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Revision 1.117 by root, Wed Jan 9 04:15:39 2008 UTC vs.
Revision 1.370 by root, Thu Jun 2 23:42:40 2011 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=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_update_now> 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 until
123	either it is interrupted or the given time interval has passed. Basically	184	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	185	this is a sub-second-resolution C<sleep ()>.
125		186
126	=item int ev_version_major ()	187	=item int ev_version_major ()
127		188
128	=item int ev_version_minor ()	189	=item int ev_version_minor ()
129		190
…		…
140	as this indicates an incompatible change. Minor versions are usually	201	as this indicates an incompatible change. Minor versions are usually
141	compatible to older versions, so a larger minor version alone is usually	202	compatible to older versions, so a larger minor version alone is usually
142	not a problem.	203	not a problem.
143		204
144	Example: Make sure we haven't accidentally been linked against the wrong	205	Example: Make sure we haven't accidentally been linked against the wrong
145	version.	206	version (note, however, that this will not detect other ABI mismatches,
		207	such as LFS or reentrancy).
146		208
147	assert (("libev version mismatch",	209	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	210	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	211	&& ev_version_minor () >= EV_VERSION_MINOR));
150		212
151	=item unsigned int ev_supported_backends ()	213	=item unsigned int ev_supported_backends ()
152		214
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	215	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	216	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	218	a description of the set values.
157		219
158	Example: make sure we have the epoll method, because yeah this is cool and	220	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	221	a must have and can we have a torrent of it please!!!11
160		222
161	assert (("sorry, no epoll, no sex",	223	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	224	ev_supported_backends () & EVBACKEND_EPOLL));
163		225
164	=item unsigned int ev_recommended_backends ()	226	=item unsigned int ev_recommended_backends ()
165		227
166	Return the set of all backends compiled into this binary of libev and also	228	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	229	also recommended for this platform, meaning it will work for most file
		230	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	231	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	232	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	233	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.	234	probe for if you specify no backends explicitly.
172		235
173	=item unsigned int ev_embeddable_backends ()	236	=item unsigned int ev_embeddable_backends ()
174		237
175	Returns the set of backends that are embeddable in other event loops. This	238	Returns the set of backends that are embeddable in other event loops. This
176	is the theoretical, all-platform, value. To find which backends	239	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	240	current system. To find which embeddable backends might be supported on
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	241	the current system, you would need to look at C<ev_embeddable_backends ()
179	recommended ones.	242	& ev_supported_backends ()>, likewise for recommended ones.
180		243
181	See the description of C<ev_embed> watchers for more info.	244	See the description of C<ev_embed> watchers for more info.
182		245
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
184		247
185	Sets the allocation function to use (the prototype is similar - the	248	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	249	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	250	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	251	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	252	or take some potentially destructive action.
190	function.	253
		254	Since some systems (at least OpenBSD and Darwin) fail to implement
		255	correct C<realloc> semantics, libev will use a wrapper around the system
		256	C<realloc> and C<free> functions by default.
191		257
192	You could override this function in high-availability programs to, say,	258	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,	259	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.	260	or even to sleep a while and retry until some memory is available.
195		261
196	Example: Replace the libev allocator with one that waits a bit and then	262	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	263	retries (example requires a standards-compliant C<realloc>).
198		264
199	static void *	265	static void *
200	persistent_realloc (void *ptr, size_t size)	266	persistent_realloc (void *ptr, size_t size)
201	{	267	{
202	for (;;)	268	for (;;)
…		…
211	}	277	}
212		278
213	...	279	...
214	ev_set_allocator (persistent_realloc);	280	ev_set_allocator (persistent_realloc);
215		281
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	282	=item ev_set_syserr_cb (void (*cb)(const char *msg))
217		283
218	Set the callback function to call on a retryable syscall error (such	284	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	285	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	286	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	287	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	288	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	289	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	290	(such as abort).
225		291
226	Example: This is basically the same thing that libev does internally, too.	292	Example: This is basically the same thing that libev does internally, too.
…		…
233	}	299	}
234		300
235	...	301	...
236	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
237		303
		304	=item ev_feed_signal (int signum)
		305
		306	This function can be used to "simulate" a signal receive. It is completely
		307	safe to call this function at any time, from any context, including signal
		308	handlers or random threads.
		309
		310	Its main use is to customise signal handling in your process, especially
		311	in the presence of threads. For example, you could block signals
		312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		313	creating any loops), and in one thread, use C<sigwait> or any other
		314	mechanism to wait for signals, then "deliver" them to libev by calling
		315	C<ev_feed_signal>.
		316
238	=back	317	=back
239		318
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
241		320
242	An event loop is described by a C<struct ev_loop *>. The library knows two	321	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	322	I<not> optional in this case unless libev 3 compatibility is disabled, as
244	events, and dynamically created loops which do not.	323	libev 3 had an C<ev_loop> function colliding with the struct name).
245		324
246	If you use threads, a common model is to run the default event loop	325	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	326	supports child process events, and dynamically created event loops which
248	create, you also create another event loop. Libev itself does no locking	327	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		328
253	=over 4	329	=over 4
254		330
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	331	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		332
257	This will initialise the default event loop if it hasn't been initialised	333	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	334	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	335	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).	336	C<ev_loop_new>.
		337
		338	If the default loop is already initialised then this function simply
		339	returns it (and ignores the flags. If that is troubling you, check
		340	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		341	flags, which should almost always be C<0>, unless the caller is also the
		342	one calling C<ev_run> or otherwise qualifies as "the main program".
261		343
262	If you don't know what event loop to use, use the one returned from this	344	If you don't know what event loop to use, use the one returned from this
263	function.	345	function (or via the C<EV_DEFAULT> macro).
		346
		347	Note that this function is I<not> thread-safe, so if you want to use it
		348	from multiple threads, you have to employ some kind of mutex (note also
		349	that this case is unlikely, as loops cannot be shared easily between
		350	threads anyway).
		351
		352	The default loop is the only loop that can handle C<ev_child> watchers,
		353	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		354	a problem for your application you can either create a dynamic loop with
		355	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		356	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		357
		358	Example: This is the most typical usage.
		359
		360	if (!ev_default_loop (0))
		361	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		362
		363	Example: Restrict libev to the select and poll backends, and do not allow
		364	environment settings to be taken into account:
		365
		366	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		367
		368	=item struct ev_loop *ev_loop_new (unsigned int flags)
		369
		370	This will create and initialise a new event loop object. If the loop
		371	could not be initialised, returns false.
		372
		373	This function is thread-safe, and one common way to use libev with
		374	threads is indeed to create one loop per thread, and using the default
		375	loop in the "main" or "initial" thread.
264		376
265	The flags argument can be used to specify special behaviour or specific	377	The flags argument can be used to specify special behaviour or specific
266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	378	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
267		379
268	The following flags are supported:	380	The following flags are supported:
…		…
274	The default flags value. Use this if you have no clue (it's the right	386	The default flags value. Use this if you have no clue (it's the right
275	thing, believe me).	387	thing, believe me).
276		388
277	=item C<EVFLAG_NOENV>	389	=item C<EVFLAG_NOENV>
278		390
279	If this flag bit is ored into the flag value (or the program runs setuid	391	If this flag bit is or'ed into the flag value (or the program runs setuid
280	or setgid) then libev will I<not> look at the environment variable	392	or setgid) then libev will I<not> look at the environment variable
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	393	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	override the flags completely if it is found in the environment. This is	394	override the flags completely if it is found in the environment. This is
283	useful to try out specific backends to test their performance, or to work	395	useful to try out specific backends to test their performance, or to work
284	around bugs.	396	around bugs.
285		397
286	=item C<EVFLAG_FORKCHECK>	398	=item C<EVFLAG_FORKCHECK>
287		399
288	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	400	Instead of calling C<ev_loop_fork> manually after a fork, you can also
289	a fork, you can also make libev check for a fork in each iteration by	401	make libev check for a fork in each iteration by enabling this flag.
290	enabling this flag.
291		402
292	This works by calling C<getpid ()> on every iteration of the loop,	403	This works by calling C<getpid ()> on every iteration of the loop,
293	and thus this might slow down your event loop if you do a lot of loop	404	and thus this might slow down your event loop if you do a lot of loop
294	iterations and little real work, but is usually not noticeable (on my	405	iterations and little real work, but is usually not noticeable (on my
295	Linux system for example, C<getpid> is actually a simple 5-insn sequence	406	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
296	without a syscall and thus I<very> fast, but my Linux system also has	407	without a system call and thus I<very> fast, but my GNU/Linux system also has
297	C<pthread_atfork> which is even faster).	408	C<pthread_atfork> which is even faster).
298		409
299	The big advantage of this flag is that you can forget about fork (and	410	The big advantage of this flag is that you can forget about fork (and
300	forget about forgetting to tell libev about forking) when you use this	411	forget about forgetting to tell libev about forking) when you use this
301	flag.	412	flag.
302		413
303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	414	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
304	environment variable.	415	environment variable.
		416
		417	=item C<EVFLAG_NOINOTIFY>
		418
		419	When this flag is specified, then libev will not attempt to use the
		420	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		421	testing, this flag can be useful to conserve inotify file descriptors, as
		422	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		423
		424	=item C<EVFLAG_SIGNALFD>
		425
		426	When this flag is specified, then libev will attempt to use the
		427	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		428	delivers signals synchronously, which makes it both faster and might make
		429	it possible to get the queued signal data. It can also simplify signal
		430	handling with threads, as long as you properly block signals in your
		431	threads that are not interested in handling them.
		432
		433	Signalfd will not be used by default as this changes your signal mask, and
		434	there are a lot of shoddy libraries and programs (glib's threadpool for
		435	example) that can't properly initialise their signal masks.
		436
		437	=item C<EVFLAG_NOSIGMASK>
		438
		439	When this flag is specified, then libev will avoid to modify the signal
		440	mask. Specifically, this means you ahve to make sure signals are unblocked
		441	when you want to receive them.
		442
		443	This behaviour is useful when you want to do your own signal handling, or
		444	want to handle signals only in specific threads and want to avoid libev
		445	unblocking the signals.
		446
		447	It's also required by POSIX in a threaded program, as libev calls
		448	C<sigprocmask>, whose behaviour is officially unspecified.
		449
		450	This flag's behaviour will become the default in future versions of libev.
305		451
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	452	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		453
308	This is your standard select(2) backend. Not I<completely> standard, as	454	This is your standard select(2) backend. Not I<completely> standard, as
309	libev tries to roll its own fd_set with no limits on the number of fds,	455	libev tries to roll its own fd_set with no limits on the number of fds,
310	but if that fails, expect a fairly low limit on the number of fds when	456	but if that fails, expect a fairly low limit on the number of fds when
311	using this backend. It doesn't scale too well (O(highest_fd)), but its	457	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	usually the fastest backend for a low number of (low-numbered :) fds.	458	usually the fastest backend for a low number of (low-numbered :) fds.
313		459
314	To get good performance out of this backend you need a high amount of	460	To get good performance out of this backend you need a high amount of
315	parallelity (most of the file descriptors should be busy). If you are	461	parallelism (most of the file descriptors should be busy). If you are
316	writing a server, you should C<accept ()> in a loop to accept as many	462	writing a server, you should C<accept ()> in a loop to accept as many
317	connections as possible during one iteration. You might also want to have	463	connections as possible during one iteration. You might also want to have
318	a look at C<ev_set_io_collect_interval ()> to increase the amount of	464	a look at C<ev_set_io_collect_interval ()> to increase the amount of
319	readyness notifications you get per iteration.	465	readiness notifications you get per iteration.
		466
		467	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		468	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		469	C<exceptfds> set on that platform).
320		470
321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	471	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
322		472
323	And this is your standard poll(2) backend. It's more complicated	473	And this is your standard poll(2) backend. It's more complicated
324	than select, but handles sparse fds better and has no artificial	474	than select, but handles sparse fds better and has no artificial
325	limit on the number of fds you can use (except it will slow down	475	limit on the number of fds you can use (except it will slow down
326	considerably with a lot of inactive fds). It scales similarly to select,	476	considerably with a lot of inactive fds). It scales similarly to select,
327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	477	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
328	performance tips.	478	performance tips.
329		479
		480	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		481	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		482
330	=item C<EVBACKEND_EPOLL> (value 4, Linux)	483	=item C<EVBACKEND_EPOLL> (value 4, Linux)
331		484
		485	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		486	kernels).
		487
332	For few fds, this backend is a bit little slower than poll and select,	488	For few fds, this backend is a bit little slower than poll and select, but
333	but it scales phenomenally better. While poll and select usually scale	489	it scales phenomenally better. While poll and select usually scale like
334	like O(total_fds) where n is the total number of fds (or the highest fd),	490	O(total_fds) where total_fds is the total number of fds (or the highest
335	epoll scales either O(1) or O(active_fds). The epoll design has a number	491	fd), epoll scales either O(1) or O(active_fds).
336	of shortcomings, such as silently dropping events in some hard-to-detect	492
337	cases and rewiring a syscall per fd change, no fork support and bad	493	The epoll mechanism deserves honorable mention as the most misdesigned
338	support for dup.	494	of the more advanced event mechanisms: mere annoyances include silently
		495	dropping file descriptors, requiring a system call per change per file
		496	descriptor (and unnecessary guessing of parameters), problems with dup,
		497	returning before the timeout value, resulting in additional iterations
		498	(and only giving 5ms accuracy while select on the same platform gives
		499	0.1ms) and so on. The biggest issue is fork races, however - if a program
		500	forks then I<both> parent and child process have to recreate the epoll
		501	set, which can take considerable time (one syscall per file descriptor)
		502	and is of course hard to detect.
		503
		504	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		505	but of course I<doesn't>, and epoll just loves to report events for
		506	totally I<different> file descriptors (even already closed ones, so
		507	one cannot even remove them from the set) than registered in the set
		508	(especially on SMP systems). Libev tries to counter these spurious
		509	notifications by employing an additional generation counter and comparing
		510	that against the events to filter out spurious ones, recreating the set
		511	when required. Epoll also errornously rounds down timeouts, but gives you
		512	no way to know when and by how much, so sometimes you have to busy-wait
		513	because epoll returns immediately despite a nonzero timeout. And last
		514	not least, it also refuses to work with some file descriptors which work
		515	perfectly fine with C<select> (files, many character devices...).
		516
		517	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		518	cobbled together in a hurry, no thought to design or interaction with
		519	others. Oh, the pain, will it ever stop...
339		520
340	While stopping, setting and starting an I/O watcher in the same iteration	521	While stopping, setting and starting an I/O watcher in the same iteration
341	will result in some caching, there is still a syscall per such incident	522	will result in some caching, there is still a system call per such
342	(because the fd could point to a different file description now), so its	523	incident (because the same I<file descriptor> could point to a different
343	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	524	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
344	very well if you register events for both fds.	525	file descriptors might not work very well if you register events for both
345		526	file descriptors.
346	Please note that epoll sometimes generates spurious notifications, so you
347	need to use non-blocking I/O or other means to avoid blocking when no data
348	(or space) is available.
349		527
350	Best performance from this backend is achieved by not unregistering all	528	Best performance from this backend is achieved by not unregistering all
351	watchers for a file descriptor until it has been closed, if possible, i.e.	529	watchers for a file descriptor until it has been closed, if possible,
352	keep at least one watcher active per fd at all times.	530	i.e. keep at least one watcher active per fd at all times. Stopping and
		531	starting a watcher (without re-setting it) also usually doesn't cause
		532	extra overhead. A fork can both result in spurious notifications as well
		533	as in libev having to destroy and recreate the epoll object, which can
		534	take considerable time and thus should be avoided.
353		535
		536	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		537	faster than epoll for maybe up to a hundred file descriptors, depending on
		538	the usage. So sad.
		539
354	While nominally embeddeble in other event loops, this feature is broken in	540	While nominally embeddable in other event loops, this feature is broken in
355	all kernel versions tested so far.	541	all kernel versions tested so far.
		542
		543	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		544	C<EVBACKEND_POLL>.
356		545
357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	546	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
358		547
359	Kqueue deserves special mention, as at the time of this writing, it	548	Kqueue deserves special mention, as at the time of this writing, it
360	was broken on all BSDs except NetBSD (usually it doesn't work reliably	549	was broken on all BSDs except NetBSD (usually it doesn't work reliably
361	with anything but sockets and pipes, except on Darwin, where of course	550	with anything but sockets and pipes, except on Darwin, where of course
362	it's completely useless). For this reason it's not being "autodetected"	551	it's completely useless). Unlike epoll, however, whose brokenness
		552	is by design, these kqueue bugs can (and eventually will) be fixed
		553	without API changes to existing programs. For this reason it's not being
363	unless you explicitly specify it explicitly in the flags (i.e. using	554	"auto-detected" unless you explicitly specify it in the flags (i.e. using
364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	555	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
365	system like NetBSD.	556	system like NetBSD.
366		557
367	You still can embed kqueue into a normal poll or select backend and use it	558	You still can embed kqueue into a normal poll or select backend and use it
368	only for sockets (after having made sure that sockets work with kqueue on	559	only for sockets (after having made sure that sockets work with kqueue on
369	the target platform). See C<ev_embed> watchers for more info.	560	the target platform). See C<ev_embed> watchers for more info.
370		561
371	It scales in the same way as the epoll backend, but the interface to the	562	It scales in the same way as the epoll backend, but the interface to the
372	kernel is more efficient (which says nothing about its actual speed, of	563	kernel is more efficient (which says nothing about its actual speed, of
373	course). While stopping, setting and starting an I/O watcher does never	564	course). While stopping, setting and starting an I/O watcher does never
374	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	565	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
375	two event changes per incident, support for C<fork ()> is very bad and it	566	two event changes per incident. Support for C<fork ()> is very bad (but
376	drops fds silently in similarly hard-to-detect cases.	567	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		568	cases
377		569
378	This backend usually performs well under most conditions.	570	This backend usually performs well under most conditions.
379		571
380	While nominally embeddable in other event loops, this doesn't work	572	While nominally embeddable in other event loops, this doesn't work
381	everywhere, so you might need to test for this. And since it is broken	573	everywhere, so you might need to test for this. And since it is broken
382	almost everywhere, you should only use it when you have a lot of sockets	574	almost everywhere, you should only use it when you have a lot of sockets
383	(for which it usually works), by embedding it into another event loop	575	(for which it usually works), by embedding it into another event loop
384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	576	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
385	sockets.	577	also broken on OS X)) and, did I mention it, using it only for sockets.
		578
		579	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		580	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		581	C<NOTE_EOF>.
386		582
387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	583	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
388		584
389	This is not implemented yet (and might never be, unless you send me an	585	This is not implemented yet (and might never be, unless you send me an
390	implementation). According to reports, C</dev/poll> only supports sockets	586	implementation). According to reports, C</dev/poll> only supports sockets
…		…
394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	590	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
395		591
396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	592	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
397	it's really slow, but it still scales very well (O(active_fds)).	593	it's really slow, but it still scales very well (O(active_fds)).
398		594
399	Please note that solaris event ports can deliver a lot of spurious
400	notifications, so you need to use non-blocking I/O or other means to avoid
401	blocking when no data (or space) is available.
402
403	While this backend scales well, it requires one system call per active	595	While this backend scales well, it requires one system call per active
404	file descriptor per loop iteration. For small and medium numbers of file	596	file descriptor per loop iteration. For small and medium numbers of file
405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	597	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
406	might perform better.	598	might perform better.
407		599
408	On the positive side, ignoring the spurious readyness notifications, this	600	On the positive side, this backend actually performed fully to
409	backend actually performed to specification in all tests and is fully	601	specification in all tests and is fully embeddable, which is a rare feat
410	embeddable, which is a rare feat among the OS-specific backends.	602	among the OS-specific backends (I vastly prefer correctness over speed
		603	hacks).
		604
		605	On the negative side, the interface is I<bizarre> - so bizarre that
		606	even sun itself gets it wrong in their code examples: The event polling
		607	function sometimes returning events to the caller even though an error
		608	occurred, but with no indication whether it has done so or not (yes, it's
		609	even documented that way) - deadly for edge-triggered interfaces where
		610	you absolutely have to know whether an event occurred or not because you
		611	have to re-arm the watcher.
		612
		613	Fortunately libev seems to be able to work around these idiocies.
		614
		615	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		616	C<EVBACKEND_POLL>.
411		617
412	=item C<EVBACKEND_ALL>	618	=item C<EVBACKEND_ALL>
413		619
414	Try all backends (even potentially broken ones that wouldn't be tried	620	Try all backends (even potentially broken ones that wouldn't be tried
415	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	621	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
416	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	622	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
417		623
418	It is definitely not recommended to use this flag.	624	It is definitely not recommended to use this flag, use whatever
		625	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		626	at all.
		627
		628	=item C<EVBACKEND_MASK>
		629
		630	Not a backend at all, but a mask to select all backend bits from a
		631	C<flags> value, in case you want to mask out any backends from a flags
		632	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
419		633
420	=back	634	=back
421		635
422	If one or more of these are ored into the flags value, then only these	636	If one or more of the backend flags are or'ed into the flags value,
423	backends will be tried (in the reverse order as listed here). If none are	637	then only these backends will be tried (in the reverse order as listed
424	specified, all backends in C<ev_recommended_backends ()> will be tried.	638	here). If none are specified, all backends in C<ev_recommended_backends
425		639	()> will be tried.
426	The most typical usage is like this:
427
428	if (!ev_default_loop (0))
429	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
430
431	Restrict libev to the select and poll backends, and do not allow
432	environment settings to be taken into account:
433
434	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
435
436	Use whatever libev has to offer, but make sure that kqueue is used if
437	available (warning, breaks stuff, best use only with your own private
438	event loop and only if you know the OS supports your types of fds):
439
440	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
441
442	=item struct ev_loop *ev_loop_new (unsigned int flags)
443
444	Similar to C<ev_default_loop>, but always creates a new event loop that is
445	always distinct from the default loop. Unlike the default loop, it cannot
446	handle signal and child watchers, and attempts to do so will be greeted by
447	undefined behaviour (or a failed assertion if assertions are enabled).
448		640
449	Example: Try to create a event loop that uses epoll and nothing else.	641	Example: Try to create a event loop that uses epoll and nothing else.
450		642
451	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	643	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
452	if (!epoller)	644	if (!epoller)
453	fatal ("no epoll found here, maybe it hides under your chair");	645	fatal ("no epoll found here, maybe it hides under your chair");
454		646
		647	Example: Use whatever libev has to offer, but make sure that kqueue is
		648	used if available.
		649
		650	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		651
455	=item ev_default_destroy ()	652	=item ev_loop_destroy (loop)
456		653
457	Destroys the default loop again (frees all memory and kernel state	654	Destroys an event loop object (frees all memory and kernel state
458	etc.). None of the active event watchers will be stopped in the normal	655	etc.). None of the active event watchers will be stopped in the normal
459	sense, so e.g. C<ev_is_active> might still return true. It is your	656	sense, so e.g. C<ev_is_active> might still return true. It is your
460	responsibility to either stop all watchers cleanly yoursef I<before>	657	responsibility to either stop all watchers cleanly yourself I<before>
461	calling this function, or cope with the fact afterwards (which is usually	658	calling this function, or cope with the fact afterwards (which is usually
462	the easiest thing, you can just ignore the watchers and/or C<free ()> them	659	the easiest thing, you can just ignore the watchers and/or C<free ()> them
463	for example).	660	for example).
464		661
465	Note that certain global state, such as signal state, will not be freed by	662	Note that certain global state, such as signal state (and installed signal
466	this function, and related watchers (such as signal and child watchers)	663	handlers), will not be freed by this function, and related watchers (such
467	would need to be stopped manually.	664	as signal and child watchers) would need to be stopped manually.
468		665
469	In general it is not advisable to call this function except in the	666	This function is normally used on loop objects allocated by
470	rare occasion where you really need to free e.g. the signal handling	667	C<ev_loop_new>, but it can also be used on the default loop returned by
		668	C<ev_default_loop>, in which case it is not thread-safe.
		669
		670	Note that it is not advisable to call this function on the default loop
		671	except in the rare occasion where you really need to free its resources.
471	pipe fds. If you need dynamically allocated loops it is better to use	672	If you need dynamically allocated loops it is better to use C<ev_loop_new>
472	C<ev_loop_new> and C<ev_loop_destroy>).	673	and C<ev_loop_destroy>.
473		674
474	=item ev_loop_destroy (loop)	675	=item ev_loop_fork (loop)
475		676
476	Like C<ev_default_destroy>, but destroys an event loop created by an	677	This function sets a flag that causes subsequent C<ev_run> iterations to
477	earlier call to C<ev_loop_new>.
478
479	=item ev_default_fork ()
480
481	This function reinitialises the kernel state for backends that have	678	reinitialise the kernel state for backends that have one. Despite the
482	one. Despite the name, you can call it anytime, but it makes most sense	679	name, you can call it anytime, but it makes most sense after forking, in
483	after forking, in either the parent or child process (or both, but that	680	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
484	again makes little sense).	681	child before resuming or calling C<ev_run>.
485		682
486	You I<must> call this function in the child process after forking if and	683	Again, you I<have> to call it on I<any> loop that you want to re-use after
487	only if you want to use the event library in both processes. If you just	684	a fork, I<even if you do not plan to use the loop in the parent>. This is
488	fork+exec, you don't have to call it.	685	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		686	during fork.
		687
		688	On the other hand, you only need to call this function in the child
		689	process if and only if you want to use the event loop in the child. If
		690	you just fork+exec or create a new loop in the child, you don't have to
		691	call it at all (in fact, C<epoll> is so badly broken that it makes a
		692	difference, but libev will usually detect this case on its own and do a
		693	costly reset of the backend).
489		694
490	The function itself is quite fast and it's usually not a problem to call	695	The function itself is quite fast and it's usually not a problem to call
491	it just in case after a fork. To make this easy, the function will fit in	696	it just in case after a fork.
492	quite nicely into a call to C<pthread_atfork>:
493		697
		698	Example: Automate calling C<ev_loop_fork> on the default loop when
		699	using pthreads.
		700
		701	static void
		702	post_fork_child (void)
		703	{
		704	ev_loop_fork (EV_DEFAULT);
		705	}
		706
		707	...
494	pthread_atfork (0, 0, ev_default_fork);	708	pthread_atfork (0, 0, post_fork_child);
495		709
496	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	710	=item int ev_is_default_loop (loop)
497	without calling this function, so if you force one of those backends you
498	do not need to care.
499		711
500	=item ev_loop_fork (loop)	712	Returns true when the given loop is, in fact, the default loop, and false
		713	otherwise.
501		714
502	Like C<ev_default_fork>, but acts on an event loop created by
503	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
504	after fork, and how you do this is entirely your own problem.
505
506	=item unsigned int ev_loop_count (loop)	715	=item unsigned int ev_iteration (loop)
507		716
508	Returns the count of loop iterations for the loop, which is identical to	717	Returns the current iteration count for the event loop, which is identical
509	the number of times libev did poll for new events. It starts at C<0> and	718	to the number of times libev did poll for new events. It starts at C<0>
510	happily wraps around with enough iterations.	719	and happily wraps around with enough iterations.
511		720
512	This value can sometimes be useful as a generation counter of sorts (it	721	This value can sometimes be useful as a generation counter of sorts (it
513	"ticks" the number of loop iterations), as it roughly corresponds with	722	"ticks" the number of loop iterations), as it roughly corresponds with
514	C<ev_prepare> and C<ev_check> calls.	723	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		724	prepare and check phases.
		725
		726	=item unsigned int ev_depth (loop)
		727
		728	Returns the number of times C<ev_run> was entered minus the number of
		729	times C<ev_run> was exited normally, in other words, the recursion depth.
		730
		731	Outside C<ev_run>, this number is zero. In a callback, this number is
		732	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		733	in which case it is higher.
		734
		735	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		736	throwing an exception etc.), doesn't count as "exit" - consider this
		737	as a hint to avoid such ungentleman-like behaviour unless it's really
		738	convenient, in which case it is fully supported.
515		739
516	=item unsigned int ev_backend (loop)	740	=item unsigned int ev_backend (loop)
517		741
518	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	742	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
519	use.	743	use.
…		…
524	received events and started processing them. This timestamp does not	748	received events and started processing them. This timestamp does not
525	change as long as callbacks are being processed, and this is also the base	749	change as long as callbacks are being processed, and this is also the base
526	time used for relative timers. You can treat it as the timestamp of the	750	time used for relative timers. You can treat it as the timestamp of the
527	event occurring (or more correctly, libev finding out about it).	751	event occurring (or more correctly, libev finding out about it).
528		752
		753	=item ev_now_update (loop)
		754
		755	Establishes the current time by querying the kernel, updating the time
		756	returned by C<ev_now ()> in the progress. This is a costly operation and
		757	is usually done automatically within C<ev_run ()>.
		758
		759	This function is rarely useful, but when some event callback runs for a
		760	very long time without entering the event loop, updating libev's idea of
		761	the current time is a good idea.
		762
		763	See also L<The special problem of time updates> in the C<ev_timer> section.
		764
		765	=item ev_suspend (loop)
		766
		767	=item ev_resume (loop)
		768
		769	These two functions suspend and resume an event loop, for use when the
		770	loop is not used for a while and timeouts should not be processed.
		771
		772	A typical use case would be an interactive program such as a game: When
		773	the user presses C<^Z> to suspend the game and resumes it an hour later it
		774	would be best to handle timeouts as if no time had actually passed while
		775	the program was suspended. This can be achieved by calling C<ev_suspend>
		776	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		777	C<ev_resume> directly afterwards to resume timer processing.
		778
		779	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		780	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		781	will be rescheduled (that is, they will lose any events that would have
		782	occurred while suspended).
		783
		784	After calling C<ev_suspend> you B<must not> call I<any> function on the
		785	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		786	without a previous call to C<ev_suspend>.
		787
		788	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		789	event loop time (see C<ev_now_update>).
		790
529	=item ev_loop (loop, int flags)	791	=item ev_run (loop, int flags)
530		792
531	Finally, this is it, the event handler. This function usually is called	793	Finally, this is it, the event handler. This function usually is called
532	after you initialised all your watchers and you want to start handling	794	after you have initialised all your watchers and you want to start
533	events.	795	handling events. It will ask the operating system for any new events, call
		796	the watcher callbacks, an then repeat the whole process indefinitely: This
		797	is why event loops are called I<loops>.
