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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
6		8
7	#include <ev.h>	9	#include <ev.h>
8		10
9	=head1 EXAMPLE PROGRAM	11	=head2 EXAMPLE PROGRAM
10		12
		13	// a single header file is required
11	#include <ev.h>	14	#include <ev.h>
12		15
		16	#include <stdio.h> // for puts
		17
		18	// every watcher type has its own typedef'd struct
		19	// with the name ev_TYPE
13	ev_io stdin_watcher;	20	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	21	ev_timer timeout_watcher;
15		22
16	/* called when data readable on stdin */	23	// all watcher callbacks have a similar signature
		24	// this callback is called when data is readable on stdin
17	static void	25	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	26	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	27	{
20	/* puts ("stdin ready"); */	28	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	29	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	30	// with its corresponding stop function.
		31	ev_io_stop (EV_A_ w);
		32
		33	// this causes all nested ev_run's to stop iterating
		34	ev_break (EV_A_ EVBREAK_ALL);
23	}	35	}
24		36
		37	// another callback, this time for a time-out
25	static void	38	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	39	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	40	{
28	/* puts ("timeout"); */	41	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	42	// this causes the innermost ev_run to stop iterating
		43	ev_break (EV_A_ EVBREAK_ONE);
30	}	44	}
31		45
32	int	46	int
33	main (void)	47	main (void)
34	{	48	{
35	struct ev_loop *loop = ev_default_loop (0);	49	// use the default event loop unless you have special needs
		50	struct ev_loop *loop = EV_DEFAULT;
36		51
37	/* initialise an io watcher, then start it */	52	// initialise an io watcher, then start it
		53	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
40		56
		57	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	58	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
44		61
45	/* loop till timeout or data ready */	62	// now wait for events to arrive
46	ev_loop (loop, 0);	63	ev_run (loop, 0);
47		64
		65	// break was called, so exit
48	return 0;	66	return 0;
49	}	67	}
50		68
51	=head1 DESCRIPTION	69	=head1 ABOUT THIS DOCUMENT
52		70
		71	This document documents the libev software package.
		72
53	The newest version of this document is also available as a html-formatted	73	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	74	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	75	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		76
		77	While this document tries to be as complete as possible in documenting
		78	libev, its usage and the rationale behind its design, it is not a tutorial
		79	on event-based programming, nor will it introduce event-based programming
		80	with libev.
		81
		82	Familiarity with event based programming techniques in general is assumed
		83	throughout this document.
		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
		93	=head1 ABOUT LIBEV
56		94
57	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occuring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	97	these event sources and provide your program with events.
60		98
61	To do this, it must take more or less complete control over your process	99	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	100	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	101	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	103	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	104	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	106	watcher.
69		107
70	=head1 FEATURES	108	=head2 FEATURES
71		109
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	114	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	115	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	116	(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	117	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	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(C<ev_fork>).	119	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		120	limited support for fork events (C<ev_fork>).
82		121
83	It also is quite fast (see this	122	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	123	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	124	for example).
86		125
87	=head1 CONVENTIONS	126	=head2 CONVENTIONS
88		127
89	Libev is very configurable. In this manual the default configuration will	128	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	129	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	130	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	131	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>	132	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.	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		134	this argument.
95		135
96	=head1 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
97		137
98	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	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	140	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	141	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	142	too. It usually aliases to the C<double> type in C. When you need to do
103	it, you should treat it as such.	143	any calculations on it, you should treat it as some floating point value.
		144
		145	Unlike the name component C<stamp> might indicate, it is also used for
		146	time differences (e.g. delays) throughout libev.
		147
		148	=head1 ERROR HANDLING
		149
		150	Libev knows three classes of errors: operating system errors, usage errors
		151	and internal errors (bugs).
		152
		153	When libev catches an operating system error it cannot handle (for example
		154	a system call indicating a condition libev cannot fix), it calls the callback
		155	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		156	abort. The default is to print a diagnostic message and to call C<abort
		157	()>.
		158
		159	When libev detects a usage error such as a negative timer interval, then
		160	it will print a diagnostic message and abort (via the C<assert> mechanism,
		161	so C<NDEBUG> will disable this checking): these are programming errors in
		162	the libev caller and need to be fixed there.
		163
		164	Libev also has a few internal error-checking C<assert>ions, and also has
		165	extensive consistency checking code. These do not trigger under normal
		166	circumstances, as they indicate either a bug in libev or worse.
		167
104		168
105	=head1 GLOBAL FUNCTIONS	169	=head1 GLOBAL FUNCTIONS
106		170
107	These functions can be called anytime, even before initialising the	171	These functions can be called anytime, even before initialising the
108	library in any way.	172	library in any way.
…		…
111		175
112	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
113		177
114	Returns the current time as libev would use it. Please note that the	178	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	179	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	180	you actually want to know. Also interesting is the combination of
		181	C<ev_now_update> and C<ev_now>.
		182
		183	=item ev_sleep (ev_tstamp interval)
		184
		185	Sleep for the given interval: The current thread will be blocked
		186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
		190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
117		194
118	=item int ev_version_major ()	195	=item int ev_version_major ()
119		196
120	=item int ev_version_minor ()	197	=item int ev_version_minor ()
121		198
122	You can find out the major and minor version numbers of the library	199	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	200	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	201	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	202	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	203	version of the library your program was compiled against.
127		204
		205	These version numbers refer to the ABI version of the library, not the
		206	release version.
		207
128	Usually, it's a good idea to terminate if the major versions mismatch,	208	Usually, it's a good idea to terminate if the major versions mismatch,
129	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
130	compatible to older versions, so a larger minor version alone is usually	210	compatible to older versions, so a larger minor version alone is usually
131	not a problem.	211	not a problem.
132		212
133	Example: Make sure we haven't accidentally been linked against the wrong	213	Example: Make sure we haven't accidentally been linked against the wrong
134	version.	214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
135		216
136	assert (("libev version mismatch",	217	assert (("libev version mismatch",
137	ev_version_major () == EV_VERSION_MAJOR	218	ev_version_major () == EV_VERSION_MAJOR
138	&& ev_version_minor () >= EV_VERSION_MINOR));	219	&& ev_version_minor () >= EV_VERSION_MINOR));
139		220
140	=item unsigned int ev_supported_backends ()	221	=item unsigned int ev_supported_backends ()
141		222
142	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	223	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
143	value) compiled into this binary of libev (independent of their	224	value) compiled into this binary of libev (independent of their
…		…
145	a description of the set values.	226	a description of the set values.
146		227
147	Example: make sure we have the epoll method, because yeah this is cool and	228	Example: make sure we have the epoll method, because yeah this is cool and
148	a must have and can we have a torrent of it please!!!11	229	a must have and can we have a torrent of it please!!!11
149		230
150	assert (("sorry, no epoll, no sex",	231	assert (("sorry, no epoll, no sex",
151	ev_supported_backends () & EVBACKEND_EPOLL));	232	ev_supported_backends () & EVBACKEND_EPOLL));
152		233
153	=item unsigned int ev_recommended_backends ()	234	=item unsigned int ev_recommended_backends ()
154		235
155	Return the set of all backends compiled into this binary of libev and also	236	Return the set of all backends compiled into this binary of libev and
156	recommended for this platform. This set is often smaller than the one	237	also recommended for this platform, meaning it will work for most file
		238	descriptor types. This set is often smaller than the one returned by
157	returned by C<ev_supported_backends>, as for example kqueue is broken on	239	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
158	most BSDs and will not be autodetected unless you explicitly request it	240	and will not be auto-detected unless you explicitly request it (assuming
159	(assuming you know what you are doing). This is the set of backends that	241	you know what you are doing). This is the set of backends that libev will
160	libev will probe for if you specify no backends explicitly.	242	probe for if you specify no backends explicitly.
161		243
162	=item unsigned int ev_embeddable_backends ()	244	=item unsigned int ev_embeddable_backends ()
163		245
164	Returns the set of backends that are embeddable in other event loops. This	246	Returns the set of backends that are embeddable in other event loops. This
165	is the theoretical, all-platform, value. To find which backends	247	value is platform-specific but can include backends not available on the
166	might be supported on the current system, you would need to look at	248	current system. To find which embeddable backends might be supported on
167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	249	the current system, you would need to look at C<ev_embeddable_backends ()
168	recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
169		251
170	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
171		253
172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
173		255
174	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
175	semantics is identical - to the realloc C function). It is used to	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
176	allocate and free memory (no surprises here). If it returns zero when	258	used to allocate and free memory (no surprises here). If it returns zero
177	memory needs to be allocated, the library might abort or take some	259	when memory needs to be allocated (C<size != 0>), the library might abort
178	potentially destructive action. The default is your system realloc	260	or take some potentially destructive action.
179	function.	261
		262	Since some systems (at least OpenBSD and Darwin) fail to implement
		263	correct C<realloc> semantics, libev will use a wrapper around the system
		264	C<realloc> and C<free> functions by default.
180		265
181	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
182	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
183	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
184		269
		270	Example: The following is the C<realloc> function that libev itself uses
		271	which should work with C<realloc> and C<free> functions of all kinds and
		272	is probably a good basis for your own implementation.
		273
		274	static void *
		275	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		276	{
		277	if (size)
		278	return realloc (ptr, size);
		279
		280	free (ptr);
		281	return 0;
		282	}
		283
185	Example: Replace the libev allocator with one that waits a bit and then	284	Example: Replace the libev allocator with one that waits a bit and then
186	retries).	285	retries.
187		286
188	static void *	287	static void *
189	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
190	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
191	for (;;)	296	for (;;)
192	{	297	{
193	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
194		299
195	if (newptr)	300	if (newptr)
…		…
200	}	305	}
201		306
202	...	307	...
203	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
204		309
205	=item ev_set_syserr_cb (void (*cb)(const char *msg));	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
206		311
207	Set the callback function to call on a retryable syscall error (such	312	Set the callback function to call on a retryable system call error (such
208	as failed select, poll, epoll_wait). The message is a printable string	313	as failed select, poll, epoll_wait). The message is a printable string
209	indicating the system call or subsystem causing the problem. If this	314	indicating the system call or subsystem causing the problem. If this
210	callback is set, then libev will expect it to remedy the sitution, no	315	callback is set, then libev will expect it to remedy the situation, no
211	matter what, when it returns. That is, libev will generally retry the	316	matter what, when it returns. That is, libev will generally retry the
212	requested operation, or, if the condition doesn't go away, do bad stuff	317	requested operation, or, if the condition doesn't go away, do bad stuff
213	(such as abort).	318	(such as abort).
214		319
215	Example: This is basically the same thing that libev does internally, too.	320	Example: This is basically the same thing that libev does internally, too.
…		…
222	}	327	}
223		328
224	...	329	...
225	ev_set_syserr_cb (fatal_error);	330	ev_set_syserr_cb (fatal_error);
226		331
		332	=item ev_feed_signal (int signum)
		333
		334	This function can be used to "simulate" a signal receive. It is completely
		335	safe to call this function at any time, from any context, including signal
		336	handlers or random threads.
		337
		338	Its main use is to customise signal handling in your process, especially
		339	in the presence of threads. For example, you could block signals
		340	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		341	creating any loops), and in one thread, use C<sigwait> or any other
		342	mechanism to wait for signals, then "deliver" them to libev by calling
		343	C<ev_feed_signal>.
		344
227	=back	345	=back
228		346
229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	347	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
230		348
231	An event loop is described by a C<struct ev_loop *>. The library knows two	349	An event loop is described by a C<struct ev_loop *> (the C<struct> is
232	types of such loops, the I<default> loop, which supports signals and child	350	I<not> optional in this case unless libev 3 compatibility is disabled, as
233	events, and dynamically created loops which do not.	351	libev 3 had an C<ev_loop> function colliding with the struct name).
234		352
235	If you use threads, a common model is to run the default event loop	353	The library knows two types of such loops, the I<default> loop, which
236	in your main thread (or in a separate thread) and for each thread you	354	supports child process events, and dynamically created event loops which
237	create, you also create another event loop. Libev itself does no locking	355	do not.
238	whatsoever, so if you mix calls to the same event loop in different
239	threads, make sure you lock (this is usually a bad idea, though, even if
240	done correctly, because it's hideous and inefficient).
241		356
242	=over 4	357	=over 4
243		358
244	=item struct ev_loop *ev_default_loop (unsigned int flags)	359	=item struct ev_loop *ev_default_loop (unsigned int flags)
245		360
246	This will initialise the default event loop if it hasn't been initialised	361	This returns the "default" event loop object, which is what you should
247	yet and return it. If the default loop could not be initialised, returns	362	normally use when you just need "the event loop". Event loop objects and
248	false. If it already was initialised it simply returns it (and ignores the	363	the C<flags> parameter are described in more detail in the entry for
249	flags. If that is troubling you, check C<ev_backend ()> afterwards).	364	C<ev_loop_new>.
		365
		366	If the default loop is already initialised then this function simply
		367	returns it (and ignores the flags. If that is troubling you, check
		368	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		369	flags, which should almost always be C<0>, unless the caller is also the
		370	one calling C<ev_run> or otherwise qualifies as "the main program".
250		371
251	If you don't know what event loop to use, use the one returned from this	372	If you don't know what event loop to use, use the one returned from this
252	function.	373	function (or via the C<EV_DEFAULT> macro).
		374
		375	Note that this function is I<not> thread-safe, so if you want to use it
		376	from multiple threads, you have to employ some kind of mutex (note also
		377	that this case is unlikely, as loops cannot be shared easily between
		378	threads anyway).
		379
		380	The default loop is the only loop that can handle C<ev_child> watchers,
		381	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		382	a problem for your application you can either create a dynamic loop with
		383	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		384	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		385
		386	Example: This is the most typical usage.
		387
		388	if (!ev_default_loop (0))
		389	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		390
		391	Example: Restrict libev to the select and poll backends, and do not allow
		392	environment settings to be taken into account:
		393
		394	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		395
		396	=item struct ev_loop *ev_loop_new (unsigned int flags)
		397
		398	This will create and initialise a new event loop object. If the loop
		399	could not be initialised, returns false.
		400
		401	This function is thread-safe, and one common way to use libev with
		402	threads is indeed to create one loop per thread, and using the default
		403	loop in the "main" or "initial" thread.
253		404
254	The flags argument can be used to specify special behaviour or specific	405	The flags argument can be used to specify special behaviour or specific
255	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	406	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
256		407
257	The following flags are supported:	408	The following flags are supported:
…		…
263	The default flags value. Use this if you have no clue (it's the right	414	The default flags value. Use this if you have no clue (it's the right
264	thing, believe me).	415	thing, believe me).
265		416
266	=item C<EVFLAG_NOENV>	417	=item C<EVFLAG_NOENV>
267		418
268	If this flag bit is ored into the flag value (or the program runs setuid	419	If this flag bit is or'ed into the flag value (or the program runs setuid
269	or setgid) then libev will I<not> look at the environment variable	420	or setgid) then libev will I<not> look at the environment variable
270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
271	override the flags completely if it is found in the environment. This is	422	override the flags completely if it is found in the environment. This is
272	useful to try out specific backends to test their performance, or to work	423	useful to try out specific backends to test their performance, to work
273	around bugs.	424	around bugs, or to make libev threadsafe (accessing environment variables
		425	cannot be done in a threadsafe way, but usually it works if no other
		426	thread modifies them).
274		427
275	=item C<EVFLAG_FORKCHECK>	428	=item C<EVFLAG_FORKCHECK>
276		429
277	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	430	Instead of calling C<ev_loop_fork> manually after a fork, you can also
278	a fork, you can also make libev check for a fork in each iteration by	431	make libev check for a fork in each iteration by enabling this flag.
279	enabling this flag.
280		432
281	This works by calling C<getpid ()> on every iteration of the loop,	433	This works by calling C<getpid ()> on every iteration of the loop,
282	and thus this might slow down your event loop if you do a lot of loop	434	and thus this might slow down your event loop if you do a lot of loop
283	iterations and little real work, but is usually not noticeable (on my	435	iterations and little real work, but is usually not noticeable (on my
284	Linux system for example, C<getpid> is actually a simple 5-insn sequence	436	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
285	without a syscall and thus I<very> fast, but my Linux system also has	437	sequence without a system call and thus I<very> fast, but my GNU/Linux
286	C<pthread_atfork> which is even faster).	438	system also has C<pthread_atfork> which is even faster). (Update: glibc
		439	versions 2.25 apparently removed the C<getpid> optimisation again).
287		440
288	The big advantage of this flag is that you can forget about fork (and	441	The big advantage of this flag is that you can forget about fork (and
289	forget about forgetting to tell libev about forking) when you use this	442	forget about forgetting to tell libev about forking, although you still
290	flag.	443	have to ignore C<SIGPIPE>) when you use this flag.
291		444
292	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	445	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
293	environment variable.	446	environment variable.
		447
		448	=item C<EVFLAG_NOINOTIFY>
		449
		450	When this flag is specified, then libev will not attempt to use the
		451	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		452	testing, this flag can be useful to conserve inotify file descriptors, as
		453	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		454
		455	=item C<EVFLAG_SIGNALFD>
		456
		457	When this flag is specified, then libev will attempt to use the
		458	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		459	delivers signals synchronously, which makes it both faster and might make
		460	it possible to get the queued signal data. It can also simplify signal
		461	handling with threads, as long as you properly block signals in your
		462	threads that are not interested in handling them.
		463
		464	Signalfd will not be used by default as this changes your signal mask, and
		465	there are a lot of shoddy libraries and programs (glib's threadpool for
		466	example) that can't properly initialise their signal masks.
		467
		468	=item C<EVFLAG_NOSIGMASK>
		469
		470	When this flag is specified, then libev will avoid to modify the signal
		471	mask. Specifically, this means you have to make sure signals are unblocked
		472	when you want to receive them.
		473
		474	This behaviour is useful when you want to do your own signal handling, or
		475	want to handle signals only in specific threads and want to avoid libev
		476	unblocking the signals.
		477
		478	It's also required by POSIX in a threaded program, as libev calls
		479	C<sigprocmask>, whose behaviour is officially unspecified.
		480
		481	This flag's behaviour will become the default in future versions of libev.
294		482
295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
296		484
297	This is your standard select(2) backend. Not I<completely> standard, as	485	This is your standard select(2) backend. Not I<completely> standard, as
298	libev tries to roll its own fd_set with no limits on the number of fds,	486	libev tries to roll its own fd_set with no limits on the number of fds,
299	but if that fails, expect a fairly low limit on the number of fds when	487	but if that fails, expect a fairly low limit on the number of fds when
300	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	488	using this backend. It doesn't scale too well (O(highest_fd)), but its
301	the fastest backend for a low number of fds.	489	usually the fastest backend for a low number of (low-numbered :) fds.
		490
		491	To get good performance out of this backend you need a high amount of
		492	parallelism (most of the file descriptors should be busy). If you are
		493	writing a server, you should C<accept ()> in a loop to accept as many
		494	connections as possible during one iteration. You might also want to have
		495	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		496	readiness notifications you get per iteration.
		497
		498	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		499	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		500	C<exceptfds> set on that platform).
302		501
303	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	502	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
304		503
305	And this is your standard poll(2) backend. It's more complicated than	504	And this is your standard poll(2) backend. It's more complicated
306	select, but handles sparse fds better and has no artificial limit on the	505	than select, but handles sparse fds better and has no artificial
307	number of fds you can use (except it will slow down considerably with a	506	limit on the number of fds you can use (except it will slow down
308	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	507	considerably with a lot of inactive fds). It scales similarly to select,
		508	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		509	performance tips.
		510
		511	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		512	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
309		513
310	=item C<EVBACKEND_EPOLL> (value 4, Linux)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
311		515
		516	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		517	kernels).
		518
312	For few fds, this backend is a bit little slower than poll and select,	519	For few fds, this backend is a bit little slower than poll and select, but
313	but it scales phenomenally better. While poll and select usually scale like	520	it scales phenomenally better. While poll and select usually scale like
314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	521	O(total_fds) where total_fds is the total number of fds (or the highest
315	either O(1) or O(active_fds).	522	fd), epoll scales either O(1) or O(active_fds).
316		523
		524	The epoll mechanism deserves honorable mention as the most misdesigned
		525	of the more advanced event mechanisms: mere annoyances include silently
		526	dropping file descriptors, requiring a system call per change per file
		527	descriptor (and unnecessary guessing of parameters), problems with dup,
		528	returning before the timeout value, resulting in additional iterations
		529	(and only giving 5ms accuracy while select on the same platform gives
		530	0.1ms) and so on. The biggest issue is fork races, however - if a program
		531	forks then I<both> parent and child process have to recreate the epoll
		532	set, which can take considerable time (one syscall per file descriptor)
		533	and is of course hard to detect.
		534
		535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		536	but of course I<doesn't>, and epoll just loves to report events for
		537	totally I<different> file descriptors (even already closed ones, so
		538	one cannot even remove them from the set) than registered in the set
		539	(especially on SMP systems). Libev tries to counter these spurious
		540	notifications by employing an additional generation counter and comparing
		541	that against the events to filter out spurious ones, recreating the set
		542	when required. Epoll also erroneously rounds down timeouts, but gives you
		543	no way to know when and by how much, so sometimes you have to busy-wait
		544	because epoll returns immediately despite a nonzero timeout. And last
		545	not least, it also refuses to work with some file descriptors which work
		546	perfectly fine with C<select> (files, many character devices...).
		547
		548	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		549	cobbled together in a hurry, no thought to design or interaction with
		550	others. Oh, the pain, will it ever stop...
		551
317	While stopping and starting an I/O watcher in the same iteration will	552	While stopping, setting and starting an I/O watcher in the same iteration
318	result in some caching, there is still a syscall per such incident	553	will result in some caching, there is still a system call per such
319	(because the fd could point to a different file description now), so its	554	incident (because the same I<file descriptor> could point to a different
320	best to avoid that. Also, dup()ed file descriptors might not work very	555	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
321	well if you register events for both fds.	556	file descriptors might not work very well if you register events for both
		557	file descriptors.
322		558
323	Please note that epoll sometimes generates spurious notifications, so you	559	Best performance from this backend is achieved by not unregistering all
324	need to use non-blocking I/O or other means to avoid blocking when no data	560	watchers for a file descriptor until it has been closed, if possible,
325	(or space) is available.	561	i.e. keep at least one watcher active per fd at all times. Stopping and
		562	starting a watcher (without re-setting it) also usually doesn't cause
		563	extra overhead. A fork can both result in spurious notifications as well
		564	as in libev having to destroy and recreate the epoll object, which can
		565	take considerable time and thus should be avoided.
		566
		567	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		568	faster than epoll for maybe up to a hundred file descriptors, depending on
		569	the usage. So sad.
		570
		571	While nominally embeddable in other event loops, this feature is broken in
		572	a lot of kernel revisions, but probably(!) works in current versions.
		573
		574	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		575	C<EVBACKEND_POLL>.
		576
		577	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		578
		579	Use the linux-specific linux aio (I<not> C<< aio(7) >>) event interface
		580	available in post-4.18 kernels.
		581
		582	If this backend works for you (as of this writing, it was very
		583	experimental and only supports a subset of file types), it is the best
		584	event interface available on linux and might be well worth it enabling it
		585	- if it isn't available in your kernel this will be detected and another
		586	backend will be chosen.
		587
		588	This backend can batch oneshot requests and uses a user-space ring buffer
		589	to receive events. It also doesn't suffer from most of the design problems
		590	of epoll (such as not being able to remove event sources from the epoll
		591	set), and generally sounds too good to be true. Because, this being the
		592	linux kernel, of course it suffers from a whole new set of limitations.
		593
		594	For one, it is not easily embeddable (but probably could be done using
		595	an event fd at some extra overhead). It also is subject to various
		596	arbitrary limits that can be configured in F</proc/sys/fs/aio-max-nr>
		597	and F</proc/sys/fs/aio-nr>), which could lead to it being skipped during
		598	initialisation.
		599
		600	Most problematic in practise, however, is that, like kqueue, it requires
		601	special support from drivers, and, not surprisingly, not all drivers
		602	implement it. For example, in linux 4.19, tcp sockets, pipes, event fds,
		603	files, F</dev/null> and a few others are supported, but ttys are not, so
		604	this is not (yet?) a generic event polling interface but is probably still
		605	be very useful in a web server or similar program.
		606
		607	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		608	C<EVBACKEND_POLL>.
326		609
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	610	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		611
329	Kqueue deserves special mention, as at the time of this writing, it	612	Kqueue deserves special mention, as at the time of this writing, it
330	was broken on all BSDs except NetBSD (usually it doesn't work with	613	was broken on all BSDs except NetBSD (usually it doesn't work reliably
331	anything but sockets and pipes, except on Darwin, where of course its	614	with anything but sockets and pipes, except on Darwin, where of course
332	completely useless). For this reason its not being "autodetected"	615	it's completely useless). Unlike epoll, however, whose brokenness
		616	is by design, these kqueue bugs can (and eventually will) be fixed
		617	without API changes to existing programs. For this reason it's not being
333	unless you explicitly specify it explicitly in the flags (i.e. using	618	"auto-detected" unless you explicitly specify it in the flags (i.e. using
334	C<EVBACKEND_KQUEUE>).	619	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		620	system like NetBSD.
		621
		622	You still can embed kqueue into a normal poll or select backend and use it
		623	only for sockets (after having made sure that sockets work with kqueue on
		624	the target platform). See C<ev_embed> watchers for more info.
335		625
336	It scales in the same way as the epoll backend, but the interface to the	626	It scales in the same way as the epoll backend, but the interface to the
337	kernel is more efficient (which says nothing about its actual speed, of	627	kernel is more efficient (which says nothing about its actual speed, of
338	course). While starting and stopping an I/O watcher does not cause an	628	course). While stopping, setting and starting an I/O watcher does never
339	extra syscall as with epoll, it still adds up to four event changes per	629	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
340	incident, so its best to avoid that.	630	two event changes per incident. Support for C<fork ()> is very bad (you
		631	might have to leak fd's on fork, but it's more sane than epoll) and it
		632	drops fds silently in similarly hard-to-detect cases.
		633
		634	This backend usually performs well under most conditions.
		635
		636	While nominally embeddable in other event loops, this doesn't work
		637	everywhere, so you might need to test for this. And since it is broken
		638	almost everywhere, you should only use it when you have a lot of sockets
		639	(for which it usually works), by embedding it into another event loop
		640	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		641	also broken on OS X)) and, did I mention it, using it only for sockets.
		642
		643	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		644	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		645	C<NOTE_EOF>.
341		646
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	647	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		648
344	This is not implemented yet (and might never be).	649	This is not implemented yet (and might never be, unless you send me an
		650	implementation). According to reports, C</dev/poll> only supports sockets
		651	and is not embeddable, which would limit the usefulness of this backend
		652	immensely.
345		653
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	654	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		655
348	This uses the Solaris 10 port mechanism. As with everything on Solaris,	656	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
349	it's really slow, but it still scales very well (O(active_fds)).	657	it's really slow, but it still scales very well (O(active_fds)).
350		658
351	Please note that solaris ports can result in a lot of spurious	659	While this backend scales well, it requires one system call per active
352	notifications, so you need to use non-blocking I/O or other means to avoid	660	file descriptor per loop iteration. For small and medium numbers of file
353	blocking when no data (or space) is available.	661	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		662	might perform better.
		663
		664	On the positive side, this backend actually performed fully to
		665	specification in all tests and is fully embeddable, which is a rare feat
		666	among the OS-specific backends (I vastly prefer correctness over speed
		667	hacks).
		668
		669	On the negative side, the interface is I<bizarre> - so bizarre that
		670	even sun itself gets it wrong in their code examples: The event polling
		671	function sometimes returns events to the caller even though an error
		672	occurred, but with no indication whether it has done so or not (yes, it's
		673	even documented that way) - deadly for edge-triggered interfaces where you
		674	absolutely have to know whether an event occurred or not because you have
		675	to re-arm the watcher.
		676
		677	Fortunately libev seems to be able to work around these idiocies.
		678
		679	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		680	C<EVBACKEND_POLL>.
354		681
355	=item C<EVBACKEND_ALL>	682	=item C<EVBACKEND_ALL>
356		683
357	Try all backends (even potentially broken ones that wouldn't be tried	684	Try all backends (even potentially broken ones that wouldn't be tried
358	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	685	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	686	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		687
		688	It is definitely not recommended to use this flag, use whatever
		689	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		690	at all.
		691
		692	=item C<EVBACKEND_MASK>
		693
		694	Not a backend at all, but a mask to select all backend bits from a
		695	C<flags> value, in case you want to mask out any backends from a flags
		696	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
		697
361	=back	698	=back
362		699
363	If one or more of these are ored into the flags value, then only these	700	If one or more of the backend flags are or'ed into the flags value,
364	backends will be tried (in the reverse order as given here). If none are	701	then only these backends will be tried (in the reverse order as listed
365	specified, most compiled-in backend will be tried, usually in reverse	702	here). If none are specified, all backends in C<ev_recommended_backends
366	order of their flag values :)	703	()> will be tried.
367
368	The most typical usage is like this:
369
370	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372
373	Restrict libev to the select and poll backends, and do not allow
374	environment settings to be taken into account:
375
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377
378	Use whatever libev has to offer, but make sure that kqueue is used if
379	available (warning, breaks stuff, best use only with your own private
380	event loop and only if you know the OS supports your types of fds):
381
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383
384	=item struct ev_loop *ev_loop_new (unsigned int flags)
385
386	Similar to C<ev_default_loop>, but always creates a new event loop that is
387	always distinct from the default loop. Unlike the default loop, it cannot
388	handle signal and child watchers, and attempts to do so will be greeted by
389	undefined behaviour (or a failed assertion if assertions are enabled).
390		704
391	Example: Try to create a event loop that uses epoll and nothing else.	705	Example: Try to create a event loop that uses epoll and nothing else.
392		706
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	707	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	708	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	709	fatal ("no epoll found here, maybe it hides under your chair");
396		710
		711	Example: Use whatever libev has to offer, but make sure that kqueue is
		712	used if available.
		713
		714	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		715
		716	Example: Similarly, on linux, you mgiht want to take advantage of the
		717	linux aio backend if possible, but fall back to something else if that
		718	isn't available.
		719
		720	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
		721
397	=item ev_default_destroy ()	722	=item ev_loop_destroy (loop)
398		723
399	Destroys the default loop again (frees all memory and kernel state	724	Destroys an event loop object (frees all memory and kernel state
400	etc.). None of the active event watchers will be stopped in the normal	725	etc.). None of the active event watchers will be stopped in the normal
401	sense, so e.g. C<ev_is_active> might still return true. It is your	726	sense, so e.g. C<ev_is_active> might still return true. It is your
402	responsibility to either stop all watchers cleanly yoursef I<before>	727	responsibility to either stop all watchers cleanly yourself I<before>
403	calling this function, or cope with the fact afterwards (which is usually	728	calling this function, or cope with the fact afterwards (which is usually
404	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	729	the easiest thing, you can just ignore the watchers and/or C<free ()> them
405	for example).	730	for example).
406		731
		732	Note that certain global state, such as signal state (and installed signal
		733	handlers), will not be freed by this function, and related watchers (such
		734	as signal and child watchers) would need to be stopped manually.
		735
		736	This function is normally used on loop objects allocated by
		737	C<ev_loop_new>, but it can also be used on the default loop returned by
		738	C<ev_default_loop>, in which case it is not thread-safe.
		739
		740	Note that it is not advisable to call this function on the default loop
		741	except in the rare occasion where you really need to free its resources.
		742	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		743	and C<ev_loop_destroy>.
		744
407	=item ev_loop_destroy (loop)	745	=item ev_loop_fork (loop)
408		746
409	Like C<ev_default_destroy>, but destroys an event loop created by an	747	This function sets a flag that causes subsequent C<ev_run> iterations
410	earlier call to C<ev_loop_new>.
