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Revision 1.105 by root, Sun Dec 23 03:50:10 2007 UTC vs.
Revision 1.416 by root, Sun May 6 13:42:10 2012 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#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 occurring), 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
…		…
70	=head2 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	=head2 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	=head2 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 some floatingpoint value. Unlike the name	141	any calculations on it, you should treat it as some floating point value.
		142
104	component C<stamp> might indicate, it is also used for time differences	143	Unlike the name component C<stamp> might indicate, it is also used for
105	throughout libev.	144	time differences (e.g. delays) throughout libev.
		145
		146	=head1 ERROR HANDLING
		147
		148	Libev knows three classes of errors: operating system errors, usage errors
		149	and internal errors (bugs).
		150
		151	When libev catches an operating system error it cannot handle (for example
		152	a system call indicating a condition libev cannot fix), it calls the callback
		153	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		154	abort. The default is to print a diagnostic message and to call C<abort
		155	()>.
		156
		157	When libev detects a usage error such as a negative timer interval, then
		158	it will print a diagnostic message and abort (via the C<assert> mechanism,
		159	so C<NDEBUG> will disable this checking): these are programming errors in
		160	the libev caller and need to be fixed there.
		161
		162	Libev also has a few internal error-checking C<assert>ions, and also has
		163	extensive consistency checking code. These do not trigger under normal
		164	circumstances, as they indicate either a bug in libev or worse.
		165
106		166
107	=head1 GLOBAL FUNCTIONS	167	=head1 GLOBAL FUNCTIONS
108		168
109	These functions can be called anytime, even before initialising the	169	These functions can be called anytime, even before initialising the
110	library in any way.	170	library in any way.
…		…
113		173
114	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
115		175
116	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
117	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
118	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>.
119		180
120	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
121		182
122	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
123	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
124	this is a subsecond-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
125		192
126	=item int ev_version_major ()	193	=item int ev_version_major ()
127		194
128	=item int ev_version_minor ()	195	=item int ev_version_minor ()
129		196
…		…
140	as this indicates an incompatible change. Minor versions are usually	207	as this indicates an incompatible change. Minor versions are usually
141	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
142	not a problem.	209	not a problem.
143		210
144	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
145	version.	212	version (note, however, that this will not detect other ABI mismatches,
		213	such as LFS or reentrancy).
146		214
147	assert (("libev version mismatch",	215	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	216	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	217	&& ev_version_minor () >= EV_VERSION_MINOR));
150		218
151	=item unsigned int ev_supported_backends ()	219	=item unsigned int ev_supported_backends ()
152		220
153	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_*>
154	value) compiled into this binary of libev (independent of their	222	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	224	a description of the set values.
157		225
158	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
159	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
160		228
161	assert (("sorry, no epoll, no sex",	229	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	230	ev_supported_backends () & EVBACKEND_EPOLL));
163		231
164	=item unsigned int ev_recommended_backends ()	232	=item unsigned int ev_recommended_backends ()
165		233
166	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
167	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
168	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
169	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
170	(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
171	libev will probe for if you specify no backends explicitly.	240	probe for if you specify no backends explicitly.
172		241
173	=item unsigned int ev_embeddable_backends ()	242	=item unsigned int ev_embeddable_backends ()
174		243
175	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
176	is the theoretical, all-platform, value. To find which backends	245	value is platform-specific but can include backends not available on the
177	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
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	247	the current system, you would need to look at C<ev_embeddable_backends ()
179	recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
180		249
181	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
182		251
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
184		253
185	Sets the allocation function to use (the prototype is similar - the	254	Sets the allocation function to use (the prototype is similar - the
186	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
187	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
188	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
189	potentially destructive action. The default is your system realloc	258	or take some potentially destructive action.
190	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.
191		263
192	You could override this function in high-availability programs to, say,	264	You could override this function in high-availability programs to, say,
193	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,
194	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.
195		267
196	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
197	retries).	269	retries (example requires a standards-compliant C<realloc>).
198		270
199	static void *	271	static void *
200	persistent_realloc (void *ptr, size_t size)	272	persistent_realloc (void *ptr, size_t size)
201	{	273	{
202	for (;;)	274	for (;;)
…		…
211	}	283	}
212		284
213	...	285	...
214	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
215		287
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	288	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
217		289
218	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
219	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
220	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
221	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
222	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
223	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
224	(such as abort).	296	(such as abort).
225		297
226	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.
…		…
233	}	305	}
234		306
235	...	307	...
236	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
237		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
238	=back	323	=back
239		324
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
241		326
242	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
243	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
244	events, and dynamically created loops which do not.	329	libev 3 had an C<ev_loop> function colliding with the struct name).
245		330
246	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
247	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
248	create, you also create another event loop. Libev itself does no locking	333	do not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		334
253	=over 4	335	=over 4
254		336
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		338
257	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
258	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
259	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
260	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".
261		349
262	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
263	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.
264		382
265	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
266	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>).
267		385
268	The following flags are supported:	386	The following flags are supported:
…		…
274	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
275	thing, believe me).	393	thing, believe me).
276		394
277	=item C<EVFLAG_NOENV>	395	=item C<EVFLAG_NOENV>
278		396
279	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
280	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
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	399	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	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
283	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
284	around bugs.	402	around bugs.
285		403
286	=item C<EVFLAG_FORKCHECK>	404	=item C<EVFLAG_FORKCHECK>
287		405
288	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
289	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.
290	enabling this flag.
291		408
292	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,
293	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
294	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
295	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
296	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
297	C<pthread_atfork> which is even faster).	414	C<pthread_atfork> which is even faster).
298		415
299	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
300	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
301	flag.	418	flag.
302		419
303	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>
304	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.
305		457
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		459
308	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
309	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,
310	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
311	using this backend. It doesn't scale too well (O(highest_fd)), but its	463	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	usually the fastest backend for a low number of (low-numbered :) fds.	464	usually the fastest backend for a low number of (low-numbered :) fds.
313		465
314	To get good performance out of this backend you need a high amount of	466	To get good performance out of this backend you need a high amount of
315	parallelity (most of the file descriptors should be busy). If you are	467	parallelism (most of the file descriptors should be busy). If you are
316	writing a server, you should C<accept ()> in a loop to accept as many	468	writing a server, you should C<accept ()> in a loop to accept as many
317	connections as possible during one iteration. You might also want to have	469	connections as possible during one iteration. You might also want to have
318	a look at C<ev_set_io_collect_interval ()> to increase the amount of	470	a look at C<ev_set_io_collect_interval ()> to increase the amount of
319	readyness notifications you get per iteration.	471	readiness notifications you get per iteration.
		472
		473	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		474	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		475	C<exceptfds> set on that platform).
320		476
321	=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)
322		478
323	And this is your standard poll(2) backend. It's more complicated	479	And this is your standard poll(2) backend. It's more complicated
324	than select, but handles sparse fds better and has no artificial	480	than select, but handles sparse fds better and has no artificial
325	limit on the number of fds you can use (except it will slow down	481	limit on the number of fds you can use (except it will slow down
326	considerably with a lot of inactive fds). It scales similarly to select,	482	considerably with a lot of inactive fds). It scales similarly to select,
327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	483	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
328	performance tips.	484	performance tips.
329		485
		486	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		487	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		488
330	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
331		490
		491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		492	kernels).
		493
332	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
333	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
334	like O(total_fds) where n is the total number of fds (or the highest fd),	496	O(total_fds) where total_fds is the total number of fds (or the highest
335	epoll scales either O(1) or O(active_fds). The epoll design has a number	497	fd), epoll scales either O(1) or O(active_fds).
336	of shortcomings, such as silently dropping events in some hard-to-detect	498
337	cases and rewiring a syscall per fd change, no fork support and bad	499	The epoll mechanism deserves honorable mention as the most misdesigned
338	support for dup.	500	of the more advanced event mechanisms: mere annoyances include silently
		501	dropping file descriptors, requiring a system call per change per file
		502	descriptor (and unnecessary guessing of parameters), problems with dup,
		503	returning before the timeout value, resulting in additional iterations
		504	(and only giving 5ms accuracy while select on the same platform gives
		505	0.1ms) and so on. The biggest issue is fork races, however - if a program
		506	forks then I<both> parent and child process have to recreate the epoll
		507	set, which can take considerable time (one syscall per file descriptor)
		508	and is of course hard to detect.
		509
		510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		511	but of course I<doesn't>, and epoll just loves to report events for
		512	totally I<different> file descriptors (even already closed ones, so
		513	one cannot even remove them from the set) than registered in the set
		514	(especially on SMP systems). Libev tries to counter these spurious
		515	notifications by employing an additional generation counter and comparing
		516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
		520	not least, it also refuses to work with some file descriptors which work
		521	perfectly fine with C<select> (files, many character devices...).
		522
		523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
339		526
340	While stopping, setting and starting an I/O watcher in the same iteration	527	While stopping, setting and starting an I/O watcher in the same iteration
341	will result in some caching, there is still a syscall per such incident	528	will result in some caching, there is still a system call per such
342	(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
343	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
344	very well if you register events for both fds.	531	file descriptors might not work very well if you register events for both
345		532	file descriptors.
346	Please note that epoll sometimes generates spurious notifications, so you
347	need to use non-blocking I/O or other means to avoid blocking when no data
348	(or space) is available.
349		533
350	Best performance from this backend is achieved by not unregistering all	534	Best performance from this backend is achieved by not unregistering all
351	watchers for a file descriptor until it has been closed, if possible, i.e.	535	watchers for a file descriptor until it has been closed, if possible,
352	keep at least one watcher active per fd at all times.	536	i.e. keep at least one watcher active per fd at all times. Stopping and
		537	starting a watcher (without re-setting it) also usually doesn't cause
		538	extra overhead. A fork can both result in spurious notifications as well
		539	as in libev having to destroy and recreate the epoll object, which can
		540	take considerable time and thus should be avoided.
353		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
354	While nominally embeddeble in other event loops, this feature is broken in	546	While nominally embeddable in other event loops, this feature is broken in
355	all kernel versions tested so far.	547	all kernel versions tested so far.
		548
		549	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		550	C<EVBACKEND_POLL>.
356		551
357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	552	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
358		553
359	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
360	was broken on all BSDs except NetBSD (usually it doesn't work reliably	555	was broken on all BSDs except NetBSD (usually it doesn't work reliably
361	with anything but sockets and pipes, except on Darwin, where of course	556	with anything but sockets and pipes, except on Darwin, where of course
362	it's completely useless). For this reason it's not being "autodetected"	557	it's completely useless). Unlike epoll, however, whose brokenness
		558	is by design, these kqueue bugs can (and eventually will) be fixed
		559	without API changes to existing programs. For this reason it's not being
363	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
364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	561	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
365	system like NetBSD.	562	system like NetBSD.
366		563
367	You still can embed kqueue into a normal poll or select backend and use it	564	You still can embed kqueue into a normal poll or select backend and use it
368	only for sockets (after having made sure that sockets work with kqueue on	565	only for sockets (after having made sure that sockets work with kqueue on
369	the target platform). See C<ev_embed> watchers for more info.	566	the target platform). See C<ev_embed> watchers for more info.
370		567
371	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
372	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
373	course). While stopping, setting and starting an I/O watcher does never	570	course). While stopping, setting and starting an I/O watcher does never
374	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
375	two event changes per incident, support for C<fork ()> is very bad and it	572	two event changes per incident. Support for C<fork ()> is very bad (you
		573	might have to leak fd's on fork, but it's more sane than epoll) and it
376	drops fds silently in similarly hard-to-detect cases.	574	drops fds silently in similarly hard-to-detect cases
377		575
378	This backend usually performs well under most conditions.	576	This backend usually performs well under most conditions.
379		577
380	While nominally embeddable in other event loops, this doesn't work	578	While nominally embeddable in other event loops, this doesn't work
381	everywhere, so you might need to test for this. And since it is broken	579	everywhere, so you might need to test for this. And since it is broken
382	almost everywhere, you should only use it when you have a lot of sockets	580	almost everywhere, you should only use it when you have a lot of sockets
383	(for which it usually works), by embedding it into another event loop	581	(for which it usually works), by embedding it into another event loop
384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	582	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
385	sockets.	583	also broken on OS X)) and, did I mention it, using it only for sockets.
		584
		585	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		586	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		587	C<NOTE_EOF>.
386		588
387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	589	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
388		590
389	This is not implemented yet (and might never be, unless you send me an	591	This is not implemented yet (and might never be, unless you send me an
390	implementation). According to reports, C</dev/poll> only supports sockets	592	implementation). According to reports, C</dev/poll> only supports sockets
…		…
394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
395		597
396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
397	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)).
398		600
399	Please note that solaris event ports can deliver a lot of spurious
400	notifications, so you need to use non-blocking I/O or other means to avoid
401	blocking when no data (or space) is available.
402
403	While this backend scales well, it requires one system call per active	601	While this backend scales well, it requires one system call per active
404	file descriptor per loop iteration. For small and medium numbers of file	602	file descriptor per loop iteration. For small and medium numbers of file
405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
406	might perform better.	604	might perform better.
407		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>.
		623
408	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
409		625
410	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
411	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
412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
413		629
414	It is definitely not recommended to use this flag.	630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
415		639
416	=back	640	=back
417		641
418	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,
419	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
420	specified, most compiled-in backend will be tried, usually in reverse	644	here). If none are specified, all backends in C<ev_recommended_backends
421	order of their flag values :)	645	()> will be tried.
422
423	The most typical usage is like this:
424
425	if (!ev_default_loop (0))
426	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
427
428	Restrict libev to the select and poll backends, and do not allow
429	environment settings to be taken into account:
430
431	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
432
433	Use whatever libev has to offer, but make sure that kqueue is used if
434	available (warning, breaks stuff, best use only with your own private
435	event loop and only if you know the OS supports your types of fds):
436
437	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
438
439	=item struct ev_loop *ev_loop_new (unsigned int flags)
440
441	Similar to C<ev_default_loop>, but always creates a new event loop that is
442	always distinct from the default loop. Unlike the default loop, it cannot
443	handle signal and child watchers, and attempts to do so will be greeted by
444	undefined behaviour (or a failed assertion if assertions are enabled).
445		646
446	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.
447		648
448	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	649	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
449	if (!epoller)	650	if (!epoller)
450	fatal ("no epoll found here, maybe it hides under your chair");	651	fatal ("no epoll found here, maybe it hides under your chair");
451		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
452	=item ev_default_destroy ()	658	=item ev_loop_destroy (loop)
453		659
454	Destroys the default loop again (frees all memory and kernel state	660	Destroys an event loop object (frees all memory and kernel state
455	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
456	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
457	responsibility to either stop all watchers cleanly yoursef I<before>	663	responsibility to either stop all watchers cleanly yourself I<before>
458	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
459	the easiest thing, you can just ignore the watchers and/or C<free ()> them	665	the easiest thing, you can just ignore the watchers and/or C<free ()> them
460	for example).	666	for example).
461		667
462	Note that certain global state, such as signal state, will not be freed by	668	Note that certain global state, such as signal state (and installed signal
463	this function, and related watchers (such as signal and child watchers)	669	handlers), will not be freed by this function, and related watchers (such
464	would need to be stopped manually.	670	as signal and child watchers) would need to be stopped manually.
465		671
466	In general it is not advisable to call this function except in the	672	This function is normally used on loop objects allocated by
467	rare occasion where you really need to free e.g. the signal handling	673	C<ev_loop_new>, but it can also be used on the default loop returned by
		674	C<ev_default_loop>, in which case it is not thread-safe.
		675
		676	Note that it is not advisable to call this function on the default loop
		677	except in the rare occasion where you really need to free its resources.
468	pipe fds. If you need dynamically allocated loops it is better to use	678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
469	C<ev_loop_new> and C<ev_loop_destroy>).	679	and C<ev_loop_destroy>.
470		680
471	=item ev_loop_destroy (loop)	681	=item ev_loop_fork (loop)
472		682
473	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
474	earlier call to C<ev_loop_new>.
475
476	=item ev_default_fork ()
477
478	This function reinitialises the kernel state for backends that have	684	reinitialise the kernel state for backends that have one. Despite the
479	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
480	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
481	again makes little sense).	687	child before resuming or calling C<ev_run>.
482		688
483	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
484	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
485	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).
486		700
487	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
488	it just in case after a fork. To make this easy, the function will fit in	702	it just in case after a fork.
489	quite nicely into a call to C<pthread_atfork>:
490		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	...
491	pthread_atfork (0, 0, ev_default_fork);	714	pthread_atfork (0, 0, post_fork_child);
492		715
493	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	716	=item int ev_is_default_loop (loop)
494	without calling this function, so if you force one of those backends you
495	do not need to care.
496		717
497	=item ev_loop_fork (loop)	718	Returns true when the given loop is, in fact, the default loop, and false
		719	otherwise.
498		720
499	Like C<ev_default_fork>, but acts on an event loop created by
500	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
501	after fork, and how you do this is entirely your own problem.
502
503	=item unsigned int ev_loop_count (loop)	721	=item unsigned int ev_iteration (loop)
504		722
505	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
506	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>
507	happily wraps around with enough iterations.	725	and happily wraps around with enough iterations.
508		726
509	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
510	"ticks" the number of loop iterations), as it roughly corresponds with	728	"ticks" the number of loop iterations), as it roughly corresponds with
511	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.
512		745
513	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
514		747
515	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
516	use.	749	use.
…		…
521	received events and started processing them. This timestamp does not	754	received events and started processing them. This timestamp does not
522	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
523	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
524	event occurring (or more correctly, libev finding out about it).	757	event occurring (or more correctly, libev finding out about it).
525		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
526	=item ev_loop (loop, int flags)	797	=item bool ev_run (loop, int flags)
527		798
528	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
529	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
530	events.	801	handling events. It will ask the operating system for any new events, call
		802	the watcher callbacks, and then repeat the whole process indefinitely: This
		803	is why event loops are called I<loops>.
531		804
532	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
533	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.
534		808
		809	The return value is false if there are no more active watchers (which
		810	usually means "all jobs done" or "deadlock"), and true in all other cases
		811	(which usually means " you should call C<ev_run> again").
		812
535	Please note that an explicit C<ev_unloop> is usually better than	813	Please note that an explicit C<ev_break> is usually better than
536	relying on all watchers to be stopped when deciding when a program has	814	relying on all watchers to be stopped when deciding when a program has
537	finished (especially in interactive programs), but having a program that	815	finished (especially in interactive programs), but having a program
538	automatically loops as long as it has to and no longer by virtue of	816	that automatically loops as long as it has to and no longer by virtue
539	relying on its watchers stopping correctly is a thing of beauty.	817	of relying on its watchers stopping correctly, that is truly a thing of
		818	beauty.
540		819
		820	This function is I<mostly> exception-safe - you can break out of a
		821	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		822	exception and so on. This does not decrement the C<ev_depth> value, nor
		823	will it clear any outstanding C<EVBREAK_ONE> breaks.
		824
541	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	825	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
542	those events and any outstanding ones, but will not block your process in	826	those events and any already outstanding ones, but will not wait and
543	case there are no events and will return after one iteration of the loop.	827	block your process in case there are no events and will return after one
		828	iteration of the loop. This is sometimes useful to poll and handle new
		829	events while doing lengthy calculations, to keep the program responsive.
544		830
545	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	831	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
546	neccessary) and will handle those and any outstanding ones. It will block	832	necessary) and will handle those and any already outstanding ones. It
547	your process until at least one new event arrives, and will return after	833	will block your process until at least one new event arrives (which could
548	one iteration of the loop. This is useful if you are waiting for some	834	be an event internal to libev itself, so there is no guarantee that a
549	external event in conjunction with something not expressible using other	835	user-registered callback will be called), and will return after one
		836	iteration of the loop.
		837
		838	This is useful if you are waiting for some external event in conjunction
		839	with something not expressible using other libev watchers (i.e. "roll your
550	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	840	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
551	usually a better approach for this kind of thing.	841	usually a better approach for this kind of thing.
552		842
553	Here are the gory details of what C<ev_loop> does:	843	Here are the gory details of what C<ev_run> does (this is for your
		844	understanding, not a guarantee that things will work exactly like this in
		845	future versions):
554		846
		847	- Increment loop depth.
		848	- Reset the ev_break status.
555	- Before the first iteration, call any pending watchers.	849	- Before the first iteration, call any pending watchers.
556	* If there are no active watchers (reference count is zero), return.	850	LOOP:
557	- Queue all prepare watchers and then call all outstanding watchers.	851	- If EVFLAG_FORKCHECK was used, check for a fork.
		852	- If a fork was detected (by any means), queue and call all fork watchers.
		853	- Queue and call all prepare watchers.
		854	- If ev_break was called, goto FINISH.
558	- If we have been forked, recreate the kernel state.	855	- If we have been forked, detach and recreate the kernel state
		856	as to not disturb the other process.
559	- Update the kernel state with all outstanding changes.	857	- Update the kernel state with all outstanding changes.
560	- Update the "event loop time".	858	- Update the "event loop time" (ev_now ()).
561	- Calculate for how long to block.	859	- Calculate for how long to sleep or block, if at all
		860	(active idle watchers, EVRUN_NOWAIT or not having
		861	any active watchers at all will result in not sleeping).
		862	- Sleep if the I/O and timer collect interval say so.
		863	- Increment loop iteration counter.
562	- Block the process, waiting for any events.	864	- Block the process, waiting for any events.
563	- Queue all outstanding I/O (fd) events.	865	- Queue all outstanding I/O (fd) events.
564	- Update the "event loop time" and do time jump handling.	866	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
565	- Queue all outstanding timers.	867	- Queue all expired timers.
566	- Queue all outstanding periodics.	868	- Queue all expired periodics.
567	- If no events are pending now, queue all idle watchers.	869	- Queue all idle watchers with priority higher than that of pending events.
568	- Queue all check watchers.	870	- Queue all check watchers.
569	- Call all queued watchers in reverse order (i.e. check watchers first).	871	- Call all queued watchers in reverse order (i.e. check watchers first).
570	Signals and child watchers are implemented as I/O watchers, and will	872	Signals and child watchers are implemented as I/O watchers, and will
571	be handled here by queueing them when their watcher gets executed.	873	be handled here by queueing them when their watcher gets executed.
572	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	874	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
573	were used, return, otherwise continue with step *.	875	were used, or there are no active watchers, goto FINISH, otherwise
		876	continue with step LOOP.
		877	FINISH:
		878	- Reset the ev_break status iff it was EVBREAK_ONE.
		879	- Decrement the loop depth.
		880	- Return.
574		881
575	Example: Queue some jobs and then loop until no events are outsanding	882	Example: Queue some jobs and then loop until no events are outstanding
576	anymore.	883	anymore.
577		884
578	... queue jobs here, make sure they register event watchers as long	885	... queue jobs here, make sure they register event watchers as long
579	... as they still have work to do (even an idle watcher will do..)	886	... as they still have work to do (even an idle watcher will do..)
580	ev_loop (my_loop, 0);	887	ev_run (my_loop, 0);
581	... jobs done. yeah!	888	... jobs done or somebody called break. yeah!
582		889
583	=item ev_unloop (loop, how)	890	=item ev_break (loop, how)
584		891
585	Can be used to make a call to C<ev_loop> return early (but only after it	892	Can be used to make a call to C<ev_run> return early (but only after it
586	has processed all outstanding events). The C<how> argument must be either	893	has processed all outstanding events). The C<how> argument must be either
587	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	894	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
588	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	895	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		896
		897	This "break state" will be cleared on the next call to C<ev_run>.
		898
		899	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		900	which case it will have no effect.
589		901
590	=item ev_ref (loop)	902	=item ev_ref (loop)
591		903
592	=item ev_unref (loop)	904	=item ev_unref (loop)
593		905
594	Ref/unref can be used to add or remove a reference count on the event	906	Ref/unref can be used to add or remove a reference count on the event
595	loop: Every watcher keeps one reference, and as long as the reference	907	loop: Every watcher keeps one reference, and as long as the reference
596	count is nonzero, C<ev_loop> will not return on its own. If you have	908	count is nonzero, C<ev_run> will not return on its own.
597	a watcher you never unregister that should not keep C<ev_loop> from	909
598	returning, ev_unref() after starting, and ev_ref() before stopping it. For	910	This is useful when you have a watcher that you never intend to
		911	unregister, but that nevertheless should not keep C<ev_run> from
		912	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		913	before stopping it.
		914
599	example, libev itself uses this for its internal signal pipe: It is not	915	As an example, libev itself uses this for its internal signal pipe: It
600	visible to the libev user and should not keep C<ev_loop> from exiting if	916	is not visible to the libev user and should not keep C<ev_run> from
601	no event watchers registered by it are active. It is also an excellent	917	exiting if no event watchers registered by it are active. It is also an
602	way to do this for generic recurring timers or from within third-party	918	excellent way to do this for generic recurring timers or from within
603	libraries. Just remember to I<unref after start> and I<ref before stop>.	919	third-party libraries. Just remember to I<unref after start> and I<ref
		920	before stop> (but only if the watcher wasn't active before, or was active
		921	before, respectively. Note also that libev might stop watchers itself
		922	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		923	in the callback).
604		924
605	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	925	Example: Create a signal watcher, but keep it from keeping C<ev_run>
606	running when nothing else is active.	926	running when nothing else is active.
607		927
608	struct ev_signal exitsig;	928	ev_signal exitsig;
609	ev_signal_init (&exitsig, sig_cb, SIGINT);	929	ev_signal_init (&exitsig, sig_cb, SIGINT);
610	ev_signal_start (loop, &exitsig);	930	ev_signal_start (loop, &exitsig);
611	evf_unref (loop);	931	ev_unref (loop);
612		932
613	Example: For some weird reason, unregister the above signal handler again.	933	Example: For some weird reason, unregister the above signal handler again.
614		934
615	ev_ref (loop);	935	ev_ref (loop);
616	ev_signal_stop (loop, &exitsig);	936	ev_signal_stop (loop, &exitsig);
617		937
618	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	938	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
619		939
620	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	940	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
621		941
622	These advanced functions influence the time that libev will spend waiting	942	These advanced functions influence the time that libev will spend waiting
623	for events. Both are by default C<0>, meaning that libev will try to	943	for events. Both time intervals are by default C<0>, meaning that libev
624	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	944	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		945	latency.
625		946
626	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	947	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
627	allows libev to delay invocation of I/O and timer/periodic callbacks to	948	allows libev to delay invocation of I/O and timer/periodic callbacks
628	increase efficiency of loop iterations.	949	to increase efficiency of loop iterations (or to increase power-saving
		950	opportunities).
629		951
630	The background is that sometimes your program runs just fast enough to	952	The idea is that sometimes your program runs just fast enough to handle
631	handle one (or very few) event(s) per loop iteration. While this makes	953	one (or very few) event(s) per loop iteration. While this makes the
632	the program responsive, it also wastes a lot of CPU time to poll for new	954	program responsive, it also wastes a lot of CPU time to poll for new
633	events, especially with backends like C<select ()> which have a high	955	events, especially with backends like C<select ()> which have a high
634	overhead for the actual polling but can deliver many events at once.	956	overhead for the actual polling but can deliver many events at once.
635		957
636	By setting a higher I<io collect interval> you allow libev to spend more	958	By setting a higher I<io collect interval> you allow libev to spend more
637	time collecting I/O events, so you can handle more events per iteration,	959	time collecting I/O events, so you can handle more events per iteration,
638	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	960	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
639	C<ev_timer>) will be not affected. Setting this to a non-null value will	961	C<ev_timer>) will not be affected. Setting this to a non-null value will
640	introduce an additional C<ev_sleep ()> call into most loop iterations.	962	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		963	sleep time ensures that libev will not poll for I/O events more often then
		964	once per this interval, on average (as long as the host time resolution is
		965	good enough).
641		966
642	Likewise, by setting a higher I<timeout collect interval> you allow libev	967	Likewise, by setting a higher I<timeout collect interval> you allow libev
643	to spend more time collecting timeouts, at the expense of increased	968	to spend more time collecting timeouts, at the expense of increased
644	latency (the watcher callback will be called later). C<ev_io> watchers	969	latency/jitter/inexactness (the watcher callback will be called
645	will not be affected. Setting this to a non-null value will not introduce	970	later). C<ev_io> watchers will not be affected. Setting this to a non-null
646	any overhead in libev.	971	value will not introduce any overhead in libev.
647		972
648	Many (busy) programs can usually benefit by setting the io collect	973	Many (busy) programs can usually benefit by setting the I/O collect
649	interval to a value near C<0.1> or so, which is often enough for	974	interval to a value near C<0.1> or so, which is often enough for
650	interactive servers (of course not for games), likewise for timeouts. It	975	interactive servers (of course not for games), likewise for timeouts. It
651	usually doesn't make much sense to set it to a lower value than C<0.01>,	976	usually doesn't make much sense to set it to a lower value than C<0.01>,
652	as this approsaches the timing granularity of most systems.	977	as this approaches the timing granularity of most systems. Note that if
		978	you do transactions with the outside world and you can't increase the
		979	parallelity, then this setting will limit your transaction rate (if you
		980	need to poll once per transaction and the I/O collect interval is 0.01,
		981	then you can't do more than 100 transactions per second).
		982
		983	Setting the I<timeout collect interval> can improve the opportunity for
		984	saving power, as the program will "bundle" timer callback invocations that
		985	are "near" in time together, by delaying some, thus reducing the number of
		986	times the process sleeps and wakes up again. Another useful technique to
		987	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		988	they fire on, say, one-second boundaries only.
