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…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	#include <ev.h>
		12
		13	ev_io stdin_watcher;
		14	ev_timer timeout_watcher;
		15
		16	/* called when data readable on stdin */
		17	static void
		18	stdin_cb (EV_P_ struct ev_io *w, int revents)
		19	{
		20	/* puts ("stdin ready"); */
		21	ev_io_stop (EV_A_ w); /* just a syntax example */
		22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
		23	}
		24
		25	static void
		26	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		27	{
		28	/* puts ("timeout"); */
		29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
		30	}
		31
		32	int
		33	main (void)
		34	{
		35	struct ev_loop *loop = ev_default_loop (0);
		36
		37	/* initialise an io watcher, then start it */
		38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		39	ev_io_start (loop, &stdin_watcher);
		40
		41	/* simple non-repeating 5.5 second timeout */
		42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		43	ev_timer_start (loop, &timeout_watcher);
		44
		45	/* loop till timeout or data ready */
		46	ev_loop (loop, 0);
		47
		48	return 0;
		49	}
		50
9	=head1 DESCRIPTION	51	=head1 DESCRIPTION
10		52
		53	The newest version of this document is also available as a html-formatted
		54	web page you might find easier to navigate when reading it for the first
		55	time: L<http://cvs.schmorp.de/libev/ev.html>.
		56
11	Libev is an event loop: you register interest in certain events (such as a	57	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	58	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	59	these event sources and provide your program with events.
14		60
15	To do this, it must take more or less complete control over your process	61	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	62	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	63	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	65	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	66	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	67	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	68	watcher.
23		69
24	=head1 FEATURES	70	=head2 FEATURES
25		71
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	76	with customised rescheduling (C<ev_periodic>), synchronous signals
		77	(C<ev_signal>), process status change events (C<ev_child>), and event
		78	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		80	file watchers (C<ev_stat>) and even limited support for fork events
		81	(C<ev_fork>).
		82
		83	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	85	for example).
33		86
34	=head1 CONVENTIONS	87	=head2 CONVENTIONS
35		88
36	Libev is very configurable. In this manual the default configuration	89	Libev is very configurable. In this manual the default configuration will
37	will be described, which supports multiple event loops. For more info	90	be described, which supports multiple event loops. For more info about
38	about various configuration options please have a look at the file	91	various configuration options please have a look at B<EMBED> section in
39	F<README.embed> in the libev distribution. If libev was configured without	92	this manual. If libev was configured without support for multiple event
40	support for multiple event loops, then all functions taking an initial	93	loops, then all functions taking an initial argument of name C<loop>
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	94	(which is always of type C<struct ev_loop *>) will not have this argument.
42	will not have this argument.
43		95
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	96	=head2 TIME REPRESENTATION
45		97
46	Libev represents time as a single floating point number, representing the	98	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	99	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	100	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	101	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	102	to the C<double> type in C, and when you need to do any calculations on
		103	it, you should treat it as some floatingpoint value. Unlike the name
		104	component C<stamp> might indicate, it is also used for time differences
		105	throughout libev.
		106
		107	=head1 GLOBAL FUNCTIONS
		108
		109	These functions can be called anytime, even before initialising the
		110	library in any way.
51		111
52	=over 4	112	=over 4
53		113
54	=item ev_tstamp ev_time ()	114	=item ev_tstamp ev_time ()
55		115
56	Returns the current time as libev would use it.	116	Returns the current time as libev would use it. Please note that the
		117	C<ev_now> function is usually faster and also often returns the timestamp
		118	you actually want to know.
		119
		120	=item ev_sleep (ev_tstamp interval)
		121
		122	Sleep for the given interval: The current thread will be blocked until
		123	either it is interrupted or the given time interval has passed. Basically
		124	this is a subsecond-resolution C<sleep ()>.
57		125
58	=item int ev_version_major ()	126	=item int ev_version_major ()
59		127
60	=item int ev_version_minor ()	128	=item int ev_version_minor ()
61		129
62	You can find out the major and minor version numbers of the library	130	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	131	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	132	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	133	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	134	version of the library your program was compiled against.
67		135
		136	These version numbers refer to the ABI version of the library, not the
		137	release version.
		138
68	Usually, its a good idea to terminate if the major versions mismatch,	139	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	140	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	141	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	142	not a problem.
72		143
		144	Example: Make sure we haven't accidentally been linked against the wrong
		145	version.
		146
		147	assert (("libev version mismatch",
		148	ev_version_major () == EV_VERSION_MAJOR
		149	&& ev_version_minor () >= EV_VERSION_MINOR));
		150
		151	=item unsigned int ev_supported_backends ()
		152
		153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		154	value) compiled into this binary of libev (independent of their
		155	availability on the system you are running on). See C<ev_default_loop> for
		156	a description of the set values.
		157
		158	Example: make sure we have the epoll method, because yeah this is cool and
		159	a must have and can we have a torrent of it please!!!11
		160
		161	assert (("sorry, no epoll, no sex",
		162	ev_supported_backends () & EVBACKEND_EPOLL));
		163
		164	=item unsigned int ev_recommended_backends ()
		165
		166	Return the set of all backends compiled into this binary of libev and also
		167	recommended for this platform. This set is often smaller than the one
		168	returned by C<ev_supported_backends>, as for example kqueue is broken on
		169	most BSDs and will not be autodetected unless you explicitly request it
		170	(assuming you know what you are doing). This is the set of backends that
		171	libev will probe for if you specify no backends explicitly.
		172
		173	=item unsigned int ev_embeddable_backends ()
		174
		175	Returns the set of backends that are embeddable in other event loops. This
		176	is the theoretical, all-platform, value. To find which backends
		177	might be supported on the current system, you would need to look at
		178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		179	recommended ones.
		180
		181	See the description of C<ev_embed> watchers for more info.
		182
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
74		184
75	Sets the allocation function to use (the prototype is similar to the	185	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	186	semantics is identical - to the realloc C function). It is used to
77	and free memory (no surprises here). If it returns zero when memory	187	allocate and free memory (no surprises here). If it returns zero when
78	needs to be allocated, the library might abort or take some potentially	188	memory needs to be allocated, the library might abort or take some
79	destructive action. The default is your system realloc function.	189	potentially destructive action. The default is your system realloc
		190	function.
80		191
81	You could override this function in high-availability programs to, say,	192	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,	193	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.	194	or even to sleep a while and retry until some memory is available.
		195
		196	Example: Replace the libev allocator with one that waits a bit and then
		197	retries).
		198
		199	static void *
		200	persistent_realloc (void *ptr, size_t size)
		201	{
		202	for (;;)
		203	{
		204	void *newptr = realloc (ptr, size);
		205
		206	if (newptr)
		207	return newptr;
		208
		209	sleep (60);
		210	}
		211	}
		212
		213	...
		214	ev_set_allocator (persistent_realloc);
84		215
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	216	=item ev_set_syserr_cb (void (*cb)(const char *msg));
86		217
87	Set the callback function to call on a retryable syscall error (such	218	Set the callback function to call on a retryable syscall error (such
88	as failed select, poll, epoll_wait). The message is a printable string	219	as failed select, poll, epoll_wait). The message is a printable string
…		…
90	callback is set, then libev will expect it to remedy the sitution, no	221	callback is set, then libev will expect it to remedy the sitution, no
91	matter what, when it returns. That is, libev will generally retry the	222	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	223	requested operation, or, if the condition doesn't go away, do bad stuff
93	(such as abort).	224	(such as abort).
94		225
		226	Example: This is basically the same thing that libev does internally, too.
		227
		228	static void
		229	fatal_error (const char *msg)
		230	{
		231	perror (msg);
		232	abort ();
		233	}
		234
		235	...
		236	ev_set_syserr_cb (fatal_error);
		237
95	=back	238	=back
96		239
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98		241
99	An event loop is described by a C<struct ev_loop *>. The library knows two	242	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	243	types of such loops, the I<default> loop, which supports signals and child
101	events, and dynamically created loops which do not.	244	events, and dynamically created loops which do not.
102		245
103	If you use threads, a common model is to run the default event loop	246	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	247	in your main thread (or in a separate thread) and for each thread you
105	create, you also create another event loop. Libev itself does no locking	248	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	249	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	250	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because its hideous and inefficient).	251	done correctly, because it's hideous and inefficient).
109		252
110	=over 4	253	=over 4
111		254
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	255	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		256
114	This will initialise the default event loop if it hasn't been initialised	257	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	258	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	259	false. If it already was initialised it simply returns it (and ignores the
117	flags).	260	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		261
119	If you don't know what event loop to use, use the one returned from this	262	If you don't know what event loop to use, use the one returned from this
120	function.	263	function.
121		264
122	The flags argument can be used to specify special behaviour or specific	265	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).	266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		267
125	It supports the following flags:	268	The following flags are supported:
126		269
127	=over 4	270	=over 4
128		271
129	=item EVFLAG_AUTO	272	=item C<EVFLAG_AUTO>
130		273
131	The default flags value. Use this if you have no clue (its the right	274	The default flags value. Use this if you have no clue (it's the right
132	thing, believe me).	275	thing, believe me).
133		276
134	=item EVFLAG_NOENV	277	=item C<EVFLAG_NOENV>
135		278
136	If this flag bit is ored into the flag value (or the program runs setuid	279	If this flag bit is ored into the flag value (or the program runs setuid
137	or setgid) then libev will I<not> look at the environment variable	280	or setgid) then libev will I<not> look at the environment variable
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	282	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	283	useful to try out specific backends to test their performance, or to work
141	around bugs.	284	around bugs.
142		285
		286	=item C<EVFLAG_FORKCHECK>
		287
		288	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		289	a fork, you can also make libev check for a fork in each iteration by
		290	enabling this flag.
		291
		292	This works by calling C<getpid ()> on every iteration of the loop,
		293	and thus this might slow down your event loop if you do a lot of loop
		294	iterations and little real work, but is usually not noticeable (on my
		295	Linux system for example, C<getpid> is actually a simple 5-insn sequence
		296	without a syscall and thus I<very> fast, but my Linux system also has
		297	C<pthread_atfork> which is even faster).
		298
		299	The big advantage of this flag is that you can forget about fork (and
		300	forget about forgetting to tell libev about forking) when you use this
		301	flag.
		302
		303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		304	environment variable.
		305
143	=item EVMETHOD_SELECT portable select backend	306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		307
145	=item EVMETHOD_POLL poll backend (everywhere except windows)	308	This is your standard select(2) backend. Not I<completely> standard, as
		309	libev tries to roll its own fd_set with no limits on the number of fds,
		310	but if that fails, expect a fairly low limit on the number of fds when
		311	using this backend. It doesn't scale too well (O(highest_fd)), but its
		312	usually the fastest backend for a low number of (low-numbered :) fds.
146		313
147	=item EVMETHOD_EPOLL linux only	314	To get good performance out of this backend you need a high amount of
		315	parallelity (most of the file descriptors should be busy). If you are
		316	writing a server, you should C<accept ()> in a loop to accept as many
		317	connections as possible during one iteration. You might also want to have
		318	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		319	readyness notifications you get per iteration.
148		320
149	=item EVMETHOD_KQUEUE some bsds only	321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
150		322
151	=item EVMETHOD_DEVPOLL solaris 8 only	323	And this is your standard poll(2) backend. It's more complicated
		324	than select, but handles sparse fds better and has no artificial
		325	limit on the number of fds you can use (except it will slow down
		326	considerably with a lot of inactive fds). It scales similarly to select,
		327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		328	performance tips.
152		329
153	=item EVMETHOD_PORT solaris 10 only	330	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		331
		332	For few fds, this backend is a bit little slower than poll and select,
		333	but it scales phenomenally better. While poll and select usually scale
		334	like O(total_fds) where n is the total number of fds (or the highest fd),
		335	epoll scales either O(1) or O(active_fds). The epoll design has a number
		336	of shortcomings, such as silently dropping events in some hard-to-detect
		337	cases and rewiring a syscall per fd change, no fork support and bad
		338	support for dup.
		339
		340	While stopping, setting and starting an I/O watcher in the same iteration
		341	will result in some caching, there is still a syscall per such incident
		342	(because the fd could point to a different file description now), so its
		343	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		344	very well if you register events for both fds.
		345
		346	Please note that epoll sometimes generates spurious notifications, so you
		347	need to use non-blocking I/O or other means to avoid blocking when no data
		348	(or space) is available.
