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Revision 1.282 by root, Wed Mar 10 08:19:39 2010 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_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_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_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_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_loop (0);
		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_loop (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	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
10		84
11	Libev is an event loop: you register interest in certain events (such as a	85	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	86	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	87	these event sources and provide your program with events.
14		88
15	To do this, it must take more or less complete control over your process	89	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	90	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	94	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	95	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	96	watcher.
23		97
24	=head1 FEATURES	98	=head2 FEATURES
25		99
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
		104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
		105	timers (C<ev_timer>), absolute timers with customised rescheduling
		106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
29	events (related to SIGCHLD), and event watchers dealing with the event	107	change events (C<ev_child>), and event watchers dealing with the event
30	loop mechanism itself (idle, prepare and check watchers).	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
		109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
31		111
		112	It also is quite fast (see this
		113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
		114	for example).
		115
32	=head1 CONVENTIONS	116	=head2 CONVENTIONS
33		117
34	Libev is very configurable. In this manual the default configuration	118	Libev is very configurable. In this manual the default (and most common)
35	will be described, which supports multiple event loops. For more info	119	configuration will be described, which supports multiple event loops. For
36	about various configuraiton options please have a look at the file	120	more info about various configuration options please have a look at
37	F<README.embed> in the libev distribution. If libev was configured without	121	B<EMBED> section in this manual. If libev was configured without support
38	support for multiple event loops, then all functions taking an initial	122	for multiple event loops, then all functions taking an initial argument of
39	argument of name C<loop> (which is always of type C<struct ev_loop *>)	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
40	will not have this argument.	124	this argument.
41		125
42	=head1 TIME AND OTHER GLOBAL FUNCTIONS	126	=head2 TIME REPRESENTATION
43		127
44	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
45	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
46	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
47	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
48	to the double type in C.	132	aliases to the C<double> type in C. When you need to do any calculations
		133	on it, you should treat it as some floating point value. Unlike the name
		134	component C<stamp> might indicate, it is also used for time differences
		135	throughout libev.
		136
		137	=head1 ERROR HANDLING
		138
		139	Libev knows three classes of errors: operating system errors, usage errors
		140	and internal errors (bugs).
		141
		142	When libev catches an operating system error it cannot handle (for example
		143	a system call indicating a condition libev cannot fix), it calls the callback
		144	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		145	abort. The default is to print a diagnostic message and to call C<abort
		146	()>.
		147
		148	When libev detects a usage error such as a negative timer interval, then
		149	it will print a diagnostic message and abort (via the C<assert> mechanism,
		150	so C<NDEBUG> will disable this checking): these are programming errors in
		151	the libev caller and need to be fixed there.
		152
		153	Libev also has a few internal error-checking C<assert>ions, and also has
		154	extensive consistency checking code. These do not trigger under normal
		155	circumstances, as they indicate either a bug in libev or worse.
		156
		157
		158	=head1 GLOBAL FUNCTIONS
		159
		160	These functions can be called anytime, even before initialising the
		161	library in any way.
49		162
50	=over 4	163	=over 4
51		164
52	=item ev_tstamp ev_time ()	165	=item ev_tstamp ev_time ()
53		166
54	Returns the current time as libev would use it.	167	Returns the current time as libev would use it. Please note that the
		168	C<ev_now> function is usually faster and also often returns the timestamp
		169	you actually want to know.
		170
		171	=item ev_sleep (ev_tstamp interval)
		172
		173	Sleep for the given interval: The current thread will be blocked until
		174	either it is interrupted or the given time interval has passed. Basically
		175	this is a sub-second-resolution C<sleep ()>.
55		176
56	=item int ev_version_major ()	177	=item int ev_version_major ()
57		178
58	=item int ev_version_minor ()	179	=item int ev_version_minor ()
59		180
60	You can find out the major and minor version numbers of the library	181	You can find out the major and minor ABI version numbers of the library
61	you linked against by calling the functions C<ev_version_major> and	182	you linked against by calling the functions C<ev_version_major> and
62	C<ev_version_minor>. If you want, you can compare against the global	183	C<ev_version_minor>. If you want, you can compare against the global
63	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	184	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
64	version of the library your program was compiled against.	185	version of the library your program was compiled against.
65		186
		187	These version numbers refer to the ABI version of the library, not the
		188	release version.
		189
66	Usually, its a good idea to terminate if the major versions mismatch,	190	Usually, it's a good idea to terminate if the major versions mismatch,
67	as this indicates an incompatible change. Minor versions are usually	191	as this indicates an incompatible change. Minor versions are usually
68	compatible to older versions, so a larger minor version alone is usually	192	compatible to older versions, so a larger minor version alone is usually
69	not a problem.	193	not a problem.
70		194
		195	Example: Make sure we haven't accidentally been linked against the wrong
		196	version.
		197
		198	assert (("libev version mismatch",
		199	ev_version_major () == EV_VERSION_MAJOR
		200	&& ev_version_minor () >= EV_VERSION_MINOR));
		201
		202	=item unsigned int ev_supported_backends ()
		203
		204	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		205	value) compiled into this binary of libev (independent of their
		206	availability on the system you are running on). See C<ev_default_loop> for
		207	a description of the set values.
		208
		209	Example: make sure we have the epoll method, because yeah this is cool and
		210	a must have and can we have a torrent of it please!!!11
		211
		212	assert (("sorry, no epoll, no sex",
		213	ev_supported_backends () & EVBACKEND_EPOLL));
		214
		215	=item unsigned int ev_recommended_backends ()
		216
		217	Return the set of all backends compiled into this binary of libev and also
		218	recommended for this platform. This set is often smaller than the one
		219	returned by C<ev_supported_backends>, as for example kqueue is broken on
		220	most BSDs and will not be auto-detected unless you explicitly request it
		221	(assuming you know what you are doing). This is the set of backends that
		222	libev will probe for if you specify no backends explicitly.
		223
		224	=item unsigned int ev_embeddable_backends ()
		225
		226	Returns the set of backends that are embeddable in other event loops. This
		227	is the theoretical, all-platform, value. To find which backends
		228	might be supported on the current system, you would need to look at
		229	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		230	recommended ones.
		231
		232	See the description of C<ev_embed> watchers for more info.
		233
71	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	234	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
72		235
73	Sets the allocation function to use (the prototype is similar to the	236	Sets the allocation function to use (the prototype is similar - the
74	realloc function). It is used to allocate and free memory (no surprises	237	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
75	here). If it returns zero when memory needs to be allocated, the library	238	used to allocate and free memory (no surprises here). If it returns zero
		239	when memory needs to be allocated (C<size != 0>), the library might abort
76	might abort or take some potentially destructive action. The default is	240	or take some potentially destructive action.
77	your system realloc function.	241
		242	Since some systems (at least OpenBSD and Darwin) fail to implement
		243	correct C<realloc> semantics, libev will use a wrapper around the system
		244	C<realloc> and C<free> functions by default.
78		245
79	You could override this function in high-availability programs to, say,	246	You could override this function in high-availability programs to, say,
80	free some memory if it cannot allocate memory, to use a special allocator,	247	free some memory if it cannot allocate memory, to use a special allocator,
81	or even to sleep a while and retry until some memory is available.	248	or even to sleep a while and retry until some memory is available.
82		249
		250	Example: Replace the libev allocator with one that waits a bit and then
		251	retries (example requires a standards-compliant C<realloc>).
		252
		253	static void *
		254	persistent_realloc (void *ptr, size_t size)
		255	{
		256	for (;;)
		257	{
		258	void *newptr = realloc (ptr, size);
		259
		260	if (newptr)
		261	return newptr;
		262
		263	sleep (60);
		264	}
		265	}
		266
		267	...
		268	ev_set_allocator (persistent_realloc);
		269
83	=item ev_set_syserr_cb (void (*cb)(const char *msg));	270	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
84		271
85	Set the callback function to call on a retryable syscall error (such	272	Set the callback function to call on a retryable system call error (such
86	as failed select, poll, epoll_wait). The message is a printable string	273	as failed select, poll, epoll_wait). The message is a printable string
87	indicating the system call or subsystem causing the problem. If this	274	indicating the system call or subsystem causing the problem. If this
88	callback is set, then libev will expect it to remedy the sitution, no	275	callback is set, then libev will expect it to remedy the situation, no
89	matter what, when it returns. That is, libev will geenrally retry the	276	matter what, when it returns. That is, libev will generally retry the
90	requested operation, or, if the condition doesn't go away, do bad stuff	277	requested operation, or, if the condition doesn't go away, do bad stuff
91	(such as abort).	278	(such as abort).
92		279
		280	Example: This is basically the same thing that libev does internally, too.
		281
		282	static void
		283	fatal_error (const char *msg)
		284	{
		285	perror (msg);
		286	abort ();
		287	}
		288
		289	...
		290	ev_set_syserr_cb (fatal_error);
		291
93	=back	292	=back
94		293
95	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
96		295
97	An event loop is described by a C<struct ev_loop *>. The library knows two	296	An event loop is described by a C<struct ev_loop *> (the C<struct>
98	types of such loops, the I<default> loop, which supports signals and child	297	is I<not> optional in this case, as there is also an C<ev_loop>
99	events, and dynamically created loops which do not.	298	I<function>).
100		299
101	If you use threads, a common model is to run the default event loop	300	The library knows two types of such loops, the I<default> loop, which
102	in your main thread (or in a separate thrad) and for each thread you	301	supports signals and child events, and dynamically created loops which do
103	create, you also create another event loop. Libev itself does no lockign	302	not.
104	whatsoever, so if you mix calls to different event loops, make sure you
105	lock (this is usually a bad idea, though, even if done right).
106		303
107	=over 4	304	=over 4
108		305
109	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
110		307
111	This will initialise the default event loop if it hasn't been initialised	308	This will initialise the default event loop if it hasn't been initialised
112	yet and return it. If the default loop could not be initialised, returns	309	yet and return it. If the default loop could not be initialised, returns
113	false. If it already was initialised it simply returns it (and ignores the	310	false. If it already was initialised it simply returns it (and ignores the
114	flags).	311	flags. If that is troubling you, check C<ev_backend ()> afterwards).
115		312
116	If you don't know what event loop to use, use the one returned from this	313	If you don't know what event loop to use, use the one returned from this
117	function.	314	function.
118		315
		316	Note that this function is I<not> thread-safe, so if you want to use it
		317	from multiple threads, you have to lock (note also that this is unlikely,
		318	as loops cannot be shared easily between threads anyway).
		319
		320	The default loop is the only loop that can handle C<ev_signal> and
		321	C<ev_child> watchers, and to do this, it always registers a handler
		322	for C<SIGCHLD>. If this is a problem for your application you can either
		323	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		324	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		325	C<ev_default_init>.
		326
119	The flags argument can be used to specify special behaviour or specific	327	The flags argument can be used to specify special behaviour or specific
120	backends to use, and is usually specified as 0 (or EVFLAG_AUTO)	328	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
121		329
122	It supports the following flags:	330	The following flags are supported:
123		331
124	=over 4	332	=over 4
125		333
126	=item EVFLAG_AUTO	334	=item C<EVFLAG_AUTO>
127		335
128	The default flags value. Use this if you have no clue (its the right	336	The default flags value. Use this if you have no clue (it's the right
129	thing, believe me).	337	thing, believe me).
130		338
131	=item EVFLAG_NOENV	339	=item C<EVFLAG_NOENV>
132		340
133	If this flag bit is ored into the flag value then libev will I<not> look	341	If this flag bit is or'ed into the flag value (or the program runs setuid
134	at the environment variable C<LIBEV_FLAGS>. Otherwise (the default), this	342	or setgid) then libev will I<not> look at the environment variable
135	environment variable will override the flags completely. This is useful	343	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
		344	override the flags completely if it is found in the environment. This is
136	to try out specific backends to tets their performance, or to work around	345	useful to try out specific backends to test their performance, or to work
137	bugs.	346	around bugs.
138		347
		348	=item C<EVFLAG_FORKCHECK>
		349
		350	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		351	a fork, you can also make libev check for a fork in each iteration by
		352	enabling this flag.
		353
		354	This works by calling C<getpid ()> on every iteration of the loop,
		355	and thus this might slow down your event loop if you do a lot of loop
		356	iterations and little real work, but is usually not noticeable (on my
		357	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		358	without a system call and thus I<very> fast, but my GNU/Linux system also has
		359	C<pthread_atfork> which is even faster).
		360
		361	The big advantage of this flag is that you can forget about fork (and
		362	forget about forgetting to tell libev about forking) when you use this
		363	flag.
		364
		365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		366	environment variable.
		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_SIGNALFD>
		376
		377	When this flag is specified, then libev will attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		379	delivers signals synchronously, which makes it both faster and might make
		380	it possible to get the queued signal data. It can also simplify signal
		381	handling with threads, as long as you properly block signals in your
		382	threads that are not interested in handling them.
		383
		384	Signalfd will not be used by default as this changes your signal mask, and
		385	there are a lot of shoddy libraries and programs (glib's threadpool for
		386	example) that can't properly initialise their signal masks.
		387
139	=item EVMETHOD_SELECT portable select backend	388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
140		389
141	=item EVMETHOD_POLL poll backend (everywhere except windows)	390	This is your standard select(2) backend. Not I<completely> standard, as
		391	libev tries to roll its own fd_set with no limits on the number of fds,
		392	but if that fails, expect a fairly low limit on the number of fds when
		393	using this backend. It doesn't scale too well (O(highest_fd)), but its
		394	usually the fastest backend for a low number of (low-numbered :) fds.
142		395
143	=item EVMETHOD_EPOLL linux only	396	To get good performance out of this backend you need a high amount of
		397	parallelism (most of the file descriptors should be busy). If you are
		398	writing a server, you should C<accept ()> in a loop to accept as many
		399	connections as possible during one iteration. You might also want to have
		400	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		401	readiness notifications you get per iteration.
144		402
145	=item EVMETHOD_KQUEUE some bsds only	403	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		404	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		405	C<exceptfds> set on that platform).
146		406
147	=item EVMETHOD_DEVPOLL solaris 8 only	407	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
148		408
149	=item EVMETHOD_PORT solaris 10 only	409	And this is your standard poll(2) backend. It's more complicated
		410	than select, but handles sparse fds better and has no artificial
		411	limit on the number of fds you can use (except it will slow down
		412	considerably with a lot of inactive fds). It scales similarly to select,
		413	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		414	performance tips.
150		415
151	If one or more of these are ored into the flags value, then only these	416	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
152	backends will be tried (in the reverse order as given here). If one are	417	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
153	specified, any backend will do.	418
		419	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		420
		421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		422	kernels).
		423
		424	For few fds, this backend is a bit little slower than poll and select,
		425	but it scales phenomenally better. While poll and select usually scale
		426	like O(total_fds) where n is the total number of fds (or the highest fd),
		427	epoll scales either O(1) or O(active_fds).
		428
		429	The epoll mechanism deserves honorable mention as the most misdesigned
		430	of the more advanced event mechanisms: mere annoyances include silently
		431	dropping file descriptors, requiring a system call per change per file
		432	descriptor (and unnecessary guessing of parameters), problems with dup and
		433	so on. The biggest issue is fork races, however - if a program forks then
		434	I<both> parent and child process have to recreate the epoll set, which can
		435	take considerable time (one syscall per file descriptor) and is of course
		436	hard to detect.
		437
		438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		439	of course I<doesn't>, and epoll just loves to report events for totally
		440	I<different> file descriptors (even already closed ones, so one cannot
		441	even remove them from the set) than registered in the set (especially
		442	on SMP systems). Libev tries to counter these spurious notifications by
		443	employing an additional generation counter and comparing that against the
		444	events to filter out spurious ones, recreating the set when required.
		445
		446	While stopping, setting and starting an I/O watcher in the same iteration
		447	will result in some caching, there is still a system call per such
		448	incident (because the same I<file descriptor> could point to a different
		449	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
		450	file descriptors might not work very well if you register events for both
		451	file descriptors.
		452
		453	Best performance from this backend is achieved by not unregistering all
		454	watchers for a file descriptor until it has been closed, if possible,
		455	i.e. keep at least one watcher active per fd at all times. Stopping and
		456	starting a watcher (without re-setting it) also usually doesn't cause
		457	extra overhead. A fork can both result in spurious notifications as well
		458	as in libev having to destroy and recreate the epoll object, which can
		459	take considerable time and thus should be avoided.
		460
		461	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		462	faster than epoll for maybe up to a hundred file descriptors, depending on
		463	the usage. So sad.
		464
		465	While nominally embeddable in other event loops, this feature is broken in
		466	all kernel versions tested so far.
		467
		468	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		469	C<EVBACKEND_POLL>.
		470
		471	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		472
		473	Kqueue deserves special mention, as at the time of this writing, it
		474	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		475	with anything but sockets and pipes, except on Darwin, where of course
		476	it's completely useless). Unlike epoll, however, whose brokenness
		477	is by design, these kqueue bugs can (and eventually will) be fixed
		478	without API changes to existing programs. For this reason it's not being
		479	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		480	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		481	system like NetBSD.
		482
		483	You still can embed kqueue into a normal poll or select backend and use it
		484	only for sockets (after having made sure that sockets work with kqueue on
		485	the target platform). See C<ev_embed> watchers for more info.
		486
		487	It scales in the same way as the epoll backend, but the interface to the
		488	kernel is more efficient (which says nothing about its actual speed, of
		489	course). While stopping, setting and starting an I/O watcher does never
		490	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		491	two event changes per incident. Support for C<fork ()> is very bad (but
		492	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		493	cases
		494
		495	This backend usually performs well under most conditions.
		496
		497	While nominally embeddable in other event loops, this doesn't work
		498	everywhere, so you might need to test for this. And since it is broken
		499	almost everywhere, you should only use it when you have a lot of sockets
		500	(for which it usually works), by embedding it into another event loop
		501	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		502	also broken on OS X)) and, did I mention it, using it only for sockets.
		503
		504	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		505	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		506	C<NOTE_EOF>.
		507
		508	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		509
		510	This is not implemented yet (and might never be, unless you send me an
		511	implementation). According to reports, C</dev/poll> only supports sockets
		512	and is not embeddable, which would limit the usefulness of this backend
		513	immensely.
		514
		515	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		516
		517	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		518	it's really slow, but it still scales very well (O(active_fds)).
		519
		520	Please note that Solaris event ports can deliver a lot of spurious
		521	notifications, so you need to use non-blocking I/O or other means to avoid
		522	blocking when no data (or space) is available.
		523
		524	While this backend scales well, it requires one system call per active
		525	file descriptor per loop iteration. For small and medium numbers of file
		526	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		527	might perform better.
		528
		529	On the positive side, with the exception of the spurious readiness
		530	notifications, this backend actually performed fully to specification
		531	in all tests and is fully embeddable, which is a rare feat among the
		532	OS-specific backends (I vastly prefer correctness over speed hacks).
		533
		534	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		535	C<EVBACKEND_POLL>.
		536
		537	=item C<EVBACKEND_ALL>
		538
		539	Try all backends (even potentially broken ones that wouldn't be tried
		540	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		541	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		542
		543	It is definitely not recommended to use this flag.
154		544
155	=back	545	=back
		546
		547	If one or more of the backend flags are or'ed into the flags value,
		548	then only these backends will be tried (in the reverse order as listed
		549	here). If none are specified, all backends in C<ev_recommended_backends
		550	()> will be tried.
		551
		552	Example: This is the most typical usage.
		553
		554	if (!ev_default_loop (0))
		555	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		556
		557	Example: Restrict libev to the select and poll backends, and do not allow
		558	environment settings to be taken into account:
		559
		560	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		561
		562	Example: Use whatever libev has to offer, but make sure that kqueue is
		563	used if available (warning, breaks stuff, best use only with your own
		564	private event loop and only if you know the OS supports your types of
		565	fds):
		566
		567	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
156		568
157	=item struct ev_loop *ev_loop_new (unsigned int flags)	569	=item struct ev_loop *ev_loop_new (unsigned int flags)
158		570
159	Similar to C<ev_default_loop>, but always creates a new event loop that is	571	Similar to C<ev_default_loop>, but always creates a new event loop that is
160	always distinct from the default loop. Unlike the default loop, it cannot	572	always distinct from the default loop. Unlike the default loop, it cannot
161	handle signal and child watchers, and attempts to do so will be greeted by	573	handle signal and child watchers, and attempts to do so will be greeted by
162	undefined behaviour (or a failed assertion if assertions are enabled).	574	undefined behaviour (or a failed assertion if assertions are enabled).
163		575
		576	Note that this function I<is> thread-safe, and the recommended way to use
		577	libev with threads is indeed to create one loop per thread, and using the
		578	default loop in the "main" or "initial" thread.
		579
		580	Example: Try to create a event loop that uses epoll and nothing else.
		581
		582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		583	if (!epoller)
		584	fatal ("no epoll found here, maybe it hides under your chair");
		585
164	=item ev_default_destroy ()	586	=item ev_default_destroy ()
165		587
166	Destroys the default loop again (frees all memory and kernel state	588	Destroys the default loop again (frees all memory and kernel state
167	etc.). This stops all registered event watchers (by not touching them in	589	etc.). None of the active event watchers will be stopped in the normal
168	any way whatsoever, although you cnanot rely on this :).	590	sense, so e.g. C<ev_is_active> might still return true. It is your
		591	responsibility to either stop all watchers cleanly yourself I<before>
		592	calling this function, or cope with the fact afterwards (which is usually
		593	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		594	for example).
		595
		596	Note that certain global state, such as signal state (and installed signal
		597	handlers), will not be freed by this function, and related watchers (such
		598	as signal and child watchers) would need to be stopped manually.
		599
		600	In general it is not advisable to call this function except in the
		601	rare occasion where you really need to free e.g. the signal handling
		602	pipe fds. If you need dynamically allocated loops it is better to use
		603	C<ev_loop_new> and C<ev_loop_destroy>.
169		604
170	=item ev_loop_destroy (loop)	605	=item ev_loop_destroy (loop)
171		606
172	Like C<ev_default_destroy>, but destroys an event loop created by an	607	Like C<ev_default_destroy>, but destroys an event loop created by an
173	earlier call to C<ev_loop_new>.	608	earlier call to C<ev_loop_new>.
174		609
175	=item ev_default_fork ()	610	=item ev_default_fork ()
176		611
		612	This function sets a flag that causes subsequent C<ev_loop> iterations
177	This function reinitialises the kernel state for backends that have	613	to reinitialise the kernel state for backends that have one. Despite the
178	one. Despite the name, you can call it anytime, but it makes most sense	614	name, you can call it anytime, but it makes most sense after forking, in
179	after forking, in either the parent or child process (or both, but that	615	the child process (or both child and parent, but that again makes little
180	again makes little sense).	616	sense). You I<must> call it in the child before using any of the libev
		617	functions, and it will only take effect at the next C<ev_loop> iteration.