534		798
535	If the flags argument is specified as C<0>, it will not return until	799	If the flags argument is specified as C<0>, it will keep handling events
536	either no event watchers are active anymore or C<ev_unloop> was called.	800	until either no event watchers are active anymore or C<ev_break> was
		801	called.
537		802
538	Please note that an explicit C<ev_unloop> is usually better than	803	Please note that an explicit C<ev_break> is usually better than
539	relying on all watchers to be stopped when deciding when a program has	804	relying on all watchers to be stopped when deciding when a program has
540	finished (especially in interactive programs), but having a program that	805	finished (especially in interactive programs), but having a program
541	automatically loops as long as it has to and no longer by virtue of	806	that automatically loops as long as it has to and no longer by virtue
542	relying on its watchers stopping correctly is a thing of beauty.	807	of relying on its watchers stopping correctly, that is truly a thing of
		808	beauty.
543		809
		810	This function is also I<mostly> exception-safe - you can break out of
		811	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		812	exception and so on. This does not decrement the C<ev_depth> value, nor
		813	will it clear any outstanding C<EVBREAK_ONE> breaks.
		814
544	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	815	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
545	those events and any outstanding ones, but will not block your process in	816	those events and any already outstanding ones, but will not wait and
546	case there are no events and will return after one iteration of the loop.	817	block your process in case there are no events and will return after one
		818	iteration of the loop. This is sometimes useful to poll and handle new
		819	events while doing lengthy calculations, to keep the program responsive.
547		820
548	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	821	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
549	neccessary) and will handle those and any outstanding ones. It will block	822	necessary) and will handle those and any already outstanding ones. It
550	your process until at least one new event arrives, and will return after	823	will block your process until at least one new event arrives (which could
551	one iteration of the loop. This is useful if you are waiting for some	824	be an event internal to libev itself, so there is no guarantee that a
552	external event in conjunction with something not expressible using other	825	user-registered callback will be called), and will return after one
		826	iteration of the loop.
		827
		828	This is useful if you are waiting for some external event in conjunction
		829	with something not expressible using other libev watchers (i.e. "roll your
553	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	830	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
554	usually a better approach for this kind of thing.	831	usually a better approach for this kind of thing.
555		832
556	Here are the gory details of what C<ev_loop> does:	833	Here are the gory details of what C<ev_run> does (this is for your
		834	understanding, not a guarantee that things will work exactly like this in
		835	future versions):
557		836
		837	- Increment loop depth.
		838	- Reset the ev_break status.
558	- Before the first iteration, call any pending watchers.	839	- Before the first iteration, call any pending watchers.
		840	LOOP:
559	* If EVFLAG_FORKCHECK was used, check for a fork.	841	- If EVFLAG_FORKCHECK was used, check for a fork.
560	- If a fork was detected, queue and call all fork watchers.	842	- If a fork was detected (by any means), queue and call all fork watchers.
561	- Queue and call all prepare watchers.	843	- Queue and call all prepare watchers.
		844	- If ev_break was called, goto FINISH.
562	- If we have been forked, recreate the kernel state.	845	- If we have been forked, detach and recreate the kernel state
		846	as to not disturb the other process.
563	- Update the kernel state with all outstanding changes.	847	- Update the kernel state with all outstanding changes.
564	- Update the "event loop time".	848	- Update the "event loop time" (ev_now ()).
565	- Calculate for how long to sleep or block, if at all	849	- Calculate for how long to sleep or block, if at all
566	(active idle watchers, EVLOOP_NONBLOCK or not having	850	(active idle watchers, EVRUN_NOWAIT or not having
567	any active watchers at all will result in not sleeping).	851	any active watchers at all will result in not sleeping).
568	- Sleep if the I/O and timer collect interval say so.	852	- Sleep if the I/O and timer collect interval say so.
		853	- Increment loop iteration counter.
569	- Block the process, waiting for any events.	854	- Block the process, waiting for any events.
570	- Queue all outstanding I/O (fd) events.	855	- Queue all outstanding I/O (fd) events.
571	- Update the "event loop time" and do time jump handling.	856	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
572	- Queue all outstanding timers.	857	- Queue all expired timers.
573	- Queue all outstanding periodics.	858	- Queue all expired periodics.
574	- If no events are pending now, queue all idle watchers.	859	- Queue all idle watchers with priority higher than that of pending events.
575	- Queue all check watchers.	860	- Queue all check watchers.
576	- Call all queued watchers in reverse order (i.e. check watchers first).	861	- Call all queued watchers in reverse order (i.e. check watchers first).
577	Signals and child watchers are implemented as I/O watchers, and will	862	Signals and child watchers are implemented as I/O watchers, and will
578	be handled here by queueing them when their watcher gets executed.	863	be handled here by queueing them when their watcher gets executed.
579	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	864	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
580	were used, or there are no active watchers, return, otherwise	865	were used, or there are no active watchers, goto FINISH, otherwise
581	continue with step *.	866	continue with step LOOP.
		867	FINISH:
		868	- Reset the ev_break status iff it was EVBREAK_ONE.
		869	- Decrement the loop depth.
		870	- Return.
582		871
583	Example: Queue some jobs and then loop until no events are outstanding	872	Example: Queue some jobs and then loop until no events are outstanding
584	anymore.	873	anymore.
585		874
586	... queue jobs here, make sure they register event watchers as long	875	... queue jobs here, make sure they register event watchers as long
587	... as they still have work to do (even an idle watcher will do..)	876	... as they still have work to do (even an idle watcher will do..)
588	ev_loop (my_loop, 0);	877	ev_run (my_loop, 0);
589	... jobs done. yeah!	878	... jobs done or somebody called break. yeah!
590		879
591	=item ev_unloop (loop, how)	880	=item ev_break (loop, how)
592		881
593	Can be used to make a call to C<ev_loop> return early (but only after it	882	Can be used to make a call to C<ev_run> return early (but only after it
594	has processed all outstanding events). The C<how> argument must be either	883	has processed all outstanding events). The C<how> argument must be either
595	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	884	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
596	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	885	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
597		886
598	This "unloop state" will be cleared when entering C<ev_loop> again.	887	This "break state" will be cleared on the next call to C<ev_run>.
		888
		889	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		890	which case it will have no effect.
599		891
600	=item ev_ref (loop)	892	=item ev_ref (loop)
601		893
602	=item ev_unref (loop)	894	=item ev_unref (loop)
603		895
604	Ref/unref can be used to add or remove a reference count on the event	896	Ref/unref can be used to add or remove a reference count on the event
605	loop: Every watcher keeps one reference, and as long as the reference	897	loop: Every watcher keeps one reference, and as long as the reference
606	count is nonzero, C<ev_loop> will not return on its own. If you have	898	count is nonzero, C<ev_run> will not return on its own.
607	a watcher you never unregister that should not keep C<ev_loop> from	899
608	returning, ev_unref() after starting, and ev_ref() before stopping it. For	900	This is useful when you have a watcher that you never intend to
		901	unregister, but that nevertheless should not keep C<ev_run> from
		902	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		903	before stopping it.
		904
609	example, libev itself uses this for its internal signal pipe: It is not	905	As an example, libev itself uses this for its internal signal pipe: It
610	visible to the libev user and should not keep C<ev_loop> from exiting if	906	is not visible to the libev user and should not keep C<ev_run> from
611	no event watchers registered by it are active. It is also an excellent	907	exiting if no event watchers registered by it are active. It is also an
612	way to do this for generic recurring timers or from within third-party	908	excellent way to do this for generic recurring timers or from within
613	libraries. Just remember to I<unref after start> and I<ref before stop>	909	third-party libraries. Just remember to I<unref after start> and I<ref
614	(but only if the watcher wasn't active before, or was active before,	910	before stop> (but only if the watcher wasn't active before, or was active
615	respectively).	911	before, respectively. Note also that libev might stop watchers itself
		912	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		913	in the callback).
616		914
617	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	915	Example: Create a signal watcher, but keep it from keeping C<ev_run>
618	running when nothing else is active.	916	running when nothing else is active.
619		917
620	struct ev_signal exitsig;	918	ev_signal exitsig;
621	ev_signal_init (&exitsig, sig_cb, SIGINT);	919	ev_signal_init (&exitsig, sig_cb, SIGINT);
622	ev_signal_start (loop, &exitsig);	920	ev_signal_start (loop, &exitsig);
623	evf_unref (loop);	921	ev_unref (loop);
624		922
625	Example: For some weird reason, unregister the above signal handler again.	923	Example: For some weird reason, unregister the above signal handler again.
626		924
627	ev_ref (loop);	925	ev_ref (loop);
628	ev_signal_stop (loop, &exitsig);	926	ev_signal_stop (loop, &exitsig);
629		927
630	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	928	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
631		929
632	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	930	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
633		931
634	These advanced functions influence the time that libev will spend waiting	932	These advanced functions influence the time that libev will spend waiting
635	for events. Both are by default C<0>, meaning that libev will try to	933	for events. Both time intervals are by default C<0>, meaning that libev
636	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	934	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		935	latency.
637		936
638	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	937	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
639	allows libev to delay invocation of I/O and timer/periodic callbacks to	938	allows libev to delay invocation of I/O and timer/periodic callbacks
640	increase efficiency of loop iterations.	939	to increase efficiency of loop iterations (or to increase power-saving
		940	opportunities).
641		941
642	The background is that sometimes your program runs just fast enough to	942	The idea is that sometimes your program runs just fast enough to handle
643	handle one (or very few) event(s) per loop iteration. While this makes	943	one (or very few) event(s) per loop iteration. While this makes the
644	the program responsive, it also wastes a lot of CPU time to poll for new	944	program responsive, it also wastes a lot of CPU time to poll for new
645	events, especially with backends like C<select ()> which have a high	945	events, especially with backends like C<select ()> which have a high
646	overhead for the actual polling but can deliver many events at once.	946	overhead for the actual polling but can deliver many events at once.
647		947
648	By setting a higher I<io collect interval> you allow libev to spend more	948	By setting a higher I<io collect interval> you allow libev to spend more
649	time collecting I/O events, so you can handle more events per iteration,	949	time collecting I/O events, so you can handle more events per iteration,
650	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	950	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
651	C<ev_timer>) will be not affected. Setting this to a non-null value will	951	C<ev_timer>) will be not affected. Setting this to a non-null value will
652	introduce an additional C<ev_sleep ()> call into most loop iterations.	952	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		953	sleep time ensures that libev will not poll for I/O events more often then
		954	once per this interval, on average.
653		955
654	Likewise, by setting a higher I<timeout collect interval> you allow libev	956	Likewise, by setting a higher I<timeout collect interval> you allow libev
655	to spend more time collecting timeouts, at the expense of increased	957	to spend more time collecting timeouts, at the expense of increased
656	latency (the watcher callback will be called later). C<ev_io> watchers	958	latency/jitter/inexactness (the watcher callback will be called
657	will not be affected. Setting this to a non-null value will not introduce	959	later). C<ev_io> watchers will not be affected. Setting this to a non-null
658	any overhead in libev.	960	value will not introduce any overhead in libev.
659		961
660	Many (busy) programs can usually benefit by setting the io collect	962	Many (busy) programs can usually benefit by setting the I/O collect
661	interval to a value near C<0.1> or so, which is often enough for	963	interval to a value near C<0.1> or so, which is often enough for
662	interactive servers (of course not for games), likewise for timeouts. It	964	interactive servers (of course not for games), likewise for timeouts. It
663	usually doesn't make much sense to set it to a lower value than C<0.01>,	965	usually doesn't make much sense to set it to a lower value than C<0.01>,
664	as this approsaches the timing granularity of most systems.	966	as this approaches the timing granularity of most systems. Note that if
		967	you do transactions with the outside world and you can't increase the
		968	parallelity, then this setting will limit your transaction rate (if you
		969	need to poll once per transaction and the I/O collect interval is 0.01,
		970	then you can't do more than 100 transactions per second).
		971
		972	Setting the I<timeout collect interval> can improve the opportunity for
		973	saving power, as the program will "bundle" timer callback invocations that
		974	are "near" in time together, by delaying some, thus reducing the number of
		975	times the process sleeps and wakes up again. Another useful technique to
		976	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		977	they fire on, say, one-second boundaries only.
		978
		979	Example: we only need 0.1s timeout granularity, and we wish not to poll
		980	more often than 100 times per second:
		981
		982	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		983	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		984
		985	=item ev_invoke_pending (loop)
		986
		987	This call will simply invoke all pending watchers while resetting their
		988	pending state. Normally, C<ev_run> does this automatically when required,
		989	but when overriding the invoke callback this call comes handy. This
		990	function can be invoked from a watcher - this can be useful for example
		991	when you want to do some lengthy calculation and want to pass further
		992	event handling to another thread (you still have to make sure only one
		993	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		994
		995	=item int ev_pending_count (loop)
		996
		997	Returns the number of pending watchers - zero indicates that no watchers
		998	are pending.
		999
		1000	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1001
		1002	This overrides the invoke pending functionality of the loop: Instead of
		1003	invoking all pending watchers when there are any, C<ev_run> will call
		1004	this callback instead. This is useful, for example, when you want to
		1005	invoke the actual watchers inside another context (another thread etc.).
		1006
		1007	If you want to reset the callback, use C<ev_invoke_pending> as new
		1008	callback.
		1009
		1010	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1011
		1012	Sometimes you want to share the same loop between multiple threads. This
		1013	can be done relatively simply by putting mutex_lock/unlock calls around
		1014	each call to a libev function.
		1015
		1016	However, C<ev_run> can run an indefinite time, so it is not feasible
		1017	to wait for it to return. One way around this is to wake up the event
		1018	loop via C<ev_break> and C<av_async_send>, another way is to set these
		1019	I<release> and I<acquire> callbacks on the loop.
		1020
		1021	When set, then C<release> will be called just before the thread is
		1022	suspended waiting for new events, and C<acquire> is called just
		1023	afterwards.
		1024
		1025	Ideally, C<release> will just call your mutex_unlock function, and
		1026	C<acquire> will just call the mutex_lock function again.
		1027
		1028	While event loop modifications are allowed between invocations of
		1029	C<release> and C<acquire> (that's their only purpose after all), no
		1030	modifications done will affect the event loop, i.e. adding watchers will
		1031	have no effect on the set of file descriptors being watched, or the time
		1032	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1033	to take note of any changes you made.
		1034
		1035	In theory, threads executing C<ev_run> will be async-cancel safe between
		1036	invocations of C<release> and C<acquire>.
		1037
		1038	See also the locking example in the C<THREADS> section later in this
		1039	document.
		1040
		1041	=item ev_set_userdata (loop, void *data)
		1042
		1043	=item void *ev_userdata (loop)
		1044
		1045	Set and retrieve a single C<void *> associated with a loop. When
		1046	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1047	C<0>.
		1048
		1049	These two functions can be used to associate arbitrary data with a loop,
		1050	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1051	C<acquire> callbacks described above, but of course can be (ab-)used for
		1052	any other purpose as well.
		1053
		1054	=item ev_verify (loop)
		1055
		1056	This function only does something when C<EV_VERIFY> support has been
		1057	compiled in, which is the default for non-minimal builds. It tries to go
		1058	through all internal structures and checks them for validity. If anything
		1059	is found to be inconsistent, it will print an error message to standard
		1060	error and call C<abort ()>.
		1061
		1062	This can be used to catch bugs inside libev itself: under normal
		1063	circumstances, this function will never abort as of course libev keeps its
		1064	data structures consistent.
665		1065
666	=back	1066	=back
667		1067
668		1068
669	=head1 ANATOMY OF A WATCHER	1069	=head1 ANATOMY OF A WATCHER
670		1070
		1071	In the following description, uppercase C<TYPE> in names stands for the
		1072	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1073	watchers and C<ev_io_start> for I/O watchers.
		1074
671	A watcher is a structure that you create and register to record your	1075	A watcher is an opaque structure that you allocate and register to record
672	interest in some event. For instance, if you want to wait for STDIN to	1076	your interest in some event. To make a concrete example, imagine you want
673	become readable, you would create an C<ev_io> watcher for that:	1077	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1078	for that:
674		1079
675	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1080	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
676	{	1081	{
677	ev_io_stop (w);	1082	ev_io_stop (w);
678	ev_unloop (loop, EVUNLOOP_ALL);	1083	ev_break (loop, EVBREAK_ALL);
679	}	1084	}
680		1085
681	struct ev_loop *loop = ev_default_loop (0);	1086	struct ev_loop *loop = ev_default_loop (0);
		1087
682	struct ev_io stdin_watcher;	1088	ev_io stdin_watcher;
		1089
683	ev_init (&stdin_watcher, my_cb);	1090	ev_init (&stdin_watcher, my_cb);
684	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1091	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
685	ev_io_start (loop, &stdin_watcher);	1092	ev_io_start (loop, &stdin_watcher);
		1093
686	ev_loop (loop, 0);	1094	ev_run (loop, 0);
687		1095
688	As you can see, you are responsible for allocating the memory for your	1096	As you can see, you are responsible for allocating the memory for your
689	watcher structures (and it is usually a bad idea to do this on the stack,	1097	watcher structures (and it is I<usually> a bad idea to do this on the
690	although this can sometimes be quite valid).	1098	stack).
691		1099
		1100	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1101	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1102
692	Each watcher structure must be initialised by a call to C<ev_init	1103	Each watcher structure must be initialised by a call to C<ev_init (watcher
693	(watcher *, callback)>, which expects a callback to be provided. This	1104	*, callback)>, which expects a callback to be provided. This callback is
694	callback gets invoked each time the event occurs (or, in the case of io	1105	invoked each time the event occurs (or, in the case of I/O watchers, each
695	watchers, each time the event loop detects that the file descriptor given	1106	time the event loop detects that the file descriptor given is readable
696	is readable and/or writable).	1107	and/or writable).
697		1108
698	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1109	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
699	with arguments specific to this watcher type. There is also a macro	1110	macro to configure it, with arguments specific to the watcher type. There
700	to combine initialisation and setting in one call: C<< ev_<type>_init	1111	is also a macro to combine initialisation and setting in one call: C<<
701	(watcher *, callback, ...) >>.	1112	ev_TYPE_init (watcher *, callback, ...) >>.
702		1113
703	To make the watcher actually watch out for events, you have to start it	1114	To make the watcher actually watch out for events, you have to start it
704	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1115	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
705	*) >>), and you can stop watching for events at any time by calling the	1116	*) >>), and you can stop watching for events at any time by calling the
706	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1117	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
707		1118
708	As long as your watcher is active (has been started but not stopped) you	1119	As long as your watcher is active (has been started but not stopped) you
709	must not touch the values stored in it. Most specifically you must never	1120	must not touch the values stored in it. Most specifically you must never
710	reinitialise it or call its C<set> macro.	1121	reinitialise it or call its C<ev_TYPE_set> macro.
711		1122
712	Each and every callback receives the event loop pointer as first, the	1123	Each and every callback receives the event loop pointer as first, the
713	registered watcher structure as second, and a bitset of received events as	1124	registered watcher structure as second, and a bitset of received events as
714	third argument.	1125	third argument.
715		1126
…		…
724	=item C<EV_WRITE>	1135	=item C<EV_WRITE>
725		1136
726	The file descriptor in the C<ev_io> watcher has become readable and/or	1137	The file descriptor in the C<ev_io> watcher has become readable and/or
727	writable.	1138	writable.
728		1139
729	=item C<EV_TIMEOUT>	1140	=item C<EV_TIMER>
730		1141
731	The C<ev_timer> watcher has timed out.	1142	The C<ev_timer> watcher has timed out.
732		1143
733	=item C<EV_PERIODIC>	1144	=item C<EV_PERIODIC>
734		1145
…		…
752		1163
753	=item C<EV_PREPARE>	1164	=item C<EV_PREPARE>
754		1165
755	=item C<EV_CHECK>	1166	=item C<EV_CHECK>
756		1167
757	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1168	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
758	to gather new events, and all C<ev_check> watchers are invoked just after	1169	to gather new events, and all C<ev_check> watchers are invoked just after
759	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1170	C<ev_run> has gathered them, but before it invokes any callbacks for any
760	received events. Callbacks of both watcher types can start and stop as	1171	received events. Callbacks of both watcher types can start and stop as
761	many watchers as they want, and all of them will be taken into account	1172	many watchers as they want, and all of them will be taken into account
762	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1173	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
763	C<ev_loop> from blocking).	1174	C<ev_run> from blocking).
764		1175
765	=item C<EV_EMBED>	1176	=item C<EV_EMBED>
766		1177
767	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1178	The embedded event loop specified in the C<ev_embed> watcher needs attention.
768		1179
769	=item C<EV_FORK>	1180	=item C<EV_FORK>
770		1181
771	The event loop has been resumed in the child process after fork (see	1182	The event loop has been resumed in the child process after fork (see
772	C<ev_fork>).	1183	C<ev_fork>).
773		1184
		1185	=item C<EV_CLEANUP>
		1186
		1187	The event loop is about to be destroyed (see C<ev_cleanup>).
		1188
		1189	=item C<EV_ASYNC>
		1190
		1191	The given async watcher has been asynchronously notified (see C<ev_async>).
		1192
		1193	=item C<EV_CUSTOM>
		1194
		1195	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1196	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1197
774	=item C<EV_ERROR>	1198	=item C<EV_ERROR>
775		1199
776	An unspecified error has occured, the watcher has been stopped. This might	1200	An unspecified error has occurred, the watcher has been stopped. This might
777	happen because the watcher could not be properly started because libev	1201	happen because the watcher could not be properly started because libev
778	ran out of memory, a file descriptor was found to be closed or any other	1202	ran out of memory, a file descriptor was found to be closed or any other
		1203	problem. Libev considers these application bugs.
		1204
779	problem. You best act on it by reporting the problem and somehow coping	1205	You best act on it by reporting the problem and somehow coping with the
780	with the watcher being stopped.	1206	watcher being stopped. Note that well-written programs should not receive
		1207	an error ever, so when your watcher receives it, this usually indicates a
		1208	bug in your program.
781		1209
782	Libev will usually signal a few "dummy" events together with an error,	1210	Libev will usually signal a few "dummy" events together with an error, for
783	for example it might indicate that a fd is readable or writable, and if	1211	example it might indicate that a fd is readable or writable, and if your
784	your callbacks is well-written it can just attempt the operation and cope	1212	callbacks is well-written it can just attempt the operation and cope with
785	with the error from read() or write(). This will not work in multithreaded	1213	the error from read() or write(). This will not work in multi-threaded
786	programs, though, so beware.	1214	programs, though, as the fd could already be closed and reused for another
		1215	thing, so beware.
787		1216
788	=back	1217	=back
789		1218
790	=head2 GENERIC WATCHER FUNCTIONS	1219	=head2 GENERIC WATCHER FUNCTIONS
791
792	In the following description, C<TYPE> stands for the watcher type,
793	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
794		1220
795	=over 4	1221	=over 4
796		1222
797	=item C<ev_init> (ev_TYPE *watcher, callback)	1223	=item C<ev_init> (ev_TYPE *watcher, callback)
798		1224
…		…
804	which rolls both calls into one.	1230	which rolls both calls into one.
805		1231
806	You can reinitialise a watcher at any time as long as it has been stopped	1232	You can reinitialise a watcher at any time as long as it has been stopped
807	(or never started) and there are no pending events outstanding.	1233	(or never started) and there are no pending events outstanding.
808		1234
809	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1235	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
810	int revents)>.	1236	int revents)>.
811		1237
		1238	Example: Initialise an C<ev_io> watcher in two steps.
		1239
		1240	ev_io w;
		1241	ev_init (&w, my_cb);
		1242	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1243
812	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1244	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
813		1245
814	This macro initialises the type-specific parts of a watcher. You need to	1246	This macro initialises the type-specific parts of a watcher. You need to
815	call C<ev_init> at least once before you call this macro, but you can	1247	call C<ev_init> at least once before you call this macro, but you can
816	call C<ev_TYPE_set> any number of times. You must not, however, call this	1248	call C<ev_TYPE_set> any number of times. You must not, however, call this
817	macro on a watcher that is active (it can be pending, however, which is a	1249	macro on a watcher that is active (it can be pending, however, which is a
818	difference to the C<ev_init> macro).	1250	difference to the C<ev_init> macro).
819		1251
820	Although some watcher types do not have type-specific arguments	1252	Although some watcher types do not have type-specific arguments
821	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1253	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
822		1254
		1255	See C<ev_init>, above, for an example.
		1256
823	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1257	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
824		1258
825	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1259	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
826	calls into a single call. This is the most convinient method to initialise	1260	calls into a single call. This is the most convenient method to initialise
827	a watcher. The same limitations apply, of course.	1261	a watcher. The same limitations apply, of course.
828		1262
		1263	Example: Initialise and set an C<ev_io> watcher in one step.
		1264
		1265	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1266
829	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1267	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
830		1268
831	Starts (activates) the given watcher. Only active watchers will receive	1269	Starts (activates) the given watcher. Only active watchers will receive
832	events. If the watcher is already active nothing will happen.	1270	events. If the watcher is already active nothing will happen.
833		1271
		1272	Example: Start the C<ev_io> watcher that is being abused as example in this
		1273	whole section.
		1274
		1275	ev_io_start (EV_DEFAULT_UC, &w);
		1276
834	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1277	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
835		1278
836	Stops the given watcher again (if active) and clears the pending	1279	Stops the given watcher if active, and clears the pending status (whether
		1280	the watcher was active or not).
		1281
837	status. It is possible that stopped watchers are pending (for example,	1282	It is possible that stopped watchers are pending - for example,
838	non-repeating timers are being stopped when they become pending), but	1283	non-repeating timers are being stopped when they become pending - but
839	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1284	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
840	you want to free or reuse the memory used by the watcher it is therefore a	1285	pending. If you want to free or reuse the memory used by the watcher it is
841	good idea to always call its C<ev_TYPE_stop> function.	1286	therefore a good idea to always call its C<ev_TYPE_stop> function.
842		1287
843	=item bool ev_is_active (ev_TYPE *watcher)	1288	=item bool ev_is_active (ev_TYPE *watcher)
844		1289
845	Returns a true value iff the watcher is active (i.e. it has been started	1290	Returns a true value iff the watcher is active (i.e. it has been started
846	and not yet been stopped). As long as a watcher is active you must not modify	1291	and not yet been stopped). As long as a watcher is active you must not modify
…		…
862	=item ev_cb_set (ev_TYPE *watcher, callback)	1307	=item ev_cb_set (ev_TYPE *watcher, callback)
863		1308
864	Change the callback. You can change the callback at virtually any time	1309	Change the callback. You can change the callback at virtually any time
865	(modulo threads).	1310	(modulo threads).
866		1311
867	=item ev_set_priority (ev_TYPE *watcher, priority)	1312	=item ev_set_priority (ev_TYPE *watcher, int priority)
868		1313
869	=item int ev_priority (ev_TYPE *watcher)	1314	=item int ev_priority (ev_TYPE *watcher)
870		1315
871	Set and query the priority of the watcher. The priority is a small	1316	Set and query the priority of the watcher. The priority is a small
872	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1317	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
873	(default: C<-2>). Pending watchers with higher priority will be invoked	1318	(default: C<-2>). Pending watchers with higher priority will be invoked
874	before watchers with lower priority, but priority will not keep watchers	1319	before watchers with lower priority, but priority will not keep watchers
875	from being executed (except for C<ev_idle> watchers).	1320	from being executed (except for C<ev_idle> watchers).
876		1321
877	This means that priorities are I<only> used for ordering callback
878	invocation after new events have been received. This is useful, for
879	example, to reduce latency after idling, or more often, to bind two
880	watchers on the same event and make sure one is called first.
881
882	If you need to suppress invocation when higher priority events are pending	1322	If you need to suppress invocation when higher priority events are pending
883	you need to look at C<ev_idle> watchers, which provide this functionality.	1323	you need to look at C<ev_idle> watchers, which provide this functionality.
884		1324
885	You I<must not> change the priority of a watcher as long as it is active or	1325	You I<must not> change the priority of a watcher as long as it is active or
886	pending.	1326	pending.
887		1327
		1328	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1329	fine, as long as you do not mind that the priority value you query might
		1330	or might not have been clamped to the valid range.
		1331
888	The default priority used by watchers when no priority has been set is	1332	The default priority used by watchers when no priority has been set is
889	always C<0>, which is supposed to not be too high and not be too low :).	1333	always C<0>, which is supposed to not be too high and not be too low :).
890		1334
891	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1335	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
892	fine, as long as you do not mind that the priority value you query might	1336	priorities.
893	or might not have been adjusted to be within valid range.
894		1337
895	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1338	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
896		1339
897	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1340	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
898	C<loop> nor C<revents> need to be valid as long as the watcher callback	1341	C<loop> nor C<revents> need to be valid as long as the watcher callback
899	can deal with that fact.	1342	can deal with that fact, as both are simply passed through to the
		1343	callback.
900		1344
901	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1345	=item int ev_clear_pending (loop, ev_TYPE *watcher)
902		1346
903	If the watcher is pending, this function returns clears its pending status	1347	If the watcher is pending, this function clears its pending status and
904	and returns its C<revents> bitset (as if its callback was invoked). If the	1348	returns its C<revents> bitset (as if its callback was invoked). If the
905	watcher isn't pending it does nothing and returns C<0>.	1349	watcher isn't pending it does nothing and returns C<0>.
906		1350
		1351	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1352	callback to be invoked, which can be accomplished with this function.
		1353
		1354	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1355
		1356	Feeds the given event set into the event loop, as if the specified event
		1357	had happened for the specified watcher (which must be a pointer to an
		1358	initialised but not necessarily started event watcher). Obviously you must
		1359	not free the watcher as long as it has pending events.
		1360
		1361	Stopping the watcher, letting libev invoke it, or calling
		1362	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1363	not started in the first place.
		1364
		1365	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1366	functions that do not need a watcher.
		1367
907	=back	1368	=back
908		1369
		1370	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1371	OWN COMPOSITE WATCHERS> idioms.
909		1372
910	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1373	=head2 WATCHER STATES
911		1374
912	Each watcher has, by default, a member C<void *data> that you can change	1375	There are various watcher states mentioned throughout this manual -
913	and read at any time, libev will completely ignore it. This can be used	1376	active, pending and so on. In this section these states and the rules to
914	to associate arbitrary data with your watcher. If you need more data and	1377	transition between them will be described in more detail - and while these
915	don't want to allocate memory and store a pointer to it in that data	1378	rules might look complicated, they usually do "the right thing".