		989
		990	Example: we only need 0.1s timeout granularity, and we wish not to poll
		991	more often than 100 times per second:
		992
		993	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		994	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		995
		996	=item ev_invoke_pending (loop)
		997
		998	This call will simply invoke all pending watchers while resetting their
		999	pending state. Normally, C<ev_run> does this automatically when required,
		1000	but when overriding the invoke callback this call comes handy. This
		1001	function can be invoked from a watcher - this can be useful for example
		1002	when you want to do some lengthy calculation and want to pass further
		1003	event handling to another thread (you still have to make sure only one
		1004	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1005
		1006	=item int ev_pending_count (loop)
		1007
		1008	Returns the number of pending watchers - zero indicates that no watchers
		1009	are pending.
		1010
		1011	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1012
		1013	This overrides the invoke pending functionality of the loop: Instead of
		1014	invoking all pending watchers when there are any, C<ev_run> will call
		1015	this callback instead. This is useful, for example, when you want to
		1016	invoke the actual watchers inside another context (another thread etc.).
		1017
		1018	If you want to reset the callback, use C<ev_invoke_pending> as new
		1019	callback.
		1020
		1021	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1022
		1023	Sometimes you want to share the same loop between multiple threads. This
		1024	can be done relatively simply by putting mutex_lock/unlock calls around
		1025	each call to a libev function.
		1026
		1027	However, C<ev_run> can run an indefinite time, so it is not feasible
		1028	to wait for it to return. One way around this is to wake up the event
		1029	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1030	I<release> and I<acquire> callbacks on the loop.
		1031
		1032	When set, then C<release> will be called just before the thread is
		1033	suspended waiting for new events, and C<acquire> is called just
		1034	afterwards.
		1035
		1036	Ideally, C<release> will just call your mutex_unlock function, and
		1037	C<acquire> will just call the mutex_lock function again.
		1038
		1039	While event loop modifications are allowed between invocations of
		1040	C<release> and C<acquire> (that's their only purpose after all), no
		1041	modifications done will affect the event loop, i.e. adding watchers will
		1042	have no effect on the set of file descriptors being watched, or the time
		1043	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1044	to take note of any changes you made.
		1045
		1046	In theory, threads executing C<ev_run> will be async-cancel safe between
		1047	invocations of C<release> and C<acquire>.
		1048
		1049	See also the locking example in the C<THREADS> section later in this
		1050	document.
		1051
		1052	=item ev_set_userdata (loop, void *data)
		1053
		1054	=item void *ev_userdata (loop)
		1055
		1056	Set and retrieve a single C<void *> associated with a loop. When
		1057	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1058	C<0>.
		1059
		1060	These two functions can be used to associate arbitrary data with a loop,
		1061	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1062	C<acquire> callbacks described above, but of course can be (ab-)used for
		1063	any other purpose as well.
		1064
		1065	=item ev_verify (loop)
		1066
		1067	This function only does something when C<EV_VERIFY> support has been
		1068	compiled in, which is the default for non-minimal builds. It tries to go
		1069	through all internal structures and checks them for validity. If anything
		1070	is found to be inconsistent, it will print an error message to standard
		1071	error and call C<abort ()>.
		1072
		1073	This can be used to catch bugs inside libev itself: under normal
		1074	circumstances, this function will never abort as of course libev keeps its
		1075	data structures consistent.
653		1076
654	=back	1077	=back
655		1078
656		1079
657	=head1 ANATOMY OF A WATCHER	1080	=head1 ANATOMY OF A WATCHER
658		1081
		1082	In the following description, uppercase C<TYPE> in names stands for the
		1083	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1084	watchers and C<ev_io_start> for I/O watchers.
		1085
659	A watcher is a structure that you create and register to record your	1086	A watcher is an opaque structure that you allocate and register to record
660	interest in some event. For instance, if you want to wait for STDIN to	1087	your interest in some event. To make a concrete example, imagine you want
661	become readable, you would create an C<ev_io> watcher for that:	1088	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1089	for that:
662		1090
663	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1091	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
664	{	1092	{
665	ev_io_stop (w);	1093	ev_io_stop (w);
666	ev_unloop (loop, EVUNLOOP_ALL);	1094	ev_break (loop, EVBREAK_ALL);
667	}	1095	}
668		1096
669	struct ev_loop *loop = ev_default_loop (0);	1097	struct ev_loop *loop = ev_default_loop (0);
		1098
670	struct ev_io stdin_watcher;	1099	ev_io stdin_watcher;
		1100
671	ev_init (&stdin_watcher, my_cb);	1101	ev_init (&stdin_watcher, my_cb);
672	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1102	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
673	ev_io_start (loop, &stdin_watcher);	1103	ev_io_start (loop, &stdin_watcher);
		1104
674	ev_loop (loop, 0);	1105	ev_run (loop, 0);
675		1106
676	As you can see, you are responsible for allocating the memory for your	1107	As you can see, you are responsible for allocating the memory for your
677	watcher structures (and it is usually a bad idea to do this on the stack,	1108	watcher structures (and it is I<usually> a bad idea to do this on the
678	although this can sometimes be quite valid).	1109	stack).
679		1110
		1111	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1112	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1113
680	Each watcher structure must be initialised by a call to C<ev_init	1114	Each watcher structure must be initialised by a call to C<ev_init (watcher
681	(watcher *, callback)>, which expects a callback to be provided. This	1115	*, callback)>, which expects a callback to be provided. This callback is
682	callback gets invoked each time the event occurs (or, in the case of io	1116	invoked each time the event occurs (or, in the case of I/O watchers, each
683	watchers, each time the event loop detects that the file descriptor given	1117	time the event loop detects that the file descriptor given is readable
684	is readable and/or writable).	1118	and/or writable).
685		1119
686	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1120	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
687	with arguments specific to this watcher type. There is also a macro	1121	macro to configure it, with arguments specific to the watcher type. There
688	to combine initialisation and setting in one call: C<< ev_<type>_init	1122	is also a macro to combine initialisation and setting in one call: C<<
689	(watcher *, callback, ...) >>.	1123	ev_TYPE_init (watcher *, callback, ...) >>.
690		1124
691	To make the watcher actually watch out for events, you have to start it	1125	To make the watcher actually watch out for events, you have to start it
692	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1126	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
693	*) >>), and you can stop watching for events at any time by calling the	1127	*) >>), and you can stop watching for events at any time by calling the
694	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1128	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
695		1129
696	As long as your watcher is active (has been started but not stopped) you	1130	As long as your watcher is active (has been started but not stopped) you
697	must not touch the values stored in it. Most specifically you must never	1131	must not touch the values stored in it. Most specifically you must never
698	reinitialise it or call its C<set> macro.	1132	reinitialise it or call its C<ev_TYPE_set> macro.
699		1133
700	Each and every callback receives the event loop pointer as first, the	1134	Each and every callback receives the event loop pointer as first, the
701	registered watcher structure as second, and a bitset of received events as	1135	registered watcher structure as second, and a bitset of received events as
702	third argument.	1136	third argument.
703		1137
…		…
712	=item C<EV_WRITE>	1146	=item C<EV_WRITE>
713		1147
714	The file descriptor in the C<ev_io> watcher has become readable and/or	1148	The file descriptor in the C<ev_io> watcher has become readable and/or
715	writable.	1149	writable.
716		1150
717	=item C<EV_TIMEOUT>	1151	=item C<EV_TIMER>
718		1152
719	The C<ev_timer> watcher has timed out.	1153	The C<ev_timer> watcher has timed out.
720		1154
721	=item C<EV_PERIODIC>	1155	=item C<EV_PERIODIC>
722		1156
…		…
740		1174
741	=item C<EV_PREPARE>	1175	=item C<EV_PREPARE>
742		1176
743	=item C<EV_CHECK>	1177	=item C<EV_CHECK>
744		1178
745	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1179	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
746	to gather new events, and all C<ev_check> watchers are invoked just after	1180	gather new events, and all C<ev_check> watchers are queued (not invoked)
747	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1181	just after C<ev_run> has gathered them, but before it queues any callbacks
		1182	for any received events. That means C<ev_prepare> watchers are the last
		1183	watchers invoked before the event loop sleeps or polls for new events, and
		1184	C<ev_check> watchers will be invoked before any other watchers of the same
		1185	or lower priority within an event loop iteration.
		1186
748	received events. Callbacks of both watcher types can start and stop as	1187	Callbacks of both watcher types can start and stop as many watchers as
749	many watchers as they want, and all of them will be taken into account	1188	they want, and all of them will be taken into account (for example, a
750	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1189	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
751	C<ev_loop> from blocking).	1190	blocking).
752		1191
753	=item C<EV_EMBED>	1192	=item C<EV_EMBED>
754		1193
755	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1194	The embedded event loop specified in the C<ev_embed> watcher needs attention.
756		1195
757	=item C<EV_FORK>	1196	=item C<EV_FORK>
758		1197
759	The event loop has been resumed in the child process after fork (see	1198	The event loop has been resumed in the child process after fork (see
760	C<ev_fork>).	1199	C<ev_fork>).
761		1200
		1201	=item C<EV_CLEANUP>
		1202
		1203	The event loop is about to be destroyed (see C<ev_cleanup>).
		1204
		1205	=item C<EV_ASYNC>
		1206
		1207	The given async watcher has been asynchronously notified (see C<ev_async>).
		1208
		1209	=item C<EV_CUSTOM>
		1210
		1211	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1212	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1213
762	=item C<EV_ERROR>	1214	=item C<EV_ERROR>
763		1215
764	An unspecified error has occured, the watcher has been stopped. This might	1216	An unspecified error has occurred, the watcher has been stopped. This might
765	happen because the watcher could not be properly started because libev	1217	happen because the watcher could not be properly started because libev
766	ran out of memory, a file descriptor was found to be closed or any other	1218	ran out of memory, a file descriptor was found to be closed or any other
		1219	problem. Libev considers these application bugs.
		1220
767	problem. You best act on it by reporting the problem and somehow coping	1221	You best act on it by reporting the problem and somehow coping with the
768	with the watcher being stopped.	1222	watcher being stopped. Note that well-written programs should not receive
		1223	an error ever, so when your watcher receives it, this usually indicates a
		1224	bug in your program.
769		1225
770	Libev will usually signal a few "dummy" events together with an error,	1226	Libev will usually signal a few "dummy" events together with an error, for
771	for example it might indicate that a fd is readable or writable, and if	1227	example it might indicate that a fd is readable or writable, and if your
772	your callbacks is well-written it can just attempt the operation and cope	1228	callbacks is well-written it can just attempt the operation and cope with
773	with the error from read() or write(). This will not work in multithreaded	1229	the error from read() or write(). This will not work in multi-threaded
774	programs, though, so beware.	1230	programs, though, as the fd could already be closed and reused for another
		1231	thing, so beware.
775		1232
776	=back	1233	=back
777		1234
778	=head2 GENERIC WATCHER FUNCTIONS	1235	=head2 GENERIC WATCHER FUNCTIONS
779
780	In the following description, C<TYPE> stands for the watcher type,
781	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
782		1236
783	=over 4	1237	=over 4
784		1238
785	=item C<ev_init> (ev_TYPE *watcher, callback)	1239	=item C<ev_init> (ev_TYPE *watcher, callback)
786		1240
…		…
792	which rolls both calls into one.	1246	which rolls both calls into one.
793		1247
794	You can reinitialise a watcher at any time as long as it has been stopped	1248	You can reinitialise a watcher at any time as long as it has been stopped
795	(or never started) and there are no pending events outstanding.	1249	(or never started) and there are no pending events outstanding.
796		1250
797	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1251	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
798	int revents)>.	1252	int revents)>.
799		1253
		1254	Example: Initialise an C<ev_io> watcher in two steps.
		1255
		1256	ev_io w;
		1257	ev_init (&w, my_cb);
		1258	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1259
800	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1260	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
801		1261
802	This macro initialises the type-specific parts of a watcher. You need to	1262	This macro initialises the type-specific parts of a watcher. You need to
803	call C<ev_init> at least once before you call this macro, but you can	1263	call C<ev_init> at least once before you call this macro, but you can
804	call C<ev_TYPE_set> any number of times. You must not, however, call this	1264	call C<ev_TYPE_set> any number of times. You must not, however, call this
805	macro on a watcher that is active (it can be pending, however, which is a	1265	macro on a watcher that is active (it can be pending, however, which is a
806	difference to the C<ev_init> macro).	1266	difference to the C<ev_init> macro).
807		1267
808	Although some watcher types do not have type-specific arguments	1268	Although some watcher types do not have type-specific arguments
809	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1269	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
810		1270
		1271	See C<ev_init>, above, for an example.
		1272
811	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1273	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
812		1274
813	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1275	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
814	calls into a single call. This is the most convinient method to initialise	1276	calls into a single call. This is the most convenient method to initialise
815	a watcher. The same limitations apply, of course.	1277	a watcher. The same limitations apply, of course.
816		1278
		1279	Example: Initialise and set an C<ev_io> watcher in one step.
		1280
		1281	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1282
817	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1283	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
818		1284
819	Starts (activates) the given watcher. Only active watchers will receive	1285	Starts (activates) the given watcher. Only active watchers will receive
820	events. If the watcher is already active nothing will happen.	1286	events. If the watcher is already active nothing will happen.
821		1287
		1288	Example: Start the C<ev_io> watcher that is being abused as example in this
		1289	whole section.
		1290
		1291	ev_io_start (EV_DEFAULT_UC, &w);
		1292
822	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1293	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
823		1294
824	Stops the given watcher again (if active) and clears the pending	1295	Stops the given watcher if active, and clears the pending status (whether
		1296	the watcher was active or not).
		1297
825	status. It is possible that stopped watchers are pending (for example,	1298	It is possible that stopped watchers are pending - for example,
826	non-repeating timers are being stopped when they become pending), but	1299	non-repeating timers are being stopped when they become pending - but
827	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1300	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
828	you want to free or reuse the memory used by the watcher it is therefore a	1301	pending. If you want to free or reuse the memory used by the watcher it is
829	good idea to always call its C<ev_TYPE_stop> function.	1302	therefore a good idea to always call its C<ev_TYPE_stop> function.
830		1303
831	=item bool ev_is_active (ev_TYPE *watcher)	1304	=item bool ev_is_active (ev_TYPE *watcher)
832		1305
833	Returns a true value iff the watcher is active (i.e. it has been started	1306	Returns a true value iff the watcher is active (i.e. it has been started
834	and not yet been stopped). As long as a watcher is active you must not modify	1307	and not yet been stopped). As long as a watcher is active you must not modify
…		…
845		1318
846	=item callback ev_cb (ev_TYPE *watcher)	1319	=item callback ev_cb (ev_TYPE *watcher)
847		1320
848	Returns the callback currently set on the watcher.	1321	Returns the callback currently set on the watcher.
849		1322
850	=item ev_cb_set (ev_TYPE *watcher, callback)	1323	=item ev_set_cb (ev_TYPE *watcher, callback)
851		1324
852	Change the callback. You can change the callback at virtually any time	1325	Change the callback. You can change the callback at virtually any time
853	(modulo threads).	1326	(modulo threads).
854		1327
855	=item ev_set_priority (ev_TYPE *watcher, priority)	1328	=item ev_set_priority (ev_TYPE *watcher, int priority)
856		1329
857	=item int ev_priority (ev_TYPE *watcher)	1330	=item int ev_priority (ev_TYPE *watcher)
858		1331
859	Set and query the priority of the watcher. The priority is a small	1332	Set and query the priority of the watcher. The priority is a small
860	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1333	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
861	(default: C<-2>). Pending watchers with higher priority will be invoked	1334	(default: C<-2>). Pending watchers with higher priority will be invoked
862	before watchers with lower priority, but priority will not keep watchers	1335	before watchers with lower priority, but priority will not keep watchers
863	from being executed (except for C<ev_idle> watchers).	1336	from being executed (except for C<ev_idle> watchers).
864		1337
865	This means that priorities are I<only> used for ordering callback
866	invocation after new events have been received. This is useful, for
867	example, to reduce latency after idling, or more often, to bind two
868	watchers on the same event and make sure one is called first.
869
870	If you need to suppress invocation when higher priority events are pending	1338	If you need to suppress invocation when higher priority events are pending
871	you need to look at C<ev_idle> watchers, which provide this functionality.	1339	you need to look at C<ev_idle> watchers, which provide this functionality.
872		1340
873	You I<must not> change the priority of a watcher as long as it is active or	1341	You I<must not> change the priority of a watcher as long as it is active or
874	pending.	1342	pending.
875		1343
		1344	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1345	fine, as long as you do not mind that the priority value you query might
		1346	or might not have been clamped to the valid range.
		1347
876	The default priority used by watchers when no priority has been set is	1348	The default priority used by watchers when no priority has been set is
877	always C<0>, which is supposed to not be too high and not be too low :).	1349	always C<0>, which is supposed to not be too high and not be too low :).
878		1350
879	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1351	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
880	fine, as long as you do not mind that the priority value you query might	1352	priorities.
881	or might not have been adjusted to be within valid range.
882		1353
883	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1354	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
884		1355
885	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1356	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
886	C<loop> nor C<revents> need to be valid as long as the watcher callback	1357	C<loop> nor C<revents> need to be valid as long as the watcher callback
887	can deal with that fact.	1358	can deal with that fact, as both are simply passed through to the
		1359	callback.
888		1360
889	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1361	=item int ev_clear_pending (loop, ev_TYPE *watcher)
890		1362
891	If the watcher is pending, this function returns clears its pending status	1363	If the watcher is pending, this function clears its pending status and
892	and returns its C<revents> bitset (as if its callback was invoked). If the	1364	returns its C<revents> bitset (as if its callback was invoked). If the
893	watcher isn't pending it does nothing and returns C<0>.	1365	watcher isn't pending it does nothing and returns C<0>.
894		1366
		1367	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1368	callback to be invoked, which can be accomplished with this function.
		1369
		1370	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1371
		1372	Feeds the given event set into the event loop, as if the specified event
		1373	had happened for the specified watcher (which must be a pointer to an
		1374	initialised but not necessarily started event watcher). Obviously you must
		1375	not free the watcher as long as it has pending events.
		1376
		1377	Stopping the watcher, letting libev invoke it, or calling
		1378	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1379	not started in the first place.
		1380
		1381	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1382	functions that do not need a watcher.
		1383
895	=back	1384	=back
896		1385
		1386	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1387	OWN COMPOSITE WATCHERS> idioms.
897		1388
898	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1389	=head2 WATCHER STATES
899		1390
900	Each watcher has, by default, a member C<void *data> that you can change	1391	There are various watcher states mentioned throughout this manual -
901	and read at any time, libev will completely ignore it. This can be used	1392	active, pending and so on. In this section these states and the rules to
902	to associate arbitrary data with your watcher. If you need more data and	1393	transition between them will be described in more detail - and while these
903	don't want to allocate memory and store a pointer to it in that data	1394	rules might look complicated, they usually do "the right thing".
904	member, you can also "subclass" the watcher type and provide your own
905	data:
906		1395
907	struct my_io	1396	=over 4
908	{
909	struct ev_io io;
910	int otherfd;
911	void *somedata;
912	struct whatever *mostinteresting;
913	}
914		1397
915	And since your callback will be called with a pointer to the watcher, you	1398	=item initialiased
916	can cast it back to your own type:
917		1399
918	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1400	Before a watcher can be registered with the event loop it has to be
919	{	1401	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
920	struct my_io *w = (struct my_io *)w_;	1402	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
921	...
922	}
923		1403
924	More interesting and less C-conformant ways of casting your callback type	1404	In this state it is simply some block of memory that is suitable for
925	instead have been omitted.	1405	use in an event loop. It can be moved around, freed, reused etc. at
		1406	will - as long as you either keep the memory contents intact, or call
		1407	C<ev_TYPE_init> again.
926		1408
927	Another common scenario is having some data structure with multiple	1409	=item started/running/active
928	watchers:
929		1410
930	struct my_biggy	1411	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
931	{	1412	property of the event loop, and is actively waiting for events. While in
932	int some_data;	1413	this state it cannot be accessed (except in a few documented ways), moved,
933	ev_timer t1;	1414	freed or anything else - the only legal thing is to keep a pointer to it,
934	ev_timer t2;	1415	and call libev functions on it that are documented to work on active watchers.
935	}
936		1416
937	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1417	=item pending
938	you need to use C<offsetof>:
939		1418
940	#include <stddef.h>	1419	If a watcher is active and libev determines that an event it is interested
		1420	in has occurred (such as a timer expiring), it will become pending. It will
		1421	stay in this pending state until either it is stopped or its callback is
		1422	about to be invoked, so it is not normally pending inside the watcher
		1423	callback.
941		1424
		1425	The watcher might or might not be active while it is pending (for example,
		1426	an expired non-repeating timer can be pending but no longer active). If it
		1427	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1428	but it is still property of the event loop at this time, so cannot be
		1429	moved, freed or reused. And if it is active the rules described in the
		1430	previous item still apply.
		1431
		1432	It is also possible to feed an event on a watcher that is not active (e.g.
		1433	via C<ev_feed_event>), in which case it becomes pending without being
		1434	active.
		1435
		1436	=item stopped
		1437
		1438	A watcher can be stopped implicitly by libev (in which case it might still
		1439	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1440	latter will clear any pending state the watcher might be in, regardless
		1441	of whether it was active or not, so stopping a watcher explicitly before
		1442	freeing it is often a good idea.
		1443
		1444	While stopped (and not pending) the watcher is essentially in the
		1445	initialised state, that is, it can be reused, moved, modified in any way
		1446	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1447	it again).
		1448
		1449	=back
		1450
		1451	=head2 WATCHER PRIORITY MODELS
		1452
		1453	Many event loops support I<watcher priorities>, which are usually small
		1454	integers that influence the ordering of event callback invocation
		1455	between watchers in some way, all else being equal.
		1456
		1457	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1458	description for the more technical details such as the actual priority
		1459	range.
		1460
		1461	There are two common ways how these these priorities are being interpreted
		1462	by event loops:
		1463
		1464	In the more common lock-out model, higher priorities "lock out" invocation
		1465	of lower priority watchers, which means as long as higher priority
		1466	watchers receive events, lower priority watchers are not being invoked.
		1467
		1468	The less common only-for-ordering model uses priorities solely to order
		1469	callback invocation within a single event loop iteration: Higher priority
		1470	watchers are invoked before lower priority ones, but they all get invoked
		1471	before polling for new events.
		1472
		1473	Libev uses the second (only-for-ordering) model for all its watchers
		1474	except for idle watchers (which use the lock-out model).
		1475
		1476	The rationale behind this is that implementing the lock-out model for
		1477	watchers is not well supported by most kernel interfaces, and most event
		1478	libraries will just poll for the same events again and again as long as
		1479	their callbacks have not been executed, which is very inefficient in the
		1480	common case of one high-priority watcher locking out a mass of lower
		1481	priority ones.
		1482
		1483	Static (ordering) priorities are most useful when you have two or more
		1484	watchers handling the same resource: a typical usage example is having an
		1485	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1486	timeouts. Under load, data might be received while the program handles
		1487	other jobs, but since timers normally get invoked first, the timeout
		1488	handler will be executed before checking for data. In that case, giving
		1489	the timer a lower priority than the I/O watcher ensures that I/O will be
		1490	handled first even under adverse conditions (which is usually, but not
		1491	always, what you want).
		1492
		1493	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1494	will only be executed when no same or higher priority watchers have
		1495	received events, they can be used to implement the "lock-out" model when
		1496	required.
		1497
		1498	For example, to emulate how many other event libraries handle priorities,
		1499	you can associate an C<ev_idle> watcher to each such watcher, and in
		1500	the normal watcher callback, you just start the idle watcher. The real
		1501	processing is done in the idle watcher callback. This causes libev to
		1502	continuously poll and process kernel event data for the watcher, but when
		1503	the lock-out case is known to be rare (which in turn is rare :), this is
		1504	workable.
		1505
		1506	Usually, however, the lock-out model implemented that way will perform
		1507	miserably under the type of load it was designed to handle. In that case,
		1508	it might be preferable to stop the real watcher before starting the
		1509	idle watcher, so the kernel will not have to process the event in case
		1510	the actual processing will be delayed for considerable time.
		1511
		1512	Here is an example of an I/O watcher that should run at a strictly lower
		1513	priority than the default, and which should only process data when no
		1514	other events are pending:
		1515
		1516	ev_idle idle; // actual processing watcher
		1517	ev_io io; // actual event watcher
		1518
942	static void	1519	static void
943	t1_cb (EV_P_ struct ev_timer *w, int revents)	1520	io_cb (EV_P_ ev_io *w, int revents)
944	{	1521	{
945	struct my_biggy big = (struct my_biggy *	1522	// stop the I/O watcher, we received the event, but
946	(((char *)w) - offsetof (struct my_biggy, t1));	1523	// are not yet ready to handle it.
		1524	ev_io_stop (EV_A_ w);
		1525
		1526	// start the idle watcher to handle the actual event.
		1527	// it will not be executed as long as other watchers
		1528	// with the default priority are receiving events.
		1529	ev_idle_start (EV_A_ &idle);
947	}	1530	}
948		1531
949	static void	1532	static void
950	t2_cb (EV_P_ struct ev_timer *w, int revents)	1533	idle_cb (EV_P_ ev_idle *w, int revents)
951	{	1534	{
952	struct my_biggy big = (struct my_biggy *	1535	// actual processing
953	(((char *)w) - offsetof (struct my_biggy, t2));	1536	read (STDIN_FILENO, ...);
		1537
		1538	// have to start the I/O watcher again, as
		1539	// we have handled the event
		1540	ev_io_start (EV_P_ &io);
954	}	1541	}
		1542
		1543	// initialisation
		1544	ev_idle_init (&idle, idle_cb);
		1545	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1546	ev_io_start (EV_DEFAULT_ &io);
		1547
		1548	In the "real" world, it might also be beneficial to start a timer, so that
		1549	low-priority connections can not be locked out forever under load. This
		1550	enables your program to keep a lower latency for important connections
		1551	during short periods of high load, while not completely locking out less
		1552	important ones.
955		1553
956		1554
957	=head1 WATCHER TYPES	1555	=head1 WATCHER TYPES
958		1556
959	This section describes each watcher in detail, but will not repeat	1557	This section describes each watcher in detail, but will not repeat
…		…
983	In general you can register as many read and/or write event watchers per	1581	In general you can register as many read and/or write event watchers per
984	fd as you want (as long as you don't confuse yourself). Setting all file	1582	fd as you want (as long as you don't confuse yourself). Setting all file
985	descriptors to non-blocking mode is also usually a good idea (but not	1583	descriptors to non-blocking mode is also usually a good idea (but not
986	required if you know what you are doing).	1584	required if you know what you are doing).
987		1585
988	You have to be careful with dup'ed file descriptors, though. Some backends
989	(the linux epoll backend is a notable example) cannot handle dup'ed file
990	descriptors correctly if you register interest in two or more fds pointing
991	to the same underlying file/socket/etc. description (that is, they share
992	the same underlying "file open").
993
994	If you must do this, then force the use of a known-to-be-good backend
995	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
996	C<EVBACKEND_POLL>).
997
998	Another thing you have to watch out for is that it is quite easy to	1586	Another thing you have to watch out for is that it is quite easy to
999	receive "spurious" readyness notifications, that is your callback might	1587	receive "spurious" readiness notifications, that is, your callback might
1000	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1588	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1001	because there is no data. Not only are some backends known to create a	1589	because there is no data. It is very easy to get into this situation even
1002	lot of those (for example solaris ports), it is very easy to get into	1590	with a relatively standard program structure. Thus it is best to always
1003	this situation even with a relatively standard program structure. Thus	1591	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1004	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1005	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1592	preferable to a program hanging until some data arrives.
1006		1593
1007	If you cannot run the fd in non-blocking mode (for example you should not	1594	If you cannot run the fd in non-blocking mode (for example you should
1008	play around with an Xlib connection), then you have to seperately re-test	1595	not play around with an Xlib connection), then you have to separately
1009	whether a file descriptor is really ready with a known-to-be good interface	1596	re-test whether a file descriptor is really ready with a known-to-be good
1010	such as poll (fortunately in our Xlib example, Xlib already does this on	1597	interface such as poll (fortunately in the case of Xlib, it already does
1011	its own, so its quite safe to use).	1598	this on its own, so its quite safe to use). Some people additionally
		1599	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1600	indefinitely.
		1601
		1602	But really, best use non-blocking mode.
1012		1603
1013	=head3 The special problem of disappearing file descriptors	1604	=head3 The special problem of disappearing file descriptors
1014		1605
1015	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1606	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1016	descriptor (either by calling C<close> explicitly or by any other means,	1607	descriptor (either due to calling C<close> explicitly or any other means,
1017	such as C<dup>). The reason is that you register interest in some file	1608	such as C<dup2>). The reason is that you register interest in some file
1018	descriptor, but when it goes away, the operating system will silently drop	1609	descriptor, but when it goes away, the operating system will silently drop
1019	this interest. If another file descriptor with the same number then is	1610	this interest. If another file descriptor with the same number then is
1020	registered with libev, there is no efficient way to see that this is, in	1611	registered with libev, there is no efficient way to see that this is, in
1021	fact, a different file descriptor.	1612	fact, a different file descriptor.
1022		1613
…		…
1033		1624
1034	=head3 The special problem of dup'ed file descriptors	1625	=head3 The special problem of dup'ed file descriptors
1035		1626
1036	Some backends (e.g. epoll), cannot register events for file descriptors,	1627	Some backends (e.g. epoll), cannot register events for file descriptors,
1037	but only events for the underlying file descriptions. That means when you	1628	but only events for the underlying file descriptions. That means when you
1038	have C<dup ()>'ed file descriptors and register events for them, only one	1629	have C<dup ()>'ed file descriptors or weirder constellations, and register
1039	file descriptor might actually receive events.	1630	events for them, only one file descriptor might actually receive events.
