ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.16 by root, Mon Nov 12 08:47:14 2007 UTC vs.
Revision 1.379 by root, Tue Jul 12 23:32:10 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_update_now> 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 C<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 C<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 C<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 C<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 C<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 C<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 C<EVMETHOD_DEVPOLL> (solaris 8 only)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
152		490
153	=item C<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<av_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 C<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 can check whether an event is active by calling the C<ev_is_active
305	(watcher *)> macro. To see whether an event is outstanding (but the
306	callback for it has not been called yet) you can use the C<ev_is_pending
307	(watcher *)> macro.
308		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
…		…
321	=item C<EV_WRITE>	1142	=item C<EV_WRITE>
322		1143
323	The file descriptor in the C<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 C<EV_TIMEOUT>	1147	=item C<EV_TIMER>
327		1148
328	The C<ev_timer> watcher has timed out.	1149	The C<ev_timer> watcher has timed out.
329		1150
330	=item C<EV_PERIODIC>	1151	=item C<EV_PERIODIC>
331		1152
…		…
337		1158
338	=item C<EV_CHILD>	1159	=item C<EV_CHILD>
339		1160
340	The pid specified in the C<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 C<EV_IDLE>	1167	=item C<EV_IDLE>
343		1168
344	The C<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 C<EV_PREPARE>	1171	=item C<EV_PREPARE>
347		1172
348	=item C<EV_CHECK>	1173	=item C<EV_CHECK>
349		1174
350	All C<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 C<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 C<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).
		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>).
357		1204
358	=item C<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 can be used
378	to associate arbitrary data with your watcher. If you need more data and
379	don't want to allocate memory and store a pointer to it in that data
380	member, you can also "subclass" the watcher type and provide your own
381	data:
382		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 C<ev_io> - is this 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 can 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 C<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 C<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). If multiple timers become ready during the
		1777	same loop iteration then the ones with earlier time-out values are invoked
		1778	before ones of the same priority with later time-out values (but this is
		1779	no longer true when a callback calls C<ev_run> recursively).
		1780
		1781	=head3 Be smart about timeouts
		1782
		1783	Many real-world problems involve some kind of timeout, usually for error
		1784	recovery. A typical example is an HTTP request - if the other side hangs,
		1785	you want to raise some error after a while.
		1786
		1787	What follows are some ways to handle this problem, from obvious and
		1788	inefficient to smart and efficient.
		1789
		1790	In the following, a 60 second activity timeout is assumed - a timeout that
		1791	gets reset to 60 seconds each time there is activity (e.g. each time some
		1792	data or other life sign was received).
		1793
		1794	=over 4
		1795
		1796	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1797
		1798	This is the most obvious, but not the most simple way: In the beginning,
		1799	start the watcher:
		1800
		1801	ev_timer_init (timer, callback, 60., 0.);
		1802	ev_timer_start (loop, timer);
		1803
		1804	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1805	and start it again:
		1806
		1807	ev_timer_stop (loop, timer);
		1808	ev_timer_set (timer, 60., 0.);
		1809	ev_timer_start (loop, timer);
		1810
		1811	This is relatively simple to implement, but means that each time there is
		1812	some activity, libev will first have to remove the timer from its internal
		1813	data structure and then add it again. Libev tries to be fast, but it's
		1814	still not a constant-time operation.
		1815
		1816	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1817
		1818	This is the easiest way, and involves using C<ev_timer_again> instead of
		1819	C<ev_timer_start>.
		1820
		1821	To implement this, configure an C<ev_timer> with a C<repeat> value
		1822	of C<60> and then call C<ev_timer_again> at start and each time you
		1823	successfully read or write some data. If you go into an idle state where
		1824	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1825	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1826
		1827	That means you can ignore both the C<ev_timer_start> function and the
		1828	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1829	member and C<ev_timer_again>.
		1830
		1831	At start:
		1832
		1833	ev_init (timer, callback);
		1834	timer->repeat = 60.;
		1835	ev_timer_again (loop, timer);
		1836
		1837	Each time there is some activity:
		1838
		1839	ev_timer_again (loop, timer);
		1840
		1841	It is even possible to change the time-out on the fly, regardless of
		1842	whether the watcher is active or not:
		1843
		1844	timer->repeat = 30.;
		1845	ev_timer_again (loop, timer);
		1846
		1847	This is slightly more efficient then stopping/starting the timer each time
		1848	you want to modify its timeout value, as libev does not have to completely
		1849	remove and re-insert the timer from/into its internal data structure.
		1850
		1851	It is, however, even simpler than the "obvious" way to do it.
		1852
		1853	=item 3. Let the timer time out, but then re-arm it as required.
		1854
		1855	This method is more tricky, but usually most efficient: Most timeouts are
		1856	relatively long compared to the intervals between other activity - in
		1857	our example, within 60 seconds, there are usually many I/O events with
		1858	associated activity resets.
		1859
		1860	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1861	but remember the time of last activity, and check for a real timeout only
		1862	within the callback:
		1863
		1864	ev_tstamp last_activity; // time of last activity
		1865
		1866	static void
		1867	callback (EV_P_ ev_timer *w, int revents)
		1868	{
		1869	ev_tstamp now = ev_now (EV_A);
		1870	ev_tstamp timeout = last_activity + 60.;
		1871
		1872	// if last_activity + 60. is older than now, we did time out
		1873	if (timeout < now)
		1874	{
		1875	// timeout occurred, take action
		1876	}
		1877	else
		1878	{
		1879	// callback was invoked, but there was some activity, re-arm
		1880	// the watcher to fire in last_activity + 60, which is
		1881	// guaranteed to be in the future, so "again" is positive:
		1882	w->repeat = timeout - now;
		1883	ev_timer_again (EV_A_ w);
		1884	}
		1885	}
		1886
		1887	To summarise the callback: first calculate the real timeout (defined
		1888	as "60 seconds after the last activity"), then check if that time has
		1889	been reached, which means something I<did>, in fact, time out. Otherwise
		1890	the callback was invoked too early (C<timeout> is in the future), so
		1891	re-schedule the timer to fire at that future time, to see if maybe we have
		1892	a timeout then.
		1893
		1894	Note how C<ev_timer_again> is used, taking advantage of the
		1895	C<ev_timer_again> optimisation when the timer is already running.
		1896
		1897	This scheme causes more callback invocations (about one every 60 seconds
		1898	minus half the average time between activity), but virtually no calls to
		1899	libev to change the timeout.
		1900
		1901	To start the timer, simply initialise the watcher and set C<last_activity>
		1902	to the current time (meaning we just have some activity :), then call the
		1903	callback, which will "do the right thing" and start the timer:
		1904
		1905	ev_init (timer, callback);
		1906	last_activity = ev_now (loop);
		1907	callback (loop, timer, EV_TIMER);
		1908
		1909	And when there is some activity, simply store the current time in
		1910	C<last_activity>, no libev calls at all:
		1911
		1912	last_activity = ev_now (loop);
		1913
		1914	This technique is slightly more complex, but in most cases where the
		1915	time-out is unlikely to be triggered, much more efficient.
		1916
		1917	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1918	callback :) - just change the timeout and invoke the callback, which will
		1919	fix things for you.
		1920
		1921	=item 4. Wee, just use a double-linked list for your timeouts.
		1922
		1923	If there is not one request, but many thousands (millions...), all
		1924	employing some kind of timeout with the same timeout value, then one can
		1925	do even better:
		1926
		1927	When starting the timeout, calculate the timeout value and put the timeout
		1928	at the I<end> of the list.
		1929
		1930	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1931	the list is expected to fire (for example, using the technique #3).
		1932
		1933	When there is some activity, remove the timer from the list, recalculate
		1934	the timeout, append it to the end of the list again, and make sure to
		1935	update the C<ev_timer> if it was taken from the beginning of the list.
		1936
		1937	This way, one can manage an unlimited number of timeouts in O(1) time for
		1938	starting, stopping and updating the timers, at the expense of a major
		1939	complication, and having to use a constant timeout. The constant timeout
		1940	ensures that the list stays sorted.
		1941
		1942	=back
		1943
		1944	So which method the best?
		1945
		1946	Method #2 is a simple no-brain-required solution that is adequate in most
		1947	situations. Method #3 requires a bit more thinking, but handles many cases
		1948	better, and isn't very complicated either. In most case, choosing either
		1949	one is fine, with #3 being better in typical situations.
		1950
		1951	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1952	rather complicated, but extremely efficient, something that really pays
		1953	off after the first million or so of active timers, i.e. it's usually
		1954	overkill :)
		1955
		1956	=head3 The special problem of time updates
		1957
		1958	Establishing the current time is a costly operation (it usually takes at
		1959	least two system calls): EV therefore updates its idea of the current
		1960	time only before and after C<ev_run> collects new events, which causes a
		1961	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1962	lots of events in one iteration.
453		1963
454	The relative timeouts are calculated relative to the C<ev_now ()>	1964	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	1965	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	1966	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	1967	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:	1968	timeout on the current time, use something like this to adjust for this:
459		1969
460	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1970	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
461		1971
		1972	If the event loop is suspended for a long time, you can also force an
		1973	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		1974	()>.
		1975
		1976	=head3 The special problems of suspended animation
		1977
		1978	When you leave the server world it is quite customary to hit machines that
		1979	can suspend/hibernate - what happens to the clocks during such a suspend?
		1980
		1981	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1982	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1983	to run until the system is suspended, but they will not advance while the
		1984	system is suspended. That means, on resume, it will be as if the program
		1985	was frozen for a few seconds, but the suspend time will not be counted
		1986	towards C<ev_timer> when a monotonic clock source is used. The real time
		1987	clock advanced as expected, but if it is used as sole clocksource, then a
		1988	long suspend would be detected as a time jump by libev, and timers would
		1989	be adjusted accordingly.
		1990
		1991	I would not be surprised to see different behaviour in different between
		1992	operating systems, OS versions or even different hardware.
		1993
		1994	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1995	time jump in the monotonic clocks and the realtime clock. If the program
		1996	is suspended for a very long time, and monotonic clock sources are in use,
		1997	then you can expect C<ev_timer>s to expire as the full suspension time
		1998	will be counted towards the timers. When no monotonic clock source is in
		1999	use, then libev will again assume a timejump and adjust accordingly.
		2000
		2001	It might be beneficial for this latter case to call C<ev_suspend>
		2002	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2003	deterministic behaviour in this case (you can do nothing against
		2004	C<SIGSTOP>).
		2005
		2006	=head3 Watcher-Specific Functions and Data Members
		2007
462	=over 4	2008	=over 4
463		2009
464	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2010	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465		2011
466	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2012	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
467		2013
468	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2014	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	2015	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	2016	reached. If it is positive, then the timer will automatically be
471	later, again, and again, until stopped manually.	2017	configured to trigger again C<repeat> seconds later, again, and again,
		2018	until stopped manually.
472		2019
473	The timer itself will do a best-effort at avoiding drift, that is, if you	2020	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	2021	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	2022	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	2023	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.	2024	do stuff) the timer will not fire more than once per event loop iteration.
478		2025
479	=item ev_timer_again (loop)	2026	=item ev_timer_again (loop, ev_timer *)
480		2027
481	This will act as if the timer timed out and restart it again if it is	2028	This will act as if the timer timed out and restarts it again if it is
482	repeating. The exact semantics are:	2029	repeating. The exact semantics are:
483		2030
		2031	If the timer is pending, its pending status is cleared.
		2032
484	If the timer is started but nonrepeating, stop it.	2033	If the timer is started but non-repeating, stop it (as if it timed out).
485		2034
486	If the timer is repeating, either start it if necessary (with the repeat	2035	If the timer is repeating, either start it if necessary (with the
487	value), or reset the running timer to the repeat value.	2036	C<repeat> value), or reset the running timer to the C<repeat> value.
488		2037
489	This sounds a bit complicated, but here is a useful and typical	2038	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	2039	usage example.
491	timeout, that is, you want to be called when there have been, say, 60	2040
492	seconds of inactivity on the socket. The easiest way to do this is to	2041	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
493	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	2042
494	time you successfully read or write some data. If you go into an idle	2043	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	2044	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.	2045	the timeout value currently configured.
		2046
		2047	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2048	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2049	will return C<4>. When the timer expires and is restarted, it will return
		2050	roughly C<7> (likely slightly less as callback invocation takes some time,
		2051	too), and so on.
		2052
		2053	=item ev_tstamp repeat [read-write]
		2054
		2055	The current C<repeat> value. Will be used each time the watcher times out
		2056	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2057	which is also when any modifications are taken into account.
497		2058
498	=back	2059	=back
499		2060
		2061	=head3 Examples
		2062
		2063	Example: Create a timer that fires after 60 seconds.
		2064
		2065	static void
		2066	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2067	{
		2068	.. one minute over, w is actually stopped right here
		2069	}
		2070
		2071	ev_timer mytimer;
		2072	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		2073	ev_timer_start (loop, &mytimer);
		2074
		2075	Example: Create a timeout timer that times out after 10 seconds of
		2076	inactivity.
		2077
		2078	static void
		2079	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2080	{
		2081	.. ten seconds without any activity
		2082	}
		2083
		2084	ev_timer mytimer;
		2085	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		2086	ev_timer_again (&mytimer); /* start timer */
		2087	ev_run (loop, 0);
		2088
		2089	// and in some piece of code that gets executed on any "activity":
		2090	// reset the timeout to start ticking again at 10 seconds
		2091	ev_timer_again (&mytimer);
		2092
		2093
500	=head2 C<ev_periodic> - to cron or not to cron	2094	=head2 C<ev_periodic> - to cron or not to cron?
501		2095
502	Periodic watchers are also timers of a kind, but they are very versatile	2096	Periodic watchers are also timers of a kind, but they are very versatile
503	(and unfortunately a bit complex).	2097	(and unfortunately a bit complex).
504		2098
505	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2099	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	2100	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	2101	(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 ()	2102	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	2103	time, and time jumps are not uncommon (e.g. when you adjust your
510	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2104	wrist-watch).
511	roughly 10 seconds later and of course not if you reset your system time
512	again).
513		2105
514	They can also be used to implement vastly more complex timers, such as	2106	You can tell a periodic watcher to trigger after some specific point
		2107	in time: for example, if you tell a periodic watcher to trigger "in 10
		2108	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2109	not a delay) and then reset your system clock to January of the previous
		2110	year, then it will take a year or more to trigger the event (unlike an
		2111	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2112	it, as it uses a relative timeout).
		2113
		2114	C<ev_periodic> watchers can also be used to implement vastly more complex
515	triggering an event on eahc midnight, local time.	2115	timers, such as triggering an event on each "midnight, local time", or
		2116	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2117	those cannot react to time jumps.
		2118
		2119	As with timers, the callback is guaranteed to be invoked only when the
		2120	point in time where it is supposed to trigger has passed. If multiple
		2121	timers become ready during the same loop iteration then the ones with
		2122	earlier time-out values are invoked before ones with later time-out values
		2123	(but this is no longer true when a callback calls C<ev_run> recursively).
		2124
		2125	=head3 Watcher-Specific Functions and Data Members
516		2126
517	=over 4	2127	=over 4
518		2128
519	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2129	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
520		2130
521	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2131	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
522		2132
523	Lots of arguments, lets sort it out... There are basically three modes of	2133	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:	2134	operation, and we will explain them from simplest to most complex:
525
526		2135
527	=over 4	2136	=over 4
528		2137
529	=item * absolute timer (interval = reschedule_cb = 0)	2138	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
530		2139
531	In this configuration the watcher triggers an event at the wallclock time	2140	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,	2141	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	2142	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.	2143	will be stopped and invoked when the system clock reaches or surpasses
		2144	this point in time.
535		2145
536	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2146	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
537		2147
538	In this mode the watcher will always be scheduled to time out at the next	2148	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	2149	C<offset + N * interval> time (for some integer N, which can also be
540	of any time jumps.	2150	negative) and then repeat, regardless of any time jumps. The C<offset>
		2151	argument is merely an offset into the C<interval> periods.
541		2152
542	This can be used to create timers that do not drift with respect to system	2153	This can be used to create timers that do not drift with respect to the
543	time:	2154	system clock, for example, here is an C<ev_periodic> that triggers each
		2155	hour, on the hour (with respect to UTC):
544		2156
545	ev_periodic_set (&periodic, 0., 3600., 0);	2157	ev_periodic_set (&periodic, 0., 3600., 0);
546		2158
547	This doesn't mean there will always be 3600 seconds in between triggers,	2159	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	2160	but only that the callback will be called when the system time shows a
549	full hour (UTC), or more correctly, when the system time is evenly divisible	2161	full hour (UTC), or more correctly, when the system time is evenly divisible
550	by 3600.	2162	by 3600.