916	member, you can also "subclass" the watcher type and provide your own
917	data:
918		1379
919	struct my_io	1380	=over 4
920	{
921	struct ev_io io;
922	int otherfd;
923	void *somedata;
924	struct whatever *mostinteresting;
925	}
926		1381
927	And since your callback will be called with a pointer to the watcher, you	1382	=item initialiased
928	can cast it back to your own type:
929		1383
930	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1384	Before a watcher can be registered with the event looop it has to be
931	{	1385	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
932	struct my_io *w = (struct my_io *)w_;	1386	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
933	...
934	}
935		1387
936	More interesting and less C-conformant ways of casting your callback type	1388	In this state it is simply some block of memory that is suitable for
937	instead have been omitted.	1389	use in an event loop. It can be moved around, freed, reused etc. at
		1390	will - as long as you either keep the memory contents intact, or call
		1391	C<ev_TYPE_init> again.
938		1392
939	Another common scenario is having some data structure with multiple	1393	=item started/running/active
940	watchers:
941		1394
942	struct my_biggy	1395	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
943	{	1396	property of the event loop, and is actively waiting for events. While in
944	int some_data;	1397	this state it cannot be accessed (except in a few documented ways), moved,
945	ev_timer t1;	1398	freed or anything else - the only legal thing is to keep a pointer to it,
946	ev_timer t2;	1399	and call libev functions on it that are documented to work on active watchers.
947	}
948		1400
949	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1401	=item pending
950	you need to use C<offsetof>:
951		1402
952	#include <stddef.h>	1403	If a watcher is active and libev determines that an event it is interested
		1404	in has occurred (such as a timer expiring), it will become pending. It will
		1405	stay in this pending state until either it is stopped or its callback is
		1406	about to be invoked, so it is not normally pending inside the watcher
		1407	callback.
953		1408
		1409	The watcher might or might not be active while it is pending (for example,
		1410	an expired non-repeating timer can be pending but no longer active). If it
		1411	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1412	but it is still property of the event loop at this time, so cannot be
		1413	moved, freed or reused. And if it is active the rules described in the
		1414	previous item still apply.
		1415
		1416	It is also possible to feed an event on a watcher that is not active (e.g.
		1417	via C<ev_feed_event>), in which case it becomes pending without being
		1418	active.
		1419
		1420	=item stopped
		1421
		1422	A watcher can be stopped implicitly by libev (in which case it might still
		1423	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1424	latter will clear any pending state the watcher might be in, regardless
		1425	of whether it was active or not, so stopping a watcher explicitly before
		1426	freeing it is often a good idea.
		1427
		1428	While stopped (and not pending) the watcher is essentially in the
		1429	initialised state, that is, it can be reused, moved, modified in any way
		1430	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1431	it again).
		1432
		1433	=back
		1434
		1435	=head2 WATCHER PRIORITY MODELS
		1436
		1437	Many event loops support I<watcher priorities>, which are usually small
		1438	integers that influence the ordering of event callback invocation
		1439	between watchers in some way, all else being equal.
		1440
		1441	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1442	description for the more technical details such as the actual priority
		1443	range.
		1444
		1445	There are two common ways how these these priorities are being interpreted
		1446	by event loops:
		1447
		1448	In the more common lock-out model, higher priorities "lock out" invocation
		1449	of lower priority watchers, which means as long as higher priority
		1450	watchers receive events, lower priority watchers are not being invoked.
		1451
		1452	The less common only-for-ordering model uses priorities solely to order
		1453	callback invocation within a single event loop iteration: Higher priority
		1454	watchers are invoked before lower priority ones, but they all get invoked
		1455	before polling for new events.
		1456
		1457	Libev uses the second (only-for-ordering) model for all its watchers
		1458	except for idle watchers (which use the lock-out model).
		1459
		1460	The rationale behind this is that implementing the lock-out model for
		1461	watchers is not well supported by most kernel interfaces, and most event
		1462	libraries will just poll for the same events again and again as long as
		1463	their callbacks have not been executed, which is very inefficient in the
		1464	common case of one high-priority watcher locking out a mass of lower
		1465	priority ones.
		1466
		1467	Static (ordering) priorities are most useful when you have two or more
		1468	watchers handling the same resource: a typical usage example is having an
		1469	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1470	timeouts. Under load, data might be received while the program handles
		1471	other jobs, but since timers normally get invoked first, the timeout
		1472	handler will be executed before checking for data. In that case, giving
		1473	the timer a lower priority than the I/O watcher ensures that I/O will be
		1474	handled first even under adverse conditions (which is usually, but not
		1475	always, what you want).
		1476
		1477	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1478	will only be executed when no same or higher priority watchers have
		1479	received events, they can be used to implement the "lock-out" model when
		1480	required.
		1481
		1482	For example, to emulate how many other event libraries handle priorities,
		1483	you can associate an C<ev_idle> watcher to each such watcher, and in
		1484	the normal watcher callback, you just start the idle watcher. The real
		1485	processing is done in the idle watcher callback. This causes libev to
		1486	continuously poll and process kernel event data for the watcher, but when
		1487	the lock-out case is known to be rare (which in turn is rare :), this is
		1488	workable.
		1489
		1490	Usually, however, the lock-out model implemented that way will perform
		1491	miserably under the type of load it was designed to handle. In that case,
		1492	it might be preferable to stop the real watcher before starting the
		1493	idle watcher, so the kernel will not have to process the event in case
		1494	the actual processing will be delayed for considerable time.
		1495
		1496	Here is an example of an I/O watcher that should run at a strictly lower
		1497	priority than the default, and which should only process data when no
		1498	other events are pending:
		1499
		1500	ev_idle idle; // actual processing watcher
		1501	ev_io io; // actual event watcher
		1502
954	static void	1503	static void
955	t1_cb (EV_P_ struct ev_timer *w, int revents)	1504	io_cb (EV_P_ ev_io *w, int revents)
956	{	1505	{
957	struct my_biggy big = (struct my_biggy *	1506	// stop the I/O watcher, we received the event, but
958	(((char *)w) - offsetof (struct my_biggy, t1));	1507	// are not yet ready to handle it.
		1508	ev_io_stop (EV_A_ w);
		1509
		1510	// start the idle watcher to handle the actual event.
		1511	// it will not be executed as long as other watchers
		1512	// with the default priority are receiving events.
		1513	ev_idle_start (EV_A_ &idle);
959	}	1514	}
960		1515
961	static void	1516	static void
962	t2_cb (EV_P_ struct ev_timer *w, int revents)	1517	idle_cb (EV_P_ ev_idle *w, int revents)
963	{	1518	{
964	struct my_biggy big = (struct my_biggy *	1519	// actual processing
965	(((char *)w) - offsetof (struct my_biggy, t2));	1520	read (STDIN_FILENO, ...);
		1521
		1522	// have to start the I/O watcher again, as
		1523	// we have handled the event
		1524	ev_io_start (EV_P_ &io);
966	}	1525	}
		1526
		1527	// initialisation
		1528	ev_idle_init (&idle, idle_cb);
		1529	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1530	ev_io_start (EV_DEFAULT_ &io);
		1531
		1532	In the "real" world, it might also be beneficial to start a timer, so that
		1533	low-priority connections can not be locked out forever under load. This
		1534	enables your program to keep a lower latency for important connections
		1535	during short periods of high load, while not completely locking out less
		1536	important ones.
967		1537
968		1538
969	=head1 WATCHER TYPES	1539	=head1 WATCHER TYPES
970		1540
971	This section describes each watcher in detail, but will not repeat	1541	This section describes each watcher in detail, but will not repeat
…		…
995	In general you can register as many read and/or write event watchers per	1565	In general you can register as many read and/or write event watchers per
996	fd as you want (as long as you don't confuse yourself). Setting all file	1566	fd as you want (as long as you don't confuse yourself). Setting all file
997	descriptors to non-blocking mode is also usually a good idea (but not	1567	descriptors to non-blocking mode is also usually a good idea (but not
998	required if you know what you are doing).	1568	required if you know what you are doing).
999		1569
1000	If you must do this, then force the use of a known-to-be-good backend
1001	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1002	C<EVBACKEND_POLL>).
1003
1004	Another thing you have to watch out for is that it is quite easy to	1570	Another thing you have to watch out for is that it is quite easy to
1005	receive "spurious" readyness notifications, that is your callback might	1571	receive "spurious" readiness notifications, that is, your callback might
1006	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1572	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1007	because there is no data. Not only are some backends known to create a	1573	because there is no data. It is very easy to get into this situation even
1008	lot of those (for example solaris ports), it is very easy to get into	1574	with a relatively standard program structure. Thus it is best to always
1009	this situation even with a relatively standard program structure. Thus	1575	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1010	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1011	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1576	preferable to a program hanging until some data arrives.
1012		1577
1013	If you cannot run the fd in non-blocking mode (for example you should not	1578	If you cannot run the fd in non-blocking mode (for example you should
1014	play around with an Xlib connection), then you have to seperately re-test	1579	not play around with an Xlib connection), then you have to separately
1015	whether a file descriptor is really ready with a known-to-be good interface	1580	re-test whether a file descriptor is really ready with a known-to-be good
1016	such as poll (fortunately in our Xlib example, Xlib already does this on	1581	interface such as poll (fortunately in the case of Xlib, it already does
1017	its own, so its quite safe to use).	1582	this on its own, so its quite safe to use). Some people additionally
		1583	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1584	indefinitely.
		1585
		1586	But really, best use non-blocking mode.
1018		1587
1019	=head3 The special problem of disappearing file descriptors	1588	=head3 The special problem of disappearing file descriptors
1020		1589
1021	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1590	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1022	descriptor (either by calling C<close> explicitly or by any other means,	1591	descriptor (either due to calling C<close> explicitly or any other means,
1023	such as C<dup>). The reason is that you register interest in some file	1592	such as C<dup2>). The reason is that you register interest in some file
1024	descriptor, but when it goes away, the operating system will silently drop	1593	descriptor, but when it goes away, the operating system will silently drop
1025	this interest. If another file descriptor with the same number then is	1594	this interest. If another file descriptor with the same number then is
1026	registered with libev, there is no efficient way to see that this is, in	1595	registered with libev, there is no efficient way to see that this is, in
1027	fact, a different file descriptor.	1596	fact, a different file descriptor.
1028		1597
…		…
1046		1615
1047	There is no workaround possible except not registering events	1616	There is no workaround possible except not registering events
1048	for potentially C<dup ()>'ed file descriptors, or to resort to	1617	for potentially C<dup ()>'ed file descriptors, or to resort to
1049	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1618	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1050		1619
		1620	=head3 The special problem of files
		1621
		1622	Many people try to use C<select> (or libev) on file descriptors
		1623	representing files, and expect it to become ready when their program
		1624	doesn't block on disk accesses (which can take a long time on their own).
		1625
		1626	However, this cannot ever work in the "expected" way - you get a readiness
		1627	notification as soon as the kernel knows whether and how much data is
		1628	there, and in the case of open files, that's always the case, so you
		1629	always get a readiness notification instantly, and your read (or possibly
		1630	write) will still block on the disk I/O.
		1631
		1632	Another way to view it is that in the case of sockets, pipes, character
		1633	devices and so on, there is another party (the sender) that delivers data
		1634	on its own, but in the case of files, there is no such thing: the disk
		1635	will not send data on its own, simply because it doesn't know what you
		1636	wish to read - you would first have to request some data.
		1637
		1638	Since files are typically not-so-well supported by advanced notification
		1639	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1640	to files, even though you should not use it. The reason for this is
		1641	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1642	usually a tty, often a pipe, but also sometimes files or special devices
		1643	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1644	F</dev/urandom>), and even though the file might better be served with
		1645	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1646	it "just works" instead of freezing.
		1647
		1648	So avoid file descriptors pointing to files when you know it (e.g. use
		1649	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1650	when you rarely read from a file instead of from a socket, and want to
		1651	reuse the same code path.
		1652
1051	=head3 The special problem of fork	1653	=head3 The special problem of fork
1052		1654
1053	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1655	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1054	useless behaviour. Libev fully supports fork, but needs to be told about	1656	useless behaviour. Libev fully supports fork, but needs to be told about
1055	it in the child.	1657	it in the child if you want to continue to use it in the child.
1056		1658
1057	To support fork in your programs, you either have to call	1659	To support fork in your child processes, you have to call C<ev_loop_fork
1058	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1660	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1059	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1661	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1060	C<EVBACKEND_POLL>.
1061		1662
		1663	=head3 The special problem of SIGPIPE
		1664
		1665	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1666	when writing to a pipe whose other end has been closed, your program gets
		1667	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1668	this is sensible behaviour, for daemons, this is usually undesirable.
		1669
		1670	So when you encounter spurious, unexplained daemon exits, make sure you
		1671	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1672	somewhere, as that would have given you a big clue).
		1673
		1674	=head3 The special problem of accept()ing when you can't
		1675
		1676	Many implementations of the POSIX C<accept> function (for example,
		1677	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1678	connection from the pending queue in all error cases.
		1679
		1680	For example, larger servers often run out of file descriptors (because
		1681	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1682	rejecting the connection, leading to libev signalling readiness on
		1683	the next iteration again (the connection still exists after all), and
		1684	typically causing the program to loop at 100% CPU usage.
		1685
		1686	Unfortunately, the set of errors that cause this issue differs between
		1687	operating systems, there is usually little the app can do to remedy the
		1688	situation, and no known thread-safe method of removing the connection to
		1689	cope with overload is known (to me).
		1690
		1691	One of the easiest ways to handle this situation is to just ignore it
		1692	- when the program encounters an overload, it will just loop until the
		1693	situation is over. While this is a form of busy waiting, no OS offers an
		1694	event-based way to handle this situation, so it's the best one can do.
		1695
		1696	A better way to handle the situation is to log any errors other than
		1697	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1698	messages, and continue as usual, which at least gives the user an idea of
		1699	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1700	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1701	usage.
		1702
		1703	If your program is single-threaded, then you could also keep a dummy file
		1704	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1705	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1706	close that fd, and create a new dummy fd. This will gracefully refuse
		1707	clients under typical overload conditions.
		1708
		1709	The last way to handle it is to simply log the error and C<exit>, as
		1710	is often done with C<malloc> failures, but this results in an easy
		1711	opportunity for a DoS attack.
1062		1712
1063	=head3 Watcher-Specific Functions	1713	=head3 Watcher-Specific Functions
1064		1714
1065	=over 4	1715	=over 4
1066		1716
1067	=item ev_io_init (ev_io *, callback, int fd, int events)	1717	=item ev_io_init (ev_io *, callback, int fd, int events)
1068		1718
1069	=item ev_io_set (ev_io *, int fd, int events)	1719	=item ev_io_set (ev_io *, int fd, int events)
1070		1720
1071	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1721	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1072	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1722	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1073	C<EV_READ | EV_WRITE> to receive the given events.	1723	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1074		1724
1075	=item int fd [read-only]	1725	=item int fd [read-only]
1076		1726
1077	The file descriptor being watched.	1727	The file descriptor being watched.
1078		1728
…		…
1086		1736
1087	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1737	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1088	readable, but only once. Since it is likely line-buffered, you could	1738	readable, but only once. Since it is likely line-buffered, you could
1089	attempt to read a whole line in the callback.	1739	attempt to read a whole line in the callback.
1090		1740
1091	static void	1741	static void
1092	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1742	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1093	{	1743	{
1094	ev_io_stop (loop, w);	1744	ev_io_stop (loop, w);
1095	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1745	.. read from stdin here (or from w->fd) and handle any I/O errors
1096	}	1746	}
1097		1747
1098	...	1748	...
1099	struct ev_loop *loop = ev_default_init (0);	1749	struct ev_loop *loop = ev_default_init (0);
1100	struct ev_io stdin_readable;	1750	ev_io stdin_readable;
1101	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1751	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1102	ev_io_start (loop, &stdin_readable);	1752	ev_io_start (loop, &stdin_readable);
1103	ev_loop (loop, 0);	1753	ev_run (loop, 0);
1104		1754
1105		1755
1106	=head2 C<ev_timer> - relative and optionally repeating timeouts	1756	=head2 C<ev_timer> - relative and optionally repeating timeouts
1107		1757
1108	Timer watchers are simple relative timers that generate an event after a	1758	Timer watchers are simple relative timers that generate an event after a
1109	given time, and optionally repeating in regular intervals after that.	1759	given time, and optionally repeating in regular intervals after that.
1110		1760
1111	The timers are based on real time, that is, if you register an event that	1761	The timers are based on real time, that is, if you register an event that
1112	times out after an hour and you reset your system clock to last years	1762	times out after an hour and you reset your system clock to January last
1113	time, it will still time out after (roughly) and hour. "Roughly" because	1763	year, it will still time out after (roughly) one hour. "Roughly" because
1114	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1764	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1115	monotonic clock option helps a lot here).	1765	monotonic clock option helps a lot here).
		1766
		1767	The callback is guaranteed to be invoked only I<after> its timeout has
		1768	passed (not I<at>, so on systems with very low-resolution clocks this
		1769	might introduce a small delay). If multiple timers become ready during the
		1770	same loop iteration then the ones with earlier time-out values are invoked
		1771	before ones of the same priority with later time-out values (but this is
		1772	no longer true when a callback calls C<ev_run> recursively).
		1773
		1774	=head3 Be smart about timeouts
		1775
		1776	Many real-world problems involve some kind of timeout, usually for error
		1777	recovery. A typical example is an HTTP request - if the other side hangs,
		1778	you want to raise some error after a while.
		1779
		1780	What follows are some ways to handle this problem, from obvious and
		1781	inefficient to smart and efficient.
		1782
		1783	In the following, a 60 second activity timeout is assumed - a timeout that
		1784	gets reset to 60 seconds each time there is activity (e.g. each time some
		1785	data or other life sign was received).
		1786
		1787	=over 4
		1788
		1789	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1790
		1791	This is the most obvious, but not the most simple way: In the beginning,
		1792	start the watcher:
		1793
		1794	ev_timer_init (timer, callback, 60., 0.);
		1795	ev_timer_start (loop, timer);
		1796
		1797	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1798	and start it again:
		1799
		1800	ev_timer_stop (loop, timer);
		1801	ev_timer_set (timer, 60., 0.);
		1802	ev_timer_start (loop, timer);
		1803
		1804	This is relatively simple to implement, but means that each time there is
		1805	some activity, libev will first have to remove the timer from its internal
		1806	data structure and then add it again. Libev tries to be fast, but it's
		1807	still not a constant-time operation.
		1808
		1809	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1810
		1811	This is the easiest way, and involves using C<ev_timer_again> instead of
		1812	C<ev_timer_start>.
		1813
		1814	To implement this, configure an C<ev_timer> with a C<repeat> value
		1815	of C<60> and then call C<ev_timer_again> at start and each time you
		1816	successfully read or write some data. If you go into an idle state where
		1817	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1818	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1819
		1820	That means you can ignore both the C<ev_timer_start> function and the
		1821	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1822	member and C<ev_timer_again>.
		1823
		1824	At start:
		1825
		1826	ev_init (timer, callback);
		1827	timer->repeat = 60.;
		1828	ev_timer_again (loop, timer);
		1829
		1830	Each time there is some activity:
		1831
		1832	ev_timer_again (loop, timer);
		1833
		1834	It is even possible to change the time-out on the fly, regardless of
		1835	whether the watcher is active or not:
		1836
		1837	timer->repeat = 30.;
		1838	ev_timer_again (loop, timer);
		1839
		1840	This is slightly more efficient then stopping/starting the timer each time
		1841	you want to modify its timeout value, as libev does not have to completely
		1842	remove and re-insert the timer from/into its internal data structure.
		1843
		1844	It is, however, even simpler than the "obvious" way to do it.
		1845
		1846	=item 3. Let the timer time out, but then re-arm it as required.
		1847
		1848	This method is more tricky, but usually most efficient: Most timeouts are
		1849	relatively long compared to the intervals between other activity - in
		1850	our example, within 60 seconds, there are usually many I/O events with
		1851	associated activity resets.
		1852
		1853	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1854	but remember the time of last activity, and check for a real timeout only
		1855	within the callback:
		1856
		1857	ev_tstamp last_activity; // time of last activity
		1858
		1859	static void
		1860	callback (EV_P_ ev_timer *w, int revents)
		1861	{
		1862	ev_tstamp now = ev_now (EV_A);
		1863	ev_tstamp timeout = last_activity + 60.;
		1864
		1865	// if last_activity + 60. is older than now, we did time out
		1866	if (timeout < now)
		1867	{
		1868	// timeout occurred, take action
		1869	}
		1870	else
		1871	{
		1872	// callback was invoked, but there was some activity, re-arm
		1873	// the watcher to fire in last_activity + 60, which is
		1874	// guaranteed to be in the future, so "again" is positive:
		1875	w->repeat = timeout - now;
		1876	ev_timer_again (EV_A_ w);
		1877	}
		1878	}
		1879
		1880	To summarise the callback: first calculate the real timeout (defined
		1881	as "60 seconds after the last activity"), then check if that time has
		1882	been reached, which means something I<did>, in fact, time out. Otherwise
		1883	the callback was invoked too early (C<timeout> is in the future), so
		1884	re-schedule the timer to fire at that future time, to see if maybe we have
		1885	a timeout then.
		1886
		1887	Note how C<ev_timer_again> is used, taking advantage of the
		1888	C<ev_timer_again> optimisation when the timer is already running.
		1889
		1890	This scheme causes more callback invocations (about one every 60 seconds
		1891	minus half the average time between activity), but virtually no calls to
		1892	libev to change the timeout.
		1893
		1894	To start the timer, simply initialise the watcher and set C<last_activity>
		1895	to the current time (meaning we just have some activity :), then call the
		1896	callback, which will "do the right thing" and start the timer:
		1897
		1898	ev_init (timer, callback);
		1899	last_activity = ev_now (loop);
		1900	callback (loop, timer, EV_TIMER);
		1901
		1902	And when there is some activity, simply store the current time in
		1903	C<last_activity>, no libev calls at all:
		1904
		1905	last_activity = ev_now (loop);
		1906
		1907	This technique is slightly more complex, but in most cases where the
		1908	time-out is unlikely to be triggered, much more efficient.
		1909
		1910	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1911	callback :) - just change the timeout and invoke the callback, which will
		1912	fix things for you.
		1913
		1914	=item 4. Wee, just use a double-linked list for your timeouts.
		1915
		1916	If there is not one request, but many thousands (millions...), all
		1917	employing some kind of timeout with the same timeout value, then one can
		1918	do even better:
		1919
		1920	When starting the timeout, calculate the timeout value and put the timeout
		1921	at the I<end> of the list.
		1922
		1923	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1924	the list is expected to fire (for example, using the technique #3).
		1925
		1926	When there is some activity, remove the timer from the list, recalculate
		1927	the timeout, append it to the end of the list again, and make sure to
		1928	update the C<ev_timer> if it was taken from the beginning of the list.
		1929
		1930	This way, one can manage an unlimited number of timeouts in O(1) time for
		1931	starting, stopping and updating the timers, at the expense of a major
		1932	complication, and having to use a constant timeout. The constant timeout
		1933	ensures that the list stays sorted.
		1934
		1935	=back
		1936
		1937	So which method the best?
		1938
		1939	Method #2 is a simple no-brain-required solution that is adequate in most
		1940	situations. Method #3 requires a bit more thinking, but handles many cases
		1941	better, and isn't very complicated either. In most case, choosing either
		1942	one is fine, with #3 being better in typical situations.
		1943
		1944	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1945	rather complicated, but extremely efficient, something that really pays
		1946	off after the first million or so of active timers, i.e. it's usually
		1947	overkill :)
		1948
		1949	=head3 The special problem of time updates
		1950
		1951	Establishing the current time is a costly operation (it usually takes at
		1952	least two system calls): EV therefore updates its idea of the current
		1953	time only before and after C<ev_run> collects new events, which causes a
		1954	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1955	lots of events in one iteration.
1116		1956
1117	The relative timeouts are calculated relative to the C<ev_now ()>	1957	The relative timeouts are calculated relative to the C<ev_now ()>
1118	time. This is usually the right thing as this timestamp refers to the time	1958	time. This is usually the right thing as this timestamp refers to the time
1119	of the event triggering whatever timeout you are modifying/starting. If	1959	of the event triggering whatever timeout you are modifying/starting. If
1120	you suspect event processing to be delayed and you I<need> to base the timeout	1960	you suspect event processing to be delayed and you I<need> to base the
1121	on the current time, use something like this to adjust for this:	1961	timeout on the current time, use something like this to adjust for this:
1122		1962
1123	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1963	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1124		1964
1125	The callback is guarenteed to be invoked only when its timeout has passed,	1965	If the event loop is suspended for a long time, you can also force an
1126	but if multiple timers become ready during the same loop iteration then	1966	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1127	order of execution is undefined.	1967	()>.
		1968
		1969	=head3 The special problems of suspended animation
		1970
		1971	When you leave the server world it is quite customary to hit machines that
		1972	can suspend/hibernate - what happens to the clocks during such a suspend?
		1973
		1974	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1975	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1976	to run until the system is suspended, but they will not advance while the
		1977	system is suspended. That means, on resume, it will be as if the program
		1978	was frozen for a few seconds, but the suspend time will not be counted
		1979	towards C<ev_timer> when a monotonic clock source is used. The real time
		1980	clock advanced as expected, but if it is used as sole clocksource, then a
		1981	long suspend would be detected as a time jump by libev, and timers would
		1982	be adjusted accordingly.
		1983
		1984	I would not be surprised to see different behaviour in different between
		1985	operating systems, OS versions or even different hardware.
		1986
		1987	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1988	time jump in the monotonic clocks and the realtime clock. If the program
		1989	is suspended for a very long time, and monotonic clock sources are in use,
		1990	then you can expect C<ev_timer>s to expire as the full suspension time
		1991	will be counted towards the timers. When no monotonic clock source is in
		1992	use, then libev will again assume a timejump and adjust accordingly.
		1993
		1994	It might be beneficial for this latter case to call C<ev_suspend>
		1995	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1996	deterministic behaviour in this case (you can do nothing against
		1997	C<SIGSTOP>).
1128		1998
1129	=head3 Watcher-Specific Functions and Data Members	1999	=head3 Watcher-Specific Functions and Data Members
1130		2000
1131	=over 4	2001	=over 4
1132		2002
1133	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2003	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1134		2004
1135	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2005	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1136		2006
1137	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2007	Configure the timer to trigger after C<after> seconds. If C<repeat>
1138	C<0.>, then it will automatically be stopped. If it is positive, then the	2008	is C<0.>, then it will automatically be stopped once the timeout is
1139	timer will automatically be configured to trigger again C<repeat> seconds	2009	reached. If it is positive, then the timer will automatically be
1140	later, again, and again, until stopped manually.	2010	configured to trigger again C<repeat> seconds later, again, and again,
		2011	until stopped manually.
1141		2012
1142	The timer itself will do a best-effort at avoiding drift, that is, if you	2013	The timer itself will do a best-effort at avoiding drift, that is, if
1143	configure a timer to trigger every 10 seconds, then it will trigger at	2014	you configure a timer to trigger every 10 seconds, then it will normally
1144	exactly 10 second intervals. If, however, your program cannot keep up with	2015	trigger at exactly 10 second intervals. If, however, your program cannot
1145	the timer (because it takes longer than those 10 seconds to do stuff) the	2016	keep up with the timer (because it takes longer than those 10 seconds to
1146	timer will not fire more than once per event loop iteration.	2017	do stuff) the timer will not fire more than once per event loop iteration.
1147		2018
1148	=item ev_timer_again (loop)	2019	=item ev_timer_again (loop, ev_timer *)
1149		2020
1150	This will act as if the timer timed out and restart it again if it is	2021	This will act as if the timer timed out and restart it again if it is
1151	repeating. The exact semantics are:	2022	repeating. The exact semantics are:
1152		2023
1153	If the timer is pending, its pending status is cleared.	2024	If the timer is pending, its pending status is cleared.
1154		2025
1155	If the timer is started but nonrepeating, stop it (as if it timed out).	2026	If the timer is started but non-repeating, stop it (as if it timed out).
1156		2027
1157	If the timer is repeating, either start it if necessary (with the	2028	If the timer is repeating, either start it if necessary (with the
1158	C<repeat> value), or reset the running timer to the C<repeat> value.	2029	C<repeat> value), or reset the running timer to the C<repeat> value.
1159		2030
1160	This sounds a bit complicated, but here is a useful and typical	2031	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1161	example: Imagine you have a tcp connection and you want a so-called idle	2032	usage example.
1162	timeout, that is, you want to be called when there have been, say, 60
1163	seconds of inactivity on the socket. The easiest way to do this is to
1164	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1165	C<ev_timer_again> each time you successfully read or write some data. If
1166	you go into an idle state where you do not expect data to travel on the
1167	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1168	automatically restart it if need be.
1169		2033
1170	That means you can ignore the C<after> value and C<ev_timer_start>	2034	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1171	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1172		2035
1173	ev_timer_init (timer, callback, 0., 5.);	2036	Returns the remaining time until a timer fires. If the timer is active,
1174	ev_timer_again (loop, timer);	2037	then this time is relative to the current event loop time, otherwise it's
1175	...	2038	the timeout value currently configured.
1176	timer->again = 17.;
1177	ev_timer_again (loop, timer);
1178	...
1179	timer->again = 10.;
1180	ev_timer_again (loop, timer);
1181		2039
1182	This is more slightly efficient then stopping/starting the timer each time	2040	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1183	you want to modify its timeout value.	2041	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2042	will return C<4>. When the timer expires and is restarted, it will return
		2043	roughly C<7> (likely slightly less as callback invocation takes some time,
		2044	too), and so on.
1184		2045
1185	=item ev_tstamp repeat [read-write]	2046	=item ev_tstamp repeat [read-write]
1186		2047
1187	The current C<repeat> value. Will be used each time the watcher times out	2048	The current C<repeat> value. Will be used each time the watcher times out
1188	or C<ev_timer_again> is called and determines the next timeout (if any),	2049	or C<ev_timer_again> is called, and determines the next timeout (if any),
1189	which is also when any modifications are taken into account.	2050	which is also when any modifications are taken into account.
