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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
6		8
7	#include <ev.h>	9	#include <ev.h>
8		10
9	=head1 DESCRIPTION	11	=head2 EXAMPLE PROGRAM
		12
		13	// a single header file is required
		14	#include <ev.h>
		15
		16	#include <stdio.h> // for puts
		17
		18	// every watcher type has its own typedef'd struct
		19	// with the name ev_TYPE
		20	ev_io stdin_watcher;
		21	ev_timer timeout_watcher;
		22
		23	// all watcher callbacks have a similar signature
		24	// this callback is called when data is readable on stdin
		25	static void
		26	stdin_cb (EV_P_ ev_io *w, int revents)
		27	{
		28	puts ("stdin ready");
		29	// for one-shot events, one must manually stop the watcher
		30	// with its corresponding stop function.
		31	ev_io_stop (EV_A_ w);
		32
		33	// this causes all nested ev_run's to stop iterating
		34	ev_break (EV_A_ EVBREAK_ALL);
		35	}
		36
		37	// another callback, this time for a time-out
		38	static void
		39	timeout_cb (EV_P_ ev_timer *w, int revents)
		40	{
		41	puts ("timeout");
		42	// this causes the innermost ev_run to stop iterating
		43	ev_break (EV_A_ EVBREAK_ONE);
		44	}
		45
		46	int
		47	main (void)
		48	{
		49	// use the default event loop unless you have special needs
		50	struct ev_loop *loop = EV_DEFAULT;
		51
		52	// initialise an io watcher, then start it
		53	// this one will watch for stdin to become readable
		54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		55	ev_io_start (loop, &stdin_watcher);
		56
		57	// initialise a timer watcher, then start it
		58	// simple non-repeating 5.5 second timeout
		59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		60	ev_timer_start (loop, &timeout_watcher);
		61
		62	// now wait for events to arrive
		63	ev_run (loop, 0);
		64
		65	// break was called, so exit
		66	return 0;
		67	}
		68
		69	=head1 ABOUT THIS DOCUMENT
		70
		71	This document documents the libev software package.
		72
		73	The newest version of this document is also available as an html-formatted
		74	web page you might find easier to navigate when reading it for the first
		75	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		76
		77	While this document tries to be as complete as possible in documenting
		78	libev, its usage and the rationale behind its design, it is not a tutorial
		79	on event-based programming, nor will it introduce event-based programming
		80	with libev.
		81
		82	Familiarity with event based programming techniques in general is assumed
		83	throughout this document.
		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
		92
		93	=head1 ABOUT LIBEV
10		94
11	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	97	these event sources and provide your program with events.
14		98
15	To do this, it must take more or less complete control over your process	99	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	100	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	101	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	103	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	104	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	105	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	106	watcher.
23		107
24	=head1 FEATURES	108	=head2 FEATURES
25		109
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	110	Libev supports C<select>, C<poll>, the Linux-specific aio and C<epoll>
27	kqueue mechanisms for file descriptor events, relative timers, absolute	111	interfaces, the BSD-specific C<kqueue> and the Solaris-specific event port
28	timers with customised rescheduling, signal events, process status change	112	mechanisms for file descriptor events (C<ev_io>), the Linux C<inotify>
		113	interface (for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
		114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
		115	timers (C<ev_timer>), absolute timers with customised rescheduling
		116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
29	events (related to SIGCHLD), and event watchers dealing with the event	117	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	118	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
		119	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		120	limited support for fork events (C<ev_fork>).
		121
		122	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	123	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	124	for example).
33		125
34	=head1 CONVENTIONS	126	=head2 CONVENTIONS
35		127
36	Libev is very configurable. In this manual the default configuration	128	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	129	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	130	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	131	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	132	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 *>)	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	134	this argument.
43		135
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	136	=head2 TIME REPRESENTATION
45		137
46	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	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	140	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	141	ask). This type is called C<ev_tstamp>, which is what you should use
50	to the double type in C.	142	too. It usually aliases to the C<double> type in C. When you need to do
		143	any calculations on it, you should treat it as some floating point value.
		144
		145	Unlike the name component C<stamp> might indicate, it is also used for
		146	time differences (e.g. delays) throughout libev.
		147
		148	=head1 ERROR HANDLING
		149
		150	Libev knows three classes of errors: operating system errors, usage errors
		151	and internal errors (bugs).
		152
		153	When libev catches an operating system error it cannot handle (for example
		154	a system call indicating a condition libev cannot fix), it calls the callback
		155	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		156	abort. The default is to print a diagnostic message and to call C<abort
		157	()>.
		158
		159	When libev detects a usage error such as a negative timer interval, then
		160	it will print a diagnostic message and abort (via the C<assert> mechanism,
		161	so C<NDEBUG> will disable this checking): these are programming errors in
		162	the libev caller and need to be fixed there.
		163
		164	Libev also has a few internal error-checking C<assert>ions, and also has
		165	extensive consistency checking code. These do not trigger under normal
		166	circumstances, as they indicate either a bug in libev or worse.
		167
		168
		169	=head1 GLOBAL FUNCTIONS
		170
		171	These functions can be called anytime, even before initialising the
		172	library in any way.
51		173
52	=over 4	174	=over 4
53		175
54	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
55		177
56	Returns the current time as libev would use it.	178	Returns the current time as libev would use it. Please note that the
		179	C<ev_now> function is usually faster and also often returns the timestamp
		180	you actually want to know. Also interesting is the combination of
		181	C<ev_now_update> and C<ev_now>.
		182
		183	=item ev_sleep (ev_tstamp interval)
		184
		185	Sleep for the given interval: The current thread will be blocked
		186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
		190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
57		194
58	=item int ev_version_major ()	195	=item int ev_version_major ()
59		196
60	=item int ev_version_minor ()	197	=item int ev_version_minor ()
61		198
62	You can find out the major and minor version numbers of the library	199	You can find out the major and minor ABI version numbers of the library
63	you linked against by calling the functions C<ev_version_major> and	200	you linked against by calling the functions C<ev_version_major> and
64	C<ev_version_minor>. If you want, you can compare against the global	201	C<ev_version_minor>. If you want, you can compare against the global
65	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	202	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	203	version of the library your program was compiled against.
67		204
		205	These version numbers refer to the ABI version of the library, not the
		206	release version.
		207
68	Usually, it's a good idea to terminate if the major versions mismatch,	208	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	210	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	211	not a problem.
72		212
		213	Example: Make sure we haven't accidentally been linked against the wrong
		214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
		216
		217	assert (("libev version mismatch",
		218	ev_version_major () == EV_VERSION_MAJOR
		219	&& ev_version_minor () >= EV_VERSION_MINOR));
		220
		221	=item unsigned int ev_supported_backends ()
		222
		223	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		224	value) compiled into this binary of libev (independent of their
		225	availability on the system you are running on). See C<ev_default_loop> for
		226	a description of the set values.
		227
		228	Example: make sure we have the epoll method, because yeah this is cool and
		229	a must have and can we have a torrent of it please!!!11
		230
		231	assert (("sorry, no epoll, no sex",
		232	ev_supported_backends () & EVBACKEND_EPOLL));
		233
		234	=item unsigned int ev_recommended_backends ()
		235
		236	Return the set of all backends compiled into this binary of libev and
		237	also recommended for this platform, meaning it will work for most file
		238	descriptor types. This set is often smaller than the one returned by
		239	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
		240	and will not be auto-detected unless you explicitly request it (assuming
		241	you know what you are doing). This is the set of backends that libev will
		242	probe for if you specify no backends explicitly.
		243
		244	=item unsigned int ev_embeddable_backends ()
		245
		246	Returns the set of backends that are embeddable in other event loops. This
		247	value is platform-specific but can include backends not available on the
		248	current system. To find which embeddable backends might be supported on
		249	the current system, you would need to look at C<ev_embeddable_backends ()
		250	& ev_supported_backends ()>, likewise for recommended ones.
		251
		252	See the description of C<ev_embed> watchers for more info.
		253
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
74		255
75	Sets the allocation function to use (the prototype is similar to the	256	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
77	and free memory (no surprises here). If it returns zero when memory	258	used to allocate and free memory (no surprises here). If it returns zero
78	needs to be allocated, the library might abort or take some potentially	259	when memory needs to be allocated (C<size != 0>), the library might abort
79	destructive action. The default is your system realloc function.	260	or take some potentially destructive action.
		261
		262	Since some systems (at least OpenBSD and Darwin) fail to implement
		263	correct C<realloc> semantics, libev will use a wrapper around the system
		264	C<realloc> and C<free> functions by default.
80		265
81	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
82	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
83	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
84		269
		270	Example: The following is the C<realloc> function that libev itself uses
		271	which should work with C<realloc> and C<free> functions of all kinds and
		272	is probably a good basis for your own implementation.
		273
		274	static void *
		275	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		276	{
		277	if (size)
		278	return realloc (ptr, size);
		279
		280	free (ptr);
		281	return 0;
		282	}
		283
		284	Example: Replace the libev allocator with one that waits a bit and then
		285	retries.
		286
		287	static void *
		288	persistent_realloc (void *ptr, size_t size)
		289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
		296	for (;;)
		297	{
		298	void *newptr = realloc (ptr, size);
		299
		300	if (newptr)
		301	return newptr;
		302
		303	sleep (60);
		304	}
		305	}
		306
		307	...
		308	ev_set_allocator (persistent_realloc);
		309
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
86		311
87	Set the callback function to call on a retryable syscall error (such	312	Set the callback function to call on a retryable system call error (such
88	as failed select, poll, epoll_wait). The message is a printable string	313	as failed select, poll, epoll_wait). The message is a printable string
89	indicating the system call or subsystem causing the problem. If this	314	indicating the system call or subsystem causing the problem. If this
90	callback is set, then libev will expect it to remedy the sitution, no	315	callback is set, then libev will expect it to remedy the situation, no
91	matter what, when it returns. That is, libev will generally retry the	316	matter what, when it returns. That is, libev will generally retry the
92	requested operation, or, if the condition doesn't go away, do bad stuff	317	requested operation, or, if the condition doesn't go away, do bad stuff
93	(such as abort).	318	(such as abort).
94		319
		320	Example: This is basically the same thing that libev does internally, too.
		321
		322	static void
		323	fatal_error (const char *msg)
		324	{
		325	perror (msg);
		326	abort ();
		327	}
		328
		329	...
		330	ev_set_syserr_cb (fatal_error);
		331
		332	=item ev_feed_signal (int signum)
		333
		334	This function can be used to "simulate" a signal receive. It is completely
		335	safe to call this function at any time, from any context, including signal
		336	handlers or random threads.
		337
		338	Its main use is to customise signal handling in your process, especially
		339	in the presence of threads. For example, you could block signals
		340	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		341	creating any loops), and in one thread, use C<sigwait> or any other
		342	mechanism to wait for signals, then "deliver" them to libev by calling
		343	C<ev_feed_signal>.
		344
95	=back	345	=back
96		346
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	347	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
98		348
99	An event loop is described by a C<struct ev_loop *>. The library knows two	349	An event loop is described by a C<struct ev_loop *> (the C<struct> is
100	types of such loops, the I<default> loop, which supports signals and child	350	I<not> optional in this case unless libev 3 compatibility is disabled, as
101	events, and dynamically created loops which do not.	351	libev 3 had an C<ev_loop> function colliding with the struct name).
102		352
103	If you use threads, a common model is to run the default event loop	353	The library knows two types of such loops, the I<default> loop, which
104	in your main thread (or in a separate thrad) and for each thread you	354	supports child process events, and dynamically created event loops which
105	create, you also create another event loop. Libev itself does no locking	355	do not.
106	whatsoever, so if you mix calls to the same event loop in different
107	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because it's hideous and inefficient).
109		356
110	=over 4	357	=over 4
111		358
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	359	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		360
114	This will initialise the default event loop if it hasn't been initialised	361	This returns the "default" event loop object, which is what you should
115	yet and return it. If the default loop could not be initialised, returns	362	normally use when you just need "the event loop". Event loop objects and
116	false. If it already was initialised it simply returns it (and ignores the	363	the C<flags> parameter are described in more detail in the entry for
117	flags).	364	C<ev_loop_new>.
		365
		366	If the default loop is already initialised then this function simply
		367	returns it (and ignores the flags. If that is troubling you, check
		368	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		369	flags, which should almost always be C<0>, unless the caller is also the
		370	one calling C<ev_run> or otherwise qualifies as "the main program".
118		371
119	If you don't know what event loop to use, use the one returned from this	372	If you don't know what event loop to use, use the one returned from this
120	function.	373	function (or via the C<EV_DEFAULT> macro).
		374
		375	Note that this function is I<not> thread-safe, so if you want to use it
		376	from multiple threads, you have to employ some kind of mutex (note also
		377	that this case is unlikely, as loops cannot be shared easily between
		378	threads anyway).
		379
		380	The default loop is the only loop that can handle C<ev_child> watchers,
		381	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		382	a problem for your application you can either create a dynamic loop with
		383	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		384	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		385
		386	Example: This is the most typical usage.
		387
		388	if (!ev_default_loop (0))
		389	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		390
		391	Example: Restrict libev to the select and poll backends, and do not allow
		392	environment settings to be taken into account:
		393
		394	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		395
		396	=item struct ev_loop *ev_loop_new (unsigned int flags)
		397
		398	This will create and initialise a new event loop object. If the loop
		399	could not be initialised, returns false.
		400
		401	This function is thread-safe, and one common way to use libev with
		402	threads is indeed to create one loop per thread, and using the default
		403	loop in the "main" or "initial" thread.
121		404
122	The flags argument can be used to specify special behaviour or specific	405	The flags argument can be used to specify special behaviour or specific
123	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	406	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		407
125	It supports the following flags:	408	The following flags are supported:
126		409
127	=over 4	410	=over 4
128		411
129	=item C<EVFLAG_AUTO>	412	=item C<EVFLAG_AUTO>
130		413
131	The default flags value. Use this if you have no clue (it's the right	414	The default flags value. Use this if you have no clue (it's the right
132	thing, believe me).	415	thing, believe me).
133		416
134	=item C<EVFLAG_NOENV>	417	=item C<EVFLAG_NOENV>
135		418
136	If this flag bit is ored into the flag value (or the program runs setuid	419	If this flag bit is or'ed into the flag value (or the program runs setuid
137	or setgid) then libev will I<not> look at the environment variable	420	or setgid) then libev will I<not> look at the environment variable
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	422	override the flags completely if it is found in the environment. This is
140	useful to try out specific backends to test their performance, or to work	423	useful to try out specific backends to test their performance, to work
141	around bugs.	424	around bugs, or to make libev threadsafe (accessing environment variables
		425	cannot be done in a threadsafe way, but usually it works if no other
		426	thread modifies them).
142		427
		428	=item C<EVFLAG_FORKCHECK>
		429
		430	Instead of calling C<ev_loop_fork> manually after a fork, you can also
		431	make libev check for a fork in each iteration by enabling this flag.
		432
		433	This works by calling C<getpid ()> on every iteration of the loop,
		434	and thus this might slow down your event loop if you do a lot of loop
		435	iterations and little real work, but is usually not noticeable (on my
		436	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
		437	sequence without a system call and thus I<very> fast, but my GNU/Linux
		438	system also has C<pthread_atfork> which is even faster). (Update: glibc
		439	versions 2.25 apparently removed the C<getpid> optimisation again).
		440
		441	The big advantage of this flag is that you can forget about fork (and
		442	forget about forgetting to tell libev about forking, although you still
		443	have to ignore C<SIGPIPE>) when you use this flag.
		444
		445	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		446	environment variable.
		447
		448	=item C<EVFLAG_NOINOTIFY>
		449
		450	When this flag is specified, then libev will not attempt to use the
		451	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		452	testing, this flag can be useful to conserve inotify file descriptors, as
		453	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		454
		455	=item C<EVFLAG_SIGNALFD>
		456
		457	When this flag is specified, then libev will attempt to use the
		458	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		459	delivers signals synchronously, which makes it both faster and might make
		460	it possible to get the queued signal data. It can also simplify signal
		461	handling with threads, as long as you properly block signals in your
		462	threads that are not interested in handling them.
		463
		464	Signalfd will not be used by default as this changes your signal mask, and
		465	there are a lot of shoddy libraries and programs (glib's threadpool for
		466	example) that can't properly initialise their signal masks.
		467
		468	=item C<EVFLAG_NOSIGMASK>
		469
		470	When this flag is specified, then libev will avoid to modify the signal
		471	mask. Specifically, this means you have to make sure signals are unblocked
		472	when you want to receive them.
		473
		474	This behaviour is useful when you want to do your own signal handling, or
		475	want to handle signals only in specific threads and want to avoid libev
		476	unblocking the signals.
		477
		478	It's also required by POSIX in a threaded program, as libev calls
		479	C<sigprocmask>, whose behaviour is officially unspecified.
		480
		481	This flag's behaviour will become the default in future versions of libev.
		482
143	=item C<EVMETHOD_SELECT> (portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		484
		485	This is your standard select(2) backend. Not I<completely> standard, as
		486	libev tries to roll its own fd_set with no limits on the number of fds,
		487	but if that fails, expect a fairly low limit on the number of fds when
		488	using this backend. It doesn't scale too well (O(highest_fd)), but its
		489	usually the fastest backend for a low number of (low-numbered :) fds.
		490
		491	To get good performance out of this backend you need a high amount of
		492	parallelism (most of the file descriptors should be busy). If you are
		493	writing a server, you should C<accept ()> in a loop to accept as many
		494	connections as possible during one iteration. You might also want to have
		495	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		496	readiness notifications you get per iteration.
		497
		498	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		499	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		500	C<exceptfds> set on that platform).
		501
145	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	502	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
146		503
147	=item C<EVMETHOD_EPOLL> (linux only)	504	And this is your standard poll(2) backend. It's more complicated
		505	than select, but handles sparse fds better and has no artificial
		506	limit on the number of fds you can use (except it will slow down
		507	considerably with a lot of inactive fds). It scales similarly to select,
		508	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		509	performance tips.
148		510
149	=item C<EVMETHOD_KQUEUE> (some bsds only)	511	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		512	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
150		513
151	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
152		515
153	=item C<EVMETHOD_PORT> (solaris 10 only)	516	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		517	kernels).
154		518
155	If one or more of these are ored into the flags value, then only these	519	For few fds, this backend is a bit little slower than poll and select, but
156	backends will be tried (in the reverse order as given here). If one are	520	it scales phenomenally better. While poll and select usually scale like
157	specified, any backend will do.	521	O(total_fds) where total_fds is the total number of fds (or the highest
		522	fd), epoll scales either O(1) or O(active_fds).
		523
		524	The epoll mechanism deserves honorable mention as the most misdesigned
		525	of the more advanced event mechanisms: mere annoyances include silently
		526	dropping file descriptors, requiring a system call per change per file
		527	descriptor (and unnecessary guessing of parameters), problems with dup,
		528	returning before the timeout value, resulting in additional iterations
		529	(and only giving 5ms accuracy while select on the same platform gives
		530	0.1ms) and so on. The biggest issue is fork races, however - if a program
		531	forks then I<both> parent and child process have to recreate the epoll
		532	set, which can take considerable time (one syscall per file descriptor)
		533	and is of course hard to detect.
		534
		535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		536	but of course I<doesn't>, and epoll just loves to report events for
		537	totally I<different> file descriptors (even already closed ones, so
		538	one cannot even remove them from the set) than registered in the set
		539	(especially on SMP systems). Libev tries to counter these spurious
		540	notifications by employing an additional generation counter and comparing
		541	that against the events to filter out spurious ones, recreating the set
		542	when required. Epoll also erroneously rounds down timeouts, but gives you
		543	no way to know when and by how much, so sometimes you have to busy-wait
		544	because epoll returns immediately despite a nonzero timeout. And last
		545	not least, it also refuses to work with some file descriptors which work
		546	perfectly fine with C<select> (files, many character devices...).
		547
		548	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		549	cobbled together in a hurry, no thought to design or interaction with
		550	others. Oh, the pain, will it ever stop...
		551
		552	While stopping, setting and starting an I/O watcher in the same iteration
		553	will result in some caching, there is still a system call per such
		554	incident (because the same I<file descriptor> could point to a different
		555	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
		556	file descriptors might not work very well if you register events for both
		557	file descriptors.
		558
		559	Best performance from this backend is achieved by not unregistering all
		560	watchers for a file descriptor until it has been closed, if possible,
		561	i.e. keep at least one watcher active per fd at all times. Stopping and
		562	starting a watcher (without re-setting it) also usually doesn't cause
		563	extra overhead. A fork can both result in spurious notifications as well
		564	as in libev having to destroy and recreate the epoll object, which can
		565	take considerable time and thus should be avoided.
		566
		567	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		568	faster than epoll for maybe up to a hundred file descriptors, depending on
		569	the usage. So sad.
		570
		571	While nominally embeddable in other event loops, this feature is broken in
		572	a lot of kernel revisions, but probably(!) works in current versions.
		573
		574	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		575	C<EVBACKEND_POLL>.
		576
		577	=item C<EVBACKEND_LINUXAIO> (value 64, Linux)
		578
		579	Use the linux-specific linux aio (I<not> C<< aio(7) >> but C<<
		580	io_submit(2) >>) event interface available in post-4.18 kernels.
		581
		582	If this backend works for you (as of this writing, it was very
		583	experimental), it is the best event interface available on linux and might
		584	be well worth enabling it - if it isn't available in your kernel this will
		585	be detected and this backend will be skipped.
		586
		587	This backend can batch oneshot requests and supports a user-space ring
		588	buffer to receive events. It also doesn't suffer from most of the design
		589	problems of epoll (such as not being able to remove event sources from the
		590	epoll set), and generally sounds too good to be true. Because, this being
		591	the linux kernel, of course it suffers from a whole new set of limitations.
		592
		593	For one, it is not easily embeddable (but probably could be done using
		594	an event fd at some extra overhead). It also is subject to a system wide
		595	limit that can be configured in F</proc/sys/fs/aio-max-nr> - each loop
		596	currently requires C<61> of this number. If no aio requests are left, this
		597	backend will be skipped during initialisation.
		598
		599	Most problematic in practise, however, is that not all file descriptors
		600	work with it. For example, in linux 5.1, tcp sockets, pipes, event fds,
		601	files, F</dev/null> and a few others are supported, but ttys do not work
		602	properly (a known bug that the kernel developers don't care about, see
		603	L<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
		604	(yet?) a generic event polling interface.
		605
		606	Overall, it seems the linux developers just don't want it to have a
		607	generic event handling mechanism other than C<select> or C<poll>.
		608
		609	To work around the fd type problem, the current version of libev uses
		610	epoll as a fallback for file deescriptor types that do not work. Epoll
		611	is used in, kind of, slow mode that hopefully avoids most of its design
		612	problems and requires 1-3 extra syscalls per active fd every iteration.
		613
		614	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		615	C<EVBACKEND_POLL>.
		616
		617	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		618
		619	Kqueue deserves special mention, as at the time of this writing, it
		620	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		621	with anything but sockets and pipes, except on Darwin, where of course
		622	it's completely useless). Unlike epoll, however, whose brokenness
		623	is by design, these kqueue bugs can (and eventually will) be fixed
		624	without API changes to existing programs. For this reason it's not being
		625	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		626	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		627	system like NetBSD.
		628
		629	You still can embed kqueue into a normal poll or select backend and use it
		630	only for sockets (after having made sure that sockets work with kqueue on
		631	the target platform). See C<ev_embed> watchers for more info.
		632
		633	It scales in the same way as the epoll backend, but the interface to the
		634	kernel is more efficient (which says nothing about its actual speed, of
		635	course). While stopping, setting and starting an I/O watcher does never
		636	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		637	two event changes per incident. Support for C<fork ()> is very bad (you
		638	might have to leak fd's on fork, but it's more sane than epoll) and it
		639	drops fds silently in similarly hard-to-detect cases.
		640
		641	This backend usually performs well under most conditions.
		642
		643	While nominally embeddable in other event loops, this doesn't work
		644	everywhere, so you might need to test for this. And since it is broken
		645	almost everywhere, you should only use it when you have a lot of sockets
		646	(for which it usually works), by embedding it into another event loop
		647	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		648	also broken on OS X)) and, did I mention it, using it only for sockets.
		649
		650	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		651	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		652	C<NOTE_EOF>.
		653
		654	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		655
		656	This is not implemented yet (and might never be, unless you send me an
		657	implementation). According to reports, C</dev/poll> only supports sockets
		658	and is not embeddable, which would limit the usefulness of this backend
		659	immensely.
		660
		661	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		662
		663	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		664	it's really slow, but it still scales very well (O(active_fds)).
		665
		666	While this backend scales well, it requires one system call per active
		667	file descriptor per loop iteration. For small and medium numbers of file
		668	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		669	might perform better.
		670
		671	On the positive side, this backend actually performed fully to
		672	specification in all tests and is fully embeddable, which is a rare feat
		673	among the OS-specific backends (I vastly prefer correctness over speed
		674	hacks).
		675
		676	On the negative side, the interface is I<bizarre> - so bizarre that
		677	even sun itself gets it wrong in their code examples: The event polling
		678	function sometimes returns events to the caller even though an error
		679	occurred, but with no indication whether it has done so or not (yes, it's
		680	even documented that way) - deadly for edge-triggered interfaces where you
		681	absolutely have to know whether an event occurred or not because you have
		682	to re-arm the watcher.
		683
		684	Fortunately libev seems to be able to work around these idiocies.
		685
		686	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		687	C<EVBACKEND_POLL>.
		688
		689	=item C<EVBACKEND_ALL>
		690
		691	Try all backends (even potentially broken ones that wouldn't be tried
		692	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		693	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		694
		695	It is definitely not recommended to use this flag, use whatever
		696	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		697	at all.
		698
		699	=item C<EVBACKEND_MASK>
		700
		701	Not a backend at all, but a mask to select all backend bits from a
		702	C<flags> value, in case you want to mask out any backends from a flags
		703	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
158		704
159	=back	705	=back
160		706
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	707	If one or more of the backend flags are or'ed into the flags value,
		708	then only these backends will be tried (in the reverse order as listed
		709	here). If none are specified, all backends in C<ev_recommended_backends
		710	()> will be tried.
162		711
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	712	Example: Try to create a event loop that uses epoll and nothing else.
164	always distinct from the default loop. Unlike the default loop, it cannot
165	handle signal and child watchers, and attempts to do so will be greeted by
166	undefined behaviour (or a failed assertion if assertions are enabled).
167		713
168	=item ev_default_destroy ()	714	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		715	if (!epoller)
		716	fatal ("no epoll found here, maybe it hides under your chair");
169		717
170	Destroys the default loop again (frees all memory and kernel state	718	Example: Use whatever libev has to offer, but make sure that kqueue is
171	etc.). This stops all registered event watchers (by not touching them in	719	used if available.
172	any way whatsoever, although you cannot rely on this :).	720
		721	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		722
		723	Example: Similarly, on linux, you mgiht want to take advantage of the
		724	linux aio backend if possible, but fall back to something else if that
		725	isn't available.
		726
		727	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
173		728
174	=item ev_loop_destroy (loop)	729	=item ev_loop_destroy (loop)
175		730
176	Like C<ev_default_destroy>, but destroys an event loop created by an	731	Destroys an event loop object (frees all memory and kernel state
177	earlier call to C<ev_loop_new>.	732	etc.). None of the active event watchers will be stopped in the normal
		733	sense, so e.g. C<ev_is_active> might still return true. It is your
		734	responsibility to either stop all watchers cleanly yourself I<before>
		735	calling this function, or cope with the fact afterwards (which is usually
		736	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		737	for example).