411
412	=item ev_default_fork ()
413
414	This function reinitialises the kernel state for backends that have	748	to reinitialise the kernel state for backends that have one. Despite
415	one. Despite the name, you can call it anytime, but it makes most sense	749	the name, you can call it anytime you are allowed to start or stop
416	after forking, in either the parent or child process (or both, but that	750	watchers (except inside an C<ev_prepare> callback), but it makes most
417	again makes little sense).	751	sense after forking, in the child process. You I<must> call it (or use
		752	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
418		753
419	You I<must> call this function in the child process after forking if and	754	In addition, if you want to reuse a loop (via this function or
420	only if you want to use the event library in both processes. If you just	755	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
421	fork+exec, you don't have to call it.	756
		757	Again, you I<have> to call it on I<any> loop that you want to re-use after
		758	a fork, I<even if you do not plan to use the loop in the parent>. This is
		759	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		760	during fork.
		761
		762	On the other hand, you only need to call this function in the child
		763	process if and only if you want to use the event loop in the child. If
		764	you just fork+exec or create a new loop in the child, you don't have to
		765	call it at all (in fact, C<epoll> is so badly broken that it makes a
		766	difference, but libev will usually detect this case on its own and do a
		767	costly reset of the backend).
422		768
423	The function itself is quite fast and it's usually not a problem to call	769	The function itself is quite fast and it's usually not a problem to call
424	it just in case after a fork. To make this easy, the function will fit in	770	it just in case after a fork.
425	quite nicely into a call to C<pthread_atfork>:
426		771
		772	Example: Automate calling C<ev_loop_fork> on the default loop when
		773	using pthreads.
		774
		775	static void
		776	post_fork_child (void)
		777	{
		778	ev_loop_fork (EV_DEFAULT);
		779	}
		780
		781	...
427	pthread_atfork (0, 0, ev_default_fork);	782	pthread_atfork (0, 0, post_fork_child);
428		783
429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	784	=item int ev_is_default_loop (loop)
430	without calling this function, so if you force one of those backends you
431	do not need to care.
432		785
433	=item ev_loop_fork (loop)	786	Returns true when the given loop is, in fact, the default loop, and false
		787	otherwise.
434		788
435	Like C<ev_default_fork>, but acts on an event loop created by
436	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
437	after fork, and how you do this is entirely your own problem.
438
439	=item unsigned int ev_loop_count (loop)	789	=item unsigned int ev_iteration (loop)
440		790
441	Returns the count of loop iterations for the loop, which is identical to	791	Returns the current iteration count for the event loop, which is identical
442	the number of times libev did poll for new events. It starts at C<0> and	792	to the number of times libev did poll for new events. It starts at C<0>
443	happily wraps around with enough iterations.	793	and happily wraps around with enough iterations.
444		794
445	This value can sometimes be useful as a generation counter of sorts (it	795	This value can sometimes be useful as a generation counter of sorts (it
446	"ticks" the number of loop iterations), as it roughly corresponds with	796	"ticks" the number of loop iterations), as it roughly corresponds with
447	C<ev_prepare> and C<ev_check> calls.	797	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		798	prepare and check phases.
		799
		800	=item unsigned int ev_depth (loop)
		801
		802	Returns the number of times C<ev_run> was entered minus the number of
		803	times C<ev_run> was exited normally, in other words, the recursion depth.
		804
		805	Outside C<ev_run>, this number is zero. In a callback, this number is
		806	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		807	in which case it is higher.
		808
		809	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		810	throwing an exception etc.), doesn't count as "exit" - consider this
		811	as a hint to avoid such ungentleman-like behaviour unless it's really
		812	convenient, in which case it is fully supported.
448		813
449	=item unsigned int ev_backend (loop)	814	=item unsigned int ev_backend (loop)
450		815
451	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	816	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
452	use.	817	use.
…		…
455		820
456	Returns the current "event loop time", which is the time the event loop	821	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	822	received events and started processing them. This timestamp does not
458	change as long as callbacks are being processed, and this is also the base	823	change as long as callbacks are being processed, and this is also the base
459	time used for relative timers. You can treat it as the timestamp of the	824	time used for relative timers. You can treat it as the timestamp of the
460	event occuring (or more correctly, libev finding out about it).	825	event occurring (or more correctly, libev finding out about it).
461		826
		827	=item ev_now_update (loop)
		828
		829	Establishes the current time by querying the kernel, updating the time
		830	returned by C<ev_now ()> in the progress. This is a costly operation and
		831	is usually done automatically within C<ev_run ()>.
		832
		833	This function is rarely useful, but when some event callback runs for a
		834	very long time without entering the event loop, updating libev's idea of
		835	the current time is a good idea.
		836
		837	See also L</The special problem of time updates> in the C<ev_timer> section.
		838
		839	=item ev_suspend (loop)
		840
		841	=item ev_resume (loop)
		842
		843	These two functions suspend and resume an event loop, for use when the
		844	loop is not used for a while and timeouts should not be processed.
		845
		846	A typical use case would be an interactive program such as a game: When
		847	the user presses C<^Z> to suspend the game and resumes it an hour later it
		848	would be best to handle timeouts as if no time had actually passed while
		849	the program was suspended. This can be achieved by calling C<ev_suspend>
		850	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		851	C<ev_resume> directly afterwards to resume timer processing.
		852
		853	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		854	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		855	will be rescheduled (that is, they will lose any events that would have
		856	occurred while suspended).
		857
		858	After calling C<ev_suspend> you B<must not> call I<any> function on the
		859	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		860	without a previous call to C<ev_suspend>.
		861
		862	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		863	event loop time (see C<ev_now_update>).
		864
462	=item ev_loop (loop, int flags)	865	=item bool ev_run (loop, int flags)
463		866
464	Finally, this is it, the event handler. This function usually is called	867	Finally, this is it, the event handler. This function usually is called
465	after you initialised all your watchers and you want to start handling	868	after you have initialised all your watchers and you want to start
466	events.	869	handling events. It will ask the operating system for any new events, call
		870	the watcher callbacks, and then repeat the whole process indefinitely: This
		871	is why event loops are called I<loops>.
467		872
468	If the flags argument is specified as C<0>, it will not return until	873	If the flags argument is specified as C<0>, it will keep handling events
469	either no event watchers are active anymore or C<ev_unloop> was called.	874	until either no event watchers are active anymore or C<ev_break> was
		875	called.
470		876
		877	The return value is false if there are no more active watchers (which
		878	usually means "all jobs done" or "deadlock"), and true in all other cases
		879	(which usually means " you should call C<ev_run> again").
		880
471	Please note that an explicit C<ev_unloop> is usually better than	881	Please note that an explicit C<ev_break> is usually better than
472	relying on all watchers to be stopped when deciding when a program has	882	relying on all watchers to be stopped when deciding when a program has
473	finished (especially in interactive programs), but having a program that	883	finished (especially in interactive programs), but having a program
474	automatically loops as long as it has to and no longer by virtue of	884	that automatically loops as long as it has to and no longer by virtue
475	relying on its watchers stopping correctly is a thing of beauty.	885	of relying on its watchers stopping correctly, that is truly a thing of
		886	beauty.
476		887
		888	This function is I<mostly> exception-safe - you can break out of a
		889	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		890	exception and so on. This does not decrement the C<ev_depth> value, nor
		891	will it clear any outstanding C<EVBREAK_ONE> breaks.
		892
477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	893	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
478	those events and any outstanding ones, but will not block your process in	894	those events and any already outstanding ones, but will not wait and
479	case there are no events and will return after one iteration of the loop.	895	block your process in case there are no events and will return after one
		896	iteration of the loop. This is sometimes useful to poll and handle new
		897	events while doing lengthy calculations, to keep the program responsive.
480		898
481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	899	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
482	neccessary) and will handle those and any outstanding ones. It will block	900	necessary) and will handle those and any already outstanding ones. It
483	your process until at least one new event arrives, and will return after	901	will block your process until at least one new event arrives (which could
484	one iteration of the loop. This is useful if you are waiting for some	902	be an event internal to libev itself, so there is no guarantee that a
485	external event in conjunction with something not expressible using other	903	user-registered callback will be called), and will return after one
		904	iteration of the loop.
		905
		906	This is useful if you are waiting for some external event in conjunction
		907	with something not expressible using other libev watchers (i.e. "roll your
486	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	908	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
487	usually a better approach for this kind of thing.	909	usually a better approach for this kind of thing.
488		910
489	Here are the gory details of what C<ev_loop> does:	911	Here are the gory details of what C<ev_run> does (this is for your
		912	understanding, not a guarantee that things will work exactly like this in
		913	future versions):
490		914
491	* If there are no active watchers (reference count is zero), return.	915	- Increment loop depth.
492	- Queue prepare watchers and then call all outstanding watchers.	916	- Reset the ev_break status.
		917	- Before the first iteration, call any pending watchers.
		918	LOOP:
		919	- If EVFLAG_FORKCHECK was used, check for a fork.
		920	- If a fork was detected (by any means), queue and call all fork watchers.
		921	- Queue and call all prepare watchers.
		922	- If ev_break was called, goto FINISH.
493	- If we have been forked, recreate the kernel state.	923	- If we have been forked, detach and recreate the kernel state
		924	as to not disturb the other process.
494	- Update the kernel state with all outstanding changes.	925	- Update the kernel state with all outstanding changes.
495	- Update the "event loop time".	926	- Update the "event loop time" (ev_now ()).
496	- Calculate for how long to block.	927	- Calculate for how long to sleep or block, if at all
		928	(active idle watchers, EVRUN_NOWAIT or not having
		929	any active watchers at all will result in not sleeping).
		930	- Sleep if the I/O and timer collect interval say so.
		931	- Increment loop iteration counter.
497	- Block the process, waiting for any events.	932	- Block the process, waiting for any events.
498	- Queue all outstanding I/O (fd) events.	933	- Queue all outstanding I/O (fd) events.
499	- Update the "event loop time" and do time jump handling.	934	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
500	- Queue all outstanding timers.	935	- Queue all expired timers.
501	- Queue all outstanding periodics.	936	- Queue all expired periodics.
502	- If no events are pending now, queue all idle watchers.	937	- Queue all idle watchers with priority higher than that of pending events.
503	- Queue all check watchers.	938	- Queue all check watchers.
504	- Call all queued watchers in reverse order (i.e. check watchers first).	939	- Call all queued watchers in reverse order (i.e. check watchers first).
505	Signals and child watchers are implemented as I/O watchers, and will	940	Signals and child watchers are implemented as I/O watchers, and will
506	be handled here by queueing them when their watcher gets executed.	941	be handled here by queueing them when their watcher gets executed.
507	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	942	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
508	were used, return, otherwise continue with step *.	943	were used, or there are no active watchers, goto FINISH, otherwise
		944	continue with step LOOP.
		945	FINISH:
		946	- Reset the ev_break status iff it was EVBREAK_ONE.
		947	- Decrement the loop depth.
		948	- Return.
509		949
510	Example: Queue some jobs and then loop until no events are outsanding	950	Example: Queue some jobs and then loop until no events are outstanding
511	anymore.	951	anymore.
512		952
513	... queue jobs here, make sure they register event watchers as long	953	... queue jobs here, make sure they register event watchers as long
514	... as they still have work to do (even an idle watcher will do..)	954	... as they still have work to do (even an idle watcher will do..)
515	ev_loop (my_loop, 0);	955	ev_run (my_loop, 0);
516	... jobs done. yeah!	956	... jobs done or somebody called break. yeah!
517		957
518	=item ev_unloop (loop, how)	958	=item ev_break (loop, how)
519		959
520	Can be used to make a call to C<ev_loop> return early (but only after it	960	Can be used to make a call to C<ev_run> return early (but only after it
521	has processed all outstanding events). The C<how> argument must be either	961	has processed all outstanding events). The C<how> argument must be either
522	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	962	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
523	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	963	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		964
		965	This "break state" will be cleared on the next call to C<ev_run>.
		966
		967	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		968	which case it will have no effect.
524		969
525	=item ev_ref (loop)	970	=item ev_ref (loop)
526		971
527	=item ev_unref (loop)	972	=item ev_unref (loop)
528		973
529	Ref/unref can be used to add or remove a reference count on the event	974	Ref/unref can be used to add or remove a reference count on the event
530	loop: Every watcher keeps one reference, and as long as the reference	975	loop: Every watcher keeps one reference, and as long as the reference
531	count is nonzero, C<ev_loop> will not return on its own. If you have	976	count is nonzero, C<ev_run> will not return on its own.
532	a watcher you never unregister that should not keep C<ev_loop> from	977
533	returning, ev_unref() after starting, and ev_ref() before stopping it. For	978	This is useful when you have a watcher that you never intend to
		979	unregister, but that nevertheless should not keep C<ev_run> from
		980	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		981	before stopping it.
		982
534	example, libev itself uses this for its internal signal pipe: It is not	983	As an example, libev itself uses this for its internal signal pipe: It
535	visible to the libev user and should not keep C<ev_loop> from exiting if	984	is not visible to the libev user and should not keep C<ev_run> from
536	no event watchers registered by it are active. It is also an excellent	985	exiting if no event watchers registered by it are active. It is also an
537	way to do this for generic recurring timers or from within third-party	986	excellent way to do this for generic recurring timers or from within
538	libraries. Just remember to I<unref after start> and I<ref before stop>.	987	third-party libraries. Just remember to I<unref after start> and I<ref
		988	before stop> (but only if the watcher wasn't active before, or was active
		989	before, respectively. Note also that libev might stop watchers itself
		990	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		991	in the callback).
539		992
540	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	993	Example: Create a signal watcher, but keep it from keeping C<ev_run>
541	running when nothing else is active.	994	running when nothing else is active.
542		995
543	struct ev_signal exitsig;	996	ev_signal exitsig;
544	ev_signal_init (&exitsig, sig_cb, SIGINT);	997	ev_signal_init (&exitsig, sig_cb, SIGINT);
545	ev_signal_start (loop, &exitsig);	998	ev_signal_start (loop, &exitsig);
546	evf_unref (loop);	999	ev_unref (loop);
547		1000
548	Example: For some weird reason, unregister the above signal handler again.	1001	Example: For some weird reason, unregister the above signal handler again.
549		1002
550	ev_ref (loop);	1003	ev_ref (loop);
551	ev_signal_stop (loop, &exitsig);	1004	ev_signal_stop (loop, &exitsig);
		1005
		1006	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		1007
		1008	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		1009
		1010	These advanced functions influence the time that libev will spend waiting
		1011	for events. Both time intervals are by default C<0>, meaning that libev
		1012	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		1013	latency.
		1014
		1015	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		1016	allows libev to delay invocation of I/O and timer/periodic callbacks
		1017	to increase efficiency of loop iterations (or to increase power-saving
		1018	opportunities).
		1019
		1020	The idea is that sometimes your program runs just fast enough to handle
		1021	one (or very few) event(s) per loop iteration. While this makes the
		1022	program responsive, it also wastes a lot of CPU time to poll for new
		1023	events, especially with backends like C<select ()> which have a high
		1024	overhead for the actual polling but can deliver many events at once.
		1025
		1026	By setting a higher I<io collect interval> you allow libev to spend more
		1027	time collecting I/O events, so you can handle more events per iteration,
		1028	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		1029	C<ev_timer>) will not be affected. Setting this to a non-null value will
		1030	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		1031	sleep time ensures that libev will not poll for I/O events more often then
		1032	once per this interval, on average (as long as the host time resolution is
		1033	good enough).
		1034
		1035	Likewise, by setting a higher I<timeout collect interval> you allow libev
		1036	to spend more time collecting timeouts, at the expense of increased
		1037	latency/jitter/inexactness (the watcher callback will be called
		1038	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		1039	value will not introduce any overhead in libev.
		1040
		1041	Many (busy) programs can usually benefit by setting the I/O collect
		1042	interval to a value near C<0.1> or so, which is often enough for
		1043	interactive servers (of course not for games), likewise for timeouts. It
		1044	usually doesn't make much sense to set it to a lower value than C<0.01>,
		1045	as this approaches the timing granularity of most systems. Note that if
		1046	you do transactions with the outside world and you can't increase the
		1047	parallelity, then this setting will limit your transaction rate (if you
		1048	need to poll once per transaction and the I/O collect interval is 0.01,
		1049	then you can't do more than 100 transactions per second).
		1050
		1051	Setting the I<timeout collect interval> can improve the opportunity for
		1052	saving power, as the program will "bundle" timer callback invocations that
		1053	are "near" in time together, by delaying some, thus reducing the number of
		1054	times the process sleeps and wakes up again. Another useful technique to
		1055	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		1056	they fire on, say, one-second boundaries only.
		1057
		1058	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1059	more often than 100 times per second:
		1060
		1061	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1062	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1063
		1064	=item ev_invoke_pending (loop)
		1065
		1066	This call will simply invoke all pending watchers while resetting their
		1067	pending state. Normally, C<ev_run> does this automatically when required,
		1068	but when overriding the invoke callback this call comes handy. This
		1069	function can be invoked from a watcher - this can be useful for example
		1070	when you want to do some lengthy calculation and want to pass further
		1071	event handling to another thread (you still have to make sure only one
		1072	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1073
		1074	=item int ev_pending_count (loop)
		1075
		1076	Returns the number of pending watchers - zero indicates that no watchers
		1077	are pending.
		1078
		1079	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1080
		1081	This overrides the invoke pending functionality of the loop: Instead of
		1082	invoking all pending watchers when there are any, C<ev_run> will call
		1083	this callback instead. This is useful, for example, when you want to
		1084	invoke the actual watchers inside another context (another thread etc.).
		1085
		1086	If you want to reset the callback, use C<ev_invoke_pending> as new
		1087	callback.
		1088
		1089	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1090
		1091	Sometimes you want to share the same loop between multiple threads. This
		1092	can be done relatively simply by putting mutex_lock/unlock calls around
		1093	each call to a libev function.
		1094
		1095	However, C<ev_run> can run an indefinite time, so it is not feasible
		1096	to wait for it to return. One way around this is to wake up the event
		1097	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1098	I<release> and I<acquire> callbacks on the loop.
		1099
		1100	When set, then C<release> will be called just before the thread is
		1101	suspended waiting for new events, and C<acquire> is called just
		1102	afterwards.
		1103
		1104	Ideally, C<release> will just call your mutex_unlock function, and
		1105	C<acquire> will just call the mutex_lock function again.
		1106
		1107	While event loop modifications are allowed between invocations of
		1108	C<release> and C<acquire> (that's their only purpose after all), no
		1109	modifications done will affect the event loop, i.e. adding watchers will
		1110	have no effect on the set of file descriptors being watched, or the time
		1111	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1112	to take note of any changes you made.
		1113
		1114	In theory, threads executing C<ev_run> will be async-cancel safe between
		1115	invocations of C<release> and C<acquire>.
		1116
		1117	See also the locking example in the C<THREADS> section later in this
		1118	document.
		1119
		1120	=item ev_set_userdata (loop, void *data)
		1121
		1122	=item void *ev_userdata (loop)
		1123
		1124	Set and retrieve a single C<void *> associated with a loop. When
		1125	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1126	C<0>.
		1127
		1128	These two functions can be used to associate arbitrary data with a loop,
		1129	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1130	C<acquire> callbacks described above, but of course can be (ab-)used for
		1131	any other purpose as well.
		1132
		1133	=item ev_verify (loop)
		1134
		1135	This function only does something when C<EV_VERIFY> support has been
		1136	compiled in, which is the default for non-minimal builds. It tries to go
		1137	through all internal structures and checks them for validity. If anything
		1138	is found to be inconsistent, it will print an error message to standard
		1139	error and call C<abort ()>.
		1140
		1141	This can be used to catch bugs inside libev itself: under normal
		1142	circumstances, this function will never abort as of course libev keeps its
		1143	data structures consistent.
552		1144
553	=back	1145	=back
554		1146
555		1147
556	=head1 ANATOMY OF A WATCHER	1148	=head1 ANATOMY OF A WATCHER
557		1149
		1150	In the following description, uppercase C<TYPE> in names stands for the
		1151	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1152	watchers and C<ev_io_start> for I/O watchers.
		1153
558	A watcher is a structure that you create and register to record your	1154	A watcher is an opaque structure that you allocate and register to record
559	interest in some event. For instance, if you want to wait for STDIN to	1155	your interest in some event. To make a concrete example, imagine you want
560	become readable, you would create an C<ev_io> watcher for that:	1156	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1157	for that:
561		1158
562	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1159	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
563	{	1160	{
564	ev_io_stop (w);	1161	ev_io_stop (w);
565	ev_unloop (loop, EVUNLOOP_ALL);	1162	ev_break (loop, EVBREAK_ALL);
566	}	1163	}
567		1164
568	struct ev_loop *loop = ev_default_loop (0);	1165	struct ev_loop *loop = ev_default_loop (0);
		1166
569	struct ev_io stdin_watcher;	1167	ev_io stdin_watcher;
		1168
570	ev_init (&stdin_watcher, my_cb);	1169	ev_init (&stdin_watcher, my_cb);
571	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1170	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
572	ev_io_start (loop, &stdin_watcher);	1171	ev_io_start (loop, &stdin_watcher);
		1172
573	ev_loop (loop, 0);	1173	ev_run (loop, 0);
574		1174
575	As you can see, you are responsible for allocating the memory for your	1175	As you can see, you are responsible for allocating the memory for your
576	watcher structures (and it is usually a bad idea to do this on the stack,	1176	watcher structures (and it is I<usually> a bad idea to do this on the
577	although this can sometimes be quite valid).	1177	stack).
578		1178
		1179	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1180	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1181
579	Each watcher structure must be initialised by a call to C<ev_init	1182	Each watcher structure must be initialised by a call to C<ev_init (watcher
580	(watcher *, callback)>, which expects a callback to be provided. This	1183	*, callback)>, which expects a callback to be provided. This callback is
581	callback gets invoked each time the event occurs (or, in the case of io	1184	invoked each time the event occurs (or, in the case of I/O watchers, each
582	watchers, each time the event loop detects that the file descriptor given	1185	time the event loop detects that the file descriptor given is readable
583	is readable and/or writable).	1186	and/or writable).
584		1187
585	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1188	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
586	with arguments specific to this watcher type. There is also a macro	1189	macro to configure it, with arguments specific to the watcher type. There
587	to combine initialisation and setting in one call: C<< ev_<type>_init	1190	is also a macro to combine initialisation and setting in one call: C<<
588	(watcher *, callback, ...) >>.	1191	ev_TYPE_init (watcher *, callback, ...) >>.
589		1192
590	To make the watcher actually watch out for events, you have to start it	1193	To make the watcher actually watch out for events, you have to start it
591	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1194	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
592	*) >>), and you can stop watching for events at any time by calling the	1195	*) >>), and you can stop watching for events at any time by calling the
593	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1196	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
594		1197
595	As long as your watcher is active (has been started but not stopped) you	1198	As long as your watcher is active (has been started but not stopped) you
596	must not touch the values stored in it. Most specifically you must never	1199	must not touch the values stored in it. Most specifically you must never
597	reinitialise it or call its C<set> macro.	1200	reinitialise it or call its C<ev_TYPE_set> macro.
598		1201
599	Each and every callback receives the event loop pointer as first, the	1202	Each and every callback receives the event loop pointer as first, the
600	registered watcher structure as second, and a bitset of received events as	1203	registered watcher structure as second, and a bitset of received events as
601	third argument.	1204	third argument.
602		1205
…		…
611	=item C<EV_WRITE>	1214	=item C<EV_WRITE>
612		1215
613	The file descriptor in the C<ev_io> watcher has become readable and/or	1216	The file descriptor in the C<ev_io> watcher has become readable and/or
614	writable.	1217	writable.
615		1218
616	=item C<EV_TIMEOUT>	1219	=item C<EV_TIMER>
617		1220
618	The C<ev_timer> watcher has timed out.	1221	The C<ev_timer> watcher has timed out.
619		1222
620	=item C<EV_PERIODIC>	1223	=item C<EV_PERIODIC>
621		1224
…		…
639		1242
640	=item C<EV_PREPARE>	1243	=item C<EV_PREPARE>
641		1244
642	=item C<EV_CHECK>	1245	=item C<EV_CHECK>
643		1246
644	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1247	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
645	to gather new events, and all C<ev_check> watchers are invoked just after	1248	gather new events, and all C<ev_check> watchers are queued (not invoked)
646	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1249	just after C<ev_run> has gathered them, but before it queues any callbacks
		1250	for any received events. That means C<ev_prepare> watchers are the last
		1251	watchers invoked before the event loop sleeps or polls for new events, and
		1252	C<ev_check> watchers will be invoked before any other watchers of the same
		1253	or lower priority within an event loop iteration.
		1254
647	received events. Callbacks of both watcher types can start and stop as	1255	Callbacks of both watcher types can start and stop as many watchers as
648	many watchers as they want, and all of them will be taken into account	1256	they want, and all of them will be taken into account (for example, a
649	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1257	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
650	C<ev_loop> from blocking).	1258	blocking).
651		1259
652	=item C<EV_EMBED>	1260	=item C<EV_EMBED>
653		1261
654	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1262	The embedded event loop specified in the C<ev_embed> watcher needs attention.
655		1263
656	=item C<EV_FORK>	1264	=item C<EV_FORK>
657		1265
658	The event loop has been resumed in the child process after fork (see	1266	The event loop has been resumed in the child process after fork (see
659	C<ev_fork>).	1267	C<ev_fork>).
660		1268
		1269	=item C<EV_CLEANUP>
		1270
		1271	The event loop is about to be destroyed (see C<ev_cleanup>).
		1272
		1273	=item C<EV_ASYNC>
		1274
		1275	The given async watcher has been asynchronously notified (see C<ev_async>).
		1276
		1277	=item C<EV_CUSTOM>
		1278
		1279	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1280	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1281
661	=item C<EV_ERROR>	1282	=item C<EV_ERROR>
662		1283
663	An unspecified error has occured, the watcher has been stopped. This might	1284	An unspecified error has occurred, the watcher has been stopped. This might
664	happen because the watcher could not be properly started because libev	1285	happen because the watcher could not be properly started because libev
665	ran out of memory, a file descriptor was found to be closed or any other	1286	ran out of memory, a file descriptor was found to be closed or any other
		1287	problem. Libev considers these application bugs.
		1288
666	problem. You best act on it by reporting the problem and somehow coping	1289	You best act on it by reporting the problem and somehow coping with the
667	with the watcher being stopped.	1290	watcher being stopped. Note that well-written programs should not receive
		1291	an error ever, so when your watcher receives it, this usually indicates a
		1292	bug in your program.
668		1293
669	Libev will usually signal a few "dummy" events together with an error,	1294	Libev will usually signal a few "dummy" events together with an error, for
670	for example it might indicate that a fd is readable or writable, and if	1295	example it might indicate that a fd is readable or writable, and if your
671	your callbacks is well-written it can just attempt the operation and cope	1296	callbacks is well-written it can just attempt the operation and cope with
672	with the error from read() or write(). This will not work in multithreaded	1297	the error from read() or write(). This will not work in multi-threaded
673	programs, though, so beware.	1298	programs, though, as the fd could already be closed and reused for another
		1299	thing, so beware.
674		1300
675	=back	1301	=back
676		1302
677	=head2 GENERIC WATCHER FUNCTIONS	1303	=head2 GENERIC WATCHER FUNCTIONS
678
679	In the following description, C<TYPE> stands for the watcher type,
680	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
681		1304
682	=over 4	1305	=over 4
683		1306
684	=item C<ev_init> (ev_TYPE *watcher, callback)	1307	=item C<ev_init> (ev_TYPE *watcher, callback)
685		1308
…		…
691	which rolls both calls into one.	1314	which rolls both calls into one.
692		1315
693	You can reinitialise a watcher at any time as long as it has been stopped	1316	You can reinitialise a watcher at any time as long as it has been stopped
694	(or never started) and there are no pending events outstanding.	1317	(or never started) and there are no pending events outstanding.
695		1318
696	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1319	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
697	int revents)>.	1320	int revents)>.
698		1321
		1322	Example: Initialise an C<ev_io> watcher in two steps.
		1323
		1324	ev_io w;
		1325	ev_init (&w, my_cb);
		1326	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1327
699	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1328	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
700		1329
701	This macro initialises the type-specific parts of a watcher. You need to	1330	This macro initialises the type-specific parts of a watcher. You need to
702	call C<ev_init> at least once before you call this macro, but you can	1331	call C<ev_init> at least once before you call this macro, but you can
703	call C<ev_TYPE_set> any number of times. You must not, however, call this	1332	call C<ev_TYPE_set> any number of times. You must not, however, call this
704	macro on a watcher that is active (it can be pending, however, which is a	1333	macro on a watcher that is active (it can be pending, however, which is a
705	difference to the C<ev_init> macro).	1334	difference to the C<ev_init> macro).
706		1335
707	Although some watcher types do not have type-specific arguments	1336	Although some watcher types do not have type-specific arguments
708	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1337	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
709		1338
		1339	See C<ev_init>, above, for an example.
		1340
710	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1341	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
711		1342
712	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1343	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
713	calls into a single call. This is the most convinient method to initialise	1344	calls into a single call. This is the most convenient method to initialise
714	a watcher. The same limitations apply, of course.	1345	a watcher. The same limitations apply, of course.
715		1346
		1347	Example: Initialise and set an C<ev_io> watcher in one step.
		1348
		1349	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1350
716	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1351	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
717		1352
718	Starts (activates) the given watcher. Only active watchers will receive	1353	Starts (activates) the given watcher. Only active watchers will receive
719	events. If the watcher is already active nothing will happen.	1354	events. If the watcher is already active nothing will happen.
720		1355
		1356	Example: Start the C<ev_io> watcher that is being abused as example in this
		1357	whole section.
		1358
		1359	ev_io_start (EV_DEFAULT_UC, &w);
		1360
721	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1361	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
722		1362
723	Stops the given watcher again (if active) and clears the pending	1363	Stops the given watcher if active, and clears the pending status (whether
		1364	the watcher was active or not).
		1365
724	status. It is possible that stopped watchers are pending (for example,	1366	It is possible that stopped watchers are pending - for example,
725	non-repeating timers are being stopped when they become pending), but	1367	non-repeating timers are being stopped when they become pending - but
726	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1368	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
727	you want to free or reuse the memory used by the watcher it is therefore a	1369	pending. If you want to free or reuse the memory used by the watcher it is
728	good idea to always call its C<ev_TYPE_stop> function.	1370	therefore a good idea to always call its C<ev_TYPE_stop> function.
729		1371
730	=item bool ev_is_active (ev_TYPE *watcher)	1372	=item bool ev_is_active (ev_TYPE *watcher)
731		1373
732	Returns a true value iff the watcher is active (i.e. it has been started	1374	Returns a true value iff the watcher is active (i.e. it has been started
733	and not yet been stopped). As long as a watcher is active you must not modify	1375	and not yet been stopped). As long as a watcher is active you must not modify
…		…
744		1386
745	=item callback ev_cb (ev_TYPE *watcher)	1387	=item callback ev_cb (ev_TYPE *watcher)
746		1388
747	Returns the callback currently set on the watcher.	1389	Returns the callback currently set on the watcher.
748		1390
749	=item ev_cb_set (ev_TYPE *watcher, callback)	1391	=item ev_set_cb (ev_TYPE *watcher, callback)
750		1392
751	Change the callback. You can change the callback at virtually any time	1393	Change the callback. You can change the callback at virtually any time
752	(modulo threads).	1394	(modulo threads).
753		1395
754	=item ev_set_priority (ev_TYPE *watcher, priority)	1396	=item ev_set_priority (ev_TYPE *watcher, int priority)
755		1397
756	=item int ev_priority (ev_TYPE *watcher)	1398	=item int ev_priority (ev_TYPE *watcher)
757		1399
758	Set and query the priority of the watcher. The priority is a small	1400	Set and query the priority of the watcher. The priority is a small
759	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1401	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
760	(default: C<-2>). Pending watchers with higher priority will be invoked	1402	(default: C<-2>). Pending watchers with higher priority will be invoked
761	before watchers with lower priority, but priority will not keep watchers	1403	before watchers with lower priority, but priority will not keep watchers
762	from being executed (except for C<ev_idle> watchers).	1404	from being executed (except for C<ev_idle> watchers).
