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Revision 1.407 by root, Thu May 3 16:02:52 2012 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 DESCRIPTION	9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
		18	ev_io stdin_watcher;
		19	ev_timer timeout_watcher;
		20
		21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
		23	static void
		24	stdin_cb (EV_P_ ev_io *w, int revents)
		25	{
		26	puts ("stdin ready");
		27	// for one-shot events, one must manually stop the watcher
		28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_run's to stop iterating
		32	ev_break (EV_A_ EVBREAK_ALL);
		33	}
		34
		35	// another callback, this time for a time-out
		36	static void
		37	timeout_cb (EV_P_ ev_timer *w, int revents)
		38	{
		39	puts ("timeout");
		40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
		42	}
		43
		44	int
		45	main (void)
		46	{
		47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = EV_DEFAULT;
		49
		50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
		52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		53	ev_io_start (loop, &stdin_watcher);
		54
		55	// initialise a timer watcher, then start it
		56	// simple non-repeating 5.5 second timeout
		57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		58	ev_timer_start (loop, &timeout_watcher);
		59
		60	// now wait for events to arrive
		61	ev_run (loop, 0);
		62
		63	// break was called, so exit
		64	return 0;
		65	}
		66
		67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
		90
		91	=head1 ABOUT LIBEV
10		92
11	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	95	these event sources and provide your program with events.
14		96
15	To do this, it must take more or less complete control over your process	97	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	98	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	99	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	101	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	102	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	103	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	104	watcher.
23		105
24	=head1 FEATURES	106	=head2 FEATURES
25		107
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
		112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
		113	timers (C<ev_timer>), absolute timers with customised rescheduling
		114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
29	events (related to SIGCHLD), and event watchers dealing with the event	115	change events (C<ev_child>), and event watchers dealing with the event
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
		117	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		118	limited support for fork events (C<ev_fork>).
		119
		120	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	121	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	122	for example).
33		123
34	=head1 CONVENTIONS	124	=head2 CONVENTIONS
35		125
36	Libev is very configurable. In this manual the default configuration	126	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	127	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	128	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	129	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	130	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	131	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	132	this argument.
43		133
44	=head1 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
45		135
46	Libev represents time as a single floating point number, representing the	136	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	137	the (fractional) number of seconds since the (POSIX) epoch (in practice
48	the beginning of 1970, details are complicated, don't ask). This type is	138	somewhere near the beginning of 1970, details are complicated, don't
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	139	ask). This type is called C<ev_tstamp>, which is what you should use
50	to the C<double> type in C, and when you need to do any calculations on	140	too. It usually aliases to the C<double> type in C. When you need to do
51	it, you should treat it as such.	141	any calculations on it, you should treat it as some floating point value.
		142
		143	Unlike the name component C<stamp> might indicate, it is also used for
		144	time differences (e.g. delays) throughout libev.
		145
		146	=head1 ERROR HANDLING
		147
		148	Libev knows three classes of errors: operating system errors, usage errors
		149	and internal errors (bugs).
		150
		151	When libev catches an operating system error it cannot handle (for example
		152	a system call indicating a condition libev cannot fix), it calls the callback
		153	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		154	abort. The default is to print a diagnostic message and to call C<abort
		155	()>.
		156
		157	When libev detects a usage error such as a negative timer interval, then
		158	it will print a diagnostic message and abort (via the C<assert> mechanism,
		159	so C<NDEBUG> will disable this checking): these are programming errors in
		160	the libev caller and need to be fixed there.
		161
		162	Libev also has a few internal error-checking C<assert>ions, and also has
		163	extensive consistency checking code. These do not trigger under normal
		164	circumstances, as they indicate either a bug in libev or worse.
52		165
53		166
54	=head1 GLOBAL FUNCTIONS	167	=head1 GLOBAL FUNCTIONS
55		168
56	These functions can be called anytime, even before initialising the	169	These functions can be called anytime, even before initialising the
…		…
60		173
61	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
62		175
63	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
64	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
65	you actually want to know.	178	you actually want to know. Also interesting is the combination of
		179	C<ev_now_update> and C<ev_now>.
		180
		181	=item ev_sleep (ev_tstamp interval)
		182
		183	Sleep for the given interval: The current thread will be blocked
		184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
		188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
66		192
67	=item int ev_version_major ()	193	=item int ev_version_major ()
68		194
69	=item int ev_version_minor ()	195	=item int ev_version_minor ()
70		196
71	You can find out the major and minor version numbers of the library	197	You can find out the major and minor ABI version numbers of the library
72	you linked against by calling the functions C<ev_version_major> and	198	you linked against by calling the functions C<ev_version_major> and
73	C<ev_version_minor>. If you want, you can compare against the global	199	C<ev_version_minor>. If you want, you can compare against the global
74	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	200	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
75	version of the library your program was compiled against.	201	version of the library your program was compiled against.
76		202
		203	These version numbers refer to the ABI version of the library, not the
		204	release version.
		205
77	Usually, it's a good idea to terminate if the major versions mismatch,	206	Usually, it's a good idea to terminate if the major versions mismatch,
78	as this indicates an incompatible change. Minor versions are usually	207	as this indicates an incompatible change. Minor versions are usually
79	compatible to older versions, so a larger minor version alone is usually	208	compatible to older versions, so a larger minor version alone is usually
80	not a problem.	209	not a problem.
81		210
82	Example: make sure we haven't accidentally been linked against the wrong	211	Example: Make sure we haven't accidentally been linked against the wrong
83	version:	212	version (note, however, that this will not detect other ABI mismatches,
		213	such as LFS or reentrancy).
84		214
85	assert (("libev version mismatch",	215	assert (("libev version mismatch",
86	ev_version_major () == EV_VERSION_MAJOR	216	ev_version_major () == EV_VERSION_MAJOR
87	&& ev_version_minor () >= EV_VERSION_MINOR));	217	&& ev_version_minor () >= EV_VERSION_MINOR));
88		218
89	=item unsigned int ev_supported_backends ()	219	=item unsigned int ev_supported_backends ()
90		220
91	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	221	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
92	value) compiled into this binary of libev (independent of their	222	value) compiled into this binary of libev (independent of their
…		…
94	a description of the set values.	224	a description of the set values.
95		225
96	Example: make sure we have the epoll method, because yeah this is cool and	226	Example: make sure we have the epoll method, because yeah this is cool and
97	a must have and can we have a torrent of it please!!!11	227	a must have and can we have a torrent of it please!!!11
98		228
99	assert (("sorry, no epoll, no sex",	229	assert (("sorry, no epoll, no sex",
100	ev_supported_backends () & EVBACKEND_EPOLL));	230	ev_supported_backends () & EVBACKEND_EPOLL));
101		231
102	=item unsigned int ev_recommended_backends ()	232	=item unsigned int ev_recommended_backends ()
103		233
104	Return the set of all backends compiled into this binary of libev and also	234	Return the set of all backends compiled into this binary of libev and
105	recommended for this platform. This set is often smaller than the one	235	also recommended for this platform, meaning it will work for most file
		236	descriptor types. This set is often smaller than the one returned by
106	returned by C<ev_supported_backends>, as for example kqueue is broken on	237	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
107	most BSDs and will not be autodetected unless you explicitly request it	238	and will not be auto-detected unless you explicitly request it (assuming
108	(assuming you know what you are doing). This is the set of backends that	239	you know what you are doing). This is the set of backends that libev will
109	libev will probe for if you specify no backends explicitly.	240	probe for if you specify no backends explicitly.
110		241
111	=item unsigned int ev_embeddable_backends ()	242	=item unsigned int ev_embeddable_backends ()
112		243
113	Returns the set of backends that are embeddable in other event loops. This	244	Returns the set of backends that are embeddable in other event loops. This
114	is the theoretical, all-platform, value. To find which backends	245	value is platform-specific but can include backends not available on the
115	might be supported on the current system, you would need to look at	246	current system. To find which embeddable backends might be supported on
116	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	247	the current system, you would need to look at C<ev_embeddable_backends ()
117	recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
118		249
119	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
120		251
121	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
122		253
123	Sets the allocation function to use (the prototype is similar to the	254	Sets the allocation function to use (the prototype is similar - the
124	realloc C function, the semantics are identical). It is used to allocate	255	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
125	and free memory (no surprises here). If it returns zero when memory	256	used to allocate and free memory (no surprises here). If it returns zero
126	needs to be allocated, the library might abort or take some potentially	257	when memory needs to be allocated (C<size != 0>), the library might abort
127	destructive action. The default is your system realloc function.	258	or take some potentially destructive action.
		259
		260	Since some systems (at least OpenBSD and Darwin) fail to implement
		261	correct C<realloc> semantics, libev will use a wrapper around the system
		262	C<realloc> and C<free> functions by default.
128		263
129	You could override this function in high-availability programs to, say,	264	You could override this function in high-availability programs to, say,
130	free some memory if it cannot allocate memory, to use a special allocator,	265	free some memory if it cannot allocate memory, to use a special allocator,
131	or even to sleep a while and retry until some memory is available.	266	or even to sleep a while and retry until some memory is available.
132		267
133	Example: replace the libev allocator with one that waits a bit and then	268	Example: Replace the libev allocator with one that waits a bit and then
134	retries: better than mine).	269	retries (example requires a standards-compliant C<realloc>).
135		270
136	static void *	271	static void *
137	persistent_realloc (void *ptr, long size)	272	persistent_realloc (void *ptr, size_t size)
138	{	273	{
139	for (;;)	274	for (;;)
140	{	275	{
141	void *newptr = realloc (ptr, size);	276	void *newptr = realloc (ptr, size);
142		277
…		…
148	}	283	}
149		284
150	...	285	...
151	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
152		287
153	=item ev_set_syserr_cb (void (*cb)(const char *msg));	288	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
154		289
155	Set the callback function to call on a retryable syscall error (such	290	Set the callback function to call on a retryable system call error (such
156	as failed select, poll, epoll_wait). The message is a printable string	291	as failed select, poll, epoll_wait). The message is a printable string
157	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
158	callback is set, then libev will expect it to remedy the sitution, no	293	callback is set, then libev will expect it to remedy the situation, no
159	matter what, when it returns. That is, libev will generally retry the	294	matter what, when it returns. That is, libev will generally retry the
160	requested operation, or, if the condition doesn't go away, do bad stuff	295	requested operation, or, if the condition doesn't go away, do bad stuff
161	(such as abort).	296	(such as abort).
162		297
163	Example: do the same thing as libev does internally:	298	Example: This is basically the same thing that libev does internally, too.
164		299
165	static void	300	static void
166	fatal_error (const char *msg)	301	fatal_error (const char *msg)
167	{	302	{
168	perror (msg);	303	perror (msg);
…		…
170	}	305	}
171		306
172	...	307	...
173	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
174		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
175	=back	323	=back
176		324
177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
178		326
179	An event loop is described by a C<struct ev_loop *>. The library knows two	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
180	types of such loops, the I<default> loop, which supports signals and child	328	I<not> optional in this case unless libev 3 compatibility is disabled, as
181	events, and dynamically created loops which do not.	329	libev 3 had an C<ev_loop> function colliding with the struct name).
182		330
183	If you use threads, a common model is to run the default event loop	331	The library knows two types of such loops, the I<default> loop, which
184	in your main thread (or in a separate thread) and for each thread you	332	supports child process events, and dynamically created event loops which
185	create, you also create another event loop. Libev itself does no locking	333	do not.
186	whatsoever, so if you mix calls to the same event loop in different
187	threads, make sure you lock (this is usually a bad idea, though, even if
188	done correctly, because it's hideous and inefficient).
189		334
190	=over 4	335	=over 4
191		336
192	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
193		338
194	This will initialise the default event loop if it hasn't been initialised	339	This returns the "default" event loop object, which is what you should
195	yet and return it. If the default loop could not be initialised, returns	340	normally use when you just need "the event loop". Event loop objects and
196	false. If it already was initialised it simply returns it (and ignores the	341	the C<flags> parameter are described in more detail in the entry for
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	342	C<ev_loop_new>.
		343
		344	If the default loop is already initialised then this function simply
		345	returns it (and ignores the flags. If that is troubling you, check
		346	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		347	flags, which should almost always be C<0>, unless the caller is also the
		348	one calling C<ev_run> or otherwise qualifies as "the main program".
198		349
199	If you don't know what event loop to use, use the one returned from this	350	If you don't know what event loop to use, use the one returned from this
200	function.	351	function (or via the C<EV_DEFAULT> macro).
		352
		353	Note that this function is I<not> thread-safe, so if you want to use it
		354	from multiple threads, you have to employ some kind of mutex (note also
		355	that this case is unlikely, as loops cannot be shared easily between
		356	threads anyway).
		357
		358	The default loop is the only loop that can handle C<ev_child> watchers,
		359	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		360	a problem for your application you can either create a dynamic loop with
		361	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		362	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		363
		364	Example: This is the most typical usage.
		365
		366	if (!ev_default_loop (0))
		367	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		368
		369	Example: Restrict libev to the select and poll backends, and do not allow
		370	environment settings to be taken into account:
		371
		372	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		373
		374	=item struct ev_loop *ev_loop_new (unsigned int flags)
		375
		376	This will create and initialise a new event loop object. If the loop
		377	could not be initialised, returns false.
		378
		379	This function is thread-safe, and one common way to use libev with
		380	threads is indeed to create one loop per thread, and using the default
		381	loop in the "main" or "initial" thread.
201		382
202	The flags argument can be used to specify special behaviour or specific	383	The flags argument can be used to specify special behaviour or specific
203	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	384	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		385
205	The following flags are supported:	386	The following flags are supported:
…		…
211	The default flags value. Use this if you have no clue (it's the right	392	The default flags value. Use this if you have no clue (it's the right
212	thing, believe me).	393	thing, believe me).
213		394
214	=item C<EVFLAG_NOENV>	395	=item C<EVFLAG_NOENV>
215		396
216	If this flag bit is ored into the flag value (or the program runs setuid	397	If this flag bit is or'ed into the flag value (or the program runs setuid
217	or setgid) then libev will I<not> look at the environment variable	398	or setgid) then libev will I<not> look at the environment variable
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	399	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	400	override the flags completely if it is found in the environment. This is
220	useful to try out specific backends to test their performance, or to work	401	useful to try out specific backends to test their performance, or to work
221	around bugs.	402	around bugs.
222		403
		404	=item C<EVFLAG_FORKCHECK>
		405
		406	Instead of calling C<ev_loop_fork> manually after a fork, you can also
		407	make libev check for a fork in each iteration by enabling this flag.
		408
		409	This works by calling C<getpid ()> on every iteration of the loop,
		410	and thus this might slow down your event loop if you do a lot of loop
		411	iterations and little real work, but is usually not noticeable (on my
		412	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		413	without a system call and thus I<very> fast, but my GNU/Linux system also has
		414	C<pthread_atfork> which is even faster).
		415
		416	The big advantage of this flag is that you can forget about fork (and
		417	forget about forgetting to tell libev about forking) when you use this
		418	flag.
		419
		420	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		421	environment variable.
		422
		423	=item C<EVFLAG_NOINOTIFY>
		424
		425	When this flag is specified, then libev will not attempt to use the
		426	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		427	testing, this flag can be useful to conserve inotify file descriptors, as
		428	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		429
		430	=item C<EVFLAG_SIGNALFD>
		431
		432	When this flag is specified, then libev will attempt to use the
		433	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		434	delivers signals synchronously, which makes it both faster and might make
		435	it possible to get the queued signal data. It can also simplify signal
		436	handling with threads, as long as you properly block signals in your
		437	threads that are not interested in handling them.
		438
		439	Signalfd will not be used by default as this changes your signal mask, and
		440	there are a lot of shoddy libraries and programs (glib's threadpool for
		441	example) that can't properly initialise their signal masks.
		442
		443	=item C<EVFLAG_NOSIGMASK>
		444
		445	When this flag is specified, then libev will avoid to modify the signal
		446	mask. Specifically, this means you have to make sure signals are unblocked
		447	when you want to receive them.
		448
		449	This behaviour is useful when you want to do your own signal handling, or
		450	want to handle signals only in specific threads and want to avoid libev
		451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
		455
		456	This flag's behaviour will become the default in future versions of libev.
		457
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		459
225	This is your standard select(2) backend. Not I<completely> standard, as	460	This is your standard select(2) backend. Not I<completely> standard, as
226	libev tries to roll its own fd_set with no limits on the number of fds,	461	libev tries to roll its own fd_set with no limits on the number of fds,
227	but if that fails, expect a fairly low limit on the number of fds when	462	but if that fails, expect a fairly low limit on the number of fds when
228	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	463	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	464	usually the fastest backend for a low number of (low-numbered :) fds.
		465
		466	To get good performance out of this backend you need a high amount of
		467	parallelism (most of the file descriptors should be busy). If you are
		468	writing a server, you should C<accept ()> in a loop to accept as many
		469	connections as possible during one iteration. You might also want to have
		470	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		471	readiness notifications you get per iteration.
		472
		473	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		474	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		475	C<exceptfds> set on that platform).
230		476
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	477	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		478
233	And this is your standard poll(2) backend. It's more complicated than	479	And this is your standard poll(2) backend. It's more complicated
234	select, but handles sparse fds better and has no artificial limit on the	480	than select, but handles sparse fds better and has no artificial
235	number of fds you can use (except it will slow down considerably with a	481	limit on the number of fds you can use (except it will slow down
236	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	482	considerably with a lot of inactive fds). It scales similarly to select,
		483	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		484	performance tips.
		485
		486	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		487	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
237		488
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		490
		491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		492	kernels).
		493
240	For few fds, this backend is a bit little slower than poll and select,	494	For few fds, this backend is a bit little slower than poll and select, but
241	but it scales phenomenally better. While poll and select usually scale like	495	it scales phenomenally better. While poll and select usually scale like
242	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	496	O(total_fds) where total_fds is the total number of fds (or the highest
243	either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
244		498
		499	The epoll mechanism deserves honorable mention as the most misdesigned
		500	of the more advanced event mechanisms: mere annoyances include silently
		501	dropping file descriptors, requiring a system call per change per file
		502	descriptor (and unnecessary guessing of parameters), problems with dup,
		503	returning before the timeout value, resulting in additional iterations
		504	(and only giving 5ms accuracy while select on the same platform gives
		505	0.1ms) and so on. The biggest issue is fork races, however - if a program
		506	forks then I<both> parent and child process have to recreate the epoll
		507	set, which can take considerable time (one syscall per file descriptor)
		508	and is of course hard to detect.
		509
		510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		511	but of course I<doesn't>, and epoll just loves to report events for
		512	totally I<different> file descriptors (even already closed ones, so
		513	one cannot even remove them from the set) than registered in the set
		514	(especially on SMP systems). Libev tries to counter these spurious
		515	notifications by employing an additional generation counter and comparing
		516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
		520	not least, it also refuses to work with some file descriptors which work
		521	perfectly fine with C<select> (files, many character devices...).
		522
		523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
		526
245	While stopping and starting an I/O watcher in the same iteration will	527	While stopping, setting and starting an I/O watcher in the same iteration
246	result in some caching, there is still a syscall per such incident	528	will result in some caching, there is still a system call per such
247	(because the fd could point to a different file description now), so its	529	incident (because the same I<file descriptor> could point to a different
248	best to avoid that. Also, dup()ed file descriptors might not work very	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
249	well if you register events for both fds.	531	file descriptors might not work very well if you register events for both
		532	file descriptors.
250		533
251	Please note that epoll sometimes generates spurious notifications, so you	534	Best performance from this backend is achieved by not unregistering all
252	need to use non-blocking I/O or other means to avoid blocking when no data	535	watchers for a file descriptor until it has been closed, if possible,
253	(or space) is available.	536	i.e. keep at least one watcher active per fd at all times. Stopping and
		537	starting a watcher (without re-setting it) also usually doesn't cause
		538	extra overhead. A fork can both result in spurious notifications as well
		539	as in libev having to destroy and recreate the epoll object, which can
		540	take considerable time and thus should be avoided.
		541
		542	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		543	faster than epoll for maybe up to a hundred file descriptors, depending on
		544	the usage. So sad.
		545
		546	While nominally embeddable in other event loops, this feature is broken in
		547	all kernel versions tested so far.
		548
		549	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		550	C<EVBACKEND_POLL>.
254		551
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	552	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		553
257	Kqueue deserves special mention, as at the time of this writing, it	554	Kqueue deserves special mention, as at the time of this writing, it
258	was broken on all BSDs except NetBSD (usually it doesn't work with	555	was broken on all BSDs except NetBSD (usually it doesn't work reliably
259	anything but sockets and pipes, except on Darwin, where of course its	556	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	557	it's completely useless). Unlike epoll, however, whose brokenness
		558	is by design, these kqueue bugs can (and eventually will) be fixed
		559	without API changes to existing programs. For this reason it's not being
261	unless you explicitly specify it explicitly in the flags (i.e. using	560	"auto-detected" unless you explicitly specify it in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	561	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		562	system like NetBSD.
		563
		564	You still can embed kqueue into a normal poll or select backend and use it
		565	only for sockets (after having made sure that sockets work with kqueue on
		566	the target platform). See C<ev_embed> watchers for more info.
263		567
264	It scales in the same way as the epoll backend, but the interface to the	568	It scales in the same way as the epoll backend, but the interface to the
265	kernel is more efficient (which says nothing about its actual speed, of	569	kernel is more efficient (which says nothing about its actual speed, of
266	course). While starting and stopping an I/O watcher does not cause an	570	course). While stopping, setting and starting an I/O watcher does never
267	extra syscall as with epoll, it still adds up to four event changes per	571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	572	two event changes per incident. Support for C<fork ()> is very bad (you
		573	might have to leak fd's on fork, but it's more sane than epoll) and it
		574	drops fds silently in similarly hard-to-detect cases
		575
		576	This backend usually performs well under most conditions.
		577
		578	While nominally embeddable in other event loops, this doesn't work
		579	everywhere, so you might need to test for this. And since it is broken
		580	almost everywhere, you should only use it when you have a lot of sockets
		581	(for which it usually works), by embedding it into another event loop
		582	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		583	also broken on OS X)) and, did I mention it, using it only for sockets.
		584
		585	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		586	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		587	C<NOTE_EOF>.
269		588
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	589	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		590
272	This is not implemented yet (and might never be).	591	This is not implemented yet (and might never be, unless you send me an
		592	implementation). According to reports, C</dev/poll> only supports sockets
		593	and is not embeddable, which would limit the usefulness of this backend
		594	immensely.
273		595
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		597
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
277	it's really slow, but it still scales very well (O(active_fds)).	599	it's really slow, but it still scales very well (O(active_fds)).
278		600
279	Please note that solaris ports can result in a lot of spurious	601	While this backend scales well, it requires one system call per active
280	notifications, so you need to use non-blocking I/O or other means to avoid	602	file descriptor per loop iteration. For small and medium numbers of file
281	blocking when no data (or space) is available.	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		604	might perform better.
		605
		606	On the positive side, this backend actually performed fully to
		607	specification in all tests and is fully embeddable, which is a rare feat
		608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returns events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where you
		616	absolutely have to know whether an event occurred or not because you have
		617	to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
		620
		621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		622	C<EVBACKEND_POLL>.
282		623
283	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
284		625
285	Try all backends (even potentially broken ones that wouldn't be tried	626	Try all backends (even potentially broken ones that wouldn't be tried
286	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	627	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		629
		630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
		639
289	=back	640	=back
290		641
291	If one or more of these are ored into the flags value, then only these	642	If one or more of the backend flags are or'ed into the flags value,
292	backends will be tried (in the reverse order as given here). If none are	643	then only these backends will be tried (in the reverse order as listed
293	specified, most compiled-in backend will be tried, usually in reverse	644	here). If none are specified, all backends in C<ev_recommended_backends
294	order of their flag values :)	645	()> will be tried.
295		646
296	The most typical usage is like this:
297
298	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
300
301	Restrict libev to the select and poll backends, and do not allow
302	environment settings to be taken into account:
303
304	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
305
306	Use whatever libev has to offer, but make sure that kqueue is used if
307	available (warning, breaks stuff, best use only with your own private
308	event loop and only if you know the OS supports your types of fds):
309
310	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
311
312	=item struct ev_loop *ev_loop_new (unsigned int flags)
313
314	Similar to C<ev_default_loop>, but always creates a new event loop that is
315	always distinct from the default loop. Unlike the default loop, it cannot
316	handle signal and child watchers, and attempts to do so will be greeted by
317	undefined behaviour (or a failed assertion if assertions are enabled).
318
319	Example: try to create a event loop that uses epoll and nothing else.	647	Example: Try to create a event loop that uses epoll and nothing else.
320		648
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	649	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	650	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	651	fatal ("no epoll found here, maybe it hides under your chair");
324		652
325	=item ev_default_destroy ()	653	Example: Use whatever libev has to offer, but make sure that kqueue is
		654	used if available.
326		655
327	Destroys the default loop again (frees all memory and kernel state	656	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
328	etc.). This stops all registered event watchers (by not touching them in
329	any way whatsoever, although you cannot rely on this :).
330		657
331	=item ev_loop_destroy (loop)	658	=item ev_loop_destroy (loop)
332		659
333	Like C<ev_default_destroy>, but destroys an event loop created by an	660	Destroys an event loop object (frees all memory and kernel state
334	earlier call to C<ev_loop_new>.	661	etc.). None of the active event watchers will be stopped in the normal
		662	sense, so e.g. C<ev_is_active> might still return true. It is your
		663	responsibility to either stop all watchers cleanly yourself I<before>
		664	calling this function, or cope with the fact afterwards (which is usually
		665	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		666	for example).
335		667
336	=item ev_default_fork ()	668	Note that certain global state, such as signal state (and installed signal
		669	handlers), will not be freed by this function, and related watchers (such
		670	as signal and child watchers) would need to be stopped manually.
337		671
		672	This function is normally used on loop objects allocated by
		673	C<ev_loop_new>, but it can also be used on the default loop returned by
		674	C<ev_default_loop>, in which case it is not thread-safe.
		675
		676	Note that it is not advisable to call this function on the default loop
		677	except in the rare occasion where you really need to free its resources.
		678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		679	and C<ev_loop_destroy>.
		680
		681	=item ev_loop_fork (loop)
		682
		683	This function sets a flag that causes subsequent C<ev_run> iterations to
338	This function reinitialises the kernel state for backends that have	684	reinitialise the kernel state for backends that have one. Despite the
339	one. Despite the name, you can call it anytime, but it makes most sense	685	name, you can call it anytime, but it makes most sense after forking, in
340	after forking, in either the parent or child process (or both, but that	686	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
341	again makes little sense).	687	child before resuming or calling C<ev_run>.
342		688
343	You I<must> call this function in the child process after forking if and	689	Again, you I<have> to call it on I<any> loop that you want to re-use after
344	only if you want to use the event library in both processes. If you just	690	a fork, I<even if you do not plan to use the loop in the parent>. This is
345	fork+exec, you don't have to call it.	691	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		692	during fork.
		693
		694	On the other hand, you only need to call this function in the child
		695	process if and only if you want to use the event loop in the child. If
		696	you just fork+exec or create a new loop in the child, you don't have to
		697	call it at all (in fact, C<epoll> is so badly broken that it makes a
		698	difference, but libev will usually detect this case on its own and do a
		699	costly reset of the backend).
346		700
347	The function itself is quite fast and it's usually not a problem to call	701	The function itself is quite fast and it's usually not a problem to call
348	it just in case after a fork. To make this easy, the function will fit in	702	it just in case after a fork.
349	quite nicely into a call to C<pthread_atfork>:
350		703
		704	Example: Automate calling C<ev_loop_fork> on the default loop when
		705	using pthreads.
		706
		707	static void
		708	post_fork_child (void)
		709	{
		710	ev_loop_fork (EV_DEFAULT);
		711	}
		712
		713	...
