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Revision 1.388 by root, Tue Dec 20 04:08:35 2011 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 DESCRIPTION	9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
		18	ev_io stdin_watcher;
		19	ev_timer timeout_watcher;
		20
		21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
		23	static void
		24	stdin_cb (EV_P_ ev_io *w, int revents)
		25	{
		26	puts ("stdin ready");
		27	// for one-shot events, one must manually stop the watcher
		28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_run's to stop iterating
		32	ev_break (EV_A_ EVBREAK_ALL);
		33	}
		34
		35	// another callback, this time for a time-out
		36	static void
		37	timeout_cb (EV_P_ ev_timer *w, int revents)
		38	{
		39	puts ("timeout");
		40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
		42	}
		43
		44	int
		45	main (void)
		46	{
		47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = EV_DEFAULT;
		49
		50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
		52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		53	ev_io_start (loop, &stdin_watcher);
		54
		55	// initialise a timer watcher, then start it
		56	// simple non-repeating 5.5 second timeout
		57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		58	ev_timer_start (loop, &timeout_watcher);
		59
		60	// now wait for events to arrive
		61	ev_run (loop, 0);
		62
		63	// break was called, so exit
		64	return 0;
		65	}
		66
		67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
		90
		91	=head1 ABOUT LIBEV
10		92
11	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	95	these event sources and provide your program with events.
14		96
15	To do this, it must take more or less complete control over your process	97	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	98	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	99	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	101	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	102	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	103	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	104	watcher.
23		105
24	=head1 FEATURES	106	=head2 FEATURES
25		107
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
		112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
		113	timers (C<ev_timer>), absolute timers with customised rescheduling
		114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
29	events (related to SIGCHLD), and event watchers dealing with the event	115	change events (C<ev_child>), and event watchers dealing with the event
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
		117	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		118	limited support for fork events (C<ev_fork>).
		119
		120	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	121	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	122	for example).
33		123
34	=head1 CONVENTIONS	124	=head2 CONVENTIONS
35		125
36	Libev is very configurable. In this manual the default configuration	126	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	127	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	128	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	129	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	130	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	131	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	132	this argument.
43		133
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	134	=head2 TIME REPRESENTATION
45		135
46	Libev represents time as a single floating point number, representing the	136	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	137	the (fractional) number of seconds since the (POSIX) epoch (in practice
48	the beginning of 1970, details are complicated, don't ask). This type is	138	somewhere near the beginning of 1970, details are complicated, don't
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	139	ask). This type is called C<ev_tstamp>, which is what you should use
50	to the double type in C.	140	too. It usually aliases to the C<double> type in C. When you need to do
		141	any calculations on it, you should treat it as some floating point value.
		142
		143	Unlike the name component C<stamp> might indicate, it is also used for
		144	time differences (e.g. delays) throughout libev.
		145
		146	=head1 ERROR HANDLING
		147
		148	Libev knows three classes of errors: operating system errors, usage errors
		149	and internal errors (bugs).
		150
		151	When libev catches an operating system error it cannot handle (for example
		152	a system call indicating a condition libev cannot fix), it calls the callback
		153	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		154	abort. The default is to print a diagnostic message and to call C<abort
		155	()>.
		156
		157	When libev detects a usage error such as a negative timer interval, then
		158	it will print a diagnostic message and abort (via the C<assert> mechanism,
		159	so C<NDEBUG> will disable this checking): these are programming errors in
		160	the libev caller and need to be fixed there.
		161
		162	Libev also has a few internal error-checking C<assert>ions, and also has
		163	extensive consistency checking code. These do not trigger under normal
		164	circumstances, as they indicate either a bug in libev or worse.
		165
		166
		167	=head1 GLOBAL FUNCTIONS
		168
		169	These functions can be called anytime, even before initialising the
		170	library in any way.
51		171
52	=over 4	172	=over 4
53		173
54	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
55		175
56	Returns the current time as libev would use it.	176	Returns the current time as libev would use it. Please note that the
		177	C<ev_now> function is usually faster and also often returns the timestamp
		178	you actually want to know. Also interesting is the combination of
		179	C<ev_now_update> and C<ev_now>.
		180
		181	=item ev_sleep (ev_tstamp interval)
		182
		183	Sleep for the given interval: The current thread will be blocked
		184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
		188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
57		192
58	=item int ev_version_major ()	193	=item int ev_version_major ()
59		194
60	=item int ev_version_minor ()	195	=item int ev_version_minor ()
61		196
62	You can find out the major and minor version numbers of the library	197	You can find out the major and minor ABI version numbers of the library
63	you linked against by calling the functions C<ev_version_major> and	198	you linked against by calling the functions C<ev_version_major> and
64	C<ev_version_minor>. If you want, you can compare against the global	199	C<ev_version_minor>. If you want, you can compare against the global
65	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	200	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	201	version of the library your program was compiled against.
67		202
		203	These version numbers refer to the ABI version of the library, not the
		204	release version.
		205
68	Usually, it's a good idea to terminate if the major versions mismatch,	206	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	207	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	208	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	209	not a problem.
72		210
		211	Example: Make sure we haven't accidentally been linked against the wrong
		212	version (note, however, that this will not detect other ABI mismatches,
		213	such as LFS or reentrancy).
		214
		215	assert (("libev version mismatch",
		216	ev_version_major () == EV_VERSION_MAJOR
		217	&& ev_version_minor () >= EV_VERSION_MINOR));
		218
		219	=item unsigned int ev_supported_backends ()
		220
		221	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		222	value) compiled into this binary of libev (independent of their
		223	availability on the system you are running on). See C<ev_default_loop> for
		224	a description of the set values.
		225
		226	Example: make sure we have the epoll method, because yeah this is cool and
		227	a must have and can we have a torrent of it please!!!11
		228
		229	assert (("sorry, no epoll, no sex",
		230	ev_supported_backends () & EVBACKEND_EPOLL));
		231
		232	=item unsigned int ev_recommended_backends ()
		233
		234	Return the set of all backends compiled into this binary of libev and
		235	also recommended for this platform, meaning it will work for most file
		236	descriptor types. This set is often smaller than the one returned by
		237	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
		238	and will not be auto-detected unless you explicitly request it (assuming
		239	you know what you are doing). This is the set of backends that libev will
		240	probe for if you specify no backends explicitly.
		241
		242	=item unsigned int ev_embeddable_backends ()
		243
		244	Returns the set of backends that are embeddable in other event loops. This
		245	value is platform-specific but can include backends not available on the
		246	current system. To find which embeddable backends might be supported on
		247	the current system, you would need to look at C<ev_embeddable_backends ()
		248	& ev_supported_backends ()>, likewise for recommended ones.
		249
		250	See the description of C<ev_embed> watchers for more info.
		251
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
74		253
75	Sets the allocation function to use (the prototype is similar to the	254	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	255	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
77	and free memory (no surprises here). If it returns zero when memory	256	used to allocate and free memory (no surprises here). If it returns zero
78	needs to be allocated, the library might abort or take some potentially	257	when memory needs to be allocated (C<size != 0>), the library might abort
79	destructive action. The default is your system realloc function.	258	or take some potentially destructive action.
		259
		260	Since some systems (at least OpenBSD and Darwin) fail to implement
		261	correct C<realloc> semantics, libev will use a wrapper around the system
		262	C<realloc> and C<free> functions by default.
80		263
81	You could override this function in high-availability programs to, say,	264	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,	265	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.	266	or even to sleep a while and retry until some memory is available.
84		267
		268	Example: Replace the libev allocator with one that waits a bit and then
		269	retries (example requires a standards-compliant C<realloc>).
		270
		271	static void *
		272	persistent_realloc (void *ptr, size_t size)
		273	{
		274	for (;;)
		275	{
		276	void *newptr = realloc (ptr, size);
		277
		278	if (newptr)
		279	return newptr;
		280
		281	sleep (60);
		282	}
		283	}
		284
		285	...
		286	ev_set_allocator (persistent_realloc);
		287
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	288	=item ev_set_syserr_cb (void (*cb)(const char *msg))
86		289
87	Set the callback function to call on a retryable syscall error (such	290	Set the callback function to call on a retryable system call error (such
88	as failed select, poll, epoll_wait). The message is a printable string	291	as failed select, poll, epoll_wait). The message is a printable string
89	indicating the system call or subsystem causing the problem. If this	292	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	293	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	294	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	295	requested operation, or, if the condition doesn't go away, do bad stuff
93	(such as abort).	296	(such as abort).
94		297
		298	Example: This is basically the same thing that libev does internally, too.
		299
		300	static void
		301	fatal_error (const char *msg)
		302	{
		303	perror (msg);
		304	abort ();
		305	}
		306
		307	...
		308	ev_set_syserr_cb (fatal_error);
		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
95	=back	323	=back
96		324
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
98		326
99	An event loop is described by a C<struct ev_loop *>. The library knows two	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
100	types of such loops, the I<default> loop, which supports signals and child	328	I<not> optional in this case unless libev 3 compatibility is disabled, as
101	events, and dynamically created loops which do not.	329	libev 3 had an C<ev_loop> function colliding with the struct name).
102		330
103	If you use threads, a common model is to run the default event loop	331	The library knows two types of such loops, the I<default> loop, which
104	in your main thread (or in a separate thrad) and for each thread you	332	supports child process events, and dynamically created event loops which
105	create, you also create another event loop. Libev itself does no locking	333	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		334
110	=over 4	335	=over 4
111		336
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		338
114	This will initialise the default event loop if it hasn't been initialised	339	This returns the "default" event loop object, which is what you should
115	yet and return it. If the default loop could not be initialised, returns	340	normally use when you just need "the event loop". Event loop objects and
116	false. If it already was initialised it simply returns it (and ignores the	341	the C<flags> parameter are described in more detail in the entry for
117	flags).	342	C<ev_loop_new>.
		343
		344	If the default loop is already initialised then this function simply
		345	returns it (and ignores the flags. If that is troubling you, check
		346	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		347	flags, which should almost always be C<0>, unless the caller is also the
		348	one calling C<ev_run> or otherwise qualifies as "the main program".
118		349
119	If you don't know what event loop to use, use the one returned from this	350	If you don't know what event loop to use, use the one returned from this
120	function.	351	function (or via the C<EV_DEFAULT> macro).
		352
		353	Note that this function is I<not> thread-safe, so if you want to use it
		354	from multiple threads, you have to employ some kind of mutex (note also
		355	that this case is unlikely, as loops cannot be shared easily between
		356	threads anyway).
		357
		358	The default loop is the only loop that can handle C<ev_child> watchers,
		359	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		360	a problem for your application you can either create a dynamic loop with
		361	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		362	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		363
		364	Example: This is the most typical usage.
		365
		366	if (!ev_default_loop (0))
		367	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		368
		369	Example: Restrict libev to the select and poll backends, and do not allow
		370	environment settings to be taken into account:
		371
		372	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		373
		374	=item struct ev_loop *ev_loop_new (unsigned int flags)
		375
		376	This will create and initialise a new event loop object. If the loop
		377	could not be initialised, returns false.
		378
		379	This function is thread-safe, and one common way to use libev with
		380	threads is indeed to create one loop per thread, and using the default
		381	loop in the "main" or "initial" thread.
121		382
122	The flags argument can be used to specify special behaviour or specific	383	The flags argument can be used to specify special behaviour or specific
123	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	384	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		385
125	It supports the following flags:	386	The following flags are supported:
126		387
127	=over 4	388	=over 4
128		389
129	=item EVFLAG_AUTO	390	=item C<EVFLAG_AUTO>
130		391
131	The default flags value. Use this if you have no clue (it's the right	392	The default flags value. Use this if you have no clue (it's the right
132	thing, believe me).	393	thing, believe me).
133		394
134	=item EVFLAG_NOENV	395	=item C<EVFLAG_NOENV>
135		396
136	If this flag bit is ored into the flag value (or the program runs setuid	397	If this flag bit is or'ed into the flag value (or the program runs setuid
137	or setgid) then libev will I<not> look at the environment variable	398	or setgid) then libev will I<not> look at the environment variable
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	399	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	400	override the flags completely if it is found in the environment. This is
140	useful to try out specific backends to test their performance, or to work	401	useful to try out specific backends to test their performance, or to work
141	around bugs.	402	around bugs.
142		403
		404	=item C<EVFLAG_FORKCHECK>
		405
		406	Instead of calling C<ev_loop_fork> manually after a fork, you can also
		407	make libev check for a fork in each iteration by enabling this flag.
		408
		409	This works by calling C<getpid ()> on every iteration of the loop,
		410	and thus this might slow down your event loop if you do a lot of loop
		411	iterations and little real work, but is usually not noticeable (on my
		412	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		413	without a system call and thus I<very> fast, but my GNU/Linux system also has
		414	C<pthread_atfork> which is even faster).
		415
		416	The big advantage of this flag is that you can forget about fork (and
		417	forget about forgetting to tell libev about forking) when you use this
		418	flag.
		419
		420	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		421	environment variable.
		422
		423	=item C<EVFLAG_NOINOTIFY>
		424
		425	When this flag is specified, then libev will not attempt to use the
		426	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		427	testing, this flag can be useful to conserve inotify file descriptors, as
		428	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		429
		430	=item C<EVFLAG_SIGNALFD>
		431
		432	When this flag is specified, then libev will attempt to use the
		433	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		434	delivers signals synchronously, which makes it both faster and might make
		435	it possible to get the queued signal data. It can also simplify signal
		436	handling with threads, as long as you properly block signals in your
		437	threads that are not interested in handling them.
		438
		439	Signalfd will not be used by default as this changes your signal mask, and
		440	there are a lot of shoddy libraries and programs (glib's threadpool for
		441	example) that can't properly initialise their signal masks.
		442
		443	=item C<EVFLAG_NOSIGMASK>
		444
		445	When this flag is specified, then libev will avoid to modify the signal
		446	mask. Specifically, this means you have to make sure signals are unblocked
		447	when you want to receive them.
		448
		449	This behaviour is useful when you want to do your own signal handling, or
		450	want to handle signals only in specific threads and want to avoid libev
		451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
		455
		456	This flag's behaviour will become the default in future versions of libev.
		457
143	=item EVMETHOD_SELECT (portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		459
		460	This is your standard select(2) backend. Not I<completely> standard, as
		461	libev tries to roll its own fd_set with no limits on the number of fds,
		462	but if that fails, expect a fairly low limit on the number of fds when
		463	using this backend. It doesn't scale too well (O(highest_fd)), but its
		464	usually the fastest backend for a low number of (low-numbered :) fds.
		465
		466	To get good performance out of this backend you need a high amount of
		467	parallelism (most of the file descriptors should be busy). If you are
		468	writing a server, you should C<accept ()> in a loop to accept as many
		469	connections as possible during one iteration. You might also want to have
		470	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		471	readiness notifications you get per iteration.
		472
		473	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		474	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		475	C<exceptfds> set on that platform).
		476
145	=item EVMETHOD_POLL (poll backend, available everywhere except on windows)	477	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
146		478
147	=item EVMETHOD_EPOLL (linux only)	479	And this is your standard poll(2) backend. It's more complicated
		480	than select, but handles sparse fds better and has no artificial
		481	limit on the number of fds you can use (except it will slow down
		482	considerably with a lot of inactive fds). It scales similarly to select,
		483	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		484	performance tips.
148		485
149	=item EVMETHOD_KQUEUE (some bsds only)	486	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		487	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
150		488
151	=item EVMETHOD_DEVPOLL (solaris 8 only)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
152		490
153	=item EVMETHOD_PORT (solaris 10 only)	491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		492	kernels).
154		493
155	If one or more of these are ored into the flags value, then only these	494	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	495	it scales phenomenally better. While poll and select usually scale like
157	specified, any backend will do.	496	O(total_fds) where total_fds is the total number of fds (or the highest
		497	fd), epoll scales either O(1) or O(active_fds).
		498
		499	The epoll mechanism deserves honorable mention as the most misdesigned
		500	of the more advanced event mechanisms: mere annoyances include silently
		501	dropping file descriptors, requiring a system call per change per file
		502	descriptor (and unnecessary guessing of parameters), problems with dup,
		503	returning before the timeout value, resulting in additional iterations
		504	(and only giving 5ms accuracy while select on the same platform gives
		505	0.1ms) and so on. The biggest issue is fork races, however - if a program
		506	forks then I<both> parent and child process have to recreate the epoll
		507	set, which can take considerable time (one syscall per file descriptor)
		508	and is of course hard to detect.
		509
		510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
		511	but of course I<doesn't>, and epoll just loves to report events for
		512	totally I<different> file descriptors (even already closed ones, so
		513	one cannot even remove them from the set) than registered in the set
		514	(especially on SMP systems). Libev tries to counter these spurious
		515	notifications by employing an additional generation counter and comparing
		516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
		520	not least, it also refuses to work with some file descriptors which work
		521	perfectly fine with C<select> (files, many character devices...).
		522
		523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
		526
		527	While stopping, setting and starting an I/O watcher in the same iteration
		528	will result in some caching, there is still a system call per such
		529	incident (because the same I<file descriptor> could point to a different
		530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
		531	file descriptors might not work very well if you register events for both
		532	file descriptors.
		533
		534	Best performance from this backend is achieved by not unregistering all
		535	watchers for a file descriptor until it has been closed, if possible,
		536	i.e. keep at least one watcher active per fd at all times. Stopping and
		537	starting a watcher (without re-setting it) also usually doesn't cause
		538	extra overhead. A fork can both result in spurious notifications as well
		539	as in libev having to destroy and recreate the epoll object, which can
		540	take considerable time and thus should be avoided.
		541
		542	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		543	faster than epoll for maybe up to a hundred file descriptors, depending on
		544	the usage. So sad.
		545
		546	While nominally embeddable in other event loops, this feature is broken in
		547	all kernel versions tested so far.
		548
		549	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		550	C<EVBACKEND_POLL>.
		551
		552	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		553
		554	Kqueue deserves special mention, as at the time of this writing, it
		555	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		556	with anything but sockets and pipes, except on Darwin, where of course
		557	it's completely useless). Unlike epoll, however, whose brokenness
		558	is by design, these kqueue bugs can (and eventually will) be fixed
		559	without API changes to existing programs. For this reason it's not being
		560	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		561	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		562	system like NetBSD.
		563
		564	You still can embed kqueue into a normal poll or select backend and use it
		565	only for sockets (after having made sure that sockets work with kqueue on
		566	the target platform). See C<ev_embed> watchers for more info.
		567
		568	It scales in the same way as the epoll backend, but the interface to the
		569	kernel is more efficient (which says nothing about its actual speed, of
		570	course). While stopping, setting and starting an I/O watcher does never
		571	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		572	two event changes per incident. Support for C<fork ()> is very bad (but
		573	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		574	cases
		575
		576	This backend usually performs well under most conditions.
		577
		578	While nominally embeddable in other event loops, this doesn't work
		579	everywhere, so you might need to test for this. And since it is broken
		580	almost everywhere, you should only use it when you have a lot of sockets
		581	(for which it usually works), by embedding it into another event loop
		582	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		583	also broken on OS X)) and, did I mention it, using it only for sockets.
		584
		585	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		586	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		587	C<NOTE_EOF>.
		588
		589	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		590
		591	This is not implemented yet (and might never be, unless you send me an
		592	implementation). According to reports, C</dev/poll> only supports sockets
		593	and is not embeddable, which would limit the usefulness of this backend
		594	immensely.
		595
		596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		597
		598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		599	it's really slow, but it still scales very well (O(active_fds)).
		600
		601	While this backend scales well, it requires one system call per active
		602	file descriptor per loop iteration. For small and medium numbers of file
		603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		604	might perform better.
		605
		606	On the positive side, this backend actually performed fully to
		607	specification in all tests and is fully embeddable, which is a rare feat
		608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returns events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where you
		616	absolutely have to know whether an event occurred or not because you have
		617	to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
		620
		621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		622	C<EVBACKEND_POLL>.
		623
		624	=item C<EVBACKEND_ALL>
		625
		626	Try all backends (even potentially broken ones that wouldn't be tried
		627	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		629
		630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
158		639
159	=back	640	=back
160		641
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	642	If one or more of the backend flags are or'ed into the flags value,
		643	then only these backends will be tried (in the reverse order as listed
		644	here). If none are specified, all backends in C<ev_recommended_backends
		645	()> will be tried.
162		646
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	647	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		648
168	=item ev_default_destroy ()	649	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		650	if (!epoller)
		651	fatal ("no epoll found here, maybe it hides under your chair");
169		652
170	Destroys the default loop again (frees all memory and kernel state	653	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	654	used if available.
172	any way whatsoever, although you cannot rely on this :).	655
		656	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
173		657
174	=item ev_loop_destroy (loop)	658	=item ev_loop_destroy (loop)
175		659
176	Like C<ev_default_destroy>, but destroys an event loop created by an	660	Destroys an event loop object (frees all memory and kernel state
177	earlier call to C<ev_loop_new>.	661	etc.). None of the active event watchers will be stopped in the normal
		662	sense, so e.g. C<ev_is_active> might still return true. It is your
		663	responsibility to either stop all watchers cleanly yourself I<before>
		664	calling this function, or cope with the fact afterwards (which is usually
		665	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		666	for example).
178		667
179	=item ev_default_fork ()	668	Note that certain global state, such as signal state (and installed signal
		669	handlers), will not be freed by this function, and related watchers (such
		670	as signal and child watchers) would need to be stopped manually.
180		671
		672	This function is normally used on loop objects allocated by
		673	C<ev_loop_new>, but it can also be used on the default loop returned by
		674	C<ev_default_loop>, in which case it is not thread-safe.
		675
		676	Note that it is not advisable to call this function on the default loop
		677	except in the rare occasion where you really need to free its resources.
		678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		679	and C<ev_loop_destroy>.
		680
		681	=item ev_loop_fork (loop)
		682
		683	This function sets a flag that causes subsequent C<ev_run> iterations to
181	This function reinitialises the kernel state for backends that have	684	reinitialise the kernel state for backends that have one. Despite the
182	one. Despite the name, you can call it anytime, but it makes most sense	685	name, you can call it anytime, but it makes most sense after forking, in
183	after forking, in either the parent or child process (or both, but that	686	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
184	again makes little sense).	687	child before resuming or calling C<ev_run>.
185		688
186	You I<must> call this function after forking if and only if you want to	689	Again, you I<have> to call it on I<any> loop that you want to re-use after
187	use the event library in both processes. If you just fork+exec, you don't	690	a fork, I<even if you do not plan to use the loop in the parent>. This is
188	have to call it.	691	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		692	during fork.
		693
		694	On the other hand, you only need to call this function in the child
		695	process if and only if you want to use the event loop in the child. If
		696	you just fork+exec or create a new loop in the child, you don't have to
		697	call it at all (in fact, C<epoll> is so badly broken that it makes a
		698	difference, but libev will usually detect this case on its own and do a
		699	costly reset of the backend).
189		700
190	The function itself is quite fast and it's usually not a problem to call	701	The function itself is quite fast and it's usually not a problem to call
191	it just in case after a fork. To make this easy, the function will fit in	702	it just in case after a fork.
192	quite nicely into a call to C<pthread_atfork>:
193		703
		704	Example: Automate calling C<ev_loop_fork> on the default loop when
		705	using pthreads.
		706
		707	static void
		708	post_fork_child (void)
		709	{
		710	ev_loop_fork (EV_DEFAULT);
		711	}
		712
		713	...
194	pthread_atfork (0, 0, ev_default_fork);	714	pthread_atfork (0, 0, post_fork_child);
195		715
196	=item ev_loop_fork (loop)	716	=item int ev_is_default_loop (loop)
197		717
198	Like C<ev_default_fork>, but acts on an event loop created by	718	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	719	otherwise.
200	after fork, and how you do this is entirely your own problem.
201		720
		721	=item unsigned int ev_iteration (loop)
		722
		723	Returns the current iteration count for the event loop, which is identical
		724	to the number of times libev did poll for new events. It starts at C<0>
		725	and happily wraps around with enough iterations.
		726
		727	This value can sometimes be useful as a generation counter of sorts (it
		728	"ticks" the number of loop iterations), as it roughly corresponds with
		729	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		730	prepare and check phases.
		731
202	=item unsigned int ev_method (loop)	732	=item unsigned int ev_depth (loop)
203		733
		734	Returns the number of times C<ev_run> was entered minus the number of
		735	times C<ev_run> was exited normally, in other words, the recursion depth.
		736
		737	Outside C<ev_run>, this number is zero. In a callback, this number is
		738	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		739	in which case it is higher.
		740
		741	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		742	throwing an exception etc.), doesn't count as "exit" - consider this
		743	as a hint to avoid such ungentleman-like behaviour unless it's really
		744	convenient, in which case it is fully supported.
		745
		746	=item unsigned int ev_backend (loop)
		747
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	748	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	749	use.
206		750
207	=item ev_tstamp ev_now (loop)	751	=item ev_tstamp ev_now (loop)
208		752
209	Returns the current "event loop time", which is the time the event loop	753	Returns the current "event loop time", which is the time the event loop
210	got events and started processing them. This timestamp does not change	754	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	755	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	756	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).	757	event occurring (or more correctly, libev finding out about it).
