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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
6		8
7	#include <ev.h>	9	#include <ev.h>
8		10
9	=head1 EXAMPLE PROGRAM	11	=head2 EXAMPLE PROGRAM
10		12
		13	// a single header file is required
11	#include <ev.h>	14	#include <ev.h>
12		15
		16	#include <stdio.h> // for puts
		17
		18	// every watcher type has its own typedef'd struct
		19	// with the name ev_TYPE
13	ev_io stdin_watcher;	20	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	21	ev_timer timeout_watcher;
15		22
16	/* called when data readable on stdin */	23	// all watcher callbacks have a similar signature
		24	// this callback is called when data is readable on stdin
17	static void	25	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	26	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	27	{
20	/* puts ("stdin ready"); */	28	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	29	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	30	// with its corresponding stop function.
		31	ev_io_stop (EV_A_ w);
		32
		33	// this causes all nested ev_run's to stop iterating
		34	ev_break (EV_A_ EVBREAK_ALL);
23	}	35	}
24		36
		37	// another callback, this time for a time-out
25	static void	38	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	39	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	40	{
28	/* puts ("timeout"); */	41	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	42	// this causes the innermost ev_run to stop iterating
		43	ev_break (EV_A_ EVBREAK_ONE);
30	}	44	}
31		45
32	int	46	int
33	main (void)	47	main (void)
34	{	48	{
35	struct ev_loop *loop = ev_default_loop (0);	49	// use the default event loop unless you have special needs
		50	struct ev_loop *loop = EV_DEFAULT;
36		51
37	/* initialise an io watcher, then start it */	52	// initialise an io watcher, then start it
		53	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
40		56
		57	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	58	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
44		61
45	/* loop till timeout or data ready */	62	// now wait for events to arrive
46	ev_loop (loop, 0);	63	ev_run (loop, 0);
47		64
		65	// break was called, so exit
48	return 0;	66	return 0;
49	}	67	}
50		68
51	=head1 DESCRIPTION	69	=head1 ABOUT THIS DOCUMENT
52		70
		71	This document documents the libev software package.
		72
53	The newest version of this document is also available as a html-formatted	73	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	74	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	75	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		76
		77	While this document tries to be as complete as possible in documenting
		78	libev, its usage and the rationale behind its design, it is not a tutorial
		79	on event-based programming, nor will it introduce event-based programming
		80	with libev.
		81
		82	Familiarity with event based programming techniques in general is assumed
		83	throughout this document.
		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
		93	=head1 ABOUT LIBEV
56		94
57	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occuring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	97	these event sources and provide your program with events.
60		98
61	To do this, it must take more or less complete control over your process	99	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	100	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	101	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	103	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	104	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	106	watcher.
69		107
70	=head1 FEATURES	108	=head2 FEATURES
71		109
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	110	Libev supports C<select>, C<poll>, the Linux-specific 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	=head1 CONVENTIONS	126	=head2 CONVENTIONS
88		127
89	Libev is very configurable. In this manual the default configuration will	128	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	129	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	130	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	131	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	132	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		134	this argument.
95		135
96	=head1 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
97		137
98	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	the (fractional) number of seconds since the (POSIX) epoch (in practice
100	the beginning of 1970, details are complicated, don't ask). This type is	140	somewhere near the beginning of 1970, details are complicated, don't
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	141	ask). This type is called C<ev_tstamp>, which is what you should use
102	to the C<double> type in C, and when you need to do any calculations on	142	too. It usually aliases to the C<double> type in C. When you need to do
103	it, you should treat it as such.	143	any calculations on it, you should treat it as some floating point value.
		144
		145	Unlike the name component C<stamp> might indicate, it is also used for
		146	time differences (e.g. delays) throughout libev.
		147
		148	=head1 ERROR HANDLING
		149
		150	Libev knows three classes of errors: operating system errors, usage errors
		151	and internal errors (bugs).
		152
		153	When libev catches an operating system error it cannot handle (for example
		154	a system call indicating a condition libev cannot fix), it calls the callback
		155	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		156	abort. The default is to print a diagnostic message and to call C<abort
		157	()>.
		158
		159	When libev detects a usage error such as a negative timer interval, then
		160	it will print a diagnostic message and abort (via the C<assert> mechanism,
		161	so C<NDEBUG> will disable this checking): these are programming errors in
		162	the libev caller and need to be fixed there.
		163
		164	Libev also has a few internal error-checking C<assert>ions, and also has
		165	extensive consistency checking code. These do not trigger under normal
		166	circumstances, as they indicate either a bug in libev or worse.
		167
104		168
105	=head1 GLOBAL FUNCTIONS	169	=head1 GLOBAL FUNCTIONS
106		170
107	These functions can be called anytime, even before initialising the	171	These functions can be called anytime, even before initialising the
108	library in any way.	172	library in any way.
…		…
111		175
112	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
113		177
114	Returns the current time as libev would use it. Please note that the	178	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	179	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	180	you actually want to know. Also interesting is the combination of
		181	C<ev_now_update> and C<ev_now>.
		182
		183	=item ev_sleep (ev_tstamp interval)
		184
		185	Sleep for the given interval: The current thread will be blocked
		186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
		190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
117		194
118	=item int ev_version_major ()	195	=item int ev_version_major ()
119		196
120	=item int ev_version_minor ()	197	=item int ev_version_minor ()
121		198
122	You can find out the major and minor version numbers of the library	199	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	200	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	201	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	202	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	203	version of the library your program was compiled against.
127		204
		205	These version numbers refer to the ABI version of the library, not the
		206	release version.
		207
128	Usually, it's a good idea to terminate if the major versions mismatch,	208	Usually, it's a good idea to terminate if the major versions mismatch,
129	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
130	compatible to older versions, so a larger minor version alone is usually	210	compatible to older versions, so a larger minor version alone is usually
131	not a problem.	211	not a problem.
132		212
133	Example: Make sure we haven't accidentally been linked against the wrong	213	Example: Make sure we haven't accidentally been linked against the wrong
134	version.	214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
135		216
136	assert (("libev version mismatch",	217	assert (("libev version mismatch",
137	ev_version_major () == EV_VERSION_MAJOR	218	ev_version_major () == EV_VERSION_MAJOR
138	&& ev_version_minor () >= EV_VERSION_MINOR));	219	&& ev_version_minor () >= EV_VERSION_MINOR));
139		220
140	=item unsigned int ev_supported_backends ()	221	=item unsigned int ev_supported_backends ()
141		222
142	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	223	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
143	value) compiled into this binary of libev (independent of their	224	value) compiled into this binary of libev (independent of their
…		…
145	a description of the set values.	226	a description of the set values.
146		227
147	Example: make sure we have the epoll method, because yeah this is cool and	228	Example: make sure we have the epoll method, because yeah this is cool and
148	a must have and can we have a torrent of it please!!!11	229	a must have and can we have a torrent of it please!!!11
149		230
150	assert (("sorry, no epoll, no sex",	231	assert (("sorry, no epoll, no sex",
151	ev_supported_backends () & EVBACKEND_EPOLL));	232	ev_supported_backends () & EVBACKEND_EPOLL));
152		233
153	=item unsigned int ev_recommended_backends ()	234	=item unsigned int ev_recommended_backends ()
154		235
155	Return the set of all backends compiled into this binary of libev and also	236	Return the set of all backends compiled into this binary of libev and
156	recommended for this platform. This set is often smaller than the one	237	also recommended for this platform, meaning it will work for most file
		238	descriptor types. This set is often smaller than the one returned by
157	returned by C<ev_supported_backends>, as for example kqueue is broken on	239	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
158	most BSDs and will not be autodetected unless you explicitly request it	240	and will not be auto-detected unless you explicitly request it (assuming
159	(assuming you know what you are doing). This is the set of backends that	241	you know what you are doing). This is the set of backends that libev will
160	libev will probe for if you specify no backends explicitly.	242	probe for if you specify no backends explicitly.
161		243
162	=item unsigned int ev_embeddable_backends ()	244	=item unsigned int ev_embeddable_backends ()
163		245
164	Returns the set of backends that are embeddable in other event loops. This	246	Returns the set of backends that are embeddable in other event loops. This
165	is the theoretical, all-platform, value. To find which backends	247	value is platform-specific but can include backends not available on the
166	might be supported on the current system, you would need to look at	248	current system. To find which embeddable backends might be supported on
167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	249	the current system, you would need to look at C<ev_embeddable_backends ()
168	recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
169		251
170	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
171		253
172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
173		255
174	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
175	semantics is identical - to the realloc C function). It is used to	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
176	allocate and free memory (no surprises here). If it returns zero when	258	used to allocate and free memory (no surprises here). If it returns zero
177	memory needs to be allocated, the library might abort or take some	259	when memory needs to be allocated (C<size != 0>), the library might abort
178	potentially destructive action. The default is your system realloc	260	or take some potentially destructive action.
179	function.	261
		262	Since some systems (at least OpenBSD and Darwin) fail to implement
		263	correct C<realloc> semantics, libev will use a wrapper around the system
		264	C<realloc> and C<free> functions by default.
180		265
181	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
182	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
183	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
184		269
185	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
186	retries).	271	retries (example requires a standards-compliant C<realloc>).
187		272
188	static void *	273	static void *
189	persistent_realloc (void *ptr, size_t size)	274	persistent_realloc (void *ptr, size_t size)
190	{	275	{
191	for (;;)	276	for (;;)
…		…
200	}	285	}
201		286
202	...	287	...
203	ev_set_allocator (persistent_realloc);	288	ev_set_allocator (persistent_realloc);
204		289
205	=item ev_set_syserr_cb (void (*cb)(const char *msg));	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
206		291
207	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
208	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
209	indicating the system call or subsystem causing the problem. If this	294	indicating the system call or subsystem causing the problem. If this
210	callback is set, then libev will expect it to remedy the sitution, no	295	callback is set, then libev will expect it to remedy the situation, no
211	matter what, when it returns. That is, libev will generally retry the	296	matter what, when it returns. That is, libev will generally retry the
212	requested operation, or, if the condition doesn't go away, do bad stuff	297	requested operation, or, if the condition doesn't go away, do bad stuff
213	(such as abort).	298	(such as abort).
214		299
215	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.
…		…
222	}	307	}
223		308
224	...	309	...
225	ev_set_syserr_cb (fatal_error);	310	ev_set_syserr_cb (fatal_error);
226		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
227	=back	325	=back
228		326
229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
230		328
231	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
232	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
233	events, and dynamically created loops which do not.	331	libev 3 had an C<ev_loop> function colliding with the struct name).
234		332
235	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
236	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
237	create, you also create another event loop. Libev itself does no locking	335	do not.
238	whatsoever, so if you mix calls to the same event loop in different
239	threads, make sure you lock (this is usually a bad idea, though, even if
240	done correctly, because it's hideous and inefficient).
241		336
242	=over 4	337	=over 4
243		338
244	=item struct ev_loop *ev_default_loop (unsigned int flags)	339	=item struct ev_loop *ev_default_loop (unsigned int flags)
245		340
246	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
247	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
248	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
249	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".
250		351
251	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
252	function.	353	function (or via the C<EV_DEFAULT> macro).
		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
		360	The default loop is the only loop that can handle C<ev_child> watchers,
		361	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		362	a problem for your application you can either create a dynamic loop with
		363	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		364	C<SIGCHLD> signal handler I<after> calling 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.
253		384
254	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
255	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>).
256		387
257	The following flags are supported:	388	The following flags are supported:
…		…
263	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
264	thing, believe me).	395	thing, believe me).
265		396
266	=item C<EVFLAG_NOENV>	397	=item C<EVFLAG_NOENV>
267		398
268	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
269	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
270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
271	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
272	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
273	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).
274		407
275	=item C<EVFLAG_FORKCHECK>	408	=item C<EVFLAG_FORKCHECK>
276		409
277	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
278	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.
279	enabling this flag.
280		412
281	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,
282	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
283	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
284	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
285	without a syscall and thus I<very> fast, but my Linux system also has	417	sequence without a system call and thus I<very> fast, but my GNU/Linux
286	C<pthread_atfork> which is even faster).	418	system also has C<pthread_atfork> which is even faster). (Update: glibc
		419	versions 2.25 apparently removed the C<getpid> optimisation again).
287		420
288	The big advantage of this flag is that you can forget about fork (and	421	The big advantage of this flag is that you can forget about fork (and
289	forget about forgetting to tell libev about forking) when you use this	422	forget about forgetting to tell libev about forking, although you still
290	flag.	423	have to ignore C<SIGPIPE>) when you use this flag.
291		424
292	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	425	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
293	environment variable.	426	environment variable.
		427
		428	=item C<EVFLAG_NOINOTIFY>
		429
		430	When this flag is specified, then libev will not attempt to use the
		431	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		432	testing, this flag can be useful to conserve inotify file descriptors, as
		433	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		434
		435	=item C<EVFLAG_SIGNALFD>
		436
		437	When this flag is specified, then libev will attempt to use the
		438	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		439	delivers signals synchronously, which makes it both faster and might make
		440	it possible to get the queued signal data. It can also simplify signal
		441	handling with threads, as long as you properly block signals in your
		442	threads that are not interested in handling them.
		443
		444	Signalfd will not be used by default as this changes your signal mask, and
		445	there are a lot of shoddy libraries and programs (glib's threadpool for
		446	example) that can't properly initialise their signal masks.
		447
		448	=item C<EVFLAG_NOSIGMASK>
		449
		450	When this flag is specified, then libev will avoid to modify the signal
		451	mask. Specifically, this means you have to make sure signals are unblocked
		452	when you want to receive them.
		453
		454	This behaviour is useful when you want to do your own signal handling, or
		455	want to handle signals only in specific threads and want to avoid libev
		456	unblocking the signals.
		457
		458	It's also required by POSIX in a threaded program, as libev calls
		459	C<sigprocmask>, whose behaviour is officially unspecified.
		460
		461	This flag's behaviour will become the default in future versions of libev.
294		462
295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	463	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
296		464
297	This is your standard select(2) backend. Not I<completely> standard, as	465	This is your standard select(2) backend. Not I<completely> standard, as
298	libev tries to roll its own fd_set with no limits on the number of fds,	466	libev tries to roll its own fd_set with no limits on the number of fds,
299	but if that fails, expect a fairly low limit on the number of fds when	467	but if that fails, expect a fairly low limit on the number of fds when
300	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	468	using this backend. It doesn't scale too well (O(highest_fd)), but its
301	the fastest backend for a low number of fds.	469	usually the fastest backend for a low number of (low-numbered :) fds.
		470
		471	To get good performance out of this backend you need a high amount of
		472	parallelism (most of the file descriptors should be busy). If you are
		473	writing a server, you should C<accept ()> in a loop to accept as many
		474	connections as possible during one iteration. You might also want to have
		475	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		476	readiness notifications you get per iteration.
		477
		478	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		479	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		480	C<exceptfds> set on that platform).
302		481
303	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	482	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
304		483
305	And this is your standard poll(2) backend. It's more complicated than	484	And this is your standard poll(2) backend. It's more complicated
306	select, but handles sparse fds better and has no artificial limit on the	485	than select, but handles sparse fds better and has no artificial
307	number of fds you can use (except it will slow down considerably with a	486	limit on the number of fds you can use (except it will slow down
308	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	487	considerably with a lot of inactive fds). It scales similarly to select,
		488	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		489	performance tips.
		490
		491	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		492	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
309		493
310	=item C<EVBACKEND_EPOLL> (value 4, Linux)	494	=item C<EVBACKEND_EPOLL> (value 4, Linux)
311		495
		496	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		497	kernels).
		498
312	For few fds, this backend is a bit little slower than poll and select,	499	For few fds, this backend is a bit little slower than poll and select, but
313	but it scales phenomenally better. While poll and select usually scale like	500	it scales phenomenally better. While poll and select usually scale like
314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	501	O(total_fds) where total_fds is the total number of fds (or the highest
315	either O(1) or O(active_fds).	502	fd), epoll scales either O(1) or O(active_fds).
316		503
		504	The epoll mechanism deserves honorable mention as the most misdesigned
		505	of the more advanced event mechanisms: mere annoyances include silently
		506	dropping file descriptors, requiring a system call per change per file
		507	descriptor (and unnecessary guessing of parameters), problems with dup,
		508	returning before the timeout value, resulting in additional iterations
		509	(and only giving 5ms accuracy while select on the same platform gives
		510	0.1ms) and so on. The biggest issue is fork races, however - if a program
		511	forks then I<both> parent and child process have to recreate the epoll
		512	set, which can take considerable time (one syscall per file descriptor)
		513	and is of course hard to detect.
		514
		515	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		516	but of course I<doesn't>, and epoll just loves to report events for
		517	totally I<different> file descriptors (even already closed ones, so
		518	one cannot even remove them from the set) than registered in the set
		519	(especially on SMP systems). Libev tries to counter these spurious
		520	notifications by employing an additional generation counter and comparing
		521	that against the events to filter out spurious ones, recreating the set
		522	when required. Epoll also erroneously rounds down timeouts, but gives you
		523	no way to know when and by how much, so sometimes you have to busy-wait
		524	because epoll returns immediately despite a nonzero timeout. And last
		525	not least, it also refuses to work with some file descriptors which work
		526	perfectly fine with C<select> (files, many character devices...).
		527
		528	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		529	cobbled together in a hurry, no thought to design or interaction with
		530	others. Oh, the pain, will it ever stop...
		531
317	While stopping and starting an I/O watcher in the same iteration will	532	While stopping, setting and starting an I/O watcher in the same iteration
318	result in some caching, there is still a syscall per such incident	533	will result in some caching, there is still a system call per such
319	(because the fd could point to a different file description now), so its	534	incident (because the same I<file descriptor> could point to a different
320	best to avoid that. Also, dup()ed file descriptors might not work very	535	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
321	well if you register events for both fds.	536	file descriptors might not work very well if you register events for both
		537	file descriptors.
322		538
323	Please note that epoll sometimes generates spurious notifications, so you	539	Best performance from this backend is achieved by not unregistering all
324	need to use non-blocking I/O or other means to avoid blocking when no data	540	watchers for a file descriptor until it has been closed, if possible,
325	(or space) is available.	541	i.e. keep at least one watcher active per fd at all times. Stopping and
		542	starting a watcher (without re-setting it) also usually doesn't cause
		543	extra overhead. A fork can both result in spurious notifications as well
		544	as in libev having to destroy and recreate the epoll object, which can
		545	take considerable time and thus should be avoided.
		546
		547	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		548	faster than epoll for maybe up to a hundred file descriptors, depending on
		549	the usage. So sad.
		550
		551	While nominally embeddable in other event loops, this feature is broken in
		552	all kernel versions tested so far.
		553
		554	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		555	C<EVBACKEND_POLL>.
326		556
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	557	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		558
329	Kqueue deserves special mention, as at the time of this writing, it	559	Kqueue deserves special mention, as at the time of this writing, it
330	was broken on all BSDs except NetBSD (usually it doesn't work with	560	was broken on all BSDs except NetBSD (usually it doesn't work reliably
331	anything but sockets and pipes, except on Darwin, where of course its	561	with anything but sockets and pipes, except on Darwin, where of course
332	completely useless). For this reason its not being "autodetected"	562	it's completely useless). Unlike epoll, however, whose brokenness
		563	is by design, these kqueue bugs can (and eventually will) be fixed
		564	without API changes to existing programs. For this reason it's not being
333	unless you explicitly specify it explicitly in the flags (i.e. using	565	"auto-detected" unless you explicitly specify it in the flags (i.e. using
334	C<EVBACKEND_KQUEUE>).	566	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		567	system like NetBSD.
		568
		569	You still can embed kqueue into a normal poll or select backend and use it
		570	only for sockets (after having made sure that sockets work with kqueue on
		571	the target platform). See C<ev_embed> watchers for more info.
335		572
336	It scales in the same way as the epoll backend, but the interface to the	573	It scales in the same way as the epoll backend, but the interface to the
337	kernel is more efficient (which says nothing about its actual speed, of	574	kernel is more efficient (which says nothing about its actual speed, of
338	course). While starting and stopping an I/O watcher does not cause an	575	course). While stopping, setting and starting an I/O watcher does never
339	extra syscall as with epoll, it still adds up to four event changes per	576	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
340	incident, so its best to avoid that.	577	two event changes per incident. Support for C<fork ()> is very bad (you
		578	might have to leak fd's on fork, but it's more sane than epoll) and it
		579	drops fds silently in similarly hard-to-detect cases.
		580
		581	This backend usually performs well under most conditions.
		582
		583	While nominally embeddable in other event loops, this doesn't work
		584	everywhere, so you might need to test for this. And since it is broken
		585	almost everywhere, you should only use it when you have a lot of sockets
		586	(for which it usually works), by embedding it into another event loop
		587	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		588	also broken on OS X)) and, did I mention it, using it only for sockets.
		589
		590	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		591	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		592	C<NOTE_EOF>.
341		593
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	594	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		595
344	This is not implemented yet (and might never be).	596	This is not implemented yet (and might never be, unless you send me an
		597	implementation). According to reports, C</dev/poll> only supports sockets
		598	and is not embeddable, which would limit the usefulness of this backend
		599	immensely.
345		600
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	601	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		602
348	This uses the Solaris 10 port mechanism. As with everything on Solaris,	603	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
349	it's really slow, but it still scales very well (O(active_fds)).	604	it's really slow, but it still scales very well (O(active_fds)).
350		605
351	Please note that solaris ports can result in a lot of spurious	606	While this backend scales well, it requires one system call per active
352	notifications, so you need to use non-blocking I/O or other means to avoid	607	file descriptor per loop iteration. For small and medium numbers of file
353	blocking when no data (or space) is available.	608	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		609	might perform better.
		610
		611	On the positive side, this backend actually performed fully to
		612	specification in all tests and is fully embeddable, which is a rare feat
		613	among the OS-specific backends (I vastly prefer correctness over speed
		614	hacks).
		615
		616	On the negative side, the interface is I<bizarre> - so bizarre that
		617	even sun itself gets it wrong in their code examples: The event polling
		618	function sometimes returns events to the caller even though an error
		619	occurred, but with no indication whether it has done so or not (yes, it's
		620	even documented that way) - deadly for edge-triggered interfaces where you
		621	absolutely have to know whether an event occurred or not because you have
		622	to re-arm the watcher.
		623
		624	Fortunately libev seems to be able to work around these idiocies.
		625
		626	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		627	C<EVBACKEND_POLL>.
354		628
355	=item C<EVBACKEND_ALL>	629	=item C<EVBACKEND_ALL>
356		630
357	Try all backends (even potentially broken ones that wouldn't be tried	631	Try all backends (even potentially broken ones that wouldn't be tried
358	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	632	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	633	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		634
		635	It is definitely not recommended to use this flag, use whatever
		636	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		637	at all.
		638
		639	=item C<EVBACKEND_MASK>
		640
		641	Not a backend at all, but a mask to select all backend bits from a
		642	C<flags> value, in case you want to mask out any backends from a flags
		643	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
		644
361	=back	645	=back
362		646
363	If one or more of these are ored into the flags value, then only these	647	If one or more of the backend flags are or'ed into the flags value,
364	backends will be tried (in the reverse order as given here). If none are	648	then only these backends will be tried (in the reverse order as listed
365	specified, most compiled-in backend will be tried, usually in reverse	649	here). If none are specified, all backends in C<ev_recommended_backends
366	order of their flag values :)	650	()> will be tried.
367
368	The most typical usage is like this:
369
370	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372
373	Restrict libev to the select and poll backends, and do not allow
374	environment settings to be taken into account:
375
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377
378	Use whatever libev has to offer, but make sure that kqueue is used if
379	available (warning, breaks stuff, best use only with your own private
380	event loop and only if you know the OS supports your types of fds):
381
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383
384	=item struct ev_loop *ev_loop_new (unsigned int flags)
385
386	Similar to C<ev_default_loop>, but always creates a new event loop that is
387	always distinct from the default loop. Unlike the default loop, it cannot
388	handle signal and child watchers, and attempts to do so will be greeted by
389	undefined behaviour (or a failed assertion if assertions are enabled).
390		651
391	Example: Try to create a event loop that uses epoll and nothing else.	652	Example: Try to create a event loop that uses epoll and nothing else.
392		653
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	654	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	655	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	656	fatal ("no epoll found here, maybe it hides under your chair");
396		657
		658	Example: Use whatever libev has to offer, but make sure that kqueue is
		659	used if available.
		660
		661	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		662
397	=item ev_default_destroy ()	663	=item ev_loop_destroy (loop)
398		664
399	Destroys the default loop again (frees all memory and kernel state	665	Destroys an event loop object (frees all memory and kernel state
400	etc.). None of the active event watchers will be stopped in the normal	666	etc.). None of the active event watchers will be stopped in the normal
401	sense, so e.g. C<ev_is_active> might still return true. It is your	667	sense, so e.g. C<ev_is_active> might still return true. It is your
402	responsibility to either stop all watchers cleanly yoursef I<before>	668	responsibility to either stop all watchers cleanly yourself I<before>
403	calling this function, or cope with the fact afterwards (which is usually	669	calling this function, or cope with the fact afterwards (which is usually
404	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	670	the easiest thing, you can just ignore the watchers and/or C<free ()> them
405	for example).	671	for example).
406		672
		673	Note that certain global state, such as signal state (and installed signal
		674	handlers), will not be freed by this function, and related watchers (such
		675	as signal and child watchers) would need to be stopped manually.
		676
		677	This function is normally used on loop objects allocated by
		678	C<ev_loop_new>, but it can also be used on the default loop returned by
		679	C<ev_default_loop>, in which case it is not thread-safe.
		680
		681	Note that it is not advisable to call this function on the default loop
		682	except in the rare occasion where you really need to free its resources.
		683	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		684	and C<ev_loop_destroy>.
		685
407	=item ev_loop_destroy (loop)	686	=item ev_loop_fork (loop)
408		687
409	Like C<ev_default_destroy>, but destroys an event loop created by an	688	This function sets a flag that causes subsequent C<ev_run> iterations
410	earlier call to C<ev_loop_new>.
411
412	=item ev_default_fork ()
413
414	This function reinitialises the kernel state for backends that have	689	to reinitialise the kernel state for backends that have one. Despite
415	one. Despite the name, you can call it anytime, but it makes most sense	690	the name, you can call it anytime you are allowed to start or stop
416	after forking, in either the parent or child process (or both, but that	691	watchers (except inside an C<ev_prepare> callback), but it makes most
417	again makes little sense).	692	sense after forking, in the child process. You I<must> call it (or use
		693	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
418		694
419	You I<must> call this function in the child process after forking if and	695	In addition, if you want to reuse a loop (via this function or
420	only if you want to use the event library in both processes. If you just	696	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
421	fork+exec, you don't have to call it.	697
		698	Again, you I<have> to call it on I<any> loop that you want to re-use after
		699	a fork, I<even if you do not plan to use the loop in the parent>. This is
		700	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		701	during fork.
		702
		703	On the other hand, you only need to call this function in the child
		704	process if and only if you want to use the event loop in the child. If
		705	you just fork+exec or create a new loop in the child, you don't have to
		706	call it at all (in fact, C<epoll> is so badly broken that it makes a
		707	difference, but libev will usually detect this case on its own and do a
		708	costly reset of the backend).
422		709
423	The function itself is quite fast and it's usually not a problem to call	710	The function itself is quite fast and it's usually not a problem to call
424	it just in case after a fork. To make this easy, the function will fit in	711	it just in case after a fork.
425	quite nicely into a call to C<pthread_atfork>:
426		712
		713	Example: Automate calling C<ev_loop_fork> on the default loop when
		714	using pthreads.
		715
		716	static void
		717	post_fork_child (void)
		718	{
		719	ev_loop_fork (EV_DEFAULT);
		720	}
		721
		722	...
427	pthread_atfork (0, 0, ev_default_fork);	723	pthread_atfork (0, 0, post_fork_child);
428		724
429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	725	=item int ev_is_default_loop (loop)
430	without calling this function, so if you force one of those backends you
431	do not need to care.
432		726
433	=item ev_loop_fork (loop)	727	Returns true when the given loop is, in fact, the default loop, and false
		728	otherwise.
434		729
435	Like C<ev_default_fork>, but acts on an event loop created by
436	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
437	after fork, and how you do this is entirely your own problem.
438
439	=item unsigned int ev_loop_count (loop)	730	=item unsigned int ev_iteration (loop)
440		731
441	Returns the count of loop iterations for the loop, which is identical to	732	Returns the current iteration count for the event loop, which is identical
442	the number of times libev did poll for new events. It starts at C<0> and	733	to the number of times libev did poll for new events. It starts at C<0>
443	happily wraps around with enough iterations.	734	and happily wraps around with enough iterations.
444		735
445	This value can sometimes be useful as a generation counter of sorts (it	736	This value can sometimes be useful as a generation counter of sorts (it
446	"ticks" the number of loop iterations), as it roughly corresponds with	737	"ticks" the number of loop iterations), as it roughly corresponds with
447	C<ev_prepare> and C<ev_check> calls.	738	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		739	prepare and check phases.
		740
		741	=item unsigned int ev_depth (loop)
		742
		743	Returns the number of times C<ev_run> was entered minus the number of
		744	times C<ev_run> was exited normally, in other words, the recursion depth.
		745
		746	Outside C<ev_run>, this number is zero. In a callback, this number is
		747	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		748	in which case it is higher.
		749
		750	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		751	throwing an exception etc.), doesn't count as "exit" - consider this
		752	as a hint to avoid such ungentleman-like behaviour unless it's really
		753	convenient, in which case it is fully supported.
448		754
449	=item unsigned int ev_backend (loop)	755	=item unsigned int ev_backend (loop)
450		756
451	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	757	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
452	use.	758	use.
…		…
455		761
456	Returns the current "event loop time", which is the time the event loop	762	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	763	received events and started processing them. This timestamp does not
458	change as long as callbacks are being processed, and this is also the base	764	change as long as callbacks are being processed, and this is also the base
459	time used for relative timers. You can treat it as the timestamp of the	765	time used for relative timers. You can treat it as the timestamp of the
460	event occuring (or more correctly, libev finding out about it).	766	event occurring (or more correctly, libev finding out about it).
461		767
		768	=item ev_now_update (loop)
		769
		770	Establishes the current time by querying the kernel, updating the time
		771	returned by C<ev_now ()> in the progress. This is a costly operation and
		772	is usually done automatically within C<ev_run ()>.
		773
		774	This function is rarely useful, but when some event callback runs for a
		775	very long time without entering the event loop, updating libev's idea of
		776	the current time is a good idea.
		777
		778	See also L</The special problem of time updates> in the C<ev_timer> section.
		779
		780	=item ev_suspend (loop)
		781
		782	=item ev_resume (loop)
		783
		784	These two functions suspend and resume an event loop, for use when the
		785	loop is not used for a while and timeouts should not be processed.
		786
		787	A typical use case would be an interactive program such as a game: When
		788	the user presses C<^Z> to suspend the game and resumes it an hour later it
		789	would be best to handle timeouts as if no time had actually passed while
		790	the program was suspended. This can be achieved by calling C<ev_suspend>
		791	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		792	C<ev_resume> directly afterwards to resume timer processing.
		793
		794	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		795	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		796	will be rescheduled (that is, they will lose any events that would have
		797	occurred while suspended).
		798
		799	After calling C<ev_suspend> you B<must not> call I<any> function on the
		800	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		801	without a previous call to C<ev_suspend>.
		802
		803	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		804	event loop time (see C<ev_now_update>).