1190		2051
1191	=back	2052	=back
1192		2053
1193	=head3 Examples	2054	=head3 Examples
1194		2055
1195	Example: Create a timer that fires after 60 seconds.	2056	Example: Create a timer that fires after 60 seconds.
1196		2057
1197	static void	2058	static void
1198	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2059	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1199	{	2060	{
1200	.. one minute over, w is actually stopped right here	2061	.. one minute over, w is actually stopped right here
1201	}	2062	}
1202		2063
1203	struct ev_timer mytimer;	2064	ev_timer mytimer;
1204	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2065	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1205	ev_timer_start (loop, &mytimer);	2066	ev_timer_start (loop, &mytimer);
1206		2067
1207	Example: Create a timeout timer that times out after 10 seconds of	2068	Example: Create a timeout timer that times out after 10 seconds of
1208	inactivity.	2069	inactivity.
1209		2070
1210	static void	2071	static void
1211	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2072	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1212	{	2073	{
1213	.. ten seconds without any activity	2074	.. ten seconds without any activity
1214	}	2075	}
1215		2076
1216	struct ev_timer mytimer;	2077	ev_timer mytimer;
1217	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2078	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1218	ev_timer_again (&mytimer); /* start timer */	2079	ev_timer_again (&mytimer); /* start timer */
1219	ev_loop (loop, 0);	2080	ev_run (loop, 0);
1220		2081
1221	// and in some piece of code that gets executed on any "activity":	2082	// and in some piece of code that gets executed on any "activity":
1222	// reset the timeout to start ticking again at 10 seconds	2083	// reset the timeout to start ticking again at 10 seconds
1223	ev_timer_again (&mytimer);	2084	ev_timer_again (&mytimer);
1224		2085
1225		2086
1226	=head2 C<ev_periodic> - to cron or not to cron?	2087	=head2 C<ev_periodic> - to cron or not to cron?
1227		2088
1228	Periodic watchers are also timers of a kind, but they are very versatile	2089	Periodic watchers are also timers of a kind, but they are very versatile
1229	(and unfortunately a bit complex).	2090	(and unfortunately a bit complex).
1230		2091
1231	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2092	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1232	but on wallclock time (absolute time). You can tell a periodic watcher	2093	relative time, the physical time that passes) but on wall clock time
1233	to trigger "at" some specific point in time. For example, if you tell a	2094	(absolute time, the thing you can read on your calender or clock). The
1234	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2095	difference is that wall clock time can run faster or slower than real
1235	+ 10.>) and then reset your system clock to the last year, then it will	2096	time, and time jumps are not uncommon (e.g. when you adjust your
1236	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2097	wrist-watch).
1237	roughly 10 seconds later).
1238		2098
1239	They can also be used to implement vastly more complex timers, such as	2099	You can tell a periodic watcher to trigger after some specific point
1240	triggering an event on each midnight, local time or other, complicated,	2100	in time: for example, if you tell a periodic watcher to trigger "in 10
1241	rules.	2101	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2102	not a delay) and then reset your system clock to January of the previous
		2103	year, then it will take a year or more to trigger the event (unlike an
		2104	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2105	it, as it uses a relative timeout).
1242		2106
		2107	C<ev_periodic> watchers can also be used to implement vastly more complex
		2108	timers, such as triggering an event on each "midnight, local time", or
		2109	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2110	those cannot react to time jumps.
		2111
1243	As with timers, the callback is guarenteed to be invoked only when the	2112	As with timers, the callback is guaranteed to be invoked only when the
1244	time (C<at>) has been passed, but if multiple periodic timers become ready	2113	point in time where it is supposed to trigger has passed. If multiple
1245	during the same loop iteration then order of execution is undefined.	2114	timers become ready during the same loop iteration then the ones with
		2115	earlier time-out values are invoked before ones with later time-out values
		2116	(but this is no longer true when a callback calls C<ev_run> recursively).
1246		2117
1247	=head3 Watcher-Specific Functions and Data Members	2118	=head3 Watcher-Specific Functions and Data Members
1248		2119
1249	=over 4	2120	=over 4
1250		2121
1251	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2122	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1252		2123
1253	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2124	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1254		2125
1255	Lots of arguments, lets sort it out... There are basically three modes of	2126	Lots of arguments, let's sort it out... There are basically three modes of
1256	operation, and we will explain them from simplest to complex:	2127	operation, and we will explain them from simplest to most complex:
1257		2128
1258	=over 4	2129	=over 4
1259		2130
1260	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2131	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1261		2132
1262	In this configuration the watcher triggers an event at the wallclock time	2133	In this configuration the watcher triggers an event after the wall clock
1263	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2134	time C<offset> has passed. It will not repeat and will not adjust when a
1264	that is, if it is to be run at January 1st 2011 then it will run when the	2135	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1265	system time reaches or surpasses this time.	2136	will be stopped and invoked when the system clock reaches or surpasses
		2137	this point in time.
1266		2138
1267	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2139	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1268		2140
1269	In this mode the watcher will always be scheduled to time out at the next	2141	In this mode the watcher will always be scheduled to time out at the next
1270	C<at + N * interval> time (for some integer N, which can also be negative)	2142	C<offset + N * interval> time (for some integer N, which can also be
1271	and then repeat, regardless of any time jumps.	2143	negative) and then repeat, regardless of any time jumps. The C<offset>
		2144	argument is merely an offset into the C<interval> periods.
1272		2145
1273	This can be used to create timers that do not drift with respect to system	2146	This can be used to create timers that do not drift with respect to the
1274	time:	2147	system clock, for example, here is an C<ev_periodic> that triggers each
		2148	hour, on the hour (with respect to UTC):
1275		2149
1276	ev_periodic_set (&periodic, 0., 3600., 0);	2150	ev_periodic_set (&periodic, 0., 3600., 0);
1277		2151
1278	This doesn't mean there will always be 3600 seconds in between triggers,	2152	This doesn't mean there will always be 3600 seconds in between triggers,
1279	but only that the the callback will be called when the system time shows a	2153	but only that the callback will be called when the system time shows a
1280	full hour (UTC), or more correctly, when the system time is evenly divisible	2154	full hour (UTC), or more correctly, when the system time is evenly divisible
1281	by 3600.	2155	by 3600.
1282		2156
1283	Another way to think about it (for the mathematically inclined) is that	2157	Another way to think about it (for the mathematically inclined) is that
1284	C<ev_periodic> will try to run the callback in this mode at the next possible	2158	C<ev_periodic> will try to run the callback in this mode at the next possible
1285	time where C<time = at (mod interval)>, regardless of any time jumps.	2159	time where C<time = offset (mod interval)>, regardless of any time jumps.
1286		2160
1287	For numerical stability it is preferable that the C<at> value is near	2161	The C<interval> I<MUST> be positive, and for numerical stability, the
1288	C<ev_now ()> (the current time), but there is no range requirement for	2162	interval value should be higher than C<1/8192> (which is around 100
1289	this value.	2163	microseconds) and C<offset> should be higher than C<0> and should have
		2164	at most a similar magnitude as the current time (say, within a factor of
		2165	ten). Typical values for offset are, in fact, C<0> or something between
		2166	C<0> and C<interval>, which is also the recommended range.
1290		2167
		2168	Note also that there is an upper limit to how often a timer can fire (CPU
		2169	speed for example), so if C<interval> is very small then timing stability
		2170	will of course deteriorate. Libev itself tries to be exact to be about one
		2171	millisecond (if the OS supports it and the machine is fast enough).
		2172
1291	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2173	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1292		2174
1293	In this mode the values for C<interval> and C<at> are both being	2175	In this mode the values for C<interval> and C<offset> are both being
1294	ignored. Instead, each time the periodic watcher gets scheduled, the	2176	ignored. Instead, each time the periodic watcher gets scheduled, the
1295	reschedule callback will be called with the watcher as first, and the	2177	reschedule callback will be called with the watcher as first, and the
1296	current time as second argument.	2178	current time as second argument.
1297		2179
1298	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2180	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1299	ever, or make any event loop modifications>. If you need to stop it,	2181	or make ANY other event loop modifications whatsoever, unless explicitly
1300	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2182	allowed by documentation here>.
1301	starting an C<ev_prepare> watcher, which is legal).
1302		2183
		2184	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2185	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2186	only event loop modification you are allowed to do).
		2187
1303	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2188	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1304	ev_tstamp now)>, e.g.:	2189	*w, ev_tstamp now)>, e.g.:
1305		2190
		2191	static ev_tstamp
1306	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2192	my_rescheduler (ev_periodic *w, ev_tstamp now)
1307	{	2193	{
1308	return now + 60.;	2194	return now + 60.;
1309	}	2195	}
1310		2196
1311	It must return the next time to trigger, based on the passed time value	2197	It must return the next time to trigger, based on the passed time value
1312	(that is, the lowest time value larger than to the second argument). It	2198	(that is, the lowest time value larger than to the second argument). It
1313	will usually be called just before the callback will be triggered, but	2199	will usually be called just before the callback will be triggered, but
1314	might be called at other times, too.	2200	might be called at other times, too.
1315		2201
1316	NOTE: I<< This callback must always return a time that is later than the	2202	NOTE: I<< This callback must always return a time that is higher than or
1317	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2203	equal to the passed C<now> value >>.
1318		2204
1319	This can be used to create very complex timers, such as a timer that	2205	This can be used to create very complex timers, such as a timer that
1320	triggers on each midnight, local time. To do this, you would calculate the	2206	triggers on "next midnight, local time". To do this, you would calculate the
1321	next midnight after C<now> and return the timestamp value for this. How	2207	next midnight after C<now> and return the timestamp value for this. How
1322	you do this is, again, up to you (but it is not trivial, which is the main	2208	you do this is, again, up to you (but it is not trivial, which is the main
1323	reason I omitted it as an example).	2209	reason I omitted it as an example).
1324		2210
1325	=back	2211	=back
…		…
1329	Simply stops and restarts the periodic watcher again. This is only useful	2215	Simply stops and restarts the periodic watcher again. This is only useful
1330	when you changed some parameters or the reschedule callback would return	2216	when you changed some parameters or the reschedule callback would return
1331	a different time than the last time it was called (e.g. in a crond like	2217	a different time than the last time it was called (e.g. in a crond like
1332	program when the crontabs have changed).	2218	program when the crontabs have changed).
1333		2219
		2220	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2221
		2222	When active, returns the absolute time that the watcher is supposed
		2223	to trigger next. This is not the same as the C<offset> argument to
		2224	C<ev_periodic_set>, but indeed works even in interval and manual
		2225	rescheduling modes.
		2226
1334	=item ev_tstamp offset [read-write]	2227	=item ev_tstamp offset [read-write]
1335		2228
1336	When repeating, this contains the offset value, otherwise this is the	2229	When repeating, this contains the offset value, otherwise this is the
1337	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2230	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2231	although libev might modify this value for better numerical stability).
1338		2232
1339	Can be modified any time, but changes only take effect when the periodic	2233	Can be modified any time, but changes only take effect when the periodic
1340	timer fires or C<ev_periodic_again> is being called.	2234	timer fires or C<ev_periodic_again> is being called.
1341		2235
1342	=item ev_tstamp interval [read-write]	2236	=item ev_tstamp interval [read-write]
1343		2237
1344	The current interval value. Can be modified any time, but changes only	2238	The current interval value. Can be modified any time, but changes only
1345	take effect when the periodic timer fires or C<ev_periodic_again> is being	2239	take effect when the periodic timer fires or C<ev_periodic_again> is being
1346	called.	2240	called.
1347		2241
1348	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2242	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1349		2243
1350	The current reschedule callback, or C<0>, if this functionality is	2244	The current reschedule callback, or C<0>, if this functionality is
1351	switched off. Can be changed any time, but changes only take effect when	2245	switched off. Can be changed any time, but changes only take effect when
1352	the periodic timer fires or C<ev_periodic_again> is being called.	2246	the periodic timer fires or C<ev_periodic_again> is being called.
1353		2247
1354	=item ev_tstamp at [read-only]
1355
1356	When active, contains the absolute time that the watcher is supposed to
1357	trigger next.
1358
1359	=back	2248	=back
1360		2249
1361	=head3 Examples	2250	=head3 Examples
1362		2251
1363	Example: Call a callback every hour, or, more precisely, whenever the	2252	Example: Call a callback every hour, or, more precisely, whenever the
1364	system clock is divisible by 3600. The callback invocation times have	2253	system time is divisible by 3600. The callback invocation times have
1365	potentially a lot of jittering, but good long-term stability.	2254	potentially a lot of jitter, but good long-term stability.
1366		2255
1367	static void	2256	static void
1368	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2257	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1369	{	2258	{
1370	... its now a full hour (UTC, or TAI or whatever your clock follows)	2259	... its now a full hour (UTC, or TAI or whatever your clock follows)
1371	}	2260	}
1372		2261
1373	struct ev_periodic hourly_tick;	2262	ev_periodic hourly_tick;
1374	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2263	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1375	ev_periodic_start (loop, &hourly_tick);	2264	ev_periodic_start (loop, &hourly_tick);
1376		2265
1377	Example: The same as above, but use a reschedule callback to do it:	2266	Example: The same as above, but use a reschedule callback to do it:
1378		2267
1379	#include <math.h>	2268	#include <math.h>
1380		2269
1381	static ev_tstamp	2270	static ev_tstamp
1382	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2271	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1383	{	2272	{
1384	return fmod (now, 3600.) + 3600.;	2273	return now + (3600. - fmod (now, 3600.));
1385	}	2274	}
1386		2275
1387	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2276	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1388		2277
1389	Example: Call a callback every hour, starting now:	2278	Example: Call a callback every hour, starting now:
1390		2279
1391	struct ev_periodic hourly_tick;	2280	ev_periodic hourly_tick;
1392	ev_periodic_init (&hourly_tick, clock_cb,	2281	ev_periodic_init (&hourly_tick, clock_cb,
1393	fmod (ev_now (loop), 3600.), 3600., 0);	2282	fmod (ev_now (loop), 3600.), 3600., 0);
1394	ev_periodic_start (loop, &hourly_tick);	2283	ev_periodic_start (loop, &hourly_tick);
1395		2284
1396		2285
1397	=head2 C<ev_signal> - signal me when a signal gets signalled!	2286	=head2 C<ev_signal> - signal me when a signal gets signalled!
1398		2287
1399	Signal watchers will trigger an event when the process receives a specific	2288	Signal watchers will trigger an event when the process receives a specific
1400	signal one or more times. Even though signals are very asynchronous, libev	2289	signal one or more times. Even though signals are very asynchronous, libev
1401	will try it's best to deliver signals synchronously, i.e. as part of the	2290	will try its best to deliver signals synchronously, i.e. as part of the
1402	normal event processing, like any other event.	2291	normal event processing, like any other event.
1403		2292
		2293	If you want signals to be delivered truly asynchronously, just use
		2294	C<sigaction> as you would do without libev and forget about sharing
		2295	the signal. You can even use C<ev_async> from a signal handler to
		2296	synchronously wake up an event loop.
		2297
1404	You can configure as many watchers as you like per signal. Only when the	2298	You can configure as many watchers as you like for the same signal, but
		2299	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2300	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2301	C<SIGINT> in both the default loop and another loop at the same time. At
		2302	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2303
1405	first watcher gets started will libev actually register a signal watcher	2304	When the first watcher gets started will libev actually register something
1406	with the kernel (thus it coexists with your own signal handlers as long	2305	with the kernel (thus it coexists with your own signal handlers as long as
1407	as you don't register any with libev). Similarly, when the last signal	2306	you don't register any with libev for the same signal).
1408	watcher for a signal is stopped libev will reset the signal handler to	2307
1409	SIG_DFL (regardless of what it was set to before).	2308	If possible and supported, libev will install its handlers with
		2309	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2310	not be unduly interrupted. If you have a problem with system calls getting
		2311	interrupted by signals you can block all signals in an C<ev_check> watcher
		2312	and unblock them in an C<ev_prepare> watcher.
		2313
		2314	=head3 The special problem of inheritance over fork/execve/pthread_create
		2315
		2316	Both the signal mask (C<sigprocmask>) and the signal disposition
		2317	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2318	stopping it again), that is, libev might or might not block the signal,
		2319	and might or might not set or restore the installed signal handler (but
		2320	see C<EVFLAG_NOSIGMASK>).
		2321
		2322	While this does not matter for the signal disposition (libev never
		2323	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2324	C<execve>), this matters for the signal mask: many programs do not expect
		2325	certain signals to be blocked.
		2326
		2327	This means that before calling C<exec> (from the child) you should reset
		2328	the signal mask to whatever "default" you expect (all clear is a good
		2329	choice usually).
		2330
		2331	The simplest way to ensure that the signal mask is reset in the child is
		2332	to install a fork handler with C<pthread_atfork> that resets it. That will
		2333	catch fork calls done by libraries (such as the libc) as well.
		2334
		2335	In current versions of libev, the signal will not be blocked indefinitely
		2336	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2337	the window of opportunity for problems, it will not go away, as libev
		2338	I<has> to modify the signal mask, at least temporarily.
		2339
		2340	So I can't stress this enough: I<If you do not reset your signal mask when
		2341	you expect it to be empty, you have a race condition in your code>. This
		2342	is not a libev-specific thing, this is true for most event libraries.
		2343
		2344	=head3 The special problem of threads signal handling
		2345
		2346	POSIX threads has problematic signal handling semantics, specifically,
		2347	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2348	threads in a process block signals, which is hard to achieve.
		2349
		2350	When you want to use sigwait (or mix libev signal handling with your own
		2351	for the same signals), you can tackle this problem by globally blocking
		2352	all signals before creating any threads (or creating them with a fully set
		2353	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2354	loops. Then designate one thread as "signal receiver thread" which handles
		2355	these signals. You can pass on any signals that libev might be interested
		2356	in by calling C<ev_feed_signal>.
1410		2357
1411	=head3 Watcher-Specific Functions and Data Members	2358	=head3 Watcher-Specific Functions and Data Members
1412		2359
1413	=over 4	2360	=over 4
1414		2361
…		…
1423		2370
1424	The signal the watcher watches out for.	2371	The signal the watcher watches out for.
1425		2372
1426	=back	2373	=back
1427		2374
		2375	=head3 Examples
		2376
		2377	Example: Try to exit cleanly on SIGINT.
		2378
		2379	static void
		2380	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2381	{
		2382	ev_break (loop, EVBREAK_ALL);
		2383	}
		2384
		2385	ev_signal signal_watcher;
		2386	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2387	ev_signal_start (loop, &signal_watcher);
		2388
1428		2389
1429	=head2 C<ev_child> - watch out for process status changes	2390	=head2 C<ev_child> - watch out for process status changes
1430		2391
1431	Child watchers trigger when your process receives a SIGCHLD in response to	2392	Child watchers trigger when your process receives a SIGCHLD in response to
1432	some child status changes (most typically when a child of yours dies).	2393	some child status changes (most typically when a child of yours dies or
		2394	exits). It is permissible to install a child watcher I<after> the child
		2395	has been forked (which implies it might have already exited), as long
		2396	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2397	forking and then immediately registering a watcher for the child is fine,
		2398	but forking and registering a watcher a few event loop iterations later or
		2399	in the next callback invocation is not.
		2400
		2401	Only the default event loop is capable of handling signals, and therefore
		2402	you can only register child watchers in the default event loop.
		2403
		2404	Due to some design glitches inside libev, child watchers will always be
		2405	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2406	libev)
		2407
		2408	=head3 Process Interaction
		2409
		2410	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2411	initialised. This is necessary to guarantee proper behaviour even if the
		2412	first child watcher is started after the child exits. The occurrence
		2413	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2414	synchronously as part of the event loop processing. Libev always reaps all
		2415	children, even ones not watched.
		2416
		2417	=head3 Overriding the Built-In Processing
		2418
		2419	Libev offers no special support for overriding the built-in child
		2420	processing, but if your application collides with libev's default child
		2421	handler, you can override it easily by installing your own handler for
		2422	C<SIGCHLD> after initialising the default loop, and making sure the
		2423	default loop never gets destroyed. You are encouraged, however, to use an
		2424	event-based approach to child reaping and thus use libev's support for
		2425	that, so other libev users can use C<ev_child> watchers freely.
		2426
		2427	=head3 Stopping the Child Watcher
		2428
		2429	Currently, the child watcher never gets stopped, even when the
		2430	child terminates, so normally one needs to stop the watcher in the
		2431	callback. Future versions of libev might stop the watcher automatically
		2432	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2433	problem).
1433		2434
1434	=head3 Watcher-Specific Functions and Data Members	2435	=head3 Watcher-Specific Functions and Data Members
1435		2436
1436	=over 4	2437	=over 4
1437		2438
1438	=item ev_child_init (ev_child *, callback, int pid)	2439	=item ev_child_init (ev_child *, callback, int pid, int trace)
1439		2440
1440	=item ev_child_set (ev_child *, int pid)	2441	=item ev_child_set (ev_child *, int pid, int trace)
1441		2442
1442	Configures the watcher to wait for status changes of process C<pid> (or	2443	Configures the watcher to wait for status changes of process C<pid> (or
1443	I<any> process if C<pid> is specified as C<0>). The callback can look	2444	I<any> process if C<pid> is specified as C<0>). The callback can look
1444	at the C<rstatus> member of the C<ev_child> watcher structure to see	2445	at the C<rstatus> member of the C<ev_child> watcher structure to see
1445	the status word (use the macros from C<sys/wait.h> and see your systems	2446	the status word (use the macros from C<sys/wait.h> and see your systems
1446	C<waitpid> documentation). The C<rpid> member contains the pid of the	2447	C<waitpid> documentation). The C<rpid> member contains the pid of the
1447	process causing the status change.	2448	process causing the status change. C<trace> must be either C<0> (only
		2449	activate the watcher when the process terminates) or C<1> (additionally
		2450	activate the watcher when the process is stopped or continued).
1448		2451
1449	=item int pid [read-only]	2452	=item int pid [read-only]
1450		2453
1451	The process id this watcher watches out for, or C<0>, meaning any process id.	2454	The process id this watcher watches out for, or C<0>, meaning any process id.
1452		2455
…		…
1461		2464
1462	=back	2465	=back
1463		2466
1464	=head3 Examples	2467	=head3 Examples
1465		2468
1466	Example: Try to exit cleanly on SIGINT and SIGTERM.	2469	Example: C<fork()> a new process and install a child handler to wait for
		2470	its completion.
1467		2471
		2472	ev_child cw;
		2473
1468	static void	2474	static void
1469	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2475	child_cb (EV_P_ ev_child *w, int revents)
1470	{	2476	{
1471	ev_unloop (loop, EVUNLOOP_ALL);	2477	ev_child_stop (EV_A_ w);
		2478	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1472	}	2479	}
1473		2480
1474	struct ev_signal signal_watcher;	2481	pid_t pid = fork ();
1475	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2482
1476	ev_signal_start (loop, &sigint_cb);	2483	if (pid < 0)
		2484	// error
		2485	else if (pid == 0)
		2486	{
		2487	// the forked child executes here
		2488	exit (1);
		2489	}
		2490	else
		2491	{
		2492	ev_child_init (&cw, child_cb, pid, 0);
		2493	ev_child_start (EV_DEFAULT_ &cw);
		2494	}
1477		2495
1478		2496
1479	=head2 C<ev_stat> - did the file attributes just change?	2497	=head2 C<ev_stat> - did the file attributes just change?
1480		2498
1481	This watches a filesystem path for attribute changes. That is, it calls	2499	This watches a file system path for attribute changes. That is, it calls
1482	C<stat> regularly (or when the OS says it changed) and sees if it changed	2500	C<stat> on that path in regular intervals (or when the OS says it changed)
1483	compared to the last time, invoking the callback if it did.	2501	and sees if it changed compared to the last time, invoking the callback if
		2502	it did.
1484		2503
1485	The path does not need to exist: changing from "path exists" to "path does	2504	The path does not need to exist: changing from "path exists" to "path does
1486	not exist" is a status change like any other. The condition "path does	2505	not exist" is a status change like any other. The condition "path does not
1487	not exist" is signified by the C<st_nlink> field being zero (which is	2506	exist" (or more correctly "path cannot be stat'ed") is signified by the
1488	otherwise always forced to be at least one) and all the other fields of	2507	C<st_nlink> field being zero (which is otherwise always forced to be at
1489	the stat buffer having unspecified contents.	2508	least one) and all the other fields of the stat buffer having unspecified
		2509	contents.
1490		2510
1491	The path I<should> be absolute and I<must not> end in a slash. If it is	2511	The path I<must not> end in a slash or contain special components such as
		2512	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1492	relative and your working directory changes, the behaviour is undefined.	2513	your working directory changes, then the behaviour is undefined.
1493		2514
1494	Since there is no standard to do this, the portable implementation simply	2515	Since there is no portable change notification interface available, the
1495	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2516	portable implementation simply calls C<stat(2)> regularly on the path
1496	can specify a recommended polling interval for this case. If you specify	2517	to see if it changed somehow. You can specify a recommended polling
1497	a polling interval of C<0> (highly recommended!) then a I<suitable,	2518	interval for this case. If you specify a polling interval of C<0> (highly
1498	unspecified default> value will be used (which you can expect to be around	2519	recommended!) then a I<suitable, unspecified default> value will be used
1499	five seconds, although this might change dynamically). Libev will also	2520	(which you can expect to be around five seconds, although this might
1500	impose a minimum interval which is currently around C<0.1>, but thats	2521	change dynamically). Libev will also impose a minimum interval which is
1501	usually overkill.	2522	currently around C<0.1>, but that's usually overkill.
1502		2523
1503	This watcher type is not meant for massive numbers of stat watchers,	2524	This watcher type is not meant for massive numbers of stat watchers,
1504	as even with OS-supported change notifications, this can be	2525	as even with OS-supported change notifications, this can be
1505	resource-intensive.	2526	resource-intensive.
1506		2527
1507	At the time of this writing, only the Linux inotify interface is	2528	At the time of this writing, the only OS-specific interface implemented
1508	implemented (implementing kqueue support is left as an exercise for the	2529	is the Linux inotify interface (implementing kqueue support is left as an
1509	reader). Inotify will be used to give hints only and should not change the	2530	exercise for the reader. Note, however, that the author sees no way of
1510	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2531	implementing C<ev_stat> semantics with kqueue, except as a hint).
1511	to fall back to regular polling again even with inotify, but changes are
1512	usually detected immediately, and if the file exists there will be no
1513	polling.
1514		2532
1515	=head3 Inotify	2533	=head3 ABI Issues (Largefile Support)
1516		2534
		2535	Libev by default (unless the user overrides this) uses the default
		2536	compilation environment, which means that on systems with large file
		2537	support disabled by default, you get the 32 bit version of the stat
		2538	structure. When using the library from programs that change the ABI to
		2539	use 64 bit file offsets the programs will fail. In that case you have to
		2540	compile libev with the same flags to get binary compatibility. This is
		2541	obviously the case with any flags that change the ABI, but the problem is
		2542	most noticeably displayed with ev_stat and large file support.
		2543
		2544	The solution for this is to lobby your distribution maker to make large
		2545	file interfaces available by default (as e.g. FreeBSD does) and not
		2546	optional. Libev cannot simply switch on large file support because it has
		2547	to exchange stat structures with application programs compiled using the
		2548	default compilation environment.
		2549
		2550	=head3 Inotify and Kqueue
		2551
1517	When C<inotify (7)> support has been compiled into libev (generally only	2552	When C<inotify (7)> support has been compiled into libev and present at
1518	available on Linux) and present at runtime, it will be used to speed up	2553	runtime, it will be used to speed up change detection where possible. The
1519	change detection where possible. The inotify descriptor will be created lazily	2554	inotify descriptor will be created lazily when the first C<ev_stat>
1520	when the first C<ev_stat> watcher is being started.	2555	watcher is being started.
1521		2556
1522	Inotify presense does not change the semantics of C<ev_stat> watchers	2557	Inotify presence does not change the semantics of C<ev_stat> watchers
1523	except that changes might be detected earlier, and in some cases, to avoid	2558	except that changes might be detected earlier, and in some cases, to avoid
1524	making regular C<stat> calls. Even in the presense of inotify support	2559	making regular C<stat> calls. Even in the presence of inotify support
1525	there are many cases where libev has to resort to regular C<stat> polling.	2560	there are many cases where libev has to resort to regular C<stat> polling,
		2561	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2562	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2563	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2564	xfs are fully working) libev usually gets away without polling.
1526		2565
1527	(There is no support for kqueue, as apparently it cannot be used to	2566	There is no support for kqueue, as apparently it cannot be used to
1528	implement this functionality, due to the requirement of having a file	2567	implement this functionality, due to the requirement of having a file
1529	descriptor open on the object at all times).	2568	descriptor open on the object at all times, and detecting renames, unlinks
		2569	etc. is difficult.
		2570
		2571	=head3 C<stat ()> is a synchronous operation
		2572
		2573	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2574	the process. The exception are C<ev_stat> watchers - those call C<stat
		2575	()>, which is a synchronous operation.
		2576
		2577	For local paths, this usually doesn't matter: unless the system is very
		2578	busy or the intervals between stat's are large, a stat call will be fast,
		2579	as the path data is usually in memory already (except when starting the
		2580	watcher).
		2581
		2582	For networked file systems, calling C<stat ()> can block an indefinite
		2583	time due to network issues, and even under good conditions, a stat call
		2584	often takes multiple milliseconds.
		2585
		2586	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2587	paths, although this is fully supported by libev.
1530		2588
1531	=head3 The special problem of stat time resolution	2589	=head3 The special problem of stat time resolution
1532		2590
1533	The C<stat ()> syscall only supports full-second resolution portably, and	2591	The C<stat ()> system call only supports full-second resolution portably,
1534	even on systems where the resolution is higher, many filesystems still	2592	and even on systems where the resolution is higher, most file systems
1535	only support whole seconds.	2593	still only support whole seconds.
1536		2594
1537	That means that, if the time is the only thing that changes, you might	2595	That means that, if the time is the only thing that changes, you can
1538	miss updates: on the first update, C<ev_stat> detects a change and calls	2596	easily miss updates: on the first update, C<ev_stat> detects a change and
1539	your callback, which does something. When there is another update within	2597	calls your callback, which does something. When there is another update
1540	the same second, C<ev_stat> will be unable to detect it.	2598	within the same second, C<ev_stat> will be unable to detect unless the
		2599	stat data does change in other ways (e.g. file size).