351	pthread_atfork (0, 0, ev_default_fork);	714	pthread_atfork (0, 0, post_fork_child);
352		715
353	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	716	=item int ev_is_default_loop (loop)
354	without calling this function, so if you force one of those backends you
355	do not need to care.
356		717
357	=item ev_loop_fork (loop)	718	Returns true when the given loop is, in fact, the default loop, and false
		719	otherwise.
358		720
359	Like C<ev_default_fork>, but acts on an event loop created by	721	=item unsigned int ev_iteration (loop)
360	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	722
361	after fork, and how you do this is entirely your own problem.	723	Returns the current iteration count for the event loop, which is identical
		724	to the number of times libev did poll for new events. It starts at C<0>
		725	and happily wraps around with enough iterations.
		726
		727	This value can sometimes be useful as a generation counter of sorts (it
		728	"ticks" the number of loop iterations), as it roughly corresponds with
		729	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		730	prepare and check phases.
		731
		732	=item unsigned int ev_depth (loop)
		733
		734	Returns the number of times C<ev_run> was entered minus the number of
		735	times C<ev_run> was exited normally, in other words, the recursion depth.
		736
		737	Outside C<ev_run>, this number is zero. In a callback, this number is
		738	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		739	in which case it is higher.
		740
		741	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		742	throwing an exception etc.), doesn't count as "exit" - consider this
		743	as a hint to avoid such ungentleman-like behaviour unless it's really
		744	convenient, in which case it is fully supported.
362		745
363	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
364		747
365	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	748	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
366	use.	749	use.
…		…
369		752
370	Returns the current "event loop time", which is the time the event loop	753	Returns the current "event loop time", which is the time the event loop
371	received events and started processing them. This timestamp does not	754	received events and started processing them. This timestamp does not
372	change as long as callbacks are being processed, and this is also the base	755	change as long as callbacks are being processed, and this is also the base
373	time used for relative timers. You can treat it as the timestamp of the	756	time used for relative timers. You can treat it as the timestamp of the
374	event occuring (or more correctly, libev finding out about it).	757	event occurring (or more correctly, libev finding out about it).
375		758
		759	=item ev_now_update (loop)
		760
		761	Establishes the current time by querying the kernel, updating the time
		762	returned by C<ev_now ()> in the progress. This is a costly operation and
		763	is usually done automatically within C<ev_run ()>.
		764
		765	This function is rarely useful, but when some event callback runs for a
		766	very long time without entering the event loop, updating libev's idea of
		767	the current time is a good idea.
		768
		769	See also L<The special problem of time updates> in the C<ev_timer> section.
		770
		771	=item ev_suspend (loop)
		772
		773	=item ev_resume (loop)
		774
		775	These two functions suspend and resume an event loop, for use when the
		776	loop is not used for a while and timeouts should not be processed.
		777
		778	A typical use case would be an interactive program such as a game: When
		779	the user presses C<^Z> to suspend the game and resumes it an hour later it
		780	would be best to handle timeouts as if no time had actually passed while
		781	the program was suspended. This can be achieved by calling C<ev_suspend>
		782	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		783	C<ev_resume> directly afterwards to resume timer processing.
		784
		785	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		786	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		787	will be rescheduled (that is, they will lose any events that would have
		788	occurred while suspended).
		789
		790	After calling C<ev_suspend> you B<must not> call I<any> function on the
		791	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		792	without a previous call to C<ev_suspend>.
		793
		794	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		795	event loop time (see C<ev_now_update>).
		796
376	=item ev_loop (loop, int flags)	797	=item bool ev_run (loop, int flags)
377		798
378	Finally, this is it, the event handler. This function usually is called	799	Finally, this is it, the event handler. This function usually is called
379	after you initialised all your watchers and you want to start handling	800	after you have initialised all your watchers and you want to start
380	events.	801	handling events. It will ask the operating system for any new events, call
		802	the watcher callbacks, and then repeat the whole process indefinitely: This
		803	is why event loops are called I<loops>.
381		804
382	If the flags argument is specified as C<0>, it will not return until	805	If the flags argument is specified as C<0>, it will keep handling events
383	either no event watchers are active anymore or C<ev_unloop> was called.	806	until either no event watchers are active anymore or C<ev_break> was
		807	called.
384		808
		809	The return value is false if there are no more active watchers (which
		810	usually means "all jobs done" or "deadlock"), and true in all other cases
		811	(which usually means " you should call C<ev_run> again").
		812
385	Please note that an explicit C<ev_unloop> is usually better than	813	Please note that an explicit C<ev_break> is usually better than
386	relying on all watchers to be stopped when deciding when a program has	814	relying on all watchers to be stopped when deciding when a program has
387	finished (especially in interactive programs), but having a program that	815	finished (especially in interactive programs), but having a program
388	automatically loops as long as it has to and no longer by virtue of	816	that automatically loops as long as it has to and no longer by virtue
389	relying on its watchers stopping correctly is a thing of beauty.	817	of relying on its watchers stopping correctly, that is truly a thing of
		818	beauty.
390		819
		820	This function is I<mostly> exception-safe - you can break out of a
		821	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		822	exception and so on. This does not decrement the C<ev_depth> value, nor
		823	will it clear any outstanding C<EVBREAK_ONE> breaks.
		824
391	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	825	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
392	those events and any outstanding ones, but will not block your process in	826	those events and any already outstanding ones, but will not wait and
393	case there are no events and will return after one iteration of the loop.	827	block your process in case there are no events and will return after one
		828	iteration of the loop. This is sometimes useful to poll and handle new
		829	events while doing lengthy calculations, to keep the program responsive.
394		830
395	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	831	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
396	neccessary) and will handle those and any outstanding ones. It will block	832	necessary) and will handle those and any already outstanding ones. It
397	your process until at least one new event arrives, and will return after	833	will block your process until at least one new event arrives (which could
398	one iteration of the loop. This is useful if you are waiting for some	834	be an event internal to libev itself, so there is no guarantee that a
399	external event in conjunction with something not expressible using other	835	user-registered callback will be called), and will return after one
		836	iteration of the loop.
		837
		838	This is useful if you are waiting for some external event in conjunction
		839	with something not expressible using other libev watchers (i.e. "roll your
400	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	840	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
401	usually a better approach for this kind of thing.	841	usually a better approach for this kind of thing.
402		842
403	Here are the gory details of what C<ev_loop> does:	843	Here are the gory details of what C<ev_run> does (this is for your
		844	understanding, not a guarantee that things will work exactly like this in
		845	future versions):
404		846
405	* If there are no active watchers (reference count is zero), return.	847	- Increment loop depth.
406	- Queue prepare watchers and then call all outstanding watchers.	848	- Reset the ev_break status.
		849	- Before the first iteration, call any pending watchers.
		850	LOOP:
		851	- If EVFLAG_FORKCHECK was used, check for a fork.
		852	- If a fork was detected (by any means), queue and call all fork watchers.
		853	- Queue and call all prepare watchers.
		854	- If ev_break was called, goto FINISH.
407	- If we have been forked, recreate the kernel state.	855	- If we have been forked, detach and recreate the kernel state
		856	as to not disturb the other process.
408	- Update the kernel state with all outstanding changes.	857	- Update the kernel state with all outstanding changes.
409	- Update the "event loop time".	858	- Update the "event loop time" (ev_now ()).
410	- Calculate for how long to block.	859	- Calculate for how long to sleep or block, if at all
		860	(active idle watchers, EVRUN_NOWAIT or not having
		861	any active watchers at all will result in not sleeping).
		862	- Sleep if the I/O and timer collect interval say so.
		863	- Increment loop iteration counter.
411	- Block the process, waiting for any events.	864	- Block the process, waiting for any events.
412	- Queue all outstanding I/O (fd) events.	865	- Queue all outstanding I/O (fd) events.
413	- Update the "event loop time" and do time jump handling.	866	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
414	- Queue all outstanding timers.	867	- Queue all expired timers.
415	- Queue all outstanding periodics.	868	- Queue all expired periodics.
416	- If no events are pending now, queue all idle watchers.	869	- Queue all idle watchers with priority higher than that of pending events.
417	- Queue all check watchers.	870	- Queue all check watchers.
418	- Call all queued watchers in reverse order (i.e. check watchers first).	871	- Call all queued watchers in reverse order (i.e. check watchers first).
419	Signals and child watchers are implemented as I/O watchers, and will	872	Signals and child watchers are implemented as I/O watchers, and will
420	be handled here by queueing them when their watcher gets executed.	873	be handled here by queueing them when their watcher gets executed.
421	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	874	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
422	were used, return, otherwise continue with step *.	875	were used, or there are no active watchers, goto FINISH, otherwise
		876	continue with step LOOP.
		877	FINISH:
		878	- Reset the ev_break status iff it was EVBREAK_ONE.
		879	- Decrement the loop depth.
		880	- Return.
423		881
424	Example: queue some jobs and then loop until no events are outsanding	882	Example: Queue some jobs and then loop until no events are outstanding
425	anymore.	883	anymore.
426		884
427	... queue jobs here, make sure they register event watchers as long	885	... queue jobs here, make sure they register event watchers as long
428	... as they still have work to do (even an idle watcher will do..)	886	... as they still have work to do (even an idle watcher will do..)
429	ev_loop (my_loop, 0);	887	ev_run (my_loop, 0);
430	... jobs done. yeah!	888	... jobs done or somebody called break. yeah!
431		889
432	=item ev_unloop (loop, how)	890	=item ev_break (loop, how)
433		891
434	Can be used to make a call to C<ev_loop> return early (but only after it	892	Can be used to make a call to C<ev_run> return early (but only after it
435	has processed all outstanding events). The C<how> argument must be either	893	has processed all outstanding events). The C<how> argument must be either
436	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	894	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
437	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	895	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		896
		897	This "break state" will be cleared on the next call to C<ev_run>.
		898
		899	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		900	which case it will have no effect.
438		901
439	=item ev_ref (loop)	902	=item ev_ref (loop)
440		903
441	=item ev_unref (loop)	904	=item ev_unref (loop)
442		905
443	Ref/unref can be used to add or remove a reference count on the event	906	Ref/unref can be used to add or remove a reference count on the event
444	loop: Every watcher keeps one reference, and as long as the reference	907	loop: Every watcher keeps one reference, and as long as the reference
445	count is nonzero, C<ev_loop> will not return on its own. If you have	908	count is nonzero, C<ev_run> will not return on its own.
446	a watcher you never unregister that should not keep C<ev_loop> from	909
447	returning, ev_unref() after starting, and ev_ref() before stopping it. For	910	This is useful when you have a watcher that you never intend to
		911	unregister, but that nevertheless should not keep C<ev_run> from
		912	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		913	before stopping it.
		914
448	example, libev itself uses this for its internal signal pipe: It is not	915	As an example, libev itself uses this for its internal signal pipe: It
449	visible to the libev user and should not keep C<ev_loop> from exiting if	916	is not visible to the libev user and should not keep C<ev_run> from
450	no event watchers registered by it are active. It is also an excellent	917	exiting if no event watchers registered by it are active. It is also an
451	way to do this for generic recurring timers or from within third-party	918	excellent way to do this for generic recurring timers or from within
452	libraries. Just remember to I<unref after start> and I<ref before stop>.	919	third-party libraries. Just remember to I<unref after start> and I<ref
		920	before stop> (but only if the watcher wasn't active before, or was active
		921	before, respectively. Note also that libev might stop watchers itself
		922	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		923	in the callback).
453		924
454	Example: create a signal watcher, but keep it from keeping C<ev_loop>	925	Example: Create a signal watcher, but keep it from keeping C<ev_run>
455	running when nothing else is active.	926	running when nothing else is active.
456		927
457	struct dv_signal exitsig;	928	ev_signal exitsig;
458	ev_signal_init (&exitsig, sig_cb, SIGINT);	929	ev_signal_init (&exitsig, sig_cb, SIGINT);
459	ev_signal_start (myloop, &exitsig);	930	ev_signal_start (loop, &exitsig);
460	evf_unref (myloop);	931	ev_unref (loop);
461		932
462	Example: for some weird reason, unregister the above signal handler again.	933	Example: For some weird reason, unregister the above signal handler again.
463		934
464	ev_ref (myloop);	935	ev_ref (loop);
465	ev_signal_stop (myloop, &exitsig);	936	ev_signal_stop (loop, &exitsig);
		937
		938	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		939
		940	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		941
		942	These advanced functions influence the time that libev will spend waiting
		943	for events. Both time intervals are by default C<0>, meaning that libev
		944	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		945	latency.
		946
		947	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		948	allows libev to delay invocation of I/O and timer/periodic callbacks
		949	to increase efficiency of loop iterations (or to increase power-saving
		950	opportunities).
		951
		952	The idea is that sometimes your program runs just fast enough to handle
		953	one (or very few) event(s) per loop iteration. While this makes the
		954	program responsive, it also wastes a lot of CPU time to poll for new
		955	events, especially with backends like C<select ()> which have a high
		956	overhead for the actual polling but can deliver many events at once.
		957
		958	By setting a higher I<io collect interval> you allow libev to spend more
		959	time collecting I/O events, so you can handle more events per iteration,
		960	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		961	C<ev_timer>) will not be affected. Setting this to a non-null value will
		962	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		963	sleep time ensures that libev will not poll for I/O events more often then
		964	once per this interval, on average (as long as the host time resolution is
		965	good enough).
		966
		967	Likewise, by setting a higher I<timeout collect interval> you allow libev
		968	to spend more time collecting timeouts, at the expense of increased
		969	latency/jitter/inexactness (the watcher callback will be called
		970	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		971	value will not introduce any overhead in libev.
		972
		973	Many (busy) programs can usually benefit by setting the I/O collect
		974	interval to a value near C<0.1> or so, which is often enough for
		975	interactive servers (of course not for games), likewise for timeouts. It
		976	usually doesn't make much sense to set it to a lower value than C<0.01>,
		977	as this approaches the timing granularity of most systems. Note that if
		978	you do transactions with the outside world and you can't increase the
		979	parallelity, then this setting will limit your transaction rate (if you
		980	need to poll once per transaction and the I/O collect interval is 0.01,
		981	then you can't do more than 100 transactions per second).
		982
		983	Setting the I<timeout collect interval> can improve the opportunity for
		984	saving power, as the program will "bundle" timer callback invocations that
		985	are "near" in time together, by delaying some, thus reducing the number of
		986	times the process sleeps and wakes up again. Another useful technique to
		987	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		988	they fire on, say, one-second boundaries only.
		989
		990	Example: we only need 0.1s timeout granularity, and we wish not to poll
		991	more often than 100 times per second:
		992
		993	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		994	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		995
		996	=item ev_invoke_pending (loop)
		997
		998	This call will simply invoke all pending watchers while resetting their
		999	pending state. Normally, C<ev_run> does this automatically when required,
		1000	but when overriding the invoke callback this call comes handy. This
		1001	function can be invoked from a watcher - this can be useful for example
		1002	when you want to do some lengthy calculation and want to pass further
		1003	event handling to another thread (you still have to make sure only one
		1004	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1005
		1006	=item int ev_pending_count (loop)
		1007
		1008	Returns the number of pending watchers - zero indicates that no watchers
		1009	are pending.
		1010
		1011	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1012
		1013	This overrides the invoke pending functionality of the loop: Instead of
		1014	invoking all pending watchers when there are any, C<ev_run> will call
		1015	this callback instead. This is useful, for example, when you want to
		1016	invoke the actual watchers inside another context (another thread etc.).
		1017
		1018	If you want to reset the callback, use C<ev_invoke_pending> as new
		1019	callback.
		1020
		1021	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1022
		1023	Sometimes you want to share the same loop between multiple threads. This
		1024	can be done relatively simply by putting mutex_lock/unlock calls around
		1025	each call to a libev function.
		1026
		1027	However, C<ev_run> can run an indefinite time, so it is not feasible
		1028	to wait for it to return. One way around this is to wake up the event
		1029	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1030	I<release> and I<acquire> callbacks on the loop.
		1031
		1032	When set, then C<release> will be called just before the thread is
		1033	suspended waiting for new events, and C<acquire> is called just
		1034	afterwards.
		1035
		1036	Ideally, C<release> will just call your mutex_unlock function, and
		1037	C<acquire> will just call the mutex_lock function again.
		1038
		1039	While event loop modifications are allowed between invocations of
		1040	C<release> and C<acquire> (that's their only purpose after all), no
		1041	modifications done will affect the event loop, i.e. adding watchers will
		1042	have no effect on the set of file descriptors being watched, or the time
		1043	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1044	to take note of any changes you made.
		1045
		1046	In theory, threads executing C<ev_run> will be async-cancel safe between
		1047	invocations of C<release> and C<acquire>.
		1048
		1049	See also the locking example in the C<THREADS> section later in this
		1050	document.
		1051
		1052	=item ev_set_userdata (loop, void *data)
		1053
		1054	=item void *ev_userdata (loop)
		1055
		1056	Set and retrieve a single C<void *> associated with a loop. When
		1057	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1058	C<0>.
		1059
		1060	These two functions can be used to associate arbitrary data with a loop,
		1061	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1062	C<acquire> callbacks described above, but of course can be (ab-)used for
		1063	any other purpose as well.
		1064
		1065	=item ev_verify (loop)
		1066
		1067	This function only does something when C<EV_VERIFY> support has been
		1068	compiled in, which is the default for non-minimal builds. It tries to go
		1069	through all internal structures and checks them for validity. If anything
		1070	is found to be inconsistent, it will print an error message to standard
		1071	error and call C<abort ()>.
		1072
		1073	This can be used to catch bugs inside libev itself: under normal
		1074	circumstances, this function will never abort as of course libev keeps its
		1075	data structures consistent.
466		1076
467	=back	1077	=back
468		1078
		1079
469	=head1 ANATOMY OF A WATCHER	1080	=head1 ANATOMY OF A WATCHER
470		1081
		1082	In the following description, uppercase C<TYPE> in names stands for the
		1083	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1084	watchers and C<ev_io_start> for I/O watchers.
		1085
471	A watcher is a structure that you create and register to record your	1086	A watcher is an opaque structure that you allocate and register to record
472	interest in some event. For instance, if you want to wait for STDIN to	1087	your interest in some event. To make a concrete example, imagine you want
473	become readable, you would create an C<ev_io> watcher for that:	1088	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1089	for that:
474		1090
475	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1091	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
476	{	1092	{
477	ev_io_stop (w);	1093	ev_io_stop (w);
478	ev_unloop (loop, EVUNLOOP_ALL);	1094	ev_break (loop, EVBREAK_ALL);
479	}	1095	}
480		1096
481	struct ev_loop *loop = ev_default_loop (0);	1097	struct ev_loop *loop = ev_default_loop (0);
		1098
482	struct ev_io stdin_watcher;	1099	ev_io stdin_watcher;
		1100
483	ev_init (&stdin_watcher, my_cb);	1101	ev_init (&stdin_watcher, my_cb);
484	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1102	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
485	ev_io_start (loop, &stdin_watcher);	1103	ev_io_start (loop, &stdin_watcher);
		1104
486	ev_loop (loop, 0);	1105	ev_run (loop, 0);
487		1106
488	As you can see, you are responsible for allocating the memory for your	1107	As you can see, you are responsible for allocating the memory for your
489	watcher structures (and it is usually a bad idea to do this on the stack,	1108	watcher structures (and it is I<usually> a bad idea to do this on the
490	although this can sometimes be quite valid).	1109	stack).
491		1110
		1111	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1112	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1113
492	Each watcher structure must be initialised by a call to C<ev_init	1114	Each watcher structure must be initialised by a call to C<ev_init (watcher
493	(watcher *, callback)>, which expects a callback to be provided. This	1115	*, callback)>, which expects a callback to be provided. This callback is
494	callback gets invoked each time the event occurs (or, in the case of io	1116	invoked each time the event occurs (or, in the case of I/O watchers, each
495	watchers, each time the event loop detects that the file descriptor given	1117	time the event loop detects that the file descriptor given is readable
496	is readable and/or writable).	1118	and/or writable).
497		1119
498	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1120	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
499	with arguments specific to this watcher type. There is also a macro	1121	macro to configure it, with arguments specific to the watcher type. There
500	to combine initialisation and setting in one call: C<< ev_<type>_init	1122	is also a macro to combine initialisation and setting in one call: C<<
501	(watcher *, callback, ...) >>.	1123	ev_TYPE_init (watcher *, callback, ...) >>.
502		1124
503	To make the watcher actually watch out for events, you have to start it	1125	To make the watcher actually watch out for events, you have to start it
504	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1126	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
505	*) >>), and you can stop watching for events at any time by calling the	1127	*) >>), and you can stop watching for events at any time by calling the
506	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1128	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
507		1129
508	As long as your watcher is active (has been started but not stopped) you	1130	As long as your watcher is active (has been started but not stopped) you
509	must not touch the values stored in it. Most specifically you must never	1131	must not touch the values stored in it. Most specifically you must never
510	reinitialise it or call its set macro.	1132	reinitialise it or call its C<ev_TYPE_set> macro.
511
512	You can check whether an event is active by calling the C<ev_is_active
513	(watcher *)> macro. To see whether an event is outstanding (but the
514	callback for it has not been called yet) you can use the C<ev_is_pending
515	(watcher *)> macro.
516		1133
517	Each and every callback receives the event loop pointer as first, the	1134	Each and every callback receives the event loop pointer as first, the
518	registered watcher structure as second, and a bitset of received events as	1135	registered watcher structure as second, and a bitset of received events as
519	third argument.	1136	third argument.
520		1137
…		…
529	=item C<EV_WRITE>	1146	=item C<EV_WRITE>
530		1147
531	The file descriptor in the C<ev_io> watcher has become readable and/or	1148	The file descriptor in the C<ev_io> watcher has become readable and/or
532	writable.	1149	writable.
533		1150
534	=item C<EV_TIMEOUT>	1151	=item C<EV_TIMER>
535		1152
536	The C<ev_timer> watcher has timed out.	1153	The C<ev_timer> watcher has timed out.
537		1154
538	=item C<EV_PERIODIC>	1155	=item C<EV_PERIODIC>
539		1156
…		…
545		1162
546	=item C<EV_CHILD>	1163	=item C<EV_CHILD>
547		1164
548	The pid specified in the C<ev_child> watcher has received a status change.	1165	The pid specified in the C<ev_child> watcher has received a status change.
549		1166
		1167	=item C<EV_STAT>
		1168
		1169	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1170
550	=item C<EV_IDLE>	1171	=item C<EV_IDLE>
551		1172
552	The C<ev_idle> watcher has determined that you have nothing better to do.	1173	The C<ev_idle> watcher has determined that you have nothing better to do.
553		1174
554	=item C<EV_PREPARE>	1175	=item C<EV_PREPARE>
555		1176
556	=item C<EV_CHECK>	1177	=item C<EV_CHECK>
557		1178
558	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1179	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
559	to gather new events, and all C<ev_check> watchers are invoked just after	1180	gather new events, and all C<ev_check> watchers are queued (not invoked)
560	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1181	just after C<ev_run> has gathered them, but before it queues any callbacks
		1182	for any received events. That means C<ev_prepare> watchers are the last
		1183	watchers invoked before the event loop sleeps or polls for new events, and
		1184	C<ev_check> watchers will be invoked before any other watchers of the same
		1185	or lower priority within an event loop iteration.
		1186
561	received events. Callbacks of both watcher types can start and stop as	1187	Callbacks of both watcher types can start and stop as many watchers as
562	many watchers as they want, and all of them will be taken into account	1188	they want, and all of them will be taken into account (for example, a
563	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1189	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
564	C<ev_loop> from blocking).	1190	blocking).
		1191
		1192	=item C<EV_EMBED>
		1193
		1194	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1195
		1196	=item C<EV_FORK>
		1197
		1198	The event loop has been resumed in the child process after fork (see
		1199	C<ev_fork>).
		1200
		1201	=item C<EV_CLEANUP>
		1202
		1203	The event loop is about to be destroyed (see C<ev_cleanup>).
		1204
		1205	=item C<EV_ASYNC>
		1206
		1207	The given async watcher has been asynchronously notified (see C<ev_async>).
		1208
		1209	=item C<EV_CUSTOM>
		1210
		1211	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1212	by libev users to signal watchers (e.g. via C<ev_feed_event>).
565		1213
566	=item C<EV_ERROR>	1214	=item C<EV_ERROR>
567		1215
568	An unspecified error has occured, the watcher has been stopped. This might	1216	An unspecified error has occurred, the watcher has been stopped. This might
569	happen because the watcher could not be properly started because libev	1217	happen because the watcher could not be properly started because libev
570	ran out of memory, a file descriptor was found to be closed or any other	1218	ran out of memory, a file descriptor was found to be closed or any other
		1219	problem. Libev considers these application bugs.
		1220
571	problem. You best act on it by reporting the problem and somehow coping	1221	You best act on it by reporting the problem and somehow coping with the
572	with the watcher being stopped.	1222	watcher being stopped. Note that well-written programs should not receive
		1223	an error ever, so when your watcher receives it, this usually indicates a
		1224	bug in your program.
573		1225
574	Libev will usually signal a few "dummy" events together with an error,	1226	Libev will usually signal a few "dummy" events together with an error, for
575	for example it might indicate that a fd is readable or writable, and if	1227	example it might indicate that a fd is readable or writable, and if your
576	your callbacks is well-written it can just attempt the operation and cope	1228	callbacks is well-written it can just attempt the operation and cope with
577	with the error from read() or write(). This will not work in multithreaded	1229	the error from read() or write(). This will not work in multi-threaded
578	programs, though, so beware.	1230	programs, though, as the fd could already be closed and reused for another
		1231	thing, so beware.
579		1232
580	=back	1233	=back
581		1234
582	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1235	=head2 GENERIC WATCHER FUNCTIONS
583		1236
584	Each watcher has, by default, a member C<void *data> that you can change	1237	=over 4
585	and read at any time, libev will completely ignore it. This can be used
586	to associate arbitrary data with your watcher. If you need more data and
587	don't want to allocate memory and store a pointer to it in that data
588	member, you can also "subclass" the watcher type and provide your own
589	data:
590		1238
591	struct my_io	1239	=item C<ev_init> (ev_TYPE *watcher, callback)
		1240
		1241	This macro initialises the generic portion of a watcher. The contents
		1242	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1243	the generic parts of the watcher are initialised, you I<need> to call
		1244	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1245	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1246	which rolls both calls into one.
		1247
		1248	You can reinitialise a watcher at any time as long as it has been stopped
		1249	(or never started) and there are no pending events outstanding.
		1250
		1251	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1252	int revents)>.
		1253
		1254	Example: Initialise an C<ev_io> watcher in two steps.
		1255
		1256	ev_io w;
		1257	ev_init (&w, my_cb);
		1258	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1259
		1260	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1261
		1262	This macro initialises the type-specific parts of a watcher. You need to
		1263	call C<ev_init> at least once before you call this macro, but you can
		1264	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1265	macro on a watcher that is active (it can be pending, however, which is a
		1266	difference to the C<ev_init> macro).
		1267
		1268	Although some watcher types do not have type-specific arguments
		1269	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1270
		1271	See C<ev_init>, above, for an example.
		1272
		1273	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1274
		1275	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1276	calls into a single call. This is the most convenient method to initialise
		1277	a watcher. The same limitations apply, of course.
		1278
		1279	Example: Initialise and set an C<ev_io> watcher in one step.
		1280
		1281	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1282
		1283	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1284
		1285	Starts (activates) the given watcher. Only active watchers will receive
		1286	events. If the watcher is already active nothing will happen.
		1287
		1288	Example: Start the C<ev_io> watcher that is being abused as example in this
		1289	whole section.
		1290
		1291	ev_io_start (EV_DEFAULT_UC, &w);
		1292
		1293	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1294
		1295	Stops the given watcher if active, and clears the pending status (whether
		1296	the watcher was active or not).