763		1405
764	This means that priorities are I<only> used for ordering callback
765	invocation after new events have been received. This is useful, for
766	example, to reduce latency after idling, or more often, to bind two
767	watchers on the same event and make sure one is called first.
768
769	If you need to suppress invocation when higher priority events are pending	1406	If you need to suppress invocation when higher priority events are pending
770	you need to look at C<ev_idle> watchers, which provide this functionality.	1407	you need to look at C<ev_idle> watchers, which provide this functionality.
771		1408
772	You I<must not> change the priority of a watcher as long as it is active or	1409	You I<must not> change the priority of a watcher as long as it is active or
773	pending.	1410	pending.
774		1411
		1412	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1413	fine, as long as you do not mind that the priority value you query might
		1414	or might not have been clamped to the valid range.
		1415
775	The default priority used by watchers when no priority has been set is	1416	The default priority used by watchers when no priority has been set is
776	always C<0>, which is supposed to not be too high and not be too low :).	1417	always C<0>, which is supposed to not be too high and not be too low :).
777		1418
778	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1419	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
779	fine, as long as you do not mind that the priority value you query might	1420	priorities.
780	or might not have been adjusted to be within valid range.
781		1421
782	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1422	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
783		1423
784	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1424	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
785	C<loop> nor C<revents> need to be valid as long as the watcher callback	1425	C<loop> nor C<revents> need to be valid as long as the watcher callback
786	can deal with that fact.	1426	can deal with that fact, as both are simply passed through to the
		1427	callback.
787		1428
788	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1429	=item int ev_clear_pending (loop, ev_TYPE *watcher)
789		1430
790	If the watcher is pending, this function returns clears its pending status	1431	If the watcher is pending, this function clears its pending status and
791	and returns its C<revents> bitset (as if its callback was invoked). If the	1432	returns its C<revents> bitset (as if its callback was invoked). If the
792	watcher isn't pending it does nothing and returns C<0>.	1433	watcher isn't pending it does nothing and returns C<0>.
793		1434
		1435	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1436	callback to be invoked, which can be accomplished with this function.
		1437
		1438	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1439
		1440	Feeds the given event set into the event loop, as if the specified event
		1441	had happened for the specified watcher (which must be a pointer to an
		1442	initialised but not necessarily started event watcher). Obviously you must
		1443	not free the watcher as long as it has pending events.
		1444
		1445	Stopping the watcher, letting libev invoke it, or calling
		1446	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1447	not started in the first place.
		1448
		1449	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1450	functions that do not need a watcher.
		1451
794	=back	1452	=back
795		1453
		1454	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1455	OWN COMPOSITE WATCHERS> idioms.
796		1456
797	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1457	=head2 WATCHER STATES
798		1458
799	Each watcher has, by default, a member C<void *data> that you can change	1459	There are various watcher states mentioned throughout this manual -
800	and read at any time, libev will completely ignore it. This can be used	1460	active, pending and so on. In this section these states and the rules to
801	to associate arbitrary data with your watcher. If you need more data and	1461	transition between them will be described in more detail - and while these
802	don't want to allocate memory and store a pointer to it in that data	1462	rules might look complicated, they usually do "the right thing".
803	member, you can also "subclass" the watcher type and provide your own
804	data:
805		1463
806	struct my_io	1464	=over 4
807	{
808	struct ev_io io;
809	int otherfd;
810	void *somedata;
811	struct whatever *mostinteresting;
812	}
813		1465
814	And since your callback will be called with a pointer to the watcher, you	1466	=item initialised
815	can cast it back to your own type:
816		1467
817	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1468	Before a watcher can be registered with the event loop it has to be
818	{	1469	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
819	struct my_io *w = (struct my_io *)w_;	1470	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
820	...
821	}
822		1471
823	More interesting and less C-conformant ways of casting your callback type	1472	In this state it is simply some block of memory that is suitable for
824	instead have been omitted.	1473	use in an event loop. It can be moved around, freed, reused etc. at
		1474	will - as long as you either keep the memory contents intact, or call
		1475	C<ev_TYPE_init> again.
825		1476
826	Another common scenario is having some data structure with multiple	1477	=item started/running/active
827	watchers:
828		1478
829	struct my_biggy	1479	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
830	{	1480	property of the event loop, and is actively waiting for events. While in
831	int some_data;	1481	this state it cannot be accessed (except in a few documented ways), moved,
832	ev_timer t1;	1482	freed or anything else - the only legal thing is to keep a pointer to it,
833	ev_timer t2;	1483	and call libev functions on it that are documented to work on active watchers.
834	}
835		1484
836	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1485	=item pending
837	you need to use C<offsetof>:
838		1486
839	#include <stddef.h>	1487	If a watcher is active and libev determines that an event it is interested
		1488	in has occurred (such as a timer expiring), it will become pending. It will
		1489	stay in this pending state until either it is stopped or its callback is
		1490	about to be invoked, so it is not normally pending inside the watcher
		1491	callback.
840		1492
		1493	The watcher might or might not be active while it is pending (for example,
		1494	an expired non-repeating timer can be pending but no longer active). If it
		1495	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1496	but it is still property of the event loop at this time, so cannot be
		1497	moved, freed or reused. And if it is active the rules described in the
		1498	previous item still apply.
		1499
		1500	It is also possible to feed an event on a watcher that is not active (e.g.
		1501	via C<ev_feed_event>), in which case it becomes pending without being
		1502	active.
		1503
		1504	=item stopped
		1505
		1506	A watcher can be stopped implicitly by libev (in which case it might still
		1507	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1508	latter will clear any pending state the watcher might be in, regardless
		1509	of whether it was active or not, so stopping a watcher explicitly before
		1510	freeing it is often a good idea.
		1511
		1512	While stopped (and not pending) the watcher is essentially in the
		1513	initialised state, that is, it can be reused, moved, modified in any way
		1514	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1515	it again).
		1516
		1517	=back
		1518
		1519	=head2 WATCHER PRIORITY MODELS
		1520
		1521	Many event loops support I<watcher priorities>, which are usually small
		1522	integers that influence the ordering of event callback invocation
		1523	between watchers in some way, all else being equal.
		1524
		1525	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1526	description for the more technical details such as the actual priority
		1527	range.
		1528
		1529	There are two common ways how these these priorities are being interpreted
		1530	by event loops:
		1531
		1532	In the more common lock-out model, higher priorities "lock out" invocation
		1533	of lower priority watchers, which means as long as higher priority
		1534	watchers receive events, lower priority watchers are not being invoked.
		1535
		1536	The less common only-for-ordering model uses priorities solely to order
		1537	callback invocation within a single event loop iteration: Higher priority
		1538	watchers are invoked before lower priority ones, but they all get invoked
		1539	before polling for new events.
		1540
		1541	Libev uses the second (only-for-ordering) model for all its watchers
		1542	except for idle watchers (which use the lock-out model).
		1543
		1544	The rationale behind this is that implementing the lock-out model for
		1545	watchers is not well supported by most kernel interfaces, and most event
		1546	libraries will just poll for the same events again and again as long as
		1547	their callbacks have not been executed, which is very inefficient in the
		1548	common case of one high-priority watcher locking out a mass of lower
		1549	priority ones.
		1550
		1551	Static (ordering) priorities are most useful when you have two or more
		1552	watchers handling the same resource: a typical usage example is having an
		1553	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1554	timeouts. Under load, data might be received while the program handles
		1555	other jobs, but since timers normally get invoked first, the timeout
		1556	handler will be executed before checking for data. In that case, giving
		1557	the timer a lower priority than the I/O watcher ensures that I/O will be
		1558	handled first even under adverse conditions (which is usually, but not
		1559	always, what you want).
		1560
		1561	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1562	will only be executed when no same or higher priority watchers have
		1563	received events, they can be used to implement the "lock-out" model when
		1564	required.
		1565
		1566	For example, to emulate how many other event libraries handle priorities,
		1567	you can associate an C<ev_idle> watcher to each such watcher, and in
		1568	the normal watcher callback, you just start the idle watcher. The real
		1569	processing is done in the idle watcher callback. This causes libev to
		1570	continuously poll and process kernel event data for the watcher, but when
		1571	the lock-out case is known to be rare (which in turn is rare :), this is
		1572	workable.
		1573
		1574	Usually, however, the lock-out model implemented that way will perform
		1575	miserably under the type of load it was designed to handle. In that case,
		1576	it might be preferable to stop the real watcher before starting the
		1577	idle watcher, so the kernel will not have to process the event in case
		1578	the actual processing will be delayed for considerable time.
		1579
		1580	Here is an example of an I/O watcher that should run at a strictly lower
		1581	priority than the default, and which should only process data when no
		1582	other events are pending:
		1583
		1584	ev_idle idle; // actual processing watcher
		1585	ev_io io; // actual event watcher
		1586
841	static void	1587	static void
842	t1_cb (EV_P_ struct ev_timer *w, int revents)	1588	io_cb (EV_P_ ev_io *w, int revents)
843	{	1589	{
844	struct my_biggy big = (struct my_biggy *	1590	// stop the I/O watcher, we received the event, but
845	(((char *)w) - offsetof (struct my_biggy, t1));	1591	// are not yet ready to handle it.
		1592	ev_io_stop (EV_A_ w);
		1593
		1594	// start the idle watcher to handle the actual event.
		1595	// it will not be executed as long as other watchers
		1596	// with the default priority are receiving events.
		1597	ev_idle_start (EV_A_ &idle);
846	}	1598	}
847		1599
848	static void	1600	static void
849	t2_cb (EV_P_ struct ev_timer *w, int revents)	1601	idle_cb (EV_P_ ev_idle *w, int revents)
850	{	1602	{
851	struct my_biggy big = (struct my_biggy *	1603	// actual processing
852	(((char *)w) - offsetof (struct my_biggy, t2));	1604	read (STDIN_FILENO, ...);
		1605
		1606	// have to start the I/O watcher again, as
		1607	// we have handled the event
		1608	ev_io_start (EV_P_ &io);
853	}	1609	}
		1610
		1611	// initialisation
		1612	ev_idle_init (&idle, idle_cb);
		1613	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1614	ev_io_start (EV_DEFAULT_ &io);
		1615
		1616	In the "real" world, it might also be beneficial to start a timer, so that
		1617	low-priority connections can not be locked out forever under load. This
		1618	enables your program to keep a lower latency for important connections
		1619	during short periods of high load, while not completely locking out less
		1620	important ones.
854		1621
855		1622
856	=head1 WATCHER TYPES	1623	=head1 WATCHER TYPES
857		1624
858	This section describes each watcher in detail, but will not repeat	1625	This section describes each watcher in detail, but will not repeat
…		…
882	In general you can register as many read and/or write event watchers per	1649	In general you can register as many read and/or write event watchers per
883	fd as you want (as long as you don't confuse yourself). Setting all file	1650	fd as you want (as long as you don't confuse yourself). Setting all file
884	descriptors to non-blocking mode is also usually a good idea (but not	1651	descriptors to non-blocking mode is also usually a good idea (but not
885	required if you know what you are doing).	1652	required if you know what you are doing).
886		1653
887	You have to be careful with dup'ed file descriptors, though. Some backends
888	(the linux epoll backend is a notable example) cannot handle dup'ed file
889	descriptors correctly if you register interest in two or more fds pointing
890	to the same underlying file/socket/etc. description (that is, they share
891	the same underlying "file open").
892
893	If you must do this, then force the use of a known-to-be-good backend
894	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
895	C<EVBACKEND_POLL>).
896
897	Another thing you have to watch out for is that it is quite easy to	1654	Another thing you have to watch out for is that it is quite easy to
898	receive "spurious" readyness notifications, that is your callback might	1655	receive "spurious" readiness notifications, that is, your callback might
899	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1656	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
900	because there is no data. Not only are some backends known to create a	1657	because there is no data. It is very easy to get into this situation even
901	lot of those (for example solaris ports), it is very easy to get into	1658	with a relatively standard program structure. Thus it is best to always
902	this situation even with a relatively standard program structure. Thus	1659	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
903	it is best to always use non-blocking I/O: An extra C<read>(2) returning
904	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1660	preferable to a program hanging until some data arrives.
905		1661
906	If you cannot run the fd in non-blocking mode (for example you should not	1662	If you cannot run the fd in non-blocking mode (for example you should
907	play around with an Xlib connection), then you have to seperately re-test	1663	not play around with an Xlib connection), then you have to separately
908	whether a file descriptor is really ready with a known-to-be good interface	1664	re-test whether a file descriptor is really ready with a known-to-be good
909	such as poll (fortunately in our Xlib example, Xlib already does this on	1665	interface such as poll (fortunately in the case of Xlib, it already does
910	its own, so its quite safe to use).	1666	this on its own, so its quite safe to use). Some people additionally
		1667	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1668	indefinitely.
		1669
		1670	But really, best use non-blocking mode.
		1671
		1672	=head3 The special problem of disappearing file descriptors
		1673
		1674	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
		1675	a file descriptor (either due to calling C<close> explicitly or any other
		1676	means, such as C<dup2>). The reason is that you register interest in some
		1677	file descriptor, but when it goes away, the operating system will silently
		1678	drop this interest. If another file descriptor with the same number then
		1679	is registered with libev, there is no efficient way to see that this is,
		1680	in fact, a different file descriptor.
		1681
		1682	To avoid having to explicitly tell libev about such cases, libev follows
		1683	the following policy: Each time C<ev_io_set> is being called, libev
		1684	will assume that this is potentially a new file descriptor, otherwise
		1685	it is assumed that the file descriptor stays the same. That means that
		1686	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1687	descriptor even if the file descriptor number itself did not change.
		1688
		1689	This is how one would do it normally anyway, the important point is that
		1690	the libev application should not optimise around libev but should leave
		1691	optimisations to libev.
		1692
		1693	=head3 The special problem of dup'ed file descriptors
		1694
		1695	Some backends (e.g. epoll), cannot register events for file descriptors,
		1696	but only events for the underlying file descriptions. That means when you
		1697	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1698	events for them, only one file descriptor might actually receive events.
		1699
		1700	There is no workaround possible except not registering events
		1701	for potentially C<dup ()>'ed file descriptors, or to resort to
		1702	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1703
		1704	=head3 The special problem of files
		1705
		1706	Many people try to use C<select> (or libev) on file descriptors
		1707	representing files, and expect it to become ready when their program
		1708	doesn't block on disk accesses (which can take a long time on their own).
		1709
		1710	However, this cannot ever work in the "expected" way - you get a readiness
		1711	notification as soon as the kernel knows whether and how much data is
		1712	there, and in the case of open files, that's always the case, so you
		1713	always get a readiness notification instantly, and your read (or possibly
		1714	write) will still block on the disk I/O.
		1715
		1716	Another way to view it is that in the case of sockets, pipes, character
		1717	devices and so on, there is another party (the sender) that delivers data
		1718	on its own, but in the case of files, there is no such thing: the disk
		1719	will not send data on its own, simply because it doesn't know what you
		1720	wish to read - you would first have to request some data.
		1721
		1722	Since files are typically not-so-well supported by advanced notification
		1723	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1724	to files, even though you should not use it. The reason for this is
		1725	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1726	usually a tty, often a pipe, but also sometimes files or special devices
		1727	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1728	F</dev/urandom>), and even though the file might better be served with
		1729	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1730	it "just works" instead of freezing.
		1731
		1732	So avoid file descriptors pointing to files when you know it (e.g. use
		1733	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1734	when you rarely read from a file instead of from a socket, and want to
		1735	reuse the same code path.
		1736
		1737	=head3 The special problem of fork
		1738
		1739	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
		1740	at all or exhibit useless behaviour. Libev fully supports fork, but needs
		1741	to be told about it in the child if you want to continue to use it in the
		1742	child.
		1743
		1744	To support fork in your child processes, you have to call C<ev_loop_fork
		1745	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1746	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1747
		1748	=head3 The special problem of SIGPIPE
		1749
		1750	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1751	when writing to a pipe whose other end has been closed, your program gets
		1752	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1753	this is sensible behaviour, for daemons, this is usually undesirable.
		1754
		1755	So when you encounter spurious, unexplained daemon exits, make sure you
		1756	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1757	somewhere, as that would have given you a big clue).
		1758
		1759	=head3 The special problem of accept()ing when you can't
		1760
		1761	Many implementations of the POSIX C<accept> function (for example,
		1762	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1763	connection from the pending queue in all error cases.
		1764
		1765	For example, larger servers often run out of file descriptors (because
		1766	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1767	rejecting the connection, leading to libev signalling readiness on
		1768	the next iteration again (the connection still exists after all), and
		1769	typically causing the program to loop at 100% CPU usage.
		1770
		1771	Unfortunately, the set of errors that cause this issue differs between
		1772	operating systems, there is usually little the app can do to remedy the
		1773	situation, and no known thread-safe method of removing the connection to
		1774	cope with overload is known (to me).
		1775
		1776	One of the easiest ways to handle this situation is to just ignore it
		1777	- when the program encounters an overload, it will just loop until the
		1778	situation is over. While this is a form of busy waiting, no OS offers an
		1779	event-based way to handle this situation, so it's the best one can do.
		1780
		1781	A better way to handle the situation is to log any errors other than
		1782	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1783	messages, and continue as usual, which at least gives the user an idea of
		1784	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1785	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1786	usage.
		1787
		1788	If your program is single-threaded, then you could also keep a dummy file
		1789	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1790	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1791	close that fd, and create a new dummy fd. This will gracefully refuse
		1792	clients under typical overload conditions.
		1793
		1794	The last way to handle it is to simply log the error and C<exit>, as
		1795	is often done with C<malloc> failures, but this results in an easy
		1796	opportunity for a DoS attack.
		1797
		1798	=head3 Watcher-Specific Functions
911		1799
912	=over 4	1800	=over 4
913		1801
914	=item ev_io_init (ev_io *, callback, int fd, int events)	1802	=item ev_io_init (ev_io *, callback, int fd, int events)
915		1803
916	=item ev_io_set (ev_io *, int fd, int events)	1804	=item ev_io_set (ev_io *, int fd, int events)
917		1805
918	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1806	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
919	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1807	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
920	C<EV_READ | EV_WRITE> to receive the given events.	1808	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
921		1809
922	=item int fd [read-only]	1810	=item int fd [read-only]
923		1811
924	The file descriptor being watched.	1812	The file descriptor being watched.
925		1813
926	=item int events [read-only]	1814	=item int events [read-only]
927		1815
928	The events being watched.	1816	The events being watched.
929		1817
930	=back	1818	=back
		1819
		1820	=head3 Examples
931		1821
932	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1822	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
933	readable, but only once. Since it is likely line-buffered, you could	1823	readable, but only once. Since it is likely line-buffered, you could
934	attempt to read a whole line in the callback.	1824	attempt to read a whole line in the callback.
935		1825
936	static void	1826	static void
937	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1827	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
938	{	1828	{
939	ev_io_stop (loop, w);	1829	ev_io_stop (loop, w);
940	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1830	.. read from stdin here (or from w->fd) and handle any I/O errors
941	}	1831	}
942		1832
943	...	1833	...
944	struct ev_loop *loop = ev_default_init (0);	1834	struct ev_loop *loop = ev_default_init (0);
945	struct ev_io stdin_readable;	1835	ev_io stdin_readable;
946	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1836	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
947	ev_io_start (loop, &stdin_readable);	1837	ev_io_start (loop, &stdin_readable);
948	ev_loop (loop, 0);	1838	ev_run (loop, 0);
949		1839
950		1840
951	=head2 C<ev_timer> - relative and optionally repeating timeouts	1841	=head2 C<ev_timer> - relative and optionally repeating timeouts
952		1842
953	Timer watchers are simple relative timers that generate an event after a	1843	Timer watchers are simple relative timers that generate an event after a
954	given time, and optionally repeating in regular intervals after that.	1844	given time, and optionally repeating in regular intervals after that.
955		1845
956	The timers are based on real time, that is, if you register an event that	1846	The timers are based on real time, that is, if you register an event that
957	times out after an hour and you reset your system clock to last years	1847	times out after an hour and you reset your system clock to January last
958	time, it will still time out after (roughly) and hour. "Roughly" because	1848	year, it will still time out after (roughly) one hour. "Roughly" because
959	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1849	detecting time jumps is hard, and some inaccuracies are unavoidable (the
960	monotonic clock option helps a lot here).	1850	monotonic clock option helps a lot here).
		1851
		1852	The callback is guaranteed to be invoked only I<after> its timeout has
		1853	passed (not I<at>, so on systems with very low-resolution clocks this
		1854	might introduce a small delay, see "the special problem of being too
		1855	early", below). If multiple timers become ready during the same loop
		1856	iteration then the ones with earlier time-out values are invoked before
		1857	ones of the same priority with later time-out values (but this is no
		1858	longer true when a callback calls C<ev_run> recursively).
		1859
		1860	=head3 Be smart about timeouts
		1861
		1862	Many real-world problems involve some kind of timeout, usually for error
		1863	recovery. A typical example is an HTTP request - if the other side hangs,
		1864	you want to raise some error after a while.
		1865
		1866	What follows are some ways to handle this problem, from obvious and
		1867	inefficient to smart and efficient.
		1868
		1869	In the following, a 60 second activity timeout is assumed - a timeout that
		1870	gets reset to 60 seconds each time there is activity (e.g. each time some
		1871	data or other life sign was received).
		1872
		1873	=over 4
		1874
		1875	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1876
		1877	This is the most obvious, but not the most simple way: In the beginning,
		1878	start the watcher:
		1879
		1880	ev_timer_init (timer, callback, 60., 0.);
		1881	ev_timer_start (loop, timer);
		1882
		1883	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1884	and start it again:
		1885
		1886	ev_timer_stop (loop, timer);
		1887	ev_timer_set (timer, 60., 0.);
		1888	ev_timer_start (loop, timer);
		1889
		1890	This is relatively simple to implement, but means that each time there is
		1891	some activity, libev will first have to remove the timer from its internal
		1892	data structure and then add it again. Libev tries to be fast, but it's
		1893	still not a constant-time operation.
		1894
		1895	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1896
		1897	This is the easiest way, and involves using C<ev_timer_again> instead of
		1898	C<ev_timer_start>.
		1899
		1900	To implement this, configure an C<ev_timer> with a C<repeat> value
		1901	of C<60> and then call C<ev_timer_again> at start and each time you
		1902	successfully read or write some data. If you go into an idle state where
		1903	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1904	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1905
		1906	That means you can ignore both the C<ev_timer_start> function and the
		1907	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1908	member and C<ev_timer_again>.
		1909
		1910	At start:
		1911
		1912	ev_init (timer, callback);
		1913	timer->repeat = 60.;
		1914	ev_timer_again (loop, timer);
		1915
		1916	Each time there is some activity:
		1917
		1918	ev_timer_again (loop, timer);
		1919
		1920	It is even possible to change the time-out on the fly, regardless of
		1921	whether the watcher is active or not:
		1922
		1923	timer->repeat = 30.;
		1924	ev_timer_again (loop, timer);
		1925
		1926	This is slightly more efficient then stopping/starting the timer each time
		1927	you want to modify its timeout value, as libev does not have to completely
		1928	remove and re-insert the timer from/into its internal data structure.
		1929
		1930	It is, however, even simpler than the "obvious" way to do it.
		1931
		1932	=item 3. Let the timer time out, but then re-arm it as required.
		1933
		1934	This method is more tricky, but usually most efficient: Most timeouts are
		1935	relatively long compared to the intervals between other activity - in
		1936	our example, within 60 seconds, there are usually many I/O events with
		1937	associated activity resets.
		1938
		1939	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1940	but remember the time of last activity, and check for a real timeout only
		1941	within the callback:
		1942
		1943	ev_tstamp timeout = 60.;
		1944	ev_tstamp last_activity; // time of last activity
		1945	ev_timer timer;
		1946
		1947	static void
		1948	callback (EV_P_ ev_timer *w, int revents)
		1949	{
		1950	// calculate when the timeout would happen
		1951	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1952
		1953	// if negative, it means we the timeout already occurred
		1954	if (after < 0.)
		1955	{
		1956	// timeout occurred, take action
		1957	}
		1958	else
		1959	{
		1960	// callback was invoked, but there was some recent
		1961	// activity. simply restart the timer to time out
		1962	// after "after" seconds, which is the earliest time
		1963	// the timeout can occur.
		1964	ev_timer_set (w, after, 0.);
		1965	ev_timer_start (EV_A_ w);
		1966	}
		1967	}
		1968
		1969	To summarise the callback: first calculate in how many seconds the
		1970	timeout will occur (by calculating the absolute time when it would occur,
		1971	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1972	(EV_A)> from that).
		1973
		1974	If this value is negative, then we are already past the timeout, i.e. we
		1975	timed out, and need to do whatever is needed in this case.
		1976
		1977	Otherwise, we now the earliest time at which the timeout would trigger,
		1978	and simply start the timer with this timeout value.
		1979
		1980	In other words, each time the callback is invoked it will check whether
		1981	the timeout occurred. If not, it will simply reschedule itself to check
		1982	again at the earliest time it could time out. Rinse. Repeat.
		1983
		1984	This scheme causes more callback invocations (about one every 60 seconds
		1985	minus half the average time between activity), but virtually no calls to
		1986	libev to change the timeout.
		1987
		1988	To start the machinery, simply initialise the watcher and set
		1989	C<last_activity> to the current time (meaning there was some activity just
		1990	now), then call the callback, which will "do the right thing" and start
		1991	the timer:
		1992
		1993	last_activity = ev_now (EV_A);
		1994	ev_init (&timer, callback);
		1995	callback (EV_A_ &timer, 0);
		1996
		1997	When there is some activity, simply store the current time in
		1998	C<last_activity>, no libev calls at all:
		1999
		2000	if (activity detected)
		2001	last_activity = ev_now (EV_A);
		2002
		2003	When your timeout value changes, then the timeout can be changed by simply
		2004	providing a new value, stopping the timer and calling the callback, which
		2005	will again do the right thing (for example, time out immediately :).
		2006
		2007	timeout = new_value;
		2008	ev_timer_stop (EV_A_ &timer);
		2009	callback (EV_A_ &timer, 0);
		2010
		2011	This technique is slightly more complex, but in most cases where the
		2012	time-out is unlikely to be triggered, much more efficient.
		2013
		2014	=item 4. Wee, just use a double-linked list for your timeouts.
		2015
		2016	If there is not one request, but many thousands (millions...), all
		2017	employing some kind of timeout with the same timeout value, then one can
		2018	do even better:
		2019
		2020	When starting the timeout, calculate the timeout value and put the timeout
		2021	at the I<end> of the list.
		2022
		2023	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		2024	the list is expected to fire (for example, using the technique #3).
		2025
		2026	When there is some activity, remove the timer from the list, recalculate
		2027	the timeout, append it to the end of the list again, and make sure to
		2028	update the C<ev_timer> if it was taken from the beginning of the list.
		2029
		2030	This way, one can manage an unlimited number of timeouts in O(1) time for
		2031	starting, stopping and updating the timers, at the expense of a major
		2032	complication, and having to use a constant timeout. The constant timeout
		2033	ensures that the list stays sorted.
		2034
		2035	=back
		2036
		2037	So which method the best?
		2038
		2039	Method #2 is a simple no-brain-required solution that is adequate in most
		2040	situations. Method #3 requires a bit more thinking, but handles many cases
		2041	better, and isn't very complicated either. In most case, choosing either
		2042	one is fine, with #3 being better in typical situations.
		2043
		2044	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		2045	rather complicated, but extremely efficient, something that really pays
		2046	off after the first million or so of active timers, i.e. it's usually
		2047	overkill :)
		2048
		2049	=head3 The special problem of being too early
		2050
		2051	If you ask a timer to call your callback after three seconds, then
		2052	you expect it to be invoked after three seconds - but of course, this
		2053	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2054	guaranteed to any precision by libev - imagine somebody suspending the
		2055	process with a STOP signal for a few hours for example.
		2056
		2057	So, libev tries to invoke your callback as soon as possible I<after> the
		2058	delay has occurred, but cannot guarantee this.
		2059
		2060	A less obvious failure mode is calling your callback too early: many event
		2061	loops compare timestamps with a "elapsed delay >= requested delay", but
		2062	this can cause your callback to be invoked much earlier than you would
		2063	expect.
		2064
		2065	To see why, imagine a system with a clock that only offers full second
		2066	resolution (think windows if you can't come up with a broken enough OS
		2067	yourself). If you schedule a one-second timer at the time 500.9, then the
		2068	event loop will schedule your timeout to elapse at a system time of 500
		2069	(500.9 truncated to the resolution) + 1, or 501.
		2070
		2071	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2072	501" and invoke the callback 0.1s after it was started, even though a
		2073	one-second delay was requested - this is being "too early", despite best
		2074	intentions.
		2075
		2076	This is the reason why libev will never invoke the callback if the elapsed
		2077	delay equals the requested delay, but only when the elapsed delay is
		2078	larger than the requested delay. In the example above, libev would only invoke
		2079	the callback at system time 502, or 1.1s after the timer was started.
		2080
		2081	So, while libev cannot guarantee that your callback will be invoked
		2082	exactly when requested, it I<can> and I<does> guarantee that the requested
		2083	delay has actually elapsed, or in other words, it always errs on the "too
		2084	late" side of things.
		2085
		2086	=head3 The special problem of time updates
		2087
		2088	Establishing the current time is a costly operation (it usually takes
		2089	at least one system call): EV therefore updates its idea of the current
		2090	time only before and after C<ev_run> collects new events, which causes a
		2091	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2092	lots of events in one iteration.
961		2093
962	The relative timeouts are calculated relative to the C<ev_now ()>	2094	The relative timeouts are calculated relative to the C<ev_now ()>
963	time. This is usually the right thing as this timestamp refers to the time	2095	time. This is usually the right thing as this timestamp refers to the time
964	of the event triggering whatever timeout you are modifying/starting. If	2096	of the event triggering whatever timeout you are modifying/starting. If
965	you suspect event processing to be delayed and you I<need> to base the timeout	2097	you suspect event processing to be delayed and you I<need> to base the
966	on the current time, use something like this to adjust for this:	2098	timeout on the current time, use something like the following to adjust
		2099	for it:
967		2100
968	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2101	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
969		2102
970	The callback is guarenteed to be invoked only when its timeout has passed,	2103	If the event loop is suspended for a long time, you can also force an
971	but if multiple timers become ready during the same loop iteration then	2104	update of the time returned by C<ev_now ()> by calling C<ev_now_update
972	order of execution is undefined.	2105	()>, although that will push the event time of all outstanding events
		2106	further into the future.
		2107
		2108	=head3 The special problem of unsynchronised clocks
		2109
		2110	Modern systems have a variety of clocks - libev itself uses the normal
		2111	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2112	jumps).
		2113
		2114	Neither of these clocks is synchronised with each other or any other clock
		2115	on the system, so C<ev_time ()> might return a considerably different time
		2116	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2117	a call to C<gettimeofday> might return a second count that is one higher
		2118	than a directly following call to C<time>.
		2119
		2120	The moral of this is to only compare libev-related timestamps with
		2121	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2122	a second or so.
		2123
		2124	One more problem arises due to this lack of synchronisation: if libev uses
		2125	the system monotonic clock and you compare timestamps from C<ev_time>
		2126	or C<ev_now> from when you started your timer and when your callback is
		2127	invoked, you will find that sometimes the callback is a bit "early".
		2128
		2129	This is because C<ev_timer>s work in real time, not wall clock time, so
		2130	libev makes sure your callback is not invoked before the delay happened,
		2131	I<measured according to the real time>, not the system clock.
		2132
		2133	If your timeouts are based on a physical timescale (e.g. "time out this
		2134	connection after 100 seconds") then this shouldn't bother you as it is
		2135	exactly the right behaviour.