178		738
179	=item ev_default_fork ()	739	Note that certain global state, such as signal state (and installed signal
		740	handlers), will not be freed by this function, and related watchers (such
		741	as signal and child watchers) would need to be stopped manually.
180		742
		743	This function is normally used on loop objects allocated by
		744	C<ev_loop_new>, but it can also be used on the default loop returned by
		745	C<ev_default_loop>, in which case it is not thread-safe.
		746
		747	Note that it is not advisable to call this function on the default loop
		748	except in the rare occasion where you really need to free its resources.
		749	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		750	and C<ev_loop_destroy>.
		751
		752	=item ev_loop_fork (loop)
		753
		754	This function sets a flag that causes subsequent C<ev_run> iterations
181	This function reinitialises the kernel state for backends that have	755	to reinitialise the kernel state for backends that have one. Despite
182	one. Despite the name, you can call it anytime, but it makes most sense	756	the name, you can call it anytime you are allowed to start or stop
183	after forking, in either the parent or child process (or both, but that	757	watchers (except inside an C<ev_prepare> callback), but it makes most
184	again makes little sense).	758	sense after forking, in the child process. You I<must> call it (or use
		759	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
185		760
186	You I<must> call this function after forking if and only if you want to	761	In addition, if you want to reuse a loop (via this function or
187	use the event library in both processes. If you just fork+exec, you don't	762	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
188	have to call it.	763
		764	Again, you I<have> to call it on I<any> loop that you want to re-use after
		765	a fork, I<even if you do not plan to use the loop in the parent>. This is
		766	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		767	during fork.
		768
		769	On the other hand, you only need to call this function in the child
		770	process if and only if you want to use the event loop in the child. If
		771	you just fork+exec or create a new loop in the child, you don't have to
		772	call it at all (in fact, C<epoll> is so badly broken that it makes a
		773	difference, but libev will usually detect this case on its own and do a
		774	costly reset of the backend).
189		775
190	The function itself is quite fast and it's usually not a problem to call	776	The function itself is quite fast and it's usually not a problem to call
191	it just in case after a fork. To make this easy, the function will fit in	777	it just in case after a fork.
192	quite nicely into a call to C<pthread_atfork>:
193		778
		779	Example: Automate calling C<ev_loop_fork> on the default loop when
		780	using pthreads.
		781
		782	static void
		783	post_fork_child (void)
		784	{
		785	ev_loop_fork (EV_DEFAULT);
		786	}
		787
		788	...
194	pthread_atfork (0, 0, ev_default_fork);	789	pthread_atfork (0, 0, post_fork_child);
195		790
196	=item ev_loop_fork (loop)	791	=item int ev_is_default_loop (loop)
197		792
198	Like C<ev_default_fork>, but acts on an event loop created by	793	Returns true when the given loop is, in fact, the default loop, and false
199	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	794	otherwise.
200	after fork, and how you do this is entirely your own problem.
201		795
		796	=item unsigned int ev_iteration (loop)
		797
		798	Returns the current iteration count for the event loop, which is identical
		799	to the number of times libev did poll for new events. It starts at C<0>
		800	and happily wraps around with enough iterations.
		801
		802	This value can sometimes be useful as a generation counter of sorts (it
		803	"ticks" the number of loop iterations), as it roughly corresponds with
		804	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		805	prepare and check phases.
		806
202	=item unsigned int ev_method (loop)	807	=item unsigned int ev_depth (loop)
203		808
		809	Returns the number of times C<ev_run> was entered minus the number of
		810	times C<ev_run> was exited normally, in other words, the recursion depth.
		811
		812	Outside C<ev_run>, this number is zero. In a callback, this number is
		813	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		814	in which case it is higher.
		815
		816	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		817	throwing an exception etc.), doesn't count as "exit" - consider this
		818	as a hint to avoid such ungentleman-like behaviour unless it's really
		819	convenient, in which case it is fully supported.
		820
		821	=item unsigned int ev_backend (loop)
		822
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	823	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	824	use.
206		825
207	=item ev_tstamp ev_now (loop)	826	=item ev_tstamp ev_now (loop)
208		827
209	Returns the current "event loop time", which is the time the event loop	828	Returns the current "event loop time", which is the time the event loop
210	got events and started processing them. This timestamp does not change	829	received events and started processing them. This timestamp does not
211	as long as callbacks are being processed, and this is also the base time	830	change as long as callbacks are being processed, and this is also the base
212	used for relative timers. You can treat it as the timestamp of the event	831	time used for relative timers. You can treat it as the timestamp of the
213	occuring (or more correctly, the mainloop finding out about it).	832	event occurring (or more correctly, libev finding out about it).
214		833
		834	=item ev_now_update (loop)
		835
		836	Establishes the current time by querying the kernel, updating the time
		837	returned by C<ev_now ()> in the progress. This is a costly operation and
		838	is usually done automatically within C<ev_run ()>.
		839
		840	This function is rarely useful, but when some event callback runs for a
		841	very long time without entering the event loop, updating libev's idea of
		842	the current time is a good idea.
		843
		844	See also L</The special problem of time updates> in the C<ev_timer> section.
		845
		846	=item ev_suspend (loop)
		847
		848	=item ev_resume (loop)
		849
		850	These two functions suspend and resume an event loop, for use when the
		851	loop is not used for a while and timeouts should not be processed.
		852
		853	A typical use case would be an interactive program such as a game: When
		854	the user presses C<^Z> to suspend the game and resumes it an hour later it
		855	would be best to handle timeouts as if no time had actually passed while
		856	the program was suspended. This can be achieved by calling C<ev_suspend>
		857	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		858	C<ev_resume> directly afterwards to resume timer processing.
		859
		860	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		861	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		862	will be rescheduled (that is, they will lose any events that would have
		863	occurred while suspended).
		864
		865	After calling C<ev_suspend> you B<must not> call I<any> function on the
		866	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		867	without a previous call to C<ev_suspend>.
		868
		869	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		870	event loop time (see C<ev_now_update>).
		871
215	=item ev_loop (loop, int flags)	872	=item bool ev_run (loop, int flags)
216		873
217	Finally, this is it, the event handler. This function usually is called	874	Finally, this is it, the event handler. This function usually is called
218	after you initialised all your watchers and you want to start handling	875	after you have initialised all your watchers and you want to start
219	events.	876	handling events. It will ask the operating system for any new events, call
		877	the watcher callbacks, and then repeat the whole process indefinitely: This
		878	is why event loops are called I<loops>.
220		879
221	If the flags argument is specified as 0, it will not return until either	880	If the flags argument is specified as C<0>, it will keep handling events
222	no event watchers are active anymore or C<ev_unloop> was called.	881	until either no event watchers are active anymore or C<ev_break> was
		882	called.
223		883
		884	The return value is false if there are no more active watchers (which
		885	usually means "all jobs done" or "deadlock"), and true in all other cases
		886	(which usually means " you should call C<ev_run> again").
		887
		888	Please note that an explicit C<ev_break> is usually better than
		889	relying on all watchers to be stopped when deciding when a program has
		890	finished (especially in interactive programs), but having a program
		891	that automatically loops as long as it has to and no longer by virtue
		892	of relying on its watchers stopping correctly, that is truly a thing of
		893	beauty.
		894
		895	This function is I<mostly> exception-safe - you can break out of a
		896	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		897	exception and so on. This does not decrement the C<ev_depth> value, nor
		898	will it clear any outstanding C<EVBREAK_ONE> breaks.
		899
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	900	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
225	those events and any outstanding ones, but will not block your process in	901	those events and any already outstanding ones, but will not wait and
226	case there are no events and will return after one iteration of the loop.	902	block your process in case there are no events and will return after one
		903	iteration of the loop. This is sometimes useful to poll and handle new
		904	events while doing lengthy calculations, to keep the program responsive.
227		905
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	906	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
229	neccessary) and will handle those and any outstanding ones. It will block	907	necessary) and will handle those and any already outstanding ones. It
230	your process until at least one new event arrives, and will return after	908	will block your process until at least one new event arrives (which could
		909	be an event internal to libev itself, so there is no guarantee that a
		910	user-registered callback will be called), and will return after one
231	one iteration of the loop.	911	iteration of the loop.
232		912
233	This flags value could be used to implement alternative looping	913	This is useful if you are waiting for some external event in conjunction
234	constructs, but the C<prepare> and C<check> watchers provide a better and	914	with something not expressible using other libev watchers (i.e. "roll your
235	more generic mechanism.	915	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		916	usually a better approach for this kind of thing.
236		917
		918	Here are the gory details of what C<ev_run> does (this is for your
		919	understanding, not a guarantee that things will work exactly like this in
		920	future versions):
		921
		922	- Increment loop depth.
		923	- Reset the ev_break status.
		924	- Before the first iteration, call any pending watchers.
		925	LOOP:
		926	- If EVFLAG_FORKCHECK was used, check for a fork.
		927	- If a fork was detected (by any means), queue and call all fork watchers.
		928	- Queue and call all prepare watchers.
		929	- If ev_break was called, goto FINISH.
		930	- If we have been forked, detach and recreate the kernel state
		931	as to not disturb the other process.
		932	- Update the kernel state with all outstanding changes.
		933	- Update the "event loop time" (ev_now ()).
		934	- Calculate for how long to sleep or block, if at all
		935	(active idle watchers, EVRUN_NOWAIT or not having
		936	any active watchers at all will result in not sleeping).
		937	- Sleep if the I/O and timer collect interval say so.
		938	- Increment loop iteration counter.
		939	- Block the process, waiting for any events.
		940	- Queue all outstanding I/O (fd) events.
		941	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		942	- Queue all expired timers.
		943	- Queue all expired periodics.
		944	- Queue all idle watchers with priority higher than that of pending events.
		945	- Queue all check watchers.
		946	- Call all queued watchers in reverse order (i.e. check watchers first).
		947	Signals and child watchers are implemented as I/O watchers, and will
		948	be handled here by queueing them when their watcher gets executed.
		949	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
		950	were used, or there are no active watchers, goto FINISH, otherwise
		951	continue with step LOOP.
		952	FINISH:
		953	- Reset the ev_break status iff it was EVBREAK_ONE.
		954	- Decrement the loop depth.
		955	- Return.
		956
		957	Example: Queue some jobs and then loop until no events are outstanding
		958	anymore.
		959
		960	... queue jobs here, make sure they register event watchers as long
		961	... as they still have work to do (even an idle watcher will do..)
		962	ev_run (my_loop, 0);
		963	... jobs done or somebody called break. yeah!
		964
237	=item ev_unloop (loop, how)	965	=item ev_break (loop, how)
238		966
239	Can be used to make a call to C<ev_loop> return early (but only after it	967	Can be used to make a call to C<ev_run> return early (but only after it
240	has processed all outstanding events). The C<how> argument must be either	968	has processed all outstanding events). The C<how> argument must be either
241	C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or	969	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
242	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	970	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		971
		972	This "break state" will be cleared on the next call to C<ev_run>.
		973
		974	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		975	which case it will have no effect.
243		976
244	=item ev_ref (loop)	977	=item ev_ref (loop)
245		978
246	=item ev_unref (loop)	979	=item ev_unref (loop)
247		980
248	Ref/unref can be used to add or remove a reference count on the event	981	Ref/unref can be used to add or remove a reference count on the event
249	loop: Every watcher keeps one reference, and as long as the reference	982	loop: Every watcher keeps one reference, and as long as the reference
250	count is nonzero, C<ev_loop> will not return on its own. If you have	983	count is nonzero, C<ev_run> will not return on its own.
251	a watcher you never unregister that should not keep C<ev_loop> from	984
252	returning, ev_unref() after starting, and ev_ref() before stopping it. For	985	This is useful when you have a watcher that you never intend to
		986	unregister, but that nevertheless should not keep C<ev_run> from
		987	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		988	before stopping it.
		989
253	example, libev itself uses this for its internal signal pipe: It is not	990	As an example, libev itself uses this for its internal signal pipe: It
254	visible to the libev user and should not keep C<ev_loop> from exiting if	991	is not visible to the libev user and should not keep C<ev_run> from
255	no event watchers registered by it are active. It is also an excellent	992	exiting if no event watchers registered by it are active. It is also an
256	way to do this for generic recurring timers or from within third-party	993	excellent way to do this for generic recurring timers or from within
257	libraries. Just remember to I<unref after start> and I<ref before stop>.	994	third-party libraries. Just remember to I<unref after start> and I<ref
		995	before stop> (but only if the watcher wasn't active before, or was active
		996	before, respectively. Note also that libev might stop watchers itself
		997	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		998	in the callback).
		999
		1000	Example: Create a signal watcher, but keep it from keeping C<ev_run>
		1001	running when nothing else is active.
		1002
		1003	ev_signal exitsig;
		1004	ev_signal_init (&exitsig, sig_cb, SIGINT);
		1005	ev_signal_start (loop, &exitsig);
		1006	ev_unref (loop);
		1007
		1008	Example: For some weird reason, unregister the above signal handler again.
		1009
		1010	ev_ref (loop);
		1011	ev_signal_stop (loop, &exitsig);
		1012
		1013	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		1014
		1015	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		1016
		1017	These advanced functions influence the time that libev will spend waiting
		1018	for events. Both time intervals are by default C<0>, meaning that libev
		1019	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		1020	latency.
		1021
		1022	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		1023	allows libev to delay invocation of I/O and timer/periodic callbacks
		1024	to increase efficiency of loop iterations (or to increase power-saving
		1025	opportunities).
		1026
		1027	The idea is that sometimes your program runs just fast enough to handle
		1028	one (or very few) event(s) per loop iteration. While this makes the
		1029	program responsive, it also wastes a lot of CPU time to poll for new
		1030	events, especially with backends like C<select ()> which have a high
		1031	overhead for the actual polling but can deliver many events at once.
		1032
		1033	By setting a higher I<io collect interval> you allow libev to spend more
		1034	time collecting I/O events, so you can handle more events per iteration,
		1035	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		1036	C<ev_timer>) will not be affected. Setting this to a non-null value will
		1037	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		1038	sleep time ensures that libev will not poll for I/O events more often then
		1039	once per this interval, on average (as long as the host time resolution is
		1040	good enough).
		1041
		1042	Likewise, by setting a higher I<timeout collect interval> you allow libev
		1043	to spend more time collecting timeouts, at the expense of increased
		1044	latency/jitter/inexactness (the watcher callback will be called
		1045	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		1046	value will not introduce any overhead in libev.
		1047
		1048	Many (busy) programs can usually benefit by setting the I/O collect
		1049	interval to a value near C<0.1> or so, which is often enough for
		1050	interactive servers (of course not for games), likewise for timeouts. It
		1051	usually doesn't make much sense to set it to a lower value than C<0.01>,
		1052	as this approaches the timing granularity of most systems. Note that if
		1053	you do transactions with the outside world and you can't increase the
		1054	parallelity, then this setting will limit your transaction rate (if you
		1055	need to poll once per transaction and the I/O collect interval is 0.01,
		1056	then you can't do more than 100 transactions per second).
		1057
		1058	Setting the I<timeout collect interval> can improve the opportunity for
		1059	saving power, as the program will "bundle" timer callback invocations that
		1060	are "near" in time together, by delaying some, thus reducing the number of
		1061	times the process sleeps and wakes up again. Another useful technique to
		1062	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		1063	they fire on, say, one-second boundaries only.
		1064
		1065	Example: we only need 0.1s timeout granularity, and we wish not to poll
		1066	more often than 100 times per second:
		1067
		1068	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		1069	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		1070
		1071	=item ev_invoke_pending (loop)
		1072
		1073	This call will simply invoke all pending watchers while resetting their
		1074	pending state. Normally, C<ev_run> does this automatically when required,
		1075	but when overriding the invoke callback this call comes handy. This
		1076	function can be invoked from a watcher - this can be useful for example
		1077	when you want to do some lengthy calculation and want to pass further
		1078	event handling to another thread (you still have to make sure only one
		1079	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1080
		1081	=item int ev_pending_count (loop)
		1082
		1083	Returns the number of pending watchers - zero indicates that no watchers
		1084	are pending.
		1085
		1086	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1087
		1088	This overrides the invoke pending functionality of the loop: Instead of
		1089	invoking all pending watchers when there are any, C<ev_run> will call
		1090	this callback instead. This is useful, for example, when you want to
		1091	invoke the actual watchers inside another context (another thread etc.).
		1092
		1093	If you want to reset the callback, use C<ev_invoke_pending> as new
		1094	callback.
		1095
		1096	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
		1097
		1098	Sometimes you want to share the same loop between multiple threads. This
		1099	can be done relatively simply by putting mutex_lock/unlock calls around
		1100	each call to a libev function.
		1101
		1102	However, C<ev_run> can run an indefinite time, so it is not feasible
		1103	to wait for it to return. One way around this is to wake up the event
		1104	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1105	I<release> and I<acquire> callbacks on the loop.
		1106
		1107	When set, then C<release> will be called just before the thread is
		1108	suspended waiting for new events, and C<acquire> is called just
		1109	afterwards.
		1110
		1111	Ideally, C<release> will just call your mutex_unlock function, and
		1112	C<acquire> will just call the mutex_lock function again.
		1113
		1114	While event loop modifications are allowed between invocations of
		1115	C<release> and C<acquire> (that's their only purpose after all), no
		1116	modifications done will affect the event loop, i.e. adding watchers will
		1117	have no effect on the set of file descriptors being watched, or the time
		1118	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1119	to take note of any changes you made.
		1120
		1121	In theory, threads executing C<ev_run> will be async-cancel safe between
		1122	invocations of C<release> and C<acquire>.
		1123
		1124	See also the locking example in the C<THREADS> section later in this
		1125	document.
		1126
		1127	=item ev_set_userdata (loop, void *data)
		1128
		1129	=item void *ev_userdata (loop)
		1130
		1131	Set and retrieve a single C<void *> associated with a loop. When
		1132	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1133	C<0>.
		1134
		1135	These two functions can be used to associate arbitrary data with a loop,
		1136	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1137	C<acquire> callbacks described above, but of course can be (ab-)used for
		1138	any other purpose as well.
		1139
		1140	=item ev_verify (loop)
		1141
		1142	This function only does something when C<EV_VERIFY> support has been
		1143	compiled in, which is the default for non-minimal builds. It tries to go
		1144	through all internal structures and checks them for validity. If anything
		1145	is found to be inconsistent, it will print an error message to standard
		1146	error and call C<abort ()>.
		1147
		1148	This can be used to catch bugs inside libev itself: under normal
		1149	circumstances, this function will never abort as of course libev keeps its
		1150	data structures consistent.
258		1151
259	=back	1152	=back
260		1153
		1154
261	=head1 ANATOMY OF A WATCHER	1155	=head1 ANATOMY OF A WATCHER
262		1156
		1157	In the following description, uppercase C<TYPE> in names stands for the
		1158	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1159	watchers and C<ev_io_start> for I/O watchers.
		1160
263	A watcher is a structure that you create and register to record your	1161	A watcher is an opaque structure that you allocate and register to record
264	interest in some event. For instance, if you want to wait for STDIN to	1162	your interest in some event. To make a concrete example, imagine you want
265	become readable, you would create an C<ev_io> watcher for that:	1163	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1164	for that:
266		1165
267	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1166	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
268	{	1167	{
269	ev_io_stop (w);	1168	ev_io_stop (w);
270	ev_unloop (loop, EVUNLOOP_ALL);	1169	ev_break (loop, EVBREAK_ALL);
271	}	1170	}
272		1171
273	struct ev_loop *loop = ev_default_loop (0);	1172	struct ev_loop *loop = ev_default_loop (0);
		1173
274	struct ev_io stdin_watcher;	1174	ev_io stdin_watcher;
		1175
275	ev_init (&stdin_watcher, my_cb);	1176	ev_init (&stdin_watcher, my_cb);
276	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1177	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
277	ev_io_start (loop, &stdin_watcher);	1178	ev_io_start (loop, &stdin_watcher);
		1179
278	ev_loop (loop, 0);	1180	ev_run (loop, 0);
279		1181
280	As you can see, you are responsible for allocating the memory for your	1182	As you can see, you are responsible for allocating the memory for your
281	watcher structures (and it is usually a bad idea to do this on the stack,	1183	watcher structures (and it is I<usually> a bad idea to do this on the
282	although this can sometimes be quite valid).	1184	stack).
283		1185
		1186	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1187	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1188
284	Each watcher structure must be initialised by a call to C<ev_init	1189	Each watcher structure must be initialised by a call to C<ev_init (watcher
285	(watcher *, callback)>, which expects a callback to be provided. This	1190	*, callback)>, which expects a callback to be provided. This callback is
286	callback gets invoked each time the event occurs (or, in the case of io	1191	invoked each time the event occurs (or, in the case of I/O watchers, each
287	watchers, each time the event loop detects that the file descriptor given	1192	time the event loop detects that the file descriptor given is readable
288	is readable and/or writable).	1193	and/or writable).
289		1194
290	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1195	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
291	with arguments specific to this watcher type. There is also a macro	1196	macro to configure it, with arguments specific to the watcher type. There
292	to combine initialisation and setting in one call: C<< ev_<type>_init	1197	is also a macro to combine initialisation and setting in one call: C<<
293	(watcher *, callback, ...) >>.	1198	ev_TYPE_init (watcher *, callback, ...) >>.
294		1199
295	To make the watcher actually watch out for events, you have to start it	1200	To make the watcher actually watch out for events, you have to start it
296	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1201	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
297	*) >>), and you can stop watching for events at any time by calling the	1202	*) >>), and you can stop watching for events at any time by calling the
298	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1203	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
299		1204
300	As long as your watcher is active (has been started but not stopped) you	1205	As long as your watcher is active (has been started but not stopped) you
301	must not touch the values stored in it. Most specifically you must never	1206	must not touch the values stored in it. Most specifically you must never
302	reinitialise it or call its set method.	1207	reinitialise it or call its C<ev_TYPE_set> macro.
303
304	You can check whether an event is active by calling the C<ev_is_active
305	(watcher *)> macro. To see whether an event is outstanding (but the
306	callback for it has not been called yet) you can use the C<ev_is_pending
307	(watcher *)> macro.
308		1208
309	Each and every callback receives the event loop pointer as first, the	1209	Each and every callback receives the event loop pointer as first, the
310	registered watcher structure as second, and a bitset of received events as	1210	registered watcher structure as second, and a bitset of received events as
311	third argument.	1211	third argument.
312		1212
…		…
321	=item C<EV_WRITE>	1221	=item C<EV_WRITE>
322		1222
323	The file descriptor in the C<ev_io> watcher has become readable and/or	1223	The file descriptor in the C<ev_io> watcher has become readable and/or
324	writable.	1224	writable.
325		1225
326	=item C<EV_TIMEOUT>	1226	=item C<EV_TIMER>
327		1227
328	The C<ev_timer> watcher has timed out.	1228	The C<ev_timer> watcher has timed out.
329		1229
330	=item C<EV_PERIODIC>	1230	=item C<EV_PERIODIC>
331		1231
…		…
337		1237
338	=item C<EV_CHILD>	1238	=item C<EV_CHILD>
339		1239
340	The pid specified in the C<ev_child> watcher has received a status change.	1240	The pid specified in the C<ev_child> watcher has received a status change.
341		1241
		1242	=item C<EV_STAT>
		1243
		1244	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1245
342	=item C<EV_IDLE>	1246	=item C<EV_IDLE>
343		1247
344	The C<ev_idle> watcher has determined that you have nothing better to do.	1248	The C<ev_idle> watcher has determined that you have nothing better to do.
345		1249
346	=item C<EV_PREPARE>	1250	=item C<EV_PREPARE>
347		1251
348	=item C<EV_CHECK>	1252	=item C<EV_CHECK>
349		1253
350	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1254	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
351	to gather new events, and all C<ev_check> watchers are invoked just after	1255	gather new events, and all C<ev_check> watchers are queued (not invoked)
352	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1256	just after C<ev_run> has gathered them, but before it queues any callbacks
		1257	for any received events. That means C<ev_prepare> watchers are the last
		1258	watchers invoked before the event loop sleeps or polls for new events, and
		1259	C<ev_check> watchers will be invoked before any other watchers of the same
		1260	or lower priority within an event loop iteration.
		1261
353	received events. Callbacks of both watcher types can start and stop as	1262	Callbacks of both watcher types can start and stop as many watchers as
354	many watchers as they want, and all of them will be taken into account	1263	they want, and all of them will be taken into account (for example, a
355	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1264	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
356	C<ev_loop> from blocking).	1265	blocking).
		1266
		1267	=item C<EV_EMBED>
		1268
		1269	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1270
		1271	=item C<EV_FORK>
		1272
		1273	The event loop has been resumed in the child process after fork (see
		1274	C<ev_fork>).
		1275
		1276	=item C<EV_CLEANUP>
		1277
		1278	The event loop is about to be destroyed (see C<ev_cleanup>).
		1279
		1280	=item C<EV_ASYNC>
		1281
		1282	The given async watcher has been asynchronously notified (see C<ev_async>).
		1283
		1284	=item C<EV_CUSTOM>
		1285
		1286	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1287	by libev users to signal watchers (e.g. via C<ev_feed_event>).
357		1288
358	=item C<EV_ERROR>	1289	=item C<EV_ERROR>
359		1290
360	An unspecified error has occured, the watcher has been stopped. This might	1291	An unspecified error has occurred, the watcher has been stopped. This might
361	happen because the watcher could not be properly started because libev	1292	happen because the watcher could not be properly started because libev
362	ran out of memory, a file descriptor was found to be closed or any other	1293	ran out of memory, a file descriptor was found to be closed or any other
		1294	problem. Libev considers these application bugs.
		1295
363	problem. You best act on it by reporting the problem and somehow coping	1296	You best act on it by reporting the problem and somehow coping with the
364	with the watcher being stopped.	1297	watcher being stopped. Note that well-written programs should not receive
		1298	an error ever, so when your watcher receives it, this usually indicates a
		1299	bug in your program.
365		1300
366	Libev will usually signal a few "dummy" events together with an error,	1301	Libev will usually signal a few "dummy" events together with an error, for
367	for example it might indicate that a fd is readable or writable, and if	1302	example it might indicate that a fd is readable or writable, and if your
368	your callbacks is well-written it can just attempt the operation and cope	1303	callbacks is well-written it can just attempt the operation and cope with
369	with the error from read() or write(). This will not work in multithreaded	1304	the error from read() or write(). This will not work in multi-threaded
370	programs, though, so beware.	1305	programs, though, as the fd could already be closed and reused for another
		1306	thing, so beware.
371		1307
372	=back	1308	=back
373		1309
374	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1310	=head2 GENERIC WATCHER FUNCTIONS
375		1311
376	Each watcher has, by default, a member C<void *data> that you can change	1312	=over 4
377	and read at any time, libev will completely ignore it. This can be used
378	to associate arbitrary data with your watcher. If you need more data and
379	don't want to allocate memory and store a pointer to it in that data
380	member, you can also "subclass" the watcher type and provide your own
381	data:
382		1313
383	struct my_io	1314	=item C<ev_init> (ev_TYPE *watcher, callback)
		1315
		1316	This macro initialises the generic portion of a watcher. The contents
		1317	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1318	the generic parts of the watcher are initialised, you I<need> to call
		1319	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1320	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1321	which rolls both calls into one.
