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Revision 1.8 by root, Mon Nov 12 08:20:02 2007 UTC vs.
Revision 1.197 by root, Tue Oct 21 20:52:30 2008 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
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_<type>
		16	ev_io stdin_watcher;
		17	ev_timer timeout_watcher;
		18
		19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
		21	static void
		22	stdin_cb (EV_P_ struct ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	struct ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
8		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	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	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	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	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	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	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	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 *>)	108	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	117	to the C<double> type in C, and when you need to do any calculations on
		118	it, you should treat it as some floating point value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 ERROR HANDLING
		123
		124	Libev knows three classes of errors: operating system errors, usage errors
		125	and internal errors (bugs).
		126
		127	When libev catches an operating system error it cannot handle (for example
		128	a system call indicating a condition libev cannot fix), it calls the callback
		129	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		130	abort. The default is to print a diagnostic message and to call C<abort
		131	()>.
		132
		133	When libev detects a usage error such as a negative timer interval, then
		134	it will print a diagnostic message and abort (via the C<assert> mechanism,
		135	so C<NDEBUG> will disable this checking): these are programming errors in
		136	the libev caller and need to be fixed there.
		137
		138	Libev also has a few internal error-checking C<assert>ions, and also has
		139	extensive consistency checking code. These do not trigger under normal
		140	circumstances, as they indicate either a bug in libev or worse.
		141
		142
		143	=head1 GLOBAL FUNCTIONS
		144
		145	These functions can be called anytime, even before initialising the
		146	library in any way.
51		147
52	=over 4	148	=over 4
53		149
54	=item ev_tstamp ev_time ()	150	=item ev_tstamp ev_time ()
55		151
56	Returns the current time as libev would use it.	152	Returns the current time as libev would use it. Please note that the
		153	C<ev_now> function is usually faster and also often returns the timestamp
		154	you actually want to know.
		155
		156	=item ev_sleep (ev_tstamp interval)
		157
		158	Sleep for the given interval: The current thread will be blocked until
		159	either it is interrupted or the given time interval has passed. Basically
		160	this is a sub-second-resolution C<sleep ()>.
57		161
58	=item int ev_version_major ()	162	=item int ev_version_major ()
59		163
60	=item int ev_version_minor ()	164	=item int ev_version_minor ()
61		165
62	You can find out the major and minor version numbers of the library	166	You can find out the major and minor ABI version numbers of the library
63	you linked against by calling the functions C<ev_version_major> and	167	you linked against by calling the functions C<ev_version_major> and
64	C<ev_version_minor>. If you want, you can compare against the global	168	C<ev_version_minor>. If you want, you can compare against the global
65	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	169	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	170	version of the library your program was compiled against.
67		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
68	Usually, its a good idea to terminate if the major versions mismatch,	175	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	177	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	178	not a problem.
72		179
		180	Example: Make sure we haven't accidentally been linked against the wrong
		181	version.
		182
		183	assert (("libev version mismatch",
		184	ev_version_major () == EV_VERSION_MAJOR
		185	&& ev_version_minor () >= EV_VERSION_MINOR));
		186
		187	=item unsigned int ev_supported_backends ()
		188
		189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		190	value) compiled into this binary of libev (independent of their
		191	availability on the system you are running on). See C<ev_default_loop> for
		192	a description of the set values.
		193
		194	Example: make sure we have the epoll method, because yeah this is cool and
		195	a must have and can we have a torrent of it please!!!11
		196
		197	assert (("sorry, no epoll, no sex",
		198	ev_supported_backends () & EVBACKEND_EPOLL));
		199
		200	=item unsigned int ev_recommended_backends ()
		201
		202	Return the set of all backends compiled into this binary of libev and also
		203	recommended for this platform. This set is often smaller than the one
		204	returned by C<ev_supported_backends>, as for example kqueue is broken on
		205	most BSDs and will not be auto-detected unless you explicitly request it
		206	(assuming you know what you are doing). This is the set of backends that
		207	libev will probe for if you specify no backends explicitly.
		208
		209	=item unsigned int ev_embeddable_backends ()
		210
		211	Returns the set of backends that are embeddable in other event loops. This
		212	is the theoretical, all-platform, value. To find which backends
		213	might be supported on the current system, you would need to look at
		214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		215	recommended ones.
		216
		217	See the description of C<ev_embed> watchers for more info.
		218
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
74		220
75	Sets the allocation function to use (the prototype is similar to the	221	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
77	and free memory (no surprises here). If it returns zero when memory	223	used to allocate and free memory (no surprises here). If it returns zero
78	needs to be allocated, the library might abort or take some potentially	224	when memory needs to be allocated (C<size != 0>), the library might abort
79	destructive action. The default is your system realloc function.	225	or take some potentially destructive action.
		226
		227	Since some systems (at least OpenBSD and Darwin) fail to implement
		228	correct C<realloc> semantics, libev will use a wrapper around the system
		229	C<realloc> and C<free> functions by default.
80		230
81	You could override this function in high-availability programs to, say,	231	You could override this function in high-availability programs to, say,
82	free some memory if it cannot allocate memory, to use a special allocator,	232	free some memory if it cannot allocate memory, to use a special allocator,
83	or even to sleep a while and retry until some memory is available.	233	or even to sleep a while and retry until some memory is available.
84		234
		235	Example: Replace the libev allocator with one that waits a bit and then
		236	retries (example requires a standards-compliant C<realloc>).
		237
		238	static void *
		239	persistent_realloc (void *ptr, size_t size)
		240	{
		241	for (;;)
		242	{
		243	void *newptr = realloc (ptr, size);
		244
		245	if (newptr)
		246	return newptr;
		247
		248	sleep (60);
		249	}
		250	}
		251
		252	...
		253	ev_set_allocator (persistent_realloc);
		254
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
86		256
87	Set the callback function to call on a retryable syscall error (such	257	Set the callback function to call on a retryable system call error (such
88	as failed select, poll, epoll_wait). The message is a printable string	258	as failed select, poll, epoll_wait). The message is a printable string
89	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
90	callback is set, then libev will expect it to remedy the sitution, no	260	callback is set, then libev will expect it to remedy the situation, no
91	matter what, when it returns. That is, libev will generally retry the	261	matter what, when it returns. That is, libev will generally retry the
92	requested operation, or, if the condition doesn't go away, do bad stuff	262	requested operation, or, if the condition doesn't go away, do bad stuff
93	(such as abort).	263	(such as abort).
94		264
		265	Example: This is basically the same thing that libev does internally, too.
		266
		267	static void
		268	fatal_error (const char *msg)
		269	{
		270	perror (msg);
		271	abort ();
		272	}
		273
		274	...
		275	ev_set_syserr_cb (fatal_error);
		276
95	=back	277	=back
96		278
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98		280
99	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<struct ev_loop *>. The library knows two
100	types of such loops, the I<default> loop, which supports signals and child	282	types of such loops, the I<default> loop, which supports signals and child
101	events, and dynamically created loops which do not.	283	events, and dynamically created loops which do not.
102		284
103	If you use threads, a common model is to run the default event loop
104	in your main thread (or in a separate thrad) and for each thread you
105	create, you also create another event loop. Libev itself does no locking
106	whatsoever, so if you mix calls to the same event loop in different
107	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because its hideous and inefficient).
109
110	=over 4	285	=over 4
111		286
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	287	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		288
114	This will initialise the default event loop if it hasn't been initialised	289	This will initialise the default event loop if it hasn't been initialised
115	yet and return it. If the default loop could not be initialised, returns	290	yet and return it. If the default loop could not be initialised, returns
116	false. If it already was initialised it simply returns it (and ignores the	291	false. If it already was initialised it simply returns it (and ignores the
117	flags).	292	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		293
119	If you don't know what event loop to use, use the one returned from this	294	If you don't know what event loop to use, use the one returned from this
120	function.	295	function.
121		296
		297	Note that this function is I<not> thread-safe, so if you want to use it
		298	from multiple threads, you have to lock (note also that this is unlikely,
		299	as loops cannot bes hared easily between threads anyway).
		300
		301	The default loop is the only loop that can handle C<ev_signal> and
		302	C<ev_child> watchers, and to do this, it always registers a handler
		303	for C<SIGCHLD>. If this is a problem for your application you can either
		304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		306	C<ev_default_init>.
		307
122	The flags argument can be used to specify special behaviour or specific	308	The flags argument can be used to specify special behaviour or specific
123	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	309	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		310
125	It supports the following flags:	311	The following flags are supported:
126		312
127	=over 4	313	=over 4
128		314
129	=item EVFLAG_AUTO	315	=item C<EVFLAG_AUTO>
130		316
131	The default flags value. Use this if you have no clue (its the right	317	The default flags value. Use this if you have no clue (it's the right
132	thing, believe me).	318	thing, believe me).
133		319
134	=item EVFLAG_NOENV	320	=item C<EVFLAG_NOENV>
135		321
136	If this flag bit is ored into the flag value (or the program runs setuid	322	If this flag bit is or'ed into the flag value (or the program runs setuid
137	or setgid) then libev will I<not> look at the environment variable	323	or setgid) then libev will I<not> look at the environment variable
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	325	override the flags completely if it is found in the environment. This is
140	useful to try out specific backends to test their performance, or to work	326	useful to try out specific backends to test their performance, or to work
141	around bugs.	327	around bugs.
142		328
		329	=item C<EVFLAG_FORKCHECK>
		330
		331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		332	a fork, you can also make libev check for a fork in each iteration by
		333	enabling this flag.
		334
		335	This works by calling C<getpid ()> on every iteration of the loop,
		336	and thus this might slow down your event loop if you do a lot of loop
		337	iterations and little real work, but is usually not noticeable (on my
		338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		339	without a system call and thus I<very> fast, but my GNU/Linux system also has
		340	C<pthread_atfork> which is even faster).
		341
		342	The big advantage of this flag is that you can forget about fork (and
		343	forget about forgetting to tell libev about forking) when you use this
		344	flag.
		345
		346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		347	environment variable.
		348
143	=item EVMETHOD_SELECT portable select backend	349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		350
145	=item EVMETHOD_POLL poll backend (everywhere except windows)	351	This is your standard select(2) backend. Not I<completely> standard, as
		352	libev tries to roll its own fd_set with no limits on the number of fds,
		353	but if that fails, expect a fairly low limit on the number of fds when
		354	using this backend. It doesn't scale too well (O(highest_fd)), but its
		355	usually the fastest backend for a low number of (low-numbered :) fds.
146		356
147	=item EVMETHOD_EPOLL linux only	357	To get good performance out of this backend you need a high amount of
		358	parallelism (most of the file descriptors should be busy). If you are
		359	writing a server, you should C<accept ()> in a loop to accept as many
		360	connections as possible during one iteration. You might also want to have
		361	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		362	readiness notifications you get per iteration.
148		363
149	=item EVMETHOD_KQUEUE some bsds only	364	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		365	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		366	C<exceptfds> set on that platform).
150		367
151	=item EVMETHOD_DEVPOLL solaris 8 only	368	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
152		369
153	=item EVMETHOD_PORT solaris 10 only	370	And this is your standard poll(2) backend. It's more complicated
		371	than select, but handles sparse fds better and has no artificial
		372	limit on the number of fds you can use (except it will slow down
		373	considerably with a lot of inactive fds). It scales similarly to select,
		374	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		375	performance tips.
154		376
155	If one or more of these are ored into the flags value, then only these	377	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
156	backends will be tried (in the reverse order as given here). If one are	378	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
157	specified, any backend will do.	379
		380	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		381
		382	For few fds, this backend is a bit little slower than poll and select,
		383	but it scales phenomenally better. While poll and select usually scale
		384	like O(total_fds) where n is the total number of fds (or the highest fd),
		385	epoll scales either O(1) or O(active_fds). The epoll design has a number
		386	of shortcomings, such as silently dropping events in some hard-to-detect
		387	cases and requiring a system call per fd change, no fork support and bad
		388	support for dup.
		389
		390	While stopping, setting and starting an I/O watcher in the same iteration
		391	will result in some caching, there is still a system call per such incident
		392	(because the fd could point to a different file description now), so its
		393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		394	very well if you register events for both fds.
		395
		396	Please note that epoll sometimes generates spurious notifications, so you
		397	need to use non-blocking I/O or other means to avoid blocking when no data
		398	(or space) is available.
		399
		400	Best performance from this backend is achieved by not unregistering all
		401	watchers for a file descriptor until it has been closed, if possible,
		402	i.e. keep at least one watcher active per fd at all times. Stopping and
		403	starting a watcher (without re-setting it) also usually doesn't cause
		404	extra overhead.
		405
		406	While nominally embeddable in other event loops, this feature is broken in
		407	all kernel versions tested so far.
		408
		409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		410	C<EVBACKEND_POLL>.
		411
		412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		413
		414	Kqueue deserves special mention, as at the time of this writing, it was
		415	broken on all BSDs except NetBSD (usually it doesn't work reliably with
		416	anything but sockets and pipes, except on Darwin, where of course it's
		417	completely useless). For this reason it's not being "auto-detected" unless
		418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or
		419	libev was compiled on a known-to-be-good (-enough) system like NetBSD.
		420
		421	You still can embed kqueue into a normal poll or select backend and use it
		422	only for sockets (after having made sure that sockets work with kqueue on
		423	the target platform). See C<ev_embed> watchers for more info.
		424
		425	It scales in the same way as the epoll backend, but the interface to the
		426	kernel is more efficient (which says nothing about its actual speed, of
		427	course). While stopping, setting and starting an I/O watcher does never
		428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		429	two event changes per incident. Support for C<fork ()> is very bad and it
		430	drops fds silently in similarly hard-to-detect cases.
		431
		432	This backend usually performs well under most conditions.
		433
		434	While nominally embeddable in other event loops, this doesn't work
		435	everywhere, so you might need to test for this. And since it is broken
		436	almost everywhere, you should only use it when you have a lot of sockets
		437	(for which it usually works), by embedding it into another event loop
		438	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
		439	using it only for sockets.
		440
		441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		442	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		443	C<NOTE_EOF>.
		444
		445	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		446
		447	This is not implemented yet (and might never be, unless you send me an
		448	implementation). According to reports, C</dev/poll> only supports sockets
		449	and is not embeddable, which would limit the usefulness of this backend
		450	immensely.
		451
		452	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		453
		454	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		455	it's really slow, but it still scales very well (O(active_fds)).
		456
		457	Please note that Solaris event ports can deliver a lot of spurious
		458	notifications, so you need to use non-blocking I/O or other means to avoid
		459	blocking when no data (or space) is available.
		460
		461	While this backend scales well, it requires one system call per active
		462	file descriptor per loop iteration. For small and medium numbers of file
		463	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		464	might perform better.
		465
		466	On the positive side, with the exception of the spurious readiness
		467	notifications, this backend actually performed fully to specification
		468	in all tests and is fully embeddable, which is a rare feat among the
		469	OS-specific backends.
		470
		471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		472	C<EVBACKEND_POLL>.
		473
		474	=item C<EVBACKEND_ALL>
		475
		476	Try all backends (even potentially broken ones that wouldn't be tried
		477	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		478	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		479
		480	It is definitely not recommended to use this flag.
158		481
159	=back	482	=back
		483
		484	If one or more of these are or'ed into the flags value, then only these
		485	backends will be tried (in the reverse order as listed here). If none are
		486	specified, all backends in C<ev_recommended_backends ()> will be tried.
		487
		488	Example: This is the most typical usage.
		489
		490	if (!ev_default_loop (0))
		491	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		492
		493	Example: Restrict libev to the select and poll backends, and do not allow
		494	environment settings to be taken into account:
		495
		496	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		497
		498	Example: Use whatever libev has to offer, but make sure that kqueue is
		499	used if available (warning, breaks stuff, best use only with your own
		500	private event loop and only if you know the OS supports your types of
		501	fds):
		502
		503	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		504
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	505	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		506
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	507	Similar to C<ev_default_loop>, but always creates a new event loop that is
164	always distinct from the default loop. Unlike the default loop, it cannot	508	always distinct from the default loop. Unlike the default loop, it cannot
165	handle signal and child watchers, and attempts to do so will be greeted by	509	handle signal and child watchers, and attempts to do so will be greeted by
166	undefined behaviour (or a failed assertion if assertions are enabled).	510	undefined behaviour (or a failed assertion if assertions are enabled).
167		511
		512	Note that this function I<is> thread-safe, and the recommended way to use
		513	libev with threads is indeed to create one loop per thread, and using the
		514	default loop in the "main" or "initial" thread.
		515
		516	Example: Try to create a event loop that uses epoll and nothing else.
		517
		518	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		519	if (!epoller)
		520	fatal ("no epoll found here, maybe it hides under your chair");
		521
168	=item ev_default_destroy ()	522	=item ev_default_destroy ()
169		523
170	Destroys the default loop again (frees all memory and kernel state	524	Destroys the default loop again (frees all memory and kernel state
171	etc.). This stops all registered event watchers (by not touching them in	525	etc.). None of the active event watchers will be stopped in the normal
172	any way whatsoever, although you cnanot rely on this :).	526	sense, so e.g. C<ev_is_active> might still return true. It is your
		527	responsibility to either stop all watchers cleanly yourself I<before>
		528	calling this function, or cope with the fact afterwards (which is usually
		529	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		530	for example).
		531
		532	Note that certain global state, such as signal state, will not be freed by
		533	this function, and related watchers (such as signal and child watchers)
		534	would need to be stopped manually.
		535
		536	In general it is not advisable to call this function except in the
		537	rare occasion where you really need to free e.g. the signal handling
		538	pipe fds. If you need dynamically allocated loops it is better to use
		539	C<ev_loop_new> and C<ev_loop_destroy>).
173		540
174	=item ev_loop_destroy (loop)	541	=item ev_loop_destroy (loop)
175		542
176	Like C<ev_default_destroy>, but destroys an event loop created by an	543	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	544	earlier call to C<ev_loop_new>.
