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Revision 1.121 by root, Mon Jan 28 12:13:54 2008 UTC vs.
Revision 1.404 by root, Sat Apr 28 12:10:07 2012 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_run's to stop iterating
		32	ev_break (EV_A_ EVBREAK_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
35	struct ev_loop *loop = ev_default_loop (0);	47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = EV_DEFAULT;
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_run (loop, 0);
47		62
		63	// break was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
		90
		91	=head1 ABOUT LIBEV
56		92
57	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occurring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	95	these event sources and provide your program with events.
60		96
…		…
70	=head2 FEATURES	106	=head2 FEATURES
71		107
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
77	(C<ev_signal>), process status change events (C<ev_child>), and event	113	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	115	change events (C<ev_child>), and event watchers dealing with the event
80	file watchers (C<ev_stat>) and even limited support for fork events	116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(C<ev_fork>).	117	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		118	limited support for fork events (C<ev_fork>).
82		119
83	It also is quite fast (see this	120	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	121	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	122	for example).
86		123
87	=head2 CONVENTIONS	124	=head2 CONVENTIONS
88		125
89	Libev is very configurable. In this manual the default configuration will	126	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	127	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	128	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	129	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	130	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	131	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		132	this argument.
95		133
96	=head2 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
97		135
98	Libev represents time as a single floating point number, representing the	136	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	137	the (fractional) number of seconds since the (POSIX) epoch (in practice
100	the beginning of 1970, details are complicated, don't ask). This type is	138	somewhere near the beginning of 1970, details are complicated, don't
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	139	ask). This type is called C<ev_tstamp>, which is what you should use
102	to the C<double> type in C, and when you need to do any calculations on	140	too. It usually aliases to the C<double> type in C. When you need to do
103	it, you should treat it as some floatingpoint value. Unlike the name	141	any calculations on it, you should treat it as some floating point value.
		142
104	component C<stamp> might indicate, it is also used for time differences	143	Unlike the name component C<stamp> might indicate, it is also used for
105	throughout libev.	144	time differences (e.g. delays) throughout libev.
		145
		146	=head1 ERROR HANDLING
		147
		148	Libev knows three classes of errors: operating system errors, usage errors
		149	and internal errors (bugs).
		150
		151	When libev catches an operating system error it cannot handle (for example
		152	a system call indicating a condition libev cannot fix), it calls the callback
		153	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		154	abort. The default is to print a diagnostic message and to call C<abort
		155	()>.
		156
		157	When libev detects a usage error such as a negative timer interval, then
		158	it will print a diagnostic message and abort (via the C<assert> mechanism,
		159	so C<NDEBUG> will disable this checking): these are programming errors in
		160	the libev caller and need to be fixed there.
		161
		162	Libev also has a few internal error-checking C<assert>ions, and also has
		163	extensive consistency checking code. These do not trigger under normal
		164	circumstances, as they indicate either a bug in libev or worse.
		165
106		166
107	=head1 GLOBAL FUNCTIONS	167	=head1 GLOBAL FUNCTIONS
108		168
109	These functions can be called anytime, even before initialising the	169	These functions can be called anytime, even before initialising the
110	library in any way.	170	library in any way.
…		…
113		173
114	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
115		175
116	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
117	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
118	you actually want to know.	178	you actually want to know. Also interesting is the combination of
		179	C<ev_now_update> and C<ev_now>.
119		180
120	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
121		182
122	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
123	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
124	this is a subsecond-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
125		192
126	=item int ev_version_major ()	193	=item int ev_version_major ()
127		194
128	=item int ev_version_minor ()	195	=item int ev_version_minor ()
129		196
…		…
140	as this indicates an incompatible change. Minor versions are usually	207	as this indicates an incompatible change. Minor versions are usually
141	compatible to older versions, so a larger minor version alone is usually	208	compatible to older versions, so a larger minor version alone is usually
142	not a problem.	209	not a problem.
143		210
144	Example: Make sure we haven't accidentally been linked against the wrong	211	Example: Make sure we haven't accidentally been linked against the wrong
145	version.	212	version (note, however, that this will not detect other ABI mismatches,
		213	such as LFS or reentrancy).
146		214
147	assert (("libev version mismatch",	215	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	216	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	217	&& ev_version_minor () >= EV_VERSION_MINOR));
150		218
151	=item unsigned int ev_supported_backends ()	219	=item unsigned int ev_supported_backends ()
152		220
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	221	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	222	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	224	a description of the set values.
157		225
158	Example: make sure we have the epoll method, because yeah this is cool and	226	Example: make sure we have the epoll method, because yeah this is cool and
159	a must have and can we have a torrent of it please!!!11	227	a must have and can we have a torrent of it please!!!11
160		228
161	assert (("sorry, no epoll, no sex",	229	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	230	ev_supported_backends () & EVBACKEND_EPOLL));
163		231
164	=item unsigned int ev_recommended_backends ()	232	=item unsigned int ev_recommended_backends ()
165		233
166	Return the set of all backends compiled into this binary of libev and also	234	Return the set of all backends compiled into this binary of libev and
167	recommended for this platform. This set is often smaller than the one	235	also recommended for this platform, meaning it will work for most file
		236	descriptor types. This set is often smaller than the one returned by
168	returned by C<ev_supported_backends>, as for example kqueue is broken on	237	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
169	most BSDs and will not be autodetected unless you explicitly request it	238	and will not be auto-detected unless you explicitly request it (assuming
170	(assuming you know what you are doing). This is the set of backends that	239	you know what you are doing). This is the set of backends that libev will
171	libev will probe for if you specify no backends explicitly.	240	probe for if you specify no backends explicitly.
172		241
173	=item unsigned int ev_embeddable_backends ()	242	=item unsigned int ev_embeddable_backends ()
174		243
175	Returns the set of backends that are embeddable in other event loops. This	244	Returns the set of backends that are embeddable in other event loops. This
176	is the theoretical, all-platform, value. To find which backends	245	value is platform-specific but can include backends not available on the
177	might be supported on the current system, you would need to look at	246	current system. To find which embeddable backends might be supported on
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	247	the current system, you would need to look at C<ev_embeddable_backends ()
179	recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
180		249
181	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
182		251
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
184		253
185	Sets the allocation function to use (the prototype is similar - the	254	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	255	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
187	allocate and free memory (no surprises here). If it returns zero when	256	used to allocate and free memory (no surprises here). If it returns zero
188	memory needs to be allocated, the library might abort or take some	257	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	258	or take some potentially destructive action.
190	function.	259
		260	Since some systems (at least OpenBSD and Darwin) fail to implement
		261	correct C<realloc> semantics, libev will use a wrapper around the system
		262	C<realloc> and C<free> functions by default.
191		263
192	You could override this function in high-availability programs to, say,	264	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	265	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	266	or even to sleep a while and retry until some memory is available.
195		267
196	Example: Replace the libev allocator with one that waits a bit and then	268	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	269	retries (example requires a standards-compliant C<realloc>).
198		270
199	static void *	271	static void *
200	persistent_realloc (void *ptr, size_t size)	272	persistent_realloc (void *ptr, size_t size)
201	{	273	{
202	for (;;)	274	for (;;)
…		…
211	}	283	}
212		284
213	...	285	...
214	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
215		287
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	288	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
217		289
218	Set the callback function to call on a retryable syscall error (such	290	Set the callback function to call on a retryable system call error (such
219	as failed select, poll, epoll_wait). The message is a printable string	291	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
221	callback is set, then libev will expect it to remedy the sitution, no	293	callback is set, then libev will expect it to remedy the situation, no
222	matter what, when it returns. That is, libev will generally retry the	294	matter what, when it returns. That is, libev will generally retry the
223	requested operation, or, if the condition doesn't go away, do bad stuff	295	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	296	(such as abort).
225		297
226	Example: This is basically the same thing that libev does internally, too.	298	Example: This is basically the same thing that libev does internally, too.
…		…
233	}	305	}
234		306
235	...	307	...
236	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
237		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
238	=back	323	=back
239		324
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
241		326
242	An event loop is described by a C<struct ev_loop *>. The library knows two	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
243	types of such loops, the I<default> loop, which supports signals and child	328	I<not> optional in this case unless libev 3 compatibility is disabled, as
244	events, and dynamically created loops which do not.	329	libev 3 had an C<ev_loop> function colliding with the struct name).
245		330
246	If you use threads, a common model is to run the default event loop	331	The library knows two types of such loops, the I<default> loop, which
247	in your main thread (or in a separate thread) and for each thread you	332	supports child process events, and dynamically created event loops which
248	create, you also create another event loop. Libev itself does no locking	333	do not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		334
253	=over 4	335	=over 4
254		336
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		338
257	This will initialise the default event loop if it hasn't been initialised	339	This returns the "default" event loop object, which is what you should
258	yet and return it. If the default loop could not be initialised, returns	340	normally use when you just need "the event loop". Event loop objects and
259	false. If it already was initialised it simply returns it (and ignores the	341	the C<flags> parameter are described in more detail in the entry for
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	342	C<ev_loop_new>.
		343
		344	If the default loop is already initialised then this function simply
		345	returns it (and ignores the flags. If that is troubling you, check
		346	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		347	flags, which should almost always be C<0>, unless the caller is also the
		348	one calling C<ev_run> or otherwise qualifies as "the main program".
261		349
262	If you don't know what event loop to use, use the one returned from this	350	If you don't know what event loop to use, use the one returned from this
263	function.	351	function (or via the C<EV_DEFAULT> macro).
264		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
265	The default loop is the only loop that can handle C<ev_signal> and	358	The default loop is the only loop that can handle C<ev_child> watchers,
266	C<ev_child> watchers, and to do this, it always registers a handler	359	and to do this, it always registers a handler for C<SIGCHLD>. If this is
267	for C<SIGCHLD>. If this is a problem for your app you can either	360	a problem for your application you can either create a dynamic loop with
268	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	361	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
269	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	362	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
270	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.
271		382
272	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
273	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>).
274		385
275	The following flags are supported:	386	The following flags are supported:
…		…
281	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
282	thing, believe me).	393	thing, believe me).
283		394
284	=item C<EVFLAG_NOENV>	395	=item C<EVFLAG_NOENV>
285		396
286	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
287	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
288	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	399	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
289	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
290	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
291	around bugs.	402	around bugs.
292		403
293	=item C<EVFLAG_FORKCHECK>	404	=item C<EVFLAG_FORKCHECK>
294		405
295	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
296	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.
297	enabling this flag.
298		408
299	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,
300	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
301	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
302	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
303	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
304	C<pthread_atfork> which is even faster).	414	C<pthread_atfork> which is even faster).
305		415
306	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
307	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
308	flag.	418	flag.
309		419
310	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>
311	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.
312		457
313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
314		459
315	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
316	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,
317	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
318	using this backend. It doesn't scale too well (O(highest_fd)), but its	463	using this backend. It doesn't scale too well (O(highest_fd)), but its
319	usually the fastest backend for a low number of (low-numbered :) fds.	464	usually the fastest backend for a low number of (low-numbered :) fds.
320		465
321	To get good performance out of this backend you need a high amount of	466	To get good performance out of this backend you need a high amount of
322	parallelity (most of the file descriptors should be busy). If you are	467	parallelism (most of the file descriptors should be busy). If you are
323	writing a server, you should C<accept ()> in a loop to accept as many	468	writing a server, you should C<accept ()> in a loop to accept as many
324	connections as possible during one iteration. You might also want to have	469	connections as possible during one iteration. You might also want to have
325	a look at C<ev_set_io_collect_interval ()> to increase the amount of	470	a look at C<ev_set_io_collect_interval ()> to increase the amount of
326	readyness notifications you get per iteration.	471	readiness notifications you get per iteration.
		472
		473	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		474	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		475	C<exceptfds> set on that platform).
327		476
328	=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)
329		478
330	And this is your standard poll(2) backend. It's more complicated	479	And this is your standard poll(2) backend. It's more complicated
331	than select, but handles sparse fds better and has no artificial	480	than select, but handles sparse fds better and has no artificial
332	limit on the number of fds you can use (except it will slow down	481	limit on the number of fds you can use (except it will slow down
333	considerably with a lot of inactive fds). It scales similarly to select,	482	considerably with a lot of inactive fds). It scales similarly to select,
334	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	483	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
335	performance tips.	484	performance tips.
336		485
		486	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		487	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		488
337	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
338		490
		491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		492	kernels).
		493
339	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
340	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
341	like O(total_fds) where n is the total number of fds (or the highest fd),	496	O(total_fds) where total_fds is the total number of fds (or the highest
342	epoll scales either O(1) or O(active_fds). The epoll design has a number	497	fd), epoll scales either O(1) or O(active_fds).
343	of shortcomings, such as silently dropping events in some hard-to-detect	498
344	cases and rewiring a syscall per fd change, no fork support and bad	499	The epoll mechanism deserves honorable mention as the most misdesigned
345	support for dup.	500	of the more advanced event mechanisms: mere annoyances include silently
		501	dropping file descriptors, requiring a system call per change per file
		502	descriptor (and unnecessary guessing of parameters), problems with dup,
		503	returning before the timeout value, resulting in additional iterations
		504	(and only giving 5ms accuracy while select on the same platform gives
		505	0.1ms) and so on. The biggest issue is fork races, however - if a program
		506	forks then I<both> parent and child process have to recreate the epoll
		507	set, which can take considerable time (one syscall per file descriptor)
		508	and is of course hard to detect.
		509
		510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		511	but of course I<doesn't>, and epoll just loves to report events for
		512	totally I<different> file descriptors (even already closed ones, so
		513	one cannot even remove them from the set) than registered in the set
		514	(especially on SMP systems). Libev tries to counter these spurious
		515	notifications by employing an additional generation counter and comparing
		516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
		520	not least, it also refuses to work with some file descriptors which work
		521	perfectly fine with C<select> (files, many character devices...).
		522
		523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
346		526
347	While stopping, setting and starting an I/O watcher in the same iteration	527	While stopping, setting and starting an I/O watcher in the same iteration
348	will result in some caching, there is still a syscall per such incident	528	will result in some caching, there is still a system call per such
349	(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
350	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
351	very well if you register events for both fds.	531	file descriptors might not work very well if you register events for both
352		532	file descriptors.
353	Please note that epoll sometimes generates spurious notifications, so you
354	need to use non-blocking I/O or other means to avoid blocking when no data
355	(or space) is available.
356		533
357	Best performance from this backend is achieved by not unregistering all	534	Best performance from this backend is achieved by not unregistering all
358	watchers for a file descriptor until it has been closed, if possible, i.e.	535	watchers for a file descriptor until it has been closed, if possible,
359	keep at least one watcher active per fd at all times.	536	i.e. keep at least one watcher active per fd at all times. Stopping and
		537	starting a watcher (without re-setting it) also usually doesn't cause
		538	extra overhead. A fork can both result in spurious notifications as well
		539	as in libev having to destroy and recreate the epoll object, which can
		540	take considerable time and thus should be avoided.
360		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
361	While nominally embeddeble in other event loops, this feature is broken in	546	While nominally embeddable in other event loops, this feature is broken in
362	all kernel versions tested so far.	547	all kernel versions tested so far.
		548
		549	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		550	C<EVBACKEND_POLL>.
363		551
364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	552	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
365		553
366	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
367	was broken on all BSDs except NetBSD (usually it doesn't work reliably	555	was broken on all BSDs except NetBSD (usually it doesn't work reliably
368	with anything but sockets and pipes, except on Darwin, where of course	556	with anything but sockets and pipes, except on Darwin, where of course
369	it's completely useless). For this reason it's not being "autodetected"	557	it's completely useless). Unlike epoll, however, whose brokenness
		558	is by design, these kqueue bugs can (and eventually will) be fixed
		559	without API changes to existing programs. For this reason it's not being
370	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
371	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	561	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
372	system like NetBSD.	562	system like NetBSD.
373		563
374	You still can embed kqueue into a normal poll or select backend and use it	564	You still can embed kqueue into a normal poll or select backend and use it
375	only for sockets (after having made sure that sockets work with kqueue on	565	only for sockets (after having made sure that sockets work with kqueue on
376	the target platform). See C<ev_embed> watchers for more info.	566	the target platform). See C<ev_embed> watchers for more info.
377		567
378	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
379	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
380	course). While stopping, setting and starting an I/O watcher does never	570	course). While stopping, setting and starting an I/O watcher does never
381	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
382	two event changes per incident, support for C<fork ()> is very bad and it	572	two event changes per incident. Support for C<fork ()> is very bad (you
		573	might have to leak fd's on fork, but it's more sane than epoll) and it
383	drops fds silently in similarly hard-to-detect cases.	574	drops fds silently in similarly hard-to-detect cases
384		575
385	This backend usually performs well under most conditions.	576	This backend usually performs well under most conditions.
386		577
387	While nominally embeddable in other event loops, this doesn't work	578	While nominally embeddable in other event loops, this doesn't work
388	everywhere, so you might need to test for this. And since it is broken	579	everywhere, so you might need to test for this. And since it is broken
389	almost everywhere, you should only use it when you have a lot of sockets	580	almost everywhere, you should only use it when you have a lot of sockets
390	(for which it usually works), by embedding it into another event loop	581	(for which it usually works), by embedding it into another event loop
391	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	582	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
392	sockets.	583	also broken on OS X)) and, did I mention it, using it only for sockets.
		584
		585	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		586	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		587	C<NOTE_EOF>.
393		588
394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	589	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
395		590
396	This is not implemented yet (and might never be, unless you send me an	591	This is not implemented yet (and might never be, unless you send me an
397	implementation). According to reports, C</dev/poll> only supports sockets	592	implementation). According to reports, C</dev/poll> only supports sockets
…		…
401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
402		597
403	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
404	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)).
405		600
406	Please note that solaris event ports can deliver a lot of spurious
407	notifications, so you need to use non-blocking I/O or other means to avoid
408	blocking when no data (or space) is available.
409
410	While this backend scales well, it requires one system call per active	601	While this backend scales well, it requires one system call per active
411	file descriptor per loop iteration. For small and medium numbers of file	602	file descriptor per loop iteration. For small and medium numbers of file
412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
413	might perform better.	604	might perform better.
414		605
415	On the positive side, ignoring the spurious readyness notifications, this	606	On the positive side, this backend actually performed fully to
416	backend actually performed to specification in all tests and is fully	607	specification in all tests and is fully embeddable, which is a rare feat
417	embeddable, which is a rare feat among the OS-specific backends.	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>.
418		623
419	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
420		625
421	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
422	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
423	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
424		629
425	It is definitely not recommended to use this flag.	630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
426		639
427	=back	640	=back
428		641
429	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,
430	backends will be tried (in the reverse order as listed here). If none are	643	then only these backends will be tried (in the reverse order as listed
431	specified, all backends in C<ev_recommended_backends ()> will be tried.	644	here). If none are specified, all backends in C<ev_recommended_backends
432		645	()> will be tried.
433	The most typical usage is like this:
434
435	if (!ev_default_loop (0))
436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
437
438	Restrict libev to the select and poll backends, and do not allow
439	environment settings to be taken into account:
440
441	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
442
443	Use whatever libev has to offer, but make sure that kqueue is used if
444	available (warning, breaks stuff, best use only with your own private
445	event loop and only if you know the OS supports your types of fds):
446
447	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
448
449	=item struct ev_loop *ev_loop_new (unsigned int flags)
450
451	Similar to C<ev_default_loop>, but always creates a new event loop that is
452	always distinct from the default loop. Unlike the default loop, it cannot
453	handle signal and child watchers, and attempts to do so will be greeted by
454	undefined behaviour (or a failed assertion if assertions are enabled).
455		646
456	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.
457		648
458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	649	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
459	if (!epoller)	650	if (!epoller)
460	fatal ("no epoll found here, maybe it hides under your chair");	651	fatal ("no epoll found here, maybe it hides under your chair");
461		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
462	=item ev_default_destroy ()	658	=item ev_loop_destroy (loop)
463		659
464	Destroys the default loop again (frees all memory and kernel state	660	Destroys an event loop object (frees all memory and kernel state
465	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
466	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
467	responsibility to either stop all watchers cleanly yoursef I<before>	663	responsibility to either stop all watchers cleanly yourself I<before>
468	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
469	the easiest thing, you can just ignore the watchers and/or C<free ()> them	665	the easiest thing, you can just ignore the watchers and/or C<free ()> them
470	for example).	666	for example).
471		667
472	Note that certain global state, such as signal state, will not be freed by	668	Note that certain global state, such as signal state (and installed signal
473	this function, and related watchers (such as signal and child watchers)	669	handlers), will not be freed by this function, and related watchers (such
474	would need to be stopped manually.	670	as signal and child watchers) would need to be stopped manually.
475		671
476	In general it is not advisable to call this function except in the	672	This function is normally used on loop objects allocated by
477	rare occasion where you really need to free e.g. the signal handling	673	C<ev_loop_new>, but it can also be used on the default loop returned by
		674	C<ev_default_loop>, in which case it is not thread-safe.
		675
		676	Note that it is not advisable to call this function on the default loop
		677	except in the rare occasion where you really need to free its resources.
478	pipe fds. If you need dynamically allocated loops it is better to use	678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
479	C<ev_loop_new> and C<ev_loop_destroy>).	679	and C<ev_loop_destroy>.
480		680
481	=item ev_loop_destroy (loop)	681	=item ev_loop_fork (loop)
482		682
483	Like C<ev_default_destroy>, but destroys an event loop created by an
484	earlier call to C<ev_loop_new>.
485
486	=item ev_default_fork ()
487
488	This function sets a flag that causes subsequent C<ev_loop> iterations	683	This function sets a flag that causes subsequent C<ev_run> iterations to
489	to reinitialise the kernel state for backends that have one. Despite the	684	reinitialise the kernel state for backends that have one. Despite the
490	name, you can call it anytime, but it makes most sense after forking, in	685	name, you can call it anytime, but it makes most sense after forking, in
491	the child process (or both child and parent, but that again makes little	686	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
492	sense). You I<must> call it in the child before using any of the libev	687	child before resuming or calling C<ev_run>.
493	functions, and it will only take effect at the next C<ev_loop> iteration.	688
		689	Again, you I<have> to call it on I<any> loop that you want to re-use after
		690	a fork, I<even if you do not plan to use the loop in the parent>. This is
		691	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		692	during fork.
494		693
495	On the other hand, you only need to call this function in the child	694	On the other hand, you only need to call this function in the child
496	process if and only if you want to use the event library in the child. If	695	process if and only if you want to use the event loop in the child. If
497	you just fork+exec, you don't have to call it at all.	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).
498		700
499	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
500	it just in case after a fork. To make this easy, the function will fit in	702	it just in case after a fork.
501	quite nicely into a call to C<pthread_atfork>:
502		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	...
503	pthread_atfork (0, 0, ev_default_fork);	714	pthread_atfork (0, 0, post_fork_child);
504		715
505	=item ev_loop_fork (loop)	716	=item int ev_is_default_loop (loop)
506		717
507	Like C<ev_default_fork>, but acts on an event loop created by	718	Returns true when the given loop is, in fact, the default loop, and false
508	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	719	otherwise.
509	after fork, and how you do this is entirely your own problem.
510		720
511	=item unsigned int ev_loop_count (loop)	721	=item unsigned int ev_iteration (loop)
512		722
513	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
514	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>
515	happily wraps around with enough iterations.	725	and happily wraps around with enough iterations.
516		726
517	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
518	"ticks" the number of loop iterations), as it roughly corresponds with	728	"ticks" the number of loop iterations), as it roughly corresponds with
519	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.
520		745
521	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
522		747
523	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
524	use.	749	use.
…		…
529	received events and started processing them. This timestamp does not	754	received events and started processing them. This timestamp does not
530	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
531	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
532	event occurring (or more correctly, libev finding out about it).	757	event occurring (or more correctly, libev finding out about it).
533		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
534	=item ev_loop (loop, int flags)	797	=item bool ev_run (loop, int flags)
535		798
536	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
537	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
538	events.	801	handling events. It will ask the operating system for any new events, call
		802	the watcher callbacks, and then repeat the whole process indefinitely: This
		803	is why event loops are called I<loops>.
539		804
540	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
541	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.
542		808
		809	The return value is false if there are no more active watchers (which
		810	usually means "all jobs done" or "deadlock"), and true in all other cases
		811	(which usually means " you should call C<ev_run> again").
		812
543	Please note that an explicit C<ev_unloop> is usually better than	813	Please note that an explicit C<ev_break> is usually better than
544	relying on all watchers to be stopped when deciding when a program has	814	relying on all watchers to be stopped when deciding when a program has
545	finished (especially in interactive programs), but having a program that	815	finished (especially in interactive programs), but having a program
546	automatically loops as long as it has to and no longer by virtue of	816	that automatically loops as long as it has to and no longer by virtue
547	relying on its watchers stopping correctly is a thing of beauty.	817	of relying on its watchers stopping correctly, that is truly a thing of
		818	beauty.
548		819
		820	This function is I<mostly> exception-safe - you can break out of a
		821	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		822	exception and so on. This does not decrement the C<ev_depth> value, nor
		823	will it clear any outstanding C<EVBREAK_ONE> breaks.
		824
549	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	825	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
550	those events and any outstanding ones, but will not block your process in	826	those events and any already outstanding ones, but will not wait and
551	case there are no events and will return after one iteration of the loop.	827	block your process in case there are no events and will return after one
		828	iteration of the loop. This is sometimes useful to poll and handle new
		829	events while doing lengthy calculations, to keep the program responsive.
552		830
553	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	831	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
554	neccessary) and will handle those and any outstanding ones. It will block	832	necessary) and will handle those and any already outstanding ones. It
555	your process until at least one new event arrives, and will return after	833	will block your process until at least one new event arrives (which could
556	one iteration of the loop. This is useful if you are waiting for some	834	be an event internal to libev itself, so there is no guarantee that a
557	external event in conjunction with something not expressible using other	835	user-registered callback will be called), and will return after one
		836	iteration of the loop.
		837
		838	This is useful if you are waiting for some external event in conjunction
		839	with something not expressible using other libev watchers (i.e. "roll your
558	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	840	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
559	usually a better approach for this kind of thing.	841	usually a better approach for this kind of thing.
560		842
561	Here are the gory details of what C<ev_loop> does:	843	Here are the gory details of what C<ev_run> does (this is for your
		844	understanding, not a guarantee that things will work exactly like this in
		845	future versions):
562		846
		847	- Increment loop depth.
		848	- Reset the ev_break status.
563	- Before the first iteration, call any pending watchers.	849	- Before the first iteration, call any pending watchers.
		850	LOOP:
564	* If EVFLAG_FORKCHECK was used, check for a fork.	851	- If EVFLAG_FORKCHECK was used, check for a fork.
565	- If a fork was detected, queue and call all fork watchers.	852	- If a fork was detected (by any means), queue and call all fork watchers.
566	- Queue and call all prepare watchers.	853	- Queue and call all prepare watchers.
		854	- If ev_break was called, goto FINISH.
567	- If we have been forked, recreate the kernel state.	855	- If we have been forked, detach and recreate the kernel state
		856	as to not disturb the other process.
568	- Update the kernel state with all outstanding changes.	857	- Update the kernel state with all outstanding changes.
569	- Update the "event loop time".	858	- Update the "event loop time" (ev_now ()).
570	- Calculate for how long to sleep or block, if at all	859	- Calculate for how long to sleep or block, if at all
571	(active idle watchers, EVLOOP_NONBLOCK or not having	860	(active idle watchers, EVRUN_NOWAIT or not having
572	any active watchers at all will result in not sleeping).	861	any active watchers at all will result in not sleeping).
573	- Sleep if the I/O and timer collect interval say so.	862	- Sleep if the I/O and timer collect interval say so.
		863	- Increment loop iteration counter.
574	- Block the process, waiting for any events.	864	- Block the process, waiting for any events.
575	- Queue all outstanding I/O (fd) events.	865	- Queue all outstanding I/O (fd) events.
576	- Update the "event loop time" and do time jump handling.	866	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
577	- Queue all outstanding timers.	867	- Queue all expired timers.
578	- Queue all outstanding periodics.	868	- Queue all expired periodics.
579	- If no events are pending now, queue all idle watchers.	869	- Queue all idle watchers with priority higher than that of pending events.
580	- Queue all check watchers.	870	- Queue all check watchers.
581	- Call all queued watchers in reverse order (i.e. check watchers first).	871	- Call all queued watchers in reverse order (i.e. check watchers first).
582	Signals and child watchers are implemented as I/O watchers, and will	872	Signals and child watchers are implemented as I/O watchers, and will
583	be handled here by queueing them when their watcher gets executed.	873	be handled here by queueing them when their watcher gets executed.
584	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	874	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
585	were used, or there are no active watchers, return, otherwise	875	were used, or there are no active watchers, goto FINISH, otherwise
586	continue with step *.	876	continue with step LOOP.
		877	FINISH:
		878	- Reset the ev_break status iff it was EVBREAK_ONE.
		879	- Decrement the loop depth.
		880	- Return.
587		881
588	Example: Queue some jobs and then loop until no events are outstanding	882	Example: Queue some jobs and then loop until no events are outstanding
589	anymore.	883	anymore.
590		884
591	... queue jobs here, make sure they register event watchers as long	885	... queue jobs here, make sure they register event watchers as long
592	... as they still have work to do (even an idle watcher will do..)	886	... as they still have work to do (even an idle watcher will do..)
593	ev_loop (my_loop, 0);	887	ev_run (my_loop, 0);
594	... jobs done. yeah!	888	... jobs done or somebody called break. yeah!
595		889
596	=item ev_unloop (loop, how)	890	=item ev_break (loop, how)
597		891
598	Can be used to make a call to C<ev_loop> return early (but only after it	892	Can be used to make a call to C<ev_run> return early (but only after it
599	has processed all outstanding events). The C<how> argument must be either	893	has processed all outstanding events). The C<how> argument must be either
600	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	894	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
601	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	895	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
602		896
603	This "unloop state" will be cleared when entering C<ev_loop> again.	897	This "break state" will be cleared on the next call to C<ev_run>.
		898
		899	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		900	which case it will have no effect.
604		901
605	=item ev_ref (loop)	902	=item ev_ref (loop)
606		903
607	=item ev_unref (loop)	904	=item ev_unref (loop)
608		905
609	Ref/unref can be used to add or remove a reference count on the event	906	Ref/unref can be used to add or remove a reference count on the event
610	loop: Every watcher keeps one reference, and as long as the reference	907	loop: Every watcher keeps one reference, and as long as the reference
611	count is nonzero, C<ev_loop> will not return on its own. If you have	908	count is nonzero, C<ev_run> will not return on its own.