551		2163
552	Another way to think about it (for the mathematically inclined) is that	2164	Another way to think about it (for the mathematically inclined) is that
553	C<ev_periodic> will try to run the callback in this mode at the next possible	2165	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.	2166	time where C<time = offset (mod interval)>, regardless of any time jumps.
555		2167
		2168	The C<interval> I<MUST> be positive, and for numerical stability, the
		2169	interval value should be higher than C<1/8192> (which is around 100
		2170	microseconds) and C<offset> should be higher than C<0> and should have
		2171	at most a similar magnitude as the current time (say, within a factor of
		2172	ten). Typical values for offset are, in fact, C<0> or something between
		2173	C<0> and C<interval>, which is also the recommended range.
		2174
		2175	Note also that there is an upper limit to how often a timer can fire (CPU
		2176	speed for example), so if C<interval> is very small then timing stability
		2177	will of course deteriorate. Libev itself tries to be exact to be about one
		2178	millisecond (if the OS supports it and the machine is fast enough).
		2179
556	=item * manual reschedule mode (reschedule_cb = callback)	2180	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
557		2181
558	In this mode the values for C<interval> and C<at> are both being	2182	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	2183	ignored. Instead, each time the periodic watcher gets scheduled, the
560	reschedule callback will be called with the watcher as first, and the	2184	reschedule callback will be called with the watcher as first, and the
561	current time as second argument.	2185	current time as second argument.
562		2186
563	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	2187	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
564	periodic watcher, ever, or make any event loop modifications>. If you need	2188	or make ANY other event loop modifications whatsoever, unless explicitly
		2189	allowed by documentation here>.
		2190
565	to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.	2191	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2192	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2193	only event loop modification you are allowed to do).
566		2194
567	Also, I<< this callback must always return a time that is later than the
568	passed C<now> value >>. Not even C<now> itself will be ok.
569
570	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2195	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
571	ev_tstamp now)>, e.g.:	2196	*w, ev_tstamp now)>, e.g.:
572		2197
		2198	static ev_tstamp
573	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2199	my_rescheduler (ev_periodic *w, ev_tstamp now)
574	{	2200	{
575	return now + 60.;	2201	return now + 60.;
576	}	2202	}
577		2203
578	It must return the next time to trigger, based on the passed time value	2204	It must return the next time to trigger, based on the passed time value
579	(that is, the lowest time value larger than to the second argument). It	2205	(that is, the lowest time value larger than to the second argument). It
580	will usually be called just before the callback will be triggered, but	2206	will usually be called just before the callback will be triggered, but
581	might be called at other times, too.	2207	might be called at other times, too.
582		2208
		2209	NOTE: I<< This callback must always return a time that is higher than or
		2210	equal to the passed C<now> value >>.
		2211
583	This can be used to create very complex timers, such as a timer that	2212	This can be used to create very complex timers, such as a timer that
584	triggers on each midnight, local time. To do this, you would calculate the	2213	triggers on "next midnight, local time". To do this, you would calculate the
585	next midnight after C<now> and return the timestamp value for this. How you do this	2214	next midnight after C<now> and return the timestamp value for this. How
586	is, again, up to you (but it is not trivial).	2215	you do this is, again, up to you (but it is not trivial, which is the main
		2216	reason I omitted it as an example).
587		2217
588	=back	2218	=back
589		2219
590	=item ev_periodic_again (loop, ev_periodic *)	2220	=item ev_periodic_again (loop, ev_periodic *)
591		2221
592	Simply stops and restarts the periodic watcher again. This is only useful	2222	Simply stops and restarts the periodic watcher again. This is only useful
593	when you changed some parameters or the reschedule callback would return	2223	when you changed some parameters or the reschedule callback would return
594	a different time than the last time it was called (e.g. in a crond like	2224	a different time than the last time it was called (e.g. in a crond like
595	program when the crontabs have changed).	2225	program when the crontabs have changed).
596		2226
		2227	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2228
		2229	When active, returns the absolute time that the watcher is supposed
		2230	to trigger next. This is not the same as the C<offset> argument to
		2231	C<ev_periodic_set>, but indeed works even in interval and manual
		2232	rescheduling modes.
		2233
		2234	=item ev_tstamp offset [read-write]
		2235
		2236	When repeating, this contains the offset value, otherwise this is the
		2237	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2238	although libev might modify this value for better numerical stability).
		2239
		2240	Can be modified any time, but changes only take effect when the periodic
		2241	timer fires or C<ev_periodic_again> is being called.
		2242
		2243	=item ev_tstamp interval [read-write]
		2244
		2245	The current interval value. Can be modified any time, but changes only
		2246	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2247	called.
		2248
		2249	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2250
		2251	The current reschedule callback, or C<0>, if this functionality is
		2252	switched off. Can be changed any time, but changes only take effect when
		2253	the periodic timer fires or C<ev_periodic_again> is being called.
		2254
597	=back	2255	=back
598		2256
		2257	=head3 Examples
		2258
		2259	Example: Call a callback every hour, or, more precisely, whenever the
		2260	system time is divisible by 3600. The callback invocation times have
		2261	potentially a lot of jitter, but good long-term stability.
		2262
		2263	static void
		2264	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
		2265	{
		2266	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2267	}
		2268
		2269	ev_periodic hourly_tick;
		2270	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2271	ev_periodic_start (loop, &hourly_tick);
		2272
		2273	Example: The same as above, but use a reschedule callback to do it:
		2274
		2275	#include <math.h>
		2276
		2277	static ev_tstamp
		2278	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2279	{
		2280	return now + (3600. - fmod (now, 3600.));
		2281	}
		2282
		2283	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2284
		2285	Example: Call a callback every hour, starting now:
		2286
		2287	ev_periodic hourly_tick;
		2288	ev_periodic_init (&hourly_tick, clock_cb,
		2289	fmod (ev_now (loop), 3600.), 3600., 0);
		2290	ev_periodic_start (loop, &hourly_tick);
		2291
		2292
599	=head2 C<ev_signal> - signal me when a signal gets signalled	2293	=head2 C<ev_signal> - signal me when a signal gets signalled!
600		2294
601	Signal watchers will trigger an event when the process receives a specific	2295	Signal watchers will trigger an event when the process receives a specific
602	signal one or more times. Even though signals are very asynchronous, libev	2296	signal one or more times. Even though signals are very asynchronous, libev
603	will try it's best to deliver signals synchronously, i.e. as part of the	2297	will try its best to deliver signals synchronously, i.e. as part of the
604	normal event processing, like any other event.	2298	normal event processing, like any other event.
605		2299
		2300	If you want signals to be delivered truly asynchronously, just use
		2301	C<sigaction> as you would do without libev and forget about sharing
		2302	the signal. You can even use C<ev_async> from a signal handler to
		2303	synchronously wake up an event loop.
		2304
606	You can configure as many watchers as you like per signal. Only when the	2305	You can configure as many watchers as you like for the same signal, but
		2306	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2307	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2308	C<SIGINT> in both the default loop and another loop at the same time. At
		2309	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2310
607	first watcher gets started will libev actually register a signal watcher	2311	When the first watcher gets started will libev actually register something
608	with the kernel (thus it coexists with your own signal handlers as long	2312	with the kernel (thus it coexists with your own signal handlers as long as
609	as you don't register any with libev). Similarly, when the last signal	2313	you don't register any with libev for the same signal).
610	watcher for a signal is stopped libev will reset the signal handler to	2314
611	SIG_DFL (regardless of what it was set to before).	2315	If possible and supported, libev will install its handlers with
		2316	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2317	not be unduly interrupted. If you have a problem with system calls getting
		2318	interrupted by signals you can block all signals in an C<ev_check> watcher
		2319	and unblock them in an C<ev_prepare> watcher.
		2320
		2321	=head3 The special problem of inheritance over fork/execve/pthread_create
		2322
		2323	Both the signal mask (C<sigprocmask>) and the signal disposition
		2324	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2325	stopping it again), that is, libev might or might not block the signal,
		2326	and might or might not set or restore the installed signal handler (but
		2327	see C<EVFLAG_NOSIGMASK>).
		2328
		2329	While this does not matter for the signal disposition (libev never
		2330	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2331	C<execve>), this matters for the signal mask: many programs do not expect
		2332	certain signals to be blocked.
		2333
		2334	This means that before calling C<exec> (from the child) you should reset
		2335	the signal mask to whatever "default" you expect (all clear is a good
		2336	choice usually).
		2337
		2338	The simplest way to ensure that the signal mask is reset in the child is
		2339	to install a fork handler with C<pthread_atfork> that resets it. That will
		2340	catch fork calls done by libraries (such as the libc) as well.
		2341
		2342	In current versions of libev, the signal will not be blocked indefinitely
		2343	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2344	the window of opportunity for problems, it will not go away, as libev
		2345	I<has> to modify the signal mask, at least temporarily.
		2346
		2347	So I can't stress this enough: I<If you do not reset your signal mask when
		2348	you expect it to be empty, you have a race condition in your code>. This
		2349	is not a libev-specific thing, this is true for most event libraries.
		2350
		2351	=head3 The special problem of threads signal handling
		2352
		2353	POSIX threads has problematic signal handling semantics, specifically,
		2354	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2355	threads in a process block signals, which is hard to achieve.
		2356
		2357	When you want to use sigwait (or mix libev signal handling with your own
		2358	for the same signals), you can tackle this problem by globally blocking
		2359	all signals before creating any threads (or creating them with a fully set
		2360	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2361	loops. Then designate one thread as "signal receiver thread" which handles
		2362	these signals. You can pass on any signals that libev might be interested
		2363	in by calling C<ev_feed_signal>.
		2364
		2365	=head3 Watcher-Specific Functions and Data Members
612		2366
613	=over 4	2367	=over 4
614		2368
615	=item ev_signal_init (ev_signal *, callback, int signum)	2369	=item ev_signal_init (ev_signal *, callback, int signum)
616		2370
617	=item ev_signal_set (ev_signal *, int signum)	2371	=item ev_signal_set (ev_signal *, int signum)
618		2372
619	Configures the watcher to trigger on the given signal number (usually one	2373	Configures the watcher to trigger on the given signal number (usually one
620	of the C<SIGxxx> constants).	2374	of the C<SIGxxx> constants).
621		2375
		2376	=item int signum [read-only]
		2377
		2378	The signal the watcher watches out for.
		2379
622	=back	2380	=back
623		2381
		2382	=head3 Examples
		2383
		2384	Example: Try to exit cleanly on SIGINT.
		2385
		2386	static void
		2387	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2388	{
		2389	ev_break (loop, EVBREAK_ALL);
		2390	}
		2391
		2392	ev_signal signal_watcher;
		2393	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2394	ev_signal_start (loop, &signal_watcher);
		2395
		2396
624	=head2 C<ev_child> - wait for pid status changes	2397	=head2 C<ev_child> - watch out for process status changes
625		2398
626	Child watchers trigger when your process receives a SIGCHLD in response to	2399	Child watchers trigger when your process receives a SIGCHLD in response to
627	some child status changes (most typically when a child of yours dies).	2400	some child status changes (most typically when a child of yours dies or
		2401	exits). It is permissible to install a child watcher I<after> the child
		2402	has been forked (which implies it might have already exited), as long
		2403	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2404	forking and then immediately registering a watcher for the child is fine,
		2405	but forking and registering a watcher a few event loop iterations later or
		2406	in the next callback invocation is not.
		2407
		2408	Only the default event loop is capable of handling signals, and therefore
		2409	you can only register child watchers in the default event loop.
		2410
		2411	Due to some design glitches inside libev, child watchers will always be
		2412	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2413	libev)
		2414
		2415	=head3 Process Interaction
		2416
		2417	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2418	initialised. This is necessary to guarantee proper behaviour even if the
		2419	first child watcher is started after the child exits. The occurrence
		2420	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2421	synchronously as part of the event loop processing. Libev always reaps all
		2422	children, even ones not watched.
		2423
		2424	=head3 Overriding the Built-In Processing
		2425
		2426	Libev offers no special support for overriding the built-in child
		2427	processing, but if your application collides with libev's default child
		2428	handler, you can override it easily by installing your own handler for
		2429	C<SIGCHLD> after initialising the default loop, and making sure the
		2430	default loop never gets destroyed. You are encouraged, however, to use an
		2431	event-based approach to child reaping and thus use libev's support for
		2432	that, so other libev users can use C<ev_child> watchers freely.
		2433
		2434	=head3 Stopping the Child Watcher
		2435
		2436	Currently, the child watcher never gets stopped, even when the
		2437	child terminates, so normally one needs to stop the watcher in the
		2438	callback. Future versions of libev might stop the watcher automatically
		2439	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2440	problem).
		2441
		2442	=head3 Watcher-Specific Functions and Data Members
628		2443
629	=over 4	2444	=over 4
630		2445
631	=item ev_child_init (ev_child *, callback, int pid)	2446	=item ev_child_init (ev_child *, callback, int pid, int trace)
632		2447
633	=item ev_child_set (ev_child *, int pid)	2448	=item ev_child_set (ev_child *, int pid, int trace)
634		2449
635	Configures the watcher to wait for status changes of process C<pid> (or	2450	Configures the watcher to wait for status changes of process C<pid> (or
636	I<any> process if C<pid> is specified as C<0>). The callback can look	2451	I<any> process if C<pid> is specified as C<0>). The callback can look
637	at the C<rstatus> member of the C<ev_child> watcher structure to see	2452	at the C<rstatus> member of the C<ev_child> watcher structure to see
638	the status word (use the macros from C<sys/wait.h> and see your systems	2453	the status word (use the macros from C<sys/wait.h> and see your systems
639	C<waitpid> documentation). The C<rpid> member contains the pid of the	2454	C<waitpid> documentation). The C<rpid> member contains the pid of the
640	process causing the status change.	2455	process causing the status change. C<trace> must be either C<0> (only
		2456	activate the watcher when the process terminates) or C<1> (additionally
		2457	activate the watcher when the process is stopped or continued).
		2458
		2459	=item int pid [read-only]
		2460
		2461	The process id this watcher watches out for, or C<0>, meaning any process id.
		2462
		2463	=item int rpid [read-write]
		2464
		2465	The process id that detected a status change.
		2466
		2467	=item int rstatus [read-write]
		2468
		2469	The process exit/trace status caused by C<rpid> (see your systems
		2470	C<waitpid> and C<sys/wait.h> documentation for details).
641		2471
642	=back	2472	=back
643		2473
		2474	=head3 Examples
		2475
		2476	Example: C<fork()> a new process and install a child handler to wait for
		2477	its completion.
		2478
		2479	ev_child cw;
		2480
		2481	static void
		2482	child_cb (EV_P_ ev_child *w, int revents)
		2483	{
		2484	ev_child_stop (EV_A_ w);
		2485	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2486	}
		2487
		2488	pid_t pid = fork ();
		2489
		2490	if (pid < 0)
		2491	// error
		2492	else if (pid == 0)
		2493	{
		2494	// the forked child executes here
		2495	exit (1);
		2496	}
		2497	else
		2498	{
		2499	ev_child_init (&cw, child_cb, pid, 0);
		2500	ev_child_start (EV_DEFAULT_ &cw);
		2501	}
		2502
		2503
		2504	=head2 C<ev_stat> - did the file attributes just change?
		2505
		2506	This watches a file system path for attribute changes. That is, it calls
		2507	C<stat> on that path in regular intervals (or when the OS says it changed)
		2508	and sees if it changed compared to the last time, invoking the callback if
		2509	it did.
		2510
		2511	The path does not need to exist: changing from "path exists" to "path does
		2512	not exist" is a status change like any other. The condition "path does not
		2513	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2514	C<st_nlink> field being zero (which is otherwise always forced to be at
		2515	least one) and all the other fields of the stat buffer having unspecified
		2516	contents.
		2517
		2518	The path I<must not> end in a slash or contain special components such as
		2519	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2520	your working directory changes, then the behaviour is undefined.
		2521
		2522	Since there is no portable change notification interface available, the
		2523	portable implementation simply calls C<stat(2)> regularly on the path
		2524	to see if it changed somehow. You can specify a recommended polling
		2525	interval for this case. If you specify a polling interval of C<0> (highly
		2526	recommended!) then a I<suitable, unspecified default> value will be used
		2527	(which you can expect to be around five seconds, although this might
		2528	change dynamically). Libev will also impose a minimum interval which is
		2529	currently around C<0.1>, but that's usually overkill.