1541		2600
1542	The solution to this is to delay acting on a change for a second (or till	2601	The solution to this is to delay acting on a change for slightly more
1543	the next second boundary), using a roughly one-second delay C<ev_timer>	2602	than a second (or till slightly after the next full second boundary), using
1544	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2603	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1545	is added to work around small timing inconsistencies of some operating	2604	ev_timer_again (loop, w)>).
1546	systems.	2605
		2606	The C<.02> offset is added to work around small timing inconsistencies
		2607	of some operating systems (where the second counter of the current time
		2608	might be be delayed. One such system is the Linux kernel, where a call to
		2609	C<gettimeofday> might return a timestamp with a full second later than
		2610	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2611	update file times then there will be a small window where the kernel uses
		2612	the previous second to update file times but libev might already execute
		2613	the timer callback).
1547		2614
1548	=head3 Watcher-Specific Functions and Data Members	2615	=head3 Watcher-Specific Functions and Data Members
1549		2616
1550	=over 4	2617	=over 4
1551		2618
…		…
1557	C<path>. The C<interval> is a hint on how quickly a change is expected to	2624	C<path>. The C<interval> is a hint on how quickly a change is expected to
1558	be detected and should normally be specified as C<0> to let libev choose	2625	be detected and should normally be specified as C<0> to let libev choose
1559	a suitable value. The memory pointed to by C<path> must point to the same	2626	a suitable value. The memory pointed to by C<path> must point to the same
1560	path for as long as the watcher is active.	2627	path for as long as the watcher is active.
1561		2628
1562	The callback will be receive C<EV_STAT> when a change was detected,	2629	The callback will receive an C<EV_STAT> event when a change was detected,
1563	relative to the attributes at the time the watcher was started (or the	2630	relative to the attributes at the time the watcher was started (or the
1564	last change was detected).	2631	last change was detected).
1565		2632
1566	=item ev_stat_stat (ev_stat *)	2633	=item ev_stat_stat (loop, ev_stat *)
1567		2634
1568	Updates the stat buffer immediately with new values. If you change the	2635	Updates the stat buffer immediately with new values. If you change the
1569	watched path in your callback, you could call this fucntion to avoid	2636	watched path in your callback, you could call this function to avoid
1570	detecting this change (while introducing a race condition). Can also be	2637	detecting this change (while introducing a race condition if you are not
1571	useful simply to find out the new values.	2638	the only one changing the path). Can also be useful simply to find out the
		2639	new values.
1572		2640
1573	=item ev_statdata attr [read-only]	2641	=item ev_statdata attr [read-only]
1574		2642
1575	The most-recently detected attributes of the file. Although the type is of	2643	The most-recently detected attributes of the file. Although the type is
1576	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2644	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1577	suitable for your system. If the C<st_nlink> member is C<0>, then there	2645	suitable for your system, but you can only rely on the POSIX-standardised
		2646	members to be present. If the C<st_nlink> member is C<0>, then there was
1578	was some error while C<stat>ing the file.	2647	some error while C<stat>ing the file.
1579		2648
1580	=item ev_statdata prev [read-only]	2649	=item ev_statdata prev [read-only]
1581		2650
1582	The previous attributes of the file. The callback gets invoked whenever	2651	The previous attributes of the file. The callback gets invoked whenever
1583	C<prev> != C<attr>.	2652	C<prev> != C<attr>, or, more precisely, one or more of these members
		2653	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2654	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1584		2655
1585	=item ev_tstamp interval [read-only]	2656	=item ev_tstamp interval [read-only]
1586		2657
1587	The specified interval.	2658	The specified interval.
1588		2659
1589	=item const char *path [read-only]	2660	=item const char *path [read-only]
1590		2661
1591	The filesystem path that is being watched.	2662	The file system path that is being watched.
1592		2663
1593	=back	2664	=back
1594		2665
1595	=head3 Examples	2666	=head3 Examples
1596		2667
1597	Example: Watch C</etc/passwd> for attribute changes.	2668	Example: Watch C</etc/passwd> for attribute changes.
1598		2669
1599	static void	2670	static void
1600	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2671	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1601	{	2672	{
1602	/* /etc/passwd changed in some way */	2673	/* /etc/passwd changed in some way */
1603	if (w->attr.st_nlink)	2674	if (w->attr.st_nlink)
1604	{	2675	{
1605	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2676	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1606	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2677	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1607	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2678	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1608	}	2679	}
1609	else	2680	else
1610	/* you shalt not abuse printf for puts */	2681	/* you shalt not abuse printf for puts */
1611	puts ("wow, /etc/passwd is not there, expect problems. "	2682	puts ("wow, /etc/passwd is not there, expect problems. "
1612	"if this is windows, they already arrived\n");	2683	"if this is windows, they already arrived\n");
1613	}	2684	}
1614		2685
1615	...	2686	...
1616	ev_stat passwd;	2687	ev_stat passwd;
1617		2688
1618	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2689	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1619	ev_stat_start (loop, &passwd);	2690	ev_stat_start (loop, &passwd);
1620		2691
1621	Example: Like above, but additionally use a one-second delay so we do not	2692	Example: Like above, but additionally use a one-second delay so we do not
1622	miss updates (however, frequent updates will delay processing, too, so	2693	miss updates (however, frequent updates will delay processing, too, so
1623	one might do the work both on C<ev_stat> callback invocation I<and> on	2694	one might do the work both on C<ev_stat> callback invocation I<and> on
1624	C<ev_timer> callback invocation).	2695	C<ev_timer> callback invocation).
1625		2696
1626	static ev_stat passwd;	2697	static ev_stat passwd;
1627	static ev_timer timer;	2698	static ev_timer timer;
1628		2699
1629	static void	2700	static void
1630	timer_cb (EV_P_ ev_timer *w, int revents)	2701	timer_cb (EV_P_ ev_timer *w, int revents)
1631	{	2702	{
1632	ev_timer_stop (EV_A_ w);	2703	ev_timer_stop (EV_A_ w);
1633		2704
1634	/* now it's one second after the most recent passwd change */	2705	/* now it's one second after the most recent passwd change */
1635	}	2706	}
1636		2707
1637	static void	2708	static void
1638	stat_cb (EV_P_ ev_stat *w, int revents)	2709	stat_cb (EV_P_ ev_stat *w, int revents)
1639	{	2710	{
1640	/* reset the one-second timer */	2711	/* reset the one-second timer */
1641	ev_timer_again (EV_A_ &timer);	2712	ev_timer_again (EV_A_ &timer);
1642	}	2713	}
1643		2714
1644	...	2715	...
1645	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2716	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1646	ev_stat_start (loop, &passwd);	2717	ev_stat_start (loop, &passwd);
1647	ev_timer_init (&timer, timer_cb, 0., 1.01);	2718	ev_timer_init (&timer, timer_cb, 0., 1.02);
1648		2719
1649		2720
1650	=head2 C<ev_idle> - when you've got nothing better to do...	2721	=head2 C<ev_idle> - when you've got nothing better to do...
1651		2722
1652	Idle watchers trigger events when no other events of the same or higher	2723	Idle watchers trigger events when no other events of the same or higher
1653	priority are pending (prepare, check and other idle watchers do not	2724	priority are pending (prepare, check and other idle watchers do not count
1654	count).	2725	as receiving "events").
1655		2726
1656	That is, as long as your process is busy handling sockets or timeouts	2727	That is, as long as your process is busy handling sockets or timeouts
1657	(or even signals, imagine) of the same or higher priority it will not be	2728	(or even signals, imagine) of the same or higher priority it will not be
1658	triggered. But when your process is idle (or only lower-priority watchers	2729	triggered. But when your process is idle (or only lower-priority watchers
1659	are pending), the idle watchers are being called once per event loop	2730	are pending), the idle watchers are being called once per event loop
…		…
1670		2741
1671	=head3 Watcher-Specific Functions and Data Members	2742	=head3 Watcher-Specific Functions and Data Members
1672		2743
1673	=over 4	2744	=over 4
1674		2745
1675	=item ev_idle_init (ev_signal *, callback)	2746	=item ev_idle_init (ev_idle *, callback)
1676		2747
1677	Initialises and configures the idle watcher - it has no parameters of any	2748	Initialises and configures the idle watcher - it has no parameters of any
1678	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2749	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1679	believe me.	2750	believe me.
1680		2751
…		…
1683	=head3 Examples	2754	=head3 Examples
1684		2755
1685	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2756	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1686	callback, free it. Also, use no error checking, as usual.	2757	callback, free it. Also, use no error checking, as usual.
1687		2758
1688	static void	2759	static void
1689	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2760	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1690	{	2761	{
1691	free (w);	2762	free (w);
1692	// now do something you wanted to do when the program has	2763	// now do something you wanted to do when the program has
1693	// no longer asnything immediate to do.	2764	// no longer anything immediate to do.
1694	}	2765	}
1695		2766
1696	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2767	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1697	ev_idle_init (idle_watcher, idle_cb);	2768	ev_idle_init (idle_watcher, idle_cb);
1698	ev_idle_start (loop, idle_cb);	2769	ev_idle_start (loop, idle_watcher);
1699		2770
1700		2771
1701	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2772	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1702		2773
1703	Prepare and check watchers are usually (but not always) used in tandem:	2774	Prepare and check watchers are usually (but not always) used in pairs:
1704	prepare watchers get invoked before the process blocks and check watchers	2775	prepare watchers get invoked before the process blocks and check watchers
1705	afterwards.	2776	afterwards.
1706		2777
1707	You I<must not> call C<ev_loop> or similar functions that enter	2778	You I<must not> call C<ev_run> or similar functions that enter
1708	the current event loop from either C<ev_prepare> or C<ev_check>	2779	the current event loop from either C<ev_prepare> or C<ev_check>
1709	watchers. Other loops than the current one are fine, however. The	2780	watchers. Other loops than the current one are fine, however. The
1710	rationale behind this is that you do not need to check for recursion in	2781	rationale behind this is that you do not need to check for recursion in
1711	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2782	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1712	C<ev_check> so if you have one watcher of each kind they will always be	2783	C<ev_check> so if you have one watcher of each kind they will always be
1713	called in pairs bracketing the blocking call.	2784	called in pairs bracketing the blocking call.
1714		2785
1715	Their main purpose is to integrate other event mechanisms into libev and	2786	Their main purpose is to integrate other event mechanisms into libev and
1716	their use is somewhat advanced. This could be used, for example, to track	2787	their use is somewhat advanced. They could be used, for example, to track
1717	variable changes, implement your own watchers, integrate net-snmp or a	2788	variable changes, implement your own watchers, integrate net-snmp or a
1718	coroutine library and lots more. They are also occasionally useful if	2789	coroutine library and lots more. They are also occasionally useful if
1719	you cache some data and want to flush it before blocking (for example,	2790	you cache some data and want to flush it before blocking (for example,
1720	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2791	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1721	watcher).	2792	watcher).
1722		2793
1723	This is done by examining in each prepare call which file descriptors need	2794	This is done by examining in each prepare call which file descriptors
1724	to be watched by the other library, registering C<ev_io> watchers for	2795	need to be watched by the other library, registering C<ev_io> watchers
1725	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2796	for them and starting an C<ev_timer> watcher for any timeouts (many
1726	provide just this functionality). Then, in the check watcher you check for	2797	libraries provide exactly this functionality). Then, in the check watcher,
1727	any events that occured (by checking the pending status of all watchers	2798	you check for any events that occurred (by checking the pending status
1728	and stopping them) and call back into the library. The I/O and timer	2799	of all watchers and stopping them) and call back into the library. The
1729	callbacks will never actually be called (but must be valid nevertheless,	2800	I/O and timer callbacks will never actually be called (but must be valid
1730	because you never know, you know?).	2801	nevertheless, because you never know, you know?).
1731		2802
1732	As another example, the Perl Coro module uses these hooks to integrate	2803	As another example, the Perl Coro module uses these hooks to integrate
1733	coroutines into libev programs, by yielding to other active coroutines	2804	coroutines into libev programs, by yielding to other active coroutines
1734	during each prepare and only letting the process block if no coroutines	2805	during each prepare and only letting the process block if no coroutines
1735	are ready to run (it's actually more complicated: it only runs coroutines	2806	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1738	loop from blocking if lower-priority coroutines are active, thus mapping	2809	loop from blocking if lower-priority coroutines are active, thus mapping
1739	low-priority coroutines to idle/background tasks).	2810	low-priority coroutines to idle/background tasks).
1740		2811
1741	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2812	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1742	priority, to ensure that they are being run before any other watchers	2813	priority, to ensure that they are being run before any other watchers
		2814	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2815
1743	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2816	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1744	too) should not activate ("feed") events into libev. While libev fully	2817	activate ("feed") events into libev. While libev fully supports this, they
1745	supports this, they will be called before other C<ev_check> watchers	2818	might get executed before other C<ev_check> watchers did their job. As
1746	did their job. As C<ev_check> watchers are often used to embed other	2819	C<ev_check> watchers are often used to embed other (non-libev) event
1747	(non-libev) event loops those other event loops might be in an unusable	2820	loops those other event loops might be in an unusable state until their
1748	state until their C<ev_check> watcher ran (always remind yourself to	2821	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1749	coexist peacefully with others).	2822	others).
1750		2823
1751	=head3 Watcher-Specific Functions and Data Members	2824	=head3 Watcher-Specific Functions and Data Members
1752		2825
1753	=over 4	2826	=over 4
1754		2827
…		…
1756		2829
1757	=item ev_check_init (ev_check *, callback)	2830	=item ev_check_init (ev_check *, callback)
1758		2831
1759	Initialises and configures the prepare or check watcher - they have no	2832	Initialises and configures the prepare or check watcher - they have no
1760	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2833	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1761	macros, but using them is utterly, utterly and completely pointless.	2834	macros, but using them is utterly, utterly, utterly and completely
		2835	pointless.
1762		2836
1763	=back	2837	=back
1764		2838
1765	=head3 Examples	2839	=head3 Examples
1766		2840
1767	There are a number of principal ways to embed other event loops or modules	2841	There are a number of principal ways to embed other event loops or modules
1768	into libev. Here are some ideas on how to include libadns into libev	2842	into libev. Here are some ideas on how to include libadns into libev
1769	(there is a Perl module named C<EV::ADNS> that does this, which you could	2843	(there is a Perl module named C<EV::ADNS> that does this, which you could
1770	use for an actually working example. Another Perl module named C<EV::Glib>	2844	use as a working example. Another Perl module named C<EV::Glib> embeds a
1771	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2845	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1772	into the Glib event loop).	2846	Glib event loop).
1773		2847
1774	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2848	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1775	and in a check watcher, destroy them and call into libadns. What follows	2849	and in a check watcher, destroy them and call into libadns. What follows
1776	is pseudo-code only of course. This requires you to either use a low	2850	is pseudo-code only of course. This requires you to either use a low
1777	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2851	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1778	the callbacks for the IO/timeout watchers might not have been called yet.	2852	the callbacks for the IO/timeout watchers might not have been called yet.
1779		2853
1780	static ev_io iow [nfd];	2854	static ev_io iow [nfd];
1781	static ev_timer tw;	2855	static ev_timer tw;
1782		2856
1783	static void	2857	static void
1784	io_cb (ev_loop *loop, ev_io *w, int revents)	2858	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1785	{	2859	{
1786	}	2860	}
1787		2861
1788	// create io watchers for each fd and a timer before blocking	2862	// create io watchers for each fd and a timer before blocking
1789	static void	2863	static void
1790	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2864	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1791	{	2865	{
1792	int timeout = 3600000;	2866	int timeout = 3600000;
1793	struct pollfd fds [nfd];	2867	struct pollfd fds [nfd];
1794	// actual code will need to loop here and realloc etc.	2868	// actual code will need to loop here and realloc etc.
1795	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2869	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1796		2870
1797	/* the callback is illegal, but won't be called as we stop during check */	2871	/* the callback is illegal, but won't be called as we stop during check */
1798	ev_timer_init (&tw, 0, timeout * 1e-3);	2872	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1799	ev_timer_start (loop, &tw);	2873	ev_timer_start (loop, &tw);
1800		2874
1801	// create one ev_io per pollfd	2875	// create one ev_io per pollfd
1802	for (int i = 0; i < nfd; ++i)	2876	for (int i = 0; i < nfd; ++i)
1803	{	2877	{
1804	ev_io_init (iow + i, io_cb, fds [i].fd,	2878	ev_io_init (iow + i, io_cb, fds [i].fd,
1805	((fds [i].events & POLLIN ? EV_READ : 0)	2879	((fds [i].events & POLLIN ? EV_READ : 0)
1806	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2880	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1807		2881
1808	fds [i].revents = 0;	2882	fds [i].revents = 0;
1809	ev_io_start (loop, iow + i);	2883	ev_io_start (loop, iow + i);
1810	}	2884	}
1811	}	2885	}
1812		2886
1813	// stop all watchers after blocking	2887	// stop all watchers after blocking
1814	static void	2888	static void
1815	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2889	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1816	{	2890	{
1817	ev_timer_stop (loop, &tw);	2891	ev_timer_stop (loop, &tw);
1818		2892
1819	for (int i = 0; i < nfd; ++i)	2893	for (int i = 0; i < nfd; ++i)
1820	{	2894	{
1821	// set the relevant poll flags	2895	// set the relevant poll flags
1822	// could also call adns_processreadable etc. here	2896	// could also call adns_processreadable etc. here
1823	struct pollfd *fd = fds + i;	2897	struct pollfd *fd = fds + i;
1824	int revents = ev_clear_pending (iow + i);	2898	int revents = ev_clear_pending (iow + i);
1825	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2899	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1826	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2900	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1827		2901
1828	// now stop the watcher	2902	// now stop the watcher
1829	ev_io_stop (loop, iow + i);	2903	ev_io_stop (loop, iow + i);
1830	}	2904	}
1831		2905
1832	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2906	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1833	}	2907	}
1834		2908
1835	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2909	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1836	in the prepare watcher and would dispose of the check watcher.	2910	in the prepare watcher and would dispose of the check watcher.
1837		2911
1838	Method 3: If the module to be embedded supports explicit event	2912	Method 3: If the module to be embedded supports explicit event
1839	notification (adns does), you can also make use of the actual watcher	2913	notification (libadns does), you can also make use of the actual watcher
1840	callbacks, and only destroy/create the watchers in the prepare watcher.	2914	callbacks, and only destroy/create the watchers in the prepare watcher.
1841		2915
1842	static void	2916	static void
1843	timer_cb (EV_P_ ev_timer *w, int revents)	2917	timer_cb (EV_P_ ev_timer *w, int revents)
1844	{	2918	{
1845	adns_state ads = (adns_state)w->data;	2919	adns_state ads = (adns_state)w->data;
1846	update_now (EV_A);	2920	update_now (EV_A);
1847		2921
1848	adns_processtimeouts (ads, &tv_now);	2922	adns_processtimeouts (ads, &tv_now);
1849	}	2923	}
1850		2924
1851	static void	2925	static void
1852	io_cb (EV_P_ ev_io *w, int revents)	2926	io_cb (EV_P_ ev_io *w, int revents)
1853	{	2927	{
1854	adns_state ads = (adns_state)w->data;	2928	adns_state ads = (adns_state)w->data;
1855	update_now (EV_A);	2929	update_now (EV_A);
1856		2930
1857	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2931	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1858	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2932	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1859	}	2933	}
1860		2934
1861	// do not ever call adns_afterpoll	2935	// do not ever call adns_afterpoll
1862		2936
1863	Method 4: Do not use a prepare or check watcher because the module you	2937	Method 4: Do not use a prepare or check watcher because the module you
1864	want to embed is too inflexible to support it. Instead, youc na override	2938	want to embed is not flexible enough to support it. Instead, you can
1865	their poll function. The drawback with this solution is that the main	2939	override their poll function. The drawback with this solution is that the
1866	loop is now no longer controllable by EV. The C<Glib::EV> module does	2940	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1867	this.	2941	this approach, effectively embedding EV as a client into the horrible
		2942	libglib event loop.
1868		2943
1869	static gint	2944	static gint
1870	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2945	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1871	{	2946	{
1872	int got_events = 0;	2947	int got_events = 0;
1873		2948
1874	for (n = 0; n < nfds; ++n)	2949	for (n = 0; n < nfds; ++n)
1875	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2950	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1876		2951
1877	if (timeout >= 0)	2952	if (timeout >= 0)
1878	// create/start timer	2953	// create/start timer
1879		2954
1880	// poll	2955	// poll
1881	ev_loop (EV_A_ 0);	2956	ev_run (EV_A_ 0);
1882		2957
1883	// stop timer again	2958	// stop timer again
1884	if (timeout >= 0)	2959	if (timeout >= 0)
1885	ev_timer_stop (EV_A_ &to);	2960	ev_timer_stop (EV_A_ &to);
1886		2961
1887	// stop io watchers again - their callbacks should have set	2962	// stop io watchers again - their callbacks should have set
1888	for (n = 0; n < nfds; ++n)	2963	for (n = 0; n < nfds; ++n)
1889	ev_io_stop (EV_A_ iow [n]);	2964	ev_io_stop (EV_A_ iow [n]);
1890		2965
1891	return got_events;	2966	return got_events;
1892	}	2967	}
1893		2968
1894		2969
1895	=head2 C<ev_embed> - when one backend isn't enough...	2970	=head2 C<ev_embed> - when one backend isn't enough...
1896		2971
1897	This is a rather advanced watcher type that lets you embed one event loop	2972	This is a rather advanced watcher type that lets you embed one event loop
…		…
1903	prioritise I/O.	2978	prioritise I/O.
1904		2979
1905	As an example for a bug workaround, the kqueue backend might only support	2980	As an example for a bug workaround, the kqueue backend might only support
1906	sockets on some platform, so it is unusable as generic backend, but you	2981	sockets on some platform, so it is unusable as generic backend, but you
1907	still want to make use of it because you have many sockets and it scales	2982	still want to make use of it because you have many sockets and it scales
1908	so nicely. In this case, you would create a kqueue-based loop and embed it	2983	so nicely. In this case, you would create a kqueue-based loop and embed
1909	into your default loop (which might use e.g. poll). Overall operation will	2984	it into your default loop (which might use e.g. poll). Overall operation
1910	be a bit slower because first libev has to poll and then call kevent, but	2985	will be a bit slower because first libev has to call C<poll> and then
1911	at least you can use both at what they are best.	2986	C<kevent>, but at least you can use both mechanisms for what they are
		2987	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1912		2988
1913	As for prioritising I/O: rarely you have the case where some fds have	2989	As for prioritising I/O: under rare circumstances you have the case where
1914	to be watched and handled very quickly (with low latency), and even	2990	some fds have to be watched and handled very quickly (with low latency),
1915	priorities and idle watchers might have too much overhead. In this case	2991	and even priorities and idle watchers might have too much overhead. In
1916	you would put all the high priority stuff in one loop and all the rest in	2992	this case you would put all the high priority stuff in one loop and all
1917	a second one, and embed the second one in the first.	2993	the rest in a second one, and embed the second one in the first.
1918		2994
1919	As long as the watcher is active, the callback will be invoked every time	2995	As long as the watcher is active, the callback will be invoked every
1920	there might be events pending in the embedded loop. The callback must then	2996	time there might be events pending in the embedded loop. The callback
1921	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2997	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1922	their callbacks (you could also start an idle watcher to give the embedded	2998	sweep and invoke their callbacks (the callback doesn't need to invoke the
1923	loop strictly lower priority for example). You can also set the callback	2999	C<ev_embed_sweep> function directly, it could also start an idle watcher
1924	to C<0>, in which case the embed watcher will automatically execute the	3000	to give the embedded loop strictly lower priority for example).
1925	embedded loop sweep.
1926		3001
1927	As long as the watcher is started it will automatically handle events. The	3002	You can also set the callback to C<0>, in which case the embed watcher
1928	callback will be invoked whenever some events have been handled. You can	3003	will automatically execute the embedded loop sweep whenever necessary.
1929	set the callback to C<0> to avoid having to specify one if you are not
1930	interested in that.
1931		3004
1932	Also, there have not currently been made special provisions for forking:	3005	Fork detection will be handled transparently while the C<ev_embed> watcher
1933	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3006	is active, i.e., the embedded loop will automatically be forked when the
1934	but you will also have to stop and restart any C<ev_embed> watchers	3007	embedding loop forks. In other cases, the user is responsible for calling
1935	yourself.	3008	C<ev_loop_fork> on the embedded loop.
1936		3009
1937	Unfortunately, not all backends are embeddable, only the ones returned by	3010	Unfortunately, not all backends are embeddable: only the ones returned by
1938	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3011	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1939	portable one.	3012	portable one.
1940		3013
1941	So when you want to use this feature you will always have to be prepared	3014	So when you want to use this feature you will always have to be prepared
1942	that you cannot get an embeddable loop. The recommended way to get around	3015	that you cannot get an embeddable loop. The recommended way to get around
1943	this is to have a separate variables for your embeddable loop, try to	3016	this is to have a separate variables for your embeddable loop, try to
1944	create it, and if that fails, use the normal loop for everything.	3017	create it, and if that fails, use the normal loop for everything.
1945		3018
		3019	=head3 C<ev_embed> and fork
		3020
		3021	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3022	automatically be applied to the embedded loop as well, so no special
		3023	fork handling is required in that case. When the watcher is not running,
		3024	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3025	as applicable.
		3026
1946	=head3 Watcher-Specific Functions and Data Members	3027	=head3 Watcher-Specific Functions and Data Members
1947		3028
1948	=over 4	3029	=over 4
1949		3030
1950	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3031	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
1953		3034
1954	Configures the watcher to embed the given loop, which must be	3035	Configures the watcher to embed the given loop, which must be
1955	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3036	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1956	invoked automatically, otherwise it is the responsibility of the callback	3037	invoked automatically, otherwise it is the responsibility of the callback
1957	to invoke it (it will continue to be called until the sweep has been done,	3038	to invoke it (it will continue to be called until the sweep has been done,
1958	if you do not want thta, you need to temporarily stop the embed watcher).	3039	if you do not want that, you need to temporarily stop the embed watcher).
1959		3040
1960	=item ev_embed_sweep (loop, ev_embed *)	3041	=item ev_embed_sweep (loop, ev_embed *)
1961		3042
1962	Make a single, non-blocking sweep over the embedded loop. This works	3043	Make a single, non-blocking sweep over the embedded loop. This works
1963	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3044	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1964	apropriate way for embedded loops.	3045	appropriate way for embedded loops.
1965		3046
1966	=item struct ev_loop *other [read-only]	3047	=item struct ev_loop *other [read-only]
1967		3048
1968	The embedded event loop.	3049	The embedded event loop.
1969		3050
…		…
1971		3052
1972	=head3 Examples	3053	=head3 Examples
1973		3054
1974	Example: Try to get an embeddable event loop and embed it into the default	3055	Example: Try to get an embeddable event loop and embed it into the default
1975	event loop. If that is not possible, use the default loop. The default	3056	event loop. If that is not possible, use the default loop. The default
1976	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	3057	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1977	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	3058	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1978	used).	3059	used).
1979		3060
1980	struct ev_loop *loop_hi = ev_default_init (0);	3061	struct ev_loop *loop_hi = ev_default_init (0);
1981	struct ev_loop *loop_lo = 0;	3062	struct ev_loop *loop_lo = 0;
1982	struct ev_embed embed;	3063	ev_embed embed;
1983		3064
1984	// see if there is a chance of getting one that works	3065	// see if there is a chance of getting one that works
1985	// (remember that a flags value of 0 means autodetection)	3066	// (remember that a flags value of 0 means autodetection)
1986	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3067	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1987	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3068	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1988	: 0;	3069	: 0;
1989		3070
1990	// if we got one, then embed it, otherwise default to loop_hi	3071	// if we got one, then embed it, otherwise default to loop_hi
1991	if (loop_lo)	3072	if (loop_lo)
1992	{	3073	{
1993	ev_embed_init (&embed, 0, loop_lo);	3074	ev_embed_init (&embed, 0, loop_lo);
1994	ev_embed_start (loop_hi, &embed);	3075	ev_embed_start (loop_hi, &embed);
1995	}	3076	}
1996	else	3077	else
1997	loop_lo = loop_hi;	3078	loop_lo = loop_hi;
1998		3079
1999	Example: Check if kqueue is available but not recommended and create	3080	Example: Check if kqueue is available but not recommended and create
2000	a kqueue backend for use with sockets (which usually work with any	3081	a kqueue backend for use with sockets (which usually work with any
2001	kqueue implementation). Store the kqueue/socket-only event loop in	3082	kqueue implementation). Store the kqueue/socket-only event loop in
2002	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3083	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2003		3084
2004	struct ev_loop *loop = ev_default_init (0);	3085	struct ev_loop *loop = ev_default_init (0);
2005	struct ev_loop *loop_socket = 0;	3086	struct ev_loop *loop_socket = 0;
2006	struct ev_embed embed;	3087	ev_embed embed;
2007		3088
2008	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3089	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2009	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3090	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2010	{	3091	{
2011	ev_embed_init (&embed, 0, loop_socket);	3092	ev_embed_init (&embed, 0, loop_socket);
2012	ev_embed_start (loop, &embed);	3093	ev_embed_start (loop, &embed);
2013	}	3094	}
2014		3095
2015	if (!loop_socket)	3096	if (!loop_socket)
2016	loop_socket = loop;	3097	loop_socket = loop;
2017		3098
2018	// now use loop_socket for all sockets, and loop for everything else	3099	// now use loop_socket for all sockets, and loop for everything else
2019		3100
2020		3101
2021	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3102	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2022		3103
2023	Fork watchers are called when a C<fork ()> was detected (usually because	3104	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2026	event loop blocks next and before C<ev_check> watchers are being called,	3107	event loop blocks next and before C<ev_check> watchers are being called,
2027	and only in the child after the fork. If whoever good citizen calling	3108	and only in the child after the fork. If whoever good citizen calling
2028	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3109	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2029	handlers will be invoked, too, of course.	3110	handlers will be invoked, too, of course.
2030		3111
		3112	=head3 The special problem of life after fork - how is it possible?
		3113
		3114	Most uses of C<fork()> consist of forking, then some simple calls to set
		3115	up/change the process environment, followed by a call to C<exec()>. This
		3116	sequence should be handled by libev without any problems.