		1297
		1298	It is possible that stopped watchers are pending - for example,
		1299	non-repeating timers are being stopped when they become pending - but
		1300	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1301	pending. If you want to free or reuse the memory used by the watcher it is
		1302	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1303
		1304	=item bool ev_is_active (ev_TYPE *watcher)
		1305
		1306	Returns a true value iff the watcher is active (i.e. it has been started
		1307	and not yet been stopped). As long as a watcher is active you must not modify
		1308	it.
		1309
		1310	=item bool ev_is_pending (ev_TYPE *watcher)
		1311
		1312	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1313	events but its callback has not yet been invoked). As long as a watcher
		1314	is pending (but not active) you must not call an init function on it (but
		1315	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1316	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1317	it).
		1318
		1319	=item callback ev_cb (ev_TYPE *watcher)
		1320
		1321	Returns the callback currently set on the watcher.
		1322
		1323	=item ev_cb_set (ev_TYPE *watcher, callback)
		1324
		1325	Change the callback. You can change the callback at virtually any time
		1326	(modulo threads).
		1327
		1328	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1329
		1330	=item int ev_priority (ev_TYPE *watcher)
		1331
		1332	Set and query the priority of the watcher. The priority is a small
		1333	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1334	(default: C<-2>). Pending watchers with higher priority will be invoked
		1335	before watchers with lower priority, but priority will not keep watchers
		1336	from being executed (except for C<ev_idle> watchers).
		1337
		1338	If you need to suppress invocation when higher priority events are pending
		1339	you need to look at C<ev_idle> watchers, which provide this functionality.
		1340
		1341	You I<must not> change the priority of a watcher as long as it is active or
		1342	pending.
		1343
		1344	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1345	fine, as long as you do not mind that the priority value you query might
		1346	or might not have been clamped to the valid range.
		1347
		1348	The default priority used by watchers when no priority has been set is
		1349	always C<0>, which is supposed to not be too high and not be too low :).
		1350
		1351	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1352	priorities.
		1353
		1354	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1355
		1356	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1357	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1358	can deal with that fact, as both are simply passed through to the
		1359	callback.
		1360
		1361	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1362
		1363	If the watcher is pending, this function clears its pending status and
		1364	returns its C<revents> bitset (as if its callback was invoked). If the
		1365	watcher isn't pending it does nothing and returns C<0>.
		1366
		1367	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1368	callback to be invoked, which can be accomplished with this function.
		1369
		1370	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1371
		1372	Feeds the given event set into the event loop, as if the specified event
		1373	had happened for the specified watcher (which must be a pointer to an
		1374	initialised but not necessarily started event watcher). Obviously you must
		1375	not free the watcher as long as it has pending events.
		1376
		1377	Stopping the watcher, letting libev invoke it, or calling
		1378	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1379	not started in the first place.
		1380
		1381	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1382	functions that do not need a watcher.
		1383
		1384	=back
		1385
		1386	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1387	OWN COMPOSITE WATCHERS> idioms.
		1388
		1389	=head2 WATCHER STATES
		1390
		1391	There are various watcher states mentioned throughout this manual -
		1392	active, pending and so on. In this section these states and the rules to
		1393	transition between them will be described in more detail - and while these
		1394	rules might look complicated, they usually do "the right thing".
		1395
		1396	=over 4
		1397
		1398	=item initialiased
		1399
		1400	Before a watcher can be registered with the event loop it has to be
		1401	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1402	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1403
		1404	In this state it is simply some block of memory that is suitable for
		1405	use in an event loop. It can be moved around, freed, reused etc. at
		1406	will - as long as you either keep the memory contents intact, or call
		1407	C<ev_TYPE_init> again.
		1408
		1409	=item started/running/active
		1410
		1411	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1412	property of the event loop, and is actively waiting for events. While in
		1413	this state it cannot be accessed (except in a few documented ways), moved,
		1414	freed or anything else - the only legal thing is to keep a pointer to it,
		1415	and call libev functions on it that are documented to work on active watchers.
		1416
		1417	=item pending
		1418
		1419	If a watcher is active and libev determines that an event it is interested
		1420	in has occurred (such as a timer expiring), it will become pending. It will
		1421	stay in this pending state until either it is stopped or its callback is
		1422	about to be invoked, so it is not normally pending inside the watcher
		1423	callback.
		1424
		1425	The watcher might or might not be active while it is pending (for example,
		1426	an expired non-repeating timer can be pending but no longer active). If it
		1427	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1428	but it is still property of the event loop at this time, so cannot be
		1429	moved, freed or reused. And if it is active the rules described in the
		1430	previous item still apply.
		1431
		1432	It is also possible to feed an event on a watcher that is not active (e.g.
		1433	via C<ev_feed_event>), in which case it becomes pending without being
		1434	active.
		1435
		1436	=item stopped
		1437
		1438	A watcher can be stopped implicitly by libev (in which case it might still
		1439	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1440	latter will clear any pending state the watcher might be in, regardless
		1441	of whether it was active or not, so stopping a watcher explicitly before
		1442	freeing it is often a good idea.
		1443
		1444	While stopped (and not pending) the watcher is essentially in the
		1445	initialised state, that is, it can be reused, moved, modified in any way
		1446	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1447	it again).
		1448
		1449	=back
		1450
		1451	=head2 WATCHER PRIORITY MODELS
		1452
		1453	Many event loops support I<watcher priorities>, which are usually small
		1454	integers that influence the ordering of event callback invocation
		1455	between watchers in some way, all else being equal.
		1456
		1457	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1458	description for the more technical details such as the actual priority
		1459	range.
		1460
		1461	There are two common ways how these these priorities are being interpreted
		1462	by event loops:
		1463
		1464	In the more common lock-out model, higher priorities "lock out" invocation
		1465	of lower priority watchers, which means as long as higher priority
		1466	watchers receive events, lower priority watchers are not being invoked.
		1467
		1468	The less common only-for-ordering model uses priorities solely to order
		1469	callback invocation within a single event loop iteration: Higher priority
		1470	watchers are invoked before lower priority ones, but they all get invoked
		1471	before polling for new events.
		1472
		1473	Libev uses the second (only-for-ordering) model for all its watchers
		1474	except for idle watchers (which use the lock-out model).
		1475
		1476	The rationale behind this is that implementing the lock-out model for
		1477	watchers is not well supported by most kernel interfaces, and most event
		1478	libraries will just poll for the same events again and again as long as
		1479	their callbacks have not been executed, which is very inefficient in the
		1480	common case of one high-priority watcher locking out a mass of lower
		1481	priority ones.
		1482
		1483	Static (ordering) priorities are most useful when you have two or more
		1484	watchers handling the same resource: a typical usage example is having an
		1485	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1486	timeouts. Under load, data might be received while the program handles
		1487	other jobs, but since timers normally get invoked first, the timeout
		1488	handler will be executed before checking for data. In that case, giving
		1489	the timer a lower priority than the I/O watcher ensures that I/O will be
		1490	handled first even under adverse conditions (which is usually, but not
		1491	always, what you want).
		1492
		1493	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1494	will only be executed when no same or higher priority watchers have
		1495	received events, they can be used to implement the "lock-out" model when
		1496	required.
		1497
		1498	For example, to emulate how many other event libraries handle priorities,
		1499	you can associate an C<ev_idle> watcher to each such watcher, and in
		1500	the normal watcher callback, you just start the idle watcher. The real
		1501	processing is done in the idle watcher callback. This causes libev to
		1502	continuously poll and process kernel event data for the watcher, but when
		1503	the lock-out case is known to be rare (which in turn is rare :), this is
		1504	workable.
		1505
		1506	Usually, however, the lock-out model implemented that way will perform
		1507	miserably under the type of load it was designed to handle. In that case,
		1508	it might be preferable to stop the real watcher before starting the
		1509	idle watcher, so the kernel will not have to process the event in case
		1510	the actual processing will be delayed for considerable time.
		1511
		1512	Here is an example of an I/O watcher that should run at a strictly lower
		1513	priority than the default, and which should only process data when no
		1514	other events are pending:
		1515
		1516	ev_idle idle; // actual processing watcher
		1517	ev_io io; // actual event watcher
		1518
		1519	static void
		1520	io_cb (EV_P_ ev_io *w, int revents)
592	{	1521	{
593	struct ev_io io;	1522	// stop the I/O watcher, we received the event, but
594	int otherfd;	1523	// are not yet ready to handle it.
595	void *somedata;	1524	ev_io_stop (EV_A_ w);
596	struct whatever *mostinteresting;	1525
		1526	// start the idle watcher to handle the actual event.
		1527	// it will not be executed as long as other watchers
		1528	// with the default priority are receiving events.
		1529	ev_idle_start (EV_A_ &idle);
597	}	1530	}
598		1531
599	And since your callback will be called with a pointer to the watcher, you	1532	static void
600	can cast it back to your own type:	1533	idle_cb (EV_P_ ev_idle *w, int revents)
601
602	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
603	{	1534	{
604	struct my_io *w = (struct my_io *)w_;	1535	// actual processing
605	...	1536	read (STDIN_FILENO, ...);
		1537
		1538	// have to start the I/O watcher again, as
		1539	// we have handled the event
		1540	ev_io_start (EV_P_ &io);
606	}	1541	}
607		1542
608	More interesting and less C-conformant ways of catsing your callback type	1543	// initialisation
609	have been omitted....	1544	ev_idle_init (&idle, idle_cb);
		1545	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1546	ev_io_start (EV_DEFAULT_ &io);
		1547
		1548	In the "real" world, it might also be beneficial to start a timer, so that
		1549	low-priority connections can not be locked out forever under load. This
		1550	enables your program to keep a lower latency for important connections
		1551	during short periods of high load, while not completely locking out less
		1552	important ones.
610		1553
611		1554
612	=head1 WATCHER TYPES	1555	=head1 WATCHER TYPES
613		1556
614	This section describes each watcher in detail, but will not repeat	1557	This section describes each watcher in detail, but will not repeat
615	information given in the last section.	1558	information given in the last section. Any initialisation/set macros,
		1559	functions and members specific to the watcher type are explained.
616		1560
		1561	Members are additionally marked with either I<[read-only]>, meaning that,
		1562	while the watcher is active, you can look at the member and expect some
		1563	sensible content, but you must not modify it (you can modify it while the
		1564	watcher is stopped to your hearts content), or I<[read-write]>, which
		1565	means you can expect it to have some sensible content while the watcher
		1566	is active, but you can also modify it. Modifying it may not do something
		1567	sensible or take immediate effect (or do anything at all), but libev will
		1568	not crash or malfunction in any way.
617		1569
		1570
618	=head2 C<ev_io> - is this file descriptor readable or writable	1571	=head2 C<ev_io> - is this file descriptor readable or writable?
619		1572
620	I/O watchers check whether a file descriptor is readable or writable	1573	I/O watchers check whether a file descriptor is readable or writable
621	in each iteration of the event loop (This behaviour is called	1574	in each iteration of the event loop, or, more precisely, when reading
622	level-triggering because you keep receiving events as long as the	1575	would not block the process and writing would at least be able to write
623	condition persists. Remember you can stop the watcher if you don't want to	1576	some data. This behaviour is called level-triggering because you keep
624	act on the event and neither want to receive future events).	1577	receiving events as long as the condition persists. Remember you can stop
		1578	the watcher if you don't want to act on the event and neither want to
		1579	receive future events.
625		1580
626	In general you can register as many read and/or write event watchers per	1581	In general you can register as many read and/or write event watchers per
627	fd as you want (as long as you don't confuse yourself). Setting all file	1582	fd as you want (as long as you don't confuse yourself). Setting all file
628	descriptors to non-blocking mode is also usually a good idea (but not	1583	descriptors to non-blocking mode is also usually a good idea (but not
629	required if you know what you are doing).	1584	required if you know what you are doing).
630		1585
631	You have to be careful with dup'ed file descriptors, though. Some backends	1586	Another thing you have to watch out for is that it is quite easy to
632	(the linux epoll backend is a notable example) cannot handle dup'ed file	1587	receive "spurious" readiness notifications, that is, your callback might
633	descriptors correctly if you register interest in two or more fds pointing	1588	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
634	to the same underlying file/socket etc. description (that is, they share	1589	because there is no data. It is very easy to get into this situation even
635	the same underlying "file open").	1590	with a relatively standard program structure. Thus it is best to always
		1591	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
		1592	preferable to a program hanging until some data arrives.
636		1593
637	If you must do this, then force the use of a known-to-be-good backend	1594	If you cannot run the fd in non-blocking mode (for example you should
638	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1595	not play around with an Xlib connection), then you have to separately
639	C<EVBACKEND_POLL>).	1596	re-test whether a file descriptor is really ready with a known-to-be good
		1597	interface such as poll (fortunately in the case of Xlib, it already does
		1598	this on its own, so its quite safe to use). Some people additionally
		1599	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1600	indefinitely.
		1601
		1602	But really, best use non-blocking mode.
		1603
		1604	=head3 The special problem of disappearing file descriptors
		1605
		1606	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1607	descriptor (either due to calling C<close> explicitly or any other means,
		1608	such as C<dup2>). The reason is that you register interest in some file
		1609	descriptor, but when it goes away, the operating system will silently drop
		1610	this interest. If another file descriptor with the same number then is
		1611	registered with libev, there is no efficient way to see that this is, in
		1612	fact, a different file descriptor.
		1613
		1614	To avoid having to explicitly tell libev about such cases, libev follows
		1615	the following policy: Each time C<ev_io_set> is being called, libev
		1616	will assume that this is potentially a new file descriptor, otherwise
		1617	it is assumed that the file descriptor stays the same. That means that
		1618	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1619	descriptor even if the file descriptor number itself did not change.
		1620
		1621	This is how one would do it normally anyway, the important point is that
		1622	the libev application should not optimise around libev but should leave
		1623	optimisations to libev.
		1624
		1625	=head3 The special problem of dup'ed file descriptors
		1626
		1627	Some backends (e.g. epoll), cannot register events for file descriptors,
		1628	but only events for the underlying file descriptions. That means when you
		1629	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1630	events for them, only one file descriptor might actually receive events.
		1631
		1632	There is no workaround possible except not registering events
		1633	for potentially C<dup ()>'ed file descriptors, or to resort to
		1634	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1635
		1636	=head3 The special problem of files
		1637
		1638	Many people try to use C<select> (or libev) on file descriptors
		1639	representing files, and expect it to become ready when their program
		1640	doesn't block on disk accesses (which can take a long time on their own).
		1641
		1642	However, this cannot ever work in the "expected" way - you get a readiness
		1643	notification as soon as the kernel knows whether and how much data is
		1644	there, and in the case of open files, that's always the case, so you
		1645	always get a readiness notification instantly, and your read (or possibly
		1646	write) will still block on the disk I/O.
		1647
		1648	Another way to view it is that in the case of sockets, pipes, character
		1649	devices and so on, there is another party (the sender) that delivers data
		1650	on its own, but in the case of files, there is no such thing: the disk
		1651	will not send data on its own, simply because it doesn't know what you
		1652	wish to read - you would first have to request some data.
		1653
		1654	Since files are typically not-so-well supported by advanced notification
		1655	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1656	to files, even though you should not use it. The reason for this is
		1657	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1658	usually a tty, often a pipe, but also sometimes files or special devices
		1659	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1660	F</dev/urandom>), and even though the file might better be served with
		1661	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1662	it "just works" instead of freezing.
		1663
		1664	So avoid file descriptors pointing to files when you know it (e.g. use
		1665	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1666	when you rarely read from a file instead of from a socket, and want to
		1667	reuse the same code path.
		1668
		1669	=head3 The special problem of fork
		1670
		1671	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1672	useless behaviour. Libev fully supports fork, but needs to be told about
		1673	it in the child if you want to continue to use it in the child.
		1674
		1675	To support fork in your child processes, you have to call C<ev_loop_fork
		1676	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1677	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1678
		1679	=head3 The special problem of SIGPIPE
		1680
		1681	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1682	when writing to a pipe whose other end has been closed, your program gets
		1683	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1684	this is sensible behaviour, for daemons, this is usually undesirable.
		1685
		1686	So when you encounter spurious, unexplained daemon exits, make sure you
		1687	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1688	somewhere, as that would have given you a big clue).
		1689
		1690	=head3 The special problem of accept()ing when you can't
		1691
		1692	Many implementations of the POSIX C<accept> function (for example,
		1693	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1694	connection from the pending queue in all error cases.
		1695
		1696	For example, larger servers often run out of file descriptors (because
		1697	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1698	rejecting the connection, leading to libev signalling readiness on
		1699	the next iteration again (the connection still exists after all), and
		1700	typically causing the program to loop at 100% CPU usage.
		1701
		1702	Unfortunately, the set of errors that cause this issue differs between
		1703	operating systems, there is usually little the app can do to remedy the
		1704	situation, and no known thread-safe method of removing the connection to
		1705	cope with overload is known (to me).
		1706
		1707	One of the easiest ways to handle this situation is to just ignore it
		1708	- when the program encounters an overload, it will just loop until the
		1709	situation is over. While this is a form of busy waiting, no OS offers an
		1710	event-based way to handle this situation, so it's the best one can do.
		1711
		1712	A better way to handle the situation is to log any errors other than
		1713	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1714	messages, and continue as usual, which at least gives the user an idea of
		1715	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1716	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1717	usage.
		1718
		1719	If your program is single-threaded, then you could also keep a dummy file
		1720	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1721	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1722	close that fd, and create a new dummy fd. This will gracefully refuse
		1723	clients under typical overload conditions.
		1724
		1725	The last way to handle it is to simply log the error and C<exit>, as
		1726	is often done with C<malloc> failures, but this results in an easy
		1727	opportunity for a DoS attack.
		1728
		1729	=head3 Watcher-Specific Functions
640		1730
641	=over 4	1731	=over 4
642		1732
643	=item ev_io_init (ev_io *, callback, int fd, int events)	1733	=item ev_io_init (ev_io *, callback, int fd, int events)
644		1734
645	=item ev_io_set (ev_io *, int fd, int events)	1735	=item ev_io_set (ev_io *, int fd, int events)
646		1736
647	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1737	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
648	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1738	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
649	EV_WRITE> to receive the given events.	1739	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
650		1740
651	Please note that most of the more scalable backend mechanisms (for example	1741	=item int fd [read-only]
652	epoll and solaris ports) can result in spurious readyness notifications	1742
653	for file descriptors, so you practically need to use non-blocking I/O (and	1743	The file descriptor being watched.
654	treat callback invocation as hint only), or retest separately with a safe	1744
655	interface before doing I/O (XLib can do this), or force the use of either	1745	=item int events [read-only]
656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this	1746
657	problem. Also note that it is quite easy to have your callback invoked	1747	The events being watched.
658	when the readyness condition is no longer valid even when employing
659	typical ways of handling events, so its a good idea to use non-blocking
660	I/O unconditionally.
661		1748
662	=back	1749	=back
663		1750
		1751	=head3 Examples
		1752
664	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1753	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
665	readable, but only once. Since it is likely line-buffered, you could	1754	readable, but only once. Since it is likely line-buffered, you could
666	attempt to read a whole line in the callback:	1755	attempt to read a whole line in the callback.
667		1756
668	static void	1757	static void
669	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1758	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
670	{	1759	{
671	ev_io_stop (loop, w);	1760	ev_io_stop (loop, w);
672	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1761	.. read from stdin here (or from w->fd) and handle any I/O errors
673	}	1762	}
674		1763
675	...	1764	...
676	struct ev_loop *loop = ev_default_init (0);	1765	struct ev_loop *loop = ev_default_init (0);
677	struct ev_io stdin_readable;	1766	ev_io stdin_readable;
678	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1767	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
679	ev_io_start (loop, &stdin_readable);	1768	ev_io_start (loop, &stdin_readable);
680	ev_loop (loop, 0);	1769	ev_run (loop, 0);
681		1770
682		1771
683	=head2 C<ev_timer> - relative and optionally recurring timeouts	1772	=head2 C<ev_timer> - relative and optionally repeating timeouts
684		1773
685	Timer watchers are simple relative timers that generate an event after a	1774	Timer watchers are simple relative timers that generate an event after a
686	given time, and optionally repeating in regular intervals after that.	1775	given time, and optionally repeating in regular intervals after that.
687		1776
688	The timers are based on real time, that is, if you register an event that	1777	The timers are based on real time, that is, if you register an event that
689	times out after an hour and you reset your system clock to last years	1778	times out after an hour and you reset your system clock to January last
690	time, it will still time out after (roughly) and hour. "Roughly" because	1779	year, it will still time out after (roughly) one hour. "Roughly" because
691	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1780	detecting time jumps is hard, and some inaccuracies are unavoidable (the
692	monotonic clock option helps a lot here).	1781	monotonic clock option helps a lot here).
		1782
		1783	The callback is guaranteed to be invoked only I<after> its timeout has
		1784	passed (not I<at>, so on systems with very low-resolution clocks this
		1785	might introduce a small delay, see "the special problem of being too
		1786	early", below). If multiple timers become ready during the same loop
		1787	iteration then the ones with earlier time-out values are invoked before
		1788	ones of the same priority with later time-out values (but this is no
		1789	longer true when a callback calls C<ev_run> recursively).
		1790
		1791	=head3 Be smart about timeouts
		1792
		1793	Many real-world problems involve some kind of timeout, usually for error
		1794	recovery. A typical example is an HTTP request - if the other side hangs,
		1795	you want to raise some error after a while.
		1796
		1797	What follows are some ways to handle this problem, from obvious and
		1798	inefficient to smart and efficient.
		1799
		1800	In the following, a 60 second activity timeout is assumed - a timeout that
		1801	gets reset to 60 seconds each time there is activity (e.g. each time some
		1802	data or other life sign was received).
		1803
		1804	=over 4
		1805
		1806	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1807
		1808	This is the most obvious, but not the most simple way: In the beginning,
		1809	start the watcher:
		1810
		1811	ev_timer_init (timer, callback, 60., 0.);
		1812	ev_timer_start (loop, timer);
		1813
		1814	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1815	and start it again:
		1816
		1817	ev_timer_stop (loop, timer);
		1818	ev_timer_set (timer, 60., 0.);
		1819	ev_timer_start (loop, timer);
		1820
		1821	This is relatively simple to implement, but means that each time there is
		1822	some activity, libev will first have to remove the timer from its internal
		1823	data structure and then add it again. Libev tries to be fast, but it's
		1824	still not a constant-time operation.
		1825
		1826	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1827
		1828	This is the easiest way, and involves using C<ev_timer_again> instead of
		1829	C<ev_timer_start>.
		1830
		1831	To implement this, configure an C<ev_timer> with a C<repeat> value
		1832	of C<60> and then call C<ev_timer_again> at start and each time you
		1833	successfully read or write some data. If you go into an idle state where
		1834	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1835	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1836
		1837	That means you can ignore both the C<ev_timer_start> function and the
		1838	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1839	member and C<ev_timer_again>.
		1840
		1841	At start:
		1842
		1843	ev_init (timer, callback);
		1844	timer->repeat = 60.;
		1845	ev_timer_again (loop, timer);
		1846
		1847	Each time there is some activity:
		1848
		1849	ev_timer_again (loop, timer);
		1850
		1851	It is even possible to change the time-out on the fly, regardless of
		1852	whether the watcher is active or not:
		1853
		1854	timer->repeat = 30.;
		1855	ev_timer_again (loop, timer);
		1856
		1857	This is slightly more efficient then stopping/starting the timer each time
		1858	you want to modify its timeout value, as libev does not have to completely
		1859	remove and re-insert the timer from/into its internal data structure.
		1860
		1861	It is, however, even simpler than the "obvious" way to do it.
		1862
		1863	=item 3. Let the timer time out, but then re-arm it as required.
		1864
		1865	This method is more tricky, but usually most efficient: Most timeouts are
		1866	relatively long compared to the intervals between other activity - in
		1867	our example, within 60 seconds, there are usually many I/O events with
		1868	associated activity resets.
		1869
		1870	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1871	but remember the time of last activity, and check for a real timeout only
		1872	within the callback:
		1873
		1874	ev_tstamp timeout = 60.;
		1875	ev_tstamp last_activity; // time of last activity
		1876	ev_timer timer;
		1877
		1878	static void
		1879	callback (EV_P_ ev_timer *w, int revents)
		1880	{
		1881	// calculate when the timeout would happen
		1882	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1883
		1884	// if negative, it means we the timeout already occurred
		1885	if (after < 0.)
		1886	{
		1887	// timeout occurred, take action
		1888	}
		1889	else
		1890	{
		1891	// callback was invoked, but there was some recent
		1892	// activity. simply restart the timer to time out
		1893	// after "after" seconds, which is the earliest time
		1894	// the timeout can occur.
		1895	ev_timer_set (w, after, 0.);
		1896	ev_timer_start (EV_A_ w);
		1897	}
		1898	}
		1899
		1900	To summarise the callback: first calculate in how many seconds the
		1901	timeout will occur (by calculating the absolute time when it would occur,
		1902	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1903	(EV_A)> from that).
		1904
		1905	If this value is negative, then we are already past the timeout, i.e. we
		1906	timed out, and need to do whatever is needed in this case.
		1907
		1908	Otherwise, we now the earliest time at which the timeout would trigger,
		1909	and simply start the timer with this timeout value.
		1910
		1911	In other words, each time the callback is invoked it will check whether
		1912	the timeout occurred. If not, it will simply reschedule itself to check
		1913	again at the earliest time it could time out. Rinse. Repeat.
		1914
		1915	This scheme causes more callback invocations (about one every 60 seconds
		1916	minus half the average time between activity), but virtually no calls to
		1917	libev to change the timeout.
		1918
		1919	To start the machinery, simply initialise the watcher and set
		1920	C<last_activity> to the current time (meaning there was some activity just
		1921	now), then call the callback, which will "do the right thing" and start
		1922	the timer:
		1923
		1924	last_activity = ev_now (EV_A);
		1925	ev_init (&timer, callback);
		1926	callback (EV_A_ &timer, 0);
		1927
		1928	When there is some activity, simply store the current time in
		1929	C<last_activity>, no libev calls at all:
		1930
		1931	if (activity detected)
		1932	last_activity = ev_now (EV_A);
		1933
		1934	When your timeout value changes, then the timeout can be changed by simply
		1935	providing a new value, stopping the timer and calling the callback, which
		1936	will again do the right thing (for example, time out immediately :).
		1937
		1938	timeout = new_value;
		1939	ev_timer_stop (EV_A_ &timer);
		1940	callback (EV_A_ &timer, 0);
		1941
		1942	This technique is slightly more complex, but in most cases where the
		1943	time-out is unlikely to be triggered, much more efficient.
		1944
		1945	=item 4. Wee, just use a double-linked list for your timeouts.
		1946
		1947	If there is not one request, but many thousands (millions...), all
		1948	employing some kind of timeout with the same timeout value, then one can
		1949	do even better:
		1950
		1951	When starting the timeout, calculate the timeout value and put the timeout
		1952	at the I<end> of the list.
		1953
		1954	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1955	the list is expected to fire (for example, using the technique #3).
		1956
		1957	When there is some activity, remove the timer from the list, recalculate
		1958	the timeout, append it to the end of the list again, and make sure to
		1959	update the C<ev_timer> if it was taken from the beginning of the list.
		1960
		1961	This way, one can manage an unlimited number of timeouts in O(1) time for
		1962	starting, stopping and updating the timers, at the expense of a major
		1963	complication, and having to use a constant timeout. The constant timeout
		1964	ensures that the list stays sorted.
		1965
		1966	=back
		1967
		1968	So which method the best?
		1969
		1970	Method #2 is a simple no-brain-required solution that is adequate in most
		1971	situations. Method #3 requires a bit more thinking, but handles many cases
		1972	better, and isn't very complicated either. In most case, choosing either
		1973	one is fine, with #3 being better in typical situations.
		1974
		1975	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1976	rather complicated, but extremely efficient, something that really pays
		1977	off after the first million or so of active timers, i.e. it's usually
		1978	overkill :)
		1979
		1980	=head3 The special problem of being too early
		1981
		1982	If you ask a timer to call your callback after three seconds, then
		1983	you expect it to be invoked after three seconds - but of course, this
		1984	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1985	guaranteed to any precision by libev - imagine somebody suspending the
		1986	process with a STOP signal for a few hours for example.
