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…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 DESCRIPTION	9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
		18	ev_io stdin_watcher;
		19	ev_timer timeout_watcher;
		20
		21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
		23	static void
		24	stdin_cb (EV_P_ ev_io *w, int revents)
		25	{
		26	puts ("stdin ready");
		27	// for one-shot events, one must manually stop the watcher
		28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_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). It also is quite	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>).
		111
		112	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	114	for example).
33		115
34	=head1 CONVENTIONS	116	=head2 CONVENTIONS
35		117
36	Libev is very configurable. In this manual the default configuration	118	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	119	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	120	more info about various configuration options please have a look at
39	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
40	support for multiple event loops, then all functions taking an initial	122	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	123	name C<loop> (which is always of type C<ev_loop *>) will not have
42	will not have this argument.	124	this argument.
43		125
44	=head1 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
45		127
46	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
48	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
49	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
50	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
51		157
52	=head1 GLOBAL FUNCTIONS	158	=head1 GLOBAL FUNCTIONS
53		159
54	These functions can be called anytime, even before initialising the	160	These functions can be called anytime, even before initialising the
55	library in any way.	161	library in any way.
…		…
60		166
61	Returns the current time as libev would use it. Please note that the	167	Returns the current time as libev would use it. Please note that the
62	C<ev_now> function is usually faster and also often returns the timestamp	168	C<ev_now> function is usually faster and also often returns the timestamp
63	you actually want to know.	169	you actually want to know.
64		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 ()>.
		176
65	=item int ev_version_major ()	177	=item int ev_version_major ()
66		178
67	=item int ev_version_minor ()	179	=item int ev_version_minor ()
68		180
69	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
70	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
71	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
72	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
73	version of the library your program was compiled against.	185	version of the library your program was compiled against.
74		186
		187	These version numbers refer to the ABI version of the library, not the
		188	release version.
		189
75	Usually, it's a good idea to terminate if the major versions mismatch,	190	Usually, it's a good idea to terminate if the major versions mismatch,
76	as this indicates an incompatible change. Minor versions are usually	191	as this indicates an incompatible change. Minor versions are usually
77	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
78	not a problem.	193	not a problem.
79		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
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	234	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
81		235
82	Sets the allocation function to use (the prototype is similar to the	236	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	237	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
84	and free memory (no surprises here). If it returns zero when memory	238	used to allocate and free memory (no surprises here). If it returns zero
85	needs to be allocated, the library might abort or take some potentially	239	when memory needs to be allocated (C<size != 0>), the library might abort
86	destructive action. The default is your system realloc function.	240	or take some potentially destructive action.
		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.
87		245
88	You could override this function in high-availability programs to, say,	246	You could override this function in high-availability programs to, say,
89	free some memory if it cannot allocate memory, to use a special allocator,	247	free some memory if it cannot allocate memory, to use a special allocator,
90	or even to sleep a while and retry until some memory is available.	248	or even to sleep a while and retry until some memory is available.
91		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
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	270	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
93		271
94	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
95	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
96	indicating the system call or subsystem causing the problem. If this	274	indicating the system call or subsystem causing the problem. If this
97	callback is set, then libev will expect it to remedy the sitution, no	275	callback is set, then libev will expect it to remedy the situation, no
98	matter what, when it returns. That is, libev will generally retry the	276	matter what, when it returns. That is, libev will generally retry the
99	requested operation, or, if the condition doesn't go away, do bad stuff	277	requested operation, or, if the condition doesn't go away, do bad stuff
100	(such as abort).	278	(such as abort).
101		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
102	=back	292	=back
103		293
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		295
106	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>
107	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>
108	events, and dynamically created loops which do not.	298	I<function>).
109		299
110	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
111	in your main thread (or in a separate thread) and for each thread you	301	supports signals and child events, and dynamically created loops which do
112	create, you also create another event loop. Libev itself does no locking	302	not.
113	whatsoever, so if you mix calls to the same event loop in different
114	threads, make sure you lock (this is usually a bad idea, though, even if
115	done correctly, because it's hideous and inefficient).
116		303
117	=over 4	304	=over 4
118		305
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		307
121	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
122	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
123	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
124	flags).	311	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		312
126	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
127	function.	314	function.
128		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
129	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
130	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>).
131		329
132	It supports the following flags:	330	The following flags are supported:
133		331
134	=over 4	332	=over 4
135		333
136	=item C<EVFLAG_AUTO>	334	=item C<EVFLAG_AUTO>
137		335
138	The default flags value. Use this if you have no clue (it's the right	336	The default flags value. Use this if you have no clue (it's the right
139	thing, believe me).	337	thing, believe me).
140		338
141	=item C<EVFLAG_NOENV>	339	=item C<EVFLAG_NOENV>
142		340
143	If this flag bit is ored into the flag value (or the program runs setuid	341	If this flag bit is or'ed into the flag value (or the program runs setuid
144	or setgid) then libev will I<not> look at the environment variable	342	or setgid) then libev will I<not> look at the environment variable
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	343	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	344	override the flags completely if it is found in the environment. This is
147	useful to try out specific backends to test their performance, or to work	345	useful to try out specific backends to test their performance, or to work
148	around bugs.	346	around bugs.
149		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_NOSIGNALFD>
		376
		377	When this flag is specified, then libev will not attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		379	probably only useful to work around any bugs in libev. Consequently, this
		380	flag might go away once the signalfd functionality is considered stable,
		381	so it's useful mostly in environment variables and not in program code.
		382
150	=item C<EVMETHOD_SELECT> (value 1, portable select backend)	383	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		384
152	This is your standard select(2) backend. Not I<completely> standard, as	385	This is your standard select(2) backend. Not I<completely> standard, as
153	libev tries to roll its own fd_set with no limits on the number of fds,	386	libev tries to roll its own fd_set with no limits on the number of fds,
154	but if that fails, expect a fairly low limit on the number of fds when	387	but if that fails, expect a fairly low limit on the number of fds when
155	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	388	using this backend. It doesn't scale too well (O(highest_fd)), but its
156	the fastest backend for a low number of fds.	389	usually the fastest backend for a low number of (low-numbered :) fds.
157		390
		391	To get good performance out of this backend you need a high amount of
		392	parallelism (most of the file descriptors should be busy). If you are
		393	writing a server, you should C<accept ()> in a loop to accept as many
		394	connections as possible during one iteration. You might also want to have
		395	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		396	readiness notifications you get per iteration.
		397
		398	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		399	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		400	C<exceptfds> set on that platform).
		401
158	=item C<EVMETHOD_POLL> (value 2, poll backend, available everywhere except on windows)	402	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
159		403
160	And this is your standard poll(2) backend. It's more complicated than	404	And this is your standard poll(2) backend. It's more complicated
161	select, but handles sparse fds better and has no artificial limit on the	405	than select, but handles sparse fds better and has no artificial
162	number of fds you can use (except it will slow down considerably with a	406	limit on the number of fds you can use (except it will slow down
163	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	407	considerably with a lot of inactive fds). It scales similarly to select,
		408	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		409	performance tips.
164		410
		411	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		412	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		413
165	=item C<EVMETHOD_EPOLL> (value 4, Linux)	414	=item C<EVBACKEND_EPOLL> (value 4, Linux)
166		415
167	For few fds, this backend is a bit little slower than poll and select,	416	For few fds, this backend is a bit little slower than poll and select,
168	but it scales phenomenally better. While poll and select usually scale like	417	but it scales phenomenally better. While poll and select usually scale
169	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	418	like O(total_fds) where n is the total number of fds (or the highest fd),
170	either O(1) or O(active_fds).	419	epoll scales either O(1) or O(active_fds).
171		420
		421	The epoll mechanism deserves honorable mention as the most misdesigned
		422	of the more advanced event mechanisms: mere annoyances include silently
		423	dropping file descriptors, requiring a system call per change per file
		424	descriptor (and unnecessary guessing of parameters), problems with dup and
		425	so on. The biggest issue is fork races, however - if a program forks then
		426	I<both> parent and child process have to recreate the epoll set, which can
		427	take considerable time (one syscall per file descriptor) and is of course
		428	hard to detect.
		429
		430	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		431	of course I<doesn't>, and epoll just loves to report events for totally
		432	I<different> file descriptors (even already closed ones, so one cannot
		433	even remove them from the set) than registered in the set (especially
		434	on SMP systems). Libev tries to counter these spurious notifications by
		435	employing an additional generation counter and comparing that against the
		436	events to filter out spurious ones, recreating the set when required.
		437
172	While stopping and starting an I/O watcher in the same iteration will	438	While stopping, setting and starting an I/O watcher in the same iteration
173	result in some caching, there is still a syscall per such incident	439	will result in some caching, there is still a system call per such
174	(because the fd could point to a different file description now), so its	440	incident (because the same I<file descriptor> could point to a different
175	best to avoid that. Also, dup()ed file descriptors might not work very	441	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
176	well if you register events for both fds.	442	file descriptors might not work very well if you register events for both
		443	file descriptors.
177		444
		445	Best performance from this backend is achieved by not unregistering all
		446	watchers for a file descriptor until it has been closed, if possible,
		447	i.e. keep at least one watcher active per fd at all times. Stopping and
		448	starting a watcher (without re-setting it) also usually doesn't cause
		449	extra overhead. A fork can both result in spurious notifications as well
		450	as in libev having to destroy and recreate the epoll object, which can
		451	take considerable time and thus should be avoided.
		452
		453	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		454	faster than epoll for maybe up to a hundred file descriptors, depending on
		455	the usage. So sad.
		456
		457	While nominally embeddable in other event loops, this feature is broken in
		458	all kernel versions tested so far.
		459
		460	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		461	C<EVBACKEND_POLL>.
		462
178	=item C<EVMETHOD_KQUEUE> (value 8, most BSD clones)	463	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
179		464
180	Kqueue deserves special mention, as at the time of this writing, it	465	Kqueue deserves special mention, as at the time of this writing, it
181	was broken on all BSDs except NetBSD (usually it doesn't work with	466	was broken on all BSDs except NetBSD (usually it doesn't work reliably
182	anything but sockets and pipes, except on Darwin, where of course its	467	with anything but sockets and pipes, except on Darwin, where of course
183	completely useless). For this reason its not being "autodetected" unless	468	it's completely useless). Unlike epoll, however, whose brokenness
184	you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).	469	is by design, these kqueue bugs can (and eventually will) be fixed
		470	without API changes to existing programs. For this reason it's not being
		471	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		472	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		473	system like NetBSD.
		474
		475	You still can embed kqueue into a normal poll or select backend and use it
		476	only for sockets (after having made sure that sockets work with kqueue on
		477	the target platform). See C<ev_embed> watchers for more info.
185		478
186	It scales in the same way as the epoll backend, but the interface to the	479	It scales in the same way as the epoll backend, but the interface to the
187	kernel is more efficient (which says nothing about its actual speed, of	480	kernel is more efficient (which says nothing about its actual speed, of
188	course). While starting and stopping an I/O watcher does not cause an	481	course). While stopping, setting and starting an I/O watcher does never
189	extra syscall as with epoll, it still adds up to four event changes per	482	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
190	incident, so its best to avoid that.	483	two event changes per incident. Support for C<fork ()> is very bad (but
		484	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		485	cases
191		486
		487	This backend usually performs well under most conditions.
		488
		489	While nominally embeddable in other event loops, this doesn't work
		490	everywhere, so you might need to test for this. And since it is broken
		491	almost everywhere, you should only use it when you have a lot of sockets
		492	(for which it usually works), by embedding it into another event loop
		493	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		494	also broken on OS X)) and, did I mention it, using it only for sockets.
		495
		496	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		497	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		498	C<NOTE_EOF>.
		499
192	=item C<EVMETHOD_DEVPOLL> (value 16, Solaris 8)	500	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
193		501
194	This is not implemented yet (and might never be).	502	This is not implemented yet (and might never be, unless you send me an
		503	implementation). According to reports, C</dev/poll> only supports sockets
		504	and is not embeddable, which would limit the usefulness of this backend
		505	immensely.
195		506
196	=item C<EVMETHOD_PORT> (value 32, Solaris 10)	507	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
197		508
198	This uses the Solaris 10 port mechanism. As with everything on Solaris,	509	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
199	it's really slow, but it still scales very well (O(active_fds)).	510	it's really slow, but it still scales very well (O(active_fds)).
200		511
		512	Please note that Solaris event ports can deliver a lot of spurious
		513	notifications, so you need to use non-blocking I/O or other means to avoid
		514	blocking when no data (or space) is available.
		515
		516	While this backend scales well, it requires one system call per active
		517	file descriptor per loop iteration. For small and medium numbers of file
		518	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		519	might perform better.
		520
		521	On the positive side, with the exception of the spurious readiness
		522	notifications, this backend actually performed fully to specification
		523	in all tests and is fully embeddable, which is a rare feat among the
		524	OS-specific backends (I vastly prefer correctness over speed hacks).
		525
		526	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		527	C<EVBACKEND_POLL>.
		528
201	=item C<EVMETHOD_ALL>	529	=item C<EVBACKEND_ALL>
202		530
203	Try all backends (even potentially broken ones that wouldn't be tried	531	Try all backends (even potentially broken ones that wouldn't be tried
204	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	532	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
205	C<EVMETHOD_ALL & ~EVMETHOD_KQUEUE>.	533	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		534
		535	It is definitely not recommended to use this flag.
206		536
207	=back	537	=back
208		538
209	If one or more of these are ored into the flags value, then only these	539	If one or more of the backend flags are or'ed into the flags value,
210	backends will be tried (in the reverse order as given here). If none are	540	then only these backends will be tried (in the reverse order as listed
211	specified, most compiled-in backend will be tried, usually in reverse	541	here). If none are specified, all backends in C<ev_recommended_backends
212	order of their flag values :)	542	()> will be tried.
		543
		544	Example: This is the most typical usage.
		545
		546	if (!ev_default_loop (0))
		547	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		548
		549	Example: Restrict libev to the select and poll backends, and do not allow
		550	environment settings to be taken into account:
		551
		552	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		553
		554	Example: Use whatever libev has to offer, but make sure that kqueue is
		555	used if available (warning, breaks stuff, best use only with your own
		556	private event loop and only if you know the OS supports your types of
		557	fds):
		558
		559	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
213		560
214	=item struct ev_loop *ev_loop_new (unsigned int flags)	561	=item struct ev_loop *ev_loop_new (unsigned int flags)
215		562
216	Similar to C<ev_default_loop>, but always creates a new event loop that is	563	Similar to C<ev_default_loop>, but always creates a new event loop that is
217	always distinct from the default loop. Unlike the default loop, it cannot	564	always distinct from the default loop. Unlike the default loop, it cannot
218	handle signal and child watchers, and attempts to do so will be greeted by	565	handle signal and child watchers, and attempts to do so will be greeted by
219	undefined behaviour (or a failed assertion if assertions are enabled).	566	undefined behaviour (or a failed assertion if assertions are enabled).
220		567
		568	Note that this function I<is> thread-safe, and the recommended way to use
		569	libev with threads is indeed to create one loop per thread, and using the
		570	default loop in the "main" or "initial" thread.
		571
		572	Example: Try to create a event loop that uses epoll and nothing else.
		573
		574	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		575	if (!epoller)
		576	fatal ("no epoll found here, maybe it hides under your chair");
		577
221	=item ev_default_destroy ()	578	=item ev_default_destroy ()
222		579
223	Destroys the default loop again (frees all memory and kernel state	580	Destroys the default loop again (frees all memory and kernel state
224	etc.). This stops all registered event watchers (by not touching them in	581	etc.). None of the active event watchers will be stopped in the normal
225	any way whatsoever, although you cannot rely on this :).	582	sense, so e.g. C<ev_is_active> might still return true. It is your
		583	responsibility to either stop all watchers cleanly yourself I<before>
		584	calling this function, or cope with the fact afterwards (which is usually
		585	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		586	for example).
		587
		588	Note that certain global state, such as signal state (and installed signal
		589	handlers), will not be freed by this function, and related watchers (such
		590	as signal and child watchers) would need to be stopped manually.
		591
		592	In general it is not advisable to call this function except in the
		593	rare occasion where you really need to free e.g. the signal handling
		594	pipe fds. If you need dynamically allocated loops it is better to use
		595	C<ev_loop_new> and C<ev_loop_destroy>).
226		596
227	=item ev_loop_destroy (loop)	597	=item ev_loop_destroy (loop)
228		598
229	Like C<ev_default_destroy>, but destroys an event loop created by an	599	Like C<ev_default_destroy>, but destroys an event loop created by an
230	earlier call to C<ev_loop_new>.	600	earlier call to C<ev_loop_new>.
231		601
232	=item ev_default_fork ()	602	=item ev_default_fork ()
233		603
		604	This function sets a flag that causes subsequent C<ev_loop> iterations
234	This function reinitialises the kernel state for backends that have	605	to reinitialise the kernel state for backends that have one. Despite the
235	one. Despite the name, you can call it anytime, but it makes most sense	606	name, you can call it anytime, but it makes most sense after forking, in
236	after forking, in either the parent or child process (or both, but that	607	the child process (or both child and parent, but that again makes little
237	again makes little sense).	608	sense). You I<must> call it in the child before using any of the libev
		609	functions, and it will only take effect at the next C<ev_loop> iteration.
238		610
239	You I<must> call this function in the child process after forking if and	611	On the other hand, you only need to call this function in the child
240	only if you want to use the event library in both processes. If you just	612	process if and only if you want to use the event library in the child. If
241	fork+exec, you don't have to call it.	613	you just fork+exec, you don't have to call it at all.
242		614
243	The function itself is quite fast and it's usually not a problem to call	615	The function itself is quite fast and it's usually not a problem to call
244	it just in case after a fork. To make this easy, the function will fit in	616	it just in case after a fork. To make this easy, the function will fit in
245	quite nicely into a call to C<pthread_atfork>:	617	quite nicely into a call to C<pthread_atfork>:
246		618
…		…
248		620
249	=item ev_loop_fork (loop)	621	=item ev_loop_fork (loop)
250		622
251	Like C<ev_default_fork>, but acts on an event loop created by	623	Like C<ev_default_fork>, but acts on an event loop created by
252	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	624	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
253	after fork, and how you do this is entirely your own problem.	625	after fork that you want to re-use in the child, and how you do this is
		626	entirely your own problem.
254		627
		628	=item int ev_is_default_loop (loop)
		629
		630	Returns true when the given loop is, in fact, the default loop, and false
		631	otherwise.
		632
		633	=item unsigned int ev_loop_count (loop)
		634
		635	Returns the count of loop iterations for the loop, which is identical to
		636	the number of times libev did poll for new events. It starts at C<0> and
		637	happily wraps around with enough iterations.
		638
		639	This value can sometimes be useful as a generation counter of sorts (it
		640	"ticks" the number of loop iterations), as it roughly corresponds with
		641	C<ev_prepare> and C<ev_check> calls.
		642
		643	=item unsigned int ev_loop_depth (loop)
		644
		645	Returns the number of times C<ev_loop> was entered minus the number of
		646	times C<ev_loop> was exited, in other words, the recursion depth.
		647
		648	Outside C<ev_loop>, this number is zero. In a callback, this number is
		649	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		650	in which case it is higher.
		651
		652	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		653	etc.), doesn't count as exit.
		654
255	=item unsigned int ev_method (loop)	655	=item unsigned int ev_backend (loop)
256		656
257	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	657	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
258	use.	658	use.
259		659
260	=item ev_tstamp ev_now (loop)	660	=item ev_tstamp ev_now (loop)
261		661
262	Returns the current "event loop time", which is the time the event loop	662	Returns the current "event loop time", which is the time the event loop
263	got events and started processing them. This timestamp does not change	663	received events and started processing them. This timestamp does not
264	as long as callbacks are being processed, and this is also the base time	664	change as long as callbacks are being processed, and this is also the base
265	used for relative timers. You can treat it as the timestamp of the event	665	time used for relative timers. You can treat it as the timestamp of the
266	occuring (or more correctly, the mainloop finding out about it).	666	event occurring (or more correctly, libev finding out about it).
		667
		668	=item ev_now_update (loop)
		669
		670	Establishes the current time by querying the kernel, updating the time
		671	returned by C<ev_now ()> in the progress. This is a costly operation and
		672	is usually done automatically within C<ev_loop ()>.
		673
		674	This function is rarely useful, but when some event callback runs for a
		675	very long time without entering the event loop, updating libev's idea of
		676	the current time is a good idea.
		677
		678	See also L<The special problem of time updates> in the C<ev_timer> section.
		679
		680	=item ev_suspend (loop)
		681
		682	=item ev_resume (loop)
		683
		684	These two functions suspend and resume a loop, for use when the loop is
		685	not used for a while and timeouts should not be processed.
		686
		687	A typical use case would be an interactive program such as a game: When
		688	the user presses C<^Z> to suspend the game and resumes it an hour later it
		689	would be best to handle timeouts as if no time had actually passed while
		690	the program was suspended. This can be achieved by calling C<ev_suspend>
		691	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		692	C<ev_resume> directly afterwards to resume timer processing.
		693
		694	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		695	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		696	will be rescheduled (that is, they will lose any events that would have
		697	occured while suspended).
		698
		699	After calling C<ev_suspend> you B<must not> call I<any> function on the
		700	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		701	without a previous call to C<ev_suspend>.
		702
		703	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		704	event loop time (see C<ev_now_update>).
267		705
268	=item ev_loop (loop, int flags)	706	=item ev_loop (loop, int flags)
269		707
270	Finally, this is it, the event handler. This function usually is called	708	Finally, this is it, the event handler. This function usually is called
271	after you initialised all your watchers and you want to start handling	709	after you initialised all your watchers and you want to start handling
272	events.	710	events.