214		758
		759	=item ev_now_update (loop)
		760
		761	Establishes the current time by querying the kernel, updating the time
		762	returned by C<ev_now ()> in the progress. This is a costly operation and
		763	is usually done automatically within C<ev_run ()>.
		764
		765	This function is rarely useful, but when some event callback runs for a
		766	very long time without entering the event loop, updating libev's idea of
		767	the current time is a good idea.
		768
		769	See also L<The special problem of time updates> in the C<ev_timer> section.
		770
		771	=item ev_suspend (loop)
		772
		773	=item ev_resume (loop)
		774
		775	These two functions suspend and resume an event loop, for use when the
		776	loop is not used for a while and timeouts should not be processed.
		777
		778	A typical use case would be an interactive program such as a game: When
		779	the user presses C<^Z> to suspend the game and resumes it an hour later it
		780	would be best to handle timeouts as if no time had actually passed while
		781	the program was suspended. This can be achieved by calling C<ev_suspend>
		782	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		783	C<ev_resume> directly afterwards to resume timer processing.
		784
		785	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		786	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		787	will be rescheduled (that is, they will lose any events that would have
		788	occurred while suspended).
		789
		790	After calling C<ev_suspend> you B<must not> call I<any> function on the
		791	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		792	without a previous call to C<ev_suspend>.
		793
		794	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		795	event loop time (see C<ev_now_update>).
		796
215	=item ev_loop (loop, int flags)	797	=item ev_run (loop, int flags)
216		798
217	Finally, this is it, the event handler. This function usually is called	799	Finally, this is it, the event handler. This function usually is called
218	after you initialised all your watchers and you want to start handling	800	after you have initialised all your watchers and you want to start
219	events.	801	handling events. It will ask the operating system for any new events, call
		802	the watcher callbacks, an then repeat the whole process indefinitely: This
		803	is why event loops are called I<loops>.
220		804
221	If the flags argument is specified as 0, it will not return until either	805	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.	806	until either no event watchers are active anymore or C<ev_break> was
		807	called.
223		808
		809	Please note that an explicit C<ev_break> is usually better than
		810	relying on all watchers to be stopped when deciding when a program has
		811	finished (especially in interactive programs), but having a program
		812	that automatically loops as long as it has to and no longer by virtue
		813	of relying on its watchers stopping correctly, that is truly a thing of
		814	beauty.
		815
		816	This function is also I<mostly> exception-safe - you can break out of
		817	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		818	exception and so on. This does not decrement the C<ev_depth> value, nor
		819	will it clear any outstanding C<EVBREAK_ONE> breaks.
		820
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	821	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	822	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.	823	block your process in case there are no events and will return after one
		824	iteration of the loop. This is sometimes useful to poll and handle new
		825	events while doing lengthy calculations, to keep the program responsive.
227		826
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	827	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	828	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	829	will block your process until at least one new event arrives (which could
		830	be an event internal to libev itself, so there is no guarantee that a
		831	user-registered callback will be called), and will return after one
231	one iteration of the loop.	832	iteration of the loop.
232		833
233	This flags value could be used to implement alternative looping	834	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	835	with something not expressible using other libev watchers (i.e. "roll your
235	more generic mechanism.	836	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		837	usually a better approach for this kind of thing.
236		838
		839	Here are the gory details of what C<ev_run> does (this is for your
		840	understanding, not a guarantee that things will work exactly like this in
		841	future versions):
		842
		843	- Increment loop depth.
		844	- Reset the ev_break status.
		845	- Before the first iteration, call any pending watchers.
		846	LOOP:
		847	- If EVFLAG_FORKCHECK was used, check for a fork.
		848	- If a fork was detected (by any means), queue and call all fork watchers.
		849	- Queue and call all prepare watchers.
		850	- If ev_break was called, goto FINISH.
		851	- If we have been forked, detach and recreate the kernel state
		852	as to not disturb the other process.
		853	- Update the kernel state with all outstanding changes.
		854	- Update the "event loop time" (ev_now ()).
		855	- Calculate for how long to sleep or block, if at all
		856	(active idle watchers, EVRUN_NOWAIT or not having
		857	any active watchers at all will result in not sleeping).
		858	- Sleep if the I/O and timer collect interval say so.
		859	- Increment loop iteration counter.
		860	- Block the process, waiting for any events.
		861	- Queue all outstanding I/O (fd) events.
		862	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		863	- Queue all expired timers.
		864	- Queue all expired periodics.
		865	- Queue all idle watchers with priority higher than that of pending events.
		866	- Queue all check watchers.
		867	- Call all queued watchers in reverse order (i.e. check watchers first).
		868	Signals and child watchers are implemented as I/O watchers, and will
		869	be handled here by queueing them when their watcher gets executed.
		870	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
		871	were used, or there are no active watchers, goto FINISH, otherwise
		872	continue with step LOOP.
		873	FINISH:
		874	- Reset the ev_break status iff it was EVBREAK_ONE.
		875	- Decrement the loop depth.
		876	- Return.
		877
		878	Example: Queue some jobs and then loop until no events are outstanding
		879	anymore.
		880
		881	... queue jobs here, make sure they register event watchers as long
		882	... as they still have work to do (even an idle watcher will do..)
		883	ev_run (my_loop, 0);
		884	... jobs done or somebody called break. yeah!
		885
237	=item ev_unloop (loop, how)	886	=item ev_break (loop, how)
238		887
239	Can be used to make a call to C<ev_loop> return early (but only after it	888	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	889	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	890	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.	891	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		892
		893	This "break state" will be cleared on the next call to C<ev_run>.
		894
		895	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		896	which case it will have no effect.
243		897
244	=item ev_ref (loop)	898	=item ev_ref (loop)
245		899
246	=item ev_unref (loop)	900	=item ev_unref (loop)
247		901
248	Ref/unref can be used to add or remove a reference count on the event	902	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	903	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	904	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	905
252	returning, ev_unref() after starting, and ev_ref() before stopping it. For	906	This is useful when you have a watcher that you never intend to
		907	unregister, but that nevertheless should not keep C<ev_run> from
		908	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		909	before stopping it.
		910
253	example, libev itself uses this for its internal signal pipe: It is not	911	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	912	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	913	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	914	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>.	915	third-party libraries. Just remember to I<unref after start> and I<ref
		916	before stop> (but only if the watcher wasn't active before, or was active
		917	before, respectively. Note also that libev might stop watchers itself
		918	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		919	in the callback).
		920
		921	Example: Create a signal watcher, but keep it from keeping C<ev_run>
		922	running when nothing else is active.
		923
		924	ev_signal exitsig;
		925	ev_signal_init (&exitsig, sig_cb, SIGINT);
		926	ev_signal_start (loop, &exitsig);
		927	ev_unref (loop);
		928
		929	Example: For some weird reason, unregister the above signal handler again.
		930
		931	ev_ref (loop);
		932	ev_signal_stop (loop, &exitsig);
		933
		934	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		935
		936	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		937
		938	These advanced functions influence the time that libev will spend waiting
		939	for events. Both time intervals are by default C<0>, meaning that libev
		940	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		941	latency.
		942
		943	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		944	allows libev to delay invocation of I/O and timer/periodic callbacks
		945	to increase efficiency of loop iterations (or to increase power-saving
		946	opportunities).
		947
		948	The idea is that sometimes your program runs just fast enough to handle
		949	one (or very few) event(s) per loop iteration. While this makes the
		950	program responsive, it also wastes a lot of CPU time to poll for new
		951	events, especially with backends like C<select ()> which have a high
		952	overhead for the actual polling but can deliver many events at once.
		953
		954	By setting a higher I<io collect interval> you allow libev to spend more
		955	time collecting I/O events, so you can handle more events per iteration,
		956	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		957	C<ev_timer>) will not be affected. Setting this to a non-null value will
		958	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		959	sleep time ensures that libev will not poll for I/O events more often then
		960	once per this interval, on average (as long as the host time resolution is
		961	good enough).
		962
		963	Likewise, by setting a higher I<timeout collect interval> you allow libev
		964	to spend more time collecting timeouts, at the expense of increased
		965	latency/jitter/inexactness (the watcher callback will be called
		966	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		967	value will not introduce any overhead in libev.
		968
		969	Many (busy) programs can usually benefit by setting the I/O collect
		970	interval to a value near C<0.1> or so, which is often enough for
		971	interactive servers (of course not for games), likewise for timeouts. It
		972	usually doesn't make much sense to set it to a lower value than C<0.01>,
		973	as this approaches the timing granularity of most systems. Note that if
		974	you do transactions with the outside world and you can't increase the
		975	parallelity, then this setting will limit your transaction rate (if you
		976	need to poll once per transaction and the I/O collect interval is 0.01,
		977	then you can't do more than 100 transactions per second).
		978
		979	Setting the I<timeout collect interval> can improve the opportunity for
		980	saving power, as the program will "bundle" timer callback invocations that
		981	are "near" in time together, by delaying some, thus reducing the number of
		982	times the process sleeps and wakes up again. Another useful technique to
		983	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		984	they fire on, say, one-second boundaries only.
		985
		986	Example: we only need 0.1s timeout granularity, and we wish not to poll
		987	more often than 100 times per second:
		988
		989	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		990	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		991
		992	=item ev_invoke_pending (loop)
		993
		994	This call will simply invoke all pending watchers while resetting their
		995	pending state. Normally, C<ev_run> does this automatically when required,
		996	but when overriding the invoke callback this call comes handy. This
		997	function can be invoked from a watcher - this can be useful for example
		998	when you want to do some lengthy calculation and want to pass further
		999	event handling to another thread (you still have to make sure only one
		1000	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		1001
		1002	=item int ev_pending_count (loop)
		1003
		1004	Returns the number of pending watchers - zero indicates that no watchers
		1005	are pending.
		1006
		1007	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		1008
		1009	This overrides the invoke pending functionality of the loop: Instead of
		1010	invoking all pending watchers when there are any, C<ev_run> will call
		1011	this callback instead. This is useful, for example, when you want to
		1012	invoke the actual watchers inside another context (another thread etc.).
		1013
		1014	If you want to reset the callback, use C<ev_invoke_pending> as new
		1015	callback.
		1016
		1017	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		1018
		1019	Sometimes you want to share the same loop between multiple threads. This
		1020	can be done relatively simply by putting mutex_lock/unlock calls around
		1021	each call to a libev function.
		1022
		1023	However, C<ev_run> can run an indefinite time, so it is not feasible
		1024	to wait for it to return. One way around this is to wake up the event
		1025	loop via C<ev_break> and C<ev_async_send>, another way is to set these
		1026	I<release> and I<acquire> callbacks on the loop.
		1027
		1028	When set, then C<release> will be called just before the thread is
		1029	suspended waiting for new events, and C<acquire> is called just
		1030	afterwards.
		1031
		1032	Ideally, C<release> will just call your mutex_unlock function, and
		1033	C<acquire> will just call the mutex_lock function again.
		1034
		1035	While event loop modifications are allowed between invocations of
		1036	C<release> and C<acquire> (that's their only purpose after all), no
		1037	modifications done will affect the event loop, i.e. adding watchers will
		1038	have no effect on the set of file descriptors being watched, or the time
		1039	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1040	to take note of any changes you made.
		1041
		1042	In theory, threads executing C<ev_run> will be async-cancel safe between
		1043	invocations of C<release> and C<acquire>.
		1044
		1045	See also the locking example in the C<THREADS> section later in this
		1046	document.
		1047
		1048	=item ev_set_userdata (loop, void *data)
		1049
		1050	=item void *ev_userdata (loop)
		1051
		1052	Set and retrieve a single C<void *> associated with a loop. When
		1053	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1054	C<0>.
		1055
		1056	These two functions can be used to associate arbitrary data with a loop,
		1057	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1058	C<acquire> callbacks described above, but of course can be (ab-)used for
		1059	any other purpose as well.
		1060
		1061	=item ev_verify (loop)
		1062
		1063	This function only does something when C<EV_VERIFY> support has been
		1064	compiled in, which is the default for non-minimal builds. It tries to go
		1065	through all internal structures and checks them for validity. If anything
		1066	is found to be inconsistent, it will print an error message to standard
		1067	error and call C<abort ()>.
		1068
		1069	This can be used to catch bugs inside libev itself: under normal
		1070	circumstances, this function will never abort as of course libev keeps its
		1071	data structures consistent.
258		1072
259	=back	1073	=back
260		1074
		1075
261	=head1 ANATOMY OF A WATCHER	1076	=head1 ANATOMY OF A WATCHER
262		1077
		1078	In the following description, uppercase C<TYPE> in names stands for the
		1079	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1080	watchers and C<ev_io_start> for I/O watchers.
		1081
263	A watcher is a structure that you create and register to record your	1082	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	1083	your interest in some event. To make a concrete example, imagine you want
265	become readable, you would create an ev_io watcher for that:	1084	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1085	for that:
266		1086
267	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1087	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
268	{	1088	{
269	ev_io_stop (w);	1089	ev_io_stop (w);
270	ev_unloop (loop, EVUNLOOP_ALL);	1090	ev_break (loop, EVBREAK_ALL);
271	}	1091	}
272		1092
273	struct ev_loop *loop = ev_default_loop (0);	1093	struct ev_loop *loop = ev_default_loop (0);
		1094
274	struct ev_io stdin_watcher;	1095	ev_io stdin_watcher;
		1096
275	ev_init (&stdin_watcher, my_cb);	1097	ev_init (&stdin_watcher, my_cb);
276	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1098	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
277	ev_io_start (loop, &stdin_watcher);	1099	ev_io_start (loop, &stdin_watcher);
		1100
278	ev_loop (loop, 0);	1101	ev_run (loop, 0);
279		1102
280	As you can see, you are responsible for allocating the memory for your	1103	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,	1104	watcher structures (and it is I<usually> a bad idea to do this on the
282	although this can sometimes be quite valid).	1105	stack).
283		1106
		1107	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1108	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1109
284	Each watcher structure must be initialised by a call to C<ev_init	1110	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	1111	*, 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	1112	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	1113	time the event loop detects that the file descriptor given is readable
288	is readable and/or writable).	1114	and/or writable).
289		1115
290	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1116	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	1117	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	1118	is also a macro to combine initialisation and setting in one call: C<<
293	(watcher *, callback, ...) >>.	1119	ev_TYPE_init (watcher *, callback, ...) >>.
294		1120
295	To make the watcher actually watch out for events, you have to start it	1121	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	1122	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	1123	*) >>), and you can stop watching for events at any time by calling the
298	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1124	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
299		1125
300	As long as your watcher is active (has been started but not stopped) you	1126	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	1127	must not touch the values stored in it. Most specifically you must never
302	reinitialise it or call its set method.	1128	reinitialise it or call its C<ev_TYPE_set> macro.
303
304	You cna 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 cna use the C<ev_is_pending
307	(watcher *)> macro.
308		1129
309	Each and every callback receives the event loop pointer as first, the	1130	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	1131	registered watcher structure as second, and a bitset of received events as
311	third argument.	1132	third argument.
312		1133
313	The rceeived events usually include a single bit per event type received	1134	The received events usually include a single bit per event type received
314	(you can receive multiple events at the same time). The possible bit masks	1135	(you can receive multiple events at the same time). The possible bit masks
315	are:	1136	are:
316		1137
317	=over 4	1138	=over 4
318		1139
319	=item EV_READ	1140	=item C<EV_READ>
320		1141
321	=item EV_WRITE	1142	=item C<EV_WRITE>
322		1143
323	The file descriptor in the ev_io watcher has become readable and/or	1144	The file descriptor in the C<ev_io> watcher has become readable and/or
324	writable.	1145	writable.
325		1146
326	=item EV_TIMEOUT	1147	=item C<EV_TIMER>
327		1148
328	The ev_timer watcher has timed out.	1149	The C<ev_timer> watcher has timed out.
329		1150
330	=item EV_PERIODIC	1151	=item C<EV_PERIODIC>
331		1152
332	The ev_periodic watcher has timed out.	1153	The C<ev_periodic> watcher has timed out.
333		1154
334	=item EV_SIGNAL	1155	=item C<EV_SIGNAL>
335		1156
336	The signal specified in the ev_signal watcher has been received by a thread.	1157	The signal specified in the C<ev_signal> watcher has been received by a thread.
337		1158
338	=item EV_CHILD	1159	=item C<EV_CHILD>
339		1160
340	The pid specified in the ev_child watcher has received a status change.	1161	The pid specified in the C<ev_child> watcher has received a status change.
341		1162
		1163	=item C<EV_STAT>
		1164
		1165	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1166
342	=item EV_IDLE	1167	=item C<EV_IDLE>
343		1168
344	The ev_idle watcher has determined that you have nothing better to do.	1169	The C<ev_idle> watcher has determined that you have nothing better to do.
345		1170
346	=item EV_PREPARE	1171	=item C<EV_PREPARE>
347		1172
348	=item EV_CHECK	1173	=item C<EV_CHECK>
349		1174
350	All ev_prepare watchers are invoked just I<before> C<ev_loop> starts	1175	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
351	to gather new events, and all ev_check watchers are invoked just after	1176	to gather new events, and all C<ev_check> watchers are invoked just after
352	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1177	C<ev_run> has gathered them, but before it invokes any callbacks for any
353	received events. Callbacks of both watcher types can start and stop as	1178	received events. Callbacks of both watcher types can start and stop as
354	many watchers as they want, and all of them will be taken into account	1179	many watchers as they want, and all of them will be taken into account
355	(for example, a ev_prepare watcher might start an idle watcher to keep	1180	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
356	C<ev_loop> from blocking).	1181	C<ev_run> from blocking).
357		1182
		1183	=item C<EV_EMBED>
		1184
		1185	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1186
		1187	=item C<EV_FORK>
		1188
		1189	The event loop has been resumed in the child process after fork (see
		1190	C<ev_fork>).
		1191
		1192	=item C<EV_CLEANUP>
		1193
		1194	The event loop is about to be destroyed (see C<ev_cleanup>).
		1195
		1196	=item C<EV_ASYNC>
		1197
		1198	The given async watcher has been asynchronously notified (see C<ev_async>).
		1199
		1200	=item C<EV_CUSTOM>
		1201
		1202	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1203	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1204
358	=item EV_ERROR	1205	=item C<EV_ERROR>
359		1206
360	An unspecified error has occured, the watcher has been stopped. This might	1207	An unspecified error has occurred, the watcher has been stopped. This might
361	happen because the watcher could not be properly started because libev	1208	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	1209	ran out of memory, a file descriptor was found to be closed or any other
		1210	problem. Libev considers these application bugs.
		1211
363	problem. You best act on it by reporting the problem and somehow coping	1212	You best act on it by reporting the problem and somehow coping with the
364	with the watcher being stopped.	1213	watcher being stopped. Note that well-written programs should not receive
		1214	an error ever, so when your watcher receives it, this usually indicates a
		1215	bug in your program.
365		1216
366	Libev will usually signal a few "dummy" events together with an error,	1217	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	1218	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	1219	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	1220	the error from read() or write(). This will not work in multi-threaded
370	programs, though, so beware.	1221	programs, though, as the fd could already be closed and reused for another
		1222	thing, so beware.
371		1223
372	=back	1224	=back
373		1225
374	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1226	=head2 GENERIC WATCHER FUNCTIONS
375		1227
376	Each watcher has, by default, a member C<void *data> that you can change	1228	=over 4
377	and read at any time, libev will completely ignore it. This cna 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		1229
383	struct my_io	1230	=item C<ev_init> (ev_TYPE *watcher, callback)
		1231
		1232	This macro initialises the generic portion of a watcher. The contents
		1233	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1234	the generic parts of the watcher are initialised, you I<need> to call
		1235	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1236	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1237	which rolls both calls into one.
		1238
		1239	You can reinitialise a watcher at any time as long as it has been stopped
		1240	(or never started) and there are no pending events outstanding.
		1241
		1242	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1243	int revents)>.
		1244
		1245	Example: Initialise an C<ev_io> watcher in two steps.
		1246
		1247	ev_io w;
		1248	ev_init (&w, my_cb);
		1249	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1250
		1251	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1252
		1253	This macro initialises the type-specific parts of a watcher. You need to
		1254	call C<ev_init> at least once before you call this macro, but you can
		1255	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1256	macro on a watcher that is active (it can be pending, however, which is a
		1257	difference to the C<ev_init> macro).
		1258
		1259	Although some watcher types do not have type-specific arguments
		1260	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1261
		1262	See C<ev_init>, above, for an example.
		1263
		1264	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1265
		1266	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1267	calls into a single call. This is the most convenient method to initialise
		1268	a watcher. The same limitations apply, of course.
		1269
		1270	Example: Initialise and set an C<ev_io> watcher in one step.
		1271
		1272	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1273
		1274	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1275
		1276	Starts (activates) the given watcher. Only active watchers will receive
		1277	events. If the watcher is already active nothing will happen.
		1278
		1279	Example: Start the C<ev_io> watcher that is being abused as example in this
		1280	whole section.
		1281
		1282	ev_io_start (EV_DEFAULT_UC, &w);
		1283
		1284	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1285
		1286	Stops the given watcher if active, and clears the pending status (whether
		1287	the watcher was active or not).
		1288
		1289	It is possible that stopped watchers are pending - for example,
		1290	non-repeating timers are being stopped when they become pending - but
		1291	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1292	pending. If you want to free or reuse the memory used by the watcher it is
		1293	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1294
		1295	=item bool ev_is_active (ev_TYPE *watcher)
		1296
		1297	Returns a true value iff the watcher is active (i.e. it has been started
		1298	and not yet been stopped). As long as a watcher is active you must not modify
		1299	it.
		1300
		1301	=item bool ev_is_pending (ev_TYPE *watcher)
		1302
		1303	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1304	events but its callback has not yet been invoked). As long as a watcher
		1305	is pending (but not active) you must not call an init function on it (but
		1306	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1307	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1308	it).
		1309
		1310	=item callback ev_cb (ev_TYPE *watcher)
		1311
		1312	Returns the callback currently set on the watcher.
		1313
		1314	=item ev_cb_set (ev_TYPE *watcher, callback)
		1315
		1316	Change the callback. You can change the callback at virtually any time
		1317	(modulo threads).
		1318
		1319	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1320
		1321	=item int ev_priority (ev_TYPE *watcher)
		1322
		1323	Set and query the priority of the watcher. The priority is a small
		1324	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1325	(default: C<-2>). Pending watchers with higher priority will be invoked
		1326	before watchers with lower priority, but priority will not keep watchers
		1327	from being executed (except for C<ev_idle> watchers).
		1328
		1329	If you need to suppress invocation when higher priority events are pending
		1330	you need to look at C<ev_idle> watchers, which provide this functionality.
		1331
		1332	You I<must not> change the priority of a watcher as long as it is active or
		1333	pending.
		1334
		1335	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1336	fine, as long as you do not mind that the priority value you query might
		1337	or might not have been clamped to the valid range.
		1338
		1339	The default priority used by watchers when no priority has been set is
		1340	always C<0>, which is supposed to not be too high and not be too low :).
		1341
		1342	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1343	priorities.
		1344
		1345	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1346
		1347	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1348	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1349	can deal with that fact, as both are simply passed through to the
		1350	callback.
		1351
		1352	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1353
		1354	If the watcher is pending, this function clears its pending status and
		1355	returns its C<revents> bitset (as if its callback was invoked). If the
		1356	watcher isn't pending it does nothing and returns C<0>.
		1357
		1358	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1359	callback to be invoked, which can be accomplished with this function.
		1360
		1361	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1362
		1363	Feeds the given event set into the event loop, as if the specified event
		1364	had happened for the specified watcher (which must be a pointer to an
		1365	initialised but not necessarily started event watcher). Obviously you must
		1366	not free the watcher as long as it has pending events.
		1367
		1368	Stopping the watcher, letting libev invoke it, or calling
		1369	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1370	not started in the first place.
		1371
		1372	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1373	functions that do not need a watcher.
		1374
		1375	=back
		1376
		1377	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1378	OWN COMPOSITE WATCHERS> idioms.
		1379
		1380	=head2 WATCHER STATES
		1381
		1382	There are various watcher states mentioned throughout this manual -
		1383	active, pending and so on. In this section these states and the rules to
		1384	transition between them will be described in more detail - and while these
		1385	rules might look complicated, they usually do "the right thing".
		1386
		1387	=over 4
		1388
		1389	=item initialiased
		1390
		1391	Before a watcher can be registered with the event loop it has to be
		1392	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1393	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1394
		1395	In this state it is simply some block of memory that is suitable for
		1396	use in an event loop. It can be moved around, freed, reused etc. at
		1397	will - as long as you either keep the memory contents intact, or call
		1398	C<ev_TYPE_init> again.
		1399
		1400	=item started/running/active
		1401
		1402	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1403	property of the event loop, and is actively waiting for events. While in
		1404	this state it cannot be accessed (except in a few documented ways), moved,
		1405	freed or anything else - the only legal thing is to keep a pointer to it,
		1406	and call libev functions on it that are documented to work on active watchers.