		1987
		1988	So, libev tries to invoke your callback as soon as possible I<after> the
		1989	delay has occurred, but cannot guarantee this.
		1990
		1991	A less obvious failure mode is calling your callback too early: many event
		1992	loops compare timestamps with a "elapsed delay >= requested delay", but
		1993	this can cause your callback to be invoked much earlier than you would
		1994	expect.
		1995
		1996	To see why, imagine a system with a clock that only offers full second
		1997	resolution (think windows if you can't come up with a broken enough OS
		1998	yourself). If you schedule a one-second timer at the time 500.9, then the
		1999	event loop will schedule your timeout to elapse at a system time of 500
		2000	(500.9 truncated to the resolution) + 1, or 501.
		2001
		2002	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2003	501" and invoke the callback 0.1s after it was started, even though a
		2004	one-second delay was requested - this is being "too early", despite best
		2005	intentions.
		2006
		2007	This is the reason why libev will never invoke the callback if the elapsed
		2008	delay equals the requested delay, but only when the elapsed delay is
		2009	larger than the requested delay. In the example above, libev would only invoke
		2010	the callback at system time 502, or 1.1s after the timer was started.
		2011
		2012	So, while libev cannot guarantee that your callback will be invoked
		2013	exactly when requested, it I<can> and I<does> guarantee that the requested
		2014	delay has actually elapsed, or in other words, it always errs on the "too
		2015	late" side of things.
		2016
		2017	=head3 The special problem of time updates
		2018
		2019	Establishing the current time is a costly operation (it usually takes
		2020	at least one system call): EV therefore updates its idea of the current
		2021	time only before and after C<ev_run> collects new events, which causes a
		2022	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2023	lots of events in one iteration.
693		2024
694	The relative timeouts are calculated relative to the C<ev_now ()>	2025	The relative timeouts are calculated relative to the C<ev_now ()>
695	time. This is usually the right thing as this timestamp refers to the time	2026	time. This is usually the right thing as this timestamp refers to the time
696	of the event triggering whatever timeout you are modifying/starting. If	2027	of the event triggering whatever timeout you are modifying/starting. If
697	you suspect event processing to be delayed and you I<need> to base the timeout	2028	you suspect event processing to be delayed and you I<need> to base the
698	on the current time, use something like this to adjust for this:	2029	timeout on the current time, use something like this to adjust for this:
699		2030
700	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2031	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
701		2032
702	The callback is guarenteed to be invoked only when its timeout has passed,	2033	If the event loop is suspended for a long time, you can also force an
703	but if multiple timers become ready during the same loop iteration then	2034	update of the time returned by C<ev_now ()> by calling C<ev_now_update
704	order of execution is undefined.	2035	()>.
		2036
		2037	=head3 The special problem of unsynchronised clocks
		2038
		2039	Modern systems have a variety of clocks - libev itself uses the normal
		2040	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2041	jumps).
		2042
		2043	Neither of these clocks is synchronised with each other or any other clock
		2044	on the system, so C<ev_time ()> might return a considerably different time
		2045	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2046	a call to C<gettimeofday> might return a second count that is one higher
		2047	than a directly following call to C<time>.
		2048
		2049	The moral of this is to only compare libev-related timestamps with
		2050	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2051	a second or so.
		2052
		2053	One more problem arises due to this lack of synchronisation: if libev uses
		2054	the system monotonic clock and you compare timestamps from C<ev_time>
		2055	or C<ev_now> from when you started your timer and when your callback is
		2056	invoked, you will find that sometimes the callback is a bit "early".
		2057
		2058	This is because C<ev_timer>s work in real time, not wall clock time, so
		2059	libev makes sure your callback is not invoked before the delay happened,
		2060	I<measured according to the real time>, not the system clock.
		2061
		2062	If your timeouts are based on a physical timescale (e.g. "time out this
		2063	connection after 100 seconds") then this shouldn't bother you as it is
		2064	exactly the right behaviour.
		2065
		2066	If you want to compare wall clock/system timestamps to your timers, then
		2067	you need to use C<ev_periodic>s, as these are based on the wall clock
		2068	time, where your comparisons will always generate correct results.
		2069
		2070	=head3 The special problems of suspended animation
		2071
		2072	When you leave the server world it is quite customary to hit machines that
		2073	can suspend/hibernate - what happens to the clocks during such a suspend?
		2074
		2075	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2076	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2077	to run until the system is suspended, but they will not advance while the
		2078	system is suspended. That means, on resume, it will be as if the program
		2079	was frozen for a few seconds, but the suspend time will not be counted
		2080	towards C<ev_timer> when a monotonic clock source is used. The real time
		2081	clock advanced as expected, but if it is used as sole clocksource, then a
		2082	long suspend would be detected as a time jump by libev, and timers would
		2083	be adjusted accordingly.
		2084
		2085	I would not be surprised to see different behaviour in different between
		2086	operating systems, OS versions or even different hardware.
		2087
		2088	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2089	time jump in the monotonic clocks and the realtime clock. If the program
		2090	is suspended for a very long time, and monotonic clock sources are in use,
		2091	then you can expect C<ev_timer>s to expire as the full suspension time
		2092	will be counted towards the timers. When no monotonic clock source is in
		2093	use, then libev will again assume a timejump and adjust accordingly.
		2094
		2095	It might be beneficial for this latter case to call C<ev_suspend>
		2096	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2097	deterministic behaviour in this case (you can do nothing against
		2098	C<SIGSTOP>).
		2099
		2100	=head3 Watcher-Specific Functions and Data Members
705		2101
706	=over 4	2102	=over 4
707		2103
708	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2104	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
709		2105
710	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2106	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
711		2107
712	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2108	Configure the timer to trigger after C<after> seconds. If C<repeat>
713	C<0.>, then it will automatically be stopped. If it is positive, then the	2109	is C<0.>, then it will automatically be stopped once the timeout is
714	timer will automatically be configured to trigger again C<repeat> seconds	2110	reached. If it is positive, then the timer will automatically be
715	later, again, and again, until stopped manually.	2111	configured to trigger again C<repeat> seconds later, again, and again,
		2112	until stopped manually.
716		2113
717	The timer itself will do a best-effort at avoiding drift, that is, if you	2114	The timer itself will do a best-effort at avoiding drift, that is, if
718	configure a timer to trigger every 10 seconds, then it will trigger at	2115	you configure a timer to trigger every 10 seconds, then it will normally
719	exactly 10 second intervals. If, however, your program cannot keep up with	2116	trigger at exactly 10 second intervals. If, however, your program cannot
720	the timer (because it takes longer than those 10 seconds to do stuff) the	2117	keep up with the timer (because it takes longer than those 10 seconds to
721	timer will not fire more than once per event loop iteration.	2118	do stuff) the timer will not fire more than once per event loop iteration.
722		2119
723	=item ev_timer_again (loop)	2120	=item ev_timer_again (loop, ev_timer *)
724		2121
725	This will act as if the timer timed out and restart it again if it is	2122	This will act as if the timer timed out, and restarts it again if it is
726	repeating. The exact semantics are:	2123	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2124	timeout to the C<repeat> value and calling C<ev_timer_start>.
727		2125
		2126	The exact semantics are as in the following rules, all of which will be
		2127	applied to the watcher:
		2128
		2129	=over 4
		2130
		2131	=item If the timer is pending, the pending status is always cleared.
		2132
728	If the timer is started but nonrepeating, stop it.	2133	=item If the timer is started but non-repeating, stop it (as if it timed
		2134	out, without invoking it).
729		2135
730	If the timer is repeating, either start it if necessary (with the repeat	2136	=item If the timer is repeating, make the C<repeat> value the new timeout
731	value), or reset the running timer to the repeat value.	2137	and start the timer, if necessary.
732
733	This sounds a bit complicated, but here is a useful and typical
734	example: Imagine you have a tcp connection and you want a so-called idle
735	timeout, that is, you want to be called when there have been, say, 60
736	seconds of inactivity on the socket. The easiest way to do this is to
737	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each
738	time you successfully read or write some data. If you go into an idle
739	state where you do not expect data to travel on the socket, you can stop
740	the timer, and again will automatically restart it if need be.
741		2138
742	=back	2139	=back
743		2140
		2141	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
		2142	usage example.
		2143
		2144	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
		2145
		2146	Returns the remaining time until a timer fires. If the timer is active,
		2147	then this time is relative to the current event loop time, otherwise it's
		2148	the timeout value currently configured.
		2149
		2150	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2151	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2152	will return C<4>. When the timer expires and is restarted, it will return
		2153	roughly C<7> (likely slightly less as callback invocation takes some time,
		2154	too), and so on.
		2155
		2156	=item ev_tstamp repeat [read-write]
		2157
		2158	The current C<repeat> value. Will be used each time the watcher times out
		2159	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2160	which is also when any modifications are taken into account.
		2161
		2162	=back
		2163
		2164	=head3 Examples
		2165
744	Example: create a timer that fires after 60 seconds.	2166	Example: Create a timer that fires after 60 seconds.
745		2167
746	static void	2168	static void
747	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2169	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
748	{	2170	{
749	.. one minute over, w is actually stopped right here	2171	.. one minute over, w is actually stopped right here
750	}	2172	}
751		2173
752	struct ev_timer mytimer;	2174	ev_timer mytimer;
753	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2175	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
754	ev_timer_start (loop, &mytimer);	2176	ev_timer_start (loop, &mytimer);
755		2177
756	Example: create a timeout timer that times out after 10 seconds of	2178	Example: Create a timeout timer that times out after 10 seconds of
757	inactivity.	2179	inactivity.
758		2180
759	static void	2181	static void
760	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2182	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
761	{	2183	{
762	.. ten seconds without any activity	2184	.. ten seconds without any activity
763	}	2185	}
764		2186
765	struct ev_timer mytimer;	2187	ev_timer mytimer;
766	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2188	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
767	ev_timer_again (&mytimer); /* start timer */	2189	ev_timer_again (&mytimer); /* start timer */
768	ev_loop (loop, 0);	2190	ev_run (loop, 0);
769		2191
770	// and in some piece of code that gets executed on any "activity":	2192	// and in some piece of code that gets executed on any "activity":
771	// reset the timeout to start ticking again at 10 seconds	2193	// reset the timeout to start ticking again at 10 seconds
772	ev_timer_again (&mytimer);	2194	ev_timer_again (&mytimer);
773		2195
774		2196
775	=head2 C<ev_periodic> - to cron or not to cron	2197	=head2 C<ev_periodic> - to cron or not to cron?
776		2198
777	Periodic watchers are also timers of a kind, but they are very versatile	2199	Periodic watchers are also timers of a kind, but they are very versatile
778	(and unfortunately a bit complex).	2200	(and unfortunately a bit complex).
779		2201
780	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2202	Unlike C<ev_timer>, periodic watchers are not based on real time (or
781	but on wallclock time (absolute time). You can tell a periodic watcher	2203	relative time, the physical time that passes) but on wall clock time
782	to trigger "at" some specific point in time. For example, if you tell a	2204	(absolute time, the thing you can read on your calender or clock). The
783	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	2205	difference is that wall clock time can run faster or slower than real
784	+ 10.>) and then reset your system clock to the last year, then it will	2206	time, and time jumps are not uncommon (e.g. when you adjust your
785	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2207	wrist-watch).
786	roughly 10 seconds later and of course not if you reset your system time
787	again).
788		2208
789	They can also be used to implement vastly more complex timers, such as	2209	You can tell a periodic watcher to trigger after some specific point
		2210	in time: for example, if you tell a periodic watcher to trigger "in 10
		2211	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2212	not a delay) and then reset your system clock to January of the previous
		2213	year, then it will take a year or more to trigger the event (unlike an
		2214	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2215	it, as it uses a relative timeout).
		2216
		2217	C<ev_periodic> watchers can also be used to implement vastly more complex
790	triggering an event on eahc midnight, local time.	2218	timers, such as triggering an event on each "midnight, local time", or
		2219	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2220	those cannot react to time jumps.
791		2221
792	As with timers, the callback is guarenteed to be invoked only when the	2222	As with timers, the callback is guaranteed to be invoked only when the
793	time (C<at>) has been passed, but if multiple periodic timers become ready	2223	point in time where it is supposed to trigger has passed. If multiple
794	during the same loop iteration then order of execution is undefined.	2224	timers become ready during the same loop iteration then the ones with
		2225	earlier time-out values are invoked before ones with later time-out values
		2226	(but this is no longer true when a callback calls C<ev_run> recursively).
		2227
		2228	=head3 Watcher-Specific Functions and Data Members
795		2229
796	=over 4	2230	=over 4
797		2231
798	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2232	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
799		2233
800	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2234	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
801		2235
802	Lots of arguments, lets sort it out... There are basically three modes of	2236	Lots of arguments, let's sort it out... There are basically three modes of
803	operation, and we will explain them from simplest to complex:	2237	operation, and we will explain them from simplest to most complex:
804		2238
805	=over 4	2239	=over 4
806		2240
807	=item * absolute timer (interval = reschedule_cb = 0)	2241	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
808		2242
809	In this configuration the watcher triggers an event at the wallclock time	2243	In this configuration the watcher triggers an event after the wall clock
810	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2244	time C<offset> has passed. It will not repeat and will not adjust when a
811	that is, if it is to be run at January 1st 2011 then it will run when the	2245	time jump occurs, that is, if it is to be run at January 1st 2011 then it
812	system time reaches or surpasses this time.	2246	will be stopped and invoked when the system clock reaches or surpasses
		2247	this point in time.
813		2248
814	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2249	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
815		2250
816	In this mode the watcher will always be scheduled to time out at the next	2251	In this mode the watcher will always be scheduled to time out at the next
817	C<at + N * interval> time (for some integer N) and then repeat, regardless	2252	C<offset + N * interval> time (for some integer N, which can also be
818	of any time jumps.	2253	negative) and then repeat, regardless of any time jumps. The C<offset>
		2254	argument is merely an offset into the C<interval> periods.
819		2255
820	This can be used to create timers that do not drift with respect to system	2256	This can be used to create timers that do not drift with respect to the
821	time:	2257	system clock, for example, here is an C<ev_periodic> that triggers each
		2258	hour, on the hour (with respect to UTC):
822		2259
823	ev_periodic_set (&periodic, 0., 3600., 0);	2260	ev_periodic_set (&periodic, 0., 3600., 0);
824		2261
825	This doesn't mean there will always be 3600 seconds in between triggers,	2262	This doesn't mean there will always be 3600 seconds in between triggers,
826	but only that the the callback will be called when the system time shows a	2263	but only that the callback will be called when the system time shows a
827	full hour (UTC), or more correctly, when the system time is evenly divisible	2264	full hour (UTC), or more correctly, when the system time is evenly divisible
828	by 3600.	2265	by 3600.
829		2266
830	Another way to think about it (for the mathematically inclined) is that	2267	Another way to think about it (for the mathematically inclined) is that
831	C<ev_periodic> will try to run the callback in this mode at the next possible	2268	C<ev_periodic> will try to run the callback in this mode at the next possible
832	time where C<time = at (mod interval)>, regardless of any time jumps.	2269	time where C<time = offset (mod interval)>, regardless of any time jumps.
833		2270
		2271	The C<interval> I<MUST> be positive, and for numerical stability, the
		2272	interval value should be higher than C<1/8192> (which is around 100
		2273	microseconds) and C<offset> should be higher than C<0> and should have
		2274	at most a similar magnitude as the current time (say, within a factor of
		2275	ten). Typical values for offset are, in fact, C<0> or something between
		2276	C<0> and C<interval>, which is also the recommended range.
		2277
		2278	Note also that there is an upper limit to how often a timer can fire (CPU
		2279	speed for example), so if C<interval> is very small then timing stability
		2280	will of course deteriorate. Libev itself tries to be exact to be about one
		2281	millisecond (if the OS supports it and the machine is fast enough).
		2282
834	=item * manual reschedule mode (reschedule_cb = callback)	2283	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
835		2284
836	In this mode the values for C<interval> and C<at> are both being	2285	In this mode the values for C<interval> and C<offset> are both being
837	ignored. Instead, each time the periodic watcher gets scheduled, the	2286	ignored. Instead, each time the periodic watcher gets scheduled, the
838	reschedule callback will be called with the watcher as first, and the	2287	reschedule callback will be called with the watcher as first, and the
839	current time as second argument.	2288	current time as second argument.
840		2289
841	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2290	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
842	ever, or make any event loop modifications>. If you need to stop it,	2291	or make ANY other event loop modifications whatsoever, unless explicitly
843	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2292	allowed by documentation here>.
844	starting a prepare watcher).
845		2293
		2294	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2295	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2296	only event loop modification you are allowed to do).
		2297
846	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2298	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
847	ev_tstamp now)>, e.g.:	2299	*w, ev_tstamp now)>, e.g.:
848		2300
		2301	static ev_tstamp
849	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2302	my_rescheduler (ev_periodic *w, ev_tstamp now)
850	{	2303	{
851	return now + 60.;	2304	return now + 60.;
852	}	2305	}
853		2306
854	It must return the next time to trigger, based on the passed time value	2307	It must return the next time to trigger, based on the passed time value
855	(that is, the lowest time value larger than to the second argument). It	2308	(that is, the lowest time value larger than to the second argument). It
856	will usually be called just before the callback will be triggered, but	2309	will usually be called just before the callback will be triggered, but
857	might be called at other times, too.	2310	might be called at other times, too.
858		2311
859	NOTE: I<< This callback must always return a time that is later than the	2312	NOTE: I<< This callback must always return a time that is higher than or
860	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2313	equal to the passed C<now> value >>.
861		2314
862	This can be used to create very complex timers, such as a timer that	2315	This can be used to create very complex timers, such as a timer that
863	triggers on each midnight, local time. To do this, you would calculate the	2316	triggers on "next midnight, local time". To do this, you would calculate the
864	next midnight after C<now> and return the timestamp value for this. How	2317	next midnight after C<now> and return the timestamp value for this. How
865	you do this is, again, up to you (but it is not trivial, which is the main	2318	you do this is, again, up to you (but it is not trivial, which is the main
866	reason I omitted it as an example).	2319	reason I omitted it as an example).
867		2320
868	=back	2321	=back
…		…
872	Simply stops and restarts the periodic watcher again. This is only useful	2325	Simply stops and restarts the periodic watcher again. This is only useful
873	when you changed some parameters or the reschedule callback would return	2326	when you changed some parameters or the reschedule callback would return
874	a different time than the last time it was called (e.g. in a crond like	2327	a different time than the last time it was called (e.g. in a crond like
875	program when the crontabs have changed).	2328	program when the crontabs have changed).
876		2329
		2330	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2331
		2332	When active, returns the absolute time that the watcher is supposed
		2333	to trigger next. This is not the same as the C<offset> argument to
		2334	C<ev_periodic_set>, but indeed works even in interval and manual
		2335	rescheduling modes.
		2336
		2337	=item ev_tstamp offset [read-write]
		2338
		2339	When repeating, this contains the offset value, otherwise this is the
		2340	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2341	although libev might modify this value for better numerical stability).
		2342
		2343	Can be modified any time, but changes only take effect when the periodic
		2344	timer fires or C<ev_periodic_again> is being called.
		2345
		2346	=item ev_tstamp interval [read-write]
		2347
		2348	The current interval value. Can be modified any time, but changes only
		2349	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2350	called.
		2351
		2352	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2353
		2354	The current reschedule callback, or C<0>, if this functionality is
		2355	switched off. Can be changed any time, but changes only take effect when
		2356	the periodic timer fires or C<ev_periodic_again> is being called.
		2357
877	=back	2358	=back
878		2359
		2360	=head3 Examples
		2361
879	Example: call a callback every hour, or, more precisely, whenever the	2362	Example: Call a callback every hour, or, more precisely, whenever the
880	system clock is divisible by 3600. The callback invocation times have	2363	system time is divisible by 3600. The callback invocation times have
881	potentially a lot of jittering, but good long-term stability.	2364	potentially a lot of jitter, but good long-term stability.
882		2365
883	static void	2366	static void
884	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2367	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
885	{	2368	{
886	... its now a full hour (UTC, or TAI or whatever your clock follows)	2369	... its now a full hour (UTC, or TAI or whatever your clock follows)
887	}	2370	}
888		2371
889	struct ev_periodic hourly_tick;	2372	ev_periodic hourly_tick;
890	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2373	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
891	ev_periodic_start (loop, &hourly_tick);	2374	ev_periodic_start (loop, &hourly_tick);
892		2375
893	Example: the same as above, but use a reschedule callback to do it:	2376	Example: The same as above, but use a reschedule callback to do it:
894		2377
895	#include <math.h>	2378	#include <math.h>
896		2379
897	static ev_tstamp	2380	static ev_tstamp
898	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2381	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
899	{	2382	{
900	return fmod (now, 3600.) + 3600.;	2383	return now + (3600. - fmod (now, 3600.));
901	}	2384	}
902		2385
903	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2386	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
904		2387
905	Example: call a callback every hour, starting now:	2388	Example: Call a callback every hour, starting now:
906		2389
907	struct ev_periodic hourly_tick;	2390	ev_periodic hourly_tick;
908	ev_periodic_init (&hourly_tick, clock_cb,	2391	ev_periodic_init (&hourly_tick, clock_cb,
909	fmod (ev_now (loop), 3600.), 3600., 0);	2392	fmod (ev_now (loop), 3600.), 3600., 0);
910	ev_periodic_start (loop, &hourly_tick);	2393	ev_periodic_start (loop, &hourly_tick);
911		2394
912		2395
913	=head2 C<ev_signal> - signal me when a signal gets signalled	2396	=head2 C<ev_signal> - signal me when a signal gets signalled!
914		2397
915	Signal watchers will trigger an event when the process receives a specific	2398	Signal watchers will trigger an event when the process receives a specific
916	signal one or more times. Even though signals are very asynchronous, libev	2399	signal one or more times. Even though signals are very asynchronous, libev
917	will try it's best to deliver signals synchronously, i.e. as part of the	2400	will try its best to deliver signals synchronously, i.e. as part of the
918	normal event processing, like any other event.	2401	normal event processing, like any other event.
919		2402
		2403	If you want signals to be delivered truly asynchronously, just use
		2404	C<sigaction> as you would do without libev and forget about sharing
		2405	the signal. You can even use C<ev_async> from a signal handler to
		2406	synchronously wake up an event loop.
		2407
920	You can configure as many watchers as you like per signal. Only when the	2408	You can configure as many watchers as you like for the same signal, but
		2409	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2410	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2411	C<SIGINT> in both the default loop and another loop at the same time. At
		2412	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2413
921	first watcher gets started will libev actually register a signal watcher	2414	When the first watcher gets started will libev actually register something
922	with the kernel (thus it coexists with your own signal handlers as long	2415	with the kernel (thus it coexists with your own signal handlers as long as
923	as you don't register any with libev). Similarly, when the last signal	2416	you don't register any with libev for the same signal).
924	watcher for a signal is stopped libev will reset the signal handler to	2417
925	SIG_DFL (regardless of what it was set to before).	2418	If possible and supported, libev will install its handlers with
		2419	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2420	not be unduly interrupted. If you have a problem with system calls getting
		2421	interrupted by signals you can block all signals in an C<ev_check> watcher
		2422	and unblock them in an C<ev_prepare> watcher.
		2423
		2424	=head3 The special problem of inheritance over fork/execve/pthread_create
		2425
		2426	Both the signal mask (C<sigprocmask>) and the signal disposition
		2427	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2428	stopping it again), that is, libev might or might not block the signal,
		2429	and might or might not set or restore the installed signal handler (but
		2430	see C<EVFLAG_NOSIGMASK>).
		2431
		2432	While this does not matter for the signal disposition (libev never
		2433	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2434	C<execve>), this matters for the signal mask: many programs do not expect
		2435	certain signals to be blocked.
		2436
		2437	This means that before calling C<exec> (from the child) you should reset
		2438	the signal mask to whatever "default" you expect (all clear is a good
		2439	choice usually).
		2440
		2441	The simplest way to ensure that the signal mask is reset in the child is
		2442	to install a fork handler with C<pthread_atfork> that resets it. That will
		2443	catch fork calls done by libraries (such as the libc) as well.
		2444
		2445	In current versions of libev, the signal will not be blocked indefinitely
		2446	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2447	the window of opportunity for problems, it will not go away, as libev
		2448	I<has> to modify the signal mask, at least temporarily.
		2449
		2450	So I can't stress this enough: I<If you do not reset your signal mask when
		2451	you expect it to be empty, you have a race condition in your code>. This
		2452	is not a libev-specific thing, this is true for most event libraries.
		2453
		2454	=head3 The special problem of threads signal handling
		2455
		2456	POSIX threads has problematic signal handling semantics, specifically,
		2457	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2458	threads in a process block signals, which is hard to achieve.
		2459
		2460	When you want to use sigwait (or mix libev signal handling with your own
		2461	for the same signals), you can tackle this problem by globally blocking
		2462	all signals before creating any threads (or creating them with a fully set
		2463	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2464	loops. Then designate one thread as "signal receiver thread" which handles
		2465	these signals. You can pass on any signals that libev might be interested
		2466	in by calling C<ev_feed_signal>.
		2467
		2468	=head3 Watcher-Specific Functions and Data Members
926		2469
927	=over 4	2470	=over 4
928		2471
929	=item ev_signal_init (ev_signal *, callback, int signum)	2472	=item ev_signal_init (ev_signal *, callback, int signum)
930		2473
931	=item ev_signal_set (ev_signal *, int signum)	2474	=item ev_signal_set (ev_signal *, int signum)
932		2475
933	Configures the watcher to trigger on the given signal number (usually one	2476	Configures the watcher to trigger on the given signal number (usually one
934	of the C<SIGxxx> constants).	2477	of the C<SIGxxx> constants).
935		2478
		2479	=item int signum [read-only]
		2480
		2481	The signal the watcher watches out for.
		2482
936	=back	2483	=back
937		2484
		2485	=head3 Examples
938		2486
		2487	Example: Try to exit cleanly on SIGINT.
		2488
		2489	static void
		2490	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2491	{
		2492	ev_break (loop, EVBREAK_ALL);
		2493	}
		2494
		2495	ev_signal signal_watcher;
		2496	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2497	ev_signal_start (loop, &signal_watcher);
		2498
		2499
939	=head2 C<ev_child> - wait for pid status changes	2500	=head2 C<ev_child> - watch out for process status changes
940		2501
941	Child watchers trigger when your process receives a SIGCHLD in response to	2502	Child watchers trigger when your process receives a SIGCHLD in response to
942	some child status changes (most typically when a child of yours dies).	2503	some child status changes (most typically when a child of yours dies or
		2504	exits). It is permissible to install a child watcher I<after> the child
		2505	has been forked (which implies it might have already exited), as long
		2506	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2507	forking and then immediately registering a watcher for the child is fine,
		2508	but forking and registering a watcher a few event loop iterations later or
		2509	in the next callback invocation is not.
		2510
		2511	Only the default event loop is capable of handling signals, and therefore
		2512	you can only register child watchers in the default event loop.
		2513
		2514	Due to some design glitches inside libev, child watchers will always be
		2515	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2516	libev)
		2517
		2518	=head3 Process Interaction
		2519
		2520	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2521	initialised. This is necessary to guarantee proper behaviour even if the
		2522	first child watcher is started after the child exits. The occurrence
		2523	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2524	synchronously as part of the event loop processing. Libev always reaps all
		2525	children, even ones not watched.
		2526
		2527	=head3 Overriding the Built-In Processing
		2528
		2529	Libev offers no special support for overriding the built-in child
		2530	processing, but if your application collides with libev's default child
		2531	handler, you can override it easily by installing your own handler for
		2532	C<SIGCHLD> after initialising the default loop, and making sure the
		2533	default loop never gets destroyed. You are encouraged, however, to use an
		2534	event-based approach to child reaping and thus use libev's support for
		2535	that, so other libev users can use C<ev_child> watchers freely.