181		618
182	You I<must> call this function after forking if and only if you want to	619	On the other hand, you only need to call this function in the child
183	use the event library in both processes. If you just fork+exec, you don't	620	process if and only if you want to use the event library in the child. If
184	have to call it.	621	you just fork+exec, you don't have to call it at all.
185		622
186	The function itself is quite fast and its usually not a problem to call	623	The function itself is quite fast and it's usually not a problem to call
187	it just in case after a fork. To make this easy, the function will fit in	624	it just in case after a fork. To make this easy, the function will fit in
188	quite nicely into a call to C<pthread_atfork>:	625	quite nicely into a call to C<pthread_atfork>:
189		626
190	pthread_atfork (0, 0, ev_default_fork);	627	pthread_atfork (0, 0, ev_default_fork);
191		628
192	=item ev_loop_fork (loop)	629	=item ev_loop_fork (loop)
193		630
194	Like C<ev_default_fork>, but acts on an event loop created by	631	Like C<ev_default_fork>, but acts on an event loop created by
195	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	632	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
196	after fork, and how you do this is entirely your own problem.	633	after fork that you want to re-use in the child, and how you do this is
		634	entirely your own problem.
197		635
		636	=item int ev_is_default_loop (loop)
		637
		638	Returns true when the given loop is, in fact, the default loop, and false
		639	otherwise.
		640
		641	=item unsigned int ev_loop_count (loop)
		642
		643	Returns the count of loop iterations for the loop, which is identical to
		644	the number of times libev did poll for new events. It starts at C<0> and
		645	happily wraps around with enough iterations.
		646
		647	This value can sometimes be useful as a generation counter of sorts (it
		648	"ticks" the number of loop iterations), as it roughly corresponds with
		649	C<ev_prepare> and C<ev_check> calls.
		650
		651	=item unsigned int ev_loop_depth (loop)
		652
		653	Returns the number of times C<ev_loop> was entered minus the number of
		654	times C<ev_loop> was exited, in other words, the recursion depth.
		655
		656	Outside C<ev_loop>, this number is zero. In a callback, this number is
		657	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		658	in which case it is higher.
		659
		660	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		661	etc.), doesn't count as exit.
		662
198	=item unsigned int ev_method (loop)	663	=item unsigned int ev_backend (loop)
199		664
200	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	665	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
201	use.	666	use.
202		667
203	=item ev_tstamp = ev_now (loop)	668	=item ev_tstamp ev_now (loop)
204		669
205	Returns the current "event loop time", which is the time the event loop	670	Returns the current "event loop time", which is the time the event loop
206	got events and started processing them. This timestamp does not change	671	received events and started processing them. This timestamp does not
207	as long as callbacks are being processed, and this is also the base time	672	change as long as callbacks are being processed, and this is also the base
208	used for relative timers. You can treat it as the timestamp of the event	673	time used for relative timers. You can treat it as the timestamp of the
209	occuring (or more correctly, the mainloop finding out about it).	674	event occurring (or more correctly, libev finding out about it).
		675
		676	=item ev_now_update (loop)
		677
		678	Establishes the current time by querying the kernel, updating the time
		679	returned by C<ev_now ()> in the progress. This is a costly operation and
		680	is usually done automatically within C<ev_loop ()>.
		681
		682	This function is rarely useful, but when some event callback runs for a
		683	very long time without entering the event loop, updating libev's idea of
		684	the current time is a good idea.
		685
		686	See also L<The special problem of time updates> in the C<ev_timer> section.
		687
		688	=item ev_suspend (loop)
		689
		690	=item ev_resume (loop)
		691
		692	These two functions suspend and resume a loop, for use when the loop is
		693	not used for a while and timeouts should not be processed.
		694
		695	A typical use case would be an interactive program such as a game: When
		696	the user presses C<^Z> to suspend the game and resumes it an hour later it
		697	would be best to handle timeouts as if no time had actually passed while
		698	the program was suspended. This can be achieved by calling C<ev_suspend>
		699	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		700	C<ev_resume> directly afterwards to resume timer processing.
		701
		702	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		703	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		704	will be rescheduled (that is, they will lose any events that would have
		705	occured while suspended).
		706
		707	After calling C<ev_suspend> you B<must not> call I<any> function on the
		708	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		709	without a previous call to C<ev_suspend>.
		710
		711	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		712	event loop time (see C<ev_now_update>).
210		713
211	=item ev_loop (loop, int flags)	714	=item ev_loop (loop, int flags)
212		715
213	Finally, this is it, the event handler. This function usually is called	716	Finally, this is it, the event handler. This function usually is called
214	after you initialised all your watchers and you want to start handling	717	after you have initialised all your watchers and you want to start
215	events.	718	handling events.
216		719
217	If the flags argument is specified as 0, it will not return until either	720	If the flags argument is specified as C<0>, it will not return until
218	no event watchers are active anymore or C<ev_unloop> was called.	721	either no event watchers are active anymore or C<ev_unloop> was called.
		722
		723	Please note that an explicit C<ev_unloop> is usually better than
		724	relying on all watchers to be stopped when deciding when a program has
		725	finished (especially in interactive programs), but having a program
		726	that automatically loops as long as it has to and no longer by virtue
		727	of relying on its watchers stopping correctly, that is truly a thing of
		728	beauty.
219		729
220	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	730	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
221	those events and any outstanding ones, but will not block your process in	731	those events and any already outstanding ones, but will not block your
222	case there are no events.	732	process in case there are no events and will return after one iteration of
		733	the loop.
223		734
224	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	735	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
225	neccessary) and will handle those and any outstanding ones. It will block	736	necessary) and will handle those and any already outstanding ones. It
226	your process until at least one new event arrives.	737	will block your process until at least one new event arrives (which could
		738	be an event internal to libev itself, so there is no guarantee that a
		739	user-registered callback will be called), and will return after one
		740	iteration of the loop.
227		741
228	This flags value could be used to implement alternative looping	742	This is useful if you are waiting for some external event in conjunction
229	constructs, but the C<prepare> and C<check> watchers provide a better and	743	with something not expressible using other libev watchers (i.e. "roll your
230	more generic mechanism.	744	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		745	usually a better approach for this kind of thing.
		746
		747	Here are the gory details of what C<ev_loop> does:
		748
		749	- Before the first iteration, call any pending watchers.
		750	* If EVFLAG_FORKCHECK was used, check for a fork.
		751	- If a fork was detected (by any means), queue and call all fork watchers.
		752	- Queue and call all prepare watchers.
		753	- If we have been forked, detach and recreate the kernel state
		754	as to not disturb the other process.
		755	- Update the kernel state with all outstanding changes.
		756	- Update the "event loop time" (ev_now ()).
		757	- Calculate for how long to sleep or block, if at all
		758	(active idle watchers, EVLOOP_NONBLOCK or not having
		759	any active watchers at all will result in not sleeping).
		760	- Sleep if the I/O and timer collect interval say so.
		761	- Block the process, waiting for any events.
		762	- Queue all outstanding I/O (fd) events.
		763	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		764	- Queue all expired timers.
		765	- Queue all expired periodics.
		766	- Unless any events are pending now, queue all idle watchers.
		767	- Queue all check watchers.
		768	- Call all queued watchers in reverse order (i.e. check watchers first).
		769	Signals and child watchers are implemented as I/O watchers, and will
		770	be handled here by queueing them when their watcher gets executed.
		771	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		772	were used, or there are no active watchers, return, otherwise
		773	continue with step *.
		774
		775	Example: Queue some jobs and then loop until no events are outstanding
		776	anymore.
		777
		778	... queue jobs here, make sure they register event watchers as long
		779	... as they still have work to do (even an idle watcher will do..)
		780	ev_loop (my_loop, 0);
		781	... jobs done or somebody called unloop. yeah!
231		782
232	=item ev_unloop (loop, how)	783	=item ev_unloop (loop, how)
233		784
234	Can be used to make a call to C<ev_loop> return early. The C<how> argument	785	Can be used to make a call to C<ev_loop> return early (but only after it
		786	has processed all outstanding events). The C<how> argument must be either
235	must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop>	787	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
236	call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop>	788	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
237	calls return.	789
		790	This "unloop state" will be cleared when entering C<ev_loop> again.
		791
		792	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
238		793
239	=item ev_ref (loop)	794	=item ev_ref (loop)
240		795
241	=item ev_unref (loop)	796	=item ev_unref (loop)
242		797
243	Ref/unref can be used to add or remove a refcount on the event loop: Every	798	Ref/unref can be used to add or remove a reference count on the event
244	watcher keeps one reference. If you have a long-runing watcher you never	799	loop: Every watcher keeps one reference, and as long as the reference
245	unregister that should not keep ev_loop from running, ev_unref() after	800	count is nonzero, C<ev_loop> will not return on its own.
246	starting, and ev_ref() before stopping it. Libev itself uses this for	801
247	example for its internal signal pipe: It is not visible to you as a user	802	This is useful when you have a watcher that you never intend to
248	and should not keep C<ev_loop> from exiting if the work is done. It is	803	unregister, but that nevertheless should not keep C<ev_loop> from
		804	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		805	before stopping it.
		806
		807	As an example, libev itself uses this for its internal signal pipe: It
		808	is not visible to the libev user and should not keep C<ev_loop> from
		809	exiting if no event watchers registered by it are active. It is also an
249	also an excellent way to do this for generic recurring timers or from	810	excellent way to do this for generic recurring timers or from within
250	within third-party libraries. Just remember to unref after start and ref	811	third-party libraries. Just remember to I<unref after start> and I<ref
251	before stop.	812	before stop> (but only if the watcher wasn't active before, or was active
		813	before, respectively. Note also that libev might stop watchers itself
		814	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		815	in the callback).
		816
		817	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		818	running when nothing else is active.
		819
		820	ev_signal exitsig;
		821	ev_signal_init (&exitsig, sig_cb, SIGINT);
		822	ev_signal_start (loop, &exitsig);
		823	evf_unref (loop);
		824
		825	Example: For some weird reason, unregister the above signal handler again.
		826
		827	ev_ref (loop);
		828	ev_signal_stop (loop, &exitsig);
		829
		830	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		831
		832	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		833
		834	These advanced functions influence the time that libev will spend waiting
		835	for events. Both time intervals are by default C<0>, meaning that libev
		836	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		837	latency.
		838
		839	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		840	allows libev to delay invocation of I/O and timer/periodic callbacks
		841	to increase efficiency of loop iterations (or to increase power-saving
		842	opportunities).
		843
		844	The idea is that sometimes your program runs just fast enough to handle
		845	one (or very few) event(s) per loop iteration. While this makes the
		846	program responsive, it also wastes a lot of CPU time to poll for new
		847	events, especially with backends like C<select ()> which have a high
		848	overhead for the actual polling but can deliver many events at once.
		849
		850	By setting a higher I<io collect interval> you allow libev to spend more
		851	time collecting I/O events, so you can handle more events per iteration,
		852	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		853	C<ev_timer>) will be not affected. Setting this to a non-null value will
		854	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		855	sleep time ensures that libev will not poll for I/O events more often then
		856	once per this interval, on average.
		857
		858	Likewise, by setting a higher I<timeout collect interval> you allow libev
		859	to spend more time collecting timeouts, at the expense of increased
		860	latency/jitter/inexactness (the watcher callback will be called
		861	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		862	value will not introduce any overhead in libev.
		863
		864	Many (busy) programs can usually benefit by setting the I/O collect
		865	interval to a value near C<0.1> or so, which is often enough for
		866	interactive servers (of course not for games), likewise for timeouts. It
		867	usually doesn't make much sense to set it to a lower value than C<0.01>,
		868	as this approaches the timing granularity of most systems. Note that if
		869	you do transactions with the outside world and you can't increase the
		870	parallelity, then this setting will limit your transaction rate (if you
		871	need to poll once per transaction and the I/O collect interval is 0.01,
		872	then you can't do more than 100 transations per second).
		873
		874	Setting the I<timeout collect interval> can improve the opportunity for
		875	saving power, as the program will "bundle" timer callback invocations that
		876	are "near" in time together, by delaying some, thus reducing the number of
		877	times the process sleeps and wakes up again. Another useful technique to
		878	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		879	they fire on, say, one-second boundaries only.
		880
		881	Example: we only need 0.1s timeout granularity, and we wish not to poll
		882	more often than 100 times per second:
		883
		884	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		885	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		886
		887	=item ev_invoke_pending (loop)
		888
		889	This call will simply invoke all pending watchers while resetting their
		890	pending state. Normally, C<ev_loop> does this automatically when required,
		891	but when overriding the invoke callback this call comes handy.
		892
		893	=item int ev_pending_count (loop)
		894
		895	Returns the number of pending watchers - zero indicates that no watchers
		896	are pending.
		897
		898	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		899
		900	This overrides the invoke pending functionality of the loop: Instead of
		901	invoking all pending watchers when there are any, C<ev_loop> will call
		902	this callback instead. This is useful, for example, when you want to
		903	invoke the actual watchers inside another context (another thread etc.).
		904
		905	If you want to reset the callback, use C<ev_invoke_pending> as new
		906	callback.
		907
		908	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		909
		910	Sometimes you want to share the same loop between multiple threads. This
		911	can be done relatively simply by putting mutex_lock/unlock calls around
		912	each call to a libev function.
		913
		914	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		915	wait for it to return. One way around this is to wake up the loop via
		916	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		917	and I<acquire> callbacks on the loop.
		918
		919	When set, then C<release> will be called just before the thread is
		920	suspended waiting for new events, and C<acquire> is called just
		921	afterwards.
		922
		923	Ideally, C<release> will just call your mutex_unlock function, and
		924	C<acquire> will just call the mutex_lock function again.
		925
		926	While event loop modifications are allowed between invocations of
		927	C<release> and C<acquire> (that's their only purpose after all), no
		928	modifications done will affect the event loop, i.e. adding watchers will
		929	have no effect on the set of file descriptors being watched, or the time
		930	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		931	to take note of any changes you made.
		932
		933	In theory, threads executing C<ev_loop> will be async-cancel safe between
		934	invocations of C<release> and C<acquire>.
		935
		936	See also the locking example in the C<THREADS> section later in this
		937	document.
		938
		939	=item ev_set_userdata (loop, void *data)
		940
		941	=item ev_userdata (loop)
		942
		943	Set and retrieve a single C<void *> associated with a loop. When
		944	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		945	C<0.>
		946
		947	These two functions can be used to associate arbitrary data with a loop,
		948	and are intended solely for the C<invoke_pending_cb>, C<release> and
		949	C<acquire> callbacks described above, but of course can be (ab-)used for
		950	any other purpose as well.
		951
		952	=item ev_loop_verify (loop)
		953
		954	This function only does something when C<EV_VERIFY> support has been
		955	compiled in, which is the default for non-minimal builds. It tries to go
		956	through all internal structures and checks them for validity. If anything
		957	is found to be inconsistent, it will print an error message to standard
		958	error and call C<abort ()>.
		959
		960	This can be used to catch bugs inside libev itself: under normal
		961	circumstances, this function will never abort as of course libev keeps its
		962	data structures consistent.
252		963
253	=back	964	=back
254		965
		966
255	=head1 ANATOMY OF A WATCHER	967	=head1 ANATOMY OF A WATCHER
		968
		969	In the following description, uppercase C<TYPE> in names stands for the
		970	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		971	watchers and C<ev_io_start> for I/O watchers.
256		972
257	A watcher is a structure that you create and register to record your	973	A watcher is a structure that you create and register to record your
258	interest in some event. For instance, if you want to wait for STDIN to	974	interest in some event. For instance, if you want to wait for STDIN to
259	become readable, you would create an ev_io watcher for that:	975	become readable, you would create an C<ev_io> watcher for that:
260		976
261	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	977	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
262	{	978	{
263	ev_io_stop (w);	979	ev_io_stop (w);
264	ev_unloop (loop, EVUNLOOP_ALL);	980	ev_unloop (loop, EVUNLOOP_ALL);
265	}	981	}
266		982
267	struct ev_loop *loop = ev_default_loop (0);	983	struct ev_loop *loop = ev_default_loop (0);
		984
268	struct ev_io stdin_watcher;	985	ev_io stdin_watcher;
		986
269	ev_init (&stdin_watcher, my_cb);	987	ev_init (&stdin_watcher, my_cb);
270	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	988	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
271	ev_io_start (loop, &stdin_watcher);	989	ev_io_start (loop, &stdin_watcher);
		990
272	ev_loop (loop, 0);	991	ev_loop (loop, 0);
273		992
274	As you can see, you are responsible for allocating the memory for your	993	As you can see, you are responsible for allocating the memory for your
275	watcher structures (and it is usually a bad idea to do this on the stack,	994	watcher structures (and it is I<usually> a bad idea to do this on the
276	although this can sometimes be quite valid).	995	stack).
		996
		997	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		998	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
277		999
278	Each watcher structure must be initialised by a call to C<ev_init	1000	Each watcher structure must be initialised by a call to C<ev_init
279	(watcher *, callback)>, which expects a callback to be provided. This	1001	(watcher *, callback)>, which expects a callback to be provided. This
280	callback gets invoked each time the event occurs (or, in the case of io	1002	callback gets invoked each time the event occurs (or, in the case of I/O
281	watchers, each time the event loop detects that the file descriptor given	1003	watchers, each time the event loop detects that the file descriptor given
282	is readable and/or writable).	1004	is readable and/or writable).
283		1005
284	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1006	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
285	with arguments specific to this watcher type. There is also a macro	1007	macro to configure it, with arguments specific to the watcher type. There
286	to combine initialisation and setting in one call: C<< ev_<type>_init	1008	is also a macro to combine initialisation and setting in one call: C<<
287	(watcher *, callback, ...) >>.	1009	ev_TYPE_init (watcher *, callback, ...) >>.
288		1010
289	To make the watcher actually watch out for events, you have to start it	1011	To make the watcher actually watch out for events, you have to start it
290	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1012	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
291	*) >>), and you can stop watching for events at any time by calling the	1013	*) >>), and you can stop watching for events at any time by calling the
292	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1014	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
293		1015
294	As long as your watcher is active (has been started but not stopped) you	1016	As long as your watcher is active (has been started but not stopped) you
295	must not touch the values stored in it. Most specifically you must never	1017	must not touch the values stored in it. Most specifically you must never
296	reinitialise it or call its set method.	1018	reinitialise it or call its C<ev_TYPE_set> macro.
297
298	You cna check whether an event is active by calling the C<ev_is_active
299	(watcher *)> macro. To see whether an event is outstanding (but the
300	callback for it has not been called yet) you cna use the C<ev_is_pending
301	(watcher *)> macro.
302		1019
303	Each and every callback receives the event loop pointer as first, the	1020	Each and every callback receives the event loop pointer as first, the
304	registered watcher structure as second, and a bitset of received events as	1021	registered watcher structure as second, and a bitset of received events as
305	third argument.	1022	third argument.
306		1023
307	The rceeived events usually include a single bit per event type received	1024	The received events usually include a single bit per event type received
308	(you can receive multiple events at the same time). The possible bit masks	1025	(you can receive multiple events at the same time). The possible bit masks
309	are:	1026	are:
310		1027
311	=over 4	1028	=over 4
312		1029
313	=item EV_READ	1030	=item C<EV_READ>
314		1031
315	=item EV_WRITE	1032	=item C<EV_WRITE>
316		1033
317	The file descriptor in the ev_io watcher has become readable and/or	1034	The file descriptor in the C<ev_io> watcher has become readable and/or
318	writable.	1035	writable.
319		1036
320	=item EV_TIMEOUT	1037	=item C<EV_TIMEOUT>
321		1038
322	The ev_timer watcher has timed out.	1039	The C<ev_timer> watcher has timed out.
323		1040
324	=item EV_PERIODIC	1041	=item C<EV_PERIODIC>
325		1042
326	The ev_periodic watcher has timed out.	1043	The C<ev_periodic> watcher has timed out.
327		1044
328	=item EV_SIGNAL	1045	=item C<EV_SIGNAL>
329		1046
330	The signal specified in the ev_signal watcher has been received by a thread.	1047	The signal specified in the C<ev_signal> watcher has been received by a thread.
331		1048
332	=item EV_CHILD	1049	=item C<EV_CHILD>
333		1050
334	The pid specified in the ev_child watcher has received a status change.	1051	The pid specified in the C<ev_child> watcher has received a status change.
335		1052
		1053	=item C<EV_STAT>
		1054
		1055	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1056
336	=item EV_IDLE	1057	=item C<EV_IDLE>
337		1058
338	The ev_idle watcher has determined that you have nothing better to do.	1059	The C<ev_idle> watcher has determined that you have nothing better to do.
339		1060
340	=item EV_PREPARE	1061	=item C<EV_PREPARE>
341		1062
342	=item EV_CHECK	1063	=item C<EV_CHECK>
343		1064
344	All ev_prepare watchers are invoked just I<before> C<ev_loop> starts	1065	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
345	to gather new events, and all ev_check watchers are invoked just after	1066	to gather new events, and all C<ev_check> watchers are invoked just after
346	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1067	C<ev_loop> has gathered them, but before it invokes any callbacks for any
347	received events. Callbacks of both watcher types can start and stop as	1068	received events. Callbacks of both watcher types can start and stop as
348	many watchers as they want, and all of them will be taken into account	1069	many watchers as they want, and all of them will be taken into account
349	(for example, a ev_prepare watcher might start an idle watcher to keep	1070	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
350	C<ev_loop> from blocking).	1071	C<ev_loop> from blocking).
351		1072
		1073	=item C<EV_EMBED>
		1074
		1075	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1076
		1077	=item C<EV_FORK>
		1078
		1079	The event loop has been resumed in the child process after fork (see
		1080	C<ev_fork>).
		1081
		1082	=item C<EV_ASYNC>
		1083
		1084	The given async watcher has been asynchronously notified (see C<ev_async>).
		1085
		1086	=item C<EV_CUSTOM>
		1087
		1088	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1089	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1090
352	=item EV_ERROR	1091	=item C<EV_ERROR>
353		1092
354	An unspecified error has occured, the watcher has been stopped. This might	1093	An unspecified error has occurred, the watcher has been stopped. This might
355	happen because the watcher could not be properly started because libev	1094	happen because the watcher could not be properly started because libev
356	ran out of memory, a file descriptor was found to be closed or any other	1095	ran out of memory, a file descriptor was found to be closed or any other
		1096	problem. Libev considers these application bugs.
		1097
357	problem. You best act on it by reporting the problem and somehow coping	1098	You best act on it by reporting the problem and somehow coping with the
358	with the watcher being stopped.	1099	watcher being stopped. Note that well-written programs should not receive
		1100	an error ever, so when your watcher receives it, this usually indicates a
		1101	bug in your program.