		2530
		2531	This watcher type is not meant for massive numbers of stat watchers,
		2532	as even with OS-supported change notifications, this can be
		2533	resource-intensive.
		2534
		2535	At the time of this writing, the only OS-specific interface implemented
		2536	is the Linux inotify interface (implementing kqueue support is left as an
		2537	exercise for the reader. Note, however, that the author sees no way of
		2538	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2539
		2540	=head3 ABI Issues (Largefile Support)
		2541
		2542	Libev by default (unless the user overrides this) uses the default
		2543	compilation environment, which means that on systems with large file
		2544	support disabled by default, you get the 32 bit version of the stat
		2545	structure. When using the library from programs that change the ABI to
		2546	use 64 bit file offsets the programs will fail. In that case you have to
		2547	compile libev with the same flags to get binary compatibility. This is
		2548	obviously the case with any flags that change the ABI, but the problem is
		2549	most noticeably displayed with ev_stat and large file support.
		2550
		2551	The solution for this is to lobby your distribution maker to make large
		2552	file interfaces available by default (as e.g. FreeBSD does) and not
		2553	optional. Libev cannot simply switch on large file support because it has
		2554	to exchange stat structures with application programs compiled using the
		2555	default compilation environment.
		2556
		2557	=head3 Inotify and Kqueue
		2558
		2559	When C<inotify (7)> support has been compiled into libev and present at
		2560	runtime, it will be used to speed up change detection where possible. The
		2561	inotify descriptor will be created lazily when the first C<ev_stat>
		2562	watcher is being started.
		2563
		2564	Inotify presence does not change the semantics of C<ev_stat> watchers
		2565	except that changes might be detected earlier, and in some cases, to avoid
		2566	making regular C<stat> calls. Even in the presence of inotify support
		2567	there are many cases where libev has to resort to regular C<stat> polling,
		2568	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2569	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2570	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2571	xfs are fully working) libev usually gets away without polling.
		2572
		2573	There is no support for kqueue, as apparently it cannot be used to
		2574	implement this functionality, due to the requirement of having a file
		2575	descriptor open on the object at all times, and detecting renames, unlinks
		2576	etc. is difficult.
		2577
		2578	=head3 C<stat ()> is a synchronous operation
		2579
		2580	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2581	the process. The exception are C<ev_stat> watchers - those call C<stat
		2582	()>, which is a synchronous operation.
		2583
		2584	For local paths, this usually doesn't matter: unless the system is very
		2585	busy or the intervals between stat's are large, a stat call will be fast,
		2586	as the path data is usually in memory already (except when starting the
		2587	watcher).
		2588
		2589	For networked file systems, calling C<stat ()> can block an indefinite
		2590	time due to network issues, and even under good conditions, a stat call
		2591	often takes multiple milliseconds.
		2592
		2593	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2594	paths, although this is fully supported by libev.
		2595
		2596	=head3 The special problem of stat time resolution
		2597
		2598	The C<stat ()> system call only supports full-second resolution portably,
		2599	and even on systems where the resolution is higher, most file systems
		2600	still only support whole seconds.
		2601
		2602	That means that, if the time is the only thing that changes, you can
		2603	easily miss updates: on the first update, C<ev_stat> detects a change and
		2604	calls your callback, which does something. When there is another update
		2605	within the same second, C<ev_stat> will be unable to detect unless the
		2606	stat data does change in other ways (e.g. file size).
		2607
		2608	The solution to this is to delay acting on a change for slightly more
		2609	than a second (or till slightly after the next full second boundary), using
		2610	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2611	ev_timer_again (loop, w)>).
		2612
		2613	The C<.02> offset is added to work around small timing inconsistencies
		2614	of some operating systems (where the second counter of the current time
		2615	might be be delayed. One such system is the Linux kernel, where a call to
		2616	C<gettimeofday> might return a timestamp with a full second later than
		2617	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2618	update file times then there will be a small window where the kernel uses
		2619	the previous second to update file times but libev might already execute
		2620	the timer callback).
		2621
		2622	=head3 Watcher-Specific Functions and Data Members
		2623
		2624	=over 4
		2625
		2626	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2627
		2628	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2629
		2630	Configures the watcher to wait for status changes of the given
		2631	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2632	be detected and should normally be specified as C<0> to let libev choose
		2633	a suitable value. The memory pointed to by C<path> must point to the same
		2634	path for as long as the watcher is active.
		2635
		2636	The callback will receive an C<EV_STAT> event when a change was detected,
		2637	relative to the attributes at the time the watcher was started (or the
		2638	last change was detected).
		2639
		2640	=item ev_stat_stat (loop, ev_stat *)
		2641
		2642	Updates the stat buffer immediately with new values. If you change the
		2643	watched path in your callback, you could call this function to avoid
		2644	detecting this change (while introducing a race condition if you are not
		2645	the only one changing the path). Can also be useful simply to find out the
		2646	new values.
		2647
		2648	=item ev_statdata attr [read-only]
		2649
		2650	The most-recently detected attributes of the file. Although the type is
		2651	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2652	suitable for your system, but you can only rely on the POSIX-standardised
		2653	members to be present. If the C<st_nlink> member is C<0>, then there was
		2654	some error while C<stat>ing the file.
		2655
		2656	=item ev_statdata prev [read-only]
		2657
		2658	The previous attributes of the file. The callback gets invoked whenever
		2659	C<prev> != C<attr>, or, more precisely, one or more of these members
		2660	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2661	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2662
		2663	=item ev_tstamp interval [read-only]
		2664
		2665	The specified interval.
		2666
		2667	=item const char *path [read-only]
		2668
		2669	The file system path that is being watched.
		2670
		2671	=back
		2672
		2673	=head3 Examples
		2674
		2675	Example: Watch C</etc/passwd> for attribute changes.
		2676
		2677	static void
		2678	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2679	{
		2680	/* /etc/passwd changed in some way */
		2681	if (w->attr.st_nlink)
		2682	{
		2683	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2684	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2685	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2686	}
		2687	else
		2688	/* you shalt not abuse printf for puts */
		2689	puts ("wow, /etc/passwd is not there, expect problems. "
		2690	"if this is windows, they already arrived\n");
		2691	}
		2692
		2693	...
		2694	ev_stat passwd;
		2695
		2696	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2697	ev_stat_start (loop, &passwd);
		2698
		2699	Example: Like above, but additionally use a one-second delay so we do not
		2700	miss updates (however, frequent updates will delay processing, too, so
		2701	one might do the work both on C<ev_stat> callback invocation I<and> on
		2702	C<ev_timer> callback invocation).
		2703
		2704	static ev_stat passwd;
		2705	static ev_timer timer;
		2706
		2707	static void
		2708	timer_cb (EV_P_ ev_timer *w, int revents)
		2709	{
		2710	ev_timer_stop (EV_A_ w);
		2711
		2712	/* now it's one second after the most recent passwd change */
		2713	}
		2714
		2715	static void
		2716	stat_cb (EV_P_ ev_stat *w, int revents)
		2717	{
		2718	/* reset the one-second timer */
		2719	ev_timer_again (EV_A_ &timer);
		2720	}
		2721
		2722	...
		2723	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2724	ev_stat_start (loop, &passwd);
		2725	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2726
		2727
644	=head2 C<ev_idle> - when you've got nothing better to do	2728	=head2 C<ev_idle> - when you've got nothing better to do...
645		2729
646	Idle watchers trigger events when there are no other events are pending	2730	Idle watchers trigger events when no other events of the same or higher
647	(prepare, check and other idle watchers do not count). That is, as long	2731	priority are pending (prepare, check and other idle watchers do not count
648	as your process is busy handling sockets or timeouts (or even signals,	2732	as receiving "events").
649	imagine) it will not be triggered. But when your process is idle all idle	2733
650	watchers are being called again and again, once per event loop iteration -	2734	That is, as long as your process is busy handling sockets or timeouts
		2735	(or even signals, imagine) of the same or higher priority it will not be
		2736	triggered. But when your process is idle (or only lower-priority watchers
		2737	are pending), the idle watchers are being called once per event loop
651	until stopped, that is, or your process receives more events and becomes	2738	iteration - until stopped, that is, or your process receives more events
652	busy.	2739	and becomes busy again with higher priority stuff.
653		2740
654	The most noteworthy effect is that as long as any idle watchers are	2741	The most noteworthy effect is that as long as any idle watchers are
655	active, the process will not block when waiting for new events.	2742	active, the process will not block when waiting for new events.
656		2743
657	Apart from keeping your process non-blocking (which is a useful	2744	Apart from keeping your process non-blocking (which is a useful
658	effect on its own sometimes), idle watchers are a good place to do	2745	effect on its own sometimes), idle watchers are a good place to do
659	"pseudo-background processing", or delay processing stuff to after the	2746	"pseudo-background processing", or delay processing stuff to after the
660	event loop has handled all outstanding events.	2747	event loop has handled all outstanding events.
661		2748
		2749	=head3 Watcher-Specific Functions and Data Members
		2750
662	=over 4	2751	=over 4
663		2752
664	=item ev_idle_init (ev_signal *, callback)	2753	=item ev_idle_init (ev_idle *, callback)
665		2754
666	Initialises and configures the idle watcher - it has no parameters of any	2755	Initialises and configures the idle watcher - it has no parameters of any
667	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2756	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
668	believe me.	2757	believe me.
669		2758
670	=back	2759	=back
671		2760
		2761	=head3 Examples
		2762
		2763	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2764	callback, free it. Also, use no error checking, as usual.
		2765
		2766	static void
		2767	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2768	{
		2769	free (w);
		2770	// now do something you wanted to do when the program has
		2771	// no longer anything immediate to do.
		2772	}
		2773
		2774	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2775	ev_idle_init (idle_watcher, idle_cb);
		2776	ev_idle_start (loop, idle_watcher);
		2777
		2778
672	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2779	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
673		2780
674	Prepare and check watchers are usually (but not always) used in tandem:	2781	Prepare and check watchers are usually (but not always) used in pairs:
675	Prepare watchers get invoked before the process blocks and check watchers	2782	prepare watchers get invoked before the process blocks and check watchers
676	afterwards.	2783	afterwards.
677		2784
		2785	You I<must not> call C<ev_run> or similar functions that enter
		2786	the current event loop from either C<ev_prepare> or C<ev_check>
		2787	watchers. Other loops than the current one are fine, however. The
		2788	rationale behind this is that you do not need to check for recursion in
		2789	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2790	C<ev_check> so if you have one watcher of each kind they will always be
		2791	called in pairs bracketing the blocking call.
		2792
678	Their main purpose is to integrate other event mechanisms into libev. This	2793	Their main purpose is to integrate other event mechanisms into libev and
679	could be used, for example, to track variable changes, implement your own	2794	their use is somewhat advanced. They could be used, for example, to track
680	watchers, integrate net-snmp or a coroutine library and lots more.	2795	variable changes, implement your own watchers, integrate net-snmp or a
		2796	coroutine library and lots more. They are also occasionally useful if
		2797	you cache some data and want to flush it before blocking (for example,
		2798	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2799	watcher).
681		2800
682	This is done by examining in each prepare call which file descriptors need	2801	This is done by examining in each prepare call which file descriptors
683	to be watched by the other library, registering C<ev_io> watchers for	2802	need to be watched by the other library, registering C<ev_io> watchers
684	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2803	for them and starting an C<ev_timer> watcher for any timeouts (many
685	provide just this functionality). Then, in the check watcher you check for	2804	libraries provide exactly this functionality). Then, in the check watcher,
686	any events that occured (by checking the pending status of all watchers	2805	you check for any events that occurred (by checking the pending status
687	and stopping them) and call back into the library. The I/O and timer	2806	of all watchers and stopping them) and call back into the library. The
688	callbacks will never actually be called (but must be valid neverthelles,	2807	I/O and timer callbacks will never actually be called (but must be valid
689	because you never know, you know?).	2808	nevertheless, because you never know, you know?).
690		2809
691	As another example, the Perl Coro module uses these hooks to integrate	2810	As another example, the Perl Coro module uses these hooks to integrate
692	coroutines into libev programs, by yielding to other active coroutines	2811	coroutines into libev programs, by yielding to other active coroutines
693	during each prepare and only letting the process block if no coroutines	2812	during each prepare and only letting the process block if no coroutines
694	are ready to run (its actually more complicated, it only runs coroutines	2813	are ready to run (it's actually more complicated: it only runs coroutines
695	with priority higher than the event loop and one lower priority once,	2814	with priority higher than or equal to the event loop and one coroutine
696	using idle watchers to keep the event loop from blocking if lower-priority	2815	of lower priority, but only once, using idle watchers to keep the event
697	coroutines exist, thus mapping low-priority coroutines to idle/background	2816	loop from blocking if lower-priority coroutines are active, thus mapping
698	tasks).	2817	low-priority coroutines to idle/background tasks).
		2818
		2819	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2820	priority, to ensure that they are being run before any other watchers
		2821	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2822
		2823	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2824	activate ("feed") events into libev. While libev fully supports this, they
		2825	might get executed before other C<ev_check> watchers did their job. As
		2826	C<ev_check> watchers are often used to embed other (non-libev) event
		2827	loops those other event loops might be in an unusable state until their
		2828	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2829	others).
		2830
		2831	=head3 Watcher-Specific Functions and Data Members
699		2832
700	=over 4	2833	=over 4
701		2834
702	=item ev_prepare_init (ev_prepare *, callback)	2835	=item ev_prepare_init (ev_prepare *, callback)
703		2836
704	=item ev_check_init (ev_check *, callback)	2837	=item ev_check_init (ev_check *, callback)
705		2838
706	Initialises and configures the prepare or check watcher - they have no	2839	Initialises and configures the prepare or check watcher - they have no
707	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2840	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
708	macros, but using them is utterly, utterly and completely pointless.	2841	macros, but using them is utterly, utterly, utterly and completely
		2842	pointless.
709		2843
710	=back	2844	=back
711		2845
		2846	=head3 Examples
		2847
		2848	There are a number of principal ways to embed other event loops or modules
		2849	into libev. Here are some ideas on how to include libadns into libev
		2850	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2851	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2852	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2853	Glib event loop).
		2854
		2855	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2856	and in a check watcher, destroy them and call into libadns. What follows
		2857	is pseudo-code only of course. This requires you to either use a low
		2858	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2859	the callbacks for the IO/timeout watchers might not have been called yet.
		2860
		2861	static ev_io iow [nfd];
		2862	static ev_timer tw;
		2863
		2864	static void
		2865	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2866	{
		2867	}
		2868
		2869	// create io watchers for each fd and a timer before blocking
		2870	static void
		2871	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2872	{
		2873	int timeout = 3600000;
		2874	struct pollfd fds [nfd];
		2875	// actual code will need to loop here and realloc etc.
		2876	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2877
		2878	/* the callback is illegal, but won't be called as we stop during check */
		2879	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		2880	ev_timer_start (loop, &tw);
		2881
		2882	// create one ev_io per pollfd
		2883	for (int i = 0; i < nfd; ++i)
		2884	{
		2885	ev_io_init (iow + i, io_cb, fds [i].fd,
		2886	((fds [i].events & POLLIN ? EV_READ : 0)
		2887	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2888
		2889	fds [i].revents = 0;
		2890	ev_io_start (loop, iow + i);
		2891	}
		2892	}
		2893
		2894	// stop all watchers after blocking
		2895	static void
		2896	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2897	{
		2898	ev_timer_stop (loop, &tw);
		2899
		2900	for (int i = 0; i < nfd; ++i)
		2901	{
		2902	// set the relevant poll flags
		2903	// could also call adns_processreadable etc. here
		2904	struct pollfd *fd = fds + i;
		2905	int revents = ev_clear_pending (iow + i);
		2906	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2907	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2908
		2909	// now stop the watcher
		2910	ev_io_stop (loop, iow + i);
		2911	}
		2912
		2913	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2914	}
		2915
		2916	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2917	in the prepare watcher and would dispose of the check watcher.
		2918
		2919	Method 3: If the module to be embedded supports explicit event
		2920	notification (libadns does), you can also make use of the actual watcher
		2921	callbacks, and only destroy/create the watchers in the prepare watcher.
