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Revision 1.358 by sf-exg, Tue Jan 11 08:43:48 2011 UTC

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

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