359		1102
360	Libev will usually signal a few "dummy" events together with an error,	1103	Libev will usually signal a few "dummy" events together with an error, for
361	for example it might indicate that a fd is readable or writable, and if	1104	example it might indicate that a fd is readable or writable, and if your
362	your callbacks is well-written it can just attempt the operation and cope	1105	callbacks is well-written it can just attempt the operation and cope with
363	with the error from read() or write(). This will not work in multithreaded	1106	the error from read() or write(). This will not work in multi-threaded
364	programs, though, so beware.	1107	programs, though, as the fd could already be closed and reused for another
		1108	thing, so beware.
365		1109
366	=back	1110	=back
367		1111
		1112	=head2 GENERIC WATCHER FUNCTIONS
		1113
		1114	=over 4
		1115
		1116	=item C<ev_init> (ev_TYPE *watcher, callback)
		1117
		1118	This macro initialises the generic portion of a watcher. The contents
		1119	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1120	the generic parts of the watcher are initialised, you I<need> to call
		1121	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1122	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1123	which rolls both calls into one.
		1124
		1125	You can reinitialise a watcher at any time as long as it has been stopped
		1126	(or never started) and there are no pending events outstanding.
		1127
		1128	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1129	int revents)>.
		1130
		1131	Example: Initialise an C<ev_io> watcher in two steps.
		1132
		1133	ev_io w;
		1134	ev_init (&w, my_cb);
		1135	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1136
		1137	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1138
		1139	This macro initialises the type-specific parts of a watcher. You need to
		1140	call C<ev_init> at least once before you call this macro, but you can
		1141	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1142	macro on a watcher that is active (it can be pending, however, which is a
		1143	difference to the C<ev_init> macro).
		1144
		1145	Although some watcher types do not have type-specific arguments
		1146	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1147
		1148	See C<ev_init>, above, for an example.
		1149
		1150	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1151
		1152	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1153	calls into a single call. This is the most convenient method to initialise
		1154	a watcher. The same limitations apply, of course.
		1155
		1156	Example: Initialise and set an C<ev_io> watcher in one step.
		1157
		1158	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1159
		1160	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1161
		1162	Starts (activates) the given watcher. Only active watchers will receive
		1163	events. If the watcher is already active nothing will happen.
		1164
		1165	Example: Start the C<ev_io> watcher that is being abused as example in this
		1166	whole section.
		1167
		1168	ev_io_start (EV_DEFAULT_UC, &w);
		1169
		1170	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1171
		1172	Stops the given watcher if active, and clears the pending status (whether
		1173	the watcher was active or not).
		1174
		1175	It is possible that stopped watchers are pending - for example,
		1176	non-repeating timers are being stopped when they become pending - but
		1177	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1178	pending. If you want to free or reuse the memory used by the watcher it is
		1179	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1180
		1181	=item bool ev_is_active (ev_TYPE *watcher)
		1182
		1183	Returns a true value iff the watcher is active (i.e. it has been started
		1184	and not yet been stopped). As long as a watcher is active you must not modify
		1185	it.
		1186
		1187	=item bool ev_is_pending (ev_TYPE *watcher)
		1188
		1189	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1190	events but its callback has not yet been invoked). As long as a watcher
		1191	is pending (but not active) you must not call an init function on it (but
		1192	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1193	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1194	it).
		1195
		1196	=item callback ev_cb (ev_TYPE *watcher)
		1197
		1198	Returns the callback currently set on the watcher.
		1199
		1200	=item ev_cb_set (ev_TYPE *watcher, callback)
		1201
		1202	Change the callback. You can change the callback at virtually any time
		1203	(modulo threads).
		1204
		1205	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1206
		1207	=item int ev_priority (ev_TYPE *watcher)
		1208
		1209	Set and query the priority of the watcher. The priority is a small
		1210	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1211	(default: C<-2>). Pending watchers with higher priority will be invoked
		1212	before watchers with lower priority, but priority will not keep watchers
		1213	from being executed (except for C<ev_idle> watchers).
		1214
		1215	If you need to suppress invocation when higher priority events are pending
		1216	you need to look at C<ev_idle> watchers, which provide this functionality.
		1217
		1218	You I<must not> change the priority of a watcher as long as it is active or
		1219	pending.
		1220
		1221	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1222	fine, as long as you do not mind that the priority value you query might
		1223	or might not have been clamped to the valid range.
		1224
		1225	The default priority used by watchers when no priority has been set is
		1226	always C<0>, which is supposed to not be too high and not be too low :).
		1227
		1228	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1229	priorities.
		1230
		1231	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1232
		1233	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1234	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1235	can deal with that fact, as both are simply passed through to the
		1236	callback.
		1237
		1238	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1239
		1240	If the watcher is pending, this function clears its pending status and
		1241	returns its C<revents> bitset (as if its callback was invoked). If the
		1242	watcher isn't pending it does nothing and returns C<0>.
		1243
		1244	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1245	callback to be invoked, which can be accomplished with this function.
		1246
		1247	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1248
		1249	Feeds the given event set into the event loop, as if the specified event
		1250	had happened for the specified watcher (which must be a pointer to an
		1251	initialised but not necessarily started event watcher). Obviously you must
		1252	not free the watcher as long as it has pending events.
		1253
		1254	Stopping the watcher, letting libev invoke it, or calling
		1255	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1256	not started in the first place.
		1257
		1258	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1259	functions that do not need a watcher.
		1260
		1261	=back
		1262
		1263
368	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1264	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
369		1265
370	Each watcher has, by default, a member C<void *data> that you can change	1266	Each watcher has, by default, a member C<void *data> that you can change
371	and read at any time, libev will completely ignore it. This cna be used	1267	and read at any time: libev will completely ignore it. This can be used
372	to associate arbitrary data with your watcher. If you need more data and	1268	to associate arbitrary data with your watcher. If you need more data and
373	don't want to allocate memory and store a pointer to it in that data	1269	don't want to allocate memory and store a pointer to it in that data
374	member, you can also "subclass" the watcher type and provide your own	1270	member, you can also "subclass" the watcher type and provide your own
375	data:	1271	data:
376		1272
377	struct my_io	1273	struct my_io
378	{	1274	{
379	struct ev_io io;	1275	ev_io io;
380	int otherfd;	1276	int otherfd;
381	void *somedata;	1277	void *somedata;
382	struct whatever *mostinteresting;	1278	struct whatever *mostinteresting;
383	}	1279	};
		1280
		1281	...
		1282	struct my_io w;
		1283	ev_io_init (&w.io, my_cb, fd, EV_READ);
384		1284
385	And since your callback will be called with a pointer to the watcher, you	1285	And since your callback will be called with a pointer to the watcher, you
386	can cast it back to your own type:	1286	can cast it back to your own type:
387		1287
388	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1288	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
389	{	1289	{
390	struct my_io *w = (struct my_io *)w_;	1290	struct my_io *w = (struct my_io *)w_;
391	...	1291	...
392	}	1292	}
393		1293
394	More interesting and less C-conformant ways of catsing your callback type	1294	More interesting and less C-conformant ways of casting your callback type
395	have been omitted....	1295	instead have been omitted.
		1296
		1297	Another common scenario is to use some data structure with multiple
		1298	embedded watchers:
		1299
		1300	struct my_biggy
		1301	{
		1302	int some_data;
		1303	ev_timer t1;
		1304	ev_timer t2;
		1305	}
		1306
		1307	In this case getting the pointer to C<my_biggy> is a bit more
		1308	complicated: Either you store the address of your C<my_biggy> struct
		1309	in the C<data> member of the watcher (for woozies), or you need to use
		1310	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1311	programmers):
		1312
		1313	#include <stddef.h>
		1314
		1315	static void
		1316	t1_cb (EV_P_ ev_timer *w, int revents)
		1317	{
		1318	struct my_biggy big = (struct my_biggy *)
		1319	(((char *)w) - offsetof (struct my_biggy, t1));
		1320	}
		1321
		1322	static void
		1323	t2_cb (EV_P_ ev_timer *w, int revents)
		1324	{
		1325	struct my_biggy big = (struct my_biggy *)
		1326	(((char *)w) - offsetof (struct my_biggy, t2));
		1327	}
		1328
		1329	=head2 WATCHER PRIORITY MODELS
		1330
		1331	Many event loops support I<watcher priorities>, which are usually small
		1332	integers that influence the ordering of event callback invocation
		1333	between watchers in some way, all else being equal.
		1334
		1335	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1336	description for the more technical details such as the actual priority
		1337	range.
		1338
		1339	There are two common ways how these these priorities are being interpreted
		1340	by event loops:
		1341
		1342	In the more common lock-out model, higher priorities "lock out" invocation
		1343	of lower priority watchers, which means as long as higher priority
		1344	watchers receive events, lower priority watchers are not being invoked.
		1345
		1346	The less common only-for-ordering model uses priorities solely to order
		1347	callback invocation within a single event loop iteration: Higher priority
		1348	watchers are invoked before lower priority ones, but they all get invoked
		1349	before polling for new events.
		1350
		1351	Libev uses the second (only-for-ordering) model for all its watchers
		1352	except for idle watchers (which use the lock-out model).
		1353
		1354	The rationale behind this is that implementing the lock-out model for
		1355	watchers is not well supported by most kernel interfaces, and most event
		1356	libraries will just poll for the same events again and again as long as
		1357	their callbacks have not been executed, which is very inefficient in the
		1358	common case of one high-priority watcher locking out a mass of lower
		1359	priority ones.
		1360
		1361	Static (ordering) priorities are most useful when you have two or more
		1362	watchers handling the same resource: a typical usage example is having an
		1363	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1364	timeouts. Under load, data might be received while the program handles
		1365	other jobs, but since timers normally get invoked first, the timeout
		1366	handler will be executed before checking for data. In that case, giving
		1367	the timer a lower priority than the I/O watcher ensures that I/O will be
		1368	handled first even under adverse conditions (which is usually, but not
		1369	always, what you want).
		1370
		1371	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1372	will only be executed when no same or higher priority watchers have
		1373	received events, they can be used to implement the "lock-out" model when
		1374	required.
		1375
		1376	For example, to emulate how many other event libraries handle priorities,
		1377	you can associate an C<ev_idle> watcher to each such watcher, and in
		1378	the normal watcher callback, you just start the idle watcher. The real
		1379	processing is done in the idle watcher callback. This causes libev to
		1380	continously poll and process kernel event data for the watcher, but when
		1381	the lock-out case is known to be rare (which in turn is rare :), this is
		1382	workable.
		1383
		1384	Usually, however, the lock-out model implemented that way will perform
		1385	miserably under the type of load it was designed to handle. In that case,
		1386	it might be preferable to stop the real watcher before starting the
		1387	idle watcher, so the kernel will not have to process the event in case
		1388	the actual processing will be delayed for considerable time.
		1389
		1390	Here is an example of an I/O watcher that should run at a strictly lower
		1391	priority than the default, and which should only process data when no
		1392	other events are pending:
		1393
		1394	ev_idle idle; // actual processing watcher
		1395	ev_io io; // actual event watcher
		1396
		1397	static void
		1398	io_cb (EV_P_ ev_io *w, int revents)
		1399	{
		1400	// stop the I/O watcher, we received the event, but
		1401	// are not yet ready to handle it.
		1402	ev_io_stop (EV_A_ w);
		1403
		1404	// start the idle watcher to ahndle the actual event.
		1405	// it will not be executed as long as other watchers
		1406	// with the default priority are receiving events.
		1407	ev_idle_start (EV_A_ &idle);
		1408	}
		1409
		1410	static void
		1411	idle_cb (EV_P_ ev_idle *w, int revents)
		1412	{
		1413	// actual processing
		1414	read (STDIN_FILENO, ...);
		1415
		1416	// have to start the I/O watcher again, as
		1417	// we have handled the event
		1418	ev_io_start (EV_P_ &io);
		1419	}
		1420
		1421	// initialisation
		1422	ev_idle_init (&idle, idle_cb);
		1423	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1424	ev_io_start (EV_DEFAULT_ &io);
		1425
		1426	In the "real" world, it might also be beneficial to start a timer, so that
		1427	low-priority connections can not be locked out forever under load. This
		1428	enables your program to keep a lower latency for important connections
		1429	during short periods of high load, while not completely locking out less
		1430	important ones.
396		1431
397		1432
398	=head1 WATCHER TYPES	1433	=head1 WATCHER TYPES
399		1434
400	This section describes each watcher in detail, but will not repeat	1435	This section describes each watcher in detail, but will not repeat
401	information given in the last section.	1436	information given in the last section. Any initialisation/set macros,
		1437	functions and members specific to the watcher type are explained.
402		1438
		1439	Members are additionally marked with either I<[read-only]>, meaning that,
		1440	while the watcher is active, you can look at the member and expect some
		1441	sensible content, but you must not modify it (you can modify it while the
		1442	watcher is stopped to your hearts content), or I<[read-write]>, which
		1443	means you can expect it to have some sensible content while the watcher
		1444	is active, but you can also modify it. Modifying it may not do something
		1445	sensible or take immediate effect (or do anything at all), but libev will
		1446	not crash or malfunction in any way.
		1447
		1448
403	=head2 struct ev_io - is my file descriptor readable or writable	1449	=head2 C<ev_io> - is this file descriptor readable or writable?
404		1450
405	I/O watchers check whether a file descriptor is readable or writable	1451	I/O watchers check whether a file descriptor is readable or writable
406	in each iteration of the event loop (This behaviour is called	1452	in each iteration of the event loop, or, more precisely, when reading
407	level-triggering because you keep receiving events as long as the	1453	would not block the process and writing would at least be able to write
408	condition persists. Remember you cna stop the watcher if you don't want to	1454	some data. This behaviour is called level-triggering because you keep
409	act on the event and neither want to receive future events).	1455	receiving events as long as the condition persists. Remember you can stop
		1456	the watcher if you don't want to act on the event and neither want to
		1457	receive future events.
		1458
		1459	In general you can register as many read and/or write event watchers per
		1460	fd as you want (as long as you don't confuse yourself). Setting all file
		1461	descriptors to non-blocking mode is also usually a good idea (but not
		1462	required if you know what you are doing).
		1463
		1464	If you cannot use non-blocking mode, then force the use of a
		1465	known-to-be-good backend (at the time of this writing, this includes only
		1466	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1467	descriptors for which non-blocking operation makes no sense (such as
		1468	files) - libev doesn't guarentee any specific behaviour in that case.
		1469
		1470	Another thing you have to watch out for is that it is quite easy to
		1471	receive "spurious" readiness notifications, that is your callback might
		1472	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1473	because there is no data. Not only are some backends known to create a
		1474	lot of those (for example Solaris ports), it is very easy to get into
		1475	this situation even with a relatively standard program structure. Thus
		1476	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1477	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1478
		1479	If you cannot run the fd in non-blocking mode (for example you should
		1480	not play around with an Xlib connection), then you have to separately
		1481	re-test whether a file descriptor is really ready with a known-to-be good
		1482	interface such as poll (fortunately in our Xlib example, Xlib already
		1483	does this on its own, so its quite safe to use). Some people additionally
		1484	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1485	indefinitely.
		1486
		1487	But really, best use non-blocking mode.
		1488
		1489	=head3 The special problem of disappearing file descriptors
		1490
		1491	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1492	descriptor (either due to calling C<close> explicitly or any other means,
		1493	such as C<dup2>). The reason is that you register interest in some file
		1494	descriptor, but when it goes away, the operating system will silently drop
		1495	this interest. If another file descriptor with the same number then is
		1496	registered with libev, there is no efficient way to see that this is, in
		1497	fact, a different file descriptor.
		1498
		1499	To avoid having to explicitly tell libev about such cases, libev follows
		1500	the following policy: Each time C<ev_io_set> is being called, libev
		1501	will assume that this is potentially a new file descriptor, otherwise
		1502	it is assumed that the file descriptor stays the same. That means that
		1503	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1504	descriptor even if the file descriptor number itself did not change.
		1505
		1506	This is how one would do it normally anyway, the important point is that
		1507	the libev application should not optimise around libev but should leave
		1508	optimisations to libev.
		1509
		1510	=head3 The special problem of dup'ed file descriptors
		1511
		1512	Some backends (e.g. epoll), cannot register events for file descriptors,
		1513	but only events for the underlying file descriptions. That means when you
		1514	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1515	events for them, only one file descriptor might actually receive events.
		1516
		1517	There is no workaround possible except not registering events
		1518	for potentially C<dup ()>'ed file descriptors, or to resort to
		1519	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1520
		1521	=head3 The special problem of fork
		1522
		1523	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1524	useless behaviour. Libev fully supports fork, but needs to be told about
		1525	it in the child.
		1526
		1527	To support fork in your programs, you either have to call
		1528	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1529	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1530	C<EVBACKEND_POLL>.
		1531
		1532	=head3 The special problem of SIGPIPE
		1533
		1534	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1535	when writing to a pipe whose other end has been closed, your program gets
		1536	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1537	this is sensible behaviour, for daemons, this is usually undesirable.
		1538
		1539	So when you encounter spurious, unexplained daemon exits, make sure you
		1540	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1541	somewhere, as that would have given you a big clue).
		1542
		1543
		1544	=head3 Watcher-Specific Functions
410		1545
411	=over 4	1546	=over 4
412		1547
413	=item ev_io_init (ev_io *, callback, int fd, int events)	1548	=item ev_io_init (ev_io *, callback, int fd, int events)
414		1549
415	=item ev_io_set (ev_io *, int fd, int events)	1550	=item ev_io_set (ev_io *, int fd, int events)
416		1551
417	Configures an ev_io watcher. The fd is the file descriptor to rceeive	1552	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
418	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1553	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
419	EV_WRITE> to receive the given events.	1554	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1555
		1556	=item int fd [read-only]
		1557
		1558	The file descriptor being watched.
		1559
		1560	=item int events [read-only]
		1561
		1562	The events being watched.
420		1563
421	=back	1564	=back
422		1565
		1566	=head3 Examples
		1567
		1568	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1569	readable, but only once. Since it is likely line-buffered, you could
		1570	attempt to read a whole line in the callback.
		1571
		1572	static void
		1573	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1574	{
		1575	ev_io_stop (loop, w);
		1576	.. read from stdin here (or from w->fd) and handle any I/O errors
		1577	}
		1578
		1579	...
		1580	struct ev_loop *loop = ev_default_init (0);
		1581	ev_io stdin_readable;
		1582	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1583	ev_io_start (loop, &stdin_readable);
		1584	ev_loop (loop, 0);
		1585
		1586
423	=head2 struct ev_timer - relative and optionally recurring timeouts	1587	=head2 C<ev_timer> - relative and optionally repeating timeouts
424		1588
425	Timer watchers are simple relative timers that generate an event after a	1589	Timer watchers are simple relative timers that generate an event after a
426	given time, and optionally repeating in regular intervals after that.	1590	given time, and optionally repeating in regular intervals after that.
427		1591
428	The timers are based on real time, that is, if you register an event that	1592	The timers are based on real time, that is, if you register an event that
429	times out after an hour and youreset your system clock to last years	1593	times out after an hour and you reset your system clock to January last
430	time, it will still time out after (roughly) and hour. "Roughly" because	1594	year, it will still time out after (roughly) one hour. "Roughly" because
431	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1595	detecting time jumps is hard, and some inaccuracies are unavoidable (the
432	monotonic clock option helps a lot here).	1596	monotonic clock option helps a lot here).
433		1597
		1598	The callback is guaranteed to be invoked only I<after> its timeout has
		1599	passed (not I<at>, so on systems with very low-resolution clocks this
		1600	might introduce a small delay). If multiple timers become ready during the
		1601	same loop iteration then the ones with earlier time-out values are invoked
		1602	before ones of the same priority with later time-out values (but this is
		1603	no longer true when a callback calls C<ev_loop> recursively).
		1604
		1605	=head3 Be smart about timeouts
		1606
		1607	Many real-world problems involve some kind of timeout, usually for error
		1608	recovery. A typical example is an HTTP request - if the other side hangs,
		1609	you want to raise some error after a while.
		1610
		1611	What follows are some ways to handle this problem, from obvious and
		1612	inefficient to smart and efficient.
		1613
		1614	In the following, a 60 second activity timeout is assumed - a timeout that
		1615	gets reset to 60 seconds each time there is activity (e.g. each time some
		1616	data or other life sign was received).
		1617
434	=over 4	1618	=over 4
435		1619
		1620	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1621
		1622	This is the most obvious, but not the most simple way: In the beginning,
		1623	start the watcher:
		1624
		1625	ev_timer_init (timer, callback, 60., 0.);
		1626	ev_timer_start (loop, timer);
		1627
		1628	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1629	and start it again:
		1630
		1631	ev_timer_stop (loop, timer);
		1632	ev_timer_set (timer, 60., 0.);
		1633	ev_timer_start (loop, timer);
		1634
		1635	This is relatively simple to implement, but means that each time there is
		1636	some activity, libev will first have to remove the timer from its internal
		1637	data structure and then add it again. Libev tries to be fast, but it's
		1638	still not a constant-time operation.
		1639
		1640	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1641
		1642	This is the easiest way, and involves using C<ev_timer_again> instead of
		1643	C<ev_timer_start>.
		1644
		1645	To implement this, configure an C<ev_timer> with a C<repeat> value
		1646	of C<60> and then call C<ev_timer_again> at start and each time you
		1647	successfully read or write some data. If you go into an idle state where
		1648	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1649	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1650
		1651	That means you can ignore both the C<ev_timer_start> function and the
		1652	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1653	member and C<ev_timer_again>.
		1654
		1655	At start:
		1656
		1657	ev_init (timer, callback);
		1658	timer->repeat = 60.;
		1659	ev_timer_again (loop, timer);
		1660
		1661	Each time there is some activity:
		1662
		1663	ev_timer_again (loop, timer);
		1664
		1665	It is even possible to change the time-out on the fly, regardless of
		1666	whether the watcher is active or not:
		1667
		1668	timer->repeat = 30.;
		1669	ev_timer_again (loop, timer);
		1670
		1671	This is slightly more efficient then stopping/starting the timer each time
		1672	you want to modify its timeout value, as libev does not have to completely
		1673	remove and re-insert the timer from/into its internal data structure.
		1674
		1675	It is, however, even simpler than the "obvious" way to do it.
		1676
		1677	=item 3. Let the timer time out, but then re-arm it as required.
		1678
		1679	This method is more tricky, but usually most efficient: Most timeouts are
		1680	relatively long compared to the intervals between other activity - in
		1681	our example, within 60 seconds, there are usually many I/O events with
		1682	associated activity resets.
