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Revision 1.84 by root, Wed Dec 12 22:26:37 2007 UTC vs.
Revision 1.385 by root, Tue Nov 29 15:10:05 2011 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_run's to stop iterating
		32	ev_break (EV_A_ EVBREAK_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
35	struct ev_loop *loop = ev_default_loop (0);	47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = EV_DEFAULT;
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_run (loop, 0);
47		62
		63	// break was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
		90
		91	=head1 ABOUT LIBEV
56		92
57	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occuring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	95	these event sources and provide your program with events.
60		96
61	To do this, it must take more or less complete control over your process	97	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	98	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	99	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	101	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	102	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	103	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	104	watcher.
69		105
70	=head1 FEATURES	106	=head2 FEATURES
71		107
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
77	(C<ev_signal>), process status change events (C<ev_child>), and event	113	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	115	change events (C<ev_child>), and event watchers dealing with the event
80	file watchers (C<ev_stat>) and even limited support for fork events	116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(C<ev_fork>).	117	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		118	limited support for fork events (C<ev_fork>).
82		119
83	It also is quite fast (see this	120	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	121	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	122	for example).
86		123
87	=head1 CONVENTIONS	124	=head2 CONVENTIONS
88		125
89	Libev is very configurable. In this manual the default configuration will	126	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	127	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	128	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	129	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	130	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	131	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		132	this argument.
95		133
96	=head1 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
97		135
98	Libev represents time as a single floating point number, representing the	136	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	137	the (fractional) number of seconds since the (POSIX) epoch (in practice
100	the beginning of 1970, details are complicated, don't ask). This type is	138	somewhere near the beginning of 1970, details are complicated, don't
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	139	ask). This type is called C<ev_tstamp>, which is what you should use
102	to the C<double> type in C, and when you need to do any calculations on	140	too. It usually aliases to the C<double> type in C. When you need to do
103	it, you should treat it as such.	141	any calculations on it, you should treat it as some floating point value.
		142
		143	Unlike the name component C<stamp> might indicate, it is also used for
		144	time differences (e.g. delays) throughout libev.
		145
		146	=head1 ERROR HANDLING
		147
		148	Libev knows three classes of errors: operating system errors, usage errors
		149	and internal errors (bugs).
		150
		151	When libev catches an operating system error it cannot handle (for example
		152	a system call indicating a condition libev cannot fix), it calls the callback
		153	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		154	abort. The default is to print a diagnostic message and to call C<abort
		155	()>.
		156
		157	When libev detects a usage error such as a negative timer interval, then
		158	it will print a diagnostic message and abort (via the C<assert> mechanism,
		159	so C<NDEBUG> will disable this checking): these are programming errors in
		160	the libev caller and need to be fixed there.
		161
		162	Libev also has a few internal error-checking C<assert>ions, and also has
		163	extensive consistency checking code. These do not trigger under normal
		164	circumstances, as they indicate either a bug in libev or worse.
		165
104		166
105	=head1 GLOBAL FUNCTIONS	167	=head1 GLOBAL FUNCTIONS
106		168
107	These functions can be called anytime, even before initialising the	169	These functions can be called anytime, even before initialising the
108	library in any way.	170	library in any way.
…		…
111		173
112	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
113		175
114	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	178	you actually want to know. Also interesting is the combination of
		179	C<ev_now_update> and C<ev_now>.
		180
		181	=item ev_sleep (ev_tstamp interval)
		182
		183	Sleep for the given interval: The current thread will be blocked
		184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
		188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
117		192
118	=item int ev_version_major ()	193	=item int ev_version_major ()
119		194
120	=item int ev_version_minor ()	195	=item int ev_version_minor ()
121		196
…		…
132	as this indicates an incompatible change. Minor versions are usually	207	as this indicates an incompatible change. Minor versions are usually
133	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
134	not a problem.	209	not a problem.
135		210
136	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
137	version.	212	version (note, however, that this will not detect other ABI mismatches,
		213	such as LFS or reentrancy).
138		214
139	assert (("libev version mismatch",	215	assert (("libev version mismatch",
140	ev_version_major () == EV_VERSION_MAJOR	216	ev_version_major () == EV_VERSION_MAJOR
141	&& ev_version_minor () >= EV_VERSION_MINOR));	217	&& ev_version_minor () >= EV_VERSION_MINOR));
142		218
143	=item unsigned int ev_supported_backends ()	219	=item unsigned int ev_supported_backends ()
144		220
145	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_*>
146	value) compiled into this binary of libev (independent of their	222	value) compiled into this binary of libev (independent of their
…		…
148	a description of the set values.	224	a description of the set values.
149		225
150	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
151	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
152		228
153	assert (("sorry, no epoll, no sex",	229	assert (("sorry, no epoll, no sex",
154	ev_supported_backends () & EVBACKEND_EPOLL));	230	ev_supported_backends () & EVBACKEND_EPOLL));
155		231
156	=item unsigned int ev_recommended_backends ()	232	=item unsigned int ev_recommended_backends ()
157		233
158	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
159	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
160	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
161	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
162	(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
163	libev will probe for if you specify no backends explicitly.	240	probe for if you specify no backends explicitly.
164		241
165	=item unsigned int ev_embeddable_backends ()	242	=item unsigned int ev_embeddable_backends ()
166		243
167	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
168	is the theoretical, all-platform, value. To find which backends	245	value is platform-specific but can include backends not available on the
169	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
170	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	247	the current system, you would need to look at C<ev_embeddable_backends ()
171	recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
172		249
173	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
174		251
175	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
176		253
177	Sets the allocation function to use (the prototype is similar - the	254	Sets the allocation function to use (the prototype is similar - the
178	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
179	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
180	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
181	potentially destructive action. The default is your system realloc	258	or take some potentially destructive action.
182	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.
183		263
184	You could override this function in high-availability programs to, say,	264	You could override this function in high-availability programs to, say,
185	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,
186	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.
187		267
188	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
189	retries).	269	retries (example requires a standards-compliant C<realloc>).
190		270
191	static void *	271	static void *
192	persistent_realloc (void *ptr, size_t size)	272	persistent_realloc (void *ptr, size_t size)
193	{	273	{
194	for (;;)	274	for (;;)
…		…
203	}	283	}
204		284
205	...	285	...
206	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
207		287
208	=item ev_set_syserr_cb (void (*cb)(const char *msg));	288	=item ev_set_syserr_cb (void (*cb)(const char *msg))
209		289
210	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
211	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
212	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
213	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
214	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
215	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
216	(such as abort).	296	(such as abort).
217		297
218	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.
…		…
225	}	305	}
226		306
227	...	307	...
228	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
229		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
230	=back	323	=back
231		324
232	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
233		326
234	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
235	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
236	events, and dynamically created loops which do not.	329	libev 3 had an C<ev_loop> function colliding with the struct name).
237		330
238	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
239	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
240	create, you also create another event loop. Libev itself does no locking	333	do not.
241	whatsoever, so if you mix calls to the same event loop in different
242	threads, make sure you lock (this is usually a bad idea, though, even if
243	done correctly, because it's hideous and inefficient).
244		334
245	=over 4	335	=over 4
246		336
247	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
248		338
249	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
250	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
251	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
252	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".
253		349
254	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
255	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.
256		382
257	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
258	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>).
259		385
260	The following flags are supported:	386	The following flags are supported:
…		…
266	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
267	thing, believe me).	393	thing, believe me).
268		394
269	=item C<EVFLAG_NOENV>	395	=item C<EVFLAG_NOENV>
270		396
271	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
272	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
273	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	399	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
274	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
275	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
276	around bugs.	402	around bugs.
277		403
278	=item C<EVFLAG_FORKCHECK>	404	=item C<EVFLAG_FORKCHECK>
279		405
280	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
281	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.
282	enabling this flag.
283		408
284	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,
285	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
286	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
287	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
288	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
289	C<pthread_atfork> which is even faster).	414	C<pthread_atfork> which is even faster).
290		415
291	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
292	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
293	flag.	418	flag.
294		419
295	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>
296	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.
297		457
298	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
299		459
300	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
301	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,
302	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
303	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	463	using this backend. It doesn't scale too well (O(highest_fd)), but its
304	the fastest backend for a low number of fds.	464	usually the fastest backend for a low number of (low-numbered :) fds.
		465
		466	To get good performance out of this backend you need a high amount of
		467	parallelism (most of the file descriptors should be busy). If you are
		468	writing a server, you should C<accept ()> in a loop to accept as many
		469	connections as possible during one iteration. You might also want to have
		470	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		471	readiness notifications you get per iteration.
		472
		473	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		474	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		475	C<exceptfds> set on that platform).
305		476
306	=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)
307		478
308	And this is your standard poll(2) backend. It's more complicated than	479	And this is your standard poll(2) backend. It's more complicated
309	select, but handles sparse fds better and has no artificial limit on the	480	than select, but handles sparse fds better and has no artificial
310	number of fds you can use (except it will slow down considerably with a	481	limit on the number of fds you can use (except it will slow down
311	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	482	considerably with a lot of inactive fds). It scales similarly to select,
		483	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		484	performance tips.
		485
		486	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		487	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
312		488
313	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
314		490
		491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		492	kernels).
		493
315	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
316	but it scales phenomenally better. While poll and select usually scale like	495	it scales phenomenally better. While poll and select usually scale like
317	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	496	O(total_fds) where total_fds is the total number of fds (or the highest
318	either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
319		498
		499	The epoll mechanism deserves honorable mention as the most misdesigned
		500	of the more advanced event mechanisms: mere annoyances include silently
		501	dropping file descriptors, requiring a system call per change per file
		502	descriptor (and unnecessary guessing of parameters), problems with dup,
		503	returning before the timeout value, resulting in additional iterations
		504	(and only giving 5ms accuracy while select on the same platform gives
		505	0.1ms) and so on. The biggest issue is fork races, however - if a program
		506	forks then I<both> parent and child process have to recreate the epoll
		507	set, which can take considerable time (one syscall per file descriptor)
		508	and is of course hard to detect.
		509
		510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		511	but of course I<doesn't>, and epoll just loves to report events for
		512	totally I<different> file descriptors (even already closed ones, so
		513	one cannot even remove them from the set) than registered in the set
		514	(especially on SMP systems). Libev tries to counter these spurious
		515	notifications by employing an additional generation counter and comparing
		516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
		520	not least, it also refuses to work with some file descriptors which work
		521	perfectly fine with C<select> (files, many character devices...).
		522
		523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
		526
320	While stopping and starting an I/O watcher in the same iteration will	527	While stopping, setting and starting an I/O watcher in the same iteration
321	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
322	(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
323	best to avoid that. Also, dup()ed file descriptors might not work very	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
324	well if you register events for both fds.	531	file descriptors might not work very well if you register events for both
		532	file descriptors.
325		533
326	Please note that epoll sometimes generates spurious notifications, so you	534	Best performance from this backend is achieved by not unregistering all
327	need to use non-blocking I/O or other means to avoid blocking when no data	535	watchers for a file descriptor until it has been closed, if possible,
328	(or space) is available.	536	i.e. keep at least one watcher active per fd at all times. Stopping and
		537	starting a watcher (without re-setting it) also usually doesn't cause
		538	extra overhead. A fork can both result in spurious notifications as well
		539	as in libev having to destroy and recreate the epoll object, which can
		540	take considerable time and thus should be avoided.
		541
		542	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		543	faster than epoll for maybe up to a hundred file descriptors, depending on
		544	the usage. So sad.
		545
		546	While nominally embeddable in other event loops, this feature is broken in
		547	all kernel versions tested so far.
		548
		549	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		550	C<EVBACKEND_POLL>.
329		551
330	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	552	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
331		553
332	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
333	was broken on all BSDs except NetBSD (usually it doesn't work with	555	was broken on all BSDs except NetBSD (usually it doesn't work reliably
334	anything but sockets and pipes, except on Darwin, where of course its	556	with anything but sockets and pipes, except on Darwin, where of course
335	completely useless). For this reason its not being "autodetected"	557	it's completely useless). Unlike epoll, however, whose brokenness
		558	is by design, these kqueue bugs can (and eventually will) be fixed
		559	without API changes to existing programs. For this reason it's not being
336	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
337	C<EVBACKEND_KQUEUE>).	561	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		562	system like NetBSD.
		563
		564	You still can embed kqueue into a normal poll or select backend and use it
		565	only for sockets (after having made sure that sockets work with kqueue on
		566	the target platform). See C<ev_embed> watchers for more info.
338		567
339	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
340	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
341	course). While starting and stopping an I/O watcher does not cause an	570	course). While stopping, setting and starting an I/O watcher does never
342	extra syscall as with epoll, it still adds up to four event changes per	571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
343	incident, so its best to avoid that.	572	two event changes per incident. Support for C<fork ()> is very bad (but
		573	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		574	cases
		575
		576	This backend usually performs well under most conditions.
		577
		578	While nominally embeddable in other event loops, this doesn't work
		579	everywhere, so you might need to test for this. And since it is broken
		580	almost everywhere, you should only use it when you have a lot of sockets
		581	(for which it usually works), by embedding it into another event loop
		582	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		583	also broken on OS X)) and, did I mention it, using it only for sockets.
		584
		585	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		586	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		587	C<NOTE_EOF>.
344		588
345	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	589	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
346		590
347	This is not implemented yet (and might never be).	591	This is not implemented yet (and might never be, unless you send me an
		592	implementation). According to reports, C</dev/poll> only supports sockets
		593	and is not embeddable, which would limit the usefulness of this backend
		594	immensely.
348		595
349	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
350		597
351	This uses the Solaris 10 port mechanism. As with everything on Solaris,	598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
352	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)).
353		600
354	Please note that solaris ports can result in a lot of spurious	601	While this backend scales well, it requires one system call per active
355	notifications, so you need to use non-blocking I/O or other means to avoid	602	file descriptor per loop iteration. For small and medium numbers of file
356	blocking when no data (or space) is available.	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		604	might perform better.
		605
		606	On the positive side, this backend actually performed fully to
		607	specification in all tests and is fully embeddable, which is a rare feat
		608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returns events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where you
		616	absolutely have to know whether an event occurred or not because you have
		617	to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
		620
		621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		622	C<EVBACKEND_POLL>.
357		623
358	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
359		625
360	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
361	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
362	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
363		629
		630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
		639
364	=back	640	=back
365		641
366	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,
367	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
368	specified, most compiled-in backend will be tried, usually in reverse	644	here). If none are specified, all backends in C<ev_recommended_backends
369	order of their flag values :)	645	()> will be tried.
370
371	The most typical usage is like this:
372
373	if (!ev_default_loop (0))
374	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
375
376	Restrict libev to the select and poll backends, and do not allow
377	environment settings to be taken into account:
378
379	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
380
381	Use whatever libev has to offer, but make sure that kqueue is used if
382	available (warning, breaks stuff, best use only with your own private
383	event loop and only if you know the OS supports your types of fds):
384
385	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
386
387	=item struct ev_loop *ev_loop_new (unsigned int flags)
388
389	Similar to C<ev_default_loop>, but always creates a new event loop that is
390	always distinct from the default loop. Unlike the default loop, it cannot
391	handle signal and child watchers, and attempts to do so will be greeted by
392	undefined behaviour (or a failed assertion if assertions are enabled).
393		646
394	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.
395		648
396	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	649	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
397	if (!epoller)	650	if (!epoller)
398	fatal ("no epoll found here, maybe it hides under your chair");	651	fatal ("no epoll found here, maybe it hides under your chair");
399		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
400	=item ev_default_destroy ()	658	=item ev_loop_destroy (loop)
401		659
402	Destroys the default loop again (frees all memory and kernel state	660	Destroys an event loop object (frees all memory and kernel state
403	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
404	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
405	responsibility to either stop all watchers cleanly yoursef I<before>	663	responsibility to either stop all watchers cleanly yourself I<before>
406	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
407	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	665	the easiest thing, you can just ignore the watchers and/or C<free ()> them
408	for example).	666	for example).
409		667
		668	Note that certain global state, such as signal state (and installed signal
		669	handlers), will not be freed by this function, and related watchers (such
		670	as signal and child watchers) would need to be stopped manually.
		671
		672	This function is normally used on loop objects allocated by
		673	C<ev_loop_new>, but it can also be used on the default loop returned by
		674	C<ev_default_loop>, in which case it is not thread-safe.
		675
		676	Note that it is not advisable to call this function on the default loop
		677	except in the rare occasion where you really need to free its resources.
		678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		679	and C<ev_loop_destroy>.
		680
410	=item ev_loop_destroy (loop)	681	=item ev_loop_fork (loop)
411		682
412	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
413	earlier call to C<ev_loop_new>.
414
415	=item ev_default_fork ()
416
417	This function reinitialises the kernel state for backends that have	684	reinitialise the kernel state for backends that have one. Despite the
418	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
419	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
420	again makes little sense).	687	child before resuming or calling C<ev_run>.
421		688
422	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
423	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
424	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).
425		700
426	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
427	it just in case after a fork. To make this easy, the function will fit in	702	it just in case after a fork.
428	quite nicely into a call to C<pthread_atfork>:
429		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	...
430	pthread_atfork (0, 0, ev_default_fork);	714	pthread_atfork (0, 0, post_fork_child);
431		715
432	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	716	=item int ev_is_default_loop (loop)
433	without calling this function, so if you force one of those backends you
434	do not need to care.
435		717
436	=item ev_loop_fork (loop)	718	Returns true when the given loop is, in fact, the default loop, and false
		719	otherwise.
437		720
438	Like C<ev_default_fork>, but acts on an event loop created by
439	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
440	after fork, and how you do this is entirely your own problem.
441
442	=item unsigned int ev_loop_count (loop)	721	=item unsigned int ev_iteration (loop)
443		722
444	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
445	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>
446	happily wraps around with enough iterations.	725	and happily wraps around with enough iterations.
447		726
448	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
449	"ticks" the number of loop iterations), as it roughly corresponds with	728	"ticks" the number of loop iterations), as it roughly corresponds with
450	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.
451		745
452	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
453		747
454	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
455	use.	749	use.
…		…
458		752
459	Returns the current "event loop time", which is the time the event loop	753	Returns the current "event loop time", which is the time the event loop
460	received events and started processing them. This timestamp does not	754	received events and started processing them. This timestamp does not
461	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
462	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
463	event occuring (or more correctly, libev finding out about it).	757	event occurring (or more correctly, libev finding out about it).
464		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
465	=item ev_loop (loop, int flags)	797	=item ev_run (loop, int flags)
466		798
467	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
468	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
469	events.	801	handling events. It will ask the operating system for any new events, call
		802	the watcher callbacks, an then repeat the whole process indefinitely: This
		803	is why event loops are called I<loops>.
470		804
471	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
472	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.
473		808
474	Please note that an explicit C<ev_unloop> is usually better than	809	Please note that an explicit C<ev_break> is usually better than
475	relying on all watchers to be stopped when deciding when a program has	810	relying on all watchers to be stopped when deciding when a program has
476	finished (especially in interactive programs), but having a program that	811	finished (especially in interactive programs), but having a program
477	automatically loops as long as it has to and no longer by virtue of	812	that automatically loops as long as it has to and no longer by virtue
478	relying on its watchers stopping correctly is a thing of beauty.	813	of relying on its watchers stopping correctly, that is truly a thing of
		814	beauty.
479		815
		816	This function is also I<mostly> exception-safe - you can break out of
		817	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		818	exception and so on. This does not decrement the C<ev_depth> value, nor
		819	will it clear any outstanding C<EVBREAK_ONE> breaks.
		820
480	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	821	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
481	those events and any outstanding ones, but will not block your process in	822	those events and any already outstanding ones, but will not wait and
482	case there are no events and will return after one iteration of the loop.	823	block your process in case there are no events and will return after one
		824	iteration of the loop. This is sometimes useful to poll and handle new
		825	events while doing lengthy calculations, to keep the program responsive.
483		826
484	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	827	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
485	neccessary) and will handle those and any outstanding ones. It will block	828	necessary) and will handle those and any already outstanding ones. It
486	your process until at least one new event arrives, and will return after	829	will block your process until at least one new event arrives (which could
487	one iteration of the loop. This is useful if you are waiting for some	830	be an event internal to libev itself, so there is no guarantee that a
488	external event in conjunction with something not expressible using other	831	user-registered callback will be called), and will return after one
		832	iteration of the loop.
		833
		834	This is useful if you are waiting for some external event in conjunction
		835	with something not expressible using other libev watchers (i.e. "roll your
489	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	836	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
490	usually a better approach for this kind of thing.	837	usually a better approach for this kind of thing.
491		838
492	Here are the gory details of what C<ev_loop> does:	839	Here are the gory details of what C<ev_run> does (this is for your
		840	understanding, not a guarantee that things will work exactly like this in
		841	future versions):
493		842
		843	- Increment loop depth.
		844	- Reset the ev_break status.
494	- Before the first iteration, call any pending watchers.	845	- Before the first iteration, call any pending watchers.
495	* If there are no active watchers (reference count is zero), return.	846	LOOP:
496	- Queue all prepare watchers and then call all outstanding watchers.	847	- If EVFLAG_FORKCHECK was used, check for a fork.
		848	- If a fork was detected (by any means), queue and call all fork watchers.
		849	- Queue and call all prepare watchers.
		850	- If ev_break was called, goto FINISH.
497	- If we have been forked, recreate the kernel state.	851	- If we have been forked, detach and recreate the kernel state
		852	as to not disturb the other process.
498	- Update the kernel state with all outstanding changes.	853	- Update the kernel state with all outstanding changes.
499	- Update the "event loop time".	854	- Update the "event loop time" (ev_now ()).
500	- Calculate for how long to block.	855	- Calculate for how long to sleep or block, if at all
		856	(active idle watchers, EVRUN_NOWAIT or not having
		857	any active watchers at all will result in not sleeping).
		858	- Sleep if the I/O and timer collect interval say so.
		859	- Increment loop iteration counter.
501	- Block the process, waiting for any events.	860	- Block the process, waiting for any events.
502	- Queue all outstanding I/O (fd) events.	861	- Queue all outstanding I/O (fd) events.
503	- Update the "event loop time" and do time jump handling.	862	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
504	- Queue all outstanding timers.	863	- Queue all expired timers.
505	- Queue all outstanding periodics.	864	- Queue all expired periodics.
506	- If no events are pending now, queue all idle watchers.	865	- Queue all idle watchers with priority higher than that of pending events.
507	- Queue all check watchers.	866	- Queue all check watchers.
508	- Call all queued watchers in reverse order (i.e. check watchers first).	867	- Call all queued watchers in reverse order (i.e. check watchers first).
509	Signals and child watchers are implemented as I/O watchers, and will	868	Signals and child watchers are implemented as I/O watchers, and will
510	be handled here by queueing them when their watcher gets executed.	869	be handled here by queueing them when their watcher gets executed.
511	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	870	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
512	were used, return, otherwise continue with step *.	871	were used, or there are no active watchers, goto FINISH, otherwise
		872	continue with step LOOP.
		873	FINISH:
		874	- Reset the ev_break status iff it was EVBREAK_ONE.
		875	- Decrement the loop depth.
		876	- Return.
513		877
514	Example: Queue some jobs and then loop until no events are outsanding	878	Example: Queue some jobs and then loop until no events are outstanding
515	anymore.	879	anymore.
516		880
517	... queue jobs here, make sure they register event watchers as long	881	... queue jobs here, make sure they register event watchers as long
518	... as they still have work to do (even an idle watcher will do..)	882	... as they still have work to do (even an idle watcher will do..)
519	ev_loop (my_loop, 0);	883	ev_run (my_loop, 0);
520	... jobs done. yeah!	884	... jobs done or somebody called break. yeah!
521		885
522	=item ev_unloop (loop, how)	886	=item ev_break (loop, how)
523		887
524	Can be used to make a call to C<ev_loop> return early (but only after it	888	Can be used to make a call to C<ev_run> return early (but only after it
525	has processed all outstanding events). The C<how> argument must be either	889	has processed all outstanding events). The C<how> argument must be either
526	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	890	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
527	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	891	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		892
		893	This "break state" will be cleared on the next call to C<ev_run>.
		894
		895	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		896	which case it will have no effect.
528		897
529	=item ev_ref (loop)	898	=item ev_ref (loop)
530		899
531	=item ev_unref (loop)	900	=item ev_unref (loop)
532		901
533	Ref/unref can be used to add or remove a reference count on the event	902	Ref/unref can be used to add or remove a reference count on the event
534	loop: Every watcher keeps one reference, and as long as the reference	903	loop: Every watcher keeps one reference, and as long as the reference
535	count is nonzero, C<ev_loop> will not return on its own. If you have	904	count is nonzero, C<ev_run> will not return on its own.
536	a watcher you never unregister that should not keep C<ev_loop> from	905
537	returning, ev_unref() after starting, and ev_ref() before stopping it. For	906	This is useful when you have a watcher that you never intend to
		907	unregister, but that nevertheless should not keep C<ev_run> from
		908	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		909	before stopping it.
		910
538	example, libev itself uses this for its internal signal pipe: It is not	911	As an example, libev itself uses this for its internal signal pipe: It
539	visible to the libev user and should not keep C<ev_loop> from exiting if	912	is not visible to the libev user and should not keep C<ev_run> from
540	no event watchers registered by it are active. It is also an excellent	913	exiting if no event watchers registered by it are active. It is also an
541	way to do this for generic recurring timers or from within third-party	914	excellent way to do this for generic recurring timers or from within
542	libraries. Just remember to I<unref after start> and I<ref before stop>.	915	third-party libraries. Just remember to I<unref after start> and I<ref
		916	before stop> (but only if the watcher wasn't active before, or was active
		917	before, respectively. Note also that libev might stop watchers itself
		918	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		919	in the callback).
543		920
544	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	921	Example: Create a signal watcher, but keep it from keeping C<ev_run>
545	running when nothing else is active.	922	running when nothing else is active.
546		923
547	struct ev_signal exitsig;	924	ev_signal exitsig;
548	ev_signal_init (&exitsig, sig_cb, SIGINT);	925	ev_signal_init (&exitsig, sig_cb, SIGINT);
549	ev_signal_start (loop, &exitsig);	926	ev_signal_start (loop, &exitsig);
550	evf_unref (loop);	927	ev_unref (loop);
551		928
552	Example: For some weird reason, unregister the above signal handler again.	929	Example: For some weird reason, unregister the above signal handler again.
553		930
554	ev_ref (loop);	931	ev_ref (loop);
555	ev_signal_stop (loop, &exitsig);	932	ev_signal_stop (loop, &exitsig);
		933
		934	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		935
		936	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		937
		938	These advanced functions influence the time that libev will spend waiting
		939	for events. Both time intervals are by default C<0>, meaning that libev
		940	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		941	latency.
		942
		943	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		944	allows libev to delay invocation of I/O and timer/periodic callbacks
		945	to increase efficiency of loop iterations (or to increase power-saving
		946	opportunities).
		947
		948	The idea is that sometimes your program runs just fast enough to handle
		949	one (or very few) event(s) per loop iteration. While this makes the
		950	program responsive, it also wastes a lot of CPU time to poll for new
		951	events, especially with backends like C<select ()> which have a high
		952	overhead for the actual polling but can deliver many events at once.
		953
		954	By setting a higher I<io collect interval> you allow libev to spend more
		955	time collecting I/O events, so you can handle more events per iteration,
		956	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		957	C<ev_timer>) will not be affected. Setting this to a non-null value will
		958	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		959	sleep time ensures that libev will not poll for I/O events more often then
		960	once per this interval, on average (as long as the host time resolution is
		961	good enough).
		962
		963	Likewise, by setting a higher I<timeout collect interval> you allow libev
		964	to spend more time collecting timeouts, at the expense of increased
		965	latency/jitter/inexactness (the watcher callback will be called
		966	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		967	value will not introduce any overhead in libev.
		968
		969	Many (busy) programs can usually benefit by setting the I/O collect
		970	interval to a value near C<0.1> or so, which is often enough for
		971	interactive servers (of course not for games), likewise for timeouts. It
		972	usually doesn't make much sense to set it to a lower value than C<0.01>,
		973	as this approaches the timing granularity of most systems. Note that if
		974	you do transactions with the outside world and you can't increase the
		975	parallelity, then this setting will limit your transaction rate (if you
		976	need to poll once per transaction and the I/O collect interval is 0.01,
		977	then you can't do more than 100 transactions per second).
		978
		979	Setting the I<timeout collect interval> can improve the opportunity for
		980	saving power, as the program will "bundle" timer callback invocations that
		981	are "near" in time together, by delaying some, thus reducing the number of
		982	times the process sleeps and wakes up again. Another useful technique to
		983	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		984	they fire on, say, one-second boundaries only.