		2536
		2537	=head3 Stopping the Child Watcher
		2538
		2539	Currently, the child watcher never gets stopped, even when the
		2540	child terminates, so normally one needs to stop the watcher in the
		2541	callback. Future versions of libev might stop the watcher automatically
		2542	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2543	problem).
		2544
		2545	=head3 Watcher-Specific Functions and Data Members
943		2546
944	=over 4	2547	=over 4
945		2548
946	=item ev_child_init (ev_child *, callback, int pid)	2549	=item ev_child_init (ev_child *, callback, int pid, int trace)
947		2550
948	=item ev_child_set (ev_child *, int pid)	2551	=item ev_child_set (ev_child *, int pid, int trace)
949		2552
950	Configures the watcher to wait for status changes of process C<pid> (or	2553	Configures the watcher to wait for status changes of process C<pid> (or
951	I<any> process if C<pid> is specified as C<0>). The callback can look	2554	I<any> process if C<pid> is specified as C<0>). The callback can look
952	at the C<rstatus> member of the C<ev_child> watcher structure to see	2555	at the C<rstatus> member of the C<ev_child> watcher structure to see
953	the status word (use the macros from C<sys/wait.h> and see your systems	2556	the status word (use the macros from C<sys/wait.h> and see your systems
954	C<waitpid> documentation). The C<rpid> member contains the pid of the	2557	C<waitpid> documentation). The C<rpid> member contains the pid of the
955	process causing the status change.	2558	process causing the status change. C<trace> must be either C<0> (only
		2559	activate the watcher when the process terminates) or C<1> (additionally
		2560	activate the watcher when the process is stopped or continued).
		2561
		2562	=item int pid [read-only]
		2563
		2564	The process id this watcher watches out for, or C<0>, meaning any process id.
		2565
		2566	=item int rpid [read-write]
		2567
		2568	The process id that detected a status change.
		2569
		2570	=item int rstatus [read-write]
		2571
		2572	The process exit/trace status caused by C<rpid> (see your systems
		2573	C<waitpid> and C<sys/wait.h> documentation for details).
956		2574
957	=back	2575	=back
958		2576
959	Example: try to exit cleanly on SIGINT and SIGTERM.	2577	=head3 Examples
960		2578
		2579	Example: C<fork()> a new process and install a child handler to wait for
		2580	its completion.
		2581
		2582	ev_child cw;
		2583
961	static void	2584	static void
962	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2585	child_cb (EV_P_ ev_child *w, int revents)
963	{	2586	{
964	ev_unloop (loop, EVUNLOOP_ALL);	2587	ev_child_stop (EV_A_ w);
		2588	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
965	}	2589	}
966		2590
967	struct ev_signal signal_watcher;	2591	pid_t pid = fork ();
968	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
969	ev_signal_start (loop, &sigint_cb);
970		2592
		2593	if (pid < 0)
		2594	// error
		2595	else if (pid == 0)
		2596	{
		2597	// the forked child executes here
		2598	exit (1);
		2599	}
		2600	else
		2601	{
		2602	ev_child_init (&cw, child_cb, pid, 0);
		2603	ev_child_start (EV_DEFAULT_ &cw);
		2604	}
971		2605
		2606
		2607	=head2 C<ev_stat> - did the file attributes just change?
		2608
		2609	This watches a file system path for attribute changes. That is, it calls
		2610	C<stat> on that path in regular intervals (or when the OS says it changed)
		2611	and sees if it changed compared to the last time, invoking the callback if
		2612	it did.
		2613
		2614	The path does not need to exist: changing from "path exists" to "path does
		2615	not exist" is a status change like any other. The condition "path does not
		2616	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2617	C<st_nlink> field being zero (which is otherwise always forced to be at
		2618	least one) and all the other fields of the stat buffer having unspecified
		2619	contents.
		2620
		2621	The path I<must not> end in a slash or contain special components such as
		2622	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2623	your working directory changes, then the behaviour is undefined.
		2624
		2625	Since there is no portable change notification interface available, the
		2626	portable implementation simply calls C<stat(2)> regularly on the path
		2627	to see if it changed somehow. You can specify a recommended polling
		2628	interval for this case. If you specify a polling interval of C<0> (highly
		2629	recommended!) then a I<suitable, unspecified default> value will be used
		2630	(which you can expect to be around five seconds, although this might
		2631	change dynamically). Libev will also impose a minimum interval which is
		2632	currently around C<0.1>, but that's usually overkill.
		2633
		2634	This watcher type is not meant for massive numbers of stat watchers,
		2635	as even with OS-supported change notifications, this can be
		2636	resource-intensive.
		2637
		2638	At the time of this writing, the only OS-specific interface implemented
		2639	is the Linux inotify interface (implementing kqueue support is left as an
		2640	exercise for the reader. Note, however, that the author sees no way of
		2641	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2642
		2643	=head3 ABI Issues (Largefile Support)
		2644
		2645	Libev by default (unless the user overrides this) uses the default
		2646	compilation environment, which means that on systems with large file
		2647	support disabled by default, you get the 32 bit version of the stat
		2648	structure. When using the library from programs that change the ABI to
		2649	use 64 bit file offsets the programs will fail. In that case you have to
		2650	compile libev with the same flags to get binary compatibility. This is
		2651	obviously the case with any flags that change the ABI, but the problem is
		2652	most noticeably displayed with ev_stat and large file support.
		2653
		2654	The solution for this is to lobby your distribution maker to make large
		2655	file interfaces available by default (as e.g. FreeBSD does) and not
		2656	optional. Libev cannot simply switch on large file support because it has
		2657	to exchange stat structures with application programs compiled using the
		2658	default compilation environment.
		2659
		2660	=head3 Inotify and Kqueue
		2661
		2662	When C<inotify (7)> support has been compiled into libev and present at
		2663	runtime, it will be used to speed up change detection where possible. The
		2664	inotify descriptor will be created lazily when the first C<ev_stat>
		2665	watcher is being started.
		2666
		2667	Inotify presence does not change the semantics of C<ev_stat> watchers
		2668	except that changes might be detected earlier, and in some cases, to avoid
		2669	making regular C<stat> calls. Even in the presence of inotify support
		2670	there are many cases where libev has to resort to regular C<stat> polling,
		2671	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2672	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2673	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2674	xfs are fully working) libev usually gets away without polling.
		2675
		2676	There is no support for kqueue, as apparently it cannot be used to
		2677	implement this functionality, due to the requirement of having a file
		2678	descriptor open on the object at all times, and detecting renames, unlinks
		2679	etc. is difficult.
		2680
		2681	=head3 C<stat ()> is a synchronous operation
		2682
		2683	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2684	the process. The exception are C<ev_stat> watchers - those call C<stat
		2685	()>, which is a synchronous operation.
		2686
		2687	For local paths, this usually doesn't matter: unless the system is very
		2688	busy or the intervals between stat's are large, a stat call will be fast,
		2689	as the path data is usually in memory already (except when starting the
		2690	watcher).
		2691
		2692	For networked file systems, calling C<stat ()> can block an indefinite
		2693	time due to network issues, and even under good conditions, a stat call
		2694	often takes multiple milliseconds.
		2695
		2696	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2697	paths, although this is fully supported by libev.
		2698
		2699	=head3 The special problem of stat time resolution
		2700
		2701	The C<stat ()> system call only supports full-second resolution portably,
		2702	and even on systems where the resolution is higher, most file systems
		2703	still only support whole seconds.
		2704
		2705	That means that, if the time is the only thing that changes, you can
		2706	easily miss updates: on the first update, C<ev_stat> detects a change and
		2707	calls your callback, which does something. When there is another update
		2708	within the same second, C<ev_stat> will be unable to detect unless the
		2709	stat data does change in other ways (e.g. file size).
		2710
		2711	The solution to this is to delay acting on a change for slightly more
		2712	than a second (or till slightly after the next full second boundary), using
		2713	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2714	ev_timer_again (loop, w)>).
		2715
		2716	The C<.02> offset is added to work around small timing inconsistencies
		2717	of some operating systems (where the second counter of the current time
		2718	might be be delayed. One such system is the Linux kernel, where a call to
		2719	C<gettimeofday> might return a timestamp with a full second later than
		2720	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2721	update file times then there will be a small window where the kernel uses
		2722	the previous second to update file times but libev might already execute
		2723	the timer callback).
		2724
		2725	=head3 Watcher-Specific Functions and Data Members
		2726
		2727	=over 4
		2728
		2729	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2730
		2731	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2732
		2733	Configures the watcher to wait for status changes of the given
		2734	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2735	be detected and should normally be specified as C<0> to let libev choose
		2736	a suitable value. The memory pointed to by C<path> must point to the same
		2737	path for as long as the watcher is active.
		2738
		2739	The callback will receive an C<EV_STAT> event when a change was detected,
		2740	relative to the attributes at the time the watcher was started (or the
		2741	last change was detected).
		2742
		2743	=item ev_stat_stat (loop, ev_stat *)
		2744
		2745	Updates the stat buffer immediately with new values. If you change the
		2746	watched path in your callback, you could call this function to avoid
		2747	detecting this change (while introducing a race condition if you are not
		2748	the only one changing the path). Can also be useful simply to find out the
		2749	new values.
		2750
		2751	=item ev_statdata attr [read-only]
		2752
		2753	The most-recently detected attributes of the file. Although the type is
		2754	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2755	suitable for your system, but you can only rely on the POSIX-standardised
		2756	members to be present. If the C<st_nlink> member is C<0>, then there was
		2757	some error while C<stat>ing the file.
		2758
		2759	=item ev_statdata prev [read-only]
		2760
		2761	The previous attributes of the file. The callback gets invoked whenever
		2762	C<prev> != C<attr>, or, more precisely, one or more of these members
		2763	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2764	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2765
		2766	=item ev_tstamp interval [read-only]
		2767
		2768	The specified interval.
		2769
		2770	=item const char *path [read-only]
		2771
		2772	The file system path that is being watched.
		2773
		2774	=back
		2775
		2776	=head3 Examples
		2777
		2778	Example: Watch C</etc/passwd> for attribute changes.
		2779
		2780	static void
		2781	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2782	{
		2783	/* /etc/passwd changed in some way */
		2784	if (w->attr.st_nlink)
		2785	{
		2786	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2787	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2788	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2789	}
		2790	else
		2791	/* you shalt not abuse printf for puts */
		2792	puts ("wow, /etc/passwd is not there, expect problems. "
		2793	"if this is windows, they already arrived\n");
		2794	}
		2795
		2796	...
		2797	ev_stat passwd;
		2798
		2799	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2800	ev_stat_start (loop, &passwd);
		2801
		2802	Example: Like above, but additionally use a one-second delay so we do not
		2803	miss updates (however, frequent updates will delay processing, too, so
		2804	one might do the work both on C<ev_stat> callback invocation I<and> on
		2805	C<ev_timer> callback invocation).
		2806
		2807	static ev_stat passwd;
		2808	static ev_timer timer;
		2809
		2810	static void
		2811	timer_cb (EV_P_ ev_timer *w, int revents)
		2812	{
		2813	ev_timer_stop (EV_A_ w);
		2814
		2815	/* now it's one second after the most recent passwd change */
		2816	}
		2817
		2818	static void
		2819	stat_cb (EV_P_ ev_stat *w, int revents)
		2820	{
		2821	/* reset the one-second timer */
		2822	ev_timer_again (EV_A_ &timer);
		2823	}
		2824
		2825	...
		2826	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2827	ev_stat_start (loop, &passwd);
		2828	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2829
		2830
972	=head2 C<ev_idle> - when you've got nothing better to do	2831	=head2 C<ev_idle> - when you've got nothing better to do...
973		2832
974	Idle watchers trigger events when there are no other events are pending	2833	Idle watchers trigger events when no other events of the same or higher
975	(prepare, check and other idle watchers do not count). That is, as long	2834	priority are pending (prepare, check and other idle watchers do not count
976	as your process is busy handling sockets or timeouts (or even signals,	2835	as receiving "events").
977	imagine) it will not be triggered. But when your process is idle all idle	2836
978	watchers are being called again and again, once per event loop iteration -	2837	That is, as long as your process is busy handling sockets or timeouts
		2838	(or even signals, imagine) of the same or higher priority it will not be
		2839	triggered. But when your process is idle (or only lower-priority watchers
		2840	are pending), the idle watchers are being called once per event loop
979	until stopped, that is, or your process receives more events and becomes	2841	iteration - until stopped, that is, or your process receives more events
980	busy.	2842	and becomes busy again with higher priority stuff.
981		2843
982	The most noteworthy effect is that as long as any idle watchers are	2844	The most noteworthy effect is that as long as any idle watchers are
983	active, the process will not block when waiting for new events.	2845	active, the process will not block when waiting for new events.
984		2846
985	Apart from keeping your process non-blocking (which is a useful	2847	Apart from keeping your process non-blocking (which is a useful
986	effect on its own sometimes), idle watchers are a good place to do	2848	effect on its own sometimes), idle watchers are a good place to do
987	"pseudo-background processing", or delay processing stuff to after the	2849	"pseudo-background processing", or delay processing stuff to after the
988	event loop has handled all outstanding events.	2850	event loop has handled all outstanding events.
989		2851
		2852	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2853
		2854	As long as there is at least one active idle watcher, libev will never
		2855	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2856	For this to work, the idle watcher doesn't need to be invoked at all - the
		2857	lowest priority will do.
		2858
		2859	This mode of operation can be useful together with an C<ev_check> watcher,
		2860	to do something on each event loop iteration - for example to balance load
		2861	between different connections.
		2862
		2863	See L<Abusing an C<ev_check> watcher for its side-effect> for a longer
		2864	example.
		2865
		2866	=head3 Watcher-Specific Functions and Data Members
		2867
990	=over 4	2868	=over 4
991		2869
992	=item ev_idle_init (ev_signal *, callback)	2870	=item ev_idle_init (ev_idle *, callback)
993		2871
994	Initialises and configures the idle watcher - it has no parameters of any	2872	Initialises and configures the idle watcher - it has no parameters of any
995	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2873	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
996	believe me.	2874	believe me.
997		2875
998	=back	2876	=back
999		2877
		2878	=head3 Examples
		2879
1000	Example: dynamically allocate an C<ev_idle>, start it, and in the	2880	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1001	callback, free it. Alos, use no error checking, as usual.	2881	callback, free it. Also, use no error checking, as usual.
1002		2882
1003	static void	2883	static void
1004	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2884	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1005	{	2885	{
		2886	// stop the watcher
		2887	ev_idle_stop (loop, w);
		2888
		2889	// now we can free it
1006	free (w);	2890	free (w);
		2891
1007	// now do something you wanted to do when the program has	2892	// now do something you wanted to do when the program has
1008	// no longer asnything immediate to do.	2893	// no longer anything immediate to do.
1009	}	2894	}
1010		2895
1011	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2896	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1012	ev_idle_init (idle_watcher, idle_cb);	2897	ev_idle_init (idle_watcher, idle_cb);
1013	ev_idle_start (loop, idle_cb);	2898	ev_idle_start (loop, idle_watcher);
1014		2899
1015		2900
1016	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2901	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1017		2902
1018	Prepare and check watchers are usually (but not always) used in tandem:	2903	Prepare and check watchers are often (but not always) used in pairs:
1019	prepare watchers get invoked before the process blocks and check watchers	2904	prepare watchers get invoked before the process blocks and check watchers
1020	afterwards.	2905	afterwards.
1021		2906
		2907	You I<must not> call C<ev_run> or similar functions that enter
		2908	the current event loop from either C<ev_prepare> or C<ev_check>
		2909	watchers. Other loops than the current one are fine, however. The
		2910	rationale behind this is that you do not need to check for recursion in
		2911	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2912	C<ev_check> so if you have one watcher of each kind they will always be
		2913	called in pairs bracketing the blocking call.
		2914
1022	Their main purpose is to integrate other event mechanisms into libev and	2915	Their main purpose is to integrate other event mechanisms into libev and
1023	their use is somewhat advanced. This could be used, for example, to track	2916	their use is somewhat advanced. They could be used, for example, to track
1024	variable changes, implement your own watchers, integrate net-snmp or a	2917	variable changes, implement your own watchers, integrate net-snmp or a
1025	coroutine library and lots more.	2918	coroutine library and lots more. They are also occasionally useful if
		2919	you cache some data and want to flush it before blocking (for example,
		2920	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2921	watcher).
1026		2922
1027	This is done by examining in each prepare call which file descriptors need	2923	This is done by examining in each prepare call which file descriptors
1028	to be watched by the other library, registering C<ev_io> watchers for	2924	need to be watched by the other library, registering C<ev_io> watchers
1029	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2925	for them and starting an C<ev_timer> watcher for any timeouts (many
1030	provide just this functionality). Then, in the check watcher you check for	2926	libraries provide exactly this functionality). Then, in the check watcher,
1031	any events that occured (by checking the pending status of all watchers	2927	you check for any events that occurred (by checking the pending status
1032	and stopping them) and call back into the library. The I/O and timer	2928	of all watchers and stopping them) and call back into the library. The
1033	callbacks will never actually be called (but must be valid nevertheless,	2929	I/O and timer callbacks will never actually be called (but must be valid
1034	because you never know, you know?).	2930	nevertheless, because you never know, you know?).
1035		2931
1036	As another example, the Perl Coro module uses these hooks to integrate	2932	As another example, the Perl Coro module uses these hooks to integrate
1037	coroutines into libev programs, by yielding to other active coroutines	2933	coroutines into libev programs, by yielding to other active coroutines
1038	during each prepare and only letting the process block if no coroutines	2934	during each prepare and only letting the process block if no coroutines
1039	are ready to run (it's actually more complicated: it only runs coroutines	2935	are ready to run (it's actually more complicated: it only runs coroutines
1040	with priority higher than or equal to the event loop and one coroutine	2936	with priority higher than or equal to the event loop and one coroutine
1041	of lower priority, but only once, using idle watchers to keep the event	2937	of lower priority, but only once, using idle watchers to keep the event
1042	loop from blocking if lower-priority coroutines are active, thus mapping	2938	loop from blocking if lower-priority coroutines are active, thus mapping
1043	low-priority coroutines to idle/background tasks).	2939	low-priority coroutines to idle/background tasks).
1044		2940
		2941	When used for this purpose, it is recommended to give C<ev_check> watchers
		2942	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		2943	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2944	watchers).
		2945
		2946	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2947	activate ("feed") events into libev. While libev fully supports this, they
		2948	might get executed before other C<ev_check> watchers did their job. As
		2949	C<ev_check> watchers are often used to embed other (non-libev) event
		2950	loops those other event loops might be in an unusable state until their
		2951	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2952	others).
		2953
		2954	=head3 Abusing an C<ev_check> watcher for its side-effect
		2955
		2956	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2957	useful because they are called once per event loop iteration. For
		2958	example, if you want to handle a large number of connections fairly, you
		2959	normally only do a bit of work for each active connection, and if there
		2960	is more work to do, you wait for the next event loop iteration, so other
		2961	connections have a chance of making progress.
		2962
		2963	Using an C<ev_check> watcher is almost enough: it will be called on the
		2964	next event loop iteration. However, that isn't as soon as possible -
		2965	without external events, your C<ev_check> watcher will not be invoked.
		2966
		2967
		2968	This is where C<ev_idle> watchers come in handy - all you need is a
		2969	single global idle watcher that is active as long as you have one active
		2970	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2971	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2972	invoked. Neither watcher alone can do that.
		2973
		2974	=head3 Watcher-Specific Functions and Data Members
		2975
1045	=over 4	2976	=over 4
1046		2977
1047	=item ev_prepare_init (ev_prepare *, callback)	2978	=item ev_prepare_init (ev_prepare *, callback)
1048		2979
1049	=item ev_check_init (ev_check *, callback)	2980	=item ev_check_init (ev_check *, callback)
1050		2981
1051	Initialises and configures the prepare or check watcher - they have no	2982	Initialises and configures the prepare or check watcher - they have no
1052	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2983	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1053	macros, but using them is utterly, utterly and completely pointless.	2984	macros, but using them is utterly, utterly, utterly and completely
		2985	pointless.
1054		2986
1055	=back	2987	=back
1056		2988
1057	Example: *TODO*.	2989	=head3 Examples
1058		2990
		2991	There are a number of principal ways to embed other event loops or modules
		2992	into libev. Here are some ideas on how to include libadns into libev
		2993	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2994	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2995	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2996	Glib event loop).
1059		2997
		2998	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2999	and in a check watcher, destroy them and call into libadns. What follows
		3000	is pseudo-code only of course. This requires you to either use a low
		3001	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		3002	the callbacks for the IO/timeout watchers might not have been called yet.
		3003
		3004	static ev_io iow [nfd];
		3005	static ev_timer tw;
		3006
		3007	static void
		3008	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		3009	{
		3010	}
		3011
		3012	// create io watchers for each fd and a timer before blocking
		3013	static void
		3014	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		3015	{
		3016	int timeout = 3600000;
		3017	struct pollfd fds [nfd];
		3018	// actual code will need to loop here and realloc etc.
		3019	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		3020
		3021	/* the callback is illegal, but won't be called as we stop during check */
		3022	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		3023	ev_timer_start (loop, &tw);
		3024
		3025	// create one ev_io per pollfd
		3026	for (int i = 0; i < nfd; ++i)
		3027	{
		3028	ev_io_init (iow + i, io_cb, fds [i].fd,
		3029	((fds [i].events & POLLIN ? EV_READ : 0)
		3030	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		3031
		3032	fds [i].revents = 0;
		3033	ev_io_start (loop, iow + i);
		3034	}
		3035	}
		3036
		3037	// stop all watchers after blocking
		3038	static void
		3039	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		3040	{
		3041	ev_timer_stop (loop, &tw);
		3042
		3043	for (int i = 0; i < nfd; ++i)
		3044	{
		3045	// set the relevant poll flags
		3046	// could also call adns_processreadable etc. here
		3047	struct pollfd *fd = fds + i;
		3048	int revents = ev_clear_pending (iow + i);
		3049	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		3050	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		3051
		3052	// now stop the watcher
		3053	ev_io_stop (loop, iow + i);
		3054	}
		3055
		3056	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		3057	}
		3058
		3059	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		3060	in the prepare watcher and would dispose of the check watcher.
		3061
		3062	Method 3: If the module to be embedded supports explicit event
		3063	notification (libadns does), you can also make use of the actual watcher
		3064	callbacks, and only destroy/create the watchers in the prepare watcher.
		3065
		3066	static void
		3067	timer_cb (EV_P_ ev_timer *w, int revents)
		3068	{
		3069	adns_state ads = (adns_state)w->data;
		3070	update_now (EV_A);
		3071
		3072	adns_processtimeouts (ads, &tv_now);
		3073	}
		3074
		3075	static void
		3076	io_cb (EV_P_ ev_io *w, int revents)
		3077	{
		3078	adns_state ads = (adns_state)w->data;
		3079	update_now (EV_A);
		3080
		3081	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		3082	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		3083	}
		3084
		3085	// do not ever call adns_afterpoll
		3086
		3087	Method 4: Do not use a prepare or check watcher because the module you
		3088	want to embed is not flexible enough to support it. Instead, you can
		3089	override their poll function. The drawback with this solution is that the
		3090	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		3091	this approach, effectively embedding EV as a client into the horrible
		3092	libglib event loop.
		3093
		3094	static gint
		3095	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		3096	{
		3097	int got_events = 0;
		3098
		3099	for (n = 0; n < nfds; ++n)
		3100	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		3101
		3102	if (timeout >= 0)
		3103	// create/start timer
		3104
		3105	// poll
		3106	ev_run (EV_A_ 0);
		3107
		3108	// stop timer again
		3109	if (timeout >= 0)
		3110	ev_timer_stop (EV_A_ &to);
		3111
		3112	// stop io watchers again - their callbacks should have set
		3113	for (n = 0; n < nfds; ++n)
		3114	ev_io_stop (EV_A_ iow [n]);
		3115
		3116	return got_events;
		3117	}
		3118
		3119
1060	=head2 C<ev_embed> - when one backend isn't enough	3120	=head2 C<ev_embed> - when one backend isn't enough...
1061		3121
1062	This is a rather advanced watcher type that lets you embed one event loop	3122	This is a rather advanced watcher type that lets you embed one event loop
1063	into another.	3123	into another (currently only C<ev_io> events are supported in the embedded
		3124	loop, other types of watchers might be handled in a delayed or incorrect
		3125	fashion and must not be used).
1064		3126
1065	There are primarily two reasons you would want that: work around bugs and	3127	There are primarily two reasons you would want that: work around bugs and
1066	prioritise I/O.	3128	prioritise I/O.
1067		3129
1068	As an example for a bug workaround, the kqueue backend might only support	3130	As an example for a bug workaround, the kqueue backend might only support
1069	sockets on some platform, so it is unusable as generic backend, but you	3131	sockets on some platform, so it is unusable as generic backend, but you
1070	still want to make use of it because you have many sockets and it scales	3132	still want to make use of it because you have many sockets and it scales
1071	so nicely. In this case, you would create a kqueue-based loop and embed it	3133	so nicely. In this case, you would create a kqueue-based loop and embed
1072	into your default loop (which might use e.g. poll). Overall operation will	3134	it into your default loop (which might use e.g. poll). Overall operation
1073	be a bit slower because first libev has to poll and then call kevent, but	3135	will be a bit slower because first libev has to call C<poll> and then
1074	at least you can use both at what they are best.	3136	C<kevent>, but at least you can use both mechanisms for what they are
		3137	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1075		3138
1076	As for prioritising I/O: rarely you have the case where some fds have	3139	As for prioritising I/O: under rare circumstances you have the case where
1077	to be watched and handled very quickly (with low latency), and even	3140	some fds have to be watched and handled very quickly (with low latency),
1078	priorities and idle watchers might have too much overhead. In this case	3141	and even priorities and idle watchers might have too much overhead. In
1079	you would put all the high priority stuff in one loop and all the rest in	3142	this case you would put all the high priority stuff in one loop and all
1080	a second one, and embed the second one in the first.	3143	the rest in a second one, and embed the second one in the first.
1081		3144
1082	As long as the watcher is started it will automatically handle events. The	3145	As long as the watcher is active, the callback will be invoked every
1083	callback will be invoked whenever some events have been handled. You can	3146	time there might be events pending in the embedded loop. The callback
1084	set the callback to C<0> to avoid having to specify one if you are not	3147	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1085	interested in that.	3148	sweep and invoke their callbacks (the callback doesn't need to invoke the
		3149	C<ev_embed_sweep> function directly, it could also start an idle watcher
		3150	to give the embedded loop strictly lower priority for example).
1086		3151
1087	Also, there have not currently been made special provisions for forking:	3152	You can also set the callback to C<0>, in which case the embed watcher
1088	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3153	will automatically execute the embedded loop sweep whenever necessary.
1089	but you will also have to stop and restart any C<ev_embed> watchers
1090	yourself.
1091		3154
		3155	Fork detection will be handled transparently while the C<ev_embed> watcher
		3156	is active, i.e., the embedded loop will automatically be forked when the
		3157	embedding loop forks. In other cases, the user is responsible for calling
		3158	C<ev_loop_fork> on the embedded loop.
		3159
1092	Unfortunately, not all backends are embeddable, only the ones returned by	3160	Unfortunately, not all backends are embeddable: only the ones returned by
1093	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3161	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1094	portable one.	3162	portable one.
1095		3163
1096	So when you want to use this feature you will always have to be prepared	3164	So when you want to use this feature you will always have to be prepared
1097	that you cannot get an embeddable loop. The recommended way to get around	3165	that you cannot get an embeddable loop. The recommended way to get around
1098	this is to have a separate variables for your embeddable loop, try to	3166	this is to have a separate variables for your embeddable loop, try to
1099	create it, and if that fails, use the normal loop for everything:	3167	create it, and if that fails, use the normal loop for everything.
