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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	=head2 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 occurring), 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
…		…
70	=head2 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 C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	112	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	113	(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	=head2 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	=head2 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 some floatingpoint value. Unlike the name	143	any calculations on it, you should treat it as some floating point value.
		144
104	component C<stamp> might indicate, it is also used for time differences	145	Unlike the name component C<stamp> might indicate, it is also used for
105	throughout libev.	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
106		168
107	=head1 GLOBAL FUNCTIONS	169	=head1 GLOBAL FUNCTIONS
108		170
109	These functions can be called anytime, even before initialising the	171	These functions can be called anytime, even before initialising the
110	library in any way.	172	library in any way.
…		…
113		175
114	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
115		177
116	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
117	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
118	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>.
119		182
120	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
121		184
122	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
123	either it is interrupted or the given time interval has passed. Basically	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
124	this is a subsecond-resolution C<sleep ()>.	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 >>).
125		194
126	=item int ev_version_major ()	195	=item int ev_version_major ()
127		196
128	=item int ev_version_minor ()	197	=item int ev_version_minor ()
129		198
…		…
140	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
141	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
142	not a problem.	211	not a problem.
143		212
144	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
145	version.	214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
146		216
147	assert (("libev version mismatch",	217	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	218	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	219	&& ev_version_minor () >= EV_VERSION_MINOR));
150		220
151	=item unsigned int ev_supported_backends ()	221	=item unsigned int ev_supported_backends ()
152		222
153	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_*>
154	value) compiled into this binary of libev (independent of their	224	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	226	a description of the set values.
157		227
158	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
159	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
160		230
161	assert (("sorry, no epoll, no sex",	231	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	232	ev_supported_backends () & EVBACKEND_EPOLL));
163		233
164	=item unsigned int ev_recommended_backends ()	234	=item unsigned int ev_recommended_backends ()
165		235
166	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
167	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
168	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
169	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
170	(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
171	libev will probe for if you specify no backends explicitly.	242	probe for if you specify no backends explicitly.
172		243
173	=item unsigned int ev_embeddable_backends ()	244	=item unsigned int ev_embeddable_backends ()
174		245
175	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
176	is the theoretical, all-platform, value. To find which backends	247	value is platform-specific but can include backends not available on the
177	might be supported on the current system, you would need to look at	248	current system. To find which embeddable backends might be supported on
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	249	the current system, you would need to look at C<ev_embeddable_backends ()
179	recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
180		251
181	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
182		253
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
184		255
185	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
186	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
187	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
188	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
189	potentially destructive action. The default is your system realloc	260	or take some potentially destructive action.
190	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.
191		265
192	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
195		269
196	Example: Replace the libev allocator with one that waits a bit and then	270	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	271	retries (example requires a standards-compliant C<realloc>).
198		272
199	static void *	273	static void *
200	persistent_realloc (void *ptr, size_t size)	274	persistent_realloc (void *ptr, size_t size)
201	{	275	{
202	for (;;)	276	for (;;)
…		…
211	}	285	}
212		286
213	...	287	...
214	ev_set_allocator (persistent_realloc);	288	ev_set_allocator (persistent_realloc);
215		289
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
217		291
218	Set the callback function to call on a retryable syscall error (such	292	Set the callback function to call on a retryable system call error (such
219	as failed select, poll, epoll_wait). The message is a printable string	293	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	294	indicating the system call or subsystem causing the problem. If this
221	callback is set, then libev will expect it to remedy the sitution, no	295	callback is set, then libev will expect it to remedy the situation, no
222	matter what, when it returns. That is, libev will generally retry the	296	matter what, when it returns. That is, libev will generally retry the
223	requested operation, or, if the condition doesn't go away, do bad stuff	297	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	298	(such as abort).
225		299
226	Example: This is basically the same thing that libev does internally, too.	300	Example: This is basically the same thing that libev does internally, too.
…		…
233	}	307	}
234		308
235	...	309	...
236	ev_set_syserr_cb (fatal_error);	310	ev_set_syserr_cb (fatal_error);
237		311
		312	=item ev_feed_signal (int signum)
		313
		314	This function can be used to "simulate" a signal receive. It is completely
		315	safe to call this function at any time, from any context, including signal
		316	handlers or random threads.
		317
		318	Its main use is to customise signal handling in your process, especially
		319	in the presence of threads. For example, you could block signals
		320	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		321	creating any loops), and in one thread, use C<sigwait> or any other
		322	mechanism to wait for signals, then "deliver" them to libev by calling
		323	C<ev_feed_signal>.
		324
238	=back	325	=back
239		326
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
241		328
242	An event loop is described by a C<struct ev_loop *>. The library knows two	329	An event loop is described by a C<struct ev_loop *> (the C<struct> is
243	types of such loops, the I<default> loop, which supports signals and child	330	I<not> optional in this case unless libev 3 compatibility is disabled, as
244	events, and dynamically created loops which do not.	331	libev 3 had an C<ev_loop> function colliding with the struct name).
245		332
246	If you use threads, a common model is to run the default event loop	333	The library knows two types of such loops, the I<default> loop, which
247	in your main thread (or in a separate thread) and for each thread you	334	supports child process events, and dynamically created event loops which
248	create, you also create another event loop. Libev itself does no locking	335	do not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		336
253	=over 4	337	=over 4
254		338
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	339	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		340
257	This will initialise the default event loop if it hasn't been initialised	341	This returns the "default" event loop object, which is what you should
258	yet and return it. If the default loop could not be initialised, returns	342	normally use when you just need "the event loop". Event loop objects and
259	false. If it already was initialised it simply returns it (and ignores the	343	the C<flags> parameter are described in more detail in the entry for
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	344	C<ev_loop_new>.
		345
		346	If the default loop is already initialised then this function simply
		347	returns it (and ignores the flags. If that is troubling you, check
		348	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		349	flags, which should almost always be C<0>, unless the caller is also the
		350	one calling C<ev_run> or otherwise qualifies as "the main program".
261		351
262	If you don't know what event loop to use, use the one returned from this	352	If you don't know what event loop to use, use the one returned from this
263	function.	353	function (or via the C<EV_DEFAULT> macro).
264		354
		355	Note that this function is I<not> thread-safe, so if you want to use it
		356	from multiple threads, you have to employ some kind of mutex (note also
		357	that this case is unlikely, as loops cannot be shared easily between
		358	threads anyway).
		359
265	The default loop is the only loop that can handle C<ev_signal> and	360	The default loop is the only loop that can handle C<ev_child> watchers,
266	C<ev_child> watchers, and to do this, it always registers a handler	361	and to do this, it always registers a handler for C<SIGCHLD>. If this is
267	for C<SIGCHLD>. If this is a problem for your app you can either	362	a problem for your application you can either create a dynamic loop with
268	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	363	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
269	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	364	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
270	C<ev_default_init>.	365
		366	Example: This is the most typical usage.
		367
		368	if (!ev_default_loop (0))
		369	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		370
		371	Example: Restrict libev to the select and poll backends, and do not allow
		372	environment settings to be taken into account:
		373
		374	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		375
		376	=item struct ev_loop *ev_loop_new (unsigned int flags)
		377
		378	This will create and initialise a new event loop object. If the loop
		379	could not be initialised, returns false.
		380
		381	This function is thread-safe, and one common way to use libev with
		382	threads is indeed to create one loop per thread, and using the default
		383	loop in the "main" or "initial" thread.
271		384
272	The flags argument can be used to specify special behaviour or specific	385	The flags argument can be used to specify special behaviour or specific
273	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	386	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
274		387
275	The following flags are supported:	388	The following flags are supported:
…		…
281	The default flags value. Use this if you have no clue (it's the right	394	The default flags value. Use this if you have no clue (it's the right
282	thing, believe me).	395	thing, believe me).
283		396
284	=item C<EVFLAG_NOENV>	397	=item C<EVFLAG_NOENV>
285		398
286	If this flag bit is ored into the flag value (or the program runs setuid	399	If this flag bit is or'ed into the flag value (or the program runs setuid
287	or setgid) then libev will I<not> look at the environment variable	400	or setgid) then libev will I<not> look at the environment variable
288	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
289	override the flags completely if it is found in the environment. This is	402	override the flags completely if it is found in the environment. This is
290	useful to try out specific backends to test their performance, or to work	403	useful to try out specific backends to test their performance, to work
291	around bugs.	404	around bugs, or to make libev threadsafe (accessing environment variables
		405	cannot be done in a threadsafe way, but usually it works if no other
		406	thread modifies them).
292		407
293	=item C<EVFLAG_FORKCHECK>	408	=item C<EVFLAG_FORKCHECK>
294		409
295	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	410	Instead of calling C<ev_loop_fork> manually after a fork, you can also
296	a fork, you can also make libev check for a fork in each iteration by	411	make libev check for a fork in each iteration by enabling this flag.
297	enabling this flag.
298		412
299	This works by calling C<getpid ()> on every iteration of the loop,	413	This works by calling C<getpid ()> on every iteration of the loop,
300	and thus this might slow down your event loop if you do a lot of loop	414	and thus this might slow down your event loop if you do a lot of loop
301	iterations and little real work, but is usually not noticeable (on my	415	iterations and little real work, but is usually not noticeable (on my
302	Linux system for example, C<getpid> is actually a simple 5-insn sequence	416	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
303	without a syscall and thus I<very> fast, but my Linux system also has	417	without a system call and thus I<very> fast, but my GNU/Linux system also has
304	C<pthread_atfork> which is even faster).	418	C<pthread_atfork> which is even faster).
305		419
306	The big advantage of this flag is that you can forget about fork (and	420	The big advantage of this flag is that you can forget about fork (and
307	forget about forgetting to tell libev about forking) when you use this	421	forget about forgetting to tell libev about forking) when you use this
308	flag.	422	flag.
309		423
310	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	424	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
311	environment variable.	425	environment variable.
		426
		427	=item C<EVFLAG_NOINOTIFY>
		428
		429	When this flag is specified, then libev will not attempt to use the
		430	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		431	testing, this flag can be useful to conserve inotify file descriptors, as
		432	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		433
		434	=item C<EVFLAG_SIGNALFD>
		435
		436	When this flag is specified, then libev will attempt to use the
		437	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		438	delivers signals synchronously, which makes it both faster and might make
		439	it possible to get the queued signal data. It can also simplify signal
		440	handling with threads, as long as you properly block signals in your
		441	threads that are not interested in handling them.
		442
		443	Signalfd will not be used by default as this changes your signal mask, and
		444	there are a lot of shoddy libraries and programs (glib's threadpool for
		445	example) that can't properly initialise their signal masks.
		446
		447	=item C<EVFLAG_NOSIGMASK>
		448
		449	When this flag is specified, then libev will avoid to modify the signal
		450	mask. Specifically, this means you have to make sure signals are unblocked
		451	when you want to receive them.
		452
		453	This behaviour is useful when you want to do your own signal handling, or
		454	want to handle signals only in specific threads and want to avoid libev
		455	unblocking the signals.
		456
		457	It's also required by POSIX in a threaded program, as libev calls
		458	C<sigprocmask>, whose behaviour is officially unspecified.
		459
		460	This flag's behaviour will become the default in future versions of libev.
312		461
313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	462	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
314		463
315	This is your standard select(2) backend. Not I<completely> standard, as	464	This is your standard select(2) backend. Not I<completely> standard, as
316	libev tries to roll its own fd_set with no limits on the number of fds,	465	libev tries to roll its own fd_set with no limits on the number of fds,
317	but if that fails, expect a fairly low limit on the number of fds when	466	but if that fails, expect a fairly low limit on the number of fds when
318	using this backend. It doesn't scale too well (O(highest_fd)), but its	467	using this backend. It doesn't scale too well (O(highest_fd)), but its
319	usually the fastest backend for a low number of (low-numbered :) fds.	468	usually the fastest backend for a low number of (low-numbered :) fds.
320		469
321	To get good performance out of this backend you need a high amount of	470	To get good performance out of this backend you need a high amount of
322	parallelity (most of the file descriptors should be busy). If you are	471	parallelism (most of the file descriptors should be busy). If you are
323	writing a server, you should C<accept ()> in a loop to accept as many	472	writing a server, you should C<accept ()> in a loop to accept as many
324	connections as possible during one iteration. You might also want to have	473	connections as possible during one iteration. You might also want to have
325	a look at C<ev_set_io_collect_interval ()> to increase the amount of	474	a look at C<ev_set_io_collect_interval ()> to increase the amount of
326	readyness notifications you get per iteration.	475	readiness notifications you get per iteration.
		476
		477	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		478	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		479	C<exceptfds> set on that platform).
327		480
328	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	481	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
329		482
330	And this is your standard poll(2) backend. It's more complicated	483	And this is your standard poll(2) backend. It's more complicated
331	than select, but handles sparse fds better and has no artificial	484	than select, but handles sparse fds better and has no artificial
332	limit on the number of fds you can use (except it will slow down	485	limit on the number of fds you can use (except it will slow down
333	considerably with a lot of inactive fds). It scales similarly to select,	486	considerably with a lot of inactive fds). It scales similarly to select,
334	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	487	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
335	performance tips.	488	performance tips.
336		489
		490	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		491	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		492
337	=item C<EVBACKEND_EPOLL> (value 4, Linux)	493	=item C<EVBACKEND_EPOLL> (value 4, Linux)
338		494
		495	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		496	kernels).
		497
339	For few fds, this backend is a bit little slower than poll and select,	498	For few fds, this backend is a bit little slower than poll and select, but
340	but it scales phenomenally better. While poll and select usually scale	499	it scales phenomenally better. While poll and select usually scale like
341	like O(total_fds) where n is the total number of fds (or the highest fd),	500	O(total_fds) where total_fds is the total number of fds (or the highest
342	epoll scales either O(1) or O(active_fds). The epoll design has a number	501	fd), epoll scales either O(1) or O(active_fds).
343	of shortcomings, such as silently dropping events in some hard-to-detect	502
344	cases and rewiring a syscall per fd change, no fork support and bad	503	The epoll mechanism deserves honorable mention as the most misdesigned
345	support for dup.	504	of the more advanced event mechanisms: mere annoyances include silently
		505	dropping file descriptors, requiring a system call per change per file
		506	descriptor (and unnecessary guessing of parameters), problems with dup,
		507	returning before the timeout value, resulting in additional iterations
		508	(and only giving 5ms accuracy while select on the same platform gives
		509	0.1ms) and so on. The biggest issue is fork races, however - if a program
		510	forks then I<both> parent and child process have to recreate the epoll
		511	set, which can take considerable time (one syscall per file descriptor)
		512	and is of course hard to detect.
		513
		514	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		515	but of course I<doesn't>, and epoll just loves to report events for
		516	totally I<different> file descriptors (even already closed ones, so
		517	one cannot even remove them from the set) than registered in the set
		518	(especially on SMP systems). Libev tries to counter these spurious
		519	notifications by employing an additional generation counter and comparing
		520	that against the events to filter out spurious ones, recreating the set
		521	when required. Epoll also erroneously rounds down timeouts, but gives you
		522	no way to know when and by how much, so sometimes you have to busy-wait
		523	because epoll returns immediately despite a nonzero timeout. And last
		524	not least, it also refuses to work with some file descriptors which work
		525	perfectly fine with C<select> (files, many character devices...).
		526
		527	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		528	cobbled together in a hurry, no thought to design or interaction with
		529	others. Oh, the pain, will it ever stop...
346		530
347	While stopping, setting and starting an I/O watcher in the same iteration	531	While stopping, setting and starting an I/O watcher in the same iteration
348	will result in some caching, there is still a syscall per such incident	532	will result in some caching, there is still a system call per such
349	(because the fd could point to a different file description now), so its	533	incident (because the same I<file descriptor> could point to a different
350	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	534	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
351	very well if you register events for both fds.	535	file descriptors might not work very well if you register events for both
352		536	file descriptors.
353	Please note that epoll sometimes generates spurious notifications, so you
354	need to use non-blocking I/O or other means to avoid blocking when no data
355	(or space) is available.
356		537
357	Best performance from this backend is achieved by not unregistering all	538	Best performance from this backend is achieved by not unregistering all
358	watchers for a file descriptor until it has been closed, if possible, i.e.	539	watchers for a file descriptor until it has been closed, if possible,
359	keep at least one watcher active per fd at all times.	540	i.e. keep at least one watcher active per fd at all times. Stopping and
		541	starting a watcher (without re-setting it) also usually doesn't cause
		542	extra overhead. A fork can both result in spurious notifications as well
		543	as in libev having to destroy and recreate the epoll object, which can
		544	take considerable time and thus should be avoided.
360		545
		546	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		547	faster than epoll for maybe up to a hundred file descriptors, depending on
		548	the usage. So sad.
		549
361	While nominally embeddeble in other event loops, this feature is broken in	550	While nominally embeddable in other event loops, this feature is broken in
362	all kernel versions tested so far.	551	all kernel versions tested so far.
		552
		553	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		554	C<EVBACKEND_POLL>.
363		555
364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	556	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
365		557
366	Kqueue deserves special mention, as at the time of this writing, it	558	Kqueue deserves special mention, as at the time of this writing, it
367	was broken on all BSDs except NetBSD (usually it doesn't work reliably	559	was broken on all BSDs except NetBSD (usually it doesn't work reliably
368	with anything but sockets and pipes, except on Darwin, where of course	560	with anything but sockets and pipes, except on Darwin, where of course
369	it's completely useless). For this reason it's not being "autodetected"	561	it's completely useless). Unlike epoll, however, whose brokenness
		562	is by design, these kqueue bugs can (and eventually will) be fixed
		563	without API changes to existing programs. For this reason it's not being
370	unless you explicitly specify it explicitly in the flags (i.e. using	564	"auto-detected" unless you explicitly specify it in the flags (i.e. using
371	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	565	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
372	system like NetBSD.	566	system like NetBSD.
373		567
374	You still can embed kqueue into a normal poll or select backend and use it	568	You still can embed kqueue into a normal poll or select backend and use it
375	only for sockets (after having made sure that sockets work with kqueue on	569	only for sockets (after having made sure that sockets work with kqueue on
376	the target platform). See C<ev_embed> watchers for more info.	570	the target platform). See C<ev_embed> watchers for more info.
377		571
378	It scales in the same way as the epoll backend, but the interface to the	572	It scales in the same way as the epoll backend, but the interface to the
379	kernel is more efficient (which says nothing about its actual speed, of	573	kernel is more efficient (which says nothing about its actual speed, of
380	course). While stopping, setting and starting an I/O watcher does never	574	course). While stopping, setting and starting an I/O watcher does never
381	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	575	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
382	two event changes per incident, support for C<fork ()> is very bad and it	576	two event changes per incident. Support for C<fork ()> is very bad (you
		577	might have to leak fd's on fork, but it's more sane than epoll) and it
383	drops fds silently in similarly hard-to-detect cases.	578	drops fds silently in similarly hard-to-detect cases.
384		579
385	This backend usually performs well under most conditions.	580	This backend usually performs well under most conditions.
386		581
387	While nominally embeddable in other event loops, this doesn't work	582	While nominally embeddable in other event loops, this doesn't work
388	everywhere, so you might need to test for this. And since it is broken	583	everywhere, so you might need to test for this. And since it is broken
389	almost everywhere, you should only use it when you have a lot of sockets	584	almost everywhere, you should only use it when you have a lot of sockets
390	(for which it usually works), by embedding it into another event loop	585	(for which it usually works), by embedding it into another event loop
391	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	586	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
392	sockets.	587	also broken on OS X)) and, did I mention it, using it only for sockets.
		588
		589	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		590	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		591	C<NOTE_EOF>.
393		592
394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	593	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
395		594
396	This is not implemented yet (and might never be, unless you send me an	595	This is not implemented yet (and might never be, unless you send me an
397	implementation). According to reports, C</dev/poll> only supports sockets	596	implementation). According to reports, C</dev/poll> only supports sockets
…		…
401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	600	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
402		601
403	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	602	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
404	it's really slow, but it still scales very well (O(active_fds)).	603	it's really slow, but it still scales very well (O(active_fds)).
405		604
406	Please note that solaris event ports can deliver a lot of spurious
407	notifications, so you need to use non-blocking I/O or other means to avoid
408	blocking when no data (or space) is available.
409
410	While this backend scales well, it requires one system call per active	605	While this backend scales well, it requires one system call per active
411	file descriptor per loop iteration. For small and medium numbers of file	606	file descriptor per loop iteration. For small and medium numbers of file
412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	607	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
413	might perform better.	608	might perform better.
414		609
415	On the positive side, ignoring the spurious readyness notifications, this	610	On the positive side, this backend actually performed fully to
416	backend actually performed to specification in all tests and is fully	611	specification in all tests and is fully embeddable, which is a rare feat
417	embeddable, which is a rare feat among the OS-specific backends.	612	among the OS-specific backends (I vastly prefer correctness over speed
		613	hacks).
		614
		615	On the negative side, the interface is I<bizarre> - so bizarre that
		616	even sun itself gets it wrong in their code examples: The event polling
		617	function sometimes returns events to the caller even though an error
		618	occurred, but with no indication whether it has done so or not (yes, it's
		619	even documented that way) - deadly for edge-triggered interfaces where you
		620	absolutely have to know whether an event occurred or not because you have
		621	to re-arm the watcher.
		622
		623	Fortunately libev seems to be able to work around these idiocies.
		624
		625	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		626	C<EVBACKEND_POLL>.
418		627
419	=item C<EVBACKEND_ALL>	628	=item C<EVBACKEND_ALL>
420		629
421	Try all backends (even potentially broken ones that wouldn't be tried	630	Try all backends (even potentially broken ones that wouldn't be tried
422	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	631	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
423	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	632	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
424		633
425	It is definitely not recommended to use this flag.	634	It is definitely not recommended to use this flag, use whatever
		635	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		636	at all.
		637
		638	=item C<EVBACKEND_MASK>
		639
		640	Not a backend at all, but a mask to select all backend bits from a
		641	C<flags> value, in case you want to mask out any backends from a flags
		642	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
426		643
427	=back	644	=back
428		645
429	If one or more of these are ored into the flags value, then only these	646	If one or more of the backend flags are or'ed into the flags value,
430	backends will be tried (in the reverse order as listed here). If none are	647	then only these backends will be tried (in the reverse order as listed
431	specified, all backends in C<ev_recommended_backends ()> will be tried.	648	here). If none are specified, all backends in C<ev_recommended_backends
432		649	()> will be tried.
433	The most typical usage is like this:
434
435	if (!ev_default_loop (0))
436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
437
438	Restrict libev to the select and poll backends, and do not allow
439	environment settings to be taken into account:
440
441	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
442
443	Use whatever libev has to offer, but make sure that kqueue is used if
444	available (warning, breaks stuff, best use only with your own private
445	event loop and only if you know the OS supports your types of fds):
446
447	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
448
449	=item struct ev_loop *ev_loop_new (unsigned int flags)
450
451	Similar to C<ev_default_loop>, but always creates a new event loop that is
452	always distinct from the default loop. Unlike the default loop, it cannot
453	handle signal and child watchers, and attempts to do so will be greeted by
454	undefined behaviour (or a failed assertion if assertions are enabled).
455		650
456	Example: Try to create a event loop that uses epoll and nothing else.	651	Example: Try to create a event loop that uses epoll and nothing else.
457		652
458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	653	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
459	if (!epoller)	654	if (!epoller)
460	fatal ("no epoll found here, maybe it hides under your chair");	655	fatal ("no epoll found here, maybe it hides under your chair");
461		656
		657	Example: Use whatever libev has to offer, but make sure that kqueue is
		658	used if available.
		659
		660	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		661
462	=item ev_default_destroy ()	662	=item ev_loop_destroy (loop)
463		663
464	Destroys the default loop again (frees all memory and kernel state	664	Destroys an event loop object (frees all memory and kernel state
465	etc.). None of the active event watchers will be stopped in the normal	665	etc.). None of the active event watchers will be stopped in the normal
466	sense, so e.g. C<ev_is_active> might still return true. It is your	666	sense, so e.g. C<ev_is_active> might still return true. It is your
467	responsibility to either stop all watchers cleanly yoursef I<before>	667	responsibility to either stop all watchers cleanly yourself I<before>
468	calling this function, or cope with the fact afterwards (which is usually	668	calling this function, or cope with the fact afterwards (which is usually
469	the easiest thing, you can just ignore the watchers and/or C<free ()> them	669	the easiest thing, you can just ignore the watchers and/or C<free ()> them
470	for example).	670	for example).
471		671
472	Note that certain global state, such as signal state, will not be freed by	672	Note that certain global state, such as signal state (and installed signal
473	this function, and related watchers (such as signal and child watchers)	673	handlers), will not be freed by this function, and related watchers (such
474	would need to be stopped manually.	674	as signal and child watchers) would need to be stopped manually.
475		675
476	In general it is not advisable to call this function except in the	676	This function is normally used on loop objects allocated by
477	rare occasion where you really need to free e.g. the signal handling	677	C<ev_loop_new>, but it can also be used on the default loop returned by
		678	C<ev_default_loop>, in which case it is not thread-safe.
		679
		680	Note that it is not advisable to call this function on the default loop
		681	except in the rare occasion where you really need to free its resources.
478	pipe fds. If you need dynamically allocated loops it is better to use	682	If you need dynamically allocated loops it is better to use C<ev_loop_new>
479	C<ev_loop_new> and C<ev_loop_destroy>).	683	and C<ev_loop_destroy>.
480		684
481	=item ev_loop_destroy (loop)	685	=item ev_loop_fork (loop)
482		686
483	Like C<ev_default_destroy>, but destroys an event loop created by an
484	earlier call to C<ev_loop_new>.
485
486	=item ev_default_fork ()
487
488	This function sets a flag that causes subsequent C<ev_loop> iterations	687	This function sets a flag that causes subsequent C<ev_run> iterations to
489	to reinitialise the kernel state for backends that have one. Despite the	688	reinitialise the kernel state for backends that have one. Despite the
490	name, you can call it anytime, but it makes most sense after forking, in	689	name, you can call it anytime, but it makes most sense after forking, in
491	the child process (or both child and parent, but that again makes little	690	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
492	sense). You I<must> call it in the child before using any of the libev	691	child before resuming or calling C<ev_run>.
493	functions, and it will only take effect at the next C<ev_loop> iteration.	692
		693	Again, you I<have> to call it on I<any> loop that you want to re-use after
		694	a fork, I<even if you do not plan to use the loop in the parent>. This is
		695	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		696	during fork.
494		697
495	On the other hand, you only need to call this function in the child	698	On the other hand, you only need to call this function in the child
496	process if and only if you want to use the event library in the child. If	699	process if and only if you want to use the event loop in the child. If
497	you just fork+exec, you don't have to call it at all.	700	you just fork+exec or create a new loop in the child, you don't have to
		701	call it at all (in fact, C<epoll> is so badly broken that it makes a
		702	difference, but libev will usually detect this case on its own and do a
		703	costly reset of the backend).
498		704
499	The function itself is quite fast and it's usually not a problem to call	705	The function itself is quite fast and it's usually not a problem to call
500	it just in case after a fork. To make this easy, the function will fit in	706	it just in case after a fork.
501	quite nicely into a call to C<pthread_atfork>:
502		707
		708	Example: Automate calling C<ev_loop_fork> on the default loop when
		709	using pthreads.
		710
		711	static void
		712	post_fork_child (void)
		713	{
		714	ev_loop_fork (EV_DEFAULT);
		715	}
		716
		717	...
503	pthread_atfork (0, 0, ev_default_fork);	718	pthread_atfork (0, 0, post_fork_child);
504
505	=item ev_loop_fork (loop)
506
507	Like C<ev_default_fork>, but acts on an event loop created by
508	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
509	after fork, and how you do this is entirely your own problem.
510		719
511	=item int ev_is_default_loop (loop)	720	=item int ev_is_default_loop (loop)
512		721
513	Returns true when the given loop actually is the default loop, false otherwise.	722	Returns true when the given loop is, in fact, the default loop, and false
		723	otherwise.
514		724
515	=item unsigned int ev_loop_count (loop)	725	=item unsigned int ev_iteration (loop)
516		726
517	Returns the count of loop iterations for the loop, which is identical to	727	Returns the current iteration count for the event loop, which is identical
518	the number of times libev did poll for new events. It starts at C<0> and	728	to the number of times libev did poll for new events. It starts at C<0>
519	happily wraps around with enough iterations.	729	and happily wraps around with enough iterations.
520		730
521	This value can sometimes be useful as a generation counter of sorts (it	731	This value can sometimes be useful as a generation counter of sorts (it
522	"ticks" the number of loop iterations), as it roughly corresponds with	732	"ticks" the number of loop iterations), as it roughly corresponds with
523	C<ev_prepare> and C<ev_check> calls.	733	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		734	prepare and check phases.
		735
		736	=item unsigned int ev_depth (loop)
		737
		738	Returns the number of times C<ev_run> was entered minus the number of
		739	times C<ev_run> was exited normally, in other words, the recursion depth.
		740
		741	Outside C<ev_run>, this number is zero. In a callback, this number is
		742	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		743	in which case it is higher.
		744
		745	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		746	throwing an exception etc.), doesn't count as "exit" - consider this
		747	as a hint to avoid such ungentleman-like behaviour unless it's really
		748	convenient, in which case it is fully supported.
524		749
525	=item unsigned int ev_backend (loop)	750	=item unsigned int ev_backend (loop)
526		751
527	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	752	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
528	use.	753	use.
…		…
533	received events and started processing them. This timestamp does not	758	received events and started processing them. This timestamp does not
534	change as long as callbacks are being processed, and this is also the base	759	change as long as callbacks are being processed, and this is also the base
535	time used for relative timers. You can treat it as the timestamp of the	760	time used for relative timers. You can treat it as the timestamp of the
536	event occurring (or more correctly, libev finding out about it).	761	event occurring (or more correctly, libev finding out about it).
537		762
		763	=item ev_now_update (loop)
		764
		765	Establishes the current time by querying the kernel, updating the time
		766	returned by C<ev_now ()> in the progress. This is a costly operation and
		767	is usually done automatically within C<ev_run ()>.
		768
		769	This function is rarely useful, but when some event callback runs for a
		770	very long time without entering the event loop, updating libev's idea of
		771	the current time is a good idea.
		772
		773	See also L</The special problem of time updates> in the C<ev_timer> section.
		774
		775	=item ev_suspend (loop)
		776
		777	=item ev_resume (loop)
		778
		779	These two functions suspend and resume an event loop, for use when the
		780	loop is not used for a while and timeouts should not be processed.
		781
		782	A typical use case would be an interactive program such as a game: When
		783	the user presses C<^Z> to suspend the game and resumes it an hour later it
		784	would be best to handle timeouts as if no time had actually passed while
		785	the program was suspended. This can be achieved by calling C<ev_suspend>
		786	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		787	C<ev_resume> directly afterwards to resume timer processing.
		788
		789	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		790	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		791	will be rescheduled (that is, they will lose any events that would have
		792	occurred while suspended).
		793
		794	After calling C<ev_suspend> you B<must not> call I<any> function on the
		795	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		796	without a previous call to C<ev_suspend>.
		797
		798	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		799	event loop time (see C<ev_now_update>).
		800
538	=item ev_loop (loop, int flags)	801	=item bool ev_run (loop, int flags)
539		802
540	Finally, this is it, the event handler. This function usually is called	803	Finally, this is it, the event handler. This function usually is called
541	after you initialised all your watchers and you want to start handling	804	after you have initialised all your watchers and you want to start
542	events.	805	handling events. It will ask the operating system for any new events, call
		806	the watcher callbacks, and then repeat the whole process indefinitely: This
		807	is why event loops are called I<loops>.
543		808
544	If the flags argument is specified as C<0>, it will not return until	809	If the flags argument is specified as C<0>, it will keep handling events
545	either no event watchers are active anymore or C<ev_unloop> was called.	810	until either no event watchers are active anymore or C<ev_break> was
		811	called.
546		812
		813	The return value is false if there are no more active watchers (which
		814	usually means "all jobs done" or "deadlock"), and true in all other cases
		815	(which usually means " you should call C<ev_run> again").