		1322
		1323	You can reinitialise a watcher at any time as long as it has been stopped
		1324	(or never started) and there are no pending events outstanding.
		1325
		1326	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1327	int revents)>.
		1328
		1329	Example: Initialise an C<ev_io> watcher in two steps.
		1330
		1331	ev_io w;
		1332	ev_init (&w, my_cb);
		1333	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1334
		1335	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1336
		1337	This macro initialises the type-specific parts of a watcher. You need to
		1338	call C<ev_init> at least once before you call this macro, but you can
		1339	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1340	macro on a watcher that is active (it can be pending, however, which is a
		1341	difference to the C<ev_init> macro).
		1342
		1343	Although some watcher types do not have type-specific arguments
		1344	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1345
		1346	See C<ev_init>, above, for an example.
		1347
		1348	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1349
		1350	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1351	calls into a single call. This is the most convenient method to initialise
		1352	a watcher. The same limitations apply, of course.
		1353
		1354	Example: Initialise and set an C<ev_io> watcher in one step.
		1355
		1356	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1357
		1358	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1359
		1360	Starts (activates) the given watcher. Only active watchers will receive
		1361	events. If the watcher is already active nothing will happen.
		1362
		1363	Example: Start the C<ev_io> watcher that is being abused as example in this
		1364	whole section.
		1365
		1366	ev_io_start (EV_DEFAULT_UC, &w);
		1367
		1368	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1369
		1370	Stops the given watcher if active, and clears the pending status (whether
		1371	the watcher was active or not).
		1372
		1373	It is possible that stopped watchers are pending - for example,
		1374	non-repeating timers are being stopped when they become pending - but
		1375	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1376	pending. If you want to free or reuse the memory used by the watcher it is
		1377	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1378
		1379	=item bool ev_is_active (ev_TYPE *watcher)
		1380
		1381	Returns a true value iff the watcher is active (i.e. it has been started
		1382	and not yet been stopped). As long as a watcher is active you must not modify
		1383	it.
		1384
		1385	=item bool ev_is_pending (ev_TYPE *watcher)
		1386
		1387	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1388	events but its callback has not yet been invoked). As long as a watcher
		1389	is pending (but not active) you must not call an init function on it (but
		1390	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1391	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1392	it).
		1393
		1394	=item callback ev_cb (ev_TYPE *watcher)
		1395
		1396	Returns the callback currently set on the watcher.
		1397
		1398	=item ev_set_cb (ev_TYPE *watcher, callback)
		1399
		1400	Change the callback. You can change the callback at virtually any time
		1401	(modulo threads).
		1402
		1403	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1404
		1405	=item int ev_priority (ev_TYPE *watcher)
		1406
		1407	Set and query the priority of the watcher. The priority is a small
		1408	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1409	(default: C<-2>). Pending watchers with higher priority will be invoked
		1410	before watchers with lower priority, but priority will not keep watchers
		1411	from being executed (except for C<ev_idle> watchers).
		1412
		1413	If you need to suppress invocation when higher priority events are pending
		1414	you need to look at C<ev_idle> watchers, which provide this functionality.
		1415
		1416	You I<must not> change the priority of a watcher as long as it is active or
		1417	pending.
		1418
		1419	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1420	fine, as long as you do not mind that the priority value you query might
		1421	or might not have been clamped to the valid range.
		1422
		1423	The default priority used by watchers when no priority has been set is
		1424	always C<0>, which is supposed to not be too high and not be too low :).
		1425
		1426	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1427	priorities.
		1428
		1429	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1430
		1431	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1432	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1433	can deal with that fact, as both are simply passed through to the
		1434	callback.
		1435
		1436	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1437
		1438	If the watcher is pending, this function clears its pending status and
		1439	returns its C<revents> bitset (as if its callback was invoked). If the
		1440	watcher isn't pending it does nothing and returns C<0>.
		1441
		1442	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1443	callback to be invoked, which can be accomplished with this function.
		1444
		1445	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1446
		1447	Feeds the given event set into the event loop, as if the specified event
		1448	had happened for the specified watcher (which must be a pointer to an
		1449	initialised but not necessarily started event watcher). Obviously you must
		1450	not free the watcher as long as it has pending events.
		1451
		1452	Stopping the watcher, letting libev invoke it, or calling
		1453	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1454	not started in the first place.
		1455
		1456	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1457	functions that do not need a watcher.
		1458
		1459	=back
		1460
		1461	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1462	OWN COMPOSITE WATCHERS> idioms.
		1463
		1464	=head2 WATCHER STATES
		1465
		1466	There are various watcher states mentioned throughout this manual -
		1467	active, pending and so on. In this section these states and the rules to
		1468	transition between them will be described in more detail - and while these
		1469	rules might look complicated, they usually do "the right thing".
		1470
		1471	=over 4
		1472
		1473	=item initialised
		1474
		1475	Before a watcher can be registered with the event loop it has to be
		1476	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1477	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1478
		1479	In this state it is simply some block of memory that is suitable for
		1480	use in an event loop. It can be moved around, freed, reused etc. at
		1481	will - as long as you either keep the memory contents intact, or call
		1482	C<ev_TYPE_init> again.
		1483
		1484	=item started/running/active
		1485
		1486	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1487	property of the event loop, and is actively waiting for events. While in
		1488	this state it cannot be accessed (except in a few documented ways), moved,
		1489	freed or anything else - the only legal thing is to keep a pointer to it,
		1490	and call libev functions on it that are documented to work on active watchers.
		1491
		1492	=item pending
		1493
		1494	If a watcher is active and libev determines that an event it is interested
		1495	in has occurred (such as a timer expiring), it will become pending. It will
		1496	stay in this pending state until either it is stopped or its callback is
		1497	about to be invoked, so it is not normally pending inside the watcher
		1498	callback.
		1499
		1500	The watcher might or might not be active while it is pending (for example,
		1501	an expired non-repeating timer can be pending but no longer active). If it
		1502	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1503	but it is still property of the event loop at this time, so cannot be
		1504	moved, freed or reused. And if it is active the rules described in the
		1505	previous item still apply.
		1506
		1507	It is also possible to feed an event on a watcher that is not active (e.g.
		1508	via C<ev_feed_event>), in which case it becomes pending without being
		1509	active.
		1510
		1511	=item stopped
		1512
		1513	A watcher can be stopped implicitly by libev (in which case it might still
		1514	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1515	latter will clear any pending state the watcher might be in, regardless
		1516	of whether it was active or not, so stopping a watcher explicitly before
		1517	freeing it is often a good idea.
		1518
		1519	While stopped (and not pending) the watcher is essentially in the
		1520	initialised state, that is, it can be reused, moved, modified in any way
		1521	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1522	it again).
		1523
		1524	=back
		1525
		1526	=head2 WATCHER PRIORITY MODELS
		1527
		1528	Many event loops support I<watcher priorities>, which are usually small
		1529	integers that influence the ordering of event callback invocation
		1530	between watchers in some way, all else being equal.
		1531
		1532	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1533	description for the more technical details such as the actual priority
		1534	range.
		1535
		1536	There are two common ways how these these priorities are being interpreted
		1537	by event loops:
		1538
		1539	In the more common lock-out model, higher priorities "lock out" invocation
		1540	of lower priority watchers, which means as long as higher priority
		1541	watchers receive events, lower priority watchers are not being invoked.
		1542
		1543	The less common only-for-ordering model uses priorities solely to order
		1544	callback invocation within a single event loop iteration: Higher priority
		1545	watchers are invoked before lower priority ones, but they all get invoked
		1546	before polling for new events.
		1547
		1548	Libev uses the second (only-for-ordering) model for all its watchers
		1549	except for idle watchers (which use the lock-out model).
		1550
		1551	The rationale behind this is that implementing the lock-out model for
		1552	watchers is not well supported by most kernel interfaces, and most event
		1553	libraries will just poll for the same events again and again as long as
		1554	their callbacks have not been executed, which is very inefficient in the
		1555	common case of one high-priority watcher locking out a mass of lower
		1556	priority ones.
		1557
		1558	Static (ordering) priorities are most useful when you have two or more
		1559	watchers handling the same resource: a typical usage example is having an
		1560	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1561	timeouts. Under load, data might be received while the program handles
		1562	other jobs, but since timers normally get invoked first, the timeout
		1563	handler will be executed before checking for data. In that case, giving
		1564	the timer a lower priority than the I/O watcher ensures that I/O will be
		1565	handled first even under adverse conditions (which is usually, but not
		1566	always, what you want).
		1567
		1568	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1569	will only be executed when no same or higher priority watchers have
		1570	received events, they can be used to implement the "lock-out" model when
		1571	required.
		1572
		1573	For example, to emulate how many other event libraries handle priorities,
		1574	you can associate an C<ev_idle> watcher to each such watcher, and in
		1575	the normal watcher callback, you just start the idle watcher. The real
		1576	processing is done in the idle watcher callback. This causes libev to
		1577	continuously poll and process kernel event data for the watcher, but when
		1578	the lock-out case is known to be rare (which in turn is rare :), this is
		1579	workable.
		1580
		1581	Usually, however, the lock-out model implemented that way will perform
		1582	miserably under the type of load it was designed to handle. In that case,
		1583	it might be preferable to stop the real watcher before starting the
		1584	idle watcher, so the kernel will not have to process the event in case
		1585	the actual processing will be delayed for considerable time.
		1586
		1587	Here is an example of an I/O watcher that should run at a strictly lower
		1588	priority than the default, and which should only process data when no
		1589	other events are pending:
		1590
		1591	ev_idle idle; // actual processing watcher
		1592	ev_io io; // actual event watcher
		1593
		1594	static void
		1595	io_cb (EV_P_ ev_io *w, int revents)
384	{	1596	{
385	struct ev_io io;	1597	// stop the I/O watcher, we received the event, but
386	int otherfd;	1598	// are not yet ready to handle it.
387	void *somedata;	1599	ev_io_stop (EV_A_ w);
388	struct whatever *mostinteresting;	1600
		1601	// start the idle watcher to handle the actual event.
		1602	// it will not be executed as long as other watchers
		1603	// with the default priority are receiving events.
		1604	ev_idle_start (EV_A_ &idle);
389	}	1605	}
390		1606
391	And since your callback will be called with a pointer to the watcher, you	1607	static void
392	can cast it back to your own type:	1608	idle_cb (EV_P_ ev_idle *w, int revents)
393
394	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
395	{	1609	{
396	struct my_io *w = (struct my_io *)w_;	1610	// actual processing
397	...	1611	read (STDIN_FILENO, ...);
		1612
		1613	// have to start the I/O watcher again, as
		1614	// we have handled the event
		1615	ev_io_start (EV_P_ &io);
398	}	1616	}
399		1617
400	More interesting and less C-conformant ways of catsing your callback type	1618	// initialisation
401	have been omitted....	1619	ev_idle_init (&idle, idle_cb);
		1620	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1621	ev_io_start (EV_DEFAULT_ &io);
		1622
		1623	In the "real" world, it might also be beneficial to start a timer, so that
		1624	low-priority connections can not be locked out forever under load. This
		1625	enables your program to keep a lower latency for important connections
		1626	during short periods of high load, while not completely locking out less
		1627	important ones.
402		1628
403		1629
404	=head1 WATCHER TYPES	1630	=head1 WATCHER TYPES
405		1631
406	This section describes each watcher in detail, but will not repeat	1632	This section describes each watcher in detail, but will not repeat
407	information given in the last section.	1633	information given in the last section. Any initialisation/set macros,
		1634	functions and members specific to the watcher type are explained.
408		1635
		1636	Members are additionally marked with either I<[read-only]>, meaning that,
		1637	while the watcher is active, you can look at the member and expect some
		1638	sensible content, but you must not modify it (you can modify it while the
		1639	watcher is stopped to your hearts content), or I<[read-write]>, which
		1640	means you can expect it to have some sensible content while the watcher
		1641	is active, but you can also modify it. Modifying it may not do something
		1642	sensible or take immediate effect (or do anything at all), but libev will
		1643	not crash or malfunction in any way.
		1644
		1645
409	=head2 C<ev_io> - is this file descriptor readable or writable	1646	=head2 C<ev_io> - is this file descriptor readable or writable?
410		1647
411	I/O watchers check whether a file descriptor is readable or writable	1648	I/O watchers check whether a file descriptor is readable or writable
412	in each iteration of the event loop (This behaviour is called	1649	in each iteration of the event loop, or, more precisely, when reading
413	level-triggering because you keep receiving events as long as the	1650	would not block the process and writing would at least be able to write
414	condition persists. Remember you can stop the watcher if you don't want to	1651	some data. This behaviour is called level-triggering because you keep
415	act on the event and neither want to receive future events).	1652	receiving events as long as the condition persists. Remember you can stop
		1653	the watcher if you don't want to act on the event and neither want to
		1654	receive future events.
416		1655
417	In general you can register as many read and/or write event watchers oer	1656	In general you can register as many read and/or write event watchers per
418	fd as you want (as long as you don't confuse yourself). Setting all file	1657	fd as you want (as long as you don't confuse yourself). Setting all file
419	descriptors to non-blocking mode is also usually a good idea (but not	1658	descriptors to non-blocking mode is also usually a good idea (but not
420	required if you know what you are doing).	1659	required if you know what you are doing).
421		1660
422	You have to be careful with dup'ed file descriptors, though. Some backends	1661	Another thing you have to watch out for is that it is quite easy to
423	(the linux epoll backend is a notable example) cannot handle dup'ed file	1662	receive "spurious" readiness notifications, that is, your callback might
424	descriptors correctly if you register interest in two or more fds pointing	1663	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
425	to the same file/socket etc. description.	1664	because there is no data. It is very easy to get into this situation even
		1665	with a relatively standard program structure. Thus it is best to always
		1666	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
		1667	preferable to a program hanging until some data arrives.
426		1668
427	If you must do this, then force the use of a known-to-be-good backend	1669	If you cannot run the fd in non-blocking mode (for example you should
428	(at the time of this writing, this includes only EVMETHOD_SELECT and	1670	not play around with an Xlib connection), then you have to separately
429	EVMETHOD_POLL).	1671	re-test whether a file descriptor is really ready with a known-to-be good
		1672	interface such as poll (fortunately in the case of Xlib, it already does
		1673	this on its own, so its quite safe to use). Some people additionally
		1674	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1675	indefinitely.
		1676
		1677	But really, best use non-blocking mode.
		1678
		1679	=head3 The special problem of disappearing file descriptors
		1680
		1681	Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
		1682	a file descriptor (either due to calling C<close> explicitly or any other
		1683	means, such as C<dup2>). The reason is that you register interest in some
		1684	file descriptor, but when it goes away, the operating system will silently
		1685	drop this interest. If another file descriptor with the same number then
		1686	is registered with libev, there is no efficient way to see that this is,
		1687	in fact, a different file descriptor.
		1688
		1689	To avoid having to explicitly tell libev about such cases, libev follows
		1690	the following policy: Each time C<ev_io_set> is being called, libev
		1691	will assume that this is potentially a new file descriptor, otherwise
		1692	it is assumed that the file descriptor stays the same. That means that
		1693	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1694	descriptor even if the file descriptor number itself did not change.
		1695
		1696	This is how one would do it normally anyway, the important point is that
		1697	the libev application should not optimise around libev but should leave
		1698	optimisations to libev.
		1699
		1700	=head3 The special problem of dup'ed file descriptors
		1701
		1702	Some backends (e.g. epoll), cannot register events for file descriptors,
		1703	but only events for the underlying file descriptions. That means when you
		1704	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1705	events for them, only one file descriptor might actually receive events.
		1706
		1707	There is no workaround possible except not registering events
		1708	for potentially C<dup ()>'ed file descriptors, or to resort to
		1709	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1710
		1711	=head3 The special problem of files
		1712
		1713	Many people try to use C<select> (or libev) on file descriptors
		1714	representing files, and expect it to become ready when their program
		1715	doesn't block on disk accesses (which can take a long time on their own).
		1716
		1717	However, this cannot ever work in the "expected" way - you get a readiness
		1718	notification as soon as the kernel knows whether and how much data is
		1719	there, and in the case of open files, that's always the case, so you
		1720	always get a readiness notification instantly, and your read (or possibly
		1721	write) will still block on the disk I/O.
		1722
		1723	Another way to view it is that in the case of sockets, pipes, character
		1724	devices and so on, there is another party (the sender) that delivers data
		1725	on its own, but in the case of files, there is no such thing: the disk
		1726	will not send data on its own, simply because it doesn't know what you
		1727	wish to read - you would first have to request some data.
		1728
		1729	Since files are typically not-so-well supported by advanced notification
		1730	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1731	to files, even though you should not use it. The reason for this is
		1732	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1733	usually a tty, often a pipe, but also sometimes files or special devices
		1734	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1735	F</dev/urandom>), and even though the file might better be served with
		1736	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1737	it "just works" instead of freezing.
		1738
		1739	So avoid file descriptors pointing to files when you know it (e.g. use
		1740	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1741	when you rarely read from a file instead of from a socket, and want to
		1742	reuse the same code path.
		1743
		1744	=head3 The special problem of fork
		1745
		1746	Some backends (epoll, kqueue, probably linuxaio) do not support C<fork ()>
		1747	at all or exhibit useless behaviour. Libev fully supports fork, but needs
		1748	to be told about it in the child if you want to continue to use it in the
		1749	child.
		1750
		1751	To support fork in your child processes, you have to call C<ev_loop_fork
		1752	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1753	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1754
		1755	=head3 The special problem of SIGPIPE
		1756
		1757	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1758	when writing to a pipe whose other end has been closed, your program gets
		1759	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1760	this is sensible behaviour, for daemons, this is usually undesirable.
		1761
		1762	So when you encounter spurious, unexplained daemon exits, make sure you
		1763	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1764	somewhere, as that would have given you a big clue).
		1765
		1766	=head3 The special problem of accept()ing when you can't
		1767
		1768	Many implementations of the POSIX C<accept> function (for example,
		1769	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1770	connection from the pending queue in all error cases.
		1771
		1772	For example, larger servers often run out of file descriptors (because
		1773	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1774	rejecting the connection, leading to libev signalling readiness on
		1775	the next iteration again (the connection still exists after all), and
		1776	typically causing the program to loop at 100% CPU usage.
		1777
		1778	Unfortunately, the set of errors that cause this issue differs between
		1779	operating systems, there is usually little the app can do to remedy the
		1780	situation, and no known thread-safe method of removing the connection to
		1781	cope with overload is known (to me).
		1782
		1783	One of the easiest ways to handle this situation is to just ignore it
		1784	- when the program encounters an overload, it will just loop until the
		1785	situation is over. While this is a form of busy waiting, no OS offers an
		1786	event-based way to handle this situation, so it's the best one can do.
		1787
		1788	A better way to handle the situation is to log any errors other than
		1789	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1790	messages, and continue as usual, which at least gives the user an idea of
		1791	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1792	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1793	usage.
		1794
		1795	If your program is single-threaded, then you could also keep a dummy file
		1796	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1797	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1798	close that fd, and create a new dummy fd. This will gracefully refuse
		1799	clients under typical overload conditions.
		1800
		1801	The last way to handle it is to simply log the error and C<exit>, as
		1802	is often done with C<malloc> failures, but this results in an easy
		1803	opportunity for a DoS attack.
		1804
		1805	=head3 Watcher-Specific Functions
430		1806
431	=over 4	1807	=over 4
432		1808
433	=item ev_io_init (ev_io *, callback, int fd, int events)	1809	=item ev_io_init (ev_io *, callback, int fd, int events)
434		1810
435	=item ev_io_set (ev_io *, int fd, int events)	1811	=item ev_io_set (ev_io *, int fd, int events)
436		1812
437	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1813	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
438	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1814	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
439	EV_WRITE> to receive the given events.	1815	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1816
		1817	=item int fd [read-only]
		1818
		1819	The file descriptor being watched.
		1820
		1821	=item int events [read-only]
		1822
		1823	The events being watched.
440		1824
441	=back	1825	=back
442		1826
		1827	=head3 Examples
		1828
		1829	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1830	readable, but only once. Since it is likely line-buffered, you could
		1831	attempt to read a whole line in the callback.
		1832
		1833	static void
		1834	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1835	{
		1836	ev_io_stop (loop, w);
		1837	.. read from stdin here (or from w->fd) and handle any I/O errors
		1838	}
		1839
		1840	...
		1841	struct ev_loop *loop = ev_default_init (0);
		1842	ev_io stdin_readable;
		1843	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1844	ev_io_start (loop, &stdin_readable);
		1845	ev_run (loop, 0);
		1846
		1847
443	=head2 C<ev_timer> - relative and optionally recurring timeouts	1848	=head2 C<ev_timer> - relative and optionally repeating timeouts
444		1849
445	Timer watchers are simple relative timers that generate an event after a	1850	Timer watchers are simple relative timers that generate an event after a
446	given time, and optionally repeating in regular intervals after that.	1851	given time, and optionally repeating in regular intervals after that.
447		1852
448	The timers are based on real time, that is, if you register an event that	1853	The timers are based on real time, that is, if you register an event that
449	times out after an hour and youreset your system clock to last years	1854	times out after an hour and you reset your system clock to January last
450	time, it will still time out after (roughly) and hour. "Roughly" because	1855	year, it will still time out after (roughly) one hour. "Roughly" because
451	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1856	detecting time jumps is hard, and some inaccuracies are unavoidable (the
452	monotonic clock option helps a lot here).	1857	monotonic clock option helps a lot here).
		1858
		1859	The callback is guaranteed to be invoked only I<after> its timeout has
		1860	passed (not I<at>, so on systems with very low-resolution clocks this
		1861	might introduce a small delay, see "the special problem of being too
		1862	early", below). If multiple timers become ready during the same loop
		1863	iteration then the ones with earlier time-out values are invoked before
		1864	ones of the same priority with later time-out values (but this is no
		1865	longer true when a callback calls C<ev_run> recursively).
		1866
		1867	=head3 Be smart about timeouts
		1868
		1869	Many real-world problems involve some kind of timeout, usually for error
		1870	recovery. A typical example is an HTTP request - if the other side hangs,
		1871	you want to raise some error after a while.
		1872
		1873	What follows are some ways to handle this problem, from obvious and
		1874	inefficient to smart and efficient.
		1875
		1876	In the following, a 60 second activity timeout is assumed - a timeout that
		1877	gets reset to 60 seconds each time there is activity (e.g. each time some
		1878	data or other life sign was received).
		1879
		1880	=over 4
		1881
		1882	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1883
		1884	This is the most obvious, but not the most simple way: In the beginning,
		1885	start the watcher:
		1886
		1887	ev_timer_init (timer, callback, 60., 0.);
		1888	ev_timer_start (loop, timer);
		1889
		1890	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1891	and start it again:
		1892
		1893	ev_timer_stop (loop, timer);
		1894	ev_timer_set (timer, 60., 0.);
		1895	ev_timer_start (loop, timer);
		1896
		1897	This is relatively simple to implement, but means that each time there is
		1898	some activity, libev will first have to remove the timer from its internal
		1899	data structure and then add it again. Libev tries to be fast, but it's
		1900	still not a constant-time operation.
		1901
		1902	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1903
		1904	This is the easiest way, and involves using C<ev_timer_again> instead of
		1905	C<ev_timer_start>.
		1906
		1907	To implement this, configure an C<ev_timer> with a C<repeat> value
		1908	of C<60> and then call C<ev_timer_again> at start and each time you
		1909	successfully read or write some data. If you go into an idle state where
		1910	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1911	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1912
		1913	That means you can ignore both the C<ev_timer_start> function and the
		1914	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1915	member and C<ev_timer_again>.
		1916
		1917	At start:
		1918
		1919	ev_init (timer, callback);
		1920	timer->repeat = 60.;
		1921	ev_timer_again (loop, timer);
		1922
		1923	Each time there is some activity:
		1924
		1925	ev_timer_again (loop, timer);
		1926
		1927	It is even possible to change the time-out on the fly, regardless of
		1928	whether the watcher is active or not:
		1929
		1930	timer->repeat = 30.;
		1931	ev_timer_again (loop, timer);
		1932
		1933	This is slightly more efficient then stopping/starting the timer each time
		1934	you want to modify its timeout value, as libev does not have to completely
		1935	remove and re-insert the timer from/into its internal data structure.
		1936
		1937	It is, however, even simpler than the "obvious" way to do it.
		1938
		1939	=item 3. Let the timer time out, but then re-arm it as required.
		1940
		1941	This method is more tricky, but usually most efficient: Most timeouts are
		1942	relatively long compared to the intervals between other activity - in
		1943	our example, within 60 seconds, there are usually many I/O events with
		1944	associated activity resets.
		1945
		1946	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1947	but remember the time of last activity, and check for a real timeout only
		1948	within the callback:
		1949
		1950	ev_tstamp timeout = 60.;
		1951	ev_tstamp last_activity; // time of last activity
		1952	ev_timer timer;
		1953
		1954	static void
		1955	callback (EV_P_ ev_timer *w, int revents)
		1956	{
		1957	// calculate when the timeout would happen
		1958	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1959
		1960	// if negative, it means we the timeout already occurred
		1961	if (after < 0.)
		1962	{
		1963	// timeout occurred, take action
		1964	}
		1965	else
		1966	{
		1967	// callback was invoked, but there was some recent
		1968	// activity. simply restart the timer to time out
		1969	// after "after" seconds, which is the earliest time
		1970	// the timeout can occur.
		1971	ev_timer_set (w, after, 0.);
		1972	ev_timer_start (EV_A_ w);
		1973	}
		1974	}
		1975
		1976	To summarise the callback: first calculate in how many seconds the
		1977	timeout will occur (by calculating the absolute time when it would occur,
		1978	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1979	(EV_A)> from that).
		1980
		1981	If this value is negative, then we are already past the timeout, i.e. we
		1982	timed out, and need to do whatever is needed in this case.
		1983
		1984	Otherwise, we now the earliest time at which the timeout would trigger,
		1985	and simply start the timer with this timeout value.
		1986
		1987	In other words, each time the callback is invoked it will check whether
		1988	the timeout occurred. If not, it will simply reschedule itself to check
		1989	again at the earliest time it could time out. Rinse. Repeat.
		1990
		1991	This scheme causes more callback invocations (about one every 60 seconds
		1992	minus half the average time between activity), but virtually no calls to
		1993	libev to change the timeout.
		1994
		1995	To start the machinery, simply initialise the watcher and set
		1996	C<last_activity> to the current time (meaning there was some activity just
		1997	now), then call the callback, which will "do the right thing" and start
		1998	the timer:
		1999
		2000	last_activity = ev_now (EV_A);
		2001	ev_init (&timer, callback);
		2002	callback (EV_A_ &timer, 0);
		2003
		2004	When there is some activity, simply store the current time in
		2005	C<last_activity>, no libev calls at all:
		2006
		2007	if (activity detected)
		2008	last_activity = ev_now (EV_A);
		2009
		2010	When your timeout value changes, then the timeout can be changed by simply
		2011	providing a new value, stopping the timer and calling the callback, which
		2012	will again do the right thing (for example, time out immediately :).
		2013
		2014	timeout = new_value;
		2015	ev_timer_stop (EV_A_ &timer);
		2016	callback (EV_A_ &timer, 0);
		2017
		2018	This technique is slightly more complex, but in most cases where the
		2019	time-out is unlikely to be triggered, much more efficient.
		2020
		2021	=item 4. Wee, just use a double-linked list for your timeouts.