273		711
274	If the flags argument is specified as 0, it will not return until either	712	If the flags argument is specified as C<0>, it will not return until
275	no event watchers are active anymore or C<ev_unloop> was called.	713	either no event watchers are active anymore or C<ev_unloop> was called.
		714
		715	Please note that an explicit C<ev_unloop> is usually better than
		716	relying on all watchers to be stopped when deciding when a program has
		717	finished (especially in interactive programs), but having a program
		718	that automatically loops as long as it has to and no longer by virtue
		719	of relying on its watchers stopping correctly, that is truly a thing of
		720	beauty.
276		721
277	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	722	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
278	those events and any outstanding ones, but will not block your process in	723	those events and any already outstanding ones, but will not block your
279	case there are no events and will return after one iteration of the loop.	724	process in case there are no events and will return after one iteration of
		725	the loop.
280		726
281	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	727	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
282	neccessary) and will handle those and any outstanding ones. It will block	728	necessary) and will handle those and any already outstanding ones. It
283	your process until at least one new event arrives, and will return after	729	will block your process until at least one new event arrives (which could
		730	be an event internal to libev itself, so there is no guarantee that a
		731	user-registered callback will be called), and will return after one
284	one iteration of the loop.	732	iteration of the loop.
285		733
286	This flags value could be used to implement alternative looping	734	This is useful if you are waiting for some external event in conjunction
287	constructs, but the C<prepare> and C<check> watchers provide a better and	735	with something not expressible using other libev watchers (i.e. "roll your
288	more generic mechanism.	736	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		737	usually a better approach for this kind of thing.
289		738
290	Here are the gory details of what ev_loop does:	739	Here are the gory details of what C<ev_loop> does:
291		740
292	1. If there are no active watchers (reference count is zero), return.	741	- Before the first iteration, call any pending watchers.
		742	* If EVFLAG_FORKCHECK was used, check for a fork.
		743	- If a fork was detected (by any means), queue and call all fork watchers.
293	2. Queue and immediately call all prepare watchers.	744	- Queue and call all prepare watchers.
294	3. If we have been forked, recreate the kernel state.	745	- If we have been forked, detach and recreate the kernel state
		746	as to not disturb the other process.
295	4. Update the kernel state with all outstanding changes.	747	- Update the kernel state with all outstanding changes.
296	5. Update the "event loop time".	748	- Update the "event loop time" (ev_now ()).
297	6. Calculate for how long to block.	749	- Calculate for how long to sleep or block, if at all
		750	(active idle watchers, EVLOOP_NONBLOCK or not having
		751	any active watchers at all will result in not sleeping).
		752	- Sleep if the I/O and timer collect interval say so.
298	7. Block the process, waiting for events.	753	- Block the process, waiting for any events.
		754	- Queue all outstanding I/O (fd) events.
299	8. Update the "event loop time" and do time jump handling.	755	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
300	9. Queue all outstanding timers.	756	- Queue all expired timers.
301	10. Queue all outstanding periodics.	757	- Queue all expired periodics.
302	11. If no events are pending now, queue all idle watchers.	758	- Unless any events are pending now, queue all idle watchers.
303	12. Queue all check watchers.	759	- Queue all check watchers.
304	13. Call all queued watchers in reverse order (i.e. check watchers first).	760	- Call all queued watchers in reverse order (i.e. check watchers first).
		761	Signals and child watchers are implemented as I/O watchers, and will
		762	be handled here by queueing them when their watcher gets executed.
305	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	763	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
306	was used, return, otherwise continue with step #1.	764	were used, or there are no active watchers, return, otherwise
		765	continue with step *.
		766
		767	Example: Queue some jobs and then loop until no events are outstanding
		768	anymore.
		769
		770	... queue jobs here, make sure they register event watchers as long
		771	... as they still have work to do (even an idle watcher will do..)
		772	ev_loop (my_loop, 0);
		773	... jobs done or somebody called unloop. yeah!
307		774
308	=item ev_unloop (loop, how)	775	=item ev_unloop (loop, how)
309		776
310	Can be used to make a call to C<ev_loop> return early (but only after it	777	Can be used to make a call to C<ev_loop> return early (but only after it
311	has processed all outstanding events). The C<how> argument must be either	778	has processed all outstanding events). The C<how> argument must be either
312	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	779	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
313	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	780	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
314		781
		782	This "unloop state" will be cleared when entering C<ev_loop> again.
		783
		784	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		785
315	=item ev_ref (loop)	786	=item ev_ref (loop)
316		787
317	=item ev_unref (loop)	788	=item ev_unref (loop)
318		789
319	Ref/unref can be used to add or remove a reference count on the event	790	Ref/unref can be used to add or remove a reference count on the event
320	loop: Every watcher keeps one reference, and as long as the reference	791	loop: Every watcher keeps one reference, and as long as the reference
321	count is nonzero, C<ev_loop> will not return on its own. If you have	792	count is nonzero, C<ev_loop> will not return on its own.
		793
322	a watcher you never unregister that should not keep C<ev_loop> from	794	If you have a watcher you never unregister that should not keep C<ev_loop>
323	returning, ev_unref() after starting, and ev_ref() before stopping it. For	795	from returning, call ev_unref() after starting, and ev_ref() before
		796	stopping it.
		797
324	example, libev itself uses this for its internal signal pipe: It is not	798	As an example, libev itself uses this for its internal signal pipe: It
325	visible to the libev user and should not keep C<ev_loop> from exiting if	799	is not visible to the libev user and should not keep C<ev_loop> from
326	no event watchers registered by it are active. It is also an excellent	800	exiting if no event watchers registered by it are active. It is also an
327	way to do this for generic recurring timers or from within third-party	801	excellent way to do this for generic recurring timers or from within
328	libraries. Just remember to I<unref after start> and I<ref before stop>.	802	third-party libraries. Just remember to I<unref after start> and I<ref
		803	before stop> (but only if the watcher wasn't active before, or was active
		804	before, respectively. Note also that libev might stop watchers itself
		805	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		806	in the callback).
		807
		808	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		809	running when nothing else is active.
		810
		811	ev_signal exitsig;
		812	ev_signal_init (&exitsig, sig_cb, SIGINT);
		813	ev_signal_start (loop, &exitsig);
		814	evf_unref (loop);
		815
		816	Example: For some weird reason, unregister the above signal handler again.
		817
		818	ev_ref (loop);
		819	ev_signal_stop (loop, &exitsig);
		820
		821	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		822
		823	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		824
		825	These advanced functions influence the time that libev will spend waiting
		826	for events. Both time intervals are by default C<0>, meaning that libev
		827	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		828	latency.
		829
		830	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		831	allows libev to delay invocation of I/O and timer/periodic callbacks
		832	to increase efficiency of loop iterations (or to increase power-saving
		833	opportunities).
		834
		835	The idea is that sometimes your program runs just fast enough to handle
		836	one (or very few) event(s) per loop iteration. While this makes the
		837	program responsive, it also wastes a lot of CPU time to poll for new
		838	events, especially with backends like C<select ()> which have a high
		839	overhead for the actual polling but can deliver many events at once.
		840
		841	By setting a higher I<io collect interval> you allow libev to spend more
		842	time collecting I/O events, so you can handle more events per iteration,
		843	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		844	C<ev_timer>) will be not affected. Setting this to a non-null value will
		845	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		846	sleep time ensures that libev will not poll for I/O events more often then
		847	once per this interval, on average.
		848
		849	Likewise, by setting a higher I<timeout collect interval> you allow libev
		850	to spend more time collecting timeouts, at the expense of increased
		851	latency/jitter/inexactness (the watcher callback will be called
		852	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		853	value will not introduce any overhead in libev.
		854
		855	Many (busy) programs can usually benefit by setting the I/O collect
		856	interval to a value near C<0.1> or so, which is often enough for
		857	interactive servers (of course not for games), likewise for timeouts. It
		858	usually doesn't make much sense to set it to a lower value than C<0.01>,
		859	as this approaches the timing granularity of most systems. Note that if
		860	you do transactions with the outside world and you can't increase the
		861	parallelity, then this setting will limit your transaction rate (if you
		862	need to poll once per transaction and the I/O collect interval is 0.01,
		863	then you can't do more than 100 transations per second).
		864
		865	Setting the I<timeout collect interval> can improve the opportunity for
		866	saving power, as the program will "bundle" timer callback invocations that
		867	are "near" in time together, by delaying some, thus reducing the number of
		868	times the process sleeps and wakes up again. Another useful technique to
		869	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		870	they fire on, say, one-second boundaries only.
		871
		872	Example: we only need 0.1s timeout granularity, and we wish not to poll
		873	more often than 100 times per second:
		874
		875	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		876	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		877
		878	=item ev_invoke_pending (loop)
		879
		880	This call will simply invoke all pending watchers while resetting their
		881	pending state. Normally, C<ev_loop> does this automatically when required,
		882	but when overriding the invoke callback this call comes handy.
		883
		884	=item int ev_pending_count (loop)
		885
		886	Returns the number of pending watchers - zero indicates that no watchers
		887	are pending.
		888
		889	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		890
		891	This overrides the invoke pending functionality of the loop: Instead of
		892	invoking all pending watchers when there are any, C<ev_loop> will call
		893	this callback instead. This is useful, for example, when you want to
		894	invoke the actual watchers inside another context (another thread etc.).
		895
		896	If you want to reset the callback, use C<ev_invoke_pending> as new
		897	callback.
		898
		899	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		900
		901	Sometimes you want to share the same loop between multiple threads. This
		902	can be done relatively simply by putting mutex_lock/unlock calls around
		903	each call to a libev function.
		904
		905	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		906	wait for it to return. One way around this is to wake up the loop via
		907	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		908	and I<acquire> callbacks on the loop.
		909
		910	When set, then C<release> will be called just before the thread is
		911	suspended waiting for new events, and C<acquire> is called just
		912	afterwards.
		913
		914	Ideally, C<release> will just call your mutex_unlock function, and
		915	C<acquire> will just call the mutex_lock function again.
		916
		917	While event loop modifications are allowed between invocations of
		918	C<release> and C<acquire> (that's their only purpose after all), no
		919	modifications done will affect the event loop, i.e. adding watchers will
		920	have no effect on the set of file descriptors being watched, or the time
		921	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		922	to take note of any changes you made.
		923
		924	In theory, threads executing C<ev_loop> will be async-cancel safe between
		925	invocations of C<release> and C<acquire>.
		926
		927	See also the locking example in the C<THREADS> section later in this
		928	document.
		929
		930	=item ev_set_userdata (loop, void *data)
		931
		932	=item ev_userdata (loop)
		933
		934	Set and retrieve a single C<void *> associated with a loop. When
		935	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		936	C<0.>
		937
		938	These two functions can be used to associate arbitrary data with a loop,
		939	and are intended solely for the C<invoke_pending_cb>, C<release> and
		940	C<acquire> callbacks described above, but of course can be (ab-)used for
		941	any other purpose as well.
		942
		943	=item ev_loop_verify (loop)
		944
		945	This function only does something when C<EV_VERIFY> support has been
		946	compiled in, which is the default for non-minimal builds. It tries to go
		947	through all internal structures and checks them for validity. If anything
		948	is found to be inconsistent, it will print an error message to standard
		949	error and call C<abort ()>.
		950
		951	This can be used to catch bugs inside libev itself: under normal
		952	circumstances, this function will never abort as of course libev keeps its
		953	data structures consistent.
329		954
330	=back	955	=back
331		956
		957
332	=head1 ANATOMY OF A WATCHER	958	=head1 ANATOMY OF A WATCHER
		959
		960	In the following description, uppercase C<TYPE> in names stands for the
		961	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		962	watchers and C<ev_io_start> for I/O watchers.
333		963
334	A watcher is a structure that you create and register to record your	964	A watcher is a structure that you create and register to record your
335	interest in some event. For instance, if you want to wait for STDIN to	965	interest in some event. For instance, if you want to wait for STDIN to
336	become readable, you would create an C<ev_io> watcher for that:	966	become readable, you would create an C<ev_io> watcher for that:
337		967
338	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	968	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
339	{	969	{
340	ev_io_stop (w);	970	ev_io_stop (w);
341	ev_unloop (loop, EVUNLOOP_ALL);	971	ev_unloop (loop, EVUNLOOP_ALL);
342	}	972	}
343		973
344	struct ev_loop *loop = ev_default_loop (0);	974	struct ev_loop *loop = ev_default_loop (0);
		975
345	struct ev_io stdin_watcher;	976	ev_io stdin_watcher;
		977
346	ev_init (&stdin_watcher, my_cb);	978	ev_init (&stdin_watcher, my_cb);
347	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	979	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
348	ev_io_start (loop, &stdin_watcher);	980	ev_io_start (loop, &stdin_watcher);
		981
349	ev_loop (loop, 0);	982	ev_loop (loop, 0);
350		983
351	As you can see, you are responsible for allocating the memory for your	984	As you can see, you are responsible for allocating the memory for your
352	watcher structures (and it is usually a bad idea to do this on the stack,	985	watcher structures (and it is I<usually> a bad idea to do this on the
353	although this can sometimes be quite valid).	986	stack).
		987
		988	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		989	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
354		990
355	Each watcher structure must be initialised by a call to C<ev_init	991	Each watcher structure must be initialised by a call to C<ev_init
356	(watcher *, callback)>, which expects a callback to be provided. This	992	(watcher *, callback)>, which expects a callback to be provided. This
357	callback gets invoked each time the event occurs (or, in the case of io	993	callback gets invoked each time the event occurs (or, in the case of I/O
358	watchers, each time the event loop detects that the file descriptor given	994	watchers, each time the event loop detects that the file descriptor given
359	is readable and/or writable).	995	is readable and/or writable).
360		996
361	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	997	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
362	with arguments specific to this watcher type. There is also a macro	998	macro to configure it, with arguments specific to the watcher type. There
363	to combine initialisation and setting in one call: C<< ev_<type>_init	999	is also a macro to combine initialisation and setting in one call: C<<
364	(watcher *, callback, ...) >>.	1000	ev_TYPE_init (watcher *, callback, ...) >>.
365		1001
366	To make the watcher actually watch out for events, you have to start it	1002	To make the watcher actually watch out for events, you have to start it
367	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1003	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
368	*) >>), and you can stop watching for events at any time by calling the	1004	*) >>), and you can stop watching for events at any time by calling the
369	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1005	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
370		1006
371	As long as your watcher is active (has been started but not stopped) you	1007	As long as your watcher is active (has been started but not stopped) you
372	must not touch the values stored in it. Most specifically you must never	1008	must not touch the values stored in it. Most specifically you must never
373	reinitialise it or call its set method.	1009	reinitialise it or call its C<ev_TYPE_set> macro.
374
375	You can check whether an event is active by calling the C<ev_is_active
376	(watcher *)> macro. To see whether an event is outstanding (but the
377	callback for it has not been called yet) you can use the C<ev_is_pending
378	(watcher *)> macro.
379		1010
380	Each and every callback receives the event loop pointer as first, the	1011	Each and every callback receives the event loop pointer as first, the
381	registered watcher structure as second, and a bitset of received events as	1012	registered watcher structure as second, and a bitset of received events as
382	third argument.	1013	third argument.
383		1014
…		…
407	The signal specified in the C<ev_signal> watcher has been received by a thread.	1038	The signal specified in the C<ev_signal> watcher has been received by a thread.
408		1039
409	=item C<EV_CHILD>	1040	=item C<EV_CHILD>
410		1041
411	The pid specified in the C<ev_child> watcher has received a status change.	1042	The pid specified in the C<ev_child> watcher has received a status change.
		1043
		1044	=item C<EV_STAT>
		1045
		1046	The path specified in the C<ev_stat> watcher changed its attributes somehow.
412		1047
413	=item C<EV_IDLE>	1048	=item C<EV_IDLE>
414		1049
415	The C<ev_idle> watcher has determined that you have nothing better to do.	1050	The C<ev_idle> watcher has determined that you have nothing better to do.
416		1051
…		…
424	received events. Callbacks of both watcher types can start and stop as	1059	received events. Callbacks of both watcher types can start and stop as
425	many watchers as they want, and all of them will be taken into account	1060	many watchers as they want, and all of them will be taken into account
426	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1061	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
427	C<ev_loop> from blocking).	1062	C<ev_loop> from blocking).
428		1063
		1064	=item C<EV_EMBED>
		1065
		1066	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1067
		1068	=item C<EV_FORK>
		1069
		1070	The event loop has been resumed in the child process after fork (see
		1071	C<ev_fork>).
		1072
		1073	=item C<EV_ASYNC>
		1074
		1075	The given async watcher has been asynchronously notified (see C<ev_async>).
		1076
		1077	=item C<EV_CUSTOM>
		1078
		1079	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1080	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1081
429	=item C<EV_ERROR>	1082	=item C<EV_ERROR>
430		1083
431	An unspecified error has occured, the watcher has been stopped. This might	1084	An unspecified error has occurred, the watcher has been stopped. This might
432	happen because the watcher could not be properly started because libev	1085	happen because the watcher could not be properly started because libev
433	ran out of memory, a file descriptor was found to be closed or any other	1086	ran out of memory, a file descriptor was found to be closed or any other
		1087	problem. Libev considers these application bugs.
		1088
434	problem. You best act on it by reporting the problem and somehow coping	1089	You best act on it by reporting the problem and somehow coping with the
435	with the watcher being stopped.	1090	watcher being stopped. Note that well-written programs should not receive
		1091	an error ever, so when your watcher receives it, this usually indicates a
		1092	bug in your program.
436		1093
437	Libev will usually signal a few "dummy" events together with an error,	1094	Libev will usually signal a few "dummy" events together with an error, for
438	for example it might indicate that a fd is readable or writable, and if	1095	example it might indicate that a fd is readable or writable, and if your
439	your callbacks is well-written it can just attempt the operation and cope	1096	callbacks is well-written it can just attempt the operation and cope with
440	with the error from read() or write(). This will not work in multithreaded	1097	the error from read() or write(). This will not work in multi-threaded
441	programs, though, so beware.	1098	programs, though, as the fd could already be closed and reused for another
		1099	thing, so beware.
442		1100
443	=back	1101	=back
444		1102
		1103	=head2 GENERIC WATCHER FUNCTIONS
		1104
		1105	=over 4
		1106
		1107	=item C<ev_init> (ev_TYPE *watcher, callback)
		1108
		1109	This macro initialises the generic portion of a watcher. The contents
		1110	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1111	the generic parts of the watcher are initialised, you I<need> to call
		1112	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1113	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1114	which rolls both calls into one.
		1115
		1116	You can reinitialise a watcher at any time as long as it has been stopped
		1117	(or never started) and there are no pending events outstanding.
		1118
		1119	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1120	int revents)>.
		1121
		1122	Example: Initialise an C<ev_io> watcher in two steps.
		1123
		1124	ev_io w;
		1125	ev_init (&w, my_cb);
		1126	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1127
		1128	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		1129
		1130	This macro initialises the type-specific parts of a watcher. You need to
		1131	call C<ev_init> at least once before you call this macro, but you can
		1132	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1133	macro on a watcher that is active (it can be pending, however, which is a
		1134	difference to the C<ev_init> macro).
		1135
		1136	Although some watcher types do not have type-specific arguments
		1137	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1138
		1139	See C<ev_init>, above, for an example.
		1140
		1141	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1142
		1143	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1144	calls into a single call. This is the most convenient method to initialise
		1145	a watcher. The same limitations apply, of course.
		1146
		1147	Example: Initialise and set an C<ev_io> watcher in one step.
		1148
		1149	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1150
		1151	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		1152
		1153	Starts (activates) the given watcher. Only active watchers will receive
		1154	events. If the watcher is already active nothing will happen.
		1155
		1156	Example: Start the C<ev_io> watcher that is being abused as example in this
		1157	whole section.
		1158
		1159	ev_io_start (EV_DEFAULT_UC, &w);
		1160
		1161	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		1162
		1163	Stops the given watcher if active, and clears the pending status (whether
		1164	the watcher was active or not).
		1165
		1166	It is possible that stopped watchers are pending - for example,
		1167	non-repeating timers are being stopped when they become pending - but
		1168	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1169	pending. If you want to free or reuse the memory used by the watcher it is
		1170	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1171
		1172	=item bool ev_is_active (ev_TYPE *watcher)
		1173
		1174	Returns a true value iff the watcher is active (i.e. it has been started
		1175	and not yet been stopped). As long as a watcher is active you must not modify
		1176	it.
		1177
		1178	=item bool ev_is_pending (ev_TYPE *watcher)
		1179
		1180	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1181	events but its callback has not yet been invoked). As long as a watcher
		1182	is pending (but not active) you must not call an init function on it (but
		1183	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1184	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1185	it).
		1186
		1187	=item callback ev_cb (ev_TYPE *watcher)
		1188
		1189	Returns the callback currently set on the watcher.
		1190
		1191	=item ev_cb_set (ev_TYPE *watcher, callback)
		1192
		1193	Change the callback. You can change the callback at virtually any time
		1194	(modulo threads).
		1195
		1196	=item ev_set_priority (ev_TYPE *watcher, priority)
		1197
		1198	=item int ev_priority (ev_TYPE *watcher)
		1199
		1200	Set and query the priority of the watcher. The priority is a small
		1201	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1202	(default: C<-2>). Pending watchers with higher priority will be invoked
		1203	before watchers with lower priority, but priority will not keep watchers
		1204	from being executed (except for C<ev_idle> watchers).
		1205
		1206	If you need to suppress invocation when higher priority events are pending
		1207	you need to look at C<ev_idle> watchers, which provide this functionality.
		1208
		1209	You I<must not> change the priority of a watcher as long as it is active or
		1210	pending.
		1211
		1212	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1213	fine, as long as you do not mind that the priority value you query might
		1214	or might not have been clamped to the valid range.