		349
		350	Best performance from this backend is achieved by not unregistering all
		351	watchers for a file descriptor until it has been closed, if possible, i.e.
		352	keep at least one watcher active per fd at all times.
		353
		354	While nominally embeddeble in other event loops, this feature is broken in
		355	all kernel versions tested so far.
		356
		357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		358
		359	Kqueue deserves special mention, as at the time of this writing, it
		360	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		361	with anything but sockets and pipes, except on Darwin, where of course
		362	it's completely useless). For this reason it's not being "autodetected"
		363	unless you explicitly specify it explicitly in the flags (i.e. using
		364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		365	system like NetBSD.
		366
		367	You still can embed kqueue into a normal poll or select backend and use it
		368	only for sockets (after having made sure that sockets work with kqueue on
		369	the target platform). See C<ev_embed> watchers for more info.
		370
		371	It scales in the same way as the epoll backend, but the interface to the
		372	kernel is more efficient (which says nothing about its actual speed, of
		373	course). While stopping, setting and starting an I/O watcher does never
		374	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
		375	two event changes per incident, support for C<fork ()> is very bad and it
		376	drops fds silently in similarly hard-to-detect cases.
		377
		378	This backend usually performs well under most conditions.
		379
		380	While nominally embeddable in other event loops, this doesn't work
		381	everywhere, so you might need to test for this. And since it is broken
		382	almost everywhere, you should only use it when you have a lot of sockets
		383	(for which it usually works), by embedding it into another event loop
		384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		385	sockets.
		386
		387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		388
		389	This is not implemented yet (and might never be, unless you send me an
		390	implementation). According to reports, C</dev/poll> only supports sockets
		391	and is not embeddable, which would limit the usefulness of this backend
		392	immensely.
		393
		394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		395
		396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		397	it's really slow, but it still scales very well (O(active_fds)).
		398
		399	Please note that solaris event ports can deliver a lot of spurious
		400	notifications, so you need to use non-blocking I/O or other means to avoid
		401	blocking when no data (or space) is available.
		402
		403	While this backend scales well, it requires one system call per active
		404	file descriptor per loop iteration. For small and medium numbers of file
		405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		406	might perform better.
		407
		408	=item C<EVBACKEND_ALL>
		409
		410	Try all backends (even potentially broken ones that wouldn't be tried
		411	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		413
		414	It is definitely not recommended to use this flag.
		415
		416	=back
154		417
155	If one or more of these are ored into the flags value, then only these	418	If one or more of these are ored into the flags value, then only these
156	backends will be tried (in the reverse order as given here). If one are	419	backends will be tried (in the reverse order as given here). If none are
157	specified, any backend will do.	420	specified, most compiled-in backend will be tried, usually in reverse
		421	order of their flag values :)
158		422
159	=back	423	The most typical usage is like this:
		424
		425	if (!ev_default_loop (0))
		426	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		427
		428	Restrict libev to the select and poll backends, and do not allow
		429	environment settings to be taken into account:
		430
		431	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		432
		433	Use whatever libev has to offer, but make sure that kqueue is used if
		434	available (warning, breaks stuff, best use only with your own private
		435	event loop and only if you know the OS supports your types of fds):
		436
		437	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		438
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	439	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		440
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	441	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	442	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	443	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).	444	undefined behaviour (or a failed assertion if assertions are enabled).
167		445
		446	Example: Try to create a event loop that uses epoll and nothing else.
		447
		448	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		449	if (!epoller)
		450	fatal ("no epoll found here, maybe it hides under your chair");
		451
168	=item ev_default_destroy ()	452	=item ev_default_destroy ()
169		453
170	Destroys the default loop again (frees all memory and kernel state	454	Destroys the default loop again (frees all memory and kernel state
171	etc.). This stops all registered event watchers (by not touching them in	455	etc.). None of the active event watchers will be stopped in the normal
172	any way whatsoever, although you cnanot rely on this :).	456	sense, so e.g. C<ev_is_active> might still return true. It is your
		457	responsibility to either stop all watchers cleanly yoursef I<before>
		458	calling this function, or cope with the fact afterwards (which is usually
		459	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		460	for example).
		461
		462	Note that certain global state, such as signal state, will not be freed by
		463	this function, and related watchers (such as signal and child watchers)
		464	would need to be stopped manually.
		465
		466	In general it is not advisable to call this function except in the
		467	rare occasion where you really need to free e.g. the signal handling
		468	pipe fds. If you need dynamically allocated loops it is better to use
		469	C<ev_loop_new> and C<ev_loop_destroy>).
173		470
174	=item ev_loop_destroy (loop)	471	=item ev_loop_destroy (loop)
175		472
176	Like C<ev_default_destroy>, but destroys an event loop created by an	473	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	474	earlier call to C<ev_loop_new>.
…		…
181	This function reinitialises the kernel state for backends that have	478	This function reinitialises the kernel state for backends that have
182	one. Despite the name, you can call it anytime, but it makes most sense	479	one. Despite the name, you can call it anytime, but it makes most sense
183	after forking, in either the parent or child process (or both, but that	480	after forking, in either the parent or child process (or both, but that
184	again makes little sense).	481	again makes little sense).
185		482
186	You I<must> call this function after forking if and only if you want to	483	You I<must> call this function in the child process after forking if and
187	use the event library in both processes. If you just fork+exec, you don't	484	only if you want to use the event library in both processes. If you just
188	have to call it.	485	fork+exec, you don't have to call it.
189		486
190	The function itself is quite fast and its usually not a problem to call	487	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	488	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>:	489	quite nicely into a call to C<pthread_atfork>:
193		490
194	pthread_atfork (0, 0, ev_default_fork);	491	pthread_atfork (0, 0, ev_default_fork);
		492
		493	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
		494	without calling this function, so if you force one of those backends you
		495	do not need to care.
195		496
196	=item ev_loop_fork (loop)	497	=item ev_loop_fork (loop)
197		498
198	Like C<ev_default_fork>, but acts on an event loop created by	499	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	500	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.	501	after fork, and how you do this is entirely your own problem.
201		502
		503	=item unsigned int ev_loop_count (loop)
		504
		505	Returns the count of loop iterations for the loop, which is identical to
		506	the number of times libev did poll for new events. It starts at C<0> and
		507	happily wraps around with enough iterations.
		508
		509	This value can sometimes be useful as a generation counter of sorts (it
		510	"ticks" the number of loop iterations), as it roughly corresponds with
		511	C<ev_prepare> and C<ev_check> calls.
		512
202	=item unsigned int ev_method (loop)	513	=item unsigned int ev_backend (loop)
203		514
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	515	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	516	use.
206		517
207	=item ev_tstamp = ev_now (loop)	518	=item ev_tstamp ev_now (loop)
208		519
209	Returns the current "event loop time", which is the time the event loop	520	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	521	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	522	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	523	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).	524	event occurring (or more correctly, libev finding out about it).
214		525
215	=item ev_loop (loop, int flags)	526	=item ev_loop (loop, int flags)
216		527
217	Finally, this is it, the event handler. This function usually is called	528	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	529	after you initialised all your watchers and you want to start handling
219	events.	530	events.
220		531
221	If the flags argument is specified as 0, it will not return until either	532	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.	533	either no event watchers are active anymore or C<ev_unloop> was called.
		534
		535	Please note that an explicit C<ev_unloop> is usually better than
		536	relying on all watchers to be stopped when deciding when a program has
		537	finished (especially in interactive programs), but having a program that
		538	automatically loops as long as it has to and no longer by virtue of
		539	relying on its watchers stopping correctly is a thing of beauty.
223		540
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	541	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	542	those events and any outstanding ones, but will not block your process in
226	case there are no events.	543	case there are no events and will return after one iteration of the loop.
227		544
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	545	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	546	neccessary) and will handle those and any outstanding ones. It will block
230	your process until at least one new event arrives.	547	your process until at least one new event arrives, and will return after
		548	one iteration of the loop. This is useful if you are waiting for some
		549	external event in conjunction with something not expressible using other
		550	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		551	usually a better approach for this kind of thing.
231		552
232	This flags value could be used to implement alternative looping	553	Here are the gory details of what C<ev_loop> does:
233	constructs, but the C<prepare> and C<check> watchers provide a better and	554
234	more generic mechanism.	555	- Before the first iteration, call any pending watchers.
		556	* If EVFLAG_FORKCHECK was used, check for a fork.
		557	- If a fork was detected, queue and call all fork watchers.
		558	- Queue and call all prepare watchers.
		559	- If we have been forked, recreate the kernel state.
		560	- Update the kernel state with all outstanding changes.
		561	- Update the "event loop time".
		562	- Calculate for how long to sleep or block, if at all
		563	(active idle watchers, EVLOOP_NONBLOCK or not having
		564	any active watchers at all will result in not sleeping).
		565	- Sleep if the I/O and timer collect interval say so.
		566	- Block the process, waiting for any events.
		567	- Queue all outstanding I/O (fd) events.
		568	- Update the "event loop time" and do time jump handling.
		569	- Queue all outstanding timers.
		570	- Queue all outstanding periodics.
		571	- If no events are pending now, queue all idle watchers.
		572	- Queue all check watchers.
		573	- Call all queued watchers in reverse order (i.e. check watchers first).
		574	Signals and child watchers are implemented as I/O watchers, and will
		575	be handled here by queueing them when their watcher gets executed.
		576	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		577	were used, or there are no active watchers, return, otherwise
		578	continue with step *.
		579
		580	Example: Queue some jobs and then loop until no events are outstanding
		581	anymore.
		582
		583	... queue jobs here, make sure they register event watchers as long
		584	... as they still have work to do (even an idle watcher will do..)
		585	ev_loop (my_loop, 0);
		586	... jobs done. yeah!
235		587
236	=item ev_unloop (loop, how)	588	=item ev_unloop (loop, how)
237		589
238	Can be used to make a call to C<ev_loop> return early. The C<how> argument	590	Can be used to make a call to C<ev_loop> return early (but only after it
		591	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>	592	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>	593	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
241	calls return.	594
		595	This "unloop state" will be cleared when entering C<ev_loop> again.
242		596
243	=item ev_ref (loop)	597	=item ev_ref (loop)
244		598
245	=item ev_unref (loop)	599	=item ev_unref (loop)
246		600
247	Ref/unref can be used to add or remove a refcount on the event loop: Every	601	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	602	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	603	count is nonzero, C<ev_loop> will not return on its own. If you have
250	starting, and ev_ref() before stopping it. Libev itself uses this for	604	a watcher you never unregister that should not keep C<ev_loop> from
251	example for its internal signal pipe: It is not visible to you as a user	605	returning, ev_unref() after starting, and ev_ref() before stopping it. For
252	and should not keep C<ev_loop> from exiting if the work is done. It is	606	example, libev itself uses this for its internal signal pipe: It is not
253	also an excellent way to do this for generic recurring timers or from	607	visible to the libev user and should not keep C<ev_loop> from exiting if
254	within third-party libraries. Just remember to unref after start and ref	608	no event watchers registered by it are active. It is also an excellent
255	before stop.	609	way to do this for generic recurring timers or from within third-party
		610	libraries. Just remember to I<unref after start> and I<ref before stop>
		611	(but only if the watcher wasn't active before, or was active before,
		612	respectively).
		613
		614	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		615	running when nothing else is active.
		616
		617	struct ev_signal exitsig;
		618	ev_signal_init (&exitsig, sig_cb, SIGINT);
		619	ev_signal_start (loop, &exitsig);
		620	evf_unref (loop);
		621
		622	Example: For some weird reason, unregister the above signal handler again.
		623
		624	ev_ref (loop);
		625	ev_signal_stop (loop, &exitsig);
		626
		627	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		628
		629	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		630
		631	These advanced functions influence the time that libev will spend waiting
		632	for events. Both are by default C<0>, meaning that libev will try to
		633	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		634
		635	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		636	allows libev to delay invocation of I/O and timer/periodic callbacks to
		637	increase efficiency of loop iterations.
		638
		639	The background is that sometimes your program runs just fast enough to
		640	handle one (or very few) event(s) per loop iteration. While this makes
		641	the program responsive, it also wastes a lot of CPU time to poll for new
		642	events, especially with backends like C<select ()> which have a high
		643	overhead for the actual polling but can deliver many events at once.
		644
		645	By setting a higher I<io collect interval> you allow libev to spend more
		646	time collecting I/O events, so you can handle more events per iteration,
		647	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		648	C<ev_timer>) will be not affected. Setting this to a non-null value will
		649	introduce an additional C<ev_sleep ()> call into most loop iterations.