612	a watcher you never unregister that should not keep C<ev_loop> from	909
613	returning, ev_unref() after starting, and ev_ref() before stopping it. For	910	This is useful when you have a watcher that you never intend to
		911	unregister, but that nevertheless should not keep C<ev_run> from
		912	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		913	before stopping it.
		914
614	example, libev itself uses this for its internal signal pipe: It is not	915	As an example, libev itself uses this for its internal signal pipe: It
615	visible to the libev user and should not keep C<ev_loop> from exiting if	916	is not visible to the libev user and should not keep C<ev_run> from
616	no event watchers registered by it are active. It is also an excellent	917	exiting if no event watchers registered by it are active. It is also an
617	way to do this for generic recurring timers or from within third-party	918	excellent way to do this for generic recurring timers or from within
618	libraries. Just remember to I<unref after start> and I<ref before stop>	919	third-party libraries. Just remember to I<unref after start> and I<ref
619	(but only if the watcher wasn't active before, or was active before,	920	before stop> (but only if the watcher wasn't active before, or was active
620	respectively).	921	before, respectively. Note also that libev might stop watchers itself
		922	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		923	in the callback).
621		924
622	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	925	Example: Create a signal watcher, but keep it from keeping C<ev_run>
623	running when nothing else is active.	926	running when nothing else is active.
624		927
625	struct ev_signal exitsig;	928	ev_signal exitsig;
626	ev_signal_init (&exitsig, sig_cb, SIGINT);	929	ev_signal_init (&exitsig, sig_cb, SIGINT);
627	ev_signal_start (loop, &exitsig);	930	ev_signal_start (loop, &exitsig);
628	evf_unref (loop);	931	ev_unref (loop);
629		932
630	Example: For some weird reason, unregister the above signal handler again.	933	Example: For some weird reason, unregister the above signal handler again.
631		934
632	ev_ref (loop);	935	ev_ref (loop);
633	ev_signal_stop (loop, &exitsig);	936	ev_signal_stop (loop, &exitsig);
634		937
635	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	938	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
636		939
637	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	940	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
638		941
639	These advanced functions influence the time that libev will spend waiting	942	These advanced functions influence the time that libev will spend waiting
640	for events. Both are by default C<0>, meaning that libev will try to	943	for events. Both time intervals are by default C<0>, meaning that libev
641	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	944	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		945	latency.
642		946
643	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	947	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
644	allows libev to delay invocation of I/O and timer/periodic callbacks to	948	allows libev to delay invocation of I/O and timer/periodic callbacks
645	increase efficiency of loop iterations.	949	to increase efficiency of loop iterations (or to increase power-saving
		950	opportunities).
646		951
647	The background is that sometimes your program runs just fast enough to	952	The idea is that sometimes your program runs just fast enough to handle
648	handle one (or very few) event(s) per loop iteration. While this makes	953	one (or very few) event(s) per loop iteration. While this makes the
649	the program responsive, it also wastes a lot of CPU time to poll for new	954	program responsive, it also wastes a lot of CPU time to poll for new
650	events, especially with backends like C<select ()> which have a high	955	events, especially with backends like C<select ()> which have a high
651	overhead for the actual polling but can deliver many events at once.	956	overhead for the actual polling but can deliver many events at once.
652		957
653	By setting a higher I<io collect interval> you allow libev to spend more	958	By setting a higher I<io collect interval> you allow libev to spend more
654	time collecting I/O events, so you can handle more events per iteration,	959	time collecting I/O events, so you can handle more events per iteration,
655	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	960	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
656	C<ev_timer>) will be not affected. Setting this to a non-null value will	961	C<ev_timer>) will not be affected. Setting this to a non-null value will
657	introduce an additional C<ev_sleep ()> call into most loop iterations.	962	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		963	sleep time ensures that libev will not poll for I/O events more often then
		964	once per this interval, on average (as long as the host time resolution is
		965	good enough).
658		966
659	Likewise, by setting a higher I<timeout collect interval> you allow libev	967	Likewise, by setting a higher I<timeout collect interval> you allow libev
660	to spend more time collecting timeouts, at the expense of increased	968	to spend more time collecting timeouts, at the expense of increased
661	latency (the watcher callback will be called later). C<ev_io> watchers	969	latency/jitter/inexactness (the watcher callback will be called
662	will not be affected. Setting this to a non-null value will not introduce	970	later). C<ev_io> watchers will not be affected. Setting this to a non-null
663	any overhead in libev.	971	value will not introduce any overhead in libev.
664		972
665	Many (busy) programs can usually benefit by setting the io collect	973	Many (busy) programs can usually benefit by setting the I/O collect
666	interval to a value near C<0.1> or so, which is often enough for	974	interval to a value near C<0.1> or so, which is often enough for
667	interactive servers (of course not for games), likewise for timeouts. It	975	interactive servers (of course not for games), likewise for timeouts. It
668	usually doesn't make much sense to set it to a lower value than C<0.01>,	976	usually doesn't make much sense to set it to a lower value than C<0.01>,
669	as this approsaches the timing granularity of most systems.	977	as this approaches the timing granularity of most systems. Note that if
		978	you do transactions with the outside world and you can't increase the
		979	parallelity, then this setting will limit your transaction rate (if you
		980	need to poll once per transaction and the I/O collect interval is 0.01,
		981	then you can't do more than 100 transactions per second).
		982
		983	Setting the I<timeout collect interval> can improve the opportunity for
		984	saving power, as the program will "bundle" timer callback invocations that
		985	are "near" in time together, by delaying some, thus reducing the number of
		986	times the process sleeps and wakes up again. Another useful technique to
		987	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		988	they fire on, say, one-second boundaries only.
		989
		990	Example: we only need 0.1s timeout granularity, and we wish not to poll
		991	more often than 100 times per second:
		992
		993	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		994	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		995
		996	=item ev_invoke_pending (loop)
		997
		998	This call will simply invoke all pending watchers while resetting their
		999	pending state. Normally, C<ev_run> does this automatically when required,
		1000	but when overriding the invoke callback this call comes handy. This
		1001	function can be invoked from a watcher - this can be useful for example
		1002	when you want to do some lengthy calculation and want to pass further
		1003	event handling to another thread (you still have to make sure only one
		1004	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1005
		1006	=item int ev_pending_count (loop)
		1007
		1008	Returns the number of pending watchers - zero indicates that no watchers
		1009	are pending.
		1010
		1011	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1012
		1013	This overrides the invoke pending functionality of the loop: Instead of
		1014	invoking all pending watchers when there are any, C<ev_run> will call
		1015	this callback instead. This is useful, for example, when you want to
		1016	invoke the actual watchers inside another context (another thread etc.).
		1017
		1018	If you want to reset the callback, use C<ev_invoke_pending> as new
		1019	callback.
		1020
		1021	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1022
		1023	Sometimes you want to share the same loop between multiple threads. This
		1024	can be done relatively simply by putting mutex_lock/unlock calls around
		1025	each call to a libev function.
		1026
		1027	However, C<ev_run> can run an indefinite time, so it is not feasible
		1028	to wait for it to return. One way around this is to wake up the event
		1029	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1030	I<release> and I<acquire> callbacks on the loop.
		1031
		1032	When set, then C<release> will be called just before the thread is
		1033	suspended waiting for new events, and C<acquire> is called just
		1034	afterwards.
		1035
		1036	Ideally, C<release> will just call your mutex_unlock function, and
		1037	C<acquire> will just call the mutex_lock function again.
		1038
		1039	While event loop modifications are allowed between invocations of
		1040	C<release> and C<acquire> (that's their only purpose after all), no
		1041	modifications done will affect the event loop, i.e. adding watchers will
		1042	have no effect on the set of file descriptors being watched, or the time
		1043	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1044	to take note of any changes you made.
		1045
		1046	In theory, threads executing C<ev_run> will be async-cancel safe between
		1047	invocations of C<release> and C<acquire>.
		1048
		1049	See also the locking example in the C<THREADS> section later in this
		1050	document.
		1051
		1052	=item ev_set_userdata (loop, void *data)
		1053
		1054	=item void *ev_userdata (loop)
		1055
		1056	Set and retrieve a single C<void *> associated with a loop. When
		1057	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1058	C<0>.
		1059
		1060	These two functions can be used to associate arbitrary data with a loop,
		1061	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1062	C<acquire> callbacks described above, but of course can be (ab-)used for
		1063	any other purpose as well.
		1064
		1065	=item ev_verify (loop)
		1066
		1067	This function only does something when C<EV_VERIFY> support has been
		1068	compiled in, which is the default for non-minimal builds. It tries to go
		1069	through all internal structures and checks them for validity. If anything
		1070	is found to be inconsistent, it will print an error message to standard
		1071	error and call C<abort ()>.
		1072
		1073	This can be used to catch bugs inside libev itself: under normal
		1074	circumstances, this function will never abort as of course libev keeps its
		1075	data structures consistent.
670		1076
671	=back	1077	=back
672		1078
673		1079
674	=head1 ANATOMY OF A WATCHER	1080	=head1 ANATOMY OF A WATCHER
675		1081
		1082	In the following description, uppercase C<TYPE> in names stands for the
		1083	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1084	watchers and C<ev_io_start> for I/O watchers.
		1085
676	A watcher is a structure that you create and register to record your	1086	A watcher is an opaque structure that you allocate and register to record
677	interest in some event. For instance, if you want to wait for STDIN to	1087	your interest in some event. To make a concrete example, imagine you want
678	become readable, you would create an C<ev_io> watcher for that:	1088	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1089	for that:
679		1090
680	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1091	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
681	{	1092	{
682	ev_io_stop (w);	1093	ev_io_stop (w);
683	ev_unloop (loop, EVUNLOOP_ALL);	1094	ev_break (loop, EVBREAK_ALL);
684	}	1095	}
685		1096
686	struct ev_loop *loop = ev_default_loop (0);	1097	struct ev_loop *loop = ev_default_loop (0);
		1098
687	struct ev_io stdin_watcher;	1099	ev_io stdin_watcher;
		1100
688	ev_init (&stdin_watcher, my_cb);	1101	ev_init (&stdin_watcher, my_cb);
689	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1102	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
690	ev_io_start (loop, &stdin_watcher);	1103	ev_io_start (loop, &stdin_watcher);
		1104
691	ev_loop (loop, 0);	1105	ev_run (loop, 0);
692		1106
693	As you can see, you are responsible for allocating the memory for your	1107	As you can see, you are responsible for allocating the memory for your
694	watcher structures (and it is usually a bad idea to do this on the stack,	1108	watcher structures (and it is I<usually> a bad idea to do this on the
695	although this can sometimes be quite valid).	1109	stack).
696		1110
		1111	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1112	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1113
697	Each watcher structure must be initialised by a call to C<ev_init	1114	Each watcher structure must be initialised by a call to C<ev_init (watcher
698	(watcher *, callback)>, which expects a callback to be provided. This	1115	*, callback)>, which expects a callback to be provided. This callback is
699	callback gets invoked each time the event occurs (or, in the case of io	1116	invoked each time the event occurs (or, in the case of I/O watchers, each
700	watchers, each time the event loop detects that the file descriptor given	1117	time the event loop detects that the file descriptor given is readable
701	is readable and/or writable).	1118	and/or writable).
702		1119
703	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1120	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
704	with arguments specific to this watcher type. There is also a macro	1121	macro to configure it, with arguments specific to the watcher type. There
705	to combine initialisation and setting in one call: C<< ev_<type>_init	1122	is also a macro to combine initialisation and setting in one call: C<<
706	(watcher *, callback, ...) >>.	1123	ev_TYPE_init (watcher *, callback, ...) >>.
707		1124
708	To make the watcher actually watch out for events, you have to start it	1125	To make the watcher actually watch out for events, you have to start it
709	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1126	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
710	*) >>), and you can stop watching for events at any time by calling the	1127	*) >>), and you can stop watching for events at any time by calling the
711	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1128	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
712		1129
713	As long as your watcher is active (has been started but not stopped) you	1130	As long as your watcher is active (has been started but not stopped) you
714	must not touch the values stored in it. Most specifically you must never	1131	must not touch the values stored in it. Most specifically you must never
715	reinitialise it or call its C<set> macro.	1132	reinitialise it or call its C<ev_TYPE_set> macro.
716		1133
717	Each and every callback receives the event loop pointer as first, the	1134	Each and every callback receives the event loop pointer as first, the
718	registered watcher structure as second, and a bitset of received events as	1135	registered watcher structure as second, and a bitset of received events as
719	third argument.	1136	third argument.
720		1137
…		…
729	=item C<EV_WRITE>	1146	=item C<EV_WRITE>
730		1147
731	The file descriptor in the C<ev_io> watcher has become readable and/or	1148	The file descriptor in the C<ev_io> watcher has become readable and/or
732	writable.	1149	writable.
733		1150
734	=item C<EV_TIMEOUT>	1151	=item C<EV_TIMER>
735		1152
736	The C<ev_timer> watcher has timed out.	1153	The C<ev_timer> watcher has timed out.
737		1154
738	=item C<EV_PERIODIC>	1155	=item C<EV_PERIODIC>
739		1156
…		…
757		1174
758	=item C<EV_PREPARE>	1175	=item C<EV_PREPARE>
759		1176
760	=item C<EV_CHECK>	1177	=item C<EV_CHECK>
761		1178
762	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1179	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
763	to gather new events, and all C<ev_check> watchers are invoked just after	1180	to gather new events, and all C<ev_check> watchers are invoked just after
764	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1181	C<ev_run> has gathered them, but before it invokes any callbacks for any
765	received events. Callbacks of both watcher types can start and stop as	1182	received events. Callbacks of both watcher types can start and stop as
766	many watchers as they want, and all of them will be taken into account	1183	many watchers as they want, and all of them will be taken into account
767	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1184	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
768	C<ev_loop> from blocking).	1185	C<ev_run> from blocking).
769		1186
770	=item C<EV_EMBED>	1187	=item C<EV_EMBED>
771		1188
772	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1189	The embedded event loop specified in the C<ev_embed> watcher needs attention.
773		1190
774	=item C<EV_FORK>	1191	=item C<EV_FORK>
775		1192
776	The event loop has been resumed in the child process after fork (see	1193	The event loop has been resumed in the child process after fork (see
777	C<ev_fork>).	1194	C<ev_fork>).
778		1195
		1196	=item C<EV_CLEANUP>
		1197
		1198	The event loop is about to be destroyed (see C<ev_cleanup>).
		1199
		1200	=item C<EV_ASYNC>
		1201
		1202	The given async watcher has been asynchronously notified (see C<ev_async>).
		1203
		1204	=item C<EV_CUSTOM>
		1205
		1206	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1207	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1208
779	=item C<EV_ERROR>	1209	=item C<EV_ERROR>
780		1210
781	An unspecified error has occured, the watcher has been stopped. This might	1211	An unspecified error has occurred, the watcher has been stopped. This might
782	happen because the watcher could not be properly started because libev	1212	happen because the watcher could not be properly started because libev
783	ran out of memory, a file descriptor was found to be closed or any other	1213	ran out of memory, a file descriptor was found to be closed or any other
		1214	problem. Libev considers these application bugs.
		1215
784	problem. You best act on it by reporting the problem and somehow coping	1216	You best act on it by reporting the problem and somehow coping with the
785	with the watcher being stopped.	1217	watcher being stopped. Note that well-written programs should not receive
		1218	an error ever, so when your watcher receives it, this usually indicates a
		1219	bug in your program.
786		1220
787	Libev will usually signal a few "dummy" events together with an error,	1221	Libev will usually signal a few "dummy" events together with an error, for
788	for example it might indicate that a fd is readable or writable, and if	1222	example it might indicate that a fd is readable or writable, and if your
789	your callbacks is well-written it can just attempt the operation and cope	1223	callbacks is well-written it can just attempt the operation and cope with
790	with the error from read() or write(). This will not work in multithreaded	1224	the error from read() or write(). This will not work in multi-threaded
791	programs, though, so beware.	1225	programs, though, as the fd could already be closed and reused for another
		1226	thing, so beware.
792		1227
793	=back	1228	=back
794		1229
795	=head2 GENERIC WATCHER FUNCTIONS	1230	=head2 GENERIC WATCHER FUNCTIONS
796
797	In the following description, C<TYPE> stands for the watcher type,
798	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
799		1231
800	=over 4	1232	=over 4
801		1233
802	=item C<ev_init> (ev_TYPE *watcher, callback)	1234	=item C<ev_init> (ev_TYPE *watcher, callback)
803		1235
…		…
809	which rolls both calls into one.	1241	which rolls both calls into one.
810		1242
811	You can reinitialise a watcher at any time as long as it has been stopped	1243	You can reinitialise a watcher at any time as long as it has been stopped
812	(or never started) and there are no pending events outstanding.	1244	(or never started) and there are no pending events outstanding.
813		1245
814	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1246	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
815	int revents)>.	1247	int revents)>.
816		1248
		1249	Example: Initialise an C<ev_io> watcher in two steps.
		1250
		1251	ev_io w;
		1252	ev_init (&w, my_cb);
		1253	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1254
817	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1255	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
818		1256
819	This macro initialises the type-specific parts of a watcher. You need to	1257	This macro initialises the type-specific parts of a watcher. You need to
820	call C<ev_init> at least once before you call this macro, but you can	1258	call C<ev_init> at least once before you call this macro, but you can
821	call C<ev_TYPE_set> any number of times. You must not, however, call this	1259	call C<ev_TYPE_set> any number of times. You must not, however, call this
822	macro on a watcher that is active (it can be pending, however, which is a	1260	macro on a watcher that is active (it can be pending, however, which is a
823	difference to the C<ev_init> macro).	1261	difference to the C<ev_init> macro).
824		1262
825	Although some watcher types do not have type-specific arguments	1263	Although some watcher types do not have type-specific arguments
826	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1264	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
827		1265
		1266	See C<ev_init>, above, for an example.
		1267
828	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1268	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
829		1269
830	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1270	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
831	calls into a single call. This is the most convinient method to initialise	1271	calls into a single call. This is the most convenient method to initialise
832	a watcher. The same limitations apply, of course.	1272	a watcher. The same limitations apply, of course.
833		1273
		1274	Example: Initialise and set an C<ev_io> watcher in one step.
		1275
		1276	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1277
834	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1278	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
835		1279
836	Starts (activates) the given watcher. Only active watchers will receive	1280	Starts (activates) the given watcher. Only active watchers will receive
837	events. If the watcher is already active nothing will happen.	1281	events. If the watcher is already active nothing will happen.
838		1282
		1283	Example: Start the C<ev_io> watcher that is being abused as example in this
		1284	whole section.
		1285
		1286	ev_io_start (EV_DEFAULT_UC, &w);
		1287
839	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1288	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
840		1289
841	Stops the given watcher again (if active) and clears the pending	1290	Stops the given watcher if active, and clears the pending status (whether
		1291	the watcher was active or not).
		1292
842	status. It is possible that stopped watchers are pending (for example,	1293	It is possible that stopped watchers are pending - for example,
843	non-repeating timers are being stopped when they become pending), but	1294	non-repeating timers are being stopped when they become pending - but
844	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1295	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
845	you want to free or reuse the memory used by the watcher it is therefore a	1296	pending. If you want to free or reuse the memory used by the watcher it is
846	good idea to always call its C<ev_TYPE_stop> function.	1297	therefore a good idea to always call its C<ev_TYPE_stop> function.
847		1298
848	=item bool ev_is_active (ev_TYPE *watcher)	1299	=item bool ev_is_active (ev_TYPE *watcher)
849		1300
850	Returns a true value iff the watcher is active (i.e. it has been started	1301	Returns a true value iff the watcher is active (i.e. it has been started
851	and not yet been stopped). As long as a watcher is active you must not modify	1302	and not yet been stopped). As long as a watcher is active you must not modify
…		…
867	=item ev_cb_set (ev_TYPE *watcher, callback)	1318	=item ev_cb_set (ev_TYPE *watcher, callback)
868		1319
869	Change the callback. You can change the callback at virtually any time	1320	Change the callback. You can change the callback at virtually any time
870	(modulo threads).	1321	(modulo threads).
871		1322
872	=item ev_set_priority (ev_TYPE *watcher, priority)	1323	=item ev_set_priority (ev_TYPE *watcher, int priority)
873		1324
874	=item int ev_priority (ev_TYPE *watcher)	1325	=item int ev_priority (ev_TYPE *watcher)
875		1326
876	Set and query the priority of the watcher. The priority is a small	1327	Set and query the priority of the watcher. The priority is a small
877	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1328	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
878	(default: C<-2>). Pending watchers with higher priority will be invoked	1329	(default: C<-2>). Pending watchers with higher priority will be invoked
879	before watchers with lower priority, but priority will not keep watchers	1330	before watchers with lower priority, but priority will not keep watchers
880	from being executed (except for C<ev_idle> watchers).	1331	from being executed (except for C<ev_idle> watchers).
881		1332
882	This means that priorities are I<only> used for ordering callback
883	invocation after new events have been received. This is useful, for
884	example, to reduce latency after idling, or more often, to bind two
885	watchers on the same event and make sure one is called first.
886
887	If you need to suppress invocation when higher priority events are pending	1333	If you need to suppress invocation when higher priority events are pending
888	you need to look at C<ev_idle> watchers, which provide this functionality.	1334	you need to look at C<ev_idle> watchers, which provide this functionality.
889		1335
890	You I<must not> change the priority of a watcher as long as it is active or	1336	You I<must not> change the priority of a watcher as long as it is active or
891	pending.	1337	pending.
892		1338
		1339	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1340	fine, as long as you do not mind that the priority value you query might
		1341	or might not have been clamped to the valid range.
		1342
893	The default priority used by watchers when no priority has been set is	1343	The default priority used by watchers when no priority has been set is
894	always C<0>, which is supposed to not be too high and not be too low :).	1344	always C<0>, which is supposed to not be too high and not be too low :).
895		1345
896	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1346	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
897	fine, as long as you do not mind that the priority value you query might	1347	priorities.
898	or might not have been adjusted to be within valid range.
899		1348
900	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1349	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
901		1350
902	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1351	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
903	C<loop> nor C<revents> need to be valid as long as the watcher callback	1352	C<loop> nor C<revents> need to be valid as long as the watcher callback
904	can deal with that fact.	1353	can deal with that fact, as both are simply passed through to the
		1354	callback.
905		1355
906	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1356	=item int ev_clear_pending (loop, ev_TYPE *watcher)
907		1357
908	If the watcher is pending, this function returns clears its pending status	1358	If the watcher is pending, this function clears its pending status and
909	and returns its C<revents> bitset (as if its callback was invoked). If the	1359	returns its C<revents> bitset (as if its callback was invoked). If the
910	watcher isn't pending it does nothing and returns C<0>.	1360	watcher isn't pending it does nothing and returns C<0>.
911		1361
		1362	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1363	callback to be invoked, which can be accomplished with this function.
		1364
		1365	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1366
		1367	Feeds the given event set into the event loop, as if the specified event
		1368	had happened for the specified watcher (which must be a pointer to an
		1369	initialised but not necessarily started event watcher). Obviously you must
		1370	not free the watcher as long as it has pending events.
		1371
		1372	Stopping the watcher, letting libev invoke it, or calling
		1373	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1374	not started in the first place.
		1375
		1376	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1377	functions that do not need a watcher.
		1378
912	=back	1379	=back
913		1380
		1381	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1382	OWN COMPOSITE WATCHERS> idioms.
914		1383
915	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1384	=head2 WATCHER STATES
916		1385
917	Each watcher has, by default, a member C<void *data> that you can change	1386	There are various watcher states mentioned throughout this manual -
918	and read at any time, libev will completely ignore it. This can be used	1387	active, pending and so on. In this section these states and the rules to
919	to associate arbitrary data with your watcher. If you need more data and	1388	transition between them will be described in more detail - and while these
920	don't want to allocate memory and store a pointer to it in that data	1389	rules might look complicated, they usually do "the right thing".
921	member, you can also "subclass" the watcher type and provide your own
922	data:
923		1390
924	struct my_io	1391	=over 4
925	{
926	struct ev_io io;
927	int otherfd;
928	void *somedata;
929	struct whatever *mostinteresting;
930	}
931		1392
932	And since your callback will be called with a pointer to the watcher, you	1393	=item initialiased
933	can cast it back to your own type:
934		1394
935	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1395	Before a watcher can be registered with the event loop it has to be
936	{	1396	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
937	struct my_io *w = (struct my_io *)w_;	1397	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
938	...
939	}
940		1398
941	More interesting and less C-conformant ways of casting your callback type	1399	In this state it is simply some block of memory that is suitable for
942	instead have been omitted.	1400	use in an event loop. It can be moved around, freed, reused etc. at
		1401	will - as long as you either keep the memory contents intact, or call
		1402	C<ev_TYPE_init> again.
943		1403
944	Another common scenario is having some data structure with multiple	1404	=item started/running/active
945	watchers:
946		1405
947	struct my_biggy	1406	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
948	{	1407	property of the event loop, and is actively waiting for events. While in
949	int some_data;	1408	this state it cannot be accessed (except in a few documented ways), moved,
950	ev_timer t1;	1409	freed or anything else - the only legal thing is to keep a pointer to it,
951	ev_timer t2;	1410	and call libev functions on it that are documented to work on active watchers.
952	}
953		1411
954	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1412	=item pending
955	you need to use C<offsetof>:
956		1413
957	#include <stddef.h>	1414	If a watcher is active and libev determines that an event it is interested
		1415	in has occurred (such as a timer expiring), it will become pending. It will
		1416	stay in this pending state until either it is stopped or its callback is
		1417	about to be invoked, so it is not normally pending inside the watcher
		1418	callback.
958		1419
		1420	The watcher might or might not be active while it is pending (for example,
		1421	an expired non-repeating timer can be pending but no longer active). If it
		1422	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1423	but it is still property of the event loop at this time, so cannot be
		1424	moved, freed or reused. And if it is active the rules described in the
		1425	previous item still apply.
		1426
		1427	It is also possible to feed an event on a watcher that is not active (e.g.
		1428	via C<ev_feed_event>), in which case it becomes pending without being
		1429	active.
		1430
		1431	=item stopped
		1432
		1433	A watcher can be stopped implicitly by libev (in which case it might still
		1434	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1435	latter will clear any pending state the watcher might be in, regardless
		1436	of whether it was active or not, so stopping a watcher explicitly before
		1437	freeing it is often a good idea.
		1438
		1439	While stopped (and not pending) the watcher is essentially in the
		1440	initialised state, that is, it can be reused, moved, modified in any way
		1441	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1442	it again).
		1443
		1444	=back
		1445
		1446	=head2 WATCHER PRIORITY MODELS
		1447
		1448	Many event loops support I<watcher priorities>, which are usually small
		1449	integers that influence the ordering of event callback invocation
		1450	between watchers in some way, all else being equal.
		1451
		1452	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1453	description for the more technical details such as the actual priority
		1454	range.
		1455
		1456	There are two common ways how these these priorities are being interpreted
		1457	by event loops:
		1458
		1459	In the more common lock-out model, higher priorities "lock out" invocation
		1460	of lower priority watchers, which means as long as higher priority
		1461	watchers receive events, lower priority watchers are not being invoked.
		1462
		1463	The less common only-for-ordering model uses priorities solely to order
		1464	callback invocation within a single event loop iteration: Higher priority
		1465	watchers are invoked before lower priority ones, but they all get invoked
		1466	before polling for new events.
		1467
		1468	Libev uses the second (only-for-ordering) model for all its watchers
		1469	except for idle watchers (which use the lock-out model).
		1470
		1471	The rationale behind this is that implementing the lock-out model for
		1472	watchers is not well supported by most kernel interfaces, and most event
		1473	libraries will just poll for the same events again and again as long as
		1474	their callbacks have not been executed, which is very inefficient in the
		1475	common case of one high-priority watcher locking out a mass of lower
		1476	priority ones.
		1477
		1478	Static (ordering) priorities are most useful when you have two or more
		1479	watchers handling the same resource: a typical usage example is having an
		1480	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1481	timeouts. Under load, data might be received while the program handles
		1482	other jobs, but since timers normally get invoked first, the timeout
		1483	handler will be executed before checking for data. In that case, giving
		1484	the timer a lower priority than the I/O watcher ensures that I/O will be
		1485	handled first even under adverse conditions (which is usually, but not
		1486	always, what you want).
		1487
		1488	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1489	will only be executed when no same or higher priority watchers have
		1490	received events, they can be used to implement the "lock-out" model when
		1491	required.
		1492
		1493	For example, to emulate how many other event libraries handle priorities,
		1494	you can associate an C<ev_idle> watcher to each such watcher, and in
		1495	the normal watcher callback, you just start the idle watcher. The real
		1496	processing is done in the idle watcher callback. This causes libev to
		1497	continuously poll and process kernel event data for the watcher, but when
		1498	the lock-out case is known to be rare (which in turn is rare :), this is
		1499	workable.
		1500
		1501	Usually, however, the lock-out model implemented that way will perform
		1502	miserably under the type of load it was designed to handle. In that case,
		1503	it might be preferable to stop the real watcher before starting the
		1504	idle watcher, so the kernel will not have to process the event in case
		1505	the actual processing will be delayed for considerable time.
		1506
		1507	Here is an example of an I/O watcher that should run at a strictly lower
		1508	priority than the default, and which should only process data when no
		1509	other events are pending:
		1510
		1511	ev_idle idle; // actual processing watcher
		1512	ev_io io; // actual event watcher
		1513
959	static void	1514	static void
960	t1_cb (EV_P_ struct ev_timer *w, int revents)	1515	io_cb (EV_P_ ev_io *w, int revents)
961	{	1516	{
962	struct my_biggy big = (struct my_biggy *	1517	// stop the I/O watcher, we received the event, but
963	(((char *)w) - offsetof (struct my_biggy, t1));	1518	// are not yet ready to handle it.
		1519	ev_io_stop (EV_A_ w);
		1520
		1521	// start the idle watcher to handle the actual event.
		1522	// it will not be executed as long as other watchers
		1523	// with the default priority are receiving events.
