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Revision 1.115 by root, Mon Dec 31 01:32:59 2007 UTC vs.
Revision 1.352 by root, Mon Jan 10 14:30:15 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	// unloop 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	This flag's behaviour will become the default in future versions of libev.
305		448
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		450
308	This is your standard select(2) backend. Not I<completely> standard, as	451	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,	452	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	453	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	454	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.	455	usually the fastest backend for a low number of (low-numbered :) fds.
313		456
314	To get good performance out of this backend you need a high amount of	457	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	458	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	459	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	460	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	461	a look at C<ev_set_io_collect_interval ()> to increase the amount of
319	readyness notifications you get per iteration.	462	readiness notifications you get per iteration.
		463
		464	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		465	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		466	C<exceptfds> set on that platform).
320		467
321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	468	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
322		469
323	And this is your standard poll(2) backend. It's more complicated	470	And this is your standard poll(2) backend. It's more complicated
324	than select, but handles sparse fds better and has no artificial	471	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	472	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,	473	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	474	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
328	performance tips.	475	performance tips.
329		476
		477	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		478	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		479
330	=item C<EVBACKEND_EPOLL> (value 4, Linux)	480	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		481
		482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		483	kernels).
331		484
332	For few fds, this backend is a bit little slower than poll and select,	485	For few fds, this backend is a bit little slower than poll and select,
333	but it scales phenomenally better. While poll and select usually scale	486	but it scales phenomenally better. While poll and select usually scale
334	like O(total_fds) where n is the total number of fds (or the highest fd),	487	like O(total_fds) where n is the total number of fds (or the highest fd),
335	epoll scales either O(1) or O(active_fds). The epoll design has a number	488	epoll scales either O(1) or O(active_fds).
336	of shortcomings, such as silently dropping events in some hard-to-detect	489
337	cases and rewiring a syscall per fd change, no fork support and bad	490	The epoll mechanism deserves honorable mention as the most misdesigned
338	support for dup.	491	of the more advanced event mechanisms: mere annoyances include silently
		492	dropping file descriptors, requiring a system call per change per file
		493	descriptor (and unnecessary guessing of parameters), problems with dup,
		494	returning before the timeout value, resulting in additional iterations
		495	(and only giving 5ms accuracy while select on the same platform gives
		496	0.1ms) and so on. The biggest issue is fork races, however - if a program
		497	forks then I<both> parent and child process have to recreate the epoll
		498	set, which can take considerable time (one syscall per file descriptor)
		499	and is of course hard to detect.
		500
		501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		502	of course I<doesn't>, and epoll just loves to report events for totally
		503	I<different> file descriptors (even already closed ones, so one cannot
		504	even remove them from the set) than registered in the set (especially
		505	on SMP systems). Libev tries to counter these spurious notifications by
		506	employing an additional generation counter and comparing that against the
		507	events to filter out spurious ones, recreating the set when required. Last
		508	not least, it also refuses to work with some file descriptors which work
		509	perfectly fine with C<select> (files, many character devices...).
		510
		511	Epoll is truly the train wreck analog among event poll mechanisms.
339		512
340	While stopping, setting and starting an I/O watcher in the same iteration	513	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	514	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	515	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	516	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
344	very well if you register events for both fds.	517	file descriptors might not work very well if you register events for both
345		518	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		519
350	Best performance from this backend is achieved by not unregistering all	520	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.	521	watchers for a file descriptor until it has been closed, if possible,
352	keep at least one watcher active per fd at all times.	522	i.e. keep at least one watcher active per fd at all times. Stopping and
		523	starting a watcher (without re-setting it) also usually doesn't cause
		524	extra overhead. A fork can both result in spurious notifications as well
		525	as in libev having to destroy and recreate the epoll object, which can
		526	take considerable time and thus should be avoided.
353		527
		528	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		529	faster than epoll for maybe up to a hundred file descriptors, depending on
		530	the usage. So sad.
		531
354	While nominally embeddeble in other event loops, this feature is broken in	532	While nominally embeddable in other event loops, this feature is broken in
355	all kernel versions tested so far.	533	all kernel versions tested so far.
		534
		535	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		536	C<EVBACKEND_POLL>.
356		537
357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	538	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
358		539
359	Kqueue deserves special mention, as at the time of this writing, it	540	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	541	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	542	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"	543	it's completely useless). Unlike epoll, however, whose brokenness
		544	is by design, these kqueue bugs can (and eventually will) be fixed
		545	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	546	"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)	547	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
365	system like NetBSD.	548	system like NetBSD.
366		549
367	You still can embed kqueue into a normal poll or select backend and use it	550	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	551	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.	552	the target platform). See C<ev_embed> watchers for more info.
370		553
371	It scales in the same way as the epoll backend, but the interface to the	554	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	555	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	556	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	557	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	558	two event changes per incident. Support for C<fork ()> is very bad (but
376	drops fds silently in similarly hard-to-detect cases.	559	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		560	cases
377		561
378	This backend usually performs well under most conditions.	562	This backend usually performs well under most conditions.
379		563
380	While nominally embeddable in other event loops, this doesn't work	564	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	565	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	566	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	567	(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	568	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
385	sockets.	569	also broken on OS X)) and, did I mention it, using it only for sockets.
		570
		571	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		572	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		573	C<NOTE_EOF>.
386		574
387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	575	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
388		576
389	This is not implemented yet (and might never be, unless you send me an	577	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	578	implementation). According to reports, C</dev/poll> only supports sockets
…		…
394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	582	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
395		583
396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	584	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)).	585	it's really slow, but it still scales very well (O(active_fds)).
398		586
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	587	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	588	file descriptor per loop iteration. For small and medium numbers of file
405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	589	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
406	might perform better.	590	might perform better.
407		591
		592	On the positive side, this backend actually performed fully to
		593	specification in all tests and is fully embeddable, which is a rare feat
		594	among the OS-specific backends (I vastly prefer correctness over speed
		595	hacks).
		596
		597	On the negative side, the interface is I<bizarre> - so bizarre that
		598	even sun itself gets it wrong in their code examples: The event polling
		599	function sometimes returning events to the caller even though an error
		600	occured, but with no indication whether it has done so or not (yes, it's
		601	even documented that way) - deadly for edge-triggered interfaces where
		602	you absolutely have to know whether an event occured or not because you
		603	have to re-arm the watcher.
		604
		605	Fortunately libev seems to be able to work around these idiocies.
		606
		607	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		608	C<EVBACKEND_POLL>.
		609
408	=item C<EVBACKEND_ALL>	610	=item C<EVBACKEND_ALL>
409		611
410	Try all backends (even potentially broken ones that wouldn't be tried	612	Try all backends (even potentially broken ones that wouldn't be tried
411	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	613	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	614	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
413		615
414	It is definitely not recommended to use this flag.	616	It is definitely not recommended to use this flag, use whatever
		617	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		618	at all.
		619
		620	=item C<EVBACKEND_MASK>
		621
		622	Not a backend at all, but a mask to select all backend bits from a
		623	C<flags> value, in case you want to mask out any backends from a flags
		624	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
415		625
416	=back	626	=back
417		627
418	If one or more of these are ored into the flags value, then only these	628	If one or more of the backend flags are or'ed into the flags value,
419	backends will be tried (in the reverse order as given here). If none are	629	then only these backends will be tried (in the reverse order as listed
420	specified, most compiled-in backend will be tried, usually in reverse	630	here). If none are specified, all backends in C<ev_recommended_backends
421	order of their flag values :)	631	()> will be tried.
422
423	The most typical usage is like this:
424
425	if (!ev_default_loop (0))
426	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
427
428	Restrict libev to the select and poll backends, and do not allow
429	environment settings to be taken into account:
430
431	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
432
433	Use whatever libev has to offer, but make sure that kqueue is used if
434	available (warning, breaks stuff, best use only with your own private
435	event loop and only if you know the OS supports your types of fds):
436
437	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
438
439	=item struct ev_loop *ev_loop_new (unsigned int flags)
440
441	Similar to C<ev_default_loop>, but always creates a new event loop that is
442	always distinct from the default loop. Unlike the default loop, it cannot
443	handle signal and child watchers, and attempts to do so will be greeted by
444	undefined behaviour (or a failed assertion if assertions are enabled).
445		632
446	Example: Try to create a event loop that uses epoll and nothing else.	633	Example: Try to create a event loop that uses epoll and nothing else.
447		634
448	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	635	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
449	if (!epoller)	636	if (!epoller)
450	fatal ("no epoll found here, maybe it hides under your chair");	637	fatal ("no epoll found here, maybe it hides under your chair");
451		638
		639	Example: Use whatever libev has to offer, but make sure that kqueue is
		640	used if available.
		641
		642	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		643
452	=item ev_default_destroy ()	644	=item ev_loop_destroy (loop)
453		645
454	Destroys the default loop again (frees all memory and kernel state	646	Destroys an event loop object (frees all memory and kernel state
455	etc.). None of the active event watchers will be stopped in the normal	647	etc.). None of the active event watchers will be stopped in the normal
456	sense, so e.g. C<ev_is_active> might still return true. It is your	648	sense, so e.g. C<ev_is_active> might still return true. It is your
457	responsibility to either stop all watchers cleanly yoursef I<before>	649	responsibility to either stop all watchers cleanly yourself I<before>
458	calling this function, or cope with the fact afterwards (which is usually	650	calling this function, or cope with the fact afterwards (which is usually
459	the easiest thing, you can just ignore the watchers and/or C<free ()> them	651	the easiest thing, you can just ignore the watchers and/or C<free ()> them
460	for example).	652	for example).
461		653
462	Note that certain global state, such as signal state, will not be freed by	654	Note that certain global state, such as signal state (and installed signal
463	this function, and related watchers (such as signal and child watchers)	655	handlers), will not be freed by this function, and related watchers (such
464	would need to be stopped manually.	656	as signal and child watchers) would need to be stopped manually.
465		657
466	In general it is not advisable to call this function except in the	658	This function is normally used on loop objects allocated by
467	rare occasion where you really need to free e.g. the signal handling	659	C<ev_loop_new>, but it can also be used on the default loop returned by
		660	C<ev_default_loop>, in which case it is not thread-safe.
		661
		662	Note that it is not advisable to call this function on the default loop
		663	except in the rare occasion where you really need to free its resources.
468	pipe fds. If you need dynamically allocated loops it is better to use	664	If you need dynamically allocated loops it is better to use C<ev_loop_new>
469	C<ev_loop_new> and C<ev_loop_destroy>).	665	and C<ev_loop_destroy>.
470		666
471	=item ev_loop_destroy (loop)	667	=item ev_loop_fork (loop)
472		668
473	Like C<ev_default_destroy>, but destroys an event loop created by an	669	This function sets a flag that causes subsequent C<ev_run> iterations to
474	earlier call to C<ev_loop_new>.
475
476	=item ev_default_fork ()
477
478	This function reinitialises the kernel state for backends that have	670	reinitialise the kernel state for backends that have one. Despite the
479	one. Despite the name, you can call it anytime, but it makes most sense	671	name, you can call it anytime, but it makes most sense after forking, in
480	after forking, in either the parent or child process (or both, but that	672	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
481	again makes little sense).	673	child before resuming or calling C<ev_run>.
482		674
483	You I<must> call this function in the child process after forking if and	675	Again, you I<have> to call it on I<any> loop that you want to re-use after
484	only if you want to use the event library in both processes. If you just	676	a fork, I<even if you do not plan to use the loop in the parent>. This is
485	fork+exec, you don't have to call it.	677	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		678	during fork.
		679
		680	On the other hand, you only need to call this function in the child
		681	process if and only if you want to use the event loop in the child. If
		682	you just fork+exec or create a new loop in the child, you don't have to
		683	call it at all (in fact, C<epoll> is so badly broken that it makes a
		684	difference, but libev will usually detect this case on its own and do a
		685	costly reset of the backend).
486		686
487	The function itself is quite fast and it's usually not a problem to call	687	The function itself is quite fast and it's usually not a problem to call
488	it just in case after a fork. To make this easy, the function will fit in	688	it just in case after a fork.
489	quite nicely into a call to C<pthread_atfork>:
490		689
		690	Example: Automate calling C<ev_loop_fork> on the default loop when
		691	using pthreads.
		692
		693	static void
		694	post_fork_child (void)
		695	{
		696	ev_loop_fork (EV_DEFAULT);
		697	}
		698
		699	...
491	pthread_atfork (0, 0, ev_default_fork);	700	pthread_atfork (0, 0, post_fork_child);
492		701
493	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	702	=item int ev_is_default_loop (loop)
494	without calling this function, so if you force one of those backends you
495	do not need to care.
496		703
497	=item ev_loop_fork (loop)	704	Returns true when the given loop is, in fact, the default loop, and false
		705	otherwise.
498		706
499	Like C<ev_default_fork>, but acts on an event loop created by
500	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
501	after fork, and how you do this is entirely your own problem.
502
503	=item unsigned int ev_loop_count (loop)	707	=item unsigned int ev_iteration (loop)
504		708
505	Returns the count of loop iterations for the loop, which is identical to	709	Returns the current iteration count for the event loop, which is identical
506	the number of times libev did poll for new events. It starts at C<0> and	710	to the number of times libev did poll for new events. It starts at C<0>
507	happily wraps around with enough iterations.	711	and happily wraps around with enough iterations.
508		712
509	This value can sometimes be useful as a generation counter of sorts (it	713	This value can sometimes be useful as a generation counter of sorts (it
510	"ticks" the number of loop iterations), as it roughly corresponds with	714	"ticks" the number of loop iterations), as it roughly corresponds with
511	C<ev_prepare> and C<ev_check> calls.	715	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		716	prepare and check phases.
		717
		718	=item unsigned int ev_depth (loop)
		719
		720	Returns the number of times C<ev_run> was entered minus the number of
		721	times C<ev_run> was exited normally, in other words, the recursion depth.
		722
		723	Outside C<ev_run>, this number is zero. In a callback, this number is
		724	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		725	in which case it is higher.
		726
		727	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		728	throwing an exception etc.), doesn't count as "exit" - consider this
		729	as a hint to avoid such ungentleman-like behaviour unless it's really
		730	convenient, in which case it is fully supported.
512		731
513	=item unsigned int ev_backend (loop)	732	=item unsigned int ev_backend (loop)
514		733
515	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	734	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
516	use.	735	use.
…		…
521	received events and started processing them. This timestamp does not	740	received events and started processing them. This timestamp does not
522	change as long as callbacks are being processed, and this is also the base	741	change as long as callbacks are being processed, and this is also the base
523	time used for relative timers. You can treat it as the timestamp of the	742	time used for relative timers. You can treat it as the timestamp of the
524	event occurring (or more correctly, libev finding out about it).	743	event occurring (or more correctly, libev finding out about it).
525		744
		745	=item ev_now_update (loop)
		746
		747	Establishes the current time by querying the kernel, updating the time
		748	returned by C<ev_now ()> in the progress. This is a costly operation and
		749	is usually done automatically within C<ev_run ()>.
		750
		751	This function is rarely useful, but when some event callback runs for a
		752	very long time without entering the event loop, updating libev's idea of
		753	the current time is a good idea.
		754
		755	See also L<The special problem of time updates> in the C<ev_timer> section.
		756
		757	=item ev_suspend (loop)
		758
		759	=item ev_resume (loop)
		760
		761	These two functions suspend and resume an event loop, for use when the
		762	loop is not used for a while and timeouts should not be processed.
		763
		764	A typical use case would be an interactive program such as a game: When
		765	the user presses C<^Z> to suspend the game and resumes it an hour later it
		766	would be best to handle timeouts as if no time had actually passed while
		767	the program was suspended. This can be achieved by calling C<ev_suspend>
		768	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		769	C<ev_resume> directly afterwards to resume timer processing.
		770
		771	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		772	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		773	will be rescheduled (that is, they will lose any events that would have
		774	occurred while suspended).
		775
		776	After calling C<ev_suspend> you B<must not> call I<any> function on the
		777	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		778	without a previous call to C<ev_suspend>.
		779
		780	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		781	event loop time (see C<ev_now_update>).
		782
526	=item ev_loop (loop, int flags)	783	=item ev_run (loop, int flags)
527		784
528	Finally, this is it, the event handler. This function usually is called	785	Finally, this is it, the event handler. This function usually is called
529	after you initialised all your watchers and you want to start handling	786	after you have initialised all your watchers and you want to start
530	events.	787	handling events. It will ask the operating system for any new events, call
		788	the watcher callbacks, an then repeat the whole process indefinitely: This
		789	is why event loops are called I<loops>.
531		790
532	If the flags argument is specified as C<0>, it will not return until	791	If the flags argument is specified as C<0>, it will keep handling events
533	either no event watchers are active anymore or C<ev_unloop> was called.	792	until either no event watchers are active anymore or C<ev_break> was
		793	called.
534		794
535	Please note that an explicit C<ev_unloop> is usually better than	795	Please note that an explicit C<ev_break> is usually better than
536	relying on all watchers to be stopped when deciding when a program has	796	relying on all watchers to be stopped when deciding when a program has
537	finished (especially in interactive programs), but having a program that	797	finished (especially in interactive programs), but having a program
538	automatically loops as long as it has to and no longer by virtue of	798	that automatically loops as long as it has to and no longer by virtue
539	relying on its watchers stopping correctly is a thing of beauty.	799	of relying on its watchers stopping correctly, that is truly a thing of
		800	beauty.
540		801
		802	This function is also I<mostly> exception-safe - you can break out of
		803	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		804	exception and so on. This does not decrement the C<ev_depth> value, nor
		805	will it clear any outstanding C<EVBREAK_ONE> breaks.
		806
541	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	807	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
542	those events and any outstanding ones, but will not block your process in	808	those events and any already outstanding ones, but will not wait and
543	case there are no events and will return after one iteration of the loop.	809	block your process in case there are no events and will return after one
		810	iteration of the loop. This is sometimes useful to poll and handle new
		811	events while doing lengthy calculations, to keep the program responsive.
544		812
545	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	813	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
546	neccessary) and will handle those and any outstanding ones. It will block	814	necessary) and will handle those and any already outstanding ones. It
547	your process until at least one new event arrives, and will return after	815	will block your process until at least one new event arrives (which could
548	one iteration of the loop. This is useful if you are waiting for some	816	be an event internal to libev itself, so there is no guarantee that a
549	external event in conjunction with something not expressible using other	817	user-registered callback will be called), and will return after one
		818	iteration of the loop.
		819
		820	This is useful if you are waiting for some external event in conjunction
		821	with something not expressible using other libev watchers (i.e. "roll your
550	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	822	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
551	usually a better approach for this kind of thing.	823	usually a better approach for this kind of thing.
552		824
553	Here are the gory details of what C<ev_loop> does:	825	Here are the gory details of what C<ev_run> does:
554		826
		827	- Increment loop depth.
		828	- Reset the ev_break status.
555	- Before the first iteration, call any pending watchers.	829	- Before the first iteration, call any pending watchers.
		830	LOOP:
556	* If EVFLAG_FORKCHECK was used, check for a fork.	831	- If EVFLAG_FORKCHECK was used, check for a fork.
557	- If a fork was detected, queue and call all fork watchers.	832	- If a fork was detected (by any means), queue and call all fork watchers.
558	- Queue and call all prepare watchers.	833	- Queue and call all prepare watchers.
		834	- If ev_break was called, goto FINISH.
559	- If we have been forked, recreate the kernel state.	835	- If we have been forked, detach and recreate the kernel state
		836	as to not disturb the other process.
560	- Update the kernel state with all outstanding changes.	837	- Update the kernel state with all outstanding changes.
561	- Update the "event loop time".	838	- Update the "event loop time" (ev_now ()).
562	- Calculate for how long to sleep or block, if at all	839	- Calculate for how long to sleep or block, if at all
563	(active idle watchers, EVLOOP_NONBLOCK or not having	840	(active idle watchers, EVRUN_NOWAIT or not having
564	any active watchers at all will result in not sleeping).	841	any active watchers at all will result in not sleeping).
565	- Sleep if the I/O and timer collect interval say so.	842	- Sleep if the I/O and timer collect interval say so.
		843	- Increment loop iteration counter.
566	- Block the process, waiting for any events.	844	- Block the process, waiting for any events.
567	- Queue all outstanding I/O (fd) events.	845	- Queue all outstanding I/O (fd) events.
568	- Update the "event loop time" and do time jump handling.	846	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
569	- Queue all outstanding timers.	847	- Queue all expired timers.
570	- Queue all outstanding periodics.	848	- Queue all expired periodics.
571	- If no events are pending now, queue all idle watchers.	849	- Queue all idle watchers with priority higher than that of pending events.
572	- Queue all check watchers.	850	- Queue all check watchers.
573	- Call all queued watchers in reverse order (i.e. check watchers first).	851	- Call all queued watchers in reverse order (i.e. check watchers first).
574	Signals and child watchers are implemented as I/O watchers, and will	852	Signals and child watchers are implemented as I/O watchers, and will
575	be handled here by queueing them when their watcher gets executed.	853	be handled here by queueing them when their watcher gets executed.
576	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	854	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
577	were used, or there are no active watchers, return, otherwise	855	were used, or there are no active watchers, goto FINISH, otherwise
578	continue with step *.	856	continue with step LOOP.
		857	FINISH:
		858	- Reset the ev_break status iff it was EVBREAK_ONE.
		859	- Decrement the loop depth.
		860	- Return.
579		861
580	Example: Queue some jobs and then loop until no events are outstanding	862	Example: Queue some jobs and then loop until no events are outstanding
581	anymore.	863	anymore.
582		864
583	... queue jobs here, make sure they register event watchers as long	865	... queue jobs here, make sure they register event watchers as long
584	... as they still have work to do (even an idle watcher will do..)	866	... as they still have work to do (even an idle watcher will do..)
585	ev_loop (my_loop, 0);	867	ev_run (my_loop, 0);
586	... jobs done. yeah!	868	... jobs done or somebody called unloop. yeah!
587		869
588	=item ev_unloop (loop, how)	870	=item ev_break (loop, how)
589		871
590	Can be used to make a call to C<ev_loop> return early (but only after it	872	Can be used to make a call to C<ev_run> return early (but only after it
591	has processed all outstanding events). The C<how> argument must be either	873	has processed all outstanding events). The C<how> argument must be either
592	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	874	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
593	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	875	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
594		876
595	This "unloop state" will be cleared when entering C<ev_loop> again.	877	This "break state" will be cleared on the next call to C<ev_run>.
		878
		879	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		880	which case it will have no effect.
596		881
597	=item ev_ref (loop)	882	=item ev_ref (loop)
598		883
599	=item ev_unref (loop)	884	=item ev_unref (loop)
600		885
601	Ref/unref can be used to add or remove a reference count on the event	886	Ref/unref can be used to add or remove a reference count on the event
602	loop: Every watcher keeps one reference, and as long as the reference	887	loop: Every watcher keeps one reference, and as long as the reference
603	count is nonzero, C<ev_loop> will not return on its own. If you have	888	count is nonzero, C<ev_run> will not return on its own.
604	a watcher you never unregister that should not keep C<ev_loop> from	889
605	returning, ev_unref() after starting, and ev_ref() before stopping it. For	890	This is useful when you have a watcher that you never intend to
		891	unregister, but that nevertheless should not keep C<ev_run> from
		892	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		893	before stopping it.
		894
606	example, libev itself uses this for its internal signal pipe: It is not	895	As an example, libev itself uses this for its internal signal pipe: It
607	visible to the libev user and should not keep C<ev_loop> from exiting if	896	is not visible to the libev user and should not keep C<ev_run> from
608	no event watchers registered by it are active. It is also an excellent	897	exiting if no event watchers registered by it are active. It is also an
609	way to do this for generic recurring timers or from within third-party	898	excellent way to do this for generic recurring timers or from within
610	libraries. Just remember to I<unref after start> and I<ref before stop>.	899	third-party libraries. Just remember to I<unref after start> and I<ref
		900	before stop> (but only if the watcher wasn't active before, or was active
		901	before, respectively. Note also that libev might stop watchers itself
		902	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		903	in the callback).
611		904
612	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	905	Example: Create a signal watcher, but keep it from keeping C<ev_run>
613	running when nothing else is active.	906	running when nothing else is active.
614		907
615	struct ev_signal exitsig;	908	ev_signal exitsig;
616	ev_signal_init (&exitsig, sig_cb, SIGINT);	909	ev_signal_init (&exitsig, sig_cb, SIGINT);
617	ev_signal_start (loop, &exitsig);	910	ev_signal_start (loop, &exitsig);
618	evf_unref (loop);	911	ev_unref (loop);
619		912
620	Example: For some weird reason, unregister the above signal handler again.	913	Example: For some weird reason, unregister the above signal handler again.
621		914
622	ev_ref (loop);	915	ev_ref (loop);
623	ev_signal_stop (loop, &exitsig);	916	ev_signal_stop (loop, &exitsig);
624		917
625	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	918	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
626		919
627	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	920	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
628		921
629	These advanced functions influence the time that libev will spend waiting	922	These advanced functions influence the time that libev will spend waiting
630	for events. Both are by default C<0>, meaning that libev will try to	923	for events. Both time intervals are by default C<0>, meaning that libev
631	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	924	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		925	latency.
632		926
633	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	927	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
634	allows libev to delay invocation of I/O and timer/periodic callbacks to	928	allows libev to delay invocation of I/O and timer/periodic callbacks
635	increase efficiency of loop iterations.	929	to increase efficiency of loop iterations (or to increase power-saving
		930	opportunities).
636		931
637	The background is that sometimes your program runs just fast enough to	932	The idea is that sometimes your program runs just fast enough to handle
638	handle one (or very few) event(s) per loop iteration. While this makes	933	one (or very few) event(s) per loop iteration. While this makes the
639	the program responsive, it also wastes a lot of CPU time to poll for new	934	program responsive, it also wastes a lot of CPU time to poll for new
640	events, especially with backends like C<select ()> which have a high	935	events, especially with backends like C<select ()> which have a high
641	overhead for the actual polling but can deliver many events at once.	936	overhead for the actual polling but can deliver many events at once.
642		937
643	By setting a higher I<io collect interval> you allow libev to spend more	938	By setting a higher I<io collect interval> you allow libev to spend more
644	time collecting I/O events, so you can handle more events per iteration,	939	time collecting I/O events, so you can handle more events per iteration,
645	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	940	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
646	C<ev_timer>) will be not affected. Setting this to a non-null value will	941	C<ev_timer>) will be not affected. Setting this to a non-null value will
647	introduce an additional C<ev_sleep ()> call into most loop iterations.	942	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		943	sleep time ensures that libev will not poll for I/O events more often then
		944	once per this interval, on average.
648		945
649	Likewise, by setting a higher I<timeout collect interval> you allow libev	946	Likewise, by setting a higher I<timeout collect interval> you allow libev
650	to spend more time collecting timeouts, at the expense of increased	947	to spend more time collecting timeouts, at the expense of increased
651	latency (the watcher callback will be called later). C<ev_io> watchers	948	latency/jitter/inexactness (the watcher callback will be called
652	will not be affected. Setting this to a non-null value will not introduce	949	later). C<ev_io> watchers will not be affected. Setting this to a non-null
653	any overhead in libev.	950	value will not introduce any overhead in libev.
654		951
655	Many (busy) programs can usually benefit by setting the io collect	952	Many (busy) programs can usually benefit by setting the I/O collect
656	interval to a value near C<0.1> or so, which is often enough for	953	interval to a value near C<0.1> or so, which is often enough for
657	interactive servers (of course not for games), likewise for timeouts. It	954	interactive servers (of course not for games), likewise for timeouts. It
658	usually doesn't make much sense to set it to a lower value than C<0.01>,	955	usually doesn't make much sense to set it to a lower value than C<0.01>,
659	as this approsaches the timing granularity of most systems.	956	as this approaches the timing granularity of most systems. Note that if
		957	you do transactions with the outside world and you can't increase the
		958	parallelity, then this setting will limit your transaction rate (if you
		959	need to poll once per transaction and the I/O collect interval is 0.01,
		960	then you can't do more than 100 transactions per second).
