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Revision 1.349 by root, Mon Jan 10 01:58:55 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	// unloop was called, so exit
		64	return 0;
		65	}
		66
		67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
		90
		91	=head1 ABOUT LIBEV
10		92
11	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	95	these event sources and provide your program with events.
14		96
15	To do this, it must take more or less complete control over your process	97	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	98	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	99	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	101	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	102	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	103	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	104	watcher.
23		105
24	=head1 FEATURES	106	=head2 FEATURES
25		107
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	108	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	109	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	110	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		111	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
		112	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
		113	timers (C<ev_timer>), absolute timers with customised rescheduling
		114	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
29	events (related to SIGCHLD), and event watchers dealing with the event	115	change events (C<ev_child>), and event watchers dealing with the event
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	116	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
		117	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		118	limited support for fork events (C<ev_fork>).
		119
		120	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	121	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	122	for example).
33		123
34	=head1 CONVENTIONS	124	=head2 CONVENTIONS
35		125
36	Libev is very configurable. In this manual the default configuration	126	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	127	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	128	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	129	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	130	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	131	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	132	this argument.
43		133
44	=head1 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
45		135
46	Libev represents time as a single floating point number, representing the	136	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	137	the (fractional) number of seconds since the (POSIX) epoch (in practice
48	the beginning of 1970, details are complicated, don't ask). This type is	138	somewhere near the beginning of 1970, details are complicated, don't
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	139	ask). This type is called C<ev_tstamp>, which is what you should use
50	to the 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
51		166
52	=head1 GLOBAL FUNCTIONS	167	=head1 GLOBAL FUNCTIONS
53		168
54	These functions can be called anytime, even before initialising the	169	These functions can be called anytime, even before initialising the
55	library in any way.	170	library in any way.
…		…
58		173
59	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
60		175
61	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
62	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
63	you actually want to know.	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 until
		184	either it is interrupted or the given time interval has passed. Basically
		185	this is a sub-second-resolution C<sleep ()>.
64		186
65	=item int ev_version_major ()	187	=item int ev_version_major ()
66		188
67	=item int ev_version_minor ()	189	=item int ev_version_minor ()
68		190
69	You can find out the major and minor version numbers of the library	191	You can find out the major and minor ABI version numbers of the library
70	you linked against by calling the functions C<ev_version_major> and	192	you linked against by calling the functions C<ev_version_major> and
71	C<ev_version_minor>. If you want, you can compare against the global	193	C<ev_version_minor>. If you want, you can compare against the global
72	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	194	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
73	version of the library your program was compiled against.	195	version of the library your program was compiled against.
74		196
		197	These version numbers refer to the ABI version of the library, not the
		198	release version.
		199
75	Usually, it's a good idea to terminate if the major versions mismatch,	200	Usually, it's a good idea to terminate if the major versions mismatch,
76	as this indicates an incompatible change. Minor versions are usually	201	as this indicates an incompatible change. Minor versions are usually
77	compatible to older versions, so a larger minor version alone is usually	202	compatible to older versions, so a larger minor version alone is usually
78	not a problem.	203	not a problem.
79		204
		205	Example: Make sure we haven't accidentally been linked against the wrong
		206	version (note, however, that this will not detect other ABI mismatches,
		207	such as LFS or reentrancy).
		208
		209	assert (("libev version mismatch",
		210	ev_version_major () == EV_VERSION_MAJOR
		211	&& ev_version_minor () >= EV_VERSION_MINOR));
		212
		213	=item unsigned int ev_supported_backends ()
		214
		215	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		216	value) compiled into this binary of libev (independent of their
		217	availability on the system you are running on). See C<ev_default_loop> for
		218	a description of the set values.
		219
		220	Example: make sure we have the epoll method, because yeah this is cool and
		221	a must have and can we have a torrent of it please!!!11
		222
		223	assert (("sorry, no epoll, no sex",
		224	ev_supported_backends () & EVBACKEND_EPOLL));
		225
		226	=item unsigned int ev_recommended_backends ()
		227
		228	Return the set of all backends compiled into this binary of libev and
		229	also recommended for this platform, meaning it will work for most file
		230	descriptor types. This set is often smaller than the one returned by
		231	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
		232	and will not be auto-detected unless you explicitly request it (assuming
		233	you know what you are doing). This is the set of backends that libev will
		234	probe for if you specify no backends explicitly.
		235
		236	=item unsigned int ev_embeddable_backends ()
		237
		238	Returns the set of backends that are embeddable in other event loops. This
		239	value is platform-specific but can include backends not available on the
		240	current system. To find which embeddable backends might be supported on
		241	the current system, you would need to look at C<ev_embeddable_backends ()
		242	& ev_supported_backends ()>, likewise for recommended ones.
		243
		244	See the description of C<ev_embed> watchers for more info.
		245
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
81		247
82	Sets the allocation function to use (the prototype is similar to the	248	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	249	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
84	and free memory (no surprises here). If it returns zero when memory	250	used to allocate and free memory (no surprises here). If it returns zero
85	needs to be allocated, the library might abort or take some potentially	251	when memory needs to be allocated (C<size != 0>), the library might abort
86	destructive action. The default is your system realloc function.	252	or take some potentially destructive action.
		253
		254	Since some systems (at least OpenBSD and Darwin) fail to implement
		255	correct C<realloc> semantics, libev will use a wrapper around the system
		256	C<realloc> and C<free> functions by default.
87		257
88	You could override this function in high-availability programs to, say,	258	You could override this function in high-availability programs to, say,
89	free some memory if it cannot allocate memory, to use a special allocator,	259	free some memory if it cannot allocate memory, to use a special allocator,
90	or even to sleep a while and retry until some memory is available.	260	or even to sleep a while and retry until some memory is available.
91		261
		262	Example: Replace the libev allocator with one that waits a bit and then
		263	retries (example requires a standards-compliant C<realloc>).
		264
		265	static void *
		266	persistent_realloc (void *ptr, size_t size)
		267	{
		268	for (;;)
		269	{
		270	void *newptr = realloc (ptr, size);
		271
		272	if (newptr)
		273	return newptr;
		274
		275	sleep (60);
		276	}
		277	}
		278
		279	...
		280	ev_set_allocator (persistent_realloc);
		281
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	282	=item ev_set_syserr_cb (void (*cb)(const char *msg))
93		283
94	Set the callback function to call on a retryable syscall error (such	284	Set the callback function to call on a retryable system call error (such
95	as failed select, poll, epoll_wait). The message is a printable string	285	as failed select, poll, epoll_wait). The message is a printable string
96	indicating the system call or subsystem causing the problem. If this	286	indicating the system call or subsystem causing the problem. If this
97	callback is set, then libev will expect it to remedy the sitution, no	287	callback is set, then libev will expect it to remedy the situation, no
98	matter what, when it returns. That is, libev will generally retry the	288	matter what, when it returns. That is, libev will generally retry the
99	requested operation, or, if the condition doesn't go away, do bad stuff	289	requested operation, or, if the condition doesn't go away, do bad stuff
100	(such as abort).	290	(such as abort).
101		291
		292	Example: This is basically the same thing that libev does internally, too.
		293
		294	static void
		295	fatal_error (const char *msg)
		296	{
		297	perror (msg);
		298	abort ();
		299	}
		300
		301	...
		302	ev_set_syserr_cb (fatal_error);
		303
		304	=item ev_feed_signal (int signum)
		305
		306	This function can be used to "simulate" a signal receive. It is completely
		307	safe to call this function at any time, from any context, including signal
		308	handlers or random threads.
		309
		310	It's main use is to customise signal handling in your process, especially
		311	in the presence of threads. For example, you could block signals
		312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		313	creating any loops), and in one thread, use C<sigwait> or any other
		314	mechanism to wait for signals, then "deliver" them to libev by calling
		315	C<ev_feed_signal>.
		316
102	=back	317	=back
103		318
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
105		320
106	An event loop is described by a C<struct ev_loop *>. The library knows two	321	An event loop is described by a C<struct ev_loop *> (the C<struct> is
107	types of such loops, the I<default> loop, which supports signals and child	322	I<not> optional in this case unless libev 3 compatibility is disabled, as
108	events, and dynamically created loops which do not.	323	libev 3 had an C<ev_loop> function colliding with the struct name).
109		324
110	If you use threads, a common model is to run the default event loop	325	The library knows two types of such loops, the I<default> loop, which
111	in your main thread (or in a separate thread) and for each thread you	326	supports child process events, and dynamically created event loops which
112	create, you also create another event loop. Libev itself does no locking	327	do not.
113	whatsoever, so if you mix calls to the same event loop in different
114	threads, make sure you lock (this is usually a bad idea, though, even if
115	done correctly, because it's hideous and inefficient).
116		328
117	=over 4	329	=over 4
118		330
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	331	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		332
121	This will initialise the default event loop if it hasn't been initialised	333	This returns the "default" event loop object, which is what you should
122	yet and return it. If the default loop could not be initialised, returns	334	normally use when you just need "the event loop". Event loop objects and
123	false. If it already was initialised it simply returns it (and ignores the	335	the C<flags> parameter are described in more detail in the entry for
124	flags).	336	C<ev_loop_new>.
		337
		338	If the default loop is already initialised then this function simply
		339	returns it (and ignores the flags. If that is troubling you, check
		340	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		341	flags, which should almost always be C<0>, unless the caller is also the
		342	one calling C<ev_run> or otherwise qualifies as "the main program".
125		343
126	If you don't know what event loop to use, use the one returned from this	344	If you don't know what event loop to use, use the one returned from this
127	function.	345	function (or via the C<EV_DEFAULT> macro).
		346
		347	Note that this function is I<not> thread-safe, so if you want to use it
		348	from multiple threads, you have to employ some kind of mutex (note also
		349	that this case is unlikely, as loops cannot be shared easily between
		350	threads anyway).
		351
		352	The default loop is the only loop that can handle C<ev_child> watchers,
		353	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		354	a problem for your application you can either create a dynamic loop with
		355	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		356	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		357
		358	Example: This is the most typical usage.
		359
		360	if (!ev_default_loop (0))
		361	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		362
		363	Example: Restrict libev to the select and poll backends, and do not allow
		364	environment settings to be taken into account:
		365
		366	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		367
		368	=item struct ev_loop *ev_loop_new (unsigned int flags)
		369
		370	This will create and initialise a new event loop object. If the loop
		371	could not be initialised, returns false.
		372
		373	This function is thread-safe, and one common way to use libev with
		374	threads is indeed to create one loop per thread, and using the default
		375	loop in the "main" or "initial" thread.
128		376
129	The flags argument can be used to specify special behaviour or specific	377	The flags argument can be used to specify special behaviour or specific
130	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	378	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		379
132	It supports the following flags:	380	The following flags are supported:
133		381
134	=over 4	382	=over 4
135		383
136	=item C<EVFLAG_AUTO>	384	=item C<EVFLAG_AUTO>
137		385
138	The default flags value. Use this if you have no clue (it's the right	386	The default flags value. Use this if you have no clue (it's the right
139	thing, believe me).	387	thing, believe me).
140		388
141	=item C<EVFLAG_NOENV>	389	=item C<EVFLAG_NOENV>
142		390
143	If this flag bit is ored into the flag value (or the program runs setuid	391	If this flag bit is or'ed into the flag value (or the program runs setuid
144	or setgid) then libev will I<not> look at the environment variable	392	or setgid) then libev will I<not> look at the environment variable
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	393	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	394	override the flags completely if it is found in the environment. This is
147	useful to try out specific backends to test their performance, or to work	395	useful to try out specific backends to test their performance, or to work
148	around bugs.	396	around bugs.
149		397
		398	=item C<EVFLAG_FORKCHECK>
		399
		400	Instead of calling C<ev_loop_fork> manually after a fork, you can also
		401	make libev check for a fork in each iteration by enabling this flag.
		402
		403	This works by calling C<getpid ()> on every iteration of the loop,
		404	and thus this might slow down your event loop if you do a lot of loop
		405	iterations and little real work, but is usually not noticeable (on my
		406	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		407	without a system call and thus I<very> fast, but my GNU/Linux system also has
		408	C<pthread_atfork> which is even faster).
		409
		410	The big advantage of this flag is that you can forget about fork (and
		411	forget about forgetting to tell libev about forking) when you use this
		412	flag.
		413
		414	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		415	environment variable.
		416
		417	=item C<EVFLAG_NOINOTIFY>
		418
		419	When this flag is specified, then libev will not attempt to use the
		420	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
		421	testing, this flag can be useful to conserve inotify file descriptors, as
		422	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		423
		424	=item C<EVFLAG_SIGNALFD>
		425
		426	When this flag is specified, then libev will attempt to use the
		427	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
		428	delivers signals synchronously, which makes it both faster and might make
		429	it possible to get the queued signal data. It can also simplify signal
		430	handling with threads, as long as you properly block signals in your
		431	threads that are not interested in handling them.
		432
		433	Signalfd will not be used by default as this changes your signal mask, and
		434	there are a lot of shoddy libraries and programs (glib's threadpool for
		435	example) that can't properly initialise their signal masks.
		436
		437	=item C<EVFLAG_NOSIGMASK>
		438
		439	When this flag is specified, then libev will avoid to modify the signal
		440	mask. Specifically, this means you ahve to make sure signals are unblocked
		441	when you want to receive them.
		442
		443	This behaviour is useful when you want to do your own signal handling, or
		444	want to handle signals only in specific threads and want to avoid libev
		445	unblocking the signals.
		446
		447	This flag's behaviour will become the default in future versions of libev.
		448
150	=item C<EVMETHOD_SELECT> (value 1, portable select backend)	449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		450
152	This is your standard select(2) backend. Not I<completely> standard, as	451	This is your standard select(2) backend. Not I<completely> standard, as
153	libev tries to roll its own fd_set with no limits on the number of fds,	452	libev tries to roll its own fd_set with no limits on the number of fds,
154	but if that fails, expect a fairly low limit on the number of fds when	453	but if that fails, expect a fairly low limit on the number of fds when
155	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	454	using this backend. It doesn't scale too well (O(highest_fd)), but its
156	the fastest backend for a low number of fds.	455	usually the fastest backend for a low number of (low-numbered :) fds.
157		456
		457	To get good performance out of this backend you need a high amount of
		458	parallelism (most of the file descriptors should be busy). If you are
		459	writing a server, you should C<accept ()> in a loop to accept as many
		460	connections as possible during one iteration. You might also want to have
		461	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		462	readiness notifications you get per iteration.
		463
		464	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		465	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		466	C<exceptfds> set on that platform).
		467
158	=item C<EVMETHOD_POLL> (value 2, poll backend, available everywhere except on windows)	468	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
159		469
160	And this is your standard poll(2) backend. It's more complicated than	470	And this is your standard poll(2) backend. It's more complicated
161	select, but handles sparse fds better and has no artificial limit on the	471	than select, but handles sparse fds better and has no artificial
162	number of fds you can use (except it will slow down considerably with a	472	limit on the number of fds you can use (except it will slow down
163	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	473	considerably with a lot of inactive fds). It scales similarly to select,
		474	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		475	performance tips.
164		476
		477	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		478	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		479
165	=item C<EVMETHOD_EPOLL> (value 4, Linux)	480	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		481
		482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		483	kernels).
166		484
167	For few fds, this backend is a bit little slower than poll and select,	485	For few fds, this backend is a bit little slower than poll and select,
168	but it scales phenomenally better. While poll and select usually scale like	486	but it scales phenomenally better. While poll and select usually scale
169	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	487	like O(total_fds) where n is the total number of fds (or the highest fd),
170	either O(1) or O(active_fds).	488	epoll scales either O(1) or O(active_fds).
171		489
		490	The epoll mechanism deserves honorable mention as the most misdesigned
		491	of the more advanced event mechanisms: mere annoyances include silently
		492	dropping file descriptors, requiring a system call per change per file
		493	descriptor (and unnecessary guessing of parameters), problems with dup,
		494	returning before the timeout value, resulting in additional iterations
		495	(and only giving 5ms accuracy while select on the same platform gives
		496	0.1ms) and so on. The biggest issue is fork races, however - if a program
		497	forks then I<both> parent and child process have to recreate the epoll
		498	set, which can take considerable time (one syscall per file descriptor)
		499	and is of course hard to detect.
		500
		501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		502	of course I<doesn't>, and epoll just loves to report events for totally
		503	I<different> file descriptors (even already closed ones, so one cannot
		504	even remove them from the set) than registered in the set (especially
		505	on SMP systems). Libev tries to counter these spurious notifications by
		506	employing an additional generation counter and comparing that against the
		507	events to filter out spurious ones, recreating the set when required. Last
		508	not least, it also refuses to work with some file descriptors which work
		509	perfectly fine with C<select> (files, many character devices...).
		510
		511	Epoll is truly the train wreck analog among event poll mechanisms.
		512
172	While stopping and starting an I/O watcher in the same iteration will	513	While stopping, setting and starting an I/O watcher in the same iteration
173	result in some caching, there is still a syscall per such incident	514	will result in some caching, there is still a system call per such
174	(because the fd could point to a different file description now), so its	515	incident (because the same I<file descriptor> could point to a different
175	best to avoid that. Also, dup()ed file descriptors might not work very	516	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
176	well if you register events for both fds.	517	file descriptors might not work very well if you register events for both
		518	file descriptors.
177		519
		520	Best performance from this backend is achieved by not unregistering all
		521	watchers for a file descriptor until it has been closed, if possible,
		522	i.e. keep at least one watcher active per fd at all times. Stopping and
		523	starting a watcher (without re-setting it) also usually doesn't cause
		524	extra overhead. A fork can both result in spurious notifications as well
		525	as in libev having to destroy and recreate the epoll object, which can
		526	take considerable time and thus should be avoided.
		527
		528	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		529	faster than epoll for maybe up to a hundred file descriptors, depending on
		530	the usage. So sad.
		531
		532	While nominally embeddable in other event loops, this feature is broken in
		533	all kernel versions tested so far.
		534
		535	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		536	C<EVBACKEND_POLL>.
		537
178	=item C<EVMETHOD_KQUEUE> (value 8, most BSD clones)	538	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
179		539
180	Kqueue deserves special mention, as at the time of this writing, it	540	Kqueue deserves special mention, as at the time of this writing, it
181	was broken on all BSDs except NetBSD (usually it doesn't work with	541	was broken on all BSDs except NetBSD (usually it doesn't work reliably
182	anything but sockets and pipes, except on Darwin, where of course its	542	with anything but sockets and pipes, except on Darwin, where of course
183	completely useless). For this reason its not being "autodetected" unless	543	it's completely useless). Unlike epoll, however, whose brokenness
184	you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).	544	is by design, these kqueue bugs can (and eventually will) be fixed
		545	without API changes to existing programs. For this reason it's not being
		546	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		547	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		548	system like NetBSD.
		549
		550	You still can embed kqueue into a normal poll or select backend and use it
		551	only for sockets (after having made sure that sockets work with kqueue on
		552	the target platform). See C<ev_embed> watchers for more info.
185		553
186	It scales in the same way as the epoll backend, but the interface to the	554	It scales in the same way as the epoll backend, but the interface to the
187	kernel is more efficient (which says nothing about its actual speed, of	555	kernel is more efficient (which says nothing about its actual speed, of
188	course). While starting and stopping an I/O watcher does not cause an	556	course). While stopping, setting and starting an I/O watcher does never
189	extra syscall as with epoll, it still adds up to four event changes per	557	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
190	incident, so its best to avoid that.	558	two event changes per incident. Support for C<fork ()> is very bad (but
		559	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		560	cases
191		561
		562	This backend usually performs well under most conditions.
		563
		564	While nominally embeddable in other event loops, this doesn't work
		565	everywhere, so you might need to test for this. And since it is broken
		566	almost everywhere, you should only use it when you have a lot of sockets
		567	(for which it usually works), by embedding it into another event loop
		568	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		569	also broken on OS X)) and, did I mention it, using it only for sockets.
		570
		571	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		572	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		573	C<NOTE_EOF>.
		574
192	=item C<EVMETHOD_DEVPOLL> (value 16, Solaris 8)	575	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
193		576
194	This is not implemented yet (and might never be).	577	This is not implemented yet (and might never be, unless you send me an
		578	implementation). According to reports, C</dev/poll> only supports sockets
		579	and is not embeddable, which would limit the usefulness of this backend
		580	immensely.
195		581
196	=item C<EVMETHOD_PORT> (value 32, Solaris 10)	582	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
197		583
198	This uses the Solaris 10 port mechanism. As with everything on Solaris,	584	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
199	it's really slow, but it still scales very well (O(active_fds)).	585	it's really slow, but it still scales very well (O(active_fds)).
200		586
		587	Please note that Solaris event ports can deliver a lot of spurious
		588	notifications, so you need to use non-blocking I/O or other means to avoid
		589	blocking when no data (or space) is available.
		590
		591	While this backend scales well, it requires one system call per active
		592	file descriptor per loop iteration. For small and medium numbers of file
		593	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		594	might perform better.
		595
		596	On the positive side, with the exception of the spurious readiness
		597	notifications, this backend actually performed fully to specification
		598	in all tests and is fully embeddable, which is a rare feat among the
		599	OS-specific backends (I vastly prefer correctness over speed hacks).
		600
		601	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		602	C<EVBACKEND_POLL>.
		603
201	=item C<EVMETHOD_ALL>	604	=item C<EVBACKEND_ALL>
202		605
203	Try all backends (even potentially broken ones that wouldn't be tried	606	Try all backends (even potentially broken ones that wouldn't be tried
204	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	607	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
205	C<EVMETHOD_ALL & ~EVMETHOD_KQUEUE>.	608	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		609
		610	It is definitely not recommended to use this flag, use whatever
		611	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		612	at all.
		613
		614	=item C<EVBACKEND_MASK>
		615
		616	Not a backend at all, but a mask to select all backend bits from a
		617	C<flags> value, in case you want to mask out any backends from a flags
		618	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
206		619
207	=back	620	=back
208		621
209	If one or more of these are ored into the flags value, then only these	622	If one or more of the backend flags are or'ed into the flags value,
210	backends will be tried (in the reverse order as given here). If none are	623	then only these backends will be tried (in the reverse order as listed
211	specified, most compiled-in backend will be tried, usually in reverse	624	here). If none are specified, all backends in C<ev_recommended_backends
212	order of their flag values :)	625	()> will be tried.
213		626
214	=item struct ev_loop *ev_loop_new (unsigned int flags)	627	Example: Try to create a event loop that uses epoll and nothing else.
215		628
216	Similar to C<ev_default_loop>, but always creates a new event loop that is	629	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
217	always distinct from the default loop. Unlike the default loop, it cannot	630	if (!epoller)
218	handle signal and child watchers, and attempts to do so will be greeted by	631	fatal ("no epoll found here, maybe it hides under your chair");
219	undefined behaviour (or a failed assertion if assertions are enabled).
220		632
221	=item ev_default_destroy ()	633	Example: Use whatever libev has to offer, but make sure that kqueue is
		634	used if available.
222		635
223	Destroys the default loop again (frees all memory and kernel state	636	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
224	etc.). This stops all registered event watchers (by not touching them in
225	any way whatsoever, although you cannot rely on this :).
226		637
227	=item ev_loop_destroy (loop)	638	=item ev_loop_destroy (loop)
228		639
229	Like C<ev_default_destroy>, but destroys an event loop created by an	640	Destroys an event loop object (frees all memory and kernel state
230	earlier call to C<ev_loop_new>.	641	etc.). None of the active event watchers will be stopped in the normal
		642	sense, so e.g. C<ev_is_active> might still return true. It is your
		643	responsibility to either stop all watchers cleanly yourself I<before>
		644	calling this function, or cope with the fact afterwards (which is usually
		645	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		646	for example).
231		647
232	=item ev_default_fork ()	648	Note that certain global state, such as signal state (and installed signal
		649	handlers), will not be freed by this function, and related watchers (such
		650	as signal and child watchers) would need to be stopped manually.
233		651
		652	This function is normally used on loop objects allocated by
		653	C<ev_loop_new>, but it can also be used on the default loop returned by
		654	C<ev_default_loop>, in which case it is not thread-safe.
		655
		656	Note that it is not advisable to call this function on the default loop
		657	except in the rare occasion where you really need to free its resources.
		658	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		659	and C<ev_loop_destroy>.
		660
		661	=item ev_loop_fork (loop)
		662
		663	This function sets a flag that causes subsequent C<ev_run> iterations to
234	This function reinitialises the kernel state for backends that have	664	reinitialise the kernel state for backends that have one. Despite the
235	one. Despite the name, you can call it anytime, but it makes most sense	665	name, you can call it anytime, but it makes most sense after forking, in
236	after forking, in either the parent or child process (or both, but that	666	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
237	again makes little sense).	667	child before resuming or calling C<ev_run>.
238		668
239	You I<must> call this function in the child process after forking if and	669	Again, you I<have> to call it on I<any> loop that you want to re-use after
240	only if you want to use the event library in both processes. If you just	670	a fork, I<even if you do not plan to use the loop in the parent>. This is
241	fork+exec, you don't have to call it.	671	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		672	during fork.