		1683
		1684	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1685	but remember the time of last activity, and check for a real timeout only
		1686	within the callback:
		1687
		1688	ev_tstamp last_activity; // time of last activity
		1689
		1690	static void
		1691	callback (EV_P_ ev_timer *w, int revents)
		1692	{
		1693	ev_tstamp now = ev_now (EV_A);
		1694	ev_tstamp timeout = last_activity + 60.;
		1695
		1696	// if last_activity + 60. is older than now, we did time out
		1697	if (timeout < now)
		1698	{
		1699	// timeout occured, take action
		1700	}
		1701	else
		1702	{
		1703	// callback was invoked, but there was some activity, re-arm
		1704	// the watcher to fire in last_activity + 60, which is
		1705	// guaranteed to be in the future, so "again" is positive:
		1706	w->repeat = timeout - now;
		1707	ev_timer_again (EV_A_ w);
		1708	}
		1709	}
		1710
		1711	To summarise the callback: first calculate the real timeout (defined
		1712	as "60 seconds after the last activity"), then check if that time has
		1713	been reached, which means something I<did>, in fact, time out. Otherwise
		1714	the callback was invoked too early (C<timeout> is in the future), so
		1715	re-schedule the timer to fire at that future time, to see if maybe we have
		1716	a timeout then.
		1717
		1718	Note how C<ev_timer_again> is used, taking advantage of the
		1719	C<ev_timer_again> optimisation when the timer is already running.
		1720
		1721	This scheme causes more callback invocations (about one every 60 seconds
		1722	minus half the average time between activity), but virtually no calls to
		1723	libev to change the timeout.
		1724
		1725	To start the timer, simply initialise the watcher and set C<last_activity>
		1726	to the current time (meaning we just have some activity :), then call the
		1727	callback, which will "do the right thing" and start the timer:
		1728
		1729	ev_init (timer, callback);
		1730	last_activity = ev_now (loop);
		1731	callback (loop, timer, EV_TIMEOUT);
		1732
		1733	And when there is some activity, simply store the current time in
		1734	C<last_activity>, no libev calls at all:
		1735
		1736	last_actiivty = ev_now (loop);
		1737
		1738	This technique is slightly more complex, but in most cases where the
		1739	time-out is unlikely to be triggered, much more efficient.
		1740
		1741	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1742	callback :) - just change the timeout and invoke the callback, which will
		1743	fix things for you.
		1744
		1745	=item 4. Wee, just use a double-linked list for your timeouts.
		1746
		1747	If there is not one request, but many thousands (millions...), all
		1748	employing some kind of timeout with the same timeout value, then one can
		1749	do even better:
		1750
		1751	When starting the timeout, calculate the timeout value and put the timeout
		1752	at the I<end> of the list.
		1753
		1754	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1755	the list is expected to fire (for example, using the technique #3).
		1756
		1757	When there is some activity, remove the timer from the list, recalculate
		1758	the timeout, append it to the end of the list again, and make sure to
		1759	update the C<ev_timer> if it was taken from the beginning of the list.
		1760
		1761	This way, one can manage an unlimited number of timeouts in O(1) time for
		1762	starting, stopping and updating the timers, at the expense of a major
		1763	complication, and having to use a constant timeout. The constant timeout
		1764	ensures that the list stays sorted.
		1765
		1766	=back
		1767
		1768	So which method the best?
		1769
		1770	Method #2 is a simple no-brain-required solution that is adequate in most
		1771	situations. Method #3 requires a bit more thinking, but handles many cases
		1772	better, and isn't very complicated either. In most case, choosing either
		1773	one is fine, with #3 being better in typical situations.
		1774
		1775	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1776	rather complicated, but extremely efficient, something that really pays
		1777	off after the first million or so of active timers, i.e. it's usually
		1778	overkill :)
		1779
		1780	=head3 The special problem of time updates
		1781
		1782	Establishing the current time is a costly operation (it usually takes at
		1783	least two system calls): EV therefore updates its idea of the current
		1784	time only before and after C<ev_loop> collects new events, which causes a
		1785	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1786	lots of events in one iteration.
		1787
		1788	The relative timeouts are calculated relative to the C<ev_now ()>
		1789	time. This is usually the right thing as this timestamp refers to the time
		1790	of the event triggering whatever timeout you are modifying/starting. If
		1791	you suspect event processing to be delayed and you I<need> to base the
		1792	timeout on the current time, use something like this to adjust for this:
		1793
		1794	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1795
		1796	If the event loop is suspended for a long time, you can also force an
		1797	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		1798	()>.
		1799
		1800	=head3 The special problems of suspended animation
		1801
		1802	When you leave the server world it is quite customary to hit machines that
		1803	can suspend/hibernate - what happens to the clocks during such a suspend?
		1804
		1805	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1806	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1807	to run until the system is suspended, but they will not advance while the
		1808	system is suspended. That means, on resume, it will be as if the program
		1809	was frozen for a few seconds, but the suspend time will not be counted
		1810	towards C<ev_timer> when a monotonic clock source is used. The real time
		1811	clock advanced as expected, but if it is used as sole clocksource, then a
		1812	long suspend would be detected as a time jump by libev, and timers would
		1813	be adjusted accordingly.
		1814
		1815	I would not be surprised to see different behaviour in different between
		1816	operating systems, OS versions or even different hardware.
		1817
		1818	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1819	time jump in the monotonic clocks and the realtime clock. If the program
		1820	is suspended for a very long time, and monotonic clock sources are in use,
		1821	then you can expect C<ev_timer>s to expire as the full suspension time
		1822	will be counted towards the timers. When no monotonic clock source is in
		1823	use, then libev will again assume a timejump and adjust accordingly.
		1824
		1825	It might be beneficial for this latter case to call C<ev_suspend>
		1826	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1827	deterministic behaviour in this case (you can do nothing against
		1828	C<SIGSTOP>).
		1829
		1830	=head3 Watcher-Specific Functions and Data Members
		1831
		1832	=over 4
		1833
436	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1834	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
437		1835
438	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1836	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
439		1837
440	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1838	Configure the timer to trigger after C<after> seconds. If C<repeat>
441	C<0.>, then it will automatically be stopped. If it is positive, then the	1839	is C<0.>, then it will automatically be stopped once the timeout is
442	timer will automatically be configured to trigger again C<repeat> seconds	1840	reached. If it is positive, then the timer will automatically be
443	later, again, and again, until stopped manually.	1841	configured to trigger again C<repeat> seconds later, again, and again,
		1842	until stopped manually.
444		1843
445	The timer itself will do a best-effort at avoiding drift, that is, if you	1844	The timer itself will do a best-effort at avoiding drift, that is, if
446	configure a timer to trigger every 10 seconds, then it will trigger at	1845	you configure a timer to trigger every 10 seconds, then it will normally
447	exactly 10 second intervals. If, however, your program cannot keep up with	1846	trigger at exactly 10 second intervals. If, however, your program cannot
448	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1847	keep up with the timer (because it takes longer than those 10 seconds to
449	timer will not fire more than once per event loop iteration.	1848	do stuff) the timer will not fire more than once per event loop iteration.
450		1849
451	=item ev_timer_again (loop)	1850	=item ev_timer_again (loop, ev_timer *)
452		1851
453	This will act as if the timer timed out and restart it again if it is	1852	This will act as if the timer timed out and restart it again if it is
454	repeating. The exact semantics are:	1853	repeating. The exact semantics are:
455		1854
		1855	If the timer is pending, its pending status is cleared.
		1856
456	If the timer is started but nonrepeating, stop it.	1857	If the timer is started but non-repeating, stop it (as if it timed out).
457		1858
458	If the timer is repeating, either start it if necessary (with the repeat	1859	If the timer is repeating, either start it if necessary (with the
459	value), or reset the running timer to the repeat value.	1860	C<repeat> value), or reset the running timer to the C<repeat> value.
460		1861
461	This sounds a bit complicated, but here is a useful and typical	1862	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
462	example: Imagine you have a tcp connection and you want a so-called idle	1863	usage example.
463	timeout, that is, you want to be called when there have been, say, 60	1864
464	seconds of inactivity on the socket. The easiest way to do this is to	1865	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
465	configure an ev_timer with after=repeat=60 and calling ev_timer_again each	1866
466	time you successfully read or write some data. If you go into an idle	1867	Returns the remaining time until a timer fires. If the timer is active,
467	state where you do not expect data to travel on the socket, you can stop	1868	then this time is relative to the current event loop time, otherwise it's
468	the timer, and again will automatically restart it if need be.	1869	the timeout value currently configured.
		1870
		1871	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1872	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1873	will return C<4>. When the timer expires and is restarted, it will return
		1874	roughly C<7> (likely slightly less as callback invocation takes some time,
		1875	too), and so on.
		1876
		1877	=item ev_tstamp repeat [read-write]
		1878
		1879	The current C<repeat> value. Will be used each time the watcher times out
		1880	or C<ev_timer_again> is called, and determines the next timeout (if any),
		1881	which is also when any modifications are taken into account.
469		1882
470	=back	1883	=back
471		1884
		1885	=head3 Examples
		1886
		1887	Example: Create a timer that fires after 60 seconds.
		1888
		1889	static void
		1890	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1891	{
		1892	.. one minute over, w is actually stopped right here
		1893	}
		1894
		1895	ev_timer mytimer;
		1896	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1897	ev_timer_start (loop, &mytimer);
		1898
		1899	Example: Create a timeout timer that times out after 10 seconds of
		1900	inactivity.
		1901
		1902	static void
		1903	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1904	{
		1905	.. ten seconds without any activity
		1906	}
		1907
		1908	ev_timer mytimer;
		1909	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1910	ev_timer_again (&mytimer); /* start timer */
		1911	ev_loop (loop, 0);
		1912
		1913	// and in some piece of code that gets executed on any "activity":
		1914	// reset the timeout to start ticking again at 10 seconds
		1915	ev_timer_again (&mytimer);
		1916
		1917
472	=head2 ev_periodic - to cron or not to cron it	1918	=head2 C<ev_periodic> - to cron or not to cron?
473		1919
474	Periodic watchers are also timers of a kind, but they are very versatile	1920	Periodic watchers are also timers of a kind, but they are very versatile
475	(and unfortunately a bit complex).	1921	(and unfortunately a bit complex).
476		1922
477	Unlike ev_timer's, they are not based on real time (or relative time)	1923	Unlike C<ev_timer>, periodic watchers are not based on real time (or
478	but on wallclock time (absolute time). You can tell a periodic watcher	1924	relative time, the physical time that passes) but on wall clock time
479	to trigger "at" some specific point in time. For example, if you tell a	1925	(absolute time, the thing you can read on your calender or clock). The
480	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1926	difference is that wall clock time can run faster or slower than real
481	+ 10.>) and then reset your system clock to the last year, then it will	1927	time, and time jumps are not uncommon (e.g. when you adjust your
482	take a year to trigger the event (unlike an ev_timer, which would trigger	1928	wrist-watch).
483	roughly 10 seconds later and of course not if you reset your system time
484	again).
485		1929
486	They can also be used to implement vastly more complex timers, such as	1930	You can tell a periodic watcher to trigger after some specific point
		1931	in time: for example, if you tell a periodic watcher to trigger "in 10
		1932	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1933	not a delay) and then reset your system clock to January of the previous
		1934	year, then it will take a year or more to trigger the event (unlike an
		1935	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1936	it, as it uses a relative timeout).
		1937
		1938	C<ev_periodic> watchers can also be used to implement vastly more complex
487	triggering an event on eahc midnight, local time.	1939	timers, such as triggering an event on each "midnight, local time", or
		1940	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1941	those cannot react to time jumps.
		1942
		1943	As with timers, the callback is guaranteed to be invoked only when the
		1944	point in time where it is supposed to trigger has passed. If multiple
		1945	timers become ready during the same loop iteration then the ones with
		1946	earlier time-out values are invoked before ones with later time-out values
		1947	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1948
		1949	=head3 Watcher-Specific Functions and Data Members
488		1950
489	=over 4	1951	=over 4
490		1952
491	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1953	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
492		1954
493	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1955	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
494		1956
495	Lots of arguments, lets sort it out... There are basically three modes of	1957	Lots of arguments, let's sort it out... There are basically three modes of
496	operation, and we will explain them from simplest to complex:	1958	operation, and we will explain them from simplest to most complex:
497
498		1959
499	=over 4	1960	=over 4
500		1961
501	=item * absolute timer (interval = reschedule_cb = 0)	1962	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
502		1963
503	In this configuration the watcher triggers an event at the wallclock time	1964	In this configuration the watcher triggers an event after the wall clock
504	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1965	time C<offset> has passed. It will not repeat and will not adjust when a
505	that is, if it is to be run at January 1st 2011 then it will run when the	1966	time jump occurs, that is, if it is to be run at January 1st 2011 then it
506	system time reaches or surpasses this time.	1967	will be stopped and invoked when the system clock reaches or surpasses
		1968	this point in time.
507		1969
508	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1970	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
509		1971
510	In this mode the watcher will always be scheduled to time out at the next	1972	In this mode the watcher will always be scheduled to time out at the next
511	C<at + N * interval> time (for some integer N) and then repeat, regardless	1973	C<offset + N * interval> time (for some integer N, which can also be
512	of any time jumps.	1974	negative) and then repeat, regardless of any time jumps. The C<offset>
		1975	argument is merely an offset into the C<interval> periods.
513		1976
514	This can be used to create timers that do not drift with respect to system	1977	This can be used to create timers that do not drift with respect to the
515	time:	1978	system clock, for example, here is an C<ev_periodic> that triggers each
		1979	hour, on the hour (with respect to UTC):
516		1980
517	ev_periodic_set (&periodic, 0., 3600., 0);	1981	ev_periodic_set (&periodic, 0., 3600., 0);
518		1982
519	This doesn't mean there will always be 3600 seconds in between triggers,	1983	This doesn't mean there will always be 3600 seconds in between triggers,
520	but only that the the callback will be called when the system time shows a	1984	but only that the callback will be called when the system time shows a
521	full hour (UTC), or more correct, when the system time is evenly divisible	1985	full hour (UTC), or more correctly, when the system time is evenly divisible
522	by 3600.	1986	by 3600.
523		1987
524	Another way to think about it (for the mathematically inclined) is that	1988	Another way to think about it (for the mathematically inclined) is that
525	ev_periodic will try to run the callback in this mode at the next possible	1989	C<ev_periodic> will try to run the callback in this mode at the next possible
526	time where C<time = at (mod interval)>, regardless of any time jumps.	1990	time where C<time = offset (mod interval)>, regardless of any time jumps.
527		1991
		1992	For numerical stability it is preferable that the C<offset> value is near
		1993	C<ev_now ()> (the current time), but there is no range requirement for
		1994	this value, and in fact is often specified as zero.
		1995
		1996	Note also that there is an upper limit to how often a timer can fire (CPU
		1997	speed for example), so if C<interval> is very small then timing stability
		1998	will of course deteriorate. Libev itself tries to be exact to be about one
		1999	millisecond (if the OS supports it and the machine is fast enough).
		2000
528	=item * manual reschedule mode (reschedule_cb = callback)	2001	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
529		2002
530	In this mode the values for C<interval> and C<at> are both being	2003	In this mode the values for C<interval> and C<offset> are both being
531	ignored. Instead, each time the periodic watcher gets scheduled, the	2004	ignored. Instead, each time the periodic watcher gets scheduled, the
532	reschedule callback will be called with the watcher as first, and the	2005	reschedule callback will be called with the watcher as first, and the
533	current time as second argument.	2006	current time as second argument.
534		2007
535	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	2008	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
536	periodic watcher, ever, or make any event loop modificstions>. If you need	2009	or make ANY other event loop modifications whatsoever, unless explicitly
537	to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.	2010	allowed by documentation here>.
538		2011
		2012	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2013	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2014	only event loop modification you are allowed to do).
		2015
539	Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2016	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
540	ev_tstamp now)>, e.g.:	2017	*w, ev_tstamp now)>, e.g.:
541		2018
		2019	static ev_tstamp
542	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2020	my_rescheduler (ev_periodic *w, ev_tstamp now)
543	{	2021	{
544	return now + 60.;	2022	return now + 60.;
545	}	2023	}
546		2024
547	It must return the next time to trigger, based on the passed time value	2025	It must return the next time to trigger, based on the passed time value
548	(that is, the lowest time value larger than to the second argument). It	2026	(that is, the lowest time value larger than to the second argument). It
549	will usually be called just before the callback will be triggered, but	2027	will usually be called just before the callback will be triggered, but
550	might be called at other times, too.	2028	might be called at other times, too.
551		2029
		2030	NOTE: I<< This callback must always return a time that is higher than or
		2031	equal to the passed C<now> value >>.
		2032
552	This can be used to create very complex timers, such as a timer that	2033	This can be used to create very complex timers, such as a timer that
553	triggers on each midnight, local time. To do this, you would calculate the	2034	triggers on "next midnight, local time". To do this, you would calculate the
554	next midnight after C<now> and return the timestamp value for this. How you do this	2035	next midnight after C<now> and return the timestamp value for this. How
555	is, again, up to you (but it is not trivial).	2036	you do this is, again, up to you (but it is not trivial, which is the main
		2037	reason I omitted it as an example).
556		2038
557	=back	2039	=back
558		2040
559	=item ev_periodic_again (loop, ev_periodic *)	2041	=item ev_periodic_again (loop, ev_periodic *)
560		2042
561	Simply stops and restarts the periodic watcher again. This is only useful	2043	Simply stops and restarts the periodic watcher again. This is only useful
562	when you changed some parameters or the reschedule callback would return	2044	when you changed some parameters or the reschedule callback would return
563	a different time than the last time it was called (e.g. in a crond like	2045	a different time than the last time it was called (e.g. in a crond like
564	program when the crontabs have changed).	2046	program when the crontabs have changed).
565		2047
		2048	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2049
		2050	When active, returns the absolute time that the watcher is supposed
		2051	to trigger next. This is not the same as the C<offset> argument to
		2052	C<ev_periodic_set>, but indeed works even in interval and manual
		2053	rescheduling modes.
		2054
		2055	=item ev_tstamp offset [read-write]
		2056
		2057	When repeating, this contains the offset value, otherwise this is the
		2058	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2059	although libev might modify this value for better numerical stability).
		2060
		2061	Can be modified any time, but changes only take effect when the periodic
		2062	timer fires or C<ev_periodic_again> is being called.
		2063
		2064	=item ev_tstamp interval [read-write]
		2065
		2066	The current interval value. Can be modified any time, but changes only
		2067	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2068	called.
		2069
		2070	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2071
		2072	The current reschedule callback, or C<0>, if this functionality is
		2073	switched off. Can be changed any time, but changes only take effect when
		2074	the periodic timer fires or C<ev_periodic_again> is being called.
		2075
566	=back	2076	=back
567		2077
		2078	=head3 Examples
		2079
		2080	Example: Call a callback every hour, or, more precisely, whenever the
		2081	system time is divisible by 3600. The callback invocation times have
		2082	potentially a lot of jitter, but good long-term stability.
		2083
		2084	static void
		2085	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
		2086	{
		2087	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2088	}
		2089
		2090	ev_periodic hourly_tick;
		2091	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2092	ev_periodic_start (loop, &hourly_tick);
		2093
		2094	Example: The same as above, but use a reschedule callback to do it:
		2095
		2096	#include <math.h>
		2097
		2098	static ev_tstamp
		2099	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2100	{
		2101	return now + (3600. - fmod (now, 3600.));
		2102	}
		2103
		2104	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2105
		2106	Example: Call a callback every hour, starting now:
		2107
		2108	ev_periodic hourly_tick;
		2109	ev_periodic_init (&hourly_tick, clock_cb,
		2110	fmod (ev_now (loop), 3600.), 3600., 0);
		2111	ev_periodic_start (loop, &hourly_tick);
		2112
		2113
568	=head2 ev_signal - signal me when a signal gets signalled	2114	=head2 C<ev_signal> - signal me when a signal gets signalled!
569		2115
570	Signal watchers will trigger an event when the process receives a specific	2116	Signal watchers will trigger an event when the process receives a specific
571	signal one or more times. Even though signals are very asynchronous, libev	2117	signal one or more times. Even though signals are very asynchronous, libev
572	will try its best to deliver signals synchronously, i.e. as part of the	2118	will try it's best to deliver signals synchronously, i.e. as part of the
573	normal event processing, like any other event.	2119	normal event processing, like any other event.
574		2120
		2121	If you want signals to be delivered truly asynchronously, just use
		2122	C<sigaction> as you would do without libev and forget about sharing
		2123	the signal. You can even use C<ev_async> from a signal handler to
		2124	synchronously wake up an event loop.
		2125
575	You cna configure as many watchers as you like per signal. Only when the	2126	You can configure as many watchers as you like for the same signal, but
		2127	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2128	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2129	C<SIGINT> in both the default loop and another loop at the same time. At
		2130	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2131
576	first watcher gets started will libev actually register a signal watcher	2132	When the first watcher gets started will libev actually register something
577	with the kernel (thus it coexists with your own signal handlers as long	2133	with the kernel (thus it coexists with your own signal handlers as long as
578	as you don't register any with libev). Similarly, when the last signal	2134	you don't register any with libev for the same signal).
579	watcher for a signal is stopped libev will reset the signal handler to	2135
580	SIG_DFL (regardless of what it was set to before).	2136	If possible and supported, libev will install its handlers with
		2137	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2138	not be unduly interrupted. If you have a problem with system calls getting
		2139	interrupted by signals you can block all signals in an C<ev_check> watcher
		2140	and unblock them in an C<ev_prepare> watcher.
		2141
		2142	=head3 The special problem of inheritance over fork/execve/pthread_create
		2143
		2144	Both the signal mask (C<sigprocmask>) and the signal disposition
		2145	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2146	stopping it again), that is, libev might or might not block the signal,
		2147	and might or might not set or restore the installed signal handler.
		2148
		2149	While this does not matter for the signal disposition (libev never
		2150	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2151	C<execve>), this matters for the signal mask: many programs do not expect
		2152	certain signals to be blocked.
		2153
		2154	This means that before calling C<exec> (from the child) you should reset
		2155	the signal mask to whatever "default" you expect (all clear is a good
		2156	choice usually).
		2157
		2158	The simplest way to ensure that the signal mask is reset in the child is
		2159	to install a fork handler with C<pthread_atfork> that resets it. That will
		2160	catch fork calls done by libraries (such as the libc) as well.
		2161
		2162	In current versions of libev, the signal will not be blocked indefinitely
		2163	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2164	the window of opportunity for problems, it will not go away, as libev
		2165	I<has> to modify the signal mask, at least temporarily.
		2166
		2167	So I can't stress this enough: I<If you do not reset your signal mask when
		2168	you expect it to be empty, you have a race condition in your code>. This
		2169	is not a libev-specific thing, this is true for most event libraries.