		650
		651	Likewise, by setting a higher I<timeout collect interval> you allow libev
		652	to spend more time collecting timeouts, at the expense of increased
		653	latency (the watcher callback will be called later). C<ev_io> watchers
		654	will not be affected. Setting this to a non-null value will not introduce
		655	any overhead in libev.
		656
		657	Many (busy) programs can usually benefit by setting the io collect
		658	interval to a value near C<0.1> or so, which is often enough for
		659	interactive servers (of course not for games), likewise for timeouts. It
		660	usually doesn't make much sense to set it to a lower value than C<0.01>,
		661	as this approsaches the timing granularity of most systems.
256		662
257	=back	663	=back
		664
258		665
259	=head1 ANATOMY OF A WATCHER	666	=head1 ANATOMY OF A WATCHER
260		667
261	A watcher is a structure that you create and register to record your	668	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	669	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:	670	become readable, you would create an C<ev_io> watcher for that:
264		671
265	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	672	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
266	{	673	{
267	ev_io_stop (w);	674	ev_io_stop (w);
268	ev_unloop (loop, EVUNLOOP_ALL);	675	ev_unloop (loop, EVUNLOOP_ALL);
…		…
295	*) >>), and you can stop watching for events at any time by calling the	702	*) >>), and you can stop watching for events at any time by calling the
296	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	703	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
297		704
298	As long as your watcher is active (has been started but not stopped) you	705	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	706	must not touch the values stored in it. Most specifically you must never
300	reinitialise it or call its set method.	707	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		708
307	Each and every callback receives the event loop pointer as first, the	709	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	710	registered watcher structure as second, and a bitset of received events as
309	third argument.	711	third argument.
310		712
311	The rceeived events usually include a single bit per event type received	713	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	714	(you can receive multiple events at the same time). The possible bit masks
313	are:	715	are:
314		716
315	=over 4	717	=over 4
316		718
317	=item EV_READ	719	=item C<EV_READ>
318		720
319	=item EV_WRITE	721	=item C<EV_WRITE>
320		722
321	The file descriptor in the ev_io watcher has become readable and/or	723	The file descriptor in the C<ev_io> watcher has become readable and/or
322	writable.	724	writable.
323		725
324	=item EV_TIMEOUT	726	=item C<EV_TIMEOUT>
325		727
326	The ev_timer watcher has timed out.	728	The C<ev_timer> watcher has timed out.
327		729
328	=item EV_PERIODIC	730	=item C<EV_PERIODIC>
329		731
330	The ev_periodic watcher has timed out.	732	The C<ev_periodic> watcher has timed out.
331		733
332	=item EV_SIGNAL	734	=item C<EV_SIGNAL>
333		735
334	The signal specified in the ev_signal watcher has been received by a thread.	736	The signal specified in the C<ev_signal> watcher has been received by a thread.
335		737
336	=item EV_CHILD	738	=item C<EV_CHILD>
337		739
338	The pid specified in the ev_child watcher has received a status change.	740	The pid specified in the C<ev_child> watcher has received a status change.
339		741
		742	=item C<EV_STAT>
		743
		744	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		745
340	=item EV_IDLE	746	=item C<EV_IDLE>
341		747
342	The ev_idle watcher has determined that you have nothing better to do.	748	The C<ev_idle> watcher has determined that you have nothing better to do.
343		749
344	=item EV_PREPARE	750	=item C<EV_PREPARE>
345		751
346	=item EV_CHECK	752	=item C<EV_CHECK>
347		753
348	All ev_prepare watchers are invoked just I<before> C<ev_loop> starts	754	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	755	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	756	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	757	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	758	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	759	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
354	C<ev_loop> from blocking).	760	C<ev_loop> from blocking).
355		761
		762	=item C<EV_EMBED>
		763
		764	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		765
		766	=item C<EV_FORK>
		767
		768	The event loop has been resumed in the child process after fork (see
		769	C<ev_fork>).
		770
356	=item EV_ERROR	771	=item C<EV_ERROR>
357		772
358	An unspecified error has occured, the watcher has been stopped. This might	773	An unspecified error has occured, the watcher has been stopped. This might
359	happen because the watcher could not be properly started because libev	774	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	775	ran out of memory, a file descriptor was found to be closed or any other
361	problem. You best act on it by reporting the problem and somehow coping	776	problem. You best act on it by reporting the problem and somehow coping
…		…
367	with the error from read() or write(). This will not work in multithreaded	782	with the error from read() or write(). This will not work in multithreaded
368	programs, though, so beware.	783	programs, though, so beware.
369		784
370	=back	785	=back
371		786
		787	=head2 GENERIC WATCHER FUNCTIONS
		788
		789	In the following description, C<TYPE> stands for the watcher type,
		790	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		791
		792	=over 4
		793
		794	=item C<ev_init> (ev_TYPE *watcher, callback)
		795
		796	This macro initialises the generic portion of a watcher. The contents
		797	of the watcher object can be arbitrary (so C<malloc> will do). Only
		798	the generic parts of the watcher are initialised, you I<need> to call
		799	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		800	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		801	which rolls both calls into one.
		802
		803	You can reinitialise a watcher at any time as long as it has been stopped
		804	(or never started) and there are no pending events outstanding.
		805
		806	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		807	int revents)>.
		808
		809	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		810
		811	This macro initialises the type-specific parts of a watcher. You need to
		812	call C<ev_init> at least once before you call this macro, but you can
		813	call C<ev_TYPE_set> any number of times. You must not, however, call this
		814	macro on a watcher that is active (it can be pending, however, which is a
		815	difference to the C<ev_init> macro).
		816
		817	Although some watcher types do not have type-specific arguments
		818	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		819
		820	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		821
		822	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		823	calls into a single call. This is the most convinient method to initialise
		824	a watcher. The same limitations apply, of course.
		825
		826	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		827
		828	Starts (activates) the given watcher. Only active watchers will receive
		829	events. If the watcher is already active nothing will happen.
		830
		831	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		832
		833	Stops the given watcher again (if active) and clears the pending
		834	status. It is possible that stopped watchers are pending (for example,
		835	non-repeating timers are being stopped when they become pending), but
		836	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		837	you want to free or reuse the memory used by the watcher it is therefore a
		838	good idea to always call its C<ev_TYPE_stop> function.
		839
		840	=item bool ev_is_active (ev_TYPE *watcher)
		841
		842	Returns a true value iff the watcher is active (i.e. it has been started
		843	and not yet been stopped). As long as a watcher is active you must not modify
		844	it.
		845
		846	=item bool ev_is_pending (ev_TYPE *watcher)
		847
		848	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		849	events but its callback has not yet been invoked). As long as a watcher
		850	is pending (but not active) you must not call an init function on it (but
		851	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		852	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		853	it).
		854
		855	=item callback ev_cb (ev_TYPE *watcher)
		856
		857	Returns the callback currently set on the watcher.
		858
		859	=item ev_cb_set (ev_TYPE *watcher, callback)
		860
		861	Change the callback. You can change the callback at virtually any time
		862	(modulo threads).
		863
		864	=item ev_set_priority (ev_TYPE *watcher, priority)
		865
		866	=item int ev_priority (ev_TYPE *watcher)
		867
		868	Set and query the priority of the watcher. The priority is a small
		869	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		870	(default: C<-2>). Pending watchers with higher priority will be invoked
		871	before watchers with lower priority, but priority will not keep watchers
		872	from being executed (except for C<ev_idle> watchers).
		873
		874	This means that priorities are I<only> used for ordering callback
		875	invocation after new events have been received. This is useful, for
		876	example, to reduce latency after idling, or more often, to bind two
		877	watchers on the same event and make sure one is called first.
		878
		879	If you need to suppress invocation when higher priority events are pending
		880	you need to look at C<ev_idle> watchers, which provide this functionality.
		881
		882	You I<must not> change the priority of a watcher as long as it is active or
		883	pending.
		884
		885	The default priority used by watchers when no priority has been set is
		886	always C<0>, which is supposed to not be too high and not be too low :).
		887
		888	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		889	fine, as long as you do not mind that the priority value you query might
		890	or might not have been adjusted to be within valid range.
		891
		892	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		893
		894	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		895	C<loop> nor C<revents> need to be valid as long as the watcher callback
		896	can deal with that fact.
		897
		898	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		899
		900	If the watcher is pending, this function returns clears its pending status
		901	and returns its C<revents> bitset (as if its callback was invoked). If the
		902	watcher isn't pending it does nothing and returns C<0>.
		903
		904	=back
		905
		906
372	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	907	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
373		908
374	Each watcher has, by default, a member C<void *data> that you can change	909	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	910	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	911	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	912	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	913	member, you can also "subclass" the watcher type and provide your own
379	data:	914	data:
380		915
…		…
393	{	928	{
394	struct my_io *w = (struct my_io *)w_;	929	struct my_io *w = (struct my_io *)w_;
395	...	930	...
396	}	931	}
397		932
398	More interesting and less C-conformant ways of catsing your callback type	933	More interesting and less C-conformant ways of casting your callback type
399	have been omitted....	934	instead have been omitted.
		935
		936	Another common scenario is having some data structure with multiple
		937	watchers:
		938
		939	struct my_biggy
		940	{
		941	int some_data;
		942	ev_timer t1;
		943	ev_timer t2;
		944	}
		945
		946	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		947	you need to use C<offsetof>:
		948
		949	#include <stddef.h>
		950
		951	static void
		952	t1_cb (EV_P_ struct ev_timer *w, int revents)
		953	{
		954	struct my_biggy big = (struct my_biggy *
		955	(((char *)w) - offsetof (struct my_biggy, t1));
		956	}
		957
		958	static void
		959	t2_cb (EV_P_ struct ev_timer *w, int revents)
		960	{
		961	struct my_biggy big = (struct my_biggy *
		962	(((char *)w) - offsetof (struct my_biggy, t2));
		963	}
400		964
401		965
402	=head1 WATCHER TYPES	966	=head1 WATCHER TYPES
403		967
404	This section describes each watcher in detail, but will not repeat	968	This section describes each watcher in detail, but will not repeat
405	information given in the last section.	969	information given in the last section. Any initialisation/set macros,
		970	functions and members specific to the watcher type are explained.
406		971
		972	Members are additionally marked with either I<[read-only]>, meaning that,
		973	while the watcher is active, you can look at the member and expect some
		974	sensible content, but you must not modify it (you can modify it while the
		975	watcher is stopped to your hearts content), or I<[read-write]>, which
		976	means you can expect it to have some sensible content while the watcher
		977	is active, but you can also modify it. Modifying it may not do something
		978	sensible or take immediate effect (or do anything at all), but libev will
		979	not crash or malfunction in any way.
		980
		981
407	=head2 struct ev_io - is my file descriptor readable or writable	982	=head2 C<ev_io> - is this file descriptor readable or writable?
408		983
409	I/O watchers check whether a file descriptor is readable or writable	984	I/O watchers check whether a file descriptor is readable or writable
410	in each iteration of the event loop (This behaviour is called	985	in each iteration of the event loop, or, more precisely, when reading
411	level-triggering because you keep receiving events as long as the	986	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	987	some data. This behaviour is called level-triggering because you keep
413	act on the event and neither want to receive future events).	988	receiving events as long as the condition persists. Remember you can stop
		989	the watcher if you don't want to act on the event and neither want to
		990	receive future events.
414		991
415	In general you can register as many read and/or write event watchers oer	992	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	993	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	994	descriptors to non-blocking mode is also usually a good idea (but not
418	required if you know what you are doing).	995	required if you know what you are doing).
419		996
420	You have to be careful with dup'ed file descriptors, though. Some backends
421	(the linux epoll backend is a notable example) cannot handle dup'ed file
422	descriptors correctly if you register interest in two or more fds pointing
423	to the same file/socket etc. description.
424
425	If you must do this, then force the use of a known-to-be-good backend	997	If you must do this, then force the use of a known-to-be-good backend
426	(at the time of this writing, this includes only EVMETHOD_SELECT and	998	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
427	EVMETHOD_POLL).	999	C<EVBACKEND_POLL>).
		1000
		1001	Another thing you have to watch out for is that it is quite easy to
		1002	receive "spurious" readyness notifications, that is your callback might
		1003	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1004	because there is no data. Not only are some backends known to create a
		1005	lot of those (for example solaris ports), it is very easy to get into
		1006	this situation even with a relatively standard program structure. Thus
		1007	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1008	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1009
		1010	If you cannot run the fd in non-blocking mode (for example you should not
		1011	play around with an Xlib connection), then you have to seperately re-test
		1012	whether a file descriptor is really ready with a known-to-be good interface
		1013	such as poll (fortunately in our Xlib example, Xlib already does this on
		1014	its own, so its quite safe to use).