178		545
179	=item ev_default_fork ()	546	=item ev_default_fork ()
180		547
		548	This function sets a flag that causes subsequent C<ev_loop> iterations
181	This function reinitialises the kernel state for backends that have	549	to reinitialise the kernel state for backends that have one. Despite the
182	one. Despite the name, you can call it anytime, but it makes most sense	550	name, you can call it anytime, but it makes most sense after forking, in
183	after forking, in either the parent or child process (or both, but that	551	the child process (or both child and parent, but that again makes little
184	again makes little sense).	552	sense). You I<must> call it in the child before using any of the libev
		553	functions, and it will only take effect at the next C<ev_loop> iteration.
185		554
186	You I<must> call this function after forking if and only if you want to	555	On the other hand, you only need to call this function in the child
187	use the event library in both processes. If you just fork+exec, you don't	556	process if and only if you want to use the event library in the child. If
188	have to call it.	557	you just fork+exec, you don't have to call it at all.
189		558
190	The function itself is quite fast and its usually not a problem to call	559	The function itself is quite fast and it's usually not a problem to call
191	it just in case after a fork. To make this easy, the function will fit in	560	it just in case after a fork. To make this easy, the function will fit in
192	quite nicely into a call to C<pthread_atfork>:	561	quite nicely into a call to C<pthread_atfork>:
193		562
194	pthread_atfork (0, 0, ev_default_fork);	563	pthread_atfork (0, 0, ev_default_fork);
195		564
196	=item ev_loop_fork (loop)	565	=item ev_loop_fork (loop)
197		566
198	Like C<ev_default_fork>, but acts on an event loop created by	567	Like C<ev_default_fork>, but acts on an event loop created by
199	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	568	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
200	after fork, and how you do this is entirely your own problem.	569	after fork that you want to re-use in the child, and how you do this is
		570	entirely your own problem.
201		571
		572	=item int ev_is_default_loop (loop)
		573
		574	Returns true when the given loop is, in fact, the default loop, and false
		575	otherwise.
		576
		577	=item unsigned int ev_loop_count (loop)
		578
		579	Returns the count of loop iterations for the loop, which is identical to
		580	the number of times libev did poll for new events. It starts at C<0> and
		581	happily wraps around with enough iterations.
		582
		583	This value can sometimes be useful as a generation counter of sorts (it
		584	"ticks" the number of loop iterations), as it roughly corresponds with
		585	C<ev_prepare> and C<ev_check> calls.
		586
202	=item unsigned int ev_method (loop)	587	=item unsigned int ev_backend (loop)
203		588
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	589	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	590	use.
206		591
207	=item ev_tstamp = ev_now (loop)	592	=item ev_tstamp ev_now (loop)
208		593
209	Returns the current "event loop time", which is the time the event loop	594	Returns the current "event loop time", which is the time the event loop
210	got events and started processing them. This timestamp does not change	595	received events and started processing them. This timestamp does not
211	as long as callbacks are being processed, and this is also the base time	596	change as long as callbacks are being processed, and this is also the base
212	used for relative timers. You can treat it as the timestamp of the event	597	time used for relative timers. You can treat it as the timestamp of the
213	occuring (or more correctly, the mainloop finding out about it).	598	event occurring (or more correctly, libev finding out about it).
		599
		600	=item ev_now_update (loop)
		601
		602	Establishes the current time by querying the kernel, updating the time
		603	returned by C<ev_now ()> in the progress. This is a costly operation and
		604	is usually done automatically within C<ev_loop ()>.
		605
		606	This function is rarely useful, but when some event callback runs for a
		607	very long time without entering the event loop, updating libev's idea of
		608	the current time is a good idea.
		609
		610	See also "The special problem of time updates" in the C<ev_timer> section.
214		611
215	=item ev_loop (loop, int flags)	612	=item ev_loop (loop, int flags)
216		613
217	Finally, this is it, the event handler. This function usually is called	614	Finally, this is it, the event handler. This function usually is called
218	after you initialised all your watchers and you want to start handling	615	after you initialised all your watchers and you want to start handling
219	events.	616	events.
220		617
221	If the flags argument is specified as 0, it will not return until either	618	If the flags argument is specified as C<0>, it will not return until
222	no event watchers are active anymore or C<ev_unloop> was called.	619	either no event watchers are active anymore or C<ev_unloop> was called.
		620
		621	Please note that an explicit C<ev_unloop> is usually better than
		622	relying on all watchers to be stopped when deciding when a program has
		623	finished (especially in interactive programs), but having a program
		624	that automatically loops as long as it has to and no longer by virtue
		625	of relying on its watchers stopping correctly, that is truly a thing of
		626	beauty.
223		627
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	628	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
225	those events and any outstanding ones, but will not block your process in	629	those events and any already outstanding ones, but will not block your
226	case there are no events.	630	process in case there are no events and will return after one iteration of
		631	the loop.
227		632
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
229	neccessary) and will handle those and any outstanding ones. It will block	634	necessary) and will handle those and any already outstanding ones. It
230	your process until at least one new event arrives.	635	will block your process until at least one new event arrives (which could
		636	be an event internal to libev itself, so there is no guarentee that a
		637	user-registered callback will be called), and will return after one
		638	iteration of the loop.
231		639
232	This flags value could be used to implement alternative looping	640	This is useful if you are waiting for some external event in conjunction
233	constructs, but the C<prepare> and C<check> watchers provide a better and	641	with something not expressible using other libev watchers (i.e. "roll your
234	more generic mechanism.	642	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		643	usually a better approach for this kind of thing.
		644
		645	Here are the gory details of what C<ev_loop> does:
		646
		647	- Before the first iteration, call any pending watchers.
		648	* If EVFLAG_FORKCHECK was used, check for a fork.
		649	- If a fork was detected (by any means), queue and call all fork watchers.
		650	- Queue and call all prepare watchers.
		651	- If we have been forked, detach and recreate the kernel state
		652	as to not disturb the other process.
		653	- Update the kernel state with all outstanding changes.
		654	- Update the "event loop time" (ev_now ()).
		655	- Calculate for how long to sleep or block, if at all
		656	(active idle watchers, EVLOOP_NONBLOCK or not having
		657	any active watchers at all will result in not sleeping).
		658	- Sleep if the I/O and timer collect interval say so.
		659	- Block the process, waiting for any events.
		660	- Queue all outstanding I/O (fd) events.
		661	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		662	- Queue all expired timers.
		663	- Queue all expired periodics.
		664	- Unless any events are pending now, queue all idle watchers.
		665	- Queue all check watchers.
		666	- Call all queued watchers in reverse order (i.e. check watchers first).
		667	Signals and child watchers are implemented as I/O watchers, and will
		668	be handled here by queueing them when their watcher gets executed.
		669	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		670	were used, or there are no active watchers, return, otherwise
		671	continue with step *.
		672
		673	Example: Queue some jobs and then loop until no events are outstanding
		674	anymore.
		675
		676	... queue jobs here, make sure they register event watchers as long
		677	... as they still have work to do (even an idle watcher will do..)
		678	ev_loop (my_loop, 0);
		679	... jobs done or somebody called unloop. yeah!
235		680
236	=item ev_unloop (loop, how)	681	=item ev_unloop (loop, how)
237		682
238	Can be used to make a call to C<ev_loop> return early. The C<how> argument	683	Can be used to make a call to C<ev_loop> return early (but only after it
		684	has processed all outstanding events). The C<how> argument must be either
239	must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop>	685	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
240	call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop>	686	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
241	calls return.	687
		688	This "unloop state" will be cleared when entering C<ev_loop> again.
		689
		690	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
242		691
243	=item ev_ref (loop)	692	=item ev_ref (loop)
244		693
245	=item ev_unref (loop)	694	=item ev_unref (loop)
246		695
247	Ref/unref can be used to add or remove a refcount on the event loop: Every	696	Ref/unref can be used to add or remove a reference count on the event
248	watcher keeps one reference. If you have a long-runing watcher you never	697	loop: Every watcher keeps one reference, and as long as the reference
249	unregister that should not keep ev_loop from running, ev_unref() after	698	count is nonzero, C<ev_loop> will not return on its own.
250	starting, and ev_ref() before stopping it. Libev itself uses this for	699
251	example for its internal signal pipe: It is not visible to you as a user	700	If you have a watcher you never unregister that should not keep C<ev_loop>
252	and should not keep C<ev_loop> from exiting if the work is done. It is	701	from returning, call ev_unref() after starting, and ev_ref() before
253	also an excellent way to do this for generic recurring timers or from	702	stopping it.
254	within third-party libraries. Just remember to unref after start and ref	703
255	before stop.	704	As an example, libev itself uses this for its internal signal pipe: It is
		705	not visible to the libev user and should not keep C<ev_loop> from exiting
		706	if no event watchers registered by it are active. It is also an excellent
		707	way to do this for generic recurring timers or from within third-party
		708	libraries. Just remember to I<unref after start> and I<ref before stop>
		709	(but only if the watcher wasn't active before, or was active before,
		710	respectively).
		711
		712	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		713	running when nothing else is active.
		714
		715	struct ev_signal exitsig;
		716	ev_signal_init (&exitsig, sig_cb, SIGINT);
		717	ev_signal_start (loop, &exitsig);
		718	evf_unref (loop);
		719
		720	Example: For some weird reason, unregister the above signal handler again.
		721
		722	ev_ref (loop);
		723	ev_signal_stop (loop, &exitsig);
		724
		725	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		726
		727	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		728
		729	These advanced functions influence the time that libev will spend waiting
		730	for events. Both time intervals are by default C<0>, meaning that libev
		731	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		732	latency.
		733
		734	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		735	allows libev to delay invocation of I/O and timer/periodic callbacks
		736	to increase efficiency of loop iterations (or to increase power-saving
		737	opportunities).
		738
		739	The idea is that sometimes your program runs just fast enough to handle
		740	one (or very few) event(s) per loop iteration. While this makes the
		741	program responsive, it also wastes a lot of CPU time to poll for new
		742	events, especially with backends like C<select ()> which have a high
		743	overhead for the actual polling but can deliver many events at once.
		744
		745	By setting a higher I<io collect interval> you allow libev to spend more
		746	time collecting I/O events, so you can handle more events per iteration,
		747	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		748	C<ev_timer>) will be not affected. Setting this to a non-null value will
		749	introduce an additional C<ev_sleep ()> call into most loop iterations.
		750
		751	Likewise, by setting a higher I<timeout collect interval> you allow libev
		752	to spend more time collecting timeouts, at the expense of increased
		753	latency/jitter/inexactness (the watcher callback will be called
		754	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		755	value will not introduce any overhead in libev.
		756
		757	Many (busy) programs can usually benefit by setting the I/O collect
		758	interval to a value near C<0.1> or so, which is often enough for
		759	interactive servers (of course not for games), likewise for timeouts. It
		760	usually doesn't make much sense to set it to a lower value than C<0.01>,
		761	as this approaches the timing granularity of most systems.
		762
		763	Setting the I<timeout collect interval> can improve the opportunity for
		764	saving power, as the program will "bundle" timer callback invocations that
		765	are "near" in time together, by delaying some, thus reducing the number of
		766	times the process sleeps and wakes up again. Another useful technique to
		767	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		768	they fire on, say, one-second boundaries only.
		769
		770	=item ev_loop_verify (loop)
		771
		772	This function only does something when C<EV_VERIFY> support has been
		773	compiled in. which is the default for non-minimal builds. It tries to go
		774	through all internal structures and checks them for validity. If anything
		775	is found to be inconsistent, it will print an error message to standard
		776	error and call C<abort ()>.
		777
		778	This can be used to catch bugs inside libev itself: under normal
		779	circumstances, this function will never abort as of course libev keeps its
		780	data structures consistent.
256		781
257	=back	782	=back
		783
258		784
259	=head1 ANATOMY OF A WATCHER	785	=head1 ANATOMY OF A WATCHER
260		786
261	A watcher is a structure that you create and register to record your	787	A watcher is a structure that you create and register to record your
262	interest in some event. For instance, if you want to wait for STDIN to	788	interest in some event. For instance, if you want to wait for STDIN to
263	become readable, you would create an ev_io watcher for that:	789	become readable, you would create an C<ev_io> watcher for that:
264		790
265	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	791	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
266	{	792	{
267	ev_io_stop (w);	793	ev_io_stop (w);
268	ev_unloop (loop, EVUNLOOP_ALL);	794	ev_unloop (loop, EVUNLOOP_ALL);
269	}	795	}
270		796
271	struct ev_loop *loop = ev_default_loop (0);	797	struct ev_loop *loop = ev_default_loop (0);
272	struct ev_io stdin_watcher;	798	struct ev_io stdin_watcher;
273	ev_init (&stdin_watcher, my_cb);	799	ev_init (&stdin_watcher, my_cb);
274	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
275	ev_io_start (loop, &stdin_watcher);	801	ev_io_start (loop, &stdin_watcher);
276	ev_loop (loop, 0);	802	ev_loop (loop, 0);
277		803
278	As you can see, you are responsible for allocating the memory for your	804	As you can see, you are responsible for allocating the memory for your
279	watcher structures (and it is usually a bad idea to do this on the stack,	805	watcher structures (and it is usually a bad idea to do this on the stack,
280	although this can sometimes be quite valid).	806	although this can sometimes be quite valid).
281		807
282	Each watcher structure must be initialised by a call to C<ev_init	808	Each watcher structure must be initialised by a call to C<ev_init
283	(watcher *, callback)>, which expects a callback to be provided. This	809	(watcher *, callback)>, which expects a callback to be provided. This
284	callback gets invoked each time the event occurs (or, in the case of io	810	callback gets invoked each time the event occurs (or, in the case of I/O
285	watchers, each time the event loop detects that the file descriptor given	811	watchers, each time the event loop detects that the file descriptor given
286	is readable and/or writable).	812	is readable and/or writable).
287		813
288	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro
289	with arguments specific to this watcher type. There is also a macro	815	with arguments specific to this watcher type. There is also a macro
…		…
295	*) >>), and you can stop watching for events at any time by calling the	821	*) >>), and you can stop watching for events at any time by calling the
296	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
297		823
298	As long as your watcher is active (has been started but not stopped) you	824	As long as your watcher is active (has been started but not stopped) you
299	must not touch the values stored in it. Most specifically you must never	825	must not touch the values stored in it. Most specifically you must never
300	reinitialise it or call its set method.	826	reinitialise it or call its C<set> macro.
301
302	You cna check whether an event is active by calling the C<ev_is_active
303	(watcher *)> macro. To see whether an event is outstanding (but the
304	callback for it has not been called yet) you cna use the C<ev_is_pending
305	(watcher *)> macro.
306		827
307	Each and every callback receives the event loop pointer as first, the	828	Each and every callback receives the event loop pointer as first, the
308	registered watcher structure as second, and a bitset of received events as	829	registered watcher structure as second, and a bitset of received events as
309	third argument.	830	third argument.
310		831
311	The rceeived events usually include a single bit per event type received	832	The received events usually include a single bit per event type received
312	(you can receive multiple events at the same time). The possible bit masks	833	(you can receive multiple events at the same time). The possible bit masks
313	are:	834	are:
314		835
315	=over 4	836	=over 4
316		837
317	=item EV_READ	838	=item C<EV_READ>
318		839
319	=item EV_WRITE	840	=item C<EV_WRITE>
320		841
321	The file descriptor in the ev_io watcher has become readable and/or	842	The file descriptor in the C<ev_io> watcher has become readable and/or
322	writable.	843	writable.
323		844
324	=item EV_TIMEOUT	845	=item C<EV_TIMEOUT>
325		846
326	The ev_timer watcher has timed out.	847	The C<ev_timer> watcher has timed out.
327		848
328	=item EV_PERIODIC	849	=item C<EV_PERIODIC>
329		850
330	The ev_periodic watcher has timed out.	851	The C<ev_periodic> watcher has timed out.
331		852
332	=item EV_SIGNAL	853	=item C<EV_SIGNAL>
333		854
334	The signal specified in the ev_signal watcher has been received by a thread.	855	The signal specified in the C<ev_signal> watcher has been received by a thread.
335		856
336	=item EV_CHILD	857	=item C<EV_CHILD>
337		858
338	The pid specified in the ev_child watcher has received a status change.	859	The pid specified in the C<ev_child> watcher has received a status change.
339		860
		861	=item C<EV_STAT>
		862
		863	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		864
340	=item EV_IDLE	865	=item C<EV_IDLE>
341		866
342	The ev_idle watcher has determined that you have nothing better to do.	867	The C<ev_idle> watcher has determined that you have nothing better to do.
343		868
344	=item EV_PREPARE	869	=item C<EV_PREPARE>
345		870
346	=item EV_CHECK	871	=item C<EV_CHECK>
347		872
348	All ev_prepare watchers are invoked just I<before> C<ev_loop> starts	873	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
349	to gather new events, and all ev_check watchers are invoked just after	874	to gather new events, and all C<ev_check> watchers are invoked just after
350	C<ev_loop> has gathered them, but before it invokes any callbacks for any	875	C<ev_loop> has gathered them, but before it invokes any callbacks for any
351	received events. Callbacks of both watcher types can start and stop as	876	received events. Callbacks of both watcher types can start and stop as
352	many watchers as they want, and all of them will be taken into account	877	many watchers as they want, and all of them will be taken into account
353	(for example, a ev_prepare watcher might start an idle watcher to keep	878	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
354	C<ev_loop> from blocking).	879	C<ev_loop> from blocking).
355		880
		881	=item C<EV_EMBED>
		882
		883	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		884
		885	=item C<EV_FORK>
		886
		887	The event loop has been resumed in the child process after fork (see
		888	C<ev_fork>).
		889
		890	=item C<EV_ASYNC>
		891
		892	The given async watcher has been asynchronously notified (see C<ev_async>).
		893
356	=item EV_ERROR	894	=item C<EV_ERROR>
357		895
358	An unspecified error has occured, the watcher has been stopped. This might	896	An unspecified error has occurred, the watcher has been stopped. This might
359	happen because the watcher could not be properly started because libev	897	happen because the watcher could not be properly started because libev
360	ran out of memory, a file descriptor was found to be closed or any other	898	ran out of memory, a file descriptor was found to be closed or any other
		899	problem. Libev considers these application bugs.
		900
361	problem. You best act on it by reporting the problem and somehow coping	901	You best act on it by reporting the problem and somehow coping with the
362	with the watcher being stopped.	902	watcher being stopped. Note that well-written programs should not receive
		903	an error ever, so when your watcher receives it, this usually indicates a
		904	bug in your program.