		985
		986	Example: we only need 0.1s timeout granularity, and we wish not to poll
		987	more often than 100 times per second:
		988
		989	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		990	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		991
		992	=item ev_invoke_pending (loop)
		993
		994	This call will simply invoke all pending watchers while resetting their
		995	pending state. Normally, C<ev_run> does this automatically when required,
		996	but when overriding the invoke callback this call comes handy. This
		997	function can be invoked from a watcher - this can be useful for example
		998	when you want to do some lengthy calculation and want to pass further
		999	event handling to another thread (you still have to make sure only one
		1000	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1001
		1002	=item int ev_pending_count (loop)
		1003
		1004	Returns the number of pending watchers - zero indicates that no watchers
		1005	are pending.
		1006
		1007	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1008
		1009	This overrides the invoke pending functionality of the loop: Instead of
		1010	invoking all pending watchers when there are any, C<ev_run> will call
		1011	this callback instead. This is useful, for example, when you want to
		1012	invoke the actual watchers inside another context (another thread etc.).
		1013
		1014	If you want to reset the callback, use C<ev_invoke_pending> as new
		1015	callback.
		1016
		1017	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1018
		1019	Sometimes you want to share the same loop between multiple threads. This
		1020	can be done relatively simply by putting mutex_lock/unlock calls around
		1021	each call to a libev function.
		1022
		1023	However, C<ev_run> can run an indefinite time, so it is not feasible
		1024	to wait for it to return. One way around this is to wake up the event
		1025	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1026	I<release> and I<acquire> callbacks on the loop.
		1027
		1028	When set, then C<release> will be called just before the thread is
		1029	suspended waiting for new events, and C<acquire> is called just
		1030	afterwards.
		1031
		1032	Ideally, C<release> will just call your mutex_unlock function, and
		1033	C<acquire> will just call the mutex_lock function again.
		1034
		1035	While event loop modifications are allowed between invocations of
		1036	C<release> and C<acquire> (that's their only purpose after all), no
		1037	modifications done will affect the event loop, i.e. adding watchers will
		1038	have no effect on the set of file descriptors being watched, or the time
		1039	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1040	to take note of any changes you made.
		1041
		1042	In theory, threads executing C<ev_run> will be async-cancel safe between
		1043	invocations of C<release> and C<acquire>.
		1044
		1045	See also the locking example in the C<THREADS> section later in this
		1046	document.
		1047
		1048	=item ev_set_userdata (loop, void *data)
		1049
		1050	=item void *ev_userdata (loop)
		1051
		1052	Set and retrieve a single C<void *> associated with a loop. When
		1053	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1054	C<0>.
		1055
		1056	These two functions can be used to associate arbitrary data with a loop,
		1057	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1058	C<acquire> callbacks described above, but of course can be (ab-)used for
		1059	any other purpose as well.
		1060
		1061	=item ev_verify (loop)
		1062
		1063	This function only does something when C<EV_VERIFY> support has been
		1064	compiled in, which is the default for non-minimal builds. It tries to go
		1065	through all internal structures and checks them for validity. If anything
		1066	is found to be inconsistent, it will print an error message to standard
		1067	error and call C<abort ()>.
		1068
		1069	This can be used to catch bugs inside libev itself: under normal
		1070	circumstances, this function will never abort as of course libev keeps its
		1071	data structures consistent.
556		1072
557	=back	1073	=back
558		1074
559		1075
560	=head1 ANATOMY OF A WATCHER	1076	=head1 ANATOMY OF A WATCHER
561		1077
		1078	In the following description, uppercase C<TYPE> in names stands for the
		1079	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1080	watchers and C<ev_io_start> for I/O watchers.
		1081
562	A watcher is a structure that you create and register to record your	1082	A watcher is an opaque structure that you allocate and register to record
563	interest in some event. For instance, if you want to wait for STDIN to	1083	your interest in some event. To make a concrete example, imagine you want
564	become readable, you would create an C<ev_io> watcher for that:	1084	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1085	for that:
565		1086
566	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1087	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
567	{	1088	{
568	ev_io_stop (w);	1089	ev_io_stop (w);
569	ev_unloop (loop, EVUNLOOP_ALL);	1090	ev_break (loop, EVBREAK_ALL);
570	}	1091	}
571		1092
572	struct ev_loop *loop = ev_default_loop (0);	1093	struct ev_loop *loop = ev_default_loop (0);
		1094
573	struct ev_io stdin_watcher;	1095	ev_io stdin_watcher;
		1096
574	ev_init (&stdin_watcher, my_cb);	1097	ev_init (&stdin_watcher, my_cb);
575	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1098	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
576	ev_io_start (loop, &stdin_watcher);	1099	ev_io_start (loop, &stdin_watcher);
		1100
577	ev_loop (loop, 0);	1101	ev_run (loop, 0);
578		1102
579	As you can see, you are responsible for allocating the memory for your	1103	As you can see, you are responsible for allocating the memory for your
580	watcher structures (and it is usually a bad idea to do this on the stack,	1104	watcher structures (and it is I<usually> a bad idea to do this on the
581	although this can sometimes be quite valid).	1105	stack).
582		1106
		1107	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1108	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1109
583	Each watcher structure must be initialised by a call to C<ev_init	1110	Each watcher structure must be initialised by a call to C<ev_init (watcher
584	(watcher *, callback)>, which expects a callback to be provided. This	1111	*, callback)>, which expects a callback to be provided. This callback is
585	callback gets invoked each time the event occurs (or, in the case of io	1112	invoked each time the event occurs (or, in the case of I/O watchers, each
586	watchers, each time the event loop detects that the file descriptor given	1113	time the event loop detects that the file descriptor given is readable
587	is readable and/or writable).	1114	and/or writable).
588		1115
589	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1116	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
590	with arguments specific to this watcher type. There is also a macro	1117	macro to configure it, with arguments specific to the watcher type. There
591	to combine initialisation and setting in one call: C<< ev_<type>_init	1118	is also a macro to combine initialisation and setting in one call: C<<
592	(watcher *, callback, ...) >>.	1119	ev_TYPE_init (watcher *, callback, ...) >>.
593		1120
594	To make the watcher actually watch out for events, you have to start it	1121	To make the watcher actually watch out for events, you have to start it
595	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1122	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
596	*) >>), and you can stop watching for events at any time by calling the	1123	*) >>), and you can stop watching for events at any time by calling the
597	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1124	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
598		1125
599	As long as your watcher is active (has been started but not stopped) you	1126	As long as your watcher is active (has been started but not stopped) you
600	must not touch the values stored in it. Most specifically you must never	1127	must not touch the values stored in it. Most specifically you must never
601	reinitialise it or call its C<set> macro.	1128	reinitialise it or call its C<ev_TYPE_set> macro.
602		1129
603	Each and every callback receives the event loop pointer as first, the	1130	Each and every callback receives the event loop pointer as first, the
604	registered watcher structure as second, and a bitset of received events as	1131	registered watcher structure as second, and a bitset of received events as
605	third argument.	1132	third argument.
606		1133
…		…
615	=item C<EV_WRITE>	1142	=item C<EV_WRITE>
616		1143
617	The file descriptor in the C<ev_io> watcher has become readable and/or	1144	The file descriptor in the C<ev_io> watcher has become readable and/or
618	writable.	1145	writable.
619		1146
620	=item C<EV_TIMEOUT>	1147	=item C<EV_TIMER>
621		1148
622	The C<ev_timer> watcher has timed out.	1149	The C<ev_timer> watcher has timed out.
623		1150
624	=item C<EV_PERIODIC>	1151	=item C<EV_PERIODIC>
625		1152
…		…
643		1170
644	=item C<EV_PREPARE>	1171	=item C<EV_PREPARE>
645		1172
646	=item C<EV_CHECK>	1173	=item C<EV_CHECK>
647		1174
648	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1175	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
649	to gather new events, and all C<ev_check> watchers are invoked just after	1176	to gather new events, and all C<ev_check> watchers are invoked just after
650	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1177	C<ev_run> has gathered them, but before it invokes any callbacks for any
651	received events. Callbacks of both watcher types can start and stop as	1178	received events. Callbacks of both watcher types can start and stop as
652	many watchers as they want, and all of them will be taken into account	1179	many watchers as they want, and all of them will be taken into account
653	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1180	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
654	C<ev_loop> from blocking).	1181	C<ev_run> from blocking).
655		1182
656	=item C<EV_EMBED>	1183	=item C<EV_EMBED>
657		1184
658	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1185	The embedded event loop specified in the C<ev_embed> watcher needs attention.
659		1186
660	=item C<EV_FORK>	1187	=item C<EV_FORK>
661		1188
662	The event loop has been resumed in the child process after fork (see	1189	The event loop has been resumed in the child process after fork (see
663	C<ev_fork>).	1190	C<ev_fork>).
664		1191
		1192	=item C<EV_CLEANUP>
		1193
		1194	The event loop is about to be destroyed (see C<ev_cleanup>).
		1195
		1196	=item C<EV_ASYNC>
		1197
		1198	The given async watcher has been asynchronously notified (see C<ev_async>).
		1199
		1200	=item C<EV_CUSTOM>
		1201
		1202	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1203	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1204
665	=item C<EV_ERROR>	1205	=item C<EV_ERROR>
666		1206
667	An unspecified error has occured, the watcher has been stopped. This might	1207	An unspecified error has occurred, the watcher has been stopped. This might
668	happen because the watcher could not be properly started because libev	1208	happen because the watcher could not be properly started because libev
669	ran out of memory, a file descriptor was found to be closed or any other	1209	ran out of memory, a file descriptor was found to be closed or any other
		1210	problem. Libev considers these application bugs.
		1211
670	problem. You best act on it by reporting the problem and somehow coping	1212	You best act on it by reporting the problem and somehow coping with the
671	with the watcher being stopped.	1213	watcher being stopped. Note that well-written programs should not receive
		1214	an error ever, so when your watcher receives it, this usually indicates a
		1215	bug in your program.
672		1216
673	Libev will usually signal a few "dummy" events together with an error,	1217	Libev will usually signal a few "dummy" events together with an error, for
674	for example it might indicate that a fd is readable or writable, and if	1218	example it might indicate that a fd is readable or writable, and if your
675	your callbacks is well-written it can just attempt the operation and cope	1219	callbacks is well-written it can just attempt the operation and cope with
676	with the error from read() or write(). This will not work in multithreaded	1220	the error from read() or write(). This will not work in multi-threaded
677	programs, though, so beware.	1221	programs, though, as the fd could already be closed and reused for another
		1222	thing, so beware.
678		1223
679	=back	1224	=back
680		1225
681	=head2 GENERIC WATCHER FUNCTIONS	1226	=head2 GENERIC WATCHER FUNCTIONS
682
683	In the following description, C<TYPE> stands for the watcher type,
684	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
685		1227
686	=over 4	1228	=over 4
687		1229
688	=item C<ev_init> (ev_TYPE *watcher, callback)	1230	=item C<ev_init> (ev_TYPE *watcher, callback)
689		1231
…		…
695	which rolls both calls into one.	1237	which rolls both calls into one.
696		1238
697	You can reinitialise a watcher at any time as long as it has been stopped	1239	You can reinitialise a watcher at any time as long as it has been stopped
698	(or never started) and there are no pending events outstanding.	1240	(or never started) and there are no pending events outstanding.
699		1241
700	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1242	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
701	int revents)>.	1243	int revents)>.
702		1244
		1245	Example: Initialise an C<ev_io> watcher in two steps.
		1246
		1247	ev_io w;
		1248	ev_init (&w, my_cb);
		1249	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1250
703	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1251	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
704		1252
705	This macro initialises the type-specific parts of a watcher. You need to	1253	This macro initialises the type-specific parts of a watcher. You need to
706	call C<ev_init> at least once before you call this macro, but you can	1254	call C<ev_init> at least once before you call this macro, but you can
707	call C<ev_TYPE_set> any number of times. You must not, however, call this	1255	call C<ev_TYPE_set> any number of times. You must not, however, call this
708	macro on a watcher that is active (it can be pending, however, which is a	1256	macro on a watcher that is active (it can be pending, however, which is a
709	difference to the C<ev_init> macro).	1257	difference to the C<ev_init> macro).
710		1258
711	Although some watcher types do not have type-specific arguments	1259	Although some watcher types do not have type-specific arguments
712	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1260	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
713		1261
		1262	See C<ev_init>, above, for an example.
		1263
714	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1264	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
715		1265
716	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1266	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
717	calls into a single call. This is the most convinient method to initialise	1267	calls into a single call. This is the most convenient method to initialise
718	a watcher. The same limitations apply, of course.	1268	a watcher. The same limitations apply, of course.
719		1269
		1270	Example: Initialise and set an C<ev_io> watcher in one step.
		1271
		1272	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1273
720	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1274	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
721		1275
722	Starts (activates) the given watcher. Only active watchers will receive	1276	Starts (activates) the given watcher. Only active watchers will receive
723	events. If the watcher is already active nothing will happen.	1277	events. If the watcher is already active nothing will happen.
724		1278
		1279	Example: Start the C<ev_io> watcher that is being abused as example in this
		1280	whole section.
		1281
		1282	ev_io_start (EV_DEFAULT_UC, &w);
		1283
725	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1284	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
726		1285
727	Stops the given watcher again (if active) and clears the pending	1286	Stops the given watcher if active, and clears the pending status (whether
		1287	the watcher was active or not).
		1288
728	status. It is possible that stopped watchers are pending (for example,	1289	It is possible that stopped watchers are pending - for example,
729	non-repeating timers are being stopped when they become pending), but	1290	non-repeating timers are being stopped when they become pending - but
730	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1291	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
731	you want to free or reuse the memory used by the watcher it is therefore a	1292	pending. If you want to free or reuse the memory used by the watcher it is
732	good idea to always call its C<ev_TYPE_stop> function.	1293	therefore a good idea to always call its C<ev_TYPE_stop> function.
733		1294
734	=item bool ev_is_active (ev_TYPE *watcher)	1295	=item bool ev_is_active (ev_TYPE *watcher)
735		1296
736	Returns a true value iff the watcher is active (i.e. it has been started	1297	Returns a true value iff the watcher is active (i.e. it has been started
737	and not yet been stopped). As long as a watcher is active you must not modify	1298	and not yet been stopped). As long as a watcher is active you must not modify
…		…
753	=item ev_cb_set (ev_TYPE *watcher, callback)	1314	=item ev_cb_set (ev_TYPE *watcher, callback)
754		1315
755	Change the callback. You can change the callback at virtually any time	1316	Change the callback. You can change the callback at virtually any time
756	(modulo threads).	1317	(modulo threads).
757		1318
758	=item ev_set_priority (ev_TYPE *watcher, priority)	1319	=item ev_set_priority (ev_TYPE *watcher, int priority)
759		1320
760	=item int ev_priority (ev_TYPE *watcher)	1321	=item int ev_priority (ev_TYPE *watcher)
761		1322
762	Set and query the priority of the watcher. The priority is a small	1323	Set and query the priority of the watcher. The priority is a small
763	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1324	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
764	(default: C<-2>). Pending watchers with higher priority will be invoked	1325	(default: C<-2>). Pending watchers with higher priority will be invoked
765	before watchers with lower priority, but priority will not keep watchers	1326	before watchers with lower priority, but priority will not keep watchers
766	from being executed (except for C<ev_idle> watchers).	1327	from being executed (except for C<ev_idle> watchers).
767		1328
768	This means that priorities are I<only> used for ordering callback
769	invocation after new events have been received. This is useful, for
770	example, to reduce latency after idling, or more often, to bind two
771	watchers on the same event and make sure one is called first.
772
773	If you need to suppress invocation when higher priority events are pending	1329	If you need to suppress invocation when higher priority events are pending
774	you need to look at C<ev_idle> watchers, which provide this functionality.	1330	you need to look at C<ev_idle> watchers, which provide this functionality.
775		1331
776	You I<must not> change the priority of a watcher as long as it is active or	1332	You I<must not> change the priority of a watcher as long as it is active or
777	pending.	1333	pending.
778		1334
		1335	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1336	fine, as long as you do not mind that the priority value you query might
		1337	or might not have been clamped to the valid range.
		1338
779	The default priority used by watchers when no priority has been set is	1339	The default priority used by watchers when no priority has been set is
780	always C<0>, which is supposed to not be too high and not be too low :).	1340	always C<0>, which is supposed to not be too high and not be too low :).
781		1341
782	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1342	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
783	fine, as long as you do not mind that the priority value you query might	1343	priorities.
784	or might not have been adjusted to be within valid range.
785		1344
786	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1345	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
787		1346
788	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1347	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
789	C<loop> nor C<revents> need to be valid as long as the watcher callback	1348	C<loop> nor C<revents> need to be valid as long as the watcher callback
790	can deal with that fact.	1349	can deal with that fact, as both are simply passed through to the
		1350	callback.
791		1351
792	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1352	=item int ev_clear_pending (loop, ev_TYPE *watcher)
793		1353
794	If the watcher is pending, this function returns clears its pending status	1354	If the watcher is pending, this function clears its pending status and
795	and returns its C<revents> bitset (as if its callback was invoked). If the	1355	returns its C<revents> bitset (as if its callback was invoked). If the
796	watcher isn't pending it does nothing and returns C<0>.	1356	watcher isn't pending it does nothing and returns C<0>.
797		1357
		1358	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1359	callback to be invoked, which can be accomplished with this function.
		1360
		1361	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1362
		1363	Feeds the given event set into the event loop, as if the specified event
		1364	had happened for the specified watcher (which must be a pointer to an
		1365	initialised but not necessarily started event watcher). Obviously you must
		1366	not free the watcher as long as it has pending events.
		1367
		1368	Stopping the watcher, letting libev invoke it, or calling
		1369	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1370	not started in the first place.
		1371
		1372	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1373	functions that do not need a watcher.
		1374
798	=back	1375	=back
799		1376
		1377	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1378	OWN COMPOSITE WATCHERS> idioms.
800		1379
801	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1380	=head2 WATCHER STATES
802		1381
803	Each watcher has, by default, a member C<void *data> that you can change	1382	There are various watcher states mentioned throughout this manual -
804	and read at any time, libev will completely ignore it. This can be used	1383	active, pending and so on. In this section these states and the rules to
805	to associate arbitrary data with your watcher. If you need more data and	1384	transition between them will be described in more detail - and while these
806	don't want to allocate memory and store a pointer to it in that data	1385	rules might look complicated, they usually do "the right thing".
807	member, you can also "subclass" the watcher type and provide your own
808	data:
809		1386
810	struct my_io	1387	=over 4
811	{
812	struct ev_io io;
813	int otherfd;
814	void *somedata;
815	struct whatever *mostinteresting;
816	}
817		1388
818	And since your callback will be called with a pointer to the watcher, you	1389	=item initialiased
819	can cast it back to your own type:
820		1390
821	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1391	Before a watcher can be registered with the event loop it has to be
822	{	1392	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
823	struct my_io *w = (struct my_io *)w_;	1393	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
824	...
825	}
826		1394
827	More interesting and less C-conformant ways of casting your callback type	1395	In this state it is simply some block of memory that is suitable for
828	instead have been omitted.	1396	use in an event loop. It can be moved around, freed, reused etc. at
		1397	will - as long as you either keep the memory contents intact, or call
		1398	C<ev_TYPE_init> again.
829		1399
830	Another common scenario is having some data structure with multiple	1400	=item started/running/active
831	watchers:
832		1401
833	struct my_biggy	1402	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
834	{	1403	property of the event loop, and is actively waiting for events. While in
835	int some_data;	1404	this state it cannot be accessed (except in a few documented ways), moved,
836	ev_timer t1;	1405	freed or anything else - the only legal thing is to keep a pointer to it,
837	ev_timer t2;	1406	and call libev functions on it that are documented to work on active watchers.
838	}
839		1407
840	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1408	=item pending
841	you need to use C<offsetof>:
842		1409
843	#include <stddef.h>	1410	If a watcher is active and libev determines that an event it is interested
		1411	in has occurred (such as a timer expiring), it will become pending. It will
		1412	stay in this pending state until either it is stopped or its callback is
		1413	about to be invoked, so it is not normally pending inside the watcher
		1414	callback.
844		1415
		1416	The watcher might or might not be active while it is pending (for example,
		1417	an expired non-repeating timer can be pending but no longer active). If it
		1418	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1419	but it is still property of the event loop at this time, so cannot be
		1420	moved, freed or reused. And if it is active the rules described in the
		1421	previous item still apply.
		1422
		1423	It is also possible to feed an event on a watcher that is not active (e.g.
		1424	via C<ev_feed_event>), in which case it becomes pending without being
		1425	active.
		1426
		1427	=item stopped
		1428
		1429	A watcher can be stopped implicitly by libev (in which case it might still
		1430	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1431	latter will clear any pending state the watcher might be in, regardless
		1432	of whether it was active or not, so stopping a watcher explicitly before
		1433	freeing it is often a good idea.
		1434
		1435	While stopped (and not pending) the watcher is essentially in the
		1436	initialised state, that is, it can be reused, moved, modified in any way
		1437	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1438	it again).
		1439
		1440	=back
		1441
		1442	=head2 WATCHER PRIORITY MODELS
		1443
		1444	Many event loops support I<watcher priorities>, which are usually small
		1445	integers that influence the ordering of event callback invocation
		1446	between watchers in some way, all else being equal.
		1447
		1448	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1449	description for the more technical details such as the actual priority
		1450	range.
		1451
		1452	There are two common ways how these these priorities are being interpreted
		1453	by event loops:
		1454
		1455	In the more common lock-out model, higher priorities "lock out" invocation
		1456	of lower priority watchers, which means as long as higher priority
		1457	watchers receive events, lower priority watchers are not being invoked.
		1458
		1459	The less common only-for-ordering model uses priorities solely to order
		1460	callback invocation within a single event loop iteration: Higher priority
		1461	watchers are invoked before lower priority ones, but they all get invoked
		1462	before polling for new events.
		1463
		1464	Libev uses the second (only-for-ordering) model for all its watchers
		1465	except for idle watchers (which use the lock-out model).
		1466
		1467	The rationale behind this is that implementing the lock-out model for
		1468	watchers is not well supported by most kernel interfaces, and most event
		1469	libraries will just poll for the same events again and again as long as
		1470	their callbacks have not been executed, which is very inefficient in the
		1471	common case of one high-priority watcher locking out a mass of lower
		1472	priority ones.
		1473
		1474	Static (ordering) priorities are most useful when you have two or more
		1475	watchers handling the same resource: a typical usage example is having an
		1476	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1477	timeouts. Under load, data might be received while the program handles
		1478	other jobs, but since timers normally get invoked first, the timeout
		1479	handler will be executed before checking for data. In that case, giving
		1480	the timer a lower priority than the I/O watcher ensures that I/O will be
		1481	handled first even under adverse conditions (which is usually, but not
		1482	always, what you want).
		1483
		1484	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1485	will only be executed when no same or higher priority watchers have
		1486	received events, they can be used to implement the "lock-out" model when
		1487	required.
		1488
		1489	For example, to emulate how many other event libraries handle priorities,
		1490	you can associate an C<ev_idle> watcher to each such watcher, and in
		1491	the normal watcher callback, you just start the idle watcher. The real
		1492	processing is done in the idle watcher callback. This causes libev to
		1493	continuously poll and process kernel event data for the watcher, but when
		1494	the lock-out case is known to be rare (which in turn is rare :), this is
		1495	workable.
		1496
		1497	Usually, however, the lock-out model implemented that way will perform
		1498	miserably under the type of load it was designed to handle. In that case,
		1499	it might be preferable to stop the real watcher before starting the
		1500	idle watcher, so the kernel will not have to process the event in case
		1501	the actual processing will be delayed for considerable time.
		1502
		1503	Here is an example of an I/O watcher that should run at a strictly lower
		1504	priority than the default, and which should only process data when no
		1505	other events are pending:
		1506
		1507	ev_idle idle; // actual processing watcher
		1508	ev_io io; // actual event watcher
		1509
845	static void	1510	static void
846	t1_cb (EV_P_ struct ev_timer *w, int revents)	1511	io_cb (EV_P_ ev_io *w, int revents)
847	{	1512	{
848	struct my_biggy big = (struct my_biggy *	1513	// stop the I/O watcher, we received the event, but
849	(((char *)w) - offsetof (struct my_biggy, t1));	1514	// are not yet ready to handle it.
		1515	ev_io_stop (EV_A_ w);
		1516
		1517	// start the idle watcher to handle the actual event.
		1518	// it will not be executed as long as other watchers
		1519	// with the default priority are receiving events.
		1520	ev_idle_start (EV_A_ &idle);
850	}	1521	}
851		1522
852	static void	1523	static void
853	t2_cb (EV_P_ struct ev_timer *w, int revents)	1524	idle_cb (EV_P_ ev_idle *w, int revents)
854	{	1525	{
855	struct my_biggy big = (struct my_biggy *	1526	// actual processing
856	(((char *)w) - offsetof (struct my_biggy, t2));	1527	read (STDIN_FILENO, ...);
		1528
		1529	// have to start the I/O watcher again, as
		1530	// we have handled the event
		1531	ev_io_start (EV_P_ &io);
857	}	1532	}
		1533
		1534	// initialisation
		1535	ev_idle_init (&idle, idle_cb);
		1536	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1537	ev_io_start (EV_DEFAULT_ &io);
		1538
		1539	In the "real" world, it might also be beneficial to start a timer, so that
		1540	low-priority connections can not be locked out forever under load. This
		1541	enables your program to keep a lower latency for important connections
		1542	during short periods of high load, while not completely locking out less
		1543	important ones.
858		1544
859		1545
860	=head1 WATCHER TYPES	1546	=head1 WATCHER TYPES
861		1547
862	This section describes each watcher in detail, but will not repeat	1548	This section describes each watcher in detail, but will not repeat
…		…
886	In general you can register as many read and/or write event watchers per	1572	In general you can register as many read and/or write event watchers per
887	fd as you want (as long as you don't confuse yourself). Setting all file	1573	fd as you want (as long as you don't confuse yourself). Setting all file
888	descriptors to non-blocking mode is also usually a good idea (but not	1574	descriptors to non-blocking mode is also usually a good idea (but not
889	required if you know what you are doing).	1575	required if you know what you are doing).
890		1576
891	You have to be careful with dup'ed file descriptors, though. Some backends
892	(the linux epoll backend is a notable example) cannot handle dup'ed file
893	descriptors correctly if you register interest in two or more fds pointing
894	to the same underlying file/socket/etc. description (that is, they share
895	the same underlying "file open").
896
897	If you must do this, then force the use of a known-to-be-good backend
898	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
899	C<EVBACKEND_POLL>).
900
901	Another thing you have to watch out for is that it is quite easy to	1577	Another thing you have to watch out for is that it is quite easy to
902	receive "spurious" readyness notifications, that is your callback might	1578	receive "spurious" readiness notifications, that is, your callback might
903	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1579	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
904	because there is no data. Not only are some backends known to create a	1580	because there is no data. It is very easy to get into this situation even
905	lot of those (for example solaris ports), it is very easy to get into	1581	with a relatively standard program structure. Thus it is best to always
906	this situation even with a relatively standard program structure. Thus	1582	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
907	it is best to always use non-blocking I/O: An extra C<read>(2) returning
908	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1583	preferable to a program hanging until some data arrives.
909		1584
910	If you cannot run the fd in non-blocking mode (for example you should not	1585	If you cannot run the fd in non-blocking mode (for example you should
911	play around with an Xlib connection), then you have to seperately re-test	1586	not play around with an Xlib connection), then you have to separately
912	whether a file descriptor is really ready with a known-to-be good interface	1587	re-test whether a file descriptor is really ready with a known-to-be good
913	such as poll (fortunately in our Xlib example, Xlib already does this on	1588	interface such as poll (fortunately in the case of Xlib, it already does
914	its own, so its quite safe to use).	1589	this on its own, so its quite safe to use). Some people additionally
		1590	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1591	indefinitely.
		1592
		1593	But really, best use non-blocking mode.
915		1594
916	=head3 The special problem of disappearing file descriptors	1595	=head3 The special problem of disappearing file descriptors
917		1596
918	Some backends (e.g kqueue, epoll) need to be told about closing a file	1597	Some backends (e.g. kqueue, epoll) need to be told about closing a file
919	descriptor (either by calling C<close> explicitly or by any other means,	1598	descriptor (either due to calling C<close> explicitly or any other means,
920	such as C<dup>). The reason is that you register interest in some file	1599	such as C<dup2>). The reason is that you register interest in some file
921	descriptor, but when it goes away, the operating system will silently drop	1600	descriptor, but when it goes away, the operating system will silently drop
922	this interest. If another file descriptor with the same number then is	1601	this interest. If another file descriptor with the same number then is
923	registered with libev, there is no efficient way to see that this is, in	1602	registered with libev, there is no efficient way to see that this is, in
924	fact, a different file descriptor.	1603	fact, a different file descriptor.