1100		3168
1101	struct ev_loop *loop_hi = ev_default_init (0);	3169	=head3 C<ev_embed> and fork
1102	struct ev_loop *loop_lo = 0;
1103	struct ev_embed embed;
1104
1105	// see if there is a chance of getting one that works
1106	// (remember that a flags value of 0 means autodetection)
1107	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1108	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1109	: 0;
1110		3170
1111	// if we got one, then embed it, otherwise default to loop_hi	3171	While the C<ev_embed> watcher is running, forks in the embedding loop will
1112	if (loop_lo)	3172	automatically be applied to the embedded loop as well, so no special
1113	{	3173	fork handling is required in that case. When the watcher is not running,
1114	ev_embed_init (&embed, 0, loop_lo);	3174	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1115	ev_embed_start (loop_hi, &embed);	3175	as applicable.
1116	}	3176
1117	else	3177	=head3 Watcher-Specific Functions and Data Members
1118	loop_lo = loop_hi;
1119		3178
1120	=over 4	3179	=over 4
1121		3180
1122	=item ev_embed_init (ev_embed *, callback, struct ev_loop *loop)	3181	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1123		3182
1124	=item ev_embed_set (ev_embed *, callback, struct ev_loop *loop)	3183	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
1125		3184
1126	Configures the watcher to embed the given loop, which must be embeddable.	3185	Configures the watcher to embed the given loop, which must be
		3186	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		3187	invoked automatically, otherwise it is the responsibility of the callback
		3188	to invoke it (it will continue to be called until the sweep has been done,
		3189	if you do not want that, you need to temporarily stop the embed watcher).
		3190
		3191	=item ev_embed_sweep (loop, ev_embed *)
		3192
		3193	Make a single, non-blocking sweep over the embedded loop. This works
		3194	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
		3195	appropriate way for embedded loops.
		3196
		3197	=item struct ev_loop *other [read-only]
		3198
		3199	The embedded event loop.
1127		3200
1128	=back	3201	=back
1129		3202
		3203	=head3 Examples
		3204
		3205	Example: Try to get an embeddable event loop and embed it into the default
		3206	event loop. If that is not possible, use the default loop. The default
		3207	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3208	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3209	used).
		3210
		3211	struct ev_loop *loop_hi = ev_default_init (0);
		3212	struct ev_loop *loop_lo = 0;
		3213	ev_embed embed;
		3214
		3215	// see if there is a chance of getting one that works
		3216	// (remember that a flags value of 0 means autodetection)
		3217	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3218	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3219	: 0;
		3220
		3221	// if we got one, then embed it, otherwise default to loop_hi
		3222	if (loop_lo)
		3223	{
		3224	ev_embed_init (&embed, 0, loop_lo);
		3225	ev_embed_start (loop_hi, &embed);
		3226	}
		3227	else
		3228	loop_lo = loop_hi;
		3229
		3230	Example: Check if kqueue is available but not recommended and create
		3231	a kqueue backend for use with sockets (which usually work with any
		3232	kqueue implementation). Store the kqueue/socket-only event loop in
		3233	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3234
		3235	struct ev_loop *loop = ev_default_init (0);
		3236	struct ev_loop *loop_socket = 0;
		3237	ev_embed embed;
		3238
		3239	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3240	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3241	{
		3242	ev_embed_init (&embed, 0, loop_socket);
		3243	ev_embed_start (loop, &embed);
		3244	}
		3245
		3246	if (!loop_socket)
		3247	loop_socket = loop;
		3248
		3249	// now use loop_socket for all sockets, and loop for everything else
		3250
		3251
		3252	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3253
		3254	Fork watchers are called when a C<fork ()> was detected (usually because
		3255	whoever is a good citizen cared to tell libev about it by calling
		3256	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		3257	event loop blocks next and before C<ev_check> watchers are being called,
		3258	and only in the child after the fork. If whoever good citizen calling
		3259	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		3260	handlers will be invoked, too, of course.
		3261
		3262	=head3 The special problem of life after fork - how is it possible?
		3263
		3264	Most uses of C<fork()> consist of forking, then some simple calls to set
		3265	up/change the process environment, followed by a call to C<exec()>. This
		3266	sequence should be handled by libev without any problems.
		3267
		3268	This changes when the application actually wants to do event handling
		3269	in the child, or both parent in child, in effect "continuing" after the
		3270	fork.
		3271
		3272	The default mode of operation (for libev, with application help to detect
		3273	forks) is to duplicate all the state in the child, as would be expected
		3274	when I<either> the parent I<or> the child process continues.
		3275
		3276	When both processes want to continue using libev, then this is usually the
		3277	wrong result. In that case, usually one process (typically the parent) is
		3278	supposed to continue with all watchers in place as before, while the other
		3279	process typically wants to start fresh, i.e. without any active watchers.
		3280
		3281	The cleanest and most efficient way to achieve that with libev is to
		3282	simply create a new event loop, which of course will be "empty", and
		3283	use that for new watchers. This has the advantage of not touching more
		3284	memory than necessary, and thus avoiding the copy-on-write, and the
		3285	disadvantage of having to use multiple event loops (which do not support
		3286	signal watchers).
		3287
		3288	When this is not possible, or you want to use the default loop for
		3289	other reasons, then in the process that wants to start "fresh", call
		3290	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3291	Destroying the default loop will "orphan" (not stop) all registered
		3292	watchers, so you have to be careful not to execute code that modifies
		3293	those watchers. Note also that in that case, you have to re-register any
		3294	signal watchers.
		3295
		3296	=head3 Watcher-Specific Functions and Data Members
		3297
		3298	=over 4
		3299
		3300	=item ev_fork_init (ev_fork *, callback)
		3301
		3302	Initialises and configures the fork watcher - it has no parameters of any
		3303	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3304	really.
		3305
		3306	=back
		3307
		3308
		3309	=head2 C<ev_cleanup> - even the best things end
		3310
		3311	Cleanup watchers are called just before the event loop is being destroyed
		3312	by a call to C<ev_loop_destroy>.
		3313
		3314	While there is no guarantee that the event loop gets destroyed, cleanup
		3315	watchers provide a convenient method to install cleanup hooks for your
		3316	program, worker threads and so on - you just to make sure to destroy the
		3317	loop when you want them to be invoked.
		3318
		3319	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3320	all other watchers, they do not keep a reference to the event loop (which
		3321	makes a lot of sense if you think about it). Like all other watchers, you
		3322	can call libev functions in the callback, except C<ev_cleanup_start>.
		3323
		3324	=head3 Watcher-Specific Functions and Data Members
		3325
		3326	=over 4
		3327
		3328	=item ev_cleanup_init (ev_cleanup *, callback)
		3329
		3330	Initialises and configures the cleanup watcher - it has no parameters of
		3331	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3332	pointless, I assure you.
		3333
		3334	=back
		3335
		3336	Example: Register an atexit handler to destroy the default loop, so any
		3337	cleanup functions are called.
		3338
		3339	static void
		3340	program_exits (void)
		3341	{
		3342	ev_loop_destroy (EV_DEFAULT_UC);
		3343	}
		3344
		3345	...
		3346	atexit (program_exits);
		3347
		3348
		3349	=head2 C<ev_async> - how to wake up an event loop
		3350
		3351	In general, you cannot use an C<ev_loop> from multiple threads or other
		3352	asynchronous sources such as signal handlers (as opposed to multiple event
		3353	loops - those are of course safe to use in different threads).
		3354
		3355	Sometimes, however, you need to wake up an event loop you do not control,
		3356	for example because it belongs to another thread. This is what C<ev_async>
		3357	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3358	it by calling C<ev_async_send>, which is thread- and signal safe.
		3359
		3360	This functionality is very similar to C<ev_signal> watchers, as signals,
		3361	too, are asynchronous in nature, and signals, too, will be compressed
		3362	(i.e. the number of callback invocations may be less than the number of
		3363	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3364	of "global async watchers" by using a watcher on an otherwise unused
		3365	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3366	even without knowing which loop owns the signal.
		3367
		3368	=head3 Queueing
		3369
		3370	C<ev_async> does not support queueing of data in any way. The reason
		3371	is that the author does not know of a simple (or any) algorithm for a
		3372	multiple-writer-single-reader queue that works in all cases and doesn't
		3373	need elaborate support such as pthreads or unportable memory access
		3374	semantics.
		3375
		3376	That means that if you want to queue data, you have to provide your own
		3377	queue. But at least I can tell you how to implement locking around your
		3378	queue:
		3379
		3380	=over 4
		3381
		3382	=item queueing from a signal handler context
		3383
		3384	To implement race-free queueing, you simply add to the queue in the signal
		3385	handler but you block the signal handler in the watcher callback. Here is
		3386	an example that does that for some fictitious SIGUSR1 handler:
		3387
		3388	static ev_async mysig;
		3389
		3390	static void
		3391	sigusr1_handler (void)
		3392	{
		3393	sometype data;
		3394
		3395	// no locking etc.
		3396	queue_put (data);
		3397	ev_async_send (EV_DEFAULT_ &mysig);
		3398	}
		3399
		3400	static void
		3401	mysig_cb (EV_P_ ev_async *w, int revents)
		3402	{
		3403	sometype data;
		3404	sigset_t block, prev;
		3405
		3406	sigemptyset (&block);
		3407	sigaddset (&block, SIGUSR1);
		3408	sigprocmask (SIG_BLOCK, &block, &prev);
		3409
		3410	while (queue_get (&data))
		3411	process (data);
		3412
		3413	if (sigismember (&prev, SIGUSR1)
		3414	sigprocmask (SIG_UNBLOCK, &block, 0);
		3415	}
		3416
		3417	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3418	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3419	either...).
		3420
		3421	=item queueing from a thread context
		3422
		3423	The strategy for threads is different, as you cannot (easily) block
		3424	threads but you can easily preempt them, so to queue safely you need to
		3425	employ a traditional mutex lock, such as in this pthread example:
		3426
		3427	static ev_async mysig;
		3428	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3429
		3430	static void
		3431	otherthread (void)
		3432	{
		3433	// only need to lock the actual queueing operation
		3434	pthread_mutex_lock (&mymutex);
		3435	queue_put (data);
		3436	pthread_mutex_unlock (&mymutex);
		3437
		3438	ev_async_send (EV_DEFAULT_ &mysig);
		3439	}
		3440
		3441	static void
		3442	mysig_cb (EV_P_ ev_async *w, int revents)
		3443	{
		3444	pthread_mutex_lock (&mymutex);
		3445
		3446	while (queue_get (&data))
		3447	process (data);
		3448
		3449	pthread_mutex_unlock (&mymutex);
		3450	}
		3451
		3452	=back
		3453
		3454
		3455	=head3 Watcher-Specific Functions and Data Members
		3456
		3457	=over 4
		3458
		3459	=item ev_async_init (ev_async *, callback)
		3460
		3461	Initialises and configures the async watcher - it has no parameters of any
		3462	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3463	trust me.
		3464
		3465	=item ev_async_send (loop, ev_async *)
		3466
		3467	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3468	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3469	returns.
		3470
		3471	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3472	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3473	embedding section below on what exactly this means).
		3474
		3475	Note that, as with other watchers in libev, multiple events might get
		3476	compressed into a single callback invocation (another way to look at
		3477	this is that C<ev_async> watchers are level-triggered: they are set on
		3478	C<ev_async_send>, reset when the event loop detects that).
		3479
		3480	This call incurs the overhead of at most one extra system call per event
		3481	loop iteration, if the event loop is blocked, and no syscall at all if
		3482	the event loop (or your program) is processing events. That means that
		3483	repeated calls are basically free (there is no need to avoid calls for
		3484	performance reasons) and that the overhead becomes smaller (typically
		3485	zero) under load.
		3486
		3487	=item bool = ev_async_pending (ev_async *)
		3488
		3489	Returns a non-zero value when C<ev_async_send> has been called on the
		3490	watcher but the event has not yet been processed (or even noted) by the
		3491	event loop.
		3492
		3493	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3494	the loop iterates next and checks for the watcher to have become active,
		3495	it will reset the flag again. C<ev_async_pending> can be used to very
		3496	quickly check whether invoking the loop might be a good idea.
		3497
		3498	Not that this does I<not> check whether the watcher itself is pending,
		3499	only whether it has been requested to make this watcher pending: there
		3500	is a time window between the event loop checking and resetting the async
		3501	notification, and the callback being invoked.
		3502
		3503	=back
		3504
1130		3505
1131	=head1 OTHER FUNCTIONS	3506	=head1 OTHER FUNCTIONS
1132		3507
1133	There are some other functions of possible interest. Described. Here. Now.	3508	There are some other functions of possible interest. Described. Here. Now.
1134		3509
1135	=over 4	3510	=over 4
1136		3511
1137	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3512	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1138		3513
1139	This function combines a simple timer and an I/O watcher, calls your	3514	This function combines a simple timer and an I/O watcher, calls your
1140	callback on whichever event happens first and automatically stop both	3515	callback on whichever event happens first and automatically stops both
1141	watchers. This is useful if you want to wait for a single event on an fd	3516	watchers. This is useful if you want to wait for a single event on an fd
1142	or timeout without having to allocate/configure/start/stop/free one or	3517	or timeout without having to allocate/configure/start/stop/free one or
1143	more watchers yourself.	3518	more watchers yourself.
1144		3519
1145	If C<fd> is less than 0, then no I/O watcher will be started and events	3520	If C<fd> is less than 0, then no I/O watcher will be started and the
1146	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3521	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1147	C<events> set will be craeted and started.	3522	the given C<fd> and C<events> set will be created and started.
1148		3523
1149	If C<timeout> is less than 0, then no timeout watcher will be	3524	If C<timeout> is less than 0, then no timeout watcher will be
1150	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3525	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1151	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3526	repeat = 0) will be started. C<0> is a valid timeout.
1152	dubious value.
1153		3527
1154	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3528	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1155	passed an C<revents> set like normal event callbacks (a combination of	3529	passed an C<revents> set like normal event callbacks (a combination of
1156	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3530	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1157	value passed to C<ev_once>:	3531	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3532	a timeout and an io event at the same time - you probably should give io
		3533	events precedence.
1158		3534
		3535	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3536
1159	static void stdin_ready (int revents, void *arg)	3537	static void stdin_ready (int revents, void *arg)
		3538	{
		3539	if (revents & EV_READ)
		3540	/* stdin might have data for us, joy! */;
		3541	else if (revents & EV_TIMER)
		3542	/* doh, nothing entered */;
		3543	}
		3544
		3545	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3546
		3547	=item ev_feed_fd_event (loop, int fd, int revents)
		3548
		3549	Feed an event on the given fd, as if a file descriptor backend detected
		3550	the given events.
		3551
		3552	=item ev_feed_signal_event (loop, int signum)
		3553
		3554	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3555	which is async-safe.
		3556
		3557	=back
		3558
		3559
		3560	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3561
		3562	This section explains some common idioms that are not immediately
		3563	obvious. Note that examples are sprinkled over the whole manual, and this
		3564	section only contains stuff that wouldn't fit anywhere else.
		3565
		3566	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3567
		3568	Each watcher has, by default, a C<void *data> member that you can read
		3569	or modify at any time: libev will completely ignore it. This can be used
		3570	to associate arbitrary data with your watcher. If you need more data and
		3571	don't want to allocate memory separately and store a pointer to it in that
		3572	data member, you can also "subclass" the watcher type and provide your own
		3573	data:
		3574
		3575	struct my_io
		3576	{
		3577	ev_io io;
		3578	int otherfd;
		3579	void *somedata;
		3580	struct whatever *mostinteresting;
		3581	};
		3582
		3583	...
		3584	struct my_io w;
		3585	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3586
		3587	And since your callback will be called with a pointer to the watcher, you
		3588	can cast it back to your own type:
		3589
		3590	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3591	{
		3592	struct my_io *w = (struct my_io *)w_;
		3593	...
		3594	}
		3595
		3596	More interesting and less C-conformant ways of casting your callback
		3597	function type instead have been omitted.
		3598
		3599	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3600
		3601	Another common scenario is to use some data structure with multiple
		3602	embedded watchers, in effect creating your own watcher that combines
		3603	multiple libev event sources into one "super-watcher":
		3604
		3605	struct my_biggy
		3606	{
		3607	int some_data;
		3608	ev_timer t1;
		3609	ev_timer t2;
		3610	}
		3611
		3612	In this case getting the pointer to C<my_biggy> is a bit more
		3613	complicated: Either you store the address of your C<my_biggy> struct in
		3614	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3615	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3616	real programmers):
		3617
		3618	#include <stddef.h>
		3619
		3620	static void
		3621	t1_cb (EV_P_ ev_timer *w, int revents)
		3622	{
		3623	struct my_biggy big = (struct my_biggy *)
		3624	(((char *)w) - offsetof (struct my_biggy, t1));
		3625	}
		3626
		3627	static void
		3628	t2_cb (EV_P_ ev_timer *w, int revents)
		3629	{
		3630	struct my_biggy big = (struct my_biggy *)
		3631	(((char *)w) - offsetof (struct my_biggy, t2));
		3632	}
		3633
		3634	=head2 AVOIDING FINISHING BEFORE RETURNING
		3635
		3636	Often you have structures like this in event-based programs:
		3637
		3638	callback ()
1160	{	3639	{
1161	if (revents & EV_TIMEOUT)	3640	free (request);
1162	/* doh, nothing entered */;
1163	else if (revents & EV_READ)
1164	/* stdin might have data for us, joy! */;
1165	}	3641	}
1166		3642
1167	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3643	request = start_new_request (..., callback);
1168		3644
1169	=item ev_feed_event (loop, watcher, int events)	3645	The intent is to start some "lengthy" operation. The C<request> could be
		3646	used to cancel the operation, or do other things with it.
1170		3647
1171	Feeds the given event set into the event loop, as if the specified event	3648	It's not uncommon to have code paths in C<start_new_request> that
1172	had happened for the specified watcher (which must be a pointer to an	3649	immediately invoke the callback, for example, to report errors. Or you add
1173	initialised but not necessarily started event watcher).	3650	some caching layer that finds that it can skip the lengthy aspects of the
		3651	operation and simply invoke the callback with the result.
1174		3652
1175	=item ev_feed_fd_event (loop, int fd, int revents)	3653	The problem here is that this will happen I<before> C<start_new_request>
		3654	has returned, so C<request> is not set.
1176		3655
1177	Feed an event on the given fd, as if a file descriptor backend detected	3656	Even if you pass the request by some safer means to the callback, you
1178	the given events it.	3657	might want to do something to the request after starting it, such as
		3658	canceling it, which probably isn't working so well when the callback has
		3659	already been invoked.
1179		3660
1180	=item ev_feed_signal_event (loop, int signum)	3661	A common way around all these issues is to make sure that
		3662	C<start_new_request> I<always> returns before the callback is invoked. If
		3663	C<start_new_request> immediately knows the result, it can artificially
		3664	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3665	for example, or more sneakily, by reusing an existing (stopped) watcher
		3666	and pushing it into the pending queue:
1181		3667
1182	Feed an event as if the given signal occured (loop must be the default loop!).	3668	ev_set_cb (watcher, callback);
		3669	ev_feed_event (EV_A_ watcher, 0);
1183		3670
1184	=back	3671	This way, C<start_new_request> can safely return before the callback is
		3672	invoked, while not delaying callback invocation too much.
		3673
		3674	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3675
		3676	Often (especially in GUI toolkits) there are places where you have
		3677	I<modal> interaction, which is most easily implemented by recursively
		3678	invoking C<ev_run>.
		3679
		3680	This brings the problem of exiting - a callback might want to finish the
		3681	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3682	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3683	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3684	other combination: In these cases, C<ev_break> will not work alone.
		3685
		3686	The solution is to maintain "break this loop" variable for each C<ev_run>
		3687	invocation, and use a loop around C<ev_run> until the condition is
		3688	triggered, using C<EVRUN_ONCE>:
		3689
		3690	// main loop
		3691	int exit_main_loop = 0;
		3692
		3693	while (!exit_main_loop)
		3694	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3695
		3696	// in a modal watcher
		3697	int exit_nested_loop = 0;
		3698
		3699	while (!exit_nested_loop)
		3700	ev_run (EV_A_ EVRUN_ONCE);
		3701
		3702	To exit from any of these loops, just set the corresponding exit variable:
		3703
		3704	// exit modal loop
		3705	exit_nested_loop = 1;
		3706
		3707	// exit main program, after modal loop is finished
		3708	exit_main_loop = 1;
		3709
		3710	// exit both
		3711	exit_main_loop = exit_nested_loop = 1;
		3712
		3713	=head2 THREAD LOCKING EXAMPLE
		3714
		3715	Here is a fictitious example of how to run an event loop in a different
		3716	thread from where callbacks are being invoked and watchers are
		3717	created/added/removed.
		3718
		3719	For a real-world example, see the C<EV::Loop::Async> perl module,
		3720	which uses exactly this technique (which is suited for many high-level
		3721	languages).
		3722
		3723	The example uses a pthread mutex to protect the loop data, a condition
		3724	variable to wait for callback invocations, an async watcher to notify the
		3725	event loop thread and an unspecified mechanism to wake up the main thread.
		3726
		3727	First, you need to associate some data with the event loop:
		3728
		3729	typedef struct {
		3730	mutex_t lock; /* global loop lock */
		3731	ev_async async_w;
		3732	thread_t tid;
		3733	cond_t invoke_cv;
		3734	} userdata;
		3735
		3736	void prepare_loop (EV_P)
		3737	{
		3738	// for simplicity, we use a static userdata struct.
		3739	static userdata u;
		3740
		3741	ev_async_init (&u->async_w, async_cb);
		3742	ev_async_start (EV_A_ &u->async_w);
		3743
		3744	pthread_mutex_init (&u->lock, 0);
		3745	pthread_cond_init (&u->invoke_cv, 0);
		3746
		3747	// now associate this with the loop
		3748	ev_set_userdata (EV_A_ u);
		3749	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3750	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3751
		3752	// then create the thread running ev_run
		3753	pthread_create (&u->tid, 0, l_run, EV_A);
		3754	}
		3755
		3756	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3757	solely to wake up the event loop so it takes notice of any new watchers
		3758	that might have been added:
		3759
		3760	static void
		3761	async_cb (EV_P_ ev_async *w, int revents)
		3762	{
		3763	// just used for the side effects
		3764	}
		3765
		3766	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3767	protecting the loop data, respectively.
		3768
		3769	static void
		3770	l_release (EV_P)
		3771	{
		3772	userdata *u = ev_userdata (EV_A);
		3773	pthread_mutex_unlock (&u->lock);
		3774	}
		3775
		3776	static void
		3777	l_acquire (EV_P)
		3778	{
		3779	userdata *u = ev_userdata (EV_A);
		3780	pthread_mutex_lock (&u->lock);
		3781	}
		3782
		3783	The event loop thread first acquires the mutex, and then jumps straight
		3784	into C<ev_run>:
		3785
		3786	void *
		3787	l_run (void *thr_arg)
		3788	{
		3789	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3790
		3791	l_acquire (EV_A);
		3792	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3793	ev_run (EV_A_ 0);
		3794	l_release (EV_A);
		3795
		3796	return 0;
		3797	}
		3798
		3799	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3800	signal the main thread via some unspecified mechanism (signals? pipe
		3801	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3802	have been called (in a while loop because a) spurious wakeups are possible
		3803	and b) skipping inter-thread-communication when there are no pending
		3804	watchers is very beneficial):
		3805
		3806	static void
		3807	l_invoke (EV_P)
		3808	{
		3809	userdata *u = ev_userdata (EV_A);
		3810
		3811	while (ev_pending_count (EV_A))
		3812	{
		3813	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3814	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3815	}
		3816	}
		3817
		3818	Now, whenever the main thread gets told to invoke pending watchers, it
		3819	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3820	thread to continue:
		3821
		3822	static void
		3823	real_invoke_pending (EV_P)
		3824	{
		3825	userdata *u = ev_userdata (EV_A);
		3826
		3827	pthread_mutex_lock (&u->lock);
		3828	ev_invoke_pending (EV_A);
		3829	pthread_cond_signal (&u->invoke_cv);
		3830	pthread_mutex_unlock (&u->lock);
		3831	}
		3832
		3833	Whenever you want to start/stop a watcher or do other modifications to an
		3834	event loop, you will now have to lock:
		3835
		3836	ev_timer timeout_watcher;
		3837	userdata *u = ev_userdata (EV_A);
		3838
		3839	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3840
		3841	pthread_mutex_lock (&u->lock);
		3842	ev_timer_start (EV_A_ &timeout_watcher);
		3843	ev_async_send (EV_A_ &u->async_w);
		3844	pthread_mutex_unlock (&u->lock);
		3845
		3846	Note that sending the C<ev_async> watcher is required because otherwise
		3847	an event loop currently blocking in the kernel will have no knowledge
		3848	about the newly added timer. By waking up the loop it will pick up any new
		3849	watchers in the next event loop iteration.
		3850
		3851	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3852
		3853	While the overhead of a callback that e.g. schedules a thread is small, it
		3854	is still an overhead. If you embed libev, and your main usage is with some
		3855	kind of threads or coroutines, you might want to customise libev so that
		3856	doesn't need callbacks anymore.
		3857
		3858	Imagine you have coroutines that you can switch to using a function
		3859	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3860	and that due to some magic, the currently active coroutine is stored in a
		3861	global called C<current_coro>. Then you can build your own "wait for libev
		3862	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3863	the differing C<;> conventions):
		3864
		3865	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3866	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3867
		3868	That means instead of having a C callback function, you store the
		3869	coroutine to switch to in each watcher, and instead of having libev call
		3870	your callback, you instead have it switch to that coroutine.
		3871
		3872	A coroutine might now wait for an event with a function called
		3873	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3874	matter when, or whether the watcher is active or not when this function is
		3875	called):
		3876
		3877	void
		3878	wait_for_event (ev_watcher *w)
		3879	{
		3880	ev_cb_set (w) = current_coro;
		3881	switch_to (libev_coro);
		3882	}
		3883
		3884	That basically suspends the coroutine inside C<wait_for_event> and
		3885	continues the libev coroutine, which, when appropriate, switches back to
		3886	this or any other coroutine.
		3887
		3888	You can do similar tricks if you have, say, threads with an event queue -
		3889	instead of storing a coroutine, you store the queue object and instead of
		3890	switching to a coroutine, you push the watcher onto the queue and notify
		3891	any waiters.
		3892
		3893	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3894	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3895
		3896	// my_ev.h
		3897	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3898	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3899	#include "../libev/ev.h"
		3900
		3901	// my_ev.c
		3902	#define EV_H "my_ev.h"
		3903	#include "../libev/ev.c"
		3904
		3905	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3906	F<my_ev.c> into your project. When properly specifying include paths, you
		3907	can even use F<ev.h> as header file name directly.
1185		3908
1186		3909
1187	=head1 LIBEVENT EMULATION	3910	=head1 LIBEVENT EMULATION
1188		3911
1189	Libev offers a compatibility emulation layer for libevent. It cannot	3912	Libev offers a compatibility emulation layer for libevent. It cannot
1190	emulate the internals of libevent, so here are some usage hints:	3913	emulate the internals of libevent, so here are some usage hints:
1191		3914
1192	=over 4	3915	=over 4
		3916
		3917	=item * Only the libevent-1.4.1-beta API is being emulated.
		3918
		3919	This was the newest libevent version available when libev was implemented,
		3920	and is still mostly unchanged in 2010.
1193		3921
1194	=item * Use it by including <event.h>, as usual.	3922	=item * Use it by including <event.h>, as usual.
1195		3923
1196	=item * The following members are fully supported: ev_base, ev_callback,	3924	=item * The following members are fully supported: ev_base, ev_callback,
1197	ev_arg, ev_fd, ev_res, ev_events.	3925	ev_arg, ev_fd, ev_res, ev_events.