		2170
		2171	=head3 Watcher-Specific Functions and Data Members
581		2172
582	=over 4	2173	=over 4
583		2174
584	=item ev_signal_init (ev_signal *, callback, int signum)	2175	=item ev_signal_init (ev_signal *, callback, int signum)
585		2176
586	=item ev_signal_set (ev_signal *, int signum)	2177	=item ev_signal_set (ev_signal *, int signum)
587		2178
588	Configures the watcher to trigger on the given signal number (usually one	2179	Configures the watcher to trigger on the given signal number (usually one
589	of the C<SIGxxx> constants).	2180	of the C<SIGxxx> constants).
590		2181
		2182	=item int signum [read-only]
		2183
		2184	The signal the watcher watches out for.
		2185
591	=back	2186	=back
592		2187
		2188	=head3 Examples
		2189
		2190	Example: Try to exit cleanly on SIGINT.
		2191
		2192	static void
		2193	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2194	{
		2195	ev_unloop (loop, EVUNLOOP_ALL);
		2196	}
		2197
		2198	ev_signal signal_watcher;
		2199	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2200	ev_signal_start (loop, &signal_watcher);
		2201
		2202
593	=head2 ev_child - wait for pid status changes	2203	=head2 C<ev_child> - watch out for process status changes
594		2204
595	Child watchers trigger when your process receives a SIGCHLD in response to	2205	Child watchers trigger when your process receives a SIGCHLD in response to
596	some child status changes (most typically when a child of yours dies).	2206	some child status changes (most typically when a child of yours dies or
		2207	exits). It is permissible to install a child watcher I<after> the child
		2208	has been forked (which implies it might have already exited), as long
		2209	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2210	forking and then immediately registering a watcher for the child is fine,
		2211	but forking and registering a watcher a few event loop iterations later or
		2212	in the next callback invocation is not.
		2213
		2214	Only the default event loop is capable of handling signals, and therefore
		2215	you can only register child watchers in the default event loop.
		2216
		2217	Due to some design glitches inside libev, child watchers will always be
		2218	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2219	libev)
		2220
		2221	=head3 Process Interaction
		2222
		2223	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2224	initialised. This is necessary to guarantee proper behaviour even if the
		2225	first child watcher is started after the child exits. The occurrence
		2226	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2227	synchronously as part of the event loop processing. Libev always reaps all
		2228	children, even ones not watched.
		2229
		2230	=head3 Overriding the Built-In Processing
		2231
		2232	Libev offers no special support for overriding the built-in child
		2233	processing, but if your application collides with libev's default child
		2234	handler, you can override it easily by installing your own handler for
		2235	C<SIGCHLD> after initialising the default loop, and making sure the
		2236	default loop never gets destroyed. You are encouraged, however, to use an
		2237	event-based approach to child reaping and thus use libev's support for
		2238	that, so other libev users can use C<ev_child> watchers freely.
		2239
		2240	=head3 Stopping the Child Watcher
		2241
		2242	Currently, the child watcher never gets stopped, even when the
		2243	child terminates, so normally one needs to stop the watcher in the
		2244	callback. Future versions of libev might stop the watcher automatically
		2245	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2246	problem).
		2247
		2248	=head3 Watcher-Specific Functions and Data Members
597		2249
598	=over 4	2250	=over 4
599		2251
600	=item ev_child_init (ev_child *, callback, int pid)	2252	=item ev_child_init (ev_child *, callback, int pid, int trace)
601		2253
602	=item ev_child_set (ev_child *, int pid)	2254	=item ev_child_set (ev_child *, int pid, int trace)
603		2255
604	Configures the watcher to wait for status changes of process C<pid> (or	2256	Configures the watcher to wait for status changes of process C<pid> (or
605	I<any> process if C<pid> is specified as C<0>). The callback can look	2257	I<any> process if C<pid> is specified as C<0>). The callback can look
606	at the C<rstatus> member of the C<ev_child> watcher structure to see	2258	at the C<rstatus> member of the C<ev_child> watcher structure to see
607	the status word (use the macros from C<sys/wait.h>). The C<rpid> member	2259	the status word (use the macros from C<sys/wait.h> and see your systems
608	contains the pid of the process causing the status change.	2260	C<waitpid> documentation). The C<rpid> member contains the pid of the
		2261	process causing the status change. C<trace> must be either C<0> (only
		2262	activate the watcher when the process terminates) or C<1> (additionally
		2263	activate the watcher when the process is stopped or continued).
		2264
		2265	=item int pid [read-only]
		2266
		2267	The process id this watcher watches out for, or C<0>, meaning any process id.
		2268
		2269	=item int rpid [read-write]
		2270
		2271	The process id that detected a status change.
		2272
		2273	=item int rstatus [read-write]
		2274
		2275	The process exit/trace status caused by C<rpid> (see your systems
		2276	C<waitpid> and C<sys/wait.h> documentation for details).
609		2277
610	=back	2278	=back
611		2279
		2280	=head3 Examples
		2281
		2282	Example: C<fork()> a new process and install a child handler to wait for
		2283	its completion.
		2284
		2285	ev_child cw;
		2286
		2287	static void
		2288	child_cb (EV_P_ ev_child *w, int revents)
		2289	{
		2290	ev_child_stop (EV_A_ w);
		2291	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2292	}
		2293
		2294	pid_t pid = fork ();
		2295
		2296	if (pid < 0)
		2297	// error
		2298	else if (pid == 0)
		2299	{
		2300	// the forked child executes here
		2301	exit (1);
		2302	}
		2303	else
		2304	{
		2305	ev_child_init (&cw, child_cb, pid, 0);
		2306	ev_child_start (EV_DEFAULT_ &cw);
		2307	}
		2308
		2309
		2310	=head2 C<ev_stat> - did the file attributes just change?
		2311
		2312	This watches a file system path for attribute changes. That is, it calls
		2313	C<stat> on that path in regular intervals (or when the OS says it changed)
		2314	and sees if it changed compared to the last time, invoking the callback if
		2315	it did.
		2316
		2317	The path does not need to exist: changing from "path exists" to "path does
		2318	not exist" is a status change like any other. The condition "path does not
		2319	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2320	C<st_nlink> field being zero (which is otherwise always forced to be at
		2321	least one) and all the other fields of the stat buffer having unspecified
		2322	contents.
		2323
		2324	The path I<must not> end in a slash or contain special components such as
		2325	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2326	your working directory changes, then the behaviour is undefined.
		2327
		2328	Since there is no portable change notification interface available, the
		2329	portable implementation simply calls C<stat(2)> regularly on the path
		2330	to see if it changed somehow. You can specify a recommended polling
		2331	interval for this case. If you specify a polling interval of C<0> (highly
		2332	recommended!) then a I<suitable, unspecified default> value will be used
		2333	(which you can expect to be around five seconds, although this might
		2334	change dynamically). Libev will also impose a minimum interval which is
		2335	currently around C<0.1>, but that's usually overkill.
		2336
		2337	This watcher type is not meant for massive numbers of stat watchers,
		2338	as even with OS-supported change notifications, this can be
		2339	resource-intensive.
		2340
		2341	At the time of this writing, the only OS-specific interface implemented
		2342	is the Linux inotify interface (implementing kqueue support is left as an
		2343	exercise for the reader. Note, however, that the author sees no way of
		2344	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2345
		2346	=head3 ABI Issues (Largefile Support)
		2347
		2348	Libev by default (unless the user overrides this) uses the default
		2349	compilation environment, which means that on systems with large file
		2350	support disabled by default, you get the 32 bit version of the stat
		2351	structure. When using the library from programs that change the ABI to
		2352	use 64 bit file offsets the programs will fail. In that case you have to
		2353	compile libev with the same flags to get binary compatibility. This is
		2354	obviously the case with any flags that change the ABI, but the problem is
		2355	most noticeably displayed with ev_stat and large file support.
		2356
		2357	The solution for this is to lobby your distribution maker to make large
		2358	file interfaces available by default (as e.g. FreeBSD does) and not
		2359	optional. Libev cannot simply switch on large file support because it has
		2360	to exchange stat structures with application programs compiled using the
		2361	default compilation environment.
		2362
		2363	=head3 Inotify and Kqueue
		2364
		2365	When C<inotify (7)> support has been compiled into libev and present at
		2366	runtime, it will be used to speed up change detection where possible. The
		2367	inotify descriptor will be created lazily when the first C<ev_stat>
		2368	watcher is being started.
		2369
		2370	Inotify presence does not change the semantics of C<ev_stat> watchers
		2371	except that changes might be detected earlier, and in some cases, to avoid
		2372	making regular C<stat> calls. Even in the presence of inotify support
		2373	there are many cases where libev has to resort to regular C<stat> polling,
		2374	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2375	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2376	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2377	xfs are fully working) libev usually gets away without polling.
		2378
		2379	There is no support for kqueue, as apparently it cannot be used to
		2380	implement this functionality, due to the requirement of having a file
		2381	descriptor open on the object at all times, and detecting renames, unlinks
		2382	etc. is difficult.
		2383
		2384	=head3 C<stat ()> is a synchronous operation
		2385
		2386	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2387	the process. The exception are C<ev_stat> watchers - those call C<stat
		2388	()>, which is a synchronous operation.
		2389
		2390	For local paths, this usually doesn't matter: unless the system is very
		2391	busy or the intervals between stat's are large, a stat call will be fast,
		2392	as the path data is usually in memory already (except when starting the
		2393	watcher).
		2394
		2395	For networked file systems, calling C<stat ()> can block an indefinite
		2396	time due to network issues, and even under good conditions, a stat call
		2397	often takes multiple milliseconds.
		2398
		2399	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2400	paths, although this is fully supported by libev.
		2401
		2402	=head3 The special problem of stat time resolution
		2403
		2404	The C<stat ()> system call only supports full-second resolution portably,
		2405	and even on systems where the resolution is higher, most file systems
		2406	still only support whole seconds.
		2407
		2408	That means that, if the time is the only thing that changes, you can
		2409	easily miss updates: on the first update, C<ev_stat> detects a change and
		2410	calls your callback, which does something. When there is another update
		2411	within the same second, C<ev_stat> will be unable to detect unless the
		2412	stat data does change in other ways (e.g. file size).
		2413
		2414	The solution to this is to delay acting on a change for slightly more
		2415	than a second (or till slightly after the next full second boundary), using
		2416	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2417	ev_timer_again (loop, w)>).
		2418
		2419	The C<.02> offset is added to work around small timing inconsistencies
		2420	of some operating systems (where the second counter of the current time
		2421	might be be delayed. One such system is the Linux kernel, where a call to
		2422	C<gettimeofday> might return a timestamp with a full second later than
		2423	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2424	update file times then there will be a small window where the kernel uses
		2425	the previous second to update file times but libev might already execute
		2426	the timer callback).
		2427
		2428	=head3 Watcher-Specific Functions and Data Members
		2429
		2430	=over 4
		2431
		2432	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2433
		2434	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2435
		2436	Configures the watcher to wait for status changes of the given
		2437	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2438	be detected and should normally be specified as C<0> to let libev choose
		2439	a suitable value. The memory pointed to by C<path> must point to the same
		2440	path for as long as the watcher is active.
		2441
		2442	The callback will receive an C<EV_STAT> event when a change was detected,
		2443	relative to the attributes at the time the watcher was started (or the
		2444	last change was detected).
		2445
		2446	=item ev_stat_stat (loop, ev_stat *)
		2447
		2448	Updates the stat buffer immediately with new values. If you change the
		2449	watched path in your callback, you could call this function to avoid
		2450	detecting this change (while introducing a race condition if you are not
		2451	the only one changing the path). Can also be useful simply to find out the
		2452	new values.
		2453
		2454	=item ev_statdata attr [read-only]
		2455
		2456	The most-recently detected attributes of the file. Although the type is
		2457	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2458	suitable for your system, but you can only rely on the POSIX-standardised
		2459	members to be present. If the C<st_nlink> member is C<0>, then there was
		2460	some error while C<stat>ing the file.
		2461
		2462	=item ev_statdata prev [read-only]
		2463
		2464	The previous attributes of the file. The callback gets invoked whenever
		2465	C<prev> != C<attr>, or, more precisely, one or more of these members
		2466	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2467	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2468
		2469	=item ev_tstamp interval [read-only]
		2470
		2471	The specified interval.
		2472
		2473	=item const char *path [read-only]
		2474
		2475	The file system path that is being watched.
		2476
		2477	=back
		2478
		2479	=head3 Examples
		2480
		2481	Example: Watch C</etc/passwd> for attribute changes.
		2482
		2483	static void
		2484	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2485	{
		2486	/* /etc/passwd changed in some way */
		2487	if (w->attr.st_nlink)
		2488	{
		2489	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2490	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2491	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2492	}
		2493	else
		2494	/* you shalt not abuse printf for puts */
		2495	puts ("wow, /etc/passwd is not there, expect problems. "
		2496	"if this is windows, they already arrived\n");
		2497	}
		2498
		2499	...
		2500	ev_stat passwd;
		2501
		2502	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2503	ev_stat_start (loop, &passwd);
		2504
		2505	Example: Like above, but additionally use a one-second delay so we do not
		2506	miss updates (however, frequent updates will delay processing, too, so
		2507	one might do the work both on C<ev_stat> callback invocation I<and> on
		2508	C<ev_timer> callback invocation).
		2509
		2510	static ev_stat passwd;
		2511	static ev_timer timer;
		2512
		2513	static void
		2514	timer_cb (EV_P_ ev_timer *w, int revents)
		2515	{
		2516	ev_timer_stop (EV_A_ w);
		2517
		2518	/* now it's one second after the most recent passwd change */
		2519	}
		2520
		2521	static void
		2522	stat_cb (EV_P_ ev_stat *w, int revents)
		2523	{
		2524	/* reset the one-second timer */
		2525	ev_timer_again (EV_A_ &timer);
		2526	}
		2527
		2528	...
		2529	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2530	ev_stat_start (loop, &passwd);
		2531	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2532
		2533
612	=head2 ev_idle - when you've got nothing better to do	2534	=head2 C<ev_idle> - when you've got nothing better to do...
613		2535
614	Idle watchers trigger events when there are no other I/O or timer (or	2536	Idle watchers trigger events when no other events of the same or higher
615	periodic) events pending. That is, as long as your process is busy	2537	priority are pending (prepare, check and other idle watchers do not count
616	handling sockets or timeouts it will not be called. But when your process	2538	as receiving "events").
617	is idle all idle watchers are being called again and again - until	2539
		2540	That is, as long as your process is busy handling sockets or timeouts
		2541	(or even signals, imagine) of the same or higher priority it will not be
		2542	triggered. But when your process is idle (or only lower-priority watchers
		2543	are pending), the idle watchers are being called once per event loop
618	stopped, that is, or your process receives more events.	2544	iteration - until stopped, that is, or your process receives more events
		2545	and becomes busy again with higher priority stuff.
619		2546
620	The most noteworthy effect is that as long as any idle watchers are	2547	The most noteworthy effect is that as long as any idle watchers are
621	active, the process will not block when waiting for new events.	2548	active, the process will not block when waiting for new events.
622		2549
623	Apart from keeping your process non-blocking (which is a useful	2550	Apart from keeping your process non-blocking (which is a useful
624	effect on its own sometimes), idle watchers are a good place to do	2551	effect on its own sometimes), idle watchers are a good place to do
625	"pseudo-background processing", or delay processing stuff to after the	2552	"pseudo-background processing", or delay processing stuff to after the
626	event loop has handled all outstanding events.	2553	event loop has handled all outstanding events.
627		2554
		2555	=head3 Watcher-Specific Functions and Data Members
		2556
628	=over 4	2557	=over 4
629		2558
630	=item ev_idle_init (ev_signal *, callback)	2559	=item ev_idle_init (ev_idle *, callback)
631		2560
632	Initialises and configures the idle watcher - it has no parameters of any	2561	Initialises and configures the idle watcher - it has no parameters of any
633	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2562	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
634	believe me.	2563	believe me.
635		2564
636	=back	2565	=back
637		2566
638	=head2 prepare and check - your hooks into the event loop	2567	=head3 Examples
639		2568
		2569	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2570	callback, free it. Also, use no error checking, as usual.
		2571
		2572	static void
		2573	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2574	{
		2575	free (w);
		2576	// now do something you wanted to do when the program has
		2577	// no longer anything immediate to do.
		2578	}
		2579
		2580	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2581	ev_idle_init (idle_watcher, idle_cb);
		2582	ev_idle_start (loop, idle_watcher);
		2583
		2584
		2585	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		2586
640	Prepare and check watchers usually (but not always) are used in	2587	Prepare and check watchers are usually (but not always) used in pairs:
641	tandom. Prepare watchers get invoked before the process blocks and check	2588	prepare watchers get invoked before the process blocks and check watchers
642	watchers afterwards.	2589	afterwards.
643		2590
		2591	You I<must not> call C<ev_loop> or similar functions that enter
		2592	the current event loop from either C<ev_prepare> or C<ev_check>
		2593	watchers. Other loops than the current one are fine, however. The
		2594	rationale behind this is that you do not need to check for recursion in
		2595	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2596	C<ev_check> so if you have one watcher of each kind they will always be
		2597	called in pairs bracketing the blocking call.
		2598
644	Their main purpose is to integrate other event mechanisms into libev. This	2599	Their main purpose is to integrate other event mechanisms into libev and
645	could be used, for example, to track variable changes, implement your own	2600	their use is somewhat advanced. They could be used, for example, to track
646	watchers, integrate net-snmp or a coroutine library and lots more.	2601	variable changes, implement your own watchers, integrate net-snmp or a
		2602	coroutine library and lots more. They are also occasionally useful if
		2603	you cache some data and want to flush it before blocking (for example,
		2604	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2605	watcher).
647		2606
648	This is done by examining in each prepare call which file descriptors need	2607	This is done by examining in each prepare call which file descriptors
649	to be watched by the other library, registering ev_io watchers for them	2608	need to be watched by the other library, registering C<ev_io> watchers
650	and starting an ev_timer watcher for any timeouts (many libraries provide	2609	for them and starting an C<ev_timer> watcher for any timeouts (many
651	just this functionality). Then, in the check watcher you check for any	2610	libraries provide exactly this functionality). Then, in the check watcher,
652	events that occured (by making your callbacks set soem flags for example)	2611	you check for any events that occurred (by checking the pending status
653	and call back into the library.	2612	of all watchers and stopping them) and call back into the library. The
		2613	I/O and timer callbacks will never actually be called (but must be valid
		2614	nevertheless, because you never know, you know?).
654		2615
655	As another example, the perl Coro module uses these hooks to integrate	2616	As another example, the Perl Coro module uses these hooks to integrate
656	coroutines into libev programs, by yielding to other active coroutines	2617	coroutines into libev programs, by yielding to other active coroutines
657	during each prepare and only letting the process block if no coroutines	2618	during each prepare and only letting the process block if no coroutines
658	are ready to run.	2619	are ready to run (it's actually more complicated: it only runs coroutines
		2620	with priority higher than or equal to the event loop and one coroutine
		2621	of lower priority, but only once, using idle watchers to keep the event
		2622	loop from blocking if lower-priority coroutines are active, thus mapping
		2623	low-priority coroutines to idle/background tasks).
		2624
		2625	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2626	priority, to ensure that they are being run before any other watchers
		2627	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2628
		2629	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2630	activate ("feed") events into libev. While libev fully supports this, they
		2631	might get executed before other C<ev_check> watchers did their job. As
		2632	C<ev_check> watchers are often used to embed other (non-libev) event
		2633	loops those other event loops might be in an unusable state until their
		2634	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2635	others).
		2636
		2637	=head3 Watcher-Specific Functions and Data Members
659		2638
660	=over 4	2639	=over 4
661		2640
662	=item ev_prepare_init (ev_prepare *, callback)	2641	=item ev_prepare_init (ev_prepare *, callback)
663		2642
664	=item ev_check_init (ev_check *, callback)	2643	=item ev_check_init (ev_check *, callback)
665		2644
666	Initialises and configures the prepare or check watcher - they have no	2645	Initialises and configures the prepare or check watcher - they have no
667	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2646	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
668	macros, but using them is utterly, utterly pointless.	2647	macros, but using them is utterly, utterly, utterly and completely
		2648	pointless.
669		2649
670	=back	2650	=back
671		2651
		2652	=head3 Examples
		2653
		2654	There are a number of principal ways to embed other event loops or modules
		2655	into libev. Here are some ideas on how to include libadns into libev
		2656	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2657	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2658	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2659	Glib event loop).
		2660
		2661	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2662	and in a check watcher, destroy them and call into libadns. What follows
		2663	is pseudo-code only of course. This requires you to either use a low
		2664	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2665	the callbacks for the IO/timeout watchers might not have been called yet.
		2666
		2667	static ev_io iow [nfd];
		2668	static ev_timer tw;
		2669
		2670	static void
		2671	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2672	{
		2673	}
		2674
		2675	// create io watchers for each fd and a timer before blocking
		2676	static void
		2677	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2678	{
		2679	int timeout = 3600000;
		2680	struct pollfd fds [nfd];
		2681	// actual code will need to loop here and realloc etc.
		2682	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2683
		2684	/* the callback is illegal, but won't be called as we stop during check */
		2685	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		2686	ev_timer_start (loop, &tw);
		2687
		2688	// create one ev_io per pollfd
		2689	for (int i = 0; i < nfd; ++i)
		2690	{
		2691	ev_io_init (iow + i, io_cb, fds [i].fd,
		2692	((fds [i].events & POLLIN ? EV_READ : 0)
		2693	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2694
		2695	fds [i].revents = 0;
		2696	ev_io_start (loop, iow + i);
		2697	}
		2698	}
		2699
		2700	// stop all watchers after blocking
		2701	static void
		2702	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2703	{
		2704	ev_timer_stop (loop, &tw);
		2705
		2706	for (int i = 0; i < nfd; ++i)
		2707	{
		2708	// set the relevant poll flags
		2709	// could also call adns_processreadable etc. here
		2710	struct pollfd *fd = fds + i;
		2711	int revents = ev_clear_pending (iow + i);
		2712	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2713	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2714
		2715	// now stop the watcher
		2716	ev_io_stop (loop, iow + i);
		2717	}
		2718
		2719	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2720	}
		2721
		2722	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2723	in the prepare watcher and would dispose of the check watcher.
		2724
		2725	Method 3: If the module to be embedded supports explicit event
		2726	notification (libadns does), you can also make use of the actual watcher
		2727	callbacks, and only destroy/create the watchers in the prepare watcher.