		1524	ev_idle_start (EV_A_ &idle);
964	}	1525	}
965		1526
966	static void	1527	static void
967	t2_cb (EV_P_ struct ev_timer *w, int revents)	1528	idle_cb (EV_P_ ev_idle *w, int revents)
968	{	1529	{
969	struct my_biggy big = (struct my_biggy *	1530	// actual processing
970	(((char *)w) - offsetof (struct my_biggy, t2));	1531	read (STDIN_FILENO, ...);
		1532
		1533	// have to start the I/O watcher again, as
		1534	// we have handled the event
		1535	ev_io_start (EV_P_ &io);
971	}	1536	}
		1537
		1538	// initialisation
		1539	ev_idle_init (&idle, idle_cb);
		1540	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1541	ev_io_start (EV_DEFAULT_ &io);
		1542
		1543	In the "real" world, it might also be beneficial to start a timer, so that
		1544	low-priority connections can not be locked out forever under load. This
		1545	enables your program to keep a lower latency for important connections
		1546	during short periods of high load, while not completely locking out less
		1547	important ones.
972		1548
973		1549
974	=head1 WATCHER TYPES	1550	=head1 WATCHER TYPES
975		1551
976	This section describes each watcher in detail, but will not repeat	1552	This section describes each watcher in detail, but will not repeat
…		…
1000	In general you can register as many read and/or write event watchers per	1576	In general you can register as many read and/or write event watchers per
1001	fd as you want (as long as you don't confuse yourself). Setting all file	1577	fd as you want (as long as you don't confuse yourself). Setting all file
1002	descriptors to non-blocking mode is also usually a good idea (but not	1578	descriptors to non-blocking mode is also usually a good idea (but not
1003	required if you know what you are doing).	1579	required if you know what you are doing).
1004		1580
1005	If you must do this, then force the use of a known-to-be-good backend
1006	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1007	C<EVBACKEND_POLL>).
1008
1009	Another thing you have to watch out for is that it is quite easy to	1581	Another thing you have to watch out for is that it is quite easy to
1010	receive "spurious" readyness notifications, that is your callback might	1582	receive "spurious" readiness notifications, that is, your callback might
1011	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1583	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1012	because there is no data. Not only are some backends known to create a	1584	because there is no data. It is very easy to get into this situation even
1013	lot of those (for example solaris ports), it is very easy to get into	1585	with a relatively standard program structure. Thus it is best to always
1014	this situation even with a relatively standard program structure. Thus	1586	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1015	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1016	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1587	preferable to a program hanging until some data arrives.
1017		1588
1018	If you cannot run the fd in non-blocking mode (for example you should not	1589	If you cannot run the fd in non-blocking mode (for example you should
1019	play around with an Xlib connection), then you have to seperately re-test	1590	not play around with an Xlib connection), then you have to separately
1020	whether a file descriptor is really ready with a known-to-be good interface	1591	re-test whether a file descriptor is really ready with a known-to-be good
1021	such as poll (fortunately in our Xlib example, Xlib already does this on	1592	interface such as poll (fortunately in the case of Xlib, it already does
1022	its own, so its quite safe to use).	1593	this on its own, so its quite safe to use). Some people additionally
		1594	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1595	indefinitely.
		1596
		1597	But really, best use non-blocking mode.
1023		1598
1024	=head3 The special problem of disappearing file descriptors	1599	=head3 The special problem of disappearing file descriptors
1025		1600
1026	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1601	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1027	descriptor (either by calling C<close> explicitly or by any other means,	1602	descriptor (either due to calling C<close> explicitly or any other means,
1028	such as C<dup>). The reason is that you register interest in some file	1603	such as C<dup2>). The reason is that you register interest in some file
1029	descriptor, but when it goes away, the operating system will silently drop	1604	descriptor, but when it goes away, the operating system will silently drop
1030	this interest. If another file descriptor with the same number then is	1605	this interest. If another file descriptor with the same number then is
1031	registered with libev, there is no efficient way to see that this is, in	1606	registered with libev, there is no efficient way to see that this is, in
1032	fact, a different file descriptor.	1607	fact, a different file descriptor.
1033		1608
…		…
1051		1626
1052	There is no workaround possible except not registering events	1627	There is no workaround possible except not registering events
1053	for potentially C<dup ()>'ed file descriptors, or to resort to	1628	for potentially C<dup ()>'ed file descriptors, or to resort to
1054	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1629	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1055		1630
		1631	=head3 The special problem of files
		1632
		1633	Many people try to use C<select> (or libev) on file descriptors
		1634	representing files, and expect it to become ready when their program
		1635	doesn't block on disk accesses (which can take a long time on their own).
		1636
		1637	However, this cannot ever work in the "expected" way - you get a readiness
		1638	notification as soon as the kernel knows whether and how much data is
		1639	there, and in the case of open files, that's always the case, so you
		1640	always get a readiness notification instantly, and your read (or possibly
		1641	write) will still block on the disk I/O.
		1642
		1643	Another way to view it is that in the case of sockets, pipes, character
		1644	devices and so on, there is another party (the sender) that delivers data
		1645	on its own, but in the case of files, there is no such thing: the disk
		1646	will not send data on its own, simply because it doesn't know what you
		1647	wish to read - you would first have to request some data.
		1648
		1649	Since files are typically not-so-well supported by advanced notification
		1650	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1651	to files, even though you should not use it. The reason for this is
		1652	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1653	usually a tty, often a pipe, but also sometimes files or special devices
		1654	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1655	F</dev/urandom>), and even though the file might better be served with
		1656	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1657	it "just works" instead of freezing.
		1658
		1659	So avoid file descriptors pointing to files when you know it (e.g. use
		1660	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1661	when you rarely read from a file instead of from a socket, and want to
		1662	reuse the same code path.
		1663
1056	=head3 The special problem of fork	1664	=head3 The special problem of fork
1057		1665
1058	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1666	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1059	useless behaviour. Libev fully supports fork, but needs to be told about	1667	useless behaviour. Libev fully supports fork, but needs to be told about
1060	it in the child.	1668	it in the child if you want to continue to use it in the child.
1061		1669
1062	To support fork in your programs, you either have to call	1670	To support fork in your child processes, you have to call C<ev_loop_fork
1063	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1671	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1064	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1672	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1065	C<EVBACKEND_POLL>.
1066		1673
		1674	=head3 The special problem of SIGPIPE
		1675
		1676	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1677	when writing to a pipe whose other end has been closed, your program gets
		1678	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1679	this is sensible behaviour, for daemons, this is usually undesirable.
		1680
		1681	So when you encounter spurious, unexplained daemon exits, make sure you
		1682	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1683	somewhere, as that would have given you a big clue).
		1684
		1685	=head3 The special problem of accept()ing when you can't
		1686
		1687	Many implementations of the POSIX C<accept> function (for example,
		1688	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1689	connection from the pending queue in all error cases.
		1690
		1691	For example, larger servers often run out of file descriptors (because
		1692	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1693	rejecting the connection, leading to libev signalling readiness on
		1694	the next iteration again (the connection still exists after all), and
		1695	typically causing the program to loop at 100% CPU usage.
		1696
		1697	Unfortunately, the set of errors that cause this issue differs between
		1698	operating systems, there is usually little the app can do to remedy the
		1699	situation, and no known thread-safe method of removing the connection to
		1700	cope with overload is known (to me).
		1701
		1702	One of the easiest ways to handle this situation is to just ignore it
		1703	- when the program encounters an overload, it will just loop until the
		1704	situation is over. While this is a form of busy waiting, no OS offers an
		1705	event-based way to handle this situation, so it's the best one can do.
		1706
		1707	A better way to handle the situation is to log any errors other than
		1708	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1709	messages, and continue as usual, which at least gives the user an idea of
		1710	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1711	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1712	usage.
		1713
		1714	If your program is single-threaded, then you could also keep a dummy file
		1715	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1716	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1717	close that fd, and create a new dummy fd. This will gracefully refuse
		1718	clients under typical overload conditions.
		1719
		1720	The last way to handle it is to simply log the error and C<exit>, as
		1721	is often done with C<malloc> failures, but this results in an easy
		1722	opportunity for a DoS attack.
1067		1723
1068	=head3 Watcher-Specific Functions	1724	=head3 Watcher-Specific Functions
1069		1725
1070	=over 4	1726	=over 4
1071		1727
1072	=item ev_io_init (ev_io *, callback, int fd, int events)	1728	=item ev_io_init (ev_io *, callback, int fd, int events)
1073		1729
1074	=item ev_io_set (ev_io *, int fd, int events)	1730	=item ev_io_set (ev_io *, int fd, int events)
1075		1731
1076	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1732	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1077	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1733	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1078	C<EV_READ | EV_WRITE> to receive the given events.	1734	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1079		1735
1080	=item int fd [read-only]	1736	=item int fd [read-only]
1081		1737
1082	The file descriptor being watched.	1738	The file descriptor being watched.
1083		1739
…		…
1091		1747
1092	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1748	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1093	readable, but only once. Since it is likely line-buffered, you could	1749	readable, but only once. Since it is likely line-buffered, you could
1094	attempt to read a whole line in the callback.	1750	attempt to read a whole line in the callback.
1095		1751
1096	static void	1752	static void
1097	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1753	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1098	{	1754	{
1099	ev_io_stop (loop, w);	1755	ev_io_stop (loop, w);
1100	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1756	.. read from stdin here (or from w->fd) and handle any I/O errors
1101	}	1757	}
1102		1758
1103	...	1759	...
1104	struct ev_loop *loop = ev_default_init (0);	1760	struct ev_loop *loop = ev_default_init (0);
1105	struct ev_io stdin_readable;	1761	ev_io stdin_readable;
1106	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1762	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1107	ev_io_start (loop, &stdin_readable);	1763	ev_io_start (loop, &stdin_readable);
1108	ev_loop (loop, 0);	1764	ev_run (loop, 0);
1109		1765
1110		1766
1111	=head2 C<ev_timer> - relative and optionally repeating timeouts	1767	=head2 C<ev_timer> - relative and optionally repeating timeouts
1112		1768
1113	Timer watchers are simple relative timers that generate an event after a	1769	Timer watchers are simple relative timers that generate an event after a
1114	given time, and optionally repeating in regular intervals after that.	1770	given time, and optionally repeating in regular intervals after that.
1115		1771
1116	The timers are based on real time, that is, if you register an event that	1772	The timers are based on real time, that is, if you register an event that
1117	times out after an hour and you reset your system clock to last years	1773	times out after an hour and you reset your system clock to January last
1118	time, it will still time out after (roughly) and hour. "Roughly" because	1774	year, it will still time out after (roughly) one hour. "Roughly" because
1119	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1775	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1120	monotonic clock option helps a lot here).	1776	monotonic clock option helps a lot here).
		1777
		1778	The callback is guaranteed to be invoked only I<after> its timeout has
		1779	passed (not I<at>, so on systems with very low-resolution clocks this
		1780	might introduce a small delay, see "the special problem of being too
		1781	early", below). If multiple timers become ready during the same loop
		1782	iteration then the ones with earlier time-out values are invoked before
		1783	ones of the same priority with later time-out values (but this is no
		1784	longer true when a callback calls C<ev_run> recursively).
		1785
		1786	=head3 Be smart about timeouts
		1787
		1788	Many real-world problems involve some kind of timeout, usually for error
		1789	recovery. A typical example is an HTTP request - if the other side hangs,
		1790	you want to raise some error after a while.
		1791
		1792	What follows are some ways to handle this problem, from obvious and
		1793	inefficient to smart and efficient.
		1794
		1795	In the following, a 60 second activity timeout is assumed - a timeout that
		1796	gets reset to 60 seconds each time there is activity (e.g. each time some
		1797	data or other life sign was received).
		1798
		1799	=over 4
		1800
		1801	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1802
		1803	This is the most obvious, but not the most simple way: In the beginning,
		1804	start the watcher:
		1805
		1806	ev_timer_init (timer, callback, 60., 0.);
		1807	ev_timer_start (loop, timer);
		1808
		1809	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1810	and start it again:
		1811
		1812	ev_timer_stop (loop, timer);
		1813	ev_timer_set (timer, 60., 0.);
		1814	ev_timer_start (loop, timer);
		1815
		1816	This is relatively simple to implement, but means that each time there is
		1817	some activity, libev will first have to remove the timer from its internal
		1818	data structure and then add it again. Libev tries to be fast, but it's
		1819	still not a constant-time operation.
		1820
		1821	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1822
		1823	This is the easiest way, and involves using C<ev_timer_again> instead of
		1824	C<ev_timer_start>.
		1825
		1826	To implement this, configure an C<ev_timer> with a C<repeat> value
		1827	of C<60> and then call C<ev_timer_again> at start and each time you
		1828	successfully read or write some data. If you go into an idle state where
		1829	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1830	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1831
		1832	That means you can ignore both the C<ev_timer_start> function and the
		1833	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1834	member and C<ev_timer_again>.
		1835
		1836	At start:
		1837
		1838	ev_init (timer, callback);
		1839	timer->repeat = 60.;
		1840	ev_timer_again (loop, timer);
		1841
		1842	Each time there is some activity:
		1843
		1844	ev_timer_again (loop, timer);
		1845
		1846	It is even possible to change the time-out on the fly, regardless of
		1847	whether the watcher is active or not:
		1848
		1849	timer->repeat = 30.;
		1850	ev_timer_again (loop, timer);
		1851
		1852	This is slightly more efficient then stopping/starting the timer each time
		1853	you want to modify its timeout value, as libev does not have to completely
		1854	remove and re-insert the timer from/into its internal data structure.
		1855
		1856	It is, however, even simpler than the "obvious" way to do it.
		1857
		1858	=item 3. Let the timer time out, but then re-arm it as required.
		1859
		1860	This method is more tricky, but usually most efficient: Most timeouts are
		1861	relatively long compared to the intervals between other activity - in
		1862	our example, within 60 seconds, there are usually many I/O events with
		1863	associated activity resets.
		1864
		1865	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1866	but remember the time of last activity, and check for a real timeout only
		1867	within the callback:
		1868
		1869	ev_tstamp timeout = 60.;
		1870	ev_tstamp last_activity; // time of last activity
		1871	ev_timer timer;
		1872
		1873	static void
		1874	callback (EV_P_ ev_timer *w, int revents)
		1875	{
		1876	// calculate when the timeout would happen
		1877	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1878
		1879	// if negative, it means we the timeout already occurred
		1880	if (after < 0.)
		1881	{
		1882	// timeout occurred, take action
		1883	}
		1884	else
		1885	{
		1886	// callback was invoked, but there was some recent
		1887	// activity. simply restart the timer to time out
		1888	// after "after" seconds, which is the earliest time
		1889	// the timeout can occur.
		1890	ev_timer_set (w, after, 0.);
		1891	ev_timer_start (EV_A_ w);
		1892	}
		1893	}
		1894
		1895	To summarise the callback: first calculate in how many seconds the
		1896	timeout will occur (by calculating the absolute time when it would occur,
		1897	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1898	(EV_A)> from that).
		1899
		1900	If this value is negative, then we are already past the timeout, i.e. we
		1901	timed out, and need to do whatever is needed in this case.
		1902
		1903	Otherwise, we now the earliest time at which the timeout would trigger,
		1904	and simply start the timer with this timeout value.
		1905
		1906	In other words, each time the callback is invoked it will check whether
		1907	the timeout occurred. If not, it will simply reschedule itself to check
		1908	again at the earliest time it could time out. Rinse. Repeat.
		1909
		1910	This scheme causes more callback invocations (about one every 60 seconds
		1911	minus half the average time between activity), but virtually no calls to
		1912	libev to change the timeout.
		1913
		1914	To start the machinery, simply initialise the watcher and set
		1915	C<last_activity> to the current time (meaning there was some activity just
		1916	now), then call the callback, which will "do the right thing" and start
		1917	the timer:
		1918
		1919	last_activity = ev_now (EV_A);
		1920	ev_init (&timer, callback);
		1921	callback (EV_A_ &timer, 0);
		1922
		1923	When there is some activity, simply store the current time in
		1924	C<last_activity>, no libev calls at all:
		1925
		1926	if (activity detected)
		1927	last_activity = ev_now (EV_A);
		1928
		1929	When your timeout value changes, then the timeout can be changed by simply
		1930	providing a new value, stopping the timer and calling the callback, which
		1931	will again do the right thing (for example, time out immediately :).
		1932
		1933	timeout = new_value;
		1934	ev_timer_stop (EV_A_ &timer);
		1935	callback (EV_A_ &timer, 0);
		1936
		1937	This technique is slightly more complex, but in most cases where the
		1938	time-out is unlikely to be triggered, much more efficient.
		1939
		1940	=item 4. Wee, just use a double-linked list for your timeouts.
		1941
		1942	If there is not one request, but many thousands (millions...), all
		1943	employing some kind of timeout with the same timeout value, then one can
		1944	do even better:
		1945
		1946	When starting the timeout, calculate the timeout value and put the timeout
		1947	at the I<end> of the list.
		1948
		1949	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1950	the list is expected to fire (for example, using the technique #3).
		1951
		1952	When there is some activity, remove the timer from the list, recalculate
		1953	the timeout, append it to the end of the list again, and make sure to
		1954	update the C<ev_timer> if it was taken from the beginning of the list.
		1955
		1956	This way, one can manage an unlimited number of timeouts in O(1) time for
		1957	starting, stopping and updating the timers, at the expense of a major
		1958	complication, and having to use a constant timeout. The constant timeout
		1959	ensures that the list stays sorted.
		1960
		1961	=back
		1962
		1963	So which method the best?
		1964
		1965	Method #2 is a simple no-brain-required solution that is adequate in most
		1966	situations. Method #3 requires a bit more thinking, but handles many cases
		1967	better, and isn't very complicated either. In most case, choosing either
		1968	one is fine, with #3 being better in typical situations.
		1969
		1970	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1971	rather complicated, but extremely efficient, something that really pays
		1972	off after the first million or so of active timers, i.e. it's usually
		1973	overkill :)
		1974
		1975	=head3 The special problem of being too early
		1976
		1977	If you ask a timer to call your callback after three seconds, then
		1978	you expect it to be invoked after three seconds - but of course, this
		1979	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1980	guaranteed to any precision by libev - imagine somebody suspending the
		1981	process with a STOP signal for a few hours for example.
		1982
		1983	So, libev tries to invoke your callback as soon as possible I<after> the
		1984	delay has occurred, but cannot guarantee this.
		1985
		1986	A less obvious failure mode is calling your callback too early: many event
		1987	loops compare timestamps with a "elapsed delay >= requested delay", but
		1988	this can cause your callback to be invoked much earlier than you would
		1989	expect.
		1990
		1991	To see why, imagine a system with a clock that only offers full second
		1992	resolution (think windows if you can't come up with a broken enough OS
		1993	yourself). If you schedule a one-second timer at the time 500.9, then the
		1994	event loop will schedule your timeout to elapse at a system time of 500
		1995	(500.9 truncated to the resolution) + 1, or 501.
		1996
		1997	If an event library looks at the timeout 0.1s later, it will see "501 >=
		1998	501" and invoke the callback 0.1s after it was started, even though a
		1999	one-second delay was requested - this is being "too early", despite best
		2000	intentions.
		2001
		2002	This is the reason why libev will never invoke the callback if the elapsed
		2003	delay equals the requested delay, but only when the elapsed delay is
		2004	larger than the requested delay. In the example above, libev would only invoke
		2005	the callback at system time 502, or 1.1s after the timer was started.
		2006
		2007	So, while libev cannot guarantee that your callback will be invoked
		2008	exactly when requested, it I<can> and I<does> guarantee that the requested
		2009	delay has actually elapsed, or in other words, it always errs on the "too
		2010	late" side of things.
		2011
		2012	=head3 The special problem of time updates
		2013
		2014	Establishing the current time is a costly operation (it usually takes
		2015	at least one system call): EV therefore updates its idea of the current
		2016	time only before and after C<ev_run> collects new events, which causes a
		2017	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2018	lots of events in one iteration.
1121		2019
1122	The relative timeouts are calculated relative to the C<ev_now ()>	2020	The relative timeouts are calculated relative to the C<ev_now ()>
1123	time. This is usually the right thing as this timestamp refers to the time	2021	time. This is usually the right thing as this timestamp refers to the time
1124	of the event triggering whatever timeout you are modifying/starting. If	2022	of the event triggering whatever timeout you are modifying/starting. If
1125	you suspect event processing to be delayed and you I<need> to base the timeout	2023	you suspect event processing to be delayed and you I<need> to base the
1126	on the current time, use something like this to adjust for this:	2024	timeout on the current time, use something like this to adjust for this:
1127		2025
1128	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2026	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1129		2027
1130	The callback is guarenteed to be invoked only when its timeout has passed,	2028	If the event loop is suspended for a long time, you can also force an
1131	but if multiple timers become ready during the same loop iteration then	2029	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1132	order of execution is undefined.	2030	()>.
		2031
		2032	=head3 The special problem of unsynchronised clocks
		2033
		2034	Modern systems have a variety of clocks - libev itself uses the normal
		2035	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2036	jumps).
		2037
		2038	Neither of these clocks is synchronised with each other or any other clock
		2039	on the system, so C<ev_time ()> might return a considerably different time
		2040	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2041	a call to C<gettimeofday> might return a second count that is one higher
		2042	than a directly following call to C<time>.
		2043
		2044	The moral of this is to only compare libev-related timestamps with
		2045	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2046	a second or so.
		2047
		2048	One more problem arises due to this lack of synchronisation: if libev uses
		2049	the system monotonic clock and you compare timestamps from C<ev_time>
		2050	or C<ev_now> from when you started your timer and when your callback is
		2051	invoked, you will find that sometimes the callback is a bit "early".
		2052
		2053	This is because C<ev_timer>s work in real time, not wall clock time, so
		2054	libev makes sure your callback is not invoked before the delay happened,
		2055	I<measured according to the real time>, not the system clock.
		2056
		2057	If your timeouts are based on a physical timescale (e.g. "time out this
		2058	connection after 100 seconds") then this shouldn't bother you as it is
		2059	exactly the right behaviour.
		2060
		2061	If you want to compare wall clock/system timestamps to your timers, then
		2062	you need to use C<ev_periodic>s, as these are based on the wall clock
		2063	time, where your comparisons will always generate correct results.
		2064
		2065	=head3 The special problems of suspended animation
		2066
		2067	When you leave the server world it is quite customary to hit machines that
		2068	can suspend/hibernate - what happens to the clocks during such a suspend?
		2069
		2070	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2071	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2072	to run until the system is suspended, but they will not advance while the
		2073	system is suspended. That means, on resume, it will be as if the program
		2074	was frozen for a few seconds, but the suspend time will not be counted
		2075	towards C<ev_timer> when a monotonic clock source is used. The real time
		2076	clock advanced as expected, but if it is used as sole clocksource, then a
		2077	long suspend would be detected as a time jump by libev, and timers would
		2078	be adjusted accordingly.
		2079
		2080	I would not be surprised to see different behaviour in different between
		2081	operating systems, OS versions or even different hardware.
		2082
		2083	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2084	time jump in the monotonic clocks and the realtime clock. If the program
		2085	is suspended for a very long time, and monotonic clock sources are in use,
		2086	then you can expect C<ev_timer>s to expire as the full suspension time
		2087	will be counted towards the timers. When no monotonic clock source is in
		2088	use, then libev will again assume a timejump and adjust accordingly.
		2089
		2090	It might be beneficial for this latter case to call C<ev_suspend>
		2091	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2092	deterministic behaviour in this case (you can do nothing against
		2093	C<SIGSTOP>).
1133		2094
1134	=head3 Watcher-Specific Functions and Data Members	2095	=head3 Watcher-Specific Functions and Data Members
1135		2096
1136	=over 4	2097	=over 4
1137		2098
1138	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2099	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1139		2100
1140	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2101	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1141		2102
1142	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2103	Configure the timer to trigger after C<after> seconds. If C<repeat>
1143	C<0.>, then it will automatically be stopped. If it is positive, then the	2104	is C<0.>, then it will automatically be stopped once the timeout is
1144	timer will automatically be configured to trigger again C<repeat> seconds	2105	reached. If it is positive, then the timer will automatically be
1145	later, again, and again, until stopped manually.	2106	configured to trigger again C<repeat> seconds later, again, and again,
		2107	until stopped manually.
1146		2108
1147	The timer itself will do a best-effort at avoiding drift, that is, if you	2109	The timer itself will do a best-effort at avoiding drift, that is, if
1148	configure a timer to trigger every 10 seconds, then it will trigger at	2110	you configure a timer to trigger every 10 seconds, then it will normally
1149	exactly 10 second intervals. If, however, your program cannot keep up with	2111	trigger at exactly 10 second intervals. If, however, your program cannot
1150	the timer (because it takes longer than those 10 seconds to do stuff) the	2112	keep up with the timer (because it takes longer than those 10 seconds to
1151	timer will not fire more than once per event loop iteration.	2113	do stuff) the timer will not fire more than once per event loop iteration.
1152		2114
1153	=item ev_timer_again (loop)	2115	=item ev_timer_again (loop, ev_timer *)
1154		2116
1155	This will act as if the timer timed out and restart it again if it is	2117	This will act as if the timer timed out, and restarts it again if it is
1156	repeating. The exact semantics are:	2118	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2119	timeout to the C<repeat> value and calling C<ev_timer_start>.
1157		2120
		2121	The exact semantics are as in the following rules, all of which will be
		2122	applied to the watcher:
		2123
		2124	=over 4
		2125
1158	If the timer is pending, its pending status is cleared.	2126	=item If the timer is pending, the pending status is always cleared.
1159		2127
1160	If the timer is started but nonrepeating, stop it (as if it timed out).	2128	=item If the timer is started but non-repeating, stop it (as if it timed
		2129	out, without invoking it).
1161		2130
1162	If the timer is repeating, either start it if necessary (with the	2131	=item If the timer is repeating, make the C<repeat> value the new timeout
1163	C<repeat> value), or reset the running timer to the C<repeat> value.	2132	and start the timer, if necessary.
1164		2133
1165	This sounds a bit complicated, but here is a useful and typical	2134	=back
1166	example: Imagine you have a tcp connection and you want a so-called idle
1167	timeout, that is, you want to be called when there have been, say, 60
1168	seconds of inactivity on the socket. The easiest way to do this is to
1169	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1170	C<ev_timer_again> each time you successfully read or write some data. If
1171	you go into an idle state where you do not expect data to travel on the
1172	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1173	automatically restart it if need be.
1174		2135
1175	That means you can ignore the C<after> value and C<ev_timer_start>	2136	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1176	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2137	usage example.
1177		2138
1178	ev_timer_init (timer, callback, 0., 5.);	2139	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1179	ev_timer_again (loop, timer);
1180	...
1181	timer->again = 17.;
1182	ev_timer_again (loop, timer);
1183	...
1184	timer->again = 10.;
1185	ev_timer_again (loop, timer);
1186		2140
1187	This is more slightly efficient then stopping/starting the timer each time	2141	Returns the remaining time until a timer fires. If the timer is active,
1188	you want to modify its timeout value.	2142	then this time is relative to the current event loop time, otherwise it's
		2143	the timeout value currently configured.
		2144
		2145	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2146	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2147	will return C<4>. When the timer expires and is restarted, it will return
		2148	roughly C<7> (likely slightly less as callback invocation takes some time,
		2149	too), and so on.
1189		2150
1190	=item ev_tstamp repeat [read-write]	2151	=item ev_tstamp repeat [read-write]
1191		2152
1192	The current C<repeat> value. Will be used each time the watcher times out	2153	The current C<repeat> value. Will be used each time the watcher times out
1193	or C<ev_timer_again> is called and determines the next timeout (if any),	2154	or C<ev_timer_again> is called, and determines the next timeout (if any),
1194	which is also when any modifications are taken into account.	2155	which is also when any modifications are taken into account.
1195		2156
1196	=back	2157	=back
1197		2158
1198	=head3 Examples	2159	=head3 Examples
1199		2160
1200	Example: Create a timer that fires after 60 seconds.	2161	Example: Create a timer that fires after 60 seconds.
1201		2162
1202	static void	2163	static void
1203	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2164	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1204	{	2165	{
1205	.. one minute over, w is actually stopped right here	2166	.. one minute over, w is actually stopped right here
1206	}	2167	}
1207		2168
1208	struct ev_timer mytimer;	2169	ev_timer mytimer;
1209	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2170	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1210	ev_timer_start (loop, &mytimer);	2171	ev_timer_start (loop, &mytimer);
1211		2172
1212	Example: Create a timeout timer that times out after 10 seconds of	2173	Example: Create a timeout timer that times out after 10 seconds of
1213	inactivity.	2174	inactivity.
1214		2175
1215	static void	2176	static void
1216	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2177	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1217	{	2178	{
1218	.. ten seconds without any activity	2179	.. ten seconds without any activity
1219	}	2180	}
1220		2181
1221	struct ev_timer mytimer;	2182	ev_timer mytimer;
1222	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2183	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1223	ev_timer_again (&mytimer); /* start timer */	2184	ev_timer_again (&mytimer); /* start timer */
1224	ev_loop (loop, 0);	2185	ev_run (loop, 0);
1225		2186
1226	// and in some piece of code that gets executed on any "activity":	2187	// and in some piece of code that gets executed on any "activity":
1227	// reset the timeout to start ticking again at 10 seconds	2188	// reset the timeout to start ticking again at 10 seconds
1228	ev_timer_again (&mytimer);	2189	ev_timer_again (&mytimer);
1229		2190
1230		2191
1231	=head2 C<ev_periodic> - to cron or not to cron?	2192	=head2 C<ev_periodic> - to cron or not to cron?
1232		2193
1233	Periodic watchers are also timers of a kind, but they are very versatile	2194	Periodic watchers are also timers of a kind, but they are very versatile
1234	(and unfortunately a bit complex).	2195	(and unfortunately a bit complex).
1235		2196
1236	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2197	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1237	but on wallclock time (absolute time). You can tell a periodic watcher	2198	relative time, the physical time that passes) but on wall clock time
1238	to trigger "at" some specific point in time. For example, if you tell a	2199	(absolute time, the thing you can read on your calender or clock). The
1239	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2200	difference is that wall clock time can run faster or slower than real
1240	+ 10.>) and then reset your system clock to the last year, then it will	2201	time, and time jumps are not uncommon (e.g. when you adjust your
1241	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2202	wrist-watch).
1242	roughly 10 seconds later).
1243		2203
1244	They can also be used to implement vastly more complex timers, such as	2204	You can tell a periodic watcher to trigger after some specific point
1245	triggering an event on each midnight, local time or other, complicated,	2205	in time: for example, if you tell a periodic watcher to trigger "in 10
1246	rules.	2206	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2207	not a delay) and then reset your system clock to January of the previous
		2208	year, then it will take a year or more to trigger the event (unlike an
		2209	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2210	it, as it uses a relative timeout).