363		905
364	Libev will usually signal a few "dummy" events together with an error,	906	Libev will usually signal a few "dummy" events together with an error, for
365	for example it might indicate that a fd is readable or writable, and if	907	example it might indicate that a fd is readable or writable, and if your
366	your callbacks is well-written it can just attempt the operation and cope	908	callbacks is well-written it can just attempt the operation and cope with
367	with the error from read() or write(). This will not work in multithreaded	909	the error from read() or write(). This will not work in multi-threaded
368	programs, though, so beware.	910	programs, though, as the fd could already be closed and reused for another
		911	thing, so beware.
369		912
370	=back	913	=back
371		914
		915	=head2 GENERIC WATCHER FUNCTIONS
		916
		917	In the following description, C<TYPE> stands for the watcher type,
		918	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		919
		920	=over 4
		921
		922	=item C<ev_init> (ev_TYPE *watcher, callback)
		923
		924	This macro initialises the generic portion of a watcher. The contents
		925	of the watcher object can be arbitrary (so C<malloc> will do). Only
		926	the generic parts of the watcher are initialised, you I<need> to call
		927	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		928	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		929	which rolls both calls into one.
		930
		931	You can reinitialise a watcher at any time as long as it has been stopped
		932	(or never started) and there are no pending events outstanding.
		933
		934	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		935	int revents)>.
		936
		937	Example: Initialise an C<ev_io> watcher in two steps.
		938
		939	ev_io w;
		940	ev_init (&w, my_cb);
		941	ev_io_set (&w, STDIN_FILENO, EV_READ);
		942
		943	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		944
		945	This macro initialises the type-specific parts of a watcher. You need to
		946	call C<ev_init> at least once before you call this macro, but you can
		947	call C<ev_TYPE_set> any number of times. You must not, however, call this
		948	macro on a watcher that is active (it can be pending, however, which is a
		949	difference to the C<ev_init> macro).
		950
		951	Although some watcher types do not have type-specific arguments
		952	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		953
		954	See C<ev_init>, above, for an example.
		955
		956	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		957
		958	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		959	calls into a single call. This is the most convenient method to initialise
		960	a watcher. The same limitations apply, of course.
		961
		962	Example: Initialise and set an C<ev_io> watcher in one step.
		963
		964	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		965
		966	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		967
		968	Starts (activates) the given watcher. Only active watchers will receive
		969	events. If the watcher is already active nothing will happen.
		970
		971	Example: Start the C<ev_io> watcher that is being abused as example in this
		972	whole section.
		973
		974	ev_io_start (EV_DEFAULT_UC, &w);
		975
		976	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		977
		978	Stops the given watcher if active, and clears the pending status (whether
		979	the watcher was active or not).
		980
		981	It is possible that stopped watchers are pending - for example,
		982	non-repeating timers are being stopped when they become pending - but
		983	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		984	pending. If you want to free or reuse the memory used by the watcher it is
		985	therefore a good idea to always call its C<ev_TYPE_stop> function.
		986
		987	=item bool ev_is_active (ev_TYPE *watcher)
		988
		989	Returns a true value iff the watcher is active (i.e. it has been started
		990	and not yet been stopped). As long as a watcher is active you must not modify
		991	it.
		992
		993	=item bool ev_is_pending (ev_TYPE *watcher)
		994
		995	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		996	events but its callback has not yet been invoked). As long as a watcher
		997	is pending (but not active) you must not call an init function on it (but
		998	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		999	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1000	it).
		1001
		1002	=item callback ev_cb (ev_TYPE *watcher)
		1003
		1004	Returns the callback currently set on the watcher.
		1005
		1006	=item ev_cb_set (ev_TYPE *watcher, callback)
		1007
		1008	Change the callback. You can change the callback at virtually any time
		1009	(modulo threads).
		1010
		1011	=item ev_set_priority (ev_TYPE *watcher, priority)
		1012
		1013	=item int ev_priority (ev_TYPE *watcher)
		1014
		1015	Set and query the priority of the watcher. The priority is a small
		1016	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1017	(default: C<-2>). Pending watchers with higher priority will be invoked
		1018	before watchers with lower priority, but priority will not keep watchers
		1019	from being executed (except for C<ev_idle> watchers).
		1020
		1021	This means that priorities are I<only> used for ordering callback
		1022	invocation after new events have been received. This is useful, for
		1023	example, to reduce latency after idling, or more often, to bind two
		1024	watchers on the same event and make sure one is called first.
		1025
		1026	If you need to suppress invocation when higher priority events are pending
		1027	you need to look at C<ev_idle> watchers, which provide this functionality.
		1028
		1029	You I<must not> change the priority of a watcher as long as it is active or
		1030	pending.
		1031
		1032	The default priority used by watchers when no priority has been set is
		1033	always C<0>, which is supposed to not be too high and not be too low :).
		1034
		1035	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1036	fine, as long as you do not mind that the priority value you query might
		1037	or might not have been adjusted to be within valid range.
		1038
		1039	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1040
		1041	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1042	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1043	can deal with that fact, as both are simply passed through to the
		1044	callback.
		1045
		1046	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1047
		1048	If the watcher is pending, this function clears its pending status and
		1049	returns its C<revents> bitset (as if its callback was invoked). If the
		1050	watcher isn't pending it does nothing and returns C<0>.
		1051
		1052	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1053	callback to be invoked, which can be accomplished with this function.
		1054
		1055	=back
		1056
		1057
372	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1058	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
373		1059
374	Each watcher has, by default, a member C<void *data> that you can change	1060	Each watcher has, by default, a member C<void *data> that you can change
375	and read at any time, libev will completely ignore it. This cna be used	1061	and read at any time: libev will completely ignore it. This can be used
376	to associate arbitrary data with your watcher. If you need more data and	1062	to associate arbitrary data with your watcher. If you need more data and
377	don't want to allocate memory and store a pointer to it in that data	1063	don't want to allocate memory and store a pointer to it in that data
378	member, you can also "subclass" the watcher type and provide your own	1064	member, you can also "subclass" the watcher type and provide your own
379	data:	1065	data:
380		1066
381	struct my_io	1067	struct my_io
382	{	1068	{
383	struct ev_io io;	1069	struct ev_io io;
384	int otherfd;	1070	int otherfd;
385	void *somedata;	1071	void *somedata;
386	struct whatever *mostinteresting;	1072	struct whatever *mostinteresting;
387	}	1073	};
		1074
		1075	...
		1076	struct my_io w;
		1077	ev_io_init (&w.io, my_cb, fd, EV_READ);
388		1078
389	And since your callback will be called with a pointer to the watcher, you	1079	And since your callback will be called with a pointer to the watcher, you
390	can cast it back to your own type:	1080	can cast it back to your own type:
391		1081
392	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1082	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
393	{	1083	{
394	struct my_io *w = (struct my_io *)w_;	1084	struct my_io *w = (struct my_io *)w_;
395	...	1085	...
396	}	1086	}
397		1087
398	More interesting and less C-conformant ways of catsing your callback type	1088	More interesting and less C-conformant ways of casting your callback type
399	have been omitted....	1089	instead have been omitted.
		1090
		1091	Another common scenario is to use some data structure with multiple
		1092	embedded watchers:
		1093
		1094	struct my_biggy
		1095	{
		1096	int some_data;
		1097	ev_timer t1;
		1098	ev_timer t2;
		1099	}
		1100
		1101	In this case getting the pointer to C<my_biggy> is a bit more
		1102	complicated: Either you store the address of your C<my_biggy> struct
		1103	in the C<data> member of the watcher (for woozies), or you need to use
		1104	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1105	programmers):
		1106
		1107	#include <stddef.h>
		1108
		1109	static void
		1110	t1_cb (EV_P_ struct ev_timer *w, int revents)
		1111	{
		1112	struct my_biggy big = (struct my_biggy *
		1113	(((char *)w) - offsetof (struct my_biggy, t1));
		1114	}
		1115
		1116	static void
		1117	t2_cb (EV_P_ struct ev_timer *w, int revents)
		1118	{
		1119	struct my_biggy big = (struct my_biggy *
		1120	(((char *)w) - offsetof (struct my_biggy, t2));
		1121	}
400		1122
401		1123
402	=head1 WATCHER TYPES	1124	=head1 WATCHER TYPES
403		1125
404	This section describes each watcher in detail, but will not repeat	1126	This section describes each watcher in detail, but will not repeat
405	information given in the last section.	1127	information given in the last section. Any initialisation/set macros,
		1128	functions and members specific to the watcher type are explained.
406		1129
		1130	Members are additionally marked with either I<[read-only]>, meaning that,
		1131	while the watcher is active, you can look at the member and expect some
		1132	sensible content, but you must not modify it (you can modify it while the
		1133	watcher is stopped to your hearts content), or I<[read-write]>, which
		1134	means you can expect it to have some sensible content while the watcher
		1135	is active, but you can also modify it. Modifying it may not do something
		1136	sensible or take immediate effect (or do anything at all), but libev will
		1137	not crash or malfunction in any way.
		1138
		1139
407	=head2 struct ev_io - is my file descriptor readable or writable	1140	=head2 C<ev_io> - is this file descriptor readable or writable?
408		1141
409	I/O watchers check whether a file descriptor is readable or writable	1142	I/O watchers check whether a file descriptor is readable or writable
410	in each iteration of the event loop (This behaviour is called	1143	in each iteration of the event loop, or, more precisely, when reading
411	level-triggering because you keep receiving events as long as the	1144	would not block the process and writing would at least be able to write
412	condition persists. Remember you cna stop the watcher if you don't want to	1145	some data. This behaviour is called level-triggering because you keep
413	act on the event and neither want to receive future events).	1146	receiving events as long as the condition persists. Remember you can stop
		1147	the watcher if you don't want to act on the event and neither want to
		1148	receive future events.
414		1149
415	In general you can register as many read and/or write event watchers oer	1150	In general you can register as many read and/or write event watchers per
416	fd as you want (as long as you don't confuse yourself). Setting all file	1151	fd as you want (as long as you don't confuse yourself). Setting all file
417	descriptors to non-blocking mode is also usually a good idea (but not	1152	descriptors to non-blocking mode is also usually a good idea (but not
418	required if you know what you are doing).	1153	required if you know what you are doing).
419		1154
420	You have to be careful with dup'ed file descriptors, though. Some backends	1155	If you cannot use non-blocking mode, then force the use of a
421	(the linux epoll backend is a notable example) cannot handle dup'ed file	1156	known-to-be-good backend (at the time of this writing, this includes only
422	descriptors correctly if you register interest in two or more fds pointing	1157	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
423	to the same file/socket etc. description.
424		1158
425	If you must do this, then force the use of a known-to-be-good backend	1159	Another thing you have to watch out for is that it is quite easy to
426	(at the time of this writing, this includes only EVMETHOD_SELECT and	1160	receive "spurious" readiness notifications, that is your callback might
427	EVMETHOD_POLL).	1161	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1162	because there is no data. Not only are some backends known to create a
		1163	lot of those (for example Solaris ports), it is very easy to get into
		1164	this situation even with a relatively standard program structure. Thus
		1165	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1166	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1167
		1168	If you cannot run the fd in non-blocking mode (for example you should
		1169	not play around with an Xlib connection), then you have to separately
		1170	re-test whether a file descriptor is really ready with a known-to-be good
		1171	interface such as poll (fortunately in our Xlib example, Xlib already
		1172	does this on its own, so its quite safe to use). Some people additionally
		1173	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1174	indefinitely.
		1175
		1176	But really, best use non-blocking mode.
		1177
		1178	=head3 The special problem of disappearing file descriptors
		1179
		1180	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1181	descriptor (either due to calling C<close> explicitly or any other means,
		1182	such as C<dup2>). The reason is that you register interest in some file
		1183	descriptor, but when it goes away, the operating system will silently drop
		1184	this interest. If another file descriptor with the same number then is
		1185	registered with libev, there is no efficient way to see that this is, in
		1186	fact, a different file descriptor.
		1187
		1188	To avoid having to explicitly tell libev about such cases, libev follows
		1189	the following policy: Each time C<ev_io_set> is being called, libev
		1190	will assume that this is potentially a new file descriptor, otherwise
		1191	it is assumed that the file descriptor stays the same. That means that
		1192	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1193	descriptor even if the file descriptor number itself did not change.
		1194
		1195	This is how one would do it normally anyway, the important point is that
		1196	the libev application should not optimise around libev but should leave
		1197	optimisations to libev.
		1198
		1199	=head3 The special problem of dup'ed file descriptors
		1200
		1201	Some backends (e.g. epoll), cannot register events for file descriptors,
		1202	but only events for the underlying file descriptions. That means when you
		1203	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1204	events for them, only one file descriptor might actually receive events.
		1205
		1206	There is no workaround possible except not registering events
		1207	for potentially C<dup ()>'ed file descriptors, or to resort to
		1208	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1209
		1210	=head3 The special problem of fork
		1211
		1212	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1213	useless behaviour. Libev fully supports fork, but needs to be told about
		1214	it in the child.
		1215
		1216	To support fork in your programs, you either have to call
		1217	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1218	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1219	C<EVBACKEND_POLL>.
		1220
		1221	=head3 The special problem of SIGPIPE
		1222
		1223	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1224	when writing to a pipe whose other end has been closed, your program gets
		1225	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1226	this is sensible behaviour, for daemons, this is usually undesirable.
		1227
		1228	So when you encounter spurious, unexplained daemon exits, make sure you
		1229	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1230	somewhere, as that would have given you a big clue).
		1231
		1232
		1233	=head3 Watcher-Specific Functions
428		1234
429	=over 4	1235	=over 4
430		1236
431	=item ev_io_init (ev_io *, callback, int fd, int events)	1237	=item ev_io_init (ev_io *, callback, int fd, int events)
432		1238
433	=item ev_io_set (ev_io *, int fd, int events)	1239	=item ev_io_set (ev_io *, int fd, int events)
434		1240
435	Configures an ev_io watcher. The fd is the file descriptor to rceeive	1241	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
436	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1242	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
437	EV_WRITE> to receive the given events.	1243	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1244
		1245	=item int fd [read-only]
		1246
		1247	The file descriptor being watched.
		1248
		1249	=item int events [read-only]
		1250
		1251	The events being watched.
438		1252
439	=back	1253	=back
440		1254
		1255	=head3 Examples
		1256
		1257	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1258	readable, but only once. Since it is likely line-buffered, you could
		1259	attempt to read a whole line in the callback.
		1260
		1261	static void
		1262	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1263	{
		1264	ev_io_stop (loop, w);
		1265	.. read from stdin here (or from w->fd) and handle any I/O errors
		1266	}
		1267
		1268	...
		1269	struct ev_loop *loop = ev_default_init (0);
		1270	struct ev_io stdin_readable;
		1271	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1272	ev_io_start (loop, &stdin_readable);
		1273	ev_loop (loop, 0);
		1274
		1275
441	=head2 struct ev_timer - relative and optionally recurring timeouts	1276	=head2 C<ev_timer> - relative and optionally repeating timeouts
442		1277
443	Timer watchers are simple relative timers that generate an event after a	1278	Timer watchers are simple relative timers that generate an event after a
444	given time, and optionally repeating in regular intervals after that.	1279	given time, and optionally repeating in regular intervals after that.
445		1280
446	The timers are based on real time, that is, if you register an event that	1281	The timers are based on real time, that is, if you register an event that
447	times out after an hour and youreset your system clock to last years	1282	times out after an hour and you reset your system clock to January last
448	time, it will still time out after (roughly) and hour. "Roughly" because	1283	year, it will still time out after (roughly) one hour. "Roughly" because
449	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1284	detecting time jumps is hard, and some inaccuracies are unavoidable (the
450	monotonic clock option helps a lot here).	1285	monotonic clock option helps a lot here).
451		1286
		1287	The callback is guaranteed to be invoked only I<after> its timeout has
		1288	passed, but if multiple timers become ready during the same loop iteration
		1289	then order of execution is undefined.
		1290
		1291	=head3 The special problem of time updates
		1292
		1293	Establishing the current time is a costly operation (it usually takes at
		1294	least two system calls): EV therefore updates its idea of the current
		1295	time only before and after C<ev_loop> collects new events, which causes a
		1296	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1297	lots of events in one iteration.
		1298
		1299	The relative timeouts are calculated relative to the C<ev_now ()>
		1300	time. This is usually the right thing as this timestamp refers to the time
		1301	of the event triggering whatever timeout you are modifying/starting. If
		1302	you suspect event processing to be delayed and you I<need> to base the
		1303	timeout on the current time, use something like this to adjust for this:
		1304
		1305	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1306
		1307	If the event loop is suspended for a long time, you can also force an
		1308	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		1309	()>.
		1310
		1311	=head3 Watcher-Specific Functions and Data Members
		1312
452	=over 4	1313	=over 4
453		1314
454	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1315	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
455		1316
456	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1317	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
457		1318
458	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1319	Configure the timer to trigger after C<after> seconds. If C<repeat>
459	C<0.>, then it will automatically be stopped. If it is positive, then the	1320	is C<0.>, then it will automatically be stopped once the timeout is
460	timer will automatically be configured to trigger again C<repeat> seconds	1321	reached. If it is positive, then the timer will automatically be
461	later, again, and again, until stopped manually.	1322	configured to trigger again C<repeat> seconds later, again, and again,
		1323	until stopped manually.
462		1324
463	The timer itself will do a best-effort at avoiding drift, that is, if you	1325	The timer itself will do a best-effort at avoiding drift, that is, if
464	configure a timer to trigger every 10 seconds, then it will trigger at	1326	you configure a timer to trigger every 10 seconds, then it will normally
465	exactly 10 second intervals. If, however, your program cannot keep up with	1327	trigger at exactly 10 second intervals. If, however, your program cannot
466	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1328	keep up with the timer (because it takes longer than those 10 seconds to
467	timer will not fire more than once per event loop iteration.	1329	do stuff) the timer will not fire more than once per event loop iteration.