		816
547	Please note that an explicit C<ev_unloop> is usually better than	817	Please note that an explicit C<ev_break> is usually better than
548	relying on all watchers to be stopped when deciding when a program has	818	relying on all watchers to be stopped when deciding when a program has
549	finished (especially in interactive programs), but having a program that	819	finished (especially in interactive programs), but having a program
550	automatically loops as long as it has to and no longer by virtue of	820	that automatically loops as long as it has to and no longer by virtue
551	relying on its watchers stopping correctly is a thing of beauty.	821	of relying on its watchers stopping correctly, that is truly a thing of
		822	beauty.
552		823
		824	This function is I<mostly> exception-safe - you can break out of a
		825	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		826	exception and so on. This does not decrement the C<ev_depth> value, nor
		827	will it clear any outstanding C<EVBREAK_ONE> breaks.
		828
553	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	829	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
554	those events and any outstanding ones, but will not block your process in	830	those events and any already outstanding ones, but will not wait and
555	case there are no events and will return after one iteration of the loop.	831	block your process in case there are no events and will return after one
		832	iteration of the loop. This is sometimes useful to poll and handle new
		833	events while doing lengthy calculations, to keep the program responsive.
556		834
557	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	835	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
558	neccessary) and will handle those and any outstanding ones. It will block	836	necessary) and will handle those and any already outstanding ones. It
559	your process until at least one new event arrives, and will return after	837	will block your process until at least one new event arrives (which could
560	one iteration of the loop. This is useful if you are waiting for some	838	be an event internal to libev itself, so there is no guarantee that a
561	external event in conjunction with something not expressible using other	839	user-registered callback will be called), and will return after one
		840	iteration of the loop.
		841
		842	This is useful if you are waiting for some external event in conjunction
		843	with something not expressible using other libev watchers (i.e. "roll your
562	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	844	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
563	usually a better approach for this kind of thing.	845	usually a better approach for this kind of thing.
564		846
565	Here are the gory details of what C<ev_loop> does:	847	Here are the gory details of what C<ev_run> does (this is for your
		848	understanding, not a guarantee that things will work exactly like this in
		849	future versions):
566		850
		851	- Increment loop depth.
		852	- Reset the ev_break status.
567	- Before the first iteration, call any pending watchers.	853	- Before the first iteration, call any pending watchers.
		854	LOOP:
568	* If EVFLAG_FORKCHECK was used, check for a fork.	855	- If EVFLAG_FORKCHECK was used, check for a fork.
569	- If a fork was detected, queue and call all fork watchers.	856	- If a fork was detected (by any means), queue and call all fork watchers.
570	- Queue and call all prepare watchers.	857	- Queue and call all prepare watchers.
		858	- If ev_break was called, goto FINISH.
571	- If we have been forked, recreate the kernel state.	859	- If we have been forked, detach and recreate the kernel state
		860	as to not disturb the other process.
572	- Update the kernel state with all outstanding changes.	861	- Update the kernel state with all outstanding changes.
573	- Update the "event loop time".	862	- Update the "event loop time" (ev_now ()).
574	- Calculate for how long to sleep or block, if at all	863	- Calculate for how long to sleep or block, if at all
575	(active idle watchers, EVLOOP_NONBLOCK or not having	864	(active idle watchers, EVRUN_NOWAIT or not having
576	any active watchers at all will result in not sleeping).	865	any active watchers at all will result in not sleeping).
577	- Sleep if the I/O and timer collect interval say so.	866	- Sleep if the I/O and timer collect interval say so.
		867	- Increment loop iteration counter.
578	- Block the process, waiting for any events.	868	- Block the process, waiting for any events.
579	- Queue all outstanding I/O (fd) events.	869	- Queue all outstanding I/O (fd) events.
580	- Update the "event loop time" and do time jump handling.	870	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
581	- Queue all outstanding timers.	871	- Queue all expired timers.
582	- Queue all outstanding periodics.	872	- Queue all expired periodics.
583	- If no events are pending now, queue all idle watchers.	873	- Queue all idle watchers with priority higher than that of pending events.
584	- Queue all check watchers.	874	- Queue all check watchers.
585	- Call all queued watchers in reverse order (i.e. check watchers first).	875	- Call all queued watchers in reverse order (i.e. check watchers first).
586	Signals and child watchers are implemented as I/O watchers, and will	876	Signals and child watchers are implemented as I/O watchers, and will
587	be handled here by queueing them when their watcher gets executed.	877	be handled here by queueing them when their watcher gets executed.
588	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	878	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
589	were used, or there are no active watchers, return, otherwise	879	were used, or there are no active watchers, goto FINISH, otherwise
590	continue with step *.	880	continue with step LOOP.
		881	FINISH:
		882	- Reset the ev_break status iff it was EVBREAK_ONE.
		883	- Decrement the loop depth.
		884	- Return.
591		885
592	Example: Queue some jobs and then loop until no events are outstanding	886	Example: Queue some jobs and then loop until no events are outstanding
593	anymore.	887	anymore.
594		888
595	... queue jobs here, make sure they register event watchers as long	889	... queue jobs here, make sure they register event watchers as long
596	... as they still have work to do (even an idle watcher will do..)	890	... as they still have work to do (even an idle watcher will do..)
597	ev_loop (my_loop, 0);	891	ev_run (my_loop, 0);
598	... jobs done. yeah!	892	... jobs done or somebody called break. yeah!
599		893
600	=item ev_unloop (loop, how)	894	=item ev_break (loop, how)
601		895
602	Can be used to make a call to C<ev_loop> return early (but only after it	896	Can be used to make a call to C<ev_run> return early (but only after it
603	has processed all outstanding events). The C<how> argument must be either	897	has processed all outstanding events). The C<how> argument must be either
604	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	898	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
605	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	899	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
606		900
607	This "unloop state" will be cleared when entering C<ev_loop> again.	901	This "break state" will be cleared on the next call to C<ev_run>.
		902
		903	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		904	which case it will have no effect.
608		905
609	=item ev_ref (loop)	906	=item ev_ref (loop)
610		907
611	=item ev_unref (loop)	908	=item ev_unref (loop)
612		909
613	Ref/unref can be used to add or remove a reference count on the event	910	Ref/unref can be used to add or remove a reference count on the event
614	loop: Every watcher keeps one reference, and as long as the reference	911	loop: Every watcher keeps one reference, and as long as the reference
615	count is nonzero, C<ev_loop> will not return on its own. If you have	912	count is nonzero, C<ev_run> will not return on its own.
616	a watcher you never unregister that should not keep C<ev_loop> from	913
617	returning, ev_unref() after starting, and ev_ref() before stopping it. For	914	This is useful when you have a watcher that you never intend to
		915	unregister, but that nevertheless should not keep C<ev_run> from
		916	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		917	before stopping it.
		918
618	example, libev itself uses this for its internal signal pipe: It is not	919	As an example, libev itself uses this for its internal signal pipe: It
619	visible to the libev user and should not keep C<ev_loop> from exiting if	920	is not visible to the libev user and should not keep C<ev_run> from
620	no event watchers registered by it are active. It is also an excellent	921	exiting if no event watchers registered by it are active. It is also an
621	way to do this for generic recurring timers or from within third-party	922	excellent way to do this for generic recurring timers or from within
622	libraries. Just remember to I<unref after start> and I<ref before stop>	923	third-party libraries. Just remember to I<unref after start> and I<ref
623	(but only if the watcher wasn't active before, or was active before,	924	before stop> (but only if the watcher wasn't active before, or was active
624	respectively).	925	before, respectively. Note also that libev might stop watchers itself
		926	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		927	in the callback).
625		928
626	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	929	Example: Create a signal watcher, but keep it from keeping C<ev_run>
627	running when nothing else is active.	930	running when nothing else is active.
628		931
629	struct ev_signal exitsig;	932	ev_signal exitsig;
630	ev_signal_init (&exitsig, sig_cb, SIGINT);	933	ev_signal_init (&exitsig, sig_cb, SIGINT);
631	ev_signal_start (loop, &exitsig);	934	ev_signal_start (loop, &exitsig);
632	evf_unref (loop);	935	ev_unref (loop);
633		936
634	Example: For some weird reason, unregister the above signal handler again.	937	Example: For some weird reason, unregister the above signal handler again.
635		938
636	ev_ref (loop);	939	ev_ref (loop);
637	ev_signal_stop (loop, &exitsig);	940	ev_signal_stop (loop, &exitsig);
638		941
639	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	942	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
640		943
641	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	944	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
642		945
643	These advanced functions influence the time that libev will spend waiting	946	These advanced functions influence the time that libev will spend waiting
644	for events. Both are by default C<0>, meaning that libev will try to	947	for events. Both time intervals are by default C<0>, meaning that libev
645	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	948	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		949	latency.
646		950
647	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	951	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
648	allows libev to delay invocation of I/O and timer/periodic callbacks to	952	allows libev to delay invocation of I/O and timer/periodic callbacks
649	increase efficiency of loop iterations.	953	to increase efficiency of loop iterations (or to increase power-saving
		954	opportunities).
650		955
651	The background is that sometimes your program runs just fast enough to	956	The idea is that sometimes your program runs just fast enough to handle
652	handle one (or very few) event(s) per loop iteration. While this makes	957	one (or very few) event(s) per loop iteration. While this makes the
653	the program responsive, it also wastes a lot of CPU time to poll for new	958	program responsive, it also wastes a lot of CPU time to poll for new
654	events, especially with backends like C<select ()> which have a high	959	events, especially with backends like C<select ()> which have a high
655	overhead for the actual polling but can deliver many events at once.	960	overhead for the actual polling but can deliver many events at once.
656		961
657	By setting a higher I<io collect interval> you allow libev to spend more	962	By setting a higher I<io collect interval> you allow libev to spend more
658	time collecting I/O events, so you can handle more events per iteration,	963	time collecting I/O events, so you can handle more events per iteration,
659	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	964	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
660	C<ev_timer>) will be not affected. Setting this to a non-null value will	965	C<ev_timer>) will not be affected. Setting this to a non-null value will
661	introduce an additional C<ev_sleep ()> call into most loop iterations.	966	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		967	sleep time ensures that libev will not poll for I/O events more often then
		968	once per this interval, on average (as long as the host time resolution is
		969	good enough).
662		970
663	Likewise, by setting a higher I<timeout collect interval> you allow libev	971	Likewise, by setting a higher I<timeout collect interval> you allow libev
664	to spend more time collecting timeouts, at the expense of increased	972	to spend more time collecting timeouts, at the expense of increased
665	latency (the watcher callback will be called later). C<ev_io> watchers	973	latency/jitter/inexactness (the watcher callback will be called
666	will not be affected. Setting this to a non-null value will not introduce	974	later). C<ev_io> watchers will not be affected. Setting this to a non-null
667	any overhead in libev.	975	value will not introduce any overhead in libev.
668		976
669	Many (busy) programs can usually benefit by setting the io collect	977	Many (busy) programs can usually benefit by setting the I/O collect
670	interval to a value near C<0.1> or so, which is often enough for	978	interval to a value near C<0.1> or so, which is often enough for
671	interactive servers (of course not for games), likewise for timeouts. It	979	interactive servers (of course not for games), likewise for timeouts. It
672	usually doesn't make much sense to set it to a lower value than C<0.01>,	980	usually doesn't make much sense to set it to a lower value than C<0.01>,
673	as this approsaches the timing granularity of most systems.	981	as this approaches the timing granularity of most systems. Note that if
		982	you do transactions with the outside world and you can't increase the
		983	parallelity, then this setting will limit your transaction rate (if you
		984	need to poll once per transaction and the I/O collect interval is 0.01,
		985	then you can't do more than 100 transactions per second).
		986
		987	Setting the I<timeout collect interval> can improve the opportunity for
		988	saving power, as the program will "bundle" timer callback invocations that
		989	are "near" in time together, by delaying some, thus reducing the number of
		990	times the process sleeps and wakes up again. Another useful technique to
		991	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		992	they fire on, say, one-second boundaries only.
		993
		994	Example: we only need 0.1s timeout granularity, and we wish not to poll
		995	more often than 100 times per second:
		996
		997	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		998	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		999
		1000	=item ev_invoke_pending (loop)
		1001
		1002	This call will simply invoke all pending watchers while resetting their
		1003	pending state. Normally, C<ev_run> does this automatically when required,
		1004	but when overriding the invoke callback this call comes handy. This
		1005	function can be invoked from a watcher - this can be useful for example
		1006	when you want to do some lengthy calculation and want to pass further
		1007	event handling to another thread (you still have to make sure only one
		1008	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1009
		1010	=item int ev_pending_count (loop)
		1011
		1012	Returns the number of pending watchers - zero indicates that no watchers
		1013	are pending.
		1014
		1015	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1016
		1017	This overrides the invoke pending functionality of the loop: Instead of
		1018	invoking all pending watchers when there are any, C<ev_run> will call
		1019	this callback instead. This is useful, for example, when you want to
		1020	invoke the actual watchers inside another context (another thread etc.).
		1021
		1022	If you want to reset the callback, use C<ev_invoke_pending> as new
		1023	callback.
		1024
		1025	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1026
		1027	Sometimes you want to share the same loop between multiple threads. This
		1028	can be done relatively simply by putting mutex_lock/unlock calls around
		1029	each call to a libev function.
		1030
		1031	However, C<ev_run> can run an indefinite time, so it is not feasible
		1032	to wait for it to return. One way around this is to wake up the event
		1033	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1034	I<release> and I<acquire> callbacks on the loop.
		1035
		1036	When set, then C<release> will be called just before the thread is
		1037	suspended waiting for new events, and C<acquire> is called just
		1038	afterwards.
		1039
		1040	Ideally, C<release> will just call your mutex_unlock function, and
		1041	C<acquire> will just call the mutex_lock function again.
		1042
		1043	While event loop modifications are allowed between invocations of
		1044	C<release> and C<acquire> (that's their only purpose after all), no
		1045	modifications done will affect the event loop, i.e. adding watchers will
		1046	have no effect on the set of file descriptors being watched, or the time
		1047	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1048	to take note of any changes you made.
		1049
		1050	In theory, threads executing C<ev_run> will be async-cancel safe between
		1051	invocations of C<release> and C<acquire>.
		1052
		1053	See also the locking example in the C<THREADS> section later in this
		1054	document.
		1055
		1056	=item ev_set_userdata (loop, void *data)
		1057
		1058	=item void *ev_userdata (loop)
		1059
		1060	Set and retrieve a single C<void *> associated with a loop. When
		1061	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1062	C<0>.
		1063
		1064	These two functions can be used to associate arbitrary data with a loop,
		1065	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1066	C<acquire> callbacks described above, but of course can be (ab-)used for
		1067	any other purpose as well.
		1068
		1069	=item ev_verify (loop)
		1070
		1071	This function only does something when C<EV_VERIFY> support has been
		1072	compiled in, which is the default for non-minimal builds. It tries to go
		1073	through all internal structures and checks them for validity. If anything
		1074	is found to be inconsistent, it will print an error message to standard
		1075	error and call C<abort ()>.
		1076
		1077	This can be used to catch bugs inside libev itself: under normal
		1078	circumstances, this function will never abort as of course libev keeps its
		1079	data structures consistent.
674		1080
675	=back	1081	=back
676		1082
677		1083
678	=head1 ANATOMY OF A WATCHER	1084	=head1 ANATOMY OF A WATCHER
679		1085
		1086	In the following description, uppercase C<TYPE> in names stands for the
		1087	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1088	watchers and C<ev_io_start> for I/O watchers.
		1089
680	A watcher is a structure that you create and register to record your	1090	A watcher is an opaque structure that you allocate and register to record
681	interest in some event. For instance, if you want to wait for STDIN to	1091	your interest in some event. To make a concrete example, imagine you want
682	become readable, you would create an C<ev_io> watcher for that:	1092	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1093	for that:
683		1094
684	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1095	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
685	{	1096	{
686	ev_io_stop (w);	1097	ev_io_stop (w);
687	ev_unloop (loop, EVUNLOOP_ALL);	1098	ev_break (loop, EVBREAK_ALL);
688	}	1099	}
689		1100
690	struct ev_loop *loop = ev_default_loop (0);	1101	struct ev_loop *loop = ev_default_loop (0);
		1102
691	struct ev_io stdin_watcher;	1103	ev_io stdin_watcher;
		1104
692	ev_init (&stdin_watcher, my_cb);	1105	ev_init (&stdin_watcher, my_cb);
693	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1106	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
694	ev_io_start (loop, &stdin_watcher);	1107	ev_io_start (loop, &stdin_watcher);
		1108
695	ev_loop (loop, 0);	1109	ev_run (loop, 0);
696		1110
697	As you can see, you are responsible for allocating the memory for your	1111	As you can see, you are responsible for allocating the memory for your
698	watcher structures (and it is usually a bad idea to do this on the stack,	1112	watcher structures (and it is I<usually> a bad idea to do this on the
699	although this can sometimes be quite valid).	1113	stack).
700		1114
		1115	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1116	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1117
701	Each watcher structure must be initialised by a call to C<ev_init	1118	Each watcher structure must be initialised by a call to C<ev_init (watcher
702	(watcher *, callback)>, which expects a callback to be provided. This	1119	*, callback)>, which expects a callback to be provided. This callback is
703	callback gets invoked each time the event occurs (or, in the case of io	1120	invoked each time the event occurs (or, in the case of I/O watchers, each
704	watchers, each time the event loop detects that the file descriptor given	1121	time the event loop detects that the file descriptor given is readable
705	is readable and/or writable).	1122	and/or writable).
706		1123
707	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1124	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
708	with arguments specific to this watcher type. There is also a macro	1125	macro to configure it, with arguments specific to the watcher type. There
709	to combine initialisation and setting in one call: C<< ev_<type>_init	1126	is also a macro to combine initialisation and setting in one call: C<<
710	(watcher *, callback, ...) >>.	1127	ev_TYPE_init (watcher *, callback, ...) >>.
711		1128
712	To make the watcher actually watch out for events, you have to start it	1129	To make the watcher actually watch out for events, you have to start it
713	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1130	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
714	*) >>), and you can stop watching for events at any time by calling the	1131	*) >>), and you can stop watching for events at any time by calling the
715	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1132	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
716		1133
717	As long as your watcher is active (has been started but not stopped) you	1134	As long as your watcher is active (has been started but not stopped) you
718	must not touch the values stored in it. Most specifically you must never	1135	must not touch the values stored in it. Most specifically you must never
719	reinitialise it or call its C<set> macro.	1136	reinitialise it or call its C<ev_TYPE_set> macro.
720		1137
721	Each and every callback receives the event loop pointer as first, the	1138	Each and every callback receives the event loop pointer as first, the
722	registered watcher structure as second, and a bitset of received events as	1139	registered watcher structure as second, and a bitset of received events as
723	third argument.	1140	third argument.
724		1141
…		…
733	=item C<EV_WRITE>	1150	=item C<EV_WRITE>
734		1151
735	The file descriptor in the C<ev_io> watcher has become readable and/or	1152	The file descriptor in the C<ev_io> watcher has become readable and/or
736	writable.	1153	writable.
737		1154
738	=item C<EV_TIMEOUT>	1155	=item C<EV_TIMER>
739		1156
740	The C<ev_timer> watcher has timed out.	1157	The C<ev_timer> watcher has timed out.
741		1158
742	=item C<EV_PERIODIC>	1159	=item C<EV_PERIODIC>
743		1160
…		…
761		1178
762	=item C<EV_PREPARE>	1179	=item C<EV_PREPARE>
763		1180
764	=item C<EV_CHECK>	1181	=item C<EV_CHECK>
765		1182
766	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1183	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
767	to gather new events, and all C<ev_check> watchers are invoked just after	1184	gather new events, and all C<ev_check> watchers are queued (not invoked)
768	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1185	just after C<ev_run> has gathered them, but before it queues any callbacks
		1186	for any received events. That means C<ev_prepare> watchers are the last
		1187	watchers invoked before the event loop sleeps or polls for new events, and
		1188	C<ev_check> watchers will be invoked before any other watchers of the same
		1189	or lower priority within an event loop iteration.
		1190
769	received events. Callbacks of both watcher types can start and stop as	1191	Callbacks of both watcher types can start and stop as many watchers as
770	many watchers as they want, and all of them will be taken into account	1192	they want, and all of them will be taken into account (for example, a
771	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1193	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
772	C<ev_loop> from blocking).	1194	blocking).
773		1195
774	=item C<EV_EMBED>	1196	=item C<EV_EMBED>
775		1197
776	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1198	The embedded event loop specified in the C<ev_embed> watcher needs attention.
777		1199
778	=item C<EV_FORK>	1200	=item C<EV_FORK>
779		1201
780	The event loop has been resumed in the child process after fork (see	1202	The event loop has been resumed in the child process after fork (see
781	C<ev_fork>).	1203	C<ev_fork>).
782		1204
		1205	=item C<EV_CLEANUP>
		1206
		1207	The event loop is about to be destroyed (see C<ev_cleanup>).
		1208
783	=item C<EV_ASYNC>	1209	=item C<EV_ASYNC>
784		1210
785	The given async watcher has been asynchronously notified (see C<ev_async>).	1211	The given async watcher has been asynchronously notified (see C<ev_async>).
786		1212
		1213	=item C<EV_CUSTOM>
		1214
		1215	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1216	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1217
787	=item C<EV_ERROR>	1218	=item C<EV_ERROR>
788		1219
789	An unspecified error has occured, the watcher has been stopped. This might	1220	An unspecified error has occurred, the watcher has been stopped. This might
790	happen because the watcher could not be properly started because libev	1221	happen because the watcher could not be properly started because libev
791	ran out of memory, a file descriptor was found to be closed or any other	1222	ran out of memory, a file descriptor was found to be closed or any other
		1223	problem. Libev considers these application bugs.
		1224
792	problem. You best act on it by reporting the problem and somehow coping	1225	You best act on it by reporting the problem and somehow coping with the
793	with the watcher being stopped.	1226	watcher being stopped. Note that well-written programs should not receive
		1227	an error ever, so when your watcher receives it, this usually indicates a
		1228	bug in your program.
794		1229
795	Libev will usually signal a few "dummy" events together with an error,	1230	Libev will usually signal a few "dummy" events together with an error, for
796	for example it might indicate that a fd is readable or writable, and if	1231	example it might indicate that a fd is readable or writable, and if your
797	your callbacks is well-written it can just attempt the operation and cope	1232	callbacks is well-written it can just attempt the operation and cope with
798	with the error from read() or write(). This will not work in multithreaded	1233	the error from read() or write(). This will not work in multi-threaded
799	programs, though, so beware.	1234	programs, though, as the fd could already be closed and reused for another
		1235	thing, so beware.
800		1236
801	=back	1237	=back
802		1238
803	=head2 GENERIC WATCHER FUNCTIONS	1239	=head2 GENERIC WATCHER FUNCTIONS
804
805	In the following description, C<TYPE> stands for the watcher type,
806	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
807		1240
808	=over 4	1241	=over 4
809		1242
810	=item C<ev_init> (ev_TYPE *watcher, callback)	1243	=item C<ev_init> (ev_TYPE *watcher, callback)
811		1244
…		…
817	which rolls both calls into one.	1250	which rolls both calls into one.
818		1251
819	You can reinitialise a watcher at any time as long as it has been stopped	1252	You can reinitialise a watcher at any time as long as it has been stopped
820	(or never started) and there are no pending events outstanding.	1253	(or never started) and there are no pending events outstanding.
821		1254
822	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1255	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
823	int revents)>.	1256	int revents)>.
824		1257
		1258	Example: Initialise an C<ev_io> watcher in two steps.
		1259
		1260	ev_io w;
		1261	ev_init (&w, my_cb);
		1262	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1263
825	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1264	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
826		1265
827	This macro initialises the type-specific parts of a watcher. You need to	1266	This macro initialises the type-specific parts of a watcher. You need to
828	call C<ev_init> at least once before you call this macro, but you can	1267	call C<ev_init> at least once before you call this macro, but you can
829	call C<ev_TYPE_set> any number of times. You must not, however, call this	1268	call C<ev_TYPE_set> any number of times. You must not, however, call this
830	macro on a watcher that is active (it can be pending, however, which is a	1269	macro on a watcher that is active (it can be pending, however, which is a
831	difference to the C<ev_init> macro).	1270	difference to the C<ev_init> macro).
832		1271
833	Although some watcher types do not have type-specific arguments	1272	Although some watcher types do not have type-specific arguments
834	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1273	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
835		1274
		1275	See C<ev_init>, above, for an example.
		1276
836	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1277	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
837		1278
838	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1279	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
839	calls into a single call. This is the most convinient method to initialise	1280	calls into a single call. This is the most convenient method to initialise
840	a watcher. The same limitations apply, of course.	1281	a watcher. The same limitations apply, of course.
841		1282
		1283	Example: Initialise and set an C<ev_io> watcher in one step.
		1284
		1285	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1286
842	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1287	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
843		1288
844	Starts (activates) the given watcher. Only active watchers will receive	1289	Starts (activates) the given watcher. Only active watchers will receive
845	events. If the watcher is already active nothing will happen.	1290	events. If the watcher is already active nothing will happen.
846		1291
		1292	Example: Start the C<ev_io> watcher that is being abused as example in this
		1293	whole section.
		1294
		1295	ev_io_start (EV_DEFAULT_UC, &w);
		1296
847	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1297	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
848		1298
849	Stops the given watcher again (if active) and clears the pending	1299	Stops the given watcher if active, and clears the pending status (whether
		1300	the watcher was active or not).
		1301
850	status. It is possible that stopped watchers are pending (for example,	1302	It is possible that stopped watchers are pending - for example,
851	non-repeating timers are being stopped when they become pending), but	1303	non-repeating timers are being stopped when they become pending - but
852	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1304	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
853	you want to free or reuse the memory used by the watcher it is therefore a	1305	pending. If you want to free or reuse the memory used by the watcher it is
854	good idea to always call its C<ev_TYPE_stop> function.	1306	therefore a good idea to always call its C<ev_TYPE_stop> function.
855		1307
856	=item bool ev_is_active (ev_TYPE *watcher)	1308	=item bool ev_is_active (ev_TYPE *watcher)
857		1309
858	Returns a true value iff the watcher is active (i.e. it has been started	1310	Returns a true value iff the watcher is active (i.e. it has been started
859	and not yet been stopped). As long as a watcher is active you must not modify	1311	and not yet been stopped). As long as a watcher is active you must not modify
…		…
870		1322
871	=item callback ev_cb (ev_TYPE *watcher)	1323	=item callback ev_cb (ev_TYPE *watcher)
872		1324
873	Returns the callback currently set on the watcher.	1325	Returns the callback currently set on the watcher.
874		1326
875	=item ev_cb_set (ev_TYPE *watcher, callback)	1327	=item ev_set_cb (ev_TYPE *watcher, callback)
876		1328
877	Change the callback. You can change the callback at virtually any time	1329	Change the callback. You can change the callback at virtually any time
878	(modulo threads).	1330	(modulo threads).
879		1331
880	=item ev_set_priority (ev_TYPE *watcher, priority)	1332	=item ev_set_priority (ev_TYPE *watcher, int priority)
881		1333
882	=item int ev_priority (ev_TYPE *watcher)	1334	=item int ev_priority (ev_TYPE *watcher)
883		1335
884	Set and query the priority of the watcher. The priority is a small	1336	Set and query the priority of the watcher. The priority is a small
885	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1337	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
886	(default: C<-2>). Pending watchers with higher priority will be invoked	1338	(default: C<-2>). Pending watchers with higher priority will be invoked
887	before watchers with lower priority, but priority will not keep watchers	1339	before watchers with lower priority, but priority will not keep watchers
888	from being executed (except for C<ev_idle> watchers).	1340	from being executed (except for C<ev_idle> watchers).
889		1341
890	This means that priorities are I<only> used for ordering callback
891	invocation after new events have been received. This is useful, for
892	example, to reduce latency after idling, or more often, to bind two
893	watchers on the same event and make sure one is called first.
894
895	If you need to suppress invocation when higher priority events are pending	1342	If you need to suppress invocation when higher priority events are pending
896	you need to look at C<ev_idle> watchers, which provide this functionality.	1343	you need to look at C<ev_idle> watchers, which provide this functionality.
897		1344
898	You I<must not> change the priority of a watcher as long as it is active or	1345	You I<must not> change the priority of a watcher as long as it is active or
899	pending.	1346	pending.
900		1347
		1348	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1349	fine, as long as you do not mind that the priority value you query might
		1350	or might not have been clamped to the valid range.
		1351
901	The default priority used by watchers when no priority has been set is	1352	The default priority used by watchers when no priority has been set is
902	always C<0>, which is supposed to not be too high and not be too low :).	1353	always C<0>, which is supposed to not be too high and not be too low :).
903		1354
904	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1355	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
905	fine, as long as you do not mind that the priority value you query might	1356	priorities.
906	or might not have been adjusted to be within valid range.
907		1357
908	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1358	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
909		1359
910	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1360	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
911	C<loop> nor C<revents> need to be valid as long as the watcher callback	1361	C<loop> nor C<revents> need to be valid as long as the watcher callback
912	can deal with that fact.	1362	can deal with that fact, as both are simply passed through to the
		1363	callback.
913		1364
914	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1365	=item int ev_clear_pending (loop, ev_TYPE *watcher)
915		1366
916	If the watcher is pending, this function returns clears its pending status	1367	If the watcher is pending, this function clears its pending status and
917	and returns its C<revents> bitset (as if its callback was invoked). If the	1368	returns its C<revents> bitset (as if its callback was invoked). If the
918	watcher isn't pending it does nothing and returns C<0>.	1369	watcher isn't pending it does nothing and returns C<0>.
919		1370
		1371	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1372	callback to be invoked, which can be accomplished with this function.
		1373
		1374	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1375
		1376	Feeds the given event set into the event loop, as if the specified event
		1377	had happened for the specified watcher (which must be a pointer to an
		1378	initialised but not necessarily started event watcher). Obviously you must
		1379	not free the watcher as long as it has pending events.
		1380
		1381	Stopping the watcher, letting libev invoke it, or calling
		1382	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1383	not started in the first place.
		1384
		1385	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1386	functions that do not need a watcher.
		1387
920	=back	1388	=back
921		1389
		1390	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1391	OWN COMPOSITE WATCHERS> idioms.
922		1392
923	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1393	=head2 WATCHER STATES
924		1394
925	Each watcher has, by default, a member C<void *data> that you can change	1395	There are various watcher states mentioned throughout this manual -
926	and read at any time, libev will completely ignore it. This can be used	1396	active, pending and so on. In this section these states and the rules to
927	to associate arbitrary data with your watcher. If you need more data and	1397	transition between them will be described in more detail - and while these
928	don't want to allocate memory and store a pointer to it in that data	1398	rules might look complicated, they usually do "the right thing".
929	member, you can also "subclass" the watcher type and provide your own
930	data:
931		1399
932	struct my_io	1400	=over 4
933	{
934	struct ev_io io;
935	int otherfd;
936	void *somedata;
937	struct whatever *mostinteresting;
938	}
939		1401
940	And since your callback will be called with a pointer to the watcher, you	1402	=item initialised
941	can cast it back to your own type:
942		1403
943	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1404	Before a watcher can be registered with the event loop it has to be
944	{	1405	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
945	struct my_io *w = (struct my_io *)w_;	1406	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
946	...
947	}
948		1407
949	More interesting and less C-conformant ways of casting your callback type	1408	In this state it is simply some block of memory that is suitable for
950	instead have been omitted.	1409	use in an event loop. It can be moved around, freed, reused etc. at
		1410	will - as long as you either keep the memory contents intact, or call
		1411	C<ev_TYPE_init> again.
951		1412
952	Another common scenario is having some data structure with multiple	1413	=item started/running/active
953	watchers:
954		1414
955	struct my_biggy	1415	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
956	{	1416	property of the event loop, and is actively waiting for events. While in
957	int some_data;	1417	this state it cannot be accessed (except in a few documented ways), moved,
958	ev_timer t1;	1418	freed or anything else - the only legal thing is to keep a pointer to it,
959	ev_timer t2;	1419	and call libev functions on it that are documented to work on active watchers.
960	}
961		1420
962	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1421	=item pending
963	you need to use C<offsetof>:
964		1422
965	#include <stddef.h>	1423	If a watcher is active and libev determines that an event it is interested
		1424	in has occurred (such as a timer expiring), it will become pending. It will
		1425	stay in this pending state until either it is stopped or its callback is
		1426	about to be invoked, so it is not normally pending inside the watcher
		1427	callback.