925		1604
…		…
932		1611
933	This is how one would do it normally anyway, the important point is that	1612	This is how one would do it normally anyway, the important point is that
934	the libev application should not optimise around libev but should leave	1613	the libev application should not optimise around libev but should leave
935	optimisations to libev.	1614	optimisations to libev.
936		1615
		1616	=head3 The special problem of dup'ed file descriptors
		1617
		1618	Some backends (e.g. epoll), cannot register events for file descriptors,
		1619	but only events for the underlying file descriptions. That means when you
		1620	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1621	events for them, only one file descriptor might actually receive events.
		1622
		1623	There is no workaround possible except not registering events
		1624	for potentially C<dup ()>'ed file descriptors, or to resort to
		1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1626
		1627	=head3 The special problem of files
		1628
		1629	Many people try to use C<select> (or libev) on file descriptors
		1630	representing files, and expect it to become ready when their program
		1631	doesn't block on disk accesses (which can take a long time on their own).
		1632
		1633	However, this cannot ever work in the "expected" way - you get a readiness
		1634	notification as soon as the kernel knows whether and how much data is
		1635	there, and in the case of open files, that's always the case, so you
		1636	always get a readiness notification instantly, and your read (or possibly
		1637	write) will still block on the disk I/O.
		1638
		1639	Another way to view it is that in the case of sockets, pipes, character
		1640	devices and so on, there is another party (the sender) that delivers data
		1641	on its own, but in the case of files, there is no such thing: the disk
		1642	will not send data on its own, simply because it doesn't know what you
		1643	wish to read - you would first have to request some data.
		1644
		1645	Since files are typically not-so-well supported by advanced notification
		1646	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1647	to files, even though you should not use it. The reason for this is
		1648	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1649	usually a tty, often a pipe, but also sometimes files or special devices
		1650	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1651	F</dev/urandom>), and even though the file might better be served with
		1652	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1653	it "just works" instead of freezing.
		1654
		1655	So avoid file descriptors pointing to files when you know it (e.g. use
		1656	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1657	when you rarely read from a file instead of from a socket, and want to
		1658	reuse the same code path.
		1659
		1660	=head3 The special problem of fork
		1661
		1662	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1663	useless behaviour. Libev fully supports fork, but needs to be told about
		1664	it in the child if you want to continue to use it in the child.
		1665
		1666	To support fork in your child processes, you have to call C<ev_loop_fork
		1667	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1669
		1670	=head3 The special problem of SIGPIPE
		1671
		1672	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1673	when writing to a pipe whose other end has been closed, your program gets
		1674	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1675	this is sensible behaviour, for daemons, this is usually undesirable.
		1676
		1677	So when you encounter spurious, unexplained daemon exits, make sure you
		1678	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1679	somewhere, as that would have given you a big clue).
		1680
		1681	=head3 The special problem of accept()ing when you can't
		1682
		1683	Many implementations of the POSIX C<accept> function (for example,
		1684	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1685	connection from the pending queue in all error cases.
		1686
		1687	For example, larger servers often run out of file descriptors (because
		1688	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1689	rejecting the connection, leading to libev signalling readiness on
		1690	the next iteration again (the connection still exists after all), and
		1691	typically causing the program to loop at 100% CPU usage.
		1692
		1693	Unfortunately, the set of errors that cause this issue differs between
		1694	operating systems, there is usually little the app can do to remedy the
		1695	situation, and no known thread-safe method of removing the connection to
		1696	cope with overload is known (to me).
		1697
		1698	One of the easiest ways to handle this situation is to just ignore it
		1699	- when the program encounters an overload, it will just loop until the
		1700	situation is over. While this is a form of busy waiting, no OS offers an
		1701	event-based way to handle this situation, so it's the best one can do.
		1702
		1703	A better way to handle the situation is to log any errors other than
		1704	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1705	messages, and continue as usual, which at least gives the user an idea of
		1706	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1707	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1708	usage.
		1709
		1710	If your program is single-threaded, then you could also keep a dummy file
		1711	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1712	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1713	close that fd, and create a new dummy fd. This will gracefully refuse
		1714	clients under typical overload conditions.
		1715
		1716	The last way to handle it is to simply log the error and C<exit>, as
		1717	is often done with C<malloc> failures, but this results in an easy
		1718	opportunity for a DoS attack.
937		1719
938	=head3 Watcher-Specific Functions	1720	=head3 Watcher-Specific Functions
939		1721
940	=over 4	1722	=over 4
941		1723
942	=item ev_io_init (ev_io *, callback, int fd, int events)	1724	=item ev_io_init (ev_io *, callback, int fd, int events)
943		1725
944	=item ev_io_set (ev_io *, int fd, int events)	1726	=item ev_io_set (ev_io *, int fd, int events)
945		1727
946	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1728	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
947	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1729	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
948	C<EV_READ | EV_WRITE> to receive the given events.	1730	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
949		1731
950	=item int fd [read-only]	1732	=item int fd [read-only]
951		1733
952	The file descriptor being watched.	1734	The file descriptor being watched.
953		1735
954	=item int events [read-only]	1736	=item int events [read-only]
955		1737
956	The events being watched.	1738	The events being watched.
957		1739
958	=back	1740	=back
		1741
		1742	=head3 Examples
959		1743
960	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1744	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
961	readable, but only once. Since it is likely line-buffered, you could	1745	readable, but only once. Since it is likely line-buffered, you could
962	attempt to read a whole line in the callback.	1746	attempt to read a whole line in the callback.
963		1747
964	static void	1748	static void
965	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1749	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
966	{	1750	{
967	ev_io_stop (loop, w);	1751	ev_io_stop (loop, w);
968	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1752	.. read from stdin here (or from w->fd) and handle any I/O errors
969	}	1753	}
970		1754
971	...	1755	...
972	struct ev_loop *loop = ev_default_init (0);	1756	struct ev_loop *loop = ev_default_init (0);
973	struct ev_io stdin_readable;	1757	ev_io stdin_readable;
974	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1758	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
975	ev_io_start (loop, &stdin_readable);	1759	ev_io_start (loop, &stdin_readable);
976	ev_loop (loop, 0);	1760	ev_run (loop, 0);
977		1761
978		1762
979	=head2 C<ev_timer> - relative and optionally repeating timeouts	1763	=head2 C<ev_timer> - relative and optionally repeating timeouts
980		1764
981	Timer watchers are simple relative timers that generate an event after a	1765	Timer watchers are simple relative timers that generate an event after a
982	given time, and optionally repeating in regular intervals after that.	1766	given time, and optionally repeating in regular intervals after that.
983		1767
984	The timers are based on real time, that is, if you register an event that	1768	The timers are based on real time, that is, if you register an event that
985	times out after an hour and you reset your system clock to last years	1769	times out after an hour and you reset your system clock to January last
986	time, it will still time out after (roughly) and hour. "Roughly" because	1770	year, it will still time out after (roughly) one hour. "Roughly" because
987	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1771	detecting time jumps is hard, and some inaccuracies are unavoidable (the
988	monotonic clock option helps a lot here).	1772	monotonic clock option helps a lot here).
		1773
		1774	The callback is guaranteed to be invoked only I<after> its timeout has
		1775	passed (not I<at>, so on systems with very low-resolution clocks this
		1776	might introduce a small delay, see "the special problem of being too
		1777	early", below). If multiple timers become ready during the same loop
		1778	iteration then the ones with earlier time-out values are invoked before
		1779	ones of the same priority with later time-out values (but this is no
		1780	longer true when a callback calls C<ev_run> recursively).
		1781
		1782	=head3 Be smart about timeouts
		1783
		1784	Many real-world problems involve some kind of timeout, usually for error
		1785	recovery. A typical example is an HTTP request - if the other side hangs,
		1786	you want to raise some error after a while.
		1787
		1788	What follows are some ways to handle this problem, from obvious and
		1789	inefficient to smart and efficient.
		1790
		1791	In the following, a 60 second activity timeout is assumed - a timeout that
		1792	gets reset to 60 seconds each time there is activity (e.g. each time some
		1793	data or other life sign was received).
		1794
		1795	=over 4
		1796
		1797	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1798
		1799	This is the most obvious, but not the most simple way: In the beginning,
		1800	start the watcher:
		1801
		1802	ev_timer_init (timer, callback, 60., 0.);
		1803	ev_timer_start (loop, timer);
		1804
		1805	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1806	and start it again:
		1807
		1808	ev_timer_stop (loop, timer);
		1809	ev_timer_set (timer, 60., 0.);
		1810	ev_timer_start (loop, timer);
		1811
		1812	This is relatively simple to implement, but means that each time there is
		1813	some activity, libev will first have to remove the timer from its internal
		1814	data structure and then add it again. Libev tries to be fast, but it's
		1815	still not a constant-time operation.
		1816
		1817	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1818
		1819	This is the easiest way, and involves using C<ev_timer_again> instead of
		1820	C<ev_timer_start>.
		1821
		1822	To implement this, configure an C<ev_timer> with a C<repeat> value
		1823	of C<60> and then call C<ev_timer_again> at start and each time you
		1824	successfully read or write some data. If you go into an idle state where
		1825	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1826	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1827
		1828	That means you can ignore both the C<ev_timer_start> function and the
		1829	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1830	member and C<ev_timer_again>.
		1831
		1832	At start:
		1833
		1834	ev_init (timer, callback);
		1835	timer->repeat = 60.;
		1836	ev_timer_again (loop, timer);
		1837
		1838	Each time there is some activity:
		1839
		1840	ev_timer_again (loop, timer);
		1841
		1842	It is even possible to change the time-out on the fly, regardless of
		1843	whether the watcher is active or not:
		1844
		1845	timer->repeat = 30.;
		1846	ev_timer_again (loop, timer);
		1847
		1848	This is slightly more efficient then stopping/starting the timer each time
		1849	you want to modify its timeout value, as libev does not have to completely
		1850	remove and re-insert the timer from/into its internal data structure.
		1851
		1852	It is, however, even simpler than the "obvious" way to do it.
		1853
		1854	=item 3. Let the timer time out, but then re-arm it as required.
		1855
		1856	This method is more tricky, but usually most efficient: Most timeouts are
		1857	relatively long compared to the intervals between other activity - in
		1858	our example, within 60 seconds, there are usually many I/O events with
		1859	associated activity resets.
		1860
		1861	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1862	but remember the time of last activity, and check for a real timeout only
		1863	within the callback:
		1864
		1865	ev_tstamp last_activity; // time of last activity
		1866
		1867	static void
		1868	callback (EV_P_ ev_timer *w, int revents)
		1869	{
		1870	ev_tstamp now = ev_now (EV_A);
		1871	ev_tstamp timeout = last_activity + 60.;
		1872
		1873	// if last_activity + 60. is older than now, we did time out
		1874	if (timeout < now)
		1875	{
		1876	// timeout occurred, take action
		1877	}
		1878	else
		1879	{
		1880	// callback was invoked, but there was some activity, re-arm
		1881	// the watcher to fire in last_activity + 60, which is
		1882	// guaranteed to be in the future, so "again" is positive:
		1883	w->repeat = timeout - now;
		1884	ev_timer_again (EV_A_ w);
		1885	}
		1886	}
		1887
		1888	To summarise the callback: first calculate the real timeout (defined
		1889	as "60 seconds after the last activity"), then check if that time has
		1890	been reached, which means something I<did>, in fact, time out. Otherwise
		1891	the callback was invoked too early (C<timeout> is in the future), so
		1892	re-schedule the timer to fire at that future time, to see if maybe we have
		1893	a timeout then.
		1894
		1895	Note how C<ev_timer_again> is used, taking advantage of the
		1896	C<ev_timer_again> optimisation when the timer is already running.
		1897
		1898	This scheme causes more callback invocations (about one every 60 seconds
		1899	minus half the average time between activity), but virtually no calls to
		1900	libev to change the timeout.
		1901
		1902	To start the timer, simply initialise the watcher and set C<last_activity>
		1903	to the current time (meaning we just have some activity :), then call the
		1904	callback, which will "do the right thing" and start the timer:
		1905
		1906	ev_init (timer, callback);
		1907	last_activity = ev_now (loop);
		1908	callback (loop, timer, EV_TIMER);
		1909
		1910	And when there is some activity, simply store the current time in
		1911	C<last_activity>, no libev calls at all:
		1912
		1913	last_activity = ev_now (loop);
		1914
		1915	This technique is slightly more complex, but in most cases where the
		1916	time-out is unlikely to be triggered, much more efficient.
		1917
		1918	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1919	callback :) - just change the timeout and invoke the callback, which will
		1920	fix things for you.
		1921
		1922	=item 4. Wee, just use a double-linked list for your timeouts.
		1923
		1924	If there is not one request, but many thousands (millions...), all
		1925	employing some kind of timeout with the same timeout value, then one can
		1926	do even better:
		1927
		1928	When starting the timeout, calculate the timeout value and put the timeout
		1929	at the I<end> of the list.
		1930
		1931	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1932	the list is expected to fire (for example, using the technique #3).
		1933
		1934	When there is some activity, remove the timer from the list, recalculate
		1935	the timeout, append it to the end of the list again, and make sure to
		1936	update the C<ev_timer> if it was taken from the beginning of the list.
		1937
		1938	This way, one can manage an unlimited number of timeouts in O(1) time for
		1939	starting, stopping and updating the timers, at the expense of a major
		1940	complication, and having to use a constant timeout. The constant timeout
		1941	ensures that the list stays sorted.
		1942
		1943	=back
		1944
		1945	So which method the best?
		1946
		1947	Method #2 is a simple no-brain-required solution that is adequate in most
		1948	situations. Method #3 requires a bit more thinking, but handles many cases
		1949	better, and isn't very complicated either. In most case, choosing either
		1950	one is fine, with #3 being better in typical situations.
		1951
		1952	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1953	rather complicated, but extremely efficient, something that really pays
		1954	off after the first million or so of active timers, i.e. it's usually
		1955	overkill :)
		1956
		1957	=head3 The special problem of being too early
		1958
		1959	If you ask a timer to call your callback after three seconds, then
		1960	you expect it to be invoked after three seconds - but of course, this
		1961	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1962	guaranteed to any precision by libev - imagine somebody suspending the
		1963	process a STOP signal for a few hours for example.
		1964
		1965	So, libev tries to invoke your callback as soon as possible I<after> the
		1966	delay has occurred, but cannot guarantee this.
		1967
		1968	A less obvious failure mode is calling your callback too early: many event
		1969	loops compare timestamps with a "elapsed delay >= requested delay", but
		1970	this can cause your callback to be invoked much earlier than you would
		1971	expect.
		1972
		1973	To see why, imagine a system with a clock that only offers full second
		1974	resolution (think windows if you can't come up with a broken enough OS
		1975	yourself). If you schedule a one-second timer at the time 500.9, then the
		1976	event loop will schedule your timeout to elapse at a system time of 500
		1977	(500.9 truncated to the resolution) + 1, or 501.
		1978
		1979	If an event library looks at the timeout 0.1s later, it will see "501 >=
		1980	501" and invoke the callback 0.1s after it was started, even though a
		1981	one-second delay was requested - this is being "too early", despite best
		1982	intentions.
		1983
		1984	This is the reason why libev will never invoke the callback if the elapsed
		1985	delay equals the requested delay, but only when the elapsed delay is
		1986	larger than the requested delay. In the example above, libev would only invoke
		1987	the callback at system time 502, or 1.1s after the timer was started.
		1988
		1989	So, while libev cannot guarantee that your callback will be invoked
		1990	exactly when requested, it I<can> and I<does> guarantee that the requested
		1991	delay has actually elapsed, or in other words, it always errs on the "too
		1992	late" side of things.
		1993
		1994	=head3 The special problem of time updates
		1995
		1996	Establishing the current time is a costly operation (it usually takes
		1997	at least one system call): EV therefore updates its idea of the current
		1998	time only before and after C<ev_run> collects new events, which causes a
		1999	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2000	lots of events in one iteration.
989		2001
990	The relative timeouts are calculated relative to the C<ev_now ()>	2002	The relative timeouts are calculated relative to the C<ev_now ()>
991	time. This is usually the right thing as this timestamp refers to the time	2003	time. This is usually the right thing as this timestamp refers to the time
992	of the event triggering whatever timeout you are modifying/starting. If	2004	of the event triggering whatever timeout you are modifying/starting. If
993	you suspect event processing to be delayed and you I<need> to base the timeout	2005	you suspect event processing to be delayed and you I<need> to base the
994	on the current time, use something like this to adjust for this:	2006	timeout on the current time, use something like this to adjust for this:
995		2007
996	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2008	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
997		2009
998	The callback is guarenteed to be invoked only when its timeout has passed,	2010	If the event loop is suspended for a long time, you can also force an
999	but if multiple timers become ready during the same loop iteration then	2011	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1000	order of execution is undefined.	2012	()>.
		2013
		2014	=head3 The special problem of unsynchronised clocks
		2015
		2016	Modern systems have a variety of clocks - libev itself uses the normal
		2017	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2018	jumps).
		2019
		2020	Neither of these clocks is synchronised with each other or any other clock
		2021	on the system, so C<ev_time ()> might return a considerably different time
		2022	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2023	a call to C<gettimeofday> might return a second count that is one higher
		2024	than a directly following call to C<time>.
		2025
		2026	The moral of this is to only compare libev-related timestamps with
		2027	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2028	a second or so.
		2029
		2030	One more problem arises due to this lack of synchronisation: if libev uses
		2031	the system monotonic clock and you compare timestamps from C<ev_time>
		2032	or C<ev_now> from when you started your timer and when your callback is
		2033	invoked, you will find that sometimes the callback is a bit "early".
		2034
		2035	This is because C<ev_timer>s work in real time, not wall clock time, so
		2036	libev makes sure your callback is not invoked before the delay happened,
		2037	I<measured according to the real time>, not the system clock.
		2038
		2039	If your timeouts are based on a physical timescale (e.g. "time out this
		2040	connection after 100 seconds") then this shouldn't bother you as it is
		2041	exactly the right behaviour.
		2042
		2043	If you want to compare wall clock/system timestamps to your timers, then
		2044	you need to use C<ev_periodic>s, as these are based on the wall clock
		2045	time, where your comparisons will always generate correct results.
		2046
		2047	=head3 The special problems of suspended animation
		2048
		2049	When you leave the server world it is quite customary to hit machines that
		2050	can suspend/hibernate - what happens to the clocks during such a suspend?
		2051
		2052	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2053	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2054	to run until the system is suspended, but they will not advance while the
		2055	system is suspended. That means, on resume, it will be as if the program
		2056	was frozen for a few seconds, but the suspend time will not be counted
		2057	towards C<ev_timer> when a monotonic clock source is used. The real time
		2058	clock advanced as expected, but if it is used as sole clocksource, then a
		2059	long suspend would be detected as a time jump by libev, and timers would
		2060	be adjusted accordingly.
		2061
		2062	I would not be surprised to see different behaviour in different between
		2063	operating systems, OS versions or even different hardware.
		2064
		2065	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2066	time jump in the monotonic clocks and the realtime clock. If the program
		2067	is suspended for a very long time, and monotonic clock sources are in use,
		2068	then you can expect C<ev_timer>s to expire as the full suspension time
		2069	will be counted towards the timers. When no monotonic clock source is in
		2070	use, then libev will again assume a timejump and adjust accordingly.
		2071
		2072	It might be beneficial for this latter case to call C<ev_suspend>
		2073	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2074	deterministic behaviour in this case (you can do nothing against
		2075	C<SIGSTOP>).
1001		2076
1002	=head3 Watcher-Specific Functions and Data Members	2077	=head3 Watcher-Specific Functions and Data Members
1003		2078
1004	=over 4	2079	=over 4
1005		2080
1006	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2081	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1007		2082
1008	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2083	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1009		2084
1010	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2085	Configure the timer to trigger after C<after> seconds. If C<repeat>
1011	C<0.>, then it will automatically be stopped. If it is positive, then the	2086	is C<0.>, then it will automatically be stopped once the timeout is
1012	timer will automatically be configured to trigger again C<repeat> seconds	2087	reached. If it is positive, then the timer will automatically be
1013	later, again, and again, until stopped manually.	2088	configured to trigger again C<repeat> seconds later, again, and again,
		2089	until stopped manually.
1014		2090
1015	The timer itself will do a best-effort at avoiding drift, that is, if you	2091	The timer itself will do a best-effort at avoiding drift, that is, if
1016	configure a timer to trigger every 10 seconds, then it will trigger at	2092	you configure a timer to trigger every 10 seconds, then it will normally
1017	exactly 10 second intervals. If, however, your program cannot keep up with	2093	trigger at exactly 10 second intervals. If, however, your program cannot
1018	the timer (because it takes longer than those 10 seconds to do stuff) the	2094	keep up with the timer (because it takes longer than those 10 seconds to
1019	timer will not fire more than once per event loop iteration.	2095	do stuff) the timer will not fire more than once per event loop iteration.
1020		2096
1021	=item ev_timer_again (loop)	2097	=item ev_timer_again (loop, ev_timer *)
1022		2098
1023	This will act as if the timer timed out and restart it again if it is	2099	This will act as if the timer timed out and restarts it again if it is
1024	repeating. The exact semantics are:	2100	repeating. The exact semantics are:
1025		2101
1026	If the timer is pending, its pending status is cleared.	2102	If the timer is pending, its pending status is cleared.
1027		2103
1028	If the timer is started but nonrepeating, stop it (as if it timed out).	2104	If the timer is started but non-repeating, stop it (as if it timed out).
1029		2105
1030	If the timer is repeating, either start it if necessary (with the	2106	If the timer is repeating, either start it if necessary (with the
1031	C<repeat> value), or reset the running timer to the C<repeat> value.	2107	C<repeat> value), or reset the running timer to the C<repeat> value.
1032		2108
1033	This sounds a bit complicated, but here is a useful and typical	2109	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1034	example: Imagine you have a tcp connection and you want a so-called idle	2110	usage example.
1035	timeout, that is, you want to be called when there have been, say, 60
1036	seconds of inactivity on the socket. The easiest way to do this is to
1037	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1038	C<ev_timer_again> each time you successfully read or write some data. If
1039	you go into an idle state where you do not expect data to travel on the
1040	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1041	automatically restart it if need be.
1042		2111
1043	That means you can ignore the C<after> value and C<ev_timer_start>	2112	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1044	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1045		2113
1046	ev_timer_init (timer, callback, 0., 5.);	2114	Returns the remaining time until a timer fires. If the timer is active,
1047	ev_timer_again (loop, timer);	2115	then this time is relative to the current event loop time, otherwise it's
1048	...	2116	the timeout value currently configured.
1049	timer->again = 17.;
1050	ev_timer_again (loop, timer);
1051	...
1052	timer->again = 10.;
1053	ev_timer_again (loop, timer);
1054		2117
1055	This is more slightly efficient then stopping/starting the timer each time	2118	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1056	you want to modify its timeout value.	2119	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2120	will return C<4>. When the timer expires and is restarted, it will return
		2121	roughly C<7> (likely slightly less as callback invocation takes some time,
		2122	too), and so on.
1057		2123
1058	=item ev_tstamp repeat [read-write]	2124	=item ev_tstamp repeat [read-write]
1059		2125
1060	The current C<repeat> value. Will be used each time the watcher times out	2126	The current C<repeat> value. Will be used each time the watcher times out
1061	or C<ev_timer_again> is called and determines the next timeout (if any),	2127	or C<ev_timer_again> is called, and determines the next timeout (if any),
1062	which is also when any modifications are taken into account.	2128	which is also when any modifications are taken into account.
1063		2129
1064	=back	2130	=back
1065		2131
		2132	=head3 Examples
		2133
1066	Example: Create a timer that fires after 60 seconds.	2134	Example: Create a timer that fires after 60 seconds.
1067		2135
1068	static void	2136	static void
1069	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2137	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1070	{	2138	{
1071	.. one minute over, w is actually stopped right here	2139	.. one minute over, w is actually stopped right here
1072	}	2140	}
1073		2141
1074	struct ev_timer mytimer;	2142	ev_timer mytimer;
1075	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2143	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1076	ev_timer_start (loop, &mytimer);	2144	ev_timer_start (loop, &mytimer);
1077		2145
1078	Example: Create a timeout timer that times out after 10 seconds of	2146	Example: Create a timeout timer that times out after 10 seconds of
1079	inactivity.	2147	inactivity.
1080		2148
1081	static void	2149	static void
1082	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2150	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1083	{	2151	{
1084	.. ten seconds without any activity	2152	.. ten seconds without any activity
1085	}	2153	}
1086		2154
1087	struct ev_timer mytimer;	2155	ev_timer mytimer;
1088	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2156	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1089	ev_timer_again (&mytimer); /* start timer */	2157	ev_timer_again (&mytimer); /* start timer */
1090	ev_loop (loop, 0);	2158	ev_run (loop, 0);
1091		2159
1092	// and in some piece of code that gets executed on any "activity":	2160	// and in some piece of code that gets executed on any "activity":
1093	// reset the timeout to start ticking again at 10 seconds	2161	// reset the timeout to start ticking again at 10 seconds
1094	ev_timer_again (&mytimer);	2162	ev_timer_again (&mytimer);
1095		2163
1096		2164
1097	=head2 C<ev_periodic> - to cron or not to cron?	2165	=head2 C<ev_periodic> - to cron or not to cron?
1098		2166
1099	Periodic watchers are also timers of a kind, but they are very versatile	2167	Periodic watchers are also timers of a kind, but they are very versatile
1100	(and unfortunately a bit complex).	2168	(and unfortunately a bit complex).
1101		2169
1102	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2170	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1103	but on wallclock time (absolute time). You can tell a periodic watcher	2171	relative time, the physical time that passes) but on wall clock time
1104	to trigger "at" some specific point in time. For example, if you tell a	2172	(absolute time, the thing you can read on your calender or clock). The
1105	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2173	difference is that wall clock time can run faster or slower than real
1106	+ 10.>) and then reset your system clock to the last year, then it will	2174	time, and time jumps are not uncommon (e.g. when you adjust your
1107	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2175	wrist-watch).
1108	roughly 10 seconds later).
1109		2176
1110	They can also be used to implement vastly more complex timers, such as	2177	You can tell a periodic watcher to trigger after some specific point
1111	triggering an event on each midnight, local time or other, complicated,	2178	in time: for example, if you tell a periodic watcher to trigger "in 10
1112	rules.	2179	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2180	not a delay) and then reset your system clock to January of the previous
		2181	year, then it will take a year or more to trigger the event (unlike an
		2182	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2183	it, as it uses a relative timeout).
1113		2184
		2185	C<ev_periodic> watchers can also be used to implement vastly more complex
		2186	timers, such as triggering an event on each "midnight, local time", or
		2187	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2188	those cannot react to time jumps.
		2189
1114	As with timers, the callback is guarenteed to be invoked only when the	2190	As with timers, the callback is guaranteed to be invoked only when the
1115	time (C<at>) has been passed, but if multiple periodic timers become ready	2191	point in time where it is supposed to trigger has passed. If multiple
1116	during the same loop iteration then order of execution is undefined.	2192	timers become ready during the same loop iteration then the ones with
		2193	earlier time-out values are invoked before ones with later time-out values
		2194	(but this is no longer true when a callback calls C<ev_run> recursively).
1117		2195
1118	=head3 Watcher-Specific Functions and Data Members	2196	=head3 Watcher-Specific Functions and Data Members
1119		2197
1120	=over 4	2198	=over 4
1121		2199
1122	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2200	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1123		2201
1124	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2202	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1125		2203
1126	Lots of arguments, lets sort it out... There are basically three modes of	2204	Lots of arguments, let's sort it out... There are basically three modes of
1127	operation, and we will explain them from simplest to complex:	2205	operation, and we will explain them from simplest to most complex:
1128		2206
1129	=over 4	2207	=over 4
1130		2208
1131	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2209	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1132		2210
1133	In this configuration the watcher triggers an event at the wallclock time	2211	In this configuration the watcher triggers an event after the wall clock
1134	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2212	time C<offset> has passed. It will not repeat and will not adjust when a
1135	that is, if it is to be run at January 1st 2011 then it will run when the	2213	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1136	system time reaches or surpasses this time.	2214	will be stopped and invoked when the system clock reaches or surpasses
		2215	this point in time.