		805
462	=item ev_loop (loop, int flags)	806	=item bool ev_run (loop, int flags)
463		807
464	Finally, this is it, the event handler. This function usually is called	808	Finally, this is it, the event handler. This function usually is called
465	after you initialised all your watchers and you want to start handling	809	after you have initialised all your watchers and you want to start
466	events.	810	handling events. It will ask the operating system for any new events, call
		811	the watcher callbacks, and then repeat the whole process indefinitely: This
		812	is why event loops are called I<loops>.
467		813
468	If the flags argument is specified as C<0>, it will not return until	814	If the flags argument is specified as C<0>, it will keep handling events
469	either no event watchers are active anymore or C<ev_unloop> was called.	815	until either no event watchers are active anymore or C<ev_break> was
		816	called.
470		817
		818	The return value is false if there are no more active watchers (which
		819	usually means "all jobs done" or "deadlock"), and true in all other cases
		820	(which usually means " you should call C<ev_run> again").
		821
471	Please note that an explicit C<ev_unloop> is usually better than	822	Please note that an explicit C<ev_break> is usually better than
472	relying on all watchers to be stopped when deciding when a program has	823	relying on all watchers to be stopped when deciding when a program has
473	finished (especially in interactive programs), but having a program that	824	finished (especially in interactive programs), but having a program
474	automatically loops as long as it has to and no longer by virtue of	825	that automatically loops as long as it has to and no longer by virtue
475	relying on its watchers stopping correctly is a thing of beauty.	826	of relying on its watchers stopping correctly, that is truly a thing of
		827	beauty.
476		828
		829	This function is I<mostly> exception-safe - you can break out of a
		830	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		831	exception and so on. This does not decrement the C<ev_depth> value, nor
		832	will it clear any outstanding C<EVBREAK_ONE> breaks.
		833
477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	834	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
478	those events and any outstanding ones, but will not block your process in	835	those events and any already outstanding ones, but will not wait and
479	case there are no events and will return after one iteration of the loop.	836	block your process in case there are no events and will return after one
		837	iteration of the loop. This is sometimes useful to poll and handle new
		838	events while doing lengthy calculations, to keep the program responsive.
480		839
481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	840	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
482	neccessary) and will handle those and any outstanding ones. It will block	841	necessary) and will handle those and any already outstanding ones. It
483	your process until at least one new event arrives, and will return after	842	will block your process until at least one new event arrives (which could
484	one iteration of the loop. This is useful if you are waiting for some	843	be an event internal to libev itself, so there is no guarantee that a
485	external event in conjunction with something not expressible using other	844	user-registered callback will be called), and will return after one
		845	iteration of the loop.
		846
		847	This is useful if you are waiting for some external event in conjunction
		848	with something not expressible using other libev watchers (i.e. "roll your
486	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	849	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
487	usually a better approach for this kind of thing.	850	usually a better approach for this kind of thing.
488		851
489	Here are the gory details of what C<ev_loop> does:	852	Here are the gory details of what C<ev_run> does (this is for your
		853	understanding, not a guarantee that things will work exactly like this in
		854	future versions):
490		855
		856	- Increment loop depth.
		857	- Reset the ev_break status.
491	- Before the first iteration, call any pending watchers.	858	- Before the first iteration, call any pending watchers.
492	* If there are no active watchers (reference count is zero), return.	859	LOOP:
493	- Queue all prepare watchers and then call all outstanding watchers.	860	- If EVFLAG_FORKCHECK was used, check for a fork.
		861	- If a fork was detected (by any means), queue and call all fork watchers.
		862	- Queue and call all prepare watchers.
		863	- If ev_break was called, goto FINISH.
494	- If we have been forked, recreate the kernel state.	864	- If we have been forked, detach and recreate the kernel state
		865	as to not disturb the other process.
495	- Update the kernel state with all outstanding changes.	866	- Update the kernel state with all outstanding changes.
496	- Update the "event loop time".	867	- Update the "event loop time" (ev_now ()).
497	- Calculate for how long to block.	868	- Calculate for how long to sleep or block, if at all
		869	(active idle watchers, EVRUN_NOWAIT or not having
		870	any active watchers at all will result in not sleeping).
		871	- Sleep if the I/O and timer collect interval say so.
		872	- Increment loop iteration counter.
498	- Block the process, waiting for any events.	873	- Block the process, waiting for any events.
499	- Queue all outstanding I/O (fd) events.	874	- Queue all outstanding I/O (fd) events.
500	- Update the "event loop time" and do time jump handling.	875	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
501	- Queue all outstanding timers.	876	- Queue all expired timers.
502	- Queue all outstanding periodics.	877	- Queue all expired periodics.
503	- If no events are pending now, queue all idle watchers.	878	- Queue all idle watchers with priority higher than that of pending events.
504	- Queue all check watchers.	879	- Queue all check watchers.
505	- Call all queued watchers in reverse order (i.e. check watchers first).	880	- Call all queued watchers in reverse order (i.e. check watchers first).
506	Signals and child watchers are implemented as I/O watchers, and will	881	Signals and child watchers are implemented as I/O watchers, and will
507	be handled here by queueing them when their watcher gets executed.	882	be handled here by queueing them when their watcher gets executed.
508	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	883	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
509	were used, return, otherwise continue with step *.	884	were used, or there are no active watchers, goto FINISH, otherwise
		885	continue with step LOOP.
		886	FINISH:
		887	- Reset the ev_break status iff it was EVBREAK_ONE.
		888	- Decrement the loop depth.
		889	- Return.
510		890
511	Example: Queue some jobs and then loop until no events are outsanding	891	Example: Queue some jobs and then loop until no events are outstanding
512	anymore.	892	anymore.
513		893
514	... queue jobs here, make sure they register event watchers as long	894	... queue jobs here, make sure they register event watchers as long
515	... as they still have work to do (even an idle watcher will do..)	895	... as they still have work to do (even an idle watcher will do..)
516	ev_loop (my_loop, 0);	896	ev_run (my_loop, 0);
517	... jobs done. yeah!	897	... jobs done or somebody called break. yeah!
518		898
519	=item ev_unloop (loop, how)	899	=item ev_break (loop, how)
520		900
521	Can be used to make a call to C<ev_loop> return early (but only after it	901	Can be used to make a call to C<ev_run> return early (but only after it
522	has processed all outstanding events). The C<how> argument must be either	902	has processed all outstanding events). The C<how> argument must be either
523	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	903	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
524	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	904	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		905
		906	This "break state" will be cleared on the next call to C<ev_run>.
		907
		908	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		909	which case it will have no effect.
525		910
526	=item ev_ref (loop)	911	=item ev_ref (loop)
527		912
528	=item ev_unref (loop)	913	=item ev_unref (loop)
529		914
530	Ref/unref can be used to add or remove a reference count on the event	915	Ref/unref can be used to add or remove a reference count on the event
531	loop: Every watcher keeps one reference, and as long as the reference	916	loop: Every watcher keeps one reference, and as long as the reference
532	count is nonzero, C<ev_loop> will not return on its own. If you have	917	count is nonzero, C<ev_run> will not return on its own.
533	a watcher you never unregister that should not keep C<ev_loop> from	918
534	returning, ev_unref() after starting, and ev_ref() before stopping it. For	919	This is useful when you have a watcher that you never intend to
		920	unregister, but that nevertheless should not keep C<ev_run> from
		921	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		922	before stopping it.
		923
535	example, libev itself uses this for its internal signal pipe: It is not	924	As an example, libev itself uses this for its internal signal pipe: It
536	visible to the libev user and should not keep C<ev_loop> from exiting if	925	is not visible to the libev user and should not keep C<ev_run> from
537	no event watchers registered by it are active. It is also an excellent	926	exiting if no event watchers registered by it are active. It is also an
538	way to do this for generic recurring timers or from within third-party	927	excellent way to do this for generic recurring timers or from within
539	libraries. Just remember to I<unref after start> and I<ref before stop>.	928	third-party libraries. Just remember to I<unref after start> and I<ref
		929	before stop> (but only if the watcher wasn't active before, or was active
		930	before, respectively. Note also that libev might stop watchers itself
		931	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		932	in the callback).
540		933
541	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	934	Example: Create a signal watcher, but keep it from keeping C<ev_run>
542	running when nothing else is active.	935	running when nothing else is active.
543		936
544	struct ev_signal exitsig;	937	ev_signal exitsig;
545	ev_signal_init (&exitsig, sig_cb, SIGINT);	938	ev_signal_init (&exitsig, sig_cb, SIGINT);
546	ev_signal_start (loop, &exitsig);	939	ev_signal_start (loop, &exitsig);
547	evf_unref (loop);	940	ev_unref (loop);
548		941
549	Example: For some weird reason, unregister the above signal handler again.	942	Example: For some weird reason, unregister the above signal handler again.
550		943
551	ev_ref (loop);	944	ev_ref (loop);
552	ev_signal_stop (loop, &exitsig);	945	ev_signal_stop (loop, &exitsig);
		946
		947	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		948
		949	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		950
		951	These advanced functions influence the time that libev will spend waiting
		952	for events. Both time intervals are by default C<0>, meaning that libev
		953	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		954	latency.
		955
		956	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		957	allows libev to delay invocation of I/O and timer/periodic callbacks
		958	to increase efficiency of loop iterations (or to increase power-saving
		959	opportunities).
		960
		961	The idea is that sometimes your program runs just fast enough to handle
		962	one (or very few) event(s) per loop iteration. While this makes the
		963	program responsive, it also wastes a lot of CPU time to poll for new
		964	events, especially with backends like C<select ()> which have a high
		965	overhead for the actual polling but can deliver many events at once.
		966
		967	By setting a higher I<io collect interval> you allow libev to spend more
		968	time collecting I/O events, so you can handle more events per iteration,
		969	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		970	C<ev_timer>) will not be affected. Setting this to a non-null value will
		971	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		972	sleep time ensures that libev will not poll for I/O events more often then
		973	once per this interval, on average (as long as the host time resolution is
		974	good enough).
		975
		976	Likewise, by setting a higher I<timeout collect interval> you allow libev
		977	to spend more time collecting timeouts, at the expense of increased
		978	latency/jitter/inexactness (the watcher callback will be called
		979	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		980	value will not introduce any overhead in libev.
		981
		982	Many (busy) programs can usually benefit by setting the I/O collect
		983	interval to a value near C<0.1> or so, which is often enough for
		984	interactive servers (of course not for games), likewise for timeouts. It
		985	usually doesn't make much sense to set it to a lower value than C<0.01>,
		986	as this approaches the timing granularity of most systems. Note that if
		987	you do transactions with the outside world and you can't increase the
		988	parallelity, then this setting will limit your transaction rate (if you
		989	need to poll once per transaction and the I/O collect interval is 0.01,
		990	then you can't do more than 100 transactions per second).
		991
		992	Setting the I<timeout collect interval> can improve the opportunity for
		993	saving power, as the program will "bundle" timer callback invocations that
		994	are "near" in time together, by delaying some, thus reducing the number of
		995	times the process sleeps and wakes up again. Another useful technique to
		996	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		997	they fire on, say, one-second boundaries only.
		998
		999	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1000	more often than 100 times per second:
		1001
		1002	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1003	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1004
		1005	=item ev_invoke_pending (loop)
		1006
		1007	This call will simply invoke all pending watchers while resetting their
		1008	pending state. Normally, C<ev_run> does this automatically when required,
		1009	but when overriding the invoke callback this call comes handy. This
		1010	function can be invoked from a watcher - this can be useful for example
		1011	when you want to do some lengthy calculation and want to pass further
		1012	event handling to another thread (you still have to make sure only one
		1013	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1014
		1015	=item int ev_pending_count (loop)
		1016
		1017	Returns the number of pending watchers - zero indicates that no watchers
		1018	are pending.
		1019
		1020	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1021
		1022	This overrides the invoke pending functionality of the loop: Instead of
		1023	invoking all pending watchers when there are any, C<ev_run> will call
		1024	this callback instead. This is useful, for example, when you want to
		1025	invoke the actual watchers inside another context (another thread etc.).
		1026
		1027	If you want to reset the callback, use C<ev_invoke_pending> as new
		1028	callback.
		1029
		1030	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1031
		1032	Sometimes you want to share the same loop between multiple threads. This
		1033	can be done relatively simply by putting mutex_lock/unlock calls around
		1034	each call to a libev function.
		1035
		1036	However, C<ev_run> can run an indefinite time, so it is not feasible
		1037	to wait for it to return. One way around this is to wake up the event
		1038	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1039	I<release> and I<acquire> callbacks on the loop.
		1040
		1041	When set, then C<release> will be called just before the thread is
		1042	suspended waiting for new events, and C<acquire> is called just
		1043	afterwards.
		1044
		1045	Ideally, C<release> will just call your mutex_unlock function, and
		1046	C<acquire> will just call the mutex_lock function again.
		1047
		1048	While event loop modifications are allowed between invocations of
		1049	C<release> and C<acquire> (that's their only purpose after all), no
		1050	modifications done will affect the event loop, i.e. adding watchers will
		1051	have no effect on the set of file descriptors being watched, or the time
		1052	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1053	to take note of any changes you made.
		1054
		1055	In theory, threads executing C<ev_run> will be async-cancel safe between
		1056	invocations of C<release> and C<acquire>.
		1057
		1058	See also the locking example in the C<THREADS> section later in this
		1059	document.
		1060
		1061	=item ev_set_userdata (loop, void *data)
		1062
		1063	=item void *ev_userdata (loop)
		1064
		1065	Set and retrieve a single C<void *> associated with a loop. When
		1066	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1067	C<0>.
		1068
		1069	These two functions can be used to associate arbitrary data with a loop,
		1070	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1071	C<acquire> callbacks described above, but of course can be (ab-)used for
		1072	any other purpose as well.
		1073
		1074	=item ev_verify (loop)
		1075
		1076	This function only does something when C<EV_VERIFY> support has been
		1077	compiled in, which is the default for non-minimal builds. It tries to go
		1078	through all internal structures and checks them for validity. If anything
		1079	is found to be inconsistent, it will print an error message to standard
		1080	error and call C<abort ()>.
		1081
		1082	This can be used to catch bugs inside libev itself: under normal
		1083	circumstances, this function will never abort as of course libev keeps its
		1084	data structures consistent.
553		1085
554	=back	1086	=back
555		1087
556		1088
557	=head1 ANATOMY OF A WATCHER	1089	=head1 ANATOMY OF A WATCHER
558		1090
		1091	In the following description, uppercase C<TYPE> in names stands for the
		1092	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1093	watchers and C<ev_io_start> for I/O watchers.
		1094
559	A watcher is a structure that you create and register to record your	1095	A watcher is an opaque structure that you allocate and register to record
560	interest in some event. For instance, if you want to wait for STDIN to	1096	your interest in some event. To make a concrete example, imagine you want
561	become readable, you would create an C<ev_io> watcher for that:	1097	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1098	for that:
562		1099
563	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1100	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
564	{	1101	{
565	ev_io_stop (w);	1102	ev_io_stop (w);
566	ev_unloop (loop, EVUNLOOP_ALL);	1103	ev_break (loop, EVBREAK_ALL);
567	}	1104	}
568		1105
569	struct ev_loop *loop = ev_default_loop (0);	1106	struct ev_loop *loop = ev_default_loop (0);
		1107
570	struct ev_io stdin_watcher;	1108	ev_io stdin_watcher;
		1109
571	ev_init (&stdin_watcher, my_cb);	1110	ev_init (&stdin_watcher, my_cb);
572	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1111	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
573	ev_io_start (loop, &stdin_watcher);	1112	ev_io_start (loop, &stdin_watcher);
		1113
574	ev_loop (loop, 0);	1114	ev_run (loop, 0);
575		1115
576	As you can see, you are responsible for allocating the memory for your	1116	As you can see, you are responsible for allocating the memory for your
577	watcher structures (and it is usually a bad idea to do this on the stack,	1117	watcher structures (and it is I<usually> a bad idea to do this on the
578	although this can sometimes be quite valid).	1118	stack).
579		1119
		1120	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1121	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1122
580	Each watcher structure must be initialised by a call to C<ev_init	1123	Each watcher structure must be initialised by a call to C<ev_init (watcher
581	(watcher *, callback)>, which expects a callback to be provided. This	1124	*, callback)>, which expects a callback to be provided. This callback is
582	callback gets invoked each time the event occurs (or, in the case of io	1125	invoked each time the event occurs (or, in the case of I/O watchers, each
583	watchers, each time the event loop detects that the file descriptor given	1126	time the event loop detects that the file descriptor given is readable
584	is readable and/or writable).	1127	and/or writable).
585		1128
586	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1129	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
587	with arguments specific to this watcher type. There is also a macro	1130	macro to configure it, with arguments specific to the watcher type. There
588	to combine initialisation and setting in one call: C<< ev_<type>_init	1131	is also a macro to combine initialisation and setting in one call: C<<
589	(watcher *, callback, ...) >>.	1132	ev_TYPE_init (watcher *, callback, ...) >>.
590		1133
591	To make the watcher actually watch out for events, you have to start it	1134	To make the watcher actually watch out for events, you have to start it
592	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1135	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
593	*) >>), and you can stop watching for events at any time by calling the	1136	*) >>), and you can stop watching for events at any time by calling the
594	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1137	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
595		1138
596	As long as your watcher is active (has been started but not stopped) you	1139	As long as your watcher is active (has been started but not stopped) you
597	must not touch the values stored in it. Most specifically you must never	1140	must not touch the values stored in it. Most specifically you must never
598	reinitialise it or call its C<set> macro.	1141	reinitialise it or call its C<ev_TYPE_set> macro.
599		1142
600	Each and every callback receives the event loop pointer as first, the	1143	Each and every callback receives the event loop pointer as first, the
601	registered watcher structure as second, and a bitset of received events as	1144	registered watcher structure as second, and a bitset of received events as
602	third argument.	1145	third argument.
603		1146
…		…
612	=item C<EV_WRITE>	1155	=item C<EV_WRITE>
613		1156
614	The file descriptor in the C<ev_io> watcher has become readable and/or	1157	The file descriptor in the C<ev_io> watcher has become readable and/or
615	writable.	1158	writable.
616		1159
617	=item C<EV_TIMEOUT>	1160	=item C<EV_TIMER>
618		1161
619	The C<ev_timer> watcher has timed out.	1162	The C<ev_timer> watcher has timed out.
620		1163
621	=item C<EV_PERIODIC>	1164	=item C<EV_PERIODIC>
622		1165
…		…
640		1183
641	=item C<EV_PREPARE>	1184	=item C<EV_PREPARE>
642		1185
643	=item C<EV_CHECK>	1186	=item C<EV_CHECK>
644		1187
645	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1188	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
646	to gather new events, and all C<ev_check> watchers are invoked just after	1189	gather new events, and all C<ev_check> watchers are queued (not invoked)
647	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1190	just after C<ev_run> has gathered them, but before it queues any callbacks
		1191	for any received events. That means C<ev_prepare> watchers are the last
		1192	watchers invoked before the event loop sleeps or polls for new events, and
		1193	C<ev_check> watchers will be invoked before any other watchers of the same
		1194	or lower priority within an event loop iteration.
		1195
648	received events. Callbacks of both watcher types can start and stop as	1196	Callbacks of both watcher types can start and stop as many watchers as
649	many watchers as they want, and all of them will be taken into account	1197	they want, and all of them will be taken into account (for example, a
650	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1198	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
651	C<ev_loop> from blocking).	1199	blocking).
652		1200
653	=item C<EV_EMBED>	1201	=item C<EV_EMBED>
654		1202
655	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1203	The embedded event loop specified in the C<ev_embed> watcher needs attention.
656		1204
657	=item C<EV_FORK>	1205	=item C<EV_FORK>
658		1206
659	The event loop has been resumed in the child process after fork (see	1207	The event loop has been resumed in the child process after fork (see
660	C<ev_fork>).	1208	C<ev_fork>).
661		1209
		1210	=item C<EV_CLEANUP>
		1211
		1212	The event loop is about to be destroyed (see C<ev_cleanup>).
		1213
		1214	=item C<EV_ASYNC>
		1215
		1216	The given async watcher has been asynchronously notified (see C<ev_async>).
		1217
		1218	=item C<EV_CUSTOM>
		1219
		1220	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1221	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1222
662	=item C<EV_ERROR>	1223	=item C<EV_ERROR>
663		1224
664	An unspecified error has occured, the watcher has been stopped. This might	1225	An unspecified error has occurred, the watcher has been stopped. This might
665	happen because the watcher could not be properly started because libev	1226	happen because the watcher could not be properly started because libev
666	ran out of memory, a file descriptor was found to be closed or any other	1227	ran out of memory, a file descriptor was found to be closed or any other
		1228	problem. Libev considers these application bugs.
		1229
667	problem. You best act on it by reporting the problem and somehow coping	1230	You best act on it by reporting the problem and somehow coping with the
668	with the watcher being stopped.	1231	watcher being stopped. Note that well-written programs should not receive
		1232	an error ever, so when your watcher receives it, this usually indicates a
		1233	bug in your program.
669		1234
670	Libev will usually signal a few "dummy" events together with an error,	1235	Libev will usually signal a few "dummy" events together with an error, for
671	for example it might indicate that a fd is readable or writable, and if	1236	example it might indicate that a fd is readable or writable, and if your
672	your callbacks is well-written it can just attempt the operation and cope	1237	callbacks is well-written it can just attempt the operation and cope with
673	with the error from read() or write(). This will not work in multithreaded	1238	the error from read() or write(). This will not work in multi-threaded
674	programs, though, so beware.	1239	programs, though, as the fd could already be closed and reused for another
		1240	thing, so beware.
675		1241
676	=back	1242	=back
677		1243
678	=head2 GENERIC WATCHER FUNCTIONS	1244	=head2 GENERIC WATCHER FUNCTIONS
679
680	In the following description, C<TYPE> stands for the watcher type,
681	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
682		1245
683	=over 4	1246	=over 4
684		1247
685	=item C<ev_init> (ev_TYPE *watcher, callback)	1248	=item C<ev_init> (ev_TYPE *watcher, callback)
686		1249
…		…
692	which rolls both calls into one.	1255	which rolls both calls into one.
693		1256
694	You can reinitialise a watcher at any time as long as it has been stopped	1257	You can reinitialise a watcher at any time as long as it has been stopped
695	(or never started) and there are no pending events outstanding.	1258	(or never started) and there are no pending events outstanding.
696		1259
697	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1260	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
698	int revents)>.	1261	int revents)>.
699		1262
		1263	Example: Initialise an C<ev_io> watcher in two steps.
		1264
		1265	ev_io w;
		1266	ev_init (&w, my_cb);
		1267	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1268
700	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1269	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
701		1270
702	This macro initialises the type-specific parts of a watcher. You need to	1271	This macro initialises the type-specific parts of a watcher. You need to
703	call C<ev_init> at least once before you call this macro, but you can	1272	call C<ev_init> at least once before you call this macro, but you can
704	call C<ev_TYPE_set> any number of times. You must not, however, call this	1273	call C<ev_TYPE_set> any number of times. You must not, however, call this
705	macro on a watcher that is active (it can be pending, however, which is a	1274	macro on a watcher that is active (it can be pending, however, which is a
706	difference to the C<ev_init> macro).	1275	difference to the C<ev_init> macro).
707		1276
708	Although some watcher types do not have type-specific arguments	1277	Although some watcher types do not have type-specific arguments
709	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1278	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
710		1279
		1280	See C<ev_init>, above, for an example.
		1281
711	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1282	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
712		1283
713	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1284	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
714	calls into a single call. This is the most convinient method to initialise	1285	calls into a single call. This is the most convenient method to initialise
715	a watcher. The same limitations apply, of course.	1286	a watcher. The same limitations apply, of course.
716		1287
		1288	Example: Initialise and set an C<ev_io> watcher in one step.
		1289
		1290	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1291
717	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1292	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
718		1293
719	Starts (activates) the given watcher. Only active watchers will receive	1294	Starts (activates) the given watcher. Only active watchers will receive
720	events. If the watcher is already active nothing will happen.	1295	events. If the watcher is already active nothing will happen.
721		1296
		1297	Example: Start the C<ev_io> watcher that is being abused as example in this
		1298	whole section.
		1299
		1300	ev_io_start (EV_DEFAULT_UC, &w);
		1301
722	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1302	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
723		1303
724	Stops the given watcher again (if active) and clears the pending	1304	Stops the given watcher if active, and clears the pending status (whether
		1305	the watcher was active or not).
		1306
725	status. It is possible that stopped watchers are pending (for example,	1307	It is possible that stopped watchers are pending - for example,
726	non-repeating timers are being stopped when they become pending), but	1308	non-repeating timers are being stopped when they become pending - but
727	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1309	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
728	you want to free or reuse the memory used by the watcher it is therefore a	1310	pending. If you want to free or reuse the memory used by the watcher it is
729	good idea to always call its C<ev_TYPE_stop> function.	1311	therefore a good idea to always call its C<ev_TYPE_stop> function.
730		1312
731	=item bool ev_is_active (ev_TYPE *watcher)	1313	=item bool ev_is_active (ev_TYPE *watcher)
732		1314
733	Returns a true value iff the watcher is active (i.e. it has been started	1315	Returns a true value iff the watcher is active (i.e. it has been started
734	and not yet been stopped). As long as a watcher is active you must not modify	1316	and not yet been stopped). As long as a watcher is active you must not modify
…		…
745		1327
746	=item callback ev_cb (ev_TYPE *watcher)	1328	=item callback ev_cb (ev_TYPE *watcher)
747		1329
748	Returns the callback currently set on the watcher.	1330	Returns the callback currently set on the watcher.
749		1331
750	=item ev_cb_set (ev_TYPE *watcher, callback)	1332	=item ev_set_cb (ev_TYPE *watcher, callback)
751		1333
752	Change the callback. You can change the callback at virtually any time	1334	Change the callback. You can change the callback at virtually any time
753	(modulo threads).	1335	(modulo threads).
754		1336
755	=item ev_set_priority (ev_TYPE *watcher, priority)	1337	=item ev_set_priority (ev_TYPE *watcher, int priority)
756		1338
757	=item int ev_priority (ev_TYPE *watcher)	1339	=item int ev_priority (ev_TYPE *watcher)
758		1340
759	Set and query the priority of the watcher. The priority is a small	1341	Set and query the priority of the watcher. The priority is a small
760	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1342	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
761	(default: C<-2>). Pending watchers with higher priority will be invoked	1343	(default: C<-2>). Pending watchers with higher priority will be invoked
762	before watchers with lower priority, but priority will not keep watchers	1344	before watchers with lower priority, but priority will not keep watchers
763	from being executed (except for C<ev_idle> watchers).	1345	from being executed (except for C<ev_idle> watchers).
764		1346
765	This means that priorities are I<only> used for ordering callback
766	invocation after new events have been received. This is useful, for
767	example, to reduce latency after idling, or more often, to bind two
768	watchers on the same event and make sure one is called first.
769
770	If you need to suppress invocation when higher priority events are pending	1347	If you need to suppress invocation when higher priority events are pending
771	you need to look at C<ev_idle> watchers, which provide this functionality.	1348	you need to look at C<ev_idle> watchers, which provide this functionality.
772		1349
773	You I<must not> change the priority of a watcher as long as it is active or	1350	You I<must not> change the priority of a watcher as long as it is active or
774	pending.	1351	pending.
775		1352
		1353	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1354	fine, as long as you do not mind that the priority value you query might
		1355	or might not have been clamped to the valid range.
		1356
776	The default priority used by watchers when no priority has been set is	1357	The default priority used by watchers when no priority has been set is
777	always C<0>, which is supposed to not be too high and not be too low :).	1358	always C<0>, which is supposed to not be too high and not be too low :).
778		1359
779	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1360	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
780	fine, as long as you do not mind that the priority value you query might	1361	priorities.
781	or might not have been adjusted to be within valid range.
782		1362
783	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1363	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
784		1364
785	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1365	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
786	C<loop> nor C<revents> need to be valid as long as the watcher callback	1366	C<loop> nor C<revents> need to be valid as long as the watcher callback
787	can deal with that fact.	1367	can deal with that fact, as both are simply passed through to the
		1368	callback.
788		1369
789	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1370	=item int ev_clear_pending (loop, ev_TYPE *watcher)
790		1371
791	If the watcher is pending, this function returns clears its pending status	1372	If the watcher is pending, this function clears its pending status and
792	and returns its C<revents> bitset (as if its callback was invoked). If the	1373	returns its C<revents> bitset (as if its callback was invoked). If the
793	watcher isn't pending it does nothing and returns C<0>.	1374	watcher isn't pending it does nothing and returns C<0>.
794		1375
		1376	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1377	callback to be invoked, which can be accomplished with this function.
		1378
		1379	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1380
		1381	Feeds the given event set into the event loop, as if the specified event
		1382	had happened for the specified watcher (which must be a pointer to an
		1383	initialised but not necessarily started event watcher). Obviously you must
		1384	not free the watcher as long as it has pending events.
		1385
		1386	Stopping the watcher, letting libev invoke it, or calling
		1387	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1388	not started in the first place.
		1389
		1390	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1391	functions that do not need a watcher.
		1392
795	=back	1393	=back
796		1394
		1395	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1396	OWN COMPOSITE WATCHERS> idioms.
797		1397
798	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1398	=head2 WATCHER STATES
799		1399
800	Each watcher has, by default, a member C<void *data> that you can change	1400	There are various watcher states mentioned throughout this manual -
801	and read at any time, libev will completely ignore it. This can be used	1401	active, pending and so on. In this section these states and the rules to
802	to associate arbitrary data with your watcher. If you need more data and	1402	transition between them will be described in more detail - and while these
803	don't want to allocate memory and store a pointer to it in that data	1403	rules might look complicated, they usually do "the right thing".
804	member, you can also "subclass" the watcher type and provide your own
805	data:
806		1404
807	struct my_io	1405	=over 4
808	{
809	struct ev_io io;
810	int otherfd;
811	void *somedata;
812	struct whatever *mostinteresting;
813	}
814		1406
815	And since your callback will be called with a pointer to the watcher, you	1407	=item initialised
816	can cast it back to your own type:
817		1408
818	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1409	Before a watcher can be registered with the event loop it has to be
819	{	1410	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
820	struct my_io *w = (struct my_io *)w_;	1411	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
821	...
822	}
823		1412
824	More interesting and less C-conformant ways of casting your callback type	1413	In this state it is simply some block of memory that is suitable for
825	instead have been omitted.	1414	use in an event loop. It can be moved around, freed, reused etc. at
		1415	will - as long as you either keep the memory contents intact, or call
		1416	C<ev_TYPE_init> again.
826		1417
827	Another common scenario is having some data structure with multiple	1418	=item started/running/active
828	watchers:
829		1419
830	struct my_biggy	1420	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
831	{	1421	property of the event loop, and is actively waiting for events. While in
832	int some_data;	1422	this state it cannot be accessed (except in a few documented ways), moved,
833	ev_timer t1;	1423	freed or anything else - the only legal thing is to keep a pointer to it,
834	ev_timer t2;	1424	and call libev functions on it that are documented to work on active watchers.
835	}
836		1425
837	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1426	=item pending
838	you need to use C<offsetof>:
839		1427
840	#include <stddef.h>	1428	If a watcher is active and libev determines that an event it is interested
		1429	in has occurred (such as a timer expiring), it will become pending. It will
		1430	stay in this pending state until either it is stopped or its callback is
		1431	about to be invoked, so it is not normally pending inside the watcher
		1432	callback.