		673
		674	On the other hand, you only need to call this function in the child
		675	process if and only if you want to use the event loop in the child. If
		676	you just fork+exec or create a new loop in the child, you don't have to
		677	call it at all (in fact, C<epoll> is so badly broken that it makes a
		678	difference, but libev will usually detect this case on its own and do a
		679	costly reset of the backend).
242		680
243	The function itself is quite fast and it's usually not a problem to call	681	The function itself is quite fast and it's usually not a problem to call
244	it just in case after a fork. To make this easy, the function will fit in	682	it just in case after a fork.
245	quite nicely into a call to C<pthread_atfork>:
246		683
		684	Example: Automate calling C<ev_loop_fork> on the default loop when
		685	using pthreads.
		686
		687	static void
		688	post_fork_child (void)
		689	{
		690	ev_loop_fork (EV_DEFAULT);
		691	}
		692
		693	...
247	pthread_atfork (0, 0, ev_default_fork);	694	pthread_atfork (0, 0, post_fork_child);
248		695
249	=item ev_loop_fork (loop)	696	=item int ev_is_default_loop (loop)
250		697
251	Like C<ev_default_fork>, but acts on an event loop created by	698	Returns true when the given loop is, in fact, the default loop, and false
252	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	699	otherwise.
253	after fork, and how you do this is entirely your own problem.
254		700
		701	=item unsigned int ev_iteration (loop)
		702
		703	Returns the current iteration count for the event loop, which is identical
		704	to the number of times libev did poll for new events. It starts at C<0>
		705	and happily wraps around with enough iterations.
		706
		707	This value can sometimes be useful as a generation counter of sorts (it
		708	"ticks" the number of loop iterations), as it roughly corresponds with
		709	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		710	prepare and check phases.
		711
255	=item unsigned int ev_method (loop)	712	=item unsigned int ev_depth (loop)
256		713
		714	Returns the number of times C<ev_run> was entered minus the number of
		715	times C<ev_run> was exited normally, in other words, the recursion depth.
		716
		717	Outside C<ev_run>, this number is zero. In a callback, this number is
		718	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		719	in which case it is higher.
		720
		721	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
		722	throwing an exception etc.), doesn't count as "exit" - consider this
		723	as a hint to avoid such ungentleman-like behaviour unless it's really
		724	convenient, in which case it is fully supported.
		725
		726	=item unsigned int ev_backend (loop)
		727
257	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	728	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
258	use.	729	use.
259		730
260	=item ev_tstamp ev_now (loop)	731	=item ev_tstamp ev_now (loop)
261		732
262	Returns the current "event loop time", which is the time the event loop	733	Returns the current "event loop time", which is the time the event loop
263	got events and started processing them. This timestamp does not change	734	received events and started processing them. This timestamp does not
264	as long as callbacks are being processed, and this is also the base time	735	change as long as callbacks are being processed, and this is also the base
265	used for relative timers. You can treat it as the timestamp of the event	736	time used for relative timers. You can treat it as the timestamp of the
266	occuring (or more correctly, the mainloop finding out about it).	737	event occurring (or more correctly, libev finding out about it).
267		738
		739	=item ev_now_update (loop)
		740
		741	Establishes the current time by querying the kernel, updating the time
		742	returned by C<ev_now ()> in the progress. This is a costly operation and
		743	is usually done automatically within C<ev_run ()>.
		744
		745	This function is rarely useful, but when some event callback runs for a
		746	very long time without entering the event loop, updating libev's idea of
		747	the current time is a good idea.
		748
		749	See also L<The special problem of time updates> in the C<ev_timer> section.
		750
		751	=item ev_suspend (loop)
		752
		753	=item ev_resume (loop)
		754
		755	These two functions suspend and resume an event loop, for use when the
		756	loop is not used for a while and timeouts should not be processed.
		757
		758	A typical use case would be an interactive program such as a game: When
		759	the user presses C<^Z> to suspend the game and resumes it an hour later it
		760	would be best to handle timeouts as if no time had actually passed while
		761	the program was suspended. This can be achieved by calling C<ev_suspend>
		762	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		763	C<ev_resume> directly afterwards to resume timer processing.
		764
		765	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		766	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		767	will be rescheduled (that is, they will lose any events that would have
		768	occurred while suspended).
		769
		770	After calling C<ev_suspend> you B<must not> call I<any> function on the
		771	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		772	without a previous call to C<ev_suspend>.
		773
		774	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		775	event loop time (see C<ev_now_update>).
		776
268	=item ev_loop (loop, int flags)	777	=item ev_run (loop, int flags)
269		778
270	Finally, this is it, the event handler. This function usually is called	779	Finally, this is it, the event handler. This function usually is called
271	after you initialised all your watchers and you want to start handling	780	after you have initialised all your watchers and you want to start
272	events.	781	handling events. It will ask the operating system for any new events, call
		782	the watcher callbacks, an then repeat the whole process indefinitely: This
		783	is why event loops are called I<loops>.
273		784
274	If the flags argument is specified as 0, it will not return until either	785	If the flags argument is specified as C<0>, it will keep handling events
275	no event watchers are active anymore or C<ev_unloop> was called.	786	until either no event watchers are active anymore or C<ev_break> was
		787	called.
276		788
		789	Please note that an explicit C<ev_break> is usually better than
		790	relying on all watchers to be stopped when deciding when a program has
		791	finished (especially in interactive programs), but having a program
		792	that automatically loops as long as it has to and no longer by virtue
		793	of relying on its watchers stopping correctly, that is truly a thing of
		794	beauty.
		795
		796	This function is also I<mostly> exception-safe - you can break out of
		797	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		798	exception and so on. This does not decrement the C<ev_depth> value, nor
		799	will it clear any outstanding C<EVBREAK_ONE> breaks.
		800
277	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	801	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
278	those events and any outstanding ones, but will not block your process in	802	those events and any already outstanding ones, but will not wait and
279	case there are no events and will return after one iteration of the loop.	803	block your process in case there are no events and will return after one
		804	iteration of the loop. This is sometimes useful to poll and handle new
		805	events while doing lengthy calculations, to keep the program responsive.
280		806
281	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	807	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
282	neccessary) and will handle those and any outstanding ones. It will block	808	necessary) and will handle those and any already outstanding ones. It
283	your process until at least one new event arrives, and will return after	809	will block your process until at least one new event arrives (which could
		810	be an event internal to libev itself, so there is no guarantee that a
		811	user-registered callback will be called), and will return after one
284	one iteration of the loop.	812	iteration of the loop.
285		813
286	This flags value could be used to implement alternative looping	814	This is useful if you are waiting for some external event in conjunction
287	constructs, but the C<prepare> and C<check> watchers provide a better and	815	with something not expressible using other libev watchers (i.e. "roll your
288	more generic mechanism.	816	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		817	usually a better approach for this kind of thing.
289		818
290	Here are the gory details of what ev_loop does:	819	Here are the gory details of what C<ev_run> does:
291		820
292	1. If there are no active watchers (reference count is zero), return.	821	- Increment loop depth.
		822	- Reset the ev_break status.
		823	- Before the first iteration, call any pending watchers.
		824	LOOP:
		825	- If EVFLAG_FORKCHECK was used, check for a fork.
		826	- If a fork was detected (by any means), queue and call all fork watchers.
293	2. Queue and immediately call all prepare watchers.	827	- Queue and call all prepare watchers.
		828	- If ev_break was called, goto FINISH.
294	3. If we have been forked, recreate the kernel state.	829	- If we have been forked, detach and recreate the kernel state
		830	as to not disturb the other process.
295	4. Update the kernel state with all outstanding changes.	831	- Update the kernel state with all outstanding changes.
296	5. Update the "event loop time".	832	- Update the "event loop time" (ev_now ()).
297	6. Calculate for how long to block.	833	- Calculate for how long to sleep or block, if at all
		834	(active idle watchers, EVRUN_NOWAIT or not having
		835	any active watchers at all will result in not sleeping).
		836	- Sleep if the I/O and timer collect interval say so.
		837	- Increment loop iteration counter.
298	7. Block the process, waiting for events.	838	- Block the process, waiting for any events.
		839	- Queue all outstanding I/O (fd) events.
299	8. Update the "event loop time" and do time jump handling.	840	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
300	9. Queue all outstanding timers.	841	- Queue all expired timers.
301	10. Queue all outstanding periodics.	842	- Queue all expired periodics.
302	11. If no events are pending now, queue all idle watchers.	843	- Queue all idle watchers with priority higher than that of pending events.
303	12. Queue all check watchers.	844	- Queue all check watchers.
304	13. Call all queued watchers in reverse order (i.e. check watchers first).	845	- Call all queued watchers in reverse order (i.e. check watchers first).
305	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	846	Signals and child watchers are implemented as I/O watchers, and will
306	was used, return, otherwise continue with step #1.	847	be handled here by queueing them when their watcher gets executed.
		848	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
		849	were used, or there are no active watchers, goto FINISH, otherwise
		850	continue with step LOOP.
		851	FINISH:
		852	- Reset the ev_break status iff it was EVBREAK_ONE.
		853	- Decrement the loop depth.
		854	- Return.
307		855
		856	Example: Queue some jobs and then loop until no events are outstanding
		857	anymore.
		858
		859	... queue jobs here, make sure they register event watchers as long
		860	... as they still have work to do (even an idle watcher will do..)
		861	ev_run (my_loop, 0);
		862	... jobs done or somebody called unloop. yeah!
		863
308	=item ev_unloop (loop, how)	864	=item ev_break (loop, how)
309		865
310	Can be used to make a call to C<ev_loop> return early (but only after it	866	Can be used to make a call to C<ev_run> return early (but only after it
311	has processed all outstanding events). The C<how> argument must be either	867	has processed all outstanding events). The C<how> argument must be either
312	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	868	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
313	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	869	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		870
		871	This "break state" will be cleared on the next call to C<ev_run>.
		872
		873	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		874	which case it will have no effect.
314		875
315	=item ev_ref (loop)	876	=item ev_ref (loop)
316		877
317	=item ev_unref (loop)	878	=item ev_unref (loop)
318		879
319	Ref/unref can be used to add or remove a reference count on the event	880	Ref/unref can be used to add or remove a reference count on the event
320	loop: Every watcher keeps one reference, and as long as the reference	881	loop: Every watcher keeps one reference, and as long as the reference
321	count is nonzero, C<ev_loop> will not return on its own. If you have	882	count is nonzero, C<ev_run> will not return on its own.
322	a watcher you never unregister that should not keep C<ev_loop> from	883
323	returning, ev_unref() after starting, and ev_ref() before stopping it. For	884	This is useful when you have a watcher that you never intend to
		885	unregister, but that nevertheless should not keep C<ev_run> from
		886	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		887	before stopping it.
		888
324	example, libev itself uses this for its internal signal pipe: It is not	889	As an example, libev itself uses this for its internal signal pipe: It
325	visible to the libev user and should not keep C<ev_loop> from exiting if	890	is not visible to the libev user and should not keep C<ev_run> from
326	no event watchers registered by it are active. It is also an excellent	891	exiting if no event watchers registered by it are active. It is also an
327	way to do this for generic recurring timers or from within third-party	892	excellent way to do this for generic recurring timers or from within
328	libraries. Just remember to I<unref after start> and I<ref before stop>.	893	third-party libraries. Just remember to I<unref after start> and I<ref
		894	before stop> (but only if the watcher wasn't active before, or was active
		895	before, respectively. Note also that libev might stop watchers itself
		896	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		897	in the callback).
		898
		899	Example: Create a signal watcher, but keep it from keeping C<ev_run>
		900	running when nothing else is active.
		901
		902	ev_signal exitsig;
		903	ev_signal_init (&exitsig, sig_cb, SIGINT);
		904	ev_signal_start (loop, &exitsig);
		905	ev_unref (loop);
		906
		907	Example: For some weird reason, unregister the above signal handler again.
		908
		909	ev_ref (loop);
		910	ev_signal_stop (loop, &exitsig);
		911
		912	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		913
		914	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		915
		916	These advanced functions influence the time that libev will spend waiting
		917	for events. Both time intervals are by default C<0>, meaning that libev
		918	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		919	latency.
		920
		921	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		922	allows libev to delay invocation of I/O and timer/periodic callbacks
		923	to increase efficiency of loop iterations (or to increase power-saving
		924	opportunities).
		925
		926	The idea is that sometimes your program runs just fast enough to handle
		927	one (or very few) event(s) per loop iteration. While this makes the
		928	program responsive, it also wastes a lot of CPU time to poll for new
		929	events, especially with backends like C<select ()> which have a high
		930	overhead for the actual polling but can deliver many events at once.
		931
		932	By setting a higher I<io collect interval> you allow libev to spend more
		933	time collecting I/O events, so you can handle more events per iteration,
		934	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		935	C<ev_timer>) will be not affected. Setting this to a non-null value will
		936	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		937	sleep time ensures that libev will not poll for I/O events more often then
		938	once per this interval, on average.
		939
		940	Likewise, by setting a higher I<timeout collect interval> you allow libev
		941	to spend more time collecting timeouts, at the expense of increased
		942	latency/jitter/inexactness (the watcher callback will be called
		943	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		944	value will not introduce any overhead in libev.
		945
		946	Many (busy) programs can usually benefit by setting the I/O collect
		947	interval to a value near C<0.1> or so, which is often enough for
		948	interactive servers (of course not for games), likewise for timeouts. It
		949	usually doesn't make much sense to set it to a lower value than C<0.01>,
		950	as this approaches the timing granularity of most systems. Note that if
		951	you do transactions with the outside world and you can't increase the
		952	parallelity, then this setting will limit your transaction rate (if you
		953	need to poll once per transaction and the I/O collect interval is 0.01,
		954	then you can't do more than 100 transactions per second).
		955
		956	Setting the I<timeout collect interval> can improve the opportunity for
		957	saving power, as the program will "bundle" timer callback invocations that
		958	are "near" in time together, by delaying some, thus reducing the number of
		959	times the process sleeps and wakes up again. Another useful technique to
		960	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		961	they fire on, say, one-second boundaries only.
		962
		963	Example: we only need 0.1s timeout granularity, and we wish not to poll
		964	more often than 100 times per second:
		965
		966	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		967	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		968
		969	=item ev_invoke_pending (loop)
		970
		971	This call will simply invoke all pending watchers while resetting their
		972	pending state. Normally, C<ev_run> does this automatically when required,
		973	but when overriding the invoke callback this call comes handy. This
		974	function can be invoked from a watcher - this can be useful for example
		975	when you want to do some lengthy calculation and want to pass further
		976	event handling to another thread (you still have to make sure only one
		977	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		978
		979	=item int ev_pending_count (loop)
		980
		981	Returns the number of pending watchers - zero indicates that no watchers
		982	are pending.
		983
		984	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		985
		986	This overrides the invoke pending functionality of the loop: Instead of
		987	invoking all pending watchers when there are any, C<ev_run> will call
		988	this callback instead. This is useful, for example, when you want to
		989	invoke the actual watchers inside another context (another thread etc.).
		990
		991	If you want to reset the callback, use C<ev_invoke_pending> as new
		992	callback.
		993
		994	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		995
		996	Sometimes you want to share the same loop between multiple threads. This
		997	can be done relatively simply by putting mutex_lock/unlock calls around
		998	each call to a libev function.
		999
		1000	However, C<ev_run> can run an indefinite time, so it is not feasible
		1001	to wait for it to return. One way around this is to wake up the event
		1002	loop via C<ev_break> and C<av_async_send>, another way is to set these
		1003	I<release> and I<acquire> callbacks on the loop.
		1004
		1005	When set, then C<release> will be called just before the thread is
		1006	suspended waiting for new events, and C<acquire> is called just
		1007	afterwards.
		1008
		1009	Ideally, C<release> will just call your mutex_unlock function, and
		1010	C<acquire> will just call the mutex_lock function again.
		1011
		1012	While event loop modifications are allowed between invocations of
		1013	C<release> and C<acquire> (that's their only purpose after all), no
		1014	modifications done will affect the event loop, i.e. adding watchers will
		1015	have no effect on the set of file descriptors being watched, or the time
		1016	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		1017	to take note of any changes you made.
		1018
		1019	In theory, threads executing C<ev_run> will be async-cancel safe between
		1020	invocations of C<release> and C<acquire>.
		1021
		1022	See also the locking example in the C<THREADS> section later in this
		1023	document.
		1024
		1025	=item ev_set_userdata (loop, void *data)
		1026
		1027	=item void *ev_userdata (loop)
		1028
		1029	Set and retrieve a single C<void *> associated with a loop. When
		1030	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		1031	C<0>.
		1032
		1033	These two functions can be used to associate arbitrary data with a loop,
		1034	and are intended solely for the C<invoke_pending_cb>, C<release> and
		1035	C<acquire> callbacks described above, but of course can be (ab-)used for
		1036	any other purpose as well.
		1037
		1038	=item ev_verify (loop)
		1039
		1040	This function only does something when C<EV_VERIFY> support has been
		1041	compiled in, which is the default for non-minimal builds. It tries to go
		1042	through all internal structures and checks them for validity. If anything
		1043	is found to be inconsistent, it will print an error message to standard
		1044	error and call C<abort ()>.
		1045
		1046	This can be used to catch bugs inside libev itself: under normal
		1047	circumstances, this function will never abort as of course libev keeps its
		1048	data structures consistent.
329		1049
330	=back	1050	=back
331		1051
		1052
332	=head1 ANATOMY OF A WATCHER	1053	=head1 ANATOMY OF A WATCHER
333		1054
		1055	In the following description, uppercase C<TYPE> in names stands for the
		1056	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1057	watchers and C<ev_io_start> for I/O watchers.
		1058
334	A watcher is a structure that you create and register to record your	1059	A watcher is an opaque structure that you allocate and register to record
335	interest in some event. For instance, if you want to wait for STDIN to	1060	your interest in some event. To make a concrete example, imagine you want
336	become readable, you would create an C<ev_io> watcher for that:	1061	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1062	for that:
337		1063
338	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1064	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
339	{	1065	{
340	ev_io_stop (w);	1066	ev_io_stop (w);
341	ev_unloop (loop, EVUNLOOP_ALL);	1067	ev_break (loop, EVBREAK_ALL);
342	}	1068	}
343		1069
344	struct ev_loop *loop = ev_default_loop (0);	1070	struct ev_loop *loop = ev_default_loop (0);
		1071
345	struct ev_io stdin_watcher;	1072	ev_io stdin_watcher;
		1073
346	ev_init (&stdin_watcher, my_cb);	1074	ev_init (&stdin_watcher, my_cb);
347	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1075	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
348	ev_io_start (loop, &stdin_watcher);	1076	ev_io_start (loop, &stdin_watcher);
		1077
349	ev_loop (loop, 0);	1078	ev_run (loop, 0);
350		1079
351	As you can see, you are responsible for allocating the memory for your	1080	As you can see, you are responsible for allocating the memory for your
352	watcher structures (and it is usually a bad idea to do this on the stack,	1081	watcher structures (and it is I<usually> a bad idea to do this on the
353	although this can sometimes be quite valid).	1082	stack).
354		1083
		1084	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1085	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1086
355	Each watcher structure must be initialised by a call to C<ev_init	1087	Each watcher structure must be initialised by a call to C<ev_init (watcher
356	(watcher *, callback)>, which expects a callback to be provided. This	1088	*, callback)>, which expects a callback to be provided. This callback is
357	callback gets invoked each time the event occurs (or, in the case of io	1089	invoked each time the event occurs (or, in the case of I/O watchers, each
358	watchers, each time the event loop detects that the file descriptor given	1090	time the event loop detects that the file descriptor given is readable
359	is readable and/or writable).	1091	and/or writable).
360		1092
361	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1093	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
362	with arguments specific to this watcher type. There is also a macro	1094	macro to configure it, with arguments specific to the watcher type. There
363	to combine initialisation and setting in one call: C<< ev_<type>_init	1095	is also a macro to combine initialisation and setting in one call: C<<
364	(watcher *, callback, ...) >>.	1096	ev_TYPE_init (watcher *, callback, ...) >>.
365		1097
366	To make the watcher actually watch out for events, you have to start it	1098	To make the watcher actually watch out for events, you have to start it
367	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1099	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
368	*) >>), and you can stop watching for events at any time by calling the	1100	*) >>), and you can stop watching for events at any time by calling the
369	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1101	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
370		1102
371	As long as your watcher is active (has been started but not stopped) you	1103	As long as your watcher is active (has been started but not stopped) you
372	must not touch the values stored in it. Most specifically you must never	1104	must not touch the values stored in it. Most specifically you must never
373	reinitialise it or call its set method.	1105	reinitialise it or call its C<ev_TYPE_set> macro.
374
375	You can check whether an event is active by calling the C<ev_is_active
376	(watcher *)> macro. To see whether an event is outstanding (but the
377	callback for it has not been called yet) you can use the C<ev_is_pending
378	(watcher *)> macro.
379		1106
380	Each and every callback receives the event loop pointer as first, the	1107	Each and every callback receives the event loop pointer as first, the
381	registered watcher structure as second, and a bitset of received events as	1108	registered watcher structure as second, and a bitset of received events as
382	third argument.	1109	third argument.
383		1110
…		…
392	=item C<EV_WRITE>	1119	=item C<EV_WRITE>
393		1120
394	The file descriptor in the C<ev_io> watcher has become readable and/or	1121	The file descriptor in the C<ev_io> watcher has become readable and/or
395	writable.	1122	writable.
396		1123
397	=item C<EV_TIMEOUT>	1124	=item C<EV_TIMER>
398		1125
399	The C<ev_timer> watcher has timed out.	1126	The C<ev_timer> watcher has timed out.
400		1127
401	=item C<EV_PERIODIC>	1128	=item C<EV_PERIODIC>
402		1129
…		…
408		1135
409	=item C<EV_CHILD>	1136	=item C<EV_CHILD>
410		1137
411	The pid specified in the C<ev_child> watcher has received a status change.	1138	The pid specified in the C<ev_child> watcher has received a status change.
412		1139
		1140	=item C<EV_STAT>
		1141
		1142	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1143
413	=item C<EV_IDLE>	1144	=item C<EV_IDLE>
414		1145
415	The C<ev_idle> watcher has determined that you have nothing better to do.	1146	The C<ev_idle> watcher has determined that you have nothing better to do.
416		1147
417	=item C<EV_PREPARE>	1148	=item C<EV_PREPARE>
418		1149
419	=item C<EV_CHECK>	1150	=item C<EV_CHECK>
420		1151
421	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1152	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
422	to gather new events, and all C<ev_check> watchers are invoked just after	1153	to gather new events, and all C<ev_check> watchers are invoked just after
423	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1154	C<ev_run> has gathered them, but before it invokes any callbacks for any
424	received events. Callbacks of both watcher types can start and stop as	1155	received events. Callbacks of both watcher types can start and stop as
425	many watchers as they want, and all of them will be taken into account	1156	many watchers as they want, and all of them will be taken into account
426	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1157	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
427	C<ev_loop> from blocking).	1158	C<ev_run> from blocking).
		1159
		1160	=item C<EV_EMBED>
		1161
		1162	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1163
		1164	=item C<EV_FORK>
		1165
		1166	The event loop has been resumed in the child process after fork (see
		1167	C<ev_fork>).
		1168
		1169	=item C<EV_CLEANUP>
		1170
		1171	The event loop is about to be destroyed (see C<ev_cleanup>).
		1172
		1173	=item C<EV_ASYNC>
		1174
		1175	The given async watcher has been asynchronously notified (see C<ev_async>).
		1176
		1177	=item C<EV_CUSTOM>
		1178
		1179	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1180	by libev users to signal watchers (e.g. via C<ev_feed_event>).
428		1181
429	=item C<EV_ERROR>	1182	=item C<EV_ERROR>
430		1183
431	An unspecified error has occured, the watcher has been stopped. This might	1184	An unspecified error has occurred, the watcher has been stopped. This might
432	happen because the watcher could not be properly started because libev	1185	happen because the watcher could not be properly started because libev
433	ran out of memory, a file descriptor was found to be closed or any other	1186	ran out of memory, a file descriptor was found to be closed or any other
		1187	problem. Libev considers these application bugs.
		1188
434	problem. You best act on it by reporting the problem and somehow coping	1189	You best act on it by reporting the problem and somehow coping with the
435	with the watcher being stopped.	1190	watcher being stopped. Note that well-written programs should not receive
		1191	an error ever, so when your watcher receives it, this usually indicates a
		1192	bug in your program.
436		1193
437	Libev will usually signal a few "dummy" events together with an error,	1194	Libev will usually signal a few "dummy" events together with an error, for
438	for example it might indicate that a fd is readable or writable, and if	1195	example it might indicate that a fd is readable or writable, and if your
439	your callbacks is well-written it can just attempt the operation and cope	1196	callbacks is well-written it can just attempt the operation and cope with
440	with the error from read() or write(). This will not work in multithreaded	1197	the error from read() or write(). This will not work in multi-threaded
441	programs, though, so beware.	1198	programs, though, as the fd could already be closed and reused for another
		1199	thing, so beware.