1137		2216
1138	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2217	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1139		2218
1140	In this mode the watcher will always be scheduled to time out at the next	2219	In this mode the watcher will always be scheduled to time out at the next
1141	C<at + N * interval> time (for some integer N, which can also be negative)	2220	C<offset + N * interval> time (for some integer N, which can also be
1142	and then repeat, regardless of any time jumps.	2221	negative) and then repeat, regardless of any time jumps. The C<offset>
		2222	argument is merely an offset into the C<interval> periods.
1143		2223
1144	This can be used to create timers that do not drift with respect to system	2224	This can be used to create timers that do not drift with respect to the
1145	time:	2225	system clock, for example, here is an C<ev_periodic> that triggers each
		2226	hour, on the hour (with respect to UTC):
1146		2227
1147	ev_periodic_set (&periodic, 0., 3600., 0);	2228	ev_periodic_set (&periodic, 0., 3600., 0);
1148		2229
1149	This doesn't mean there will always be 3600 seconds in between triggers,	2230	This doesn't mean there will always be 3600 seconds in between triggers,
1150	but only that the the callback will be called when the system time shows a	2231	but only that the callback will be called when the system time shows a
1151	full hour (UTC), or more correctly, when the system time is evenly divisible	2232	full hour (UTC), or more correctly, when the system time is evenly divisible
1152	by 3600.	2233	by 3600.
1153		2234
1154	Another way to think about it (for the mathematically inclined) is that	2235	Another way to think about it (for the mathematically inclined) is that
1155	C<ev_periodic> will try to run the callback in this mode at the next possible	2236	C<ev_periodic> will try to run the callback in this mode at the next possible
1156	time where C<time = at (mod interval)>, regardless of any time jumps.	2237	time where C<time = offset (mod interval)>, regardless of any time jumps.
1157		2238
1158	For numerical stability it is preferable that the C<at> value is near	2239	The C<interval> I<MUST> be positive, and for numerical stability, the
1159	C<ev_now ()> (the current time), but there is no range requirement for	2240	interval value should be higher than C<1/8192> (which is around 100
1160	this value.	2241	microseconds) and C<offset> should be higher than C<0> and should have
		2242	at most a similar magnitude as the current time (say, within a factor of
		2243	ten). Typical values for offset are, in fact, C<0> or something between
		2244	C<0> and C<interval>, which is also the recommended range.
1161		2245
		2246	Note also that there is an upper limit to how often a timer can fire (CPU
		2247	speed for example), so if C<interval> is very small then timing stability
		2248	will of course deteriorate. Libev itself tries to be exact to be about one
		2249	millisecond (if the OS supports it and the machine is fast enough).
		2250
1162	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2251	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1163		2252
1164	In this mode the values for C<interval> and C<at> are both being	2253	In this mode the values for C<interval> and C<offset> are both being
1165	ignored. Instead, each time the periodic watcher gets scheduled, the	2254	ignored. Instead, each time the periodic watcher gets scheduled, the
1166	reschedule callback will be called with the watcher as first, and the	2255	reschedule callback will be called with the watcher as first, and the
1167	current time as second argument.	2256	current time as second argument.
1168		2257
1169	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2258	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1170	ever, or make any event loop modifications>. If you need to stop it,	2259	or make ANY other event loop modifications whatsoever, unless explicitly
1171	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2260	allowed by documentation here>.
1172	starting an C<ev_prepare> watcher, which is legal).
1173		2261
		2262	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2263	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2264	only event loop modification you are allowed to do).
		2265
1174	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2266	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1175	ev_tstamp now)>, e.g.:	2267	*w, ev_tstamp now)>, e.g.:
1176		2268
		2269	static ev_tstamp
1177	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2270	my_rescheduler (ev_periodic *w, ev_tstamp now)
1178	{	2271	{
1179	return now + 60.;	2272	return now + 60.;
1180	}	2273	}
1181		2274
1182	It must return the next time to trigger, based on the passed time value	2275	It must return the next time to trigger, based on the passed time value
1183	(that is, the lowest time value larger than to the second argument). It	2276	(that is, the lowest time value larger than to the second argument). It
1184	will usually be called just before the callback will be triggered, but	2277	will usually be called just before the callback will be triggered, but
1185	might be called at other times, too.	2278	might be called at other times, too.
1186		2279
1187	NOTE: I<< This callback must always return a time that is later than the	2280	NOTE: I<< This callback must always return a time that is higher than or
1188	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2281	equal to the passed C<now> value >>.
1189		2282
1190	This can be used to create very complex timers, such as a timer that	2283	This can be used to create very complex timers, such as a timer that
1191	triggers on each midnight, local time. To do this, you would calculate the	2284	triggers on "next midnight, local time". To do this, you would calculate the
1192	next midnight after C<now> and return the timestamp value for this. How	2285	next midnight after C<now> and return the timestamp value for this. How
1193	you do this is, again, up to you (but it is not trivial, which is the main	2286	you do this is, again, up to you (but it is not trivial, which is the main
1194	reason I omitted it as an example).	2287	reason I omitted it as an example).
1195		2288
1196	=back	2289	=back
…		…
1200	Simply stops and restarts the periodic watcher again. This is only useful	2293	Simply stops and restarts the periodic watcher again. This is only useful
1201	when you changed some parameters or the reschedule callback would return	2294	when you changed some parameters or the reschedule callback would return
1202	a different time than the last time it was called (e.g. in a crond like	2295	a different time than the last time it was called (e.g. in a crond like
1203	program when the crontabs have changed).	2296	program when the crontabs have changed).
1204		2297
		2298	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2299
		2300	When active, returns the absolute time that the watcher is supposed
		2301	to trigger next. This is not the same as the C<offset> argument to
		2302	C<ev_periodic_set>, but indeed works even in interval and manual
		2303	rescheduling modes.
		2304
1205	=item ev_tstamp offset [read-write]	2305	=item ev_tstamp offset [read-write]
1206		2306
1207	When repeating, this contains the offset value, otherwise this is the	2307	When repeating, this contains the offset value, otherwise this is the
1208	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2308	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2309	although libev might modify this value for better numerical stability).
1209		2310
1210	Can be modified any time, but changes only take effect when the periodic	2311	Can be modified any time, but changes only take effect when the periodic
1211	timer fires or C<ev_periodic_again> is being called.	2312	timer fires or C<ev_periodic_again> is being called.
1212		2313
1213	=item ev_tstamp interval [read-write]	2314	=item ev_tstamp interval [read-write]
1214		2315
1215	The current interval value. Can be modified any time, but changes only	2316	The current interval value. Can be modified any time, but changes only
1216	take effect when the periodic timer fires or C<ev_periodic_again> is being	2317	take effect when the periodic timer fires or C<ev_periodic_again> is being
1217	called.	2318	called.
1218		2319
1219	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2320	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1220		2321
1221	The current reschedule callback, or C<0>, if this functionality is	2322	The current reschedule callback, or C<0>, if this functionality is
1222	switched off. Can be changed any time, but changes only take effect when	2323	switched off. Can be changed any time, but changes only take effect when
1223	the periodic timer fires or C<ev_periodic_again> is being called.	2324	the periodic timer fires or C<ev_periodic_again> is being called.
1224		2325
1225	=back	2326	=back
1226		2327
		2328	=head3 Examples
		2329
1227	Example: Call a callback every hour, or, more precisely, whenever the	2330	Example: Call a callback every hour, or, more precisely, whenever the
1228	system clock is divisible by 3600. The callback invocation times have	2331	system time is divisible by 3600. The callback invocation times have
1229	potentially a lot of jittering, but good long-term stability.	2332	potentially a lot of jitter, but good long-term stability.
1230		2333
1231	static void	2334	static void
1232	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2335	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1233	{	2336	{
1234	... its now a full hour (UTC, or TAI or whatever your clock follows)	2337	... its now a full hour (UTC, or TAI or whatever your clock follows)
1235	}	2338	}
1236		2339
1237	struct ev_periodic hourly_tick;	2340	ev_periodic hourly_tick;
1238	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2341	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1239	ev_periodic_start (loop, &hourly_tick);	2342	ev_periodic_start (loop, &hourly_tick);
1240		2343
1241	Example: The same as above, but use a reschedule callback to do it:	2344	Example: The same as above, but use a reschedule callback to do it:
1242		2345
1243	#include <math.h>	2346	#include <math.h>
1244		2347
1245	static ev_tstamp	2348	static ev_tstamp
1246	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2349	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1247	{	2350	{
1248	return fmod (now, 3600.) + 3600.;	2351	return now + (3600. - fmod (now, 3600.));
1249	}	2352	}
1250		2353
1251	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2354	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1252		2355
1253	Example: Call a callback every hour, starting now:	2356	Example: Call a callback every hour, starting now:
1254		2357
1255	struct ev_periodic hourly_tick;	2358	ev_periodic hourly_tick;
1256	ev_periodic_init (&hourly_tick, clock_cb,	2359	ev_periodic_init (&hourly_tick, clock_cb,
1257	fmod (ev_now (loop), 3600.), 3600., 0);	2360	fmod (ev_now (loop), 3600.), 3600., 0);
1258	ev_periodic_start (loop, &hourly_tick);	2361	ev_periodic_start (loop, &hourly_tick);
1259		2362
1260		2363
1261	=head2 C<ev_signal> - signal me when a signal gets signalled!	2364	=head2 C<ev_signal> - signal me when a signal gets signalled!
1262		2365
1263	Signal watchers will trigger an event when the process receives a specific	2366	Signal watchers will trigger an event when the process receives a specific
1264	signal one or more times. Even though signals are very asynchronous, libev	2367	signal one or more times. Even though signals are very asynchronous, libev
1265	will try it's best to deliver signals synchronously, i.e. as part of the	2368	will try its best to deliver signals synchronously, i.e. as part of the
1266	normal event processing, like any other event.	2369	normal event processing, like any other event.
1267		2370
		2371	If you want signals to be delivered truly asynchronously, just use
		2372	C<sigaction> as you would do without libev and forget about sharing
		2373	the signal. You can even use C<ev_async> from a signal handler to
		2374	synchronously wake up an event loop.
		2375
1268	You can configure as many watchers as you like per signal. Only when the	2376	You can configure as many watchers as you like for the same signal, but
		2377	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2378	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2379	C<SIGINT> in both the default loop and another loop at the same time. At
		2380	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2381
1269	first watcher gets started will libev actually register a signal watcher	2382	When the first watcher gets started will libev actually register something
1270	with the kernel (thus it coexists with your own signal handlers as long	2383	with the kernel (thus it coexists with your own signal handlers as long as
1271	as you don't register any with libev). Similarly, when the last signal	2384	you don't register any with libev for the same signal).
1272	watcher for a signal is stopped libev will reset the signal handler to	2385
1273	SIG_DFL (regardless of what it was set to before).	2386	If possible and supported, libev will install its handlers with
		2387	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2388	not be unduly interrupted. If you have a problem with system calls getting
		2389	interrupted by signals you can block all signals in an C<ev_check> watcher
		2390	and unblock them in an C<ev_prepare> watcher.
		2391
		2392	=head3 The special problem of inheritance over fork/execve/pthread_create
		2393
		2394	Both the signal mask (C<sigprocmask>) and the signal disposition
		2395	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2396	stopping it again), that is, libev might or might not block the signal,
		2397	and might or might not set or restore the installed signal handler (but
		2398	see C<EVFLAG_NOSIGMASK>).
		2399
		2400	While this does not matter for the signal disposition (libev never
		2401	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2402	C<execve>), this matters for the signal mask: many programs do not expect
		2403	certain signals to be blocked.
		2404
		2405	This means that before calling C<exec> (from the child) you should reset
		2406	the signal mask to whatever "default" you expect (all clear is a good
		2407	choice usually).
		2408
		2409	The simplest way to ensure that the signal mask is reset in the child is
		2410	to install a fork handler with C<pthread_atfork> that resets it. That will
		2411	catch fork calls done by libraries (such as the libc) as well.
		2412
		2413	In current versions of libev, the signal will not be blocked indefinitely
		2414	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2415	the window of opportunity for problems, it will not go away, as libev
		2416	I<has> to modify the signal mask, at least temporarily.
		2417
		2418	So I can't stress this enough: I<If you do not reset your signal mask when
		2419	you expect it to be empty, you have a race condition in your code>. This
		2420	is not a libev-specific thing, this is true for most event libraries.
		2421
		2422	=head3 The special problem of threads signal handling
		2423
		2424	POSIX threads has problematic signal handling semantics, specifically,
		2425	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2426	threads in a process block signals, which is hard to achieve.
		2427
		2428	When you want to use sigwait (or mix libev signal handling with your own
		2429	for the same signals), you can tackle this problem by globally blocking
		2430	all signals before creating any threads (or creating them with a fully set
		2431	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2432	loops. Then designate one thread as "signal receiver thread" which handles
		2433	these signals. You can pass on any signals that libev might be interested
		2434	in by calling C<ev_feed_signal>.
1274		2435
1275	=head3 Watcher-Specific Functions and Data Members	2436	=head3 Watcher-Specific Functions and Data Members
1276		2437
1277	=over 4	2438	=over 4
1278		2439
…		…
1287		2448
1288	The signal the watcher watches out for.	2449	The signal the watcher watches out for.
1289		2450
1290	=back	2451	=back
1291		2452
		2453	=head3 Examples
		2454
		2455	Example: Try to exit cleanly on SIGINT.
		2456
		2457	static void
		2458	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2459	{
		2460	ev_break (loop, EVBREAK_ALL);
		2461	}
		2462
		2463	ev_signal signal_watcher;
		2464	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2465	ev_signal_start (loop, &signal_watcher);
		2466
1292		2467
1293	=head2 C<ev_child> - watch out for process status changes	2468	=head2 C<ev_child> - watch out for process status changes
1294		2469
1295	Child watchers trigger when your process receives a SIGCHLD in response to	2470	Child watchers trigger when your process receives a SIGCHLD in response to
1296	some child status changes (most typically when a child of yours dies).	2471	some child status changes (most typically when a child of yours dies or
		2472	exits). It is permissible to install a child watcher I<after> the child
		2473	has been forked (which implies it might have already exited), as long
		2474	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2475	forking and then immediately registering a watcher for the child is fine,
		2476	but forking and registering a watcher a few event loop iterations later or
		2477	in the next callback invocation is not.
		2478
		2479	Only the default event loop is capable of handling signals, and therefore
		2480	you can only register child watchers in the default event loop.
		2481
		2482	Due to some design glitches inside libev, child watchers will always be
		2483	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2484	libev)
		2485
		2486	=head3 Process Interaction
		2487
		2488	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2489	initialised. This is necessary to guarantee proper behaviour even if the
		2490	first child watcher is started after the child exits. The occurrence
		2491	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2492	synchronously as part of the event loop processing. Libev always reaps all
		2493	children, even ones not watched.
		2494
		2495	=head3 Overriding the Built-In Processing
		2496
		2497	Libev offers no special support for overriding the built-in child
		2498	processing, but if your application collides with libev's default child
		2499	handler, you can override it easily by installing your own handler for
		2500	C<SIGCHLD> after initialising the default loop, and making sure the
		2501	default loop never gets destroyed. You are encouraged, however, to use an
		2502	event-based approach to child reaping and thus use libev's support for
		2503	that, so other libev users can use C<ev_child> watchers freely.
		2504
		2505	=head3 Stopping the Child Watcher
		2506
		2507	Currently, the child watcher never gets stopped, even when the
		2508	child terminates, so normally one needs to stop the watcher in the
		2509	callback. Future versions of libev might stop the watcher automatically
		2510	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2511	problem).
1297		2512
1298	=head3 Watcher-Specific Functions and Data Members	2513	=head3 Watcher-Specific Functions and Data Members
1299		2514
1300	=over 4	2515	=over 4
1301		2516
1302	=item ev_child_init (ev_child *, callback, int pid)	2517	=item ev_child_init (ev_child *, callback, int pid, int trace)
1303		2518
1304	=item ev_child_set (ev_child *, int pid)	2519	=item ev_child_set (ev_child *, int pid, int trace)
1305		2520
1306	Configures the watcher to wait for status changes of process C<pid> (or	2521	Configures the watcher to wait for status changes of process C<pid> (or
1307	I<any> process if C<pid> is specified as C<0>). The callback can look	2522	I<any> process if C<pid> is specified as C<0>). The callback can look
1308	at the C<rstatus> member of the C<ev_child> watcher structure to see	2523	at the C<rstatus> member of the C<ev_child> watcher structure to see
1309	the status word (use the macros from C<sys/wait.h> and see your systems	2524	the status word (use the macros from C<sys/wait.h> and see your systems
1310	C<waitpid> documentation). The C<rpid> member contains the pid of the	2525	C<waitpid> documentation). The C<rpid> member contains the pid of the
1311	process causing the status change.	2526	process causing the status change. C<trace> must be either C<0> (only
		2527	activate the watcher when the process terminates) or C<1> (additionally
		2528	activate the watcher when the process is stopped or continued).
1312		2529
1313	=item int pid [read-only]	2530	=item int pid [read-only]
1314		2531
1315	The process id this watcher watches out for, or C<0>, meaning any process id.	2532	The process id this watcher watches out for, or C<0>, meaning any process id.
1316		2533
…		…
1323	The process exit/trace status caused by C<rpid> (see your systems	2540	The process exit/trace status caused by C<rpid> (see your systems
1324	C<waitpid> and C<sys/wait.h> documentation for details).	2541	C<waitpid> and C<sys/wait.h> documentation for details).
1325		2542
1326	=back	2543	=back
1327		2544
1328	Example: Try to exit cleanly on SIGINT and SIGTERM.	2545	=head3 Examples
1329		2546
		2547	Example: C<fork()> a new process and install a child handler to wait for
		2548	its completion.
		2549
		2550	ev_child cw;
		2551
1330	static void	2552	static void
1331	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2553	child_cb (EV_P_ ev_child *w, int revents)
1332	{	2554	{
1333	ev_unloop (loop, EVUNLOOP_ALL);	2555	ev_child_stop (EV_A_ w);
		2556	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1334	}	2557	}
1335		2558
1336	struct ev_signal signal_watcher;	2559	pid_t pid = fork ();
1337	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2560
1338	ev_signal_start (loop, &sigint_cb);	2561	if (pid < 0)
		2562	// error
		2563	else if (pid == 0)
		2564	{
		2565	// the forked child executes here
		2566	exit (1);
		2567	}
		2568	else
		2569	{
		2570	ev_child_init (&cw, child_cb, pid, 0);
		2571	ev_child_start (EV_DEFAULT_ &cw);
		2572	}
1339		2573
1340		2574
1341	=head2 C<ev_stat> - did the file attributes just change?	2575	=head2 C<ev_stat> - did the file attributes just change?
1342		2576
1343	This watches a filesystem path for attribute changes. That is, it calls	2577	This watches a file system path for attribute changes. That is, it calls
1344	C<stat> regularly (or when the OS says it changed) and sees if it changed	2578	C<stat> on that path in regular intervals (or when the OS says it changed)
1345	compared to the last time, invoking the callback if it did.	2579	and sees if it changed compared to the last time, invoking the callback if
		2580	it did.
1346		2581
1347	The path does not need to exist: changing from "path exists" to "path does	2582	The path does not need to exist: changing from "path exists" to "path does
1348	not exist" is a status change like any other. The condition "path does	2583	not exist" is a status change like any other. The condition "path does not
1349	not exist" is signified by the C<st_nlink> field being zero (which is	2584	exist" (or more correctly "path cannot be stat'ed") is signified by the
1350	otherwise always forced to be at least one) and all the other fields of	2585	C<st_nlink> field being zero (which is otherwise always forced to be at
1351	the stat buffer having unspecified contents.	2586	least one) and all the other fields of the stat buffer having unspecified
		2587	contents.
1352		2588
1353	The path I<should> be absolute and I<must not> end in a slash. If it is	2589	The path I<must not> end in a slash or contain special components such as
		2590	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1354	relative and your working directory changes, the behaviour is undefined.	2591	your working directory changes, then the behaviour is undefined.
1355		2592
1356	Since there is no standard to do this, the portable implementation simply	2593	Since there is no portable change notification interface available, the
1357	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2594	portable implementation simply calls C<stat(2)> regularly on the path
1358	can specify a recommended polling interval for this case. If you specify	2595	to see if it changed somehow. You can specify a recommended polling
1359	a polling interval of C<0> (highly recommended!) then a I<suitable,	2596	interval for this case. If you specify a polling interval of C<0> (highly
1360	unspecified default> value will be used (which you can expect to be around	2597	recommended!) then a I<suitable, unspecified default> value will be used
1361	five seconds, although this might change dynamically). Libev will also	2598	(which you can expect to be around five seconds, although this might
1362	impose a minimum interval which is currently around C<0.1>, but thats	2599	change dynamically). Libev will also impose a minimum interval which is
1363	usually overkill.	2600	currently around C<0.1>, but that's usually overkill.
1364		2601
1365	This watcher type is not meant for massive numbers of stat watchers,	2602	This watcher type is not meant for massive numbers of stat watchers,
1366	as even with OS-supported change notifications, this can be	2603	as even with OS-supported change notifications, this can be
1367	resource-intensive.	2604	resource-intensive.
1368		2605
1369	At the time of this writing, only the Linux inotify interface is	2606	At the time of this writing, the only OS-specific interface implemented
1370	implemented (implementing kqueue support is left as an exercise for the	2607	is the Linux inotify interface (implementing kqueue support is left as an
1371	reader). Inotify will be used to give hints only and should not change the	2608	exercise for the reader. Note, however, that the author sees no way of
1372	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2609	implementing C<ev_stat> semantics with kqueue, except as a hint).
1373	to fall back to regular polling again even with inotify, but changes are	2610
1374	usually detected immediately, and if the file exists there will be no	2611	=head3 ABI Issues (Largefile Support)
1375	polling.	2612
		2613	Libev by default (unless the user overrides this) uses the default
		2614	compilation environment, which means that on systems with large file
		2615	support disabled by default, you get the 32 bit version of the stat
		2616	structure. When using the library from programs that change the ABI to
		2617	use 64 bit file offsets the programs will fail. In that case you have to
		2618	compile libev with the same flags to get binary compatibility. This is
		2619	obviously the case with any flags that change the ABI, but the problem is
		2620	most noticeably displayed with ev_stat and large file support.
		2621
		2622	The solution for this is to lobby your distribution maker to make large
		2623	file interfaces available by default (as e.g. FreeBSD does) and not
		2624	optional. Libev cannot simply switch on large file support because it has
		2625	to exchange stat structures with application programs compiled using the
		2626	default compilation environment.
		2627
		2628	=head3 Inotify and Kqueue
		2629
		2630	When C<inotify (7)> support has been compiled into libev and present at
		2631	runtime, it will be used to speed up change detection where possible. The
		2632	inotify descriptor will be created lazily when the first C<ev_stat>
		2633	watcher is being started.
		2634
		2635	Inotify presence does not change the semantics of C<ev_stat> watchers
		2636	except that changes might be detected earlier, and in some cases, to avoid
		2637	making regular C<stat> calls. Even in the presence of inotify support
		2638	there are many cases where libev has to resort to regular C<stat> polling,
		2639	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2640	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2641	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2642	xfs are fully working) libev usually gets away without polling.
		2643
		2644	There is no support for kqueue, as apparently it cannot be used to
		2645	implement this functionality, due to the requirement of having a file
		2646	descriptor open on the object at all times, and detecting renames, unlinks
		2647	etc. is difficult.
		2648
		2649	=head3 C<stat ()> is a synchronous operation
		2650
		2651	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2652	the process. The exception are C<ev_stat> watchers - those call C<stat
		2653	()>, which is a synchronous operation.
		2654
		2655	For local paths, this usually doesn't matter: unless the system is very
		2656	busy or the intervals between stat's are large, a stat call will be fast,
		2657	as the path data is usually in memory already (except when starting the
		2658	watcher).
		2659
		2660	For networked file systems, calling C<stat ()> can block an indefinite
		2661	time due to network issues, and even under good conditions, a stat call
		2662	often takes multiple milliseconds.
		2663
		2664	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2665	paths, although this is fully supported by libev.
		2666
		2667	=head3 The special problem of stat time resolution
		2668
		2669	The C<stat ()> system call only supports full-second resolution portably,
		2670	and even on systems where the resolution is higher, most file systems
		2671	still only support whole seconds.
		2672
		2673	That means that, if the time is the only thing that changes, you can
		2674	easily miss updates: on the first update, C<ev_stat> detects a change and
		2675	calls your callback, which does something. When there is another update
		2676	within the same second, C<ev_stat> will be unable to detect unless the
		2677	stat data does change in other ways (e.g. file size).
		2678
		2679	The solution to this is to delay acting on a change for slightly more
		2680	than a second (or till slightly after the next full second boundary), using
		2681	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2682	ev_timer_again (loop, w)>).
		2683
		2684	The C<.02> offset is added to work around small timing inconsistencies
		2685	of some operating systems (where the second counter of the current time
		2686	might be be delayed. One such system is the Linux kernel, where a call to
		2687	C<gettimeofday> might return a timestamp with a full second later than
		2688	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2689	update file times then there will be a small window where the kernel uses
		2690	the previous second to update file times but libev might already execute
		2691	the timer callback).
1376		2692
1377	=head3 Watcher-Specific Functions and Data Members	2693	=head3 Watcher-Specific Functions and Data Members
1378		2694
1379	=over 4	2695	=over 4
1380		2696
…		…
1386	C<path>. The C<interval> is a hint on how quickly a change is expected to	2702	C<path>. The C<interval> is a hint on how quickly a change is expected to
1387	be detected and should normally be specified as C<0> to let libev choose	2703	be detected and should normally be specified as C<0> to let libev choose
1388	a suitable value. The memory pointed to by C<path> must point to the same	2704	a suitable value. The memory pointed to by C<path> must point to the same
1389	path for as long as the watcher is active.	2705	path for as long as the watcher is active.
1390		2706
1391	The callback will be receive C<EV_STAT> when a change was detected,	2707	The callback will receive an C<EV_STAT> event when a change was detected,
1392	relative to the attributes at the time the watcher was started (or the	2708	relative to the attributes at the time the watcher was started (or the
1393	last change was detected).	2709	last change was detected).
1394		2710
1395	=item ev_stat_stat (ev_stat *)	2711	=item ev_stat_stat (loop, ev_stat *)
1396		2712
1397	Updates the stat buffer immediately with new values. If you change the	2713	Updates the stat buffer immediately with new values. If you change the
1398	watched path in your callback, you could call this fucntion to avoid	2714	watched path in your callback, you could call this function to avoid
1399	detecting this change (while introducing a race condition). Can also be	2715	detecting this change (while introducing a race condition if you are not
1400	useful simply to find out the new values.	2716	the only one changing the path). Can also be useful simply to find out the
		2717	new values.
1401		2718
1402	=item ev_statdata attr [read-only]	2719	=item ev_statdata attr [read-only]
1403		2720
1404	The most-recently detected attributes of the file. Although the type is of	2721	The most-recently detected attributes of the file. Although the type is
1405	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2722	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1406	suitable for your system. If the C<st_nlink> member is C<0>, then there	2723	suitable for your system, but you can only rely on the POSIX-standardised
		2724	members to be present. If the C<st_nlink> member is C<0>, then there was
1407	was some error while C<stat>ing the file.	2725	some error while C<stat>ing the file.
1408		2726
1409	=item ev_statdata prev [read-only]	2727	=item ev_statdata prev [read-only]
1410		2728
1411	The previous attributes of the file. The callback gets invoked whenever	2729	The previous attributes of the file. The callback gets invoked whenever
1412	C<prev> != C<attr>.	2730	C<prev> != C<attr>, or, more precisely, one or more of these members
		2731	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2732	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1413		2733
1414	=item ev_tstamp interval [read-only]	2734	=item ev_tstamp interval [read-only]
1415		2735
1416	The specified interval.	2736	The specified interval.
1417		2737
1418	=item const char *path [read-only]	2738	=item const char *path [read-only]
1419		2739
1420	The filesystem path that is being watched.	2740	The file system path that is being watched.
1421		2741
1422	=back	2742	=back
1423		2743
		2744	=head3 Examples
		2745
1424	Example: Watch C</etc/passwd> for attribute changes.	2746	Example: Watch C</etc/passwd> for attribute changes.
1425		2747
1426	static void	2748	static void
1427	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2749	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1428	{	2750	{
1429	/* /etc/passwd changed in some way */	2751	/* /etc/passwd changed in some way */
1430	if (w->attr.st_nlink)	2752	if (w->attr.st_nlink)
1431	{	2753	{
1432	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2754	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1433	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2755	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1434	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2756	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1435	}	2757	}
1436	else	2758	else
1437	/* you shalt not abuse printf for puts */	2759	/* you shalt not abuse printf for puts */
1438	puts ("wow, /etc/passwd is not there, expect problems. "	2760	puts ("wow, /etc/passwd is not there, expect problems. "
1439	"if this is windows, they already arrived\n");	2761	"if this is windows, they already arrived\n");
1440	}	2762	}
1441		2763
1442	...	2764	...