841		1433
		1434	The watcher might or might not be active while it is pending (for example,
		1435	an expired non-repeating timer can be pending but no longer active). If it
		1436	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1437	but it is still property of the event loop at this time, so cannot be
		1438	moved, freed or reused. And if it is active the rules described in the
		1439	previous item still apply.
		1440
		1441	It is also possible to feed an event on a watcher that is not active (e.g.
		1442	via C<ev_feed_event>), in which case it becomes pending without being
		1443	active.
		1444
		1445	=item stopped
		1446
		1447	A watcher can be stopped implicitly by libev (in which case it might still
		1448	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1449	latter will clear any pending state the watcher might be in, regardless
		1450	of whether it was active or not, so stopping a watcher explicitly before
		1451	freeing it is often a good idea.
		1452
		1453	While stopped (and not pending) the watcher is essentially in the
		1454	initialised state, that is, it can be reused, moved, modified in any way
		1455	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1456	it again).
		1457
		1458	=back
		1459
		1460	=head2 WATCHER PRIORITY MODELS
		1461
		1462	Many event loops support I<watcher priorities>, which are usually small
		1463	integers that influence the ordering of event callback invocation
		1464	between watchers in some way, all else being equal.
		1465
		1466	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1467	description for the more technical details such as the actual priority
		1468	range.
		1469
		1470	There are two common ways how these these priorities are being interpreted
		1471	by event loops:
		1472
		1473	In the more common lock-out model, higher priorities "lock out" invocation
		1474	of lower priority watchers, which means as long as higher priority
		1475	watchers receive events, lower priority watchers are not being invoked.
		1476
		1477	The less common only-for-ordering model uses priorities solely to order
		1478	callback invocation within a single event loop iteration: Higher priority
		1479	watchers are invoked before lower priority ones, but they all get invoked
		1480	before polling for new events.
		1481
		1482	Libev uses the second (only-for-ordering) model for all its watchers
		1483	except for idle watchers (which use the lock-out model).
		1484
		1485	The rationale behind this is that implementing the lock-out model for
		1486	watchers is not well supported by most kernel interfaces, and most event
		1487	libraries will just poll for the same events again and again as long as
		1488	their callbacks have not been executed, which is very inefficient in the
		1489	common case of one high-priority watcher locking out a mass of lower
		1490	priority ones.
		1491
		1492	Static (ordering) priorities are most useful when you have two or more
		1493	watchers handling the same resource: a typical usage example is having an
		1494	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1495	timeouts. Under load, data might be received while the program handles
		1496	other jobs, but since timers normally get invoked first, the timeout
		1497	handler will be executed before checking for data. In that case, giving
		1498	the timer a lower priority than the I/O watcher ensures that I/O will be
		1499	handled first even under adverse conditions (which is usually, but not
		1500	always, what you want).
		1501
		1502	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1503	will only be executed when no same or higher priority watchers have
		1504	received events, they can be used to implement the "lock-out" model when
		1505	required.
		1506
		1507	For example, to emulate how many other event libraries handle priorities,
		1508	you can associate an C<ev_idle> watcher to each such watcher, and in
		1509	the normal watcher callback, you just start the idle watcher. The real
		1510	processing is done in the idle watcher callback. This causes libev to
		1511	continuously poll and process kernel event data for the watcher, but when
		1512	the lock-out case is known to be rare (which in turn is rare :), this is
		1513	workable.
		1514
		1515	Usually, however, the lock-out model implemented that way will perform
		1516	miserably under the type of load it was designed to handle. In that case,
		1517	it might be preferable to stop the real watcher before starting the
		1518	idle watcher, so the kernel will not have to process the event in case
		1519	the actual processing will be delayed for considerable time.
		1520
		1521	Here is an example of an I/O watcher that should run at a strictly lower
		1522	priority than the default, and which should only process data when no
		1523	other events are pending:
		1524
		1525	ev_idle idle; // actual processing watcher
		1526	ev_io io; // actual event watcher
		1527
842	static void	1528	static void
843	t1_cb (EV_P_ struct ev_timer *w, int revents)	1529	io_cb (EV_P_ ev_io *w, int revents)
844	{	1530	{
845	struct my_biggy big = (struct my_biggy *	1531	// stop the I/O watcher, we received the event, but
846	(((char *)w) - offsetof (struct my_biggy, t1));	1532	// are not yet ready to handle it.
		1533	ev_io_stop (EV_A_ w);
		1534
		1535	// start the idle watcher to handle the actual event.
		1536	// it will not be executed as long as other watchers
		1537	// with the default priority are receiving events.
		1538	ev_idle_start (EV_A_ &idle);
847	}	1539	}
848		1540
849	static void	1541	static void
850	t2_cb (EV_P_ struct ev_timer *w, int revents)	1542	idle_cb (EV_P_ ev_idle *w, int revents)
851	{	1543	{
852	struct my_biggy big = (struct my_biggy *	1544	// actual processing
853	(((char *)w) - offsetof (struct my_biggy, t2));	1545	read (STDIN_FILENO, ...);
		1546
		1547	// have to start the I/O watcher again, as
		1548	// we have handled the event
		1549	ev_io_start (EV_P_ &io);
854	}	1550	}
		1551
		1552	// initialisation
		1553	ev_idle_init (&idle, idle_cb);
		1554	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1555	ev_io_start (EV_DEFAULT_ &io);
		1556
		1557	In the "real" world, it might also be beneficial to start a timer, so that
		1558	low-priority connections can not be locked out forever under load. This
		1559	enables your program to keep a lower latency for important connections
		1560	during short periods of high load, while not completely locking out less
		1561	important ones.
855		1562
856		1563
857	=head1 WATCHER TYPES	1564	=head1 WATCHER TYPES
858		1565
859	This section describes each watcher in detail, but will not repeat	1566	This section describes each watcher in detail, but will not repeat
…		…
883	In general you can register as many read and/or write event watchers per	1590	In general you can register as many read and/or write event watchers per
884	fd as you want (as long as you don't confuse yourself). Setting all file	1591	fd as you want (as long as you don't confuse yourself). Setting all file
885	descriptors to non-blocking mode is also usually a good idea (but not	1592	descriptors to non-blocking mode is also usually a good idea (but not
886	required if you know what you are doing).	1593	required if you know what you are doing).
887		1594
888	You have to be careful with dup'ed file descriptors, though. Some backends
889	(the linux epoll backend is a notable example) cannot handle dup'ed file
890	descriptors correctly if you register interest in two or more fds pointing
891	to the same underlying file/socket/etc. description (that is, they share
892	the same underlying "file open").
893
894	If you must do this, then force the use of a known-to-be-good backend
895	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
896	C<EVBACKEND_POLL>).
897
898	Another thing you have to watch out for is that it is quite easy to	1595	Another thing you have to watch out for is that it is quite easy to
899	receive "spurious" readyness notifications, that is your callback might	1596	receive "spurious" readiness notifications, that is, your callback might
900	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1597	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
901	because there is no data. Not only are some backends known to create a	1598	because there is no data. It is very easy to get into this situation even
902	lot of those (for example solaris ports), it is very easy to get into	1599	with a relatively standard program structure. Thus it is best to always
903	this situation even with a relatively standard program structure. Thus	1600	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
904	it is best to always use non-blocking I/O: An extra C<read>(2) returning
905	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1601	preferable to a program hanging until some data arrives.
906		1602
907	If you cannot run the fd in non-blocking mode (for example you should not	1603	If you cannot run the fd in non-blocking mode (for example you should
908	play around with an Xlib connection), then you have to seperately re-test	1604	not play around with an Xlib connection), then you have to separately
909	whether a file descriptor is really ready with a known-to-be good interface	1605	re-test whether a file descriptor is really ready with a known-to-be good
910	such as poll (fortunately in our Xlib example, Xlib already does this on	1606	interface such as poll (fortunately in the case of Xlib, it already does
911	its own, so its quite safe to use).	1607	this on its own, so its quite safe to use). Some people additionally
		1608	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1609	indefinitely.
		1610
		1611	But really, best use non-blocking mode.
		1612
		1613	=head3 The special problem of disappearing file descriptors
		1614
		1615	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1616	descriptor (either due to calling C<close> explicitly or any other means,
		1617	such as C<dup2>). The reason is that you register interest in some file
		1618	descriptor, but when it goes away, the operating system will silently drop
		1619	this interest. If another file descriptor with the same number then is
		1620	registered with libev, there is no efficient way to see that this is, in
		1621	fact, a different file descriptor.
		1622
		1623	To avoid having to explicitly tell libev about such cases, libev follows
		1624	the following policy: Each time C<ev_io_set> is being called, libev
		1625	will assume that this is potentially a new file descriptor, otherwise
		1626	it is assumed that the file descriptor stays the same. That means that
		1627	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1628	descriptor even if the file descriptor number itself did not change.
		1629
		1630	This is how one would do it normally anyway, the important point is that
		1631	the libev application should not optimise around libev but should leave
		1632	optimisations to libev.
		1633
		1634	=head3 The special problem of dup'ed file descriptors
		1635
		1636	Some backends (e.g. epoll), cannot register events for file descriptors,
		1637	but only events for the underlying file descriptions. That means when you
		1638	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1639	events for them, only one file descriptor might actually receive events.
		1640
		1641	There is no workaround possible except not registering events
		1642	for potentially C<dup ()>'ed file descriptors, or to resort to
		1643	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1644
		1645	=head3 The special problem of files
		1646
		1647	Many people try to use C<select> (or libev) on file descriptors
		1648	representing files, and expect it to become ready when their program
		1649	doesn't block on disk accesses (which can take a long time on their own).
		1650
		1651	However, this cannot ever work in the "expected" way - you get a readiness
		1652	notification as soon as the kernel knows whether and how much data is
		1653	there, and in the case of open files, that's always the case, so you
		1654	always get a readiness notification instantly, and your read (or possibly
		1655	write) will still block on the disk I/O.
		1656
		1657	Another way to view it is that in the case of sockets, pipes, character
		1658	devices and so on, there is another party (the sender) that delivers data
		1659	on its own, but in the case of files, there is no such thing: the disk
		1660	will not send data on its own, simply because it doesn't know what you
		1661	wish to read - you would first have to request some data.
		1662
		1663	Since files are typically not-so-well supported by advanced notification
		1664	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1665	to files, even though you should not use it. The reason for this is
		1666	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1667	usually a tty, often a pipe, but also sometimes files or special devices
		1668	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1669	F</dev/urandom>), and even though the file might better be served with
		1670	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1671	it "just works" instead of freezing.
		1672
		1673	So avoid file descriptors pointing to files when you know it (e.g. use
		1674	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1675	when you rarely read from a file instead of from a socket, and want to
		1676	reuse the same code path.
		1677
		1678	=head3 The special problem of fork
		1679
		1680	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1681	useless behaviour. Libev fully supports fork, but needs to be told about
		1682	it in the child if you want to continue to use it in the child.
		1683
		1684	To support fork in your child processes, you have to call C<ev_loop_fork
		1685	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1686	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1687
		1688	=head3 The special problem of SIGPIPE
		1689
		1690	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1691	when writing to a pipe whose other end has been closed, your program gets
		1692	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1693	this is sensible behaviour, for daemons, this is usually undesirable.
		1694
		1695	So when you encounter spurious, unexplained daemon exits, make sure you
		1696	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1697	somewhere, as that would have given you a big clue).
		1698
		1699	=head3 The special problem of accept()ing when you can't
		1700
		1701	Many implementations of the POSIX C<accept> function (for example,
		1702	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1703	connection from the pending queue in all error cases.
		1704
		1705	For example, larger servers often run out of file descriptors (because
		1706	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1707	rejecting the connection, leading to libev signalling readiness on
		1708	the next iteration again (the connection still exists after all), and
		1709	typically causing the program to loop at 100% CPU usage.
		1710
		1711	Unfortunately, the set of errors that cause this issue differs between
		1712	operating systems, there is usually little the app can do to remedy the
		1713	situation, and no known thread-safe method of removing the connection to
		1714	cope with overload is known (to me).
		1715
		1716	One of the easiest ways to handle this situation is to just ignore it
		1717	- when the program encounters an overload, it will just loop until the
		1718	situation is over. While this is a form of busy waiting, no OS offers an
		1719	event-based way to handle this situation, so it's the best one can do.
		1720
		1721	A better way to handle the situation is to log any errors other than
		1722	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1723	messages, and continue as usual, which at least gives the user an idea of
		1724	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1725	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1726	usage.
		1727
		1728	If your program is single-threaded, then you could also keep a dummy file
		1729	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1730	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1731	close that fd, and create a new dummy fd. This will gracefully refuse
		1732	clients under typical overload conditions.
		1733
		1734	The last way to handle it is to simply log the error and C<exit>, as
		1735	is often done with C<malloc> failures, but this results in an easy
		1736	opportunity for a DoS attack.
		1737
		1738	=head3 Watcher-Specific Functions
912		1739
913	=over 4	1740	=over 4
914		1741
915	=item ev_io_init (ev_io *, callback, int fd, int events)	1742	=item ev_io_init (ev_io *, callback, int fd, int events)
916		1743
917	=item ev_io_set (ev_io *, int fd, int events)	1744	=item ev_io_set (ev_io *, int fd, int events)
918		1745
919	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1746	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
920	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1747	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
921	C<EV_READ | EV_WRITE> to receive the given events.	1748	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
922		1749
923	=item int fd [read-only]	1750	=item int fd [read-only]
924		1751
925	The file descriptor being watched.	1752	The file descriptor being watched.
926		1753
927	=item int events [read-only]	1754	=item int events [read-only]
928		1755
929	The events being watched.	1756	The events being watched.
930		1757
931	=back	1758	=back
		1759
		1760	=head3 Examples
932		1761
933	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1762	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
934	readable, but only once. Since it is likely line-buffered, you could	1763	readable, but only once. Since it is likely line-buffered, you could
935	attempt to read a whole line in the callback.	1764	attempt to read a whole line in the callback.
936		1765
937	static void	1766	static void
938	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1767	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
939	{	1768	{
940	ev_io_stop (loop, w);	1769	ev_io_stop (loop, w);
941	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1770	.. read from stdin here (or from w->fd) and handle any I/O errors
942	}	1771	}
943		1772
944	...	1773	...
945	struct ev_loop *loop = ev_default_init (0);	1774	struct ev_loop *loop = ev_default_init (0);
946	struct ev_io stdin_readable;	1775	ev_io stdin_readable;
947	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1776	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
948	ev_io_start (loop, &stdin_readable);	1777	ev_io_start (loop, &stdin_readable);
949	ev_loop (loop, 0);	1778	ev_run (loop, 0);
950		1779
951		1780
952	=head2 C<ev_timer> - relative and optionally repeating timeouts	1781	=head2 C<ev_timer> - relative and optionally repeating timeouts
953		1782
954	Timer watchers are simple relative timers that generate an event after a	1783	Timer watchers are simple relative timers that generate an event after a
955	given time, and optionally repeating in regular intervals after that.	1784	given time, and optionally repeating in regular intervals after that.
956		1785
957	The timers are based on real time, that is, if you register an event that	1786	The timers are based on real time, that is, if you register an event that
958	times out after an hour and you reset your system clock to last years	1787	times out after an hour and you reset your system clock to January last
959	time, it will still time out after (roughly) and hour. "Roughly" because	1788	year, it will still time out after (roughly) one hour. "Roughly" because
960	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1789	detecting time jumps is hard, and some inaccuracies are unavoidable (the
961	monotonic clock option helps a lot here).	1790	monotonic clock option helps a lot here).
		1791
		1792	The callback is guaranteed to be invoked only I<after> its timeout has
		1793	passed (not I<at>, so on systems with very low-resolution clocks this
		1794	might introduce a small delay, see "the special problem of being too
		1795	early", below). If multiple timers become ready during the same loop
		1796	iteration then the ones with earlier time-out values are invoked before
		1797	ones of the same priority with later time-out values (but this is no
		1798	longer true when a callback calls C<ev_run> recursively).
		1799
		1800	=head3 Be smart about timeouts
		1801
		1802	Many real-world problems involve some kind of timeout, usually for error
		1803	recovery. A typical example is an HTTP request - if the other side hangs,
		1804	you want to raise some error after a while.
		1805
		1806	What follows are some ways to handle this problem, from obvious and
		1807	inefficient to smart and efficient.
		1808
		1809	In the following, a 60 second activity timeout is assumed - a timeout that
		1810	gets reset to 60 seconds each time there is activity (e.g. each time some
		1811	data or other life sign was received).
		1812
		1813	=over 4
		1814
		1815	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1816
		1817	This is the most obvious, but not the most simple way: In the beginning,
		1818	start the watcher:
		1819
		1820	ev_timer_init (timer, callback, 60., 0.);
		1821	ev_timer_start (loop, timer);
		1822
		1823	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1824	and start it again:
		1825
		1826	ev_timer_stop (loop, timer);
		1827	ev_timer_set (timer, 60., 0.);
		1828	ev_timer_start (loop, timer);
		1829
		1830	This is relatively simple to implement, but means that each time there is
		1831	some activity, libev will first have to remove the timer from its internal
		1832	data structure and then add it again. Libev tries to be fast, but it's
		1833	still not a constant-time operation.
		1834
		1835	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1836
		1837	This is the easiest way, and involves using C<ev_timer_again> instead of
		1838	C<ev_timer_start>.
		1839
		1840	To implement this, configure an C<ev_timer> with a C<repeat> value
		1841	of C<60> and then call C<ev_timer_again> at start and each time you
		1842	successfully read or write some data. If you go into an idle state where
		1843	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1844	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1845
		1846	That means you can ignore both the C<ev_timer_start> function and the
		1847	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1848	member and C<ev_timer_again>.
		1849
		1850	At start:
		1851
		1852	ev_init (timer, callback);
		1853	timer->repeat = 60.;
		1854	ev_timer_again (loop, timer);
		1855
		1856	Each time there is some activity:
		1857
		1858	ev_timer_again (loop, timer);
		1859
		1860	It is even possible to change the time-out on the fly, regardless of
		1861	whether the watcher is active or not:
		1862
		1863	timer->repeat = 30.;
		1864	ev_timer_again (loop, timer);
		1865
		1866	This is slightly more efficient then stopping/starting the timer each time
		1867	you want to modify its timeout value, as libev does not have to completely
		1868	remove and re-insert the timer from/into its internal data structure.
		1869
		1870	It is, however, even simpler than the "obvious" way to do it.
		1871
		1872	=item 3. Let the timer time out, but then re-arm it as required.
		1873
		1874	This method is more tricky, but usually most efficient: Most timeouts are
		1875	relatively long compared to the intervals between other activity - in
		1876	our example, within 60 seconds, there are usually many I/O events with
		1877	associated activity resets.
		1878
		1879	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1880	but remember the time of last activity, and check for a real timeout only
		1881	within the callback:
		1882
		1883	ev_tstamp timeout = 60.;
		1884	ev_tstamp last_activity; // time of last activity
		1885	ev_timer timer;
		1886
		1887	static void
		1888	callback (EV_P_ ev_timer *w, int revents)
		1889	{
		1890	// calculate when the timeout would happen
		1891	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1892
		1893	// if negative, it means we the timeout already occurred
		1894	if (after < 0.)
		1895	{
		1896	// timeout occurred, take action
		1897	}
		1898	else
		1899	{
		1900	// callback was invoked, but there was some recent
		1901	// activity. simply restart the timer to time out
		1902	// after "after" seconds, which is the earliest time
		1903	// the timeout can occur.
		1904	ev_timer_set (w, after, 0.);
		1905	ev_timer_start (EV_A_ w);
		1906	}
		1907	}
		1908
		1909	To summarise the callback: first calculate in how many seconds the
		1910	timeout will occur (by calculating the absolute time when it would occur,
		1911	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1912	(EV_A)> from that).
		1913
		1914	If this value is negative, then we are already past the timeout, i.e. we
		1915	timed out, and need to do whatever is needed in this case.
		1916
		1917	Otherwise, we now the earliest time at which the timeout would trigger,
		1918	and simply start the timer with this timeout value.
		1919
		1920	In other words, each time the callback is invoked it will check whether
		1921	the timeout occurred. If not, it will simply reschedule itself to check
		1922	again at the earliest time it could time out. Rinse. Repeat.
		1923
		1924	This scheme causes more callback invocations (about one every 60 seconds
		1925	minus half the average time between activity), but virtually no calls to
		1926	libev to change the timeout.
		1927
		1928	To start the machinery, simply initialise the watcher and set
		1929	C<last_activity> to the current time (meaning there was some activity just
		1930	now), then call the callback, which will "do the right thing" and start
		1931	the timer:
		1932
		1933	last_activity = ev_now (EV_A);
		1934	ev_init (&timer, callback);
		1935	callback (EV_A_ &timer, 0);
		1936
		1937	When there is some activity, simply store the current time in
		1938	C<last_activity>, no libev calls at all:
		1939
		1940	if (activity detected)
		1941	last_activity = ev_now (EV_A);
		1942
		1943	When your timeout value changes, then the timeout can be changed by simply
		1944	providing a new value, stopping the timer and calling the callback, which
		1945	will again do the right thing (for example, time out immediately :).
		1946
		1947	timeout = new_value;
		1948	ev_timer_stop (EV_A_ &timer);
		1949	callback (EV_A_ &timer, 0);
		1950
		1951	This technique is slightly more complex, but in most cases where the
		1952	time-out is unlikely to be triggered, much more efficient.
		1953
		1954	=item 4. Wee, just use a double-linked list for your timeouts.
		1955
		1956	If there is not one request, but many thousands (millions...), all
		1957	employing some kind of timeout with the same timeout value, then one can
		1958	do even better:
		1959
		1960	When starting the timeout, calculate the timeout value and put the timeout
		1961	at the I<end> of the list.
		1962
		1963	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1964	the list is expected to fire (for example, using the technique #3).
		1965
		1966	When there is some activity, remove the timer from the list, recalculate
		1967	the timeout, append it to the end of the list again, and make sure to
		1968	update the C<ev_timer> if it was taken from the beginning of the list.
		1969
		1970	This way, one can manage an unlimited number of timeouts in O(1) time for
		1971	starting, stopping and updating the timers, at the expense of a major
		1972	complication, and having to use a constant timeout. The constant timeout
		1973	ensures that the list stays sorted.
		1974
		1975	=back
		1976
		1977	So which method the best?
		1978
		1979	Method #2 is a simple no-brain-required solution that is adequate in most
		1980	situations. Method #3 requires a bit more thinking, but handles many cases
		1981	better, and isn't very complicated either. In most case, choosing either
		1982	one is fine, with #3 being better in typical situations.
		1983
		1984	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1985	rather complicated, but extremely efficient, something that really pays
		1986	off after the first million or so of active timers, i.e. it's usually
		1987	overkill :)
		1988
		1989	=head3 The special problem of being too early
		1990
		1991	If you ask a timer to call your callback after three seconds, then
		1992	you expect it to be invoked after three seconds - but of course, this
		1993	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1994	guaranteed to any precision by libev - imagine somebody suspending the
		1995	process with a STOP signal for a few hours for example.
		1996
		1997	So, libev tries to invoke your callback as soon as possible I<after> the
		1998	delay has occurred, but cannot guarantee this.
		1999
		2000	A less obvious failure mode is calling your callback too early: many event
		2001	loops compare timestamps with a "elapsed delay >= requested delay", but
		2002	this can cause your callback to be invoked much earlier than you would
		2003	expect.
		2004
		2005	To see why, imagine a system with a clock that only offers full second
		2006	resolution (think windows if you can't come up with a broken enough OS
		2007	yourself). If you schedule a one-second timer at the time 500.9, then the
		2008	event loop will schedule your timeout to elapse at a system time of 500
		2009	(500.9 truncated to the resolution) + 1, or 501.
		2010
		2011	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2012	501" and invoke the callback 0.1s after it was started, even though a
		2013	one-second delay was requested - this is being "too early", despite best
		2014	intentions.
		2015
		2016	This is the reason why libev will never invoke the callback if the elapsed
		2017	delay equals the requested delay, but only when the elapsed delay is
		2018	larger than the requested delay. In the example above, libev would only invoke
		2019	the callback at system time 502, or 1.1s after the timer was started.
		2020
		2021	So, while libev cannot guarantee that your callback will be invoked
		2022	exactly when requested, it I<can> and I<does> guarantee that the requested
		2023	delay has actually elapsed, or in other words, it always errs on the "too
		2024	late" side of things.
		2025
		2026	=head3 The special problem of time updates
		2027
		2028	Establishing the current time is a costly operation (it usually takes
		2029	at least one system call): EV therefore updates its idea of the current
		2030	time only before and after C<ev_run> collects new events, which causes a
		2031	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2032	lots of events in one iteration.
962		2033
963	The relative timeouts are calculated relative to the C<ev_now ()>	2034	The relative timeouts are calculated relative to the C<ev_now ()>
964	time. This is usually the right thing as this timestamp refers to the time	2035	time. This is usually the right thing as this timestamp refers to the time
965	of the event triggering whatever timeout you are modifying/starting. If	2036	of the event triggering whatever timeout you are modifying/starting. If
966	you suspect event processing to be delayed and you I<need> to base the timeout	2037	you suspect event processing to be delayed and you I<need> to base the
967	on the current time, use something like this to adjust for this:	2038	timeout on the current time, use something like the following to adjust
		2039	for it:
968		2040
969	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2041	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
970		2042
971	The callback is guarenteed to be invoked only when its timeout has passed,	2043	If the event loop is suspended for a long time, you can also force an
972	but if multiple timers become ready during the same loop iteration then	2044	update of the time returned by C<ev_now ()> by calling C<ev_now_update
973	order of execution is undefined.	2045	()>, although that will push the event time of all outstanding events
		2046	further into the future.
		2047
		2048	=head3 The special problem of unsynchronised clocks
		2049
		2050	Modern systems have a variety of clocks - libev itself uses the normal
		2051	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2052	jumps).
		2053
		2054	Neither of these clocks is synchronised with each other or any other clock
		2055	on the system, so C<ev_time ()> might return a considerably different time
		2056	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2057	a call to C<gettimeofday> might return a second count that is one higher
		2058	than a directly following call to C<time>.
		2059
		2060	The moral of this is to only compare libev-related timestamps with
		2061	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2062	a second or so.
		2063
		2064	One more problem arises due to this lack of synchronisation: if libev uses
		2065	the system monotonic clock and you compare timestamps from C<ev_time>
		2066	or C<ev_now> from when you started your timer and when your callback is
		2067	invoked, you will find that sometimes the callback is a bit "early".
		2068
		2069	This is because C<ev_timer>s work in real time, not wall clock time, so
		2070	libev makes sure your callback is not invoked before the delay happened,
		2071	I<measured according to the real time>, not the system clock.
		2072
		2073	If your timeouts are based on a physical timescale (e.g. "time out this
		2074	connection after 100 seconds") then this shouldn't bother you as it is
		2075	exactly the right behaviour.
		2076
		2077	If you want to compare wall clock/system timestamps to your timers, then
		2078	you need to use C<ev_periodic>s, as these are based on the wall clock
		2079	time, where your comparisons will always generate correct results.
		2080
		2081	=head3 The special problems of suspended animation
		2082
		2083	When you leave the server world it is quite customary to hit machines that
		2084	can suspend/hibernate - what happens to the clocks during such a suspend?
		2085
		2086	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2087	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2088	to run until the system is suspended, but they will not advance while the
		2089	system is suspended. That means, on resume, it will be as if the program
		2090	was frozen for a few seconds, but the suspend time will not be counted
		2091	towards C<ev_timer> when a monotonic clock source is used. The real time
		2092	clock advanced as expected, but if it is used as sole clocksource, then a
		2093	long suspend would be detected as a time jump by libev, and timers would
		2094	be adjusted accordingly.
		2095
		2096	I would not be surprised to see different behaviour in different between
		2097	operating systems, OS versions or even different hardware.
		2098
		2099	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2100	time jump in the monotonic clocks and the realtime clock. If the program
		2101	is suspended for a very long time, and monotonic clock sources are in use,
		2102	then you can expect C<ev_timer>s to expire as the full suspension time
		2103	will be counted towards the timers. When no monotonic clock source is in
		2104	use, then libev will again assume a timejump and adjust accordingly.
		2105
		2106	It might be beneficial for this latter case to call C<ev_suspend>
		2107	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2108	deterministic behaviour in this case (you can do nothing against
		2109	C<SIGSTOP>).
		2110
		2111	=head3 Watcher-Specific Functions and Data Members
974		2112
975	=over 4	2113	=over 4
976		2114
977	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2115	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
978		2116
979	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2117	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
980		2118
981	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2119	Configure the timer to trigger after C<after> seconds (fractional and
982	C<0.>, then it will automatically be stopped. If it is positive, then the	2120	negative values are supported). If C<repeat> is C<0.>, then it will
		2121	automatically be stopped once the timeout is reached. If it is positive,
983	timer will automatically be configured to trigger again C<repeat> seconds	2122	then the timer will automatically be configured to trigger again C<repeat>
984	later, again, and again, until stopped manually.	2123	seconds later, again, and again, until stopped manually.
985		2124
986	The timer itself will do a best-effort at avoiding drift, that is, if you	2125	The timer itself will do a best-effort at avoiding drift, that is, if
987	configure a timer to trigger every 10 seconds, then it will trigger at	2126	you configure a timer to trigger every 10 seconds, then it will normally
988	exactly 10 second intervals. If, however, your program cannot keep up with	2127	trigger at exactly 10 second intervals. If, however, your program cannot
989	the timer (because it takes longer than those 10 seconds to do stuff) the	2128	keep up with the timer (because it takes longer than those 10 seconds to
990	timer will not fire more than once per event loop iteration.	2129	do stuff) the timer will not fire more than once per event loop iteration.
991		2130
992	=item ev_timer_again (loop)	2131	=item ev_timer_again (loop, ev_timer *)
993		2132
994	This will act as if the timer timed out and restart it again if it is	2133	This will act as if the timer timed out, and restarts it again if it is
995	repeating. The exact semantics are:	2134	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2135	timeout to the C<repeat> value and calling C<ev_timer_start>.
996		2136
		2137	The exact semantics are as in the following rules, all of which will be
		2138	applied to the watcher:
		2139
		2140	=over 4
		2141
997	If the timer is pending, its pending status is cleared.	2142	=item If the timer is pending, the pending status is always cleared.
998		2143
999	If the timer is started but nonrepeating, stop it (as if it timed out).	2144	=item If the timer is started but non-repeating, stop it (as if it timed
		2145	out, without invoking it).
1000		2146
1001	If the timer is repeating, either start it if necessary (with the	2147	=item If the timer is repeating, make the C<repeat> value the new timeout
1002	C<repeat> value), or reset the running timer to the C<repeat> value.	2148	and start the timer, if necessary.
1003		2149
1004	This sounds a bit complicated, but here is a useful and typical	2150	=back
1005	example: Imagine you have a tcp connection and you want a so-called idle
1006	timeout, that is, you want to be called when there have been, say, 60
1007	seconds of inactivity on the socket. The easiest way to do this is to
1008	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1009	C<ev_timer_again> each time you successfully read or write some data. If
1010	you go into an idle state where you do not expect data to travel on the
1011	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1012	automatically restart it if need be.
1013		2151
1014	That means you can ignore the C<after> value and C<ev_timer_start>	2152	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1015	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2153	usage example.