		1215
		1216	The default priority used by watchers when no priority has been set is
		1217	always C<0>, which is supposed to not be too high and not be too low :).
		1218
		1219	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1220	priorities.
		1221
		1222	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1223
		1224	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1225	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1226	can deal with that fact, as both are simply passed through to the
		1227	callback.
		1228
		1229	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1230
		1231	If the watcher is pending, this function clears its pending status and
		1232	returns its C<revents> bitset (as if its callback was invoked). If the
		1233	watcher isn't pending it does nothing and returns C<0>.
		1234
		1235	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1236	callback to be invoked, which can be accomplished with this function.
		1237
		1238	=back
		1239
		1240
445	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1241	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
446		1242
447	Each watcher has, by default, a member C<void *data> that you can change	1243	Each watcher has, by default, a member C<void *data> that you can change
448	and read at any time, libev will completely ignore it. This can be used	1244	and read at any time: libev will completely ignore it. This can be used
449	to associate arbitrary data with your watcher. If you need more data and	1245	to associate arbitrary data with your watcher. If you need more data and
450	don't want to allocate memory and store a pointer to it in that data	1246	don't want to allocate memory and store a pointer to it in that data
451	member, you can also "subclass" the watcher type and provide your own	1247	member, you can also "subclass" the watcher type and provide your own
452	data:	1248	data:
453		1249
454	struct my_io	1250	struct my_io
455	{	1251	{
456	struct ev_io io;	1252	ev_io io;
457	int otherfd;	1253	int otherfd;
458	void *somedata;	1254	void *somedata;
459	struct whatever *mostinteresting;	1255	struct whatever *mostinteresting;
460	}	1256	};
		1257
		1258	...
		1259	struct my_io w;
		1260	ev_io_init (&w.io, my_cb, fd, EV_READ);
461		1261
462	And since your callback will be called with a pointer to the watcher, you	1262	And since your callback will be called with a pointer to the watcher, you
463	can cast it back to your own type:	1263	can cast it back to your own type:
464		1264
465	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1265	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
466	{	1266	{
467	struct my_io *w = (struct my_io *)w_;	1267	struct my_io *w = (struct my_io *)w_;
468	...	1268	...
469	}	1269	}
470		1270
471	More interesting and less C-conformant ways of catsing your callback type	1271	More interesting and less C-conformant ways of casting your callback type
472	have been omitted....	1272	instead have been omitted.
		1273
		1274	Another common scenario is to use some data structure with multiple
		1275	embedded watchers:
		1276
		1277	struct my_biggy
		1278	{
		1279	int some_data;
		1280	ev_timer t1;
		1281	ev_timer t2;
		1282	}
		1283
		1284	In this case getting the pointer to C<my_biggy> is a bit more
		1285	complicated: Either you store the address of your C<my_biggy> struct
		1286	in the C<data> member of the watcher (for woozies), or you need to use
		1287	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1288	programmers):
		1289
		1290	#include <stddef.h>
		1291
		1292	static void
		1293	t1_cb (EV_P_ ev_timer *w, int revents)
		1294	{
		1295	struct my_biggy big = (struct my_biggy *)
		1296	(((char *)w) - offsetof (struct my_biggy, t1));
		1297	}
		1298
		1299	static void
		1300	t2_cb (EV_P_ ev_timer *w, int revents)
		1301	{
		1302	struct my_biggy big = (struct my_biggy *)
		1303	(((char *)w) - offsetof (struct my_biggy, t2));
		1304	}
		1305
		1306	=head2 WATCHER PRIORITY MODELS
		1307
		1308	Many event loops support I<watcher priorities>, which are usually small
		1309	integers that influence the ordering of event callback invocation
		1310	between watchers in some way, all else being equal.
		1311
		1312	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1313	description for the more technical details such as the actual priority
		1314	range.
		1315
		1316	There are two common ways how these these priorities are being interpreted
		1317	by event loops:
		1318
		1319	In the more common lock-out model, higher priorities "lock out" invocation
		1320	of lower priority watchers, which means as long as higher priority
		1321	watchers receive events, lower priority watchers are not being invoked.
		1322
		1323	The less common only-for-ordering model uses priorities solely to order
		1324	callback invocation within a single event loop iteration: Higher priority
		1325	watchers are invoked before lower priority ones, but they all get invoked
		1326	before polling for new events.
		1327
		1328	Libev uses the second (only-for-ordering) model for all its watchers
		1329	except for idle watchers (which use the lock-out model).
		1330
		1331	The rationale behind this is that implementing the lock-out model for
		1332	watchers is not well supported by most kernel interfaces, and most event
		1333	libraries will just poll for the same events again and again as long as
		1334	their callbacks have not been executed, which is very inefficient in the
		1335	common case of one high-priority watcher locking out a mass of lower
		1336	priority ones.
		1337
		1338	Static (ordering) priorities are most useful when you have two or more
		1339	watchers handling the same resource: a typical usage example is having an
		1340	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1341	timeouts. Under load, data might be received while the program handles
		1342	other jobs, but since timers normally get invoked first, the timeout
		1343	handler will be executed before checking for data. In that case, giving
		1344	the timer a lower priority than the I/O watcher ensures that I/O will be
		1345	handled first even under adverse conditions (which is usually, but not
		1346	always, what you want).
		1347
		1348	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1349	will only be executed when no same or higher priority watchers have
		1350	received events, they can be used to implement the "lock-out" model when
		1351	required.
		1352
		1353	For example, to emulate how many other event libraries handle priorities,
		1354	you can associate an C<ev_idle> watcher to each such watcher, and in
		1355	the normal watcher callback, you just start the idle watcher. The real
		1356	processing is done in the idle watcher callback. This causes libev to
		1357	continously poll and process kernel event data for the watcher, but when
		1358	the lock-out case is known to be rare (which in turn is rare :), this is
		1359	workable.
		1360
		1361	Usually, however, the lock-out model implemented that way will perform
		1362	miserably under the type of load it was designed to handle. In that case,
		1363	it might be preferable to stop the real watcher before starting the
		1364	idle watcher, so the kernel will not have to process the event in case
		1365	the actual processing will be delayed for considerable time.
		1366
		1367	Here is an example of an I/O watcher that should run at a strictly lower
		1368	priority than the default, and which should only process data when no
		1369	other events are pending:
		1370
		1371	ev_idle idle; // actual processing watcher
		1372	ev_io io; // actual event watcher
		1373
		1374	static void
		1375	io_cb (EV_P_ ev_io *w, int revents)
		1376	{
		1377	// stop the I/O watcher, we received the event, but
		1378	// are not yet ready to handle it.
		1379	ev_io_stop (EV_A_ w);
		1380
		1381	// start the idle watcher to ahndle the actual event.
		1382	// it will not be executed as long as other watchers
		1383	// with the default priority are receiving events.
		1384	ev_idle_start (EV_A_ &idle);
		1385	}
		1386
		1387	static void
		1388	idle_cb (EV_P_ ev_idle *w, int revents)
		1389	{
		1390	// actual processing
		1391	read (STDIN_FILENO, ...);
		1392
		1393	// have to start the I/O watcher again, as
		1394	// we have handled the event
		1395	ev_io_start (EV_P_ &io);
		1396	}
		1397
		1398	// initialisation
		1399	ev_idle_init (&idle, idle_cb);
		1400	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1401	ev_io_start (EV_DEFAULT_ &io);
		1402
		1403	In the "real" world, it might also be beneficial to start a timer, so that
		1404	low-priority connections can not be locked out forever under load. This
		1405	enables your program to keep a lower latency for important connections
		1406	during short periods of high load, while not completely locking out less
		1407	important ones.
473		1408
474		1409
475	=head1 WATCHER TYPES	1410	=head1 WATCHER TYPES
476		1411
477	This section describes each watcher in detail, but will not repeat	1412	This section describes each watcher in detail, but will not repeat
478	information given in the last section.	1413	information given in the last section. Any initialisation/set macros,
		1414	functions and members specific to the watcher type are explained.
479		1415
		1416	Members are additionally marked with either I<[read-only]>, meaning that,
		1417	while the watcher is active, you can look at the member and expect some
		1418	sensible content, but you must not modify it (you can modify it while the
		1419	watcher is stopped to your hearts content), or I<[read-write]>, which
		1420	means you can expect it to have some sensible content while the watcher
		1421	is active, but you can also modify it. Modifying it may not do something
		1422	sensible or take immediate effect (or do anything at all), but libev will
		1423	not crash or malfunction in any way.
		1424
		1425
480	=head2 C<ev_io> - is this file descriptor readable or writable	1426	=head2 C<ev_io> - is this file descriptor readable or writable?
481		1427
482	I/O watchers check whether a file descriptor is readable or writable	1428	I/O watchers check whether a file descriptor is readable or writable
483	in each iteration of the event loop (This behaviour is called	1429	in each iteration of the event loop, or, more precisely, when reading
484	level-triggering because you keep receiving events as long as the	1430	would not block the process and writing would at least be able to write
485	condition persists. Remember you can stop the watcher if you don't want to	1431	some data. This behaviour is called level-triggering because you keep
486	act on the event and neither want to receive future events).	1432	receiving events as long as the condition persists. Remember you can stop
		1433	the watcher if you don't want to act on the event and neither want to
		1434	receive future events.
487		1435
488	In general you can register as many read and/or write event watchers per	1436	In general you can register as many read and/or write event watchers per
489	fd as you want (as long as you don't confuse yourself). Setting all file	1437	fd as you want (as long as you don't confuse yourself). Setting all file
490	descriptors to non-blocking mode is also usually a good idea (but not	1438	descriptors to non-blocking mode is also usually a good idea (but not
491	required if you know what you are doing).	1439	required if you know what you are doing).
492		1440
493	You have to be careful with dup'ed file descriptors, though. Some backends	1441	If you cannot use non-blocking mode, then force the use of a
494	(the linux epoll backend is a notable example) cannot handle dup'ed file	1442	known-to-be-good backend (at the time of this writing, this includes only
495	descriptors correctly if you register interest in two or more fds pointing	1443	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
496	to the same underlying file/socket etc. description (that is, they share	1444	descriptors for which non-blocking operation makes no sense (such as
497	the same underlying "file open").	1445	files) - libev doesn't guarentee any specific behaviour in that case.
498		1446
499	If you must do this, then force the use of a known-to-be-good backend	1447	Another thing you have to watch out for is that it is quite easy to
500	(at the time of this writing, this includes only EVMETHOD_SELECT and	1448	receive "spurious" readiness notifications, that is your callback might
501	EVMETHOD_POLL).	1449	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1450	because there is no data. Not only are some backends known to create a
		1451	lot of those (for example Solaris ports), it is very easy to get into
		1452	this situation even with a relatively standard program structure. Thus
		1453	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1454	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1455
		1456	If you cannot run the fd in non-blocking mode (for example you should
		1457	not play around with an Xlib connection), then you have to separately
		1458	re-test whether a file descriptor is really ready with a known-to-be good
		1459	interface such as poll (fortunately in our Xlib example, Xlib already
		1460	does this on its own, so its quite safe to use). Some people additionally
		1461	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1462	indefinitely.
		1463
		1464	But really, best use non-blocking mode.
		1465
		1466	=head3 The special problem of disappearing file descriptors
		1467
		1468	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1469	descriptor (either due to calling C<close> explicitly or any other means,
		1470	such as C<dup2>). The reason is that you register interest in some file
		1471	descriptor, but when it goes away, the operating system will silently drop
		1472	this interest. If another file descriptor with the same number then is
		1473	registered with libev, there is no efficient way to see that this is, in
		1474	fact, a different file descriptor.
		1475
		1476	To avoid having to explicitly tell libev about such cases, libev follows
		1477	the following policy: Each time C<ev_io_set> is being called, libev
		1478	will assume that this is potentially a new file descriptor, otherwise
		1479	it is assumed that the file descriptor stays the same. That means that
		1480	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1481	descriptor even if the file descriptor number itself did not change.
		1482
		1483	This is how one would do it normally anyway, the important point is that
		1484	the libev application should not optimise around libev but should leave
		1485	optimisations to libev.
		1486
		1487	=head3 The special problem of dup'ed file descriptors
		1488
		1489	Some backends (e.g. epoll), cannot register events for file descriptors,
		1490	but only events for the underlying file descriptions. That means when you
		1491	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1492	events for them, only one file descriptor might actually receive events.
		1493
		1494	There is no workaround possible except not registering events
		1495	for potentially C<dup ()>'ed file descriptors, or to resort to
		1496	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1497
		1498	=head3 The special problem of fork
		1499
		1500	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1501	useless behaviour. Libev fully supports fork, but needs to be told about
		1502	it in the child.
		1503
		1504	To support fork in your programs, you either have to call
		1505	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1506	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1507	C<EVBACKEND_POLL>.
		1508
		1509	=head3 The special problem of SIGPIPE
		1510
		1511	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1512	when writing to a pipe whose other end has been closed, your program gets
		1513	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1514	this is sensible behaviour, for daemons, this is usually undesirable.
		1515
		1516	So when you encounter spurious, unexplained daemon exits, make sure you
		1517	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1518	somewhere, as that would have given you a big clue).
		1519
		1520
		1521	=head3 Watcher-Specific Functions
502		1522
503	=over 4	1523	=over 4
504		1524
505	=item ev_io_init (ev_io *, callback, int fd, int events)	1525	=item ev_io_init (ev_io *, callback, int fd, int events)
506		1526
507	=item ev_io_set (ev_io *, int fd, int events)	1527	=item ev_io_set (ev_io *, int fd, int events)
508		1528
509	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1529	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
510	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1530	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
511	EV_WRITE> to receive the given events.	1531	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1532
		1533	=item int fd [read-only]
		1534
		1535	The file descriptor being watched.
		1536
		1537	=item int events [read-only]
		1538
		1539	The events being watched.
512		1540
513	=back	1541	=back
514		1542
		1543	=head3 Examples
		1544
		1545	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1546	readable, but only once. Since it is likely line-buffered, you could
		1547	attempt to read a whole line in the callback.
		1548
		1549	static void
		1550	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1551	{
		1552	ev_io_stop (loop, w);
		1553	.. read from stdin here (or from w->fd) and handle any I/O errors
		1554	}
		1555
		1556	...
		1557	struct ev_loop *loop = ev_default_init (0);
		1558	ev_io stdin_readable;
		1559	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1560	ev_io_start (loop, &stdin_readable);
		1561	ev_loop (loop, 0);
		1562
		1563
515	=head2 C<ev_timer> - relative and optionally recurring timeouts	1564	=head2 C<ev_timer> - relative and optionally repeating timeouts
516		1565
517	Timer watchers are simple relative timers that generate an event after a	1566	Timer watchers are simple relative timers that generate an event after a
518	given time, and optionally repeating in regular intervals after that.	1567	given time, and optionally repeating in regular intervals after that.
519		1568
520	The timers are based on real time, that is, if you register an event that	1569	The timers are based on real time, that is, if you register an event that
521	times out after an hour and you reset your system clock to last years	1570	times out after an hour and you reset your system clock to January last
522	time, it will still time out after (roughly) and hour. "Roughly" because	1571	year, it will still time out after (roughly) one hour. "Roughly" because
523	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1572	detecting time jumps is hard, and some inaccuracies are unavoidable (the
524	monotonic clock option helps a lot here).	1573	monotonic clock option helps a lot here).
		1574
		1575	The callback is guaranteed to be invoked only I<after> its timeout has
		1576	passed (not I<at>, so on systems with very low-resolution clocks this
		1577	might introduce a small delay). If multiple timers become ready during the
		1578	same loop iteration then the ones with earlier time-out values are invoked
		1579	before ones of the same priority with later time-out values (but this is
		1580	no longer true when a callback calls C<ev_loop> recursively).
		1581
		1582	=head3 Be smart about timeouts
		1583
		1584	Many real-world problems involve some kind of timeout, usually for error
		1585	recovery. A typical example is an HTTP request - if the other side hangs,
		1586	you want to raise some error after a while.
		1587
		1588	What follows are some ways to handle this problem, from obvious and
		1589	inefficient to smart and efficient.
		1590
		1591	In the following, a 60 second activity timeout is assumed - a timeout that
		1592	gets reset to 60 seconds each time there is activity (e.g. each time some
		1593	data or other life sign was received).
		1594
		1595	=over 4
		1596
		1597	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1598
		1599	This is the most obvious, but not the most simple way: In the beginning,
		1600	start the watcher:
		1601
		1602	ev_timer_init (timer, callback, 60., 0.);
		1603	ev_timer_start (loop, timer);
		1604
		1605	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1606	and start it again:
		1607
		1608	ev_timer_stop (loop, timer);
		1609	ev_timer_set (timer, 60., 0.);
		1610	ev_timer_start (loop, timer);
		1611
		1612	This is relatively simple to implement, but means that each time there is
		1613	some activity, libev will first have to remove the timer from its internal
		1614	data structure and then add it again. Libev tries to be fast, but it's
		1615	still not a constant-time operation.
		1616
		1617	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1618
		1619	This is the easiest way, and involves using C<ev_timer_again> instead of
		1620	C<ev_timer_start>.
		1621
		1622	To implement this, configure an C<ev_timer> with a C<repeat> value
		1623	of C<60> and then call C<ev_timer_again> at start and each time you
		1624	successfully read or write some data. If you go into an idle state where
		1625	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1626	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1627
		1628	That means you can ignore both the C<ev_timer_start> function and the
		1629	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1630	member and C<ev_timer_again>.
		1631
		1632	At start:
		1633
		1634	ev_init (timer, callback);
		1635	timer->repeat = 60.;
		1636	ev_timer_again (loop, timer);
		1637
		1638	Each time there is some activity:
		1639
		1640	ev_timer_again (loop, timer);
		1641
		1642	It is even possible to change the time-out on the fly, regardless of
		1643	whether the watcher is active or not:
		1644
		1645	timer->repeat = 30.;
		1646	ev_timer_again (loop, timer);
		1647
		1648	This is slightly more efficient then stopping/starting the timer each time
		1649	you want to modify its timeout value, as libev does not have to completely
		1650	remove and re-insert the timer from/into its internal data structure.
		1651
		1652	It is, however, even simpler than the "obvious" way to do it.
		1653
		1654	=item 3. Let the timer time out, but then re-arm it as required.
		1655
		1656	This method is more tricky, but usually most efficient: Most timeouts are
		1657	relatively long compared to the intervals between other activity - in
		1658	our example, within 60 seconds, there are usually many I/O events with
		1659	associated activity resets.
		1660
		1661	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1662	but remember the time of last activity, and check for a real timeout only
		1663	within the callback:
		1664
		1665	ev_tstamp last_activity; // time of last activity
		1666
		1667	static void
		1668	callback (EV_P_ ev_timer *w, int revents)
		1669	{
		1670	ev_tstamp now = ev_now (EV_A);
		1671	ev_tstamp timeout = last_activity + 60.;
		1672
		1673	// if last_activity + 60. is older than now, we did time out
		1674	if (timeout < now)
		1675	{
		1676	// timeout occured, take action
		1677	}
		1678	else
		1679	{
		1680	// callback was invoked, but there was some activity, re-arm
		1681	// the watcher to fire in last_activity + 60, which is
		1682	// guaranteed to be in the future, so "again" is positive:
		1683	w->repeat = timeout - now;
		1684	ev_timer_again (EV_A_ w);
		1685	}
		1686	}
		1687
		1688	To summarise the callback: first calculate the real timeout (defined
		1689	as "60 seconds after the last activity"), then check if that time has
		1690	been reached, which means something I<did>, in fact, time out. Otherwise
		1691	the callback was invoked too early (C<timeout> is in the future), so
		1692	re-schedule the timer to fire at that future time, to see if maybe we have
		1693	a timeout then.
		1694
		1695	Note how C<ev_timer_again> is used, taking advantage of the
		1696	C<ev_timer_again> optimisation when the timer is already running.
		1697
		1698	This scheme causes more callback invocations (about one every 60 seconds
		1699	minus half the average time between activity), but virtually no calls to
		1700	libev to change the timeout.
		1701
		1702	To start the timer, simply initialise the watcher and set C<last_activity>
		1703	to the current time (meaning we just have some activity :), then call the
		1704	callback, which will "do the right thing" and start the timer:
		1705
		1706	ev_init (timer, callback);
		1707	last_activity = ev_now (loop);
		1708	callback (loop, timer, EV_TIMEOUT);
		1709
		1710	And when there is some activity, simply store the current time in
		1711	C<last_activity>, no libev calls at all:
		1712
		1713	last_actiivty = ev_now (loop);
		1714
		1715	This technique is slightly more complex, but in most cases where the
		1716	time-out is unlikely to be triggered, much more efficient.
		1717
		1718	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1719	callback :) - just change the timeout and invoke the callback, which will
		1720	fix things for you.
		1721
		1722	=item 4. Wee, just use a double-linked list for your timeouts.
		1723
		1724	If there is not one request, but many thousands (millions...), all
		1725	employing some kind of timeout with the same timeout value, then one can
		1726	do even better:
		1727
		1728	When starting the timeout, calculate the timeout value and put the timeout
		1729	at the I<end> of the list.
		1730
		1731	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1732	the list is expected to fire (for example, using the technique #3).
		1733
		1734	When there is some activity, remove the timer from the list, recalculate
		1735	the timeout, append it to the end of the list again, and make sure to
		1736	update the C<ev_timer> if it was taken from the beginning of the list.
		1737
		1738	This way, one can manage an unlimited number of timeouts in O(1) time for
		1739	starting, stopping and updating the timers, at the expense of a major
		1740	complication, and having to use a constant timeout. The constant timeout
		1741	ensures that the list stays sorted.