…		…
1202		3930
1203	=item * Priorities are not currently supported. Initialising priorities	3931	=item * Priorities are not currently supported. Initialising priorities
1204	will fail and all watchers will have the same priority, even though there	3932	will fail and all watchers will have the same priority, even though there
1205	is an ev_pri field.	3933	is an ev_pri field.
1206		3934
		3935	=item * In libevent, the last base created gets the signals, in libev, the
		3936	base that registered the signal gets the signals.
		3937
1207	=item * Other members are not supported.	3938	=item * Other members are not supported.
1208		3939
1209	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3940	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1210	to use the libev header file and library.	3941	to use the libev header file and library.
1211		3942
1212	=back	3943	=back
1213		3944
1214	=head1 C++ SUPPORT	3945	=head1 C++ SUPPORT
1215		3946
1216	TBD.	3947	=head2 C API
		3948
		3949	The normal C API should work fine when used from C++: both ev.h and the
		3950	libev sources can be compiled as C++. Therefore, code that uses the C API
		3951	will work fine.
		3952
		3953	Proper exception specifications might have to be added to callbacks passed
		3954	to libev: exceptions may be thrown only from watcher callbacks, all
		3955	other callbacks (allocator, syserr, loop acquire/release and periodioc
		3956	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3957	()> specification. If you have code that needs to be compiled as both C
		3958	and C++ you can use the C<EV_THROW> macro for this:
		3959
		3960	static void
		3961	fatal_error (const char *msg) EV_THROW
		3962	{
		3963	perror (msg);
		3964	abort ();
		3965	}
		3966
		3967	...
		3968	ev_set_syserr_cb (fatal_error);
		3969
		3970	The only API functions that can currently throw exceptions are C<ev_run>,
		3971	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3972	because it runs cleanup watchers).
		3973
		3974	Throwing exceptions in watcher callbacks is only supported if libev itself
		3975	is compiled with a C++ compiler or your C and C++ environments allow
		3976	throwing exceptions through C libraries (most do).
		3977
		3978	=head2 C++ API
		3979
		3980	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3981	you to use some convenience methods to start/stop watchers and also change
		3982	the callback model to a model using method callbacks on objects.
		3983
		3984	To use it,
		3985
		3986	#include <ev++.h>
		3987
		3988	This automatically includes F<ev.h> and puts all of its definitions (many
		3989	of them macros) into the global namespace. All C++ specific things are
		3990	put into the C<ev> namespace. It should support all the same embedding
		3991	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3992
		3993	Care has been taken to keep the overhead low. The only data member the C++
		3994	classes add (compared to plain C-style watchers) is the event loop pointer
		3995	that the watcher is associated with (or no additional members at all if
		3996	you disable C<EV_MULTIPLICITY> when embedding libev).
		3997
		3998	Currently, functions, static and non-static member functions and classes
		3999	with C<operator ()> can be used as callbacks. Other types should be easy
		4000	to add as long as they only need one additional pointer for context. If
		4001	you need support for other types of functors please contact the author
		4002	(preferably after implementing it).
		4003
		4004	For all this to work, your C++ compiler either has to use the same calling
		4005	conventions as your C compiler (for static member functions), or you have
		4006	to embed libev and compile libev itself as C++.
		4007
		4008	Here is a list of things available in the C<ev> namespace:
		4009
		4010	=over 4
		4011
		4012	=item C<ev::READ>, C<ev::WRITE> etc.
		4013
		4014	These are just enum values with the same values as the C<EV_READ> etc.
		4015	macros from F<ev.h>.
		4016
		4017	=item C<ev::tstamp>, C<ev::now>
		4018
		4019	Aliases to the same types/functions as with the C<ev_> prefix.
		4020
		4021	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		4022
		4023	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		4024	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		4025	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		4026	defined by many implementations.
		4027
		4028	All of those classes have these methods:
		4029
		4030	=over 4
		4031
		4032	=item ev::TYPE::TYPE ()
		4033
		4034	=item ev::TYPE::TYPE (loop)
		4035
		4036	=item ev::TYPE::~TYPE
		4037
		4038	The constructor (optionally) takes an event loop to associate the watcher
		4039	with. If it is omitted, it will use C<EV_DEFAULT>.
		4040
		4041	The constructor calls C<ev_init> for you, which means you have to call the
		4042	C<set> method before starting it.
		4043
		4044	It will not set a callback, however: You have to call the templated C<set>
		4045	method to set a callback before you can start the watcher.
		4046
		4047	(The reason why you have to use a method is a limitation in C++ which does
		4048	not allow explicit template arguments for constructors).
		4049
		4050	The destructor automatically stops the watcher if it is active.
		4051
		4052	=item w->set<class, &class::method> (object *)
		4053
		4054	This method sets the callback method to call. The method has to have a
		4055	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		4056	first argument and the C<revents> as second. The object must be given as
		4057	parameter and is stored in the C<data> member of the watcher.
		4058
		4059	This method synthesizes efficient thunking code to call your method from
		4060	the C callback that libev requires. If your compiler can inline your
		4061	callback (i.e. it is visible to it at the place of the C<set> call and
		4062	your compiler is good :), then the method will be fully inlined into the
		4063	thunking function, making it as fast as a direct C callback.
		4064
		4065	Example: simple class declaration and watcher initialisation
		4066
		4067	struct myclass
		4068	{
		4069	void io_cb (ev::io &w, int revents) { }
		4070	}
		4071
		4072	myclass obj;
		4073	ev::io iow;
		4074	iow.set <myclass, &myclass::io_cb> (&obj);
		4075
		4076	=item w->set (object *)
		4077
		4078	This is a variation of a method callback - leaving out the method to call
		4079	will default the method to C<operator ()>, which makes it possible to use
		4080	functor objects without having to manually specify the C<operator ()> all
		4081	the time. Incidentally, you can then also leave out the template argument
		4082	list.
		4083
		4084	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4085	int revents)>.
		4086
		4087	See the method-C<set> above for more details.
		4088
		4089	Example: use a functor object as callback.
		4090
		4091	struct myfunctor
		4092	{
		4093	void operator() (ev::io &w, int revents)
		4094	{
		4095	...
		4096	}
		4097	}
		4098
		4099	myfunctor f;
		4100
		4101	ev::io w;
		4102	w.set (&f);
		4103
		4104	=item w->set<function> (void *data = 0)
		4105
		4106	Also sets a callback, but uses a static method or plain function as
		4107	callback. The optional C<data> argument will be stored in the watcher's
		4108	C<data> member and is free for you to use.
		4109
		4110	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		4111
		4112	See the method-C<set> above for more details.
		4113
		4114	Example: Use a plain function as callback.
		4115
		4116	static void io_cb (ev::io &w, int revents) { }
		4117	iow.set <io_cb> ();
		4118
		4119	=item w->set (loop)
		4120
		4121	Associates a different C<struct ev_loop> with this watcher. You can only
		4122	do this when the watcher is inactive (and not pending either).
		4123
		4124	=item w->set ([arguments])
		4125
		4126	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
		4127	method or a suitable start method must be called at least once. Unlike the
		4128	C counterpart, an active watcher gets automatically stopped and restarted
		4129	when reconfiguring it with this method.
		4130
		4131	=item w->start ()
		4132
		4133	Starts the watcher. Note that there is no C<loop> argument, as the
		4134	constructor already stores the event loop.
		4135
		4136	=item w->start ([arguments])
		4137
		4138	Instead of calling C<set> and C<start> methods separately, it is often
		4139	convenient to wrap them in one call. Uses the same type of arguments as
		4140	the configure C<set> method of the watcher.
		4141
		4142	=item w->stop ()
		4143
		4144	Stops the watcher if it is active. Again, no C<loop> argument.
		4145
		4146	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		4147
		4148	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		4149	C<ev_TYPE_again> function.
		4150
		4151	=item w->sweep () (C<ev::embed> only)
		4152
		4153	Invokes C<ev_embed_sweep>.
		4154
		4155	=item w->update () (C<ev::stat> only)
		4156
		4157	Invokes C<ev_stat_stat>.
		4158
		4159	=back
		4160
		4161	=back
		4162
		4163	Example: Define a class with two I/O and idle watchers, start the I/O
		4164	watchers in the constructor.
		4165
		4166	class myclass
		4167	{
		4168	ev::io io ; void io_cb (ev::io &w, int revents);
		4169	ev::io io2 ; void io2_cb (ev::io &w, int revents);
		4170	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		4171
		4172	myclass (int fd)
		4173	{
		4174	io .set <myclass, &myclass::io_cb > (this);
		4175	io2 .set <myclass, &myclass::io2_cb > (this);
		4176	idle.set <myclass, &myclass::idle_cb> (this);
		4177
		4178	io.set (fd, ev::WRITE); // configure the watcher
		4179	io.start (); // start it whenever convenient
		4180
		4181	io2.start (fd, ev::READ); // set + start in one call
		4182	}
		4183	};
		4184
		4185
		4186	=head1 OTHER LANGUAGE BINDINGS
		4187
		4188	Libev does not offer other language bindings itself, but bindings for a
		4189	number of languages exist in the form of third-party packages. If you know
		4190	any interesting language binding in addition to the ones listed here, drop
		4191	me a note.
		4192
		4193	=over 4
		4194
		4195	=item Perl
		4196
		4197	The EV module implements the full libev API and is actually used to test
		4198	libev. EV is developed together with libev. Apart from the EV core module,
		4199	there are additional modules that implement libev-compatible interfaces
		4200	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4201	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4202	and C<EV::Glib>).
		4203
		4204	It can be found and installed via CPAN, its homepage is at
		4205	L<http://software.schmorp.de/pkg/EV>.
		4206
		4207	=item Python
		4208
		4209	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4210	seems to be quite complete and well-documented.
		4211
		4212	=item Ruby
		4213
		4214	Tony Arcieri has written a ruby extension that offers access to a subset
		4215	of the libev API and adds file handle abstractions, asynchronous DNS and
		4216	more on top of it. It can be found via gem servers. Its homepage is at
		4217	L<http://rev.rubyforge.org/>.
		4218
		4219	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4220	makes rev work even on mingw.
		4221
		4222	=item Haskell
		4223
		4224	A haskell binding to libev is available at
		4225	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4226
		4227	=item D
		4228
		4229	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4230	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4231
		4232	=item Ocaml
		4233
		4234	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4235	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4236
		4237	=item Lua
		4238
		4239	Brian Maher has written a partial interface to libev for lua (at the
		4240	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4241	L<http://github.com/brimworks/lua-ev>.
		4242
		4243	=back
		4244
		4245
		4246	=head1 MACRO MAGIC
		4247
		4248	Libev can be compiled with a variety of options, the most fundamental
		4249	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		4250	functions and callbacks have an initial C<struct ev_loop *> argument.
		4251
		4252	To make it easier to write programs that cope with either variant, the
		4253	following macros are defined:
		4254
		4255	=over 4
		4256
		4257	=item C<EV_A>, C<EV_A_>
		4258
		4259	This provides the loop I<argument> for functions, if one is required ("ev
		4260	loop argument"). The C<EV_A> form is used when this is the sole argument,
		4261	C<EV_A_> is used when other arguments are following. Example:
		4262
		4263	ev_unref (EV_A);
		4264	ev_timer_add (EV_A_ watcher);
		4265	ev_run (EV_A_ 0);
		4266
		4267	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		4268	which is often provided by the following macro.
		4269
		4270	=item C<EV_P>, C<EV_P_>
		4271
		4272	This provides the loop I<parameter> for functions, if one is required ("ev
		4273	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		4274	C<EV_P_> is used when other parameters are following. Example:
		4275
		4276	// this is how ev_unref is being declared
		4277	static void ev_unref (EV_P);
		4278
		4279	// this is how you can declare your typical callback
		4280	static void cb (EV_P_ ev_timer *w, int revents)
		4281
		4282	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		4283	suitable for use with C<EV_A>.
		4284
		4285	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		4286
		4287	Similar to the other two macros, this gives you the value of the default
		4288	loop, if multiple loops are supported ("ev loop default"). The default loop
		4289	will be initialised if it isn't already initialised.
		4290
		4291	For non-multiplicity builds, these macros do nothing, so you always have
		4292	to initialise the loop somewhere.
		4293
		4294	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4295
		4296	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4297	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4298	is undefined when the default loop has not been initialised by a previous
		4299	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4300
		4301	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4302	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		4303
		4304	=back
		4305
		4306	Example: Declare and initialise a check watcher, utilising the above
		4307	macros so it will work regardless of whether multiple loops are supported
		4308	or not.
		4309
		4310	static void
		4311	check_cb (EV_P_ ev_timer *w, int revents)
		4312	{
		4313	ev_check_stop (EV_A_ w);
		4314	}
		4315
		4316	ev_check check;
		4317	ev_check_init (&check, check_cb);
		4318	ev_check_start (EV_DEFAULT_ &check);
		4319	ev_run (EV_DEFAULT_ 0);
		4320
		4321	=head1 EMBEDDING
		4322
		4323	Libev can (and often is) directly embedded into host
		4324	applications. Examples of applications that embed it include the Deliantra
		4325	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		4326	and rxvt-unicode.
		4327
		4328	The goal is to enable you to just copy the necessary files into your
		4329	source directory without having to change even a single line in them, so
		4330	you can easily upgrade by simply copying (or having a checked-out copy of
		4331	libev somewhere in your source tree).
		4332
		4333	=head2 FILESETS
		4334
		4335	Depending on what features you need you need to include one or more sets of files
		4336	in your application.
		4337
		4338	=head3 CORE EVENT LOOP
		4339
		4340	To include only the libev core (all the C<ev_*> functions), with manual
		4341	configuration (no autoconf):
		4342
		4343	#define EV_STANDALONE 1
		4344	#include "ev.c"
		4345
		4346	This will automatically include F<ev.h>, too, and should be done in a
		4347	single C source file only to provide the function implementations. To use
		4348	it, do the same for F<ev.h> in all files wishing to use this API (best
		4349	done by writing a wrapper around F<ev.h> that you can include instead and
		4350	where you can put other configuration options):
		4351
		4352	#define EV_STANDALONE 1
		4353	#include "ev.h"
		4354
		4355	Both header files and implementation files can be compiled with a C++
		4356	compiler (at least, that's a stated goal, and breakage will be treated
		4357	as a bug).
		4358
		4359	You need the following files in your source tree, or in a directory
		4360	in your include path (e.g. in libev/ when using -Ilibev):
		4361
		4362	ev.h
		4363	ev.c
		4364	ev_vars.h
		4365	ev_wrap.h
		4366
		4367	ev_win32.c required on win32 platforms only
		4368
		4369	ev_select.c only when select backend is enabled (which is enabled by default)
		4370	ev_poll.c only when poll backend is enabled (disabled by default)
		4371	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		4372	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		4373	ev_port.c only when the solaris port backend is enabled (disabled by default)
		4374
		4375	F<ev.c> includes the backend files directly when enabled, so you only need
		4376	to compile this single file.
		4377
		4378	=head3 LIBEVENT COMPATIBILITY API
		4379
		4380	To include the libevent compatibility API, also include:
		4381
		4382	#include "event.c"
		4383
		4384	in the file including F<ev.c>, and:
		4385
		4386	#include "event.h"
		4387
		4388	in the files that want to use the libevent API. This also includes F<ev.h>.
		4389
		4390	You need the following additional files for this:
		4391
		4392	event.h
		4393	event.c
		4394
		4395	=head3 AUTOCONF SUPPORT
		4396
		4397	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		4398	whatever way you want, you can also C<m4_include([libev.m4])> in your
		4399	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		4400	include F<config.h> and configure itself accordingly.
		4401
		4402	For this of course you need the m4 file:
		4403
		4404	libev.m4
		4405
		4406	=head2 PREPROCESSOR SYMBOLS/MACROS
		4407
		4408	Libev can be configured via a variety of preprocessor symbols you have to
		4409	define before including (or compiling) any of its files. The default in
		4410	the absence of autoconf is documented for every option.
		4411
		4412	Symbols marked with "(h)" do not change the ABI, and can have different
		4413	values when compiling libev vs. including F<ev.h>, so it is permissible
		4414	to redefine them before including F<ev.h> without breaking compatibility
		4415	to a compiled library. All other symbols change the ABI, which means all
		4416	users of libev and the libev code itself must be compiled with compatible
		4417	settings.
		4418
		4419	=over 4
		4420
		4421	=item EV_COMPAT3 (h)
		4422
		4423	Backwards compatibility is a major concern for libev. This is why this
		4424	release of libev comes with wrappers for the functions and symbols that
		4425	have been renamed between libev version 3 and 4.
		4426
		4427	You can disable these wrappers (to test compatibility with future
		4428	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4429	sources. This has the additional advantage that you can drop the C<struct>
		4430	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4431	typedef in that case.
		4432
		4433	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4434	and in some even more future version the compatibility code will be
		4435	removed completely.
		4436
		4437	=item EV_STANDALONE (h)
		4438
		4439	Must always be C<1> if you do not use autoconf configuration, which
		4440	keeps libev from including F<config.h>, and it also defines dummy
		4441	implementations for some libevent functions (such as logging, which is not
		4442	supported). It will also not define any of the structs usually found in
		4443	F<event.h> that are not directly supported by the libev core alone.
		4444
		4445	In standalone mode, libev will still try to automatically deduce the
		4446	configuration, but has to be more conservative.
		4447
		4448	=item EV_USE_FLOOR
		4449
		4450	If defined to be C<1>, libev will use the C<floor ()> function for its
		4451	periodic reschedule calculations, otherwise libev will fall back on a
		4452	portable (slower) implementation. If you enable this, you usually have to
		4453	link against libm or something equivalent. Enabling this when the C<floor>
		4454	function is not available will fail, so the safe default is to not enable
		4455	this.
		4456
		4457	=item EV_USE_MONOTONIC
		4458
		4459	If defined to be C<1>, libev will try to detect the availability of the
		4460	monotonic clock option at both compile time and runtime. Otherwise no
		4461	use of the monotonic clock option will be attempted. If you enable this,
		4462	you usually have to link against librt or something similar. Enabling it
		4463	when the functionality isn't available is safe, though, although you have
		4464	to make sure you link against any libraries where the C<clock_gettime>
		4465	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		4466
		4467	=item EV_USE_REALTIME
		4468
		4469	If defined to be C<1>, libev will try to detect the availability of the
		4470	real-time clock option at compile time (and assume its availability
		4471	at runtime if successful). Otherwise no use of the real-time clock
		4472	option will be attempted. This effectively replaces C<gettimeofday>
		4473	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		4474	correctness. See the note about libraries in the description of
		4475	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4476	C<EV_USE_CLOCK_SYSCALL>.
		4477
		4478	=item EV_USE_CLOCK_SYSCALL
		4479
		4480	If defined to be C<1>, libev will try to use a direct syscall instead
		4481	of calling the system-provided C<clock_gettime> function. This option
		4482	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4483	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4484	programs needlessly. Using a direct syscall is slightly slower (in
		4485	theory), because no optimised vdso implementation can be used, but avoids
		4486	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4487	higher, as it simplifies linking (no need for C<-lrt>).
		4488
		4489	=item EV_USE_NANOSLEEP
		4490
		4491	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4492	and will use it for delays. Otherwise it will use C<select ()>.
		4493
		4494	=item EV_USE_EVENTFD
		4495
		4496	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4497	available and will probe for kernel support at runtime. This will improve
		4498	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4499	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4500	2.7 or newer, otherwise disabled.
		4501
		4502	=item EV_USE_SELECT
		4503
		4504	If undefined or defined to be C<1>, libev will compile in support for the
		4505	C<select>(2) backend. No attempt at auto-detection will be done: if no
		4506	other method takes over, select will be it. Otherwise the select backend
		4507	will not be compiled in.
		4508
		4509	=item EV_SELECT_USE_FD_SET
		4510
		4511	If defined to C<1>, then the select backend will use the system C<fd_set>
		4512	structure. This is useful if libev doesn't compile due to a missing
		4513	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		4514	on exotic systems. This usually limits the range of file descriptors to
		4515	some low limit such as 1024 or might have other limitations (winsocket
		4516	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		4517	configures the maximum size of the C<fd_set>.
		4518
		4519	=item EV_SELECT_IS_WINSOCKET
		4520
		4521	When defined to C<1>, the select backend will assume that
		4522	select/socket/connect etc. don't understand file descriptors but
		4523	wants osf handles on win32 (this is the case when the select to
		4524	be used is the winsock select). This means that it will call
		4525	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		4526	it is assumed that all these functions actually work on fds, even
		4527	on win32. Should not be defined on non-win32 platforms.
		4528
		4529	=item EV_FD_TO_WIN32_HANDLE(fd)
		4530
		4531	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4532	file descriptors to socket handles. When not defining this symbol (the
		4533	default), then libev will call C<_get_osfhandle>, which is usually
		4534	correct. In some cases, programs use their own file descriptor management,
		4535	in which case they can provide this function to map fds to socket handles.
		4536
		4537	=item EV_WIN32_HANDLE_TO_FD(handle)
		4538
		4539	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4540	using the standard C<_open_osfhandle> function. For programs implementing
		4541	their own fd to handle mapping, overwriting this function makes it easier
		4542	to do so. This can be done by defining this macro to an appropriate value.
		4543
		4544	=item EV_WIN32_CLOSE_FD(fd)
		4545
		4546	If programs implement their own fd to handle mapping on win32, then this
		4547	macro can be used to override the C<close> function, useful to unregister
		4548	file descriptors again. Note that the replacement function has to close
		4549	the underlying OS handle.
		4550
		4551	=item EV_USE_POLL
		4552
		4553	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		4554	backend. Otherwise it will be enabled on non-win32 platforms. It
		4555	takes precedence over select.
		4556
		4557	=item EV_USE_EPOLL
		4558
		4559	If defined to be C<1>, libev will compile in support for the Linux
		4560	C<epoll>(7) backend. Its availability will be detected at runtime,
		4561	otherwise another method will be used as fallback. This is the preferred
		4562	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4563	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4564
		4565	=item EV_USE_KQUEUE
		4566
		4567	If defined to be C<1>, libev will compile in support for the BSD style
		4568	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		4569	otherwise another method will be used as fallback. This is the preferred
		4570	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		4571	supports some types of fds correctly (the only platform we found that
		4572	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		4573	not be used unless explicitly requested. The best way to use it is to find
		4574	out whether kqueue supports your type of fd properly and use an embedded
		4575	kqueue loop.
		4576
		4577	=item EV_USE_PORT
		4578
		4579	If defined to be C<1>, libev will compile in support for the Solaris
		4580	10 port style backend. Its availability will be detected at runtime,
		4581	otherwise another method will be used as fallback. This is the preferred
		4582	backend for Solaris 10 systems.
		4583
		4584	=item EV_USE_DEVPOLL
		4585
		4586	Reserved for future expansion, works like the USE symbols above.
		4587
		4588	=item EV_USE_INOTIFY
		4589
		4590	If defined to be C<1>, libev will compile in support for the Linux inotify
		4591	interface to speed up C<ev_stat> watchers. Its actual availability will
		4592	be detected at runtime. If undefined, it will be enabled if the headers
		4593	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4594
		4595	=item EV_NO_SMP
		4596
		4597	If defined to be C<1>, libev will assume that memory is always coherent
		4598	between threads, that is, threads can be used, but threads never run on
		4599	different cpus (or different cpu cores). This reduces dependencies
		4600	and makes libev faster.
		4601
		4602	=item EV_NO_THREADS
		4603
		4604	If defined to be C<1>, libev will assume that it will never be called
		4605	from different threads, which is a stronger assumption than C<EV_NO_SMP>,
		4606	above. This reduces dependencies and makes libev faster.
		4607
		4608	=item EV_ATOMIC_T
		4609
		4610	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4611	access is atomic and serialised with respect to other threads or signal
		4612	contexts. No such type is easily found in the C language, so you can
		4613	provide your own type that you know is safe for your purposes. It is used
		4614	both for signal handler "locking" as well as for signal and thread safety
		4615	in C<ev_async> watchers.
		4616
		4617	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4618	(from F<signal.h>), which is usually good enough on most platforms,
		4619	although strictly speaking using a type that also implies a memory fence
		4620	is required.
		4621
		4622	=item EV_H (h)
		4623
		4624	The name of the F<ev.h> header file used to include it. The default if
		4625	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		4626	used to virtually rename the F<ev.h> header file in case of conflicts.
		4627
		4628	=item EV_CONFIG_H (h)
		4629
		4630	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		4631	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		4632	C<EV_H>, above.
		4633
		4634	=item EV_EVENT_H (h)
		4635
		4636	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		4637	of how the F<event.h> header can be found, the default is C<"event.h">.
		4638
		4639	=item EV_PROTOTYPES (h)
		4640
		4641	If defined to be C<0>, then F<ev.h> will not define any function
		4642	prototypes, but still define all the structs and other symbols. This is
		4643	occasionally useful if you want to provide your own wrapper functions
		4644	around libev functions.
		4645
		4646	=item EV_MULTIPLICITY
		4647
		4648	If undefined or defined to C<1>, then all event-loop-specific functions
		4649	will have the C<struct ev_loop *> as first argument, and you can create
		4650	additional independent event loops. Otherwise there will be no support
		4651	for multiple event loops and there is no first event loop pointer
		4652	argument. Instead, all functions act on the single default loop.
		4653
		4654	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4655	default loop when multiplicity is switched off - you always have to
		4656	initialise the loop manually in this case.
		4657
		4658	=item EV_MINPRI
		4659
		4660	=item EV_MAXPRI
		4661
		4662	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4663	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4664	provide for more priorities by overriding those symbols (usually defined
		4665	to be C<-2> and C<2>, respectively).
		4666
		4667	When doing priority-based operations, libev usually has to linearly search
		4668	all the priorities, so having many of them (hundreds) uses a lot of space
		4669	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4670	fine.
		4671
		4672	If your embedding application does not need any priorities, defining these
		4673	both to C<0> will save some memory and CPU.
		4674
		4675	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4676	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4677	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4678
		4679	If undefined or defined to be C<1> (and the platform supports it), then
		4680	the respective watcher type is supported. If defined to be C<0>, then it
		4681	is not. Disabling watcher types mainly saves code size.
		4682
		4683	=item EV_FEATURES
		4684
		4685	If you need to shave off some kilobytes of code at the expense of some
		4686	speed (but with the full API), you can define this symbol to request
		4687	certain subsets of functionality. The default is to enable all features
		4688	that can be enabled on the platform.
		4689
		4690	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4691	with some broad features you want) and then selectively re-enable
		4692	additional parts you want, for example if you want everything minimal,
		4693	but multiple event loop support, async and child watchers and the poll
		4694	backend, use this:
		4695
		4696	#define EV_FEATURES 0
		4697	#define EV_MULTIPLICITY 1
		4698	#define EV_USE_POLL 1
		4699	#define EV_CHILD_ENABLE 1
		4700	#define EV_ASYNC_ENABLE 1
		4701
		4702	The actual value is a bitset, it can be a combination of the following
		4703	values (by default, all of these are enabled):
		4704
		4705	=over 4
		4706
		4707	=item C<1> - faster/larger code
		4708
		4709	Use larger code to speed up some operations.
		4710
		4711	Currently this is used to override some inlining decisions (enlarging the
		4712	code size by roughly 30% on amd64).
		4713
		4714	When optimising for size, use of compiler flags such as C<-Os> with
		4715	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4716	assertions.
		4717
		4718	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4719	(e.g. gcc with C<-Os>).
		4720
		4721	=item C<2> - faster/larger data structures
		4722
		4723	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4724	hash table sizes and so on. This will usually further increase code size
		4725	and can additionally have an effect on the size of data structures at
		4726	runtime.
		4727
		4728	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4729	(e.g. gcc with C<-Os>).
		4730
		4731	=item C<4> - full API configuration
		4732
		4733	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4734	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4735
		4736	=item C<8> - full API
		4737
		4738	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4739	details on which parts of the API are still available without this
		4740	feature, and do not complain if this subset changes over time.