		1015
		1016	=head3 The special problem of disappearing file descriptors
		1017
		1018	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1019	descriptor (either by calling C<close> explicitly or by any other means,
		1020	such as C<dup>). The reason is that you register interest in some file
		1021	descriptor, but when it goes away, the operating system will silently drop
		1022	this interest. If another file descriptor with the same number then is
		1023	registered with libev, there is no efficient way to see that this is, in
		1024	fact, a different file descriptor.
		1025
		1026	To avoid having to explicitly tell libev about such cases, libev follows
		1027	the following policy: Each time C<ev_io_set> is being called, libev
		1028	will assume that this is potentially a new file descriptor, otherwise
		1029	it is assumed that the file descriptor stays the same. That means that
		1030	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1031	descriptor even if the file descriptor number itself did not change.
		1032
		1033	This is how one would do it normally anyway, the important point is that
		1034	the libev application should not optimise around libev but should leave
		1035	optimisations to libev.
		1036
		1037	=head3 The special problem of dup'ed file descriptors
		1038
		1039	Some backends (e.g. epoll), cannot register events for file descriptors,
		1040	but only events for the underlying file descriptions. That means when you
		1041	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1042	events for them, only one file descriptor might actually receive events.
		1043
		1044	There is no workaround possible except not registering events
		1045	for potentially C<dup ()>'ed file descriptors, or to resort to
		1046	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1047
		1048	=head3 The special problem of fork
		1049
		1050	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1051	useless behaviour. Libev fully supports fork, but needs to be told about
		1052	it in the child.
		1053
		1054	To support fork in your programs, you either have to call
		1055	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1056	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1057	C<EVBACKEND_POLL>.
		1058
		1059
		1060	=head3 Watcher-Specific Functions
428		1061
429	=over 4	1062	=over 4
430		1063
431	=item ev_io_init (ev_io *, callback, int fd, int events)	1064	=item ev_io_init (ev_io *, callback, int fd, int events)
432		1065
433	=item ev_io_set (ev_io *, int fd, int events)	1066	=item ev_io_set (ev_io *, int fd, int events)
434		1067
435	Configures an ev_io watcher. The fd is the file descriptor to rceeive	1068	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 |	1069	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
437	EV_WRITE> to receive the given events.	1070	C<EV_READ | EV_WRITE> to receive the given events.
		1071
		1072	=item int fd [read-only]
		1073
		1074	The file descriptor being watched.
		1075
		1076	=item int events [read-only]
		1077
		1078	The events being watched.
438		1079
439	=back	1080	=back
440		1081
		1082	=head3 Examples
		1083
		1084	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1085	readable, but only once. Since it is likely line-buffered, you could
		1086	attempt to read a whole line in the callback.
		1087
		1088	static void
		1089	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1090	{
		1091	ev_io_stop (loop, w);
		1092	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1093	}
		1094
		1095	...
		1096	struct ev_loop *loop = ev_default_init (0);
		1097	struct ev_io stdin_readable;
		1098	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1099	ev_io_start (loop, &stdin_readable);
		1100	ev_loop (loop, 0);
		1101
		1102
441	=head2 struct ev_timer - relative and optionally recurring timeouts	1103	=head2 C<ev_timer> - relative and optionally repeating timeouts
442		1104
443	Timer watchers are simple relative timers that generate an event after a	1105	Timer watchers are simple relative timers that generate an event after a
444	given time, and optionally repeating in regular intervals after that.	1106	given time, and optionally repeating in regular intervals after that.
445		1107
446	The timers are based on real time, that is, if you register an event that	1108	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	1109	times out after an hour and you reset your system clock to last years
448	time, it will still time out after (roughly) and hour. "Roughly" because	1110	time, it will still time out after (roughly) and hour. "Roughly" because
449	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1111	detecting time jumps is hard, and some inaccuracies are unavoidable (the
450	monotonic clock option helps a lot here).	1112	monotonic clock option helps a lot here).
		1113
		1114	The relative timeouts are calculated relative to the C<ev_now ()>
		1115	time. This is usually the right thing as this timestamp refers to the time
		1116	of the event triggering whatever timeout you are modifying/starting. If
		1117	you suspect event processing to be delayed and you I<need> to base the timeout
		1118	on the current time, use something like this to adjust for this:
		1119
		1120	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1121
		1122	The callback is guarenteed to be invoked only when its timeout has passed,
		1123	but if multiple timers become ready during the same loop iteration then
		1124	order of execution is undefined.
		1125
		1126	=head3 Watcher-Specific Functions and Data Members
451		1127
452	=over 4	1128	=over 4
453		1129
454	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1130	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
455		1131
…		…
461	later, again, and again, until stopped manually.	1137	later, again, and again, until stopped manually.
462		1138
463	The timer itself will do a best-effort at avoiding drift, that is, if you	1139	The timer itself will do a best-effort at avoiding drift, that is, if you
464	configure a timer to trigger every 10 seconds, then it will trigger at	1140	configure a timer to trigger every 10 seconds, then it will trigger at
465	exactly 10 second intervals. If, however, your program cannot keep up with	1141	exactly 10 second intervals. If, however, your program cannot keep up with
466	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1142	the timer (because it takes longer than those 10 seconds to do stuff) the
467	timer will not fire more than once per event loop iteration.	1143	timer will not fire more than once per event loop iteration.
468		1144
469	=item ev_timer_again (loop)	1145	=item ev_timer_again (loop)
470		1146
471	This will act as if the timer timed out and restart it again if it is	1147	This will act as if the timer timed out and restart it again if it is
472	repeating. The exact semantics are:	1148	repeating. The exact semantics are:
473		1149
		1150	If the timer is pending, its pending status is cleared.
		1151
474	If the timer is started but nonrepeating, stop it.	1152	If the timer is started but nonrepeating, stop it (as if it timed out).
475		1153
476	If the timer is repeating, either start it if necessary (with the repeat	1154	If the timer is repeating, either start it if necessary (with the
477	value), or reset the running timer to the repeat value.	1155	C<repeat> value), or reset the running timer to the C<repeat> value.
478		1156
479	This sounds a bit complicated, but here is a useful and typical	1157	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	1158	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	1159	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	1160	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	1161	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	1162	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	1163	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.	1164	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1165	automatically restart it if need be.
		1166
		1167	That means you can ignore the C<after> value and C<ev_timer_start>
		1168	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1169
		1170	ev_timer_init (timer, callback, 0., 5.);
		1171	ev_timer_again (loop, timer);
		1172	...
		1173	timer->again = 17.;
		1174	ev_timer_again (loop, timer);
		1175	...
		1176	timer->again = 10.;
		1177	ev_timer_again (loop, timer);
		1178
		1179	This is more slightly efficient then stopping/starting the timer each time
		1180	you want to modify its timeout value.
		1181
		1182	=item ev_tstamp repeat [read-write]
		1183
		1184	The current C<repeat> value. Will be used each time the watcher times out
		1185	or C<ev_timer_again> is called and determines the next timeout (if any),
		1186	which is also when any modifications are taken into account.
487		1187
488	=back	1188	=back
489		1189
		1190	=head3 Examples
		1191
		1192	Example: Create a timer that fires after 60 seconds.
		1193
		1194	static void
		1195	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1196	{
		1197	.. one minute over, w is actually stopped right here
		1198	}
		1199
		1200	struct ev_timer mytimer;
		1201	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1202	ev_timer_start (loop, &mytimer);
		1203
		1204	Example: Create a timeout timer that times out after 10 seconds of
		1205	inactivity.
		1206
		1207	static void
		1208	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1209	{
		1210	.. ten seconds without any activity
		1211	}
		1212
		1213	struct ev_timer mytimer;
		1214	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1215	ev_timer_again (&mytimer); /* start timer */
		1216	ev_loop (loop, 0);
		1217
		1218	// and in some piece of code that gets executed on any "activity":
		1219	// reset the timeout to start ticking again at 10 seconds
		1220	ev_timer_again (&mytimer);
		1221
		1222
490	=head2 ev_periodic - to cron or not to cron it	1223	=head2 C<ev_periodic> - to cron or not to cron?
491		1224
492	Periodic watchers are also timers of a kind, but they are very versatile	1225	Periodic watchers are also timers of a kind, but they are very versatile
493	(and unfortunately a bit complex).	1226	(and unfortunately a bit complex).
494		1227
495	Unlike ev_timer's, they are not based on real time (or relative time)	1228	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	1229	but on wallclock time (absolute time). You can tell a periodic watcher
497	to trigger "at" some specific point in time. For example, if you tell a	1230	to trigger "at" 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 ()	1231	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
499	+ 10.>) and then reset your system clock to the last year, then it will	1232	+ 10.>) and then reset your system clock to the last year, then it will
500	take a year to trigger the event (unlike an ev_timer, which would trigger	1233	take a year to trigger the event (unlike an C<ev_timer>, which would trigger
501	roughly 10 seconds later and of course not if you reset your system time	1234	roughly 10 seconds later).
502	again).
503		1235
504	They can also be used to implement vastly more complex timers, such as	1236	They can also be used to implement vastly more complex timers, such as
505	triggering an event on eahc midnight, local time.	1237	triggering an event on each midnight, local time or other, complicated,
		1238	rules.
		1239
		1240	As with timers, the callback is guarenteed to be invoked only when the
		1241	time (C<at>) has been passed, but if multiple periodic timers become ready
		1242	during the same loop iteration then order of execution is undefined.
		1243
		1244	=head3 Watcher-Specific Functions and Data Members
506		1245
507	=over 4	1246	=over 4
508		1247
509	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1248	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
510		1249
511	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1250	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
512		1251
513	Lots of arguments, lets sort it out... There are basically three modes of	1252	Lots of arguments, lets sort it out... There are basically three modes of
514	operation, and we will explain them from simplest to complex:	1253	operation, and we will explain them from simplest to complex:
515		1254
516
517	=over 4	1255	=over 4
518		1256
519	=item * absolute timer (interval = reschedule_cb = 0)	1257	=item * absolute timer (at = time, interval = reschedule_cb = 0)
520		1258
521	In this configuration the watcher triggers an event at the wallclock time	1259	In this configuration the watcher triggers an event at the wallclock time
522	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1260	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
523	that is, if it is to be run at January 1st 2011 then it will run when the	1261	that is, if it is to be run at January 1st 2011 then it will run when the
524	system time reaches or surpasses this time.	1262	system time reaches or surpasses this time.
525		1263
526	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1264	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
527		1265
528	In this mode the watcher will always be scheduled to time out at the next	1266	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	1267	C<at + N * interval> time (for some integer N, which can also be negative)
530	of any time jumps.	1268	and then repeat, regardless of any time jumps.
531		1269
532	This can be used to create timers that do not drift with respect to system	1270	This can be used to create timers that do not drift with respect to system
533	time:	1271	time:
534		1272
535	ev_periodic_set (&periodic, 0., 3600., 0);	1273	ev_periodic_set (&periodic, 0., 3600., 0);
536		1274
537	This doesn't mean there will always be 3600 seconds in between triggers,	1275	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	1276	but only that the 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	1277	full hour (UTC), or more correctly, when the system time is evenly divisible
540	by 3600.	1278	by 3600.
541		1279
542	Another way to think about it (for the mathematically inclined) is that	1280	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	1281	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.	1282	time where C<time = at (mod interval)>, regardless of any time jumps.
545		1283
		1284	For numerical stability it is preferable that the C<at> value is near
		1285	C<ev_now ()> (the current time), but there is no range requirement for
		1286	this value.
		1287
546	=item * manual reschedule mode (reschedule_cb = callback)	1288	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
547		1289
548	In this mode the values for C<interval> and C<at> are both being	1290	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	1291	ignored. Instead, each time the periodic watcher gets scheduled, the
550	reschedule callback will be called with the watcher as first, and the	1292	reschedule callback will be called with the watcher as first, and the
551	current time as second argument.	1293	current time as second argument.
552		1294
553	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1295	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	1296	ever, or make any event loop modifications>. If you need to stop it,
555	to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.	1297	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
		1298	starting an C<ev_prepare> watcher, which is legal).