		3117
		3118	This changes when the application actually wants to do event handling
		3119	in the child, or both parent in child, in effect "continuing" after the
		3120	fork.
		3121
		3122	The default mode of operation (for libev, with application help to detect
		3123	forks) is to duplicate all the state in the child, as would be expected
		3124	when I<either> the parent I<or> the child process continues.
		3125
		3126	When both processes want to continue using libev, then this is usually the
		3127	wrong result. In that case, usually one process (typically the parent) is
		3128	supposed to continue with all watchers in place as before, while the other
		3129	process typically wants to start fresh, i.e. without any active watchers.
		3130
		3131	The cleanest and most efficient way to achieve that with libev is to
		3132	simply create a new event loop, which of course will be "empty", and
		3133	use that for new watchers. This has the advantage of not touching more
		3134	memory than necessary, and thus avoiding the copy-on-write, and the
		3135	disadvantage of having to use multiple event loops (which do not support
		3136	signal watchers).
		3137
		3138	When this is not possible, or you want to use the default loop for
		3139	other reasons, then in the process that wants to start "fresh", call
		3140	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3141	Destroying the default loop will "orphan" (not stop) all registered
		3142	watchers, so you have to be careful not to execute code that modifies
		3143	those watchers. Note also that in that case, you have to re-register any
		3144	signal watchers.
		3145
2031	=head3 Watcher-Specific Functions and Data Members	3146	=head3 Watcher-Specific Functions and Data Members
2032		3147
2033	=over 4	3148	=over 4
2034		3149
2035	=item ev_fork_init (ev_signal *, callback)	3150	=item ev_fork_init (ev_fork *, callback)
2036		3151
2037	Initialises and configures the fork watcher - it has no parameters of any	3152	Initialises and configures the fork watcher - it has no parameters of any
2038	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3153	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2039	believe me.	3154	really.
2040		3155
2041	=back	3156	=back
2042		3157
2043		3158
		3159	=head2 C<ev_cleanup> - even the best things end
		3160
		3161	Cleanup watchers are called just before the event loop is being destroyed
		3162	by a call to C<ev_loop_destroy>.
		3163
		3164	While there is no guarantee that the event loop gets destroyed, cleanup
		3165	watchers provide a convenient method to install cleanup hooks for your
		3166	program, worker threads and so on - you just to make sure to destroy the
		3167	loop when you want them to be invoked.
		3168
		3169	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3170	all other watchers, they do not keep a reference to the event loop (which
		3171	makes a lot of sense if you think about it). Like all other watchers, you
		3172	can call libev functions in the callback, except C<ev_cleanup_start>.
		3173
		3174	=head3 Watcher-Specific Functions and Data Members
		3175
		3176	=over 4
		3177
		3178	=item ev_cleanup_init (ev_cleanup *, callback)
		3179
		3180	Initialises and configures the cleanup watcher - it has no parameters of
		3181	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3182	pointless, I assure you.
		3183
		3184	=back
		3185
		3186	Example: Register an atexit handler to destroy the default loop, so any
		3187	cleanup functions are called.
		3188
		3189	static void
		3190	program_exits (void)
		3191	{
		3192	ev_loop_destroy (EV_DEFAULT_UC);
		3193	}
		3194
		3195	...
		3196	atexit (program_exits);
		3197
		3198
		3199	=head2 C<ev_async> - how to wake up an event loop
		3200
		3201	In general, you cannot use an C<ev_loop> from multiple threads or other
		3202	asynchronous sources such as signal handlers (as opposed to multiple event
		3203	loops - those are of course safe to use in different threads).
		3204
		3205	Sometimes, however, you need to wake up an event loop you do not control,
		3206	for example because it belongs to another thread. This is what C<ev_async>
		3207	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3208	it by calling C<ev_async_send>, which is thread- and signal safe.
		3209
		3210	This functionality is very similar to C<ev_signal> watchers, as signals,
		3211	too, are asynchronous in nature, and signals, too, will be compressed
		3212	(i.e. the number of callback invocations may be less than the number of
		3213	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3214	of "global async watchers" by using a watcher on an otherwise unused
		3215	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3216	even without knowing which loop owns the signal.
		3217
		3218	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3219	just the default loop.
		3220
		3221	=head3 Queueing
		3222
		3223	C<ev_async> does not support queueing of data in any way. The reason
		3224	is that the author does not know of a simple (or any) algorithm for a
		3225	multiple-writer-single-reader queue that works in all cases and doesn't
		3226	need elaborate support such as pthreads or unportable memory access
		3227	semantics.
		3228
		3229	That means that if you want to queue data, you have to provide your own
		3230	queue. But at least I can tell you how to implement locking around your
		3231	queue:
		3232
		3233	=over 4
		3234
		3235	=item queueing from a signal handler context
		3236
		3237	To implement race-free queueing, you simply add to the queue in the signal
		3238	handler but you block the signal handler in the watcher callback. Here is
		3239	an example that does that for some fictitious SIGUSR1 handler:
		3240
		3241	static ev_async mysig;
		3242
		3243	static void
		3244	sigusr1_handler (void)
		3245	{
		3246	sometype data;
		3247
		3248	// no locking etc.
		3249	queue_put (data);
		3250	ev_async_send (EV_DEFAULT_ &mysig);
		3251	}
		3252
		3253	static void
		3254	mysig_cb (EV_P_ ev_async *w, int revents)
		3255	{
		3256	sometype data;
		3257	sigset_t block, prev;
		3258
		3259	sigemptyset (&block);
		3260	sigaddset (&block, SIGUSR1);
		3261	sigprocmask (SIG_BLOCK, &block, &prev);
		3262
		3263	while (queue_get (&data))
		3264	process (data);
		3265
		3266	if (sigismember (&prev, SIGUSR1)
		3267	sigprocmask (SIG_UNBLOCK, &block, 0);
		3268	}
		3269
		3270	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3271	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3272	either...).
		3273
		3274	=item queueing from a thread context
		3275
		3276	The strategy for threads is different, as you cannot (easily) block
		3277	threads but you can easily preempt them, so to queue safely you need to
		3278	employ a traditional mutex lock, such as in this pthread example:
		3279
		3280	static ev_async mysig;
		3281	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3282
		3283	static void
		3284	otherthread (void)
		3285	{
		3286	// only need to lock the actual queueing operation
		3287	pthread_mutex_lock (&mymutex);
		3288	queue_put (data);
		3289	pthread_mutex_unlock (&mymutex);
		3290
		3291	ev_async_send (EV_DEFAULT_ &mysig);
		3292	}
		3293
		3294	static void
		3295	mysig_cb (EV_P_ ev_async *w, int revents)
		3296	{
		3297	pthread_mutex_lock (&mymutex);
		3298
		3299	while (queue_get (&data))
		3300	process (data);
		3301
		3302	pthread_mutex_unlock (&mymutex);
		3303	}
		3304
		3305	=back
		3306
		3307
		3308	=head3 Watcher-Specific Functions and Data Members
		3309
		3310	=over 4
		3311
		3312	=item ev_async_init (ev_async *, callback)
		3313
		3314	Initialises and configures the async watcher - it has no parameters of any
		3315	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3316	trust me.
		3317
		3318	=item ev_async_send (loop, ev_async *)
		3319
		3320	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3321	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3322	returns.
		3323
		3324	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3325	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3326	embedding section below on what exactly this means).
		3327
		3328	Note that, as with other watchers in libev, multiple events might get
		3329	compressed into a single callback invocation (another way to look at this
		3330	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3331	reset when the event loop detects that).
		3332
		3333	This call incurs the overhead of a system call only once per event loop
		3334	iteration, so while the overhead might be noticeable, it doesn't apply to
		3335	repeated calls to C<ev_async_send> for the same event loop.
		3336
		3337	=item bool = ev_async_pending (ev_async *)
		3338
		3339	Returns a non-zero value when C<ev_async_send> has been called on the
		3340	watcher but the event has not yet been processed (or even noted) by the
		3341	event loop.
		3342
		3343	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3344	the loop iterates next and checks for the watcher to have become active,
		3345	it will reset the flag again. C<ev_async_pending> can be used to very
		3346	quickly check whether invoking the loop might be a good idea.
		3347
		3348	Not that this does I<not> check whether the watcher itself is pending,
		3349	only whether it has been requested to make this watcher pending: there
		3350	is a time window between the event loop checking and resetting the async
		3351	notification, and the callback being invoked.
		3352
		3353	=back
		3354
		3355
2044	=head1 OTHER FUNCTIONS	3356	=head1 OTHER FUNCTIONS
2045		3357
2046	There are some other functions of possible interest. Described. Here. Now.	3358	There are some other functions of possible interest. Described. Here. Now.
2047		3359
2048	=over 4	3360	=over 4
2049		3361
2050	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3362	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2051		3363
2052	This function combines a simple timer and an I/O watcher, calls your	3364	This function combines a simple timer and an I/O watcher, calls your
2053	callback on whichever event happens first and automatically stop both	3365	callback on whichever event happens first and automatically stops both
2054	watchers. This is useful if you want to wait for a single event on an fd	3366	watchers. This is useful if you want to wait for a single event on an fd
2055	or timeout without having to allocate/configure/start/stop/free one or	3367	or timeout without having to allocate/configure/start/stop/free one or
2056	more watchers yourself.	3368	more watchers yourself.
2057		3369
2058	If C<fd> is less than 0, then no I/O watcher will be started and events	3370	If C<fd> is less than 0, then no I/O watcher will be started and the
2059	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3371	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2060	C<events> set will be craeted and started.	3372	the given C<fd> and C<events> set will be created and started.
2061		3373
2062	If C<timeout> is less than 0, then no timeout watcher will be	3374	If C<timeout> is less than 0, then no timeout watcher will be
2063	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3375	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2064	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3376	repeat = 0) will be started. C<0> is a valid timeout.
2065	dubious value.
2066		3377
2067	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3378	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2068	passed an C<revents> set like normal event callbacks (a combination of	3379	passed an C<revents> set like normal event callbacks (a combination of
2069	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3380	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2070	value passed to C<ev_once>:	3381	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3382	a timeout and an io event at the same time - you probably should give io
		3383	events precedence.
2071		3384
		3385	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3386
2072	static void stdin_ready (int revents, void *arg)	3387	static void stdin_ready (int revents, void *arg)
2073	{	3388	{
2074	if (revents & EV_TIMEOUT)
2075	/* doh, nothing entered */;
2076	else if (revents & EV_READ)	3389	if (revents & EV_READ)
2077	/* stdin might have data for us, joy! */;	3390	/* stdin might have data for us, joy! */;
		3391	else if (revents & EV_TIMER)
		3392	/* doh, nothing entered */;
2078	}	3393	}
2079		3394
2080	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3395	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2081		3396
2082	=item ev_feed_event (ev_loop *, watcher *, int revents)
2083
2084	Feeds the given event set into the event loop, as if the specified event
2085	had happened for the specified watcher (which must be a pointer to an
2086	initialised but not necessarily started event watcher).
2087
2088	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3397	=item ev_feed_fd_event (loop, int fd, int revents)
2089		3398
2090	Feed an event on the given fd, as if a file descriptor backend detected	3399	Feed an event on the given fd, as if a file descriptor backend detected
2091	the given events it.	3400	the given events it.
2092		3401
2093	=item ev_feed_signal_event (ev_loop *loop, int signum)	3402	=item ev_feed_signal_event (loop, int signum)
2094		3403
2095	Feed an event as if the given signal occured (C<loop> must be the default	3404	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2096	loop!).	3405	which is async-safe.
2097		3406
2098	=back	3407	=back
		3408
		3409
		3410	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3411
		3412	This section explains some common idioms that are not immediately
		3413	obvious. Note that examples are sprinkled over the whole manual, and this
		3414	section only contains stuff that wouldn't fit anywhere else.
		3415
		3416	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3417
		3418	Each watcher has, by default, a C<void *data> member that you can read
		3419	or modify at any time: libev will completely ignore it. This can be used
		3420	to associate arbitrary data with your watcher. If you need more data and
		3421	don't want to allocate memory separately and store a pointer to it in that
		3422	data member, you can also "subclass" the watcher type and provide your own
		3423	data:
		3424
		3425	struct my_io
		3426	{
		3427	ev_io io;
		3428	int otherfd;
		3429	void *somedata;
		3430	struct whatever *mostinteresting;
		3431	};
		3432
		3433	...
		3434	struct my_io w;
		3435	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3436
		3437	And since your callback will be called with a pointer to the watcher, you
		3438	can cast it back to your own type:
		3439
		3440	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3441	{
		3442	struct my_io *w = (struct my_io *)w_;
		3443	...
		3444	}
		3445
		3446	More interesting and less C-conformant ways of casting your callback
		3447	function type instead have been omitted.
		3448
		3449	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3450
		3451	Another common scenario is to use some data structure with multiple
		3452	embedded watchers, in effect creating your own watcher that combines
		3453	multiple libev event sources into one "super-watcher":
		3454
		3455	struct my_biggy
		3456	{
		3457	int some_data;
		3458	ev_timer t1;
		3459	ev_timer t2;
		3460	}
		3461
		3462	In this case getting the pointer to C<my_biggy> is a bit more
		3463	complicated: Either you store the address of your C<my_biggy> struct in
		3464	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3465	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3466	real programmers):
		3467
		3468	#include <stddef.h>
		3469
		3470	static void
		3471	t1_cb (EV_P_ ev_timer *w, int revents)
		3472	{
		3473	struct my_biggy big = (struct my_biggy *)
		3474	(((char *)w) - offsetof (struct my_biggy, t1));
		3475	}
		3476
		3477	static void
		3478	t2_cb (EV_P_ ev_timer *w, int revents)
		3479	{
		3480	struct my_biggy big = (struct my_biggy *)
		3481	(((char *)w) - offsetof (struct my_biggy, t2));
		3482	}
		3483
		3484	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3485
		3486	Often (especially in GUI toolkits) there are places where you have
		3487	I<modal> interaction, which is most easily implemented by recursively
		3488	invoking C<ev_run>.
		3489
		3490	This brings the problem of exiting - a callback might want to finish the
		3491	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3492	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3493	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3494	other combination: In these cases, C<ev_break> will not work alone.
		3495
		3496	The solution is to maintain "break this loop" variable for each C<ev_run>
		3497	invocation, and use a loop around C<ev_run> until the condition is
		3498	triggered, using C<EVRUN_ONCE>:
		3499
		3500	// main loop
		3501	int exit_main_loop = 0;
		3502
		3503	while (!exit_main_loop)
		3504	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3505
		3506	// in a model watcher
		3507	int exit_nested_loop = 0;
		3508
		3509	while (!exit_nested_loop)
		3510	ev_run (EV_A_ EVRUN_ONCE);
		3511
		3512	To exit from any of these loops, just set the corresponding exit variable:
		3513
		3514	// exit modal loop
		3515	exit_nested_loop = 1;
		3516
		3517	// exit main program, after modal loop is finished
		3518	exit_main_loop = 1;
		3519
		3520	// exit both
		3521	exit_main_loop = exit_nested_loop = 1;
		3522
		3523	=head2 THREAD LOCKING EXAMPLE
		3524
		3525	Here is a fictitious example of how to run an event loop in a different
		3526	thread from where callbacks are being invoked and watchers are
		3527	created/added/removed.
		3528
		3529	For a real-world example, see the C<EV::Loop::Async> perl module,
		3530	which uses exactly this technique (which is suited for many high-level
		3531	languages).
		3532
		3533	The example uses a pthread mutex to protect the loop data, a condition
		3534	variable to wait for callback invocations, an async watcher to notify the
		3535	event loop thread and an unspecified mechanism to wake up the main thread.
		3536
		3537	First, you need to associate some data with the event loop:
		3538
		3539	typedef struct {
		3540	mutex_t lock; /* global loop lock */
		3541	ev_async async_w;
		3542	thread_t tid;
		3543	cond_t invoke_cv;
		3544	} userdata;
		3545
		3546	void prepare_loop (EV_P)
		3547	{
		3548	// for simplicity, we use a static userdata struct.
		3549	static userdata u;
		3550
		3551	ev_async_init (&u->async_w, async_cb);
		3552	ev_async_start (EV_A_ &u->async_w);
		3553
		3554	pthread_mutex_init (&u->lock, 0);
		3555	pthread_cond_init (&u->invoke_cv, 0);
		3556
		3557	// now associate this with the loop
		3558	ev_set_userdata (EV_A_ u);
		3559	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3560	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3561
		3562	// then create the thread running ev_run
		3563	pthread_create (&u->tid, 0, l_run, EV_A);
		3564	}
		3565
		3566	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3567	solely to wake up the event loop so it takes notice of any new watchers
		3568	that might have been added:
		3569
		3570	static void
		3571	async_cb (EV_P_ ev_async *w, int revents)
		3572	{
		3573	// just used for the side effects
		3574	}
		3575
		3576	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3577	protecting the loop data, respectively.
		3578
		3579	static void
		3580	l_release (EV_P)
		3581	{
		3582	userdata *u = ev_userdata (EV_A);
		3583	pthread_mutex_unlock (&u->lock);
		3584	}
		3585
		3586	static void
		3587	l_acquire (EV_P)
		3588	{
		3589	userdata *u = ev_userdata (EV_A);
		3590	pthread_mutex_lock (&u->lock);
		3591	}
		3592
		3593	The event loop thread first acquires the mutex, and then jumps straight
		3594	into C<ev_run>:
		3595
		3596	void *
		3597	l_run (void *thr_arg)
		3598	{
		3599	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3600
		3601	l_acquire (EV_A);
		3602	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3603	ev_run (EV_A_ 0);
		3604	l_release (EV_A);
		3605
		3606	return 0;
		3607	}
		3608
		3609	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3610	signal the main thread via some unspecified mechanism (signals? pipe
		3611	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3612	have been called (in a while loop because a) spurious wakeups are possible
		3613	and b) skipping inter-thread-communication when there are no pending
		3614	watchers is very beneficial):
		3615
		3616	static void
		3617	l_invoke (EV_P)
		3618	{
		3619	userdata *u = ev_userdata (EV_A);
		3620
		3621	while (ev_pending_count (EV_A))
		3622	{
		3623	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3624	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3625	}
		3626	}
		3627
		3628	Now, whenever the main thread gets told to invoke pending watchers, it
		3629	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3630	thread to continue:
		3631
		3632	static void
		3633	real_invoke_pending (EV_P)
		3634	{
		3635	userdata *u = ev_userdata (EV_A);
		3636
		3637	pthread_mutex_lock (&u->lock);
		3638	ev_invoke_pending (EV_A);
		3639	pthread_cond_signal (&u->invoke_cv);
		3640	pthread_mutex_unlock (&u->lock);
		3641	}
		3642
		3643	Whenever you want to start/stop a watcher or do other modifications to an
		3644	event loop, you will now have to lock:
		3645
		3646	ev_timer timeout_watcher;
		3647	userdata *u = ev_userdata (EV_A);
		3648
		3649	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3650
		3651	pthread_mutex_lock (&u->lock);
		3652	ev_timer_start (EV_A_ &timeout_watcher);
		3653	ev_async_send (EV_A_ &u->async_w);
		3654	pthread_mutex_unlock (&u->lock);
		3655
		3656	Note that sending the C<ev_async> watcher is required because otherwise
		3657	an event loop currently blocking in the kernel will have no knowledge
		3658	about the newly added timer. By waking up the loop it will pick up any new
		3659	watchers in the next event loop iteration.
		3660
		3661	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3662
		3663	While the overhead of a callback that e.g. schedules a thread is small, it
		3664	is still an overhead. If you embed libev, and your main usage is with some
		3665	kind of threads or coroutines, you might want to customise libev so that
		3666	doesn't need callbacks anymore.
		3667
		3668	Imagine you have coroutines that you can switch to using a function
		3669	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3670	and that due to some magic, the currently active coroutine is stored in a
		3671	global called C<current_coro>. Then you can build your own "wait for libev
		3672	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3673	the differing C<;> conventions):
		3674
		3675	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3676	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3677
		3678	That means instead of having a C callback function, you store the
		3679	coroutine to switch to in each watcher, and instead of having libev call
		3680	your callback, you instead have it switch to that coroutine.
		3681
		3682	A coroutine might now wait for an event with a function called
		3683	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3684	matter when, or whether the watcher is active or not when this function is
		3685	called):
		3686
		3687	void
		3688	wait_for_event (ev_watcher *w)
		3689	{
		3690	ev_cb_set (w) = current_coro;
		3691	switch_to (libev_coro);
		3692	}
		3693
		3694	That basically suspends the coroutine inside C<wait_for_event> and
		3695	continues the libev coroutine, which, when appropriate, switches back to
		3696	this or any other coroutine. I am sure if you sue this your own :)
		3697
		3698	You can do similar tricks if you have, say, threads with an event queue -
		3699	instead of storing a coroutine, you store the queue object and instead of
		3700	switching to a coroutine, you push the watcher onto the queue and notify
		3701	any waiters.
		3702
		3703	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3704	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3705
		3706	// my_ev.h
		3707	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3708	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3709	#include "../libev/ev.h"
		3710
		3711	// my_ev.c
		3712	#define EV_H "my_ev.h"
		3713	#include "../libev/ev.c"
		3714
		3715	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3716	F<my_ev.c> into your project. When properly specifying include paths, you
		3717	can even use F<ev.h> as header file name directly.
2099		3718
2100		3719
2101	=head1 LIBEVENT EMULATION	3720	=head1 LIBEVENT EMULATION
2102		3721
2103	Libev offers a compatibility emulation layer for libevent. It cannot	3722	Libev offers a compatibility emulation layer for libevent. It cannot
2104	emulate the internals of libevent, so here are some usage hints:	3723	emulate the internals of libevent, so here are some usage hints:
2105		3724
2106	=over 4	3725	=over 4
		3726
		3727	=item * Only the libevent-1.4.1-beta API is being emulated.
		3728
		3729	This was the newest libevent version available when libev was implemented,
		3730	and is still mostly unchanged in 2010.
2107		3731
2108	=item * Use it by including <event.h>, as usual.	3732	=item * Use it by including <event.h>, as usual.
2109		3733
2110	=item * The following members are fully supported: ev_base, ev_callback,	3734	=item * The following members are fully supported: ev_base, ev_callback,
2111	ev_arg, ev_fd, ev_res, ev_events.	3735	ev_arg, ev_fd, ev_res, ev_events.
…		…
2116		3740
2117	=item * Priorities are not currently supported. Initialising priorities	3741	=item * Priorities are not currently supported. Initialising priorities
2118	will fail and all watchers will have the same priority, even though there	3742	will fail and all watchers will have the same priority, even though there
2119	is an ev_pri field.	3743	is an ev_pri field.
2120		3744
		3745	=item * In libevent, the last base created gets the signals, in libev, the
		3746	base that registered the signal gets the signals.
		3747
2121	=item * Other members are not supported.	3748	=item * Other members are not supported.
2122		3749
2123	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3750	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2124	to use the libev header file and library.	3751	to use the libev header file and library.
2125		3752
2126	=back	3753	=back
2127		3754
2128	=head1 C++ SUPPORT	3755	=head1 C++ SUPPORT
2129		3756
2130	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3757	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2131	you to use some convinience methods to start/stop watchers and also change	3758	you to use some convenience methods to start/stop watchers and also change
2132	the callback model to a model using method callbacks on objects.	3759	the callback model to a model using method callbacks on objects.
2133		3760
2134	To use it,	3761	To use it,
2135		3762
2136	#include <ev++.h>	3763	#include <ev++.h>
2137		3764
2138	This automatically includes F<ev.h> and puts all of its definitions (many	3765	This automatically includes F<ev.h> and puts all of its definitions (many
2139	of them macros) into the global namespace. All C++ specific things are	3766	of them macros) into the global namespace. All C++ specific things are
2140	put into the C<ev> namespace. It should support all the same embedding	3767	put into the C<ev> namespace. It should support all the same embedding
2141	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3768	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2143	Care has been taken to keep the overhead low. The only data member the C++	3770	Care has been taken to keep the overhead low. The only data member the C++
2144	classes add (compared to plain C-style watchers) is the event loop pointer	3771	classes add (compared to plain C-style watchers) is the event loop pointer
2145	that the watcher is associated with (or no additional members at all if	3772	that the watcher is associated with (or no additional members at all if
2146	you disable C<EV_MULTIPLICITY> when embedding libev).	3773	you disable C<EV_MULTIPLICITY> when embedding libev).
2147		3774
2148	Currently, functions, and static and non-static member functions can be	3775	Currently, functions, static and non-static member functions and classes
2149	used as callbacks. Other types should be easy to add as long as they only	3776	with C<operator ()> can be used as callbacks. Other types should be easy
2150	need one additional pointer for context. If you need support for other	3777	to add as long as they only need one additional pointer for context. If
2151	types of functors please contact the author (preferably after implementing	3778	you need support for other types of functors please contact the author
2152	it).	3779	(preferably after implementing it).
2153		3780
2154	Here is a list of things available in the C<ev> namespace:	3781	Here is a list of things available in the C<ev> namespace:
2155		3782
2156	=over 4	3783	=over 4
2157		3784
…		…
2175		3802
2176	=over 4	3803	=over 4
2177		3804
2178	=item ev::TYPE::TYPE ()	3805	=item ev::TYPE::TYPE ()
2179		3806
2180	=item ev::TYPE::TYPE (struct ev_loop *)	3807	=item ev::TYPE::TYPE (loop)
2181		3808
2182	=item ev::TYPE::~TYPE	3809	=item ev::TYPE::~TYPE
2183		3810
2184	The constructor (optionally) takes an event loop to associate the watcher	3811	The constructor (optionally) takes an event loop to associate the watcher
2185	with. If it is omitted, it will use C<EV_DEFAULT>.	3812	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2208	your compiler is good :), then the method will be fully inlined into the	3835	your compiler is good :), then the method will be fully inlined into the
2209	thunking function, making it as fast as a direct C callback.	3836	thunking function, making it as fast as a direct C callback.
2210		3837
2211	Example: simple class declaration and watcher initialisation	3838	Example: simple class declaration and watcher initialisation
2212		3839
2213	struct myclass	3840	struct myclass
2214	{	3841	{
2215	void io_cb (ev::io &w, int revents) { }	3842	void io_cb (ev::io &w, int revents) { }
2216	}	3843	}
2217		3844
2218	myclass obj;	3845	myclass obj;
2219	ev::io iow;	3846	ev::io iow;
2220	iow.set <myclass, &myclass::io_cb> (&obj);	3847	iow.set <myclass, &myclass::io_cb> (&obj);
		3848
		3849	=item w->set (object *)
		3850
		3851	This is a variation of a method callback - leaving out the method to call
		3852	will default the method to C<operator ()>, which makes it possible to use
		3853	functor objects without having to manually specify the C<operator ()> all
		3854	the time. Incidentally, you can then also leave out the template argument
		3855	list.
		3856
		3857	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3858	int revents)>.
		3859
		3860	See the method-C<set> above for more details.
		3861
		3862	Example: use a functor object as callback.
		3863
		3864	struct myfunctor
		3865	{
		3866	void operator() (ev::io &w, int revents)
		3867	{
		3868	...
		3869	}
		3870	}
		3871
		3872	myfunctor f;
		3873
		3874	ev::io w;
		3875	w.set (&f);
2221		3876
2222	=item w->set<function> (void *data = 0)	3877	=item w->set<function> (void *data = 0)
2223		3878
2224	Also sets a callback, but uses a static method or plain function as	3879	Also sets a callback, but uses a static method or plain function as
2225	callback. The optional C<data> argument will be stored in the watcher's	3880	callback. The optional C<data> argument will be stored in the watcher's
…		…
2227		3882
2228	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3883	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2229		3884
2230	See the method-C<set> above for more details.	3885	See the method-C<set> above for more details.
2231		3886
2232	Example:	3887	Example: Use a plain function as callback.
2233		3888
2234	static void io_cb (ev::io &w, int revents) { }	3889	static void io_cb (ev::io &w, int revents) { }
2235	iow.set <io_cb> ();	3890	iow.set <io_cb> ();
2236		3891
2237	=item w->set (struct ev_loop *)	3892	=item w->set (loop)
2238		3893
2239	Associates a different C<struct ev_loop> with this watcher. You can only	3894	Associates a different C<struct ev_loop> with this watcher. You can only
2240	do this when the watcher is inactive (and not pending either).	3895	do this when the watcher is inactive (and not pending either).
2241		3896
2242	=item w->set ([args])	3897	=item w->set ([arguments])
2243		3898
2244	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3899	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2245	called at least once. Unlike the C counterpart, an active watcher gets	3900	method or a suitable start method must be called at least once. Unlike the
2246	automatically stopped and restarted when reconfiguring it with this	3901	C counterpart, an active watcher gets automatically stopped and restarted
2247	method.	3902	when reconfiguring it with this method.
2248		3903
2249	=item w->start ()	3904	=item w->start ()
2250		3905
2251	Starts the watcher. Note that there is no C<loop> argument, as the	3906	Starts the watcher. Note that there is no C<loop> argument, as the
2252	constructor already stores the event loop.	3907	constructor already stores the event loop.
2253		3908
		3909	=item w->start ([arguments])
		3910
		3911	Instead of calling C<set> and C<start> methods separately, it is often
		3912	convenient to wrap them in one call. Uses the same type of arguments as
		3913	the configure C<set> method of the watcher.
		3914
2254	=item w->stop ()	3915	=item w->stop ()
2255		3916
2256	Stops the watcher if it is active. Again, no C<loop> argument.	3917	Stops the watcher if it is active. Again, no C<loop> argument.
2257		3918
2258	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3919	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2270		3931
2271	=back	3932	=back
2272		3933
2273	=back	3934	=back
2274		3935
2275	Example: Define a class with an IO and idle watcher, start one of them in	3936	Example: Define a class with two I/O and idle watchers, start the I/O
2276	the constructor.	3937	watchers in the constructor.