468		1330
469	=item ev_timer_again (loop)	1331	=item ev_timer_again (loop, ev_timer *)
470		1332
471	This will act as if the timer timed out and restart it again if it is	1333	This will act as if the timer timed out and restart it again if it is
472	repeating. The exact semantics are:	1334	repeating. The exact semantics are:
473		1335
		1336	If the timer is pending, its pending status is cleared.
		1337
474	If the timer is started but nonrepeating, stop it.	1338	If the timer is started but non-repeating, stop it (as if it timed out).
475		1339
476	If the timer is repeating, either start it if necessary (with the repeat	1340	If the timer is repeating, either start it if necessary (with the
477	value), or reset the running timer to the repeat value.	1341	C<repeat> value), or reset the running timer to the C<repeat> value.
478		1342
479	This sounds a bit complicated, but here is a useful and typical	1343	This sounds a bit complicated, but here is a useful and typical
480	example: Imagine you have a tcp connection and you want a so-called idle	1344	example: Imagine you have a TCP connection and you want a so-called idle
481	timeout, that is, you want to be called when there have been, say, 60	1345	timeout, that is, you want to be called when there have been, say, 60
482	seconds of inactivity on the socket. The easiest way to do this is to	1346	seconds of inactivity on the socket. The easiest way to do this is to
483	configure an ev_timer with after=repeat=60 and calling ev_timer_again each	1347	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
484	time you successfully read or write some data. If you go into an idle	1348	C<ev_timer_again> each time you successfully read or write some data. If
485	state where you do not expect data to travel on the socket, you can stop	1349	you go into an idle state where you do not expect data to travel on the
486	the timer, and again will automatically restart it if need be.	1350	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1351	automatically restart it if need be.
		1352
		1353	That means you can ignore the C<after> value and C<ev_timer_start>
		1354	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1355
		1356	ev_timer_init (timer, callback, 0., 5.);
		1357	ev_timer_again (loop, timer);
		1358	...
		1359	timer->again = 17.;
		1360	ev_timer_again (loop, timer);
		1361	...
		1362	timer->again = 10.;
		1363	ev_timer_again (loop, timer);
		1364
		1365	This is more slightly efficient then stopping/starting the timer each time
		1366	you want to modify its timeout value.
		1367
		1368	Note, however, that it is often even more efficient to remember the
		1369	time of the last activity and let the timer time-out naturally. In the
		1370	callback, you then check whether the time-out is real, or, if there was
		1371	some activity, you reschedule the watcher to time-out in "last_activity +
		1372	timeout - ev_now ()" seconds.
		1373
		1374	=item ev_tstamp repeat [read-write]
		1375
		1376	The current C<repeat> value. Will be used each time the watcher times out
		1377	or C<ev_timer_again> is called, and determines the next timeout (if any),
		1378	which is also when any modifications are taken into account.
487		1379
488	=back	1380	=back
489		1381
		1382	=head3 Examples
		1383
		1384	Example: Create a timer that fires after 60 seconds.
		1385
		1386	static void
		1387	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1388	{
		1389	.. one minute over, w is actually stopped right here
		1390	}
		1391
		1392	struct ev_timer mytimer;
		1393	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1394	ev_timer_start (loop, &mytimer);
		1395
		1396	Example: Create a timeout timer that times out after 10 seconds of
		1397	inactivity.
		1398
		1399	static void
		1400	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1401	{
		1402	.. ten seconds without any activity
		1403	}
		1404
		1405	struct ev_timer mytimer;
		1406	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1407	ev_timer_again (&mytimer); /* start timer */
		1408	ev_loop (loop, 0);
		1409
		1410	// and in some piece of code that gets executed on any "activity":
		1411	// reset the timeout to start ticking again at 10 seconds
		1412	ev_timer_again (&mytimer);
		1413
		1414
490	=head2 ev_periodic - to cron or not to cron it	1415	=head2 C<ev_periodic> - to cron or not to cron?
491		1416
492	Periodic watchers are also timers of a kind, but they are very versatile	1417	Periodic watchers are also timers of a kind, but they are very versatile
493	(and unfortunately a bit complex).	1418	(and unfortunately a bit complex).
494		1419
495	Unlike ev_timer's, they are not based on real time (or relative time)	1420	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
496	but on wallclock time (absolute time). You can tell a periodic watcher	1421	but on wall clock time (absolute time). You can tell a periodic watcher
497	to trigger "at" some specific point in time. For example, if you tell a	1422	to trigger after some specific point in time. For example, if you tell a
498	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1423	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
499	+ 10.>) and then reset your system clock to the last year, then it will	1424	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1425	clock to January of the previous year, then it will take more than year
500	take a year to trigger the event (unlike an ev_timer, which would trigger	1426	to trigger the event (unlike an C<ev_timer>, which would still trigger
501	roughly 10 seconds later and of course not if you reset your system time	1427	roughly 10 seconds later as it uses a relative timeout).
502	again).
503		1428
504	They can also be used to implement vastly more complex timers, such as	1429	C<ev_periodic>s can also be used to implement vastly more complex timers,
505	triggering an event on eahc midnight, local time.	1430	such as triggering an event on each "midnight, local time", or other
		1431	complicated rules.
		1432
		1433	As with timers, the callback is guaranteed to be invoked only when the
		1434	time (C<at>) has passed, but if multiple periodic timers become ready
		1435	during the same loop iteration, then order of execution is undefined.
		1436
		1437	=head3 Watcher-Specific Functions and Data Members
506		1438
507	=over 4	1439	=over 4
508		1440
509	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1441	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
510		1442
511	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1443	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
512		1444
513	Lots of arguments, lets sort it out... There are basically three modes of	1445	Lots of arguments, lets sort it out... There are basically three modes of
514	operation, and we will explain them from simplest to complex:	1446	operation, and we will explain them from simplest to most complex:
515
516		1447
517	=over 4	1448	=over 4
518		1449
519	=item * absolute timer (interval = reschedule_cb = 0)	1450	=item * absolute timer (at = time, interval = reschedule_cb = 0)
520		1451
521	In this configuration the watcher triggers an event at the wallclock time	1452	In this configuration the watcher triggers an event after the wall clock
522	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1453	time C<at> has passed. It will not repeat and will not adjust when a time
523	that is, if it is to be run at January 1st 2011 then it will run when the	1454	jump occurs, that is, if it is to be run at January 1st 2011 then it will
524	system time reaches or surpasses this time.	1455	only run when the system clock reaches or surpasses this time.
525		1456
526	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1457	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
527		1458
528	In this mode the watcher will always be scheduled to time out at the next	1459	In this mode the watcher will always be scheduled to time out at the next
529	C<at + N * interval> time (for some integer N) and then repeat, regardless	1460	C<at + N * interval> time (for some integer N, which can also be negative)
530	of any time jumps.	1461	and then repeat, regardless of any time jumps.
531		1462
532	This can be used to create timers that do not drift with respect to system	1463	This can be used to create timers that do not drift with respect to the
533	time:	1464	system clock, for example, here is a C<ev_periodic> that triggers each
		1465	hour, on the hour:
534		1466
535	ev_periodic_set (&periodic, 0., 3600., 0);	1467	ev_periodic_set (&periodic, 0., 3600., 0);
536		1468
537	This doesn't mean there will always be 3600 seconds in between triggers,	1469	This doesn't mean there will always be 3600 seconds in between triggers,
538	but only that the the callback will be called when the system time shows a	1470	but only that the callback will be called when the system time shows a
539	full hour (UTC), or more correct, when the system time is evenly divisible	1471	full hour (UTC), or more correctly, when the system time is evenly divisible
540	by 3600.	1472	by 3600.
541		1473
542	Another way to think about it (for the mathematically inclined) is that	1474	Another way to think about it (for the mathematically inclined) is that
543	ev_periodic will try to run the callback in this mode at the next possible	1475	C<ev_periodic> will try to run the callback in this mode at the next possible
544	time where C<time = at (mod interval)>, regardless of any time jumps.	1476	time where C<time = at (mod interval)>, regardless of any time jumps.
545		1477
		1478	For numerical stability it is preferable that the C<at> value is near
		1479	C<ev_now ()> (the current time), but there is no range requirement for
		1480	this value, and in fact is often specified as zero.
		1481
		1482	Note also that there is an upper limit to how often a timer can fire (CPU
		1483	speed for example), so if C<interval> is very small then timing stability
		1484	will of course deteriorate. Libev itself tries to be exact to be about one
		1485	millisecond (if the OS supports it and the machine is fast enough).
		1486
546	=item * manual reschedule mode (reschedule_cb = callback)	1487	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
547		1488
548	In this mode the values for C<interval> and C<at> are both being	1489	In this mode the values for C<interval> and C<at> are both being
549	ignored. Instead, each time the periodic watcher gets scheduled, the	1490	ignored. Instead, each time the periodic watcher gets scheduled, the
550	reschedule callback will be called with the watcher as first, and the	1491	reschedule callback will be called with the watcher as first, and the
551	current time as second argument.	1492	current time as second argument.
552		1493
553	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1494	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
554	periodic watcher, ever, or make any event loop modificstions>. If you need	1495	ever, or make ANY event loop modifications whatsoever>.
555	to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
556		1496
		1497	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1498	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1499	only event loop modification you are allowed to do).
		1500
557	Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1501	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
558	ev_tstamp now)>, e.g.:	1502	*w, ev_tstamp now)>, e.g.:
559		1503
560	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1504	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
561	{	1505	{
562	return now + 60.;	1506	return now + 60.;
563	}	1507	}
…		…
565	It must return the next time to trigger, based on the passed time value	1509	It must return the next time to trigger, based on the passed time value
566	(that is, the lowest time value larger than to the second argument). It	1510	(that is, the lowest time value larger than to the second argument). It
567	will usually be called just before the callback will be triggered, but	1511	will usually be called just before the callback will be triggered, but
568	might be called at other times, too.	1512	might be called at other times, too.
569		1513
		1514	NOTE: I<< This callback must always return a time that is higher than or
		1515	equal to the passed C<now> value >>.
		1516
570	This can be used to create very complex timers, such as a timer that	1517	This can be used to create very complex timers, such as a timer that
571	triggers on each midnight, local time. To do this, you would calculate the	1518	triggers on "next midnight, local time". To do this, you would calculate the
572	next midnight after C<now> and return the timestamp value for this. How you do this	1519	next midnight after C<now> and return the timestamp value for this. How
573	is, again, up to you (but it is not trivial).	1520	you do this is, again, up to you (but it is not trivial, which is the main
		1521	reason I omitted it as an example).
574		1522
575	=back	1523	=back
576		1524
577	=item ev_periodic_again (loop, ev_periodic *)	1525	=item ev_periodic_again (loop, ev_periodic *)
578		1526
579	Simply stops and restarts the periodic watcher again. This is only useful	1527	Simply stops and restarts the periodic watcher again. This is only useful
580	when you changed some parameters or the reschedule callback would return	1528	when you changed some parameters or the reschedule callback would return
581	a different time than the last time it was called (e.g. in a crond like	1529	a different time than the last time it was called (e.g. in a crond like
582	program when the crontabs have changed).	1530	program when the crontabs have changed).
583		1531
		1532	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1533
		1534	When active, returns the absolute time that the watcher is supposed to
		1535	trigger next.
		1536
		1537	=item ev_tstamp offset [read-write]
		1538
		1539	When repeating, this contains the offset value, otherwise this is the
		1540	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1541
		1542	Can be modified any time, but changes only take effect when the periodic
		1543	timer fires or C<ev_periodic_again> is being called.
		1544
		1545	=item ev_tstamp interval [read-write]
		1546
		1547	The current interval value. Can be modified any time, but changes only
		1548	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1549	called.
		1550
		1551	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1552
		1553	The current reschedule callback, or C<0>, if this functionality is
		1554	switched off. Can be changed any time, but changes only take effect when
		1555	the periodic timer fires or C<ev_periodic_again> is being called.
		1556
584	=back	1557	=back
585		1558
		1559	=head3 Examples
		1560
		1561	Example: Call a callback every hour, or, more precisely, whenever the
		1562	system time is divisible by 3600. The callback invocation times have
		1563	potentially a lot of jitter, but good long-term stability.
		1564
		1565	static void
		1566	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1567	{
		1568	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1569	}
		1570
		1571	struct ev_periodic hourly_tick;
		1572	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1573	ev_periodic_start (loop, &hourly_tick);
		1574
		1575	Example: The same as above, but use a reschedule callback to do it:
		1576
		1577	#include <math.h>
		1578
		1579	static ev_tstamp
		1580	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1581	{
		1582	return now + (3600. - fmod (now, 3600.));
		1583	}
		1584
		1585	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1586
		1587	Example: Call a callback every hour, starting now:
		1588
		1589	struct ev_periodic hourly_tick;
		1590	ev_periodic_init (&hourly_tick, clock_cb,
		1591	fmod (ev_now (loop), 3600.), 3600., 0);
		1592	ev_periodic_start (loop, &hourly_tick);
		1593
		1594
586	=head2 ev_signal - signal me when a signal gets signalled	1595	=head2 C<ev_signal> - signal me when a signal gets signalled!
587		1596
588	Signal watchers will trigger an event when the process receives a specific	1597	Signal watchers will trigger an event when the process receives a specific
589	signal one or more times. Even though signals are very asynchronous, libev	1598	signal one or more times. Even though signals are very asynchronous, libev
590	will try its best to deliver signals synchronously, i.e. as part of the	1599	will try it's best to deliver signals synchronously, i.e. as part of the
591	normal event processing, like any other event.	1600	normal event processing, like any other event.
592		1601
		1602	If you want signals asynchronously, just use C<sigaction> as you would
		1603	do without libev and forget about sharing the signal. You can even use
		1604	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1605
593	You cna configure as many watchers as you like per signal. Only when the	1606	You can configure as many watchers as you like per signal. Only when the
594	first watcher gets started will libev actually register a signal watcher	1607	first watcher gets started will libev actually register a signal handler
595	with the kernel (thus it coexists with your own signal handlers as long	1608	with the kernel (thus it coexists with your own signal handlers as long as
596	as you don't register any with libev). Similarly, when the last signal	1609	you don't register any with libev for the same signal). Similarly, when
597	watcher for a signal is stopped libev will reset the signal handler to	1610	the last signal watcher for a signal is stopped, libev will reset the
598	SIG_DFL (regardless of what it was set to before).	1611	signal handler to SIG_DFL (regardless of what it was set to before).
		1612
		1613	If possible and supported, libev will install its handlers with
		1614	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1615	interrupted. If you have a problem with system calls getting interrupted by
		1616	signals you can block all signals in an C<ev_check> watcher and unblock
		1617	them in an C<ev_prepare> watcher.
		1618
		1619	=head3 Watcher-Specific Functions and Data Members
599		1620
600	=over 4	1621	=over 4
601		1622
602	=item ev_signal_init (ev_signal *, callback, int signum)	1623	=item ev_signal_init (ev_signal *, callback, int signum)
603		1624
604	=item ev_signal_set (ev_signal *, int signum)	1625	=item ev_signal_set (ev_signal *, int signum)
605		1626
606	Configures the watcher to trigger on the given signal number (usually one	1627	Configures the watcher to trigger on the given signal number (usually one
607	of the C<SIGxxx> constants).	1628	of the C<SIGxxx> constants).
608		1629
		1630	=item int signum [read-only]
		1631
		1632	The signal the watcher watches out for.
		1633
609	=back	1634	=back
610		1635
		1636	=head3 Examples
		1637
		1638	Example: Try to exit cleanly on SIGINT.
		1639
		1640	static void
		1641	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1642	{
		1643	ev_unloop (loop, EVUNLOOP_ALL);
		1644	}
		1645
		1646	struct ev_signal signal_watcher;
		1647	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1648	ev_signal_start (loop, &signal_watcher);
		1649
		1650
611	=head2 ev_child - wait for pid status changes	1651	=head2 C<ev_child> - watch out for process status changes
612		1652
613	Child watchers trigger when your process receives a SIGCHLD in response to	1653	Child watchers trigger when your process receives a SIGCHLD in response to
614	some child status changes (most typically when a child of yours dies).	1654	some child status changes (most typically when a child of yours dies or
		1655	exits). It is permissible to install a child watcher I<after> the child
		1656	has been forked (which implies it might have already exited), as long
		1657	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1658	forking and then immediately registering a watcher for the child is fine,
		1659	but forking and registering a watcher a few event loop iterations later is
		1660	not.
		1661
		1662	Only the default event loop is capable of handling signals, and therefore
		1663	you can only register child watchers in the default event loop.
		1664
		1665	=head3 Process Interaction
		1666
		1667	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1668	initialised. This is necessary to guarantee proper behaviour even if
		1669	the first child watcher is started after the child exits. The occurrence
		1670	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1671	synchronously as part of the event loop processing. Libev always reaps all
		1672	children, even ones not watched.
		1673
		1674	=head3 Overriding the Built-In Processing
		1675
		1676	Libev offers no special support for overriding the built-in child
		1677	processing, but if your application collides with libev's default child
		1678	handler, you can override it easily by installing your own handler for
		1679	C<SIGCHLD> after initialising the default loop, and making sure the
		1680	default loop never gets destroyed. You are encouraged, however, to use an
		1681	event-based approach to child reaping and thus use libev's support for
		1682	that, so other libev users can use C<ev_child> watchers freely.
		1683
		1684	=head3 Stopping the Child Watcher
		1685
		1686	Currently, the child watcher never gets stopped, even when the
		1687	child terminates, so normally one needs to stop the watcher in the
		1688	callback. Future versions of libev might stop the watcher automatically
		1689	when a child exit is detected.
		1690
		1691	=head3 Watcher-Specific Functions and Data Members
615		1692
616	=over 4	1693	=over 4
617		1694
618	=item ev_child_init (ev_child *, callback, int pid)	1695	=item ev_child_init (ev_child *, callback, int pid, int trace)
619		1696
620	=item ev_child_set (ev_child *, int pid)	1697	=item ev_child_set (ev_child *, int pid, int trace)
621		1698
622	Configures the watcher to wait for status changes of process C<pid> (or	1699	Configures the watcher to wait for status changes of process C<pid> (or
623	I<any> process if C<pid> is specified as C<0>). The callback can look	1700	I<any> process if C<pid> is specified as C<0>). The callback can look
624	at the C<rstatus> member of the C<ev_child> watcher structure to see	1701	at the C<rstatus> member of the C<ev_child> watcher structure to see
625	the status word (use the macros from C<sys/wait.h>). The C<rpid> member	1702	the status word (use the macros from C<sys/wait.h> and see your systems
626	contains the pid of the process causing the status change.	1703	C<waitpid> documentation). The C<rpid> member contains the pid of the
		1704	process causing the status change. C<trace> must be either C<0> (only
		1705	activate the watcher when the process terminates) or C<1> (additionally
		1706	activate the watcher when the process is stopped or continued).