		2922
		2923	static void
		2924	timer_cb (EV_P_ ev_timer *w, int revents)
		2925	{
		2926	adns_state ads = (adns_state)w->data;
		2927	update_now (EV_A);
		2928
		2929	adns_processtimeouts (ads, &tv_now);
		2930	}
		2931
		2932	static void
		2933	io_cb (EV_P_ ev_io *w, int revents)
		2934	{
		2935	adns_state ads = (adns_state)w->data;
		2936	update_now (EV_A);
		2937
		2938	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2939	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2940	}
		2941
		2942	// do not ever call adns_afterpoll
		2943
		2944	Method 4: Do not use a prepare or check watcher because the module you
		2945	want to embed is not flexible enough to support it. Instead, you can
		2946	override their poll function. The drawback with this solution is that the
		2947	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2948	this approach, effectively embedding EV as a client into the horrible
		2949	libglib event loop.
		2950
		2951	static gint
		2952	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2953	{
		2954	int got_events = 0;
		2955
		2956	for (n = 0; n < nfds; ++n)
		2957	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2958
		2959	if (timeout >= 0)
		2960	// create/start timer
		2961
		2962	// poll
		2963	ev_run (EV_A_ 0);
		2964
		2965	// stop timer again
		2966	if (timeout >= 0)
		2967	ev_timer_stop (EV_A_ &to);
		2968
		2969	// stop io watchers again - their callbacks should have set
		2970	for (n = 0; n < nfds; ++n)
		2971	ev_io_stop (EV_A_ iow [n]);
		2972
		2973	return got_events;
		2974	}
		2975
		2976
		2977	=head2 C<ev_embed> - when one backend isn't enough...
		2978
		2979	This is a rather advanced watcher type that lets you embed one event loop
		2980	into another (currently only C<ev_io> events are supported in the embedded
		2981	loop, other types of watchers might be handled in a delayed or incorrect
		2982	fashion and must not be used).
		2983
		2984	There are primarily two reasons you would want that: work around bugs and
		2985	prioritise I/O.
		2986
		2987	As an example for a bug workaround, the kqueue backend might only support
		2988	sockets on some platform, so it is unusable as generic backend, but you
		2989	still want to make use of it because you have many sockets and it scales
		2990	so nicely. In this case, you would create a kqueue-based loop and embed
		2991	it into your default loop (which might use e.g. poll). Overall operation
		2992	will be a bit slower because first libev has to call C<poll> and then
		2993	C<kevent>, but at least you can use both mechanisms for what they are
		2994	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2995
		2996	As for prioritising I/O: under rare circumstances you have the case where
		2997	some fds have to be watched and handled very quickly (with low latency),
		2998	and even priorities and idle watchers might have too much overhead. In
		2999	this case you would put all the high priority stuff in one loop and all
		3000	the rest in a second one, and embed the second one in the first.
		3001
		3002	As long as the watcher is active, the callback will be invoked every
		3003	time there might be events pending in the embedded loop. The callback
		3004	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		3005	sweep and invoke their callbacks (the callback doesn't need to invoke the
		3006	C<ev_embed_sweep> function directly, it could also start an idle watcher
		3007	to give the embedded loop strictly lower priority for example).
		3008
		3009	You can also set the callback to C<0>, in which case the embed watcher
		3010	will automatically execute the embedded loop sweep whenever necessary.
		3011
		3012	Fork detection will be handled transparently while the C<ev_embed> watcher
		3013	is active, i.e., the embedded loop will automatically be forked when the
		3014	embedding loop forks. In other cases, the user is responsible for calling
		3015	C<ev_loop_fork> on the embedded loop.
		3016
		3017	Unfortunately, not all backends are embeddable: only the ones returned by
		3018	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		3019	portable one.
		3020
		3021	So when you want to use this feature you will always have to be prepared
		3022	that you cannot get an embeddable loop. The recommended way to get around
		3023	this is to have a separate variables for your embeddable loop, try to
		3024	create it, and if that fails, use the normal loop for everything.
		3025
		3026	=head3 C<ev_embed> and fork
		3027
		3028	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3029	automatically be applied to the embedded loop as well, so no special
		3030	fork handling is required in that case. When the watcher is not running,
		3031	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3032	as applicable.
		3033
		3034	=head3 Watcher-Specific Functions and Data Members
		3035
		3036	=over 4
		3037
		3038	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		3039
		3040	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		3041
		3042	Configures the watcher to embed the given loop, which must be
		3043	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		3044	invoked automatically, otherwise it is the responsibility of the callback
		3045	to invoke it (it will continue to be called until the sweep has been done,
		3046	if you do not want that, you need to temporarily stop the embed watcher).
		3047
		3048	=item ev_embed_sweep (loop, ev_embed *)
		3049
		3050	Make a single, non-blocking sweep over the embedded loop. This works
		3051	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
		3052	appropriate way for embedded loops.
		3053
		3054	=item struct ev_loop *other [read-only]
		3055
		3056	The embedded event loop.
		3057
		3058	=back
		3059
		3060	=head3 Examples
		3061
		3062	Example: Try to get an embeddable event loop and embed it into the default
		3063	event loop. If that is not possible, use the default loop. The default
		3064	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3065	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3066	used).
		3067
		3068	struct ev_loop *loop_hi = ev_default_init (0);
		3069	struct ev_loop *loop_lo = 0;
		3070	ev_embed embed;
		3071
		3072	// see if there is a chance of getting one that works
		3073	// (remember that a flags value of 0 means autodetection)
		3074	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3075	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3076	: 0;
		3077
		3078	// if we got one, then embed it, otherwise default to loop_hi
		3079	if (loop_lo)
		3080	{
		3081	ev_embed_init (&embed, 0, loop_lo);
		3082	ev_embed_start (loop_hi, &embed);
		3083	}
		3084	else
		3085	loop_lo = loop_hi;
		3086
		3087	Example: Check if kqueue is available but not recommended and create
		3088	a kqueue backend for use with sockets (which usually work with any
		3089	kqueue implementation). Store the kqueue/socket-only event loop in
		3090	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3091
		3092	struct ev_loop *loop = ev_default_init (0);
		3093	struct ev_loop *loop_socket = 0;
		3094	ev_embed embed;
		3095
		3096	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3097	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3098	{
		3099	ev_embed_init (&embed, 0, loop_socket);
		3100	ev_embed_start (loop, &embed);
		3101	}
		3102
		3103	if (!loop_socket)
		3104	loop_socket = loop;
		3105
		3106	// now use loop_socket for all sockets, and loop for everything else
		3107
		3108
		3109	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3110
		3111	Fork watchers are called when a C<fork ()> was detected (usually because
		3112	whoever is a good citizen cared to tell libev about it by calling
		3113	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		3114	event loop blocks next and before C<ev_check> watchers are being called,
		3115	and only in the child after the fork. If whoever good citizen calling
		3116	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		3117	handlers will be invoked, too, of course.
		3118
		3119	=head3 The special problem of life after fork - how is it possible?
		3120
		3121	Most uses of C<fork()> consist of forking, then some simple calls to set
		3122	up/change the process environment, followed by a call to C<exec()>. This
		3123	sequence should be handled by libev without any problems.
		3124
		3125	This changes when the application actually wants to do event handling
		3126	in the child, or both parent in child, in effect "continuing" after the
		3127	fork.
		3128
		3129	The default mode of operation (for libev, with application help to detect
		3130	forks) is to duplicate all the state in the child, as would be expected
		3131	when I<either> the parent I<or> the child process continues.
		3132
		3133	When both processes want to continue using libev, then this is usually the
		3134	wrong result. In that case, usually one process (typically the parent) is
		3135	supposed to continue with all watchers in place as before, while the other
		3136	process typically wants to start fresh, i.e. without any active watchers.
		3137
		3138	The cleanest and most efficient way to achieve that with libev is to
		3139	simply create a new event loop, which of course will be "empty", and
		3140	use that for new watchers. This has the advantage of not touching more
		3141	memory than necessary, and thus avoiding the copy-on-write, and the
		3142	disadvantage of having to use multiple event loops (which do not support
		3143	signal watchers).
		3144
		3145	When this is not possible, or you want to use the default loop for
		3146	other reasons, then in the process that wants to start "fresh", call
		3147	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3148	Destroying the default loop will "orphan" (not stop) all registered
		3149	watchers, so you have to be careful not to execute code that modifies
		3150	those watchers. Note also that in that case, you have to re-register any
		3151	signal watchers.
		3152
		3153	=head3 Watcher-Specific Functions and Data Members
		3154
		3155	=over 4
		3156
		3157	=item ev_fork_init (ev_fork *, callback)
		3158
		3159	Initialises and configures the fork watcher - it has no parameters of any
		3160	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3161	really.
		3162
		3163	=back
		3164
		3165
		3166	=head2 C<ev_cleanup> - even the best things end
		3167
		3168	Cleanup watchers are called just before the event loop is being destroyed
		3169	by a call to C<ev_loop_destroy>.
		3170
		3171	While there is no guarantee that the event loop gets destroyed, cleanup
		3172	watchers provide a convenient method to install cleanup hooks for your
		3173	program, worker threads and so on - you just to make sure to destroy the
		3174	loop when you want them to be invoked.
		3175
		3176	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3177	all other watchers, they do not keep a reference to the event loop (which
		3178	makes a lot of sense if you think about it). Like all other watchers, you
		3179	can call libev functions in the callback, except C<ev_cleanup_start>.
		3180
		3181	=head3 Watcher-Specific Functions and Data Members
		3182
		3183	=over 4
		3184
		3185	=item ev_cleanup_init (ev_cleanup *, callback)
		3186
		3187	Initialises and configures the cleanup watcher - it has no parameters of
		3188	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3189	pointless, I assure you.
		3190
		3191	=back
		3192
		3193	Example: Register an atexit handler to destroy the default loop, so any
		3194	cleanup functions are called.
		3195
		3196	static void
		3197	program_exits (void)
		3198	{
		3199	ev_loop_destroy (EV_DEFAULT_UC);
		3200	}
		3201
		3202	...
		3203	atexit (program_exits);
		3204
		3205
		3206	=head2 C<ev_async> - how to wake up an event loop
		3207
		3208	In general, you cannot use an C<ev_loop> from multiple threads or other
		3209	asynchronous sources such as signal handlers (as opposed to multiple event
		3210	loops - those are of course safe to use in different threads).
		3211
		3212	Sometimes, however, you need to wake up an event loop you do not control,
		3213	for example because it belongs to another thread. This is what C<ev_async>
		3214	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3215	it by calling C<ev_async_send>, which is thread- and signal safe.
		3216
		3217	This functionality is very similar to C<ev_signal> watchers, as signals,
		3218	too, are asynchronous in nature, and signals, too, will be compressed
		3219	(i.e. the number of callback invocations may be less than the number of
		3220	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3221	of "global async watchers" by using a watcher on an otherwise unused
		3222	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3223	even without knowing which loop owns the signal.
		3224
		3225	=head3 Queueing
		3226
		3227	C<ev_async> does not support queueing of data in any way. The reason
		3228	is that the author does not know of a simple (or any) algorithm for a
		3229	multiple-writer-single-reader queue that works in all cases and doesn't
		3230	need elaborate support such as pthreads or unportable memory access
		3231	semantics.
		3232
		3233	That means that if you want to queue data, you have to provide your own
		3234	queue. But at least I can tell you how to implement locking around your
		3235	queue:
		3236
		3237	=over 4
		3238
		3239	=item queueing from a signal handler context
		3240
		3241	To implement race-free queueing, you simply add to the queue in the signal
		3242	handler but you block the signal handler in the watcher callback. Here is
		3243	an example that does that for some fictitious SIGUSR1 handler:
		3244
		3245	static ev_async mysig;
		3246
		3247	static void
		3248	sigusr1_handler (void)
		3249	{
		3250	sometype data;
		3251
		3252	// no locking etc.
		3253	queue_put (data);
		3254	ev_async_send (EV_DEFAULT_ &mysig);
		3255	}
		3256
		3257	static void
		3258	mysig_cb (EV_P_ ev_async *w, int revents)
		3259	{
		3260	sometype data;
		3261	sigset_t block, prev;
		3262
		3263	sigemptyset (&block);
		3264	sigaddset (&block, SIGUSR1);
		3265	sigprocmask (SIG_BLOCK, &block, &prev);
		3266
		3267	while (queue_get (&data))
		3268	process (data);
		3269
		3270	if (sigismember (&prev, SIGUSR1)
		3271	sigprocmask (SIG_UNBLOCK, &block, 0);
		3272	}
		3273
		3274	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3275	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3276	either...).
		3277
		3278	=item queueing from a thread context
		3279
		3280	The strategy for threads is different, as you cannot (easily) block
		3281	threads but you can easily preempt them, so to queue safely you need to
		3282	employ a traditional mutex lock, such as in this pthread example:
		3283
		3284	static ev_async mysig;
		3285	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3286
		3287	static void
		3288	otherthread (void)
		3289	{
		3290	// only need to lock the actual queueing operation
		3291	pthread_mutex_lock (&mymutex);
		3292	queue_put (data);
		3293	pthread_mutex_unlock (&mymutex);
		3294
		3295	ev_async_send (EV_DEFAULT_ &mysig);
		3296	}
		3297
		3298	static void
		3299	mysig_cb (EV_P_ ev_async *w, int revents)
		3300	{
		3301	pthread_mutex_lock (&mymutex);
		3302
		3303	while (queue_get (&data))
		3304	process (data);
		3305
		3306	pthread_mutex_unlock (&mymutex);
		3307	}
		3308
		3309	=back
		3310
		3311
		3312	=head3 Watcher-Specific Functions and Data Members
		3313
		3314	=over 4
		3315
		3316	=item ev_async_init (ev_async *, callback)
		3317
		3318	Initialises and configures the async watcher - it has no parameters of any
		3319	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3320	trust me.
		3321
		3322	=item ev_async_send (loop, ev_async *)
		3323
		3324	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3325	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3326	returns.
		3327
		3328	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3329	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3330	embedding section below on what exactly this means).
		3331
		3332	Note that, as with other watchers in libev, multiple events might get
		3333	compressed into a single callback invocation (another way to look at
		3334	this is that C<ev_async> watchers are level-triggered: they are set on
		3335	C<ev_async_send>, reset when the event loop detects that).
		3336
		3337	This call incurs the overhead of at most one extra system call per event
		3338	loop iteration, if the event loop is blocked, and no syscall at all if
		3339	the event loop (or your program) is processing events. That means that
		3340	repeated calls are basically free (there is no need to avoid calls for
		3341	performance reasons) and that the overhead becomes smaller (typically
		3342	zero) under load.
		3343
		3344	=item bool = ev_async_pending (ev_async *)
		3345
		3346	Returns a non-zero value when C<ev_async_send> has been called on the
		3347	watcher but the event has not yet been processed (or even noted) by the
		3348	event loop.
		3349
		3350	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3351	the loop iterates next and checks for the watcher to have become active,
		3352	it will reset the flag again. C<ev_async_pending> can be used to very
		3353	quickly check whether invoking the loop might be a good idea.
		3354
		3355	Not that this does I<not> check whether the watcher itself is pending,
		3356	only whether it has been requested to make this watcher pending: there
		3357	is a time window between the event loop checking and resetting the async
		3358	notification, and the callback being invoked.
		3359
		3360	=back
		3361
		3362
712	=head1 OTHER FUNCTIONS	3363	=head1 OTHER FUNCTIONS
713		3364
714	There are some other functions of possible interest. Described. Here. Now.	3365	There are some other functions of possible interest. Described. Here. Now.
715		3366
716	=over 4	3367	=over 4
717		3368
718	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3369	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
719		3370
720	This function combines a simple timer and an I/O watcher, calls your	3371	This function combines a simple timer and an I/O watcher, calls your
721	callback on whichever event happens first and automatically stop both	3372	callback on whichever event happens first and automatically stops both
722	watchers. This is useful if you want to wait for a single event on an fd	3373	watchers. This is useful if you want to wait for a single event on an fd
723	or timeout without havign to allocate/configure/start/stop/free one or	3374	or timeout without having to allocate/configure/start/stop/free one or
724	more watchers yourself.	3375	more watchers yourself.
725		3376
726	If C<fd> is less than 0, then no I/O watcher will be started and events	3377	If C<fd> is less than 0, then no I/O watcher will be started and the
727	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3378	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
728	C<events> set will be craeted and started.	3379	the given C<fd> and C<events> set will be created and started.
729		3380
730	If C<timeout> is less than 0, then no timeout watcher will be	3381	If C<timeout> is less than 0, then no timeout watcher will be
731	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3382	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
732	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3383	repeat = 0) will be started. C<0> is a valid timeout.