		1407
		1408	=item pending
		1409
		1410	If a watcher is active and libev determines that an event it is interested
		1411	in has occurred (such as a timer expiring), it will become pending. It will
		1412	stay in this pending state until either it is stopped or its callback is
		1413	about to be invoked, so it is not normally pending inside the watcher
		1414	callback.
		1415
		1416	The watcher might or might not be active while it is pending (for example,
		1417	an expired non-repeating timer can be pending but no longer active). If it
		1418	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1419	but it is still property of the event loop at this time, so cannot be
		1420	moved, freed or reused. And if it is active the rules described in the
		1421	previous item still apply.
		1422
		1423	It is also possible to feed an event on a watcher that is not active (e.g.
		1424	via C<ev_feed_event>), in which case it becomes pending without being
		1425	active.
		1426
		1427	=item stopped
		1428
		1429	A watcher can be stopped implicitly by libev (in which case it might still
		1430	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1431	latter will clear any pending state the watcher might be in, regardless
		1432	of whether it was active or not, so stopping a watcher explicitly before
		1433	freeing it is often a good idea.
		1434
		1435	While stopped (and not pending) the watcher is essentially in the
		1436	initialised state, that is, it can be reused, moved, modified in any way
		1437	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1438	it again).
		1439
		1440	=back
		1441
		1442	=head2 WATCHER PRIORITY MODELS
		1443
		1444	Many event loops support I<watcher priorities>, which are usually small
		1445	integers that influence the ordering of event callback invocation
		1446	between watchers in some way, all else being equal.
		1447
		1448	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1449	description for the more technical details such as the actual priority
		1450	range.
		1451
		1452	There are two common ways how these these priorities are being interpreted
		1453	by event loops:
		1454
		1455	In the more common lock-out model, higher priorities "lock out" invocation
		1456	of lower priority watchers, which means as long as higher priority
		1457	watchers receive events, lower priority watchers are not being invoked.
		1458
		1459	The less common only-for-ordering model uses priorities solely to order
		1460	callback invocation within a single event loop iteration: Higher priority
		1461	watchers are invoked before lower priority ones, but they all get invoked
		1462	before polling for new events.
		1463
		1464	Libev uses the second (only-for-ordering) model for all its watchers
		1465	except for idle watchers (which use the lock-out model).
		1466
		1467	The rationale behind this is that implementing the lock-out model for
		1468	watchers is not well supported by most kernel interfaces, and most event
		1469	libraries will just poll for the same events again and again as long as
		1470	their callbacks have not been executed, which is very inefficient in the
		1471	common case of one high-priority watcher locking out a mass of lower
		1472	priority ones.
		1473
		1474	Static (ordering) priorities are most useful when you have two or more
		1475	watchers handling the same resource: a typical usage example is having an
		1476	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1477	timeouts. Under load, data might be received while the program handles
		1478	other jobs, but since timers normally get invoked first, the timeout
		1479	handler will be executed before checking for data. In that case, giving
		1480	the timer a lower priority than the I/O watcher ensures that I/O will be
		1481	handled first even under adverse conditions (which is usually, but not
		1482	always, what you want).
		1483
		1484	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1485	will only be executed when no same or higher priority watchers have
		1486	received events, they can be used to implement the "lock-out" model when
		1487	required.
		1488
		1489	For example, to emulate how many other event libraries handle priorities,
		1490	you can associate an C<ev_idle> watcher to each such watcher, and in
		1491	the normal watcher callback, you just start the idle watcher. The real
		1492	processing is done in the idle watcher callback. This causes libev to
		1493	continuously poll and process kernel event data for the watcher, but when
		1494	the lock-out case is known to be rare (which in turn is rare :), this is
		1495	workable.
		1496
		1497	Usually, however, the lock-out model implemented that way will perform
		1498	miserably under the type of load it was designed to handle. In that case,
		1499	it might be preferable to stop the real watcher before starting the
		1500	idle watcher, so the kernel will not have to process the event in case
		1501	the actual processing will be delayed for considerable time.
		1502
		1503	Here is an example of an I/O watcher that should run at a strictly lower
		1504	priority than the default, and which should only process data when no
		1505	other events are pending:
		1506
		1507	ev_idle idle; // actual processing watcher
		1508	ev_io io; // actual event watcher
		1509
		1510	static void
		1511	io_cb (EV_P_ ev_io *w, int revents)
384	{	1512	{
385	struct ev_io io;	1513	// stop the I/O watcher, we received the event, but
386	int otherfd;	1514	// are not yet ready to handle it.
387	void *somedata;	1515	ev_io_stop (EV_A_ w);
388	struct whatever *mostinteresting;	1516
		1517	// start the idle watcher to handle the actual event.
		1518	// it will not be executed as long as other watchers
		1519	// with the default priority are receiving events.
		1520	ev_idle_start (EV_A_ &idle);
389	}	1521	}
390		1522
391	And since your callback will be called with a pointer to the watcher, you	1523	static void
392	can cast it back to your own type:	1524	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	{	1525	{
396	struct my_io *w = (struct my_io *)w_;	1526	// actual processing
397	...	1527	read (STDIN_FILENO, ...);
		1528
		1529	// have to start the I/O watcher again, as
		1530	// we have handled the event
		1531	ev_io_start (EV_P_ &io);
398	}	1532	}
399		1533
400	More interesting and less C-conformant ways of catsing your callback type	1534	// initialisation
401	have been omitted....	1535	ev_idle_init (&idle, idle_cb);
		1536	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1537	ev_io_start (EV_DEFAULT_ &io);
		1538
		1539	In the "real" world, it might also be beneficial to start a timer, so that
		1540	low-priority connections can not be locked out forever under load. This
		1541	enables your program to keep a lower latency for important connections
		1542	during short periods of high load, while not completely locking out less
		1543	important ones.
402		1544
403		1545
404	=head1 WATCHER TYPES	1546	=head1 WATCHER TYPES
405		1547
406	This section describes each watcher in detail, but will not repeat	1548	This section describes each watcher in detail, but will not repeat
407	information given in the last section.	1549	information given in the last section. Any initialisation/set macros,
		1550	functions and members specific to the watcher type are explained.
408		1551
		1552	Members are additionally marked with either I<[read-only]>, meaning that,
		1553	while the watcher is active, you can look at the member and expect some
		1554	sensible content, but you must not modify it (you can modify it while the
		1555	watcher is stopped to your hearts content), or I<[read-write]>, which
		1556	means you can expect it to have some sensible content while the watcher
		1557	is active, but you can also modify it. Modifying it may not do something
		1558	sensible or take immediate effect (or do anything at all), but libev will
		1559	not crash or malfunction in any way.
		1560
		1561
409	=head2 struct ev_io - is my file descriptor readable or writable	1562	=head2 C<ev_io> - is this file descriptor readable or writable?
410		1563
411	I/O watchers check whether a file descriptor is readable or writable	1564	I/O watchers check whether a file descriptor is readable or writable
412	in each iteration of the event loop (This behaviour is called	1565	in each iteration of the event loop, or, more precisely, when reading
413	level-triggering because you keep receiving events as long as the	1566	would not block the process and writing would at least be able to write
414	condition persists. Remember you cna stop the watcher if you don't want to	1567	some data. This behaviour is called level-triggering because you keep
415	act on the event and neither want to receive future events).	1568	receiving events as long as the condition persists. Remember you can stop
		1569	the watcher if you don't want to act on the event and neither want to
		1570	receive future events.
416		1571
417	In general you can register as many read and/or write event watchers oer	1572	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	1573	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	1574	descriptors to non-blocking mode is also usually a good idea (but not
420	required if you know what you are doing).	1575	required if you know what you are doing).
421		1576
422	You have to be careful with dup'ed file descriptors, though. Some backends	1577	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	1578	receive "spurious" readiness notifications, that is, your callback might
424	descriptors correctly if you register interest in two or more fds pointing	1579	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
425	to the same file/socket etc. description.	1580	because there is no data. It is very easy to get into this situation even
		1581	with a relatively standard program structure. Thus it is best to always
		1582	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
		1583	preferable to a program hanging until some data arrives.
426		1584
427	If you must do this, then force the use of a known-to-be-good backend	1585	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	1586	not play around with an Xlib connection), then you have to separately
429	EVMETHOD_POLL).	1587	re-test whether a file descriptor is really ready with a known-to-be good
		1588	interface such as poll (fortunately in the case of Xlib, it already does
		1589	this on its own, so its quite safe to use). Some people additionally
		1590	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1591	indefinitely.
		1592
		1593	But really, best use non-blocking mode.
		1594
		1595	=head3 The special problem of disappearing file descriptors
		1596
		1597	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1598	descriptor (either due to calling C<close> explicitly or any other means,
		1599	such as C<dup2>). The reason is that you register interest in some file
		1600	descriptor, but when it goes away, the operating system will silently drop
		1601	this interest. If another file descriptor with the same number then is
		1602	registered with libev, there is no efficient way to see that this is, in
		1603	fact, a different file descriptor.
		1604
		1605	To avoid having to explicitly tell libev about such cases, libev follows
		1606	the following policy: Each time C<ev_io_set> is being called, libev
		1607	will assume that this is potentially a new file descriptor, otherwise
		1608	it is assumed that the file descriptor stays the same. That means that
		1609	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1610	descriptor even if the file descriptor number itself did not change.
		1611
		1612	This is how one would do it normally anyway, the important point is that
		1613	the libev application should not optimise around libev but should leave
		1614	optimisations to libev.
		1615
		1616	=head3 The special problem of dup'ed file descriptors
		1617
		1618	Some backends (e.g. epoll), cannot register events for file descriptors,
		1619	but only events for the underlying file descriptions. That means when you
		1620	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1621	events for them, only one file descriptor might actually receive events.
		1622
		1623	There is no workaround possible except not registering events
		1624	for potentially C<dup ()>'ed file descriptors, or to resort to
		1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1626
		1627	=head3 The special problem of files
		1628
		1629	Many people try to use C<select> (or libev) on file descriptors
		1630	representing files, and expect it to become ready when their program
		1631	doesn't block on disk accesses (which can take a long time on their own).
		1632
		1633	However, this cannot ever work in the "expected" way - you get a readiness
		1634	notification as soon as the kernel knows whether and how much data is
		1635	there, and in the case of open files, that's always the case, so you
		1636	always get a readiness notification instantly, and your read (or possibly
		1637	write) will still block on the disk I/O.
		1638
		1639	Another way to view it is that in the case of sockets, pipes, character
		1640	devices and so on, there is another party (the sender) that delivers data
		1641	on its own, but in the case of files, there is no such thing: the disk
		1642	will not send data on its own, simply because it doesn't know what you
		1643	wish to read - you would first have to request some data.
		1644
		1645	Since files are typically not-so-well supported by advanced notification
		1646	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1647	to files, even though you should not use it. The reason for this is
		1648	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1649	usually a tty, often a pipe, but also sometimes files or special devices
		1650	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1651	F</dev/urandom>), and even though the file might better be served with
		1652	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1653	it "just works" instead of freezing.
		1654
		1655	So avoid file descriptors pointing to files when you know it (e.g. use
		1656	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1657	when you rarely read from a file instead of from a socket, and want to
		1658	reuse the same code path.
		1659
		1660	=head3 The special problem of fork
		1661
		1662	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1663	useless behaviour. Libev fully supports fork, but needs to be told about
		1664	it in the child if you want to continue to use it in the child.
		1665
		1666	To support fork in your child processes, you have to call C<ev_loop_fork
		1667	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
		1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1669
		1670	=head3 The special problem of SIGPIPE
		1671
		1672	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1673	when writing to a pipe whose other end has been closed, your program gets
		1674	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1675	this is sensible behaviour, for daemons, this is usually undesirable.
		1676
		1677	So when you encounter spurious, unexplained daemon exits, make sure you
		1678	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1679	somewhere, as that would have given you a big clue).
		1680
		1681	=head3 The special problem of accept()ing when you can't
		1682
		1683	Many implementations of the POSIX C<accept> function (for example,
		1684	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1685	connection from the pending queue in all error cases.
		1686
		1687	For example, larger servers often run out of file descriptors (because
		1688	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1689	rejecting the connection, leading to libev signalling readiness on
		1690	the next iteration again (the connection still exists after all), and
		1691	typically causing the program to loop at 100% CPU usage.
		1692
		1693	Unfortunately, the set of errors that cause this issue differs between
		1694	operating systems, there is usually little the app can do to remedy the
		1695	situation, and no known thread-safe method of removing the connection to
		1696	cope with overload is known (to me).
		1697
		1698	One of the easiest ways to handle this situation is to just ignore it
		1699	- when the program encounters an overload, it will just loop until the
		1700	situation is over. While this is a form of busy waiting, no OS offers an
		1701	event-based way to handle this situation, so it's the best one can do.
		1702
		1703	A better way to handle the situation is to log any errors other than
		1704	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1705	messages, and continue as usual, which at least gives the user an idea of
		1706	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1707	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1708	usage.
		1709
		1710	If your program is single-threaded, then you could also keep a dummy file
		1711	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1712	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1713	close that fd, and create a new dummy fd. This will gracefully refuse
		1714	clients under typical overload conditions.
		1715
		1716	The last way to handle it is to simply log the error and C<exit>, as
		1717	is often done with C<malloc> failures, but this results in an easy
		1718	opportunity for a DoS attack.
		1719
		1720	=head3 Watcher-Specific Functions
430		1721
431	=over 4	1722	=over 4
432		1723
433	=item ev_io_init (ev_io *, callback, int fd, int events)	1724	=item ev_io_init (ev_io *, callback, int fd, int events)
434		1725
435	=item ev_io_set (ev_io *, int fd, int events)	1726	=item ev_io_set (ev_io *, int fd, int events)
436		1727
437	Configures an ev_io watcher. The fd is the file descriptor to rceeive	1728	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 |	1729	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
439	EV_WRITE> to receive the given events.	1730	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1731
		1732	=item int fd [read-only]
		1733
		1734	The file descriptor being watched.
		1735
		1736	=item int events [read-only]
		1737
		1738	The events being watched.
440		1739
441	=back	1740	=back
442		1741
		1742	=head3 Examples
		1743
		1744	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1745	readable, but only once. Since it is likely line-buffered, you could
		1746	attempt to read a whole line in the callback.
		1747
		1748	static void
		1749	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1750	{
		1751	ev_io_stop (loop, w);
		1752	.. read from stdin here (or from w->fd) and handle any I/O errors
		1753	}
		1754
		1755	...
		1756	struct ev_loop *loop = ev_default_init (0);
		1757	ev_io stdin_readable;
		1758	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1759	ev_io_start (loop, &stdin_readable);
		1760	ev_run (loop, 0);
		1761
		1762
443	=head2 struct ev_timer - relative and optionally recurring timeouts	1763	=head2 C<ev_timer> - relative and optionally repeating timeouts
444		1764
445	Timer watchers are simple relative timers that generate an event after a	1765	Timer watchers are simple relative timers that generate an event after a
446	given time, and optionally repeating in regular intervals after that.	1766	given time, and optionally repeating in regular intervals after that.
447		1767
448	The timers are based on real time, that is, if you register an event that	1768	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	1769	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	1770	year, it will still time out after (roughly) one hour. "Roughly" because
451	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1771	detecting time jumps is hard, and some inaccuracies are unavoidable (the
452	monotonic clock option helps a lot here).	1772	monotonic clock option helps a lot here).
		1773
		1774	The callback is guaranteed to be invoked only I<after> its timeout has
		1775	passed (not I<at>, so on systems with very low-resolution clocks this
		1776	might introduce a small delay, see "the special problem of being too
		1777	early", below). If multiple timers become ready during the same loop
		1778	iteration then the ones with earlier time-out values are invoked before
		1779	ones of the same priority with later time-out values (but this is no
		1780	longer true when a callback calls C<ev_run> recursively).
		1781
		1782	=head3 Be smart about timeouts
		1783
		1784	Many real-world problems involve some kind of timeout, usually for error
		1785	recovery. A typical example is an HTTP request - if the other side hangs,
		1786	you want to raise some error after a while.
		1787
		1788	What follows are some ways to handle this problem, from obvious and
		1789	inefficient to smart and efficient.
		1790
		1791	In the following, a 60 second activity timeout is assumed - a timeout that
		1792	gets reset to 60 seconds each time there is activity (e.g. each time some
		1793	data or other life sign was received).
		1794
		1795	=over 4
		1796
		1797	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1798
		1799	This is the most obvious, but not the most simple way: In the beginning,
		1800	start the watcher:
		1801
		1802	ev_timer_init (timer, callback, 60., 0.);
		1803	ev_timer_start (loop, timer);
		1804
		1805	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1806	and start it again:
		1807
		1808	ev_timer_stop (loop, timer);
		1809	ev_timer_set (timer, 60., 0.);
		1810	ev_timer_start (loop, timer);
		1811
		1812	This is relatively simple to implement, but means that each time there is
		1813	some activity, libev will first have to remove the timer from its internal
		1814	data structure and then add it again. Libev tries to be fast, but it's
		1815	still not a constant-time operation.
		1816
		1817	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1818
		1819	This is the easiest way, and involves using C<ev_timer_again> instead of
		1820	C<ev_timer_start>.
		1821
		1822	To implement this, configure an C<ev_timer> with a C<repeat> value
		1823	of C<60> and then call C<ev_timer_again> at start and each time you
		1824	successfully read or write some data. If you go into an idle state where
		1825	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1826	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1827
		1828	That means you can ignore both the C<ev_timer_start> function and the
		1829	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1830	member and C<ev_timer_again>.
		1831
		1832	At start:
		1833
		1834	ev_init (timer, callback);
		1835	timer->repeat = 60.;
		1836	ev_timer_again (loop, timer);
		1837
		1838	Each time there is some activity:
		1839
		1840	ev_timer_again (loop, timer);
		1841
		1842	It is even possible to change the time-out on the fly, regardless of
		1843	whether the watcher is active or not:
		1844
		1845	timer->repeat = 30.;
		1846	ev_timer_again (loop, timer);
		1847
		1848	This is slightly more efficient then stopping/starting the timer each time
		1849	you want to modify its timeout value, as libev does not have to completely
		1850	remove and re-insert the timer from/into its internal data structure.
		1851
		1852	It is, however, even simpler than the "obvious" way to do it.
		1853
		1854	=item 3. Let the timer time out, but then re-arm it as required.
		1855
		1856	This method is more tricky, but usually most efficient: Most timeouts are
		1857	relatively long compared to the intervals between other activity - in
		1858	our example, within 60 seconds, there are usually many I/O events with
		1859	associated activity resets.
		1860
		1861	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1862	but remember the time of last activity, and check for a real timeout only
		1863	within the callback:
		1864
		1865	ev_tstamp timeout = 60.;
		1866	ev_tstamp last_activity; // time of last activity
		1867	ev_timer timer;
		1868
		1869	static void
		1870	callback (EV_P_ ev_timer *w, int revents)
		1871	{
		1872	// calculate when the timeout would happen
		1873	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
		1874
		1875	// if negative, it means we the timeout already occured
		1876	if (after < 0.)
		1877	{
		1878	// timeout occurred, take action
		1879	}
		1880	else
		1881	{
		1882	// callback was invoked, but there was some recent
		1883	// activity. simply restart the timer to time out
		1884	// after "after" seconds, which is the earliest time
		1885	// the timeout can occur.
		1886	ev_timer_set (w, after, 0.);
		1887	ev_timer_start (EV_A_ w);
		1888	}
		1889	}
		1890
		1891	To summarise the callback: first calculate in how many seconds the
		1892	timeout will occur (by calculating the absolute time when it would occur,
		1893	C<last_activity + timeout>, and subtracting the current time, C<ev_now
		1894	(EV_A)> from that).
		1895
		1896	If this value is negative, then we are already past the timeout, i.e. we
		1897	timed out, and need to do whatever is needed in this case.
		1898
		1899	Otherwise, we now the earliest time at which the timeout would trigger,
		1900	and simply start the timer with this timeout value.
		1901
		1902	In other words, each time the callback is invoked it will check whether
		1903	the timeout cocured. If not, it will simply reschedule itself to check
		1904	again at the earliest time it could time out. Rinse. Repeat.
		1905
		1906	This scheme causes more callback invocations (about one every 60 seconds
		1907	minus half the average time between activity), but virtually no calls to
		1908	libev to change the timeout.
		1909
		1910	To start the machinery, simply initialise the watcher and set
		1911	C<last_activity> to the current time (meaning there was some activity just
		1912	now), then call the callback, which will "do the right thing" and start
		1913	the timer:
		1914
		1915	last_activity = ev_now (EV_A);
		1916	ev_init (&timer, callback);
		1917	callback (EV_A_ &timer, 0);
		1918
		1919	When there is some activity, simply store the current time in
		1920	C<last_activity>, no libev calls at all:
		1921
		1922	if (activity detected)
		1923	last_activity = ev_now (EV_A);
		1924
		1925	When your timeout value changes, then the timeout can be changed by simply
		1926	providing a new value, stopping the timer and calling the callback, which
		1927	will agaion do the right thing (for example, time out immediately :).
		1928
		1929	timeout = new_value;
		1930	ev_timer_stop (EV_A_ &timer);
		1931	callback (EV_A_ &timer, 0);
		1932
		1933	This technique is slightly more complex, but in most cases where the
		1934	time-out is unlikely to be triggered, much more efficient.
		1935
		1936	=item 4. Wee, just use a double-linked list for your timeouts.
		1937
		1938	If there is not one request, but many thousands (millions...), all
		1939	employing some kind of timeout with the same timeout value, then one can
		1940	do even better:
		1941
		1942	When starting the timeout, calculate the timeout value and put the timeout
		1943	at the I<end> of the list.
		1944
		1945	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1946	the list is expected to fire (for example, using the technique #3).
		1947
		1948	When there is some activity, remove the timer from the list, recalculate
		1949	the timeout, append it to the end of the list again, and make sure to
		1950	update the C<ev_timer> if it was taken from the beginning of the list.
		1951
		1952	This way, one can manage an unlimited number of timeouts in O(1) time for
		1953	starting, stopping and updating the timers, at the expense of a major
		1954	complication, and having to use a constant timeout. The constant timeout
		1955	ensures that the list stays sorted.
		1956
		1957	=back
		1958
		1959	So which method the best?
		1960
		1961	Method #2 is a simple no-brain-required solution that is adequate in most
		1962	situations. Method #3 requires a bit more thinking, but handles many cases
		1963	better, and isn't very complicated either. In most case, choosing either
		1964	one is fine, with #3 being better in typical situations.
		1965
		1966	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1967	rather complicated, but extremely efficient, something that really pays
		1968	off after the first million or so of active timers, i.e. it's usually
		1969	overkill :)
		1970
		1971	=head3 The special problem of being too early
		1972
		1973	If you ask a timer to call your callback after three seconds, then
		1974	you expect it to be invoked after three seconds - but of course, this
		1975	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1976	guaranteed to any precision by libev - imagine somebody suspending the
		1977	process with a STOP signal for a few hours for example.
		1978
		1979	So, libev tries to invoke your callback as soon as possible I<after> the
		1980	delay has occurred, but cannot guarantee this.
		1981
		1982	A less obvious failure mode is calling your callback too early: many event
		1983	loops compare timestamps with a "elapsed delay >= requested delay", but
		1984	this can cause your callback to be invoked much earlier than you would
		1985	expect.
		1986
		1987	To see why, imagine a system with a clock that only offers full second
		1988	resolution (think windows if you can't come up with a broken enough OS
		1989	yourself). If you schedule a one-second timer at the time 500.9, then the
		1990	event loop will schedule your timeout to elapse at a system time of 500
		1991	(500.9 truncated to the resolution) + 1, or 501.
		1992
		1993	If an event library looks at the timeout 0.1s later, it will see "501 >=
		1994	501" and invoke the callback 0.1s after it was started, even though a
		1995	one-second delay was requested - this is being "too early", despite best
		1996	intentions.
		1997
		1998	This is the reason why libev will never invoke the callback if the elapsed
		1999	delay equals the requested delay, but only when the elapsed delay is
		2000	larger than the requested delay. In the example above, libev would only invoke
		2001	the callback at system time 502, or 1.1s after the timer was started.
		2002
		2003	So, while libev cannot guarantee that your callback will be invoked
		2004	exactly when requested, it I<can> and I<does> guarantee that the requested
		2005	delay has actually elapsed, or in other words, it always errs on the "too
		2006	late" side of things.
		2007
		2008	=head3 The special problem of time updates
		2009
		2010	Establishing the current time is a costly operation (it usually takes
		2011	at least one system call): EV therefore updates its idea of the current
		2012	time only before and after C<ev_run> collects new events, which causes a
		2013	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2014	lots of events in one iteration.
453		2015
454	The relative timeouts are calculated relative to the C<ev_now ()>	2016	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	2017	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	2018	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	2019	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:	2020	timeout on the current time, use something like this to adjust for this:
459		2021
460	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2022	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
461		2023
		2024	If the event loop is suspended for a long time, you can also force an
		2025	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		2026	()>.
		2027
		2028	=head3 The special problem of unsynchronised clocks
		2029
		2030	Modern systems have a variety of clocks - libev itself uses the normal
		2031	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2032	jumps).