2277		3938
2278	class myclass	3939	class myclass
2279	{	3940	{
2280	ev_io io; void io_cb (ev::io &w, int revents);	3941	ev::io io ; void io_cb (ev::io &w, int revents);
		3942	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2281	ev_idle idle void idle_cb (ev::idle &w, int revents);	3943	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2282		3944
2283	myclass ();	3945	myclass (int fd)
2284	}	3946	{
2285
2286	myclass::myclass (int fd)
2287	{
2288	io .set <myclass, &myclass::io_cb > (this);	3947	io .set <myclass, &myclass::io_cb > (this);
		3948	io2 .set <myclass, &myclass::io2_cb > (this);
2289	idle.set <myclass, &myclass::idle_cb> (this);	3949	idle.set <myclass, &myclass::idle_cb> (this);
2290		3950
2291	io.start (fd, ev::READ);	3951	io.set (fd, ev::WRITE); // configure the watcher
		3952	io.start (); // start it whenever convenient
		3953
		3954	io2.start (fd, ev::READ); // set + start in one call
		3955	}
2292	}	3956	};
		3957
		3958
		3959	=head1 OTHER LANGUAGE BINDINGS
		3960
		3961	Libev does not offer other language bindings itself, but bindings for a
		3962	number of languages exist in the form of third-party packages. If you know
		3963	any interesting language binding in addition to the ones listed here, drop
		3964	me a note.
		3965
		3966	=over 4
		3967
		3968	=item Perl
		3969
		3970	The EV module implements the full libev API and is actually used to test
		3971	libev. EV is developed together with libev. Apart from the EV core module,
		3972	there are additional modules that implement libev-compatible interfaces
		3973	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3974	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3975	and C<EV::Glib>).
		3976
		3977	It can be found and installed via CPAN, its homepage is at
		3978	L<http://software.schmorp.de/pkg/EV>.
		3979
		3980	=item Python
		3981
		3982	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3983	seems to be quite complete and well-documented.
		3984
		3985	=item Ruby
		3986
		3987	Tony Arcieri has written a ruby extension that offers access to a subset
		3988	of the libev API and adds file handle abstractions, asynchronous DNS and
		3989	more on top of it. It can be found via gem servers. Its homepage is at
		3990	L<http://rev.rubyforge.org/>.
		3991
		3992	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3993	makes rev work even on mingw.
		3994
		3995	=item Haskell
		3996
		3997	A haskell binding to libev is available at
		3998	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3999
		4000	=item D
		4001
		4002	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4003	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		4004
		4005	=item Ocaml
		4006
		4007	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4008	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4009
		4010	=item Lua
		4011
		4012	Brian Maher has written a partial interface to libev for lua (at the
		4013	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4014	L<http://github.com/brimworks/lua-ev>.
		4015
		4016	=back
2293		4017
2294		4018
2295	=head1 MACRO MAGIC	4019	=head1 MACRO MAGIC
2296		4020
2297	Libev can be compiled with a variety of options, the most fundamantal	4021	Libev can be compiled with a variety of options, the most fundamental
2298	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4022	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2299	functions and callbacks have an initial C<struct ev_loop *> argument.	4023	functions and callbacks have an initial C<struct ev_loop *> argument.
2300		4024
2301	To make it easier to write programs that cope with either variant, the	4025	To make it easier to write programs that cope with either variant, the
2302	following macros are defined:	4026	following macros are defined:
…		…
2307		4031
2308	This provides the loop I<argument> for functions, if one is required ("ev	4032	This provides the loop I<argument> for functions, if one is required ("ev
2309	loop argument"). The C<EV_A> form is used when this is the sole argument,	4033	loop argument"). The C<EV_A> form is used when this is the sole argument,
2310	C<EV_A_> is used when other arguments are following. Example:	4034	C<EV_A_> is used when other arguments are following. Example:
2311		4035
2312	ev_unref (EV_A);	4036	ev_unref (EV_A);
2313	ev_timer_add (EV_A_ watcher);	4037	ev_timer_add (EV_A_ watcher);
2314	ev_loop (EV_A_ 0);	4038	ev_run (EV_A_ 0);
2315		4039
2316	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4040	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2317	which is often provided by the following macro.	4041	which is often provided by the following macro.
2318		4042
2319	=item C<EV_P>, C<EV_P_>	4043	=item C<EV_P>, C<EV_P_>
2320		4044
2321	This provides the loop I<parameter> for functions, if one is required ("ev	4045	This provides the loop I<parameter> for functions, if one is required ("ev
2322	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4046	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2323	C<EV_P_> is used when other parameters are following. Example:	4047	C<EV_P_> is used when other parameters are following. Example:
2324		4048
2325	// this is how ev_unref is being declared	4049	// this is how ev_unref is being declared
2326	static void ev_unref (EV_P);	4050	static void ev_unref (EV_P);
2327		4051
2328	// this is how you can declare your typical callback	4052	// this is how you can declare your typical callback
2329	static void cb (EV_P_ ev_timer *w, int revents)	4053	static void cb (EV_P_ ev_timer *w, int revents)
2330		4054
2331	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4055	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2332	suitable for use with C<EV_A>.	4056	suitable for use with C<EV_A>.
2333		4057
2334	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4058	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2335		4059
2336	Similar to the other two macros, this gives you the value of the default	4060	Similar to the other two macros, this gives you the value of the default
2337	loop, if multiple loops are supported ("ev loop default").	4061	loop, if multiple loops are supported ("ev loop default").
		4062
		4063	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4064
		4065	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4066	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4067	is undefined when the default loop has not been initialised by a previous
		4068	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4069
		4070	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4071	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2338		4072
2339	=back	4073	=back
2340		4074
2341	Example: Declare and initialise a check watcher, utilising the above	4075	Example: Declare and initialise a check watcher, utilising the above
2342	macros so it will work regardless of whether multiple loops are supported	4076	macros so it will work regardless of whether multiple loops are supported
2343	or not.	4077	or not.
2344		4078
2345	static void	4079	static void
2346	check_cb (EV_P_ ev_timer *w, int revents)	4080	check_cb (EV_P_ ev_timer *w, int revents)
2347	{	4081	{
2348	ev_check_stop (EV_A_ w);	4082	ev_check_stop (EV_A_ w);
2349	}	4083	}
2350		4084
2351	ev_check check;	4085	ev_check check;
2352	ev_check_init (&check, check_cb);	4086	ev_check_init (&check, check_cb);
2353	ev_check_start (EV_DEFAULT_ &check);	4087	ev_check_start (EV_DEFAULT_ &check);
2354	ev_loop (EV_DEFAULT_ 0);	4088	ev_run (EV_DEFAULT_ 0);
2355		4089
2356	=head1 EMBEDDING	4090	=head1 EMBEDDING
2357		4091
2358	Libev can (and often is) directly embedded into host	4092	Libev can (and often is) directly embedded into host
2359	applications. Examples of applications that embed it include the Deliantra	4093	applications. Examples of applications that embed it include the Deliantra
…		…
2366	libev somewhere in your source tree).	4100	libev somewhere in your source tree).
2367		4101
2368	=head2 FILESETS	4102	=head2 FILESETS
2369		4103
2370	Depending on what features you need you need to include one or more sets of files	4104	Depending on what features you need you need to include one or more sets of files
2371	in your app.	4105	in your application.
2372		4106
2373	=head3 CORE EVENT LOOP	4107	=head3 CORE EVENT LOOP
2374		4108
2375	To include only the libev core (all the C<ev_*> functions), with manual	4109	To include only the libev core (all the C<ev_*> functions), with manual
2376	configuration (no autoconf):	4110	configuration (no autoconf):
2377		4111
2378	#define EV_STANDALONE 1	4112	#define EV_STANDALONE 1
2379	#include "ev.c"	4113	#include "ev.c"
2380		4114
2381	This will automatically include F<ev.h>, too, and should be done in a	4115	This will automatically include F<ev.h>, too, and should be done in a
2382	single C source file only to provide the function implementations. To use	4116	single C source file only to provide the function implementations. To use
2383	it, do the same for F<ev.h> in all files wishing to use this API (best	4117	it, do the same for F<ev.h> in all files wishing to use this API (best
2384	done by writing a wrapper around F<ev.h> that you can include instead and	4118	done by writing a wrapper around F<ev.h> that you can include instead and
2385	where you can put other configuration options):	4119	where you can put other configuration options):
2386		4120
2387	#define EV_STANDALONE 1	4121	#define EV_STANDALONE 1
2388	#include "ev.h"	4122	#include "ev.h"
2389		4123
2390	Both header files and implementation files can be compiled with a C++	4124	Both header files and implementation files can be compiled with a C++
2391	compiler (at least, thats a stated goal, and breakage will be treated	4125	compiler (at least, that's a stated goal, and breakage will be treated
2392	as a bug).	4126	as a bug).
2393		4127
2394	You need the following files in your source tree, or in a directory	4128	You need the following files in your source tree, or in a directory
2395	in your include path (e.g. in libev/ when using -Ilibev):	4129	in your include path (e.g. in libev/ when using -Ilibev):
2396		4130
2397	ev.h	4131	ev.h
2398	ev.c	4132	ev.c
2399	ev_vars.h	4133	ev_vars.h
2400	ev_wrap.h	4134	ev_wrap.h
2401		4135
2402	ev_win32.c required on win32 platforms only	4136	ev_win32.c required on win32 platforms only
2403		4137
2404	ev_select.c only when select backend is enabled (which is enabled by default)	4138	ev_select.c only when select backend is enabled (which is enabled by default)
2405	ev_poll.c only when poll backend is enabled (disabled by default)	4139	ev_poll.c only when poll backend is enabled (disabled by default)
2406	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4140	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2407	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4141	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2408	ev_port.c only when the solaris port backend is enabled (disabled by default)	4142	ev_port.c only when the solaris port backend is enabled (disabled by default)
2409		4143
2410	F<ev.c> includes the backend files directly when enabled, so you only need	4144	F<ev.c> includes the backend files directly when enabled, so you only need
2411	to compile this single file.	4145	to compile this single file.
2412		4146
2413	=head3 LIBEVENT COMPATIBILITY API	4147	=head3 LIBEVENT COMPATIBILITY API
2414		4148
2415	To include the libevent compatibility API, also include:	4149	To include the libevent compatibility API, also include:
2416		4150
2417	#include "event.c"	4151	#include "event.c"
2418		4152
2419	in the file including F<ev.c>, and:	4153	in the file including F<ev.c>, and:
2420		4154
2421	#include "event.h"	4155	#include "event.h"
2422		4156
2423	in the files that want to use the libevent API. This also includes F<ev.h>.	4157	in the files that want to use the libevent API. This also includes F<ev.h>.
2424		4158
2425	You need the following additional files for this:	4159	You need the following additional files for this:
2426		4160
2427	event.h	4161	event.h
2428	event.c	4162	event.c
2429		4163
2430	=head3 AUTOCONF SUPPORT	4164	=head3 AUTOCONF SUPPORT
2431		4165
2432	Instead of using C<EV_STANDALONE=1> and providing your config in	4166	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2433	whatever way you want, you can also C<m4_include([libev.m4])> in your	4167	whatever way you want, you can also C<m4_include([libev.m4])> in your
2434	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4168	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2435	include F<config.h> and configure itself accordingly.	4169	include F<config.h> and configure itself accordingly.
2436		4170
2437	For this of course you need the m4 file:	4171	For this of course you need the m4 file:
2438		4172
2439	libev.m4	4173	libev.m4
2440		4174
2441	=head2 PREPROCESSOR SYMBOLS/MACROS	4175	=head2 PREPROCESSOR SYMBOLS/MACROS
2442		4176
2443	Libev can be configured via a variety of preprocessor symbols you have to define	4177	Libev can be configured via a variety of preprocessor symbols you have to
2444	before including any of its files. The default is not to build for multiplicity	4178	define before including (or compiling) any of its files. The default in
2445	and only include the select backend.	4179	the absence of autoconf is documented for every option.
		4180
		4181	Symbols marked with "(h)" do not change the ABI, and can have different
		4182	values when compiling libev vs. including F<ev.h>, so it is permissible
		4183	to redefine them before including F<ev.h> without breaking compatibility
		4184	to a compiled library. All other symbols change the ABI, which means all
		4185	users of libev and the libev code itself must be compiled with compatible
		4186	settings.
2446		4187
2447	=over 4	4188	=over 4
2448		4189
		4190	=item EV_COMPAT3 (h)
		4191
		4192	Backwards compatibility is a major concern for libev. This is why this
		4193	release of libev comes with wrappers for the functions and symbols that
		4194	have been renamed between libev version 3 and 4.
		4195
		4196	You can disable these wrappers (to test compatibility with future
		4197	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4198	sources. This has the additional advantage that you can drop the C<struct>
		4199	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4200	typedef in that case.
		4201
		4202	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4203	and in some even more future version the compatibility code will be
		4204	removed completely.
		4205
2449	=item EV_STANDALONE	4206	=item EV_STANDALONE (h)
2450		4207
2451	Must always be C<1> if you do not use autoconf configuration, which	4208	Must always be C<1> if you do not use autoconf configuration, which
2452	keeps libev from including F<config.h>, and it also defines dummy	4209	keeps libev from including F<config.h>, and it also defines dummy
2453	implementations for some libevent functions (such as logging, which is not	4210	implementations for some libevent functions (such as logging, which is not
2454	supported). It will also not define any of the structs usually found in	4211	supported). It will also not define any of the structs usually found in
2455	F<event.h> that are not directly supported by the libev core alone.	4212	F<event.h> that are not directly supported by the libev core alone.
2456		4213
		4214	In standalone mode, libev will still try to automatically deduce the
		4215	configuration, but has to be more conservative.
		4216
		4217	=item EV_USE_FLOOR
		4218
		4219	If defined to be C<1>, libev will use the C<floor ()> function for its
		4220	periodic reschedule calculations, otherwise libev will fall back on a
		4221	portable (slower) implementation. If you enable this, you usually have to
		4222	link against libm or something equivalent. Enabling this when the C<floor>
		4223	function is not available will fail, so the safe default is to not enable
		4224	this.
		4225
2457	=item EV_USE_MONOTONIC	4226	=item EV_USE_MONOTONIC
2458		4227
2459	If defined to be C<1>, libev will try to detect the availability of the	4228	If defined to be C<1>, libev will try to detect the availability of the
2460	monotonic clock option at both compiletime and runtime. Otherwise no use	4229	monotonic clock option at both compile time and runtime. Otherwise no
2461	of the monotonic clock option will be attempted. If you enable this, you	4230	use of the monotonic clock option will be attempted. If you enable this,
2462	usually have to link against librt or something similar. Enabling it when	4231	you usually have to link against librt or something similar. Enabling it
2463	the functionality isn't available is safe, though, although you have	4232	when the functionality isn't available is safe, though, although you have
2464	to make sure you link against any libraries where the C<clock_gettime>	4233	to make sure you link against any libraries where the C<clock_gettime>
2465	function is hiding in (often F<-lrt>).	4234	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2466		4235
2467	=item EV_USE_REALTIME	4236	=item EV_USE_REALTIME
2468		4237
2469	If defined to be C<1>, libev will try to detect the availability of the	4238	If defined to be C<1>, libev will try to detect the availability of the
2470	realtime clock option at compiletime (and assume its availability at	4239	real-time clock option at compile time (and assume its availability
2471	runtime if successful). Otherwise no use of the realtime clock option will	4240	at runtime if successful). Otherwise no use of the real-time clock
2472	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4241	option will be attempted. This effectively replaces C<gettimeofday>
2473	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4242	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2474	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4243	correctness. See the note about libraries in the description of
		4244	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4245	C<EV_USE_CLOCK_SYSCALL>.
		4246
		4247	=item EV_USE_CLOCK_SYSCALL
		4248
		4249	If defined to be C<1>, libev will try to use a direct syscall instead
		4250	of calling the system-provided C<clock_gettime> function. This option
		4251	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4252	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4253	programs needlessly. Using a direct syscall is slightly slower (in
		4254	theory), because no optimised vdso implementation can be used, but avoids
		4255	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4256	higher, as it simplifies linking (no need for C<-lrt>).
2475		4257
2476	=item EV_USE_NANOSLEEP	4258	=item EV_USE_NANOSLEEP
2477		4259
2478	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4260	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2479	and will use it for delays. Otherwise it will use C<select ()>.	4261	and will use it for delays. Otherwise it will use C<select ()>.
2480		4262
		4263	=item EV_USE_EVENTFD
		4264
		4265	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4266	available and will probe for kernel support at runtime. This will improve
		4267	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4268	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4269	2.7 or newer, otherwise disabled.
		4270
2481	=item EV_USE_SELECT	4271	=item EV_USE_SELECT
2482		4272
2483	If undefined or defined to be C<1>, libev will compile in support for the	4273	If undefined or defined to be C<1>, libev will compile in support for the
2484	C<select>(2) backend. No attempt at autodetection will be done: if no	4274	C<select>(2) backend. No attempt at auto-detection will be done: if no
2485	other method takes over, select will be it. Otherwise the select backend	4275	other method takes over, select will be it. Otherwise the select backend
2486	will not be compiled in.	4276	will not be compiled in.
2487		4277
2488	=item EV_SELECT_USE_FD_SET	4278	=item EV_SELECT_USE_FD_SET
2489		4279
2490	If defined to C<1>, then the select backend will use the system C<fd_set>	4280	If defined to C<1>, then the select backend will use the system C<fd_set>
2491	structure. This is useful if libev doesn't compile due to a missing	4281	structure. This is useful if libev doesn't compile due to a missing
2492	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4282	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2493	exotic systems. This usually limits the range of file descriptors to some	4283	on exotic systems. This usually limits the range of file descriptors to
2494	low limit such as 1024 or might have other limitations (winsocket only	4284	some low limit such as 1024 or might have other limitations (winsocket
2495	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4285	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2496	influence the size of the C<fd_set> used.	4286	configures the maximum size of the C<fd_set>.
2497		4287
2498	=item EV_SELECT_IS_WINSOCKET	4288	=item EV_SELECT_IS_WINSOCKET
2499		4289
2500	When defined to C<1>, the select backend will assume that	4290	When defined to C<1>, the select backend will assume that
2501	select/socket/connect etc. don't understand file descriptors but	4291	select/socket/connect etc. don't understand file descriptors but
…		…
2503	be used is the winsock select). This means that it will call	4293	be used is the winsock select). This means that it will call
2504	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4294	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2505	it is assumed that all these functions actually work on fds, even	4295	it is assumed that all these functions actually work on fds, even
2506	on win32. Should not be defined on non-win32 platforms.	4296	on win32. Should not be defined on non-win32 platforms.
2507		4297
2508	=item EV_FD_TO_WIN32_HANDLE	4298	=item EV_FD_TO_WIN32_HANDLE(fd)
2509		4299
2510	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4300	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2511	file descriptors to socket handles. When not defining this symbol (the	4301	file descriptors to socket handles. When not defining this symbol (the
2512	default), then libev will call C<_get_osfhandle>, which is usually	4302	default), then libev will call C<_get_osfhandle>, which is usually
2513	correct. In some cases, programs use their own file descriptor management,	4303	correct. In some cases, programs use their own file descriptor management,
2514	in which case they can provide this function to map fds to socket handles.	4304	in which case they can provide this function to map fds to socket handles.
2515		4305
		4306	=item EV_WIN32_HANDLE_TO_FD(handle)
		4307
		4308	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4309	using the standard C<_open_osfhandle> function. For programs implementing
		4310	their own fd to handle mapping, overwriting this function makes it easier
		4311	to do so. This can be done by defining this macro to an appropriate value.
		4312
		4313	=item EV_WIN32_CLOSE_FD(fd)
		4314
		4315	If programs implement their own fd to handle mapping on win32, then this
		4316	macro can be used to override the C<close> function, useful to unregister
		4317	file descriptors again. Note that the replacement function has to close
		4318	the underlying OS handle.
		4319
2516	=item EV_USE_POLL	4320	=item EV_USE_POLL
2517		4321
2518	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4322	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2519	backend. Otherwise it will be enabled on non-win32 platforms. It	4323	backend. Otherwise it will be enabled on non-win32 platforms. It
2520	takes precedence over select.	4324	takes precedence over select.
2521		4325
2522	=item EV_USE_EPOLL	4326	=item EV_USE_EPOLL
2523		4327
2524	If defined to be C<1>, libev will compile in support for the Linux	4328	If defined to be C<1>, libev will compile in support for the Linux
2525	C<epoll>(7) backend. Its availability will be detected at runtime,	4329	C<epoll>(7) backend. Its availability will be detected at runtime,
2526	otherwise another method will be used as fallback. This is the	4330	otherwise another method will be used as fallback. This is the preferred
2527	preferred backend for GNU/Linux systems.	4331	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4332	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2528		4333
2529	=item EV_USE_KQUEUE	4334	=item EV_USE_KQUEUE
2530		4335
2531	If defined to be C<1>, libev will compile in support for the BSD style	4336	If defined to be C<1>, libev will compile in support for the BSD style
2532	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4337	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2545	otherwise another method will be used as fallback. This is the preferred	4350	otherwise another method will be used as fallback. This is the preferred
2546	backend for Solaris 10 systems.	4351	backend for Solaris 10 systems.
2547		4352
2548	=item EV_USE_DEVPOLL	4353	=item EV_USE_DEVPOLL
2549		4354
2550	reserved for future expansion, works like the USE symbols above.	4355	Reserved for future expansion, works like the USE symbols above.
2551		4356
2552	=item EV_USE_INOTIFY	4357	=item EV_USE_INOTIFY
2553		4358
2554	If defined to be C<1>, libev will compile in support for the Linux inotify	4359	If defined to be C<1>, libev will compile in support for the Linux inotify
2555	interface to speed up C<ev_stat> watchers. Its actual availability will	4360	interface to speed up C<ev_stat> watchers. Its actual availability will
2556	be detected at runtime.	4361	be detected at runtime. If undefined, it will be enabled if the headers
		4362	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2557		4363
		4364	=item EV_ATOMIC_T
		4365
		4366	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4367	access is atomic with respect to other threads or signal contexts. No such
		4368	type is easily found in the C language, so you can provide your own type
		4369	that you know is safe for your purposes. It is used both for signal handler "locking"
		4370	as well as for signal and thread safety in C<ev_async> watchers.
		4371
		4372	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4373	(from F<signal.h>), which is usually good enough on most platforms.
		4374
2558	=item EV_H	4375	=item EV_H (h)
2559		4376
2560	The name of the F<ev.h> header file used to include it. The default if	4377	The name of the F<ev.h> header file used to include it. The default if
2561	undefined is C<"ev.h"> in F<event.h> and F<ev.c>. This can be used to	4378	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2562	virtually rename the F<ev.h> header file in case of conflicts.	4379	used to virtually rename the F<ev.h> header file in case of conflicts.
2563		4380
2564	=item EV_CONFIG_H	4381	=item EV_CONFIG_H (h)
2565		4382
2566	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4383	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2567	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4384	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2568	C<EV_H>, above.	4385	C<EV_H>, above.
2569		4386
2570	=item EV_EVENT_H	4387	=item EV_EVENT_H (h)
2571		4388
2572	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4389	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2573	of how the F<event.h> header can be found, the dfeault is C<"event.h">.	4390	of how the F<event.h> header can be found, the default is C<"event.h">.
2574		4391
2575	=item EV_PROTOTYPES	4392	=item EV_PROTOTYPES (h)
2576		4393
2577	If defined to be C<0>, then F<ev.h> will not define any function	4394	If defined to be C<0>, then F<ev.h> will not define any function
2578	prototypes, but still define all the structs and other symbols. This is	4395	prototypes, but still define all the structs and other symbols. This is
2579	occasionally useful if you want to provide your own wrapper functions	4396	occasionally useful if you want to provide your own wrapper functions
2580	around libev functions.	4397	around libev functions.
…		…
2599	When doing priority-based operations, libev usually has to linearly search	4416	When doing priority-based operations, libev usually has to linearly search
2600	all the priorities, so having many of them (hundreds) uses a lot of space	4417	all the priorities, so having many of them (hundreds) uses a lot of space
2601	and time, so using the defaults of five priorities (-2 .. +2) is usually	4418	and time, so using the defaults of five priorities (-2 .. +2) is usually
2602	fine.	4419	fine.
2603		4420
2604	If your embedding app does not need any priorities, defining these both to	4421	If your embedding application does not need any priorities, defining these
2605	C<0> will save some memory and cpu.	4422	both to C<0> will save some memory and CPU.
2606		4423
2607	=item EV_PERIODIC_ENABLE	4424	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4425	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4426	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2608		4427
2609	If undefined or defined to be C<1>, then periodic timers are supported. If	4428	If undefined or defined to be C<1> (and the platform supports it), then
2610	defined to be C<0>, then they are not. Disabling them saves a few kB of	4429	the respective watcher type is supported. If defined to be C<0>, then it
2611	code.	4430	is not. Disabling watcher types mainly saves code size.
2612		4431
2613	=item EV_IDLE_ENABLE	4432	=item EV_FEATURES
2614
2615	If undefined or defined to be C<1>, then idle watchers are supported. If
2616	defined to be C<0>, then they are not. Disabling them saves a few kB of
2617	code.
2618
2619	=item EV_EMBED_ENABLE
2620
2621	If undefined or defined to be C<1>, then embed watchers are supported. If
2622	defined to be C<0>, then they are not.
2623
2624	=item EV_STAT_ENABLE
2625
2626	If undefined or defined to be C<1>, then stat watchers are supported. If
2627	defined to be C<0>, then they are not.
2628
2629	=item EV_FORK_ENABLE
2630
2631	If undefined or defined to be C<1>, then fork watchers are supported. If
2632	defined to be C<0>, then they are not.
2633
2634	=item EV_MINIMAL
2635		4433
2636	If you need to shave off some kilobytes of code at the expense of some	4434	If you need to shave off some kilobytes of code at the expense of some
2637	speed, define this symbol to C<1>. Currently only used for gcc to override	4435	speed (but with the full API), you can define this symbol to request
2638	some inlining decisions, saves roughly 30% codesize of amd64.	4436	certain subsets of functionality. The default is to enable all features
		4437	that can be enabled on the platform.
		4438
		4439	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4440	with some broad features you want) and then selectively re-enable
		4441	additional parts you want, for example if you want everything minimal,
		4442	but multiple event loop support, async and child watchers and the poll
		4443	backend, use this:
		4444
		4445	#define EV_FEATURES 0
		4446	#define EV_MULTIPLICITY 1
		4447	#define EV_USE_POLL 1
		4448	#define EV_CHILD_ENABLE 1
		4449	#define EV_ASYNC_ENABLE 1
		4450
		4451	The actual value is a bitset, it can be a combination of the following
		4452	values:
		4453
		4454	=over 4
		4455
		4456	=item C<1> - faster/larger code
		4457
		4458	Use larger code to speed up some operations.
		4459
		4460	Currently this is used to override some inlining decisions (enlarging the
		4461	code size by roughly 30% on amd64).
		4462
		4463	When optimising for size, use of compiler flags such as C<-Os> with
		4464	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4465	assertions.
		4466
		4467	=item C<2> - faster/larger data structures
		4468
		4469	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4470	hash table sizes and so on. This will usually further increase code size
		4471	and can additionally have an effect on the size of data structures at
		4472	runtime.
		4473
		4474	=item C<4> - full API configuration
		4475
		4476	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4477	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4478
		4479	=item C<8> - full API
		4480
		4481	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4482	details on which parts of the API are still available without this
		4483	feature, and do not complain if this subset changes over time.
		4484
		4485	=item C<16> - enable all optional watcher types
		4486
		4487	Enables all optional watcher types. If you want to selectively enable
		4488	only some watcher types other than I/O and timers (e.g. prepare,
		4489	embed, async, child...) you can enable them manually by defining
		4490	C<EV_watchertype_ENABLE> to C<1> instead.
		4491
		4492	=item C<32> - enable all backends
		4493
		4494	This enables all backends - without this feature, you need to enable at
		4495	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4496
		4497	=item C<64> - enable OS-specific "helper" APIs
		4498
		4499	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4500	default.
		4501
		4502	=back
		4503
		4504	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4505	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4506	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4507	watchers, timers and monotonic clock support.
		4508
		4509	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4510	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4511	your program might be left out as well - a binary starting a timer and an
		4512	I/O watcher then might come out at only 5Kb.
		4513
		4514	=item EV_AVOID_STDIO
		4515
		4516	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4517	functions (printf, scanf, perror etc.). This will increase the code size
		4518	somewhat, but if your program doesn't otherwise depend on stdio and your
		4519	libc allows it, this avoids linking in the stdio library which is quite
		4520	big.
		4521
		4522	Note that error messages might become less precise when this option is
		4523	enabled.
		4524
		4525	=item EV_NSIG
		4526
		4527	The highest supported signal number, +1 (or, the number of
		4528	signals): Normally, libev tries to deduce the maximum number of signals
		4529	automatically, but sometimes this fails, in which case it can be
		4530	specified. Also, using a lower number than detected (C<32> should be
		4531	good for about any system in existence) can save some memory, as libev
		4532	statically allocates some 12-24 bytes per signal number.
2639		4533
2640	=item EV_PID_HASHSIZE	4534	=item EV_PID_HASHSIZE
2641		4535
2642	C<ev_child> watchers use a small hash table to distribute workload by	4536	C<ev_child> watchers use a small hash table to distribute workload by
2643	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4537	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2644	than enough. If you need to manage thousands of children you might want to	4538	usually more than enough. If you need to manage thousands of children you
2645	increase this value (I<must> be a power of two).	4539	might want to increase this value (I<must> be a power of two).
2646		4540
2647	=item EV_INOTIFY_HASHSIZE	4541	=item EV_INOTIFY_HASHSIZE
2648		4542
2649	C<ev_stat> watchers use a small hash table to distribute workload by	4543	C<ev_stat> watchers use a small hash table to distribute workload by
2650	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4544	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2651	usually more than enough. If you need to manage thousands of C<ev_stat>	4545	disabled), usually more than enough. If you need to manage thousands of
2652	watchers you might want to increase this value (I<must> be a power of	4546	C<ev_stat> watchers you might want to increase this value (I<must> be a
2653	two).	4547	power of two).
		4548
		4549	=item EV_USE_4HEAP
		4550
		4551	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4552	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4553	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4554	faster performance with many (thousands) of watchers.
		4555
		4556	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4557	will be C<0>.
		4558
		4559	=item EV_HEAP_CACHE_AT
		4560
		4561	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4562	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4563	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4564	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4565	but avoids random read accesses on heap changes. This improves performance
		4566	noticeably with many (hundreds) of watchers.
		4567
		4568	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4569	will be C<0>.