1016		2154
1017	ev_timer_init (timer, callback, 0., 5.);	2155	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1018	ev_timer_again (loop, timer);
1019	...
1020	timer->again = 17.;
1021	ev_timer_again (loop, timer);
1022	...
1023	timer->again = 10.;
1024	ev_timer_again (loop, timer);
1025		2156
1026	This is more slightly efficient then stopping/starting the timer each time	2157	Returns the remaining time until a timer fires. If the timer is active,
1027	you want to modify its timeout value.	2158	then this time is relative to the current event loop time, otherwise it's
		2159	the timeout value currently configured.
		2160
		2161	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2162	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2163	will return C<4>. When the timer expires and is restarted, it will return
		2164	roughly C<7> (likely slightly less as callback invocation takes some time,
		2165	too), and so on.
1028		2166
1029	=item ev_tstamp repeat [read-write]	2167	=item ev_tstamp repeat [read-write]
1030		2168
1031	The current C<repeat> value. Will be used each time the watcher times out	2169	The current C<repeat> value. Will be used each time the watcher times out
1032	or C<ev_timer_again> is called and determines the next timeout (if any),	2170	or C<ev_timer_again> is called, and determines the next timeout (if any),
1033	which is also when any modifications are taken into account.	2171	which is also when any modifications are taken into account.
1034		2172
1035	=back	2173	=back
1036		2174
		2175	=head3 Examples
		2176
1037	Example: Create a timer that fires after 60 seconds.	2177	Example: Create a timer that fires after 60 seconds.
1038		2178
1039	static void	2179	static void
1040	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2180	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1041	{	2181	{
1042	.. one minute over, w is actually stopped right here	2182	.. one minute over, w is actually stopped right here
1043	}	2183	}
1044		2184
1045	struct ev_timer mytimer;	2185	ev_timer mytimer;
1046	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2186	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1047	ev_timer_start (loop, &mytimer);	2187	ev_timer_start (loop, &mytimer);
1048		2188
1049	Example: Create a timeout timer that times out after 10 seconds of	2189	Example: Create a timeout timer that times out after 10 seconds of
1050	inactivity.	2190	inactivity.
1051		2191
1052	static void	2192	static void
1053	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2193	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1054	{	2194	{
1055	.. ten seconds without any activity	2195	.. ten seconds without any activity
1056	}	2196	}
1057		2197
1058	struct ev_timer mytimer;	2198	ev_timer mytimer;
1059	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2199	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1060	ev_timer_again (&mytimer); /* start timer */	2200	ev_timer_again (&mytimer); /* start timer */
1061	ev_loop (loop, 0);	2201	ev_run (loop, 0);
1062		2202
1063	// and in some piece of code that gets executed on any "activity":	2203	// and in some piece of code that gets executed on any "activity":
1064	// reset the timeout to start ticking again at 10 seconds	2204	// reset the timeout to start ticking again at 10 seconds
1065	ev_timer_again (&mytimer);	2205	ev_timer_again (&mytimer);
1066		2206
1067		2207
1068	=head2 C<ev_periodic> - to cron or not to cron?	2208	=head2 C<ev_periodic> - to cron or not to cron?
1069		2209
1070	Periodic watchers are also timers of a kind, but they are very versatile	2210	Periodic watchers are also timers of a kind, but they are very versatile
1071	(and unfortunately a bit complex).	2211	(and unfortunately a bit complex).
1072		2212
1073	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2213	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1074	but on wallclock time (absolute time). You can tell a periodic watcher	2214	relative time, the physical time that passes) but on wall clock time
1075	to trigger "at" some specific point in time. For example, if you tell a	2215	(absolute time, the thing you can read on your calendar or clock). The
1076	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2216	difference is that wall clock time can run faster or slower than real
1077	+ 10.>) and then reset your system clock to the last year, then it will	2217	time, and time jumps are not uncommon (e.g. when you adjust your
1078	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2218	wrist-watch).
1079	roughly 10 seconds later).
1080		2219
1081	They can also be used to implement vastly more complex timers, such as	2220	You can tell a periodic watcher to trigger after some specific point
1082	triggering an event on each midnight, local time or other, complicated,	2221	in time: for example, if you tell a periodic watcher to trigger "in 10
1083	rules.	2222	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2223	not a delay) and then reset your system clock to January of the previous
		2224	year, then it will take a year or more to trigger the event (unlike an
		2225	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2226	it, as it uses a relative timeout).
1084		2227
		2228	C<ev_periodic> watchers can also be used to implement vastly more complex
		2229	timers, such as triggering an event on each "midnight, local time", or
		2230	other complicated rules. This cannot easily be done with C<ev_timer>
		2231	watchers, as those cannot react to time jumps.
		2232
1085	As with timers, the callback is guarenteed to be invoked only when the	2233	As with timers, the callback is guaranteed to be invoked only when the
1086	time (C<at>) has been passed, but if multiple periodic timers become ready	2234	point in time where it is supposed to trigger has passed. If multiple
1087	during the same loop iteration then order of execution is undefined.	2235	timers become ready during the same loop iteration then the ones with
		2236	earlier time-out values are invoked before ones with later time-out values
		2237	(but this is no longer true when a callback calls C<ev_run> recursively).
		2238
		2239	=head3 Watcher-Specific Functions and Data Members
1088		2240
1089	=over 4	2241	=over 4
1090		2242
1091	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2243	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1092		2244
1093	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2245	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1094		2246
1095	Lots of arguments, lets sort it out... There are basically three modes of	2247	Lots of arguments, let's sort it out... There are basically three modes of
1096	operation, and we will explain them from simplest to complex:	2248	operation, and we will explain them from simplest to most complex:
1097		2249
1098	=over 4	2250	=over 4
1099		2251
1100	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2252	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1101		2253
1102	In this configuration the watcher triggers an event at the wallclock time	2254	In this configuration the watcher triggers an event after the wall clock
1103	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2255	time C<offset> has passed. It will not repeat and will not adjust when a
1104	that is, if it is to be run at January 1st 2011 then it will run when the	2256	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1105	system time reaches or surpasses this time.	2257	will be stopped and invoked when the system clock reaches or surpasses
		2258	this point in time.
1106		2259
1107	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2260	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1108		2261
1109	In this mode the watcher will always be scheduled to time out at the next	2262	In this mode the watcher will always be scheduled to time out at the next
1110	C<at + N * interval> time (for some integer N, which can also be negative)	2263	C<offset + N * interval> time (for some integer N, which can also be
1111	and then repeat, regardless of any time jumps.	2264	negative) and then repeat, regardless of any time jumps. The C<offset>
		2265	argument is merely an offset into the C<interval> periods.
1112		2266
1113	This can be used to create timers that do not drift with respect to system	2267	This can be used to create timers that do not drift with respect to the
1114	time:	2268	system clock, for example, here is an C<ev_periodic> that triggers each
		2269	hour, on the hour (with respect to UTC):
1115		2270
1116	ev_periodic_set (&periodic, 0., 3600., 0);	2271	ev_periodic_set (&periodic, 0., 3600., 0);
1117		2272
1118	This doesn't mean there will always be 3600 seconds in between triggers,	2273	This doesn't mean there will always be 3600 seconds in between triggers,
1119	but only that the the callback will be called when the system time shows a	2274	but only that the callback will be called when the system time shows a
1120	full hour (UTC), or more correctly, when the system time is evenly divisible	2275	full hour (UTC), or more correctly, when the system time is evenly divisible
1121	by 3600.	2276	by 3600.
1122		2277
1123	Another way to think about it (for the mathematically inclined) is that	2278	Another way to think about it (for the mathematically inclined) is that
1124	C<ev_periodic> will try to run the callback in this mode at the next possible	2279	C<ev_periodic> will try to run the callback in this mode at the next possible
1125	time where C<time = at (mod interval)>, regardless of any time jumps.	2280	time where C<time = offset (mod interval)>, regardless of any time jumps.
1126		2281
1127	For numerical stability it is preferable that the C<at> value is near	2282	The C<interval> I<MUST> be positive, and for numerical stability, the
1128	C<ev_now ()> (the current time), but there is no range requirement for	2283	interval value should be higher than C<1/8192> (which is around 100
1129	this value.	2284	microseconds) and C<offset> should be higher than C<0> and should have
		2285	at most a similar magnitude as the current time (say, within a factor of
		2286	ten). Typical values for offset are, in fact, C<0> or something between
		2287	C<0> and C<interval>, which is also the recommended range.
1130		2288
		2289	Note also that there is an upper limit to how often a timer can fire (CPU
		2290	speed for example), so if C<interval> is very small then timing stability
		2291	will of course deteriorate. Libev itself tries to be exact to be about one
		2292	millisecond (if the OS supports it and the machine is fast enough).
		2293
1131	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2294	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1132		2295
1133	In this mode the values for C<interval> and C<at> are both being	2296	In this mode the values for C<interval> and C<offset> are both being
1134	ignored. Instead, each time the periodic watcher gets scheduled, the	2297	ignored. Instead, each time the periodic watcher gets scheduled, the
1135	reschedule callback will be called with the watcher as first, and the	2298	reschedule callback will be called with the watcher as first, and the
1136	current time as second argument.	2299	current time as second argument.
1137		2300
1138	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2301	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1139	ever, or make any event loop modifications>. If you need to stop it,	2302	or make ANY other event loop modifications whatsoever, unless explicitly
1140	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2303	allowed by documentation here>.
1141	starting an C<ev_prepare> watcher, which is legal).
1142		2304
		2305	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2306	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2307	only event loop modification you are allowed to do).
		2308
1143	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2309	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1144	ev_tstamp now)>, e.g.:	2310	*w, ev_tstamp now)>, e.g.:
1145		2311
		2312	static ev_tstamp
1146	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2313	my_rescheduler (ev_periodic *w, ev_tstamp now)
1147	{	2314	{
1148	return now + 60.;	2315	return now + 60.;
1149	}	2316	}
1150		2317
1151	It must return the next time to trigger, based on the passed time value	2318	It must return the next time to trigger, based on the passed time value
1152	(that is, the lowest time value larger than to the second argument). It	2319	(that is, the lowest time value larger than to the second argument). It
1153	will usually be called just before the callback will be triggered, but	2320	will usually be called just before the callback will be triggered, but
1154	might be called at other times, too.	2321	might be called at other times, too.
1155		2322
1156	NOTE: I<< This callback must always return a time that is later than the	2323	NOTE: I<< This callback must always return a time that is higher than or
1157	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2324	equal to the passed C<now> value >>.
1158		2325
1159	This can be used to create very complex timers, such as a timer that	2326	This can be used to create very complex timers, such as a timer that
1160	triggers on each midnight, local time. To do this, you would calculate the	2327	triggers on "next midnight, local time". To do this, you would calculate
1161	next midnight after C<now> and return the timestamp value for this. How	2328	the next midnight after C<now> and return the timestamp value for
1162	you do this is, again, up to you (but it is not trivial, which is the main	2329	this. Here is a (completely untested, no error checking) example on how to
1163	reason I omitted it as an example).	2330	do this:
		2331
		2332	#include <time.h>
		2333
		2334	static ev_tstamp
		2335	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2336	{
		2337	time_t tnow = (time_t)now;
		2338	struct tm tm;
		2339	localtime_r (&tnow, &tm);
		2340
		2341	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2342	++tm.tm_mday; // midnight next day
		2343
		2344	return mktime (&tm);
		2345	}
		2346
		2347	Note: this code might run into trouble on days that have more then two
		2348	midnights (beginning and end).
1164		2349
1165	=back	2350	=back
1166		2351
1167	=item ev_periodic_again (loop, ev_periodic *)	2352	=item ev_periodic_again (loop, ev_periodic *)
1168		2353
1169	Simply stops and restarts the periodic watcher again. This is only useful	2354	Simply stops and restarts the periodic watcher again. This is only useful
1170	when you changed some parameters or the reschedule callback would return	2355	when you changed some parameters or the reschedule callback would return
1171	a different time than the last time it was called (e.g. in a crond like	2356	a different time than the last time it was called (e.g. in a crond like
1172	program when the crontabs have changed).	2357	program when the crontabs have changed).
1173		2358
		2359	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2360
		2361	When active, returns the absolute time that the watcher is supposed
		2362	to trigger next. This is not the same as the C<offset> argument to
		2363	C<ev_periodic_set>, but indeed works even in interval and manual
		2364	rescheduling modes.
		2365
1174	=item ev_tstamp offset [read-write]	2366	=item ev_tstamp offset [read-write]
1175		2367
1176	When repeating, this contains the offset value, otherwise this is the	2368	When repeating, this contains the offset value, otherwise this is the
1177	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2369	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2370	although libev might modify this value for better numerical stability).
1178		2371
1179	Can be modified any time, but changes only take effect when the periodic	2372	Can be modified any time, but changes only take effect when the periodic
1180	timer fires or C<ev_periodic_again> is being called.	2373	timer fires or C<ev_periodic_again> is being called.
1181		2374
1182	=item ev_tstamp interval [read-write]	2375	=item ev_tstamp interval [read-write]
1183		2376
1184	The current interval value. Can be modified any time, but changes only	2377	The current interval value. Can be modified any time, but changes only
1185	take effect when the periodic timer fires or C<ev_periodic_again> is being	2378	take effect when the periodic timer fires or C<ev_periodic_again> is being
1186	called.	2379	called.
1187		2380
1188	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2381	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1189		2382
1190	The current reschedule callback, or C<0>, if this functionality is	2383	The current reschedule callback, or C<0>, if this functionality is
1191	switched off. Can be changed any time, but changes only take effect when	2384	switched off. Can be changed any time, but changes only take effect when
1192	the periodic timer fires or C<ev_periodic_again> is being called.	2385	the periodic timer fires or C<ev_periodic_again> is being called.
1193		2386
1194	=back	2387	=back
1195		2388
		2389	=head3 Examples
		2390
1196	Example: Call a callback every hour, or, more precisely, whenever the	2391	Example: Call a callback every hour, or, more precisely, whenever the
1197	system clock is divisible by 3600. The callback invocation times have	2392	system time is divisible by 3600. The callback invocation times have
1198	potentially a lot of jittering, but good long-term stability.	2393	potentially a lot of jitter, but good long-term stability.
1199		2394
1200	static void	2395	static void
1201	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2396	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1202	{	2397	{
1203	... its now a full hour (UTC, or TAI or whatever your clock follows)	2398	... its now a full hour (UTC, or TAI or whatever your clock follows)
1204	}	2399	}
1205		2400
1206	struct ev_periodic hourly_tick;	2401	ev_periodic hourly_tick;
1207	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2402	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1208	ev_periodic_start (loop, &hourly_tick);	2403	ev_periodic_start (loop, &hourly_tick);
1209		2404
1210	Example: The same as above, but use a reschedule callback to do it:	2405	Example: The same as above, but use a reschedule callback to do it:
1211		2406
1212	#include <math.h>	2407	#include <math.h>
1213		2408
1214	static ev_tstamp	2409	static ev_tstamp
1215	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2410	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1216	{	2411	{
1217	return fmod (now, 3600.) + 3600.;	2412	return now + (3600. - fmod (now, 3600.));
1218	}	2413	}
1219		2414
1220	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2415	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1221		2416
1222	Example: Call a callback every hour, starting now:	2417	Example: Call a callback every hour, starting now:
1223		2418
1224	struct ev_periodic hourly_tick;	2419	ev_periodic hourly_tick;
1225	ev_periodic_init (&hourly_tick, clock_cb,	2420	ev_periodic_init (&hourly_tick, clock_cb,
1226	fmod (ev_now (loop), 3600.), 3600., 0);	2421	fmod (ev_now (loop), 3600.), 3600., 0);
1227	ev_periodic_start (loop, &hourly_tick);	2422	ev_periodic_start (loop, &hourly_tick);
1228		2423
1229		2424
1230	=head2 C<ev_signal> - signal me when a signal gets signalled!	2425	=head2 C<ev_signal> - signal me when a signal gets signalled!
1231		2426
1232	Signal watchers will trigger an event when the process receives a specific	2427	Signal watchers will trigger an event when the process receives a specific
1233	signal one or more times. Even though signals are very asynchronous, libev	2428	signal one or more times. Even though signals are very asynchronous, libev
1234	will try it's best to deliver signals synchronously, i.e. as part of the	2429	will try its best to deliver signals synchronously, i.e. as part of the
1235	normal event processing, like any other event.	2430	normal event processing, like any other event.
1236		2431
		2432	If you want signals to be delivered truly asynchronously, just use
		2433	C<sigaction> as you would do without libev and forget about sharing
		2434	the signal. You can even use C<ev_async> from a signal handler to
		2435	synchronously wake up an event loop.
		2436
1237	You can configure as many watchers as you like per signal. Only when the	2437	You can configure as many watchers as you like for the same signal, but
1238	first watcher gets started will libev actually register a signal watcher	2438	only within the same loop, i.e. you can watch for C<SIGINT> in your
1239	with the kernel (thus it coexists with your own signal handlers as long	2439	default loop and for C<SIGIO> in another loop, but you cannot watch for
1240	as you don't register any with libev). Similarly, when the last signal	2440	C<SIGINT> in both the default loop and another loop at the same time. At
1241	watcher for a signal is stopped libev will reset the signal handler to	2441	the moment, C<SIGCHLD> is permanently tied to the default loop.
1242	SIG_DFL (regardless of what it was set to before).	2442
		2443	Only after the first watcher for a signal is started will libev actually
		2444	register something with the kernel. It thus coexists with your own signal
		2445	handlers as long as you don't register any with libev for the same signal.
		2446
		2447	If possible and supported, libev will install its handlers with
		2448	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2449	not be unduly interrupted. If you have a problem with system calls getting
		2450	interrupted by signals you can block all signals in an C<ev_check> watcher
		2451	and unblock them in an C<ev_prepare> watcher.
		2452
		2453	=head3 The special problem of inheritance over fork/execve/pthread_create
		2454
		2455	Both the signal mask (C<sigprocmask>) and the signal disposition
		2456	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2457	stopping it again), that is, libev might or might not block the signal,
		2458	and might or might not set or restore the installed signal handler (but
		2459	see C<EVFLAG_NOSIGMASK>).
		2460
		2461	While this does not matter for the signal disposition (libev never
		2462	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2463	C<execve>), this matters for the signal mask: many programs do not expect
		2464	certain signals to be blocked.
		2465
		2466	This means that before calling C<exec> (from the child) you should reset
		2467	the signal mask to whatever "default" you expect (all clear is a good
		2468	choice usually).
		2469
		2470	The simplest way to ensure that the signal mask is reset in the child is
		2471	to install a fork handler with C<pthread_atfork> that resets it. That will
		2472	catch fork calls done by libraries (such as the libc) as well.
		2473
		2474	In current versions of libev, the signal will not be blocked indefinitely
		2475	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2476	the window of opportunity for problems, it will not go away, as libev
		2477	I<has> to modify the signal mask, at least temporarily.
		2478
		2479	So I can't stress this enough: I<If you do not reset your signal mask when
		2480	you expect it to be empty, you have a race condition in your code>. This
		2481	is not a libev-specific thing, this is true for most event libraries.
		2482
		2483	=head3 The special problem of threads signal handling
		2484
		2485	POSIX threads has problematic signal handling semantics, specifically,
		2486	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2487	threads in a process block signals, which is hard to achieve.
		2488
		2489	When you want to use sigwait (or mix libev signal handling with your own
		2490	for the same signals), you can tackle this problem by globally blocking
		2491	all signals before creating any threads (or creating them with a fully set
		2492	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2493	loops. Then designate one thread as "signal receiver thread" which handles
		2494	these signals. You can pass on any signals that libev might be interested
		2495	in by calling C<ev_feed_signal>.
		2496
		2497	=head3 Watcher-Specific Functions and Data Members
1243		2498
1244	=over 4	2499	=over 4
1245		2500
1246	=item ev_signal_init (ev_signal *, callback, int signum)	2501	=item ev_signal_init (ev_signal *, callback, int signum)
1247		2502
…		…
1254		2509
1255	The signal the watcher watches out for.	2510	The signal the watcher watches out for.
1256		2511
1257	=back	2512	=back
1258		2513
		2514	=head3 Examples
		2515
		2516	Example: Try to exit cleanly on SIGINT.
		2517
		2518	static void
		2519	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2520	{
		2521	ev_break (loop, EVBREAK_ALL);
		2522	}
		2523
		2524	ev_signal signal_watcher;
		2525	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2526	ev_signal_start (loop, &signal_watcher);
		2527
1259		2528
1260	=head2 C<ev_child> - watch out for process status changes	2529	=head2 C<ev_child> - watch out for process status changes
1261		2530
1262	Child watchers trigger when your process receives a SIGCHLD in response to	2531	Child watchers trigger when your process receives a SIGCHLD in response to
1263	some child status changes (most typically when a child of yours dies).	2532	some child status changes (most typically when a child of yours dies or
		2533	exits). It is permissible to install a child watcher I<after> the child
		2534	has been forked (which implies it might have already exited), as long
		2535	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2536	forking and then immediately registering a watcher for the child is fine,
		2537	but forking and registering a watcher a few event loop iterations later or
		2538	in the next callback invocation is not.
		2539
		2540	Only the default event loop is capable of handling signals, and therefore
		2541	you can only register child watchers in the default event loop.
		2542
		2543	Due to some design glitches inside libev, child watchers will always be
		2544	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2545	libev)
		2546
		2547	=head3 Process Interaction
		2548
		2549	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2550	initialised. This is necessary to guarantee proper behaviour even if the
		2551	first child watcher is started after the child exits. The occurrence
		2552	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2553	synchronously as part of the event loop processing. Libev always reaps all
		2554	children, even ones not watched.
		2555
		2556	=head3 Overriding the Built-In Processing
		2557
		2558	Libev offers no special support for overriding the built-in child
		2559	processing, but if your application collides with libev's default child
		2560	handler, you can override it easily by installing your own handler for
		2561	C<SIGCHLD> after initialising the default loop, and making sure the
		2562	default loop never gets destroyed. You are encouraged, however, to use an
		2563	event-based approach to child reaping and thus use libev's support for
		2564	that, so other libev users can use C<ev_child> watchers freely.
		2565
		2566	=head3 Stopping the Child Watcher
		2567
		2568	Currently, the child watcher never gets stopped, even when the
		2569	child terminates, so normally one needs to stop the watcher in the
		2570	callback. Future versions of libev might stop the watcher automatically
		2571	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2572	problem).
		2573
		2574	=head3 Watcher-Specific Functions and Data Members
1264		2575
1265	=over 4	2576	=over 4
1266		2577
1267	=item ev_child_init (ev_child *, callback, int pid)	2578	=item ev_child_init (ev_child *, callback, int pid, int trace)
1268		2579
1269	=item ev_child_set (ev_child *, int pid)	2580	=item ev_child_set (ev_child *, int pid, int trace)
1270		2581
1271	Configures the watcher to wait for status changes of process C<pid> (or	2582	Configures the watcher to wait for status changes of process C<pid> (or
1272	I<any> process if C<pid> is specified as C<0>). The callback can look	2583	I<any> process if C<pid> is specified as C<0>). The callback can look
1273	at the C<rstatus> member of the C<ev_child> watcher structure to see	2584	at the C<rstatus> member of the C<ev_child> watcher structure to see
1274	the status word (use the macros from C<sys/wait.h> and see your systems	2585	the status word (use the macros from C<sys/wait.h> and see your systems
1275	C<waitpid> documentation). The C<rpid> member contains the pid of the	2586	C<waitpid> documentation). The C<rpid> member contains the pid of the
1276	process causing the status change.	2587	process causing the status change. C<trace> must be either C<0> (only
		2588	activate the watcher when the process terminates) or C<1> (additionally
		2589	activate the watcher when the process is stopped or continued).
1277		2590
1278	=item int pid [read-only]	2591	=item int pid [read-only]
1279		2592
1280	The process id this watcher watches out for, or C<0>, meaning any process id.	2593	The process id this watcher watches out for, or C<0>, meaning any process id.
1281		2594
…		…
1288	The process exit/trace status caused by C<rpid> (see your systems	2601	The process exit/trace status caused by C<rpid> (see your systems
1289	C<waitpid> and C<sys/wait.h> documentation for details).	2602	C<waitpid> and C<sys/wait.h> documentation for details).
1290		2603
1291	=back	2604	=back
1292		2605
1293	Example: Try to exit cleanly on SIGINT and SIGTERM.	2606	=head3 Examples
1294		2607
		2608	Example: C<fork()> a new process and install a child handler to wait for
		2609	its completion.
		2610
		2611	ev_child cw;
		2612
1295	static void	2613	static void
1296	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2614	child_cb (EV_P_ ev_child *w, int revents)
1297	{	2615	{
1298	ev_unloop (loop, EVUNLOOP_ALL);	2616	ev_child_stop (EV_A_ w);
		2617	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1299	}	2618	}
1300		2619
1301	struct ev_signal signal_watcher;	2620	pid_t pid = fork ();
1302	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2621
1303	ev_signal_start (loop, &sigint_cb);	2622	if (pid < 0)
		2623	// error
		2624	else if (pid == 0)
		2625	{
		2626	// the forked child executes here
		2627	exit (1);
		2628	}
		2629	else
		2630	{
		2631	ev_child_init (&cw, child_cb, pid, 0);
		2632	ev_child_start (EV_DEFAULT_ &cw);
		2633	}
1304		2634
1305		2635
1306	=head2 C<ev_stat> - did the file attributes just change?	2636	=head2 C<ev_stat> - did the file attributes just change?
1307		2637
1308	This watches a filesystem path for attribute changes. That is, it calls	2638	This watches a file system path for attribute changes. That is, it calls
1309	C<stat> regularly (or when the OS says it changed) and sees if it changed	2639	C<stat> on that path in regular intervals (or when the OS says it changed)
1310	compared to the last time, invoking the callback if it did.	2640	and sees if it changed compared to the last time, invoking the callback
		2641	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2642	happen after the watcher has been started will be reported.
1311		2643
1312	The path does not need to exist: changing from "path exists" to "path does	2644	The path does not need to exist: changing from "path exists" to "path does
1313	not exist" is a status change like any other. The condition "path does	2645	not exist" is a status change like any other. The condition "path does not
1314	not exist" is signified by the C<st_nlink> field being zero (which is	2646	exist" (or more correctly "path cannot be stat'ed") is signified by the
1315	otherwise always forced to be at least one) and all the other fields of	2647	C<st_nlink> field being zero (which is otherwise always forced to be at
1316	the stat buffer having unspecified contents.	2648	least one) and all the other fields of the stat buffer having unspecified
		2649	contents.
1317		2650
1318	The path I<should> be absolute and I<must not> end in a slash. If it is	2651	The path I<must not> end in a slash or contain special components such as
		2652	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1319	relative and your working directory changes, the behaviour is undefined.	2653	your working directory changes, then the behaviour is undefined.
1320		2654
1321	Since there is no standard to do this, the portable implementation simply	2655	Since there is no portable change notification interface available, the
1322	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2656	portable implementation simply calls C<stat(2)> regularly on the path
1323	can specify a recommended polling interval for this case. If you specify	2657	to see if it changed somehow. You can specify a recommended polling
1324	a polling interval of C<0> (highly recommended!) then a I<suitable,	2658	interval for this case. If you specify a polling interval of C<0> (highly
1325	unspecified default> value will be used (which you can expect to be around	2659	recommended!) then a I<suitable, unspecified default> value will be used
1326	five seconds, although this might change dynamically). Libev will also	2660	(which you can expect to be around five seconds, although this might
1327	impose a minimum interval which is currently around C<0.1>, but thats	2661	change dynamically). Libev will also impose a minimum interval which is
1328	usually overkill.	2662	currently around C<0.1>, but that's usually overkill.
1329		2663
1330	This watcher type is not meant for massive numbers of stat watchers,	2664	This watcher type is not meant for massive numbers of stat watchers,
1331	as even with OS-supported change notifications, this can be	2665	as even with OS-supported change notifications, this can be
1332	resource-intensive.	2666	resource-intensive.
1333		2667
1334	At the time of this writing, only the Linux inotify interface is	2668	At the time of this writing, the only OS-specific interface implemented
1335	implemented (implementing kqueue support is left as an exercise for the	2669	is the Linux inotify interface (implementing kqueue support is left as an
1336	reader). Inotify will be used to give hints only and should not change the	2670	exercise for the reader. Note, however, that the author sees no way of
1337	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2671	implementing C<ev_stat> semantics with kqueue, except as a hint).
1338	to fall back to regular polling again even with inotify, but changes are	2672
1339	usually detected immediately, and if the file exists there will be no	2673	=head3 ABI Issues (Largefile Support)
1340	polling.	2674
		2675	Libev by default (unless the user overrides this) uses the default
		2676	compilation environment, which means that on systems with large file
		2677	support disabled by default, you get the 32 bit version of the stat
		2678	structure. When using the library from programs that change the ABI to
		2679	use 64 bit file offsets the programs will fail. In that case you have to
		2680	compile libev with the same flags to get binary compatibility. This is
		2681	obviously the case with any flags that change the ABI, but the problem is
		2682	most noticeably displayed with ev_stat and large file support.
		2683
		2684	The solution for this is to lobby your distribution maker to make large
		2685	file interfaces available by default (as e.g. FreeBSD does) and not
		2686	optional. Libev cannot simply switch on large file support because it has
		2687	to exchange stat structures with application programs compiled using the
		2688	default compilation environment.
		2689
		2690	=head3 Inotify and Kqueue
		2691
		2692	When C<inotify (7)> support has been compiled into libev and present at
		2693	runtime, it will be used to speed up change detection where possible. The
		2694	inotify descriptor will be created lazily when the first C<ev_stat>
		2695	watcher is being started.
		2696
		2697	Inotify presence does not change the semantics of C<ev_stat> watchers
		2698	except that changes might be detected earlier, and in some cases, to avoid
		2699	making regular C<stat> calls. Even in the presence of inotify support
		2700	there are many cases where libev has to resort to regular C<stat> polling,
		2701	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2702	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2703	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2704	xfs are fully working) libev usually gets away without polling.
		2705
		2706	There is no support for kqueue, as apparently it cannot be used to
		2707	implement this functionality, due to the requirement of having a file
		2708	descriptor open on the object at all times, and detecting renames, unlinks
		2709	etc. is difficult.
		2710
		2711	=head3 C<stat ()> is a synchronous operation
		2712
		2713	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2714	the process. The exception are C<ev_stat> watchers - those call C<stat
		2715	()>, which is a synchronous operation.
		2716
		2717	For local paths, this usually doesn't matter: unless the system is very
		2718	busy or the intervals between stat's are large, a stat call will be fast,
		2719	as the path data is usually in memory already (except when starting the
		2720	watcher).
		2721
		2722	For networked file systems, calling C<stat ()> can block an indefinite
		2723	time due to network issues, and even under good conditions, a stat call
		2724	often takes multiple milliseconds.
		2725
		2726	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2727	paths, although this is fully supported by libev.
		2728
		2729	=head3 The special problem of stat time resolution
		2730
		2731	The C<stat ()> system call only supports full-second resolution portably,
		2732	and even on systems where the resolution is higher, most file systems
		2733	still only support whole seconds.
		2734
		2735	That means that, if the time is the only thing that changes, you can
		2736	easily miss updates: on the first update, C<ev_stat> detects a change and
		2737	calls your callback, which does something. When there is another update
		2738	within the same second, C<ev_stat> will be unable to detect unless the
		2739	stat data does change in other ways (e.g. file size).