		2022
		2023	If there is not one request, but many thousands (millions...), all
		2024	employing some kind of timeout with the same timeout value, then one can
		2025	do even better:
		2026
		2027	When starting the timeout, calculate the timeout value and put the timeout
		2028	at the I<end> of the list.
		2029
		2030	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		2031	the list is expected to fire (for example, using the technique #3).
		2032
		2033	When there is some activity, remove the timer from the list, recalculate
		2034	the timeout, append it to the end of the list again, and make sure to
		2035	update the C<ev_timer> if it was taken from the beginning of the list.
		2036
		2037	This way, one can manage an unlimited number of timeouts in O(1) time for
		2038	starting, stopping and updating the timers, at the expense of a major
		2039	complication, and having to use a constant timeout. The constant timeout
		2040	ensures that the list stays sorted.
		2041
		2042	=back
		2043
		2044	So which method the best?
		2045
		2046	Method #2 is a simple no-brain-required solution that is adequate in most
		2047	situations. Method #3 requires a bit more thinking, but handles many cases
		2048	better, and isn't very complicated either. In most case, choosing either
		2049	one is fine, with #3 being better in typical situations.
		2050
		2051	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		2052	rather complicated, but extremely efficient, something that really pays
		2053	off after the first million or so of active timers, i.e. it's usually
		2054	overkill :)
		2055
		2056	=head3 The special problem of being too early
		2057
		2058	If you ask a timer to call your callback after three seconds, then
		2059	you expect it to be invoked after three seconds - but of course, this
		2060	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2061	guaranteed to any precision by libev - imagine somebody suspending the
		2062	process with a STOP signal for a few hours for example.
		2063
		2064	So, libev tries to invoke your callback as soon as possible I<after> the
		2065	delay has occurred, but cannot guarantee this.
		2066
		2067	A less obvious failure mode is calling your callback too early: many event
		2068	loops compare timestamps with a "elapsed delay >= requested delay", but
		2069	this can cause your callback to be invoked much earlier than you would
		2070	expect.
		2071
		2072	To see why, imagine a system with a clock that only offers full second
		2073	resolution (think windows if you can't come up with a broken enough OS
		2074	yourself). If you schedule a one-second timer at the time 500.9, then the
		2075	event loop will schedule your timeout to elapse at a system time of 500
		2076	(500.9 truncated to the resolution) + 1, or 501.
		2077
		2078	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2079	501" and invoke the callback 0.1s after it was started, even though a
		2080	one-second delay was requested - this is being "too early", despite best
		2081	intentions.
		2082
		2083	This is the reason why libev will never invoke the callback if the elapsed
		2084	delay equals the requested delay, but only when the elapsed delay is
		2085	larger than the requested delay. In the example above, libev would only invoke
		2086	the callback at system time 502, or 1.1s after the timer was started.
		2087
		2088	So, while libev cannot guarantee that your callback will be invoked
		2089	exactly when requested, it I<can> and I<does> guarantee that the requested
		2090	delay has actually elapsed, or in other words, it always errs on the "too
		2091	late" side of things.
		2092
		2093	=head3 The special problem of time updates
		2094
		2095	Establishing the current time is a costly operation (it usually takes
		2096	at least one system call): EV therefore updates its idea of the current
		2097	time only before and after C<ev_run> collects new events, which causes a
		2098	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2099	lots of events in one iteration.
453		2100
454	The relative timeouts are calculated relative to the C<ev_now ()>	2101	The relative timeouts are calculated relative to the C<ev_now ()>
455	time. This is usually the right thing as this timestamp refers to the time	2102	time. This is usually the right thing as this timestamp refers to the time
456	of the event triggering whatever timeout you are modifying/starting. If	2103	of the event triggering whatever timeout you are modifying/starting. If
457	you suspect event processing to be delayed and you *need* to base the timeout	2104	you suspect event processing to be delayed and you I<need> to base the
458	ion the current time, use something like this to adjust for this:	2105	timeout on the current time, use something like the following to adjust
		2106	for it:
459		2107
460	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2108	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
		2109
		2110	If the event loop is suspended for a long time, you can also force an
		2111	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		2112	()>, although that will push the event time of all outstanding events
		2113	further into the future.
		2114
		2115	=head3 The special problem of unsynchronised clocks
		2116
		2117	Modern systems have a variety of clocks - libev itself uses the normal
		2118	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2119	jumps).
		2120
		2121	Neither of these clocks is synchronised with each other or any other clock
		2122	on the system, so C<ev_time ()> might return a considerably different time
		2123	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2124	a call to C<gettimeofday> might return a second count that is one higher
		2125	than a directly following call to C<time>.
		2126
		2127	The moral of this is to only compare libev-related timestamps with
		2128	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2129	a second or so.
		2130
		2131	One more problem arises due to this lack of synchronisation: if libev uses
		2132	the system monotonic clock and you compare timestamps from C<ev_time>
		2133	or C<ev_now> from when you started your timer and when your callback is
		2134	invoked, you will find that sometimes the callback is a bit "early".
		2135
		2136	This is because C<ev_timer>s work in real time, not wall clock time, so
		2137	libev makes sure your callback is not invoked before the delay happened,
		2138	I<measured according to the real time>, not the system clock.
		2139
		2140	If your timeouts are based on a physical timescale (e.g. "time out this
		2141	connection after 100 seconds") then this shouldn't bother you as it is
		2142	exactly the right behaviour.
		2143
		2144	If you want to compare wall clock/system timestamps to your timers, then
		2145	you need to use C<ev_periodic>s, as these are based on the wall clock
		2146	time, where your comparisons will always generate correct results.
		2147
		2148	=head3 The special problems of suspended animation
		2149
		2150	When you leave the server world it is quite customary to hit machines that
		2151	can suspend/hibernate - what happens to the clocks during such a suspend?
		2152
		2153	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2154	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2155	to run until the system is suspended, but they will not advance while the
		2156	system is suspended. That means, on resume, it will be as if the program
		2157	was frozen for a few seconds, but the suspend time will not be counted
		2158	towards C<ev_timer> when a monotonic clock source is used. The real time
		2159	clock advanced as expected, but if it is used as sole clocksource, then a
		2160	long suspend would be detected as a time jump by libev, and timers would
		2161	be adjusted accordingly.
		2162
		2163	I would not be surprised to see different behaviour in different between
		2164	operating systems, OS versions or even different hardware.
		2165
		2166	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2167	time jump in the monotonic clocks and the realtime clock. If the program
		2168	is suspended for a very long time, and monotonic clock sources are in use,
		2169	then you can expect C<ev_timer>s to expire as the full suspension time
		2170	will be counted towards the timers. When no monotonic clock source is in
		2171	use, then libev will again assume a timejump and adjust accordingly.
		2172
		2173	It might be beneficial for this latter case to call C<ev_suspend>
		2174	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2175	deterministic behaviour in this case (you can do nothing against
		2176	C<SIGSTOP>).
		2177
		2178	=head3 Watcher-Specific Functions and Data Members
461		2179
462	=over 4	2180	=over 4
463		2181
464	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2182	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465		2183
466	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2184	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
467		2185
468	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2186	Configure the timer to trigger after C<after> seconds (fractional and
469	C<0.>, then it will automatically be stopped. If it is positive, then the	2187	negative values are supported). If C<repeat> is C<0.>, then it will
		2188	automatically be stopped once the timeout is reached. If it is positive,
470	timer will automatically be configured to trigger again C<repeat> seconds	2189	then the timer will automatically be configured to trigger again C<repeat>
471	later, again, and again, until stopped manually.	2190	seconds later, again, and again, until stopped manually.
472		2191
473	The timer itself will do a best-effort at avoiding drift, that is, if you	2192	The timer itself will do a best-effort at avoiding drift, that is, if
474	configure a timer to trigger every 10 seconds, then it will trigger at	2193	you configure a timer to trigger every 10 seconds, then it will normally
475	exactly 10 second intervals. If, however, your program cannot keep up with	2194	trigger at exactly 10 second intervals. If, however, your program cannot
476	the timer (ecause it takes longer than those 10 seconds to do stuff) the	2195	keep up with the timer (because it takes longer than those 10 seconds to
477	timer will not fire more than once per event loop iteration.	2196	do stuff) the timer will not fire more than once per event loop iteration.
478		2197
479	=item ev_timer_again (loop)	2198	=item ev_timer_again (loop, ev_timer *)
480		2199
481	This will act as if the timer timed out and restart it again if it is	2200	This will act as if the timer timed out, and restarts it again if it is
482	repeating. The exact semantics are:	2201	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2202	timeout to the C<repeat> value and calling C<ev_timer_start>.
483		2203
		2204	The exact semantics are as in the following rules, all of which will be
		2205	applied to the watcher:
		2206
		2207	=over 4
		2208
		2209	=item If the timer is pending, the pending status is always cleared.
		2210
484	If the timer is started but nonrepeating, stop it.	2211	=item If the timer is started but non-repeating, stop it (as if it timed
		2212	out, without invoking it).
485		2213
486	If the timer is repeating, either start it if necessary (with the repeat	2214	=item If the timer is repeating, make the C<repeat> value the new timeout
487	value), or reset the running timer to the repeat value.	2215	and start the timer, if necessary.
488
489	This sounds a bit complicated, but here is a useful and typical
490	example: Imagine you have a tcp connection and you want a so-called idle
491	timeout, that is, you want to be called when there have been, say, 60
492	seconds of inactivity on the socket. The easiest way to do this is to
493	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each
494	time you successfully read or write some data. If you go into an idle
495	state where you do not expect data to travel on the socket, you can stop
496	the timer, and again will automatically restart it if need be.
497		2216
498	=back	2217	=back
499		2218
		2219	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
		2220	usage example.
		2221
		2222	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
		2223
		2224	Returns the remaining time until a timer fires. If the timer is active,
		2225	then this time is relative to the current event loop time, otherwise it's
		2226	the timeout value currently configured.
		2227
		2228	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2229	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2230	will return C<4>. When the timer expires and is restarted, it will return
		2231	roughly C<7> (likely slightly less as callback invocation takes some time,
		2232	too), and so on.
		2233
		2234	=item ev_tstamp repeat [read-write]
		2235
		2236	The current C<repeat> value. Will be used each time the watcher times out
		2237	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2238	which is also when any modifications are taken into account.
		2239
		2240	=back
		2241
		2242	=head3 Examples
		2243
		2244	Example: Create a timer that fires after 60 seconds.
		2245
		2246	static void
		2247	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2248	{
		2249	.. one minute over, w is actually stopped right here
		2250	}
		2251
		2252	ev_timer mytimer;
		2253	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		2254	ev_timer_start (loop, &mytimer);
		2255
		2256	Example: Create a timeout timer that times out after 10 seconds of
		2257	inactivity.
		2258
		2259	static void
		2260	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2261	{
		2262	.. ten seconds without any activity
		2263	}
		2264
		2265	ev_timer mytimer;
		2266	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		2267	ev_timer_again (&mytimer); /* start timer */
		2268	ev_run (loop, 0);
		2269
		2270	// and in some piece of code that gets executed on any "activity":
		2271	// reset the timeout to start ticking again at 10 seconds
		2272	ev_timer_again (&mytimer);
		2273
		2274
500	=head2 C<ev_periodic> - to cron or not to cron	2275	=head2 C<ev_periodic> - to cron or not to cron?
501		2276
502	Periodic watchers are also timers of a kind, but they are very versatile	2277	Periodic watchers are also timers of a kind, but they are very versatile
503	(and unfortunately a bit complex).	2278	(and unfortunately a bit complex).
504		2279
505	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2280	Unlike C<ev_timer>, periodic watchers are not based on real time (or
506	but on wallclock time (absolute time). You can tell a periodic watcher	2281	relative time, the physical time that passes) but on wall clock time
507	to trigger "at" some specific point in time. For example, if you tell a	2282	(absolute time, the thing you can read on your calendar or clock). The
508	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	2283	difference is that wall clock time can run faster or slower than real
509	+ 10.>) and then reset your system clock to the last year, then it will	2284	time, and time jumps are not uncommon (e.g. when you adjust your
510	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2285	wrist-watch).
511	roughly 10 seconds later and of course not if you reset your system time
512	again).
513		2286
514	They can also be used to implement vastly more complex timers, such as	2287	You can tell a periodic watcher to trigger after some specific point
		2288	in time: for example, if you tell a periodic watcher to trigger "in 10
		2289	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2290	not a delay) and then reset your system clock to January of the previous
		2291	year, then it will take a year or more to trigger the event (unlike an
		2292	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2293	it, as it uses a relative timeout).
		2294
		2295	C<ev_periodic> watchers can also be used to implement vastly more complex
515	triggering an event on eahc midnight, local time.	2296	timers, such as triggering an event on each "midnight, local time", or
		2297	other complicated rules. This cannot easily be done with C<ev_timer>
		2298	watchers, as those cannot react to time jumps.
		2299
		2300	As with timers, the callback is guaranteed to be invoked only when the
		2301	point in time where it is supposed to trigger has passed. If multiple
		2302	timers become ready during the same loop iteration then the ones with
		2303	earlier time-out values are invoked before ones with later time-out values
		2304	(but this is no longer true when a callback calls C<ev_run> recursively).
		2305
		2306	=head3 Watcher-Specific Functions and Data Members
516		2307
517	=over 4	2308	=over 4
518		2309
519	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2310	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
520		2311
521	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2312	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
522		2313
523	Lots of arguments, lets sort it out... There are basically three modes of	2314	Lots of arguments, let's sort it out... There are basically three modes of
524	operation, and we will explain them from simplest to complex:	2315	operation, and we will explain them from simplest to most complex:
525
526		2316
527	=over 4	2317	=over 4
528		2318
529	=item * absolute timer (interval = reschedule_cb = 0)	2319	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
530		2320
531	In this configuration the watcher triggers an event at the wallclock time	2321	In this configuration the watcher triggers an event after the wall clock
532	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2322	time C<offset> has passed. It will not repeat and will not adjust when a
533	that is, if it is to be run at January 1st 2011 then it will run when the	2323	time jump occurs, that is, if it is to be run at January 1st 2011 then it
534	system time reaches or surpasses this time.	2324	will be stopped and invoked when the system clock reaches or surpasses
		2325	this point in time.
535		2326
536	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2327	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
537		2328
538	In this mode the watcher will always be scheduled to time out at the next	2329	In this mode the watcher will always be scheduled to time out at the next
539	C<at + N * interval> time (for some integer N) and then repeat, regardless	2330	C<offset + N * interval> time (for some integer N, which can also be
540	of any time jumps.	2331	negative) and then repeat, regardless of any time jumps. The C<offset>
		2332	argument is merely an offset into the C<interval> periods.
541		2333
542	This can be used to create timers that do not drift with respect to system	2334	This can be used to create timers that do not drift with respect to the
543	time:	2335	system clock, for example, here is an C<ev_periodic> that triggers each
		2336	hour, on the hour (with respect to UTC):
544		2337
545	ev_periodic_set (&periodic, 0., 3600., 0);	2338	ev_periodic_set (&periodic, 0., 3600., 0);
546		2339
547	This doesn't mean there will always be 3600 seconds in between triggers,	2340	This doesn't mean there will always be 3600 seconds in between triggers,
548	but only that the the callback will be called when the system time shows a	2341	but only that the callback will be called when the system time shows a
549	full hour (UTC), or more correctly, when the system time is evenly divisible	2342	full hour (UTC), or more correctly, when the system time is evenly divisible
550	by 3600.	2343	by 3600.
551		2344
552	Another way to think about it (for the mathematically inclined) is that	2345	Another way to think about it (for the mathematically inclined) is that
553	C<ev_periodic> will try to run the callback in this mode at the next possible	2346	C<ev_periodic> will try to run the callback in this mode at the next possible
554	time where C<time = at (mod interval)>, regardless of any time jumps.	2347	time where C<time = offset (mod interval)>, regardless of any time jumps.
555		2348
		2349	The C<interval> I<MUST> be positive, and for numerical stability, the
		2350	interval value should be higher than C<1/8192> (which is around 100
		2351	microseconds) and C<offset> should be higher than C<0> and should have
		2352	at most a similar magnitude as the current time (say, within a factor of
		2353	ten). Typical values for offset are, in fact, C<0> or something between
		2354	C<0> and C<interval>, which is also the recommended range.
		2355
		2356	Note also that there is an upper limit to how often a timer can fire (CPU
		2357	speed for example), so if C<interval> is very small then timing stability
		2358	will of course deteriorate. Libev itself tries to be exact to be about one
		2359	millisecond (if the OS supports it and the machine is fast enough).
		2360
556	=item * manual reschedule mode (reschedule_cb = callback)	2361	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
557		2362
558	In this mode the values for C<interval> and C<at> are both being	2363	In this mode the values for C<interval> and C<offset> are both being
559	ignored. Instead, each time the periodic watcher gets scheduled, the	2364	ignored. Instead, each time the periodic watcher gets scheduled, the
560	reschedule callback will be called with the watcher as first, and the	2365	reschedule callback will be called with the watcher as first, and the
561	current time as second argument.	2366	current time as second argument.
562		2367
563	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	2368	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
564	periodic watcher, ever, or make any event loop modifications>. If you need	2369	or make ANY other event loop modifications whatsoever, unless explicitly
		2370	allowed by documentation here>.
		2371
565	to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.	2372	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2373	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2374	only event loop modification you are allowed to do).
566		2375
567	Also, I<< this callback must always return a time that is later than the
568	passed C<now> value >>. Not even C<now> itself will be ok.
569
570	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2376	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
571	ev_tstamp now)>, e.g.:	2377	*w, ev_tstamp now)>, e.g.:
572		2378
		2379	static ev_tstamp
573	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2380	my_rescheduler (ev_periodic *w, ev_tstamp now)
574	{	2381	{
575	return now + 60.;	2382	return now + 60.;
576	}	2383	}
577		2384
578	It must return the next time to trigger, based on the passed time value	2385	It must return the next time to trigger, based on the passed time value
579	(that is, the lowest time value larger than to the second argument). It	2386	(that is, the lowest time value larger than to the second argument). It
580	will usually be called just before the callback will be triggered, but	2387	will usually be called just before the callback will be triggered, but
581	might be called at other times, too.	2388	might be called at other times, too.
582		2389
		2390	NOTE: I<< This callback must always return a time that is higher than or
		2391	equal to the passed C<now> value >>.
		2392
583	This can be used to create very complex timers, such as a timer that	2393	This can be used to create very complex timers, such as a timer that
584	triggers on each midnight, local time. To do this, you would calculate the	2394	triggers on "next midnight, local time". To do this, you would calculate
585	next midnight after C<now> and return the timestamp value for this. How you do this	2395	the next midnight after C<now> and return the timestamp value for
586	is, again, up to you (but it is not trivial).	2396	this. Here is a (completely untested, no error checking) example on how to
		2397	do this:
		2398
		2399	#include <time.h>
		2400
		2401	static ev_tstamp
		2402	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2403	{
		2404	time_t tnow = (time_t)now;
		2405	struct tm tm;
		2406	localtime_r (&tnow, &tm);
		2407
		2408	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2409	++tm.tm_mday; // midnight next day
		2410
		2411	return mktime (&tm);
		2412	}
		2413
		2414	Note: this code might run into trouble on days that have more then two
		2415	midnights (beginning and end).
587		2416
588	=back	2417	=back
589		2418
590	=item ev_periodic_again (loop, ev_periodic *)	2419	=item ev_periodic_again (loop, ev_periodic *)
591		2420
592	Simply stops and restarts the periodic watcher again. This is only useful	2421	Simply stops and restarts the periodic watcher again. This is only useful
593	when you changed some parameters or the reschedule callback would return	2422	when you changed some parameters or the reschedule callback would return
594	a different time than the last time it was called (e.g. in a crond like	2423	a different time than the last time it was called (e.g. in a crond like
595	program when the crontabs have changed).	2424	program when the crontabs have changed).
596		2425
		2426	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2427
		2428	When active, returns the absolute time that the watcher is supposed
		2429	to trigger next. This is not the same as the C<offset> argument to
		2430	C<ev_periodic_set>, but indeed works even in interval and manual
		2431	rescheduling modes.
		2432
		2433	=item ev_tstamp offset [read-write]
		2434
		2435	When repeating, this contains the offset value, otherwise this is the
		2436	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2437	although libev might modify this value for better numerical stability).
		2438
		2439	Can be modified any time, but changes only take effect when the periodic
		2440	timer fires or C<ev_periodic_again> is being called.
		2441
		2442	=item ev_tstamp interval [read-write]
		2443
		2444	The current interval value. Can be modified any time, but changes only
		2445	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2446	called.
		2447
		2448	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2449
		2450	The current reschedule callback, or C<0>, if this functionality is
		2451	switched off. Can be changed any time, but changes only take effect when
		2452	the periodic timer fires or C<ev_periodic_again> is being called.
		2453
597	=back	2454	=back
598		2455
		2456	=head3 Examples
		2457
		2458	Example: Call a callback every hour, or, more precisely, whenever the
		2459	system time is divisible by 3600. The callback invocation times have
		2460	potentially a lot of jitter, but good long-term stability.
		2461
		2462	static void
		2463	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
		2464	{
		2465	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2466	}
		2467
		2468	ev_periodic hourly_tick;
		2469	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2470	ev_periodic_start (loop, &hourly_tick);
		2471
		2472	Example: The same as above, but use a reschedule callback to do it:
		2473
		2474	#include <math.h>
		2475
		2476	static ev_tstamp
		2477	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2478	{
		2479	return now + (3600. - fmod (now, 3600.));
		2480	}
		2481
		2482	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2483
		2484	Example: Call a callback every hour, starting now:
		2485
		2486	ev_periodic hourly_tick;
		2487	ev_periodic_init (&hourly_tick, clock_cb,
		2488	fmod (ev_now (loop), 3600.), 3600., 0);
		2489	ev_periodic_start (loop, &hourly_tick);
		2490
		2491
599	=head2 C<ev_signal> - signal me when a signal gets signalled	2492	=head2 C<ev_signal> - signal me when a signal gets signalled!
600		2493
601	Signal watchers will trigger an event when the process receives a specific	2494	Signal watchers will trigger an event when the process receives a specific
602	signal one or more times. Even though signals are very asynchronous, libev	2495	signal one or more times. Even though signals are very asynchronous, libev
603	will try it's best to deliver signals synchronously, i.e. as part of the	2496	will try its best to deliver signals synchronously, i.e. as part of the
604	normal event processing, like any other event.	2497	normal event processing, like any other event.
605		2498
		2499	If you want signals to be delivered truly asynchronously, just use
		2500	C<sigaction> as you would do without libev and forget about sharing
		2501	the signal. You can even use C<ev_async> from a signal handler to
		2502	synchronously wake up an event loop.
		2503
606	You can configure as many watchers as you like per signal. Only when the	2504	You can configure as many watchers as you like for the same signal, but
607	first watcher gets started will libev actually register a signal watcher	2505	only within the same loop, i.e. you can watch for C<SIGINT> in your
608	with the kernel (thus it coexists with your own signal handlers as long	2506	default loop and for C<SIGIO> in another loop, but you cannot watch for
609	as you don't register any with libev). Similarly, when the last signal	2507	C<SIGINT> in both the default loop and another loop at the same time. At
610	watcher for a signal is stopped libev will reset the signal handler to	2508	the moment, C<SIGCHLD> is permanently tied to the default loop.
611	SIG_DFL (regardless of what it was set to before).	2509
		2510	Only after the first watcher for a signal is started will libev actually
		2511	register something with the kernel. It thus coexists with your own signal
		2512	handlers as long as you don't register any with libev for the same signal.
		2513
		2514	If possible and supported, libev will install its handlers with
		2515	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2516	not be unduly interrupted. If you have a problem with system calls getting
		2517	interrupted by signals you can block all signals in an C<ev_check> watcher
		2518	and unblock them in an C<ev_prepare> watcher.
		2519
		2520	=head3 The special problem of inheritance over fork/execve/pthread_create
		2521
		2522	Both the signal mask (C<sigprocmask>) and the signal disposition
		2523	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2524	stopping it again), that is, libev might or might not block the signal,
		2525	and might or might not set or restore the installed signal handler (but
		2526	see C<EVFLAG_NOSIGMASK>).
		2527
		2528	While this does not matter for the signal disposition (libev never
		2529	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2530	C<execve>), this matters for the signal mask: many programs do not expect
		2531	certain signals to be blocked.
		2532
		2533	This means that before calling C<exec> (from the child) you should reset
		2534	the signal mask to whatever "default" you expect (all clear is a good
		2535	choice usually).
		2536
		2537	The simplest way to ensure that the signal mask is reset in the child is
		2538	to install a fork handler with C<pthread_atfork> that resets it. That will
		2539	catch fork calls done by libraries (such as the libc) as well.
		2540
		2541	In current versions of libev, the signal will not be blocked indefinitely
		2542	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2543	the window of opportunity for problems, it will not go away, as libev
		2544	I<has> to modify the signal mask, at least temporarily.
		2545
		2546	So I can't stress this enough: I<If you do not reset your signal mask when
		2547	you expect it to be empty, you have a race condition in your code>. This
		2548	is not a libev-specific thing, this is true for most event libraries.
		2549
		2550	=head3 The special problem of threads signal handling
		2551
		2552	POSIX threads has problematic signal handling semantics, specifically,
		2553	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2554	threads in a process block signals, which is hard to achieve.
		2555
		2556	When you want to use sigwait (or mix libev signal handling with your own
		2557	for the same signals), you can tackle this problem by globally blocking
		2558	all signals before creating any threads (or creating them with a fully set
		2559	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2560	loops. Then designate one thread as "signal receiver thread" which handles
		2561	these signals. You can pass on any signals that libev might be interested
		2562	in by calling C<ev_feed_signal>.
		2563
		2564	=head3 Watcher-Specific Functions and Data Members
612		2565
613	=over 4	2566	=over 4
614		2567
615	=item ev_signal_init (ev_signal *, callback, int signum)	2568	=item ev_signal_init (ev_signal *, callback, int signum)
616		2569
617	=item ev_signal_set (ev_signal *, int signum)	2570	=item ev_signal_set (ev_signal *, int signum)
618		2571
619	Configures the watcher to trigger on the given signal number (usually one	2572	Configures the watcher to trigger on the given signal number (usually one
620	of the C<SIGxxx> constants).	2573	of the C<SIGxxx> constants).
621		2574
		2575	=item int signum [read-only]
		2576
		2577	The signal the watcher watches out for.
		2578
622	=back	2579	=back
623		2580
		2581	=head3 Examples
		2582
		2583	Example: Try to exit cleanly on SIGINT.
		2584
		2585	static void
		2586	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2587	{
		2588	ev_break (loop, EVBREAK_ALL);
		2589	}
		2590
		2591	ev_signal signal_watcher;
		2592	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2593	ev_signal_start (loop, &signal_watcher);
		2594
		2595
624	=head2 C<ev_child> - wait for pid status changes	2596	=head2 C<ev_child> - watch out for process status changes
625		2597
626	Child watchers trigger when your process receives a SIGCHLD in response to	2598	Child watchers trigger when your process receives a SIGCHLD in response to
627	some child status changes (most typically when a child of yours dies).	2599	some child status changes (most typically when a child of yours dies or
		2600	exits). It is permissible to install a child watcher I<after> the child
		2601	has been forked (which implies it might have already exited), as long
		2602	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2603	forking and then immediately registering a watcher for the child is fine,
		2604	but forking and registering a watcher a few event loop iterations later or
		2605	in the next callback invocation is not.