733	dubious value.
734		3384
735	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3385	The callback has the type C<void (*cb)(int revents, void *arg)> and is
736	passed an events set like normal event callbacks (with a combination of	3386	passed an C<revents> set like normal event callbacks (a combination of
737	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3387	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
738	value passed to C<ev_once>:	3388	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3389	a timeout and an io event at the same time - you probably should give io
		3390	events precedence.
739		3391
		3392	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3393
740	static void stdin_ready (int revents, void *arg)	3394	static void stdin_ready (int revents, void *arg)
741	{	3395	{
742	if (revents & EV_TIMEOUT)
743	/* doh, nothing entered */;
744	else if (revents & EV_READ)	3396	if (revents & EV_READ)
745	/* stdin might have data for us, joy! */;	3397	/* stdin might have data for us, joy! */;
		3398	else if (revents & EV_TIMER)
		3399	/* doh, nothing entered */;
746	}	3400	}
747		3401
748	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3402	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
749
750	=item ev_feed_event (loop, watcher, int events)
751
752	Feeds the given event set into the event loop, as if the specified event
753	had happened for the specified watcher (which must be a pointer to an
754	initialised but not necessarily started event watcher).
755		3403
756	=item ev_feed_fd_event (loop, int fd, int revents)	3404	=item ev_feed_fd_event (loop, int fd, int revents)
757		3405
758	Feed an event on the given fd, as if a file descriptor backend detected	3406	Feed an event on the given fd, as if a file descriptor backend detected
759	the given events it.	3407	the given events it.
760		3408
761	=item ev_feed_signal_event (loop, int signum)	3409	=item ev_feed_signal_event (loop, int signum)
762		3410
763	Feed an event as if the given signal occured (loop must be the default loop!).	3411	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3412	which is async-safe.
764		3413
765	=back	3414	=back
766		3415
		3416
		3417	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3418
		3419	This section explains some common idioms that are not immediately
		3420	obvious. Note that examples are sprinkled over the whole manual, and this
		3421	section only contains stuff that wouldn't fit anywhere else.
		3422
		3423	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3424
		3425	Each watcher has, by default, a C<void *data> member that you can read
		3426	or modify at any time: libev will completely ignore it. This can be used
		3427	to associate arbitrary data with your watcher. If you need more data and
		3428	don't want to allocate memory separately and store a pointer to it in that
		3429	data member, you can also "subclass" the watcher type and provide your own
		3430	data:
		3431
		3432	struct my_io
		3433	{
		3434	ev_io io;
		3435	int otherfd;
		3436	void *somedata;
		3437	struct whatever *mostinteresting;
		3438	};
		3439
		3440	...
		3441	struct my_io w;
		3442	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3443
		3444	And since your callback will be called with a pointer to the watcher, you
		3445	can cast it back to your own type:
		3446
		3447	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3448	{
		3449	struct my_io *w = (struct my_io *)w_;
		3450	...
		3451	}
		3452
		3453	More interesting and less C-conformant ways of casting your callback
		3454	function type instead have been omitted.
		3455
		3456	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3457
		3458	Another common scenario is to use some data structure with multiple
		3459	embedded watchers, in effect creating your own watcher that combines
		3460	multiple libev event sources into one "super-watcher":
		3461
		3462	struct my_biggy
		3463	{
		3464	int some_data;
		3465	ev_timer t1;
		3466	ev_timer t2;
		3467	}
		3468
		3469	In this case getting the pointer to C<my_biggy> is a bit more
		3470	complicated: Either you store the address of your C<my_biggy> struct in
		3471	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3472	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3473	real programmers):
		3474
		3475	#include <stddef.h>
		3476
		3477	static void
		3478	t1_cb (EV_P_ ev_timer *w, int revents)
		3479	{
		3480	struct my_biggy big = (struct my_biggy *)
		3481	(((char *)w) - offsetof (struct my_biggy, t1));
		3482	}
		3483
		3484	static void
		3485	t2_cb (EV_P_ ev_timer *w, int revents)
		3486	{
		3487	struct my_biggy big = (struct my_biggy *)
		3488	(((char *)w) - offsetof (struct my_biggy, t2));
		3489	}
		3490
		3491	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3492
		3493	Often (especially in GUI toolkits) there are places where you have
		3494	I<modal> interaction, which is most easily implemented by recursively
		3495	invoking C<ev_run>.
		3496
		3497	This brings the problem of exiting - a callback might want to finish the
		3498	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3499	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3500	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3501	other combination: In these cases, C<ev_break> will not work alone.
		3502
		3503	The solution is to maintain "break this loop" variable for each C<ev_run>
		3504	invocation, and use a loop around C<ev_run> until the condition is
		3505	triggered, using C<EVRUN_ONCE>:
		3506
		3507	// main loop
		3508	int exit_main_loop = 0;
		3509
		3510	while (!exit_main_loop)
		3511	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3512
		3513	// in a model watcher
		3514	int exit_nested_loop = 0;
		3515
		3516	while (!exit_nested_loop)
		3517	ev_run (EV_A_ EVRUN_ONCE);
		3518
		3519	To exit from any of these loops, just set the corresponding exit variable:
		3520
		3521	// exit modal loop
		3522	exit_nested_loop = 1;
		3523
		3524	// exit main program, after modal loop is finished
		3525	exit_main_loop = 1;
		3526
		3527	// exit both
		3528	exit_main_loop = exit_nested_loop = 1;
		3529
		3530	=head2 THREAD LOCKING EXAMPLE
		3531
		3532	Here is a fictitious example of how to run an event loop in a different
		3533	thread from where callbacks are being invoked and watchers are
		3534	created/added/removed.
		3535
		3536	For a real-world example, see the C<EV::Loop::Async> perl module,
		3537	which uses exactly this technique (which is suited for many high-level
		3538	languages).
		3539
		3540	The example uses a pthread mutex to protect the loop data, a condition
		3541	variable to wait for callback invocations, an async watcher to notify the
		3542	event loop thread and an unspecified mechanism to wake up the main thread.
		3543
		3544	First, you need to associate some data with the event loop:
		3545
		3546	typedef struct {
		3547	mutex_t lock; /* global loop lock */
		3548	ev_async async_w;
		3549	thread_t tid;
		3550	cond_t invoke_cv;
		3551	} userdata;
		3552
		3553	void prepare_loop (EV_P)
		3554	{
		3555	// for simplicity, we use a static userdata struct.
		3556	static userdata u;
		3557
		3558	ev_async_init (&u->async_w, async_cb);
		3559	ev_async_start (EV_A_ &u->async_w);
		3560
		3561	pthread_mutex_init (&u->lock, 0);
		3562	pthread_cond_init (&u->invoke_cv, 0);
		3563
		3564	// now associate this with the loop
		3565	ev_set_userdata (EV_A_ u);
		3566	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3567	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3568
		3569	// then create the thread running ev_run
		3570	pthread_create (&u->tid, 0, l_run, EV_A);
		3571	}
		3572
		3573	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3574	solely to wake up the event loop so it takes notice of any new watchers
		3575	that might have been added:
		3576
		3577	static void
		3578	async_cb (EV_P_ ev_async *w, int revents)
		3579	{
		3580	// just used for the side effects
		3581	}
		3582
		3583	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3584	protecting the loop data, respectively.
		3585
		3586	static void
		3587	l_release (EV_P)
		3588	{
		3589	userdata *u = ev_userdata (EV_A);
		3590	pthread_mutex_unlock (&u->lock);
		3591	}
		3592
		3593	static void
		3594	l_acquire (EV_P)
		3595	{
		3596	userdata *u = ev_userdata (EV_A);
		3597	pthread_mutex_lock (&u->lock);
		3598	}
		3599
		3600	The event loop thread first acquires the mutex, and then jumps straight
		3601	into C<ev_run>:
		3602
		3603	void *
		3604	l_run (void *thr_arg)
		3605	{
		3606	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3607
		3608	l_acquire (EV_A);
		3609	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3610	ev_run (EV_A_ 0);
		3611	l_release (EV_A);
		3612
		3613	return 0;
		3614	}
		3615
		3616	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3617	signal the main thread via some unspecified mechanism (signals? pipe
		3618	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3619	have been called (in a while loop because a) spurious wakeups are possible
		3620	and b) skipping inter-thread-communication when there are no pending
		3621	watchers is very beneficial):
		3622
		3623	static void
		3624	l_invoke (EV_P)
		3625	{
		3626	userdata *u = ev_userdata (EV_A);
		3627
		3628	while (ev_pending_count (EV_A))
		3629	{
		3630	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3631	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3632	}
		3633	}
		3634
		3635	Now, whenever the main thread gets told to invoke pending watchers, it
		3636	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3637	thread to continue:
		3638
		3639	static void
		3640	real_invoke_pending (EV_P)
		3641	{
		3642	userdata *u = ev_userdata (EV_A);
		3643
		3644	pthread_mutex_lock (&u->lock);
		3645	ev_invoke_pending (EV_A);
		3646	pthread_cond_signal (&u->invoke_cv);
		3647	pthread_mutex_unlock (&u->lock);
		3648	}
		3649
		3650	Whenever you want to start/stop a watcher or do other modifications to an
		3651	event loop, you will now have to lock:
		3652
		3653	ev_timer timeout_watcher;
		3654	userdata *u = ev_userdata (EV_A);
		3655
		3656	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3657
		3658	pthread_mutex_lock (&u->lock);
		3659	ev_timer_start (EV_A_ &timeout_watcher);
		3660	ev_async_send (EV_A_ &u->async_w);
		3661	pthread_mutex_unlock (&u->lock);
		3662
		3663	Note that sending the C<ev_async> watcher is required because otherwise
		3664	an event loop currently blocking in the kernel will have no knowledge
		3665	about the newly added timer. By waking up the loop it will pick up any new
		3666	watchers in the next event loop iteration.
		3667
		3668	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3669
		3670	While the overhead of a callback that e.g. schedules a thread is small, it
		3671	is still an overhead. If you embed libev, and your main usage is with some
		3672	kind of threads or coroutines, you might want to customise libev so that
		3673	doesn't need callbacks anymore.
		3674
		3675	Imagine you have coroutines that you can switch to using a function
		3676	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3677	and that due to some magic, the currently active coroutine is stored in a
		3678	global called C<current_coro>. Then you can build your own "wait for libev
		3679	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3680	the differing C<;> conventions):
		3681
		3682	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3683	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3684
		3685	That means instead of having a C callback function, you store the
		3686	coroutine to switch to in each watcher, and instead of having libev call
		3687	your callback, you instead have it switch to that coroutine.
		3688
		3689	A coroutine might now wait for an event with a function called
		3690	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3691	matter when, or whether the watcher is active or not when this function is
		3692	called):
		3693
		3694	void
		3695	wait_for_event (ev_watcher *w)
		3696	{
		3697	ev_cb_set (w) = current_coro;
		3698	switch_to (libev_coro);
		3699	}
		3700
		3701	That basically suspends the coroutine inside C<wait_for_event> and
		3702	continues the libev coroutine, which, when appropriate, switches back to
		3703	this or any other coroutine. I am sure if you sue this your own :)
		3704
		3705	You can do similar tricks if you have, say, threads with an event queue -
		3706	instead of storing a coroutine, you store the queue object and instead of
		3707	switching to a coroutine, you push the watcher onto the queue and notify
		3708	any waiters.
		3709
		3710	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3711	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3712
		3713	// my_ev.h
		3714	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3715	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3716	#include "../libev/ev.h"
		3717
		3718	// my_ev.c
		3719	#define EV_H "my_ev.h"
		3720	#include "../libev/ev.c"
		3721
		3722	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3723	F<my_ev.c> into your project. When properly specifying include paths, you
		3724	can even use F<ev.h> as header file name directly.
		3725
		3726
		3727	=head1 LIBEVENT EMULATION
		3728
		3729	Libev offers a compatibility emulation layer for libevent. It cannot
		3730	emulate the internals of libevent, so here are some usage hints:
		3731
		3732	=over 4
		3733
		3734	=item * Only the libevent-1.4.1-beta API is being emulated.
		3735
		3736	This was the newest libevent version available when libev was implemented,
		3737	and is still mostly unchanged in 2010.
		3738
		3739	=item * Use it by including <event.h>, as usual.
		3740
		3741	=item * The following members are fully supported: ev_base, ev_callback,
		3742	ev_arg, ev_fd, ev_res, ev_events.
		3743
		3744	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		3745	maintained by libev, it does not work exactly the same way as in libevent (consider
		3746	it a private API).
		3747
		3748	=item * Priorities are not currently supported. Initialising priorities
		3749	will fail and all watchers will have the same priority, even though there
		3750	is an ev_pri field.
		3751
		3752	=item * In libevent, the last base created gets the signals, in libev, the
		3753	base that registered the signal gets the signals.
		3754
		3755	=item * Other members are not supported.
		3756
		3757	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		3758	to use the libev header file and library.
		3759
		3760	=back
		3761
		3762	=head1 C++ SUPPORT
		3763
		3764	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3765	you to use some convenience methods to start/stop watchers and also change
		3766	the callback model to a model using method callbacks on objects.
		3767
		3768	To use it,
		3769
		3770	#include <ev++.h>
		3771
		3772	This automatically includes F<ev.h> and puts all of its definitions (many
		3773	of them macros) into the global namespace. All C++ specific things are
		3774	put into the C<ev> namespace. It should support all the same embedding
		3775	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3776
		3777	Care has been taken to keep the overhead low. The only data member the C++
		3778	classes add (compared to plain C-style watchers) is the event loop pointer
		3779	that the watcher is associated with (or no additional members at all if
		3780	you disable C<EV_MULTIPLICITY> when embedding libev).
		3781
		3782	Currently, functions, static and non-static member functions and classes
		3783	with C<operator ()> can be used as callbacks. Other types should be easy
		3784	to add as long as they only need one additional pointer for context. If
		3785	you need support for other types of functors please contact the author
		3786	(preferably after implementing it).
		3787
		3788	Here is a list of things available in the C<ev> namespace:
		3789
		3790	=over 4
		3791
		3792	=item C<ev::READ>, C<ev::WRITE> etc.
		3793
		3794	These are just enum values with the same values as the C<EV_READ> etc.
		3795	macros from F<ev.h>.
		3796
		3797	=item C<ev::tstamp>, C<ev::now>
		3798
		3799	Aliases to the same types/functions as with the C<ev_> prefix.
		3800
		3801	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		3802
		3803	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		3804	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		3805	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3806	defines by many implementations.
		3807
		3808	All of those classes have these methods:
		3809
		3810	=over 4
		3811
		3812	=item ev::TYPE::TYPE ()
		3813
		3814	=item ev::TYPE::TYPE (loop)
		3815
		3816	=item ev::TYPE::~TYPE
		3817
		3818	The constructor (optionally) takes an event loop to associate the watcher
		3819	with. If it is omitted, it will use C<EV_DEFAULT>.
		3820
		3821	The constructor calls C<ev_init> for you, which means you have to call the
		3822	C<set> method before starting it.
		3823
		3824	It will not set a callback, however: You have to call the templated C<set>
		3825	method to set a callback before you can start the watcher.
		3826
		3827	(The reason why you have to use a method is a limitation in C++ which does
		3828	not allow explicit template arguments for constructors).
		3829
		3830	The destructor automatically stops the watcher if it is active.
		3831
		3832	=item w->set<class, &class::method> (object *)
		3833
		3834	This method sets the callback method to call. The method has to have a
		3835	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3836	first argument and the C<revents> as second. The object must be given as
		3837	parameter and is stored in the C<data> member of the watcher.
		3838
		3839	This method synthesizes efficient thunking code to call your method from
		3840	the C callback that libev requires. If your compiler can inline your
		3841	callback (i.e. it is visible to it at the place of the C<set> call and
		3842	your compiler is good :), then the method will be fully inlined into the
		3843	thunking function, making it as fast as a direct C callback.
		3844
		3845	Example: simple class declaration and watcher initialisation
		3846
		3847	struct myclass
		3848	{
		3849	void io_cb (ev::io &w, int revents) { }
		3850	}
		3851
		3852	myclass obj;
		3853	ev::io iow;
		3854	iow.set <myclass, &myclass::io_cb> (&obj);
		3855
		3856	=item w->set (object *)
		3857
		3858	This is a variation of a method callback - leaving out the method to call
		3859	will default the method to C<operator ()>, which makes it possible to use
		3860	functor objects without having to manually specify the C<operator ()> all
		3861	the time. Incidentally, you can then also leave out the template argument
		3862	list.