1247		2211
		2212	C<ev_periodic> watchers can also be used to implement vastly more complex
		2213	timers, such as triggering an event on each "midnight, local time", or
		2214	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2215	those cannot react to time jumps.
		2216
1248	As with timers, the callback is guarenteed to be invoked only when the	2217	As with timers, the callback is guaranteed to be invoked only when the
1249	time (C<at>) has been passed, but if multiple periodic timers become ready	2218	point in time where it is supposed to trigger has passed. If multiple
1250	during the same loop iteration then order of execution is undefined.	2219	timers become ready during the same loop iteration then the ones with
		2220	earlier time-out values are invoked before ones with later time-out values
		2221	(but this is no longer true when a callback calls C<ev_run> recursively).
1251		2222
1252	=head3 Watcher-Specific Functions and Data Members	2223	=head3 Watcher-Specific Functions and Data Members
1253		2224
1254	=over 4	2225	=over 4
1255		2226
1256	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2227	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1257		2228
1258	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2229	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1259		2230
1260	Lots of arguments, lets sort it out... There are basically three modes of	2231	Lots of arguments, let's sort it out... There are basically three modes of
1261	operation, and we will explain them from simplest to complex:	2232	operation, and we will explain them from simplest to most complex:
1262		2233
1263	=over 4	2234	=over 4
1264		2235
1265	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2236	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1266		2237
1267	In this configuration the watcher triggers an event at the wallclock time	2238	In this configuration the watcher triggers an event after the wall clock
1268	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2239	time C<offset> has passed. It will not repeat and will not adjust when a
1269	that is, if it is to be run at January 1st 2011 then it will run when the	2240	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1270	system time reaches or surpasses this time.	2241	will be stopped and invoked when the system clock reaches or surpasses
		2242	this point in time.
1271		2243
1272	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2244	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1273		2245
1274	In this mode the watcher will always be scheduled to time out at the next	2246	In this mode the watcher will always be scheduled to time out at the next
1275	C<at + N * interval> time (for some integer N, which can also be negative)	2247	C<offset + N * interval> time (for some integer N, which can also be
1276	and then repeat, regardless of any time jumps.	2248	negative) and then repeat, regardless of any time jumps. The C<offset>
		2249	argument is merely an offset into the C<interval> periods.
1277		2250
1278	This can be used to create timers that do not drift with respect to system	2251	This can be used to create timers that do not drift with respect to the
1279	time:	2252	system clock, for example, here is an C<ev_periodic> that triggers each
		2253	hour, on the hour (with respect to UTC):
1280		2254
1281	ev_periodic_set (&periodic, 0., 3600., 0);	2255	ev_periodic_set (&periodic, 0., 3600., 0);
1282		2256
1283	This doesn't mean there will always be 3600 seconds in between triggers,	2257	This doesn't mean there will always be 3600 seconds in between triggers,
1284	but only that the the callback will be called when the system time shows a	2258	but only that the callback will be called when the system time shows a
1285	full hour (UTC), or more correctly, when the system time is evenly divisible	2259	full hour (UTC), or more correctly, when the system time is evenly divisible
1286	by 3600.	2260	by 3600.
1287		2261
1288	Another way to think about it (for the mathematically inclined) is that	2262	Another way to think about it (for the mathematically inclined) is that
1289	C<ev_periodic> will try to run the callback in this mode at the next possible	2263	C<ev_periodic> will try to run the callback in this mode at the next possible
1290	time where C<time = at (mod interval)>, regardless of any time jumps.	2264	time where C<time = offset (mod interval)>, regardless of any time jumps.
1291		2265
1292	For numerical stability it is preferable that the C<at> value is near	2266	The C<interval> I<MUST> be positive, and for numerical stability, the
1293	C<ev_now ()> (the current time), but there is no range requirement for	2267	interval value should be higher than C<1/8192> (which is around 100
1294	this value.	2268	microseconds) and C<offset> should be higher than C<0> and should have
		2269	at most a similar magnitude as the current time (say, within a factor of
		2270	ten). Typical values for offset are, in fact, C<0> or something between
		2271	C<0> and C<interval>, which is also the recommended range.
1295		2272
		2273	Note also that there is an upper limit to how often a timer can fire (CPU
		2274	speed for example), so if C<interval> is very small then timing stability
		2275	will of course deteriorate. Libev itself tries to be exact to be about one
		2276	millisecond (if the OS supports it and the machine is fast enough).
		2277
1296	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2278	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1297		2279
1298	In this mode the values for C<interval> and C<at> are both being	2280	In this mode the values for C<interval> and C<offset> are both being
1299	ignored. Instead, each time the periodic watcher gets scheduled, the	2281	ignored. Instead, each time the periodic watcher gets scheduled, the
1300	reschedule callback will be called with the watcher as first, and the	2282	reschedule callback will be called with the watcher as first, and the
1301	current time as second argument.	2283	current time as second argument.
1302		2284
1303	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2285	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1304	ever, or make any event loop modifications>. If you need to stop it,	2286	or make ANY other event loop modifications whatsoever, unless explicitly
1305	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2287	allowed by documentation here>.
1306	starting an C<ev_prepare> watcher, which is legal).
1307		2288
		2289	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2290	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2291	only event loop modification you are allowed to do).
		2292
1308	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2293	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1309	ev_tstamp now)>, e.g.:	2294	*w, ev_tstamp now)>, e.g.:
1310		2295
		2296	static ev_tstamp
1311	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2297	my_rescheduler (ev_periodic *w, ev_tstamp now)
1312	{	2298	{
1313	return now + 60.;	2299	return now + 60.;
1314	}	2300	}
1315		2301
1316	It must return the next time to trigger, based on the passed time value	2302	It must return the next time to trigger, based on the passed time value
1317	(that is, the lowest time value larger than to the second argument). It	2303	(that is, the lowest time value larger than to the second argument). It
1318	will usually be called just before the callback will be triggered, but	2304	will usually be called just before the callback will be triggered, but
1319	might be called at other times, too.	2305	might be called at other times, too.
1320		2306
1321	NOTE: I<< This callback must always return a time that is later than the	2307	NOTE: I<< This callback must always return a time that is higher than or
1322	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2308	equal to the passed C<now> value >>.
1323		2309
1324	This can be used to create very complex timers, such as a timer that	2310	This can be used to create very complex timers, such as a timer that
1325	triggers on each midnight, local time. To do this, you would calculate the	2311	triggers on "next midnight, local time". To do this, you would calculate the
1326	next midnight after C<now> and return the timestamp value for this. How	2312	next midnight after C<now> and return the timestamp value for this. How
1327	you do this is, again, up to you (but it is not trivial, which is the main	2313	you do this is, again, up to you (but it is not trivial, which is the main
1328	reason I omitted it as an example).	2314	reason I omitted it as an example).
1329		2315
1330	=back	2316	=back
…		…
1334	Simply stops and restarts the periodic watcher again. This is only useful	2320	Simply stops and restarts the periodic watcher again. This is only useful
1335	when you changed some parameters or the reschedule callback would return	2321	when you changed some parameters or the reschedule callback would return
1336	a different time than the last time it was called (e.g. in a crond like	2322	a different time than the last time it was called (e.g. in a crond like
1337	program when the crontabs have changed).	2323	program when the crontabs have changed).
1338		2324
		2325	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2326
		2327	When active, returns the absolute time that the watcher is supposed
		2328	to trigger next. This is not the same as the C<offset> argument to
		2329	C<ev_periodic_set>, but indeed works even in interval and manual
		2330	rescheduling modes.
		2331
1339	=item ev_tstamp offset [read-write]	2332	=item ev_tstamp offset [read-write]
1340		2333
1341	When repeating, this contains the offset value, otherwise this is the	2334	When repeating, this contains the offset value, otherwise this is the
1342	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2335	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2336	although libev might modify this value for better numerical stability).
1343		2337
1344	Can be modified any time, but changes only take effect when the periodic	2338	Can be modified any time, but changes only take effect when the periodic
1345	timer fires or C<ev_periodic_again> is being called.	2339	timer fires or C<ev_periodic_again> is being called.
1346		2340
1347	=item ev_tstamp interval [read-write]	2341	=item ev_tstamp interval [read-write]
1348		2342
1349	The current interval value. Can be modified any time, but changes only	2343	The current interval value. Can be modified any time, but changes only
1350	take effect when the periodic timer fires or C<ev_periodic_again> is being	2344	take effect when the periodic timer fires or C<ev_periodic_again> is being
1351	called.	2345	called.
1352		2346
1353	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2347	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1354		2348
1355	The current reschedule callback, or C<0>, if this functionality is	2349	The current reschedule callback, or C<0>, if this functionality is
1356	switched off. Can be changed any time, but changes only take effect when	2350	switched off. Can be changed any time, but changes only take effect when
1357	the periodic timer fires or C<ev_periodic_again> is being called.	2351	the periodic timer fires or C<ev_periodic_again> is being called.
1358		2352
1359	=item ev_tstamp at [read-only]
1360
1361	When active, contains the absolute time that the watcher is supposed to
1362	trigger next.
1363
1364	=back	2353	=back
1365		2354
1366	=head3 Examples	2355	=head3 Examples
1367		2356
1368	Example: Call a callback every hour, or, more precisely, whenever the	2357	Example: Call a callback every hour, or, more precisely, whenever the
1369	system clock is divisible by 3600. The callback invocation times have	2358	system time is divisible by 3600. The callback invocation times have
1370	potentially a lot of jittering, but good long-term stability.	2359	potentially a lot of jitter, but good long-term stability.
1371		2360
1372	static void	2361	static void
1373	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2362	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1374	{	2363	{
1375	... its now a full hour (UTC, or TAI or whatever your clock follows)	2364	... its now a full hour (UTC, or TAI or whatever your clock follows)
1376	}	2365	}
1377		2366
1378	struct ev_periodic hourly_tick;	2367	ev_periodic hourly_tick;
1379	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2368	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1380	ev_periodic_start (loop, &hourly_tick);	2369	ev_periodic_start (loop, &hourly_tick);
1381		2370
1382	Example: The same as above, but use a reschedule callback to do it:	2371	Example: The same as above, but use a reschedule callback to do it:
1383		2372
1384	#include <math.h>	2373	#include <math.h>
1385		2374
1386	static ev_tstamp	2375	static ev_tstamp
1387	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2376	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1388	{	2377	{
1389	return fmod (now, 3600.) + 3600.;	2378	return now + (3600. - fmod (now, 3600.));
1390	}	2379	}
1391		2380
1392	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2381	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1393		2382
1394	Example: Call a callback every hour, starting now:	2383	Example: Call a callback every hour, starting now:
1395		2384
1396	struct ev_periodic hourly_tick;	2385	ev_periodic hourly_tick;
1397	ev_periodic_init (&hourly_tick, clock_cb,	2386	ev_periodic_init (&hourly_tick, clock_cb,
1398	fmod (ev_now (loop), 3600.), 3600., 0);	2387	fmod (ev_now (loop), 3600.), 3600., 0);
1399	ev_periodic_start (loop, &hourly_tick);	2388	ev_periodic_start (loop, &hourly_tick);
1400		2389
1401		2390
1402	=head2 C<ev_signal> - signal me when a signal gets signalled!	2391	=head2 C<ev_signal> - signal me when a signal gets signalled!
1403		2392
1404	Signal watchers will trigger an event when the process receives a specific	2393	Signal watchers will trigger an event when the process receives a specific
1405	signal one or more times. Even though signals are very asynchronous, libev	2394	signal one or more times. Even though signals are very asynchronous, libev
1406	will try it's best to deliver signals synchronously, i.e. as part of the	2395	will try its best to deliver signals synchronously, i.e. as part of the
1407	normal event processing, like any other event.	2396	normal event processing, like any other event.
1408		2397
		2398	If you want signals to be delivered truly asynchronously, just use
		2399	C<sigaction> as you would do without libev and forget about sharing
		2400	the signal. You can even use C<ev_async> from a signal handler to
		2401	synchronously wake up an event loop.
		2402
1409	You can configure as many watchers as you like per signal. Only when the	2403	You can configure as many watchers as you like for the same signal, but
		2404	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2405	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2406	C<SIGINT> in both the default loop and another loop at the same time. At
		2407	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2408
1410	first watcher gets started will libev actually register a signal watcher	2409	When the first watcher gets started will libev actually register something
1411	with the kernel (thus it coexists with your own signal handlers as long	2410	with the kernel (thus it coexists with your own signal handlers as long as
1412	as you don't register any with libev). Similarly, when the last signal	2411	you don't register any with libev for the same signal).
1413	watcher for a signal is stopped libev will reset the signal handler to	2412
1414	SIG_DFL (regardless of what it was set to before).	2413	If possible and supported, libev will install its handlers with
		2414	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2415	not be unduly interrupted. If you have a problem with system calls getting
		2416	interrupted by signals you can block all signals in an C<ev_check> watcher
		2417	and unblock them in an C<ev_prepare> watcher.
		2418
		2419	=head3 The special problem of inheritance over fork/execve/pthread_create
		2420
		2421	Both the signal mask (C<sigprocmask>) and the signal disposition
		2422	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2423	stopping it again), that is, libev might or might not block the signal,
		2424	and might or might not set or restore the installed signal handler (but
		2425	see C<EVFLAG_NOSIGMASK>).
		2426
		2427	While this does not matter for the signal disposition (libev never
		2428	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2429	C<execve>), this matters for the signal mask: many programs do not expect
		2430	certain signals to be blocked.
		2431
		2432	This means that before calling C<exec> (from the child) you should reset
		2433	the signal mask to whatever "default" you expect (all clear is a good
		2434	choice usually).
		2435
		2436	The simplest way to ensure that the signal mask is reset in the child is
		2437	to install a fork handler with C<pthread_atfork> that resets it. That will
		2438	catch fork calls done by libraries (such as the libc) as well.
		2439
		2440	In current versions of libev, the signal will not be blocked indefinitely
		2441	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2442	the window of opportunity for problems, it will not go away, as libev
		2443	I<has> to modify the signal mask, at least temporarily.
		2444
		2445	So I can't stress this enough: I<If you do not reset your signal mask when
		2446	you expect it to be empty, you have a race condition in your code>. This
		2447	is not a libev-specific thing, this is true for most event libraries.
		2448
		2449	=head3 The special problem of threads signal handling
		2450
		2451	POSIX threads has problematic signal handling semantics, specifically,
		2452	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2453	threads in a process block signals, which is hard to achieve.
		2454
		2455	When you want to use sigwait (or mix libev signal handling with your own
		2456	for the same signals), you can tackle this problem by globally blocking
		2457	all signals before creating any threads (or creating them with a fully set
		2458	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2459	loops. Then designate one thread as "signal receiver thread" which handles
		2460	these signals. You can pass on any signals that libev might be interested
		2461	in by calling C<ev_feed_signal>.
1415		2462
1416	=head3 Watcher-Specific Functions and Data Members	2463	=head3 Watcher-Specific Functions and Data Members
1417		2464
1418	=over 4	2465	=over 4
1419		2466
…		…
1428		2475
1429	The signal the watcher watches out for.	2476	The signal the watcher watches out for.
1430		2477
1431	=back	2478	=back
1432		2479
		2480	=head3 Examples
		2481
		2482	Example: Try to exit cleanly on SIGINT.
		2483
		2484	static void
		2485	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2486	{
		2487	ev_break (loop, EVBREAK_ALL);
		2488	}
		2489
		2490	ev_signal signal_watcher;
		2491	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2492	ev_signal_start (loop, &signal_watcher);
		2493
1433		2494
1434	=head2 C<ev_child> - watch out for process status changes	2495	=head2 C<ev_child> - watch out for process status changes
1435		2496
1436	Child watchers trigger when your process receives a SIGCHLD in response to	2497	Child watchers trigger when your process receives a SIGCHLD in response to
1437	some child status changes (most typically when a child of yours dies).	2498	some child status changes (most typically when a child of yours dies or
		2499	exits). It is permissible to install a child watcher I<after> the child
		2500	has been forked (which implies it might have already exited), as long
		2501	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2502	forking and then immediately registering a watcher for the child is fine,
		2503	but forking and registering a watcher a few event loop iterations later or
		2504	in the next callback invocation is not.
		2505
		2506	Only the default event loop is capable of handling signals, and therefore
		2507	you can only register child watchers in the default event loop.
		2508
		2509	Due to some design glitches inside libev, child watchers will always be
		2510	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2511	libev)
		2512
		2513	=head3 Process Interaction
		2514
		2515	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2516	initialised. This is necessary to guarantee proper behaviour even if the
		2517	first child watcher is started after the child exits. The occurrence
		2518	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2519	synchronously as part of the event loop processing. Libev always reaps all
		2520	children, even ones not watched.
		2521
		2522	=head3 Overriding the Built-In Processing
		2523
		2524	Libev offers no special support for overriding the built-in child
		2525	processing, but if your application collides with libev's default child
		2526	handler, you can override it easily by installing your own handler for
		2527	C<SIGCHLD> after initialising the default loop, and making sure the
		2528	default loop never gets destroyed. You are encouraged, however, to use an
		2529	event-based approach to child reaping and thus use libev's support for
		2530	that, so other libev users can use C<ev_child> watchers freely.
		2531
		2532	=head3 Stopping the Child Watcher
		2533
		2534	Currently, the child watcher never gets stopped, even when the
		2535	child terminates, so normally one needs to stop the watcher in the
		2536	callback. Future versions of libev might stop the watcher automatically
		2537	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2538	problem).
1438		2539
1439	=head3 Watcher-Specific Functions and Data Members	2540	=head3 Watcher-Specific Functions and Data Members
1440		2541
1441	=over 4	2542	=over 4
1442		2543
…		…
1468		2569
1469	=back	2570	=back
1470		2571
1471	=head3 Examples	2572	=head3 Examples
1472		2573
1473	Example: Try to exit cleanly on SIGINT and SIGTERM.	2574	Example: C<fork()> a new process and install a child handler to wait for
		2575	its completion.
1474		2576
		2577	ev_child cw;
		2578
1475	static void	2579	static void
1476	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2580	child_cb (EV_P_ ev_child *w, int revents)
1477	{	2581	{
1478	ev_unloop (loop, EVUNLOOP_ALL);	2582	ev_child_stop (EV_A_ w);
		2583	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1479	}	2584	}
1480		2585
1481	struct ev_signal signal_watcher;	2586	pid_t pid = fork ();
1482	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2587
1483	ev_signal_start (loop, &sigint_cb);	2588	if (pid < 0)
		2589	// error
		2590	else if (pid == 0)
		2591	{
		2592	// the forked child executes here
		2593	exit (1);
		2594	}
		2595	else
		2596	{
		2597	ev_child_init (&cw, child_cb, pid, 0);
		2598	ev_child_start (EV_DEFAULT_ &cw);
		2599	}
1484		2600
1485		2601
1486	=head2 C<ev_stat> - did the file attributes just change?	2602	=head2 C<ev_stat> - did the file attributes just change?
1487		2603
1488	This watches a filesystem path for attribute changes. That is, it calls	2604	This watches a file system path for attribute changes. That is, it calls
1489	C<stat> regularly (or when the OS says it changed) and sees if it changed	2605	C<stat> on that path in regular intervals (or when the OS says it changed)
1490	compared to the last time, invoking the callback if it did.	2606	and sees if it changed compared to the last time, invoking the callback if
		2607	it did.
1491		2608
1492	The path does not need to exist: changing from "path exists" to "path does	2609	The path does not need to exist: changing from "path exists" to "path does
1493	not exist" is a status change like any other. The condition "path does	2610	not exist" is a status change like any other. The condition "path does not
1494	not exist" is signified by the C<st_nlink> field being zero (which is	2611	exist" (or more correctly "path cannot be stat'ed") is signified by the
1495	otherwise always forced to be at least one) and all the other fields of	2612	C<st_nlink> field being zero (which is otherwise always forced to be at
1496	the stat buffer having unspecified contents.	2613	least one) and all the other fields of the stat buffer having unspecified
		2614	contents.
1497		2615
1498	The path I<should> be absolute and I<must not> end in a slash. If it is	2616	The path I<must not> end in a slash or contain special components such as
		2617	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1499	relative and your working directory changes, the behaviour is undefined.	2618	your working directory changes, then the behaviour is undefined.
1500		2619
1501	Since there is no standard to do this, the portable implementation simply	2620	Since there is no portable change notification interface available, the
1502	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2621	portable implementation simply calls C<stat(2)> regularly on the path
1503	can specify a recommended polling interval for this case. If you specify	2622	to see if it changed somehow. You can specify a recommended polling
1504	a polling interval of C<0> (highly recommended!) then a I<suitable,	2623	interval for this case. If you specify a polling interval of C<0> (highly
1505	unspecified default> value will be used (which you can expect to be around	2624	recommended!) then a I<suitable, unspecified default> value will be used
1506	five seconds, although this might change dynamically). Libev will also	2625	(which you can expect to be around five seconds, although this might
1507	impose a minimum interval which is currently around C<0.1>, but thats	2626	change dynamically). Libev will also impose a minimum interval which is
1508	usually overkill.	2627	currently around C<0.1>, but that's usually overkill.
1509		2628
1510	This watcher type is not meant for massive numbers of stat watchers,	2629	This watcher type is not meant for massive numbers of stat watchers,
1511	as even with OS-supported change notifications, this can be	2630	as even with OS-supported change notifications, this can be
1512	resource-intensive.	2631	resource-intensive.
1513		2632
1514	At the time of this writing, only the Linux inotify interface is	2633	At the time of this writing, the only OS-specific interface implemented
1515	implemented (implementing kqueue support is left as an exercise for the	2634	is the Linux inotify interface (implementing kqueue support is left as an
1516	reader). Inotify will be used to give hints only and should not change the	2635	exercise for the reader. Note, however, that the author sees no way of
1517	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2636	implementing C<ev_stat> semantics with kqueue, except as a hint).
1518	to fall back to regular polling again even with inotify, but changes are
1519	usually detected immediately, and if the file exists there will be no
1520	polling.
1521		2637
1522	=head3 Inotify	2638	=head3 ABI Issues (Largefile Support)
1523		2639
		2640	Libev by default (unless the user overrides this) uses the default
		2641	compilation environment, which means that on systems with large file
		2642	support disabled by default, you get the 32 bit version of the stat
		2643	structure. When using the library from programs that change the ABI to
		2644	use 64 bit file offsets the programs will fail. In that case you have to
		2645	compile libev with the same flags to get binary compatibility. This is
		2646	obviously the case with any flags that change the ABI, but the problem is
		2647	most noticeably displayed with ev_stat and large file support.
		2648
		2649	The solution for this is to lobby your distribution maker to make large
		2650	file interfaces available by default (as e.g. FreeBSD does) and not
		2651	optional. Libev cannot simply switch on large file support because it has
		2652	to exchange stat structures with application programs compiled using the
		2653	default compilation environment.
		2654
		2655	=head3 Inotify and Kqueue
		2656
1524	When C<inotify (7)> support has been compiled into libev (generally only	2657	When C<inotify (7)> support has been compiled into libev and present at
1525	available on Linux) and present at runtime, it will be used to speed up	2658	runtime, it will be used to speed up change detection where possible. The
1526	change detection where possible. The inotify descriptor will be created lazily	2659	inotify descriptor will be created lazily when the first C<ev_stat>
1527	when the first C<ev_stat> watcher is being started.	2660	watcher is being started.
1528		2661
1529	Inotify presense does not change the semantics of C<ev_stat> watchers	2662	Inotify presence does not change the semantics of C<ev_stat> watchers
1530	except that changes might be detected earlier, and in some cases, to avoid	2663	except that changes might be detected earlier, and in some cases, to avoid
1531	making regular C<stat> calls. Even in the presense of inotify support	2664	making regular C<stat> calls. Even in the presence of inotify support
1532	there are many cases where libev has to resort to regular C<stat> polling.	2665	there are many cases where libev has to resort to regular C<stat> polling,
		2666	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2667	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2668	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2669	xfs are fully working) libev usually gets away without polling.
1533		2670
1534	(There is no support for kqueue, as apparently it cannot be used to	2671	There is no support for kqueue, as apparently it cannot be used to
1535	implement this functionality, due to the requirement of having a file	2672	implement this functionality, due to the requirement of having a file
1536	descriptor open on the object at all times).	2673	descriptor open on the object at all times, and detecting renames, unlinks
		2674	etc. is difficult.
		2675
		2676	=head3 C<stat ()> is a synchronous operation
		2677
		2678	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2679	the process. The exception are C<ev_stat> watchers - those call C<stat
		2680	()>, which is a synchronous operation.
		2681
		2682	For local paths, this usually doesn't matter: unless the system is very
		2683	busy or the intervals between stat's are large, a stat call will be fast,
		2684	as the path data is usually in memory already (except when starting the
		2685	watcher).
		2686
		2687	For networked file systems, calling C<stat ()> can block an indefinite
		2688	time due to network issues, and even under good conditions, a stat call
		2689	often takes multiple milliseconds.
		2690
		2691	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2692	paths, although this is fully supported by libev.
1537		2693
1538	=head3 The special problem of stat time resolution	2694	=head3 The special problem of stat time resolution
1539		2695
1540	The C<stat ()> syscall only supports full-second resolution portably, and	2696	The C<stat ()> system call only supports full-second resolution portably,
1541	even on systems where the resolution is higher, many filesystems still	2697	and even on systems where the resolution is higher, most file systems
1542	only support whole seconds.	2698	still only support whole seconds.
1543		2699
1544	That means that, if the time is the only thing that changes, you might	2700	That means that, if the time is the only thing that changes, you can
1545	miss updates: on the first update, C<ev_stat> detects a change and calls	2701	easily miss updates: on the first update, C<ev_stat> detects a change and
1546	your callback, which does something. When there is another update within	2702	calls your callback, which does something. When there is another update
1547	the same second, C<ev_stat> will be unable to detect it.	2703	within the same second, C<ev_stat> will be unable to detect unless the
		2704	stat data does change in other ways (e.g. file size).
1548		2705
1549	The solution to this is to delay acting on a change for a second (or till	2706	The solution to this is to delay acting on a change for slightly more
1550	the next second boundary), using a roughly one-second delay C<ev_timer>	2707	than a second (or till slightly after the next full second boundary), using
1551	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2708	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1552	is added to work around small timing inconsistencies of some operating	2709	ev_timer_again (loop, w)>).
1553	systems.	2710
		2711	The C<.02> offset is added to work around small timing inconsistencies
		2712	of some operating systems (where the second counter of the current time
		2713	might be be delayed. One such system is the Linux kernel, where a call to
		2714	C<gettimeofday> might return a timestamp with a full second later than
		2715	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2716	update file times then there will be a small window where the kernel uses
		2717	the previous second to update file times but libev might already execute
		2718	the timer callback).
1554		2719
1555	=head3 Watcher-Specific Functions and Data Members	2720	=head3 Watcher-Specific Functions and Data Members
1556		2721
1557	=over 4	2722	=over 4
1558		2723
…		…
1564	C<path>. The C<interval> is a hint on how quickly a change is expected to	2729	C<path>. The C<interval> is a hint on how quickly a change is expected to
1565	be detected and should normally be specified as C<0> to let libev choose	2730	be detected and should normally be specified as C<0> to let libev choose
1566	a suitable value. The memory pointed to by C<path> must point to the same	2731	a suitable value. The memory pointed to by C<path> must point to the same
1567	path for as long as the watcher is active.	2732	path for as long as the watcher is active.
1568		2733
1569	The callback will be receive C<EV_STAT> when a change was detected,	2734	The callback will receive an C<EV_STAT> event when a change was detected,
1570	relative to the attributes at the time the watcher was started (or the	2735	relative to the attributes at the time the watcher was started (or the
1571	last change was detected).	2736	last change was detected).
1572		2737
1573	=item ev_stat_stat (ev_stat *)	2738	=item ev_stat_stat (loop, ev_stat *)
1574		2739
1575	Updates the stat buffer immediately with new values. If you change the	2740	Updates the stat buffer immediately with new values. If you change the
1576	watched path in your callback, you could call this fucntion to avoid	2741	watched path in your callback, you could call this function to avoid
1577	detecting this change (while introducing a race condition). Can also be	2742	detecting this change (while introducing a race condition if you are not
1578	useful simply to find out the new values.	2743	the only one changing the path). Can also be useful simply to find out the
		2744	new values.
1579		2745
1580	=item ev_statdata attr [read-only]	2746	=item ev_statdata attr [read-only]
1581		2747
1582	The most-recently detected attributes of the file. Although the type is of	2748	The most-recently detected attributes of the file. Although the type is
1583	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2749	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1584	suitable for your system. If the C<st_nlink> member is C<0>, then there	2750	suitable for your system, but you can only rely on the POSIX-standardised
		2751	members to be present. If the C<st_nlink> member is C<0>, then there was
1585	was some error while C<stat>ing the file.	2752	some error while C<stat>ing the file.
1586		2753
1587	=item ev_statdata prev [read-only]	2754	=item ev_statdata prev [read-only]
1588		2755
1589	The previous attributes of the file. The callback gets invoked whenever	2756	The previous attributes of the file. The callback gets invoked whenever
1590	C<prev> != C<attr>.	2757	C<prev> != C<attr>, or, more precisely, one or more of these members
		2758	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2759	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1591		2760
1592	=item ev_tstamp interval [read-only]	2761	=item ev_tstamp interval [read-only]
1593		2762
1594	The specified interval.	2763	The specified interval.
1595		2764
1596	=item const char *path [read-only]	2765	=item const char *path [read-only]
1597		2766
1598	The filesystem path that is being watched.	2767	The file system path that is being watched.
1599		2768
1600	=back	2769	=back
1601		2770
1602	=head3 Examples	2771	=head3 Examples
1603		2772
1604	Example: Watch C</etc/passwd> for attribute changes.	2773	Example: Watch C</etc/passwd> for attribute changes.
1605		2774
1606	static void	2775	static void
1607	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2776	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1608	{	2777	{
1609	/* /etc/passwd changed in some way */	2778	/* /etc/passwd changed in some way */
1610	if (w->attr.st_nlink)	2779	if (w->attr.st_nlink)
1611	{	2780	{
1612	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2781	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1613	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2782	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1614	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2783	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1615	}	2784	}
1616	else	2785	else
1617	/* you shalt not abuse printf for puts */	2786	/* you shalt not abuse printf for puts */
1618	puts ("wow, /etc/passwd is not there, expect problems. "	2787	puts ("wow, /etc/passwd is not there, expect problems. "
1619	"if this is windows, they already arrived\n");	2788	"if this is windows, they already arrived\n");
1620	}	2789	}
1621		2790
1622	...	2791	...