966		1428
		1429	The watcher might or might not be active while it is pending (for example,
		1430	an expired non-repeating timer can be pending but no longer active). If it
		1431	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1432	but it is still property of the event loop at this time, so cannot be
		1433	moved, freed or reused. And if it is active the rules described in the
		1434	previous item still apply.
		1435
		1436	It is also possible to feed an event on a watcher that is not active (e.g.
		1437	via C<ev_feed_event>), in which case it becomes pending without being
		1438	active.
		1439
		1440	=item stopped
		1441
		1442	A watcher can be stopped implicitly by libev (in which case it might still
		1443	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1444	latter will clear any pending state the watcher might be in, regardless
		1445	of whether it was active or not, so stopping a watcher explicitly before
		1446	freeing it is often a good idea.
		1447
		1448	While stopped (and not pending) the watcher is essentially in the
		1449	initialised state, that is, it can be reused, moved, modified in any way
		1450	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1451	it again).
		1452
		1453	=back
		1454
		1455	=head2 WATCHER PRIORITY MODELS
		1456
		1457	Many event loops support I<watcher priorities>, which are usually small
		1458	integers that influence the ordering of event callback invocation
		1459	between watchers in some way, all else being equal.
		1460
		1461	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1462	description for the more technical details such as the actual priority
		1463	range.
		1464
		1465	There are two common ways how these these priorities are being interpreted
		1466	by event loops:
		1467
		1468	In the more common lock-out model, higher priorities "lock out" invocation
		1469	of lower priority watchers, which means as long as higher priority
		1470	watchers receive events, lower priority watchers are not being invoked.
		1471
		1472	The less common only-for-ordering model uses priorities solely to order
		1473	callback invocation within a single event loop iteration: Higher priority
		1474	watchers are invoked before lower priority ones, but they all get invoked
		1475	before polling for new events.
		1476
		1477	Libev uses the second (only-for-ordering) model for all its watchers
		1478	except for idle watchers (which use the lock-out model).
		1479
		1480	The rationale behind this is that implementing the lock-out model for
		1481	watchers is not well supported by most kernel interfaces, and most event
		1482	libraries will just poll for the same events again and again as long as
		1483	their callbacks have not been executed, which is very inefficient in the
		1484	common case of one high-priority watcher locking out a mass of lower
		1485	priority ones.
		1486
		1487	Static (ordering) priorities are most useful when you have two or more
		1488	watchers handling the same resource: a typical usage example is having an
		1489	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1490	timeouts. Under load, data might be received while the program handles
		1491	other jobs, but since timers normally get invoked first, the timeout
		1492	handler will be executed before checking for data. In that case, giving
		1493	the timer a lower priority than the I/O watcher ensures that I/O will be
		1494	handled first even under adverse conditions (which is usually, but not
		1495	always, what you want).
		1496
		1497	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1498	will only be executed when no same or higher priority watchers have
		1499	received events, they can be used to implement the "lock-out" model when
		1500	required.
		1501
		1502	For example, to emulate how many other event libraries handle priorities,
		1503	you can associate an C<ev_idle> watcher to each such watcher, and in
		1504	the normal watcher callback, you just start the idle watcher. The real
		1505	processing is done in the idle watcher callback. This causes libev to
		1506	continuously poll and process kernel event data for the watcher, but when
		1507	the lock-out case is known to be rare (which in turn is rare :), this is
		1508	workable.
		1509
		1510	Usually, however, the lock-out model implemented that way will perform
		1511	miserably under the type of load it was designed to handle. In that case,
		1512	it might be preferable to stop the real watcher before starting the
		1513	idle watcher, so the kernel will not have to process the event in case
		1514	the actual processing will be delayed for considerable time.
		1515
		1516	Here is an example of an I/O watcher that should run at a strictly lower
		1517	priority than the default, and which should only process data when no
		1518	other events are pending:
		1519
		1520	ev_idle idle; // actual processing watcher
		1521	ev_io io; // actual event watcher
		1522
967	static void	1523	static void
968	t1_cb (EV_P_ struct ev_timer *w, int revents)	1524	io_cb (EV_P_ ev_io *w, int revents)
969	{	1525	{
970	struct my_biggy big = (struct my_biggy *	1526	// stop the I/O watcher, we received the event, but
971	(((char *)w) - offsetof (struct my_biggy, t1));	1527	// are not yet ready to handle it.
		1528	ev_io_stop (EV_A_ w);
		1529
		1530	// start the idle watcher to handle the actual event.
		1531	// it will not be executed as long as other watchers
		1532	// with the default priority are receiving events.
		1533	ev_idle_start (EV_A_ &idle);
972	}	1534	}
973		1535
974	static void	1536	static void
975	t2_cb (EV_P_ struct ev_timer *w, int revents)	1537	idle_cb (EV_P_ ev_idle *w, int revents)
976	{	1538	{
977	struct my_biggy big = (struct my_biggy *	1539	// actual processing
978	(((char *)w) - offsetof (struct my_biggy, t2));	1540	read (STDIN_FILENO, ...);
		1541
		1542	// have to start the I/O watcher again, as
		1543	// we have handled the event
		1544	ev_io_start (EV_P_ &io);
979	}	1545	}
		1546
		1547	// initialisation
		1548	ev_idle_init (&idle, idle_cb);
		1549	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1550	ev_io_start (EV_DEFAULT_ &io);
		1551
		1552	In the "real" world, it might also be beneficial to start a timer, so that
		1553	low-priority connections can not be locked out forever under load. This
		1554	enables your program to keep a lower latency for important connections
		1555	during short periods of high load, while not completely locking out less
		1556	important ones.
980		1557
981		1558
982	=head1 WATCHER TYPES	1559	=head1 WATCHER TYPES
983		1560
984	This section describes each watcher in detail, but will not repeat	1561	This section describes each watcher in detail, but will not repeat
…		…
1008	In general you can register as many read and/or write event watchers per	1585	In general you can register as many read and/or write event watchers per
1009	fd as you want (as long as you don't confuse yourself). Setting all file	1586	fd as you want (as long as you don't confuse yourself). Setting all file
1010	descriptors to non-blocking mode is also usually a good idea (but not	1587	descriptors to non-blocking mode is also usually a good idea (but not
1011	required if you know what you are doing).	1588	required if you know what you are doing).
1012		1589
1013	If you must do this, then force the use of a known-to-be-good backend
1014	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1015	C<EVBACKEND_POLL>).
1016
1017	Another thing you have to watch out for is that it is quite easy to	1590	Another thing you have to watch out for is that it is quite easy to
1018	receive "spurious" readyness notifications, that is your callback might	1591	receive "spurious" readiness notifications, that is, your callback might
1019	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1592	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1020	because there is no data. Not only are some backends known to create a	1593	because there is no data. It is very easy to get into this situation even
1021	lot of those (for example solaris ports), it is very easy to get into	1594	with a relatively standard program structure. Thus it is best to always
1022	this situation even with a relatively standard program structure. Thus	1595	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1023	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1024	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1596	preferable to a program hanging until some data arrives.
1025		1597
1026	If you cannot run the fd in non-blocking mode (for example you should not	1598	If you cannot run the fd in non-blocking mode (for example you should
1027	play around with an Xlib connection), then you have to seperately re-test	1599	not play around with an Xlib connection), then you have to separately
1028	whether a file descriptor is really ready with a known-to-be good interface	1600	re-test whether a file descriptor is really ready with a known-to-be good
1029	such as poll (fortunately in our Xlib example, Xlib already does this on	1601	interface such as poll (fortunately in the case of Xlib, it already does
1030	its own, so its quite safe to use).	1602	this on its own, so its quite safe to use). Some people additionally
		1603	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1604	indefinitely.
		1605
		1606	But really, best use non-blocking mode.
1031		1607
1032	=head3 The special problem of disappearing file descriptors	1608	=head3 The special problem of disappearing file descriptors
1033		1609
1034	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1610	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1035	descriptor (either by calling C<close> explicitly or by any other means,	1611	descriptor (either due to calling C<close> explicitly or any other means,
1036	such as C<dup>). The reason is that you register interest in some file	1612	such as C<dup2>). The reason is that you register interest in some file
1037	descriptor, but when it goes away, the operating system will silently drop	1613	descriptor, but when it goes away, the operating system will silently drop
1038	this interest. If another file descriptor with the same number then is	1614	this interest. If another file descriptor with the same number then is
1039	registered with libev, there is no efficient way to see that this is, in	1615	registered with libev, there is no efficient way to see that this is, in
1040	fact, a different file descriptor.	1616	fact, a different file descriptor.
1041		1617
…		…
1059		1635
1060	There is no workaround possible except not registering events	1636	There is no workaround possible except not registering events
1061	for potentially C<dup ()>'ed file descriptors, or to resort to	1637	for potentially C<dup ()>'ed file descriptors, or to resort to
1062	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1638	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1063		1639
		1640	=head3 The special problem of files
		1641
		1642	Many people try to use C<select> (or libev) on file descriptors
		1643	representing files, and expect it to become ready when their program
		1644	doesn't block on disk accesses (which can take a long time on their own).
		1645
		1646	However, this cannot ever work in the "expected" way - you get a readiness
		1647	notification as soon as the kernel knows whether and how much data is
		1648	there, and in the case of open files, that's always the case, so you
		1649	always get a readiness notification instantly, and your read (or possibly
		1650	write) will still block on the disk I/O.
		1651
		1652	Another way to view it is that in the case of sockets, pipes, character
		1653	devices and so on, there is another party (the sender) that delivers data
		1654	on its own, but in the case of files, there is no such thing: the disk
		1655	will not send data on its own, simply because it doesn't know what you
		1656	wish to read - you would first have to request some data.
		1657
		1658	Since files are typically not-so-well supported by advanced notification
		1659	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1660	to files, even though you should not use it. The reason for this is
		1661	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1662	usually a tty, often a pipe, but also sometimes files or special devices
		1663	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1664	F</dev/urandom>), and even though the file might better be served with
		1665	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1666	it "just works" instead of freezing.
		1667
		1668	So avoid file descriptors pointing to files when you know it (e.g. use
		1669	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1670	when you rarely read from a file instead of from a socket, and want to
		1671	reuse the same code path.
		1672
1064	=head3 The special problem of fork	1673	=head3 The special problem of fork
1065		1674
1066	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1675	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1067	useless behaviour. Libev fully supports fork, but needs to be told about	1676	useless behaviour. Libev fully supports fork, but needs to be told about
1068	it in the child.	1677	it in the child if you want to continue to use it in the child.
1069		1678
1070	To support fork in your programs, you either have to call	1679	To support fork in your child processes, you have to call C<ev_loop_fork
1071	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1680	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1072	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1681	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1073	C<EVBACKEND_POLL>.
1074		1682
		1683	=head3 The special problem of SIGPIPE
		1684
		1685	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1686	when writing to a pipe whose other end has been closed, your program gets
		1687	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1688	this is sensible behaviour, for daemons, this is usually undesirable.
		1689
		1690	So when you encounter spurious, unexplained daemon exits, make sure you
		1691	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1692	somewhere, as that would have given you a big clue).
		1693
		1694	=head3 The special problem of accept()ing when you can't
		1695
		1696	Many implementations of the POSIX C<accept> function (for example,
		1697	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1698	connection from the pending queue in all error cases.
		1699
		1700	For example, larger servers often run out of file descriptors (because
		1701	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1702	rejecting the connection, leading to libev signalling readiness on
		1703	the next iteration again (the connection still exists after all), and
		1704	typically causing the program to loop at 100% CPU usage.
		1705
		1706	Unfortunately, the set of errors that cause this issue differs between
		1707	operating systems, there is usually little the app can do to remedy the
		1708	situation, and no known thread-safe method of removing the connection to
		1709	cope with overload is known (to me).
		1710
		1711	One of the easiest ways to handle this situation is to just ignore it
		1712	- when the program encounters an overload, it will just loop until the
		1713	situation is over. While this is a form of busy waiting, no OS offers an
		1714	event-based way to handle this situation, so it's the best one can do.
		1715
		1716	A better way to handle the situation is to log any errors other than
		1717	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1718	messages, and continue as usual, which at least gives the user an idea of
		1719	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1720	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1721	usage.
		1722
		1723	If your program is single-threaded, then you could also keep a dummy file
		1724	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1725	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1726	close that fd, and create a new dummy fd. This will gracefully refuse
		1727	clients under typical overload conditions.
		1728
		1729	The last way to handle it is to simply log the error and C<exit>, as
		1730	is often done with C<malloc> failures, but this results in an easy
		1731	opportunity for a DoS attack.
1075		1732
1076	=head3 Watcher-Specific Functions	1733	=head3 Watcher-Specific Functions
1077		1734
1078	=over 4	1735	=over 4
1079		1736
1080	=item ev_io_init (ev_io *, callback, int fd, int events)	1737	=item ev_io_init (ev_io *, callback, int fd, int events)
1081		1738
1082	=item ev_io_set (ev_io *, int fd, int events)	1739	=item ev_io_set (ev_io *, int fd, int events)
1083		1740
1084	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1741	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1085	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1742	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1086	C<EV_READ | EV_WRITE> to receive the given events.	1743	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1087		1744
1088	=item int fd [read-only]	1745	=item int fd [read-only]
1089		1746
1090	The file descriptor being watched.	1747	The file descriptor being watched.
1091		1748
…		…
1099		1756
1100	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1757	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1101	readable, but only once. Since it is likely line-buffered, you could	1758	readable, but only once. Since it is likely line-buffered, you could
1102	attempt to read a whole line in the callback.	1759	attempt to read a whole line in the callback.
1103		1760
1104	static void	1761	static void
1105	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1762	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1106	{	1763	{
1107	ev_io_stop (loop, w);	1764	ev_io_stop (loop, w);
1108	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1765	.. read from stdin here (or from w->fd) and handle any I/O errors
1109	}	1766	}
1110		1767
1111	...	1768	...
1112	struct ev_loop *loop = ev_default_init (0);	1769	struct ev_loop *loop = ev_default_init (0);
1113	struct ev_io stdin_readable;	1770	ev_io stdin_readable;
1114	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1771	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1115	ev_io_start (loop, &stdin_readable);	1772	ev_io_start (loop, &stdin_readable);
1116	ev_loop (loop, 0);	1773	ev_run (loop, 0);
1117		1774
1118		1775
1119	=head2 C<ev_timer> - relative and optionally repeating timeouts	1776	=head2 C<ev_timer> - relative and optionally repeating timeouts
1120		1777
1121	Timer watchers are simple relative timers that generate an event after a	1778	Timer watchers are simple relative timers that generate an event after a
1122	given time, and optionally repeating in regular intervals after that.	1779	given time, and optionally repeating in regular intervals after that.
1123		1780
1124	The timers are based on real time, that is, if you register an event that	1781	The timers are based on real time, that is, if you register an event that
1125	times out after an hour and you reset your system clock to last years	1782	times out after an hour and you reset your system clock to January last
1126	time, it will still time out after (roughly) and hour. "Roughly" because	1783	year, it will still time out after (roughly) one hour. "Roughly" because
1127	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1784	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1128	monotonic clock option helps a lot here).	1785	monotonic clock option helps a lot here).
		1786
		1787	The callback is guaranteed to be invoked only I<after> its timeout has
		1788	passed (not I<at>, so on systems with very low-resolution clocks this
		1789	might introduce a small delay, see "the special problem of being too
		1790	early", below). If multiple timers become ready during the same loop
		1791	iteration then the ones with earlier time-out values are invoked before
		1792	ones of the same priority with later time-out values (but this is no
		1793	longer true when a callback calls C<ev_run> recursively).
		1794
		1795	=head3 Be smart about timeouts
		1796
		1797	Many real-world problems involve some kind of timeout, usually for error
		1798	recovery. A typical example is an HTTP request - if the other side hangs,
		1799	you want to raise some error after a while.
		1800
		1801	What follows are some ways to handle this problem, from obvious and
		1802	inefficient to smart and efficient.
		1803
		1804	In the following, a 60 second activity timeout is assumed - a timeout that
		1805	gets reset to 60 seconds each time there is activity (e.g. each time some
		1806	data or other life sign was received).
		1807
		1808	=over 4
		1809
		1810	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1811
		1812	This is the most obvious, but not the most simple way: In the beginning,
		1813	start the watcher:
		1814
		1815	ev_timer_init (timer, callback, 60., 0.);
		1816	ev_timer_start (loop, timer);
		1817
		1818	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1819	and start it again:
		1820
		1821	ev_timer_stop (loop, timer);
		1822	ev_timer_set (timer, 60., 0.);
		1823	ev_timer_start (loop, timer);
		1824
		1825	This is relatively simple to implement, but means that each time there is
		1826	some activity, libev will first have to remove the timer from its internal
		1827	data structure and then add it again. Libev tries to be fast, but it's
		1828	still not a constant-time operation.
		1829
		1830	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1831
		1832	This is the easiest way, and involves using C<ev_timer_again> instead of
		1833	C<ev_timer_start>.
		1834
		1835	To implement this, configure an C<ev_timer> with a C<repeat> value
		1836	of C<60> and then call C<ev_timer_again> at start and each time you
		1837	successfully read or write some data. If you go into an idle state where
		1838	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1839	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1840
		1841	That means you can ignore both the C<ev_timer_start> function and the
		1842	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1843	member and C<ev_timer_again>.
		1844
		1845	At start:
		1846
		1847	ev_init (timer, callback);
		1848	timer->repeat = 60.;
		1849	ev_timer_again (loop, timer);
		1850
		1851	Each time there is some activity:
		1852
		1853	ev_timer_again (loop, timer);
		1854
		1855	It is even possible to change the time-out on the fly, regardless of
		1856	whether the watcher is active or not:
		1857
		1858	timer->repeat = 30.;
		1859	ev_timer_again (loop, timer);
		1860
		1861	This is slightly more efficient then stopping/starting the timer each time
		1862	you want to modify its timeout value, as libev does not have to completely
		1863	remove and re-insert the timer from/into its internal data structure.
		1864
		1865	It is, however, even simpler than the "obvious" way to do it.
		1866
		1867	=item 3. Let the timer time out, but then re-arm it as required.
		1868
		1869	This method is more tricky, but usually most efficient: Most timeouts are
		1870	relatively long compared to the intervals between other activity - in
		1871	our example, within 60 seconds, there are usually many I/O events with
		1872	associated activity resets.
		1873
		1874	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1875	but remember the time of last activity, and check for a real timeout only
		1876	within the callback:
		1877
		1878	ev_tstamp timeout = 60.;
		1879	ev_tstamp last_activity; // time of last activity
		1880	ev_timer timer;
		1881
		1882	static void
		1883	callback (EV_P_ ev_timer *w, int revents)
		1884	{
		1885	// calculate when the timeout would happen
		1886	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1887
		1888	// if negative, it means we the timeout already occurred
		1889	if (after < 0.)
		1890	{
		1891	// timeout occurred, take action
		1892	}
		1893	else
		1894	{
		1895	// callback was invoked, but there was some recent
		1896	// activity. simply restart the timer to time out
		1897	// after "after" seconds, which is the earliest time
		1898	// the timeout can occur.
		1899	ev_timer_set (w, after, 0.);
		1900	ev_timer_start (EV_A_ w);
		1901	}
		1902	}
		1903
		1904	To summarise the callback: first calculate in how many seconds the
		1905	timeout will occur (by calculating the absolute time when it would occur,
		1906	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1907	(EV_A)> from that).
		1908
		1909	If this value is negative, then we are already past the timeout, i.e. we
		1910	timed out, and need to do whatever is needed in this case.
		1911
		1912	Otherwise, we now the earliest time at which the timeout would trigger,
		1913	and simply start the timer with this timeout value.
		1914
		1915	In other words, each time the callback is invoked it will check whether
		1916	the timeout occurred. If not, it will simply reschedule itself to check
		1917	again at the earliest time it could time out. Rinse. Repeat.
		1918
		1919	This scheme causes more callback invocations (about one every 60 seconds
		1920	minus half the average time between activity), but virtually no calls to
		1921	libev to change the timeout.
		1922
		1923	To start the machinery, simply initialise the watcher and set
		1924	C<last_activity> to the current time (meaning there was some activity just
		1925	now), then call the callback, which will "do the right thing" and start
		1926	the timer:
		1927
		1928	last_activity = ev_now (EV_A);
		1929	ev_init (&timer, callback);
		1930	callback (EV_A_ &timer, 0);
		1931
		1932	When there is some activity, simply store the current time in
		1933	C<last_activity>, no libev calls at all:
		1934
		1935	if (activity detected)
		1936	last_activity = ev_now (EV_A);
		1937
		1938	When your timeout value changes, then the timeout can be changed by simply
		1939	providing a new value, stopping the timer and calling the callback, which
		1940	will again do the right thing (for example, time out immediately :).
		1941
		1942	timeout = new_value;
		1943	ev_timer_stop (EV_A_ &timer);
		1944	callback (EV_A_ &timer, 0);
		1945
		1946	This technique is slightly more complex, but in most cases where the
		1947	time-out is unlikely to be triggered, much more efficient.
		1948
		1949	=item 4. Wee, just use a double-linked list for your timeouts.
		1950
		1951	If there is not one request, but many thousands (millions...), all
		1952	employing some kind of timeout with the same timeout value, then one can
		1953	do even better:
		1954
		1955	When starting the timeout, calculate the timeout value and put the timeout
		1956	at the I<end> of the list.
		1957
		1958	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1959	the list is expected to fire (for example, using the technique #3).
		1960
		1961	When there is some activity, remove the timer from the list, recalculate
		1962	the timeout, append it to the end of the list again, and make sure to
		1963	update the C<ev_timer> if it was taken from the beginning of the list.
		1964
		1965	This way, one can manage an unlimited number of timeouts in O(1) time for
		1966	starting, stopping and updating the timers, at the expense of a major
		1967	complication, and having to use a constant timeout. The constant timeout
		1968	ensures that the list stays sorted.
		1969
		1970	=back
		1971
		1972	So which method the best?
		1973
		1974	Method #2 is a simple no-brain-required solution that is adequate in most
		1975	situations. Method #3 requires a bit more thinking, but handles many cases
		1976	better, and isn't very complicated either. In most case, choosing either
		1977	one is fine, with #3 being better in typical situations.
		1978
		1979	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1980	rather complicated, but extremely efficient, something that really pays
		1981	off after the first million or so of active timers, i.e. it's usually
		1982	overkill :)
		1983
		1984	=head3 The special problem of being too early
		1985
		1986	If you ask a timer to call your callback after three seconds, then
		1987	you expect it to be invoked after three seconds - but of course, this
		1988	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1989	guaranteed to any precision by libev - imagine somebody suspending the
		1990	process with a STOP signal for a few hours for example.
		1991
		1992	So, libev tries to invoke your callback as soon as possible I<after> the
		1993	delay has occurred, but cannot guarantee this.
		1994
		1995	A less obvious failure mode is calling your callback too early: many event
		1996	loops compare timestamps with a "elapsed delay >= requested delay", but
		1997	this can cause your callback to be invoked much earlier than you would
		1998	expect.
		1999
		2000	To see why, imagine a system with a clock that only offers full second
		2001	resolution (think windows if you can't come up with a broken enough OS
		2002	yourself). If you schedule a one-second timer at the time 500.9, then the
		2003	event loop will schedule your timeout to elapse at a system time of 500
		2004	(500.9 truncated to the resolution) + 1, or 501.
		2005
		2006	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2007	501" and invoke the callback 0.1s after it was started, even though a
		2008	one-second delay was requested - this is being "too early", despite best
		2009	intentions.
		2010
		2011	This is the reason why libev will never invoke the callback if the elapsed
		2012	delay equals the requested delay, but only when the elapsed delay is
		2013	larger than the requested delay. In the example above, libev would only invoke
		2014	the callback at system time 502, or 1.1s after the timer was started.
		2015
		2016	So, while libev cannot guarantee that your callback will be invoked
		2017	exactly when requested, it I<can> and I<does> guarantee that the requested
		2018	delay has actually elapsed, or in other words, it always errs on the "too
		2019	late" side of things.
		2020
		2021	=head3 The special problem of time updates
		2022
		2023	Establishing the current time is a costly operation (it usually takes
		2024	at least one system call): EV therefore updates its idea of the current
		2025	time only before and after C<ev_run> collects new events, which causes a
		2026	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2027	lots of events in one iteration.
1129		2028
1130	The relative timeouts are calculated relative to the C<ev_now ()>	2029	The relative timeouts are calculated relative to the C<ev_now ()>
1131	time. This is usually the right thing as this timestamp refers to the time	2030	time. This is usually the right thing as this timestamp refers to the time
1132	of the event triggering whatever timeout you are modifying/starting. If	2031	of the event triggering whatever timeout you are modifying/starting. If
1133	you suspect event processing to be delayed and you I<need> to base the timeout	2032	you suspect event processing to be delayed and you I<need> to base the
1134	on the current time, use something like this to adjust for this:	2033	timeout on the current time, use something like this to adjust for this:
1135		2034
1136	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2035	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1137		2036
1138	The callback is guarenteed to be invoked only when its timeout has passed,	2037	If the event loop is suspended for a long time, you can also force an
1139	but if multiple timers become ready during the same loop iteration then	2038	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1140	order of execution is undefined.	2039	()>.
		2040
		2041	=head3 The special problem of unsynchronised clocks
		2042
		2043	Modern systems have a variety of clocks - libev itself uses the normal
		2044	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2045	jumps).
		2046
		2047	Neither of these clocks is synchronised with each other or any other clock
		2048	on the system, so C<ev_time ()> might return a considerably different time
		2049	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2050	a call to C<gettimeofday> might return a second count that is one higher
		2051	than a directly following call to C<time>.
		2052
		2053	The moral of this is to only compare libev-related timestamps with
		2054	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2055	a second or so.
		2056
		2057	One more problem arises due to this lack of synchronisation: if libev uses
		2058	the system monotonic clock and you compare timestamps from C<ev_time>
		2059	or C<ev_now> from when you started your timer and when your callback is
		2060	invoked, you will find that sometimes the callback is a bit "early".
		2061
		2062	This is because C<ev_timer>s work in real time, not wall clock time, so
		2063	libev makes sure your callback is not invoked before the delay happened,
		2064	I<measured according to the real time>, not the system clock.
		2065
		2066	If your timeouts are based on a physical timescale (e.g. "time out this
		2067	connection after 100 seconds") then this shouldn't bother you as it is
		2068	exactly the right behaviour.
		2069
		2070	If you want to compare wall clock/system timestamps to your timers, then
		2071	you need to use C<ev_periodic>s, as these are based on the wall clock
		2072	time, where your comparisons will always generate correct results.
		2073
		2074	=head3 The special problems of suspended animation
		2075
		2076	When you leave the server world it is quite customary to hit machines that
		2077	can suspend/hibernate - what happens to the clocks during such a suspend?
		2078
		2079	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2080	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2081	to run until the system is suspended, but they will not advance while the
		2082	system is suspended. That means, on resume, it will be as if the program
		2083	was frozen for a few seconds, but the suspend time will not be counted
		2084	towards C<ev_timer> when a monotonic clock source is used. The real time
		2085	clock advanced as expected, but if it is used as sole clocksource, then a
		2086	long suspend would be detected as a time jump by libev, and timers would
		2087	be adjusted accordingly.
		2088
		2089	I would not be surprised to see different behaviour in different between
		2090	operating systems, OS versions or even different hardware.
		2091
		2092	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2093	time jump in the monotonic clocks and the realtime clock. If the program
		2094	is suspended for a very long time, and monotonic clock sources are in use,
		2095	then you can expect C<ev_timer>s to expire as the full suspension time
		2096	will be counted towards the timers. When no monotonic clock source is in
		2097	use, then libev will again assume a timejump and adjust accordingly.
		2098
		2099	It might be beneficial for this latter case to call C<ev_suspend>
		2100	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2101	deterministic behaviour in this case (you can do nothing against
		2102	C<SIGSTOP>).
1141		2103
1142	=head3 Watcher-Specific Functions and Data Members	2104	=head3 Watcher-Specific Functions and Data Members
1143		2105
1144	=over 4	2106	=over 4
1145		2107
1146	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2108	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1147		2109
1148	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2110	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1149		2111
1150	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2112	Configure the timer to trigger after C<after> seconds. If C<repeat>
1151	C<0.>, then it will automatically be stopped. If it is positive, then the	2113	is C<0.>, then it will automatically be stopped once the timeout is
1152	timer will automatically be configured to trigger again C<repeat> seconds	2114	reached. If it is positive, then the timer will automatically be
1153	later, again, and again, until stopped manually.	2115	configured to trigger again C<repeat> seconds later, again, and again,
		2116	until stopped manually.
1154		2117
1155	The timer itself will do a best-effort at avoiding drift, that is, if you	2118	The timer itself will do a best-effort at avoiding drift, that is, if
1156	configure a timer to trigger every 10 seconds, then it will trigger at	2119	you configure a timer to trigger every 10 seconds, then it will normally
1157	exactly 10 second intervals. If, however, your program cannot keep up with	2120	trigger at exactly 10 second intervals. If, however, your program cannot
1158	the timer (because it takes longer than those 10 seconds to do stuff) the	2121	keep up with the timer (because it takes longer than those 10 seconds to
1159	timer will not fire more than once per event loop iteration.	2122	do stuff) the timer will not fire more than once per event loop iteration.
1160		2123
1161	=item ev_timer_again (loop, ev_timer *)	2124	=item ev_timer_again (loop, ev_timer *)
1162		2125
1163	This will act as if the timer timed out and restart it again if it is	2126	This will act as if the timer timed out, and restarts it again if it is
1164	repeating. The exact semantics are:	2127	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2128	timeout to the C<repeat> value and calling C<ev_timer_start>.
1165		2129
		2130	The exact semantics are as in the following rules, all of which will be
		2131	applied to the watcher:
		2132
		2133	=over 4
		2134
1166	If the timer is pending, its pending status is cleared.	2135	=item If the timer is pending, the pending status is always cleared.
1167		2136
1168	If the timer is started but nonrepeating, stop it (as if it timed out).	2137	=item If the timer is started but non-repeating, stop it (as if it timed
		2138	out, without invoking it).
1169		2139
1170	If the timer is repeating, either start it if necessary (with the	2140	=item If the timer is repeating, make the C<repeat> value the new timeout
1171	C<repeat> value), or reset the running timer to the C<repeat> value.	2141	and start the timer, if necessary.
1172		2142
1173	This sounds a bit complicated, but here is a useful and typical	2143	=back
1174	example: Imagine you have a tcp connection and you want a so-called idle
1175	timeout, that is, you want to be called when there have been, say, 60
1176	seconds of inactivity on the socket. The easiest way to do this is to
1177	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1178	C<ev_timer_again> each time you successfully read or write some data. If
1179	you go into an idle state where you do not expect data to travel on the
1180	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1181	automatically restart it if need be.
1182		2144
1183	That means you can ignore the C<after> value and C<ev_timer_start>	2145	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1184	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2146	usage example.
1185		2147
1186	ev_timer_init (timer, callback, 0., 5.);	2148	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1187	ev_timer_again (loop, timer);
1188	...
1189	timer->again = 17.;
1190	ev_timer_again (loop, timer);
1191	...
1192	timer->again = 10.;
1193	ev_timer_again (loop, timer);
1194		2149
1195	This is more slightly efficient then stopping/starting the timer each time	2150	Returns the remaining time until a timer fires. If the timer is active,
1196	you want to modify its timeout value.	2151	then this time is relative to the current event loop time, otherwise it's
		2152	the timeout value currently configured.
		2153
		2154	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2155	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2156	will return C<4>. When the timer expires and is restarted, it will return
		2157	roughly C<7> (likely slightly less as callback invocation takes some time,
		2158	too), and so on.
1197		2159
1198	=item ev_tstamp repeat [read-write]	2160	=item ev_tstamp repeat [read-write]
1199		2161
1200	The current C<repeat> value. Will be used each time the watcher times out	2162	The current C<repeat> value. Will be used each time the watcher times out
1201	or C<ev_timer_again> is called and determines the next timeout (if any),	2163	or C<ev_timer_again> is called, and determines the next timeout (if any),
1202	which is also when any modifications are taken into account.	2164	which is also when any modifications are taken into account.