		1742
		1743	=back
		1744
		1745	So which method the best?
		1746
		1747	Method #2 is a simple no-brain-required solution that is adequate in most
		1748	situations. Method #3 requires a bit more thinking, but handles many cases
		1749	better, and isn't very complicated either. In most case, choosing either
		1750	one is fine, with #3 being better in typical situations.
		1751
		1752	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1753	rather complicated, but extremely efficient, something that really pays
		1754	off after the first million or so of active timers, i.e. it's usually
		1755	overkill :)
		1756
		1757	=head3 The special problem of time updates
		1758
		1759	Establishing the current time is a costly operation (it usually takes at
		1760	least two system calls): EV therefore updates its idea of the current
		1761	time only before and after C<ev_loop> collects new events, which causes a
		1762	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1763	lots of events in one iteration.
525		1764
526	The relative timeouts are calculated relative to the C<ev_now ()>	1765	The relative timeouts are calculated relative to the C<ev_now ()>
527	time. This is usually the right thing as this timestamp refers to the time	1766	time. This is usually the right thing as this timestamp refers to the time
528	of the event triggering whatever timeout you are modifying/starting. If	1767	of the event triggering whatever timeout you are modifying/starting. If
529	you suspect event processing to be delayed and you I<need> to base the timeout	1768	you suspect event processing to be delayed and you I<need> to base the
530	on the current time, use something like this to adjust for this:	1769	timeout on the current time, use something like this to adjust for this:
531		1770
532	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1771	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
533		1772
534	The callback is guarenteed to be invoked only when its timeout has passed,	1773	If the event loop is suspended for a long time, you can also force an
535	but if multiple timers become ready during the same loop iteration then	1774	update of the time returned by C<ev_now ()> by calling C<ev_now_update
536	order of execution is undefined.	1775	()>.
		1776
		1777	=head3 The special problems of suspended animation
		1778
		1779	When you leave the server world it is quite customary to hit machines that
		1780	can suspend/hibernate - what happens to the clocks during such a suspend?
		1781
		1782	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1783	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1784	to run until the system is suspended, but they will not advance while the
		1785	system is suspended. That means, on resume, it will be as if the program
		1786	was frozen for a few seconds, but the suspend time will not be counted
		1787	towards C<ev_timer> when a monotonic clock source is used. The real time
		1788	clock advanced as expected, but if it is used as sole clocksource, then a
		1789	long suspend would be detected as a time jump by libev, and timers would
		1790	be adjusted accordingly.
		1791
		1792	I would not be surprised to see different behaviour in different between
		1793	operating systems, OS versions or even different hardware.
		1794
		1795	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1796	time jump in the monotonic clocks and the realtime clock. If the program
		1797	is suspended for a very long time, and monotonic clock sources are in use,
		1798	then you can expect C<ev_timer>s to expire as the full suspension time
		1799	will be counted towards the timers. When no monotonic clock source is in
		1800	use, then libev will again assume a timejump and adjust accordingly.
		1801
		1802	It might be beneficial for this latter case to call C<ev_suspend>
		1803	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1804	deterministic behaviour in this case (you can do nothing against
		1805	C<SIGSTOP>).
		1806
		1807	=head3 Watcher-Specific Functions and Data Members
537		1808
538	=over 4	1809	=over 4
539		1810
540	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1811	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
541		1812
542	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1813	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
543		1814
544	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1815	Configure the timer to trigger after C<after> seconds. If C<repeat>
545	C<0.>, then it will automatically be stopped. If it is positive, then the	1816	is C<0.>, then it will automatically be stopped once the timeout is
546	timer will automatically be configured to trigger again C<repeat> seconds	1817	reached. If it is positive, then the timer will automatically be
547	later, again, and again, until stopped manually.	1818	configured to trigger again C<repeat> seconds later, again, and again,
		1819	until stopped manually.
548		1820
549	The timer itself will do a best-effort at avoiding drift, that is, if you	1821	The timer itself will do a best-effort at avoiding drift, that is, if
550	configure a timer to trigger every 10 seconds, then it will trigger at	1822	you configure a timer to trigger every 10 seconds, then it will normally
551	exactly 10 second intervals. If, however, your program cannot keep up with	1823	trigger at exactly 10 second intervals. If, however, your program cannot
552	the timer (because it takes longer than those 10 seconds to do stuff) the	1824	keep up with the timer (because it takes longer than those 10 seconds to
553	timer will not fire more than once per event loop iteration.	1825	do stuff) the timer will not fire more than once per event loop iteration.
554		1826
555	=item ev_timer_again (loop)	1827	=item ev_timer_again (loop, ev_timer *)
556		1828
557	This will act as if the timer timed out and restart it again if it is	1829	This will act as if the timer timed out and restart it again if it is
558	repeating. The exact semantics are:	1830	repeating. The exact semantics are:
559		1831
		1832	If the timer is pending, its pending status is cleared.
		1833
560	If the timer is started but nonrepeating, stop it.	1834	If the timer is started but non-repeating, stop it (as if it timed out).
561		1835
562	If the timer is repeating, either start it if necessary (with the repeat	1836	If the timer is repeating, either start it if necessary (with the
563	value), or reset the running timer to the repeat value.	1837	C<repeat> value), or reset the running timer to the C<repeat> value.
564		1838
565	This sounds a bit complicated, but here is a useful and typical	1839	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
566	example: Imagine you have a tcp connection and you want a so-called idle	1840	usage example.
567	timeout, that is, you want to be called when there have been, say, 60	1841
568	seconds of inactivity on the socket. The easiest way to do this is to	1842	=item ev_timer_remaining (loop, ev_timer *)
569	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1843
570	time you successfully read or write some data. If you go into an idle	1844	Returns the remaining time until a timer fires. If the timer is active,
571	state where you do not expect data to travel on the socket, you can stop	1845	then this time is relative to the current event loop time, otherwise it's
572	the timer, and again will automatically restart it if need be.	1846	the timeout value currently configured.
		1847
		1848	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1849	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1850	will return C<4>. When the timer expires and is restarted, it will return
		1851	roughly C<7> (likely slightly less as callback invocation takes some time,
		1852	too), and so on.
		1853
		1854	=item ev_tstamp repeat [read-write]
		1855
		1856	The current C<repeat> value. Will be used each time the watcher times out
		1857	or C<ev_timer_again> is called, and determines the next timeout (if any),
		1858	which is also when any modifications are taken into account.
573		1859
574	=back	1860	=back
575		1861
		1862	=head3 Examples
		1863
		1864	Example: Create a timer that fires after 60 seconds.
		1865
		1866	static void
		1867	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1868	{
		1869	.. one minute over, w is actually stopped right here
		1870	}
		1871
		1872	ev_timer mytimer;
		1873	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1874	ev_timer_start (loop, &mytimer);
		1875
		1876	Example: Create a timeout timer that times out after 10 seconds of
		1877	inactivity.
		1878
		1879	static void
		1880	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1881	{
		1882	.. ten seconds without any activity
		1883	}
		1884
		1885	ev_timer mytimer;
		1886	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1887	ev_timer_again (&mytimer); /* start timer */
		1888	ev_loop (loop, 0);
		1889
		1890	// and in some piece of code that gets executed on any "activity":
		1891	// reset the timeout to start ticking again at 10 seconds
		1892	ev_timer_again (&mytimer);
		1893
		1894
576	=head2 C<ev_periodic> - to cron or not to cron	1895	=head2 C<ev_periodic> - to cron or not to cron?
577		1896
578	Periodic watchers are also timers of a kind, but they are very versatile	1897	Periodic watchers are also timers of a kind, but they are very versatile
579	(and unfortunately a bit complex).	1898	(and unfortunately a bit complex).
580		1899
581	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1900	Unlike C<ev_timer>, periodic watchers are not based on real time (or
582	but on wallclock time (absolute time). You can tell a periodic watcher	1901	relative time, the physical time that passes) but on wall clock time
583	to trigger "at" some specific point in time. For example, if you tell a	1902	(absolute time, the thing you can read on your calender or clock). The
584	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1903	difference is that wall clock time can run faster or slower than real
585	+ 10.>) and then reset your system clock to the last year, then it will	1904	time, and time jumps are not uncommon (e.g. when you adjust your
586	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1905	wrist-watch).
587	roughly 10 seconds later and of course not if you reset your system time
588	again).
589		1906
590	They can also be used to implement vastly more complex timers, such as	1907	You can tell a periodic watcher to trigger after some specific point
		1908	in time: for example, if you tell a periodic watcher to trigger "in 10
		1909	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1910	not a delay) and then reset your system clock to January of the previous
		1911	year, then it will take a year or more to trigger the event (unlike an
		1912	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1913	it, as it uses a relative timeout).
		1914
		1915	C<ev_periodic> watchers can also be used to implement vastly more complex
591	triggering an event on eahc midnight, local time.	1916	timers, such as triggering an event on each "midnight, local time", or
		1917	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1918	those cannot react to time jumps.
592		1919
593	As with timers, the callback is guarenteed to be invoked only when the	1920	As with timers, the callback is guaranteed to be invoked only when the
594	time (C<at>) has been passed, but if multiple periodic timers become ready	1921	point in time where it is supposed to trigger has passed. If multiple
595	during the same loop iteration then order of execution is undefined.	1922	timers become ready during the same loop iteration then the ones with
		1923	earlier time-out values are invoked before ones with later time-out values
		1924	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1925
		1926	=head3 Watcher-Specific Functions and Data Members
596		1927
597	=over 4	1928	=over 4
598		1929
599	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1930	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
600		1931
601	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1932	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
602		1933
603	Lots of arguments, lets sort it out... There are basically three modes of	1934	Lots of arguments, let's sort it out... There are basically three modes of
604	operation, and we will explain them from simplest to complex:	1935	operation, and we will explain them from simplest to most complex:
605		1936
606	=over 4	1937	=over 4
607		1938
608	=item * absolute timer (interval = reschedule_cb = 0)	1939	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
609		1940
610	In this configuration the watcher triggers an event at the wallclock time	1941	In this configuration the watcher triggers an event after the wall clock
611	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1942	time C<offset> has passed. It will not repeat and will not adjust when a
612	that is, if it is to be run at January 1st 2011 then it will run when the	1943	time jump occurs, that is, if it is to be run at January 1st 2011 then it
613	system time reaches or surpasses this time.	1944	will be stopped and invoked when the system clock reaches or surpasses
		1945	this point in time.
614		1946
615	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1947	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
616		1948
617	In this mode the watcher will always be scheduled to time out at the next	1949	In this mode the watcher will always be scheduled to time out at the next
618	C<at + N * interval> time (for some integer N) and then repeat, regardless	1950	C<offset + N * interval> time (for some integer N, which can also be
619	of any time jumps.	1951	negative) and then repeat, regardless of any time jumps. The C<offset>
		1952	argument is merely an offset into the C<interval> periods.
620		1953
621	This can be used to create timers that do not drift with respect to system	1954	This can be used to create timers that do not drift with respect to the
622	time:	1955	system clock, for example, here is an C<ev_periodic> that triggers each
		1956	hour, on the hour (with respect to UTC):
623		1957
624	ev_periodic_set (&periodic, 0., 3600., 0);	1958	ev_periodic_set (&periodic, 0., 3600., 0);
625		1959
626	This doesn't mean there will always be 3600 seconds in between triggers,	1960	This doesn't mean there will always be 3600 seconds in between triggers,
627	but only that the the callback will be called when the system time shows a	1961	but only that the callback will be called when the system time shows a
628	full hour (UTC), or more correctly, when the system time is evenly divisible	1962	full hour (UTC), or more correctly, when the system time is evenly divisible
629	by 3600.	1963	by 3600.
630		1964
631	Another way to think about it (for the mathematically inclined) is that	1965	Another way to think about it (for the mathematically inclined) is that
632	C<ev_periodic> will try to run the callback in this mode at the next possible	1966	C<ev_periodic> will try to run the callback in this mode at the next possible
633	time where C<time = at (mod interval)>, regardless of any time jumps.	1967	time where C<time = offset (mod interval)>, regardless of any time jumps.
634		1968
		1969	For numerical stability it is preferable that the C<offset> value is near
		1970	C<ev_now ()> (the current time), but there is no range requirement for
		1971	this value, and in fact is often specified as zero.
		1972
		1973	Note also that there is an upper limit to how often a timer can fire (CPU
		1974	speed for example), so if C<interval> is very small then timing stability
		1975	will of course deteriorate. Libev itself tries to be exact to be about one
		1976	millisecond (if the OS supports it and the machine is fast enough).
		1977
635	=item * manual reschedule mode (reschedule_cb = callback)	1978	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
636		1979
637	In this mode the values for C<interval> and C<at> are both being	1980	In this mode the values for C<interval> and C<offset> are both being
638	ignored. Instead, each time the periodic watcher gets scheduled, the	1981	ignored. Instead, each time the periodic watcher gets scheduled, the
639	reschedule callback will be called with the watcher as first, and the	1982	reschedule callback will be called with the watcher as first, and the
640	current time as second argument.	1983	current time as second argument.
641		1984
642	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1985	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
643	ever, or make any event loop modifications>. If you need to stop it,	1986	or make ANY other event loop modifications whatsoever, unless explicitly
644	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1987	allowed by documentation here>.
645	starting a prepare watcher).
646		1988
		1989	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1990	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1991	only event loop modification you are allowed to do).
		1992
647	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1993	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
648	ev_tstamp now)>, e.g.:	1994	*w, ev_tstamp now)>, e.g.:
649		1995
		1996	static ev_tstamp
650	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1997	my_rescheduler (ev_periodic *w, ev_tstamp now)
651	{	1998	{
652	return now + 60.;	1999	return now + 60.;
653	}	2000	}
654		2001
655	It must return the next time to trigger, based on the passed time value	2002	It must return the next time to trigger, based on the passed time value
656	(that is, the lowest time value larger than to the second argument). It	2003	(that is, the lowest time value larger than to the second argument). It
657	will usually be called just before the callback will be triggered, but	2004	will usually be called just before the callback will be triggered, but
658	might be called at other times, too.	2005	might be called at other times, too.
659		2006
660	NOTE: I<< This callback must always return a time that is later than the	2007	NOTE: I<< This callback must always return a time that is higher than or
661	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2008	equal to the passed C<now> value >>.
662		2009
663	This can be used to create very complex timers, such as a timer that	2010	This can be used to create very complex timers, such as a timer that
664	triggers on each midnight, local time. To do this, you would calculate the	2011	triggers on "next midnight, local time". To do this, you would calculate the
665	next midnight after C<now> and return the timestamp value for this. How	2012	next midnight after C<now> and return the timestamp value for this. How
666	you do this is, again, up to you (but it is not trivial, which is the main	2013	you do this is, again, up to you (but it is not trivial, which is the main
667	reason I omitted it as an example).	2014	reason I omitted it as an example).
668		2015
669	=back	2016	=back
…		…
673	Simply stops and restarts the periodic watcher again. This is only useful	2020	Simply stops and restarts the periodic watcher again. This is only useful
674	when you changed some parameters or the reschedule callback would return	2021	when you changed some parameters or the reschedule callback would return
675	a different time than the last time it was called (e.g. in a crond like	2022	a different time than the last time it was called (e.g. in a crond like
676	program when the crontabs have changed).	2023	program when the crontabs have changed).
677		2024
		2025	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2026
		2027	When active, returns the absolute time that the watcher is supposed
		2028	to trigger next. This is not the same as the C<offset> argument to
		2029	C<ev_periodic_set>, but indeed works even in interval and manual
		2030	rescheduling modes.
		2031
		2032	=item ev_tstamp offset [read-write]
		2033
		2034	When repeating, this contains the offset value, otherwise this is the
		2035	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2036	although libev might modify this value for better numerical stability).
		2037
		2038	Can be modified any time, but changes only take effect when the periodic
		2039	timer fires or C<ev_periodic_again> is being called.
		2040
		2041	=item ev_tstamp interval [read-write]
		2042
		2043	The current interval value. Can be modified any time, but changes only
		2044	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2045	called.
		2046
		2047	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2048
		2049	The current reschedule callback, or C<0>, if this functionality is
		2050	switched off. Can be changed any time, but changes only take effect when
		2051	the periodic timer fires or C<ev_periodic_again> is being called.
		2052
678	=back	2053	=back
679		2054
		2055	=head3 Examples
		2056
		2057	Example: Call a callback every hour, or, more precisely, whenever the
		2058	system time is divisible by 3600. The callback invocation times have
		2059	potentially a lot of jitter, but good long-term stability.
		2060
		2061	static void
		2062	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
		2063	{
		2064	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2065	}
		2066
		2067	ev_periodic hourly_tick;
		2068	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2069	ev_periodic_start (loop, &hourly_tick);
		2070
		2071	Example: The same as above, but use a reschedule callback to do it:
		2072
		2073	#include <math.h>
		2074
		2075	static ev_tstamp
		2076	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2077	{
		2078	return now + (3600. - fmod (now, 3600.));
		2079	}
		2080
		2081	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2082
		2083	Example: Call a callback every hour, starting now:
		2084
		2085	ev_periodic hourly_tick;
		2086	ev_periodic_init (&hourly_tick, clock_cb,
		2087	fmod (ev_now (loop), 3600.), 3600., 0);
		2088	ev_periodic_start (loop, &hourly_tick);
		2089
		2090
680	=head2 C<ev_signal> - signal me when a signal gets signalled	2091	=head2 C<ev_signal> - signal me when a signal gets signalled!
681		2092
682	Signal watchers will trigger an event when the process receives a specific	2093	Signal watchers will trigger an event when the process receives a specific
683	signal one or more times. Even though signals are very asynchronous, libev	2094	signal one or more times. Even though signals are very asynchronous, libev
684	will try it's best to deliver signals synchronously, i.e. as part of the	2095	will try it's best to deliver signals synchronously, i.e. as part of the
685	normal event processing, like any other event.	2096	normal event processing, like any other event.
686		2097
		2098	If you want signals to be delivered truly asynchronously, just use
		2099	C<sigaction> as you would do without libev and forget about sharing
		2100	the signal. You can even use C<ev_async> from a signal handler to
		2101	synchronously wake up an event loop.
		2102
687	You can configure as many watchers as you like per signal. Only when the	2103	You can configure as many watchers as you like for the same signal, but
		2104	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2105	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2106	C<SIGINT> in both the default loop and another loop at the same time. At
		2107	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2108
688	first watcher gets started will libev actually register a signal watcher	2109	When the first watcher gets started will libev actually register something
689	with the kernel (thus it coexists with your own signal handlers as long	2110	with the kernel (thus it coexists with your own signal handlers as long as
690	as you don't register any with libev). Similarly, when the last signal	2111	you don't register any with libev for the same signal).
691	watcher for a signal is stopped libev will reset the signal handler to	2112
692	SIG_DFL (regardless of what it was set to before).	2113	If possible and supported, libev will install its handlers with
		2114	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2115	not be unduly interrupted. If you have a problem with system calls getting
		2116	interrupted by signals you can block all signals in an C<ev_check> watcher
		2117	and unblock them in an C<ev_prepare> watcher.
		2118
		2119	=head3 The special problem of inheritance over execve
		2120
		2121	Both the signal mask (C<sigprocmask>) and the signal disposition
		2122	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2123	stopping it again), that is, libev might or might not block the signal,
		2124	and might or might not set or restore the installed signal handler.
		2125
		2126	While this does not matter for the signal disposition (libev never
		2127	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2128	C<execve>), this matters for the signal mask: many programs do not expect
		2129	certain signals to be blocked.
		2130
		2131	This means that before calling C<exec> (from the child) you should reset
		2132	the signal mask to whatever "default" you expect (all clear is a good
		2133	choice usually).
		2134
		2135	In current versions of libev, you can ensure that the signal mask is not
		2136	blocking any signals (except temporarily, so thread users watch out) by
		2137	specifying the C<EVFLAG_NOSIGNALFD> when creating the event loop. This is
		2138	not guaranteed for future versions, however.
		2139
		2140	=head3 Watcher-Specific Functions and Data Members
693		2141
694	=over 4	2142	=over 4
695		2143
696	=item ev_signal_init (ev_signal *, callback, int signum)	2144	=item ev_signal_init (ev_signal *, callback, int signum)
697		2145
698	=item ev_signal_set (ev_signal *, int signum)	2146	=item ev_signal_set (ev_signal *, int signum)
699		2147
700	Configures the watcher to trigger on the given signal number (usually one	2148	Configures the watcher to trigger on the given signal number (usually one
701	of the C<SIGxxx> constants).	2149	of the C<SIGxxx> constants).
702		2150
		2151	=item int signum [read-only]
		2152
		2153	The signal the watcher watches out for.
		2154
703	=back	2155	=back
704		2156
		2157	=head3 Examples
		2158
		2159	Example: Try to exit cleanly on SIGINT.
		2160
		2161	static void
		2162	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2163	{
		2164	ev_unloop (loop, EVUNLOOP_ALL);
		2165	}
		2166
		2167	ev_signal signal_watcher;
		2168	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2169	ev_signal_start (loop, &signal_watcher);
		2170
		2171
705	=head2 C<ev_child> - wait for pid status changes	2172	=head2 C<ev_child> - watch out for process status changes
706		2173
707	Child watchers trigger when your process receives a SIGCHLD in response to	2174	Child watchers trigger when your process receives a SIGCHLD in response to
708	some child status changes (most typically when a child of yours dies).	2175	some child status changes (most typically when a child of yours dies or
		2176	exits). It is permissible to install a child watcher I<after> the child
		2177	has been forked (which implies it might have already exited), as long
		2178	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2179	forking and then immediately registering a watcher for the child is fine,
		2180	but forking and registering a watcher a few event loop iterations later or
		2181	in the next callback invocation is not.
		2182
		2183	Only the default event loop is capable of handling signals, and therefore
		2184	you can only register child watchers in the default event loop.