		2728
		2729	static void
		2730	timer_cb (EV_P_ ev_timer *w, int revents)
		2731	{
		2732	adns_state ads = (adns_state)w->data;
		2733	update_now (EV_A);
		2734
		2735	adns_processtimeouts (ads, &tv_now);
		2736	}
		2737
		2738	static void
		2739	io_cb (EV_P_ ev_io *w, int revents)
		2740	{
		2741	adns_state ads = (adns_state)w->data;
		2742	update_now (EV_A);
		2743
		2744	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2745	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2746	}
		2747
		2748	// do not ever call adns_afterpoll
		2749
		2750	Method 4: Do not use a prepare or check watcher because the module you
		2751	want to embed is not flexible enough to support it. Instead, you can
		2752	override their poll function. The drawback with this solution is that the
		2753	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2754	this approach, effectively embedding EV as a client into the horrible
		2755	libglib event loop.
		2756
		2757	static gint
		2758	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2759	{
		2760	int got_events = 0;
		2761
		2762	for (n = 0; n < nfds; ++n)
		2763	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2764
		2765	if (timeout >= 0)
		2766	// create/start timer
		2767
		2768	// poll
		2769	ev_loop (EV_A_ 0);
		2770
		2771	// stop timer again
		2772	if (timeout >= 0)
		2773	ev_timer_stop (EV_A_ &to);
		2774
		2775	// stop io watchers again - their callbacks should have set
		2776	for (n = 0; n < nfds; ++n)
		2777	ev_io_stop (EV_A_ iow [n]);
		2778
		2779	return got_events;
		2780	}
		2781
		2782
		2783	=head2 C<ev_embed> - when one backend isn't enough...
		2784
		2785	This is a rather advanced watcher type that lets you embed one event loop
		2786	into another (currently only C<ev_io> events are supported in the embedded
		2787	loop, other types of watchers might be handled in a delayed or incorrect
		2788	fashion and must not be used).
		2789
		2790	There are primarily two reasons you would want that: work around bugs and
		2791	prioritise I/O.
		2792
		2793	As an example for a bug workaround, the kqueue backend might only support
		2794	sockets on some platform, so it is unusable as generic backend, but you
		2795	still want to make use of it because you have many sockets and it scales
		2796	so nicely. In this case, you would create a kqueue-based loop and embed
		2797	it into your default loop (which might use e.g. poll). Overall operation
		2798	will be a bit slower because first libev has to call C<poll> and then
		2799	C<kevent>, but at least you can use both mechanisms for what they are
		2800	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2801
		2802	As for prioritising I/O: under rare circumstances you have the case where
		2803	some fds have to be watched and handled very quickly (with low latency),
		2804	and even priorities and idle watchers might have too much overhead. In
		2805	this case you would put all the high priority stuff in one loop and all
		2806	the rest in a second one, and embed the second one in the first.
		2807
		2808	As long as the watcher is active, the callback will be invoked every
		2809	time there might be events pending in the embedded loop. The callback
		2810	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		2811	sweep and invoke their callbacks (the callback doesn't need to invoke the
		2812	C<ev_embed_sweep> function directly, it could also start an idle watcher
		2813	to give the embedded loop strictly lower priority for example).
		2814
		2815	You can also set the callback to C<0>, in which case the embed watcher
		2816	will automatically execute the embedded loop sweep whenever necessary.
		2817
		2818	Fork detection will be handled transparently while the C<ev_embed> watcher
		2819	is active, i.e., the embedded loop will automatically be forked when the
		2820	embedding loop forks. In other cases, the user is responsible for calling
		2821	C<ev_loop_fork> on the embedded loop.
		2822
		2823	Unfortunately, not all backends are embeddable: only the ones returned by
		2824	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2825	portable one.
		2826
		2827	So when you want to use this feature you will always have to be prepared
		2828	that you cannot get an embeddable loop. The recommended way to get around
		2829	this is to have a separate variables for your embeddable loop, try to
		2830	create it, and if that fails, use the normal loop for everything.
		2831
		2832	=head3 C<ev_embed> and fork
		2833
		2834	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2835	automatically be applied to the embedded loop as well, so no special
		2836	fork handling is required in that case. When the watcher is not running,
		2837	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2838	as applicable.
		2839
		2840	=head3 Watcher-Specific Functions and Data Members
		2841
		2842	=over 4
		2843
		2844	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2845
		2846	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2847
		2848	Configures the watcher to embed the given loop, which must be
		2849	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2850	invoked automatically, otherwise it is the responsibility of the callback
		2851	to invoke it (it will continue to be called until the sweep has been done,
		2852	if you do not want that, you need to temporarily stop the embed watcher).
		2853
		2854	=item ev_embed_sweep (loop, ev_embed *)
		2855
		2856	Make a single, non-blocking sweep over the embedded loop. This works
		2857	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2858	appropriate way for embedded loops.
		2859
		2860	=item struct ev_loop *other [read-only]
		2861
		2862	The embedded event loop.
		2863
		2864	=back
		2865
		2866	=head3 Examples
		2867
		2868	Example: Try to get an embeddable event loop and embed it into the default
		2869	event loop. If that is not possible, use the default loop. The default
		2870	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2871	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2872	used).
		2873
		2874	struct ev_loop *loop_hi = ev_default_init (0);
		2875	struct ev_loop *loop_lo = 0;
		2876	ev_embed embed;
		2877
		2878	// see if there is a chance of getting one that works
		2879	// (remember that a flags value of 0 means autodetection)
		2880	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2881	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2882	: 0;
		2883
		2884	// if we got one, then embed it, otherwise default to loop_hi
		2885	if (loop_lo)
		2886	{
		2887	ev_embed_init (&embed, 0, loop_lo);
		2888	ev_embed_start (loop_hi, &embed);
		2889	}
		2890	else
		2891	loop_lo = loop_hi;
		2892
		2893	Example: Check if kqueue is available but not recommended and create
		2894	a kqueue backend for use with sockets (which usually work with any
		2895	kqueue implementation). Store the kqueue/socket-only event loop in
		2896	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2897
		2898	struct ev_loop *loop = ev_default_init (0);
		2899	struct ev_loop *loop_socket = 0;
		2900	ev_embed embed;
		2901
		2902	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2903	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2904	{
		2905	ev_embed_init (&embed, 0, loop_socket);
		2906	ev_embed_start (loop, &embed);
		2907	}
		2908
		2909	if (!loop_socket)
		2910	loop_socket = loop;
		2911
		2912	// now use loop_socket for all sockets, and loop for everything else
		2913
		2914
		2915	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2916
		2917	Fork watchers are called when a C<fork ()> was detected (usually because
		2918	whoever is a good citizen cared to tell libev about it by calling
		2919	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2920	event loop blocks next and before C<ev_check> watchers are being called,
		2921	and only in the child after the fork. If whoever good citizen calling
		2922	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2923	handlers will be invoked, too, of course.
		2924
		2925	=head3 The special problem of life after fork - how is it possible?
		2926
		2927	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2928	up/change the process environment, followed by a call to C<exec()>. This
		2929	sequence should be handled by libev without any problems.
		2930
		2931	This changes when the application actually wants to do event handling
		2932	in the child, or both parent in child, in effect "continuing" after the
		2933	fork.
		2934
		2935	The default mode of operation (for libev, with application help to detect
		2936	forks) is to duplicate all the state in the child, as would be expected
		2937	when I<either> the parent I<or> the child process continues.
		2938
		2939	When both processes want to continue using libev, then this is usually the
		2940	wrong result. In that case, usually one process (typically the parent) is
		2941	supposed to continue with all watchers in place as before, while the other
		2942	process typically wants to start fresh, i.e. without any active watchers.
		2943
		2944	The cleanest and most efficient way to achieve that with libev is to
		2945	simply create a new event loop, which of course will be "empty", and
		2946	use that for new watchers. This has the advantage of not touching more
		2947	memory than necessary, and thus avoiding the copy-on-write, and the
		2948	disadvantage of having to use multiple event loops (which do not support
		2949	signal watchers).
		2950
		2951	When this is not possible, or you want to use the default loop for
		2952	other reasons, then in the process that wants to start "fresh", call
		2953	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2954	the default loop will "orphan" (not stop) all registered watchers, so you
		2955	have to be careful not to execute code that modifies those watchers. Note
		2956	also that in that case, you have to re-register any signal watchers.
		2957
		2958	=head3 Watcher-Specific Functions and Data Members
		2959
		2960	=over 4
		2961
		2962	=item ev_fork_init (ev_signal *, callback)
		2963
		2964	Initialises and configures the fork watcher - it has no parameters of any
		2965	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2966	believe me.
		2967
		2968	=back
		2969
		2970
		2971	=head2 C<ev_async> - how to wake up another event loop
		2972
		2973	In general, you cannot use an C<ev_loop> from multiple threads or other
		2974	asynchronous sources such as signal handlers (as opposed to multiple event
		2975	loops - those are of course safe to use in different threads).
		2976
		2977	Sometimes, however, you need to wake up another event loop you do not
		2978	control, for example because it belongs to another thread. This is what
		2979	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2980	can signal it by calling C<ev_async_send>, which is thread- and signal
		2981	safe.
		2982
		2983	This functionality is very similar to C<ev_signal> watchers, as signals,
		2984	too, are asynchronous in nature, and signals, too, will be compressed
		2985	(i.e. the number of callback invocations may be less than the number of
		2986	C<ev_async_sent> calls).
		2987
		2988	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2989	just the default loop.
		2990
		2991	=head3 Queueing
		2992
		2993	C<ev_async> does not support queueing of data in any way. The reason
		2994	is that the author does not know of a simple (or any) algorithm for a
		2995	multiple-writer-single-reader queue that works in all cases and doesn't
		2996	need elaborate support such as pthreads or unportable memory access
		2997	semantics.
		2998
		2999	That means that if you want to queue data, you have to provide your own
		3000	queue. But at least I can tell you how to implement locking around your
		3001	queue:
		3002
		3003	=over 4
		3004
		3005	=item queueing from a signal handler context
		3006
		3007	To implement race-free queueing, you simply add to the queue in the signal
		3008	handler but you block the signal handler in the watcher callback. Here is
		3009	an example that does that for some fictitious SIGUSR1 handler:
		3010
		3011	static ev_async mysig;
		3012
		3013	static void
		3014	sigusr1_handler (void)
		3015	{
		3016	sometype data;
		3017
		3018	// no locking etc.
		3019	queue_put (data);
		3020	ev_async_send (EV_DEFAULT_ &mysig);
		3021	}
		3022
		3023	static void
		3024	mysig_cb (EV_P_ ev_async *w, int revents)
		3025	{
		3026	sometype data;
		3027	sigset_t block, prev;
		3028
		3029	sigemptyset (&block);
		3030	sigaddset (&block, SIGUSR1);
		3031	sigprocmask (SIG_BLOCK, &block, &prev);
		3032
		3033	while (queue_get (&data))
		3034	process (data);
		3035
		3036	if (sigismember (&prev, SIGUSR1)
		3037	sigprocmask (SIG_UNBLOCK, &block, 0);
		3038	}
		3039
		3040	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3041	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3042	either...).
		3043
		3044	=item queueing from a thread context
		3045
		3046	The strategy for threads is different, as you cannot (easily) block
		3047	threads but you can easily preempt them, so to queue safely you need to
		3048	employ a traditional mutex lock, such as in this pthread example:
		3049
		3050	static ev_async mysig;
		3051	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3052
		3053	static void
		3054	otherthread (void)
		3055	{
		3056	// only need to lock the actual queueing operation
		3057	pthread_mutex_lock (&mymutex);
		3058	queue_put (data);
		3059	pthread_mutex_unlock (&mymutex);
		3060
		3061	ev_async_send (EV_DEFAULT_ &mysig);
		3062	}
		3063
		3064	static void
		3065	mysig_cb (EV_P_ ev_async *w, int revents)
		3066	{
		3067	pthread_mutex_lock (&mymutex);
		3068
		3069	while (queue_get (&data))
		3070	process (data);
		3071
		3072	pthread_mutex_unlock (&mymutex);
		3073	}
		3074
		3075	=back
		3076
		3077
		3078	=head3 Watcher-Specific Functions and Data Members
		3079
		3080	=over 4
		3081
		3082	=item ev_async_init (ev_async *, callback)
		3083
		3084	Initialises and configures the async watcher - it has no parameters of any
		3085	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3086	trust me.
		3087
		3088	=item ev_async_send (loop, ev_async *)
		3089
		3090	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3091	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3092	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3093	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3094	section below on what exactly this means).
		3095
		3096	Note that, as with other watchers in libev, multiple events might get
		3097	compressed into a single callback invocation (another way to look at this
		3098	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3099	reset when the event loop detects that).
		3100
		3101	This call incurs the overhead of a system call only once per event loop
		3102	iteration, so while the overhead might be noticeable, it doesn't apply to
		3103	repeated calls to C<ev_async_send> for the same event loop.
		3104
		3105	=item bool = ev_async_pending (ev_async *)
		3106
		3107	Returns a non-zero value when C<ev_async_send> has been called on the
		3108	watcher but the event has not yet been processed (or even noted) by the
		3109	event loop.
		3110
		3111	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3112	the loop iterates next and checks for the watcher to have become active,
		3113	it will reset the flag again. C<ev_async_pending> can be used to very
		3114	quickly check whether invoking the loop might be a good idea.
		3115
		3116	Not that this does I<not> check whether the watcher itself is pending,
		3117	only whether it has been requested to make this watcher pending: there
		3118	is a time window between the event loop checking and resetting the async
		3119	notification, and the callback being invoked.
		3120
		3121	=back
		3122
		3123
672	=head1 OTHER FUNCTIONS	3124	=head1 OTHER FUNCTIONS
673		3125
674	There are some other fucntions of possible interest. Described. Here. Now.	3126	There are some other functions of possible interest. Described. Here. Now.
675		3127
676	=over 4	3128	=over 4
677		3129
678	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3130	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
679		3131
680	This function combines a simple timer and an I/O watcher, calls your	3132	This function combines a simple timer and an I/O watcher, calls your
681	callback on whichever event happens first and automatically stop both	3133	callback on whichever event happens first and automatically stops both
682	watchers. This is useful if you want to wait for a single event on an fd	3134	watchers. This is useful if you want to wait for a single event on an fd
683	or timeout without havign to allocate/configure/start/stop/free one or	3135	or timeout without having to allocate/configure/start/stop/free one or
684	more watchers yourself.	3136	more watchers yourself.
685		3137
686	If C<fd> is less than 0, then no I/O watcher will be started and events is	3138	If C<fd> is less than 0, then no I/O watcher will be started and the
687	ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set	3139	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
688	will be craeted and started.	3140	the given C<fd> and C<events> set will be created and started.
689		3141
690	If C<timeout> is less than 0, then no timeout watcher will be	3142	If C<timeout> is less than 0, then no timeout watcher will be
691	started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat	3143	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
692	= 0) will be started.	3144	repeat = 0) will be started. C<0> is a valid timeout.
693		3145
694	The callback has the type C<void (*cb)(int revents, void *arg)> and	3146	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
695	gets passed an events set (normally a combination of EV_ERROR, EV_READ,	3147	passed an C<revents> set like normal event callbacks (a combination of
696	EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>:	3148	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
		3149	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3150	a timeout and an io event at the same time - you probably should give io
		3151	events precedence.
697		3152
		3153	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3154
698	static void stdin_ready (int revents, void *arg)	3155	static void stdin_ready (int revents, void *arg)
699	{	3156	{
700	if (revents & EV_TIMEOUT)
701	/* doh, nothing entered */
702	else if (revents & EV_READ)	3157	if (revents & EV_READ)
703	/* stdin might have data for us, joy! */	3158	/* stdin might have data for us, joy! */;
		3159	else if (revents & EV_TIMEOUT)
		3160	/* doh, nothing entered */;
704	}	3161	}
705		3162
706	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	3163	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
707
708	=item ev_feed_event (loop, watcher, int events)
709
710	Feeds the given event set into the event loop, as if the specified event
711	has happened for the specified watcher (which must be a pointer to an
712	initialised but not necessarily active event watcher).
713		3164
714	=item ev_feed_fd_event (loop, int fd, int revents)	3165	=item ev_feed_fd_event (loop, int fd, int revents)
715		3166
716	Feed an event on the given fd, as if a file descriptor backend detected it.	3167	Feed an event on the given fd, as if a file descriptor backend detected
		3168	the given events it.
717		3169
718	=item ev_feed_signal_event (loop, int signum)	3170	=item ev_feed_signal_event (loop, int signum)
719		3171
720	Feed an event as if the given signal occured (loop must be the default loop!).	3172	Feed an event as if the given signal occurred (C<loop> must be the default
		3173	loop!).
721		3174
722	=back	3175	=back
723		3176
		3177
		3178	=head1 LIBEVENT EMULATION
		3179
		3180	Libev offers a compatibility emulation layer for libevent. It cannot
		3181	emulate the internals of libevent, so here are some usage hints:
		3182
		3183	=over 4
		3184
		3185	=item * Use it by including <event.h>, as usual.
		3186
		3187	=item * The following members are fully supported: ev_base, ev_callback,
		3188	ev_arg, ev_fd, ev_res, ev_events.
		3189
		3190	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		3191	maintained by libev, it does not work exactly the same way as in libevent (consider
		3192	it a private API).
		3193
		3194	=item * Priorities are not currently supported. Initialising priorities
		3195	will fail and all watchers will have the same priority, even though there
		3196	is an ev_pri field.
		3197
		3198	=item * In libevent, the last base created gets the signals, in libev, the
		3199	first base created (== the default loop) gets the signals.
		3200
		3201	=item * Other members are not supported.
		3202
		3203	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		3204	to use the libev header file and library.
		3205
		3206	=back
		3207
		3208	=head1 C++ SUPPORT
		3209
		3210	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3211	you to use some convenience methods to start/stop watchers and also change
		3212	the callback model to a model using method callbacks on objects.
		3213
		3214	To use it,
		3215
		3216	#include <ev++.h>
		3217
		3218	This automatically includes F<ev.h> and puts all of its definitions (many
		3219	of them macros) into the global namespace. All C++ specific things are
		3220	put into the C<ev> namespace. It should support all the same embedding
		3221	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3222
		3223	Care has been taken to keep the overhead low. The only data member the C++
		3224	classes add (compared to plain C-style watchers) is the event loop pointer
		3225	that the watcher is associated with (or no additional members at all if
		3226	you disable C<EV_MULTIPLICITY> when embedding libev).
		3227
		3228	Currently, functions, and static and non-static member functions can be
		3229	used as callbacks. Other types should be easy to add as long as they only
		3230	need one additional pointer for context. If you need support for other
		3231	types of functors please contact the author (preferably after implementing
		3232	it).
		3233
		3234	Here is a list of things available in the C<ev> namespace:
		3235
		3236	=over 4
		3237
		3238	=item C<ev::READ>, C<ev::WRITE> etc.
		3239
		3240	These are just enum values with the same values as the C<EV_READ> etc.
		3241	macros from F<ev.h>.
		3242
		3243	=item C<ev::tstamp>, C<ev::now>
		3244
		3245	Aliases to the same types/functions as with the C<ev_> prefix.
		3246
		3247	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		3248
		3249	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		3250	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		3251	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3252	defines by many implementations.
		3253
		3254	All of those classes have these methods:
		3255
		3256	=over 4
		3257
		3258	=item ev::TYPE::TYPE ()
		3259
		3260	=item ev::TYPE::TYPE (loop)
		3261
		3262	=item ev::TYPE::~TYPE
		3263
		3264	The constructor (optionally) takes an event loop to associate the watcher
		3265	with. If it is omitted, it will use C<EV_DEFAULT>.
		3266
		3267	The constructor calls C<ev_init> for you, which means you have to call the
		3268	C<set> method before starting it.
		3269
		3270	It will not set a callback, however: You have to call the templated C<set>
		3271	method to set a callback before you can start the watcher.
		3272
		3273	(The reason why you have to use a method is a limitation in C++ which does
		3274	not allow explicit template arguments for constructors).
		3275
		3276	The destructor automatically stops the watcher if it is active.
		3277
		3278	=item w->set<class, &class::method> (object *)
		3279
		3280	This method sets the callback method to call. The method has to have a
		3281	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3282	first argument and the C<revents> as second. The object must be given as
		3283	parameter and is stored in the C<data> member of the watcher.
		3284
		3285	This method synthesizes efficient thunking code to call your method from
		3286	the C callback that libev requires. If your compiler can inline your
		3287	callback (i.e. it is visible to it at the place of the C<set> call and
		3288	your compiler is good :), then the method will be fully inlined into the
		3289	thunking function, making it as fast as a direct C callback.
		3290
		3291	Example: simple class declaration and watcher initialisation
		3292
		3293	struct myclass
		3294	{
		3295	void io_cb (ev::io &w, int revents) { }
		3296	}
		3297
		3298	myclass obj;
		3299	ev::io iow;
		3300	iow.set <myclass, &myclass::io_cb> (&obj);
		3301
		3302	=item w->set (object *)
		3303
		3304	This is an B<experimental> feature that might go away in a future version.
		3305
		3306	This is a variation of a method callback - leaving out the method to call
		3307	will default the method to C<operator ()>, which makes it possible to use
		3308	functor objects without having to manually specify the C<operator ()> all
		3309	the time. Incidentally, you can then also leave out the template argument
		3310	list.
		3311
		3312	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3313	int revents)>.
		3314
		3315	See the method-C<set> above for more details.
		3316
		3317	Example: use a functor object as callback.
		3318
		3319	struct myfunctor
		3320	{
		3321	void operator() (ev::io &w, int revents)
		3322	{
		3323	...
		3324	}
		3325	}
		3326
		3327	myfunctor f;
		3328
		3329	ev::io w;
		3330	w.set (&f);
		3331
		3332	=item w->set<function> (void *data = 0)
		3333
		3334	Also sets a callback, but uses a static method or plain function as
		3335	callback. The optional C<data> argument will be stored in the watcher's
		3336	C<data> member and is free for you to use.
		3337
		3338	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3339
		3340	See the method-C<set> above for more details.
		3341
		3342	Example: Use a plain function as callback.
		3343
		3344	static void io_cb (ev::io &w, int revents) { }
		3345	iow.set <io_cb> ();
		3346
		3347	=item w->set (loop)
		3348
		3349	Associates a different C<struct ev_loop> with this watcher. You can only
		3350	do this when the watcher is inactive (and not pending either).
		3351
		3352	=item w->set ([arguments])
		3353
		3354	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		3355	called at least once. Unlike the C counterpart, an active watcher gets
		3356	automatically stopped and restarted when reconfiguring it with this
		3357	method.
		3358
		3359	=item w->start ()
		3360
		3361	Starts the watcher. Note that there is no C<loop> argument, as the
		3362	constructor already stores the event loop.
		3363
		3364	=item w->stop ()
		3365
		3366	Stops the watcher if it is active. Again, no C<loop> argument.
		3367
		3368	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		3369
		3370	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		3371	C<ev_TYPE_again> function.