1203		2165
1204	=back	2166	=back
1205		2167
1206	=head3 Examples	2168	=head3 Examples
1207		2169
1208	Example: Create a timer that fires after 60 seconds.	2170	Example: Create a timer that fires after 60 seconds.
1209		2171
1210	static void	2172	static void
1211	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2173	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1212	{	2174	{
1213	.. one minute over, w is actually stopped right here	2175	.. one minute over, w is actually stopped right here
1214	}	2176	}
1215		2177
1216	struct ev_timer mytimer;	2178	ev_timer mytimer;
1217	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2179	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1218	ev_timer_start (loop, &mytimer);	2180	ev_timer_start (loop, &mytimer);
1219		2181
1220	Example: Create a timeout timer that times out after 10 seconds of	2182	Example: Create a timeout timer that times out after 10 seconds of
1221	inactivity.	2183	inactivity.
1222		2184
1223	static void	2185	static void
1224	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2186	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1225	{	2187	{
1226	.. ten seconds without any activity	2188	.. ten seconds without any activity
1227	}	2189	}
1228		2190
1229	struct ev_timer mytimer;	2191	ev_timer mytimer;
1230	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2192	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1231	ev_timer_again (&mytimer); /* start timer */	2193	ev_timer_again (&mytimer); /* start timer */
1232	ev_loop (loop, 0);	2194	ev_run (loop, 0);
1233		2195
1234	// and in some piece of code that gets executed on any "activity":	2196	// and in some piece of code that gets executed on any "activity":
1235	// reset the timeout to start ticking again at 10 seconds	2197	// reset the timeout to start ticking again at 10 seconds
1236	ev_timer_again (&mytimer);	2198	ev_timer_again (&mytimer);
1237		2199
1238		2200
1239	=head2 C<ev_periodic> - to cron or not to cron?	2201	=head2 C<ev_periodic> - to cron or not to cron?
1240		2202
1241	Periodic watchers are also timers of a kind, but they are very versatile	2203	Periodic watchers are also timers of a kind, but they are very versatile
1242	(and unfortunately a bit complex).	2204	(and unfortunately a bit complex).
1243		2205
1244	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2206	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1245	but on wallclock time (absolute time). You can tell a periodic watcher	2207	relative time, the physical time that passes) but on wall clock time
1246	to trigger "at" some specific point in time. For example, if you tell a	2208	(absolute time, the thing you can read on your calender or clock). The
1247	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2209	difference is that wall clock time can run faster or slower than real
1248	+ 10.>) and then reset your system clock to the last year, then it will	2210	time, and time jumps are not uncommon (e.g. when you adjust your
1249	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2211	wrist-watch).
1250	roughly 10 seconds later).
1251		2212
1252	They can also be used to implement vastly more complex timers, such as	2213	You can tell a periodic watcher to trigger after some specific point
1253	triggering an event on each midnight, local time or other, complicated,	2214	in time: for example, if you tell a periodic watcher to trigger "in 10
1254	rules.	2215	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2216	not a delay) and then reset your system clock to January of the previous
		2217	year, then it will take a year or more to trigger the event (unlike an
		2218	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2219	it, as it uses a relative timeout).
1255		2220
		2221	C<ev_periodic> watchers can also be used to implement vastly more complex
		2222	timers, such as triggering an event on each "midnight, local time", or
		2223	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2224	those cannot react to time jumps.
		2225
1256	As with timers, the callback is guarenteed to be invoked only when the	2226	As with timers, the callback is guaranteed to be invoked only when the
1257	time (C<at>) has been passed, but if multiple periodic timers become ready	2227	point in time where it is supposed to trigger has passed. If multiple
1258	during the same loop iteration then order of execution is undefined.	2228	timers become ready during the same loop iteration then the ones with
		2229	earlier time-out values are invoked before ones with later time-out values
		2230	(but this is no longer true when a callback calls C<ev_run> recursively).
1259		2231
1260	=head3 Watcher-Specific Functions and Data Members	2232	=head3 Watcher-Specific Functions and Data Members
1261		2233
1262	=over 4	2234	=over 4
1263		2235
1264	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2236	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1265		2237
1266	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2238	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1267		2239
1268	Lots of arguments, lets sort it out... There are basically three modes of	2240	Lots of arguments, let's sort it out... There are basically three modes of
1269	operation, and we will explain them from simplest to complex:	2241	operation, and we will explain them from simplest to most complex:
1270		2242
1271	=over 4	2243	=over 4
1272		2244
1273	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2245	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1274		2246
1275	In this configuration the watcher triggers an event at the wallclock time	2247	In this configuration the watcher triggers an event after the wall clock
1276	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2248	time C<offset> has passed. It will not repeat and will not adjust when a
1277	that is, if it is to be run at January 1st 2011 then it will run when the	2249	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1278	system time reaches or surpasses this time.	2250	will be stopped and invoked when the system clock reaches or surpasses
		2251	this point in time.
1279		2252
1280	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2253	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1281		2254
1282	In this mode the watcher will always be scheduled to time out at the next	2255	In this mode the watcher will always be scheduled to time out at the next
1283	C<at + N * interval> time (for some integer N, which can also be negative)	2256	C<offset + N * interval> time (for some integer N, which can also be
1284	and then repeat, regardless of any time jumps.	2257	negative) and then repeat, regardless of any time jumps. The C<offset>
		2258	argument is merely an offset into the C<interval> periods.
1285		2259
1286	This can be used to create timers that do not drift with respect to system	2260	This can be used to create timers that do not drift with respect to the
1287	time:	2261	system clock, for example, here is an C<ev_periodic> that triggers each
		2262	hour, on the hour (with respect to UTC):
1288		2263
1289	ev_periodic_set (&periodic, 0., 3600., 0);	2264	ev_periodic_set (&periodic, 0., 3600., 0);
1290		2265
1291	This doesn't mean there will always be 3600 seconds in between triggers,	2266	This doesn't mean there will always be 3600 seconds in between triggers,
1292	but only that the the callback will be called when the system time shows a	2267	but only that the callback will be called when the system time shows a
1293	full hour (UTC), or more correctly, when the system time is evenly divisible	2268	full hour (UTC), or more correctly, when the system time is evenly divisible
1294	by 3600.	2269	by 3600.
1295		2270
1296	Another way to think about it (for the mathematically inclined) is that	2271	Another way to think about it (for the mathematically inclined) is that
1297	C<ev_periodic> will try to run the callback in this mode at the next possible	2272	C<ev_periodic> will try to run the callback in this mode at the next possible
1298	time where C<time = at (mod interval)>, regardless of any time jumps.	2273	time where C<time = offset (mod interval)>, regardless of any time jumps.
1299		2274
1300	For numerical stability it is preferable that the C<at> value is near	2275	The C<interval> I<MUST> be positive, and for numerical stability, the
1301	C<ev_now ()> (the current time), but there is no range requirement for	2276	interval value should be higher than C<1/8192> (which is around 100
1302	this value.	2277	microseconds) and C<offset> should be higher than C<0> and should have
		2278	at most a similar magnitude as the current time (say, within a factor of
		2279	ten). Typical values for offset are, in fact, C<0> or something between
		2280	C<0> and C<interval>, which is also the recommended range.
1303		2281
		2282	Note also that there is an upper limit to how often a timer can fire (CPU
		2283	speed for example), so if C<interval> is very small then timing stability
		2284	will of course deteriorate. Libev itself tries to be exact to be about one
		2285	millisecond (if the OS supports it and the machine is fast enough).
		2286
1304	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2287	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1305		2288
1306	In this mode the values for C<interval> and C<at> are both being	2289	In this mode the values for C<interval> and C<offset> are both being
1307	ignored. Instead, each time the periodic watcher gets scheduled, the	2290	ignored. Instead, each time the periodic watcher gets scheduled, the
1308	reschedule callback will be called with the watcher as first, and the	2291	reschedule callback will be called with the watcher as first, and the
1309	current time as second argument.	2292	current time as second argument.
1310		2293
1311	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2294	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1312	ever, or make any event loop modifications>. If you need to stop it,	2295	or make ANY other event loop modifications whatsoever, unless explicitly
1313	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2296	allowed by documentation here>.
1314	starting an C<ev_prepare> watcher, which is legal).
1315		2297
		2298	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2299	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2300	only event loop modification you are allowed to do).
		2301
1316	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2302	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1317	ev_tstamp now)>, e.g.:	2303	*w, ev_tstamp now)>, e.g.:
1318		2304
		2305	static ev_tstamp
1319	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2306	my_rescheduler (ev_periodic *w, ev_tstamp now)
1320	{	2307	{
1321	return now + 60.;	2308	return now + 60.;
1322	}	2309	}
1323		2310
1324	It must return the next time to trigger, based on the passed time value	2311	It must return the next time to trigger, based on the passed time value
1325	(that is, the lowest time value larger than to the second argument). It	2312	(that is, the lowest time value larger than to the second argument). It
1326	will usually be called just before the callback will be triggered, but	2313	will usually be called just before the callback will be triggered, but
1327	might be called at other times, too.	2314	might be called at other times, too.
1328		2315
1329	NOTE: I<< This callback must always return a time that is later than the	2316	NOTE: I<< This callback must always return a time that is higher than or
1330	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2317	equal to the passed C<now> value >>.
1331		2318
1332	This can be used to create very complex timers, such as a timer that	2319	This can be used to create very complex timers, such as a timer that
1333	triggers on each midnight, local time. To do this, you would calculate the	2320	triggers on "next midnight, local time". To do this, you would calculate the
1334	next midnight after C<now> and return the timestamp value for this. How	2321	next midnight after C<now> and return the timestamp value for this. How
1335	you do this is, again, up to you (but it is not trivial, which is the main	2322	you do this is, again, up to you (but it is not trivial, which is the main
1336	reason I omitted it as an example).	2323	reason I omitted it as an example).
1337		2324
1338	=back	2325	=back
…		…
1342	Simply stops and restarts the periodic watcher again. This is only useful	2329	Simply stops and restarts the periodic watcher again. This is only useful
1343	when you changed some parameters or the reschedule callback would return	2330	when you changed some parameters or the reschedule callback would return
1344	a different time than the last time it was called (e.g. in a crond like	2331	a different time than the last time it was called (e.g. in a crond like
1345	program when the crontabs have changed).	2332	program when the crontabs have changed).
1346		2333
		2334	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2335
		2336	When active, returns the absolute time that the watcher is supposed
		2337	to trigger next. This is not the same as the C<offset> argument to
		2338	C<ev_periodic_set>, but indeed works even in interval and manual
		2339	rescheduling modes.
		2340
1347	=item ev_tstamp offset [read-write]	2341	=item ev_tstamp offset [read-write]
1348		2342
1349	When repeating, this contains the offset value, otherwise this is the	2343	When repeating, this contains the offset value, otherwise this is the
1350	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2344	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2345	although libev might modify this value for better numerical stability).
1351		2346
1352	Can be modified any time, but changes only take effect when the periodic	2347	Can be modified any time, but changes only take effect when the periodic
1353	timer fires or C<ev_periodic_again> is being called.	2348	timer fires or C<ev_periodic_again> is being called.
1354		2349
1355	=item ev_tstamp interval [read-write]	2350	=item ev_tstamp interval [read-write]
1356		2351
1357	The current interval value. Can be modified any time, but changes only	2352	The current interval value. Can be modified any time, but changes only
1358	take effect when the periodic timer fires or C<ev_periodic_again> is being	2353	take effect when the periodic timer fires or C<ev_periodic_again> is being
1359	called.	2354	called.
1360		2355
1361	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2356	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1362		2357
1363	The current reschedule callback, or C<0>, if this functionality is	2358	The current reschedule callback, or C<0>, if this functionality is
1364	switched off. Can be changed any time, but changes only take effect when	2359	switched off. Can be changed any time, but changes only take effect when
1365	the periodic timer fires or C<ev_periodic_again> is being called.	2360	the periodic timer fires or C<ev_periodic_again> is being called.
1366		2361
1367	=item ev_tstamp at [read-only]
1368
1369	When active, contains the absolute time that the watcher is supposed to
1370	trigger next.
1371
1372	=back	2362	=back
1373		2363
1374	=head3 Examples	2364	=head3 Examples
1375		2365
1376	Example: Call a callback every hour, or, more precisely, whenever the	2366	Example: Call a callback every hour, or, more precisely, whenever the
1377	system clock is divisible by 3600. The callback invocation times have	2367	system time is divisible by 3600. The callback invocation times have
1378	potentially a lot of jittering, but good long-term stability.	2368	potentially a lot of jitter, but good long-term stability.
1379		2369
1380	static void	2370	static void
1381	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2371	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1382	{	2372	{
1383	... its now a full hour (UTC, or TAI or whatever your clock follows)	2373	... its now a full hour (UTC, or TAI or whatever your clock follows)
1384	}	2374	}
1385		2375
1386	struct ev_periodic hourly_tick;	2376	ev_periodic hourly_tick;
1387	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2377	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1388	ev_periodic_start (loop, &hourly_tick);	2378	ev_periodic_start (loop, &hourly_tick);
1389		2379
1390	Example: The same as above, but use a reschedule callback to do it:	2380	Example: The same as above, but use a reschedule callback to do it:
1391		2381
1392	#include <math.h>	2382	#include <math.h>
1393		2383
1394	static ev_tstamp	2384	static ev_tstamp
1395	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2385	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1396	{	2386	{
1397	return fmod (now, 3600.) + 3600.;	2387	return now + (3600. - fmod (now, 3600.));
1398	}	2388	}
1399		2389
1400	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2390	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1401		2391
1402	Example: Call a callback every hour, starting now:	2392	Example: Call a callback every hour, starting now:
1403		2393
1404	struct ev_periodic hourly_tick;	2394	ev_periodic hourly_tick;
1405	ev_periodic_init (&hourly_tick, clock_cb,	2395	ev_periodic_init (&hourly_tick, clock_cb,
1406	fmod (ev_now (loop), 3600.), 3600., 0);	2396	fmod (ev_now (loop), 3600.), 3600., 0);
1407	ev_periodic_start (loop, &hourly_tick);	2397	ev_periodic_start (loop, &hourly_tick);
1408		2398
1409		2399
1410	=head2 C<ev_signal> - signal me when a signal gets signalled!	2400	=head2 C<ev_signal> - signal me when a signal gets signalled!
1411		2401
1412	Signal watchers will trigger an event when the process receives a specific	2402	Signal watchers will trigger an event when the process receives a specific
1413	signal one or more times. Even though signals are very asynchronous, libev	2403	signal one or more times. Even though signals are very asynchronous, libev
1414	will try it's best to deliver signals synchronously, i.e. as part of the	2404	will try its best to deliver signals synchronously, i.e. as part of the
1415	normal event processing, like any other event.	2405	normal event processing, like any other event.
1416		2406
		2407	If you want signals to be delivered truly asynchronously, just use
		2408	C<sigaction> as you would do without libev and forget about sharing
		2409	the signal. You can even use C<ev_async> from a signal handler to
		2410	synchronously wake up an event loop.
		2411
1417	You can configure as many watchers as you like per signal. Only when the	2412	You can configure as many watchers as you like for the same signal, but
1418	first watcher gets started will libev actually register a signal watcher	2413	only within the same loop, i.e. you can watch for C<SIGINT> in your
1419	with the kernel (thus it coexists with your own signal handlers as long	2414	default loop and for C<SIGIO> in another loop, but you cannot watch for
1420	as you don't register any with libev). Similarly, when the last signal	2415	C<SIGINT> in both the default loop and another loop at the same time. At
1421	watcher for a signal is stopped libev will reset the signal handler to	2416	the moment, C<SIGCHLD> is permanently tied to the default loop.
1422	SIG_DFL (regardless of what it was set to before).	2417
		2418	Only after the first watcher for a signal is started will libev actually
		2419	register something with the kernel. It thus coexists with your own signal
		2420	handlers as long as you don't register any with libev for the same signal.
		2421
		2422	If possible and supported, libev will install its handlers with
		2423	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2424	not be unduly interrupted. If you have a problem with system calls getting
		2425	interrupted by signals you can block all signals in an C<ev_check> watcher
		2426	and unblock them in an C<ev_prepare> watcher.
		2427
		2428	=head3 The special problem of inheritance over fork/execve/pthread_create
		2429
		2430	Both the signal mask (C<sigprocmask>) and the signal disposition
		2431	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2432	stopping it again), that is, libev might or might not block the signal,
		2433	and might or might not set or restore the installed signal handler (but
		2434	see C<EVFLAG_NOSIGMASK>).
		2435
		2436	While this does not matter for the signal disposition (libev never
		2437	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2438	C<execve>), this matters for the signal mask: many programs do not expect
		2439	certain signals to be blocked.
		2440
		2441	This means that before calling C<exec> (from the child) you should reset
		2442	the signal mask to whatever "default" you expect (all clear is a good
		2443	choice usually).
		2444
		2445	The simplest way to ensure that the signal mask is reset in the child is
		2446	to install a fork handler with C<pthread_atfork> that resets it. That will
		2447	catch fork calls done by libraries (such as the libc) as well.
		2448
		2449	In current versions of libev, the signal will not be blocked indefinitely
		2450	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2451	the window of opportunity for problems, it will not go away, as libev
		2452	I<has> to modify the signal mask, at least temporarily.
		2453
		2454	So I can't stress this enough: I<If you do not reset your signal mask when
		2455	you expect it to be empty, you have a race condition in your code>. This
		2456	is not a libev-specific thing, this is true for most event libraries.
		2457
		2458	=head3 The special problem of threads signal handling
		2459
		2460	POSIX threads has problematic signal handling semantics, specifically,
		2461	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2462	threads in a process block signals, which is hard to achieve.
		2463
		2464	When you want to use sigwait (or mix libev signal handling with your own
		2465	for the same signals), you can tackle this problem by globally blocking
		2466	all signals before creating any threads (or creating them with a fully set
		2467	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2468	loops. Then designate one thread as "signal receiver thread" which handles
		2469	these signals. You can pass on any signals that libev might be interested
		2470	in by calling C<ev_feed_signal>.
1423		2471
1424	=head3 Watcher-Specific Functions and Data Members	2472	=head3 Watcher-Specific Functions and Data Members
1425		2473
1426	=over 4	2474	=over 4
1427		2475
…		…
1438		2486
1439	=back	2487	=back
1440		2488
1441	=head3 Examples	2489	=head3 Examples
1442		2490
1443	Example: Try to exit cleanly on SIGINT and SIGTERM.	2491	Example: Try to exit cleanly on SIGINT.
1444		2492
1445	static void	2493	static void
1446	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2494	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1447	{	2495	{
1448	ev_unloop (loop, EVUNLOOP_ALL);	2496	ev_break (loop, EVBREAK_ALL);
1449	}	2497	}
1450		2498
1451	struct ev_signal signal_watcher;	2499	ev_signal signal_watcher;
1452	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2500	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1453	ev_signal_start (loop, &sigint_cb);	2501	ev_signal_start (loop, &signal_watcher);
1454		2502
1455		2503
1456	=head2 C<ev_child> - watch out for process status changes	2504	=head2 C<ev_child> - watch out for process status changes
1457		2505
1458	Child watchers trigger when your process receives a SIGCHLD in response to	2506	Child watchers trigger when your process receives a SIGCHLD in response to
1459	some child status changes (most typically when a child of yours dies). It	2507	some child status changes (most typically when a child of yours dies or
1460	is permissible to install a child watcher I<after> the child has been	2508	exits). It is permissible to install a child watcher I<after> the child
1461	forked (which implies it might have already exited), as long as the event	2509	has been forked (which implies it might have already exited), as long
1462	loop isn't entered (or is continued from a watcher).	2510	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2511	forking and then immediately registering a watcher for the child is fine,
		2512	but forking and registering a watcher a few event loop iterations later or
		2513	in the next callback invocation is not.
1463		2514
1464	Only the default event loop is capable of handling signals, and therefore	2515	Only the default event loop is capable of handling signals, and therefore
1465	you can only rgeister child watchers in the default event loop.	2516	you can only register child watchers in the default event loop.
		2517
		2518	Due to some design glitches inside libev, child watchers will always be
		2519	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2520	libev)
1466		2521
1467	=head3 Process Interaction	2522	=head3 Process Interaction
1468		2523
1469	Libev grabs C<SIGCHLD> as soon as the default event loop is	2524	Libev grabs C<SIGCHLD> as soon as the default event loop is
1470	initialised. This is necessary to guarantee proper behaviour even if	2525	initialised. This is necessary to guarantee proper behaviour even if the
1471	the first child watcher is started after the child exits. The occurance	2526	first child watcher is started after the child exits. The occurrence
1472	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2527	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1473	synchronously as part of the event loop processing. Libev always reaps all	2528	synchronously as part of the event loop processing. Libev always reaps all
1474	children, even ones not watched.	2529	children, even ones not watched.
1475		2530
1476	=head3 Overriding the Built-In Processing	2531	=head3 Overriding the Built-In Processing
…		…
1480	handler, you can override it easily by installing your own handler for	2535	handler, you can override it easily by installing your own handler for
1481	C<SIGCHLD> after initialising the default loop, and making sure the	2536	C<SIGCHLD> after initialising the default loop, and making sure the
1482	default loop never gets destroyed. You are encouraged, however, to use an	2537	default loop never gets destroyed. You are encouraged, however, to use an
1483	event-based approach to child reaping and thus use libev's support for	2538	event-based approach to child reaping and thus use libev's support for
1484	that, so other libev users can use C<ev_child> watchers freely.	2539	that, so other libev users can use C<ev_child> watchers freely.
		2540
		2541	=head3 Stopping the Child Watcher
		2542
		2543	Currently, the child watcher never gets stopped, even when the
		2544	child terminates, so normally one needs to stop the watcher in the
		2545	callback. Future versions of libev might stop the watcher automatically
		2546	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2547	problem).
1485		2548
1486	=head3 Watcher-Specific Functions and Data Members	2549	=head3 Watcher-Specific Functions and Data Members
1487		2550
1488	=over 4	2551	=over 4
1489		2552
…		…
1518	=head3 Examples	2581	=head3 Examples
1519		2582
1520	Example: C<fork()> a new process and install a child handler to wait for	2583	Example: C<fork()> a new process and install a child handler to wait for
1521	its completion.	2584	its completion.
1522		2585
1523	ev_child cw;	2586	ev_child cw;
1524		2587
1525	static void	2588	static void
1526	child_cb (EV_P_ struct ev_child *w, int revents)	2589	child_cb (EV_P_ ev_child *w, int revents)
1527	{	2590	{
1528	ev_child_stop (EV_A_ w);	2591	ev_child_stop (EV_A_ w);
1529	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2592	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1530	}	2593	}
1531		2594
1532	pid_t pid = fork ();	2595	pid_t pid = fork ();
1533		2596
1534	if (pid < 0)	2597	if (pid < 0)
1535	// error	2598	// error
1536	else if (pid == 0)	2599	else if (pid == 0)
1537	{	2600	{
1538	// the forked child executes here	2601	// the forked child executes here
1539	exit (1);	2602	exit (1);
1540	}	2603	}
1541	else	2604	else
1542	{	2605	{
1543	ev_child_init (&cw, child_cb, pid, 0);	2606	ev_child_init (&cw, child_cb, pid, 0);
1544	ev_child_start (EV_DEFAULT_ &cw);	2607	ev_child_start (EV_DEFAULT_ &cw);
1545	}	2608	}
1546		2609
1547		2610
1548	=head2 C<ev_stat> - did the file attributes just change?	2611	=head2 C<ev_stat> - did the file attributes just change?
1549		2612
1550	This watches a filesystem path for attribute changes. That is, it calls	2613	This watches a file system path for attribute changes. That is, it calls
1551	C<stat> regularly (or when the OS says it changed) and sees if it changed	2614	C<stat> on that path in regular intervals (or when the OS says it changed)
1552	compared to the last time, invoking the callback if it did.	2615	and sees if it changed compared to the last time, invoking the callback
		2616	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2617	happen after the watcher has been started will be reported.
1553		2618
1554	The path does not need to exist: changing from "path exists" to "path does	2619	The path does not need to exist: changing from "path exists" to "path does
1555	not exist" is a status change like any other. The condition "path does	2620	not exist" is a status change like any other. The condition "path does not
1556	not exist" is signified by the C<st_nlink> field being zero (which is	2621	exist" (or more correctly "path cannot be stat'ed") is signified by the
1557	otherwise always forced to be at least one) and all the other fields of	2622	C<st_nlink> field being zero (which is otherwise always forced to be at
1558	the stat buffer having unspecified contents.	2623	least one) and all the other fields of the stat buffer having unspecified
		2624	contents.
1559		2625
1560	The path I<should> be absolute and I<must not> end in a slash. If it is	2626	The path I<must not> end in a slash or contain special components such as
		2627	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1561	relative and your working directory changes, the behaviour is undefined.	2628	your working directory changes, then the behaviour is undefined.
1562		2629
1563	Since there is no standard to do this, the portable implementation simply	2630	Since there is no portable change notification interface available, the
1564	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2631	portable implementation simply calls C<stat(2)> regularly on the path
1565	can specify a recommended polling interval for this case. If you specify	2632	to see if it changed somehow. You can specify a recommended polling
1566	a polling interval of C<0> (highly recommended!) then a I<suitable,	2633	interval for this case. If you specify a polling interval of C<0> (highly
1567	unspecified default> value will be used (which you can expect to be around	2634	recommended!) then a I<suitable, unspecified default> value will be used
1568	five seconds, although this might change dynamically). Libev will also	2635	(which you can expect to be around five seconds, although this might
1569	impose a minimum interval which is currently around C<0.1>, but thats	2636	change dynamically). Libev will also impose a minimum interval which is
1570	usually overkill.	2637	currently around C<0.1>, but that's usually overkill.
1571		2638
1572	This watcher type is not meant for massive numbers of stat watchers,	2639	This watcher type is not meant for massive numbers of stat watchers,
1573	as even with OS-supported change notifications, this can be	2640	as even with OS-supported change notifications, this can be
1574	resource-intensive.	2641	resource-intensive.
1575		2642
1576	At the time of this writing, only the Linux inotify interface is	2643	At the time of this writing, the only OS-specific interface implemented
1577	implemented (implementing kqueue support is left as an exercise for the	2644	is the Linux inotify interface (implementing kqueue support is left as an
1578	reader). Inotify will be used to give hints only and should not change the	2645	exercise for the reader. Note, however, that the author sees no way of
1579	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2646	implementing C<ev_stat> semantics with kqueue, except as a hint).
1580	to fall back to regular polling again even with inotify, but changes are
1581	usually detected immediately, and if the file exists there will be no
1582	polling.
1583		2647
1584	=head3 Inotify	2648	=head3 ABI Issues (Largefile Support)
1585		2649
		2650	Libev by default (unless the user overrides this) uses the default
		2651	compilation environment, which means that on systems with large file
		2652	support disabled by default, you get the 32 bit version of the stat
		2653	structure. When using the library from programs that change the ABI to
		2654	use 64 bit file offsets the programs will fail. In that case you have to
		2655	compile libev with the same flags to get binary compatibility. This is
		2656	obviously the case with any flags that change the ABI, but the problem is
		2657	most noticeably displayed with ev_stat and large file support.
		2658
		2659	The solution for this is to lobby your distribution maker to make large
		2660	file interfaces available by default (as e.g. FreeBSD does) and not
		2661	optional. Libev cannot simply switch on large file support because it has
		2662	to exchange stat structures with application programs compiled using the
		2663	default compilation environment.
		2664
		2665	=head3 Inotify and Kqueue
		2666
1586	When C<inotify (7)> support has been compiled into libev (generally only	2667	When C<inotify (7)> support has been compiled into libev and present at
1587	available on Linux) and present at runtime, it will be used to speed up	2668	runtime, it will be used to speed up change detection where possible. The
1588	change detection where possible. The inotify descriptor will be created lazily	2669	inotify descriptor will be created lazily when the first C<ev_stat>
1589	when the first C<ev_stat> watcher is being started.	2670	watcher is being started.
1590		2671
1591	Inotify presense does not change the semantics of C<ev_stat> watchers	2672	Inotify presence does not change the semantics of C<ev_stat> watchers
1592	except that changes might be detected earlier, and in some cases, to avoid	2673	except that changes might be detected earlier, and in some cases, to avoid
1593	making regular C<stat> calls. Even in the presense of inotify support	2674	making regular C<stat> calls. Even in the presence of inotify support
1594	there are many cases where libev has to resort to regular C<stat> polling.	2675	there are many cases where libev has to resort to regular C<stat> polling,
		2676	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2677	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2678	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2679	xfs are fully working) libev usually gets away without polling.
1595		2680
1596	(There is no support for kqueue, as apparently it cannot be used to	2681	There is no support for kqueue, as apparently it cannot be used to
1597	implement this functionality, due to the requirement of having a file	2682	implement this functionality, due to the requirement of having a file
1598	descriptor open on the object at all times).	2683	descriptor open on the object at all times, and detecting renames, unlinks
		2684	etc. is difficult.
		2685
		2686	=head3 C<stat ()> is a synchronous operation
		2687
		2688	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2689	the process. The exception are C<ev_stat> watchers - those call C<stat
		2690	()>, which is a synchronous operation.
		2691
		2692	For local paths, this usually doesn't matter: unless the system is very
		2693	busy or the intervals between stat's are large, a stat call will be fast,
		2694	as the path data is usually in memory already (except when starting the
		2695	watcher).
		2696
		2697	For networked file systems, calling C<stat ()> can block an indefinite
		2698	time due to network issues, and even under good conditions, a stat call
		2699	often takes multiple milliseconds.
		2700
		2701	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2702	paths, although this is fully supported by libev.
1599		2703
1600	=head3 The special problem of stat time resolution	2704	=head3 The special problem of stat time resolution
1601		2705
1602	The C<stat ()> syscall only supports full-second resolution portably, and	2706	The C<stat ()> system call only supports full-second resolution portably,
1603	even on systems where the resolution is higher, many filesystems still	2707	and even on systems where the resolution is higher, most file systems
1604	only support whole seconds.	2708	still only support whole seconds.
1605		2709
1606	That means that, if the time is the only thing that changes, you might	2710	That means that, if the time is the only thing that changes, you can
1607	miss updates: on the first update, C<ev_stat> detects a change and calls	2711	easily miss updates: on the first update, C<ev_stat> detects a change and
1608	your callback, which does something. When there is another update within	2712	calls your callback, which does something. When there is another update
1609	the same second, C<ev_stat> will be unable to detect it.	2713	within the same second, C<ev_stat> will be unable to detect unless the
		2714	stat data does change in other ways (e.g. file size).
1610		2715
1611	The solution to this is to delay acting on a change for a second (or till	2716	The solution to this is to delay acting on a change for slightly more
1612	the next second boundary), using a roughly one-second delay C<ev_timer>	2717	than a second (or till slightly after the next full second boundary), using
1613	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2718	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1614	is added to work around small timing inconsistencies of some operating	2719	ev_timer_again (loop, w)>).
1615	systems.	2720
		2721	The C<.02> offset is added to work around small timing inconsistencies
		2722	of some operating systems (where the second counter of the current time
		2723	might be be delayed. One such system is the Linux kernel, where a call to
		2724	C<gettimeofday> might return a timestamp with a full second later than
		2725	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2726	update file times then there will be a small window where the kernel uses
		2727	the previous second to update file times but libev might already execute
		2728	the timer callback).
1616		2729
1617	=head3 Watcher-Specific Functions and Data Members	2730	=head3 Watcher-Specific Functions and Data Members
1618		2731
1619	=over 4	2732	=over 4
1620		2733
…		…
1626	C<path>. The C<interval> is a hint on how quickly a change is expected to	2739	C<path>. The C<interval> is a hint on how quickly a change is expected to
1627	be detected and should normally be specified as C<0> to let libev choose	2740	be detected and should normally be specified as C<0> to let libev choose
1628	a suitable value. The memory pointed to by C<path> must point to the same	2741	a suitable value. The memory pointed to by C<path> must point to the same
1629	path for as long as the watcher is active.	2742	path for as long as the watcher is active.
1630		2743
1631	The callback will be receive C<EV_STAT> when a change was detected,	2744	The callback will receive an C<EV_STAT> event when a change was detected,
1632	relative to the attributes at the time the watcher was started (or the	2745	relative to the attributes at the time the watcher was started (or the
1633	last change was detected).	2746	last change was detected).