442		1200
443	=back	1201	=back
444		1202
		1203	=head2 GENERIC WATCHER FUNCTIONS
		1204
		1205	=over 4
		1206
		1207	=item C<ev_init> (ev_TYPE *watcher, callback)
		1208
		1209	This macro initialises the generic portion of a watcher. The contents
		1210	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1211	the generic parts of the watcher are initialised, you I<need> to call
		1212	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1213	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1214	which rolls both calls into one.
		1215
		1216	You can reinitialise a watcher at any time as long as it has been stopped
		1217	(or never started) and there are no pending events outstanding.
		1218
		1219	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1220	int revents)>.
		1221
		1222	Example: Initialise an C<ev_io> watcher in two steps.
		1223
		1224	ev_io w;
		1225	ev_init (&w, my_cb);
		1226	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1227
		1228	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1229
		1230	This macro initialises the type-specific parts of a watcher. You need to
		1231	call C<ev_init> at least once before you call this macro, but you can
		1232	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1233	macro on a watcher that is active (it can be pending, however, which is a
		1234	difference to the C<ev_init> macro).
		1235
		1236	Although some watcher types do not have type-specific arguments
		1237	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1238
		1239	See C<ev_init>, above, for an example.
		1240
		1241	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1242
		1243	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1244	calls into a single call. This is the most convenient method to initialise
		1245	a watcher. The same limitations apply, of course.
		1246
		1247	Example: Initialise and set an C<ev_io> watcher in one step.
		1248
		1249	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1250
		1251	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1252
		1253	Starts (activates) the given watcher. Only active watchers will receive
		1254	events. If the watcher is already active nothing will happen.
		1255
		1256	Example: Start the C<ev_io> watcher that is being abused as example in this
		1257	whole section.
		1258
		1259	ev_io_start (EV_DEFAULT_UC, &w);
		1260
		1261	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1262
		1263	Stops the given watcher if active, and clears the pending status (whether
		1264	the watcher was active or not).
		1265
		1266	It is possible that stopped watchers are pending - for example,
		1267	non-repeating timers are being stopped when they become pending - but
		1268	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1269	pending. If you want to free or reuse the memory used by the watcher it is
		1270	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1271
		1272	=item bool ev_is_active (ev_TYPE *watcher)
		1273
		1274	Returns a true value iff the watcher is active (i.e. it has been started
		1275	and not yet been stopped). As long as a watcher is active you must not modify
		1276	it.
		1277
		1278	=item bool ev_is_pending (ev_TYPE *watcher)
		1279
		1280	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1281	events but its callback has not yet been invoked). As long as a watcher
		1282	is pending (but not active) you must not call an init function on it (but
		1283	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1284	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1285	it).
		1286
		1287	=item callback ev_cb (ev_TYPE *watcher)
		1288
		1289	Returns the callback currently set on the watcher.
		1290
		1291	=item ev_cb_set (ev_TYPE *watcher, callback)
		1292
		1293	Change the callback. You can change the callback at virtually any time
		1294	(modulo threads).
		1295
		1296	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1297
		1298	=item int ev_priority (ev_TYPE *watcher)
		1299
		1300	Set and query the priority of the watcher. The priority is a small
		1301	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1302	(default: C<-2>). Pending watchers with higher priority will be invoked
		1303	before watchers with lower priority, but priority will not keep watchers
		1304	from being executed (except for C<ev_idle> watchers).
		1305
		1306	If you need to suppress invocation when higher priority events are pending
		1307	you need to look at C<ev_idle> watchers, which provide this functionality.
		1308
		1309	You I<must not> change the priority of a watcher as long as it is active or
		1310	pending.
		1311
		1312	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1313	fine, as long as you do not mind that the priority value you query might
		1314	or might not have been clamped to the valid range.
		1315
		1316	The default priority used by watchers when no priority has been set is
		1317	always C<0>, which is supposed to not be too high and not be too low :).
		1318
		1319	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1320	priorities.
		1321
		1322	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1323
		1324	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1325	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1326	can deal with that fact, as both are simply passed through to the
		1327	callback.
		1328
		1329	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1330
		1331	If the watcher is pending, this function clears its pending status and
		1332	returns its C<revents> bitset (as if its callback was invoked). If the
		1333	watcher isn't pending it does nothing and returns C<0>.
		1334
		1335	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1336	callback to be invoked, which can be accomplished with this function.
		1337
		1338	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1339
		1340	Feeds the given event set into the event loop, as if the specified event
		1341	had happened for the specified watcher (which must be a pointer to an
		1342	initialised but not necessarily started event watcher). Obviously you must
		1343	not free the watcher as long as it has pending events.
		1344
		1345	Stopping the watcher, letting libev invoke it, or calling
		1346	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1347	not started in the first place.
		1348
		1349	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1350	functions that do not need a watcher.
		1351
		1352	=back
		1353
445	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1354	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
446		1355
447	Each watcher has, by default, a member C<void *data> that you can change	1356	Each watcher has, by default, a member C<void *data> that you can change
448	and read at any time, libev will completely ignore it. This can be used	1357	and read at any time: libev will completely ignore it. This can be used
449	to associate arbitrary data with your watcher. If you need more data and	1358	to associate arbitrary data with your watcher. If you need more data and
450	don't want to allocate memory and store a pointer to it in that data	1359	don't want to allocate memory and store a pointer to it in that data
451	member, you can also "subclass" the watcher type and provide your own	1360	member, you can also "subclass" the watcher type and provide your own
452	data:	1361	data:
453		1362
454	struct my_io	1363	struct my_io
455	{	1364	{
456	struct ev_io io;	1365	ev_io io;
457	int otherfd;	1366	int otherfd;
458	void *somedata;	1367	void *somedata;
459	struct whatever *mostinteresting;	1368	struct whatever *mostinteresting;
460	}	1369	};
		1370
		1371	...
		1372	struct my_io w;
		1373	ev_io_init (&w.io, my_cb, fd, EV_READ);
461		1374
462	And since your callback will be called with a pointer to the watcher, you	1375	And since your callback will be called with a pointer to the watcher, you
463	can cast it back to your own type:	1376	can cast it back to your own type:
464		1377
465	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1378	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
466	{	1379	{
467	struct my_io *w = (struct my_io *)w_;	1380	struct my_io *w = (struct my_io *)w_;
468	...	1381	...
469	}	1382	}
470		1383
471	More interesting and less C-conformant ways of catsing your callback type	1384	More interesting and less C-conformant ways of casting your callback type
472	have been omitted....	1385	instead have been omitted.
		1386
		1387	Another common scenario is to use some data structure with multiple
		1388	embedded watchers:
		1389
		1390	struct my_biggy
		1391	{
		1392	int some_data;
		1393	ev_timer t1;
		1394	ev_timer t2;
		1395	}
		1396
		1397	In this case getting the pointer to C<my_biggy> is a bit more
		1398	complicated: Either you store the address of your C<my_biggy> struct
		1399	in the C<data> member of the watcher (for woozies), or you need to use
		1400	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1401	programmers):
		1402
		1403	#include <stddef.h>
		1404
		1405	static void
		1406	t1_cb (EV_P_ ev_timer *w, int revents)
		1407	{
		1408	struct my_biggy big = (struct my_biggy *)
		1409	(((char *)w) - offsetof (struct my_biggy, t1));
		1410	}
		1411
		1412	static void
		1413	t2_cb (EV_P_ ev_timer *w, int revents)
		1414	{
		1415	struct my_biggy big = (struct my_biggy *)
		1416	(((char *)w) - offsetof (struct my_biggy, t2));
		1417	}
		1418
		1419	=head2 WATCHER STATES
		1420
		1421	There are various watcher states mentioned throughout this manual -
		1422	active, pending and so on. In this section these states and the rules to
		1423	transition between them will be described in more detail - and while these
		1424	rules might look complicated, they usually do "the right thing".
		1425
		1426	=over 4
		1427
		1428	=item initialiased
		1429
		1430	Before a watcher can be registered with the event looop it has to be
		1431	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1432	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1433
		1434	In this state it is simply some block of memory that is suitable for use
		1435	in an event loop. It can be moved around, freed, reused etc. at will.
		1436
		1437	=item started/running/active
		1438
		1439	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1440	property of the event loop, and is actively waiting for events. While in
		1441	this state it cannot be accessed (except in a few documented ways), moved,
		1442	freed or anything else - the only legal thing is to keep a pointer to it,
		1443	and call libev functions on it that are documented to work on active watchers.
		1444
		1445	=item pending
		1446
		1447	If a watcher is active and libev determines that an event it is interested
		1448	in has occurred (such as a timer expiring), it will become pending. It will
		1449	stay in this pending state until either it is stopped or its callback is
		1450	about to be invoked, so it is not normally pending inside the watcher
		1451	callback.
		1452
		1453	The watcher might or might not be active while it is pending (for example,
		1454	an expired non-repeating timer can be pending but no longer active). If it
		1455	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1456	but it is still property of the event loop at this time, so cannot be
		1457	moved, freed or reused. And if it is active the rules described in the
		1458	previous item still apply.
		1459
		1460	It is also possible to feed an event on a watcher that is not active (e.g.
		1461	via C<ev_feed_event>), in which case it becomes pending without being
		1462	active.
		1463
		1464	=item stopped
		1465
		1466	A watcher can be stopped implicitly by libev (in which case it might still
		1467	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1468	latter will clear any pending state the watcher might be in, regardless
		1469	of whether it was active or not, so stopping a watcher explicitly before
		1470	freeing it is often a good idea.
		1471
		1472	While stopped (and not pending) the watcher is essentially in the
		1473	initialised state, that is it can be reused, moved, modified in any way
		1474	you wish.
		1475
		1476	=back
		1477
		1478	=head2 WATCHER PRIORITY MODELS
		1479
		1480	Many event loops support I<watcher priorities>, which are usually small
		1481	integers that influence the ordering of event callback invocation
		1482	between watchers in some way, all else being equal.
		1483
		1484	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1485	description for the more technical details such as the actual priority
		1486	range.
		1487
		1488	There are two common ways how these these priorities are being interpreted
		1489	by event loops:
		1490
		1491	In the more common lock-out model, higher priorities "lock out" invocation
		1492	of lower priority watchers, which means as long as higher priority
		1493	watchers receive events, lower priority watchers are not being invoked.
		1494
		1495	The less common only-for-ordering model uses priorities solely to order
		1496	callback invocation within a single event loop iteration: Higher priority
		1497	watchers are invoked before lower priority ones, but they all get invoked
		1498	before polling for new events.
		1499
		1500	Libev uses the second (only-for-ordering) model for all its watchers
		1501	except for idle watchers (which use the lock-out model).
		1502
		1503	The rationale behind this is that implementing the lock-out model for
		1504	watchers is not well supported by most kernel interfaces, and most event
		1505	libraries will just poll for the same events again and again as long as
		1506	their callbacks have not been executed, which is very inefficient in the
		1507	common case of one high-priority watcher locking out a mass of lower
		1508	priority ones.
		1509
		1510	Static (ordering) priorities are most useful when you have two or more
		1511	watchers handling the same resource: a typical usage example is having an
		1512	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1513	timeouts. Under load, data might be received while the program handles
		1514	other jobs, but since timers normally get invoked first, the timeout
		1515	handler will be executed before checking for data. In that case, giving
		1516	the timer a lower priority than the I/O watcher ensures that I/O will be
		1517	handled first even under adverse conditions (which is usually, but not
		1518	always, what you want).
		1519
		1520	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1521	will only be executed when no same or higher priority watchers have
		1522	received events, they can be used to implement the "lock-out" model when
		1523	required.
		1524
		1525	For example, to emulate how many other event libraries handle priorities,
		1526	you can associate an C<ev_idle> watcher to each such watcher, and in
		1527	the normal watcher callback, you just start the idle watcher. The real
		1528	processing is done in the idle watcher callback. This causes libev to
		1529	continuously poll and process kernel event data for the watcher, but when
		1530	the lock-out case is known to be rare (which in turn is rare :), this is
		1531	workable.
		1532
		1533	Usually, however, the lock-out model implemented that way will perform
		1534	miserably under the type of load it was designed to handle. In that case,
		1535	it might be preferable to stop the real watcher before starting the
		1536	idle watcher, so the kernel will not have to process the event in case
		1537	the actual processing will be delayed for considerable time.
		1538
		1539	Here is an example of an I/O watcher that should run at a strictly lower
		1540	priority than the default, and which should only process data when no
		1541	other events are pending:
		1542
		1543	ev_idle idle; // actual processing watcher
		1544	ev_io io; // actual event watcher
		1545
		1546	static void
		1547	io_cb (EV_P_ ev_io *w, int revents)
		1548	{
		1549	// stop the I/O watcher, we received the event, but
		1550	// are not yet ready to handle it.
		1551	ev_io_stop (EV_A_ w);
		1552
		1553	// start the idle watcher to handle the actual event.
		1554	// it will not be executed as long as other watchers
		1555	// with the default priority are receiving events.
		1556	ev_idle_start (EV_A_ &idle);
		1557	}
		1558
		1559	static void
		1560	idle_cb (EV_P_ ev_idle *w, int revents)
		1561	{
		1562	// actual processing
		1563	read (STDIN_FILENO, ...);
		1564
		1565	// have to start the I/O watcher again, as
		1566	// we have handled the event
		1567	ev_io_start (EV_P_ &io);
		1568	}
		1569
		1570	// initialisation
		1571	ev_idle_init (&idle, idle_cb);
		1572	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1573	ev_io_start (EV_DEFAULT_ &io);
		1574
		1575	In the "real" world, it might also be beneficial to start a timer, so that
		1576	low-priority connections can not be locked out forever under load. This
		1577	enables your program to keep a lower latency for important connections
		1578	during short periods of high load, while not completely locking out less
		1579	important ones.
473		1580
474		1581
475	=head1 WATCHER TYPES	1582	=head1 WATCHER TYPES
476		1583
477	This section describes each watcher in detail, but will not repeat	1584	This section describes each watcher in detail, but will not repeat
478	information given in the last section.	1585	information given in the last section. Any initialisation/set macros,
		1586	functions and members specific to the watcher type are explained.
479		1587
		1588	Members are additionally marked with either I<[read-only]>, meaning that,
		1589	while the watcher is active, you can look at the member and expect some
		1590	sensible content, but you must not modify it (you can modify it while the
		1591	watcher is stopped to your hearts content), or I<[read-write]>, which
		1592	means you can expect it to have some sensible content while the watcher
		1593	is active, but you can also modify it. Modifying it may not do something
		1594	sensible or take immediate effect (or do anything at all), but libev will
		1595	not crash or malfunction in any way.
		1596
		1597
480	=head2 C<ev_io> - is this file descriptor readable or writable	1598	=head2 C<ev_io> - is this file descriptor readable or writable?
481		1599
482	I/O watchers check whether a file descriptor is readable or writable	1600	I/O watchers check whether a file descriptor is readable or writable
483	in each iteration of the event loop (This behaviour is called	1601	in each iteration of the event loop, or, more precisely, when reading
484	level-triggering because you keep receiving events as long as the	1602	would not block the process and writing would at least be able to write
485	condition persists. Remember you can stop the watcher if you don't want to	1603	some data. This behaviour is called level-triggering because you keep
486	act on the event and neither want to receive future events).	1604	receiving events as long as the condition persists. Remember you can stop
		1605	the watcher if you don't want to act on the event and neither want to
		1606	receive future events.
487		1607
488	In general you can register as many read and/or write event watchers per	1608	In general you can register as many read and/or write event watchers per
489	fd as you want (as long as you don't confuse yourself). Setting all file	1609	fd as you want (as long as you don't confuse yourself). Setting all file
490	descriptors to non-blocking mode is also usually a good idea (but not	1610	descriptors to non-blocking mode is also usually a good idea (but not
491	required if you know what you are doing).	1611	required if you know what you are doing).
492		1612
493	You have to be careful with dup'ed file descriptors, though. Some backends	1613	If you cannot use non-blocking mode, then force the use of a
494	(the linux epoll backend is a notable example) cannot handle dup'ed file	1614	known-to-be-good backend (at the time of this writing, this includes only
495	descriptors correctly if you register interest in two or more fds pointing	1615	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
496	to the same underlying file/socket etc. description (that is, they share	1616	descriptors for which non-blocking operation makes no sense (such as
497	the same underlying "file open").	1617	files) - libev doesn't guarantee any specific behaviour in that case.
498		1618
499	If you must do this, then force the use of a known-to-be-good backend	1619	Another thing you have to watch out for is that it is quite easy to
500	(at the time of this writing, this includes only EVMETHOD_SELECT and	1620	receive "spurious" readiness notifications, that is your callback might
501	EVMETHOD_POLL).	1621	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1622	because there is no data. Not only are some backends known to create a
		1623	lot of those (for example Solaris ports), it is very easy to get into
		1624	this situation even with a relatively standard program structure. Thus
		1625	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1626	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1627
		1628	If you cannot run the fd in non-blocking mode (for example you should
		1629	not play around with an Xlib connection), then you have to separately
		1630	re-test whether a file descriptor is really ready with a known-to-be good
		1631	interface such as poll (fortunately in our Xlib example, Xlib already
		1632	does this on its own, so its quite safe to use). Some people additionally
		1633	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1634	indefinitely.
		1635
		1636	But really, best use non-blocking mode.
		1637
		1638	=head3 The special problem of disappearing file descriptors
		1639
		1640	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1641	descriptor (either due to calling C<close> explicitly or any other means,
		1642	such as C<dup2>). The reason is that you register interest in some file
		1643	descriptor, but when it goes away, the operating system will silently drop
		1644	this interest. If another file descriptor with the same number then is
		1645	registered with libev, there is no efficient way to see that this is, in
		1646	fact, a different file descriptor.
		1647
		1648	To avoid having to explicitly tell libev about such cases, libev follows
		1649	the following policy: Each time C<ev_io_set> is being called, libev
		1650	will assume that this is potentially a new file descriptor, otherwise
		1651	it is assumed that the file descriptor stays the same. That means that
		1652	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1653	descriptor even if the file descriptor number itself did not change.
		1654
		1655	This is how one would do it normally anyway, the important point is that
		1656	the libev application should not optimise around libev but should leave
		1657	optimisations to libev.
		1658
		1659	=head3 The special problem of dup'ed file descriptors
		1660
		1661	Some backends (e.g. epoll), cannot register events for file descriptors,
		1662	but only events for the underlying file descriptions. That means when you
		1663	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1664	events for them, only one file descriptor might actually receive events.
		1665
		1666	There is no workaround possible except not registering events
		1667	for potentially C<dup ()>'ed file descriptors, or to resort to
		1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1669
		1670	=head3 The special problem of fork
		1671
		1672	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1673	useless behaviour. Libev fully supports fork, but needs to be told about
		1674	it in the child.
		1675
		1676	To support fork in your programs, you either have to call
		1677	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1678	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1679	C<EVBACKEND_POLL>.
		1680
		1681	=head3 The special problem of SIGPIPE
		1682
		1683	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1684	when writing to a pipe whose other end has been closed, your program gets
		1685	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1686	this is sensible behaviour, for daemons, this is usually undesirable.
		1687
		1688	So when you encounter spurious, unexplained daemon exits, make sure you
		1689	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1690	somewhere, as that would have given you a big clue).
		1691
		1692	=head3 The special problem of accept()ing when you can't
		1693
		1694	Many implementations of the POSIX C<accept> function (for example,
		1695	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1696	connection from the pending queue in all error cases.
		1697
		1698	For example, larger servers often run out of file descriptors (because
		1699	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1700	rejecting the connection, leading to libev signalling readiness on
		1701	the next iteration again (the connection still exists after all), and
		1702	typically causing the program to loop at 100% CPU usage.
		1703
		1704	Unfortunately, the set of errors that cause this issue differs between
		1705	operating systems, there is usually little the app can do to remedy the
		1706	situation, and no known thread-safe method of removing the connection to
		1707	cope with overload is known (to me).
		1708
		1709	One of the easiest ways to handle this situation is to just ignore it
		1710	- when the program encounters an overload, it will just loop until the
		1711	situation is over. While this is a form of busy waiting, no OS offers an
		1712	event-based way to handle this situation, so it's the best one can do.
		1713
		1714	A better way to handle the situation is to log any errors other than
		1715	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1716	messages, and continue as usual, which at least gives the user an idea of
		1717	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1718	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1719	usage.
		1720
		1721	If your program is single-threaded, then you could also keep a dummy file
		1722	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1723	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1724	close that fd, and create a new dummy fd. This will gracefully refuse
		1725	clients under typical overload conditions.
		1726
		1727	The last way to handle it is to simply log the error and C<exit>, as
		1728	is often done with C<malloc> failures, but this results in an easy
		1729	opportunity for a DoS attack.
		1730
		1731	=head3 Watcher-Specific Functions
502		1732
503	=over 4	1733	=over 4
504		1734
505	=item ev_io_init (ev_io *, callback, int fd, int events)	1735	=item ev_io_init (ev_io *, callback, int fd, int events)
506		1736
507	=item ev_io_set (ev_io *, int fd, int events)	1737	=item ev_io_set (ev_io *, int fd, int events)
508		1738
509	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1739	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
510	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1740	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
511	EV_WRITE> to receive the given events.	1741	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1742
		1743	=item int fd [read-only]
		1744
		1745	The file descriptor being watched.
		1746
		1747	=item int events [read-only]
		1748
		1749	The events being watched.
512		1750
513	=back	1751	=back
514		1752
		1753	=head3 Examples
		1754
		1755	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1756	readable, but only once. Since it is likely line-buffered, you could
		1757	attempt to read a whole line in the callback.
		1758
		1759	static void
		1760	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1761	{
		1762	ev_io_stop (loop, w);
		1763	.. read from stdin here (or from w->fd) and handle any I/O errors
		1764	}
		1765
		1766	...
		1767	struct ev_loop *loop = ev_default_init (0);
		1768	ev_io stdin_readable;
		1769	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1770	ev_io_start (loop, &stdin_readable);
		1771	ev_run (loop, 0);
		1772
		1773
515	=head2 C<ev_timer> - relative and optionally recurring timeouts	1774	=head2 C<ev_timer> - relative and optionally repeating timeouts
516		1775
517	Timer watchers are simple relative timers that generate an event after a	1776	Timer watchers are simple relative timers that generate an event after a
518	given time, and optionally repeating in regular intervals after that.	1777	given time, and optionally repeating in regular intervals after that.
519		1778
520	The timers are based on real time, that is, if you register an event that	1779	The timers are based on real time, that is, if you register an event that
521	times out after an hour and you reset your system clock to last years	1780	times out after an hour and you reset your system clock to January last
522	time, it will still time out after (roughly) and hour. "Roughly" because	1781	year, it will still time out after (roughly) one hour. "Roughly" because
523	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1782	detecting time jumps is hard, and some inaccuracies are unavoidable (the
524	monotonic clock option helps a lot here).	1783	monotonic clock option helps a lot here).
		1784
		1785	The callback is guaranteed to be invoked only I<after> its timeout has
		1786	passed (not I<at>, so on systems with very low-resolution clocks this
		1787	might introduce a small delay). If multiple timers become ready during the
		1788	same loop iteration then the ones with earlier time-out values are invoked
		1789	before ones of the same priority with later time-out values (but this is
		1790	no longer true when a callback calls C<ev_run> recursively).
		1791
		1792	=head3 Be smart about timeouts
		1793
		1794	Many real-world problems involve some kind of timeout, usually for error
		1795	recovery. A typical example is an HTTP request - if the other side hangs,
		1796	you want to raise some error after a while.
		1797
		1798	What follows are some ways to handle this problem, from obvious and
		1799	inefficient to smart and efficient.
		1800
		1801	In the following, a 60 second activity timeout is assumed - a timeout that
		1802	gets reset to 60 seconds each time there is activity (e.g. each time some
		1803	data or other life sign was received).
		1804
		1805	=over 4
		1806
		1807	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1808
		1809	This is the most obvious, but not the most simple way: In the beginning,
		1810	start the watcher:
		1811
		1812	ev_timer_init (timer, callback, 60., 0.);
		1813	ev_timer_start (loop, timer);
		1814
		1815	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1816	and start it again:
		1817
		1818	ev_timer_stop (loop, timer);
		1819	ev_timer_set (timer, 60., 0.);
		1820	ev_timer_start (loop, timer);
		1821
		1822	This is relatively simple to implement, but means that each time there is
		1823	some activity, libev will first have to remove the timer from its internal
		1824	data structure and then add it again. Libev tries to be fast, but it's
		1825	still not a constant-time operation.
		1826
		1827	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1828
		1829	This is the easiest way, and involves using C<ev_timer_again> instead of
		1830	C<ev_timer_start>.
		1831
		1832	To implement this, configure an C<ev_timer> with a C<repeat> value
		1833	of C<60> and then call C<ev_timer_again> at start and each time you
		1834	successfully read or write some data. If you go into an idle state where
		1835	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1836	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1837
		1838	That means you can ignore both the C<ev_timer_start> function and the
		1839	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1840	member and C<ev_timer_again>.