		961
		962	Setting the I<timeout collect interval> can improve the opportunity for
		963	saving power, as the program will "bundle" timer callback invocations that
		964	are "near" in time together, by delaying some, thus reducing the number of
		965	times the process sleeps and wakes up again. Another useful technique to
		966	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		967	they fire on, say, one-second boundaries only.
		968
		969	Example: we only need 0.1s timeout granularity, and we wish not to poll
		970	more often than 100 times per second:
		971
		972	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		973	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		974
		975	=item ev_invoke_pending (loop)
		976
		977	This call will simply invoke all pending watchers while resetting their
		978	pending state. Normally, C<ev_run> does this automatically when required,
		979	but when overriding the invoke callback this call comes handy. This
		980	function can be invoked from a watcher - this can be useful for example
		981	when you want to do some lengthy calculation and want to pass further
		982	event handling to another thread (you still have to make sure only one
		983	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		984
		985	=item int ev_pending_count (loop)
		986
		987	Returns the number of pending watchers - zero indicates that no watchers
		988	are pending.
		989
		990	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		991
		992	This overrides the invoke pending functionality of the loop: Instead of
		993	invoking all pending watchers when there are any, C<ev_run> will call
		994	this callback instead. This is useful, for example, when you want to
		995	invoke the actual watchers inside another context (another thread etc.).
		996
		997	If you want to reset the callback, use C<ev_invoke_pending> as new
		998	callback.
		999
		1000	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1001
		1002	Sometimes you want to share the same loop between multiple threads. This
		1003	can be done relatively simply by putting mutex_lock/unlock calls around
		1004	each call to a libev function.
		1005
		1006	However, C<ev_run> can run an indefinite time, so it is not feasible
		1007	to wait for it to return. One way around this is to wake up the event
		1008	loop via C<ev_break> and C<av_async_send>, another way is to set these
		1009	I<release> and I<acquire> callbacks on the loop.
		1010
		1011	When set, then C<release> will be called just before the thread is
		1012	suspended waiting for new events, and C<acquire> is called just
		1013	afterwards.
		1014
		1015	Ideally, C<release> will just call your mutex_unlock function, and
		1016	C<acquire> will just call the mutex_lock function again.
		1017
		1018	While event loop modifications are allowed between invocations of
		1019	C<release> and C<acquire> (that's their only purpose after all), no
		1020	modifications done will affect the event loop, i.e. adding watchers will
		1021	have no effect on the set of file descriptors being watched, or the time
		1022	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1023	to take note of any changes you made.
		1024
		1025	In theory, threads executing C<ev_run> will be async-cancel safe between
		1026	invocations of C<release> and C<acquire>.
		1027
		1028	See also the locking example in the C<THREADS> section later in this
		1029	document.
		1030
		1031	=item ev_set_userdata (loop, void *data)
		1032
		1033	=item void *ev_userdata (loop)
		1034
		1035	Set and retrieve a single C<void *> associated with a loop. When
		1036	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1037	C<0>.
		1038
		1039	These two functions can be used to associate arbitrary data with a loop,
		1040	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1041	C<acquire> callbacks described above, but of course can be (ab-)used for
		1042	any other purpose as well.
		1043
		1044	=item ev_verify (loop)
		1045
		1046	This function only does something when C<EV_VERIFY> support has been
		1047	compiled in, which is the default for non-minimal builds. It tries to go
		1048	through all internal structures and checks them for validity. If anything
		1049	is found to be inconsistent, it will print an error message to standard
		1050	error and call C<abort ()>.
		1051
		1052	This can be used to catch bugs inside libev itself: under normal
		1053	circumstances, this function will never abort as of course libev keeps its
		1054	data structures consistent.
660		1055
661	=back	1056	=back
662		1057
663		1058
664	=head1 ANATOMY OF A WATCHER	1059	=head1 ANATOMY OF A WATCHER
665		1060
		1061	In the following description, uppercase C<TYPE> in names stands for the
		1062	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1063	watchers and C<ev_io_start> for I/O watchers.
		1064
666	A watcher is a structure that you create and register to record your	1065	A watcher is an opaque structure that you allocate and register to record
667	interest in some event. For instance, if you want to wait for STDIN to	1066	your interest in some event. To make a concrete example, imagine you want
668	become readable, you would create an C<ev_io> watcher for that:	1067	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1068	for that:
669		1069
670	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1070	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
671	{	1071	{
672	ev_io_stop (w);	1072	ev_io_stop (w);
673	ev_unloop (loop, EVUNLOOP_ALL);	1073	ev_break (loop, EVBREAK_ALL);
674	}	1074	}
675		1075
676	struct ev_loop *loop = ev_default_loop (0);	1076	struct ev_loop *loop = ev_default_loop (0);
		1077
677	struct ev_io stdin_watcher;	1078	ev_io stdin_watcher;
		1079
678	ev_init (&stdin_watcher, my_cb);	1080	ev_init (&stdin_watcher, my_cb);
679	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1081	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
680	ev_io_start (loop, &stdin_watcher);	1082	ev_io_start (loop, &stdin_watcher);
		1083
681	ev_loop (loop, 0);	1084	ev_run (loop, 0);
682		1085
683	As you can see, you are responsible for allocating the memory for your	1086	As you can see, you are responsible for allocating the memory for your
684	watcher structures (and it is usually a bad idea to do this on the stack,	1087	watcher structures (and it is I<usually> a bad idea to do this on the
685	although this can sometimes be quite valid).	1088	stack).
686		1089
		1090	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1091	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1092
687	Each watcher structure must be initialised by a call to C<ev_init	1093	Each watcher structure must be initialised by a call to C<ev_init (watcher
688	(watcher *, callback)>, which expects a callback to be provided. This	1094	*, callback)>, which expects a callback to be provided. This callback is
689	callback gets invoked each time the event occurs (or, in the case of io	1095	invoked each time the event occurs (or, in the case of I/O watchers, each
690	watchers, each time the event loop detects that the file descriptor given	1096	time the event loop detects that the file descriptor given is readable
691	is readable and/or writable).	1097	and/or writable).
692		1098
693	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1099	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
694	with arguments specific to this watcher type. There is also a macro	1100	macro to configure it, with arguments specific to the watcher type. There
695	to combine initialisation and setting in one call: C<< ev_<type>_init	1101	is also a macro to combine initialisation and setting in one call: C<<
696	(watcher *, callback, ...) >>.	1102	ev_TYPE_init (watcher *, callback, ...) >>.
697		1103
698	To make the watcher actually watch out for events, you have to start it	1104	To make the watcher actually watch out for events, you have to start it
699	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1105	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
700	*) >>), and you can stop watching for events at any time by calling the	1106	*) >>), and you can stop watching for events at any time by calling the
701	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1107	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
702		1108
703	As long as your watcher is active (has been started but not stopped) you	1109	As long as your watcher is active (has been started but not stopped) you
704	must not touch the values stored in it. Most specifically you must never	1110	must not touch the values stored in it. Most specifically you must never
705	reinitialise it or call its C<set> macro.	1111	reinitialise it or call its C<ev_TYPE_set> macro.
706		1112
707	Each and every callback receives the event loop pointer as first, the	1113	Each and every callback receives the event loop pointer as first, the
708	registered watcher structure as second, and a bitset of received events as	1114	registered watcher structure as second, and a bitset of received events as
709	third argument.	1115	third argument.
710		1116
…		…
719	=item C<EV_WRITE>	1125	=item C<EV_WRITE>
720		1126
721	The file descriptor in the C<ev_io> watcher has become readable and/or	1127	The file descriptor in the C<ev_io> watcher has become readable and/or
722	writable.	1128	writable.
723		1129
724	=item C<EV_TIMEOUT>	1130	=item C<EV_TIMER>
725		1131
726	The C<ev_timer> watcher has timed out.	1132	The C<ev_timer> watcher has timed out.
727		1133
728	=item C<EV_PERIODIC>	1134	=item C<EV_PERIODIC>
729		1135
…		…
747		1153
748	=item C<EV_PREPARE>	1154	=item C<EV_PREPARE>
749		1155
750	=item C<EV_CHECK>	1156	=item C<EV_CHECK>
751		1157
752	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1158	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
753	to gather new events, and all C<ev_check> watchers are invoked just after	1159	to gather new events, and all C<ev_check> watchers are invoked just after
754	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1160	C<ev_run> has gathered them, but before it invokes any callbacks for any
755	received events. Callbacks of both watcher types can start and stop as	1161	received events. Callbacks of both watcher types can start and stop as
756	many watchers as they want, and all of them will be taken into account	1162	many watchers as they want, and all of them will be taken into account
757	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1163	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
758	C<ev_loop> from blocking).	1164	C<ev_run> from blocking).
759		1165
760	=item C<EV_EMBED>	1166	=item C<EV_EMBED>
761		1167
762	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1168	The embedded event loop specified in the C<ev_embed> watcher needs attention.
763		1169
764	=item C<EV_FORK>	1170	=item C<EV_FORK>
765		1171
766	The event loop has been resumed in the child process after fork (see	1172	The event loop has been resumed in the child process after fork (see
767	C<ev_fork>).	1173	C<ev_fork>).
768		1174
		1175	=item C<EV_CLEANUP>
		1176
		1177	The event loop is about to be destroyed (see C<ev_cleanup>).
		1178
		1179	=item C<EV_ASYNC>
		1180
		1181	The given async watcher has been asynchronously notified (see C<ev_async>).
		1182
		1183	=item C<EV_CUSTOM>
		1184
		1185	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1186	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1187
769	=item C<EV_ERROR>	1188	=item C<EV_ERROR>
770		1189
771	An unspecified error has occured, the watcher has been stopped. This might	1190	An unspecified error has occurred, the watcher has been stopped. This might
772	happen because the watcher could not be properly started because libev	1191	happen because the watcher could not be properly started because libev
773	ran out of memory, a file descriptor was found to be closed or any other	1192	ran out of memory, a file descriptor was found to be closed or any other
		1193	problem. Libev considers these application bugs.
		1194
774	problem. You best act on it by reporting the problem and somehow coping	1195	You best act on it by reporting the problem and somehow coping with the
775	with the watcher being stopped.	1196	watcher being stopped. Note that well-written programs should not receive
		1197	an error ever, so when your watcher receives it, this usually indicates a
		1198	bug in your program.
776		1199
777	Libev will usually signal a few "dummy" events together with an error,	1200	Libev will usually signal a few "dummy" events together with an error, for
778	for example it might indicate that a fd is readable or writable, and if	1201	example it might indicate that a fd is readable or writable, and if your
779	your callbacks is well-written it can just attempt the operation and cope	1202	callbacks is well-written it can just attempt the operation and cope with
780	with the error from read() or write(). This will not work in multithreaded	1203	the error from read() or write(). This will not work in multi-threaded
781	programs, though, so beware.	1204	programs, though, as the fd could already be closed and reused for another
		1205	thing, so beware.
782		1206
783	=back	1207	=back
784		1208
785	=head2 GENERIC WATCHER FUNCTIONS	1209	=head2 GENERIC WATCHER FUNCTIONS
786
787	In the following description, C<TYPE> stands for the watcher type,
788	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
789		1210
790	=over 4	1211	=over 4
791		1212
792	=item C<ev_init> (ev_TYPE *watcher, callback)	1213	=item C<ev_init> (ev_TYPE *watcher, callback)
793		1214
…		…
799	which rolls both calls into one.	1220	which rolls both calls into one.
800		1221
801	You can reinitialise a watcher at any time as long as it has been stopped	1222	You can reinitialise a watcher at any time as long as it has been stopped
802	(or never started) and there are no pending events outstanding.	1223	(or never started) and there are no pending events outstanding.
803		1224
804	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1225	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
805	int revents)>.	1226	int revents)>.
806		1227
		1228	Example: Initialise an C<ev_io> watcher in two steps.
		1229
		1230	ev_io w;
		1231	ev_init (&w, my_cb);
		1232	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1233
807	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1234	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
808		1235
809	This macro initialises the type-specific parts of a watcher. You need to	1236	This macro initialises the type-specific parts of a watcher. You need to
810	call C<ev_init> at least once before you call this macro, but you can	1237	call C<ev_init> at least once before you call this macro, but you can
811	call C<ev_TYPE_set> any number of times. You must not, however, call this	1238	call C<ev_TYPE_set> any number of times. You must not, however, call this
812	macro on a watcher that is active (it can be pending, however, which is a	1239	macro on a watcher that is active (it can be pending, however, which is a
813	difference to the C<ev_init> macro).	1240	difference to the C<ev_init> macro).
814		1241
815	Although some watcher types do not have type-specific arguments	1242	Although some watcher types do not have type-specific arguments
816	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1243	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
817		1244
		1245	See C<ev_init>, above, for an example.
		1246
818	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1247	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
819		1248
820	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1249	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
821	calls into a single call. This is the most convinient method to initialise	1250	calls into a single call. This is the most convenient method to initialise
822	a watcher. The same limitations apply, of course.	1251	a watcher. The same limitations apply, of course.
823		1252
		1253	Example: Initialise and set an C<ev_io> watcher in one step.
		1254
		1255	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1256
824	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1257	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
825		1258
826	Starts (activates) the given watcher. Only active watchers will receive	1259	Starts (activates) the given watcher. Only active watchers will receive
827	events. If the watcher is already active nothing will happen.	1260	events. If the watcher is already active nothing will happen.
828		1261
		1262	Example: Start the C<ev_io> watcher that is being abused as example in this
		1263	whole section.
		1264
		1265	ev_io_start (EV_DEFAULT_UC, &w);
		1266
829	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1267	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
830		1268
831	Stops the given watcher again (if active) and clears the pending	1269	Stops the given watcher if active, and clears the pending status (whether
		1270	the watcher was active or not).
		1271
832	status. It is possible that stopped watchers are pending (for example,	1272	It is possible that stopped watchers are pending - for example,
833	non-repeating timers are being stopped when they become pending), but	1273	non-repeating timers are being stopped when they become pending - but
834	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1274	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
835	you want to free or reuse the memory used by the watcher it is therefore a	1275	pending. If you want to free or reuse the memory used by the watcher it is
836	good idea to always call its C<ev_TYPE_stop> function.	1276	therefore a good idea to always call its C<ev_TYPE_stop> function.
837		1277
838	=item bool ev_is_active (ev_TYPE *watcher)	1278	=item bool ev_is_active (ev_TYPE *watcher)
839		1279
840	Returns a true value iff the watcher is active (i.e. it has been started	1280	Returns a true value iff the watcher is active (i.e. it has been started
841	and not yet been stopped). As long as a watcher is active you must not modify	1281	and not yet been stopped). As long as a watcher is active you must not modify
…		…
857	=item ev_cb_set (ev_TYPE *watcher, callback)	1297	=item ev_cb_set (ev_TYPE *watcher, callback)
858		1298
859	Change the callback. You can change the callback at virtually any time	1299	Change the callback. You can change the callback at virtually any time
860	(modulo threads).	1300	(modulo threads).
861		1301
862	=item ev_set_priority (ev_TYPE *watcher, priority)	1302	=item ev_set_priority (ev_TYPE *watcher, int priority)
863		1303
864	=item int ev_priority (ev_TYPE *watcher)	1304	=item int ev_priority (ev_TYPE *watcher)
865		1305
866	Set and query the priority of the watcher. The priority is a small	1306	Set and query the priority of the watcher. The priority is a small
867	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1307	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
868	(default: C<-2>). Pending watchers with higher priority will be invoked	1308	(default: C<-2>). Pending watchers with higher priority will be invoked
869	before watchers with lower priority, but priority will not keep watchers	1309	before watchers with lower priority, but priority will not keep watchers
870	from being executed (except for C<ev_idle> watchers).	1310	from being executed (except for C<ev_idle> watchers).
871		1311
872	This means that priorities are I<only> used for ordering callback
873	invocation after new events have been received. This is useful, for
874	example, to reduce latency after idling, or more often, to bind two
875	watchers on the same event and make sure one is called first.
876
877	If you need to suppress invocation when higher priority events are pending	1312	If you need to suppress invocation when higher priority events are pending
878	you need to look at C<ev_idle> watchers, which provide this functionality.	1313	you need to look at C<ev_idle> watchers, which provide this functionality.
879		1314
880	You I<must not> change the priority of a watcher as long as it is active or	1315	You I<must not> change the priority of a watcher as long as it is active or
881	pending.	1316	pending.
882		1317
		1318	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1319	fine, as long as you do not mind that the priority value you query might
		1320	or might not have been clamped to the valid range.
		1321
883	The default priority used by watchers when no priority has been set is	1322	The default priority used by watchers when no priority has been set is
884	always C<0>, which is supposed to not be too high and not be too low :).	1323	always C<0>, which is supposed to not be too high and not be too low :).
885		1324
886	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1325	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
887	fine, as long as you do not mind that the priority value you query might	1326	priorities.
888	or might not have been adjusted to be within valid range.
889		1327
890	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1328	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
891		1329
892	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1330	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
893	C<loop> nor C<revents> need to be valid as long as the watcher callback	1331	C<loop> nor C<revents> need to be valid as long as the watcher callback
894	can deal with that fact.	1332	can deal with that fact, as both are simply passed through to the
		1333	callback.
895		1334
896	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1335	=item int ev_clear_pending (loop, ev_TYPE *watcher)
897		1336
898	If the watcher is pending, this function returns clears its pending status	1337	If the watcher is pending, this function clears its pending status and
899	and returns its C<revents> bitset (as if its callback was invoked). If the	1338	returns its C<revents> bitset (as if its callback was invoked). If the
900	watcher isn't pending it does nothing and returns C<0>.	1339	watcher isn't pending it does nothing and returns C<0>.
901		1340
		1341	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1342	callback to be invoked, which can be accomplished with this function.
		1343
		1344	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1345
		1346	Feeds the given event set into the event loop, as if the specified event
		1347	had happened for the specified watcher (which must be a pointer to an
		1348	initialised but not necessarily started event watcher). Obviously you must
		1349	not free the watcher as long as it has pending events.
		1350
		1351	Stopping the watcher, letting libev invoke it, or calling
		1352	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1353	not started in the first place.
		1354
		1355	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1356	functions that do not need a watcher.
		1357
902	=back	1358	=back
903		1359
904
905	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1360	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
906		1361
907	Each watcher has, by default, a member C<void *data> that you can change	1362	Each watcher has, by default, a member C<void *data> that you can change
908	and read at any time, libev will completely ignore it. This can be used	1363	and read at any time: libev will completely ignore it. This can be used
909	to associate arbitrary data with your watcher. If you need more data and	1364	to associate arbitrary data with your watcher. If you need more data and
910	don't want to allocate memory and store a pointer to it in that data	1365	don't want to allocate memory and store a pointer to it in that data
911	member, you can also "subclass" the watcher type and provide your own	1366	member, you can also "subclass" the watcher type and provide your own
912	data:	1367	data:
913		1368
914	struct my_io	1369	struct my_io
915	{	1370	{
916	struct ev_io io;	1371	ev_io io;
917	int otherfd;	1372	int otherfd;
918	void *somedata;	1373	void *somedata;
919	struct whatever *mostinteresting;	1374	struct whatever *mostinteresting;
920	}	1375	};
		1376
		1377	...
		1378	struct my_io w;
		1379	ev_io_init (&w.io, my_cb, fd, EV_READ);
921		1380
922	And since your callback will be called with a pointer to the watcher, you	1381	And since your callback will be called with a pointer to the watcher, you
923	can cast it back to your own type:	1382	can cast it back to your own type:
924		1383
925	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1384	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
926	{	1385	{
927	struct my_io *w = (struct my_io *)w_;	1386	struct my_io *w = (struct my_io *)w_;
928	...	1387	...
929	}	1388	}
930		1389
931	More interesting and less C-conformant ways of casting your callback type	1390	More interesting and less C-conformant ways of casting your callback type
932	instead have been omitted.	1391	instead have been omitted.
933		1392
934	Another common scenario is having some data structure with multiple	1393	Another common scenario is to use some data structure with multiple
935	watchers:	1394	embedded watchers:
936		1395
937	struct my_biggy	1396	struct my_biggy
938	{	1397	{
939	int some_data;	1398	int some_data;
940	ev_timer t1;	1399	ev_timer t1;
941	ev_timer t2;	1400	ev_timer t2;
942	}	1401	}
943		1402
944	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1403	In this case getting the pointer to C<my_biggy> is a bit more
945	you need to use C<offsetof>:	1404	complicated: Either you store the address of your C<my_biggy> struct
		1405	in the C<data> member of the watcher (for woozies), or you need to use
		1406	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1407	programmers):
946		1408
947	#include <stddef.h>	1409	#include <stddef.h>
948		1410
949	static void	1411	static void
950	t1_cb (EV_P_ struct ev_timer *w, int revents)	1412	t1_cb (EV_P_ ev_timer *w, int revents)
951	{	1413	{
952	struct my_biggy big = (struct my_biggy *	1414	struct my_biggy big = (struct my_biggy *)
953	(((char *)w) - offsetof (struct my_biggy, t1));	1415	(((char *)w) - offsetof (struct my_biggy, t1));
954	}	1416	}
955		1417
956	static void	1418	static void
957	t2_cb (EV_P_ struct ev_timer *w, int revents)	1419	t2_cb (EV_P_ ev_timer *w, int revents)
958	{	1420	{
959	struct my_biggy big = (struct my_biggy *	1421	struct my_biggy big = (struct my_biggy *)
960	(((char *)w) - offsetof (struct my_biggy, t2));	1422	(((char *)w) - offsetof (struct my_biggy, t2));
961	}	1423	}
		1424
		1425	=head2 WATCHER STATES
		1426
		1427	There are various watcher states mentioned throughout this manual -
		1428	active, pending and so on. In this section these states and the rules to
		1429	transition between them will be described in more detail - and while these
		1430	rules might look complicated, they usually do "the right thing".
		1431
		1432	=over 4
		1433
		1434	=item initialiased
		1435
		1436	Before a watcher can be registered with the event looop it has to be
		1437	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1438	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1439
		1440	In this state it is simply some block of memory that is suitable for use
		1441	in an event loop. It can be moved around, freed, reused etc. at will.
		1442
		1443	=item started/running/active
		1444
		1445	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1446	property of the event loop, and is actively waiting for events. While in
		1447	this state it cannot be accessed (except in a few documented ways), moved,
		1448	freed or anything else - the only legal thing is to keep a pointer to it,
		1449	and call libev functions on it that are documented to work on active watchers.
		1450
		1451	=item pending
		1452
		1453	If a watcher is active and libev determines that an event it is interested
		1454	in has occurred (such as a timer expiring), it will become pending. It will
		1455	stay in this pending state until either it is stopped or its callback is
		1456	about to be invoked, so it is not normally pending inside the watcher
		1457	callback.
		1458
		1459	The watcher might or might not be active while it is pending (for example,
		1460	an expired non-repeating timer can be pending but no longer active). If it
		1461	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1462	but it is still property of the event loop at this time, so cannot be
		1463	moved, freed or reused. And if it is active the rules described in the
		1464	previous item still apply.
		1465
		1466	It is also possible to feed an event on a watcher that is not active (e.g.
		1467	via C<ev_feed_event>), in which case it becomes pending without being
		1468	active.
		1469
		1470	=item stopped
		1471
		1472	A watcher can be stopped implicitly by libev (in which case it might still
		1473	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1474	latter will clear any pending state the watcher might be in, regardless
		1475	of whether it was active or not, so stopping a watcher explicitly before
		1476	freeing it is often a good idea.
		1477
		1478	While stopped (and not pending) the watcher is essentially in the
		1479	initialised state, that is it can be reused, moved, modified in any way
		1480	you wish.
		1481
		1482	=back
		1483
		1484	=head2 WATCHER PRIORITY MODELS
		1485
		1486	Many event loops support I<watcher priorities>, which are usually small
		1487	integers that influence the ordering of event callback invocation
		1488	between watchers in some way, all else being equal.
		1489
		1490	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1491	description for the more technical details such as the actual priority
		1492	range.
		1493
		1494	There are two common ways how these these priorities are being interpreted
		1495	by event loops:
		1496
		1497	In the more common lock-out model, higher priorities "lock out" invocation
		1498	of lower priority watchers, which means as long as higher priority
		1499	watchers receive events, lower priority watchers are not being invoked.
		1500
		1501	The less common only-for-ordering model uses priorities solely to order
		1502	callback invocation within a single event loop iteration: Higher priority
		1503	watchers are invoked before lower priority ones, but they all get invoked
		1504	before polling for new events.
		1505
		1506	Libev uses the second (only-for-ordering) model for all its watchers
		1507	except for idle watchers (which use the lock-out model).
		1508
		1509	The rationale behind this is that implementing the lock-out model for
		1510	watchers is not well supported by most kernel interfaces, and most event
		1511	libraries will just poll for the same events again and again as long as
		1512	their callbacks have not been executed, which is very inefficient in the
		1513	common case of one high-priority watcher locking out a mass of lower
		1514	priority ones.
		1515
		1516	Static (ordering) priorities are most useful when you have two or more
		1517	watchers handling the same resource: a typical usage example is having an
		1518	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1519	timeouts. Under load, data might be received while the program handles
		1520	other jobs, but since timers normally get invoked first, the timeout
		1521	handler will be executed before checking for data. In that case, giving
		1522	the timer a lower priority than the I/O watcher ensures that I/O will be
		1523	handled first even under adverse conditions (which is usually, but not
		1524	always, what you want).
		1525
		1526	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1527	will only be executed when no same or higher priority watchers have
		1528	received events, they can be used to implement the "lock-out" model when
		1529	required.
		1530
		1531	For example, to emulate how many other event libraries handle priorities,
		1532	you can associate an C<ev_idle> watcher to each such watcher, and in
		1533	the normal watcher callback, you just start the idle watcher. The real
		1534	processing is done in the idle watcher callback. This causes libev to
		1535	continuously poll and process kernel event data for the watcher, but when
		1536	the lock-out case is known to be rare (which in turn is rare :), this is
		1537	workable.
		1538
		1539	Usually, however, the lock-out model implemented that way will perform
		1540	miserably under the type of load it was designed to handle. In that case,
		1541	it might be preferable to stop the real watcher before starting the
		1542	idle watcher, so the kernel will not have to process the event in case
		1543	the actual processing will be delayed for considerable time.
		1544
		1545	Here is an example of an I/O watcher that should run at a strictly lower
		1546	priority than the default, and which should only process data when no
		1547	other events are pending:
		1548
		1549	ev_idle idle; // actual processing watcher
		1550	ev_io io; // actual event watcher
		1551
		1552	static void
		1553	io_cb (EV_P_ ev_io *w, int revents)
		1554	{
		1555	// stop the I/O watcher, we received the event, but
		1556	// are not yet ready to handle it.
		1557	ev_io_stop (EV_A_ w);
		1558
		1559	// start the idle watcher to handle the actual event.
		1560	// it will not be executed as long as other watchers
		1561	// with the default priority are receiving events.
		1562	ev_idle_start (EV_A_ &idle);
		1563	}
		1564
		1565	static void
		1566	idle_cb (EV_P_ ev_idle *w, int revents)
		1567	{
		1568	// actual processing
		1569	read (STDIN_FILENO, ...);
		1570
		1571	// have to start the I/O watcher again, as
		1572	// we have handled the event
		1573	ev_io_start (EV_P_ &io);
		1574	}
		1575
		1576	// initialisation
		1577	ev_idle_init (&idle, idle_cb);
		1578	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1579	ev_io_start (EV_DEFAULT_ &io);
		1580
		1581	In the "real" world, it might also be beneficial to start a timer, so that
		1582	low-priority connections can not be locked out forever under load. This
		1583	enables your program to keep a lower latency for important connections
		1584	during short periods of high load, while not completely locking out less
		1585	important ones.