1443	ev_stat passwd;	2765	ev_stat passwd;
1444		2766
1445	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2767	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1446	ev_stat_start (loop, &passwd);	2768	ev_stat_start (loop, &passwd);
		2769
		2770	Example: Like above, but additionally use a one-second delay so we do not
		2771	miss updates (however, frequent updates will delay processing, too, so
		2772	one might do the work both on C<ev_stat> callback invocation I<and> on
		2773	C<ev_timer> callback invocation).
		2774
		2775	static ev_stat passwd;
		2776	static ev_timer timer;
		2777
		2778	static void
		2779	timer_cb (EV_P_ ev_timer *w, int revents)
		2780	{
		2781	ev_timer_stop (EV_A_ w);
		2782
		2783	/* now it's one second after the most recent passwd change */
		2784	}
		2785
		2786	static void
		2787	stat_cb (EV_P_ ev_stat *w, int revents)
		2788	{
		2789	/* reset the one-second timer */
		2790	ev_timer_again (EV_A_ &timer);
		2791	}
		2792
		2793	...
		2794	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2795	ev_stat_start (loop, &passwd);
		2796	ev_timer_init (&timer, timer_cb, 0., 1.02);
1447		2797
1448		2798
1449	=head2 C<ev_idle> - when you've got nothing better to do...	2799	=head2 C<ev_idle> - when you've got nothing better to do...
1450		2800
1451	Idle watchers trigger events when no other events of the same or higher	2801	Idle watchers trigger events when no other events of the same or higher
1452	priority are pending (prepare, check and other idle watchers do not	2802	priority are pending (prepare, check and other idle watchers do not count
1453	count).	2803	as receiving "events").
1454		2804
1455	That is, as long as your process is busy handling sockets or timeouts	2805	That is, as long as your process is busy handling sockets or timeouts
1456	(or even signals, imagine) of the same or higher priority it will not be	2806	(or even signals, imagine) of the same or higher priority it will not be
1457	triggered. But when your process is idle (or only lower-priority watchers	2807	triggered. But when your process is idle (or only lower-priority watchers
1458	are pending), the idle watchers are being called once per event loop	2808	are pending), the idle watchers are being called once per event loop
…		…
1469		2819
1470	=head3 Watcher-Specific Functions and Data Members	2820	=head3 Watcher-Specific Functions and Data Members
1471		2821
1472	=over 4	2822	=over 4
1473		2823
1474	=item ev_idle_init (ev_signal *, callback)	2824	=item ev_idle_init (ev_idle *, callback)
1475		2825
1476	Initialises and configures the idle watcher - it has no parameters of any	2826	Initialises and configures the idle watcher - it has no parameters of any
1477	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2827	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1478	believe me.	2828	believe me.
1479		2829
1480	=back	2830	=back
1481		2831
		2832	=head3 Examples
		2833
1482	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2834	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1483	callback, free it. Also, use no error checking, as usual.	2835	callback, free it. Also, use no error checking, as usual.
1484		2836
1485	static void	2837	static void
1486	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2838	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1487	{	2839	{
1488	free (w);	2840	free (w);
1489	// now do something you wanted to do when the program has	2841	// now do something you wanted to do when the program has
1490	// no longer asnything immediate to do.	2842	// no longer anything immediate to do.
1491	}	2843	}
1492		2844
1493	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2845	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1494	ev_idle_init (idle_watcher, idle_cb);	2846	ev_idle_init (idle_watcher, idle_cb);
1495	ev_idle_start (loop, idle_cb);	2847	ev_idle_start (loop, idle_watcher);
1496		2848
1497		2849
1498	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2850	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1499		2851
1500	Prepare and check watchers are usually (but not always) used in tandem:	2852	Prepare and check watchers are usually (but not always) used in pairs:
1501	prepare watchers get invoked before the process blocks and check watchers	2853	prepare watchers get invoked before the process blocks and check watchers
1502	afterwards.	2854	afterwards.
1503		2855
1504	You I<must not> call C<ev_loop> or similar functions that enter	2856	You I<must not> call C<ev_run> or similar functions that enter
1505	the current event loop from either C<ev_prepare> or C<ev_check>	2857	the current event loop from either C<ev_prepare> or C<ev_check>
1506	watchers. Other loops than the current one are fine, however. The	2858	watchers. Other loops than the current one are fine, however. The
1507	rationale behind this is that you do not need to check for recursion in	2859	rationale behind this is that you do not need to check for recursion in
1508	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2860	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1509	C<ev_check> so if you have one watcher of each kind they will always be	2861	C<ev_check> so if you have one watcher of each kind they will always be
1510	called in pairs bracketing the blocking call.	2862	called in pairs bracketing the blocking call.
1511		2863
1512	Their main purpose is to integrate other event mechanisms into libev and	2864	Their main purpose is to integrate other event mechanisms into libev and
1513	their use is somewhat advanced. This could be used, for example, to track	2865	their use is somewhat advanced. They could be used, for example, to track
1514	variable changes, implement your own watchers, integrate net-snmp or a	2866	variable changes, implement your own watchers, integrate net-snmp or a
1515	coroutine library and lots more. They are also occasionally useful if	2867	coroutine library and lots more. They are also occasionally useful if
1516	you cache some data and want to flush it before blocking (for example,	2868	you cache some data and want to flush it before blocking (for example,
1517	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2869	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1518	watcher).	2870	watcher).
1519		2871
1520	This is done by examining in each prepare call which file descriptors need	2872	This is done by examining in each prepare call which file descriptors
1521	to be watched by the other library, registering C<ev_io> watchers for	2873	need to be watched by the other library, registering C<ev_io> watchers
1522	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2874	for them and starting an C<ev_timer> watcher for any timeouts (many
1523	provide just this functionality). Then, in the check watcher you check for	2875	libraries provide exactly this functionality). Then, in the check watcher,
1524	any events that occured (by checking the pending status of all watchers	2876	you check for any events that occurred (by checking the pending status
1525	and stopping them) and call back into the library. The I/O and timer	2877	of all watchers and stopping them) and call back into the library. The
1526	callbacks will never actually be called (but must be valid nevertheless,	2878	I/O and timer callbacks will never actually be called (but must be valid
1527	because you never know, you know?).	2879	nevertheless, because you never know, you know?).
1528		2880
1529	As another example, the Perl Coro module uses these hooks to integrate	2881	As another example, the Perl Coro module uses these hooks to integrate
1530	coroutines into libev programs, by yielding to other active coroutines	2882	coroutines into libev programs, by yielding to other active coroutines
1531	during each prepare and only letting the process block if no coroutines	2883	during each prepare and only letting the process block if no coroutines
1532	are ready to run (it's actually more complicated: it only runs coroutines	2884	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1535	loop from blocking if lower-priority coroutines are active, thus mapping	2887	loop from blocking if lower-priority coroutines are active, thus mapping
1536	low-priority coroutines to idle/background tasks).	2888	low-priority coroutines to idle/background tasks).
1537		2889
1538	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2890	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1539	priority, to ensure that they are being run before any other watchers	2891	priority, to ensure that they are being run before any other watchers
		2892	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2893
1540	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2894	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1541	too) should not activate ("feed") events into libev. While libev fully	2895	activate ("feed") events into libev. While libev fully supports this, they
1542	supports this, they will be called before other C<ev_check> watchers did	2896	might get executed before other C<ev_check> watchers did their job. As
1543	their job. As C<ev_check> watchers are often used to embed other event	2897	C<ev_check> watchers are often used to embed other (non-libev) event
1544	loops those other event loops might be in an unusable state until their	2898	loops those other event loops might be in an unusable state until their
1545	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2899	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1546	others).	2900	others).
1547		2901
1548	=head3 Watcher-Specific Functions and Data Members	2902	=head3 Watcher-Specific Functions and Data Members
…		…
1553		2907
1554	=item ev_check_init (ev_check *, callback)	2908	=item ev_check_init (ev_check *, callback)
1555		2909
1556	Initialises and configures the prepare or check watcher - they have no	2910	Initialises and configures the prepare or check watcher - they have no
1557	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2911	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1558	macros, but using them is utterly, utterly and completely pointless.	2912	macros, but using them is utterly, utterly, utterly and completely
		2913	pointless.
1559		2914
1560	=back	2915	=back
		2916
		2917	=head3 Examples
1561		2918
1562	There are a number of principal ways to embed other event loops or modules	2919	There are a number of principal ways to embed other event loops or modules
1563	into libev. Here are some ideas on how to include libadns into libev	2920	into libev. Here are some ideas on how to include libadns into libev
1564	(there is a Perl module named C<EV::ADNS> that does this, which you could	2921	(there is a Perl module named C<EV::ADNS> that does this, which you could
1565	use for an actually working example. Another Perl module named C<EV::Glib>	2922	use as a working example. Another Perl module named C<EV::Glib> embeds a
1566	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2923	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1567	into the Glib event loop).	2924	Glib event loop).
1568		2925
1569	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2926	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1570	and in a check watcher, destroy them and call into libadns. What follows	2927	and in a check watcher, destroy them and call into libadns. What follows
1571	is pseudo-code only of course. This requires you to either use a low	2928	is pseudo-code only of course. This requires you to either use a low
1572	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2929	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1573	the callbacks for the IO/timeout watchers might not have been called yet.	2930	the callbacks for the IO/timeout watchers might not have been called yet.
1574		2931
1575	static ev_io iow [nfd];	2932	static ev_io iow [nfd];
1576	static ev_timer tw;	2933	static ev_timer tw;
1577		2934
1578	static void	2935	static void
1579	io_cb (ev_loop *loop, ev_io *w, int revents)	2936	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1580	{	2937	{
1581	}	2938	}
1582		2939
1583	// create io watchers for each fd and a timer before blocking	2940	// create io watchers for each fd and a timer before blocking
1584	static void	2941	static void
1585	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2942	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1586	{	2943	{
1587	int timeout = 3600000;	2944	int timeout = 3600000;
1588	struct pollfd fds [nfd];	2945	struct pollfd fds [nfd];
1589	// actual code will need to loop here and realloc etc.	2946	// actual code will need to loop here and realloc etc.
1590	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2947	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1591		2948
1592	/* the callback is illegal, but won't be called as we stop during check */	2949	/* the callback is illegal, but won't be called as we stop during check */
1593	ev_timer_init (&tw, 0, timeout * 1e-3);	2950	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1594	ev_timer_start (loop, &tw);	2951	ev_timer_start (loop, &tw);
1595		2952
1596	// create one ev_io per pollfd	2953	// create one ev_io per pollfd
1597	for (int i = 0; i < nfd; ++i)	2954	for (int i = 0; i < nfd; ++i)
1598	{	2955	{
1599	ev_io_init (iow + i, io_cb, fds [i].fd,	2956	ev_io_init (iow + i, io_cb, fds [i].fd,
1600	((fds [i].events & POLLIN ? EV_READ : 0)	2957	((fds [i].events & POLLIN ? EV_READ : 0)
1601	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2958	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1602		2959
1603	fds [i].revents = 0;	2960	fds [i].revents = 0;
1604	ev_io_start (loop, iow + i);	2961	ev_io_start (loop, iow + i);
1605	}	2962	}
1606	}	2963	}
1607		2964
1608	// stop all watchers after blocking	2965	// stop all watchers after blocking
1609	static void	2966	static void
1610	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2967	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1611	{	2968	{
1612	ev_timer_stop (loop, &tw);	2969	ev_timer_stop (loop, &tw);
1613		2970
1614	for (int i = 0; i < nfd; ++i)	2971	for (int i = 0; i < nfd; ++i)
1615	{	2972	{
1616	// set the relevant poll flags	2973	// set the relevant poll flags
1617	// could also call adns_processreadable etc. here	2974	// could also call adns_processreadable etc. here
1618	struct pollfd *fd = fds + i;	2975	struct pollfd *fd = fds + i;
1619	int revents = ev_clear_pending (iow + i);	2976	int revents = ev_clear_pending (iow + i);
1620	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2977	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1621	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2978	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1622		2979
1623	// now stop the watcher	2980	// now stop the watcher
1624	ev_io_stop (loop, iow + i);	2981	ev_io_stop (loop, iow + i);
1625	}	2982	}
1626		2983
1627	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2984	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1628	}	2985	}
1629		2986
1630	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2987	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1631	in the prepare watcher and would dispose of the check watcher.	2988	in the prepare watcher and would dispose of the check watcher.
1632		2989
1633	Method 3: If the module to be embedded supports explicit event	2990	Method 3: If the module to be embedded supports explicit event
1634	notification (adns does), you can also make use of the actual watcher	2991	notification (libadns does), you can also make use of the actual watcher
1635	callbacks, and only destroy/create the watchers in the prepare watcher.	2992	callbacks, and only destroy/create the watchers in the prepare watcher.
1636		2993
1637	static void	2994	static void
1638	timer_cb (EV_P_ ev_timer *w, int revents)	2995	timer_cb (EV_P_ ev_timer *w, int revents)
1639	{	2996	{
1640	adns_state ads = (adns_state)w->data;	2997	adns_state ads = (adns_state)w->data;
1641	update_now (EV_A);	2998	update_now (EV_A);
1642		2999
1643	adns_processtimeouts (ads, &tv_now);	3000	adns_processtimeouts (ads, &tv_now);
1644	}	3001	}
1645		3002
1646	static void	3003	static void
1647	io_cb (EV_P_ ev_io *w, int revents)	3004	io_cb (EV_P_ ev_io *w, int revents)
1648	{	3005	{
1649	adns_state ads = (adns_state)w->data;	3006	adns_state ads = (adns_state)w->data;
1650	update_now (EV_A);	3007	update_now (EV_A);
1651		3008
1652	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	3009	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1653	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	3010	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1654	}	3011	}
1655		3012
1656	// do not ever call adns_afterpoll	3013	// do not ever call adns_afterpoll
1657		3014
1658	Method 4: Do not use a prepare or check watcher because the module you	3015	Method 4: Do not use a prepare or check watcher because the module you
1659	want to embed is too inflexible to support it. Instead, youc na override	3016	want to embed is not flexible enough to support it. Instead, you can
1660	their poll function. The drawback with this solution is that the main	3017	override their poll function. The drawback with this solution is that the
1661	loop is now no longer controllable by EV. The C<Glib::EV> module does	3018	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1662	this.	3019	this approach, effectively embedding EV as a client into the horrible
		3020	libglib event loop.
1663		3021
1664	static gint	3022	static gint
1665	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3023	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1666	{	3024	{
1667	int got_events = 0;	3025	int got_events = 0;
1668		3026
1669	for (n = 0; n < nfds; ++n)	3027	for (n = 0; n < nfds; ++n)
1670	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	3028	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1671		3029
1672	if (timeout >= 0)	3030	if (timeout >= 0)
1673	// create/start timer	3031	// create/start timer
1674		3032
1675	// poll	3033	// poll
1676	ev_loop (EV_A_ 0);	3034	ev_run (EV_A_ 0);
1677		3035
1678	// stop timer again	3036	// stop timer again
1679	if (timeout >= 0)	3037	if (timeout >= 0)
1680	ev_timer_stop (EV_A_ &to);	3038	ev_timer_stop (EV_A_ &to);
1681		3039
1682	// stop io watchers again - their callbacks should have set	3040	// stop io watchers again - their callbacks should have set
1683	for (n = 0; n < nfds; ++n)	3041	for (n = 0; n < nfds; ++n)
1684	ev_io_stop (EV_A_ iow [n]);	3042	ev_io_stop (EV_A_ iow [n]);
1685		3043
1686	return got_events;	3044	return got_events;
1687	}	3045	}
1688		3046
1689		3047
1690	=head2 C<ev_embed> - when one backend isn't enough...	3048	=head2 C<ev_embed> - when one backend isn't enough...
1691		3049
1692	This is a rather advanced watcher type that lets you embed one event loop	3050	This is a rather advanced watcher type that lets you embed one event loop
…		…
1698	prioritise I/O.	3056	prioritise I/O.
1699		3057
1700	As an example for a bug workaround, the kqueue backend might only support	3058	As an example for a bug workaround, the kqueue backend might only support
1701	sockets on some platform, so it is unusable as generic backend, but you	3059	sockets on some platform, so it is unusable as generic backend, but you
1702	still want to make use of it because you have many sockets and it scales	3060	still want to make use of it because you have many sockets and it scales
1703	so nicely. In this case, you would create a kqueue-based loop and embed it	3061	so nicely. In this case, you would create a kqueue-based loop and embed
1704	into your default loop (which might use e.g. poll). Overall operation will	3062	it into your default loop (which might use e.g. poll). Overall operation
1705	be a bit slower because first libev has to poll and then call kevent, but	3063	will be a bit slower because first libev has to call C<poll> and then
1706	at least you can use both at what they are best.	3064	C<kevent>, but at least you can use both mechanisms for what they are
		3065	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1707		3066
1708	As for prioritising I/O: rarely you have the case where some fds have	3067	As for prioritising I/O: under rare circumstances you have the case where
1709	to be watched and handled very quickly (with low latency), and even	3068	some fds have to be watched and handled very quickly (with low latency),
1710	priorities and idle watchers might have too much overhead. In this case	3069	and even priorities and idle watchers might have too much overhead. In
1711	you would put all the high priority stuff in one loop and all the rest in	3070	this case you would put all the high priority stuff in one loop and all
1712	a second one, and embed the second one in the first.	3071	the rest in a second one, and embed the second one in the first.
1713		3072
1714	As long as the watcher is active, the callback will be invoked every time	3073	As long as the watcher is active, the callback will be invoked every
1715	there might be events pending in the embedded loop. The callback must then	3074	time there might be events pending in the embedded loop. The callback
1716	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3075	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1717	their callbacks (you could also start an idle watcher to give the embedded	3076	sweep and invoke their callbacks (the callback doesn't need to invoke the
1718	loop strictly lower priority for example). You can also set the callback	3077	C<ev_embed_sweep> function directly, it could also start an idle watcher
1719	to C<0>, in which case the embed watcher will automatically execute the	3078	to give the embedded loop strictly lower priority for example).
1720	embedded loop sweep.
1721		3079
1722	As long as the watcher is started it will automatically handle events. The	3080	You can also set the callback to C<0>, in which case the embed watcher
1723	callback will be invoked whenever some events have been handled. You can	3081	will automatically execute the embedded loop sweep whenever necessary.
1724	set the callback to C<0> to avoid having to specify one if you are not
1725	interested in that.
1726		3082
1727	Also, there have not currently been made special provisions for forking:	3083	Fork detection will be handled transparently while the C<ev_embed> watcher
1728	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3084	is active, i.e., the embedded loop will automatically be forked when the
1729	but you will also have to stop and restart any C<ev_embed> watchers	3085	embedding loop forks. In other cases, the user is responsible for calling
1730	yourself.	3086	C<ev_loop_fork> on the embedded loop.
1731		3087
1732	Unfortunately, not all backends are embeddable, only the ones returned by	3088	Unfortunately, not all backends are embeddable: only the ones returned by
1733	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3089	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1734	portable one.	3090	portable one.
1735		3091
1736	So when you want to use this feature you will always have to be prepared	3092	So when you want to use this feature you will always have to be prepared
1737	that you cannot get an embeddable loop. The recommended way to get around	3093	that you cannot get an embeddable loop. The recommended way to get around
1738	this is to have a separate variables for your embeddable loop, try to	3094	this is to have a separate variables for your embeddable loop, try to
1739	create it, and if that fails, use the normal loop for everything:	3095	create it, and if that fails, use the normal loop for everything.
1740		3096
1741	struct ev_loop *loop_hi = ev_default_init (0);	3097	=head3 C<ev_embed> and fork
1742	struct ev_loop *loop_lo = 0;
1743	struct ev_embed embed;
1744
1745	// see if there is a chance of getting one that works
1746	// (remember that a flags value of 0 means autodetection)
1747	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1748	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1749	: 0;
1750		3098
1751	// if we got one, then embed it, otherwise default to loop_hi	3099	While the C<ev_embed> watcher is running, forks in the embedding loop will
1752	if (loop_lo)	3100	automatically be applied to the embedded loop as well, so no special
1753	{	3101	fork handling is required in that case. When the watcher is not running,
1754	ev_embed_init (&embed, 0, loop_lo);	3102	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1755	ev_embed_start (loop_hi, &embed);	3103	as applicable.
1756	}
1757	else
1758	loop_lo = loop_hi;
1759		3104
1760	=head3 Watcher-Specific Functions and Data Members	3105	=head3 Watcher-Specific Functions and Data Members
1761		3106
1762	=over 4	3107	=over 4
1763		3108
…		…
1767		3112
1768	Configures the watcher to embed the given loop, which must be	3113	Configures the watcher to embed the given loop, which must be
1769	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3114	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1770	invoked automatically, otherwise it is the responsibility of the callback	3115	invoked automatically, otherwise it is the responsibility of the callback
1771	to invoke it (it will continue to be called until the sweep has been done,	3116	to invoke it (it will continue to be called until the sweep has been done,
1772	if you do not want thta, you need to temporarily stop the embed watcher).	3117	if you do not want that, you need to temporarily stop the embed watcher).
1773		3118
1774	=item ev_embed_sweep (loop, ev_embed *)	3119	=item ev_embed_sweep (loop, ev_embed *)
1775		3120
1776	Make a single, non-blocking sweep over the embedded loop. This works	3121	Make a single, non-blocking sweep over the embedded loop. This works
1777	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3122	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1778	apropriate way for embedded loops.	3123	appropriate way for embedded loops.
1779		3124
1780	=item struct ev_loop *loop [read-only]	3125	=item struct ev_loop *other [read-only]
1781		3126
1782	The embedded event loop.	3127	The embedded event loop.
1783		3128
1784	=back	3129	=back
		3130
		3131	=head3 Examples
		3132
		3133	Example: Try to get an embeddable event loop and embed it into the default
		3134	event loop. If that is not possible, use the default loop. The default
		3135	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3136	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3137	used).
		3138
		3139	struct ev_loop *loop_hi = ev_default_init (0);
		3140	struct ev_loop *loop_lo = 0;
		3141	ev_embed embed;
		3142
		3143	// see if there is a chance of getting one that works
		3144	// (remember that a flags value of 0 means autodetection)
		3145	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3146	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3147	: 0;
		3148
		3149	// if we got one, then embed it, otherwise default to loop_hi
		3150	if (loop_lo)
		3151	{
		3152	ev_embed_init (&embed, 0, loop_lo);
		3153	ev_embed_start (loop_hi, &embed);
		3154	}
		3155	else
		3156	loop_lo = loop_hi;
		3157
		3158	Example: Check if kqueue is available but not recommended and create
		3159	a kqueue backend for use with sockets (which usually work with any
		3160	kqueue implementation). Store the kqueue/socket-only event loop in
		3161	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3162
		3163	struct ev_loop *loop = ev_default_init (0);
		3164	struct ev_loop *loop_socket = 0;
		3165	ev_embed embed;
		3166
		3167	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3168	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3169	{
		3170	ev_embed_init (&embed, 0, loop_socket);
		3171	ev_embed_start (loop, &embed);
		3172	}
		3173
		3174	if (!loop_socket)
		3175	loop_socket = loop;
		3176
		3177	// now use loop_socket for all sockets, and loop for everything else
1785		3178
1786		3179
1787	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3180	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1788		3181
1789	Fork watchers are called when a C<fork ()> was detected (usually because	3182	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1792	event loop blocks next and before C<ev_check> watchers are being called,	3185	event loop blocks next and before C<ev_check> watchers are being called,
1793	and only in the child after the fork. If whoever good citizen calling	3186	and only in the child after the fork. If whoever good citizen calling
1794	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3187	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1795	handlers will be invoked, too, of course.	3188	handlers will be invoked, too, of course.
1796		3189
		3190	=head3 The special problem of life after fork - how is it possible?
		3191
		3192	Most uses of C<fork()> consist of forking, then some simple calls to set
		3193	up/change the process environment, followed by a call to C<exec()>. This
		3194	sequence should be handled by libev without any problems.
		3195
		3196	This changes when the application actually wants to do event handling
		3197	in the child, or both parent in child, in effect "continuing" after the
		3198	fork.
		3199
		3200	The default mode of operation (for libev, with application help to detect
		3201	forks) is to duplicate all the state in the child, as would be expected
		3202	when I<either> the parent I<or> the child process continues.
		3203
		3204	When both processes want to continue using libev, then this is usually the
		3205	wrong result. In that case, usually one process (typically the parent) is
		3206	supposed to continue with all watchers in place as before, while the other
		3207	process typically wants to start fresh, i.e. without any active watchers.
		3208
		3209	The cleanest and most efficient way to achieve that with libev is to
		3210	simply create a new event loop, which of course will be "empty", and
		3211	use that for new watchers. This has the advantage of not touching more
		3212	memory than necessary, and thus avoiding the copy-on-write, and the
		3213	disadvantage of having to use multiple event loops (which do not support
		3214	signal watchers).
		3215
		3216	When this is not possible, or you want to use the default loop for
		3217	other reasons, then in the process that wants to start "fresh", call
		3218	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3219	Destroying the default loop will "orphan" (not stop) all registered
		3220	watchers, so you have to be careful not to execute code that modifies
		3221	those watchers. Note also that in that case, you have to re-register any
		3222	signal watchers.
		3223
1797	=head3 Watcher-Specific Functions and Data Members	3224	=head3 Watcher-Specific Functions and Data Members
1798		3225
1799	=over 4	3226	=over 4
1800		3227
1801	=item ev_fork_init (ev_signal *, callback)	3228	=item ev_fork_init (ev_fork *, callback)
1802		3229
1803	Initialises and configures the fork watcher - it has no parameters of any	3230	Initialises and configures the fork watcher - it has no parameters of any
1804	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3231	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1805	believe me.	3232	really.
1806		3233
1807	=back	3234	=back
1808		3235
1809		3236
		3237	=head2 C<ev_cleanup> - even the best things end
		3238
		3239	Cleanup watchers are called just before the event loop is being destroyed
		3240	by a call to C<ev_loop_destroy>.
		3241
		3242	While there is no guarantee that the event loop gets destroyed, cleanup
		3243	watchers provide a convenient method to install cleanup hooks for your
		3244	program, worker threads and so on - you just to make sure to destroy the
		3245	loop when you want them to be invoked.
		3246
		3247	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3248	all other watchers, they do not keep a reference to the event loop (which
		3249	makes a lot of sense if you think about it). Like all other watchers, you
		3250	can call libev functions in the callback, except C<ev_cleanup_start>.
		3251
		3252	=head3 Watcher-Specific Functions and Data Members
		3253
		3254	=over 4
		3255
		3256	=item ev_cleanup_init (ev_cleanup *, callback)
		3257
		3258	Initialises and configures the cleanup watcher - it has no parameters of
		3259	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3260	pointless, I assure you.
		3261
		3262	=back
		3263
		3264	Example: Register an atexit handler to destroy the default loop, so any
		3265	cleanup functions are called.
		3266
		3267	static void
		3268	program_exits (void)
		3269	{
		3270	ev_loop_destroy (EV_DEFAULT_UC);
		3271	}
		3272
		3273	...
		3274	atexit (program_exits);
		3275
		3276
		3277	=head2 C<ev_async> - how to wake up an event loop
		3278
		3279	In general, you cannot use an C<ev_loop> from multiple threads or other
		3280	asynchronous sources such as signal handlers (as opposed to multiple event
		3281	loops - those are of course safe to use in different threads).
		3282
		3283	Sometimes, however, you need to wake up an event loop you do not control,
		3284	for example because it belongs to another thread. This is what C<ev_async>
		3285	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3286	it by calling C<ev_async_send>, which is thread- and signal safe.
		3287
		3288	This functionality is very similar to C<ev_signal> watchers, as signals,
		3289	too, are asynchronous in nature, and signals, too, will be compressed
		3290	(i.e. the number of callback invocations may be less than the number of
		3291	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3292	of "global async watchers" by using a watcher on an otherwise unused
		3293	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3294	even without knowing which loop owns the signal.