1623	ev_stat passwd;	2792	ev_stat passwd;
1624		2793
1625	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2794	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1626	ev_stat_start (loop, &passwd);	2795	ev_stat_start (loop, &passwd);
1627		2796
1628	Example: Like above, but additionally use a one-second delay so we do not	2797	Example: Like above, but additionally use a one-second delay so we do not
1629	miss updates (however, frequent updates will delay processing, too, so	2798	miss updates (however, frequent updates will delay processing, too, so
1630	one might do the work both on C<ev_stat> callback invocation I<and> on	2799	one might do the work both on C<ev_stat> callback invocation I<and> on
1631	C<ev_timer> callback invocation).	2800	C<ev_timer> callback invocation).
1632		2801
1633	static ev_stat passwd;	2802	static ev_stat passwd;
1634	static ev_timer timer;	2803	static ev_timer timer;
1635		2804
1636	static void	2805	static void
1637	timer_cb (EV_P_ ev_timer *w, int revents)	2806	timer_cb (EV_P_ ev_timer *w, int revents)
1638	{	2807	{
1639	ev_timer_stop (EV_A_ w);	2808	ev_timer_stop (EV_A_ w);
1640		2809
1641	/* now it's one second after the most recent passwd change */	2810	/* now it's one second after the most recent passwd change */
1642	}	2811	}
1643		2812
1644	static void	2813	static void
1645	stat_cb (EV_P_ ev_stat *w, int revents)	2814	stat_cb (EV_P_ ev_stat *w, int revents)
1646	{	2815	{
1647	/* reset the one-second timer */	2816	/* reset the one-second timer */
1648	ev_timer_again (EV_A_ &timer);	2817	ev_timer_again (EV_A_ &timer);
1649	}	2818	}
1650		2819
1651	...	2820	...
1652	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2821	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1653	ev_stat_start (loop, &passwd);	2822	ev_stat_start (loop, &passwd);
1654	ev_timer_init (&timer, timer_cb, 0., 1.01);	2823	ev_timer_init (&timer, timer_cb, 0., 1.02);
1655		2824
1656		2825
1657	=head2 C<ev_idle> - when you've got nothing better to do...	2826	=head2 C<ev_idle> - when you've got nothing better to do...
1658		2827
1659	Idle watchers trigger events when no other events of the same or higher	2828	Idle watchers trigger events when no other events of the same or higher
1660	priority are pending (prepare, check and other idle watchers do not	2829	priority are pending (prepare, check and other idle watchers do not count
1661	count).	2830	as receiving "events").
1662		2831
1663	That is, as long as your process is busy handling sockets or timeouts	2832	That is, as long as your process is busy handling sockets or timeouts
1664	(or even signals, imagine) of the same or higher priority it will not be	2833	(or even signals, imagine) of the same or higher priority it will not be
1665	triggered. But when your process is idle (or only lower-priority watchers	2834	triggered. But when your process is idle (or only lower-priority watchers
1666	are pending), the idle watchers are being called once per event loop	2835	are pending), the idle watchers are being called once per event loop
…		…
1677		2846
1678	=head3 Watcher-Specific Functions and Data Members	2847	=head3 Watcher-Specific Functions and Data Members
1679		2848
1680	=over 4	2849	=over 4
1681		2850
1682	=item ev_idle_init (ev_signal *, callback)	2851	=item ev_idle_init (ev_idle *, callback)
1683		2852
1684	Initialises and configures the idle watcher - it has no parameters of any	2853	Initialises and configures the idle watcher - it has no parameters of any
1685	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2854	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1686	believe me.	2855	believe me.
1687		2856
…		…
1690	=head3 Examples	2859	=head3 Examples
1691		2860
1692	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2861	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1693	callback, free it. Also, use no error checking, as usual.	2862	callback, free it. Also, use no error checking, as usual.
1694		2863
1695	static void	2864	static void
1696	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2865	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1697	{	2866	{
1698	free (w);	2867	free (w);
1699	// now do something you wanted to do when the program has	2868	// now do something you wanted to do when the program has
1700	// no longer anything immediate to do.	2869	// no longer anything immediate to do.
1701	}	2870	}
1702		2871
1703	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2872	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1704	ev_idle_init (idle_watcher, idle_cb);	2873	ev_idle_init (idle_watcher, idle_cb);
1705	ev_idle_start (loop, idle_cb);	2874	ev_idle_start (loop, idle_watcher);
1706		2875
1707		2876
1708	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2877	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1709		2878
1710	Prepare and check watchers are usually (but not always) used in tandem:	2879	Prepare and check watchers are usually (but not always) used in pairs:
1711	prepare watchers get invoked before the process blocks and check watchers	2880	prepare watchers get invoked before the process blocks and check watchers
1712	afterwards.	2881	afterwards.
1713		2882
1714	You I<must not> call C<ev_loop> or similar functions that enter	2883	You I<must not> call C<ev_run> or similar functions that enter
1715	the current event loop from either C<ev_prepare> or C<ev_check>	2884	the current event loop from either C<ev_prepare> or C<ev_check>
1716	watchers. Other loops than the current one are fine, however. The	2885	watchers. Other loops than the current one are fine, however. The
1717	rationale behind this is that you do not need to check for recursion in	2886	rationale behind this is that you do not need to check for recursion in
1718	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2887	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1719	C<ev_check> so if you have one watcher of each kind they will always be	2888	C<ev_check> so if you have one watcher of each kind they will always be
1720	called in pairs bracketing the blocking call.	2889	called in pairs bracketing the blocking call.
1721		2890
1722	Their main purpose is to integrate other event mechanisms into libev and	2891	Their main purpose is to integrate other event mechanisms into libev and
1723	their use is somewhat advanced. This could be used, for example, to track	2892	their use is somewhat advanced. They could be used, for example, to track
1724	variable changes, implement your own watchers, integrate net-snmp or a	2893	variable changes, implement your own watchers, integrate net-snmp or a
1725	coroutine library and lots more. They are also occasionally useful if	2894	coroutine library and lots more. They are also occasionally useful if
1726	you cache some data and want to flush it before blocking (for example,	2895	you cache some data and want to flush it before blocking (for example,
1727	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2896	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1728	watcher).	2897	watcher).
1729		2898
1730	This is done by examining in each prepare call which file descriptors need	2899	This is done by examining in each prepare call which file descriptors
1731	to be watched by the other library, registering C<ev_io> watchers for	2900	need to be watched by the other library, registering C<ev_io> watchers
1732	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2901	for them and starting an C<ev_timer> watcher for any timeouts (many
1733	provide just this functionality). Then, in the check watcher you check for	2902	libraries provide exactly this functionality). Then, in the check watcher,
1734	any events that occured (by checking the pending status of all watchers	2903	you check for any events that occurred (by checking the pending status
1735	and stopping them) and call back into the library. The I/O and timer	2904	of all watchers and stopping them) and call back into the library. The
1736	callbacks will never actually be called (but must be valid nevertheless,	2905	I/O and timer callbacks will never actually be called (but must be valid
1737	because you never know, you know?).	2906	nevertheless, because you never know, you know?).
1738		2907
1739	As another example, the Perl Coro module uses these hooks to integrate	2908	As another example, the Perl Coro module uses these hooks to integrate
1740	coroutines into libev programs, by yielding to other active coroutines	2909	coroutines into libev programs, by yielding to other active coroutines
1741	during each prepare and only letting the process block if no coroutines	2910	during each prepare and only letting the process block if no coroutines
1742	are ready to run (it's actually more complicated: it only runs coroutines	2911	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1745	loop from blocking if lower-priority coroutines are active, thus mapping	2914	loop from blocking if lower-priority coroutines are active, thus mapping
1746	low-priority coroutines to idle/background tasks).	2915	low-priority coroutines to idle/background tasks).
1747		2916
1748	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2917	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1749	priority, to ensure that they are being run before any other watchers	2918	priority, to ensure that they are being run before any other watchers
		2919	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2920
1750	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2921	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1751	too) should not activate ("feed") events into libev. While libev fully	2922	activate ("feed") events into libev. While libev fully supports this, they
1752	supports this, they will be called before other C<ev_check> watchers	2923	might get executed before other C<ev_check> watchers did their job. As
1753	did their job. As C<ev_check> watchers are often used to embed other	2924	C<ev_check> watchers are often used to embed other (non-libev) event
1754	(non-libev) event loops those other event loops might be in an unusable	2925	loops those other event loops might be in an unusable state until their
1755	state until their C<ev_check> watcher ran (always remind yourself to	2926	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1756	coexist peacefully with others).	2927	others).
1757		2928
1758	=head3 Watcher-Specific Functions and Data Members	2929	=head3 Watcher-Specific Functions and Data Members
1759		2930
1760	=over 4	2931	=over 4
1761		2932
…		…
1763		2934
1764	=item ev_check_init (ev_check *, callback)	2935	=item ev_check_init (ev_check *, callback)
1765		2936
1766	Initialises and configures the prepare or check watcher - they have no	2937	Initialises and configures the prepare or check watcher - they have no
1767	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2938	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1768	macros, but using them is utterly, utterly and completely pointless.	2939	macros, but using them is utterly, utterly, utterly and completely
		2940	pointless.
1769		2941
1770	=back	2942	=back
1771		2943
1772	=head3 Examples	2944	=head3 Examples
1773		2945
1774	There are a number of principal ways to embed other event loops or modules	2946	There are a number of principal ways to embed other event loops or modules
1775	into libev. Here are some ideas on how to include libadns into libev	2947	into libev. Here are some ideas on how to include libadns into libev
1776	(there is a Perl module named C<EV::ADNS> that does this, which you could	2948	(there is a Perl module named C<EV::ADNS> that does this, which you could
1777	use for an actually working example. Another Perl module named C<EV::Glib>	2949	use as a working example. Another Perl module named C<EV::Glib> embeds a
1778	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2950	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1779	into the Glib event loop).	2951	Glib event loop).
1780		2952
1781	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2953	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1782	and in a check watcher, destroy them and call into libadns. What follows	2954	and in a check watcher, destroy them and call into libadns. What follows
1783	is pseudo-code only of course. This requires you to either use a low	2955	is pseudo-code only of course. This requires you to either use a low
1784	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2956	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1785	the callbacks for the IO/timeout watchers might not have been called yet.	2957	the callbacks for the IO/timeout watchers might not have been called yet.
1786		2958
1787	static ev_io iow [nfd];	2959	static ev_io iow [nfd];
1788	static ev_timer tw;	2960	static ev_timer tw;
1789		2961
1790	static void	2962	static void
1791	io_cb (ev_loop *loop, ev_io *w, int revents)	2963	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1792	{	2964	{
1793	}	2965	}
1794		2966
1795	// create io watchers for each fd and a timer before blocking	2967	// create io watchers for each fd and a timer before blocking
1796	static void	2968	static void
1797	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2969	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1798	{	2970	{
1799	int timeout = 3600000;	2971	int timeout = 3600000;
1800	struct pollfd fds [nfd];	2972	struct pollfd fds [nfd];
1801	// actual code will need to loop here and realloc etc.	2973	// actual code will need to loop here and realloc etc.
1802	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2974	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1803		2975
1804	/* the callback is illegal, but won't be called as we stop during check */	2976	/* the callback is illegal, but won't be called as we stop during check */
1805	ev_timer_init (&tw, 0, timeout * 1e-3);	2977	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1806	ev_timer_start (loop, &tw);	2978	ev_timer_start (loop, &tw);
1807		2979
1808	// create one ev_io per pollfd	2980	// create one ev_io per pollfd
1809	for (int i = 0; i < nfd; ++i)	2981	for (int i = 0; i < nfd; ++i)
1810	{	2982	{
1811	ev_io_init (iow + i, io_cb, fds [i].fd,	2983	ev_io_init (iow + i, io_cb, fds [i].fd,
1812	((fds [i].events & POLLIN ? EV_READ : 0)	2984	((fds [i].events & POLLIN ? EV_READ : 0)
1813	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2985	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1814		2986
1815	fds [i].revents = 0;	2987	fds [i].revents = 0;
1816	ev_io_start (loop, iow + i);	2988	ev_io_start (loop, iow + i);
1817	}	2989	}
1818	}	2990	}
1819		2991
1820	// stop all watchers after blocking	2992	// stop all watchers after blocking
1821	static void	2993	static void
1822	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2994	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1823	{	2995	{
1824	ev_timer_stop (loop, &tw);	2996	ev_timer_stop (loop, &tw);
1825		2997
1826	for (int i = 0; i < nfd; ++i)	2998	for (int i = 0; i < nfd; ++i)
1827	{	2999	{
1828	// set the relevant poll flags	3000	// set the relevant poll flags
1829	// could also call adns_processreadable etc. here	3001	// could also call adns_processreadable etc. here
1830	struct pollfd *fd = fds + i;	3002	struct pollfd *fd = fds + i;
1831	int revents = ev_clear_pending (iow + i);	3003	int revents = ev_clear_pending (iow + i);
1832	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	3004	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1833	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	3005	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1834		3006
1835	// now stop the watcher	3007	// now stop the watcher
1836	ev_io_stop (loop, iow + i);	3008	ev_io_stop (loop, iow + i);
1837	}	3009	}
1838		3010
1839	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3011	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1840	}	3012	}
1841		3013
1842	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	3014	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1843	in the prepare watcher and would dispose of the check watcher.	3015	in the prepare watcher and would dispose of the check watcher.
1844		3016
1845	Method 3: If the module to be embedded supports explicit event	3017	Method 3: If the module to be embedded supports explicit event
1846	notification (adns does), you can also make use of the actual watcher	3018	notification (libadns does), you can also make use of the actual watcher
1847	callbacks, and only destroy/create the watchers in the prepare watcher.	3019	callbacks, and only destroy/create the watchers in the prepare watcher.
1848		3020
1849	static void	3021	static void
1850	timer_cb (EV_P_ ev_timer *w, int revents)	3022	timer_cb (EV_P_ ev_timer *w, int revents)
1851	{	3023	{
1852	adns_state ads = (adns_state)w->data;	3024	adns_state ads = (adns_state)w->data;
1853	update_now (EV_A);	3025	update_now (EV_A);
1854		3026
1855	adns_processtimeouts (ads, &tv_now);	3027	adns_processtimeouts (ads, &tv_now);
1856	}	3028	}
1857		3029
1858	static void	3030	static void
1859	io_cb (EV_P_ ev_io *w, int revents)	3031	io_cb (EV_P_ ev_io *w, int revents)
1860	{	3032	{
1861	adns_state ads = (adns_state)w->data;	3033	adns_state ads = (adns_state)w->data;
1862	update_now (EV_A);	3034	update_now (EV_A);
1863		3035
1864	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	3036	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1865	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	3037	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1866	}	3038	}
1867		3039
1868	// do not ever call adns_afterpoll	3040	// do not ever call adns_afterpoll
1869		3041
1870	Method 4: Do not use a prepare or check watcher because the module you	3042	Method 4: Do not use a prepare or check watcher because the module you
1871	want to embed is too inflexible to support it. Instead, youc na override	3043	want to embed is not flexible enough to support it. Instead, you can
1872	their poll function. The drawback with this solution is that the main	3044	override their poll function. The drawback with this solution is that the
1873	loop is now no longer controllable by EV. The C<Glib::EV> module does	3045	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1874	this.	3046	this approach, effectively embedding EV as a client into the horrible
		3047	libglib event loop.
1875		3048
1876	static gint	3049	static gint
1877	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3050	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1878	{	3051	{
1879	int got_events = 0;	3052	int got_events = 0;
1880		3053
1881	for (n = 0; n < nfds; ++n)	3054	for (n = 0; n < nfds; ++n)
1882	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	3055	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1883		3056
1884	if (timeout >= 0)	3057	if (timeout >= 0)
1885	// create/start timer	3058	// create/start timer
1886		3059
1887	// poll	3060	// poll
1888	ev_loop (EV_A_ 0);	3061	ev_run (EV_A_ 0);
1889		3062
1890	// stop timer again	3063	// stop timer again
1891	if (timeout >= 0)	3064	if (timeout >= 0)
1892	ev_timer_stop (EV_A_ &to);	3065	ev_timer_stop (EV_A_ &to);
1893		3066
1894	// stop io watchers again - their callbacks should have set	3067	// stop io watchers again - their callbacks should have set
1895	for (n = 0; n < nfds; ++n)	3068	for (n = 0; n < nfds; ++n)
1896	ev_io_stop (EV_A_ iow [n]);	3069	ev_io_stop (EV_A_ iow [n]);
1897		3070
1898	return got_events;	3071	return got_events;
1899	}	3072	}
1900		3073
1901		3074
1902	=head2 C<ev_embed> - when one backend isn't enough...	3075	=head2 C<ev_embed> - when one backend isn't enough...
1903		3076
1904	This is a rather advanced watcher type that lets you embed one event loop	3077	This is a rather advanced watcher type that lets you embed one event loop
…		…
1910	prioritise I/O.	3083	prioritise I/O.
1911		3084
1912	As an example for a bug workaround, the kqueue backend might only support	3085	As an example for a bug workaround, the kqueue backend might only support
1913	sockets on some platform, so it is unusable as generic backend, but you	3086	sockets on some platform, so it is unusable as generic backend, but you
1914	still want to make use of it because you have many sockets and it scales	3087	still want to make use of it because you have many sockets and it scales
1915	so nicely. In this case, you would create a kqueue-based loop and embed it	3088	so nicely. In this case, you would create a kqueue-based loop and embed
1916	into your default loop (which might use e.g. poll). Overall operation will	3089	it into your default loop (which might use e.g. poll). Overall operation
1917	be a bit slower because first libev has to poll and then call kevent, but	3090	will be a bit slower because first libev has to call C<poll> and then
1918	at least you can use both at what they are best.	3091	C<kevent>, but at least you can use both mechanisms for what they are
		3092	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1919		3093
1920	As for prioritising I/O: rarely you have the case where some fds have	3094	As for prioritising I/O: under rare circumstances you have the case where
1921	to be watched and handled very quickly (with low latency), and even	3095	some fds have to be watched and handled very quickly (with low latency),
1922	priorities and idle watchers might have too much overhead. In this case	3096	and even priorities and idle watchers might have too much overhead. In
1923	you would put all the high priority stuff in one loop and all the rest in	3097	this case you would put all the high priority stuff in one loop and all
1924	a second one, and embed the second one in the first.	3098	the rest in a second one, and embed the second one in the first.
1925		3099
1926	As long as the watcher is active, the callback will be invoked every time	3100	As long as the watcher is active, the callback will be invoked every
1927	there might be events pending in the embedded loop. The callback must then	3101	time there might be events pending in the embedded loop. The callback
1928	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3102	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1929	their callbacks (you could also start an idle watcher to give the embedded	3103	sweep and invoke their callbacks (the callback doesn't need to invoke the
1930	loop strictly lower priority for example). You can also set the callback	3104	C<ev_embed_sweep> function directly, it could also start an idle watcher
1931	to C<0>, in which case the embed watcher will automatically execute the	3105	to give the embedded loop strictly lower priority for example).
1932	embedded loop sweep.
1933		3106
1934	As long as the watcher is started it will automatically handle events. The	3107	You can also set the callback to C<0>, in which case the embed watcher
1935	callback will be invoked whenever some events have been handled. You can	3108	will automatically execute the embedded loop sweep whenever necessary.
1936	set the callback to C<0> to avoid having to specify one if you are not
1937	interested in that.
1938		3109
1939	Also, there have not currently been made special provisions for forking:	3110	Fork detection will be handled transparently while the C<ev_embed> watcher
1940	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3111	is active, i.e., the embedded loop will automatically be forked when the
1941	but you will also have to stop and restart any C<ev_embed> watchers	3112	embedding loop forks. In other cases, the user is responsible for calling
1942	yourself.	3113	C<ev_loop_fork> on the embedded loop.
1943		3114
1944	Unfortunately, not all backends are embeddable, only the ones returned by	3115	Unfortunately, not all backends are embeddable: only the ones returned by
1945	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3116	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1946	portable one.	3117	portable one.
1947		3118
1948	So when you want to use this feature you will always have to be prepared	3119	So when you want to use this feature you will always have to be prepared
1949	that you cannot get an embeddable loop. The recommended way to get around	3120	that you cannot get an embeddable loop. The recommended way to get around
1950	this is to have a separate variables for your embeddable loop, try to	3121	this is to have a separate variables for your embeddable loop, try to
1951	create it, and if that fails, use the normal loop for everything.	3122	create it, and if that fails, use the normal loop for everything.
1952		3123
		3124	=head3 C<ev_embed> and fork
		3125
		3126	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3127	automatically be applied to the embedded loop as well, so no special
		3128	fork handling is required in that case. When the watcher is not running,
		3129	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3130	as applicable.
		3131
1953	=head3 Watcher-Specific Functions and Data Members	3132	=head3 Watcher-Specific Functions and Data Members
1954		3133
1955	=over 4	3134	=over 4
1956		3135
1957	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3136	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
1960		3139
1961	Configures the watcher to embed the given loop, which must be	3140	Configures the watcher to embed the given loop, which must be
1962	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3141	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1963	invoked automatically, otherwise it is the responsibility of the callback	3142	invoked automatically, otherwise it is the responsibility of the callback
1964	to invoke it (it will continue to be called until the sweep has been done,	3143	to invoke it (it will continue to be called until the sweep has been done,
1965	if you do not want thta, you need to temporarily stop the embed watcher).	3144	if you do not want that, you need to temporarily stop the embed watcher).
1966		3145
1967	=item ev_embed_sweep (loop, ev_embed *)	3146	=item ev_embed_sweep (loop, ev_embed *)
1968		3147
1969	Make a single, non-blocking sweep over the embedded loop. This works	3148	Make a single, non-blocking sweep over the embedded loop. This works
1970	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3149	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1971	apropriate way for embedded loops.	3150	appropriate way for embedded loops.
1972		3151
1973	=item struct ev_loop *other [read-only]	3152	=item struct ev_loop *other [read-only]
1974		3153
1975	The embedded event loop.	3154	The embedded event loop.
1976		3155
…		…
1978		3157
1979	=head3 Examples	3158	=head3 Examples
1980		3159
1981	Example: Try to get an embeddable event loop and embed it into the default	3160	Example: Try to get an embeddable event loop and embed it into the default
1982	event loop. If that is not possible, use the default loop. The default	3161	event loop. If that is not possible, use the default loop. The default
1983	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	3162	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1984	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	3163	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1985	used).	3164	used).
1986		3165
1987	struct ev_loop *loop_hi = ev_default_init (0);	3166	struct ev_loop *loop_hi = ev_default_init (0);
1988	struct ev_loop *loop_lo = 0;	3167	struct ev_loop *loop_lo = 0;
1989	struct ev_embed embed;	3168	ev_embed embed;
1990		3169
1991	// see if there is a chance of getting one that works	3170	// see if there is a chance of getting one that works
1992	// (remember that a flags value of 0 means autodetection)	3171	// (remember that a flags value of 0 means autodetection)
1993	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3172	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1994	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3173	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1995	: 0;	3174	: 0;
1996		3175
1997	// if we got one, then embed it, otherwise default to loop_hi	3176	// if we got one, then embed it, otherwise default to loop_hi
1998	if (loop_lo)	3177	if (loop_lo)
1999	{	3178	{
2000	ev_embed_init (&embed, 0, loop_lo);	3179	ev_embed_init (&embed, 0, loop_lo);
2001	ev_embed_start (loop_hi, &embed);	3180	ev_embed_start (loop_hi, &embed);
2002	}	3181	}
2003	else	3182	else
2004	loop_lo = loop_hi;	3183	loop_lo = loop_hi;
2005		3184
2006	Example: Check if kqueue is available but not recommended and create	3185	Example: Check if kqueue is available but not recommended and create
2007	a kqueue backend for use with sockets (which usually work with any	3186	a kqueue backend for use with sockets (which usually work with any
2008	kqueue implementation). Store the kqueue/socket-only event loop in	3187	kqueue implementation). Store the kqueue/socket-only event loop in
2009	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3188	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2010		3189
2011	struct ev_loop *loop = ev_default_init (0);	3190	struct ev_loop *loop = ev_default_init (0);
2012	struct ev_loop *loop_socket = 0;	3191	struct ev_loop *loop_socket = 0;
2013	struct ev_embed embed;	3192	ev_embed embed;
2014		3193
2015	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3194	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2016	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3195	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2017	{	3196	{
2018	ev_embed_init (&embed, 0, loop_socket);	3197	ev_embed_init (&embed, 0, loop_socket);
2019	ev_embed_start (loop, &embed);	3198	ev_embed_start (loop, &embed);
2020	}	3199	}
2021		3200
2022	if (!loop_socket)	3201	if (!loop_socket)
2023	loop_socket = loop;	3202	loop_socket = loop;
2024		3203
2025	// now use loop_socket for all sockets, and loop for everything else	3204	// now use loop_socket for all sockets, and loop for everything else
2026		3205
2027		3206
2028	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3207	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2029		3208
2030	Fork watchers are called when a C<fork ()> was detected (usually because	3209	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2033	event loop blocks next and before C<ev_check> watchers are being called,	3212	event loop blocks next and before C<ev_check> watchers are being called,
2034	and only in the child after the fork. If whoever good citizen calling	3213	and only in the child after the fork. If whoever good citizen calling
2035	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3214	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2036	handlers will be invoked, too, of course.	3215	handlers will be invoked, too, of course.
2037		3216
		3217	=head3 The special problem of life after fork - how is it possible?
		3218
		3219	Most uses of C<fork()> consist of forking, then some simple calls to set
		3220	up/change the process environment, followed by a call to C<exec()>. This
		3221	sequence should be handled by libev without any problems.
		3222
		3223	This changes when the application actually wants to do event handling
		3224	in the child, or both parent in child, in effect "continuing" after the
		3225	fork.
		3226
		3227	The default mode of operation (for libev, with application help to detect
		3228	forks) is to duplicate all the state in the child, as would be expected
		3229	when I<either> the parent I<or> the child process continues.
		3230
		3231	When both processes want to continue using libev, then this is usually the
		3232	wrong result. In that case, usually one process (typically the parent) is
		3233	supposed to continue with all watchers in place as before, while the other
		3234	process typically wants to start fresh, i.e. without any active watchers.
		3235
		3236	The cleanest and most efficient way to achieve that with libev is to
		3237	simply create a new event loop, which of course will be "empty", and
		3238	use that for new watchers. This has the advantage of not touching more
		3239	memory than necessary, and thus avoiding the copy-on-write, and the
		3240	disadvantage of having to use multiple event loops (which do not support
		3241	signal watchers).
		3242
		3243	When this is not possible, or you want to use the default loop for
		3244	other reasons, then in the process that wants to start "fresh", call
		3245	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3246	Destroying the default loop will "orphan" (not stop) all registered
		3247	watchers, so you have to be careful not to execute code that modifies
		3248	those watchers. Note also that in that case, you have to re-register any
		3249	signal watchers.
		3250
2038	=head3 Watcher-Specific Functions and Data Members	3251	=head3 Watcher-Specific Functions and Data Members
2039		3252
2040	=over 4	3253	=over 4
2041		3254
2042	=item ev_fork_init (ev_signal *, callback)	3255	=item ev_fork_init (ev_fork *, callback)
2043		3256
2044	Initialises and configures the fork watcher - it has no parameters of any	3257	Initialises and configures the fork watcher - it has no parameters of any
2045	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3258	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2046	believe me.	3259	really.
2047		3260
2048	=back	3261	=back
2049		3262
2050		3263
		3264	=head2 C<ev_cleanup> - even the best things end
		3265
		3266	Cleanup watchers are called just before the event loop is being destroyed
		3267	by a call to C<ev_loop_destroy>.
		3268
		3269	While there is no guarantee that the event loop gets destroyed, cleanup
		3270	watchers provide a convenient method to install cleanup hooks for your
		3271	program, worker threads and so on - you just to make sure to destroy the
		3272	loop when you want them to be invoked.
		3273
		3274	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3275	all other watchers, they do not keep a reference to the event loop (which
		3276	makes a lot of sense if you think about it). Like all other watchers, you
		3277	can call libev functions in the callback, except C<ev_cleanup_start>.
		3278
		3279	=head3 Watcher-Specific Functions and Data Members
		3280
		3281	=over 4
		3282
		3283	=item ev_cleanup_init (ev_cleanup *, callback)
		3284
		3285	Initialises and configures the cleanup watcher - it has no parameters of
		3286	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3287	pointless, I assure you.
		3288
		3289	=back
		3290
		3291	Example: Register an atexit handler to destroy the default loop, so any
		3292	cleanup functions are called.
		3293
		3294	static void
		3295	program_exits (void)
		3296	{
		3297	ev_loop_destroy (EV_DEFAULT_UC);
		3298	}
		3299
		3300	...
		3301	atexit (program_exits);
		3302
		3303
		3304	=head2 C<ev_async> - how to wake up an event loop
		3305
		3306	In general, you cannot use an C<ev_loop> from multiple threads or other
		3307	asynchronous sources such as signal handlers (as opposed to multiple event
		3308	loops - those are of course safe to use in different threads).
		3309
		3310	Sometimes, however, you need to wake up an event loop you do not control,
		3311	for example because it belongs to another thread. This is what C<ev_async>
		3312	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3313	it by calling C<ev_async_send>, which is thread- and signal safe.
		3314
		3315	This functionality is very similar to C<ev_signal> watchers, as signals,
		3316	too, are asynchronous in nature, and signals, too, will be compressed
		3317	(i.e. the number of callback invocations may be less than the number of
		3318	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3319	of "global async watchers" by using a watcher on an otherwise unused
		3320	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3321	even without knowing which loop owns the signal.
		3322
		3323	=head3 Queueing
		3324
		3325	C<ev_async> does not support queueing of data in any way. The reason
		3326	is that the author does not know of a simple (or any) algorithm for a
		3327	multiple-writer-single-reader queue that works in all cases and doesn't
		3328	need elaborate support such as pthreads or unportable memory access
		3329	semantics.
		3330
		3331	That means that if you want to queue data, you have to provide your own
		3332	queue. But at least I can tell you how to implement locking around your
		3333	queue:
		3334
		3335	=over 4
		3336
		3337	=item queueing from a signal handler context
		3338
		3339	To implement race-free queueing, you simply add to the queue in the signal
		3340	handler but you block the signal handler in the watcher callback. Here is
		3341	an example that does that for some fictitious SIGUSR1 handler:
		3342
		3343	static ev_async mysig;
		3344
		3345	static void
		3346	sigusr1_handler (void)
		3347	{
		3348	sometype data;
		3349
		3350	// no locking etc.