962		1586
963		1587
964	=head1 WATCHER TYPES	1588	=head1 WATCHER TYPES
965		1589
966	This section describes each watcher in detail, but will not repeat	1590	This section describes each watcher in detail, but will not repeat
…		…
990	In general you can register as many read and/or write event watchers per	1614	In general you can register as many read and/or write event watchers per
991	fd as you want (as long as you don't confuse yourself). Setting all file	1615	fd as you want (as long as you don't confuse yourself). Setting all file
992	descriptors to non-blocking mode is also usually a good idea (but not	1616	descriptors to non-blocking mode is also usually a good idea (but not
993	required if you know what you are doing).	1617	required if you know what you are doing).
994		1618
995	If you must do this, then force the use of a known-to-be-good backend	1619	If you cannot use non-blocking mode, then force the use of a
996	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1620	known-to-be-good backend (at the time of this writing, this includes only
997	C<EVBACKEND_POLL>).	1621	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1622	descriptors for which non-blocking operation makes no sense (such as
		1623	files) - libev doesn't guarantee any specific behaviour in that case.
998		1624
999	Another thing you have to watch out for is that it is quite easy to	1625	Another thing you have to watch out for is that it is quite easy to
1000	receive "spurious" readyness notifications, that is your callback might	1626	receive "spurious" readiness notifications, that is your callback might
1001	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1627	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1002	because there is no data. Not only are some backends known to create a	1628	because there is no data. Not only are some backends known to create a
1003	lot of those (for example solaris ports), it is very easy to get into	1629	lot of those (for example Solaris ports), it is very easy to get into
1004	this situation even with a relatively standard program structure. Thus	1630	this situation even with a relatively standard program structure. Thus
1005	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1631	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1006	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1632	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1007		1633
1008	If you cannot run the fd in non-blocking mode (for example you should not	1634	If you cannot run the fd in non-blocking mode (for example you should
1009	play around with an Xlib connection), then you have to seperately re-test	1635	not play around with an Xlib connection), then you have to separately
1010	whether a file descriptor is really ready with a known-to-be good interface	1636	re-test whether a file descriptor is really ready with a known-to-be good
1011	such as poll (fortunately in our Xlib example, Xlib already does this on	1637	interface such as poll (fortunately in our Xlib example, Xlib already
1012	its own, so its quite safe to use).	1638	does this on its own, so its quite safe to use). Some people additionally
		1639	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1640	indefinitely.
		1641
		1642	But really, best use non-blocking mode.
1013		1643
1014	=head3 The special problem of disappearing file descriptors	1644	=head3 The special problem of disappearing file descriptors
1015		1645
1016	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1646	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1017	descriptor (either by calling C<close> explicitly or by any other means,	1647	descriptor (either due to calling C<close> explicitly or any other means,
1018	such as C<dup>). The reason is that you register interest in some file	1648	such as C<dup2>). The reason is that you register interest in some file
1019	descriptor, but when it goes away, the operating system will silently drop	1649	descriptor, but when it goes away, the operating system will silently drop
1020	this interest. If another file descriptor with the same number then is	1650	this interest. If another file descriptor with the same number then is
1021	registered with libev, there is no efficient way to see that this is, in	1651	registered with libev, there is no efficient way to see that this is, in
1022	fact, a different file descriptor.	1652	fact, a different file descriptor.
1023		1653
…		…
1052	To support fork in your programs, you either have to call	1682	To support fork in your programs, you either have to call
1053	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1683	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1054	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1684	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1055	C<EVBACKEND_POLL>.	1685	C<EVBACKEND_POLL>.
1056		1686
		1687	=head3 The special problem of SIGPIPE
		1688
		1689	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1690	when writing to a pipe whose other end has been closed, your program gets
		1691	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1692	this is sensible behaviour, for daemons, this is usually undesirable.
		1693
		1694	So when you encounter spurious, unexplained daemon exits, make sure you
		1695	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1696	somewhere, as that would have given you a big clue).
		1697
		1698	=head3 The special problem of accept()ing when you can't
		1699
		1700	Many implementations of the POSIX C<accept> function (for example,
		1701	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1702	connection from the pending queue in all error cases.
		1703
		1704	For example, larger servers often run out of file descriptors (because
		1705	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1706	rejecting the connection, leading to libev signalling readiness on
		1707	the next iteration again (the connection still exists after all), and
		1708	typically causing the program to loop at 100% CPU usage.
		1709
		1710	Unfortunately, the set of errors that cause this issue differs between
		1711	operating systems, there is usually little the app can do to remedy the
		1712	situation, and no known thread-safe method of removing the connection to
		1713	cope with overload is known (to me).
		1714
		1715	One of the easiest ways to handle this situation is to just ignore it
		1716	- when the program encounters an overload, it will just loop until the
		1717	situation is over. While this is a form of busy waiting, no OS offers an
		1718	event-based way to handle this situation, so it's the best one can do.
		1719
		1720	A better way to handle the situation is to log any errors other than
		1721	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1722	messages, and continue as usual, which at least gives the user an idea of
		1723	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1724	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1725	usage.
		1726
		1727	If your program is single-threaded, then you could also keep a dummy file
		1728	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1729	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1730	close that fd, and create a new dummy fd. This will gracefully refuse
		1731	clients under typical overload conditions.
		1732
		1733	The last way to handle it is to simply log the error and C<exit>, as
		1734	is often done with C<malloc> failures, but this results in an easy
		1735	opportunity for a DoS attack.
1057		1736
1058	=head3 Watcher-Specific Functions	1737	=head3 Watcher-Specific Functions
1059		1738
1060	=over 4	1739	=over 4
1061		1740
1062	=item ev_io_init (ev_io *, callback, int fd, int events)	1741	=item ev_io_init (ev_io *, callback, int fd, int events)
1063		1742
1064	=item ev_io_set (ev_io *, int fd, int events)	1743	=item ev_io_set (ev_io *, int fd, int events)
1065		1744
1066	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1745	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1067	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1746	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1068	C<EV_READ | EV_WRITE> to receive the given events.	1747	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1069		1748
1070	=item int fd [read-only]	1749	=item int fd [read-only]
1071		1750
1072	The file descriptor being watched.	1751	The file descriptor being watched.
1073		1752
…		…
1081		1760
1082	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1761	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1083	readable, but only once. Since it is likely line-buffered, you could	1762	readable, but only once. Since it is likely line-buffered, you could
1084	attempt to read a whole line in the callback.	1763	attempt to read a whole line in the callback.
1085		1764
1086	static void	1765	static void
1087	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1766	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1088	{	1767	{
1089	ev_io_stop (loop, w);	1768	ev_io_stop (loop, w);
1090	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1769	.. read from stdin here (or from w->fd) and handle any I/O errors
1091	}	1770	}
1092		1771
1093	...	1772	...
1094	struct ev_loop *loop = ev_default_init (0);	1773	struct ev_loop *loop = ev_default_init (0);
1095	struct ev_io stdin_readable;	1774	ev_io stdin_readable;
1096	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1775	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1097	ev_io_start (loop, &stdin_readable);	1776	ev_io_start (loop, &stdin_readable);
1098	ev_loop (loop, 0);	1777	ev_run (loop, 0);
1099		1778
1100		1779
1101	=head2 C<ev_timer> - relative and optionally repeating timeouts	1780	=head2 C<ev_timer> - relative and optionally repeating timeouts
1102		1781
1103	Timer watchers are simple relative timers that generate an event after a	1782	Timer watchers are simple relative timers that generate an event after a
1104	given time, and optionally repeating in regular intervals after that.	1783	given time, and optionally repeating in regular intervals after that.
1105		1784
1106	The timers are based on real time, that is, if you register an event that	1785	The timers are based on real time, that is, if you register an event that
1107	times out after an hour and you reset your system clock to last years	1786	times out after an hour and you reset your system clock to January last
1108	time, it will still time out after (roughly) and hour. "Roughly" because	1787	year, it will still time out after (roughly) one hour. "Roughly" because
1109	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1788	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1110	monotonic clock option helps a lot here).	1789	monotonic clock option helps a lot here).
		1790
		1791	The callback is guaranteed to be invoked only I<after> its timeout has
		1792	passed (not I<at>, so on systems with very low-resolution clocks this
		1793	might introduce a small delay). If multiple timers become ready during the
		1794	same loop iteration then the ones with earlier time-out values are invoked
		1795	before ones of the same priority with later time-out values (but this is
		1796	no longer true when a callback calls C<ev_run> recursively).
		1797
		1798	=head3 Be smart about timeouts
		1799
		1800	Many real-world problems involve some kind of timeout, usually for error
		1801	recovery. A typical example is an HTTP request - if the other side hangs,
		1802	you want to raise some error after a while.
		1803
		1804	What follows are some ways to handle this problem, from obvious and
		1805	inefficient to smart and efficient.
		1806
		1807	In the following, a 60 second activity timeout is assumed - a timeout that
		1808	gets reset to 60 seconds each time there is activity (e.g. each time some
		1809	data or other life sign was received).
		1810
		1811	=over 4
		1812
		1813	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1814
		1815	This is the most obvious, but not the most simple way: In the beginning,
		1816	start the watcher:
		1817
		1818	ev_timer_init (timer, callback, 60., 0.);
		1819	ev_timer_start (loop, timer);
		1820
		1821	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1822	and start it again:
		1823
		1824	ev_timer_stop (loop, timer);
		1825	ev_timer_set (timer, 60., 0.);
		1826	ev_timer_start (loop, timer);
		1827
		1828	This is relatively simple to implement, but means that each time there is
		1829	some activity, libev will first have to remove the timer from its internal
		1830	data structure and then add it again. Libev tries to be fast, but it's
		1831	still not a constant-time operation.
		1832
		1833	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1834
		1835	This is the easiest way, and involves using C<ev_timer_again> instead of
		1836	C<ev_timer_start>.
		1837
		1838	To implement this, configure an C<ev_timer> with a C<repeat> value
		1839	of C<60> and then call C<ev_timer_again> at start and each time you
		1840	successfully read or write some data. If you go into an idle state where
		1841	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1842	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1843
		1844	That means you can ignore both the C<ev_timer_start> function and the
		1845	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1846	member and C<ev_timer_again>.
		1847
		1848	At start:
		1849
		1850	ev_init (timer, callback);
		1851	timer->repeat = 60.;
		1852	ev_timer_again (loop, timer);
		1853
		1854	Each time there is some activity:
		1855
		1856	ev_timer_again (loop, timer);
		1857
		1858	It is even possible to change the time-out on the fly, regardless of
		1859	whether the watcher is active or not:
		1860
		1861	timer->repeat = 30.;
		1862	ev_timer_again (loop, timer);
		1863
		1864	This is slightly more efficient then stopping/starting the timer each time
		1865	you want to modify its timeout value, as libev does not have to completely
		1866	remove and re-insert the timer from/into its internal data structure.
		1867
		1868	It is, however, even simpler than the "obvious" way to do it.
		1869
		1870	=item 3. Let the timer time out, but then re-arm it as required.
		1871
		1872	This method is more tricky, but usually most efficient: Most timeouts are
		1873	relatively long compared to the intervals between other activity - in
		1874	our example, within 60 seconds, there are usually many I/O events with
		1875	associated activity resets.
		1876
		1877	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1878	but remember the time of last activity, and check for a real timeout only
		1879	within the callback:
		1880
		1881	ev_tstamp last_activity; // time of last activity
		1882
		1883	static void
		1884	callback (EV_P_ ev_timer *w, int revents)
		1885	{
		1886	ev_tstamp now = ev_now (EV_A);
		1887	ev_tstamp timeout = last_activity + 60.;
		1888
		1889	// if last_activity + 60. is older than now, we did time out
		1890	if (timeout < now)
		1891	{
		1892	// timeout occurred, take action
		1893	}
		1894	else
		1895	{
		1896	// callback was invoked, but there was some activity, re-arm
		1897	// the watcher to fire in last_activity + 60, which is
		1898	// guaranteed to be in the future, so "again" is positive:
		1899	w->repeat = timeout - now;
		1900	ev_timer_again (EV_A_ w);
		1901	}
		1902	}
		1903
		1904	To summarise the callback: first calculate the real timeout (defined
		1905	as "60 seconds after the last activity"), then check if that time has
		1906	been reached, which means something I<did>, in fact, time out. Otherwise
		1907	the callback was invoked too early (C<timeout> is in the future), so
		1908	re-schedule the timer to fire at that future time, to see if maybe we have
		1909	a timeout then.
		1910
		1911	Note how C<ev_timer_again> is used, taking advantage of the
		1912	C<ev_timer_again> optimisation when the timer is already running.
		1913
		1914	This scheme causes more callback invocations (about one every 60 seconds
		1915	minus half the average time between activity), but virtually no calls to
		1916	libev to change the timeout.
		1917
		1918	To start the timer, simply initialise the watcher and set C<last_activity>
		1919	to the current time (meaning we just have some activity :), then call the
		1920	callback, which will "do the right thing" and start the timer:
		1921
		1922	ev_init (timer, callback);
		1923	last_activity = ev_now (loop);
		1924	callback (loop, timer, EV_TIMER);
		1925
		1926	And when there is some activity, simply store the current time in
		1927	C<last_activity>, no libev calls at all:
		1928
		1929	last_activity = ev_now (loop);
		1930
		1931	This technique is slightly more complex, but in most cases where the
		1932	time-out is unlikely to be triggered, much more efficient.
		1933
		1934	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1935	callback :) - just change the timeout and invoke the callback, which will
		1936	fix things for you.
		1937
		1938	=item 4. Wee, just use a double-linked list for your timeouts.
		1939
		1940	If there is not one request, but many thousands (millions...), all
		1941	employing some kind of timeout with the same timeout value, then one can
		1942	do even better:
		1943
		1944	When starting the timeout, calculate the timeout value and put the timeout
		1945	at the I<end> of the list.
		1946
		1947	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1948	the list is expected to fire (for example, using the technique #3).
		1949
		1950	When there is some activity, remove the timer from the list, recalculate
		1951	the timeout, append it to the end of the list again, and make sure to
		1952	update the C<ev_timer> if it was taken from the beginning of the list.
		1953
		1954	This way, one can manage an unlimited number of timeouts in O(1) time for
		1955	starting, stopping and updating the timers, at the expense of a major
		1956	complication, and having to use a constant timeout. The constant timeout
		1957	ensures that the list stays sorted.
		1958
		1959	=back
		1960
		1961	So which method the best?
		1962
		1963	Method #2 is a simple no-brain-required solution that is adequate in most
		1964	situations. Method #3 requires a bit more thinking, but handles many cases
		1965	better, and isn't very complicated either. In most case, choosing either
		1966	one is fine, with #3 being better in typical situations.
		1967
		1968	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1969	rather complicated, but extremely efficient, something that really pays
		1970	off after the first million or so of active timers, i.e. it's usually
		1971	overkill :)
		1972
		1973	=head3 The special problem of time updates
		1974
		1975	Establishing the current time is a costly operation (it usually takes at
		1976	least two system calls): EV therefore updates its idea of the current
		1977	time only before and after C<ev_run> collects new events, which causes a
		1978	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1979	lots of events in one iteration.
1111		1980
1112	The relative timeouts are calculated relative to the C<ev_now ()>	1981	The relative timeouts are calculated relative to the C<ev_now ()>
1113	time. This is usually the right thing as this timestamp refers to the time	1982	time. This is usually the right thing as this timestamp refers to the time
1114	of the event triggering whatever timeout you are modifying/starting. If	1983	of the event triggering whatever timeout you are modifying/starting. If
1115	you suspect event processing to be delayed and you I<need> to base the timeout	1984	you suspect event processing to be delayed and you I<need> to base the
1116	on the current time, use something like this to adjust for this:	1985	timeout on the current time, use something like this to adjust for this:
1117		1986
1118	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1987	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1119		1988
1120	The callback is guarenteed to be invoked only when its timeout has passed,	1989	If the event loop is suspended for a long time, you can also force an
1121	but if multiple timers become ready during the same loop iteration then	1990	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1122	order of execution is undefined.	1991	()>.
		1992
		1993	=head3 The special problems of suspended animation
		1994
		1995	When you leave the server world it is quite customary to hit machines that
		1996	can suspend/hibernate - what happens to the clocks during such a suspend?
		1997
		1998	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1999	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2000	to run until the system is suspended, but they will not advance while the
		2001	system is suspended. That means, on resume, it will be as if the program
		2002	was frozen for a few seconds, but the suspend time will not be counted
		2003	towards C<ev_timer> when a monotonic clock source is used. The real time
		2004	clock advanced as expected, but if it is used as sole clocksource, then a
		2005	long suspend would be detected as a time jump by libev, and timers would
		2006	be adjusted accordingly.
		2007
		2008	I would not be surprised to see different behaviour in different between
		2009	operating systems, OS versions or even different hardware.
		2010
		2011	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2012	time jump in the monotonic clocks and the realtime clock. If the program
		2013	is suspended for a very long time, and monotonic clock sources are in use,
		2014	then you can expect C<ev_timer>s to expire as the full suspension time
		2015	will be counted towards the timers. When no monotonic clock source is in
		2016	use, then libev will again assume a timejump and adjust accordingly.
		2017
		2018	It might be beneficial for this latter case to call C<ev_suspend>
		2019	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2020	deterministic behaviour in this case (you can do nothing against
		2021	C<SIGSTOP>).
1123		2022
1124	=head3 Watcher-Specific Functions and Data Members	2023	=head3 Watcher-Specific Functions and Data Members
1125		2024
1126	=over 4	2025	=over 4
1127		2026
1128	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2027	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1129		2028
1130	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2029	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1131		2030
1132	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2031	Configure the timer to trigger after C<after> seconds. If C<repeat>
1133	C<0.>, then it will automatically be stopped. If it is positive, then the	2032	is C<0.>, then it will automatically be stopped once the timeout is
1134	timer will automatically be configured to trigger again C<repeat> seconds	2033	reached. If it is positive, then the timer will automatically be
1135	later, again, and again, until stopped manually.	2034	configured to trigger again C<repeat> seconds later, again, and again,
		2035	until stopped manually.
1136		2036
1137	The timer itself will do a best-effort at avoiding drift, that is, if you	2037	The timer itself will do a best-effort at avoiding drift, that is, if
1138	configure a timer to trigger every 10 seconds, then it will trigger at	2038	you configure a timer to trigger every 10 seconds, then it will normally
1139	exactly 10 second intervals. If, however, your program cannot keep up with	2039	trigger at exactly 10 second intervals. If, however, your program cannot
1140	the timer (because it takes longer than those 10 seconds to do stuff) the	2040	keep up with the timer (because it takes longer than those 10 seconds to
1141	timer will not fire more than once per event loop iteration.	2041	do stuff) the timer will not fire more than once per event loop iteration.
1142		2042
1143	=item ev_timer_again (loop)	2043	=item ev_timer_again (loop, ev_timer *)
1144		2044
1145	This will act as if the timer timed out and restart it again if it is	2045	This will act as if the timer timed out and restart it again if it is
1146	repeating. The exact semantics are:	2046	repeating. The exact semantics are:
1147		2047
1148	If the timer is pending, its pending status is cleared.	2048	If the timer is pending, its pending status is cleared.
1149		2049
1150	If the timer is started but nonrepeating, stop it (as if it timed out).	2050	If the timer is started but non-repeating, stop it (as if it timed out).
1151		2051
1152	If the timer is repeating, either start it if necessary (with the	2052	If the timer is repeating, either start it if necessary (with the
1153	C<repeat> value), or reset the running timer to the C<repeat> value.	2053	C<repeat> value), or reset the running timer to the C<repeat> value.
1154		2054
1155	This sounds a bit complicated, but here is a useful and typical	2055	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1156	example: Imagine you have a tcp connection and you want a so-called idle	2056	usage example.
1157	timeout, that is, you want to be called when there have been, say, 60
1158	seconds of inactivity on the socket. The easiest way to do this is to
1159	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1160	C<ev_timer_again> each time you successfully read or write some data. If
1161	you go into an idle state where you do not expect data to travel on the
1162	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1163	automatically restart it if need be.
1164		2057
1165	That means you can ignore the C<after> value and C<ev_timer_start>	2058	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1166	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1167		2059
1168	ev_timer_init (timer, callback, 0., 5.);	2060	Returns the remaining time until a timer fires. If the timer is active,
1169	ev_timer_again (loop, timer);	2061	then this time is relative to the current event loop time, otherwise it's
1170	...	2062	the timeout value currently configured.
1171	timer->again = 17.;
1172	ev_timer_again (loop, timer);
1173	...
1174	timer->again = 10.;
1175	ev_timer_again (loop, timer);
1176		2063
1177	This is more slightly efficient then stopping/starting the timer each time	2064	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1178	you want to modify its timeout value.	2065	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2066	will return C<4>. When the timer expires and is restarted, it will return
		2067	roughly C<7> (likely slightly less as callback invocation takes some time,
		2068	too), and so on.
1179		2069
1180	=item ev_tstamp repeat [read-write]	2070	=item ev_tstamp repeat [read-write]
1181		2071
1182	The current C<repeat> value. Will be used each time the watcher times out	2072	The current C<repeat> value. Will be used each time the watcher times out
1183	or C<ev_timer_again> is called and determines the next timeout (if any),	2073	or C<ev_timer_again> is called, and determines the next timeout (if any),
1184	which is also when any modifications are taken into account.	2074	which is also when any modifications are taken into account.
1185		2075
1186	=back	2076	=back
1187		2077
1188	=head3 Examples	2078	=head3 Examples
1189		2079
1190	Example: Create a timer that fires after 60 seconds.	2080	Example: Create a timer that fires after 60 seconds.
1191		2081
1192	static void	2082	static void
1193	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2083	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1194	{	2084	{
1195	.. one minute over, w is actually stopped right here	2085	.. one minute over, w is actually stopped right here
1196	}	2086	}
1197		2087
1198	struct ev_timer mytimer;	2088	ev_timer mytimer;
1199	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2089	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1200	ev_timer_start (loop, &mytimer);	2090	ev_timer_start (loop, &mytimer);
1201		2091
1202	Example: Create a timeout timer that times out after 10 seconds of	2092	Example: Create a timeout timer that times out after 10 seconds of
1203	inactivity.	2093	inactivity.
1204		2094
1205	static void	2095	static void
1206	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2096	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1207	{	2097	{
1208	.. ten seconds without any activity	2098	.. ten seconds without any activity
1209	}	2099	}
1210		2100
1211	struct ev_timer mytimer;	2101	ev_timer mytimer;
1212	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2102	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1213	ev_timer_again (&mytimer); /* start timer */	2103	ev_timer_again (&mytimer); /* start timer */
1214	ev_loop (loop, 0);	2104	ev_run (loop, 0);
1215		2105
1216	// and in some piece of code that gets executed on any "activity":	2106	// and in some piece of code that gets executed on any "activity":
1217	// reset the timeout to start ticking again at 10 seconds	2107	// reset the timeout to start ticking again at 10 seconds
1218	ev_timer_again (&mytimer);	2108	ev_timer_again (&mytimer);
1219		2109
1220		2110
1221	=head2 C<ev_periodic> - to cron or not to cron?	2111	=head2 C<ev_periodic> - to cron or not to cron?
1222		2112
1223	Periodic watchers are also timers of a kind, but they are very versatile	2113	Periodic watchers are also timers of a kind, but they are very versatile
1224	(and unfortunately a bit complex).	2114	(and unfortunately a bit complex).
1225		2115
1226	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2116	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1227	but on wallclock time (absolute time). You can tell a periodic watcher	2117	relative time, the physical time that passes) but on wall clock time
1228	to trigger "at" some specific point in time. For example, if you tell a	2118	(absolute time, the thing you can read on your calender or clock). The
1229	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2119	difference is that wall clock time can run faster or slower than real
1230	+ 10.>) and then reset your system clock to the last year, then it will	2120	time, and time jumps are not uncommon (e.g. when you adjust your
1231	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2121	wrist-watch).
1232	roughly 10 seconds later).
1233		2122
1234	They can also be used to implement vastly more complex timers, such as	2123	You can tell a periodic watcher to trigger after some specific point
1235	triggering an event on each midnight, local time or other, complicated,	2124	in time: for example, if you tell a periodic watcher to trigger "in 10
1236	rules.	2125	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2126	not a delay) and then reset your system clock to January of the previous
		2127	year, then it will take a year or more to trigger the event (unlike an
		2128	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2129	it, as it uses a relative timeout).
1237		2130
		2131	C<ev_periodic> watchers can also be used to implement vastly more complex
		2132	timers, such as triggering an event on each "midnight, local time", or
		2133	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2134	those cannot react to time jumps.
		2135
1238	As with timers, the callback is guarenteed to be invoked only when the	2136	As with timers, the callback is guaranteed to be invoked only when the
1239	time (C<at>) has been passed, but if multiple periodic timers become ready	2137	point in time where it is supposed to trigger has passed. If multiple
1240	during the same loop iteration then order of execution is undefined.	2138	timers become ready during the same loop iteration then the ones with
		2139	earlier time-out values are invoked before ones with later time-out values
		2140	(but this is no longer true when a callback calls C<ev_run> recursively).
1241		2141
1242	=head3 Watcher-Specific Functions and Data Members	2142	=head3 Watcher-Specific Functions and Data Members
1243		2143
1244	=over 4	2144	=over 4
1245		2145
1246	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2146	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1247		2147
1248	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2148	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1249		2149
1250	Lots of arguments, lets sort it out... There are basically three modes of	2150	Lots of arguments, let's sort it out... There are basically three modes of
1251	operation, and we will explain them from simplest to complex:	2151	operation, and we will explain them from simplest to most complex:
1252		2152
1253	=over 4	2153	=over 4
1254		2154
1255	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2155	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1256		2156
1257	In this configuration the watcher triggers an event at the wallclock time	2157	In this configuration the watcher triggers an event after the wall clock
1258	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2158	time C<offset> has passed. It will not repeat and will not adjust when a
1259	that is, if it is to be run at January 1st 2011 then it will run when the	2159	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1260	system time reaches or surpasses this time.	2160	will be stopped and invoked when the system clock reaches or surpasses
		2161	this point in time.
1261		2162
1262	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2163	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1263		2164
1264	In this mode the watcher will always be scheduled to time out at the next	2165	In this mode the watcher will always be scheduled to time out at the next
1265	C<at + N * interval> time (for some integer N, which can also be negative)	2166	C<offset + N * interval> time (for some integer N, which can also be
1266	and then repeat, regardless of any time jumps.	2167	negative) and then repeat, regardless of any time jumps. The C<offset>
		2168	argument is merely an offset into the C<interval> periods.
1267		2169
1268	This can be used to create timers that do not drift with respect to system	2170	This can be used to create timers that do not drift with respect to the
1269	time:	2171	system clock, for example, here is an C<ev_periodic> that triggers each
		2172	hour, on the hour (with respect to UTC):
1270		2173
1271	ev_periodic_set (&periodic, 0., 3600., 0);	2174	ev_periodic_set (&periodic, 0., 3600., 0);
1272		2175
1273	This doesn't mean there will always be 3600 seconds in between triggers,	2176	This doesn't mean there will always be 3600 seconds in between triggers,
1274	but only that the the callback will be called when the system time shows a	2177	but only that the callback will be called when the system time shows a
1275	full hour (UTC), or more correctly, when the system time is evenly divisible	2178	full hour (UTC), or more correctly, when the system time is evenly divisible
1276	by 3600.	2179	by 3600.
1277		2180
1278	Another way to think about it (for the mathematically inclined) is that	2181	Another way to think about it (for the mathematically inclined) is that
1279	C<ev_periodic> will try to run the callback in this mode at the next possible	2182	C<ev_periodic> will try to run the callback in this mode at the next possible
1280	time where C<time = at (mod interval)>, regardless of any time jumps.	2183	time where C<time = offset (mod interval)>, regardless of any time jumps.
1281		2184
1282	For numerical stability it is preferable that the C<at> value is near	2185	For numerical stability it is preferable that the C<offset> value is near
1283	C<ev_now ()> (the current time), but there is no range requirement for	2186	C<ev_now ()> (the current time), but there is no range requirement for
1284	this value.	2187	this value, and in fact is often specified as zero.