		2033
		2034	Neither of these clocks is synchronised with each other or any other clock
		2035	on the system, so C<ev_time ()> might return a considerably different time
		2036	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2037	a call to C<gettimeofday> might return a second count that is one higher
		2038	than a directly following call to C<time>.
		2039
		2040	The moral of this is to only compare libev-related timestamps with
		2041	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2042	a second or so.
		2043
		2044	One more problem arises due to this lack of synchronisation: if libev uses
		2045	the system monotonic clock and you compare timestamps from C<ev_time>
		2046	or C<ev_now> from when you started your timer and when your callback is
		2047	invoked, you will find that sometimes the callback is a bit "early".
		2048
		2049	This is because C<ev_timer>s work in real time, not wall clock time, so
		2050	libev makes sure your callback is not invoked before the delay happened,
		2051	I<measured according to the real time>, not the system clock.
		2052
		2053	If your timeouts are based on a physical timescale (e.g. "time out this
		2054	connection after 100 seconds") then this shouldn't bother you as it is
		2055	exactly the right behaviour.
		2056
		2057	If you want to compare wall clock/system timestamps to your timers, then
		2058	you need to use C<ev_periodic>s, as these are based on the wall clock
		2059	time, where your comparisons will always generate correct results.
		2060
		2061	=head3 The special problems of suspended animation
		2062
		2063	When you leave the server world it is quite customary to hit machines that
		2064	can suspend/hibernate - what happens to the clocks during such a suspend?
		2065
		2066	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2067	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2068	to run until the system is suspended, but they will not advance while the
		2069	system is suspended. That means, on resume, it will be as if the program
		2070	was frozen for a few seconds, but the suspend time will not be counted
		2071	towards C<ev_timer> when a monotonic clock source is used. The real time
		2072	clock advanced as expected, but if it is used as sole clocksource, then a
		2073	long suspend would be detected as a time jump by libev, and timers would
		2074	be adjusted accordingly.
		2075
		2076	I would not be surprised to see different behaviour in different between
		2077	operating systems, OS versions or even different hardware.
		2078
		2079	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2080	time jump in the monotonic clocks and the realtime clock. If the program
		2081	is suspended for a very long time, and monotonic clock sources are in use,
		2082	then you can expect C<ev_timer>s to expire as the full suspension time
		2083	will be counted towards the timers. When no monotonic clock source is in
		2084	use, then libev will again assume a timejump and adjust accordingly.
		2085
		2086	It might be beneficial for this latter case to call C<ev_suspend>
		2087	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2088	deterministic behaviour in this case (you can do nothing against
		2089	C<SIGSTOP>).
		2090
		2091	=head3 Watcher-Specific Functions and Data Members
		2092
462	=over 4	2093	=over 4
463		2094
464	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2095	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465		2096
466	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2097	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
467		2098
468	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2099	Configure the timer to trigger after C<after> seconds. If C<repeat>
469	C<0.>, then it will automatically be stopped. If it is positive, then the	2100	is C<0.>, then it will automatically be stopped once the timeout is
470	timer will automatically be configured to trigger again C<repeat> seconds	2101	reached. If it is positive, then the timer will automatically be
471	later, again, and again, until stopped manually.	2102	configured to trigger again C<repeat> seconds later, again, and again,
		2103	until stopped manually.
472		2104
473	The timer itself will do a best-effort at avoiding drift, that is, if you	2105	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	2106	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	2107	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	2108	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.	2109	do stuff) the timer will not fire more than once per event loop iteration.
478		2110
479	=item ev_timer_again (loop)	2111	=item ev_timer_again (loop, ev_timer *)
480		2112
481	This will act as if the timer timed out and restart it again if it is	2113	This will act as if the timer timed out and restarts it again if it is
482	repeating. The exact semantics are:	2114	repeating. The exact semantics are:
483		2115
		2116	If the timer is pending, its pending status is cleared.
		2117
484	If the timer is started but nonrepeating, stop it.	2118	If the timer is started but non-repeating, stop it (as if it timed out).
485		2119
486	If the timer is repeating, either start it if necessary (with the repeat	2120	If the timer is repeating, either start it if necessary (with the
487	value), or reset the running timer to the repeat value.	2121	C<repeat> value), or reset the running timer to the C<repeat> value.
488		2122
489	This sounds a bit complicated, but here is a useful and typical	2123	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
490	example: Imagine you have a tcp connection and you want a so-called idle	2124	usage example.
491	timeout, that is, you want to be called when there have been, say, 60	2125
492	seconds of inactivity on the socket. The easiest way to do this is to	2126	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
493	configure an ev_timer with after=repeat=60 and calling ev_timer_again each	2127
494	time you successfully read or write some data. If you go into an idle	2128	Returns the remaining time until a timer fires. If the timer is active,
495	state where you do not expect data to travel on the socket, you can stop	2129	then this time is relative to the current event loop time, otherwise it's
496	the timer, and again will automatically restart it if need be.	2130	the timeout value currently configured.
		2131
		2132	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2133	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2134	will return C<4>. When the timer expires and is restarted, it will return
		2135	roughly C<7> (likely slightly less as callback invocation takes some time,
		2136	too), and so on.
		2137
		2138	=item ev_tstamp repeat [read-write]
		2139
		2140	The current C<repeat> value. Will be used each time the watcher times out
		2141	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2142	which is also when any modifications are taken into account.
497		2143
498	=back	2144	=back
499		2145
		2146	=head3 Examples
		2147
		2148	Example: Create a timer that fires after 60 seconds.
		2149
		2150	static void
		2151	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2152	{
		2153	.. one minute over, w is actually stopped right here
		2154	}
		2155
		2156	ev_timer mytimer;
		2157	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		2158	ev_timer_start (loop, &mytimer);
		2159
		2160	Example: Create a timeout timer that times out after 10 seconds of
		2161	inactivity.
		2162
		2163	static void
		2164	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2165	{
		2166	.. ten seconds without any activity
		2167	}
		2168
		2169	ev_timer mytimer;
		2170	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		2171	ev_timer_again (&mytimer); /* start timer */
		2172	ev_run (loop, 0);
		2173
		2174	// and in some piece of code that gets executed on any "activity":
		2175	// reset the timeout to start ticking again at 10 seconds
		2176	ev_timer_again (&mytimer);
		2177
		2178
500	=head2 ev_periodic - to cron or not to cron it	2179	=head2 C<ev_periodic> - to cron or not to cron?
501		2180
502	Periodic watchers are also timers of a kind, but they are very versatile	2181	Periodic watchers are also timers of a kind, but they are very versatile
503	(and unfortunately a bit complex).	2182	(and unfortunately a bit complex).
504		2183
505	Unlike ev_timer's, they are not based on real time (or relative time)	2184	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	2185	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	2186	(absolute time, the thing you can read on your calender or clock). The
508	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	2187	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	2188	time, and time jumps are not uncommon (e.g. when you adjust your
510	take a year to trigger the event (unlike an ev_timer, which would trigger	2189	wrist-watch).
511	roughly 10 seconds later and of course not if you reset your system time
512	again).
513		2190
514	They can also be used to implement vastly more complex timers, such as	2191	You can tell a periodic watcher to trigger after some specific point
		2192	in time: for example, if you tell a periodic watcher to trigger "in 10
		2193	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2194	not a delay) and then reset your system clock to January of the previous
		2195	year, then it will take a year or more to trigger the event (unlike an
		2196	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2197	it, as it uses a relative timeout).
		2198
		2199	C<ev_periodic> watchers can also be used to implement vastly more complex
515	triggering an event on eahc midnight, local time.	2200	timers, such as triggering an event on each "midnight, local time", or
		2201	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2202	those cannot react to time jumps.
		2203
		2204	As with timers, the callback is guaranteed to be invoked only when the
		2205	point in time where it is supposed to trigger has passed. If multiple
		2206	timers become ready during the same loop iteration then the ones with
		2207	earlier time-out values are invoked before ones with later time-out values
		2208	(but this is no longer true when a callback calls C<ev_run> recursively).
		2209
		2210	=head3 Watcher-Specific Functions and Data Members
516		2211
517	=over 4	2212	=over 4
518		2213
519	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2214	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
520		2215
521	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2216	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
522		2217
523	Lots of arguments, lets sort it out... There are basically three modes of	2218	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:	2219	operation, and we will explain them from simplest to most complex:
525
526		2220
527	=over 4	2221	=over 4
528		2222
529	=item * absolute timer (interval = reschedule_cb = 0)	2223	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
530		2224
531	In this configuration the watcher triggers an event at the wallclock time	2225	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,	2226	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	2227	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.	2228	will be stopped and invoked when the system clock reaches or surpasses
		2229	this point in time.
535		2230
536	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2231	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
537		2232
538	In this mode the watcher will always be scheduled to time out at the next	2233	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	2234	C<offset + N * interval> time (for some integer N, which can also be
540	of any time jumps.	2235	negative) and then repeat, regardless of any time jumps. The C<offset>
		2236	argument is merely an offset into the C<interval> periods.
541		2237
542	This can be used to create timers that do not drift with respect to system	2238	This can be used to create timers that do not drift with respect to the
543	time:	2239	system clock, for example, here is an C<ev_periodic> that triggers each
		2240	hour, on the hour (with respect to UTC):
544		2241
545	ev_periodic_set (&periodic, 0., 3600., 0);	2242	ev_periodic_set (&periodic, 0., 3600., 0);
546		2243
547	This doesn't mean there will always be 3600 seconds in between triggers,	2244	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	2245	but only that the callback will be called when the system time shows a
549	full hour (UTC), or more correct, when the system time is evenly divisible	2246	full hour (UTC), or more correctly, when the system time is evenly divisible
550	by 3600.	2247	by 3600.
551		2248
552	Another way to think about it (for the mathematically inclined) is that	2249	Another way to think about it (for the mathematically inclined) is that
553	ev_periodic will try to run the callback in this mode at the next possible	2250	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.	2251	time where C<time = offset (mod interval)>, regardless of any time jumps.
555		2252
		2253	The C<interval> I<MUST> be positive, and for numerical stability, the
		2254	interval value should be higher than C<1/8192> (which is around 100
		2255	microseconds) and C<offset> should be higher than C<0> and should have
		2256	at most a similar magnitude as the current time (say, within a factor of
		2257	ten). Typical values for offset are, in fact, C<0> or something between
		2258	C<0> and C<interval>, which is also the recommended range.
		2259
		2260	Note also that there is an upper limit to how often a timer can fire (CPU
		2261	speed for example), so if C<interval> is very small then timing stability
		2262	will of course deteriorate. Libev itself tries to be exact to be about one
		2263	millisecond (if the OS supports it and the machine is fast enough).
		2264
556	=item * manual reschedule mode (reschedule_cb = callback)	2265	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
557		2266
558	In this mode the values for C<interval> and C<at> are both being	2267	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	2268	ignored. Instead, each time the periodic watcher gets scheduled, the
560	reschedule callback will be called with the watcher as first, and the	2269	reschedule callback will be called with the watcher as first, and the
561	current time as second argument.	2270	current time as second argument.
562		2271
563	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	2272	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
564	periodic watcher, ever, or make any event loop modificstions>. If you need	2273	or make ANY other event loop modifications whatsoever, unless explicitly
565	to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.	2274	allowed by documentation here>.
566		2275
		2276	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2277	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2278	only event loop modification you are allowed to do).
		2279
567	Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2280	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
568	ev_tstamp now)>, e.g.:	2281	*w, ev_tstamp now)>, e.g.:
569		2282
		2283	static ev_tstamp
570	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2284	my_rescheduler (ev_periodic *w, ev_tstamp now)
571	{	2285	{
572	return now + 60.;	2286	return now + 60.;
573	}	2287	}
574		2288
575	It must return the next time to trigger, based on the passed time value	2289	It must return the next time to trigger, based on the passed time value
576	(that is, the lowest time value larger than to the second argument). It	2290	(that is, the lowest time value larger than to the second argument). It
577	will usually be called just before the callback will be triggered, but	2291	will usually be called just before the callback will be triggered, but
578	might be called at other times, too.	2292	might be called at other times, too.
579		2293
		2294	NOTE: I<< This callback must always return a time that is higher than or
		2295	equal to the passed C<now> value >>.
		2296
580	This can be used to create very complex timers, such as a timer that	2297	This can be used to create very complex timers, such as a timer that
581	triggers on each midnight, local time. To do this, you would calculate the	2298	triggers on "next midnight, local time". To do this, you would calculate the
582	next midnight after C<now> and return the timestamp value for this. How you do this	2299	next midnight after C<now> and return the timestamp value for this. How
583	is, again, up to you (but it is not trivial).	2300	you do this is, again, up to you (but it is not trivial, which is the main
		2301	reason I omitted it as an example).
584		2302
585	=back	2303	=back
586		2304
587	=item ev_periodic_again (loop, ev_periodic *)	2305	=item ev_periodic_again (loop, ev_periodic *)
588		2306
589	Simply stops and restarts the periodic watcher again. This is only useful	2307	Simply stops and restarts the periodic watcher again. This is only useful
590	when you changed some parameters or the reschedule callback would return	2308	when you changed some parameters or the reschedule callback would return
591	a different time than the last time it was called (e.g. in a crond like	2309	a different time than the last time it was called (e.g. in a crond like
592	program when the crontabs have changed).	2310	program when the crontabs have changed).
593		2311
		2312	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2313
		2314	When active, returns the absolute time that the watcher is supposed
		2315	to trigger next. This is not the same as the C<offset> argument to
		2316	C<ev_periodic_set>, but indeed works even in interval and manual
		2317	rescheduling modes.
		2318
		2319	=item ev_tstamp offset [read-write]
		2320
		2321	When repeating, this contains the offset value, otherwise this is the
		2322	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2323	although libev might modify this value for better numerical stability).
		2324
		2325	Can be modified any time, but changes only take effect when the periodic
		2326	timer fires or C<ev_periodic_again> is being called.
		2327
		2328	=item ev_tstamp interval [read-write]
		2329
		2330	The current interval value. Can be modified any time, but changes only
		2331	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2332	called.
		2333
		2334	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2335
		2336	The current reschedule callback, or C<0>, if this functionality is
		2337	switched off. Can be changed any time, but changes only take effect when
		2338	the periodic timer fires or C<ev_periodic_again> is being called.
		2339
594	=back	2340	=back
595		2341
		2342	=head3 Examples
		2343
		2344	Example: Call a callback every hour, or, more precisely, whenever the
		2345	system time is divisible by 3600. The callback invocation times have
		2346	potentially a lot of jitter, but good long-term stability.
		2347
		2348	static void
		2349	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
		2350	{
		2351	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2352	}
		2353
		2354	ev_periodic hourly_tick;
		2355	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2356	ev_periodic_start (loop, &hourly_tick);
		2357
		2358	Example: The same as above, but use a reschedule callback to do it:
		2359
		2360	#include <math.h>
		2361
		2362	static ev_tstamp
		2363	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2364	{
		2365	return now + (3600. - fmod (now, 3600.));
		2366	}
		2367
		2368	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2369
		2370	Example: Call a callback every hour, starting now:
		2371
		2372	ev_periodic hourly_tick;
		2373	ev_periodic_init (&hourly_tick, clock_cb,
		2374	fmod (ev_now (loop), 3600.), 3600., 0);
		2375	ev_periodic_start (loop, &hourly_tick);
		2376
		2377
596	=head2 ev_signal - signal me when a signal gets signalled	2378	=head2 C<ev_signal> - signal me when a signal gets signalled!
597		2379
598	Signal watchers will trigger an event when the process receives a specific	2380	Signal watchers will trigger an event when the process receives a specific
599	signal one or more times. Even though signals are very asynchronous, libev	2381	signal one or more times. Even though signals are very asynchronous, libev
600	will try it's best to deliver signals synchronously, i.e. as part of the	2382	will try its best to deliver signals synchronously, i.e. as part of the
601	normal event processing, like any other event.	2383	normal event processing, like any other event.
602		2384
		2385	If you want signals to be delivered truly asynchronously, just use
		2386	C<sigaction> as you would do without libev and forget about sharing
		2387	the signal. You can even use C<ev_async> from a signal handler to
		2388	synchronously wake up an event loop.
		2389
603	You cna configure as many watchers as you like per signal. Only when the	2390	You can configure as many watchers as you like for the same signal, but
		2391	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2392	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2393	C<SIGINT> in both the default loop and another loop at the same time. At
		2394	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2395
604	first watcher gets started will libev actually register a signal watcher	2396	When the first watcher gets started will libev actually register something
605	with the kernel (thus it coexists with your own signal handlers as long	2397	with the kernel (thus it coexists with your own signal handlers as long as
606	as you don't register any with libev). Similarly, when the last signal	2398	you don't register any with libev for the same signal).
607	watcher for a signal is stopped libev will reset the signal handler to	2399
608	SIG_DFL (regardless of what it was set to before).	2400	If possible and supported, libev will install its handlers with
		2401	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2402	not be unduly interrupted. If you have a problem with system calls getting
		2403	interrupted by signals you can block all signals in an C<ev_check> watcher
		2404	and unblock them in an C<ev_prepare> watcher.
		2405
		2406	=head3 The special problem of inheritance over fork/execve/pthread_create
		2407
		2408	Both the signal mask (C<sigprocmask>) and the signal disposition
		2409	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2410	stopping it again), that is, libev might or might not block the signal,
		2411	and might or might not set or restore the installed signal handler (but
		2412	see C<EVFLAG_NOSIGMASK>).
		2413
		2414	While this does not matter for the signal disposition (libev never
		2415	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2416	C<execve>), this matters for the signal mask: many programs do not expect
		2417	certain signals to be blocked.
		2418
		2419	This means that before calling C<exec> (from the child) you should reset
		2420	the signal mask to whatever "default" you expect (all clear is a good
		2421	choice usually).
		2422
		2423	The simplest way to ensure that the signal mask is reset in the child is
		2424	to install a fork handler with C<pthread_atfork> that resets it. That will
		2425	catch fork calls done by libraries (such as the libc) as well.
		2426
		2427	In current versions of libev, the signal will not be blocked indefinitely
		2428	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2429	the window of opportunity for problems, it will not go away, as libev
		2430	I<has> to modify the signal mask, at least temporarily.
		2431
		2432	So I can't stress this enough: I<If you do not reset your signal mask when
		2433	you expect it to be empty, you have a race condition in your code>. This
		2434	is not a libev-specific thing, this is true for most event libraries.
		2435
		2436	=head3 The special problem of threads signal handling
		2437
		2438	POSIX threads has problematic signal handling semantics, specifically,
		2439	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2440	threads in a process block signals, which is hard to achieve.
		2441
		2442	When you want to use sigwait (or mix libev signal handling with your own
		2443	for the same signals), you can tackle this problem by globally blocking
		2444	all signals before creating any threads (or creating them with a fully set
		2445	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2446	loops. Then designate one thread as "signal receiver thread" which handles
		2447	these signals. You can pass on any signals that libev might be interested
		2448	in by calling C<ev_feed_signal>.
		2449
		2450	=head3 Watcher-Specific Functions and Data Members
609		2451
610	=over 4	2452	=over 4
611		2453
612	=item ev_signal_init (ev_signal *, callback, int signum)	2454	=item ev_signal_init (ev_signal *, callback, int signum)
613		2455
614	=item ev_signal_set (ev_signal *, int signum)	2456	=item ev_signal_set (ev_signal *, int signum)
615		2457
616	Configures the watcher to trigger on the given signal number (usually one	2458	Configures the watcher to trigger on the given signal number (usually one
617	of the C<SIGxxx> constants).	2459	of the C<SIGxxx> constants).
618		2460
		2461	=item int signum [read-only]
		2462
		2463	The signal the watcher watches out for.
		2464
619	=back	2465	=back
620		2466
		2467	=head3 Examples
		2468
		2469	Example: Try to exit cleanly on SIGINT.
		2470
		2471	static void
		2472	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2473	{
		2474	ev_break (loop, EVBREAK_ALL);
		2475	}
		2476
		2477	ev_signal signal_watcher;
		2478	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2479	ev_signal_start (loop, &signal_watcher);
		2480
		2481
621	=head2 ev_child - wait for pid status changes	2482	=head2 C<ev_child> - watch out for process status changes
622		2483
623	Child watchers trigger when your process receives a SIGCHLD in response to	2484	Child watchers trigger when your process receives a SIGCHLD in response to
624	some child status changes (most typically when a child of yours dies).	2485	some child status changes (most typically when a child of yours dies or
		2486	exits). It is permissible to install a child watcher I<after> the child
		2487	has been forked (which implies it might have already exited), as long
		2488	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2489	forking and then immediately registering a watcher for the child is fine,
		2490	but forking and registering a watcher a few event loop iterations later or
		2491	in the next callback invocation is not.
		2492
		2493	Only the default event loop is capable of handling signals, and therefore
		2494	you can only register child watchers in the default event loop.
		2495
		2496	Due to some design glitches inside libev, child watchers will always be
		2497	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2498	libev)
		2499
		2500	=head3 Process Interaction
		2501
		2502	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2503	initialised. This is necessary to guarantee proper behaviour even if the
		2504	first child watcher is started after the child exits. The occurrence
		2505	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2506	synchronously as part of the event loop processing. Libev always reaps all
		2507	children, even ones not watched.
		2508
		2509	=head3 Overriding the Built-In Processing
		2510
		2511	Libev offers no special support for overriding the built-in child
		2512	processing, but if your application collides with libev's default child
		2513	handler, you can override it easily by installing your own handler for
		2514	C<SIGCHLD> after initialising the default loop, and making sure the
		2515	default loop never gets destroyed. You are encouraged, however, to use an
		2516	event-based approach to child reaping and thus use libev's support for
		2517	that, so other libev users can use C<ev_child> watchers freely.
		2518
		2519	=head3 Stopping the Child Watcher
		2520
		2521	Currently, the child watcher never gets stopped, even when the
		2522	child terminates, so normally one needs to stop the watcher in the
		2523	callback. Future versions of libev might stop the watcher automatically
		2524	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2525	problem).
		2526
		2527	=head3 Watcher-Specific Functions and Data Members
625		2528
626	=over 4	2529	=over 4
627		2530
628	=item ev_child_init (ev_child *, callback, int pid)	2531	=item ev_child_init (ev_child *, callback, int pid, int trace)
629		2532
630	=item ev_child_set (ev_child *, int pid)	2533	=item ev_child_set (ev_child *, int pid, int trace)
631		2534
632	Configures the watcher to wait for status changes of process C<pid> (or	2535	Configures the watcher to wait for status changes of process C<pid> (or
633	I<any> process if C<pid> is specified as C<0>). The callback can look	2536	I<any> process if C<pid> is specified as C<0>). The callback can look
634	at the C<rstatus> member of the C<ev_child> watcher structure to see	2537	at the C<rstatus> member of the C<ev_child> watcher structure to see
635	the status word (use the macros from C<sys/wait.h>). The C<rpid> member	2538	the status word (use the macros from C<sys/wait.h> and see your systems
636	contains the pid of the process causing the status change.	2539	C<waitpid> documentation). The C<rpid> member contains the pid of the
		2540	process causing the status change. C<trace> must be either C<0> (only
		2541	activate the watcher when the process terminates) or C<1> (additionally
		2542	activate the watcher when the process is stopped or continued).
		2543
		2544	=item int pid [read-only]
		2545
		2546	The process id this watcher watches out for, or C<0>, meaning any process id.
		2547
		2548	=item int rpid [read-write]
		2549
		2550	The process id that detected a status change.
		2551
		2552	=item int rstatus [read-write]
		2553
		2554	The process exit/trace status caused by C<rpid> (see your systems
		2555	C<waitpid> and C<sys/wait.h> documentation for details).
637		2556
638	=back	2557	=back
639		2558
		2559	=head3 Examples
		2560
		2561	Example: C<fork()> a new process and install a child handler to wait for
		2562	its completion.
		2563
		2564	ev_child cw;
		2565
		2566	static void
		2567	child_cb (EV_P_ ev_child *w, int revents)
		2568	{
		2569	ev_child_stop (EV_A_ w);
		2570	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2571	}
		2572
		2573	pid_t pid = fork ();
		2574
		2575	if (pid < 0)
		2576	// error
		2577	else if (pid == 0)
		2578	{
		2579	// the forked child executes here
		2580	exit (1);
		2581	}
		2582	else
		2583	{
		2584	ev_child_init (&cw, child_cb, pid, 0);
		2585	ev_child_start (EV_DEFAULT_ &cw);
		2586	}
		2587
		2588
		2589	=head2 C<ev_stat> - did the file attributes just change?
		2590
		2591	This watches a file system path for attribute changes. That is, it calls
		2592	C<stat> on that path in regular intervals (or when the OS says it changed)
		2593	and sees if it changed compared to the last time, invoking the callback if
		2594	it did.
		2595
		2596	The path does not need to exist: changing from "path exists" to "path does
		2597	not exist" is a status change like any other. The condition "path does not
		2598	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2599	C<st_nlink> field being zero (which is otherwise always forced to be at
		2600	least one) and all the other fields of the stat buffer having unspecified
		2601	contents.