		2606
		2607	Only the default event loop is capable of handling signals, and therefore
		2608	you can only register child watchers in the default event loop.
		2609
		2610	Due to some design glitches inside libev, child watchers will always be
		2611	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2612	libev)
		2613
		2614	=head3 Process Interaction
		2615
		2616	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2617	initialised. This is necessary to guarantee proper behaviour even if the
		2618	first child watcher is started after the child exits. The occurrence
		2619	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2620	synchronously as part of the event loop processing. Libev always reaps all
		2621	children, even ones not watched.
		2622
		2623	=head3 Overriding the Built-In Processing
		2624
		2625	Libev offers no special support for overriding the built-in child
		2626	processing, but if your application collides with libev's default child
		2627	handler, you can override it easily by installing your own handler for
		2628	C<SIGCHLD> after initialising the default loop, and making sure the
		2629	default loop never gets destroyed. You are encouraged, however, to use an
		2630	event-based approach to child reaping and thus use libev's support for
		2631	that, so other libev users can use C<ev_child> watchers freely.
		2632
		2633	=head3 Stopping the Child Watcher
		2634
		2635	Currently, the child watcher never gets stopped, even when the
		2636	child terminates, so normally one needs to stop the watcher in the
		2637	callback. Future versions of libev might stop the watcher automatically
		2638	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2639	problem).
		2640
		2641	=head3 Watcher-Specific Functions and Data Members
628		2642
629	=over 4	2643	=over 4
630		2644
631	=item ev_child_init (ev_child *, callback, int pid)	2645	=item ev_child_init (ev_child *, callback, int pid, int trace)
632		2646
633	=item ev_child_set (ev_child *, int pid)	2647	=item ev_child_set (ev_child *, int pid, int trace)
634		2648
635	Configures the watcher to wait for status changes of process C<pid> (or	2649	Configures the watcher to wait for status changes of process C<pid> (or
636	I<any> process if C<pid> is specified as C<0>). The callback can look	2650	I<any> process if C<pid> is specified as C<0>). The callback can look
637	at the C<rstatus> member of the C<ev_child> watcher structure to see	2651	at the C<rstatus> member of the C<ev_child> watcher structure to see
638	the status word (use the macros from C<sys/wait.h> and see your systems	2652	the status word (use the macros from C<sys/wait.h> and see your systems
639	C<waitpid> documentation). The C<rpid> member contains the pid of the	2653	C<waitpid> documentation). The C<rpid> member contains the pid of the
640	process causing the status change.	2654	process causing the status change. C<trace> must be either C<0> (only
		2655	activate the watcher when the process terminates) or C<1> (additionally
		2656	activate the watcher when the process is stopped or continued).
		2657
		2658	=item int pid [read-only]
		2659
		2660	The process id this watcher watches out for, or C<0>, meaning any process id.
		2661
		2662	=item int rpid [read-write]
		2663
		2664	The process id that detected a status change.
		2665
		2666	=item int rstatus [read-write]
		2667
		2668	The process exit/trace status caused by C<rpid> (see your systems
		2669	C<waitpid> and C<sys/wait.h> documentation for details).
641		2670
642	=back	2671	=back
643		2672
		2673	=head3 Examples
		2674
		2675	Example: C<fork()> a new process and install a child handler to wait for
		2676	its completion.
		2677
		2678	ev_child cw;
		2679
		2680	static void
		2681	child_cb (EV_P_ ev_child *w, int revents)
		2682	{
		2683	ev_child_stop (EV_A_ w);
		2684	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2685	}
		2686
		2687	pid_t pid = fork ();
		2688
		2689	if (pid < 0)
		2690	// error
		2691	else if (pid == 0)
		2692	{
		2693	// the forked child executes here
		2694	exit (1);
		2695	}
		2696	else
		2697	{
		2698	ev_child_init (&cw, child_cb, pid, 0);
		2699	ev_child_start (EV_DEFAULT_ &cw);
		2700	}
		2701
		2702
		2703	=head2 C<ev_stat> - did the file attributes just change?
		2704
		2705	This watches a file system path for attribute changes. That is, it calls
		2706	C<stat> on that path in regular intervals (or when the OS says it changed)
		2707	and sees if it changed compared to the last time, invoking the callback
		2708	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2709	happen after the watcher has been started will be reported.
		2710
		2711	The path does not need to exist: changing from "path exists" to "path does
		2712	not exist" is a status change like any other. The condition "path does not
		2713	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2714	C<st_nlink> field being zero (which is otherwise always forced to be at
		2715	least one) and all the other fields of the stat buffer having unspecified
		2716	contents.
		2717
		2718	The path I<must not> end in a slash or contain special components such as
		2719	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2720	your working directory changes, then the behaviour is undefined.
		2721
		2722	Since there is no portable change notification interface available, the
		2723	portable implementation simply calls C<stat(2)> regularly on the path
		2724	to see if it changed somehow. You can specify a recommended polling
		2725	interval for this case. If you specify a polling interval of C<0> (highly
		2726	recommended!) then a I<suitable, unspecified default> value will be used
		2727	(which you can expect to be around five seconds, although this might
		2728	change dynamically). Libev will also impose a minimum interval which is
		2729	currently around C<0.1>, but that's usually overkill.
		2730
		2731	This watcher type is not meant for massive numbers of stat watchers,
		2732	as even with OS-supported change notifications, this can be
		2733	resource-intensive.
		2734
		2735	At the time of this writing, the only OS-specific interface implemented
		2736	is the Linux inotify interface (implementing kqueue support is left as an
		2737	exercise for the reader. Note, however, that the author sees no way of
		2738	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2739
		2740	=head3 ABI Issues (Largefile Support)
		2741
		2742	Libev by default (unless the user overrides this) uses the default
		2743	compilation environment, which means that on systems with large file
		2744	support disabled by default, you get the 32 bit version of the stat
		2745	structure. When using the library from programs that change the ABI to
		2746	use 64 bit file offsets the programs will fail. In that case you have to
		2747	compile libev with the same flags to get binary compatibility. This is
		2748	obviously the case with any flags that change the ABI, but the problem is
		2749	most noticeably displayed with ev_stat and large file support.
		2750
		2751	The solution for this is to lobby your distribution maker to make large
		2752	file interfaces available by default (as e.g. FreeBSD does) and not
		2753	optional. Libev cannot simply switch on large file support because it has
		2754	to exchange stat structures with application programs compiled using the
		2755	default compilation environment.
		2756
		2757	=head3 Inotify and Kqueue
		2758
		2759	When C<inotify (7)> support has been compiled into libev and present at
		2760	runtime, it will be used to speed up change detection where possible. The
		2761	inotify descriptor will be created lazily when the first C<ev_stat>
		2762	watcher is being started.
		2763
		2764	Inotify presence does not change the semantics of C<ev_stat> watchers
		2765	except that changes might be detected earlier, and in some cases, to avoid
		2766	making regular C<stat> calls. Even in the presence of inotify support
		2767	there are many cases where libev has to resort to regular C<stat> polling,
		2768	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2769	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2770	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2771	xfs are fully working) libev usually gets away without polling.
		2772
		2773	There is no support for kqueue, as apparently it cannot be used to
		2774	implement this functionality, due to the requirement of having a file
		2775	descriptor open on the object at all times, and detecting renames, unlinks
		2776	etc. is difficult.
		2777
		2778	=head3 C<stat ()> is a synchronous operation
		2779
		2780	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2781	the process. The exception are C<ev_stat> watchers - those call C<stat
		2782	()>, which is a synchronous operation.
		2783
		2784	For local paths, this usually doesn't matter: unless the system is very
		2785	busy or the intervals between stat's are large, a stat call will be fast,
		2786	as the path data is usually in memory already (except when starting the
		2787	watcher).
		2788
		2789	For networked file systems, calling C<stat ()> can block an indefinite
		2790	time due to network issues, and even under good conditions, a stat call
		2791	often takes multiple milliseconds.
		2792
		2793	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2794	paths, although this is fully supported by libev.
		2795
		2796	=head3 The special problem of stat time resolution
		2797
		2798	The C<stat ()> system call only supports full-second resolution portably,
		2799	and even on systems where the resolution is higher, most file systems
		2800	still only support whole seconds.
		2801
		2802	That means that, if the time is the only thing that changes, you can
		2803	easily miss updates: on the first update, C<ev_stat> detects a change and
		2804	calls your callback, which does something. When there is another update
		2805	within the same second, C<ev_stat> will be unable to detect unless the
		2806	stat data does change in other ways (e.g. file size).
		2807
		2808	The solution to this is to delay acting on a change for slightly more
		2809	than a second (or till slightly after the next full second boundary), using
		2810	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2811	ev_timer_again (loop, w)>).
		2812
		2813	The C<.02> offset is added to work around small timing inconsistencies
		2814	of some operating systems (where the second counter of the current time
		2815	might be be delayed. One such system is the Linux kernel, where a call to
		2816	C<gettimeofday> might return a timestamp with a full second later than
		2817	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2818	update file times then there will be a small window where the kernel uses
		2819	the previous second to update file times but libev might already execute
		2820	the timer callback).
		2821
		2822	=head3 Watcher-Specific Functions and Data Members
		2823
		2824	=over 4
		2825
		2826	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2827
		2828	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2829
		2830	Configures the watcher to wait for status changes of the given
		2831	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2832	be detected and should normally be specified as C<0> to let libev choose
		2833	a suitable value. The memory pointed to by C<path> must point to the same
		2834	path for as long as the watcher is active.
		2835
		2836	The callback will receive an C<EV_STAT> event when a change was detected,
		2837	relative to the attributes at the time the watcher was started (or the
		2838	last change was detected).
		2839
		2840	=item ev_stat_stat (loop, ev_stat *)
		2841
		2842	Updates the stat buffer immediately with new values. If you change the
		2843	watched path in your callback, you could call this function to avoid
		2844	detecting this change (while introducing a race condition if you are not
		2845	the only one changing the path). Can also be useful simply to find out the
		2846	new values.
		2847
		2848	=item ev_statdata attr [read-only]
		2849
		2850	The most-recently detected attributes of the file. Although the type is
		2851	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2852	suitable for your system, but you can only rely on the POSIX-standardised
		2853	members to be present. If the C<st_nlink> member is C<0>, then there was
		2854	some error while C<stat>ing the file.
		2855
		2856	=item ev_statdata prev [read-only]
		2857
		2858	The previous attributes of the file. The callback gets invoked whenever
		2859	C<prev> != C<attr>, or, more precisely, one or more of these members
		2860	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2861	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2862
		2863	=item ev_tstamp interval [read-only]
		2864
		2865	The specified interval.
		2866
		2867	=item const char *path [read-only]
		2868
		2869	The file system path that is being watched.
		2870
		2871	=back
		2872
		2873	=head3 Examples
		2874
		2875	Example: Watch C</etc/passwd> for attribute changes.
		2876
		2877	static void
		2878	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2879	{
		2880	/* /etc/passwd changed in some way */
		2881	if (w->attr.st_nlink)
		2882	{
		2883	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2884	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2885	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2886	}
		2887	else
		2888	/* you shalt not abuse printf for puts */
		2889	puts ("wow, /etc/passwd is not there, expect problems. "
		2890	"if this is windows, they already arrived\n");
		2891	}
		2892
		2893	...
		2894	ev_stat passwd;
		2895
		2896	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2897	ev_stat_start (loop, &passwd);
		2898
		2899	Example: Like above, but additionally use a one-second delay so we do not
		2900	miss updates (however, frequent updates will delay processing, too, so
		2901	one might do the work both on C<ev_stat> callback invocation I<and> on
		2902	C<ev_timer> callback invocation).
		2903
		2904	static ev_stat passwd;
		2905	static ev_timer timer;
		2906
		2907	static void
		2908	timer_cb (EV_P_ ev_timer *w, int revents)
		2909	{
		2910	ev_timer_stop (EV_A_ w);
		2911
		2912	/* now it's one second after the most recent passwd change */
		2913	}
		2914
		2915	static void
		2916	stat_cb (EV_P_ ev_stat *w, int revents)
		2917	{
		2918	/* reset the one-second timer */
		2919	ev_timer_again (EV_A_ &timer);
		2920	}
		2921
		2922	...
		2923	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2924	ev_stat_start (loop, &passwd);
		2925	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2926
		2927
644	=head2 C<ev_idle> - when you've got nothing better to do	2928	=head2 C<ev_idle> - when you've got nothing better to do...
645		2929
646	Idle watchers trigger events when there are no other events are pending	2930	Idle watchers trigger events when no other events of the same or higher
647	(prepare, check and other idle watchers do not count). That is, as long	2931	priority are pending (prepare, check and other idle watchers do not count
648	as your process is busy handling sockets or timeouts (or even signals,	2932	as receiving "events").
649	imagine) it will not be triggered. But when your process is idle all idle	2933
650	watchers are being called again and again, once per event loop iteration -	2934	That is, as long as your process is busy handling sockets or timeouts
		2935	(or even signals, imagine) of the same or higher priority it will not be
		2936	triggered. But when your process is idle (or only lower-priority watchers
		2937	are pending), the idle watchers are being called once per event loop
651	until stopped, that is, or your process receives more events and becomes	2938	iteration - until stopped, that is, or your process receives more events
652	busy.	2939	and becomes busy again with higher priority stuff.
653		2940
654	The most noteworthy effect is that as long as any idle watchers are	2941	The most noteworthy effect is that as long as any idle watchers are
655	active, the process will not block when waiting for new events.	2942	active, the process will not block when waiting for new events.
656		2943
657	Apart from keeping your process non-blocking (which is a useful	2944	Apart from keeping your process non-blocking (which is a useful
658	effect on its own sometimes), idle watchers are a good place to do	2945	effect on its own sometimes), idle watchers are a good place to do
659	"pseudo-background processing", or delay processing stuff to after the	2946	"pseudo-background processing", or delay processing stuff to after the
660	event loop has handled all outstanding events.	2947	event loop has handled all outstanding events.
661		2948
		2949	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2950
		2951	As long as there is at least one active idle watcher, libev will never
		2952	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2953	For this to work, the idle watcher doesn't need to be invoked at all - the
		2954	lowest priority will do.
		2955
		2956	This mode of operation can be useful together with an C<ev_check> watcher,
		2957	to do something on each event loop iteration - for example to balance load
		2958	between different connections.
		2959
		2960	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2961	example.
		2962
		2963	=head3 Watcher-Specific Functions and Data Members
		2964
662	=over 4	2965	=over 4
663		2966
664	=item ev_idle_init (ev_signal *, callback)	2967	=item ev_idle_init (ev_idle *, callback)
665		2968
666	Initialises and configures the idle watcher - it has no parameters of any	2969	Initialises and configures the idle watcher - it has no parameters of any
667	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2970	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
668	believe me.	2971	believe me.
669		2972
670	=back	2973	=back
671		2974
		2975	=head3 Examples
		2976
		2977	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2978	callback, free it. Also, use no error checking, as usual.
		2979
		2980	static void
		2981	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2982	{
		2983	// stop the watcher
		2984	ev_idle_stop (loop, w);
		2985
		2986	// now we can free it
		2987	free (w);
		2988
		2989	// now do something you wanted to do when the program has
		2990	// no longer anything immediate to do.
		2991	}
		2992
		2993	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2994	ev_idle_init (idle_watcher, idle_cb);
		2995	ev_idle_start (loop, idle_watcher);
		2996
		2997
672	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2998	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
673		2999
674	Prepare and check watchers are usually (but not always) used in tandem:	3000	Prepare and check watchers are often (but not always) used in pairs:
675	Prepare watchers get invoked before the process blocks and check watchers	3001	prepare watchers get invoked before the process blocks and check watchers
676	afterwards.	3002	afterwards.
677		3003
		3004	You I<must not> call C<ev_run> (or similar functions that enter the
		3005	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
		3006	C<ev_check> watchers. Other loops than the current one are fine,
		3007	however. The rationale behind this is that you do not need to check
		3008	for recursion in those watchers, i.e. the sequence will always be
		3009	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
		3010	kind they will always be called in pairs bracketing the blocking call.
		3011
678	Their main purpose is to integrate other event mechanisms into libev. This	3012	Their main purpose is to integrate other event mechanisms into libev and
679	could be used, for example, to track variable changes, implement your own	3013	their use is somewhat advanced. They could be used, for example, to track
680	watchers, integrate net-snmp or a coroutine library and lots more.	3014	variable changes, implement your own watchers, integrate net-snmp or a
		3015	coroutine library and lots more. They are also occasionally useful if
		3016	you cache some data and want to flush it before blocking (for example,
		3017	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		3018	watcher).
681		3019
682	This is done by examining in each prepare call which file descriptors need	3020	This is done by examining in each prepare call which file descriptors
683	to be watched by the other library, registering C<ev_io> watchers for	3021	need to be watched by the other library, registering C<ev_io> watchers
684	them and starting an C<ev_timer> watcher for any timeouts (many libraries	3022	for them and starting an C<ev_timer> watcher for any timeouts (many
685	provide just this functionality). Then, in the check watcher you check for	3023	libraries provide exactly this functionality). Then, in the check watcher,
686	any events that occured (by checking the pending status of all watchers	3024	you check for any events that occurred (by checking the pending status
687	and stopping them) and call back into the library. The I/O and timer	3025	of all watchers and stopping them) and call back into the library. The
688	callbacks will never actually be called (but must be valid neverthelles,	3026	I/O and timer callbacks will never actually be called (but must be valid
689	because you never know, you know?).	3027	nevertheless, because you never know, you know?).
690		3028
691	As another example, the Perl Coro module uses these hooks to integrate	3029	As another example, the Perl Coro module uses these hooks to integrate
692	coroutines into libev programs, by yielding to other active coroutines	3030	coroutines into libev programs, by yielding to other active coroutines
693	during each prepare and only letting the process block if no coroutines	3031	during each prepare and only letting the process block if no coroutines
694	are ready to run (its actually more complicated, it only runs coroutines	3032	are ready to run (it's actually more complicated: it only runs coroutines
695	with priority higher than the event loop and one lower priority once,	3033	with priority higher than or equal to the event loop and one coroutine
696	using idle watchers to keep the event loop from blocking if lower-priority	3034	of lower priority, but only once, using idle watchers to keep the event
697	coroutines exist, thus mapping low-priority coroutines to idle/background	3035	loop from blocking if lower-priority coroutines are active, thus mapping
698	tasks).	3036	low-priority coroutines to idle/background tasks).
		3037
		3038	When used for this purpose, it is recommended to give C<ev_check> watchers
		3039	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		3040	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		3041	watchers).
		3042
		3043	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		3044	activate ("feed") events into libev. While libev fully supports this, they
		3045	might get executed before other C<ev_check> watchers did their job. As
		3046	C<ev_check> watchers are often used to embed other (non-libev) event
		3047	loops those other event loops might be in an unusable state until their
		3048	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		3049	others).
		3050
		3051	=head3 Abusing an C<ev_check> watcher for its side-effect
		3052
		3053	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3054	useful because they are called once per event loop iteration. For
		3055	example, if you want to handle a large number of connections fairly, you
		3056	normally only do a bit of work for each active connection, and if there
		3057	is more work to do, you wait for the next event loop iteration, so other
		3058	connections have a chance of making progress.
		3059
		3060	Using an C<ev_check> watcher is almost enough: it will be called on the
		3061	next event loop iteration. However, that isn't as soon as possible -
		3062	without external events, your C<ev_check> watcher will not be invoked.
		3063
		3064	This is where C<ev_idle> watchers come in handy - all you need is a
		3065	single global idle watcher that is active as long as you have one active
		3066	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3067	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3068	invoked. Neither watcher alone can do that.
		3069
		3070	=head3 Watcher-Specific Functions and Data Members
699		3071
700	=over 4	3072	=over 4
701		3073
702	=item ev_prepare_init (ev_prepare *, callback)	3074	=item ev_prepare_init (ev_prepare *, callback)
703		3075
704	=item ev_check_init (ev_check *, callback)	3076	=item ev_check_init (ev_check *, callback)
705		3077
706	Initialises and configures the prepare or check watcher - they have no	3078	Initialises and configures the prepare or check watcher - they have no
707	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	3079	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
708	macros, but using them is utterly, utterly and completely pointless.	3080	macros, but using them is utterly, utterly, utterly and completely
		3081	pointless.
709		3082
710	=back	3083	=back
711		3084
		3085	=head3 Examples
		3086
		3087	There are a number of principal ways to embed other event loops or modules
		3088	into libev. Here are some ideas on how to include libadns into libev
		3089	(there is a Perl module named C<EV::ADNS> that does this, which you could
		3090	use as a working example. Another Perl module named C<EV::Glib> embeds a
		3091	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		3092	Glib event loop).
		3093
		3094	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		3095	and in a check watcher, destroy them and call into libadns. What follows
		3096	is pseudo-code only of course. This requires you to either use a low
		3097	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		3098	the callbacks for the IO/timeout watchers might not have been called yet.
		3099
		3100	static ev_io iow [nfd];
		3101	static ev_timer tw;
		3102
		3103	static void
		3104	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		3105	{
		3106	}
		3107
		3108	// create io watchers for each fd and a timer before blocking
		3109	static void
		3110	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		3111	{
		3112	int timeout = 3600000;
		3113	struct pollfd fds [nfd];
		3114	// actual code will need to loop here and realloc etc.
		3115	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		3116
		3117	/* the callback is illegal, but won't be called as we stop during check */
		3118	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		3119	ev_timer_start (loop, &tw);
		3120
		3121	// create one ev_io per pollfd
		3122	for (int i = 0; i < nfd; ++i)
		3123	{
		3124	ev_io_init (iow + i, io_cb, fds [i].fd,
		3125	((fds [i].events & POLLIN ? EV_READ : 0)
		3126	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		3127
		3128	fds [i].revents = 0;
		3129	ev_io_start (loop, iow + i);
		3130	}
		3131	}
		3132
		3133	// stop all watchers after blocking
		3134	static void
		3135	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		3136	{
		3137	ev_timer_stop (loop, &tw);
		3138
		3139	for (int i = 0; i < nfd; ++i)
		3140	{
		3141	// set the relevant poll flags
		3142	// could also call adns_processreadable etc. here
		3143	struct pollfd *fd = fds + i;
		3144	int revents = ev_clear_pending (iow + i);
		3145	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		3146	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		3147
		3148	// now stop the watcher
		3149	ev_io_stop (loop, iow + i);
		3150	}
		3151
		3152	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		3153	}
		3154
		3155	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		3156	in the prepare watcher and would dispose of the check watcher.
		3157
		3158	Method 3: If the module to be embedded supports explicit event
		3159	notification (libadns does), you can also make use of the actual watcher
		3160	callbacks, and only destroy/create the watchers in the prepare watcher.
		3161
		3162	static void
		3163	timer_cb (EV_P_ ev_timer *w, int revents)
		3164	{
		3165	adns_state ads = (adns_state)w->data;
		3166	update_now (EV_A);
		3167
		3168	adns_processtimeouts (ads, &tv_now);
		3169	}
		3170
		3171	static void
		3172	io_cb (EV_P_ ev_io *w, int revents)
		3173	{
		3174	adns_state ads = (adns_state)w->data;
		3175	update_now (EV_A);
		3176
		3177	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		3178	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		3179	}
		3180
		3181	// do not ever call adns_afterpoll
		3182
		3183	Method 4: Do not use a prepare or check watcher because the module you
		3184	want to embed is not flexible enough to support it. Instead, you can
		3185	override their poll function. The drawback with this solution is that the
		3186	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		3187	this approach, effectively embedding EV as a client into the horrible
		3188	libglib event loop.
		3189
		3190	static gint
		3191	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		3192	{
		3193	int got_events = 0;
		3194
		3195	for (n = 0; n < nfds; ++n)
		3196	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		3197
		3198	if (timeout >= 0)
		3199	// create/start timer
		3200
		3201	// poll
		3202	ev_run (EV_A_ 0);
		3203
		3204	// stop timer again
		3205	if (timeout >= 0)
		3206	ev_timer_stop (EV_A_ &to);
		3207
		3208	// stop io watchers again - their callbacks should have set
		3209	for (n = 0; n < nfds; ++n)
		3210	ev_io_stop (EV_A_ iow [n]);
		3211
		3212	return got_events;
		3213	}
		3214
		3215
		3216	=head2 C<ev_embed> - when one backend isn't enough...
		3217
		3218	This is a rather advanced watcher type that lets you embed one event loop
		3219	into another (currently only C<ev_io> events are supported in the embedded
		3220	loop, other types of watchers might be handled in a delayed or incorrect
		3221	fashion and must not be used).
		3222
		3223	There are primarily two reasons you would want that: work around bugs and
		3224	prioritise I/O.
		3225
		3226	As an example for a bug workaround, the kqueue backend might only support
		3227	sockets on some platform, so it is unusable as generic backend, but you
		3228	still want to make use of it because you have many sockets and it scales
		3229	so nicely. In this case, you would create a kqueue-based loop and embed
		3230	it into your default loop (which might use e.g. poll). Overall operation
		3231	will be a bit slower because first libev has to call C<poll> and then
		3232	C<kevent>, but at least you can use both mechanisms for what they are
		3233	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		3234
		3235	As for prioritising I/O: under rare circumstances you have the case where
		3236	some fds have to be watched and handled very quickly (with low latency),
		3237	and even priorities and idle watchers might have too much overhead. In
		3238	this case you would put all the high priority stuff in one loop and all
		3239	the rest in a second one, and embed the second one in the first.
		3240
		3241	As long as the watcher is active, the callback will be invoked every
		3242	time there might be events pending in the embedded loop. The callback
		3243	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		3244	sweep and invoke their callbacks (the callback doesn't need to invoke the
		3245	C<ev_embed_sweep> function directly, it could also start an idle watcher
		3246	to give the embedded loop strictly lower priority for example).
		3247
		3248	You can also set the callback to C<0>, in which case the embed watcher
		3249	will automatically execute the embedded loop sweep whenever necessary.
		3250
		3251	Fork detection will be handled transparently while the C<ev_embed> watcher
		3252	is active, i.e., the embedded loop will automatically be forked when the
		3253	embedding loop forks. In other cases, the user is responsible for calling
		3254	C<ev_loop_fork> on the embedded loop.
		3255
		3256	Unfortunately, not all backends are embeddable: only the ones returned by
		3257	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		3258	portable one.
		3259
		3260	So when you want to use this feature you will always have to be prepared
		3261	that you cannot get an embeddable loop. The recommended way to get around
		3262	this is to have a separate variables for your embeddable loop, try to
		3263	create it, and if that fails, use the normal loop for everything.
		3264
		3265	=head3 C<ev_embed> and fork
		3266
		3267	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3268	automatically be applied to the embedded loop as well, so no special
		3269	fork handling is required in that case. When the watcher is not running,
		3270	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3271	as applicable.
		3272
		3273	=head3 Watcher-Specific Functions and Data Members
		3274
		3275	=over 4
		3276
		3277	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		3278
		3279	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
		3280
		3281	Configures the watcher to embed the given loop, which must be
		3282	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		3283	invoked automatically, otherwise it is the responsibility of the callback
		3284	to invoke it (it will continue to be called until the sweep has been done,
		3285	if you do not want that, you need to temporarily stop the embed watcher).