1040		1631
1041	There is no workaround possible except not registering events	1632	There is no workaround possible except not registering events
1042	for potentially C<dup ()>'ed file descriptors, or to resort to	1633	for potentially C<dup ()>'ed file descriptors, or to resort to
1043	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1634	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1044		1635
		1636	=head3 The special problem of files
		1637
		1638	Many people try to use C<select> (or libev) on file descriptors
		1639	representing files, and expect it to become ready when their program
		1640	doesn't block on disk accesses (which can take a long time on their own).
		1641
		1642	However, this cannot ever work in the "expected" way - you get a readiness
		1643	notification as soon as the kernel knows whether and how much data is
		1644	there, and in the case of open files, that's always the case, so you
		1645	always get a readiness notification instantly, and your read (or possibly
		1646	write) will still block on the disk I/O.
		1647
		1648	Another way to view it is that in the case of sockets, pipes, character
		1649	devices and so on, there is another party (the sender) that delivers data
		1650	on its own, but in the case of files, there is no such thing: the disk
		1651	will not send data on its own, simply because it doesn't know what you
		1652	wish to read - you would first have to request some data.
		1653
		1654	Since files are typically not-so-well supported by advanced notification
		1655	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1656	to files, even though you should not use it. The reason for this is
		1657	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1658	usually a tty, often a pipe, but also sometimes files or special devices
		1659	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1660	F</dev/urandom>), and even though the file might better be served with
		1661	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1662	it "just works" instead of freezing.
		1663
		1664	So avoid file descriptors pointing to files when you know it (e.g. use
		1665	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1666	when you rarely read from a file instead of from a socket, and want to
		1667	reuse the same code path.
		1668
1045	=head3 The special problem of fork	1669	=head3 The special problem of fork
1046		1670
1047	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1671	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1048	useless behaviour. Libev fully supports fork, but needs to be told about	1672	useless behaviour. Libev fully supports fork, but needs to be told about
1049	it in the child.	1673	it in the child if you want to continue to use it in the child.
1050		1674
1051	To support fork in your programs, you either have to call	1675	To support fork in your child processes, you have to call C<ev_loop_fork
1052	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1676	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1053	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1677	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1054	C<EVBACKEND_POLL>.
1055		1678
		1679	=head3 The special problem of SIGPIPE
		1680
		1681	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1682	when writing to a pipe whose other end has been closed, your program gets
		1683	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1684	this is sensible behaviour, for daemons, this is usually undesirable.
		1685
		1686	So when you encounter spurious, unexplained daemon exits, make sure you
		1687	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1688	somewhere, as that would have given you a big clue).
		1689
		1690	=head3 The special problem of accept()ing when you can't
		1691
		1692	Many implementations of the POSIX C<accept> function (for example,
		1693	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1694	connection from the pending queue in all error cases.
		1695
		1696	For example, larger servers often run out of file descriptors (because
		1697	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1698	rejecting the connection, leading to libev signalling readiness on
		1699	the next iteration again (the connection still exists after all), and
		1700	typically causing the program to loop at 100% CPU usage.
		1701
		1702	Unfortunately, the set of errors that cause this issue differs between
		1703	operating systems, there is usually little the app can do to remedy the
		1704	situation, and no known thread-safe method of removing the connection to
		1705	cope with overload is known (to me).
		1706
		1707	One of the easiest ways to handle this situation is to just ignore it
		1708	- when the program encounters an overload, it will just loop until the
		1709	situation is over. While this is a form of busy waiting, no OS offers an
		1710	event-based way to handle this situation, so it's the best one can do.
		1711
		1712	A better way to handle the situation is to log any errors other than
		1713	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1714	messages, and continue as usual, which at least gives the user an idea of
		1715	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1716	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1717	usage.
		1718
		1719	If your program is single-threaded, then you could also keep a dummy file
		1720	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1721	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1722	close that fd, and create a new dummy fd. This will gracefully refuse
		1723	clients under typical overload conditions.
		1724
		1725	The last way to handle it is to simply log the error and C<exit>, as
		1726	is often done with C<malloc> failures, but this results in an easy
		1727	opportunity for a DoS attack.
1056		1728
1057	=head3 Watcher-Specific Functions	1729	=head3 Watcher-Specific Functions
1058		1730
1059	=over 4	1731	=over 4
1060		1732
1061	=item ev_io_init (ev_io *, callback, int fd, int events)	1733	=item ev_io_init (ev_io *, callback, int fd, int events)
1062		1734
1063	=item ev_io_set (ev_io *, int fd, int events)	1735	=item ev_io_set (ev_io *, int fd, int events)
1064		1736
1065	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1737	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1066	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1738	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1067	C<EV_READ | EV_WRITE> to receive the given events.	1739	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1068		1740
1069	=item int fd [read-only]	1741	=item int fd [read-only]
1070		1742
1071	The file descriptor being watched.	1743	The file descriptor being watched.
1072		1744
1073	=item int events [read-only]	1745	=item int events [read-only]
1074		1746
1075	The events being watched.	1747	The events being watched.
1076		1748
1077	=back	1749	=back
		1750
		1751	=head3 Examples
1078		1752
1079	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1753	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1080	readable, but only once. Since it is likely line-buffered, you could	1754	readable, but only once. Since it is likely line-buffered, you could
1081	attempt to read a whole line in the callback.	1755	attempt to read a whole line in the callback.
1082		1756
1083	static void	1757	static void
1084	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1758	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1085	{	1759	{
1086	ev_io_stop (loop, w);	1760	ev_io_stop (loop, w);
1087	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1761	.. read from stdin here (or from w->fd) and handle any I/O errors
1088	}	1762	}
1089		1763
1090	...	1764	...
1091	struct ev_loop *loop = ev_default_init (0);	1765	struct ev_loop *loop = ev_default_init (0);
1092	struct ev_io stdin_readable;	1766	ev_io stdin_readable;
1093	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1767	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1094	ev_io_start (loop, &stdin_readable);	1768	ev_io_start (loop, &stdin_readable);
1095	ev_loop (loop, 0);	1769	ev_run (loop, 0);
1096		1770
1097		1771
1098	=head2 C<ev_timer> - relative and optionally repeating timeouts	1772	=head2 C<ev_timer> - relative and optionally repeating timeouts
1099		1773
1100	Timer watchers are simple relative timers that generate an event after a	1774	Timer watchers are simple relative timers that generate an event after a
1101	given time, and optionally repeating in regular intervals after that.	1775	given time, and optionally repeating in regular intervals after that.
1102		1776
1103	The timers are based on real time, that is, if you register an event that	1777	The timers are based on real time, that is, if you register an event that
1104	times out after an hour and you reset your system clock to last years	1778	times out after an hour and you reset your system clock to January last
1105	time, it will still time out after (roughly) and hour. "Roughly" because	1779	year, it will still time out after (roughly) one hour. "Roughly" because
1106	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1780	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1107	monotonic clock option helps a lot here).	1781	monotonic clock option helps a lot here).
		1782
		1783	The callback is guaranteed to be invoked only I<after> its timeout has
		1784	passed (not I<at>, so on systems with very low-resolution clocks this
		1785	might introduce a small delay, see "the special problem of being too
		1786	early", below). If multiple timers become ready during the same loop
		1787	iteration then the ones with earlier time-out values are invoked before
		1788	ones of the same priority with later time-out values (but this is no
		1789	longer true when a callback calls C<ev_run> recursively).
		1790
		1791	=head3 Be smart about timeouts
		1792
		1793	Many real-world problems involve some kind of timeout, usually for error
		1794	recovery. A typical example is an HTTP request - if the other side hangs,
		1795	you want to raise some error after a while.
		1796
		1797	What follows are some ways to handle this problem, from obvious and
		1798	inefficient to smart and efficient.
		1799
		1800	In the following, a 60 second activity timeout is assumed - a timeout that
		1801	gets reset to 60 seconds each time there is activity (e.g. each time some
		1802	data or other life sign was received).
		1803
		1804	=over 4
		1805
		1806	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1807
		1808	This is the most obvious, but not the most simple way: In the beginning,
		1809	start the watcher:
		1810
		1811	ev_timer_init (timer, callback, 60., 0.);
		1812	ev_timer_start (loop, timer);
		1813
		1814	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1815	and start it again:
		1816
		1817	ev_timer_stop (loop, timer);
		1818	ev_timer_set (timer, 60., 0.);
		1819	ev_timer_start (loop, timer);
		1820
		1821	This is relatively simple to implement, but means that each time there is
		1822	some activity, libev will first have to remove the timer from its internal
		1823	data structure and then add it again. Libev tries to be fast, but it's
		1824	still not a constant-time operation.
		1825
		1826	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1827
		1828	This is the easiest way, and involves using C<ev_timer_again> instead of
		1829	C<ev_timer_start>.
		1830
		1831	To implement this, configure an C<ev_timer> with a C<repeat> value
		1832	of C<60> and then call C<ev_timer_again> at start and each time you
		1833	successfully read or write some data. If you go into an idle state where
		1834	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1835	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1836
		1837	That means you can ignore both the C<ev_timer_start> function and the
		1838	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1839	member and C<ev_timer_again>.
		1840
		1841	At start:
		1842
		1843	ev_init (timer, callback);
		1844	timer->repeat = 60.;
		1845	ev_timer_again (loop, timer);
		1846
		1847	Each time there is some activity:
		1848
		1849	ev_timer_again (loop, timer);
		1850
		1851	It is even possible to change the time-out on the fly, regardless of
		1852	whether the watcher is active or not:
		1853
		1854	timer->repeat = 30.;
		1855	ev_timer_again (loop, timer);
		1856
		1857	This is slightly more efficient then stopping/starting the timer each time
		1858	you want to modify its timeout value, as libev does not have to completely
		1859	remove and re-insert the timer from/into its internal data structure.
		1860
		1861	It is, however, even simpler than the "obvious" way to do it.
		1862
		1863	=item 3. Let the timer time out, but then re-arm it as required.
		1864
		1865	This method is more tricky, but usually most efficient: Most timeouts are
		1866	relatively long compared to the intervals between other activity - in
		1867	our example, within 60 seconds, there are usually many I/O events with
		1868	associated activity resets.
		1869
		1870	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1871	but remember the time of last activity, and check for a real timeout only
		1872	within the callback:
		1873
		1874	ev_tstamp timeout = 60.;
		1875	ev_tstamp last_activity; // time of last activity
		1876	ev_timer timer;
		1877
		1878	static void
		1879	callback (EV_P_ ev_timer *w, int revents)
		1880	{
		1881	// calculate when the timeout would happen
		1882	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1883
		1884	// if negative, it means we the timeout already occurred
		1885	if (after < 0.)
		1886	{
		1887	// timeout occurred, take action
		1888	}
		1889	else
		1890	{
		1891	// callback was invoked, but there was some recent
		1892	// activity. simply restart the timer to time out
		1893	// after "after" seconds, which is the earliest time
		1894	// the timeout can occur.
		1895	ev_timer_set (w, after, 0.);
		1896	ev_timer_start (EV_A_ w);
		1897	}
		1898	}
		1899
		1900	To summarise the callback: first calculate in how many seconds the
		1901	timeout will occur (by calculating the absolute time when it would occur,
		1902	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1903	(EV_A)> from that).
		1904
		1905	If this value is negative, then we are already past the timeout, i.e. we
		1906	timed out, and need to do whatever is needed in this case.
		1907
		1908	Otherwise, we now the earliest time at which the timeout would trigger,
		1909	and simply start the timer with this timeout value.
		1910
		1911	In other words, each time the callback is invoked it will check whether
		1912	the timeout occurred. If not, it will simply reschedule itself to check
		1913	again at the earliest time it could time out. Rinse. Repeat.
		1914
		1915	This scheme causes more callback invocations (about one every 60 seconds
		1916	minus half the average time between activity), but virtually no calls to
		1917	libev to change the timeout.
		1918
		1919	To start the machinery, simply initialise the watcher and set
		1920	C<last_activity> to the current time (meaning there was some activity just
		1921	now), then call the callback, which will "do the right thing" and start
		1922	the timer:
		1923
		1924	last_activity = ev_now (EV_A);
		1925	ev_init (&timer, callback);
		1926	callback (EV_A_ &timer, 0);
		1927
		1928	When there is some activity, simply store the current time in
		1929	C<last_activity>, no libev calls at all:
		1930
		1931	if (activity detected)
		1932	last_activity = ev_now (EV_A);
		1933
		1934	When your timeout value changes, then the timeout can be changed by simply
		1935	providing a new value, stopping the timer and calling the callback, which
		1936	will again do the right thing (for example, time out immediately :).
		1937
		1938	timeout = new_value;
		1939	ev_timer_stop (EV_A_ &timer);
		1940	callback (EV_A_ &timer, 0);
		1941
		1942	This technique is slightly more complex, but in most cases where the
		1943	time-out is unlikely to be triggered, much more efficient.
		1944
		1945	=item 4. Wee, just use a double-linked list for your timeouts.
		1946
		1947	If there is not one request, but many thousands (millions...), all
		1948	employing some kind of timeout with the same timeout value, then one can
		1949	do even better:
		1950
		1951	When starting the timeout, calculate the timeout value and put the timeout
		1952	at the I<end> of the list.
		1953
		1954	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1955	the list is expected to fire (for example, using the technique #3).
		1956
		1957	When there is some activity, remove the timer from the list, recalculate
		1958	the timeout, append it to the end of the list again, and make sure to
		1959	update the C<ev_timer> if it was taken from the beginning of the list.
		1960
		1961	This way, one can manage an unlimited number of timeouts in O(1) time for
		1962	starting, stopping and updating the timers, at the expense of a major
		1963	complication, and having to use a constant timeout. The constant timeout
		1964	ensures that the list stays sorted.
		1965
		1966	=back
		1967
		1968	So which method the best?
		1969
		1970	Method #2 is a simple no-brain-required solution that is adequate in most
		1971	situations. Method #3 requires a bit more thinking, but handles many cases
		1972	better, and isn't very complicated either. In most case, choosing either
		1973	one is fine, with #3 being better in typical situations.
		1974
		1975	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1976	rather complicated, but extremely efficient, something that really pays
		1977	off after the first million or so of active timers, i.e. it's usually
		1978	overkill :)
		1979
		1980	=head3 The special problem of being too early
		1981
		1982	If you ask a timer to call your callback after three seconds, then
		1983	you expect it to be invoked after three seconds - but of course, this
		1984	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1985	guaranteed to any precision by libev - imagine somebody suspending the
		1986	process with a STOP signal for a few hours for example.
		1987
		1988	So, libev tries to invoke your callback as soon as possible I<after> the
		1989	delay has occurred, but cannot guarantee this.
		1990
		1991	A less obvious failure mode is calling your callback too early: many event
		1992	loops compare timestamps with a "elapsed delay >= requested delay", but
		1993	this can cause your callback to be invoked much earlier than you would
		1994	expect.
		1995
		1996	To see why, imagine a system with a clock that only offers full second
		1997	resolution (think windows if you can't come up with a broken enough OS
		1998	yourself). If you schedule a one-second timer at the time 500.9, then the
		1999	event loop will schedule your timeout to elapse at a system time of 500
		2000	(500.9 truncated to the resolution) + 1, or 501.
		2001
		2002	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2003	501" and invoke the callback 0.1s after it was started, even though a
		2004	one-second delay was requested - this is being "too early", despite best
		2005	intentions.
		2006
		2007	This is the reason why libev will never invoke the callback if the elapsed
		2008	delay equals the requested delay, but only when the elapsed delay is
		2009	larger than the requested delay. In the example above, libev would only invoke
		2010	the callback at system time 502, or 1.1s after the timer was started.
		2011
		2012	So, while libev cannot guarantee that your callback will be invoked
		2013	exactly when requested, it I<can> and I<does> guarantee that the requested
		2014	delay has actually elapsed, or in other words, it always errs on the "too
		2015	late" side of things.
		2016
		2017	=head3 The special problem of time updates
		2018
		2019	Establishing the current time is a costly operation (it usually takes
		2020	at least one system call): EV therefore updates its idea of the current
		2021	time only before and after C<ev_run> collects new events, which causes a
		2022	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2023	lots of events in one iteration.
1108		2024
1109	The relative timeouts are calculated relative to the C<ev_now ()>	2025	The relative timeouts are calculated relative to the C<ev_now ()>
1110	time. This is usually the right thing as this timestamp refers to the time	2026	time. This is usually the right thing as this timestamp refers to the time
1111	of the event triggering whatever timeout you are modifying/starting. If	2027	of the event triggering whatever timeout you are modifying/starting. If
1112	you suspect event processing to be delayed and you I<need> to base the timeout	2028	you suspect event processing to be delayed and you I<need> to base the
1113	on the current time, use something like this to adjust for this:	2029	timeout on the current time, use something like this to adjust for this:
1114		2030
1115	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2031	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1116		2032
1117	The callback is guarenteed to be invoked only when its timeout has passed,	2033	If the event loop is suspended for a long time, you can also force an
1118	but if multiple timers become ready during the same loop iteration then	2034	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1119	order of execution is undefined.	2035	()>.
		2036
		2037	=head3 The special problem of unsynchronised clocks
		2038
		2039	Modern systems have a variety of clocks - libev itself uses the normal
		2040	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2041	jumps).
		2042
		2043	Neither of these clocks is synchronised with each other or any other clock
		2044	on the system, so C<ev_time ()> might return a considerably different time
		2045	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2046	a call to C<gettimeofday> might return a second count that is one higher
		2047	than a directly following call to C<time>.
		2048
		2049	The moral of this is to only compare libev-related timestamps with
		2050	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2051	a second or so.
		2052
		2053	One more problem arises due to this lack of synchronisation: if libev uses
		2054	the system monotonic clock and you compare timestamps from C<ev_time>
		2055	or C<ev_now> from when you started your timer and when your callback is
		2056	invoked, you will find that sometimes the callback is a bit "early".
		2057
		2058	This is because C<ev_timer>s work in real time, not wall clock time, so
		2059	libev makes sure your callback is not invoked before the delay happened,
		2060	I<measured according to the real time>, not the system clock.
		2061
		2062	If your timeouts are based on a physical timescale (e.g. "time out this
		2063	connection after 100 seconds") then this shouldn't bother you as it is
		2064	exactly the right behaviour.
		2065
		2066	If you want to compare wall clock/system timestamps to your timers, then
		2067	you need to use C<ev_periodic>s, as these are based on the wall clock
		2068	time, where your comparisons will always generate correct results.
		2069
		2070	=head3 The special problems of suspended animation
		2071
		2072	When you leave the server world it is quite customary to hit machines that
		2073	can suspend/hibernate - what happens to the clocks during such a suspend?
		2074
		2075	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2076	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2077	to run until the system is suspended, but they will not advance while the
		2078	system is suspended. That means, on resume, it will be as if the program
		2079	was frozen for a few seconds, but the suspend time will not be counted
		2080	towards C<ev_timer> when a monotonic clock source is used. The real time
		2081	clock advanced as expected, but if it is used as sole clocksource, then a
		2082	long suspend would be detected as a time jump by libev, and timers would
		2083	be adjusted accordingly.
		2084
		2085	I would not be surprised to see different behaviour in different between
		2086	operating systems, OS versions or even different hardware.
		2087
		2088	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2089	time jump in the monotonic clocks and the realtime clock. If the program
		2090	is suspended for a very long time, and monotonic clock sources are in use,
		2091	then you can expect C<ev_timer>s to expire as the full suspension time
		2092	will be counted towards the timers. When no monotonic clock source is in
		2093	use, then libev will again assume a timejump and adjust accordingly.
		2094
		2095	It might be beneficial for this latter case to call C<ev_suspend>
		2096	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2097	deterministic behaviour in this case (you can do nothing against
		2098	C<SIGSTOP>).
1120		2099
1121	=head3 Watcher-Specific Functions and Data Members	2100	=head3 Watcher-Specific Functions and Data Members
1122		2101
1123	=over 4	2102	=over 4
1124		2103
1125	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2104	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1126		2105
1127	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2106	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1128		2107
1129	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2108	Configure the timer to trigger after C<after> seconds. If C<repeat>
1130	C<0.>, then it will automatically be stopped. If it is positive, then the	2109	is C<0.>, then it will automatically be stopped once the timeout is
1131	timer will automatically be configured to trigger again C<repeat> seconds	2110	reached. If it is positive, then the timer will automatically be
1132	later, again, and again, until stopped manually.	2111	configured to trigger again C<repeat> seconds later, again, and again,
		2112	until stopped manually.
1133		2113
1134	The timer itself will do a best-effort at avoiding drift, that is, if you	2114	The timer itself will do a best-effort at avoiding drift, that is, if
1135	configure a timer to trigger every 10 seconds, then it will trigger at	2115	you configure a timer to trigger every 10 seconds, then it will normally
1136	exactly 10 second intervals. If, however, your program cannot keep up with	2116	trigger at exactly 10 second intervals. If, however, your program cannot
1137	the timer (because it takes longer than those 10 seconds to do stuff) the	2117	keep up with the timer (because it takes longer than those 10 seconds to
1138	timer will not fire more than once per event loop iteration.	2118	do stuff) the timer will not fire more than once per event loop iteration.
1139		2119
1140	=item ev_timer_again (loop)	2120	=item ev_timer_again (loop, ev_timer *)
1141		2121
1142	This will act as if the timer timed out and restart it again if it is	2122	This will act as if the timer timed out, and restarts it again if it is
1143	repeating. The exact semantics are:	2123	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2124	timeout to the C<repeat> value and calling C<ev_timer_start>.
1144		2125
		2126	The exact semantics are as in the following rules, all of which will be
		2127	applied to the watcher:
		2128
		2129	=over 4
		2130
1145	If the timer is pending, its pending status is cleared.	2131	=item If the timer is pending, the pending status is always cleared.
1146		2132
1147	If the timer is started but nonrepeating, stop it (as if it timed out).	2133	=item If the timer is started but non-repeating, stop it (as if it timed
		2134	out, without invoking it).
1148		2135
1149	If the timer is repeating, either start it if necessary (with the	2136	=item If the timer is repeating, make the C<repeat> value the new timeout
1150	C<repeat> value), or reset the running timer to the C<repeat> value.	2137	and start the timer, if necessary.
1151		2138
1152	This sounds a bit complicated, but here is a useful and typical	2139	=back
1153	example: Imagine you have a tcp connection and you want a so-called idle
1154	timeout, that is, you want to be called when there have been, say, 60
1155	seconds of inactivity on the socket. The easiest way to do this is to
1156	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1157	C<ev_timer_again> each time you successfully read or write some data. If
1158	you go into an idle state where you do not expect data to travel on the
1159	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1160	automatically restart it if need be.
1161		2140
1162	That means you can ignore the C<after> value and C<ev_timer_start>	2141	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1163	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2142	usage example.
1164		2143
1165	ev_timer_init (timer, callback, 0., 5.);	2144	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1166	ev_timer_again (loop, timer);
1167	...
1168	timer->again = 17.;
1169	ev_timer_again (loop, timer);
1170	...
1171	timer->again = 10.;
1172	ev_timer_again (loop, timer);
1173		2145
1174	This is more slightly efficient then stopping/starting the timer each time	2146	Returns the remaining time until a timer fires. If the timer is active,
1175	you want to modify its timeout value.	2147	then this time is relative to the current event loop time, otherwise it's
		2148	the timeout value currently configured.
		2149
		2150	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2151	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2152	will return C<4>. When the timer expires and is restarted, it will return
		2153	roughly C<7> (likely slightly less as callback invocation takes some time,
		2154	too), and so on.
1176		2155
1177	=item ev_tstamp repeat [read-write]	2156	=item ev_tstamp repeat [read-write]
1178		2157
1179	The current C<repeat> value. Will be used each time the watcher times out	2158	The current C<repeat> value. Will be used each time the watcher times out
1180	or C<ev_timer_again> is called and determines the next timeout (if any),	2159	or C<ev_timer_again> is called, and determines the next timeout (if any),
1181	which is also when any modifications are taken into account.	2160	which is also when any modifications are taken into account.
1182		2161
1183	=back	2162	=back
1184		2163
		2164	=head3 Examples
		2165
1185	Example: Create a timer that fires after 60 seconds.	2166	Example: Create a timer that fires after 60 seconds.
1186		2167
1187	static void	2168	static void
1188	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2169	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1189	{	2170	{
1190	.. one minute over, w is actually stopped right here	2171	.. one minute over, w is actually stopped right here
1191	}	2172	}
1192		2173
1193	struct ev_timer mytimer;	2174	ev_timer mytimer;
1194	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2175	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1195	ev_timer_start (loop, &mytimer);	2176	ev_timer_start (loop, &mytimer);
1196		2177
1197	Example: Create a timeout timer that times out after 10 seconds of	2178	Example: Create a timeout timer that times out after 10 seconds of
1198	inactivity.	2179	inactivity.
1199		2180
1200	static void	2181	static void
1201	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2182	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1202	{	2183	{
1203	.. ten seconds without any activity	2184	.. ten seconds without any activity
1204	}	2185	}
1205		2186
1206	struct ev_timer mytimer;	2187	ev_timer mytimer;
1207	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2188	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1208	ev_timer_again (&mytimer); /* start timer */	2189	ev_timer_again (&mytimer); /* start timer */
1209	ev_loop (loop, 0);	2190	ev_run (loop, 0);
1210		2191
1211	// and in some piece of code that gets executed on any "activity":	2192	// and in some piece of code that gets executed on any "activity":
1212	// reset the timeout to start ticking again at 10 seconds	2193	// reset the timeout to start ticking again at 10 seconds
1213	ev_timer_again (&mytimer);	2194	ev_timer_again (&mytimer);
1214		2195
1215		2196
1216	=head2 C<ev_periodic> - to cron or not to cron?	2197	=head2 C<ev_periodic> - to cron or not to cron?
1217		2198
1218	Periodic watchers are also timers of a kind, but they are very versatile	2199	Periodic watchers are also timers of a kind, but they are very versatile
1219	(and unfortunately a bit complex).	2200	(and unfortunately a bit complex).
1220		2201
1221	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2202	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1222	but on wallclock time (absolute time). You can tell a periodic watcher	2203	relative time, the physical time that passes) but on wall clock time
1223	to trigger "at" some specific point in time. For example, if you tell a	2204	(absolute time, the thing you can read on your calender or clock). The
1224	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2205	difference is that wall clock time can run faster or slower than real
1225	+ 10.>) and then reset your system clock to the last year, then it will	2206	time, and time jumps are not uncommon (e.g. when you adjust your
1226	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2207	wrist-watch).
1227	roughly 10 seconds later).
1228		2208
1229	They can also be used to implement vastly more complex timers, such as	2209	You can tell a periodic watcher to trigger after some specific point
1230	triggering an event on each midnight, local time or other, complicated,	2210	in time: for example, if you tell a periodic watcher to trigger "in 10
1231	rules.	2211	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2212	not a delay) and then reset your system clock to January of the previous
		2213	year, then it will take a year or more to trigger the event (unlike an
		2214	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2215	it, as it uses a relative timeout).
1232		2216
		2217	C<ev_periodic> watchers can also be used to implement vastly more complex
		2218	timers, such as triggering an event on each "midnight, local time", or
		2219	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2220	those cannot react to time jumps.
		2221
1233	As with timers, the callback is guarenteed to be invoked only when the	2222	As with timers, the callback is guaranteed to be invoked only when the
1234	time (C<at>) has been passed, but if multiple periodic timers become ready	2223	point in time where it is supposed to trigger has passed. If multiple
1235	during the same loop iteration then order of execution is undefined.	2224	timers become ready during the same loop iteration then the ones with
		2225	earlier time-out values are invoked before ones with later time-out values
		2226	(but this is no longer true when a callback calls C<ev_run> recursively).
1236		2227
1237	=head3 Watcher-Specific Functions and Data Members	2228	=head3 Watcher-Specific Functions and Data Members
1238		2229
1239	=over 4	2230	=over 4
1240		2231
1241	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2232	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1242		2233
1243	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2234	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1244		2235
1245	Lots of arguments, lets sort it out... There are basically three modes of	2236	Lots of arguments, let's sort it out... There are basically three modes of
1246	operation, and we will explain them from simplest to complex:	2237	operation, and we will explain them from simplest to most complex:
1247		2238
1248	=over 4	2239	=over 4
1249		2240
1250	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2241	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1251		2242
1252	In this configuration the watcher triggers an event at the wallclock time	2243	In this configuration the watcher triggers an event after the wall clock
1253	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2244	time C<offset> has passed. It will not repeat and will not adjust when a
1254	that is, if it is to be run at January 1st 2011 then it will run when the	2245	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1255	system time reaches or surpasses this time.	2246	will be stopped and invoked when the system clock reaches or surpasses
		2247	this point in time.
1256		2248
1257	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2249	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1258		2250
1259	In this mode the watcher will always be scheduled to time out at the next	2251	In this mode the watcher will always be scheduled to time out at the next
1260	C<at + N * interval> time (for some integer N, which can also be negative)	2252	C<offset + N * interval> time (for some integer N, which can also be
1261	and then repeat, regardless of any time jumps.	2253	negative) and then repeat, regardless of any time jumps. The C<offset>
		2254	argument is merely an offset into the C<interval> periods.