		2740
		2741	The solution to this is to delay acting on a change for slightly more
		2742	than a second (or till slightly after the next full second boundary), using
		2743	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2744	ev_timer_again (loop, w)>).
		2745
		2746	The C<.02> offset is added to work around small timing inconsistencies
		2747	of some operating systems (where the second counter of the current time
		2748	might be be delayed. One such system is the Linux kernel, where a call to
		2749	C<gettimeofday> might return a timestamp with a full second later than
		2750	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2751	update file times then there will be a small window where the kernel uses
		2752	the previous second to update file times but libev might already execute
		2753	the timer callback).
		2754
		2755	=head3 Watcher-Specific Functions and Data Members
1341		2756
1342	=over 4	2757	=over 4
1343		2758
1344	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2759	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1345		2760
…		…
1349	C<path>. The C<interval> is a hint on how quickly a change is expected to	2764	C<path>. The C<interval> is a hint on how quickly a change is expected to
1350	be detected and should normally be specified as C<0> to let libev choose	2765	be detected and should normally be specified as C<0> to let libev choose
1351	a suitable value. The memory pointed to by C<path> must point to the same	2766	a suitable value. The memory pointed to by C<path> must point to the same
1352	path for as long as the watcher is active.	2767	path for as long as the watcher is active.
1353		2768
1354	The callback will be receive C<EV_STAT> when a change was detected,	2769	The callback will receive an C<EV_STAT> event when a change was detected,
1355	relative to the attributes at the time the watcher was started (or the	2770	relative to the attributes at the time the watcher was started (or the
1356	last change was detected).	2771	last change was detected).
1357		2772
1358	=item ev_stat_stat (ev_stat *)	2773	=item ev_stat_stat (loop, ev_stat *)
1359		2774
1360	Updates the stat buffer immediately with new values. If you change the	2775	Updates the stat buffer immediately with new values. If you change the
1361	watched path in your callback, you could call this fucntion to avoid	2776	watched path in your callback, you could call this function to avoid
1362	detecting this change (while introducing a race condition). Can also be	2777	detecting this change (while introducing a race condition if you are not
1363	useful simply to find out the new values.	2778	the only one changing the path). Can also be useful simply to find out the
		2779	new values.
1364		2780
1365	=item ev_statdata attr [read-only]	2781	=item ev_statdata attr [read-only]
1366		2782
1367	The most-recently detected attributes of the file. Although the type is of	2783	The most-recently detected attributes of the file. Although the type is
1368	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2784	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1369	suitable for your system. If the C<st_nlink> member is C<0>, then there	2785	suitable for your system, but you can only rely on the POSIX-standardised
		2786	members to be present. If the C<st_nlink> member is C<0>, then there was
1370	was some error while C<stat>ing the file.	2787	some error while C<stat>ing the file.
1371		2788
1372	=item ev_statdata prev [read-only]	2789	=item ev_statdata prev [read-only]
1373		2790
1374	The previous attributes of the file. The callback gets invoked whenever	2791	The previous attributes of the file. The callback gets invoked whenever
1375	C<prev> != C<attr>.	2792	C<prev> != C<attr>, or, more precisely, one or more of these members
		2793	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2794	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1376		2795
1377	=item ev_tstamp interval [read-only]	2796	=item ev_tstamp interval [read-only]
1378		2797
1379	The specified interval.	2798	The specified interval.
1380		2799
1381	=item const char *path [read-only]	2800	=item const char *path [read-only]
1382		2801
1383	The filesystem path that is being watched.	2802	The file system path that is being watched.
1384		2803
1385	=back	2804	=back
1386		2805
		2806	=head3 Examples
		2807
1387	Example: Watch C</etc/passwd> for attribute changes.	2808	Example: Watch C</etc/passwd> for attribute changes.
1388		2809
1389	static void	2810	static void
1390	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2811	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1391	{	2812	{
1392	/* /etc/passwd changed in some way */	2813	/* /etc/passwd changed in some way */
1393	if (w->attr.st_nlink)	2814	if (w->attr.st_nlink)
1394	{	2815	{
1395	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2816	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1396	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2817	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1397	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2818	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1398	}	2819	}
1399	else	2820	else
1400	/* you shalt not abuse printf for puts */	2821	/* you shalt not abuse printf for puts */
1401	puts ("wow, /etc/passwd is not there, expect problems. "	2822	puts ("wow, /etc/passwd is not there, expect problems. "
1402	"if this is windows, they already arrived\n");	2823	"if this is windows, they already arrived\n");
1403	}	2824	}
1404		2825
1405	...	2826	...
1406	ev_stat passwd;	2827	ev_stat passwd;
1407		2828
1408	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2829	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1409	ev_stat_start (loop, &passwd);	2830	ev_stat_start (loop, &passwd);
		2831
		2832	Example: Like above, but additionally use a one-second delay so we do not
		2833	miss updates (however, frequent updates will delay processing, too, so
		2834	one might do the work both on C<ev_stat> callback invocation I<and> on
		2835	C<ev_timer> callback invocation).
		2836
		2837	static ev_stat passwd;
		2838	static ev_timer timer;
		2839
		2840	static void
		2841	timer_cb (EV_P_ ev_timer *w, int revents)
		2842	{
		2843	ev_timer_stop (EV_A_ w);
		2844
		2845	/* now it's one second after the most recent passwd change */
		2846	}
		2847
		2848	static void
		2849	stat_cb (EV_P_ ev_stat *w, int revents)
		2850	{
		2851	/* reset the one-second timer */
		2852	ev_timer_again (EV_A_ &timer);
		2853	}
		2854
		2855	...
		2856	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2857	ev_stat_start (loop, &passwd);
		2858	ev_timer_init (&timer, timer_cb, 0., 1.02);
1410		2859
1411		2860
1412	=head2 C<ev_idle> - when you've got nothing better to do...	2861	=head2 C<ev_idle> - when you've got nothing better to do...
1413		2862
1414	Idle watchers trigger events when no other events of the same or higher	2863	Idle watchers trigger events when no other events of the same or higher
1415	priority are pending (prepare, check and other idle watchers do not	2864	priority are pending (prepare, check and other idle watchers do not count
1416	count).	2865	as receiving "events").
1417		2866
1418	That is, as long as your process is busy handling sockets or timeouts	2867	That is, as long as your process is busy handling sockets or timeouts
1419	(or even signals, imagine) of the same or higher priority it will not be	2868	(or even signals, imagine) of the same or higher priority it will not be
1420	triggered. But when your process is idle (or only lower-priority watchers	2869	triggered. But when your process is idle (or only lower-priority watchers
1421	are pending), the idle watchers are being called once per event loop	2870	are pending), the idle watchers are being called once per event loop
…		…
1428	Apart from keeping your process non-blocking (which is a useful	2877	Apart from keeping your process non-blocking (which is a useful
1429	effect on its own sometimes), idle watchers are a good place to do	2878	effect on its own sometimes), idle watchers are a good place to do
1430	"pseudo-background processing", or delay processing stuff to after the	2879	"pseudo-background processing", or delay processing stuff to after the
1431	event loop has handled all outstanding events.	2880	event loop has handled all outstanding events.
1432		2881
		2882	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2883
		2884	As long as there is at least one active idle watcher, libev will never
		2885	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2886	For this to work, the idle watcher doesn't need to be invoked at all - the
		2887	lowest priority will do.
		2888
		2889	This mode of operation can be useful together with an C<ev_check> watcher,
		2890	to do something on each event loop iteration - for example to balance load
		2891	between different connections.
		2892
		2893	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2894	example.
		2895
		2896	=head3 Watcher-Specific Functions and Data Members
		2897
1433	=over 4	2898	=over 4
1434		2899
1435	=item ev_idle_init (ev_signal *, callback)	2900	=item ev_idle_init (ev_idle *, callback)
1436		2901
1437	Initialises and configures the idle watcher - it has no parameters of any	2902	Initialises and configures the idle watcher - it has no parameters of any
1438	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2903	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1439	believe me.	2904	believe me.
1440		2905
1441	=back	2906	=back
1442		2907
		2908	=head3 Examples
		2909
1443	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2910	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1444	callback, free it. Also, use no error checking, as usual.	2911	callback, free it. Also, use no error checking, as usual.
1445		2912
1446	static void	2913	static void
1447	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2914	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1448	{	2915	{
		2916	// stop the watcher
		2917	ev_idle_stop (loop, w);
		2918
		2919	// now we can free it
1449	free (w);	2920	free (w);
		2921
1450	// now do something you wanted to do when the program has	2922	// now do something you wanted to do when the program has
1451	// no longer asnything immediate to do.	2923	// no longer anything immediate to do.
1452	}	2924	}
1453		2925
1454	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2926	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1455	ev_idle_init (idle_watcher, idle_cb);	2927	ev_idle_init (idle_watcher, idle_cb);
1456	ev_idle_start (loop, idle_cb);	2928	ev_idle_start (loop, idle_watcher);
1457		2929
1458		2930
1459	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2931	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1460		2932
1461	Prepare and check watchers are usually (but not always) used in tandem:	2933	Prepare and check watchers are often (but not always) used in pairs:
1462	prepare watchers get invoked before the process blocks and check watchers	2934	prepare watchers get invoked before the process blocks and check watchers
1463	afterwards.	2935	afterwards.
1464		2936
1465	You I<must not> call C<ev_loop> or similar functions that enter	2937	You I<must not> call C<ev_run> (or similar functions that enter the
1466	the current event loop from either C<ev_prepare> or C<ev_check>	2938	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
1467	watchers. Other loops than the current one are fine, however. The	2939	C<ev_check> watchers. Other loops than the current one are fine,
1468	rationale behind this is that you do not need to check for recursion in	2940	however. The rationale behind this is that you do not need to check
1469	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2941	for recursion in those watchers, i.e. the sequence will always be
1470	C<ev_check> so if you have one watcher of each kind they will always be	2942	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
1471	called in pairs bracketing the blocking call.	2943	kind they will always be called in pairs bracketing the blocking call.
1472		2944
1473	Their main purpose is to integrate other event mechanisms into libev and	2945	Their main purpose is to integrate other event mechanisms into libev and
1474	their use is somewhat advanced. This could be used, for example, to track	2946	their use is somewhat advanced. They could be used, for example, to track
1475	variable changes, implement your own watchers, integrate net-snmp or a	2947	variable changes, implement your own watchers, integrate net-snmp or a
1476	coroutine library and lots more. They are also occasionally useful if	2948	coroutine library and lots more. They are also occasionally useful if
1477	you cache some data and want to flush it before blocking (for example,	2949	you cache some data and want to flush it before blocking (for example,
1478	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2950	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1479	watcher).	2951	watcher).
1480		2952
1481	This is done by examining in each prepare call which file descriptors need	2953	This is done by examining in each prepare call which file descriptors
1482	to be watched by the other library, registering C<ev_io> watchers for	2954	need to be watched by the other library, registering C<ev_io> watchers
1483	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2955	for them and starting an C<ev_timer> watcher for any timeouts (many
1484	provide just this functionality). Then, in the check watcher you check for	2956	libraries provide exactly this functionality). Then, in the check watcher,
1485	any events that occured (by checking the pending status of all watchers	2957	you check for any events that occurred (by checking the pending status
1486	and stopping them) and call back into the library. The I/O and timer	2958	of all watchers and stopping them) and call back into the library. The
1487	callbacks will never actually be called (but must be valid nevertheless,	2959	I/O and timer callbacks will never actually be called (but must be valid
1488	because you never know, you know?).	2960	nevertheless, because you never know, you know?).
1489		2961
1490	As another example, the Perl Coro module uses these hooks to integrate	2962	As another example, the Perl Coro module uses these hooks to integrate
1491	coroutines into libev programs, by yielding to other active coroutines	2963	coroutines into libev programs, by yielding to other active coroutines
1492	during each prepare and only letting the process block if no coroutines	2964	during each prepare and only letting the process block if no coroutines
1493	are ready to run (it's actually more complicated: it only runs coroutines	2965	are ready to run (it's actually more complicated: it only runs coroutines
1494	with priority higher than or equal to the event loop and one coroutine	2966	with priority higher than or equal to the event loop and one coroutine
1495	of lower priority, but only once, using idle watchers to keep the event	2967	of lower priority, but only once, using idle watchers to keep the event
1496	loop from blocking if lower-priority coroutines are active, thus mapping	2968	loop from blocking if lower-priority coroutines are active, thus mapping
1497	low-priority coroutines to idle/background tasks).	2969	low-priority coroutines to idle/background tasks).
1498		2970
1499	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2971	When used for this purpose, it is recommended to give C<ev_check> watchers
1500	priority, to ensure that they are being run before any other watchers	2972	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		2973	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2974	watchers).
		2975
1501	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2976	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1502	too) should not activate ("feed") events into libev. While libev fully	2977	activate ("feed") events into libev. While libev fully supports this, they
1503	supports this, they will be called before other C<ev_check> watchers did	2978	might get executed before other C<ev_check> watchers did their job. As
1504	their job. As C<ev_check> watchers are often used to embed other event	2979	C<ev_check> watchers are often used to embed other (non-libev) event
1505	loops those other event loops might be in an unusable state until their	2980	loops those other event loops might be in an unusable state until their
1506	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2981	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1507	others).	2982	others).
1508		2983
		2984	=head3 Abusing an C<ev_check> watcher for its side-effect
		2985
		2986	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2987	useful because they are called once per event loop iteration. For
		2988	example, if you want to handle a large number of connections fairly, you
		2989	normally only do a bit of work for each active connection, and if there
		2990	is more work to do, you wait for the next event loop iteration, so other
		2991	connections have a chance of making progress.
		2992
		2993	Using an C<ev_check> watcher is almost enough: it will be called on the
		2994	next event loop iteration. However, that isn't as soon as possible -
		2995	without external events, your C<ev_check> watcher will not be invoked.
		2996
		2997	This is where C<ev_idle> watchers come in handy - all you need is a
		2998	single global idle watcher that is active as long as you have one active
		2999	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3000	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3001	invoked. Neither watcher alone can do that.
		3002
		3003	=head3 Watcher-Specific Functions and Data Members
		3004
1509	=over 4	3005	=over 4
1510		3006
1511	=item ev_prepare_init (ev_prepare *, callback)	3007	=item ev_prepare_init (ev_prepare *, callback)
1512		3008
1513	=item ev_check_init (ev_check *, callback)	3009	=item ev_check_init (ev_check *, callback)
1514		3010
1515	Initialises and configures the prepare or check watcher - they have no	3011	Initialises and configures the prepare or check watcher - they have no
1516	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	3012	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1517	macros, but using them is utterly, utterly and completely pointless.	3013	macros, but using them is utterly, utterly, utterly and completely
		3014	pointless.
1518		3015
1519	=back	3016	=back
		3017
		3018	=head3 Examples
1520		3019
1521	There are a number of principal ways to embed other event loops or modules	3020	There are a number of principal ways to embed other event loops or modules
1522	into libev. Here are some ideas on how to include libadns into libev	3021	into libev. Here are some ideas on how to include libadns into libev
1523	(there is a Perl module named C<EV::ADNS> that does this, which you could	3022	(there is a Perl module named C<EV::ADNS> that does this, which you could
1524	use for an actually working example. Another Perl module named C<EV::Glib>	3023	use as a working example. Another Perl module named C<EV::Glib> embeds a
1525	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	3024	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1526	into the Glib event loop).	3025	Glib event loop).
1527		3026
1528	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	3027	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1529	and in a check watcher, destroy them and call into libadns. What follows	3028	and in a check watcher, destroy them and call into libadns. What follows
1530	is pseudo-code only of course. This requires you to either use a low	3029	is pseudo-code only of course. This requires you to either use a low
1531	priority for the check watcher or use C<ev_clear_pending> explicitly, as	3030	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1532	the callbacks for the IO/timeout watchers might not have been called yet.	3031	the callbacks for the IO/timeout watchers might not have been called yet.
1533		3032
1534	static ev_io iow [nfd];	3033	static ev_io iow [nfd];
1535	static ev_timer tw;	3034	static ev_timer tw;
1536		3035
1537	static void	3036	static void
1538	io_cb (ev_loop *loop, ev_io *w, int revents)	3037	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1539	{	3038	{
1540	}	3039	}
1541		3040
1542	// create io watchers for each fd and a timer before blocking	3041	// create io watchers for each fd and a timer before blocking
1543	static void	3042	static void
1544	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3043	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1545	{	3044	{
1546	int timeout = 3600000;	3045	int timeout = 3600000;
1547	struct pollfd fds [nfd];	3046	struct pollfd fds [nfd];
1548	// actual code will need to loop here and realloc etc.	3047	// actual code will need to loop here and realloc etc.
1549	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3048	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1550		3049
1551	/* the callback is illegal, but won't be called as we stop during check */	3050	/* the callback is illegal, but won't be called as we stop during check */
1552	ev_timer_init (&tw, 0, timeout * 1e-3);	3051	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1553	ev_timer_start (loop, &tw);	3052	ev_timer_start (loop, &tw);
1554		3053
1555	// create one ev_io per pollfd	3054	// create one ev_io per pollfd
1556	for (int i = 0; i < nfd; ++i)	3055	for (int i = 0; i < nfd; ++i)
1557	{	3056	{
1558	ev_io_init (iow + i, io_cb, fds [i].fd,	3057	ev_io_init (iow + i, io_cb, fds [i].fd,
1559	((fds [i].events & POLLIN ? EV_READ : 0)	3058	((fds [i].events & POLLIN ? EV_READ : 0)
1560	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	3059	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1561		3060
1562	fds [i].revents = 0;	3061	fds [i].revents = 0;
1563	ev_io_start (loop, iow + i);	3062	ev_io_start (loop, iow + i);
1564	}	3063	}
1565	}	3064	}
1566		3065
1567	// stop all watchers after blocking	3066	// stop all watchers after blocking
1568	static void	3067	static void
1569	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3068	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1570	{	3069	{
1571	ev_timer_stop (loop, &tw);	3070	ev_timer_stop (loop, &tw);
1572		3071
1573	for (int i = 0; i < nfd; ++i)	3072	for (int i = 0; i < nfd; ++i)
1574	{	3073	{
1575	// set the relevant poll flags	3074	// set the relevant poll flags
1576	// could also call adns_processreadable etc. here	3075	// could also call adns_processreadable etc. here
1577	struct pollfd *fd = fds + i;	3076	struct pollfd *fd = fds + i;
1578	int revents = ev_clear_pending (iow + i);	3077	int revents = ev_clear_pending (iow + i);
1579	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	3078	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1580	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	3079	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1581		3080
1582	// now stop the watcher	3081	// now stop the watcher
1583	ev_io_stop (loop, iow + i);	3082	ev_io_stop (loop, iow + i);
1584	}	3083	}
1585		3084
1586	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3085	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1587	}	3086	}
1588		3087
1589	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	3088	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1590	in the prepare watcher and would dispose of the check watcher.	3089	in the prepare watcher and would dispose of the check watcher.
1591		3090
1592	Method 3: If the module to be embedded supports explicit event	3091	Method 3: If the module to be embedded supports explicit event
1593	notification (adns does), you can also make use of the actual watcher	3092	notification (libadns does), you can also make use of the actual watcher
1594	callbacks, and only destroy/create the watchers in the prepare watcher.	3093	callbacks, and only destroy/create the watchers in the prepare watcher.
1595		3094
1596	static void	3095	static void
1597	timer_cb (EV_P_ ev_timer *w, int revents)	3096	timer_cb (EV_P_ ev_timer *w, int revents)
1598	{	3097	{
1599	adns_state ads = (adns_state)w->data;	3098	adns_state ads = (adns_state)w->data;
1600	update_now (EV_A);	3099	update_now (EV_A);
1601		3100
1602	adns_processtimeouts (ads, &tv_now);	3101	adns_processtimeouts (ads, &tv_now);
1603	}	3102	}
1604		3103
1605	static void	3104	static void
1606	io_cb (EV_P_ ev_io *w, int revents)	3105	io_cb (EV_P_ ev_io *w, int revents)
1607	{	3106	{
1608	adns_state ads = (adns_state)w->data;	3107	adns_state ads = (adns_state)w->data;
1609	update_now (EV_A);	3108	update_now (EV_A);
1610		3109
1611	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	3110	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1612	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	3111	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1613	}	3112	}
1614		3113
1615	// do not ever call adns_afterpoll	3114	// do not ever call adns_afterpoll
1616		3115
1617	Method 4: Do not use a prepare or check watcher because the module you	3116	Method 4: Do not use a prepare or check watcher because the module you
1618	want to embed is too inflexible to support it. Instead, youc na override	3117	want to embed is not flexible enough to support it. Instead, you can
1619	their poll function. The drawback with this solution is that the main	3118	override their poll function. The drawback with this solution is that the
1620	loop is now no longer controllable by EV. The C<Glib::EV> module does	3119	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1621	this.	3120	this approach, effectively embedding EV as a client into the horrible
		3121	libglib event loop.
1622		3122
1623	static gint	3123	static gint
1624	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3124	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1625	{	3125	{
1626	int got_events = 0;	3126	int got_events = 0;
1627		3127
1628	for (n = 0; n < nfds; ++n)	3128	for (n = 0; n < nfds; ++n)
1629	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	3129	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1630		3130
1631	if (timeout >= 0)	3131	if (timeout >= 0)
1632	// create/start timer	3132	// create/start timer
1633		3133
1634	// poll	3134	// poll
1635	ev_loop (EV_A_ 0);	3135	ev_run (EV_A_ 0);
1636		3136
1637	// stop timer again	3137	// stop timer again
1638	if (timeout >= 0)	3138	if (timeout >= 0)
1639	ev_timer_stop (EV_A_ &to);	3139	ev_timer_stop (EV_A_ &to);
1640		3140
1641	// stop io watchers again - their callbacks should have set	3141	// stop io watchers again - their callbacks should have set
1642	for (n = 0; n < nfds; ++n)	3142	for (n = 0; n < nfds; ++n)
1643	ev_io_stop (EV_A_ iow [n]);	3143	ev_io_stop (EV_A_ iow [n]);
1644		3144
1645	return got_events;	3145	return got_events;
1646	}	3146	}
1647		3147
1648		3148
1649	=head2 C<ev_embed> - when one backend isn't enough...	3149	=head2 C<ev_embed> - when one backend isn't enough...
1650		3150
1651	This is a rather advanced watcher type that lets you embed one event loop	3151	This is a rather advanced watcher type that lets you embed one event loop
…		…
1657	prioritise I/O.	3157	prioritise I/O.
1658		3158
1659	As an example for a bug workaround, the kqueue backend might only support	3159	As an example for a bug workaround, the kqueue backend might only support
1660	sockets on some platform, so it is unusable as generic backend, but you	3160	sockets on some platform, so it is unusable as generic backend, but you
1661	still want to make use of it because you have many sockets and it scales	3161	still want to make use of it because you have many sockets and it scales
1662	so nicely. In this case, you would create a kqueue-based loop and embed it	3162	so nicely. In this case, you would create a kqueue-based loop and embed
1663	into your default loop (which might use e.g. poll). Overall operation will	3163	it into your default loop (which might use e.g. poll). Overall operation
1664	be a bit slower because first libev has to poll and then call kevent, but	3164	will be a bit slower because first libev has to call C<poll> and then
1665	at least you can use both at what they are best.	3165	C<kevent>, but at least you can use both mechanisms for what they are
		3166	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1666		3167
1667	As for prioritising I/O: rarely you have the case where some fds have	3168	As for prioritising I/O: under rare circumstances you have the case where
1668	to be watched and handled very quickly (with low latency), and even	3169	some fds have to be watched and handled very quickly (with low latency),
1669	priorities and idle watchers might have too much overhead. In this case	3170	and even priorities and idle watchers might have too much overhead. In
1670	you would put all the high priority stuff in one loop and all the rest in	3171	this case you would put all the high priority stuff in one loop and all
1671	a second one, and embed the second one in the first.	3172	the rest in a second one, and embed the second one in the first.
1672		3173
1673	As long as the watcher is active, the callback will be invoked every time	3174	As long as the watcher is active, the callback will be invoked every
1674	there might be events pending in the embedded loop. The callback must then	3175	time there might be events pending in the embedded loop. The callback
1675	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3176	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1676	their callbacks (you could also start an idle watcher to give the embedded	3177	sweep and invoke their callbacks (the callback doesn't need to invoke the
1677	loop strictly lower priority for example). You can also set the callback	3178	C<ev_embed_sweep> function directly, it could also start an idle watcher
1678	to C<0>, in which case the embed watcher will automatically execute the	3179	to give the embedded loop strictly lower priority for example).
1679	embedded loop sweep.
1680		3180
1681	As long as the watcher is started it will automatically handle events. The	3181	You can also set the callback to C<0>, in which case the embed watcher
1682	callback will be invoked whenever some events have been handled. You can	3182	will automatically execute the embedded loop sweep whenever necessary.
1683	set the callback to C<0> to avoid having to specify one if you are not
1684	interested in that.
1685		3183
1686	Also, there have not currently been made special provisions for forking:	3184	Fork detection will be handled transparently while the C<ev_embed> watcher
1687	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3185	is active, i.e., the embedded loop will automatically be forked when the
1688	but you will also have to stop and restart any C<ev_embed> watchers	3186	embedding loop forks. In other cases, the user is responsible for calling
1689	yourself.	3187	C<ev_loop_fork> on the embedded loop.
1690		3188
1691	Unfortunately, not all backends are embeddable, only the ones returned by	3189	Unfortunately, not all backends are embeddable: only the ones returned by
1692	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3190	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1693	portable one.	3191	portable one.
1694		3192
1695	So when you want to use this feature you will always have to be prepared	3193	So when you want to use this feature you will always have to be prepared
1696	that you cannot get an embeddable loop. The recommended way to get around	3194	that you cannot get an embeddable loop. The recommended way to get around
1697	this is to have a separate variables for your embeddable loop, try to	3195	this is to have a separate variables for your embeddable loop, try to
1698	create it, and if that fails, use the normal loop for everything:	3196	create it, and if that fails, use the normal loop for everything.
1699		3197
1700	struct ev_loop *loop_hi = ev_default_init (0);	3198	=head3 C<ev_embed> and fork
1701	struct ev_loop *loop_lo = 0;
1702	struct ev_embed embed;
1703
1704	// see if there is a chance of getting one that works
1705	// (remember that a flags value of 0 means autodetection)
1706	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1707	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1708	: 0;
1709		3199
1710	// if we got one, then embed it, otherwise default to loop_hi	3200	While the C<ev_embed> watcher is running, forks in the embedding loop will
1711	if (loop_lo)	3201	automatically be applied to the embedded loop as well, so no special
1712	{	3202	fork handling is required in that case. When the watcher is not running,
1713	ev_embed_init (&embed, 0, loop_lo);	3203	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1714	ev_embed_start (loop_hi, &embed);	3204	as applicable.
1715	}	3205
1716	else	3206	=head3 Watcher-Specific Functions and Data Members
1717	loop_lo = loop_hi;
1718		3207
1719	=over 4	3208	=over 4
1720		3209
1721	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3210	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1722		3211
1723	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3212	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
1724		3213
1725	Configures the watcher to embed the given loop, which must be	3214	Configures the watcher to embed the given loop, which must be
1726	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3215	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1727	invoked automatically, otherwise it is the responsibility of the callback	3216	invoked automatically, otherwise it is the responsibility of the callback
1728	to invoke it (it will continue to be called until the sweep has been done,	3217	to invoke it (it will continue to be called until the sweep has been done,
1729	if you do not want thta, you need to temporarily stop the embed watcher).	3218	if you do not want that, you need to temporarily stop the embed watcher).
1730		3219
1731	=item ev_embed_sweep (loop, ev_embed *)	3220	=item ev_embed_sweep (loop, ev_embed *)
1732		3221
1733	Make a single, non-blocking sweep over the embedded loop. This works	3222	Make a single, non-blocking sweep over the embedded loop. This works
1734	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3223	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1735	apropriate way for embedded loops.	3224	appropriate way for embedded loops.
1736		3225
1737	=item struct ev_loop *loop [read-only]	3226	=item struct ev_loop *other [read-only]
1738		3227
1739	The embedded event loop.	3228	The embedded event loop.
1740		3229
1741	=back	3230	=back
		3231
		3232	=head3 Examples
		3233
		3234	Example: Try to get an embeddable event loop and embed it into the default
		3235	event loop. If that is not possible, use the default loop. The default
		3236	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3237	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3238	used).
		3239
		3240	struct ev_loop *loop_hi = ev_default_init (0);
		3241	struct ev_loop *loop_lo = 0;
		3242	ev_embed embed;
		3243
		3244	// see if there is a chance of getting one that works
		3245	// (remember that a flags value of 0 means autodetection)
		3246	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3247	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3248	: 0;
		3249
		3250	// if we got one, then embed it, otherwise default to loop_hi
		3251	if (loop_lo)
		3252	{
		3253	ev_embed_init (&embed, 0, loop_lo);
		3254	ev_embed_start (loop_hi, &embed);
		3255	}
		3256	else
		3257	loop_lo = loop_hi;
		3258
		3259	Example: Check if kqueue is available but not recommended and create
		3260	a kqueue backend for use with sockets (which usually work with any
		3261	kqueue implementation). Store the kqueue/socket-only event loop in
		3262	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3263
		3264	struct ev_loop *loop = ev_default_init (0);
		3265	struct ev_loop *loop_socket = 0;
		3266	ev_embed embed;
		3267
		3268	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3269	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3270	{
		3271	ev_embed_init (&embed, 0, loop_socket);
		3272	ev_embed_start (loop, &embed);
		3273	}
		3274
		3275	if (!loop_socket)
		3276	loop_socket = loop;
		3277
		3278	// now use loop_socket for all sockets, and loop for everything else
1742		3279
1743		3280
1744	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3281	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1745		3282
1746	Fork watchers are called when a C<fork ()> was detected (usually because	3283	Fork watchers are called when a C<fork ()> was detected (usually because
1747	whoever is a good citizen cared to tell libev about it by calling	3284	whoever is a good citizen cared to tell libev about it by calling
1748	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3285	C<ev_loop_fork>). The invocation is done before the event loop blocks next
1749	event loop blocks next and before C<ev_check> watchers are being called,	3286	and before C<ev_check> watchers are being called, and only in the child
1750	and only in the child after the fork. If whoever good citizen calling	3287	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
1751	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3288	and calls it in the wrong process, the fork handlers will be invoked, too,
1752	handlers will be invoked, too, of course.	3289	of course.
		3290
		3291	=head3 The special problem of life after fork - how is it possible?
		3292
		3293	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3294	up/change the process environment, followed by a call to C<exec()>. This
		3295	sequence should be handled by libev without any problems.
		3296
		3297	This changes when the application actually wants to do event handling
		3298	in the child, or both parent in child, in effect "continuing" after the
		3299	fork.
		3300
		3301	The default mode of operation (for libev, with application help to detect
		3302	forks) is to duplicate all the state in the child, as would be expected
		3303	when I<either> the parent I<or> the child process continues.
		3304
		3305	When both processes want to continue using libev, then this is usually the
		3306	wrong result. In that case, usually one process (typically the parent) is
		3307	supposed to continue with all watchers in place as before, while the other
		3308	process typically wants to start fresh, i.e. without any active watchers.
		3309
		3310	The cleanest and most efficient way to achieve that with libev is to
		3311	simply create a new event loop, which of course will be "empty", and
		3312	use that for new watchers. This has the advantage of not touching more
		3313	memory than necessary, and thus avoiding the copy-on-write, and the
		3314	disadvantage of having to use multiple event loops (which do not support
		3315	signal watchers).