1285		2188
		2189	Note also that there is an upper limit to how often a timer can fire (CPU
		2190	speed for example), so if C<interval> is very small then timing stability
		2191	will of course deteriorate. Libev itself tries to be exact to be about one
		2192	millisecond (if the OS supports it and the machine is fast enough).
		2193
1286	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2194	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1287		2195
1288	In this mode the values for C<interval> and C<at> are both being	2196	In this mode the values for C<interval> and C<offset> are both being
1289	ignored. Instead, each time the periodic watcher gets scheduled, the	2197	ignored. Instead, each time the periodic watcher gets scheduled, the
1290	reschedule callback will be called with the watcher as first, and the	2198	reschedule callback will be called with the watcher as first, and the
1291	current time as second argument.	2199	current time as second argument.
1292		2200
1293	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2201	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1294	ever, or make any event loop modifications>. If you need to stop it,	2202	or make ANY other event loop modifications whatsoever, unless explicitly
1295	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2203	allowed by documentation here>.
1296	starting an C<ev_prepare> watcher, which is legal).
1297		2204
		2205	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2206	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2207	only event loop modification you are allowed to do).
		2208
1298	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2209	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1299	ev_tstamp now)>, e.g.:	2210	*w, ev_tstamp now)>, e.g.:
1300		2211
		2212	static ev_tstamp
1301	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2213	my_rescheduler (ev_periodic *w, ev_tstamp now)
1302	{	2214	{
1303	return now + 60.;	2215	return now + 60.;
1304	}	2216	}
1305		2217
1306	It must return the next time to trigger, based on the passed time value	2218	It must return the next time to trigger, based on the passed time value
1307	(that is, the lowest time value larger than to the second argument). It	2219	(that is, the lowest time value larger than to the second argument). It
1308	will usually be called just before the callback will be triggered, but	2220	will usually be called just before the callback will be triggered, but
1309	might be called at other times, too.	2221	might be called at other times, too.
1310		2222
1311	NOTE: I<< This callback must always return a time that is later than the	2223	NOTE: I<< This callback must always return a time that is higher than or
1312	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2224	equal to the passed C<now> value >>.
1313		2225
1314	This can be used to create very complex timers, such as a timer that	2226	This can be used to create very complex timers, such as a timer that
1315	triggers on each midnight, local time. To do this, you would calculate the	2227	triggers on "next midnight, local time". To do this, you would calculate the
1316	next midnight after C<now> and return the timestamp value for this. How	2228	next midnight after C<now> and return the timestamp value for this. How
1317	you do this is, again, up to you (but it is not trivial, which is the main	2229	you do this is, again, up to you (but it is not trivial, which is the main
1318	reason I omitted it as an example).	2230	reason I omitted it as an example).
1319		2231
1320	=back	2232	=back
…		…
1324	Simply stops and restarts the periodic watcher again. This is only useful	2236	Simply stops and restarts the periodic watcher again. This is only useful
1325	when you changed some parameters or the reschedule callback would return	2237	when you changed some parameters or the reschedule callback would return
1326	a different time than the last time it was called (e.g. in a crond like	2238	a different time than the last time it was called (e.g. in a crond like
1327	program when the crontabs have changed).	2239	program when the crontabs have changed).
1328		2240
		2241	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2242
		2243	When active, returns the absolute time that the watcher is supposed
		2244	to trigger next. This is not the same as the C<offset> argument to
		2245	C<ev_periodic_set>, but indeed works even in interval and manual
		2246	rescheduling modes.
		2247
1329	=item ev_tstamp offset [read-write]	2248	=item ev_tstamp offset [read-write]
1330		2249
1331	When repeating, this contains the offset value, otherwise this is the	2250	When repeating, this contains the offset value, otherwise this is the
1332	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2251	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2252	although libev might modify this value for better numerical stability).
1333		2253
1334	Can be modified any time, but changes only take effect when the periodic	2254	Can be modified any time, but changes only take effect when the periodic
1335	timer fires or C<ev_periodic_again> is being called.	2255	timer fires or C<ev_periodic_again> is being called.
1336		2256
1337	=item ev_tstamp interval [read-write]	2257	=item ev_tstamp interval [read-write]
1338		2258
1339	The current interval value. Can be modified any time, but changes only	2259	The current interval value. Can be modified any time, but changes only
1340	take effect when the periodic timer fires or C<ev_periodic_again> is being	2260	take effect when the periodic timer fires or C<ev_periodic_again> is being
1341	called.	2261	called.
1342		2262
1343	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2263	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1344		2264
1345	The current reschedule callback, or C<0>, if this functionality is	2265	The current reschedule callback, or C<0>, if this functionality is
1346	switched off. Can be changed any time, but changes only take effect when	2266	switched off. Can be changed any time, but changes only take effect when
1347	the periodic timer fires or C<ev_periodic_again> is being called.	2267	the periodic timer fires or C<ev_periodic_again> is being called.
1348		2268
1349	=item ev_tstamp at [read-only]
1350
1351	When active, contains the absolute time that the watcher is supposed to
1352	trigger next.
1353
1354	=back	2269	=back
1355		2270
1356	=head3 Examples	2271	=head3 Examples
1357		2272
1358	Example: Call a callback every hour, or, more precisely, whenever the	2273	Example: Call a callback every hour, or, more precisely, whenever the
1359	system clock is divisible by 3600. The callback invocation times have	2274	system time is divisible by 3600. The callback invocation times have
1360	potentially a lot of jittering, but good long-term stability.	2275	potentially a lot of jitter, but good long-term stability.
1361		2276
1362	static void	2277	static void
1363	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2278	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1364	{	2279	{
1365	... its now a full hour (UTC, or TAI or whatever your clock follows)	2280	... its now a full hour (UTC, or TAI or whatever your clock follows)
1366	}	2281	}
1367		2282
1368	struct ev_periodic hourly_tick;	2283	ev_periodic hourly_tick;
1369	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2284	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1370	ev_periodic_start (loop, &hourly_tick);	2285	ev_periodic_start (loop, &hourly_tick);
1371		2286
1372	Example: The same as above, but use a reschedule callback to do it:	2287	Example: The same as above, but use a reschedule callback to do it:
1373		2288
1374	#include <math.h>	2289	#include <math.h>
1375		2290
1376	static ev_tstamp	2291	static ev_tstamp
1377	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2292	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1378	{	2293	{
1379	return fmod (now, 3600.) + 3600.;	2294	return now + (3600. - fmod (now, 3600.));
1380	}	2295	}
1381		2296
1382	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2297	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1383		2298
1384	Example: Call a callback every hour, starting now:	2299	Example: Call a callback every hour, starting now:
1385		2300
1386	struct ev_periodic hourly_tick;	2301	ev_periodic hourly_tick;
1387	ev_periodic_init (&hourly_tick, clock_cb,	2302	ev_periodic_init (&hourly_tick, clock_cb,
1388	fmod (ev_now (loop), 3600.), 3600., 0);	2303	fmod (ev_now (loop), 3600.), 3600., 0);
1389	ev_periodic_start (loop, &hourly_tick);	2304	ev_periodic_start (loop, &hourly_tick);
1390		2305
1391		2306
1392	=head2 C<ev_signal> - signal me when a signal gets signalled!	2307	=head2 C<ev_signal> - signal me when a signal gets signalled!
1393		2308
1394	Signal watchers will trigger an event when the process receives a specific	2309	Signal watchers will trigger an event when the process receives a specific
1395	signal one or more times. Even though signals are very asynchronous, libev	2310	signal one or more times. Even though signals are very asynchronous, libev
1396	will try it's best to deliver signals synchronously, i.e. as part of the	2311	will try its best to deliver signals synchronously, i.e. as part of the
1397	normal event processing, like any other event.	2312	normal event processing, like any other event.
1398		2313
		2314	If you want signals to be delivered truly asynchronously, just use
		2315	C<sigaction> as you would do without libev and forget about sharing
		2316	the signal. You can even use C<ev_async> from a signal handler to
		2317	synchronously wake up an event loop.
		2318
1399	You can configure as many watchers as you like per signal. Only when the	2319	You can configure as many watchers as you like for the same signal, but
		2320	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2321	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2322	C<SIGINT> in both the default loop and another loop at the same time. At
		2323	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2324
1400	first watcher gets started will libev actually register a signal watcher	2325	When the first watcher gets started will libev actually register something
1401	with the kernel (thus it coexists with your own signal handlers as long	2326	with the kernel (thus it coexists with your own signal handlers as long as
1402	as you don't register any with libev). Similarly, when the last signal	2327	you don't register any with libev for the same signal).
1403	watcher for a signal is stopped libev will reset the signal handler to	2328
1404	SIG_DFL (regardless of what it was set to before).	2329	If possible and supported, libev will install its handlers with
		2330	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2331	not be unduly interrupted. If you have a problem with system calls getting
		2332	interrupted by signals you can block all signals in an C<ev_check> watcher
		2333	and unblock them in an C<ev_prepare> watcher.
		2334
		2335	=head3 The special problem of inheritance over fork/execve/pthread_create
		2336
		2337	Both the signal mask (C<sigprocmask>) and the signal disposition
		2338	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2339	stopping it again), that is, libev might or might not block the signal,
		2340	and might or might not set or restore the installed signal handler.
		2341
		2342	While this does not matter for the signal disposition (libev never
		2343	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2344	C<execve>), this matters for the signal mask: many programs do not expect
		2345	certain signals to be blocked.
		2346
		2347	This means that before calling C<exec> (from the child) you should reset
		2348	the signal mask to whatever "default" you expect (all clear is a good
		2349	choice usually).
		2350
		2351	The simplest way to ensure that the signal mask is reset in the child is
		2352	to install a fork handler with C<pthread_atfork> that resets it. That will
		2353	catch fork calls done by libraries (such as the libc) as well.
		2354
		2355	In current versions of libev, the signal will not be blocked indefinitely
		2356	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2357	the window of opportunity for problems, it will not go away, as libev
		2358	I<has> to modify the signal mask, at least temporarily.
		2359
		2360	So I can't stress this enough: I<If you do not reset your signal mask when
		2361	you expect it to be empty, you have a race condition in your code>. This
		2362	is not a libev-specific thing, this is true for most event libraries.
		2363
		2364	=head3 The special problem of threads signal handling
		2365
		2366	POSIX threads has problematic signal handling semantics, specifically,
		2367	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2368	threads in a process block signals, which is hard to achieve.
		2369
		2370	When you want to use sigwait (or mix libev signal handling with your own
		2371	for the same signals), you can tackle this problem by globally blocking
		2372	all signals before creating any threads (or creating them with a fully set
		2373	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2374	loops. Then designate one thread as "signal receiver thread" which handles
		2375	these signals. You can pass on any signals that libev might be interested
		2376	in by calling C<ev_feed_signal>.
1405		2377
1406	=head3 Watcher-Specific Functions and Data Members	2378	=head3 Watcher-Specific Functions and Data Members
1407		2379
1408	=over 4	2380	=over 4
1409		2381
…		…
1418		2390
1419	The signal the watcher watches out for.	2391	The signal the watcher watches out for.
1420		2392
1421	=back	2393	=back
1422		2394
		2395	=head3 Examples
		2396
		2397	Example: Try to exit cleanly on SIGINT.
		2398
		2399	static void
		2400	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2401	{
		2402	ev_break (loop, EVBREAK_ALL);
		2403	}
		2404
		2405	ev_signal signal_watcher;
		2406	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2407	ev_signal_start (loop, &signal_watcher);
		2408
1423		2409
1424	=head2 C<ev_child> - watch out for process status changes	2410	=head2 C<ev_child> - watch out for process status changes
1425		2411
1426	Child watchers trigger when your process receives a SIGCHLD in response to	2412	Child watchers trigger when your process receives a SIGCHLD in response to
1427	some child status changes (most typically when a child of yours dies).	2413	some child status changes (most typically when a child of yours dies or
		2414	exits). It is permissible to install a child watcher I<after> the child
		2415	has been forked (which implies it might have already exited), as long
		2416	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2417	forking and then immediately registering a watcher for the child is fine,
		2418	but forking and registering a watcher a few event loop iterations later or
		2419	in the next callback invocation is not.
		2420
		2421	Only the default event loop is capable of handling signals, and therefore
		2422	you can only register child watchers in the default event loop.
		2423
		2424	Due to some design glitches inside libev, child watchers will always be
		2425	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2426	libev)
		2427
		2428	=head3 Process Interaction
		2429
		2430	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2431	initialised. This is necessary to guarantee proper behaviour even if the
		2432	first child watcher is started after the child exits. The occurrence
		2433	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2434	synchronously as part of the event loop processing. Libev always reaps all
		2435	children, even ones not watched.
		2436
		2437	=head3 Overriding the Built-In Processing
		2438
		2439	Libev offers no special support for overriding the built-in child
		2440	processing, but if your application collides with libev's default child
		2441	handler, you can override it easily by installing your own handler for
		2442	C<SIGCHLD> after initialising the default loop, and making sure the
		2443	default loop never gets destroyed. You are encouraged, however, to use an
		2444	event-based approach to child reaping and thus use libev's support for
		2445	that, so other libev users can use C<ev_child> watchers freely.
		2446
		2447	=head3 Stopping the Child Watcher
		2448
		2449	Currently, the child watcher never gets stopped, even when the
		2450	child terminates, so normally one needs to stop the watcher in the
		2451	callback. Future versions of libev might stop the watcher automatically
		2452	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2453	problem).
1428		2454
1429	=head3 Watcher-Specific Functions and Data Members	2455	=head3 Watcher-Specific Functions and Data Members
1430		2456
1431	=over 4	2457	=over 4
1432		2458
1433	=item ev_child_init (ev_child *, callback, int pid)	2459	=item ev_child_init (ev_child *, callback, int pid, int trace)
1434		2460
1435	=item ev_child_set (ev_child *, int pid)	2461	=item ev_child_set (ev_child *, int pid, int trace)
1436		2462
1437	Configures the watcher to wait for status changes of process C<pid> (or	2463	Configures the watcher to wait for status changes of process C<pid> (or
1438	I<any> process if C<pid> is specified as C<0>). The callback can look	2464	I<any> process if C<pid> is specified as C<0>). The callback can look
1439	at the C<rstatus> member of the C<ev_child> watcher structure to see	2465	at the C<rstatus> member of the C<ev_child> watcher structure to see
1440	the status word (use the macros from C<sys/wait.h> and see your systems	2466	the status word (use the macros from C<sys/wait.h> and see your systems
1441	C<waitpid> documentation). The C<rpid> member contains the pid of the	2467	C<waitpid> documentation). The C<rpid> member contains the pid of the
1442	process causing the status change.	2468	process causing the status change. C<trace> must be either C<0> (only
		2469	activate the watcher when the process terminates) or C<1> (additionally
		2470	activate the watcher when the process is stopped or continued).
1443		2471
1444	=item int pid [read-only]	2472	=item int pid [read-only]
1445		2473
1446	The process id this watcher watches out for, or C<0>, meaning any process id.	2474	The process id this watcher watches out for, or C<0>, meaning any process id.
1447		2475
…		…
1456		2484
1457	=back	2485	=back
1458		2486
1459	=head3 Examples	2487	=head3 Examples
1460		2488
1461	Example: Try to exit cleanly on SIGINT and SIGTERM.	2489	Example: C<fork()> a new process and install a child handler to wait for
		2490	its completion.
1462		2491
		2492	ev_child cw;
		2493
1463	static void	2494	static void
1464	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2495	child_cb (EV_P_ ev_child *w, int revents)
1465	{	2496	{
1466	ev_unloop (loop, EVUNLOOP_ALL);	2497	ev_child_stop (EV_A_ w);
		2498	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1467	}	2499	}
1468		2500
1469	struct ev_signal signal_watcher;	2501	pid_t pid = fork ();
1470	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2502
1471	ev_signal_start (loop, &sigint_cb);	2503	if (pid < 0)
		2504	// error
		2505	else if (pid == 0)
		2506	{
		2507	// the forked child executes here
		2508	exit (1);
		2509	}
		2510	else
		2511	{
		2512	ev_child_init (&cw, child_cb, pid, 0);
		2513	ev_child_start (EV_DEFAULT_ &cw);
		2514	}
1472		2515
1473		2516
1474	=head2 C<ev_stat> - did the file attributes just change?	2517	=head2 C<ev_stat> - did the file attributes just change?
1475		2518
1476	This watches a filesystem path for attribute changes. That is, it calls	2519	This watches a file system path for attribute changes. That is, it calls
1477	C<stat> regularly (or when the OS says it changed) and sees if it changed	2520	C<stat> on that path in regular intervals (or when the OS says it changed)
1478	compared to the last time, invoking the callback if it did.	2521	and sees if it changed compared to the last time, invoking the callback if
		2522	it did.
1479		2523
1480	The path does not need to exist: changing from "path exists" to "path does	2524	The path does not need to exist: changing from "path exists" to "path does
1481	not exist" is a status change like any other. The condition "path does	2525	not exist" is a status change like any other. The condition "path does not
1482	not exist" is signified by the C<st_nlink> field being zero (which is	2526	exist" (or more correctly "path cannot be stat'ed") is signified by the
1483	otherwise always forced to be at least one) and all the other fields of	2527	C<st_nlink> field being zero (which is otherwise always forced to be at
1484	the stat buffer having unspecified contents.	2528	least one) and all the other fields of the stat buffer having unspecified
		2529	contents.
1485		2530
1486	The path I<should> be absolute and I<must not> end in a slash. If it is	2531	The path I<must not> end in a slash or contain special components such as
		2532	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1487	relative and your working directory changes, the behaviour is undefined.	2533	your working directory changes, then the behaviour is undefined.
1488		2534
1489	Since there is no standard to do this, the portable implementation simply	2535	Since there is no portable change notification interface available, the
1490	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2536	portable implementation simply calls C<stat(2)> regularly on the path
1491	can specify a recommended polling interval for this case. If you specify	2537	to see if it changed somehow. You can specify a recommended polling
1492	a polling interval of C<0> (highly recommended!) then a I<suitable,	2538	interval for this case. If you specify a polling interval of C<0> (highly
1493	unspecified default> value will be used (which you can expect to be around	2539	recommended!) then a I<suitable, unspecified default> value will be used
1494	five seconds, although this might change dynamically). Libev will also	2540	(which you can expect to be around five seconds, although this might
1495	impose a minimum interval which is currently around C<0.1>, but thats	2541	change dynamically). Libev will also impose a minimum interval which is
1496	usually overkill.	2542	currently around C<0.1>, but that's usually overkill.
1497		2543
1498	This watcher type is not meant for massive numbers of stat watchers,	2544	This watcher type is not meant for massive numbers of stat watchers,
1499	as even with OS-supported change notifications, this can be	2545	as even with OS-supported change notifications, this can be
1500	resource-intensive.	2546	resource-intensive.
1501		2547
1502	At the time of this writing, only the Linux inotify interface is	2548	At the time of this writing, the only OS-specific interface implemented
1503	implemented (implementing kqueue support is left as an exercise for the	2549	is the Linux inotify interface (implementing kqueue support is left as an
1504	reader). Inotify will be used to give hints only and should not change the	2550	exercise for the reader. Note, however, that the author sees no way of
1505	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2551	implementing C<ev_stat> semantics with kqueue, except as a hint).
1506	to fall back to regular polling again even with inotify, but changes are
1507	usually detected immediately, and if the file exists there will be no
1508	polling.
1509		2552
1510	=head3 Inotify	2553	=head3 ABI Issues (Largefile Support)
1511		2554
		2555	Libev by default (unless the user overrides this) uses the default
		2556	compilation environment, which means that on systems with large file
		2557	support disabled by default, you get the 32 bit version of the stat
		2558	structure. When using the library from programs that change the ABI to
		2559	use 64 bit file offsets the programs will fail. In that case you have to
		2560	compile libev with the same flags to get binary compatibility. This is
		2561	obviously the case with any flags that change the ABI, but the problem is
		2562	most noticeably displayed with ev_stat and large file support.
		2563
		2564	The solution for this is to lobby your distribution maker to make large
		2565	file interfaces available by default (as e.g. FreeBSD does) and not
		2566	optional. Libev cannot simply switch on large file support because it has
		2567	to exchange stat structures with application programs compiled using the
		2568	default compilation environment.
		2569
		2570	=head3 Inotify and Kqueue
		2571
1512	When C<inotify (7)> support has been compiled into libev (generally only	2572	When C<inotify (7)> support has been compiled into libev and present at
1513	available on Linux) and present at runtime, it will be used to speed up	2573	runtime, it will be used to speed up change detection where possible. The
1514	change detection where possible. The inotify descriptor will be created lazily	2574	inotify descriptor will be created lazily when the first C<ev_stat>
1515	when the first C<ev_stat> watcher is being started.	2575	watcher is being started.
1516		2576
1517	Inotify presense does not change the semantics of C<ev_stat> watchers	2577	Inotify presence does not change the semantics of C<ev_stat> watchers
1518	except that changes might be detected earlier, and in some cases, to avoid	2578	except that changes might be detected earlier, and in some cases, to avoid
1519	making regular C<stat> calls. Even in the presense of inotify support	2579	making regular C<stat> calls. Even in the presence of inotify support
1520	there are many cases where libev has to resort to regular C<stat> polling.	2580	there are many cases where libev has to resort to regular C<stat> polling,
		2581	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2582	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2583	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2584	xfs are fully working) libev usually gets away without polling.
1521		2585
1522	(There is no support for kqueue, as apparently it cannot be used to	2586	There is no support for kqueue, as apparently it cannot be used to
1523	implement this functionality, due to the requirement of having a file	2587	implement this functionality, due to the requirement of having a file
1524	descriptor open on the object at all times).	2588	descriptor open on the object at all times, and detecting renames, unlinks
		2589	etc. is difficult.
		2590
		2591	=head3 C<stat ()> is a synchronous operation
		2592
		2593	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2594	the process. The exception are C<ev_stat> watchers - those call C<stat
		2595	()>, which is a synchronous operation.
		2596
		2597	For local paths, this usually doesn't matter: unless the system is very
		2598	busy or the intervals between stat's are large, a stat call will be fast,
		2599	as the path data is usually in memory already (except when starting the
		2600	watcher).
		2601
		2602	For networked file systems, calling C<stat ()> can block an indefinite
		2603	time due to network issues, and even under good conditions, a stat call
		2604	often takes multiple milliseconds.
		2605
		2606	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2607	paths, although this is fully supported by libev.
1525		2608
1526	=head3 The special problem of stat time resolution	2609	=head3 The special problem of stat time resolution
1527		2610
1528	The C<stat ()> syscall only supports full-second resolution portably, and	2611	The C<stat ()> system call only supports full-second resolution portably,
1529	even on systems where the resolution is higher, many filesystems still	2612	and even on systems where the resolution is higher, most file systems
1530	only support whole seconds.	2613	still only support whole seconds.
1531		2614
1532	That means that, if the time is the only thing that changes, you might	2615	That means that, if the time is the only thing that changes, you can
1533	miss updates: on the first update, C<ev_stat> detects a change and calls	2616	easily miss updates: on the first update, C<ev_stat> detects a change and
1534	your callback, which does something. When there is another update within	2617	calls your callback, which does something. When there is another update
1535	the same second, C<ev_stat> will be unable to detect it.	2618	within the same second, C<ev_stat> will be unable to detect unless the
		2619	stat data does change in other ways (e.g. file size).
1536		2620
1537	The solution to this is to delay acting on a change for a second (or till	2621	The solution to this is to delay acting on a change for slightly more
1538	the next second boundary), using a roughly one-second delay C<ev_timer>	2622	than a second (or till slightly after the next full second boundary), using
1539	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2623	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1540	is added to work around small timing inconsistencies of some operating	2624	ev_timer_again (loop, w)>).
1541	systems.	2625
		2626	The C<.02> offset is added to work around small timing inconsistencies
		2627	of some operating systems (where the second counter of the current time
		2628	might be be delayed. One such system is the Linux kernel, where a call to
		2629	C<gettimeofday> might return a timestamp with a full second later than
		2630	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2631	update file times then there will be a small window where the kernel uses
		2632	the previous second to update file times but libev might already execute
		2633	the timer callback).
1542		2634
1543	=head3 Watcher-Specific Functions and Data Members	2635	=head3 Watcher-Specific Functions and Data Members
1544		2636
1545	=over 4	2637	=over 4
1546		2638
…		…
1552	C<path>. The C<interval> is a hint on how quickly a change is expected to	2644	C<path>. The C<interval> is a hint on how quickly a change is expected to
1553	be detected and should normally be specified as C<0> to let libev choose	2645	be detected and should normally be specified as C<0> to let libev choose
1554	a suitable value. The memory pointed to by C<path> must point to the same	2646	a suitable value. The memory pointed to by C<path> must point to the same
1555	path for as long as the watcher is active.	2647	path for as long as the watcher is active.
1556		2648
1557	The callback will be receive C<EV_STAT> when a change was detected,	2649	The callback will receive an C<EV_STAT> event when a change was detected,
1558	relative to the attributes at the time the watcher was started (or the	2650	relative to the attributes at the time the watcher was started (or the
1559	last change was detected).	2651	last change was detected).
1560		2652
1561	=item ev_stat_stat (ev_stat *)	2653	=item ev_stat_stat (loop, ev_stat *)
1562		2654
1563	Updates the stat buffer immediately with new values. If you change the	2655	Updates the stat buffer immediately with new values. If you change the
1564	watched path in your callback, you could call this fucntion to avoid	2656	watched path in your callback, you could call this function to avoid
1565	detecting this change (while introducing a race condition). Can also be	2657	detecting this change (while introducing a race condition if you are not
1566	useful simply to find out the new values.	2658	the only one changing the path). Can also be useful simply to find out the
		2659	new values.
1567		2660
1568	=item ev_statdata attr [read-only]	2661	=item ev_statdata attr [read-only]
1569		2662
1570	The most-recently detected attributes of the file. Although the type is of	2663	The most-recently detected attributes of the file. Although the type is
1571	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2664	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1572	suitable for your system. If the C<st_nlink> member is C<0>, then there	2665	suitable for your system, but you can only rely on the POSIX-standardised
		2666	members to be present. If the C<st_nlink> member is C<0>, then there was
1573	was some error while C<stat>ing the file.	2667	some error while C<stat>ing the file.
1574		2668
1575	=item ev_statdata prev [read-only]	2669	=item ev_statdata prev [read-only]
1576		2670
1577	The previous attributes of the file. The callback gets invoked whenever	2671	The previous attributes of the file. The callback gets invoked whenever
1578	C<prev> != C<attr>.	2672	C<prev> != C<attr>, or, more precisely, one or more of these members
		2673	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2674	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1579		2675
1580	=item ev_tstamp interval [read-only]	2676	=item ev_tstamp interval [read-only]
1581		2677
1582	The specified interval.	2678	The specified interval.
1583		2679
1584	=item const char *path [read-only]	2680	=item const char *path [read-only]
1585		2681
1586	The filesystem path that is being watched.	2682	The file system path that is being watched.
1587		2683
1588	=back	2684	=back
1589		2685
1590	=head3 Examples	2686	=head3 Examples
1591		2687
1592	Example: Watch C</etc/passwd> for attribute changes.	2688	Example: Watch C</etc/passwd> for attribute changes.
1593		2689
1594	static void	2690	static void
1595	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2691	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1596	{	2692	{
1597	/* /etc/passwd changed in some way */	2693	/* /etc/passwd changed in some way */
1598	if (w->attr.st_nlink)	2694	if (w->attr.st_nlink)
1599	{	2695	{
1600	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2696	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1601	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2697	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1602	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2698	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1603	}	2699	}
1604	else	2700	else
1605	/* you shalt not abuse printf for puts */	2701	/* you shalt not abuse printf for puts */
1606	puts ("wow, /etc/passwd is not there, expect problems. "	2702	puts ("wow, /etc/passwd is not there, expect problems. "
1607	"if this is windows, they already arrived\n");	2703	"if this is windows, they already arrived\n");
1608	}	2704	}
1609		2705
1610	...	2706	...