		1841
		1842	At start:
		1843
		1844	ev_init (timer, callback);
		1845	timer->repeat = 60.;
		1846	ev_timer_again (loop, timer);
		1847
		1848	Each time there is some activity:
		1849
		1850	ev_timer_again (loop, timer);
		1851
		1852	It is even possible to change the time-out on the fly, regardless of
		1853	whether the watcher is active or not:
		1854
		1855	timer->repeat = 30.;
		1856	ev_timer_again (loop, timer);
		1857
		1858	This is slightly more efficient then stopping/starting the timer each time
		1859	you want to modify its timeout value, as libev does not have to completely
		1860	remove and re-insert the timer from/into its internal data structure.
		1861
		1862	It is, however, even simpler than the "obvious" way to do it.
		1863
		1864	=item 3. Let the timer time out, but then re-arm it as required.
		1865
		1866	This method is more tricky, but usually most efficient: Most timeouts are
		1867	relatively long compared to the intervals between other activity - in
		1868	our example, within 60 seconds, there are usually many I/O events with
		1869	associated activity resets.
		1870
		1871	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1872	but remember the time of last activity, and check for a real timeout only
		1873	within the callback:
		1874
		1875	ev_tstamp last_activity; // time of last activity
		1876
		1877	static void
		1878	callback (EV_P_ ev_timer *w, int revents)
		1879	{
		1880	ev_tstamp now = ev_now (EV_A);
		1881	ev_tstamp timeout = last_activity + 60.;
		1882
		1883	// if last_activity + 60. is older than now, we did time out
		1884	if (timeout < now)
		1885	{
		1886	// timeout occurred, take action
		1887	}
		1888	else
		1889	{
		1890	// callback was invoked, but there was some activity, re-arm
		1891	// the watcher to fire in last_activity + 60, which is
		1892	// guaranteed to be in the future, so "again" is positive:
		1893	w->repeat = timeout - now;
		1894	ev_timer_again (EV_A_ w);
		1895	}
		1896	}
		1897
		1898	To summarise the callback: first calculate the real timeout (defined
		1899	as "60 seconds after the last activity"), then check if that time has
		1900	been reached, which means something I<did>, in fact, time out. Otherwise
		1901	the callback was invoked too early (C<timeout> is in the future), so
		1902	re-schedule the timer to fire at that future time, to see if maybe we have
		1903	a timeout then.
		1904
		1905	Note how C<ev_timer_again> is used, taking advantage of the
		1906	C<ev_timer_again> optimisation when the timer is already running.
		1907
		1908	This scheme causes more callback invocations (about one every 60 seconds
		1909	minus half the average time between activity), but virtually no calls to
		1910	libev to change the timeout.
		1911
		1912	To start the timer, simply initialise the watcher and set C<last_activity>
		1913	to the current time (meaning we just have some activity :), then call the
		1914	callback, which will "do the right thing" and start the timer:
		1915
		1916	ev_init (timer, callback);
		1917	last_activity = ev_now (loop);
		1918	callback (loop, timer, EV_TIMER);
		1919
		1920	And when there is some activity, simply store the current time in
		1921	C<last_activity>, no libev calls at all:
		1922
		1923	last_activity = ev_now (loop);
		1924
		1925	This technique is slightly more complex, but in most cases where the
		1926	time-out is unlikely to be triggered, much more efficient.
		1927
		1928	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1929	callback :) - just change the timeout and invoke the callback, which will
		1930	fix things for you.
		1931
		1932	=item 4. Wee, just use a double-linked list for your timeouts.
		1933
		1934	If there is not one request, but many thousands (millions...), all
		1935	employing some kind of timeout with the same timeout value, then one can
		1936	do even better:
		1937
		1938	When starting the timeout, calculate the timeout value and put the timeout
		1939	at the I<end> of the list.
		1940
		1941	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1942	the list is expected to fire (for example, using the technique #3).
		1943
		1944	When there is some activity, remove the timer from the list, recalculate
		1945	the timeout, append it to the end of the list again, and make sure to
		1946	update the C<ev_timer> if it was taken from the beginning of the list.
		1947
		1948	This way, one can manage an unlimited number of timeouts in O(1) time for
		1949	starting, stopping and updating the timers, at the expense of a major
		1950	complication, and having to use a constant timeout. The constant timeout
		1951	ensures that the list stays sorted.
		1952
		1953	=back
		1954
		1955	So which method the best?
		1956
		1957	Method #2 is a simple no-brain-required solution that is adequate in most
		1958	situations. Method #3 requires a bit more thinking, but handles many cases
		1959	better, and isn't very complicated either. In most case, choosing either
		1960	one is fine, with #3 being better in typical situations.
		1961
		1962	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1963	rather complicated, but extremely efficient, something that really pays
		1964	off after the first million or so of active timers, i.e. it's usually
		1965	overkill :)
		1966
		1967	=head3 The special problem of time updates
		1968
		1969	Establishing the current time is a costly operation (it usually takes at
		1970	least two system calls): EV therefore updates its idea of the current
		1971	time only before and after C<ev_run> collects new events, which causes a
		1972	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1973	lots of events in one iteration.
525		1974
526	The relative timeouts are calculated relative to the C<ev_now ()>	1975	The relative timeouts are calculated relative to the C<ev_now ()>
527	time. This is usually the right thing as this timestamp refers to the time	1976	time. This is usually the right thing as this timestamp refers to the time
528	of the event triggering whatever timeout you are modifying/starting. If	1977	of the event triggering whatever timeout you are modifying/starting. If
529	you suspect event processing to be delayed and you I<need> to base the timeout	1978	you suspect event processing to be delayed and you I<need> to base the
530	on the current time, use something like this to adjust for this:	1979	timeout on the current time, use something like this to adjust for this:
531		1980
532	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1981	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
533		1982
534	The callback is guarenteed to be invoked only when its timeout has passed,	1983	If the event loop is suspended for a long time, you can also force an
535	but if multiple timers become ready during the same loop iteration then	1984	update of the time returned by C<ev_now ()> by calling C<ev_now_update
536	order of execution is undefined.	1985	()>.
		1986
		1987	=head3 The special problems of suspended animation
		1988
		1989	When you leave the server world it is quite customary to hit machines that
		1990	can suspend/hibernate - what happens to the clocks during such a suspend?
		1991
		1992	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1993	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1994	to run until the system is suspended, but they will not advance while the
		1995	system is suspended. That means, on resume, it will be as if the program
		1996	was frozen for a few seconds, but the suspend time will not be counted
		1997	towards C<ev_timer> when a monotonic clock source is used. The real time
		1998	clock advanced as expected, but if it is used as sole clocksource, then a
		1999	long suspend would be detected as a time jump by libev, and timers would
		2000	be adjusted accordingly.
		2001
		2002	I would not be surprised to see different behaviour in different between
		2003	operating systems, OS versions or even different hardware.
		2004
		2005	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2006	time jump in the monotonic clocks and the realtime clock. If the program
		2007	is suspended for a very long time, and monotonic clock sources are in use,
		2008	then you can expect C<ev_timer>s to expire as the full suspension time
		2009	will be counted towards the timers. When no monotonic clock source is in
		2010	use, then libev will again assume a timejump and adjust accordingly.
		2011
		2012	It might be beneficial for this latter case to call C<ev_suspend>
		2013	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2014	deterministic behaviour in this case (you can do nothing against
		2015	C<SIGSTOP>).
		2016
		2017	=head3 Watcher-Specific Functions and Data Members
537		2018
538	=over 4	2019	=over 4
539		2020
540	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2021	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
541		2022
542	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2023	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
543		2024
544	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2025	Configure the timer to trigger after C<after> seconds. If C<repeat>
545	C<0.>, then it will automatically be stopped. If it is positive, then the	2026	is C<0.>, then it will automatically be stopped once the timeout is
546	timer will automatically be configured to trigger again C<repeat> seconds	2027	reached. If it is positive, then the timer will automatically be
547	later, again, and again, until stopped manually.	2028	configured to trigger again C<repeat> seconds later, again, and again,
		2029	until stopped manually.
548		2030
549	The timer itself will do a best-effort at avoiding drift, that is, if you	2031	The timer itself will do a best-effort at avoiding drift, that is, if
550	configure a timer to trigger every 10 seconds, then it will trigger at	2032	you configure a timer to trigger every 10 seconds, then it will normally
551	exactly 10 second intervals. If, however, your program cannot keep up with	2033	trigger at exactly 10 second intervals. If, however, your program cannot
552	the timer (because it takes longer than those 10 seconds to do stuff) the	2034	keep up with the timer (because it takes longer than those 10 seconds to
553	timer will not fire more than once per event loop iteration.	2035	do stuff) the timer will not fire more than once per event loop iteration.
554		2036
555	=item ev_timer_again (loop)	2037	=item ev_timer_again (loop, ev_timer *)
556		2038
557	This will act as if the timer timed out and restart it again if it is	2039	This will act as if the timer timed out and restart it again if it is
558	repeating. The exact semantics are:	2040	repeating. The exact semantics are:
559		2041
		2042	If the timer is pending, its pending status is cleared.
		2043
560	If the timer is started but nonrepeating, stop it.	2044	If the timer is started but non-repeating, stop it (as if it timed out).
561		2045
562	If the timer is repeating, either start it if necessary (with the repeat	2046	If the timer is repeating, either start it if necessary (with the
563	value), or reset the running timer to the repeat value.	2047	C<repeat> value), or reset the running timer to the C<repeat> value.
564		2048
565	This sounds a bit complicated, but here is a useful and typical	2049	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
566	example: Imagine you have a tcp connection and you want a so-called idle	2050	usage example.
567	timeout, that is, you want to be called when there have been, say, 60	2051
568	seconds of inactivity on the socket. The easiest way to do this is to	2052	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
569	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	2053
570	time you successfully read or write some data. If you go into an idle	2054	Returns the remaining time until a timer fires. If the timer is active,
571	state where you do not expect data to travel on the socket, you can stop	2055	then this time is relative to the current event loop time, otherwise it's
572	the timer, and again will automatically restart it if need be.	2056	the timeout value currently configured.
		2057
		2058	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2059	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2060	will return C<4>. When the timer expires and is restarted, it will return
		2061	roughly C<7> (likely slightly less as callback invocation takes some time,
		2062	too), and so on.
		2063
		2064	=item ev_tstamp repeat [read-write]
		2065
		2066	The current C<repeat> value. Will be used each time the watcher times out
		2067	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2068	which is also when any modifications are taken into account.
573		2069
574	=back	2070	=back
575		2071
		2072	=head3 Examples
		2073
		2074	Example: Create a timer that fires after 60 seconds.
		2075
		2076	static void
		2077	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2078	{
		2079	.. one minute over, w is actually stopped right here
		2080	}
		2081
		2082	ev_timer mytimer;
		2083	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		2084	ev_timer_start (loop, &mytimer);
		2085
		2086	Example: Create a timeout timer that times out after 10 seconds of
		2087	inactivity.
		2088
		2089	static void
		2090	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		2091	{
		2092	.. ten seconds without any activity
		2093	}
		2094
		2095	ev_timer mytimer;
		2096	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		2097	ev_timer_again (&mytimer); /* start timer */
		2098	ev_run (loop, 0);
		2099
		2100	// and in some piece of code that gets executed on any "activity":
		2101	// reset the timeout to start ticking again at 10 seconds
		2102	ev_timer_again (&mytimer);
		2103
		2104
576	=head2 C<ev_periodic> - to cron or not to cron	2105	=head2 C<ev_periodic> - to cron or not to cron?
577		2106
578	Periodic watchers are also timers of a kind, but they are very versatile	2107	Periodic watchers are also timers of a kind, but they are very versatile
579	(and unfortunately a bit complex).	2108	(and unfortunately a bit complex).
580		2109
581	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2110	Unlike C<ev_timer>, periodic watchers are not based on real time (or
582	but on wallclock time (absolute time). You can tell a periodic watcher	2111	relative time, the physical time that passes) but on wall clock time
583	to trigger "at" some specific point in time. For example, if you tell a	2112	(absolute time, the thing you can read on your calender or clock). The
584	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	2113	difference is that wall clock time can run faster or slower than real
585	+ 10.>) and then reset your system clock to the last year, then it will	2114	time, and time jumps are not uncommon (e.g. when you adjust your
586	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2115	wrist-watch).
587	roughly 10 seconds later and of course not if you reset your system time
588	again).
589		2116
590	They can also be used to implement vastly more complex timers, such as	2117	You can tell a periodic watcher to trigger after some specific point
		2118	in time: for example, if you tell a periodic watcher to trigger "in 10
		2119	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2120	not a delay) and then reset your system clock to January of the previous
		2121	year, then it will take a year or more to trigger the event (unlike an
		2122	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2123	it, as it uses a relative timeout).
		2124
		2125	C<ev_periodic> watchers can also be used to implement vastly more complex
591	triggering an event on eahc midnight, local time.	2126	timers, such as triggering an event on each "midnight, local time", or
		2127	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2128	those cannot react to time jumps.
592		2129
593	As with timers, the callback is guarenteed to be invoked only when the	2130	As with timers, the callback is guaranteed to be invoked only when the
594	time (C<at>) has been passed, but if multiple periodic timers become ready	2131	point in time where it is supposed to trigger has passed. If multiple
595	during the same loop iteration then order of execution is undefined.	2132	timers become ready during the same loop iteration then the ones with
		2133	earlier time-out values are invoked before ones with later time-out values
		2134	(but this is no longer true when a callback calls C<ev_run> recursively).
		2135
		2136	=head3 Watcher-Specific Functions and Data Members
596		2137
597	=over 4	2138	=over 4
598		2139
599	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2140	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
600		2141
601	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2142	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
602		2143
603	Lots of arguments, lets sort it out... There are basically three modes of	2144	Lots of arguments, let's sort it out... There are basically three modes of
604	operation, and we will explain them from simplest to complex:	2145	operation, and we will explain them from simplest to most complex:
605		2146
606	=over 4	2147	=over 4
607		2148
608	=item * absolute timer (interval = reschedule_cb = 0)	2149	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
609		2150
610	In this configuration the watcher triggers an event at the wallclock time	2151	In this configuration the watcher triggers an event after the wall clock
611	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2152	time C<offset> has passed. It will not repeat and will not adjust when a
612	that is, if it is to be run at January 1st 2011 then it will run when the	2153	time jump occurs, that is, if it is to be run at January 1st 2011 then it
613	system time reaches or surpasses this time.	2154	will be stopped and invoked when the system clock reaches or surpasses
		2155	this point in time.
614		2156
615	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2157	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
616		2158
617	In this mode the watcher will always be scheduled to time out at the next	2159	In this mode the watcher will always be scheduled to time out at the next
618	C<at + N * interval> time (for some integer N) and then repeat, regardless	2160	C<offset + N * interval> time (for some integer N, which can also be
619	of any time jumps.	2161	negative) and then repeat, regardless of any time jumps. The C<offset>
		2162	argument is merely an offset into the C<interval> periods.
620		2163
621	This can be used to create timers that do not drift with respect to system	2164	This can be used to create timers that do not drift with respect to the
622	time:	2165	system clock, for example, here is an C<ev_periodic> that triggers each
		2166	hour, on the hour (with respect to UTC):
623		2167
624	ev_periodic_set (&periodic, 0., 3600., 0);	2168	ev_periodic_set (&periodic, 0., 3600., 0);
625		2169
626	This doesn't mean there will always be 3600 seconds in between triggers,	2170	This doesn't mean there will always be 3600 seconds in between triggers,
627	but only that the the callback will be called when the system time shows a	2171	but only that the callback will be called when the system time shows a
628	full hour (UTC), or more correctly, when the system time is evenly divisible	2172	full hour (UTC), or more correctly, when the system time is evenly divisible
629	by 3600.	2173	by 3600.
630		2174
631	Another way to think about it (for the mathematically inclined) is that	2175	Another way to think about it (for the mathematically inclined) is that
632	C<ev_periodic> will try to run the callback in this mode at the next possible	2176	C<ev_periodic> will try to run the callback in this mode at the next possible
633	time where C<time = at (mod interval)>, regardless of any time jumps.	2177	time where C<time = offset (mod interval)>, regardless of any time jumps.
634		2178
		2179	For numerical stability it is preferable that the C<offset> value is near
		2180	C<ev_now ()> (the current time), but there is no range requirement for
		2181	this value, and in fact is often specified as zero.
		2182
		2183	Note also that there is an upper limit to how often a timer can fire (CPU
		2184	speed for example), so if C<interval> is very small then timing stability
		2185	will of course deteriorate. Libev itself tries to be exact to be about one
		2186	millisecond (if the OS supports it and the machine is fast enough).
		2187
635	=item * manual reschedule mode (reschedule_cb = callback)	2188	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
636		2189
637	In this mode the values for C<interval> and C<at> are both being	2190	In this mode the values for C<interval> and C<offset> are both being
638	ignored. Instead, each time the periodic watcher gets scheduled, the	2191	ignored. Instead, each time the periodic watcher gets scheduled, the
639	reschedule callback will be called with the watcher as first, and the	2192	reschedule callback will be called with the watcher as first, and the
640	current time as second argument.	2193	current time as second argument.
641		2194
642	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2195	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
643	ever, or make any event loop modifications>. If you need to stop it,	2196	or make ANY other event loop modifications whatsoever, unless explicitly
644	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2197	allowed by documentation here>.
645	starting a prepare watcher).
646		2198
		2199	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2200	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2201	only event loop modification you are allowed to do).
		2202
647	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2203	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
648	ev_tstamp now)>, e.g.:	2204	*w, ev_tstamp now)>, e.g.:
649		2205
		2206	static ev_tstamp
650	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2207	my_rescheduler (ev_periodic *w, ev_tstamp now)
651	{	2208	{
652	return now + 60.;	2209	return now + 60.;
653	}	2210	}
654		2211
655	It must return the next time to trigger, based on the passed time value	2212	It must return the next time to trigger, based on the passed time value
656	(that is, the lowest time value larger than to the second argument). It	2213	(that is, the lowest time value larger than to the second argument). It
657	will usually be called just before the callback will be triggered, but	2214	will usually be called just before the callback will be triggered, but
658	might be called at other times, too.	2215	might be called at other times, too.
659		2216
660	NOTE: I<< This callback must always return a time that is later than the	2217	NOTE: I<< This callback must always return a time that is higher than or
661	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2218	equal to the passed C<now> value >>.
662		2219
663	This can be used to create very complex timers, such as a timer that	2220	This can be used to create very complex timers, such as a timer that
664	triggers on each midnight, local time. To do this, you would calculate the	2221	triggers on "next midnight, local time". To do this, you would calculate the
665	next midnight after C<now> and return the timestamp value for this. How	2222	next midnight after C<now> and return the timestamp value for this. How
666	you do this is, again, up to you (but it is not trivial, which is the main	2223	you do this is, again, up to you (but it is not trivial, which is the main
667	reason I omitted it as an example).	2224	reason I omitted it as an example).
668		2225
669	=back	2226	=back
…		…
673	Simply stops and restarts the periodic watcher again. This is only useful	2230	Simply stops and restarts the periodic watcher again. This is only useful
674	when you changed some parameters or the reschedule callback would return	2231	when you changed some parameters or the reschedule callback would return
675	a different time than the last time it was called (e.g. in a crond like	2232	a different time than the last time it was called (e.g. in a crond like
676	program when the crontabs have changed).	2233	program when the crontabs have changed).
677		2234
		2235	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2236
		2237	When active, returns the absolute time that the watcher is supposed
		2238	to trigger next. This is not the same as the C<offset> argument to
		2239	C<ev_periodic_set>, but indeed works even in interval and manual
		2240	rescheduling modes.
		2241
		2242	=item ev_tstamp offset [read-write]
		2243
		2244	When repeating, this contains the offset value, otherwise this is the
		2245	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2246	although libev might modify this value for better numerical stability).
		2247
		2248	Can be modified any time, but changes only take effect when the periodic
		2249	timer fires or C<ev_periodic_again> is being called.
		2250
		2251	=item ev_tstamp interval [read-write]
		2252
		2253	The current interval value. Can be modified any time, but changes only
		2254	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2255	called.
		2256
		2257	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2258
		2259	The current reschedule callback, or C<0>, if this functionality is
		2260	switched off. Can be changed any time, but changes only take effect when
		2261	the periodic timer fires or C<ev_periodic_again> is being called.
		2262
678	=back	2263	=back
679		2264
		2265	=head3 Examples
		2266
		2267	Example: Call a callback every hour, or, more precisely, whenever the
		2268	system time is divisible by 3600. The callback invocation times have
		2269	potentially a lot of jitter, but good long-term stability.
		2270
		2271	static void
		2272	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
		2273	{
		2274	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2275	}
		2276
		2277	ev_periodic hourly_tick;
		2278	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2279	ev_periodic_start (loop, &hourly_tick);
		2280
		2281	Example: The same as above, but use a reschedule callback to do it:
		2282
		2283	#include <math.h>
		2284
		2285	static ev_tstamp
		2286	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2287	{
		2288	return now + (3600. - fmod (now, 3600.));
		2289	}
		2290
		2291	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2292
		2293	Example: Call a callback every hour, starting now:
		2294
		2295	ev_periodic hourly_tick;
		2296	ev_periodic_init (&hourly_tick, clock_cb,
		2297	fmod (ev_now (loop), 3600.), 3600., 0);
		2298	ev_periodic_start (loop, &hourly_tick);
		2299
		2300
680	=head2 C<ev_signal> - signal me when a signal gets signalled	2301	=head2 C<ev_signal> - signal me when a signal gets signalled!
681		2302
682	Signal watchers will trigger an event when the process receives a specific	2303	Signal watchers will trigger an event when the process receives a specific
683	signal one or more times. Even though signals are very asynchronous, libev	2304	signal one or more times. Even though signals are very asynchronous, libev
684	will try it's best to deliver signals synchronously, i.e. as part of the	2305	will try its best to deliver signals synchronously, i.e. as part of the
685	normal event processing, like any other event.	2306	normal event processing, like any other event.
686		2307
		2308	If you want signals to be delivered truly asynchronously, just use
		2309	C<sigaction> as you would do without libev and forget about sharing
		2310	the signal. You can even use C<ev_async> from a signal handler to
		2311	synchronously wake up an event loop.
		2312
687	You can configure as many watchers as you like per signal. Only when the	2313	You can configure as many watchers as you like for the same signal, but
		2314	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2315	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2316	C<SIGINT> in both the default loop and another loop at the same time. At
		2317	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2318
688	first watcher gets started will libev actually register a signal watcher	2319	When the first watcher gets started will libev actually register something
689	with the kernel (thus it coexists with your own signal handlers as long	2320	with the kernel (thus it coexists with your own signal handlers as long as
690	as you don't register any with libev). Similarly, when the last signal	2321	you don't register any with libev for the same signal).
691	watcher for a signal is stopped libev will reset the signal handler to	2322
692	SIG_DFL (regardless of what it was set to before).	2323	If possible and supported, libev will install its handlers with
		2324	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2325	not be unduly interrupted. If you have a problem with system calls getting
		2326	interrupted by signals you can block all signals in an C<ev_check> watcher
		2327	and unblock them in an C<ev_prepare> watcher.
		2328
		2329	=head3 The special problem of inheritance over fork/execve/pthread_create
		2330
		2331	Both the signal mask (C<sigprocmask>) and the signal disposition
		2332	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2333	stopping it again), that is, libev might or might not block the signal,
		2334	and might or might not set or restore the installed signal handler.
		2335
		2336	While this does not matter for the signal disposition (libev never
		2337	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2338	C<execve>), this matters for the signal mask: many programs do not expect
		2339	certain signals to be blocked.
		2340
		2341	This means that before calling C<exec> (from the child) you should reset
		2342	the signal mask to whatever "default" you expect (all clear is a good
		2343	choice usually).
		2344
		2345	The simplest way to ensure that the signal mask is reset in the child is
		2346	to install a fork handler with C<pthread_atfork> that resets it. That will
		2347	catch fork calls done by libraries (such as the libc) as well.
		2348
		2349	In current versions of libev, the signal will not be blocked indefinitely
		2350	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2351	the window of opportunity for problems, it will not go away, as libev
		2352	I<has> to modify the signal mask, at least temporarily.
		2353
		2354	So I can't stress this enough: I<If you do not reset your signal mask when
		2355	you expect it to be empty, you have a race condition in your code>. This
		2356	is not a libev-specific thing, this is true for most event libraries.
		2357
		2358	=head3 The special problem of threads signal handling
		2359
		2360	POSIX threads has problematic signal handling semantics, specifically,
		2361	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2362	threads in a process block signals, which is hard to achieve.
		2363
		2364	When you want to use sigwait (or mix libev signal handling with your own
		2365	for the same signals), you can tackle this problem by globally blocking
		2366	all signals before creating any threads (or creating them with a fully set
		2367	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2368	loops. Then designate one thread as "signal receiver thread" which handles
		2369	these signals. You can pass on any signals that libev might be interested
		2370	in by calling C<ev_feed_signal>.