556		1299
557	Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1300	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
558	ev_tstamp now)>, e.g.:	1301	ev_tstamp now)>, e.g.:
559		1302
560	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1303	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
561	{	1304	{
562	return now + 60.;	1305	return now + 60.;
…		…
565	It must return the next time to trigger, based on the passed time value	1308	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	1309	(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	1310	will usually be called just before the callback will be triggered, but
568	might be called at other times, too.	1311	might be called at other times, too.
569		1312
		1313	NOTE: I<< This callback must always return a time that is later than the
		1314	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
		1315
570	This can be used to create very complex timers, such as a timer that	1316	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	1317	triggers on each 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	1318	next midnight after C<now> and return the timestamp value for this. How
573	is, again, up to you (but it is not trivial).	1319	you do this is, again, up to you (but it is not trivial, which is the main
		1320	reason I omitted it as an example).
574		1321
575	=back	1322	=back
576		1323
577	=item ev_periodic_again (loop, ev_periodic *)	1324	=item ev_periodic_again (loop, ev_periodic *)
578		1325
579	Simply stops and restarts the periodic watcher again. This is only useful	1326	Simply stops and restarts the periodic watcher again. This is only useful
580	when you changed some parameters or the reschedule callback would return	1327	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	1328	a different time than the last time it was called (e.g. in a crond like
582	program when the crontabs have changed).	1329	program when the crontabs have changed).
583		1330
		1331	=item ev_tstamp offset [read-write]
		1332
		1333	When repeating, this contains the offset value, otherwise this is the
		1334	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1335
		1336	Can be modified any time, but changes only take effect when the periodic
		1337	timer fires or C<ev_periodic_again> is being called.
		1338
		1339	=item ev_tstamp interval [read-write]
		1340
		1341	The current interval value. Can be modified any time, but changes only
		1342	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1343	called.
		1344
		1345	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1346
		1347	The current reschedule callback, or C<0>, if this functionality is
		1348	switched off. Can be changed any time, but changes only take effect when
		1349	the periodic timer fires or C<ev_periodic_again> is being called.
		1350
		1351	=item ev_tstamp at [read-only]
		1352
		1353	When active, contains the absolute time that the watcher is supposed to
		1354	trigger next.
		1355
584	=back	1356	=back
585		1357
		1358	=head3 Examples
		1359
		1360	Example: Call a callback every hour, or, more precisely, whenever the
		1361	system clock is divisible by 3600. The callback invocation times have
		1362	potentially a lot of jittering, but good long-term stability.
		1363
		1364	static void
		1365	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1366	{
		1367	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1368	}
		1369
		1370	struct ev_periodic hourly_tick;
		1371	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1372	ev_periodic_start (loop, &hourly_tick);
		1373
		1374	Example: The same as above, but use a reschedule callback to do it:
		1375
		1376	#include <math.h>
		1377
		1378	static ev_tstamp
		1379	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1380	{
		1381	return fmod (now, 3600.) + 3600.;
		1382	}
		1383
		1384	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1385
		1386	Example: Call a callback every hour, starting now:
		1387
		1388	struct ev_periodic hourly_tick;
		1389	ev_periodic_init (&hourly_tick, clock_cb,
		1390	fmod (ev_now (loop), 3600.), 3600., 0);
		1391	ev_periodic_start (loop, &hourly_tick);
		1392
		1393
586	=head2 ev_signal - signal me when a signal gets signalled	1394	=head2 C<ev_signal> - signal me when a signal gets signalled!
587		1395
588	Signal watchers will trigger an event when the process receives a specific	1396	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	1397	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	1398	will try it's best to deliver signals synchronously, i.e. as part of the
591	normal event processing, like any other event.	1399	normal event processing, like any other event.
592		1400
593	You cna configure as many watchers as you like per signal. Only when the	1401	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	1402	first watcher gets started will libev actually register a signal watcher
595	with the kernel (thus it coexists with your own signal handlers as long	1403	with the kernel (thus it coexists with your own signal handlers as long
596	as you don't register any with libev). Similarly, when the last signal	1404	as you don't register any with libev). Similarly, when the last signal
597	watcher for a signal is stopped libev will reset the signal handler to	1405	watcher for a signal is stopped libev will reset the signal handler to
598	SIG_DFL (regardless of what it was set to before).	1406	SIG_DFL (regardless of what it was set to before).
599		1407
		1408	=head3 Watcher-Specific Functions and Data Members
		1409
600	=over 4	1410	=over 4
601		1411
602	=item ev_signal_init (ev_signal *, callback, int signum)	1412	=item ev_signal_init (ev_signal *, callback, int signum)
603		1413
604	=item ev_signal_set (ev_signal *, int signum)	1414	=item ev_signal_set (ev_signal *, int signum)
605		1415
606	Configures the watcher to trigger on the given signal number (usually one	1416	Configures the watcher to trigger on the given signal number (usually one
607	of the C<SIGxxx> constants).	1417	of the C<SIGxxx> constants).
608		1418
		1419	=item int signum [read-only]
		1420
		1421	The signal the watcher watches out for.
		1422
609	=back	1423	=back
610		1424
		1425
611	=head2 ev_child - wait for pid status changes	1426	=head2 C<ev_child> - watch out for process status changes
612		1427
613	Child watchers trigger when your process receives a SIGCHLD in response to	1428	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).	1429	some child status changes (most typically when a child of yours dies).
		1430
		1431	=head3 Watcher-Specific Functions and Data Members
615		1432
616	=over 4	1433	=over 4
617		1434
618	=item ev_child_init (ev_child *, callback, int pid)	1435	=item ev_child_init (ev_child *, callback, int pid)
619		1436
620	=item ev_child_set (ev_child *, int pid)	1437	=item ev_child_set (ev_child *, int pid)
621		1438
622	Configures the watcher to wait for status changes of process C<pid> (or	1439	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	1440	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	1441	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	1442	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.	1443	C<waitpid> documentation). The C<rpid> member contains the pid of the
		1444	process causing the status change.
		1445
		1446	=item int pid [read-only]
		1447
		1448	The process id this watcher watches out for, or C<0>, meaning any process id.
		1449
		1450	=item int rpid [read-write]
		1451
		1452	The process id that detected a status change.
		1453
		1454	=item int rstatus [read-write]
		1455
		1456	The process exit/trace status caused by C<rpid> (see your systems
		1457	C<waitpid> and C<sys/wait.h> documentation for details).
627		1458
628	=back	1459	=back
629		1460
		1461	=head3 Examples
		1462
		1463	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1464
		1465	static void
		1466	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1467	{
		1468	ev_unloop (loop, EVUNLOOP_ALL);
		1469	}
		1470
		1471	struct ev_signal signal_watcher;
		1472	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1473	ev_signal_start (loop, &sigint_cb);
		1474
		1475
		1476	=head2 C<ev_stat> - did the file attributes just change?
		1477
		1478	This watches a filesystem path for attribute changes. That is, it calls
		1479	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1480	compared to the last time, invoking the callback if it did.
		1481
		1482	The path does not need to exist: changing from "path exists" to "path does
		1483	not exist" is a status change like any other. The condition "path does
		1484	not exist" is signified by the C<st_nlink> field being zero (which is
		1485	otherwise always forced to be at least one) and all the other fields of
		1486	the stat buffer having unspecified contents.
		1487
		1488	The path I<should> be absolute and I<must not> end in a slash. If it is
		1489	relative and your working directory changes, the behaviour is undefined.
		1490
		1491	Since there is no standard to do this, the portable implementation simply
		1492	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1493	can specify a recommended polling interval for this case. If you specify
		1494	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1495	unspecified default> value will be used (which you can expect to be around
		1496	five seconds, although this might change dynamically). Libev will also
		1497	impose a minimum interval which is currently around C<0.1>, but thats
		1498	usually overkill.
		1499
		1500	This watcher type is not meant for massive numbers of stat watchers,
		1501	as even with OS-supported change notifications, this can be
		1502	resource-intensive.
		1503
		1504	At the time of this writing, only the Linux inotify interface is
		1505	implemented (implementing kqueue support is left as an exercise for the
		1506	reader). Inotify will be used to give hints only and should not change the
		1507	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1508	to fall back to regular polling again even with inotify, but changes are
		1509	usually detected immediately, and if the file exists there will be no
		1510	polling.
		1511
		1512	=head3 Inotify
		1513
		1514	When C<inotify (7)> support has been compiled into libev (generally only
		1515	available on Linux) and present at runtime, it will be used to speed up
		1516	change detection where possible. The inotify descriptor will be created lazily
		1517	when the first C<ev_stat> watcher is being started.
		1518
		1519	Inotify presense does not change the semantics of C<ev_stat> watchers
		1520	except that changes might be detected earlier, and in some cases, to avoid
		1521	making regular C<stat> calls. Even in the presense of inotify support
		1522	there are many cases where libev has to resort to regular C<stat> polling.
		1523
		1524	(There is no support for kqueue, as apparently it cannot be used to
		1525	implement this functionality, due to the requirement of having a file
		1526	descriptor open on the object at all times).
		1527
		1528	=head3 The special problem of stat time resolution
		1529
		1530	The C<stat ()> syscall only supports full-second resolution portably, and
		1531	even on systems where the resolution is higher, many filesystems still
		1532	only support whole seconds.
		1533
		1534	That means that, if the time is the only thing that changes, you might
		1535	miss updates: on the first update, C<ev_stat> detects a change and calls
		1536	your callback, which does something. When there is another update within
		1537	the same second, C<ev_stat> will be unable to detect it.
		1538
		1539	The solution to this is to delay acting on a change for a second (or till
		1540	the next second boundary), using a roughly one-second delay C<ev_timer>
		1541	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1542	is added to work around small timing inconsistencies of some operating
		1543	systems.
		1544
		1545	=head3 Watcher-Specific Functions and Data Members
		1546
		1547	=over 4
		1548
		1549	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1550
		1551	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1552
		1553	Configures the watcher to wait for status changes of the given
		1554	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1555	be detected and should normally be specified as C<0> to let libev choose
		1556	a suitable value. The memory pointed to by C<path> must point to the same
		1557	path for as long as the watcher is active.
		1558
		1559	The callback will be receive C<EV_STAT> when a change was detected,
		1560	relative to the attributes at the time the watcher was started (or the
		1561	last change was detected).
		1562
		1563	=item ev_stat_stat (ev_stat *)
		1564
		1565	Updates the stat buffer immediately with new values. If you change the
		1566	watched path in your callback, you could call this fucntion to avoid
		1567	detecting this change (while introducing a race condition). Can also be
		1568	useful simply to find out the new values.
		1569
		1570	=item ev_statdata attr [read-only]
		1571
		1572	The most-recently detected attributes of the file. Although the type is of
		1573	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1574	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1575	was some error while C<stat>ing the file.
		1576
		1577	=item ev_statdata prev [read-only]
		1578
		1579	The previous attributes of the file. The callback gets invoked whenever
		1580	C<prev> != C<attr>.
		1581
		1582	=item ev_tstamp interval [read-only]
		1583
		1584	The specified interval.
		1585
		1586	=item const char *path [read-only]
		1587
		1588	The filesystem path that is being watched.
		1589
		1590	=back
		1591
		1592	=head3 Examples
		1593
		1594	Example: Watch C</etc/passwd> for attribute changes.
		1595
		1596	static void
		1597	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1598	{
		1599	/* /etc/passwd changed in some way */
		1600	if (w->attr.st_nlink)
		1601	{
		1602	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1603	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1604	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1605	}
		1606	else
		1607	/* you shalt not abuse printf for puts */
		1608	puts ("wow, /etc/passwd is not there, expect problems. "
		1609	"if this is windows, they already arrived\n");
		1610	}
		1611
		1612	...
		1613	ev_stat passwd;
		1614
		1615	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1616	ev_stat_start (loop, &passwd);
		1617
		1618	Example: Like above, but additionally use a one-second delay so we do not
		1619	miss updates (however, frequent updates will delay processing, too, so
		1620	one might do the work both on C<ev_stat> callback invocation I<and> on
		1621	C<ev_timer> callback invocation).
		1622
		1623	static ev_stat passwd;
		1624	static ev_timer timer;
		1625
		1626	static void
		1627	timer_cb (EV_P_ ev_timer *w, int revents)
		1628	{
		1629	ev_timer_stop (EV_A_ w);
		1630
		1631	/* now it's one second after the most recent passwd change */
		1632	}
		1633
		1634	static void
		1635	stat_cb (EV_P_ ev_stat *w, int revents)
		1636	{
		1637	/* reset the one-second timer */
		1638	ev_timer_again (EV_A_ &timer);
		1639	}
		1640
		1641	...
