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Revision 1.242 by root, Thu Jun 18 18:16:54 2009 UTC

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

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