1611	ev_stat passwd;	2707	ev_stat passwd;
1612		2708
1613	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2709	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1614	ev_stat_start (loop, &passwd);	2710	ev_stat_start (loop, &passwd);
1615		2711
1616	Example: Like above, but additionally use a one-second delay so we do not	2712	Example: Like above, but additionally use a one-second delay so we do not
1617	miss updates (however, frequent updates will delay processing, too, so	2713	miss updates (however, frequent updates will delay processing, too, so
1618	one might do the work both on C<ev_stat> callback invocation I<and> on	2714	one might do the work both on C<ev_stat> callback invocation I<and> on
1619	C<ev_timer> callback invocation).	2715	C<ev_timer> callback invocation).
1620		2716
1621	static ev_stat passwd;	2717	static ev_stat passwd;
1622	static ev_timer timer;	2718	static ev_timer timer;
1623		2719
1624	static void	2720	static void
1625	timer_cb (EV_P_ ev_timer *w, int revents)	2721	timer_cb (EV_P_ ev_timer *w, int revents)
1626	{	2722	{
1627	ev_timer_stop (EV_A_ w);	2723	ev_timer_stop (EV_A_ w);
1628		2724
1629	/* now it's one second after the most recent passwd change */	2725	/* now it's one second after the most recent passwd change */
1630	}	2726	}
1631		2727
1632	static void	2728	static void
1633	stat_cb (EV_P_ ev_stat *w, int revents)	2729	stat_cb (EV_P_ ev_stat *w, int revents)
1634	{	2730	{
1635	/* reset the one-second timer */	2731	/* reset the one-second timer */
1636	ev_timer_again (EV_A_ &timer);	2732	ev_timer_again (EV_A_ &timer);
1637	}	2733	}
1638		2734
1639	...	2735	...
1640	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2736	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1641	ev_stat_start (loop, &passwd);	2737	ev_stat_start (loop, &passwd);
1642	ev_timer_init (&timer, timer_cb, 0., 1.01);	2738	ev_timer_init (&timer, timer_cb, 0., 1.02);
1643		2739
1644		2740
1645	=head2 C<ev_idle> - when you've got nothing better to do...	2741	=head2 C<ev_idle> - when you've got nothing better to do...
1646		2742
1647	Idle watchers trigger events when no other events of the same or higher	2743	Idle watchers trigger events when no other events of the same or higher
1648	priority are pending (prepare, check and other idle watchers do not	2744	priority are pending (prepare, check and other idle watchers do not count
1649	count).	2745	as receiving "events").
1650		2746
1651	That is, as long as your process is busy handling sockets or timeouts	2747	That is, as long as your process is busy handling sockets or timeouts
1652	(or even signals, imagine) of the same or higher priority it will not be	2748	(or even signals, imagine) of the same or higher priority it will not be
1653	triggered. But when your process is idle (or only lower-priority watchers	2749	triggered. But when your process is idle (or only lower-priority watchers
1654	are pending), the idle watchers are being called once per event loop	2750	are pending), the idle watchers are being called once per event loop
…		…
1665		2761
1666	=head3 Watcher-Specific Functions and Data Members	2762	=head3 Watcher-Specific Functions and Data Members
1667		2763
1668	=over 4	2764	=over 4
1669		2765
1670	=item ev_idle_init (ev_signal *, callback)	2766	=item ev_idle_init (ev_idle *, callback)
1671		2767
1672	Initialises and configures the idle watcher - it has no parameters of any	2768	Initialises and configures the idle watcher - it has no parameters of any
1673	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2769	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1674	believe me.	2770	believe me.
1675		2771
…		…
1678	=head3 Examples	2774	=head3 Examples
1679		2775
1680	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2776	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1681	callback, free it. Also, use no error checking, as usual.	2777	callback, free it. Also, use no error checking, as usual.
1682		2778
1683	static void	2779	static void
1684	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2780	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1685	{	2781	{
1686	free (w);	2782	free (w);
1687	// now do something you wanted to do when the program has	2783	// now do something you wanted to do when the program has
1688	// no longer asnything immediate to do.	2784	// no longer anything immediate to do.
1689	}	2785	}
1690		2786
1691	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2787	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1692	ev_idle_init (idle_watcher, idle_cb);	2788	ev_idle_init (idle_watcher, idle_cb);
1693	ev_idle_start (loop, idle_cb);	2789	ev_idle_start (loop, idle_watcher);
1694		2790
1695		2791
1696	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2792	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1697		2793
1698	Prepare and check watchers are usually (but not always) used in tandem:	2794	Prepare and check watchers are usually (but not always) used in pairs:
1699	prepare watchers get invoked before the process blocks and check watchers	2795	prepare watchers get invoked before the process blocks and check watchers
1700	afterwards.	2796	afterwards.
1701		2797
1702	You I<must not> call C<ev_loop> or similar functions that enter	2798	You I<must not> call C<ev_run> or similar functions that enter
1703	the current event loop from either C<ev_prepare> or C<ev_check>	2799	the current event loop from either C<ev_prepare> or C<ev_check>
1704	watchers. Other loops than the current one are fine, however. The	2800	watchers. Other loops than the current one are fine, however. The
1705	rationale behind this is that you do not need to check for recursion in	2801	rationale behind this is that you do not need to check for recursion in
1706	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2802	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1707	C<ev_check> so if you have one watcher of each kind they will always be	2803	C<ev_check> so if you have one watcher of each kind they will always be
1708	called in pairs bracketing the blocking call.	2804	called in pairs bracketing the blocking call.
1709		2805
1710	Their main purpose is to integrate other event mechanisms into libev and	2806	Their main purpose is to integrate other event mechanisms into libev and
1711	their use is somewhat advanced. This could be used, for example, to track	2807	their use is somewhat advanced. They could be used, for example, to track
1712	variable changes, implement your own watchers, integrate net-snmp or a	2808	variable changes, implement your own watchers, integrate net-snmp or a
1713	coroutine library and lots more. They are also occasionally useful if	2809	coroutine library and lots more. They are also occasionally useful if
1714	you cache some data and want to flush it before blocking (for example,	2810	you cache some data and want to flush it before blocking (for example,
1715	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2811	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1716	watcher).	2812	watcher).
1717		2813
1718	This is done by examining in each prepare call which file descriptors need	2814	This is done by examining in each prepare call which file descriptors
1719	to be watched by the other library, registering C<ev_io> watchers for	2815	need to be watched by the other library, registering C<ev_io> watchers
1720	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2816	for them and starting an C<ev_timer> watcher for any timeouts (many
1721	provide just this functionality). Then, in the check watcher you check for	2817	libraries provide exactly this functionality). Then, in the check watcher,
1722	any events that occured (by checking the pending status of all watchers	2818	you check for any events that occurred (by checking the pending status
1723	and stopping them) and call back into the library. The I/O and timer	2819	of all watchers and stopping them) and call back into the library. The
1724	callbacks will never actually be called (but must be valid nevertheless,	2820	I/O and timer callbacks will never actually be called (but must be valid
1725	because you never know, you know?).	2821	nevertheless, because you never know, you know?).
1726		2822
1727	As another example, the Perl Coro module uses these hooks to integrate	2823	As another example, the Perl Coro module uses these hooks to integrate
1728	coroutines into libev programs, by yielding to other active coroutines	2824	coroutines into libev programs, by yielding to other active coroutines
1729	during each prepare and only letting the process block if no coroutines	2825	during each prepare and only letting the process block if no coroutines
1730	are ready to run (it's actually more complicated: it only runs coroutines	2826	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1733	loop from blocking if lower-priority coroutines are active, thus mapping	2829	loop from blocking if lower-priority coroutines are active, thus mapping
1734	low-priority coroutines to idle/background tasks).	2830	low-priority coroutines to idle/background tasks).
1735		2831
1736	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2832	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1737	priority, to ensure that they are being run before any other watchers	2833	priority, to ensure that they are being run before any other watchers
		2834	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2835
1738	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2836	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1739	too) should not activate ("feed") events into libev. While libev fully	2837	activate ("feed") events into libev. While libev fully supports this, they
1740	supports this, they will be called before other C<ev_check> watchers	2838	might get executed before other C<ev_check> watchers did their job. As
1741	did their job. As C<ev_check> watchers are often used to embed other	2839	C<ev_check> watchers are often used to embed other (non-libev) event
1742	(non-libev) event loops those other event loops might be in an unusable	2840	loops those other event loops might be in an unusable state until their
1743	state until their C<ev_check> watcher ran (always remind yourself to	2841	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1744	coexist peacefully with others).	2842	others).
1745		2843
1746	=head3 Watcher-Specific Functions and Data Members	2844	=head3 Watcher-Specific Functions and Data Members
1747		2845
1748	=over 4	2846	=over 4
1749		2847
…		…
1751		2849
1752	=item ev_check_init (ev_check *, callback)	2850	=item ev_check_init (ev_check *, callback)
1753		2851
1754	Initialises and configures the prepare or check watcher - they have no	2852	Initialises and configures the prepare or check watcher - they have no
1755	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2853	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1756	macros, but using them is utterly, utterly and completely pointless.	2854	macros, but using them is utterly, utterly, utterly and completely
		2855	pointless.
1757		2856
1758	=back	2857	=back
1759		2858
1760	=head3 Examples	2859	=head3 Examples
1761		2860
1762	There are a number of principal ways to embed other event loops or modules	2861	There are a number of principal ways to embed other event loops or modules
1763	into libev. Here are some ideas on how to include libadns into libev	2862	into libev. Here are some ideas on how to include libadns into libev
1764	(there is a Perl module named C<EV::ADNS> that does this, which you could	2863	(there is a Perl module named C<EV::ADNS> that does this, which you could
1765	use for an actually working example. Another Perl module named C<EV::Glib>	2864	use as a working example. Another Perl module named C<EV::Glib> embeds a
1766	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2865	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1767	into the Glib event loop).	2866	Glib event loop).
1768		2867
1769	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2868	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1770	and in a check watcher, destroy them and call into libadns. What follows	2869	and in a check watcher, destroy them and call into libadns. What follows
1771	is pseudo-code only of course. This requires you to either use a low	2870	is pseudo-code only of course. This requires you to either use a low
1772	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2871	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1773	the callbacks for the IO/timeout watchers might not have been called yet.	2872	the callbacks for the IO/timeout watchers might not have been called yet.
1774		2873
1775	static ev_io iow [nfd];	2874	static ev_io iow [nfd];
1776	static ev_timer tw;	2875	static ev_timer tw;
1777		2876
1778	static void	2877	static void
1779	io_cb (ev_loop *loop, ev_io *w, int revents)	2878	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1780	{	2879	{
1781	}	2880	}
1782		2881
1783	// create io watchers for each fd and a timer before blocking	2882	// create io watchers for each fd and a timer before blocking
1784	static void	2883	static void
1785	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2884	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1786	{	2885	{
1787	int timeout = 3600000;	2886	int timeout = 3600000;
1788	struct pollfd fds [nfd];	2887	struct pollfd fds [nfd];
1789	// actual code will need to loop here and realloc etc.	2888	// actual code will need to loop here and realloc etc.
1790	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2889	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1791		2890
1792	/* the callback is illegal, but won't be called as we stop during check */	2891	/* the callback is illegal, but won't be called as we stop during check */
1793	ev_timer_init (&tw, 0, timeout * 1e-3);	2892	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1794	ev_timer_start (loop, &tw);	2893	ev_timer_start (loop, &tw);
1795		2894
1796	// create one ev_io per pollfd	2895	// create one ev_io per pollfd
1797	for (int i = 0; i < nfd; ++i)	2896	for (int i = 0; i < nfd; ++i)
1798	{	2897	{
1799	ev_io_init (iow + i, io_cb, fds [i].fd,	2898	ev_io_init (iow + i, io_cb, fds [i].fd,
1800	((fds [i].events & POLLIN ? EV_READ : 0)	2899	((fds [i].events & POLLIN ? EV_READ : 0)
1801	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2900	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1802		2901
1803	fds [i].revents = 0;	2902	fds [i].revents = 0;
1804	ev_io_start (loop, iow + i);	2903	ev_io_start (loop, iow + i);
1805	}	2904	}
1806	}	2905	}
1807		2906
1808	// stop all watchers after blocking	2907	// stop all watchers after blocking
1809	static void	2908	static void
1810	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2909	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1811	{	2910	{
1812	ev_timer_stop (loop, &tw);	2911	ev_timer_stop (loop, &tw);
1813		2912
1814	for (int i = 0; i < nfd; ++i)	2913	for (int i = 0; i < nfd; ++i)
1815	{	2914	{
1816	// set the relevant poll flags	2915	// set the relevant poll flags
1817	// could also call adns_processreadable etc. here	2916	// could also call adns_processreadable etc. here
1818	struct pollfd *fd = fds + i;	2917	struct pollfd *fd = fds + i;
1819	int revents = ev_clear_pending (iow + i);	2918	int revents = ev_clear_pending (iow + i);
1820	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2919	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1821	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2920	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1822		2921
1823	// now stop the watcher	2922	// now stop the watcher
1824	ev_io_stop (loop, iow + i);	2923	ev_io_stop (loop, iow + i);
1825	}	2924	}
1826		2925
1827	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2926	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1828	}	2927	}
1829		2928
1830	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2929	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1831	in the prepare watcher and would dispose of the check watcher.	2930	in the prepare watcher and would dispose of the check watcher.
1832		2931
1833	Method 3: If the module to be embedded supports explicit event	2932	Method 3: If the module to be embedded supports explicit event
1834	notification (adns does), you can also make use of the actual watcher	2933	notification (libadns does), you can also make use of the actual watcher
1835	callbacks, and only destroy/create the watchers in the prepare watcher.	2934	callbacks, and only destroy/create the watchers in the prepare watcher.
1836		2935
1837	static void	2936	static void
1838	timer_cb (EV_P_ ev_timer *w, int revents)	2937	timer_cb (EV_P_ ev_timer *w, int revents)
1839	{	2938	{
1840	adns_state ads = (adns_state)w->data;	2939	adns_state ads = (adns_state)w->data;
1841	update_now (EV_A);	2940	update_now (EV_A);
1842		2941
1843	adns_processtimeouts (ads, &tv_now);	2942	adns_processtimeouts (ads, &tv_now);
1844	}	2943	}
1845		2944
1846	static void	2945	static void
1847	io_cb (EV_P_ ev_io *w, int revents)	2946	io_cb (EV_P_ ev_io *w, int revents)
1848	{	2947	{
1849	adns_state ads = (adns_state)w->data;	2948	adns_state ads = (adns_state)w->data;
1850	update_now (EV_A);	2949	update_now (EV_A);
1851		2950
1852	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2951	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1853	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2952	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1854	}	2953	}
1855		2954
1856	// do not ever call adns_afterpoll	2955	// do not ever call adns_afterpoll
1857		2956
1858	Method 4: Do not use a prepare or check watcher because the module you	2957	Method 4: Do not use a prepare or check watcher because the module you
1859	want to embed is too inflexible to support it. Instead, youc na override	2958	want to embed is not flexible enough to support it. Instead, you can
1860	their poll function. The drawback with this solution is that the main	2959	override their poll function. The drawback with this solution is that the
1861	loop is now no longer controllable by EV. The C<Glib::EV> module does	2960	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1862	this.	2961	this approach, effectively embedding EV as a client into the horrible
		2962	libglib event loop.
1863		2963
1864	static gint	2964	static gint
1865	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2965	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1866	{	2966	{
1867	int got_events = 0;	2967	int got_events = 0;
1868		2968
1869	for (n = 0; n < nfds; ++n)	2969	for (n = 0; n < nfds; ++n)
1870	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2970	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1871		2971
1872	if (timeout >= 0)	2972	if (timeout >= 0)
1873	// create/start timer	2973	// create/start timer
1874		2974
1875	// poll	2975	// poll
1876	ev_loop (EV_A_ 0);	2976	ev_run (EV_A_ 0);
1877		2977
1878	// stop timer again	2978	// stop timer again
1879	if (timeout >= 0)	2979	if (timeout >= 0)
1880	ev_timer_stop (EV_A_ &to);	2980	ev_timer_stop (EV_A_ &to);
1881		2981
1882	// stop io watchers again - their callbacks should have set	2982	// stop io watchers again - their callbacks should have set
1883	for (n = 0; n < nfds; ++n)	2983	for (n = 0; n < nfds; ++n)
1884	ev_io_stop (EV_A_ iow [n]);	2984	ev_io_stop (EV_A_ iow [n]);
1885		2985
1886	return got_events;	2986	return got_events;
1887	}	2987	}
1888		2988
1889		2989
1890	=head2 C<ev_embed> - when one backend isn't enough...	2990	=head2 C<ev_embed> - when one backend isn't enough...
1891		2991
1892	This is a rather advanced watcher type that lets you embed one event loop	2992	This is a rather advanced watcher type that lets you embed one event loop
…		…
1898	prioritise I/O.	2998	prioritise I/O.
1899		2999
1900	As an example for a bug workaround, the kqueue backend might only support	3000	As an example for a bug workaround, the kqueue backend might only support
1901	sockets on some platform, so it is unusable as generic backend, but you	3001	sockets on some platform, so it is unusable as generic backend, but you
1902	still want to make use of it because you have many sockets and it scales	3002	still want to make use of it because you have many sockets and it scales
1903	so nicely. In this case, you would create a kqueue-based loop and embed it	3003	so nicely. In this case, you would create a kqueue-based loop and embed
1904	into your default loop (which might use e.g. poll). Overall operation will	3004	it into your default loop (which might use e.g. poll). Overall operation
1905	be a bit slower because first libev has to poll and then call kevent, but	3005	will be a bit slower because first libev has to call C<poll> and then
1906	at least you can use both at what they are best.	3006	C<kevent>, but at least you can use both mechanisms for what they are
		3007	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1907		3008
1908	As for prioritising I/O: rarely you have the case where some fds have	3009	As for prioritising I/O: under rare circumstances you have the case where
1909	to be watched and handled very quickly (with low latency), and even	3010	some fds have to be watched and handled very quickly (with low latency),
1910	priorities and idle watchers might have too much overhead. In this case	3011	and even priorities and idle watchers might have too much overhead. In
1911	you would put all the high priority stuff in one loop and all the rest in	3012	this case you would put all the high priority stuff in one loop and all
1912	a second one, and embed the second one in the first.	3013	the rest in a second one, and embed the second one in the first.
1913		3014
1914	As long as the watcher is active, the callback will be invoked every time	3015	As long as the watcher is active, the callback will be invoked every
1915	there might be events pending in the embedded loop. The callback must then	3016	time there might be events pending in the embedded loop. The callback
1916	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3017	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1917	their callbacks (you could also start an idle watcher to give the embedded	3018	sweep and invoke their callbacks (the callback doesn't need to invoke the
1918	loop strictly lower priority for example). You can also set the callback	3019	C<ev_embed_sweep> function directly, it could also start an idle watcher
1919	to C<0>, in which case the embed watcher will automatically execute the	3020	to give the embedded loop strictly lower priority for example).
1920	embedded loop sweep.
1921		3021
1922	As long as the watcher is started it will automatically handle events. The	3022	You can also set the callback to C<0>, in which case the embed watcher
1923	callback will be invoked whenever some events have been handled. You can	3023	will automatically execute the embedded loop sweep whenever necessary.
1924	set the callback to C<0> to avoid having to specify one if you are not
1925	interested in that.
1926		3024
1927	Also, there have not currently been made special provisions for forking:	3025	Fork detection will be handled transparently while the C<ev_embed> watcher
1928	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3026	is active, i.e., the embedded loop will automatically be forked when the
1929	but you will also have to stop and restart any C<ev_embed> watchers	3027	embedding loop forks. In other cases, the user is responsible for calling
1930	yourself.	3028	C<ev_loop_fork> on the embedded loop.
1931		3029
1932	Unfortunately, not all backends are embeddable, only the ones returned by	3030	Unfortunately, not all backends are embeddable: only the ones returned by
1933	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3031	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1934	portable one.	3032	portable one.
1935		3033
1936	So when you want to use this feature you will always have to be prepared	3034	So when you want to use this feature you will always have to be prepared
1937	that you cannot get an embeddable loop. The recommended way to get around	3035	that you cannot get an embeddable loop. The recommended way to get around
1938	this is to have a separate variables for your embeddable loop, try to	3036	this is to have a separate variables for your embeddable loop, try to
1939	create it, and if that fails, use the normal loop for everything.	3037	create it, and if that fails, use the normal loop for everything.
1940		3038
		3039	=head3 C<ev_embed> and fork
		3040
		3041	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3042	automatically be applied to the embedded loop as well, so no special
		3043	fork handling is required in that case. When the watcher is not running,
		3044	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3045	as applicable.
		3046
1941	=head3 Watcher-Specific Functions and Data Members	3047	=head3 Watcher-Specific Functions and Data Members
1942		3048
1943	=over 4	3049	=over 4
1944		3050
1945	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3051	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
1948		3054
1949	Configures the watcher to embed the given loop, which must be	3055	Configures the watcher to embed the given loop, which must be
1950	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3056	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1951	invoked automatically, otherwise it is the responsibility of the callback	3057	invoked automatically, otherwise it is the responsibility of the callback
1952	to invoke it (it will continue to be called until the sweep has been done,	3058	to invoke it (it will continue to be called until the sweep has been done,
1953	if you do not want thta, you need to temporarily stop the embed watcher).	3059	if you do not want that, you need to temporarily stop the embed watcher).
1954		3060
1955	=item ev_embed_sweep (loop, ev_embed *)	3061	=item ev_embed_sweep (loop, ev_embed *)
1956		3062
1957	Make a single, non-blocking sweep over the embedded loop. This works	3063	Make a single, non-blocking sweep over the embedded loop. This works
1958	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3064	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1959	apropriate way for embedded loops.	3065	appropriate way for embedded loops.
1960		3066
1961	=item struct ev_loop *other [read-only]	3067	=item struct ev_loop *other [read-only]
1962		3068
1963	The embedded event loop.	3069	The embedded event loop.
1964		3070
…		…
1966		3072
1967	=head3 Examples	3073	=head3 Examples
1968		3074
1969	Example: Try to get an embeddable event loop and embed it into the default	3075	Example: Try to get an embeddable event loop and embed it into the default
1970	event loop. If that is not possible, use the default loop. The default	3076	event loop. If that is not possible, use the default loop. The default
1971	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	3077	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1972	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	3078	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1973	used).	3079	used).
1974		3080
1975	struct ev_loop *loop_hi = ev_default_init (0);	3081	struct ev_loop *loop_hi = ev_default_init (0);
1976	struct ev_loop *loop_lo = 0;	3082	struct ev_loop *loop_lo = 0;
1977	struct ev_embed embed;	3083	ev_embed embed;
1978		3084
1979	// see if there is a chance of getting one that works	3085	// see if there is a chance of getting one that works
1980	// (remember that a flags value of 0 means autodetection)	3086	// (remember that a flags value of 0 means autodetection)
1981	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3087	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1982	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3088	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1983	: 0;	3089	: 0;
1984		3090
1985	// if we got one, then embed it, otherwise default to loop_hi	3091	// if we got one, then embed it, otherwise default to loop_hi
1986	if (loop_lo)	3092	if (loop_lo)
1987	{	3093	{
1988	ev_embed_init (&embed, 0, loop_lo);	3094	ev_embed_init (&embed, 0, loop_lo);
1989	ev_embed_start (loop_hi, &embed);	3095	ev_embed_start (loop_hi, &embed);
1990	}	3096	}
1991	else	3097	else
1992	loop_lo = loop_hi;	3098	loop_lo = loop_hi;
1993		3099
1994	Example: Check if kqueue is available but not recommended and create	3100	Example: Check if kqueue is available but not recommended and create
1995	a kqueue backend for use with sockets (which usually work with any	3101	a kqueue backend for use with sockets (which usually work with any
1996	kqueue implementation). Store the kqueue/socket-only event loop in	3102	kqueue implementation). Store the kqueue/socket-only event loop in
1997	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3103	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
1998		3104
1999	struct ev_loop *loop = ev_default_init (0);	3105	struct ev_loop *loop = ev_default_init (0);
2000	struct ev_loop *loop_socket = 0;	3106	struct ev_loop *loop_socket = 0;
2001	struct ev_embed embed;	3107	ev_embed embed;
2002		3108
2003	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3109	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2004	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3110	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2005	{	3111	{
2006	ev_embed_init (&embed, 0, loop_socket);	3112	ev_embed_init (&embed, 0, loop_socket);
2007	ev_embed_start (loop, &embed);	3113	ev_embed_start (loop, &embed);
2008	}	3114	}
2009		3115
2010	if (!loop_socket)	3116	if (!loop_socket)
2011	loop_socket = loop;	3117	loop_socket = loop;
2012		3118
2013	// now use loop_socket for all sockets, and loop for everything else	3119	// now use loop_socket for all sockets, and loop for everything else
2014		3120
2015		3121
2016	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3122	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2017		3123
2018	Fork watchers are called when a C<fork ()> was detected (usually because	3124	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2021	event loop blocks next and before C<ev_check> watchers are being called,	3127	event loop blocks next and before C<ev_check> watchers are being called,
2022	and only in the child after the fork. If whoever good citizen calling	3128	and only in the child after the fork. If whoever good citizen calling
2023	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3129	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2024	handlers will be invoked, too, of course.	3130	handlers will be invoked, too, of course.
2025		3131
		3132	=head3 The special problem of life after fork - how is it possible?
		3133
		3134	Most uses of C<fork()> consist of forking, then some simple calls to set
		3135	up/change the process environment, followed by a call to C<exec()>. This
		3136	sequence should be handled by libev without any problems.
		3137
		3138	This changes when the application actually wants to do event handling
		3139	in the child, or both parent in child, in effect "continuing" after the
		3140	fork.
		3141
		3142	The default mode of operation (for libev, with application help to detect
		3143	forks) is to duplicate all the state in the child, as would be expected
		3144	when I<either> the parent I<or> the child process continues.
		3145
		3146	When both processes want to continue using libev, then this is usually the
		3147	wrong result. In that case, usually one process (typically the parent) is
		3148	supposed to continue with all watchers in place as before, while the other
		3149	process typically wants to start fresh, i.e. without any active watchers.
		3150
		3151	The cleanest and most efficient way to achieve that with libev is to
		3152	simply create a new event loop, which of course will be "empty", and
		3153	use that for new watchers. This has the advantage of not touching more
		3154	memory than necessary, and thus avoiding the copy-on-write, and the
		3155	disadvantage of having to use multiple event loops (which do not support
		3156	signal watchers).
		3157
		3158	When this is not possible, or you want to use the default loop for
		3159	other reasons, then in the process that wants to start "fresh", call
		3160	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3161	Destroying the default loop will "orphan" (not stop) all registered
		3162	watchers, so you have to be careful not to execute code that modifies
		3163	those watchers. Note also that in that case, you have to re-register any
		3164	signal watchers.
		3165
2026	=head3 Watcher-Specific Functions and Data Members	3166	=head3 Watcher-Specific Functions and Data Members
2027		3167
2028	=over 4	3168	=over 4
2029		3169
2030	=item ev_fork_init (ev_signal *, callback)	3170	=item ev_fork_init (ev_fork *, callback)
2031		3171
2032	Initialises and configures the fork watcher - it has no parameters of any	3172	Initialises and configures the fork watcher - it has no parameters of any
2033	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3173	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2034	believe me.	3174	really.
2035		3175
2036	=back	3176	=back
2037		3177
2038		3178
		3179	=head2 C<ev_cleanup> - even the best things end
		3180
		3181	Cleanup watchers are called just before the event loop is being destroyed
		3182	by a call to C<ev_loop_destroy>.
		3183
		3184	While there is no guarantee that the event loop gets destroyed, cleanup
		3185	watchers provide a convenient method to install cleanup hooks for your
		3186	program, worker threads and so on - you just to make sure to destroy the
		3187	loop when you want them to be invoked.
		3188
		3189	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3190	all other watchers, they do not keep a reference to the event loop (which
		3191	makes a lot of sense if you think about it). Like all other watchers, you
		3192	can call libev functions in the callback, except C<ev_cleanup_start>.
		3193
		3194	=head3 Watcher-Specific Functions and Data Members
		3195
		3196	=over 4
		3197
		3198	=item ev_cleanup_init (ev_cleanup *, callback)
		3199
		3200	Initialises and configures the cleanup watcher - it has no parameters of
		3201	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3202	pointless, I assure you.
		3203
		3204	=back
		3205
		3206	Example: Register an atexit handler to destroy the default loop, so any
		3207	cleanup functions are called.
		3208
		3209	static void
		3210	program_exits (void)
		3211	{
		3212	ev_loop_destroy (EV_DEFAULT_UC);
		3213	}
		3214
		3215	...
		3216	atexit (program_exits);
		3217
		3218
		3219	=head2 C<ev_async> - how to wake up an event loop
		3220
		3221	In general, you cannot use an C<ev_run> from multiple threads or other
		3222	asynchronous sources such as signal handlers (as opposed to multiple event
		3223	loops - those are of course safe to use in different threads).
		3224
		3225	Sometimes, however, you need to wake up an event loop you do not control,
		3226	for example because it belongs to another thread. This is what C<ev_async>
		3227	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3228	it by calling C<ev_async_send>, which is thread- and signal safe.
		3229
		3230	This functionality is very similar to C<ev_signal> watchers, as signals,
		3231	too, are asynchronous in nature, and signals, too, will be compressed
		3232	(i.e. the number of callback invocations may be less than the number of
		3233	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3234	of "global async watchers" by using a watcher on an otherwise unused
		3235	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3236	even without knowing which loop owns the signal.
		3237
		3238	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3239	just the default loop.
		3240
		3241	=head3 Queueing
		3242
		3243	C<ev_async> does not support queueing of data in any way. The reason
		3244	is that the author does not know of a simple (or any) algorithm for a
		3245	multiple-writer-single-reader queue that works in all cases and doesn't
		3246	need elaborate support such as pthreads or unportable memory access
		3247	semantics.
		3248
		3249	That means that if you want to queue data, you have to provide your own
		3250	queue. But at least I can tell you how to implement locking around your
		3251	queue:
		3252
		3253	=over 4
		3254
		3255	=item queueing from a signal handler context
		3256
		3257	To implement race-free queueing, you simply add to the queue in the signal
		3258	handler but you block the signal handler in the watcher callback. Here is
		3259	an example that does that for some fictitious SIGUSR1 handler:
		3260
		3261	static ev_async mysig;
		3262
		3263	static void
		3264	sigusr1_handler (void)
		3265	{
		3266	sometype data;
		3267
		3268	// no locking etc.
		3269	queue_put (data);
		3270	ev_async_send (EV_DEFAULT_ &mysig);
		3271	}
		3272
		3273	static void
		3274	mysig_cb (EV_P_ ev_async *w, int revents)
		3275	{
		3276	sometype data;
		3277	sigset_t block, prev;
		3278
		3279	sigemptyset (&block);
		3280	sigaddset (&block, SIGUSR1);
		3281	sigprocmask (SIG_BLOCK, &block, &prev);
		3282
		3283	while (queue_get (&data))
		3284	process (data);
		3285
		3286	if (sigismember (&prev, SIGUSR1)
		3287	sigprocmask (SIG_UNBLOCK, &block, 0);
		3288	}
		3289
		3290	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3291	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3292	either...).
		3293
		3294	=item queueing from a thread context
		3295
		3296	The strategy for threads is different, as you cannot (easily) block
		3297	threads but you can easily preempt them, so to queue safely you need to
		3298	employ a traditional mutex lock, such as in this pthread example:
		3299
		3300	static ev_async mysig;
		3301	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3302
		3303	static void
		3304	otherthread (void)
		3305	{
		3306	// only need to lock the actual queueing operation
		3307	pthread_mutex_lock (&mymutex);
		3308	queue_put (data);
		3309	pthread_mutex_unlock (&mymutex);
		3310
		3311	ev_async_send (EV_DEFAULT_ &mysig);
		3312	}
		3313
		3314	static void
		3315	mysig_cb (EV_P_ ev_async *w, int revents)
		3316	{
		3317	pthread_mutex_lock (&mymutex);
		3318
		3319	while (queue_get (&data))
		3320	process (data);
		3321
		3322	pthread_mutex_unlock (&mymutex);
		3323	}
		3324
		3325	=back
		3326
		3327
		3328	=head3 Watcher-Specific Functions and Data Members
		3329
		3330	=over 4
		3331
		3332	=item ev_async_init (ev_async *, callback)
		3333
		3334	Initialises and configures the async watcher - it has no parameters of any
		3335	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3336	trust me.
		3337
		3338	=item ev_async_send (loop, ev_async *)
		3339
		3340	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3341	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3342	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3343	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3344	section below on what exactly this means).
		3345
		3346	Note that, as with other watchers in libev, multiple events might get
		3347	compressed into a single callback invocation (another way to look at this
		3348	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3349	reset when the event loop detects that).
		3350
		3351	This call incurs the overhead of a system call only once per event loop
		3352	iteration, so while the overhead might be noticeable, it doesn't apply to
		3353	repeated calls to C<ev_async_send> for the same event loop.
		3354
		3355	=item bool = ev_async_pending (ev_async *)
		3356
		3357	Returns a non-zero value when C<ev_async_send> has been called on the
		3358	watcher but the event has not yet been processed (or even noted) by the
		3359	event loop.
		3360
		3361	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3362	the loop iterates next and checks for the watcher to have become active,
		3363	it will reset the flag again. C<ev_async_pending> can be used to very
		3364	quickly check whether invoking the loop might be a good idea.
		3365
		3366	Not that this does I<not> check whether the watcher itself is pending,
		3367	only whether it has been requested to make this watcher pending: there
		3368	is a time window between the event loop checking and resetting the async
		3369	notification, and the callback being invoked.
		3370
		3371	=back
		3372
		3373
2039	=head1 OTHER FUNCTIONS	3374	=head1 OTHER FUNCTIONS
2040		3375
2041	There are some other functions of possible interest. Described. Here. Now.	3376	There are some other functions of possible interest. Described. Here. Now.
2042		3377
2043	=over 4	3378	=over 4
2044		3379
2045	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3380	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2046		3381
2047	This function combines a simple timer and an I/O watcher, calls your	3382	This function combines a simple timer and an I/O watcher, calls your
2048	callback on whichever event happens first and automatically stop both	3383	callback on whichever event happens first and automatically stops both
2049	watchers. This is useful if you want to wait for a single event on an fd	3384	watchers. This is useful if you want to wait for a single event on an fd
2050	or timeout without having to allocate/configure/start/stop/free one or	3385	or timeout without having to allocate/configure/start/stop/free one or
2051	more watchers yourself.	3386	more watchers yourself.
2052		3387
2053	If C<fd> is less than 0, then no I/O watcher will be started and events	3388	If C<fd> is less than 0, then no I/O watcher will be started and the
2054	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3389	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2055	C<events> set will be craeted and started.	3390	the given C<fd> and C<events> set will be created and started.
2056		3391
2057	If C<timeout> is less than 0, then no timeout watcher will be	3392	If C<timeout> is less than 0, then no timeout watcher will be
2058	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3393	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2059	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3394	repeat = 0) will be started. C<0> is a valid timeout.
2060	dubious value.
2061		3395
2062	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3396	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2063	passed an C<revents> set like normal event callbacks (a combination of	3397	passed an C<revents> set like normal event callbacks (a combination of
2064	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3398	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2065	value passed to C<ev_once>:	3399	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3400	a timeout and an io event at the same time - you probably should give io
		3401	events precedence.
2066		3402
		3403	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3404
2067	static void stdin_ready (int revents, void *arg)	3405	static void stdin_ready (int revents, void *arg)
2068	{	3406	{
2069	if (revents & EV_TIMEOUT)
2070	/* doh, nothing entered */;
2071	else if (revents & EV_READ)	3407	if (revents & EV_READ)
2072	/* stdin might have data for us, joy! */;	3408	/* stdin might have data for us, joy! */;
		3409	else if (revents & EV_TIMER)
		3410	/* doh, nothing entered */;
2073	}	3411	}
2074		3412
2075	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3413	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2076		3414
2077	=item ev_feed_event (ev_loop *, watcher *, int revents)
2078
2079	Feeds the given event set into the event loop, as if the specified event
2080	had happened for the specified watcher (which must be a pointer to an
2081	initialised but not necessarily started event watcher).
2082
2083	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3415	=item ev_feed_fd_event (loop, int fd, int revents)
2084		3416
2085	Feed an event on the given fd, as if a file descriptor backend detected	3417	Feed an event on the given fd, as if a file descriptor backend detected
2086	the given events it.	3418	the given events it.
2087		3419
2088	=item ev_feed_signal_event (ev_loop *loop, int signum)	3420	=item ev_feed_signal_event (loop, int signum)
2089		3421
2090	Feed an event as if the given signal occured (C<loop> must be the default	3422	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
2091	loop!).	3423	which is async-safe.
		3424
		3425	=back
		3426
		3427
		3428	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3429
		3430	This section explains some common idioms that are not immediately
		3431	obvious. Note that examples are sprinkled over the whole manual, and this
		3432	section only contains stuff that wouldn't fit anywhere else.
		3433
		3434	=over 4
		3435
		3436	=item Model/nested event loop invocations and exit conditions.
		3437
		3438	Often (especially in GUI toolkits) there are places where you have
		3439	I<modal> interaction, which is most easily implemented by recursively
		3440	invoking C<ev_run>.
		3441
		3442	This brings the problem of exiting - a callback might want to finish the
		3443	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3444	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3445	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3446	other combination: In these cases, C<ev_break> will not work alone.
		3447
		3448	The solution is to maintain "break this loop" variable for each C<ev_run>
		3449	invocation, and use a loop around C<ev_run> until the condition is
		3450	triggered, using C<EVRUN_ONCE>:
		3451
		3452	// main loop
		3453	int exit_main_loop = 0;
		3454
		3455	while (!exit_main_loop)
		3456	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3457
		3458	// in a model watcher
		3459	int exit_nested_loop = 0;
		3460
		3461	while (!exit_nested_loop)
		3462	ev_run (EV_A_ EVRUN_ONCE);
		3463
		3464	To exit from any of these loops, just set the corresponding exit variable:
		3465
		3466	// exit modal loop
		3467	exit_nested_loop = 1;
		3468
		3469	// exit main program, after modal loop is finished
		3470	exit_main_loop = 1;
		3471
		3472	// exit both
		3473	exit_main_loop = exit_nested_loop = 1;
2092		3474
2093	=back	3475	=back
2094		3476
2095		3477
2096	=head1 LIBEVENT EMULATION	3478	=head1 LIBEVENT EMULATION
2097		3479
2098	Libev offers a compatibility emulation layer for libevent. It cannot	3480	Libev offers a compatibility emulation layer for libevent. It cannot
2099	emulate the internals of libevent, so here are some usage hints:	3481	emulate the internals of libevent, so here are some usage hints:
2100		3482
2101	=over 4	3483	=over 4
		3484
		3485	=item * Only the libevent-1.4.1-beta API is being emulated.
		3486
		3487	This was the newest libevent version available when libev was implemented,
		3488	and is still mostly unchanged in 2010.
2102		3489
2103	=item * Use it by including <event.h>, as usual.	3490	=item * Use it by including <event.h>, as usual.
2104		3491
2105	=item * The following members are fully supported: ev_base, ev_callback,	3492	=item * The following members are fully supported: ev_base, ev_callback,
2106	ev_arg, ev_fd, ev_res, ev_events.	3493	ev_arg, ev_fd, ev_res, ev_events.
…		…
2111		3498
2112	=item * Priorities are not currently supported. Initialising priorities	3499	=item * Priorities are not currently supported. Initialising priorities
2113	will fail and all watchers will have the same priority, even though there	3500	will fail and all watchers will have the same priority, even though there
2114	is an ev_pri field.	3501	is an ev_pri field.
2115		3502
		3503	=item * In libevent, the last base created gets the signals, in libev, the
		3504	base that registered the signal gets the signals.
		3505
2116	=item * Other members are not supported.	3506	=item * Other members are not supported.
2117		3507
2118	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3508	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2119	to use the libev header file and library.	3509	to use the libev header file and library.
2120		3510
2121	=back	3511	=back
2122		3512
2123	=head1 C++ SUPPORT	3513	=head1 C++ SUPPORT
2124		3514
2125	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3515	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2126	you to use some convinience methods to start/stop watchers and also change	3516	you to use some convenience methods to start/stop watchers and also change
2127	the callback model to a model using method callbacks on objects.	3517	the callback model to a model using method callbacks on objects.
2128		3518
2129	To use it,	3519	To use it,
2130		3520
2131	#include <ev++.h>	3521	#include <ev++.h>
2132		3522
2133	This automatically includes F<ev.h> and puts all of its definitions (many	3523	This automatically includes F<ev.h> and puts all of its definitions (many
2134	of them macros) into the global namespace. All C++ specific things are	3524	of them macros) into the global namespace. All C++ specific things are
2135	put into the C<ev> namespace. It should support all the same embedding	3525	put into the C<ev> namespace. It should support all the same embedding
2136	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3526	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2138	Care has been taken to keep the overhead low. The only data member the C++	3528	Care has been taken to keep the overhead low. The only data member the C++
2139	classes add (compared to plain C-style watchers) is the event loop pointer	3529	classes add (compared to plain C-style watchers) is the event loop pointer
2140	that the watcher is associated with (or no additional members at all if	3530	that the watcher is associated with (or no additional members at all if
2141	you disable C<EV_MULTIPLICITY> when embedding libev).	3531	you disable C<EV_MULTIPLICITY> when embedding libev).
2142		3532
2143	Currently, functions, and static and non-static member functions can be	3533	Currently, functions, static and non-static member functions and classes
2144	used as callbacks. Other types should be easy to add as long as they only	3534	with C<operator ()> can be used as callbacks. Other types should be easy
2145	need one additional pointer for context. If you need support for other	3535	to add as long as they only need one additional pointer for context. If
2146	types of functors please contact the author (preferably after implementing	3536	you need support for other types of functors please contact the author
2147	it).	3537	(preferably after implementing it).
2148		3538
2149	Here is a list of things available in the C<ev> namespace:	3539	Here is a list of things available in the C<ev> namespace:
2150		3540
2151	=over 4	3541	=over 4
2152		3542
…		…
2170		3560
2171	=over 4	3561	=over 4
2172		3562
2173	=item ev::TYPE::TYPE ()	3563	=item ev::TYPE::TYPE ()
2174		3564
2175	=item ev::TYPE::TYPE (struct ev_loop *)	3565	=item ev::TYPE::TYPE (loop)
2176		3566
2177	=item ev::TYPE::~TYPE	3567	=item ev::TYPE::~TYPE
2178		3568
2179	The constructor (optionally) takes an event loop to associate the watcher	3569	The constructor (optionally) takes an event loop to associate the watcher
2180	with. If it is omitted, it will use C<EV_DEFAULT>.	3570	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2203	your compiler is good :), then the method will be fully inlined into the	3593	your compiler is good :), then the method will be fully inlined into the
2204	thunking function, making it as fast as a direct C callback.	3594	thunking function, making it as fast as a direct C callback.
2205		3595
2206	Example: simple class declaration and watcher initialisation	3596	Example: simple class declaration and watcher initialisation
2207		3597
2208	struct myclass	3598	struct myclass
2209	{	3599	{
2210	void io_cb (ev::io &w, int revents) { }	3600	void io_cb (ev::io &w, int revents) { }
2211	}	3601	}
2212		3602
2213	myclass obj;	3603	myclass obj;
2214	ev::io iow;	3604	ev::io iow;
2215	iow.set <myclass, &myclass::io_cb> (&obj);	3605	iow.set <myclass, &myclass::io_cb> (&obj);
		3606
		3607	=item w->set (object *)
		3608
		3609	This is a variation of a method callback - leaving out the method to call
		3610	will default the method to C<operator ()>, which makes it possible to use
		3611	functor objects without having to manually specify the C<operator ()> all
		3612	the time. Incidentally, you can then also leave out the template argument
		3613	list.
		3614
		3615	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3616	int revents)>.
		3617
		3618	See the method-C<set> above for more details.
		3619
		3620	Example: use a functor object as callback.
		3621
		3622	struct myfunctor
		3623	{
		3624	void operator() (ev::io &w, int revents)
		3625	{
		3626	...
		3627	}
		3628	}
		3629
		3630	myfunctor f;
		3631
		3632	ev::io w;
		3633	w.set (&f);
2216		3634
2217	=item w->set<function> (void *data = 0)	3635	=item w->set<function> (void *data = 0)
2218		3636
2219	Also sets a callback, but uses a static method or plain function as	3637	Also sets a callback, but uses a static method or plain function as
2220	callback. The optional C<data> argument will be stored in the watcher's	3638	callback. The optional C<data> argument will be stored in the watcher's
…		…
2222		3640
2223	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3641	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2224		3642
2225	See the method-C<set> above for more details.	3643	See the method-C<set> above for more details.
2226		3644
2227	Example:	3645	Example: Use a plain function as callback.
2228		3646
2229	static void io_cb (ev::io &w, int revents) { }	3647	static void io_cb (ev::io &w, int revents) { }
2230	iow.set <io_cb> ();	3648	iow.set <io_cb> ();
2231		3649
2232	=item w->set (struct ev_loop *)	3650	=item w->set (loop)
2233		3651
2234	Associates a different C<struct ev_loop> with this watcher. You can only	3652	Associates a different C<struct ev_loop> with this watcher. You can only
2235	do this when the watcher is inactive (and not pending either).	3653	do this when the watcher is inactive (and not pending either).
2236		3654
2237	=item w->set ([args])	3655	=item w->set ([arguments])
2238		3656
2239	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3657	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2240	called at least once. Unlike the C counterpart, an active watcher gets	3658	method or a suitable start method must be called at least once. Unlike the
2241	automatically stopped and restarted when reconfiguring it with this	3659	C counterpart, an active watcher gets automatically stopped and restarted
2242	method.	3660	when reconfiguring it with this method.
2243		3661
2244	=item w->start ()	3662	=item w->start ()
2245		3663
2246	Starts the watcher. Note that there is no C<loop> argument, as the	3664	Starts the watcher. Note that there is no C<loop> argument, as the
2247	constructor already stores the event loop.	3665	constructor already stores the event loop.
2248		3666
		3667	=item w->start ([arguments])
		3668
		3669	Instead of calling C<set> and C<start> methods separately, it is often
		3670	convenient to wrap them in one call. Uses the same type of arguments as
		3671	the configure C<set> method of the watcher.
		3672
2249	=item w->stop ()	3673	=item w->stop ()
2250		3674
2251	Stops the watcher if it is active. Again, no C<loop> argument.	3675	Stops the watcher if it is active. Again, no C<loop> argument.
2252		3676
2253	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3677	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2265		3689
2266	=back	3690	=back
2267		3691
2268	=back	3692	=back
2269		3693
2270	Example: Define a class with an IO and idle watcher, start one of them in	3694	Example: Define a class with two I/O and idle watchers, start the I/O
2271	the constructor.	3695	watchers in the constructor.
2272		3696
2273	class myclass	3697	class myclass
2274	{	3698	{
2275	ev_io io; void io_cb (ev::io &w, int revents);	3699	ev::io io ; void io_cb (ev::io &w, int revents);
		3700	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2276	ev_idle idle void idle_cb (ev::idle &w, int revents);	3701	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2277		3702
2278	myclass ();	3703	myclass (int fd)
2279	}	3704	{
2280
2281	myclass::myclass (int fd)
2282	{
2283	io .set <myclass, &myclass::io_cb > (this);	3705	io .set <myclass, &myclass::io_cb > (this);
		3706	io2 .set <myclass, &myclass::io2_cb > (this);
2284	idle.set <myclass, &myclass::idle_cb> (this);	3707	idle.set <myclass, &myclass::idle_cb> (this);
2285		3708
2286	io.start (fd, ev::READ);	3709	io.set (fd, ev::WRITE); // configure the watcher
		3710	io.start (); // start it whenever convenient
		3711
		3712	io2.start (fd, ev::READ); // set + start in one call
		3713	}
2287	}	3714	};
		3715
		3716
		3717	=head1 OTHER LANGUAGE BINDINGS
		3718
		3719	Libev does not offer other language bindings itself, but bindings for a
		3720	number of languages exist in the form of third-party packages. If you know
		3721	any interesting language binding in addition to the ones listed here, drop
		3722	me a note.
		3723
		3724	=over 4
		3725
		3726	=item Perl
		3727
		3728	The EV module implements the full libev API and is actually used to test
		3729	libev. EV is developed together with libev. Apart from the EV core module,
		3730	there are additional modules that implement libev-compatible interfaces
		3731	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3732	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3733	and C<EV::Glib>).
		3734
		3735	It can be found and installed via CPAN, its homepage is at
		3736	L<http://software.schmorp.de/pkg/EV>.
		3737
		3738	=item Python
		3739
		3740	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3741	seems to be quite complete and well-documented.
		3742
		3743	=item Ruby
		3744
		3745	Tony Arcieri has written a ruby extension that offers access to a subset
		3746	of the libev API and adds file handle abstractions, asynchronous DNS and
		3747	more on top of it. It can be found via gem servers. Its homepage is at
		3748	L<http://rev.rubyforge.org/>.
		3749
		3750	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3751	makes rev work even on mingw.
		3752
		3753	=item Haskell
		3754
		3755	A haskell binding to libev is available at
		3756	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3757
		3758	=item D
		3759
		3760	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3761	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3762
		3763	=item Ocaml
		3764
		3765	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3766	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3767
		3768	=item Lua
		3769
		3770	Brian Maher has written a partial interface to libev for lua (at the
		3771	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3772	L<http://github.com/brimworks/lua-ev>.
		3773
		3774	=back
2288		3775
2289		3776
2290	=head1 MACRO MAGIC	3777	=head1 MACRO MAGIC
2291		3778
2292	Libev can be compiled with a variety of options, the most fundamantal	3779	Libev can be compiled with a variety of options, the most fundamental
2293	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3780	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2294	functions and callbacks have an initial C<struct ev_loop *> argument.	3781	functions and callbacks have an initial C<struct ev_loop *> argument.
2295		3782
2296	To make it easier to write programs that cope with either variant, the	3783	To make it easier to write programs that cope with either variant, the
2297	following macros are defined:	3784	following macros are defined:
…		…
2302		3789
2303	This provides the loop I<argument> for functions, if one is required ("ev	3790	This provides the loop I<argument> for functions, if one is required ("ev
2304	loop argument"). The C<EV_A> form is used when this is the sole argument,	3791	loop argument"). The C<EV_A> form is used when this is the sole argument,
2305	C<EV_A_> is used when other arguments are following. Example:	3792	C<EV_A_> is used when other arguments are following. Example:
2306		3793
2307	ev_unref (EV_A);	3794	ev_unref (EV_A);
2308	ev_timer_add (EV_A_ watcher);	3795	ev_timer_add (EV_A_ watcher);
2309	ev_loop (EV_A_ 0);	3796	ev_run (EV_A_ 0);
2310		3797
2311	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3798	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2312	which is often provided by the following macro.	3799	which is often provided by the following macro.
2313		3800
2314	=item C<EV_P>, C<EV_P_>	3801	=item C<EV_P>, C<EV_P_>
2315		3802
2316	This provides the loop I<parameter> for functions, if one is required ("ev	3803	This provides the loop I<parameter> for functions, if one is required ("ev
2317	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3804	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2318	C<EV_P_> is used when other parameters are following. Example:	3805	C<EV_P_> is used when other parameters are following. Example:
2319		3806
2320	// this is how ev_unref is being declared	3807	// this is how ev_unref is being declared
2321	static void ev_unref (EV_P);	3808	static void ev_unref (EV_P);
2322		3809
2323	// this is how you can declare your typical callback	3810	// this is how you can declare your typical callback
2324	static void cb (EV_P_ ev_timer *w, int revents)	3811	static void cb (EV_P_ ev_timer *w, int revents)
2325		3812
2326	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3813	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2327	suitable for use with C<EV_A>.	3814	suitable for use with C<EV_A>.
2328		3815
2329	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3816	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2330		3817
2331	Similar to the other two macros, this gives you the value of the default	3818	Similar to the other two macros, this gives you the value of the default
2332	loop, if multiple loops are supported ("ev loop default").	3819	loop, if multiple loops are supported ("ev loop default").
		3820
		3821	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3822
		3823	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3824	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3825	is undefined when the default loop has not been initialised by a previous
		3826	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3827
		3828	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3829	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2333		3830
2334	=back	3831	=back
2335		3832
2336	Example: Declare and initialise a check watcher, utilising the above	3833	Example: Declare and initialise a check watcher, utilising the above
2337	macros so it will work regardless of whether multiple loops are supported	3834	macros so it will work regardless of whether multiple loops are supported
2338	or not.	3835	or not.
2339		3836
2340	static void	3837	static void
2341	check_cb (EV_P_ ev_timer *w, int revents)	3838	check_cb (EV_P_ ev_timer *w, int revents)
2342	{	3839	{
2343	ev_check_stop (EV_A_ w);	3840	ev_check_stop (EV_A_ w);
2344	}	3841	}
2345		3842
2346	ev_check check;	3843	ev_check check;
2347	ev_check_init (&check, check_cb);	3844	ev_check_init (&check, check_cb);
2348	ev_check_start (EV_DEFAULT_ &check);	3845	ev_check_start (EV_DEFAULT_ &check);
2349	ev_loop (EV_DEFAULT_ 0);	3846	ev_run (EV_DEFAULT_ 0);
2350		3847
2351	=head1 EMBEDDING	3848	=head1 EMBEDDING
2352		3849
2353	Libev can (and often is) directly embedded into host	3850	Libev can (and often is) directly embedded into host
2354	applications. Examples of applications that embed it include the Deliantra	3851	applications. Examples of applications that embed it include the Deliantra
…		…
2361	libev somewhere in your source tree).	3858	libev somewhere in your source tree).
2362		3859
2363	=head2 FILESETS	3860	=head2 FILESETS
2364		3861
2365	Depending on what features you need you need to include one or more sets of files	3862	Depending on what features you need you need to include one or more sets of files
2366	in your app.	3863	in your application.
2367		3864
2368	=head3 CORE EVENT LOOP	3865	=head3 CORE EVENT LOOP
2369		3866
2370	To include only the libev core (all the C<ev_*> functions), with manual	3867	To include only the libev core (all the C<ev_*> functions), with manual
2371	configuration (no autoconf):	3868	configuration (no autoconf):
2372		3869
2373	#define EV_STANDALONE 1	3870	#define EV_STANDALONE 1
2374	#include "ev.c"	3871	#include "ev.c"
2375		3872
2376	This will automatically include F<ev.h>, too, and should be done in a	3873	This will automatically include F<ev.h>, too, and should be done in a
2377	single C source file only to provide the function implementations. To use	3874	single C source file only to provide the function implementations. To use
2378	it, do the same for F<ev.h> in all files wishing to use this API (best	3875	it, do the same for F<ev.h> in all files wishing to use this API (best
2379	done by writing a wrapper around F<ev.h> that you can include instead and	3876	done by writing a wrapper around F<ev.h> that you can include instead and
2380	where you can put other configuration options):	3877	where you can put other configuration options):
2381		3878
2382	#define EV_STANDALONE 1	3879	#define EV_STANDALONE 1
2383	#include "ev.h"	3880	#include "ev.h"
2384		3881
2385	Both header files and implementation files can be compiled with a C++	3882	Both header files and implementation files can be compiled with a C++
2386	compiler (at least, thats a stated goal, and breakage will be treated	3883	compiler (at least, that's a stated goal, and breakage will be treated
2387	as a bug).	3884	as a bug).