		1642	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1643	ev_stat_start (loop, &passwd);
		1644	ev_timer_init (&timer, timer_cb, 0., 1.01);
		1645
		1646
630	=head2 ev_idle - when you've got nothing better to do	1647	=head2 C<ev_idle> - when you've got nothing better to do...
631		1648
632	Idle watchers trigger events when there are no other I/O or timer (or	1649	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	1650	priority are pending (prepare, check and other idle watchers do not
634	handling sockets or timeouts it will not be called. But when your process	1651	count).
635	is idle all idle watchers are being called again and again - until	1652
		1653	That is, as long as your process is busy handling sockets or timeouts
		1654	(or even signals, imagine) of the same or higher priority it will not be
		1655	triggered. But when your process is idle (or only lower-priority watchers
		1656	are pending), the idle watchers are being called once per event loop
636	stopped, that is, or your process receives more events.	1657	iteration - until stopped, that is, or your process receives more events
		1658	and becomes busy again with higher priority stuff.
637		1659
638	The most noteworthy effect is that as long as any idle watchers are	1660	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.	1661	active, the process will not block when waiting for new events.
640		1662
641	Apart from keeping your process non-blocking (which is a useful	1663	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	1664	effect on its own sometimes), idle watchers are a good place to do
643	"pseudo-background processing", or delay processing stuff to after the	1665	"pseudo-background processing", or delay processing stuff to after the
644	event loop has handled all outstanding events.	1666	event loop has handled all outstanding events.
645		1667
		1668	=head3 Watcher-Specific Functions and Data Members
		1669
646	=over 4	1670	=over 4
647		1671
648	=item ev_idle_init (ev_signal *, callback)	1672	=item ev_idle_init (ev_signal *, callback)
649		1673
650	Initialises and configures the idle watcher - it has no parameters of any	1674	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,	1675	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
652	believe me.	1676	believe me.
653		1677
654	=back	1678	=back
655		1679
656	=head2 prepare and check - your hooks into the event loop	1680	=head3 Examples
657		1681
		1682	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1683	callback, free it. Also, use no error checking, as usual.
		1684
		1685	static void
		1686	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1687	{
		1688	free (w);
		1689	// now do something you wanted to do when the program has
		1690	// no longer asnything immediate to do.
		1691	}
		1692
		1693	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1694	ev_idle_init (idle_watcher, idle_cb);
		1695	ev_idle_start (loop, idle_cb);
		1696
		1697
		1698	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		1699
658	Prepare and check watchers usually (but not always) are used in	1700	Prepare and check watchers are usually (but not always) used in tandem:
659	tandom. Prepare watchers get invoked before the process blocks and check	1701	prepare watchers get invoked before the process blocks and check watchers
660	watchers afterwards.	1702	afterwards.
661		1703
		1704	You I<must not> call C<ev_loop> or similar functions that enter
		1705	the current event loop from either C<ev_prepare> or C<ev_check>
		1706	watchers. Other loops than the current one are fine, however. The
		1707	rationale behind this is that you do not need to check for recursion in
		1708	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1709	C<ev_check> so if you have one watcher of each kind they will always be
		1710	called in pairs bracketing the blocking call.
		1711
662	Their main purpose is to integrate other event mechanisms into libev. This	1712	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	1713	their use is somewhat advanced. This could be used, for example, to track
664	watchers, integrate net-snmp or a coroutine library and lots more.	1714	variable changes, implement your own watchers, integrate net-snmp or a
		1715	coroutine library and lots more. They are also occasionally useful if
		1716	you cache some data and want to flush it before blocking (for example,
		1717	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1718	watcher).
665		1719
666	This is done by examining in each prepare call which file descriptors need	1720	This is done by examining in each prepare call which file descriptors need
667	to be watched by the other library, registering ev_io watchers for them	1721	to be watched by the other library, registering C<ev_io> watchers for
668	and starting an ev_timer watcher for any timeouts (many libraries provide	1722	them and starting an C<ev_timer> watcher for any timeouts (many libraries
669	just this functionality). Then, in the check watcher you check for any	1723	provide just this functionality). Then, in the check watcher you check for
670	events that occured (by making your callbacks set soem flags for example)	1724	any events that occured (by checking the pending status of all watchers
671	and call back into the library.	1725	and stopping them) and call back into the library. The I/O and timer
		1726	callbacks will never actually be called (but must be valid nevertheless,
		1727	because you never know, you know?).
672		1728
673	As another example, the perl Coro module uses these hooks to integrate	1729	As another example, the Perl Coro module uses these hooks to integrate
674	coroutines into libev programs, by yielding to other active coroutines	1730	coroutines into libev programs, by yielding to other active coroutines
675	during each prepare and only letting the process block if no coroutines	1731	during each prepare and only letting the process block if no coroutines
676	are ready to run.	1732	are ready to run (it's actually more complicated: it only runs coroutines
		1733	with priority higher than or equal to the event loop and one coroutine
		1734	of lower priority, but only once, using idle watchers to keep the event
		1735	loop from blocking if lower-priority coroutines are active, thus mapping
		1736	low-priority coroutines to idle/background tasks).
		1737
		1738	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1739	priority, to ensure that they are being run before any other watchers
		1740	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1741	too) should not activate ("feed") events into libev. While libev fully
		1742	supports this, they will be called before other C<ev_check> watchers
		1743	did their job. As C<ev_check> watchers are often used to embed other
		1744	(non-libev) event loops those other event loops might be in an unusable
		1745	state until their C<ev_check> watcher ran (always remind yourself to
		1746	coexist peacefully with others).
		1747
		1748	=head3 Watcher-Specific Functions and Data Members
677		1749
678	=over 4	1750	=over 4
679		1751
680	=item ev_prepare_init (ev_prepare *, callback)	1752	=item ev_prepare_init (ev_prepare *, callback)
681		1753
682	=item ev_check_init (ev_check *, callback)	1754	=item ev_check_init (ev_check *, callback)
683		1755
684	Initialises and configures the prepare or check watcher - they have no	1756	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>	1757	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
686	macros, but using them is utterly, utterly pointless.	1758	macros, but using them is utterly, utterly and completely pointless.
687		1759
688	=back	1760	=back
689		1761
		1762	=head3 Examples
		1763
		1764	There are a number of principal ways to embed other event loops or modules
		1765	into libev. Here are some ideas on how to include libadns into libev
		1766	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1767	use for an actually working example. Another Perl module named C<EV::Glib>
		1768	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
		1769	into the Glib event loop).
		1770
		1771	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1772	and in a check watcher, destroy them and call into libadns. What follows
		1773	is pseudo-code only of course. This requires you to either use a low
		1774	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1775	the callbacks for the IO/timeout watchers might not have been called yet.
		1776
		1777	static ev_io iow [nfd];
		1778	static ev_timer tw;
		1779
		1780	static void
		1781	io_cb (ev_loop *loop, ev_io *w, int revents)
		1782	{
		1783	}
		1784
		1785	// create io watchers for each fd and a timer before blocking
		1786	static void
		1787	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1788	{
		1789	int timeout = 3600000;
		1790	struct pollfd fds [nfd];
		1791	// actual code will need to loop here and realloc etc.
		1792	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1793
		1794	/* the callback is illegal, but won't be called as we stop during check */
		1795	ev_timer_init (&tw, 0, timeout * 1e-3);
		1796	ev_timer_start (loop, &tw);
		1797
		1798	// create one ev_io per pollfd
		1799	for (int i = 0; i < nfd; ++i)
		1800	{
		1801	ev_io_init (iow + i, io_cb, fds [i].fd,
		1802	((fds [i].events & POLLIN ? EV_READ : 0)
		1803	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1804
		1805	fds [i].revents = 0;
		1806	ev_io_start (loop, iow + i);
		1807	}
		1808	}
		1809
		1810	// stop all watchers after blocking
		1811	static void
		1812	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1813	{
		1814	ev_timer_stop (loop, &tw);
		1815
		1816	for (int i = 0; i < nfd; ++i)
		1817	{
		1818	// set the relevant poll flags
		1819	// could also call adns_processreadable etc. here
		1820	struct pollfd *fd = fds + i;
		1821	int revents = ev_clear_pending (iow + i);
		1822	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1823	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1824
		1825	// now stop the watcher
		1826	ev_io_stop (loop, iow + i);
		1827	}
		1828
		1829	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1830	}
		1831
		1832	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1833	in the prepare watcher and would dispose of the check watcher.
		1834
		1835	Method 3: If the module to be embedded supports explicit event
		1836	notification (adns does), you can also make use of the actual watcher
		1837	callbacks, and only destroy/create the watchers in the prepare watcher.
		1838
		1839	static void
		1840	timer_cb (EV_P_ ev_timer *w, int revents)
		1841	{
		1842	adns_state ads = (adns_state)w->data;
		1843	update_now (EV_A);
		1844
		1845	adns_processtimeouts (ads, &tv_now);
		1846	}
		1847
		1848	static void
		1849	io_cb (EV_P_ ev_io *w, int revents)
		1850	{
		1851	adns_state ads = (adns_state)w->data;
		1852	update_now (EV_A);
		1853
		1854	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1855	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1856	}
		1857
		1858	// do not ever call adns_afterpoll
		1859
		1860	Method 4: Do not use a prepare or check watcher because the module you
		1861	want to embed is too inflexible to support it. Instead, youc na override
		1862	their poll function. The drawback with this solution is that the main
		1863	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1864	this.
		1865
		1866	static gint
		1867	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		1868	{
		1869	int got_events = 0;
		1870
		1871	for (n = 0; n < nfds; ++n)
		1872	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		1873
		1874	if (timeout >= 0)
		1875	// create/start timer
		1876
		1877	// poll
		1878	ev_loop (EV_A_ 0);
		1879
		1880	// stop timer again
		1881	if (timeout >= 0)
		1882	ev_timer_stop (EV_A_ &to);
		1883
		1884	// stop io watchers again - their callbacks should have set
		1885	for (n = 0; n < nfds; ++n)
		1886	ev_io_stop (EV_A_ iow [n]);
		1887
		1888	return got_events;
		1889	}
		1890
		1891
		1892	=head2 C<ev_embed> - when one backend isn't enough...
		1893
		1894	This is a rather advanced watcher type that lets you embed one event loop
		1895	into another (currently only C<ev_io> events are supported in the embedded
		1896	loop, other types of watchers might be handled in a delayed or incorrect
		1897	fashion and must not be used).
		1898
		1899	There are primarily two reasons you would want that: work around bugs and
		1900	prioritise I/O.
		1901
		1902	As an example for a bug workaround, the kqueue backend might only support
		1903	sockets on some platform, so it is unusable as generic backend, but you
		1904	still want to make use of it because you have many sockets and it scales
		1905	so nicely. In this case, you would create a kqueue-based loop and embed it
		1906	into your default loop (which might use e.g. poll). Overall operation will
		1907	be a bit slower because first libev has to poll and then call kevent, but
		1908	at least you can use both at what they are best.
		1909
		1910	As for prioritising I/O: rarely you have the case where some fds have
		1911	to be watched and handled very quickly (with low latency), and even
		1912	priorities and idle watchers might have too much overhead. In this case
		1913	you would put all the high priority stuff in one loop and all the rest in
		1914	a second one, and embed the second one in the first.
		1915
		1916	As long as the watcher is active, the callback will be invoked every time
		1917	there might be events pending in the embedded loop. The callback must then
		1918	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		1919	their callbacks (you could also start an idle watcher to give the embedded
		1920	loop strictly lower priority for example). You can also set the callback
		1921	to C<0>, in which case the embed watcher will automatically execute the
		1922	embedded loop sweep.
		1923
		1924	As long as the watcher is started it will automatically handle events. The
		1925	callback will be invoked whenever some events have been handled. You can
		1926	set the callback to C<0> to avoid having to specify one if you are not
		1927	interested in that.
		1928
		1929	Also, there have not currently been made special provisions for forking:
		1930	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1931	but you will also have to stop and restart any C<ev_embed> watchers
		1932	yourself.
		1933
		1934	Unfortunately, not all backends are embeddable, only the ones returned by
		1935	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1936	portable one.
		1937
		1938	So when you want to use this feature you will always have to be prepared
		1939	that you cannot get an embeddable loop. The recommended way to get around
		1940	this is to have a separate variables for your embeddable loop, try to
		1941	create it, and if that fails, use the normal loop for everything.