1634		2747
1635	=item ev_stat_stat (loop, ev_stat *)	2748	=item ev_stat_stat (loop, ev_stat *)
1636		2749
1637	Updates the stat buffer immediately with new values. If you change the	2750	Updates the stat buffer immediately with new values. If you change the
1638	watched path in your callback, you could call this fucntion to avoid	2751	watched path in your callback, you could call this function to avoid
1639	detecting this change (while introducing a race condition). Can also be	2752	detecting this change (while introducing a race condition if you are not
1640	useful simply to find out the new values.	2753	the only one changing the path). Can also be useful simply to find out the
		2754	new values.
1641		2755
1642	=item ev_statdata attr [read-only]	2756	=item ev_statdata attr [read-only]
1643		2757
1644	The most-recently detected attributes of the file. Although the type is of	2758	The most-recently detected attributes of the file. Although the type is
1645	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2759	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1646	suitable for your system. If the C<st_nlink> member is C<0>, then there	2760	suitable for your system, but you can only rely on the POSIX-standardised
		2761	members to be present. If the C<st_nlink> member is C<0>, then there was
1647	was some error while C<stat>ing the file.	2762	some error while C<stat>ing the file.
1648		2763
1649	=item ev_statdata prev [read-only]	2764	=item ev_statdata prev [read-only]
1650		2765
1651	The previous attributes of the file. The callback gets invoked whenever	2766	The previous attributes of the file. The callback gets invoked whenever
1652	C<prev> != C<attr>.	2767	C<prev> != C<attr>, or, more precisely, one or more of these members
		2768	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2769	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1653		2770
1654	=item ev_tstamp interval [read-only]	2771	=item ev_tstamp interval [read-only]
1655		2772
1656	The specified interval.	2773	The specified interval.
1657		2774
1658	=item const char *path [read-only]	2775	=item const char *path [read-only]
1659		2776
1660	The filesystem path that is being watched.	2777	The file system path that is being watched.
1661		2778
1662	=back	2779	=back
1663		2780
1664	=head3 Examples	2781	=head3 Examples
1665		2782
1666	Example: Watch C</etc/passwd> for attribute changes.	2783	Example: Watch C</etc/passwd> for attribute changes.
1667		2784
1668	static void	2785	static void
1669	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2786	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1670	{	2787	{
1671	/* /etc/passwd changed in some way */	2788	/* /etc/passwd changed in some way */
1672	if (w->attr.st_nlink)	2789	if (w->attr.st_nlink)
1673	{	2790	{
1674	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2791	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1675	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2792	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1676	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2793	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1677	}	2794	}
1678	else	2795	else
1679	/* you shalt not abuse printf for puts */	2796	/* you shalt not abuse printf for puts */
1680	puts ("wow, /etc/passwd is not there, expect problems. "	2797	puts ("wow, /etc/passwd is not there, expect problems. "
1681	"if this is windows, they already arrived\n");	2798	"if this is windows, they already arrived\n");
1682	}	2799	}
1683		2800
1684	...	2801	...
1685	ev_stat passwd;	2802	ev_stat passwd;
1686		2803
1687	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2804	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1688	ev_stat_start (loop, &passwd);	2805	ev_stat_start (loop, &passwd);
1689		2806
1690	Example: Like above, but additionally use a one-second delay so we do not	2807	Example: Like above, but additionally use a one-second delay so we do not
1691	miss updates (however, frequent updates will delay processing, too, so	2808	miss updates (however, frequent updates will delay processing, too, so
1692	one might do the work both on C<ev_stat> callback invocation I<and> on	2809	one might do the work both on C<ev_stat> callback invocation I<and> on
1693	C<ev_timer> callback invocation).	2810	C<ev_timer> callback invocation).
1694		2811
1695	static ev_stat passwd;	2812	static ev_stat passwd;
1696	static ev_timer timer;	2813	static ev_timer timer;
1697		2814
1698	static void	2815	static void
1699	timer_cb (EV_P_ ev_timer *w, int revents)	2816	timer_cb (EV_P_ ev_timer *w, int revents)
1700	{	2817	{
1701	ev_timer_stop (EV_A_ w);	2818	ev_timer_stop (EV_A_ w);
1702		2819
1703	/* now it's one second after the most recent passwd change */	2820	/* now it's one second after the most recent passwd change */
1704	}	2821	}
1705		2822
1706	static void	2823	static void
1707	stat_cb (EV_P_ ev_stat *w, int revents)	2824	stat_cb (EV_P_ ev_stat *w, int revents)
1708	{	2825	{
1709	/* reset the one-second timer */	2826	/* reset the one-second timer */
1710	ev_timer_again (EV_A_ &timer);	2827	ev_timer_again (EV_A_ &timer);
1711	}	2828	}
1712		2829
1713	...	2830	...
1714	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2831	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1715	ev_stat_start (loop, &passwd);	2832	ev_stat_start (loop, &passwd);
1716	ev_timer_init (&timer, timer_cb, 0., 1.01);	2833	ev_timer_init (&timer, timer_cb, 0., 1.02);
1717		2834
1718		2835
1719	=head2 C<ev_idle> - when you've got nothing better to do...	2836	=head2 C<ev_idle> - when you've got nothing better to do...
1720		2837
1721	Idle watchers trigger events when no other events of the same or higher	2838	Idle watchers trigger events when no other events of the same or higher
1722	priority are pending (prepare, check and other idle watchers do not	2839	priority are pending (prepare, check and other idle watchers do not count
1723	count).	2840	as receiving "events").
1724		2841
1725	That is, as long as your process is busy handling sockets or timeouts	2842	That is, as long as your process is busy handling sockets or timeouts
1726	(or even signals, imagine) of the same or higher priority it will not be	2843	(or even signals, imagine) of the same or higher priority it will not be
1727	triggered. But when your process is idle (or only lower-priority watchers	2844	triggered. But when your process is idle (or only lower-priority watchers
1728	are pending), the idle watchers are being called once per event loop	2845	are pending), the idle watchers are being called once per event loop
…		…
1735	Apart from keeping your process non-blocking (which is a useful	2852	Apart from keeping your process non-blocking (which is a useful
1736	effect on its own sometimes), idle watchers are a good place to do	2853	effect on its own sometimes), idle watchers are a good place to do
1737	"pseudo-background processing", or delay processing stuff to after the	2854	"pseudo-background processing", or delay processing stuff to after the
1738	event loop has handled all outstanding events.	2855	event loop has handled all outstanding events.
1739		2856
		2857	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2858
		2859	As long as there is at least one active idle watcher, libev will never
		2860	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2861	For this to work, the idle watcher doesn't need to be invoked at all - the
		2862	lowest priority will do.
		2863
		2864	This mode of operation can be useful together with an C<ev_check> watcher,
		2865	to do something on each event loop iteration - for example to balance load
		2866	between different connections.
		2867
		2868	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2869	example.
		2870
1740	=head3 Watcher-Specific Functions and Data Members	2871	=head3 Watcher-Specific Functions and Data Members
1741		2872
1742	=over 4	2873	=over 4
1743		2874
1744	=item ev_idle_init (ev_signal *, callback)	2875	=item ev_idle_init (ev_idle *, callback)
1745		2876
1746	Initialises and configures the idle watcher - it has no parameters of any	2877	Initialises and configures the idle watcher - it has no parameters of any
1747	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2878	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1748	believe me.	2879	believe me.
1749		2880
…		…
1752	=head3 Examples	2883	=head3 Examples
1753		2884
1754	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2885	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1755	callback, free it. Also, use no error checking, as usual.	2886	callback, free it. Also, use no error checking, as usual.
1756		2887
1757	static void	2888	static void
1758	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2889	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1759	{	2890	{
		2891	// stop the watcher
		2892	ev_idle_stop (loop, w);
		2893
		2894	// now we can free it
1760	free (w);	2895	free (w);
		2896
1761	// now do something you wanted to do when the program has	2897	// now do something you wanted to do when the program has
1762	// no longer anything immediate to do.	2898	// no longer anything immediate to do.
1763	}	2899	}
1764		2900
1765	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2901	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1766	ev_idle_init (idle_watcher, idle_cb);	2902	ev_idle_init (idle_watcher, idle_cb);
1767	ev_idle_start (loop, idle_cb);	2903	ev_idle_start (loop, idle_watcher);
1768		2904
1769		2905
1770	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2906	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1771		2907
1772	Prepare and check watchers are usually (but not always) used in tandem:	2908	Prepare and check watchers are often (but not always) used in pairs:
1773	prepare watchers get invoked before the process blocks and check watchers	2909	prepare watchers get invoked before the process blocks and check watchers
1774	afterwards.	2910	afterwards.
1775		2911
1776	You I<must not> call C<ev_loop> or similar functions that enter	2912	You I<must not> call C<ev_run> or similar functions that enter
1777	the current event loop from either C<ev_prepare> or C<ev_check>	2913	the current event loop from either C<ev_prepare> or C<ev_check>
1778	watchers. Other loops than the current one are fine, however. The	2914	watchers. Other loops than the current one are fine, however. The
1779	rationale behind this is that you do not need to check for recursion in	2915	rationale behind this is that you do not need to check for recursion in
1780	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2916	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1781	C<ev_check> so if you have one watcher of each kind they will always be	2917	C<ev_check> so if you have one watcher of each kind they will always be
1782	called in pairs bracketing the blocking call.	2918	called in pairs bracketing the blocking call.
1783		2919
1784	Their main purpose is to integrate other event mechanisms into libev and	2920	Their main purpose is to integrate other event mechanisms into libev and
1785	their use is somewhat advanced. This could be used, for example, to track	2921	their use is somewhat advanced. They could be used, for example, to track
1786	variable changes, implement your own watchers, integrate net-snmp or a	2922	variable changes, implement your own watchers, integrate net-snmp or a
1787	coroutine library and lots more. They are also occasionally useful if	2923	coroutine library and lots more. They are also occasionally useful if
1788	you cache some data and want to flush it before blocking (for example,	2924	you cache some data and want to flush it before blocking (for example,
1789	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2925	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1790	watcher).	2926	watcher).
1791		2927
1792	This is done by examining in each prepare call which file descriptors need	2928	This is done by examining in each prepare call which file descriptors
1793	to be watched by the other library, registering C<ev_io> watchers for	2929	need to be watched by the other library, registering C<ev_io> watchers
1794	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2930	for them and starting an C<ev_timer> watcher for any timeouts (many
1795	provide just this functionality). Then, in the check watcher you check for	2931	libraries provide exactly this functionality). Then, in the check watcher,
1796	any events that occured (by checking the pending status of all watchers	2932	you check for any events that occurred (by checking the pending status
1797	and stopping them) and call back into the library. The I/O and timer	2933	of all watchers and stopping them) and call back into the library. The
1798	callbacks will never actually be called (but must be valid nevertheless,	2934	I/O and timer callbacks will never actually be called (but must be valid
1799	because you never know, you know?).	2935	nevertheless, because you never know, you know?).
1800		2936
1801	As another example, the Perl Coro module uses these hooks to integrate	2937	As another example, the Perl Coro module uses these hooks to integrate
1802	coroutines into libev programs, by yielding to other active coroutines	2938	coroutines into libev programs, by yielding to other active coroutines
1803	during each prepare and only letting the process block if no coroutines	2939	during each prepare and only letting the process block if no coroutines
1804	are ready to run (it's actually more complicated: it only runs coroutines	2940	are ready to run (it's actually more complicated: it only runs coroutines
1805	with priority higher than or equal to the event loop and one coroutine	2941	with priority higher than or equal to the event loop and one coroutine
1806	of lower priority, but only once, using idle watchers to keep the event	2942	of lower priority, but only once, using idle watchers to keep the event
1807	loop from blocking if lower-priority coroutines are active, thus mapping	2943	loop from blocking if lower-priority coroutines are active, thus mapping
1808	low-priority coroutines to idle/background tasks).	2944	low-priority coroutines to idle/background tasks).
1809		2945
1810	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2946	When used for this purpose, it is recommended to give C<ev_check> watchers
1811	priority, to ensure that they are being run before any other watchers	2947	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		2948	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2949	watchers).
		2950
1812	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2951	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1813	too) should not activate ("feed") events into libev. While libev fully	2952	activate ("feed") events into libev. While libev fully supports this, they
1814	supports this, they will be called before other C<ev_check> watchers	2953	might get executed before other C<ev_check> watchers did their job. As
1815	did their job. As C<ev_check> watchers are often used to embed other	2954	C<ev_check> watchers are often used to embed other (non-libev) event
1816	(non-libev) event loops those other event loops might be in an unusable	2955	loops those other event loops might be in an unusable state until their
1817	state until their C<ev_check> watcher ran (always remind yourself to	2956	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1818	coexist peacefully with others).	2957	others).
		2958
		2959	=head3 Abusing an C<ev_check> watcher for its side-effect
		2960
		2961	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2962	useful because they are called once per event loop iteration. For
		2963	example, if you want to handle a large number of connections fairly, you
		2964	normally only do a bit of work for each active connection, and if there
		2965	is more work to do, you wait for the next event loop iteration, so other
		2966	connections have a chance of making progress.
		2967
		2968	Using an C<ev_check> watcher is almost enough: it will be called on the
		2969	next event loop iteration. However, that isn't as soon as possible -
		2970	without external events, your C<ev_check> watcher will not be invoked.
		2971
		2972	This is where C<ev_idle> watchers come in handy - all you need is a
		2973	single global idle watcher that is active as long as you have one active
		2974	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2975	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2976	invoked. Neither watcher alone can do that.
1819		2977
1820	=head3 Watcher-Specific Functions and Data Members	2978	=head3 Watcher-Specific Functions and Data Members
1821		2979
1822	=over 4	2980	=over 4
1823		2981
…		…
1825		2983
1826	=item ev_check_init (ev_check *, callback)	2984	=item ev_check_init (ev_check *, callback)
1827		2985
1828	Initialises and configures the prepare or check watcher - they have no	2986	Initialises and configures the prepare or check watcher - they have no
1829	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2987	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1830	macros, but using them is utterly, utterly and completely pointless.	2988	macros, but using them is utterly, utterly, utterly and completely
		2989	pointless.
1831		2990
1832	=back	2991	=back
1833		2992
1834	=head3 Examples	2993	=head3 Examples
1835		2994
1836	There are a number of principal ways to embed other event loops or modules	2995	There are a number of principal ways to embed other event loops or modules
1837	into libev. Here are some ideas on how to include libadns into libev	2996	into libev. Here are some ideas on how to include libadns into libev
1838	(there is a Perl module named C<EV::ADNS> that does this, which you could	2997	(there is a Perl module named C<EV::ADNS> that does this, which you could
1839	use for an actually working example. Another Perl module named C<EV::Glib>	2998	use as a working example. Another Perl module named C<EV::Glib> embeds a
1840	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2999	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1841	into the Glib event loop).	3000	Glib event loop).
1842		3001
1843	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	3002	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1844	and in a check watcher, destroy them and call into libadns. What follows	3003	and in a check watcher, destroy them and call into libadns. What follows
1845	is pseudo-code only of course. This requires you to either use a low	3004	is pseudo-code only of course. This requires you to either use a low
1846	priority for the check watcher or use C<ev_clear_pending> explicitly, as	3005	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1847	the callbacks for the IO/timeout watchers might not have been called yet.	3006	the callbacks for the IO/timeout watchers might not have been called yet.
1848		3007
1849	static ev_io iow [nfd];	3008	static ev_io iow [nfd];
1850	static ev_timer tw;	3009	static ev_timer tw;
1851		3010
1852	static void	3011	static void
1853	io_cb (ev_loop *loop, ev_io *w, int revents)	3012	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1854	{	3013	{
1855	}	3014	}
1856		3015
1857	// create io watchers for each fd and a timer before blocking	3016	// create io watchers for each fd and a timer before blocking
1858	static void	3017	static void
1859	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3018	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1860	{	3019	{
1861	int timeout = 3600000;	3020	int timeout = 3600000;
1862	struct pollfd fds [nfd];	3021	struct pollfd fds [nfd];
1863	// actual code will need to loop here and realloc etc.	3022	// actual code will need to loop here and realloc etc.
1864	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3023	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1865		3024
1866	/* the callback is illegal, but won't be called as we stop during check */	3025	/* the callback is illegal, but won't be called as we stop during check */
1867	ev_timer_init (&tw, 0, timeout * 1e-3);	3026	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1868	ev_timer_start (loop, &tw);	3027	ev_timer_start (loop, &tw);
1869		3028
1870	// create one ev_io per pollfd	3029	// create one ev_io per pollfd
1871	for (int i = 0; i < nfd; ++i)	3030	for (int i = 0; i < nfd; ++i)
1872	{	3031	{
1873	ev_io_init (iow + i, io_cb, fds [i].fd,	3032	ev_io_init (iow + i, io_cb, fds [i].fd,
1874	((fds [i].events & POLLIN ? EV_READ : 0)	3033	((fds [i].events & POLLIN ? EV_READ : 0)
1875	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	3034	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1876		3035
1877	fds [i].revents = 0;	3036	fds [i].revents = 0;
1878	ev_io_start (loop, iow + i);	3037	ev_io_start (loop, iow + i);
1879	}	3038	}
1880	}	3039	}
1881		3040
1882	// stop all watchers after blocking	3041	// stop all watchers after blocking
1883	static void	3042	static void
1884	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3043	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1885	{	3044	{
1886	ev_timer_stop (loop, &tw);	3045	ev_timer_stop (loop, &tw);
1887		3046
1888	for (int i = 0; i < nfd; ++i)	3047	for (int i = 0; i < nfd; ++i)
1889	{	3048	{
1890	// set the relevant poll flags	3049	// set the relevant poll flags
1891	// could also call adns_processreadable etc. here	3050	// could also call adns_processreadable etc. here
1892	struct pollfd *fd = fds + i;	3051	struct pollfd *fd = fds + i;
1893	int revents = ev_clear_pending (iow + i);	3052	int revents = ev_clear_pending (iow + i);
1894	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	3053	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1895	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	3054	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1896		3055
1897	// now stop the watcher	3056	// now stop the watcher
1898	ev_io_stop (loop, iow + i);	3057	ev_io_stop (loop, iow + i);
1899	}	3058	}
1900		3059
1901	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3060	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1902	}	3061	}
1903		3062
1904	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	3063	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1905	in the prepare watcher and would dispose of the check watcher.	3064	in the prepare watcher and would dispose of the check watcher.
1906		3065
1907	Method 3: If the module to be embedded supports explicit event	3066	Method 3: If the module to be embedded supports explicit event
1908	notification (adns does), you can also make use of the actual watcher	3067	notification (libadns does), you can also make use of the actual watcher
1909	callbacks, and only destroy/create the watchers in the prepare watcher.	3068	callbacks, and only destroy/create the watchers in the prepare watcher.
1910		3069
1911	static void	3070	static void
1912	timer_cb (EV_P_ ev_timer *w, int revents)	3071	timer_cb (EV_P_ ev_timer *w, int revents)
1913	{	3072	{
1914	adns_state ads = (adns_state)w->data;	3073	adns_state ads = (adns_state)w->data;
1915	update_now (EV_A);	3074	update_now (EV_A);
1916		3075
1917	adns_processtimeouts (ads, &tv_now);	3076	adns_processtimeouts (ads, &tv_now);
1918	}	3077	}
1919		3078
1920	static void	3079	static void
1921	io_cb (EV_P_ ev_io *w, int revents)	3080	io_cb (EV_P_ ev_io *w, int revents)
1922	{	3081	{
1923	adns_state ads = (adns_state)w->data;	3082	adns_state ads = (adns_state)w->data;
1924	update_now (EV_A);	3083	update_now (EV_A);
1925		3084
1926	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	3085	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1927	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	3086	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1928	}	3087	}
1929		3088
1930	// do not ever call adns_afterpoll	3089	// do not ever call adns_afterpoll
1931		3090
1932	Method 4: Do not use a prepare or check watcher because the module you	3091	Method 4: Do not use a prepare or check watcher because the module you
1933	want to embed is too inflexible to support it. Instead, youc na override	3092	want to embed is not flexible enough to support it. Instead, you can
1934	their poll function. The drawback with this solution is that the main	3093	override their poll function. The drawback with this solution is that the
1935	loop is now no longer controllable by EV. The C<Glib::EV> module does	3094	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1936	this.	3095	this approach, effectively embedding EV as a client into the horrible
		3096	libglib event loop.
1937		3097
1938	static gint	3098	static gint
1939	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3099	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1940	{	3100	{
1941	int got_events = 0;	3101	int got_events = 0;
1942		3102
1943	for (n = 0; n < nfds; ++n)	3103	for (n = 0; n < nfds; ++n)
1944	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	3104	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1945		3105
1946	if (timeout >= 0)	3106	if (timeout >= 0)
1947	// create/start timer	3107	// create/start timer
1948		3108
1949	// poll	3109	// poll
1950	ev_loop (EV_A_ 0);	3110	ev_run (EV_A_ 0);
1951		3111
1952	// stop timer again	3112	// stop timer again
1953	if (timeout >= 0)	3113	if (timeout >= 0)
1954	ev_timer_stop (EV_A_ &to);	3114	ev_timer_stop (EV_A_ &to);
1955		3115
1956	// stop io watchers again - their callbacks should have set	3116	// stop io watchers again - their callbacks should have set
1957	for (n = 0; n < nfds; ++n)	3117	for (n = 0; n < nfds; ++n)
1958	ev_io_stop (EV_A_ iow [n]);	3118	ev_io_stop (EV_A_ iow [n]);
1959		3119
1960	return got_events;	3120	return got_events;
1961	}	3121	}
1962		3122
1963		3123
1964	=head2 C<ev_embed> - when one backend isn't enough...	3124	=head2 C<ev_embed> - when one backend isn't enough...
1965		3125
1966	This is a rather advanced watcher type that lets you embed one event loop	3126	This is a rather advanced watcher type that lets you embed one event loop
…		…
1972	prioritise I/O.	3132	prioritise I/O.
1973		3133
1974	As an example for a bug workaround, the kqueue backend might only support	3134	As an example for a bug workaround, the kqueue backend might only support
1975	sockets on some platform, so it is unusable as generic backend, but you	3135	sockets on some platform, so it is unusable as generic backend, but you
1976	still want to make use of it because you have many sockets and it scales	3136	still want to make use of it because you have many sockets and it scales
1977	so nicely. In this case, you would create a kqueue-based loop and embed it	3137	so nicely. In this case, you would create a kqueue-based loop and embed
1978	into your default loop (which might use e.g. poll). Overall operation will	3138	it into your default loop (which might use e.g. poll). Overall operation
1979	be a bit slower because first libev has to poll and then call kevent, but	3139	will be a bit slower because first libev has to call C<poll> and then
1980	at least you can use both at what they are best.	3140	C<kevent>, but at least you can use both mechanisms for what they are
		3141	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1981		3142
1982	As for prioritising I/O: rarely you have the case where some fds have	3143	As for prioritising I/O: under rare circumstances you have the case where
1983	to be watched and handled very quickly (with low latency), and even	3144	some fds have to be watched and handled very quickly (with low latency),
1984	priorities and idle watchers might have too much overhead. In this case	3145	and even priorities and idle watchers might have too much overhead. In
1985	you would put all the high priority stuff in one loop and all the rest in	3146	this case you would put all the high priority stuff in one loop and all
1986	a second one, and embed the second one in the first.	3147	the rest in a second one, and embed the second one in the first.
1987		3148
1988	As long as the watcher is active, the callback will be invoked every time	3149	As long as the watcher is active, the callback will be invoked every
1989	there might be events pending in the embedded loop. The callback must then	3150	time there might be events pending in the embedded loop. The callback
1990	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3151	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1991	their callbacks (you could also start an idle watcher to give the embedded	3152	sweep and invoke their callbacks (the callback doesn't need to invoke the
1992	loop strictly lower priority for example). You can also set the callback	3153	C<ev_embed_sweep> function directly, it could also start an idle watcher
1993	to C<0>, in which case the embed watcher will automatically execute the	3154	to give the embedded loop strictly lower priority for example).
1994	embedded loop sweep.
1995		3155
1996	As long as the watcher is started it will automatically handle events. The	3156	You can also set the callback to C<0>, in which case the embed watcher
1997	callback will be invoked whenever some events have been handled. You can	3157	will automatically execute the embedded loop sweep whenever necessary.
1998	set the callback to C<0> to avoid having to specify one if you are not
1999	interested in that.
2000		3158
2001	Also, there have not currently been made special provisions for forking:	3159	Fork detection will be handled transparently while the C<ev_embed> watcher
2002	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3160	is active, i.e., the embedded loop will automatically be forked when the
2003	but you will also have to stop and restart any C<ev_embed> watchers	3161	embedding loop forks. In other cases, the user is responsible for calling
2004	yourself.	3162	C<ev_loop_fork> on the embedded loop.
2005		3163
2006	Unfortunately, not all backends are embeddable, only the ones returned by	3164	Unfortunately, not all backends are embeddable: only the ones returned by
2007	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3165	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2008	portable one.	3166	portable one.
2009		3167
2010	So when you want to use this feature you will always have to be prepared	3168	So when you want to use this feature you will always have to be prepared
2011	that you cannot get an embeddable loop. The recommended way to get around	3169	that you cannot get an embeddable loop. The recommended way to get around
2012	this is to have a separate variables for your embeddable loop, try to	3170	this is to have a separate variables for your embeddable loop, try to
2013	create it, and if that fails, use the normal loop for everything.	3171	create it, and if that fails, use the normal loop for everything.
2014		3172
		3173	=head3 C<ev_embed> and fork
		3174
		3175	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3176	automatically be applied to the embedded loop as well, so no special
		3177	fork handling is required in that case. When the watcher is not running,
		3178	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3179	as applicable.
		3180
2015	=head3 Watcher-Specific Functions and Data Members	3181	=head3 Watcher-Specific Functions and Data Members
2016		3182
2017	=over 4	3183	=over 4
2018		3184
2019	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3185	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2020		3186
2021	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3187	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2022		3188
2023	Configures the watcher to embed the given loop, which must be	3189	Configures the watcher to embed the given loop, which must be
2024	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3190	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2025	invoked automatically, otherwise it is the responsibility of the callback	3191	invoked automatically, otherwise it is the responsibility of the callback
2026	to invoke it (it will continue to be called until the sweep has been done,	3192	to invoke it (it will continue to be called until the sweep has been done,
2027	if you do not want thta, you need to temporarily stop the embed watcher).	3193	if you do not want that, you need to temporarily stop the embed watcher).
2028		3194
2029	=item ev_embed_sweep (loop, ev_embed *)	3195	=item ev_embed_sweep (loop, ev_embed *)
2030		3196
2031	Make a single, non-blocking sweep over the embedded loop. This works	3197	Make a single, non-blocking sweep over the embedded loop. This works
2032	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3198	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2033	apropriate way for embedded loops.	3199	appropriate way for embedded loops.
2034		3200
2035	=item struct ev_loop *other [read-only]	3201	=item struct ev_loop *other [read-only]
2036		3202
2037	The embedded event loop.	3203	The embedded event loop.
2038		3204
…		…
2040		3206
2041	=head3 Examples	3207	=head3 Examples
2042		3208
2043	Example: Try to get an embeddable event loop and embed it into the default	3209	Example: Try to get an embeddable event loop and embed it into the default
2044	event loop. If that is not possible, use the default loop. The default	3210	event loop. If that is not possible, use the default loop. The default
2045	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	3211	loop is stored in C<loop_hi>, while the embeddable loop is stored in
2046	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	3212	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2047	used).	3213	used).
2048		3214
2049	struct ev_loop *loop_hi = ev_default_init (0);	3215	struct ev_loop *loop_hi = ev_default_init (0);
2050	struct ev_loop *loop_lo = 0;	3216	struct ev_loop *loop_lo = 0;
2051	struct ev_embed embed;	3217	ev_embed embed;
2052		3218
2053	// see if there is a chance of getting one that works	3219	// see if there is a chance of getting one that works
2054	// (remember that a flags value of 0 means autodetection)	3220	// (remember that a flags value of 0 means autodetection)
2055	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3221	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2056	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3222	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2057	: 0;	3223	: 0;
2058		3224
2059	// if we got one, then embed it, otherwise default to loop_hi	3225	// if we got one, then embed it, otherwise default to loop_hi
2060	if (loop_lo)	3226	if (loop_lo)
2061	{	3227	{
2062	ev_embed_init (&embed, 0, loop_lo);	3228	ev_embed_init (&embed, 0, loop_lo);
2063	ev_embed_start (loop_hi, &embed);	3229	ev_embed_start (loop_hi, &embed);
2064	}	3230	}
2065	else	3231	else
2066	loop_lo = loop_hi;	3232	loop_lo = loop_hi;
2067		3233
2068	Example: Check if kqueue is available but not recommended and create	3234	Example: Check if kqueue is available but not recommended and create
2069	a kqueue backend for use with sockets (which usually work with any	3235	a kqueue backend for use with sockets (which usually work with any
2070	kqueue implementation). Store the kqueue/socket-only event loop in	3236	kqueue implementation). Store the kqueue/socket-only event loop in
2071	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3237	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2072		3238
2073	struct ev_loop *loop = ev_default_init (0);	3239	struct ev_loop *loop = ev_default_init (0);
2074	struct ev_loop *loop_socket = 0;	3240	struct ev_loop *loop_socket = 0;
2075	struct ev_embed embed;	3241	ev_embed embed;
2076		3242
2077	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3243	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2078	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3244	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2079	{	3245	{
2080	ev_embed_init (&embed, 0, loop_socket);	3246	ev_embed_init (&embed, 0, loop_socket);
2081	ev_embed_start (loop, &embed);	3247	ev_embed_start (loop, &embed);
2082	}	3248	}
2083		3249
2084	if (!loop_socket)	3250	if (!loop_socket)
2085	loop_socket = loop;	3251	loop_socket = loop;
2086		3252
2087	// now use loop_socket for all sockets, and loop for everything else	3253	// now use loop_socket for all sockets, and loop for everything else
2088		3254
2089		3255
2090	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3256	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2091		3257
2092	Fork watchers are called when a C<fork ()> was detected (usually because	3258	Fork watchers are called when a C<fork ()> was detected (usually because
2093	whoever is a good citizen cared to tell libev about it by calling	3259	whoever is a good citizen cared to tell libev about it by calling
2094	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3260	C<ev_loop_fork>). The invocation is done before the event loop blocks next
2095	event loop blocks next and before C<ev_check> watchers are being called,	3261	and before C<ev_check> watchers are being called, and only in the child
2096	and only in the child after the fork. If whoever good citizen calling	3262	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
2097	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3263	and calls it in the wrong process, the fork handlers will be invoked, too,
2098	handlers will be invoked, too, of course.	3264	of course.
		3265
		3266	=head3 The special problem of life after fork - how is it possible?
		3267
		3268	Most uses of C<fork()> consist of forking, then some simple calls to set
		3269	up/change the process environment, followed by a call to C<exec()>. This
		3270	sequence should be handled by libev without any problems.
		3271
		3272	This changes when the application actually wants to do event handling
		3273	in the child, or both parent in child, in effect "continuing" after the
		3274	fork.
		3275
		3276	The default mode of operation (for libev, with application help to detect
		3277	forks) is to duplicate all the state in the child, as would be expected
		3278	when I<either> the parent I<or> the child process continues.
		3279
		3280	When both processes want to continue using libev, then this is usually the
		3281	wrong result. In that case, usually one process (typically the parent) is
		3282	supposed to continue with all watchers in place as before, while the other
		3283	process typically wants to start fresh, i.e. without any active watchers.
		3284
		3285	The cleanest and most efficient way to achieve that with libev is to
		3286	simply create a new event loop, which of course will be "empty", and
		3287	use that for new watchers. This has the advantage of not touching more
		3288	memory than necessary, and thus avoiding the copy-on-write, and the
		3289	disadvantage of having to use multiple event loops (which do not support
		3290	signal watchers).
		3291
		3292	When this is not possible, or you want to use the default loop for
		3293	other reasons, then in the process that wants to start "fresh", call
		3294	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3295	Destroying the default loop will "orphan" (not stop) all registered
		3296	watchers, so you have to be careful not to execute code that modifies
		3297	those watchers. Note also that in that case, you have to re-register any
		3298	signal watchers.