		2185
		2186	Due to some design glitches inside libev, child watchers will always be
		2187	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2188	libev)
		2189
		2190	=head3 Process Interaction
		2191
		2192	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2193	initialised. This is necessary to guarantee proper behaviour even if the
		2194	first child watcher is started after the child exits. The occurrence
		2195	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2196	synchronously as part of the event loop processing. Libev always reaps all
		2197	children, even ones not watched.
		2198
		2199	=head3 Overriding the Built-In Processing
		2200
		2201	Libev offers no special support for overriding the built-in child
		2202	processing, but if your application collides with libev's default child
		2203	handler, you can override it easily by installing your own handler for
		2204	C<SIGCHLD> after initialising the default loop, and making sure the
		2205	default loop never gets destroyed. You are encouraged, however, to use an
		2206	event-based approach to child reaping and thus use libev's support for
		2207	that, so other libev users can use C<ev_child> watchers freely.
		2208
		2209	=head3 Stopping the Child Watcher
		2210
		2211	Currently, the child watcher never gets stopped, even when the
		2212	child terminates, so normally one needs to stop the watcher in the
		2213	callback. Future versions of libev might stop the watcher automatically
		2214	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2215	problem).
		2216
		2217	=head3 Watcher-Specific Functions and Data Members
709		2218
710	=over 4	2219	=over 4
711		2220
712	=item ev_child_init (ev_child *, callback, int pid)	2221	=item ev_child_init (ev_child *, callback, int pid, int trace)
713		2222
714	=item ev_child_set (ev_child *, int pid)	2223	=item ev_child_set (ev_child *, int pid, int trace)
715		2224
716	Configures the watcher to wait for status changes of process C<pid> (or	2225	Configures the watcher to wait for status changes of process C<pid> (or
717	I<any> process if C<pid> is specified as C<0>). The callback can look	2226	I<any> process if C<pid> is specified as C<0>). The callback can look
718	at the C<rstatus> member of the C<ev_child> watcher structure to see	2227	at the C<rstatus> member of the C<ev_child> watcher structure to see
719	the status word (use the macros from C<sys/wait.h> and see your systems	2228	the status word (use the macros from C<sys/wait.h> and see your systems
720	C<waitpid> documentation). The C<rpid> member contains the pid of the	2229	C<waitpid> documentation). The C<rpid> member contains the pid of the
721	process causing the status change.	2230	process causing the status change. C<trace> must be either C<0> (only
		2231	activate the watcher when the process terminates) or C<1> (additionally
		2232	activate the watcher when the process is stopped or continued).
		2233
		2234	=item int pid [read-only]
		2235
		2236	The process id this watcher watches out for, or C<0>, meaning any process id.
		2237
		2238	=item int rpid [read-write]
		2239
		2240	The process id that detected a status change.
		2241
		2242	=item int rstatus [read-write]
		2243
		2244	The process exit/trace status caused by C<rpid> (see your systems
		2245	C<waitpid> and C<sys/wait.h> documentation for details).
722		2246
723	=back	2247	=back
724		2248
		2249	=head3 Examples
		2250
		2251	Example: C<fork()> a new process and install a child handler to wait for
		2252	its completion.
		2253
		2254	ev_child cw;
		2255
		2256	static void
		2257	child_cb (EV_P_ ev_child *w, int revents)
		2258	{
		2259	ev_child_stop (EV_A_ w);
		2260	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2261	}
		2262
		2263	pid_t pid = fork ();
		2264
		2265	if (pid < 0)
		2266	// error
		2267	else if (pid == 0)
		2268	{
		2269	// the forked child executes here
		2270	exit (1);
		2271	}
		2272	else
		2273	{
		2274	ev_child_init (&cw, child_cb, pid, 0);
		2275	ev_child_start (EV_DEFAULT_ &cw);
		2276	}
		2277
		2278
		2279	=head2 C<ev_stat> - did the file attributes just change?
		2280
		2281	This watches a file system path for attribute changes. That is, it calls
		2282	C<stat> on that path in regular intervals (or when the OS says it changed)
		2283	and sees if it changed compared to the last time, invoking the callback if
		2284	it did.
		2285
		2286	The path does not need to exist: changing from "path exists" to "path does
		2287	not exist" is a status change like any other. The condition "path does not
		2288	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2289	C<st_nlink> field being zero (which is otherwise always forced to be at
		2290	least one) and all the other fields of the stat buffer having unspecified
		2291	contents.
		2292
		2293	The path I<must not> end in a slash or contain special components such as
		2294	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2295	your working directory changes, then the behaviour is undefined.
		2296
		2297	Since there is no portable change notification interface available, the
		2298	portable implementation simply calls C<stat(2)> regularly on the path
		2299	to see if it changed somehow. You can specify a recommended polling
		2300	interval for this case. If you specify a polling interval of C<0> (highly
		2301	recommended!) then a I<suitable, unspecified default> value will be used
		2302	(which you can expect to be around five seconds, although this might
		2303	change dynamically). Libev will also impose a minimum interval which is
		2304	currently around C<0.1>, but that's usually overkill.
		2305
		2306	This watcher type is not meant for massive numbers of stat watchers,
		2307	as even with OS-supported change notifications, this can be
		2308	resource-intensive.
		2309
		2310	At the time of this writing, the only OS-specific interface implemented
		2311	is the Linux inotify interface (implementing kqueue support is left as an
		2312	exercise for the reader. Note, however, that the author sees no way of
		2313	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2314
		2315	=head3 ABI Issues (Largefile Support)
		2316
		2317	Libev by default (unless the user overrides this) uses the default
		2318	compilation environment, which means that on systems with large file
		2319	support disabled by default, you get the 32 bit version of the stat
		2320	structure. When using the library from programs that change the ABI to
		2321	use 64 bit file offsets the programs will fail. In that case you have to
		2322	compile libev with the same flags to get binary compatibility. This is
		2323	obviously the case with any flags that change the ABI, but the problem is
		2324	most noticeably displayed with ev_stat and large file support.
		2325
		2326	The solution for this is to lobby your distribution maker to make large
		2327	file interfaces available by default (as e.g. FreeBSD does) and not
		2328	optional. Libev cannot simply switch on large file support because it has
		2329	to exchange stat structures with application programs compiled using the
		2330	default compilation environment.
		2331
		2332	=head3 Inotify and Kqueue
		2333
		2334	When C<inotify (7)> support has been compiled into libev and present at
		2335	runtime, it will be used to speed up change detection where possible. The
		2336	inotify descriptor will be created lazily when the first C<ev_stat>
		2337	watcher is being started.
		2338
		2339	Inotify presence does not change the semantics of C<ev_stat> watchers
		2340	except that changes might be detected earlier, and in some cases, to avoid
		2341	making regular C<stat> calls. Even in the presence of inotify support
		2342	there are many cases where libev has to resort to regular C<stat> polling,
		2343	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2344	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2345	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2346	xfs are fully working) libev usually gets away without polling.
		2347
		2348	There is no support for kqueue, as apparently it cannot be used to
		2349	implement this functionality, due to the requirement of having a file
		2350	descriptor open on the object at all times, and detecting renames, unlinks
		2351	etc. is difficult.
		2352
		2353	=head3 C<stat ()> is a synchronous operation
		2354
		2355	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2356	the process. The exception are C<ev_stat> watchers - those call C<stat
		2357	()>, which is a synchronous operation.
		2358
		2359	For local paths, this usually doesn't matter: unless the system is very
		2360	busy or the intervals between stat's are large, a stat call will be fast,
		2361	as the path data is usually in memory already (except when starting the
		2362	watcher).
		2363
		2364	For networked file systems, calling C<stat ()> can block an indefinite
		2365	time due to network issues, and even under good conditions, a stat call
		2366	often takes multiple milliseconds.
		2367
		2368	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2369	paths, although this is fully supported by libev.
		2370
		2371	=head3 The special problem of stat time resolution
		2372
		2373	The C<stat ()> system call only supports full-second resolution portably,
		2374	and even on systems where the resolution is higher, most file systems
		2375	still only support whole seconds.
		2376
		2377	That means that, if the time is the only thing that changes, you can
		2378	easily miss updates: on the first update, C<ev_stat> detects a change and
		2379	calls your callback, which does something. When there is another update
		2380	within the same second, C<ev_stat> will be unable to detect unless the
		2381	stat data does change in other ways (e.g. file size).
		2382
		2383	The solution to this is to delay acting on a change for slightly more
		2384	than a second (or till slightly after the next full second boundary), using
		2385	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2386	ev_timer_again (loop, w)>).
		2387
		2388	The C<.02> offset is added to work around small timing inconsistencies
		2389	of some operating systems (where the second counter of the current time
		2390	might be be delayed. One such system is the Linux kernel, where a call to
		2391	C<gettimeofday> might return a timestamp with a full second later than
		2392	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2393	update file times then there will be a small window where the kernel uses
		2394	the previous second to update file times but libev might already execute
		2395	the timer callback).
		2396
		2397	=head3 Watcher-Specific Functions and Data Members
		2398
		2399	=over 4
		2400
		2401	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2402
		2403	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2404
		2405	Configures the watcher to wait for status changes of the given
		2406	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2407	be detected and should normally be specified as C<0> to let libev choose
		2408	a suitable value. The memory pointed to by C<path> must point to the same
		2409	path for as long as the watcher is active.
		2410
		2411	The callback will receive an C<EV_STAT> event when a change was detected,
		2412	relative to the attributes at the time the watcher was started (or the
		2413	last change was detected).
		2414
		2415	=item ev_stat_stat (loop, ev_stat *)
		2416
		2417	Updates the stat buffer immediately with new values. If you change the
		2418	watched path in your callback, you could call this function to avoid
		2419	detecting this change (while introducing a race condition if you are not
		2420	the only one changing the path). Can also be useful simply to find out the
		2421	new values.
		2422
		2423	=item ev_statdata attr [read-only]
		2424
		2425	The most-recently detected attributes of the file. Although the type is
		2426	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2427	suitable for your system, but you can only rely on the POSIX-standardised
		2428	members to be present. If the C<st_nlink> member is C<0>, then there was
		2429	some error while C<stat>ing the file.
		2430
		2431	=item ev_statdata prev [read-only]
		2432
		2433	The previous attributes of the file. The callback gets invoked whenever
		2434	C<prev> != C<attr>, or, more precisely, one or more of these members
		2435	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2436	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2437
		2438	=item ev_tstamp interval [read-only]
		2439
		2440	The specified interval.
		2441
		2442	=item const char *path [read-only]
		2443
		2444	The file system path that is being watched.
		2445
		2446	=back
		2447
		2448	=head3 Examples
		2449
		2450	Example: Watch C</etc/passwd> for attribute changes.
		2451
		2452	static void
		2453	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2454	{
		2455	/* /etc/passwd changed in some way */
		2456	if (w->attr.st_nlink)
		2457	{
		2458	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2459	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2460	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2461	}
		2462	else
		2463	/* you shalt not abuse printf for puts */
		2464	puts ("wow, /etc/passwd is not there, expect problems. "
		2465	"if this is windows, they already arrived\n");
		2466	}
		2467
		2468	...
		2469	ev_stat passwd;
		2470
		2471	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2472	ev_stat_start (loop, &passwd);
		2473
		2474	Example: Like above, but additionally use a one-second delay so we do not
		2475	miss updates (however, frequent updates will delay processing, too, so
		2476	one might do the work both on C<ev_stat> callback invocation I<and> on
		2477	C<ev_timer> callback invocation).
		2478
		2479	static ev_stat passwd;
		2480	static ev_timer timer;
		2481
		2482	static void
		2483	timer_cb (EV_P_ ev_timer *w, int revents)
		2484	{
		2485	ev_timer_stop (EV_A_ w);
		2486
		2487	/* now it's one second after the most recent passwd change */
		2488	}
		2489
		2490	static void
		2491	stat_cb (EV_P_ ev_stat *w, int revents)
		2492	{
		2493	/* reset the one-second timer */
		2494	ev_timer_again (EV_A_ &timer);
		2495	}
		2496
		2497	...
		2498	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2499	ev_stat_start (loop, &passwd);
		2500	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2501
		2502
725	=head2 C<ev_idle> - when you've got nothing better to do	2503	=head2 C<ev_idle> - when you've got nothing better to do...
726		2504
727	Idle watchers trigger events when there are no other events are pending	2505	Idle watchers trigger events when no other events of the same or higher
728	(prepare, check and other idle watchers do not count). That is, as long	2506	priority are pending (prepare, check and other idle watchers do not count
729	as your process is busy handling sockets or timeouts (or even signals,	2507	as receiving "events").
730	imagine) it will not be triggered. But when your process is idle all idle	2508
731	watchers are being called again and again, once per event loop iteration -	2509	That is, as long as your process is busy handling sockets or timeouts
		2510	(or even signals, imagine) of the same or higher priority it will not be
		2511	triggered. But when your process is idle (or only lower-priority watchers
		2512	are pending), the idle watchers are being called once per event loop
732	until stopped, that is, or your process receives more events and becomes	2513	iteration - until stopped, that is, or your process receives more events
733	busy.	2514	and becomes busy again with higher priority stuff.
734		2515
735	The most noteworthy effect is that as long as any idle watchers are	2516	The most noteworthy effect is that as long as any idle watchers are
736	active, the process will not block when waiting for new events.	2517	active, the process will not block when waiting for new events.
737		2518
738	Apart from keeping your process non-blocking (which is a useful	2519	Apart from keeping your process non-blocking (which is a useful
739	effect on its own sometimes), idle watchers are a good place to do	2520	effect on its own sometimes), idle watchers are a good place to do
740	"pseudo-background processing", or delay processing stuff to after the	2521	"pseudo-background processing", or delay processing stuff to after the
741	event loop has handled all outstanding events.	2522	event loop has handled all outstanding events.
742		2523
		2524	=head3 Watcher-Specific Functions and Data Members
		2525
743	=over 4	2526	=over 4
744		2527
745	=item ev_idle_init (ev_signal *, callback)	2528	=item ev_idle_init (ev_idle *, callback)
746		2529
747	Initialises and configures the idle watcher - it has no parameters of any	2530	Initialises and configures the idle watcher - it has no parameters of any
748	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2531	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
749	believe me.	2532	believe me.
750		2533
751	=back	2534	=back
752		2535
		2536	=head3 Examples
		2537
		2538	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2539	callback, free it. Also, use no error checking, as usual.
		2540
		2541	static void
		2542	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2543	{
		2544	free (w);
		2545	// now do something you wanted to do when the program has
		2546	// no longer anything immediate to do.
		2547	}
		2548
		2549	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2550	ev_idle_init (idle_watcher, idle_cb);
		2551	ev_idle_start (loop, idle_watcher);
		2552
		2553
753	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2554	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
754		2555
755	Prepare and check watchers are usually (but not always) used in tandem:	2556	Prepare and check watchers are usually (but not always) used in pairs:
756	prepare watchers get invoked before the process blocks and check watchers	2557	prepare watchers get invoked before the process blocks and check watchers
757	afterwards.	2558	afterwards.
758		2559
		2560	You I<must not> call C<ev_loop> or similar functions that enter
		2561	the current event loop from either C<ev_prepare> or C<ev_check>
		2562	watchers. Other loops than the current one are fine, however. The
		2563	rationale behind this is that you do not need to check for recursion in
		2564	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2565	C<ev_check> so if you have one watcher of each kind they will always be
		2566	called in pairs bracketing the blocking call.
		2567
759	Their main purpose is to integrate other event mechanisms into libev. This	2568	Their main purpose is to integrate other event mechanisms into libev and
760	could be used, for example, to track variable changes, implement your own	2569	their use is somewhat advanced. They could be used, for example, to track
761	watchers, integrate net-snmp or a coroutine library and lots more.	2570	variable changes, implement your own watchers, integrate net-snmp or a
		2571	coroutine library and lots more. They are also occasionally useful if
		2572	you cache some data and want to flush it before blocking (for example,
		2573	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2574	watcher).
762		2575
763	This is done by examining in each prepare call which file descriptors need	2576	This is done by examining in each prepare call which file descriptors
764	to be watched by the other library, registering C<ev_io> watchers for	2577	need to be watched by the other library, registering C<ev_io> watchers
765	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2578	for them and starting an C<ev_timer> watcher for any timeouts (many
766	provide just this functionality). Then, in the check watcher you check for	2579	libraries provide exactly this functionality). Then, in the check watcher,
767	any events that occured (by checking the pending status of all watchers	2580	you check for any events that occurred (by checking the pending status
768	and stopping them) and call back into the library. The I/O and timer	2581	of all watchers and stopping them) and call back into the library. The
769	callbacks will never actually be called (but must be valid nevertheless,	2582	I/O and timer callbacks will never actually be called (but must be valid
770	because you never know, you know?).	2583	nevertheless, because you never know, you know?).
771		2584
772	As another example, the Perl Coro module uses these hooks to integrate	2585	As another example, the Perl Coro module uses these hooks to integrate
773	coroutines into libev programs, by yielding to other active coroutines	2586	coroutines into libev programs, by yielding to other active coroutines
774	during each prepare and only letting the process block if no coroutines	2587	during each prepare and only letting the process block if no coroutines
775	are ready to run (it's actually more complicated: it only runs coroutines	2588	are ready to run (it's actually more complicated: it only runs coroutines
776	with priority higher than or equal to the event loop and one coroutine	2589	with priority higher than or equal to the event loop and one coroutine
777	of lower priority, but only once, using idle watchers to keep the event	2590	of lower priority, but only once, using idle watchers to keep the event
778	loop from blocking if lower-priority coroutines are active, thus mapping	2591	loop from blocking if lower-priority coroutines are active, thus mapping
779	low-priority coroutines to idle/background tasks).	2592	low-priority coroutines to idle/background tasks).
780		2593
		2594	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2595	priority, to ensure that they are being run before any other watchers
		2596	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2597
		2598	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2599	activate ("feed") events into libev. While libev fully supports this, they
		2600	might get executed before other C<ev_check> watchers did their job. As
		2601	C<ev_check> watchers are often used to embed other (non-libev) event
		2602	loops those other event loops might be in an unusable state until their
		2603	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2604	others).
		2605
		2606	=head3 Watcher-Specific Functions and Data Members
		2607
781	=over 4	2608	=over 4
782		2609
783	=item ev_prepare_init (ev_prepare *, callback)	2610	=item ev_prepare_init (ev_prepare *, callback)
784		2611
785	=item ev_check_init (ev_check *, callback)	2612	=item ev_check_init (ev_check *, callback)
786		2613
787	Initialises and configures the prepare or check watcher - they have no	2614	Initialises and configures the prepare or check watcher - they have no
788	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2615	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
789	macros, but using them is utterly, utterly and completely pointless.	2616	macros, but using them is utterly, utterly, utterly and completely
		2617	pointless.
790		2618
791	=back	2619	=back
792		2620
		2621	=head3 Examples
		2622
		2623	There are a number of principal ways to embed other event loops or modules
		2624	into libev. Here are some ideas on how to include libadns into libev
		2625	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2626	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2627	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2628	Glib event loop).
		2629
		2630	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2631	and in a check watcher, destroy them and call into libadns. What follows
		2632	is pseudo-code only of course. This requires you to either use a low
		2633	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2634	the callbacks for the IO/timeout watchers might not have been called yet.
		2635
		2636	static ev_io iow [nfd];
		2637	static ev_timer tw;
		2638
		2639	static void
		2640	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2641	{
		2642	}
		2643
		2644	// create io watchers for each fd and a timer before blocking
		2645	static void
		2646	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2647	{
		2648	int timeout = 3600000;
		2649	struct pollfd fds [nfd];
		2650	// actual code will need to loop here and realloc etc.
		2651	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2652
		2653	/* the callback is illegal, but won't be called as we stop during check */
		2654	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		2655	ev_timer_start (loop, &tw);
		2656
		2657	// create one ev_io per pollfd
		2658	for (int i = 0; i < nfd; ++i)
		2659	{
		2660	ev_io_init (iow + i, io_cb, fds [i].fd,
		2661	((fds [i].events & POLLIN ? EV_READ : 0)
		2662	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2663
		2664	fds [i].revents = 0;
		2665	ev_io_start (loop, iow + i);
		2666	}
		2667	}
		2668
		2669	// stop all watchers after blocking
		2670	static void
		2671	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2672	{
		2673	ev_timer_stop (loop, &tw);
		2674
		2675	for (int i = 0; i < nfd; ++i)
		2676	{
		2677	// set the relevant poll flags
		2678	// could also call adns_processreadable etc. here
		2679	struct pollfd *fd = fds + i;
		2680	int revents = ev_clear_pending (iow + i);
		2681	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2682	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2683
		2684	// now stop the watcher
		2685	ev_io_stop (loop, iow + i);
		2686	}
		2687
		2688	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2689	}
		2690
		2691	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2692	in the prepare watcher and would dispose of the check watcher.
		2693
		2694	Method 3: If the module to be embedded supports explicit event
		2695	notification (libadns does), you can also make use of the actual watcher
		2696	callbacks, and only destroy/create the watchers in the prepare watcher.
		2697
		2698	static void
		2699	timer_cb (EV_P_ ev_timer *w, int revents)
		2700	{
		2701	adns_state ads = (adns_state)w->data;
		2702	update_now (EV_A);
		2703
		2704	adns_processtimeouts (ads, &tv_now);
		2705	}
		2706
		2707	static void
		2708	io_cb (EV_P_ ev_io *w, int revents)
		2709	{
		2710	adns_state ads = (adns_state)w->data;
		2711	update_now (EV_A);
		2712
		2713	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2714	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2715	}
		2716
		2717	// do not ever call adns_afterpoll
		2718
		2719	Method 4: Do not use a prepare or check watcher because the module you
		2720	want to embed is not flexible enough to support it. Instead, you can
		2721	override their poll function. The drawback with this solution is that the
		2722	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2723	this approach, effectively embedding EV as a client into the horrible
		2724	libglib event loop.