		3863
		3864	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3865	int revents)>.
		3866
		3867	See the method-C<set> above for more details.
		3868
		3869	Example: use a functor object as callback.
		3870
		3871	struct myfunctor
		3872	{
		3873	void operator() (ev::io &w, int revents)
		3874	{
		3875	...
		3876	}
		3877	}
		3878
		3879	myfunctor f;
		3880
		3881	ev::io w;
		3882	w.set (&f);
		3883
		3884	=item w->set<function> (void *data = 0)
		3885
		3886	Also sets a callback, but uses a static method or plain function as
		3887	callback. The optional C<data> argument will be stored in the watcher's
		3888	C<data> member and is free for you to use.
		3889
		3890	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3891
		3892	See the method-C<set> above for more details.
		3893
		3894	Example: Use a plain function as callback.
		3895
		3896	static void io_cb (ev::io &w, int revents) { }
		3897	iow.set <io_cb> ();
		3898
		3899	=item w->set (loop)
		3900
		3901	Associates a different C<struct ev_loop> with this watcher. You can only
		3902	do this when the watcher is inactive (and not pending either).
		3903
		3904	=item w->set ([arguments])
		3905
		3906	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
		3907	method or a suitable start method must be called at least once. Unlike the
		3908	C counterpart, an active watcher gets automatically stopped and restarted
		3909	when reconfiguring it with this method.
		3910
		3911	=item w->start ()
		3912
		3913	Starts the watcher. Note that there is no C<loop> argument, as the
		3914	constructor already stores the event loop.
		3915
		3916	=item w->start ([arguments])
		3917
		3918	Instead of calling C<set> and C<start> methods separately, it is often
		3919	convenient to wrap them in one call. Uses the same type of arguments as
		3920	the configure C<set> method of the watcher.
		3921
		3922	=item w->stop ()
		3923
		3924	Stops the watcher if it is active. Again, no C<loop> argument.
		3925
		3926	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		3927
		3928	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		3929	C<ev_TYPE_again> function.
		3930
		3931	=item w->sweep () (C<ev::embed> only)
		3932
		3933	Invokes C<ev_embed_sweep>.
		3934
		3935	=item w->update () (C<ev::stat> only)
		3936
		3937	Invokes C<ev_stat_stat>.
		3938
		3939	=back
		3940
		3941	=back
		3942
		3943	Example: Define a class with two I/O and idle watchers, start the I/O
		3944	watchers in the constructor.
		3945
		3946	class myclass
		3947	{
		3948	ev::io io ; void io_cb (ev::io &w, int revents);
		3949	ev::io io2 ; void io2_cb (ev::io &w, int revents);
		3950	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3951
		3952	myclass (int fd)
		3953	{
		3954	io .set <myclass, &myclass::io_cb > (this);
		3955	io2 .set <myclass, &myclass::io2_cb > (this);
		3956	idle.set <myclass, &myclass::idle_cb> (this);
		3957
		3958	io.set (fd, ev::WRITE); // configure the watcher
		3959	io.start (); // start it whenever convenient
		3960
		3961	io2.start (fd, ev::READ); // set + start in one call
		3962	}
		3963	};
		3964
		3965
		3966	=head1 OTHER LANGUAGE BINDINGS
		3967
		3968	Libev does not offer other language bindings itself, but bindings for a
		3969	number of languages exist in the form of third-party packages. If you know
		3970	any interesting language binding in addition to the ones listed here, drop
		3971	me a note.
		3972
		3973	=over 4
		3974
		3975	=item Perl
		3976
		3977	The EV module implements the full libev API and is actually used to test
		3978	libev. EV is developed together with libev. Apart from the EV core module,
		3979	there are additional modules that implement libev-compatible interfaces
		3980	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3981	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3982	and C<EV::Glib>).
		3983
		3984	It can be found and installed via CPAN, its homepage is at
		3985	L<http://software.schmorp.de/pkg/EV>.
		3986
		3987	=item Python
		3988
		3989	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3990	seems to be quite complete and well-documented.
		3991
		3992	=item Ruby
		3993
		3994	Tony Arcieri has written a ruby extension that offers access to a subset
		3995	of the libev API and adds file handle abstractions, asynchronous DNS and
		3996	more on top of it. It can be found via gem servers. Its homepage is at
		3997	L<http://rev.rubyforge.org/>.
		3998
		3999	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4000	makes rev work even on mingw.
		4001
		4002	=item Haskell
		4003
		4004	A haskell binding to libev is available at
		4005	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4006
		4007	=item D
		4008
		4009	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4010	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4011
		4012	=item Ocaml
		4013
		4014	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4015	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4016
		4017	=item Lua
		4018
		4019	Brian Maher has written a partial interface to libev for lua (at the
		4020	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4021	L<http://github.com/brimworks/lua-ev>.
		4022
		4023	=back
		4024
		4025
		4026	=head1 MACRO MAGIC
		4027
		4028	Libev can be compiled with a variety of options, the most fundamental
		4029	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		4030	functions and callbacks have an initial C<struct ev_loop *> argument.
		4031
		4032	To make it easier to write programs that cope with either variant, the
		4033	following macros are defined:
		4034
		4035	=over 4
		4036
		4037	=item C<EV_A>, C<EV_A_>
		4038
		4039	This provides the loop I<argument> for functions, if one is required ("ev
		4040	loop argument"). The C<EV_A> form is used when this is the sole argument,
		4041	C<EV_A_> is used when other arguments are following. Example:
		4042
		4043	ev_unref (EV_A);
		4044	ev_timer_add (EV_A_ watcher);
		4045	ev_run (EV_A_ 0);
		4046
		4047	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		4048	which is often provided by the following macro.
		4049
		4050	=item C<EV_P>, C<EV_P_>
		4051
		4052	This provides the loop I<parameter> for functions, if one is required ("ev
		4053	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		4054	C<EV_P_> is used when other parameters are following. Example:
		4055
		4056	// this is how ev_unref is being declared
		4057	static void ev_unref (EV_P);
		4058
		4059	// this is how you can declare your typical callback
		4060	static void cb (EV_P_ ev_timer *w, int revents)
		4061
		4062	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		4063	suitable for use with C<EV_A>.
		4064
		4065	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		4066
		4067	Similar to the other two macros, this gives you the value of the default
		4068	loop, if multiple loops are supported ("ev loop default").
		4069
		4070	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4071
		4072	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4073	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4074	is undefined when the default loop has not been initialised by a previous
		4075	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4076
		4077	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4078	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		4079
		4080	=back
		4081
		4082	Example: Declare and initialise a check watcher, utilising the above
		4083	macros so it will work regardless of whether multiple loops are supported
		4084	or not.
		4085
		4086	static void
		4087	check_cb (EV_P_ ev_timer *w, int revents)
		4088	{
		4089	ev_check_stop (EV_A_ w);
		4090	}
		4091
		4092	ev_check check;
		4093	ev_check_init (&check, check_cb);
		4094	ev_check_start (EV_DEFAULT_ &check);
		4095	ev_run (EV_DEFAULT_ 0);
		4096
		4097	=head1 EMBEDDING
		4098
		4099	Libev can (and often is) directly embedded into host
		4100	applications. Examples of applications that embed it include the Deliantra
		4101	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		4102	and rxvt-unicode.
		4103
		4104	The goal is to enable you to just copy the necessary files into your
		4105	source directory without having to change even a single line in them, so
		4106	you can easily upgrade by simply copying (or having a checked-out copy of
		4107	libev somewhere in your source tree).
		4108
		4109	=head2 FILESETS
		4110
		4111	Depending on what features you need you need to include one or more sets of files
		4112	in your application.
		4113
		4114	=head3 CORE EVENT LOOP
		4115
		4116	To include only the libev core (all the C<ev_*> functions), with manual
		4117	configuration (no autoconf):
		4118
		4119	#define EV_STANDALONE 1
		4120	#include "ev.c"
		4121
		4122	This will automatically include F<ev.h>, too, and should be done in a
		4123	single C source file only to provide the function implementations. To use
		4124	it, do the same for F<ev.h> in all files wishing to use this API (best
		4125	done by writing a wrapper around F<ev.h> that you can include instead and
		4126	where you can put other configuration options):
		4127
		4128	#define EV_STANDALONE 1
		4129	#include "ev.h"
		4130
		4131	Both header files and implementation files can be compiled with a C++
		4132	compiler (at least, that's a stated goal, and breakage will be treated
		4133	as a bug).
		4134
		4135	You need the following files in your source tree, or in a directory
		4136	in your include path (e.g. in libev/ when using -Ilibev):
		4137
		4138	ev.h
		4139	ev.c
		4140	ev_vars.h
		4141	ev_wrap.h
		4142
		4143	ev_win32.c required on win32 platforms only
		4144
		4145	ev_select.c only when select backend is enabled (which is enabled by default)
		4146	ev_poll.c only when poll backend is enabled (disabled by default)
		4147	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		4148	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		4149	ev_port.c only when the solaris port backend is enabled (disabled by default)
		4150
		4151	F<ev.c> includes the backend files directly when enabled, so you only need
		4152	to compile this single file.
		4153
		4154	=head3 LIBEVENT COMPATIBILITY API
		4155
		4156	To include the libevent compatibility API, also include:
		4157
		4158	#include "event.c"
		4159
		4160	in the file including F<ev.c>, and:
		4161
		4162	#include "event.h"
		4163
		4164	in the files that want to use the libevent API. This also includes F<ev.h>.
		4165
		4166	You need the following additional files for this:
		4167
		4168	event.h
		4169	event.c
		4170
		4171	=head3 AUTOCONF SUPPORT
		4172
		4173	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		4174	whatever way you want, you can also C<m4_include([libev.m4])> in your
		4175	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		4176	include F<config.h> and configure itself accordingly.
		4177
		4178	For this of course you need the m4 file:
		4179
		4180	libev.m4
		4181
		4182	=head2 PREPROCESSOR SYMBOLS/MACROS
		4183
		4184	Libev can be configured via a variety of preprocessor symbols you have to
		4185	define before including (or compiling) any of its files. The default in
		4186	the absence of autoconf is documented for every option.
		4187
		4188	Symbols marked with "(h)" do not change the ABI, and can have different
		4189	values when compiling libev vs. including F<ev.h>, so it is permissible
		4190	to redefine them before including F<ev.h> without breaking compatibility
		4191	to a compiled library. All other symbols change the ABI, which means all
		4192	users of libev and the libev code itself must be compiled with compatible
		4193	settings.
		4194
		4195	=over 4
		4196
		4197	=item EV_COMPAT3 (h)
		4198
		4199	Backwards compatibility is a major concern for libev. This is why this
		4200	release of libev comes with wrappers for the functions and symbols that
		4201	have been renamed between libev version 3 and 4.
		4202
		4203	You can disable these wrappers (to test compatibility with future
		4204	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4205	sources. This has the additional advantage that you can drop the C<struct>
		4206	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4207	typedef in that case.
		4208
		4209	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4210	and in some even more future version the compatibility code will be
		4211	removed completely.
		4212
		4213	=item EV_STANDALONE (h)
		4214
		4215	Must always be C<1> if you do not use autoconf configuration, which
		4216	keeps libev from including F<config.h>, and it also defines dummy
		4217	implementations for some libevent functions (such as logging, which is not
		4218	supported). It will also not define any of the structs usually found in
		4219	F<event.h> that are not directly supported by the libev core alone.
		4220
		4221	In standalone mode, libev will still try to automatically deduce the
		4222	configuration, but has to be more conservative.
		4223
		4224	=item EV_USE_FLOOR
		4225
		4226	If defined to be C<1>, libev will use the C<floor ()> function for its
		4227	periodic reschedule calculations, otherwise libev will fall back on a
		4228	portable (slower) implementation. If you enable this, you usually have to
		4229	link against libm or something equivalent. Enabling this when the C<floor>
		4230	function is not available will fail, so the safe default is to not enable
		4231	this.
		4232
		4233	=item EV_USE_MONOTONIC
		4234
		4235	If defined to be C<1>, libev will try to detect the availability of the
		4236	monotonic clock option at both compile time and runtime. Otherwise no
		4237	use of the monotonic clock option will be attempted. If you enable this,
		4238	you usually have to link against librt or something similar. Enabling it
		4239	when the functionality isn't available is safe, though, although you have
		4240	to make sure you link against any libraries where the C<clock_gettime>
		4241	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		4242
		4243	=item EV_USE_REALTIME
		4244
		4245	If defined to be C<1>, libev will try to detect the availability of the
		4246	real-time clock option at compile time (and assume its availability
		4247	at runtime if successful). Otherwise no use of the real-time clock
		4248	option will be attempted. This effectively replaces C<gettimeofday>
		4249	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		4250	correctness. See the note about libraries in the description of
		4251	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4252	C<EV_USE_CLOCK_SYSCALL>.
		4253
		4254	=item EV_USE_CLOCK_SYSCALL
		4255
		4256	If defined to be C<1>, libev will try to use a direct syscall instead
		4257	of calling the system-provided C<clock_gettime> function. This option
		4258	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4259	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4260	programs needlessly. Using a direct syscall is slightly slower (in
		4261	theory), because no optimised vdso implementation can be used, but avoids
		4262	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4263	higher, as it simplifies linking (no need for C<-lrt>).
		4264
		4265	=item EV_USE_NANOSLEEP
		4266
		4267	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4268	and will use it for delays. Otherwise it will use C<select ()>.
		4269
		4270	=item EV_USE_EVENTFD
		4271
		4272	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4273	available and will probe for kernel support at runtime. This will improve
		4274	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4275	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4276	2.7 or newer, otherwise disabled.
		4277
		4278	=item EV_USE_SELECT
		4279
		4280	If undefined or defined to be C<1>, libev will compile in support for the
		4281	C<select>(2) backend. No attempt at auto-detection will be done: if no
		4282	other method takes over, select will be it. Otherwise the select backend
		4283	will not be compiled in.
		4284
		4285	=item EV_SELECT_USE_FD_SET
		4286
		4287	If defined to C<1>, then the select backend will use the system C<fd_set>
		4288	structure. This is useful if libev doesn't compile due to a missing
		4289	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		4290	on exotic systems. This usually limits the range of file descriptors to
		4291	some low limit such as 1024 or might have other limitations (winsocket
		4292	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		4293	configures the maximum size of the C<fd_set>.
		4294
		4295	=item EV_SELECT_IS_WINSOCKET
		4296
		4297	When defined to C<1>, the select backend will assume that
		4298	select/socket/connect etc. don't understand file descriptors but
		4299	wants osf handles on win32 (this is the case when the select to
		4300	be used is the winsock select). This means that it will call
		4301	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		4302	it is assumed that all these functions actually work on fds, even
		4303	on win32. Should not be defined on non-win32 platforms.
		4304
		4305	=item EV_FD_TO_WIN32_HANDLE(fd)
		4306
		4307	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4308	file descriptors to socket handles. When not defining this symbol (the
		4309	default), then libev will call C<_get_osfhandle>, which is usually
		4310	correct. In some cases, programs use their own file descriptor management,
		4311	in which case they can provide this function to map fds to socket handles.
		4312
		4313	=item EV_WIN32_HANDLE_TO_FD(handle)
		4314
		4315	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4316	using the standard C<_open_osfhandle> function. For programs implementing
		4317	their own fd to handle mapping, overwriting this function makes it easier
		4318	to do so. This can be done by defining this macro to an appropriate value.
		4319
		4320	=item EV_WIN32_CLOSE_FD(fd)
		4321
		4322	If programs implement their own fd to handle mapping on win32, then this
		4323	macro can be used to override the C<close> function, useful to unregister
		4324	file descriptors again. Note that the replacement function has to close
		4325	the underlying OS handle.
		4326
		4327	=item EV_USE_POLL
		4328
		4329	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		4330	backend. Otherwise it will be enabled on non-win32 platforms. It
		4331	takes precedence over select.