1262		2255
1263	This can be used to create timers that do not drift with respect to system	2256	This can be used to create timers that do not drift with respect to the
1264	time:	2257	system clock, for example, here is an C<ev_periodic> that triggers each
		2258	hour, on the hour (with respect to UTC):
1265		2259
1266	ev_periodic_set (&periodic, 0., 3600., 0);	2260	ev_periodic_set (&periodic, 0., 3600., 0);
1267		2261
1268	This doesn't mean there will always be 3600 seconds in between triggers,	2262	This doesn't mean there will always be 3600 seconds in between triggers,
1269	but only that the the callback will be called when the system time shows a	2263	but only that the callback will be called when the system time shows a
1270	full hour (UTC), or more correctly, when the system time is evenly divisible	2264	full hour (UTC), or more correctly, when the system time is evenly divisible
1271	by 3600.	2265	by 3600.
1272		2266
1273	Another way to think about it (for the mathematically inclined) is that	2267	Another way to think about it (for the mathematically inclined) is that
1274	C<ev_periodic> will try to run the callback in this mode at the next possible	2268	C<ev_periodic> will try to run the callback in this mode at the next possible
1275	time where C<time = at (mod interval)>, regardless of any time jumps.	2269	time where C<time = offset (mod interval)>, regardless of any time jumps.
1276		2270
1277	For numerical stability it is preferable that the C<at> value is near	2271	The C<interval> I<MUST> be positive, and for numerical stability, the
1278	C<ev_now ()> (the current time), but there is no range requirement for	2272	interval value should be higher than C<1/8192> (which is around 100
1279	this value.	2273	microseconds) and C<offset> should be higher than C<0> and should have
		2274	at most a similar magnitude as the current time (say, within a factor of
		2275	ten). Typical values for offset are, in fact, C<0> or something between
		2276	C<0> and C<interval>, which is also the recommended range.
1280		2277
		2278	Note also that there is an upper limit to how often a timer can fire (CPU
		2279	speed for example), so if C<interval> is very small then timing stability
		2280	will of course deteriorate. Libev itself tries to be exact to be about one
		2281	millisecond (if the OS supports it and the machine is fast enough).
		2282
1281	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2283	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1282		2284
1283	In this mode the values for C<interval> and C<at> are both being	2285	In this mode the values for C<interval> and C<offset> are both being
1284	ignored. Instead, each time the periodic watcher gets scheduled, the	2286	ignored. Instead, each time the periodic watcher gets scheduled, the
1285	reschedule callback will be called with the watcher as first, and the	2287	reschedule callback will be called with the watcher as first, and the
1286	current time as second argument.	2288	current time as second argument.
1287		2289
1288	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2290	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1289	ever, or make any event loop modifications>. If you need to stop it,	2291	or make ANY other event loop modifications whatsoever, unless explicitly
1290	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2292	allowed by documentation here>.
1291	starting an C<ev_prepare> watcher, which is legal).
1292		2293
		2294	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2295	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2296	only event loop modification you are allowed to do).
		2297
1293	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2298	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1294	ev_tstamp now)>, e.g.:	2299	*w, ev_tstamp now)>, e.g.:
1295		2300
		2301	static ev_tstamp
1296	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2302	my_rescheduler (ev_periodic *w, ev_tstamp now)
1297	{	2303	{
1298	return now + 60.;	2304	return now + 60.;
1299	}	2305	}
1300		2306
1301	It must return the next time to trigger, based on the passed time value	2307	It must return the next time to trigger, based on the passed time value
1302	(that is, the lowest time value larger than to the second argument). It	2308	(that is, the lowest time value larger than to the second argument). It
1303	will usually be called just before the callback will be triggered, but	2309	will usually be called just before the callback will be triggered, but
1304	might be called at other times, too.	2310	might be called at other times, too.
1305		2311
1306	NOTE: I<< This callback must always return a time that is later than the	2312	NOTE: I<< This callback must always return a time that is higher than or
1307	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2313	equal to the passed C<now> value >>.
1308		2314
1309	This can be used to create very complex timers, such as a timer that	2315	This can be used to create very complex timers, such as a timer that
1310	triggers on each midnight, local time. To do this, you would calculate the	2316	triggers on "next midnight, local time". To do this, you would calculate the
1311	next midnight after C<now> and return the timestamp value for this. How	2317	next midnight after C<now> and return the timestamp value for this. How
1312	you do this is, again, up to you (but it is not trivial, which is the main	2318	you do this is, again, up to you (but it is not trivial, which is the main
1313	reason I omitted it as an example).	2319	reason I omitted it as an example).
1314		2320
1315	=back	2321	=back
…		…
1319	Simply stops and restarts the periodic watcher again. This is only useful	2325	Simply stops and restarts the periodic watcher again. This is only useful
1320	when you changed some parameters or the reschedule callback would return	2326	when you changed some parameters or the reschedule callback would return
1321	a different time than the last time it was called (e.g. in a crond like	2327	a different time than the last time it was called (e.g. in a crond like
1322	program when the crontabs have changed).	2328	program when the crontabs have changed).
1323		2329
		2330	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2331
		2332	When active, returns the absolute time that the watcher is supposed
		2333	to trigger next. This is not the same as the C<offset> argument to
		2334	C<ev_periodic_set>, but indeed works even in interval and manual
		2335	rescheduling modes.
		2336
1324	=item ev_tstamp offset [read-write]	2337	=item ev_tstamp offset [read-write]
1325		2338
1326	When repeating, this contains the offset value, otherwise this is the	2339	When repeating, this contains the offset value, otherwise this is the
1327	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2340	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2341	although libev might modify this value for better numerical stability).
1328		2342
1329	Can be modified any time, but changes only take effect when the periodic	2343	Can be modified any time, but changes only take effect when the periodic
1330	timer fires or C<ev_periodic_again> is being called.	2344	timer fires or C<ev_periodic_again> is being called.
1331		2345
1332	=item ev_tstamp interval [read-write]	2346	=item ev_tstamp interval [read-write]
1333		2347
1334	The current interval value. Can be modified any time, but changes only	2348	The current interval value. Can be modified any time, but changes only
1335	take effect when the periodic timer fires or C<ev_periodic_again> is being	2349	take effect when the periodic timer fires or C<ev_periodic_again> is being
1336	called.	2350	called.
1337		2351
1338	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2352	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1339		2353
1340	The current reschedule callback, or C<0>, if this functionality is	2354	The current reschedule callback, or C<0>, if this functionality is
1341	switched off. Can be changed any time, but changes only take effect when	2355	switched off. Can be changed any time, but changes only take effect when
1342	the periodic timer fires or C<ev_periodic_again> is being called.	2356	the periodic timer fires or C<ev_periodic_again> is being called.
1343		2357
1344	=item ev_tstamp at [read-only]
1345
1346	When active, contains the absolute time that the watcher is supposed to
1347	trigger next.
1348
1349	=back	2358	=back
1350		2359
		2360	=head3 Examples
		2361
1351	Example: Call a callback every hour, or, more precisely, whenever the	2362	Example: Call a callback every hour, or, more precisely, whenever the
1352	system clock is divisible by 3600. The callback invocation times have	2363	system time is divisible by 3600. The callback invocation times have
1353	potentially a lot of jittering, but good long-term stability.	2364	potentially a lot of jitter, but good long-term stability.
1354		2365
1355	static void	2366	static void
1356	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2367	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1357	{	2368	{
1358	... its now a full hour (UTC, or TAI or whatever your clock follows)	2369	... its now a full hour (UTC, or TAI or whatever your clock follows)
1359	}	2370	}
1360		2371
1361	struct ev_periodic hourly_tick;	2372	ev_periodic hourly_tick;
1362	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2373	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1363	ev_periodic_start (loop, &hourly_tick);	2374	ev_periodic_start (loop, &hourly_tick);
1364		2375
1365	Example: The same as above, but use a reschedule callback to do it:	2376	Example: The same as above, but use a reschedule callback to do it:
1366		2377
1367	#include <math.h>	2378	#include <math.h>
1368		2379
1369	static ev_tstamp	2380	static ev_tstamp
1370	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2381	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1371	{	2382	{
1372	return fmod (now, 3600.) + 3600.;	2383	return now + (3600. - fmod (now, 3600.));
1373	}	2384	}
1374		2385
1375	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2386	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1376		2387
1377	Example: Call a callback every hour, starting now:	2388	Example: Call a callback every hour, starting now:
1378		2389
1379	struct ev_periodic hourly_tick;	2390	ev_periodic hourly_tick;
1380	ev_periodic_init (&hourly_tick, clock_cb,	2391	ev_periodic_init (&hourly_tick, clock_cb,
1381	fmod (ev_now (loop), 3600.), 3600., 0);	2392	fmod (ev_now (loop), 3600.), 3600., 0);
1382	ev_periodic_start (loop, &hourly_tick);	2393	ev_periodic_start (loop, &hourly_tick);
1383		2394
1384		2395
1385	=head2 C<ev_signal> - signal me when a signal gets signalled!	2396	=head2 C<ev_signal> - signal me when a signal gets signalled!
1386		2397
1387	Signal watchers will trigger an event when the process receives a specific	2398	Signal watchers will trigger an event when the process receives a specific
1388	signal one or more times. Even though signals are very asynchronous, libev	2399	signal one or more times. Even though signals are very asynchronous, libev
1389	will try it's best to deliver signals synchronously, i.e. as part of the	2400	will try its best to deliver signals synchronously, i.e. as part of the
1390	normal event processing, like any other event.	2401	normal event processing, like any other event.
1391		2402
		2403	If you want signals to be delivered truly asynchronously, just use
		2404	C<sigaction> as you would do without libev and forget about sharing
		2405	the signal. You can even use C<ev_async> from a signal handler to
		2406	synchronously wake up an event loop.
		2407
1392	You can configure as many watchers as you like per signal. Only when the	2408	You can configure as many watchers as you like for the same signal, but
		2409	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2410	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2411	C<SIGINT> in both the default loop and another loop at the same time. At
		2412	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2413
1393	first watcher gets started will libev actually register a signal watcher	2414	When the first watcher gets started will libev actually register something
1394	with the kernel (thus it coexists with your own signal handlers as long	2415	with the kernel (thus it coexists with your own signal handlers as long as
1395	as you don't register any with libev). Similarly, when the last signal	2416	you don't register any with libev for the same signal).
1396	watcher for a signal is stopped libev will reset the signal handler to	2417
1397	SIG_DFL (regardless of what it was set to before).	2418	If possible and supported, libev will install its handlers with
		2419	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2420	not be unduly interrupted. If you have a problem with system calls getting
		2421	interrupted by signals you can block all signals in an C<ev_check> watcher
		2422	and unblock them in an C<ev_prepare> watcher.
		2423
		2424	=head3 The special problem of inheritance over fork/execve/pthread_create
		2425
		2426	Both the signal mask (C<sigprocmask>) and the signal disposition
		2427	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2428	stopping it again), that is, libev might or might not block the signal,
		2429	and might or might not set or restore the installed signal handler (but
		2430	see C<EVFLAG_NOSIGMASK>).
		2431
		2432	While this does not matter for the signal disposition (libev never
		2433	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2434	C<execve>), this matters for the signal mask: many programs do not expect
		2435	certain signals to be blocked.
		2436
		2437	This means that before calling C<exec> (from the child) you should reset
		2438	the signal mask to whatever "default" you expect (all clear is a good
		2439	choice usually).
		2440
		2441	The simplest way to ensure that the signal mask is reset in the child is
		2442	to install a fork handler with C<pthread_atfork> that resets it. That will
		2443	catch fork calls done by libraries (such as the libc) as well.
		2444
		2445	In current versions of libev, the signal will not be blocked indefinitely
		2446	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2447	the window of opportunity for problems, it will not go away, as libev
		2448	I<has> to modify the signal mask, at least temporarily.
		2449
		2450	So I can't stress this enough: I<If you do not reset your signal mask when
		2451	you expect it to be empty, you have a race condition in your code>. This
		2452	is not a libev-specific thing, this is true for most event libraries.
		2453
		2454	=head3 The special problem of threads signal handling
		2455
		2456	POSIX threads has problematic signal handling semantics, specifically,
		2457	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2458	threads in a process block signals, which is hard to achieve.
		2459
		2460	When you want to use sigwait (or mix libev signal handling with your own
		2461	for the same signals), you can tackle this problem by globally blocking
		2462	all signals before creating any threads (or creating them with a fully set
		2463	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2464	loops. Then designate one thread as "signal receiver thread" which handles
		2465	these signals. You can pass on any signals that libev might be interested
		2466	in by calling C<ev_feed_signal>.
1398		2467
1399	=head3 Watcher-Specific Functions and Data Members	2468	=head3 Watcher-Specific Functions and Data Members
1400		2469
1401	=over 4	2470	=over 4
1402		2471
…		…
1411		2480
1412	The signal the watcher watches out for.	2481	The signal the watcher watches out for.
1413		2482
1414	=back	2483	=back
1415		2484
		2485	=head3 Examples
		2486
		2487	Example: Try to exit cleanly on SIGINT.
		2488
		2489	static void
		2490	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2491	{
		2492	ev_break (loop, EVBREAK_ALL);
		2493	}
		2494
		2495	ev_signal signal_watcher;
		2496	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2497	ev_signal_start (loop, &signal_watcher);
		2498
1416		2499
1417	=head2 C<ev_child> - watch out for process status changes	2500	=head2 C<ev_child> - watch out for process status changes
1418		2501
1419	Child watchers trigger when your process receives a SIGCHLD in response to	2502	Child watchers trigger when your process receives a SIGCHLD in response to
1420	some child status changes (most typically when a child of yours dies).	2503	some child status changes (most typically when a child of yours dies or
		2504	exits). It is permissible to install a child watcher I<after> the child
		2505	has been forked (which implies it might have already exited), as long
		2506	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2507	forking and then immediately registering a watcher for the child is fine,
		2508	but forking and registering a watcher a few event loop iterations later or
		2509	in the next callback invocation is not.
		2510
		2511	Only the default event loop is capable of handling signals, and therefore
		2512	you can only register child watchers in the default event loop.
		2513
		2514	Due to some design glitches inside libev, child watchers will always be
		2515	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2516	libev)
		2517
		2518	=head3 Process Interaction
		2519
		2520	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2521	initialised. This is necessary to guarantee proper behaviour even if the
		2522	first child watcher is started after the child exits. The occurrence
		2523	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2524	synchronously as part of the event loop processing. Libev always reaps all
		2525	children, even ones not watched.
		2526
		2527	=head3 Overriding the Built-In Processing
		2528
		2529	Libev offers no special support for overriding the built-in child
		2530	processing, but if your application collides with libev's default child
		2531	handler, you can override it easily by installing your own handler for
		2532	C<SIGCHLD> after initialising the default loop, and making sure the
		2533	default loop never gets destroyed. You are encouraged, however, to use an
		2534	event-based approach to child reaping and thus use libev's support for
		2535	that, so other libev users can use C<ev_child> watchers freely.
		2536
		2537	=head3 Stopping the Child Watcher
		2538
		2539	Currently, the child watcher never gets stopped, even when the
		2540	child terminates, so normally one needs to stop the watcher in the
		2541	callback. Future versions of libev might stop the watcher automatically
		2542	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2543	problem).
1421		2544
1422	=head3 Watcher-Specific Functions and Data Members	2545	=head3 Watcher-Specific Functions and Data Members
1423		2546
1424	=over 4	2547	=over 4
1425		2548
1426	=item ev_child_init (ev_child *, callback, int pid)	2549	=item ev_child_init (ev_child *, callback, int pid, int trace)
1427		2550
1428	=item ev_child_set (ev_child *, int pid)	2551	=item ev_child_set (ev_child *, int pid, int trace)
1429		2552
1430	Configures the watcher to wait for status changes of process C<pid> (or	2553	Configures the watcher to wait for status changes of process C<pid> (or
1431	I<any> process if C<pid> is specified as C<0>). The callback can look	2554	I<any> process if C<pid> is specified as C<0>). The callback can look
1432	at the C<rstatus> member of the C<ev_child> watcher structure to see	2555	at the C<rstatus> member of the C<ev_child> watcher structure to see
1433	the status word (use the macros from C<sys/wait.h> and see your systems	2556	the status word (use the macros from C<sys/wait.h> and see your systems
1434	C<waitpid> documentation). The C<rpid> member contains the pid of the	2557	C<waitpid> documentation). The C<rpid> member contains the pid of the
1435	process causing the status change.	2558	process causing the status change. C<trace> must be either C<0> (only
		2559	activate the watcher when the process terminates) or C<1> (additionally
		2560	activate the watcher when the process is stopped or continued).
1436		2561
1437	=item int pid [read-only]	2562	=item int pid [read-only]
1438		2563
1439	The process id this watcher watches out for, or C<0>, meaning any process id.	2564	The process id this watcher watches out for, or C<0>, meaning any process id.
1440		2565
…		…
1447	The process exit/trace status caused by C<rpid> (see your systems	2572	The process exit/trace status caused by C<rpid> (see your systems
1448	C<waitpid> and C<sys/wait.h> documentation for details).	2573	C<waitpid> and C<sys/wait.h> documentation for details).
1449		2574
1450	=back	2575	=back
1451		2576
1452	Example: Try to exit cleanly on SIGINT and SIGTERM.	2577	=head3 Examples
1453		2578
		2579	Example: C<fork()> a new process and install a child handler to wait for
		2580	its completion.
		2581
		2582	ev_child cw;
		2583
1454	static void	2584	static void
1455	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2585	child_cb (EV_P_ ev_child *w, int revents)
1456	{	2586	{
1457	ev_unloop (loop, EVUNLOOP_ALL);	2587	ev_child_stop (EV_A_ w);
		2588	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1458	}	2589	}
1459		2590
1460	struct ev_signal signal_watcher;	2591	pid_t pid = fork ();
1461	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2592
1462	ev_signal_start (loop, &sigint_cb);	2593	if (pid < 0)
		2594	// error
		2595	else if (pid == 0)
		2596	{
		2597	// the forked child executes here
		2598	exit (1);
		2599	}
		2600	else
		2601	{
		2602	ev_child_init (&cw, child_cb, pid, 0);
		2603	ev_child_start (EV_DEFAULT_ &cw);
		2604	}
1463		2605
1464		2606
1465	=head2 C<ev_stat> - did the file attributes just change?	2607	=head2 C<ev_stat> - did the file attributes just change?
1466		2608
1467	This watches a filesystem path for attribute changes. That is, it calls	2609	This watches a file system path for attribute changes. That is, it calls
1468	C<stat> regularly (or when the OS says it changed) and sees if it changed	2610	C<stat> on that path in regular intervals (or when the OS says it changed)
1469	compared to the last time, invoking the callback if it did.	2611	and sees if it changed compared to the last time, invoking the callback if
		2612	it did.
1470		2613
1471	The path does not need to exist: changing from "path exists" to "path does	2614	The path does not need to exist: changing from "path exists" to "path does
1472	not exist" is a status change like any other. The condition "path does	2615	not exist" is a status change like any other. The condition "path does not
1473	not exist" is signified by the C<st_nlink> field being zero (which is	2616	exist" (or more correctly "path cannot be stat'ed") is signified by the
1474	otherwise always forced to be at least one) and all the other fields of	2617	C<st_nlink> field being zero (which is otherwise always forced to be at
1475	the stat buffer having unspecified contents.	2618	least one) and all the other fields of the stat buffer having unspecified
		2619	contents.
1476		2620
1477	The path I<should> be absolute and I<must not> end in a slash. If it is	2621	The path I<must not> end in a slash or contain special components such as
		2622	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1478	relative and your working directory changes, the behaviour is undefined.	2623	your working directory changes, then the behaviour is undefined.
1479		2624
1480	Since there is no standard to do this, the portable implementation simply	2625	Since there is no portable change notification interface available, the
1481	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2626	portable implementation simply calls C<stat(2)> regularly on the path
1482	can specify a recommended polling interval for this case. If you specify	2627	to see if it changed somehow. You can specify a recommended polling
1483	a polling interval of C<0> (highly recommended!) then a I<suitable,	2628	interval for this case. If you specify a polling interval of C<0> (highly
1484	unspecified default> value will be used (which you can expect to be around	2629	recommended!) then a I<suitable, unspecified default> value will be used
1485	five seconds, although this might change dynamically). Libev will also	2630	(which you can expect to be around five seconds, although this might
1486	impose a minimum interval which is currently around C<0.1>, but thats	2631	change dynamically). Libev will also impose a minimum interval which is
1487	usually overkill.	2632	currently around C<0.1>, but that's usually overkill.
1488		2633
1489	This watcher type is not meant for massive numbers of stat watchers,	2634	This watcher type is not meant for massive numbers of stat watchers,
1490	as even with OS-supported change notifications, this can be	2635	as even with OS-supported change notifications, this can be
1491	resource-intensive.	2636	resource-intensive.
1492		2637
1493	At the time of this writing, only the Linux inotify interface is	2638	At the time of this writing, the only OS-specific interface implemented
1494	implemented (implementing kqueue support is left as an exercise for the	2639	is the Linux inotify interface (implementing kqueue support is left as an
1495	reader). Inotify will be used to give hints only and should not change the	2640	exercise for the reader. Note, however, that the author sees no way of
1496	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2641	implementing C<ev_stat> semantics with kqueue, except as a hint).
1497	to fall back to regular polling again even with inotify, but changes are	2642
1498	usually detected immediately, and if the file exists there will be no	2643	=head3 ABI Issues (Largefile Support)
1499	polling.	2644
		2645	Libev by default (unless the user overrides this) uses the default
		2646	compilation environment, which means that on systems with large file
		2647	support disabled by default, you get the 32 bit version of the stat
		2648	structure. When using the library from programs that change the ABI to
		2649	use 64 bit file offsets the programs will fail. In that case you have to
		2650	compile libev with the same flags to get binary compatibility. This is
		2651	obviously the case with any flags that change the ABI, but the problem is
		2652	most noticeably displayed with ev_stat and large file support.
		2653
		2654	The solution for this is to lobby your distribution maker to make large
		2655	file interfaces available by default (as e.g. FreeBSD does) and not
		2656	optional. Libev cannot simply switch on large file support because it has
		2657	to exchange stat structures with application programs compiled using the
		2658	default compilation environment.
		2659
		2660	=head3 Inotify and Kqueue
		2661
		2662	When C<inotify (7)> support has been compiled into libev and present at
		2663	runtime, it will be used to speed up change detection where possible. The
		2664	inotify descriptor will be created lazily when the first C<ev_stat>
		2665	watcher is being started.
		2666
		2667	Inotify presence does not change the semantics of C<ev_stat> watchers
		2668	except that changes might be detected earlier, and in some cases, to avoid
		2669	making regular C<stat> calls. Even in the presence of inotify support
		2670	there are many cases where libev has to resort to regular C<stat> polling,
		2671	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2672	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2673	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2674	xfs are fully working) libev usually gets away without polling.
		2675
		2676	There is no support for kqueue, as apparently it cannot be used to
		2677	implement this functionality, due to the requirement of having a file
		2678	descriptor open on the object at all times, and detecting renames, unlinks
		2679	etc. is difficult.
		2680
		2681	=head3 C<stat ()> is a synchronous operation
		2682
		2683	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2684	the process. The exception are C<ev_stat> watchers - those call C<stat
		2685	()>, which is a synchronous operation.
		2686
		2687	For local paths, this usually doesn't matter: unless the system is very
		2688	busy or the intervals between stat's are large, a stat call will be fast,
		2689	as the path data is usually in memory already (except when starting the
		2690	watcher).
		2691
		2692	For networked file systems, calling C<stat ()> can block an indefinite
		2693	time due to network issues, and even under good conditions, a stat call
		2694	often takes multiple milliseconds.
		2695
		2696	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2697	paths, although this is fully supported by libev.
		2698
		2699	=head3 The special problem of stat time resolution
		2700
		2701	The C<stat ()> system call only supports full-second resolution portably,
		2702	and even on systems where the resolution is higher, most file systems
		2703	still only support whole seconds.
		2704
		2705	That means that, if the time is the only thing that changes, you can
		2706	easily miss updates: on the first update, C<ev_stat> detects a change and
		2707	calls your callback, which does something. When there is another update
		2708	within the same second, C<ev_stat> will be unable to detect unless the
		2709	stat data does change in other ways (e.g. file size).
		2710
		2711	The solution to this is to delay acting on a change for slightly more
		2712	than a second (or till slightly after the next full second boundary), using
		2713	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2714	ev_timer_again (loop, w)>).
		2715
		2716	The C<.02> offset is added to work around small timing inconsistencies
		2717	of some operating systems (where the second counter of the current time
		2718	might be be delayed. One such system is the Linux kernel, where a call to
		2719	C<gettimeofday> might return a timestamp with a full second later than
		2720	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2721	update file times then there will be a small window where the kernel uses
		2722	the previous second to update file times but libev might already execute
		2723	the timer callback).
1500		2724
1501	=head3 Watcher-Specific Functions and Data Members	2725	=head3 Watcher-Specific Functions and Data Members
1502		2726
1503	=over 4	2727	=over 4
1504		2728
…		…
1510	C<path>. The C<interval> is a hint on how quickly a change is expected to	2734	C<path>. The C<interval> is a hint on how quickly a change is expected to
1511	be detected and should normally be specified as C<0> to let libev choose	2735	be detected and should normally be specified as C<0> to let libev choose
1512	a suitable value. The memory pointed to by C<path> must point to the same	2736	a suitable value. The memory pointed to by C<path> must point to the same
1513	path for as long as the watcher is active.	2737	path for as long as the watcher is active.
1514		2738
1515	The callback will be receive C<EV_STAT> when a change was detected,	2739	The callback will receive an C<EV_STAT> event when a change was detected,
1516	relative to the attributes at the time the watcher was started (or the	2740	relative to the attributes at the time the watcher was started (or the
1517	last change was detected).	2741	last change was detected).
1518		2742
1519	=item ev_stat_stat (ev_stat *)	2743	=item ev_stat_stat (loop, ev_stat *)
1520		2744
1521	Updates the stat buffer immediately with new values. If you change the	2745	Updates the stat buffer immediately with new values. If you change the
1522	watched path in your callback, you could call this fucntion to avoid	2746	watched path in your callback, you could call this function to avoid
1523	detecting this change (while introducing a race condition). Can also be	2747	detecting this change (while introducing a race condition if you are not
1524	useful simply to find out the new values.	2748	the only one changing the path). Can also be useful simply to find out the
		2749	new values.
1525		2750
1526	=item ev_statdata attr [read-only]	2751	=item ev_statdata attr [read-only]
1527		2752
1528	The most-recently detected attributes of the file. Although the type is of	2753	The most-recently detected attributes of the file. Although the type is
1529	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2754	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1530	suitable for your system. If the C<st_nlink> member is C<0>, then there	2755	suitable for your system, but you can only rely on the POSIX-standardised
		2756	members to be present. If the C<st_nlink> member is C<0>, then there was
1531	was some error while C<stat>ing the file.	2757	some error while C<stat>ing the file.
1532		2758
1533	=item ev_statdata prev [read-only]	2759	=item ev_statdata prev [read-only]
1534		2760
1535	The previous attributes of the file. The callback gets invoked whenever	2761	The previous attributes of the file. The callback gets invoked whenever
1536	C<prev> != C<attr>.	2762	C<prev> != C<attr>, or, more precisely, one or more of these members
		2763	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2764	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1537		2765
1538	=item ev_tstamp interval [read-only]	2766	=item ev_tstamp interval [read-only]
1539		2767
1540	The specified interval.	2768	The specified interval.
1541		2769
1542	=item const char *path [read-only]	2770	=item const char *path [read-only]
1543		2771
1544	The filesystem path that is being watched.	2772	The file system path that is being watched.
1545		2773
1546	=back	2774	=back
1547		2775
		2776	=head3 Examples
		2777
1548	Example: Watch C</etc/passwd> for attribute changes.	2778	Example: Watch C</etc/passwd> for attribute changes.
1549		2779
1550	static void	2780	static void
1551	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2781	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1552	{	2782	{
1553	/* /etc/passwd changed in some way */	2783	/* /etc/passwd changed in some way */
1554	if (w->attr.st_nlink)	2784	if (w->attr.st_nlink)
1555	{	2785	{
1556	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2786	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1557	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2787	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1558	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2788	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1559	}	2789	}
1560	else	2790	else
1561	/* you shalt not abuse printf for puts */	2791	/* you shalt not abuse printf for puts */
1562	puts ("wow, /etc/passwd is not there, expect problems. "	2792	puts ("wow, /etc/passwd is not there, expect problems. "
1563	"if this is windows, they already arrived\n");	2793	"if this is windows, they already arrived\n");
1564	}	2794	}
1565		2795
1566	...	2796	...
1567	ev_stat passwd;	2797	ev_stat passwd;
1568		2798
1569	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2799	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1570	ev_stat_start (loop, &passwd);	2800	ev_stat_start (loop, &passwd);
		2801
		2802	Example: Like above, but additionally use a one-second delay so we do not
		2803	miss updates (however, frequent updates will delay processing, too, so
		2804	one might do the work both on C<ev_stat> callback invocation I<and> on
		2805	C<ev_timer> callback invocation).
		2806
		2807	static ev_stat passwd;
		2808	static ev_timer timer;
		2809
		2810	static void
		2811	timer_cb (EV_P_ ev_timer *w, int revents)
		2812	{
		2813	ev_timer_stop (EV_A_ w);
		2814
		2815	/* now it's one second after the most recent passwd change */
		2816	}
		2817
		2818	static void
		2819	stat_cb (EV_P_ ev_stat *w, int revents)
		2820	{
		2821	/* reset the one-second timer */
		2822	ev_timer_again (EV_A_ &timer);
		2823	}
		2824
		2825	...
		2826	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2827	ev_stat_start (loop, &passwd);
		2828	ev_timer_init (&timer, timer_cb, 0., 1.02);
1571		2829
1572		2830
1573	=head2 C<ev_idle> - when you've got nothing better to do...	2831	=head2 C<ev_idle> - when you've got nothing better to do...