		3372
		3373	=item w->sweep () (C<ev::embed> only)
		3374
		3375	Invokes C<ev_embed_sweep>.
		3376
		3377	=item w->update () (C<ev::stat> only)
		3378
		3379	Invokes C<ev_stat_stat>.
		3380
		3381	=back
		3382
		3383	=back
		3384
		3385	Example: Define a class with an IO and idle watcher, start one of them in
		3386	the constructor.
		3387
		3388	class myclass
		3389	{
		3390	ev::io io ; void io_cb (ev::io &w, int revents);
		3391	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3392
		3393	myclass (int fd)
		3394	{
		3395	io .set <myclass, &myclass::io_cb > (this);
		3396	idle.set <myclass, &myclass::idle_cb> (this);
		3397
		3398	io.start (fd, ev::READ);
		3399	}
		3400	};
		3401
		3402
		3403	=head1 OTHER LANGUAGE BINDINGS
		3404
		3405	Libev does not offer other language bindings itself, but bindings for a
		3406	number of languages exist in the form of third-party packages. If you know
		3407	any interesting language binding in addition to the ones listed here, drop
		3408	me a note.
		3409
		3410	=over 4
		3411
		3412	=item Perl
		3413
		3414	The EV module implements the full libev API and is actually used to test
		3415	libev. EV is developed together with libev. Apart from the EV core module,
		3416	there are additional modules that implement libev-compatible interfaces
		3417	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3418	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3419	and C<EV::Glib>).
		3420
		3421	It can be found and installed via CPAN, its homepage is at
		3422	L<http://software.schmorp.de/pkg/EV>.
		3423
		3424	=item Python
		3425
		3426	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3427	seems to be quite complete and well-documented.
		3428
		3429	=item Ruby
		3430
		3431	Tony Arcieri has written a ruby extension that offers access to a subset
		3432	of the libev API and adds file handle abstractions, asynchronous DNS and
		3433	more on top of it. It can be found via gem servers. Its homepage is at
		3434	L<http://rev.rubyforge.org/>.
		3435
		3436	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3437	makes rev work even on mingw.
		3438
		3439	=item Haskell
		3440
		3441	A haskell binding to libev is available at
		3442	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3443
		3444	=item D
		3445
		3446	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3447	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3448
		3449	=item Ocaml
		3450
		3451	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3452	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3453
		3454	=item Lua
		3455
		3456	Brian Maher has written a partial interface to libev for lua (at the
		3457	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3458	L<http://github.com/brimworks/lua-ev>.
		3459
		3460	=back
		3461
		3462
		3463	=head1 MACRO MAGIC
		3464
		3465	Libev can be compiled with a variety of options, the most fundamental
		3466	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3467	functions and callbacks have an initial C<struct ev_loop *> argument.
		3468
		3469	To make it easier to write programs that cope with either variant, the
		3470	following macros are defined:
		3471
		3472	=over 4
		3473
		3474	=item C<EV_A>, C<EV_A_>
		3475
		3476	This provides the loop I<argument> for functions, if one is required ("ev
		3477	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3478	C<EV_A_> is used when other arguments are following. Example:
		3479
		3480	ev_unref (EV_A);
		3481	ev_timer_add (EV_A_ watcher);
		3482	ev_loop (EV_A_ 0);
		3483
		3484	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3485	which is often provided by the following macro.
		3486
		3487	=item C<EV_P>, C<EV_P_>
		3488
		3489	This provides the loop I<parameter> for functions, if one is required ("ev
		3490	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3491	C<EV_P_> is used when other parameters are following. Example:
		3492
		3493	// this is how ev_unref is being declared
		3494	static void ev_unref (EV_P);
		3495
		3496	// this is how you can declare your typical callback
		3497	static void cb (EV_P_ ev_timer *w, int revents)
		3498
		3499	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3500	suitable for use with C<EV_A>.
		3501
		3502	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3503
		3504	Similar to the other two macros, this gives you the value of the default
		3505	loop, if multiple loops are supported ("ev loop default").
		3506
		3507	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3508
		3509	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3510	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3511	is undefined when the default loop has not been initialised by a previous
		3512	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3513
		3514	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3515	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3516
		3517	=back
		3518
		3519	Example: Declare and initialise a check watcher, utilising the above
		3520	macros so it will work regardless of whether multiple loops are supported
		3521	or not.
		3522
		3523	static void
		3524	check_cb (EV_P_ ev_timer *w, int revents)
		3525	{
		3526	ev_check_stop (EV_A_ w);
		3527	}
		3528
		3529	ev_check check;
		3530	ev_check_init (&check, check_cb);
		3531	ev_check_start (EV_DEFAULT_ &check);
		3532	ev_loop (EV_DEFAULT_ 0);
		3533
		3534	=head1 EMBEDDING
		3535
		3536	Libev can (and often is) directly embedded into host
		3537	applications. Examples of applications that embed it include the Deliantra
		3538	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3539	and rxvt-unicode.
		3540
		3541	The goal is to enable you to just copy the necessary files into your
		3542	source directory without having to change even a single line in them, so
		3543	you can easily upgrade by simply copying (or having a checked-out copy of
		3544	libev somewhere in your source tree).
		3545
		3546	=head2 FILESETS
		3547
		3548	Depending on what features you need you need to include one or more sets of files
		3549	in your application.
		3550
		3551	=head3 CORE EVENT LOOP
		3552
		3553	To include only the libev core (all the C<ev_*> functions), with manual
		3554	configuration (no autoconf):
		3555
		3556	#define EV_STANDALONE 1
		3557	#include "ev.c"
		3558
		3559	This will automatically include F<ev.h>, too, and should be done in a
		3560	single C source file only to provide the function implementations. To use
		3561	it, do the same for F<ev.h> in all files wishing to use this API (best
		3562	done by writing a wrapper around F<ev.h> that you can include instead and
		3563	where you can put other configuration options):
		3564
		3565	#define EV_STANDALONE 1
		3566	#include "ev.h"
		3567
		3568	Both header files and implementation files can be compiled with a C++
		3569	compiler (at least, that's a stated goal, and breakage will be treated
		3570	as a bug).
		3571
		3572	You need the following files in your source tree, or in a directory
		3573	in your include path (e.g. in libev/ when using -Ilibev):
		3574
		3575	ev.h
		3576	ev.c
		3577	ev_vars.h
		3578	ev_wrap.h
		3579
		3580	ev_win32.c required on win32 platforms only
		3581
		3582	ev_select.c only when select backend is enabled (which is enabled by default)
		3583	ev_poll.c only when poll backend is enabled (disabled by default)
		3584	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3585	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3586	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3587
		3588	F<ev.c> includes the backend files directly when enabled, so you only need
		3589	to compile this single file.
		3590
		3591	=head3 LIBEVENT COMPATIBILITY API
		3592
		3593	To include the libevent compatibility API, also include:
		3594
		3595	#include "event.c"
		3596
		3597	in the file including F<ev.c>, and:
		3598
		3599	#include "event.h"
		3600
		3601	in the files that want to use the libevent API. This also includes F<ev.h>.
		3602
		3603	You need the following additional files for this:
		3604
		3605	event.h
		3606	event.c
		3607
		3608	=head3 AUTOCONF SUPPORT
		3609
		3610	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3611	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3612	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3613	include F<config.h> and configure itself accordingly.
		3614
		3615	For this of course you need the m4 file:
		3616
		3617	libev.m4
		3618
		3619	=head2 PREPROCESSOR SYMBOLS/MACROS
		3620
		3621	Libev can be configured via a variety of preprocessor symbols you have to
		3622	define before including (or compiling) any of its files. The default in
		3623	the absence of autoconf is documented for every option.
		3624
		3625	Symbols marked with "(h)" do not change the ABI, and can have different
		3626	values when compiling libev vs. including F<ev.h>, so it is permissible
		3627	to redefine them before including F<ev.h> without breakign compatibility
		3628	to a compiled library. All other symbols change the ABI, which means all
		3629	users of libev and the libev code itself must be compiled with compatible
		3630	settings.
		3631
		3632	=over 4
		3633
		3634	=item EV_STANDALONE (h)
		3635
		3636	Must always be C<1> if you do not use autoconf configuration, which
		3637	keeps libev from including F<config.h>, and it also defines dummy
		3638	implementations for some libevent functions (such as logging, which is not
		3639	supported). It will also not define any of the structs usually found in
		3640	F<event.h> that are not directly supported by the libev core alone.
		3641
		3642	In standalone mode, libev will still try to automatically deduce the
		3643	configuration, but has to be more conservative.
		3644
		3645	=item EV_USE_MONOTONIC
		3646
		3647	If defined to be C<1>, libev will try to detect the availability of the
		3648	monotonic clock option at both compile time and runtime. Otherwise no
		3649	use of the monotonic clock option will be attempted. If you enable this,
		3650	you usually have to link against librt or something similar. Enabling it
		3651	when the functionality isn't available is safe, though, although you have
		3652	to make sure you link against any libraries where the C<clock_gettime>
		3653	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3654
		3655	=item EV_USE_REALTIME
		3656
		3657	If defined to be C<1>, libev will try to detect the availability of the
		3658	real-time clock option at compile time (and assume its availability
		3659	at runtime if successful). Otherwise no use of the real-time clock
		3660	option will be attempted. This effectively replaces C<gettimeofday>
		3661	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		3662	correctness. See the note about libraries in the description of
		3663	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3664	C<EV_USE_CLOCK_SYSCALL>.
		3665
		3666	=item EV_USE_CLOCK_SYSCALL
		3667
		3668	If defined to be C<1>, libev will try to use a direct syscall instead
		3669	of calling the system-provided C<clock_gettime> function. This option
		3670	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3671	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3672	programs needlessly. Using a direct syscall is slightly slower (in
		3673	theory), because no optimised vdso implementation can be used, but avoids
		3674	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3675	higher, as it simplifies linking (no need for C<-lrt>).
		3676
		3677	=item EV_USE_NANOSLEEP
		3678
		3679	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3680	and will use it for delays. Otherwise it will use C<select ()>.
		3681
		3682	=item EV_USE_EVENTFD
		3683
		3684	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3685	available and will probe for kernel support at runtime. This will improve
		3686	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3687	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3688	2.7 or newer, otherwise disabled.
		3689
		3690	=item EV_USE_SELECT
		3691
		3692	If undefined or defined to be C<1>, libev will compile in support for the
		3693	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3694	other method takes over, select will be it. Otherwise the select backend
		3695	will not be compiled in.
		3696
		3697	=item EV_SELECT_USE_FD_SET
		3698
		3699	If defined to C<1>, then the select backend will use the system C<fd_set>
		3700	structure. This is useful if libev doesn't compile due to a missing
		3701	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		3702	on exotic systems. This usually limits the range of file descriptors to
		3703	some low limit such as 1024 or might have other limitations (winsocket
		3704	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		3705	configures the maximum size of the C<fd_set>.
		3706
		3707	=item EV_SELECT_IS_WINSOCKET
		3708
		3709	When defined to C<1>, the select backend will assume that
		3710	select/socket/connect etc. don't understand file descriptors but
		3711	wants osf handles on win32 (this is the case when the select to
		3712	be used is the winsock select). This means that it will call
		3713	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3714	it is assumed that all these functions actually work on fds, even
		3715	on win32. Should not be defined on non-win32 platforms.
		3716
		3717	=item EV_FD_TO_WIN32_HANDLE(fd)
		3718
		3719	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3720	file descriptors to socket handles. When not defining this symbol (the
		3721	default), then libev will call C<_get_osfhandle>, which is usually
		3722	correct. In some cases, programs use their own file descriptor management,
		3723	in which case they can provide this function to map fds to socket handles.
		3724
		3725	=item EV_WIN32_HANDLE_TO_FD(handle)
		3726
		3727	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3728	using the standard C<_open_osfhandle> function. For programs implementing
		3729	their own fd to handle mapping, overwriting this function makes it easier
		3730	to do so. This can be done by defining this macro to an appropriate value.
		3731
		3732	=item EV_WIN32_CLOSE_FD(fd)
		3733
		3734	If programs implement their own fd to handle mapping on win32, then this
		3735	macro can be used to override the C<close> function, useful to unregister
		3736	file descriptors again. Note that the replacement function has to close
		3737	the underlying OS handle.
		3738
		3739	=item EV_USE_POLL
		3740
		3741	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3742	backend. Otherwise it will be enabled on non-win32 platforms. It
		3743	takes precedence over select.
		3744
		3745	=item EV_USE_EPOLL
		3746
		3747	If defined to be C<1>, libev will compile in support for the Linux
		3748	C<epoll>(7) backend. Its availability will be detected at runtime,
		3749	otherwise another method will be used as fallback. This is the preferred
		3750	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3751	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3752
		3753	=item EV_USE_KQUEUE
		3754
		3755	If defined to be C<1>, libev will compile in support for the BSD style
		3756	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3757	otherwise another method will be used as fallback. This is the preferred
		3758	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3759	supports some types of fds correctly (the only platform we found that
		3760	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3761	not be used unless explicitly requested. The best way to use it is to find
		3762	out whether kqueue supports your type of fd properly and use an embedded
		3763	kqueue loop.
		3764
		3765	=item EV_USE_PORT
		3766
		3767	If defined to be C<1>, libev will compile in support for the Solaris
		3768	10 port style backend. Its availability will be detected at runtime,
		3769	otherwise another method will be used as fallback. This is the preferred
		3770	backend for Solaris 10 systems.
		3771
		3772	=item EV_USE_DEVPOLL
		3773
		3774	Reserved for future expansion, works like the USE symbols above.
		3775
		3776	=item EV_USE_INOTIFY
		3777
		3778	If defined to be C<1>, libev will compile in support for the Linux inotify
		3779	interface to speed up C<ev_stat> watchers. Its actual availability will
		3780	be detected at runtime. If undefined, it will be enabled if the headers
		3781	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3782
		3783	=item EV_ATOMIC_T
		3784
		3785	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3786	access is atomic with respect to other threads or signal contexts. No such
		3787	type is easily found in the C language, so you can provide your own type
		3788	that you know is safe for your purposes. It is used both for signal handler "locking"
		3789	as well as for signal and thread safety in C<ev_async> watchers.
		3790
		3791	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3792	(from F<signal.h>), which is usually good enough on most platforms.
		3793
		3794	=item EV_H (h)
		3795
		3796	The name of the F<ev.h> header file used to include it. The default if
		3797	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3798	used to virtually rename the F<ev.h> header file in case of conflicts.
		3799
		3800	=item EV_CONFIG_H (h)
		3801
		3802	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3803	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3804	C<EV_H>, above.
		3805
		3806	=item EV_EVENT_H (h)
		3807
		3808	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3809	of how the F<event.h> header can be found, the default is C<"event.h">.
		3810
		3811	=item EV_PROTOTYPES (h)
		3812
		3813	If defined to be C<0>, then F<ev.h> will not define any function
		3814	prototypes, but still define all the structs and other symbols. This is
		3815	occasionally useful if you want to provide your own wrapper functions
		3816	around libev functions.
		3817
		3818	=item EV_MULTIPLICITY
		3819
		3820	If undefined or defined to C<1>, then all event-loop-specific functions
		3821	will have the C<struct ev_loop *> as first argument, and you can create
		3822	additional independent event loops. Otherwise there will be no support
		3823	for multiple event loops and there is no first event loop pointer
		3824	argument. Instead, all functions act on the single default loop.
		3825
		3826	=item EV_MINPRI
		3827
		3828	=item EV_MAXPRI
		3829
		3830	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3831	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3832	provide for more priorities by overriding those symbols (usually defined
		3833	to be C<-2> and C<2>, respectively).
		3834
		3835	When doing priority-based operations, libev usually has to linearly search
		3836	all the priorities, so having many of them (hundreds) uses a lot of space
		3837	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3838	fine.
		3839
		3840	If your embedding application does not need any priorities, defining these
		3841	both to C<0> will save some memory and CPU.
		3842
		3843	=item EV_PERIODIC_ENABLE
		3844
		3845	If undefined or defined to be C<1>, then periodic timers are supported. If
		3846	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3847	code.
		3848
		3849	=item EV_IDLE_ENABLE
		3850
		3851	If undefined or defined to be C<1>, then idle watchers are supported. If
		3852	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3853	code.
		3854
		3855	=item EV_EMBED_ENABLE
		3856
		3857	If undefined or defined to be C<1>, then embed watchers are supported. If
		3858	defined to be C<0>, then they are not. Embed watchers rely on most other
		3859	watcher types, which therefore must not be disabled.
		3860
		3861	=item EV_STAT_ENABLE
		3862
		3863	If undefined or defined to be C<1>, then stat watchers are supported. If
		3864	defined to be C<0>, then they are not.
		3865
		3866	=item EV_FORK_ENABLE
		3867
		3868	If undefined or defined to be C<1>, then fork watchers are supported. If
		3869	defined to be C<0>, then they are not.
		3870
		3871	=item EV_SIGNAL_ENABLE
		3872
		3873	If undefined or defined to be C<1>, then signal watchers are supported. If
		3874	defined to be C<0>, then they are not.
		3875
		3876	=item EV_ASYNC_ENABLE
		3877
		3878	If undefined or defined to be C<1>, then async watchers are supported. If
		3879	defined to be C<0>, then they are not.
		3880
		3881	=item EV_CHILD_ENABLE
		3882
		3883	If undefined or defined to be C<1> (and C<_WIN32> is not defined), then
		3884	child watchers are supported. If defined to be C<0>, then they are not.
		3885
		3886	=item EV_MINIMAL
		3887
		3888	If you need to shave off some kilobytes of code at the expense of some
		3889	speed (but with the full API), define this symbol to C<1>. Currently this
		3890	is used to override some inlining decisions, saves roughly 30% code size
		3891	on amd64. It also selects a much smaller 2-heap for timer management over
		3892	the default 4-heap.
		3893
		3894	You can save even more by disabling watcher types you do not need
		3895	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3896	(C<-DNDEBUG>) will usually reduce code size a lot. Disabling inotify,
		3897	eventfd and signalfd will further help, and disabling backends one doesn't
		3898	need (e.g. poll, epoll, kqueue, ports) will help further.
		3899
		3900	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3901	provide a bare-bones event library. See C<ev.h> for details on what parts
		3902	of the API are still available, and do not complain if this subset changes
		3903	over time.
		3904
		3905	This example set of settings reduces the compiled size of libev from 24Kb
		3906	to 8Kb on my GNU/Linux amd64 system (and leaves little in - there is also
		3907	an effect on the amount of memory used). With an intelligent-enough linker
		3908	further unused functions might be left out as well automatically.
		3909
		3910	// tuning and API changes
		3911	#define EV_MINIMAL 2
		3912	#define EV_MULTIPLICITY 0
		3913	#define EV_MINPRI 0
		3914	#define EV_MAXPRI 0
		3915
		3916	// OS-specific backends
		3917	#define EV_USE_INOTIFY 0
		3918	#define EV_USE_EVENTFD 0
		3919	#define EV_USE_SIGNALFD 0
		3920	#define EV_USE_REALTIME 0
		3921	#define EV_USE_MONOTONIC 0
		3922	#define EV_USE_CLOCK_SYSCALL 0
		3923
		3924	// disable all backends except select
		3925	#define EV_USE_POLL 0
		3926	#define EV_USE_PORT 0
		3927	#define EV_USE_KQUEUE 0
		3928	#define EV_USE_EPOLL 0
		3929
		3930	// disable all watcher types that cna be disabled
		3931	#define EV_STAT_ENABLE 0
		3932	#define EV_PERIODIC_ENABLE 0
		3933	#define EV_IDLE_ENABLE 0
		3934	#define EV_FORK_ENABLE 0
		3935	#define EV_SIGNAL_ENABLE 0
		3936	#define EV_CHILD_ENABLE 0
		3937	#define EV_ASYNC_ENABLE 0
		3938	#define EV_EMBED_ENABLE 0
		3939
		3940	=item EV_AVOID_STDIO
		3941
		3942	If this is set to C<1> at compiletime, then libev will avoid using stdio
		3943	functions (printf, scanf, perror etc.). This will increase the codesize
		3944	somewhat, but if your program doesn't otherwise depend on stdio and your
		3945	libc allows it, this avoids linking in the stdio library which is quite
		3946	big.
		3947
		3948	Note that error messages might become less precise when this option is
		3949	enabled.
		3950
		3951	=item EV_NSIG
		3952
		3953	The highest supported signal number, +1 (or, the number of
		3954	signals): Normally, libev tries to deduce the maximum number of signals
		3955	automatically, but sometimes this fails, in which case it can be
		3956	specified. Also, using a lower number than detected (C<32> should be
		3957	good for about any system in existance) can save some memory, as libev
		3958	statically allocates some 12-24 bytes per signal number.
		3959
		3960	=item EV_PID_HASHSIZE
		3961
		3962	C<ev_child> watchers use a small hash table to distribute workload by
		3963	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3964	than enough. If you need to manage thousands of children you might want to
		3965	increase this value (I<must> be a power of two).
		3966
		3967	=item EV_INOTIFY_HASHSIZE
		3968
		3969	C<ev_stat> watchers use a small hash table to distribute workload by
		3970	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3971	usually more than enough. If you need to manage thousands of C<ev_stat>
		3972	watchers you might want to increase this value (I<must> be a power of
		3973	two).
		3974
		3975	=item EV_USE_4HEAP
		3976
		3977	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3978	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3979	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3980	faster performance with many (thousands) of watchers.
		3981
		3982	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3983	(disabled).
		3984
		3985	=item EV_HEAP_CACHE_AT
		3986
		3987	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3988	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3989	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3990	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3991	but avoids random read accesses on heap changes. This improves performance
		3992	noticeably with many (hundreds) of watchers.
		3993
		3994	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3995	(disabled).
		3996
		3997	=item EV_VERIFY
		3998
		3999	Controls how much internal verification (see C<ev_loop_verify ()>) will
		4000	be done: If set to C<0>, no internal verification code will be compiled
		4001	in. If set to C<1>, then verification code will be compiled in, but not
		4002	called. If set to C<2>, then the internal verification code will be
		4003	called once per loop, which can slow down libev. If set to C<3>, then the
		4004	verification code will be called very frequently, which will slow down
		4005	libev considerably.
		4006
		4007	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		4008	C<0>.
		4009
		4010	=item EV_COMMON
		4011
		4012	By default, all watchers have a C<void *data> member. By redefining
		4013	this macro to a something else you can include more and other types of
		4014	members. You have to define it each time you include one of the files,
		4015	though, and it must be identical each time.
		4016
		4017	For example, the perl EV module uses something like this:
		4018
		4019	#define EV_COMMON \
		4020	SV *self; /* contains this struct */ \
		4021	SV *cb_sv, *fh /* note no trailing ";" */
		4022
		4023	=item EV_CB_DECLARE (type)
		4024
		4025	=item EV_CB_INVOKE (watcher, revents)
		4026
		4027	=item ev_set_cb (ev, cb)
		4028
		4029	Can be used to change the callback member declaration in each watcher,
		4030	and the way callbacks are invoked and set. Must expand to a struct member
		4031	definition and a statement, respectively. See the F<ev.h> header file for
		4032	their default definitions. One possible use for overriding these is to
		4033	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		4034	method calls instead of plain function calls in C++.