		4332
		4333	=item EV_USE_EPOLL
		4334
		4335	If defined to be C<1>, libev will compile in support for the Linux
		4336	C<epoll>(7) backend. Its availability will be detected at runtime,
		4337	otherwise another method will be used as fallback. This is the preferred
		4338	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4339	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4340
		4341	=item EV_USE_KQUEUE
		4342
		4343	If defined to be C<1>, libev will compile in support for the BSD style
		4344	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		4345	otherwise another method will be used as fallback. This is the preferred
		4346	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		4347	supports some types of fds correctly (the only platform we found that
		4348	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		4349	not be used unless explicitly requested. The best way to use it is to find
		4350	out whether kqueue supports your type of fd properly and use an embedded
		4351	kqueue loop.
		4352
		4353	=item EV_USE_PORT
		4354
		4355	If defined to be C<1>, libev will compile in support for the Solaris
		4356	10 port style backend. Its availability will be detected at runtime,
		4357	otherwise another method will be used as fallback. This is the preferred
		4358	backend for Solaris 10 systems.
		4359
		4360	=item EV_USE_DEVPOLL
		4361
		4362	Reserved for future expansion, works like the USE symbols above.
		4363
		4364	=item EV_USE_INOTIFY
		4365
		4366	If defined to be C<1>, libev will compile in support for the Linux inotify
		4367	interface to speed up C<ev_stat> watchers. Its actual availability will
		4368	be detected at runtime. If undefined, it will be enabled if the headers
		4369	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4370
		4371	=item EV_ATOMIC_T
		4372
		4373	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4374	access is atomic and serialised with respect to other threads or signal
		4375	contexts. No such type is easily found in the C language, so you can
		4376	provide your own type that you know is safe for your purposes. It is used
		4377	both for signal handler "locking" as well as for signal and thread safety
		4378	in C<ev_async> watchers.
		4379
		4380	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4381	(from F<signal.h>), which is usually good enough on most platforms,
		4382	although strictly speaking using a type that also implies a memory fence
		4383	is required.
		4384
		4385	=item EV_H (h)
		4386
		4387	The name of the F<ev.h> header file used to include it. The default if
		4388	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		4389	used to virtually rename the F<ev.h> header file in case of conflicts.
		4390
		4391	=item EV_CONFIG_H (h)
		4392
		4393	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		4394	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		4395	C<EV_H>, above.
		4396
		4397	=item EV_EVENT_H (h)
		4398
		4399	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		4400	of how the F<event.h> header can be found, the default is C<"event.h">.
		4401
		4402	=item EV_PROTOTYPES (h)
		4403
		4404	If defined to be C<0>, then F<ev.h> will not define any function
		4405	prototypes, but still define all the structs and other symbols. This is
		4406	occasionally useful if you want to provide your own wrapper functions
		4407	around libev functions.
		4408
		4409	=item EV_MULTIPLICITY
		4410
		4411	If undefined or defined to C<1>, then all event-loop-specific functions
		4412	will have the C<struct ev_loop *> as first argument, and you can create
		4413	additional independent event loops. Otherwise there will be no support
		4414	for multiple event loops and there is no first event loop pointer
		4415	argument. Instead, all functions act on the single default loop.
		4416
		4417	=item EV_MINPRI
		4418
		4419	=item EV_MAXPRI
		4420
		4421	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4422	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4423	provide for more priorities by overriding those symbols (usually defined
		4424	to be C<-2> and C<2>, respectively).
		4425
		4426	When doing priority-based operations, libev usually has to linearly search
		4427	all the priorities, so having many of them (hundreds) uses a lot of space
		4428	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4429	fine.
		4430
		4431	If your embedding application does not need any priorities, defining these
		4432	both to C<0> will save some memory and CPU.
		4433
		4434	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4435	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4436	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4437
		4438	If undefined or defined to be C<1> (and the platform supports it), then
		4439	the respective watcher type is supported. If defined to be C<0>, then it
		4440	is not. Disabling watcher types mainly saves code size.
		4441
		4442	=item EV_FEATURES
		4443
		4444	If you need to shave off some kilobytes of code at the expense of some
		4445	speed (but with the full API), you can define this symbol to request
		4446	certain subsets of functionality. The default is to enable all features
		4447	that can be enabled on the platform.
		4448
		4449	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4450	with some broad features you want) and then selectively re-enable
		4451	additional parts you want, for example if you want everything minimal,
		4452	but multiple event loop support, async and child watchers and the poll
		4453	backend, use this:
		4454
		4455	#define EV_FEATURES 0
		4456	#define EV_MULTIPLICITY 1
		4457	#define EV_USE_POLL 1
		4458	#define EV_CHILD_ENABLE 1
		4459	#define EV_ASYNC_ENABLE 1
		4460
		4461	The actual value is a bitset, it can be a combination of the following
		4462	values:
		4463
		4464	=over 4
		4465
		4466	=item C<1> - faster/larger code
		4467
		4468	Use larger code to speed up some operations.
		4469
		4470	Currently this is used to override some inlining decisions (enlarging the
		4471	code size by roughly 30% on amd64).
		4472
		4473	When optimising for size, use of compiler flags such as C<-Os> with
		4474	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4475	assertions.
		4476
		4477	=item C<2> - faster/larger data structures
		4478
		4479	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4480	hash table sizes and so on. This will usually further increase code size
		4481	and can additionally have an effect on the size of data structures at
		4482	runtime.
		4483
		4484	=item C<4> - full API configuration
		4485
		4486	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4487	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4488
		4489	=item C<8> - full API
		4490
		4491	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4492	details on which parts of the API are still available without this
		4493	feature, and do not complain if this subset changes over time.
		4494
		4495	=item C<16> - enable all optional watcher types
		4496
		4497	Enables all optional watcher types. If you want to selectively enable
		4498	only some watcher types other than I/O and timers (e.g. prepare,
		4499	embed, async, child...) you can enable them manually by defining
		4500	C<EV_watchertype_ENABLE> to C<1> instead.
		4501
		4502	=item C<32> - enable all backends
		4503
		4504	This enables all backends - without this feature, you need to enable at
		4505	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4506
		4507	=item C<64> - enable OS-specific "helper" APIs
		4508
		4509	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4510	default.
		4511
		4512	=back
		4513
		4514	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4515	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4516	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4517	watchers, timers and monotonic clock support.
		4518
		4519	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4520	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4521	your program might be left out as well - a binary starting a timer and an
		4522	I/O watcher then might come out at only 5Kb.
		4523
		4524	=item EV_AVOID_STDIO
		4525
		4526	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4527	functions (printf, scanf, perror etc.). This will increase the code size
		4528	somewhat, but if your program doesn't otherwise depend on stdio and your
		4529	libc allows it, this avoids linking in the stdio library which is quite
		4530	big.
		4531
		4532	Note that error messages might become less precise when this option is
		4533	enabled.
		4534
		4535	=item EV_NSIG
		4536
		4537	The highest supported signal number, +1 (or, the number of
		4538	signals): Normally, libev tries to deduce the maximum number of signals
		4539	automatically, but sometimes this fails, in which case it can be
		4540	specified. Also, using a lower number than detected (C<32> should be
		4541	good for about any system in existence) can save some memory, as libev
		4542	statically allocates some 12-24 bytes per signal number.
		4543
		4544	=item EV_PID_HASHSIZE
		4545
		4546	C<ev_child> watchers use a small hash table to distribute workload by
		4547	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4548	usually more than enough. If you need to manage thousands of children you
		4549	might want to increase this value (I<must> be a power of two).
		4550
		4551	=item EV_INOTIFY_HASHSIZE
		4552
		4553	C<ev_stat> watchers use a small hash table to distribute workload by
		4554	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4555	disabled), usually more than enough. If you need to manage thousands of
		4556	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4557	power of two).
		4558
		4559	=item EV_USE_4HEAP
		4560
		4561	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4562	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4563	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4564	faster performance with many (thousands) of watchers.
		4565
		4566	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4567	will be C<0>.
		4568
		4569	=item EV_HEAP_CACHE_AT
		4570
		4571	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4572	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4573	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4574	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4575	but avoids random read accesses on heap changes. This improves performance
		4576	noticeably with many (hundreds) of watchers.
		4577
		4578	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4579	will be C<0>.
		4580
		4581	=item EV_VERIFY
		4582
		4583	Controls how much internal verification (see C<ev_verify ()>) will
		4584	be done: If set to C<0>, no internal verification code will be compiled
		4585	in. If set to C<1>, then verification code will be compiled in, but not
		4586	called. If set to C<2>, then the internal verification code will be
		4587	called once per loop, which can slow down libev. If set to C<3>, then the
		4588	verification code will be called very frequently, which will slow down
		4589	libev considerably.
		4590
		4591	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4592	will be C<0>.
		4593
		4594	=item EV_COMMON
		4595
		4596	By default, all watchers have a C<void *data> member. By redefining
		4597	this macro to something else you can include more and other types of
		4598	members. You have to define it each time you include one of the files,
		4599	though, and it must be identical each time.
		4600
		4601	For example, the perl EV module uses something like this:
		4602
		4603	#define EV_COMMON \
		4604	SV *self; /* contains this struct */ \
		4605	SV *cb_sv, *fh /* note no trailing ";" */
		4606
		4607	=item EV_CB_DECLARE (type)
		4608
		4609	=item EV_CB_INVOKE (watcher, revents)
		4610
		4611	=item ev_set_cb (ev, cb)
		4612
		4613	Can be used to change the callback member declaration in each watcher,
		4614	and the way callbacks are invoked and set. Must expand to a struct member
		4615	definition and a statement, respectively. See the F<ev.h> header file for
		4616	their default definitions. One possible use for overriding these is to
		4617	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		4618	method calls instead of plain function calls in C++.
		4619
		4620	=back
		4621
		4622	=head2 EXPORTED API SYMBOLS
		4623
		4624	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4625	exported symbols, you can use the provided F<Symbol.*> files which list
		4626	all public symbols, one per line:
		4627
		4628	Symbols.ev for libev proper
		4629	Symbols.event for the libevent emulation
		4630
		4631	This can also be used to rename all public symbols to avoid clashes with
		4632	multiple versions of libev linked together (which is obviously bad in
		4633	itself, but sometimes it is inconvenient to avoid this).
		4634
		4635	A sed command like this will create wrapper C<#define>'s that you need to
		4636	include before including F<ev.h>:
		4637
		4638	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4639
		4640	This would create a file F<wrap.h> which essentially looks like this:
		4641
		4642	#define ev_backend myprefix_ev_backend
		4643	#define ev_check_start myprefix_ev_check_start
		4644	#define ev_check_stop myprefix_ev_check_stop
		4645	...
		4646
		4647	=head2 EXAMPLES
		4648
		4649	For a real-world example of a program the includes libev
		4650	verbatim, you can have a look at the EV perl module
		4651	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		4652	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		4653	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		4654	will be compiled. It is pretty complex because it provides its own header
		4655	file.
		4656
		4657	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		4658	that everybody includes and which overrides some configure choices:
		4659
		4660	#define EV_FEATURES 8
		4661	#define EV_USE_SELECT 1
		4662	#define EV_PREPARE_ENABLE 1
		4663	#define EV_IDLE_ENABLE 1
		4664	#define EV_SIGNAL_ENABLE 1
		4665	#define EV_CHILD_ENABLE 1
		4666	#define EV_USE_STDEXCEPT 0
		4667	#define EV_CONFIG_H <config.h>
		4668
		4669	#include "ev++.h"
		4670
		4671	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		4672
		4673	#include "ev_cpp.h"
		4674	#include "ev.c"
		4675
		4676	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
		4677
		4678	=head2 THREADS AND COROUTINES
		4679
		4680	=head3 THREADS
		4681
		4682	All libev functions are reentrant and thread-safe unless explicitly
		4683	documented otherwise, but libev implements no locking itself. This means
		4684	that you can use as many loops as you want in parallel, as long as there
		4685	are no concurrent calls into any libev function with the same loop
		4686	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4687	of course): libev guarantees that different event loops share no data
		4688	structures that need any locking.
		4689
		4690	Or to put it differently: calls with different loop parameters can be done
		4691	concurrently from multiple threads, calls with the same loop parameter
		4692	must be done serially (but can be done from different threads, as long as
		4693	only one thread ever is inside a call at any point in time, e.g. by using
		4694	a mutex per loop).
		4695
		4696	Specifically to support threads (and signal handlers), libev implements
		4697	so-called C<ev_async> watchers, which allow some limited form of
		4698	concurrency on the same event loop, namely waking it up "from the
		4699	outside".
		4700
		4701	If you want to know which design (one loop, locking, or multiple loops
		4702	without or something else still) is best for your problem, then I cannot
		4703	help you, but here is some generic advice:
		4704
		4705	=over 4
		4706
		4707	=item * most applications have a main thread: use the default libev loop
		4708	in that thread, or create a separate thread running only the default loop.
		4709
		4710	This helps integrating other libraries or software modules that use libev
		4711	themselves and don't care/know about threading.
		4712
		4713	=item * one loop per thread is usually a good model.
		4714
		4715	Doing this is almost never wrong, sometimes a better-performance model
		4716	exists, but it is always a good start.
		4717
		4718	=item * other models exist, such as the leader/follower pattern, where one
		4719	loop is handed through multiple threads in a kind of round-robin fashion.
		4720
		4721	Choosing a model is hard - look around, learn, know that usually you can do
		4722	better than you currently do :-)
		4723
		4724	=item * often you need to talk to some other thread which blocks in the
		4725	event loop.
		4726
		4727	C<ev_async> watchers can be used to wake them up from other threads safely
		4728	(or from signal contexts...).
		4729
		4730	An example use would be to communicate signals or other events that only
		4731	work in the default loop by registering the signal watcher with the
		4732	default loop and triggering an C<ev_async> watcher from the default loop
		4733	watcher callback into the event loop interested in the signal.
		4734
		4735	=back
		4736
		4737	See also L<THREAD LOCKING EXAMPLE>.
		4738
		4739	=head3 COROUTINES
		4740
		4741	Libev is very accommodating to coroutines ("cooperative threads"):
		4742	libev fully supports nesting calls to its functions from different
		4743	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4744	different coroutines, and switch freely between both coroutines running
		4745	the loop, as long as you don't confuse yourself). The only exception is
		4746	that you must not do this from C<ev_periodic> reschedule callbacks.
		4747
		4748	Care has been taken to ensure that libev does not keep local state inside
		4749	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4750	they do not call any callbacks.
		4751
		4752	=head2 COMPILER WARNINGS
		4753
		4754	Depending on your compiler and compiler settings, you might get no or a
		4755	lot of warnings when compiling libev code. Some people are apparently
		4756	scared by this.
		4757
		4758	However, these are unavoidable for many reasons. For one, each compiler
		4759	has different warnings, and each user has different tastes regarding
		4760	warning options. "Warn-free" code therefore cannot be a goal except when
		4761	targeting a specific compiler and compiler-version.
		4762
		4763	Another reason is that some compiler warnings require elaborate
		4764	workarounds, or other changes to the code that make it less clear and less
		4765	maintainable.
		4766
		4767	And of course, some compiler warnings are just plain stupid, or simply
		4768	wrong (because they don't actually warn about the condition their message
		4769	seems to warn about). For example, certain older gcc versions had some
		4770	warnings that resulted in an extreme number of false positives. These have
		4771	been fixed, but some people still insist on making code warn-free with
		4772	such buggy versions.
		4773
		4774	While libev is written to generate as few warnings as possible,
		4775	"warn-free" code is not a goal, and it is recommended not to build libev
		4776	with any compiler warnings enabled unless you are prepared to cope with
		4777	them (e.g. by ignoring them). Remember that warnings are just that:
		4778	warnings, not errors, or proof of bugs.
		4779
		4780
		4781	=head2 VALGRIND
		4782
		4783	Valgrind has a special section here because it is a popular tool that is
		4784	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4785
		4786	If you think you found a bug (memory leak, uninitialised data access etc.)
		4787	in libev, then check twice: If valgrind reports something like:
		4788
		4789	==2274== definitely lost: 0 bytes in 0 blocks.
		4790	==2274== possibly lost: 0 bytes in 0 blocks.
		4791	==2274== still reachable: 256 bytes in 1 blocks.
		4792
		4793	Then there is no memory leak, just as memory accounted to global variables
		4794	is not a memleak - the memory is still being referenced, and didn't leak.
		4795
		4796	Similarly, under some circumstances, valgrind might report kernel bugs
		4797	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4798	although an acceptable workaround has been found here), or it might be
		4799	confused.
		4800
		4801	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4802	make it into some kind of religion.
		4803
		4804	If you are unsure about something, feel free to contact the mailing list
		4805	with the full valgrind report and an explanation on why you think this
		4806	is a bug in libev (best check the archives, too :). However, don't be
		4807	annoyed when you get a brisk "this is no bug" answer and take the chance
		4808	of learning how to interpret valgrind properly.