		1942
		1943	=head3 Watcher-Specific Functions and Data Members
		1944
		1945	=over 4
		1946
		1947	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		1948
		1949	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		1950
		1951	Configures the watcher to embed the given loop, which must be
		1952	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1953	invoked automatically, otherwise it is the responsibility of the callback
		1954	to invoke it (it will continue to be called until the sweep has been done,
		1955	if you do not want thta, you need to temporarily stop the embed watcher).
		1956
		1957	=item ev_embed_sweep (loop, ev_embed *)
		1958
		1959	Make a single, non-blocking sweep over the embedded loop. This works
		1960	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1961	apropriate way for embedded loops.
		1962
		1963	=item struct ev_loop *other [read-only]
		1964
		1965	The embedded event loop.
		1966
		1967	=back
		1968
		1969	=head3 Examples
		1970
		1971	Example: Try to get an embeddable event loop and embed it into the default
		1972	event loop. If that is not possible, use the default loop. The default
		1973	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		1974	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		1975	used).
		1976
		1977	struct ev_loop *loop_hi = ev_default_init (0);
		1978	struct ev_loop *loop_lo = 0;
		1979	struct ev_embed embed;
		1980
		1981	// see if there is a chance of getting one that works
		1982	// (remember that a flags value of 0 means autodetection)
		1983	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		1984	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		1985	: 0;
		1986
		1987	// if we got one, then embed it, otherwise default to loop_hi
		1988	if (loop_lo)
		1989	{
		1990	ev_embed_init (&embed, 0, loop_lo);
		1991	ev_embed_start (loop_hi, &embed);
		1992	}
		1993	else
		1994	loop_lo = loop_hi;
		1995
		1996	Example: Check if kqueue is available but not recommended and create
		1997	a kqueue backend for use with sockets (which usually work with any
		1998	kqueue implementation). Store the kqueue/socket-only event loop in
		1999	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2000
		2001	struct ev_loop *loop = ev_default_init (0);
		2002	struct ev_loop *loop_socket = 0;
		2003	struct ev_embed embed;
		2004
		2005	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2006	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2007	{
		2008	ev_embed_init (&embed, 0, loop_socket);
		2009	ev_embed_start (loop, &embed);
		2010	}
		2011
		2012	if (!loop_socket)
		2013	loop_socket = loop;
		2014
		2015	// now use loop_socket for all sockets, and loop for everything else
		2016
		2017
		2018	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2019
		2020	Fork watchers are called when a C<fork ()> was detected (usually because
		2021	whoever is a good citizen cared to tell libev about it by calling
		2022	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2023	event loop blocks next and before C<ev_check> watchers are being called,
		2024	and only in the child after the fork. If whoever good citizen calling
		2025	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2026	handlers will be invoked, too, of course.
		2027
		2028	=head3 Watcher-Specific Functions and Data Members
		2029
		2030	=over 4
		2031
		2032	=item ev_fork_init (ev_signal *, callback)
		2033
		2034	Initialises and configures the fork watcher - it has no parameters of any
		2035	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2036	believe me.
		2037
		2038	=back
		2039
		2040
690	=head1 OTHER FUNCTIONS	2041	=head1 OTHER FUNCTIONS
691		2042
692	There are some other fucntions of possible interest. Described. Here. Now.	2043	There are some other functions of possible interest. Described. Here. Now.
693		2044
694	=over 4	2045	=over 4
695		2046
696	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2047	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
697		2048
698	This function combines a simple timer and an I/O watcher, calls your	2049	This function combines a simple timer and an I/O watcher, calls your
699	callback on whichever event happens first and automatically stop both	2050	callback on whichever event happens first and automatically stop both
700	watchers. This is useful if you want to wait for a single event on an fd	2051	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	2052	or timeout without having to allocate/configure/start/stop/free one or
702	more watchers yourself.	2053	more watchers yourself.
703		2054
704	If C<fd> is less than 0, then no I/O watcher will be started and events is	2055	If C<fd> is less than 0, then no I/O watcher will be started and events
705	ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set	2056	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
706	will be craeted and started.	2057	C<events> set will be craeted and started.
707		2058
708	If C<timeout> is less than 0, then no timeout watcher will be	2059	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	2060	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
710	= 0) will be started.	2061	repeat = 0) will be started. While C<0> is a valid timeout, it is of
		2062	dubious value.
711		2063
712	The callback has the type C<void (*cb)(int revents, void *arg)> and	2064	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,	2065	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>:	2066	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
		2067	value passed to C<ev_once>:
715		2068
716	static void stdin_ready (int revents, void *arg)	2069	static void stdin_ready (int revents, void *arg)
717	{	2070	{
718	if (revents & EV_TIMEOUT)	2071	if (revents & EV_TIMEOUT)
719	/* doh, nothing entered */	2072	/* doh, nothing entered */;
720	else if (revents & EV_READ)	2073	else if (revents & EV_READ)
721	/* stdin might have data for us, joy! */	2074	/* stdin might have data for us, joy! */;
722	}	2075	}
723		2076
724	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	2077	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
725		2078
726	=item ev_feed_event (loop, watcher, int events)	2079	=item ev_feed_event (ev_loop *, watcher *, int revents)
727		2080
728	Feeds the given event set into the event loop, as if the specified event	2081	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	2082	had happened for the specified watcher (which must be a pointer to an
730	initialised but not necessarily active event watcher).	2083	initialised but not necessarily started event watcher).
731		2084
732	=item ev_feed_fd_event (loop, int fd, int revents)	2085	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
733		2086
734	Feed an event on the given fd, as if a file descriptor backend detected it.	2087	Feed an event on the given fd, as if a file descriptor backend detected
		2088	the given events it.
735		2089
736	=item ev_feed_signal_event (loop, int signum)	2090	=item ev_feed_signal_event (ev_loop *loop, int signum)
737		2091
738	Feed an event as if the given signal occured (loop must be the default loop!).	2092	Feed an event as if the given signal occured (C<loop> must be the default
		2093	loop!).
739		2094
740	=back	2095	=back
741		2096
		2097
		2098	=head1 LIBEVENT EMULATION
		2099
		2100	Libev offers a compatibility emulation layer for libevent. It cannot
		2101	emulate the internals of libevent, so here are some usage hints:
		2102
		2103	=over 4
		2104
		2105	=item * Use it by including <event.h>, as usual.
		2106
		2107	=item * The following members are fully supported: ev_base, ev_callback,
		2108	ev_arg, ev_fd, ev_res, ev_events.
		2109
		2110	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2111	maintained by libev, it does not work exactly the same way as in libevent (consider
		2112	it a private API).
		2113
		2114	=item * Priorities are not currently supported. Initialising priorities
		2115	will fail and all watchers will have the same priority, even though there
		2116	is an ev_pri field.
		2117
		2118	=item * Other members are not supported.
		2119
		2120	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2121	to use the libev header file and library.
		2122
		2123	=back
		2124
		2125	=head1 C++ SUPPORT
		2126
		2127	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2128	you to use some convinience methods to start/stop watchers and also change
		2129	the callback model to a model using method callbacks on objects.
		2130
		2131	To use it,
		2132
		2133	#include <ev++.h>
		2134
		2135	This automatically includes F<ev.h> and puts all of its definitions (many
		2136	of them macros) into the global namespace. All C++ specific things are
		2137	put into the C<ev> namespace. It should support all the same embedding
		2138	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2139
		2140	Care has been taken to keep the overhead low. The only data member the C++
		2141	classes add (compared to plain C-style watchers) is the event loop pointer
		2142	that the watcher is associated with (or no additional members at all if
		2143	you disable C<EV_MULTIPLICITY> when embedding libev).
		2144
		2145	Currently, functions, and static and non-static member functions can be
		2146	used as callbacks. Other types should be easy to add as long as they only
		2147	need one additional pointer for context. If you need support for other
		2148	types of functors please contact the author (preferably after implementing
		2149	it).
		2150
		2151	Here is a list of things available in the C<ev> namespace:
		2152
		2153	=over 4
		2154
		2155	=item C<ev::READ>, C<ev::WRITE> etc.
		2156
		2157	These are just enum values with the same values as the C<EV_READ> etc.
		2158	macros from F<ev.h>.
		2159
		2160	=item C<ev::tstamp>, C<ev::now>
		2161
		2162	Aliases to the same types/functions as with the C<ev_> prefix.
		2163
		2164	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2165
		2166	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2167	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2168	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2169	defines by many implementations.
		2170
		2171	All of those classes have these methods:
		2172
		2173	=over 4
		2174
		2175	=item ev::TYPE::TYPE ()
		2176
		2177	=item ev::TYPE::TYPE (struct ev_loop *)
		2178
		2179	=item ev::TYPE::~TYPE
		2180
		2181	The constructor (optionally) takes an event loop to associate the watcher
		2182	with. If it is omitted, it will use C<EV_DEFAULT>.
		2183
		2184	The constructor calls C<ev_init> for you, which means you have to call the
		2185	C<set> method before starting it.
		2186
		2187	It will not set a callback, however: You have to call the templated C<set>
		2188	method to set a callback before you can start the watcher.
		2189
		2190	(The reason why you have to use a method is a limitation in C++ which does
		2191	not allow explicit template arguments for constructors).
		2192
		2193	The destructor automatically stops the watcher if it is active.
		2194
		2195	=item w->set<class, &class::method> (object *)
		2196
		2197	This method sets the callback method to call. The method has to have a
		2198	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2199	first argument and the C<revents> as second. The object must be given as
		2200	parameter and is stored in the C<data> member of the watcher.
		2201
		2202	This method synthesizes efficient thunking code to call your method from
		2203	the C callback that libev requires. If your compiler can inline your
		2204	callback (i.e. it is visible to it at the place of the C<set> call and
		2205	your compiler is good :), then the method will be fully inlined into the
		2206	thunking function, making it as fast as a direct C callback.
		2207
		2208	Example: simple class declaration and watcher initialisation
		2209
		2210	struct myclass
		2211	{
		2212	void io_cb (ev::io &w, int revents) { }
		2213	}
		2214
		2215	myclass obj;
		2216	ev::io iow;
		2217	iow.set <myclass, &myclass::io_cb> (&obj);
		2218
		2219	=item w->set<function> (void *data = 0)
		2220
		2221	Also sets a callback, but uses a static method or plain function as
		2222	callback. The optional C<data> argument will be stored in the watcher's
		2223	C<data> member and is free for you to use.
		2224
		2225	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2226
		2227	See the method-C<set> above for more details.
		2228
		2229	Example:
		2230
		2231	static void io_cb (ev::io &w, int revents) { }
		2232	iow.set <io_cb> ();
		2233
		2234	=item w->set (struct ev_loop *)
		2235
		2236	Associates a different C<struct ev_loop> with this watcher. You can only
		2237	do this when the watcher is inactive (and not pending either).
		2238
		2239	=item w->set ([args])
		2240
		2241	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2242	called at least once. Unlike the C counterpart, an active watcher gets
		2243	automatically stopped and restarted when reconfiguring it with this
		2244	method.
		2245
		2246	=item w->start ()
		2247
		2248	Starts the watcher. Note that there is no C<loop> argument, as the
		2249	constructor already stores the event loop.
		2250
		2251	=item w->stop ()
		2252
		2253	Stops the watcher if it is active. Again, no C<loop> argument.
		2254
		2255	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2256
		2257	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2258	C<ev_TYPE_again> function.
		2259
		2260	=item w->sweep () (C<ev::embed> only)
		2261
		2262	Invokes C<ev_embed_sweep>.
		2263
		2264	=item w->update () (C<ev::stat> only)
		2265
		2266	Invokes C<ev_stat_stat>.
		2267
		2268	=back
		2269
		2270	=back
		2271
		2272	Example: Define a class with an IO and idle watcher, start one of them in
		2273	the constructor.
		2274
		2275	class myclass
		2276	{
		2277	ev_io io; void io_cb (ev::io &w, int revents);
		2278	ev_idle idle void idle_cb (ev::idle &w, int revents);
		2279
		2280	myclass ();
		2281	}
		2282
		2283	myclass::myclass (int fd)
		2284	{
		2285	io .set <myclass, &myclass::io_cb > (this);
		2286	idle.set <myclass, &myclass::idle_cb> (this);
		2287
		2288	io.start (fd, ev::READ);
		2289	}
		2290
		2291
		2292	=head1 MACRO MAGIC
		2293
		2294	Libev can be compiled with a variety of options, the most fundamantal
		2295	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2296	functions and callbacks have an initial C<struct ev_loop *> argument.