		3286
		3287	=item ev_embed_sweep (loop, ev_embed *)
		3288
		3289	Make a single, non-blocking sweep over the embedded loop. This works
		3290	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
		3291	appropriate way for embedded loops.
		3292
		3293	=item struct ev_loop *other [read-only]
		3294
		3295	The embedded event loop.
		3296
		3297	=back
		3298
		3299	=head3 Examples
		3300
		3301	Example: Try to get an embeddable event loop and embed it into the default
		3302	event loop. If that is not possible, use the default loop. The default
		3303	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3304	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3305	used).
		3306
		3307	struct ev_loop *loop_hi = ev_default_init (0);
		3308	struct ev_loop *loop_lo = 0;
		3309	ev_embed embed;
		3310
		3311	// see if there is a chance of getting one that works
		3312	// (remember that a flags value of 0 means autodetection)
		3313	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3314	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3315	: 0;
		3316
		3317	// if we got one, then embed it, otherwise default to loop_hi
		3318	if (loop_lo)
		3319	{
		3320	ev_embed_init (&embed, 0, loop_lo);
		3321	ev_embed_start (loop_hi, &embed);
		3322	}
		3323	else
		3324	loop_lo = loop_hi;
		3325
		3326	Example: Check if kqueue is available but not recommended and create
		3327	a kqueue backend for use with sockets (which usually work with any
		3328	kqueue implementation). Store the kqueue/socket-only event loop in
		3329	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3330
		3331	struct ev_loop *loop = ev_default_init (0);
		3332	struct ev_loop *loop_socket = 0;
		3333	ev_embed embed;
		3334
		3335	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3336	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3337	{
		3338	ev_embed_init (&embed, 0, loop_socket);
		3339	ev_embed_start (loop, &embed);
		3340	}
		3341
		3342	if (!loop_socket)
		3343	loop_socket = loop;
		3344
		3345	// now use loop_socket for all sockets, and loop for everything else
		3346
		3347
		3348	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3349
		3350	Fork watchers are called when a C<fork ()> was detected (usually because
		3351	whoever is a good citizen cared to tell libev about it by calling
		3352	C<ev_loop_fork>). The invocation is done before the event loop blocks next
		3353	and before C<ev_check> watchers are being called, and only in the child
		3354	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
		3355	and calls it in the wrong process, the fork handlers will be invoked, too,
		3356	of course.
		3357
		3358	=head3 The special problem of life after fork - how is it possible?
		3359
		3360	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3361	up/change the process environment, followed by a call to C<exec()>. This
		3362	sequence should be handled by libev without any problems.
		3363
		3364	This changes when the application actually wants to do event handling
		3365	in the child, or both parent in child, in effect "continuing" after the
		3366	fork.
		3367
		3368	The default mode of operation (for libev, with application help to detect
		3369	forks) is to duplicate all the state in the child, as would be expected
		3370	when I<either> the parent I<or> the child process continues.
		3371
		3372	When both processes want to continue using libev, then this is usually the
		3373	wrong result. In that case, usually one process (typically the parent) is
		3374	supposed to continue with all watchers in place as before, while the other
		3375	process typically wants to start fresh, i.e. without any active watchers.
		3376
		3377	The cleanest and most efficient way to achieve that with libev is to
		3378	simply create a new event loop, which of course will be "empty", and
		3379	use that for new watchers. This has the advantage of not touching more
		3380	memory than necessary, and thus avoiding the copy-on-write, and the
		3381	disadvantage of having to use multiple event loops (which do not support
		3382	signal watchers).
		3383
		3384	When this is not possible, or you want to use the default loop for
		3385	other reasons, then in the process that wants to start "fresh", call
		3386	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3387	Destroying the default loop will "orphan" (not stop) all registered
		3388	watchers, so you have to be careful not to execute code that modifies
		3389	those watchers. Note also that in that case, you have to re-register any
		3390	signal watchers.
		3391
		3392	=head3 Watcher-Specific Functions and Data Members
		3393
		3394	=over 4
		3395
		3396	=item ev_fork_init (ev_fork *, callback)
		3397
		3398	Initialises and configures the fork watcher - it has no parameters of any
		3399	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3400	really.
		3401
		3402	=back
		3403
		3404
		3405	=head2 C<ev_cleanup> - even the best things end
		3406
		3407	Cleanup watchers are called just before the event loop is being destroyed
		3408	by a call to C<ev_loop_destroy>.
		3409
		3410	While there is no guarantee that the event loop gets destroyed, cleanup
		3411	watchers provide a convenient method to install cleanup hooks for your
		3412	program, worker threads and so on - you just to make sure to destroy the
		3413	loop when you want them to be invoked.
		3414
		3415	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3416	all other watchers, they do not keep a reference to the event loop (which
		3417	makes a lot of sense if you think about it). Like all other watchers, you
		3418	can call libev functions in the callback, except C<ev_cleanup_start>.
		3419
		3420	=head3 Watcher-Specific Functions and Data Members
		3421
		3422	=over 4
		3423
		3424	=item ev_cleanup_init (ev_cleanup *, callback)
		3425
		3426	Initialises and configures the cleanup watcher - it has no parameters of
		3427	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3428	pointless, I assure you.
		3429
		3430	=back
		3431
		3432	Example: Register an atexit handler to destroy the default loop, so any
		3433	cleanup functions are called.
		3434
		3435	static void
		3436	program_exits (void)
		3437	{
		3438	ev_loop_destroy (EV_DEFAULT_UC);
		3439	}
		3440
		3441	...
		3442	atexit (program_exits);
		3443
		3444
		3445	=head2 C<ev_async> - how to wake up an event loop
		3446
		3447	In general, you cannot use an C<ev_loop> from multiple threads or other
		3448	asynchronous sources such as signal handlers (as opposed to multiple event
		3449	loops - those are of course safe to use in different threads).
		3450
		3451	Sometimes, however, you need to wake up an event loop you do not control,
		3452	for example because it belongs to another thread. This is what C<ev_async>
		3453	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3454	it by calling C<ev_async_send>, which is thread- and signal safe.
		3455
		3456	This functionality is very similar to C<ev_signal> watchers, as signals,
		3457	too, are asynchronous in nature, and signals, too, will be compressed
		3458	(i.e. the number of callback invocations may be less than the number of
		3459	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3460	of "global async watchers" by using a watcher on an otherwise unused
		3461	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3462	even without knowing which loop owns the signal.
		3463
		3464	=head3 Queueing
		3465
		3466	C<ev_async> does not support queueing of data in any way. The reason
		3467	is that the author does not know of a simple (or any) algorithm for a
		3468	multiple-writer-single-reader queue that works in all cases and doesn't
		3469	need elaborate support such as pthreads or unportable memory access
		3470	semantics.
		3471
		3472	That means that if you want to queue data, you have to provide your own
		3473	queue. But at least I can tell you how to implement locking around your
		3474	queue:
		3475
		3476	=over 4
		3477
		3478	=item queueing from a signal handler context
		3479
		3480	To implement race-free queueing, you simply add to the queue in the signal
		3481	handler but you block the signal handler in the watcher callback. Here is
		3482	an example that does that for some fictitious SIGUSR1 handler:
		3483
		3484	static ev_async mysig;
		3485
		3486	static void
		3487	sigusr1_handler (void)
		3488	{
		3489	sometype data;
		3490
		3491	// no locking etc.
		3492	queue_put (data);
		3493	ev_async_send (EV_DEFAULT_ &mysig);
		3494	}
		3495
		3496	static void
		3497	mysig_cb (EV_P_ ev_async *w, int revents)
		3498	{
		3499	sometype data;
		3500	sigset_t block, prev;
		3501
		3502	sigemptyset (&block);
		3503	sigaddset (&block, SIGUSR1);
		3504	sigprocmask (SIG_BLOCK, &block, &prev);
		3505
		3506	while (queue_get (&data))
		3507	process (data);
		3508
		3509	if (sigismember (&prev, SIGUSR1)
		3510	sigprocmask (SIG_UNBLOCK, &block, 0);
		3511	}
		3512
		3513	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3514	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3515	either...).
		3516
		3517	=item queueing from a thread context
		3518
		3519	The strategy for threads is different, as you cannot (easily) block
		3520	threads but you can easily preempt them, so to queue safely you need to
		3521	employ a traditional mutex lock, such as in this pthread example:
		3522
		3523	static ev_async mysig;
		3524	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3525
		3526	static void
		3527	otherthread (void)
		3528	{
		3529	// only need to lock the actual queueing operation
		3530	pthread_mutex_lock (&mymutex);
		3531	queue_put (data);
		3532	pthread_mutex_unlock (&mymutex);
		3533
		3534	ev_async_send (EV_DEFAULT_ &mysig);
		3535	}
		3536
		3537	static void
		3538	mysig_cb (EV_P_ ev_async *w, int revents)
		3539	{
		3540	pthread_mutex_lock (&mymutex);
		3541
		3542	while (queue_get (&data))
		3543	process (data);
		3544
		3545	pthread_mutex_unlock (&mymutex);
		3546	}
		3547
		3548	=back
		3549
		3550
		3551	=head3 Watcher-Specific Functions and Data Members
		3552
		3553	=over 4
		3554
		3555	=item ev_async_init (ev_async *, callback)
		3556
		3557	Initialises and configures the async watcher - it has no parameters of any
		3558	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3559	trust me.
		3560
		3561	=item ev_async_send (loop, ev_async *)
		3562
		3563	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3564	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3565	returns.
		3566
		3567	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3568	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3569	embedding section below on what exactly this means).
		3570
		3571	Note that, as with other watchers in libev, multiple events might get
		3572	compressed into a single callback invocation (another way to look at
		3573	this is that C<ev_async> watchers are level-triggered: they are set on
		3574	C<ev_async_send>, reset when the event loop detects that).
		3575
		3576	This call incurs the overhead of at most one extra system call per event
		3577	loop iteration, if the event loop is blocked, and no syscall at all if
		3578	the event loop (or your program) is processing events. That means that
		3579	repeated calls are basically free (there is no need to avoid calls for
		3580	performance reasons) and that the overhead becomes smaller (typically
		3581	zero) under load.
		3582
		3583	=item bool = ev_async_pending (ev_async *)
		3584
		3585	Returns a non-zero value when C<ev_async_send> has been called on the
		3586	watcher but the event has not yet been processed (or even noted) by the
		3587	event loop.
		3588
		3589	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3590	the loop iterates next and checks for the watcher to have become active,
		3591	it will reset the flag again. C<ev_async_pending> can be used to very
		3592	quickly check whether invoking the loop might be a good idea.
		3593
		3594	Not that this does I<not> check whether the watcher itself is pending,
		3595	only whether it has been requested to make this watcher pending: there
		3596	is a time window between the event loop checking and resetting the async
		3597	notification, and the callback being invoked.
		3598
		3599	=back
		3600
		3601
712	=head1 OTHER FUNCTIONS	3602	=head1 OTHER FUNCTIONS
713		3603
714	There are some other functions of possible interest. Described. Here. Now.	3604	There are some other functions of possible interest. Described. Here. Now.
715		3605
716	=over 4	3606	=over 4
717		3607
718	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3608	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
719		3609
720	This function combines a simple timer and an I/O watcher, calls your	3610	This function combines a simple timer and an I/O watcher, calls your
721	callback on whichever event happens first and automatically stop both	3611	callback on whichever event happens first and automatically stops both
722	watchers. This is useful if you want to wait for a single event on an fd	3612	watchers. This is useful if you want to wait for a single event on an fd
723	or timeout without havign to allocate/configure/start/stop/free one or	3613	or timeout without having to allocate/configure/start/stop/free one or
724	more watchers yourself.	3614	more watchers yourself.
725		3615
726	If C<fd> is less than 0, then no I/O watcher will be started and events	3616	If C<fd> is less than 0, then no I/O watcher will be started and the
727	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3617	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
728	C<events> set will be craeted and started.	3618	the given C<fd> and C<events> set will be created and started.
729		3619
730	If C<timeout> is less than 0, then no timeout watcher will be	3620	If C<timeout> is less than 0, then no timeout watcher will be
731	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3621	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
732	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3622	repeat = 0) will be started. C<0> is a valid timeout.
733	dubious value.
734		3623
735	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3624	The callback has the type C<void (*cb)(int revents, void *arg)> and is
736	passed an events set like normal event callbacks (with a combination of	3625	passed an C<revents> set like normal event callbacks (a combination of
737	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3626	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
738	value passed to C<ev_once>:	3627	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3628	a timeout and an io event at the same time - you probably should give io
		3629	events precedence.
739		3630
		3631	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3632
740	static void stdin_ready (int revents, void *arg)	3633	static void stdin_ready (int revents, void *arg)
		3634	{
		3635	if (revents & EV_READ)
		3636	/* stdin might have data for us, joy! */;
		3637	else if (revents & EV_TIMER)
		3638	/* doh, nothing entered */;
		3639	}
		3640
		3641	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3642
		3643	=item ev_feed_fd_event (loop, int fd, int revents)
		3644
		3645	Feed an event on the given fd, as if a file descriptor backend detected
		3646	the given events.
		3647
		3648	=item ev_feed_signal_event (loop, int signum)
		3649
		3650	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3651	which is async-safe.
		3652
		3653	=back
		3654
		3655
		3656	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3657
		3658	This section explains some common idioms that are not immediately
		3659	obvious. Note that examples are sprinkled over the whole manual, and this
		3660	section only contains stuff that wouldn't fit anywhere else.
		3661
		3662	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3663
		3664	Each watcher has, by default, a C<void *data> member that you can read
		3665	or modify at any time: libev will completely ignore it. This can be used
		3666	to associate arbitrary data with your watcher. If you need more data and
		3667	don't want to allocate memory separately and store a pointer to it in that
		3668	data member, you can also "subclass" the watcher type and provide your own
		3669	data:
		3670
		3671	struct my_io
		3672	{
		3673	ev_io io;
		3674	int otherfd;
		3675	void *somedata;
		3676	struct whatever *mostinteresting;
		3677	};
		3678
		3679	...
		3680	struct my_io w;
		3681	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3682
		3683	And since your callback will be called with a pointer to the watcher, you
		3684	can cast it back to your own type:
		3685
		3686	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3687	{
		3688	struct my_io *w = (struct my_io *)w_;
		3689	...
		3690	}
		3691
		3692	More interesting and less C-conformant ways of casting your callback
		3693	function type instead have been omitted.
		3694
		3695	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3696
		3697	Another common scenario is to use some data structure with multiple
		3698	embedded watchers, in effect creating your own watcher that combines
		3699	multiple libev event sources into one "super-watcher":
		3700
		3701	struct my_biggy
		3702	{
		3703	int some_data;
		3704	ev_timer t1;
		3705	ev_timer t2;
		3706	}
		3707
		3708	In this case getting the pointer to C<my_biggy> is a bit more
		3709	complicated: Either you store the address of your C<my_biggy> struct in
		3710	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3711	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3712	real programmers):
		3713
		3714	#include <stddef.h>
		3715
		3716	static void
		3717	t1_cb (EV_P_ ev_timer *w, int revents)
		3718	{
		3719	struct my_biggy big = (struct my_biggy *)
		3720	(((char *)w) - offsetof (struct my_biggy, t1));
		3721	}
		3722
		3723	static void
		3724	t2_cb (EV_P_ ev_timer *w, int revents)
		3725	{
		3726	struct my_biggy big = (struct my_biggy *)
		3727	(((char *)w) - offsetof (struct my_biggy, t2));
		3728	}
		3729
		3730	=head2 AVOIDING FINISHING BEFORE RETURNING
		3731
		3732	Often you have structures like this in event-based programs:
		3733
		3734	callback ()
741	{	3735	{
742	if (revents & EV_TIMEOUT)	3736	free (request);
743	/* doh, nothing entered */;
744	else if (revents & EV_READ)
745	/* stdin might have data for us, joy! */;
746	}	3737	}
747		3738
748	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3739	request = start_new_request (..., callback);
749		3740
750	=item ev_feed_event (loop, watcher, int events)	3741	The intent is to start some "lengthy" operation. The C<request> could be
		3742	used to cancel the operation, or do other things with it.
751		3743
752	Feeds the given event set into the event loop, as if the specified event	3744	It's not uncommon to have code paths in C<start_new_request> that
753	had happened for the specified watcher (which must be a pointer to an	3745	immediately invoke the callback, for example, to report errors. Or you add
754	initialised but not necessarily started event watcher).	3746	some caching layer that finds that it can skip the lengthy aspects of the
		3747	operation and simply invoke the callback with the result.
755		3748
756	=item ev_feed_fd_event (loop, int fd, int revents)	3749	The problem here is that this will happen I<before> C<start_new_request>
		3750	has returned, so C<request> is not set.
757		3751
758	Feed an event on the given fd, as if a file descriptor backend detected	3752	Even if you pass the request by some safer means to the callback, you
759	the given events it.	3753	might want to do something to the request after starting it, such as
		3754	canceling it, which probably isn't working so well when the callback has
		3755	already been invoked.
760		3756
761	=item ev_feed_signal_event (loop, int signum)	3757	A common way around all these issues is to make sure that
		3758	C<start_new_request> I<always> returns before the callback is invoked. If
		3759	C<start_new_request> immediately knows the result, it can artificially
		3760	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3761	example, or more sneakily, by reusing an existing (stopped) watcher and
		3762	pushing it into the pending queue:
762		3763
763	Feed an event as if the given signal occured (loop must be the default loop!).	3764	ev_set_cb (watcher, callback);
		3765	ev_feed_event (EV_A_ watcher, 0);
		3766
		3767	This way, C<start_new_request> can safely return before the callback is
		3768	invoked, while not delaying callback invocation too much.
		3769
		3770	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3771
		3772	Often (especially in GUI toolkits) there are places where you have
		3773	I<modal> interaction, which is most easily implemented by recursively
		3774	invoking C<ev_run>.
		3775
		3776	This brings the problem of exiting - a callback might want to finish the
		3777	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3778	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3779	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3780	other combination: In these cases, a simple C<ev_break> will not work.
		3781
		3782	The solution is to maintain "break this loop" variable for each C<ev_run>
		3783	invocation, and use a loop around C<ev_run> until the condition is
		3784	triggered, using C<EVRUN_ONCE>:
		3785
		3786	// main loop
		3787	int exit_main_loop = 0;
		3788
		3789	while (!exit_main_loop)
		3790	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3791
		3792	// in a modal watcher
		3793	int exit_nested_loop = 0;
		3794
		3795	while (!exit_nested_loop)
		3796	ev_run (EV_A_ EVRUN_ONCE);
		3797
		3798	To exit from any of these loops, just set the corresponding exit variable:
		3799
		3800	// exit modal loop
		3801	exit_nested_loop = 1;
		3802
		3803	// exit main program, after modal loop is finished
		3804	exit_main_loop = 1;
		3805
		3806	// exit both
		3807	exit_main_loop = exit_nested_loop = 1;
		3808
		3809	=head2 THREAD LOCKING EXAMPLE
		3810
		3811	Here is a fictitious example of how to run an event loop in a different
		3812	thread from where callbacks are being invoked and watchers are
		3813	created/added/removed.
		3814
		3815	For a real-world example, see the C<EV::Loop::Async> perl module,
		3816	which uses exactly this technique (which is suited for many high-level
		3817	languages).
		3818
		3819	The example uses a pthread mutex to protect the loop data, a condition
		3820	variable to wait for callback invocations, an async watcher to notify the
		3821	event loop thread and an unspecified mechanism to wake up the main thread.
		3822
		3823	First, you need to associate some data with the event loop:
		3824
		3825	typedef struct {
		3826	mutex_t lock; /* global loop lock */
		3827	ev_async async_w;
		3828	thread_t tid;
		3829	cond_t invoke_cv;
		3830	} userdata;
		3831
		3832	void prepare_loop (EV_P)
		3833	{
		3834	// for simplicity, we use a static userdata struct.
		3835	static userdata u;
		3836
		3837	ev_async_init (&u->async_w, async_cb);
		3838	ev_async_start (EV_A_ &u->async_w);
		3839
		3840	pthread_mutex_init (&u->lock, 0);
		3841	pthread_cond_init (&u->invoke_cv, 0);
		3842
		3843	// now associate this with the loop
		3844	ev_set_userdata (EV_A_ u);
		3845	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3846	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3847
		3848	// then create the thread running ev_run
		3849	pthread_create (&u->tid, 0, l_run, EV_A);
		3850	}
		3851
		3852	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3853	solely to wake up the event loop so it takes notice of any new watchers
		3854	that might have been added:
		3855
		3856	static void
		3857	async_cb (EV_P_ ev_async *w, int revents)
		3858	{
		3859	// just used for the side effects
		3860	}
		3861
		3862	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3863	protecting the loop data, respectively.
		3864
		3865	static void
		3866	l_release (EV_P)
		3867	{
		3868	userdata *u = ev_userdata (EV_A);
		3869	pthread_mutex_unlock (&u->lock);
		3870	}
		3871
		3872	static void
		3873	l_acquire (EV_P)
		3874	{
		3875	userdata *u = ev_userdata (EV_A);
		3876	pthread_mutex_lock (&u->lock);
		3877	}
		3878
		3879	The event loop thread first acquires the mutex, and then jumps straight
		3880	into C<ev_run>:
		3881
		3882	void *
		3883	l_run (void *thr_arg)
		3884	{
		3885	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3886
		3887	l_acquire (EV_A);
		3888	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3889	ev_run (EV_A_ 0);
		3890	l_release (EV_A);
		3891
		3892	return 0;
		3893	}
		3894
		3895	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3896	signal the main thread via some unspecified mechanism (signals? pipe
		3897	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3898	have been called (in a while loop because a) spurious wakeups are possible
		3899	and b) skipping inter-thread-communication when there are no pending
		3900	watchers is very beneficial):
		3901
		3902	static void
		3903	l_invoke (EV_P)
		3904	{
		3905	userdata *u = ev_userdata (EV_A);
		3906
		3907	while (ev_pending_count (EV_A))
		3908	{
		3909	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3910	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3911	}
		3912	}
		3913
		3914	Now, whenever the main thread gets told to invoke pending watchers, it
		3915	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3916	thread to continue:
		3917
		3918	static void
		3919	real_invoke_pending (EV_P)
		3920	{
		3921	userdata *u = ev_userdata (EV_A);
		3922
		3923	pthread_mutex_lock (&u->lock);
		3924	ev_invoke_pending (EV_A);
		3925	pthread_cond_signal (&u->invoke_cv);
		3926	pthread_mutex_unlock (&u->lock);
		3927	}
		3928
		3929	Whenever you want to start/stop a watcher or do other modifications to an
		3930	event loop, you will now have to lock:
		3931
		3932	ev_timer timeout_watcher;
		3933	userdata *u = ev_userdata (EV_A);
		3934
		3935	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3936
		3937	pthread_mutex_lock (&u->lock);
		3938	ev_timer_start (EV_A_ &timeout_watcher);
		3939	ev_async_send (EV_A_ &u->async_w);
		3940	pthread_mutex_unlock (&u->lock);
		3941
		3942	Note that sending the C<ev_async> watcher is required because otherwise
		3943	an event loop currently blocking in the kernel will have no knowledge
		3944	about the newly added timer. By waking up the loop it will pick up any new
		3945	watchers in the next event loop iteration.
		3946
		3947	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3948
		3949	While the overhead of a callback that e.g. schedules a thread is small, it
		3950	is still an overhead. If you embed libev, and your main usage is with some
		3951	kind of threads or coroutines, you might want to customise libev so that
		3952	doesn't need callbacks anymore.
		3953
		3954	Imagine you have coroutines that you can switch to using a function
		3955	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3956	and that due to some magic, the currently active coroutine is stored in a
		3957	global called C<current_coro>. Then you can build your own "wait for libev
		3958	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3959	the differing C<;> conventions):
		3960
		3961	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3962	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3963
		3964	That means instead of having a C callback function, you store the
		3965	coroutine to switch to in each watcher, and instead of having libev call
		3966	your callback, you instead have it switch to that coroutine.
		3967
		3968	A coroutine might now wait for an event with a function called
		3969	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3970	matter when, or whether the watcher is active or not when this function is
		3971	called):
		3972
		3973	void
		3974	wait_for_event (ev_watcher *w)
		3975	{
		3976	ev_set_cb (w, current_coro);
		3977	switch_to (libev_coro);
		3978	}
		3979
		3980	That basically suspends the coroutine inside C<wait_for_event> and
		3981	continues the libev coroutine, which, when appropriate, switches back to
		3982	this or any other coroutine.
		3983
		3984	You can do similar tricks if you have, say, threads with an event queue -
		3985	instead of storing a coroutine, you store the queue object and instead of
		3986	switching to a coroutine, you push the watcher onto the queue and notify
		3987	any waiters.
		3988
		3989	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3990	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3991
		3992	// my_ev.h
		3993	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3994	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3995	#include "../libev/ev.h"
		3996
		3997	// my_ev.c
		3998	#define EV_H "my_ev.h"
		3999	#include "../libev/ev.c"
		4000
		4001	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		4002	F<my_ev.c> into your project. When properly specifying include paths, you
		4003	can even use F<ev.h> as header file name directly.
		4004
		4005
		4006	=head1 LIBEVENT EMULATION
		4007
		4008	Libev offers a compatibility emulation layer for libevent. It cannot
		4009	emulate the internals of libevent, so here are some usage hints:
		4010
		4011	=over 4
		4012
		4013	=item * Only the libevent-1.4.1-beta API is being emulated.
		4014
		4015	This was the newest libevent version available when libev was implemented,
		4016	and is still mostly unchanged in 2010.
		4017
		4018	=item * Use it by including <event.h>, as usual.
		4019
		4020	=item * The following members are fully supported: ev_base, ev_callback,
		4021	ev_arg, ev_fd, ev_res, ev_events.
		4022
		4023	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		4024	maintained by libev, it does not work exactly the same way as in libevent (consider
		4025	it a private API).
		4026
		4027	=item * Priorities are not currently supported. Initialising priorities
		4028	will fail and all watchers will have the same priority, even though there
		4029	is an ev_pri field.
		4030
		4031	=item * In libevent, the last base created gets the signals, in libev, the
		4032	base that registered the signal gets the signals.
		4033
		4034	=item * Other members are not supported.
		4035
		4036	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		4037	to use the libev header file and library.
764		4038
765	=back	4039	=back
766		4040
		4041	=head1 C++ SUPPORT
		4042
		4043	=head2 C API
		4044
		4045	The normal C API should work fine when used from C++: both ev.h and the
		4046	libev sources can be compiled as C++. Therefore, code that uses the C API
		4047	will work fine.
		4048
		4049	Proper exception specifications might have to be added to callbacks passed
		4050	to libev: exceptions may be thrown only from watcher callbacks, all other
		4051	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4052	callbacks) must not throw exceptions, and might need a C<noexcept>
		4053	specification. If you have code that needs to be compiled as both C and
		4054	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4055
		4056	static void
		4057	fatal_error (const char *msg) EV_NOEXCEPT
		4058	{
		4059	perror (msg);
		4060	abort ();
		4061	}
		4062
		4063	...
		4064	ev_set_syserr_cb (fatal_error);
		4065
		4066	The only API functions that can currently throw exceptions are C<ev_run>,
		4067	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4068	because it runs cleanup watchers).
		4069
		4070	Throwing exceptions in watcher callbacks is only supported if libev itself
		4071	is compiled with a C++ compiler or your C and C++ environments allow
		4072	throwing exceptions through C libraries (most do).