		3351	queue_put (data);
		3352	ev_async_send (EV_DEFAULT_ &mysig);
		3353	}
		3354
		3355	static void
		3356	mysig_cb (EV_P_ ev_async *w, int revents)
		3357	{
		3358	sometype data;
		3359	sigset_t block, prev;
		3360
		3361	sigemptyset (&block);
		3362	sigaddset (&block, SIGUSR1);
		3363	sigprocmask (SIG_BLOCK, &block, &prev);
		3364
		3365	while (queue_get (&data))
		3366	process (data);
		3367
		3368	if (sigismember (&prev, SIGUSR1)
		3369	sigprocmask (SIG_UNBLOCK, &block, 0);
		3370	}
		3371
		3372	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3373	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3374	either...).
		3375
		3376	=item queueing from a thread context
		3377
		3378	The strategy for threads is different, as you cannot (easily) block
		3379	threads but you can easily preempt them, so to queue safely you need to
		3380	employ a traditional mutex lock, such as in this pthread example:
		3381
		3382	static ev_async mysig;
		3383	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3384
		3385	static void
		3386	otherthread (void)
		3387	{
		3388	// only need to lock the actual queueing operation
		3389	pthread_mutex_lock (&mymutex);
		3390	queue_put (data);
		3391	pthread_mutex_unlock (&mymutex);
		3392
		3393	ev_async_send (EV_DEFAULT_ &mysig);
		3394	}
		3395
		3396	static void
		3397	mysig_cb (EV_P_ ev_async *w, int revents)
		3398	{
		3399	pthread_mutex_lock (&mymutex);
		3400
		3401	while (queue_get (&data))
		3402	process (data);
		3403
		3404	pthread_mutex_unlock (&mymutex);
		3405	}
		3406
		3407	=back
		3408
		3409
		3410	=head3 Watcher-Specific Functions and Data Members
		3411
		3412	=over 4
		3413
		3414	=item ev_async_init (ev_async *, callback)
		3415
		3416	Initialises and configures the async watcher - it has no parameters of any
		3417	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3418	trust me.
		3419
		3420	=item ev_async_send (loop, ev_async *)
		3421
		3422	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3423	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3424	returns.
		3425
		3426	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3427	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3428	embedding section below on what exactly this means).
		3429
		3430	Note that, as with other watchers in libev, multiple events might get
		3431	compressed into a single callback invocation (another way to look at
		3432	this is that C<ev_async> watchers are level-triggered: they are set on
		3433	C<ev_async_send>, reset when the event loop detects that).
		3434
		3435	This call incurs the overhead of at most one extra system call per event
		3436	loop iteration, if the event loop is blocked, and no syscall at all if
		3437	the event loop (or your program) is processing events. That means that
		3438	repeated calls are basically free (there is no need to avoid calls for
		3439	performance reasons) and that the overhead becomes smaller (typically
		3440	zero) under load.
		3441
		3442	=item bool = ev_async_pending (ev_async *)
		3443
		3444	Returns a non-zero value when C<ev_async_send> has been called on the
		3445	watcher but the event has not yet been processed (or even noted) by the
		3446	event loop.
		3447
		3448	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3449	the loop iterates next and checks for the watcher to have become active,
		3450	it will reset the flag again. C<ev_async_pending> can be used to very
		3451	quickly check whether invoking the loop might be a good idea.
		3452
		3453	Not that this does I<not> check whether the watcher itself is pending,
		3454	only whether it has been requested to make this watcher pending: there
		3455	is a time window between the event loop checking and resetting the async
		3456	notification, and the callback being invoked.
		3457
		3458	=back
		3459
		3460
2051	=head1 OTHER FUNCTIONS	3461	=head1 OTHER FUNCTIONS
2052		3462
2053	There are some other functions of possible interest. Described. Here. Now.	3463	There are some other functions of possible interest. Described. Here. Now.
2054		3464
2055	=over 4	3465	=over 4
2056		3466
2057	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3467	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2058		3468
2059	This function combines a simple timer and an I/O watcher, calls your	3469	This function combines a simple timer and an I/O watcher, calls your
2060	callback on whichever event happens first and automatically stop both	3470	callback on whichever event happens first and automatically stops both
2061	watchers. This is useful if you want to wait for a single event on an fd	3471	watchers. This is useful if you want to wait for a single event on an fd
2062	or timeout without having to allocate/configure/start/stop/free one or	3472	or timeout without having to allocate/configure/start/stop/free one or
2063	more watchers yourself.	3473	more watchers yourself.
2064		3474
2065	If C<fd> is less than 0, then no I/O watcher will be started and events	3475	If C<fd> is less than 0, then no I/O watcher will be started and the
2066	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3476	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2067	C<events> set will be craeted and started.	3477	the given C<fd> and C<events> set will be created and started.
2068		3478
2069	If C<timeout> is less than 0, then no timeout watcher will be	3479	If C<timeout> is less than 0, then no timeout watcher will be
2070	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3480	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2071	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3481	repeat = 0) will be started. C<0> is a valid timeout.
2072	dubious value.
2073		3482
2074	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3483	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2075	passed an C<revents> set like normal event callbacks (a combination of	3484	passed an C<revents> set like normal event callbacks (a combination of
2076	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3485	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2077	value passed to C<ev_once>:	3486	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3487	a timeout and an io event at the same time - you probably should give io
		3488	events precedence.
2078		3489
		3490	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3491
2079	static void stdin_ready (int revents, void *arg)	3492	static void stdin_ready (int revents, void *arg)
		3493	{
		3494	if (revents & EV_READ)
		3495	/* stdin might have data for us, joy! */;
		3496	else if (revents & EV_TIMER)
		3497	/* doh, nothing entered */;
		3498	}
		3499
		3500	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3501
		3502	=item ev_feed_fd_event (loop, int fd, int revents)
		3503
		3504	Feed an event on the given fd, as if a file descriptor backend detected
		3505	the given events.
		3506
		3507	=item ev_feed_signal_event (loop, int signum)
		3508
		3509	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3510	which is async-safe.
		3511
		3512	=back
		3513
		3514
		3515	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3516
		3517	This section explains some common idioms that are not immediately
		3518	obvious. Note that examples are sprinkled over the whole manual, and this
		3519	section only contains stuff that wouldn't fit anywhere else.
		3520
		3521	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3522
		3523	Each watcher has, by default, a C<void *data> member that you can read
		3524	or modify at any time: libev will completely ignore it. This can be used
		3525	to associate arbitrary data with your watcher. If you need more data and
		3526	don't want to allocate memory separately and store a pointer to it in that
		3527	data member, you can also "subclass" the watcher type and provide your own
		3528	data:
		3529
		3530	struct my_io
		3531	{
		3532	ev_io io;
		3533	int otherfd;
		3534	void *somedata;
		3535	struct whatever *mostinteresting;
		3536	};
		3537
		3538	...
		3539	struct my_io w;
		3540	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3541
		3542	And since your callback will be called with a pointer to the watcher, you
		3543	can cast it back to your own type:
		3544
		3545	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3546	{
		3547	struct my_io *w = (struct my_io *)w_;
		3548	...
		3549	}
		3550
		3551	More interesting and less C-conformant ways of casting your callback
		3552	function type instead have been omitted.
		3553
		3554	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3555
		3556	Another common scenario is to use some data structure with multiple
		3557	embedded watchers, in effect creating your own watcher that combines
		3558	multiple libev event sources into one "super-watcher":
		3559
		3560	struct my_biggy
		3561	{
		3562	int some_data;
		3563	ev_timer t1;
		3564	ev_timer t2;
		3565	}
		3566
		3567	In this case getting the pointer to C<my_biggy> is a bit more
		3568	complicated: Either you store the address of your C<my_biggy> struct in
		3569	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3570	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3571	real programmers):
		3572
		3573	#include <stddef.h>
		3574
		3575	static void
		3576	t1_cb (EV_P_ ev_timer *w, int revents)
		3577	{
		3578	struct my_biggy big = (struct my_biggy *)
		3579	(((char *)w) - offsetof (struct my_biggy, t1));
		3580	}
		3581
		3582	static void
		3583	t2_cb (EV_P_ ev_timer *w, int revents)
		3584	{
		3585	struct my_biggy big = (struct my_biggy *)
		3586	(((char *)w) - offsetof (struct my_biggy, t2));
		3587	}
		3588
		3589	=head2 AVOIDING FINISHING BEFORE RETURNING
		3590
		3591	Often you have structures like this in event-based programs:
		3592
		3593	callback ()
2080	{	3594	{
2081	if (revents & EV_TIMEOUT)	3595	free (request);
2082	/* doh, nothing entered */;
2083	else if (revents & EV_READ)
2084	/* stdin might have data for us, joy! */;
2085	}	3596	}
2086		3597
2087	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3598	request = start_new_request (..., callback);
2088		3599
2089	=item ev_feed_event (ev_loop *, watcher *, int revents)	3600	The intent is to start some "lengthy" operation. The C<request> could be
		3601	used to cancel the operation, or do other things with it.
2090		3602
2091	Feeds the given event set into the event loop, as if the specified event	3603	It's not uncommon to have code paths in C<start_new_request> that
2092	had happened for the specified watcher (which must be a pointer to an	3604	immediately invoke the callback, for example, to report errors. Or you add
2093	initialised but not necessarily started event watcher).	3605	some caching layer that finds that it can skip the lengthy aspects of the
		3606	operation and simply invoke the callback with the result.
2094		3607
2095	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3608	The problem here is that this will happen I<before> C<start_new_request>
		3609	has returned, so C<request> is not set.
2096		3610
2097	Feed an event on the given fd, as if a file descriptor backend detected	3611	Even if you pass the request by some safer means to the callback, you
2098	the given events it.	3612	might want to do something to the request after starting it, such as
		3613	canceling it, which probably isn't working so well when the callback has
		3614	already been invoked.
2099		3615
2100	=item ev_feed_signal_event (ev_loop *loop, int signum)	3616	A common way around all these issues is to make sure that
		3617	C<start_new_request> I<always> returns before the callback is invoked. If
		3618	C<start_new_request> immediately knows the result, it can artificially
		3619	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3620	for example, or more sneakily, by reusing an existing (stopped) watcher
		3621	and pushing it into the pending queue:
2101		3622
2102	Feed an event as if the given signal occured (C<loop> must be the default	3623	ev_set_cb (watcher, callback);
2103	loop!).	3624	ev_feed_event (EV_A_ watcher, 0);
2104		3625
2105	=back	3626	This way, C<start_new_request> can safely return before the callback is
		3627	invoked, while not delaying callback invocation too much.
		3628
		3629	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3630
		3631	Often (especially in GUI toolkits) there are places where you have
		3632	I<modal> interaction, which is most easily implemented by recursively
		3633	invoking C<ev_run>.
		3634
		3635	This brings the problem of exiting - a callback might want to finish the
		3636	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3637	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3638	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3639	other combination: In these cases, C<ev_break> will not work alone.
		3640
		3641	The solution is to maintain "break this loop" variable for each C<ev_run>
		3642	invocation, and use a loop around C<ev_run> until the condition is
		3643	triggered, using C<EVRUN_ONCE>:
		3644
		3645	// main loop
		3646	int exit_main_loop = 0;
		3647
		3648	while (!exit_main_loop)
		3649	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3650
		3651	// in a modal watcher
		3652	int exit_nested_loop = 0;
		3653
		3654	while (!exit_nested_loop)
		3655	ev_run (EV_A_ EVRUN_ONCE);
		3656
		3657	To exit from any of these loops, just set the corresponding exit variable:
		3658
		3659	// exit modal loop
		3660	exit_nested_loop = 1;
		3661
		3662	// exit main program, after modal loop is finished
		3663	exit_main_loop = 1;
		3664
		3665	// exit both
		3666	exit_main_loop = exit_nested_loop = 1;
		3667
		3668	=head2 THREAD LOCKING EXAMPLE
		3669
		3670	Here is a fictitious example of how to run an event loop in a different
		3671	thread from where callbacks are being invoked and watchers are
		3672	created/added/removed.
		3673
		3674	For a real-world example, see the C<EV::Loop::Async> perl module,
		3675	which uses exactly this technique (which is suited for many high-level
		3676	languages).
		3677
		3678	The example uses a pthread mutex to protect the loop data, a condition
		3679	variable to wait for callback invocations, an async watcher to notify the
		3680	event loop thread and an unspecified mechanism to wake up the main thread.
		3681
		3682	First, you need to associate some data with the event loop:
		3683
		3684	typedef struct {
		3685	mutex_t lock; /* global loop lock */
		3686	ev_async async_w;
		3687	thread_t tid;
		3688	cond_t invoke_cv;
		3689	} userdata;
		3690
		3691	void prepare_loop (EV_P)
		3692	{
		3693	// for simplicity, we use a static userdata struct.
		3694	static userdata u;
		3695
		3696	ev_async_init (&u->async_w, async_cb);
		3697	ev_async_start (EV_A_ &u->async_w);
		3698
		3699	pthread_mutex_init (&u->lock, 0);
		3700	pthread_cond_init (&u->invoke_cv, 0);
		3701
		3702	// now associate this with the loop
		3703	ev_set_userdata (EV_A_ u);
		3704	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3705	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3706
		3707	// then create the thread running ev_run
		3708	pthread_create (&u->tid, 0, l_run, EV_A);
		3709	}
		3710
		3711	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3712	solely to wake up the event loop so it takes notice of any new watchers
		3713	that might have been added:
		3714
		3715	static void
		3716	async_cb (EV_P_ ev_async *w, int revents)
		3717	{
		3718	// just used for the side effects
		3719	}
		3720
		3721	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3722	protecting the loop data, respectively.
		3723
		3724	static void
		3725	l_release (EV_P)
		3726	{
		3727	userdata *u = ev_userdata (EV_A);
		3728	pthread_mutex_unlock (&u->lock);
		3729	}
		3730
		3731	static void
		3732	l_acquire (EV_P)
		3733	{
		3734	userdata *u = ev_userdata (EV_A);
		3735	pthread_mutex_lock (&u->lock);
		3736	}
		3737
		3738	The event loop thread first acquires the mutex, and then jumps straight
		3739	into C<ev_run>:
		3740
		3741	void *
		3742	l_run (void *thr_arg)
		3743	{
		3744	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3745
		3746	l_acquire (EV_A);
		3747	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3748	ev_run (EV_A_ 0);
		3749	l_release (EV_A);
		3750
		3751	return 0;
		3752	}
		3753
		3754	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3755	signal the main thread via some unspecified mechanism (signals? pipe
		3756	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3757	have been called (in a while loop because a) spurious wakeups are possible
		3758	and b) skipping inter-thread-communication when there are no pending
		3759	watchers is very beneficial):
		3760
		3761	static void
		3762	l_invoke (EV_P)
		3763	{
		3764	userdata *u = ev_userdata (EV_A);
		3765
		3766	while (ev_pending_count (EV_A))
		3767	{
		3768	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3769	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3770	}
		3771	}
		3772
		3773	Now, whenever the main thread gets told to invoke pending watchers, it
		3774	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3775	thread to continue:
		3776
		3777	static void
		3778	real_invoke_pending (EV_P)
		3779	{
		3780	userdata *u = ev_userdata (EV_A);
		3781
		3782	pthread_mutex_lock (&u->lock);
		3783	ev_invoke_pending (EV_A);
		3784	pthread_cond_signal (&u->invoke_cv);
		3785	pthread_mutex_unlock (&u->lock);
		3786	}
		3787
		3788	Whenever you want to start/stop a watcher or do other modifications to an
		3789	event loop, you will now have to lock:
		3790
		3791	ev_timer timeout_watcher;
		3792	userdata *u = ev_userdata (EV_A);
		3793
		3794	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3795
		3796	pthread_mutex_lock (&u->lock);
		3797	ev_timer_start (EV_A_ &timeout_watcher);
		3798	ev_async_send (EV_A_ &u->async_w);
		3799	pthread_mutex_unlock (&u->lock);
		3800
		3801	Note that sending the C<ev_async> watcher is required because otherwise
		3802	an event loop currently blocking in the kernel will have no knowledge
		3803	about the newly added timer. By waking up the loop it will pick up any new
		3804	watchers in the next event loop iteration.
		3805
		3806	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3807
		3808	While the overhead of a callback that e.g. schedules a thread is small, it
		3809	is still an overhead. If you embed libev, and your main usage is with some
		3810	kind of threads or coroutines, you might want to customise libev so that
		3811	doesn't need callbacks anymore.
		3812
		3813	Imagine you have coroutines that you can switch to using a function
		3814	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3815	and that due to some magic, the currently active coroutine is stored in a
		3816	global called C<current_coro>. Then you can build your own "wait for libev
		3817	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3818	the differing C<;> conventions):
		3819
		3820	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3821	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3822
		3823	That means instead of having a C callback function, you store the
		3824	coroutine to switch to in each watcher, and instead of having libev call
		3825	your callback, you instead have it switch to that coroutine.
		3826
		3827	A coroutine might now wait for an event with a function called
		3828	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3829	matter when, or whether the watcher is active or not when this function is
		3830	called):
		3831
		3832	void
		3833	wait_for_event (ev_watcher *w)
		3834	{
		3835	ev_cb_set (w) = current_coro;
		3836	switch_to (libev_coro);
		3837	}
		3838
		3839	That basically suspends the coroutine inside C<wait_for_event> and
		3840	continues the libev coroutine, which, when appropriate, switches back to
		3841	this or any other coroutine.
		3842
		3843	You can do similar tricks if you have, say, threads with an event queue -
		3844	instead of storing a coroutine, you store the queue object and instead of
		3845	switching to a coroutine, you push the watcher onto the queue and notify
		3846	any waiters.
		3847
		3848	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3849	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3850
		3851	// my_ev.h
		3852	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3853	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3854	#include "../libev/ev.h"
		3855
		3856	// my_ev.c
		3857	#define EV_H "my_ev.h"
		3858	#include "../libev/ev.c"
		3859
		3860	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3861	F<my_ev.c> into your project. When properly specifying include paths, you
		3862	can even use F<ev.h> as header file name directly.
2106		3863
2107		3864
2108	=head1 LIBEVENT EMULATION	3865	=head1 LIBEVENT EMULATION
2109		3866
2110	Libev offers a compatibility emulation layer for libevent. It cannot	3867	Libev offers a compatibility emulation layer for libevent. It cannot
2111	emulate the internals of libevent, so here are some usage hints:	3868	emulate the internals of libevent, so here are some usage hints:
2112		3869
2113	=over 4	3870	=over 4
		3871
		3872	=item * Only the libevent-1.4.1-beta API is being emulated.
		3873
		3874	This was the newest libevent version available when libev was implemented,
		3875	and is still mostly unchanged in 2010.
2114		3876
2115	=item * Use it by including <event.h>, as usual.	3877	=item * Use it by including <event.h>, as usual.
2116		3878
2117	=item * The following members are fully supported: ev_base, ev_callback,	3879	=item * The following members are fully supported: ev_base, ev_callback,
2118	ev_arg, ev_fd, ev_res, ev_events.	3880	ev_arg, ev_fd, ev_res, ev_events.
…		…
2123		3885
2124	=item * Priorities are not currently supported. Initialising priorities	3886	=item * Priorities are not currently supported. Initialising priorities
2125	will fail and all watchers will have the same priority, even though there	3887	will fail and all watchers will have the same priority, even though there
2126	is an ev_pri field.	3888	is an ev_pri field.
2127		3889
		3890	=item * In libevent, the last base created gets the signals, in libev, the
		3891	base that registered the signal gets the signals.
		3892
2128	=item * Other members are not supported.	3893	=item * Other members are not supported.
2129		3894
2130	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3895	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2131	to use the libev header file and library.	3896	to use the libev header file and library.
2132		3897
2133	=back	3898	=back
2134		3899
2135	=head1 C++ SUPPORT	3900	=head1 C++ SUPPORT
2136		3901
		3902	=head2 C API
		3903
		3904	The normal C API should work fine when used from C++: both ev.h and the
		3905	libev sources can be compiled as C++. Therefore, code that uses the C API
		3906	will work fine.
		3907
		3908	Proper exception specifications might have to be added to callbacks passed
		3909	to libev: exceptions may be thrown only from watcher callbacks, all
		3910	other callbacks (allocator, syserr, loop acquire/release and periodioc
		3911	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3912	()> specification. If you have code that needs to be compiled as both C
		3913	and C++ you can use the C<EV_THROW> macro for this:
		3914
		3915	static void
		3916	fatal_error (const char *msg) EV_THROW
		3917	{
		3918	perror (msg);
		3919	abort ();
		3920	}
		3921
		3922	...
		3923	ev_set_syserr_cb (fatal_error);
		3924
		3925	The only API functions that can currently throw exceptions are C<ev_run>,
		3926	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3927	because it runs cleanup watchers).
		3928
		3929	Throwing exceptions in watcher callbacks is only supported if libev itself
		3930	is compiled with a C++ compiler or your C and C++ environments allow
		3931	throwing exceptions through C libraries (most do).
		3932
		3933	=head2 C++ API
		3934
2137	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3935	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2138	you to use some convinience methods to start/stop watchers and also change	3936	you to use some convenience methods to start/stop watchers and also change
2139	the callback model to a model using method callbacks on objects.	3937	the callback model to a model using method callbacks on objects.
2140		3938
2141	To use it,	3939	To use it,
2142		3940
2143	#include <ev++.h>	3941	#include <ev++.h>
2144		3942
2145	This automatically includes F<ev.h> and puts all of its definitions (many	3943	This automatically includes F<ev.h> and puts all of its definitions (many
2146	of them macros) into the global namespace. All C++ specific things are	3944	of them macros) into the global namespace. All C++ specific things are
2147	put into the C<ev> namespace. It should support all the same embedding	3945	put into the C<ev> namespace. It should support all the same embedding
2148	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3946	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2150	Care has been taken to keep the overhead low. The only data member the C++	3948	Care has been taken to keep the overhead low. The only data member the C++
2151	classes add (compared to plain C-style watchers) is the event loop pointer	3949	classes add (compared to plain C-style watchers) is the event loop pointer
2152	that the watcher is associated with (or no additional members at all if	3950	that the watcher is associated with (or no additional members at all if
2153	you disable C<EV_MULTIPLICITY> when embedding libev).	3951	you disable C<EV_MULTIPLICITY> when embedding libev).
2154		3952
2155	Currently, functions, and static and non-static member functions can be	3953	Currently, functions, static and non-static member functions and classes
2156	used as callbacks. Other types should be easy to add as long as they only	3954	with C<operator ()> can be used as callbacks. Other types should be easy
2157	need one additional pointer for context. If you need support for other	3955	to add as long as they only need one additional pointer for context. If
2158	types of functors please contact the author (preferably after implementing	3956	you need support for other types of functors please contact the author
2159	it).	3957	(preferably after implementing it).
		3958
		3959	For all this to work, your C++ compiler either has to use the same calling
		3960	conventions as your C compiler (for static member functions), or you have
		3961	to embed libev and compile libev itself as C++.
2160		3962
2161	Here is a list of things available in the C<ev> namespace:	3963	Here is a list of things available in the C<ev> namespace:
2162		3964
2163	=over 4	3965	=over 4
2164		3966
…		…
2174	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	3976	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2175		3977
2176	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	3978	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2177	the same name in the C<ev> namespace, with the exception of C<ev_signal>	3979	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2178	which is called C<ev::sig> to avoid clashes with the C<signal> macro	3980	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2179	defines by many implementations.	3981	defined by many implementations.
2180		3982
2181	All of those classes have these methods:	3983	All of those classes have these methods:
2182		3984
2183	=over 4	3985	=over 4
2184		3986
2185	=item ev::TYPE::TYPE ()	3987	=item ev::TYPE::TYPE ()
2186		3988
2187	=item ev::TYPE::TYPE (struct ev_loop *)	3989	=item ev::TYPE::TYPE (loop)
2188		3990
2189	=item ev::TYPE::~TYPE	3991	=item ev::TYPE::~TYPE
2190		3992
2191	The constructor (optionally) takes an event loop to associate the watcher	3993	The constructor (optionally) takes an event loop to associate the watcher
2192	with. If it is omitted, it will use C<EV_DEFAULT>.	3994	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2215	your compiler is good :), then the method will be fully inlined into the	4017	your compiler is good :), then the method will be fully inlined into the
2216	thunking function, making it as fast as a direct C callback.	4018	thunking function, making it as fast as a direct C callback.
2217		4019
2218	Example: simple class declaration and watcher initialisation	4020	Example: simple class declaration and watcher initialisation
2219		4021
2220	struct myclass	4022	struct myclass
2221	{	4023	{
2222	void io_cb (ev::io &w, int revents) { }	4024	void io_cb (ev::io &w, int revents) { }
2223	}	4025	}
2224		4026
2225	myclass obj;	4027	myclass obj;
2226	ev::io iow;	4028	ev::io iow;
2227	iow.set <myclass, &myclass::io_cb> (&obj);	4029	iow.set <myclass, &myclass::io_cb> (&obj);
		4030
		4031	=item w->set (object *)
		4032
		4033	This is a variation of a method callback - leaving out the method to call
		4034	will default the method to C<operator ()>, which makes it possible to use
		4035	functor objects without having to manually specify the C<operator ()> all
		4036	the time. Incidentally, you can then also leave out the template argument
		4037	list.
		4038
		4039	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4040	int revents)>.
		4041
		4042	See the method-C<set> above for more details.
		4043
		4044	Example: use a functor object as callback.
		4045
		4046	struct myfunctor
		4047	{
		4048	void operator() (ev::io &w, int revents)
		4049	{
		4050	...
		4051	}
		4052	}
		4053
		4054	myfunctor f;
		4055
		4056	ev::io w;
		4057	w.set (&f);
2228		4058
2229	=item w->set<function> (void *data = 0)	4059	=item w->set<function> (void *data = 0)
2230		4060
2231	Also sets a callback, but uses a static method or plain function as	4061	Also sets a callback, but uses a static method or plain function as
2232	callback. The optional C<data> argument will be stored in the watcher's	4062	callback. The optional C<data> argument will be stored in the watcher's
…		…
2234		4064
2235	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4065	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2236		4066
2237	See the method-C<set> above for more details.	4067	See the method-C<set> above for more details.
2238		4068
2239	Example:	4069	Example: Use a plain function as callback.
2240		4070
2241	static void io_cb (ev::io &w, int revents) { }	4071	static void io_cb (ev::io &w, int revents) { }
2242	iow.set <io_cb> ();	4072	iow.set <io_cb> ();
2243		4073
2244	=item w->set (struct ev_loop *)	4074	=item w->set (loop)
2245		4075
2246	Associates a different C<struct ev_loop> with this watcher. You can only	4076	Associates a different C<struct ev_loop> with this watcher. You can only
2247	do this when the watcher is inactive (and not pending either).	4077	do this when the watcher is inactive (and not pending either).
2248		4078
2249	=item w->set ([args])	4079	=item w->set ([arguments])
2250		4080
2251	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4081	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2252	called at least once. Unlike the C counterpart, an active watcher gets	4082	method or a suitable start method must be called at least once. Unlike the
2253	automatically stopped and restarted when reconfiguring it with this	4083	C counterpart, an active watcher gets automatically stopped and restarted
2254	method.	4084	when reconfiguring it with this method.
2255		4085
2256	=item w->start ()	4086	=item w->start ()
2257		4087
2258	Starts the watcher. Note that there is no C<loop> argument, as the	4088	Starts the watcher. Note that there is no C<loop> argument, as the
2259	constructor already stores the event loop.	4089	constructor already stores the event loop.
2260		4090
		4091	=item w->start ([arguments])
		4092
		4093	Instead of calling C<set> and C<start> methods separately, it is often
		4094	convenient to wrap them in one call. Uses the same type of arguments as
		4095	the configure C<set> method of the watcher.
		4096
2261	=item w->stop ()	4097	=item w->stop ()
2262		4098
2263	Stops the watcher if it is active. Again, no C<loop> argument.	4099	Stops the watcher if it is active. Again, no C<loop> argument.
2264		4100
2265	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4101	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2277		4113
2278	=back	4114	=back
2279		4115
2280	=back	4116	=back
2281		4117
2282	Example: Define a class with an IO and idle watcher, start one of them in	4118	Example: Define a class with two I/O and idle watchers, start the I/O
2283	the constructor.	4119	watchers in the constructor.
2284		4120
2285	class myclass	4121	class myclass
2286	{	4122	{
2287	ev::io io; void io_cb (ev::io &w, int revents);	4123	ev::io io ; void io_cb (ev::io &w, int revents);
		4124	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2288	ev:idle idle void idle_cb (ev::idle &w, int revents);	4125	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2289		4126
2290	myclass (int fd)	4127	myclass (int fd)
2291	{	4128	{
2292	io .set <myclass, &myclass::io_cb > (this);	4129	io .set <myclass, &myclass::io_cb > (this);
		4130	io2 .set <myclass, &myclass::io2_cb > (this);
2293	idle.set <myclass, &myclass::idle_cb> (this);	4131	idle.set <myclass, &myclass::idle_cb> (this);
2294		4132
2295	io.start (fd, ev::READ);	4133	io.set (fd, ev::WRITE); // configure the watcher
		4134	io.start (); // start it whenever convenient
		4135
		4136	io2.start (fd, ev::READ); // set + start in one call
2296	}	4137	}
2297	};	4138	};
		4139
		4140
		4141	=head1 OTHER LANGUAGE BINDINGS
		4142
		4143	Libev does not offer other language bindings itself, but bindings for a
		4144	number of languages exist in the form of third-party packages. If you know
		4145	any interesting language binding in addition to the ones listed here, drop
		4146	me a note.
		4147
		4148	=over 4
		4149
		4150	=item Perl
		4151
		4152	The EV module implements the full libev API and is actually used to test
		4153	libev. EV is developed together with libev. Apart from the EV core module,
		4154	there are additional modules that implement libev-compatible interfaces
		4155	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4156	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4157	and C<EV::Glib>).
		4158
		4159	It can be found and installed via CPAN, its homepage is at
		4160	L<http://software.schmorp.de/pkg/EV>.
		4161
		4162	=item Python
		4163
		4164	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4165	seems to be quite complete and well-documented.
		4166
		4167	=item Ruby
		4168
		4169	Tony Arcieri has written a ruby extension that offers access to a subset
		4170	of the libev API and adds file handle abstractions, asynchronous DNS and
		4171	more on top of it. It can be found via gem servers. Its homepage is at
		4172	L<http://rev.rubyforge.org/>.
		4173
		4174	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4175	makes rev work even on mingw.