		2136
		2137	If you want to compare wall clock/system timestamps to your timers, then
		2138	you need to use C<ev_periodic>s, as these are based on the wall clock
		2139	time, where your comparisons will always generate correct results.
		2140
		2141	=head3 The special problems of suspended animation
		2142
		2143	When you leave the server world it is quite customary to hit machines that
		2144	can suspend/hibernate - what happens to the clocks during such a suspend?
		2145
		2146	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2147	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2148	to run until the system is suspended, but they will not advance while the
		2149	system is suspended. That means, on resume, it will be as if the program
		2150	was frozen for a few seconds, but the suspend time will not be counted
		2151	towards C<ev_timer> when a monotonic clock source is used. The real time
		2152	clock advanced as expected, but if it is used as sole clocksource, then a
		2153	long suspend would be detected as a time jump by libev, and timers would
		2154	be adjusted accordingly.
		2155
		2156	I would not be surprised to see different behaviour in different between
		2157	operating systems, OS versions or even different hardware.
		2158
		2159	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2160	time jump in the monotonic clocks and the realtime clock. If the program
		2161	is suspended for a very long time, and monotonic clock sources are in use,
		2162	then you can expect C<ev_timer>s to expire as the full suspension time
		2163	will be counted towards the timers. When no monotonic clock source is in
		2164	use, then libev will again assume a timejump and adjust accordingly.
		2165
		2166	It might be beneficial for this latter case to call C<ev_suspend>
		2167	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2168	deterministic behaviour in this case (you can do nothing against
		2169	C<SIGSTOP>).
		2170
		2171	=head3 Watcher-Specific Functions and Data Members
973		2172
974	=over 4	2173	=over 4
975		2174
976	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2175	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
977		2176
978	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2177	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
979		2178
980	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2179	Configure the timer to trigger after C<after> seconds (fractional and
981	C<0.>, then it will automatically be stopped. If it is positive, then the	2180	negative values are supported). If C<repeat> is C<0.>, then it will
		2181	automatically be stopped once the timeout is reached. If it is positive,
982	timer will automatically be configured to trigger again C<repeat> seconds	2182	then the timer will automatically be configured to trigger again C<repeat>
983	later, again, and again, until stopped manually.	2183	seconds later, again, and again, until stopped manually.
984		2184
985	The timer itself will do a best-effort at avoiding drift, that is, if you	2185	The timer itself will do a best-effort at avoiding drift, that is, if
986	configure a timer to trigger every 10 seconds, then it will trigger at	2186	you configure a timer to trigger every 10 seconds, then it will normally
987	exactly 10 second intervals. If, however, your program cannot keep up with	2187	trigger at exactly 10 second intervals. If, however, your program cannot
988	the timer (because it takes longer than those 10 seconds to do stuff) the	2188	keep up with the timer (because it takes longer than those 10 seconds to
989	timer will not fire more than once per event loop iteration.	2189	do stuff) the timer will not fire more than once per event loop iteration.
990		2190
991	=item ev_timer_again (loop)	2191	=item ev_timer_again (loop, ev_timer *)
992		2192
993	This will act as if the timer timed out and restart it again if it is	2193	This will act as if the timer timed out, and restarts it again if it is
994	repeating. The exact semantics are:	2194	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2195	timeout to the C<repeat> value and calling C<ev_timer_start>.
995		2196
		2197	The exact semantics are as in the following rules, all of which will be
		2198	applied to the watcher:
		2199
		2200	=over 4
		2201
996	If the timer is pending, its pending status is cleared.	2202	=item If the timer is pending, the pending status is always cleared.
997		2203
998	If the timer is started but nonrepeating, stop it (as if it timed out).	2204	=item If the timer is started but non-repeating, stop it (as if it timed
		2205	out, without invoking it).
999		2206
1000	If the timer is repeating, either start it if necessary (with the	2207	=item If the timer is repeating, make the C<repeat> value the new timeout
1001	C<repeat> value), or reset the running timer to the C<repeat> value.	2208	and start the timer, if necessary.
1002		2209
1003	This sounds a bit complicated, but here is a useful and typical	2210	=back
1004	example: Imagine you have a tcp connection and you want a so-called idle
1005	timeout, that is, you want to be called when there have been, say, 60
1006	seconds of inactivity on the socket. The easiest way to do this is to
1007	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1008	C<ev_timer_again> each time you successfully read or write some data. If
1009	you go into an idle state where you do not expect data to travel on the
1010	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1011	automatically restart it if need be.
1012		2211
1013	That means you can ignore the C<after> value and C<ev_timer_start>	2212	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1014	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2213	usage example.
1015		2214
1016	ev_timer_init (timer, callback, 0., 5.);	2215	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1017	ev_timer_again (loop, timer);
1018	...
1019	timer->again = 17.;
1020	ev_timer_again (loop, timer);
1021	...
1022	timer->again = 10.;
1023	ev_timer_again (loop, timer);
1024		2216
1025	This is more slightly efficient then stopping/starting the timer each time	2217	Returns the remaining time until a timer fires. If the timer is active,
1026	you want to modify its timeout value.	2218	then this time is relative to the current event loop time, otherwise it's
		2219	the timeout value currently configured.
		2220
		2221	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2222	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2223	will return C<4>. When the timer expires and is restarted, it will return
		2224	roughly C<7> (likely slightly less as callback invocation takes some time,
		2225	too), and so on.
1027		2226
1028	=item ev_tstamp repeat [read-write]	2227	=item ev_tstamp repeat [read-write]
1029		2228
1030	The current C<repeat> value. Will be used each time the watcher times out	2229	The current C<repeat> value. Will be used each time the watcher times out
1031	or C<ev_timer_again> is called and determines the next timeout (if any),	2230	or C<ev_timer_again> is called, and determines the next timeout (if any),
1032	which is also when any modifications are taken into account.	2231	which is also when any modifications are taken into account.
1033		2232
1034	=back	2233	=back
1035		2234
		2235	=head3 Examples
		2236
1036	Example: Create a timer that fires after 60 seconds.	2237	Example: Create a timer that fires after 60 seconds.
1037		2238
1038	static void	2239	static void
1039	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2240	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1040	{	2241	{
1041	.. one minute over, w is actually stopped right here	2242	.. one minute over, w is actually stopped right here
1042	}	2243	}
1043		2244
1044	struct ev_timer mytimer;	2245	ev_timer mytimer;
1045	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2246	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1046	ev_timer_start (loop, &mytimer);	2247	ev_timer_start (loop, &mytimer);
1047		2248
1048	Example: Create a timeout timer that times out after 10 seconds of	2249	Example: Create a timeout timer that times out after 10 seconds of
1049	inactivity.	2250	inactivity.
1050		2251
1051	static void	2252	static void
1052	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2253	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1053	{	2254	{
1054	.. ten seconds without any activity	2255	.. ten seconds without any activity
1055	}	2256	}
1056		2257
1057	struct ev_timer mytimer;	2258	ev_timer mytimer;
1058	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2259	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1059	ev_timer_again (&mytimer); /* start timer */	2260	ev_timer_again (&mytimer); /* start timer */
1060	ev_loop (loop, 0);	2261	ev_run (loop, 0);
1061		2262
1062	// and in some piece of code that gets executed on any "activity":	2263	// and in some piece of code that gets executed on any "activity":
1063	// reset the timeout to start ticking again at 10 seconds	2264	// reset the timeout to start ticking again at 10 seconds
1064	ev_timer_again (&mytimer);	2265	ev_timer_again (&mytimer);
1065		2266
1066		2267
1067	=head2 C<ev_periodic> - to cron or not to cron?	2268	=head2 C<ev_periodic> - to cron or not to cron?
1068		2269
1069	Periodic watchers are also timers of a kind, but they are very versatile	2270	Periodic watchers are also timers of a kind, but they are very versatile
1070	(and unfortunately a bit complex).	2271	(and unfortunately a bit complex).
1071		2272
1072	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2273	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1073	but on wallclock time (absolute time). You can tell a periodic watcher	2274	relative time, the physical time that passes) but on wall clock time
1074	to trigger "at" some specific point in time. For example, if you tell a	2275	(absolute time, the thing you can read on your calendar or clock). The
1075	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2276	difference is that wall clock time can run faster or slower than real
1076	+ 10.>) and then reset your system clock to the last year, then it will	2277	time, and time jumps are not uncommon (e.g. when you adjust your
1077	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2278	wrist-watch).
1078	roughly 10 seconds later and of course not if you reset your system time
1079	again).
1080		2279
1081	They can also be used to implement vastly more complex timers, such as	2280	You can tell a periodic watcher to trigger after some specific point
		2281	in time: for example, if you tell a periodic watcher to trigger "in 10
		2282	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2283	not a delay) and then reset your system clock to January of the previous
		2284	year, then it will take a year or more to trigger the event (unlike an
		2285	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2286	it, as it uses a relative timeout).
		2287
		2288	C<ev_periodic> watchers can also be used to implement vastly more complex
1082	triggering an event on eahc midnight, local time.	2289	timers, such as triggering an event on each "midnight, local time", or
		2290	other complicated rules. This cannot easily be done with C<ev_timer>
		2291	watchers, as those cannot react to time jumps.
1083		2292
1084	As with timers, the callback is guarenteed to be invoked only when the	2293	As with timers, the callback is guaranteed to be invoked only when the
1085	time (C<at>) has been passed, but if multiple periodic timers become ready	2294	point in time where it is supposed to trigger has passed. If multiple
1086	during the same loop iteration then order of execution is undefined.	2295	timers become ready during the same loop iteration then the ones with
		2296	earlier time-out values are invoked before ones with later time-out values
		2297	(but this is no longer true when a callback calls C<ev_run> recursively).
		2298
		2299	=head3 Watcher-Specific Functions and Data Members
1087		2300
1088	=over 4	2301	=over 4
1089		2302
1090	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2303	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1091		2304
1092	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2305	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1093		2306
1094	Lots of arguments, lets sort it out... There are basically three modes of	2307	Lots of arguments, let's sort it out... There are basically three modes of
1095	operation, and we will explain them from simplest to complex:	2308	operation, and we will explain them from simplest to most complex:
1096		2309
1097	=over 4	2310	=over 4
1098		2311
1099	=item * absolute timer (interval = reschedule_cb = 0)	2312	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1100		2313
1101	In this configuration the watcher triggers an event at the wallclock time	2314	In this configuration the watcher triggers an event after the wall clock
1102	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2315	time C<offset> has passed. It will not repeat and will not adjust when a
1103	that is, if it is to be run at January 1st 2011 then it will run when the	2316	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1104	system time reaches or surpasses this time.	2317	will be stopped and invoked when the system clock reaches or surpasses
		2318	this point in time.
1105		2319
1106	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2320	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1107		2321
1108	In this mode the watcher will always be scheduled to time out at the next	2322	In this mode the watcher will always be scheduled to time out at the next
1109	C<at + N * interval> time (for some integer N) and then repeat, regardless	2323	C<offset + N * interval> time (for some integer N, which can also be
1110	of any time jumps.	2324	negative) and then repeat, regardless of any time jumps. The C<offset>
		2325	argument is merely an offset into the C<interval> periods.
1111		2326
1112	This can be used to create timers that do not drift with respect to system	2327	This can be used to create timers that do not drift with respect to the
1113	time:	2328	system clock, for example, here is an C<ev_periodic> that triggers each
		2329	hour, on the hour (with respect to UTC):
1114		2330
1115	ev_periodic_set (&periodic, 0., 3600., 0);	2331	ev_periodic_set (&periodic, 0., 3600., 0);
1116		2332
1117	This doesn't mean there will always be 3600 seconds in between triggers,	2333	This doesn't mean there will always be 3600 seconds in between triggers,
1118	but only that the the callback will be called when the system time shows a	2334	but only that the callback will be called when the system time shows a
1119	full hour (UTC), or more correctly, when the system time is evenly divisible	2335	full hour (UTC), or more correctly, when the system time is evenly divisible
1120	by 3600.	2336	by 3600.
1121		2337
1122	Another way to think about it (for the mathematically inclined) is that	2338	Another way to think about it (for the mathematically inclined) is that
1123	C<ev_periodic> will try to run the callback in this mode at the next possible	2339	C<ev_periodic> will try to run the callback in this mode at the next possible
1124	time where C<time = at (mod interval)>, regardless of any time jumps.	2340	time where C<time = offset (mod interval)>, regardless of any time jumps.
1125		2341
		2342	The C<interval> I<MUST> be positive, and for numerical stability, the
		2343	interval value should be higher than C<1/8192> (which is around 100
		2344	microseconds) and C<offset> should be higher than C<0> and should have
		2345	at most a similar magnitude as the current time (say, within a factor of
		2346	ten). Typical values for offset are, in fact, C<0> or something between
		2347	C<0> and C<interval>, which is also the recommended range.
		2348
		2349	Note also that there is an upper limit to how often a timer can fire (CPU
		2350	speed for example), so if C<interval> is very small then timing stability
		2351	will of course deteriorate. Libev itself tries to be exact to be about one
		2352	millisecond (if the OS supports it and the machine is fast enough).
		2353
1126	=item * manual reschedule mode (reschedule_cb = callback)	2354	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1127		2355
1128	In this mode the values for C<interval> and C<at> are both being	2356	In this mode the values for C<interval> and C<offset> are both being
1129	ignored. Instead, each time the periodic watcher gets scheduled, the	2357	ignored. Instead, each time the periodic watcher gets scheduled, the
1130	reschedule callback will be called with the watcher as first, and the	2358	reschedule callback will be called with the watcher as first, and the
1131	current time as second argument.	2359	current time as second argument.
1132		2360
1133	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2361	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1134	ever, or make any event loop modifications>. If you need to stop it,	2362	or make ANY other event loop modifications whatsoever, unless explicitly
1135	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2363	allowed by documentation here>.
1136	starting a prepare watcher).
1137		2364
		2365	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2366	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2367	only event loop modification you are allowed to do).
		2368
1138	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2369	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1139	ev_tstamp now)>, e.g.:	2370	*w, ev_tstamp now)>, e.g.:
1140		2371
		2372	static ev_tstamp
1141	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2373	my_rescheduler (ev_periodic *w, ev_tstamp now)
1142	{	2374	{
1143	return now + 60.;	2375	return now + 60.;
1144	}	2376	}
1145		2377
1146	It must return the next time to trigger, based on the passed time value	2378	It must return the next time to trigger, based on the passed time value
1147	(that is, the lowest time value larger than to the second argument). It	2379	(that is, the lowest time value larger than to the second argument). It
1148	will usually be called just before the callback will be triggered, but	2380	will usually be called just before the callback will be triggered, but
1149	might be called at other times, too.	2381	might be called at other times, too.
1150		2382
1151	NOTE: I<< This callback must always return a time that is later than the	2383	NOTE: I<< This callback must always return a time that is higher than or
1152	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2384	equal to the passed C<now> value >>.
1153		2385
1154	This can be used to create very complex timers, such as a timer that	2386	This can be used to create very complex timers, such as a timer that
1155	triggers on each midnight, local time. To do this, you would calculate the	2387	triggers on "next midnight, local time". To do this, you would calculate
1156	next midnight after C<now> and return the timestamp value for this. How	2388	the next midnight after C<now> and return the timestamp value for
1157	you do this is, again, up to you (but it is not trivial, which is the main	2389	this. Here is a (completely untested, no error checking) example on how to
1158	reason I omitted it as an example).	2390	do this:
		2391
		2392	#include <time.h>
		2393
		2394	static ev_tstamp
		2395	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2396	{
		2397	time_t tnow = (time_t)now;
		2398	struct tm tm;
		2399	localtime_r (&tnow, &tm);
		2400
		2401	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2402	++tm.tm_mday; // midnight next day
		2403
		2404	return mktime (&tm);
		2405	}
		2406
		2407	Note: this code might run into trouble on days that have more then two
		2408	midnights (beginning and end).
1159		2409
1160	=back	2410	=back
1161		2411
1162	=item ev_periodic_again (loop, ev_periodic *)	2412	=item ev_periodic_again (loop, ev_periodic *)
1163		2413
1164	Simply stops and restarts the periodic watcher again. This is only useful	2414	Simply stops and restarts the periodic watcher again. This is only useful
1165	when you changed some parameters or the reschedule callback would return	2415	when you changed some parameters or the reschedule callback would return
1166	a different time than the last time it was called (e.g. in a crond like	2416	a different time than the last time it was called (e.g. in a crond like
1167	program when the crontabs have changed).	2417	program when the crontabs have changed).
1168		2418
		2419	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2420
		2421	When active, returns the absolute time that the watcher is supposed
		2422	to trigger next. This is not the same as the C<offset> argument to
		2423	C<ev_periodic_set>, but indeed works even in interval and manual
		2424	rescheduling modes.
		2425
		2426	=item ev_tstamp offset [read-write]
		2427
		2428	When repeating, this contains the offset value, otherwise this is the
		2429	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2430	although libev might modify this value for better numerical stability).
		2431
		2432	Can be modified any time, but changes only take effect when the periodic
		2433	timer fires or C<ev_periodic_again> is being called.
		2434
1169	=item ev_tstamp interval [read-write]	2435	=item ev_tstamp interval [read-write]
1170		2436
1171	The current interval value. Can be modified any time, but changes only	2437	The current interval value. Can be modified any time, but changes only
1172	take effect when the periodic timer fires or C<ev_periodic_again> is being	2438	take effect when the periodic timer fires or C<ev_periodic_again> is being
1173	called.	2439	called.
1174		2440
1175	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2441	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1176		2442
1177	The current reschedule callback, or C<0>, if this functionality is	2443	The current reschedule callback, or C<0>, if this functionality is
1178	switched off. Can be changed any time, but changes only take effect when	2444	switched off. Can be changed any time, but changes only take effect when
1179	the periodic timer fires or C<ev_periodic_again> is being called.	2445	the periodic timer fires or C<ev_periodic_again> is being called.
1180		2446
1181	=back	2447	=back
1182		2448
		2449	=head3 Examples
		2450
1183	Example: Call a callback every hour, or, more precisely, whenever the	2451	Example: Call a callback every hour, or, more precisely, whenever the
1184	system clock is divisible by 3600. The callback invocation times have	2452	system time is divisible by 3600. The callback invocation times have
1185	potentially a lot of jittering, but good long-term stability.	2453	potentially a lot of jitter, but good long-term stability.
1186		2454
1187	static void	2455	static void
1188	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2456	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1189	{	2457	{
1190	... its now a full hour (UTC, or TAI or whatever your clock follows)	2458	... its now a full hour (UTC, or TAI or whatever your clock follows)
1191	}	2459	}
1192		2460
1193	struct ev_periodic hourly_tick;	2461	ev_periodic hourly_tick;
1194	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2462	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1195	ev_periodic_start (loop, &hourly_tick);	2463	ev_periodic_start (loop, &hourly_tick);
1196		2464
1197	Example: The same as above, but use a reschedule callback to do it:	2465	Example: The same as above, but use a reschedule callback to do it:
1198		2466
1199	#include <math.h>	2467	#include <math.h>
1200		2468
1201	static ev_tstamp	2469	static ev_tstamp
1202	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2470	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1203	{	2471	{
1204	return fmod (now, 3600.) + 3600.;	2472	return now + (3600. - fmod (now, 3600.));
1205	}	2473	}
1206		2474
1207	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2475	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1208		2476
1209	Example: Call a callback every hour, starting now:	2477	Example: Call a callback every hour, starting now:
1210		2478
1211	struct ev_periodic hourly_tick;	2479	ev_periodic hourly_tick;
1212	ev_periodic_init (&hourly_tick, clock_cb,	2480	ev_periodic_init (&hourly_tick, clock_cb,
1213	fmod (ev_now (loop), 3600.), 3600., 0);	2481	fmod (ev_now (loop), 3600.), 3600., 0);
1214	ev_periodic_start (loop, &hourly_tick);	2482	ev_periodic_start (loop, &hourly_tick);
1215		2483
1216		2484
1217	=head2 C<ev_signal> - signal me when a signal gets signalled!	2485	=head2 C<ev_signal> - signal me when a signal gets signalled!
1218		2486
1219	Signal watchers will trigger an event when the process receives a specific	2487	Signal watchers will trigger an event when the process receives a specific
1220	signal one or more times. Even though signals are very asynchronous, libev	2488	signal one or more times. Even though signals are very asynchronous, libev
1221	will try it's best to deliver signals synchronously, i.e. as part of the	2489	will try its best to deliver signals synchronously, i.e. as part of the
1222	normal event processing, like any other event.	2490	normal event processing, like any other event.
1223		2491
		2492	If you want signals to be delivered truly asynchronously, just use
		2493	C<sigaction> as you would do without libev and forget about sharing
		2494	the signal. You can even use C<ev_async> from a signal handler to
		2495	synchronously wake up an event loop.
		2496
1224	You can configure as many watchers as you like per signal. Only when the	2497	You can configure as many watchers as you like for the same signal, but
1225	first watcher gets started will libev actually register a signal watcher	2498	only within the same loop, i.e. you can watch for C<SIGINT> in your
1226	with the kernel (thus it coexists with your own signal handlers as long	2499	default loop and for C<SIGIO> in another loop, but you cannot watch for
1227	as you don't register any with libev). Similarly, when the last signal	2500	C<SIGINT> in both the default loop and another loop at the same time. At
1228	watcher for a signal is stopped libev will reset the signal handler to	2501	the moment, C<SIGCHLD> is permanently tied to the default loop.
1229	SIG_DFL (regardless of what it was set to before).	2502
		2503	Only after the first watcher for a signal is started will libev actually
		2504	register something with the kernel. It thus coexists with your own signal
		2505	handlers as long as you don't register any with libev for the same signal.
		2506
		2507	If possible and supported, libev will install its handlers with
		2508	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2509	not be unduly interrupted. If you have a problem with system calls getting
		2510	interrupted by signals you can block all signals in an C<ev_check> watcher
		2511	and unblock them in an C<ev_prepare> watcher.
		2512
		2513	=head3 The special problem of inheritance over fork/execve/pthread_create
		2514
		2515	Both the signal mask (C<sigprocmask>) and the signal disposition
		2516	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2517	stopping it again), that is, libev might or might not block the signal,
		2518	and might or might not set or restore the installed signal handler (but
		2519	see C<EVFLAG_NOSIGMASK>).
		2520
		2521	While this does not matter for the signal disposition (libev never
		2522	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2523	C<execve>), this matters for the signal mask: many programs do not expect
		2524	certain signals to be blocked.
		2525
		2526	This means that before calling C<exec> (from the child) you should reset
		2527	the signal mask to whatever "default" you expect (all clear is a good
		2528	choice usually).
		2529
		2530	The simplest way to ensure that the signal mask is reset in the child is
		2531	to install a fork handler with C<pthread_atfork> that resets it. That will
		2532	catch fork calls done by libraries (such as the libc) as well.
		2533
		2534	In current versions of libev, the signal will not be blocked indefinitely
		2535	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2536	the window of opportunity for problems, it will not go away, as libev
		2537	I<has> to modify the signal mask, at least temporarily.
		2538
		2539	So I can't stress this enough: I<If you do not reset your signal mask when
		2540	you expect it to be empty, you have a race condition in your code>. This
		2541	is not a libev-specific thing, this is true for most event libraries.
		2542
		2543	=head3 The special problem of threads signal handling
		2544
		2545	POSIX threads has problematic signal handling semantics, specifically,
		2546	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2547	threads in a process block signals, which is hard to achieve.
		2548
		2549	When you want to use sigwait (or mix libev signal handling with your own
		2550	for the same signals), you can tackle this problem by globally blocking
		2551	all signals before creating any threads (or creating them with a fully set
		2552	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2553	loops. Then designate one thread as "signal receiver thread" which handles
		2554	these signals. You can pass on any signals that libev might be interested
		2555	in by calling C<ev_feed_signal>.
		2556
		2557	=head3 Watcher-Specific Functions and Data Members
1230		2558
1231	=over 4	2559	=over 4
1232		2560
1233	=item ev_signal_init (ev_signal *, callback, int signum)	2561	=item ev_signal_init (ev_signal *, callback, int signum)
1234		2562
…		…
1241		2569
1242	The signal the watcher watches out for.	2570	The signal the watcher watches out for.
1243		2571
1244	=back	2572	=back
1245		2573
		2574	=head3 Examples
		2575
		2576	Example: Try to exit cleanly on SIGINT.
		2577
		2578	static void
		2579	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2580	{
		2581	ev_break (loop, EVBREAK_ALL);
		2582	}
		2583
		2584	ev_signal signal_watcher;
		2585	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2586	ev_signal_start (loop, &signal_watcher);
		2587
1246		2588
1247	=head2 C<ev_child> - watch out for process status changes	2589	=head2 C<ev_child> - watch out for process status changes
1248		2590
1249	Child watchers trigger when your process receives a SIGCHLD in response to	2591	Child watchers trigger when your process receives a SIGCHLD in response to
1250	some child status changes (most typically when a child of yours dies).	2592	some child status changes (most typically when a child of yours dies or
		2593	exits). It is permissible to install a child watcher I<after> the child
		2594	has been forked (which implies it might have already exited), as long
		2595	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2596	forking and then immediately registering a watcher for the child is fine,
		2597	but forking and registering a watcher a few event loop iterations later or
		2598	in the next callback invocation is not.
		2599
		2600	Only the default event loop is capable of handling signals, and therefore
		2601	you can only register child watchers in the default event loop.
		2602
		2603	Due to some design glitches inside libev, child watchers will always be
		2604	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2605	libev)
		2606
		2607	=head3 Process Interaction
		2608
		2609	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2610	initialised. This is necessary to guarantee proper behaviour even if the
		2611	first child watcher is started after the child exits. The occurrence
		2612	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2613	synchronously as part of the event loop processing. Libev always reaps all
		2614	children, even ones not watched.
		2615
		2616	=head3 Overriding the Built-In Processing
		2617
		2618	Libev offers no special support for overriding the built-in child
		2619	processing, but if your application collides with libev's default child
		2620	handler, you can override it easily by installing your own handler for
		2621	C<SIGCHLD> after initialising the default loop, and making sure the
		2622	default loop never gets destroyed. You are encouraged, however, to use an
		2623	event-based approach to child reaping and thus use libev's support for
		2624	that, so other libev users can use C<ev_child> watchers freely.
		2625
		2626	=head3 Stopping the Child Watcher
		2627
		2628	Currently, the child watcher never gets stopped, even when the
		2629	child terminates, so normally one needs to stop the watcher in the
		2630	callback. Future versions of libev might stop the watcher automatically
		2631	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2632	problem).
		2633
		2634	=head3 Watcher-Specific Functions and Data Members
1251		2635
1252	=over 4	2636	=over 4
1253		2637
1254	=item ev_child_init (ev_child *, callback, int pid)	2638	=item ev_child_init (ev_child *, callback, int pid, int trace)
1255		2639
1256	=item ev_child_set (ev_child *, int pid)	2640	=item ev_child_set (ev_child *, int pid, int trace)
1257		2641
1258	Configures the watcher to wait for status changes of process C<pid> (or	2642	Configures the watcher to wait for status changes of process C<pid> (or
1259	I<any> process if C<pid> is specified as C<0>). The callback can look	2643	I<any> process if C<pid> is specified as C<0>). The callback can look
1260	at the C<rstatus> member of the C<ev_child> watcher structure to see	2644	at the C<rstatus> member of the C<ev_child> watcher structure to see
1261	the status word (use the macros from C<sys/wait.h> and see your systems	2645	the status word (use the macros from C<sys/wait.h> and see your systems
1262	C<waitpid> documentation). The C<rpid> member contains the pid of the	2646	C<waitpid> documentation). The C<rpid> member contains the pid of the
1263	process causing the status change.	2647	process causing the status change. C<trace> must be either C<0> (only
		2648	activate the watcher when the process terminates) or C<1> (additionally
		2649	activate the watcher when the process is stopped or continued).
1264		2650
1265	=item int pid [read-only]	2651	=item int pid [read-only]
1266		2652
1267	The process id this watcher watches out for, or C<0>, meaning any process id.	2653	The process id this watcher watches out for, or C<0>, meaning any process id.
1268		2654
…		…
1275	The process exit/trace status caused by C<rpid> (see your systems	2661	The process exit/trace status caused by C<rpid> (see your systems
1276	C<waitpid> and C<sys/wait.h> documentation for details).	2662	C<waitpid> and C<sys/wait.h> documentation for details).
1277		2663
1278	=back	2664	=back
1279		2665
1280	Example: Try to exit cleanly on SIGINT and SIGTERM.	2666	=head3 Examples
1281		2667
		2668	Example: C<fork()> a new process and install a child handler to wait for
		2669	its completion.
		2670
		2671	ev_child cw;
		2672
1282	static void	2673	static void
1283	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2674	child_cb (EV_P_ ev_child *w, int revents)
1284	{	2675	{
1285	ev_unloop (loop, EVUNLOOP_ALL);	2676	ev_child_stop (EV_A_ w);
		2677	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1286	}	2678	}
1287		2679
1288	struct ev_signal signal_watcher;	2680	pid_t pid = fork ();
1289	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2681
1290	ev_signal_start (loop, &sigint_cb);	2682	if (pid < 0)
		2683	// error
		2684	else if (pid == 0)
		2685	{
		2686	// the forked child executes here
		2687	exit (1);
		2688	}
		2689	else
		2690	{
		2691	ev_child_init (&cw, child_cb, pid, 0);
		2692	ev_child_start (EV_DEFAULT_ &cw);
		2693	}
1291		2694
1292		2695
1293	=head2 C<ev_stat> - did the file attributes just change?	2696	=head2 C<ev_stat> - did the file attributes just change?
1294		2697
1295	This watches a filesystem path for attribute changes. That is, it calls	2698	This watches a file system path for attribute changes. That is, it calls
1296	C<stat> regularly (or when the OS says it changed) and sees if it changed	2699	C<stat> on that path in regular intervals (or when the OS says it changed)
1297	compared to the last time, invoking the callback if it did.	2700	and sees if it changed compared to the last time, invoking the callback
		2701	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2702	happen after the watcher has been started will be reported.
1298		2703
1299	The path does not need to exist: changing from "path exists" to "path does	2704	The path does not need to exist: changing from "path exists" to "path does
1300	not exist" is a status change like any other. The condition "path does	2705	not exist" is a status change like any other. The condition "path does not
1301	not exist" is signified by the C<st_nlink> field being zero (which is	2706	exist" (or more correctly "path cannot be stat'ed") is signified by the
1302	otherwise always forced to be at least one) and all the other fields of	2707	C<st_nlink> field being zero (which is otherwise always forced to be at
1303	the stat buffer having unspecified contents.	2708	least one) and all the other fields of the stat buffer having unspecified
		2709	contents.
1304		2710
1305	The path I<should> be absolute and I<must not> end in a slash. If it is	2711	The path I<must not> end in a slash or contain special components such as
		2712	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1306	relative and your working directory changes, the behaviour is undefined.	2713	your working directory changes, then the behaviour is undefined.
1307		2714
1308	Since there is no standard to do this, the portable implementation simply	2715	Since there is no portable change notification interface available, the
1309	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2716	portable implementation simply calls C<stat(2)> regularly on the path
1310	can specify a recommended polling interval for this case. If you specify	2717	to see if it changed somehow. You can specify a recommended polling
1311	a polling interval of C<0> (highly recommended!) then a I<suitable,	2718	interval for this case. If you specify a polling interval of C<0> (highly
1312	unspecified default> value will be used (which you can expect to be around	2719	recommended!) then a I<suitable, unspecified default> value will be used
1313	five seconds, although this might change dynamically). Libev will also	2720	(which you can expect to be around five seconds, although this might
1314	impose a minimum interval which is currently around C<0.1>, but thats	2721	change dynamically). Libev will also impose a minimum interval which is
1315	usually overkill.	2722	currently around C<0.1>, but that's usually overkill.