		2725
		2726	static gint
		2727	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2728	{
		2729	int got_events = 0;
		2730
		2731	for (n = 0; n < nfds; ++n)
		2732	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2733
		2734	if (timeout >= 0)
		2735	// create/start timer
		2736
		2737	// poll
		2738	ev_loop (EV_A_ 0);
		2739
		2740	// stop timer again
		2741	if (timeout >= 0)
		2742	ev_timer_stop (EV_A_ &to);
		2743
		2744	// stop io watchers again - their callbacks should have set
		2745	for (n = 0; n < nfds; ++n)
		2746	ev_io_stop (EV_A_ iow [n]);
		2747
		2748	return got_events;
		2749	}
		2750
		2751
		2752	=head2 C<ev_embed> - when one backend isn't enough...
		2753
		2754	This is a rather advanced watcher type that lets you embed one event loop
		2755	into another (currently only C<ev_io> events are supported in the embedded
		2756	loop, other types of watchers might be handled in a delayed or incorrect
		2757	fashion and must not be used).
		2758
		2759	There are primarily two reasons you would want that: work around bugs and
		2760	prioritise I/O.
		2761
		2762	As an example for a bug workaround, the kqueue backend might only support
		2763	sockets on some platform, so it is unusable as generic backend, but you
		2764	still want to make use of it because you have many sockets and it scales
		2765	so nicely. In this case, you would create a kqueue-based loop and embed
		2766	it into your default loop (which might use e.g. poll). Overall operation
		2767	will be a bit slower because first libev has to call C<poll> and then
		2768	C<kevent>, but at least you can use both mechanisms for what they are
		2769	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2770
		2771	As for prioritising I/O: under rare circumstances you have the case where
		2772	some fds have to be watched and handled very quickly (with low latency),
		2773	and even priorities and idle watchers might have too much overhead. In
		2774	this case you would put all the high priority stuff in one loop and all
		2775	the rest in a second one, and embed the second one in the first.
		2776
		2777	As long as the watcher is active, the callback will be invoked every
		2778	time there might be events pending in the embedded loop. The callback
		2779	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		2780	sweep and invoke their callbacks (the callback doesn't need to invoke the
		2781	C<ev_embed_sweep> function directly, it could also start an idle watcher
		2782	to give the embedded loop strictly lower priority for example).
		2783
		2784	You can also set the callback to C<0>, in which case the embed watcher
		2785	will automatically execute the embedded loop sweep whenever necessary.
		2786
		2787	Fork detection will be handled transparently while the C<ev_embed> watcher
		2788	is active, i.e., the embedded loop will automatically be forked when the
		2789	embedding loop forks. In other cases, the user is responsible for calling
		2790	C<ev_loop_fork> on the embedded loop.
		2791
		2792	Unfortunately, not all backends are embeddable: only the ones returned by
		2793	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2794	portable one.
		2795
		2796	So when you want to use this feature you will always have to be prepared
		2797	that you cannot get an embeddable loop. The recommended way to get around
		2798	this is to have a separate variables for your embeddable loop, try to
		2799	create it, and if that fails, use the normal loop for everything.
		2800
		2801	=head3 C<ev_embed> and fork
		2802
		2803	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2804	automatically be applied to the embedded loop as well, so no special
		2805	fork handling is required in that case. When the watcher is not running,
		2806	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2807	as applicable.
		2808
		2809	=head3 Watcher-Specific Functions and Data Members
		2810
		2811	=over 4
		2812
		2813	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2814
		2815	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2816
		2817	Configures the watcher to embed the given loop, which must be
		2818	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2819	invoked automatically, otherwise it is the responsibility of the callback
		2820	to invoke it (it will continue to be called until the sweep has been done,
		2821	if you do not want that, you need to temporarily stop the embed watcher).
		2822
		2823	=item ev_embed_sweep (loop, ev_embed *)
		2824
		2825	Make a single, non-blocking sweep over the embedded loop. This works
		2826	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2827	appropriate way for embedded loops.
		2828
		2829	=item struct ev_loop *other [read-only]
		2830
		2831	The embedded event loop.
		2832
		2833	=back
		2834
		2835	=head3 Examples
		2836
		2837	Example: Try to get an embeddable event loop and embed it into the default
		2838	event loop. If that is not possible, use the default loop. The default
		2839	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2840	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2841	used).
		2842
		2843	struct ev_loop *loop_hi = ev_default_init (0);
		2844	struct ev_loop *loop_lo = 0;
		2845	ev_embed embed;
		2846
		2847	// see if there is a chance of getting one that works
		2848	// (remember that a flags value of 0 means autodetection)
		2849	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2850	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2851	: 0;
		2852
		2853	// if we got one, then embed it, otherwise default to loop_hi
		2854	if (loop_lo)
		2855	{
		2856	ev_embed_init (&embed, 0, loop_lo);
		2857	ev_embed_start (loop_hi, &embed);
		2858	}
		2859	else
		2860	loop_lo = loop_hi;
		2861
		2862	Example: Check if kqueue is available but not recommended and create
		2863	a kqueue backend for use with sockets (which usually work with any
		2864	kqueue implementation). Store the kqueue/socket-only event loop in
		2865	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2866
		2867	struct ev_loop *loop = ev_default_init (0);
		2868	struct ev_loop *loop_socket = 0;
		2869	ev_embed embed;
		2870
		2871	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2872	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2873	{
		2874	ev_embed_init (&embed, 0, loop_socket);
		2875	ev_embed_start (loop, &embed);
		2876	}
		2877
		2878	if (!loop_socket)
		2879	loop_socket = loop;
		2880
		2881	// now use loop_socket for all sockets, and loop for everything else
		2882
		2883
		2884	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2885
		2886	Fork watchers are called when a C<fork ()> was detected (usually because
		2887	whoever is a good citizen cared to tell libev about it by calling
		2888	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2889	event loop blocks next and before C<ev_check> watchers are being called,
		2890	and only in the child after the fork. If whoever good citizen calling
		2891	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2892	handlers will be invoked, too, of course.
		2893
		2894	=head3 The special problem of life after fork - how is it possible?
		2895
		2896	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2897	up/change the process environment, followed by a call to C<exec()>. This
		2898	sequence should be handled by libev without any problems.
		2899
		2900	This changes when the application actually wants to do event handling
		2901	in the child, or both parent in child, in effect "continuing" after the
		2902	fork.
		2903
		2904	The default mode of operation (for libev, with application help to detect
		2905	forks) is to duplicate all the state in the child, as would be expected
		2906	when I<either> the parent I<or> the child process continues.
		2907
		2908	When both processes want to continue using libev, then this is usually the
		2909	wrong result. In that case, usually one process (typically the parent) is
		2910	supposed to continue with all watchers in place as before, while the other
		2911	process typically wants to start fresh, i.e. without any active watchers.
		2912
		2913	The cleanest and most efficient way to achieve that with libev is to
		2914	simply create a new event loop, which of course will be "empty", and
		2915	use that for new watchers. This has the advantage of not touching more
		2916	memory than necessary, and thus avoiding the copy-on-write, and the
		2917	disadvantage of having to use multiple event loops (which do not support
		2918	signal watchers).
		2919
		2920	When this is not possible, or you want to use the default loop for
		2921	other reasons, then in the process that wants to start "fresh", call
		2922	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2923	the default loop will "orphan" (not stop) all registered watchers, so you
		2924	have to be careful not to execute code that modifies those watchers. Note
		2925	also that in that case, you have to re-register any signal watchers.
		2926
		2927	=head3 Watcher-Specific Functions and Data Members
		2928
		2929	=over 4
		2930
		2931	=item ev_fork_init (ev_signal *, callback)
		2932
		2933	Initialises and configures the fork watcher - it has no parameters of any
		2934	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2935	believe me.
		2936
		2937	=back
		2938
		2939
		2940	=head2 C<ev_async> - how to wake up another event loop
		2941
		2942	In general, you cannot use an C<ev_loop> from multiple threads or other
		2943	asynchronous sources such as signal handlers (as opposed to multiple event
		2944	loops - those are of course safe to use in different threads).
		2945
		2946	Sometimes, however, you need to wake up another event loop you do not
		2947	control, for example because it belongs to another thread. This is what
		2948	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2949	can signal it by calling C<ev_async_send>, which is thread- and signal
		2950	safe.
		2951
		2952	This functionality is very similar to C<ev_signal> watchers, as signals,
		2953	too, are asynchronous in nature, and signals, too, will be compressed
		2954	(i.e. the number of callback invocations may be less than the number of
		2955	C<ev_async_sent> calls).
		2956
		2957	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2958	just the default loop.
		2959
		2960	=head3 Queueing
		2961
		2962	C<ev_async> does not support queueing of data in any way. The reason
		2963	is that the author does not know of a simple (or any) algorithm for a
		2964	multiple-writer-single-reader queue that works in all cases and doesn't
		2965	need elaborate support such as pthreads.
		2966
		2967	That means that if you want to queue data, you have to provide your own
		2968	queue. But at least I can tell you how to implement locking around your
		2969	queue:
		2970
		2971	=over 4
		2972
		2973	=item queueing from a signal handler context
		2974
		2975	To implement race-free queueing, you simply add to the queue in the signal
		2976	handler but you block the signal handler in the watcher callback. Here is
		2977	an example that does that for some fictitious SIGUSR1 handler:
		2978
		2979	static ev_async mysig;
		2980
		2981	static void
		2982	sigusr1_handler (void)
		2983	{
		2984	sometype data;
		2985
		2986	// no locking etc.
		2987	queue_put (data);
		2988	ev_async_send (EV_DEFAULT_ &mysig);
		2989	}
		2990
		2991	static void
		2992	mysig_cb (EV_P_ ev_async *w, int revents)
		2993	{
		2994	sometype data;
		2995	sigset_t block, prev;
		2996
		2997	sigemptyset (&block);
		2998	sigaddset (&block, SIGUSR1);
		2999	sigprocmask (SIG_BLOCK, &block, &prev);
		3000
		3001	while (queue_get (&data))
		3002	process (data);
		3003
		3004	if (sigismember (&prev, SIGUSR1)
		3005	sigprocmask (SIG_UNBLOCK, &block, 0);
		3006	}
		3007
		3008	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3009	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3010	either...).
		3011
		3012	=item queueing from a thread context
		3013
		3014	The strategy for threads is different, as you cannot (easily) block
		3015	threads but you can easily preempt them, so to queue safely you need to
		3016	employ a traditional mutex lock, such as in this pthread example:
		3017
		3018	static ev_async mysig;
		3019	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3020
		3021	static void
		3022	otherthread (void)
		3023	{
		3024	// only need to lock the actual queueing operation
		3025	pthread_mutex_lock (&mymutex);
		3026	queue_put (data);
		3027	pthread_mutex_unlock (&mymutex);
		3028
		3029	ev_async_send (EV_DEFAULT_ &mysig);
		3030	}
		3031
		3032	static void
		3033	mysig_cb (EV_P_ ev_async *w, int revents)
		3034	{
		3035	pthread_mutex_lock (&mymutex);
		3036
		3037	while (queue_get (&data))
		3038	process (data);
		3039
		3040	pthread_mutex_unlock (&mymutex);
		3041	}
		3042
		3043	=back
		3044
		3045
		3046	=head3 Watcher-Specific Functions and Data Members
		3047
		3048	=over 4
		3049
		3050	=item ev_async_init (ev_async *, callback)
		3051
		3052	Initialises and configures the async watcher - it has no parameters of any
		3053	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3054	trust me.
		3055
		3056	=item ev_async_send (loop, ev_async *)
		3057
		3058	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3059	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3060	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3061	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3062	section below on what exactly this means).
		3063
		3064	Note that, as with other watchers in libev, multiple events might get
		3065	compressed into a single callback invocation (another way to look at this
		3066	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3067	reset when the event loop detects that).
		3068
		3069	This call incurs the overhead of a system call only once per event loop
		3070	iteration, so while the overhead might be noticeable, it doesn't apply to
		3071	repeated calls to C<ev_async_send> for the same event loop.
		3072
		3073	=item bool = ev_async_pending (ev_async *)
		3074
		3075	Returns a non-zero value when C<ev_async_send> has been called on the
		3076	watcher but the event has not yet been processed (or even noted) by the
		3077	event loop.
		3078
		3079	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3080	the loop iterates next and checks for the watcher to have become active,
		3081	it will reset the flag again. C<ev_async_pending> can be used to very
		3082	quickly check whether invoking the loop might be a good idea.
		3083
		3084	Not that this does I<not> check whether the watcher itself is pending,
		3085	only whether it has been requested to make this watcher pending: there
		3086	is a time window between the event loop checking and resetting the async
		3087	notification, and the callback being invoked.
		3088
		3089	=back
		3090
		3091
793	=head1 OTHER FUNCTIONS	3092	=head1 OTHER FUNCTIONS
794		3093
795	There are some other functions of possible interest. Described. Here. Now.	3094	There are some other functions of possible interest. Described. Here. Now.
796		3095
797	=over 4	3096	=over 4
798		3097
799	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3098	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
800		3099
801	This function combines a simple timer and an I/O watcher, calls your	3100	This function combines a simple timer and an I/O watcher, calls your
802	callback on whichever event happens first and automatically stop both	3101	callback on whichever event happens first and automatically stops both
803	watchers. This is useful if you want to wait for a single event on an fd	3102	watchers. This is useful if you want to wait for a single event on an fd
804	or timeout without having to allocate/configure/start/stop/free one or	3103	or timeout without having to allocate/configure/start/stop/free one or
805	more watchers yourself.	3104	more watchers yourself.
806		3105
807	If C<fd> is less than 0, then no I/O watcher will be started and events	3106	If C<fd> is less than 0, then no I/O watcher will be started and the
808	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3107	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
809	C<events> set will be craeted and started.	3108	the given C<fd> and C<events> set will be created and started.
810		3109
811	If C<timeout> is less than 0, then no timeout watcher will be	3110	If C<timeout> is less than 0, then no timeout watcher will be
812	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3111	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
813	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3112	repeat = 0) will be started. C<0> is a valid timeout.
814	dubious value.
815		3113
816	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3114	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
817	passed an C<revents> set like normal event callbacks (a combination of	3115	passed an C<revents> set like normal event callbacks (a combination of
818	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3116	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
819	value passed to C<ev_once>:	3117	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3118	a timeout and an io event at the same time - you probably should give io
		3119	events precedence.
820		3120
		3121	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3122
821	static void stdin_ready (int revents, void *arg)	3123	static void stdin_ready (int revents, void *arg)
822	{	3124	{
823	if (revents & EV_TIMEOUT)
824	/* doh, nothing entered */;
825	else if (revents & EV_READ)	3125	if (revents & EV_READ)
826	/* stdin might have data for us, joy! */;	3126	/* stdin might have data for us, joy! */;
		3127	else if (revents & EV_TIMEOUT)
		3128	/* doh, nothing entered */;
827	}	3129	}
828		3130
829	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3131	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
830		3132
831	=item ev_feed_event (loop, watcher, int events)	3133	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
832		3134
833	Feeds the given event set into the event loop, as if the specified event	3135	Feeds the given event set into the event loop, as if the specified event
834	had happened for the specified watcher (which must be a pointer to an	3136	had happened for the specified watcher (which must be a pointer to an
835	initialised but not necessarily started event watcher).	3137	initialised but not necessarily started event watcher).
836		3138
837	=item ev_feed_fd_event (loop, int fd, int revents)	3139	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
838		3140
839	Feed an event on the given fd, as if a file descriptor backend detected	3141	Feed an event on the given fd, as if a file descriptor backend detected
840	the given events it.	3142	the given events it.
841		3143
842	=item ev_feed_signal_event (loop, int signum)	3144	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
843		3145
844	Feed an event as if the given signal occured (loop must be the default loop!).	3146	Feed an event as if the given signal occurred (C<loop> must be the default
		3147	loop!).
845		3148
846	=back	3149	=back
		3150
847		3151
848	=head1 LIBEVENT EMULATION	3152	=head1 LIBEVENT EMULATION
849		3153
850	Libev offers a compatibility emulation layer for libevent. It cannot	3154	Libev offers a compatibility emulation layer for libevent. It cannot
851	emulate the internals of libevent, so here are some usage hints:	3155	emulate the internals of libevent, so here are some usage hints:
…		…
863		3167
864	=item * Priorities are not currently supported. Initialising priorities	3168	=item * Priorities are not currently supported. Initialising priorities
865	will fail and all watchers will have the same priority, even though there	3169	will fail and all watchers will have the same priority, even though there
866	is an ev_pri field.	3170	is an ev_pri field.
867		3171
		3172	=item * In libevent, the last base created gets the signals, in libev, the
		3173	first base created (== the default loop) gets the signals.
		3174
868	=item * Other members are not supported.	3175	=item * Other members are not supported.
869		3176
870	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3177	=item * The libev emulation is I<not> ABI compatible to libevent, you need
871	to use the libev header file and library.	3178	to use the libev header file and library.
872		3179
873	=back	3180	=back
874		3181
875	=head1 C++ SUPPORT	3182	=head1 C++ SUPPORT
876		3183
877	TBD.	3184	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3185	you to use some convenience methods to start/stop watchers and also change
		3186	the callback model to a model using method callbacks on objects.
		3187
		3188	To use it,
		3189
		3190	#include <ev++.h>
		3191
		3192	This automatically includes F<ev.h> and puts all of its definitions (many
		3193	of them macros) into the global namespace. All C++ specific things are
		3194	put into the C<ev> namespace. It should support all the same embedding
		3195	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3196
		3197	Care has been taken to keep the overhead low. The only data member the C++
		3198	classes add (compared to plain C-style watchers) is the event loop pointer
		3199	that the watcher is associated with (or no additional members at all if
		3200	you disable C<EV_MULTIPLICITY> when embedding libev).
		3201
		3202	Currently, functions, and static and non-static member functions can be
		3203	used as callbacks. Other types should be easy to add as long as they only
		3204	need one additional pointer for context. If you need support for other
		3205	types of functors please contact the author (preferably after implementing
		3206	it).
		3207
		3208	Here is a list of things available in the C<ev> namespace:
		3209
		3210	=over 4
		3211
		3212	=item C<ev::READ>, C<ev::WRITE> etc.
		3213
		3214	These are just enum values with the same values as the C<EV_READ> etc.
		3215	macros from F<ev.h>.
		3216
		3217	=item C<ev::tstamp>, C<ev::now>
		3218
		3219	Aliases to the same types/functions as with the C<ev_> prefix.
		3220
		3221	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		3222
		3223	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		3224	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		3225	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3226	defines by many implementations.
		3227
		3228	All of those classes have these methods:
		3229
		3230	=over 4
		3231
		3232	=item ev::TYPE::TYPE ()
		3233
		3234	=item ev::TYPE::TYPE (struct ev_loop *)
		3235
		3236	=item ev::TYPE::~TYPE
		3237
		3238	The constructor (optionally) takes an event loop to associate the watcher
		3239	with. If it is omitted, it will use C<EV_DEFAULT>.
		3240
		3241	The constructor calls C<ev_init> for you, which means you have to call the
		3242	C<set> method before starting it.
		3243
		3244	It will not set a callback, however: You have to call the templated C<set>
		3245	method to set a callback before you can start the watcher.
		3246
		3247	(The reason why you have to use a method is a limitation in C++ which does
		3248	not allow explicit template arguments for constructors).
		3249
		3250	The destructor automatically stops the watcher if it is active.
		3251
		3252	=item w->set<class, &class::method> (object *)
		3253
		3254	This method sets the callback method to call. The method has to have a
		3255	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3256	first argument and the C<revents> as second. The object must be given as
		3257	parameter and is stored in the C<data> member of the watcher.
		3258
		3259	This method synthesizes efficient thunking code to call your method from
		3260	the C callback that libev requires. If your compiler can inline your
		3261	callback (i.e. it is visible to it at the place of the C<set> call and
		3262	your compiler is good :), then the method will be fully inlined into the
		3263	thunking function, making it as fast as a direct C callback.
		3264
		3265	Example: simple class declaration and watcher initialisation
		3266
		3267	struct myclass
		3268	{
		3269	void io_cb (ev::io &w, int revents) { }
		3270	}
		3271
		3272	myclass obj;
		3273	ev::io iow;
		3274	iow.set <myclass, &myclass::io_cb> (&obj);
		3275
		3276	=item w->set (object *)
		3277
		3278	This is an B<experimental> feature that might go away in a future version.
		3279
		3280	This is a variation of a method callback - leaving out the method to call
		3281	will default the method to C<operator ()>, which makes it possible to use
		3282	functor objects without having to manually specify the C<operator ()> all
		3283	the time. Incidentally, you can then also leave out the template argument
		3284	list.
		3285
		3286	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3287	int revents)>.
		3288
		3289	See the method-C<set> above for more details.
		3290
		3291	Example: use a functor object as callback.
		3292
		3293	struct myfunctor
		3294	{
		3295	void operator() (ev::io &w, int revents)
		3296	{
		3297	...
		3298	}
		3299	}
		3300
		3301	myfunctor f;
		3302
		3303	ev::io w;
		3304	w.set (&f);
		3305
		3306	=item w->set<function> (void *data = 0)
		3307
		3308	Also sets a callback, but uses a static method or plain function as
		3309	callback. The optional C<data> argument will be stored in the watcher's
		3310	C<data> member and is free for you to use.
		3311
		3312	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3313
		3314	See the method-C<set> above for more details.
		3315
		3316	Example: Use a plain function as callback.
		3317
		3318	static void io_cb (ev::io &w, int revents) { }
		3319	iow.set <io_cb> ();
		3320
		3321	=item w->set (struct ev_loop *)
		3322
		3323	Associates a different C<struct ev_loop> with this watcher. You can only
		3324	do this when the watcher is inactive (and not pending either).