		3295
		3296	=head3 Queueing
		3297
		3298	C<ev_async> does not support queueing of data in any way. The reason
		3299	is that the author does not know of a simple (or any) algorithm for a
		3300	multiple-writer-single-reader queue that works in all cases and doesn't
		3301	need elaborate support such as pthreads or unportable memory access
		3302	semantics.
		3303
		3304	That means that if you want to queue data, you have to provide your own
		3305	queue. But at least I can tell you how to implement locking around your
		3306	queue:
		3307
		3308	=over 4
		3309
		3310	=item queueing from a signal handler context
		3311
		3312	To implement race-free queueing, you simply add to the queue in the signal
		3313	handler but you block the signal handler in the watcher callback. Here is
		3314	an example that does that for some fictitious SIGUSR1 handler:
		3315
		3316	static ev_async mysig;
		3317
		3318	static void
		3319	sigusr1_handler (void)
		3320	{
		3321	sometype data;
		3322
		3323	// no locking etc.
		3324	queue_put (data);
		3325	ev_async_send (EV_DEFAULT_ &mysig);
		3326	}
		3327
		3328	static void
		3329	mysig_cb (EV_P_ ev_async *w, int revents)
		3330	{
		3331	sometype data;
		3332	sigset_t block, prev;
		3333
		3334	sigemptyset (&block);
		3335	sigaddset (&block, SIGUSR1);
		3336	sigprocmask (SIG_BLOCK, &block, &prev);
		3337
		3338	while (queue_get (&data))
		3339	process (data);
		3340
		3341	if (sigismember (&prev, SIGUSR1)
		3342	sigprocmask (SIG_UNBLOCK, &block, 0);
		3343	}
		3344
		3345	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3346	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3347	either...).
		3348
		3349	=item queueing from a thread context
		3350
		3351	The strategy for threads is different, as you cannot (easily) block
		3352	threads but you can easily preempt them, so to queue safely you need to
		3353	employ a traditional mutex lock, such as in this pthread example:
		3354
		3355	static ev_async mysig;
		3356	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3357
		3358	static void
		3359	otherthread (void)
		3360	{
		3361	// only need to lock the actual queueing operation
		3362	pthread_mutex_lock (&mymutex);
		3363	queue_put (data);
		3364	pthread_mutex_unlock (&mymutex);
		3365
		3366	ev_async_send (EV_DEFAULT_ &mysig);
		3367	}
		3368
		3369	static void
		3370	mysig_cb (EV_P_ ev_async *w, int revents)
		3371	{
		3372	pthread_mutex_lock (&mymutex);
		3373
		3374	while (queue_get (&data))
		3375	process (data);
		3376
		3377	pthread_mutex_unlock (&mymutex);
		3378	}
		3379
		3380	=back
		3381
		3382
		3383	=head3 Watcher-Specific Functions and Data Members
		3384
		3385	=over 4
		3386
		3387	=item ev_async_init (ev_async *, callback)
		3388
		3389	Initialises and configures the async watcher - it has no parameters of any
		3390	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3391	trust me.
		3392
		3393	=item ev_async_send (loop, ev_async *)
		3394
		3395	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3396	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3397	returns.
		3398
		3399	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3400	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3401	embedding section below on what exactly this means).
		3402
		3403	Note that, as with other watchers in libev, multiple events might get
		3404	compressed into a single callback invocation (another way to look at
		3405	this is that C<ev_async> watchers are level-triggered: they are set on
		3406	C<ev_async_send>, reset when the event loop detects that).
		3407
		3408	This call incurs the overhead of at most one extra system call per event
		3409	loop iteration, if the event loop is blocked, and no syscall at all if
		3410	the event loop (or your program) is processing events. That means that
		3411	repeated calls are basically free (there is no need to avoid calls for
		3412	performance reasons) and that the overhead becomes smaller (typically
		3413	zero) under load.
		3414
		3415	=item bool = ev_async_pending (ev_async *)
		3416
		3417	Returns a non-zero value when C<ev_async_send> has been called on the
		3418	watcher but the event has not yet been processed (or even noted) by the
		3419	event loop.
		3420
		3421	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3422	the loop iterates next and checks for the watcher to have become active,
		3423	it will reset the flag again. C<ev_async_pending> can be used to very
		3424	quickly check whether invoking the loop might be a good idea.
		3425
		3426	Not that this does I<not> check whether the watcher itself is pending,
		3427	only whether it has been requested to make this watcher pending: there
		3428	is a time window between the event loop checking and resetting the async
		3429	notification, and the callback being invoked.
		3430
		3431	=back
		3432
		3433
1810	=head1 OTHER FUNCTIONS	3434	=head1 OTHER FUNCTIONS
1811		3435
1812	There are some other functions of possible interest. Described. Here. Now.	3436	There are some other functions of possible interest. Described. Here. Now.
1813		3437
1814	=over 4	3438	=over 4
1815		3439
1816	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3440	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1817		3441
1818	This function combines a simple timer and an I/O watcher, calls your	3442	This function combines a simple timer and an I/O watcher, calls your
1819	callback on whichever event happens first and automatically stop both	3443	callback on whichever event happens first and automatically stops both
1820	watchers. This is useful if you want to wait for a single event on an fd	3444	watchers. This is useful if you want to wait for a single event on an fd
1821	or timeout without having to allocate/configure/start/stop/free one or	3445	or timeout without having to allocate/configure/start/stop/free one or
1822	more watchers yourself.	3446	more watchers yourself.
1823		3447
1824	If C<fd> is less than 0, then no I/O watcher will be started and events	3448	If C<fd> is less than 0, then no I/O watcher will be started and the
1825	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3449	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1826	C<events> set will be craeted and started.	3450	the given C<fd> and C<events> set will be created and started.
1827		3451
1828	If C<timeout> is less than 0, then no timeout watcher will be	3452	If C<timeout> is less than 0, then no timeout watcher will be
1829	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3453	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1830	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3454	repeat = 0) will be started. C<0> is a valid timeout.
1831	dubious value.
1832		3455
1833	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3456	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1834	passed an C<revents> set like normal event callbacks (a combination of	3457	passed an C<revents> set like normal event callbacks (a combination of
1835	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3458	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1836	value passed to C<ev_once>:	3459	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3460	a timeout and an io event at the same time - you probably should give io
		3461	events precedence.
1837		3462
		3463	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3464
1838	static void stdin_ready (int revents, void *arg)	3465	static void stdin_ready (int revents, void *arg)
1839	{	3466	{
1840	if (revents & EV_TIMEOUT)
1841	/* doh, nothing entered */;
1842	else if (revents & EV_READ)	3467	if (revents & EV_READ)
1843	/* stdin might have data for us, joy! */;	3468	/* stdin might have data for us, joy! */;
		3469	else if (revents & EV_TIMER)
		3470	/* doh, nothing entered */;
1844	}	3471	}
1845		3472
1846	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3473	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1847		3474
1848	=item ev_feed_event (ev_loop *, watcher *, int revents)
1849
1850	Feeds the given event set into the event loop, as if the specified event
1851	had happened for the specified watcher (which must be a pointer to an
1852	initialised but not necessarily started event watcher).
1853
1854	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3475	=item ev_feed_fd_event (loop, int fd, int revents)
1855		3476
1856	Feed an event on the given fd, as if a file descriptor backend detected	3477	Feed an event on the given fd, as if a file descriptor backend detected
1857	the given events it.	3478	the given events it.
1858		3479
1859	=item ev_feed_signal_event (ev_loop *loop, int signum)	3480	=item ev_feed_signal_event (loop, int signum)
1860		3481
1861	Feed an event as if the given signal occured (C<loop> must be the default	3482	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
1862	loop!).	3483	which is async-safe.
1863		3484
1864	=back	3485	=back
		3486
		3487
		3488	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3489
		3490	This section explains some common idioms that are not immediately
		3491	obvious. Note that examples are sprinkled over the whole manual, and this
		3492	section only contains stuff that wouldn't fit anywhere else.
		3493
		3494	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3495
		3496	Each watcher has, by default, a C<void *data> member that you can read
		3497	or modify at any time: libev will completely ignore it. This can be used
		3498	to associate arbitrary data with your watcher. If you need more data and
		3499	don't want to allocate memory separately and store a pointer to it in that
		3500	data member, you can also "subclass" the watcher type and provide your own
		3501	data:
		3502
		3503	struct my_io
		3504	{
		3505	ev_io io;
		3506	int otherfd;
		3507	void *somedata;
		3508	struct whatever *mostinteresting;
		3509	};
		3510
		3511	...
		3512	struct my_io w;
		3513	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3514
		3515	And since your callback will be called with a pointer to the watcher, you
		3516	can cast it back to your own type:
		3517
		3518	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3519	{
		3520	struct my_io *w = (struct my_io *)w_;
		3521	...
		3522	}
		3523
		3524	More interesting and less C-conformant ways of casting your callback
		3525	function type instead have been omitted.
		3526
		3527	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3528
		3529	Another common scenario is to use some data structure with multiple
		3530	embedded watchers, in effect creating your own watcher that combines
		3531	multiple libev event sources into one "super-watcher":
		3532
		3533	struct my_biggy
		3534	{
		3535	int some_data;
		3536	ev_timer t1;
		3537	ev_timer t2;
		3538	}
		3539
		3540	In this case getting the pointer to C<my_biggy> is a bit more
		3541	complicated: Either you store the address of your C<my_biggy> struct in
		3542	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3543	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3544	real programmers):
		3545
		3546	#include <stddef.h>
		3547
		3548	static void
		3549	t1_cb (EV_P_ ev_timer *w, int revents)
		3550	{
		3551	struct my_biggy big = (struct my_biggy *)
		3552	(((char *)w) - offsetof (struct my_biggy, t1));
		3553	}
		3554
		3555	static void
		3556	t2_cb (EV_P_ ev_timer *w, int revents)
		3557	{
		3558	struct my_biggy big = (struct my_biggy *)
		3559	(((char *)w) - offsetof (struct my_biggy, t2));
		3560	}
		3561
		3562	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3563
		3564	Often (especially in GUI toolkits) there are places where you have
		3565	I<modal> interaction, which is most easily implemented by recursively
		3566	invoking C<ev_run>.
		3567
		3568	This brings the problem of exiting - a callback might want to finish the
		3569	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3570	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3571	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3572	other combination: In these cases, C<ev_break> will not work alone.
		3573
		3574	The solution is to maintain "break this loop" variable for each C<ev_run>
		3575	invocation, and use a loop around C<ev_run> until the condition is
		3576	triggered, using C<EVRUN_ONCE>:
		3577
		3578	// main loop
		3579	int exit_main_loop = 0;
		3580
		3581	while (!exit_main_loop)
		3582	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3583
		3584	// in a model watcher
		3585	int exit_nested_loop = 0;
		3586
		3587	while (!exit_nested_loop)
		3588	ev_run (EV_A_ EVRUN_ONCE);
		3589
		3590	To exit from any of these loops, just set the corresponding exit variable:
		3591
		3592	// exit modal loop
		3593	exit_nested_loop = 1;
		3594
		3595	// exit main program, after modal loop is finished
		3596	exit_main_loop = 1;
		3597
		3598	// exit both
		3599	exit_main_loop = exit_nested_loop = 1;
		3600
		3601	=head2 THREAD LOCKING EXAMPLE
		3602
		3603	Here is a fictitious example of how to run an event loop in a different
		3604	thread from where callbacks are being invoked and watchers are
		3605	created/added/removed.
		3606
		3607	For a real-world example, see the C<EV::Loop::Async> perl module,
		3608	which uses exactly this technique (which is suited for many high-level
		3609	languages).
		3610
		3611	The example uses a pthread mutex to protect the loop data, a condition
		3612	variable to wait for callback invocations, an async watcher to notify the
		3613	event loop thread and an unspecified mechanism to wake up the main thread.
		3614
		3615	First, you need to associate some data with the event loop:
		3616
		3617	typedef struct {
		3618	mutex_t lock; /* global loop lock */
		3619	ev_async async_w;
		3620	thread_t tid;
		3621	cond_t invoke_cv;
		3622	} userdata;
		3623
		3624	void prepare_loop (EV_P)
		3625	{
		3626	// for simplicity, we use a static userdata struct.
		3627	static userdata u;
		3628
		3629	ev_async_init (&u->async_w, async_cb);
		3630	ev_async_start (EV_A_ &u->async_w);
		3631
		3632	pthread_mutex_init (&u->lock, 0);
		3633	pthread_cond_init (&u->invoke_cv, 0);
		3634
		3635	// now associate this with the loop
		3636	ev_set_userdata (EV_A_ u);
		3637	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3638	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3639
		3640	// then create the thread running ev_run
		3641	pthread_create (&u->tid, 0, l_run, EV_A);
		3642	}
		3643
		3644	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3645	solely to wake up the event loop so it takes notice of any new watchers
		3646	that might have been added:
		3647
		3648	static void
		3649	async_cb (EV_P_ ev_async *w, int revents)
		3650	{
		3651	// just used for the side effects
		3652	}
		3653
		3654	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3655	protecting the loop data, respectively.
		3656
		3657	static void
		3658	l_release (EV_P)
		3659	{
		3660	userdata *u = ev_userdata (EV_A);
		3661	pthread_mutex_unlock (&u->lock);
		3662	}
		3663
		3664	static void
		3665	l_acquire (EV_P)
		3666	{
		3667	userdata *u = ev_userdata (EV_A);
		3668	pthread_mutex_lock (&u->lock);
		3669	}
		3670
		3671	The event loop thread first acquires the mutex, and then jumps straight
		3672	into C<ev_run>:
		3673
		3674	void *
		3675	l_run (void *thr_arg)
		3676	{
		3677	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3678
		3679	l_acquire (EV_A);
		3680	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3681	ev_run (EV_A_ 0);
		3682	l_release (EV_A);
		3683
		3684	return 0;
		3685	}
		3686
		3687	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3688	signal the main thread via some unspecified mechanism (signals? pipe
		3689	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3690	have been called (in a while loop because a) spurious wakeups are possible
		3691	and b) skipping inter-thread-communication when there are no pending
		3692	watchers is very beneficial):
		3693
		3694	static void
		3695	l_invoke (EV_P)
		3696	{
		3697	userdata *u = ev_userdata (EV_A);
		3698
		3699	while (ev_pending_count (EV_A))
		3700	{
		3701	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3702	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3703	}
		3704	}
		3705
		3706	Now, whenever the main thread gets told to invoke pending watchers, it
		3707	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3708	thread to continue:
		3709
		3710	static void
		3711	real_invoke_pending (EV_P)
		3712	{
		3713	userdata *u = ev_userdata (EV_A);
		3714
		3715	pthread_mutex_lock (&u->lock);
		3716	ev_invoke_pending (EV_A);
		3717	pthread_cond_signal (&u->invoke_cv);
		3718	pthread_mutex_unlock (&u->lock);
		3719	}
		3720
		3721	Whenever you want to start/stop a watcher or do other modifications to an
		3722	event loop, you will now have to lock:
		3723
		3724	ev_timer timeout_watcher;
		3725	userdata *u = ev_userdata (EV_A);
		3726
		3727	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3728
		3729	pthread_mutex_lock (&u->lock);
		3730	ev_timer_start (EV_A_ &timeout_watcher);
		3731	ev_async_send (EV_A_ &u->async_w);
		3732	pthread_mutex_unlock (&u->lock);
		3733
		3734	Note that sending the C<ev_async> watcher is required because otherwise
		3735	an event loop currently blocking in the kernel will have no knowledge
		3736	about the newly added timer. By waking up the loop it will pick up any new
		3737	watchers in the next event loop iteration.
		3738
		3739	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3740
		3741	While the overhead of a callback that e.g. schedules a thread is small, it
		3742	is still an overhead. If you embed libev, and your main usage is with some
		3743	kind of threads or coroutines, you might want to customise libev so that
		3744	doesn't need callbacks anymore.
		3745
		3746	Imagine you have coroutines that you can switch to using a function
		3747	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3748	and that due to some magic, the currently active coroutine is stored in a
		3749	global called C<current_coro>. Then you can build your own "wait for libev
		3750	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3751	the differing C<;> conventions):
		3752
		3753	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3754	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3755
		3756	That means instead of having a C callback function, you store the
		3757	coroutine to switch to in each watcher, and instead of having libev call
		3758	your callback, you instead have it switch to that coroutine.
		3759
		3760	A coroutine might now wait for an event with a function called
		3761	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3762	matter when, or whether the watcher is active or not when this function is
		3763	called):
		3764
		3765	void
		3766	wait_for_event (ev_watcher *w)
		3767	{
		3768	ev_cb_set (w) = current_coro;
		3769	switch_to (libev_coro);
		3770	}
		3771
		3772	That basically suspends the coroutine inside C<wait_for_event> and
		3773	continues the libev coroutine, which, when appropriate, switches back to
		3774	this or any other coroutine. I am sure if you sue this your own :)
		3775
		3776	You can do similar tricks if you have, say, threads with an event queue -
		3777	instead of storing a coroutine, you store the queue object and instead of
		3778	switching to a coroutine, you push the watcher onto the queue and notify
		3779	any waiters.
		3780
		3781	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3782	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3783
		3784	// my_ev.h
		3785	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3786	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3787	#include "../libev/ev.h"
		3788
		3789	// my_ev.c
		3790	#define EV_H "my_ev.h"
		3791	#include "../libev/ev.c"
		3792
		3793	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3794	F<my_ev.c> into your project. When properly specifying include paths, you
		3795	can even use F<ev.h> as header file name directly.
1865		3796
1866		3797
1867	=head1 LIBEVENT EMULATION	3798	=head1 LIBEVENT EMULATION
1868		3799
1869	Libev offers a compatibility emulation layer for libevent. It cannot	3800	Libev offers a compatibility emulation layer for libevent. It cannot
1870	emulate the internals of libevent, so here are some usage hints:	3801	emulate the internals of libevent, so here are some usage hints:
1871		3802
1872	=over 4	3803	=over 4
		3804
		3805	=item * Only the libevent-1.4.1-beta API is being emulated.
		3806
		3807	This was the newest libevent version available when libev was implemented,
		3808	and is still mostly unchanged in 2010.
1873		3809
1874	=item * Use it by including <event.h>, as usual.	3810	=item * Use it by including <event.h>, as usual.
1875		3811
1876	=item * The following members are fully supported: ev_base, ev_callback,	3812	=item * The following members are fully supported: ev_base, ev_callback,
1877	ev_arg, ev_fd, ev_res, ev_events.	3813	ev_arg, ev_fd, ev_res, ev_events.
…		…
1882		3818
1883	=item * Priorities are not currently supported. Initialising priorities	3819	=item * Priorities are not currently supported. Initialising priorities
1884	will fail and all watchers will have the same priority, even though there	3820	will fail and all watchers will have the same priority, even though there
1885	is an ev_pri field.	3821	is an ev_pri field.
1886		3822
		3823	=item * In libevent, the last base created gets the signals, in libev, the
		3824	base that registered the signal gets the signals.
		3825
1887	=item * Other members are not supported.	3826	=item * Other members are not supported.
1888		3827
1889	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3828	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1890	to use the libev header file and library.	3829	to use the libev header file and library.
1891		3830
1892	=back	3831	=back
1893		3832
1894	=head1 C++ SUPPORT	3833	=head1 C++ SUPPORT
1895		3834
1896	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3835	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1897	you to use some convinience methods to start/stop watchers and also change	3836	you to use some convenience methods to start/stop watchers and also change
1898	the callback model to a model using method callbacks on objects.	3837	the callback model to a model using method callbacks on objects.
1899		3838
1900	To use it,	3839	To use it,
1901		3840
1902	#include <ev++.h>	3841	#include <ev++.h>
1903		3842
1904	This automatically includes F<ev.h> and puts all of its definitions (many	3843	This automatically includes F<ev.h> and puts all of its definitions (many
1905	of them macros) into the global namespace. All C++ specific things are	3844	of them macros) into the global namespace. All C++ specific things are
1906	put into the C<ev> namespace. It should support all the same embedding	3845	put into the C<ev> namespace. It should support all the same embedding
1907	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3846	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1909	Care has been taken to keep the overhead low. The only data member the C++	3848	Care has been taken to keep the overhead low. The only data member the C++
1910	classes add (compared to plain C-style watchers) is the event loop pointer	3849	classes add (compared to plain C-style watchers) is the event loop pointer
1911	that the watcher is associated with (or no additional members at all if	3850	that the watcher is associated with (or no additional members at all if
1912	you disable C<EV_MULTIPLICITY> when embedding libev).	3851	you disable C<EV_MULTIPLICITY> when embedding libev).
1913		3852
1914	Currently, functions, and static and non-static member functions can be	3853	Currently, functions, static and non-static member functions and classes
1915	used as callbacks. Other types should be easy to add as long as they only	3854	with C<operator ()> can be used as callbacks. Other types should be easy
1916	need one additional pointer for context. If you need support for other	3855	to add as long as they only need one additional pointer for context. If
1917	types of functors please contact the author (preferably after implementing	3856	you need support for other types of functors please contact the author
1918	it).	3857	(preferably after implementing it).
1919		3858
1920	Here is a list of things available in the C<ev> namespace:	3859	Here is a list of things available in the C<ev> namespace:
1921		3860
1922	=over 4	3861	=over 4
1923		3862
…		…
1941		3880
1942	=over 4	3881	=over 4
1943		3882
1944	=item ev::TYPE::TYPE ()	3883	=item ev::TYPE::TYPE ()
1945		3884
1946	=item ev::TYPE::TYPE (struct ev_loop *)	3885	=item ev::TYPE::TYPE (loop)
1947		3886
1948	=item ev::TYPE::~TYPE	3887	=item ev::TYPE::~TYPE
1949		3888
1950	The constructor (optionally) takes an event loop to associate the watcher	3889	The constructor (optionally) takes an event loop to associate the watcher
1951	with. If it is omitted, it will use C<EV_DEFAULT>.	3890	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
1974	your compiler is good :), then the method will be fully inlined into the	3913	your compiler is good :), then the method will be fully inlined into the
1975	thunking function, making it as fast as a direct C callback.	3914	thunking function, making it as fast as a direct C callback.
1976		3915
1977	Example: simple class declaration and watcher initialisation	3916	Example: simple class declaration and watcher initialisation
1978		3917
1979	struct myclass	3918	struct myclass
1980	{	3919	{
1981	void io_cb (ev::io &w, int revents) { }	3920	void io_cb (ev::io &w, int revents) { }
1982	}	3921	}
1983		3922
1984	myclass obj;	3923	myclass obj;
1985	ev::io iow;	3924	ev::io iow;
1986	iow.set <myclass, &myclass::io_cb> (&obj);	3925	iow.set <myclass, &myclass::io_cb> (&obj);
		3926
		3927	=item w->set (object *)
		3928
		3929	This is a variation of a method callback - leaving out the method to call
		3930	will default the method to C<operator ()>, which makes it possible to use
		3931	functor objects without having to manually specify the C<operator ()> all
		3932	the time. Incidentally, you can then also leave out the template argument
		3933	list.
		3934
		3935	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3936	int revents)>.
		3937
		3938	See the method-C<set> above for more details.
		3939
		3940	Example: use a functor object as callback.
		3941
		3942	struct myfunctor
		3943	{
		3944	void operator() (ev::io &w, int revents)
		3945	{
		3946	...
		3947	}
		3948	}
		3949
		3950	myfunctor f;
		3951
		3952	ev::io w;
		3953	w.set (&f);
1987		3954
1988	=item w->set<function> (void *data = 0)	3955	=item w->set<function> (void *data = 0)
1989		3956
1990	Also sets a callback, but uses a static method or plain function as	3957	Also sets a callback, but uses a static method or plain function as
1991	callback. The optional C<data> argument will be stored in the watcher's	3958	callback. The optional C<data> argument will be stored in the watcher's
…		…
1993		3960
1994	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3961	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1995		3962
1996	See the method-C<set> above for more details.	3963	See the method-C<set> above for more details.
1997		3964
1998	Example:	3965	Example: Use a plain function as callback.
1999		3966
2000	static void io_cb (ev::io &w, int revents) { }	3967	static void io_cb (ev::io &w, int revents) { }
2001	iow.set <io_cb> ();	3968	iow.set <io_cb> ();
2002		3969
2003	=item w->set (struct ev_loop *)	3970	=item w->set (loop)
2004		3971
2005	Associates a different C<struct ev_loop> with this watcher. You can only	3972	Associates a different C<struct ev_loop> with this watcher. You can only
2006	do this when the watcher is inactive (and not pending either).	3973	do this when the watcher is inactive (and not pending either).
2007		3974
2008	=item w->set ([args])	3975	=item w->set ([arguments])
2009		3976
2010	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3977	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2011	called at least once. Unlike the C counterpart, an active watcher gets	3978	method or a suitable start method must be called at least once. Unlike the
2012	automatically stopped and restarted when reconfiguring it with this	3979	C counterpart, an active watcher gets automatically stopped and restarted
2013	method.	3980	when reconfiguring it with this method.
2014		3981
2015	=item w->start ()	3982	=item w->start ()
2016		3983
2017	Starts the watcher. Note that there is no C<loop> argument, as the	3984	Starts the watcher. Note that there is no C<loop> argument, as the
2018	constructor already stores the event loop.	3985	constructor already stores the event loop.
2019		3986
		3987	=item w->start ([arguments])
		3988
		3989	Instead of calling C<set> and C<start> methods separately, it is often
		3990	convenient to wrap them in one call. Uses the same type of arguments as
		3991	the configure C<set> method of the watcher.
		3992
2020	=item w->stop ()	3993	=item w->stop ()
2021		3994
2022	Stops the watcher if it is active. Again, no C<loop> argument.	3995	Stops the watcher if it is active. Again, no C<loop> argument.
2023		3996
2024	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3997	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2036		4009
2037	=back	4010	=back
2038		4011
2039	=back	4012	=back
2040		4013
2041	Example: Define a class with an IO and idle watcher, start one of them in	4014	Example: Define a class with two I/O and idle watchers, start the I/O
2042	the constructor.	4015	watchers in the constructor.
2043		4016
2044	class myclass	4017	class myclass
2045	{	4018	{
2046	ev_io io; void io_cb (ev::io &w, int revents);	4019	ev::io io ; void io_cb (ev::io &w, int revents);
		4020	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2047	ev_idle idle void idle_cb (ev::idle &w, int revents);	4021	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2048		4022
2049	myclass ();	4023	myclass (int fd)
2050	}	4024	{
2051
2052	myclass::myclass (int fd)
2053	{
2054	io .set <myclass, &myclass::io_cb > (this);	4025	io .set <myclass, &myclass::io_cb > (this);
		4026	io2 .set <myclass, &myclass::io2_cb > (this);
2055	idle.set <myclass, &myclass::idle_cb> (this);	4027	idle.set <myclass, &myclass::idle_cb> (this);
2056		4028
2057	io.start (fd, ev::READ);	4029	io.set (fd, ev::WRITE); // configure the watcher
		4030	io.start (); // start it whenever convenient
		4031
		4032	io2.start (fd, ev::READ); // set + start in one call
		4033	}
2058	}	4034	};
		4035
		4036
		4037	=head1 OTHER LANGUAGE BINDINGS
		4038
		4039	Libev does not offer other language bindings itself, but bindings for a
		4040	number of languages exist in the form of third-party packages. If you know
		4041	any interesting language binding in addition to the ones listed here, drop
		4042	me a note.
		4043
		4044	=over 4
		4045
		4046	=item Perl
		4047
		4048	The EV module implements the full libev API and is actually used to test
		4049	libev. EV is developed together with libev. Apart from the EV core module,
		4050	there are additional modules that implement libev-compatible interfaces
		4051	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4052	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4053	and C<EV::Glib>).
		4054
		4055	It can be found and installed via CPAN, its homepage is at
		4056	L<http://software.schmorp.de/pkg/EV>.
		4057
		4058	=item Python
		4059
		4060	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4061	seems to be quite complete and well-documented.
		4062
		4063	=item Ruby
		4064
		4065	Tony Arcieri has written a ruby extension that offers access to a subset
		4066	of the libev API and adds file handle abstractions, asynchronous DNS and
		4067	more on top of it. It can be found via gem servers. Its homepage is at
		4068	L<http://rev.rubyforge.org/>.
		4069
		4070	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4071	makes rev work even on mingw.