1316		2723
1317	This watcher type is not meant for massive numbers of stat watchers,	2724	This watcher type is not meant for massive numbers of stat watchers,
1318	as even with OS-supported change notifications, this can be	2725	as even with OS-supported change notifications, this can be
1319	resource-intensive.	2726	resource-intensive.
1320		2727
1321	At the time of this writing, only the Linux inotify interface is	2728	At the time of this writing, the only OS-specific interface implemented
1322	implemented (implementing kqueue support is left as an exercise for the	2729	is the Linux inotify interface (implementing kqueue support is left as an
1323	reader). Inotify will be used to give hints only and should not change the	2730	exercise for the reader. Note, however, that the author sees no way of
1324	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2731	implementing C<ev_stat> semantics with kqueue, except as a hint).
1325	to fall back to regular polling again even with inotify, but changes are	2732
1326	usually detected immediately, and if the file exists there will be no	2733	=head3 ABI Issues (Largefile Support)
1327	polling.	2734
		2735	Libev by default (unless the user overrides this) uses the default
		2736	compilation environment, which means that on systems with large file
		2737	support disabled by default, you get the 32 bit version of the stat
		2738	structure. When using the library from programs that change the ABI to
		2739	use 64 bit file offsets the programs will fail. In that case you have to
		2740	compile libev with the same flags to get binary compatibility. This is
		2741	obviously the case with any flags that change the ABI, but the problem is
		2742	most noticeably displayed with ev_stat and large file support.
		2743
		2744	The solution for this is to lobby your distribution maker to make large
		2745	file interfaces available by default (as e.g. FreeBSD does) and not
		2746	optional. Libev cannot simply switch on large file support because it has
		2747	to exchange stat structures with application programs compiled using the
		2748	default compilation environment.
		2749
		2750	=head3 Inotify and Kqueue
		2751
		2752	When C<inotify (7)> support has been compiled into libev and present at
		2753	runtime, it will be used to speed up change detection where possible. The
		2754	inotify descriptor will be created lazily when the first C<ev_stat>
		2755	watcher is being started.
		2756
		2757	Inotify presence does not change the semantics of C<ev_stat> watchers
		2758	except that changes might be detected earlier, and in some cases, to avoid
		2759	making regular C<stat> calls. Even in the presence of inotify support
		2760	there are many cases where libev has to resort to regular C<stat> polling,
		2761	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2762	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2763	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2764	xfs are fully working) libev usually gets away without polling.
		2765
		2766	There is no support for kqueue, as apparently it cannot be used to
		2767	implement this functionality, due to the requirement of having a file
		2768	descriptor open on the object at all times, and detecting renames, unlinks
		2769	etc. is difficult.
		2770
		2771	=head3 C<stat ()> is a synchronous operation
		2772
		2773	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2774	the process. The exception are C<ev_stat> watchers - those call C<stat
		2775	()>, which is a synchronous operation.
		2776
		2777	For local paths, this usually doesn't matter: unless the system is very
		2778	busy or the intervals between stat's are large, a stat call will be fast,
		2779	as the path data is usually in memory already (except when starting the
		2780	watcher).
		2781
		2782	For networked file systems, calling C<stat ()> can block an indefinite
		2783	time due to network issues, and even under good conditions, a stat call
		2784	often takes multiple milliseconds.
		2785
		2786	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2787	paths, although this is fully supported by libev.
		2788
		2789	=head3 The special problem of stat time resolution
		2790
		2791	The C<stat ()> system call only supports full-second resolution portably,
		2792	and even on systems where the resolution is higher, most file systems
		2793	still only support whole seconds.
		2794
		2795	That means that, if the time is the only thing that changes, you can
		2796	easily miss updates: on the first update, C<ev_stat> detects a change and
		2797	calls your callback, which does something. When there is another update
		2798	within the same second, C<ev_stat> will be unable to detect unless the
		2799	stat data does change in other ways (e.g. file size).
		2800
		2801	The solution to this is to delay acting on a change for slightly more
		2802	than a second (or till slightly after the next full second boundary), using
		2803	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2804	ev_timer_again (loop, w)>).
		2805
		2806	The C<.02> offset is added to work around small timing inconsistencies
		2807	of some operating systems (where the second counter of the current time
		2808	might be be delayed. One such system is the Linux kernel, where a call to
		2809	C<gettimeofday> might return a timestamp with a full second later than
		2810	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2811	update file times then there will be a small window where the kernel uses
		2812	the previous second to update file times but libev might already execute
		2813	the timer callback).
		2814
		2815	=head3 Watcher-Specific Functions and Data Members
1328		2816
1329	=over 4	2817	=over 4
1330		2818
1331	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2819	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1332		2820
…		…
1336	C<path>. The C<interval> is a hint on how quickly a change is expected to	2824	C<path>. The C<interval> is a hint on how quickly a change is expected to
1337	be detected and should normally be specified as C<0> to let libev choose	2825	be detected and should normally be specified as C<0> to let libev choose
1338	a suitable value. The memory pointed to by C<path> must point to the same	2826	a suitable value. The memory pointed to by C<path> must point to the same
1339	path for as long as the watcher is active.	2827	path for as long as the watcher is active.
1340		2828
1341	The callback will be receive C<EV_STAT> when a change was detected,	2829	The callback will receive an C<EV_STAT> event when a change was detected,
1342	relative to the attributes at the time the watcher was started (or the	2830	relative to the attributes at the time the watcher was started (or the
1343	last change was detected).	2831	last change was detected).
1344		2832
1345	=item ev_stat_stat (ev_stat *)	2833	=item ev_stat_stat (loop, ev_stat *)
1346		2834
1347	Updates the stat buffer immediately with new values. If you change the	2835	Updates the stat buffer immediately with new values. If you change the
1348	watched path in your callback, you could call this fucntion to avoid	2836	watched path in your callback, you could call this function to avoid
1349	detecting this change (while introducing a race condition). Can also be	2837	detecting this change (while introducing a race condition if you are not
1350	useful simply to find out the new values.	2838	the only one changing the path). Can also be useful simply to find out the
		2839	new values.
1351		2840
1352	=item ev_statdata attr [read-only]	2841	=item ev_statdata attr [read-only]
1353		2842
1354	The most-recently detected attributes of the file. Although the type is of	2843	The most-recently detected attributes of the file. Although the type is
1355	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2844	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1356	suitable for your system. If the C<st_nlink> member is C<0>, then there	2845	suitable for your system, but you can only rely on the POSIX-standardised
		2846	members to be present. If the C<st_nlink> member is C<0>, then there was
1357	was some error while C<stat>ing the file.	2847	some error while C<stat>ing the file.
1358		2848
1359	=item ev_statdata prev [read-only]	2849	=item ev_statdata prev [read-only]
1360		2850
1361	The previous attributes of the file. The callback gets invoked whenever	2851	The previous attributes of the file. The callback gets invoked whenever
1362	C<prev> != C<attr>.	2852	C<prev> != C<attr>, or, more precisely, one or more of these members
		2853	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2854	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1363		2855
1364	=item ev_tstamp interval [read-only]	2856	=item ev_tstamp interval [read-only]
1365		2857
1366	The specified interval.	2858	The specified interval.
1367		2859
1368	=item const char *path [read-only]	2860	=item const char *path [read-only]
1369		2861
1370	The filesystem path that is being watched.	2862	The file system path that is being watched.
1371		2863
1372	=back	2864	=back
1373		2865
		2866	=head3 Examples
		2867
1374	Example: Watch C</etc/passwd> for attribute changes.	2868	Example: Watch C</etc/passwd> for attribute changes.
1375		2869
1376	static void	2870	static void
1377	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2871	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1378	{	2872	{
1379	/* /etc/passwd changed in some way */	2873	/* /etc/passwd changed in some way */
1380	if (w->attr.st_nlink)	2874	if (w->attr.st_nlink)
1381	{	2875	{
1382	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2876	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1383	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2877	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1384	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2878	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1385	}	2879	}
1386	else	2880	else
1387	/* you shalt not abuse printf for puts */	2881	/* you shalt not abuse printf for puts */
1388	puts ("wow, /etc/passwd is not there, expect problems. "	2882	puts ("wow, /etc/passwd is not there, expect problems. "
1389	"if this is windows, they already arrived\n");	2883	"if this is windows, they already arrived\n");
1390	}	2884	}
1391		2885
1392	...	2886	...
1393	ev_stat passwd;	2887	ev_stat passwd;
1394		2888
1395	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2889	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1396	ev_stat_start (loop, &passwd);	2890	ev_stat_start (loop, &passwd);
		2891
		2892	Example: Like above, but additionally use a one-second delay so we do not
		2893	miss updates (however, frequent updates will delay processing, too, so
		2894	one might do the work both on C<ev_stat> callback invocation I<and> on
		2895	C<ev_timer> callback invocation).
		2896
		2897	static ev_stat passwd;
		2898	static ev_timer timer;
		2899
		2900	static void
		2901	timer_cb (EV_P_ ev_timer *w, int revents)
		2902	{
		2903	ev_timer_stop (EV_A_ w);
		2904
		2905	/* now it's one second after the most recent passwd change */
		2906	}
		2907
		2908	static void
		2909	stat_cb (EV_P_ ev_stat *w, int revents)
		2910	{
		2911	/* reset the one-second timer */
		2912	ev_timer_again (EV_A_ &timer);
		2913	}
		2914
		2915	...
		2916	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2917	ev_stat_start (loop, &passwd);
		2918	ev_timer_init (&timer, timer_cb, 0., 1.02);
1397		2919
1398		2920
1399	=head2 C<ev_idle> - when you've got nothing better to do...	2921	=head2 C<ev_idle> - when you've got nothing better to do...
1400		2922
1401	Idle watchers trigger events when no other events of the same or higher	2923	Idle watchers trigger events when no other events of the same or higher
1402	priority are pending (prepare, check and other idle watchers do not	2924	priority are pending (prepare, check and other idle watchers do not count
1403	count).	2925	as receiving "events").
1404		2926
1405	That is, as long as your process is busy handling sockets or timeouts	2927	That is, as long as your process is busy handling sockets or timeouts
1406	(or even signals, imagine) of the same or higher priority it will not be	2928	(or even signals, imagine) of the same or higher priority it will not be
1407	triggered. But when your process is idle (or only lower-priority watchers	2929	triggered. But when your process is idle (or only lower-priority watchers
1408	are pending), the idle watchers are being called once per event loop	2930	are pending), the idle watchers are being called once per event loop
…		…
1415	Apart from keeping your process non-blocking (which is a useful	2937	Apart from keeping your process non-blocking (which is a useful
1416	effect on its own sometimes), idle watchers are a good place to do	2938	effect on its own sometimes), idle watchers are a good place to do
1417	"pseudo-background processing", or delay processing stuff to after the	2939	"pseudo-background processing", or delay processing stuff to after the
1418	event loop has handled all outstanding events.	2940	event loop has handled all outstanding events.
1419		2941
		2942	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2943
		2944	As long as there is at least one active idle watcher, libev will never
		2945	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2946	For this to work, the idle watcher doesn't need to be invoked at all - the
		2947	lowest priority will do.
		2948
		2949	This mode of operation can be useful together with an C<ev_check> watcher,
		2950	to do something on each event loop iteration - for example to balance load
		2951	between different connections.
		2952
		2953	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2954	example.
		2955
		2956	=head3 Watcher-Specific Functions and Data Members
		2957
1420	=over 4	2958	=over 4
1421		2959
1422	=item ev_idle_init (ev_signal *, callback)	2960	=item ev_idle_init (ev_idle *, callback)
1423		2961
1424	Initialises and configures the idle watcher - it has no parameters of any	2962	Initialises and configures the idle watcher - it has no parameters of any
1425	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2963	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1426	believe me.	2964	believe me.
1427		2965
1428	=back	2966	=back
1429		2967
		2968	=head3 Examples
		2969
1430	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2970	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1431	callback, free it. Also, use no error checking, as usual.	2971	callback, free it. Also, use no error checking, as usual.
1432		2972
1433	static void	2973	static void
1434	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2974	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1435	{	2975	{
		2976	// stop the watcher
		2977	ev_idle_stop (loop, w);
		2978
		2979	// now we can free it
1436	free (w);	2980	free (w);
		2981
1437	// now do something you wanted to do when the program has	2982	// now do something you wanted to do when the program has
1438	// no longer asnything immediate to do.	2983	// no longer anything immediate to do.
1439	}	2984	}
1440		2985
1441	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2986	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1442	ev_idle_init (idle_watcher, idle_cb);	2987	ev_idle_init (idle_watcher, idle_cb);
1443	ev_idle_start (loop, idle_cb);	2988	ev_idle_start (loop, idle_watcher);
1444		2989
1445		2990
1446	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2991	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1447		2992
1448	Prepare and check watchers are usually (but not always) used in tandem:	2993	Prepare and check watchers are often (but not always) used in pairs:
1449	prepare watchers get invoked before the process blocks and check watchers	2994	prepare watchers get invoked before the process blocks and check watchers
1450	afterwards.	2995	afterwards.
1451		2996
1452	You I<must not> call C<ev_loop> or similar functions that enter	2997	You I<must not> call C<ev_run> (or similar functions that enter the
1453	the current event loop from either C<ev_prepare> or C<ev_check>	2998	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
1454	watchers. Other loops than the current one are fine, however. The	2999	C<ev_check> watchers. Other loops than the current one are fine,
1455	rationale behind this is that you do not need to check for recursion in	3000	however. The rationale behind this is that you do not need to check
1456	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	3001	for recursion in those watchers, i.e. the sequence will always be
1457	C<ev_check> so if you have one watcher of each kind they will always be	3002	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
1458	called in pairs bracketing the blocking call.	3003	kind they will always be called in pairs bracketing the blocking call.
1459		3004
1460	Their main purpose is to integrate other event mechanisms into libev and	3005	Their main purpose is to integrate other event mechanisms into libev and
1461	their use is somewhat advanced. This could be used, for example, to track	3006	their use is somewhat advanced. They could be used, for example, to track
1462	variable changes, implement your own watchers, integrate net-snmp or a	3007	variable changes, implement your own watchers, integrate net-snmp or a
1463	coroutine library and lots more. They are also occasionally useful if	3008	coroutine library and lots more. They are also occasionally useful if
1464	you cache some data and want to flush it before blocking (for example,	3009	you cache some data and want to flush it before blocking (for example,
1465	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	3010	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1466	watcher).	3011	watcher).
1467		3012
1468	This is done by examining in each prepare call which file descriptors need	3013	This is done by examining in each prepare call which file descriptors
1469	to be watched by the other library, registering C<ev_io> watchers for	3014	need to be watched by the other library, registering C<ev_io> watchers
1470	them and starting an C<ev_timer> watcher for any timeouts (many libraries	3015	for them and starting an C<ev_timer> watcher for any timeouts (many
1471	provide just this functionality). Then, in the check watcher you check for	3016	libraries provide exactly this functionality). Then, in the check watcher,
1472	any events that occured (by checking the pending status of all watchers	3017	you check for any events that occurred (by checking the pending status
1473	and stopping them) and call back into the library. The I/O and timer	3018	of all watchers and stopping them) and call back into the library. The
1474	callbacks will never actually be called (but must be valid nevertheless,	3019	I/O and timer callbacks will never actually be called (but must be valid
1475	because you never know, you know?).	3020	nevertheless, because you never know, you know?).
1476		3021
1477	As another example, the Perl Coro module uses these hooks to integrate	3022	As another example, the Perl Coro module uses these hooks to integrate
1478	coroutines into libev programs, by yielding to other active coroutines	3023	coroutines into libev programs, by yielding to other active coroutines
1479	during each prepare and only letting the process block if no coroutines	3024	during each prepare and only letting the process block if no coroutines
1480	are ready to run (it's actually more complicated: it only runs coroutines	3025	are ready to run (it's actually more complicated: it only runs coroutines
1481	with priority higher than or equal to the event loop and one coroutine	3026	with priority higher than or equal to the event loop and one coroutine
1482	of lower priority, but only once, using idle watchers to keep the event	3027	of lower priority, but only once, using idle watchers to keep the event
1483	loop from blocking if lower-priority coroutines are active, thus mapping	3028	loop from blocking if lower-priority coroutines are active, thus mapping
1484	low-priority coroutines to idle/background tasks).	3029	low-priority coroutines to idle/background tasks).
1485		3030
		3031	When used for this purpose, it is recommended to give C<ev_check> watchers
		3032	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		3033	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3034	watchers).
		3035
		3036	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		3037	activate ("feed") events into libev. While libev fully supports this, they
		3038	might get executed before other C<ev_check> watchers did their job. As
		3039	C<ev_check> watchers are often used to embed other (non-libev) event
		3040	loops those other event loops might be in an unusable state until their
		3041	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		3042	others).
		3043
		3044	=head3 Abusing an C<ev_check> watcher for its side-effect
		3045
		3046	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3047	useful because they are called once per event loop iteration. For
		3048	example, if you want to handle a large number of connections fairly, you
		3049	normally only do a bit of work for each active connection, and if there
		3050	is more work to do, you wait for the next event loop iteration, so other
		3051	connections have a chance of making progress.
		3052
		3053	Using an C<ev_check> watcher is almost enough: it will be called on the
		3054	next event loop iteration. However, that isn't as soon as possible -
		3055	without external events, your C<ev_check> watcher will not be invoked.
		3056
		3057	This is where C<ev_idle> watchers come in handy - all you need is a
		3058	single global idle watcher that is active as long as you have one active
		3059	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3060	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3061	invoked. Neither watcher alone can do that.
		3062
		3063	=head3 Watcher-Specific Functions and Data Members
		3064
1486	=over 4	3065	=over 4
1487		3066
1488	=item ev_prepare_init (ev_prepare *, callback)	3067	=item ev_prepare_init (ev_prepare *, callback)
1489		3068
1490	=item ev_check_init (ev_check *, callback)	3069	=item ev_check_init (ev_check *, callback)
1491		3070
1492	Initialises and configures the prepare or check watcher - they have no	3071	Initialises and configures the prepare or check watcher - they have no
1493	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	3072	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1494	macros, but using them is utterly, utterly and completely pointless.	3073	macros, but using them is utterly, utterly, utterly and completely
		3074	pointless.
1495		3075
1496	=back	3076	=back
1497		3077
1498	Example: To include a library such as adns, you would add IO watchers	3078	=head3 Examples
1499	and a timeout watcher in a prepare handler, as required by libadns, and	3079
		3080	There are a number of principal ways to embed other event loops or modules
		3081	into libev. Here are some ideas on how to include libadns into libev
		3082	(there is a Perl module named C<EV::ADNS> that does this, which you could
		3083	use as a working example. Another Perl module named C<EV::Glib> embeds a
		3084	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		3085	Glib event loop).
		3086
		3087	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1500	in a check watcher, destroy them and call into libadns. What follows is	3088	and in a check watcher, destroy them and call into libadns. What follows
1501	pseudo-code only of course:	3089	is pseudo-code only of course. This requires you to either use a low
		3090	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		3091	the callbacks for the IO/timeout watchers might not have been called yet.
1502		3092
1503	static ev_io iow [nfd];	3093	static ev_io iow [nfd];
1504	static ev_timer tw;	3094	static ev_timer tw;
1505		3095
1506	static void	3096	static void
1507	io_cb (ev_loop *loop, ev_io *w, int revents)	3097	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1508	{	3098	{
1509	// set the relevant poll flags
1510	// could also call adns_processreadable etc. here
1511	struct pollfd *fd = (struct pollfd *)w->data;
1512	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1513	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1514	}	3099	}
1515		3100
1516	// create io watchers for each fd and a timer before blocking	3101	// create io watchers for each fd and a timer before blocking
1517	static void	3102	static void
1518	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3103	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1519	{	3104	{
1520	int timeout = 3600000;	3105	int timeout = 3600000;
1521	struct pollfd fds [nfd];	3106	struct pollfd fds [nfd];
1522	// actual code will need to loop here and realloc etc.	3107	// actual code will need to loop here and realloc etc.
1523	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3108	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1524		3109
1525	/* the callback is illegal, but won't be called as we stop during check */	3110	/* the callback is illegal, but won't be called as we stop during check */
1526	ev_timer_init (&tw, 0, timeout * 1e-3);	3111	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1527	ev_timer_start (loop, &tw);	3112	ev_timer_start (loop, &tw);
1528		3113
1529	// create on ev_io per pollfd	3114	// create one ev_io per pollfd
1530	for (int i = 0; i < nfd; ++i)	3115	for (int i = 0; i < nfd; ++i)
1531	{	3116	{
1532	ev_io_init (iow + i, io_cb, fds [i].fd,	3117	ev_io_init (iow + i, io_cb, fds [i].fd,
1533	((fds [i].events & POLLIN ? EV_READ : 0)	3118	((fds [i].events & POLLIN ? EV_READ : 0)
1534	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	3119	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1535		3120
1536	fds [i].revents = 0;	3121	fds [i].revents = 0;
1537	iow [i].data = fds + i;
1538	ev_io_start (loop, iow + i);	3122	ev_io_start (loop, iow + i);
1539	}	3123	}
1540	}	3124	}
1541		3125
1542	// stop all watchers after blocking	3126	// stop all watchers after blocking
1543	static void	3127	static void
1544	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3128	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1545	{	3129	{
1546	ev_timer_stop (loop, &tw);	3130	ev_timer_stop (loop, &tw);
1547		3131
1548	for (int i = 0; i < nfd; ++i)	3132	for (int i = 0; i < nfd; ++i)
		3133	{
		3134	// set the relevant poll flags
		3135	// could also call adns_processreadable etc. here
		3136	struct pollfd *fd = fds + i;
		3137	int revents = ev_clear_pending (iow + i);
		3138	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		3139	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		3140
		3141	// now stop the watcher
1549	ev_io_stop (loop, iow + i);	3142	ev_io_stop (loop, iow + i);
		3143	}
1550		3144
1551	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3145	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1552	}	3146	}
		3147
		3148	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		3149	in the prepare watcher and would dispose of the check watcher.
		3150
		3151	Method 3: If the module to be embedded supports explicit event
		3152	notification (libadns does), you can also make use of the actual watcher
		3153	callbacks, and only destroy/create the watchers in the prepare watcher.
		3154
		3155	static void
		3156	timer_cb (EV_P_ ev_timer *w, int revents)
		3157	{
		3158	adns_state ads = (adns_state)w->data;
		3159	update_now (EV_A);
		3160
		3161	adns_processtimeouts (ads, &tv_now);
		3162	}
		3163
		3164	static void
		3165	io_cb (EV_P_ ev_io *w, int revents)
		3166	{
		3167	adns_state ads = (adns_state)w->data;
		3168	update_now (EV_A);
		3169
		3170	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		3171	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		3172	}
		3173
		3174	// do not ever call adns_afterpoll
		3175
		3176	Method 4: Do not use a prepare or check watcher because the module you
		3177	want to embed is not flexible enough to support it. Instead, you can
		3178	override their poll function. The drawback with this solution is that the
		3179	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		3180	this approach, effectively embedding EV as a client into the horrible
		3181	libglib event loop.
		3182
		3183	static gint
		3184	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		3185	{
		3186	int got_events = 0;
		3187
		3188	for (n = 0; n < nfds; ++n)
		3189	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		3190
		3191	if (timeout >= 0)
		3192	// create/start timer
		3193
		3194	// poll
		3195	ev_run (EV_A_ 0);
		3196
		3197	// stop timer again
		3198	if (timeout >= 0)
		3199	ev_timer_stop (EV_A_ &to);
		3200
		3201	// stop io watchers again - their callbacks should have set
		3202	for (n = 0; n < nfds; ++n)
		3203	ev_io_stop (EV_A_ iow [n]);
		3204
		3205	return got_events;
		3206	}
1553		3207
1554		3208
1555	=head2 C<ev_embed> - when one backend isn't enough...	3209	=head2 C<ev_embed> - when one backend isn't enough...
1556		3210
1557	This is a rather advanced watcher type that lets you embed one event loop	3211	This is a rather advanced watcher type that lets you embed one event loop
…		…
1563	prioritise I/O.	3217	prioritise I/O.
1564		3218
1565	As an example for a bug workaround, the kqueue backend might only support	3219	As an example for a bug workaround, the kqueue backend might only support
1566	sockets on some platform, so it is unusable as generic backend, but you	3220	sockets on some platform, so it is unusable as generic backend, but you
1567	still want to make use of it because you have many sockets and it scales	3221	still want to make use of it because you have many sockets and it scales
1568	so nicely. In this case, you would create a kqueue-based loop and embed it	3222	so nicely. In this case, you would create a kqueue-based loop and embed
1569	into your default loop (which might use e.g. poll). Overall operation will	3223	it into your default loop (which might use e.g. poll). Overall operation
1570	be a bit slower because first libev has to poll and then call kevent, but	3224	will be a bit slower because first libev has to call C<poll> and then
1571	at least you can use both at what they are best.	3225	C<kevent>, but at least you can use both mechanisms for what they are
		3226	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1572		3227
1573	As for prioritising I/O: rarely you have the case where some fds have	3228	As for prioritising I/O: under rare circumstances you have the case where
1574	to be watched and handled very quickly (with low latency), and even	3229	some fds have to be watched and handled very quickly (with low latency),
1575	priorities and idle watchers might have too much overhead. In this case	3230	and even priorities and idle watchers might have too much overhead. In
1576	you would put all the high priority stuff in one loop and all the rest in	3231	this case you would put all the high priority stuff in one loop and all
1577	a second one, and embed the second one in the first.	3232	the rest in a second one, and embed the second one in the first.
1578		3233
1579	As long as the watcher is active, the callback will be invoked every time	3234	As long as the watcher is active, the callback will be invoked every
1580	there might be events pending in the embedded loop. The callback must then	3235	time there might be events pending in the embedded loop. The callback
1581	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3236	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1582	their callbacks (you could also start an idle watcher to give the embedded	3237	sweep and invoke their callbacks (the callback doesn't need to invoke the
1583	loop strictly lower priority for example). You can also set the callback	3238	C<ev_embed_sweep> function directly, it could also start an idle watcher
1584	to C<0>, in which case the embed watcher will automatically execute the	3239	to give the embedded loop strictly lower priority for example).
1585	embedded loop sweep.
1586		3240
1587	As long as the watcher is started it will automatically handle events. The	3241	You can also set the callback to C<0>, in which case the embed watcher
1588	callback will be invoked whenever some events have been handled. You can	3242	will automatically execute the embedded loop sweep whenever necessary.
1589	set the callback to C<0> to avoid having to specify one if you are not
1590	interested in that.
1591		3243
1592	Also, there have not currently been made special provisions for forking:	3244	Fork detection will be handled transparently while the C<ev_embed> watcher
1593	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3245	is active, i.e., the embedded loop will automatically be forked when the
1594	but you will also have to stop and restart any C<ev_embed> watchers	3246	embedding loop forks. In other cases, the user is responsible for calling
1595	yourself.	3247	C<ev_loop_fork> on the embedded loop.
1596		3248
1597	Unfortunately, not all backends are embeddable, only the ones returned by	3249	Unfortunately, not all backends are embeddable: only the ones returned by
1598	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3250	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1599	portable one.	3251	portable one.
1600		3252
1601	So when you want to use this feature you will always have to be prepared	3253	So when you want to use this feature you will always have to be prepared
1602	that you cannot get an embeddable loop. The recommended way to get around	3254	that you cannot get an embeddable loop. The recommended way to get around
1603	this is to have a separate variables for your embeddable loop, try to	3255	this is to have a separate variables for your embeddable loop, try to
1604	create it, and if that fails, use the normal loop for everything:	3256	create it, and if that fails, use the normal loop for everything.
1605		3257
1606	struct ev_loop *loop_hi = ev_default_init (0);	3258	=head3 C<ev_embed> and fork
1607	struct ev_loop *loop_lo = 0;
1608	struct ev_embed embed;
1609
1610	// see if there is a chance of getting one that works
1611	// (remember that a flags value of 0 means autodetection)
1612	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1613	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1614	: 0;
1615		3259
1616	// if we got one, then embed it, otherwise default to loop_hi	3260	While the C<ev_embed> watcher is running, forks in the embedding loop will
1617	if (loop_lo)	3261	automatically be applied to the embedded loop as well, so no special
1618	{	3262	fork handling is required in that case. When the watcher is not running,
1619	ev_embed_init (&embed, 0, loop_lo);	3263	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1620	ev_embed_start (loop_hi, &embed);	3264	as applicable.
1621	}	3265
1622	else	3266	=head3 Watcher-Specific Functions and Data Members
1623	loop_lo = loop_hi;
1624		3267
1625	=over 4	3268	=over 4
1626		3269
1627	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3270	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1628		3271
1629	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3272	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
1630		3273
1631	Configures the watcher to embed the given loop, which must be	3274	Configures the watcher to embed the given loop, which must be
1632	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3275	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1633	invoked automatically, otherwise it is the responsibility of the callback	3276	invoked automatically, otherwise it is the responsibility of the callback
1634	to invoke it (it will continue to be called until the sweep has been done,	3277	to invoke it (it will continue to be called until the sweep has been done,
1635	if you do not want thta, you need to temporarily stop the embed watcher).	3278	if you do not want that, you need to temporarily stop the embed watcher).
1636		3279
1637	=item ev_embed_sweep (loop, ev_embed *)	3280	=item ev_embed_sweep (loop, ev_embed *)
1638		3281
1639	Make a single, non-blocking sweep over the embedded loop. This works	3282	Make a single, non-blocking sweep over the embedded loop. This works
1640	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3283	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1641	apropriate way for embedded loops.	3284	appropriate way for embedded loops.
1642		3285
1643	=item struct ev_loop *loop [read-only]	3286	=item struct ev_loop *other [read-only]
1644		3287
1645	The embedded event loop.	3288	The embedded event loop.
1646		3289
1647	=back	3290	=back
		3291
		3292	=head3 Examples
		3293
		3294	Example: Try to get an embeddable event loop and embed it into the default
		3295	event loop. If that is not possible, use the default loop. The default
		3296	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3297	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3298	used).
		3299
		3300	struct ev_loop *loop_hi = ev_default_init (0);
		3301	struct ev_loop *loop_lo = 0;
		3302	ev_embed embed;
		3303
		3304	// see if there is a chance of getting one that works
		3305	// (remember that a flags value of 0 means autodetection)
		3306	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3307	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3308	: 0;
		3309
		3310	// if we got one, then embed it, otherwise default to loop_hi
		3311	if (loop_lo)
		3312	{
		3313	ev_embed_init (&embed, 0, loop_lo);
		3314	ev_embed_start (loop_hi, &embed);
		3315	}
		3316	else
		3317	loop_lo = loop_hi;
		3318
		3319	Example: Check if kqueue is available but not recommended and create
		3320	a kqueue backend for use with sockets (which usually work with any
		3321	kqueue implementation). Store the kqueue/socket-only event loop in
		3322	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3323
		3324	struct ev_loop *loop = ev_default_init (0);
		3325	struct ev_loop *loop_socket = 0;
		3326	ev_embed embed;
		3327
		3328	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3329	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3330	{
		3331	ev_embed_init (&embed, 0, loop_socket);
		3332	ev_embed_start (loop, &embed);
		3333	}
		3334
		3335	if (!loop_socket)
		3336	loop_socket = loop;
		3337
		3338	// now use loop_socket for all sockets, and loop for everything else
1648		3339
1649		3340
1650	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3341	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1651		3342
1652	Fork watchers are called when a C<fork ()> was detected (usually because	3343	Fork watchers are called when a C<fork ()> was detected (usually because
1653	whoever is a good citizen cared to tell libev about it by calling	3344	whoever is a good citizen cared to tell libev about it by calling
1654	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3345	C<ev_loop_fork>). The invocation is done before the event loop blocks next
1655	event loop blocks next and before C<ev_check> watchers are being called,	3346	and before C<ev_check> watchers are being called, and only in the child
1656	and only in the child after the fork. If whoever good citizen calling	3347	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
1657	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3348	and calls it in the wrong process, the fork handlers will be invoked, too,
1658	handlers will be invoked, too, of course.	3349	of course.
		3350
		3351	=head3 The special problem of life after fork - how is it possible?
		3352
		3353	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3354	up/change the process environment, followed by a call to C<exec()>. This
		3355	sequence should be handled by libev without any problems.
		3356
		3357	This changes when the application actually wants to do event handling
		3358	in the child, or both parent in child, in effect "continuing" after the
		3359	fork.
		3360
		3361	The default mode of operation (for libev, with application help to detect
		3362	forks) is to duplicate all the state in the child, as would be expected
		3363	when I<either> the parent I<or> the child process continues.
		3364
		3365	When both processes want to continue using libev, then this is usually the
		3366	wrong result. In that case, usually one process (typically the parent) is
		3367	supposed to continue with all watchers in place as before, while the other
		3368	process typically wants to start fresh, i.e. without any active watchers.
		3369
		3370	The cleanest and most efficient way to achieve that with libev is to
		3371	simply create a new event loop, which of course will be "empty", and
		3372	use that for new watchers. This has the advantage of not touching more
		3373	memory than necessary, and thus avoiding the copy-on-write, and the
		3374	disadvantage of having to use multiple event loops (which do not support
		3375	signal watchers).
		3376
		3377	When this is not possible, or you want to use the default loop for
		3378	other reasons, then in the process that wants to start "fresh", call
		3379	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3380	Destroying the default loop will "orphan" (not stop) all registered
		3381	watchers, so you have to be careful not to execute code that modifies
		3382	those watchers. Note also that in that case, you have to re-register any
		3383	signal watchers.
		3384
		3385	=head3 Watcher-Specific Functions and Data Members
1659		3386
1660	=over 4	3387	=over 4
1661		3388
1662	=item ev_fork_init (ev_signal *, callback)	3389	=item ev_fork_init (ev_fork *, callback)
1663		3390
1664	Initialises and configures the fork watcher - it has no parameters of any	3391	Initialises and configures the fork watcher - it has no parameters of any
1665	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3392	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1666	believe me.	3393	really.
1667		3394
1668	=back	3395	=back
1669		3396
1670		3397
		3398	=head2 C<ev_cleanup> - even the best things end
		3399
		3400	Cleanup watchers are called just before the event loop is being destroyed
		3401	by a call to C<ev_loop_destroy>.
		3402
		3403	While there is no guarantee that the event loop gets destroyed, cleanup
		3404	watchers provide a convenient method to install cleanup hooks for your
		3405	program, worker threads and so on - you just to make sure to destroy the
		3406	loop when you want them to be invoked.
		3407
		3408	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3409	all other watchers, they do not keep a reference to the event loop (which
		3410	makes a lot of sense if you think about it). Like all other watchers, you
		3411	can call libev functions in the callback, except C<ev_cleanup_start>.
		3412
		3413	=head3 Watcher-Specific Functions and Data Members
		3414
		3415	=over 4
		3416
		3417	=item ev_cleanup_init (ev_cleanup *, callback)
		3418
		3419	Initialises and configures the cleanup watcher - it has no parameters of
		3420	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3421	pointless, I assure you.
		3422
		3423	=back
		3424
		3425	Example: Register an atexit handler to destroy the default loop, so any
		3426	cleanup functions are called.
		3427
		3428	static void
		3429	program_exits (void)
		3430	{
		3431	ev_loop_destroy (EV_DEFAULT_UC);
		3432	}
		3433
		3434	...
		3435	atexit (program_exits);
		3436
		3437
		3438	=head2 C<ev_async> - how to wake up an event loop
		3439
		3440	In general, you cannot use an C<ev_loop> from multiple threads or other
		3441	asynchronous sources such as signal handlers (as opposed to multiple event
		3442	loops - those are of course safe to use in different threads).
		3443
		3444	Sometimes, however, you need to wake up an event loop you do not control,
		3445	for example because it belongs to another thread. This is what C<ev_async>
		3446	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3447	it by calling C<ev_async_send>, which is thread- and signal safe.
		3448
		3449	This functionality is very similar to C<ev_signal> watchers, as signals,
		3450	too, are asynchronous in nature, and signals, too, will be compressed
		3451	(i.e. the number of callback invocations may be less than the number of
		3452	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3453	of "global async watchers" by using a watcher on an otherwise unused
		3454	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3455	even without knowing which loop owns the signal.
		3456
		3457	=head3 Queueing
		3458
		3459	C<ev_async> does not support queueing of data in any way. The reason
		3460	is that the author does not know of a simple (or any) algorithm for a
		3461	multiple-writer-single-reader queue that works in all cases and doesn't
		3462	need elaborate support such as pthreads or unportable memory access
		3463	semantics.
		3464
		3465	That means that if you want to queue data, you have to provide your own
		3466	queue. But at least I can tell you how to implement locking around your
		3467	queue:
		3468
		3469	=over 4
		3470
		3471	=item queueing from a signal handler context
		3472
		3473	To implement race-free queueing, you simply add to the queue in the signal
		3474	handler but you block the signal handler in the watcher callback. Here is
		3475	an example that does that for some fictitious SIGUSR1 handler:
		3476
		3477	static ev_async mysig;
		3478
		3479	static void
		3480	sigusr1_handler (void)
		3481	{
		3482	sometype data;
		3483
		3484	// no locking etc.
		3485	queue_put (data);
		3486	ev_async_send (EV_DEFAULT_ &mysig);
		3487	}
		3488
		3489	static void
		3490	mysig_cb (EV_P_ ev_async *w, int revents)
		3491	{
		3492	sometype data;
		3493	sigset_t block, prev;
		3494
		3495	sigemptyset (&block);
		3496	sigaddset (&block, SIGUSR1);
		3497	sigprocmask (SIG_BLOCK, &block, &prev);
		3498
		3499	while (queue_get (&data))
		3500	process (data);
		3501
		3502	if (sigismember (&prev, SIGUSR1)
		3503	sigprocmask (SIG_UNBLOCK, &block, 0);
		3504	}
		3505
		3506	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3507	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3508	either...).
		3509
		3510	=item queueing from a thread context
		3511
		3512	The strategy for threads is different, as you cannot (easily) block
		3513	threads but you can easily preempt them, so to queue safely you need to
		3514	employ a traditional mutex lock, such as in this pthread example:
		3515
		3516	static ev_async mysig;
		3517	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3518
		3519	static void
		3520	otherthread (void)
		3521	{
		3522	// only need to lock the actual queueing operation
		3523	pthread_mutex_lock (&mymutex);
		3524	queue_put (data);
		3525	pthread_mutex_unlock (&mymutex);
		3526
		3527	ev_async_send (EV_DEFAULT_ &mysig);
		3528	}
		3529
		3530	static void
		3531	mysig_cb (EV_P_ ev_async *w, int revents)
		3532	{
		3533	pthread_mutex_lock (&mymutex);
		3534
		3535	while (queue_get (&data))
		3536	process (data);
		3537
		3538	pthread_mutex_unlock (&mymutex);
		3539	}
		3540
		3541	=back
		3542
		3543
		3544	=head3 Watcher-Specific Functions and Data Members
		3545
		3546	=over 4
		3547
		3548	=item ev_async_init (ev_async *, callback)
		3549
		3550	Initialises and configures the async watcher - it has no parameters of any
		3551	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3552	trust me.
		3553
		3554	=item ev_async_send (loop, ev_async *)
		3555
		3556	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3557	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3558	returns.
		3559
		3560	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3561	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3562	embedding section below on what exactly this means).
		3563
		3564	Note that, as with other watchers in libev, multiple events might get
		3565	compressed into a single callback invocation (another way to look at
		3566	this is that C<ev_async> watchers are level-triggered: they are set on
		3567	C<ev_async_send>, reset when the event loop detects that).
		3568
		3569	This call incurs the overhead of at most one extra system call per event
		3570	loop iteration, if the event loop is blocked, and no syscall at all if
		3571	the event loop (or your program) is processing events. That means that
		3572	repeated calls are basically free (there is no need to avoid calls for
		3573	performance reasons) and that the overhead becomes smaller (typically
		3574	zero) under load.
		3575
		3576	=item bool = ev_async_pending (ev_async *)
		3577
		3578	Returns a non-zero value when C<ev_async_send> has been called on the
		3579	watcher but the event has not yet been processed (or even noted) by the
		3580	event loop.
		3581
		3582	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3583	the loop iterates next and checks for the watcher to have become active,
		3584	it will reset the flag again. C<ev_async_pending> can be used to very
		3585	quickly check whether invoking the loop might be a good idea.
		3586
		3587	Not that this does I<not> check whether the watcher itself is pending,
		3588	only whether it has been requested to make this watcher pending: there
		3589	is a time window between the event loop checking and resetting the async
		3590	notification, and the callback being invoked.
		3591
		3592	=back
		3593
		3594
1671	=head1 OTHER FUNCTIONS	3595	=head1 OTHER FUNCTIONS
1672		3596
1673	There are some other functions of possible interest. Described. Here. Now.	3597	There are some other functions of possible interest. Described. Here. Now.
1674		3598
1675	=over 4	3599	=over 4
1676		3600
1677	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3601	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
1678		3602
1679	This function combines a simple timer and an I/O watcher, calls your	3603	This function combines a simple timer and an I/O watcher, calls your
1680	callback on whichever event happens first and automatically stop both	3604	callback on whichever event happens first and automatically stops both
1681	watchers. This is useful if you want to wait for a single event on an fd	3605	watchers. This is useful if you want to wait for a single event on an fd
1682	or timeout without having to allocate/configure/start/stop/free one or	3606	or timeout without having to allocate/configure/start/stop/free one or
1683	more watchers yourself.	3607	more watchers yourself.
1684		3608
1685	If C<fd> is less than 0, then no I/O watcher will be started and events	3609	If C<fd> is less than 0, then no I/O watcher will be started and the
1686	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3610	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1687	C<events> set will be craeted and started.	3611	the given C<fd> and C<events> set will be created and started.
1688		3612
1689	If C<timeout> is less than 0, then no timeout watcher will be	3613	If C<timeout> is less than 0, then no timeout watcher will be
1690	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3614	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1691	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3615	repeat = 0) will be started. C<0> is a valid timeout.
1692	dubious value.
1693		3616
1694	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3617	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1695	passed an C<revents> set like normal event callbacks (a combination of	3618	passed an C<revents> set like normal event callbacks (a combination of
1696	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3619	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1697	value passed to C<ev_once>:	3620	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3621	a timeout and an io event at the same time - you probably should give io
		3622	events precedence.
1698		3623
		3624	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3625
1699	static void stdin_ready (int revents, void *arg)	3626	static void stdin_ready (int revents, void *arg)
		3627	{
		3628	if (revents & EV_READ)
		3629	/* stdin might have data for us, joy! */;
		3630	else if (revents & EV_TIMER)
		3631	/* doh, nothing entered */;
		3632	}
		3633
		3634	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3635
		3636	=item ev_feed_fd_event (loop, int fd, int revents)
		3637
		3638	Feed an event on the given fd, as if a file descriptor backend detected
		3639	the given events.
		3640
		3641	=item ev_feed_signal_event (loop, int signum)
		3642
		3643	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3644	which is async-safe.
		3645
		3646	=back
		3647
		3648
		3649	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3650
		3651	This section explains some common idioms that are not immediately
		3652	obvious. Note that examples are sprinkled over the whole manual, and this
		3653	section only contains stuff that wouldn't fit anywhere else.
		3654
		3655	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3656
		3657	Each watcher has, by default, a C<void *data> member that you can read
		3658	or modify at any time: libev will completely ignore it. This can be used
		3659	to associate arbitrary data with your watcher. If you need more data and
		3660	don't want to allocate memory separately and store a pointer to it in that
		3661	data member, you can also "subclass" the watcher type and provide your own
		3662	data:
		3663
		3664	struct my_io
		3665	{
		3666	ev_io io;
		3667	int otherfd;
		3668	void *somedata;
		3669	struct whatever *mostinteresting;
		3670	};
		3671
		3672	...
		3673	struct my_io w;
		3674	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3675
		3676	And since your callback will be called with a pointer to the watcher, you
		3677	can cast it back to your own type:
		3678
		3679	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3680	{
		3681	struct my_io *w = (struct my_io *)w_;
		3682	...
		3683	}
		3684
		3685	More interesting and less C-conformant ways of casting your callback
		3686	function type instead have been omitted.
		3687
		3688	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3689
		3690	Another common scenario is to use some data structure with multiple
		3691	embedded watchers, in effect creating your own watcher that combines
		3692	multiple libev event sources into one "super-watcher":
		3693
		3694	struct my_biggy
		3695	{
		3696	int some_data;
		3697	ev_timer t1;
		3698	ev_timer t2;
		3699	}
		3700
		3701	In this case getting the pointer to C<my_biggy> is a bit more
		3702	complicated: Either you store the address of your C<my_biggy> struct in
		3703	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3704	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3705	real programmers):
		3706
		3707	#include <stddef.h>
		3708
		3709	static void
		3710	t1_cb (EV_P_ ev_timer *w, int revents)
		3711	{
		3712	struct my_biggy big = (struct my_biggy *)
		3713	(((char *)w) - offsetof (struct my_biggy, t1));
		3714	}
		3715
		3716	static void
		3717	t2_cb (EV_P_ ev_timer *w, int revents)
		3718	{
		3719	struct my_biggy big = (struct my_biggy *)
		3720	(((char *)w) - offsetof (struct my_biggy, t2));
		3721	}
		3722
		3723	=head2 AVOIDING FINISHING BEFORE RETURNING
		3724
		3725	Often you have structures like this in event-based programs:
		3726
		3727	callback ()
1700	{	3728	{
1701	if (revents & EV_TIMEOUT)	3729	free (request);
1702	/* doh, nothing entered */;
1703	else if (revents & EV_READ)
1704	/* stdin might have data for us, joy! */;
1705	}	3730	}
1706		3731
1707	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3732	request = start_new_request (..., callback);
1708		3733
1709	=item ev_feed_event (ev_loop *, watcher *, int revents)	3734	The intent is to start some "lengthy" operation. The C<request> could be
		3735	used to cancel the operation, or do other things with it.
1710		3736
1711	Feeds the given event set into the event loop, as if the specified event	3737	It's not uncommon to have code paths in C<start_new_request> that
1712	had happened for the specified watcher (which must be a pointer to an	3738	immediately invoke the callback, for example, to report errors. Or you add
1713	initialised but not necessarily started event watcher).	3739	some caching layer that finds that it can skip the lengthy aspects of the
		3740	operation and simply invoke the callback with the result.
1714		3741
1715	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3742	The problem here is that this will happen I<before> C<start_new_request>
		3743	has returned, so C<request> is not set.
1716		3744
1717	Feed an event on the given fd, as if a file descriptor backend detected	3745	Even if you pass the request by some safer means to the callback, you
1718	the given events it.	3746	might want to do something to the request after starting it, such as
		3747	canceling it, which probably isn't working so well when the callback has
		3748	already been invoked.
1719		3749
1720	=item ev_feed_signal_event (ev_loop *loop, int signum)	3750	A common way around all these issues is to make sure that
		3751	C<start_new_request> I<always> returns before the callback is invoked. If
		3752	C<start_new_request> immediately knows the result, it can artificially
		3753	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3754	example, or more sneakily, by reusing an existing (stopped) watcher and
		3755	pushing it into the pending queue:
1721		3756
1722	Feed an event as if the given signal occured (C<loop> must be the default	3757	ev_set_cb (watcher, callback);
1723	loop!).	3758	ev_feed_event (EV_A_ watcher, 0);
1724		3759
1725	=back	3760	This way, C<start_new_request> can safely return before the callback is
		3761	invoked, while not delaying callback invocation too much.
		3762
		3763	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3764
		3765	Often (especially in GUI toolkits) there are places where you have
		3766	I<modal> interaction, which is most easily implemented by recursively
		3767	invoking C<ev_run>.
		3768
		3769	This brings the problem of exiting - a callback might want to finish the
		3770	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3771	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3772	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3773	other combination: In these cases, a simple C<ev_break> will not work.
		3774
		3775	The solution is to maintain "break this loop" variable for each C<ev_run>
		3776	invocation, and use a loop around C<ev_run> until the condition is
		3777	triggered, using C<EVRUN_ONCE>:
		3778
		3779	// main loop
		3780	int exit_main_loop = 0;
		3781
		3782	while (!exit_main_loop)
		3783	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3784
		3785	// in a modal watcher
		3786	int exit_nested_loop = 0;
		3787
		3788	while (!exit_nested_loop)
		3789	ev_run (EV_A_ EVRUN_ONCE);
		3790
		3791	To exit from any of these loops, just set the corresponding exit variable:
		3792
		3793	// exit modal loop
		3794	exit_nested_loop = 1;
		3795
		3796	// exit main program, after modal loop is finished
		3797	exit_main_loop = 1;
		3798
		3799	// exit both
		3800	exit_main_loop = exit_nested_loop = 1;
		3801
		3802	=head2 THREAD LOCKING EXAMPLE
		3803
		3804	Here is a fictitious example of how to run an event loop in a different
		3805	thread from where callbacks are being invoked and watchers are
		3806	created/added/removed.
		3807
		3808	For a real-world example, see the C<EV::Loop::Async> perl module,
		3809	which uses exactly this technique (which is suited for many high-level
		3810	languages).
		3811
		3812	The example uses a pthread mutex to protect the loop data, a condition
		3813	variable to wait for callback invocations, an async watcher to notify the
		3814	event loop thread and an unspecified mechanism to wake up the main thread.
		3815
		3816	First, you need to associate some data with the event loop:
		3817
		3818	typedef struct {
		3819	mutex_t lock; /* global loop lock */
		3820	ev_async async_w;
		3821	thread_t tid;
		3822	cond_t invoke_cv;
		3823	} userdata;
		3824
		3825	void prepare_loop (EV_P)
		3826	{
		3827	// for simplicity, we use a static userdata struct.
		3828	static userdata u;
		3829
		3830	ev_async_init (&u->async_w, async_cb);
		3831	ev_async_start (EV_A_ &u->async_w);
		3832
		3833	pthread_mutex_init (&u->lock, 0);
		3834	pthread_cond_init (&u->invoke_cv, 0);
		3835
		3836	// now associate this with the loop
		3837	ev_set_userdata (EV_A_ u);
		3838	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3839	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3840
		3841	// then create the thread running ev_run
		3842	pthread_create (&u->tid, 0, l_run, EV_A);
		3843	}
		3844
		3845	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3846	solely to wake up the event loop so it takes notice of any new watchers
		3847	that might have been added:
		3848
		3849	static void
		3850	async_cb (EV_P_ ev_async *w, int revents)
		3851	{
		3852	// just used for the side effects
		3853	}
		3854
		3855	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3856	protecting the loop data, respectively.
		3857
		3858	static void
		3859	l_release (EV_P)
		3860	{
		3861	userdata *u = ev_userdata (EV_A);
		3862	pthread_mutex_unlock (&u->lock);
		3863	}
		3864
		3865	static void
		3866	l_acquire (EV_P)
		3867	{
		3868	userdata *u = ev_userdata (EV_A);
		3869	pthread_mutex_lock (&u->lock);
		3870	}
		3871
		3872	The event loop thread first acquires the mutex, and then jumps straight
		3873	into C<ev_run>:
		3874
		3875	void *
		3876	l_run (void *thr_arg)
		3877	{
		3878	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3879
		3880	l_acquire (EV_A);
		3881	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3882	ev_run (EV_A_ 0);
		3883	l_release (EV_A);
		3884
		3885	return 0;
		3886	}
		3887
		3888	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3889	signal the main thread via some unspecified mechanism (signals? pipe
		3890	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3891	have been called (in a while loop because a) spurious wakeups are possible
		3892	and b) skipping inter-thread-communication when there are no pending
		3893	watchers is very beneficial):
		3894
		3895	static void
		3896	l_invoke (EV_P)
		3897	{
		3898	userdata *u = ev_userdata (EV_A);
		3899
		3900	while (ev_pending_count (EV_A))
		3901	{
		3902	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3903	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3904	}
		3905	}
		3906
		3907	Now, whenever the main thread gets told to invoke pending watchers, it
		3908	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3909	thread to continue:
		3910
		3911	static void
		3912	real_invoke_pending (EV_P)
		3913	{
		3914	userdata *u = ev_userdata (EV_A);
		3915
		3916	pthread_mutex_lock (&u->lock);
		3917	ev_invoke_pending (EV_A);
		3918	pthread_cond_signal (&u->invoke_cv);
		3919	pthread_mutex_unlock (&u->lock);
		3920	}
		3921
		3922	Whenever you want to start/stop a watcher or do other modifications to an
		3923	event loop, you will now have to lock:
		3924
		3925	ev_timer timeout_watcher;
		3926	userdata *u = ev_userdata (EV_A);
		3927
		3928	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3929
		3930	pthread_mutex_lock (&u->lock);
		3931	ev_timer_start (EV_A_ &timeout_watcher);
		3932	ev_async_send (EV_A_ &u->async_w);
		3933	pthread_mutex_unlock (&u->lock);
		3934
		3935	Note that sending the C<ev_async> watcher is required because otherwise
		3936	an event loop currently blocking in the kernel will have no knowledge
		3937	about the newly added timer. By waking up the loop it will pick up any new
		3938	watchers in the next event loop iteration.
		3939
		3940	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3941
		3942	While the overhead of a callback that e.g. schedules a thread is small, it
		3943	is still an overhead. If you embed libev, and your main usage is with some
		3944	kind of threads or coroutines, you might want to customise libev so that
		3945	doesn't need callbacks anymore.
		3946
		3947	Imagine you have coroutines that you can switch to using a function
		3948	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3949	and that due to some magic, the currently active coroutine is stored in a
		3950	global called C<current_coro>. Then you can build your own "wait for libev
		3951	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3952	the differing C<;> conventions):
		3953
		3954	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3955	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3956
		3957	That means instead of having a C callback function, you store the
		3958	coroutine to switch to in each watcher, and instead of having libev call
		3959	your callback, you instead have it switch to that coroutine.
		3960
		3961	A coroutine might now wait for an event with a function called
		3962	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3963	matter when, or whether the watcher is active or not when this function is
		3964	called):
		3965
		3966	void
		3967	wait_for_event (ev_watcher *w)
		3968	{
		3969	ev_set_cb (w, current_coro);
		3970	switch_to (libev_coro);
		3971	}
		3972
		3973	That basically suspends the coroutine inside C<wait_for_event> and
		3974	continues the libev coroutine, which, when appropriate, switches back to
		3975	this or any other coroutine.
		3976
		3977	You can do similar tricks if you have, say, threads with an event queue -
		3978	instead of storing a coroutine, you store the queue object and instead of
		3979	switching to a coroutine, you push the watcher onto the queue and notify
		3980	any waiters.
		3981
		3982	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3983	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3984
		3985	// my_ev.h
		3986	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3987	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3988	#include "../libev/ev.h"
		3989
		3990	// my_ev.c
		3991	#define EV_H "my_ev.h"
		3992	#include "../libev/ev.c"
		3993
		3994	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3995	F<my_ev.c> into your project. When properly specifying include paths, you
		3996	can even use F<ev.h> as header file name directly.
1726		3997
1727		3998
1728	=head1 LIBEVENT EMULATION	3999	=head1 LIBEVENT EMULATION
1729		4000
1730	Libev offers a compatibility emulation layer for libevent. It cannot	4001	Libev offers a compatibility emulation layer for libevent. It cannot
1731	emulate the internals of libevent, so here are some usage hints:	4002	emulate the internals of libevent, so here are some usage hints:
1732		4003
1733	=over 4	4004	=over 4
		4005
		4006	=item * Only the libevent-1.4.1-beta API is being emulated.
		4007
		4008	This was the newest libevent version available when libev was implemented,
		4009	and is still mostly unchanged in 2010.
1734		4010
1735	=item * Use it by including <event.h>, as usual.	4011	=item * Use it by including <event.h>, as usual.
1736		4012
1737	=item * The following members are fully supported: ev_base, ev_callback,	4013	=item * The following members are fully supported: ev_base, ev_callback,
1738	ev_arg, ev_fd, ev_res, ev_events.	4014	ev_arg, ev_fd, ev_res, ev_events.
…		…
1743		4019
1744	=item * Priorities are not currently supported. Initialising priorities	4020	=item * Priorities are not currently supported. Initialising priorities
1745	will fail and all watchers will have the same priority, even though there	4021	will fail and all watchers will have the same priority, even though there
1746	is an ev_pri field.	4022	is an ev_pri field.
1747		4023
		4024	=item * In libevent, the last base created gets the signals, in libev, the
		4025	base that registered the signal gets the signals.
		4026
1748	=item * Other members are not supported.	4027	=item * Other members are not supported.
1749		4028
1750	=item * The libev emulation is I<not> ABI compatible to libevent, you need	4029	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1751	to use the libev header file and library.	4030	to use the libev header file and library.
1752		4031
1753	=back	4032	=back
1754		4033
1755	=head1 C++ SUPPORT	4034	=head1 C++ SUPPORT
1756		4035
		4036	=head2 C API
		4037
		4038	The normal C API should work fine when used from C++: both ev.h and the
		4039	libev sources can be compiled as C++. Therefore, code that uses the C API
		4040	will work fine.
		4041
		4042	Proper exception specifications might have to be added to callbacks passed
		4043	to libev: exceptions may be thrown only from watcher callbacks, all other
		4044	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4045	callbacks) must not throw exceptions, and might need a C<noexcept>
		4046	specification. If you have code that needs to be compiled as both C and
		4047	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4048
		4049	static void
		4050	fatal_error (const char *msg) EV_NOEXCEPT
		4051	{
		4052	perror (msg);
		4053	abort ();
		4054	}
		4055
		4056	...
		4057	ev_set_syserr_cb (fatal_error);
		4058
		4059	The only API functions that can currently throw exceptions are C<ev_run>,
		4060	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4061	because it runs cleanup watchers).
		4062
		4063	Throwing exceptions in watcher callbacks is only supported if libev itself
		4064	is compiled with a C++ compiler or your C and C++ environments allow
		4065	throwing exceptions through C libraries (most do).
		4066
		4067	=head2 C++ API
		4068
1757	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4069	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1758	you to use some convinience methods to start/stop watchers and also change	4070	you to use some convenience methods to start/stop watchers and also change
1759	the callback model to a model using method callbacks on objects.	4071	the callback model to a model using method callbacks on objects.
1760		4072
1761	To use it,	4073	To use it,
1762		4074
1763	#include <ev++.h>	4075	#include <ev++.h>
1764		4076
1765	This automatically includes F<ev.h> and puts all of its definitions (many	4077	This automatically includes F<ev.h> and puts all of its definitions (many
1766	of them macros) into the global namespace. All C++ specific things are	4078	of them macros) into the global namespace. All C++ specific things are
1767	put into the C<ev> namespace. It should support all the same embedding	4079	put into the C<ev> namespace. It should support all the same embedding
1768	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	4080	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1770	Care has been taken to keep the overhead low. The only data member the C++	4082	Care has been taken to keep the overhead low. The only data member the C++
1771	classes add (compared to plain C-style watchers) is the event loop pointer	4083	classes add (compared to plain C-style watchers) is the event loop pointer
1772	that the watcher is associated with (or no additional members at all if	4084	that the watcher is associated with (or no additional members at all if
1773	you disable C<EV_MULTIPLICITY> when embedding libev).	4085	you disable C<EV_MULTIPLICITY> when embedding libev).
1774		4086
1775	Currently, functions, and static and non-static member functions can be	4087	Currently, functions, static and non-static member functions and classes
1776	used as callbacks. Other types should be easy to add as long as they only	4088	with C<operator ()> can be used as callbacks. Other types should be easy
1777	need one additional pointer for context. If you need support for other	4089	to add as long as they only need one additional pointer for context. If
1778	types of functors please contact the author (preferably after implementing	4090	you need support for other types of functors please contact the author
1779	it).	4091	(preferably after implementing it).
		4092
		4093	For all this to work, your C++ compiler either has to use the same calling
		4094	conventions as your C compiler (for static member functions), or you have
		4095	to embed libev and compile libev itself as C++.
1780		4096
1781	Here is a list of things available in the C<ev> namespace:	4097	Here is a list of things available in the C<ev> namespace:
1782		4098
1783	=over 4	4099	=over 4
1784		4100
…		…
1794	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4110	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
1795		4111
1796	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4112	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
1797	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4113	the same name in the C<ev> namespace, with the exception of C<ev_signal>
1798	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4114	which is called C<ev::sig> to avoid clashes with the C<signal> macro
1799	defines by many implementations.	4115	defined by many implementations.
1800		4116
1801	All of those classes have these methods:	4117	All of those classes have these methods:
1802		4118
1803	=over 4	4119	=over 4
1804		4120
1805	=item ev::TYPE::TYPE ()	4121	=item ev::TYPE::TYPE ()
1806		4122
1807	=item ev::TYPE::TYPE (struct ev_loop *)	4123	=item ev::TYPE::TYPE (loop)
1808		4124
1809	=item ev::TYPE::~TYPE	4125	=item ev::TYPE::~TYPE
1810		4126
1811	The constructor (optionally) takes an event loop to associate the watcher	4127	The constructor (optionally) takes an event loop to associate the watcher
1812	with. If it is omitted, it will use C<EV_DEFAULT>.	4128	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
1835	your compiler is good :), then the method will be fully inlined into the	4151	your compiler is good :), then the method will be fully inlined into the
1836	thunking function, making it as fast as a direct C callback.	4152	thunking function, making it as fast as a direct C callback.
1837		4153
1838	Example: simple class declaration and watcher initialisation	4154	Example: simple class declaration and watcher initialisation
1839		4155
1840	struct myclass	4156	struct myclass
1841	{	4157	{
1842	void io_cb (ev::io &w, int revents) { }	4158	void io_cb (ev::io &w, int revents) { }
1843	}	4159	}
1844		4160
1845	myclass obj;	4161	myclass obj;
1846	ev::io iow;	4162	ev::io iow;
1847	iow.set <myclass, &myclass::io_cb> (&obj);	4163	iow.set <myclass, &myclass::io_cb> (&obj);
1848		4164
1849	=item w->set (void (*function)(watcher &w, int), void *data = 0)	4165	=item w->set (object *)
		4166
		4167	This is a variation of a method callback - leaving out the method to call
		4168	will default the method to C<operator ()>, which makes it possible to use
		4169	functor objects without having to manually specify the C<operator ()> all
		4170	the time. Incidentally, you can then also leave out the template argument
		4171	list.
		4172
		4173	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4174	int revents)>.
		4175
		4176	See the method-C<set> above for more details.
		4177
		4178	Example: use a functor object as callback.
		4179
		4180	struct myfunctor
		4181	{
		4182	void operator() (ev::io &w, int revents)
		4183	{
		4184	...
		4185	}
		4186	}
		4187
		4188	myfunctor f;
		4189
		4190	ev::io w;
		4191	w.set (&f);
		4192
		4193	=item w->set<function> (void *data = 0)
1850		4194
1851	Also sets a callback, but uses a static method or plain function as	4195	Also sets a callback, but uses a static method or plain function as
1852	callback. The optional C<data> argument will be stored in the watcher's	4196	callback. The optional C<data> argument will be stored in the watcher's
1853	C<data> member and is free for you to use.	4197	C<data> member and is free for you to use.
1854		4198
		4199	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		4200
1855	See the method-C<set> above for more details.	4201	See the method-C<set> above for more details.
1856		4202
		4203	Example: Use a plain function as callback.
		4204
		4205	static void io_cb (ev::io &w, int revents) { }
		4206	iow.set <io_cb> ();
		4207
1857	=item w->set (struct ev_loop *)	4208	=item w->set (loop)
1858		4209
1859	Associates a different C<struct ev_loop> with this watcher. You can only	4210	Associates a different C<struct ev_loop> with this watcher. You can only
1860	do this when the watcher is inactive (and not pending either).	4211	do this when the watcher is inactive (and not pending either).