		4809
		4810	If you need, for some reason, empty reports from valgrind for your project
		4811	I suggest using suppression lists.
		4812
		4813
		4814	=head1 PORTABILITY NOTES
		4815
		4816	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4817
		4818	GNU/Linux is the only common platform that supports 64 bit file/large file
		4819	interfaces but I<disables> them by default.
		4820
		4821	That means that libev compiled in the default environment doesn't support
		4822	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4823
		4824	Unfortunately, many programs try to work around this GNU/Linux issue
		4825	by enabling the large file API, which makes them incompatible with the
		4826	standard libev compiled for their system.
		4827
		4828	Likewise, libev cannot enable the large file API itself as this would
		4829	suddenly make it incompatible to the default compile time environment,
		4830	i.e. all programs not using special compile switches.
		4831
		4832	=head2 OS/X AND DARWIN BUGS
		4833
		4834	The whole thing is a bug if you ask me - basically any system interface
		4835	you touch is broken, whether it is locales, poll, kqueue or even the
		4836	OpenGL drivers.
		4837
		4838	=head3 C<kqueue> is buggy
		4839
		4840	The kqueue syscall is broken in all known versions - most versions support
		4841	only sockets, many support pipes.
		4842
		4843	Libev tries to work around this by not using C<kqueue> by default on this
		4844	rotten platform, but of course you can still ask for it when creating a
		4845	loop - embedding a socket-only kqueue loop into a select-based one is
		4846	probably going to work well.
		4847
		4848	=head3 C<poll> is buggy
		4849
		4850	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4851	implementation by something calling C<kqueue> internally around the 10.5.6
		4852	release, so now C<kqueue> I<and> C<poll> are broken.
		4853
		4854	Libev tries to work around this by not using C<poll> by default on
		4855	this rotten platform, but of course you can still ask for it when creating
		4856	a loop.
		4857
		4858	=head3 C<select> is buggy
		4859
		4860	All that's left is C<select>, and of course Apple found a way to fuck this
		4861	one up as well: On OS/X, C<select> actively limits the number of file
		4862	descriptors you can pass in to 1024 - your program suddenly crashes when
		4863	you use more.
		4864
		4865	There is an undocumented "workaround" for this - defining
		4866	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4867	work on OS/X.
		4868
		4869	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4870
		4871	=head3 C<errno> reentrancy
		4872
		4873	The default compile environment on Solaris is unfortunately so
		4874	thread-unsafe that you can't even use components/libraries compiled
		4875	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4876	defined by default. A valid, if stupid, implementation choice.
		4877
		4878	If you want to use libev in threaded environments you have to make sure
		4879	it's compiled with C<_REENTRANT> defined.
		4880
		4881	=head3 Event port backend
		4882
		4883	The scalable event interface for Solaris is called "event
		4884	ports". Unfortunately, this mechanism is very buggy in all major
		4885	releases. If you run into high CPU usage, your program freezes or you get
		4886	a large number of spurious wakeups, make sure you have all the relevant
		4887	and latest kernel patches applied. No, I don't know which ones, but there
		4888	are multiple ones to apply, and afterwards, event ports actually work
		4889	great.
		4890
		4891	If you can't get it to work, you can try running the program by setting
		4892	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4893	C<select> backends.
		4894
		4895	=head2 AIX POLL BUG
		4896
		4897	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4898	this by trying to avoid the poll backend altogether (i.e. it's not even
		4899	compiled in), which normally isn't a big problem as C<select> works fine
		4900	with large bitsets on AIX, and AIX is dead anyway.
		4901
		4902	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4903
		4904	=head3 General issues
		4905
		4906	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4907	requires, and its I/O model is fundamentally incompatible with the POSIX
		4908	model. Libev still offers limited functionality on this platform in
		4909	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4910	descriptors. This only applies when using Win32 natively, not when using
		4911	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4912	as every compiler comes with a slightly differently broken/incompatible
		4913	environment.
		4914
		4915	Lifting these limitations would basically require the full
		4916	re-implementation of the I/O system. If you are into this kind of thing,
		4917	then note that glib does exactly that for you in a very portable way (note
		4918	also that glib is the slowest event library known to man).
		4919
		4920	There is no supported compilation method available on windows except
		4921	embedding it into other applications.
		4922
		4923	Sensible signal handling is officially unsupported by Microsoft - libev
		4924	tries its best, but under most conditions, signals will simply not work.
		4925
		4926	Not a libev limitation but worth mentioning: windows apparently doesn't
		4927	accept large writes: instead of resulting in a partial write, windows will
		4928	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4929	so make sure you only write small amounts into your sockets (less than a
		4930	megabyte seems safe, but this apparently depends on the amount of memory
		4931	available).
		4932
		4933	Due to the many, low, and arbitrary limits on the win32 platform and
		4934	the abysmal performance of winsockets, using a large number of sockets
		4935	is not recommended (and not reasonable). If your program needs to use
		4936	more than a hundred or so sockets, then likely it needs to use a totally
		4937	different implementation for windows, as libev offers the POSIX readiness
		4938	notification model, which cannot be implemented efficiently on windows
		4939	(due to Microsoft monopoly games).
		4940
		4941	A typical way to use libev under windows is to embed it (see the embedding
		4942	section for details) and use the following F<evwrap.h> header file instead
		4943	of F<ev.h>:
		4944
		4945	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4946	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4947
		4948	#include "ev.h"
		4949
		4950	And compile the following F<evwrap.c> file into your project (make sure
		4951	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4952
		4953	#include "evwrap.h"
		4954	#include "ev.c"
		4955
		4956	=head3 The winsocket C<select> function
		4957
		4958	The winsocket C<select> function doesn't follow POSIX in that it
		4959	requires socket I<handles> and not socket I<file descriptors> (it is
		4960	also extremely buggy). This makes select very inefficient, and also
		4961	requires a mapping from file descriptors to socket handles (the Microsoft
		4962	C runtime provides the function C<_open_osfhandle> for this). See the
		4963	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4964	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4965
		4966	The configuration for a "naked" win32 using the Microsoft runtime
		4967	libraries and raw winsocket select is:
		4968
		4969	#define EV_USE_SELECT 1
		4970	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4971
		4972	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4973	complexity in the O(n²) range when using win32.
		4974
		4975	=head3 Limited number of file descriptors
		4976
		4977	Windows has numerous arbitrary (and low) limits on things.
		4978
		4979	Early versions of winsocket's select only supported waiting for a maximum
		4980	of C<64> handles (probably owning to the fact that all windows kernels
		4981	can only wait for C<64> things at the same time internally; Microsoft
		4982	recommends spawning a chain of threads and wait for 63 handles and the
		4983	previous thread in each. Sounds great!).
		4984
		4985	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4986	to some high number (e.g. C<2048>) before compiling the winsocket select
		4987	call (which might be in libev or elsewhere, for example, perl and many
		4988	other interpreters do their own select emulation on windows).
		4989
		4990	Another limit is the number of file descriptors in the Microsoft runtime
		4991	libraries, which by default is C<64> (there must be a hidden I<64>
		4992	fetish or something like this inside Microsoft). You can increase this
		4993	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4994	(another arbitrary limit), but is broken in many versions of the Microsoft
		4995	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4996	(depending on windows version and/or the phase of the moon). To get more,
		4997	you need to wrap all I/O functions and provide your own fd management, but
		4998	the cost of calling select (O(n²)) will likely make this unworkable.
		4999
		5000	=head2 PORTABILITY REQUIREMENTS
		5001
		5002	In addition to a working ISO-C implementation and of course the
		5003	backend-specific APIs, libev relies on a few additional extensions:
		5004
		5005	=over 4
		5006
		5007	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5008	calling conventions regardless of C<ev_watcher_type *>.
		5009
		5010	Libev assumes not only that all watcher pointers have the same internal
		5011	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5012	assumes that the same (machine) code can be used to call any watcher
		5013	callback: The watcher callbacks have different type signatures, but libev
		5014	calls them using an C<ev_watcher *> internally.
		5015
		5016	=item pointer accesses must be thread-atomic
		5017
		5018	Accessing a pointer value must be atomic, it must both be readable and
		5019	writable in one piece - this is the case on all current architectures.
		5020
		5021	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5022
		5023	The type C<sig_atomic_t volatile> (or whatever is defined as
		5024	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5025	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5026	believed to be sufficiently portable.
		5027
		5028	=item C<sigprocmask> must work in a threaded environment
		5029
		5030	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5031	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5032	pthread implementations will either allow C<sigprocmask> in the "main
		5033	thread" or will block signals process-wide, both behaviours would
		5034	be compatible with libev. Interaction between C<sigprocmask> and
		5035	C<pthread_sigmask> could complicate things, however.
		5036
		5037	The most portable way to handle signals is to block signals in all threads
		5038	except the initial one, and run the default loop in the initial thread as
		5039	well.
		5040
		5041	=item C<long> must be large enough for common memory allocation sizes
		5042
		5043	To improve portability and simplify its API, libev uses C<long> internally
		5044	instead of C<size_t> when allocating its data structures. On non-POSIX
		5045	systems (Microsoft...) this might be unexpectedly low, but is still at
		5046	least 31 bits everywhere, which is enough for hundreds of millions of
		5047	watchers.
		5048
		5049	=item C<double> must hold a time value in seconds with enough accuracy
		5050
		5051	The type C<double> is used to represent timestamps. It is required to
		5052	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5053	good enough for at least into the year 4000 with millisecond accuracy
		5054	(the design goal for libev). This requirement is overfulfilled by
		5055	implementations using IEEE 754, which is basically all existing ones.
		5056
		5057	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5058	year 2255 (and millisecond accuray till the year 287396 - by then, libev
		5059	is either obsolete or somebody patched it to use C<long double> or
		5060	something like that, just kidding).
		5061
		5062	=back
		5063
		5064	If you know of other additional requirements drop me a note.
		5065
		5066
		5067	=head1 ALGORITHMIC COMPLEXITIES
		5068
		5069	In this section the complexities of (many of) the algorithms used inside
		5070	libev will be documented. For complexity discussions about backends see
		5071	the documentation for C<ev_default_init>.
		5072
		5073	All of the following are about amortised time: If an array needs to be
		5074	extended, libev needs to realloc and move the whole array, but this
		5075	happens asymptotically rarer with higher number of elements, so O(1) might
		5076	mean that libev does a lengthy realloc operation in rare cases, but on
		5077	average it is much faster and asymptotically approaches constant time.
		5078
		5079	=over 4
		5080
		5081	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		5082
		5083	This means that, when you have a watcher that triggers in one hour and
		5084	there are 100 watchers that would trigger before that, then inserting will
		5085	have to skip roughly seven (C<ld 100>) of these watchers.
		5086
		5087	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		5088
		5089	That means that changing a timer costs less than removing/adding them,
		5090	as only the relative motion in the event queue has to be paid for.
		5091
		5092	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		5093
		5094	These just add the watcher into an array or at the head of a list.
		5095
		5096	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		5097
		5098	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		5099
		5100	These watchers are stored in lists, so they need to be walked to find the
		5101	correct watcher to remove. The lists are usually short (you don't usually
		5102	have many watchers waiting for the same fd or signal: one is typical, two
		5103	is rare).
		5104
		5105	=item Finding the next timer in each loop iteration: O(1)
		5106
		5107	By virtue of using a binary or 4-heap, the next timer is always found at a
		5108	fixed position in the storage array.
		5109
		5110	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		5111
		5112	A change means an I/O watcher gets started or stopped, which requires
		5113	libev to recalculate its status (and possibly tell the kernel, depending
		5114	on backend and whether C<ev_io_set> was used).
		5115
		5116	=item Activating one watcher (putting it into the pending state): O(1)
		5117
		5118	=item Priority handling: O(number_of_priorities)
		5119
		5120	Priorities are implemented by allocating some space for each
		5121	priority. When doing priority-based operations, libev usually has to
		5122	linearly search all the priorities, but starting/stopping and activating
		5123	watchers becomes O(1) with respect to priority handling.
		5124
		5125	=item Sending an ev_async: O(1)
		5126
		5127	=item Processing ev_async_send: O(number_of_async_watchers)
		5128
		5129	=item Processing signals: O(max_signal_number)
		5130
		5131	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5132	calls in the current loop iteration and the loop is currently
		5133	blocked. Checking for async and signal events involves iterating over all
		5134	running async watchers or all signal numbers.
		5135
		5136	=back
		5137
		5138
		5139	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5140
		5141	The major version 4 introduced some incompatible changes to the API.
		5142
		5143	At the moment, the C<ev.h> header file provides compatibility definitions
		5144	for all changes, so most programs should still compile. The compatibility
		5145	layer might be removed in later versions of libev, so better update to the
		5146	new API early than late.
		5147
		5148	=over 4
		5149
		5150	=item C<EV_COMPAT3> backwards compatibility mechanism
		5151
		5152	The backward compatibility mechanism can be controlled by
		5153	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5154	section.
		5155
		5156	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5157
		5158	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5159
		5160	ev_loop_destroy (EV_DEFAULT_UC);
		5161	ev_loop_fork (EV_DEFAULT);
		5162
		5163	=item function/symbol renames
		5164
		5165	A number of functions and symbols have been renamed:
		5166
		5167	ev_loop => ev_run
		5168	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5169	EVLOOP_ONESHOT => EVRUN_ONCE
		5170
		5171	ev_unloop => ev_break
		5172	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5173	EVUNLOOP_ONE => EVBREAK_ONE
		5174	EVUNLOOP_ALL => EVBREAK_ALL
		5175
		5176	EV_TIMEOUT => EV_TIMER
		5177
		5178	ev_loop_count => ev_iteration
		5179	ev_loop_depth => ev_depth
		5180	ev_loop_verify => ev_verify
		5181
		5182	Most functions working on C<struct ev_loop> objects don't have an
		5183	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5184	associated constants have been renamed to not collide with the C<struct
		5185	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5186	as all other watcher types. Note that C<ev_loop_fork> is still called
		5187	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5188	typedef.
		5189
		5190	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5191
		5192	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5193	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5194	and work, but the library code will of course be larger.
		5195
		5196	=back
		5197
		5198
		5199	=head1 GLOSSARY
		5200
		5201	=over 4
		5202
		5203	=item active
		5204
		5205	A watcher is active as long as it has been started and not yet stopped.
		5206	See L<WATCHER STATES> for details.
		5207
		5208	=item application
		5209
		5210	In this document, an application is whatever is using libev.
		5211
		5212	=item backend
		5213
		5214	The part of the code dealing with the operating system interfaces.
		5215
		5216	=item callback
		5217
		5218	The address of a function that is called when some event has been
		5219	detected. Callbacks are being passed the event loop, the watcher that
		5220	received the event, and the actual event bitset.
		5221
		5222	=item callback/watcher invocation
		5223
		5224	The act of calling the callback associated with a watcher.
		5225
		5226	=item event
		5227
		5228	A change of state of some external event, such as data now being available
		5229	for reading on a file descriptor, time having passed or simply not having
		5230	any other events happening anymore.
		5231
		5232	In libev, events are represented as single bits (such as C<EV_READ> or
		5233	C<EV_TIMER>).
		5234
		5235	=item event library
		5236
		5237	A software package implementing an event model and loop.
		5238
		5239	=item event loop
		5240
		5241	An entity that handles and processes external events and converts them
		5242	into callback invocations.
		5243
		5244	=item event model
		5245
		5246	The model used to describe how an event loop handles and processes
		5247	watchers and events.
		5248
		5249	=item pending
		5250
		5251	A watcher is pending as soon as the corresponding event has been
		5252	detected. See L<WATCHER STATES> for details.
		5253
		5254	=item real time
		5255
		5256	The physical time that is observed. It is apparently strictly monotonic :)
		5257
		5258	=item wall-clock time
		5259
		5260	The time and date as shown on clocks. Unlike real time, it can actually
		5261	be wrong and jump forwards and backwards, e.g. when you adjust your
		5262	clock.
		5263
		5264	=item watcher
		5265
		5266	A data structure that describes interest in certain events. Watchers need
		5267	to be started (attached to an event loop) before they can receive events.
		5268
		5269	=back
		5270
767	=head1 AUTHOR	5271	=head1 AUTHOR
768		5272
769	Marc Lehmann <libev@schmorp.de>.	5273	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5274	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
770		5275

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines