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

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