		4035
		4036	=back
		4037
		4038	=head2 EXPORTED API SYMBOLS
		4039
		4040	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4041	exported symbols, you can use the provided F<Symbol.*> files which list
		4042	all public symbols, one per line:
		4043
		4044	Symbols.ev for libev proper
		4045	Symbols.event for the libevent emulation
		4046
		4047	This can also be used to rename all public symbols to avoid clashes with
		4048	multiple versions of libev linked together (which is obviously bad in
		4049	itself, but sometimes it is inconvenient to avoid this).
		4050
		4051	A sed command like this will create wrapper C<#define>'s that you need to
		4052	include before including F<ev.h>:
		4053
		4054	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4055
		4056	This would create a file F<wrap.h> which essentially looks like this:
		4057
		4058	#define ev_backend myprefix_ev_backend
		4059	#define ev_check_start myprefix_ev_check_start
		4060	#define ev_check_stop myprefix_ev_check_stop
		4061	...
		4062
		4063	=head2 EXAMPLES
		4064
		4065	For a real-world example of a program the includes libev
		4066	verbatim, you can have a look at the EV perl module
		4067	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		4068	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		4069	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		4070	will be compiled. It is pretty complex because it provides its own header
		4071	file.
		4072
		4073	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		4074	that everybody includes and which overrides some configure choices:
		4075
		4076	#define EV_MINIMAL 1
		4077	#define EV_USE_POLL 0
		4078	#define EV_MULTIPLICITY 0
		4079	#define EV_PERIODIC_ENABLE 0
		4080	#define EV_STAT_ENABLE 0
		4081	#define EV_FORK_ENABLE 0
		4082	#define EV_CONFIG_H <config.h>
		4083	#define EV_MINPRI 0
		4084	#define EV_MAXPRI 0
		4085
		4086	#include "ev++.h"
		4087
		4088	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		4089
		4090	#include "ev_cpp.h"
		4091	#include "ev.c"
		4092
		4093	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		4094
		4095	=head2 THREADS AND COROUTINES
		4096
		4097	=head3 THREADS
		4098
		4099	All libev functions are reentrant and thread-safe unless explicitly
		4100	documented otherwise, but libev implements no locking itself. This means
		4101	that you can use as many loops as you want in parallel, as long as there
		4102	are no concurrent calls into any libev function with the same loop
		4103	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4104	of course): libev guarantees that different event loops share no data
		4105	structures that need any locking.
		4106
		4107	Or to put it differently: calls with different loop parameters can be done
		4108	concurrently from multiple threads, calls with the same loop parameter
		4109	must be done serially (but can be done from different threads, as long as
		4110	only one thread ever is inside a call at any point in time, e.g. by using
		4111	a mutex per loop).
		4112
		4113	Specifically to support threads (and signal handlers), libev implements
		4114	so-called C<ev_async> watchers, which allow some limited form of
		4115	concurrency on the same event loop, namely waking it up "from the
		4116	outside".
		4117
		4118	If you want to know which design (one loop, locking, or multiple loops
		4119	without or something else still) is best for your problem, then I cannot
		4120	help you, but here is some generic advice:
		4121
		4122	=over 4
		4123
		4124	=item * most applications have a main thread: use the default libev loop
		4125	in that thread, or create a separate thread running only the default loop.
		4126
		4127	This helps integrating other libraries or software modules that use libev
		4128	themselves and don't care/know about threading.
		4129
		4130	=item * one loop per thread is usually a good model.
		4131
		4132	Doing this is almost never wrong, sometimes a better-performance model
		4133	exists, but it is always a good start.
		4134
		4135	=item * other models exist, such as the leader/follower pattern, where one
		4136	loop is handed through multiple threads in a kind of round-robin fashion.
		4137
		4138	Choosing a model is hard - look around, learn, know that usually you can do
		4139	better than you currently do :-)
		4140
		4141	=item * often you need to talk to some other thread which blocks in the
		4142	event loop.
		4143
		4144	C<ev_async> watchers can be used to wake them up from other threads safely
		4145	(or from signal contexts...).
		4146
		4147	An example use would be to communicate signals or other events that only
		4148	work in the default loop by registering the signal watcher with the
		4149	default loop and triggering an C<ev_async> watcher from the default loop
		4150	watcher callback into the event loop interested in the signal.
		4151
		4152	=back
		4153
		4154	=head4 THREAD LOCKING EXAMPLE
		4155
		4156	Here is a fictitious example of how to run an event loop in a different
		4157	thread than where callbacks are being invoked and watchers are
		4158	created/added/removed.
		4159
		4160	For a real-world example, see the C<EV::Loop::Async> perl module,
		4161	which uses exactly this technique (which is suited for many high-level
		4162	languages).
		4163
		4164	The example uses a pthread mutex to protect the loop data, a condition
		4165	variable to wait for callback invocations, an async watcher to notify the
		4166	event loop thread and an unspecified mechanism to wake up the main thread.
		4167
		4168	First, you need to associate some data with the event loop:
		4169
		4170	typedef struct {
		4171	mutex_t lock; /* global loop lock */
		4172	ev_async async_w;
		4173	thread_t tid;
		4174	cond_t invoke_cv;
		4175	} userdata;
		4176
		4177	void prepare_loop (EV_P)
		4178	{
		4179	// for simplicity, we use a static userdata struct.
		4180	static userdata u;
		4181
		4182	ev_async_init (&u->async_w, async_cb);
		4183	ev_async_start (EV_A_ &u->async_w);
		4184
		4185	pthread_mutex_init (&u->lock, 0);
		4186	pthread_cond_init (&u->invoke_cv, 0);
		4187
		4188	// now associate this with the loop
		4189	ev_set_userdata (EV_A_ u);
		4190	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4191	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4192
		4193	// then create the thread running ev_loop
		4194	pthread_create (&u->tid, 0, l_run, EV_A);
		4195	}
		4196
		4197	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4198	solely to wake up the event loop so it takes notice of any new watchers
		4199	that might have been added:
		4200
		4201	static void
		4202	async_cb (EV_P_ ev_async *w, int revents)
		4203	{
		4204	// just used for the side effects
		4205	}
		4206
		4207	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4208	protecting the loop data, respectively.
		4209
		4210	static void
		4211	l_release (EV_P)
		4212	{
		4213	userdata *u = ev_userdata (EV_A);
		4214	pthread_mutex_unlock (&u->lock);
		4215	}
		4216
		4217	static void
		4218	l_acquire (EV_P)
		4219	{
		4220	userdata *u = ev_userdata (EV_A);
		4221	pthread_mutex_lock (&u->lock);
		4222	}
		4223
		4224	The event loop thread first acquires the mutex, and then jumps straight
		4225	into C<ev_loop>:
		4226
		4227	void *
		4228	l_run (void *thr_arg)
		4229	{
		4230	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4231
		4232	l_acquire (EV_A);
		4233	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4234	ev_loop (EV_A_ 0);
		4235	l_release (EV_A);
		4236
		4237	return 0;
		4238	}
		4239
		4240	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4241	signal the main thread via some unspecified mechanism (signals? pipe
		4242	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4243	have been called (in a while loop because a) spurious wakeups are possible
		4244	and b) skipping inter-thread-communication when there are no pending
		4245	watchers is very beneficial):
		4246
		4247	static void
		4248	l_invoke (EV_P)
		4249	{
		4250	userdata *u = ev_userdata (EV_A);
		4251
		4252	while (ev_pending_count (EV_A))
		4253	{
		4254	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4255	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4256	}
		4257	}
		4258
		4259	Now, whenever the main thread gets told to invoke pending watchers, it
		4260	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4261	thread to continue:
		4262
		4263	static void
		4264	real_invoke_pending (EV_P)
		4265	{
		4266	userdata *u = ev_userdata (EV_A);
		4267
		4268	pthread_mutex_lock (&u->lock);
		4269	ev_invoke_pending (EV_A);
		4270	pthread_cond_signal (&u->invoke_cv);
		4271	pthread_mutex_unlock (&u->lock);
		4272	}
		4273
		4274	Whenever you want to start/stop a watcher or do other modifications to an
		4275	event loop, you will now have to lock:
		4276
		4277	ev_timer timeout_watcher;
		4278	userdata *u = ev_userdata (EV_A);
		4279
		4280	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4281
		4282	pthread_mutex_lock (&u->lock);
		4283	ev_timer_start (EV_A_ &timeout_watcher);
		4284	ev_async_send (EV_A_ &u->async_w);
		4285	pthread_mutex_unlock (&u->lock);
		4286
		4287	Note that sending the C<ev_async> watcher is required because otherwise
		4288	an event loop currently blocking in the kernel will have no knowledge
		4289	about the newly added timer. By waking up the loop it will pick up any new
		4290	watchers in the next event loop iteration.
		4291
		4292	=head3 COROUTINES
		4293
		4294	Libev is very accommodating to coroutines ("cooperative threads"):
		4295	libev fully supports nesting calls to its functions from different
		4296	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4297	different coroutines, and switch freely between both coroutines running
		4298	the loop, as long as you don't confuse yourself). The only exception is
		4299	that you must not do this from C<ev_periodic> reschedule callbacks.
		4300
		4301	Care has been taken to ensure that libev does not keep local state inside
		4302	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4303	they do not call any callbacks.
		4304
		4305	=head2 COMPILER WARNINGS
		4306
		4307	Depending on your compiler and compiler settings, you might get no or a
		4308	lot of warnings when compiling libev code. Some people are apparently
		4309	scared by this.
		4310
		4311	However, these are unavoidable for many reasons. For one, each compiler
		4312	has different warnings, and each user has different tastes regarding
		4313	warning options. "Warn-free" code therefore cannot be a goal except when
		4314	targeting a specific compiler and compiler-version.
		4315
		4316	Another reason is that some compiler warnings require elaborate
		4317	workarounds, or other changes to the code that make it less clear and less
		4318	maintainable.
		4319
		4320	And of course, some compiler warnings are just plain stupid, or simply
		4321	wrong (because they don't actually warn about the condition their message
		4322	seems to warn about). For example, certain older gcc versions had some
		4323	warnings that resulted an extreme number of false positives. These have
		4324	been fixed, but some people still insist on making code warn-free with
		4325	such buggy versions.
		4326
		4327	While libev is written to generate as few warnings as possible,
		4328	"warn-free" code is not a goal, and it is recommended not to build libev
		4329	with any compiler warnings enabled unless you are prepared to cope with
		4330	them (e.g. by ignoring them). Remember that warnings are just that:
		4331	warnings, not errors, or proof of bugs.
		4332
		4333
		4334	=head2 VALGRIND
		4335
		4336	Valgrind has a special section here because it is a popular tool that is
		4337	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4338
		4339	If you think you found a bug (memory leak, uninitialised data access etc.)
		4340	in libev, then check twice: If valgrind reports something like:
		4341
		4342	==2274== definitely lost: 0 bytes in 0 blocks.
		4343	==2274== possibly lost: 0 bytes in 0 blocks.
		4344	==2274== still reachable: 256 bytes in 1 blocks.
		4345
		4346	Then there is no memory leak, just as memory accounted to global variables
		4347	is not a memleak - the memory is still being referenced, and didn't leak.
		4348
		4349	Similarly, under some circumstances, valgrind might report kernel bugs
		4350	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4351	although an acceptable workaround has been found here), or it might be
		4352	confused.
		4353
		4354	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4355	make it into some kind of religion.
		4356
		4357	If you are unsure about something, feel free to contact the mailing list
		4358	with the full valgrind report and an explanation on why you think this
		4359	is a bug in libev (best check the archives, too :). However, don't be
		4360	annoyed when you get a brisk "this is no bug" answer and take the chance
		4361	of learning how to interpret valgrind properly.
		4362
		4363	If you need, for some reason, empty reports from valgrind for your project
		4364	I suggest using suppression lists.
		4365
		4366
		4367	=head1 PORTABILITY NOTES
		4368
		4369	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4370
		4371	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4372	requires, and its I/O model is fundamentally incompatible with the POSIX
		4373	model. Libev still offers limited functionality on this platform in
		4374	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4375	descriptors. This only applies when using Win32 natively, not when using
		4376	e.g. cygwin.
		4377
		4378	Lifting these limitations would basically require the full
		4379	re-implementation of the I/O system. If you are into these kinds of
		4380	things, then note that glib does exactly that for you in a very portable
		4381	way (note also that glib is the slowest event library known to man).
		4382
		4383	There is no supported compilation method available on windows except
		4384	embedding it into other applications.
		4385
		4386	Sensible signal handling is officially unsupported by Microsoft - libev
		4387	tries its best, but under most conditions, signals will simply not work.
		4388
		4389	Not a libev limitation but worth mentioning: windows apparently doesn't
		4390	accept large writes: instead of resulting in a partial write, windows will
		4391	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4392	so make sure you only write small amounts into your sockets (less than a
		4393	megabyte seems safe, but this apparently depends on the amount of memory
		4394	available).
		4395
		4396	Due to the many, low, and arbitrary limits on the win32 platform and
		4397	the abysmal performance of winsockets, using a large number of sockets
		4398	is not recommended (and not reasonable). If your program needs to use
		4399	more than a hundred or so sockets, then likely it needs to use a totally
		4400	different implementation for windows, as libev offers the POSIX readiness
		4401	notification model, which cannot be implemented efficiently on windows
		4402	(due to Microsoft monopoly games).
		4403
		4404	A typical way to use libev under windows is to embed it (see the embedding
		4405	section for details) and use the following F<evwrap.h> header file instead
		4406	of F<ev.h>:
		4407
		4408	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4409	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4410
		4411	#include "ev.h"
		4412
		4413	And compile the following F<evwrap.c> file into your project (make sure
		4414	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4415
		4416	#include "evwrap.h"
		4417	#include "ev.c"
		4418
		4419	=over 4
		4420
		4421	=item The winsocket select function
		4422
		4423	The winsocket C<select> function doesn't follow POSIX in that it
		4424	requires socket I<handles> and not socket I<file descriptors> (it is
		4425	also extremely buggy). This makes select very inefficient, and also
		4426	requires a mapping from file descriptors to socket handles (the Microsoft
		4427	C runtime provides the function C<_open_osfhandle> for this). See the
		4428	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4429	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4430
		4431	The configuration for a "naked" win32 using the Microsoft runtime
		4432	libraries and raw winsocket select is:
		4433
		4434	#define EV_USE_SELECT 1
		4435	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4436
		4437	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4438	complexity in the O(n²) range when using win32.
		4439
		4440	=item Limited number of file descriptors
		4441
		4442	Windows has numerous arbitrary (and low) limits on things.
		4443
		4444	Early versions of winsocket's select only supported waiting for a maximum
		4445	of C<64> handles (probably owning to the fact that all windows kernels
		4446	can only wait for C<64> things at the same time internally; Microsoft
		4447	recommends spawning a chain of threads and wait for 63 handles and the
		4448	previous thread in each. Sounds great!).
		4449
		4450	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4451	to some high number (e.g. C<2048>) before compiling the winsocket select
		4452	call (which might be in libev or elsewhere, for example, perl and many
		4453	other interpreters do their own select emulation on windows).
		4454
		4455	Another limit is the number of file descriptors in the Microsoft runtime
		4456	libraries, which by default is C<64> (there must be a hidden I<64>
		4457	fetish or something like this inside Microsoft). You can increase this
		4458	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4459	(another arbitrary limit), but is broken in many versions of the Microsoft
		4460	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4461	(depending on windows version and/or the phase of the moon). To get more,
		4462	you need to wrap all I/O functions and provide your own fd management, but
		4463	the cost of calling select (O(n²)) will likely make this unworkable.
		4464
		4465	=back
		4466
		4467	=head2 PORTABILITY REQUIREMENTS
		4468
		4469	In addition to a working ISO-C implementation and of course the
		4470	backend-specific APIs, libev relies on a few additional extensions:
		4471
		4472	=over 4
		4473
		4474	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4475	calling conventions regardless of C<ev_watcher_type *>.
		4476
		4477	Libev assumes not only that all watcher pointers have the same internal
		4478	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4479	assumes that the same (machine) code can be used to call any watcher
		4480	callback: The watcher callbacks have different type signatures, but libev
		4481	calls them using an C<ev_watcher *> internally.
		4482
		4483	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4484
		4485	The type C<sig_atomic_t volatile> (or whatever is defined as
		4486	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4487	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4488	believed to be sufficiently portable.
		4489
		4490	=item C<sigprocmask> must work in a threaded environment
		4491
		4492	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4493	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4494	pthread implementations will either allow C<sigprocmask> in the "main
		4495	thread" or will block signals process-wide, both behaviours would
		4496	be compatible with libev. Interaction between C<sigprocmask> and
		4497	C<pthread_sigmask> could complicate things, however.
		4498
		4499	The most portable way to handle signals is to block signals in all threads
		4500	except the initial one, and run the default loop in the initial thread as
		4501	well.
		4502
		4503	=item C<long> must be large enough for common memory allocation sizes
		4504
		4505	To improve portability and simplify its API, libev uses C<long> internally
		4506	instead of C<size_t> when allocating its data structures. On non-POSIX
		4507	systems (Microsoft...) this might be unexpectedly low, but is still at
		4508	least 31 bits everywhere, which is enough for hundreds of millions of
		4509	watchers.
		4510
		4511	=item C<double> must hold a time value in seconds with enough accuracy
		4512
		4513	The type C<double> is used to represent timestamps. It is required to
		4514	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4515	enough for at least into the year 4000. This requirement is fulfilled by
		4516	implementations implementing IEEE 754, which is basically all existing
		4517	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4518	2200.
		4519
		4520	=back
		4521
		4522	If you know of other additional requirements drop me a note.
		4523
		4524
		4525	=head1 ALGORITHMIC COMPLEXITIES
		4526
		4527	In this section the complexities of (many of) the algorithms used inside
		4528	libev will be documented. For complexity discussions about backends see
		4529	the documentation for C<ev_default_init>.
		4530
		4531	All of the following are about amortised time: If an array needs to be
		4532	extended, libev needs to realloc and move the whole array, but this
		4533	happens asymptotically rarer with higher number of elements, so O(1) might
		4534	mean that libev does a lengthy realloc operation in rare cases, but on
		4535	average it is much faster and asymptotically approaches constant time.
		4536
		4537	=over 4
		4538
		4539	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4540
		4541	This means that, when you have a watcher that triggers in one hour and
		4542	there are 100 watchers that would trigger before that, then inserting will
		4543	have to skip roughly seven (C<ld 100>) of these watchers.
		4544
		4545	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4546
		4547	That means that changing a timer costs less than removing/adding them,
		4548	as only the relative motion in the event queue has to be paid for.
		4549
		4550	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4551
		4552	These just add the watcher into an array or at the head of a list.
		4553
		4554	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4555
		4556	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4557
		4558	These watchers are stored in lists, so they need to be walked to find the
		4559	correct watcher to remove. The lists are usually short (you don't usually
		4560	have many watchers waiting for the same fd or signal: one is typical, two
		4561	is rare).
		4562
		4563	=item Finding the next timer in each loop iteration: O(1)
		4564
		4565	By virtue of using a binary or 4-heap, the next timer is always found at a
		4566	fixed position in the storage array.
		4567
		4568	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4569
		4570	A change means an I/O watcher gets started or stopped, which requires
		4571	libev to recalculate its status (and possibly tell the kernel, depending
		4572	on backend and whether C<ev_io_set> was used).
		4573
		4574	=item Activating one watcher (putting it into the pending state): O(1)
		4575
		4576	=item Priority handling: O(number_of_priorities)
		4577
		4578	Priorities are implemented by allocating some space for each
		4579	priority. When doing priority-based operations, libev usually has to
		4580	linearly search all the priorities, but starting/stopping and activating
		4581	watchers becomes O(1) with respect to priority handling.
		4582
		4583	=item Sending an ev_async: O(1)
		4584
		4585	=item Processing ev_async_send: O(number_of_async_watchers)
		4586
		4587	=item Processing signals: O(max_signal_number)
		4588
		4589	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4590	calls in the current loop iteration. Checking for async and signal events
		4591	involves iterating over all running async watchers or all signal numbers.
		4592
		4593	=back
		4594
		4595
		4596	=head1 GLOSSARY
		4597
		4598	=over 4
		4599
		4600	=item active
		4601
		4602	A watcher is active as long as it has been started (has been attached to
		4603	an event loop) but not yet stopped (disassociated from the event loop).
		4604
		4605	=item application
		4606
		4607	In this document, an application is whatever is using libev.
		4608
		4609	=item callback
		4610
		4611	The address of a function that is called when some event has been
		4612	detected. Callbacks are being passed the event loop, the watcher that
		4613	received the event, and the actual event bitset.
		4614
		4615	=item callback invocation
		4616
		4617	The act of calling the callback associated with a watcher.
		4618
		4619	=item event
		4620
		4621	A change of state of some external event, such as data now being available
		4622	for reading on a file descriptor, time having passed or simply not having
		4623	any other events happening anymore.
		4624
		4625	In libev, events are represented as single bits (such as C<EV_READ> or
		4626	C<EV_TIMEOUT>).
		4627
		4628	=item event library
		4629
		4630	A software package implementing an event model and loop.
		4631
		4632	=item event loop
		4633
		4634	An entity that handles and processes external events and converts them
		4635	into callback invocations.
		4636
		4637	=item event model
		4638
		4639	The model used to describe how an event loop handles and processes
		4640	watchers and events.
		4641
		4642	=item pending
		4643
		4644	A watcher is pending as soon as the corresponding event has been detected,
		4645	and stops being pending as soon as the watcher will be invoked or its
		4646	pending status is explicitly cleared by the application.
		4647
		4648	A watcher can be pending, but not active. Stopping a watcher also clears
		4649	its pending status.
		4650
		4651	=item real time
		4652
		4653	The physical time that is observed. It is apparently strictly monotonic :)
		4654
		4655	=item wall-clock time
		4656
		4657	The time and date as shown on clocks. Unlike real time, it can actually
		4658	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4659	clock.
		4660
		4661	=item watcher
		4662
		4663	A data structure that describes interest in certain events. Watchers need
		4664	to be started (attached to an event loop) before they can receive events.
		4665
		4666	=item watcher invocation
		4667
		4668	The act of calling the callback associated with a watcher.
		4669
		4670	=back
		4671
724	=head1 AUTHOR	4672	=head1 AUTHOR
725		4673
726	Marc Lehmann <libev@schmorp.de>.	4674	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
727		4675

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