		4073
		4074	=head2 C++ API
		4075
		4076	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		4077	you to use some convenience methods to start/stop watchers and also change
		4078	the callback model to a model using method callbacks on objects.
		4079
		4080	To use it,
		4081
		4082	#include <ev++.h>
		4083
		4084	This automatically includes F<ev.h> and puts all of its definitions (many
		4085	of them macros) into the global namespace. All C++ specific things are
		4086	put into the C<ev> namespace. It should support all the same embedding
		4087	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		4088
		4089	Care has been taken to keep the overhead low. The only data member the C++
		4090	classes add (compared to plain C-style watchers) is the event loop pointer
		4091	that the watcher is associated with (or no additional members at all if
		4092	you disable C<EV_MULTIPLICITY> when embedding libev).
		4093
		4094	Currently, functions, static and non-static member functions and classes
		4095	with C<operator ()> can be used as callbacks. Other types should be easy
		4096	to add as long as they only need one additional pointer for context. If
		4097	you need support for other types of functors please contact the author
		4098	(preferably after implementing it).
		4099
		4100	For all this to work, your C++ compiler either has to use the same calling
		4101	conventions as your C compiler (for static member functions), or you have
		4102	to embed libev and compile libev itself as C++.
		4103
		4104	Here is a list of things available in the C<ev> namespace:
		4105
		4106	=over 4
		4107
		4108	=item C<ev::READ>, C<ev::WRITE> etc.
		4109
		4110	These are just enum values with the same values as the C<EV_READ> etc.
		4111	macros from F<ev.h>.
		4112
		4113	=item C<ev::tstamp>, C<ev::now>
		4114
		4115	Aliases to the same types/functions as with the C<ev_> prefix.
		4116
		4117	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		4118
		4119	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		4120	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		4121	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		4122	defined by many implementations.
		4123
		4124	All of those classes have these methods:
		4125
		4126	=over 4
		4127
		4128	=item ev::TYPE::TYPE ()
		4129
		4130	=item ev::TYPE::TYPE (loop)
		4131
		4132	=item ev::TYPE::~TYPE
		4133
		4134	The constructor (optionally) takes an event loop to associate the watcher
		4135	with. If it is omitted, it will use C<EV_DEFAULT>.
		4136
		4137	The constructor calls C<ev_init> for you, which means you have to call the
		4138	C<set> method before starting it.
		4139
		4140	It will not set a callback, however: You have to call the templated C<set>
		4141	method to set a callback before you can start the watcher.
		4142
		4143	(The reason why you have to use a method is a limitation in C++ which does
		4144	not allow explicit template arguments for constructors).
		4145
		4146	The destructor automatically stops the watcher if it is active.
		4147
		4148	=item w->set<class, &class::method> (object *)
		4149
		4150	This method sets the callback method to call. The method has to have a
		4151	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		4152	first argument and the C<revents> as second. The object must be given as
		4153	parameter and is stored in the C<data> member of the watcher.
		4154
		4155	This method synthesizes efficient thunking code to call your method from
		4156	the C callback that libev requires. If your compiler can inline your
		4157	callback (i.e. it is visible to it at the place of the C<set> call and
		4158	your compiler is good :), then the method will be fully inlined into the
		4159	thunking function, making it as fast as a direct C callback.
		4160
		4161	Example: simple class declaration and watcher initialisation
		4162
		4163	struct myclass
		4164	{
		4165	void io_cb (ev::io &w, int revents) { }
		4166	}
		4167
		4168	myclass obj;
		4169	ev::io iow;
		4170	iow.set <myclass, &myclass::io_cb> (&obj);
		4171
		4172	=item w->set (object *)
		4173
		4174	This is a variation of a method callback - leaving out the method to call
		4175	will default the method to C<operator ()>, which makes it possible to use
		4176	functor objects without having to manually specify the C<operator ()> all
		4177	the time. Incidentally, you can then also leave out the template argument
		4178	list.
		4179
		4180	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4181	int revents)>.
		4182
		4183	See the method-C<set> above for more details.
		4184
		4185	Example: use a functor object as callback.
		4186
		4187	struct myfunctor
		4188	{
		4189	void operator() (ev::io &w, int revents)
		4190	{
		4191	...
		4192	}
		4193	}
		4194
		4195	myfunctor f;
		4196
		4197	ev::io w;
		4198	w.set (&f);
		4199
		4200	=item w->set<function> (void *data = 0)
		4201
		4202	Also sets a callback, but uses a static method or plain function as
		4203	callback. The optional C<data> argument will be stored in the watcher's
		4204	C<data> member and is free for you to use.
		4205
		4206	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		4207
		4208	See the method-C<set> above for more details.
		4209
		4210	Example: Use a plain function as callback.
		4211
		4212	static void io_cb (ev::io &w, int revents) { }
		4213	iow.set <io_cb> ();
		4214
		4215	=item w->set (loop)
		4216
		4217	Associates a different C<struct ev_loop> with this watcher. You can only
		4218	do this when the watcher is inactive (and not pending either).
		4219
		4220	=item w->set ([arguments])
		4221
		4222	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4223	with the same arguments. Either this method or a suitable start method
		4224	must be called at least once. Unlike the C counterpart, an active watcher
		4225	gets automatically stopped and restarted when reconfiguring it with this
		4226	method.
		4227
		4228	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4229	clashing with the C<set (loop)> method.
		4230
		4231	=item w->start ()
		4232
		4233	Starts the watcher. Note that there is no C<loop> argument, as the
		4234	constructor already stores the event loop.
		4235
		4236	=item w->start ([arguments])
		4237
		4238	Instead of calling C<set> and C<start> methods separately, it is often
		4239	convenient to wrap them in one call. Uses the same type of arguments as
		4240	the configure C<set> method of the watcher.
		4241
		4242	=item w->stop ()
		4243
		4244	Stops the watcher if it is active. Again, no C<loop> argument.
		4245
		4246	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		4247
		4248	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		4249	C<ev_TYPE_again> function.
		4250
		4251	=item w->sweep () (C<ev::embed> only)
		4252
		4253	Invokes C<ev_embed_sweep>.
		4254
		4255	=item w->update () (C<ev::stat> only)
		4256
		4257	Invokes C<ev_stat_stat>.
		4258
		4259	=back
		4260
		4261	=back
		4262
		4263	Example: Define a class with two I/O and idle watchers, start the I/O
		4264	watchers in the constructor.
		4265
		4266	class myclass
		4267	{
		4268	ev::io io ; void io_cb (ev::io &w, int revents);
		4269	ev::io io2 ; void io2_cb (ev::io &w, int revents);
		4270	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		4271
		4272	myclass (int fd)
		4273	{
		4274	io .set <myclass, &myclass::io_cb > (this);
		4275	io2 .set <myclass, &myclass::io2_cb > (this);
		4276	idle.set <myclass, &myclass::idle_cb> (this);
		4277
		4278	io.set (fd, ev::WRITE); // configure the watcher
		4279	io.start (); // start it whenever convenient
		4280
		4281	io2.start (fd, ev::READ); // set + start in one call
		4282	}
		4283	};
		4284
		4285
		4286	=head1 OTHER LANGUAGE BINDINGS
		4287
		4288	Libev does not offer other language bindings itself, but bindings for a
		4289	number of languages exist in the form of third-party packages. If you know
		4290	any interesting language binding in addition to the ones listed here, drop
		4291	me a note.
		4292
		4293	=over 4
		4294
		4295	=item Perl
		4296
		4297	The EV module implements the full libev API and is actually used to test
		4298	libev. EV is developed together with libev. Apart from the EV core module,
		4299	there are additional modules that implement libev-compatible interfaces
		4300	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4301	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4302	and C<EV::Glib>).
		4303
		4304	It can be found and installed via CPAN, its homepage is at
		4305	L<http://software.schmorp.de/pkg/EV>.
		4306
		4307	=item Python
		4308
		4309	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4310	seems to be quite complete and well-documented.
		4311
		4312	=item Ruby
		4313
		4314	Tony Arcieri has written a ruby extension that offers access to a subset
		4315	of the libev API and adds file handle abstractions, asynchronous DNS and
		4316	more on top of it. It can be found via gem servers. Its homepage is at
		4317	L<http://rev.rubyforge.org/>.
		4318
		4319	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4320	makes rev work even on mingw.
		4321
		4322	=item Haskell
		4323
		4324	A haskell binding to libev is available at
		4325	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4326
		4327	=item D
		4328
		4329	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4330	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4331
		4332	=item Ocaml
		4333
		4334	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4335	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4336
		4337	=item Lua
		4338
		4339	Brian Maher has written a partial interface to libev for lua (at the
		4340	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4341	L<http://github.com/brimworks/lua-ev>.
		4342
		4343	=item Javascript
		4344
		4345	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4346
		4347	=item Others
		4348
		4349	There are others, and I stopped counting.
		4350
		4351	=back
		4352
		4353
		4354	=head1 MACRO MAGIC
		4355
		4356	Libev can be compiled with a variety of options, the most fundamental
		4357	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		4358	functions and callbacks have an initial C<struct ev_loop *> argument.
		4359
		4360	To make it easier to write programs that cope with either variant, the
		4361	following macros are defined:
		4362
		4363	=over 4
		4364
		4365	=item C<EV_A>, C<EV_A_>
		4366
		4367	This provides the loop I<argument> for functions, if one is required ("ev
		4368	loop argument"). The C<EV_A> form is used when this is the sole argument,
		4369	C<EV_A_> is used when other arguments are following. Example:
		4370
		4371	ev_unref (EV_A);
		4372	ev_timer_add (EV_A_ watcher);
		4373	ev_run (EV_A_ 0);
		4374
		4375	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		4376	which is often provided by the following macro.
		4377
		4378	=item C<EV_P>, C<EV_P_>
		4379
		4380	This provides the loop I<parameter> for functions, if one is required ("ev
		4381	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		4382	C<EV_P_> is used when other parameters are following. Example:
		4383
		4384	// this is how ev_unref is being declared
		4385	static void ev_unref (EV_P);
		4386
		4387	// this is how you can declare your typical callback
		4388	static void cb (EV_P_ ev_timer *w, int revents)
		4389
		4390	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		4391	suitable for use with C<EV_A>.
		4392
		4393	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		4394
		4395	Similar to the other two macros, this gives you the value of the default
		4396	loop, if multiple loops are supported ("ev loop default"). The default loop
		4397	will be initialised if it isn't already initialised.
		4398
		4399	For non-multiplicity builds, these macros do nothing, so you always have
		4400	to initialise the loop somewhere.
		4401
		4402	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4403
		4404	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4405	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4406	is undefined when the default loop has not been initialised by a previous
		4407	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4408
		4409	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4410	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		4411
		4412	=back
		4413
		4414	Example: Declare and initialise a check watcher, utilising the above
		4415	macros so it will work regardless of whether multiple loops are supported
		4416	or not.
		4417
		4418	static void
		4419	check_cb (EV_P_ ev_timer *w, int revents)
		4420	{
		4421	ev_check_stop (EV_A_ w);
		4422	}
		4423
		4424	ev_check check;
		4425	ev_check_init (&check, check_cb);
		4426	ev_check_start (EV_DEFAULT_ &check);
		4427	ev_run (EV_DEFAULT_ 0);
		4428
		4429	=head1 EMBEDDING
		4430
		4431	Libev can (and often is) directly embedded into host
		4432	applications. Examples of applications that embed it include the Deliantra
		4433	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		4434	and rxvt-unicode.
		4435
		4436	The goal is to enable you to just copy the necessary files into your
		4437	source directory without having to change even a single line in them, so
		4438	you can easily upgrade by simply copying (or having a checked-out copy of
		4439	libev somewhere in your source tree).
		4440
		4441	=head2 FILESETS
		4442
		4443	Depending on what features you need you need to include one or more sets of files
		4444	in your application.
		4445
		4446	=head3 CORE EVENT LOOP
		4447
		4448	To include only the libev core (all the C<ev_*> functions), with manual
		4449	configuration (no autoconf):
		4450
		4451	#define EV_STANDALONE 1
		4452	#include "ev.c"
		4453
		4454	This will automatically include F<ev.h>, too, and should be done in a
		4455	single C source file only to provide the function implementations. To use
		4456	it, do the same for F<ev.h> in all files wishing to use this API (best
		4457	done by writing a wrapper around F<ev.h> that you can include instead and
		4458	where you can put other configuration options):
		4459
		4460	#define EV_STANDALONE 1
		4461	#include "ev.h"
		4462
		4463	Both header files and implementation files can be compiled with a C++
		4464	compiler (at least, that's a stated goal, and breakage will be treated
		4465	as a bug).
		4466
		4467	You need the following files in your source tree, or in a directory
		4468	in your include path (e.g. in libev/ when using -Ilibev):
		4469
		4470	ev.h
		4471	ev.c
		4472	ev_vars.h
		4473	ev_wrap.h
		4474
		4475	ev_win32.c required on win32 platforms only
		4476
		4477	ev_select.c only when select backend is enabled
		4478	ev_poll.c only when poll backend is enabled
		4479	ev_epoll.c only when the epoll backend is enabled
		4480	ev_linuxaio.c only when the linux aio backend is enabled
		4481	ev_kqueue.c only when the kqueue backend is enabled
		4482	ev_port.c only when the solaris port backend is enabled
		4483
		4484	F<ev.c> includes the backend files directly when enabled, so you only need
		4485	to compile this single file.
		4486
		4487	=head3 LIBEVENT COMPATIBILITY API
		4488
		4489	To include the libevent compatibility API, also include:
		4490
		4491	#include "event.c"
		4492
		4493	in the file including F<ev.c>, and:
		4494
		4495	#include "event.h"
		4496
		4497	in the files that want to use the libevent API. This also includes F<ev.h>.
		4498
		4499	You need the following additional files for this:
		4500
		4501	event.h
		4502	event.c
		4503
		4504	=head3 AUTOCONF SUPPORT
		4505
		4506	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		4507	whatever way you want, you can also C<m4_include([libev.m4])> in your
		4508	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		4509	include F<config.h> and configure itself accordingly.
		4510
		4511	For this of course you need the m4 file:
		4512
		4513	libev.m4
		4514
		4515	=head2 PREPROCESSOR SYMBOLS/MACROS
		4516
		4517	Libev can be configured via a variety of preprocessor symbols you have to
		4518	define before including (or compiling) any of its files. The default in
		4519	the absence of autoconf is documented for every option.
		4520
		4521	Symbols marked with "(h)" do not change the ABI, and can have different
		4522	values when compiling libev vs. including F<ev.h>, so it is permissible
		4523	to redefine them before including F<ev.h> without breaking compatibility
		4524	to a compiled library. All other symbols change the ABI, which means all
		4525	users of libev and the libev code itself must be compiled with compatible
		4526	settings.
		4527
		4528	=over 4
		4529
		4530	=item EV_COMPAT3 (h)
		4531
		4532	Backwards compatibility is a major concern for libev. This is why this
		4533	release of libev comes with wrappers for the functions and symbols that
		4534	have been renamed between libev version 3 and 4.
		4535
		4536	You can disable these wrappers (to test compatibility with future
		4537	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4538	sources. This has the additional advantage that you can drop the C<struct>
		4539	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4540	typedef in that case.
		4541
		4542	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4543	and in some even more future version the compatibility code will be
		4544	removed completely.
		4545
		4546	=item EV_STANDALONE (h)
		4547
		4548	Must always be C<1> if you do not use autoconf configuration, which
		4549	keeps libev from including F<config.h>, and it also defines dummy
		4550	implementations for some libevent functions (such as logging, which is not
		4551	supported). It will also not define any of the structs usually found in
		4552	F<event.h> that are not directly supported by the libev core alone.
		4553
		4554	In standalone mode, libev will still try to automatically deduce the
		4555	configuration, but has to be more conservative.
		4556
		4557	=item EV_USE_FLOOR
		4558
		4559	If defined to be C<1>, libev will use the C<floor ()> function for its
		4560	periodic reschedule calculations, otherwise libev will fall back on a
		4561	portable (slower) implementation. If you enable this, you usually have to
		4562	link against libm or something equivalent. Enabling this when the C<floor>
		4563	function is not available will fail, so the safe default is to not enable
		4564	this.
		4565
		4566	=item EV_USE_MONOTONIC
		4567
		4568	If defined to be C<1>, libev will try to detect the availability of the
		4569	monotonic clock option at both compile time and runtime. Otherwise no
		4570	use of the monotonic clock option will be attempted. If you enable this,
		4571	you usually have to link against librt or something similar. Enabling it
		4572	when the functionality isn't available is safe, though, although you have
		4573	to make sure you link against any libraries where the C<clock_gettime>
		4574	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		4575
		4576	=item EV_USE_REALTIME
		4577
		4578	If defined to be C<1>, libev will try to detect the availability of the
		4579	real-time clock option at compile time (and assume its availability
		4580	at runtime if successful). Otherwise no use of the real-time clock
		4581	option will be attempted. This effectively replaces C<gettimeofday>
		4582	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		4583	correctness. See the note about libraries in the description of
		4584	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4585	C<EV_USE_CLOCK_SYSCALL>.
		4586
		4587	=item EV_USE_CLOCK_SYSCALL
		4588
		4589	If defined to be C<1>, libev will try to use a direct syscall instead
		4590	of calling the system-provided C<clock_gettime> function. This option
		4591	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4592	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4593	programs needlessly. Using a direct syscall is slightly slower (in
		4594	theory), because no optimised vdso implementation can be used, but avoids
		4595	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4596	higher, as it simplifies linking (no need for C<-lrt>).
		4597
		4598	=item EV_USE_NANOSLEEP
		4599
		4600	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4601	and will use it for delays. Otherwise it will use C<select ()>.
		4602
		4603	=item EV_USE_EVENTFD
		4604
		4605	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4606	available and will probe for kernel support at runtime. This will improve
		4607	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4608	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4609	2.7 or newer, otherwise disabled.
		4610
		4611	=item EV_USE_SELECT
		4612
		4613	If undefined or defined to be C<1>, libev will compile in support for the
		4614	C<select>(2) backend. No attempt at auto-detection will be done: if no
		4615	other method takes over, select will be it. Otherwise the select backend
		4616	will not be compiled in.
		4617
		4618	=item EV_SELECT_USE_FD_SET
		4619
		4620	If defined to C<1>, then the select backend will use the system C<fd_set>
		4621	structure. This is useful if libev doesn't compile due to a missing
		4622	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		4623	on exotic systems. This usually limits the range of file descriptors to
		4624	some low limit such as 1024 or might have other limitations (winsocket
		4625	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		4626	configures the maximum size of the C<fd_set>.
		4627
		4628	=item EV_SELECT_IS_WINSOCKET
		4629
		4630	When defined to C<1>, the select backend will assume that
		4631	select/socket/connect etc. don't understand file descriptors but
		4632	wants osf handles on win32 (this is the case when the select to
		4633	be used is the winsock select). This means that it will call
		4634	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		4635	it is assumed that all these functions actually work on fds, even
		4636	on win32. Should not be defined on non-win32 platforms.
		4637
		4638	=item EV_FD_TO_WIN32_HANDLE(fd)
		4639
		4640	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4641	file descriptors to socket handles. When not defining this symbol (the
		4642	default), then libev will call C<_get_osfhandle>, which is usually
		4643	correct. In some cases, programs use their own file descriptor management,
		4644	in which case they can provide this function to map fds to socket handles.
		4645
		4646	=item EV_WIN32_HANDLE_TO_FD(handle)
		4647
		4648	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4649	using the standard C<_open_osfhandle> function. For programs implementing
		4650	their own fd to handle mapping, overwriting this function makes it easier
		4651	to do so. This can be done by defining this macro to an appropriate value.
		4652
		4653	=item EV_WIN32_CLOSE_FD(fd)
		4654
		4655	If programs implement their own fd to handle mapping on win32, then this
		4656	macro can be used to override the C<close> function, useful to unregister
		4657	file descriptors again. Note that the replacement function has to close
		4658	the underlying OS handle.
		4659
		4660	=item EV_USE_WSASOCKET
		4661
		4662	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4663	communication socket, which works better in some environments. Otherwise,
		4664	the normal C<socket> function will be used, which works better in other
		4665	environments.
		4666
		4667	=item EV_USE_POLL
		4668
		4669	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		4670	backend. Otherwise it will be enabled on non-win32 platforms. It
		4671	takes precedence over select.
		4672
		4673	=item EV_USE_EPOLL
		4674
		4675	If defined to be C<1>, libev will compile in support for the Linux
		4676	C<epoll>(7) backend. Its availability will be detected at runtime,
		4677	otherwise another method will be used as fallback. This is the preferred
		4678	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4679	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4680
		4681	=item EV_USE_LINUXAIO
		4682
		4683	If defined to be C<1>, libev will compile in support for the Linux
		4684	aio backend. Due to it's currenbt limitations it has to be requested
		4685	explicitly. If undefined, it will be enabled on linux, otherwise
		4686	disabled.
		4687
		4688	=item EV_USE_KQUEUE
		4689
		4690	If defined to be C<1>, libev will compile in support for the BSD style
		4691	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		4692	otherwise another method will be used as fallback. This is the preferred
		4693	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		4694	supports some types of fds correctly (the only platform we found that
		4695	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		4696	not be used unless explicitly requested. The best way to use it is to find
		4697	out whether kqueue supports your type of fd properly and use an embedded
		4698	kqueue loop.
		4699
		4700	=item EV_USE_PORT
		4701
		4702	If defined to be C<1>, libev will compile in support for the Solaris
		4703	10 port style backend. Its availability will be detected at runtime,
		4704	otherwise another method will be used as fallback. This is the preferred
		4705	backend for Solaris 10 systems.
		4706
		4707	=item EV_USE_DEVPOLL
		4708
		4709	Reserved for future expansion, works like the USE symbols above.
		4710
		4711	=item EV_USE_INOTIFY
		4712
		4713	If defined to be C<1>, libev will compile in support for the Linux inotify
		4714	interface to speed up C<ev_stat> watchers. Its actual availability will
		4715	be detected at runtime. If undefined, it will be enabled if the headers
		4716	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4717
		4718	=item EV_NO_SMP
		4719
		4720	If defined to be C<1>, libev will assume that memory is always coherent
		4721	between threads, that is, threads can be used, but threads never run on
		4722	different cpus (or different cpu cores). This reduces dependencies
		4723	and makes libev faster.
		4724
		4725	=item EV_NO_THREADS
		4726
		4727	If defined to be C<1>, libev will assume that it will never be called from
		4728	different threads (that includes signal handlers), which is a stronger
		4729	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4730	libev faster.
		4731
		4732	=item EV_ATOMIC_T
		4733
		4734	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4735	access is atomic with respect to other threads or signal contexts. No
		4736	such type is easily found in the C language, so you can provide your own
		4737	type that you know is safe for your purposes. It is used both for signal
		4738	handler "locking" as well as for signal and thread safety in C<ev_async>
		4739	watchers.
		4740
		4741	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4742	(from F<signal.h>), which is usually good enough on most platforms.
		4743
		4744	=item EV_H (h)
		4745
		4746	The name of the F<ev.h> header file used to include it. The default if
		4747	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		4748	used to virtually rename the F<ev.h> header file in case of conflicts.
		4749
		4750	=item EV_CONFIG_H (h)
		4751
		4752	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		4753	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		4754	C<EV_H>, above.
		4755
		4756	=item EV_EVENT_H (h)
		4757
		4758	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		4759	of how the F<event.h> header can be found, the default is C<"event.h">.
		4760
		4761	=item EV_PROTOTYPES (h)
		4762
		4763	If defined to be C<0>, then F<ev.h> will not define any function
		4764	prototypes, but still define all the structs and other symbols. This is
		4765	occasionally useful if you want to provide your own wrapper functions
		4766	around libev functions.
		4767
		4768	=item EV_MULTIPLICITY
		4769
		4770	If undefined or defined to C<1>, then all event-loop-specific functions
		4771	will have the C<struct ev_loop *> as first argument, and you can create
		4772	additional independent event loops. Otherwise there will be no support
		4773	for multiple event loops and there is no first event loop pointer
		4774	argument. Instead, all functions act on the single default loop.
		4775
		4776	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4777	default loop when multiplicity is switched off - you always have to
		4778	initialise the loop manually in this case.
		4779
		4780	=item EV_MINPRI
		4781
		4782	=item EV_MAXPRI
		4783
		4784	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4785	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4786	provide for more priorities by overriding those symbols (usually defined
		4787	to be C<-2> and C<2>, respectively).
		4788
		4789	When doing priority-based operations, libev usually has to linearly search
		4790	all the priorities, so having many of them (hundreds) uses a lot of space
		4791	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4792	fine.
		4793
		4794	If your embedding application does not need any priorities, defining these
		4795	both to C<0> will save some memory and CPU.
		4796
		4797	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4798	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4799	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4800
		4801	If undefined or defined to be C<1> (and the platform supports it), then
		4802	the respective watcher type is supported. If defined to be C<0>, then it
		4803	is not. Disabling watcher types mainly saves code size.
		4804
		4805	=item EV_FEATURES
		4806
		4807	If you need to shave off some kilobytes of code at the expense of some
		4808	speed (but with the full API), you can define this symbol to request
		4809	certain subsets of functionality. The default is to enable all features
		4810	that can be enabled on the platform.
		4811
		4812	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4813	with some broad features you want) and then selectively re-enable
		4814	additional parts you want, for example if you want everything minimal,
		4815	but multiple event loop support, async and child watchers and the poll
		4816	backend, use this:
		4817
		4818	#define EV_FEATURES 0
		4819	#define EV_MULTIPLICITY 1
		4820	#define EV_USE_POLL 1
		4821	#define EV_CHILD_ENABLE 1
		4822	#define EV_ASYNC_ENABLE 1
		4823
		4824	The actual value is a bitset, it can be a combination of the following
		4825	values (by default, all of these are enabled):
		4826
		4827	=over 4
		4828
		4829	=item C<1> - faster/larger code
		4830
		4831	Use larger code to speed up some operations.
		4832
		4833	Currently this is used to override some inlining decisions (enlarging the
		4834	code size by roughly 30% on amd64).
		4835
		4836	When optimising for size, use of compiler flags such as C<-Os> with
		4837	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4838	assertions.
		4839
		4840	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4841	(e.g. gcc with C<-Os>).
		4842
		4843	=item C<2> - faster/larger data structures
		4844
		4845	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4846	hash table sizes and so on. This will usually further increase code size
		4847	and can additionally have an effect on the size of data structures at
		4848	runtime.
		4849
		4850	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4851	(e.g. gcc with C<-Os>).
		4852
		4853	=item C<4> - full API configuration
		4854
		4855	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4856	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4857
		4858	=item C<8> - full API
		4859
		4860	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4861	details on which parts of the API are still available without this
		4862	feature, and do not complain if this subset changes over time.
		4863
		4864	=item C<16> - enable all optional watcher types
		4865
		4866	Enables all optional watcher types. If you want to selectively enable
		4867	only some watcher types other than I/O and timers (e.g. prepare,
		4868	embed, async, child...) you can enable them manually by defining
		4869	C<EV_watchertype_ENABLE> to C<1> instead.
		4870
		4871	=item C<32> - enable all backends
		4872
		4873	This enables all backends - without this feature, you need to enable at
		4874	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4875
		4876	=item C<64> - enable OS-specific "helper" APIs
		4877
		4878	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4879	default.
		4880
		4881	=back
		4882
		4883	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4884	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4885	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4886	watchers, timers and monotonic clock support.