		3325
		3326	=item w->set ([arguments])
		3327
		3328	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		3329	called at least once. Unlike the C counterpart, an active watcher gets
		3330	automatically stopped and restarted when reconfiguring it with this
		3331	method.
		3332
		3333	=item w->start ()
		3334
		3335	Starts the watcher. Note that there is no C<loop> argument, as the
		3336	constructor already stores the event loop.
		3337
		3338	=item w->stop ()
		3339
		3340	Stops the watcher if it is active. Again, no C<loop> argument.
		3341
		3342	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		3343
		3344	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		3345	C<ev_TYPE_again> function.
		3346
		3347	=item w->sweep () (C<ev::embed> only)
		3348
		3349	Invokes C<ev_embed_sweep>.
		3350
		3351	=item w->update () (C<ev::stat> only)
		3352
		3353	Invokes C<ev_stat_stat>.
		3354
		3355	=back
		3356
		3357	=back
		3358
		3359	Example: Define a class with an IO and idle watcher, start one of them in
		3360	the constructor.
		3361
		3362	class myclass
		3363	{
		3364	ev::io io ; void io_cb (ev::io &w, int revents);
		3365	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3366
		3367	myclass (int fd)
		3368	{
		3369	io .set <myclass, &myclass::io_cb > (this);
		3370	idle.set <myclass, &myclass::idle_cb> (this);
		3371
		3372	io.start (fd, ev::READ);
		3373	}
		3374	};
		3375
		3376
		3377	=head1 OTHER LANGUAGE BINDINGS
		3378
		3379	Libev does not offer other language bindings itself, but bindings for a
		3380	number of languages exist in the form of third-party packages. If you know
		3381	any interesting language binding in addition to the ones listed here, drop
		3382	me a note.
		3383
		3384	=over 4
		3385
		3386	=item Perl
		3387
		3388	The EV module implements the full libev API and is actually used to test
		3389	libev. EV is developed together with libev. Apart from the EV core module,
		3390	there are additional modules that implement libev-compatible interfaces
		3391	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3392	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3393	and C<EV::Glib>).
		3394
		3395	It can be found and installed via CPAN, its homepage is at
		3396	L<http://software.schmorp.de/pkg/EV>.
		3397
		3398	=item Python
		3399
		3400	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3401	seems to be quite complete and well-documented.
		3402
		3403	=item Ruby
		3404
		3405	Tony Arcieri has written a ruby extension that offers access to a subset
		3406	of the libev API and adds file handle abstractions, asynchronous DNS and
		3407	more on top of it. It can be found via gem servers. Its homepage is at
		3408	L<http://rev.rubyforge.org/>.
		3409
		3410	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3411	makes rev work even on mingw.
		3412
		3413	=item Haskell
		3414
		3415	A haskell binding to libev is available at
		3416	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3417
		3418	=item D
		3419
		3420	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3421	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3422
		3423	=item Ocaml
		3424
		3425	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3426	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3427
		3428	=item Lua
		3429
		3430	Brian Maher has written a partial interface to libev
		3431	for lua (only C<ev_io> and C<ev_timer>), to be found at
		3432	L<http://github.com/brimworks/lua-ev>.
		3433
		3434	=back
		3435
		3436
		3437	=head1 MACRO MAGIC
		3438
		3439	Libev can be compiled with a variety of options, the most fundamental
		3440	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3441	functions and callbacks have an initial C<struct ev_loop *> argument.
		3442
		3443	To make it easier to write programs that cope with either variant, the
		3444	following macros are defined:
		3445
		3446	=over 4
		3447
		3448	=item C<EV_A>, C<EV_A_>
		3449
		3450	This provides the loop I<argument> for functions, if one is required ("ev
		3451	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3452	C<EV_A_> is used when other arguments are following. Example:
		3453
		3454	ev_unref (EV_A);
		3455	ev_timer_add (EV_A_ watcher);
		3456	ev_loop (EV_A_ 0);
		3457
		3458	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3459	which is often provided by the following macro.
		3460
		3461	=item C<EV_P>, C<EV_P_>
		3462
		3463	This provides the loop I<parameter> for functions, if one is required ("ev
		3464	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3465	C<EV_P_> is used when other parameters are following. Example:
		3466
		3467	// this is how ev_unref is being declared
		3468	static void ev_unref (EV_P);
		3469
		3470	// this is how you can declare your typical callback
		3471	static void cb (EV_P_ ev_timer *w, int revents)
		3472
		3473	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3474	suitable for use with C<EV_A>.
		3475
		3476	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3477
		3478	Similar to the other two macros, this gives you the value of the default
		3479	loop, if multiple loops are supported ("ev loop default").
		3480
		3481	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3482
		3483	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3484	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3485	is undefined when the default loop has not been initialised by a previous
		3486	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3487
		3488	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3489	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3490
		3491	=back
		3492
		3493	Example: Declare and initialise a check watcher, utilising the above
		3494	macros so it will work regardless of whether multiple loops are supported
		3495	or not.
		3496
		3497	static void
		3498	check_cb (EV_P_ ev_timer *w, int revents)
		3499	{
		3500	ev_check_stop (EV_A_ w);
		3501	}
		3502
		3503	ev_check check;
		3504	ev_check_init (&check, check_cb);
		3505	ev_check_start (EV_DEFAULT_ &check);
		3506	ev_loop (EV_DEFAULT_ 0);
		3507
		3508	=head1 EMBEDDING
		3509
		3510	Libev can (and often is) directly embedded into host
		3511	applications. Examples of applications that embed it include the Deliantra
		3512	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3513	and rxvt-unicode.
		3514
		3515	The goal is to enable you to just copy the necessary files into your
		3516	source directory without having to change even a single line in them, so
		3517	you can easily upgrade by simply copying (or having a checked-out copy of
		3518	libev somewhere in your source tree).
		3519
		3520	=head2 FILESETS
		3521
		3522	Depending on what features you need you need to include one or more sets of files
		3523	in your application.
		3524
		3525	=head3 CORE EVENT LOOP
		3526
		3527	To include only the libev core (all the C<ev_*> functions), with manual
		3528	configuration (no autoconf):
		3529
		3530	#define EV_STANDALONE 1
		3531	#include "ev.c"
		3532
		3533	This will automatically include F<ev.h>, too, and should be done in a
		3534	single C source file only to provide the function implementations. To use
		3535	it, do the same for F<ev.h> in all files wishing to use this API (best
		3536	done by writing a wrapper around F<ev.h> that you can include instead and
		3537	where you can put other configuration options):
		3538
		3539	#define EV_STANDALONE 1
		3540	#include "ev.h"
		3541
		3542	Both header files and implementation files can be compiled with a C++
		3543	compiler (at least, that's a stated goal, and breakage will be treated
		3544	as a bug).
		3545
		3546	You need the following files in your source tree, or in a directory
		3547	in your include path (e.g. in libev/ when using -Ilibev):
		3548
		3549	ev.h
		3550	ev.c
		3551	ev_vars.h
		3552	ev_wrap.h
		3553
		3554	ev_win32.c required on win32 platforms only
		3555
		3556	ev_select.c only when select backend is enabled (which is enabled by default)
		3557	ev_poll.c only when poll backend is enabled (disabled by default)
		3558	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3559	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3560	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3561
		3562	F<ev.c> includes the backend files directly when enabled, so you only need
		3563	to compile this single file.
		3564
		3565	=head3 LIBEVENT COMPATIBILITY API
		3566
		3567	To include the libevent compatibility API, also include:
		3568
		3569	#include "event.c"
		3570
		3571	in the file including F<ev.c>, and:
		3572
		3573	#include "event.h"
		3574
		3575	in the files that want to use the libevent API. This also includes F<ev.h>.
		3576
		3577	You need the following additional files for this:
		3578
		3579	event.h
		3580	event.c
		3581
		3582	=head3 AUTOCONF SUPPORT
		3583
		3584	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3585	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3586	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3587	include F<config.h> and configure itself accordingly.
		3588
		3589	For this of course you need the m4 file:
		3590
		3591	libev.m4
		3592
		3593	=head2 PREPROCESSOR SYMBOLS/MACROS
		3594
		3595	Libev can be configured via a variety of preprocessor symbols you have to
		3596	define before including any of its files. The default in the absence of
		3597	autoconf is documented for every option.
		3598
		3599	=over 4
		3600
		3601	=item EV_STANDALONE
		3602
		3603	Must always be C<1> if you do not use autoconf configuration, which
		3604	keeps libev from including F<config.h>, and it also defines dummy
		3605	implementations for some libevent functions (such as logging, which is not
		3606	supported). It will also not define any of the structs usually found in
		3607	F<event.h> that are not directly supported by the libev core alone.
		3608
		3609	In standalone mode, libev will still try to automatically deduce the
		3610	configuration, but has to be more conservative.
		3611
		3612	=item EV_USE_MONOTONIC
		3613
		3614	If defined to be C<1>, libev will try to detect the availability of the
		3615	monotonic clock option at both compile time and runtime. Otherwise no
		3616	use of the monotonic clock option will be attempted. If you enable this,
		3617	you usually have to link against librt or something similar. Enabling it
		3618	when the functionality isn't available is safe, though, although you have
		3619	to make sure you link against any libraries where the C<clock_gettime>
		3620	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3621
		3622	=item EV_USE_REALTIME
		3623
		3624	If defined to be C<1>, libev will try to detect the availability of the
		3625	real-time clock option at compile time (and assume its availability
		3626	at runtime if successful). Otherwise no use of the real-time clock
		3627	option will be attempted. This effectively replaces C<gettimeofday>
		3628	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		3629	correctness. See the note about libraries in the description of
		3630	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3631	C<EV_USE_CLOCK_SYSCALL>.
		3632
		3633	=item EV_USE_CLOCK_SYSCALL
		3634
		3635	If defined to be C<1>, libev will try to use a direct syscall instead
		3636	of calling the system-provided C<clock_gettime> function. This option
		3637	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3638	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3639	programs needlessly. Using a direct syscall is slightly slower (in
		3640	theory), because no optimised vdso implementation can be used, but avoids
		3641	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3642	higher, as it simplifies linking (no need for C<-lrt>).
		3643
		3644	=item EV_USE_NANOSLEEP
		3645
		3646	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3647	and will use it for delays. Otherwise it will use C<select ()>.
		3648
		3649	=item EV_USE_EVENTFD
		3650
		3651	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3652	available and will probe for kernel support at runtime. This will improve
		3653	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3654	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3655	2.7 or newer, otherwise disabled.
		3656
		3657	=item EV_USE_SELECT
		3658
		3659	If undefined or defined to be C<1>, libev will compile in support for the
		3660	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3661	other method takes over, select will be it. Otherwise the select backend
		3662	will not be compiled in.
		3663
		3664	=item EV_SELECT_USE_FD_SET
		3665
		3666	If defined to C<1>, then the select backend will use the system C<fd_set>
		3667	structure. This is useful if libev doesn't compile due to a missing
		3668	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		3669	on exotic systems. This usually limits the range of file descriptors to
		3670	some low limit such as 1024 or might have other limitations (winsocket
		3671	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		3672	configures the maximum size of the C<fd_set>.
		3673
		3674	=item EV_SELECT_IS_WINSOCKET
		3675
		3676	When defined to C<1>, the select backend will assume that
		3677	select/socket/connect etc. don't understand file descriptors but
		3678	wants osf handles on win32 (this is the case when the select to
		3679	be used is the winsock select). This means that it will call
		3680	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3681	it is assumed that all these functions actually work on fds, even
		3682	on win32. Should not be defined on non-win32 platforms.
		3683
		3684	=item EV_FD_TO_WIN32_HANDLE(fd)
		3685
		3686	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3687	file descriptors to socket handles. When not defining this symbol (the
		3688	default), then libev will call C<_get_osfhandle>, which is usually
		3689	correct. In some cases, programs use their own file descriptor management,
		3690	in which case they can provide this function to map fds to socket handles.
		3691
		3692	=item EV_WIN32_HANDLE_TO_FD(handle)
		3693
		3694	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3695	using the standard C<_open_osfhandle> function. For programs implementing
		3696	their own fd to handle mapping, overwriting this function makes it easier
		3697	to do so. This can be done by defining this macro to an appropriate value.
		3698
		3699	=item EV_WIN32_CLOSE_FD(fd)
		3700
		3701	If programs implement their own fd to handle mapping on win32, then this
		3702	macro can be used to override the C<close> function, useful to unregister
		3703	file descriptors again. Note that the replacement function has to close
		3704	the underlying OS handle.
		3705
		3706	=item EV_USE_POLL
		3707
		3708	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3709	backend. Otherwise it will be enabled on non-win32 platforms. It
		3710	takes precedence over select.
		3711
		3712	=item EV_USE_EPOLL
		3713
		3714	If defined to be C<1>, libev will compile in support for the Linux
		3715	C<epoll>(7) backend. Its availability will be detected at runtime,
		3716	otherwise another method will be used as fallback. This is the preferred
		3717	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3718	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3719
		3720	=item EV_USE_KQUEUE
		3721
		3722	If defined to be C<1>, libev will compile in support for the BSD style
		3723	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3724	otherwise another method will be used as fallback. This is the preferred
		3725	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3726	supports some types of fds correctly (the only platform we found that
		3727	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3728	not be used unless explicitly requested. The best way to use it is to find
		3729	out whether kqueue supports your type of fd properly and use an embedded
		3730	kqueue loop.
		3731
		3732	=item EV_USE_PORT
		3733
		3734	If defined to be C<1>, libev will compile in support for the Solaris
		3735	10 port style backend. Its availability will be detected at runtime,
		3736	otherwise another method will be used as fallback. This is the preferred
		3737	backend for Solaris 10 systems.
		3738
		3739	=item EV_USE_DEVPOLL
		3740
		3741	Reserved for future expansion, works like the USE symbols above.
		3742
		3743	=item EV_USE_INOTIFY
		3744
		3745	If defined to be C<1>, libev will compile in support for the Linux inotify
		3746	interface to speed up C<ev_stat> watchers. Its actual availability will
		3747	be detected at runtime. If undefined, it will be enabled if the headers
		3748	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3749
		3750	=item EV_ATOMIC_T
		3751
		3752	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3753	access is atomic with respect to other threads or signal contexts. No such
		3754	type is easily found in the C language, so you can provide your own type
		3755	that you know is safe for your purposes. It is used both for signal handler "locking"
		3756	as well as for signal and thread safety in C<ev_async> watchers.
		3757
		3758	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3759	(from F<signal.h>), which is usually good enough on most platforms.
		3760
		3761	=item EV_H
		3762
		3763	The name of the F<ev.h> header file used to include it. The default if
		3764	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3765	used to virtually rename the F<ev.h> header file in case of conflicts.
		3766
		3767	=item EV_CONFIG_H
		3768
		3769	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3770	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3771	C<EV_H>, above.
		3772
		3773	=item EV_EVENT_H
		3774
		3775	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3776	of how the F<event.h> header can be found, the default is C<"event.h">.
		3777
		3778	=item EV_PROTOTYPES
		3779
		3780	If defined to be C<0>, then F<ev.h> will not define any function
		3781	prototypes, but still define all the structs and other symbols. This is
		3782	occasionally useful if you want to provide your own wrapper functions
		3783	around libev functions.
		3784
		3785	=item EV_MULTIPLICITY
		3786
		3787	If undefined or defined to C<1>, then all event-loop-specific functions
		3788	will have the C<struct ev_loop *> as first argument, and you can create
		3789	additional independent event loops. Otherwise there will be no support
		3790	for multiple event loops and there is no first event loop pointer
		3791	argument. Instead, all functions act on the single default loop.
		3792
		3793	=item EV_MINPRI
		3794
		3795	=item EV_MAXPRI
		3796
		3797	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3798	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3799	provide for more priorities by overriding those symbols (usually defined
		3800	to be C<-2> and C<2>, respectively).
		3801
		3802	When doing priority-based operations, libev usually has to linearly search
		3803	all the priorities, so having many of them (hundreds) uses a lot of space
		3804	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3805	fine.
		3806
		3807	If your embedding application does not need any priorities, defining these
		3808	both to C<0> will save some memory and CPU.
		3809
		3810	=item EV_PERIODIC_ENABLE
		3811
		3812	If undefined or defined to be C<1>, then periodic timers are supported. If
		3813	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3814	code.
		3815
		3816	=item EV_IDLE_ENABLE
		3817
		3818	If undefined or defined to be C<1>, then idle watchers are supported. If
		3819	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3820	code.
		3821
		3822	=item EV_EMBED_ENABLE
		3823
		3824	If undefined or defined to be C<1>, then embed watchers are supported. If
		3825	defined to be C<0>, then they are not. Embed watchers rely on most other
		3826	watcher types, which therefore must not be disabled.
		3827
		3828	=item EV_STAT_ENABLE
		3829
		3830	If undefined or defined to be C<1>, then stat watchers are supported. If
		3831	defined to be C<0>, then they are not.
		3832
		3833	=item EV_FORK_ENABLE
		3834
		3835	If undefined or defined to be C<1>, then fork watchers are supported. If
		3836	defined to be C<0>, then they are not.
		3837
		3838	=item EV_ASYNC_ENABLE
		3839
		3840	If undefined or defined to be C<1>, then async watchers are supported. If
		3841	defined to be C<0>, then they are not.
		3842
		3843	=item EV_MINIMAL
		3844
		3845	If you need to shave off some kilobytes of code at the expense of some
		3846	speed (but with the full API), define this symbol to C<1>. Currently this
		3847	is used to override some inlining decisions, saves roughly 30% code size
		3848	on amd64. It also selects a much smaller 2-heap for timer management over
		3849	the default 4-heap.
		3850
		3851	You can save even more by disabling watcher types you do not need
		3852	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3853	(C<-DNDEBUG>) will usually reduce code size a lot.
		3854
		3855	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3856	provide a bare-bones event library. See C<ev.h> for details on what parts
		3857	of the API are still available, and do not complain if this subset changes
		3858	over time.
		3859
		3860	=item EV_NSIG
		3861
		3862	The highest supported signal number, +1 (or, the number of
		3863	signals): Normally, libev tries to deduce the maximum number of signals
		3864	automatically, but sometimes this fails, in which case it can be
		3865	specified. Also, using a lower number than detected (C<32> should be
		3866	good for about any system in existance) can save some memory, as libev
		3867	statically allocates some 12-24 bytes per signal number.
		3868
		3869	=item EV_PID_HASHSIZE
		3870
		3871	C<ev_child> watchers use a small hash table to distribute workload by
		3872	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3873	than enough. If you need to manage thousands of children you might want to
		3874	increase this value (I<must> be a power of two).
		3875
		3876	=item EV_INOTIFY_HASHSIZE
		3877
		3878	C<ev_stat> watchers use a small hash table to distribute workload by
		3879	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3880	usually more than enough. If you need to manage thousands of C<ev_stat>
		3881	watchers you might want to increase this value (I<must> be a power of
		3882	two).
		3883
		3884	=item EV_USE_4HEAP
		3885
		3886	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3887	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3888	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3889	faster performance with many (thousands) of watchers.
		3890
		3891	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3892	(disabled).
		3893
		3894	=item EV_HEAP_CACHE_AT
		3895
		3896	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3897	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3898	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3899	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3900	but avoids random read accesses on heap changes. This improves performance
		3901	noticeably with many (hundreds) of watchers.
		3902
		3903	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3904	(disabled).
		3905
		3906	=item EV_VERIFY
		3907
		3908	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3909	be done: If set to C<0>, no internal verification code will be compiled
		3910	in. If set to C<1>, then verification code will be compiled in, but not
		3911	called. If set to C<2>, then the internal verification code will be
		3912	called once per loop, which can slow down libev. If set to C<3>, then the
		3913	verification code will be called very frequently, which will slow down
		3914	libev considerably.
		3915
		3916	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3917	C<0>.
		3918
		3919	=item EV_COMMON
		3920
		3921	By default, all watchers have a C<void *data> member. By redefining
		3922	this macro to a something else you can include more and other types of
		3923	members. You have to define it each time you include one of the files,
		3924	though, and it must be identical each time.
		3925
		3926	For example, the perl EV module uses something like this:
		3927
		3928	#define EV_COMMON \
		3929	SV *self; /* contains this struct */ \
		3930	SV *cb_sv, *fh /* note no trailing ";" */
		3931
		3932	=item EV_CB_DECLARE (type)
		3933
		3934	=item EV_CB_INVOKE (watcher, revents)
		3935
		3936	=item ev_set_cb (ev, cb)
		3937
		3938	Can be used to change the callback member declaration in each watcher,
		3939	and the way callbacks are invoked and set. Must expand to a struct member
		3940	definition and a statement, respectively. See the F<ev.h> header file for
		3941	their default definitions. One possible use for overriding these is to
		3942	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3943	method calls instead of plain function calls in C++.
		3944
		3945	=back
		3946
		3947	=head2 EXPORTED API SYMBOLS
		3948
		3949	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3950	exported symbols, you can use the provided F<Symbol.*> files which list
		3951	all public symbols, one per line:
		3952
		3953	Symbols.ev for libev proper
		3954	Symbols.event for the libevent emulation
		3955
		3956	This can also be used to rename all public symbols to avoid clashes with
		3957	multiple versions of libev linked together (which is obviously bad in
		3958	itself, but sometimes it is inconvenient to avoid this).