		4176
		4177	=item Haskell
		4178
		4179	A haskell binding to libev is available at
		4180	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4181
		4182	=item D
		4183
		4184	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4185	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4186
		4187	=item Ocaml
		4188
		4189	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4190	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4191
		4192	=item Lua
		4193
		4194	Brian Maher has written a partial interface to libev for lua (at the
		4195	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4196	L<http://github.com/brimworks/lua-ev>.
		4197
		4198	=back
2298		4199
2299		4200
2300	=head1 MACRO MAGIC	4201	=head1 MACRO MAGIC
2301		4202
2302	Libev can be compiled with a variety of options, the most fundamantal	4203	Libev can be compiled with a variety of options, the most fundamental
2303	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4204	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2304	functions and callbacks have an initial C<struct ev_loop *> argument.	4205	functions and callbacks have an initial C<struct ev_loop *> argument.
2305		4206
2306	To make it easier to write programs that cope with either variant, the	4207	To make it easier to write programs that cope with either variant, the
2307	following macros are defined:	4208	following macros are defined:
…		…
2312		4213
2313	This provides the loop I<argument> for functions, if one is required ("ev	4214	This provides the loop I<argument> for functions, if one is required ("ev
2314	loop argument"). The C<EV_A> form is used when this is the sole argument,	4215	loop argument"). The C<EV_A> form is used when this is the sole argument,
2315	C<EV_A_> is used when other arguments are following. Example:	4216	C<EV_A_> is used when other arguments are following. Example:
2316		4217
2317	ev_unref (EV_A);	4218	ev_unref (EV_A);
2318	ev_timer_add (EV_A_ watcher);	4219	ev_timer_add (EV_A_ watcher);
2319	ev_loop (EV_A_ 0);	4220	ev_run (EV_A_ 0);
2320		4221
2321	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4222	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2322	which is often provided by the following macro.	4223	which is often provided by the following macro.
2323		4224
2324	=item C<EV_P>, C<EV_P_>	4225	=item C<EV_P>, C<EV_P_>
2325		4226
2326	This provides the loop I<parameter> for functions, if one is required ("ev	4227	This provides the loop I<parameter> for functions, if one is required ("ev
2327	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4228	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2328	C<EV_P_> is used when other parameters are following. Example:	4229	C<EV_P_> is used when other parameters are following. Example:
2329		4230
2330	// this is how ev_unref is being declared	4231	// this is how ev_unref is being declared
2331	static void ev_unref (EV_P);	4232	static void ev_unref (EV_P);
2332		4233
2333	// this is how you can declare your typical callback	4234	// this is how you can declare your typical callback
2334	static void cb (EV_P_ ev_timer *w, int revents)	4235	static void cb (EV_P_ ev_timer *w, int revents)
2335		4236
2336	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4237	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2337	suitable for use with C<EV_A>.	4238	suitable for use with C<EV_A>.
2338		4239
2339	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4240	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2340		4241
2341	Similar to the other two macros, this gives you the value of the default	4242	Similar to the other two macros, this gives you the value of the default
2342	loop, if multiple loops are supported ("ev loop default").	4243	loop, if multiple loops are supported ("ev loop default"). The default loop
		4244	will be initialised if it isn't already initialised.
		4245
		4246	For non-multiplicity builds, these macros do nothing, so you always have
		4247	to initialise the loop somewhere.
		4248
		4249	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4250
		4251	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4252	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4253	is undefined when the default loop has not been initialised by a previous
		4254	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4255
		4256	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4257	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2343		4258
2344	=back	4259	=back
2345		4260
2346	Example: Declare and initialise a check watcher, utilising the above	4261	Example: Declare and initialise a check watcher, utilising the above
2347	macros so it will work regardless of whether multiple loops are supported	4262	macros so it will work regardless of whether multiple loops are supported
2348	or not.	4263	or not.
2349		4264
2350	static void	4265	static void
2351	check_cb (EV_P_ ev_timer *w, int revents)	4266	check_cb (EV_P_ ev_timer *w, int revents)
2352	{	4267	{
2353	ev_check_stop (EV_A_ w);	4268	ev_check_stop (EV_A_ w);
2354	}	4269	}
2355		4270
2356	ev_check check;	4271	ev_check check;
2357	ev_check_init (&check, check_cb);	4272	ev_check_init (&check, check_cb);
2358	ev_check_start (EV_DEFAULT_ &check);	4273	ev_check_start (EV_DEFAULT_ &check);
2359	ev_loop (EV_DEFAULT_ 0);	4274	ev_run (EV_DEFAULT_ 0);
2360		4275
2361	=head1 EMBEDDING	4276	=head1 EMBEDDING
2362		4277
2363	Libev can (and often is) directly embedded into host	4278	Libev can (and often is) directly embedded into host
2364	applications. Examples of applications that embed it include the Deliantra	4279	applications. Examples of applications that embed it include the Deliantra
…		…
2371	libev somewhere in your source tree).	4286	libev somewhere in your source tree).
2372		4287
2373	=head2 FILESETS	4288	=head2 FILESETS
2374		4289
2375	Depending on what features you need you need to include one or more sets of files	4290	Depending on what features you need you need to include one or more sets of files
2376	in your app.	4291	in your application.
2377		4292
2378	=head3 CORE EVENT LOOP	4293	=head3 CORE EVENT LOOP
2379		4294
2380	To include only the libev core (all the C<ev_*> functions), with manual	4295	To include only the libev core (all the C<ev_*> functions), with manual
2381	configuration (no autoconf):	4296	configuration (no autoconf):
2382		4297
2383	#define EV_STANDALONE 1	4298	#define EV_STANDALONE 1
2384	#include "ev.c"	4299	#include "ev.c"
2385		4300
2386	This will automatically include F<ev.h>, too, and should be done in a	4301	This will automatically include F<ev.h>, too, and should be done in a
2387	single C source file only to provide the function implementations. To use	4302	single C source file only to provide the function implementations. To use
2388	it, do the same for F<ev.h> in all files wishing to use this API (best	4303	it, do the same for F<ev.h> in all files wishing to use this API (best
2389	done by writing a wrapper around F<ev.h> that you can include instead and	4304	done by writing a wrapper around F<ev.h> that you can include instead and
2390	where you can put other configuration options):	4305	where you can put other configuration options):
2391		4306
2392	#define EV_STANDALONE 1	4307	#define EV_STANDALONE 1
2393	#include "ev.h"	4308	#include "ev.h"
2394		4309
2395	Both header files and implementation files can be compiled with a C++	4310	Both header files and implementation files can be compiled with a C++
2396	compiler (at least, thats a stated goal, and breakage will be treated	4311	compiler (at least, that's a stated goal, and breakage will be treated
2397	as a bug).	4312	as a bug).
2398		4313
2399	You need the following files in your source tree, or in a directory	4314	You need the following files in your source tree, or in a directory
2400	in your include path (e.g. in libev/ when using -Ilibev):	4315	in your include path (e.g. in libev/ when using -Ilibev):
2401		4316
2402	ev.h	4317	ev.h
2403	ev.c	4318	ev.c
2404	ev_vars.h	4319	ev_vars.h
2405	ev_wrap.h	4320	ev_wrap.h
2406		4321
2407	ev_win32.c required on win32 platforms only	4322	ev_win32.c required on win32 platforms only
2408		4323
2409	ev_select.c only when select backend is enabled (which is enabled by default)	4324	ev_select.c only when select backend is enabled (which is enabled by default)
2410	ev_poll.c only when poll backend is enabled (disabled by default)	4325	ev_poll.c only when poll backend is enabled (disabled by default)
2411	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4326	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2412	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4327	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2413	ev_port.c only when the solaris port backend is enabled (disabled by default)	4328	ev_port.c only when the solaris port backend is enabled (disabled by default)
2414		4329
2415	F<ev.c> includes the backend files directly when enabled, so you only need	4330	F<ev.c> includes the backend files directly when enabled, so you only need
2416	to compile this single file.	4331	to compile this single file.
2417		4332
2418	=head3 LIBEVENT COMPATIBILITY API	4333	=head3 LIBEVENT COMPATIBILITY API
2419		4334
2420	To include the libevent compatibility API, also include:	4335	To include the libevent compatibility API, also include:
2421		4336
2422	#include "event.c"	4337	#include "event.c"
2423		4338
2424	in the file including F<ev.c>, and:	4339	in the file including F<ev.c>, and:
2425		4340
2426	#include "event.h"	4341	#include "event.h"
2427		4342
2428	in the files that want to use the libevent API. This also includes F<ev.h>.	4343	in the files that want to use the libevent API. This also includes F<ev.h>.
2429		4344
2430	You need the following additional files for this:	4345	You need the following additional files for this:
2431		4346
2432	event.h	4347	event.h
2433	event.c	4348	event.c
2434		4349
2435	=head3 AUTOCONF SUPPORT	4350	=head3 AUTOCONF SUPPORT
2436		4351
2437	Instead of using C<EV_STANDALONE=1> and providing your config in	4352	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2438	whatever way you want, you can also C<m4_include([libev.m4])> in your	4353	whatever way you want, you can also C<m4_include([libev.m4])> in your
2439	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4354	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2440	include F<config.h> and configure itself accordingly.	4355	include F<config.h> and configure itself accordingly.
2441		4356
2442	For this of course you need the m4 file:	4357	For this of course you need the m4 file:
2443		4358
2444	libev.m4	4359	libev.m4
2445		4360
2446	=head2 PREPROCESSOR SYMBOLS/MACROS	4361	=head2 PREPROCESSOR SYMBOLS/MACROS
2447		4362
2448	Libev can be configured via a variety of preprocessor symbols you have to define	4363	Libev can be configured via a variety of preprocessor symbols you have to
2449	before including any of its files. The default is not to build for multiplicity	4364	define before including (or compiling) any of its files. The default in
2450	and only include the select backend.	4365	the absence of autoconf is documented for every option.
		4366
		4367	Symbols marked with "(h)" do not change the ABI, and can have different
		4368	values when compiling libev vs. including F<ev.h>, so it is permissible
		4369	to redefine them before including F<ev.h> without breaking compatibility
		4370	to a compiled library. All other symbols change the ABI, which means all
		4371	users of libev and the libev code itself must be compiled with compatible
		4372	settings.
2451		4373
2452	=over 4	4374	=over 4
2453		4375
		4376	=item EV_COMPAT3 (h)
		4377
		4378	Backwards compatibility is a major concern for libev. This is why this
		4379	release of libev comes with wrappers for the functions and symbols that
		4380	have been renamed between libev version 3 and 4.
		4381
		4382	You can disable these wrappers (to test compatibility with future
		4383	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4384	sources. This has the additional advantage that you can drop the C<struct>
		4385	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4386	typedef in that case.
		4387
		4388	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4389	and in some even more future version the compatibility code will be
		4390	removed completely.
		4391
2454	=item EV_STANDALONE	4392	=item EV_STANDALONE (h)
2455		4393
2456	Must always be C<1> if you do not use autoconf configuration, which	4394	Must always be C<1> if you do not use autoconf configuration, which
2457	keeps libev from including F<config.h>, and it also defines dummy	4395	keeps libev from including F<config.h>, and it also defines dummy
2458	implementations for some libevent functions (such as logging, which is not	4396	implementations for some libevent functions (such as logging, which is not
2459	supported). It will also not define any of the structs usually found in	4397	supported). It will also not define any of the structs usually found in
2460	F<event.h> that are not directly supported by the libev core alone.	4398	F<event.h> that are not directly supported by the libev core alone.
2461		4399
		4400	In standalone mode, libev will still try to automatically deduce the
		4401	configuration, but has to be more conservative.
		4402
		4403	=item EV_USE_FLOOR
		4404
		4405	If defined to be C<1>, libev will use the C<floor ()> function for its
		4406	periodic reschedule calculations, otherwise libev will fall back on a
		4407	portable (slower) implementation. If you enable this, you usually have to
		4408	link against libm or something equivalent. Enabling this when the C<floor>
		4409	function is not available will fail, so the safe default is to not enable
		4410	this.
		4411
2462	=item EV_USE_MONOTONIC	4412	=item EV_USE_MONOTONIC
2463		4413
2464	If defined to be C<1>, libev will try to detect the availability of the	4414	If defined to be C<1>, libev will try to detect the availability of the
2465	monotonic clock option at both compiletime and runtime. Otherwise no use	4415	monotonic clock option at both compile time and runtime. Otherwise no
2466	of the monotonic clock option will be attempted. If you enable this, you	4416	use of the monotonic clock option will be attempted. If you enable this,
2467	usually have to link against librt or something similar. Enabling it when	4417	you usually have to link against librt or something similar. Enabling it
2468	the functionality isn't available is safe, though, although you have	4418	when the functionality isn't available is safe, though, although you have
2469	to make sure you link against any libraries where the C<clock_gettime>	4419	to make sure you link against any libraries where the C<clock_gettime>
2470	function is hiding in (often F<-lrt>).	4420	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2471		4421
2472	=item EV_USE_REALTIME	4422	=item EV_USE_REALTIME
2473		4423
2474	If defined to be C<1>, libev will try to detect the availability of the	4424	If defined to be C<1>, libev will try to detect the availability of the
2475	realtime clock option at compiletime (and assume its availability at	4425	real-time clock option at compile time (and assume its availability
2476	runtime if successful). Otherwise no use of the realtime clock option will	4426	at runtime if successful). Otherwise no use of the real-time clock
2477	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4427	option will be attempted. This effectively replaces C<gettimeofday>
2478	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4428	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2479	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4429	correctness. See the note about libraries in the description of
		4430	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4431	C<EV_USE_CLOCK_SYSCALL>.
		4432
		4433	=item EV_USE_CLOCK_SYSCALL
		4434
		4435	If defined to be C<1>, libev will try to use a direct syscall instead
		4436	of calling the system-provided C<clock_gettime> function. This option
		4437	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4438	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4439	programs needlessly. Using a direct syscall is slightly slower (in
		4440	theory), because no optimised vdso implementation can be used, but avoids
		4441	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4442	higher, as it simplifies linking (no need for C<-lrt>).
2480		4443
2481	=item EV_USE_NANOSLEEP	4444	=item EV_USE_NANOSLEEP
2482		4445
2483	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4446	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2484	and will use it for delays. Otherwise it will use C<select ()>.	4447	and will use it for delays. Otherwise it will use C<select ()>.
2485		4448
		4449	=item EV_USE_EVENTFD
		4450
		4451	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4452	available and will probe for kernel support at runtime. This will improve
		4453	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4454	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4455	2.7 or newer, otherwise disabled.
		4456
2486	=item EV_USE_SELECT	4457	=item EV_USE_SELECT
2487		4458
2488	If undefined or defined to be C<1>, libev will compile in support for the	4459	If undefined or defined to be C<1>, libev will compile in support for the
2489	C<select>(2) backend. No attempt at autodetection will be done: if no	4460	C<select>(2) backend. No attempt at auto-detection will be done: if no
2490	other method takes over, select will be it. Otherwise the select backend	4461	other method takes over, select will be it. Otherwise the select backend
2491	will not be compiled in.	4462	will not be compiled in.
2492		4463
2493	=item EV_SELECT_USE_FD_SET	4464	=item EV_SELECT_USE_FD_SET
2494		4465
2495	If defined to C<1>, then the select backend will use the system C<fd_set>	4466	If defined to C<1>, then the select backend will use the system C<fd_set>
2496	structure. This is useful if libev doesn't compile due to a missing	4467	structure. This is useful if libev doesn't compile due to a missing
2497	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4468	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2498	exotic systems. This usually limits the range of file descriptors to some	4469	on exotic systems. This usually limits the range of file descriptors to
2499	low limit such as 1024 or might have other limitations (winsocket only	4470	some low limit such as 1024 or might have other limitations (winsocket
2500	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4471	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2501	influence the size of the C<fd_set> used.	4472	configures the maximum size of the C<fd_set>.
2502		4473
2503	=item EV_SELECT_IS_WINSOCKET	4474	=item EV_SELECT_IS_WINSOCKET
2504		4475
2505	When defined to C<1>, the select backend will assume that	4476	When defined to C<1>, the select backend will assume that
2506	select/socket/connect etc. don't understand file descriptors but	4477	select/socket/connect etc. don't understand file descriptors but
…		…
2508	be used is the winsock select). This means that it will call	4479	be used is the winsock select). This means that it will call
2509	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4480	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2510	it is assumed that all these functions actually work on fds, even	4481	it is assumed that all these functions actually work on fds, even
2511	on win32. Should not be defined on non-win32 platforms.	4482	on win32. Should not be defined on non-win32 platforms.
2512		4483
2513	=item EV_FD_TO_WIN32_HANDLE	4484	=item EV_FD_TO_WIN32_HANDLE(fd)
2514		4485
2515	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4486	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2516	file descriptors to socket handles. When not defining this symbol (the	4487	file descriptors to socket handles. When not defining this symbol (the
2517	default), then libev will call C<_get_osfhandle>, which is usually	4488	default), then libev will call C<_get_osfhandle>, which is usually
2518	correct. In some cases, programs use their own file descriptor management,	4489	correct. In some cases, programs use their own file descriptor management,
2519	in which case they can provide this function to map fds to socket handles.	4490	in which case they can provide this function to map fds to socket handles.
2520		4491
		4492	=item EV_WIN32_HANDLE_TO_FD(handle)
		4493
		4494	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4495	using the standard C<_open_osfhandle> function. For programs implementing
		4496	their own fd to handle mapping, overwriting this function makes it easier
		4497	to do so. This can be done by defining this macro to an appropriate value.
		4498
		4499	=item EV_WIN32_CLOSE_FD(fd)
		4500
		4501	If programs implement their own fd to handle mapping on win32, then this
		4502	macro can be used to override the C<close> function, useful to unregister
		4503	file descriptors again. Note that the replacement function has to close
		4504	the underlying OS handle.
		4505
2521	=item EV_USE_POLL	4506	=item EV_USE_POLL
2522		4507
2523	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4508	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2524	backend. Otherwise it will be enabled on non-win32 platforms. It	4509	backend. Otherwise it will be enabled on non-win32 platforms. It
2525	takes precedence over select.	4510	takes precedence over select.
2526		4511
2527	=item EV_USE_EPOLL	4512	=item EV_USE_EPOLL
2528		4513
2529	If defined to be C<1>, libev will compile in support for the Linux	4514	If defined to be C<1>, libev will compile in support for the Linux
2530	C<epoll>(7) backend. Its availability will be detected at runtime,	4515	C<epoll>(7) backend. Its availability will be detected at runtime,
2531	otherwise another method will be used as fallback. This is the	4516	otherwise another method will be used as fallback. This is the preferred
2532	preferred backend for GNU/Linux systems.	4517	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4518	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2533		4519
2534	=item EV_USE_KQUEUE	4520	=item EV_USE_KQUEUE
2535		4521
2536	If defined to be C<1>, libev will compile in support for the BSD style	4522	If defined to be C<1>, libev will compile in support for the BSD style
2537	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4523	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2550	otherwise another method will be used as fallback. This is the preferred	4536	otherwise another method will be used as fallback. This is the preferred
2551	backend for Solaris 10 systems.	4537	backend for Solaris 10 systems.
2552		4538
2553	=item EV_USE_DEVPOLL	4539	=item EV_USE_DEVPOLL
2554		4540
2555	reserved for future expansion, works like the USE symbols above.	4541	Reserved for future expansion, works like the USE symbols above.
2556		4542
2557	=item EV_USE_INOTIFY	4543	=item EV_USE_INOTIFY
2558		4544
2559	If defined to be C<1>, libev will compile in support for the Linux inotify	4545	If defined to be C<1>, libev will compile in support for the Linux inotify
2560	interface to speed up C<ev_stat> watchers. Its actual availability will	4546	interface to speed up C<ev_stat> watchers. Its actual availability will
2561	be detected at runtime.	4547	be detected at runtime. If undefined, it will be enabled if the headers
		4548	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2562		4549
		4550	=item EV_NO_SMP
		4551
		4552	If defined to be C<1>, libev will assume that memory is always coherent
		4553	between threads, that is, threads can be used, but threads never run on
		4554	different cpus (or different cpu cores). This reduces dependencies
		4555	and makes libev faster.
		4556
		4557	=item EV_NO_THREADS
		4558
		4559	If defined to be C<1>, libev will assume that it will never be called
		4560	from different threads, which is a stronger assumption than C<EV_NO_SMP>,
		4561	above. This reduces dependencies and makes libev faster.
		4562
		4563	=item EV_ATOMIC_T
		4564
		4565	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4566	access is atomic and serialised with respect to other threads or signal
		4567	contexts. No such type is easily found in the C language, so you can
		4568	provide your own type that you know is safe for your purposes. It is used
		4569	both for signal handler "locking" as well as for signal and thread safety
		4570	in C<ev_async> watchers.
		4571
		4572	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4573	(from F<signal.h>), which is usually good enough on most platforms,
		4574	although strictly speaking using a type that also implies a memory fence
		4575	is required.
		4576
2563	=item EV_H	4577	=item EV_H (h)
2564		4578
2565	The name of the F<ev.h> header file used to include it. The default if	4579	The name of the F<ev.h> header file used to include it. The default if
2566	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4580	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2567	used to virtually rename the F<ev.h> header file in case of conflicts.	4581	used to virtually rename the F<ev.h> header file in case of conflicts.
2568		4582
2569	=item EV_CONFIG_H	4583	=item EV_CONFIG_H (h)
2570		4584
2571	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4585	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2572	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4586	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2573	C<EV_H>, above.	4587	C<EV_H>, above.
2574		4588
2575	=item EV_EVENT_H	4589	=item EV_EVENT_H (h)
2576		4590
2577	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4591	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2578	of how the F<event.h> header can be found, the default is C<"event.h">.	4592	of how the F<event.h> header can be found, the default is C<"event.h">.
2579		4593
2580	=item EV_PROTOTYPES	4594	=item EV_PROTOTYPES (h)
2581		4595
2582	If defined to be C<0>, then F<ev.h> will not define any function	4596	If defined to be C<0>, then F<ev.h> will not define any function
2583	prototypes, but still define all the structs and other symbols. This is	4597	prototypes, but still define all the structs and other symbols. This is
2584	occasionally useful if you want to provide your own wrapper functions	4598	occasionally useful if you want to provide your own wrapper functions
2585	around libev functions.	4599	around libev functions.
…		…
2590	will have the C<struct ev_loop *> as first argument, and you can create	4604	will have the C<struct ev_loop *> as first argument, and you can create
2591	additional independent event loops. Otherwise there will be no support	4605	additional independent event loops. Otherwise there will be no support
2592	for multiple event loops and there is no first event loop pointer	4606	for multiple event loops and there is no first event loop pointer
2593	argument. Instead, all functions act on the single default loop.	4607	argument. Instead, all functions act on the single default loop.
2594		4608
		4609	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4610	default loop when multiplicity is switched off - you always have to
		4611	initialise the loop manually in this case.
		4612
2595	=item EV_MINPRI	4613	=item EV_MINPRI
2596		4614
2597	=item EV_MAXPRI	4615	=item EV_MAXPRI
2598		4616
2599	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4617	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2604	When doing priority-based operations, libev usually has to linearly search	4622	When doing priority-based operations, libev usually has to linearly search
2605	all the priorities, so having many of them (hundreds) uses a lot of space	4623	all the priorities, so having many of them (hundreds) uses a lot of space
2606	and time, so using the defaults of five priorities (-2 .. +2) is usually	4624	and time, so using the defaults of five priorities (-2 .. +2) is usually
2607	fine.	4625	fine.
2608		4626
2609	If your embedding app does not need any priorities, defining these both to	4627	If your embedding application does not need any priorities, defining these
2610	C<0> will save some memory and cpu.	4628	both to C<0> will save some memory and CPU.
2611		4629
2612	=item EV_PERIODIC_ENABLE	4630	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4631	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4632	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2613		4633
2614	If undefined or defined to be C<1>, then periodic timers are supported. If	4634	If undefined or defined to be C<1> (and the platform supports it), then
2615	defined to be C<0>, then they are not. Disabling them saves a few kB of	4635	the respective watcher type is supported. If defined to be C<0>, then it
2616	code.	4636	is not. Disabling watcher types mainly saves code size.
2617		4637
2618	=item EV_IDLE_ENABLE	4638	=item EV_FEATURES
2619
2620	If undefined or defined to be C<1>, then idle watchers are supported. If
2621	defined to be C<0>, then they are not. Disabling them saves a few kB of
2622	code.
2623
2624	=item EV_EMBED_ENABLE
2625
2626	If undefined or defined to be C<1>, then embed watchers are supported. If
2627	defined to be C<0>, then they are not.
2628
2629	=item EV_STAT_ENABLE
2630
2631	If undefined or defined to be C<1>, then stat watchers are supported. If
2632	defined to be C<0>, then they are not.
2633
2634	=item EV_FORK_ENABLE
2635
2636	If undefined or defined to be C<1>, then fork watchers are supported. If
2637	defined to be C<0>, then they are not.
2638
2639	=item EV_MINIMAL
2640		4639
2641	If you need to shave off some kilobytes of code at the expense of some	4640	If you need to shave off some kilobytes of code at the expense of some
2642	speed, define this symbol to C<1>. Currently only used for gcc to override	4641	speed (but with the full API), you can define this symbol to request
2643	some inlining decisions, saves roughly 30% codesize of amd64.	4642	certain subsets of functionality. The default is to enable all features
		4643	that can be enabled on the platform.
		4644
		4645	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4646	with some broad features you want) and then selectively re-enable
		4647	additional parts you want, for example if you want everything minimal,
		4648	but multiple event loop support, async and child watchers and the poll
		4649	backend, use this:
		4650
		4651	#define EV_FEATURES 0
		4652	#define EV_MULTIPLICITY 1
		4653	#define EV_USE_POLL 1
		4654	#define EV_CHILD_ENABLE 1
		4655	#define EV_ASYNC_ENABLE 1
		4656
		4657	The actual value is a bitset, it can be a combination of the following
		4658	values (by default, all of these are enabled):
		4659
		4660	=over 4
		4661
		4662	=item C<1> - faster/larger code
		4663
		4664	Use larger code to speed up some operations.
		4665
		4666	Currently this is used to override some inlining decisions (enlarging the
		4667	code size by roughly 30% on amd64).
		4668
		4669	When optimising for size, use of compiler flags such as C<-Os> with
		4670	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4671	assertions.
		4672
		4673	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4674	(e.g. gcc with C<-Os>).
		4675
		4676	=item C<2> - faster/larger data structures
		4677
		4678	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4679	hash table sizes and so on. This will usually further increase code size
		4680	and can additionally have an effect on the size of data structures at
		4681	runtime.
		4682
		4683	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4684	(e.g. gcc with C<-Os>).
		4685
		4686	=item C<4> - full API configuration
		4687
		4688	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4689	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4690
		4691	=item C<8> - full API
		4692
		4693	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4694	details on which parts of the API are still available without this
		4695	feature, and do not complain if this subset changes over time.
		4696
		4697	=item C<16> - enable all optional watcher types
		4698
		4699	Enables all optional watcher types. If you want to selectively enable
		4700	only some watcher types other than I/O and timers (e.g. prepare,
		4701	embed, async, child...) you can enable them manually by defining
		4702	C<EV_watchertype_ENABLE> to C<1> instead.
		4703
		4704	=item C<32> - enable all backends
		4705
		4706	This enables all backends - without this feature, you need to enable at
		4707	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4708
		4709	=item C<64> - enable OS-specific "helper" APIs
		4710
		4711	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4712	default.
		4713
		4714	=back
		4715
		4716	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4717	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4718	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4719	watchers, timers and monotonic clock support.
		4720
		4721	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4722	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4723	your program might be left out as well - a binary starting a timer and an
		4724	I/O watcher then might come out at only 5Kb.
		4725
		4726	=item EV_API_STATIC
		4727
		4728	If this symbol is defined (by default it is not), then all identifiers
		4729	will have static linkage. This means that libev will not export any
		4730	identifiers, and you cannot link against libev anymore. This can be useful
		4731	when you embed libev, only want to use libev functions in a single file,
		4732	and do not want its identifiers to be visible.
		4733
		4734	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4735	wants to use libev.
		4736
		4737	This option only works when libev is compiled with a C compiler, as C++
		4738	doesn't support the required declaration syntax.
		4739
		4740	=item EV_AVOID_STDIO
		4741
		4742	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4743	functions (printf, scanf, perror etc.). This will increase the code size
		4744	somewhat, but if your program doesn't otherwise depend on stdio and your
		4745	libc allows it, this avoids linking in the stdio library which is quite
		4746	big.
		4747
		4748	Note that error messages might become less precise when this option is
		4749	enabled.
		4750
		4751	=item EV_NSIG
		4752
		4753	The highest supported signal number, +1 (or, the number of
		4754	signals): Normally, libev tries to deduce the maximum number of signals
		4755	automatically, but sometimes this fails, in which case it can be
		4756	specified. Also, using a lower number than detected (C<32> should be
		4757	good for about any system in existence) can save some memory, as libev
		4758	statically allocates some 12-24 bytes per signal number.
2644		4759
2645	=item EV_PID_HASHSIZE	4760	=item EV_PID_HASHSIZE
2646		4761
2647	C<ev_child> watchers use a small hash table to distribute workload by	4762	C<ev_child> watchers use a small hash table to distribute workload by
2648	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4763	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2649	than enough. If you need to manage thousands of children you might want to	4764	usually more than enough. If you need to manage thousands of children you
2650	increase this value (I<must> be a power of two).	4765	might want to increase this value (I<must> be a power of two).
2651		4766
2652	=item EV_INOTIFY_HASHSIZE	4767	=item EV_INOTIFY_HASHSIZE
2653		4768
2654	C<ev_stat> watchers use a small hash table to distribute workload by	4769	C<ev_stat> watchers use a small hash table to distribute workload by
2655	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4770	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2656	usually more than enough. If you need to manage thousands of C<ev_stat>	4771	disabled), usually more than enough. If you need to manage thousands of
2657	watchers you might want to increase this value (I<must> be a power of	4772	C<ev_stat> watchers you might want to increase this value (I<must> be a
2658	two).	4773	power of two).
		4774
		4775	=item EV_USE_4HEAP
		4776
		4777	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4778	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4779	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4780	faster performance with many (thousands) of watchers.
		4781
		4782	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4783	will be C<0>.
		4784
		4785	=item EV_HEAP_CACHE_AT
		4786
		4787	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4788	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4789	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4790	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4791	but avoids random read accesses on heap changes. This improves performance
		4792	noticeably with many (hundreds) of watchers.