		2602
		2603	The path I<must not> end in a slash or contain special components such as
		2604	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2605	your working directory changes, then the behaviour is undefined.
		2606
		2607	Since there is no portable change notification interface available, the
		2608	portable implementation simply calls C<stat(2)> regularly on the path
		2609	to see if it changed somehow. You can specify a recommended polling
		2610	interval for this case. If you specify a polling interval of C<0> (highly
		2611	recommended!) then a I<suitable, unspecified default> value will be used
		2612	(which you can expect to be around five seconds, although this might
		2613	change dynamically). Libev will also impose a minimum interval which is
		2614	currently around C<0.1>, but that's usually overkill.
		2615
		2616	This watcher type is not meant for massive numbers of stat watchers,
		2617	as even with OS-supported change notifications, this can be
		2618	resource-intensive.
		2619
		2620	At the time of this writing, the only OS-specific interface implemented
		2621	is the Linux inotify interface (implementing kqueue support is left as an
		2622	exercise for the reader. Note, however, that the author sees no way of
		2623	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2624
		2625	=head3 ABI Issues (Largefile Support)
		2626
		2627	Libev by default (unless the user overrides this) uses the default
		2628	compilation environment, which means that on systems with large file
		2629	support disabled by default, you get the 32 bit version of the stat
		2630	structure. When using the library from programs that change the ABI to
		2631	use 64 bit file offsets the programs will fail. In that case you have to
		2632	compile libev with the same flags to get binary compatibility. This is
		2633	obviously the case with any flags that change the ABI, but the problem is
		2634	most noticeably displayed with ev_stat and large file support.
		2635
		2636	The solution for this is to lobby your distribution maker to make large
		2637	file interfaces available by default (as e.g. FreeBSD does) and not
		2638	optional. Libev cannot simply switch on large file support because it has
		2639	to exchange stat structures with application programs compiled using the
		2640	default compilation environment.
		2641
		2642	=head3 Inotify and Kqueue
		2643
		2644	When C<inotify (7)> support has been compiled into libev and present at
		2645	runtime, it will be used to speed up change detection where possible. The
		2646	inotify descriptor will be created lazily when the first C<ev_stat>
		2647	watcher is being started.
		2648
		2649	Inotify presence does not change the semantics of C<ev_stat> watchers
		2650	except that changes might be detected earlier, and in some cases, to avoid
		2651	making regular C<stat> calls. Even in the presence of inotify support
		2652	there are many cases where libev has to resort to regular C<stat> polling,
		2653	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2654	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2655	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2656	xfs are fully working) libev usually gets away without polling.
		2657
		2658	There is no support for kqueue, as apparently it cannot be used to
		2659	implement this functionality, due to the requirement of having a file
		2660	descriptor open on the object at all times, and detecting renames, unlinks
		2661	etc. is difficult.
		2662
		2663	=head3 C<stat ()> is a synchronous operation
		2664
		2665	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2666	the process. The exception are C<ev_stat> watchers - those call C<stat
		2667	()>, which is a synchronous operation.
		2668
		2669	For local paths, this usually doesn't matter: unless the system is very
		2670	busy or the intervals between stat's are large, a stat call will be fast,
		2671	as the path data is usually in memory already (except when starting the
		2672	watcher).
		2673
		2674	For networked file systems, calling C<stat ()> can block an indefinite
		2675	time due to network issues, and even under good conditions, a stat call
		2676	often takes multiple milliseconds.
		2677
		2678	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2679	paths, although this is fully supported by libev.
		2680
		2681	=head3 The special problem of stat time resolution
		2682
		2683	The C<stat ()> system call only supports full-second resolution portably,
		2684	and even on systems where the resolution is higher, most file systems
		2685	still only support whole seconds.
		2686
		2687	That means that, if the time is the only thing that changes, you can
		2688	easily miss updates: on the first update, C<ev_stat> detects a change and
		2689	calls your callback, which does something. When there is another update
		2690	within the same second, C<ev_stat> will be unable to detect unless the
		2691	stat data does change in other ways (e.g. file size).
		2692
		2693	The solution to this is to delay acting on a change for slightly more
		2694	than a second (or till slightly after the next full second boundary), using
		2695	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2696	ev_timer_again (loop, w)>).
		2697
		2698	The C<.02> offset is added to work around small timing inconsistencies
		2699	of some operating systems (where the second counter of the current time
		2700	might be be delayed. One such system is the Linux kernel, where a call to
		2701	C<gettimeofday> might return a timestamp with a full second later than
		2702	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2703	update file times then there will be a small window where the kernel uses
		2704	the previous second to update file times but libev might already execute
		2705	the timer callback).
		2706
		2707	=head3 Watcher-Specific Functions and Data Members
		2708
		2709	=over 4
		2710
		2711	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2712
		2713	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2714
		2715	Configures the watcher to wait for status changes of the given
		2716	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2717	be detected and should normally be specified as C<0> to let libev choose
		2718	a suitable value. The memory pointed to by C<path> must point to the same
		2719	path for as long as the watcher is active.
		2720
		2721	The callback will receive an C<EV_STAT> event when a change was detected,
		2722	relative to the attributes at the time the watcher was started (or the
		2723	last change was detected).
		2724
		2725	=item ev_stat_stat (loop, ev_stat *)
		2726
		2727	Updates the stat buffer immediately with new values. If you change the
		2728	watched path in your callback, you could call this function to avoid
		2729	detecting this change (while introducing a race condition if you are not
		2730	the only one changing the path). Can also be useful simply to find out the
		2731	new values.
		2732
		2733	=item ev_statdata attr [read-only]
		2734
		2735	The most-recently detected attributes of the file. Although the type is
		2736	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2737	suitable for your system, but you can only rely on the POSIX-standardised
		2738	members to be present. If the C<st_nlink> member is C<0>, then there was
		2739	some error while C<stat>ing the file.
		2740
		2741	=item ev_statdata prev [read-only]
		2742
		2743	The previous attributes of the file. The callback gets invoked whenever
		2744	C<prev> != C<attr>, or, more precisely, one or more of these members
		2745	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2746	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2747
		2748	=item ev_tstamp interval [read-only]
		2749
		2750	The specified interval.
		2751
		2752	=item const char *path [read-only]
		2753
		2754	The file system path that is being watched.
		2755
		2756	=back
		2757
		2758	=head3 Examples
		2759
		2760	Example: Watch C</etc/passwd> for attribute changes.
		2761
		2762	static void
		2763	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2764	{
		2765	/* /etc/passwd changed in some way */
		2766	if (w->attr.st_nlink)
		2767	{
		2768	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2769	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2770	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2771	}
		2772	else
		2773	/* you shalt not abuse printf for puts */
		2774	puts ("wow, /etc/passwd is not there, expect problems. "
		2775	"if this is windows, they already arrived\n");
		2776	}
		2777
		2778	...
		2779	ev_stat passwd;
		2780
		2781	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2782	ev_stat_start (loop, &passwd);
		2783
		2784	Example: Like above, but additionally use a one-second delay so we do not
		2785	miss updates (however, frequent updates will delay processing, too, so
		2786	one might do the work both on C<ev_stat> callback invocation I<and> on
		2787	C<ev_timer> callback invocation).
		2788
		2789	static ev_stat passwd;
		2790	static ev_timer timer;
		2791
		2792	static void
		2793	timer_cb (EV_P_ ev_timer *w, int revents)
		2794	{
		2795	ev_timer_stop (EV_A_ w);
		2796
		2797	/* now it's one second after the most recent passwd change */
		2798	}
		2799
		2800	static void
		2801	stat_cb (EV_P_ ev_stat *w, int revents)
		2802	{
		2803	/* reset the one-second timer */
		2804	ev_timer_again (EV_A_ &timer);
		2805	}
		2806
		2807	...
		2808	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2809	ev_stat_start (loop, &passwd);
		2810	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2811
		2812
640	=head2 ev_idle - when you've got nothing better to do	2813	=head2 C<ev_idle> - when you've got nothing better to do...
641		2814
642	Idle watchers trigger events when there are no other I/O or timer (or	2815	Idle watchers trigger events when no other events of the same or higher
643	periodic) events pending. That is, as long as your process is busy	2816	priority are pending (prepare, check and other idle watchers do not count
644	handling sockets or timeouts it will not be called. But when your process	2817	as receiving "events").
645	is idle all idle watchers are being called again and again - until	2818
		2819	That is, as long as your process is busy handling sockets or timeouts
		2820	(or even signals, imagine) of the same or higher priority it will not be
		2821	triggered. But when your process is idle (or only lower-priority watchers
		2822	are pending), the idle watchers are being called once per event loop
646	stopped, that is, or your process receives more events.	2823	iteration - until stopped, that is, or your process receives more events
		2824	and becomes busy again with higher priority stuff.
647		2825
648	The most noteworthy effect is that as long as any idle watchers are	2826	The most noteworthy effect is that as long as any idle watchers are
649	active, the process will not block when waiting for new events.	2827	active, the process will not block when waiting for new events.
650		2828
651	Apart from keeping your process non-blocking (which is a useful	2829	Apart from keeping your process non-blocking (which is a useful
652	effect on its own sometimes), idle watchers are a good place to do	2830	effect on its own sometimes), idle watchers are a good place to do
653	"pseudo-background processing", or delay processing stuff to after the	2831	"pseudo-background processing", or delay processing stuff to after the
654	event loop has handled all outstanding events.	2832	event loop has handled all outstanding events.
655		2833
		2834	=head3 Watcher-Specific Functions and Data Members
		2835
656	=over 4	2836	=over 4
657		2837
658	=item ev_idle_init (ev_signal *, callback)	2838	=item ev_idle_init (ev_idle *, callback)
659		2839
660	Initialises and configures the idle watcher - it has no parameters of any	2840	Initialises and configures the idle watcher - it has no parameters of any
661	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2841	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
662	believe me.	2842	believe me.
663		2843
664	=back	2844	=back
665		2845
666	=head2 prepare and check - your hooks into the event loop	2846	=head3 Examples
667		2847
		2848	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2849	callback, free it. Also, use no error checking, as usual.
		2850
		2851	static void
		2852	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2853	{
		2854	free (w);
		2855	// now do something you wanted to do when the program has
		2856	// no longer anything immediate to do.
		2857	}
		2858
		2859	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2860	ev_idle_init (idle_watcher, idle_cb);
		2861	ev_idle_start (loop, idle_watcher);
		2862
		2863
		2864	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		2865
668	Prepare and check watchers usually (but not always) are used in	2866	Prepare and check watchers are usually (but not always) used in pairs:
669	tandom. Prepare watchers get invoked before the process blocks and check	2867	prepare watchers get invoked before the process blocks and check watchers
670	watchers afterwards.	2868	afterwards.
671		2869
		2870	You I<must not> call C<ev_run> or similar functions that enter
		2871	the current event loop from either C<ev_prepare> or C<ev_check>
		2872	watchers. Other loops than the current one are fine, however. The
		2873	rationale behind this is that you do not need to check for recursion in
		2874	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2875	C<ev_check> so if you have one watcher of each kind they will always be
		2876	called in pairs bracketing the blocking call.
		2877
672	Their main purpose is to integrate other event mechanisms into libev. This	2878	Their main purpose is to integrate other event mechanisms into libev and
673	could be used, for example, to track variable changes, implement your own	2879	their use is somewhat advanced. They could be used, for example, to track
674	watchers, integrate net-snmp or a coroutine library and lots more.	2880	variable changes, implement your own watchers, integrate net-snmp or a
		2881	coroutine library and lots more. They are also occasionally useful if
		2882	you cache some data and want to flush it before blocking (for example,
		2883	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2884	watcher).
675		2885
676	This is done by examining in each prepare call which file descriptors need	2886	This is done by examining in each prepare call which file descriptors
677	to be watched by the other library, registering ev_io watchers for them	2887	need to be watched by the other library, registering C<ev_io> watchers
678	and starting an ev_timer watcher for any timeouts (many libraries provide	2888	for them and starting an C<ev_timer> watcher for any timeouts (many
679	just this functionality). Then, in the check watcher you check for any	2889	libraries provide exactly this functionality). Then, in the check watcher,
680	events that occured (by making your callbacks set soem flags for example)	2890	you check for any events that occurred (by checking the pending status
681	and call back into the library.	2891	of all watchers and stopping them) and call back into the library. The
		2892	I/O and timer callbacks will never actually be called (but must be valid
		2893	nevertheless, because you never know, you know?).
682		2894
683	As another example, the perl Coro module uses these hooks to integrate	2895	As another example, the Perl Coro module uses these hooks to integrate
684	coroutines into libev programs, by yielding to other active coroutines	2896	coroutines into libev programs, by yielding to other active coroutines
685	during each prepare and only letting the process block if no coroutines	2897	during each prepare and only letting the process block if no coroutines
686	are ready to run.	2898	are ready to run (it's actually more complicated: it only runs coroutines
		2899	with priority higher than or equal to the event loop and one coroutine
		2900	of lower priority, but only once, using idle watchers to keep the event
		2901	loop from blocking if lower-priority coroutines are active, thus mapping
		2902	low-priority coroutines to idle/background tasks).
		2903
		2904	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2905	priority, to ensure that they are being run before any other watchers
		2906	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2907
		2908	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2909	activate ("feed") events into libev. While libev fully supports this, they
		2910	might get executed before other C<ev_check> watchers did their job. As
		2911	C<ev_check> watchers are often used to embed other (non-libev) event
		2912	loops those other event loops might be in an unusable state until their
		2913	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2914	others).
		2915
		2916	=head3 Watcher-Specific Functions and Data Members
687		2917
688	=over 4	2918	=over 4
689		2919
690	=item ev_prepare_init (ev_prepare *, callback)	2920	=item ev_prepare_init (ev_prepare *, callback)
691		2921
692	=item ev_check_init (ev_check *, callback)	2922	=item ev_check_init (ev_check *, callback)
693		2923
694	Initialises and configures the prepare or check watcher - they have no	2924	Initialises and configures the prepare or check watcher - they have no
695	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2925	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
696	macros, but using them is utterly, utterly pointless.	2926	macros, but using them is utterly, utterly, utterly and completely
		2927	pointless.
697		2928
698	=back	2929	=back
699		2930
		2931	=head3 Examples
		2932
		2933	There are a number of principal ways to embed other event loops or modules
		2934	into libev. Here are some ideas on how to include libadns into libev
		2935	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2936	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2937	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2938	Glib event loop).
		2939
		2940	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2941	and in a check watcher, destroy them and call into libadns. What follows
		2942	is pseudo-code only of course. This requires you to either use a low
		2943	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2944	the callbacks for the IO/timeout watchers might not have been called yet.
		2945
		2946	static ev_io iow [nfd];
		2947	static ev_timer tw;
		2948
		2949	static void
		2950	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2951	{
		2952	}
		2953
		2954	// create io watchers for each fd and a timer before blocking
		2955	static void
		2956	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2957	{
		2958	int timeout = 3600000;
		2959	struct pollfd fds [nfd];
		2960	// actual code will need to loop here and realloc etc.
		2961	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2962
		2963	/* the callback is illegal, but won't be called as we stop during check */
		2964	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		2965	ev_timer_start (loop, &tw);
		2966
		2967	// create one ev_io per pollfd
		2968	for (int i = 0; i < nfd; ++i)
		2969	{
		2970	ev_io_init (iow + i, io_cb, fds [i].fd,
		2971	((fds [i].events & POLLIN ? EV_READ : 0)
		2972	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2973
		2974	fds [i].revents = 0;
		2975	ev_io_start (loop, iow + i);
		2976	}
		2977	}
		2978
		2979	// stop all watchers after blocking
		2980	static void
		2981	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2982	{
		2983	ev_timer_stop (loop, &tw);
		2984
		2985	for (int i = 0; i < nfd; ++i)
		2986	{
		2987	// set the relevant poll flags
		2988	// could also call adns_processreadable etc. here
		2989	struct pollfd *fd = fds + i;
		2990	int revents = ev_clear_pending (iow + i);
		2991	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2992	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2993
		2994	// now stop the watcher
		2995	ev_io_stop (loop, iow + i);
		2996	}
		2997
		2998	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2999	}
		3000
		3001	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		3002	in the prepare watcher and would dispose of the check watcher.
		3003
		3004	Method 3: If the module to be embedded supports explicit event
		3005	notification (libadns does), you can also make use of the actual watcher
		3006	callbacks, and only destroy/create the watchers in the prepare watcher.
		3007
		3008	static void
		3009	timer_cb (EV_P_ ev_timer *w, int revents)
		3010	{
		3011	adns_state ads = (adns_state)w->data;
		3012	update_now (EV_A);
		3013
		3014	adns_processtimeouts (ads, &tv_now);
		3015	}
		3016
		3017	static void
		3018	io_cb (EV_P_ ev_io *w, int revents)
		3019	{
		3020	adns_state ads = (adns_state)w->data;
		3021	update_now (EV_A);
		3022
		3023	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		3024	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		3025	}
		3026
		3027	// do not ever call adns_afterpoll
		3028
		3029	Method 4: Do not use a prepare or check watcher because the module you
		3030	want to embed is not flexible enough to support it. Instead, you can
		3031	override their poll function. The drawback with this solution is that the
		3032	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		3033	this approach, effectively embedding EV as a client into the horrible
		3034	libglib event loop.
		3035
		3036	static gint
		3037	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		3038	{
		3039	int got_events = 0;
		3040
		3041	for (n = 0; n < nfds; ++n)
		3042	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		3043
		3044	if (timeout >= 0)
		3045	// create/start timer
		3046
		3047	// poll
		3048	ev_run (EV_A_ 0);
		3049
		3050	// stop timer again
		3051	if (timeout >= 0)
		3052	ev_timer_stop (EV_A_ &to);
		3053
		3054	// stop io watchers again - their callbacks should have set
		3055	for (n = 0; n < nfds; ++n)
		3056	ev_io_stop (EV_A_ iow [n]);
		3057
		3058	return got_events;
		3059	}
		3060
		3061
		3062	=head2 C<ev_embed> - when one backend isn't enough...
		3063
		3064	This is a rather advanced watcher type that lets you embed one event loop
		3065	into another (currently only C<ev_io> events are supported in the embedded
		3066	loop, other types of watchers might be handled in a delayed or incorrect
		3067	fashion and must not be used).
		3068
		3069	There are primarily two reasons you would want that: work around bugs and
		3070	prioritise I/O.
		3071
		3072	As an example for a bug workaround, the kqueue backend might only support
		3073	sockets on some platform, so it is unusable as generic backend, but you
		3074	still want to make use of it because you have many sockets and it scales
		3075	so nicely. In this case, you would create a kqueue-based loop and embed
		3076	it into your default loop (which might use e.g. poll). Overall operation
		3077	will be a bit slower because first libev has to call C<poll> and then
		3078	C<kevent>, but at least you can use both mechanisms for what they are
		3079	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		3080
		3081	As for prioritising I/O: under rare circumstances you have the case where
		3082	some fds have to be watched and handled very quickly (with low latency),
		3083	and even priorities and idle watchers might have too much overhead. In
		3084	this case you would put all the high priority stuff in one loop and all
		3085	the rest in a second one, and embed the second one in the first.
		3086
		3087	As long as the watcher is active, the callback will be invoked every
		3088	time there might be events pending in the embedded loop. The callback
		3089	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		3090	sweep and invoke their callbacks (the callback doesn't need to invoke the
		3091	C<ev_embed_sweep> function directly, it could also start an idle watcher
		3092	to give the embedded loop strictly lower priority for example).
		3093
		3094	You can also set the callback to C<0>, in which case the embed watcher
		3095	will automatically execute the embedded loop sweep whenever necessary.
		3096
		3097	Fork detection will be handled transparently while the C<ev_embed> watcher
		3098	is active, i.e., the embedded loop will automatically be forked when the
		3099	embedding loop forks. In other cases, the user is responsible for calling
		3100	C<ev_loop_fork> on the embedded loop.
		3101
		3102	Unfortunately, not all backends are embeddable: only the ones returned by
		3103	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		3104	portable one.
		3105
		3106	So when you want to use this feature you will always have to be prepared
		3107	that you cannot get an embeddable loop. The recommended way to get around
		3108	this is to have a separate variables for your embeddable loop, try to
		3109	create it, and if that fails, use the normal loop for everything.
		3110
		3111	=head3 C<ev_embed> and fork
		3112
		3113	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3114	automatically be applied to the embedded loop as well, so no special
		3115	fork handling is required in that case. When the watcher is not running,
		3116	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3117	as applicable.
		3118
		3119	=head3 Watcher-Specific Functions and Data Members
		3120
		3121	=over 4
		3122
		3123	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		3124
		3125	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		3126
		3127	Configures the watcher to embed the given loop, which must be
		3128	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		3129	invoked automatically, otherwise it is the responsibility of the callback
		3130	to invoke it (it will continue to be called until the sweep has been done,
		3131	if you do not want that, you need to temporarily stop the embed watcher).
		3132
		3133	=item ev_embed_sweep (loop, ev_embed *)
		3134
		3135	Make a single, non-blocking sweep over the embedded loop. This works
		3136	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
		3137	appropriate way for embedded loops.
		3138
		3139	=item struct ev_loop *other [read-only]
		3140
		3141	The embedded event loop.
		3142
		3143	=back
		3144
		3145	=head3 Examples
		3146
		3147	Example: Try to get an embeddable event loop and embed it into the default
		3148	event loop. If that is not possible, use the default loop. The default
		3149	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3150	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3151	used).
		3152
		3153	struct ev_loop *loop_hi = ev_default_init (0);
		3154	struct ev_loop *loop_lo = 0;
		3155	ev_embed embed;
		3156
		3157	// see if there is a chance of getting one that works
		3158	// (remember that a flags value of 0 means autodetection)
		3159	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3160	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3161	: 0;
		3162
		3163	// if we got one, then embed it, otherwise default to loop_hi
		3164	if (loop_lo)
		3165	{
		3166	ev_embed_init (&embed, 0, loop_lo);
		3167	ev_embed_start (loop_hi, &embed);
		3168	}
		3169	else
		3170	loop_lo = loop_hi;
		3171
		3172	Example: Check if kqueue is available but not recommended and create
		3173	a kqueue backend for use with sockets (which usually work with any
		3174	kqueue implementation). Store the kqueue/socket-only event loop in
		3175	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3176
		3177	struct ev_loop *loop = ev_default_init (0);
		3178	struct ev_loop *loop_socket = 0;
		3179	ev_embed embed;
		3180
		3181	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3182	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3183	{
		3184	ev_embed_init (&embed, 0, loop_socket);
		3185	ev_embed_start (loop, &embed);
		3186	}
		3187
		3188	if (!loop_socket)
		3189	loop_socket = loop;
		3190
		3191	// now use loop_socket for all sockets, and loop for everything else
		3192
		3193
		3194	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3195
		3196	Fork watchers are called when a C<fork ()> was detected (usually because
		3197	whoever is a good citizen cared to tell libev about it by calling
		3198	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		3199	event loop blocks next and before C<ev_check> watchers are being called,
		3200	and only in the child after the fork. If whoever good citizen calling
		3201	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		3202	handlers will be invoked, too, of course.
		3203
		3204	=head3 The special problem of life after fork - how is it possible?
		3205
		3206	Most uses of C<fork()> consist of forking, then some simple calls to set
		3207	up/change the process environment, followed by a call to C<exec()>. This
		3208	sequence should be handled by libev without any problems.
		3209
		3210	This changes when the application actually wants to do event handling
		3211	in the child, or both parent in child, in effect "continuing" after the
		3212	fork.
		3213
		3214	The default mode of operation (for libev, with application help to detect
		3215	forks) is to duplicate all the state in the child, as would be expected
		3216	when I<either> the parent I<or> the child process continues.
		3217
		3218	When both processes want to continue using libev, then this is usually the
		3219	wrong result. In that case, usually one process (typically the parent) is
		3220	supposed to continue with all watchers in place as before, while the other
		3221	process typically wants to start fresh, i.e. without any active watchers.
		3222
		3223	The cleanest and most efficient way to achieve that with libev is to
		3224	simply create a new event loop, which of course will be "empty", and
		3225	use that for new watchers. This has the advantage of not touching more
		3226	memory than necessary, and thus avoiding the copy-on-write, and the
		3227	disadvantage of having to use multiple event loops (which do not support
		3228	signal watchers).
		3229
		3230	When this is not possible, or you want to use the default loop for
		3231	other reasons, then in the process that wants to start "fresh", call
		3232	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3233	Destroying the default loop will "orphan" (not stop) all registered
		3234	watchers, so you have to be careful not to execute code that modifies
		3235	those watchers. Note also that in that case, you have to re-register any
		3236	signal watchers.
		3237
		3238	=head3 Watcher-Specific Functions and Data Members
		3239
		3240	=over 4
		3241
		3242	=item ev_fork_init (ev_fork *, callback)
		3243
		3244	Initialises and configures the fork watcher - it has no parameters of any
		3245	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3246	really.
		3247
		3248	=back
		3249
		3250
		3251	=head2 C<ev_cleanup> - even the best things end
		3252
		3253	Cleanup watchers are called just before the event loop is being destroyed
		3254	by a call to C<ev_loop_destroy>.