		4741
		4742	=item C<16> - enable all optional watcher types
		4743
		4744	Enables all optional watcher types. If you want to selectively enable
		4745	only some watcher types other than I/O and timers (e.g. prepare,
		4746	embed, async, child...) you can enable them manually by defining
		4747	C<EV_watchertype_ENABLE> to C<1> instead.
		4748
		4749	=item C<32> - enable all backends
		4750
		4751	This enables all backends - without this feature, you need to enable at
		4752	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4753
		4754	=item C<64> - enable OS-specific "helper" APIs
		4755
		4756	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4757	default.
		4758
		4759	=back
		4760
		4761	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4762	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4763	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4764	watchers, timers and monotonic clock support.
		4765
		4766	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4767	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4768	your program might be left out as well - a binary starting a timer and an
		4769	I/O watcher then might come out at only 5Kb.
		4770
		4771	=item EV_API_STATIC
		4772
		4773	If this symbol is defined (by default it is not), then all identifiers
		4774	will have static linkage. This means that libev will not export any
		4775	identifiers, and you cannot link against libev anymore. This can be useful
		4776	when you embed libev, only want to use libev functions in a single file,
		4777	and do not want its identifiers to be visible.
		4778
		4779	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4780	wants to use libev.
		4781
		4782	This option only works when libev is compiled with a C compiler, as C++
		4783	doesn't support the required declaration syntax.
		4784
		4785	=item EV_AVOID_STDIO
		4786
		4787	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4788	functions (printf, scanf, perror etc.). This will increase the code size
		4789	somewhat, but if your program doesn't otherwise depend on stdio and your
		4790	libc allows it, this avoids linking in the stdio library which is quite
		4791	big.
		4792
		4793	Note that error messages might become less precise when this option is
		4794	enabled.
		4795
		4796	=item EV_NSIG
		4797
		4798	The highest supported signal number, +1 (or, the number of
		4799	signals): Normally, libev tries to deduce the maximum number of signals
		4800	automatically, but sometimes this fails, in which case it can be
		4801	specified. Also, using a lower number than detected (C<32> should be
		4802	good for about any system in existence) can save some memory, as libev
		4803	statically allocates some 12-24 bytes per signal number.
		4804
		4805	=item EV_PID_HASHSIZE
		4806
		4807	C<ev_child> watchers use a small hash table to distribute workload by
		4808	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4809	usually more than enough. If you need to manage thousands of children you
		4810	might want to increase this value (I<must> be a power of two).
		4811
		4812	=item EV_INOTIFY_HASHSIZE
		4813
		4814	C<ev_stat> watchers use a small hash table to distribute workload by
		4815	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4816	disabled), usually more than enough. If you need to manage thousands of
		4817	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4818	power of two).
		4819
		4820	=item EV_USE_4HEAP
		4821
		4822	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4823	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4824	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4825	faster performance with many (thousands) of watchers.
		4826
		4827	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4828	will be C<0>.
		4829
		4830	=item EV_HEAP_CACHE_AT
		4831
		4832	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4833	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4834	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4835	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4836	but avoids random read accesses on heap changes. This improves performance
		4837	noticeably with many (hundreds) of watchers.
		4838
		4839	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4840	will be C<0>.
		4841
		4842	=item EV_VERIFY
		4843
		4844	Controls how much internal verification (see C<ev_verify ()>) will
		4845	be done: If set to C<0>, no internal verification code will be compiled
		4846	in. If set to C<1>, then verification code will be compiled in, but not
		4847	called. If set to C<2>, then the internal verification code will be
		4848	called once per loop, which can slow down libev. If set to C<3>, then the
		4849	verification code will be called very frequently, which will slow down
		4850	libev considerably.
		4851
		4852	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4853	will be C<0>.
		4854
		4855	=item EV_COMMON
		4856
		4857	By default, all watchers have a C<void *data> member. By redefining
		4858	this macro to something else you can include more and other types of
		4859	members. You have to define it each time you include one of the files,
		4860	though, and it must be identical each time.
		4861
		4862	For example, the perl EV module uses something like this:
		4863
		4864	#define EV_COMMON \
		4865	SV *self; /* contains this struct */ \
		4866	SV *cb_sv, *fh /* note no trailing ";" */
		4867
		4868	=item EV_CB_DECLARE (type)
		4869
		4870	=item EV_CB_INVOKE (watcher, revents)
		4871
		4872	=item ev_set_cb (ev, cb)
		4873
		4874	Can be used to change the callback member declaration in each watcher,
		4875	and the way callbacks are invoked and set. Must expand to a struct member
		4876	definition and a statement, respectively. See the F<ev.h> header file for
		4877	their default definitions. One possible use for overriding these is to
		4878	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		4879	method calls instead of plain function calls in C++.
		4880
		4881	=back
		4882
		4883	=head2 EXPORTED API SYMBOLS
		4884
		4885	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4886	exported symbols, you can use the provided F<Symbol.*> files which list
		4887	all public symbols, one per line:
		4888
		4889	Symbols.ev for libev proper
		4890	Symbols.event for the libevent emulation
		4891
		4892	This can also be used to rename all public symbols to avoid clashes with
		4893	multiple versions of libev linked together (which is obviously bad in
		4894	itself, but sometimes it is inconvenient to avoid this).
		4895
		4896	A sed command like this will create wrapper C<#define>'s that you need to
		4897	include before including F<ev.h>:
		4898
		4899	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4900
		4901	This would create a file F<wrap.h> which essentially looks like this:
		4902
		4903	#define ev_backend myprefix_ev_backend
		4904	#define ev_check_start myprefix_ev_check_start
		4905	#define ev_check_stop myprefix_ev_check_stop
		4906	...
		4907
		4908	=head2 EXAMPLES
		4909
		4910	For a real-world example of a program the includes libev
		4911	verbatim, you can have a look at the EV perl module
		4912	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		4913	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		4914	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		4915	will be compiled. It is pretty complex because it provides its own header
		4916	file.
		4917
		4918	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		4919	that everybody includes and which overrides some configure choices:
		4920
		4921	#define EV_FEATURES 8
		4922	#define EV_USE_SELECT 1
		4923	#define EV_PREPARE_ENABLE 1
		4924	#define EV_IDLE_ENABLE 1
		4925	#define EV_SIGNAL_ENABLE 1
		4926	#define EV_CHILD_ENABLE 1
		4927	#define EV_USE_STDEXCEPT 0
		4928	#define EV_CONFIG_H <config.h>
		4929
		4930	#include "ev++.h"
		4931
		4932	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		4933
		4934	#include "ev_cpp.h"
		4935	#include "ev.c"
		4936
		4937	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
		4938
		4939	=head2 THREADS AND COROUTINES
		4940
		4941	=head3 THREADS
		4942
		4943	All libev functions are reentrant and thread-safe unless explicitly
		4944	documented otherwise, but libev implements no locking itself. This means
		4945	that you can use as many loops as you want in parallel, as long as there
		4946	are no concurrent calls into any libev function with the same loop
		4947	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4948	of course): libev guarantees that different event loops share no data
		4949	structures that need any locking.
		4950
		4951	Or to put it differently: calls with different loop parameters can be done
		4952	concurrently from multiple threads, calls with the same loop parameter
		4953	must be done serially (but can be done from different threads, as long as
		4954	only one thread ever is inside a call at any point in time, e.g. by using
		4955	a mutex per loop).
		4956
		4957	Specifically to support threads (and signal handlers), libev implements
		4958	so-called C<ev_async> watchers, which allow some limited form of
		4959	concurrency on the same event loop, namely waking it up "from the
		4960	outside".
		4961
		4962	If you want to know which design (one loop, locking, or multiple loops
		4963	without or something else still) is best for your problem, then I cannot
		4964	help you, but here is some generic advice:
		4965
		4966	=over 4
		4967
		4968	=item * most applications have a main thread: use the default libev loop
		4969	in that thread, or create a separate thread running only the default loop.
		4970
		4971	This helps integrating other libraries or software modules that use libev
		4972	themselves and don't care/know about threading.
		4973
		4974	=item * one loop per thread is usually a good model.
		4975
		4976	Doing this is almost never wrong, sometimes a better-performance model
		4977	exists, but it is always a good start.
		4978
		4979	=item * other models exist, such as the leader/follower pattern, where one
		4980	loop is handed through multiple threads in a kind of round-robin fashion.
		4981
		4982	Choosing a model is hard - look around, learn, know that usually you can do
		4983	better than you currently do :-)
		4984
		4985	=item * often you need to talk to some other thread which blocks in the
		4986	event loop.
		4987
		4988	C<ev_async> watchers can be used to wake them up from other threads safely
		4989	(or from signal contexts...).
		4990
		4991	An example use would be to communicate signals or other events that only
		4992	work in the default loop by registering the signal watcher with the
		4993	default loop and triggering an C<ev_async> watcher from the default loop
		4994	watcher callback into the event loop interested in the signal.
		4995
		4996	=back
		4997
		4998	See also L<THREAD LOCKING EXAMPLE>.
		4999
		5000	=head3 COROUTINES
		5001
		5002	Libev is very accommodating to coroutines ("cooperative threads"):
		5003	libev fully supports nesting calls to its functions from different
		5004	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5005	different coroutines, and switch freely between both coroutines running
		5006	the loop, as long as you don't confuse yourself). The only exception is
		5007	that you must not do this from C<ev_periodic> reschedule callbacks.
		5008
		5009	Care has been taken to ensure that libev does not keep local state inside
		5010	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5011	they do not call any callbacks.
		5012
		5013	=head2 COMPILER WARNINGS
		5014
		5015	Depending on your compiler and compiler settings, you might get no or a
		5016	lot of warnings when compiling libev code. Some people are apparently
		5017	scared by this.
		5018
		5019	However, these are unavoidable for many reasons. For one, each compiler
		5020	has different warnings, and each user has different tastes regarding
		5021	warning options. "Warn-free" code therefore cannot be a goal except when
		5022	targeting a specific compiler and compiler-version.
		5023
		5024	Another reason is that some compiler warnings require elaborate
		5025	workarounds, or other changes to the code that make it less clear and less
		5026	maintainable.
		5027
		5028	And of course, some compiler warnings are just plain stupid, or simply
		5029	wrong (because they don't actually warn about the condition their message
		5030	seems to warn about). For example, certain older gcc versions had some
		5031	warnings that resulted in an extreme number of false positives. These have
		5032	been fixed, but some people still insist on making code warn-free with
		5033	such buggy versions.
		5034
		5035	While libev is written to generate as few warnings as possible,
		5036	"warn-free" code is not a goal, and it is recommended not to build libev
		5037	with any compiler warnings enabled unless you are prepared to cope with
		5038	them (e.g. by ignoring them). Remember that warnings are just that:
		5039	warnings, not errors, or proof of bugs.
		5040
		5041
		5042	=head2 VALGRIND
		5043
		5044	Valgrind has a special section here because it is a popular tool that is
		5045	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5046
		5047	If you think you found a bug (memory leak, uninitialised data access etc.)
		5048	in libev, then check twice: If valgrind reports something like:
		5049
		5050	==2274== definitely lost: 0 bytes in 0 blocks.
		5051	==2274== possibly lost: 0 bytes in 0 blocks.
		5052	==2274== still reachable: 256 bytes in 1 blocks.
		5053
		5054	Then there is no memory leak, just as memory accounted to global variables
		5055	is not a memleak - the memory is still being referenced, and didn't leak.
		5056
		5057	Similarly, under some circumstances, valgrind might report kernel bugs
		5058	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5059	although an acceptable workaround has been found here), or it might be
		5060	confused.
		5061
		5062	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5063	make it into some kind of religion.
		5064
		5065	If you are unsure about something, feel free to contact the mailing list
		5066	with the full valgrind report and an explanation on why you think this
		5067	is a bug in libev (best check the archives, too :). However, don't be
		5068	annoyed when you get a brisk "this is no bug" answer and take the chance
		5069	of learning how to interpret valgrind properly.
		5070
		5071	If you need, for some reason, empty reports from valgrind for your project
		5072	I suggest using suppression lists.
		5073
		5074
		5075	=head1 PORTABILITY NOTES
		5076
		5077	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5078
		5079	GNU/Linux is the only common platform that supports 64 bit file/large file
		5080	interfaces but I<disables> them by default.
		5081
		5082	That means that libev compiled in the default environment doesn't support
		5083	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5084
		5085	Unfortunately, many programs try to work around this GNU/Linux issue
		5086	by enabling the large file API, which makes them incompatible with the
		5087	standard libev compiled for their system.
		5088
		5089	Likewise, libev cannot enable the large file API itself as this would
		5090	suddenly make it incompatible to the default compile time environment,
		5091	i.e. all programs not using special compile switches.
		5092
		5093	=head2 OS/X AND DARWIN BUGS
		5094
		5095	The whole thing is a bug if you ask me - basically any system interface
		5096	you touch is broken, whether it is locales, poll, kqueue or even the
		5097	OpenGL drivers.
		5098
		5099	=head3 C<kqueue> is buggy
		5100
		5101	The kqueue syscall is broken in all known versions - most versions support
		5102	only sockets, many support pipes.
		5103
		5104	Libev tries to work around this by not using C<kqueue> by default on this
		5105	rotten platform, but of course you can still ask for it when creating a
		5106	loop - embedding a socket-only kqueue loop into a select-based one is
		5107	probably going to work well.
		5108
		5109	=head3 C<poll> is buggy
		5110
		5111	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5112	implementation by something calling C<kqueue> internally around the 10.5.6
		5113	release, so now C<kqueue> I<and> C<poll> are broken.
		5114
		5115	Libev tries to work around this by not using C<poll> by default on
		5116	this rotten platform, but of course you can still ask for it when creating
		5117	a loop.
		5118
		5119	=head3 C<select> is buggy
		5120
		5121	All that's left is C<select>, and of course Apple found a way to fuck this
		5122	one up as well: On OS/X, C<select> actively limits the number of file
		5123	descriptors you can pass in to 1024 - your program suddenly crashes when
		5124	you use more.
		5125
		5126	There is an undocumented "workaround" for this - defining
		5127	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5128	work on OS/X.
		5129
		5130	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5131
		5132	=head3 C<errno> reentrancy
		5133
		5134	The default compile environment on Solaris is unfortunately so
		5135	thread-unsafe that you can't even use components/libraries compiled
		5136	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5137	defined by default. A valid, if stupid, implementation choice.
		5138
		5139	If you want to use libev in threaded environments you have to make sure
		5140	it's compiled with C<_REENTRANT> defined.
		5141
		5142	=head3 Event port backend
		5143
		5144	The scalable event interface for Solaris is called "event
		5145	ports". Unfortunately, this mechanism is very buggy in all major
		5146	releases. If you run into high CPU usage, your program freezes or you get
		5147	a large number of spurious wakeups, make sure you have all the relevant
		5148	and latest kernel patches applied. No, I don't know which ones, but there
		5149	are multiple ones to apply, and afterwards, event ports actually work
		5150	great.
		5151
		5152	If you can't get it to work, you can try running the program by setting
		5153	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5154	C<select> backends.
		5155
		5156	=head2 AIX POLL BUG
		5157
		5158	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5159	this by trying to avoid the poll backend altogether (i.e. it's not even
		5160	compiled in), which normally isn't a big problem as C<select> works fine
		5161	with large bitsets on AIX, and AIX is dead anyway.
		5162
		5163	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5164
		5165	=head3 General issues
		5166
		5167	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5168	requires, and its I/O model is fundamentally incompatible with the POSIX
		5169	model. Libev still offers limited functionality on this platform in
		5170	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5171	descriptors. This only applies when using Win32 natively, not when using
		5172	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5173	as every compiler comes with a slightly differently broken/incompatible
		5174	environment.
		5175
		5176	Lifting these limitations would basically require the full
		5177	re-implementation of the I/O system. If you are into this kind of thing,
		5178	then note that glib does exactly that for you in a very portable way (note
		5179	also that glib is the slowest event library known to man).
		5180
		5181	There is no supported compilation method available on windows except
		5182	embedding it into other applications.
		5183
		5184	Sensible signal handling is officially unsupported by Microsoft - libev
		5185	tries its best, but under most conditions, signals will simply not work.
		5186
		5187	Not a libev limitation but worth mentioning: windows apparently doesn't
		5188	accept large writes: instead of resulting in a partial write, windows will
		5189	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5190	so make sure you only write small amounts into your sockets (less than a
		5191	megabyte seems safe, but this apparently depends on the amount of memory
		5192	available).
		5193
		5194	Due to the many, low, and arbitrary limits on the win32 platform and
		5195	the abysmal performance of winsockets, using a large number of sockets
		5196	is not recommended (and not reasonable). If your program needs to use
		5197	more than a hundred or so sockets, then likely it needs to use a totally
		5198	different implementation for windows, as libev offers the POSIX readiness
		5199	notification model, which cannot be implemented efficiently on windows
		5200	(due to Microsoft monopoly games).
		5201
		5202	A typical way to use libev under windows is to embed it (see the embedding
		5203	section for details) and use the following F<evwrap.h> header file instead
		5204	of F<ev.h>:
		5205
		5206	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5207	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5208
		5209	#include "ev.h"
		5210
		5211	And compile the following F<evwrap.c> file into your project (make sure
		5212	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5213
		5214	#include "evwrap.h"
		5215	#include "ev.c"
		5216
		5217	=head3 The winsocket C<select> function
		5218
		5219	The winsocket C<select> function doesn't follow POSIX in that it
		5220	requires socket I<handles> and not socket I<file descriptors> (it is
		5221	also extremely buggy). This makes select very inefficient, and also
		5222	requires a mapping from file descriptors to socket handles (the Microsoft
		5223	C runtime provides the function C<_open_osfhandle> for this). See the
		5224	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5225	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5226
		5227	The configuration for a "naked" win32 using the Microsoft runtime
		5228	libraries and raw winsocket select is:
		5229
		5230	#define EV_USE_SELECT 1
		5231	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5232
		5233	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5234	complexity in the O(n²) range when using win32.
		5235
		5236	=head3 Limited number of file descriptors
		5237
		5238	Windows has numerous arbitrary (and low) limits on things.
		5239
		5240	Early versions of winsocket's select only supported waiting for a maximum
		5241	of C<64> handles (probably owning to the fact that all windows kernels
		5242	can only wait for C<64> things at the same time internally; Microsoft
		5243	recommends spawning a chain of threads and wait for 63 handles and the
		5244	previous thread in each. Sounds great!).
		5245
		5246	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5247	to some high number (e.g. C<2048>) before compiling the winsocket select
		5248	call (which might be in libev or elsewhere, for example, perl and many
		5249	other interpreters do their own select emulation on windows).
		5250
		5251	Another limit is the number of file descriptors in the Microsoft runtime
		5252	libraries, which by default is C<64> (there must be a hidden I<64>
		5253	fetish or something like this inside Microsoft). You can increase this
		5254	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5255	(another arbitrary limit), but is broken in many versions of the Microsoft
		5256	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5257	(depending on windows version and/or the phase of the moon). To get more,
		5258	you need to wrap all I/O functions and provide your own fd management, but
		5259	the cost of calling select (O(n²)) will likely make this unworkable.
		5260
		5261	=head2 PORTABILITY REQUIREMENTS
		5262
		5263	In addition to a working ISO-C implementation and of course the
		5264	backend-specific APIs, libev relies on a few additional extensions:
		5265
		5266	=over 4
		5267
		5268	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5269	calling conventions regardless of C<ev_watcher_type *>.
		5270
		5271	Libev assumes not only that all watcher pointers have the same internal
		5272	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5273	assumes that the same (machine) code can be used to call any watcher
		5274	callback: The watcher callbacks have different type signatures, but libev
		5275	calls them using an C<ev_watcher *> internally.
		5276
		5277	=item pointer accesses must be thread-atomic
		5278
		5279	Accessing a pointer value must be atomic, it must both be readable and
		5280	writable in one piece - this is the case on all current architectures.
		5281
		5282	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5283
		5284	The type C<sig_atomic_t volatile> (or whatever is defined as
		5285	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5286	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5287	believed to be sufficiently portable.
		5288
		5289	=item C<sigprocmask> must work in a threaded environment
		5290
		5291	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5292	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5293	pthread implementations will either allow C<sigprocmask> in the "main
		5294	thread" or will block signals process-wide, both behaviours would
		5295	be compatible with libev. Interaction between C<sigprocmask> and
		5296	C<pthread_sigmask> could complicate things, however.
		5297
		5298	The most portable way to handle signals is to block signals in all threads
		5299	except the initial one, and run the default loop in the initial thread as
		5300	well.
		5301
		5302	=item C<long> must be large enough for common memory allocation sizes
		5303
		5304	To improve portability and simplify its API, libev uses C<long> internally
		5305	instead of C<size_t> when allocating its data structures. On non-POSIX
		5306	systems (Microsoft...) this might be unexpectedly low, but is still at
		5307	least 31 bits everywhere, which is enough for hundreds of millions of
		5308	watchers.
		5309
		5310	=item C<double> must hold a time value in seconds with enough accuracy
		5311
		5312	The type C<double> is used to represent timestamps. It is required to
		5313	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5314	good enough for at least into the year 4000 with millisecond accuracy
		5315	(the design goal for libev). This requirement is overfulfilled by
		5316	implementations using IEEE 754, which is basically all existing ones.
		5317
		5318	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5319	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5320	is either obsolete or somebody patched it to use C<long double> or
		5321	something like that, just kidding).
		5322
		5323	=back
		5324
		5325	If you know of other additional requirements drop me a note.
		5326
		5327
		5328	=head1 ALGORITHMIC COMPLEXITIES
		5329
		5330	In this section the complexities of (many of) the algorithms used inside
		5331	libev will be documented. For complexity discussions about backends see
		5332	the documentation for C<ev_default_init>.
		5333
		5334	All of the following are about amortised time: If an array needs to be
		5335	extended, libev needs to realloc and move the whole array, but this
		5336	happens asymptotically rarer with higher number of elements, so O(1) might
		5337	mean that libev does a lengthy realloc operation in rare cases, but on
		5338	average it is much faster and asymptotically approaches constant time.
		5339
		5340	=over 4
		5341
		5342	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5343
		5344	This means that, when you have a watcher that triggers in one hour and
		5345	there are 100 watchers that would trigger before that, then inserting will
		5346	have to skip roughly seven (C<ld 100>) of these watchers.
		5347
		5348	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5349
		5350	That means that changing a timer costs less than removing/adding them,
		5351	as only the relative motion in the event queue has to be paid for.
		5352
		5353	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5354
		5355	These just add the watcher into an array or at the head of a list.
		5356
		5357	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5358
		5359	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5360
		5361	These watchers are stored in lists, so they need to be walked to find the
		5362	correct watcher to remove. The lists are usually short (you don't usually
		5363	have many watchers waiting for the same fd or signal: one is typical, two
		5364	is rare).
		5365
		5366	=item Finding the next timer in each loop iteration: O(1)
		5367
		5368	By virtue of using a binary or 4-heap, the next timer is always found at a
		5369	fixed position in the storage array.
		5370
		5371	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5372
		5373	A change means an I/O watcher gets started or stopped, which requires
		5374	libev to recalculate its status (and possibly tell the kernel, depending
		5375	on backend and whether C<ev_io_set> was used).
		5376
		5377	=item Activating one watcher (putting it into the pending state): O(1)
		5378
		5379	=item Priority handling: O(number_of_priorities)
		5380
		5381	Priorities are implemented by allocating some space for each
		5382	priority. When doing priority-based operations, libev usually has to
		5383	linearly search all the priorities, but starting/stopping and activating
		5384	watchers becomes O(1) with respect to priority handling.
		5385
		5386	=item Sending an ev_async: O(1)
		5387
		5388	=item Processing ev_async_send: O(number_of_async_watchers)
		5389
		5390	=item Processing signals: O(max_signal_number)
		5391
		5392	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5393	calls in the current loop iteration and the loop is currently
		5394	blocked. Checking for async and signal events involves iterating over all
		5395	running async watchers or all signal numbers.
		5396
		5397	=back
		5398
		5399
		5400	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5401
		5402	The major version 4 introduced some incompatible changes to the API.
		5403
		5404	At the moment, the C<ev.h> header file provides compatibility definitions
		5405	for all changes, so most programs should still compile. The compatibility
		5406	layer might be removed in later versions of libev, so better update to the
		5407	new API early than late.
		5408
		5409	=over 4
		5410
		5411	=item C<EV_COMPAT3> backwards compatibility mechanism
		5412
		5413	The backward compatibility mechanism can be controlled by
		5414	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5415	section.
		5416
		5417	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5418
		5419	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5420
		5421	ev_loop_destroy (EV_DEFAULT_UC);
		5422	ev_loop_fork (EV_DEFAULT);
		5423
		5424	=item function/symbol renames
		5425
		5426	A number of functions and symbols have been renamed:
		5427
		5428	ev_loop => ev_run
		5429	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5430	EVLOOP_ONESHOT => EVRUN_ONCE
		5431
		5432	ev_unloop => ev_break
		5433	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5434	EVUNLOOP_ONE => EVBREAK_ONE
		5435	EVUNLOOP_ALL => EVBREAK_ALL
		5436
		5437	EV_TIMEOUT => EV_TIMER
		5438
		5439	ev_loop_count => ev_iteration
		5440	ev_loop_depth => ev_depth
		5441	ev_loop_verify => ev_verify
		5442
		5443	Most functions working on C<struct ev_loop> objects don't have an
		5444	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5445	associated constants have been renamed to not collide with the C<struct
		5446	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5447	as all other watcher types. Note that C<ev_loop_fork> is still called
		5448	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5449	typedef.
		5450
		5451	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5452
		5453	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5454	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5455	and work, but the library code will of course be larger.
		5456
		5457	=back
		5458
		5459
		5460	=head1 GLOSSARY
		5461
		5462	=over 4
		5463
		5464	=item active
		5465
		5466	A watcher is active as long as it has been started and not yet stopped.
		5467	See L<WATCHER STATES> for details.
		5468
		5469	=item application
		5470
		5471	In this document, an application is whatever is using libev.
		5472
		5473	=item backend
		5474
		5475	The part of the code dealing with the operating system interfaces.
		5476
		5477	=item callback
		5478
		5479	The address of a function that is called when some event has been
		5480	detected. Callbacks are being passed the event loop, the watcher that
		5481	received the event, and the actual event bitset.
		5482
		5483	=item callback/watcher invocation
		5484
		5485	The act of calling the callback associated with a watcher.
		5486
		5487	=item event
		5488
		5489	A change of state of some external event, such as data now being available
		5490	for reading on a file descriptor, time having passed or simply not having
		5491	any other events happening anymore.
		5492
		5493	In libev, events are represented as single bits (such as C<EV_READ> or
		5494	C<EV_TIMER>).
		5495
		5496	=item event library
		5497
		5498	A software package implementing an event model and loop.
		5499
		5500	=item event loop
		5501
		5502	An entity that handles and processes external events and converts them
		5503	into callback invocations.
		5504
		5505	=item event model
		5506
		5507	The model used to describe how an event loop handles and processes
		5508	watchers and events.
		5509
		5510	=item pending
		5511
		5512	A watcher is pending as soon as the corresponding event has been
		5513	detected. See L<WATCHER STATES> for details.
		5514
		5515	=item real time
		5516
		5517	The physical time that is observed. It is apparently strictly monotonic :)
		5518
		5519	=item wall-clock time
		5520
		5521	The time and date as shown on clocks. Unlike real time, it can actually
		5522	be wrong and jump forwards and backwards, e.g. when you adjust your
		5523	clock.
		5524
		5525	=item watcher
		5526
		5527	A data structure that describes interest in certain events. Watchers need
		5528	to be started (attached to an event loop) before they can receive events.
		5529
		5530	=back
1217		5531
1218	=head1 AUTHOR	5532	=head1 AUTHOR
1219		5533
1220	Marc Lehmann <libev@schmorp.de>.	5534	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5535	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
1221		5536

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