		1707
		1708	=item int pid [read-only]
		1709
		1710	The process id this watcher watches out for, or C<0>, meaning any process id.
		1711
		1712	=item int rpid [read-write]
		1713
		1714	The process id that detected a status change.
		1715
		1716	=item int rstatus [read-write]
		1717
		1718	The process exit/trace status caused by C<rpid> (see your systems
		1719	C<waitpid> and C<sys/wait.h> documentation for details).
627		1720
628	=back	1721	=back
629		1722
		1723	=head3 Examples
		1724
		1725	Example: C<fork()> a new process and install a child handler to wait for
		1726	its completion.
		1727
		1728	ev_child cw;
		1729
		1730	static void
		1731	child_cb (EV_P_ struct ev_child *w, int revents)
		1732	{
		1733	ev_child_stop (EV_A_ w);
		1734	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1735	}
		1736
		1737	pid_t pid = fork ();
		1738
		1739	if (pid < 0)
		1740	// error
		1741	else if (pid == 0)
		1742	{
		1743	// the forked child executes here
		1744	exit (1);
		1745	}
		1746	else
		1747	{
		1748	ev_child_init (&cw, child_cb, pid, 0);
		1749	ev_child_start (EV_DEFAULT_ &cw);
		1750	}
		1751
		1752
		1753	=head2 C<ev_stat> - did the file attributes just change?
		1754
		1755	This watches a file system path for attribute changes. That is, it calls
		1756	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1757	compared to the last time, invoking the callback if it did.
		1758
		1759	The path does not need to exist: changing from "path exists" to "path does
		1760	not exist" is a status change like any other. The condition "path does
		1761	not exist" is signified by the C<st_nlink> field being zero (which is
		1762	otherwise always forced to be at least one) and all the other fields of
		1763	the stat buffer having unspecified contents.
		1764
		1765	The path I<should> be absolute and I<must not> end in a slash. If it is
		1766	relative and your working directory changes, the behaviour is undefined.
		1767
		1768	Since there is no standard kernel interface to do this, the portable
		1769	implementation simply calls C<stat (2)> regularly on the path to see if
		1770	it changed somehow. You can specify a recommended polling interval for
		1771	this case. If you specify a polling interval of C<0> (highly recommended!)
		1772	then a I<suitable, unspecified default> value will be used (which
		1773	you can expect to be around five seconds, although this might change
		1774	dynamically). Libev will also impose a minimum interval which is currently
		1775	around C<0.1>, but thats usually overkill.
		1776
		1777	This watcher type is not meant for massive numbers of stat watchers,
		1778	as even with OS-supported change notifications, this can be
		1779	resource-intensive.
		1780
		1781	At the time of this writing, the only OS-specific interface implemented
		1782	is the Linux inotify interface (implementing kqueue support is left as
		1783	an exercise for the reader. Note, however, that the author sees no way
		1784	of implementing C<ev_stat> semantics with kqueue).
		1785
		1786	=head3 ABI Issues (Largefile Support)
		1787
		1788	Libev by default (unless the user overrides this) uses the default
		1789	compilation environment, which means that on systems with large file
		1790	support disabled by default, you get the 32 bit version of the stat
		1791	structure. When using the library from programs that change the ABI to
		1792	use 64 bit file offsets the programs will fail. In that case you have to
		1793	compile libev with the same flags to get binary compatibility. This is
		1794	obviously the case with any flags that change the ABI, but the problem is
		1795	most noticeably disabled with ev_stat and large file support.
		1796
		1797	The solution for this is to lobby your distribution maker to make large
		1798	file interfaces available by default (as e.g. FreeBSD does) and not
		1799	optional. Libev cannot simply switch on large file support because it has
		1800	to exchange stat structures with application programs compiled using the
		1801	default compilation environment.
		1802
		1803	=head3 Inotify and Kqueue
		1804
		1805	When C<inotify (7)> support has been compiled into libev (generally
		1806	only available with Linux 2.6.25 or above due to bugs in earlier
		1807	implementations) and present at runtime, it will be used to speed up
		1808	change detection where possible. The inotify descriptor will be created
		1809	lazily when the first C<ev_stat> watcher is being started.
		1810
		1811	Inotify presence does not change the semantics of C<ev_stat> watchers
		1812	except that changes might be detected earlier, and in some cases, to avoid
		1813	making regular C<stat> calls. Even in the presence of inotify support
		1814	there are many cases where libev has to resort to regular C<stat> polling,
		1815	but as long as the path exists, libev usually gets away without polling.
		1816
		1817	There is no support for kqueue, as apparently it cannot be used to
		1818	implement this functionality, due to the requirement of having a file
		1819	descriptor open on the object at all times, and detecting renames, unlinks
		1820	etc. is difficult.
		1821
		1822	=head3 The special problem of stat time resolution
		1823
		1824	The C<stat ()> system call only supports full-second resolution portably, and
		1825	even on systems where the resolution is higher, most file systems still
		1826	only support whole seconds.
		1827
		1828	That means that, if the time is the only thing that changes, you can
		1829	easily miss updates: on the first update, C<ev_stat> detects a change and
		1830	calls your callback, which does something. When there is another update
		1831	within the same second, C<ev_stat> will be unable to detect unless the
		1832	stat data does change in other ways (e.g. file size).
		1833
		1834	The solution to this is to delay acting on a change for slightly more
		1835	than a second (or till slightly after the next full second boundary), using
		1836	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1837	ev_timer_again (loop, w)>).
		1838
		1839	The C<.02> offset is added to work around small timing inconsistencies
		1840	of some operating systems (where the second counter of the current time
		1841	might be be delayed. One such system is the Linux kernel, where a call to
		1842	C<gettimeofday> might return a timestamp with a full second later than
		1843	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1844	update file times then there will be a small window where the kernel uses
		1845	the previous second to update file times but libev might already execute
		1846	the timer callback).
		1847
		1848	=head3 Watcher-Specific Functions and Data Members
		1849
		1850	=over 4
		1851
		1852	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1853
		1854	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1855
		1856	Configures the watcher to wait for status changes of the given
		1857	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1858	be detected and should normally be specified as C<0> to let libev choose
		1859	a suitable value. The memory pointed to by C<path> must point to the same
		1860	path for as long as the watcher is active.
		1861
		1862	The callback will receive an C<EV_STAT> event when a change was detected,
		1863	relative to the attributes at the time the watcher was started (or the
		1864	last change was detected).
		1865
		1866	=item ev_stat_stat (loop, ev_stat *)
		1867
		1868	Updates the stat buffer immediately with new values. If you change the
		1869	watched path in your callback, you could call this function to avoid
		1870	detecting this change (while introducing a race condition if you are not
		1871	the only one changing the path). Can also be useful simply to find out the
		1872	new values.
		1873
		1874	=item ev_statdata attr [read-only]
		1875
		1876	The most-recently detected attributes of the file. Although the type is
		1877	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1878	suitable for your system, but you can only rely on the POSIX-standardised
		1879	members to be present. If the C<st_nlink> member is C<0>, then there was
		1880	some error while C<stat>ing the file.
		1881
		1882	=item ev_statdata prev [read-only]
		1883
		1884	The previous attributes of the file. The callback gets invoked whenever
		1885	C<prev> != C<attr>, or, more precisely, one or more of these members
		1886	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1887	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1888
		1889	=item ev_tstamp interval [read-only]
		1890
		1891	The specified interval.
		1892
		1893	=item const char *path [read-only]
		1894
		1895	The file system path that is being watched.
		1896
		1897	=back
		1898
		1899	=head3 Examples
		1900
		1901	Example: Watch C</etc/passwd> for attribute changes.
		1902
		1903	static void
		1904	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1905	{
		1906	/* /etc/passwd changed in some way */
		1907	if (w->attr.st_nlink)
		1908	{
		1909	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1910	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1911	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1912	}
		1913	else
		1914	/* you shalt not abuse printf for puts */
		1915	puts ("wow, /etc/passwd is not there, expect problems. "
		1916	"if this is windows, they already arrived\n");
		1917	}
		1918
		1919	...
		1920	ev_stat passwd;
		1921
		1922	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1923	ev_stat_start (loop, &passwd);
		1924
		1925	Example: Like above, but additionally use a one-second delay so we do not
		1926	miss updates (however, frequent updates will delay processing, too, so
		1927	one might do the work both on C<ev_stat> callback invocation I<and> on
		1928	C<ev_timer> callback invocation).
		1929
		1930	static ev_stat passwd;
		1931	static ev_timer timer;
		1932
		1933	static void
		1934	timer_cb (EV_P_ ev_timer *w, int revents)
		1935	{
		1936	ev_timer_stop (EV_A_ w);
		1937
		1938	/* now it's one second after the most recent passwd change */
		1939	}
		1940
		1941	static void
		1942	stat_cb (EV_P_ ev_stat *w, int revents)
		1943	{
		1944	/* reset the one-second timer */
		1945	ev_timer_again (EV_A_ &timer);
		1946	}
		1947
		1948	...
		1949	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1950	ev_stat_start (loop, &passwd);
		1951	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1952
		1953
630	=head2 ev_idle - when you've got nothing better to do	1954	=head2 C<ev_idle> - when you've got nothing better to do...
631		1955
632	Idle watchers trigger events when there are no other I/O or timer (or	1956	Idle watchers trigger events when no other events of the same or higher
633	periodic) events pending. That is, as long as your process is busy	1957	priority are pending (prepare, check and other idle watchers do not count
634	handling sockets or timeouts it will not be called. But when your process	1958	as receiving "events").
635	is idle all idle watchers are being called again and again - until	1959
		1960	That is, as long as your process is busy handling sockets or timeouts
		1961	(or even signals, imagine) of the same or higher priority it will not be
		1962	triggered. But when your process is idle (or only lower-priority watchers
		1963	are pending), the idle watchers are being called once per event loop
636	stopped, that is, or your process receives more events.	1964	iteration - until stopped, that is, or your process receives more events
		1965	and becomes busy again with higher priority stuff.
637		1966
638	The most noteworthy effect is that as long as any idle watchers are	1967	The most noteworthy effect is that as long as any idle watchers are
639	active, the process will not block when waiting for new events.	1968	active, the process will not block when waiting for new events.
640		1969
641	Apart from keeping your process non-blocking (which is a useful	1970	Apart from keeping your process non-blocking (which is a useful
642	effect on its own sometimes), idle watchers are a good place to do	1971	effect on its own sometimes), idle watchers are a good place to do
643	"pseudo-background processing", or delay processing stuff to after the	1972	"pseudo-background processing", or delay processing stuff to after the
644	event loop has handled all outstanding events.	1973	event loop has handled all outstanding events.
645		1974
		1975	=head3 Watcher-Specific Functions and Data Members
		1976
646	=over 4	1977	=over 4
647		1978
648	=item ev_idle_init (ev_signal *, callback)	1979	=item ev_idle_init (ev_signal *, callback)
649		1980
650	Initialises and configures the idle watcher - it has no parameters of any	1981	Initialises and configures the idle watcher - it has no parameters of any
651	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1982	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
652	believe me.	1983	believe me.
653		1984
654	=back	1985	=back
655		1986
656	=head2 prepare and check - your hooks into the event loop	1987	=head3 Examples
657		1988
		1989	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1990	callback, free it. Also, use no error checking, as usual.
		1991
		1992	static void
		1993	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1994	{
		1995	free (w);
		1996	// now do something you wanted to do when the program has
		1997	// no longer anything immediate to do.
		1998	}
		1999
		2000	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		2001	ev_idle_init (idle_watcher, idle_cb);
		2002	ev_idle_start (loop, idle_cb);
		2003
		2004
		2005	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		2006
658	Prepare and check watchers usually (but not always) are used in	2007	Prepare and check watchers are usually (but not always) used in pairs:
659	tandom. Prepare watchers get invoked before the process blocks and check	2008	prepare watchers get invoked before the process blocks and check watchers
660	watchers afterwards.	2009	afterwards.
661		2010
		2011	You I<must not> call C<ev_loop> or similar functions that enter
		2012	the current event loop from either C<ev_prepare> or C<ev_check>
		2013	watchers. Other loops than the current one are fine, however. The
		2014	rationale behind this is that you do not need to check for recursion in
		2015	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2016	C<ev_check> so if you have one watcher of each kind they will always be
		2017	called in pairs bracketing the blocking call.
		2018
662	Their main purpose is to integrate other event mechanisms into libev. This	2019	Their main purpose is to integrate other event mechanisms into libev and
663	could be used, for example, to track variable changes, implement your own	2020	their use is somewhat advanced. They could be used, for example, to track
664	watchers, integrate net-snmp or a coroutine library and lots more.	2021	variable changes, implement your own watchers, integrate net-snmp or a
		2022	coroutine library and lots more. They are also occasionally useful if
		2023	you cache some data and want to flush it before blocking (for example,
		2024	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2025	watcher).
665		2026
666	This is done by examining in each prepare call which file descriptors need	2027	This is done by examining in each prepare call which file descriptors
667	to be watched by the other library, registering ev_io watchers for them	2028	need to be watched by the other library, registering C<ev_io> watchers
668	and starting an ev_timer watcher for any timeouts (many libraries provide	2029	for them and starting an C<ev_timer> watcher for any timeouts (many
669	just this functionality). Then, in the check watcher you check for any	2030	libraries provide exactly this functionality). Then, in the check watcher,
670	events that occured (by making your callbacks set soem flags for example)	2031	you check for any events that occurred (by checking the pending status
671	and call back into the library.	2032	of all watchers and stopping them) and call back into the library. The
		2033	I/O and timer callbacks will never actually be called (but must be valid
		2034	nevertheless, because you never know, you know?).
672		2035
673	As another example, the perl Coro module uses these hooks to integrate	2036	As another example, the Perl Coro module uses these hooks to integrate
674	coroutines into libev programs, by yielding to other active coroutines	2037	coroutines into libev programs, by yielding to other active coroutines
675	during each prepare and only letting the process block if no coroutines	2038	during each prepare and only letting the process block if no coroutines
676	are ready to run.	2039	are ready to run (it's actually more complicated: it only runs coroutines
		2040	with priority higher than or equal to the event loop and one coroutine
		2041	of lower priority, but only once, using idle watchers to keep the event
		2042	loop from blocking if lower-priority coroutines are active, thus mapping
		2043	low-priority coroutines to idle/background tasks).
		2044
		2045	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2046	priority, to ensure that they are being run before any other watchers
		2047	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2048
		2049	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2050	activate ("feed") events into libev. While libev fully supports this, they
		2051	might get executed before other C<ev_check> watchers did their job. As
		2052	C<ev_check> watchers are often used to embed other (non-libev) event
		2053	loops those other event loops might be in an unusable state until their
		2054	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2055	others).
		2056
		2057	=head3 Watcher-Specific Functions and Data Members
677		2058
678	=over 4	2059	=over 4
679		2060
680	=item ev_prepare_init (ev_prepare *, callback)	2061	=item ev_prepare_init (ev_prepare *, callback)
681		2062
682	=item ev_check_init (ev_check *, callback)	2063	=item ev_check_init (ev_check *, callback)
683		2064
684	Initialises and configures the prepare or check watcher - they have no	2065	Initialises and configures the prepare or check watcher - they have no
685	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2066	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
686	macros, but using them is utterly, utterly pointless.	2067	macros, but using them is utterly, utterly, utterly and completely
		2068	pointless.
687		2069
688	=back	2070	=back
689		2071
		2072	=head3 Examples
		2073
		2074	There are a number of principal ways to embed other event loops or modules
		2075	into libev. Here are some ideas on how to include libadns into libev
		2076	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2077	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2078	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2079	Glib event loop).
		2080
		2081	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2082	and in a check watcher, destroy them and call into libadns. What follows
		2083	is pseudo-code only of course. This requires you to either use a low
		2084	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2085	the callbacks for the IO/timeout watchers might not have been called yet.
		2086
		2087	static ev_io iow [nfd];
		2088	static ev_timer tw;
		2089
		2090	static void
		2091	io_cb (ev_loop *loop, ev_io *w, int revents)
		2092	{
		2093	}
		2094
		2095	// create io watchers for each fd and a timer before blocking
		2096	static void
		2097	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		2098	{
		2099	int timeout = 3600000;
		2100	struct pollfd fds [nfd];
		2101	// actual code will need to loop here and realloc etc.
		2102	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2103
		2104	/* the callback is illegal, but won't be called as we stop during check */
		2105	ev_timer_init (&tw, 0, timeout * 1e-3);
		2106	ev_timer_start (loop, &tw);
		2107
		2108	// create one ev_io per pollfd
		2109	for (int i = 0; i < nfd; ++i)
		2110	{
		2111	ev_io_init (iow + i, io_cb, fds [i].fd,
		2112	((fds [i].events & POLLIN ? EV_READ : 0)
		2113	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2114
		2115	fds [i].revents = 0;
		2116	ev_io_start (loop, iow + i);
		2117	}
		2118	}
		2119
		2120	// stop all watchers after blocking
		2121	static void
		2122	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		2123	{
		2124	ev_timer_stop (loop, &tw);
		2125
		2126	for (int i = 0; i < nfd; ++i)
		2127	{
		2128	// set the relevant poll flags
		2129	// could also call adns_processreadable etc. here
		2130	struct pollfd *fd = fds + i;
		2131	int revents = ev_clear_pending (iow + i);
		2132	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2133	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2134
		2135	// now stop the watcher
		2136	ev_io_stop (loop, iow + i);
		2137	}
		2138
		2139	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2140	}
		2141
		2142	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2143	in the prepare watcher and would dispose of the check watcher.