		3255
		3256	While there is no guarantee that the event loop gets destroyed, cleanup
		3257	watchers provide a convenient method to install cleanup hooks for your
		3258	program, worker threads and so on - you just to make sure to destroy the
		3259	loop when you want them to be invoked.
		3260
		3261	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3262	all other watchers, they do not keep a reference to the event loop (which
		3263	makes a lot of sense if you think about it). Like all other watchers, you
		3264	can call libev functions in the callback, except C<ev_cleanup_start>.
		3265
		3266	=head3 Watcher-Specific Functions and Data Members
		3267
		3268	=over 4
		3269
		3270	=item ev_cleanup_init (ev_cleanup *, callback)
		3271
		3272	Initialises and configures the cleanup watcher - it has no parameters of
		3273	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3274	pointless, I assure you.
		3275
		3276	=back
		3277
		3278	Example: Register an atexit handler to destroy the default loop, so any
		3279	cleanup functions are called.
		3280
		3281	static void
		3282	program_exits (void)
		3283	{
		3284	ev_loop_destroy (EV_DEFAULT_UC);
		3285	}
		3286
		3287	...
		3288	atexit (program_exits);
		3289
		3290
		3291	=head2 C<ev_async> - how to wake up an event loop
		3292
		3293	In general, you cannot use an C<ev_loop> from multiple threads or other
		3294	asynchronous sources such as signal handlers (as opposed to multiple event
		3295	loops - those are of course safe to use in different threads).
		3296
		3297	Sometimes, however, you need to wake up an event loop you do not control,
		3298	for example because it belongs to another thread. This is what C<ev_async>
		3299	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3300	it by calling C<ev_async_send>, which is thread- and signal safe.
		3301
		3302	This functionality is very similar to C<ev_signal> watchers, as signals,
		3303	too, are asynchronous in nature, and signals, too, will be compressed
		3304	(i.e. the number of callback invocations may be less than the number of
		3305	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3306	of "global async watchers" by using a watcher on an otherwise unused
		3307	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3308	even without knowing which loop owns the signal.
		3309
		3310	=head3 Queueing
		3311
		3312	C<ev_async> does not support queueing of data in any way. The reason
		3313	is that the author does not know of a simple (or any) algorithm for a
		3314	multiple-writer-single-reader queue that works in all cases and doesn't
		3315	need elaborate support such as pthreads or unportable memory access
		3316	semantics.
		3317
		3318	That means that if you want to queue data, you have to provide your own
		3319	queue. But at least I can tell you how to implement locking around your
		3320	queue:
		3321
		3322	=over 4
		3323
		3324	=item queueing from a signal handler context
		3325
		3326	To implement race-free queueing, you simply add to the queue in the signal
		3327	handler but you block the signal handler in the watcher callback. Here is
		3328	an example that does that for some fictitious SIGUSR1 handler:
		3329
		3330	static ev_async mysig;
		3331
		3332	static void
		3333	sigusr1_handler (void)
		3334	{
		3335	sometype data;
		3336
		3337	// no locking etc.
		3338	queue_put (data);
		3339	ev_async_send (EV_DEFAULT_ &mysig);
		3340	}
		3341
		3342	static void
		3343	mysig_cb (EV_P_ ev_async *w, int revents)
		3344	{
		3345	sometype data;
		3346	sigset_t block, prev;
		3347
		3348	sigemptyset (&block);
		3349	sigaddset (&block, SIGUSR1);
		3350	sigprocmask (SIG_BLOCK, &block, &prev);
		3351
		3352	while (queue_get (&data))
		3353	process (data);
		3354
		3355	if (sigismember (&prev, SIGUSR1)
		3356	sigprocmask (SIG_UNBLOCK, &block, 0);
		3357	}
		3358
		3359	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3360	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3361	either...).
		3362
		3363	=item queueing from a thread context
		3364
		3365	The strategy for threads is different, as you cannot (easily) block
		3366	threads but you can easily preempt them, so to queue safely you need to
		3367	employ a traditional mutex lock, such as in this pthread example:
		3368
		3369	static ev_async mysig;
		3370	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3371
		3372	static void
		3373	otherthread (void)
		3374	{
		3375	// only need to lock the actual queueing operation
		3376	pthread_mutex_lock (&mymutex);
		3377	queue_put (data);
		3378	pthread_mutex_unlock (&mymutex);
		3379
		3380	ev_async_send (EV_DEFAULT_ &mysig);
		3381	}
		3382
		3383	static void
		3384	mysig_cb (EV_P_ ev_async *w, int revents)
		3385	{
		3386	pthread_mutex_lock (&mymutex);
		3387
		3388	while (queue_get (&data))
		3389	process (data);
		3390
		3391	pthread_mutex_unlock (&mymutex);
		3392	}
		3393
		3394	=back
		3395
		3396
		3397	=head3 Watcher-Specific Functions and Data Members
		3398
		3399	=over 4
		3400
		3401	=item ev_async_init (ev_async *, callback)
		3402
		3403	Initialises and configures the async watcher - it has no parameters of any
		3404	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3405	trust me.
		3406
		3407	=item ev_async_send (loop, ev_async *)
		3408
		3409	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3410	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3411	returns.
		3412
		3413	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3414	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3415	embedding section below on what exactly this means).
		3416
		3417	Note that, as with other watchers in libev, multiple events might get
		3418	compressed into a single callback invocation (another way to look at
		3419	this is that C<ev_async> watchers are level-triggered: they are set on
		3420	C<ev_async_send>, reset when the event loop detects that).
		3421
		3422	This call incurs the overhead of at most one extra system call per event
		3423	loop iteration, if the event loop is blocked, and no syscall at all if
		3424	the event loop (or your program) is processing events. That means that
		3425	repeated calls are basically free (there is no need to avoid calls for
		3426	performance reasons) and that the overhead becomes smaller (typically
		3427	zero) under load.
		3428
		3429	=item bool = ev_async_pending (ev_async *)
		3430
		3431	Returns a non-zero value when C<ev_async_send> has been called on the
		3432	watcher but the event has not yet been processed (or even noted) by the
		3433	event loop.
		3434
		3435	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3436	the loop iterates next and checks for the watcher to have become active,
		3437	it will reset the flag again. C<ev_async_pending> can be used to very
		3438	quickly check whether invoking the loop might be a good idea.
		3439
		3440	Not that this does I<not> check whether the watcher itself is pending,
		3441	only whether it has been requested to make this watcher pending: there
		3442	is a time window between the event loop checking and resetting the async
		3443	notification, and the callback being invoked.
		3444
		3445	=back
		3446
		3447
700	=head1 OTHER FUNCTIONS	3448	=head1 OTHER FUNCTIONS
701		3449
702	There are some other fucntions of possible interest. Described. Here. Now.	3450	There are some other functions of possible interest. Described. Here. Now.
703		3451
704	=over 4	3452	=over 4
705		3453
706	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3454	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
707		3455
708	This function combines a simple timer and an I/O watcher, calls your	3456	This function combines a simple timer and an I/O watcher, calls your
709	callback on whichever event happens first and automatically stop both	3457	callback on whichever event happens first and automatically stops both
710	watchers. This is useful if you want to wait for a single event on an fd	3458	watchers. This is useful if you want to wait for a single event on an fd
711	or timeout without havign to allocate/configure/start/stop/free one or	3459	or timeout without having to allocate/configure/start/stop/free one or
712	more watchers yourself.	3460	more watchers yourself.
713		3461
714	If C<fd> is less than 0, then no I/O watcher will be started and events is	3462	If C<fd> is less than 0, then no I/O watcher will be started and the
715	ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set	3463	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
716	will be craeted and started.	3464	the given C<fd> and C<events> set will be created and started.
717		3465
718	If C<timeout> is less than 0, then no timeout watcher will be	3466	If C<timeout> is less than 0, then no timeout watcher will be
719	started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat	3467	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
720	= 0) will be started.	3468	repeat = 0) will be started. C<0> is a valid timeout.
721		3469
722	The callback has the type C<void (*cb)(int revents, void *arg)> and	3470	The callback has the type C<void (*cb)(int revents, void *arg)> and is
723	gets passed an events set (normally a combination of EV_ERROR, EV_READ,	3471	passed an C<revents> set like normal event callbacks (a combination of
724	EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>:	3472	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
		3473	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3474	a timeout and an io event at the same time - you probably should give io
		3475	events precedence.
725		3476
		3477	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3478
726	static void stdin_ready (int revents, void *arg)	3479	static void stdin_ready (int revents, void *arg)
		3480	{
		3481	if (revents & EV_READ)
		3482	/* stdin might have data for us, joy! */;
		3483	else if (revents & EV_TIMER)
		3484	/* doh, nothing entered */;
		3485	}
		3486
		3487	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3488
		3489	=item ev_feed_fd_event (loop, int fd, int revents)
		3490
		3491	Feed an event on the given fd, as if a file descriptor backend detected
		3492	the given events.
		3493
		3494	=item ev_feed_signal_event (loop, int signum)
		3495
		3496	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3497	which is async-safe.
		3498
		3499	=back
		3500
		3501
		3502	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3503
		3504	This section explains some common idioms that are not immediately
		3505	obvious. Note that examples are sprinkled over the whole manual, and this
		3506	section only contains stuff that wouldn't fit anywhere else.
		3507
		3508	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3509
		3510	Each watcher has, by default, a C<void *data> member that you can read
		3511	or modify at any time: libev will completely ignore it. This can be used
		3512	to associate arbitrary data with your watcher. If you need more data and
		3513	don't want to allocate memory separately and store a pointer to it in that
		3514	data member, you can also "subclass" the watcher type and provide your own
		3515	data:
		3516
		3517	struct my_io
		3518	{
		3519	ev_io io;
		3520	int otherfd;
		3521	void *somedata;
		3522	struct whatever *mostinteresting;
		3523	};
		3524
		3525	...
		3526	struct my_io w;
		3527	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3528
		3529	And since your callback will be called with a pointer to the watcher, you
		3530	can cast it back to your own type:
		3531
		3532	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3533	{
		3534	struct my_io *w = (struct my_io *)w_;
		3535	...
		3536	}
		3537
		3538	More interesting and less C-conformant ways of casting your callback
		3539	function type instead have been omitted.
		3540
		3541	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3542
		3543	Another common scenario is to use some data structure with multiple
		3544	embedded watchers, in effect creating your own watcher that combines
		3545	multiple libev event sources into one "super-watcher":
		3546
		3547	struct my_biggy
		3548	{
		3549	int some_data;
		3550	ev_timer t1;
		3551	ev_timer t2;
		3552	}
		3553
		3554	In this case getting the pointer to C<my_biggy> is a bit more
		3555	complicated: Either you store the address of your C<my_biggy> struct in
		3556	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3557	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3558	real programmers):
		3559
		3560	#include <stddef.h>
		3561
		3562	static void
		3563	t1_cb (EV_P_ ev_timer *w, int revents)
		3564	{
		3565	struct my_biggy big = (struct my_biggy *)
		3566	(((char *)w) - offsetof (struct my_biggy, t1));
		3567	}
		3568
		3569	static void
		3570	t2_cb (EV_P_ ev_timer *w, int revents)
		3571	{
		3572	struct my_biggy big = (struct my_biggy *)
		3573	(((char *)w) - offsetof (struct my_biggy, t2));
		3574	}
		3575
		3576	=head2 AVOIDING FINISHING BEFORE RETURNING
		3577
		3578	Often you have structures like this in event-based programs:
		3579
		3580	callback ()
727	{	3581	{
728	if (revents & EV_TIMEOUT)	3582	free (request);
729	/* doh, nothing entered */
730	else if (revents & EV_READ)
731	/* stdin might have data for us, joy! */
732	}	3583	}
733		3584
734	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	3585	request = start_new_request (..., callback);
735		3586
736	=item ev_feed_event (loop, watcher, int events)	3587	The intent is to start some "lengthy" operation. The C<request> could be
		3588	used to cancel the operation, or do other things with it.
737		3589
738	Feeds the given event set into the event loop, as if the specified event	3590	It's not uncommon to have code paths in C<start_new_request> that
739	has happened for the specified watcher (which must be a pointer to an	3591	immediately invoke the callback, for example, to report errors. Or you add
740	initialised but not necessarily active event watcher).	3592	some caching layer that finds that it can skip the lengthy aspects of the
		3593	operation and simply invoke the callback with the result.
741		3594
742	=item ev_feed_fd_event (loop, int fd, int revents)	3595	The problem here is that this will happen I<before> C<start_new_request>
		3596	has returned, so C<request> is not set.
743		3597
744	Feed an event on the given fd, as if a file descriptor backend detected it.	3598	Even if you pass the request by some safer means to the callback, you
		3599	might want to do something to the request after starting it, such as
		3600	canceling it, which probably isn't working so well when the callback has
		3601	already been invoked.
745		3602
746	=item ev_feed_signal_event (loop, int signum)	3603	A common way around all these issues is to make sure that
		3604	C<start_new_request> I<always> returns before the callback is invoked. If
		3605	C<start_new_request> immediately knows the result, it can artificially
		3606	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3607	for example, or more sneakily, by reusing an existing (stopped) watcher
		3608	and pushing it into the pending queue:
747		3609
748	Feed an event as if the given signal occured (loop must be the default loop!).	3610	ev_set_cb (watcher, callback);
		3611	ev_feed_event (EV_A_ watcher, 0);
		3612
		3613	This way, C<start_new_request> can safely return before the callback is
		3614	invoked, while not delaying callback invocation too much.
		3615
		3616	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3617
		3618	Often (especially in GUI toolkits) there are places where you have
		3619	I<modal> interaction, which is most easily implemented by recursively
		3620	invoking C<ev_run>.
		3621
		3622	This brings the problem of exiting - a callback might want to finish the
		3623	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3624	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3625	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3626	other combination: In these cases, C<ev_break> will not work alone.
		3627
		3628	The solution is to maintain "break this loop" variable for each C<ev_run>
		3629	invocation, and use a loop around C<ev_run> until the condition is
		3630	triggered, using C<EVRUN_ONCE>:
		3631
		3632	// main loop
		3633	int exit_main_loop = 0;
		3634
		3635	while (!exit_main_loop)
		3636	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3637
		3638	// in a model watcher
		3639	int exit_nested_loop = 0;
		3640
		3641	while (!exit_nested_loop)
		3642	ev_run (EV_A_ EVRUN_ONCE);
		3643
		3644	To exit from any of these loops, just set the corresponding exit variable:
		3645
		3646	// exit modal loop
		3647	exit_nested_loop = 1;
		3648
		3649	// exit main program, after modal loop is finished
		3650	exit_main_loop = 1;
		3651
		3652	// exit both
		3653	exit_main_loop = exit_nested_loop = 1;
		3654
		3655	=head2 THREAD LOCKING EXAMPLE
		3656
		3657	Here is a fictitious example of how to run an event loop in a different
		3658	thread from where callbacks are being invoked and watchers are
		3659	created/added/removed.
		3660
		3661	For a real-world example, see the C<EV::Loop::Async> perl module,
		3662	which uses exactly this technique (which is suited for many high-level
		3663	languages).
		3664
		3665	The example uses a pthread mutex to protect the loop data, a condition
		3666	variable to wait for callback invocations, an async watcher to notify the
		3667	event loop thread and an unspecified mechanism to wake up the main thread.
		3668
		3669	First, you need to associate some data with the event loop:
		3670
		3671	typedef struct {
		3672	mutex_t lock; /* global loop lock */
		3673	ev_async async_w;
		3674	thread_t tid;
		3675	cond_t invoke_cv;
		3676	} userdata;
		3677
		3678	void prepare_loop (EV_P)
		3679	{
		3680	// for simplicity, we use a static userdata struct.
		3681	static userdata u;
		3682
		3683	ev_async_init (&u->async_w, async_cb);
		3684	ev_async_start (EV_A_ &u->async_w);
		3685
		3686	pthread_mutex_init (&u->lock, 0);
		3687	pthread_cond_init (&u->invoke_cv, 0);
		3688
		3689	// now associate this with the loop
		3690	ev_set_userdata (EV_A_ u);
		3691	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3692	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3693
		3694	// then create the thread running ev_run
		3695	pthread_create (&u->tid, 0, l_run, EV_A);
		3696	}
		3697
		3698	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3699	solely to wake up the event loop so it takes notice of any new watchers
		3700	that might have been added:
		3701
		3702	static void
		3703	async_cb (EV_P_ ev_async *w, int revents)
		3704	{
		3705	// just used for the side effects
		3706	}
		3707
		3708	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3709	protecting the loop data, respectively.
		3710
		3711	static void
		3712	l_release (EV_P)
		3713	{
		3714	userdata *u = ev_userdata (EV_A);
		3715	pthread_mutex_unlock (&u->lock);
		3716	}
		3717
		3718	static void
		3719	l_acquire (EV_P)
		3720	{
		3721	userdata *u = ev_userdata (EV_A);
		3722	pthread_mutex_lock (&u->lock);
		3723	}
		3724
		3725	The event loop thread first acquires the mutex, and then jumps straight
		3726	into C<ev_run>:
		3727
		3728	void *
		3729	l_run (void *thr_arg)
		3730	{
		3731	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3732
		3733	l_acquire (EV_A);
		3734	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3735	ev_run (EV_A_ 0);
		3736	l_release (EV_A);
		3737
		3738	return 0;
		3739	}
		3740
		3741	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3742	signal the main thread via some unspecified mechanism (signals? pipe
		3743	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3744	have been called (in a while loop because a) spurious wakeups are possible
		3745	and b) skipping inter-thread-communication when there are no pending
		3746	watchers is very beneficial):
		3747
		3748	static void
		3749	l_invoke (EV_P)
		3750	{
		3751	userdata *u = ev_userdata (EV_A);
		3752
		3753	while (ev_pending_count (EV_A))
		3754	{
		3755	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3756	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3757	}
		3758	}
		3759
		3760	Now, whenever the main thread gets told to invoke pending watchers, it
		3761	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3762	thread to continue:
		3763
		3764	static void
		3765	real_invoke_pending (EV_P)
		3766	{
		3767	userdata *u = ev_userdata (EV_A);
		3768
		3769	pthread_mutex_lock (&u->lock);
		3770	ev_invoke_pending (EV_A);
		3771	pthread_cond_signal (&u->invoke_cv);
		3772	pthread_mutex_unlock (&u->lock);
		3773	}
		3774
		3775	Whenever you want to start/stop a watcher or do other modifications to an
		3776	event loop, you will now have to lock:
		3777
		3778	ev_timer timeout_watcher;
		3779	userdata *u = ev_userdata (EV_A);
		3780
		3781	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3782
		3783	pthread_mutex_lock (&u->lock);
		3784	ev_timer_start (EV_A_ &timeout_watcher);
		3785	ev_async_send (EV_A_ &u->async_w);
		3786	pthread_mutex_unlock (&u->lock);
		3787
		3788	Note that sending the C<ev_async> watcher is required because otherwise
		3789	an event loop currently blocking in the kernel will have no knowledge
		3790	about the newly added timer. By waking up the loop it will pick up any new
		3791	watchers in the next event loop iteration.
		3792
		3793	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3794
		3795	While the overhead of a callback that e.g. schedules a thread is small, it
		3796	is still an overhead. If you embed libev, and your main usage is with some
		3797	kind of threads or coroutines, you might want to customise libev so that
		3798	doesn't need callbacks anymore.
		3799
		3800	Imagine you have coroutines that you can switch to using a function
		3801	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3802	and that due to some magic, the currently active coroutine is stored in a
		3803	global called C<current_coro>. Then you can build your own "wait for libev
		3804	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3805	the differing C<;> conventions):
		3806
		3807	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3808	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3809
		3810	That means instead of having a C callback function, you store the
		3811	coroutine to switch to in each watcher, and instead of having libev call
		3812	your callback, you instead have it switch to that coroutine.
		3813
		3814	A coroutine might now wait for an event with a function called
		3815	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3816	matter when, or whether the watcher is active or not when this function is
		3817	called):
		3818
		3819	void
		3820	wait_for_event (ev_watcher *w)
		3821	{
		3822	ev_cb_set (w) = current_coro;
		3823	switch_to (libev_coro);
		3824	}
		3825
		3826	That basically suspends the coroutine inside C<wait_for_event> and
		3827	continues the libev coroutine, which, when appropriate, switches back to
		3828	this or any other coroutine. I am sure if you sue this your own :)
		3829
		3830	You can do similar tricks if you have, say, threads with an event queue -
		3831	instead of storing a coroutine, you store the queue object and instead of
		3832	switching to a coroutine, you push the watcher onto the queue and notify
		3833	any waiters.
		3834
		3835	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3836	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3837
		3838	// my_ev.h
		3839	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3840	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3841	#include "../libev/ev.h"
		3842
		3843	// my_ev.c
		3844	#define EV_H "my_ev.h"
		3845	#include "../libev/ev.c"
		3846
		3847	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3848	F<my_ev.c> into your project. When properly specifying include paths, you
		3849	can even use F<ev.h> as header file name directly.
		3850
		3851
		3852	=head1 LIBEVENT EMULATION
		3853
		3854	Libev offers a compatibility emulation layer for libevent. It cannot
		3855	emulate the internals of libevent, so here are some usage hints:
		3856
		3857	=over 4
		3858
		3859	=item * Only the libevent-1.4.1-beta API is being emulated.
		3860
		3861	This was the newest libevent version available when libev was implemented,
		3862	and is still mostly unchanged in 2010.
		3863
		3864	=item * Use it by including <event.h>, as usual.
		3865
		3866	=item * The following members are fully supported: ev_base, ev_callback,
		3867	ev_arg, ev_fd, ev_res, ev_events.
		3868
		3869	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		3870	maintained by libev, it does not work exactly the same way as in libevent (consider
		3871	it a private API).
		3872
		3873	=item * Priorities are not currently supported. Initialising priorities
		3874	will fail and all watchers will have the same priority, even though there
		3875	is an ev_pri field.
		3876
		3877	=item * In libevent, the last base created gets the signals, in libev, the
		3878	base that registered the signal gets the signals.
		3879
		3880	=item * Other members are not supported.
		3881
		3882	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		3883	to use the libev header file and library.
749		3884
750	=back	3885	=back
751		3886
		3887	=head1 C++ SUPPORT
		3888
		3889	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3890	you to use some convenience methods to start/stop watchers and also change
		3891	the callback model to a model using method callbacks on objects.
		3892
		3893	To use it,
		3894
		3895	#include <ev++.h>
		3896
		3897	This automatically includes F<ev.h> and puts all of its definitions (many
		3898	of them macros) into the global namespace. All C++ specific things are
		3899	put into the C<ev> namespace. It should support all the same embedding
		3900	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3901
		3902	Care has been taken to keep the overhead low. The only data member the C++
		3903	classes add (compared to plain C-style watchers) is the event loop pointer
		3904	that the watcher is associated with (or no additional members at all if
		3905	you disable C<EV_MULTIPLICITY> when embedding libev).
		3906
		3907	Currently, functions, static and non-static member functions and classes
		3908	with C<operator ()> can be used as callbacks. Other types should be easy
		3909	to add as long as they only need one additional pointer for context. If
		3910	you need support for other types of functors please contact the author
		3911	(preferably after implementing it).
		3912
		3913	Here is a list of things available in the C<ev> namespace:
		3914
		3915	=over 4
		3916
		3917	=item C<ev::READ>, C<ev::WRITE> etc.
		3918
		3919	These are just enum values with the same values as the C<EV_READ> etc.
		3920	macros from F<ev.h>.
		3921
		3922	=item C<ev::tstamp>, C<ev::now>
		3923
		3924	Aliases to the same types/functions as with the C<ev_> prefix.
		3925
		3926	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		3927
		3928	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		3929	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		3930	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3931	defines by many implementations.
		3932
		3933	All of those classes have these methods:
		3934
		3935	=over 4
		3936
		3937	=item ev::TYPE::TYPE ()
		3938
		3939	=item ev::TYPE::TYPE (loop)
		3940
		3941	=item ev::TYPE::~TYPE
		3942
		3943	The constructor (optionally) takes an event loop to associate the watcher
		3944	with. If it is omitted, it will use C<EV_DEFAULT>.
		3945
		3946	The constructor calls C<ev_init> for you, which means you have to call the
		3947	C<set> method before starting it.
		3948
		3949	It will not set a callback, however: You have to call the templated C<set>
		3950	method to set a callback before you can start the watcher.
		3951
		3952	(The reason why you have to use a method is a limitation in C++ which does
		3953	not allow explicit template arguments for constructors).
		3954
		3955	The destructor automatically stops the watcher if it is active.
		3956
		3957	=item w->set<class, &class::method> (object *)
		3958
		3959	This method sets the callback method to call. The method has to have a
		3960	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3961	first argument and the C<revents> as second. The object must be given as
		3962	parameter and is stored in the C<data> member of the watcher.
		3963
		3964	This method synthesizes efficient thunking code to call your method from
		3965	the C callback that libev requires. If your compiler can inline your
		3966	callback (i.e. it is visible to it at the place of the C<set> call and
		3967	your compiler is good :), then the method will be fully inlined into the
		3968	thunking function, making it as fast as a direct C callback.