		4887
		4888	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4889	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4890	your program might be left out as well - a binary starting a timer and an
		4891	I/O watcher then might come out at only 5Kb.
		4892
		4893	=item EV_API_STATIC
		4894
		4895	If this symbol is defined (by default it is not), then all identifiers
		4896	will have static linkage. This means that libev will not export any
		4897	identifiers, and you cannot link against libev anymore. This can be useful
		4898	when you embed libev, only want to use libev functions in a single file,
		4899	and do not want its identifiers to be visible.
		4900
		4901	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4902	wants to use libev.
		4903
		4904	This option only works when libev is compiled with a C compiler, as C++
		4905	doesn't support the required declaration syntax.
		4906
		4907	=item EV_AVOID_STDIO
		4908
		4909	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4910	functions (printf, scanf, perror etc.). This will increase the code size
		4911	somewhat, but if your program doesn't otherwise depend on stdio and your
		4912	libc allows it, this avoids linking in the stdio library which is quite
		4913	big.
		4914
		4915	Note that error messages might become less precise when this option is
		4916	enabled.
		4917
		4918	=item EV_NSIG
		4919
		4920	The highest supported signal number, +1 (or, the number of
		4921	signals): Normally, libev tries to deduce the maximum number of signals
		4922	automatically, but sometimes this fails, in which case it can be
		4923	specified. Also, using a lower number than detected (C<32> should be
		4924	good for about any system in existence) can save some memory, as libev
		4925	statically allocates some 12-24 bytes per signal number.
		4926
		4927	=item EV_PID_HASHSIZE
		4928
		4929	C<ev_child> watchers use a small hash table to distribute workload by
		4930	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4931	usually more than enough. If you need to manage thousands of children you
		4932	might want to increase this value (I<must> be a power of two).
		4933
		4934	=item EV_INOTIFY_HASHSIZE
		4935
		4936	C<ev_stat> watchers use a small hash table to distribute workload by
		4937	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4938	disabled), usually more than enough. If you need to manage thousands of
		4939	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4940	power of two).
		4941
		4942	=item EV_USE_4HEAP
		4943
		4944	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4945	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4946	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4947	faster performance with many (thousands) of watchers.
		4948
		4949	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4950	will be C<0>.
		4951
		4952	=item EV_HEAP_CACHE_AT
		4953
		4954	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4955	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4956	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4957	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4958	but avoids random read accesses on heap changes. This improves performance
		4959	noticeably with many (hundreds) of watchers.
		4960
		4961	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4962	will be C<0>.
		4963
		4964	=item EV_VERIFY
		4965
		4966	Controls how much internal verification (see C<ev_verify ()>) will
		4967	be done: If set to C<0>, no internal verification code will be compiled
		4968	in. If set to C<1>, then verification code will be compiled in, but not
		4969	called. If set to C<2>, then the internal verification code will be
		4970	called once per loop, which can slow down libev. If set to C<3>, then the
		4971	verification code will be called very frequently, which will slow down
		4972	libev considerably.
		4973
		4974	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4975	will be C<0>.
		4976
		4977	=item EV_COMMON
		4978
		4979	By default, all watchers have a C<void *data> member. By redefining
		4980	this macro to something else you can include more and other types of
		4981	members. You have to define it each time you include one of the files,
		4982	though, and it must be identical each time.
		4983
		4984	For example, the perl EV module uses something like this:
		4985
		4986	#define EV_COMMON \
		4987	SV *self; /* contains this struct */ \
		4988	SV *cb_sv, *fh /* note no trailing ";" */
		4989
		4990	=item EV_CB_DECLARE (type)
		4991
		4992	=item EV_CB_INVOKE (watcher, revents)
		4993
		4994	=item ev_set_cb (ev, cb)
		4995
		4996	Can be used to change the callback member declaration in each watcher,
		4997	and the way callbacks are invoked and set. Must expand to a struct member
		4998	definition and a statement, respectively. See the F<ev.h> header file for
		4999	their default definitions. One possible use for overriding these is to
		5000	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		5001	method calls instead of plain function calls in C++.
		5002
		5003	=back
		5004
		5005	=head2 EXPORTED API SYMBOLS
		5006
		5007	If you need to re-export the API (e.g. via a DLL) and you need a list of
		5008	exported symbols, you can use the provided F<Symbol.*> files which list
		5009	all public symbols, one per line:
		5010
		5011	Symbols.ev for libev proper
		5012	Symbols.event for the libevent emulation
		5013
		5014	This can also be used to rename all public symbols to avoid clashes with
		5015	multiple versions of libev linked together (which is obviously bad in
		5016	itself, but sometimes it is inconvenient to avoid this).
		5017
		5018	A sed command like this will create wrapper C<#define>'s that you need to
		5019	include before including F<ev.h>:
		5020
		5021	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		5022
		5023	This would create a file F<wrap.h> which essentially looks like this:
		5024
		5025	#define ev_backend myprefix_ev_backend
		5026	#define ev_check_start myprefix_ev_check_start
		5027	#define ev_check_stop myprefix_ev_check_stop
		5028	...
		5029
		5030	=head2 EXAMPLES
		5031
		5032	For a real-world example of a program the includes libev
		5033	verbatim, you can have a look at the EV perl module
		5034	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		5035	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		5036	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		5037	will be compiled. It is pretty complex because it provides its own header
		5038	file.
		5039
		5040	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		5041	that everybody includes and which overrides some configure choices:
		5042
		5043	#define EV_FEATURES 8
		5044	#define EV_USE_SELECT 1
		5045	#define EV_PREPARE_ENABLE 1
		5046	#define EV_IDLE_ENABLE 1
		5047	#define EV_SIGNAL_ENABLE 1
		5048	#define EV_CHILD_ENABLE 1
		5049	#define EV_USE_STDEXCEPT 0
		5050	#define EV_CONFIG_H <config.h>
		5051
		5052	#include "ev++.h"
		5053
		5054	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		5055
		5056	#include "ev_cpp.h"
		5057	#include "ev.c"
		5058
		5059	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
		5060
		5061	=head2 THREADS AND COROUTINES
		5062
		5063	=head3 THREADS
		5064
		5065	All libev functions are reentrant and thread-safe unless explicitly
		5066	documented otherwise, but libev implements no locking itself. This means
		5067	that you can use as many loops as you want in parallel, as long as there
		5068	are no concurrent calls into any libev function with the same loop
		5069	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		5070	of course): libev guarantees that different event loops share no data
		5071	structures that need any locking.
		5072
		5073	Or to put it differently: calls with different loop parameters can be done
		5074	concurrently from multiple threads, calls with the same loop parameter
		5075	must be done serially (but can be done from different threads, as long as
		5076	only one thread ever is inside a call at any point in time, e.g. by using
		5077	a mutex per loop).
		5078
		5079	Specifically to support threads (and signal handlers), libev implements
		5080	so-called C<ev_async> watchers, which allow some limited form of
		5081	concurrency on the same event loop, namely waking it up "from the
		5082	outside".
		5083
		5084	If you want to know which design (one loop, locking, or multiple loops
		5085	without or something else still) is best for your problem, then I cannot
		5086	help you, but here is some generic advice:
		5087
		5088	=over 4
		5089
		5090	=item * most applications have a main thread: use the default libev loop
		5091	in that thread, or create a separate thread running only the default loop.
		5092
		5093	This helps integrating other libraries or software modules that use libev
		5094	themselves and don't care/know about threading.
		5095
		5096	=item * one loop per thread is usually a good model.
		5097
		5098	Doing this is almost never wrong, sometimes a better-performance model
		5099	exists, but it is always a good start.
		5100
		5101	=item * other models exist, such as the leader/follower pattern, where one
		5102	loop is handed through multiple threads in a kind of round-robin fashion.
		5103
		5104	Choosing a model is hard - look around, learn, know that usually you can do
		5105	better than you currently do :-)
		5106
		5107	=item * often you need to talk to some other thread which blocks in the
		5108	event loop.
		5109
		5110	C<ev_async> watchers can be used to wake them up from other threads safely
		5111	(or from signal contexts...).
		5112
		5113	An example use would be to communicate signals or other events that only
		5114	work in the default loop by registering the signal watcher with the
		5115	default loop and triggering an C<ev_async> watcher from the default loop
		5116	watcher callback into the event loop interested in the signal.
		5117
		5118	=back
		5119
		5120	See also L</THREAD LOCKING EXAMPLE>.
		5121
		5122	=head3 COROUTINES
		5123
		5124	Libev is very accommodating to coroutines ("cooperative threads"):
		5125	libev fully supports nesting calls to its functions from different
		5126	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5127	different coroutines, and switch freely between both coroutines running
		5128	the loop, as long as you don't confuse yourself). The only exception is
		5129	that you must not do this from C<ev_periodic> reschedule callbacks.
		5130
		5131	Care has been taken to ensure that libev does not keep local state inside
		5132	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5133	they do not call any callbacks.
		5134
		5135	=head2 COMPILER WARNINGS
		5136
		5137	Depending on your compiler and compiler settings, you might get no or a
		5138	lot of warnings when compiling libev code. Some people are apparently
		5139	scared by this.
		5140
		5141	However, these are unavoidable for many reasons. For one, each compiler
		5142	has different warnings, and each user has different tastes regarding
		5143	warning options. "Warn-free" code therefore cannot be a goal except when
		5144	targeting a specific compiler and compiler-version.
		5145
		5146	Another reason is that some compiler warnings require elaborate
		5147	workarounds, or other changes to the code that make it less clear and less
		5148	maintainable.
		5149
		5150	And of course, some compiler warnings are just plain stupid, or simply
		5151	wrong (because they don't actually warn about the condition their message
		5152	seems to warn about). For example, certain older gcc versions had some
		5153	warnings that resulted in an extreme number of false positives. These have
		5154	been fixed, but some people still insist on making code warn-free with
		5155	such buggy versions.
		5156
		5157	While libev is written to generate as few warnings as possible,
		5158	"warn-free" code is not a goal, and it is recommended not to build libev
		5159	with any compiler warnings enabled unless you are prepared to cope with
		5160	them (e.g. by ignoring them). Remember that warnings are just that:
		5161	warnings, not errors, or proof of bugs.
		5162
		5163
		5164	=head2 VALGRIND
		5165
		5166	Valgrind has a special section here because it is a popular tool that is
		5167	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5168
		5169	If you think you found a bug (memory leak, uninitialised data access etc.)
		5170	in libev, then check twice: If valgrind reports something like:
		5171
		5172	==2274== definitely lost: 0 bytes in 0 blocks.
		5173	==2274== possibly lost: 0 bytes in 0 blocks.
		5174	==2274== still reachable: 256 bytes in 1 blocks.
		5175
		5176	Then there is no memory leak, just as memory accounted to global variables
		5177	is not a memleak - the memory is still being referenced, and didn't leak.
		5178
		5179	Similarly, under some circumstances, valgrind might report kernel bugs
		5180	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5181	although an acceptable workaround has been found here), or it might be
		5182	confused.
		5183
		5184	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5185	make it into some kind of religion.
		5186
		5187	If you are unsure about something, feel free to contact the mailing list
		5188	with the full valgrind report and an explanation on why you think this
		5189	is a bug in libev (best check the archives, too :). However, don't be
		5190	annoyed when you get a brisk "this is no bug" answer and take the chance
		5191	of learning how to interpret valgrind properly.
		5192
		5193	If you need, for some reason, empty reports from valgrind for your project
		5194	I suggest using suppression lists.
		5195
		5196
		5197	=head1 PORTABILITY NOTES
		5198
		5199	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5200
		5201	GNU/Linux is the only common platform that supports 64 bit file/large file
		5202	interfaces but I<disables> them by default.
		5203
		5204	That means that libev compiled in the default environment doesn't support
		5205	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5206
		5207	Unfortunately, many programs try to work around this GNU/Linux issue
		5208	by enabling the large file API, which makes them incompatible with the
		5209	standard libev compiled for their system.
		5210
		5211	Likewise, libev cannot enable the large file API itself as this would
		5212	suddenly make it incompatible to the default compile time environment,
		5213	i.e. all programs not using special compile switches.
		5214
		5215	=head2 OS/X AND DARWIN BUGS
		5216
		5217	The whole thing is a bug if you ask me - basically any system interface
		5218	you touch is broken, whether it is locales, poll, kqueue or even the
		5219	OpenGL drivers.
		5220
		5221	=head3 C<kqueue> is buggy
		5222
		5223	The kqueue syscall is broken in all known versions - most versions support
		5224	only sockets, many support pipes.
		5225
		5226	Libev tries to work around this by not using C<kqueue> by default on this
		5227	rotten platform, but of course you can still ask for it when creating a
		5228	loop - embedding a socket-only kqueue loop into a select-based one is
		5229	probably going to work well.
		5230
		5231	=head3 C<poll> is buggy
		5232
		5233	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5234	implementation by something calling C<kqueue> internally around the 10.5.6
		5235	release, so now C<kqueue> I<and> C<poll> are broken.
		5236
		5237	Libev tries to work around this by not using C<poll> by default on
		5238	this rotten platform, but of course you can still ask for it when creating
		5239	a loop.
		5240
		5241	=head3 C<select> is buggy
		5242
		5243	All that's left is C<select>, and of course Apple found a way to fuck this
		5244	one up as well: On OS/X, C<select> actively limits the number of file
		5245	descriptors you can pass in to 1024 - your program suddenly crashes when
		5246	you use more.
		5247
		5248	There is an undocumented "workaround" for this - defining
		5249	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5250	work on OS/X.
		5251
		5252	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5253
		5254	=head3 C<errno> reentrancy
		5255
		5256	The default compile environment on Solaris is unfortunately so
		5257	thread-unsafe that you can't even use components/libraries compiled
		5258	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5259	defined by default. A valid, if stupid, implementation choice.
		5260
		5261	If you want to use libev in threaded environments you have to make sure
		5262	it's compiled with C<_REENTRANT> defined.
		5263
		5264	=head3 Event port backend
		5265
		5266	The scalable event interface for Solaris is called "event
		5267	ports". Unfortunately, this mechanism is very buggy in all major
		5268	releases. If you run into high CPU usage, your program freezes or you get
		5269	a large number of spurious wakeups, make sure you have all the relevant
		5270	and latest kernel patches applied. No, I don't know which ones, but there
		5271	are multiple ones to apply, and afterwards, event ports actually work
		5272	great.
		5273
		5274	If you can't get it to work, you can try running the program by setting
		5275	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5276	C<select> backends.
		5277
		5278	=head2 AIX POLL BUG
		5279
		5280	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5281	this by trying to avoid the poll backend altogether (i.e. it's not even
		5282	compiled in), which normally isn't a big problem as C<select> works fine
		5283	with large bitsets on AIX, and AIX is dead anyway.
		5284
		5285	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5286
		5287	=head3 General issues
		5288
		5289	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5290	requires, and its I/O model is fundamentally incompatible with the POSIX
		5291	model. Libev still offers limited functionality on this platform in
		5292	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5293	descriptors. This only applies when using Win32 natively, not when using
		5294	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5295	as every compiler comes with a slightly differently broken/incompatible
		5296	environment.
		5297
		5298	Lifting these limitations would basically require the full
		5299	re-implementation of the I/O system. If you are into this kind of thing,
		5300	then note that glib does exactly that for you in a very portable way (note
		5301	also that glib is the slowest event library known to man).
		5302
		5303	There is no supported compilation method available on windows except
		5304	embedding it into other applications.
		5305
		5306	Sensible signal handling is officially unsupported by Microsoft - libev
		5307	tries its best, but under most conditions, signals will simply not work.
		5308
		5309	Not a libev limitation but worth mentioning: windows apparently doesn't
		5310	accept large writes: instead of resulting in a partial write, windows will
		5311	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5312	so make sure you only write small amounts into your sockets (less than a
		5313	megabyte seems safe, but this apparently depends on the amount of memory
		5314	available).
		5315
		5316	Due to the many, low, and arbitrary limits on the win32 platform and
		5317	the abysmal performance of winsockets, using a large number of sockets
		5318	is not recommended (and not reasonable). If your program needs to use
		5319	more than a hundred or so sockets, then likely it needs to use a totally
		5320	different implementation for windows, as libev offers the POSIX readiness
		5321	notification model, which cannot be implemented efficiently on windows
		5322	(due to Microsoft monopoly games).
		5323
		5324	A typical way to use libev under windows is to embed it (see the embedding
		5325	section for details) and use the following F<evwrap.h> header file instead
		5326	of F<ev.h>:
		5327
		5328	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5329	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5330
		5331	#include "ev.h"
		5332
		5333	And compile the following F<evwrap.c> file into your project (make sure
		5334	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5335
		5336	#include "evwrap.h"
		5337	#include "ev.c"
		5338
		5339	=head3 The winsocket C<select> function
		5340
		5341	The winsocket C<select> function doesn't follow POSIX in that it
		5342	requires socket I<handles> and not socket I<file descriptors> (it is
		5343	also extremely buggy). This makes select very inefficient, and also
		5344	requires a mapping from file descriptors to socket handles (the Microsoft
		5345	C runtime provides the function C<_open_osfhandle> for this). See the
		5346	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5347	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5348
		5349	The configuration for a "naked" win32 using the Microsoft runtime
		5350	libraries and raw winsocket select is:
		5351
		5352	#define EV_USE_SELECT 1
		5353	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5354
		5355	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5356	complexity in the O(n²) range when using win32.
		5357
		5358	=head3 Limited number of file descriptors
		5359
		5360	Windows has numerous arbitrary (and low) limits on things.
		5361
		5362	Early versions of winsocket's select only supported waiting for a maximum
		5363	of C<64> handles (probably owning to the fact that all windows kernels
		5364	can only wait for C<64> things at the same time internally; Microsoft
		5365	recommends spawning a chain of threads and wait for 63 handles and the
		5366	previous thread in each. Sounds great!).
		5367
		5368	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5369	to some high number (e.g. C<2048>) before compiling the winsocket select
		5370	call (which might be in libev or elsewhere, for example, perl and many
		5371	other interpreters do their own select emulation on windows).
		5372
		5373	Another limit is the number of file descriptors in the Microsoft runtime
		5374	libraries, which by default is C<64> (there must be a hidden I<64>
		5375	fetish or something like this inside Microsoft). You can increase this
		5376	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5377	(another arbitrary limit), but is broken in many versions of the Microsoft
		5378	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5379	(depending on windows version and/or the phase of the moon). To get more,
		5380	you need to wrap all I/O functions and provide your own fd management, but
		5381	the cost of calling select (O(n²)) will likely make this unworkable.
		5382
		5383	=head2 PORTABILITY REQUIREMENTS
		5384
		5385	In addition to a working ISO-C implementation and of course the
		5386	backend-specific APIs, libev relies on a few additional extensions:
		5387
		5388	=over 4
		5389
		5390	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5391	calling conventions regardless of C<ev_watcher_type *>.
		5392
		5393	Libev assumes not only that all watcher pointers have the same internal
		5394	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5395	assumes that the same (machine) code can be used to call any watcher
		5396	callback: The watcher callbacks have different type signatures, but libev
		5397	calls them using an C<ev_watcher *> internally.
		5398
		5399	=item null pointers and integer zero are represented by 0 bytes
		5400
		5401	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5402	relies on this setting pointers and integers to null.
		5403
		5404	=item pointer accesses must be thread-atomic
		5405
		5406	Accessing a pointer value must be atomic, it must both be readable and
		5407	writable in one piece - this is the case on all current architectures.
		5408
		5409	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5410
		5411	The type C<sig_atomic_t volatile> (or whatever is defined as
		5412	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5413	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5414	believed to be sufficiently portable.
		5415
		5416	=item C<sigprocmask> must work in a threaded environment
		5417
		5418	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5419	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5420	pthread implementations will either allow C<sigprocmask> in the "main
		5421	thread" or will block signals process-wide, both behaviours would
		5422	be compatible with libev. Interaction between C<sigprocmask> and
		5423	C<pthread_sigmask> could complicate things, however.
		5424
		5425	The most portable way to handle signals is to block signals in all threads
		5426	except the initial one, and run the signal handling loop in the initial
		5427	thread as well.
		5428
		5429	=item C<long> must be large enough for common memory allocation sizes
		5430
		5431	To improve portability and simplify its API, libev uses C<long> internally
		5432	instead of C<size_t> when allocating its data structures. On non-POSIX
		5433	systems (Microsoft...) this might be unexpectedly low, but is still at
		5434	least 31 bits everywhere, which is enough for hundreds of millions of
		5435	watchers.
		5436
		5437	=item C<double> must hold a time value in seconds with enough accuracy
		5438
		5439	The type C<double> is used to represent timestamps. It is required to
		5440	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5441	good enough for at least into the year 4000 with millisecond accuracy
		5442	(the design goal for libev). This requirement is overfulfilled by
		5443	implementations using IEEE 754, which is basically all existing ones.
		5444
		5445	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5446	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5447	is either obsolete or somebody patched it to use C<long double> or
		5448	something like that, just kidding).
		5449
		5450	=back
		5451
		5452	If you know of other additional requirements drop me a note.
		5453
		5454
		5455	=head1 ALGORITHMIC COMPLEXITIES
		5456
		5457	In this section the complexities of (many of) the algorithms used inside
		5458	libev will be documented. For complexity discussions about backends see
		5459	the documentation for C<ev_default_init>.
		5460
		5461	All of the following are about amortised time: If an array needs to be
		5462	extended, libev needs to realloc and move the whole array, but this
		5463	happens asymptotically rarer with higher number of elements, so O(1) might
		5464	mean that libev does a lengthy realloc operation in rare cases, but on
		5465	average it is much faster and asymptotically approaches constant time.
		5466
		5467	=over 4
		5468
		5469	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5470
		5471	This means that, when you have a watcher that triggers in one hour and
		5472	there are 100 watchers that would trigger before that, then inserting will
		5473	have to skip roughly seven (C<ld 100>) of these watchers.
		5474
		5475	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5476
		5477	That means that changing a timer costs less than removing/adding them,
		5478	as only the relative motion in the event queue has to be paid for.
		5479
		5480	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5481
		5482	These just add the watcher into an array or at the head of a list.
		5483
		5484	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5485
		5486	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5487
		5488	These watchers are stored in lists, so they need to be walked to find the
		5489	correct watcher to remove. The lists are usually short (you don't usually
		5490	have many watchers waiting for the same fd or signal: one is typical, two
		5491	is rare).
		5492
		5493	=item Finding the next timer in each loop iteration: O(1)
		5494
		5495	By virtue of using a binary or 4-heap, the next timer is always found at a
		5496	fixed position in the storage array.
		5497
		5498	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5499
		5500	A change means an I/O watcher gets started or stopped, which requires
		5501	libev to recalculate its status (and possibly tell the kernel, depending
		5502	on backend and whether C<ev_io_set> was used).
		5503
		5504	=item Activating one watcher (putting it into the pending state): O(1)
		5505
		5506	=item Priority handling: O(number_of_priorities)
		5507
		5508	Priorities are implemented by allocating some space for each
		5509	priority. When doing priority-based operations, libev usually has to
		5510	linearly search all the priorities, but starting/stopping and activating
		5511	watchers becomes O(1) with respect to priority handling.
		5512
		5513	=item Sending an ev_async: O(1)
		5514
		5515	=item Processing ev_async_send: O(number_of_async_watchers)
		5516
		5517	=item Processing signals: O(max_signal_number)
		5518
		5519	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5520	calls in the current loop iteration and the loop is currently
		5521	blocked. Checking for async and signal events involves iterating over all
		5522	running async watchers or all signal numbers.
		5523
		5524	=back
		5525
		5526
		5527	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5528
		5529	The major version 4 introduced some incompatible changes to the API.
		5530
		5531	At the moment, the C<ev.h> header file provides compatibility definitions
		5532	for all changes, so most programs should still compile. The compatibility
		5533	layer might be removed in later versions of libev, so better update to the
		5534	new API early than late.
		5535
		5536	=over 4
		5537
		5538	=item C<EV_COMPAT3> backwards compatibility mechanism
		5539
		5540	The backward compatibility mechanism can be controlled by
		5541	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5542	section.
		5543
		5544	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5545
		5546	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5547
		5548	ev_loop_destroy (EV_DEFAULT_UC);
		5549	ev_loop_fork (EV_DEFAULT);
		5550
		5551	=item function/symbol renames
		5552
		5553	A number of functions and symbols have been renamed:
		5554
		5555	ev_loop => ev_run
		5556	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5557	EVLOOP_ONESHOT => EVRUN_ONCE
		5558
		5559	ev_unloop => ev_break
		5560	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5561	EVUNLOOP_ONE => EVBREAK_ONE
		5562	EVUNLOOP_ALL => EVBREAK_ALL
		5563
		5564	EV_TIMEOUT => EV_TIMER
		5565
		5566	ev_loop_count => ev_iteration
		5567	ev_loop_depth => ev_depth
		5568	ev_loop_verify => ev_verify
		5569
		5570	Most functions working on C<struct ev_loop> objects don't have an
		5571	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5572	associated constants have been renamed to not collide with the C<struct
		5573	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5574	as all other watcher types. Note that C<ev_loop_fork> is still called
		5575	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5576	typedef.
		5577
		5578	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5579
		5580	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5581	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5582	and work, but the library code will of course be larger.
		5583
		5584	=back
		5585
		5586
		5587	=head1 GLOSSARY
		5588
		5589	=over 4
		5590
		5591	=item active
		5592
		5593	A watcher is active as long as it has been started and not yet stopped.
		5594	See L</WATCHER STATES> for details.
		5595
		5596	=item application
		5597
		5598	In this document, an application is whatever is using libev.
		5599
		5600	=item backend
		5601
		5602	The part of the code dealing with the operating system interfaces.
		5603
		5604	=item callback
		5605
		5606	The address of a function that is called when some event has been
		5607	detected. Callbacks are being passed the event loop, the watcher that
		5608	received the event, and the actual event bitset.
		5609
		5610	=item callback/watcher invocation
		5611
		5612	The act of calling the callback associated with a watcher.
		5613
		5614	=item event
		5615
		5616	A change of state of some external event, such as data now being available
		5617	for reading on a file descriptor, time having passed or simply not having
		5618	any other events happening anymore.
		5619
		5620	In libev, events are represented as single bits (such as C<EV_READ> or
		5621	C<EV_TIMER>).
		5622
		5623	=item event library
		5624
		5625	A software package implementing an event model and loop.
		5626
		5627	=item event loop
		5628
		5629	An entity that handles and processes external events and converts them
		5630	into callback invocations.
		5631
		5632	=item event model
		5633
		5634	The model used to describe how an event loop handles and processes
		5635	watchers and events.
		5636
		5637	=item pending
		5638
		5639	A watcher is pending as soon as the corresponding event has been
		5640	detected. See L</WATCHER STATES> for details.
		5641
		5642	=item real time
		5643
		5644	The physical time that is observed. It is apparently strictly monotonic :)
		5645
		5646	=item wall-clock time
		5647
		5648	The time and date as shown on clocks. Unlike real time, it can actually
		5649	be wrong and jump forwards and backwards, e.g. when you adjust your
		5650	clock.
		5651
		5652	=item watcher
		5653
		5654	A data structure that describes interest in certain events. Watchers need
		5655	to be started (attached to an event loop) before they can receive events.
		5656
		5657	=back
		5658
767	=head1 AUTHOR	5659	=head1 AUTHOR
768		5660
769	Marc Lehmann <libev@schmorp.de>.	5661	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5662	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
770		5663

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