		4570
		4571	=item EV_VERIFY
		4572
		4573	Controls how much internal verification (see C<ev_verify ()>) will
		4574	be done: If set to C<0>, no internal verification code will be compiled
		4575	in. If set to C<1>, then verification code will be compiled in, but not
		4576	called. If set to C<2>, then the internal verification code will be
		4577	called once per loop, which can slow down libev. If set to C<3>, then the
		4578	verification code will be called very frequently, which will slow down
		4579	libev considerably.
		4580
		4581	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4582	will be C<0>.
2654		4583
2655	=item EV_COMMON	4584	=item EV_COMMON
2656		4585
2657	By default, all watchers have a C<void *data> member. By redefining	4586	By default, all watchers have a C<void *data> member. By redefining
2658	this macro to a something else you can include more and other types of	4587	this macro to something else you can include more and other types of
2659	members. You have to define it each time you include one of the files,	4588	members. You have to define it each time you include one of the files,
2660	though, and it must be identical each time.	4589	though, and it must be identical each time.
2661		4590
2662	For example, the perl EV module uses something like this:	4591	For example, the perl EV module uses something like this:
2663		4592
2664	#define EV_COMMON \	4593	#define EV_COMMON \
2665	SV *self; /* contains this struct */ \	4594	SV *self; /* contains this struct */ \
2666	SV *cb_sv, *fh /* note no trailing ";" */	4595	SV *cb_sv, *fh /* note no trailing ";" */
2667		4596
2668	=item EV_CB_DECLARE (type)	4597	=item EV_CB_DECLARE (type)
2669		4598
2670	=item EV_CB_INVOKE (watcher, revents)	4599	=item EV_CB_INVOKE (watcher, revents)
2671		4600
…		…
2676	definition and a statement, respectively. See the F<ev.h> header file for	4605	definition and a statement, respectively. See the F<ev.h> header file for
2677	their default definitions. One possible use for overriding these is to	4606	their default definitions. One possible use for overriding these is to
2678	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4607	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2679	method calls instead of plain function calls in C++.	4608	method calls instead of plain function calls in C++.
2680		4609
		4610	=back
		4611
2681	=head2 EXPORTED API SYMBOLS	4612	=head2 EXPORTED API SYMBOLS
2682		4613
2683	If you need to re-export the API (e.g. via a dll) and you need a list of	4614	If you need to re-export the API (e.g. via a DLL) and you need a list of
2684	exported symbols, you can use the provided F<Symbol.*> files which list	4615	exported symbols, you can use the provided F<Symbol.*> files which list
2685	all public symbols, one per line:	4616	all public symbols, one per line:
2686		4617
2687	Symbols.ev for libev proper	4618	Symbols.ev for libev proper
2688	Symbols.event for the libevent emulation	4619	Symbols.event for the libevent emulation
2689		4620
2690	This can also be used to rename all public symbols to avoid clashes with	4621	This can also be used to rename all public symbols to avoid clashes with
2691	multiple versions of libev linked together (which is obviously bad in	4622	multiple versions of libev linked together (which is obviously bad in
2692	itself, but sometimes it is inconvinient to avoid this).	4623	itself, but sometimes it is inconvenient to avoid this).
2693		4624
2694	A sed command like this will create wrapper C<#define>'s that you need to	4625	A sed command like this will create wrapper C<#define>'s that you need to
2695	include before including F<ev.h>:	4626	include before including F<ev.h>:
2696		4627
2697	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4628	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2714	file.	4645	file.
2715		4646
2716	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4647	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2717	that everybody includes and which overrides some configure choices:	4648	that everybody includes and which overrides some configure choices:
2718		4649
2719	#define EV_MINIMAL 1	4650	#define EV_FEATURES 8
2720	#define EV_USE_POLL 0	4651	#define EV_USE_SELECT 1
2721	#define EV_MULTIPLICITY 0
2722	#define EV_PERIODIC_ENABLE 0	4652	#define EV_PREPARE_ENABLE 1
		4653	#define EV_IDLE_ENABLE 1
2723	#define EV_STAT_ENABLE 0	4654	#define EV_SIGNAL_ENABLE 1
2724	#define EV_FORK_ENABLE 0	4655	#define EV_CHILD_ENABLE 1
		4656	#define EV_USE_STDEXCEPT 0
2725	#define EV_CONFIG_H <config.h>	4657	#define EV_CONFIG_H <config.h>
2726	#define EV_MINPRI 0
2727	#define EV_MAXPRI 0
2728		4658
2729	#include "ev++.h"	4659	#include "ev++.h"
2730		4660
2731	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4661	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2732		4662
2733	#include "ev_cpp.h"	4663	#include "ev_cpp.h"
2734	#include "ev.c"	4664	#include "ev.c"
2735		4665
		4666	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2736		4667
2737	=head1 COMPLEXITIES	4668	=head2 THREADS AND COROUTINES
2738		4669
2739	In this section the complexities of (many of) the algorithms used inside	4670	=head3 THREADS
2740	libev will be explained. For complexity discussions about backends see the
2741	documentation for C<ev_default_init>.
2742		4671
2743	All of the following are about amortised time: If an array needs to be	4672	All libev functions are reentrant and thread-safe unless explicitly
2744	extended, libev needs to realloc and move the whole array, but this	4673	documented otherwise, but libev implements no locking itself. This means
2745	happens asymptotically never with higher number of elements, so O(1) might	4674	that you can use as many loops as you want in parallel, as long as there
2746	mean it might do a lengthy realloc operation in rare cases, but on average	4675	are no concurrent calls into any libev function with the same loop
2747	it is much faster and asymptotically approaches constant time.	4676	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4677	of course): libev guarantees that different event loops share no data
		4678	structures that need any locking.
		4679
		4680	Or to put it differently: calls with different loop parameters can be done
		4681	concurrently from multiple threads, calls with the same loop parameter
		4682	must be done serially (but can be done from different threads, as long as
		4683	only one thread ever is inside a call at any point in time, e.g. by using
		4684	a mutex per loop).
		4685
		4686	Specifically to support threads (and signal handlers), libev implements
		4687	so-called C<ev_async> watchers, which allow some limited form of
		4688	concurrency on the same event loop, namely waking it up "from the
		4689	outside".
		4690
		4691	If you want to know which design (one loop, locking, or multiple loops
		4692	without or something else still) is best for your problem, then I cannot
		4693	help you, but here is some generic advice:
2748		4694
2749	=over 4	4695	=over 4
2750		4696
2751	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4697	=item * most applications have a main thread: use the default libev loop
		4698	in that thread, or create a separate thread running only the default loop.
2752		4699
2753	This means that, when you have a watcher that triggers in one hour and	4700	This helps integrating other libraries or software modules that use libev
2754	there are 100 watchers that would trigger before that then inserting will	4701	themselves and don't care/know about threading.
2755	have to skip roughly seven (C<ld 100>) of these watchers.
2756		4702
2757	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4703	=item * one loop per thread is usually a good model.
2758		4704
2759	That means that changing a timer costs less than removing/adding them	4705	Doing this is almost never wrong, sometimes a better-performance model
2760	as only the relative motion in the event queue has to be paid for.	4706	exists, but it is always a good start.
2761		4707
2762	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4708	=item * other models exist, such as the leader/follower pattern, where one
		4709	loop is handed through multiple threads in a kind of round-robin fashion.
2763		4710
2764	These just add the watcher into an array or at the head of a list.	4711	Choosing a model is hard - look around, learn, know that usually you can do
		4712	better than you currently do :-)
2765		4713
2766	=item Stopping check/prepare/idle watchers: O(1)	4714	=item * often you need to talk to some other thread which blocks in the
		4715	event loop.
2767		4716
2768	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4717	C<ev_async> watchers can be used to wake them up from other threads safely
		4718	(or from signal contexts...).
2769		4719
2770	These watchers are stored in lists then need to be walked to find the	4720	An example use would be to communicate signals or other events that only
2771	correct watcher to remove. The lists are usually short (you don't usually	4721	work in the default loop by registering the signal watcher with the
2772	have many watchers waiting for the same fd or signal).	4722	default loop and triggering an C<ev_async> watcher from the default loop
2773		4723	watcher callback into the event loop interested in the signal.
2774	=item Finding the next timer in each loop iteration: O(1)
2775
2776	By virtue of using a binary heap, the next timer is always found at the
2777	beginning of the storage array.
2778
2779	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2780
2781	A change means an I/O watcher gets started or stopped, which requires
2782	libev to recalculate its status (and possibly tell the kernel, depending
2783	on backend and wether C<ev_io_set> was used).
2784
2785	=item Activating one watcher (putting it into the pending state): O(1)
2786
2787	=item Priority handling: O(number_of_priorities)
2788
2789	Priorities are implemented by allocating some space for each
2790	priority. When doing priority-based operations, libev usually has to
2791	linearly search all the priorities, but starting/stopping and activating
2792	watchers becomes O(1) w.r.t. prioritiy handling.
2793		4724
2794	=back	4725	=back
2795		4726
		4727	See also L<THREAD LOCKING EXAMPLE>.
2796		4728
2797	=head1 Win32 platform limitations and workarounds	4729	=head3 COROUTINES
		4730
		4731	Libev is very accommodating to coroutines ("cooperative threads"):
		4732	libev fully supports nesting calls to its functions from different
		4733	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4734	different coroutines, and switch freely between both coroutines running
		4735	the loop, as long as you don't confuse yourself). The only exception is
		4736	that you must not do this from C<ev_periodic> reschedule callbacks.
		4737
		4738	Care has been taken to ensure that libev does not keep local state inside
		4739	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4740	they do not call any callbacks.
		4741
		4742	=head2 COMPILER WARNINGS
		4743
		4744	Depending on your compiler and compiler settings, you might get no or a
		4745	lot of warnings when compiling libev code. Some people are apparently
		4746	scared by this.
		4747
		4748	However, these are unavoidable for many reasons. For one, each compiler
		4749	has different warnings, and each user has different tastes regarding
		4750	warning options. "Warn-free" code therefore cannot be a goal except when
		4751	targeting a specific compiler and compiler-version.
		4752
		4753	Another reason is that some compiler warnings require elaborate
		4754	workarounds, or other changes to the code that make it less clear and less
		4755	maintainable.
		4756
		4757	And of course, some compiler warnings are just plain stupid, or simply
		4758	wrong (because they don't actually warn about the condition their message
		4759	seems to warn about). For example, certain older gcc versions had some
		4760	warnings that resulted in an extreme number of false positives. These have
		4761	been fixed, but some people still insist on making code warn-free with
		4762	such buggy versions.
		4763
		4764	While libev is written to generate as few warnings as possible,
		4765	"warn-free" code is not a goal, and it is recommended not to build libev
		4766	with any compiler warnings enabled unless you are prepared to cope with
		4767	them (e.g. by ignoring them). Remember that warnings are just that:
		4768	warnings, not errors, or proof of bugs.
		4769
		4770
		4771	=head2 VALGRIND
		4772
		4773	Valgrind has a special section here because it is a popular tool that is
		4774	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4775
		4776	If you think you found a bug (memory leak, uninitialised data access etc.)
		4777	in libev, then check twice: If valgrind reports something like:
		4778
		4779	==2274== definitely lost: 0 bytes in 0 blocks.
		4780	==2274== possibly lost: 0 bytes in 0 blocks.
		4781	==2274== still reachable: 256 bytes in 1 blocks.
		4782
		4783	Then there is no memory leak, just as memory accounted to global variables
		4784	is not a memleak - the memory is still being referenced, and didn't leak.
		4785
		4786	Similarly, under some circumstances, valgrind might report kernel bugs
		4787	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4788	although an acceptable workaround has been found here), or it might be
		4789	confused.
		4790
		4791	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4792	make it into some kind of religion.
		4793
		4794	If you are unsure about something, feel free to contact the mailing list
		4795	with the full valgrind report and an explanation on why you think this
		4796	is a bug in libev (best check the archives, too :). However, don't be
		4797	annoyed when you get a brisk "this is no bug" answer and take the chance
		4798	of learning how to interpret valgrind properly.
		4799
		4800	If you need, for some reason, empty reports from valgrind for your project
		4801	I suggest using suppression lists.
		4802
		4803
		4804	=head1 PORTABILITY NOTES
		4805
		4806	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4807
		4808	GNU/Linux is the only common platform that supports 64 bit file/large file
		4809	interfaces but I<disables> them by default.
		4810
		4811	That means that libev compiled in the default environment doesn't support
		4812	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4813
		4814	Unfortunately, many programs try to work around this GNU/Linux issue
		4815	by enabling the large file API, which makes them incompatible with the
		4816	standard libev compiled for their system.
		4817
		4818	Likewise, libev cannot enable the large file API itself as this would
		4819	suddenly make it incompatible to the default compile time environment,
		4820	i.e. all programs not using special compile switches.
		4821
		4822	=head2 OS/X AND DARWIN BUGS
		4823
		4824	The whole thing is a bug if you ask me - basically any system interface
		4825	you touch is broken, whether it is locales, poll, kqueue or even the
		4826	OpenGL drivers.
		4827
		4828	=head3 C<kqueue> is buggy
		4829
		4830	The kqueue syscall is broken in all known versions - most versions support
		4831	only sockets, many support pipes.
		4832
		4833	Libev tries to work around this by not using C<kqueue> by default on this
		4834	rotten platform, but of course you can still ask for it when creating a
		4835	loop - embedding a socket-only kqueue loop into a select-based one is
		4836	probably going to work well.
		4837
		4838	=head3 C<poll> is buggy
		4839
		4840	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4841	implementation by something calling C<kqueue> internally around the 10.5.6
		4842	release, so now C<kqueue> I<and> C<poll> are broken.
		4843
		4844	Libev tries to work around this by not using C<poll> by default on
		4845	this rotten platform, but of course you can still ask for it when creating
		4846	a loop.
		4847
		4848	=head3 C<select> is buggy
		4849
		4850	All that's left is C<select>, and of course Apple found a way to fuck this
		4851	one up as well: On OS/X, C<select> actively limits the number of file
		4852	descriptors you can pass in to 1024 - your program suddenly crashes when
		4853	you use more.
		4854
		4855	There is an undocumented "workaround" for this - defining
		4856	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4857	work on OS/X.
		4858
		4859	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4860
		4861	=head3 C<errno> reentrancy
		4862
		4863	The default compile environment on Solaris is unfortunately so
		4864	thread-unsafe that you can't even use components/libraries compiled
		4865	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4866	defined by default. A valid, if stupid, implementation choice.
		4867
		4868	If you want to use libev in threaded environments you have to make sure
		4869	it's compiled with C<_REENTRANT> defined.
		4870
		4871	=head3 Event port backend
		4872
		4873	The scalable event interface for Solaris is called "event
		4874	ports". Unfortunately, this mechanism is very buggy in all major
		4875	releases. If you run into high CPU usage, your program freezes or you get
		4876	a large number of spurious wakeups, make sure you have all the relevant
		4877	and latest kernel patches applied. No, I don't know which ones, but there
		4878	are multiple ones to apply, and afterwards, event ports actually work
		4879	great.
		4880
		4881	If you can't get it to work, you can try running the program by setting
		4882	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4883	C<select> backends.
		4884
		4885	=head2 AIX POLL BUG
		4886
		4887	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4888	this by trying to avoid the poll backend altogether (i.e. it's not even
		4889	compiled in), which normally isn't a big problem as C<select> works fine
		4890	with large bitsets on AIX, and AIX is dead anyway.
		4891
		4892	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4893
		4894	=head3 General issues
2798		4895
2799	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4896	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2800	requires, and its I/O model is fundamentally incompatible with the POSIX	4897	requires, and its I/O model is fundamentally incompatible with the POSIX
2801	model. Libev still offers limited functionality on this platform in	4898	model. Libev still offers limited functionality on this platform in
2802	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4899	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2803	descriptors. This only applies when using Win32 natively, not when using	4900	descriptors. This only applies when using Win32 natively, not when using
2804	e.g. cygwin.	4901	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4902	as every compielr comes with a slightly differently broken/incompatible
		4903	environment.
		4904
		4905	Lifting these limitations would basically require the full
		4906	re-implementation of the I/O system. If you are into this kind of thing,
		4907	then note that glib does exactly that for you in a very portable way (note
		4908	also that glib is the slowest event library known to man).
2805		4909
2806	There is no supported compilation method available on windows except	4910	There is no supported compilation method available on windows except
2807	embedding it into other applications.	4911	embedding it into other applications.
2808		4912
		4913	Sensible signal handling is officially unsupported by Microsoft - libev
		4914	tries its best, but under most conditions, signals will simply not work.
		4915
		4916	Not a libev limitation but worth mentioning: windows apparently doesn't
		4917	accept large writes: instead of resulting in a partial write, windows will
		4918	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4919	so make sure you only write small amounts into your sockets (less than a
		4920	megabyte seems safe, but this apparently depends on the amount of memory
		4921	available).
		4922
2809	Due to the many, low, and arbitrary limits on the win32 platform and the	4923	Due to the many, low, and arbitrary limits on the win32 platform and
2810	abysmal performance of winsockets, using a large number of sockets is not	4924	the abysmal performance of winsockets, using a large number of sockets
2811	recommended (and not reasonable). If your program needs to use more than	4925	is not recommended (and not reasonable). If your program needs to use
2812	a hundred or so sockets, then likely it needs to use a totally different	4926	more than a hundred or so sockets, then likely it needs to use a totally
2813	implementation for windows, as libev offers the POSIX model, which cannot	4927	different implementation for windows, as libev offers the POSIX readiness
2814	be implemented efficiently on windows (microsoft monopoly games).	4928	notification model, which cannot be implemented efficiently on windows
		4929	(due to Microsoft monopoly games).
2815		4930
2816	=over 4	4931	A typical way to use libev under windows is to embed it (see the embedding
		4932	section for details) and use the following F<evwrap.h> header file instead
		4933	of F<ev.h>:
2817		4934
		4935	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4936	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4937
		4938	#include "ev.h"
		4939
		4940	And compile the following F<evwrap.c> file into your project (make sure
		4941	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4942
		4943	#include "evwrap.h"
		4944	#include "ev.c"
		4945
2818	=item The winsocket select function	4946	=head3 The winsocket C<select> function
2819		4947
2820	The winsocket C<select> function doesn't follow POSIX in that it requires	4948	The winsocket C<select> function doesn't follow POSIX in that it
2821	socket I<handles> and not socket I<file descriptors>. This makes select	4949	requires socket I<handles> and not socket I<file descriptors> (it is
2822	very inefficient, and also requires a mapping from file descriptors	4950	also extremely buggy). This makes select very inefficient, and also
2823	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4951	requires a mapping from file descriptors to socket handles (the Microsoft
2824	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4952	C runtime provides the function C<_open_osfhandle> for this). See the
2825	symbols for more info.	4953	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4954	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
2826		4955
2827	The configuration for a "naked" win32 using the microsoft runtime	4956	The configuration for a "naked" win32 using the Microsoft runtime
2828	libraries and raw winsocket select is:	4957	libraries and raw winsocket select is:
2829		4958
2830	#define EV_USE_SELECT 1	4959	#define EV_USE_SELECT 1
2831	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4960	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2832		4961
2833	Note that winsockets handling of fd sets is O(n), so you can easily get a	4962	Note that winsockets handling of fd sets is O(n), so you can easily get a
2834	complexity in the O(n²) range when using win32.	4963	complexity in the O(n²) range when using win32.
2835		4964
2836	=item Limited number of file descriptors	4965	=head3 Limited number of file descriptors
2837		4966
2838	Windows has numerous arbitrary (and low) limits on things. Early versions	4967	Windows has numerous arbitrary (and low) limits on things.
2839	of winsocket's select only supported waiting for a max. of C<64> handles	4968
		4969	Early versions of winsocket's select only supported waiting for a maximum
2840	(probably owning to the fact that all windows kernels can only wait for	4970	of C<64> handles (probably owning to the fact that all windows kernels
2841	C<64> things at the same time internally; microsoft recommends spawning a	4971	can only wait for C<64> things at the same time internally; Microsoft
2842	chain of threads and wait for 63 handles and the previous thread in each).	4972	recommends spawning a chain of threads and wait for 63 handles and the
		4973	previous thread in each. Sounds great!).
2843		4974
2844	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4975	Newer versions support more handles, but you need to define C<FD_SETSIZE>
2845	to some high number (e.g. C<2048>) before compiling the winsocket select	4976	to some high number (e.g. C<2048>) before compiling the winsocket select
2846	call (which might be in libev or elsewhere, for example, perl does its own	4977	call (which might be in libev or elsewhere, for example, perl and many
2847	select emulation on windows).	4978	other interpreters do their own select emulation on windows).
2848		4979
2849	Another limit is the number of file descriptors in the microsoft runtime	4980	Another limit is the number of file descriptors in the Microsoft runtime
2850	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4981	libraries, which by default is C<64> (there must be a hidden I<64>
2851	or something like this inside microsoft). You can increase this by calling	4982	fetish or something like this inside Microsoft). You can increase this
2852	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4983	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
2853	arbitrary limit), but is broken in many versions of the microsoft runtime	4984	(another arbitrary limit), but is broken in many versions of the Microsoft
2854	libraries.
2855
2856	This might get you to about C<512> or C<2048> sockets (depending on	4985	runtime libraries. This might get you to about C<512> or C<2048> sockets
2857	windows version and/or the phase of the moon). To get more, you need to	4986	(depending on windows version and/or the phase of the moon). To get more,
2858	wrap all I/O functions and provide your own fd management, but the cost of	4987	you need to wrap all I/O functions and provide your own fd management, but
2859	calling select (O(n²)) will likely make this unworkable.	4988	the cost of calling select (O(n²)) will likely make this unworkable.
		4989
		4990	=head2 PORTABILITY REQUIREMENTS
		4991
		4992	In addition to a working ISO-C implementation and of course the
		4993	backend-specific APIs, libev relies on a few additional extensions:
		4994
		4995	=over 4
		4996
		4997	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4998	calling conventions regardless of C<ev_watcher_type *>.
		4999
		5000	Libev assumes not only that all watcher pointers have the same internal
		5001	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5002	assumes that the same (machine) code can be used to call any watcher
		5003	callback: The watcher callbacks have different type signatures, but libev
		5004	calls them using an C<ev_watcher *> internally.
		5005
		5006	=item pointer accesses must be thread-atomic
		5007
		5008	Accessing a pointer value must be atomic, it must both be readable and
		5009	writable in one piece - this is the case on all current architectures.
		5010
		5011	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5012
		5013	The type C<sig_atomic_t volatile> (or whatever is defined as
		5014	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5015	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5016	believed to be sufficiently portable.
		5017
		5018	=item C<sigprocmask> must work in a threaded environment
		5019
		5020	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5021	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5022	pthread implementations will either allow C<sigprocmask> in the "main
		5023	thread" or will block signals process-wide, both behaviours would
		5024	be compatible with libev. Interaction between C<sigprocmask> and
		5025	C<pthread_sigmask> could complicate things, however.
		5026
		5027	The most portable way to handle signals is to block signals in all threads
		5028	except the initial one, and run the default loop in the initial thread as
		5029	well.
		5030
		5031	=item C<long> must be large enough for common memory allocation sizes
		5032
		5033	To improve portability and simplify its API, libev uses C<long> internally
		5034	instead of C<size_t> when allocating its data structures. On non-POSIX
		5035	systems (Microsoft...) this might be unexpectedly low, but is still at
		5036	least 31 bits everywhere, which is enough for hundreds of millions of
		5037	watchers.
		5038
		5039	=item C<double> must hold a time value in seconds with enough accuracy
		5040
		5041	The type C<double> is used to represent timestamps. It is required to
		5042	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5043	good enough for at least into the year 4000 with millisecond accuracy
		5044	(the design goal for libev). This requirement is overfulfilled by
		5045	implementations using IEEE 754, which is basically all existing ones. With
		5046	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
2860		5047
2861	=back	5048	=back
2862		5049
		5050	If you know of other additional requirements drop me a note.
		5051
		5052
		5053	=head1 ALGORITHMIC COMPLEXITIES
		5054
		5055	In this section the complexities of (many of) the algorithms used inside
		5056	libev will be documented. For complexity discussions about backends see
		5057	the documentation for C<ev_default_init>.
		5058
		5059	All of the following are about amortised time: If an array needs to be
		5060	extended, libev needs to realloc and move the whole array, but this
		5061	happens asymptotically rarer with higher number of elements, so O(1) might
		5062	mean that libev does a lengthy realloc operation in rare cases, but on
		5063	average it is much faster and asymptotically approaches constant time.
		5064
		5065	=over 4
		5066
		5067	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5068
		5069	This means that, when you have a watcher that triggers in one hour and
		5070	there are 100 watchers that would trigger before that, then inserting will
		5071	have to skip roughly seven (C<ld 100>) of these watchers.
		5072
		5073	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5074
		5075	That means that changing a timer costs less than removing/adding them,
		5076	as only the relative motion in the event queue has to be paid for.
		5077
		5078	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5079
		5080	These just add the watcher into an array or at the head of a list.
		5081
		5082	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5083
		5084	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5085
		5086	These watchers are stored in lists, so they need to be walked to find the
		5087	correct watcher to remove. The lists are usually short (you don't usually
		5088	have many watchers waiting for the same fd or signal: one is typical, two
		5089	is rare).
		5090
		5091	=item Finding the next timer in each loop iteration: O(1)
		5092
		5093	By virtue of using a binary or 4-heap, the next timer is always found at a
		5094	fixed position in the storage array.
		5095
		5096	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5097
		5098	A change means an I/O watcher gets started or stopped, which requires
		5099	libev to recalculate its status (and possibly tell the kernel, depending
		5100	on backend and whether C<ev_io_set> was used).
		5101
		5102	=item Activating one watcher (putting it into the pending state): O(1)
		5103
		5104	=item Priority handling: O(number_of_priorities)
		5105
		5106	Priorities are implemented by allocating some space for each
		5107	priority. When doing priority-based operations, libev usually has to
		5108	linearly search all the priorities, but starting/stopping and activating
		5109	watchers becomes O(1) with respect to priority handling.
		5110
		5111	=item Sending an ev_async: O(1)
		5112
		5113	=item Processing ev_async_send: O(number_of_async_watchers)
		5114
		5115	=item Processing signals: O(max_signal_number)
		5116
		5117	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5118	calls in the current loop iteration. Checking for async and signal events
		5119	involves iterating over all running async watchers or all signal numbers.
		5120
		5121	=back
		5122
		5123
		5124	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5125
		5126	The major version 4 introduced some incompatible changes to the API.
		5127
		5128	At the moment, the C<ev.h> header file provides compatibility definitions
		5129	for all changes, so most programs should still compile. The compatibility
		5130	layer might be removed in later versions of libev, so better update to the
		5131	new API early than late.
		5132
		5133	=over 4
		5134
		5135	=item C<EV_COMPAT3> backwards compatibility mechanism
		5136
		5137	The backward compatibility mechanism can be controlled by
		5138	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5139	section.
		5140
		5141	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5142
		5143	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5144
		5145	ev_loop_destroy (EV_DEFAULT_UC);
		5146	ev_loop_fork (EV_DEFAULT);
		5147
		5148	=item function/symbol renames
		5149
		5150	A number of functions and symbols have been renamed:
		5151
		5152	ev_loop => ev_run
		5153	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5154	EVLOOP_ONESHOT => EVRUN_ONCE
		5155
		5156	ev_unloop => ev_break
		5157	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5158	EVUNLOOP_ONE => EVBREAK_ONE
		5159	EVUNLOOP_ALL => EVBREAK_ALL
		5160
		5161	EV_TIMEOUT => EV_TIMER
		5162
		5163	ev_loop_count => ev_iteration
		5164	ev_loop_depth => ev_depth
		5165	ev_loop_verify => ev_verify
		5166
		5167	Most functions working on C<struct ev_loop> objects don't have an
		5168	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5169	associated constants have been renamed to not collide with the C<struct
		5170	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5171	as all other watcher types. Note that C<ev_loop_fork> is still called
		5172	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5173	typedef.
		5174
		5175	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5176
		5177	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5178	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5179	and work, but the library code will of course be larger.
		5180
		5181	=back
		5182
		5183
		5184	=head1 GLOSSARY
		5185
		5186	=over 4
		5187
		5188	=item active
		5189
		5190	A watcher is active as long as it has been started and not yet stopped.
		5191	See L<WATCHER STATES> for details.
		5192
		5193	=item application
		5194
		5195	In this document, an application is whatever is using libev.
		5196
		5197	=item backend
		5198
		5199	The part of the code dealing with the operating system interfaces.
		5200
		5201	=item callback
		5202
		5203	The address of a function that is called when some event has been
		5204	detected. Callbacks are being passed the event loop, the watcher that
		5205	received the event, and the actual event bitset.
		5206
		5207	=item callback/watcher invocation
		5208
		5209	The act of calling the callback associated with a watcher.
		5210
		5211	=item event
		5212
		5213	A change of state of some external event, such as data now being available
		5214	for reading on a file descriptor, time having passed or simply not having
		5215	any other events happening anymore.
		5216
		5217	In libev, events are represented as single bits (such as C<EV_READ> or
		5218	C<EV_TIMER>).
		5219
		5220	=item event library
		5221
		5222	A software package implementing an event model and loop.
		5223
		5224	=item event loop
		5225
		5226	An entity that handles and processes external events and converts them
		5227	into callback invocations.
		5228
		5229	=item event model
		5230
		5231	The model used to describe how an event loop handles and processes
		5232	watchers and events.
		5233
		5234	=item pending
		5235
		5236	A watcher is pending as soon as the corresponding event has been
		5237	detected. See L<WATCHER STATES> for details.
		5238
		5239	=item real time
		5240
		5241	The physical time that is observed. It is apparently strictly monotonic :)
		5242
		5243	=item wall-clock time
		5244
		5245	The time and date as shown on clocks. Unlike real time, it can actually
		5246	be wrong and jump forwards and backwards, e.g. when you adjust your
		5247	clock.
		5248
		5249	=item watcher
		5250
		5251	A data structure that describes interest in certain events. Watchers need
		5252	to be started (attached to an event loop) before they can receive events.
		5253
		5254	=back
2863		5255
2864	=head1 AUTHOR	5256	=head1 AUTHOR
2865		5257
2866	Marc Lehmann <libev@schmorp.de>.	5258	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5259	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
2867		5260

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