		3316
		3317	When this is not possible, or you want to use the default loop for
		3318	other reasons, then in the process that wants to start "fresh", call
		3319	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3320	Destroying the default loop will "orphan" (not stop) all registered
		3321	watchers, so you have to be careful not to execute code that modifies
		3322	those watchers. Note also that in that case, you have to re-register any
		3323	signal watchers.
		3324
		3325	=head3 Watcher-Specific Functions and Data Members
1753		3326
1754	=over 4	3327	=over 4
1755		3328
1756	=item ev_fork_init (ev_signal *, callback)	3329	=item ev_fork_init (ev_fork *, callback)
1757		3330
1758	Initialises and configures the fork watcher - it has no parameters of any	3331	Initialises and configures the fork watcher - it has no parameters of any
1759	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3332	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1760	believe me.	3333	really.
1761		3334
1762	=back	3335	=back
1763		3336
1764		3337
		3338	=head2 C<ev_cleanup> - even the best things end
		3339
		3340	Cleanup watchers are called just before the event loop is being destroyed
		3341	by a call to C<ev_loop_destroy>.
		3342
		3343	While there is no guarantee that the event loop gets destroyed, cleanup
		3344	watchers provide a convenient method to install cleanup hooks for your
		3345	program, worker threads and so on - you just to make sure to destroy the
		3346	loop when you want them to be invoked.
		3347
		3348	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3349	all other watchers, they do not keep a reference to the event loop (which
		3350	makes a lot of sense if you think about it). Like all other watchers, you
		3351	can call libev functions in the callback, except C<ev_cleanup_start>.
		3352
		3353	=head3 Watcher-Specific Functions and Data Members
		3354
		3355	=over 4
		3356
		3357	=item ev_cleanup_init (ev_cleanup *, callback)
		3358
		3359	Initialises and configures the cleanup watcher - it has no parameters of
		3360	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3361	pointless, I assure you.
		3362
		3363	=back
		3364
		3365	Example: Register an atexit handler to destroy the default loop, so any
		3366	cleanup functions are called.
		3367
		3368	static void
		3369	program_exits (void)
		3370	{
		3371	ev_loop_destroy (EV_DEFAULT_UC);
		3372	}
		3373
		3374	...
		3375	atexit (program_exits);
		3376
		3377
		3378	=head2 C<ev_async> - how to wake up an event loop
		3379
		3380	In general, you cannot use an C<ev_loop> from multiple threads or other
		3381	asynchronous sources such as signal handlers (as opposed to multiple event
		3382	loops - those are of course safe to use in different threads).
		3383
		3384	Sometimes, however, you need to wake up an event loop you do not control,
		3385	for example because it belongs to another thread. This is what C<ev_async>
		3386	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3387	it by calling C<ev_async_send>, which is thread- and signal safe.
		3388
		3389	This functionality is very similar to C<ev_signal> watchers, as signals,
		3390	too, are asynchronous in nature, and signals, too, will be compressed
		3391	(i.e. the number of callback invocations may be less than the number of
		3392	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3393	of "global async watchers" by using a watcher on an otherwise unused
		3394	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3395	even without knowing which loop owns the signal.
		3396
		3397	=head3 Queueing
		3398
		3399	C<ev_async> does not support queueing of data in any way. The reason
		3400	is that the author does not know of a simple (or any) algorithm for a
		3401	multiple-writer-single-reader queue that works in all cases and doesn't
		3402	need elaborate support such as pthreads or unportable memory access
		3403	semantics.
		3404
		3405	That means that if you want to queue data, you have to provide your own
		3406	queue. But at least I can tell you how to implement locking around your
		3407	queue:
		3408
		3409	=over 4
		3410
		3411	=item queueing from a signal handler context
		3412
		3413	To implement race-free queueing, you simply add to the queue in the signal
		3414	handler but you block the signal handler in the watcher callback. Here is
		3415	an example that does that for some fictitious SIGUSR1 handler:
		3416
		3417	static ev_async mysig;
		3418
		3419	static void
		3420	sigusr1_handler (void)
		3421	{
		3422	sometype data;
		3423
		3424	// no locking etc.
		3425	queue_put (data);
		3426	ev_async_send (EV_DEFAULT_ &mysig);
		3427	}
		3428
		3429	static void
		3430	mysig_cb (EV_P_ ev_async *w, int revents)
		3431	{
		3432	sometype data;
		3433	sigset_t block, prev;
		3434
		3435	sigemptyset (&block);
		3436	sigaddset (&block, SIGUSR1);
		3437	sigprocmask (SIG_BLOCK, &block, &prev);
		3438
		3439	while (queue_get (&data))
		3440	process (data);
		3441
		3442	if (sigismember (&prev, SIGUSR1)
		3443	sigprocmask (SIG_UNBLOCK, &block, 0);
		3444	}
		3445
		3446	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3447	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3448	either...).
		3449
		3450	=item queueing from a thread context
		3451
		3452	The strategy for threads is different, as you cannot (easily) block
		3453	threads but you can easily preempt them, so to queue safely you need to
		3454	employ a traditional mutex lock, such as in this pthread example:
		3455
		3456	static ev_async mysig;
		3457	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3458
		3459	static void
		3460	otherthread (void)
		3461	{
		3462	// only need to lock the actual queueing operation
		3463	pthread_mutex_lock (&mymutex);
		3464	queue_put (data);
		3465	pthread_mutex_unlock (&mymutex);
		3466
		3467	ev_async_send (EV_DEFAULT_ &mysig);
		3468	}
		3469
		3470	static void
		3471	mysig_cb (EV_P_ ev_async *w, int revents)
		3472	{
		3473	pthread_mutex_lock (&mymutex);
		3474
		3475	while (queue_get (&data))
		3476	process (data);
		3477
		3478	pthread_mutex_unlock (&mymutex);
		3479	}
		3480
		3481	=back
		3482
		3483
		3484	=head3 Watcher-Specific Functions and Data Members
		3485
		3486	=over 4
		3487
		3488	=item ev_async_init (ev_async *, callback)
		3489
		3490	Initialises and configures the async watcher - it has no parameters of any
		3491	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3492	trust me.
		3493
		3494	=item ev_async_send (loop, ev_async *)
		3495
		3496	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3497	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3498	returns.
		3499
		3500	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3501	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3502	embedding section below on what exactly this means).
		3503
		3504	Note that, as with other watchers in libev, multiple events might get
		3505	compressed into a single callback invocation (another way to look at
		3506	this is that C<ev_async> watchers are level-triggered: they are set on
		3507	C<ev_async_send>, reset when the event loop detects that).
		3508
		3509	This call incurs the overhead of at most one extra system call per event
		3510	loop iteration, if the event loop is blocked, and no syscall at all if
		3511	the event loop (or your program) is processing events. That means that
		3512	repeated calls are basically free (there is no need to avoid calls for
		3513	performance reasons) and that the overhead becomes smaller (typically
		3514	zero) under load.
		3515
		3516	=item bool = ev_async_pending (ev_async *)
		3517
		3518	Returns a non-zero value when C<ev_async_send> has been called on the
		3519	watcher but the event has not yet been processed (or even noted) by the
		3520	event loop.
		3521
		3522	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3523	the loop iterates next and checks for the watcher to have become active,
		3524	it will reset the flag again. C<ev_async_pending> can be used to very
		3525	quickly check whether invoking the loop might be a good idea.
		3526
		3527	Not that this does I<not> check whether the watcher itself is pending,
		3528	only whether it has been requested to make this watcher pending: there
		3529	is a time window between the event loop checking and resetting the async
		3530	notification, and the callback being invoked.
		3531
		3532	=back
		3533
		3534
1765	=head1 OTHER FUNCTIONS	3535	=head1 OTHER FUNCTIONS
1766		3536
1767	There are some other functions of possible interest. Described. Here. Now.	3537	There are some other functions of possible interest. Described. Here. Now.
1768		3538
1769	=over 4	3539	=over 4
1770		3540
1771	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3541	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
1772		3542
1773	This function combines a simple timer and an I/O watcher, calls your	3543	This function combines a simple timer and an I/O watcher, calls your
1774	callback on whichever event happens first and automatically stop both	3544	callback on whichever event happens first and automatically stops both
1775	watchers. This is useful if you want to wait for a single event on an fd	3545	watchers. This is useful if you want to wait for a single event on an fd
1776	or timeout without having to allocate/configure/start/stop/free one or	3546	or timeout without having to allocate/configure/start/stop/free one or
1777	more watchers yourself.	3547	more watchers yourself.
1778		3548
1779	If C<fd> is less than 0, then no I/O watcher will be started and events	3549	If C<fd> is less than 0, then no I/O watcher will be started and the
1780	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3550	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1781	C<events> set will be craeted and started.	3551	the given C<fd> and C<events> set will be created and started.
1782		3552
1783	If C<timeout> is less than 0, then no timeout watcher will be	3553	If C<timeout> is less than 0, then no timeout watcher will be
1784	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3554	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1785	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3555	repeat = 0) will be started. C<0> is a valid timeout.
1786	dubious value.
1787		3556
1788	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3557	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1789	passed an C<revents> set like normal event callbacks (a combination of	3558	passed an C<revents> set like normal event callbacks (a combination of
1790	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3559	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1791	value passed to C<ev_once>:	3560	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3561	a timeout and an io event at the same time - you probably should give io
		3562	events precedence.
1792		3563
		3564	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3565
1793	static void stdin_ready (int revents, void *arg)	3566	static void stdin_ready (int revents, void *arg)
		3567	{
		3568	if (revents & EV_READ)
		3569	/* stdin might have data for us, joy! */;
		3570	else if (revents & EV_TIMER)
		3571	/* doh, nothing entered */;
		3572	}
		3573
		3574	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3575
		3576	=item ev_feed_fd_event (loop, int fd, int revents)
		3577
		3578	Feed an event on the given fd, as if a file descriptor backend detected
		3579	the given events.
		3580
		3581	=item ev_feed_signal_event (loop, int signum)
		3582
		3583	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3584	which is async-safe.
		3585
		3586	=back
		3587
		3588
		3589	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3590
		3591	This section explains some common idioms that are not immediately
		3592	obvious. Note that examples are sprinkled over the whole manual, and this
		3593	section only contains stuff that wouldn't fit anywhere else.
		3594
		3595	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3596
		3597	Each watcher has, by default, a C<void *data> member that you can read
		3598	or modify at any time: libev will completely ignore it. This can be used
		3599	to associate arbitrary data with your watcher. If you need more data and
		3600	don't want to allocate memory separately and store a pointer to it in that
		3601	data member, you can also "subclass" the watcher type and provide your own
		3602	data:
		3603
		3604	struct my_io
		3605	{
		3606	ev_io io;
		3607	int otherfd;
		3608	void *somedata;
		3609	struct whatever *mostinteresting;
		3610	};
		3611
		3612	...
		3613	struct my_io w;
		3614	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3615
		3616	And since your callback will be called with a pointer to the watcher, you
		3617	can cast it back to your own type:
		3618
		3619	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3620	{
		3621	struct my_io *w = (struct my_io *)w_;
		3622	...
		3623	}
		3624
		3625	More interesting and less C-conformant ways of casting your callback
		3626	function type instead have been omitted.
		3627
		3628	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3629
		3630	Another common scenario is to use some data structure with multiple
		3631	embedded watchers, in effect creating your own watcher that combines
		3632	multiple libev event sources into one "super-watcher":
		3633
		3634	struct my_biggy
		3635	{
		3636	int some_data;
		3637	ev_timer t1;
		3638	ev_timer t2;
		3639	}
		3640
		3641	In this case getting the pointer to C<my_biggy> is a bit more
		3642	complicated: Either you store the address of your C<my_biggy> struct in
		3643	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3644	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3645	real programmers):
		3646
		3647	#include <stddef.h>
		3648
		3649	static void
		3650	t1_cb (EV_P_ ev_timer *w, int revents)
		3651	{
		3652	struct my_biggy big = (struct my_biggy *)
		3653	(((char *)w) - offsetof (struct my_biggy, t1));
		3654	}
		3655
		3656	static void
		3657	t2_cb (EV_P_ ev_timer *w, int revents)
		3658	{
		3659	struct my_biggy big = (struct my_biggy *)
		3660	(((char *)w) - offsetof (struct my_biggy, t2));
		3661	}
		3662
		3663	=head2 AVOIDING FINISHING BEFORE RETURNING
		3664
		3665	Often you have structures like this in event-based programs:
		3666
		3667	callback ()
1794	{	3668	{
1795	if (revents & EV_TIMEOUT)	3669	free (request);
1796	/* doh, nothing entered */;
1797	else if (revents & EV_READ)
1798	/* stdin might have data for us, joy! */;
1799	}	3670	}
1800		3671
1801	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3672	request = start_new_request (..., callback);
1802		3673
1803	=item ev_feed_event (ev_loop *, watcher *, int revents)	3674	The intent is to start some "lengthy" operation. The C<request> could be
		3675	used to cancel the operation, or do other things with it.
1804		3676
1805	Feeds the given event set into the event loop, as if the specified event	3677	It's not uncommon to have code paths in C<start_new_request> that
1806	had happened for the specified watcher (which must be a pointer to an	3678	immediately invoke the callback, for example, to report errors. Or you add
1807	initialised but not necessarily started event watcher).	3679	some caching layer that finds that it can skip the lengthy aspects of the
		3680	operation and simply invoke the callback with the result.
1808		3681
1809	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3682	The problem here is that this will happen I<before> C<start_new_request>
		3683	has returned, so C<request> is not set.
1810		3684
1811	Feed an event on the given fd, as if a file descriptor backend detected	3685	Even if you pass the request by some safer means to the callback, you
1812	the given events it.	3686	might want to do something to the request after starting it, such as
		3687	canceling it, which probably isn't working so well when the callback has
		3688	already been invoked.
1813		3689
1814	=item ev_feed_signal_event (ev_loop *loop, int signum)	3690	A common way around all these issues is to make sure that
		3691	C<start_new_request> I<always> returns before the callback is invoked. If
		3692	C<start_new_request> immediately knows the result, it can artificially
		3693	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3694	example, or more sneakily, by reusing an existing (stopped) watcher and
		3695	pushing it into the pending queue:
1815		3696
1816	Feed an event as if the given signal occured (C<loop> must be the default	3697	ev_set_cb (watcher, callback);
1817	loop!).	3698	ev_feed_event (EV_A_ watcher, 0);
1818		3699
1819	=back	3700	This way, C<start_new_request> can safely return before the callback is
		3701	invoked, while not delaying callback invocation too much.
		3702
		3703	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3704
		3705	Often (especially in GUI toolkits) there are places where you have
		3706	I<modal> interaction, which is most easily implemented by recursively
		3707	invoking C<ev_run>.
		3708
		3709	This brings the problem of exiting - a callback might want to finish the
		3710	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3711	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3712	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3713	other combination: In these cases, a simple C<ev_break> will not work.
		3714
		3715	The solution is to maintain "break this loop" variable for each C<ev_run>
		3716	invocation, and use a loop around C<ev_run> until the condition is
		3717	triggered, using C<EVRUN_ONCE>:
		3718
		3719	// main loop
		3720	int exit_main_loop = 0;
		3721
		3722	while (!exit_main_loop)
		3723	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3724
		3725	// in a modal watcher
		3726	int exit_nested_loop = 0;
		3727
		3728	while (!exit_nested_loop)
		3729	ev_run (EV_A_ EVRUN_ONCE);
		3730
		3731	To exit from any of these loops, just set the corresponding exit variable:
		3732
		3733	// exit modal loop
		3734	exit_nested_loop = 1;
		3735
		3736	// exit main program, after modal loop is finished
		3737	exit_main_loop = 1;
		3738
		3739	// exit both
		3740	exit_main_loop = exit_nested_loop = 1;
		3741
		3742	=head2 THREAD LOCKING EXAMPLE
		3743
		3744	Here is a fictitious example of how to run an event loop in a different
		3745	thread from where callbacks are being invoked and watchers are
		3746	created/added/removed.
		3747
		3748	For a real-world example, see the C<EV::Loop::Async> perl module,
		3749	which uses exactly this technique (which is suited for many high-level
		3750	languages).
		3751
		3752	The example uses a pthread mutex to protect the loop data, a condition
		3753	variable to wait for callback invocations, an async watcher to notify the
		3754	event loop thread and an unspecified mechanism to wake up the main thread.
		3755
		3756	First, you need to associate some data with the event loop:
		3757
		3758	typedef struct {
		3759	mutex_t lock; /* global loop lock */
		3760	ev_async async_w;
		3761	thread_t tid;
		3762	cond_t invoke_cv;
		3763	} userdata;
		3764
		3765	void prepare_loop (EV_P)
		3766	{
		3767	// for simplicity, we use a static userdata struct.
		3768	static userdata u;
		3769
		3770	ev_async_init (&u->async_w, async_cb);
		3771	ev_async_start (EV_A_ &u->async_w);
		3772
		3773	pthread_mutex_init (&u->lock, 0);
		3774	pthread_cond_init (&u->invoke_cv, 0);
		3775
		3776	// now associate this with the loop
		3777	ev_set_userdata (EV_A_ u);
		3778	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3779	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3780
		3781	// then create the thread running ev_run
		3782	pthread_create (&u->tid, 0, l_run, EV_A);
		3783	}
		3784
		3785	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3786	solely to wake up the event loop so it takes notice of any new watchers
		3787	that might have been added:
		3788
		3789	static void
		3790	async_cb (EV_P_ ev_async *w, int revents)
		3791	{
		3792	// just used for the side effects
		3793	}
		3794
		3795	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3796	protecting the loop data, respectively.
		3797
		3798	static void
		3799	l_release (EV_P)
		3800	{
		3801	userdata *u = ev_userdata (EV_A);
		3802	pthread_mutex_unlock (&u->lock);
		3803	}
		3804
		3805	static void
		3806	l_acquire (EV_P)
		3807	{
		3808	userdata *u = ev_userdata (EV_A);
		3809	pthread_mutex_lock (&u->lock);
		3810	}
		3811
		3812	The event loop thread first acquires the mutex, and then jumps straight
		3813	into C<ev_run>:
		3814
		3815	void *
		3816	l_run (void *thr_arg)
		3817	{
		3818	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3819
		3820	l_acquire (EV_A);
		3821	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3822	ev_run (EV_A_ 0);
		3823	l_release (EV_A);
		3824
		3825	return 0;
		3826	}
		3827
		3828	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3829	signal the main thread via some unspecified mechanism (signals? pipe
		3830	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3831	have been called (in a while loop because a) spurious wakeups are possible
		3832	and b) skipping inter-thread-communication when there are no pending
		3833	watchers is very beneficial):
		3834
		3835	static void
		3836	l_invoke (EV_P)
		3837	{
		3838	userdata *u = ev_userdata (EV_A);
		3839
		3840	while (ev_pending_count (EV_A))
		3841	{
		3842	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3843	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3844	}
		3845	}
		3846
		3847	Now, whenever the main thread gets told to invoke pending watchers, it
		3848	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3849	thread to continue:
		3850
		3851	static void
		3852	real_invoke_pending (EV_P)
		3853	{
		3854	userdata *u = ev_userdata (EV_A);
		3855
		3856	pthread_mutex_lock (&u->lock);
		3857	ev_invoke_pending (EV_A);
		3858	pthread_cond_signal (&u->invoke_cv);
		3859	pthread_mutex_unlock (&u->lock);
		3860	}
		3861
		3862	Whenever you want to start/stop a watcher or do other modifications to an
		3863	event loop, you will now have to lock:
		3864
		3865	ev_timer timeout_watcher;
		3866	userdata *u = ev_userdata (EV_A);
		3867
		3868	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3869
		3870	pthread_mutex_lock (&u->lock);
		3871	ev_timer_start (EV_A_ &timeout_watcher);
		3872	ev_async_send (EV_A_ &u->async_w);
		3873	pthread_mutex_unlock (&u->lock);
		3874
		3875	Note that sending the C<ev_async> watcher is required because otherwise
		3876	an event loop currently blocking in the kernel will have no knowledge
		3877	about the newly added timer. By waking up the loop it will pick up any new
		3878	watchers in the next event loop iteration.
		3879
		3880	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3881
		3882	While the overhead of a callback that e.g. schedules a thread is small, it
		3883	is still an overhead. If you embed libev, and your main usage is with some
		3884	kind of threads or coroutines, you might want to customise libev so that
		3885	doesn't need callbacks anymore.
		3886
		3887	Imagine you have coroutines that you can switch to using a function
		3888	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3889	and that due to some magic, the currently active coroutine is stored in a
		3890	global called C<current_coro>. Then you can build your own "wait for libev
		3891	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3892	the differing C<;> conventions):
		3893
		3894	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3895	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3896
		3897	That means instead of having a C callback function, you store the
		3898	coroutine to switch to in each watcher, and instead of having libev call
		3899	your callback, you instead have it switch to that coroutine.
		3900
		3901	A coroutine might now wait for an event with a function called
		3902	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3903	matter when, or whether the watcher is active or not when this function is
		3904	called):
		3905
		3906	void
		3907	wait_for_event (ev_watcher *w)
		3908	{
		3909	ev_set_cb (w, current_coro);
		3910	switch_to (libev_coro);
		3911	}
		3912
		3913	That basically suspends the coroutine inside C<wait_for_event> and
		3914	continues the libev coroutine, which, when appropriate, switches back to
		3915	this or any other coroutine.
		3916
		3917	You can do similar tricks if you have, say, threads with an event queue -
		3918	instead of storing a coroutine, you store the queue object and instead of
		3919	switching to a coroutine, you push the watcher onto the queue and notify
		3920	any waiters.
		3921
		3922	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3923	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3924
		3925	// my_ev.h
		3926	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3927	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3928	#include "../libev/ev.h"
		3929
		3930	// my_ev.c
		3931	#define EV_H "my_ev.h"
		3932	#include "../libev/ev.c"
		3933
		3934	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3935	F<my_ev.c> into your project. When properly specifying include paths, you
		3936	can even use F<ev.h> as header file name directly.
1820		3937
1821		3938
1822	=head1 LIBEVENT EMULATION	3939	=head1 LIBEVENT EMULATION
1823		3940
1824	Libev offers a compatibility emulation layer for libevent. It cannot	3941	Libev offers a compatibility emulation layer for libevent. It cannot
1825	emulate the internals of libevent, so here are some usage hints:	3942	emulate the internals of libevent, so here are some usage hints:
1826		3943
1827	=over 4	3944	=over 4
		3945
		3946	=item * Only the libevent-1.4.1-beta API is being emulated.
		3947
		3948	This was the newest libevent version available when libev was implemented,
		3949	and is still mostly unchanged in 2010.
1828		3950
1829	=item * Use it by including <event.h>, as usual.	3951	=item * Use it by including <event.h>, as usual.
1830		3952
1831	=item * The following members are fully supported: ev_base, ev_callback,	3953	=item * The following members are fully supported: ev_base, ev_callback,
1832	ev_arg, ev_fd, ev_res, ev_events.	3954	ev_arg, ev_fd, ev_res, ev_events.
…		…
1837		3959
1838	=item * Priorities are not currently supported. Initialising priorities	3960	=item * Priorities are not currently supported. Initialising priorities
1839	will fail and all watchers will have the same priority, even though there	3961	will fail and all watchers will have the same priority, even though there
1840	is an ev_pri field.	3962	is an ev_pri field.
1841		3963
		3964	=item * In libevent, the last base created gets the signals, in libev, the
		3965	base that registered the signal gets the signals.
		3966
1842	=item * Other members are not supported.	3967	=item * Other members are not supported.
1843		3968
1844	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3969	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1845	to use the libev header file and library.	3970	to use the libev header file and library.
1846		3971
1847	=back	3972	=back
1848		3973
1849	=head1 C++ SUPPORT	3974	=head1 C++ SUPPORT
1850		3975
		3976	=head2 C API
		3977
		3978	The normal C API should work fine when used from C++: both ev.h and the
		3979	libev sources can be compiled as C++. Therefore, code that uses the C API
		3980	will work fine.
		3981
		3982	Proper exception specifications might have to be added to callbacks passed
		3983	to libev: exceptions may be thrown only from watcher callbacks, all other
		3984	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		3985	callbacks) must not throw exceptions, and might need a C<noexcept>
		3986	specification. If you have code that needs to be compiled as both C and
		3987	C++ you can use the C<EV_NOEXCEPT> macro for this:
		3988
		3989	static void
		3990	fatal_error (const char *msg) EV_NOEXCEPT
		3991	{
		3992	perror (msg);
		3993	abort ();
		3994	}
		3995
		3996	...
		3997	ev_set_syserr_cb (fatal_error);
		3998
		3999	The only API functions that can currently throw exceptions are C<ev_run>,
		4000	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4001	because it runs cleanup watchers).
		4002
		4003	Throwing exceptions in watcher callbacks is only supported if libev itself
		4004	is compiled with a C++ compiler or your C and C++ environments allow
		4005	throwing exceptions through C libraries (most do).
		4006
		4007	=head2 C++ API
		4008
1851	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4009	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1852	you to use some convinience methods to start/stop watchers and also change	4010	you to use some convenience methods to start/stop watchers and also change
1853	the callback model to a model using method callbacks on objects.	4011	the callback model to a model using method callbacks on objects.
1854		4012
1855	To use it,	4013	To use it,
1856		4014
1857	#include <ev++.h>	4015	#include <ev++.h>
1858		4016
1859	This automatically includes F<ev.h> and puts all of its definitions (many	4017	This automatically includes F<ev.h> and puts all of its definitions (many
1860	of them macros) into the global namespace. All C++ specific things are	4018	of them macros) into the global namespace. All C++ specific things are
1861	put into the C<ev> namespace. It should support all the same embedding	4019	put into the C<ev> namespace. It should support all the same embedding
1862	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	4020	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1864	Care has been taken to keep the overhead low. The only data member the C++	4022	Care has been taken to keep the overhead low. The only data member the C++
1865	classes add (compared to plain C-style watchers) is the event loop pointer	4023	classes add (compared to plain C-style watchers) is the event loop pointer
1866	that the watcher is associated with (or no additional members at all if	4024	that the watcher is associated with (or no additional members at all if
1867	you disable C<EV_MULTIPLICITY> when embedding libev).	4025	you disable C<EV_MULTIPLICITY> when embedding libev).
1868		4026
1869	Currently, functions, and static and non-static member functions can be	4027	Currently, functions, static and non-static member functions and classes
1870	used as callbacks. Other types should be easy to add as long as they only	4028	with C<operator ()> can be used as callbacks. Other types should be easy
1871	need one additional pointer for context. If you need support for other	4029	to add as long as they only need one additional pointer for context. If
1872	types of functors please contact the author (preferably after implementing	4030	you need support for other types of functors please contact the author
1873	it).	4031	(preferably after implementing it).
		4032
		4033	For all this to work, your C++ compiler either has to use the same calling
		4034	conventions as your C compiler (for static member functions), or you have
		4035	to embed libev and compile libev itself as C++.
1874		4036
1875	Here is a list of things available in the C<ev> namespace:	4037	Here is a list of things available in the C<ev> namespace:
1876		4038
1877	=over 4	4039	=over 4
1878		4040
…		…
1888	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4050	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
1889		4051
1890	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4052	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
1891	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4053	the same name in the C<ev> namespace, with the exception of C<ev_signal>
1892	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4054	which is called C<ev::sig> to avoid clashes with the C<signal> macro
1893	defines by many implementations.	4055	defined by many implementations.
1894		4056
1895	All of those classes have these methods:	4057	All of those classes have these methods:
1896		4058
1897	=over 4	4059	=over 4
1898		4060
1899	=item ev::TYPE::TYPE ()	4061	=item ev::TYPE::TYPE ()
1900		4062
1901	=item ev::TYPE::TYPE (struct ev_loop *)	4063	=item ev::TYPE::TYPE (loop)
1902		4064
1903	=item ev::TYPE::~TYPE	4065	=item ev::TYPE::~TYPE
1904		4066
1905	The constructor (optionally) takes an event loop to associate the watcher	4067	The constructor (optionally) takes an event loop to associate the watcher
1906	with. If it is omitted, it will use C<EV_DEFAULT>.	4068	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
1929	your compiler is good :), then the method will be fully inlined into the	4091	your compiler is good :), then the method will be fully inlined into the
1930	thunking function, making it as fast as a direct C callback.	4092	thunking function, making it as fast as a direct C callback.
1931		4093
1932	Example: simple class declaration and watcher initialisation	4094	Example: simple class declaration and watcher initialisation
1933		4095
1934	struct myclass	4096	struct myclass
1935	{	4097	{
1936	void io_cb (ev::io &w, int revents) { }	4098	void io_cb (ev::io &w, int revents) { }
1937	}	4099	}
1938		4100
1939	myclass obj;	4101	myclass obj;
1940	ev::io iow;	4102	ev::io iow;
1941	iow.set <myclass, &myclass::io_cb> (&obj);	4103	iow.set <myclass, &myclass::io_cb> (&obj);
		4104
		4105	=item w->set (object *)
		4106
		4107	This is a variation of a method callback - leaving out the method to call
		4108	will default the method to C<operator ()>, which makes it possible to use
		4109	functor objects without having to manually specify the C<operator ()> all
		4110	the time. Incidentally, you can then also leave out the template argument
		4111	list.
		4112
		4113	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4114	int revents)>.
		4115
		4116	See the method-C<set> above for more details.
		4117
		4118	Example: use a functor object as callback.
		4119
		4120	struct myfunctor
		4121	{
		4122	void operator() (ev::io &w, int revents)
		4123	{
		4124	...
		4125	}
		4126	}
		4127
		4128	myfunctor f;
		4129
		4130	ev::io w;
		4131	w.set (&f);
1942		4132
1943	=item w->set<function> (void *data = 0)	4133	=item w->set<function> (void *data = 0)
1944		4134
1945	Also sets a callback, but uses a static method or plain function as	4135	Also sets a callback, but uses a static method or plain function as
1946	callback. The optional C<data> argument will be stored in the watcher's	4136	callback. The optional C<data> argument will be stored in the watcher's
…		…
1948		4138
1949	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4139	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1950		4140
1951	See the method-C<set> above for more details.	4141	See the method-C<set> above for more details.
1952		4142
1953	Example:	4143	Example: Use a plain function as callback.
1954		4144
1955	static void io_cb (ev::io &w, int revents) { }	4145	static void io_cb (ev::io &w, int revents) { }
1956	iow.set <io_cb> ();	4146	iow.set <io_cb> ();
1957		4147
1958	=item w->set (struct ev_loop *)	4148	=item w->set (loop)
1959		4149
1960	Associates a different C<struct ev_loop> with this watcher. You can only	4150	Associates a different C<struct ev_loop> with this watcher. You can only
1961	do this when the watcher is inactive (and not pending either).	4151	do this when the watcher is inactive (and not pending either).
1962		4152
1963	=item w->set ([args])	4153	=item w->set ([arguments])
1964		4154
1965	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4155	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4156	with the same arguments. Either this method or a suitable start method
1966	called at least once. Unlike the C counterpart, an active watcher gets	4157	must be called at least once. Unlike the C counterpart, an active watcher
1967	automatically stopped and restarted when reconfiguring it with this	4158	gets automatically stopped and restarted when reconfiguring it with this
1968	method.	4159	method.
		4160
		4161	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4162	clashing with the C<set (loop)> method.