		4072
		4073	=item Haskell
		4074
		4075	A haskell binding to libev is available at
		4076	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4077
		4078	=item D
		4079
		4080	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4081	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4082
		4083	=item Ocaml
		4084
		4085	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4086	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4087
		4088	=item Lua
		4089
		4090	Brian Maher has written a partial interface to libev for lua (at the
		4091	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4092	L<http://github.com/brimworks/lua-ev>.
		4093
		4094	=back
2059		4095
2060		4096
2061	=head1 MACRO MAGIC	4097	=head1 MACRO MAGIC
2062		4098
2063	Libev can be compiled with a variety of options, the most fundamantal	4099	Libev can be compiled with a variety of options, the most fundamental
2064	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4100	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2065	functions and callbacks have an initial C<struct ev_loop *> argument.	4101	functions and callbacks have an initial C<struct ev_loop *> argument.
2066		4102
2067	To make it easier to write programs that cope with either variant, the	4103	To make it easier to write programs that cope with either variant, the
2068	following macros are defined:	4104	following macros are defined:
…		…
2073		4109
2074	This provides the loop I<argument> for functions, if one is required ("ev	4110	This provides the loop I<argument> for functions, if one is required ("ev
2075	loop argument"). The C<EV_A> form is used when this is the sole argument,	4111	loop argument"). The C<EV_A> form is used when this is the sole argument,
2076	C<EV_A_> is used when other arguments are following. Example:	4112	C<EV_A_> is used when other arguments are following. Example:
2077		4113
2078	ev_unref (EV_A);	4114	ev_unref (EV_A);
2079	ev_timer_add (EV_A_ watcher);	4115	ev_timer_add (EV_A_ watcher);
2080	ev_loop (EV_A_ 0);	4116	ev_run (EV_A_ 0);
2081		4117
2082	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4118	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2083	which is often provided by the following macro.	4119	which is often provided by the following macro.
2084		4120
2085	=item C<EV_P>, C<EV_P_>	4121	=item C<EV_P>, C<EV_P_>
2086		4122
2087	This provides the loop I<parameter> for functions, if one is required ("ev	4123	This provides the loop I<parameter> for functions, if one is required ("ev
2088	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4124	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2089	C<EV_P_> is used when other parameters are following. Example:	4125	C<EV_P_> is used when other parameters are following. Example:
2090		4126
2091	// this is how ev_unref is being declared	4127	// this is how ev_unref is being declared
2092	static void ev_unref (EV_P);	4128	static void ev_unref (EV_P);
2093		4129
2094	// this is how you can declare your typical callback	4130	// this is how you can declare your typical callback
2095	static void cb (EV_P_ ev_timer *w, int revents)	4131	static void cb (EV_P_ ev_timer *w, int revents)
2096		4132
2097	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4133	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2098	suitable for use with C<EV_A>.	4134	suitable for use with C<EV_A>.
2099		4135
2100	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4136	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2101		4137
2102	Similar to the other two macros, this gives you the value of the default	4138	Similar to the other two macros, this gives you the value of the default
2103	loop, if multiple loops are supported ("ev loop default").	4139	loop, if multiple loops are supported ("ev loop default"). The default loop
		4140	will be initialised if it isn't already initialised.
		4141
		4142	For non-multiplicity builds, these macros do nothing, so you always have
		4143	to initialise the loop somewhere.
		4144
		4145	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4146
		4147	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4148	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4149	is undefined when the default loop has not been initialised by a previous
		4150	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4151
		4152	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4153	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2104		4154
2105	=back	4155	=back
2106		4156
2107	Example: Declare and initialise a check watcher, utilising the above	4157	Example: Declare and initialise a check watcher, utilising the above
2108	macros so it will work regardless of whether multiple loops are supported	4158	macros so it will work regardless of whether multiple loops are supported
2109	or not.	4159	or not.
2110		4160
2111	static void	4161	static void
2112	check_cb (EV_P_ ev_timer *w, int revents)	4162	check_cb (EV_P_ ev_timer *w, int revents)
2113	{	4163	{
2114	ev_check_stop (EV_A_ w);	4164	ev_check_stop (EV_A_ w);
2115	}	4165	}
2116		4166
2117	ev_check check;	4167	ev_check check;
2118	ev_check_init (&check, check_cb);	4168	ev_check_init (&check, check_cb);
2119	ev_check_start (EV_DEFAULT_ &check);	4169	ev_check_start (EV_DEFAULT_ &check);
2120	ev_loop (EV_DEFAULT_ 0);	4170	ev_run (EV_DEFAULT_ 0);
2121		4171
2122	=head1 EMBEDDING	4172	=head1 EMBEDDING
2123		4173
2124	Libev can (and often is) directly embedded into host	4174	Libev can (and often is) directly embedded into host
2125	applications. Examples of applications that embed it include the Deliantra	4175	applications. Examples of applications that embed it include the Deliantra
2126	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	4176	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2127	and rxvt-unicode.	4177	and rxvt-unicode.
2128		4178
2129	The goal is to enable you to just copy the neecssary files into your	4179	The goal is to enable you to just copy the necessary files into your
2130	source directory without having to change even a single line in them, so	4180	source directory without having to change even a single line in them, so
2131	you can easily upgrade by simply copying (or having a checked-out copy of	4181	you can easily upgrade by simply copying (or having a checked-out copy of
2132	libev somewhere in your source tree).	4182	libev somewhere in your source tree).
2133		4183
2134	=head2 FILESETS	4184	=head2 FILESETS
2135		4185
2136	Depending on what features you need you need to include one or more sets of files	4186	Depending on what features you need you need to include one or more sets of files
2137	in your app.	4187	in your application.
2138		4188
2139	=head3 CORE EVENT LOOP	4189	=head3 CORE EVENT LOOP
2140		4190
2141	To include only the libev core (all the C<ev_*> functions), with manual	4191	To include only the libev core (all the C<ev_*> functions), with manual
2142	configuration (no autoconf):	4192	configuration (no autoconf):
2143		4193
2144	#define EV_STANDALONE 1	4194	#define EV_STANDALONE 1
2145	#include "ev.c"	4195	#include "ev.c"
2146		4196
2147	This will automatically include F<ev.h>, too, and should be done in a	4197	This will automatically include F<ev.h>, too, and should be done in a
2148	single C source file only to provide the function implementations. To use	4198	single C source file only to provide the function implementations. To use
2149	it, do the same for F<ev.h> in all files wishing to use this API (best	4199	it, do the same for F<ev.h> in all files wishing to use this API (best
2150	done by writing a wrapper around F<ev.h> that you can include instead and	4200	done by writing a wrapper around F<ev.h> that you can include instead and
2151	where you can put other configuration options):	4201	where you can put other configuration options):
2152		4202
2153	#define EV_STANDALONE 1	4203	#define EV_STANDALONE 1
2154	#include "ev.h"	4204	#include "ev.h"
2155		4205
2156	Both header files and implementation files can be compiled with a C++	4206	Both header files and implementation files can be compiled with a C++
2157	compiler (at least, thats a stated goal, and breakage will be treated	4207	compiler (at least, that's a stated goal, and breakage will be treated
2158	as a bug).	4208	as a bug).
2159		4209
2160	You need the following files in your source tree, or in a directory	4210	You need the following files in your source tree, or in a directory
2161	in your include path (e.g. in libev/ when using -Ilibev):	4211	in your include path (e.g. in libev/ when using -Ilibev):
2162		4212
2163	ev.h	4213	ev.h
2164	ev.c	4214	ev.c
2165	ev_vars.h	4215	ev_vars.h
2166	ev_wrap.h	4216	ev_wrap.h
2167		4217
2168	ev_win32.c required on win32 platforms only	4218	ev_win32.c required on win32 platforms only
2169		4219
2170	ev_select.c only when select backend is enabled (which is enabled by default)	4220	ev_select.c only when select backend is enabled (which is enabled by default)
2171	ev_poll.c only when poll backend is enabled (disabled by default)	4221	ev_poll.c only when poll backend is enabled (disabled by default)
2172	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4222	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2173	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4223	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2174	ev_port.c only when the solaris port backend is enabled (disabled by default)	4224	ev_port.c only when the solaris port backend is enabled (disabled by default)
2175		4225
2176	F<ev.c> includes the backend files directly when enabled, so you only need	4226	F<ev.c> includes the backend files directly when enabled, so you only need
2177	to compile this single file.	4227	to compile this single file.
2178		4228
2179	=head3 LIBEVENT COMPATIBILITY API	4229	=head3 LIBEVENT COMPATIBILITY API
2180		4230
2181	To include the libevent compatibility API, also include:	4231	To include the libevent compatibility API, also include:
2182		4232
2183	#include "event.c"	4233	#include "event.c"
2184		4234
2185	in the file including F<ev.c>, and:	4235	in the file including F<ev.c>, and:
2186		4236
2187	#include "event.h"	4237	#include "event.h"
2188		4238
2189	in the files that want to use the libevent API. This also includes F<ev.h>.	4239	in the files that want to use the libevent API. This also includes F<ev.h>.
2190		4240
2191	You need the following additional files for this:	4241	You need the following additional files for this:
2192		4242
2193	event.h	4243	event.h
2194	event.c	4244	event.c
2195		4245
2196	=head3 AUTOCONF SUPPORT	4246	=head3 AUTOCONF SUPPORT
2197		4247
2198	Instead of using C<EV_STANDALONE=1> and providing your config in	4248	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2199	whatever way you want, you can also C<m4_include([libev.m4])> in your	4249	whatever way you want, you can also C<m4_include([libev.m4])> in your
2200	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4250	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2201	include F<config.h> and configure itself accordingly.	4251	include F<config.h> and configure itself accordingly.
2202		4252
2203	For this of course you need the m4 file:	4253	For this of course you need the m4 file:
2204		4254
2205	libev.m4	4255	libev.m4
2206		4256
2207	=head2 PREPROCESSOR SYMBOLS/MACROS	4257	=head2 PREPROCESSOR SYMBOLS/MACROS
2208		4258
2209	Libev can be configured via a variety of preprocessor symbols you have to define	4259	Libev can be configured via a variety of preprocessor symbols you have to
2210	before including any of its files. The default is not to build for multiplicity	4260	define before including (or compiling) any of its files. The default in
2211	and only include the select backend.	4261	the absence of autoconf is documented for every option.
		4262
		4263	Symbols marked with "(h)" do not change the ABI, and can have different
		4264	values when compiling libev vs. including F<ev.h>, so it is permissible
		4265	to redefine them before including F<ev.h> without breaking compatibility
		4266	to a compiled library. All other symbols change the ABI, which means all
		4267	users of libev and the libev code itself must be compiled with compatible
		4268	settings.
2212		4269
2213	=over 4	4270	=over 4
2214		4271
		4272	=item EV_COMPAT3 (h)
		4273
		4274	Backwards compatibility is a major concern for libev. This is why this
		4275	release of libev comes with wrappers for the functions and symbols that
		4276	have been renamed between libev version 3 and 4.
		4277
		4278	You can disable these wrappers (to test compatibility with future
		4279	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4280	sources. This has the additional advantage that you can drop the C<struct>
		4281	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4282	typedef in that case.
		4283
		4284	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4285	and in some even more future version the compatibility code will be
		4286	removed completely.
		4287
2215	=item EV_STANDALONE	4288	=item EV_STANDALONE (h)
2216		4289
2217	Must always be C<1> if you do not use autoconf configuration, which	4290	Must always be C<1> if you do not use autoconf configuration, which
2218	keeps libev from including F<config.h>, and it also defines dummy	4291	keeps libev from including F<config.h>, and it also defines dummy
2219	implementations for some libevent functions (such as logging, which is not	4292	implementations for some libevent functions (such as logging, which is not
2220	supported). It will also not define any of the structs usually found in	4293	supported). It will also not define any of the structs usually found in
2221	F<event.h> that are not directly supported by the libev core alone.	4294	F<event.h> that are not directly supported by the libev core alone.
2222		4295
		4296	In standalone mode, libev will still try to automatically deduce the
		4297	configuration, but has to be more conservative.
		4298
		4299	=item EV_USE_FLOOR
		4300
		4301	If defined to be C<1>, libev will use the C<floor ()> function for its
		4302	periodic reschedule calculations, otherwise libev will fall back on a
		4303	portable (slower) implementation. If you enable this, you usually have to
		4304	link against libm or something equivalent. Enabling this when the C<floor>
		4305	function is not available will fail, so the safe default is to not enable
		4306	this.
		4307
2223	=item EV_USE_MONOTONIC	4308	=item EV_USE_MONOTONIC
2224		4309
2225	If defined to be C<1>, libev will try to detect the availability of the	4310	If defined to be C<1>, libev will try to detect the availability of the
2226	monotonic clock option at both compiletime and runtime. Otherwise no use	4311	monotonic clock option at both compile time and runtime. Otherwise no
2227	of the monotonic clock option will be attempted. If you enable this, you	4312	use of the monotonic clock option will be attempted. If you enable this,
2228	usually have to link against librt or something similar. Enabling it when	4313	you usually have to link against librt or something similar. Enabling it
2229	the functionality isn't available is safe, though, althoguh you have	4314	when the functionality isn't available is safe, though, although you have
2230	to make sure you link against any libraries where the C<clock_gettime>	4315	to make sure you link against any libraries where the C<clock_gettime>
2231	function is hiding in (often F<-lrt>).	4316	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2232		4317
2233	=item EV_USE_REALTIME	4318	=item EV_USE_REALTIME
2234		4319
2235	If defined to be C<1>, libev will try to detect the availability of the	4320	If defined to be C<1>, libev will try to detect the availability of the
2236	realtime clock option at compiletime (and assume its availability at	4321	real-time clock option at compile time (and assume its availability
2237	runtime if successful). Otherwise no use of the realtime clock option will	4322	at runtime if successful). Otherwise no use of the real-time clock
2238	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4323	option will be attempted. This effectively replaces C<gettimeofday>
2239	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	4324	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2240	in the description of C<EV_USE_MONOTONIC>, though.	4325	correctness. See the note about libraries in the description of
		4326	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4327	C<EV_USE_CLOCK_SYSCALL>.
		4328
		4329	=item EV_USE_CLOCK_SYSCALL
		4330
		4331	If defined to be C<1>, libev will try to use a direct syscall instead
		4332	of calling the system-provided C<clock_gettime> function. This option
		4333	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4334	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4335	programs needlessly. Using a direct syscall is slightly slower (in
		4336	theory), because no optimised vdso implementation can be used, but avoids
		4337	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4338	higher, as it simplifies linking (no need for C<-lrt>).
		4339
		4340	=item EV_USE_NANOSLEEP
		4341
		4342	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4343	and will use it for delays. Otherwise it will use C<select ()>.
		4344
		4345	=item EV_USE_EVENTFD
		4346
		4347	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4348	available and will probe for kernel support at runtime. This will improve
		4349	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4350	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4351	2.7 or newer, otherwise disabled.
2241		4352
2242	=item EV_USE_SELECT	4353	=item EV_USE_SELECT
2243		4354
2244	If undefined or defined to be C<1>, libev will compile in support for the	4355	If undefined or defined to be C<1>, libev will compile in support for the
2245	C<select>(2) backend. No attempt at autodetection will be done: if no	4356	C<select>(2) backend. No attempt at auto-detection will be done: if no
2246	other method takes over, select will be it. Otherwise the select backend	4357	other method takes over, select will be it. Otherwise the select backend
2247	will not be compiled in.	4358	will not be compiled in.
2248		4359
2249	=item EV_SELECT_USE_FD_SET	4360	=item EV_SELECT_USE_FD_SET
2250		4361
2251	If defined to C<1>, then the select backend will use the system C<fd_set>	4362	If defined to C<1>, then the select backend will use the system C<fd_set>
2252	structure. This is useful if libev doesn't compile due to a missing	4363	structure. This is useful if libev doesn't compile due to a missing
2253	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4364	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2254	exotic systems. This usually limits the range of file descriptors to some	4365	on exotic systems. This usually limits the range of file descriptors to
2255	low limit such as 1024 or might have other limitations (winsocket only	4366	some low limit such as 1024 or might have other limitations (winsocket
2256	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4367	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2257	influence the size of the C<fd_set> used.	4368	configures the maximum size of the C<fd_set>.
2258		4369
2259	=item EV_SELECT_IS_WINSOCKET	4370	=item EV_SELECT_IS_WINSOCKET
2260		4371
2261	When defined to C<1>, the select backend will assume that	4372	When defined to C<1>, the select backend will assume that
2262	select/socket/connect etc. don't understand file descriptors but	4373	select/socket/connect etc. don't understand file descriptors but
…		…
2264	be used is the winsock select). This means that it will call	4375	be used is the winsock select). This means that it will call
2265	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4376	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2266	it is assumed that all these functions actually work on fds, even	4377	it is assumed that all these functions actually work on fds, even
2267	on win32. Should not be defined on non-win32 platforms.	4378	on win32. Should not be defined on non-win32 platforms.
2268		4379
		4380	=item EV_FD_TO_WIN32_HANDLE(fd)
		4381
		4382	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4383	file descriptors to socket handles. When not defining this symbol (the
		4384	default), then libev will call C<_get_osfhandle>, which is usually
		4385	correct. In some cases, programs use their own file descriptor management,
		4386	in which case they can provide this function to map fds to socket handles.
		4387
		4388	=item EV_WIN32_HANDLE_TO_FD(handle)
		4389
		4390	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4391	using the standard C<_open_osfhandle> function. For programs implementing
		4392	their own fd to handle mapping, overwriting this function makes it easier
		4393	to do so. This can be done by defining this macro to an appropriate value.
		4394
		4395	=item EV_WIN32_CLOSE_FD(fd)
		4396
		4397	If programs implement their own fd to handle mapping on win32, then this
		4398	macro can be used to override the C<close> function, useful to unregister
		4399	file descriptors again. Note that the replacement function has to close
		4400	the underlying OS handle.
		4401
2269	=item EV_USE_POLL	4402	=item EV_USE_POLL
2270		4403
2271	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4404	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2272	backend. Otherwise it will be enabled on non-win32 platforms. It	4405	backend. Otherwise it will be enabled on non-win32 platforms. It
2273	takes precedence over select.	4406	takes precedence over select.
2274		4407
2275	=item EV_USE_EPOLL	4408	=item EV_USE_EPOLL
2276		4409
2277	If defined to be C<1>, libev will compile in support for the Linux	4410	If defined to be C<1>, libev will compile in support for the Linux
2278	C<epoll>(7) backend. Its availability will be detected at runtime,	4411	C<epoll>(7) backend. Its availability will be detected at runtime,
2279	otherwise another method will be used as fallback. This is the	4412	otherwise another method will be used as fallback. This is the preferred
2280	preferred backend for GNU/Linux systems.	4413	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4414	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2281		4415
2282	=item EV_USE_KQUEUE	4416	=item EV_USE_KQUEUE
2283		4417
2284	If defined to be C<1>, libev will compile in support for the BSD style	4418	If defined to be C<1>, libev will compile in support for the BSD style
2285	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4419	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2298	otherwise another method will be used as fallback. This is the preferred	4432	otherwise another method will be used as fallback. This is the preferred
2299	backend for Solaris 10 systems.	4433	backend for Solaris 10 systems.
2300		4434
2301	=item EV_USE_DEVPOLL	4435	=item EV_USE_DEVPOLL
2302		4436
2303	reserved for future expansion, works like the USE symbols above.	4437	Reserved for future expansion, works like the USE symbols above.
2304		4438
2305	=item EV_USE_INOTIFY	4439	=item EV_USE_INOTIFY
2306		4440
2307	If defined to be C<1>, libev will compile in support for the Linux inotify	4441	If defined to be C<1>, libev will compile in support for the Linux inotify
2308	interface to speed up C<ev_stat> watchers. Its actual availability will	4442	interface to speed up C<ev_stat> watchers. Its actual availability will
2309	be detected at runtime.	4443	be detected at runtime. If undefined, it will be enabled if the headers
		4444	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2310		4445
		4446	=item EV_ATOMIC_T
		4447
		4448	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4449	access is atomic and serialised with respect to other threads or signal
		4450	contexts. No such type is easily found in the C language, so you can
		4451	provide your own type that you know is safe for your purposes. It is used
		4452	both for signal handler "locking" as well as for signal and thread safety
		4453	in C<ev_async> watchers.
		4454
		4455	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4456	(from F<signal.h>), which is usually good enough on most platforms,
		4457	although strictly speaking using a type that also implies a memory fence
		4458	is required.
		4459
2311	=item EV_H	4460	=item EV_H (h)
2312		4461
2313	The name of the F<ev.h> header file used to include it. The default if	4462	The name of the F<ev.h> header file used to include it. The default if
2314	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4463	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2315	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4464	used to virtually rename the F<ev.h> header file in case of conflicts.
2316		4465
2317	=item EV_CONFIG_H	4466	=item EV_CONFIG_H (h)
2318		4467
2319	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4468	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2320	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4469	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2321	C<EV_H>, above.	4470	C<EV_H>, above.
2322		4471
2323	=item EV_EVENT_H	4472	=item EV_EVENT_H (h)
2324		4473
2325	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4474	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2326	of how the F<event.h> header can be found.	4475	of how the F<event.h> header can be found, the default is C<"event.h">.
2327		4476
2328	=item EV_PROTOTYPES	4477	=item EV_PROTOTYPES (h)
2329		4478
2330	If defined to be C<0>, then F<ev.h> will not define any function	4479	If defined to be C<0>, then F<ev.h> will not define any function
2331	prototypes, but still define all the structs and other symbols. This is	4480	prototypes, but still define all the structs and other symbols. This is
2332	occasionally useful if you want to provide your own wrapper functions	4481	occasionally useful if you want to provide your own wrapper functions
2333	around libev functions.	4482	around libev functions.
…		…
2338	will have the C<struct ev_loop *> as first argument, and you can create	4487	will have the C<struct ev_loop *> as first argument, and you can create
2339	additional independent event loops. Otherwise there will be no support	4488	additional independent event loops. Otherwise there will be no support
2340	for multiple event loops and there is no first event loop pointer	4489	for multiple event loops and there is no first event loop pointer
2341	argument. Instead, all functions act on the single default loop.	4490	argument. Instead, all functions act on the single default loop.
2342		4491
		4492	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4493	default loop when multiplicity is switched off - you always have to
		4494	initialise the loop manually in this case.
		4495
2343	=item EV_MINPRI	4496	=item EV_MINPRI
2344		4497
2345	=item EV_MAXPRI	4498	=item EV_MAXPRI
2346		4499
2347	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4500	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2352	When doing priority-based operations, libev usually has to linearly search	4505	When doing priority-based operations, libev usually has to linearly search
2353	all the priorities, so having many of them (hundreds) uses a lot of space	4506	all the priorities, so having many of them (hundreds) uses a lot of space
2354	and time, so using the defaults of five priorities (-2 .. +2) is usually	4507	and time, so using the defaults of five priorities (-2 .. +2) is usually
2355	fine.	4508	fine.
2356		4509
2357	If your embedding app does not need any priorities, defining these both to	4510	If your embedding application does not need any priorities, defining these
2358	C<0> will save some memory and cpu.	4511	both to C<0> will save some memory and CPU.
2359		4512
2360	=item EV_PERIODIC_ENABLE	4513	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4514	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4515	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2361		4516
2362	If undefined or defined to be C<1>, then periodic timers are supported. If	4517	If undefined or defined to be C<1> (and the platform supports it), then
2363	defined to be C<0>, then they are not. Disabling them saves a few kB of	4518	the respective watcher type is supported. If defined to be C<0>, then it
2364	code.	4519	is not. Disabling watcher types mainly saves code size.
2365		4520
2366	=item EV_IDLE_ENABLE	4521	=item EV_FEATURES
2367
2368	If undefined or defined to be C<1>, then idle watchers are supported. If
2369	defined to be C<0>, then they are not. Disabling them saves a few kB of
2370	code.
2371
2372	=item EV_EMBED_ENABLE
2373
2374	If undefined or defined to be C<1>, then embed watchers are supported. If
2375	defined to be C<0>, then they are not.
2376
2377	=item EV_STAT_ENABLE
2378
2379	If undefined or defined to be C<1>, then stat watchers are supported. If
2380	defined to be C<0>, then they are not.
2381
2382	=item EV_FORK_ENABLE
2383
2384	If undefined or defined to be C<1>, then fork watchers are supported. If
2385	defined to be C<0>, then they are not.
2386
2387	=item EV_MINIMAL
2388		4522
2389	If you need to shave off some kilobytes of code at the expense of some	4523	If you need to shave off some kilobytes of code at the expense of some
2390	speed, define this symbol to C<1>. Currently only used for gcc to override	4524	speed (but with the full API), you can define this symbol to request
2391	some inlining decisions, saves roughly 30% codesize of amd64.	4525	certain subsets of functionality. The default is to enable all features
		4526	that can be enabled on the platform.
		4527
		4528	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4529	with some broad features you want) and then selectively re-enable
		4530	additional parts you want, for example if you want everything minimal,
		4531	but multiple event loop support, async and child watchers and the poll
		4532	backend, use this:
		4533
		4534	#define EV_FEATURES 0
		4535	#define EV_MULTIPLICITY 1
		4536	#define EV_USE_POLL 1
		4537	#define EV_CHILD_ENABLE 1
		4538	#define EV_ASYNC_ENABLE 1
		4539
		4540	The actual value is a bitset, it can be a combination of the following
		4541	values:
		4542
		4543	=over 4
		4544
		4545	=item C<1> - faster/larger code
		4546
		4547	Use larger code to speed up some operations.
		4548
		4549	Currently this is used to override some inlining decisions (enlarging the
		4550	code size by roughly 30% on amd64).
		4551
		4552	When optimising for size, use of compiler flags such as C<-Os> with
		4553	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4554	assertions.
		4555
		4556	=item C<2> - faster/larger data structures
		4557
		4558	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4559	hash table sizes and so on. This will usually further increase code size
		4560	and can additionally have an effect on the size of data structures at
		4561	runtime.
		4562
		4563	=item C<4> - full API configuration
		4564
		4565	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4566	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4567
		4568	=item C<8> - full API
		4569
		4570	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4571	details on which parts of the API are still available without this
		4572	feature, and do not complain if this subset changes over time.
		4573
		4574	=item C<16> - enable all optional watcher types
		4575
		4576	Enables all optional watcher types. If you want to selectively enable
		4577	only some watcher types other than I/O and timers (e.g. prepare,
		4578	embed, async, child...) you can enable them manually by defining
		4579	C<EV_watchertype_ENABLE> to C<1> instead.
		4580
		4581	=item C<32> - enable all backends
		4582
		4583	This enables all backends - without this feature, you need to enable at
		4584	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4585
		4586	=item C<64> - enable OS-specific "helper" APIs
		4587
		4588	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4589	default.
		4590
		4591	=back
		4592
		4593	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4594	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4595	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4596	watchers, timers and monotonic clock support.
		4597
		4598	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4599	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4600	your program might be left out as well - a binary starting a timer and an
		4601	I/O watcher then might come out at only 5Kb.
		4602
		4603	=item EV_AVOID_STDIO
		4604
		4605	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4606	functions (printf, scanf, perror etc.). This will increase the code size
		4607	somewhat, but if your program doesn't otherwise depend on stdio and your
		4608	libc allows it, this avoids linking in the stdio library which is quite
		4609	big.
		4610
		4611	Note that error messages might become less precise when this option is
		4612	enabled.
		4613
		4614	=item EV_NSIG
		4615
		4616	The highest supported signal number, +1 (or, the number of
		4617	signals): Normally, libev tries to deduce the maximum number of signals
		4618	automatically, but sometimes this fails, in which case it can be
		4619	specified. Also, using a lower number than detected (C<32> should be
		4620	good for about any system in existence) can save some memory, as libev
		4621	statically allocates some 12-24 bytes per signal number.
2392		4622
2393	=item EV_PID_HASHSIZE	4623	=item EV_PID_HASHSIZE
2394		4624
2395	C<ev_child> watchers use a small hash table to distribute workload by	4625	C<ev_child> watchers use a small hash table to distribute workload by
2396	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4626	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2397	than enough. If you need to manage thousands of children you might want to	4627	usually more than enough. If you need to manage thousands of children you
2398	increase this value (I<must> be a power of two).	4628	might want to increase this value (I<must> be a power of two).
2399		4629
2400	=item EV_INOTIFY_HASHSIZE	4630	=item EV_INOTIFY_HASHSIZE
2401		4631
2402	C<ev_staz> watchers use a small hash table to distribute workload by	4632	C<ev_stat> watchers use a small hash table to distribute workload by
2403	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4633	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2404	usually more than enough. If you need to manage thousands of C<ev_stat>	4634	disabled), usually more than enough. If you need to manage thousands of
2405	watchers you might want to increase this value (I<must> be a power of	4635	C<ev_stat> watchers you might want to increase this value (I<must> be a
2406	two).	4636	power of two).