		2371
		2372	=head3 Watcher-Specific Functions and Data Members
693		2373
694	=over 4	2374	=over 4
695		2375
696	=item ev_signal_init (ev_signal *, callback, int signum)	2376	=item ev_signal_init (ev_signal *, callback, int signum)
697		2377
698	=item ev_signal_set (ev_signal *, int signum)	2378	=item ev_signal_set (ev_signal *, int signum)
699		2379
700	Configures the watcher to trigger on the given signal number (usually one	2380	Configures the watcher to trigger on the given signal number (usually one
701	of the C<SIGxxx> constants).	2381	of the C<SIGxxx> constants).
702		2382
		2383	=item int signum [read-only]
		2384
		2385	The signal the watcher watches out for.
		2386
703	=back	2387	=back
704		2388
		2389	=head3 Examples
		2390
		2391	Example: Try to exit cleanly on SIGINT.
		2392
		2393	static void
		2394	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2395	{
		2396	ev_break (loop, EVBREAK_ALL);
		2397	}
		2398
		2399	ev_signal signal_watcher;
		2400	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2401	ev_signal_start (loop, &signal_watcher);
		2402
		2403
705	=head2 C<ev_child> - wait for pid status changes	2404	=head2 C<ev_child> - watch out for process status changes
706		2405
707	Child watchers trigger when your process receives a SIGCHLD in response to	2406	Child watchers trigger when your process receives a SIGCHLD in response to
708	some child status changes (most typically when a child of yours dies).	2407	some child status changes (most typically when a child of yours dies or
		2408	exits). It is permissible to install a child watcher I<after> the child
		2409	has been forked (which implies it might have already exited), as long
		2410	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2411	forking and then immediately registering a watcher for the child is fine,
		2412	but forking and registering a watcher a few event loop iterations later or
		2413	in the next callback invocation is not.
		2414
		2415	Only the default event loop is capable of handling signals, and therefore
		2416	you can only register child watchers in the default event loop.
		2417
		2418	Due to some design glitches inside libev, child watchers will always be
		2419	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2420	libev)
		2421
		2422	=head3 Process Interaction
		2423
		2424	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2425	initialised. This is necessary to guarantee proper behaviour even if the
		2426	first child watcher is started after the child exits. The occurrence
		2427	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2428	synchronously as part of the event loop processing. Libev always reaps all
		2429	children, even ones not watched.
		2430
		2431	=head3 Overriding the Built-In Processing
		2432
		2433	Libev offers no special support for overriding the built-in child
		2434	processing, but if your application collides with libev's default child
		2435	handler, you can override it easily by installing your own handler for
		2436	C<SIGCHLD> after initialising the default loop, and making sure the
		2437	default loop never gets destroyed. You are encouraged, however, to use an
		2438	event-based approach to child reaping and thus use libev's support for
		2439	that, so other libev users can use C<ev_child> watchers freely.
		2440
		2441	=head3 Stopping the Child Watcher
		2442
		2443	Currently, the child watcher never gets stopped, even when the
		2444	child terminates, so normally one needs to stop the watcher in the
		2445	callback. Future versions of libev might stop the watcher automatically
		2446	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2447	problem).
		2448
		2449	=head3 Watcher-Specific Functions and Data Members
709		2450
710	=over 4	2451	=over 4
711		2452
712	=item ev_child_init (ev_child *, callback, int pid)	2453	=item ev_child_init (ev_child *, callback, int pid, int trace)
713		2454
714	=item ev_child_set (ev_child *, int pid)	2455	=item ev_child_set (ev_child *, int pid, int trace)
715		2456
716	Configures the watcher to wait for status changes of process C<pid> (or	2457	Configures the watcher to wait for status changes of process C<pid> (or
717	I<any> process if C<pid> is specified as C<0>). The callback can look	2458	I<any> process if C<pid> is specified as C<0>). The callback can look
718	at the C<rstatus> member of the C<ev_child> watcher structure to see	2459	at the C<rstatus> member of the C<ev_child> watcher structure to see
719	the status word (use the macros from C<sys/wait.h> and see your systems	2460	the status word (use the macros from C<sys/wait.h> and see your systems
720	C<waitpid> documentation). The C<rpid> member contains the pid of the	2461	C<waitpid> documentation). The C<rpid> member contains the pid of the
721	process causing the status change.	2462	process causing the status change. C<trace> must be either C<0> (only
		2463	activate the watcher when the process terminates) or C<1> (additionally
		2464	activate the watcher when the process is stopped or continued).
		2465
		2466	=item int pid [read-only]
		2467
		2468	The process id this watcher watches out for, or C<0>, meaning any process id.
		2469
		2470	=item int rpid [read-write]
		2471
		2472	The process id that detected a status change.
		2473
		2474	=item int rstatus [read-write]
		2475
		2476	The process exit/trace status caused by C<rpid> (see your systems
		2477	C<waitpid> and C<sys/wait.h> documentation for details).
722		2478
723	=back	2479	=back
724		2480
		2481	=head3 Examples
		2482
		2483	Example: C<fork()> a new process and install a child handler to wait for
		2484	its completion.
		2485
		2486	ev_child cw;
		2487
		2488	static void
		2489	child_cb (EV_P_ ev_child *w, int revents)
		2490	{
		2491	ev_child_stop (EV_A_ w);
		2492	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2493	}
		2494
		2495	pid_t pid = fork ();
		2496
		2497	if (pid < 0)
		2498	// error
		2499	else if (pid == 0)
		2500	{
		2501	// the forked child executes here
		2502	exit (1);
		2503	}
		2504	else
		2505	{
		2506	ev_child_init (&cw, child_cb, pid, 0);
		2507	ev_child_start (EV_DEFAULT_ &cw);
		2508	}
		2509
		2510
		2511	=head2 C<ev_stat> - did the file attributes just change?
		2512
		2513	This watches a file system path for attribute changes. That is, it calls
		2514	C<stat> on that path in regular intervals (or when the OS says it changed)
		2515	and sees if it changed compared to the last time, invoking the callback if
		2516	it did.
		2517
		2518	The path does not need to exist: changing from "path exists" to "path does
		2519	not exist" is a status change like any other. The condition "path does not
		2520	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2521	C<st_nlink> field being zero (which is otherwise always forced to be at
		2522	least one) and all the other fields of the stat buffer having unspecified
		2523	contents.
		2524
		2525	The path I<must not> end in a slash or contain special components such as
		2526	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2527	your working directory changes, then the behaviour is undefined.
		2528
		2529	Since there is no portable change notification interface available, the
		2530	portable implementation simply calls C<stat(2)> regularly on the path
		2531	to see if it changed somehow. You can specify a recommended polling
		2532	interval for this case. If you specify a polling interval of C<0> (highly
		2533	recommended!) then a I<suitable, unspecified default> value will be used
		2534	(which you can expect to be around five seconds, although this might
		2535	change dynamically). Libev will also impose a minimum interval which is
		2536	currently around C<0.1>, but that's usually overkill.
		2537
		2538	This watcher type is not meant for massive numbers of stat watchers,
		2539	as even with OS-supported change notifications, this can be
		2540	resource-intensive.
		2541
		2542	At the time of this writing, the only OS-specific interface implemented
		2543	is the Linux inotify interface (implementing kqueue support is left as an
		2544	exercise for the reader. Note, however, that the author sees no way of
		2545	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2546
		2547	=head3 ABI Issues (Largefile Support)
		2548
		2549	Libev by default (unless the user overrides this) uses the default
		2550	compilation environment, which means that on systems with large file
		2551	support disabled by default, you get the 32 bit version of the stat
		2552	structure. When using the library from programs that change the ABI to
		2553	use 64 bit file offsets the programs will fail. In that case you have to
		2554	compile libev with the same flags to get binary compatibility. This is
		2555	obviously the case with any flags that change the ABI, but the problem is
		2556	most noticeably displayed with ev_stat and large file support.
		2557
		2558	The solution for this is to lobby your distribution maker to make large
		2559	file interfaces available by default (as e.g. FreeBSD does) and not
		2560	optional. Libev cannot simply switch on large file support because it has
		2561	to exchange stat structures with application programs compiled using the
		2562	default compilation environment.
		2563
		2564	=head3 Inotify and Kqueue
		2565
		2566	When C<inotify (7)> support has been compiled into libev and present at
		2567	runtime, it will be used to speed up change detection where possible. The
		2568	inotify descriptor will be created lazily when the first C<ev_stat>
		2569	watcher is being started.
		2570
		2571	Inotify presence does not change the semantics of C<ev_stat> watchers
		2572	except that changes might be detected earlier, and in some cases, to avoid
		2573	making regular C<stat> calls. Even in the presence of inotify support
		2574	there are many cases where libev has to resort to regular C<stat> polling,
		2575	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2576	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2577	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2578	xfs are fully working) libev usually gets away without polling.
		2579
		2580	There is no support for kqueue, as apparently it cannot be used to
		2581	implement this functionality, due to the requirement of having a file
		2582	descriptor open on the object at all times, and detecting renames, unlinks
		2583	etc. is difficult.
		2584
		2585	=head3 C<stat ()> is a synchronous operation
		2586
		2587	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2588	the process. The exception are C<ev_stat> watchers - those call C<stat
		2589	()>, which is a synchronous operation.
		2590
		2591	For local paths, this usually doesn't matter: unless the system is very
		2592	busy or the intervals between stat's are large, a stat call will be fast,
		2593	as the path data is usually in memory already (except when starting the
		2594	watcher).
		2595
		2596	For networked file systems, calling C<stat ()> can block an indefinite
		2597	time due to network issues, and even under good conditions, a stat call
		2598	often takes multiple milliseconds.
		2599
		2600	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2601	paths, although this is fully supported by libev.
		2602
		2603	=head3 The special problem of stat time resolution
		2604
		2605	The C<stat ()> system call only supports full-second resolution portably,
		2606	and even on systems where the resolution is higher, most file systems
		2607	still only support whole seconds.
		2608
		2609	That means that, if the time is the only thing that changes, you can
		2610	easily miss updates: on the first update, C<ev_stat> detects a change and
		2611	calls your callback, which does something. When there is another update
		2612	within the same second, C<ev_stat> will be unable to detect unless the
		2613	stat data does change in other ways (e.g. file size).
		2614
		2615	The solution to this is to delay acting on a change for slightly more
		2616	than a second (or till slightly after the next full second boundary), using
		2617	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2618	ev_timer_again (loop, w)>).
		2619
		2620	The C<.02> offset is added to work around small timing inconsistencies
		2621	of some operating systems (where the second counter of the current time
		2622	might be be delayed. One such system is the Linux kernel, where a call to
		2623	C<gettimeofday> might return a timestamp with a full second later than
		2624	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2625	update file times then there will be a small window where the kernel uses
		2626	the previous second to update file times but libev might already execute
		2627	the timer callback).
		2628
		2629	=head3 Watcher-Specific Functions and Data Members
		2630
		2631	=over 4
		2632
		2633	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2634
		2635	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2636
		2637	Configures the watcher to wait for status changes of the given
		2638	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2639	be detected and should normally be specified as C<0> to let libev choose
		2640	a suitable value. The memory pointed to by C<path> must point to the same
		2641	path for as long as the watcher is active.
		2642
		2643	The callback will receive an C<EV_STAT> event when a change was detected,
		2644	relative to the attributes at the time the watcher was started (or the
		2645	last change was detected).
		2646
		2647	=item ev_stat_stat (loop, ev_stat *)
		2648
		2649	Updates the stat buffer immediately with new values. If you change the
		2650	watched path in your callback, you could call this function to avoid
		2651	detecting this change (while introducing a race condition if you are not
		2652	the only one changing the path). Can also be useful simply to find out the
		2653	new values.
		2654
		2655	=item ev_statdata attr [read-only]
		2656
		2657	The most-recently detected attributes of the file. Although the type is
		2658	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2659	suitable for your system, but you can only rely on the POSIX-standardised
		2660	members to be present. If the C<st_nlink> member is C<0>, then there was
		2661	some error while C<stat>ing the file.
		2662
		2663	=item ev_statdata prev [read-only]
		2664
		2665	The previous attributes of the file. The callback gets invoked whenever
		2666	C<prev> != C<attr>, or, more precisely, one or more of these members
		2667	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2668	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2669
		2670	=item ev_tstamp interval [read-only]
		2671
		2672	The specified interval.
		2673
		2674	=item const char *path [read-only]
		2675
		2676	The file system path that is being watched.
		2677
		2678	=back
		2679
		2680	=head3 Examples
		2681
		2682	Example: Watch C</etc/passwd> for attribute changes.
		2683
		2684	static void
		2685	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2686	{
		2687	/* /etc/passwd changed in some way */
		2688	if (w->attr.st_nlink)
		2689	{
		2690	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2691	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2692	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2693	}
		2694	else
		2695	/* you shalt not abuse printf for puts */
		2696	puts ("wow, /etc/passwd is not there, expect problems. "
		2697	"if this is windows, they already arrived\n");
		2698	}
		2699
		2700	...
		2701	ev_stat passwd;
		2702
		2703	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2704	ev_stat_start (loop, &passwd);
		2705
		2706	Example: Like above, but additionally use a one-second delay so we do not
		2707	miss updates (however, frequent updates will delay processing, too, so
		2708	one might do the work both on C<ev_stat> callback invocation I<and> on
		2709	C<ev_timer> callback invocation).
		2710
		2711	static ev_stat passwd;
		2712	static ev_timer timer;
		2713
		2714	static void
		2715	timer_cb (EV_P_ ev_timer *w, int revents)
		2716	{
		2717	ev_timer_stop (EV_A_ w);
		2718
		2719	/* now it's one second after the most recent passwd change */
		2720	}
		2721
		2722	static void
		2723	stat_cb (EV_P_ ev_stat *w, int revents)
		2724	{
		2725	/* reset the one-second timer */
		2726	ev_timer_again (EV_A_ &timer);
		2727	}
		2728
		2729	...
		2730	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2731	ev_stat_start (loop, &passwd);
		2732	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2733
		2734
725	=head2 C<ev_idle> - when you've got nothing better to do	2735	=head2 C<ev_idle> - when you've got nothing better to do...
726		2736
727	Idle watchers trigger events when there are no other events are pending	2737	Idle watchers trigger events when no other events of the same or higher
728	(prepare, check and other idle watchers do not count). That is, as long	2738	priority are pending (prepare, check and other idle watchers do not count
729	as your process is busy handling sockets or timeouts (or even signals,	2739	as receiving "events").
730	imagine) it will not be triggered. But when your process is idle all idle	2740
731	watchers are being called again and again, once per event loop iteration -	2741	That is, as long as your process is busy handling sockets or timeouts
		2742	(or even signals, imagine) of the same or higher priority it will not be
		2743	triggered. But when your process is idle (or only lower-priority watchers
		2744	are pending), the idle watchers are being called once per event loop
732	until stopped, that is, or your process receives more events and becomes	2745	iteration - until stopped, that is, or your process receives more events
733	busy.	2746	and becomes busy again with higher priority stuff.
734		2747
735	The most noteworthy effect is that as long as any idle watchers are	2748	The most noteworthy effect is that as long as any idle watchers are
736	active, the process will not block when waiting for new events.	2749	active, the process will not block when waiting for new events.
737		2750
738	Apart from keeping your process non-blocking (which is a useful	2751	Apart from keeping your process non-blocking (which is a useful
739	effect on its own sometimes), idle watchers are a good place to do	2752	effect on its own sometimes), idle watchers are a good place to do
740	"pseudo-background processing", or delay processing stuff to after the	2753	"pseudo-background processing", or delay processing stuff to after the
741	event loop has handled all outstanding events.	2754	event loop has handled all outstanding events.
742		2755
		2756	=head3 Watcher-Specific Functions and Data Members
		2757
743	=over 4	2758	=over 4
744		2759
745	=item ev_idle_init (ev_signal *, callback)	2760	=item ev_idle_init (ev_idle *, callback)
746		2761
747	Initialises and configures the idle watcher - it has no parameters of any	2762	Initialises and configures the idle watcher - it has no parameters of any
748	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2763	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
749	believe me.	2764	believe me.
750		2765
751	=back	2766	=back
752		2767
		2768	=head3 Examples
		2769
		2770	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2771	callback, free it. Also, use no error checking, as usual.
		2772
		2773	static void
		2774	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2775	{
		2776	free (w);
		2777	// now do something you wanted to do when the program has
		2778	// no longer anything immediate to do.
		2779	}
		2780
		2781	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2782	ev_idle_init (idle_watcher, idle_cb);
		2783	ev_idle_start (loop, idle_watcher);
		2784
		2785
753	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2786	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
754		2787
755	Prepare and check watchers are usually (but not always) used in tandem:	2788	Prepare and check watchers are usually (but not always) used in pairs:
756	prepare watchers get invoked before the process blocks and check watchers	2789	prepare watchers get invoked before the process blocks and check watchers
757	afterwards.	2790	afterwards.
758		2791
		2792	You I<must not> call C<ev_run> or similar functions that enter
		2793	the current event loop from either C<ev_prepare> or C<ev_check>
		2794	watchers. Other loops than the current one are fine, however. The
		2795	rationale behind this is that you do not need to check for recursion in
		2796	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2797	C<ev_check> so if you have one watcher of each kind they will always be
		2798	called in pairs bracketing the blocking call.
		2799
759	Their main purpose is to integrate other event mechanisms into libev. This	2800	Their main purpose is to integrate other event mechanisms into libev and
760	could be used, for example, to track variable changes, implement your own	2801	their use is somewhat advanced. They could be used, for example, to track
761	watchers, integrate net-snmp or a coroutine library and lots more.	2802	variable changes, implement your own watchers, integrate net-snmp or a
		2803	coroutine library and lots more. They are also occasionally useful if
		2804	you cache some data and want to flush it before blocking (for example,
		2805	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2806	watcher).
762		2807
763	This is done by examining in each prepare call which file descriptors need	2808	This is done by examining in each prepare call which file descriptors
764	to be watched by the other library, registering C<ev_io> watchers for	2809	need to be watched by the other library, registering C<ev_io> watchers
765	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2810	for them and starting an C<ev_timer> watcher for any timeouts (many
766	provide just this functionality). Then, in the check watcher you check for	2811	libraries provide exactly this functionality). Then, in the check watcher,
767	any events that occured (by checking the pending status of all watchers	2812	you check for any events that occurred (by checking the pending status
768	and stopping them) and call back into the library. The I/O and timer	2813	of all watchers and stopping them) and call back into the library. The
769	callbacks will never actually be called (but must be valid nevertheless,	2814	I/O and timer callbacks will never actually be called (but must be valid
770	because you never know, you know?).	2815	nevertheless, because you never know, you know?).
771		2816
772	As another example, the Perl Coro module uses these hooks to integrate	2817	As another example, the Perl Coro module uses these hooks to integrate
773	coroutines into libev programs, by yielding to other active coroutines	2818	coroutines into libev programs, by yielding to other active coroutines
774	during each prepare and only letting the process block if no coroutines	2819	during each prepare and only letting the process block if no coroutines
775	are ready to run (it's actually more complicated: it only runs coroutines	2820	are ready to run (it's actually more complicated: it only runs coroutines
776	with priority higher than or equal to the event loop and one coroutine	2821	with priority higher than or equal to the event loop and one coroutine
777	of lower priority, but only once, using idle watchers to keep the event	2822	of lower priority, but only once, using idle watchers to keep the event
778	loop from blocking if lower-priority coroutines are active, thus mapping	2823	loop from blocking if lower-priority coroutines are active, thus mapping
779	low-priority coroutines to idle/background tasks).	2824	low-priority coroutines to idle/background tasks).
780		2825
		2826	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2827	priority, to ensure that they are being run before any other watchers
		2828	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2829
		2830	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2831	activate ("feed") events into libev. While libev fully supports this, they
		2832	might get executed before other C<ev_check> watchers did their job. As
		2833	C<ev_check> watchers are often used to embed other (non-libev) event
		2834	loops those other event loops might be in an unusable state until their
		2835	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2836	others).
		2837
		2838	=head3 Watcher-Specific Functions and Data Members
		2839
781	=over 4	2840	=over 4
782		2841
783	=item ev_prepare_init (ev_prepare *, callback)	2842	=item ev_prepare_init (ev_prepare *, callback)
784		2843
785	=item ev_check_init (ev_check *, callback)	2844	=item ev_check_init (ev_check *, callback)
786		2845
787	Initialises and configures the prepare or check watcher - they have no	2846	Initialises and configures the prepare or check watcher - they have no
788	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2847	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
789	macros, but using them is utterly, utterly and completely pointless.	2848	macros, but using them is utterly, utterly, utterly and completely
		2849	pointless.
790		2850
791	=back	2851	=back
792		2852
		2853	=head3 Examples
		2854
		2855	There are a number of principal ways to embed other event loops or modules
		2856	into libev. Here are some ideas on how to include libadns into libev
		2857	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2858	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2859	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2860	Glib event loop).
		2861
		2862	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2863	and in a check watcher, destroy them and call into libadns. What follows
		2864	is pseudo-code only of course. This requires you to either use a low
		2865	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2866	the callbacks for the IO/timeout watchers might not have been called yet.
		2867
		2868	static ev_io iow [nfd];
		2869	static ev_timer tw;
		2870
		2871	static void
		2872	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2873	{
		2874	}
		2875
		2876	// create io watchers for each fd and a timer before blocking
		2877	static void
		2878	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2879	{
		2880	int timeout = 3600000;
		2881	struct pollfd fds [nfd];
		2882	// actual code will need to loop here and realloc etc.
		2883	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2884
		2885	/* the callback is illegal, but won't be called as we stop during check */
		2886	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		2887	ev_timer_start (loop, &tw);
		2888
		2889	// create one ev_io per pollfd
		2890	for (int i = 0; i < nfd; ++i)
		2891	{
		2892	ev_io_init (iow + i, io_cb, fds [i].fd,
		2893	((fds [i].events & POLLIN ? EV_READ : 0)
		2894	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2895
		2896	fds [i].revents = 0;
		2897	ev_io_start (loop, iow + i);
		2898	}
		2899	}
		2900
		2901	// stop all watchers after blocking
		2902	static void
		2903	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2904	{
		2905	ev_timer_stop (loop, &tw);
		2906
		2907	for (int i = 0; i < nfd; ++i)
		2908	{
		2909	// set the relevant poll flags
		2910	// could also call adns_processreadable etc. here
		2911	struct pollfd *fd = fds + i;
		2912	int revents = ev_clear_pending (iow + i);
		2913	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2914	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2915
		2916	// now stop the watcher
		2917	ev_io_stop (loop, iow + i);
		2918	}
		2919
		2920	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2921	}
		2922
		2923	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2924	in the prepare watcher and would dispose of the check watcher.
		2925
		2926	Method 3: If the module to be embedded supports explicit event
		2927	notification (libadns does), you can also make use of the actual watcher
		2928	callbacks, and only destroy/create the watchers in the prepare watcher.
		2929
		2930	static void
		2931	timer_cb (EV_P_ ev_timer *w, int revents)
		2932	{
		2933	adns_state ads = (adns_state)w->data;
		2934	update_now (EV_A);
		2935
		2936	adns_processtimeouts (ads, &tv_now);
		2937	}
		2938
		2939	static void
		2940	io_cb (EV_P_ ev_io *w, int revents)
		2941	{
		2942	adns_state ads = (adns_state)w->data;
		2943	update_now (EV_A);
		2944
		2945	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2946	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2947	}
		2948
		2949	// do not ever call adns_afterpoll
		2950
		2951	Method 4: Do not use a prepare or check watcher because the module you
		2952	want to embed is not flexible enough to support it. Instead, you can
		2953	override their poll function. The drawback with this solution is that the
		2954	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2955	this approach, effectively embedding EV as a client into the horrible
		2956	libglib event loop.
		2957
		2958	static gint
		2959	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2960	{
		2961	int got_events = 0;
		2962
		2963	for (n = 0; n < nfds; ++n)
		2964	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2965
		2966	if (timeout >= 0)
		2967	// create/start timer
		2968
		2969	// poll
		2970	ev_run (EV_A_ 0);
		2971
		2972	// stop timer again
		2973	if (timeout >= 0)
		2974	ev_timer_stop (EV_A_ &to);
		2975
		2976	// stop io watchers again - their callbacks should have set
		2977	for (n = 0; n < nfds; ++n)
		2978	ev_io_stop (EV_A_ iow [n]);
		2979
		2980	return got_events;
		2981	}
		2982
		2983
		2984	=head2 C<ev_embed> - when one backend isn't enough...
		2985
		2986	This is a rather advanced watcher type that lets you embed one event loop
		2987	into another (currently only C<ev_io> events are supported in the embedded
		2988	loop, other types of watchers might be handled in a delayed or incorrect
		2989	fashion and must not be used).
		2990
		2991	There are primarily two reasons you would want that: work around bugs and
		2992	prioritise I/O.