1861		4212
1862	=item w->set ([args])	4213	=item w->set ([arguments])
1863		4214
1864	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4215	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4216	with the same arguments. Either this method or a suitable start method
1865	called at least once. Unlike the C counterpart, an active watcher gets	4217	must be called at least once. Unlike the C counterpart, an active watcher
1866	automatically stopped and restarted when reconfiguring it with this	4218	gets automatically stopped and restarted when reconfiguring it with this
1867	method.	4219	method.
		4220
		4221	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4222	clashing with the C<set (loop)> method.
1868		4223
1869	=item w->start ()	4224	=item w->start ()
1870		4225
1871	Starts the watcher. Note that there is no C<loop> argument, as the	4226	Starts the watcher. Note that there is no C<loop> argument, as the
1872	constructor already stores the event loop.	4227	constructor already stores the event loop.
1873		4228
		4229	=item w->start ([arguments])
		4230
		4231	Instead of calling C<set> and C<start> methods separately, it is often
		4232	convenient to wrap them in one call. Uses the same type of arguments as
		4233	the configure C<set> method of the watcher.
		4234
1874	=item w->stop ()	4235	=item w->stop ()
1875		4236
1876	Stops the watcher if it is active. Again, no C<loop> argument.	4237	Stops the watcher if it is active. Again, no C<loop> argument.
1877		4238
1878	=item w->again () C<ev::timer>, C<ev::periodic> only	4239	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1879		4240
1880	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	4241	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1881	C<ev_TYPE_again> function.	4242	C<ev_TYPE_again> function.
1882		4243
1883	=item w->sweep () C<ev::embed> only	4244	=item w->sweep () (C<ev::embed> only)
1884		4245
1885	Invokes C<ev_embed_sweep>.	4246	Invokes C<ev_embed_sweep>.
1886		4247
1887	=item w->update () C<ev::stat> only	4248	=item w->update () (C<ev::stat> only)
1888		4249
1889	Invokes C<ev_stat_stat>.	4250	Invokes C<ev_stat_stat>.
1890		4251
1891	=back	4252	=back
1892		4253
1893	=back	4254	=back
1894		4255
1895	Example: Define a class with an IO and idle watcher, start one of them in	4256	Example: Define a class with two I/O and idle watchers, start the I/O
1896	the constructor.	4257	watchers in the constructor.
1897		4258
1898	class myclass	4259	class myclass
1899	{	4260	{
1900	ev_io io; void io_cb (ev::io &w, int revents);	4261	ev::io io ; void io_cb (ev::io &w, int revents);
		4262	ev::io io2 ; void io2_cb (ev::io &w, int revents);
1901	ev_idle idle void idle_cb (ev::idle &w, int revents);	4263	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1902		4264
1903	myclass ();	4265	myclass (int fd)
1904	}	4266	{
1905
1906	myclass::myclass (int fd)
1907	{
1908	io .set <myclass, &myclass::io_cb > (this);	4267	io .set <myclass, &myclass::io_cb > (this);
		4268	io2 .set <myclass, &myclass::io2_cb > (this);
1909	idle.set <myclass, &myclass::idle_cb> (this);	4269	idle.set <myclass, &myclass::idle_cb> (this);
1910		4270
1911	io.start (fd, ev::READ);	4271	io.set (fd, ev::WRITE); // configure the watcher
		4272	io.start (); // start it whenever convenient
		4273
		4274	io2.start (fd, ev::READ); // set + start in one call
		4275	}
1912	}	4276	};
		4277
		4278
		4279	=head1 OTHER LANGUAGE BINDINGS
		4280
		4281	Libev does not offer other language bindings itself, but bindings for a
		4282	number of languages exist in the form of third-party packages. If you know
		4283	any interesting language binding in addition to the ones listed here, drop
		4284	me a note.
		4285
		4286	=over 4
		4287
		4288	=item Perl
		4289
		4290	The EV module implements the full libev API and is actually used to test
		4291	libev. EV is developed together with libev. Apart from the EV core module,
		4292	there are additional modules that implement libev-compatible interfaces
		4293	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4294	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4295	and C<EV::Glib>).
		4296
		4297	It can be found and installed via CPAN, its homepage is at
		4298	L<http://software.schmorp.de/pkg/EV>.
		4299
		4300	=item Python
		4301
		4302	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4303	seems to be quite complete and well-documented.
		4304
		4305	=item Ruby
		4306
		4307	Tony Arcieri has written a ruby extension that offers access to a subset
		4308	of the libev API and adds file handle abstractions, asynchronous DNS and
		4309	more on top of it. It can be found via gem servers. Its homepage is at
		4310	L<http://rev.rubyforge.org/>.
		4311
		4312	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4313	makes rev work even on mingw.
		4314
		4315	=item Haskell
		4316
		4317	A haskell binding to libev is available at
		4318	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4319
		4320	=item D
		4321
		4322	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4323	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4324
		4325	=item Ocaml
		4326
		4327	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4328	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4329
		4330	=item Lua
		4331
		4332	Brian Maher has written a partial interface to libev for lua (at the
		4333	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4334	L<http://github.com/brimworks/lua-ev>.
		4335
		4336	=item Javascript
		4337
		4338	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4339
		4340	=item Others
		4341
		4342	There are others, and I stopped counting.
		4343
		4344	=back
1913		4345
1914		4346
1915	=head1 MACRO MAGIC	4347	=head1 MACRO MAGIC
1916		4348
1917	Libev can be compiled with a variety of options, the most fundemantal is	4349	Libev can be compiled with a variety of options, the most fundamental
1918	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	4350	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1919	callbacks have an initial C<struct ev_loop *> argument.	4351	functions and callbacks have an initial C<struct ev_loop *> argument.
1920		4352
1921	To make it easier to write programs that cope with either variant, the	4353	To make it easier to write programs that cope with either variant, the
1922	following macros are defined:	4354	following macros are defined:
1923		4355
1924	=over 4	4356	=over 4
…		…
1927		4359
1928	This provides the loop I<argument> for functions, if one is required ("ev	4360	This provides the loop I<argument> for functions, if one is required ("ev
1929	loop argument"). The C<EV_A> form is used when this is the sole argument,	4361	loop argument"). The C<EV_A> form is used when this is the sole argument,
1930	C<EV_A_> is used when other arguments are following. Example:	4362	C<EV_A_> is used when other arguments are following. Example:
1931		4363
1932	ev_unref (EV_A);	4364	ev_unref (EV_A);
1933	ev_timer_add (EV_A_ watcher);	4365	ev_timer_add (EV_A_ watcher);
1934	ev_loop (EV_A_ 0);	4366	ev_run (EV_A_ 0);
1935		4367
1936	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4368	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1937	which is often provided by the following macro.	4369	which is often provided by the following macro.
1938		4370
1939	=item C<EV_P>, C<EV_P_>	4371	=item C<EV_P>, C<EV_P_>
1940		4372
1941	This provides the loop I<parameter> for functions, if one is required ("ev	4373	This provides the loop I<parameter> for functions, if one is required ("ev
1942	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4374	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1943	C<EV_P_> is used when other parameters are following. Example:	4375	C<EV_P_> is used when other parameters are following. Example:
1944		4376
1945	// this is how ev_unref is being declared	4377	// this is how ev_unref is being declared
1946	static void ev_unref (EV_P);	4378	static void ev_unref (EV_P);
1947		4379
1948	// this is how you can declare your typical callback	4380	// this is how you can declare your typical callback
1949	static void cb (EV_P_ ev_timer *w, int revents)	4381	static void cb (EV_P_ ev_timer *w, int revents)
1950		4382
1951	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4383	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1952	suitable for use with C<EV_A>.	4384	suitable for use with C<EV_A>.
1953		4385
1954	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4386	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1955		4387
1956	Similar to the other two macros, this gives you the value of the default	4388	Similar to the other two macros, this gives you the value of the default
1957	loop, if multiple loops are supported ("ev loop default").	4389	loop, if multiple loops are supported ("ev loop default"). The default loop
		4390	will be initialised if it isn't already initialised.
		4391
		4392	For non-multiplicity builds, these macros do nothing, so you always have
		4393	to initialise the loop somewhere.
		4394
		4395	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4396
		4397	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4398	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4399	is undefined when the default loop has not been initialised by a previous
		4400	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4401
		4402	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4403	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
1958		4404
1959	=back	4405	=back
1960		4406
1961	Example: Declare and initialise a check watcher, utilising the above	4407	Example: Declare and initialise a check watcher, utilising the above
1962	macros so it will work regardless of whether multiple loops are supported	4408	macros so it will work regardless of whether multiple loops are supported
1963	or not.	4409	or not.
1964		4410
1965	static void	4411	static void
1966	check_cb (EV_P_ ev_timer *w, int revents)	4412	check_cb (EV_P_ ev_timer *w, int revents)
1967	{	4413	{
1968	ev_check_stop (EV_A_ w);	4414	ev_check_stop (EV_A_ w);
1969	}	4415	}
1970		4416
1971	ev_check check;	4417	ev_check check;
1972	ev_check_init (&check, check_cb);	4418	ev_check_init (&check, check_cb);
1973	ev_check_start (EV_DEFAULT_ &check);	4419	ev_check_start (EV_DEFAULT_ &check);
1974	ev_loop (EV_DEFAULT_ 0);	4420	ev_run (EV_DEFAULT_ 0);
1975		4421
1976	=head1 EMBEDDING	4422	=head1 EMBEDDING
1977		4423
1978	Libev can (and often is) directly embedded into host	4424	Libev can (and often is) directly embedded into host
1979	applications. Examples of applications that embed it include the Deliantra	4425	applications. Examples of applications that embed it include the Deliantra
1980	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	4426	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1981	and rxvt-unicode.	4427	and rxvt-unicode.
1982		4428
1983	The goal is to enable you to just copy the neecssary files into your	4429	The goal is to enable you to just copy the necessary files into your
1984	source directory without having to change even a single line in them, so	4430	source directory without having to change even a single line in them, so
1985	you can easily upgrade by simply copying (or having a checked-out copy of	4431	you can easily upgrade by simply copying (or having a checked-out copy of
1986	libev somewhere in your source tree).	4432	libev somewhere in your source tree).
1987		4433
1988	=head2 FILESETS	4434	=head2 FILESETS
1989		4435
1990	Depending on what features you need you need to include one or more sets of files	4436	Depending on what features you need you need to include one or more sets of files
1991	in your app.	4437	in your application.
1992		4438
1993	=head3 CORE EVENT LOOP	4439	=head3 CORE EVENT LOOP
1994		4440
1995	To include only the libev core (all the C<ev_*> functions), with manual	4441	To include only the libev core (all the C<ev_*> functions), with manual
1996	configuration (no autoconf):	4442	configuration (no autoconf):
1997		4443
1998	#define EV_STANDALONE 1	4444	#define EV_STANDALONE 1
1999	#include "ev.c"	4445	#include "ev.c"
2000		4446
2001	This will automatically include F<ev.h>, too, and should be done in a	4447	This will automatically include F<ev.h>, too, and should be done in a
2002	single C source file only to provide the function implementations. To use	4448	single C source file only to provide the function implementations. To use
2003	it, do the same for F<ev.h> in all files wishing to use this API (best	4449	it, do the same for F<ev.h> in all files wishing to use this API (best
2004	done by writing a wrapper around F<ev.h> that you can include instead and	4450	done by writing a wrapper around F<ev.h> that you can include instead and
2005	where you can put other configuration options):	4451	where you can put other configuration options):
2006		4452
2007	#define EV_STANDALONE 1	4453	#define EV_STANDALONE 1
2008	#include "ev.h"	4454	#include "ev.h"
2009		4455
2010	Both header files and implementation files can be compiled with a C++	4456	Both header files and implementation files can be compiled with a C++
2011	compiler (at least, thats a stated goal, and breakage will be treated	4457	compiler (at least, that's a stated goal, and breakage will be treated
2012	as a bug).	4458	as a bug).
2013		4459
2014	You need the following files in your source tree, or in a directory	4460	You need the following files in your source tree, or in a directory
2015	in your include path (e.g. in libev/ when using -Ilibev):	4461	in your include path (e.g. in libev/ when using -Ilibev):
2016		4462
2017	ev.h	4463	ev.h
2018	ev.c	4464	ev.c
2019	ev_vars.h	4465	ev_vars.h
2020	ev_wrap.h	4466	ev_wrap.h
2021		4467
2022	ev_win32.c required on win32 platforms only	4468	ev_win32.c required on win32 platforms only
2023		4469
2024	ev_select.c only when select backend is enabled (which is enabled by default)	4470	ev_select.c only when select backend is enabled
2025	ev_poll.c only when poll backend is enabled (disabled by default)	4471	ev_poll.c only when poll backend is enabled
2026	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4472	ev_epoll.c only when the epoll backend is enabled
		4473	ev_linuxaio.c only when the linux aio backend is enabled
2027	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4474	ev_kqueue.c only when the kqueue backend is enabled
2028	ev_port.c only when the solaris port backend is enabled (disabled by default)	4475	ev_port.c only when the solaris port backend is enabled
2029		4476
2030	F<ev.c> includes the backend files directly when enabled, so you only need	4477	F<ev.c> includes the backend files directly when enabled, so you only need
2031	to compile this single file.	4478	to compile this single file.
2032		4479
2033	=head3 LIBEVENT COMPATIBILITY API	4480	=head3 LIBEVENT COMPATIBILITY API
2034		4481
2035	To include the libevent compatibility API, also include:	4482	To include the libevent compatibility API, also include:
2036		4483
2037	#include "event.c"	4484	#include "event.c"
2038		4485
2039	in the file including F<ev.c>, and:	4486	in the file including F<ev.c>, and:
2040		4487
2041	#include "event.h"	4488	#include "event.h"
2042		4489
2043	in the files that want to use the libevent API. This also includes F<ev.h>.	4490	in the files that want to use the libevent API. This also includes F<ev.h>.
2044		4491
2045	You need the following additional files for this:	4492	You need the following additional files for this:
2046		4493
2047	event.h	4494	event.h
2048	event.c	4495	event.c
2049		4496
2050	=head3 AUTOCONF SUPPORT	4497	=head3 AUTOCONF SUPPORT
2051		4498
2052	Instead of using C<EV_STANDALONE=1> and providing your config in	4499	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2053	whatever way you want, you can also C<m4_include([libev.m4])> in your	4500	whatever way you want, you can also C<m4_include([libev.m4])> in your
2054	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4501	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2055	include F<config.h> and configure itself accordingly.	4502	include F<config.h> and configure itself accordingly.
2056		4503
2057	For this of course you need the m4 file:	4504	For this of course you need the m4 file:
2058		4505
2059	libev.m4	4506	libev.m4
2060		4507
2061	=head2 PREPROCESSOR SYMBOLS/MACROS	4508	=head2 PREPROCESSOR SYMBOLS/MACROS
2062		4509
2063	Libev can be configured via a variety of preprocessor symbols you have to define	4510	Libev can be configured via a variety of preprocessor symbols you have to
2064	before including any of its files. The default is not to build for multiplicity	4511	define before including (or compiling) any of its files. The default in
2065	and only include the select backend.	4512	the absence of autoconf is documented for every option.
		4513
		4514	Symbols marked with "(h)" do not change the ABI, and can have different
		4515	values when compiling libev vs. including F<ev.h>, so it is permissible
		4516	to redefine them before including F<ev.h> without breaking compatibility
		4517	to a compiled library. All other symbols change the ABI, which means all
		4518	users of libev and the libev code itself must be compiled with compatible
		4519	settings.
2066		4520
2067	=over 4	4521	=over 4
2068		4522
		4523	=item EV_COMPAT3 (h)
		4524
		4525	Backwards compatibility is a major concern for libev. This is why this
		4526	release of libev comes with wrappers for the functions and symbols that
		4527	have been renamed between libev version 3 and 4.
		4528
		4529	You can disable these wrappers (to test compatibility with future
		4530	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4531	sources. This has the additional advantage that you can drop the C<struct>
		4532	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4533	typedef in that case.
		4534
		4535	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4536	and in some even more future version the compatibility code will be
		4537	removed completely.
		4538
2069	=item EV_STANDALONE	4539	=item EV_STANDALONE (h)
2070		4540
2071	Must always be C<1> if you do not use autoconf configuration, which	4541	Must always be C<1> if you do not use autoconf configuration, which
2072	keeps libev from including F<config.h>, and it also defines dummy	4542	keeps libev from including F<config.h>, and it also defines dummy
2073	implementations for some libevent functions (such as logging, which is not	4543	implementations for some libevent functions (such as logging, which is not
2074	supported). It will also not define any of the structs usually found in	4544	supported). It will also not define any of the structs usually found in
2075	F<event.h> that are not directly supported by the libev core alone.	4545	F<event.h> that are not directly supported by the libev core alone.
2076		4546
		4547	In standalone mode, libev will still try to automatically deduce the
		4548	configuration, but has to be more conservative.
		4549
		4550	=item EV_USE_FLOOR
		4551
		4552	If defined to be C<1>, libev will use the C<floor ()> function for its
		4553	periodic reschedule calculations, otherwise libev will fall back on a
		4554	portable (slower) implementation. If you enable this, you usually have to
		4555	link against libm or something equivalent. Enabling this when the C<floor>
		4556	function is not available will fail, so the safe default is to not enable
		4557	this.
		4558
2077	=item EV_USE_MONOTONIC	4559	=item EV_USE_MONOTONIC
2078		4560
2079	If defined to be C<1>, libev will try to detect the availability of the	4561	If defined to be C<1>, libev will try to detect the availability of the
2080	monotonic clock option at both compiletime and runtime. Otherwise no use	4562	monotonic clock option at both compile time and runtime. Otherwise no
2081	of the monotonic clock option will be attempted. If you enable this, you	4563	use of the monotonic clock option will be attempted. If you enable this,
2082	usually have to link against librt or something similar. Enabling it when	4564	you usually have to link against librt or something similar. Enabling it
2083	the functionality isn't available is safe, though, althoguh you have	4565	when the functionality isn't available is safe, though, although you have
2084	to make sure you link against any libraries where the C<clock_gettime>	4566	to make sure you link against any libraries where the C<clock_gettime>
2085	function is hiding in (often F<-lrt>).	4567	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2086		4568
2087	=item EV_USE_REALTIME	4569	=item EV_USE_REALTIME
2088		4570
2089	If defined to be C<1>, libev will try to detect the availability of the	4571	If defined to be C<1>, libev will try to detect the availability of the
2090	realtime clock option at compiletime (and assume its availability at	4572	real-time clock option at compile time (and assume its availability
2091	runtime if successful). Otherwise no use of the realtime clock option will	4573	at runtime if successful). Otherwise no use of the real-time clock
2092	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4574	option will be attempted. This effectively replaces C<gettimeofday>
2093	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	4575	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2094	in the description of C<EV_USE_MONOTONIC>, though.	4576	correctness. See the note about libraries in the description of
		4577	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4578	C<EV_USE_CLOCK_SYSCALL>.
		4579
		4580	=item EV_USE_CLOCK_SYSCALL
		4581
		4582	If defined to be C<1>, libev will try to use a direct syscall instead
		4583	of calling the system-provided C<clock_gettime> function. This option
		4584	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4585	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4586	programs needlessly. Using a direct syscall is slightly slower (in
		4587	theory), because no optimised vdso implementation can be used, but avoids
		4588	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4589	higher, as it simplifies linking (no need for C<-lrt>).
		4590
		4591	=item EV_USE_NANOSLEEP
		4592
		4593	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4594	and will use it for delays. Otherwise it will use C<select ()>.
		4595
		4596	=item EV_USE_EVENTFD
		4597
		4598	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4599	available and will probe for kernel support at runtime. This will improve
		4600	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4601	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4602	2.7 or newer, otherwise disabled.
2095		4603
2096	=item EV_USE_SELECT	4604	=item EV_USE_SELECT
2097		4605
2098	If undefined or defined to be C<1>, libev will compile in support for the	4606	If undefined or defined to be C<1>, libev will compile in support for the
2099	C<select>(2) backend. No attempt at autodetection will be done: if no	4607	C<select>(2) backend. No attempt at auto-detection will be done: if no
2100	other method takes over, select will be it. Otherwise the select backend	4608	other method takes over, select will be it. Otherwise the select backend
2101	will not be compiled in.	4609	will not be compiled in.
2102		4610
2103	=item EV_SELECT_USE_FD_SET	4611	=item EV_SELECT_USE_FD_SET
2104		4612
2105	If defined to C<1>, then the select backend will use the system C<fd_set>	4613	If defined to C<1>, then the select backend will use the system C<fd_set>
2106	structure. This is useful if libev doesn't compile due to a missing	4614	structure. This is useful if libev doesn't compile due to a missing
2107	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4615	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2108	exotic systems. This usually limits the range of file descriptors to some	4616	on exotic systems. This usually limits the range of file descriptors to
2109	low limit such as 1024 or might have other limitations (winsocket only	4617	some low limit such as 1024 or might have other limitations (winsocket
2110	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4618	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2111	influence the size of the C<fd_set> used.	4619	configures the maximum size of the C<fd_set>.
2112		4620
2113	=item EV_SELECT_IS_WINSOCKET	4621	=item EV_SELECT_IS_WINSOCKET
2114		4622
2115	When defined to C<1>, the select backend will assume that	4623	When defined to C<1>, the select backend will assume that
2116	select/socket/connect etc. don't understand file descriptors but	4624	select/socket/connect etc. don't understand file descriptors but
…		…
2118	be used is the winsock select). This means that it will call	4626	be used is the winsock select). This means that it will call
2119	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4627	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2120	it is assumed that all these functions actually work on fds, even	4628	it is assumed that all these functions actually work on fds, even
2121	on win32. Should not be defined on non-win32 platforms.	4629	on win32. Should not be defined on non-win32 platforms.
2122		4630
		4631	=item EV_FD_TO_WIN32_HANDLE(fd)
		4632
		4633	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4634	file descriptors to socket handles. When not defining this symbol (the
		4635	default), then libev will call C<_get_osfhandle>, which is usually
		4636	correct. In some cases, programs use their own file descriptor management,
		4637	in which case they can provide this function to map fds to socket handles.
		4638
		4639	=item EV_WIN32_HANDLE_TO_FD(handle)
		4640
		4641	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4642	using the standard C<_open_osfhandle> function. For programs implementing
		4643	their own fd to handle mapping, overwriting this function makes it easier
		4644	to do so. This can be done by defining this macro to an appropriate value.
		4645
		4646	=item EV_WIN32_CLOSE_FD(fd)
		4647
		4648	If programs implement their own fd to handle mapping on win32, then this
		4649	macro can be used to override the C<close> function, useful to unregister
		4650	file descriptors again. Note that the replacement function has to close
		4651	the underlying OS handle.
		4652
		4653	=item EV_USE_WSASOCKET
		4654
		4655	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4656	communication socket, which works better in some environments. Otherwise,
		4657	the normal C<socket> function will be used, which works better in other
		4658	environments.
		4659
2123	=item EV_USE_POLL	4660	=item EV_USE_POLL
2124		4661
2125	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4662	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2126	backend. Otherwise it will be enabled on non-win32 platforms. It	4663	backend. Otherwise it will be enabled on non-win32 platforms. It
2127	takes precedence over select.	4664	takes precedence over select.
2128		4665
2129	=item EV_USE_EPOLL	4666	=item EV_USE_EPOLL
2130		4667
2131	If defined to be C<1>, libev will compile in support for the Linux	4668	If defined to be C<1>, libev will compile in support for the Linux
2132	C<epoll>(7) backend. Its availability will be detected at runtime,	4669	C<epoll>(7) backend. Its availability will be detected at runtime,
2133	otherwise another method will be used as fallback. This is the	4670	otherwise another method will be used as fallback. This is the preferred
2134	preferred backend for GNU/Linux systems.	4671	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4672	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4673
		4674	=item EV_USE_LINUXAIO
		4675
		4676	If defined to be C<1>, libev will compile in support for the Linux
		4677	aio backend. Due to it's currenbt limitations it has to be requested
		4678	explicitly. If undefined, it will be enabled on linux, otherwise
		4679	disabled.
2135		4680
2136	=item EV_USE_KQUEUE	4681	=item EV_USE_KQUEUE
2137		4682
2138	If defined to be C<1>, libev will compile in support for the BSD style	4683	If defined to be C<1>, libev will compile in support for the BSD style
2139	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4684	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2152	otherwise another method will be used as fallback. This is the preferred	4697	otherwise another method will be used as fallback. This is the preferred
2153	backend for Solaris 10 systems.	4698	backend for Solaris 10 systems.
2154		4699
2155	=item EV_USE_DEVPOLL	4700	=item EV_USE_DEVPOLL
2156		4701
2157	reserved for future expansion, works like the USE symbols above.	4702	Reserved for future expansion, works like the USE symbols above.
2158		4703
2159	=item EV_USE_INOTIFY	4704	=item EV_USE_INOTIFY
2160		4705
2161	If defined to be C<1>, libev will compile in support for the Linux inotify	4706	If defined to be C<1>, libev will compile in support for the Linux inotify
2162	interface to speed up C<ev_stat> watchers. Its actual availability will	4707	interface to speed up C<ev_stat> watchers. Its actual availability will
2163	be detected at runtime.	4708	be detected at runtime. If undefined, it will be enabled if the headers
		4709	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2164		4710
		4711	=item EV_NO_SMP
		4712
		4713	If defined to be C<1>, libev will assume that memory is always coherent
		4714	between threads, that is, threads can be used, but threads never run on
		4715	different cpus (or different cpu cores). This reduces dependencies
		4716	and makes libev faster.
		4717
		4718	=item EV_NO_THREADS
		4719
		4720	If defined to be C<1>, libev will assume that it will never be called from
		4721	different threads (that includes signal handlers), which is a stronger
		4722	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4723	libev faster.
		4724
		4725	=item EV_ATOMIC_T
		4726
		4727	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4728	access is atomic with respect to other threads or signal contexts. No
		4729	such type is easily found in the C language, so you can provide your own
		4730	type that you know is safe for your purposes. It is used both for signal
		4731	handler "locking" as well as for signal and thread safety in C<ev_async>
		4732	watchers.
		4733
		4734	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4735	(from F<signal.h>), which is usually good enough on most platforms.
		4736
2165	=item EV_H	4737	=item EV_H (h)
2166		4738
2167	The name of the F<ev.h> header file used to include it. The default if	4739	The name of the F<ev.h> header file used to include it. The default if
2168	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4740	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2169	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4741	used to virtually rename the F<ev.h> header file in case of conflicts.
2170		4742
2171	=item EV_CONFIG_H	4743	=item EV_CONFIG_H (h)
2172		4744
2173	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4745	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2174	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4746	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2175	C<EV_H>, above.	4747	C<EV_H>, above.
2176		4748
2177	=item EV_EVENT_H	4749	=item EV_EVENT_H (h)
2178		4750
2179	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4751	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2180	of how the F<event.h> header can be found.	4752	of how the F<event.h> header can be found, the default is C<"event.h">.
2181		4753
2182	=item EV_PROTOTYPES	4754	=item EV_PROTOTYPES (h)
2183		4755
2184	If defined to be C<0>, then F<ev.h> will not define any function	4756	If defined to be C<0>, then F<ev.h> will not define any function
2185	prototypes, but still define all the structs and other symbols. This is	4757	prototypes, but still define all the structs and other symbols. This is
2186	occasionally useful if you want to provide your own wrapper functions	4758	occasionally useful if you want to provide your own wrapper functions
2187	around libev functions.	4759	around libev functions.
…		…
2192	will have the C<struct ev_loop *> as first argument, and you can create	4764	will have the C<struct ev_loop *> as first argument, and you can create
2193	additional independent event loops. Otherwise there will be no support	4765	additional independent event loops. Otherwise there will be no support
2194	for multiple event loops and there is no first event loop pointer	4766	for multiple event loops and there is no first event loop pointer
2195	argument. Instead, all functions act on the single default loop.	4767	argument. Instead, all functions act on the single default loop.
2196		4768
		4769	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4770	default loop when multiplicity is switched off - you always have to
		4771	initialise the loop manually in this case.
		4772
2197	=item EV_MINPRI	4773	=item EV_MINPRI
2198		4774
2199	=item EV_MAXPRI	4775	=item EV_MAXPRI
2200		4776
2201	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4777	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2206	When doing priority-based operations, libev usually has to linearly search	4782	When doing priority-based operations, libev usually has to linearly search
2207	all the priorities, so having many of them (hundreds) uses a lot of space	4783	all the priorities, so having many of them (hundreds) uses a lot of space
2208	and time, so using the defaults of five priorities (-2 .. +2) is usually	4784	and time, so using the defaults of five priorities (-2 .. +2) is usually
2209	fine.	4785	fine.
2210		4786
2211	If your embedding app does not need any priorities, defining these both to	4787	If your embedding application does not need any priorities, defining these
2212	C<0> will save some memory and cpu.	4788	both to C<0> will save some memory and CPU.
2213		4789
2214	=item EV_PERIODIC_ENABLE	4790	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4791	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4792	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2215		4793
2216	If undefined or defined to be C<1>, then periodic timers are supported. If	4794	If undefined or defined to be C<1> (and the platform supports it), then
2217	defined to be C<0>, then they are not. Disabling them saves a few kB of	4795	the respective watcher type is supported. If defined to be C<0>, then it
2218	code.	4796	is not. Disabling watcher types mainly saves code size.
2219		4797
2220	=item EV_IDLE_ENABLE	4798	=item EV_FEATURES
2221
2222	If undefined or defined to be C<1>, then idle watchers are supported. If
2223	defined to be C<0>, then they are not. Disabling them saves a few kB of
2224	code.
2225
2226	=item EV_EMBED_ENABLE
2227
2228	If undefined or defined to be C<1>, then embed watchers are supported. If
2229	defined to be C<0>, then they are not.
2230
2231	=item EV_STAT_ENABLE
2232
2233	If undefined or defined to be C<1>, then stat watchers are supported. If
2234	defined to be C<0>, then they are not.
2235
2236	=item EV_FORK_ENABLE
2237
2238	If undefined or defined to be C<1>, then fork watchers are supported. If
2239	defined to be C<0>, then they are not.
2240
2241	=item EV_MINIMAL
2242		4799
2243	If you need to shave off some kilobytes of code at the expense of some	4800	If you need to shave off some kilobytes of code at the expense of some
2244	speed, define this symbol to C<1>. Currently only used for gcc to override	4801	speed (but with the full API), you can define this symbol to request
2245	some inlining decisions, saves roughly 30% codesize of amd64.	4802	certain subsets of functionality. The default is to enable all features
		4803	that can be enabled on the platform.
		4804
		4805	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4806	with some broad features you want) and then selectively re-enable
		4807	additional parts you want, for example if you want everything minimal,
		4808	but multiple event loop support, async and child watchers and the poll
		4809	backend, use this:
		4810
		4811	#define EV_FEATURES 0
		4812	#define EV_MULTIPLICITY 1
		4813	#define EV_USE_POLL 1
		4814	#define EV_CHILD_ENABLE 1
		4815	#define EV_ASYNC_ENABLE 1
		4816
		4817	The actual value is a bitset, it can be a combination of the following
		4818	values (by default, all of these are enabled):
		4819
		4820	=over 4
		4821
		4822	=item C<1> - faster/larger code
		4823
		4824	Use larger code to speed up some operations.
		4825
		4826	Currently this is used to override some inlining decisions (enlarging the
		4827	code size by roughly 30% on amd64).
		4828
		4829	When optimising for size, use of compiler flags such as C<-Os> with
		4830	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4831	assertions.
		4832
		4833	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4834	(e.g. gcc with C<-Os>).
		4835
		4836	=item C<2> - faster/larger data structures
		4837
		4838	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4839	hash table sizes and so on. This will usually further increase code size
		4840	and can additionally have an effect on the size of data structures at
		4841	runtime.
		4842
		4843	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4844	(e.g. gcc with C<-Os>).