2388		3885
2389	You need the following files in your source tree, or in a directory	3886	You need the following files in your source tree, or in a directory
2390	in your include path (e.g. in libev/ when using -Ilibev):	3887	in your include path (e.g. in libev/ when using -Ilibev):
2391		3888
2392	ev.h	3889	ev.h
2393	ev.c	3890	ev.c
2394	ev_vars.h	3891	ev_vars.h
2395	ev_wrap.h	3892	ev_wrap.h
2396		3893
2397	ev_win32.c required on win32 platforms only	3894	ev_win32.c required on win32 platforms only
2398		3895
2399	ev_select.c only when select backend is enabled (which is enabled by default)	3896	ev_select.c only when select backend is enabled (which is enabled by default)
2400	ev_poll.c only when poll backend is enabled (disabled by default)	3897	ev_poll.c only when poll backend is enabled (disabled by default)
2401	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3898	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2402	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3899	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2403	ev_port.c only when the solaris port backend is enabled (disabled by default)	3900	ev_port.c only when the solaris port backend is enabled (disabled by default)
2404		3901
2405	F<ev.c> includes the backend files directly when enabled, so you only need	3902	F<ev.c> includes the backend files directly when enabled, so you only need
2406	to compile this single file.	3903	to compile this single file.
2407		3904
2408	=head3 LIBEVENT COMPATIBILITY API	3905	=head3 LIBEVENT COMPATIBILITY API
2409		3906
2410	To include the libevent compatibility API, also include:	3907	To include the libevent compatibility API, also include:
2411		3908
2412	#include "event.c"	3909	#include "event.c"
2413		3910
2414	in the file including F<ev.c>, and:	3911	in the file including F<ev.c>, and:
2415		3912
2416	#include "event.h"	3913	#include "event.h"
2417		3914
2418	in the files that want to use the libevent API. This also includes F<ev.h>.	3915	in the files that want to use the libevent API. This also includes F<ev.h>.
2419		3916
2420	You need the following additional files for this:	3917	You need the following additional files for this:
2421		3918
2422	event.h	3919	event.h
2423	event.c	3920	event.c
2424		3921
2425	=head3 AUTOCONF SUPPORT	3922	=head3 AUTOCONF SUPPORT
2426		3923
2427	Instead of using C<EV_STANDALONE=1> and providing your config in	3924	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2428	whatever way you want, you can also C<m4_include([libev.m4])> in your	3925	whatever way you want, you can also C<m4_include([libev.m4])> in your
2429	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3926	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2430	include F<config.h> and configure itself accordingly.	3927	include F<config.h> and configure itself accordingly.
2431		3928
2432	For this of course you need the m4 file:	3929	For this of course you need the m4 file:
2433		3930
2434	libev.m4	3931	libev.m4
2435		3932
2436	=head2 PREPROCESSOR SYMBOLS/MACROS	3933	=head2 PREPROCESSOR SYMBOLS/MACROS
2437		3934
2438	Libev can be configured via a variety of preprocessor symbols you have to define	3935	Libev can be configured via a variety of preprocessor symbols you have to
2439	before including any of its files. The default is not to build for multiplicity	3936	define before including (or compiling) any of its files. The default in
2440	and only include the select backend.	3937	the absence of autoconf is documented for every option.
		3938
		3939	Symbols marked with "(h)" do not change the ABI, and can have different
		3940	values when compiling libev vs. including F<ev.h>, so it is permissible
		3941	to redefine them before including F<ev.h> without breaking compatibility
		3942	to a compiled library. All other symbols change the ABI, which means all
		3943	users of libev and the libev code itself must be compiled with compatible
		3944	settings.
2441		3945
2442	=over 4	3946	=over 4
2443		3947
		3948	=item EV_COMPAT3 (h)
		3949
		3950	Backwards compatibility is a major concern for libev. This is why this
		3951	release of libev comes with wrappers for the functions and symbols that
		3952	have been renamed between libev version 3 and 4.
		3953
		3954	You can disable these wrappers (to test compatibility with future
		3955	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3956	sources. This has the additional advantage that you can drop the C<struct>
		3957	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3958	typedef in that case.
		3959
		3960	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3961	and in some even more future version the compatibility code will be
		3962	removed completely.
		3963
2444	=item EV_STANDALONE	3964	=item EV_STANDALONE (h)
2445		3965
2446	Must always be C<1> if you do not use autoconf configuration, which	3966	Must always be C<1> if you do not use autoconf configuration, which
2447	keeps libev from including F<config.h>, and it also defines dummy	3967	keeps libev from including F<config.h>, and it also defines dummy
2448	implementations for some libevent functions (such as logging, which is not	3968	implementations for some libevent functions (such as logging, which is not
2449	supported). It will also not define any of the structs usually found in	3969	supported). It will also not define any of the structs usually found in
2450	F<event.h> that are not directly supported by the libev core alone.	3970	F<event.h> that are not directly supported by the libev core alone.
2451		3971
		3972	In standalone mode, libev will still try to automatically deduce the
		3973	configuration, but has to be more conservative.
		3974
2452	=item EV_USE_MONOTONIC	3975	=item EV_USE_MONOTONIC
2453		3976
2454	If defined to be C<1>, libev will try to detect the availability of the	3977	If defined to be C<1>, libev will try to detect the availability of the
2455	monotonic clock option at both compiletime and runtime. Otherwise no use	3978	monotonic clock option at both compile time and runtime. Otherwise no
2456	of the monotonic clock option will be attempted. If you enable this, you	3979	use of the monotonic clock option will be attempted. If you enable this,
2457	usually have to link against librt or something similar. Enabling it when	3980	you usually have to link against librt or something similar. Enabling it
2458	the functionality isn't available is safe, though, although you have	3981	when the functionality isn't available is safe, though, although you have
2459	to make sure you link against any libraries where the C<clock_gettime>	3982	to make sure you link against any libraries where the C<clock_gettime>
2460	function is hiding in (often F<-lrt>).	3983	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2461		3984
2462	=item EV_USE_REALTIME	3985	=item EV_USE_REALTIME
2463		3986
2464	If defined to be C<1>, libev will try to detect the availability of the	3987	If defined to be C<1>, libev will try to detect the availability of the
2465	realtime clock option at compiletime (and assume its availability at	3988	real-time clock option at compile time (and assume its availability
2466	runtime if successful). Otherwise no use of the realtime clock option will	3989	at runtime if successful). Otherwise no use of the real-time clock
2467	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3990	option will be attempted. This effectively replaces C<gettimeofday>
2468	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3991	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2469	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3992	correctness. See the note about libraries in the description of
		3993	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3994	C<EV_USE_CLOCK_SYSCALL>.
		3995
		3996	=item EV_USE_CLOCK_SYSCALL
		3997
		3998	If defined to be C<1>, libev will try to use a direct syscall instead
		3999	of calling the system-provided C<clock_gettime> function. This option
		4000	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4001	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4002	programs needlessly. Using a direct syscall is slightly slower (in
		4003	theory), because no optimised vdso implementation can be used, but avoids
		4004	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4005	higher, as it simplifies linking (no need for C<-lrt>).
2470		4006
2471	=item EV_USE_NANOSLEEP	4007	=item EV_USE_NANOSLEEP
2472		4008
2473	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4009	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2474	and will use it for delays. Otherwise it will use C<select ()>.	4010	and will use it for delays. Otherwise it will use C<select ()>.
2475		4011
		4012	=item EV_USE_EVENTFD
		4013
		4014	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4015	available and will probe for kernel support at runtime. This will improve
		4016	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4017	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4018	2.7 or newer, otherwise disabled.
		4019
2476	=item EV_USE_SELECT	4020	=item EV_USE_SELECT
2477		4021
2478	If undefined or defined to be C<1>, libev will compile in support for the	4022	If undefined or defined to be C<1>, libev will compile in support for the
2479	C<select>(2) backend. No attempt at autodetection will be done: if no	4023	C<select>(2) backend. No attempt at auto-detection will be done: if no
2480	other method takes over, select will be it. Otherwise the select backend	4024	other method takes over, select will be it. Otherwise the select backend
2481	will not be compiled in.	4025	will not be compiled in.
2482		4026
2483	=item EV_SELECT_USE_FD_SET	4027	=item EV_SELECT_USE_FD_SET
2484		4028
2485	If defined to C<1>, then the select backend will use the system C<fd_set>	4029	If defined to C<1>, then the select backend will use the system C<fd_set>
2486	structure. This is useful if libev doesn't compile due to a missing	4030	structure. This is useful if libev doesn't compile due to a missing
2487	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4031	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2488	exotic systems. This usually limits the range of file descriptors to some	4032	on exotic systems. This usually limits the range of file descriptors to
2489	low limit such as 1024 or might have other limitations (winsocket only	4033	some low limit such as 1024 or might have other limitations (winsocket
2490	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4034	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2491	influence the size of the C<fd_set> used.	4035	configures the maximum size of the C<fd_set>.
2492		4036
2493	=item EV_SELECT_IS_WINSOCKET	4037	=item EV_SELECT_IS_WINSOCKET
2494		4038
2495	When defined to C<1>, the select backend will assume that	4039	When defined to C<1>, the select backend will assume that
2496	select/socket/connect etc. don't understand file descriptors but	4040	select/socket/connect etc. don't understand file descriptors but
…		…
2498	be used is the winsock select). This means that it will call	4042	be used is the winsock select). This means that it will call
2499	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4043	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2500	it is assumed that all these functions actually work on fds, even	4044	it is assumed that all these functions actually work on fds, even
2501	on win32. Should not be defined on non-win32 platforms.	4045	on win32. Should not be defined on non-win32 platforms.
2502		4046
2503	=item EV_FD_TO_WIN32_HANDLE	4047	=item EV_FD_TO_WIN32_HANDLE(fd)
2504		4048
2505	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4049	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2506	file descriptors to socket handles. When not defining this symbol (the	4050	file descriptors to socket handles. When not defining this symbol (the
2507	default), then libev will call C<_get_osfhandle>, which is usually	4051	default), then libev will call C<_get_osfhandle>, which is usually
2508	correct. In some cases, programs use their own file descriptor management,	4052	correct. In some cases, programs use their own file descriptor management,
2509	in which case they can provide this function to map fds to socket handles.	4053	in which case they can provide this function to map fds to socket handles.
2510		4054
		4055	=item EV_WIN32_HANDLE_TO_FD(handle)
		4056
		4057	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4058	using the standard C<_open_osfhandle> function. For programs implementing
		4059	their own fd to handle mapping, overwriting this function makes it easier
		4060	to do so. This can be done by defining this macro to an appropriate value.
		4061
		4062	=item EV_WIN32_CLOSE_FD(fd)
		4063
		4064	If programs implement their own fd to handle mapping on win32, then this
		4065	macro can be used to override the C<close> function, useful to unregister
		4066	file descriptors again. Note that the replacement function has to close
		4067	the underlying OS handle.
		4068
2511	=item EV_USE_POLL	4069	=item EV_USE_POLL
2512		4070
2513	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4071	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2514	backend. Otherwise it will be enabled on non-win32 platforms. It	4072	backend. Otherwise it will be enabled on non-win32 platforms. It
2515	takes precedence over select.	4073	takes precedence over select.
2516		4074
2517	=item EV_USE_EPOLL	4075	=item EV_USE_EPOLL
2518		4076
2519	If defined to be C<1>, libev will compile in support for the Linux	4077	If defined to be C<1>, libev will compile in support for the Linux
2520	C<epoll>(7) backend. Its availability will be detected at runtime,	4078	C<epoll>(7) backend. Its availability will be detected at runtime,
2521	otherwise another method will be used as fallback. This is the	4079	otherwise another method will be used as fallback. This is the preferred
2522	preferred backend for GNU/Linux systems.	4080	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4081	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2523		4082
2524	=item EV_USE_KQUEUE	4083	=item EV_USE_KQUEUE
2525		4084
2526	If defined to be C<1>, libev will compile in support for the BSD style	4085	If defined to be C<1>, libev will compile in support for the BSD style
2527	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4086	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2540	otherwise another method will be used as fallback. This is the preferred	4099	otherwise another method will be used as fallback. This is the preferred
2541	backend for Solaris 10 systems.	4100	backend for Solaris 10 systems.
2542		4101
2543	=item EV_USE_DEVPOLL	4102	=item EV_USE_DEVPOLL
2544		4103
2545	reserved for future expansion, works like the USE symbols above.	4104	Reserved for future expansion, works like the USE symbols above.
2546		4105
2547	=item EV_USE_INOTIFY	4106	=item EV_USE_INOTIFY
2548		4107
2549	If defined to be C<1>, libev will compile in support for the Linux inotify	4108	If defined to be C<1>, libev will compile in support for the Linux inotify
2550	interface to speed up C<ev_stat> watchers. Its actual availability will	4109	interface to speed up C<ev_stat> watchers. Its actual availability will
2551	be detected at runtime.	4110	be detected at runtime. If undefined, it will be enabled if the headers
		4111	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2552		4112
		4113	=item EV_ATOMIC_T
		4114
		4115	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4116	access is atomic with respect to other threads or signal contexts. No such
		4117	type is easily found in the C language, so you can provide your own type
		4118	that you know is safe for your purposes. It is used both for signal handler "locking"
		4119	as well as for signal and thread safety in C<ev_async> watchers.
		4120
		4121	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4122	(from F<signal.h>), which is usually good enough on most platforms.
		4123
2553	=item EV_H	4124	=item EV_H (h)
2554		4125
2555	The name of the F<ev.h> header file used to include it. The default if	4126	The name of the F<ev.h> header file used to include it. The default if
2556	undefined is C<"ev.h"> in F<event.h> and F<ev.c>. This can be used to	4127	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2557	virtually rename the F<ev.h> header file in case of conflicts.	4128	used to virtually rename the F<ev.h> header file in case of conflicts.
2558		4129
2559	=item EV_CONFIG_H	4130	=item EV_CONFIG_H (h)
2560		4131
2561	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4132	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2562	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4133	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2563	C<EV_H>, above.	4134	C<EV_H>, above.
2564		4135
2565	=item EV_EVENT_H	4136	=item EV_EVENT_H (h)
2566		4137
2567	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4138	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2568	of how the F<event.h> header can be found, the dfeault is C<"event.h">.	4139	of how the F<event.h> header can be found, the default is C<"event.h">.
2569		4140
2570	=item EV_PROTOTYPES	4141	=item EV_PROTOTYPES (h)
2571		4142
2572	If defined to be C<0>, then F<ev.h> will not define any function	4143	If defined to be C<0>, then F<ev.h> will not define any function
2573	prototypes, but still define all the structs and other symbols. This is	4144	prototypes, but still define all the structs and other symbols. This is
2574	occasionally useful if you want to provide your own wrapper functions	4145	occasionally useful if you want to provide your own wrapper functions
2575	around libev functions.	4146	around libev functions.
…		…
2594	When doing priority-based operations, libev usually has to linearly search	4165	When doing priority-based operations, libev usually has to linearly search
2595	all the priorities, so having many of them (hundreds) uses a lot of space	4166	all the priorities, so having many of them (hundreds) uses a lot of space
2596	and time, so using the defaults of five priorities (-2 .. +2) is usually	4167	and time, so using the defaults of five priorities (-2 .. +2) is usually
2597	fine.	4168	fine.
2598		4169
2599	If your embedding app does not need any priorities, defining these both to	4170	If your embedding application does not need any priorities, defining these
2600	C<0> will save some memory and cpu.	4171	both to C<0> will save some memory and CPU.
2601		4172
2602	=item EV_PERIODIC_ENABLE	4173	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4174	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4175	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2603		4176
2604	If undefined or defined to be C<1>, then periodic timers are supported. If	4177	If undefined or defined to be C<1> (and the platform supports it), then
2605	defined to be C<0>, then they are not. Disabling them saves a few kB of	4178	the respective watcher type is supported. If defined to be C<0>, then it
2606	code.	4179	is not. Disabling watcher types mainly saves code size.
2607		4180
2608	=item EV_IDLE_ENABLE	4181	=item EV_FEATURES
2609
2610	If undefined or defined to be C<1>, then idle watchers are supported. If
2611	defined to be C<0>, then they are not. Disabling them saves a few kB of
2612	code.
2613
2614	=item EV_EMBED_ENABLE
2615
2616	If undefined or defined to be C<1>, then embed watchers are supported. If
2617	defined to be C<0>, then they are not.
2618
2619	=item EV_STAT_ENABLE
2620
2621	If undefined or defined to be C<1>, then stat watchers are supported. If
2622	defined to be C<0>, then they are not.
2623
2624	=item EV_FORK_ENABLE
2625
2626	If undefined or defined to be C<1>, then fork watchers are supported. If
2627	defined to be C<0>, then they are not.
2628
2629	=item EV_MINIMAL
2630		4182
2631	If you need to shave off some kilobytes of code at the expense of some	4183	If you need to shave off some kilobytes of code at the expense of some
2632	speed, define this symbol to C<1>. Currently only used for gcc to override	4184	speed (but with the full API), you can define this symbol to request
2633	some inlining decisions, saves roughly 30% codesize of amd64.	4185	certain subsets of functionality. The default is to enable all features
		4186	that can be enabled on the platform.
		4187
		4188	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4189	with some broad features you want) and then selectively re-enable
		4190	additional parts you want, for example if you want everything minimal,
		4191	but multiple event loop support, async and child watchers and the poll
		4192	backend, use this:
		4193
		4194	#define EV_FEATURES 0
		4195	#define EV_MULTIPLICITY 1
		4196	#define EV_USE_POLL 1
		4197	#define EV_CHILD_ENABLE 1
		4198	#define EV_ASYNC_ENABLE 1
		4199
		4200	The actual value is a bitset, it can be a combination of the following
		4201	values:
		4202
		4203	=over 4
		4204
		4205	=item C<1> - faster/larger code
		4206
		4207	Use larger code to speed up some operations.
		4208
		4209	Currently this is used to override some inlining decisions (enlarging the
		4210	code size by roughly 30% on amd64).
		4211
		4212	When optimising for size, use of compiler flags such as C<-Os> with
		4213	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4214	assertions.
		4215
		4216	=item C<2> - faster/larger data structures
		4217
		4218	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4219	hash table sizes and so on. This will usually further increase code size
		4220	and can additionally have an effect on the size of data structures at
		4221	runtime.
		4222
		4223	=item C<4> - full API configuration
		4224
		4225	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4226	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4227
		4228	=item C<8> - full API
		4229
		4230	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4231	details on which parts of the API are still available without this
		4232	feature, and do not complain if this subset changes over time.
		4233
		4234	=item C<16> - enable all optional watcher types
		4235
		4236	Enables all optional watcher types. If you want to selectively enable
		4237	only some watcher types other than I/O and timers (e.g. prepare,
		4238	embed, async, child...) you can enable them manually by defining
		4239	C<EV_watchertype_ENABLE> to C<1> instead.
		4240
		4241	=item C<32> - enable all backends
		4242
		4243	This enables all backends - without this feature, you need to enable at
		4244	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4245
		4246	=item C<64> - enable OS-specific "helper" APIs
		4247
		4248	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4249	default.
		4250
		4251	=back
		4252
		4253	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4254	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4255	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4256	watchers, timers and monotonic clock support.
		4257
		4258	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4259	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4260	your program might be left out as well - a binary starting a timer and an
		4261	I/O watcher then might come out at only 5Kb.
		4262
		4263	=item EV_AVOID_STDIO
		4264
		4265	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4266	functions (printf, scanf, perror etc.). This will increase the code size
		4267	somewhat, but if your program doesn't otherwise depend on stdio and your
		4268	libc allows it, this avoids linking in the stdio library which is quite
		4269	big.
		4270
		4271	Note that error messages might become less precise when this option is
		4272	enabled.
		4273
		4274	=item EV_NSIG
		4275
		4276	The highest supported signal number, +1 (or, the number of
		4277	signals): Normally, libev tries to deduce the maximum number of signals
		4278	automatically, but sometimes this fails, in which case it can be
		4279	specified. Also, using a lower number than detected (C<32> should be
		4280	good for about any system in existence) can save some memory, as libev
		4281	statically allocates some 12-24 bytes per signal number.
2634		4282
2635	=item EV_PID_HASHSIZE	4283	=item EV_PID_HASHSIZE
2636		4284
2637	C<ev_child> watchers use a small hash table to distribute workload by	4285	C<ev_child> watchers use a small hash table to distribute workload by
2638	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4286	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2639	than enough. If you need to manage thousands of children you might want to	4287	usually more than enough. If you need to manage thousands of children you
2640	increase this value (I<must> be a power of two).	4288	might want to increase this value (I<must> be a power of two).
2641		4289
2642	=item EV_INOTIFY_HASHSIZE	4290	=item EV_INOTIFY_HASHSIZE
2643		4291
2644	C<ev_stat> watchers use a small hash table to distribute workload by	4292	C<ev_stat> watchers use a small hash table to distribute workload by
2645	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4293	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2646	usually more than enough. If you need to manage thousands of C<ev_stat>	4294	disabled), usually more than enough. If you need to manage thousands of
2647	watchers you might want to increase this value (I<must> be a power of	4295	C<ev_stat> watchers you might want to increase this value (I<must> be a
2648	two).	4296	power of two).
		4297
		4298	=item EV_USE_4HEAP
		4299
		4300	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4301	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4302	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4303	faster performance with many (thousands) of watchers.
		4304
		4305	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4306	will be C<0>.
		4307
		4308	=item EV_HEAP_CACHE_AT
		4309
		4310	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4311	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4312	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4313	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4314	but avoids random read accesses on heap changes. This improves performance
		4315	noticeably with many (hundreds) of watchers.
		4316
		4317	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4318	will be C<0>.
		4319
		4320	=item EV_VERIFY
		4321
		4322	Controls how much internal verification (see C<ev_verify ()>) will
		4323	be done: If set to C<0>, no internal verification code will be compiled
		4324	in. If set to C<1>, then verification code will be compiled in, but not
		4325	called. If set to C<2>, then the internal verification code will be
		4326	called once per loop, which can slow down libev. If set to C<3>, then the
		4327	verification code will be called very frequently, which will slow down
		4328	libev considerably.
		4329
		4330	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4331	will be C<0>.
2649		4332
2650	=item EV_COMMON	4333	=item EV_COMMON
2651		4334
2652	By default, all watchers have a C<void *data> member. By redefining	4335	By default, all watchers have a C<void *data> member. By redefining
2653	this macro to a something else you can include more and other types of	4336	this macro to something else you can include more and other types of
2654	members. You have to define it each time you include one of the files,	4337	members. You have to define it each time you include one of the files,
2655	though, and it must be identical each time.	4338	though, and it must be identical each time.
2656		4339
2657	For example, the perl EV module uses something like this:	4340	For example, the perl EV module uses something like this:
2658		4341
2659	#define EV_COMMON \	4342	#define EV_COMMON \
2660	SV *self; /* contains this struct */ \	4343	SV *self; /* contains this struct */ \
2661	SV *cb_sv, *fh /* note no trailing ";" */	4344	SV *cb_sv, *fh /* note no trailing ";" */
2662		4345
2663	=item EV_CB_DECLARE (type)	4346	=item EV_CB_DECLARE (type)
2664		4347
2665	=item EV_CB_INVOKE (watcher, revents)	4348	=item EV_CB_INVOKE (watcher, revents)
2666		4349
…		…
2671	definition and a statement, respectively. See the F<ev.h> header file for	4354	definition and a statement, respectively. See the F<ev.h> header file for
2672	their default definitions. One possible use for overriding these is to	4355	their default definitions. One possible use for overriding these is to
2673	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4356	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2674	method calls instead of plain function calls in C++.	4357	method calls instead of plain function calls in C++.
2675		4358
		4359	=back
		4360
2676	=head2 EXPORTED API SYMBOLS	4361	=head2 EXPORTED API SYMBOLS
2677		4362
2678	If you need to re-export the API (e.g. via a dll) and you need a list of	4363	If you need to re-export the API (e.g. via a DLL) and you need a list of
2679	exported symbols, you can use the provided F<Symbol.*> files which list	4364	exported symbols, you can use the provided F<Symbol.*> files which list
2680	all public symbols, one per line:	4365	all public symbols, one per line:
2681		4366
2682	Symbols.ev for libev proper	4367	Symbols.ev for libev proper
2683	Symbols.event for the libevent emulation	4368	Symbols.event for the libevent emulation
2684		4369
2685	This can also be used to rename all public symbols to avoid clashes with	4370	This can also be used to rename all public symbols to avoid clashes with
2686	multiple versions of libev linked together (which is obviously bad in	4371	multiple versions of libev linked together (which is obviously bad in
2687	itself, but sometimes it is inconvinient to avoid this).	4372	itself, but sometimes it is inconvenient to avoid this).
2688		4373
2689	A sed command like this will create wrapper C<#define>'s that you need to	4374	A sed command like this will create wrapper C<#define>'s that you need to
2690	include before including F<ev.h>:	4375	include before including F<ev.h>:
2691		4376
2692	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4377	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2709	file.	4394	file.
2710		4395
2711	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4396	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2712	that everybody includes and which overrides some configure choices:	4397	that everybody includes and which overrides some configure choices:
2713		4398
2714	#define EV_MINIMAL 1	4399	#define EV_FEATURES 8
2715	#define EV_USE_POLL 0	4400	#define EV_USE_SELECT 1
2716	#define EV_MULTIPLICITY 0
2717	#define EV_PERIODIC_ENABLE 0	4401	#define EV_PREPARE_ENABLE 1
		4402	#define EV_IDLE_ENABLE 1
2718	#define EV_STAT_ENABLE 0	4403	#define EV_SIGNAL_ENABLE 1
2719	#define EV_FORK_ENABLE 0	4404	#define EV_CHILD_ENABLE 1
		4405	#define EV_USE_STDEXCEPT 0
2720	#define EV_CONFIG_H <config.h>	4406	#define EV_CONFIG_H <config.h>
2721	#define EV_MINPRI 0
2722	#define EV_MAXPRI 0
2723		4407
2724	#include "ev++.h"	4408	#include "ev++.h"
2725		4409
2726	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4410	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2727		4411
2728	#include "ev_cpp.h"	4412	#include "ev_cpp.h"
2729	#include "ev.c"	4413	#include "ev.c"
2730		4414
		4415	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2731		4416
2732	=head1 COMPLEXITIES	4417	=head2 THREADS AND COROUTINES
2733		4418
2734	In this section the complexities of (many of) the algorithms used inside	4419	=head3 THREADS
2735	libev will be explained. For complexity discussions about backends see the
2736	documentation for C<ev_default_init>.
2737		4420
2738	All of the following are about amortised time: If an array needs to be	4421	All libev functions are reentrant and thread-safe unless explicitly
2739	extended, libev needs to realloc and move the whole array, but this	4422	documented otherwise, but libev implements no locking itself. This means
2740	happens asymptotically never with higher number of elements, so O(1) might	4423	that you can use as many loops as you want in parallel, as long as there
2741	mean it might do a lengthy realloc operation in rare cases, but on average	4424	are no concurrent calls into any libev function with the same loop
2742	it is much faster and asymptotically approaches constant time.	4425	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4426	of course): libev guarantees that different event loops share no data
		4427	structures that need any locking.
		4428
		4429	Or to put it differently: calls with different loop parameters can be done
		4430	concurrently from multiple threads, calls with the same loop parameter
		4431	must be done serially (but can be done from different threads, as long as
		4432	only one thread ever is inside a call at any point in time, e.g. by using
		4433	a mutex per loop).
		4434
		4435	Specifically to support threads (and signal handlers), libev implements
		4436	so-called C<ev_async> watchers, which allow some limited form of
		4437	concurrency on the same event loop, namely waking it up "from the
		4438	outside".
		4439
		4440	If you want to know which design (one loop, locking, or multiple loops
		4441	without or something else still) is best for your problem, then I cannot
		4442	help you, but here is some generic advice:
2743		4443
2744	=over 4	4444	=over 4
2745		4445
2746	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4446	=item * most applications have a main thread: use the default libev loop
		4447	in that thread, or create a separate thread running only the default loop.
2747		4448
2748	This means that, when you have a watcher that triggers in one hour and	4449	This helps integrating other libraries or software modules that use libev
2749	there are 100 watchers that would trigger before that then inserting will	4450	themselves and don't care/know about threading.
2750	have to skip roughly seven (C<ld 100>) of these watchers.