		3969
		3970	Example: simple class declaration and watcher initialisation
		3971
		3972	struct myclass
		3973	{
		3974	void io_cb (ev::io &w, int revents) { }
		3975	}
		3976
		3977	myclass obj;
		3978	ev::io iow;
		3979	iow.set <myclass, &myclass::io_cb> (&obj);
		3980
		3981	=item w->set (object *)
		3982
		3983	This is a variation of a method callback - leaving out the method to call
		3984	will default the method to C<operator ()>, which makes it possible to use
		3985	functor objects without having to manually specify the C<operator ()> all
		3986	the time. Incidentally, you can then also leave out the template argument
		3987	list.
		3988
		3989	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3990	int revents)>.
		3991
		3992	See the method-C<set> above for more details.
		3993
		3994	Example: use a functor object as callback.
		3995
		3996	struct myfunctor
		3997	{
		3998	void operator() (ev::io &w, int revents)
		3999	{
		4000	...
		4001	}
		4002	}
		4003
		4004	myfunctor f;
		4005
		4006	ev::io w;
		4007	w.set (&f);
		4008
		4009	=item w->set<function> (void *data = 0)
		4010
		4011	Also sets a callback, but uses a static method or plain function as
		4012	callback. The optional C<data> argument will be stored in the watcher's
		4013	C<data> member and is free for you to use.
		4014
		4015	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		4016
		4017	See the method-C<set> above for more details.
		4018
		4019	Example: Use a plain function as callback.
		4020
		4021	static void io_cb (ev::io &w, int revents) { }
		4022	iow.set <io_cb> ();
		4023
		4024	=item w->set (loop)
		4025
		4026	Associates a different C<struct ev_loop> with this watcher. You can only
		4027	do this when the watcher is inactive (and not pending either).
		4028
		4029	=item w->set ([arguments])
		4030
		4031	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
		4032	method or a suitable start method must be called at least once. Unlike the
		4033	C counterpart, an active watcher gets automatically stopped and restarted
		4034	when reconfiguring it with this method.
		4035
		4036	=item w->start ()
		4037
		4038	Starts the watcher. Note that there is no C<loop> argument, as the
		4039	constructor already stores the event loop.
		4040
		4041	=item w->start ([arguments])
		4042
		4043	Instead of calling C<set> and C<start> methods separately, it is often
		4044	convenient to wrap them in one call. Uses the same type of arguments as
		4045	the configure C<set> method of the watcher.
		4046
		4047	=item w->stop ()
		4048
		4049	Stops the watcher if it is active. Again, no C<loop> argument.
		4050
		4051	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		4052
		4053	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		4054	C<ev_TYPE_again> function.
		4055
		4056	=item w->sweep () (C<ev::embed> only)
		4057
		4058	Invokes C<ev_embed_sweep>.
		4059
		4060	=item w->update () (C<ev::stat> only)
		4061
		4062	Invokes C<ev_stat_stat>.
		4063
		4064	=back
		4065
		4066	=back
		4067
		4068	Example: Define a class with two I/O and idle watchers, start the I/O
		4069	watchers in the constructor.
		4070
		4071	class myclass
		4072	{
		4073	ev::io io ; void io_cb (ev::io &w, int revents);
		4074	ev::io io2 ; void io2_cb (ev::io &w, int revents);
		4075	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		4076
		4077	myclass (int fd)
		4078	{
		4079	io .set <myclass, &myclass::io_cb > (this);
		4080	io2 .set <myclass, &myclass::io2_cb > (this);
		4081	idle.set <myclass, &myclass::idle_cb> (this);
		4082
		4083	io.set (fd, ev::WRITE); // configure the watcher
		4084	io.start (); // start it whenever convenient
		4085
		4086	io2.start (fd, ev::READ); // set + start in one call
		4087	}
		4088	};
		4089
		4090
		4091	=head1 OTHER LANGUAGE BINDINGS
		4092
		4093	Libev does not offer other language bindings itself, but bindings for a
		4094	number of languages exist in the form of third-party packages. If you know
		4095	any interesting language binding in addition to the ones listed here, drop
		4096	me a note.
		4097
		4098	=over 4
		4099
		4100	=item Perl
		4101
		4102	The EV module implements the full libev API and is actually used to test
		4103	libev. EV is developed together with libev. Apart from the EV core module,
		4104	there are additional modules that implement libev-compatible interfaces
		4105	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4106	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4107	and C<EV::Glib>).
		4108
		4109	It can be found and installed via CPAN, its homepage is at
		4110	L<http://software.schmorp.de/pkg/EV>.
		4111
		4112	=item Python
		4113
		4114	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4115	seems to be quite complete and well-documented.
		4116
		4117	=item Ruby
		4118
		4119	Tony Arcieri has written a ruby extension that offers access to a subset
		4120	of the libev API and adds file handle abstractions, asynchronous DNS and
		4121	more on top of it. It can be found via gem servers. Its homepage is at
		4122	L<http://rev.rubyforge.org/>.
		4123
		4124	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4125	makes rev work even on mingw.
		4126
		4127	=item Haskell
		4128
		4129	A haskell binding to libev is available at
		4130	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4131
		4132	=item D
		4133
		4134	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4135	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4136
		4137	=item Ocaml
		4138
		4139	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4140	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4141
		4142	=item Lua
		4143
		4144	Brian Maher has written a partial interface to libev for lua (at the
		4145	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4146	L<http://github.com/brimworks/lua-ev>.
		4147
		4148	=back
		4149
		4150
		4151	=head1 MACRO MAGIC
		4152
		4153	Libev can be compiled with a variety of options, the most fundamental
		4154	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		4155	functions and callbacks have an initial C<struct ev_loop *> argument.
		4156
		4157	To make it easier to write programs that cope with either variant, the
		4158	following macros are defined:
		4159
		4160	=over 4
		4161
		4162	=item C<EV_A>, C<EV_A_>
		4163
		4164	This provides the loop I<argument> for functions, if one is required ("ev
		4165	loop argument"). The C<EV_A> form is used when this is the sole argument,
		4166	C<EV_A_> is used when other arguments are following. Example:
		4167
		4168	ev_unref (EV_A);
		4169	ev_timer_add (EV_A_ watcher);
		4170	ev_run (EV_A_ 0);
		4171
		4172	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		4173	which is often provided by the following macro.
		4174
		4175	=item C<EV_P>, C<EV_P_>
		4176
		4177	This provides the loop I<parameter> for functions, if one is required ("ev
		4178	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		4179	C<EV_P_> is used when other parameters are following. Example:
		4180
		4181	// this is how ev_unref is being declared
		4182	static void ev_unref (EV_P);
		4183
		4184	// this is how you can declare your typical callback
		4185	static void cb (EV_P_ ev_timer *w, int revents)
		4186
		4187	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		4188	suitable for use with C<EV_A>.
		4189
		4190	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		4191
		4192	Similar to the other two macros, this gives you the value of the default
		4193	loop, if multiple loops are supported ("ev loop default"). The default loop
		4194	will be initialised if it isn't already initialised.
		4195
		4196	For non-multiplicity builds, these macros do nothing, so you always have
		4197	to initialise the loop somewhere.
		4198
		4199	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4200
		4201	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4202	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4203	is undefined when the default loop has not been initialised by a previous
		4204	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4205
		4206	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4207	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		4208
		4209	=back
		4210
		4211	Example: Declare and initialise a check watcher, utilising the above
		4212	macros so it will work regardless of whether multiple loops are supported
		4213	or not.
		4214
		4215	static void
		4216	check_cb (EV_P_ ev_timer *w, int revents)
		4217	{
		4218	ev_check_stop (EV_A_ w);
		4219	}
		4220
		4221	ev_check check;
		4222	ev_check_init (&check, check_cb);
		4223	ev_check_start (EV_DEFAULT_ &check);
		4224	ev_run (EV_DEFAULT_ 0);
		4225
		4226	=head1 EMBEDDING
		4227
		4228	Libev can (and often is) directly embedded into host
		4229	applications. Examples of applications that embed it include the Deliantra
		4230	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		4231	and rxvt-unicode.
		4232
		4233	The goal is to enable you to just copy the necessary files into your
		4234	source directory without having to change even a single line in them, so
		4235	you can easily upgrade by simply copying (or having a checked-out copy of
		4236	libev somewhere in your source tree).
		4237
		4238	=head2 FILESETS
		4239
		4240	Depending on what features you need you need to include one or more sets of files
		4241	in your application.
		4242
		4243	=head3 CORE EVENT LOOP
		4244
		4245	To include only the libev core (all the C<ev_*> functions), with manual
		4246	configuration (no autoconf):
		4247
		4248	#define EV_STANDALONE 1
		4249	#include "ev.c"
		4250
		4251	This will automatically include F<ev.h>, too, and should be done in a
		4252	single C source file only to provide the function implementations. To use
		4253	it, do the same for F<ev.h> in all files wishing to use this API (best
		4254	done by writing a wrapper around F<ev.h> that you can include instead and
		4255	where you can put other configuration options):
		4256
		4257	#define EV_STANDALONE 1
		4258	#include "ev.h"
		4259
		4260	Both header files and implementation files can be compiled with a C++
		4261	compiler (at least, that's a stated goal, and breakage will be treated
		4262	as a bug).
		4263
		4264	You need the following files in your source tree, or in a directory
		4265	in your include path (e.g. in libev/ when using -Ilibev):
		4266
		4267	ev.h
		4268	ev.c
		4269	ev_vars.h
		4270	ev_wrap.h
		4271
		4272	ev_win32.c required on win32 platforms only
		4273
		4274	ev_select.c only when select backend is enabled (which is enabled by default)
		4275	ev_poll.c only when poll backend is enabled (disabled by default)
		4276	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		4277	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		4278	ev_port.c only when the solaris port backend is enabled (disabled by default)
		4279
		4280	F<ev.c> includes the backend files directly when enabled, so you only need
		4281	to compile this single file.
		4282
		4283	=head3 LIBEVENT COMPATIBILITY API
		4284
		4285	To include the libevent compatibility API, also include:
		4286
		4287	#include "event.c"
		4288
		4289	in the file including F<ev.c>, and:
		4290
		4291	#include "event.h"
		4292
		4293	in the files that want to use the libevent API. This also includes F<ev.h>.
		4294
		4295	You need the following additional files for this:
		4296
		4297	event.h
		4298	event.c
		4299
		4300	=head3 AUTOCONF SUPPORT
		4301
		4302	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		4303	whatever way you want, you can also C<m4_include([libev.m4])> in your
		4304	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		4305	include F<config.h> and configure itself accordingly.
		4306
		4307	For this of course you need the m4 file:
		4308
		4309	libev.m4
		4310
		4311	=head2 PREPROCESSOR SYMBOLS/MACROS
		4312
		4313	Libev can be configured via a variety of preprocessor symbols you have to
		4314	define before including (or compiling) any of its files. The default in
		4315	the absence of autoconf is documented for every option.
		4316
		4317	Symbols marked with "(h)" do not change the ABI, and can have different
		4318	values when compiling libev vs. including F<ev.h>, so it is permissible
		4319	to redefine them before including F<ev.h> without breaking compatibility
		4320	to a compiled library. All other symbols change the ABI, which means all
		4321	users of libev and the libev code itself must be compiled with compatible
		4322	settings.
		4323
		4324	=over 4
		4325
		4326	=item EV_COMPAT3 (h)
		4327
		4328	Backwards compatibility is a major concern for libev. This is why this
		4329	release of libev comes with wrappers for the functions and symbols that
		4330	have been renamed between libev version 3 and 4.
		4331
		4332	You can disable these wrappers (to test compatibility with future
		4333	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4334	sources. This has the additional advantage that you can drop the C<struct>
		4335	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4336	typedef in that case.
		4337
		4338	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4339	and in some even more future version the compatibility code will be
		4340	removed completely.
		4341
		4342	=item EV_STANDALONE (h)
		4343
		4344	Must always be C<1> if you do not use autoconf configuration, which
		4345	keeps libev from including F<config.h>, and it also defines dummy
		4346	implementations for some libevent functions (such as logging, which is not
		4347	supported). It will also not define any of the structs usually found in
		4348	F<event.h> that are not directly supported by the libev core alone.
		4349
		4350	In standalone mode, libev will still try to automatically deduce the
		4351	configuration, but has to be more conservative.
		4352
		4353	=item EV_USE_FLOOR
		4354
		4355	If defined to be C<1>, libev will use the C<floor ()> function for its
		4356	periodic reschedule calculations, otherwise libev will fall back on a
		4357	portable (slower) implementation. If you enable this, you usually have to
		4358	link against libm or something equivalent. Enabling this when the C<floor>
		4359	function is not available will fail, so the safe default is to not enable
		4360	this.
		4361
		4362	=item EV_USE_MONOTONIC
		4363
		4364	If defined to be C<1>, libev will try to detect the availability of the
		4365	monotonic clock option at both compile time and runtime. Otherwise no
		4366	use of the monotonic clock option will be attempted. If you enable this,
		4367	you usually have to link against librt or something similar. Enabling it
		4368	when the functionality isn't available is safe, though, although you have
		4369	to make sure you link against any libraries where the C<clock_gettime>
		4370	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		4371
		4372	=item EV_USE_REALTIME
		4373
		4374	If defined to be C<1>, libev will try to detect the availability of the
		4375	real-time clock option at compile time (and assume its availability
		4376	at runtime if successful). Otherwise no use of the real-time clock
		4377	option will be attempted. This effectively replaces C<gettimeofday>
		4378	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		4379	correctness. See the note about libraries in the description of
		4380	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4381	C<EV_USE_CLOCK_SYSCALL>.
		4382
		4383	=item EV_USE_CLOCK_SYSCALL
		4384
		4385	If defined to be C<1>, libev will try to use a direct syscall instead
		4386	of calling the system-provided C<clock_gettime> function. This option
		4387	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4388	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4389	programs needlessly. Using a direct syscall is slightly slower (in
		4390	theory), because no optimised vdso implementation can be used, but avoids
		4391	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4392	higher, as it simplifies linking (no need for C<-lrt>).
		4393
		4394	=item EV_USE_NANOSLEEP
		4395
		4396	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4397	and will use it for delays. Otherwise it will use C<select ()>.
		4398
		4399	=item EV_USE_EVENTFD
		4400
		4401	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4402	available and will probe for kernel support at runtime. This will improve
		4403	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4404	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4405	2.7 or newer, otherwise disabled.
		4406
		4407	=item EV_USE_SELECT
		4408
		4409	If undefined or defined to be C<1>, libev will compile in support for the
		4410	C<select>(2) backend. No attempt at auto-detection will be done: if no
		4411	other method takes over, select will be it. Otherwise the select backend
		4412	will not be compiled in.
		4413
		4414	=item EV_SELECT_USE_FD_SET
		4415
		4416	If defined to C<1>, then the select backend will use the system C<fd_set>
		4417	structure. This is useful if libev doesn't compile due to a missing
		4418	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		4419	on exotic systems. This usually limits the range of file descriptors to
		4420	some low limit such as 1024 or might have other limitations (winsocket
		4421	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		4422	configures the maximum size of the C<fd_set>.
		4423
		4424	=item EV_SELECT_IS_WINSOCKET
		4425
		4426	When defined to C<1>, the select backend will assume that
		4427	select/socket/connect etc. don't understand file descriptors but
		4428	wants osf handles on win32 (this is the case when the select to
		4429	be used is the winsock select). This means that it will call
		4430	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		4431	it is assumed that all these functions actually work on fds, even
		4432	on win32. Should not be defined on non-win32 platforms.
		4433
		4434	=item EV_FD_TO_WIN32_HANDLE(fd)
		4435
		4436	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4437	file descriptors to socket handles. When not defining this symbol (the
		4438	default), then libev will call C<_get_osfhandle>, which is usually
		4439	correct. In some cases, programs use their own file descriptor management,
		4440	in which case they can provide this function to map fds to socket handles.
		4441
		4442	=item EV_WIN32_HANDLE_TO_FD(handle)
		4443
		4444	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4445	using the standard C<_open_osfhandle> function. For programs implementing
		4446	their own fd to handle mapping, overwriting this function makes it easier
		4447	to do so. This can be done by defining this macro to an appropriate value.
		4448
		4449	=item EV_WIN32_CLOSE_FD(fd)
		4450
		4451	If programs implement their own fd to handle mapping on win32, then this
		4452	macro can be used to override the C<close> function, useful to unregister
		4453	file descriptors again. Note that the replacement function has to close
		4454	the underlying OS handle.
		4455
		4456	=item EV_USE_POLL
		4457
		4458	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		4459	backend. Otherwise it will be enabled on non-win32 platforms. It
		4460	takes precedence over select.
		4461
		4462	=item EV_USE_EPOLL
		4463
		4464	If defined to be C<1>, libev will compile in support for the Linux
		4465	C<epoll>(7) backend. Its availability will be detected at runtime,
		4466	otherwise another method will be used as fallback. This is the preferred
		4467	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4468	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4469
		4470	=item EV_USE_KQUEUE
		4471
		4472	If defined to be C<1>, libev will compile in support for the BSD style
		4473	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		4474	otherwise another method will be used as fallback. This is the preferred
		4475	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		4476	supports some types of fds correctly (the only platform we found that
		4477	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		4478	not be used unless explicitly requested. The best way to use it is to find
		4479	out whether kqueue supports your type of fd properly and use an embedded
		4480	kqueue loop.
		4481
		4482	=item EV_USE_PORT
		4483
		4484	If defined to be C<1>, libev will compile in support for the Solaris
		4485	10 port style backend. Its availability will be detected at runtime,
		4486	otherwise another method will be used as fallback. This is the preferred
		4487	backend for Solaris 10 systems.
		4488
		4489	=item EV_USE_DEVPOLL
		4490
		4491	Reserved for future expansion, works like the USE symbols above.
		4492
		4493	=item EV_USE_INOTIFY
		4494
		4495	If defined to be C<1>, libev will compile in support for the Linux inotify
		4496	interface to speed up C<ev_stat> watchers. Its actual availability will
		4497	be detected at runtime. If undefined, it will be enabled if the headers
		4498	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4499
		4500	=item EV_ATOMIC_T
		4501
		4502	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4503	access is atomic and serialised with respect to other threads or signal
		4504	contexts. No such type is easily found in the C language, so you can
		4505	provide your own type that you know is safe for your purposes. It is used
		4506	both for signal handler "locking" as well as for signal and thread safety
		4507	in C<ev_async> watchers.
		4508
		4509	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4510	(from F<signal.h>), which is usually good enough on most platforms,
		4511	although strictly speaking using a type that also implies a memory fence
		4512	is required.
		4513
		4514	=item EV_H (h)
		4515
		4516	The name of the F<ev.h> header file used to include it. The default if
		4517	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		4518	used to virtually rename the F<ev.h> header file in case of conflicts.
		4519
		4520	=item EV_CONFIG_H (h)
		4521
		4522	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		4523	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		4524	C<EV_H>, above.
		4525
		4526	=item EV_EVENT_H (h)
		4527
		4528	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		4529	of how the F<event.h> header can be found, the default is C<"event.h">.
		4530
		4531	=item EV_PROTOTYPES (h)
		4532
		4533	If defined to be C<0>, then F<ev.h> will not define any function
		4534	prototypes, but still define all the structs and other symbols. This is
		4535	occasionally useful if you want to provide your own wrapper functions
		4536	around libev functions.
		4537
		4538	=item EV_MULTIPLICITY
		4539
		4540	If undefined or defined to C<1>, then all event-loop-specific functions
		4541	will have the C<struct ev_loop *> as first argument, and you can create
		4542	additional independent event loops. Otherwise there will be no support
		4543	for multiple event loops and there is no first event loop pointer
		4544	argument. Instead, all functions act on the single default loop.
		4545
		4546	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4547	default loop when multiplicity is switched off - you always have to
		4548	initialise the loop manually in this case.
		4549
		4550	=item EV_MINPRI
		4551
		4552	=item EV_MAXPRI
		4553
		4554	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4555	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4556	provide for more priorities by overriding those symbols (usually defined
		4557	to be C<-2> and C<2>, respectively).
		4558
		4559	When doing priority-based operations, libev usually has to linearly search
		4560	all the priorities, so having many of them (hundreds) uses a lot of space
		4561	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4562	fine.
		4563
		4564	If your embedding application does not need any priorities, defining these
		4565	both to C<0> will save some memory and CPU.
		4566
		4567	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4568	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4569	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4570
		4571	If undefined or defined to be C<1> (and the platform supports it), then
		4572	the respective watcher type is supported. If defined to be C<0>, then it
		4573	is not. Disabling watcher types mainly saves code size.
		4574
		4575	=item EV_FEATURES
		4576
		4577	If you need to shave off some kilobytes of code at the expense of some
		4578	speed (but with the full API), you can define this symbol to request
		4579	certain subsets of functionality. The default is to enable all features
		4580	that can be enabled on the platform.
		4581
		4582	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4583	with some broad features you want) and then selectively re-enable
		4584	additional parts you want, for example if you want everything minimal,
		4585	but multiple event loop support, async and child watchers and the poll
		4586	backend, use this:
		4587
		4588	#define EV_FEATURES 0
		4589	#define EV_MULTIPLICITY 1
		4590	#define EV_USE_POLL 1
		4591	#define EV_CHILD_ENABLE 1
		4592	#define EV_ASYNC_ENABLE 1
		4593
		4594	The actual value is a bitset, it can be a combination of the following
		4595	values:
		4596
		4597	=over 4
		4598
		4599	=item C<1> - faster/larger code
		4600
		4601	Use larger code to speed up some operations.
		4602
		4603	Currently this is used to override some inlining decisions (enlarging the
		4604	code size by roughly 30% on amd64).
		4605
		4606	When optimising for size, use of compiler flags such as C<-Os> with
		4607	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4608	assertions.
		4609
		4610	=item C<2> - faster/larger data structures
		4611
		4612	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4613	hash table sizes and so on. This will usually further increase code size
		4614	and can additionally have an effect on the size of data structures at
		4615	runtime.
		4616
		4617	=item C<4> - full API configuration
		4618
		4619	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4620	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4621
		4622	=item C<8> - full API
		4623
		4624	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4625	details on which parts of the API are still available without this
		4626	feature, and do not complain if this subset changes over time.
		4627
		4628	=item C<16> - enable all optional watcher types
		4629
		4630	Enables all optional watcher types. If you want to selectively enable
		4631	only some watcher types other than I/O and timers (e.g. prepare,
		4632	embed, async, child...) you can enable them manually by defining
		4633	C<EV_watchertype_ENABLE> to C<1> instead.
		4634
		4635	=item C<32> - enable all backends
		4636
		4637	This enables all backends - without this feature, you need to enable at
		4638	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4639
		4640	=item C<64> - enable OS-specific "helper" APIs
		4641
		4642	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4643	default.
		4644
		4645	=back
		4646
		4647	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4648	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4649	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4650	watchers, timers and monotonic clock support.
		4651
		4652	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4653	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4654	your program might be left out as well - a binary starting a timer and an
		4655	I/O watcher then might come out at only 5Kb.
		4656
		4657	=item EV_API_STATIC
		4658
		4659	If this symbol is defined (by default it is not), then all identifiers
		4660	will have static linkage. This means that libev will not export any
		4661	identifiers, and you cannot link against libev anymore. This can be useful
		4662	when you embed libev, only want to use libev functions in a single file,
		4663	and do not want its identifiers to be visible.
		4664
		4665	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4666	wants to use libev.
		4667
		4668	=item EV_AVOID_STDIO
		4669
		4670	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4671	functions (printf, scanf, perror etc.). This will increase the code size
		4672	somewhat, but if your program doesn't otherwise depend on stdio and your
		4673	libc allows it, this avoids linking in the stdio library which is quite
		4674	big.
		4675
		4676	Note that error messages might become less precise when this option is
		4677	enabled.
		4678
		4679	=item EV_NSIG
		4680
		4681	The highest supported signal number, +1 (or, the number of
		4682	signals): Normally, libev tries to deduce the maximum number of signals
		4683	automatically, but sometimes this fails, in which case it can be
		4684	specified. Also, using a lower number than detected (C<32> should be
		4685	good for about any system in existence) can save some memory, as libev
		4686	statically allocates some 12-24 bytes per signal number.
		4687
		4688	=item EV_PID_HASHSIZE
		4689
		4690	C<ev_child> watchers use a small hash table to distribute workload by
		4691	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4692	usually more than enough. If you need to manage thousands of children you
		4693	might want to increase this value (I<must> be a power of two).
		4694
		4695	=item EV_INOTIFY_HASHSIZE
		4696
		4697	C<ev_stat> watchers use a small hash table to distribute workload by
		4698	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4699	disabled), usually more than enough. If you need to manage thousands of
		4700	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4701	power of two).
		4702
		4703	=item EV_USE_4HEAP
		4704
		4705	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4706	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4707	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4708	faster performance with many (thousands) of watchers.
		4709
		4710	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4711	will be C<0>.