2099		3299
2100	=head3 Watcher-Specific Functions and Data Members	3300	=head3 Watcher-Specific Functions and Data Members
2101		3301
2102	=over 4	3302	=over 4
2103		3303
2104	=item ev_fork_init (ev_signal *, callback)	3304	=item ev_fork_init (ev_fork *, callback)
2105		3305
2106	Initialises and configures the fork watcher - it has no parameters of any	3306	Initialises and configures the fork watcher - it has no parameters of any
2107	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3307	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
2108	believe me.	3308	really.
2109		3309
2110	=back	3310	=back
2111		3311
2112		3312
		3313	=head2 C<ev_cleanup> - even the best things end
		3314
		3315	Cleanup watchers are called just before the event loop is being destroyed
		3316	by a call to C<ev_loop_destroy>.
		3317
		3318	While there is no guarantee that the event loop gets destroyed, cleanup
		3319	watchers provide a convenient method to install cleanup hooks for your
		3320	program, worker threads and so on - you just to make sure to destroy the
		3321	loop when you want them to be invoked.
		3322
		3323	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3324	all other watchers, they do not keep a reference to the event loop (which
		3325	makes a lot of sense if you think about it). Like all other watchers, you
		3326	can call libev functions in the callback, except C<ev_cleanup_start>.
		3327
		3328	=head3 Watcher-Specific Functions and Data Members
		3329
		3330	=over 4
		3331
		3332	=item ev_cleanup_init (ev_cleanup *, callback)
		3333
		3334	Initialises and configures the cleanup watcher - it has no parameters of
		3335	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3336	pointless, I assure you.
		3337
		3338	=back
		3339
		3340	Example: Register an atexit handler to destroy the default loop, so any
		3341	cleanup functions are called.
		3342
		3343	static void
		3344	program_exits (void)
		3345	{
		3346	ev_loop_destroy (EV_DEFAULT_UC);
		3347	}
		3348
		3349	...
		3350	atexit (program_exits);
		3351
		3352
2113	=head2 C<ev_async> - how to wake up another event loop	3353	=head2 C<ev_async> - how to wake up an event loop
2114		3354
2115	In general, you cannot use an C<ev_loop> from multiple threads or other	3355	In general, you cannot use an C<ev_loop> from multiple threads or other
2116	asynchronous sources such as signal handlers (as opposed to multiple event	3356	asynchronous sources such as signal handlers (as opposed to multiple event
2117	loops - those are of course safe to use in different threads).	3357	loops - those are of course safe to use in different threads).
2118		3358
2119	Sometimes, however, you need to wake up another event loop you do not	3359	Sometimes, however, you need to wake up an event loop you do not control,
2120	control, for example because it belongs to another thread. This is what	3360	for example because it belongs to another thread. This is what C<ev_async>
2121	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3361	watchers do: as long as the C<ev_async> watcher is active, you can signal
2122	can signal it by calling C<ev_async_send>, which is thread- and signal	3362	it by calling C<ev_async_send>, which is thread- and signal safe.
2123	safe.
2124		3363
2125	This functionality is very similar to C<ev_signal> watchers, as signals,	3364	This functionality is very similar to C<ev_signal> watchers, as signals,
2126	too, are asynchronous in nature, and signals, too, will be compressed	3365	too, are asynchronous in nature, and signals, too, will be compressed
2127	(i.e. the number of callback invocations may be less than the number of	3366	(i.e. the number of callback invocations may be less than the number of
2128	C<ev_async_sent> calls).	3367	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
2129		3368	of "global async watchers" by using a watcher on an otherwise unused
2130	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3369	signal, and C<ev_feed_signal> to signal this watcher from another thread,
2131	just the default loop.	3370	even without knowing which loop owns the signal.
2132		3371
2133	=head3 Queueing	3372	=head3 Queueing
2134		3373
2135	C<ev_async> does not support queueing of data in any way. The reason	3374	C<ev_async> does not support queueing of data in any way. The reason
2136	is that the author does not know of a simple (or any) algorithm for a	3375	is that the author does not know of a simple (or any) algorithm for a
2137	multiple-writer-single-reader queue that works in all cases and doesn't	3376	multiple-writer-single-reader queue that works in all cases and doesn't
2138	need elaborate support such as pthreads.	3377	need elaborate support such as pthreads or unportable memory access
		3378	semantics.
2139		3379
2140	That means that if you want to queue data, you have to provide your own	3380	That means that if you want to queue data, you have to provide your own
2141	queue. But at least I can tell you would implement locking around your	3381	queue. But at least I can tell you how to implement locking around your
2142	queue:	3382	queue:
2143		3383
2144	=over 4	3384	=over 4
2145		3385
2146	=item queueing from a signal handler context	3386	=item queueing from a signal handler context
2147		3387
2148	To implement race-free queueing, you simply add to the queue in the signal	3388	To implement race-free queueing, you simply add to the queue in the signal
2149	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3389	handler but you block the signal handler in the watcher callback. Here is
2150	some fictitiuous SIGUSR1 handler:	3390	an example that does that for some fictitious SIGUSR1 handler:
2151		3391
2152	static ev_async mysig;	3392	static ev_async mysig;
2153		3393
2154	static void	3394	static void
2155	sigusr1_handler (void)	3395	sigusr1_handler (void)
…		…
2221	=over 4	3461	=over 4
2222		3462
2223	=item ev_async_init (ev_async *, callback)	3463	=item ev_async_init (ev_async *, callback)
2224		3464
2225	Initialises and configures the async watcher - it has no parameters of any	3465	Initialises and configures the async watcher - it has no parameters of any
2226	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3466	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2227	believe me.	3467	trust me.
2228		3468
2229	=item ev_async_send (loop, ev_async *)	3469	=item ev_async_send (loop, ev_async *)
2230		3470
2231	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3471	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2232	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3472	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3473	returns.
		3474
2233	C<ev_feed_event>, this call is safe to do in other threads, signal or	3475	Unlike C<ev_feed_event>, this call is safe to do from other threads,
2234	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding	3476	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
2235	section below on what exactly this means).	3477	embedding section below on what exactly this means).
2236		3478
2237	This call incurs the overhead of a syscall only once per loop iteration,	3479	Note that, as with other watchers in libev, multiple events might get
2238	so while the overhead might be noticable, it doesn't apply to repeated	3480	compressed into a single callback invocation (another way to look at
2239	calls to C<ev_async_send>.	3481	this is that C<ev_async> watchers are level-triggered: they are set on
		3482	C<ev_async_send>, reset when the event loop detects that).
		3483
		3484	This call incurs the overhead of at most one extra system call per event
		3485	loop iteration, if the event loop is blocked, and no syscall at all if
		3486	the event loop (or your program) is processing events. That means that
		3487	repeated calls are basically free (there is no need to avoid calls for
		3488	performance reasons) and that the overhead becomes smaller (typically
		3489	zero) under load.
		3490
		3491	=item bool = ev_async_pending (ev_async *)
		3492
		3493	Returns a non-zero value when C<ev_async_send> has been called on the
		3494	watcher but the event has not yet been processed (or even noted) by the
		3495	event loop.
		3496
		3497	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3498	the loop iterates next and checks for the watcher to have become active,
		3499	it will reset the flag again. C<ev_async_pending> can be used to very
		3500	quickly check whether invoking the loop might be a good idea.
		3501
		3502	Not that this does I<not> check whether the watcher itself is pending,
		3503	only whether it has been requested to make this watcher pending: there
		3504	is a time window between the event loop checking and resetting the async
		3505	notification, and the callback being invoked.
2240		3506
2241	=back	3507	=back
2242		3508
2243		3509
2244	=head1 OTHER FUNCTIONS	3510	=head1 OTHER FUNCTIONS
…		…
2248	=over 4	3514	=over 4
2249		3515
2250	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3516	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2251		3517
2252	This function combines a simple timer and an I/O watcher, calls your	3518	This function combines a simple timer and an I/O watcher, calls your
2253	callback on whichever event happens first and automatically stop both	3519	callback on whichever event happens first and automatically stops both
2254	watchers. This is useful if you want to wait for a single event on an fd	3520	watchers. This is useful if you want to wait for a single event on an fd
2255	or timeout without having to allocate/configure/start/stop/free one or	3521	or timeout without having to allocate/configure/start/stop/free one or
2256	more watchers yourself.	3522	more watchers yourself.
2257		3523
2258	If C<fd> is less than 0, then no I/O watcher will be started and events	3524	If C<fd> is less than 0, then no I/O watcher will be started and the
2259	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3525	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2260	C<events> set will be craeted and started.	3526	the given C<fd> and C<events> set will be created and started.
2261		3527
2262	If C<timeout> is less than 0, then no timeout watcher will be	3528	If C<timeout> is less than 0, then no timeout watcher will be
2263	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3529	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2264	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3530	repeat = 0) will be started. C<0> is a valid timeout.
2265	dubious value.
2266		3531
2267	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3532	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2268	passed an C<revents> set like normal event callbacks (a combination of	3533	passed an C<revents> set like normal event callbacks (a combination of
2269	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3534	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2270	value passed to C<ev_once>:	3535	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3536	a timeout and an io event at the same time - you probably should give io
		3537	events precedence.
2271		3538
		3539	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3540
2272	static void stdin_ready (int revents, void *arg)	3541	static void stdin_ready (int revents, void *arg)
		3542	{
		3543	if (revents & EV_READ)
		3544	/* stdin might have data for us, joy! */;
		3545	else if (revents & EV_TIMER)
		3546	/* doh, nothing entered */;
		3547	}
		3548
		3549	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3550
		3551	=item ev_feed_fd_event (loop, int fd, int revents)
		3552
		3553	Feed an event on the given fd, as if a file descriptor backend detected
		3554	the given events.
		3555
		3556	=item ev_feed_signal_event (loop, int signum)
		3557
		3558	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3559	which is async-safe.
		3560
		3561	=back
		3562
		3563
		3564	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3565
		3566	This section explains some common idioms that are not immediately
		3567	obvious. Note that examples are sprinkled over the whole manual, and this
		3568	section only contains stuff that wouldn't fit anywhere else.
		3569
		3570	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3571
		3572	Each watcher has, by default, a C<void *data> member that you can read
		3573	or modify at any time: libev will completely ignore it. This can be used
		3574	to associate arbitrary data with your watcher. If you need more data and
		3575	don't want to allocate memory separately and store a pointer to it in that
		3576	data member, you can also "subclass" the watcher type and provide your own
		3577	data:
		3578
		3579	struct my_io
		3580	{
		3581	ev_io io;
		3582	int otherfd;
		3583	void *somedata;
		3584	struct whatever *mostinteresting;
		3585	};
		3586
		3587	...
		3588	struct my_io w;
		3589	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3590
		3591	And since your callback will be called with a pointer to the watcher, you
		3592	can cast it back to your own type:
		3593
		3594	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3595	{
		3596	struct my_io *w = (struct my_io *)w_;
		3597	...
		3598	}
		3599
		3600	More interesting and less C-conformant ways of casting your callback
		3601	function type instead have been omitted.
		3602
		3603	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3604
		3605	Another common scenario is to use some data structure with multiple
		3606	embedded watchers, in effect creating your own watcher that combines
		3607	multiple libev event sources into one "super-watcher":
		3608
		3609	struct my_biggy
		3610	{
		3611	int some_data;
		3612	ev_timer t1;
		3613	ev_timer t2;
		3614	}
		3615
		3616	In this case getting the pointer to C<my_biggy> is a bit more
		3617	complicated: Either you store the address of your C<my_biggy> struct in
		3618	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3619	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3620	real programmers):
		3621
		3622	#include <stddef.h>
		3623
		3624	static void
		3625	t1_cb (EV_P_ ev_timer *w, int revents)
		3626	{
		3627	struct my_biggy big = (struct my_biggy *)
		3628	(((char *)w) - offsetof (struct my_biggy, t1));
		3629	}
		3630
		3631	static void
		3632	t2_cb (EV_P_ ev_timer *w, int revents)
		3633	{
		3634	struct my_biggy big = (struct my_biggy *)
		3635	(((char *)w) - offsetof (struct my_biggy, t2));
		3636	}
		3637
		3638	=head2 AVOIDING FINISHING BEFORE RETURNING
		3639
		3640	Often you have structures like this in event-based programs:
		3641
		3642	callback ()
2273	{	3643	{
2274	if (revents & EV_TIMEOUT)	3644	free (request);
2275	/* doh, nothing entered */;
2276	else if (revents & EV_READ)
2277	/* stdin might have data for us, joy! */;
2278	}	3645	}
2279		3646
2280	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3647	request = start_new_request (..., callback);
2281		3648
2282	=item ev_feed_event (ev_loop *, watcher *, int revents)	3649	The intent is to start some "lengthy" operation. The C<request> could be
		3650	used to cancel the operation, or do other things with it.
2283		3651
2284	Feeds the given event set into the event loop, as if the specified event	3652	It's not uncommon to have code paths in C<start_new_request> that
2285	had happened for the specified watcher (which must be a pointer to an	3653	immediately invoke the callback, for example, to report errors. Or you add
2286	initialised but not necessarily started event watcher).	3654	some caching layer that finds that it can skip the lengthy aspects of the
		3655	operation and simply invoke the callback with the result.
2287		3656
2288	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3657	The problem here is that this will happen I<before> C<start_new_request>
		3658	has returned, so C<request> is not set.
2289		3659
2290	Feed an event on the given fd, as if a file descriptor backend detected	3660	Even if you pass the request by some safer means to the callback, you
2291	the given events it.	3661	might want to do something to the request after starting it, such as
		3662	canceling it, which probably isn't working so well when the callback has
		3663	already been invoked.
2292		3664
2293	=item ev_feed_signal_event (ev_loop *loop, int signum)	3665	A common way around all these issues is to make sure that
		3666	C<start_new_request> I<always> returns before the callback is invoked. If
		3667	C<start_new_request> immediately knows the result, it can artificially
		3668	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3669	example, or more sneakily, by reusing an existing (stopped) watcher and
		3670	pushing it into the pending queue:
2294		3671
2295	Feed an event as if the given signal occured (C<loop> must be the default	3672	ev_set_cb (watcher, callback);
2296	loop!).	3673	ev_feed_event (EV_A_ watcher, 0);
2297		3674
2298	=back	3675	This way, C<start_new_request> can safely return before the callback is
		3676	invoked, while not delaying callback invocation too much.
		3677
		3678	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3679
		3680	Often (especially in GUI toolkits) there are places where you have
		3681	I<modal> interaction, which is most easily implemented by recursively
		3682	invoking C<ev_run>.
		3683
		3684	This brings the problem of exiting - a callback might want to finish the
		3685	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3686	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3687	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3688	other combination: In these cases, a simple C<ev_break> will not work.
		3689
		3690	The solution is to maintain "break this loop" variable for each C<ev_run>
		3691	invocation, and use a loop around C<ev_run> until the condition is
		3692	triggered, using C<EVRUN_ONCE>:
		3693
		3694	// main loop
		3695	int exit_main_loop = 0;
		3696
		3697	while (!exit_main_loop)
		3698	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3699
		3700	// in a modal watcher
		3701	int exit_nested_loop = 0;
		3702
		3703	while (!exit_nested_loop)
		3704	ev_run (EV_A_ EVRUN_ONCE);
		3705
		3706	To exit from any of these loops, just set the corresponding exit variable:
		3707
		3708	// exit modal loop
		3709	exit_nested_loop = 1;
		3710
		3711	// exit main program, after modal loop is finished
		3712	exit_main_loop = 1;
		3713
		3714	// exit both
		3715	exit_main_loop = exit_nested_loop = 1;
		3716
		3717	=head2 THREAD LOCKING EXAMPLE
		3718
		3719	Here is a fictitious example of how to run an event loop in a different
		3720	thread from where callbacks are being invoked and watchers are
		3721	created/added/removed.
		3722
		3723	For a real-world example, see the C<EV::Loop::Async> perl module,
		3724	which uses exactly this technique (which is suited for many high-level
		3725	languages).
		3726
		3727	The example uses a pthread mutex to protect the loop data, a condition
		3728	variable to wait for callback invocations, an async watcher to notify the
		3729	event loop thread and an unspecified mechanism to wake up the main thread.
		3730
		3731	First, you need to associate some data with the event loop:
		3732
		3733	typedef struct {
		3734	mutex_t lock; /* global loop lock */
		3735	ev_async async_w;
		3736	thread_t tid;
		3737	cond_t invoke_cv;
		3738	} userdata;
		3739
		3740	void prepare_loop (EV_P)
		3741	{
		3742	// for simplicity, we use a static userdata struct.
		3743	static userdata u;
		3744
		3745	ev_async_init (&u->async_w, async_cb);
		3746	ev_async_start (EV_A_ &u->async_w);
		3747
		3748	pthread_mutex_init (&u->lock, 0);
		3749	pthread_cond_init (&u->invoke_cv, 0);
		3750
		3751	// now associate this with the loop
		3752	ev_set_userdata (EV_A_ u);
		3753	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3754	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3755
		3756	// then create the thread running ev_run
		3757	pthread_create (&u->tid, 0, l_run, EV_A);
		3758	}
		3759
		3760	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3761	solely to wake up the event loop so it takes notice of any new watchers
		3762	that might have been added:
		3763
		3764	static void
		3765	async_cb (EV_P_ ev_async *w, int revents)
		3766	{
		3767	// just used for the side effects
		3768	}
		3769
		3770	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3771	protecting the loop data, respectively.
		3772
		3773	static void
		3774	l_release (EV_P)
		3775	{
		3776	userdata *u = ev_userdata (EV_A);
		3777	pthread_mutex_unlock (&u->lock);
		3778	}
		3779
		3780	static void
		3781	l_acquire (EV_P)
		3782	{
		3783	userdata *u = ev_userdata (EV_A);
		3784	pthread_mutex_lock (&u->lock);
		3785	}
		3786
		3787	The event loop thread first acquires the mutex, and then jumps straight
		3788	into C<ev_run>:
		3789
		3790	void *
		3791	l_run (void *thr_arg)
		3792	{
		3793	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3794
		3795	l_acquire (EV_A);
		3796	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3797	ev_run (EV_A_ 0);
		3798	l_release (EV_A);
		3799
		3800	return 0;
		3801	}
		3802
		3803	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3804	signal the main thread via some unspecified mechanism (signals? pipe
		3805	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3806	have been called (in a while loop because a) spurious wakeups are possible
		3807	and b) skipping inter-thread-communication when there are no pending
		3808	watchers is very beneficial):
		3809
		3810	static void
		3811	l_invoke (EV_P)
		3812	{
		3813	userdata *u = ev_userdata (EV_A);
		3814
		3815	while (ev_pending_count (EV_A))
		3816	{
		3817	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3818	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3819	}
		3820	}
		3821
		3822	Now, whenever the main thread gets told to invoke pending watchers, it
		3823	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3824	thread to continue:
		3825
		3826	static void
		3827	real_invoke_pending (EV_P)
		3828	{
		3829	userdata *u = ev_userdata (EV_A);
		3830
		3831	pthread_mutex_lock (&u->lock);
		3832	ev_invoke_pending (EV_A);
		3833	pthread_cond_signal (&u->invoke_cv);
		3834	pthread_mutex_unlock (&u->lock);
		3835	}
		3836
		3837	Whenever you want to start/stop a watcher or do other modifications to an
		3838	event loop, you will now have to lock:
		3839
		3840	ev_timer timeout_watcher;
		3841	userdata *u = ev_userdata (EV_A);
		3842
		3843	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3844
		3845	pthread_mutex_lock (&u->lock);
		3846	ev_timer_start (EV_A_ &timeout_watcher);
		3847	ev_async_send (EV_A_ &u->async_w);
		3848	pthread_mutex_unlock (&u->lock);
		3849
		3850	Note that sending the C<ev_async> watcher is required because otherwise
		3851	an event loop currently blocking in the kernel will have no knowledge
		3852	about the newly added timer. By waking up the loop it will pick up any new
		3853	watchers in the next event loop iteration.
		3854
		3855	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3856
		3857	While the overhead of a callback that e.g. schedules a thread is small, it
		3858	is still an overhead. If you embed libev, and your main usage is with some
		3859	kind of threads or coroutines, you might want to customise libev so that
		3860	doesn't need callbacks anymore.
		3861
		3862	Imagine you have coroutines that you can switch to using a function
		3863	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3864	and that due to some magic, the currently active coroutine is stored in a
		3865	global called C<current_coro>. Then you can build your own "wait for libev
		3866	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3867	the differing C<;> conventions):
		3868
		3869	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3870	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3871
		3872	That means instead of having a C callback function, you store the
		3873	coroutine to switch to in each watcher, and instead of having libev call
		3874	your callback, you instead have it switch to that coroutine.
		3875
		3876	A coroutine might now wait for an event with a function called
		3877	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3878	matter when, or whether the watcher is active or not when this function is
		3879	called):
		3880
		3881	void
		3882	wait_for_event (ev_watcher *w)
		3883	{
		3884	ev_set_cb (w, current_coro);
		3885	switch_to (libev_coro);
		3886	}
		3887
		3888	That basically suspends the coroutine inside C<wait_for_event> and
		3889	continues the libev coroutine, which, when appropriate, switches back to
		3890	this or any other coroutine.
		3891
		3892	You can do similar tricks if you have, say, threads with an event queue -
		3893	instead of storing a coroutine, you store the queue object and instead of
		3894	switching to a coroutine, you push the watcher onto the queue and notify
		3895	any waiters.
		3896
		3897	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3898	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3899
		3900	// my_ev.h
		3901	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3902	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3903	#include "../libev/ev.h"
		3904
		3905	// my_ev.c
		3906	#define EV_H "my_ev.h"
		3907	#include "../libev/ev.c"
		3908
		3909	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3910	F<my_ev.c> into your project. When properly specifying include paths, you
		3911	can even use F<ev.h> as header file name directly.
2299		3912
2300		3913
2301	=head1 LIBEVENT EMULATION	3914	=head1 LIBEVENT EMULATION
2302		3915
2303	Libev offers a compatibility emulation layer for libevent. It cannot	3916	Libev offers a compatibility emulation layer for libevent. It cannot
2304	emulate the internals of libevent, so here are some usage hints:	3917	emulate the internals of libevent, so here are some usage hints:
2305		3918
2306	=over 4	3919	=over 4
		3920
		3921	=item * Only the libevent-1.4.1-beta API is being emulated.
		3922
		3923	This was the newest libevent version available when libev was implemented,
		3924	and is still mostly unchanged in 2010.
2307		3925
2308	=item * Use it by including <event.h>, as usual.	3926	=item * Use it by including <event.h>, as usual.
2309		3927
2310	=item * The following members are fully supported: ev_base, ev_callback,	3928	=item * The following members are fully supported: ev_base, ev_callback,
2311	ev_arg, ev_fd, ev_res, ev_events.	3929	ev_arg, ev_fd, ev_res, ev_events.
…		…
2316		3934
2317	=item * Priorities are not currently supported. Initialising priorities	3935	=item * Priorities are not currently supported. Initialising priorities
2318	will fail and all watchers will have the same priority, even though there	3936	will fail and all watchers will have the same priority, even though there
2319	is an ev_pri field.	3937	is an ev_pri field.
2320		3938
		3939	=item * In libevent, the last base created gets the signals, in libev, the
		3940	base that registered the signal gets the signals.
		3941
2321	=item * Other members are not supported.	3942	=item * Other members are not supported.
2322		3943
2323	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3944	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2324	to use the libev header file and library.	3945	to use the libev header file and library.
2325		3946
2326	=back	3947	=back
2327		3948
2328	=head1 C++ SUPPORT	3949	=head1 C++ SUPPORT
2329		3950
		3951	=head2 C API
		3952
		3953	The normal C API should work fine when used from C++: both ev.h and the
		3954	libev sources can be compiled as C++. Therefore, code that uses the C API
		3955	will work fine.
		3956
		3957	Proper exception specifications might have to be added to callbacks passed
		3958	to libev: exceptions may be thrown only from watcher callbacks, all
		3959	other callbacks (allocator, syserr, loop acquire/release and periodic
		3960	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3961	()> specification. If you have code that needs to be compiled as both C
		3962	and C++ you can use the C<EV_THROW> macro for this:
		3963
		3964	static void
		3965	fatal_error (const char *msg) EV_THROW
		3966	{
		3967	perror (msg);
		3968	abort ();
		3969	}
		3970
		3971	...
		3972	ev_set_syserr_cb (fatal_error);
		3973
		3974	The only API functions that can currently throw exceptions are C<ev_run>,
		3975	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3976	because it runs cleanup watchers).
		3977
		3978	Throwing exceptions in watcher callbacks is only supported if libev itself
		3979	is compiled with a C++ compiler or your C and C++ environments allow
		3980	throwing exceptions through C libraries (most do).
		3981
		3982	=head2 C++ API
		3983
2330	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3984	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2331	you to use some convinience methods to start/stop watchers and also change	3985	you to use some convenience methods to start/stop watchers and also change
2332	the callback model to a model using method callbacks on objects.	3986	the callback model to a model using method callbacks on objects.
2333		3987
2334	To use it,	3988	To use it,
2335		3989
2336	#include <ev++.h>	3990	#include <ev++.h>
2337		3991
2338	This automatically includes F<ev.h> and puts all of its definitions (many	3992	This automatically includes F<ev.h> and puts all of its definitions (many
2339	of them macros) into the global namespace. All C++ specific things are	3993	of them macros) into the global namespace. All C++ specific things are
2340	put into the C<ev> namespace. It should support all the same embedding	3994	put into the C<ev> namespace. It should support all the same embedding
2341	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3995	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2343	Care has been taken to keep the overhead low. The only data member the C++	3997	Care has been taken to keep the overhead low. The only data member the C++
2344	classes add (compared to plain C-style watchers) is the event loop pointer	3998	classes add (compared to plain C-style watchers) is the event loop pointer
2345	that the watcher is associated with (or no additional members at all if	3999	that the watcher is associated with (or no additional members at all if
2346	you disable C<EV_MULTIPLICITY> when embedding libev).	4000	you disable C<EV_MULTIPLICITY> when embedding libev).
2347		4001
2348	Currently, functions, and static and non-static member functions can be	4002	Currently, functions, static and non-static member functions and classes
2349	used as callbacks. Other types should be easy to add as long as they only	4003	with C<operator ()> can be used as callbacks. Other types should be easy
2350	need one additional pointer for context. If you need support for other	4004	to add as long as they only need one additional pointer for context. If
2351	types of functors please contact the author (preferably after implementing	4005	you need support for other types of functors please contact the author
2352	it).	4006	(preferably after implementing it).
		4007
		4008	For all this to work, your C++ compiler either has to use the same calling
		4009	conventions as your C compiler (for static member functions), or you have
		4010	to embed libev and compile libev itself as C++.
2353		4011
2354	Here is a list of things available in the C<ev> namespace:	4012	Here is a list of things available in the C<ev> namespace:
2355		4013
2356	=over 4	4014	=over 4
2357		4015
…		…
2367	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4025	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2368		4026
2369	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4027	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2370	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4028	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2371	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4029	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2372	defines by many implementations.	4030	defined by many implementations.
2373		4031
2374	All of those classes have these methods:	4032	All of those classes have these methods:
2375		4033
2376	=over 4	4034	=over 4
2377		4035
2378	=item ev::TYPE::TYPE ()	4036	=item ev::TYPE::TYPE ()
2379		4037
2380	=item ev::TYPE::TYPE (struct ev_loop *)	4038	=item ev::TYPE::TYPE (loop)
2381		4039
2382	=item ev::TYPE::~TYPE	4040	=item ev::TYPE::~TYPE
2383		4041
2384	The constructor (optionally) takes an event loop to associate the watcher	4042	The constructor (optionally) takes an event loop to associate the watcher
2385	with. If it is omitted, it will use C<EV_DEFAULT>.	4043	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2408	your compiler is good :), then the method will be fully inlined into the	4066	your compiler is good :), then the method will be fully inlined into the
2409	thunking function, making it as fast as a direct C callback.	4067	thunking function, making it as fast as a direct C callback.
2410		4068
2411	Example: simple class declaration and watcher initialisation	4069	Example: simple class declaration and watcher initialisation
2412		4070
2413	struct myclass	4071	struct myclass
2414	{	4072	{
2415	void io_cb (ev::io &w, int revents) { }	4073	void io_cb (ev::io &w, int revents) { }
2416	}	4074	}
2417		4075
2418	myclass obj;	4076	myclass obj;
2419	ev::io iow;	4077	ev::io iow;
2420	iow.set <myclass, &myclass::io_cb> (&obj);	4078	iow.set <myclass, &myclass::io_cb> (&obj);
		4079
		4080	=item w->set (object *)
		4081
		4082	This is a variation of a method callback - leaving out the method to call
		4083	will default the method to C<operator ()>, which makes it possible to use
		4084	functor objects without having to manually specify the C<operator ()> all
		4085	the time. Incidentally, you can then also leave out the template argument
		4086	list.
		4087
		4088	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4089	int revents)>.
		4090
		4091	See the method-C<set> above for more details.
		4092
		4093	Example: use a functor object as callback.
		4094
		4095	struct myfunctor
		4096	{
		4097	void operator() (ev::io &w, int revents)
		4098	{
		4099	...
		4100	}
		4101	}
		4102
		4103	myfunctor f;
		4104
		4105	ev::io w;
		4106	w.set (&f);
2421		4107
2422	=item w->set<function> (void *data = 0)	4108	=item w->set<function> (void *data = 0)
2423		4109
2424	Also sets a callback, but uses a static method or plain function as	4110	Also sets a callback, but uses a static method or plain function as
2425	callback. The optional C<data> argument will be stored in the watcher's	4111	callback. The optional C<data> argument will be stored in the watcher's
…		…
2427		4113
2428	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4114	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2429		4115
2430	See the method-C<set> above for more details.	4116	See the method-C<set> above for more details.
2431		4117
2432	Example:	4118	Example: Use a plain function as callback.
2433		4119
2434	static void io_cb (ev::io &w, int revents) { }	4120	static void io_cb (ev::io &w, int revents) { }
2435	iow.set <io_cb> ();	4121	iow.set <io_cb> ();
2436		4122
2437	=item w->set (struct ev_loop *)	4123	=item w->set (loop)
2438		4124
2439	Associates a different C<struct ev_loop> with this watcher. You can only	4125	Associates a different C<struct ev_loop> with this watcher. You can only
2440	do this when the watcher is inactive (and not pending either).	4126	do this when the watcher is inactive (and not pending either).
2441		4127
2442	=item w->set ([args])	4128	=item w->set ([arguments])
2443		4129
2444	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4130	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4131	with the same arguments. Either this method or a suitable start method
2445	called at least once. Unlike the C counterpart, an active watcher gets	4132	must be called at least once. Unlike the C counterpart, an active watcher
2446	automatically stopped and restarted when reconfiguring it with this	4133	gets automatically stopped and restarted when reconfiguring it with this
2447	method.	4134	method.
		4135
		4136	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4137	clashing with the C<set (loop)> method.
2448		4138
2449	=item w->start ()	4139	=item w->start ()
2450		4140
2451	Starts the watcher. Note that there is no C<loop> argument, as the	4141	Starts the watcher. Note that there is no C<loop> argument, as the
2452	constructor already stores the event loop.	4142	constructor already stores the event loop.
2453		4143
		4144	=item w->start ([arguments])
		4145
		4146	Instead of calling C<set> and C<start> methods separately, it is often
		4147	convenient to wrap them in one call. Uses the same type of arguments as
		4148	the configure C<set> method of the watcher.
		4149
2454	=item w->stop ()	4150	=item w->stop ()
2455		4151
2456	Stops the watcher if it is active. Again, no C<loop> argument.	4152	Stops the watcher if it is active. Again, no C<loop> argument.
2457		4153
2458	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4154	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2470		4166
2471	=back	4167	=back
2472		4168
2473	=back	4169	=back
2474		4170
2475	Example: Define a class with an IO and idle watcher, start one of them in	4171	Example: Define a class with two I/O and idle watchers, start the I/O
2476	the constructor.	4172	watchers in the constructor.