		2144
		2145	Method 3: If the module to be embedded supports explicit event
		2146	notification (libadns does), you can also make use of the actual watcher
		2147	callbacks, and only destroy/create the watchers in the prepare watcher.
		2148
		2149	static void
		2150	timer_cb (EV_P_ ev_timer *w, int revents)
		2151	{
		2152	adns_state ads = (adns_state)w->data;
		2153	update_now (EV_A);
		2154
		2155	adns_processtimeouts (ads, &tv_now);
		2156	}
		2157
		2158	static void
		2159	io_cb (EV_P_ ev_io *w, int revents)
		2160	{
		2161	adns_state ads = (adns_state)w->data;
		2162	update_now (EV_A);
		2163
		2164	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2165	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2166	}
		2167
		2168	// do not ever call adns_afterpoll
		2169
		2170	Method 4: Do not use a prepare or check watcher because the module you
		2171	want to embed is not flexible enough to support it. Instead, you can
		2172	override their poll function. The drawback with this solution is that the
		2173	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2174	this approach, effectively embedding EV as a client into the horrible
		2175	libglib event loop.
		2176
		2177	static gint
		2178	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2179	{
		2180	int got_events = 0;
		2181
		2182	for (n = 0; n < nfds; ++n)
		2183	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2184
		2185	if (timeout >= 0)
		2186	// create/start timer
		2187
		2188	// poll
		2189	ev_loop (EV_A_ 0);
		2190
		2191	// stop timer again
		2192	if (timeout >= 0)
		2193	ev_timer_stop (EV_A_ &to);
		2194
		2195	// stop io watchers again - their callbacks should have set
		2196	for (n = 0; n < nfds; ++n)
		2197	ev_io_stop (EV_A_ iow [n]);
		2198
		2199	return got_events;
		2200	}
		2201
		2202
		2203	=head2 C<ev_embed> - when one backend isn't enough...
		2204
		2205	This is a rather advanced watcher type that lets you embed one event loop
		2206	into another (currently only C<ev_io> events are supported in the embedded
		2207	loop, other types of watchers might be handled in a delayed or incorrect
		2208	fashion and must not be used).
		2209
		2210	There are primarily two reasons you would want that: work around bugs and
		2211	prioritise I/O.
		2212
		2213	As an example for a bug workaround, the kqueue backend might only support
		2214	sockets on some platform, so it is unusable as generic backend, but you
		2215	still want to make use of it because you have many sockets and it scales
		2216	so nicely. In this case, you would create a kqueue-based loop and embed
		2217	it into your default loop (which might use e.g. poll). Overall operation
		2218	will be a bit slower because first libev has to call C<poll> and then
		2219	C<kevent>, but at least you can use both mechanisms for what they are
		2220	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2221
		2222	As for prioritising I/O: under rare circumstances you have the case where
		2223	some fds have to be watched and handled very quickly (with low latency),
		2224	and even priorities and idle watchers might have too much overhead. In
		2225	this case you would put all the high priority stuff in one loop and all
		2226	the rest in a second one, and embed the second one in the first.
		2227
		2228	As long as the watcher is active, the callback will be invoked every time
		2229	there might be events pending in the embedded loop. The callback must then
		2230	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2231	their callbacks (you could also start an idle watcher to give the embedded
		2232	loop strictly lower priority for example). You can also set the callback
		2233	to C<0>, in which case the embed watcher will automatically execute the
		2234	embedded loop sweep.
		2235
		2236	As long as the watcher is started it will automatically handle events. The
		2237	callback will be invoked whenever some events have been handled. You can
		2238	set the callback to C<0> to avoid having to specify one if you are not
		2239	interested in that.
		2240
		2241	Also, there have not currently been made special provisions for forking:
		2242	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2243	but you will also have to stop and restart any C<ev_embed> watchers
		2244	yourself - but you can use a fork watcher to handle this automatically,
		2245	and future versions of libev might do just that.
		2246
		2247	Unfortunately, not all backends are embeddable: only the ones returned by
		2248	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2249	portable one.
		2250
		2251	So when you want to use this feature you will always have to be prepared
		2252	that you cannot get an embeddable loop. The recommended way to get around
		2253	this is to have a separate variables for your embeddable loop, try to
		2254	create it, and if that fails, use the normal loop for everything.
		2255
		2256	=head3 C<ev_embed> and fork
		2257
		2258	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2259	automatically be applied to the embedded loop as well, so no special
		2260	fork handling is required in that case. When the watcher is not running,
		2261	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2262	as applicable.
		2263
		2264	=head3 Watcher-Specific Functions and Data Members
		2265
		2266	=over 4
		2267
		2268	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2269
		2270	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2271
		2272	Configures the watcher to embed the given loop, which must be
		2273	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2274	invoked automatically, otherwise it is the responsibility of the callback
		2275	to invoke it (it will continue to be called until the sweep has been done,
		2276	if you do not want that, you need to temporarily stop the embed watcher).
		2277
		2278	=item ev_embed_sweep (loop, ev_embed *)
		2279
		2280	Make a single, non-blocking sweep over the embedded loop. This works
		2281	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2282	appropriate way for embedded loops.
		2283
		2284	=item struct ev_loop *other [read-only]
		2285
		2286	The embedded event loop.
		2287
		2288	=back
		2289
		2290	=head3 Examples
		2291
		2292	Example: Try to get an embeddable event loop and embed it into the default
		2293	event loop. If that is not possible, use the default loop. The default
		2294	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2295	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2296	used).
		2297
		2298	struct ev_loop *loop_hi = ev_default_init (0);
		2299	struct ev_loop *loop_lo = 0;
		2300	struct ev_embed embed;
		2301
		2302	// see if there is a chance of getting one that works
		2303	// (remember that a flags value of 0 means autodetection)
		2304	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2305	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2306	: 0;
		2307
		2308	// if we got one, then embed it, otherwise default to loop_hi
		2309	if (loop_lo)
		2310	{
		2311	ev_embed_init (&embed, 0, loop_lo);
		2312	ev_embed_start (loop_hi, &embed);
		2313	}
		2314	else
		2315	loop_lo = loop_hi;
		2316
		2317	Example: Check if kqueue is available but not recommended and create
		2318	a kqueue backend for use with sockets (which usually work with any
		2319	kqueue implementation). Store the kqueue/socket-only event loop in
		2320	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2321
		2322	struct ev_loop *loop = ev_default_init (0);
		2323	struct ev_loop *loop_socket = 0;
		2324	struct ev_embed embed;
		2325
		2326	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2327	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2328	{
		2329	ev_embed_init (&embed, 0, loop_socket);
		2330	ev_embed_start (loop, &embed);
		2331	}
		2332
		2333	if (!loop_socket)
		2334	loop_socket = loop;
		2335
		2336	// now use loop_socket for all sockets, and loop for everything else
		2337
		2338
		2339	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2340
		2341	Fork watchers are called when a C<fork ()> was detected (usually because
		2342	whoever is a good citizen cared to tell libev about it by calling
		2343	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2344	event loop blocks next and before C<ev_check> watchers are being called,
		2345	and only in the child after the fork. If whoever good citizen calling
		2346	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2347	handlers will be invoked, too, of course.
		2348
		2349	=head3 Watcher-Specific Functions and Data Members
		2350
		2351	=over 4
		2352
		2353	=item ev_fork_init (ev_signal *, callback)
		2354
		2355	Initialises and configures the fork watcher - it has no parameters of any
		2356	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2357	believe me.
		2358
		2359	=back
		2360
		2361
		2362	=head2 C<ev_async> - how to wake up another event loop
		2363
		2364	In general, you cannot use an C<ev_loop> from multiple threads or other
		2365	asynchronous sources such as signal handlers (as opposed to multiple event
		2366	loops - those are of course safe to use in different threads).
		2367
		2368	Sometimes, however, you need to wake up another event loop you do not
		2369	control, for example because it belongs to another thread. This is what
		2370	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2371	can signal it by calling C<ev_async_send>, which is thread- and signal
		2372	safe.
		2373
		2374	This functionality is very similar to C<ev_signal> watchers, as signals,
		2375	too, are asynchronous in nature, and signals, too, will be compressed
		2376	(i.e. the number of callback invocations may be less than the number of
		2377	C<ev_async_sent> calls).
		2378
		2379	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2380	just the default loop.
		2381
		2382	=head3 Queueing
		2383
		2384	C<ev_async> does not support queueing of data in any way. The reason
		2385	is that the author does not know of a simple (or any) algorithm for a
		2386	multiple-writer-single-reader queue that works in all cases and doesn't
		2387	need elaborate support such as pthreads.
		2388
		2389	That means that if you want to queue data, you have to provide your own
		2390	queue. But at least I can tell you how to implement locking around your
		2391	queue:
		2392
		2393	=over 4
		2394
		2395	=item queueing from a signal handler context
		2396
		2397	To implement race-free queueing, you simply add to the queue in the signal
		2398	handler but you block the signal handler in the watcher callback. Here is
		2399	an example that does that for some fictitious SIGUSR1 handler:
		2400
		2401	static ev_async mysig;
		2402
		2403	static void
		2404	sigusr1_handler (void)
		2405	{
		2406	sometype data;
		2407
		2408	// no locking etc.
		2409	queue_put (data);
		2410	ev_async_send (EV_DEFAULT_ &mysig);
		2411	}
		2412
		2413	static void
		2414	mysig_cb (EV_P_ ev_async *w, int revents)
		2415	{
		2416	sometype data;
		2417	sigset_t block, prev;
		2418
		2419	sigemptyset (&block);
		2420	sigaddset (&block, SIGUSR1);
		2421	sigprocmask (SIG_BLOCK, &block, &prev);
		2422
		2423	while (queue_get (&data))
		2424	process (data);
		2425
		2426	if (sigismember (&prev, SIGUSR1)
		2427	sigprocmask (SIG_UNBLOCK, &block, 0);
		2428	}
		2429
		2430	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2431	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2432	either...).
		2433
		2434	=item queueing from a thread context
		2435
		2436	The strategy for threads is different, as you cannot (easily) block
		2437	threads but you can easily preempt them, so to queue safely you need to
		2438	employ a traditional mutex lock, such as in this pthread example:
		2439
		2440	static ev_async mysig;
		2441	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2442
		2443	static void
		2444	otherthread (void)
		2445	{
		2446	// only need to lock the actual queueing operation
		2447	pthread_mutex_lock (&mymutex);
		2448	queue_put (data);
		2449	pthread_mutex_unlock (&mymutex);
		2450
		2451	ev_async_send (EV_DEFAULT_ &mysig);
		2452	}
		2453
		2454	static void
		2455	mysig_cb (EV_P_ ev_async *w, int revents)
		2456	{
		2457	pthread_mutex_lock (&mymutex);
		2458
		2459	while (queue_get (&data))
		2460	process (data);
		2461
		2462	pthread_mutex_unlock (&mymutex);
		2463	}
		2464
		2465	=back
		2466
		2467
		2468	=head3 Watcher-Specific Functions and Data Members
		2469
		2470	=over 4
		2471
		2472	=item ev_async_init (ev_async *, callback)
		2473
		2474	Initialises and configures the async watcher - it has no parameters of any
		2475	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2476	trust me.
		2477
		2478	=item ev_async_send (loop, ev_async *)
		2479
		2480	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2481	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2482	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2483	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2484	section below on what exactly this means).
		2485
		2486	This call incurs the overhead of a system call only once per loop iteration,
		2487	so while the overhead might be noticeable, it doesn't apply to repeated
		2488	calls to C<ev_async_send>.
		2489
		2490	=item bool = ev_async_pending (ev_async *)
		2491
		2492	Returns a non-zero value when C<ev_async_send> has been called on the
		2493	watcher but the event has not yet been processed (or even noted) by the
		2494	event loop.
		2495
		2496	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2497	the loop iterates next and checks for the watcher to have become active,
		2498	it will reset the flag again. C<ev_async_pending> can be used to very
		2499	quickly check whether invoking the loop might be a good idea.
		2500
		2501	Not that this does I<not> check whether the watcher itself is pending, only
		2502	whether it has been requested to make this watcher pending.
		2503
		2504	=back
		2505
		2506
690	=head1 OTHER FUNCTIONS	2507	=head1 OTHER FUNCTIONS
691		2508
692	There are some other fucntions of possible interest. Described. Here. Now.	2509	There are some other functions of possible interest. Described. Here. Now.
693		2510
694	=over 4	2511	=over 4
695		2512
696	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2513	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
697		2514
698	This function combines a simple timer and an I/O watcher, calls your	2515	This function combines a simple timer and an I/O watcher, calls your
699	callback on whichever event happens first and automatically stop both	2516	callback on whichever event happens first and automatically stops both
700	watchers. This is useful if you want to wait for a single event on an fd	2517	watchers. This is useful if you want to wait for a single event on an fd
701	or timeout without havign to allocate/configure/start/stop/free one or	2518	or timeout without having to allocate/configure/start/stop/free one or
702	more watchers yourself.	2519	more watchers yourself.
703		2520
704	If C<fd> is less than 0, then no I/O watcher will be started and events is	2521	If C<fd> is less than 0, then no I/O watcher will be started and the
705	ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set	2522	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
706	will be craeted and started.	2523	the given C<fd> and C<events> set will be created and started.
707		2524
708	If C<timeout> is less than 0, then no timeout watcher will be	2525	If C<timeout> is less than 0, then no timeout watcher will be
709	started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat	2526	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
710	= 0) will be started.	2527	repeat = 0) will be started. C<0> is a valid timeout.
711		2528
712	The callback has the type C<void (*cb)(int revents, void *arg)> and	2529	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
713	gets passed an events set (normally a combination of EV_ERROR, EV_READ,	2530	passed an C<revents> set like normal event callbacks (a combination of
714	EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>:	2531	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
		2532	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2533	a timeout and an io event at the same time - you probably should give io
		2534	events precedence.
715		2535
		2536	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2537
716	static void stdin_ready (int revents, void *arg)	2538	static void stdin_ready (int revents, void *arg)
717	{	2539	{
718	if (revents & EV_TIMEOUT)
719	/* doh, nothing entered */
720	else if (revents & EV_READ)	2540	if (revents & EV_READ)
721	/* stdin might have data for us, joy! */	2541	/* stdin might have data for us, joy! */;
		2542	else if (revents & EV_TIMEOUT)
		2543	/* doh, nothing entered */;
722	}	2544	}
723		2545
724	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	2546	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
725		2547
726	=item ev_feed_event (loop, watcher, int events)	2548	=item ev_feed_event (ev_loop *, watcher *, int revents)
727		2549
728	Feeds the given event set into the event loop, as if the specified event	2550	Feeds the given event set into the event loop, as if the specified event
729	has happened for the specified watcher (which must be a pointer to an	2551	had happened for the specified watcher (which must be a pointer to an
730	initialised but not necessarily active event watcher).	2552	initialised but not necessarily started event watcher).
731		2553
732	=item ev_feed_fd_event (loop, int fd, int revents)	2554	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
733		2555
734	Feed an event on the given fd, as if a file descriptor backend detected it.	2556	Feed an event on the given fd, as if a file descriptor backend detected
		2557	the given events it.
735		2558
736	=item ev_feed_signal_event (loop, int signum)	2559	=item ev_feed_signal_event (ev_loop *loop, int signum)
737		2560
738	Feed an event as if the given signal occured (loop must be the default loop!).	2561	Feed an event as if the given signal occurred (C<loop> must be the default
		2562	loop!).
739		2563
740	=back	2564	=back
741		2565
		2566
		2567	=head1 LIBEVENT EMULATION
		2568
		2569	Libev offers a compatibility emulation layer for libevent. It cannot
		2570	emulate the internals of libevent, so here are some usage hints:
		2571
		2572	=over 4
		2573
		2574	=item * Use it by including <event.h>, as usual.
		2575
		2576	=item * The following members are fully supported: ev_base, ev_callback,
		2577	ev_arg, ev_fd, ev_res, ev_events.
		2578
		2579	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2580	maintained by libev, it does not work exactly the same way as in libevent (consider
		2581	it a private API).
		2582
		2583	=item * Priorities are not currently supported. Initialising priorities
		2584	will fail and all watchers will have the same priority, even though there
		2585	is an ev_pri field.
		2586
		2587	=item * In libevent, the last base created gets the signals, in libev, the
		2588	first base created (== the default loop) gets the signals.
		2589
		2590	=item * Other members are not supported.
		2591
		2592	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2593	to use the libev header file and library.
		2594
		2595	=back
		2596
		2597	=head1 C++ SUPPORT
		2598
		2599	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2600	you to use some convenience methods to start/stop watchers and also change
		2601	the callback model to a model using method callbacks on objects.
		2602
		2603	To use it,
		2604
		2605	#include <ev++.h>
		2606
		2607	This automatically includes F<ev.h> and puts all of its definitions (many
		2608	of them macros) into the global namespace. All C++ specific things are
		2609	put into the C<ev> namespace. It should support all the same embedding
		2610	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2611
		2612	Care has been taken to keep the overhead low. The only data member the C++
		2613	classes add (compared to plain C-style watchers) is the event loop pointer
		2614	that the watcher is associated with (or no additional members at all if
		2615	you disable C<EV_MULTIPLICITY> when embedding libev).
		2616
		2617	Currently, functions, and static and non-static member functions can be
		2618	used as callbacks. Other types should be easy to add as long as they only
		2619	need one additional pointer for context. If you need support for other
		2620	types of functors please contact the author (preferably after implementing
		2621	it).
		2622
		2623	Here is a list of things available in the C<ev> namespace:
		2624
		2625	=over 4
		2626
		2627	=item C<ev::READ>, C<ev::WRITE> etc.
		2628
		2629	These are just enum values with the same values as the C<EV_READ> etc.
		2630	macros from F<ev.h>.
		2631
		2632	=item C<ev::tstamp>, C<ev::now>
		2633
		2634	Aliases to the same types/functions as with the C<ev_> prefix.
		2635
		2636	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2637
		2638	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2639	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2640	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2641	defines by many implementations.
		2642
		2643	All of those classes have these methods:
		2644
		2645	=over 4
		2646
		2647	=item ev::TYPE::TYPE ()
		2648
		2649	=item ev::TYPE::TYPE (struct ev_loop *)
		2650
		2651	=item ev::TYPE::~TYPE
		2652
		2653	The constructor (optionally) takes an event loop to associate the watcher
		2654	with. If it is omitted, it will use C<EV_DEFAULT>.