2751		4451
2752	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4452	=item * one loop per thread is usually a good model.
2753		4453
2754	That means that changing a timer costs less than removing/adding them	4454	Doing this is almost never wrong, sometimes a better-performance model
2755	as only the relative motion in the event queue has to be paid for.	4455	exists, but it is always a good start.
2756		4456
2757	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4457	=item * other models exist, such as the leader/follower pattern, where one
		4458	loop is handed through multiple threads in a kind of round-robin fashion.
2758		4459
2759	These just add the watcher into an array or at the head of a list.	4460	Choosing a model is hard - look around, learn, know that usually you can do
		4461	better than you currently do :-)
2760		4462
2761	=item Stopping check/prepare/idle watchers: O(1)	4463	=item * often you need to talk to some other thread which blocks in the
		4464	event loop.
2762		4465
2763	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4466	C<ev_async> watchers can be used to wake them up from other threads safely
		4467	(or from signal contexts...).
2764		4468
2765	These watchers are stored in lists then need to be walked to find the	4469	An example use would be to communicate signals or other events that only
2766	correct watcher to remove. The lists are usually short (you don't usually	4470	work in the default loop by registering the signal watcher with the
2767	have many watchers waiting for the same fd or signal).	4471	default loop and triggering an C<ev_async> watcher from the default loop
2768		4472	watcher callback into the event loop interested in the signal.
2769	=item Finding the next timer in each loop iteration: O(1)
2770
2771	By virtue of using a binary heap, the next timer is always found at the
2772	beginning of the storage array.
2773
2774	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2775
2776	A change means an I/O watcher gets started or stopped, which requires
2777	libev to recalculate its status (and possibly tell the kernel, depending
2778	on backend and wether C<ev_io_set> was used).
2779
2780	=item Activating one watcher (putting it into the pending state): O(1)
2781
2782	=item Priority handling: O(number_of_priorities)
2783
2784	Priorities are implemented by allocating some space for each
2785	priority. When doing priority-based operations, libev usually has to
2786	linearly search all the priorities, but starting/stopping and activating
2787	watchers becomes O(1) w.r.t. prioritiy handling.
2788		4473
2789	=back	4474	=back
2790		4475
		4476	=head4 THREAD LOCKING EXAMPLE
2791		4477
2792	=head1 Win32 platform limitations and workarounds	4478	Here is a fictitious example of how to run an event loop in a different
		4479	thread than where callbacks are being invoked and watchers are
		4480	created/added/removed.
		4481
		4482	For a real-world example, see the C<EV::Loop::Async> perl module,
		4483	which uses exactly this technique (which is suited for many high-level
		4484	languages).
		4485
		4486	The example uses a pthread mutex to protect the loop data, a condition
		4487	variable to wait for callback invocations, an async watcher to notify the
		4488	event loop thread and an unspecified mechanism to wake up the main thread.
		4489
		4490	First, you need to associate some data with the event loop:
		4491
		4492	typedef struct {
		4493	mutex_t lock; /* global loop lock */
		4494	ev_async async_w;
		4495	thread_t tid;
		4496	cond_t invoke_cv;
		4497	} userdata;
		4498
		4499	void prepare_loop (EV_P)
		4500	{
		4501	// for simplicity, we use a static userdata struct.
		4502	static userdata u;
		4503
		4504	ev_async_init (&u->async_w, async_cb);
		4505	ev_async_start (EV_A_ &u->async_w);
		4506
		4507	pthread_mutex_init (&u->lock, 0);
		4508	pthread_cond_init (&u->invoke_cv, 0);
		4509
		4510	// now associate this with the loop
		4511	ev_set_userdata (EV_A_ u);
		4512	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4513	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4514
		4515	// then create the thread running ev_loop
		4516	pthread_create (&u->tid, 0, l_run, EV_A);
		4517	}
		4518
		4519	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4520	solely to wake up the event loop so it takes notice of any new watchers
		4521	that might have been added:
		4522
		4523	static void
		4524	async_cb (EV_P_ ev_async *w, int revents)
		4525	{
		4526	// just used for the side effects
		4527	}
		4528
		4529	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4530	protecting the loop data, respectively.
		4531
		4532	static void
		4533	l_release (EV_P)
		4534	{
		4535	userdata *u = ev_userdata (EV_A);
		4536	pthread_mutex_unlock (&u->lock);
		4537	}
		4538
		4539	static void
		4540	l_acquire (EV_P)
		4541	{
		4542	userdata *u = ev_userdata (EV_A);
		4543	pthread_mutex_lock (&u->lock);
		4544	}
		4545
		4546	The event loop thread first acquires the mutex, and then jumps straight
		4547	into C<ev_run>:
		4548
		4549	void *
		4550	l_run (void *thr_arg)
		4551	{
		4552	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4553
		4554	l_acquire (EV_A);
		4555	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4556	ev_run (EV_A_ 0);
		4557	l_release (EV_A);
		4558
		4559	return 0;
		4560	}
		4561
		4562	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4563	signal the main thread via some unspecified mechanism (signals? pipe
		4564	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4565	have been called (in a while loop because a) spurious wakeups are possible
		4566	and b) skipping inter-thread-communication when there are no pending
		4567	watchers is very beneficial):
		4568
		4569	static void
		4570	l_invoke (EV_P)
		4571	{
		4572	userdata *u = ev_userdata (EV_A);
		4573
		4574	while (ev_pending_count (EV_A))
		4575	{
		4576	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4577	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4578	}
		4579	}
		4580
		4581	Now, whenever the main thread gets told to invoke pending watchers, it
		4582	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4583	thread to continue:
		4584
		4585	static void
		4586	real_invoke_pending (EV_P)
		4587	{
		4588	userdata *u = ev_userdata (EV_A);
		4589
		4590	pthread_mutex_lock (&u->lock);
		4591	ev_invoke_pending (EV_A);
		4592	pthread_cond_signal (&u->invoke_cv);
		4593	pthread_mutex_unlock (&u->lock);
		4594	}
		4595
		4596	Whenever you want to start/stop a watcher or do other modifications to an
		4597	event loop, you will now have to lock:
		4598
		4599	ev_timer timeout_watcher;
		4600	userdata *u = ev_userdata (EV_A);
		4601
		4602	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4603
		4604	pthread_mutex_lock (&u->lock);
		4605	ev_timer_start (EV_A_ &timeout_watcher);
		4606	ev_async_send (EV_A_ &u->async_w);
		4607	pthread_mutex_unlock (&u->lock);
		4608
		4609	Note that sending the C<ev_async> watcher is required because otherwise
		4610	an event loop currently blocking in the kernel will have no knowledge
		4611	about the newly added timer. By waking up the loop it will pick up any new
		4612	watchers in the next event loop iteration.
		4613
		4614	=head3 COROUTINES
		4615
		4616	Libev is very accommodating to coroutines ("cooperative threads"):
		4617	libev fully supports nesting calls to its functions from different
		4618	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4619	different coroutines, and switch freely between both coroutines running
		4620	the loop, as long as you don't confuse yourself). The only exception is
		4621	that you must not do this from C<ev_periodic> reschedule callbacks.
		4622
		4623	Care has been taken to ensure that libev does not keep local state inside
		4624	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4625	they do not call any callbacks.
		4626
		4627	=head2 COMPILER WARNINGS
		4628
		4629	Depending on your compiler and compiler settings, you might get no or a
		4630	lot of warnings when compiling libev code. Some people are apparently
		4631	scared by this.
		4632
		4633	However, these are unavoidable for many reasons. For one, each compiler
		4634	has different warnings, and each user has different tastes regarding
		4635	warning options. "Warn-free" code therefore cannot be a goal except when
		4636	targeting a specific compiler and compiler-version.
		4637
		4638	Another reason is that some compiler warnings require elaborate
		4639	workarounds, or other changes to the code that make it less clear and less
		4640	maintainable.
		4641
		4642	And of course, some compiler warnings are just plain stupid, or simply
		4643	wrong (because they don't actually warn about the condition their message
		4644	seems to warn about). For example, certain older gcc versions had some
		4645	warnings that resulted in an extreme number of false positives. These have
		4646	been fixed, but some people still insist on making code warn-free with
		4647	such buggy versions.
		4648
		4649	While libev is written to generate as few warnings as possible,
		4650	"warn-free" code is not a goal, and it is recommended not to build libev
		4651	with any compiler warnings enabled unless you are prepared to cope with
		4652	them (e.g. by ignoring them). Remember that warnings are just that:
		4653	warnings, not errors, or proof of bugs.
		4654
		4655
		4656	=head2 VALGRIND
		4657
		4658	Valgrind has a special section here because it is a popular tool that is
		4659	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4660
		4661	If you think you found a bug (memory leak, uninitialised data access etc.)
		4662	in libev, then check twice: If valgrind reports something like:
		4663
		4664	==2274== definitely lost: 0 bytes in 0 blocks.
		4665	==2274== possibly lost: 0 bytes in 0 blocks.
		4666	==2274== still reachable: 256 bytes in 1 blocks.
		4667
		4668	Then there is no memory leak, just as memory accounted to global variables
		4669	is not a memleak - the memory is still being referenced, and didn't leak.
		4670
		4671	Similarly, under some circumstances, valgrind might report kernel bugs
		4672	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4673	although an acceptable workaround has been found here), or it might be
		4674	confused.
		4675
		4676	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4677	make it into some kind of religion.
		4678
		4679	If you are unsure about something, feel free to contact the mailing list
		4680	with the full valgrind report and an explanation on why you think this
		4681	is a bug in libev (best check the archives, too :). However, don't be
		4682	annoyed when you get a brisk "this is no bug" answer and take the chance
		4683	of learning how to interpret valgrind properly.
		4684
		4685	If you need, for some reason, empty reports from valgrind for your project
		4686	I suggest using suppression lists.
		4687
		4688
		4689	=head1 PORTABILITY NOTES
		4690
		4691	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4692
		4693	GNU/Linux is the only common platform that supports 64 bit file/large file
		4694	interfaces but I<disables> them by default.
		4695
		4696	That means that libev compiled in the default environment doesn't support
		4697	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4698
		4699	Unfortunately, many programs try to work around this GNU/Linux issue
		4700	by enabling the large file API, which makes them incompatible with the
		4701	standard libev compiled for their system.
		4702
		4703	Likewise, libev cannot enable the large file API itself as this would
		4704	suddenly make it incompatible to the default compile time environment,
		4705	i.e. all programs not using special compile switches.
		4706
		4707	=head2 OS/X AND DARWIN BUGS
		4708
		4709	The whole thing is a bug if you ask me - basically any system interface
		4710	you touch is broken, whether it is locales, poll, kqueue or even the
		4711	OpenGL drivers.
		4712
		4713	=head3 C<kqueue> is buggy
		4714
		4715	The kqueue syscall is broken in all known versions - most versions support
		4716	only sockets, many support pipes.
		4717
		4718	Libev tries to work around this by not using C<kqueue> by default on this
		4719	rotten platform, but of course you can still ask for it when creating a
		4720	loop - embedding a socket-only kqueue loop into a select-based one is
		4721	probably going to work well.
		4722
		4723	=head3 C<poll> is buggy
		4724
		4725	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4726	implementation by something calling C<kqueue> internally around the 10.5.6
		4727	release, so now C<kqueue> I<and> C<poll> are broken.
		4728
		4729	Libev tries to work around this by not using C<poll> by default on
		4730	this rotten platform, but of course you can still ask for it when creating
		4731	a loop.
		4732
		4733	=head3 C<select> is buggy
		4734
		4735	All that's left is C<select>, and of course Apple found a way to fuck this
		4736	one up as well: On OS/X, C<select> actively limits the number of file
		4737	descriptors you can pass in to 1024 - your program suddenly crashes when
		4738	you use more.
		4739
		4740	There is an undocumented "workaround" for this - defining
		4741	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4742	work on OS/X.
		4743
		4744	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4745
		4746	=head3 C<errno> reentrancy
		4747
		4748	The default compile environment on Solaris is unfortunately so
		4749	thread-unsafe that you can't even use components/libraries compiled
		4750	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4751	defined by default. A valid, if stupid, implementation choice.
		4752
		4753	If you want to use libev in threaded environments you have to make sure
		4754	it's compiled with C<_REENTRANT> defined.
		4755
		4756	=head3 Event port backend
		4757
		4758	The scalable event interface for Solaris is called "event
		4759	ports". Unfortunately, this mechanism is very buggy in all major
		4760	releases. If you run into high CPU usage, your program freezes or you get
		4761	a large number of spurious wakeups, make sure you have all the relevant
		4762	and latest kernel patches applied. No, I don't know which ones, but there
		4763	are multiple ones to apply, and afterwards, event ports actually work
		4764	great.
		4765
		4766	If you can't get it to work, you can try running the program by setting
		4767	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4768	C<select> backends.
		4769
		4770	=head2 AIX POLL BUG
		4771
		4772	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4773	this by trying to avoid the poll backend altogether (i.e. it's not even
		4774	compiled in), which normally isn't a big problem as C<select> works fine
		4775	with large bitsets on AIX, and AIX is dead anyway.
		4776
		4777	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4778
		4779	=head3 General issues
2793		4780
2794	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4781	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2795	requires, and its I/O model is fundamentally incompatible with the POSIX	4782	requires, and its I/O model is fundamentally incompatible with the POSIX
2796	model. Libev still offers limited functionality on this platform in	4783	model. Libev still offers limited functionality on this platform in
2797	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4784	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2798	descriptors. This only applies when using Win32 natively, not when using	4785	descriptors. This only applies when using Win32 natively, not when using
2799	e.g. cygwin.	4786	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4787	as every compielr comes with a slightly differently broken/incompatible
		4788	environment.
		4789
		4790	Lifting these limitations would basically require the full
		4791	re-implementation of the I/O system. If you are into this kind of thing,
		4792	then note that glib does exactly that for you in a very portable way (note
		4793	also that glib is the slowest event library known to man).
2800		4794
2801	There is no supported compilation method available on windows except	4795	There is no supported compilation method available on windows except
2802	embedding it into other applications.	4796	embedding it into other applications.
2803		4797
		4798	Sensible signal handling is officially unsupported by Microsoft - libev
		4799	tries its best, but under most conditions, signals will simply not work.
		4800
		4801	Not a libev limitation but worth mentioning: windows apparently doesn't
		4802	accept large writes: instead of resulting in a partial write, windows will
		4803	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4804	so make sure you only write small amounts into your sockets (less than a
		4805	megabyte seems safe, but this apparently depends on the amount of memory
		4806	available).
		4807
2804	Due to the many, low, and arbitrary limits on the win32 platform and the	4808	Due to the many, low, and arbitrary limits on the win32 platform and
2805	abysmal performance of winsockets, using a large number of sockets is not	4809	the abysmal performance of winsockets, using a large number of sockets
2806	recommended (and not reasonable). If your program needs to use more than	4810	is not recommended (and not reasonable). If your program needs to use
2807	a hundred or so sockets, then likely it needs to use a totally different	4811	more than a hundred or so sockets, then likely it needs to use a totally
2808	implementation for windows, as libev offers the POSIX model, which cannot	4812	different implementation for windows, as libev offers the POSIX readiness
2809	be implemented efficiently on windows (microsoft monopoly games).	4813	notification model, which cannot be implemented efficiently on windows
		4814	(due to Microsoft monopoly games).
2810		4815
2811	=over 4	4816	A typical way to use libev under windows is to embed it (see the embedding
		4817	section for details) and use the following F<evwrap.h> header file instead
		4818	of F<ev.h>:
2812		4819
		4820	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4821	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4822
		4823	#include "ev.h"
		4824
		4825	And compile the following F<evwrap.c> file into your project (make sure
		4826	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4827
		4828	#include "evwrap.h"
		4829	#include "ev.c"
		4830
2813	=item The winsocket select function	4831	=head3 The winsocket C<select> function
2814		4832
2815	The winsocket C<select> function doesn't follow POSIX in that it requires	4833	The winsocket C<select> function doesn't follow POSIX in that it
2816	socket I<handles> and not socket I<file descriptors>. This makes select	4834	requires socket I<handles> and not socket I<file descriptors> (it is
2817	very inefficient, and also requires a mapping from file descriptors	4835	also extremely buggy). This makes select very inefficient, and also
2818	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4836	requires a mapping from file descriptors to socket handles (the Microsoft
2819	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4837	C runtime provides the function C<_open_osfhandle> for this). See the
2820	symbols for more info.	4838	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4839	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
2821		4840
2822	The configuration for a "naked" win32 using the microsoft runtime	4841	The configuration for a "naked" win32 using the Microsoft runtime
2823	libraries and raw winsocket select is:	4842	libraries and raw winsocket select is:
2824		4843
2825	#define EV_USE_SELECT 1	4844	#define EV_USE_SELECT 1
2826	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4845	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2827		4846
2828	Note that winsockets handling of fd sets is O(n), so you can easily get a	4847	Note that winsockets handling of fd sets is O(n), so you can easily get a
2829	complexity in the O(n²) range when using win32.	4848	complexity in the O(n²) range when using win32.
2830		4849
2831	=item Limited number of file descriptors	4850	=head3 Limited number of file descriptors
2832		4851
2833	Windows has numerous arbitrary (and low) limits on things. Early versions	4852	Windows has numerous arbitrary (and low) limits on things.
2834	of winsocket's select only supported waiting for a max. of C<64> handles	4853
		4854	Early versions of winsocket's select only supported waiting for a maximum
2835	(probably owning to the fact that all windows kernels can only wait for	4855	of C<64> handles (probably owning to the fact that all windows kernels
2836	C<64> things at the same time internally; microsoft recommends spawning a	4856	can only wait for C<64> things at the same time internally; Microsoft
2837	chain of threads and wait for 63 handles and the previous thread in each).	4857	recommends spawning a chain of threads and wait for 63 handles and the
		4858	previous thread in each. Sounds great!).
2838		4859
2839	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4860	Newer versions support more handles, but you need to define C<FD_SETSIZE>
2840	to some high number (e.g. C<2048>) before compiling the winsocket select	4861	to some high number (e.g. C<2048>) before compiling the winsocket select
2841	call (which might be in libev or elsewhere, for example, perl does its own	4862	call (which might be in libev or elsewhere, for example, perl and many
2842	select emulation on windows).	4863	other interpreters do their own select emulation on windows).
2843		4864
2844	Another limit is the number of file descriptors in the microsoft runtime	4865	Another limit is the number of file descriptors in the Microsoft runtime
2845	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4866	libraries, which by default is C<64> (there must be a hidden I<64>
2846	or something like this inside microsoft). You can increase this by calling	4867	fetish or something like this inside Microsoft). You can increase this
2847	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4868	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
2848	arbitrary limit), but is broken in many versions of the microsoft runtime	4869	(another arbitrary limit), but is broken in many versions of the Microsoft
2849	libraries.
2850
2851	This might get you to about C<512> or C<2048> sockets (depending on	4870	runtime libraries. This might get you to about C<512> or C<2048> sockets
2852	windows version and/or the phase of the moon). To get more, you need to	4871	(depending on windows version and/or the phase of the moon). To get more,
2853	wrap all I/O functions and provide your own fd management, but the cost of	4872	you need to wrap all I/O functions and provide your own fd management, but
2854	calling select (O(n²)) will likely make this unworkable.	4873	the cost of calling select (O(n²)) will likely make this unworkable.
		4874
		4875	=head2 PORTABILITY REQUIREMENTS
		4876
		4877	In addition to a working ISO-C implementation and of course the
		4878	backend-specific APIs, libev relies on a few additional extensions:
		4879
		4880	=over 4
		4881
		4882	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4883	calling conventions regardless of C<ev_watcher_type *>.
		4884
		4885	Libev assumes not only that all watcher pointers have the same internal
		4886	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4887	assumes that the same (machine) code can be used to call any watcher
		4888	callback: The watcher callbacks have different type signatures, but libev
		4889	calls them using an C<ev_watcher *> internally.
		4890
		4891	=item pointer accesses must be thread-atomic
		4892
		4893	Accessing a pointer value must be atomic, it must both be readable and
		4894	writable in one piece - this is the case on all current architectures.
		4895
		4896	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4897
		4898	The type C<sig_atomic_t volatile> (or whatever is defined as
		4899	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4900	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4901	believed to be sufficiently portable.
		4902
		4903	=item C<sigprocmask> must work in a threaded environment
		4904
		4905	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4906	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4907	pthread implementations will either allow C<sigprocmask> in the "main
		4908	thread" or will block signals process-wide, both behaviours would
		4909	be compatible with libev. Interaction between C<sigprocmask> and
		4910	C<pthread_sigmask> could complicate things, however.
		4911
		4912	The most portable way to handle signals is to block signals in all threads
		4913	except the initial one, and run the default loop in the initial thread as
		4914	well.
		4915
		4916	=item C<long> must be large enough for common memory allocation sizes
		4917
		4918	To improve portability and simplify its API, libev uses C<long> internally
		4919	instead of C<size_t> when allocating its data structures. On non-POSIX
		4920	systems (Microsoft...) this might be unexpectedly low, but is still at
		4921	least 31 bits everywhere, which is enough for hundreds of millions of
		4922	watchers.
		4923
		4924	=item C<double> must hold a time value in seconds with enough accuracy
		4925
		4926	The type C<double> is used to represent timestamps. It is required to
		4927	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4928	good enough for at least into the year 4000 with millisecond accuracy
		4929	(the design goal for libev). This requirement is overfulfilled by
		4930	implementations using IEEE 754, which is basically all existing ones. With
		4931	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
2855		4932
2856	=back	4933	=back
2857		4934
		4935	If you know of other additional requirements drop me a note.
		4936
		4937
		4938	=head1 ALGORITHMIC COMPLEXITIES
		4939
		4940	In this section the complexities of (many of) the algorithms used inside
		4941	libev will be documented. For complexity discussions about backends see
		4942	the documentation for C<ev_default_init>.
		4943
		4944	All of the following are about amortised time: If an array needs to be
		4945	extended, libev needs to realloc and move the whole array, but this
		4946	happens asymptotically rarer with higher number of elements, so O(1) might
		4947	mean that libev does a lengthy realloc operation in rare cases, but on
		4948	average it is much faster and asymptotically approaches constant time.
		4949
		4950	=over 4
		4951
		4952	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4953
		4954	This means that, when you have a watcher that triggers in one hour and
		4955	there are 100 watchers that would trigger before that, then inserting will
		4956	have to skip roughly seven (C<ld 100>) of these watchers.
		4957
		4958	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4959
		4960	That means that changing a timer costs less than removing/adding them,
		4961	as only the relative motion in the event queue has to be paid for.
		4962
		4963	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4964
		4965	These just add the watcher into an array or at the head of a list.
		4966
		4967	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4968
		4969	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4970
		4971	These watchers are stored in lists, so they need to be walked to find the
		4972	correct watcher to remove. The lists are usually short (you don't usually
		4973	have many watchers waiting for the same fd or signal: one is typical, two
		4974	is rare).
		4975
		4976	=item Finding the next timer in each loop iteration: O(1)
		4977
		4978	By virtue of using a binary or 4-heap, the next timer is always found at a
		4979	fixed position in the storage array.
		4980
		4981	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4982
		4983	A change means an I/O watcher gets started or stopped, which requires
		4984	libev to recalculate its status (and possibly tell the kernel, depending
		4985	on backend and whether C<ev_io_set> was used).
		4986
		4987	=item Activating one watcher (putting it into the pending state): O(1)
		4988
		4989	=item Priority handling: O(number_of_priorities)
		4990
		4991	Priorities are implemented by allocating some space for each
		4992	priority. When doing priority-based operations, libev usually has to
		4993	linearly search all the priorities, but starting/stopping and activating
		4994	watchers becomes O(1) with respect to priority handling.
		4995
		4996	=item Sending an ev_async: O(1)
		4997
		4998	=item Processing ev_async_send: O(number_of_async_watchers)
		4999
		5000	=item Processing signals: O(max_signal_number)
		5001
		5002	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5003	calls in the current loop iteration. Checking for async and signal events
		5004	involves iterating over all running async watchers or all signal numbers.
		5005
		5006	=back
		5007
		5008
		5009	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5010
		5011	The major version 4 introduced some incompatible changes to the API.
		5012
		5013	At the moment, the C<ev.h> header file provides compatibility definitions
		5014	for all changes, so most programs should still compile. The compatibility
		5015	layer might be removed in later versions of libev, so better update to the
		5016	new API early than late.
		5017
		5018	=over 4
		5019
		5020	=item C<EV_COMPAT3> backwards compatibility mechanism
		5021
		5022	The backward compatibility mechanism can be controlled by
		5023	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5024	section.
		5025
		5026	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5027
		5028	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5029
		5030	ev_loop_destroy (EV_DEFAULT_UC);
		5031	ev_loop_fork (EV_DEFAULT);
		5032
		5033	=item function/symbol renames
		5034
		5035	A number of functions and symbols have been renamed:
		5036
		5037	ev_loop => ev_run
		5038	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5039	EVLOOP_ONESHOT => EVRUN_ONCE
		5040
		5041	ev_unloop => ev_break
		5042	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5043	EVUNLOOP_ONE => EVBREAK_ONE
		5044	EVUNLOOP_ALL => EVBREAK_ALL
		5045
		5046	EV_TIMEOUT => EV_TIMER
		5047
		5048	ev_loop_count => ev_iteration
		5049	ev_loop_depth => ev_depth
		5050	ev_loop_verify => ev_verify
		5051
		5052	Most functions working on C<struct ev_loop> objects don't have an
		5053	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5054	associated constants have been renamed to not collide with the C<struct
		5055	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5056	as all other watcher types. Note that C<ev_loop_fork> is still called
		5057	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5058	typedef.
		5059
		5060	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5061
		5062	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5063	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5064	and work, but the library code will of course be larger.
		5065
		5066	=back
		5067
		5068
		5069	=head1 GLOSSARY
		5070
		5071	=over 4
		5072
		5073	=item active
		5074
		5075	A watcher is active as long as it has been started and not yet stopped.
		5076	See L<WATCHER STATES> for details.
		5077
		5078	=item application
		5079
		5080	In this document, an application is whatever is using libev.
		5081
		5082	=item backend
		5083
		5084	The part of the code dealing with the operating system interfaces.
		5085
		5086	=item callback
		5087
		5088	The address of a function that is called when some event has been
		5089	detected. Callbacks are being passed the event loop, the watcher that
		5090	received the event, and the actual event bitset.
		5091
		5092	=item callback/watcher invocation
		5093
		5094	The act of calling the callback associated with a watcher.
		5095
		5096	=item event
		5097
		5098	A change of state of some external event, such as data now being available
		5099	for reading on a file descriptor, time having passed or simply not having
		5100	any other events happening anymore.
		5101
		5102	In libev, events are represented as single bits (such as C<EV_READ> or
		5103	C<EV_TIMER>).
		5104
		5105	=item event library
		5106
		5107	A software package implementing an event model and loop.
		5108
		5109	=item event loop
		5110
		5111	An entity that handles and processes external events and converts them
		5112	into callback invocations.
		5113
		5114	=item event model
		5115
		5116	The model used to describe how an event loop handles and processes
		5117	watchers and events.
		5118
		5119	=item pending
		5120
		5121	A watcher is pending as soon as the corresponding event has been
		5122	detected. See L<WATCHER STATES> for details.
		5123
		5124	=item real time
		5125
		5126	The physical time that is observed. It is apparently strictly monotonic :)
		5127
		5128	=item wall-clock time
		5129
		5130	The time and date as shown on clocks. Unlike real time, it can actually
		5131	be wrong and jump forwards and backwards, e.g. when the you adjust your
		5132	clock.
		5133
		5134	=item watcher
		5135
		5136	A data structure that describes interest in certain events. Watchers need
		5137	to be started (attached to an event loop) before they can receive events.
		5138
		5139	=back
2858		5140
2859	=head1 AUTHOR	5141	=head1 AUTHOR
2860		5142
2861	Marc Lehmann <libev@schmorp.de>.	5143	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5144	Magnusson and Emanuele Giaquinta.
2862		5145

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