1574		2832
1575	Idle watchers trigger events when no other events of the same or higher	2833	Idle watchers trigger events when no other events of the same or higher
1576	priority are pending (prepare, check and other idle watchers do not	2834	priority are pending (prepare, check and other idle watchers do not count
1577	count).	2835	as receiving "events").
1578		2836
1579	That is, as long as your process is busy handling sockets or timeouts	2837	That is, as long as your process is busy handling sockets or timeouts
1580	(or even signals, imagine) of the same or higher priority it will not be	2838	(or even signals, imagine) of the same or higher priority it will not be
1581	triggered. But when your process is idle (or only lower-priority watchers	2839	triggered. But when your process is idle (or only lower-priority watchers
1582	are pending), the idle watchers are being called once per event loop	2840	are pending), the idle watchers are being called once per event loop
…		…
1589	Apart from keeping your process non-blocking (which is a useful	2847	Apart from keeping your process non-blocking (which is a useful
1590	effect on its own sometimes), idle watchers are a good place to do	2848	effect on its own sometimes), idle watchers are a good place to do
1591	"pseudo-background processing", or delay processing stuff to after the	2849	"pseudo-background processing", or delay processing stuff to after the
1592	event loop has handled all outstanding events.	2850	event loop has handled all outstanding events.
1593		2851
		2852	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2853
		2854	As long as there is at least one active idle watcher, libev will never
		2855	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2856	For this to work, the idle watcher doesn't need to be invoked at all - the
		2857	lowest priority will do.
		2858
		2859	This mode of operation can be useful together with an C<ev_check> watcher,
		2860	to do something on each event loop iteration - for example to balance load
		2861	between different connections.
		2862
		2863	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2864	example.
		2865
1594	=head3 Watcher-Specific Functions and Data Members	2866	=head3 Watcher-Specific Functions and Data Members
1595		2867
1596	=over 4	2868	=over 4
1597		2869
1598	=item ev_idle_init (ev_signal *, callback)	2870	=item ev_idle_init (ev_idle *, callback)
1599		2871
1600	Initialises and configures the idle watcher - it has no parameters of any	2872	Initialises and configures the idle watcher - it has no parameters of any
1601	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2873	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1602	believe me.	2874	believe me.
1603		2875
1604	=back	2876	=back
1605		2877
		2878	=head3 Examples
		2879
1606	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2880	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1607	callback, free it. Also, use no error checking, as usual.	2881	callback, free it. Also, use no error checking, as usual.
1608		2882
1609	static void	2883	static void
1610	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2884	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1611	{	2885	{
		2886	// stop the watcher
		2887	ev_idle_stop (loop, w);
		2888
		2889	// now we can free it
1612	free (w);	2890	free (w);
		2891
1613	// now do something you wanted to do when the program has	2892	// now do something you wanted to do when the program has
1614	// no longer asnything immediate to do.	2893	// no longer anything immediate to do.
1615	}	2894	}
1616		2895
1617	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2896	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1618	ev_idle_init (idle_watcher, idle_cb);	2897	ev_idle_init (idle_watcher, idle_cb);
1619	ev_idle_start (loop, idle_cb);	2898	ev_idle_start (loop, idle_watcher);
1620		2899
1621		2900
1622	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2901	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1623		2902
1624	Prepare and check watchers are usually (but not always) used in tandem:	2903	Prepare and check watchers are often (but not always) used in pairs:
1625	prepare watchers get invoked before the process blocks and check watchers	2904	prepare watchers get invoked before the process blocks and check watchers
1626	afterwards.	2905	afterwards.
1627		2906
1628	You I<must not> call C<ev_loop> or similar functions that enter	2907	You I<must not> call C<ev_run> or similar functions that enter
1629	the current event loop from either C<ev_prepare> or C<ev_check>	2908	the current event loop from either C<ev_prepare> or C<ev_check>
1630	watchers. Other loops than the current one are fine, however. The	2909	watchers. Other loops than the current one are fine, however. The
1631	rationale behind this is that you do not need to check for recursion in	2910	rationale behind this is that you do not need to check for recursion in
1632	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2911	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1633	C<ev_check> so if you have one watcher of each kind they will always be	2912	C<ev_check> so if you have one watcher of each kind they will always be
1634	called in pairs bracketing the blocking call.	2913	called in pairs bracketing the blocking call.
1635		2914
1636	Their main purpose is to integrate other event mechanisms into libev and	2915	Their main purpose is to integrate other event mechanisms into libev and
1637	their use is somewhat advanced. This could be used, for example, to track	2916	their use is somewhat advanced. They could be used, for example, to track
1638	variable changes, implement your own watchers, integrate net-snmp or a	2917	variable changes, implement your own watchers, integrate net-snmp or a
1639	coroutine library and lots more. They are also occasionally useful if	2918	coroutine library and lots more. They are also occasionally useful if
1640	you cache some data and want to flush it before blocking (for example,	2919	you cache some data and want to flush it before blocking (for example,
1641	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2920	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1642	watcher).	2921	watcher).
1643		2922
1644	This is done by examining in each prepare call which file descriptors need	2923	This is done by examining in each prepare call which file descriptors
1645	to be watched by the other library, registering C<ev_io> watchers for	2924	need to be watched by the other library, registering C<ev_io> watchers
1646	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2925	for them and starting an C<ev_timer> watcher for any timeouts (many
1647	provide just this functionality). Then, in the check watcher you check for	2926	libraries provide exactly this functionality). Then, in the check watcher,
1648	any events that occured (by checking the pending status of all watchers	2927	you check for any events that occurred (by checking the pending status
1649	and stopping them) and call back into the library. The I/O and timer	2928	of all watchers and stopping them) and call back into the library. The
1650	callbacks will never actually be called (but must be valid nevertheless,	2929	I/O and timer callbacks will never actually be called (but must be valid
1651	because you never know, you know?).	2930	nevertheless, because you never know, you know?).
1652		2931
1653	As another example, the Perl Coro module uses these hooks to integrate	2932	As another example, the Perl Coro module uses these hooks to integrate
1654	coroutines into libev programs, by yielding to other active coroutines	2933	coroutines into libev programs, by yielding to other active coroutines
1655	during each prepare and only letting the process block if no coroutines	2934	during each prepare and only letting the process block if no coroutines
1656	are ready to run (it's actually more complicated: it only runs coroutines	2935	are ready to run (it's actually more complicated: it only runs coroutines
1657	with priority higher than or equal to the event loop and one coroutine	2936	with priority higher than or equal to the event loop and one coroutine
1658	of lower priority, but only once, using idle watchers to keep the event	2937	of lower priority, but only once, using idle watchers to keep the event
1659	loop from blocking if lower-priority coroutines are active, thus mapping	2938	loop from blocking if lower-priority coroutines are active, thus mapping
1660	low-priority coroutines to idle/background tasks).	2939	low-priority coroutines to idle/background tasks).
1661		2940
1662	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2941	When used for this purpose, it is recommended to give C<ev_check> watchers
1663	priority, to ensure that they are being run before any other watchers	2942	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		2943	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2944	watchers).
		2945
1664	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2946	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1665	too) should not activate ("feed") events into libev. While libev fully	2947	activate ("feed") events into libev. While libev fully supports this, they
1666	supports this, they will be called before other C<ev_check> watchers	2948	might get executed before other C<ev_check> watchers did their job. As
1667	did their job. As C<ev_check> watchers are often used to embed other	2949	C<ev_check> watchers are often used to embed other (non-libev) event
1668	(non-libev) event loops those other event loops might be in an unusable	2950	loops those other event loops might be in an unusable state until their
1669	state until their C<ev_check> watcher ran (always remind yourself to	2951	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1670	coexist peacefully with others).	2952	others).
		2953
		2954	=head3 Abusing an C<ev_check> watcher for its side-effect
		2955
		2956	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2957	useful because they are called once per event loop iteration. For
		2958	example, if you want to handle a large number of connections fairly, you
		2959	normally only do a bit of work for each active connection, and if there
		2960	is more work to do, you wait for the next event loop iteration, so other
		2961	connections have a chance of making progress.
		2962
		2963	Using an C<ev_check> watcher is almost enough: it will be called on the
		2964	next event loop iteration. However, that isn't as soon as possible -
		2965	without external events, your C<ev_check> watcher will not be invoked.
		2966
		2967
		2968	This is where C<ev_idle> watchers come in handy - all you need is a
		2969	single global idle watcher that is active as long as you have one active
		2970	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2971	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2972	invoked. Neither watcher alone can do that.
1671		2973
1672	=head3 Watcher-Specific Functions and Data Members	2974	=head3 Watcher-Specific Functions and Data Members
1673		2975
1674	=over 4	2976	=over 4
1675		2977
…		…
1677		2979
1678	=item ev_check_init (ev_check *, callback)	2980	=item ev_check_init (ev_check *, callback)
1679		2981
1680	Initialises and configures the prepare or check watcher - they have no	2982	Initialises and configures the prepare or check watcher - they have no
1681	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2983	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1682	macros, but using them is utterly, utterly and completely pointless.	2984	macros, but using them is utterly, utterly, utterly and completely
		2985	pointless.
1683		2986
1684	=back	2987	=back
		2988
		2989	=head3 Examples
1685		2990
1686	There are a number of principal ways to embed other event loops or modules	2991	There are a number of principal ways to embed other event loops or modules
1687	into libev. Here are some ideas on how to include libadns into libev	2992	into libev. Here are some ideas on how to include libadns into libev
1688	(there is a Perl module named C<EV::ADNS> that does this, which you could	2993	(there is a Perl module named C<EV::ADNS> that does this, which you could
1689	use for an actually working example. Another Perl module named C<EV::Glib>	2994	use as a working example. Another Perl module named C<EV::Glib> embeds a
1690	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2995	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1691	into the Glib event loop).	2996	Glib event loop).
1692		2997
1693	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2998	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1694	and in a check watcher, destroy them and call into libadns. What follows	2999	and in a check watcher, destroy them and call into libadns. What follows
1695	is pseudo-code only of course. This requires you to either use a low	3000	is pseudo-code only of course. This requires you to either use a low
1696	priority for the check watcher or use C<ev_clear_pending> explicitly, as	3001	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1697	the callbacks for the IO/timeout watchers might not have been called yet.	3002	the callbacks for the IO/timeout watchers might not have been called yet.
1698		3003
1699	static ev_io iow [nfd];	3004	static ev_io iow [nfd];
1700	static ev_timer tw;	3005	static ev_timer tw;
1701		3006
1702	static void	3007	static void
1703	io_cb (ev_loop *loop, ev_io *w, int revents)	3008	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1704	{	3009	{
1705	}	3010	}
1706		3011
1707	// create io watchers for each fd and a timer before blocking	3012	// create io watchers for each fd and a timer before blocking
1708	static void	3013	static void
1709	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3014	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1710	{	3015	{
1711	int timeout = 3600000;	3016	int timeout = 3600000;
1712	struct pollfd fds [nfd];	3017	struct pollfd fds [nfd];
1713	// actual code will need to loop here and realloc etc.	3018	// actual code will need to loop here and realloc etc.
1714	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3019	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1715		3020
1716	/* the callback is illegal, but won't be called as we stop during check */	3021	/* the callback is illegal, but won't be called as we stop during check */
1717	ev_timer_init (&tw, 0, timeout * 1e-3);	3022	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1718	ev_timer_start (loop, &tw);	3023	ev_timer_start (loop, &tw);
1719		3024
1720	// create one ev_io per pollfd	3025	// create one ev_io per pollfd
1721	for (int i = 0; i < nfd; ++i)	3026	for (int i = 0; i < nfd; ++i)
1722	{	3027	{
1723	ev_io_init (iow + i, io_cb, fds [i].fd,	3028	ev_io_init (iow + i, io_cb, fds [i].fd,
1724	((fds [i].events & POLLIN ? EV_READ : 0)	3029	((fds [i].events & POLLIN ? EV_READ : 0)
1725	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	3030	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1726		3031
1727	fds [i].revents = 0;	3032	fds [i].revents = 0;
1728	ev_io_start (loop, iow + i);	3033	ev_io_start (loop, iow + i);
1729	}	3034	}
1730	}	3035	}
1731		3036
1732	// stop all watchers after blocking	3037	// stop all watchers after blocking
1733	static void	3038	static void
1734	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3039	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1735	{	3040	{
1736	ev_timer_stop (loop, &tw);	3041	ev_timer_stop (loop, &tw);
1737		3042
1738	for (int i = 0; i < nfd; ++i)	3043	for (int i = 0; i < nfd; ++i)
1739	{	3044	{
1740	// set the relevant poll flags	3045	// set the relevant poll flags
1741	// could also call adns_processreadable etc. here	3046	// could also call adns_processreadable etc. here
1742	struct pollfd *fd = fds + i;	3047	struct pollfd *fd = fds + i;
1743	int revents = ev_clear_pending (iow + i);	3048	int revents = ev_clear_pending (iow + i);
1744	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	3049	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1745	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	3050	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1746		3051
1747	// now stop the watcher	3052	// now stop the watcher
1748	ev_io_stop (loop, iow + i);	3053	ev_io_stop (loop, iow + i);
1749	}	3054	}
1750		3055
1751	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3056	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1752	}	3057	}
1753		3058
1754	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	3059	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1755	in the prepare watcher and would dispose of the check watcher.	3060	in the prepare watcher and would dispose of the check watcher.
1756		3061
1757	Method 3: If the module to be embedded supports explicit event	3062	Method 3: If the module to be embedded supports explicit event
1758	notification (adns does), you can also make use of the actual watcher	3063	notification (libadns does), you can also make use of the actual watcher
1759	callbacks, and only destroy/create the watchers in the prepare watcher.	3064	callbacks, and only destroy/create the watchers in the prepare watcher.
1760		3065
1761	static void	3066	static void
1762	timer_cb (EV_P_ ev_timer *w, int revents)	3067	timer_cb (EV_P_ ev_timer *w, int revents)
1763	{	3068	{
1764	adns_state ads = (adns_state)w->data;	3069	adns_state ads = (adns_state)w->data;
1765	update_now (EV_A);	3070	update_now (EV_A);
1766		3071
1767	adns_processtimeouts (ads, &tv_now);	3072	adns_processtimeouts (ads, &tv_now);
1768	}	3073	}
1769		3074
1770	static void	3075	static void
1771	io_cb (EV_P_ ev_io *w, int revents)	3076	io_cb (EV_P_ ev_io *w, int revents)
1772	{	3077	{
1773	adns_state ads = (adns_state)w->data;	3078	adns_state ads = (adns_state)w->data;
1774	update_now (EV_A);	3079	update_now (EV_A);
1775		3080
1776	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	3081	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1777	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	3082	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1778	}	3083	}
1779		3084
1780	// do not ever call adns_afterpoll	3085	// do not ever call adns_afterpoll
1781		3086
1782	Method 4: Do not use a prepare or check watcher because the module you	3087	Method 4: Do not use a prepare or check watcher because the module you
1783	want to embed is too inflexible to support it. Instead, youc na override	3088	want to embed is not flexible enough to support it. Instead, you can
1784	their poll function. The drawback with this solution is that the main	3089	override their poll function. The drawback with this solution is that the
1785	loop is now no longer controllable by EV. The C<Glib::EV> module does	3090	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1786	this.	3091	this approach, effectively embedding EV as a client into the horrible
		3092	libglib event loop.
1787		3093
1788	static gint	3094	static gint
1789	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3095	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1790	{	3096	{
1791	int got_events = 0;	3097	int got_events = 0;
1792		3098
1793	for (n = 0; n < nfds; ++n)	3099	for (n = 0; n < nfds; ++n)
1794	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	3100	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1795		3101
1796	if (timeout >= 0)	3102	if (timeout >= 0)
1797	// create/start timer	3103	// create/start timer
1798		3104
1799	// poll	3105	// poll
1800	ev_loop (EV_A_ 0);	3106	ev_run (EV_A_ 0);
1801		3107
1802	// stop timer again	3108	// stop timer again
1803	if (timeout >= 0)	3109	if (timeout >= 0)
1804	ev_timer_stop (EV_A_ &to);	3110	ev_timer_stop (EV_A_ &to);
1805		3111
1806	// stop io watchers again - their callbacks should have set	3112	// stop io watchers again - their callbacks should have set
1807	for (n = 0; n < nfds; ++n)	3113	for (n = 0; n < nfds; ++n)
1808	ev_io_stop (EV_A_ iow [n]);	3114	ev_io_stop (EV_A_ iow [n]);
1809		3115
1810	return got_events;	3116	return got_events;
1811	}	3117	}
1812		3118
1813		3119
1814	=head2 C<ev_embed> - when one backend isn't enough...	3120	=head2 C<ev_embed> - when one backend isn't enough...
1815		3121
1816	This is a rather advanced watcher type that lets you embed one event loop	3122	This is a rather advanced watcher type that lets you embed one event loop
…		…
1822	prioritise I/O.	3128	prioritise I/O.
1823		3129
1824	As an example for a bug workaround, the kqueue backend might only support	3130	As an example for a bug workaround, the kqueue backend might only support
1825	sockets on some platform, so it is unusable as generic backend, but you	3131	sockets on some platform, so it is unusable as generic backend, but you
1826	still want to make use of it because you have many sockets and it scales	3132	still want to make use of it because you have many sockets and it scales
1827	so nicely. In this case, you would create a kqueue-based loop and embed it	3133	so nicely. In this case, you would create a kqueue-based loop and embed
1828	into your default loop (which might use e.g. poll). Overall operation will	3134	it into your default loop (which might use e.g. poll). Overall operation
1829	be a bit slower because first libev has to poll and then call kevent, but	3135	will be a bit slower because first libev has to call C<poll> and then
1830	at least you can use both at what they are best.	3136	C<kevent>, but at least you can use both mechanisms for what they are
		3137	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1831		3138
1832	As for prioritising I/O: rarely you have the case where some fds have	3139	As for prioritising I/O: under rare circumstances you have the case where
1833	to be watched and handled very quickly (with low latency), and even	3140	some fds have to be watched and handled very quickly (with low latency),
1834	priorities and idle watchers might have too much overhead. In this case	3141	and even priorities and idle watchers might have too much overhead. In
1835	you would put all the high priority stuff in one loop and all the rest in	3142	this case you would put all the high priority stuff in one loop and all
1836	a second one, and embed the second one in the first.	3143	the rest in a second one, and embed the second one in the first.
1837		3144
1838	As long as the watcher is active, the callback will be invoked every time	3145	As long as the watcher is active, the callback will be invoked every
1839	there might be events pending in the embedded loop. The callback must then	3146	time there might be events pending in the embedded loop. The callback
1840	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3147	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1841	their callbacks (you could also start an idle watcher to give the embedded	3148	sweep and invoke their callbacks (the callback doesn't need to invoke the
1842	loop strictly lower priority for example). You can also set the callback	3149	C<ev_embed_sweep> function directly, it could also start an idle watcher
1843	to C<0>, in which case the embed watcher will automatically execute the	3150	to give the embedded loop strictly lower priority for example).
1844	embedded loop sweep.
1845		3151
1846	As long as the watcher is started it will automatically handle events. The	3152	You can also set the callback to C<0>, in which case the embed watcher
1847	callback will be invoked whenever some events have been handled. You can	3153	will automatically execute the embedded loop sweep whenever necessary.
1848	set the callback to C<0> to avoid having to specify one if you are not
1849	interested in that.
1850		3154
1851	Also, there have not currently been made special provisions for forking:	3155	Fork detection will be handled transparently while the C<ev_embed> watcher
1852	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3156	is active, i.e., the embedded loop will automatically be forked when the
1853	but you will also have to stop and restart any C<ev_embed> watchers	3157	embedding loop forks. In other cases, the user is responsible for calling
1854	yourself.	3158	C<ev_loop_fork> on the embedded loop.
1855		3159
1856	Unfortunately, not all backends are embeddable, only the ones returned by	3160	Unfortunately, not all backends are embeddable: only the ones returned by
1857	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3161	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1858	portable one.	3162	portable one.
1859		3163
1860	So when you want to use this feature you will always have to be prepared	3164	So when you want to use this feature you will always have to be prepared
1861	that you cannot get an embeddable loop. The recommended way to get around	3165	that you cannot get an embeddable loop. The recommended way to get around
1862	this is to have a separate variables for your embeddable loop, try to	3166	this is to have a separate variables for your embeddable loop, try to
1863	create it, and if that fails, use the normal loop for everything:	3167	create it, and if that fails, use the normal loop for everything.
1864		3168
1865	struct ev_loop *loop_hi = ev_default_init (0);	3169	=head3 C<ev_embed> and fork
1866	struct ev_loop *loop_lo = 0;
1867	struct ev_embed embed;
1868
1869	// see if there is a chance of getting one that works
1870	// (remember that a flags value of 0 means autodetection)
1871	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1872	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1873	: 0;
1874		3170
1875	// if we got one, then embed it, otherwise default to loop_hi	3171	While the C<ev_embed> watcher is running, forks in the embedding loop will
1876	if (loop_lo)	3172	automatically be applied to the embedded loop as well, so no special
1877	{	3173	fork handling is required in that case. When the watcher is not running,
1878	ev_embed_init (&embed, 0, loop_lo);	3174	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1879	ev_embed_start (loop_hi, &embed);	3175	as applicable.
1880	}
1881	else
1882	loop_lo = loop_hi;
1883		3176
1884	=head3 Watcher-Specific Functions and Data Members	3177	=head3 Watcher-Specific Functions and Data Members
1885		3178
1886	=over 4	3179	=over 4
1887		3180
…		…
1891		3184
1892	Configures the watcher to embed the given loop, which must be	3185	Configures the watcher to embed the given loop, which must be
1893	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3186	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1894	invoked automatically, otherwise it is the responsibility of the callback	3187	invoked automatically, otherwise it is the responsibility of the callback
1895	to invoke it (it will continue to be called until the sweep has been done,	3188	to invoke it (it will continue to be called until the sweep has been done,
1896	if you do not want thta, you need to temporarily stop the embed watcher).	3189	if you do not want that, you need to temporarily stop the embed watcher).
1897		3190
1898	=item ev_embed_sweep (loop, ev_embed *)	3191	=item ev_embed_sweep (loop, ev_embed *)
1899		3192
1900	Make a single, non-blocking sweep over the embedded loop. This works	3193	Make a single, non-blocking sweep over the embedded loop. This works
1901	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3194	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1902	apropriate way for embedded loops.	3195	appropriate way for embedded loops.
1903		3196
1904	=item struct ev_loop *other [read-only]	3197	=item struct ev_loop *other [read-only]
1905		3198
1906	The embedded event loop.	3199	The embedded event loop.
1907		3200
1908	=back	3201	=back
		3202
		3203	=head3 Examples
		3204
		3205	Example: Try to get an embeddable event loop and embed it into the default
		3206	event loop. If that is not possible, use the default loop. The default
		3207	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3208	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3209	used).
		3210
		3211	struct ev_loop *loop_hi = ev_default_init (0);
		3212	struct ev_loop *loop_lo = 0;
		3213	ev_embed embed;
		3214
		3215	// see if there is a chance of getting one that works
		3216	// (remember that a flags value of 0 means autodetection)
		3217	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3218	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3219	: 0;
		3220
		3221	// if we got one, then embed it, otherwise default to loop_hi
		3222	if (loop_lo)
		3223	{
		3224	ev_embed_init (&embed, 0, loop_lo);
		3225	ev_embed_start (loop_hi, &embed);
		3226	}
		3227	else
		3228	loop_lo = loop_hi;
		3229
		3230	Example: Check if kqueue is available but not recommended and create
		3231	a kqueue backend for use with sockets (which usually work with any
		3232	kqueue implementation). Store the kqueue/socket-only event loop in
		3233	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3234
		3235	struct ev_loop *loop = ev_default_init (0);
		3236	struct ev_loop *loop_socket = 0;
		3237	ev_embed embed;
		3238
		3239	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3240	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3241	{
		3242	ev_embed_init (&embed, 0, loop_socket);
		3243	ev_embed_start (loop, &embed);
		3244	}
		3245
		3246	if (!loop_socket)
		3247	loop_socket = loop;
		3248
		3249	// now use loop_socket for all sockets, and loop for everything else
1909		3250
1910		3251
1911	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3252	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1912		3253
1913	Fork watchers are called when a C<fork ()> was detected (usually because	3254	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1916	event loop blocks next and before C<ev_check> watchers are being called,	3257	event loop blocks next and before C<ev_check> watchers are being called,
1917	and only in the child after the fork. If whoever good citizen calling	3258	and only in the child after the fork. If whoever good citizen calling
1918	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3259	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1919	handlers will be invoked, too, of course.	3260	handlers will be invoked, too, of course.
1920		3261
		3262	=head3 The special problem of life after fork - how is it possible?
		3263
		3264	Most uses of C<fork()> consist of forking, then some simple calls to set
		3265	up/change the process environment, followed by a call to C<exec()>. This
		3266	sequence should be handled by libev without any problems.
		3267
		3268	This changes when the application actually wants to do event handling
		3269	in the child, or both parent in child, in effect "continuing" after the
		3270	fork.
		3271
		3272	The default mode of operation (for libev, with application help to detect
		3273	forks) is to duplicate all the state in the child, as would be expected
		3274	when I<either> the parent I<or> the child process continues.
		3275
		3276	When both processes want to continue using libev, then this is usually the
		3277	wrong result. In that case, usually one process (typically the parent) is
		3278	supposed to continue with all watchers in place as before, while the other
		3279	process typically wants to start fresh, i.e. without any active watchers.
		3280
		3281	The cleanest and most efficient way to achieve that with libev is to
		3282	simply create a new event loop, which of course will be "empty", and
		3283	use that for new watchers. This has the advantage of not touching more
		3284	memory than necessary, and thus avoiding the copy-on-write, and the
		3285	disadvantage of having to use multiple event loops (which do not support
		3286	signal watchers).
		3287
		3288	When this is not possible, or you want to use the default loop for
		3289	other reasons, then in the process that wants to start "fresh", call
		3290	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3291	Destroying the default loop will "orphan" (not stop) all registered
		3292	watchers, so you have to be careful not to execute code that modifies
		3293	those watchers. Note also that in that case, you have to re-register any
		3294	signal watchers.
		3295
1921	=head3 Watcher-Specific Functions and Data Members	3296	=head3 Watcher-Specific Functions and Data Members
1922		3297
1923	=over 4	3298	=over 4
1924		3299
1925	=item ev_fork_init (ev_signal *, callback)	3300	=item ev_fork_init (ev_fork *, callback)
1926		3301
1927	Initialises and configures the fork watcher - it has no parameters of any	3302	Initialises and configures the fork watcher - it has no parameters of any
1928	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3303	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1929	believe me.	3304	really.
1930		3305
1931	=back	3306	=back
1932		3307
1933		3308
		3309	=head2 C<ev_cleanup> - even the best things end
		3310
		3311	Cleanup watchers are called just before the event loop is being destroyed
		3312	by a call to C<ev_loop_destroy>.
		3313
		3314	While there is no guarantee that the event loop gets destroyed, cleanup
		3315	watchers provide a convenient method to install cleanup hooks for your
		3316	program, worker threads and so on - you just to make sure to destroy the
		3317	loop when you want them to be invoked.
		3318
		3319	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3320	all other watchers, they do not keep a reference to the event loop (which
		3321	makes a lot of sense if you think about it). Like all other watchers, you
		3322	can call libev functions in the callback, except C<ev_cleanup_start>.
		3323
		3324	=head3 Watcher-Specific Functions and Data Members
		3325
		3326	=over 4
		3327
		3328	=item ev_cleanup_init (ev_cleanup *, callback)
		3329
		3330	Initialises and configures the cleanup watcher - it has no parameters of
		3331	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3332	pointless, I assure you.
		3333
		3334	=back
		3335
		3336	Example: Register an atexit handler to destroy the default loop, so any
		3337	cleanup functions are called.
		3338
		3339	static void
		3340	program_exits (void)
		3341	{
		3342	ev_loop_destroy (EV_DEFAULT_UC);
		3343	}
		3344
		3345	...
		3346	atexit (program_exits);
		3347
		3348
		3349	=head2 C<ev_async> - how to wake up an event loop
		3350
		3351	In general, you cannot use an C<ev_loop> from multiple threads or other
		3352	asynchronous sources such as signal handlers (as opposed to multiple event
		3353	loops - those are of course safe to use in different threads).
		3354
		3355	Sometimes, however, you need to wake up an event loop you do not control,
		3356	for example because it belongs to another thread. This is what C<ev_async>
		3357	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3358	it by calling C<ev_async_send>, which is thread- and signal safe.
		3359
		3360	This functionality is very similar to C<ev_signal> watchers, as signals,
		3361	too, are asynchronous in nature, and signals, too, will be compressed
		3362	(i.e. the number of callback invocations may be less than the number of
		3363	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3364	of "global async watchers" by using a watcher on an otherwise unused
		3365	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3366	even without knowing which loop owns the signal.
		3367
		3368	=head3 Queueing
		3369
		3370	C<ev_async> does not support queueing of data in any way. The reason
		3371	is that the author does not know of a simple (or any) algorithm for a
		3372	multiple-writer-single-reader queue that works in all cases and doesn't
		3373	need elaborate support such as pthreads or unportable memory access
		3374	semantics.