2477		4173
2478	class myclass	4174	class myclass
2479	{	4175	{
2480	ev::io io; void io_cb (ev::io &w, int revents);	4176	ev::io io ; void io_cb (ev::io &w, int revents);
		4177	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2481	ev:idle idle void idle_cb (ev::idle &w, int revents);	4178	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2482		4179
2483	myclass (int fd)	4180	myclass (int fd)
2484	{	4181	{
2485	io .set <myclass, &myclass::io_cb > (this);	4182	io .set <myclass, &myclass::io_cb > (this);
		4183	io2 .set <myclass, &myclass::io2_cb > (this);
2486	idle.set <myclass, &myclass::idle_cb> (this);	4184	idle.set <myclass, &myclass::idle_cb> (this);
2487		4185
2488	io.start (fd, ev::READ);	4186	io.set (fd, ev::WRITE); // configure the watcher
		4187	io.start (); // start it whenever convenient
		4188
		4189	io2.start (fd, ev::READ); // set + start in one call
2489	}	4190	}
2490	};	4191	};
		4192
		4193
		4194	=head1 OTHER LANGUAGE BINDINGS
		4195
		4196	Libev does not offer other language bindings itself, but bindings for a
		4197	number of languages exist in the form of third-party packages. If you know
		4198	any interesting language binding in addition to the ones listed here, drop
		4199	me a note.
		4200
		4201	=over 4
		4202
		4203	=item Perl
		4204
		4205	The EV module implements the full libev API and is actually used to test
		4206	libev. EV is developed together with libev. Apart from the EV core module,
		4207	there are additional modules that implement libev-compatible interfaces
		4208	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4209	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4210	and C<EV::Glib>).
		4211
		4212	It can be found and installed via CPAN, its homepage is at
		4213	L<http://software.schmorp.de/pkg/EV>.
		4214
		4215	=item Python
		4216
		4217	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4218	seems to be quite complete and well-documented.
		4219
		4220	=item Ruby
		4221
		4222	Tony Arcieri has written a ruby extension that offers access to a subset
		4223	of the libev API and adds file handle abstractions, asynchronous DNS and
		4224	more on top of it. It can be found via gem servers. Its homepage is at
		4225	L<http://rev.rubyforge.org/>.
		4226
		4227	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4228	makes rev work even on mingw.
		4229
		4230	=item Haskell
		4231
		4232	A haskell binding to libev is available at
		4233	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4234
		4235	=item D
		4236
		4237	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4238	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4239
		4240	=item Ocaml
		4241
		4242	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4243	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4244
		4245	=item Lua
		4246
		4247	Brian Maher has written a partial interface to libev for lua (at the
		4248	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4249	L<http://github.com/brimworks/lua-ev>.
		4250
		4251	=item Javascript
		4252
		4253	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4254
		4255	=item Others
		4256
		4257	There are others, and I stopped counting.
		4258
		4259	=back
2491		4260
2492		4261
2493	=head1 MACRO MAGIC	4262	=head1 MACRO MAGIC
2494		4263
2495	Libev can be compiled with a variety of options, the most fundamantal	4264	Libev can be compiled with a variety of options, the most fundamental
2496	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4265	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2497	functions and callbacks have an initial C<struct ev_loop *> argument.	4266	functions and callbacks have an initial C<struct ev_loop *> argument.
2498		4267
2499	To make it easier to write programs that cope with either variant, the	4268	To make it easier to write programs that cope with either variant, the
2500	following macros are defined:	4269	following macros are defined:
…		…
2505		4274
2506	This provides the loop I<argument> for functions, if one is required ("ev	4275	This provides the loop I<argument> for functions, if one is required ("ev
2507	loop argument"). The C<EV_A> form is used when this is the sole argument,	4276	loop argument"). The C<EV_A> form is used when this is the sole argument,
2508	C<EV_A_> is used when other arguments are following. Example:	4277	C<EV_A_> is used when other arguments are following. Example:
2509		4278
2510	ev_unref (EV_A);	4279	ev_unref (EV_A);
2511	ev_timer_add (EV_A_ watcher);	4280	ev_timer_add (EV_A_ watcher);
2512	ev_loop (EV_A_ 0);	4281	ev_run (EV_A_ 0);
2513		4282
2514	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4283	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2515	which is often provided by the following macro.	4284	which is often provided by the following macro.
2516		4285
2517	=item C<EV_P>, C<EV_P_>	4286	=item C<EV_P>, C<EV_P_>
2518		4287
2519	This provides the loop I<parameter> for functions, if one is required ("ev	4288	This provides the loop I<parameter> for functions, if one is required ("ev
2520	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4289	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2521	C<EV_P_> is used when other parameters are following. Example:	4290	C<EV_P_> is used when other parameters are following. Example:
2522		4291
2523	// this is how ev_unref is being declared	4292	// this is how ev_unref is being declared
2524	static void ev_unref (EV_P);	4293	static void ev_unref (EV_P);
2525		4294
2526	// this is how you can declare your typical callback	4295	// this is how you can declare your typical callback
2527	static void cb (EV_P_ ev_timer *w, int revents)	4296	static void cb (EV_P_ ev_timer *w, int revents)
2528		4297
2529	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4298	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2530	suitable for use with C<EV_A>.	4299	suitable for use with C<EV_A>.
2531		4300
2532	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4301	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2533		4302
2534	Similar to the other two macros, this gives you the value of the default	4303	Similar to the other two macros, this gives you the value of the default
2535	loop, if multiple loops are supported ("ev loop default").	4304	loop, if multiple loops are supported ("ev loop default"). The default loop
		4305	will be initialised if it isn't already initialised.
		4306
		4307	For non-multiplicity builds, these macros do nothing, so you always have
		4308	to initialise the loop somewhere.
		4309
		4310	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4311
		4312	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4313	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4314	is undefined when the default loop has not been initialised by a previous
		4315	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4316
		4317	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4318	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2536		4319
2537	=back	4320	=back
2538		4321
2539	Example: Declare and initialise a check watcher, utilising the above	4322	Example: Declare and initialise a check watcher, utilising the above
2540	macros so it will work regardless of whether multiple loops are supported	4323	macros so it will work regardless of whether multiple loops are supported
2541	or not.	4324	or not.
2542		4325
2543	static void	4326	static void
2544	check_cb (EV_P_ ev_timer *w, int revents)	4327	check_cb (EV_P_ ev_timer *w, int revents)
2545	{	4328	{
2546	ev_check_stop (EV_A_ w);	4329	ev_check_stop (EV_A_ w);
2547	}	4330	}
2548		4331
2549	ev_check check;	4332	ev_check check;
2550	ev_check_init (&check, check_cb);	4333	ev_check_init (&check, check_cb);
2551	ev_check_start (EV_DEFAULT_ &check);	4334	ev_check_start (EV_DEFAULT_ &check);
2552	ev_loop (EV_DEFAULT_ 0);	4335	ev_run (EV_DEFAULT_ 0);
2553		4336
2554	=head1 EMBEDDING	4337	=head1 EMBEDDING
2555		4338
2556	Libev can (and often is) directly embedded into host	4339	Libev can (and often is) directly embedded into host
2557	applications. Examples of applications that embed it include the Deliantra	4340	applications. Examples of applications that embed it include the Deliantra
…		…
2564	libev somewhere in your source tree).	4347	libev somewhere in your source tree).
2565		4348
2566	=head2 FILESETS	4349	=head2 FILESETS
2567		4350
2568	Depending on what features you need you need to include one or more sets of files	4351	Depending on what features you need you need to include one or more sets of files
2569	in your app.	4352	in your application.
2570		4353
2571	=head3 CORE EVENT LOOP	4354	=head3 CORE EVENT LOOP
2572		4355
2573	To include only the libev core (all the C<ev_*> functions), with manual	4356	To include only the libev core (all the C<ev_*> functions), with manual
2574	configuration (no autoconf):	4357	configuration (no autoconf):
2575		4358
2576	#define EV_STANDALONE 1	4359	#define EV_STANDALONE 1
2577	#include "ev.c"	4360	#include "ev.c"
2578		4361
2579	This will automatically include F<ev.h>, too, and should be done in a	4362	This will automatically include F<ev.h>, too, and should be done in a
2580	single C source file only to provide the function implementations. To use	4363	single C source file only to provide the function implementations. To use
2581	it, do the same for F<ev.h> in all files wishing to use this API (best	4364	it, do the same for F<ev.h> in all files wishing to use this API (best
2582	done by writing a wrapper around F<ev.h> that you can include instead and	4365	done by writing a wrapper around F<ev.h> that you can include instead and
2583	where you can put other configuration options):	4366	where you can put other configuration options):
2584		4367
2585	#define EV_STANDALONE 1	4368	#define EV_STANDALONE 1
2586	#include "ev.h"	4369	#include "ev.h"
2587		4370
2588	Both header files and implementation files can be compiled with a C++	4371	Both header files and implementation files can be compiled with a C++
2589	compiler (at least, thats a stated goal, and breakage will be treated	4372	compiler (at least, that's a stated goal, and breakage will be treated
2590	as a bug).	4373	as a bug).
2591		4374
2592	You need the following files in your source tree, or in a directory	4375	You need the following files in your source tree, or in a directory
2593	in your include path (e.g. in libev/ when using -Ilibev):	4376	in your include path (e.g. in libev/ when using -Ilibev):
2594		4377
2595	ev.h	4378	ev.h
2596	ev.c	4379	ev.c
2597	ev_vars.h	4380	ev_vars.h
2598	ev_wrap.h	4381	ev_wrap.h
2599		4382
2600	ev_win32.c required on win32 platforms only	4383	ev_win32.c required on win32 platforms only
2601		4384
2602	ev_select.c only when select backend is enabled (which is enabled by default)	4385	ev_select.c only when select backend is enabled (which is enabled by default)
2603	ev_poll.c only when poll backend is enabled (disabled by default)	4386	ev_poll.c only when poll backend is enabled (disabled by default)
2604	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4387	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2605	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4388	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2606	ev_port.c only when the solaris port backend is enabled (disabled by default)	4389	ev_port.c only when the solaris port backend is enabled (disabled by default)
2607		4390
2608	F<ev.c> includes the backend files directly when enabled, so you only need	4391	F<ev.c> includes the backend files directly when enabled, so you only need
2609	to compile this single file.	4392	to compile this single file.
2610		4393
2611	=head3 LIBEVENT COMPATIBILITY API	4394	=head3 LIBEVENT COMPATIBILITY API
2612		4395
2613	To include the libevent compatibility API, also include:	4396	To include the libevent compatibility API, also include:
2614		4397
2615	#include "event.c"	4398	#include "event.c"
2616		4399
2617	in the file including F<ev.c>, and:	4400	in the file including F<ev.c>, and:
2618		4401
2619	#include "event.h"	4402	#include "event.h"
2620		4403
2621	in the files that want to use the libevent API. This also includes F<ev.h>.	4404	in the files that want to use the libevent API. This also includes F<ev.h>.
2622		4405
2623	You need the following additional files for this:	4406	You need the following additional files for this:
2624		4407
2625	event.h	4408	event.h
2626	event.c	4409	event.c
2627		4410
2628	=head3 AUTOCONF SUPPORT	4411	=head3 AUTOCONF SUPPORT
2629		4412
2630	Instead of using C<EV_STANDALONE=1> and providing your config in	4413	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2631	whatever way you want, you can also C<m4_include([libev.m4])> in your	4414	whatever way you want, you can also C<m4_include([libev.m4])> in your
2632	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4415	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2633	include F<config.h> and configure itself accordingly.	4416	include F<config.h> and configure itself accordingly.
2634		4417
2635	For this of course you need the m4 file:	4418	For this of course you need the m4 file:
2636		4419
2637	libev.m4	4420	libev.m4
2638		4421
2639	=head2 PREPROCESSOR SYMBOLS/MACROS	4422	=head2 PREPROCESSOR SYMBOLS/MACROS
2640		4423
2641	Libev can be configured via a variety of preprocessor symbols you have to define	4424	Libev can be configured via a variety of preprocessor symbols you have to
2642	before including any of its files. The default is not to build for multiplicity	4425	define before including (or compiling) any of its files. The default in
2643	and only include the select backend.	4426	the absence of autoconf is documented for every option.
		4427
		4428	Symbols marked with "(h)" do not change the ABI, and can have different
		4429	values when compiling libev vs. including F<ev.h>, so it is permissible
		4430	to redefine them before including F<ev.h> without breaking compatibility
		4431	to a compiled library. All other symbols change the ABI, which means all
		4432	users of libev and the libev code itself must be compiled with compatible
		4433	settings.
2644		4434
2645	=over 4	4435	=over 4
2646		4436
		4437	=item EV_COMPAT3 (h)
		4438
		4439	Backwards compatibility is a major concern for libev. This is why this
		4440	release of libev comes with wrappers for the functions and symbols that
		4441	have been renamed between libev version 3 and 4.
		4442
		4443	You can disable these wrappers (to test compatibility with future
		4444	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4445	sources. This has the additional advantage that you can drop the C<struct>
		4446	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4447	typedef in that case.
		4448
		4449	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4450	and in some even more future version the compatibility code will be
		4451	removed completely.
		4452
2647	=item EV_STANDALONE	4453	=item EV_STANDALONE (h)
2648		4454
2649	Must always be C<1> if you do not use autoconf configuration, which	4455	Must always be C<1> if you do not use autoconf configuration, which
2650	keeps libev from including F<config.h>, and it also defines dummy	4456	keeps libev from including F<config.h>, and it also defines dummy
2651	implementations for some libevent functions (such as logging, which is not	4457	implementations for some libevent functions (such as logging, which is not
2652	supported). It will also not define any of the structs usually found in	4458	supported). It will also not define any of the structs usually found in
2653	F<event.h> that are not directly supported by the libev core alone.	4459	F<event.h> that are not directly supported by the libev core alone.
2654		4460
		4461	In standalone mode, libev will still try to automatically deduce the
		4462	configuration, but has to be more conservative.
		4463
		4464	=item EV_USE_FLOOR
		4465
		4466	If defined to be C<1>, libev will use the C<floor ()> function for its
		4467	periodic reschedule calculations, otherwise libev will fall back on a
		4468	portable (slower) implementation. If you enable this, you usually have to
		4469	link against libm or something equivalent. Enabling this when the C<floor>
		4470	function is not available will fail, so the safe default is to not enable
		4471	this.
		4472
2655	=item EV_USE_MONOTONIC	4473	=item EV_USE_MONOTONIC
2656		4474
2657	If defined to be C<1>, libev will try to detect the availability of the	4475	If defined to be C<1>, libev will try to detect the availability of the
2658	monotonic clock option at both compiletime and runtime. Otherwise no use	4476	monotonic clock option at both compile time and runtime. Otherwise no
2659	of the monotonic clock option will be attempted. If you enable this, you	4477	use of the monotonic clock option will be attempted. If you enable this,
2660	usually have to link against librt or something similar. Enabling it when	4478	you usually have to link against librt or something similar. Enabling it
2661	the functionality isn't available is safe, though, although you have	4479	when the functionality isn't available is safe, though, although you have
2662	to make sure you link against any libraries where the C<clock_gettime>	4480	to make sure you link against any libraries where the C<clock_gettime>
2663	function is hiding in (often F<-lrt>).	4481	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2664		4482
2665	=item EV_USE_REALTIME	4483	=item EV_USE_REALTIME
2666		4484
2667	If defined to be C<1>, libev will try to detect the availability of the	4485	If defined to be C<1>, libev will try to detect the availability of the
2668	realtime clock option at compiletime (and assume its availability at	4486	real-time clock option at compile time (and assume its availability
2669	runtime if successful). Otherwise no use of the realtime clock option will	4487	at runtime if successful). Otherwise no use of the real-time clock
2670	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4488	option will be attempted. This effectively replaces C<gettimeofday>
2671	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4489	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2672	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4490	correctness. See the note about libraries in the description of
		4491	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4492	C<EV_USE_CLOCK_SYSCALL>.
		4493
		4494	=item EV_USE_CLOCK_SYSCALL
		4495
		4496	If defined to be C<1>, libev will try to use a direct syscall instead
		4497	of calling the system-provided C<clock_gettime> function. This option
		4498	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4499	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4500	programs needlessly. Using a direct syscall is slightly slower (in
		4501	theory), because no optimised vdso implementation can be used, but avoids
		4502	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4503	higher, as it simplifies linking (no need for C<-lrt>).
2673		4504
2674	=item EV_USE_NANOSLEEP	4505	=item EV_USE_NANOSLEEP
2675		4506
2676	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4507	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2677	and will use it for delays. Otherwise it will use C<select ()>.	4508	and will use it for delays. Otherwise it will use C<select ()>.
2678		4509
		4510	=item EV_USE_EVENTFD
		4511
		4512	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4513	available and will probe for kernel support at runtime. This will improve
		4514	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4515	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4516	2.7 or newer, otherwise disabled.
		4517
2679	=item EV_USE_SELECT	4518	=item EV_USE_SELECT
2680		4519
2681	If undefined or defined to be C<1>, libev will compile in support for the	4520	If undefined or defined to be C<1>, libev will compile in support for the
2682	C<select>(2) backend. No attempt at autodetection will be done: if no	4521	C<select>(2) backend. No attempt at auto-detection will be done: if no
2683	other method takes over, select will be it. Otherwise the select backend	4522	other method takes over, select will be it. Otherwise the select backend
2684	will not be compiled in.	4523	will not be compiled in.
2685		4524
2686	=item EV_SELECT_USE_FD_SET	4525	=item EV_SELECT_USE_FD_SET
2687		4526
2688	If defined to C<1>, then the select backend will use the system C<fd_set>	4527	If defined to C<1>, then the select backend will use the system C<fd_set>
2689	structure. This is useful if libev doesn't compile due to a missing	4528	structure. This is useful if libev doesn't compile due to a missing
2690	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4529	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2691	exotic systems. This usually limits the range of file descriptors to some	4530	on exotic systems. This usually limits the range of file descriptors to
2692	low limit such as 1024 or might have other limitations (winsocket only	4531	some low limit such as 1024 or might have other limitations (winsocket
2693	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4532	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2694	influence the size of the C<fd_set> used.	4533	configures the maximum size of the C<fd_set>.
2695		4534
2696	=item EV_SELECT_IS_WINSOCKET	4535	=item EV_SELECT_IS_WINSOCKET
2697		4536
2698	When defined to C<1>, the select backend will assume that	4537	When defined to C<1>, the select backend will assume that
2699	select/socket/connect etc. don't understand file descriptors but	4538	select/socket/connect etc. don't understand file descriptors but
…		…
2701	be used is the winsock select). This means that it will call	4540	be used is the winsock select). This means that it will call
2702	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4541	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2703	it is assumed that all these functions actually work on fds, even	4542	it is assumed that all these functions actually work on fds, even
2704	on win32. Should not be defined on non-win32 platforms.	4543	on win32. Should not be defined on non-win32 platforms.
2705		4544
2706	=item EV_FD_TO_WIN32_HANDLE	4545	=item EV_FD_TO_WIN32_HANDLE(fd)
2707		4546
2708	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	4547	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2709	file descriptors to socket handles. When not defining this symbol (the	4548	file descriptors to socket handles. When not defining this symbol (the
2710	default), then libev will call C<_get_osfhandle>, which is usually	4549	default), then libev will call C<_get_osfhandle>, which is usually
2711	correct. In some cases, programs use their own file descriptor management,	4550	correct. In some cases, programs use their own file descriptor management,
2712	in which case they can provide this function to map fds to socket handles.	4551	in which case they can provide this function to map fds to socket handles.
2713		4552
		4553	=item EV_WIN32_HANDLE_TO_FD(handle)
		4554
		4555	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4556	using the standard C<_open_osfhandle> function. For programs implementing
		4557	their own fd to handle mapping, overwriting this function makes it easier
		4558	to do so. This can be done by defining this macro to an appropriate value.
		4559
		4560	=item EV_WIN32_CLOSE_FD(fd)
		4561
		4562	If programs implement their own fd to handle mapping on win32, then this
		4563	macro can be used to override the C<close> function, useful to unregister
		4564	file descriptors again. Note that the replacement function has to close
		4565	the underlying OS handle.
		4566
		4567	=item EV_USE_WSASOCKET
		4568
		4569	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4570	communication socket, which works better in some environments. Otherwise,
		4571	the normal C<socket> function will be used, which works better in other
		4572	environments.
		4573
2714	=item EV_USE_POLL	4574	=item EV_USE_POLL
2715		4575
2716	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4576	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2717	backend. Otherwise it will be enabled on non-win32 platforms. It	4577	backend. Otherwise it will be enabled on non-win32 platforms. It
2718	takes precedence over select.	4578	takes precedence over select.
2719		4579
2720	=item EV_USE_EPOLL	4580	=item EV_USE_EPOLL
2721		4581
2722	If defined to be C<1>, libev will compile in support for the Linux	4582	If defined to be C<1>, libev will compile in support for the Linux
2723	C<epoll>(7) backend. Its availability will be detected at runtime,	4583	C<epoll>(7) backend. Its availability will be detected at runtime,
2724	otherwise another method will be used as fallback. This is the	4584	otherwise another method will be used as fallback. This is the preferred
2725	preferred backend for GNU/Linux systems.	4585	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4586	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2726		4587
2727	=item EV_USE_KQUEUE	4588	=item EV_USE_KQUEUE
2728		4589
2729	If defined to be C<1>, libev will compile in support for the BSD style	4590	If defined to be C<1>, libev will compile in support for the BSD style
2730	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4591	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2743	otherwise another method will be used as fallback. This is the preferred	4604	otherwise another method will be used as fallback. This is the preferred
2744	backend for Solaris 10 systems.	4605	backend for Solaris 10 systems.
2745		4606
2746	=item EV_USE_DEVPOLL	4607	=item EV_USE_DEVPOLL
2747		4608
2748	reserved for future expansion, works like the USE symbols above.	4609	Reserved for future expansion, works like the USE symbols above.
2749		4610
2750	=item EV_USE_INOTIFY	4611	=item EV_USE_INOTIFY
2751		4612
2752	If defined to be C<1>, libev will compile in support for the Linux inotify	4613	If defined to be C<1>, libev will compile in support for the Linux inotify
2753	interface to speed up C<ev_stat> watchers. Its actual availability will	4614	interface to speed up C<ev_stat> watchers. Its actual availability will
2754	be detected at runtime.	4615	be detected at runtime. If undefined, it will be enabled if the headers
		4616	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4617
		4618	=item EV_NO_SMP
		4619
		4620	If defined to be C<1>, libev will assume that memory is always coherent
		4621	between threads, that is, threads can be used, but threads never run on
		4622	different cpus (or different cpu cores). This reduces dependencies
		4623	and makes libev faster.
		4624
		4625	=item EV_NO_THREADS
		4626
		4627	If defined to be C<1>, libev will assume that it will never be called from
		4628	different threads (that includes signal handlers), which is a stronger
		4629	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4630	libev faster.
2755		4631
2756	=item EV_ATOMIC_T	4632	=item EV_ATOMIC_T
2757		4633
2758	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4634	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2759	access is atomic with respect to other threads or signal contexts. No such	4635	access is atomic with respect to other threads or signal contexts. No
2760	type is easily found in the C language, so you can provide your own type	4636	such type is easily found in the C language, so you can provide your own
2761	that you know is safe for your purposes. It is used both for signal handler "locking"	4637	type that you know is safe for your purposes. It is used both for signal
2762	as well as for signal and thread safety in C<ev_async> watchers.	4638	handler "locking" as well as for signal and thread safety in C<ev_async>
		4639	watchers.
2763		4640
2764	In the absense of this define, libev will use C<sig_atomic_t volatile>	4641	In the absence of this define, libev will use C<sig_atomic_t volatile>
2765	(from F<signal.h>), which is usually good enough on most platforms.	4642	(from F<signal.h>), which is usually good enough on most platforms.
2766		4643
2767	=item EV_H	4644	=item EV_H (h)
2768		4645
2769	The name of the F<ev.h> header file used to include it. The default if	4646	The name of the F<ev.h> header file used to include it. The default if
2770	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4647	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2771	used to virtually rename the F<ev.h> header file in case of conflicts.	4648	used to virtually rename the F<ev.h> header file in case of conflicts.
2772		4649
2773	=item EV_CONFIG_H	4650	=item EV_CONFIG_H (h)
2774		4651
2775	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4652	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2776	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4653	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2777	C<EV_H>, above.	4654	C<EV_H>, above.
2778		4655
2779	=item EV_EVENT_H	4656	=item EV_EVENT_H (h)
2780		4657
2781	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4658	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2782	of how the F<event.h> header can be found, the default is C<"event.h">.	4659	of how the F<event.h> header can be found, the default is C<"event.h">.
2783		4660
2784	=item EV_PROTOTYPES	4661	=item EV_PROTOTYPES (h)
2785		4662
2786	If defined to be C<0>, then F<ev.h> will not define any function	4663	If defined to be C<0>, then F<ev.h> will not define any function
2787	prototypes, but still define all the structs and other symbols. This is	4664	prototypes, but still define all the structs and other symbols. This is
2788	occasionally useful if you want to provide your own wrapper functions	4665	occasionally useful if you want to provide your own wrapper functions
2789	around libev functions.	4666	around libev functions.
…		…
2794	will have the C<struct ev_loop *> as first argument, and you can create	4671	will have the C<struct ev_loop *> as first argument, and you can create
2795	additional independent event loops. Otherwise there will be no support	4672	additional independent event loops. Otherwise there will be no support
2796	for multiple event loops and there is no first event loop pointer	4673	for multiple event loops and there is no first event loop pointer
2797	argument. Instead, all functions act on the single default loop.	4674	argument. Instead, all functions act on the single default loop.
2798		4675
		4676	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4677	default loop when multiplicity is switched off - you always have to
		4678	initialise the loop manually in this case.
		4679
2799	=item EV_MINPRI	4680	=item EV_MINPRI
2800		4681
2801	=item EV_MAXPRI	4682	=item EV_MAXPRI
2802		4683
2803	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4684	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2808	When doing priority-based operations, libev usually has to linearly search	4689	When doing priority-based operations, libev usually has to linearly search
2809	all the priorities, so having many of them (hundreds) uses a lot of space	4690	all the priorities, so having many of them (hundreds) uses a lot of space
2810	and time, so using the defaults of five priorities (-2 .. +2) is usually	4691	and time, so using the defaults of five priorities (-2 .. +2) is usually
2811	fine.	4692	fine.
2812		4693
2813	If your embedding app does not need any priorities, defining these both to	4694	If your embedding application does not need any priorities, defining these
2814	C<0> will save some memory and cpu.	4695	both to C<0> will save some memory and CPU.
2815		4696
2816	=item EV_PERIODIC_ENABLE	4697	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4698	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4699	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2817		4700
2818	If undefined or defined to be C<1>, then periodic timers are supported. If	4701	If undefined or defined to be C<1> (and the platform supports it), then
2819	defined to be C<0>, then they are not. Disabling them saves a few kB of	4702	the respective watcher type is supported. If defined to be C<0>, then it
2820	code.	4703	is not. Disabling watcher types mainly saves code size.
2821		4704
2822	=item EV_IDLE_ENABLE	4705	=item EV_FEATURES
2823
2824	If undefined or defined to be C<1>, then idle watchers are supported. If
2825	defined to be C<0>, then they are not. Disabling them saves a few kB of
2826	code.
2827
2828	=item EV_EMBED_ENABLE
2829
2830	If undefined or defined to be C<1>, then embed watchers are supported. If
2831	defined to be C<0>, then they are not.
2832
2833	=item EV_STAT_ENABLE
2834
2835	If undefined or defined to be C<1>, then stat watchers are supported. If
2836	defined to be C<0>, then they are not.
2837
2838	=item EV_FORK_ENABLE
2839
2840	If undefined or defined to be C<1>, then fork watchers are supported. If
2841	defined to be C<0>, then they are not.
2842
2843	=item EV_ASYNC_ENABLE
2844
2845	If undefined or defined to be C<1>, then async watchers are supported. If
2846	defined to be C<0>, then they are not.
2847
2848	=item EV_MINIMAL
2849		4706
2850	If you need to shave off some kilobytes of code at the expense of some	4707	If you need to shave off some kilobytes of code at the expense of some
2851	speed, define this symbol to C<1>. Currently only used for gcc to override	4708	speed (but with the full API), you can define this symbol to request
2852	some inlining decisions, saves roughly 30% codesize of amd64.	4709	certain subsets of functionality. The default is to enable all features
		4710	that can be enabled on the platform.
		4711
		4712	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4713	with some broad features you want) and then selectively re-enable
		4714	additional parts you want, for example if you want everything minimal,
		4715	but multiple event loop support, async and child watchers and the poll
		4716	backend, use this:
		4717
		4718	#define EV_FEATURES 0
		4719	#define EV_MULTIPLICITY 1
		4720	#define EV_USE_POLL 1
		4721	#define EV_CHILD_ENABLE 1
		4722	#define EV_ASYNC_ENABLE 1
		4723
		4724	The actual value is a bitset, it can be a combination of the following
		4725	values (by default, all of these are enabled):
		4726
		4727	=over 4
		4728
		4729	=item C<1> - faster/larger code
		4730
		4731	Use larger code to speed up some operations.
		4732
		4733	Currently this is used to override some inlining decisions (enlarging the
		4734	code size by roughly 30% on amd64).
		4735
		4736	When optimising for size, use of compiler flags such as C<-Os> with
		4737	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4738	assertions.
		4739
		4740	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4741	(e.g. gcc with C<-Os>).
		4742
		4743	=item C<2> - faster/larger data structures
		4744
		4745	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4746	hash table sizes and so on. This will usually further increase code size
		4747	and can additionally have an effect on the size of data structures at
		4748	runtime.
		4749
		4750	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4751	(e.g. gcc with C<-Os>).
		4752
		4753	=item C<4> - full API configuration
		4754
		4755	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4756	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4757
		4758	=item C<8> - full API
		4759
		4760	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4761	details on which parts of the API are still available without this
		4762	feature, and do not complain if this subset changes over time.
		4763
		4764	=item C<16> - enable all optional watcher types
		4765
		4766	Enables all optional watcher types. If you want to selectively enable
		4767	only some watcher types other than I/O and timers (e.g. prepare,
		4768	embed, async, child...) you can enable them manually by defining
		4769	C<EV_watchertype_ENABLE> to C<1> instead.
		4770
		4771	=item C<32> - enable all backends
		4772
		4773	This enables all backends - without this feature, you need to enable at
		4774	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4775
		4776	=item C<64> - enable OS-specific "helper" APIs
		4777
		4778	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4779	default.
		4780
		4781	=back
		4782
		4783	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4784	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4785	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4786	watchers, timers and monotonic clock support.
		4787
		4788	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4789	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4790	your program might be left out as well - a binary starting a timer and an
		4791	I/O watcher then might come out at only 5Kb.
		4792
		4793	=item EV_API_STATIC
		4794
		4795	If this symbol is defined (by default it is not), then all identifiers
		4796	will have static linkage. This means that libev will not export any
		4797	identifiers, and you cannot link against libev anymore. This can be useful
		4798	when you embed libev, only want to use libev functions in a single file,
		4799	and do not want its identifiers to be visible.
		4800
		4801	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4802	wants to use libev.
		4803
		4804	This option only works when libev is compiled with a C compiler, as C++
		4805	doesn't support the required declaration syntax.
		4806
		4807	=item EV_AVOID_STDIO
		4808
		4809	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4810	functions (printf, scanf, perror etc.). This will increase the code size
		4811	somewhat, but if your program doesn't otherwise depend on stdio and your
		4812	libc allows it, this avoids linking in the stdio library which is quite
		4813	big.
		4814
		4815	Note that error messages might become less precise when this option is
		4816	enabled.
		4817
		4818	=item EV_NSIG
		4819
		4820	The highest supported signal number, +1 (or, the number of
		4821	signals): Normally, libev tries to deduce the maximum number of signals
		4822	automatically, but sometimes this fails, in which case it can be
		4823	specified. Also, using a lower number than detected (C<32> should be
		4824	good for about any system in existence) can save some memory, as libev
		4825	statically allocates some 12-24 bytes per signal number.
2853		4826
2854	=item EV_PID_HASHSIZE	4827	=item EV_PID_HASHSIZE
2855		4828
2856	C<ev_child> watchers use a small hash table to distribute workload by	4829	C<ev_child> watchers use a small hash table to distribute workload by
2857	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4830	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2858	than enough. If you need to manage thousands of children you might want to	4831	usually more than enough. If you need to manage thousands of children you
2859	increase this value (I<must> be a power of two).	4832	might want to increase this value (I<must> be a power of two).