		4793
		4794	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4795	will be C<0>.
		4796
		4797	=item EV_VERIFY
		4798
		4799	Controls how much internal verification (see C<ev_verify ()>) will
		4800	be done: If set to C<0>, no internal verification code will be compiled
		4801	in. If set to C<1>, then verification code will be compiled in, but not
		4802	called. If set to C<2>, then the internal verification code will be
		4803	called once per loop, which can slow down libev. If set to C<3>, then the
		4804	verification code will be called very frequently, which will slow down
		4805	libev considerably.
		4806
		4807	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4808	will be C<0>.
2659		4809
2660	=item EV_COMMON	4810	=item EV_COMMON
2661		4811
2662	By default, all watchers have a C<void *data> member. By redefining	4812	By default, all watchers have a C<void *data> member. By redefining
2663	this macro to a something else you can include more and other types of	4813	this macro to something else you can include more and other types of
2664	members. You have to define it each time you include one of the files,	4814	members. You have to define it each time you include one of the files,
2665	though, and it must be identical each time.	4815	though, and it must be identical each time.
2666		4816
2667	For example, the perl EV module uses something like this:	4817	For example, the perl EV module uses something like this:
2668		4818
2669	#define EV_COMMON \	4819	#define EV_COMMON \
2670	SV *self; /* contains this struct */ \	4820	SV *self; /* contains this struct */ \
2671	SV *cb_sv, *fh /* note no trailing ";" */	4821	SV *cb_sv, *fh /* note no trailing ";" */
2672		4822
2673	=item EV_CB_DECLARE (type)	4823	=item EV_CB_DECLARE (type)
2674		4824
2675	=item EV_CB_INVOKE (watcher, revents)	4825	=item EV_CB_INVOKE (watcher, revents)
2676		4826
…		…
2681	definition and a statement, respectively. See the F<ev.h> header file for	4831	definition and a statement, respectively. See the F<ev.h> header file for
2682	their default definitions. One possible use for overriding these is to	4832	their default definitions. One possible use for overriding these is to
2683	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4833	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2684	method calls instead of plain function calls in C++.	4834	method calls instead of plain function calls in C++.
2685		4835
		4836	=back
		4837
2686	=head2 EXPORTED API SYMBOLS	4838	=head2 EXPORTED API SYMBOLS
2687		4839
2688	If you need to re-export the API (e.g. via a dll) and you need a list of	4840	If you need to re-export the API (e.g. via a DLL) and you need a list of
2689	exported symbols, you can use the provided F<Symbol.*> files which list	4841	exported symbols, you can use the provided F<Symbol.*> files which list
2690	all public symbols, one per line:	4842	all public symbols, one per line:
2691		4843
2692	Symbols.ev for libev proper	4844	Symbols.ev for libev proper
2693	Symbols.event for the libevent emulation	4845	Symbols.event for the libevent emulation
2694		4846
2695	This can also be used to rename all public symbols to avoid clashes with	4847	This can also be used to rename all public symbols to avoid clashes with
2696	multiple versions of libev linked together (which is obviously bad in	4848	multiple versions of libev linked together (which is obviously bad in
2697	itself, but sometimes it is inconvinient to avoid this).	4849	itself, but sometimes it is inconvenient to avoid this).
2698		4850
2699	A sed command like this will create wrapper C<#define>'s that you need to	4851	A sed command like this will create wrapper C<#define>'s that you need to
2700	include before including F<ev.h>:	4852	include before including F<ev.h>:
2701		4853
2702	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4854	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2719	file.	4871	file.
2720		4872
2721	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4873	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2722	that everybody includes and which overrides some configure choices:	4874	that everybody includes and which overrides some configure choices:
2723		4875
2724	#define EV_MINIMAL 1	4876	#define EV_FEATURES 8
2725	#define EV_USE_POLL 0	4877	#define EV_USE_SELECT 1
2726	#define EV_MULTIPLICITY 0
2727	#define EV_PERIODIC_ENABLE 0	4878	#define EV_PREPARE_ENABLE 1
		4879	#define EV_IDLE_ENABLE 1
2728	#define EV_STAT_ENABLE 0	4880	#define EV_SIGNAL_ENABLE 1
2729	#define EV_FORK_ENABLE 0	4881	#define EV_CHILD_ENABLE 1
		4882	#define EV_USE_STDEXCEPT 0
2730	#define EV_CONFIG_H <config.h>	4883	#define EV_CONFIG_H <config.h>
2731	#define EV_MINPRI 0
2732	#define EV_MAXPRI 0
2733		4884
2734	#include "ev++.h"	4885	#include "ev++.h"
2735		4886
2736	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4887	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2737		4888
2738	#include "ev_cpp.h"	4889	#include "ev_cpp.h"
2739	#include "ev.c"	4890	#include "ev.c"
2740		4891
		4892	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2741		4893
2742	=head1 COMPLEXITIES	4894	=head2 THREADS AND COROUTINES
2743		4895
2744	In this section the complexities of (many of) the algorithms used inside	4896	=head3 THREADS
2745	libev will be explained. For complexity discussions about backends see the
2746	documentation for C<ev_default_init>.
2747		4897
2748	All of the following are about amortised time: If an array needs to be	4898	All libev functions are reentrant and thread-safe unless explicitly
2749	extended, libev needs to realloc and move the whole array, but this	4899	documented otherwise, but libev implements no locking itself. This means
2750	happens asymptotically never with higher number of elements, so O(1) might	4900	that you can use as many loops as you want in parallel, as long as there
2751	mean it might do a lengthy realloc operation in rare cases, but on average	4901	are no concurrent calls into any libev function with the same loop
2752	it is much faster and asymptotically approaches constant time.	4902	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4903	of course): libev guarantees that different event loops share no data
		4904	structures that need any locking.
		4905
		4906	Or to put it differently: calls with different loop parameters can be done
		4907	concurrently from multiple threads, calls with the same loop parameter
		4908	must be done serially (but can be done from different threads, as long as
		4909	only one thread ever is inside a call at any point in time, e.g. by using
		4910	a mutex per loop).
		4911
		4912	Specifically to support threads (and signal handlers), libev implements
		4913	so-called C<ev_async> watchers, which allow some limited form of
		4914	concurrency on the same event loop, namely waking it up "from the
		4915	outside".
		4916
		4917	If you want to know which design (one loop, locking, or multiple loops
		4918	without or something else still) is best for your problem, then I cannot
		4919	help you, but here is some generic advice:
2753		4920
2754	=over 4	4921	=over 4
2755		4922
2756	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4923	=item * most applications have a main thread: use the default libev loop
		4924	in that thread, or create a separate thread running only the default loop.
2757		4925
2758	This means that, when you have a watcher that triggers in one hour and	4926	This helps integrating other libraries or software modules that use libev
2759	there are 100 watchers that would trigger before that then inserting will	4927	themselves and don't care/know about threading.
2760	have to skip roughly seven (C<ld 100>) of these watchers.
2761		4928
2762	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4929	=item * one loop per thread is usually a good model.
2763		4930
2764	That means that changing a timer costs less than removing/adding them	4931	Doing this is almost never wrong, sometimes a better-performance model
2765	as only the relative motion in the event queue has to be paid for.	4932	exists, but it is always a good start.
2766		4933
2767	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4934	=item * other models exist, such as the leader/follower pattern, where one
		4935	loop is handed through multiple threads in a kind of round-robin fashion.
2768		4936
2769	These just add the watcher into an array or at the head of a list.	4937	Choosing a model is hard - look around, learn, know that usually you can do
		4938	better than you currently do :-)
2770		4939
2771	=item Stopping check/prepare/idle watchers: O(1)	4940	=item * often you need to talk to some other thread which blocks in the
		4941	event loop.
2772		4942
2773	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4943	C<ev_async> watchers can be used to wake them up from other threads safely
		4944	(or from signal contexts...).
2774		4945
2775	These watchers are stored in lists then need to be walked to find the	4946	An example use would be to communicate signals or other events that only
2776	correct watcher to remove. The lists are usually short (you don't usually	4947	work in the default loop by registering the signal watcher with the
2777	have many watchers waiting for the same fd or signal).	4948	default loop and triggering an C<ev_async> watcher from the default loop
2778		4949	watcher callback into the event loop interested in the signal.
2779	=item Finding the next timer in each loop iteration: O(1)
2780
2781	By virtue of using a binary heap, the next timer is always found at the
2782	beginning of the storage array.
2783
2784	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2785
2786	A change means an I/O watcher gets started or stopped, which requires
2787	libev to recalculate its status (and possibly tell the kernel, depending
2788	on backend and wether C<ev_io_set> was used).
2789
2790	=item Activating one watcher (putting it into the pending state): O(1)
2791
2792	=item Priority handling: O(number_of_priorities)
2793
2794	Priorities are implemented by allocating some space for each
2795	priority. When doing priority-based operations, libev usually has to
2796	linearly search all the priorities, but starting/stopping and activating
2797	watchers becomes O(1) w.r.t. prioritiy handling.
2798		4950
2799	=back	4951	=back
2800		4952
		4953	See also L<THREAD LOCKING EXAMPLE>.
2801		4954
2802	=head1 Win32 platform limitations and workarounds	4955	=head3 COROUTINES
		4956
		4957	Libev is very accommodating to coroutines ("cooperative threads"):
		4958	libev fully supports nesting calls to its functions from different
		4959	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4960	different coroutines, and switch freely between both coroutines running
		4961	the loop, as long as you don't confuse yourself). The only exception is
		4962	that you must not do this from C<ev_periodic> reschedule callbacks.
		4963
		4964	Care has been taken to ensure that libev does not keep local state inside
		4965	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4966	they do not call any callbacks.
		4967
		4968	=head2 COMPILER WARNINGS
		4969
		4970	Depending on your compiler and compiler settings, you might get no or a
		4971	lot of warnings when compiling libev code. Some people are apparently
		4972	scared by this.
		4973
		4974	However, these are unavoidable for many reasons. For one, each compiler
		4975	has different warnings, and each user has different tastes regarding
		4976	warning options. "Warn-free" code therefore cannot be a goal except when
		4977	targeting a specific compiler and compiler-version.
		4978
		4979	Another reason is that some compiler warnings require elaborate
		4980	workarounds, or other changes to the code that make it less clear and less
		4981	maintainable.
		4982
		4983	And of course, some compiler warnings are just plain stupid, or simply
		4984	wrong (because they don't actually warn about the condition their message
		4985	seems to warn about). For example, certain older gcc versions had some
		4986	warnings that resulted in an extreme number of false positives. These have
		4987	been fixed, but some people still insist on making code warn-free with
		4988	such buggy versions.
		4989
		4990	While libev is written to generate as few warnings as possible,
		4991	"warn-free" code is not a goal, and it is recommended not to build libev
		4992	with any compiler warnings enabled unless you are prepared to cope with
		4993	them (e.g. by ignoring them). Remember that warnings are just that:
		4994	warnings, not errors, or proof of bugs.
		4995
		4996
		4997	=head2 VALGRIND
		4998
		4999	Valgrind has a special section here because it is a popular tool that is
		5000	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5001
		5002	If you think you found a bug (memory leak, uninitialised data access etc.)
		5003	in libev, then check twice: If valgrind reports something like:
		5004
		5005	==2274== definitely lost: 0 bytes in 0 blocks.
		5006	==2274== possibly lost: 0 bytes in 0 blocks.
		5007	==2274== still reachable: 256 bytes in 1 blocks.
		5008
		5009	Then there is no memory leak, just as memory accounted to global variables
		5010	is not a memleak - the memory is still being referenced, and didn't leak.
		5011
		5012	Similarly, under some circumstances, valgrind might report kernel bugs
		5013	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5014	although an acceptable workaround has been found here), or it might be
		5015	confused.
		5016
		5017	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5018	make it into some kind of religion.
		5019
		5020	If you are unsure about something, feel free to contact the mailing list
		5021	with the full valgrind report and an explanation on why you think this
		5022	is a bug in libev (best check the archives, too :). However, don't be
		5023	annoyed when you get a brisk "this is no bug" answer and take the chance
		5024	of learning how to interpret valgrind properly.
		5025
		5026	If you need, for some reason, empty reports from valgrind for your project
		5027	I suggest using suppression lists.
		5028
		5029
		5030	=head1 PORTABILITY NOTES
		5031
		5032	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5033
		5034	GNU/Linux is the only common platform that supports 64 bit file/large file
		5035	interfaces but I<disables> them by default.
		5036
		5037	That means that libev compiled in the default environment doesn't support
		5038	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5039
		5040	Unfortunately, many programs try to work around this GNU/Linux issue
		5041	by enabling the large file API, which makes them incompatible with the
		5042	standard libev compiled for their system.
		5043
		5044	Likewise, libev cannot enable the large file API itself as this would
		5045	suddenly make it incompatible to the default compile time environment,
		5046	i.e. all programs not using special compile switches.
		5047
		5048	=head2 OS/X AND DARWIN BUGS
		5049
		5050	The whole thing is a bug if you ask me - basically any system interface
		5051	you touch is broken, whether it is locales, poll, kqueue or even the
		5052	OpenGL drivers.
		5053
		5054	=head3 C<kqueue> is buggy
		5055
		5056	The kqueue syscall is broken in all known versions - most versions support
		5057	only sockets, many support pipes.
		5058
		5059	Libev tries to work around this by not using C<kqueue> by default on this
		5060	rotten platform, but of course you can still ask for it when creating a
		5061	loop - embedding a socket-only kqueue loop into a select-based one is
		5062	probably going to work well.
		5063
		5064	=head3 C<poll> is buggy
		5065
		5066	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5067	implementation by something calling C<kqueue> internally around the 10.5.6
		5068	release, so now C<kqueue> I<and> C<poll> are broken.
		5069
		5070	Libev tries to work around this by not using C<poll> by default on
		5071	this rotten platform, but of course you can still ask for it when creating
		5072	a loop.
		5073
		5074	=head3 C<select> is buggy
		5075
		5076	All that's left is C<select>, and of course Apple found a way to fuck this
		5077	one up as well: On OS/X, C<select> actively limits the number of file
		5078	descriptors you can pass in to 1024 - your program suddenly crashes when
		5079	you use more.
		5080
		5081	There is an undocumented "workaround" for this - defining
		5082	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5083	work on OS/X.
		5084
		5085	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5086
		5087	=head3 C<errno> reentrancy
		5088
		5089	The default compile environment on Solaris is unfortunately so
		5090	thread-unsafe that you can't even use components/libraries compiled
		5091	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5092	defined by default. A valid, if stupid, implementation choice.
		5093
		5094	If you want to use libev in threaded environments you have to make sure
		5095	it's compiled with C<_REENTRANT> defined.
		5096
		5097	=head3 Event port backend
		5098
		5099	The scalable event interface for Solaris is called "event
		5100	ports". Unfortunately, this mechanism is very buggy in all major
		5101	releases. If you run into high CPU usage, your program freezes or you get
		5102	a large number of spurious wakeups, make sure you have all the relevant
		5103	and latest kernel patches applied. No, I don't know which ones, but there
		5104	are multiple ones to apply, and afterwards, event ports actually work
		5105	great.
		5106
		5107	If you can't get it to work, you can try running the program by setting
		5108	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5109	C<select> backends.
		5110
		5111	=head2 AIX POLL BUG
		5112
		5113	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5114	this by trying to avoid the poll backend altogether (i.e. it's not even
		5115	compiled in), which normally isn't a big problem as C<select> works fine
		5116	with large bitsets on AIX, and AIX is dead anyway.
		5117
		5118	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5119
		5120	=head3 General issues
2803		5121
2804	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5122	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2805	requires, and its I/O model is fundamentally incompatible with the POSIX	5123	requires, and its I/O model is fundamentally incompatible with the POSIX
2806	model. Libev still offers limited functionality on this platform in	5124	model. Libev still offers limited functionality on this platform in
2807	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5125	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2808	descriptors. This only applies when using Win32 natively, not when using	5126	descriptors. This only applies when using Win32 natively, not when using
2809	e.g. cygwin.	5127	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5128	as every compiler comes with a slightly differently broken/incompatible
		5129	environment.
		5130
		5131	Lifting these limitations would basically require the full
		5132	re-implementation of the I/O system. If you are into this kind of thing,
		5133	then note that glib does exactly that for you in a very portable way (note
		5134	also that glib is the slowest event library known to man).
2810		5135
2811	There is no supported compilation method available on windows except	5136	There is no supported compilation method available on windows except
2812	embedding it into other applications.	5137	embedding it into other applications.
2813		5138
		5139	Sensible signal handling is officially unsupported by Microsoft - libev
		5140	tries its best, but under most conditions, signals will simply not work.
		5141
		5142	Not a libev limitation but worth mentioning: windows apparently doesn't
		5143	accept large writes: instead of resulting in a partial write, windows will
		5144	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5145	so make sure you only write small amounts into your sockets (less than a
		5146	megabyte seems safe, but this apparently depends on the amount of memory
		5147	available).
		5148
2814	Due to the many, low, and arbitrary limits on the win32 platform and the	5149	Due to the many, low, and arbitrary limits on the win32 platform and
2815	abysmal performance of winsockets, using a large number of sockets is not	5150	the abysmal performance of winsockets, using a large number of sockets
2816	recommended (and not reasonable). If your program needs to use more than	5151	is not recommended (and not reasonable). If your program needs to use
2817	a hundred or so sockets, then likely it needs to use a totally different	5152	more than a hundred or so sockets, then likely it needs to use a totally
2818	implementation for windows, as libev offers the POSIX model, which cannot	5153	different implementation for windows, as libev offers the POSIX readiness
2819	be implemented efficiently on windows (microsoft monopoly games).	5154	notification model, which cannot be implemented efficiently on windows
		5155	(due to Microsoft monopoly games).
2820		5156
2821	=over 4	5157	A typical way to use libev under windows is to embed it (see the embedding
		5158	section for details) and use the following F<evwrap.h> header file instead
		5159	of F<ev.h>:
2822		5160
		5161	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5162	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5163
		5164	#include "ev.h"
		5165
		5166	And compile the following F<evwrap.c> file into your project (make sure
		5167	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5168
		5169	#include "evwrap.h"
		5170	#include "ev.c"
		5171
2823	=item The winsocket select function	5172	=head3 The winsocket C<select> function
2824		5173
2825	The winsocket C<select> function doesn't follow POSIX in that it requires	5174	The winsocket C<select> function doesn't follow POSIX in that it
2826	socket I<handles> and not socket I<file descriptors>. This makes select	5175	requires socket I<handles> and not socket I<file descriptors> (it is
2827	very inefficient, and also requires a mapping from file descriptors	5176	also extremely buggy). This makes select very inefficient, and also
2828	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	5177	requires a mapping from file descriptors to socket handles (the Microsoft
2829	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	5178	C runtime provides the function C<_open_osfhandle> for this). See the
2830	symbols for more info.	5179	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5180	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
2831		5181
2832	The configuration for a "naked" win32 using the microsoft runtime	5182	The configuration for a "naked" win32 using the Microsoft runtime
2833	libraries and raw winsocket select is:	5183	libraries and raw winsocket select is:
2834		5184
2835	#define EV_USE_SELECT 1	5185	#define EV_USE_SELECT 1
2836	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5186	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2837		5187
2838	Note that winsockets handling of fd sets is O(n), so you can easily get a	5188	Note that winsockets handling of fd sets is O(n), so you can easily get a
2839	complexity in the O(n²) range when using win32.	5189	complexity in the O(n²) range when using win32.
2840		5190
2841	=item Limited number of file descriptors	5191	=head3 Limited number of file descriptors
2842		5192
2843	Windows has numerous arbitrary (and low) limits on things. Early versions	5193	Windows has numerous arbitrary (and low) limits on things.
2844	of winsocket's select only supported waiting for a max. of C<64> handles	5194
		5195	Early versions of winsocket's select only supported waiting for a maximum
2845	(probably owning to the fact that all windows kernels can only wait for	5196	of C<64> handles (probably owning to the fact that all windows kernels
2846	C<64> things at the same time internally; microsoft recommends spawning a	5197	can only wait for C<64> things at the same time internally; Microsoft
2847	chain of threads and wait for 63 handles and the previous thread in each).	5198	recommends spawning a chain of threads and wait for 63 handles and the
		5199	previous thread in each. Sounds great!).
2848		5200
2849	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5201	Newer versions support more handles, but you need to define C<FD_SETSIZE>
2850	to some high number (e.g. C<2048>) before compiling the winsocket select	5202	to some high number (e.g. C<2048>) before compiling the winsocket select
2851	call (which might be in libev or elsewhere, for example, perl does its own	5203	call (which might be in libev or elsewhere, for example, perl and many
2852	select emulation on windows).	5204	other interpreters do their own select emulation on windows).
2853		5205
2854	Another limit is the number of file descriptors in the microsoft runtime	5206	Another limit is the number of file descriptors in the Microsoft runtime
2855	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5207	libraries, which by default is C<64> (there must be a hidden I<64>
2856	or something like this inside microsoft). You can increase this by calling	5208	fetish or something like this inside Microsoft). You can increase this
2857	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5209	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
2858	arbitrary limit), but is broken in many versions of the microsoft runtime	5210	(another arbitrary limit), but is broken in many versions of the Microsoft
2859	libraries.
2860
2861	This might get you to about C<512> or C<2048> sockets (depending on	5211	runtime libraries. This might get you to about C<512> or C<2048> sockets
2862	windows version and/or the phase of the moon). To get more, you need to	5212	(depending on windows version and/or the phase of the moon). To get more,
2863	wrap all I/O functions and provide your own fd management, but the cost of	5213	you need to wrap all I/O functions and provide your own fd management, but
2864	calling select (O(n²)) will likely make this unworkable.	5214	the cost of calling select (O(n²)) will likely make this unworkable.
		5215
		5216	=head2 PORTABILITY REQUIREMENTS
		5217
		5218	In addition to a working ISO-C implementation and of course the
		5219	backend-specific APIs, libev relies on a few additional extensions:
		5220
		5221	=over 4
		5222
		5223	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5224	calling conventions regardless of C<ev_watcher_type *>.
		5225
		5226	Libev assumes not only that all watcher pointers have the same internal
		5227	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5228	assumes that the same (machine) code can be used to call any watcher
		5229	callback: The watcher callbacks have different type signatures, but libev
		5230	calls them using an C<ev_watcher *> internally.
		5231
		5232	=item pointer accesses must be thread-atomic
		5233
		5234	Accessing a pointer value must be atomic, it must both be readable and
		5235	writable in one piece - this is the case on all current architectures.
		5236
		5237	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5238
		5239	The type C<sig_atomic_t volatile> (or whatever is defined as
		5240	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5241	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5242	believed to be sufficiently portable.
		5243
		5244	=item C<sigprocmask> must work in a threaded environment
		5245
		5246	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5247	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5248	pthread implementations will either allow C<sigprocmask> in the "main
		5249	thread" or will block signals process-wide, both behaviours would
		5250	be compatible with libev. Interaction between C<sigprocmask> and
		5251	C<pthread_sigmask> could complicate things, however.
		5252
		5253	The most portable way to handle signals is to block signals in all threads
		5254	except the initial one, and run the default loop in the initial thread as
		5255	well.
		5256
		5257	=item C<long> must be large enough for common memory allocation sizes
		5258
		5259	To improve portability and simplify its API, libev uses C<long> internally
		5260	instead of C<size_t> when allocating its data structures. On non-POSIX
		5261	systems (Microsoft...) this might be unexpectedly low, but is still at
		5262	least 31 bits everywhere, which is enough for hundreds of millions of
		5263	watchers.
		5264
		5265	=item C<double> must hold a time value in seconds with enough accuracy
		5266
		5267	The type C<double> is used to represent timestamps. It is required to
		5268	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5269	good enough for at least into the year 4000 with millisecond accuracy
		5270	(the design goal for libev). This requirement is overfulfilled by
		5271	implementations using IEEE 754, which is basically all existing ones.
		5272
		5273	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5274	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5275	is either obsolete or somebody patched it to use C<long double> or
		5276	something like that, just kidding).
2865		5277
2866	=back	5278	=back
2867		5279
		5280	If you know of other additional requirements drop me a note.
		5281
		5282
		5283	=head1 ALGORITHMIC COMPLEXITIES
		5284
		5285	In this section the complexities of (many of) the algorithms used inside
		5286	libev will be documented. For complexity discussions about backends see
		5287	the documentation for C<ev_default_init>.
		5288
		5289	All of the following are about amortised time: If an array needs to be
		5290	extended, libev needs to realloc and move the whole array, but this
		5291	happens asymptotically rarer with higher number of elements, so O(1) might
		5292	mean that libev does a lengthy realloc operation in rare cases, but on
		5293	average it is much faster and asymptotically approaches constant time.
		5294
		5295	=over 4
		5296
		5297	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5298
		5299	This means that, when you have a watcher that triggers in one hour and
		5300	there are 100 watchers that would trigger before that, then inserting will
		5301	have to skip roughly seven (C<ld 100>) of these watchers.
		5302
		5303	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5304
		5305	That means that changing a timer costs less than removing/adding them,
		5306	as only the relative motion in the event queue has to be paid for.
		5307
		5308	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5309
		5310	These just add the watcher into an array or at the head of a list.
		5311
		5312	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5313
		5314	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5315
		5316	These watchers are stored in lists, so they need to be walked to find the
		5317	correct watcher to remove. The lists are usually short (you don't usually
		5318	have many watchers waiting for the same fd or signal: one is typical, two
		5319	is rare).
		5320
		5321	=item Finding the next timer in each loop iteration: O(1)
		5322
		5323	By virtue of using a binary or 4-heap, the next timer is always found at a
		5324	fixed position in the storage array.
		5325
		5326	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5327
		5328	A change means an I/O watcher gets started or stopped, which requires
		5329	libev to recalculate its status (and possibly tell the kernel, depending
		5330	on backend and whether C<ev_io_set> was used).
		5331
		5332	=item Activating one watcher (putting it into the pending state): O(1)
		5333
		5334	=item Priority handling: O(number_of_priorities)
		5335
		5336	Priorities are implemented by allocating some space for each
		5337	priority. When doing priority-based operations, libev usually has to
		5338	linearly search all the priorities, but starting/stopping and activating
		5339	watchers becomes O(1) with respect to priority handling.
		5340
		5341	=item Sending an ev_async: O(1)
		5342
		5343	=item Processing ev_async_send: O(number_of_async_watchers)
		5344
		5345	=item Processing signals: O(max_signal_number)
		5346
		5347	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5348	calls in the current loop iteration and the loop is currently
		5349	blocked. Checking for async and signal events involves iterating over all
		5350	running async watchers or all signal numbers.
		5351
		5352	=back
		5353
		5354
		5355	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5356
		5357	The major version 4 introduced some incompatible changes to the API.
		5358
		5359	At the moment, the C<ev.h> header file provides compatibility definitions
		5360	for all changes, so most programs should still compile. The compatibility
		5361	layer might be removed in later versions of libev, so better update to the
		5362	new API early than late.
		5363
		5364	=over 4
		5365
		5366	=item C<EV_COMPAT3> backwards compatibility mechanism
		5367
		5368	The backward compatibility mechanism can be controlled by
		5369	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5370	section.
		5371
		5372	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5373
		5374	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5375
		5376	ev_loop_destroy (EV_DEFAULT_UC);
		5377	ev_loop_fork (EV_DEFAULT);
		5378
		5379	=item function/symbol renames
		5380
		5381	A number of functions and symbols have been renamed:
		5382
		5383	ev_loop => ev_run
		5384	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5385	EVLOOP_ONESHOT => EVRUN_ONCE
		5386
		5387	ev_unloop => ev_break
		5388	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5389	EVUNLOOP_ONE => EVBREAK_ONE
		5390	EVUNLOOP_ALL => EVBREAK_ALL
		5391
		5392	EV_TIMEOUT => EV_TIMER
		5393
		5394	ev_loop_count => ev_iteration
		5395	ev_loop_depth => ev_depth
		5396	ev_loop_verify => ev_verify
		5397
		5398	Most functions working on C<struct ev_loop> objects don't have an
		5399	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5400	associated constants have been renamed to not collide with the C<struct
		5401	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5402	as all other watcher types. Note that C<ev_loop_fork> is still called
		5403	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5404	typedef.
		5405
		5406	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5407
		5408	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5409	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5410	and work, but the library code will of course be larger.
		5411
		5412	=back
		5413
		5414
		5415	=head1 GLOSSARY
		5416
		5417	=over 4
		5418
		5419	=item active
		5420
		5421	A watcher is active as long as it has been started and not yet stopped.
		5422	See L<WATCHER STATES> for details.
		5423
		5424	=item application
		5425
		5426	In this document, an application is whatever is using libev.
		5427
		5428	=item backend
		5429
		5430	The part of the code dealing with the operating system interfaces.
		5431
		5432	=item callback
		5433
		5434	The address of a function that is called when some event has been
		5435	detected. Callbacks are being passed the event loop, the watcher that
		5436	received the event, and the actual event bitset.
		5437
		5438	=item callback/watcher invocation
		5439
		5440	The act of calling the callback associated with a watcher.
		5441
		5442	=item event
		5443
		5444	A change of state of some external event, such as data now being available
		5445	for reading on a file descriptor, time having passed or simply not having
		5446	any other events happening anymore.
		5447
		5448	In libev, events are represented as single bits (such as C<EV_READ> or
		5449	C<EV_TIMER>).
		5450
		5451	=item event library
		5452
		5453	A software package implementing an event model and loop.
		5454
		5455	=item event loop
		5456
		5457	An entity that handles and processes external events and converts them
		5458	into callback invocations.
		5459
		5460	=item event model
		5461
		5462	The model used to describe how an event loop handles and processes
		5463	watchers and events.
		5464
		5465	=item pending
		5466
		5467	A watcher is pending as soon as the corresponding event has been
		5468	detected. See L<WATCHER STATES> for details.
		5469
		5470	=item real time
		5471
		5472	The physical time that is observed. It is apparently strictly monotonic :)
		5473
		5474	=item wall-clock time
		5475
		5476	The time and date as shown on clocks. Unlike real time, it can actually
		5477	be wrong and jump forwards and backwards, e.g. when you adjust your
		5478	clock.
		5479
		5480	=item watcher
		5481
		5482	A data structure that describes interest in certain events. Watchers need
		5483	to be started (attached to an event loop) before they can receive events.
		5484
		5485	=back
2868		5486
2869	=head1 AUTHOR	5487	=head1 AUTHOR
2870		5488
2871	Marc Lehmann <libev@schmorp.de>.	5489	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5490	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
2872		5491

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