1969		4163
1970	=item w->start ()	4164	=item w->start ()
1971		4165
1972	Starts the watcher. Note that there is no C<loop> argument, as the	4166	Starts the watcher. Note that there is no C<loop> argument, as the
1973	constructor already stores the event loop.	4167	constructor already stores the event loop.
1974		4168
		4169	=item w->start ([arguments])
		4170
		4171	Instead of calling C<set> and C<start> methods separately, it is often
		4172	convenient to wrap them in one call. Uses the same type of arguments as
		4173	the configure C<set> method of the watcher.
		4174
1975	=item w->stop ()	4175	=item w->stop ()
1976		4176
1977	Stops the watcher if it is active. Again, no C<loop> argument.	4177	Stops the watcher if it is active. Again, no C<loop> argument.
1978		4178
1979	=item w->again () C<ev::timer>, C<ev::periodic> only	4179	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1980		4180
1981	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	4181	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1982	C<ev_TYPE_again> function.	4182	C<ev_TYPE_again> function.
1983		4183
1984	=item w->sweep () C<ev::embed> only	4184	=item w->sweep () (C<ev::embed> only)
1985		4185
1986	Invokes C<ev_embed_sweep>.	4186	Invokes C<ev_embed_sweep>.
1987		4187
1988	=item w->update () C<ev::stat> only	4188	=item w->update () (C<ev::stat> only)
1989		4189
1990	Invokes C<ev_stat_stat>.	4190	Invokes C<ev_stat_stat>.
1991		4191
1992	=back	4192	=back
1993		4193
1994	=back	4194	=back
1995		4195
1996	Example: Define a class with an IO and idle watcher, start one of them in	4196	Example: Define a class with two I/O and idle watchers, start the I/O
1997	the constructor.	4197	watchers in the constructor.
1998		4198
1999	class myclass	4199	class myclass
2000	{	4200	{
2001	ev_io io; void io_cb (ev::io &w, int revents);	4201	ev::io io ; void io_cb (ev::io &w, int revents);
		4202	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2002	ev_idle idle void idle_cb (ev::idle &w, int revents);	4203	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2003		4204
2004	myclass ();	4205	myclass (int fd)
2005	}	4206	{
2006
2007	myclass::myclass (int fd)
2008	{
2009	io .set <myclass, &myclass::io_cb > (this);	4207	io .set <myclass, &myclass::io_cb > (this);
		4208	io2 .set <myclass, &myclass::io2_cb > (this);
2010	idle.set <myclass, &myclass::idle_cb> (this);	4209	idle.set <myclass, &myclass::idle_cb> (this);
2011		4210
2012	io.start (fd, ev::READ);	4211	io.set (fd, ev::WRITE); // configure the watcher
		4212	io.start (); // start it whenever convenient
		4213
		4214	io2.start (fd, ev::READ); // set + start in one call
		4215	}
2013	}	4216	};
		4217
		4218
		4219	=head1 OTHER LANGUAGE BINDINGS
		4220
		4221	Libev does not offer other language bindings itself, but bindings for a
		4222	number of languages exist in the form of third-party packages. If you know
		4223	any interesting language binding in addition to the ones listed here, drop
		4224	me a note.
		4225
		4226	=over 4
		4227
		4228	=item Perl
		4229
		4230	The EV module implements the full libev API and is actually used to test
		4231	libev. EV is developed together with libev. Apart from the EV core module,
		4232	there are additional modules that implement libev-compatible interfaces
		4233	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4234	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4235	and C<EV::Glib>).
		4236
		4237	It can be found and installed via CPAN, its homepage is at
		4238	L<http://software.schmorp.de/pkg/EV>.
		4239
		4240	=item Python
		4241
		4242	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4243	seems to be quite complete and well-documented.
		4244
		4245	=item Ruby
		4246
		4247	Tony Arcieri has written a ruby extension that offers access to a subset
		4248	of the libev API and adds file handle abstractions, asynchronous DNS and
		4249	more on top of it. It can be found via gem servers. Its homepage is at
		4250	L<http://rev.rubyforge.org/>.
		4251
		4252	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4253	makes rev work even on mingw.
		4254
		4255	=item Haskell
		4256
		4257	A haskell binding to libev is available at
		4258	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4259
		4260	=item D
		4261
		4262	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4263	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4264
		4265	=item Ocaml
		4266
		4267	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4268	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4269
		4270	=item Lua
		4271
		4272	Brian Maher has written a partial interface to libev for lua (at the
		4273	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4274	L<http://github.com/brimworks/lua-ev>.
		4275
		4276	=item Javascript
		4277
		4278	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4279
		4280	=item Others
		4281
		4282	There are others, and I stopped counting.
		4283
		4284	=back
2014		4285
2015		4286
2016	=head1 MACRO MAGIC	4287	=head1 MACRO MAGIC
2017		4288
2018	Libev can be compiled with a variety of options, the most fundemantal is	4289	Libev can be compiled with a variety of options, the most fundamental
2019	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	4290	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2020	callbacks have an initial C<struct ev_loop *> argument.	4291	functions and callbacks have an initial C<struct ev_loop *> argument.
2021		4292
2022	To make it easier to write programs that cope with either variant, the	4293	To make it easier to write programs that cope with either variant, the
2023	following macros are defined:	4294	following macros are defined:
2024		4295
2025	=over 4	4296	=over 4
…		…
2028		4299
2029	This provides the loop I<argument> for functions, if one is required ("ev	4300	This provides the loop I<argument> for functions, if one is required ("ev
2030	loop argument"). The C<EV_A> form is used when this is the sole argument,	4301	loop argument"). The C<EV_A> form is used when this is the sole argument,
2031	C<EV_A_> is used when other arguments are following. Example:	4302	C<EV_A_> is used when other arguments are following. Example:
2032		4303
2033	ev_unref (EV_A);	4304	ev_unref (EV_A);
2034	ev_timer_add (EV_A_ watcher);	4305	ev_timer_add (EV_A_ watcher);
2035	ev_loop (EV_A_ 0);	4306	ev_run (EV_A_ 0);
2036		4307
2037	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4308	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2038	which is often provided by the following macro.	4309	which is often provided by the following macro.
2039		4310
2040	=item C<EV_P>, C<EV_P_>	4311	=item C<EV_P>, C<EV_P_>
2041		4312
2042	This provides the loop I<parameter> for functions, if one is required ("ev	4313	This provides the loop I<parameter> for functions, if one is required ("ev
2043	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4314	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2044	C<EV_P_> is used when other parameters are following. Example:	4315	C<EV_P_> is used when other parameters are following. Example:
2045		4316
2046	// this is how ev_unref is being declared	4317	// this is how ev_unref is being declared
2047	static void ev_unref (EV_P);	4318	static void ev_unref (EV_P);
2048		4319
2049	// this is how you can declare your typical callback	4320	// this is how you can declare your typical callback
2050	static void cb (EV_P_ ev_timer *w, int revents)	4321	static void cb (EV_P_ ev_timer *w, int revents)
2051		4322
2052	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4323	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2053	suitable for use with C<EV_A>.	4324	suitable for use with C<EV_A>.
2054		4325
2055	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4326	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2056		4327
2057	Similar to the other two macros, this gives you the value of the default	4328	Similar to the other two macros, this gives you the value of the default
2058	loop, if multiple loops are supported ("ev loop default").	4329	loop, if multiple loops are supported ("ev loop default"). The default loop
		4330	will be initialised if it isn't already initialised.
		4331
		4332	For non-multiplicity builds, these macros do nothing, so you always have
		4333	to initialise the loop somewhere.
		4334
		4335	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4336
		4337	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4338	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4339	is undefined when the default loop has not been initialised by a previous
		4340	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4341
		4342	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4343	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2059		4344
2060	=back	4345	=back
2061		4346
2062	Example: Declare and initialise a check watcher, utilising the above	4347	Example: Declare and initialise a check watcher, utilising the above
2063	macros so it will work regardless of whether multiple loops are supported	4348	macros so it will work regardless of whether multiple loops are supported
2064	or not.	4349	or not.
2065		4350
2066	static void	4351	static void
2067	check_cb (EV_P_ ev_timer *w, int revents)	4352	check_cb (EV_P_ ev_timer *w, int revents)
2068	{	4353	{
2069	ev_check_stop (EV_A_ w);	4354	ev_check_stop (EV_A_ w);
2070	}	4355	}
2071		4356
2072	ev_check check;	4357	ev_check check;
2073	ev_check_init (&check, check_cb);	4358	ev_check_init (&check, check_cb);
2074	ev_check_start (EV_DEFAULT_ &check);	4359	ev_check_start (EV_DEFAULT_ &check);
2075	ev_loop (EV_DEFAULT_ 0);	4360	ev_run (EV_DEFAULT_ 0);
2076		4361
2077	=head1 EMBEDDING	4362	=head1 EMBEDDING
2078		4363
2079	Libev can (and often is) directly embedded into host	4364	Libev can (and often is) directly embedded into host
2080	applications. Examples of applications that embed it include the Deliantra	4365	applications. Examples of applications that embed it include the Deliantra
2081	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	4366	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2082	and rxvt-unicode.	4367	and rxvt-unicode.
2083		4368
2084	The goal is to enable you to just copy the neecssary files into your	4369	The goal is to enable you to just copy the necessary files into your
2085	source directory without having to change even a single line in them, so	4370	source directory without having to change even a single line in them, so
2086	you can easily upgrade by simply copying (or having a checked-out copy of	4371	you can easily upgrade by simply copying (or having a checked-out copy of
2087	libev somewhere in your source tree).	4372	libev somewhere in your source tree).
2088		4373
2089	=head2 FILESETS	4374	=head2 FILESETS
2090		4375
2091	Depending on what features you need you need to include one or more sets of files	4376	Depending on what features you need you need to include one or more sets of files
2092	in your app.	4377	in your application.
2093		4378
2094	=head3 CORE EVENT LOOP	4379	=head3 CORE EVENT LOOP
2095		4380
2096	To include only the libev core (all the C<ev_*> functions), with manual	4381	To include only the libev core (all the C<ev_*> functions), with manual
2097	configuration (no autoconf):	4382	configuration (no autoconf):
2098		4383
2099	#define EV_STANDALONE 1	4384	#define EV_STANDALONE 1
2100	#include "ev.c"	4385	#include "ev.c"
2101		4386
2102	This will automatically include F<ev.h>, too, and should be done in a	4387	This will automatically include F<ev.h>, too, and should be done in a
2103	single C source file only to provide the function implementations. To use	4388	single C source file only to provide the function implementations. To use
2104	it, do the same for F<ev.h> in all files wishing to use this API (best	4389	it, do the same for F<ev.h> in all files wishing to use this API (best
2105	done by writing a wrapper around F<ev.h> that you can include instead and	4390	done by writing a wrapper around F<ev.h> that you can include instead and
2106	where you can put other configuration options):	4391	where you can put other configuration options):
2107		4392
2108	#define EV_STANDALONE 1	4393	#define EV_STANDALONE 1
2109	#include "ev.h"	4394	#include "ev.h"
2110		4395
2111	Both header files and implementation files can be compiled with a C++	4396	Both header files and implementation files can be compiled with a C++
2112	compiler (at least, thats a stated goal, and breakage will be treated	4397	compiler (at least, that's a stated goal, and breakage will be treated
2113	as a bug).	4398	as a bug).
2114		4399
2115	You need the following files in your source tree, or in a directory	4400	You need the following files in your source tree, or in a directory
2116	in your include path (e.g. in libev/ when using -Ilibev):	4401	in your include path (e.g. in libev/ when using -Ilibev):
2117		4402
2118	ev.h	4403	ev.h
2119	ev.c	4404	ev.c
2120	ev_vars.h	4405	ev_vars.h
2121	ev_wrap.h	4406	ev_wrap.h
2122		4407
2123	ev_win32.c required on win32 platforms only	4408	ev_win32.c required on win32 platforms only
2124		4409
2125	ev_select.c only when select backend is enabled (which is enabled by default)	4410	ev_select.c only when select backend is enabled
2126	ev_poll.c only when poll backend is enabled (disabled by default)	4411	ev_poll.c only when poll backend is enabled
2127	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4412	ev_epoll.c only when the epoll backend is enabled
2128	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4413	ev_kqueue.c only when the kqueue backend is enabled
2129	ev_port.c only when the solaris port backend is enabled (disabled by default)	4414	ev_port.c only when the solaris port backend is enabled
2130		4415
2131	F<ev.c> includes the backend files directly when enabled, so you only need	4416	F<ev.c> includes the backend files directly when enabled, so you only need
2132	to compile this single file.	4417	to compile this single file.
2133		4418
2134	=head3 LIBEVENT COMPATIBILITY API	4419	=head3 LIBEVENT COMPATIBILITY API
2135		4420
2136	To include the libevent compatibility API, also include:	4421	To include the libevent compatibility API, also include:
2137		4422
2138	#include "event.c"	4423	#include "event.c"
2139		4424
2140	in the file including F<ev.c>, and:	4425	in the file including F<ev.c>, and:
2141		4426
2142	#include "event.h"	4427	#include "event.h"
2143		4428
2144	in the files that want to use the libevent API. This also includes F<ev.h>.	4429	in the files that want to use the libevent API. This also includes F<ev.h>.
2145		4430
2146	You need the following additional files for this:	4431	You need the following additional files for this:
2147		4432
2148	event.h	4433	event.h
2149	event.c	4434	event.c
2150		4435
2151	=head3 AUTOCONF SUPPORT	4436	=head3 AUTOCONF SUPPORT
2152		4437
2153	Instead of using C<EV_STANDALONE=1> and providing your config in	4438	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2154	whatever way you want, you can also C<m4_include([libev.m4])> in your	4439	whatever way you want, you can also C<m4_include([libev.m4])> in your
2155	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4440	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2156	include F<config.h> and configure itself accordingly.	4441	include F<config.h> and configure itself accordingly.
2157		4442
2158	For this of course you need the m4 file:	4443	For this of course you need the m4 file:
2159		4444
2160	libev.m4	4445	libev.m4
2161		4446
2162	=head2 PREPROCESSOR SYMBOLS/MACROS	4447	=head2 PREPROCESSOR SYMBOLS/MACROS
2163		4448
2164	Libev can be configured via a variety of preprocessor symbols you have to define	4449	Libev can be configured via a variety of preprocessor symbols you have to
2165	before including any of its files. The default is not to build for multiplicity	4450	define before including (or compiling) any of its files. The default in
2166	and only include the select backend.	4451	the absence of autoconf is documented for every option.
		4452
		4453	Symbols marked with "(h)" do not change the ABI, and can have different
		4454	values when compiling libev vs. including F<ev.h>, so it is permissible
		4455	to redefine them before including F<ev.h> without breaking compatibility
		4456	to a compiled library. All other symbols change the ABI, which means all
		4457	users of libev and the libev code itself must be compiled with compatible
		4458	settings.
2167		4459
2168	=over 4	4460	=over 4
2169		4461
		4462	=item EV_COMPAT3 (h)
		4463
		4464	Backwards compatibility is a major concern for libev. This is why this
		4465	release of libev comes with wrappers for the functions and symbols that
		4466	have been renamed between libev version 3 and 4.
		4467
		4468	You can disable these wrappers (to test compatibility with future
		4469	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4470	sources. This has the additional advantage that you can drop the C<struct>
		4471	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4472	typedef in that case.
		4473
		4474	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4475	and in some even more future version the compatibility code will be
		4476	removed completely.
		4477
2170	=item EV_STANDALONE	4478	=item EV_STANDALONE (h)
2171		4479
2172	Must always be C<1> if you do not use autoconf configuration, which	4480	Must always be C<1> if you do not use autoconf configuration, which
2173	keeps libev from including F<config.h>, and it also defines dummy	4481	keeps libev from including F<config.h>, and it also defines dummy
2174	implementations for some libevent functions (such as logging, which is not	4482	implementations for some libevent functions (such as logging, which is not
2175	supported). It will also not define any of the structs usually found in	4483	supported). It will also not define any of the structs usually found in
2176	F<event.h> that are not directly supported by the libev core alone.	4484	F<event.h> that are not directly supported by the libev core alone.
2177		4485
		4486	In standalone mode, libev will still try to automatically deduce the
		4487	configuration, but has to be more conservative.
		4488
		4489	=item EV_USE_FLOOR
		4490
		4491	If defined to be C<1>, libev will use the C<floor ()> function for its
		4492	periodic reschedule calculations, otherwise libev will fall back on a
		4493	portable (slower) implementation. If you enable this, you usually have to
		4494	link against libm or something equivalent. Enabling this when the C<floor>
		4495	function is not available will fail, so the safe default is to not enable
		4496	this.
		4497
2178	=item EV_USE_MONOTONIC	4498	=item EV_USE_MONOTONIC
2179		4499
2180	If defined to be C<1>, libev will try to detect the availability of the	4500	If defined to be C<1>, libev will try to detect the availability of the
2181	monotonic clock option at both compiletime and runtime. Otherwise no use	4501	monotonic clock option at both compile time and runtime. Otherwise no
2182	of the monotonic clock option will be attempted. If you enable this, you	4502	use of the monotonic clock option will be attempted. If you enable this,
2183	usually have to link against librt or something similar. Enabling it when	4503	you usually have to link against librt or something similar. Enabling it
2184	the functionality isn't available is safe, though, althoguh you have	4504	when the functionality isn't available is safe, though, although you have
2185	to make sure you link against any libraries where the C<clock_gettime>	4505	to make sure you link against any libraries where the C<clock_gettime>
2186	function is hiding in (often F<-lrt>).	4506	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2187		4507
2188	=item EV_USE_REALTIME	4508	=item EV_USE_REALTIME
2189		4509
2190	If defined to be C<1>, libev will try to detect the availability of the	4510	If defined to be C<1>, libev will try to detect the availability of the
2191	realtime clock option at compiletime (and assume its availability at	4511	real-time clock option at compile time (and assume its availability
2192	runtime if successful). Otherwise no use of the realtime clock option will	4512	at runtime if successful). Otherwise no use of the real-time clock
2193	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4513	option will be attempted. This effectively replaces C<gettimeofday>
2194	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	4514	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2195	in the description of C<EV_USE_MONOTONIC>, though.	4515	correctness. See the note about libraries in the description of
		4516	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4517	C<EV_USE_CLOCK_SYSCALL>.
		4518
		4519	=item EV_USE_CLOCK_SYSCALL
		4520
		4521	If defined to be C<1>, libev will try to use a direct syscall instead
		4522	of calling the system-provided C<clock_gettime> function. This option
		4523	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4524	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4525	programs needlessly. Using a direct syscall is slightly slower (in
		4526	theory), because no optimised vdso implementation can be used, but avoids
		4527	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4528	higher, as it simplifies linking (no need for C<-lrt>).
		4529
		4530	=item EV_USE_NANOSLEEP
		4531
		4532	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4533	and will use it for delays. Otherwise it will use C<select ()>.
		4534
		4535	=item EV_USE_EVENTFD
		4536
		4537	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4538	available and will probe for kernel support at runtime. This will improve
		4539	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4540	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4541	2.7 or newer, otherwise disabled.
2196		4542
2197	=item EV_USE_SELECT	4543	=item EV_USE_SELECT
2198		4544
2199	If undefined or defined to be C<1>, libev will compile in support for the	4545	If undefined or defined to be C<1>, libev will compile in support for the
2200	C<select>(2) backend. No attempt at autodetection will be done: if no	4546	C<select>(2) backend. No attempt at auto-detection will be done: if no
2201	other method takes over, select will be it. Otherwise the select backend	4547	other method takes over, select will be it. Otherwise the select backend
2202	will not be compiled in.	4548	will not be compiled in.
2203		4549
2204	=item EV_SELECT_USE_FD_SET	4550	=item EV_SELECT_USE_FD_SET
2205		4551
2206	If defined to C<1>, then the select backend will use the system C<fd_set>	4552	If defined to C<1>, then the select backend will use the system C<fd_set>
2207	structure. This is useful if libev doesn't compile due to a missing	4553	structure. This is useful if libev doesn't compile due to a missing
2208	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4554	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2209	exotic systems. This usually limits the range of file descriptors to some	4555	on exotic systems. This usually limits the range of file descriptors to
2210	low limit such as 1024 or might have other limitations (winsocket only	4556	some low limit such as 1024 or might have other limitations (winsocket
2211	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4557	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2212	influence the size of the C<fd_set> used.	4558	configures the maximum size of the C<fd_set>.
2213		4559
2214	=item EV_SELECT_IS_WINSOCKET	4560	=item EV_SELECT_IS_WINSOCKET
2215		4561
2216	When defined to C<1>, the select backend will assume that	4562	When defined to C<1>, the select backend will assume that
2217	select/socket/connect etc. don't understand file descriptors but	4563	select/socket/connect etc. don't understand file descriptors but
…		…
2219	be used is the winsock select). This means that it will call	4565	be used is the winsock select). This means that it will call
2220	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4566	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2221	it is assumed that all these functions actually work on fds, even	4567	it is assumed that all these functions actually work on fds, even
2222	on win32. Should not be defined on non-win32 platforms.	4568	on win32. Should not be defined on non-win32 platforms.
2223		4569
		4570	=item EV_FD_TO_WIN32_HANDLE(fd)
		4571
		4572	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4573	file descriptors to socket handles. When not defining this symbol (the
		4574	default), then libev will call C<_get_osfhandle>, which is usually
		4575	correct. In some cases, programs use their own file descriptor management,
		4576	in which case they can provide this function to map fds to socket handles.
		4577
		4578	=item EV_WIN32_HANDLE_TO_FD(handle)
		4579
		4580	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4581	using the standard C<_open_osfhandle> function. For programs implementing
		4582	their own fd to handle mapping, overwriting this function makes it easier
		4583	to do so. This can be done by defining this macro to an appropriate value.
		4584
		4585	=item EV_WIN32_CLOSE_FD(fd)
		4586
		4587	If programs implement their own fd to handle mapping on win32, then this
		4588	macro can be used to override the C<close> function, useful to unregister
		4589	file descriptors again. Note that the replacement function has to close
		4590	the underlying OS handle.
		4591
		4592	=item EV_USE_WSASOCKET
		4593
		4594	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4595	communication socket, which works better in some environments. Otherwise,
		4596	the normal C<socket> function will be used, which works better in other
		4597	environments.
		4598
2224	=item EV_USE_POLL	4599	=item EV_USE_POLL
2225		4600
2226	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4601	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2227	backend. Otherwise it will be enabled on non-win32 platforms. It	4602	backend. Otherwise it will be enabled on non-win32 platforms. It
2228	takes precedence over select.	4603	takes precedence over select.
2229		4604
2230	=item EV_USE_EPOLL	4605	=item EV_USE_EPOLL
2231		4606
2232	If defined to be C<1>, libev will compile in support for the Linux	4607	If defined to be C<1>, libev will compile in support for the Linux
2233	C<epoll>(7) backend. Its availability will be detected at runtime,	4608	C<epoll>(7) backend. Its availability will be detected at runtime,
2234	otherwise another method will be used as fallback. This is the	4609	otherwise another method will be used as fallback. This is the preferred
2235	preferred backend for GNU/Linux systems.	4610	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4611	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2236		4612
2237	=item EV_USE_KQUEUE	4613	=item EV_USE_KQUEUE
2238		4614
2239	If defined to be C<1>, libev will compile in support for the BSD style	4615	If defined to be C<1>, libev will compile in support for the BSD style
2240	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4616	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2253	otherwise another method will be used as fallback. This is the preferred	4629	otherwise another method will be used as fallback. This is the preferred
2254	backend for Solaris 10 systems.	4630	backend for Solaris 10 systems.
2255		4631
2256	=item EV_USE_DEVPOLL	4632	=item EV_USE_DEVPOLL
2257		4633
2258	reserved for future expansion, works like the USE symbols above.	4634	Reserved for future expansion, works like the USE symbols above.
2259		4635
2260	=item EV_USE_INOTIFY	4636	=item EV_USE_INOTIFY
2261		4637
2262	If defined to be C<1>, libev will compile in support for the Linux inotify	4638	If defined to be C<1>, libev will compile in support for the Linux inotify
2263	interface to speed up C<ev_stat> watchers. Its actual availability will	4639	interface to speed up C<ev_stat> watchers. Its actual availability will
2264	be detected at runtime.	4640	be detected at runtime. If undefined, it will be enabled if the headers
		4641	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2265		4642
		4643	=item EV_NO_SMP
		4644
		4645	If defined to be C<1>, libev will assume that memory is always coherent
		4646	between threads, that is, threads can be used, but threads never run on
		4647	different cpus (or different cpu cores). This reduces dependencies
		4648	and makes libev faster.
		4649
		4650	=item EV_NO_THREADS
		4651
		4652	If defined to be C<1>, libev will assume that it will never be called from
		4653	different threads (that includes signal handlers), which is a stronger
		4654	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4655	libev faster.
		4656
		4657	=item EV_ATOMIC_T
		4658
		4659	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4660	access is atomic with respect to other threads or signal contexts. No
		4661	such type is easily found in the C language, so you can provide your own
		4662	type that you know is safe for your purposes. It is used both for signal
		4663	handler "locking" as well as for signal and thread safety in C<ev_async>
		4664	watchers.
		4665
		4666	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4667	(from F<signal.h>), which is usually good enough on most platforms.
		4668
2266	=item EV_H	4669	=item EV_H (h)
2267		4670
2268	The name of the F<ev.h> header file used to include it. The default if	4671	The name of the F<ev.h> header file used to include it. The default if
2269	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4672	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2270	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4673	used to virtually rename the F<ev.h> header file in case of conflicts.
2271		4674
2272	=item EV_CONFIG_H	4675	=item EV_CONFIG_H (h)
2273		4676
2274	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4677	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2275	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4678	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2276	C<EV_H>, above.	4679	C<EV_H>, above.
2277		4680
2278	=item EV_EVENT_H	4681	=item EV_EVENT_H (h)
2279		4682
2280	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4683	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2281	of how the F<event.h> header can be found.	4684	of how the F<event.h> header can be found, the default is C<"event.h">.
2282		4685
2283	=item EV_PROTOTYPES	4686	=item EV_PROTOTYPES (h)
2284		4687
2285	If defined to be C<0>, then F<ev.h> will not define any function	4688	If defined to be C<0>, then F<ev.h> will not define any function
2286	prototypes, but still define all the structs and other symbols. This is	4689	prototypes, but still define all the structs and other symbols. This is
2287	occasionally useful if you want to provide your own wrapper functions	4690	occasionally useful if you want to provide your own wrapper functions
2288	around libev functions.	4691	around libev functions.
…		…
2293	will have the C<struct ev_loop *> as first argument, and you can create	4696	will have the C<struct ev_loop *> as first argument, and you can create
2294	additional independent event loops. Otherwise there will be no support	4697	additional independent event loops. Otherwise there will be no support
2295	for multiple event loops and there is no first event loop pointer	4698	for multiple event loops and there is no first event loop pointer
2296	argument. Instead, all functions act on the single default loop.	4699	argument. Instead, all functions act on the single default loop.
2297		4700
		4701	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4702	default loop when multiplicity is switched off - you always have to
		4703	initialise the loop manually in this case.
		4704
2298	=item EV_MINPRI	4705	=item EV_MINPRI
2299		4706
2300	=item EV_MAXPRI	4707	=item EV_MAXPRI
2301		4708
2302	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4709	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2307	When doing priority-based operations, libev usually has to linearly search	4714	When doing priority-based operations, libev usually has to linearly search
2308	all the priorities, so having many of them (hundreds) uses a lot of space	4715	all the priorities, so having many of them (hundreds) uses a lot of space
2309	and time, so using the defaults of five priorities (-2 .. +2) is usually	4716	and time, so using the defaults of five priorities (-2 .. +2) is usually
2310	fine.	4717	fine.
2311		4718
2312	If your embedding app does not need any priorities, defining these both to	4719	If your embedding application does not need any priorities, defining these
2313	C<0> will save some memory and cpu.	4720	both to C<0> will save some memory and CPU.
2314		4721
2315	=item EV_PERIODIC_ENABLE	4722	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4723	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4724	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2316		4725
2317	If undefined or defined to be C<1>, then periodic timers are supported. If	4726	If undefined or defined to be C<1> (and the platform supports it), then
2318	defined to be C<0>, then they are not. Disabling them saves a few kB of	4727	the respective watcher type is supported. If defined to be C<0>, then it
2319	code.	4728	is not. Disabling watcher types mainly saves code size.
2320		4729
2321	=item EV_IDLE_ENABLE	4730	=item EV_FEATURES
2322
2323	If undefined or defined to be C<1>, then idle watchers are supported. If
2324	defined to be C<0>, then they are not. Disabling them saves a few kB of
2325	code.
2326
2327	=item EV_EMBED_ENABLE
2328
2329	If undefined or defined to be C<1>, then embed watchers are supported. If
2330	defined to be C<0>, then they are not.
2331
2332	=item EV_STAT_ENABLE
2333
2334	If undefined or defined to be C<1>, then stat watchers are supported. If
2335	defined to be C<0>, then they are not.
2336
2337	=item EV_FORK_ENABLE
2338
2339	If undefined or defined to be C<1>, then fork watchers are supported. If
2340	defined to be C<0>, then they are not.
2341
2342	=item EV_MINIMAL
2343		4731
2344	If you need to shave off some kilobytes of code at the expense of some	4732	If you need to shave off some kilobytes of code at the expense of some
2345	speed, define this symbol to C<1>. Currently only used for gcc to override	4733	speed (but with the full API), you can define this symbol to request
2346	some inlining decisions, saves roughly 30% codesize of amd64.	4734	certain subsets of functionality. The default is to enable all features
		4735	that can be enabled on the platform.
		4736
		4737	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4738	with some broad features you want) and then selectively re-enable
		4739	additional parts you want, for example if you want everything minimal,
		4740	but multiple event loop support, async and child watchers and the poll
		4741	backend, use this:
		4742
		4743	#define EV_FEATURES 0
		4744	#define EV_MULTIPLICITY 1
		4745	#define EV_USE_POLL 1
		4746	#define EV_CHILD_ENABLE 1
		4747	#define EV_ASYNC_ENABLE 1
		4748
		4749	The actual value is a bitset, it can be a combination of the following
		4750	values (by default, all of these are enabled):
		4751
		4752	=over 4
		4753
		4754	=item C<1> - faster/larger code
		4755
		4756	Use larger code to speed up some operations.
		4757
		4758	Currently this is used to override some inlining decisions (enlarging the
		4759	code size by roughly 30% on amd64).
		4760
		4761	When optimising for size, use of compiler flags such as C<-Os> with
		4762	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4763	assertions.
		4764
		4765	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4766	(e.g. gcc with C<-Os>).
		4767
		4768	=item C<2> - faster/larger data structures
		4769
		4770	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4771	hash table sizes and so on. This will usually further increase code size
		4772	and can additionally have an effect on the size of data structures at
		4773	runtime.
		4774
		4775	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4776	(e.g. gcc with C<-Os>).
		4777
		4778	=item C<4> - full API configuration
		4779
		4780	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4781	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4782
		4783	=item C<8> - full API
		4784
		4785	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4786	details on which parts of the API are still available without this
		4787	feature, and do not complain if this subset changes over time.