		2993
		2994	As an example for a bug workaround, the kqueue backend might only support
		2995	sockets on some platform, so it is unusable as generic backend, but you
		2996	still want to make use of it because you have many sockets and it scales
		2997	so nicely. In this case, you would create a kqueue-based loop and embed
		2998	it into your default loop (which might use e.g. poll). Overall operation
		2999	will be a bit slower because first libev has to call C<poll> and then
		3000	C<kevent>, but at least you can use both mechanisms for what they are
		3001	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		3002
		3003	As for prioritising I/O: under rare circumstances you have the case where
		3004	some fds have to be watched and handled very quickly (with low latency),
		3005	and even priorities and idle watchers might have too much overhead. In
		3006	this case you would put all the high priority stuff in one loop and all
		3007	the rest in a second one, and embed the second one in the first.
		3008
		3009	As long as the watcher is active, the callback will be invoked every
		3010	time there might be events pending in the embedded loop. The callback
		3011	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		3012	sweep and invoke their callbacks (the callback doesn't need to invoke the
		3013	C<ev_embed_sweep> function directly, it could also start an idle watcher
		3014	to give the embedded loop strictly lower priority for example).
		3015
		3016	You can also set the callback to C<0>, in which case the embed watcher
		3017	will automatically execute the embedded loop sweep whenever necessary.
		3018
		3019	Fork detection will be handled transparently while the C<ev_embed> watcher
		3020	is active, i.e., the embedded loop will automatically be forked when the
		3021	embedding loop forks. In other cases, the user is responsible for calling
		3022	C<ev_loop_fork> on the embedded loop.
		3023
		3024	Unfortunately, not all backends are embeddable: only the ones returned by
		3025	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		3026	portable one.
		3027
		3028	So when you want to use this feature you will always have to be prepared
		3029	that you cannot get an embeddable loop. The recommended way to get around
		3030	this is to have a separate variables for your embeddable loop, try to
		3031	create it, and if that fails, use the normal loop for everything.
		3032
		3033	=head3 C<ev_embed> and fork
		3034
		3035	While the C<ev_embed> watcher is running, forks in the embedding loop will
		3036	automatically be applied to the embedded loop as well, so no special
		3037	fork handling is required in that case. When the watcher is not running,
		3038	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		3039	as applicable.
		3040
		3041	=head3 Watcher-Specific Functions and Data Members
		3042
		3043	=over 4
		3044
		3045	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		3046
		3047	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		3048
		3049	Configures the watcher to embed the given loop, which must be
		3050	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		3051	invoked automatically, otherwise it is the responsibility of the callback
		3052	to invoke it (it will continue to be called until the sweep has been done,
		3053	if you do not want that, you need to temporarily stop the embed watcher).
		3054
		3055	=item ev_embed_sweep (loop, ev_embed *)
		3056
		3057	Make a single, non-blocking sweep over the embedded loop. This works
		3058	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
		3059	appropriate way for embedded loops.
		3060
		3061	=item struct ev_loop *other [read-only]
		3062
		3063	The embedded event loop.
		3064
		3065	=back
		3066
		3067	=head3 Examples
		3068
		3069	Example: Try to get an embeddable event loop and embed it into the default
		3070	event loop. If that is not possible, use the default loop. The default
		3071	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3072	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3073	used).
		3074
		3075	struct ev_loop *loop_hi = ev_default_init (0);
		3076	struct ev_loop *loop_lo = 0;
		3077	ev_embed embed;
		3078
		3079	// see if there is a chance of getting one that works
		3080	// (remember that a flags value of 0 means autodetection)
		3081	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3082	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3083	: 0;
		3084
		3085	// if we got one, then embed it, otherwise default to loop_hi
		3086	if (loop_lo)
		3087	{
		3088	ev_embed_init (&embed, 0, loop_lo);
		3089	ev_embed_start (loop_hi, &embed);
		3090	}
		3091	else
		3092	loop_lo = loop_hi;
		3093
		3094	Example: Check if kqueue is available but not recommended and create
		3095	a kqueue backend for use with sockets (which usually work with any
		3096	kqueue implementation). Store the kqueue/socket-only event loop in
		3097	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3098
		3099	struct ev_loop *loop = ev_default_init (0);
		3100	struct ev_loop *loop_socket = 0;
		3101	ev_embed embed;
		3102
		3103	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3104	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3105	{
		3106	ev_embed_init (&embed, 0, loop_socket);
		3107	ev_embed_start (loop, &embed);
		3108	}
		3109
		3110	if (!loop_socket)
		3111	loop_socket = loop;
		3112
		3113	// now use loop_socket for all sockets, and loop for everything else
		3114
		3115
		3116	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3117
		3118	Fork watchers are called when a C<fork ()> was detected (usually because
		3119	whoever is a good citizen cared to tell libev about it by calling
		3120	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		3121	event loop blocks next and before C<ev_check> watchers are being called,
		3122	and only in the child after the fork. If whoever good citizen calling
		3123	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		3124	handlers will be invoked, too, of course.
		3125
		3126	=head3 The special problem of life after fork - how is it possible?
		3127
		3128	Most uses of C<fork()> consist of forking, then some simple calls to set
		3129	up/change the process environment, followed by a call to C<exec()>. This
		3130	sequence should be handled by libev without any problems.
		3131
		3132	This changes when the application actually wants to do event handling
		3133	in the child, or both parent in child, in effect "continuing" after the
		3134	fork.
		3135
		3136	The default mode of operation (for libev, with application help to detect
		3137	forks) is to duplicate all the state in the child, as would be expected
		3138	when I<either> the parent I<or> the child process continues.
		3139
		3140	When both processes want to continue using libev, then this is usually the
		3141	wrong result. In that case, usually one process (typically the parent) is
		3142	supposed to continue with all watchers in place as before, while the other
		3143	process typically wants to start fresh, i.e. without any active watchers.
		3144
		3145	The cleanest and most efficient way to achieve that with libev is to
		3146	simply create a new event loop, which of course will be "empty", and
		3147	use that for new watchers. This has the advantage of not touching more
		3148	memory than necessary, and thus avoiding the copy-on-write, and the
		3149	disadvantage of having to use multiple event loops (which do not support
		3150	signal watchers).
		3151
		3152	When this is not possible, or you want to use the default loop for
		3153	other reasons, then in the process that wants to start "fresh", call
		3154	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3155	Destroying the default loop will "orphan" (not stop) all registered
		3156	watchers, so you have to be careful not to execute code that modifies
		3157	those watchers. Note also that in that case, you have to re-register any
		3158	signal watchers.
		3159
		3160	=head3 Watcher-Specific Functions and Data Members
		3161
		3162	=over 4
		3163
		3164	=item ev_fork_init (ev_fork *, callback)
		3165
		3166	Initialises and configures the fork watcher - it has no parameters of any
		3167	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3168	really.
		3169
		3170	=back
		3171
		3172
		3173	=head2 C<ev_cleanup> - even the best things end
		3174
		3175	Cleanup watchers are called just before the event loop is being destroyed
		3176	by a call to C<ev_loop_destroy>.
		3177
		3178	While there is no guarantee that the event loop gets destroyed, cleanup
		3179	watchers provide a convenient method to install cleanup hooks for your
		3180	program, worker threads and so on - you just to make sure to destroy the
		3181	loop when you want them to be invoked.
		3182
		3183	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3184	all other watchers, they do not keep a reference to the event loop (which
		3185	makes a lot of sense if you think about it). Like all other watchers, you
		3186	can call libev functions in the callback, except C<ev_cleanup_start>.
		3187
		3188	=head3 Watcher-Specific Functions and Data Members
		3189
		3190	=over 4
		3191
		3192	=item ev_cleanup_init (ev_cleanup *, callback)
		3193
		3194	Initialises and configures the cleanup watcher - it has no parameters of
		3195	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3196	pointless, I assure you.
		3197
		3198	=back
		3199
		3200	Example: Register an atexit handler to destroy the default loop, so any
		3201	cleanup functions are called.
		3202
		3203	static void
		3204	program_exits (void)
		3205	{
		3206	ev_loop_destroy (EV_DEFAULT_UC);
		3207	}
		3208
		3209	...
		3210	atexit (program_exits);
		3211
		3212
		3213	=head2 C<ev_async> - how to wake up an event loop
		3214
		3215	In general, you cannot use an C<ev_run> from multiple threads or other
		3216	asynchronous sources such as signal handlers (as opposed to multiple event
		3217	loops - those are of course safe to use in different threads).
		3218
		3219	Sometimes, however, you need to wake up an event loop you do not control,
		3220	for example because it belongs to another thread. This is what C<ev_async>
		3221	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3222	it by calling C<ev_async_send>, which is thread- and signal safe.
		3223
		3224	This functionality is very similar to C<ev_signal> watchers, as signals,
		3225	too, are asynchronous in nature, and signals, too, will be compressed
		3226	(i.e. the number of callback invocations may be less than the number of
		3227	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3228	of "global async watchers" by using a watcher on an otherwise unused
		3229	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3230	even without knowing which loop owns the signal.
		3231
		3232	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3233	just the default loop.
		3234
		3235	=head3 Queueing
		3236
		3237	C<ev_async> does not support queueing of data in any way. The reason
		3238	is that the author does not know of a simple (or any) algorithm for a
		3239	multiple-writer-single-reader queue that works in all cases and doesn't
		3240	need elaborate support such as pthreads or unportable memory access
		3241	semantics.
		3242
		3243	That means that if you want to queue data, you have to provide your own
		3244	queue. But at least I can tell you how to implement locking around your
		3245	queue:
		3246
		3247	=over 4
		3248
		3249	=item queueing from a signal handler context
		3250
		3251	To implement race-free queueing, you simply add to the queue in the signal
		3252	handler but you block the signal handler in the watcher callback. Here is
		3253	an example that does that for some fictitious SIGUSR1 handler:
		3254
		3255	static ev_async mysig;
		3256
		3257	static void
		3258	sigusr1_handler (void)
		3259	{
		3260	sometype data;
		3261
		3262	// no locking etc.
		3263	queue_put (data);
		3264	ev_async_send (EV_DEFAULT_ &mysig);
		3265	}
		3266
		3267	static void
		3268	mysig_cb (EV_P_ ev_async *w, int revents)
		3269	{
		3270	sometype data;
		3271	sigset_t block, prev;
		3272
		3273	sigemptyset (&block);
		3274	sigaddset (&block, SIGUSR1);
		3275	sigprocmask (SIG_BLOCK, &block, &prev);
		3276
		3277	while (queue_get (&data))
		3278	process (data);
		3279
		3280	if (sigismember (&prev, SIGUSR1)
		3281	sigprocmask (SIG_UNBLOCK, &block, 0);
		3282	}
		3283
		3284	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3285	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3286	either...).
		3287
		3288	=item queueing from a thread context
		3289
		3290	The strategy for threads is different, as you cannot (easily) block
		3291	threads but you can easily preempt them, so to queue safely you need to
		3292	employ a traditional mutex lock, such as in this pthread example:
		3293
		3294	static ev_async mysig;
		3295	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3296
		3297	static void
		3298	otherthread (void)
		3299	{
		3300	// only need to lock the actual queueing operation
		3301	pthread_mutex_lock (&mymutex);
		3302	queue_put (data);
		3303	pthread_mutex_unlock (&mymutex);
		3304
		3305	ev_async_send (EV_DEFAULT_ &mysig);
		3306	}
		3307
		3308	static void
		3309	mysig_cb (EV_P_ ev_async *w, int revents)
		3310	{
		3311	pthread_mutex_lock (&mymutex);
		3312
		3313	while (queue_get (&data))
		3314	process (data);
		3315
		3316	pthread_mutex_unlock (&mymutex);
		3317	}
		3318
		3319	=back
		3320
		3321
		3322	=head3 Watcher-Specific Functions and Data Members
		3323
		3324	=over 4
		3325
		3326	=item ev_async_init (ev_async *, callback)
		3327
		3328	Initialises and configures the async watcher - it has no parameters of any
		3329	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3330	trust me.
		3331
		3332	=item ev_async_send (loop, ev_async *)
		3333
		3334	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3335	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3336	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3337	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3338	section below on what exactly this means).
		3339
		3340	Note that, as with other watchers in libev, multiple events might get
		3341	compressed into a single callback invocation (another way to look at this
		3342	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3343	reset when the event loop detects that).
		3344
		3345	This call incurs the overhead of a system call only once per event loop
		3346	iteration, so while the overhead might be noticeable, it doesn't apply to
		3347	repeated calls to C<ev_async_send> for the same event loop.
		3348
		3349	=item bool = ev_async_pending (ev_async *)
		3350
		3351	Returns a non-zero value when C<ev_async_send> has been called on the
		3352	watcher but the event has not yet been processed (or even noted) by the
		3353	event loop.
		3354
		3355	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3356	the loop iterates next and checks for the watcher to have become active,
		3357	it will reset the flag again. C<ev_async_pending> can be used to very
		3358	quickly check whether invoking the loop might be a good idea.
		3359
		3360	Not that this does I<not> check whether the watcher itself is pending,
		3361	only whether it has been requested to make this watcher pending: there
		3362	is a time window between the event loop checking and resetting the async
		3363	notification, and the callback being invoked.
		3364
		3365	=back
		3366
		3367
793	=head1 OTHER FUNCTIONS	3368	=head1 OTHER FUNCTIONS
794		3369
795	There are some other functions of possible interest. Described. Here. Now.	3370	There are some other functions of possible interest. Described. Here. Now.
796		3371
797	=over 4	3372	=over 4
798		3373
799	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3374	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
800		3375
801	This function combines a simple timer and an I/O watcher, calls your	3376	This function combines a simple timer and an I/O watcher, calls your
802	callback on whichever event happens first and automatically stop both	3377	callback on whichever event happens first and automatically stops both
803	watchers. This is useful if you want to wait for a single event on an fd	3378	watchers. This is useful if you want to wait for a single event on an fd
804	or timeout without having to allocate/configure/start/stop/free one or	3379	or timeout without having to allocate/configure/start/stop/free one or
805	more watchers yourself.	3380	more watchers yourself.
806		3381
807	If C<fd> is less than 0, then no I/O watcher will be started and events	3382	If C<fd> is less than 0, then no I/O watcher will be started and the
808	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3383	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
809	C<events> set will be craeted and started.	3384	the given C<fd> and C<events> set will be created and started.
810		3385
811	If C<timeout> is less than 0, then no timeout watcher will be	3386	If C<timeout> is less than 0, then no timeout watcher will be
812	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3387	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
813	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3388	repeat = 0) will be started. C<0> is a valid timeout.
814	dubious value.
815		3389
816	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3390	The callback has the type C<void (*cb)(int revents, void *arg)> and is
817	passed an C<revents> set like normal event callbacks (a combination of	3391	passed an C<revents> set like normal event callbacks (a combination of
818	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3392	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
819	value passed to C<ev_once>:	3393	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3394	a timeout and an io event at the same time - you probably should give io
		3395	events precedence.
820		3396
		3397	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3398
821	static void stdin_ready (int revents, void *arg)	3399	static void stdin_ready (int revents, void *arg)
822	{	3400	{
823	if (revents & EV_TIMEOUT)
824	/* doh, nothing entered */;
825	else if (revents & EV_READ)	3401	if (revents & EV_READ)
826	/* stdin might have data for us, joy! */;	3402	/* stdin might have data for us, joy! */;
		3403	else if (revents & EV_TIMER)
		3404	/* doh, nothing entered */;
827	}	3405	}
828		3406
829	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3407	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
830
831	=item ev_feed_event (loop, watcher, int events)
832
833	Feeds the given event set into the event loop, as if the specified event
834	had happened for the specified watcher (which must be a pointer to an
835	initialised but not necessarily started event watcher).
836		3408
837	=item ev_feed_fd_event (loop, int fd, int revents)	3409	=item ev_feed_fd_event (loop, int fd, int revents)
838		3410
839	Feed an event on the given fd, as if a file descriptor backend detected	3411	Feed an event on the given fd, as if a file descriptor backend detected
840	the given events it.	3412	the given events it.
841		3413
842	=item ev_feed_signal_event (loop, int signum)	3414	=item ev_feed_signal_event (loop, int signum)
843		3415
844	Feed an event as if the given signal occured (loop must be the default loop!).	3416	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3417	which is async-safe.
845		3418
846	=back	3419	=back
		3420
		3421
		3422	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3423
		3424	This section explains some common idioms that are not immediately
		3425	obvious. Note that examples are sprinkled over the whole manual, and this
		3426	section only contains stuff that wouldn't fit anywhere else.
		3427
		3428	=over 4
		3429
		3430	=item Model/nested event loop invocations and exit conditions.
		3431
		3432	Often (especially in GUI toolkits) there are places where you have
		3433	I<modal> interaction, which is most easily implemented by recursively
		3434	invoking C<ev_run>.
		3435
		3436	This brings the problem of exiting - a callback might want to finish the
		3437	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3438	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3439	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3440	other combination: In these cases, C<ev_break> will not work alone.
		3441
		3442	The solution is to maintain "break this loop" variable for each C<ev_run>
		3443	invocation, and use a loop around C<ev_run> until the condition is
		3444	triggered, using C<EVRUN_ONCE>:
		3445
		3446	// main loop
		3447	int exit_main_loop = 0;
		3448
		3449	while (!exit_main_loop)
		3450	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3451
		3452	// in a model watcher
		3453	int exit_nested_loop = 0;
		3454
		3455	while (!exit_nested_loop)
		3456	ev_run (EV_A_ EVRUN_ONCE);
		3457
		3458	To exit from any of these loops, just set the corresponding exit variable:
		3459
		3460	// exit modal loop
		3461	exit_nested_loop = 1;
		3462
		3463	// exit main program, after modal loop is finished
		3464	exit_main_loop = 1;
		3465
		3466	// exit both
		3467	exit_main_loop = exit_nested_loop = 1;
		3468
		3469	=back
		3470
847		3471
848	=head1 LIBEVENT EMULATION	3472	=head1 LIBEVENT EMULATION
849		3473
850	Libev offers a compatibility emulation layer for libevent. It cannot	3474	Libev offers a compatibility emulation layer for libevent. It cannot
851	emulate the internals of libevent, so here are some usage hints:	3475	emulate the internals of libevent, so here are some usage hints:
852		3476
853	=over 4	3477	=over 4
		3478
		3479	=item * Only the libevent-1.4.1-beta API is being emulated.
		3480
		3481	This was the newest libevent version available when libev was implemented,
		3482	and is still mostly unchanged in 2010.
854		3483
855	=item * Use it by including <event.h>, as usual.	3484	=item * Use it by including <event.h>, as usual.
856		3485
857	=item * The following members are fully supported: ev_base, ev_callback,	3486	=item * The following members are fully supported: ev_base, ev_callback,
858	ev_arg, ev_fd, ev_res, ev_events.	3487	ev_arg, ev_fd, ev_res, ev_events.
…		…
863		3492
864	=item * Priorities are not currently supported. Initialising priorities	3493	=item * Priorities are not currently supported. Initialising priorities
865	will fail and all watchers will have the same priority, even though there	3494	will fail and all watchers will have the same priority, even though there
866	is an ev_pri field.	3495	is an ev_pri field.
867		3496
		3497	=item * In libevent, the last base created gets the signals, in libev, the
		3498	base that registered the signal gets the signals.
		3499
868	=item * Other members are not supported.	3500	=item * Other members are not supported.
869		3501
870	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3502	=item * The libev emulation is I<not> ABI compatible to libevent, you need
871	to use the libev header file and library.	3503	to use the libev header file and library.
872		3504
873	=back	3505	=back
874		3506
875	=head1 C++ SUPPORT	3507	=head1 C++ SUPPORT
876		3508
877	TBD.	3509	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3510	you to use some convenience methods to start/stop watchers and also change
		3511	the callback model to a model using method callbacks on objects.
		3512
		3513	To use it,
		3514
		3515	#include <ev++.h>
		3516
		3517	This automatically includes F<ev.h> and puts all of its definitions (many
		3518	of them macros) into the global namespace. All C++ specific things are
		3519	put into the C<ev> namespace. It should support all the same embedding
		3520	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3521
		3522	Care has been taken to keep the overhead low. The only data member the C++
		3523	classes add (compared to plain C-style watchers) is the event loop pointer
		3524	that the watcher is associated with (or no additional members at all if
		3525	you disable C<EV_MULTIPLICITY> when embedding libev).
		3526
		3527	Currently, functions, static and non-static member functions and classes
		3528	with C<operator ()> can be used as callbacks. Other types should be easy
		3529	to add as long as they only need one additional pointer for context. If
		3530	you need support for other types of functors please contact the author
		3531	(preferably after implementing it).
		3532
		3533	Here is a list of things available in the C<ev> namespace:
		3534
		3535	=over 4
		3536
		3537	=item C<ev::READ>, C<ev::WRITE> etc.
		3538
		3539	These are just enum values with the same values as the C<EV_READ> etc.
		3540	macros from F<ev.h>.
		3541
		3542	=item C<ev::tstamp>, C<ev::now>
		3543
		3544	Aliases to the same types/functions as with the C<ev_> prefix.
		3545
		3546	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		3547
		3548	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		3549	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		3550	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3551	defines by many implementations.
		3552
		3553	All of those classes have these methods:
		3554
		3555	=over 4
		3556
		3557	=item ev::TYPE::TYPE ()
		3558
		3559	=item ev::TYPE::TYPE (loop)
		3560
		3561	=item ev::TYPE::~TYPE
		3562
		3563	The constructor (optionally) takes an event loop to associate the watcher
		3564	with. If it is omitted, it will use C<EV_DEFAULT>.
		3565
		3566	The constructor calls C<ev_init> for you, which means you have to call the
		3567	C<set> method before starting it.
		3568
		3569	It will not set a callback, however: You have to call the templated C<set>
		3570	method to set a callback before you can start the watcher.
		3571
		3572	(The reason why you have to use a method is a limitation in C++ which does
		3573	not allow explicit template arguments for constructors).
		3574
		3575	The destructor automatically stops the watcher if it is active.
		3576
		3577	=item w->set<class, &class::method> (object *)
		3578
		3579	This method sets the callback method to call. The method has to have a
		3580	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3581	first argument and the C<revents> as second. The object must be given as
		3582	parameter and is stored in the C<data> member of the watcher.
		3583
		3584	This method synthesizes efficient thunking code to call your method from
		3585	the C callback that libev requires. If your compiler can inline your
		3586	callback (i.e. it is visible to it at the place of the C<set> call and
		3587	your compiler is good :), then the method will be fully inlined into the
		3588	thunking function, making it as fast as a direct C callback.
		3589
		3590	Example: simple class declaration and watcher initialisation
		3591
		3592	struct myclass
		3593	{
		3594	void io_cb (ev::io &w, int revents) { }
		3595	}
		3596
		3597	myclass obj;
		3598	ev::io iow;
		3599	iow.set <myclass, &myclass::io_cb> (&obj);
		3600
		3601	=item w->set (object *)
		3602
		3603	This is a variation of a method callback - leaving out the method to call
		3604	will default the method to C<operator ()>, which makes it possible to use
		3605	functor objects without having to manually specify the C<operator ()> all
		3606	the time. Incidentally, you can then also leave out the template argument
		3607	list.
		3608
		3609	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3610	int revents)>.
		3611
		3612	See the method-C<set> above for more details.
		3613
		3614	Example: use a functor object as callback.
		3615
		3616	struct myfunctor
		3617	{
		3618	void operator() (ev::io &w, int revents)
		3619	{
		3620	...
		3621	}
		3622	}
		3623
		3624	myfunctor f;
		3625
		3626	ev::io w;
		3627	w.set (&f);
		3628
		3629	=item w->set<function> (void *data = 0)
		3630
		3631	Also sets a callback, but uses a static method or plain function as
		3632	callback. The optional C<data> argument will be stored in the watcher's
		3633	C<data> member and is free for you to use.
		3634
		3635	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3636
		3637	See the method-C<set> above for more details.
		3638
		3639	Example: Use a plain function as callback.
		3640
		3641	static void io_cb (ev::io &w, int revents) { }
		3642	iow.set <io_cb> ();
		3643
		3644	=item w->set (loop)
		3645
		3646	Associates a different C<struct ev_loop> with this watcher. You can only
		3647	do this when the watcher is inactive (and not pending either).
		3648
		3649	=item w->set ([arguments])
		3650
		3651	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
		3652	method or a suitable start method must be called at least once. Unlike the
		3653	C counterpart, an active watcher gets automatically stopped and restarted
		3654	when reconfiguring it with this method.
		3655
		3656	=item w->start ()
		3657
		3658	Starts the watcher. Note that there is no C<loop> argument, as the
		3659	constructor already stores the event loop.
		3660
		3661	=item w->start ([arguments])
		3662
		3663	Instead of calling C<set> and C<start> methods separately, it is often
		3664	convenient to wrap them in one call. Uses the same type of arguments as
		3665	the configure C<set> method of the watcher.
		3666
		3667	=item w->stop ()
		3668
		3669	Stops the watcher if it is active. Again, no C<loop> argument.
		3670
		3671	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		3672
		3673	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		3674	C<ev_TYPE_again> function.