		3375
		3376	That means that if you want to queue data, you have to provide your own
		3377	queue. But at least I can tell you how to implement locking around your
		3378	queue:
		3379
		3380	=over 4
		3381
		3382	=item queueing from a signal handler context
		3383
		3384	To implement race-free queueing, you simply add to the queue in the signal
		3385	handler but you block the signal handler in the watcher callback. Here is
		3386	an example that does that for some fictitious SIGUSR1 handler:
		3387
		3388	static ev_async mysig;
		3389
		3390	static void
		3391	sigusr1_handler (void)
		3392	{
		3393	sometype data;
		3394
		3395	// no locking etc.
		3396	queue_put (data);
		3397	ev_async_send (EV_DEFAULT_ &mysig);
		3398	}
		3399
		3400	static void
		3401	mysig_cb (EV_P_ ev_async *w, int revents)
		3402	{
		3403	sometype data;
		3404	sigset_t block, prev;
		3405
		3406	sigemptyset (&block);
		3407	sigaddset (&block, SIGUSR1);
		3408	sigprocmask (SIG_BLOCK, &block, &prev);
		3409
		3410	while (queue_get (&data))
		3411	process (data);
		3412
		3413	if (sigismember (&prev, SIGUSR1)
		3414	sigprocmask (SIG_UNBLOCK, &block, 0);
		3415	}
		3416
		3417	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3418	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3419	either...).
		3420
		3421	=item queueing from a thread context
		3422
		3423	The strategy for threads is different, as you cannot (easily) block
		3424	threads but you can easily preempt them, so to queue safely you need to
		3425	employ a traditional mutex lock, such as in this pthread example:
		3426
		3427	static ev_async mysig;
		3428	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3429
		3430	static void
		3431	otherthread (void)
		3432	{
		3433	// only need to lock the actual queueing operation
		3434	pthread_mutex_lock (&mymutex);
		3435	queue_put (data);
		3436	pthread_mutex_unlock (&mymutex);
		3437
		3438	ev_async_send (EV_DEFAULT_ &mysig);
		3439	}
		3440
		3441	static void
		3442	mysig_cb (EV_P_ ev_async *w, int revents)
		3443	{
		3444	pthread_mutex_lock (&mymutex);
		3445
		3446	while (queue_get (&data))
		3447	process (data);
		3448
		3449	pthread_mutex_unlock (&mymutex);
		3450	}
		3451
		3452	=back
		3453
		3454
		3455	=head3 Watcher-Specific Functions and Data Members
		3456
		3457	=over 4
		3458
		3459	=item ev_async_init (ev_async *, callback)
		3460
		3461	Initialises and configures the async watcher - it has no parameters of any
		3462	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3463	trust me.
		3464
		3465	=item ev_async_send (loop, ev_async *)
		3466
		3467	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3468	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3469	returns.
		3470
		3471	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3472	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3473	embedding section below on what exactly this means).
		3474
		3475	Note that, as with other watchers in libev, multiple events might get
		3476	compressed into a single callback invocation (another way to look at
		3477	this is that C<ev_async> watchers are level-triggered: they are set on
		3478	C<ev_async_send>, reset when the event loop detects that).
		3479
		3480	This call incurs the overhead of at most one extra system call per event
		3481	loop iteration, if the event loop is blocked, and no syscall at all if
		3482	the event loop (or your program) is processing events. That means that
		3483	repeated calls are basically free (there is no need to avoid calls for
		3484	performance reasons) and that the overhead becomes smaller (typically
		3485	zero) under load.
		3486
		3487	=item bool = ev_async_pending (ev_async *)
		3488
		3489	Returns a non-zero value when C<ev_async_send> has been called on the
		3490	watcher but the event has not yet been processed (or even noted) by the
		3491	event loop.
		3492
		3493	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3494	the loop iterates next and checks for the watcher to have become active,
		3495	it will reset the flag again. C<ev_async_pending> can be used to very
		3496	quickly check whether invoking the loop might be a good idea.
		3497
		3498	Not that this does I<not> check whether the watcher itself is pending,
		3499	only whether it has been requested to make this watcher pending: there
		3500	is a time window between the event loop checking and resetting the async
		3501	notification, and the callback being invoked.
		3502
		3503	=back
		3504
		3505
1934	=head1 OTHER FUNCTIONS	3506	=head1 OTHER FUNCTIONS
1935		3507
1936	There are some other functions of possible interest. Described. Here. Now.	3508	There are some other functions of possible interest. Described. Here. Now.
1937		3509
1938	=over 4	3510	=over 4
1939		3511
1940	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3512	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1941		3513
1942	This function combines a simple timer and an I/O watcher, calls your	3514	This function combines a simple timer and an I/O watcher, calls your
1943	callback on whichever event happens first and automatically stop both	3515	callback on whichever event happens first and automatically stops both
1944	watchers. This is useful if you want to wait for a single event on an fd	3516	watchers. This is useful if you want to wait for a single event on an fd
1945	or timeout without having to allocate/configure/start/stop/free one or	3517	or timeout without having to allocate/configure/start/stop/free one or
1946	more watchers yourself.	3518	more watchers yourself.
1947		3519
1948	If C<fd> is less than 0, then no I/O watcher will be started and events	3520	If C<fd> is less than 0, then no I/O watcher will be started and the
1949	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3521	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1950	C<events> set will be craeted and started.	3522	the given C<fd> and C<events> set will be created and started.
1951		3523
1952	If C<timeout> is less than 0, then no timeout watcher will be	3524	If C<timeout> is less than 0, then no timeout watcher will be
1953	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3525	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1954	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3526	repeat = 0) will be started. C<0> is a valid timeout.
1955	dubious value.
1956		3527
1957	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3528	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1958	passed an C<revents> set like normal event callbacks (a combination of	3529	passed an C<revents> set like normal event callbacks (a combination of
1959	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3530	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1960	value passed to C<ev_once>:	3531	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3532	a timeout and an io event at the same time - you probably should give io
		3533	events precedence.
1961		3534
		3535	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3536
1962	static void stdin_ready (int revents, void *arg)	3537	static void stdin_ready (int revents, void *arg)
		3538	{
		3539	if (revents & EV_READ)
		3540	/* stdin might have data for us, joy! */;
		3541	else if (revents & EV_TIMER)
		3542	/* doh, nothing entered */;
		3543	}
		3544
		3545	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3546
		3547	=item ev_feed_fd_event (loop, int fd, int revents)
		3548
		3549	Feed an event on the given fd, as if a file descriptor backend detected
		3550	the given events.
		3551
		3552	=item ev_feed_signal_event (loop, int signum)
		3553
		3554	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3555	which is async-safe.
		3556
		3557	=back
		3558
		3559
		3560	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3561
		3562	This section explains some common idioms that are not immediately
		3563	obvious. Note that examples are sprinkled over the whole manual, and this
		3564	section only contains stuff that wouldn't fit anywhere else.
		3565
		3566	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3567
		3568	Each watcher has, by default, a C<void *data> member that you can read
		3569	or modify at any time: libev will completely ignore it. This can be used
		3570	to associate arbitrary data with your watcher. If you need more data and
		3571	don't want to allocate memory separately and store a pointer to it in that
		3572	data member, you can also "subclass" the watcher type and provide your own
		3573	data:
		3574
		3575	struct my_io
		3576	{
		3577	ev_io io;
		3578	int otherfd;
		3579	void *somedata;
		3580	struct whatever *mostinteresting;
		3581	};
		3582
		3583	...
		3584	struct my_io w;
		3585	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3586
		3587	And since your callback will be called with a pointer to the watcher, you
		3588	can cast it back to your own type:
		3589
		3590	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3591	{
		3592	struct my_io *w = (struct my_io *)w_;
		3593	...
		3594	}
		3595
		3596	More interesting and less C-conformant ways of casting your callback
		3597	function type instead have been omitted.
		3598
		3599	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3600
		3601	Another common scenario is to use some data structure with multiple
		3602	embedded watchers, in effect creating your own watcher that combines
		3603	multiple libev event sources into one "super-watcher":
		3604
		3605	struct my_biggy
		3606	{
		3607	int some_data;
		3608	ev_timer t1;
		3609	ev_timer t2;
		3610	}
		3611
		3612	In this case getting the pointer to C<my_biggy> is a bit more
		3613	complicated: Either you store the address of your C<my_biggy> struct in
		3614	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3615	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3616	real programmers):
		3617
		3618	#include <stddef.h>
		3619
		3620	static void
		3621	t1_cb (EV_P_ ev_timer *w, int revents)
		3622	{
		3623	struct my_biggy big = (struct my_biggy *)
		3624	(((char *)w) - offsetof (struct my_biggy, t1));
		3625	}
		3626
		3627	static void
		3628	t2_cb (EV_P_ ev_timer *w, int revents)
		3629	{
		3630	struct my_biggy big = (struct my_biggy *)
		3631	(((char *)w) - offsetof (struct my_biggy, t2));
		3632	}
		3633
		3634	=head2 AVOIDING FINISHING BEFORE RETURNING
		3635
		3636	Often you have structures like this in event-based programs:
		3637
		3638	callback ()
1963	{	3639	{
1964	if (revents & EV_TIMEOUT)	3640	free (request);
1965	/* doh, nothing entered */;
1966	else if (revents & EV_READ)
1967	/* stdin might have data for us, joy! */;
1968	}	3641	}
1969		3642
1970	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3643	request = start_new_request (..., callback);
1971		3644
1972	=item ev_feed_event (ev_loop *, watcher *, int revents)	3645	The intent is to start some "lengthy" operation. The C<request> could be
		3646	used to cancel the operation, or do other things with it.
1973		3647
1974	Feeds the given event set into the event loop, as if the specified event	3648	It's not uncommon to have code paths in C<start_new_request> that
1975	had happened for the specified watcher (which must be a pointer to an	3649	immediately invoke the callback, for example, to report errors. Or you add
1976	initialised but not necessarily started event watcher).	3650	some caching layer that finds that it can skip the lengthy aspects of the
		3651	operation and simply invoke the callback with the result.
1977		3652
1978	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3653	The problem here is that this will happen I<before> C<start_new_request>
		3654	has returned, so C<request> is not set.
1979		3655
1980	Feed an event on the given fd, as if a file descriptor backend detected	3656	Even if you pass the request by some safer means to the callback, you
1981	the given events it.	3657	might want to do something to the request after starting it, such as
		3658	canceling it, which probably isn't working so well when the callback has
		3659	already been invoked.
1982		3660
1983	=item ev_feed_signal_event (ev_loop *loop, int signum)	3661	A common way around all these issues is to make sure that
		3662	C<start_new_request> I<always> returns before the callback is invoked. If
		3663	C<start_new_request> immediately knows the result, it can artificially
		3664	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3665	for example, or more sneakily, by reusing an existing (stopped) watcher
		3666	and pushing it into the pending queue:
1984		3667
1985	Feed an event as if the given signal occured (C<loop> must be the default	3668	ev_set_cb (watcher, callback);
1986	loop!).	3669	ev_feed_event (EV_A_ watcher, 0);
1987		3670
1988	=back	3671	This way, C<start_new_request> can safely return before the callback is
		3672	invoked, while not delaying callback invocation too much.
		3673
		3674	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3675
		3676	Often (especially in GUI toolkits) there are places where you have
		3677	I<modal> interaction, which is most easily implemented by recursively
		3678	invoking C<ev_run>.
		3679
		3680	This brings the problem of exiting - a callback might want to finish the
		3681	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3682	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3683	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3684	other combination: In these cases, C<ev_break> will not work alone.
		3685
		3686	The solution is to maintain "break this loop" variable for each C<ev_run>
		3687	invocation, and use a loop around C<ev_run> until the condition is
		3688	triggered, using C<EVRUN_ONCE>:
		3689
		3690	// main loop
		3691	int exit_main_loop = 0;
		3692
		3693	while (!exit_main_loop)
		3694	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3695
		3696	// in a modal watcher
		3697	int exit_nested_loop = 0;
		3698
		3699	while (!exit_nested_loop)
		3700	ev_run (EV_A_ EVRUN_ONCE);
		3701
		3702	To exit from any of these loops, just set the corresponding exit variable:
		3703
		3704	// exit modal loop
		3705	exit_nested_loop = 1;
		3706
		3707	// exit main program, after modal loop is finished
		3708	exit_main_loop = 1;
		3709
		3710	// exit both
		3711	exit_main_loop = exit_nested_loop = 1;
		3712
		3713	=head2 THREAD LOCKING EXAMPLE
		3714
		3715	Here is a fictitious example of how to run an event loop in a different
		3716	thread from where callbacks are being invoked and watchers are
		3717	created/added/removed.
		3718
		3719	For a real-world example, see the C<EV::Loop::Async> perl module,
		3720	which uses exactly this technique (which is suited for many high-level
		3721	languages).
		3722
		3723	The example uses a pthread mutex to protect the loop data, a condition
		3724	variable to wait for callback invocations, an async watcher to notify the
		3725	event loop thread and an unspecified mechanism to wake up the main thread.
		3726
		3727	First, you need to associate some data with the event loop:
		3728
		3729	typedef struct {
		3730	mutex_t lock; /* global loop lock */
		3731	ev_async async_w;
		3732	thread_t tid;
		3733	cond_t invoke_cv;
		3734	} userdata;
		3735
		3736	void prepare_loop (EV_P)
		3737	{
		3738	// for simplicity, we use a static userdata struct.
		3739	static userdata u;
		3740
		3741	ev_async_init (&u->async_w, async_cb);
		3742	ev_async_start (EV_A_ &u->async_w);
		3743
		3744	pthread_mutex_init (&u->lock, 0);
		3745	pthread_cond_init (&u->invoke_cv, 0);
		3746
		3747	// now associate this with the loop
		3748	ev_set_userdata (EV_A_ u);
		3749	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3750	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3751
		3752	// then create the thread running ev_run
		3753	pthread_create (&u->tid, 0, l_run, EV_A);
		3754	}
		3755
		3756	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3757	solely to wake up the event loop so it takes notice of any new watchers
		3758	that might have been added:
		3759
		3760	static void
		3761	async_cb (EV_P_ ev_async *w, int revents)
		3762	{
		3763	// just used for the side effects
		3764	}
		3765
		3766	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3767	protecting the loop data, respectively.
		3768
		3769	static void
		3770	l_release (EV_P)
		3771	{
		3772	userdata *u = ev_userdata (EV_A);
		3773	pthread_mutex_unlock (&u->lock);
		3774	}
		3775
		3776	static void
		3777	l_acquire (EV_P)
		3778	{
		3779	userdata *u = ev_userdata (EV_A);
		3780	pthread_mutex_lock (&u->lock);
		3781	}
		3782
		3783	The event loop thread first acquires the mutex, and then jumps straight
		3784	into C<ev_run>:
		3785
		3786	void *
		3787	l_run (void *thr_arg)
		3788	{
		3789	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3790
		3791	l_acquire (EV_A);
		3792	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3793	ev_run (EV_A_ 0);
		3794	l_release (EV_A);
		3795
		3796	return 0;
		3797	}
		3798
		3799	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3800	signal the main thread via some unspecified mechanism (signals? pipe
		3801	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3802	have been called (in a while loop because a) spurious wakeups are possible
		3803	and b) skipping inter-thread-communication when there are no pending
		3804	watchers is very beneficial):
		3805
		3806	static void
		3807	l_invoke (EV_P)
		3808	{
		3809	userdata *u = ev_userdata (EV_A);
		3810
		3811	while (ev_pending_count (EV_A))
		3812	{
		3813	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3814	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3815	}
		3816	}
		3817
		3818	Now, whenever the main thread gets told to invoke pending watchers, it
		3819	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3820	thread to continue:
		3821
		3822	static void
		3823	real_invoke_pending (EV_P)
		3824	{
		3825	userdata *u = ev_userdata (EV_A);
		3826
		3827	pthread_mutex_lock (&u->lock);
		3828	ev_invoke_pending (EV_A);
		3829	pthread_cond_signal (&u->invoke_cv);
		3830	pthread_mutex_unlock (&u->lock);
		3831	}
		3832
		3833	Whenever you want to start/stop a watcher or do other modifications to an
		3834	event loop, you will now have to lock:
		3835
		3836	ev_timer timeout_watcher;
		3837	userdata *u = ev_userdata (EV_A);
		3838
		3839	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3840
		3841	pthread_mutex_lock (&u->lock);
		3842	ev_timer_start (EV_A_ &timeout_watcher);
		3843	ev_async_send (EV_A_ &u->async_w);
		3844	pthread_mutex_unlock (&u->lock);
		3845
		3846	Note that sending the C<ev_async> watcher is required because otherwise
		3847	an event loop currently blocking in the kernel will have no knowledge
		3848	about the newly added timer. By waking up the loop it will pick up any new
		3849	watchers in the next event loop iteration.
		3850
		3851	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3852
		3853	While the overhead of a callback that e.g. schedules a thread is small, it
		3854	is still an overhead. If you embed libev, and your main usage is with some
		3855	kind of threads or coroutines, you might want to customise libev so that
		3856	doesn't need callbacks anymore.
		3857
		3858	Imagine you have coroutines that you can switch to using a function
		3859	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3860	and that due to some magic, the currently active coroutine is stored in a
		3861	global called C<current_coro>. Then you can build your own "wait for libev
		3862	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3863	the differing C<;> conventions):
		3864
		3865	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3866	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3867
		3868	That means instead of having a C callback function, you store the
		3869	coroutine to switch to in each watcher, and instead of having libev call
		3870	your callback, you instead have it switch to that coroutine.
		3871
		3872	A coroutine might now wait for an event with a function called
		3873	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3874	matter when, or whether the watcher is active or not when this function is
		3875	called):
		3876
		3877	void
		3878	wait_for_event (ev_watcher *w)
		3879	{
		3880	ev_set_cb (w, current_coro);
		3881	switch_to (libev_coro);
		3882	}
		3883
		3884	That basically suspends the coroutine inside C<wait_for_event> and
		3885	continues the libev coroutine, which, when appropriate, switches back to
		3886	this or any other coroutine.
		3887
		3888	You can do similar tricks if you have, say, threads with an event queue -
		3889	instead of storing a coroutine, you store the queue object and instead of
		3890	switching to a coroutine, you push the watcher onto the queue and notify
		3891	any waiters.
		3892
		3893	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3894	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3895
		3896	// my_ev.h
		3897	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3898	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3899	#include "../libev/ev.h"
		3900
		3901	// my_ev.c
		3902	#define EV_H "my_ev.h"
		3903	#include "../libev/ev.c"
		3904
		3905	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3906	F<my_ev.c> into your project. When properly specifying include paths, you
		3907	can even use F<ev.h> as header file name directly.
1989		3908
1990		3909
1991	=head1 LIBEVENT EMULATION	3910	=head1 LIBEVENT EMULATION
1992		3911
1993	Libev offers a compatibility emulation layer for libevent. It cannot	3912	Libev offers a compatibility emulation layer for libevent. It cannot
1994	emulate the internals of libevent, so here are some usage hints:	3913	emulate the internals of libevent, so here are some usage hints:
1995		3914
1996	=over 4	3915	=over 4
		3916
		3917	=item * Only the libevent-1.4.1-beta API is being emulated.
		3918
		3919	This was the newest libevent version available when libev was implemented,
		3920	and is still mostly unchanged in 2010.
1997		3921
1998	=item * Use it by including <event.h>, as usual.	3922	=item * Use it by including <event.h>, as usual.
1999		3923
2000	=item * The following members are fully supported: ev_base, ev_callback,	3924	=item * The following members are fully supported: ev_base, ev_callback,
2001	ev_arg, ev_fd, ev_res, ev_events.	3925	ev_arg, ev_fd, ev_res, ev_events.
…		…
2006		3930
2007	=item * Priorities are not currently supported. Initialising priorities	3931	=item * Priorities are not currently supported. Initialising priorities
2008	will fail and all watchers will have the same priority, even though there	3932	will fail and all watchers will have the same priority, even though there
2009	is an ev_pri field.	3933	is an ev_pri field.
2010		3934
		3935	=item * In libevent, the last base created gets the signals, in libev, the
		3936	base that registered the signal gets the signals.
		3937
2011	=item * Other members are not supported.	3938	=item * Other members are not supported.
2012		3939
2013	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3940	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2014	to use the libev header file and library.	3941	to use the libev header file and library.
2015		3942
2016	=back	3943	=back
2017		3944
2018	=head1 C++ SUPPORT	3945	=head1 C++ SUPPORT
2019		3946
		3947	=head2 C API
		3948
		3949	The normal C API should work fine when used from C++: both ev.h and the
		3950	libev sources can be compiled as C++. Therefore, code that uses the C API
		3951	will work fine.
		3952
		3953	Proper exception specifications might have to be added to callbacks passed
		3954	to libev: exceptions may be thrown only from watcher callbacks, all
		3955	other callbacks (allocator, syserr, loop acquire/release and periodioc
		3956	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3957	()> specification. If you have code that needs to be compiled as both C
		3958	and C++ you can use the C<EV_THROW> macro for this:
		3959
		3960	static void
		3961	fatal_error (const char *msg) EV_THROW
		3962	{
		3963	perror (msg);
		3964	abort ();
		3965	}
		3966
		3967	...
		3968	ev_set_syserr_cb (fatal_error);
		3969
		3970	The only API functions that can currently throw exceptions are C<ev_run>,
		3971	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3972	because it runs cleanup watchers).
		3973
		3974	Throwing exceptions in watcher callbacks is only supported if libev itself
		3975	is compiled with a C++ compiler or your C and C++ environments allow
		3976	throwing exceptions through C libraries (most do).
		3977
		3978	=head2 C++ API
		3979
2020	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3980	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2021	you to use some convinience methods to start/stop watchers and also change	3981	you to use some convenience methods to start/stop watchers and also change
2022	the callback model to a model using method callbacks on objects.	3982	the callback model to a model using method callbacks on objects.
2023		3983
2024	To use it,	3984	To use it,
2025		3985
2026	#include <ev++.h>	3986	#include <ev++.h>
2027		3987
2028	This automatically includes F<ev.h> and puts all of its definitions (many	3988	This automatically includes F<ev.h> and puts all of its definitions (many
2029	of them macros) into the global namespace. All C++ specific things are	3989	of them macros) into the global namespace. All C++ specific things are
2030	put into the C<ev> namespace. It should support all the same embedding	3990	put into the C<ev> namespace. It should support all the same embedding
2031	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3991	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2033	Care has been taken to keep the overhead low. The only data member the C++	3993	Care has been taken to keep the overhead low. The only data member the C++
2034	classes add (compared to plain C-style watchers) is the event loop pointer	3994	classes add (compared to plain C-style watchers) is the event loop pointer
2035	that the watcher is associated with (or no additional members at all if	3995	that the watcher is associated with (or no additional members at all if
2036	you disable C<EV_MULTIPLICITY> when embedding libev).	3996	you disable C<EV_MULTIPLICITY> when embedding libev).
2037		3997
2038	Currently, functions, and static and non-static member functions can be	3998	Currently, functions, static and non-static member functions and classes
2039	used as callbacks. Other types should be easy to add as long as they only	3999	with C<operator ()> can be used as callbacks. Other types should be easy
2040	need one additional pointer for context. If you need support for other	4000	to add as long as they only need one additional pointer for context. If
2041	types of functors please contact the author (preferably after implementing	4001	you need support for other types of functors please contact the author
2042	it).	4002	(preferably after implementing it).
		4003
		4004	For all this to work, your C++ compiler either has to use the same calling
		4005	conventions as your C compiler (for static member functions), or you have
		4006	to embed libev and compile libev itself as C++.
2043		4007
2044	Here is a list of things available in the C<ev> namespace:	4008	Here is a list of things available in the C<ev> namespace:
2045		4009
2046	=over 4	4010	=over 4
2047		4011
…		…
2057	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4021	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2058		4022
2059	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4023	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2060	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4024	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2061	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4025	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2062	defines by many implementations.	4026	defined by many implementations.
2063		4027
2064	All of those classes have these methods:	4028	All of those classes have these methods:
2065		4029
2066	=over 4	4030	=over 4
2067		4031
2068	=item ev::TYPE::TYPE ()	4032	=item ev::TYPE::TYPE ()
2069		4033
2070	=item ev::TYPE::TYPE (struct ev_loop *)	4034	=item ev::TYPE::TYPE (loop)
2071		4035
2072	=item ev::TYPE::~TYPE	4036	=item ev::TYPE::~TYPE
2073		4037
2074	The constructor (optionally) takes an event loop to associate the watcher	4038	The constructor (optionally) takes an event loop to associate the watcher
2075	with. If it is omitted, it will use C<EV_DEFAULT>.	4039	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2098	your compiler is good :), then the method will be fully inlined into the	4062	your compiler is good :), then the method will be fully inlined into the
2099	thunking function, making it as fast as a direct C callback.	4063	thunking function, making it as fast as a direct C callback.
2100		4064
2101	Example: simple class declaration and watcher initialisation	4065	Example: simple class declaration and watcher initialisation
2102		4066
2103	struct myclass	4067	struct myclass
2104	{	4068	{
2105	void io_cb (ev::io &w, int revents) { }	4069	void io_cb (ev::io &w, int revents) { }
2106	}	4070	}
2107		4071
2108	myclass obj;	4072	myclass obj;
2109	ev::io iow;	4073	ev::io iow;
2110	iow.set <myclass, &myclass::io_cb> (&obj);	4074	iow.set <myclass, &myclass::io_cb> (&obj);
		4075
		4076	=item w->set (object *)
		4077
		4078	This is a variation of a method callback - leaving out the method to call
		4079	will default the method to C<operator ()>, which makes it possible to use
		4080	functor objects without having to manually specify the C<operator ()> all
		4081	the time. Incidentally, you can then also leave out the template argument
		4082	list.
		4083
		4084	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4085	int revents)>.
		4086
		4087	See the method-C<set> above for more details.
		4088
		4089	Example: use a functor object as callback.
		4090
		4091	struct myfunctor
		4092	{
		4093	void operator() (ev::io &w, int revents)
		4094	{
		4095	...
		4096	}
		4097	}
		4098
		4099	myfunctor f;
		4100
		4101	ev::io w;
		4102	w.set (&f);
2111		4103
2112	=item w->set<function> (void *data = 0)	4104	=item w->set<function> (void *data = 0)
2113		4105
2114	Also sets a callback, but uses a static method or plain function as	4106	Also sets a callback, but uses a static method or plain function as
2115	callback. The optional C<data> argument will be stored in the watcher's	4107	callback. The optional C<data> argument will be stored in the watcher's
…		…
2117		4109
2118	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4110	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2119		4111
2120	See the method-C<set> above for more details.	4112	See the method-C<set> above for more details.
2121		4113
2122	Example:	4114	Example: Use a plain function as callback.
2123		4115
2124	static void io_cb (ev::io &w, int revents) { }	4116	static void io_cb (ev::io &w, int revents) { }
2125	iow.set <io_cb> ();	4117	iow.set <io_cb> ();
2126		4118
2127	=item w->set (struct ev_loop *)	4119	=item w->set (loop)
2128		4120
2129	Associates a different C<struct ev_loop> with this watcher. You can only	4121	Associates a different C<struct ev_loop> with this watcher. You can only
2130	do this when the watcher is inactive (and not pending either).	4122	do this when the watcher is inactive (and not pending either).
2131		4123
2132	=item w->set ([args])	4124	=item w->set ([arguments])
2133		4125
2134	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4126	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2135	called at least once. Unlike the C counterpart, an active watcher gets	4127	method or a suitable start method must be called at least once. Unlike the
2136	automatically stopped and restarted when reconfiguring it with this	4128	C counterpart, an active watcher gets automatically stopped and restarted
2137	method.	4129	when reconfiguring it with this method.
2138		4130
2139	=item w->start ()	4131	=item w->start ()
2140		4132
2141	Starts the watcher. Note that there is no C<loop> argument, as the	4133	Starts the watcher. Note that there is no C<loop> argument, as the
2142	constructor already stores the event loop.	4134	constructor already stores the event loop.
2143		4135
		4136	=item w->start ([arguments])
		4137
		4138	Instead of calling C<set> and C<start> methods separately, it is often
		4139	convenient to wrap them in one call. Uses the same type of arguments as
		4140	the configure C<set> method of the watcher.
		4141
2144	=item w->stop ()	4142	=item w->stop ()
2145		4143
2146	Stops the watcher if it is active. Again, no C<loop> argument.	4144	Stops the watcher if it is active. Again, no C<loop> argument.
2147		4145
2148	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4146	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2160		4158
2161	=back	4159	=back
2162		4160
2163	=back	4161	=back
2164		4162
2165	Example: Define a class with an IO and idle watcher, start one of them in	4163	Example: Define a class with two I/O and idle watchers, start the I/O
2166	the constructor.	4164	watchers in the constructor.
2167		4165
2168	class myclass	4166	class myclass
2169	{	4167	{
2170	ev_io io; void io_cb (ev::io &w, int revents);	4168	ev::io io ; void io_cb (ev::io &w, int revents);
		4169	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2171	ev_idle idle void idle_cb (ev::idle &w, int revents);	4170	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2172		4171
2173	myclass ();	4172	myclass (int fd)
2174	}	4173	{
2175
2176	myclass::myclass (int fd)
2177	{
2178	io .set <myclass, &myclass::io_cb > (this);	4174	io .set <myclass, &myclass::io_cb > (this);
		4175	io2 .set <myclass, &myclass::io2_cb > (this);
2179	idle.set <myclass, &myclass::idle_cb> (this);	4176	idle.set <myclass, &myclass::idle_cb> (this);
2180		4177
2181	io.start (fd, ev::READ);	4178	io.set (fd, ev::WRITE); // configure the watcher
		4179	io.start (); // start it whenever convenient
		4180
		4181	io2.start (fd, ev::READ); // set + start in one call
		4182	}
2182	}	4183	};
		4184
		4185
		4186	=head1 OTHER LANGUAGE BINDINGS
		4187
		4188	Libev does not offer other language bindings itself, but bindings for a
		4189	number of languages exist in the form of third-party packages. If you know
		4190	any interesting language binding in addition to the ones listed here, drop
		4191	me a note.