		4637
		4638	=item EV_USE_4HEAP
		4639
		4640	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4641	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4642	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4643	faster performance with many (thousands) of watchers.
		4644
		4645	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4646	will be C<0>.
		4647
		4648	=item EV_HEAP_CACHE_AT
		4649
		4650	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4651	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4652	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4653	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4654	but avoids random read accesses on heap changes. This improves performance
		4655	noticeably with many (hundreds) of watchers.
		4656
		4657	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4658	will be C<0>.
		4659
		4660	=item EV_VERIFY
		4661
		4662	Controls how much internal verification (see C<ev_verify ()>) will
		4663	be done: If set to C<0>, no internal verification code will be compiled
		4664	in. If set to C<1>, then verification code will be compiled in, but not
		4665	called. If set to C<2>, then the internal verification code will be
		4666	called once per loop, which can slow down libev. If set to C<3>, then the
		4667	verification code will be called very frequently, which will slow down
		4668	libev considerably.
		4669
		4670	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4671	will be C<0>.
2407		4672
2408	=item EV_COMMON	4673	=item EV_COMMON
2409		4674
2410	By default, all watchers have a C<void *data> member. By redefining	4675	By default, all watchers have a C<void *data> member. By redefining
2411	this macro to a something else you can include more and other types of	4676	this macro to something else you can include more and other types of
2412	members. You have to define it each time you include one of the files,	4677	members. You have to define it each time you include one of the files,
2413	though, and it must be identical each time.	4678	though, and it must be identical each time.
2414		4679
2415	For example, the perl EV module uses something like this:	4680	For example, the perl EV module uses something like this:
2416		4681
2417	#define EV_COMMON \	4682	#define EV_COMMON \
2418	SV *self; /* contains this struct */ \	4683	SV *self; /* contains this struct */ \
2419	SV *cb_sv, *fh /* note no trailing ";" */	4684	SV *cb_sv, *fh /* note no trailing ";" */
2420		4685
2421	=item EV_CB_DECLARE (type)	4686	=item EV_CB_DECLARE (type)
2422		4687
2423	=item EV_CB_INVOKE (watcher, revents)	4688	=item EV_CB_INVOKE (watcher, revents)
2424		4689
2425	=item ev_set_cb (ev, cb)	4690	=item ev_set_cb (ev, cb)
2426		4691
2427	Can be used to change the callback member declaration in each watcher,	4692	Can be used to change the callback member declaration in each watcher,
2428	and the way callbacks are invoked and set. Must expand to a struct member	4693	and the way callbacks are invoked and set. Must expand to a struct member
2429	definition and a statement, respectively. See the F<ev.v> header file for	4694	definition and a statement, respectively. See the F<ev.h> header file for
2430	their default definitions. One possible use for overriding these is to	4695	their default definitions. One possible use for overriding these is to
2431	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4696	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2432	method calls instead of plain function calls in C++.	4697	method calls instead of plain function calls in C++.
		4698
		4699	=back
		4700
		4701	=head2 EXPORTED API SYMBOLS
		4702
		4703	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4704	exported symbols, you can use the provided F<Symbol.*> files which list
		4705	all public symbols, one per line:
		4706
		4707	Symbols.ev for libev proper
		4708	Symbols.event for the libevent emulation
		4709
		4710	This can also be used to rename all public symbols to avoid clashes with
		4711	multiple versions of libev linked together (which is obviously bad in
		4712	itself, but sometimes it is inconvenient to avoid this).
		4713
		4714	A sed command like this will create wrapper C<#define>'s that you need to
		4715	include before including F<ev.h>:
		4716
		4717	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4718
		4719	This would create a file F<wrap.h> which essentially looks like this:
		4720
		4721	#define ev_backend myprefix_ev_backend
		4722	#define ev_check_start myprefix_ev_check_start
		4723	#define ev_check_stop myprefix_ev_check_stop
		4724	...
2433		4725
2434	=head2 EXAMPLES	4726	=head2 EXAMPLES
2435		4727
2436	For a real-world example of a program the includes libev	4728	For a real-world example of a program the includes libev
2437	verbatim, you can have a look at the EV perl module	4729	verbatim, you can have a look at the EV perl module
…		…
2442	file.	4734	file.
2443		4735
2444	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4736	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2445	that everybody includes and which overrides some configure choices:	4737	that everybody includes and which overrides some configure choices:
2446		4738
2447	#define EV_MINIMAL 1	4739	#define EV_FEATURES 8
2448	#define EV_USE_POLL 0	4740	#define EV_USE_SELECT 1
2449	#define EV_MULTIPLICITY 0
2450	#define EV_PERIODIC_ENABLE 0	4741	#define EV_PREPARE_ENABLE 1
		4742	#define EV_IDLE_ENABLE 1
2451	#define EV_STAT_ENABLE 0	4743	#define EV_SIGNAL_ENABLE 1
2452	#define EV_FORK_ENABLE 0	4744	#define EV_CHILD_ENABLE 1
		4745	#define EV_USE_STDEXCEPT 0
2453	#define EV_CONFIG_H <config.h>	4746	#define EV_CONFIG_H <config.h>
2454	#define EV_MINPRI 0
2455	#define EV_MAXPRI 0
2456		4747
2457	#include "ev++.h"	4748	#include "ev++.h"
2458		4749
2459	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4750	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2460		4751
2461	#include "ev_cpp.h"	4752	#include "ev_cpp.h"
2462	#include "ev.c"	4753	#include "ev.c"
2463		4754
		4755	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2464		4756
		4757	=head2 THREADS AND COROUTINES
		4758
		4759	=head3 THREADS
		4760
		4761	All libev functions are reentrant and thread-safe unless explicitly
		4762	documented otherwise, but libev implements no locking itself. This means
		4763	that you can use as many loops as you want in parallel, as long as there
		4764	are no concurrent calls into any libev function with the same loop
		4765	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4766	of course): libev guarantees that different event loops share no data
		4767	structures that need any locking.
		4768
		4769	Or to put it differently: calls with different loop parameters can be done
		4770	concurrently from multiple threads, calls with the same loop parameter
		4771	must be done serially (but can be done from different threads, as long as
		4772	only one thread ever is inside a call at any point in time, e.g. by using
		4773	a mutex per loop).
		4774
		4775	Specifically to support threads (and signal handlers), libev implements
		4776	so-called C<ev_async> watchers, which allow some limited form of
		4777	concurrency on the same event loop, namely waking it up "from the
		4778	outside".
		4779
		4780	If you want to know which design (one loop, locking, or multiple loops
		4781	without or something else still) is best for your problem, then I cannot
		4782	help you, but here is some generic advice:
		4783
		4784	=over 4
		4785
		4786	=item * most applications have a main thread: use the default libev loop
		4787	in that thread, or create a separate thread running only the default loop.
		4788
		4789	This helps integrating other libraries or software modules that use libev
		4790	themselves and don't care/know about threading.
		4791
		4792	=item * one loop per thread is usually a good model.
		4793
		4794	Doing this is almost never wrong, sometimes a better-performance model
		4795	exists, but it is always a good start.
		4796
		4797	=item * other models exist, such as the leader/follower pattern, where one
		4798	loop is handed through multiple threads in a kind of round-robin fashion.
		4799
		4800	Choosing a model is hard - look around, learn, know that usually you can do
		4801	better than you currently do :-)
		4802
		4803	=item * often you need to talk to some other thread which blocks in the
		4804	event loop.
		4805
		4806	C<ev_async> watchers can be used to wake them up from other threads safely
		4807	(or from signal contexts...).
		4808
		4809	An example use would be to communicate signals or other events that only
		4810	work in the default loop by registering the signal watcher with the
		4811	default loop and triggering an C<ev_async> watcher from the default loop
		4812	watcher callback into the event loop interested in the signal.
		4813
		4814	=back
		4815
		4816	See also L<THREAD LOCKING EXAMPLE>.
		4817
		4818	=head3 COROUTINES
		4819
		4820	Libev is very accommodating to coroutines ("cooperative threads"):
		4821	libev fully supports nesting calls to its functions from different
		4822	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4823	different coroutines, and switch freely between both coroutines running
		4824	the loop, as long as you don't confuse yourself). The only exception is
		4825	that you must not do this from C<ev_periodic> reschedule callbacks.
		4826
		4827	Care has been taken to ensure that libev does not keep local state inside
		4828	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4829	they do not call any callbacks.
		4830
		4831	=head2 COMPILER WARNINGS
		4832
		4833	Depending on your compiler and compiler settings, you might get no or a
		4834	lot of warnings when compiling libev code. Some people are apparently
		4835	scared by this.
		4836
		4837	However, these are unavoidable for many reasons. For one, each compiler
		4838	has different warnings, and each user has different tastes regarding
		4839	warning options. "Warn-free" code therefore cannot be a goal except when
		4840	targeting a specific compiler and compiler-version.
		4841
		4842	Another reason is that some compiler warnings require elaborate
		4843	workarounds, or other changes to the code that make it less clear and less
		4844	maintainable.
		4845
		4846	And of course, some compiler warnings are just plain stupid, or simply
		4847	wrong (because they don't actually warn about the condition their message
		4848	seems to warn about). For example, certain older gcc versions had some
		4849	warnings that resulted in an extreme number of false positives. These have
		4850	been fixed, but some people still insist on making code warn-free with
		4851	such buggy versions.
		4852
		4853	While libev is written to generate as few warnings as possible,
		4854	"warn-free" code is not a goal, and it is recommended not to build libev
		4855	with any compiler warnings enabled unless you are prepared to cope with
		4856	them (e.g. by ignoring them). Remember that warnings are just that:
		4857	warnings, not errors, or proof of bugs.
		4858
		4859
		4860	=head2 VALGRIND
		4861
		4862	Valgrind has a special section here because it is a popular tool that is
		4863	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4864
		4865	If you think you found a bug (memory leak, uninitialised data access etc.)
		4866	in libev, then check twice: If valgrind reports something like:
		4867
		4868	==2274== definitely lost: 0 bytes in 0 blocks.
		4869	==2274== possibly lost: 0 bytes in 0 blocks.
		4870	==2274== still reachable: 256 bytes in 1 blocks.
		4871
		4872	Then there is no memory leak, just as memory accounted to global variables
		4873	is not a memleak - the memory is still being referenced, and didn't leak.
		4874
		4875	Similarly, under some circumstances, valgrind might report kernel bugs
		4876	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4877	although an acceptable workaround has been found here), or it might be
		4878	confused.
		4879
		4880	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4881	make it into some kind of religion.
		4882
		4883	If you are unsure about something, feel free to contact the mailing list
		4884	with the full valgrind report and an explanation on why you think this
		4885	is a bug in libev (best check the archives, too :). However, don't be
		4886	annoyed when you get a brisk "this is no bug" answer and take the chance
		4887	of learning how to interpret valgrind properly.
		4888
		4889	If you need, for some reason, empty reports from valgrind for your project
		4890	I suggest using suppression lists.
		4891
		4892
		4893	=head1 PORTABILITY NOTES
		4894
		4895	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4896
		4897	GNU/Linux is the only common platform that supports 64 bit file/large file
		4898	interfaces but I<disables> them by default.
		4899
		4900	That means that libev compiled in the default environment doesn't support
		4901	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4902
		4903	Unfortunately, many programs try to work around this GNU/Linux issue
		4904	by enabling the large file API, which makes them incompatible with the
		4905	standard libev compiled for their system.
		4906
		4907	Likewise, libev cannot enable the large file API itself as this would
		4908	suddenly make it incompatible to the default compile time environment,
		4909	i.e. all programs not using special compile switches.
		4910
		4911	=head2 OS/X AND DARWIN BUGS
		4912
		4913	The whole thing is a bug if you ask me - basically any system interface
		4914	you touch is broken, whether it is locales, poll, kqueue or even the
		4915	OpenGL drivers.
		4916
		4917	=head3 C<kqueue> is buggy
		4918
		4919	The kqueue syscall is broken in all known versions - most versions support
		4920	only sockets, many support pipes.
		4921
		4922	Libev tries to work around this by not using C<kqueue> by default on this
		4923	rotten platform, but of course you can still ask for it when creating a
		4924	loop - embedding a socket-only kqueue loop into a select-based one is
		4925	probably going to work well.
		4926
		4927	=head3 C<poll> is buggy
		4928
		4929	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4930	implementation by something calling C<kqueue> internally around the 10.5.6
		4931	release, so now C<kqueue> I<and> C<poll> are broken.
		4932
		4933	Libev tries to work around this by not using C<poll> by default on
		4934	this rotten platform, but of course you can still ask for it when creating
		4935	a loop.
		4936
		4937	=head3 C<select> is buggy
		4938
		4939	All that's left is C<select>, and of course Apple found a way to fuck this
		4940	one up as well: On OS/X, C<select> actively limits the number of file
		4941	descriptors you can pass in to 1024 - your program suddenly crashes when
		4942	you use more.
		4943
		4944	There is an undocumented "workaround" for this - defining
		4945	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4946	work on OS/X.
		4947
		4948	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4949
		4950	=head3 C<errno> reentrancy
		4951
		4952	The default compile environment on Solaris is unfortunately so
		4953	thread-unsafe that you can't even use components/libraries compiled
		4954	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4955	defined by default. A valid, if stupid, implementation choice.
		4956
		4957	If you want to use libev in threaded environments you have to make sure
		4958	it's compiled with C<_REENTRANT> defined.
		4959
		4960	=head3 Event port backend
		4961
		4962	The scalable event interface for Solaris is called "event
		4963	ports". Unfortunately, this mechanism is very buggy in all major
		4964	releases. If you run into high CPU usage, your program freezes or you get
		4965	a large number of spurious wakeups, make sure you have all the relevant
		4966	and latest kernel patches applied. No, I don't know which ones, but there
		4967	are multiple ones to apply, and afterwards, event ports actually work
		4968	great.
		4969
		4970	If you can't get it to work, you can try running the program by setting
		4971	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4972	C<select> backends.
		4973
		4974	=head2 AIX POLL BUG
		4975
		4976	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4977	this by trying to avoid the poll backend altogether (i.e. it's not even
		4978	compiled in), which normally isn't a big problem as C<select> works fine
		4979	with large bitsets on AIX, and AIX is dead anyway.
		4980
		4981	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4982
		4983	=head3 General issues
		4984
		4985	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4986	requires, and its I/O model is fundamentally incompatible with the POSIX
		4987	model. Libev still offers limited functionality on this platform in
		4988	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4989	descriptors. This only applies when using Win32 natively, not when using
		4990	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4991	as every compiler comes with a slightly differently broken/incompatible
		4992	environment.
		4993
		4994	Lifting these limitations would basically require the full
		4995	re-implementation of the I/O system. If you are into this kind of thing,
		4996	then note that glib does exactly that for you in a very portable way (note
		4997	also that glib is the slowest event library known to man).
		4998
		4999	There is no supported compilation method available on windows except
		5000	embedding it into other applications.
		5001
		5002	Sensible signal handling is officially unsupported by Microsoft - libev
		5003	tries its best, but under most conditions, signals will simply not work.
		5004
		5005	Not a libev limitation but worth mentioning: windows apparently doesn't
		5006	accept large writes: instead of resulting in a partial write, windows will
		5007	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5008	so make sure you only write small amounts into your sockets (less than a
		5009	megabyte seems safe, but this apparently depends on the amount of memory
		5010	available).
		5011
		5012	Due to the many, low, and arbitrary limits on the win32 platform and
		5013	the abysmal performance of winsockets, using a large number of sockets
		5014	is not recommended (and not reasonable). If your program needs to use
		5015	more than a hundred or so sockets, then likely it needs to use a totally
		5016	different implementation for windows, as libev offers the POSIX readiness
		5017	notification model, which cannot be implemented efficiently on windows
		5018	(due to Microsoft monopoly games).
		5019
		5020	A typical way to use libev under windows is to embed it (see the embedding
		5021	section for details) and use the following F<evwrap.h> header file instead
		5022	of F<ev.h>:
		5023
		5024	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5025	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5026
		5027	#include "ev.h"
		5028
		5029	And compile the following F<evwrap.c> file into your project (make sure
		5030	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5031
		5032	#include "evwrap.h"
		5033	#include "ev.c"
		5034
		5035	=head3 The winsocket C<select> function
		5036
		5037	The winsocket C<select> function doesn't follow POSIX in that it
		5038	requires socket I<handles> and not socket I<file descriptors> (it is
		5039	also extremely buggy). This makes select very inefficient, and also
		5040	requires a mapping from file descriptors to socket handles (the Microsoft
		5041	C runtime provides the function C<_open_osfhandle> for this). See the
		5042	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5043	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5044
		5045	The configuration for a "naked" win32 using the Microsoft runtime
		5046	libraries and raw winsocket select is:
		5047
		5048	#define EV_USE_SELECT 1
		5049	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5050
		5051	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5052	complexity in the O(n²) range when using win32.
		5053
		5054	=head3 Limited number of file descriptors
		5055
		5056	Windows has numerous arbitrary (and low) limits on things.
		5057
		5058	Early versions of winsocket's select only supported waiting for a maximum
		5059	of C<64> handles (probably owning to the fact that all windows kernels
		5060	can only wait for C<64> things at the same time internally; Microsoft
		5061	recommends spawning a chain of threads and wait for 63 handles and the
		5062	previous thread in each. Sounds great!).
		5063
		5064	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5065	to some high number (e.g. C<2048>) before compiling the winsocket select
		5066	call (which might be in libev or elsewhere, for example, perl and many
		5067	other interpreters do their own select emulation on windows).
		5068
		5069	Another limit is the number of file descriptors in the Microsoft runtime
		5070	libraries, which by default is C<64> (there must be a hidden I<64>
		5071	fetish or something like this inside Microsoft). You can increase this
		5072	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5073	(another arbitrary limit), but is broken in many versions of the Microsoft
		5074	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5075	(depending on windows version and/or the phase of the moon). To get more,
		5076	you need to wrap all I/O functions and provide your own fd management, but
		5077	the cost of calling select (O(n²)) will likely make this unworkable.
		5078
		5079	=head2 PORTABILITY REQUIREMENTS
		5080
		5081	In addition to a working ISO-C implementation and of course the
		5082	backend-specific APIs, libev relies on a few additional extensions:
		5083
		5084	=over 4
		5085
		5086	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5087	calling conventions regardless of C<ev_watcher_type *>.
		5088
		5089	Libev assumes not only that all watcher pointers have the same internal
		5090	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5091	assumes that the same (machine) code can be used to call any watcher
		5092	callback: The watcher callbacks have different type signatures, but libev
		5093	calls them using an C<ev_watcher *> internally.
		5094
		5095	=item pointer accesses must be thread-atomic
		5096
		5097	Accessing a pointer value must be atomic, it must both be readable and
		5098	writable in one piece - this is the case on all current architectures.
		5099
		5100	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5101
		5102	The type C<sig_atomic_t volatile> (or whatever is defined as
		5103	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5104	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5105	believed to be sufficiently portable.
		5106
		5107	=item C<sigprocmask> must work in a threaded environment
		5108
		5109	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5110	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5111	pthread implementations will either allow C<sigprocmask> in the "main
		5112	thread" or will block signals process-wide, both behaviours would
		5113	be compatible with libev. Interaction between C<sigprocmask> and
		5114	C<pthread_sigmask> could complicate things, however.
		5115
		5116	The most portable way to handle signals is to block signals in all threads
		5117	except the initial one, and run the default loop in the initial thread as
		5118	well.
		5119
		5120	=item C<long> must be large enough for common memory allocation sizes
		5121
		5122	To improve portability and simplify its API, libev uses C<long> internally
		5123	instead of C<size_t> when allocating its data structures. On non-POSIX
		5124	systems (Microsoft...) this might be unexpectedly low, but is still at
		5125	least 31 bits everywhere, which is enough for hundreds of millions of
		5126	watchers.
		5127
		5128	=item C<double> must hold a time value in seconds with enough accuracy
		5129
		5130	The type C<double> is used to represent timestamps. It is required to
		5131	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5132	good enough for at least into the year 4000 with millisecond accuracy
		5133	(the design goal for libev). This requirement is overfulfilled by
		5134	implementations using IEEE 754, which is basically all existing ones.
		5135
		5136	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5137	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5138	is either obsolete or somebody patched it to use C<long double> or
		5139	something like that, just kidding).
		5140
		5141	=back
		5142
		5143	If you know of other additional requirements drop me a note.
		5144
		5145
2465	=head1 COMPLEXITIES	5146	=head1 ALGORITHMIC COMPLEXITIES
2466		5147
2467	In this section the complexities of (many of) the algorithms used inside	5148	In this section the complexities of (many of) the algorithms used inside
2468	libev will be explained. For complexity discussions about backends see the	5149	libev will be documented. For complexity discussions about backends see
2469	documentation for C<ev_default_init>.	5150	the documentation for C<ev_default_init>.
2470		5151
2471	All of the following are about amortised time: If an array needs to be	5152	All of the following are about amortised time: If an array needs to be
2472	extended, libev needs to realloc and move the whole array, but this	5153	extended, libev needs to realloc and move the whole array, but this
2473	happens asymptotically never with higher number of elements, so O(1) might	5154	happens asymptotically rarer with higher number of elements, so O(1) might
2474	mean it might do a lengthy realloc operation in rare cases, but on average	5155	mean that libev does a lengthy realloc operation in rare cases, but on
2475	it is much faster and asymptotically approaches constant time.	5156	average it is much faster and asymptotically approaches constant time.
2476		5157
2477	=over 4	5158	=over 4
2478		5159
2479	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5160	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2480		5161
2481	This means that, when you have a watcher that triggers in one hour and	5162	This means that, when you have a watcher that triggers in one hour and
2482	there are 100 watchers that would trigger before that then inserting will	5163	there are 100 watchers that would trigger before that, then inserting will
2483	have to skip those 100 watchers.	5164	have to skip roughly seven (C<ld 100>) of these watchers.
2484		5165
2485	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	5166	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2486		5167
2487	That means that for changing a timer costs less than removing/adding them	5168	That means that changing a timer costs less than removing/adding them,
2488	as only the relative motion in the event queue has to be paid for.	5169	as only the relative motion in the event queue has to be paid for.
2489		5170
2490	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	5171	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2491		5172
2492	These just add the watcher into an array or at the head of a list.	5173	These just add the watcher into an array or at the head of a list.
		5174
2493	=item Stopping check/prepare/idle watchers: O(1)	5175	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2494		5176
2495	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5177	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2496		5178
2497	These watchers are stored in lists then need to be walked to find the	5179	These watchers are stored in lists, so they need to be walked to find the
2498	correct watcher to remove. The lists are usually short (you don't usually	5180	correct watcher to remove. The lists are usually short (you don't usually
2499	have many watchers waiting for the same fd or signal).	5181	have many watchers waiting for the same fd or signal: one is typical, two
		5182	is rare).
2500		5183
2501	=item Finding the next timer per loop iteration: O(1)	5184	=item Finding the next timer in each loop iteration: O(1)
		5185
		5186	By virtue of using a binary or 4-heap, the next timer is always found at a
		5187	fixed position in the storage array.
2502		5188
2503	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	5189	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2504		5190
2505	A change means an I/O watcher gets started or stopped, which requires	5191	A change means an I/O watcher gets started or stopped, which requires
2506	libev to recalculate its status (and possibly tell the kernel).	5192	libev to recalculate its status (and possibly tell the kernel, depending
		5193	on backend and whether C<ev_io_set> was used).
2507		5194
2508	=item Activating one watcher: O(1)	5195	=item Activating one watcher (putting it into the pending state): O(1)
2509		5196
2510	=item Priority handling: O(number_of_priorities)	5197	=item Priority handling: O(number_of_priorities)
2511		5198
2512	Priorities are implemented by allocating some space for each	5199	Priorities are implemented by allocating some space for each
2513	priority. When doing priority-based operations, libev usually has to	5200	priority. When doing priority-based operations, libev usually has to
2514	linearly search all the priorities.	5201	linearly search all the priorities, but starting/stopping and activating
		5202	watchers becomes O(1) with respect to priority handling.
		5203
		5204	=item Sending an ev_async: O(1)
		5205
		5206	=item Processing ev_async_send: O(number_of_async_watchers)
		5207
		5208	=item Processing signals: O(max_signal_number)
		5209
		5210	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5211	calls in the current loop iteration and the loop is currently
		5212	blocked. Checking for async and signal events involves iterating over all
		5213	running async watchers or all signal numbers.
2515		5214
2516	=back	5215	=back
2517		5216
2518		5217
		5218	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5219
		5220	The major version 4 introduced some incompatible changes to the API.
		5221
		5222	At the moment, the C<ev.h> header file provides compatibility definitions
		5223	for all changes, so most programs should still compile. The compatibility
		5224	layer might be removed in later versions of libev, so better update to the
		5225	new API early than late.
		5226
		5227	=over 4
		5228
		5229	=item C<EV_COMPAT3> backwards compatibility mechanism
		5230
		5231	The backward compatibility mechanism can be controlled by
		5232	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5233	section.
		5234
		5235	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5236
		5237	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5238
		5239	ev_loop_destroy (EV_DEFAULT_UC);
		5240	ev_loop_fork (EV_DEFAULT);
		5241
		5242	=item function/symbol renames
		5243
		5244	A number of functions and symbols have been renamed:
		5245
		5246	ev_loop => ev_run
		5247	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5248	EVLOOP_ONESHOT => EVRUN_ONCE
		5249
		5250	ev_unloop => ev_break
		5251	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5252	EVUNLOOP_ONE => EVBREAK_ONE
		5253	EVUNLOOP_ALL => EVBREAK_ALL
		5254
		5255	EV_TIMEOUT => EV_TIMER
		5256
		5257	ev_loop_count => ev_iteration
		5258	ev_loop_depth => ev_depth
		5259	ev_loop_verify => ev_verify
		5260
		5261	Most functions working on C<struct ev_loop> objects don't have an
		5262	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5263	associated constants have been renamed to not collide with the C<struct
		5264	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5265	as all other watcher types. Note that C<ev_loop_fork> is still called
		5266	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5267	typedef.
		5268
		5269	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5270
		5271	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5272	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5273	and work, but the library code will of course be larger.
		5274
		5275	=back
		5276
		5277
		5278	=head1 GLOSSARY
		5279
		5280	=over 4
		5281
		5282	=item active
		5283
		5284	A watcher is active as long as it has been started and not yet stopped.
		5285	See L<WATCHER STATES> for details.
		5286
		5287	=item application
		5288
		5289	In this document, an application is whatever is using libev.
		5290
		5291	=item backend
		5292
		5293	The part of the code dealing with the operating system interfaces.
		5294
		5295	=item callback
		5296
		5297	The address of a function that is called when some event has been
		5298	detected. Callbacks are being passed the event loop, the watcher that
		5299	received the event, and the actual event bitset.
		5300
		5301	=item callback/watcher invocation
		5302
		5303	The act of calling the callback associated with a watcher.
		5304
		5305	=item event
		5306
		5307	A change of state of some external event, such as data now being available
		5308	for reading on a file descriptor, time having passed or simply not having
		5309	any other events happening anymore.
		5310
		5311	In libev, events are represented as single bits (such as C<EV_READ> or
		5312	C<EV_TIMER>).
		5313
		5314	=item event library
		5315
		5316	A software package implementing an event model and loop.
		5317
		5318	=item event loop
		5319
		5320	An entity that handles and processes external events and converts them
		5321	into callback invocations.
		5322
		5323	=item event model
		5324
		5325	The model used to describe how an event loop handles and processes
		5326	watchers and events.
		5327
		5328	=item pending
		5329
		5330	A watcher is pending as soon as the corresponding event has been
		5331	detected. See L<WATCHER STATES> for details.
		5332
		5333	=item real time
		5334
		5335	The physical time that is observed. It is apparently strictly monotonic :)
		5336
		5337	=item wall-clock time
		5338
		5339	The time and date as shown on clocks. Unlike real time, it can actually
		5340	be wrong and jump forwards and backwards, e.g. when you adjust your
		5341	clock.
		5342
		5343	=item watcher
		5344
		5345	A data structure that describes interest in certain events. Watchers need
		5346	to be started (attached to an event loop) before they can receive events.
		5347
		5348	=back
		5349
2519	=head1 AUTHOR	5350	=head1 AUTHOR
2520		5351
2521	Marc Lehmann <libev@schmorp.de>.	5352	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5353	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
2522		5354

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