		3675
		3676	=item w->sweep () (C<ev::embed> only)
		3677
		3678	Invokes C<ev_embed_sweep>.
		3679
		3680	=item w->update () (C<ev::stat> only)
		3681
		3682	Invokes C<ev_stat_stat>.
		3683
		3684	=back
		3685
		3686	=back
		3687
		3688	Example: Define a class with two I/O and idle watchers, start the I/O
		3689	watchers in the constructor.
		3690
		3691	class myclass
		3692	{
		3693	ev::io io ; void io_cb (ev::io &w, int revents);
		3694	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
		3695	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3696
		3697	myclass (int fd)
		3698	{
		3699	io .set <myclass, &myclass::io_cb > (this);
		3700	io2 .set <myclass, &myclass::io2_cb > (this);
		3701	idle.set <myclass, &myclass::idle_cb> (this);
		3702
		3703	io.set (fd, ev::WRITE); // configure the watcher
		3704	io.start (); // start it whenever convenient
		3705
		3706	io2.start (fd, ev::READ); // set + start in one call
		3707	}
		3708	};
		3709
		3710
		3711	=head1 OTHER LANGUAGE BINDINGS
		3712
		3713	Libev does not offer other language bindings itself, but bindings for a
		3714	number of languages exist in the form of third-party packages. If you know
		3715	any interesting language binding in addition to the ones listed here, drop
		3716	me a note.
		3717
		3718	=over 4
		3719
		3720	=item Perl
		3721
		3722	The EV module implements the full libev API and is actually used to test
		3723	libev. EV is developed together with libev. Apart from the EV core module,
		3724	there are additional modules that implement libev-compatible interfaces
		3725	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3726	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3727	and C<EV::Glib>).
		3728
		3729	It can be found and installed via CPAN, its homepage is at
		3730	L<http://software.schmorp.de/pkg/EV>.
		3731
		3732	=item Python
		3733
		3734	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3735	seems to be quite complete and well-documented.
		3736
		3737	=item Ruby
		3738
		3739	Tony Arcieri has written a ruby extension that offers access to a subset
		3740	of the libev API and adds file handle abstractions, asynchronous DNS and
		3741	more on top of it. It can be found via gem servers. Its homepage is at
		3742	L<http://rev.rubyforge.org/>.
		3743
		3744	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3745	makes rev work even on mingw.
		3746
		3747	=item Haskell
		3748
		3749	A haskell binding to libev is available at
		3750	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3751
		3752	=item D
		3753
		3754	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3755	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3756
		3757	=item Ocaml
		3758
		3759	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3760	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3761
		3762	=item Lua
		3763
		3764	Brian Maher has written a partial interface to libev for lua (at the
		3765	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3766	L<http://github.com/brimworks/lua-ev>.
		3767
		3768	=back
		3769
		3770
		3771	=head1 MACRO MAGIC
		3772
		3773	Libev can be compiled with a variety of options, the most fundamental
		3774	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3775	functions and callbacks have an initial C<struct ev_loop *> argument.
		3776
		3777	To make it easier to write programs that cope with either variant, the
		3778	following macros are defined:
		3779
		3780	=over 4
		3781
		3782	=item C<EV_A>, C<EV_A_>
		3783
		3784	This provides the loop I<argument> for functions, if one is required ("ev
		3785	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3786	C<EV_A_> is used when other arguments are following. Example:
		3787
		3788	ev_unref (EV_A);
		3789	ev_timer_add (EV_A_ watcher);
		3790	ev_run (EV_A_ 0);
		3791
		3792	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3793	which is often provided by the following macro.
		3794
		3795	=item C<EV_P>, C<EV_P_>
		3796
		3797	This provides the loop I<parameter> for functions, if one is required ("ev
		3798	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3799	C<EV_P_> is used when other parameters are following. Example:
		3800
		3801	// this is how ev_unref is being declared
		3802	static void ev_unref (EV_P);
		3803
		3804	// this is how you can declare your typical callback
		3805	static void cb (EV_P_ ev_timer *w, int revents)
		3806
		3807	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3808	suitable for use with C<EV_A>.
		3809
		3810	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3811
		3812	Similar to the other two macros, this gives you the value of the default
		3813	loop, if multiple loops are supported ("ev loop default").
		3814
		3815	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3816
		3817	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3818	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3819	is undefined when the default loop has not been initialised by a previous
		3820	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3821
		3822	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3823	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3824
		3825	=back
		3826
		3827	Example: Declare and initialise a check watcher, utilising the above
		3828	macros so it will work regardless of whether multiple loops are supported
		3829	or not.
		3830
		3831	static void
		3832	check_cb (EV_P_ ev_timer *w, int revents)
		3833	{
		3834	ev_check_stop (EV_A_ w);
		3835	}
		3836
		3837	ev_check check;
		3838	ev_check_init (&check, check_cb);
		3839	ev_check_start (EV_DEFAULT_ &check);
		3840	ev_run (EV_DEFAULT_ 0);
		3841
		3842	=head1 EMBEDDING
		3843
		3844	Libev can (and often is) directly embedded into host
		3845	applications. Examples of applications that embed it include the Deliantra
		3846	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3847	and rxvt-unicode.
		3848
		3849	The goal is to enable you to just copy the necessary files into your
		3850	source directory without having to change even a single line in them, so
		3851	you can easily upgrade by simply copying (or having a checked-out copy of
		3852	libev somewhere in your source tree).
		3853
		3854	=head2 FILESETS
		3855
		3856	Depending on what features you need you need to include one or more sets of files
		3857	in your application.
		3858
		3859	=head3 CORE EVENT LOOP
		3860
		3861	To include only the libev core (all the C<ev_*> functions), with manual
		3862	configuration (no autoconf):
		3863
		3864	#define EV_STANDALONE 1
		3865	#include "ev.c"
		3866
		3867	This will automatically include F<ev.h>, too, and should be done in a
		3868	single C source file only to provide the function implementations. To use
		3869	it, do the same for F<ev.h> in all files wishing to use this API (best
		3870	done by writing a wrapper around F<ev.h> that you can include instead and
		3871	where you can put other configuration options):
		3872
		3873	#define EV_STANDALONE 1
		3874	#include "ev.h"
		3875
		3876	Both header files and implementation files can be compiled with a C++
		3877	compiler (at least, that's a stated goal, and breakage will be treated
		3878	as a bug).
		3879
		3880	You need the following files in your source tree, or in a directory
		3881	in your include path (e.g. in libev/ when using -Ilibev):
		3882
		3883	ev.h
		3884	ev.c
		3885	ev_vars.h
		3886	ev_wrap.h
		3887
		3888	ev_win32.c required on win32 platforms only
		3889
		3890	ev_select.c only when select backend is enabled (which is enabled by default)
		3891	ev_poll.c only when poll backend is enabled (disabled by default)
		3892	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3893	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3894	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3895
		3896	F<ev.c> includes the backend files directly when enabled, so you only need
		3897	to compile this single file.
		3898
		3899	=head3 LIBEVENT COMPATIBILITY API
		3900
		3901	To include the libevent compatibility API, also include:
		3902
		3903	#include "event.c"
		3904
		3905	in the file including F<ev.c>, and:
		3906
		3907	#include "event.h"
		3908
		3909	in the files that want to use the libevent API. This also includes F<ev.h>.
		3910
		3911	You need the following additional files for this:
		3912
		3913	event.h
		3914	event.c
		3915
		3916	=head3 AUTOCONF SUPPORT
		3917
		3918	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3919	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3920	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3921	include F<config.h> and configure itself accordingly.
		3922
		3923	For this of course you need the m4 file:
		3924
		3925	libev.m4
		3926
		3927	=head2 PREPROCESSOR SYMBOLS/MACROS
		3928
		3929	Libev can be configured via a variety of preprocessor symbols you have to
		3930	define before including (or compiling) any of its files. The default in
		3931	the absence of autoconf is documented for every option.
		3932
		3933	Symbols marked with "(h)" do not change the ABI, and can have different
		3934	values when compiling libev vs. including F<ev.h>, so it is permissible
		3935	to redefine them before including F<ev.h> without breaking compatibility
		3936	to a compiled library. All other symbols change the ABI, which means all
		3937	users of libev and the libev code itself must be compiled with compatible
		3938	settings.
		3939
		3940	=over 4
		3941
		3942	=item EV_COMPAT3 (h)
		3943
		3944	Backwards compatibility is a major concern for libev. This is why this
		3945	release of libev comes with wrappers for the functions and symbols that
		3946	have been renamed between libev version 3 and 4.
		3947
		3948	You can disable these wrappers (to test compatibility with future
		3949	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3950	sources. This has the additional advantage that you can drop the C<struct>
		3951	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3952	typedef in that case.
		3953
		3954	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3955	and in some even more future version the compatibility code will be
		3956	removed completely.
		3957
		3958	=item EV_STANDALONE (h)
		3959
		3960	Must always be C<1> if you do not use autoconf configuration, which
		3961	keeps libev from including F<config.h>, and it also defines dummy
		3962	implementations for some libevent functions (such as logging, which is not
		3963	supported). It will also not define any of the structs usually found in
		3964	F<event.h> that are not directly supported by the libev core alone.
		3965
		3966	In standalone mode, libev will still try to automatically deduce the
		3967	configuration, but has to be more conservative.
		3968
		3969	=item EV_USE_MONOTONIC
		3970
		3971	If defined to be C<1>, libev will try to detect the availability of the
		3972	monotonic clock option at both compile time and runtime. Otherwise no
		3973	use of the monotonic clock option will be attempted. If you enable this,
		3974	you usually have to link against librt or something similar. Enabling it
		3975	when the functionality isn't available is safe, though, although you have
		3976	to make sure you link against any libraries where the C<clock_gettime>
		3977	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3978
		3979	=item EV_USE_REALTIME
		3980
		3981	If defined to be C<1>, libev will try to detect the availability of the
		3982	real-time clock option at compile time (and assume its availability
		3983	at runtime if successful). Otherwise no use of the real-time clock
		3984	option will be attempted. This effectively replaces C<gettimeofday>
		3985	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		3986	correctness. See the note about libraries in the description of
		3987	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3988	C<EV_USE_CLOCK_SYSCALL>.
		3989
		3990	=item EV_USE_CLOCK_SYSCALL
		3991
		3992	If defined to be C<1>, libev will try to use a direct syscall instead
		3993	of calling the system-provided C<clock_gettime> function. This option
		3994	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3995	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3996	programs needlessly. Using a direct syscall is slightly slower (in
		3997	theory), because no optimised vdso implementation can be used, but avoids
		3998	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3999	higher, as it simplifies linking (no need for C<-lrt>).
		4000
		4001	=item EV_USE_NANOSLEEP
		4002
		4003	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		4004	and will use it for delays. Otherwise it will use C<select ()>.
		4005
		4006	=item EV_USE_EVENTFD
		4007
		4008	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4009	available and will probe for kernel support at runtime. This will improve
		4010	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4011	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4012	2.7 or newer, otherwise disabled.
		4013
		4014	=item EV_USE_SELECT
		4015
		4016	If undefined or defined to be C<1>, libev will compile in support for the
		4017	C<select>(2) backend. No attempt at auto-detection will be done: if no
		4018	other method takes over, select will be it. Otherwise the select backend
		4019	will not be compiled in.
		4020
		4021	=item EV_SELECT_USE_FD_SET
		4022
		4023	If defined to C<1>, then the select backend will use the system C<fd_set>
		4024	structure. This is useful if libev doesn't compile due to a missing
		4025	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		4026	on exotic systems. This usually limits the range of file descriptors to
		4027	some low limit such as 1024 or might have other limitations (winsocket
		4028	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		4029	configures the maximum size of the C<fd_set>.
		4030
		4031	=item EV_SELECT_IS_WINSOCKET
		4032
		4033	When defined to C<1>, the select backend will assume that
		4034	select/socket/connect etc. don't understand file descriptors but
		4035	wants osf handles on win32 (this is the case when the select to
		4036	be used is the winsock select). This means that it will call
		4037	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		4038	it is assumed that all these functions actually work on fds, even
		4039	on win32. Should not be defined on non-win32 platforms.
		4040
		4041	=item EV_FD_TO_WIN32_HANDLE(fd)
		4042
		4043	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4044	file descriptors to socket handles. When not defining this symbol (the
		4045	default), then libev will call C<_get_osfhandle>, which is usually
		4046	correct. In some cases, programs use their own file descriptor management,
		4047	in which case they can provide this function to map fds to socket handles.
		4048
		4049	=item EV_WIN32_HANDLE_TO_FD(handle)
		4050
		4051	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4052	using the standard C<_open_osfhandle> function. For programs implementing
		4053	their own fd to handle mapping, overwriting this function makes it easier
		4054	to do so. This can be done by defining this macro to an appropriate value.
		4055
		4056	=item EV_WIN32_CLOSE_FD(fd)
		4057
		4058	If programs implement their own fd to handle mapping on win32, then this
		4059	macro can be used to override the C<close> function, useful to unregister
		4060	file descriptors again. Note that the replacement function has to close
		4061	the underlying OS handle.
		4062
		4063	=item EV_USE_POLL
		4064
		4065	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		4066	backend. Otherwise it will be enabled on non-win32 platforms. It
		4067	takes precedence over select.
		4068
		4069	=item EV_USE_EPOLL
		4070
		4071	If defined to be C<1>, libev will compile in support for the Linux
		4072	C<epoll>(7) backend. Its availability will be detected at runtime,
		4073	otherwise another method will be used as fallback. This is the preferred
		4074	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4075	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4076
		4077	=item EV_USE_KQUEUE
		4078
		4079	If defined to be C<1>, libev will compile in support for the BSD style
		4080	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		4081	otherwise another method will be used as fallback. This is the preferred
		4082	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		4083	supports some types of fds correctly (the only platform we found that
		4084	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		4085	not be used unless explicitly requested. The best way to use it is to find
		4086	out whether kqueue supports your type of fd properly and use an embedded
		4087	kqueue loop.
		4088
		4089	=item EV_USE_PORT
		4090
		4091	If defined to be C<1>, libev will compile in support for the Solaris
		4092	10 port style backend. Its availability will be detected at runtime,
		4093	otherwise another method will be used as fallback. This is the preferred
		4094	backend for Solaris 10 systems.
		4095
		4096	=item EV_USE_DEVPOLL
		4097
		4098	Reserved for future expansion, works like the USE symbols above.
		4099
		4100	=item EV_USE_INOTIFY
		4101
		4102	If defined to be C<1>, libev will compile in support for the Linux inotify
		4103	interface to speed up C<ev_stat> watchers. Its actual availability will
		4104	be detected at runtime. If undefined, it will be enabled if the headers
		4105	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		4106
		4107	=item EV_ATOMIC_T
		4108
		4109	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4110	access is atomic with respect to other threads or signal contexts. No such
		4111	type is easily found in the C language, so you can provide your own type
		4112	that you know is safe for your purposes. It is used both for signal handler "locking"
		4113	as well as for signal and thread safety in C<ev_async> watchers.
		4114
		4115	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4116	(from F<signal.h>), which is usually good enough on most platforms.
		4117
		4118	=item EV_H (h)
		4119
		4120	The name of the F<ev.h> header file used to include it. The default if
		4121	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		4122	used to virtually rename the F<ev.h> header file in case of conflicts.
		4123
		4124	=item EV_CONFIG_H (h)
		4125
		4126	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		4127	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		4128	C<EV_H>, above.
		4129
		4130	=item EV_EVENT_H (h)
		4131
		4132	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		4133	of how the F<event.h> header can be found, the default is C<"event.h">.
		4134
		4135	=item EV_PROTOTYPES (h)
		4136
		4137	If defined to be C<0>, then F<ev.h> will not define any function
		4138	prototypes, but still define all the structs and other symbols. This is
		4139	occasionally useful if you want to provide your own wrapper functions
		4140	around libev functions.
		4141
		4142	=item EV_MULTIPLICITY
		4143
		4144	If undefined or defined to C<1>, then all event-loop-specific functions
		4145	will have the C<struct ev_loop *> as first argument, and you can create
		4146	additional independent event loops. Otherwise there will be no support
		4147	for multiple event loops and there is no first event loop pointer
		4148	argument. Instead, all functions act on the single default loop.
		4149
		4150	=item EV_MINPRI
		4151
		4152	=item EV_MAXPRI
		4153
		4154	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4155	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4156	provide for more priorities by overriding those symbols (usually defined
		4157	to be C<-2> and C<2>, respectively).
		4158
		4159	When doing priority-based operations, libev usually has to linearly search
		4160	all the priorities, so having many of them (hundreds) uses a lot of space
		4161	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4162	fine.
		4163
		4164	If your embedding application does not need any priorities, defining these
		4165	both to C<0> will save some memory and CPU.
		4166
		4167	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4168	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4169	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4170
		4171	If undefined or defined to be C<1> (and the platform supports it), then
		4172	the respective watcher type is supported. If defined to be C<0>, then it
		4173	is not. Disabling watcher types mainly saves code size.
		4174
		4175	=item EV_FEATURES
		4176
		4177	If you need to shave off some kilobytes of code at the expense of some
		4178	speed (but with the full API), you can define this symbol to request
		4179	certain subsets of functionality. The default is to enable all features
		4180	that can be enabled on the platform.
		4181
		4182	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4183	with some broad features you want) and then selectively re-enable
		4184	additional parts you want, for example if you want everything minimal,
		4185	but multiple event loop support, async and child watchers and the poll
		4186	backend, use this:
		4187
		4188	#define EV_FEATURES 0
		4189	#define EV_MULTIPLICITY 1
		4190	#define EV_USE_POLL 1
		4191	#define EV_CHILD_ENABLE 1
		4192	#define EV_ASYNC_ENABLE 1
		4193
		4194	The actual value is a bitset, it can be a combination of the following
		4195	values:
		4196
		4197	=over 4
		4198
		4199	=item C<1> - faster/larger code
		4200
		4201	Use larger code to speed up some operations.
		4202
		4203	Currently this is used to override some inlining decisions (enlarging the
		4204	code size by roughly 30% on amd64).
		4205
		4206	When optimising for size, use of compiler flags such as C<-Os> with
		4207	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4208	assertions.
		4209
		4210	=item C<2> - faster/larger data structures
		4211
		4212	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4213	hash table sizes and so on. This will usually further increase code size
		4214	and can additionally have an effect on the size of data structures at
		4215	runtime.
		4216
		4217	=item C<4> - full API configuration
		4218
		4219	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4220	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4221
		4222	=item C<8> - full API
		4223
		4224	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4225	details on which parts of the API are still available without this
		4226	feature, and do not complain if this subset changes over time.
		4227
		4228	=item C<16> - enable all optional watcher types
		4229
		4230	Enables all optional watcher types. If you want to selectively enable
		4231	only some watcher types other than I/O and timers (e.g. prepare,
		4232	embed, async, child...) you can enable them manually by defining
		4233	C<EV_watchertype_ENABLE> to C<1> instead.
		4234
		4235	=item C<32> - enable all backends
		4236
		4237	This enables all backends - without this feature, you need to enable at
		4238	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4239
		4240	=item C<64> - enable OS-specific "helper" APIs
		4241
		4242	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4243	default.
		4244
		4245	=back
		4246
		4247	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4248	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4249	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4250	watchers, timers and monotonic clock support.
		4251
		4252	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4253	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4254	your program might be left out as well - a binary starting a timer and an
		4255	I/O watcher then might come out at only 5Kb.
		4256
		4257	=item EV_AVOID_STDIO
		4258
		4259	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4260	functions (printf, scanf, perror etc.). This will increase the code size
		4261	somewhat, but if your program doesn't otherwise depend on stdio and your
		4262	libc allows it, this avoids linking in the stdio library which is quite
		4263	big.
		4264
		4265	Note that error messages might become less precise when this option is
		4266	enabled.
		4267
		4268	=item EV_NSIG
		4269
		4270	The highest supported signal number, +1 (or, the number of
		4271	signals): Normally, libev tries to deduce the maximum number of signals
		4272	automatically, but sometimes this fails, in which case it can be
		4273	specified. Also, using a lower number than detected (C<32> should be
		4274	good for about any system in existence) can save some memory, as libev
		4275	statically allocates some 12-24 bytes per signal number.
		4276
		4277	=item EV_PID_HASHSIZE
		4278
		4279	C<ev_child> watchers use a small hash table to distribute workload by
		4280	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4281	usually more than enough. If you need to manage thousands of children you
		4282	might want to increase this value (I<must> be a power of two).
		4283
		4284	=item EV_INOTIFY_HASHSIZE
		4285
		4286	C<ev_stat> watchers use a small hash table to distribute workload by
		4287	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4288	disabled), usually more than enough. If you need to manage thousands of
		4289	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4290	power of two).
		4291
		4292	=item EV_USE_4HEAP
		4293
		4294	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4295	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4296	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4297	faster performance with many (thousands) of watchers.
		4298
		4299	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4300	will be C<0>.
		4301
		4302	=item EV_HEAP_CACHE_AT
		4303
		4304	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4305	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4306	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4307	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4308	but avoids random read accesses on heap changes. This improves performance
		4309	noticeably with many (hundreds) of watchers.
		4310
		4311	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4312	will be C<0>.
		4313
		4314	=item EV_VERIFY
		4315
		4316	Controls how much internal verification (see C<ev_verify ()>) will
		4317	be done: If set to C<0>, no internal verification code will be compiled
		4318	in. If set to C<1>, then verification code will be compiled in, but not
		4319	called. If set to C<2>, then the internal verification code will be
		4320	called once per loop, which can slow down libev. If set to C<3>, then the
		4321	verification code will be called very frequently, which will slow down
		4322	libev considerably.
		4323
		4324	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4325	will be C<0>.
		4326
		4327	=item EV_COMMON
		4328
		4329	By default, all watchers have a C<void *data> member. By redefining
		4330	this macro to something else you can include more and other types of
		4331	members. You have to define it each time you include one of the files,
		4332	though, and it must be identical each time.
		4333
		4334	For example, the perl EV module uses something like this:
		4335
		4336	#define EV_COMMON \
		4337	SV *self; /* contains this struct */ \
		4338	SV *cb_sv, *fh /* note no trailing ";" */
		4339
		4340	=item EV_CB_DECLARE (type)
		4341
		4342	=item EV_CB_INVOKE (watcher, revents)
		4343
		4344	=item ev_set_cb (ev, cb)
		4345
		4346	Can be used to change the callback member declaration in each watcher,
		4347	and the way callbacks are invoked and set. Must expand to a struct member
		4348	definition and a statement, respectively. See the F<ev.h> header file for
		4349	their default definitions. One possible use for overriding these is to
		4350	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		4351	method calls instead of plain function calls in C++.
		4352
		4353	=back
		4354
		4355	=head2 EXPORTED API SYMBOLS
		4356
		4357	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4358	exported symbols, you can use the provided F<Symbol.*> files which list
		4359	all public symbols, one per line:
		4360
		4361	Symbols.ev for libev proper
		4362	Symbols.event for the libevent emulation
		4363
		4364	This can also be used to rename all public symbols to avoid clashes with
		4365	multiple versions of libev linked together (which is obviously bad in
		4366	itself, but sometimes it is inconvenient to avoid this).
		4367
		4368	A sed command like this will create wrapper C<#define>'s that you need to
		4369	include before including F<ev.h>:
		4370
		4371	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4372
		4373	This would create a file F<wrap.h> which essentially looks like this:
		4374
		4375	#define ev_backend myprefix_ev_backend
		4376	#define ev_check_start myprefix_ev_check_start
		4377	#define ev_check_stop myprefix_ev_check_stop
		4378	...
		4379
		4380	=head2 EXAMPLES
		4381
		4382	For a real-world example of a program the includes libev
		4383	verbatim, you can have a look at the EV perl module
		4384	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		4385	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		4386	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		4387	will be compiled. It is pretty complex because it provides its own header
		4388	file.
		4389
		4390	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		4391	that everybody includes and which overrides some configure choices:
		4392
		4393	#define EV_FEATURES 8
		4394	#define EV_USE_SELECT 1
		4395	#define EV_PREPARE_ENABLE 1
		4396	#define EV_IDLE_ENABLE 1
		4397	#define EV_SIGNAL_ENABLE 1
		4398	#define EV_CHILD_ENABLE 1
		4399	#define EV_USE_STDEXCEPT 0
		4400	#define EV_CONFIG_H <config.h>
		4401
		4402	#include "ev++.h"
		4403
		4404	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		4405
		4406	#include "ev_cpp.h"
		4407	#include "ev.c"
		4408
		4409	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		4410
		4411	=head2 THREADS AND COROUTINES
		4412
		4413	=head3 THREADS
		4414
		4415	All libev functions are reentrant and thread-safe unless explicitly
		4416	documented otherwise, but libev implements no locking itself. This means
		4417	that you can use as many loops as you want in parallel, as long as there
		4418	are no concurrent calls into any libev function with the same loop
		4419	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4420	of course): libev guarantees that different event loops share no data
		4421	structures that need any locking.
		4422
		4423	Or to put it differently: calls with different loop parameters can be done
		4424	concurrently from multiple threads, calls with the same loop parameter
		4425	must be done serially (but can be done from different threads, as long as
		4426	only one thread ever is inside a call at any point in time, e.g. by using
		4427	a mutex per loop).