2860		4833
2861	=item EV_INOTIFY_HASHSIZE	4834	=item EV_INOTIFY_HASHSIZE
2862		4835
2863	C<ev_stat> watchers use a small hash table to distribute workload by	4836	C<ev_stat> watchers use a small hash table to distribute workload by
2864	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4837	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2865	usually more than enough. If you need to manage thousands of C<ev_stat>	4838	disabled), usually more than enough. If you need to manage thousands of
2866	watchers you might want to increase this value (I<must> be a power of	4839	C<ev_stat> watchers you might want to increase this value (I<must> be a
2867	two).	4840	power of two).
		4841
		4842	=item EV_USE_4HEAP
		4843
		4844	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4845	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4846	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4847	faster performance with many (thousands) of watchers.
		4848
		4849	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4850	will be C<0>.
		4851
		4852	=item EV_HEAP_CACHE_AT
		4853
		4854	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4855	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4856	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4857	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4858	but avoids random read accesses on heap changes. This improves performance
		4859	noticeably with many (hundreds) of watchers.
		4860
		4861	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4862	will be C<0>.
		4863
		4864	=item EV_VERIFY
		4865
		4866	Controls how much internal verification (see C<ev_verify ()>) will
		4867	be done: If set to C<0>, no internal verification code will be compiled
		4868	in. If set to C<1>, then verification code will be compiled in, but not
		4869	called. If set to C<2>, then the internal verification code will be
		4870	called once per loop, which can slow down libev. If set to C<3>, then the
		4871	verification code will be called very frequently, which will slow down
		4872	libev considerably.
		4873
		4874	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4875	will be C<0>.
2868		4876
2869	=item EV_COMMON	4877	=item EV_COMMON
2870		4878
2871	By default, all watchers have a C<void *data> member. By redefining	4879	By default, all watchers have a C<void *data> member. By redefining
2872	this macro to a something else you can include more and other types of	4880	this macro to something else you can include more and other types of
2873	members. You have to define it each time you include one of the files,	4881	members. You have to define it each time you include one of the files,
2874	though, and it must be identical each time.	4882	though, and it must be identical each time.
2875		4883
2876	For example, the perl EV module uses something like this:	4884	For example, the perl EV module uses something like this:
2877		4885
2878	#define EV_COMMON \	4886	#define EV_COMMON \
2879	SV *self; /* contains this struct */ \	4887	SV *self; /* contains this struct */ \
2880	SV *cb_sv, *fh /* note no trailing ";" */	4888	SV *cb_sv, *fh /* note no trailing ";" */
2881		4889
2882	=item EV_CB_DECLARE (type)	4890	=item EV_CB_DECLARE (type)
2883		4891
2884	=item EV_CB_INVOKE (watcher, revents)	4892	=item EV_CB_INVOKE (watcher, revents)
2885		4893
…		…
2890	definition and a statement, respectively. See the F<ev.h> header file for	4898	definition and a statement, respectively. See the F<ev.h> header file for
2891	their default definitions. One possible use for overriding these is to	4899	their default definitions. One possible use for overriding these is to
2892	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4900	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2893	method calls instead of plain function calls in C++.	4901	method calls instead of plain function calls in C++.
2894		4902
		4903	=back
		4904
2895	=head2 EXPORTED API SYMBOLS	4905	=head2 EXPORTED API SYMBOLS
2896		4906
2897	If you need to re-export the API (e.g. via a dll) and you need a list of	4907	If you need to re-export the API (e.g. via a DLL) and you need a list of
2898	exported symbols, you can use the provided F<Symbol.*> files which list	4908	exported symbols, you can use the provided F<Symbol.*> files which list
2899	all public symbols, one per line:	4909	all public symbols, one per line:
2900		4910
2901	Symbols.ev for libev proper	4911	Symbols.ev for libev proper
2902	Symbols.event for the libevent emulation	4912	Symbols.event for the libevent emulation
2903		4913
2904	This can also be used to rename all public symbols to avoid clashes with	4914	This can also be used to rename all public symbols to avoid clashes with
2905	multiple versions of libev linked together (which is obviously bad in	4915	multiple versions of libev linked together (which is obviously bad in
2906	itself, but sometimes it is inconvinient to avoid this).	4916	itself, but sometimes it is inconvenient to avoid this).
2907		4917
2908	A sed command like this will create wrapper C<#define>'s that you need to	4918	A sed command like this will create wrapper C<#define>'s that you need to
2909	include before including F<ev.h>:	4919	include before including F<ev.h>:
2910		4920
2911	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4921	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2928	file.	4938	file.
2929		4939
2930	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4940	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2931	that everybody includes and which overrides some configure choices:	4941	that everybody includes and which overrides some configure choices:
2932		4942
2933	#define EV_MINIMAL 1	4943	#define EV_FEATURES 8
2934	#define EV_USE_POLL 0	4944	#define EV_USE_SELECT 1
2935	#define EV_MULTIPLICITY 0
2936	#define EV_PERIODIC_ENABLE 0	4945	#define EV_PREPARE_ENABLE 1
		4946	#define EV_IDLE_ENABLE 1
2937	#define EV_STAT_ENABLE 0	4947	#define EV_SIGNAL_ENABLE 1
2938	#define EV_FORK_ENABLE 0	4948	#define EV_CHILD_ENABLE 1
		4949	#define EV_USE_STDEXCEPT 0
2939	#define EV_CONFIG_H <config.h>	4950	#define EV_CONFIG_H <config.h>
2940	#define EV_MINPRI 0
2941	#define EV_MAXPRI 0
2942		4951
2943	#include "ev++.h"	4952	#include "ev++.h"
2944		4953
2945	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4954	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2946		4955
2947	#include "ev_cpp.h"	4956	#include "ev_cpp.h"
2948	#include "ev.c"	4957	#include "ev.c"
2949		4958
		4959	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2950		4960
2951	=head1 COMPLEXITIES	4961	=head2 THREADS AND COROUTINES
2952		4962
2953	In this section the complexities of (many of) the algorithms used inside	4963	=head3 THREADS
2954	libev will be explained. For complexity discussions about backends see the
2955	documentation for C<ev_default_init>.
2956		4964
2957	All of the following are about amortised time: If an array needs to be	4965	All libev functions are reentrant and thread-safe unless explicitly
2958	extended, libev needs to realloc and move the whole array, but this	4966	documented otherwise, but libev implements no locking itself. This means
2959	happens asymptotically never with higher number of elements, so O(1) might	4967	that you can use as many loops as you want in parallel, as long as there
2960	mean it might do a lengthy realloc operation in rare cases, but on average	4968	are no concurrent calls into any libev function with the same loop
2961	it is much faster and asymptotically approaches constant time.	4969	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4970	of course): libev guarantees that different event loops share no data
		4971	structures that need any locking.
		4972
		4973	Or to put it differently: calls with different loop parameters can be done
		4974	concurrently from multiple threads, calls with the same loop parameter
		4975	must be done serially (but can be done from different threads, as long as
		4976	only one thread ever is inside a call at any point in time, e.g. by using
		4977	a mutex per loop).
		4978
		4979	Specifically to support threads (and signal handlers), libev implements
		4980	so-called C<ev_async> watchers, which allow some limited form of
		4981	concurrency on the same event loop, namely waking it up "from the
		4982	outside".
		4983
		4984	If you want to know which design (one loop, locking, or multiple loops
		4985	without or something else still) is best for your problem, then I cannot
		4986	help you, but here is some generic advice:
2962		4987
2963	=over 4	4988	=over 4
2964		4989
2965	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4990	=item * most applications have a main thread: use the default libev loop
		4991	in that thread, or create a separate thread running only the default loop.
2966		4992
2967	This means that, when you have a watcher that triggers in one hour and	4993	This helps integrating other libraries or software modules that use libev
2968	there are 100 watchers that would trigger before that then inserting will	4994	themselves and don't care/know about threading.
2969	have to skip roughly seven (C<ld 100>) of these watchers.
2970		4995
2971	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4996	=item * one loop per thread is usually a good model.
2972		4997
2973	That means that changing a timer costs less than removing/adding them	4998	Doing this is almost never wrong, sometimes a better-performance model
2974	as only the relative motion in the event queue has to be paid for.	4999	exists, but it is always a good start.
2975		5000
2976	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	5001	=item * other models exist, such as the leader/follower pattern, where one
		5002	loop is handed through multiple threads in a kind of round-robin fashion.
2977		5003
2978	These just add the watcher into an array or at the head of a list.	5004	Choosing a model is hard - look around, learn, know that usually you can do
		5005	better than you currently do :-)
2979		5006
2980	=item Stopping check/prepare/idle/fork/async watchers: O(1)	5007	=item * often you need to talk to some other thread which blocks in the
		5008	event loop.
2981		5009
2982	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5010	C<ev_async> watchers can be used to wake them up from other threads safely
		5011	(or from signal contexts...).
2983		5012
2984	These watchers are stored in lists then need to be walked to find the	5013	An example use would be to communicate signals or other events that only
2985	correct watcher to remove. The lists are usually short (you don't usually	5014	work in the default loop by registering the signal watcher with the
2986	have many watchers waiting for the same fd or signal).	5015	default loop and triggering an C<ev_async> watcher from the default loop
2987		5016	watcher callback into the event loop interested in the signal.
2988	=item Finding the next timer in each loop iteration: O(1)
2989
2990	By virtue of using a binary heap, the next timer is always found at the
2991	beginning of the storage array.
2992
2993	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2994
2995	A change means an I/O watcher gets started or stopped, which requires
2996	libev to recalculate its status (and possibly tell the kernel, depending
2997	on backend and wether C<ev_io_set> was used).
2998
2999	=item Activating one watcher (putting it into the pending state): O(1)
3000
3001	=item Priority handling: O(number_of_priorities)
3002
3003	Priorities are implemented by allocating some space for each
3004	priority. When doing priority-based operations, libev usually has to
3005	linearly search all the priorities, but starting/stopping and activating
3006	watchers becomes O(1) w.r.t. priority handling.
3007
3008	=item Sending an ev_async: O(1)
3009
3010	=item Processing ev_async_send: O(number_of_async_watchers)
3011
3012	=item Processing signals: O(max_signal_number)
3013
3014	Sending involves a syscall I<iff> there were no other C<ev_async_send>
3015	calls in the current loop iteration. Checking for async and signal events
3016	involves iterating over all running async watchers or all signal numbers.
3017		5017
3018	=back	5018	=back
3019		5019
		5020	See also L</THREAD LOCKING EXAMPLE>.
3020		5021
3021	=head1 Win32 platform limitations and workarounds	5022	=head3 COROUTINES
		5023
		5024	Libev is very accommodating to coroutines ("cooperative threads"):
		5025	libev fully supports nesting calls to its functions from different
		5026	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5027	different coroutines, and switch freely between both coroutines running
		5028	the loop, as long as you don't confuse yourself). The only exception is
		5029	that you must not do this from C<ev_periodic> reschedule callbacks.
		5030
		5031	Care has been taken to ensure that libev does not keep local state inside
		5032	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5033	they do not call any callbacks.
		5034
		5035	=head2 COMPILER WARNINGS
		5036
		5037	Depending on your compiler and compiler settings, you might get no or a
		5038	lot of warnings when compiling libev code. Some people are apparently
		5039	scared by this.
		5040
		5041	However, these are unavoidable for many reasons. For one, each compiler
		5042	has different warnings, and each user has different tastes regarding
		5043	warning options. "Warn-free" code therefore cannot be a goal except when
		5044	targeting a specific compiler and compiler-version.
		5045
		5046	Another reason is that some compiler warnings require elaborate
		5047	workarounds, or other changes to the code that make it less clear and less
		5048	maintainable.
		5049
		5050	And of course, some compiler warnings are just plain stupid, or simply
		5051	wrong (because they don't actually warn about the condition their message
		5052	seems to warn about). For example, certain older gcc versions had some
		5053	warnings that resulted in an extreme number of false positives. These have
		5054	been fixed, but some people still insist on making code warn-free with
		5055	such buggy versions.
		5056
		5057	While libev is written to generate as few warnings as possible,
		5058	"warn-free" code is not a goal, and it is recommended not to build libev
		5059	with any compiler warnings enabled unless you are prepared to cope with
		5060	them (e.g. by ignoring them). Remember that warnings are just that:
		5061	warnings, not errors, or proof of bugs.
		5062
		5063
		5064	=head2 VALGRIND
		5065
		5066	Valgrind has a special section here because it is a popular tool that is
		5067	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5068
		5069	If you think you found a bug (memory leak, uninitialised data access etc.)
		5070	in libev, then check twice: If valgrind reports something like:
		5071
		5072	==2274== definitely lost: 0 bytes in 0 blocks.
		5073	==2274== possibly lost: 0 bytes in 0 blocks.
		5074	==2274== still reachable: 256 bytes in 1 blocks.
		5075
		5076	Then there is no memory leak, just as memory accounted to global variables
		5077	is not a memleak - the memory is still being referenced, and didn't leak.
		5078
		5079	Similarly, under some circumstances, valgrind might report kernel bugs
		5080	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5081	although an acceptable workaround has been found here), or it might be
		5082	confused.
		5083
		5084	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5085	make it into some kind of religion.
		5086
		5087	If you are unsure about something, feel free to contact the mailing list
		5088	with the full valgrind report and an explanation on why you think this
		5089	is a bug in libev (best check the archives, too :). However, don't be
		5090	annoyed when you get a brisk "this is no bug" answer and take the chance
		5091	of learning how to interpret valgrind properly.
		5092
		5093	If you need, for some reason, empty reports from valgrind for your project
		5094	I suggest using suppression lists.
		5095
		5096
		5097	=head1 PORTABILITY NOTES
		5098
		5099	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5100
		5101	GNU/Linux is the only common platform that supports 64 bit file/large file
		5102	interfaces but I<disables> them by default.
		5103
		5104	That means that libev compiled in the default environment doesn't support
		5105	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5106
		5107	Unfortunately, many programs try to work around this GNU/Linux issue
		5108	by enabling the large file API, which makes them incompatible with the
		5109	standard libev compiled for their system.
		5110
		5111	Likewise, libev cannot enable the large file API itself as this would
		5112	suddenly make it incompatible to the default compile time environment,
		5113	i.e. all programs not using special compile switches.
		5114
		5115	=head2 OS/X AND DARWIN BUGS
		5116
		5117	The whole thing is a bug if you ask me - basically any system interface
		5118	you touch is broken, whether it is locales, poll, kqueue or even the
		5119	OpenGL drivers.
		5120
		5121	=head3 C<kqueue> is buggy
		5122
		5123	The kqueue syscall is broken in all known versions - most versions support
		5124	only sockets, many support pipes.
		5125
		5126	Libev tries to work around this by not using C<kqueue> by default on this
		5127	rotten platform, but of course you can still ask for it when creating a
		5128	loop - embedding a socket-only kqueue loop into a select-based one is
		5129	probably going to work well.
		5130
		5131	=head3 C<poll> is buggy
		5132
		5133	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5134	implementation by something calling C<kqueue> internally around the 10.5.6
		5135	release, so now C<kqueue> I<and> C<poll> are broken.
		5136
		5137	Libev tries to work around this by not using C<poll> by default on
		5138	this rotten platform, but of course you can still ask for it when creating
		5139	a loop.
		5140
		5141	=head3 C<select> is buggy
		5142
		5143	All that's left is C<select>, and of course Apple found a way to fuck this
		5144	one up as well: On OS/X, C<select> actively limits the number of file
		5145	descriptors you can pass in to 1024 - your program suddenly crashes when
		5146	you use more.
		5147
		5148	There is an undocumented "workaround" for this - defining
		5149	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5150	work on OS/X.
		5151
		5152	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5153
		5154	=head3 C<errno> reentrancy
		5155
		5156	The default compile environment on Solaris is unfortunately so
		5157	thread-unsafe that you can't even use components/libraries compiled
		5158	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5159	defined by default. A valid, if stupid, implementation choice.
		5160
		5161	If you want to use libev in threaded environments you have to make sure
		5162	it's compiled with C<_REENTRANT> defined.
		5163
		5164	=head3 Event port backend
		5165
		5166	The scalable event interface for Solaris is called "event
		5167	ports". Unfortunately, this mechanism is very buggy in all major
		5168	releases. If you run into high CPU usage, your program freezes or you get
		5169	a large number of spurious wakeups, make sure you have all the relevant
		5170	and latest kernel patches applied. No, I don't know which ones, but there
		5171	are multiple ones to apply, and afterwards, event ports actually work
		5172	great.
		5173
		5174	If you can't get it to work, you can try running the program by setting
		5175	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5176	C<select> backends.
		5177
		5178	=head2 AIX POLL BUG
		5179
		5180	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5181	this by trying to avoid the poll backend altogether (i.e. it's not even
		5182	compiled in), which normally isn't a big problem as C<select> works fine
		5183	with large bitsets on AIX, and AIX is dead anyway.
		5184
		5185	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5186
		5187	=head3 General issues
3022		5188
3023	Win32 doesn't support any of the standards (e.g. POSIX) that libev	5189	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3024	requires, and its I/O model is fundamentally incompatible with the POSIX	5190	requires, and its I/O model is fundamentally incompatible with the POSIX
3025	model. Libev still offers limited functionality on this platform in	5191	model. Libev still offers limited functionality on this platform in
3026	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5192	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3027	descriptors. This only applies when using Win32 natively, not when using	5193	descriptors. This only applies when using Win32 natively, not when using
3028	e.g. cygwin.	5194	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5195	as every compiler comes with a slightly differently broken/incompatible
		5196	environment.
		5197
		5198	Lifting these limitations would basically require the full
		5199	re-implementation of the I/O system. If you are into this kind of thing,
		5200	then note that glib does exactly that for you in a very portable way (note
		5201	also that glib is the slowest event library known to man).
3029		5202
3030	There is no supported compilation method available on windows except	5203	There is no supported compilation method available on windows except
3031	embedding it into other applications.	5204	embedding it into other applications.
3032		5205
		5206	Sensible signal handling is officially unsupported by Microsoft - libev
		5207	tries its best, but under most conditions, signals will simply not work.
		5208
		5209	Not a libev limitation but worth mentioning: windows apparently doesn't
		5210	accept large writes: instead of resulting in a partial write, windows will
		5211	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5212	so make sure you only write small amounts into your sockets (less than a
		5213	megabyte seems safe, but this apparently depends on the amount of memory
		5214	available).
		5215
3033	Due to the many, low, and arbitrary limits on the win32 platform and the	5216	Due to the many, low, and arbitrary limits on the win32 platform and
3034	abysmal performance of winsockets, using a large number of sockets is not	5217	the abysmal performance of winsockets, using a large number of sockets
3035	recommended (and not reasonable). If your program needs to use more than	5218	is not recommended (and not reasonable). If your program needs to use
3036	a hundred or so sockets, then likely it needs to use a totally different	5219	more than a hundred or so sockets, then likely it needs to use a totally
3037	implementation for windows, as libev offers the POSIX model, which cannot	5220	different implementation for windows, as libev offers the POSIX readiness
3038	be implemented efficiently on windows (microsoft monopoly games).	5221	notification model, which cannot be implemented efficiently on windows
		5222	(due to Microsoft monopoly games).
3039		5223
3040	=over 4	5224	A typical way to use libev under windows is to embed it (see the embedding
		5225	section for details) and use the following F<evwrap.h> header file instead
		5226	of F<ev.h>:
3041		5227
		5228	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5229	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5230
		5231	#include "ev.h"
		5232
		5233	And compile the following F<evwrap.c> file into your project (make sure
		5234	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5235
		5236	#include "evwrap.h"
		5237	#include "ev.c"
		5238
3042	=item The winsocket select function	5239	=head3 The winsocket C<select> function
3043		5240
3044	The winsocket C<select> function doesn't follow POSIX in that it requires	5241	The winsocket C<select> function doesn't follow POSIX in that it
3045	socket I<handles> and not socket I<file descriptors>. This makes select	5242	requires socket I<handles> and not socket I<file descriptors> (it is
3046	very inefficient, and also requires a mapping from file descriptors	5243	also extremely buggy). This makes select very inefficient, and also
3047	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	5244	requires a mapping from file descriptors to socket handles (the Microsoft
3048	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	5245	C runtime provides the function C<_open_osfhandle> for this). See the
3049	symbols for more info.	5246	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5247	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
3050		5248
3051	The configuration for a "naked" win32 using the microsoft runtime	5249	The configuration for a "naked" win32 using the Microsoft runtime
3052	libraries and raw winsocket select is:	5250	libraries and raw winsocket select is:
3053		5251
3054	#define EV_USE_SELECT 1	5252	#define EV_USE_SELECT 1
3055	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	5253	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3056		5254
3057	Note that winsockets handling of fd sets is O(n), so you can easily get a	5255	Note that winsockets handling of fd sets is O(n), so you can easily get a
3058	complexity in the O(n²) range when using win32.	5256	complexity in the O(n²) range when using win32.
3059		5257
3060	=item Limited number of file descriptors	5258	=head3 Limited number of file descriptors
3061		5259
3062	Windows has numerous arbitrary (and low) limits on things. Early versions	5260	Windows has numerous arbitrary (and low) limits on things.
3063	of winsocket's select only supported waiting for a max. of C<64> handles	5261
		5262	Early versions of winsocket's select only supported waiting for a maximum
3064	(probably owning to the fact that all windows kernels can only wait for	5263	of C<64> handles (probably owning to the fact that all windows kernels
3065	C<64> things at the same time internally; microsoft recommends spawning a	5264	can only wait for C<64> things at the same time internally; Microsoft
3066	chain of threads and wait for 63 handles and the previous thread in each).	5265	recommends spawning a chain of threads and wait for 63 handles and the
		5266	previous thread in each. Sounds great!).
3067		5267
3068	Newer versions support more handles, but you need to define C<FD_SETSIZE>	5268	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3069	to some high number (e.g. C<2048>) before compiling the winsocket select	5269	to some high number (e.g. C<2048>) before compiling the winsocket select
3070	call (which might be in libev or elsewhere, for example, perl does its own	5270	call (which might be in libev or elsewhere, for example, perl and many
3071	select emulation on windows).	5271	other interpreters do their own select emulation on windows).
3072		5272
3073	Another limit is the number of file descriptors in the microsoft runtime	5273	Another limit is the number of file descriptors in the Microsoft runtime
3074	libraries, which by default is C<64> (there must be a hidden I<64> fetish	5274	libraries, which by default is C<64> (there must be a hidden I<64>
3075	or something like this inside microsoft). You can increase this by calling	5275	fetish or something like this inside Microsoft). You can increase this
3076	C<_setmaxstdio>, which can increase this limit to C<2048> (another	5276	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3077	arbitrary limit), but is broken in many versions of the microsoft runtime	5277	(another arbitrary limit), but is broken in many versions of the Microsoft
3078	libraries.
3079
3080	This might get you to about C<512> or C<2048> sockets (depending on	5278	runtime libraries. This might get you to about C<512> or C<2048> sockets
3081	windows version and/or the phase of the moon). To get more, you need to	5279	(depending on windows version and/or the phase of the moon). To get more,
3082	wrap all I/O functions and provide your own fd management, but the cost of	5280	you need to wrap all I/O functions and provide your own fd management, but
3083	calling select (O(n²)) will likely make this unworkable.	5281	the cost of calling select (O(n²)) will likely make this unworkable.
		5282
		5283	=head2 PORTABILITY REQUIREMENTS
		5284
		5285	In addition to a working ISO-C implementation and of course the
		5286	backend-specific APIs, libev relies on a few additional extensions:
		5287
		5288	=over 4
		5289
		5290	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5291	calling conventions regardless of C<ev_watcher_type *>.
		5292
		5293	Libev assumes not only that all watcher pointers have the same internal
		5294	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5295	assumes that the same (machine) code can be used to call any watcher
		5296	callback: The watcher callbacks have different type signatures, but libev
		5297	calls them using an C<ev_watcher *> internally.
		5298
		5299	=item pointer accesses must be thread-atomic
		5300
		5301	Accessing a pointer value must be atomic, it must both be readable and
		5302	writable in one piece - this is the case on all current architectures.
		5303
		5304	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5305
		5306	The type C<sig_atomic_t volatile> (or whatever is defined as
		5307	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5308	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5309	believed to be sufficiently portable.
		5310
		5311	=item C<sigprocmask> must work in a threaded environment
		5312
		5313	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5314	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5315	pthread implementations will either allow C<sigprocmask> in the "main
		5316	thread" or will block signals process-wide, both behaviours would
		5317	be compatible with libev. Interaction between C<sigprocmask> and
		5318	C<pthread_sigmask> could complicate things, however.
		5319
		5320	The most portable way to handle signals is to block signals in all threads
		5321	except the initial one, and run the signal handling loop in the initial
		5322	thread as well.
		5323
		5324	=item C<long> must be large enough for common memory allocation sizes
		5325
		5326	To improve portability and simplify its API, libev uses C<long> internally
		5327	instead of C<size_t> when allocating its data structures. On non-POSIX
		5328	systems (Microsoft...) this might be unexpectedly low, but is still at
		5329	least 31 bits everywhere, which is enough for hundreds of millions of
		5330	watchers.
		5331
		5332	=item C<double> must hold a time value in seconds with enough accuracy
		5333
		5334	The type C<double> is used to represent timestamps. It is required to
		5335	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5336	good enough for at least into the year 4000 with millisecond accuracy
		5337	(the design goal for libev). This requirement is overfulfilled by
		5338	implementations using IEEE 754, which is basically all existing ones.
		5339
		5340	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5341	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5342	is either obsolete or somebody patched it to use C<long double> or
		5343	something like that, just kidding).
3084		5344
3085	=back	5345	=back
3086		5346
		5347	If you know of other additional requirements drop me a note.
		5348
		5349
		5350	=head1 ALGORITHMIC COMPLEXITIES
		5351
		5352	In this section the complexities of (many of) the algorithms used inside
		5353	libev will be documented. For complexity discussions about backends see
		5354	the documentation for C<ev_default_init>.
		5355
		5356	All of the following are about amortised time: If an array needs to be
		5357	extended, libev needs to realloc and move the whole array, but this
		5358	happens asymptotically rarer with higher number of elements, so O(1) might
		5359	mean that libev does a lengthy realloc operation in rare cases, but on
		5360	average it is much faster and asymptotically approaches constant time.
		5361
		5362	=over 4
		5363
		5364	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5365
		5366	This means that, when you have a watcher that triggers in one hour and
		5367	there are 100 watchers that would trigger before that, then inserting will
		5368	have to skip roughly seven (C<ld 100>) of these watchers.
		5369
		5370	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5371
		5372	That means that changing a timer costs less than removing/adding them,
		5373	as only the relative motion in the event queue has to be paid for.
		5374
		5375	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5376
		5377	These just add the watcher into an array or at the head of a list.
		5378
		5379	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5380
		5381	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5382
		5383	These watchers are stored in lists, so they need to be walked to find the
		5384	correct watcher to remove. The lists are usually short (you don't usually
		5385	have many watchers waiting for the same fd or signal: one is typical, two
		5386	is rare).
		5387
		5388	=item Finding the next timer in each loop iteration: O(1)
		5389
		5390	By virtue of using a binary or 4-heap, the next timer is always found at a
		5391	fixed position in the storage array.
		5392
		5393	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5394
		5395	A change means an I/O watcher gets started or stopped, which requires
		5396	libev to recalculate its status (and possibly tell the kernel, depending
		5397	on backend and whether C<ev_io_set> was used).
		5398
		5399	=item Activating one watcher (putting it into the pending state): O(1)
		5400
		5401	=item Priority handling: O(number_of_priorities)
		5402
		5403	Priorities are implemented by allocating some space for each
		5404	priority. When doing priority-based operations, libev usually has to
		5405	linearly search all the priorities, but starting/stopping and activating
		5406	watchers becomes O(1) with respect to priority handling.
		5407
		5408	=item Sending an ev_async: O(1)
		5409
		5410	=item Processing ev_async_send: O(number_of_async_watchers)
		5411
		5412	=item Processing signals: O(max_signal_number)
		5413
		5414	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5415	calls in the current loop iteration and the loop is currently
		5416	blocked. Checking for async and signal events involves iterating over all
		5417	running async watchers or all signal numbers.
		5418
		5419	=back
		5420
		5421
		5422	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5423
		5424	The major version 4 introduced some incompatible changes to the API.
		5425
		5426	At the moment, the C<ev.h> header file provides compatibility definitions
		5427	for all changes, so most programs should still compile. The compatibility
		5428	layer might be removed in later versions of libev, so better update to the
		5429	new API early than late.
		5430
		5431	=over 4
		5432
		5433	=item C<EV_COMPAT3> backwards compatibility mechanism
		5434
		5435	The backward compatibility mechanism can be controlled by
		5436	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5437	section.
		5438
		5439	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5440
		5441	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5442
		5443	ev_loop_destroy (EV_DEFAULT_UC);
		5444	ev_loop_fork (EV_DEFAULT);
		5445
		5446	=item function/symbol renames
		5447
		5448	A number of functions and symbols have been renamed:
		5449
		5450	ev_loop => ev_run
		5451	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5452	EVLOOP_ONESHOT => EVRUN_ONCE
		5453
		5454	ev_unloop => ev_break
		5455	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5456	EVUNLOOP_ONE => EVBREAK_ONE
		5457	EVUNLOOP_ALL => EVBREAK_ALL
		5458
		5459	EV_TIMEOUT => EV_TIMER
		5460
		5461	ev_loop_count => ev_iteration
		5462	ev_loop_depth => ev_depth
		5463	ev_loop_verify => ev_verify
		5464
		5465	Most functions working on C<struct ev_loop> objects don't have an
		5466	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5467	associated constants have been renamed to not collide with the C<struct
		5468	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5469	as all other watcher types. Note that C<ev_loop_fork> is still called
		5470	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5471	typedef.
		5472
		5473	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5474
		5475	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5476	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5477	and work, but the library code will of course be larger.
		5478
		5479	=back
		5480
		5481
		5482	=head1 GLOSSARY
		5483
		5484	=over 4
		5485
		5486	=item active
		5487
		5488	A watcher is active as long as it has been started and not yet stopped.
		5489	See L</WATCHER STATES> for details.
		5490
		5491	=item application
		5492
		5493	In this document, an application is whatever is using libev.
		5494
		5495	=item backend
		5496
		5497	The part of the code dealing with the operating system interfaces.
		5498
		5499	=item callback
		5500
		5501	The address of a function that is called when some event has been
		5502	detected. Callbacks are being passed the event loop, the watcher that
		5503	received the event, and the actual event bitset.
		5504
		5505	=item callback/watcher invocation
		5506
		5507	The act of calling the callback associated with a watcher.
		5508
		5509	=item event
		5510
		5511	A change of state of some external event, such as data now being available
		5512	for reading on a file descriptor, time having passed or simply not having
		5513	any other events happening anymore.
		5514
		5515	In libev, events are represented as single bits (such as C<EV_READ> or
		5516	C<EV_TIMER>).
		5517
		5518	=item event library
		5519
		5520	A software package implementing an event model and loop.
		5521
		5522	=item event loop
		5523
		5524	An entity that handles and processes external events and converts them
		5525	into callback invocations.
		5526
		5527	=item event model
		5528
		5529	The model used to describe how an event loop handles and processes
		5530	watchers and events.
		5531
		5532	=item pending
		5533
		5534	A watcher is pending as soon as the corresponding event has been
		5535	detected. See L</WATCHER STATES> for details.
		5536
		5537	=item real time
		5538
		5539	The physical time that is observed. It is apparently strictly monotonic :)
		5540
		5541	=item wall-clock time
		5542
		5543	The time and date as shown on clocks. Unlike real time, it can actually
		5544	be wrong and jump forwards and backwards, e.g. when you adjust your
		5545	clock.
		5546
		5547	=item watcher
		5548
		5549	A data structure that describes interest in certain events. Watchers need
		5550	to be started (attached to an event loop) before they can receive events.
		5551
		5552	=back
3087		5553
3088	=head1 AUTHOR	5554	=head1 AUTHOR
3089		5555
3090	Marc Lehmann <libev@schmorp.de>.	5556	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5557	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
3091		5558

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