		4712
		4713	=item EV_HEAP_CACHE_AT
		4714
		4715	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4716	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4717	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4718	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4719	but avoids random read accesses on heap changes. This improves performance
		4720	noticeably with many (hundreds) of watchers.
		4721
		4722	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4723	will be C<0>.
		4724
		4725	=item EV_VERIFY
		4726
		4727	Controls how much internal verification (see C<ev_verify ()>) will
		4728	be done: If set to C<0>, no internal verification code will be compiled
		4729	in. If set to C<1>, then verification code will be compiled in, but not
		4730	called. If set to C<2>, then the internal verification code will be
		4731	called once per loop, which can slow down libev. If set to C<3>, then the
		4732	verification code will be called very frequently, which will slow down
		4733	libev considerably.
		4734
		4735	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4736	will be C<0>.
		4737
		4738	=item EV_COMMON
		4739
		4740	By default, all watchers have a C<void *data> member. By redefining
		4741	this macro to something else you can include more and other types of
		4742	members. You have to define it each time you include one of the files,
		4743	though, and it must be identical each time.
		4744
		4745	For example, the perl EV module uses something like this:
		4746
		4747	#define EV_COMMON \
		4748	SV *self; /* contains this struct */ \
		4749	SV *cb_sv, *fh /* note no trailing ";" */
		4750
		4751	=item EV_CB_DECLARE (type)
		4752
		4753	=item EV_CB_INVOKE (watcher, revents)
		4754
		4755	=item ev_set_cb (ev, cb)
		4756
		4757	Can be used to change the callback member declaration in each watcher,
		4758	and the way callbacks are invoked and set. Must expand to a struct member
		4759	definition and a statement, respectively. See the F<ev.h> header file for
		4760	their default definitions. One possible use for overriding these is to
		4761	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		4762	method calls instead of plain function calls in C++.
		4763
		4764	=back
		4765
		4766	=head2 EXPORTED API SYMBOLS
		4767
		4768	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4769	exported symbols, you can use the provided F<Symbol.*> files which list
		4770	all public symbols, one per line:
		4771
		4772	Symbols.ev for libev proper
		4773	Symbols.event for the libevent emulation
		4774
		4775	This can also be used to rename all public symbols to avoid clashes with
		4776	multiple versions of libev linked together (which is obviously bad in
		4777	itself, but sometimes it is inconvenient to avoid this).
		4778
		4779	A sed command like this will create wrapper C<#define>'s that you need to
		4780	include before including F<ev.h>:
		4781
		4782	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4783
		4784	This would create a file F<wrap.h> which essentially looks like this:
		4785
		4786	#define ev_backend myprefix_ev_backend
		4787	#define ev_check_start myprefix_ev_check_start
		4788	#define ev_check_stop myprefix_ev_check_stop
		4789	...
		4790
		4791	=head2 EXAMPLES
		4792
		4793	For a real-world example of a program the includes libev
		4794	verbatim, you can have a look at the EV perl module
		4795	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		4796	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		4797	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		4798	will be compiled. It is pretty complex because it provides its own header
		4799	file.
		4800
		4801	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		4802	that everybody includes and which overrides some configure choices:
		4803
		4804	#define EV_FEATURES 8
		4805	#define EV_USE_SELECT 1
		4806	#define EV_PREPARE_ENABLE 1
		4807	#define EV_IDLE_ENABLE 1
		4808	#define EV_SIGNAL_ENABLE 1
		4809	#define EV_CHILD_ENABLE 1
		4810	#define EV_USE_STDEXCEPT 0
		4811	#define EV_CONFIG_H <config.h>
		4812
		4813	#include "ev++.h"
		4814
		4815	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		4816
		4817	#include "ev_cpp.h"
		4818	#include "ev.c"
		4819
		4820	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
		4821
		4822	=head2 THREADS AND COROUTINES
		4823
		4824	=head3 THREADS
		4825
		4826	All libev functions are reentrant and thread-safe unless explicitly
		4827	documented otherwise, but libev implements no locking itself. This means
		4828	that you can use as many loops as you want in parallel, as long as there
		4829	are no concurrent calls into any libev function with the same loop
		4830	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4831	of course): libev guarantees that different event loops share no data
		4832	structures that need any locking.
		4833
		4834	Or to put it differently: calls with different loop parameters can be done
		4835	concurrently from multiple threads, calls with the same loop parameter
		4836	must be done serially (but can be done from different threads, as long as
		4837	only one thread ever is inside a call at any point in time, e.g. by using
		4838	a mutex per loop).
		4839
		4840	Specifically to support threads (and signal handlers), libev implements
		4841	so-called C<ev_async> watchers, which allow some limited form of
		4842	concurrency on the same event loop, namely waking it up "from the
		4843	outside".
		4844
		4845	If you want to know which design (one loop, locking, or multiple loops
		4846	without or something else still) is best for your problem, then I cannot
		4847	help you, but here is some generic advice:
		4848
		4849	=over 4
		4850
		4851	=item * most applications have a main thread: use the default libev loop
		4852	in that thread, or create a separate thread running only the default loop.
		4853
		4854	This helps integrating other libraries or software modules that use libev
		4855	themselves and don't care/know about threading.
		4856
		4857	=item * one loop per thread is usually a good model.
		4858
		4859	Doing this is almost never wrong, sometimes a better-performance model
		4860	exists, but it is always a good start.
		4861
		4862	=item * other models exist, such as the leader/follower pattern, where one
		4863	loop is handed through multiple threads in a kind of round-robin fashion.
		4864
		4865	Choosing a model is hard - look around, learn, know that usually you can do
		4866	better than you currently do :-)
		4867
		4868	=item * often you need to talk to some other thread which blocks in the
		4869	event loop.
		4870
		4871	C<ev_async> watchers can be used to wake them up from other threads safely
		4872	(or from signal contexts...).
		4873
		4874	An example use would be to communicate signals or other events that only
		4875	work in the default loop by registering the signal watcher with the
		4876	default loop and triggering an C<ev_async> watcher from the default loop
		4877	watcher callback into the event loop interested in the signal.
		4878
		4879	=back
		4880
		4881	See also L<THREAD LOCKING EXAMPLE>.
		4882
		4883	=head3 COROUTINES
		4884
		4885	Libev is very accommodating to coroutines ("cooperative threads"):
		4886	libev fully supports nesting calls to its functions from different
		4887	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4888	different coroutines, and switch freely between both coroutines running
		4889	the loop, as long as you don't confuse yourself). The only exception is
		4890	that you must not do this from C<ev_periodic> reschedule callbacks.
		4891
		4892	Care has been taken to ensure that libev does not keep local state inside
		4893	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4894	they do not call any callbacks.
		4895
		4896	=head2 COMPILER WARNINGS
		4897
		4898	Depending on your compiler and compiler settings, you might get no or a
		4899	lot of warnings when compiling libev code. Some people are apparently
		4900	scared by this.
		4901
		4902	However, these are unavoidable for many reasons. For one, each compiler
		4903	has different warnings, and each user has different tastes regarding
		4904	warning options. "Warn-free" code therefore cannot be a goal except when
		4905	targeting a specific compiler and compiler-version.
		4906
		4907	Another reason is that some compiler warnings require elaborate
		4908	workarounds, or other changes to the code that make it less clear and less
		4909	maintainable.
		4910
		4911	And of course, some compiler warnings are just plain stupid, or simply
		4912	wrong (because they don't actually warn about the condition their message
		4913	seems to warn about). For example, certain older gcc versions had some
		4914	warnings that resulted in an extreme number of false positives. These have
		4915	been fixed, but some people still insist on making code warn-free with
		4916	such buggy versions.
		4917
		4918	While libev is written to generate as few warnings as possible,
		4919	"warn-free" code is not a goal, and it is recommended not to build libev
		4920	with any compiler warnings enabled unless you are prepared to cope with
		4921	them (e.g. by ignoring them). Remember that warnings are just that:
		4922	warnings, not errors, or proof of bugs.
		4923
		4924
		4925	=head2 VALGRIND
		4926
		4927	Valgrind has a special section here because it is a popular tool that is
		4928	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4929
		4930	If you think you found a bug (memory leak, uninitialised data access etc.)
		4931	in libev, then check twice: If valgrind reports something like:
		4932
		4933	==2274== definitely lost: 0 bytes in 0 blocks.
		4934	==2274== possibly lost: 0 bytes in 0 blocks.
		4935	==2274== still reachable: 256 bytes in 1 blocks.
		4936
		4937	Then there is no memory leak, just as memory accounted to global variables
		4938	is not a memleak - the memory is still being referenced, and didn't leak.
		4939
		4940	Similarly, under some circumstances, valgrind might report kernel bugs
		4941	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4942	although an acceptable workaround has been found here), or it might be
		4943	confused.
		4944
		4945	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4946	make it into some kind of religion.
		4947
		4948	If you are unsure about something, feel free to contact the mailing list
		4949	with the full valgrind report and an explanation on why you think this
		4950	is a bug in libev (best check the archives, too :). However, don't be
		4951	annoyed when you get a brisk "this is no bug" answer and take the chance
		4952	of learning how to interpret valgrind properly.
		4953
		4954	If you need, for some reason, empty reports from valgrind for your project
		4955	I suggest using suppression lists.
		4956
		4957
		4958	=head1 PORTABILITY NOTES
		4959
		4960	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4961
		4962	GNU/Linux is the only common platform that supports 64 bit file/large file
		4963	interfaces but I<disables> them by default.
		4964
		4965	That means that libev compiled in the default environment doesn't support
		4966	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4967
		4968	Unfortunately, many programs try to work around this GNU/Linux issue
		4969	by enabling the large file API, which makes them incompatible with the
		4970	standard libev compiled for their system.
		4971
		4972	Likewise, libev cannot enable the large file API itself as this would
		4973	suddenly make it incompatible to the default compile time environment,
		4974	i.e. all programs not using special compile switches.
		4975
		4976	=head2 OS/X AND DARWIN BUGS
		4977
		4978	The whole thing is a bug if you ask me - basically any system interface
		4979	you touch is broken, whether it is locales, poll, kqueue or even the
		4980	OpenGL drivers.
		4981
		4982	=head3 C<kqueue> is buggy
		4983
		4984	The kqueue syscall is broken in all known versions - most versions support
		4985	only sockets, many support pipes.
		4986
		4987	Libev tries to work around this by not using C<kqueue> by default on this
		4988	rotten platform, but of course you can still ask for it when creating a
		4989	loop - embedding a socket-only kqueue loop into a select-based one is
		4990	probably going to work well.
		4991
		4992	=head3 C<poll> is buggy
		4993
		4994	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4995	implementation by something calling C<kqueue> internally around the 10.5.6
		4996	release, so now C<kqueue> I<and> C<poll> are broken.
		4997
		4998	Libev tries to work around this by not using C<poll> by default on
		4999	this rotten platform, but of course you can still ask for it when creating
		5000	a loop.
		5001
		5002	=head3 C<select> is buggy
		5003
		5004	All that's left is C<select>, and of course Apple found a way to fuck this
		5005	one up as well: On OS/X, C<select> actively limits the number of file
		5006	descriptors you can pass in to 1024 - your program suddenly crashes when
		5007	you use more.
		5008
		5009	There is an undocumented "workaround" for this - defining
		5010	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5011	work on OS/X.
		5012
		5013	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5014
		5015	=head3 C<errno> reentrancy
		5016
		5017	The default compile environment on Solaris is unfortunately so
		5018	thread-unsafe that you can't even use components/libraries compiled
		5019	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5020	defined by default. A valid, if stupid, implementation choice.
		5021
		5022	If you want to use libev in threaded environments you have to make sure
		5023	it's compiled with C<_REENTRANT> defined.
		5024
		5025	=head3 Event port backend
		5026
		5027	The scalable event interface for Solaris is called "event
		5028	ports". Unfortunately, this mechanism is very buggy in all major
		5029	releases. If you run into high CPU usage, your program freezes or you get
		5030	a large number of spurious wakeups, make sure you have all the relevant
		5031	and latest kernel patches applied. No, I don't know which ones, but there
		5032	are multiple ones to apply, and afterwards, event ports actually work
		5033	great.
		5034
		5035	If you can't get it to work, you can try running the program by setting
		5036	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5037	C<select> backends.
		5038
		5039	=head2 AIX POLL BUG
		5040
		5041	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5042	this by trying to avoid the poll backend altogether (i.e. it's not even
		5043	compiled in), which normally isn't a big problem as C<select> works fine
		5044	with large bitsets on AIX, and AIX is dead anyway.
		5045
		5046	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5047
		5048	=head3 General issues
		5049
		5050	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5051	requires, and its I/O model is fundamentally incompatible with the POSIX
		5052	model. Libev still offers limited functionality on this platform in
		5053	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5054	descriptors. This only applies when using Win32 natively, not when using
		5055	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5056	as every compiler comes with a slightly differently broken/incompatible
		5057	environment.
		5058
		5059	Lifting these limitations would basically require the full
		5060	re-implementation of the I/O system. If you are into this kind of thing,
		5061	then note that glib does exactly that for you in a very portable way (note
		5062	also that glib is the slowest event library known to man).
		5063
		5064	There is no supported compilation method available on windows except
		5065	embedding it into other applications.
		5066
		5067	Sensible signal handling is officially unsupported by Microsoft - libev
		5068	tries its best, but under most conditions, signals will simply not work.
		5069
		5070	Not a libev limitation but worth mentioning: windows apparently doesn't
		5071	accept large writes: instead of resulting in a partial write, windows will
		5072	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5073	so make sure you only write small amounts into your sockets (less than a
		5074	megabyte seems safe, but this apparently depends on the amount of memory
		5075	available).
		5076
		5077	Due to the many, low, and arbitrary limits on the win32 platform and
		5078	the abysmal performance of winsockets, using a large number of sockets
		5079	is not recommended (and not reasonable). If your program needs to use
		5080	more than a hundred or so sockets, then likely it needs to use a totally
		5081	different implementation for windows, as libev offers the POSIX readiness
		5082	notification model, which cannot be implemented efficiently on windows
		5083	(due to Microsoft monopoly games).
		5084
		5085	A typical way to use libev under windows is to embed it (see the embedding
		5086	section for details) and use the following F<evwrap.h> header file instead
		5087	of F<ev.h>:
		5088
		5089	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5090	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5091
		5092	#include "ev.h"
		5093
		5094	And compile the following F<evwrap.c> file into your project (make sure
		5095	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5096
		5097	#include "evwrap.h"
		5098	#include "ev.c"
		5099
		5100	=head3 The winsocket C<select> function
		5101
		5102	The winsocket C<select> function doesn't follow POSIX in that it
		5103	requires socket I<handles> and not socket I<file descriptors> (it is
		5104	also extremely buggy). This makes select very inefficient, and also
		5105	requires a mapping from file descriptors to socket handles (the Microsoft
		5106	C runtime provides the function C<_open_osfhandle> for this). See the
		5107	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5108	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5109
		5110	The configuration for a "naked" win32 using the Microsoft runtime
		5111	libraries and raw winsocket select is:
		5112
		5113	#define EV_USE_SELECT 1
		5114	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5115
		5116	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5117	complexity in the O(n²) range when using win32.
		5118
		5119	=head3 Limited number of file descriptors
		5120
		5121	Windows has numerous arbitrary (and low) limits on things.
		5122
		5123	Early versions of winsocket's select only supported waiting for a maximum
		5124	of C<64> handles (probably owning to the fact that all windows kernels
		5125	can only wait for C<64> things at the same time internally; Microsoft
		5126	recommends spawning a chain of threads and wait for 63 handles and the
		5127	previous thread in each. Sounds great!).
		5128
		5129	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5130	to some high number (e.g. C<2048>) before compiling the winsocket select
		5131	call (which might be in libev or elsewhere, for example, perl and many
		5132	other interpreters do their own select emulation on windows).
		5133
		5134	Another limit is the number of file descriptors in the Microsoft runtime
		5135	libraries, which by default is C<64> (there must be a hidden I<64>
		5136	fetish or something like this inside Microsoft). You can increase this
		5137	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5138	(another arbitrary limit), but is broken in many versions of the Microsoft
		5139	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5140	(depending on windows version and/or the phase of the moon). To get more,
		5141	you need to wrap all I/O functions and provide your own fd management, but
		5142	the cost of calling select (O(n²)) will likely make this unworkable.
		5143
		5144	=head2 PORTABILITY REQUIREMENTS
		5145
		5146	In addition to a working ISO-C implementation and of course the
		5147	backend-specific APIs, libev relies on a few additional extensions:
		5148
		5149	=over 4
		5150
		5151	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5152	calling conventions regardless of C<ev_watcher_type *>.
		5153
		5154	Libev assumes not only that all watcher pointers have the same internal
		5155	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5156	assumes that the same (machine) code can be used to call any watcher
		5157	callback: The watcher callbacks have different type signatures, but libev
		5158	calls them using an C<ev_watcher *> internally.
		5159
		5160	=item pointer accesses must be thread-atomic
		5161
		5162	Accessing a pointer value must be atomic, it must both be readable and
		5163	writable in one piece - this is the case on all current architectures.
		5164
		5165	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5166
		5167	The type C<sig_atomic_t volatile> (or whatever is defined as
		5168	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5169	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5170	believed to be sufficiently portable.
		5171
		5172	=item C<sigprocmask> must work in a threaded environment
		5173
		5174	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5175	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5176	pthread implementations will either allow C<sigprocmask> in the "main
		5177	thread" or will block signals process-wide, both behaviours would
		5178	be compatible with libev. Interaction between C<sigprocmask> and
		5179	C<pthread_sigmask> could complicate things, however.
		5180
		5181	The most portable way to handle signals is to block signals in all threads
		5182	except the initial one, and run the default loop in the initial thread as
		5183	well.
		5184
		5185	=item C<long> must be large enough for common memory allocation sizes
		5186
		5187	To improve portability and simplify its API, libev uses C<long> internally
		5188	instead of C<size_t> when allocating its data structures. On non-POSIX
		5189	systems (Microsoft...) this might be unexpectedly low, but is still at
		5190	least 31 bits everywhere, which is enough for hundreds of millions of
		5191	watchers.
		5192
		5193	=item C<double> must hold a time value in seconds with enough accuracy
		5194
		5195	The type C<double> is used to represent timestamps. It is required to
		5196	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5197	good enough for at least into the year 4000 with millisecond accuracy
		5198	(the design goal for libev). This requirement is overfulfilled by
		5199	implementations using IEEE 754, which is basically all existing ones.
		5200
		5201	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5202	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5203	is either obsolete or somebody patched it to use C<long double> or
		5204	something like that, just kidding).
		5205
		5206	=back
		5207
		5208	If you know of other additional requirements drop me a note.
		5209
		5210
		5211	=head1 ALGORITHMIC COMPLEXITIES
		5212
		5213	In this section the complexities of (many of) the algorithms used inside
		5214	libev will be documented. For complexity discussions about backends see
		5215	the documentation for C<ev_default_init>.
		5216
		5217	All of the following are about amortised time: If an array needs to be
		5218	extended, libev needs to realloc and move the whole array, but this
		5219	happens asymptotically rarer with higher number of elements, so O(1) might
		5220	mean that libev does a lengthy realloc operation in rare cases, but on
		5221	average it is much faster and asymptotically approaches constant time.
		5222
		5223	=over 4
		5224
		5225	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5226
		5227	This means that, when you have a watcher that triggers in one hour and
		5228	there are 100 watchers that would trigger before that, then inserting will
		5229	have to skip roughly seven (C<ld 100>) of these watchers.
		5230
		5231	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5232
		5233	That means that changing a timer costs less than removing/adding them,
		5234	as only the relative motion in the event queue has to be paid for.
		5235
		5236	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5237
		5238	These just add the watcher into an array or at the head of a list.
		5239
		5240	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5241
		5242	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5243
		5244	These watchers are stored in lists, so they need to be walked to find the
		5245	correct watcher to remove. The lists are usually short (you don't usually
		5246	have many watchers waiting for the same fd or signal: one is typical, two
		5247	is rare).
		5248
		5249	=item Finding the next timer in each loop iteration: O(1)
		5250
		5251	By virtue of using a binary or 4-heap, the next timer is always found at a
		5252	fixed position in the storage array.
		5253
		5254	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5255
		5256	A change means an I/O watcher gets started or stopped, which requires
		5257	libev to recalculate its status (and possibly tell the kernel, depending
		5258	on backend and whether C<ev_io_set> was used).
		5259
		5260	=item Activating one watcher (putting it into the pending state): O(1)
		5261
		5262	=item Priority handling: O(number_of_priorities)
		5263
		5264	Priorities are implemented by allocating some space for each
		5265	priority. When doing priority-based operations, libev usually has to
		5266	linearly search all the priorities, but starting/stopping and activating
		5267	watchers becomes O(1) with respect to priority handling.
		5268
		5269	=item Sending an ev_async: O(1)
		5270
		5271	=item Processing ev_async_send: O(number_of_async_watchers)
		5272
		5273	=item Processing signals: O(max_signal_number)
		5274
		5275	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5276	calls in the current loop iteration and the loop is currently
		5277	blocked. Checking for async and signal events involves iterating over all
		5278	running async watchers or all signal numbers.
		5279
		5280	=back
		5281
		5282
		5283	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5284
		5285	The major version 4 introduced some incompatible changes to the API.
		5286
		5287	At the moment, the C<ev.h> header file provides compatibility definitions
		5288	for all changes, so most programs should still compile. The compatibility
		5289	layer might be removed in later versions of libev, so better update to the
		5290	new API early than late.
		5291
		5292	=over 4
		5293
		5294	=item C<EV_COMPAT3> backwards compatibility mechanism
		5295
		5296	The backward compatibility mechanism can be controlled by
		5297	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5298	section.
		5299
		5300	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5301
		5302	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5303
		5304	ev_loop_destroy (EV_DEFAULT_UC);
		5305	ev_loop_fork (EV_DEFAULT);
		5306
		5307	=item function/symbol renames
		5308
		5309	A number of functions and symbols have been renamed:
		5310
		5311	ev_loop => ev_run
		5312	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5313	EVLOOP_ONESHOT => EVRUN_ONCE
		5314
		5315	ev_unloop => ev_break
		5316	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5317	EVUNLOOP_ONE => EVBREAK_ONE
		5318	EVUNLOOP_ALL => EVBREAK_ALL
		5319
		5320	EV_TIMEOUT => EV_TIMER
		5321
		5322	ev_loop_count => ev_iteration
		5323	ev_loop_depth => ev_depth
		5324	ev_loop_verify => ev_verify
		5325
		5326	Most functions working on C<struct ev_loop> objects don't have an
		5327	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5328	associated constants have been renamed to not collide with the C<struct
		5329	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5330	as all other watcher types. Note that C<ev_loop_fork> is still called
		5331	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5332	typedef.
		5333
		5334	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5335
		5336	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5337	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5338	and work, but the library code will of course be larger.
		5339
		5340	=back
		5341
		5342
		5343	=head1 GLOSSARY
		5344
		5345	=over 4
		5346
		5347	=item active
		5348
		5349	A watcher is active as long as it has been started and not yet stopped.
		5350	See L<WATCHER STATES> for details.
		5351
		5352	=item application
		5353
		5354	In this document, an application is whatever is using libev.
		5355
		5356	=item backend
		5357
		5358	The part of the code dealing with the operating system interfaces.
		5359
		5360	=item callback
		5361
		5362	The address of a function that is called when some event has been
		5363	detected. Callbacks are being passed the event loop, the watcher that
		5364	received the event, and the actual event bitset.
		5365
		5366	=item callback/watcher invocation
		5367
		5368	The act of calling the callback associated with a watcher.
		5369
		5370	=item event
		5371
		5372	A change of state of some external event, such as data now being available
		5373	for reading on a file descriptor, time having passed or simply not having
		5374	any other events happening anymore.
		5375
		5376	In libev, events are represented as single bits (such as C<EV_READ> or
		5377	C<EV_TIMER>).
		5378
		5379	=item event library
		5380
		5381	A software package implementing an event model and loop.
		5382
		5383	=item event loop
		5384
		5385	An entity that handles and processes external events and converts them
		5386	into callback invocations.
		5387
		5388	=item event model
		5389
		5390	The model used to describe how an event loop handles and processes
		5391	watchers and events.
		5392
		5393	=item pending
		5394
		5395	A watcher is pending as soon as the corresponding event has been
		5396	detected. See L<WATCHER STATES> for details.
		5397
		5398	=item real time
		5399
		5400	The physical time that is observed. It is apparently strictly monotonic :)
		5401
		5402	=item wall-clock time
		5403
		5404	The time and date as shown on clocks. Unlike real time, it can actually
		5405	be wrong and jump forwards and backwards, e.g. when you adjust your
		5406	clock.
		5407
		5408	=item watcher
		5409
		5410	A data structure that describes interest in certain events. Watchers need
		5411	to be started (attached to an event loop) before they can receive events.
		5412
		5413	=back
		5414
752	=head1 AUTHOR	5415	=head1 AUTHOR
753		5416
754	Marc Lehmann <libev@schmorp.de>.	5417	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5418	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
755		5419

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