		4428
		4429	Specifically to support threads (and signal handlers), libev implements
		4430	so-called C<ev_async> watchers, which allow some limited form of
		4431	concurrency on the same event loop, namely waking it up "from the
		4432	outside".
		4433
		4434	If you want to know which design (one loop, locking, or multiple loops
		4435	without or something else still) is best for your problem, then I cannot
		4436	help you, but here is some generic advice:
		4437
		4438	=over 4
		4439
		4440	=item * most applications have a main thread: use the default libev loop
		4441	in that thread, or create a separate thread running only the default loop.
		4442
		4443	This helps integrating other libraries or software modules that use libev
		4444	themselves and don't care/know about threading.
		4445
		4446	=item * one loop per thread is usually a good model.
		4447
		4448	Doing this is almost never wrong, sometimes a better-performance model
		4449	exists, but it is always a good start.
		4450
		4451	=item * other models exist, such as the leader/follower pattern, where one
		4452	loop is handed through multiple threads in a kind of round-robin fashion.
		4453
		4454	Choosing a model is hard - look around, learn, know that usually you can do
		4455	better than you currently do :-)
		4456
		4457	=item * often you need to talk to some other thread which blocks in the
		4458	event loop.
		4459
		4460	C<ev_async> watchers can be used to wake them up from other threads safely
		4461	(or from signal contexts...).
		4462
		4463	An example use would be to communicate signals or other events that only
		4464	work in the default loop by registering the signal watcher with the
		4465	default loop and triggering an C<ev_async> watcher from the default loop
		4466	watcher callback into the event loop interested in the signal.
		4467
		4468	=back
		4469
		4470	=head4 THREAD LOCKING EXAMPLE
		4471
		4472	Here is a fictitious example of how to run an event loop in a different
		4473	thread than where callbacks are being invoked and watchers are
		4474	created/added/removed.
		4475
		4476	For a real-world example, see the C<EV::Loop::Async> perl module,
		4477	which uses exactly this technique (which is suited for many high-level
		4478	languages).
		4479
		4480	The example uses a pthread mutex to protect the loop data, a condition
		4481	variable to wait for callback invocations, an async watcher to notify the
		4482	event loop thread and an unspecified mechanism to wake up the main thread.
		4483
		4484	First, you need to associate some data with the event loop:
		4485
		4486	typedef struct {
		4487	mutex_t lock; /* global loop lock */
		4488	ev_async async_w;
		4489	thread_t tid;
		4490	cond_t invoke_cv;
		4491	} userdata;
		4492
		4493	void prepare_loop (EV_P)
		4494	{
		4495	// for simplicity, we use a static userdata struct.
		4496	static userdata u;
		4497
		4498	ev_async_init (&u->async_w, async_cb);
		4499	ev_async_start (EV_A_ &u->async_w);
		4500
		4501	pthread_mutex_init (&u->lock, 0);
		4502	pthread_cond_init (&u->invoke_cv, 0);
		4503
		4504	// now associate this with the loop
		4505	ev_set_userdata (EV_A_ u);
		4506	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4507	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4508
		4509	// then create the thread running ev_loop
		4510	pthread_create (&u->tid, 0, l_run, EV_A);
		4511	}
		4512
		4513	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4514	solely to wake up the event loop so it takes notice of any new watchers
		4515	that might have been added:
		4516
		4517	static void
		4518	async_cb (EV_P_ ev_async *w, int revents)
		4519	{
		4520	// just used for the side effects
		4521	}
		4522
		4523	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4524	protecting the loop data, respectively.
		4525
		4526	static void
		4527	l_release (EV_P)
		4528	{
		4529	userdata *u = ev_userdata (EV_A);
		4530	pthread_mutex_unlock (&u->lock);
		4531	}
		4532
		4533	static void
		4534	l_acquire (EV_P)
		4535	{
		4536	userdata *u = ev_userdata (EV_A);
		4537	pthread_mutex_lock (&u->lock);
		4538	}
		4539
		4540	The event loop thread first acquires the mutex, and then jumps straight
		4541	into C<ev_run>:
		4542
		4543	void *
		4544	l_run (void *thr_arg)
		4545	{
		4546	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4547
		4548	l_acquire (EV_A);
		4549	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4550	ev_run (EV_A_ 0);
		4551	l_release (EV_A);
		4552
		4553	return 0;
		4554	}
		4555
		4556	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4557	signal the main thread via some unspecified mechanism (signals? pipe
		4558	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4559	have been called (in a while loop because a) spurious wakeups are possible
		4560	and b) skipping inter-thread-communication when there are no pending
		4561	watchers is very beneficial):
		4562
		4563	static void
		4564	l_invoke (EV_P)
		4565	{
		4566	userdata *u = ev_userdata (EV_A);
		4567
		4568	while (ev_pending_count (EV_A))
		4569	{
		4570	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4571	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4572	}
		4573	}
		4574
		4575	Now, whenever the main thread gets told to invoke pending watchers, it
		4576	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4577	thread to continue:
		4578
		4579	static void
		4580	real_invoke_pending (EV_P)
		4581	{
		4582	userdata *u = ev_userdata (EV_A);
		4583
		4584	pthread_mutex_lock (&u->lock);
		4585	ev_invoke_pending (EV_A);
		4586	pthread_cond_signal (&u->invoke_cv);
		4587	pthread_mutex_unlock (&u->lock);
		4588	}
		4589
		4590	Whenever you want to start/stop a watcher or do other modifications to an
		4591	event loop, you will now have to lock:
		4592
		4593	ev_timer timeout_watcher;
		4594	userdata *u = ev_userdata (EV_A);
		4595
		4596	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4597
		4598	pthread_mutex_lock (&u->lock);
		4599	ev_timer_start (EV_A_ &timeout_watcher);
		4600	ev_async_send (EV_A_ &u->async_w);
		4601	pthread_mutex_unlock (&u->lock);
		4602
		4603	Note that sending the C<ev_async> watcher is required because otherwise
		4604	an event loop currently blocking in the kernel will have no knowledge
		4605	about the newly added timer. By waking up the loop it will pick up any new
		4606	watchers in the next event loop iteration.
		4607
		4608	=head3 COROUTINES
		4609
		4610	Libev is very accommodating to coroutines ("cooperative threads"):
		4611	libev fully supports nesting calls to its functions from different
		4612	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4613	different coroutines, and switch freely between both coroutines running
		4614	the loop, as long as you don't confuse yourself). The only exception is
		4615	that you must not do this from C<ev_periodic> reschedule callbacks.
		4616
		4617	Care has been taken to ensure that libev does not keep local state inside
		4618	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4619	they do not call any callbacks.
		4620
		4621	=head2 COMPILER WARNINGS
		4622
		4623	Depending on your compiler and compiler settings, you might get no or a
		4624	lot of warnings when compiling libev code. Some people are apparently
		4625	scared by this.
		4626
		4627	However, these are unavoidable for many reasons. For one, each compiler
		4628	has different warnings, and each user has different tastes regarding
		4629	warning options. "Warn-free" code therefore cannot be a goal except when
		4630	targeting a specific compiler and compiler-version.
		4631
		4632	Another reason is that some compiler warnings require elaborate
		4633	workarounds, or other changes to the code that make it less clear and less
		4634	maintainable.
		4635
		4636	And of course, some compiler warnings are just plain stupid, or simply
		4637	wrong (because they don't actually warn about the condition their message
		4638	seems to warn about). For example, certain older gcc versions had some
		4639	warnings that resulted in an extreme number of false positives. These have
		4640	been fixed, but some people still insist on making code warn-free with
		4641	such buggy versions.
		4642
		4643	While libev is written to generate as few warnings as possible,
		4644	"warn-free" code is not a goal, and it is recommended not to build libev
		4645	with any compiler warnings enabled unless you are prepared to cope with
		4646	them (e.g. by ignoring them). Remember that warnings are just that:
		4647	warnings, not errors, or proof of bugs.
		4648
		4649
		4650	=head2 VALGRIND
		4651
		4652	Valgrind has a special section here because it is a popular tool that is
		4653	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4654
		4655	If you think you found a bug (memory leak, uninitialised data access etc.)
		4656	in libev, then check twice: If valgrind reports something like:
		4657
		4658	==2274== definitely lost: 0 bytes in 0 blocks.
		4659	==2274== possibly lost: 0 bytes in 0 blocks.
		4660	==2274== still reachable: 256 bytes in 1 blocks.
		4661
		4662	Then there is no memory leak, just as memory accounted to global variables
		4663	is not a memleak - the memory is still being referenced, and didn't leak.
		4664
		4665	Similarly, under some circumstances, valgrind might report kernel bugs
		4666	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4667	although an acceptable workaround has been found here), or it might be
		4668	confused.
		4669
		4670	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4671	make it into some kind of religion.
		4672
		4673	If you are unsure about something, feel free to contact the mailing list
		4674	with the full valgrind report and an explanation on why you think this
		4675	is a bug in libev (best check the archives, too :). However, don't be
		4676	annoyed when you get a brisk "this is no bug" answer and take the chance
		4677	of learning how to interpret valgrind properly.
		4678
		4679	If you need, for some reason, empty reports from valgrind for your project
		4680	I suggest using suppression lists.
		4681
		4682
		4683	=head1 PORTABILITY NOTES
		4684
		4685	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4686
		4687	GNU/Linux is the only common platform that supports 64 bit file/large file
		4688	interfaces but I<disables> them by default.
		4689
		4690	That means that libev compiled in the default environment doesn't support
		4691	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4692
		4693	Unfortunately, many programs try to work around this GNU/Linux issue
		4694	by enabling the large file API, which makes them incompatible with the
		4695	standard libev compiled for their system.
		4696
		4697	Likewise, libev cannot enable the large file API itself as this would
		4698	suddenly make it incompatible to the default compile time environment,
		4699	i.e. all programs not using special compile switches.
		4700
		4701	=head2 OS/X AND DARWIN BUGS
		4702
		4703	The whole thing is a bug if you ask me - basically any system interface
		4704	you touch is broken, whether it is locales, poll, kqueue or even the
		4705	OpenGL drivers.
		4706
		4707	=head3 C<kqueue> is buggy
		4708
		4709	The kqueue syscall is broken in all known versions - most versions support
		4710	only sockets, many support pipes.
		4711
		4712	Libev tries to work around this by not using C<kqueue> by default on this
		4713	rotten platform, but of course you can still ask for it when creating a
		4714	loop - embedding a socket-only kqueue loop into a select-based one is
		4715	probably going to work well.
		4716
		4717	=head3 C<poll> is buggy
		4718
		4719	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4720	implementation by something calling C<kqueue> internally around the 10.5.6
		4721	release, so now C<kqueue> I<and> C<poll> are broken.
		4722
		4723	Libev tries to work around this by not using C<poll> by default on
		4724	this rotten platform, but of course you can still ask for it when creating
		4725	a loop.
		4726
		4727	=head3 C<select> is buggy
		4728
		4729	All that's left is C<select>, and of course Apple found a way to fuck this
		4730	one up as well: On OS/X, C<select> actively limits the number of file
		4731	descriptors you can pass in to 1024 - your program suddenly crashes when
		4732	you use more.
		4733
		4734	There is an undocumented "workaround" for this - defining
		4735	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4736	work on OS/X.
		4737
		4738	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4739
		4740	=head3 C<errno> reentrancy
		4741
		4742	The default compile environment on Solaris is unfortunately so
		4743	thread-unsafe that you can't even use components/libraries compiled
		4744	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4745	defined by default. A valid, if stupid, implementation choice.
		4746
		4747	If you want to use libev in threaded environments you have to make sure
		4748	it's compiled with C<_REENTRANT> defined.
		4749
		4750	=head3 Event port backend
		4751
		4752	The scalable event interface for Solaris is called "event
		4753	ports". Unfortunately, this mechanism is very buggy in all major
		4754	releases. If you run into high CPU usage, your program freezes or you get
		4755	a large number of spurious wakeups, make sure you have all the relevant
		4756	and latest kernel patches applied. No, I don't know which ones, but there
		4757	are multiple ones to apply, and afterwards, event ports actually work
		4758	great.
		4759
		4760	If you can't get it to work, you can try running the program by setting
		4761	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4762	C<select> backends.
		4763
		4764	=head2 AIX POLL BUG
		4765
		4766	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4767	this by trying to avoid the poll backend altogether (i.e. it's not even
		4768	compiled in), which normally isn't a big problem as C<select> works fine
		4769	with large bitsets on AIX, and AIX is dead anyway.
		4770
		4771	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4772
		4773	=head3 General issues
		4774
		4775	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4776	requires, and its I/O model is fundamentally incompatible with the POSIX
		4777	model. Libev still offers limited functionality on this platform in
		4778	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4779	descriptors. This only applies when using Win32 natively, not when using
		4780	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4781	as every compielr comes with a slightly differently broken/incompatible
		4782	environment.
		4783
		4784	Lifting these limitations would basically require the full
		4785	re-implementation of the I/O system. If you are into this kind of thing,
		4786	then note that glib does exactly that for you in a very portable way (note
		4787	also that glib is the slowest event library known to man).
		4788
		4789	There is no supported compilation method available on windows except
		4790	embedding it into other applications.
		4791
		4792	Sensible signal handling is officially unsupported by Microsoft - libev
		4793	tries its best, but under most conditions, signals will simply not work.
		4794
		4795	Not a libev limitation but worth mentioning: windows apparently doesn't
		4796	accept large writes: instead of resulting in a partial write, windows will
		4797	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4798	so make sure you only write small amounts into your sockets (less than a
		4799	megabyte seems safe, but this apparently depends on the amount of memory
		4800	available).
		4801
		4802	Due to the many, low, and arbitrary limits on the win32 platform and
		4803	the abysmal performance of winsockets, using a large number of sockets
		4804	is not recommended (and not reasonable). If your program needs to use
		4805	more than a hundred or so sockets, then likely it needs to use a totally
		4806	different implementation for windows, as libev offers the POSIX readiness
		4807	notification model, which cannot be implemented efficiently on windows
		4808	(due to Microsoft monopoly games).
		4809
		4810	A typical way to use libev under windows is to embed it (see the embedding
		4811	section for details) and use the following F<evwrap.h> header file instead
		4812	of F<ev.h>:
		4813
		4814	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4815	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4816
		4817	#include "ev.h"
		4818
		4819	And compile the following F<evwrap.c> file into your project (make sure
		4820	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4821
		4822	#include "evwrap.h"
		4823	#include "ev.c"
		4824
		4825	=head3 The winsocket C<select> function
		4826
		4827	The winsocket C<select> function doesn't follow POSIX in that it
		4828	requires socket I<handles> and not socket I<file descriptors> (it is
		4829	also extremely buggy). This makes select very inefficient, and also
		4830	requires a mapping from file descriptors to socket handles (the Microsoft
		4831	C runtime provides the function C<_open_osfhandle> for this). See the
		4832	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4833	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4834
		4835	The configuration for a "naked" win32 using the Microsoft runtime
		4836	libraries and raw winsocket select is:
		4837
		4838	#define EV_USE_SELECT 1
		4839	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4840
		4841	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4842	complexity in the O(n²) range when using win32.
		4843
		4844	=head3 Limited number of file descriptors
		4845
		4846	Windows has numerous arbitrary (and low) limits on things.
		4847
		4848	Early versions of winsocket's select only supported waiting for a maximum
		4849	of C<64> handles (probably owning to the fact that all windows kernels
		4850	can only wait for C<64> things at the same time internally; Microsoft
		4851	recommends spawning a chain of threads and wait for 63 handles and the
		4852	previous thread in each. Sounds great!).
		4853
		4854	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4855	to some high number (e.g. C<2048>) before compiling the winsocket select
		4856	call (which might be in libev or elsewhere, for example, perl and many
		4857	other interpreters do their own select emulation on windows).
		4858
		4859	Another limit is the number of file descriptors in the Microsoft runtime
		4860	libraries, which by default is C<64> (there must be a hidden I<64>
		4861	fetish or something like this inside Microsoft). You can increase this
		4862	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4863	(another arbitrary limit), but is broken in many versions of the Microsoft
		4864	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4865	(depending on windows version and/or the phase of the moon). To get more,
		4866	you need to wrap all I/O functions and provide your own fd management, but
		4867	the cost of calling select (O(n²)) will likely make this unworkable.
		4868
		4869	=head2 PORTABILITY REQUIREMENTS
		4870
		4871	In addition to a working ISO-C implementation and of course the
		4872	backend-specific APIs, libev relies on a few additional extensions:
		4873
		4874	=over 4
		4875
		4876	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4877	calling conventions regardless of C<ev_watcher_type *>.
		4878
		4879	Libev assumes not only that all watcher pointers have the same internal
		4880	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4881	assumes that the same (machine) code can be used to call any watcher
		4882	callback: The watcher callbacks have different type signatures, but libev
		4883	calls them using an C<ev_watcher *> internally.
		4884
		4885	=item pointer accesses must be thread-atomic
		4886
		4887	Accessing a pointer value must be atomic, it must both be readable and
		4888	writable in one piece - this is the case on all current architectures.
		4889
		4890	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4891
		4892	The type C<sig_atomic_t volatile> (or whatever is defined as
		4893	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4894	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4895	believed to be sufficiently portable.
		4896
		4897	=item C<sigprocmask> must work in a threaded environment
		4898
		4899	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4900	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4901	pthread implementations will either allow C<sigprocmask> in the "main
		4902	thread" or will block signals process-wide, both behaviours would
		4903	be compatible with libev. Interaction between C<sigprocmask> and
		4904	C<pthread_sigmask> could complicate things, however.
		4905
		4906	The most portable way to handle signals is to block signals in all threads
		4907	except the initial one, and run the default loop in the initial thread as
		4908	well.
		4909
		4910	=item C<long> must be large enough for common memory allocation sizes
		4911
		4912	To improve portability and simplify its API, libev uses C<long> internally
		4913	instead of C<size_t> when allocating its data structures. On non-POSIX
		4914	systems (Microsoft...) this might be unexpectedly low, but is still at
		4915	least 31 bits everywhere, which is enough for hundreds of millions of
		4916	watchers.
		4917
		4918	=item C<double> must hold a time value in seconds with enough accuracy
		4919
		4920	The type C<double> is used to represent timestamps. It is required to
		4921	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4922	good enough for at least into the year 4000 with millisecond accuracy
		4923	(the design goal for libev). This requirement is overfulfilled by
		4924	implementations using IEEE 754, which is basically all existing ones. With
		4925	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4926
		4927	=back
		4928
		4929	If you know of other additional requirements drop me a note.
		4930
		4931
		4932	=head1 ALGORITHMIC COMPLEXITIES
		4933
		4934	In this section the complexities of (many of) the algorithms used inside
		4935	libev will be documented. For complexity discussions about backends see
		4936	the documentation for C<ev_default_init>.
		4937
		4938	All of the following are about amortised time: If an array needs to be
		4939	extended, libev needs to realloc and move the whole array, but this
		4940	happens asymptotically rarer with higher number of elements, so O(1) might
		4941	mean that libev does a lengthy realloc operation in rare cases, but on
		4942	average it is much faster and asymptotically approaches constant time.
		4943
		4944	=over 4
		4945
		4946	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4947
		4948	This means that, when you have a watcher that triggers in one hour and
		4949	there are 100 watchers that would trigger before that, then inserting will
		4950	have to skip roughly seven (C<ld 100>) of these watchers.
		4951
		4952	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4953
		4954	That means that changing a timer costs less than removing/adding them,
		4955	as only the relative motion in the event queue has to be paid for.
		4956
		4957	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4958
		4959	These just add the watcher into an array or at the head of a list.
		4960
		4961	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4962
		4963	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4964
		4965	These watchers are stored in lists, so they need to be walked to find the
		4966	correct watcher to remove. The lists are usually short (you don't usually
		4967	have many watchers waiting for the same fd or signal: one is typical, two
		4968	is rare).
		4969
		4970	=item Finding the next timer in each loop iteration: O(1)
		4971
		4972	By virtue of using a binary or 4-heap, the next timer is always found at a
		4973	fixed position in the storage array.
		4974
		4975	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4976
		4977	A change means an I/O watcher gets started or stopped, which requires
		4978	libev to recalculate its status (and possibly tell the kernel, depending
		4979	on backend and whether C<ev_io_set> was used).
		4980
		4981	=item Activating one watcher (putting it into the pending state): O(1)
		4982
		4983	=item Priority handling: O(number_of_priorities)
		4984
		4985	Priorities are implemented by allocating some space for each
		4986	priority. When doing priority-based operations, libev usually has to
		4987	linearly search all the priorities, but starting/stopping and activating
		4988	watchers becomes O(1) with respect to priority handling.
		4989
		4990	=item Sending an ev_async: O(1)
		4991
		4992	=item Processing ev_async_send: O(number_of_async_watchers)
		4993
		4994	=item Processing signals: O(max_signal_number)
		4995
		4996	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4997	calls in the current loop iteration. Checking for async and signal events
		4998	involves iterating over all running async watchers or all signal numbers.
		4999
		5000	=back
		5001
		5002
		5003	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5004
		5005	The major version 4 introduced some incompatible changes to the API.
		5006
		5007	At the moment, the C<ev.h> header file provides compatibility definitions
		5008	for all changes, so most programs should still compile. The compatibility
		5009	layer might be removed in later versions of libev, so better update to the
		5010	new API early than late.
		5011
		5012	=over 4
		5013
		5014	=item C<EV_COMPAT3> backwards compatibility mechanism
		5015
		5016	The backward compatibility mechanism can be controlled by
		5017	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5018	section.
		5019
		5020	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5021
		5022	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5023
		5024	ev_loop_destroy (EV_DEFAULT_UC);
		5025	ev_loop_fork (EV_DEFAULT);
		5026
		5027	=item function/symbol renames
		5028
		5029	A number of functions and symbols have been renamed:
		5030
		5031	ev_loop => ev_run
		5032	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5033	EVLOOP_ONESHOT => EVRUN_ONCE
		5034
		5035	ev_unloop => ev_break
		5036	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5037	EVUNLOOP_ONE => EVBREAK_ONE
		5038	EVUNLOOP_ALL => EVBREAK_ALL
		5039
		5040	EV_TIMEOUT => EV_TIMER
		5041
		5042	ev_loop_count => ev_iteration
		5043	ev_loop_depth => ev_depth
		5044	ev_loop_verify => ev_verify
		5045
		5046	Most functions working on C<struct ev_loop> objects don't have an
		5047	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5048	associated constants have been renamed to not collide with the C<struct
		5049	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5050	as all other watcher types. Note that C<ev_loop_fork> is still called
		5051	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5052	typedef.
		5053
		5054	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5055
		5056	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5057	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5058	and work, but the library code will of course be larger.
		5059
		5060	=back
		5061
		5062
		5063	=head1 GLOSSARY
		5064
		5065	=over 4
		5066
		5067	=item active
		5068
		5069	A watcher is active as long as it has been started and not yet stopped.
		5070	See L<WATCHER STATES> for details.
		5071
		5072	=item application
		5073
		5074	In this document, an application is whatever is using libev.
		5075
		5076	=item backend
		5077
		5078	The part of the code dealing with the operating system interfaces.
		5079
		5080	=item callback
		5081
		5082	The address of a function that is called when some event has been
		5083	detected. Callbacks are being passed the event loop, the watcher that
		5084	received the event, and the actual event bitset.
		5085
		5086	=item callback/watcher invocation
		5087
		5088	The act of calling the callback associated with a watcher.
		5089
		5090	=item event
		5091
		5092	A change of state of some external event, such as data now being available
		5093	for reading on a file descriptor, time having passed or simply not having
		5094	any other events happening anymore.
		5095
		5096	In libev, events are represented as single bits (such as C<EV_READ> or
		5097	C<EV_TIMER>).
		5098
		5099	=item event library
		5100
		5101	A software package implementing an event model and loop.
		5102
		5103	=item event loop
		5104
		5105	An entity that handles and processes external events and converts them
		5106	into callback invocations.
		5107
		5108	=item event model
		5109
		5110	The model used to describe how an event loop handles and processes
		5111	watchers and events.
		5112
		5113	=item pending
		5114
		5115	A watcher is pending as soon as the corresponding event has been
		5116	detected. See L<WATCHER STATES> for details.
		5117
		5118	=item real time
		5119
		5120	The physical time that is observed. It is apparently strictly monotonic :)
		5121
		5122	=item wall-clock time
		5123
		5124	The time and date as shown on clocks. Unlike real time, it can actually
		5125	be wrong and jump forwards and backwards, e.g. when the you adjust your
		5126	clock.
		5127
		5128	=item watcher
		5129
		5130	A data structure that describes interest in certain events. Watchers need
		5131	to be started (attached to an event loop) before they can receive events.
		5132
		5133	=back
878		5134
879	=head1 AUTHOR	5135	=head1 AUTHOR
880		5136
881	Marc Lehmann <libev@schmorp.de>.	5137	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5138	Magnusson and Emanuele Giaquinta.
882		5139

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