		4845
		4846	=item C<4> - full API configuration
		4847
		4848	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4849	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4850
		4851	=item C<8> - full API
		4852
		4853	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4854	details on which parts of the API are still available without this
		4855	feature, and do not complain if this subset changes over time.
		4856
		4857	=item C<16> - enable all optional watcher types
		4858
		4859	Enables all optional watcher types. If you want to selectively enable
		4860	only some watcher types other than I/O and timers (e.g. prepare,
		4861	embed, async, child...) you can enable them manually by defining
		4862	C<EV_watchertype_ENABLE> to C<1> instead.
		4863
		4864	=item C<32> - enable all backends
		4865
		4866	This enables all backends - without this feature, you need to enable at
		4867	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4868
		4869	=item C<64> - enable OS-specific "helper" APIs
		4870
		4871	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4872	default.
		4873
		4874	=back
		4875
		4876	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4877	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4878	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4879	watchers, timers and monotonic clock support.
		4880
		4881	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4882	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4883	your program might be left out as well - a binary starting a timer and an
		4884	I/O watcher then might come out at only 5Kb.
		4885
		4886	=item EV_API_STATIC
		4887
		4888	If this symbol is defined (by default it is not), then all identifiers
		4889	will have static linkage. This means that libev will not export any
		4890	identifiers, and you cannot link against libev anymore. This can be useful
		4891	when you embed libev, only want to use libev functions in a single file,
		4892	and do not want its identifiers to be visible.
		4893
		4894	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4895	wants to use libev.
		4896
		4897	This option only works when libev is compiled with a C compiler, as C++
		4898	doesn't support the required declaration syntax.
		4899
		4900	=item EV_AVOID_STDIO
		4901
		4902	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4903	functions (printf, scanf, perror etc.). This will increase the code size
		4904	somewhat, but if your program doesn't otherwise depend on stdio and your
		4905	libc allows it, this avoids linking in the stdio library which is quite
		4906	big.
		4907
		4908	Note that error messages might become less precise when this option is
		4909	enabled.
		4910
		4911	=item EV_NSIG
		4912
		4913	The highest supported signal number, +1 (or, the number of
		4914	signals): Normally, libev tries to deduce the maximum number of signals
		4915	automatically, but sometimes this fails, in which case it can be
		4916	specified. Also, using a lower number than detected (C<32> should be
		4917	good for about any system in existence) can save some memory, as libev
		4918	statically allocates some 12-24 bytes per signal number.
2246		4919
2247	=item EV_PID_HASHSIZE	4920	=item EV_PID_HASHSIZE
2248		4921
2249	C<ev_child> watchers use a small hash table to distribute workload by	4922	C<ev_child> watchers use a small hash table to distribute workload by
2250	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4923	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2251	than enough. If you need to manage thousands of children you might want to	4924	usually more than enough. If you need to manage thousands of children you
2252	increase this value (I<must> be a power of two).	4925	might want to increase this value (I<must> be a power of two).
2253		4926
2254	=item EV_INOTIFY_HASHSIZE	4927	=item EV_INOTIFY_HASHSIZE
2255		4928
2256	C<ev_staz> watchers use a small hash table to distribute workload by	4929	C<ev_stat> watchers use a small hash table to distribute workload by
2257	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4930	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2258	usually more than enough. If you need to manage thousands of C<ev_stat>	4931	disabled), usually more than enough. If you need to manage thousands of
2259	watchers you might want to increase this value (I<must> be a power of	4932	C<ev_stat> watchers you might want to increase this value (I<must> be a
2260	two).	4933	power of two).
		4934
		4935	=item EV_USE_4HEAP
		4936
		4937	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4938	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4939	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4940	faster performance with many (thousands) of watchers.
		4941
		4942	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4943	will be C<0>.
		4944
		4945	=item EV_HEAP_CACHE_AT
		4946
		4947	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4948	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4949	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4950	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4951	but avoids random read accesses on heap changes. This improves performance
		4952	noticeably with many (hundreds) of watchers.
		4953
		4954	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4955	will be C<0>.
		4956
		4957	=item EV_VERIFY
		4958
		4959	Controls how much internal verification (see C<ev_verify ()>) will
		4960	be done: If set to C<0>, no internal verification code will be compiled
		4961	in. If set to C<1>, then verification code will be compiled in, but not
		4962	called. If set to C<2>, then the internal verification code will be
		4963	called once per loop, which can slow down libev. If set to C<3>, then the
		4964	verification code will be called very frequently, which will slow down
		4965	libev considerably.
		4966
		4967	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4968	will be C<0>.
2261		4969
2262	=item EV_COMMON	4970	=item EV_COMMON
2263		4971
2264	By default, all watchers have a C<void *data> member. By redefining	4972	By default, all watchers have a C<void *data> member. By redefining
2265	this macro to a something else you can include more and other types of	4973	this macro to something else you can include more and other types of
2266	members. You have to define it each time you include one of the files,	4974	members. You have to define it each time you include one of the files,
2267	though, and it must be identical each time.	4975	though, and it must be identical each time.
2268		4976
2269	For example, the perl EV module uses something like this:	4977	For example, the perl EV module uses something like this:
2270		4978
2271	#define EV_COMMON \	4979	#define EV_COMMON \
2272	SV *self; /* contains this struct */ \	4980	SV *self; /* contains this struct */ \
2273	SV *cb_sv, *fh /* note no trailing ";" */	4981	SV *cb_sv, *fh /* note no trailing ";" */
2274		4982
2275	=item EV_CB_DECLARE (type)	4983	=item EV_CB_DECLARE (type)
2276		4984
2277	=item EV_CB_INVOKE (watcher, revents)	4985	=item EV_CB_INVOKE (watcher, revents)
2278		4986
2279	=item ev_set_cb (ev, cb)	4987	=item ev_set_cb (ev, cb)
2280		4988
2281	Can be used to change the callback member declaration in each watcher,	4989	Can be used to change the callback member declaration in each watcher,
2282	and the way callbacks are invoked and set. Must expand to a struct member	4990	and the way callbacks are invoked and set. Must expand to a struct member
2283	definition and a statement, respectively. See the F<ev.v> header file for	4991	definition and a statement, respectively. See the F<ev.h> header file for
2284	their default definitions. One possible use for overriding these is to	4992	their default definitions. One possible use for overriding these is to
2285	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4993	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2286	method calls instead of plain function calls in C++.	4994	method calls instead of plain function calls in C++.
		4995
		4996	=back
		4997
		4998	=head2 EXPORTED API SYMBOLS
		4999
		5000	If you need to re-export the API (e.g. via a DLL) and you need a list of
		5001	exported symbols, you can use the provided F<Symbol.*> files which list
		5002	all public symbols, one per line:
		5003
		5004	Symbols.ev for libev proper
		5005	Symbols.event for the libevent emulation
		5006
		5007	This can also be used to rename all public symbols to avoid clashes with
		5008	multiple versions of libev linked together (which is obviously bad in
		5009	itself, but sometimes it is inconvenient to avoid this).
		5010
		5011	A sed command like this will create wrapper C<#define>'s that you need to
		5012	include before including F<ev.h>:
		5013
		5014	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		5015
		5016	This would create a file F<wrap.h> which essentially looks like this:
		5017
		5018	#define ev_backend myprefix_ev_backend
		5019	#define ev_check_start myprefix_ev_check_start
		5020	#define ev_check_stop myprefix_ev_check_stop
		5021	...
2287		5022
2288	=head2 EXAMPLES	5023	=head2 EXAMPLES
2289		5024
2290	For a real-world example of a program the includes libev	5025	For a real-world example of a program the includes libev
2291	verbatim, you can have a look at the EV perl module	5026	verbatim, you can have a look at the EV perl module
…		…
2296	file.	5031	file.
2297		5032
2298	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	5033	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2299	that everybody includes and which overrides some configure choices:	5034	that everybody includes and which overrides some configure choices:
2300		5035
2301	#define EV_MINIMAL 1	5036	#define EV_FEATURES 8
2302	#define EV_USE_POLL 0	5037	#define EV_USE_SELECT 1
2303	#define EV_MULTIPLICITY 0
2304	#define EV_PERIODIC_ENABLE 0	5038	#define EV_PREPARE_ENABLE 1
		5039	#define EV_IDLE_ENABLE 1
2305	#define EV_STAT_ENABLE 0	5040	#define EV_SIGNAL_ENABLE 1
2306	#define EV_FORK_ENABLE 0	5041	#define EV_CHILD_ENABLE 1
		5042	#define EV_USE_STDEXCEPT 0
2307	#define EV_CONFIG_H <config.h>	5043	#define EV_CONFIG_H <config.h>
2308	#define EV_MINPRI 0
2309	#define EV_MAXPRI 0
2310		5044
2311	#include "ev++.h"	5045	#include "ev++.h"
2312		5046
2313	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	5047	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2314		5048
2315	#include "ev_cpp.h"	5049	#include "ev_cpp.h"
2316	#include "ev.c"	5050	#include "ev.c"
2317		5051
		5052	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2318		5053
		5054	=head2 THREADS AND COROUTINES
		5055
		5056	=head3 THREADS
		5057
		5058	All libev functions are reentrant and thread-safe unless explicitly
		5059	documented otherwise, but libev implements no locking itself. This means
		5060	that you can use as many loops as you want in parallel, as long as there
		5061	are no concurrent calls into any libev function with the same loop
		5062	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		5063	of course): libev guarantees that different event loops share no data
		5064	structures that need any locking.
		5065
		5066	Or to put it differently: calls with different loop parameters can be done
		5067	concurrently from multiple threads, calls with the same loop parameter
		5068	must be done serially (but can be done from different threads, as long as
		5069	only one thread ever is inside a call at any point in time, e.g. by using
		5070	a mutex per loop).
		5071
		5072	Specifically to support threads (and signal handlers), libev implements
		5073	so-called C<ev_async> watchers, which allow some limited form of
		5074	concurrency on the same event loop, namely waking it up "from the
		5075	outside".
		5076
		5077	If you want to know which design (one loop, locking, or multiple loops
		5078	without or something else still) is best for your problem, then I cannot
		5079	help you, but here is some generic advice:
		5080
		5081	=over 4
		5082
		5083	=item * most applications have a main thread: use the default libev loop
		5084	in that thread, or create a separate thread running only the default loop.
		5085
		5086	This helps integrating other libraries or software modules that use libev
		5087	themselves and don't care/know about threading.
		5088
		5089	=item * one loop per thread is usually a good model.
		5090
		5091	Doing this is almost never wrong, sometimes a better-performance model
		5092	exists, but it is always a good start.
		5093
		5094	=item * other models exist, such as the leader/follower pattern, where one
		5095	loop is handed through multiple threads in a kind of round-robin fashion.
		5096
		5097	Choosing a model is hard - look around, learn, know that usually you can do
		5098	better than you currently do :-)
		5099
		5100	=item * often you need to talk to some other thread which blocks in the
		5101	event loop.
		5102
		5103	C<ev_async> watchers can be used to wake them up from other threads safely
		5104	(or from signal contexts...).
		5105
		5106	An example use would be to communicate signals or other events that only
		5107	work in the default loop by registering the signal watcher with the
		5108	default loop and triggering an C<ev_async> watcher from the default loop
		5109	watcher callback into the event loop interested in the signal.
		5110
		5111	=back
		5112
		5113	See also L</THREAD LOCKING EXAMPLE>.
		5114
		5115	=head3 COROUTINES
		5116
		5117	Libev is very accommodating to coroutines ("cooperative threads"):
		5118	libev fully supports nesting calls to its functions from different
		5119	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5120	different coroutines, and switch freely between both coroutines running
		5121	the loop, as long as you don't confuse yourself). The only exception is
		5122	that you must not do this from C<ev_periodic> reschedule callbacks.
		5123
		5124	Care has been taken to ensure that libev does not keep local state inside
		5125	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5126	they do not call any callbacks.
		5127
		5128	=head2 COMPILER WARNINGS
		5129
		5130	Depending on your compiler and compiler settings, you might get no or a
		5131	lot of warnings when compiling libev code. Some people are apparently
		5132	scared by this.
		5133
		5134	However, these are unavoidable for many reasons. For one, each compiler
		5135	has different warnings, and each user has different tastes regarding
		5136	warning options. "Warn-free" code therefore cannot be a goal except when
		5137	targeting a specific compiler and compiler-version.
		5138
		5139	Another reason is that some compiler warnings require elaborate
		5140	workarounds, or other changes to the code that make it less clear and less
		5141	maintainable.
		5142
		5143	And of course, some compiler warnings are just plain stupid, or simply
		5144	wrong (because they don't actually warn about the condition their message
		5145	seems to warn about). For example, certain older gcc versions had some
		5146	warnings that resulted in an extreme number of false positives. These have
		5147	been fixed, but some people still insist on making code warn-free with
		5148	such buggy versions.
		5149
		5150	While libev is written to generate as few warnings as possible,
		5151	"warn-free" code is not a goal, and it is recommended not to build libev
		5152	with any compiler warnings enabled unless you are prepared to cope with
		5153	them (e.g. by ignoring them). Remember that warnings are just that:
		5154	warnings, not errors, or proof of bugs.
		5155
		5156
		5157	=head2 VALGRIND
		5158
		5159	Valgrind has a special section here because it is a popular tool that is
		5160	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5161
		5162	If you think you found a bug (memory leak, uninitialised data access etc.)
		5163	in libev, then check twice: If valgrind reports something like:
		5164
		5165	==2274== definitely lost: 0 bytes in 0 blocks.
		5166	==2274== possibly lost: 0 bytes in 0 blocks.
		5167	==2274== still reachable: 256 bytes in 1 blocks.
		5168
		5169	Then there is no memory leak, just as memory accounted to global variables
		5170	is not a memleak - the memory is still being referenced, and didn't leak.
		5171
		5172	Similarly, under some circumstances, valgrind might report kernel bugs
		5173	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5174	although an acceptable workaround has been found here), or it might be
		5175	confused.
		5176
		5177	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5178	make it into some kind of religion.
		5179
		5180	If you are unsure about something, feel free to contact the mailing list
		5181	with the full valgrind report and an explanation on why you think this
		5182	is a bug in libev (best check the archives, too :). However, don't be
		5183	annoyed when you get a brisk "this is no bug" answer and take the chance
		5184	of learning how to interpret valgrind properly.
		5185
		5186	If you need, for some reason, empty reports from valgrind for your project
		5187	I suggest using suppression lists.
		5188
		5189
		5190	=head1 PORTABILITY NOTES
		5191
		5192	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5193
		5194	GNU/Linux is the only common platform that supports 64 bit file/large file
		5195	interfaces but I<disables> them by default.
		5196
		5197	That means that libev compiled in the default environment doesn't support
		5198	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5199
		5200	Unfortunately, many programs try to work around this GNU/Linux issue
		5201	by enabling the large file API, which makes them incompatible with the
		5202	standard libev compiled for their system.
		5203
		5204	Likewise, libev cannot enable the large file API itself as this would
		5205	suddenly make it incompatible to the default compile time environment,
		5206	i.e. all programs not using special compile switches.
		5207
		5208	=head2 OS/X AND DARWIN BUGS
		5209
		5210	The whole thing is a bug if you ask me - basically any system interface
		5211	you touch is broken, whether it is locales, poll, kqueue or even the
		5212	OpenGL drivers.
		5213
		5214	=head3 C<kqueue> is buggy
		5215
		5216	The kqueue syscall is broken in all known versions - most versions support
		5217	only sockets, many support pipes.
		5218
		5219	Libev tries to work around this by not using C<kqueue> by default on this
		5220	rotten platform, but of course you can still ask for it when creating a
		5221	loop - embedding a socket-only kqueue loop into a select-based one is
		5222	probably going to work well.
		5223
		5224	=head3 C<poll> is buggy
		5225
		5226	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5227	implementation by something calling C<kqueue> internally around the 10.5.6
		5228	release, so now C<kqueue> I<and> C<poll> are broken.
		5229
		5230	Libev tries to work around this by not using C<poll> by default on
		5231	this rotten platform, but of course you can still ask for it when creating
		5232	a loop.
		5233
		5234	=head3 C<select> is buggy
		5235
		5236	All that's left is C<select>, and of course Apple found a way to fuck this
		5237	one up as well: On OS/X, C<select> actively limits the number of file
		5238	descriptors you can pass in to 1024 - your program suddenly crashes when
		5239	you use more.
		5240
		5241	There is an undocumented "workaround" for this - defining
		5242	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5243	work on OS/X.
		5244
		5245	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5246
		5247	=head3 C<errno> reentrancy
		5248
		5249	The default compile environment on Solaris is unfortunately so
		5250	thread-unsafe that you can't even use components/libraries compiled
		5251	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5252	defined by default. A valid, if stupid, implementation choice.
		5253
		5254	If you want to use libev in threaded environments you have to make sure
		5255	it's compiled with C<_REENTRANT> defined.
		5256
		5257	=head3 Event port backend
		5258
		5259	The scalable event interface for Solaris is called "event
		5260	ports". Unfortunately, this mechanism is very buggy in all major
		5261	releases. If you run into high CPU usage, your program freezes or you get
		5262	a large number of spurious wakeups, make sure you have all the relevant
		5263	and latest kernel patches applied. No, I don't know which ones, but there
		5264	are multiple ones to apply, and afterwards, event ports actually work
		5265	great.
		5266
		5267	If you can't get it to work, you can try running the program by setting
		5268	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5269	C<select> backends.
		5270
		5271	=head2 AIX POLL BUG
		5272
		5273	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5274	this by trying to avoid the poll backend altogether (i.e. it's not even
		5275	compiled in), which normally isn't a big problem as C<select> works fine
		5276	with large bitsets on AIX, and AIX is dead anyway.
		5277
		5278	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5279
		5280	=head3 General issues
		5281
		5282	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5283	requires, and its I/O model is fundamentally incompatible with the POSIX
		5284	model. Libev still offers limited functionality on this platform in
		5285	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5286	descriptors. This only applies when using Win32 natively, not when using
		5287	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5288	as every compiler comes with a slightly differently broken/incompatible
		5289	environment.
		5290
		5291	Lifting these limitations would basically require the full
		5292	re-implementation of the I/O system. If you are into this kind of thing,
		5293	then note that glib does exactly that for you in a very portable way (note
		5294	also that glib is the slowest event library known to man).
		5295
		5296	There is no supported compilation method available on windows except
		5297	embedding it into other applications.
		5298
		5299	Sensible signal handling is officially unsupported by Microsoft - libev
		5300	tries its best, but under most conditions, signals will simply not work.
		5301
		5302	Not a libev limitation but worth mentioning: windows apparently doesn't
		5303	accept large writes: instead of resulting in a partial write, windows will
		5304	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5305	so make sure you only write small amounts into your sockets (less than a
		5306	megabyte seems safe, but this apparently depends on the amount of memory
		5307	available).
		5308
		5309	Due to the many, low, and arbitrary limits on the win32 platform and
		5310	the abysmal performance of winsockets, using a large number of sockets
		5311	is not recommended (and not reasonable). If your program needs to use
		5312	more than a hundred or so sockets, then likely it needs to use a totally
		5313	different implementation for windows, as libev offers the POSIX readiness
		5314	notification model, which cannot be implemented efficiently on windows
		5315	(due to Microsoft monopoly games).
		5316
		5317	A typical way to use libev under windows is to embed it (see the embedding
		5318	section for details) and use the following F<evwrap.h> header file instead
		5319	of F<ev.h>:
		5320
		5321	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5322	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5323
		5324	#include "ev.h"
		5325
		5326	And compile the following F<evwrap.c> file into your project (make sure
		5327	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5328
		5329	#include "evwrap.h"
		5330	#include "ev.c"
		5331
		5332	=head3 The winsocket C<select> function
		5333
		5334	The winsocket C<select> function doesn't follow POSIX in that it
		5335	requires socket I<handles> and not socket I<file descriptors> (it is
		5336	also extremely buggy). This makes select very inefficient, and also
		5337	requires a mapping from file descriptors to socket handles (the Microsoft
		5338	C runtime provides the function C<_open_osfhandle> for this). See the
		5339	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5340	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5341
		5342	The configuration for a "naked" win32 using the Microsoft runtime
		5343	libraries and raw winsocket select is:
		5344
		5345	#define EV_USE_SELECT 1
		5346	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5347
		5348	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5349	complexity in the O(n²) range when using win32.
		5350
		5351	=head3 Limited number of file descriptors
		5352
		5353	Windows has numerous arbitrary (and low) limits on things.
		5354
		5355	Early versions of winsocket's select only supported waiting for a maximum
		5356	of C<64> handles (probably owning to the fact that all windows kernels
		5357	can only wait for C<64> things at the same time internally; Microsoft
		5358	recommends spawning a chain of threads and wait for 63 handles and the
		5359	previous thread in each. Sounds great!).
		5360
		5361	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5362	to some high number (e.g. C<2048>) before compiling the winsocket select
		5363	call (which might be in libev or elsewhere, for example, perl and many
		5364	other interpreters do their own select emulation on windows).
		5365
		5366	Another limit is the number of file descriptors in the Microsoft runtime
		5367	libraries, which by default is C<64> (there must be a hidden I<64>
		5368	fetish or something like this inside Microsoft). You can increase this
		5369	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5370	(another arbitrary limit), but is broken in many versions of the Microsoft
		5371	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5372	(depending on windows version and/or the phase of the moon). To get more,
		5373	you need to wrap all I/O functions and provide your own fd management, but
		5374	the cost of calling select (O(n²)) will likely make this unworkable.
		5375
		5376	=head2 PORTABILITY REQUIREMENTS
		5377
		5378	In addition to a working ISO-C implementation and of course the
		5379	backend-specific APIs, libev relies on a few additional extensions:
		5380
		5381	=over 4
		5382
		5383	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5384	calling conventions regardless of C<ev_watcher_type *>.
		5385
		5386	Libev assumes not only that all watcher pointers have the same internal
		5387	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5388	assumes that the same (machine) code can be used to call any watcher
		5389	callback: The watcher callbacks have different type signatures, but libev
		5390	calls them using an C<ev_watcher *> internally.
		5391
		5392	=item null pointers and integer zero are represented by 0 bytes
		5393
		5394	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5395	relies on this setting pointers and integers to null.
		5396
		5397	=item pointer accesses must be thread-atomic
		5398
		5399	Accessing a pointer value must be atomic, it must both be readable and
		5400	writable in one piece - this is the case on all current architectures.
		5401
		5402	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5403
		5404	The type C<sig_atomic_t volatile> (or whatever is defined as
		5405	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5406	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5407	believed to be sufficiently portable.
		5408
		5409	=item C<sigprocmask> must work in a threaded environment
		5410
		5411	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5412	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5413	pthread implementations will either allow C<sigprocmask> in the "main
		5414	thread" or will block signals process-wide, both behaviours would
		5415	be compatible with libev. Interaction between C<sigprocmask> and
		5416	C<pthread_sigmask> could complicate things, however.
		5417
		5418	The most portable way to handle signals is to block signals in all threads
		5419	except the initial one, and run the signal handling loop in the initial
		5420	thread as well.
		5421
		5422	=item C<long> must be large enough for common memory allocation sizes
		5423
		5424	To improve portability and simplify its API, libev uses C<long> internally
		5425	instead of C<size_t> when allocating its data structures. On non-POSIX
		5426	systems (Microsoft...) this might be unexpectedly low, but is still at
		5427	least 31 bits everywhere, which is enough for hundreds of millions of
		5428	watchers.
		5429
		5430	=item C<double> must hold a time value in seconds with enough accuracy
		5431
		5432	The type C<double> is used to represent timestamps. It is required to
		5433	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5434	good enough for at least into the year 4000 with millisecond accuracy
		5435	(the design goal for libev). This requirement is overfulfilled by
		5436	implementations using IEEE 754, which is basically all existing ones.
		5437
		5438	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5439	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5440	is either obsolete or somebody patched it to use C<long double> or
		5441	something like that, just kidding).
		5442
		5443	=back
		5444
		5445	If you know of other additional requirements drop me a note.
		5446
		5447
2319	=head1 COMPLEXITIES	5448	=head1 ALGORITHMIC COMPLEXITIES
2320		5449
2321	In this section the complexities of (many of) the algorithms used inside	5450	In this section the complexities of (many of) the algorithms used inside
2322	libev will be explained. For complexity discussions about backends see the	5451	libev will be documented. For complexity discussions about backends see
2323	documentation for C<ev_default_init>.	5452	the documentation for C<ev_default_init>.
2324		5453
2325	All of the following are about amortised time: If an array needs to be	5454	All of the following are about amortised time: If an array needs to be
2326	extended, libev needs to realloc and move the whole array, but this	5455	extended, libev needs to realloc and move the whole array, but this
2327	happens asymptotically never with higher number of elements, so O(1) might	5456	happens asymptotically rarer with higher number of elements, so O(1) might
2328	mean it might do a lengthy realloc operation in rare cases, but on average	5457	mean that libev does a lengthy realloc operation in rare cases, but on
2329	it is much faster and asymptotically approaches constant time.	5458	average it is much faster and asymptotically approaches constant time.
2330		5459
2331	=over 4	5460	=over 4
2332		5461
2333	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5462	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2334		5463
2335	This means that, when you have a watcher that triggers in one hour and	5464	This means that, when you have a watcher that triggers in one hour and
2336	there are 100 watchers that would trigger before that then inserting will	5465	there are 100 watchers that would trigger before that, then inserting will
2337	have to skip those 100 watchers.	5466	have to skip roughly seven (C<ld 100>) of these watchers.
2338		5467
2339	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	5468	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2340		5469
2341	That means that for changing a timer costs less than removing/adding them	5470	That means that changing a timer costs less than removing/adding them,
2342	as only the relative motion in the event queue has to be paid for.	5471	as only the relative motion in the event queue has to be paid for.
2343		5472
2344	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	5473	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2345		5474
2346	These just add the watcher into an array or at the head of a list.	5475	These just add the watcher into an array or at the head of a list.
		5476
2347	=item Stopping check/prepare/idle watchers: O(1)	5477	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2348		5478
2349	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5479	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2350		5480
2351	These watchers are stored in lists then need to be walked to find the	5481	These watchers are stored in lists, so they need to be walked to find the
2352	correct watcher to remove. The lists are usually short (you don't usually	5482	correct watcher to remove. The lists are usually short (you don't usually
2353	have many watchers waiting for the same fd or signal).	5483	have many watchers waiting for the same fd or signal: one is typical, two
		5484	is rare).
2354		5485
2355	=item Finding the next timer per loop iteration: O(1)	5486	=item Finding the next timer in each loop iteration: O(1)
		5487
		5488	By virtue of using a binary or 4-heap, the next timer is always found at a
		5489	fixed position in the storage array.
2356		5490
2357	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	5491	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2358		5492
2359	A change means an I/O watcher gets started or stopped, which requires	5493	A change means an I/O watcher gets started or stopped, which requires
2360	libev to recalculate its status (and possibly tell the kernel).	5494	libev to recalculate its status (and possibly tell the kernel, depending
		5495	on backend and whether C<ev_io_set> was used).
2361		5496
2362	=item Activating one watcher: O(1)	5497	=item Activating one watcher (putting it into the pending state): O(1)
2363		5498
2364	=item Priority handling: O(number_of_priorities)	5499	=item Priority handling: O(number_of_priorities)
2365		5500
2366	Priorities are implemented by allocating some space for each	5501	Priorities are implemented by allocating some space for each
2367	priority. When doing priority-based operations, libev usually has to	5502	priority. When doing priority-based operations, libev usually has to
2368	linearly search all the priorities.	5503	linearly search all the priorities, but starting/stopping and activating
		5504	watchers becomes O(1) with respect to priority handling.
		5505
		5506	=item Sending an ev_async: O(1)
		5507
		5508	=item Processing ev_async_send: O(number_of_async_watchers)
		5509
		5510	=item Processing signals: O(max_signal_number)
		5511
		5512	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5513	calls in the current loop iteration and the loop is currently
		5514	blocked. Checking for async and signal events involves iterating over all
		5515	running async watchers or all signal numbers.
2369		5516
2370	=back	5517	=back
2371		5518
2372		5519
		5520	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5521
		5522	The major version 4 introduced some incompatible changes to the API.
		5523
		5524	At the moment, the C<ev.h> header file provides compatibility definitions
		5525	for all changes, so most programs should still compile. The compatibility
		5526	layer might be removed in later versions of libev, so better update to the
		5527	new API early than late.
		5528
		5529	=over 4
		5530
		5531	=item C<EV_COMPAT3> backwards compatibility mechanism
		5532
		5533	The backward compatibility mechanism can be controlled by
		5534	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5535	section.
		5536
		5537	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5538
		5539	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5540
		5541	ev_loop_destroy (EV_DEFAULT_UC);
		5542	ev_loop_fork (EV_DEFAULT);
		5543
		5544	=item function/symbol renames
		5545
		5546	A number of functions and symbols have been renamed:
		5547
		5548	ev_loop => ev_run
		5549	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5550	EVLOOP_ONESHOT => EVRUN_ONCE
		5551
		5552	ev_unloop => ev_break
		5553	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5554	EVUNLOOP_ONE => EVBREAK_ONE
		5555	EVUNLOOP_ALL => EVBREAK_ALL
		5556
		5557	EV_TIMEOUT => EV_TIMER
		5558
		5559	ev_loop_count => ev_iteration
		5560	ev_loop_depth => ev_depth
		5561	ev_loop_verify => ev_verify
		5562
		5563	Most functions working on C<struct ev_loop> objects don't have an
		5564	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5565	associated constants have been renamed to not collide with the C<struct
		5566	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5567	as all other watcher types. Note that C<ev_loop_fork> is still called
		5568	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5569	typedef.
		5570
		5571	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5572
		5573	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5574	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5575	and work, but the library code will of course be larger.
		5576
		5577	=back
		5578
		5579
		5580	=head1 GLOSSARY
		5581
		5582	=over 4
		5583
		5584	=item active
		5585
		5586	A watcher is active as long as it has been started and not yet stopped.
		5587	See L</WATCHER STATES> for details.
		5588
		5589	=item application
		5590
		5591	In this document, an application is whatever is using libev.
		5592
		5593	=item backend
		5594
		5595	The part of the code dealing with the operating system interfaces.
		5596
		5597	=item callback
		5598
		5599	The address of a function that is called when some event has been
		5600	detected. Callbacks are being passed the event loop, the watcher that
		5601	received the event, and the actual event bitset.
		5602
		5603	=item callback/watcher invocation
		5604
		5605	The act of calling the callback associated with a watcher.
		5606
		5607	=item event
		5608
		5609	A change of state of some external event, such as data now being available
		5610	for reading on a file descriptor, time having passed or simply not having
		5611	any other events happening anymore.
		5612
		5613	In libev, events are represented as single bits (such as C<EV_READ> or
		5614	C<EV_TIMER>).
		5615
		5616	=item event library
		5617
		5618	A software package implementing an event model and loop.
		5619
		5620	=item event loop
		5621
		5622	An entity that handles and processes external events and converts them
		5623	into callback invocations.
		5624
		5625	=item event model
		5626
		5627	The model used to describe how an event loop handles and processes
		5628	watchers and events.
		5629
		5630	=item pending
		5631
		5632	A watcher is pending as soon as the corresponding event has been
		5633	detected. See L</WATCHER STATES> for details.
		5634
		5635	=item real time
		5636
		5637	The physical time that is observed. It is apparently strictly monotonic :)
		5638
		5639	=item wall-clock time
		5640
		5641	The time and date as shown on clocks. Unlike real time, it can actually
		5642	be wrong and jump forwards and backwards, e.g. when you adjust your
		5643	clock.
		5644
		5645	=item watcher
		5646
		5647	A data structure that describes interest in certain events. Watchers need
		5648	to be started (attached to an event loop) before they can receive events.
		5649
		5650	=back
		5651
2373	=head1 AUTHOR	5652	=head1 AUTHOR
2374		5653
2375	Marc Lehmann <libev@schmorp.de>.	5654	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5655	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
2376		5656

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