		4192
		4193	=over 4
		4194
		4195	=item Perl
		4196
		4197	The EV module implements the full libev API and is actually used to test
		4198	libev. EV is developed together with libev. Apart from the EV core module,
		4199	there are additional modules that implement libev-compatible interfaces
		4200	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4201	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4202	and C<EV::Glib>).
		4203
		4204	It can be found and installed via CPAN, its homepage is at
		4205	L<http://software.schmorp.de/pkg/EV>.
		4206
		4207	=item Python
		4208
		4209	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4210	seems to be quite complete and well-documented.
		4211
		4212	=item Ruby
		4213
		4214	Tony Arcieri has written a ruby extension that offers access to a subset
		4215	of the libev API and adds file handle abstractions, asynchronous DNS and
		4216	more on top of it. It can be found via gem servers. Its homepage is at
		4217	L<http://rev.rubyforge.org/>.
		4218
		4219	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4220	makes rev work even on mingw.
		4221
		4222	=item Haskell
		4223
		4224	A haskell binding to libev is available at
		4225	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4226
		4227	=item D
		4228
		4229	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4230	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4231
		4232	=item Ocaml
		4233
		4234	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4235	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4236
		4237	=item Lua
		4238
		4239	Brian Maher has written a partial interface to libev for lua (at the
		4240	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4241	L<http://github.com/brimworks/lua-ev>.
		4242
		4243	=item Javascript
		4244
		4245	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4246
		4247	=item Others
		4248
		4249	There are others, and I stopped counting.
		4250
		4251	=back
2183		4252
2184		4253
2185	=head1 MACRO MAGIC	4254	=head1 MACRO MAGIC
2186		4255
2187	Libev can be compiled with a variety of options, the most fundamantal	4256	Libev can be compiled with a variety of options, the most fundamental
2188	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4257	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2189	functions and callbacks have an initial C<struct ev_loop *> argument.	4258	functions and callbacks have an initial C<struct ev_loop *> argument.
2190		4259
2191	To make it easier to write programs that cope with either variant, the	4260	To make it easier to write programs that cope with either variant, the
2192	following macros are defined:	4261	following macros are defined:
…		…
2197		4266
2198	This provides the loop I<argument> for functions, if one is required ("ev	4267	This provides the loop I<argument> for functions, if one is required ("ev
2199	loop argument"). The C<EV_A> form is used when this is the sole argument,	4268	loop argument"). The C<EV_A> form is used when this is the sole argument,
2200	C<EV_A_> is used when other arguments are following. Example:	4269	C<EV_A_> is used when other arguments are following. Example:
2201		4270
2202	ev_unref (EV_A);	4271	ev_unref (EV_A);
2203	ev_timer_add (EV_A_ watcher);	4272	ev_timer_add (EV_A_ watcher);
2204	ev_loop (EV_A_ 0);	4273	ev_run (EV_A_ 0);
2205		4274
2206	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4275	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2207	which is often provided by the following macro.	4276	which is often provided by the following macro.
2208		4277
2209	=item C<EV_P>, C<EV_P_>	4278	=item C<EV_P>, C<EV_P_>
2210		4279
2211	This provides the loop I<parameter> for functions, if one is required ("ev	4280	This provides the loop I<parameter> for functions, if one is required ("ev
2212	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4281	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2213	C<EV_P_> is used when other parameters are following. Example:	4282	C<EV_P_> is used when other parameters are following. Example:
2214		4283
2215	// this is how ev_unref is being declared	4284	// this is how ev_unref is being declared
2216	static void ev_unref (EV_P);	4285	static void ev_unref (EV_P);
2217		4286
2218	// this is how you can declare your typical callback	4287	// this is how you can declare your typical callback
2219	static void cb (EV_P_ ev_timer *w, int revents)	4288	static void cb (EV_P_ ev_timer *w, int revents)
2220		4289
2221	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4290	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2222	suitable for use with C<EV_A>.	4291	suitable for use with C<EV_A>.
2223		4292
2224	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4293	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2225		4294
2226	Similar to the other two macros, this gives you the value of the default	4295	Similar to the other two macros, this gives you the value of the default
2227	loop, if multiple loops are supported ("ev loop default").	4296	loop, if multiple loops are supported ("ev loop default"). The default loop
		4297	will be initialised if it isn't already initialised.
		4298
		4299	For non-multiplicity builds, these macros do nothing, so you always have
		4300	to initialise the loop somewhere.
		4301
		4302	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4303
		4304	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4305	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4306	is undefined when the default loop has not been initialised by a previous
		4307	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4308
		4309	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4310	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2228		4311
2229	=back	4312	=back
2230		4313
2231	Example: Declare and initialise a check watcher, utilising the above	4314	Example: Declare and initialise a check watcher, utilising the above
2232	macros so it will work regardless of whether multiple loops are supported	4315	macros so it will work regardless of whether multiple loops are supported
2233	or not.	4316	or not.
2234		4317
2235	static void	4318	static void
2236	check_cb (EV_P_ ev_timer *w, int revents)	4319	check_cb (EV_P_ ev_timer *w, int revents)
2237	{	4320	{
2238	ev_check_stop (EV_A_ w);	4321	ev_check_stop (EV_A_ w);
2239	}	4322	}
2240		4323
2241	ev_check check;	4324	ev_check check;
2242	ev_check_init (&check, check_cb);	4325	ev_check_init (&check, check_cb);
2243	ev_check_start (EV_DEFAULT_ &check);	4326	ev_check_start (EV_DEFAULT_ &check);
2244	ev_loop (EV_DEFAULT_ 0);	4327	ev_run (EV_DEFAULT_ 0);
2245		4328
2246	=head1 EMBEDDING	4329	=head1 EMBEDDING
2247		4330
2248	Libev can (and often is) directly embedded into host	4331	Libev can (and often is) directly embedded into host
2249	applications. Examples of applications that embed it include the Deliantra	4332	applications. Examples of applications that embed it include the Deliantra
…		…
2256	libev somewhere in your source tree).	4339	libev somewhere in your source tree).
2257		4340
2258	=head2 FILESETS	4341	=head2 FILESETS
2259		4342
2260	Depending on what features you need you need to include one or more sets of files	4343	Depending on what features you need you need to include one or more sets of files
2261	in your app.	4344	in your application.
2262		4345
2263	=head3 CORE EVENT LOOP	4346	=head3 CORE EVENT LOOP
2264		4347
2265	To include only the libev core (all the C<ev_*> functions), with manual	4348	To include only the libev core (all the C<ev_*> functions), with manual
2266	configuration (no autoconf):	4349	configuration (no autoconf):
2267		4350
2268	#define EV_STANDALONE 1	4351	#define EV_STANDALONE 1
2269	#include "ev.c"	4352	#include "ev.c"
2270		4353
2271	This will automatically include F<ev.h>, too, and should be done in a	4354	This will automatically include F<ev.h>, too, and should be done in a
2272	single C source file only to provide the function implementations. To use	4355	single C source file only to provide the function implementations. To use
2273	it, do the same for F<ev.h> in all files wishing to use this API (best	4356	it, do the same for F<ev.h> in all files wishing to use this API (best
2274	done by writing a wrapper around F<ev.h> that you can include instead and	4357	done by writing a wrapper around F<ev.h> that you can include instead and
2275	where you can put other configuration options):	4358	where you can put other configuration options):
2276		4359
2277	#define EV_STANDALONE 1	4360	#define EV_STANDALONE 1
2278	#include "ev.h"	4361	#include "ev.h"
2279		4362
2280	Both header files and implementation files can be compiled with a C++	4363	Both header files and implementation files can be compiled with a C++
2281	compiler (at least, thats a stated goal, and breakage will be treated	4364	compiler (at least, that's a stated goal, and breakage will be treated
2282	as a bug).	4365	as a bug).
2283		4366
2284	You need the following files in your source tree, or in a directory	4367	You need the following files in your source tree, or in a directory
2285	in your include path (e.g. in libev/ when using -Ilibev):	4368	in your include path (e.g. in libev/ when using -Ilibev):
2286		4369
2287	ev.h	4370	ev.h
2288	ev.c	4371	ev.c
2289	ev_vars.h	4372	ev_vars.h
2290	ev_wrap.h	4373	ev_wrap.h
2291		4374
2292	ev_win32.c required on win32 platforms only	4375	ev_win32.c required on win32 platforms only
2293		4376
2294	ev_select.c only when select backend is enabled (which is enabled by default)	4377	ev_select.c only when select backend is enabled (which is enabled by default)
2295	ev_poll.c only when poll backend is enabled (disabled by default)	4378	ev_poll.c only when poll backend is enabled (disabled by default)
2296	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4379	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2297	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4380	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2298	ev_port.c only when the solaris port backend is enabled (disabled by default)	4381	ev_port.c only when the solaris port backend is enabled (disabled by default)
2299		4382
2300	F<ev.c> includes the backend files directly when enabled, so you only need	4383	F<ev.c> includes the backend files directly when enabled, so you only need
2301	to compile this single file.	4384	to compile this single file.
2302		4385
2303	=head3 LIBEVENT COMPATIBILITY API	4386	=head3 LIBEVENT COMPATIBILITY API
2304		4387
2305	To include the libevent compatibility API, also include:	4388	To include the libevent compatibility API, also include:
2306		4389
2307	#include "event.c"	4390	#include "event.c"
2308		4391
2309	in the file including F<ev.c>, and:	4392	in the file including F<ev.c>, and:
2310		4393
2311	#include "event.h"	4394	#include "event.h"
2312		4395
2313	in the files that want to use the libevent API. This also includes F<ev.h>.	4396	in the files that want to use the libevent API. This also includes F<ev.h>.
2314		4397
2315	You need the following additional files for this:	4398	You need the following additional files for this:
2316		4399
2317	event.h	4400	event.h
2318	event.c	4401	event.c
2319		4402
2320	=head3 AUTOCONF SUPPORT	4403	=head3 AUTOCONF SUPPORT
2321		4404
2322	Instead of using C<EV_STANDALONE=1> and providing your config in	4405	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2323	whatever way you want, you can also C<m4_include([libev.m4])> in your	4406	whatever way you want, you can also C<m4_include([libev.m4])> in your
2324	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4407	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2325	include F<config.h> and configure itself accordingly.	4408	include F<config.h> and configure itself accordingly.
2326		4409
2327	For this of course you need the m4 file:	4410	For this of course you need the m4 file:
2328		4411
2329	libev.m4	4412	libev.m4
2330		4413
2331	=head2 PREPROCESSOR SYMBOLS/MACROS	4414	=head2 PREPROCESSOR SYMBOLS/MACROS
2332		4415
2333	Libev can be configured via a variety of preprocessor symbols you have to define	4416	Libev can be configured via a variety of preprocessor symbols you have to
2334	before including any of its files. The default is not to build for multiplicity	4417	define before including (or compiling) any of its files. The default in
2335	and only include the select backend.	4418	the absence of autoconf is documented for every option.
		4419
		4420	Symbols marked with "(h)" do not change the ABI, and can have different
		4421	values when compiling libev vs. including F<ev.h>, so it is permissible
		4422	to redefine them before including F<ev.h> without breaking compatibility
		4423	to a compiled library. All other symbols change the ABI, which means all
		4424	users of libev and the libev code itself must be compiled with compatible
		4425	settings.
2336		4426
2337	=over 4	4427	=over 4
2338		4428
		4429	=item EV_COMPAT3 (h)
		4430
		4431	Backwards compatibility is a major concern for libev. This is why this
		4432	release of libev comes with wrappers for the functions and symbols that
		4433	have been renamed between libev version 3 and 4.
		4434
		4435	You can disable these wrappers (to test compatibility with future
		4436	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4437	sources. This has the additional advantage that you can drop the C<struct>
		4438	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4439	typedef in that case.
		4440
		4441	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4442	and in some even more future version the compatibility code will be
		4443	removed completely.
		4444
2339	=item EV_STANDALONE	4445	=item EV_STANDALONE (h)
2340		4446
2341	Must always be C<1> if you do not use autoconf configuration, which	4447	Must always be C<1> if you do not use autoconf configuration, which
2342	keeps libev from including F<config.h>, and it also defines dummy	4448	keeps libev from including F<config.h>, and it also defines dummy
2343	implementations for some libevent functions (such as logging, which is not	4449	implementations for some libevent functions (such as logging, which is not
2344	supported). It will also not define any of the structs usually found in	4450	supported). It will also not define any of the structs usually found in
2345	F<event.h> that are not directly supported by the libev core alone.	4451	F<event.h> that are not directly supported by the libev core alone.
2346		4452
		4453	In standalone mode, libev will still try to automatically deduce the
		4454	configuration, but has to be more conservative.
		4455
		4456	=item EV_USE_FLOOR
		4457
		4458	If defined to be C<1>, libev will use the C<floor ()> function for its
		4459	periodic reschedule calculations, otherwise libev will fall back on a
		4460	portable (slower) implementation. If you enable this, you usually have to
		4461	link against libm or something equivalent. Enabling this when the C<floor>
		4462	function is not available will fail, so the safe default is to not enable
		4463	this.
		4464
2347	=item EV_USE_MONOTONIC	4465	=item EV_USE_MONOTONIC
2348		4466
2349	If defined to be C<1>, libev will try to detect the availability of the	4467	If defined to be C<1>, libev will try to detect the availability of the
2350	monotonic clock option at both compiletime and runtime. Otherwise no use	4468	monotonic clock option at both compile time and runtime. Otherwise no
2351	of the monotonic clock option will be attempted. If you enable this, you	4469	use of the monotonic clock option will be attempted. If you enable this,
2352	usually have to link against librt or something similar. Enabling it when	4470	you usually have to link against librt or something similar. Enabling it
2353	the functionality isn't available is safe, though, although you have	4471	when the functionality isn't available is safe, though, although you have
2354	to make sure you link against any libraries where the C<clock_gettime>	4472	to make sure you link against any libraries where the C<clock_gettime>
2355	function is hiding in (often F<-lrt>).	4473	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2356		4474
2357	=item EV_USE_REALTIME	4475	=item EV_USE_REALTIME
2358		4476
2359	If defined to be C<1>, libev will try to detect the availability of the	4477	If defined to be C<1>, libev will try to detect the availability of the
2360	realtime clock option at compiletime (and assume its availability at	4478	real-time clock option at compile time (and assume its availability
2361	runtime if successful). Otherwise no use of the realtime clock option will	4479	at runtime if successful). Otherwise no use of the real-time clock
2362	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4480	option will be attempted. This effectively replaces C<gettimeofday>
2363	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4481	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2364	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4482	correctness. See the note about libraries in the description of
		4483	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4484	C<EV_USE_CLOCK_SYSCALL>.
		4485
		4486	=item EV_USE_CLOCK_SYSCALL
		4487
		4488	If defined to be C<1>, libev will try to use a direct syscall instead
		4489	of calling the system-provided C<clock_gettime> function. This option
		4490	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4491	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4492	programs needlessly. Using a direct syscall is slightly slower (in
		4493	theory), because no optimised vdso implementation can be used, but avoids
		4494	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4495	higher, as it simplifies linking (no need for C<-lrt>).
2365		4496
2366	=item EV_USE_NANOSLEEP	4497	=item EV_USE_NANOSLEEP
2367		4498
2368	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4499	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2369	and will use it for delays. Otherwise it will use C<select ()>.	4500	and will use it for delays. Otherwise it will use C<select ()>.
2370		4501
		4502	=item EV_USE_EVENTFD
		4503
		4504	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4505	available and will probe for kernel support at runtime. This will improve
		4506	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4507	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4508	2.7 or newer, otherwise disabled.
		4509
2371	=item EV_USE_SELECT	4510	=item EV_USE_SELECT
2372		4511
2373	If undefined or defined to be C<1>, libev will compile in support for the	4512	If undefined or defined to be C<1>, libev will compile in support for the
2374	C<select>(2) backend. No attempt at autodetection will be done: if no	4513	C<select>(2) backend. No attempt at auto-detection will be done: if no
2375	other method takes over, select will be it. Otherwise the select backend	4514	other method takes over, select will be it. Otherwise the select backend
2376	will not be compiled in.	4515	will not be compiled in.
2377		4516
2378	=item EV_SELECT_USE_FD_SET	4517	=item EV_SELECT_USE_FD_SET
2379		4518
2380	If defined to C<1>, then the select backend will use the system C<fd_set>	4519	If defined to C<1>, then the select backend will use the system C<fd_set>
2381	structure. This is useful if libev doesn't compile due to a missing	4520	structure. This is useful if libev doesn't compile due to a missing
2382	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4521	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2383	exotic systems. This usually limits the range of file descriptors to some	4522	on exotic systems. This usually limits the range of file descriptors to
2384	low limit such as 1024 or might have other limitations (winsocket only	4523	some low limit such as 1024 or might have other limitations (winsocket
2385	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4524	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2386	influence the size of the C<fd_set> used.	4525	configures the maximum size of the C<fd_set>.
2387		4526
2388	=item EV_SELECT_IS_WINSOCKET	4527	=item EV_SELECT_IS_WINSOCKET
2389		4528
2390	When defined to C<1>, the select backend will assume that	4529	When defined to C<1>, the select backend will assume that
2391	select/socket/connect etc. don't understand file descriptors but	4530	select/socket/connect etc. don't understand file descriptors but
…		…
2393	be used is the winsock select). This means that it will call	4532	be used is the winsock select). This means that it will call
2394	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4533	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2395	it is assumed that all these functions actually work on fds, even	4534	it is assumed that all these functions actually work on fds, even
2396	on win32. Should not be defined on non-win32 platforms.	4535	on win32. Should not be defined on non-win32 platforms.
2397		4536
		4537	=item EV_FD_TO_WIN32_HANDLE(fd)
		4538
		4539	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4540	file descriptors to socket handles. When not defining this symbol (the
		4541	default), then libev will call C<_get_osfhandle>, which is usually
		4542	correct. In some cases, programs use their own file descriptor management,
		4543	in which case they can provide this function to map fds to socket handles.
		4544
		4545	=item EV_WIN32_HANDLE_TO_FD(handle)
		4546
		4547	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4548	using the standard C<_open_osfhandle> function. For programs implementing
		4549	their own fd to handle mapping, overwriting this function makes it easier
		4550	to do so. This can be done by defining this macro to an appropriate value.
		4551
		4552	=item EV_WIN32_CLOSE_FD(fd)
		4553
		4554	If programs implement their own fd to handle mapping on win32, then this
		4555	macro can be used to override the C<close> function, useful to unregister
		4556	file descriptors again. Note that the replacement function has to close
		4557	the underlying OS handle.
		4558
2398	=item EV_USE_POLL	4559	=item EV_USE_POLL
2399		4560
2400	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4561	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2401	backend. Otherwise it will be enabled on non-win32 platforms. It	4562	backend. Otherwise it will be enabled on non-win32 platforms. It
2402	takes precedence over select.	4563	takes precedence over select.
2403		4564
2404	=item EV_USE_EPOLL	4565	=item EV_USE_EPOLL
2405		4566
2406	If defined to be C<1>, libev will compile in support for the Linux	4567	If defined to be C<1>, libev will compile in support for the Linux
2407	C<epoll>(7) backend. Its availability will be detected at runtime,	4568	C<epoll>(7) backend. Its availability will be detected at runtime,
2408	otherwise another method will be used as fallback. This is the	4569	otherwise another method will be used as fallback. This is the preferred
2409	preferred backend for GNU/Linux systems.	4570	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4571	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2410		4572
2411	=item EV_USE_KQUEUE	4573	=item EV_USE_KQUEUE
2412		4574
2413	If defined to be C<1>, libev will compile in support for the BSD style	4575	If defined to be C<1>, libev will compile in support for the BSD style
2414	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4576	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2427	otherwise another method will be used as fallback. This is the preferred	4589	otherwise another method will be used as fallback. This is the preferred
2428	backend for Solaris 10 systems.	4590	backend for Solaris 10 systems.
2429		4591
2430	=item EV_USE_DEVPOLL	4592	=item EV_USE_DEVPOLL
2431		4593
2432	reserved for future expansion, works like the USE symbols above.	4594	Reserved for future expansion, works like the USE symbols above.
2433		4595
2434	=item EV_USE_INOTIFY	4596	=item EV_USE_INOTIFY
2435		4597
2436	If defined to be C<1>, libev will compile in support for the Linux inotify	4598	If defined to be C<1>, libev will compile in support for the Linux inotify
2437	interface to speed up C<ev_stat> watchers. Its actual availability will	4599	interface to speed up C<ev_stat> watchers. Its actual availability will
2438	be detected at runtime.	4600	be detected at runtime. If undefined, it will be enabled if the headers
		4601	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2439		4602
		4603	=item EV_NO_SMP
		4604
		4605	If defined to be C<1>, libev will assume that memory is always coherent
		4606	between threads, that is, threads can be used, but threads never run on
		4607	different cpus (or different cpu cores). This reduces dependencies
		4608	and makes libev faster.
		4609
		4610	=item EV_NO_THREADS
		4611
		4612	If defined to be C<1>, libev will assume that it will never be called
		4613	from different threads, which is a stronger assumption than C<EV_NO_SMP>,
		4614	above. This reduces dependencies and makes libev faster.
		4615
		4616	=item EV_ATOMIC_T
		4617
		4618	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4619	access is atomic and serialised with respect to other threads or signal
		4620	contexts. No such type is easily found in the C language, so you can
		4621	provide your own type that you know is safe for your purposes. It is used
		4622	both for signal handler "locking" as well as for signal and thread safety
		4623	in C<ev_async> watchers.
		4624
		4625	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4626	(from F<signal.h>), which is usually good enough on most platforms,
		4627	although strictly speaking using a type that also implies a memory fence
		4628	is required.
		4629
2440	=item EV_H	4630	=item EV_H (h)
2441		4631
2442	The name of the F<ev.h> header file used to include it. The default if	4632	The name of the F<ev.h> header file used to include it. The default if
2443	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4633	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2444	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4634	used to virtually rename the F<ev.h> header file in case of conflicts.
2445		4635
2446	=item EV_CONFIG_H	4636	=item EV_CONFIG_H (h)
2447		4637
2448	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4638	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2449	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4639	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2450	C<EV_H>, above.	4640	C<EV_H>, above.
2451		4641
2452	=item EV_EVENT_H	4642	=item EV_EVENT_H (h)
2453		4643
2454	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4644	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2455	of how the F<event.h> header can be found.	4645	of how the F<event.h> header can be found, the default is C<"event.h">.
2456		4646
2457	=item EV_PROTOTYPES	4647	=item EV_PROTOTYPES (h)
2458		4648
2459	If defined to be C<0>, then F<ev.h> will not define any function	4649	If defined to be C<0>, then F<ev.h> will not define any function
2460	prototypes, but still define all the structs and other symbols. This is	4650	prototypes, but still define all the structs and other symbols. This is
2461	occasionally useful if you want to provide your own wrapper functions	4651	occasionally useful if you want to provide your own wrapper functions
2462	around libev functions.	4652	around libev functions.
…		…
2467	will have the C<struct ev_loop *> as first argument, and you can create	4657	will have the C<struct ev_loop *> as first argument, and you can create
2468	additional independent event loops. Otherwise there will be no support	4658	additional independent event loops. Otherwise there will be no support
2469	for multiple event loops and there is no first event loop pointer	4659	for multiple event loops and there is no first event loop pointer
2470	argument. Instead, all functions act on the single default loop.	4660	argument. Instead, all functions act on the single default loop.
2471		4661
		4662	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4663	default loop when multiplicity is switched off - you always have to
		4664	initialise the loop manually in this case.
		4665
2472	=item EV_MINPRI	4666	=item EV_MINPRI
2473		4667
2474	=item EV_MAXPRI	4668	=item EV_MAXPRI
2475		4669
2476	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4670	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2481	When doing priority-based operations, libev usually has to linearly search	4675	When doing priority-based operations, libev usually has to linearly search
2482	all the priorities, so having many of them (hundreds) uses a lot of space	4676	all the priorities, so having many of them (hundreds) uses a lot of space
2483	and time, so using the defaults of five priorities (-2 .. +2) is usually	4677	and time, so using the defaults of five priorities (-2 .. +2) is usually
2484	fine.	4678	fine.
2485		4679
2486	If your embedding app does not need any priorities, defining these both to	4680	If your embedding application does not need any priorities, defining these
2487	C<0> will save some memory and cpu.	4681	both to C<0> will save some memory and CPU.
2488		4682
2489	=item EV_PERIODIC_ENABLE	4683	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4684	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4685	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2490		4686
2491	If undefined or defined to be C<1>, then periodic timers are supported. If	4687	If undefined or defined to be C<1> (and the platform supports it), then
2492	defined to be C<0>, then they are not. Disabling them saves a few kB of	4688	the respective watcher type is supported. If defined to be C<0>, then it
2493	code.	4689	is not. Disabling watcher types mainly saves code size.
2494		4690
2495	=item EV_IDLE_ENABLE	4691	=item EV_FEATURES
2496
2497	If undefined or defined to be C<1>, then idle watchers are supported. If
2498	defined to be C<0>, then they are not. Disabling them saves a few kB of
2499	code.
2500
2501	=item EV_EMBED_ENABLE
2502
2503	If undefined or defined to be C<1>, then embed watchers are supported. If
2504	defined to be C<0>, then they are not.
2505
2506	=item EV_STAT_ENABLE
2507
2508	If undefined or defined to be C<1>, then stat watchers are supported. If
2509	defined to be C<0>, then they are not.
2510
2511	=item EV_FORK_ENABLE
2512
2513	If undefined or defined to be C<1>, then fork watchers are supported. If
2514	defined to be C<0>, then they are not.
2515
2516	=item EV_MINIMAL
2517		4692
2518	If you need to shave off some kilobytes of code at the expense of some	4693	If you need to shave off some kilobytes of code at the expense of some
2519	speed, define this symbol to C<1>. Currently only used for gcc to override	4694	speed (but with the full API), you can define this symbol to request
2520	some inlining decisions, saves roughly 30% codesize of amd64.	4695	certain subsets of functionality. The default is to enable all features
		4696	that can be enabled on the platform.
		4697
		4698	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4699	with some broad features you want) and then selectively re-enable
		4700	additional parts you want, for example if you want everything minimal,
		4701	but multiple event loop support, async and child watchers and the poll
		4702	backend, use this:
		4703
		4704	#define EV_FEATURES 0
		4705	#define EV_MULTIPLICITY 1
		4706	#define EV_USE_POLL 1
		4707	#define EV_CHILD_ENABLE 1
		4708	#define EV_ASYNC_ENABLE 1
		4709
		4710	The actual value is a bitset, it can be a combination of the following
		4711	values (by default, all of these are enabled):
		4712
		4713	=over 4
		4714
		4715	=item C<1> - faster/larger code
		4716
		4717	Use larger code to speed up some operations.
		4718
		4719	Currently this is used to override some inlining decisions (enlarging the
		4720	code size by roughly 30% on amd64).
		4721
		4722	When optimising for size, use of compiler flags such as C<-Os> with
		4723	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4724	assertions.
		4725
		4726	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4727	(e.g. gcc with C<-Os>).
		4728
		4729	=item C<2> - faster/larger data structures
		4730
		4731	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4732	hash table sizes and so on. This will usually further increase code size
		4733	and can additionally have an effect on the size of data structures at
		4734	runtime.
		4735
		4736	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4737	(e.g. gcc with C<-Os>).
		4738
		4739	=item C<4> - full API configuration
		4740
		4741	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4742	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4743
		4744	=item C<8> - full API
		4745
		4746	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4747	details on which parts of the API are still available without this
		4748	feature, and do not complain if this subset changes over time.
		4749
		4750	=item C<16> - enable all optional watcher types
		4751
		4752	Enables all optional watcher types. If you want to selectively enable
		4753	only some watcher types other than I/O and timers (e.g. prepare,
		4754	embed, async, child...) you can enable them manually by defining
		4755	C<EV_watchertype_ENABLE> to C<1> instead.
		4756
		4757	=item C<32> - enable all backends
		4758
		4759	This enables all backends - without this feature, you need to enable at
		4760	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4761
		4762	=item C<64> - enable OS-specific "helper" APIs
		4763
		4764	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4765	default.
		4766
		4767	=back
		4768
		4769	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4770	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4771	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4772	watchers, timers and monotonic clock support.
		4773
		4774	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4775	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4776	your program might be left out as well - a binary starting a timer and an
		4777	I/O watcher then might come out at only 5Kb.
		4778
		4779	=item EV_API_STATIC
		4780
		4781	If this symbol is defined (by default it is not), then all identifiers
		4782	will have static linkage. This means that libev will not export any
		4783	identifiers, and you cannot link against libev anymore. This can be useful
		4784	when you embed libev, only want to use libev functions in a single file,
		4785	and do not want its identifiers to be visible.
		4786
		4787	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4788	wants to use libev.
		4789
		4790	This option only works when libev is compiled with a C compiler, as C++
		4791	doesn't support the required declaration syntax.
		4792
		4793	=item EV_AVOID_STDIO
		4794
		4795	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4796	functions (printf, scanf, perror etc.). This will increase the code size
		4797	somewhat, but if your program doesn't otherwise depend on stdio and your
		4798	libc allows it, this avoids linking in the stdio library which is quite
		4799	big.
		4800
		4801	Note that error messages might become less precise when this option is
		4802	enabled.