		2655
		2656	The constructor calls C<ev_init> for you, which means you have to call the
		2657	C<set> method before starting it.
		2658
		2659	It will not set a callback, however: You have to call the templated C<set>
		2660	method to set a callback before you can start the watcher.
		2661
		2662	(The reason why you have to use a method is a limitation in C++ which does
		2663	not allow explicit template arguments for constructors).
		2664
		2665	The destructor automatically stops the watcher if it is active.
		2666
		2667	=item w->set<class, &class::method> (object *)
		2668
		2669	This method sets the callback method to call. The method has to have a
		2670	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2671	first argument and the C<revents> as second. The object must be given as
		2672	parameter and is stored in the C<data> member of the watcher.
		2673
		2674	This method synthesizes efficient thunking code to call your method from
		2675	the C callback that libev requires. If your compiler can inline your
		2676	callback (i.e. it is visible to it at the place of the C<set> call and
		2677	your compiler is good :), then the method will be fully inlined into the
		2678	thunking function, making it as fast as a direct C callback.
		2679
		2680	Example: simple class declaration and watcher initialisation
		2681
		2682	struct myclass
		2683	{
		2684	void io_cb (ev::io &w, int revents) { }
		2685	}
		2686
		2687	myclass obj;
		2688	ev::io iow;
		2689	iow.set <myclass, &myclass::io_cb> (&obj);
		2690
		2691	=item w->set<function> (void *data = 0)
		2692
		2693	Also sets a callback, but uses a static method or plain function as
		2694	callback. The optional C<data> argument will be stored in the watcher's
		2695	C<data> member and is free for you to use.
		2696
		2697	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2698
		2699	See the method-C<set> above for more details.
		2700
		2701	Example: Use a plain function as callback.
		2702
		2703	static void io_cb (ev::io &w, int revents) { }
		2704	iow.set <io_cb> ();
		2705
		2706	=item w->set (struct ev_loop *)
		2707
		2708	Associates a different C<struct ev_loop> with this watcher. You can only
		2709	do this when the watcher is inactive (and not pending either).
		2710
		2711	=item w->set ([arguments])
		2712
		2713	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2714	called at least once. Unlike the C counterpart, an active watcher gets
		2715	automatically stopped and restarted when reconfiguring it with this
		2716	method.
		2717
		2718	=item w->start ()
		2719
		2720	Starts the watcher. Note that there is no C<loop> argument, as the
		2721	constructor already stores the event loop.
		2722
		2723	=item w->stop ()
		2724
		2725	Stops the watcher if it is active. Again, no C<loop> argument.
		2726
		2727	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2728
		2729	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2730	C<ev_TYPE_again> function.
		2731
		2732	=item w->sweep () (C<ev::embed> only)
		2733
		2734	Invokes C<ev_embed_sweep>.
		2735
		2736	=item w->update () (C<ev::stat> only)
		2737
		2738	Invokes C<ev_stat_stat>.
		2739
		2740	=back
		2741
		2742	=back
		2743
		2744	Example: Define a class with an IO and idle watcher, start one of them in
		2745	the constructor.
		2746
		2747	class myclass
		2748	{
		2749	ev::io io ; void io_cb (ev::io &w, int revents);
		2750	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		2751
		2752	myclass (int fd)
		2753	{
		2754	io .set <myclass, &myclass::io_cb > (this);
		2755	idle.set <myclass, &myclass::idle_cb> (this);
		2756
		2757	io.start (fd, ev::READ);
		2758	}
		2759	};
		2760
		2761
		2762	=head1 OTHER LANGUAGE BINDINGS
		2763
		2764	Libev does not offer other language bindings itself, but bindings for a
		2765	number of languages exist in the form of third-party packages. If you know
		2766	any interesting language binding in addition to the ones listed here, drop
		2767	me a note.
		2768
		2769	=over 4
		2770
		2771	=item Perl
		2772
		2773	The EV module implements the full libev API and is actually used to test
		2774	libev. EV is developed together with libev. Apart from the EV core module,
		2775	there are additional modules that implement libev-compatible interfaces
		2776	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2777	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2778	and C<EV::Glib>).
		2779
		2780	It can be found and installed via CPAN, its homepage is at
		2781	L<http://software.schmorp.de/pkg/EV>.
		2782
		2783	=item Python
		2784
		2785	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2786	seems to be quite complete and well-documented. Note, however, that the
		2787	patch they require for libev is outright dangerous as it breaks the ABI
		2788	for everybody else, and therefore, should never be applied in an installed
		2789	libev (if python requires an incompatible ABI then it needs to embed
		2790	libev).
		2791
		2792	=item Ruby
		2793
		2794	Tony Arcieri has written a ruby extension that offers access to a subset
		2795	of the libev API and adds file handle abstractions, asynchronous DNS and
		2796	more on top of it. It can be found via gem servers. Its homepage is at
		2797	L<http://rev.rubyforge.org/>.
		2798
		2799	=item D
		2800
		2801	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2802	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2803
		2804	=back
		2805
		2806
		2807	=head1 MACRO MAGIC
		2808
		2809	Libev can be compiled with a variety of options, the most fundamental
		2810	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2811	functions and callbacks have an initial C<struct ev_loop *> argument.
		2812
		2813	To make it easier to write programs that cope with either variant, the
		2814	following macros are defined:
		2815
		2816	=over 4
		2817
		2818	=item C<EV_A>, C<EV_A_>
		2819
		2820	This provides the loop I<argument> for functions, if one is required ("ev
		2821	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2822	C<EV_A_> is used when other arguments are following. Example:
		2823
		2824	ev_unref (EV_A);
		2825	ev_timer_add (EV_A_ watcher);
		2826	ev_loop (EV_A_ 0);
		2827
		2828	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2829	which is often provided by the following macro.
		2830
		2831	=item C<EV_P>, C<EV_P_>
		2832
		2833	This provides the loop I<parameter> for functions, if one is required ("ev
		2834	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2835	C<EV_P_> is used when other parameters are following. Example:
		2836
		2837	// this is how ev_unref is being declared
		2838	static void ev_unref (EV_P);
		2839
		2840	// this is how you can declare your typical callback
		2841	static void cb (EV_P_ ev_timer *w, int revents)
		2842
		2843	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2844	suitable for use with C<EV_A>.
		2845
		2846	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2847
		2848	Similar to the other two macros, this gives you the value of the default
		2849	loop, if multiple loops are supported ("ev loop default").
		2850
		2851	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2852
		2853	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2854	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2855	is undefined when the default loop has not been initialised by a previous
		2856	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2857
		2858	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2859	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2860
		2861	=back
		2862
		2863	Example: Declare and initialise a check watcher, utilising the above
		2864	macros so it will work regardless of whether multiple loops are supported
		2865	or not.
		2866
		2867	static void
		2868	check_cb (EV_P_ ev_timer *w, int revents)
		2869	{
		2870	ev_check_stop (EV_A_ w);
		2871	}
		2872
		2873	ev_check check;
		2874	ev_check_init (&check, check_cb);
		2875	ev_check_start (EV_DEFAULT_ &check);
		2876	ev_loop (EV_DEFAULT_ 0);
		2877
		2878	=head1 EMBEDDING
		2879
		2880	Libev can (and often is) directly embedded into host
		2881	applications. Examples of applications that embed it include the Deliantra
		2882	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2883	and rxvt-unicode.
		2884
		2885	The goal is to enable you to just copy the necessary files into your
		2886	source directory without having to change even a single line in them, so
		2887	you can easily upgrade by simply copying (or having a checked-out copy of
		2888	libev somewhere in your source tree).
		2889
		2890	=head2 FILESETS
		2891
		2892	Depending on what features you need you need to include one or more sets of files
		2893	in your application.
		2894
		2895	=head3 CORE EVENT LOOP
		2896
		2897	To include only the libev core (all the C<ev_*> functions), with manual
		2898	configuration (no autoconf):
		2899
		2900	#define EV_STANDALONE 1
		2901	#include "ev.c"
		2902
		2903	This will automatically include F<ev.h>, too, and should be done in a
		2904	single C source file only to provide the function implementations. To use
		2905	it, do the same for F<ev.h> in all files wishing to use this API (best
		2906	done by writing a wrapper around F<ev.h> that you can include instead and
		2907	where you can put other configuration options):
		2908
		2909	#define EV_STANDALONE 1
		2910	#include "ev.h"
		2911
		2912	Both header files and implementation files can be compiled with a C++
		2913	compiler (at least, thats a stated goal, and breakage will be treated
		2914	as a bug).
		2915
		2916	You need the following files in your source tree, or in a directory
		2917	in your include path (e.g. in libev/ when using -Ilibev):
		2918
		2919	ev.h
		2920	ev.c
		2921	ev_vars.h
		2922	ev_wrap.h
		2923
		2924	ev_win32.c required on win32 platforms only
		2925
		2926	ev_select.c only when select backend is enabled (which is enabled by default)
		2927	ev_poll.c only when poll backend is enabled (disabled by default)
		2928	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2929	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2930	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2931
		2932	F<ev.c> includes the backend files directly when enabled, so you only need
		2933	to compile this single file.
		2934
		2935	=head3 LIBEVENT COMPATIBILITY API
		2936
		2937	To include the libevent compatibility API, also include:
		2938
		2939	#include "event.c"
		2940
		2941	in the file including F<ev.c>, and:
		2942
		2943	#include "event.h"
		2944
		2945	in the files that want to use the libevent API. This also includes F<ev.h>.
		2946
		2947	You need the following additional files for this:
		2948
		2949	event.h
		2950	event.c
		2951
		2952	=head3 AUTOCONF SUPPORT
		2953
		2954	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		2955	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2956	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2957	include F<config.h> and configure itself accordingly.
		2958
		2959	For this of course you need the m4 file:
		2960
		2961	libev.m4
		2962
		2963	=head2 PREPROCESSOR SYMBOLS/MACROS
		2964
		2965	Libev can be configured via a variety of preprocessor symbols you have to
		2966	define before including any of its files. The default in the absence of
		2967	autoconf is documented for every option.
		2968
		2969	=over 4
		2970
		2971	=item EV_STANDALONE
		2972
		2973	Must always be C<1> if you do not use autoconf configuration, which
		2974	keeps libev from including F<config.h>, and it also defines dummy
		2975	implementations for some libevent functions (such as logging, which is not
		2976	supported). It will also not define any of the structs usually found in
		2977	F<event.h> that are not directly supported by the libev core alone.
		2978
		2979	=item EV_USE_MONOTONIC
		2980
		2981	If defined to be C<1>, libev will try to detect the availability of the
		2982	monotonic clock option at both compile time and runtime. Otherwise no use
		2983	of the monotonic clock option will be attempted. If you enable this, you
		2984	usually have to link against librt or something similar. Enabling it when
		2985	the functionality isn't available is safe, though, although you have
		2986	to make sure you link against any libraries where the C<clock_gettime>
		2987	function is hiding in (often F<-lrt>).
		2988
		2989	=item EV_USE_REALTIME
		2990
		2991	If defined to be C<1>, libev will try to detect the availability of the
		2992	real-time clock option at compile time (and assume its availability at
		2993	runtime if successful). Otherwise no use of the real-time clock option will
		2994	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2995	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2996	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2997
		2998	=item EV_USE_NANOSLEEP
		2999
		3000	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3001	and will use it for delays. Otherwise it will use C<select ()>.
		3002
		3003	=item EV_USE_EVENTFD
		3004
		3005	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3006	available and will probe for kernel support at runtime. This will improve
		3007	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3008	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3009	2.7 or newer, otherwise disabled.
		3010
		3011	=item EV_USE_SELECT
		3012
		3013	If undefined or defined to be C<1>, libev will compile in support for the
		3014	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3015	other method takes over, select will be it. Otherwise the select backend
		3016	will not be compiled in.
		3017
		3018	=item EV_SELECT_USE_FD_SET
		3019
		3020	If defined to C<1>, then the select backend will use the system C<fd_set>
		3021	structure. This is useful if libev doesn't compile due to a missing
		3022	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		3023	exotic systems. This usually limits the range of file descriptors to some
		3024	low limit such as 1024 or might have other limitations (winsocket only
		3025	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		3026	influence the size of the C<fd_set> used.
		3027
		3028	=item EV_SELECT_IS_WINSOCKET
		3029
		3030	When defined to C<1>, the select backend will assume that
		3031	select/socket/connect etc. don't understand file descriptors but
		3032	wants osf handles on win32 (this is the case when the select to
		3033	be used is the winsock select). This means that it will call
		3034	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3035	it is assumed that all these functions actually work on fds, even
		3036	on win32. Should not be defined on non-win32 platforms.
		3037
		3038	=item EV_FD_TO_WIN32_HANDLE
		3039
		3040	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3041	file descriptors to socket handles. When not defining this symbol (the
		3042	default), then libev will call C<_get_osfhandle>, which is usually
		3043	correct. In some cases, programs use their own file descriptor management,
		3044	in which case they can provide this function to map fds to socket handles.
		3045
		3046	=item EV_USE_POLL
		3047
		3048	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3049	backend. Otherwise it will be enabled on non-win32 platforms. It
		3050	takes precedence over select.
		3051
		3052	=item EV_USE_EPOLL
		3053
		3054	If defined to be C<1>, libev will compile in support for the Linux
		3055	C<epoll>(7) backend. Its availability will be detected at runtime,
		3056	otherwise another method will be used as fallback. This is the preferred
		3057	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3058	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3059
		3060	=item EV_USE_KQUEUE
		3061
		3062	If defined to be C<1>, libev will compile in support for the BSD style
		3063	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3064	otherwise another method will be used as fallback. This is the preferred
		3065	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3066	supports some types of fds correctly (the only platform we found that
		3067	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3068	not be used unless explicitly requested. The best way to use it is to find
		3069	out whether kqueue supports your type of fd properly and use an embedded
		3070	kqueue loop.
		3071
		3072	=item EV_USE_PORT
		3073
		3074	If defined to be C<1>, libev will compile in support for the Solaris
		3075	10 port style backend. Its availability will be detected at runtime,
		3076	otherwise another method will be used as fallback. This is the preferred
		3077	backend for Solaris 10 systems.
		3078
		3079	=item EV_USE_DEVPOLL
		3080
		3081	Reserved for future expansion, works like the USE symbols above.
		3082
		3083	=item EV_USE_INOTIFY
		3084
		3085	If defined to be C<1>, libev will compile in support for the Linux inotify
		3086	interface to speed up C<ev_stat> watchers. Its actual availability will
		3087	be detected at runtime. If undefined, it will be enabled if the headers
		3088	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3089
		3090	=item EV_ATOMIC_T
		3091
		3092	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3093	access is atomic with respect to other threads or signal contexts. No such
		3094	type is easily found in the C language, so you can provide your own type
		3095	that you know is safe for your purposes. It is used both for signal handler "locking"
		3096	as well as for signal and thread safety in C<ev_async> watchers.
		3097
		3098	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3099	(from F<signal.h>), which is usually good enough on most platforms.
		3100
		3101	=item EV_H
		3102
		3103	The name of the F<ev.h> header file used to include it. The default if
		3104	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3105	used to virtually rename the F<ev.h> header file in case of conflicts.
		3106
		3107	=item EV_CONFIG_H
		3108
		3109	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3110	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3111	C<EV_H>, above.
		3112
		3113	=item EV_EVENT_H
		3114
		3115	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3116	of how the F<event.h> header can be found, the default is C<"event.h">.
		3117
		3118	=item EV_PROTOTYPES
		3119
		3120	If defined to be C<0>, then F<ev.h> will not define any function
		3121	prototypes, but still define all the structs and other symbols. This is
		3122	occasionally useful if you want to provide your own wrapper functions
		3123	around libev functions.
		3124
		3125	=item EV_MULTIPLICITY
		3126
		3127	If undefined or defined to C<1>, then all event-loop-specific functions
		3128	will have the C<struct ev_loop *> as first argument, and you can create
		3129	additional independent event loops. Otherwise there will be no support
		3130	for multiple event loops and there is no first event loop pointer
		3131	argument. Instead, all functions act on the single default loop.
		3132
		3133	=item EV_MINPRI
		3134
		3135	=item EV_MAXPRI
		3136
		3137	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3138	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3139	provide for more priorities by overriding those symbols (usually defined
		3140	to be C<-2> and C<2>, respectively).
		3141
		3142	When doing priority-based operations, libev usually has to linearly search
		3143	all the priorities, so having many of them (hundreds) uses a lot of space
		3144	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3145	fine.
		3146
		3147	If your embedding application does not need any priorities, defining these
		3148	both to C<0> will save some memory and CPU.
		3149
		3150	=item EV_PERIODIC_ENABLE
		3151
		3152	If undefined or defined to be C<1>, then periodic timers are supported. If
		3153	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3154	code.
		3155
		3156	=item EV_IDLE_ENABLE
		3157
		3158	If undefined or defined to be C<1>, then idle watchers are supported. If
		3159	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3160	code.
		3161
		3162	=item EV_EMBED_ENABLE
		3163
		3164	If undefined or defined to be C<1>, then embed watchers are supported. If
		3165	defined to be C<0>, then they are not. Embed watchers rely on most other
		3166	watcher types, which therefore must not be disabled.
		3167
		3168	=item EV_STAT_ENABLE
		3169
		3170	If undefined or defined to be C<1>, then stat watchers are supported. If
		3171	defined to be C<0>, then they are not.
		3172
		3173	=item EV_FORK_ENABLE
		3174
		3175	If undefined or defined to be C<1>, then fork watchers are supported. If
		3176	defined to be C<0>, then they are not.
		3177
		3178	=item EV_ASYNC_ENABLE
		3179
		3180	If undefined or defined to be C<1>, then async watchers are supported. If
		3181	defined to be C<0>, then they are not.
		3182
		3183	=item EV_MINIMAL
		3184
		3185	If you need to shave off some kilobytes of code at the expense of some
		3186	speed, define this symbol to C<1>. Currently this is used to override some
		3187	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3188	much smaller 2-heap for timer management over the default 4-heap.