		4788
		4789	=item C<16> - enable all optional watcher types
		4790
		4791	Enables all optional watcher types. If you want to selectively enable
		4792	only some watcher types other than I/O and timers (e.g. prepare,
		4793	embed, async, child...) you can enable them manually by defining
		4794	C<EV_watchertype_ENABLE> to C<1> instead.
		4795
		4796	=item C<32> - enable all backends
		4797
		4798	This enables all backends - without this feature, you need to enable at
		4799	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4800
		4801	=item C<64> - enable OS-specific "helper" APIs
		4802
		4803	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4804	default.
		4805
		4806	=back
		4807
		4808	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4809	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4810	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4811	watchers, timers and monotonic clock support.
		4812
		4813	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4814	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4815	your program might be left out as well - a binary starting a timer and an
		4816	I/O watcher then might come out at only 5Kb.
		4817
		4818	=item EV_API_STATIC
		4819
		4820	If this symbol is defined (by default it is not), then all identifiers
		4821	will have static linkage. This means that libev will not export any
		4822	identifiers, and you cannot link against libev anymore. This can be useful
		4823	when you embed libev, only want to use libev functions in a single file,
		4824	and do not want its identifiers to be visible.
		4825
		4826	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4827	wants to use libev.
		4828
		4829	This option only works when libev is compiled with a C compiler, as C++
		4830	doesn't support the required declaration syntax.
		4831
		4832	=item EV_AVOID_STDIO
		4833
		4834	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4835	functions (printf, scanf, perror etc.). This will increase the code size
		4836	somewhat, but if your program doesn't otherwise depend on stdio and your
		4837	libc allows it, this avoids linking in the stdio library which is quite
		4838	big.
		4839
		4840	Note that error messages might become less precise when this option is
		4841	enabled.
		4842
		4843	=item EV_NSIG
		4844
		4845	The highest supported signal number, +1 (or, the number of
		4846	signals): Normally, libev tries to deduce the maximum number of signals
		4847	automatically, but sometimes this fails, in which case it can be
		4848	specified. Also, using a lower number than detected (C<32> should be
		4849	good for about any system in existence) can save some memory, as libev
		4850	statically allocates some 12-24 bytes per signal number.
2347		4851
2348	=item EV_PID_HASHSIZE	4852	=item EV_PID_HASHSIZE
2349		4853
2350	C<ev_child> watchers use a small hash table to distribute workload by	4854	C<ev_child> watchers use a small hash table to distribute workload by
2351	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4855	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2352	than enough. If you need to manage thousands of children you might want to	4856	usually more than enough. If you need to manage thousands of children you
2353	increase this value (I<must> be a power of two).	4857	might want to increase this value (I<must> be a power of two).
2354		4858
2355	=item EV_INOTIFY_HASHSIZE	4859	=item EV_INOTIFY_HASHSIZE
2356		4860
2357	C<ev_staz> watchers use a small hash table to distribute workload by	4861	C<ev_stat> watchers use a small hash table to distribute workload by
2358	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4862	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2359	usually more than enough. If you need to manage thousands of C<ev_stat>	4863	disabled), usually more than enough. If you need to manage thousands of
2360	watchers you might want to increase this value (I<must> be a power of	4864	C<ev_stat> watchers you might want to increase this value (I<must> be a
2361	two).	4865	power of two).
		4866
		4867	=item EV_USE_4HEAP
		4868
		4869	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4870	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4871	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4872	faster performance with many (thousands) of watchers.
		4873
		4874	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4875	will be C<0>.
		4876
		4877	=item EV_HEAP_CACHE_AT
		4878
		4879	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4880	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4881	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4882	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4883	but avoids random read accesses on heap changes. This improves performance
		4884	noticeably with many (hundreds) of watchers.
		4885
		4886	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4887	will be C<0>.
		4888
		4889	=item EV_VERIFY
		4890
		4891	Controls how much internal verification (see C<ev_verify ()>) will
		4892	be done: If set to C<0>, no internal verification code will be compiled
		4893	in. If set to C<1>, then verification code will be compiled in, but not
		4894	called. If set to C<2>, then the internal verification code will be
		4895	called once per loop, which can slow down libev. If set to C<3>, then the
		4896	verification code will be called very frequently, which will slow down
		4897	libev considerably.
		4898
		4899	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4900	will be C<0>.
2362		4901
2363	=item EV_COMMON	4902	=item EV_COMMON
2364		4903
2365	By default, all watchers have a C<void *data> member. By redefining	4904	By default, all watchers have a C<void *data> member. By redefining
2366	this macro to a something else you can include more and other types of	4905	this macro to something else you can include more and other types of
2367	members. You have to define it each time you include one of the files,	4906	members. You have to define it each time you include one of the files,
2368	though, and it must be identical each time.	4907	though, and it must be identical each time.
2369		4908
2370	For example, the perl EV module uses something like this:	4909	For example, the perl EV module uses something like this:
2371		4910
2372	#define EV_COMMON \	4911	#define EV_COMMON \
2373	SV *self; /* contains this struct */ \	4912	SV *self; /* contains this struct */ \
2374	SV *cb_sv, *fh /* note no trailing ";" */	4913	SV *cb_sv, *fh /* note no trailing ";" */
2375		4914
2376	=item EV_CB_DECLARE (type)	4915	=item EV_CB_DECLARE (type)
2377		4916
2378	=item EV_CB_INVOKE (watcher, revents)	4917	=item EV_CB_INVOKE (watcher, revents)
2379		4918
2380	=item ev_set_cb (ev, cb)	4919	=item ev_set_cb (ev, cb)
2381		4920
2382	Can be used to change the callback member declaration in each watcher,	4921	Can be used to change the callback member declaration in each watcher,
2383	and the way callbacks are invoked and set. Must expand to a struct member	4922	and the way callbacks are invoked and set. Must expand to a struct member
2384	definition and a statement, respectively. See the F<ev.v> header file for	4923	definition and a statement, respectively. See the F<ev.h> header file for
2385	their default definitions. One possible use for overriding these is to	4924	their default definitions. One possible use for overriding these is to
2386	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4925	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2387	method calls instead of plain function calls in C++.	4926	method calls instead of plain function calls in C++.
		4927
		4928	=back
		4929
		4930	=head2 EXPORTED API SYMBOLS
		4931
		4932	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4933	exported symbols, you can use the provided F<Symbol.*> files which list
		4934	all public symbols, one per line:
		4935
		4936	Symbols.ev for libev proper
		4937	Symbols.event for the libevent emulation
		4938
		4939	This can also be used to rename all public symbols to avoid clashes with
		4940	multiple versions of libev linked together (which is obviously bad in
		4941	itself, but sometimes it is inconvenient to avoid this).
		4942
		4943	A sed command like this will create wrapper C<#define>'s that you need to
		4944	include before including F<ev.h>:
		4945
		4946	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4947
		4948	This would create a file F<wrap.h> which essentially looks like this:
		4949
		4950	#define ev_backend myprefix_ev_backend
		4951	#define ev_check_start myprefix_ev_check_start
		4952	#define ev_check_stop myprefix_ev_check_stop
		4953	...
2388		4954
2389	=head2 EXAMPLES	4955	=head2 EXAMPLES
2390		4956
2391	For a real-world example of a program the includes libev	4957	For a real-world example of a program the includes libev
2392	verbatim, you can have a look at the EV perl module	4958	verbatim, you can have a look at the EV perl module
…		…
2397	file.	4963	file.
2398		4964
2399	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4965	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2400	that everybody includes and which overrides some configure choices:	4966	that everybody includes and which overrides some configure choices:
2401		4967
2402	#define EV_MINIMAL 1	4968	#define EV_FEATURES 8
2403	#define EV_USE_POLL 0	4969	#define EV_USE_SELECT 1
2404	#define EV_MULTIPLICITY 0
2405	#define EV_PERIODIC_ENABLE 0	4970	#define EV_PREPARE_ENABLE 1
		4971	#define EV_IDLE_ENABLE 1
2406	#define EV_STAT_ENABLE 0	4972	#define EV_SIGNAL_ENABLE 1
2407	#define EV_FORK_ENABLE 0	4973	#define EV_CHILD_ENABLE 1
		4974	#define EV_USE_STDEXCEPT 0
2408	#define EV_CONFIG_H <config.h>	4975	#define EV_CONFIG_H <config.h>
2409	#define EV_MINPRI 0
2410	#define EV_MAXPRI 0
2411		4976
2412	#include "ev++.h"	4977	#include "ev++.h"
2413		4978
2414	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4979	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2415		4980
2416	#include "ev_cpp.h"	4981	#include "ev_cpp.h"
2417	#include "ev.c"	4982	#include "ev.c"
2418		4983
		4984	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2419		4985
		4986	=head2 THREADS AND COROUTINES
		4987
		4988	=head3 THREADS
		4989
		4990	All libev functions are reentrant and thread-safe unless explicitly
		4991	documented otherwise, but libev implements no locking itself. This means
		4992	that you can use as many loops as you want in parallel, as long as there
		4993	are no concurrent calls into any libev function with the same loop
		4994	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4995	of course): libev guarantees that different event loops share no data
		4996	structures that need any locking.
		4997
		4998	Or to put it differently: calls with different loop parameters can be done
		4999	concurrently from multiple threads, calls with the same loop parameter
		5000	must be done serially (but can be done from different threads, as long as
		5001	only one thread ever is inside a call at any point in time, e.g. by using
		5002	a mutex per loop).
		5003
		5004	Specifically to support threads (and signal handlers), libev implements
		5005	so-called C<ev_async> watchers, which allow some limited form of
		5006	concurrency on the same event loop, namely waking it up "from the
		5007	outside".
		5008
		5009	If you want to know which design (one loop, locking, or multiple loops
		5010	without or something else still) is best for your problem, then I cannot
		5011	help you, but here is some generic advice:
		5012
		5013	=over 4
		5014
		5015	=item * most applications have a main thread: use the default libev loop
		5016	in that thread, or create a separate thread running only the default loop.
		5017
		5018	This helps integrating other libraries or software modules that use libev
		5019	themselves and don't care/know about threading.
		5020
		5021	=item * one loop per thread is usually a good model.
		5022
		5023	Doing this is almost never wrong, sometimes a better-performance model
		5024	exists, but it is always a good start.
		5025
		5026	=item * other models exist, such as the leader/follower pattern, where one
		5027	loop is handed through multiple threads in a kind of round-robin fashion.
		5028
		5029	Choosing a model is hard - look around, learn, know that usually you can do
		5030	better than you currently do :-)
		5031
		5032	=item * often you need to talk to some other thread which blocks in the
		5033	event loop.
		5034
		5035	C<ev_async> watchers can be used to wake them up from other threads safely
		5036	(or from signal contexts...).
		5037
		5038	An example use would be to communicate signals or other events that only
		5039	work in the default loop by registering the signal watcher with the
		5040	default loop and triggering an C<ev_async> watcher from the default loop
		5041	watcher callback into the event loop interested in the signal.
		5042
		5043	=back
		5044
		5045	See also L</THREAD LOCKING EXAMPLE>.
		5046
		5047	=head3 COROUTINES
		5048
		5049	Libev is very accommodating to coroutines ("cooperative threads"):
		5050	libev fully supports nesting calls to its functions from different
		5051	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5052	different coroutines, and switch freely between both coroutines running
		5053	the loop, as long as you don't confuse yourself). The only exception is
		5054	that you must not do this from C<ev_periodic> reschedule callbacks.
		5055
		5056	Care has been taken to ensure that libev does not keep local state inside
		5057	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5058	they do not call any callbacks.
		5059
		5060	=head2 COMPILER WARNINGS
		5061
		5062	Depending on your compiler and compiler settings, you might get no or a
		5063	lot of warnings when compiling libev code. Some people are apparently
		5064	scared by this.
		5065
		5066	However, these are unavoidable for many reasons. For one, each compiler
		5067	has different warnings, and each user has different tastes regarding
		5068	warning options. "Warn-free" code therefore cannot be a goal except when
		5069	targeting a specific compiler and compiler-version.
		5070
		5071	Another reason is that some compiler warnings require elaborate
		5072	workarounds, or other changes to the code that make it less clear and less
		5073	maintainable.
		5074
		5075	And of course, some compiler warnings are just plain stupid, or simply
		5076	wrong (because they don't actually warn about the condition their message
		5077	seems to warn about). For example, certain older gcc versions had some
		5078	warnings that resulted in an extreme number of false positives. These have
		5079	been fixed, but some people still insist on making code warn-free with
		5080	such buggy versions.
		5081
		5082	While libev is written to generate as few warnings as possible,
		5083	"warn-free" code is not a goal, and it is recommended not to build libev
		5084	with any compiler warnings enabled unless you are prepared to cope with
		5085	them (e.g. by ignoring them). Remember that warnings are just that:
		5086	warnings, not errors, or proof of bugs.
		5087
		5088
		5089	=head2 VALGRIND
		5090
		5091	Valgrind has a special section here because it is a popular tool that is
		5092	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5093
		5094	If you think you found a bug (memory leak, uninitialised data access etc.)
		5095	in libev, then check twice: If valgrind reports something like:
		5096
		5097	==2274== definitely lost: 0 bytes in 0 blocks.
		5098	==2274== possibly lost: 0 bytes in 0 blocks.
		5099	==2274== still reachable: 256 bytes in 1 blocks.
		5100
		5101	Then there is no memory leak, just as memory accounted to global variables
		5102	is not a memleak - the memory is still being referenced, and didn't leak.
		5103
		5104	Similarly, under some circumstances, valgrind might report kernel bugs
		5105	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5106	although an acceptable workaround has been found here), or it might be
		5107	confused.
		5108
		5109	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5110	make it into some kind of religion.
		5111
		5112	If you are unsure about something, feel free to contact the mailing list
		5113	with the full valgrind report and an explanation on why you think this
		5114	is a bug in libev (best check the archives, too :). However, don't be
		5115	annoyed when you get a brisk "this is no bug" answer and take the chance
		5116	of learning how to interpret valgrind properly.
		5117
		5118	If you need, for some reason, empty reports from valgrind for your project
		5119	I suggest using suppression lists.
		5120
		5121
		5122	=head1 PORTABILITY NOTES
		5123
		5124	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5125
		5126	GNU/Linux is the only common platform that supports 64 bit file/large file
		5127	interfaces but I<disables> them by default.
		5128
		5129	That means that libev compiled in the default environment doesn't support
		5130	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5131
		5132	Unfortunately, many programs try to work around this GNU/Linux issue
		5133	by enabling the large file API, which makes them incompatible with the
		5134	standard libev compiled for their system.
		5135
		5136	Likewise, libev cannot enable the large file API itself as this would
		5137	suddenly make it incompatible to the default compile time environment,
		5138	i.e. all programs not using special compile switches.
		5139
		5140	=head2 OS/X AND DARWIN BUGS
		5141
		5142	The whole thing is a bug if you ask me - basically any system interface
		5143	you touch is broken, whether it is locales, poll, kqueue or even the
		5144	OpenGL drivers.
		5145
		5146	=head3 C<kqueue> is buggy
		5147
		5148	The kqueue syscall is broken in all known versions - most versions support
		5149	only sockets, many support pipes.
		5150
		5151	Libev tries to work around this by not using C<kqueue> by default on this
		5152	rotten platform, but of course you can still ask for it when creating a
		5153	loop - embedding a socket-only kqueue loop into a select-based one is
		5154	probably going to work well.
		5155
		5156	=head3 C<poll> is buggy
		5157
		5158	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5159	implementation by something calling C<kqueue> internally around the 10.5.6
		5160	release, so now C<kqueue> I<and> C<poll> are broken.
		5161
		5162	Libev tries to work around this by not using C<poll> by default on
		5163	this rotten platform, but of course you can still ask for it when creating
		5164	a loop.
		5165
		5166	=head3 C<select> is buggy
		5167
		5168	All that's left is C<select>, and of course Apple found a way to fuck this
		5169	one up as well: On OS/X, C<select> actively limits the number of file
		5170	descriptors you can pass in to 1024 - your program suddenly crashes when
		5171	you use more.
		5172
		5173	There is an undocumented "workaround" for this - defining
		5174	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5175	work on OS/X.
		5176
		5177	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5178
		5179	=head3 C<errno> reentrancy
		5180
		5181	The default compile environment on Solaris is unfortunately so
		5182	thread-unsafe that you can't even use components/libraries compiled
		5183	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5184	defined by default. A valid, if stupid, implementation choice.
		5185
		5186	If you want to use libev in threaded environments you have to make sure
		5187	it's compiled with C<_REENTRANT> defined.
		5188
		5189	=head3 Event port backend
		5190
		5191	The scalable event interface for Solaris is called "event
		5192	ports". Unfortunately, this mechanism is very buggy in all major
		5193	releases. If you run into high CPU usage, your program freezes or you get
		5194	a large number of spurious wakeups, make sure you have all the relevant
		5195	and latest kernel patches applied. No, I don't know which ones, but there
		5196	are multiple ones to apply, and afterwards, event ports actually work
		5197	great.
		5198
		5199	If you can't get it to work, you can try running the program by setting
		5200	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5201	C<select> backends.
		5202
		5203	=head2 AIX POLL BUG
		5204
		5205	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5206	this by trying to avoid the poll backend altogether (i.e. it's not even
		5207	compiled in), which normally isn't a big problem as C<select> works fine
		5208	with large bitsets on AIX, and AIX is dead anyway.
		5209
		5210	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5211
		5212	=head3 General issues
		5213
		5214	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5215	requires, and its I/O model is fundamentally incompatible with the POSIX
		5216	model. Libev still offers limited functionality on this platform in
		5217	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5218	descriptors. This only applies when using Win32 natively, not when using
		5219	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5220	as every compiler comes with a slightly differently broken/incompatible
		5221	environment.
		5222
		5223	Lifting these limitations would basically require the full
		5224	re-implementation of the I/O system. If you are into this kind of thing,
		5225	then note that glib does exactly that for you in a very portable way (note
		5226	also that glib is the slowest event library known to man).
		5227
		5228	There is no supported compilation method available on windows except
		5229	embedding it into other applications.
		5230
		5231	Sensible signal handling is officially unsupported by Microsoft - libev
		5232	tries its best, but under most conditions, signals will simply not work.
		5233
		5234	Not a libev limitation but worth mentioning: windows apparently doesn't
		5235	accept large writes: instead of resulting in a partial write, windows will
		5236	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5237	so make sure you only write small amounts into your sockets (less than a
		5238	megabyte seems safe, but this apparently depends on the amount of memory
		5239	available).
		5240
		5241	Due to the many, low, and arbitrary limits on the win32 platform and
		5242	the abysmal performance of winsockets, using a large number of sockets
		5243	is not recommended (and not reasonable). If your program needs to use
		5244	more than a hundred or so sockets, then likely it needs to use a totally
		5245	different implementation for windows, as libev offers the POSIX readiness
		5246	notification model, which cannot be implemented efficiently on windows
		5247	(due to Microsoft monopoly games).
		5248
		5249	A typical way to use libev under windows is to embed it (see the embedding
		5250	section for details) and use the following F<evwrap.h> header file instead
		5251	of F<ev.h>:
		5252
		5253	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5254	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5255
		5256	#include "ev.h"
		5257
		5258	And compile the following F<evwrap.c> file into your project (make sure
		5259	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5260
		5261	#include "evwrap.h"
		5262	#include "ev.c"
		5263
		5264	=head3 The winsocket C<select> function
		5265
		5266	The winsocket C<select> function doesn't follow POSIX in that it
		5267	requires socket I<handles> and not socket I<file descriptors> (it is
		5268	also extremely buggy). This makes select very inefficient, and also
		5269	requires a mapping from file descriptors to socket handles (the Microsoft
		5270	C runtime provides the function C<_open_osfhandle> for this). See the
		5271	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5272	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5273
		5274	The configuration for a "naked" win32 using the Microsoft runtime
		5275	libraries and raw winsocket select is:
		5276
		5277	#define EV_USE_SELECT 1
		5278	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5279
		5280	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5281	complexity in the O(n²) range when using win32.
		5282
		5283	=head3 Limited number of file descriptors
		5284
		5285	Windows has numerous arbitrary (and low) limits on things.
		5286
		5287	Early versions of winsocket's select only supported waiting for a maximum
		5288	of C<64> handles (probably owning to the fact that all windows kernels
		5289	can only wait for C<64> things at the same time internally; Microsoft
		5290	recommends spawning a chain of threads and wait for 63 handles and the
		5291	previous thread in each. Sounds great!).
		5292
		5293	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5294	to some high number (e.g. C<2048>) before compiling the winsocket select
		5295	call (which might be in libev or elsewhere, for example, perl and many
		5296	other interpreters do their own select emulation on windows).
		5297
		5298	Another limit is the number of file descriptors in the Microsoft runtime
		5299	libraries, which by default is C<64> (there must be a hidden I<64>
		5300	fetish or something like this inside Microsoft). You can increase this
		5301	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5302	(another arbitrary limit), but is broken in many versions of the Microsoft
		5303	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5304	(depending on windows version and/or the phase of the moon). To get more,
		5305	you need to wrap all I/O functions and provide your own fd management, but
		5306	the cost of calling select (O(n²)) will likely make this unworkable.
		5307
		5308	=head2 PORTABILITY REQUIREMENTS
		5309
		5310	In addition to a working ISO-C implementation and of course the
		5311	backend-specific APIs, libev relies on a few additional extensions:
		5312
		5313	=over 4
		5314
		5315	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5316	calling conventions regardless of C<ev_watcher_type *>.
		5317
		5318	Libev assumes not only that all watcher pointers have the same internal
		5319	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5320	assumes that the same (machine) code can be used to call any watcher
		5321	callback: The watcher callbacks have different type signatures, but libev
		5322	calls them using an C<ev_watcher *> internally.
		5323
		5324	=item null pointers and integer zero are represented by 0 bytes
		5325
		5326	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5327	relies on this setting pointers and integers to null.
		5328
		5329	=item pointer accesses must be thread-atomic
		5330
		5331	Accessing a pointer value must be atomic, it must both be readable and
		5332	writable in one piece - this is the case on all current architectures.
		5333
		5334	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5335
		5336	The type C<sig_atomic_t volatile> (or whatever is defined as
		5337	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5338	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5339	believed to be sufficiently portable.
		5340
		5341	=item C<sigprocmask> must work in a threaded environment
		5342
		5343	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5344	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5345	pthread implementations will either allow C<sigprocmask> in the "main
		5346	thread" or will block signals process-wide, both behaviours would
		5347	be compatible with libev. Interaction between C<sigprocmask> and
		5348	C<pthread_sigmask> could complicate things, however.
		5349
		5350	The most portable way to handle signals is to block signals in all threads
		5351	except the initial one, and run the signal handling loop in the initial
		5352	thread as well.
		5353
		5354	=item C<long> must be large enough for common memory allocation sizes
		5355
		5356	To improve portability and simplify its API, libev uses C<long> internally
		5357	instead of C<size_t> when allocating its data structures. On non-POSIX
		5358	systems (Microsoft...) this might be unexpectedly low, but is still at
		5359	least 31 bits everywhere, which is enough for hundreds of millions of
		5360	watchers.
		5361
		5362	=item C<double> must hold a time value in seconds with enough accuracy
		5363
		5364	The type C<double> is used to represent timestamps. It is required to
		5365	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5366	good enough for at least into the year 4000 with millisecond accuracy
		5367	(the design goal for libev). This requirement is overfulfilled by
		5368	implementations using IEEE 754, which is basically all existing ones.
		5369
		5370	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5371	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5372	is either obsolete or somebody patched it to use C<long double> or
		5373	something like that, just kidding).
		5374
		5375	=back
		5376
		5377	If you know of other additional requirements drop me a note.
		5378
		5379
2420	=head1 COMPLEXITIES	5380	=head1 ALGORITHMIC COMPLEXITIES
2421		5381
2422	In this section the complexities of (many of) the algorithms used inside	5382	In this section the complexities of (many of) the algorithms used inside
2423	libev will be explained. For complexity discussions about backends see the	5383	libev will be documented. For complexity discussions about backends see
2424	documentation for C<ev_default_init>.	5384	the documentation for C<ev_default_init>.
2425		5385
2426	All of the following are about amortised time: If an array needs to be	5386	All of the following are about amortised time: If an array needs to be
2427	extended, libev needs to realloc and move the whole array, but this	5387	extended, libev needs to realloc and move the whole array, but this
2428	happens asymptotically never with higher number of elements, so O(1) might	5388	happens asymptotically rarer with higher number of elements, so O(1) might
2429	mean it might do a lengthy realloc operation in rare cases, but on average	5389	mean that libev does a lengthy realloc operation in rare cases, but on
2430	it is much faster and asymptotically approaches constant time.	5390	average it is much faster and asymptotically approaches constant time.
2431		5391
2432	=over 4	5392	=over 4
2433		5393
2434	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5394	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2435		5395
2436	This means that, when you have a watcher that triggers in one hour and	5396	This means that, when you have a watcher that triggers in one hour and
2437	there are 100 watchers that would trigger before that then inserting will	5397	there are 100 watchers that would trigger before that, then inserting will
2438	have to skip those 100 watchers.	5398	have to skip roughly seven (C<ld 100>) of these watchers.
2439		5399
2440	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	5400	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2441		5401
2442	That means that for changing a timer costs less than removing/adding them	5402	That means that changing a timer costs less than removing/adding them,
2443	as only the relative motion in the event queue has to be paid for.	5403	as only the relative motion in the event queue has to be paid for.
2444		5404
2445	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	5405	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2446		5406
2447	These just add the watcher into an array or at the head of a list.	5407	These just add the watcher into an array or at the head of a list.
		5408
2448	=item Stopping check/prepare/idle watchers: O(1)	5409	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2449		5410
2450	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5411	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2451		5412
2452	These watchers are stored in lists then need to be walked to find the	5413	These watchers are stored in lists, so they need to be walked to find the
2453	correct watcher to remove. The lists are usually short (you don't usually	5414	correct watcher to remove. The lists are usually short (you don't usually
2454	have many watchers waiting for the same fd or signal).	5415	have many watchers waiting for the same fd or signal: one is typical, two
		5416	is rare).
2455		5417
2456	=item Finding the next timer per loop iteration: O(1)	5418	=item Finding the next timer in each loop iteration: O(1)
		5419
		5420	By virtue of using a binary or 4-heap, the next timer is always found at a
		5421	fixed position in the storage array.
2457		5422
2458	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	5423	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2459		5424
2460	A change means an I/O watcher gets started or stopped, which requires	5425	A change means an I/O watcher gets started or stopped, which requires
2461	libev to recalculate its status (and possibly tell the kernel).	5426	libev to recalculate its status (and possibly tell the kernel, depending
		5427	on backend and whether C<ev_io_set> was used).
2462		5428
2463	=item Activating one watcher: O(1)	5429	=item Activating one watcher (putting it into the pending state): O(1)
2464		5430
2465	=item Priority handling: O(number_of_priorities)	5431	=item Priority handling: O(number_of_priorities)
2466		5432
2467	Priorities are implemented by allocating some space for each	5433	Priorities are implemented by allocating some space for each
2468	priority. When doing priority-based operations, libev usually has to	5434	priority. When doing priority-based operations, libev usually has to
2469	linearly search all the priorities.	5435	linearly search all the priorities, but starting/stopping and activating
		5436	watchers becomes O(1) with respect to priority handling.
		5437
		5438	=item Sending an ev_async: O(1)
		5439
		5440	=item Processing ev_async_send: O(number_of_async_watchers)
		5441
		5442	=item Processing signals: O(max_signal_number)
		5443
		5444	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5445	calls in the current loop iteration and the loop is currently
		5446	blocked. Checking for async and signal events involves iterating over all
		5447	running async watchers or all signal numbers.
2470		5448
2471	=back	5449	=back
2472		5450
2473		5451
		5452	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5453
		5454	The major version 4 introduced some incompatible changes to the API.
		5455
		5456	At the moment, the C<ev.h> header file provides compatibility definitions
		5457	for all changes, so most programs should still compile. The compatibility
		5458	layer might be removed in later versions of libev, so better update to the
		5459	new API early than late.
		5460
		5461	=over 4
		5462
		5463	=item C<EV_COMPAT3> backwards compatibility mechanism
		5464
		5465	The backward compatibility mechanism can be controlled by
		5466	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5467	section.
		5468
		5469	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5470
		5471	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5472
		5473	ev_loop_destroy (EV_DEFAULT_UC);
		5474	ev_loop_fork (EV_DEFAULT);
		5475
		5476	=item function/symbol renames
		5477
		5478	A number of functions and symbols have been renamed:
		5479
		5480	ev_loop => ev_run
		5481	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5482	EVLOOP_ONESHOT => EVRUN_ONCE
		5483
		5484	ev_unloop => ev_break
		5485	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5486	EVUNLOOP_ONE => EVBREAK_ONE
		5487	EVUNLOOP_ALL => EVBREAK_ALL
		5488
		5489	EV_TIMEOUT => EV_TIMER
		5490
		5491	ev_loop_count => ev_iteration
		5492	ev_loop_depth => ev_depth
		5493	ev_loop_verify => ev_verify
		5494
		5495	Most functions working on C<struct ev_loop> objects don't have an
		5496	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5497	associated constants have been renamed to not collide with the C<struct
		5498	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5499	as all other watcher types. Note that C<ev_loop_fork> is still called
		5500	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5501	typedef.
		5502
		5503	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5504
		5505	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5506	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5507	and work, but the library code will of course be larger.
		5508
		5509	=back
		5510
		5511
		5512	=head1 GLOSSARY
		5513
		5514	=over 4
		5515
		5516	=item active
		5517
		5518	A watcher is active as long as it has been started and not yet stopped.
		5519	See L</WATCHER STATES> for details.
		5520
		5521	=item application
		5522
		5523	In this document, an application is whatever is using libev.
		5524
		5525	=item backend
		5526
		5527	The part of the code dealing with the operating system interfaces.
		5528
		5529	=item callback
		5530
		5531	The address of a function that is called when some event has been
		5532	detected. Callbacks are being passed the event loop, the watcher that
		5533	received the event, and the actual event bitset.
		5534
		5535	=item callback/watcher invocation
		5536
		5537	The act of calling the callback associated with a watcher.
		5538
		5539	=item event
		5540
		5541	A change of state of some external event, such as data now being available
		5542	for reading on a file descriptor, time having passed or simply not having
		5543	any other events happening anymore.
		5544
		5545	In libev, events are represented as single bits (such as C<EV_READ> or
		5546	C<EV_TIMER>).
		5547
		5548	=item event library
		5549
		5550	A software package implementing an event model and loop.
		5551
		5552	=item event loop
		5553
		5554	An entity that handles and processes external events and converts them
		5555	into callback invocations.
		5556
		5557	=item event model
		5558
		5559	The model used to describe how an event loop handles and processes
		5560	watchers and events.
		5561
		5562	=item pending
		5563
		5564	A watcher is pending as soon as the corresponding event has been
		5565	detected. See L</WATCHER STATES> for details.
		5566
		5567	=item real time
		5568
		5569	The physical time that is observed. It is apparently strictly monotonic :)
		5570
		5571	=item wall-clock time
		5572
		5573	The time and date as shown on clocks. Unlike real time, it can actually
		5574	be wrong and jump forwards and backwards, e.g. when you adjust your
		5575	clock.
		5576
		5577	=item watcher
		5578
		5579	A data structure that describes interest in certain events. Watchers need
		5580	to be started (attached to an event loop) before they can receive events.
		5581
		5582	=back
		5583
2474	=head1 AUTHOR	5584	=head1 AUTHOR
2475		5585
2476	Marc Lehmann <libev@schmorp.de>.	5586	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5587	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
2477		5588

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