		4803
		4804	=item EV_NSIG
		4805
		4806	The highest supported signal number, +1 (or, the number of
		4807	signals): Normally, libev tries to deduce the maximum number of signals
		4808	automatically, but sometimes this fails, in which case it can be
		4809	specified. Also, using a lower number than detected (C<32> should be
		4810	good for about any system in existence) can save some memory, as libev
		4811	statically allocates some 12-24 bytes per signal number.
2521		4812
2522	=item EV_PID_HASHSIZE	4813	=item EV_PID_HASHSIZE
2523		4814
2524	C<ev_child> watchers use a small hash table to distribute workload by	4815	C<ev_child> watchers use a small hash table to distribute workload by
2525	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4816	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2526	than enough. If you need to manage thousands of children you might want to	4817	usually more than enough. If you need to manage thousands of children you
2527	increase this value (I<must> be a power of two).	4818	might want to increase this value (I<must> be a power of two).
2528		4819
2529	=item EV_INOTIFY_HASHSIZE	4820	=item EV_INOTIFY_HASHSIZE
2530		4821
2531	C<ev_stat> watchers use a small hash table to distribute workload by	4822	C<ev_stat> watchers use a small hash table to distribute workload by
2532	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4823	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2533	usually more than enough. If you need to manage thousands of C<ev_stat>	4824	disabled), usually more than enough. If you need to manage thousands of
2534	watchers you might want to increase this value (I<must> be a power of	4825	C<ev_stat> watchers you might want to increase this value (I<must> be a
2535	two).	4826	power of two).
		4827
		4828	=item EV_USE_4HEAP
		4829
		4830	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4831	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4832	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4833	faster performance with many (thousands) of watchers.
		4834
		4835	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4836	will be C<0>.
		4837
		4838	=item EV_HEAP_CACHE_AT
		4839
		4840	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4841	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4842	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4843	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4844	but avoids random read accesses on heap changes. This improves performance
		4845	noticeably with many (hundreds) of watchers.
		4846
		4847	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4848	will be C<0>.
		4849
		4850	=item EV_VERIFY
		4851
		4852	Controls how much internal verification (see C<ev_verify ()>) will
		4853	be done: If set to C<0>, no internal verification code will be compiled
		4854	in. If set to C<1>, then verification code will be compiled in, but not
		4855	called. If set to C<2>, then the internal verification code will be
		4856	called once per loop, which can slow down libev. If set to C<3>, then the
		4857	verification code will be called very frequently, which will slow down
		4858	libev considerably.
		4859
		4860	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4861	will be C<0>.
2536		4862
2537	=item EV_COMMON	4863	=item EV_COMMON
2538		4864
2539	By default, all watchers have a C<void *data> member. By redefining	4865	By default, all watchers have a C<void *data> member. By redefining
2540	this macro to a something else you can include more and other types of	4866	this macro to something else you can include more and other types of
2541	members. You have to define it each time you include one of the files,	4867	members. You have to define it each time you include one of the files,
2542	though, and it must be identical each time.	4868	though, and it must be identical each time.
2543		4869
2544	For example, the perl EV module uses something like this:	4870	For example, the perl EV module uses something like this:
2545		4871
2546	#define EV_COMMON \	4872	#define EV_COMMON \
2547	SV *self; /* contains this struct */ \	4873	SV *self; /* contains this struct */ \
2548	SV *cb_sv, *fh /* note no trailing ";" */	4874	SV *cb_sv, *fh /* note no trailing ";" */
2549		4875
2550	=item EV_CB_DECLARE (type)	4876	=item EV_CB_DECLARE (type)
2551		4877
2552	=item EV_CB_INVOKE (watcher, revents)	4878	=item EV_CB_INVOKE (watcher, revents)
2553		4879
…		…
2558	definition and a statement, respectively. See the F<ev.h> header file for	4884	definition and a statement, respectively. See the F<ev.h> header file for
2559	their default definitions. One possible use for overriding these is to	4885	their default definitions. One possible use for overriding these is to
2560	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4886	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2561	method calls instead of plain function calls in C++.	4887	method calls instead of plain function calls in C++.
2562		4888
		4889	=back
		4890
2563	=head2 EXPORTED API SYMBOLS	4891	=head2 EXPORTED API SYMBOLS
2564		4892
2565	If you need to re-export the API (e.g. via a dll) and you need a list of	4893	If you need to re-export the API (e.g. via a DLL) and you need a list of
2566	exported symbols, you can use the provided F<Symbol.*> files which list	4894	exported symbols, you can use the provided F<Symbol.*> files which list
2567	all public symbols, one per line:	4895	all public symbols, one per line:
2568		4896
2569	Symbols.ev for libev proper	4897	Symbols.ev for libev proper
2570	Symbols.event for the libevent emulation	4898	Symbols.event for the libevent emulation
2571		4899
2572	This can also be used to rename all public symbols to avoid clashes with	4900	This can also be used to rename all public symbols to avoid clashes with
2573	multiple versions of libev linked together (which is obviously bad in	4901	multiple versions of libev linked together (which is obviously bad in
2574	itself, but sometimes it is inconvinient to avoid this).	4902	itself, but sometimes it is inconvenient to avoid this).
2575		4903
2576	A sed command like this will create wrapper C<#define>'s that you need to	4904	A sed command like this will create wrapper C<#define>'s that you need to
2577	include before including F<ev.h>:	4905	include before including F<ev.h>:
2578		4906
2579	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4907	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2596	file.	4924	file.
2597		4925
2598	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4926	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2599	that everybody includes and which overrides some configure choices:	4927	that everybody includes and which overrides some configure choices:
2600		4928
2601	#define EV_MINIMAL 1	4929	#define EV_FEATURES 8
2602	#define EV_USE_POLL 0	4930	#define EV_USE_SELECT 1
2603	#define EV_MULTIPLICITY 0
2604	#define EV_PERIODIC_ENABLE 0	4931	#define EV_PREPARE_ENABLE 1
		4932	#define EV_IDLE_ENABLE 1
2605	#define EV_STAT_ENABLE 0	4933	#define EV_SIGNAL_ENABLE 1
2606	#define EV_FORK_ENABLE 0	4934	#define EV_CHILD_ENABLE 1
		4935	#define EV_USE_STDEXCEPT 0
2607	#define EV_CONFIG_H <config.h>	4936	#define EV_CONFIG_H <config.h>
2608	#define EV_MINPRI 0
2609	#define EV_MAXPRI 0
2610		4937
2611	#include "ev++.h"	4938	#include "ev++.h"
2612		4939
2613	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4940	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2614		4941
2615	#include "ev_cpp.h"	4942	#include "ev_cpp.h"
2616	#include "ev.c"	4943	#include "ev.c"
2617		4944
		4945	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2618		4946
		4947	=head2 THREADS AND COROUTINES
		4948
		4949	=head3 THREADS
		4950
		4951	All libev functions are reentrant and thread-safe unless explicitly
		4952	documented otherwise, but libev implements no locking itself. This means
		4953	that you can use as many loops as you want in parallel, as long as there
		4954	are no concurrent calls into any libev function with the same loop
		4955	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4956	of course): libev guarantees that different event loops share no data
		4957	structures that need any locking.
		4958
		4959	Or to put it differently: calls with different loop parameters can be done
		4960	concurrently from multiple threads, calls with the same loop parameter
		4961	must be done serially (but can be done from different threads, as long as
		4962	only one thread ever is inside a call at any point in time, e.g. by using
		4963	a mutex per loop).
		4964
		4965	Specifically to support threads (and signal handlers), libev implements
		4966	so-called C<ev_async> watchers, which allow some limited form of
		4967	concurrency on the same event loop, namely waking it up "from the
		4968	outside".
		4969
		4970	If you want to know which design (one loop, locking, or multiple loops
		4971	without or something else still) is best for your problem, then I cannot
		4972	help you, but here is some generic advice:
		4973
		4974	=over 4
		4975
		4976	=item * most applications have a main thread: use the default libev loop
		4977	in that thread, or create a separate thread running only the default loop.
		4978
		4979	This helps integrating other libraries or software modules that use libev
		4980	themselves and don't care/know about threading.
		4981
		4982	=item * one loop per thread is usually a good model.
		4983
		4984	Doing this is almost never wrong, sometimes a better-performance model
		4985	exists, but it is always a good start.
		4986
		4987	=item * other models exist, such as the leader/follower pattern, where one
		4988	loop is handed through multiple threads in a kind of round-robin fashion.
		4989
		4990	Choosing a model is hard - look around, learn, know that usually you can do
		4991	better than you currently do :-)
		4992
		4993	=item * often you need to talk to some other thread which blocks in the
		4994	event loop.
		4995
		4996	C<ev_async> watchers can be used to wake them up from other threads safely
		4997	(or from signal contexts...).
		4998
		4999	An example use would be to communicate signals or other events that only
		5000	work in the default loop by registering the signal watcher with the
		5001	default loop and triggering an C<ev_async> watcher from the default loop
		5002	watcher callback into the event loop interested in the signal.
		5003
		5004	=back
		5005
		5006	See also L</THREAD LOCKING EXAMPLE>.
		5007
		5008	=head3 COROUTINES
		5009
		5010	Libev is very accommodating to coroutines ("cooperative threads"):
		5011	libev fully supports nesting calls to its functions from different
		5012	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5013	different coroutines, and switch freely between both coroutines running
		5014	the loop, as long as you don't confuse yourself). The only exception is
		5015	that you must not do this from C<ev_periodic> reschedule callbacks.
		5016
		5017	Care has been taken to ensure that libev does not keep local state inside
		5018	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5019	they do not call any callbacks.
		5020
		5021	=head2 COMPILER WARNINGS
		5022
		5023	Depending on your compiler and compiler settings, you might get no or a
		5024	lot of warnings when compiling libev code. Some people are apparently
		5025	scared by this.
		5026
		5027	However, these are unavoidable for many reasons. For one, each compiler
		5028	has different warnings, and each user has different tastes regarding
		5029	warning options. "Warn-free" code therefore cannot be a goal except when
		5030	targeting a specific compiler and compiler-version.
		5031
		5032	Another reason is that some compiler warnings require elaborate
		5033	workarounds, or other changes to the code that make it less clear and less
		5034	maintainable.
		5035
		5036	And of course, some compiler warnings are just plain stupid, or simply
		5037	wrong (because they don't actually warn about the condition their message
		5038	seems to warn about). For example, certain older gcc versions had some
		5039	warnings that resulted in an extreme number of false positives. These have
		5040	been fixed, but some people still insist on making code warn-free with
		5041	such buggy versions.
		5042
		5043	While libev is written to generate as few warnings as possible,
		5044	"warn-free" code is not a goal, and it is recommended not to build libev
		5045	with any compiler warnings enabled unless you are prepared to cope with
		5046	them (e.g. by ignoring them). Remember that warnings are just that:
		5047	warnings, not errors, or proof of bugs.
		5048
		5049
		5050	=head2 VALGRIND
		5051
		5052	Valgrind has a special section here because it is a popular tool that is
		5053	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5054
		5055	If you think you found a bug (memory leak, uninitialised data access etc.)
		5056	in libev, then check twice: If valgrind reports something like:
		5057
		5058	==2274== definitely lost: 0 bytes in 0 blocks.
		5059	==2274== possibly lost: 0 bytes in 0 blocks.
		5060	==2274== still reachable: 256 bytes in 1 blocks.
		5061
		5062	Then there is no memory leak, just as memory accounted to global variables
		5063	is not a memleak - the memory is still being referenced, and didn't leak.
		5064
		5065	Similarly, under some circumstances, valgrind might report kernel bugs
		5066	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5067	although an acceptable workaround has been found here), or it might be
		5068	confused.
		5069
		5070	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5071	make it into some kind of religion.
		5072
		5073	If you are unsure about something, feel free to contact the mailing list
		5074	with the full valgrind report and an explanation on why you think this
		5075	is a bug in libev (best check the archives, too :). However, don't be
		5076	annoyed when you get a brisk "this is no bug" answer and take the chance
		5077	of learning how to interpret valgrind properly.
		5078
		5079	If you need, for some reason, empty reports from valgrind for your project
		5080	I suggest using suppression lists.
		5081
		5082
		5083	=head1 PORTABILITY NOTES
		5084
		5085	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5086
		5087	GNU/Linux is the only common platform that supports 64 bit file/large file
		5088	interfaces but I<disables> them by default.
		5089
		5090	That means that libev compiled in the default environment doesn't support
		5091	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5092
		5093	Unfortunately, many programs try to work around this GNU/Linux issue
		5094	by enabling the large file API, which makes them incompatible with the
		5095	standard libev compiled for their system.
		5096
		5097	Likewise, libev cannot enable the large file API itself as this would
		5098	suddenly make it incompatible to the default compile time environment,
		5099	i.e. all programs not using special compile switches.
		5100
		5101	=head2 OS/X AND DARWIN BUGS
		5102
		5103	The whole thing is a bug if you ask me - basically any system interface
		5104	you touch is broken, whether it is locales, poll, kqueue or even the
		5105	OpenGL drivers.
		5106
		5107	=head3 C<kqueue> is buggy
		5108
		5109	The kqueue syscall is broken in all known versions - most versions support
		5110	only sockets, many support pipes.
		5111
		5112	Libev tries to work around this by not using C<kqueue> by default on this
		5113	rotten platform, but of course you can still ask for it when creating a
		5114	loop - embedding a socket-only kqueue loop into a select-based one is
		5115	probably going to work well.
		5116
		5117	=head3 C<poll> is buggy
		5118
		5119	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5120	implementation by something calling C<kqueue> internally around the 10.5.6
		5121	release, so now C<kqueue> I<and> C<poll> are broken.
		5122
		5123	Libev tries to work around this by not using C<poll> by default on
		5124	this rotten platform, but of course you can still ask for it when creating
		5125	a loop.
		5126
		5127	=head3 C<select> is buggy
		5128
		5129	All that's left is C<select>, and of course Apple found a way to fuck this
		5130	one up as well: On OS/X, C<select> actively limits the number of file
		5131	descriptors you can pass in to 1024 - your program suddenly crashes when
		5132	you use more.
		5133
		5134	There is an undocumented "workaround" for this - defining
		5135	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5136	work on OS/X.
		5137
		5138	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5139
		5140	=head3 C<errno> reentrancy
		5141
		5142	The default compile environment on Solaris is unfortunately so
		5143	thread-unsafe that you can't even use components/libraries compiled
		5144	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5145	defined by default. A valid, if stupid, implementation choice.
		5146
		5147	If you want to use libev in threaded environments you have to make sure
		5148	it's compiled with C<_REENTRANT> defined.
		5149
		5150	=head3 Event port backend
		5151
		5152	The scalable event interface for Solaris is called "event
		5153	ports". Unfortunately, this mechanism is very buggy in all major
		5154	releases. If you run into high CPU usage, your program freezes or you get
		5155	a large number of spurious wakeups, make sure you have all the relevant
		5156	and latest kernel patches applied. No, I don't know which ones, but there
		5157	are multiple ones to apply, and afterwards, event ports actually work
		5158	great.
		5159
		5160	If you can't get it to work, you can try running the program by setting
		5161	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5162	C<select> backends.
		5163
		5164	=head2 AIX POLL BUG
		5165
		5166	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5167	this by trying to avoid the poll backend altogether (i.e. it's not even
		5168	compiled in), which normally isn't a big problem as C<select> works fine
		5169	with large bitsets on AIX, and AIX is dead anyway.
		5170
		5171	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5172
		5173	=head3 General issues
		5174
		5175	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5176	requires, and its I/O model is fundamentally incompatible with the POSIX
		5177	model. Libev still offers limited functionality on this platform in
		5178	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5179	descriptors. This only applies when using Win32 natively, not when using
		5180	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5181	as every compiler comes with a slightly differently broken/incompatible
		5182	environment.
		5183
		5184	Lifting these limitations would basically require the full
		5185	re-implementation of the I/O system. If you are into this kind of thing,
		5186	then note that glib does exactly that for you in a very portable way (note
		5187	also that glib is the slowest event library known to man).
		5188
		5189	There is no supported compilation method available on windows except
		5190	embedding it into other applications.
		5191
		5192	Sensible signal handling is officially unsupported by Microsoft - libev
		5193	tries its best, but under most conditions, signals will simply not work.
		5194
		5195	Not a libev limitation but worth mentioning: windows apparently doesn't
		5196	accept large writes: instead of resulting in a partial write, windows will
		5197	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5198	so make sure you only write small amounts into your sockets (less than a
		5199	megabyte seems safe, but this apparently depends on the amount of memory
		5200	available).
		5201
		5202	Due to the many, low, and arbitrary limits on the win32 platform and
		5203	the abysmal performance of winsockets, using a large number of sockets
		5204	is not recommended (and not reasonable). If your program needs to use
		5205	more than a hundred or so sockets, then likely it needs to use a totally
		5206	different implementation for windows, as libev offers the POSIX readiness
		5207	notification model, which cannot be implemented efficiently on windows
		5208	(due to Microsoft monopoly games).
		5209
		5210	A typical way to use libev under windows is to embed it (see the embedding
		5211	section for details) and use the following F<evwrap.h> header file instead
		5212	of F<ev.h>:
		5213
		5214	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5215	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5216
		5217	#include "ev.h"
		5218
		5219	And compile the following F<evwrap.c> file into your project (make sure
		5220	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5221
		5222	#include "evwrap.h"
		5223	#include "ev.c"
		5224
		5225	=head3 The winsocket C<select> function
		5226
		5227	The winsocket C<select> function doesn't follow POSIX in that it
		5228	requires socket I<handles> and not socket I<file descriptors> (it is
		5229	also extremely buggy). This makes select very inefficient, and also
		5230	requires a mapping from file descriptors to socket handles (the Microsoft
		5231	C runtime provides the function C<_open_osfhandle> for this). See the
		5232	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5233	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5234
		5235	The configuration for a "naked" win32 using the Microsoft runtime
		5236	libraries and raw winsocket select is:
		5237
		5238	#define EV_USE_SELECT 1
		5239	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5240
		5241	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5242	complexity in the O(n²) range when using win32.
		5243
		5244	=head3 Limited number of file descriptors
		5245
		5246	Windows has numerous arbitrary (and low) limits on things.
		5247
		5248	Early versions of winsocket's select only supported waiting for a maximum
		5249	of C<64> handles (probably owning to the fact that all windows kernels
		5250	can only wait for C<64> things at the same time internally; Microsoft
		5251	recommends spawning a chain of threads and wait for 63 handles and the
		5252	previous thread in each. Sounds great!).
		5253
		5254	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5255	to some high number (e.g. C<2048>) before compiling the winsocket select
		5256	call (which might be in libev or elsewhere, for example, perl and many
		5257	other interpreters do their own select emulation on windows).
		5258
		5259	Another limit is the number of file descriptors in the Microsoft runtime
		5260	libraries, which by default is C<64> (there must be a hidden I<64>
		5261	fetish or something like this inside Microsoft). You can increase this
		5262	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5263	(another arbitrary limit), but is broken in many versions of the Microsoft
		5264	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5265	(depending on windows version and/or the phase of the moon). To get more,
		5266	you need to wrap all I/O functions and provide your own fd management, but
		5267	the cost of calling select (O(n²)) will likely make this unworkable.
		5268
		5269	=head2 PORTABILITY REQUIREMENTS
		5270
		5271	In addition to a working ISO-C implementation and of course the
		5272	backend-specific APIs, libev relies on a few additional extensions:
		5273
		5274	=over 4
		5275
		5276	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5277	calling conventions regardless of C<ev_watcher_type *>.
		5278
		5279	Libev assumes not only that all watcher pointers have the same internal
		5280	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5281	assumes that the same (machine) code can be used to call any watcher
		5282	callback: The watcher callbacks have different type signatures, but libev
		5283	calls them using an C<ev_watcher *> internally.
		5284
		5285	=item pointer accesses must be thread-atomic
		5286
		5287	Accessing a pointer value must be atomic, it must both be readable and
		5288	writable in one piece - this is the case on all current architectures.
		5289
		5290	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5291
		5292	The type C<sig_atomic_t volatile> (or whatever is defined as
		5293	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5294	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5295	believed to be sufficiently portable.
		5296
		5297	=item C<sigprocmask> must work in a threaded environment
		5298
		5299	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5300	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5301	pthread implementations will either allow C<sigprocmask> in the "main
		5302	thread" or will block signals process-wide, both behaviours would
		5303	be compatible with libev. Interaction between C<sigprocmask> and
		5304	C<pthread_sigmask> could complicate things, however.
		5305
		5306	The most portable way to handle signals is to block signals in all threads
		5307	except the initial one, and run the default loop in the initial thread as
		5308	well.
		5309
		5310	=item C<long> must be large enough for common memory allocation sizes
		5311
		5312	To improve portability and simplify its API, libev uses C<long> internally
		5313	instead of C<size_t> when allocating its data structures. On non-POSIX
		5314	systems (Microsoft...) this might be unexpectedly low, but is still at
		5315	least 31 bits everywhere, which is enough for hundreds of millions of
		5316	watchers.
		5317
		5318	=item C<double> must hold a time value in seconds with enough accuracy
		5319
		5320	The type C<double> is used to represent timestamps. It is required to
		5321	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5322	good enough for at least into the year 4000 with millisecond accuracy
		5323	(the design goal for libev). This requirement is overfulfilled by
		5324	implementations using IEEE 754, which is basically all existing ones.
		5325
		5326	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5327	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5328	is either obsolete or somebody patched it to use C<long double> or
		5329	something like that, just kidding).
		5330
		5331	=back
		5332
		5333	If you know of other additional requirements drop me a note.
		5334
		5335
2619	=head1 COMPLEXITIES	5336	=head1 ALGORITHMIC COMPLEXITIES
2620		5337
2621	In this section the complexities of (many of) the algorithms used inside	5338	In this section the complexities of (many of) the algorithms used inside
2622	libev will be explained. For complexity discussions about backends see the	5339	libev will be documented. For complexity discussions about backends see
2623	documentation for C<ev_default_init>.	5340	the documentation for C<ev_default_init>.
2624		5341
2625	All of the following are about amortised time: If an array needs to be	5342	All of the following are about amortised time: If an array needs to be
2626	extended, libev needs to realloc and move the whole array, but this	5343	extended, libev needs to realloc and move the whole array, but this
2627	happens asymptotically never with higher number of elements, so O(1) might	5344	happens asymptotically rarer with higher number of elements, so O(1) might
2628	mean it might do a lengthy realloc operation in rare cases, but on average	5345	mean that libev does a lengthy realloc operation in rare cases, but on
2629	it is much faster and asymptotically approaches constant time.	5346	average it is much faster and asymptotically approaches constant time.
2630		5347
2631	=over 4	5348	=over 4
2632		5349
2633	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5350	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2634		5351
2635	This means that, when you have a watcher that triggers in one hour and	5352	This means that, when you have a watcher that triggers in one hour and
2636	there are 100 watchers that would trigger before that then inserting will	5353	there are 100 watchers that would trigger before that, then inserting will
2637	have to skip those 100 watchers.	5354	have to skip roughly seven (C<ld 100>) of these watchers.
2638		5355
2639	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	5356	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2640		5357
2641	That means that for changing a timer costs less than removing/adding them	5358	That means that changing a timer costs less than removing/adding them,
2642	as only the relative motion in the event queue has to be paid for.	5359	as only the relative motion in the event queue has to be paid for.
2643		5360
2644	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	5361	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2645		5362
2646	These just add the watcher into an array or at the head of a list.	5363	These just add the watcher into an array or at the head of a list.
		5364
2647	=item Stopping check/prepare/idle watchers: O(1)	5365	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2648		5366
2649	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5367	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2650		5368
2651	These watchers are stored in lists then need to be walked to find the	5369	These watchers are stored in lists, so they need to be walked to find the
2652	correct watcher to remove. The lists are usually short (you don't usually	5370	correct watcher to remove. The lists are usually short (you don't usually
2653	have many watchers waiting for the same fd or signal).	5371	have many watchers waiting for the same fd or signal: one is typical, two
		5372	is rare).
2654		5373
2655	=item Finding the next timer per loop iteration: O(1)	5374	=item Finding the next timer in each loop iteration: O(1)
		5375
		5376	By virtue of using a binary or 4-heap, the next timer is always found at a
		5377	fixed position in the storage array.
2656		5378
2657	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	5379	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2658		5380
2659	A change means an I/O watcher gets started or stopped, which requires	5381	A change means an I/O watcher gets started or stopped, which requires
2660	libev to recalculate its status (and possibly tell the kernel).	5382	libev to recalculate its status (and possibly tell the kernel, depending
		5383	on backend and whether C<ev_io_set> was used).
2661		5384
2662	=item Activating one watcher: O(1)	5385	=item Activating one watcher (putting it into the pending state): O(1)
2663		5386
2664	=item Priority handling: O(number_of_priorities)	5387	=item Priority handling: O(number_of_priorities)
2665		5388
2666	Priorities are implemented by allocating some space for each	5389	Priorities are implemented by allocating some space for each
2667	priority. When doing priority-based operations, libev usually has to	5390	priority. When doing priority-based operations, libev usually has to
2668	linearly search all the priorities.	5391	linearly search all the priorities, but starting/stopping and activating
		5392	watchers becomes O(1) with respect to priority handling.
		5393
		5394	=item Sending an ev_async: O(1)
		5395
		5396	=item Processing ev_async_send: O(number_of_async_watchers)
		5397
		5398	=item Processing signals: O(max_signal_number)
		5399
		5400	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5401	calls in the current loop iteration and the loop is currently
		5402	blocked. Checking for async and signal events involves iterating over all
		5403	running async watchers or all signal numbers.
2669		5404
2670	=back	5405	=back
2671		5406
2672		5407
		5408	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5409
		5410	The major version 4 introduced some incompatible changes to the API.
		5411
		5412	At the moment, the C<ev.h> header file provides compatibility definitions
		5413	for all changes, so most programs should still compile. The compatibility
		5414	layer might be removed in later versions of libev, so better update to the
		5415	new API early than late.
		5416
		5417	=over 4
		5418
		5419	=item C<EV_COMPAT3> backwards compatibility mechanism
		5420
		5421	The backward compatibility mechanism can be controlled by
		5422	C<EV_COMPAT3>. See L</PREPROCESSOR SYMBOLS/MACROS> in the L</EMBEDDING>
		5423	section.
		5424
		5425	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5426
		5427	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5428
		5429	ev_loop_destroy (EV_DEFAULT_UC);
		5430	ev_loop_fork (EV_DEFAULT);
		5431
		5432	=item function/symbol renames
		5433
		5434	A number of functions and symbols have been renamed:
		5435
		5436	ev_loop => ev_run
		5437	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5438	EVLOOP_ONESHOT => EVRUN_ONCE
		5439
		5440	ev_unloop => ev_break
		5441	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5442	EVUNLOOP_ONE => EVBREAK_ONE
		5443	EVUNLOOP_ALL => EVBREAK_ALL
		5444
		5445	EV_TIMEOUT => EV_TIMER
		5446
		5447	ev_loop_count => ev_iteration
		5448	ev_loop_depth => ev_depth
		5449	ev_loop_verify => ev_verify
		5450
		5451	Most functions working on C<struct ev_loop> objects don't have an
		5452	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5453	associated constants have been renamed to not collide with the C<struct
		5454	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5455	as all other watcher types. Note that C<ev_loop_fork> is still called
		5456	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5457	typedef.
		5458
		5459	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5460
		5461	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5462	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5463	and work, but the library code will of course be larger.
		5464
		5465	=back
		5466
		5467
		5468	=head1 GLOSSARY
		5469
		5470	=over 4
		5471
		5472	=item active
		5473
		5474	A watcher is active as long as it has been started and not yet stopped.
		5475	See L</WATCHER STATES> for details.
		5476
		5477	=item application
		5478
		5479	In this document, an application is whatever is using libev.
		5480
		5481	=item backend
		5482
		5483	The part of the code dealing with the operating system interfaces.
		5484
		5485	=item callback
		5486
		5487	The address of a function that is called when some event has been
		5488	detected. Callbacks are being passed the event loop, the watcher that
		5489	received the event, and the actual event bitset.
		5490
		5491	=item callback/watcher invocation
		5492
		5493	The act of calling the callback associated with a watcher.
		5494
		5495	=item event
		5496
		5497	A change of state of some external event, such as data now being available
		5498	for reading on a file descriptor, time having passed or simply not having
		5499	any other events happening anymore.
		5500
		5501	In libev, events are represented as single bits (such as C<EV_READ> or
		5502	C<EV_TIMER>).
		5503
		5504	=item event library
		5505
		5506	A software package implementing an event model and loop.
		5507
		5508	=item event loop
		5509
		5510	An entity that handles and processes external events and converts them
		5511	into callback invocations.
		5512
		5513	=item event model
		5514
		5515	The model used to describe how an event loop handles and processes
		5516	watchers and events.
		5517
		5518	=item pending
		5519
		5520	A watcher is pending as soon as the corresponding event has been
		5521	detected. See L</WATCHER STATES> for details.
		5522
		5523	=item real time
		5524
		5525	The physical time that is observed. It is apparently strictly monotonic :)
		5526
		5527	=item wall-clock time
		5528
		5529	The time and date as shown on clocks. Unlike real time, it can actually
		5530	be wrong and jump forwards and backwards, e.g. when you adjust your
		5531	clock.
		5532
		5533	=item watcher
		5534
		5535	A data structure that describes interest in certain events. Watchers need
		5536	to be started (attached to an event loop) before they can receive events.
		5537
		5538	=back
		5539
2673	=head1 AUTHOR	5540	=head1 AUTHOR
2674		5541
2675	Marc Lehmann <libev@schmorp.de>.	5542	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5543	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
2676		5544

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