		3959
		3960	A sed command like this will create wrapper C<#define>'s that you need to
		3961	include before including F<ev.h>:
		3962
		3963	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3964
		3965	This would create a file F<wrap.h> which essentially looks like this:
		3966
		3967	#define ev_backend myprefix_ev_backend
		3968	#define ev_check_start myprefix_ev_check_start
		3969	#define ev_check_stop myprefix_ev_check_stop
		3970	...
		3971
		3972	=head2 EXAMPLES
		3973
		3974	For a real-world example of a program the includes libev
		3975	verbatim, you can have a look at the EV perl module
		3976	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3977	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3978	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3979	will be compiled. It is pretty complex because it provides its own header
		3980	file.
		3981
		3982	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3983	that everybody includes and which overrides some configure choices:
		3984
		3985	#define EV_MINIMAL 1
		3986	#define EV_USE_POLL 0
		3987	#define EV_MULTIPLICITY 0
		3988	#define EV_PERIODIC_ENABLE 0
		3989	#define EV_STAT_ENABLE 0
		3990	#define EV_FORK_ENABLE 0
		3991	#define EV_CONFIG_H <config.h>
		3992	#define EV_MINPRI 0
		3993	#define EV_MAXPRI 0
		3994
		3995	#include "ev++.h"
		3996
		3997	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3998
		3999	#include "ev_cpp.h"
		4000	#include "ev.c"
		4001
		4002	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		4003
		4004	=head2 THREADS AND COROUTINES
		4005
		4006	=head3 THREADS
		4007
		4008	All libev functions are reentrant and thread-safe unless explicitly
		4009	documented otherwise, but libev implements no locking itself. This means
		4010	that you can use as many loops as you want in parallel, as long as there
		4011	are no concurrent calls into any libev function with the same loop
		4012	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4013	of course): libev guarantees that different event loops share no data
		4014	structures that need any locking.
		4015
		4016	Or to put it differently: calls with different loop parameters can be done
		4017	concurrently from multiple threads, calls with the same loop parameter
		4018	must be done serially (but can be done from different threads, as long as
		4019	only one thread ever is inside a call at any point in time, e.g. by using
		4020	a mutex per loop).
		4021
		4022	Specifically to support threads (and signal handlers), libev implements
		4023	so-called C<ev_async> watchers, which allow some limited form of
		4024	concurrency on the same event loop, namely waking it up "from the
		4025	outside".
		4026
		4027	If you want to know which design (one loop, locking, or multiple loops
		4028	without or something else still) is best for your problem, then I cannot
		4029	help you, but here is some generic advice:
		4030
		4031	=over 4
		4032
		4033	=item * most applications have a main thread: use the default libev loop
		4034	in that thread, or create a separate thread running only the default loop.
		4035
		4036	This helps integrating other libraries or software modules that use libev
		4037	themselves and don't care/know about threading.
		4038
		4039	=item * one loop per thread is usually a good model.
		4040
		4041	Doing this is almost never wrong, sometimes a better-performance model
		4042	exists, but it is always a good start.
		4043
		4044	=item * other models exist, such as the leader/follower pattern, where one
		4045	loop is handed through multiple threads in a kind of round-robin fashion.
		4046
		4047	Choosing a model is hard - look around, learn, know that usually you can do
		4048	better than you currently do :-)
		4049
		4050	=item * often you need to talk to some other thread which blocks in the
		4051	event loop.
		4052
		4053	C<ev_async> watchers can be used to wake them up from other threads safely
		4054	(or from signal contexts...).
		4055
		4056	An example use would be to communicate signals or other events that only
		4057	work in the default loop by registering the signal watcher with the
		4058	default loop and triggering an C<ev_async> watcher from the default loop
		4059	watcher callback into the event loop interested in the signal.
		4060
		4061	=back
		4062
		4063	=head4 THREAD LOCKING EXAMPLE
		4064
		4065	Here is a fictitious example of how to run an event loop in a different
		4066	thread than where callbacks are being invoked and watchers are
		4067	created/added/removed.
		4068
		4069	For a real-world example, see the C<EV::Loop::Async> perl module,
		4070	which uses exactly this technique (which is suited for many high-level
		4071	languages).
		4072
		4073	The example uses a pthread mutex to protect the loop data, a condition
		4074	variable to wait for callback invocations, an async watcher to notify the
		4075	event loop thread and an unspecified mechanism to wake up the main thread.
		4076
		4077	First, you need to associate some data with the event loop:
		4078
		4079	typedef struct {
		4080	mutex_t lock; /* global loop lock */
		4081	ev_async async_w;
		4082	thread_t tid;
		4083	cond_t invoke_cv;
		4084	} userdata;
		4085
		4086	void prepare_loop (EV_P)
		4087	{
		4088	// for simplicity, we use a static userdata struct.
		4089	static userdata u;
		4090
		4091	ev_async_init (&u->async_w, async_cb);
		4092	ev_async_start (EV_A_ &u->async_w);
		4093
		4094	pthread_mutex_init (&u->lock, 0);
		4095	pthread_cond_init (&u->invoke_cv, 0);
		4096
		4097	// now associate this with the loop
		4098	ev_set_userdata (EV_A_ u);
		4099	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4100	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4101
		4102	// then create the thread running ev_loop
		4103	pthread_create (&u->tid, 0, l_run, EV_A);
		4104	}
		4105
		4106	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4107	solely to wake up the event loop so it takes notice of any new watchers
		4108	that might have been added:
		4109
		4110	static void
		4111	async_cb (EV_P_ ev_async *w, int revents)
		4112	{
		4113	// just used for the side effects
		4114	}
		4115
		4116	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4117	protecting the loop data, respectively.
		4118
		4119	static void
		4120	l_release (EV_P)
		4121	{
		4122	userdata *u = ev_userdata (EV_A);
		4123	pthread_mutex_unlock (&u->lock);
		4124	}
		4125
		4126	static void
		4127	l_acquire (EV_P)
		4128	{
		4129	userdata *u = ev_userdata (EV_A);
		4130	pthread_mutex_lock (&u->lock);
		4131	}
		4132
		4133	The event loop thread first acquires the mutex, and then jumps straight
		4134	into C<ev_loop>:
		4135
		4136	void *
		4137	l_run (void *thr_arg)
		4138	{
		4139	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4140
		4141	l_acquire (EV_A);
		4142	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4143	ev_loop (EV_A_ 0);
		4144	l_release (EV_A);
		4145
		4146	return 0;
		4147	}
		4148
		4149	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4150	signal the main thread via some unspecified mechanism (signals? pipe
		4151	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4152	have been called (in a while loop because a) spurious wakeups are possible
		4153	and b) skipping inter-thread-communication when there are no pending
		4154	watchers is very beneficial):
		4155
		4156	static void
		4157	l_invoke (EV_P)
		4158	{
		4159	userdata *u = ev_userdata (EV_A);
		4160
		4161	while (ev_pending_count (EV_A))
		4162	{
		4163	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4164	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4165	}
		4166	}
		4167
		4168	Now, whenever the main thread gets told to invoke pending watchers, it
		4169	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4170	thread to continue:
		4171
		4172	static void
		4173	real_invoke_pending (EV_P)
		4174	{
		4175	userdata *u = ev_userdata (EV_A);
		4176
		4177	pthread_mutex_lock (&u->lock);
		4178	ev_invoke_pending (EV_A);
		4179	pthread_cond_signal (&u->invoke_cv);
		4180	pthread_mutex_unlock (&u->lock);
		4181	}
		4182
		4183	Whenever you want to start/stop a watcher or do other modifications to an
		4184	event loop, you will now have to lock:
		4185
		4186	ev_timer timeout_watcher;
		4187	userdata *u = ev_userdata (EV_A);
		4188
		4189	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4190
		4191	pthread_mutex_lock (&u->lock);
		4192	ev_timer_start (EV_A_ &timeout_watcher);
		4193	ev_async_send (EV_A_ &u->async_w);
		4194	pthread_mutex_unlock (&u->lock);
		4195
		4196	Note that sending the C<ev_async> watcher is required because otherwise
		4197	an event loop currently blocking in the kernel will have no knowledge
		4198	about the newly added timer. By waking up the loop it will pick up any new
		4199	watchers in the next event loop iteration.
		4200
		4201	=head3 COROUTINES
		4202
		4203	Libev is very accommodating to coroutines ("cooperative threads"):
		4204	libev fully supports nesting calls to its functions from different
		4205	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4206	different coroutines, and switch freely between both coroutines running
		4207	the loop, as long as you don't confuse yourself). The only exception is
		4208	that you must not do this from C<ev_periodic> reschedule callbacks.
		4209
		4210	Care has been taken to ensure that libev does not keep local state inside
		4211	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4212	they do not call any callbacks.
		4213
		4214	=head2 COMPILER WARNINGS
		4215
		4216	Depending on your compiler and compiler settings, you might get no or a
		4217	lot of warnings when compiling libev code. Some people are apparently
		4218	scared by this.
		4219
		4220	However, these are unavoidable for many reasons. For one, each compiler
		4221	has different warnings, and each user has different tastes regarding
		4222	warning options. "Warn-free" code therefore cannot be a goal except when
		4223	targeting a specific compiler and compiler-version.
		4224
		4225	Another reason is that some compiler warnings require elaborate
		4226	workarounds, or other changes to the code that make it less clear and less
		4227	maintainable.
		4228
		4229	And of course, some compiler warnings are just plain stupid, or simply
		4230	wrong (because they don't actually warn about the condition their message
		4231	seems to warn about). For example, certain older gcc versions had some
		4232	warnings that resulted an extreme number of false positives. These have
		4233	been fixed, but some people still insist on making code warn-free with
		4234	such buggy versions.
		4235
		4236	While libev is written to generate as few warnings as possible,
		4237	"warn-free" code is not a goal, and it is recommended not to build libev
		4238	with any compiler warnings enabled unless you are prepared to cope with
		4239	them (e.g. by ignoring them). Remember that warnings are just that:
		4240	warnings, not errors, or proof of bugs.
		4241
		4242
		4243	=head2 VALGRIND
		4244
		4245	Valgrind has a special section here because it is a popular tool that is
		4246	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4247
		4248	If you think you found a bug (memory leak, uninitialised data access etc.)
		4249	in libev, then check twice: If valgrind reports something like:
		4250
		4251	==2274== definitely lost: 0 bytes in 0 blocks.
		4252	==2274== possibly lost: 0 bytes in 0 blocks.
		4253	==2274== still reachable: 256 bytes in 1 blocks.
		4254
		4255	Then there is no memory leak, just as memory accounted to global variables
		4256	is not a memleak - the memory is still being referenced, and didn't leak.
		4257
		4258	Similarly, under some circumstances, valgrind might report kernel bugs
		4259	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4260	although an acceptable workaround has been found here), or it might be
		4261	confused.
		4262
		4263	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4264	make it into some kind of religion.
		4265
		4266	If you are unsure about something, feel free to contact the mailing list
		4267	with the full valgrind report and an explanation on why you think this
		4268	is a bug in libev (best check the archives, too :). However, don't be
		4269	annoyed when you get a brisk "this is no bug" answer and take the chance
		4270	of learning how to interpret valgrind properly.
		4271
		4272	If you need, for some reason, empty reports from valgrind for your project
		4273	I suggest using suppression lists.
		4274
		4275
		4276	=head1 PORTABILITY NOTES
		4277
		4278	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4279
		4280	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4281	requires, and its I/O model is fundamentally incompatible with the POSIX
		4282	model. Libev still offers limited functionality on this platform in
		4283	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4284	descriptors. This only applies when using Win32 natively, not when using
		4285	e.g. cygwin.
		4286
		4287	Lifting these limitations would basically require the full
		4288	re-implementation of the I/O system. If you are into these kinds of
		4289	things, then note that glib does exactly that for you in a very portable
		4290	way (note also that glib is the slowest event library known to man).
		4291
		4292	There is no supported compilation method available on windows except
		4293	embedding it into other applications.
		4294
		4295	Sensible signal handling is officially unsupported by Microsoft - libev
		4296	tries its best, but under most conditions, signals will simply not work.
		4297
		4298	Not a libev limitation but worth mentioning: windows apparently doesn't
		4299	accept large writes: instead of resulting in a partial write, windows will
		4300	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4301	so make sure you only write small amounts into your sockets (less than a
		4302	megabyte seems safe, but this apparently depends on the amount of memory
		4303	available).
		4304
		4305	Due to the many, low, and arbitrary limits on the win32 platform and
		4306	the abysmal performance of winsockets, using a large number of sockets
		4307	is not recommended (and not reasonable). If your program needs to use
		4308	more than a hundred or so sockets, then likely it needs to use a totally
		4309	different implementation for windows, as libev offers the POSIX readiness
		4310	notification model, which cannot be implemented efficiently on windows
		4311	(due to Microsoft monopoly games).
		4312
		4313	A typical way to use libev under windows is to embed it (see the embedding
		4314	section for details) and use the following F<evwrap.h> header file instead
		4315	of F<ev.h>:
		4316
		4317	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4318	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4319
		4320	#include "ev.h"
		4321
		4322	And compile the following F<evwrap.c> file into your project (make sure
		4323	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4324
		4325	#include "evwrap.h"
		4326	#include "ev.c"
		4327
		4328	=over 4
		4329
		4330	=item The winsocket select function
		4331
		4332	The winsocket C<select> function doesn't follow POSIX in that it
		4333	requires socket I<handles> and not socket I<file descriptors> (it is
		4334	also extremely buggy). This makes select very inefficient, and also
		4335	requires a mapping from file descriptors to socket handles (the Microsoft
		4336	C runtime provides the function C<_open_osfhandle> for this). See the
		4337	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4338	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4339
		4340	The configuration for a "naked" win32 using the Microsoft runtime
		4341	libraries and raw winsocket select is:
		4342
		4343	#define EV_USE_SELECT 1
		4344	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4345
		4346	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4347	complexity in the O(n²) range when using win32.
		4348
		4349	=item Limited number of file descriptors
		4350
		4351	Windows has numerous arbitrary (and low) limits on things.
		4352
		4353	Early versions of winsocket's select only supported waiting for a maximum
		4354	of C<64> handles (probably owning to the fact that all windows kernels
		4355	can only wait for C<64> things at the same time internally; Microsoft
		4356	recommends spawning a chain of threads and wait for 63 handles and the
		4357	previous thread in each. Sounds great!).
		4358
		4359	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4360	to some high number (e.g. C<2048>) before compiling the winsocket select
		4361	call (which might be in libev or elsewhere, for example, perl and many
		4362	other interpreters do their own select emulation on windows).
		4363
		4364	Another limit is the number of file descriptors in the Microsoft runtime
		4365	libraries, which by default is C<64> (there must be a hidden I<64>
		4366	fetish or something like this inside Microsoft). You can increase this
		4367	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4368	(another arbitrary limit), but is broken in many versions of the Microsoft
		4369	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4370	(depending on windows version and/or the phase of the moon). To get more,
		4371	you need to wrap all I/O functions and provide your own fd management, but
		4372	the cost of calling select (O(n²)) will likely make this unworkable.
		4373
		4374	=back
		4375
		4376	=head2 PORTABILITY REQUIREMENTS
		4377
		4378	In addition to a working ISO-C implementation and of course the
		4379	backend-specific APIs, libev relies on a few additional extensions:
		4380
		4381	=over 4
		4382
		4383	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4384	calling conventions regardless of C<ev_watcher_type *>.
		4385
		4386	Libev assumes not only that all watcher pointers have the same internal
		4387	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4388	assumes that the same (machine) code can be used to call any watcher
		4389	callback: The watcher callbacks have different type signatures, but libev
		4390	calls them using an C<ev_watcher *> internally.
		4391
		4392	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4393
		4394	The type C<sig_atomic_t volatile> (or whatever is defined as
		4395	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4396	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4397	believed to be sufficiently portable.
		4398
		4399	=item C<sigprocmask> must work in a threaded environment
		4400
		4401	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4402	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4403	pthread implementations will either allow C<sigprocmask> in the "main
		4404	thread" or will block signals process-wide, both behaviours would
		4405	be compatible with libev. Interaction between C<sigprocmask> and
		4406	C<pthread_sigmask> could complicate things, however.
		4407
		4408	The most portable way to handle signals is to block signals in all threads
		4409	except the initial one, and run the default loop in the initial thread as
		4410	well.
		4411
		4412	=item C<long> must be large enough for common memory allocation sizes
		4413
		4414	To improve portability and simplify its API, libev uses C<long> internally
		4415	instead of C<size_t> when allocating its data structures. On non-POSIX
		4416	systems (Microsoft...) this might be unexpectedly low, but is still at
		4417	least 31 bits everywhere, which is enough for hundreds of millions of
		4418	watchers.
		4419
		4420	=item C<double> must hold a time value in seconds with enough accuracy
		4421
		4422	The type C<double> is used to represent timestamps. It is required to
		4423	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4424	enough for at least into the year 4000. This requirement is fulfilled by
		4425	implementations implementing IEEE 754, which is basically all existing
		4426	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4427	2200.
		4428
		4429	=back
		4430
		4431	If you know of other additional requirements drop me a note.
		4432
		4433
		4434	=head1 ALGORITHMIC COMPLEXITIES
		4435
		4436	In this section the complexities of (many of) the algorithms used inside
		4437	libev will be documented. For complexity discussions about backends see
		4438	the documentation for C<ev_default_init>.
		4439
		4440	All of the following are about amortised time: If an array needs to be
		4441	extended, libev needs to realloc and move the whole array, but this
		4442	happens asymptotically rarer with higher number of elements, so O(1) might
		4443	mean that libev does a lengthy realloc operation in rare cases, but on
		4444	average it is much faster and asymptotically approaches constant time.
		4445
		4446	=over 4
		4447
		4448	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4449
		4450	This means that, when you have a watcher that triggers in one hour and
		4451	there are 100 watchers that would trigger before that, then inserting will
		4452	have to skip roughly seven (C<ld 100>) of these watchers.
		4453
		4454	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4455
		4456	That means that changing a timer costs less than removing/adding them,
		4457	as only the relative motion in the event queue has to be paid for.
		4458
		4459	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4460
		4461	These just add the watcher into an array or at the head of a list.
		4462
		4463	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4464
		4465	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4466
		4467	These watchers are stored in lists, so they need to be walked to find the
		4468	correct watcher to remove. The lists are usually short (you don't usually
		4469	have many watchers waiting for the same fd or signal: one is typical, two
		4470	is rare).
		4471
		4472	=item Finding the next timer in each loop iteration: O(1)
		4473
		4474	By virtue of using a binary or 4-heap, the next timer is always found at a
		4475	fixed position in the storage array.
		4476
		4477	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4478
		4479	A change means an I/O watcher gets started or stopped, which requires
		4480	libev to recalculate its status (and possibly tell the kernel, depending
		4481	on backend and whether C<ev_io_set> was used).
		4482
		4483	=item Activating one watcher (putting it into the pending state): O(1)
		4484
		4485	=item Priority handling: O(number_of_priorities)
		4486
		4487	Priorities are implemented by allocating some space for each
		4488	priority. When doing priority-based operations, libev usually has to
		4489	linearly search all the priorities, but starting/stopping and activating
		4490	watchers becomes O(1) with respect to priority handling.
		4491
		4492	=item Sending an ev_async: O(1)
		4493
		4494	=item Processing ev_async_send: O(number_of_async_watchers)
		4495
		4496	=item Processing signals: O(max_signal_number)
		4497
		4498	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4499	calls in the current loop iteration. Checking for async and signal events
		4500	involves iterating over all running async watchers or all signal numbers.
		4501
		4502	=back
		4503
		4504
		4505	=head1 GLOSSARY
		4506
		4507	=over 4
		4508
		4509	=item active
		4510
		4511	A watcher is active as long as it has been started (has been attached to
		4512	an event loop) but not yet stopped (disassociated from the event loop).
		4513
		4514	=item application
		4515
		4516	In this document, an application is whatever is using libev.
		4517
		4518	=item callback
		4519
		4520	The address of a function that is called when some event has been
		4521	detected. Callbacks are being passed the event loop, the watcher that
		4522	received the event, and the actual event bitset.
		4523
		4524	=item callback invocation
		4525
		4526	The act of calling the callback associated with a watcher.
		4527
		4528	=item event
		4529
		4530	A change of state of some external event, such as data now being available
		4531	for reading on a file descriptor, time having passed or simply not having
		4532	any other events happening anymore.
		4533
		4534	In libev, events are represented as single bits (such as C<EV_READ> or
		4535	C<EV_TIMEOUT>).
		4536
		4537	=item event library
		4538
		4539	A software package implementing an event model and loop.
		4540
		4541	=item event loop
		4542
		4543	An entity that handles and processes external events and converts them
		4544	into callback invocations.
		4545
		4546	=item event model
		4547
		4548	The model used to describe how an event loop handles and processes
		4549	watchers and events.
		4550
		4551	=item pending
		4552
		4553	A watcher is pending as soon as the corresponding event has been detected,
		4554	and stops being pending as soon as the watcher will be invoked or its
		4555	pending status is explicitly cleared by the application.
		4556
		4557	A watcher can be pending, but not active. Stopping a watcher also clears
		4558	its pending status.
		4559
		4560	=item real time
		4561
		4562	The physical time that is observed. It is apparently strictly monotonic :)
		4563
		4564	=item wall-clock time
		4565
		4566	The time and date as shown on clocks. Unlike real time, it can actually
		4567	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4568	clock.
		4569
		4570	=item watcher
		4571
		4572	A data structure that describes interest in certain events. Watchers need
		4573	to be started (attached to an event loop) before they can receive events.
		4574
		4575	=item watcher invocation
		4576
		4577	The act of calling the callback associated with a watcher.
		4578
		4579	=back
878		4580
879	=head1 AUTHOR	4581	=head1 AUTHOR
880		4582
881	Marc Lehmann <libev@schmorp.de>.	4583	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
882		4584

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