		3189
		3190	=item EV_PID_HASHSIZE
		3191
		3192	C<ev_child> watchers use a small hash table to distribute workload by
		3193	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3194	than enough. If you need to manage thousands of children you might want to
		3195	increase this value (I<must> be a power of two).
		3196
		3197	=item EV_INOTIFY_HASHSIZE
		3198
		3199	C<ev_stat> watchers use a small hash table to distribute workload by
		3200	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3201	usually more than enough. If you need to manage thousands of C<ev_stat>
		3202	watchers you might want to increase this value (I<must> be a power of
		3203	two).
		3204
		3205	=item EV_USE_4HEAP
		3206
		3207	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3208	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3209	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3210	faster performance with many (thousands) of watchers.
		3211
		3212	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3213	(disabled).
		3214
		3215	=item EV_HEAP_CACHE_AT
		3216
		3217	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3218	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3219	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3220	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3221	but avoids random read accesses on heap changes. This improves performance
		3222	noticeably with many (hundreds) of watchers.
		3223
		3224	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3225	(disabled).
		3226
		3227	=item EV_VERIFY
		3228
		3229	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3230	be done: If set to C<0>, no internal verification code will be compiled
		3231	in. If set to C<1>, then verification code will be compiled in, but not
		3232	called. If set to C<2>, then the internal verification code will be
		3233	called once per loop, which can slow down libev. If set to C<3>, then the
		3234	verification code will be called very frequently, which will slow down
		3235	libev considerably.
		3236
		3237	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3238	C<0>.
		3239
		3240	=item EV_COMMON
		3241
		3242	By default, all watchers have a C<void *data> member. By redefining
		3243	this macro to a something else you can include more and other types of
		3244	members. You have to define it each time you include one of the files,
		3245	though, and it must be identical each time.
		3246
		3247	For example, the perl EV module uses something like this:
		3248
		3249	#define EV_COMMON \
		3250	SV *self; /* contains this struct */ \
		3251	SV *cb_sv, *fh /* note no trailing ";" */
		3252
		3253	=item EV_CB_DECLARE (type)
		3254
		3255	=item EV_CB_INVOKE (watcher, revents)
		3256
		3257	=item ev_set_cb (ev, cb)
		3258
		3259	Can be used to change the callback member declaration in each watcher,
		3260	and the way callbacks are invoked and set. Must expand to a struct member
		3261	definition and a statement, respectively. See the F<ev.h> header file for
		3262	their default definitions. One possible use for overriding these is to
		3263	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3264	method calls instead of plain function calls in C++.
		3265
		3266	=back
		3267
		3268	=head2 EXPORTED API SYMBOLS
		3269
		3270	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3271	exported symbols, you can use the provided F<Symbol.*> files which list
		3272	all public symbols, one per line:
		3273
		3274	Symbols.ev for libev proper
		3275	Symbols.event for the libevent emulation
		3276
		3277	This can also be used to rename all public symbols to avoid clashes with
		3278	multiple versions of libev linked together (which is obviously bad in
		3279	itself, but sometimes it is inconvenient to avoid this).
		3280
		3281	A sed command like this will create wrapper C<#define>'s that you need to
		3282	include before including F<ev.h>:
		3283
		3284	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3285
		3286	This would create a file F<wrap.h> which essentially looks like this:
		3287
		3288	#define ev_backend myprefix_ev_backend
		3289	#define ev_check_start myprefix_ev_check_start
		3290	#define ev_check_stop myprefix_ev_check_stop
		3291	...
		3292
		3293	=head2 EXAMPLES
		3294
		3295	For a real-world example of a program the includes libev
		3296	verbatim, you can have a look at the EV perl module
		3297	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3298	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3299	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3300	will be compiled. It is pretty complex because it provides its own header
		3301	file.
		3302
		3303	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3304	that everybody includes and which overrides some configure choices:
		3305
		3306	#define EV_MINIMAL 1
		3307	#define EV_USE_POLL 0
		3308	#define EV_MULTIPLICITY 0
		3309	#define EV_PERIODIC_ENABLE 0
		3310	#define EV_STAT_ENABLE 0
		3311	#define EV_FORK_ENABLE 0
		3312	#define EV_CONFIG_H <config.h>
		3313	#define EV_MINPRI 0
		3314	#define EV_MAXPRI 0
		3315
		3316	#include "ev++.h"
		3317
		3318	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3319
		3320	#include "ev_cpp.h"
		3321	#include "ev.c"
		3322
		3323	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3324
		3325	=head2 THREADS AND COROUTINES
		3326
		3327	=head3 THREADS
		3328
		3329	All libev functions are reentrant and thread-safe unless explicitly
		3330	documented otherwise, but libev implements no locking itself. This means
		3331	that you can use as many loops as you want in parallel, as long as there
		3332	are no concurrent calls into any libev function with the same loop
		3333	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3334	of course): libev guarantees that different event loops share no data
		3335	structures that need any locking.
		3336
		3337	Or to put it differently: calls with different loop parameters can be done
		3338	concurrently from multiple threads, calls with the same loop parameter
		3339	must be done serially (but can be done from different threads, as long as
		3340	only one thread ever is inside a call at any point in time, e.g. by using
		3341	a mutex per loop).
		3342
		3343	Specifically to support threads (and signal handlers), libev implements
		3344	so-called C<ev_async> watchers, which allow some limited form of
		3345	concurrency on the same event loop, namely waking it up "from the
		3346	outside".
		3347
		3348	If you want to know which design (one loop, locking, or multiple loops
		3349	without or something else still) is best for your problem, then I cannot
		3350	help you, but here is some generic advice:
		3351
		3352	=over 4
		3353
		3354	=item * most applications have a main thread: use the default libev loop
		3355	in that thread, or create a separate thread running only the default loop.
		3356
		3357	This helps integrating other libraries or software modules that use libev
		3358	themselves and don't care/know about threading.
		3359
		3360	=item * one loop per thread is usually a good model.
		3361
		3362	Doing this is almost never wrong, sometimes a better-performance model
		3363	exists, but it is always a good start.
		3364
		3365	=item * other models exist, such as the leader/follower pattern, where one
		3366	loop is handed through multiple threads in a kind of round-robin fashion.
		3367
		3368	Choosing a model is hard - look around, learn, know that usually you can do
		3369	better than you currently do :-)
		3370
		3371	=item * often you need to talk to some other thread which blocks in the
		3372	event loop.
		3373
		3374	C<ev_async> watchers can be used to wake them up from other threads safely
		3375	(or from signal contexts...).
		3376
		3377	An example use would be to communicate signals or other events that only
		3378	work in the default loop by registering the signal watcher with the
		3379	default loop and triggering an C<ev_async> watcher from the default loop
		3380	watcher callback into the event loop interested in the signal.
		3381
		3382	=back
		3383
		3384	=head3 COROUTINES
		3385
		3386	Libev is very accommodating to coroutines ("cooperative threads"):
		3387	libev fully supports nesting calls to its functions from different
		3388	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3389	different coroutines, and switch freely between both coroutines running the
		3390	loop, as long as you don't confuse yourself). The only exception is that
		3391	you must not do this from C<ev_periodic> reschedule callbacks.
		3392
		3393	Care has been taken to ensure that libev does not keep local state inside
		3394	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3395	they do not clal any callbacks.
		3396
		3397	=head2 COMPILER WARNINGS
		3398
		3399	Depending on your compiler and compiler settings, you might get no or a
		3400	lot of warnings when compiling libev code. Some people are apparently
		3401	scared by this.
		3402
		3403	However, these are unavoidable for many reasons. For one, each compiler
		3404	has different warnings, and each user has different tastes regarding
		3405	warning options. "Warn-free" code therefore cannot be a goal except when
		3406	targeting a specific compiler and compiler-version.
		3407
		3408	Another reason is that some compiler warnings require elaborate
		3409	workarounds, or other changes to the code that make it less clear and less
		3410	maintainable.
		3411
		3412	And of course, some compiler warnings are just plain stupid, or simply
		3413	wrong (because they don't actually warn about the condition their message
		3414	seems to warn about). For example, certain older gcc versions had some
		3415	warnings that resulted an extreme number of false positives. These have
		3416	been fixed, but some people still insist on making code warn-free with
		3417	such buggy versions.
		3418
		3419	While libev is written to generate as few warnings as possible,
		3420	"warn-free" code is not a goal, and it is recommended not to build libev
		3421	with any compiler warnings enabled unless you are prepared to cope with
		3422	them (e.g. by ignoring them). Remember that warnings are just that:
		3423	warnings, not errors, or proof of bugs.
		3424
		3425
		3426	=head2 VALGRIND
		3427
		3428	Valgrind has a special section here because it is a popular tool that is
		3429	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3430
		3431	If you think you found a bug (memory leak, uninitialised data access etc.)
		3432	in libev, then check twice: If valgrind reports something like:
		3433
		3434	==2274== definitely lost: 0 bytes in 0 blocks.
		3435	==2274== possibly lost: 0 bytes in 0 blocks.
		3436	==2274== still reachable: 256 bytes in 1 blocks.
		3437
		3438	Then there is no memory leak, just as memory accounted to global variables
		3439	is not a memleak - the memory is still being refernced, and didn't leak.
		3440
		3441	Similarly, under some circumstances, valgrind might report kernel bugs
		3442	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3443	although an acceptable workaround has been found here), or it might be
		3444	confused.
		3445
		3446	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3447	make it into some kind of religion.
		3448
		3449	If you are unsure about something, feel free to contact the mailing list
		3450	with the full valgrind report and an explanation on why you think this
		3451	is a bug in libev (best check the archives, too :). However, don't be
		3452	annoyed when you get a brisk "this is no bug" answer and take the chance
		3453	of learning how to interpret valgrind properly.
		3454
		3455	If you need, for some reason, empty reports from valgrind for your project
		3456	I suggest using suppression lists.
		3457
		3458
		3459	=head1 PORTABILITY NOTES
		3460
		3461	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3462
		3463	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3464	requires, and its I/O model is fundamentally incompatible with the POSIX
		3465	model. Libev still offers limited functionality on this platform in
		3466	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3467	descriptors. This only applies when using Win32 natively, not when using
		3468	e.g. cygwin.
		3469
		3470	Lifting these limitations would basically require the full
		3471	re-implementation of the I/O system. If you are into these kinds of
		3472	things, then note that glib does exactly that for you in a very portable
		3473	way (note also that glib is the slowest event library known to man).
		3474
		3475	There is no supported compilation method available on windows except
		3476	embedding it into other applications.
		3477
		3478	Not a libev limitation but worth mentioning: windows apparently doesn't
		3479	accept large writes: instead of resulting in a partial write, windows will
		3480	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3481	so make sure you only write small amounts into your sockets (less than a
		3482	megabyte seems safe, but this apparently depends on the amount of memory
		3483	available).
		3484
		3485	Due to the many, low, and arbitrary limits on the win32 platform and
		3486	the abysmal performance of winsockets, using a large number of sockets
		3487	is not recommended (and not reasonable). If your program needs to use
		3488	more than a hundred or so sockets, then likely it needs to use a totally
		3489	different implementation for windows, as libev offers the POSIX readiness
		3490	notification model, which cannot be implemented efficiently on windows
		3491	(Microsoft monopoly games).
		3492
		3493	A typical way to use libev under windows is to embed it (see the embedding
		3494	section for details) and use the following F<evwrap.h> header file instead
		3495	of F<ev.h>:
		3496
		3497	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3498	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3499
		3500	#include "ev.h"
		3501
		3502	And compile the following F<evwrap.c> file into your project (make sure
		3503	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3504
		3505	#include "evwrap.h"
		3506	#include "ev.c"
		3507
		3508	=over 4
		3509
		3510	=item The winsocket select function
		3511
		3512	The winsocket C<select> function doesn't follow POSIX in that it
		3513	requires socket I<handles> and not socket I<file descriptors> (it is
		3514	also extremely buggy). This makes select very inefficient, and also
		3515	requires a mapping from file descriptors to socket handles (the Microsoft
		3516	C runtime provides the function C<_open_osfhandle> for this). See the
		3517	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3518	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3519
		3520	The configuration for a "naked" win32 using the Microsoft runtime
		3521	libraries and raw winsocket select is:
		3522
		3523	#define EV_USE_SELECT 1
		3524	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3525
		3526	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3527	complexity in the O(n²) range when using win32.
		3528
		3529	=item Limited number of file descriptors
		3530
		3531	Windows has numerous arbitrary (and low) limits on things.
		3532
		3533	Early versions of winsocket's select only supported waiting for a maximum
		3534	of C<64> handles (probably owning to the fact that all windows kernels
		3535	can only wait for C<64> things at the same time internally; Microsoft
		3536	recommends spawning a chain of threads and wait for 63 handles and the
		3537	previous thread in each. Great).
		3538
		3539	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3540	to some high number (e.g. C<2048>) before compiling the winsocket select
		3541	call (which might be in libev or elsewhere, for example, perl does its own
		3542	select emulation on windows).
		3543
		3544	Another limit is the number of file descriptors in the Microsoft runtime
		3545	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3546	or something like this inside Microsoft). You can increase this by calling
		3547	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3548	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3549	libraries.
		3550
		3551	This might get you to about C<512> or C<2048> sockets (depending on
		3552	windows version and/or the phase of the moon). To get more, you need to
		3553	wrap all I/O functions and provide your own fd management, but the cost of
		3554	calling select (O(n²)) will likely make this unworkable.
		3555
		3556	=back
		3557
		3558	=head2 PORTABILITY REQUIREMENTS
		3559
		3560	In addition to a working ISO-C implementation and of course the
		3561	backend-specific APIs, libev relies on a few additional extensions:
		3562
		3563	=over 4
		3564
		3565	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3566	calling conventions regardless of C<ev_watcher_type *>.
		3567
		3568	Libev assumes not only that all watcher pointers have the same internal
		3569	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3570	assumes that the same (machine) code can be used to call any watcher
		3571	callback: The watcher callbacks have different type signatures, but libev
		3572	calls them using an C<ev_watcher *> internally.
		3573
		3574	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3575
		3576	The type C<sig_atomic_t volatile> (or whatever is defined as
		3577	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3578	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3579	believed to be sufficiently portable.
		3580
		3581	=item C<sigprocmask> must work in a threaded environment
		3582
		3583	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3584	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3585	pthread implementations will either allow C<sigprocmask> in the "main
		3586	thread" or will block signals process-wide, both behaviours would
		3587	be compatible with libev. Interaction between C<sigprocmask> and
		3588	C<pthread_sigmask> could complicate things, however.
		3589
		3590	The most portable way to handle signals is to block signals in all threads
		3591	except the initial one, and run the default loop in the initial thread as
		3592	well.
		3593
		3594	=item C<long> must be large enough for common memory allocation sizes
		3595
		3596	To improve portability and simplify its API, libev uses C<long> internally
		3597	instead of C<size_t> when allocating its data structures. On non-POSIX
		3598	systems (Microsoft...) this might be unexpectedly low, but is still at
		3599	least 31 bits everywhere, which is enough for hundreds of millions of
		3600	watchers.
		3601
		3602	=item C<double> must hold a time value in seconds with enough accuracy
		3603
		3604	The type C<double> is used to represent timestamps. It is required to
		3605	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3606	enough for at least into the year 4000. This requirement is fulfilled by
		3607	implementations implementing IEEE 754 (basically all existing ones).
		3608
		3609	=back
		3610
		3611	If you know of other additional requirements drop me a note.
		3612
		3613
		3614	=head1 ALGORITHMIC COMPLEXITIES
		3615
		3616	In this section the complexities of (many of) the algorithms used inside
		3617	libev will be documented. For complexity discussions about backends see
		3618	the documentation for C<ev_default_init>.
		3619
		3620	All of the following are about amortised time: If an array needs to be
		3621	extended, libev needs to realloc and move the whole array, but this
		3622	happens asymptotically rarer with higher number of elements, so O(1) might
		3623	mean that libev does a lengthy realloc operation in rare cases, but on
		3624	average it is much faster and asymptotically approaches constant time.
		3625
		3626	=over 4
		3627
		3628	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3629
		3630	This means that, when you have a watcher that triggers in one hour and
		3631	there are 100 watchers that would trigger before that, then inserting will
		3632	have to skip roughly seven (C<ld 100>) of these watchers.
		3633
		3634	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3635
		3636	That means that changing a timer costs less than removing/adding them,
		3637	as only the relative motion in the event queue has to be paid for.
		3638
		3639	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3640
		3641	These just add the watcher into an array or at the head of a list.
		3642
		3643	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3644
		3645	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3646
		3647	These watchers are stored in lists, so they need to be walked to find the
		3648	correct watcher to remove. The lists are usually short (you don't usually
		3649	have many watchers waiting for the same fd or signal: one is typical, two
		3650	is rare).
		3651
		3652	=item Finding the next timer in each loop iteration: O(1)
		3653
		3654	By virtue of using a binary or 4-heap, the next timer is always found at a
		3655	fixed position in the storage array.
		3656
		3657	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3658
		3659	A change means an I/O watcher gets started or stopped, which requires
		3660	libev to recalculate its status (and possibly tell the kernel, depending
		3661	on backend and whether C<ev_io_set> was used).
		3662
		3663	=item Activating one watcher (putting it into the pending state): O(1)
		3664
		3665	=item Priority handling: O(number_of_priorities)
		3666
		3667	Priorities are implemented by allocating some space for each
		3668	priority. When doing priority-based operations, libev usually has to
		3669	linearly search all the priorities, but starting/stopping and activating
		3670	watchers becomes O(1) with respect to priority handling.
		3671
		3672	=item Sending an ev_async: O(1)
		3673
		3674	=item Processing ev_async_send: O(number_of_async_watchers)
		3675
		3676	=item Processing signals: O(max_signal_number)
		3677
		3678	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3679	calls in the current loop iteration. Checking for async and signal events
		3680	involves iterating over all running async watchers or all signal numbers.
		3681
		3682	=back
		3683
		3684
742	=head1 AUTHOR	3685	=head1 AUTHOR
743		3686
744	Marc Lehmann <libev@schmorp.de>.	3687	Marc Lehmann <libev@schmorp.de>.
745		3688

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