		2297
		2298	To make it easier to write programs that cope with either variant, the
		2299	following macros are defined:
		2300
		2301	=over 4
		2302
		2303	=item C<EV_A>, C<EV_A_>
		2304
		2305	This provides the loop I<argument> for functions, if one is required ("ev
		2306	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2307	C<EV_A_> is used when other arguments are following. Example:
		2308
		2309	ev_unref (EV_A);
		2310	ev_timer_add (EV_A_ watcher);
		2311	ev_loop (EV_A_ 0);
		2312
		2313	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2314	which is often provided by the following macro.
		2315
		2316	=item C<EV_P>, C<EV_P_>
		2317
		2318	This provides the loop I<parameter> for functions, if one is required ("ev
		2319	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2320	C<EV_P_> is used when other parameters are following. Example:
		2321
		2322	// this is how ev_unref is being declared
		2323	static void ev_unref (EV_P);
		2324
		2325	// this is how you can declare your typical callback
		2326	static void cb (EV_P_ ev_timer *w, int revents)
		2327
		2328	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2329	suitable for use with C<EV_A>.
		2330
		2331	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2332
		2333	Similar to the other two macros, this gives you the value of the default
		2334	loop, if multiple loops are supported ("ev loop default").
		2335
		2336	=back
		2337
		2338	Example: Declare and initialise a check watcher, utilising the above
		2339	macros so it will work regardless of whether multiple loops are supported
		2340	or not.
		2341
		2342	static void
		2343	check_cb (EV_P_ ev_timer *w, int revents)
		2344	{
		2345	ev_check_stop (EV_A_ w);
		2346	}
		2347
		2348	ev_check check;
		2349	ev_check_init (&check, check_cb);
		2350	ev_check_start (EV_DEFAULT_ &check);
		2351	ev_loop (EV_DEFAULT_ 0);
		2352
		2353	=head1 EMBEDDING
		2354
		2355	Libev can (and often is) directly embedded into host
		2356	applications. Examples of applications that embed it include the Deliantra
		2357	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2358	and rxvt-unicode.
		2359
		2360	The goal is to enable you to just copy the necessary files into your
		2361	source directory without having to change even a single line in them, so
		2362	you can easily upgrade by simply copying (or having a checked-out copy of
		2363	libev somewhere in your source tree).
		2364
		2365	=head2 FILESETS
		2366
		2367	Depending on what features you need you need to include one or more sets of files
		2368	in your app.
		2369
		2370	=head3 CORE EVENT LOOP
		2371
		2372	To include only the libev core (all the C<ev_*> functions), with manual
		2373	configuration (no autoconf):
		2374
		2375	#define EV_STANDALONE 1
		2376	#include "ev.c"
		2377
		2378	This will automatically include F<ev.h>, too, and should be done in a
		2379	single C source file only to provide the function implementations. To use
		2380	it, do the same for F<ev.h> in all files wishing to use this API (best
		2381	done by writing a wrapper around F<ev.h> that you can include instead and
		2382	where you can put other configuration options):
		2383
		2384	#define EV_STANDALONE 1
		2385	#include "ev.h"
		2386
		2387	Both header files and implementation files can be compiled with a C++
		2388	compiler (at least, thats a stated goal, and breakage will be treated
		2389	as a bug).
		2390
		2391	You need the following files in your source tree, or in a directory
		2392	in your include path (e.g. in libev/ when using -Ilibev):
		2393
		2394	ev.h
		2395	ev.c
		2396	ev_vars.h
		2397	ev_wrap.h
		2398
		2399	ev_win32.c required on win32 platforms only
		2400
		2401	ev_select.c only when select backend is enabled (which is enabled by default)
		2402	ev_poll.c only when poll backend is enabled (disabled by default)
		2403	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2404	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2405	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2406
		2407	F<ev.c> includes the backend files directly when enabled, so you only need
		2408	to compile this single file.
		2409
		2410	=head3 LIBEVENT COMPATIBILITY API
		2411
		2412	To include the libevent compatibility API, also include:
		2413
		2414	#include "event.c"
		2415
		2416	in the file including F<ev.c>, and:
		2417
		2418	#include "event.h"
		2419
		2420	in the files that want to use the libevent API. This also includes F<ev.h>.
		2421
		2422	You need the following additional files for this:
		2423
		2424	event.h
		2425	event.c
		2426
		2427	=head3 AUTOCONF SUPPORT
		2428
		2429	Instead of using C<EV_STANDALONE=1> and providing your config in
		2430	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2431	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2432	include F<config.h> and configure itself accordingly.
		2433
		2434	For this of course you need the m4 file:
		2435
		2436	libev.m4
		2437
		2438	=head2 PREPROCESSOR SYMBOLS/MACROS
		2439
		2440	Libev can be configured via a variety of preprocessor symbols you have to define
		2441	before including any of its files. The default is not to build for multiplicity
		2442	and only include the select backend.
		2443
		2444	=over 4
		2445
		2446	=item EV_STANDALONE
		2447
		2448	Must always be C<1> if you do not use autoconf configuration, which
		2449	keeps libev from including F<config.h>, and it also defines dummy
		2450	implementations for some libevent functions (such as logging, which is not
		2451	supported). It will also not define any of the structs usually found in
		2452	F<event.h> that are not directly supported by the libev core alone.
		2453
		2454	=item EV_USE_MONOTONIC
		2455
		2456	If defined to be C<1>, libev will try to detect the availability of the
		2457	monotonic clock option at both compiletime and runtime. Otherwise no use
		2458	of the monotonic clock option will be attempted. If you enable this, you
		2459	usually have to link against librt or something similar. Enabling it when
		2460	the functionality isn't available is safe, though, although you have
		2461	to make sure you link against any libraries where the C<clock_gettime>
		2462	function is hiding in (often F<-lrt>).
		2463
		2464	=item EV_USE_REALTIME
		2465
		2466	If defined to be C<1>, libev will try to detect the availability of the
		2467	realtime clock option at compiletime (and assume its availability at
		2468	runtime if successful). Otherwise no use of the realtime clock option will
		2469	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2470	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2471	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2472
		2473	=item EV_USE_NANOSLEEP
		2474
		2475	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2476	and will use it for delays. Otherwise it will use C<select ()>.
		2477
		2478	=item EV_USE_SELECT
		2479
		2480	If undefined or defined to be C<1>, libev will compile in support for the
		2481	C<select>(2) backend. No attempt at autodetection will be done: if no
		2482	other method takes over, select will be it. Otherwise the select backend
		2483	will not be compiled in.
		2484
		2485	=item EV_SELECT_USE_FD_SET
		2486
		2487	If defined to C<1>, then the select backend will use the system C<fd_set>
		2488	structure. This is useful if libev doesn't compile due to a missing
		2489	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2490	exotic systems. This usually limits the range of file descriptors to some
		2491	low limit such as 1024 or might have other limitations (winsocket only
		2492	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2493	influence the size of the C<fd_set> used.
		2494
		2495	=item EV_SELECT_IS_WINSOCKET
		2496
		2497	When defined to C<1>, the select backend will assume that
		2498	select/socket/connect etc. don't understand file descriptors but
		2499	wants osf handles on win32 (this is the case when the select to
		2500	be used is the winsock select). This means that it will call
		2501	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2502	it is assumed that all these functions actually work on fds, even
		2503	on win32. Should not be defined on non-win32 platforms.
		2504
		2505	=item EV_FD_TO_WIN32_HANDLE
		2506
		2507	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2508	file descriptors to socket handles. When not defining this symbol (the
		2509	default), then libev will call C<_get_osfhandle>, which is usually
		2510	correct. In some cases, programs use their own file descriptor management,
		2511	in which case they can provide this function to map fds to socket handles.
		2512
		2513	=item EV_USE_POLL
		2514
		2515	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2516	backend. Otherwise it will be enabled on non-win32 platforms. It
		2517	takes precedence over select.
		2518
		2519	=item EV_USE_EPOLL
		2520
		2521	If defined to be C<1>, libev will compile in support for the Linux
		2522	C<epoll>(7) backend. Its availability will be detected at runtime,
		2523	otherwise another method will be used as fallback. This is the
		2524	preferred backend for GNU/Linux systems.
		2525
		2526	=item EV_USE_KQUEUE
		2527
		2528	If defined to be C<1>, libev will compile in support for the BSD style
		2529	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2530	otherwise another method will be used as fallback. This is the preferred
		2531	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2532	supports some types of fds correctly (the only platform we found that
		2533	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2534	not be used unless explicitly requested. The best way to use it is to find
		2535	out whether kqueue supports your type of fd properly and use an embedded
		2536	kqueue loop.
		2537
		2538	=item EV_USE_PORT
		2539
		2540	If defined to be C<1>, libev will compile in support for the Solaris
		2541	10 port style backend. Its availability will be detected at runtime,
		2542	otherwise another method will be used as fallback. This is the preferred
		2543	backend for Solaris 10 systems.
		2544
		2545	=item EV_USE_DEVPOLL
		2546
		2547	reserved for future expansion, works like the USE symbols above.
		2548
		2549	=item EV_USE_INOTIFY
		2550
		2551	If defined to be C<1>, libev will compile in support for the Linux inotify
		2552	interface to speed up C<ev_stat> watchers. Its actual availability will
		2553	be detected at runtime.
		2554
		2555	=item EV_H
		2556
		2557	The name of the F<ev.h> header file used to include it. The default if
		2558	undefined is C<"ev.h"> in F<event.h> and F<ev.c>. This can be used to
		2559	virtually rename the F<ev.h> header file in case of conflicts.
		2560
		2561	=item EV_CONFIG_H
		2562
		2563	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2564	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2565	C<EV_H>, above.
		2566
		2567	=item EV_EVENT_H
		2568
		2569	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2570	of how the F<event.h> header can be found, the dfeault is C<"event.h">.
		2571
		2572	=item EV_PROTOTYPES
		2573
		2574	If defined to be C<0>, then F<ev.h> will not define any function
		2575	prototypes, but still define all the structs and other symbols. This is
		2576	occasionally useful if you want to provide your own wrapper functions
		2577	around libev functions.
		2578
		2579	=item EV_MULTIPLICITY
		2580
		2581	If undefined or defined to C<1>, then all event-loop-specific functions
		2582	will have the C<struct ev_loop *> as first argument, and you can create
		2583	additional independent event loops. Otherwise there will be no support
		2584	for multiple event loops and there is no first event loop pointer
		2585	argument. Instead, all functions act on the single default loop.
		2586
		2587	=item EV_MINPRI
		2588
		2589	=item EV_MAXPRI
		2590
		2591	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2592	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2593	provide for more priorities by overriding those symbols (usually defined
		2594	to be C<-2> and C<2>, respectively).
		2595
		2596	When doing priority-based operations, libev usually has to linearly search
		2597	all the priorities, so having many of them (hundreds) uses a lot of space
		2598	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2599	fine.
		2600
		2601	If your embedding app does not need any priorities, defining these both to
		2602	C<0> will save some memory and cpu.
		2603
		2604	=item EV_PERIODIC_ENABLE
		2605
		2606	If undefined or defined to be C<1>, then periodic timers are supported. If
		2607	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2608	code.
		2609
		2610	=item EV_IDLE_ENABLE
		2611
		2612	If undefined or defined to be C<1>, then idle watchers are supported. If
		2613	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2614	code.
		2615
		2616	=item EV_EMBED_ENABLE
		2617
		2618	If undefined or defined to be C<1>, then embed watchers are supported. If
		2619	defined to be C<0>, then they are not.
		2620
		2621	=item EV_STAT_ENABLE
		2622
		2623	If undefined or defined to be C<1>, then stat watchers are supported. If
		2624	defined to be C<0>, then they are not.
		2625
		2626	=item EV_FORK_ENABLE
		2627
		2628	If undefined or defined to be C<1>, then fork watchers are supported. If
		2629	defined to be C<0>, then they are not.
		2630
		2631	=item EV_MINIMAL
		2632
		2633	If you need to shave off some kilobytes of code at the expense of some
		2634	speed, define this symbol to C<1>. Currently only used for gcc to override
		2635	some inlining decisions, saves roughly 30% codesize of amd64.
		2636
		2637	=item EV_PID_HASHSIZE
		2638
		2639	C<ev_child> watchers use a small hash table to distribute workload by
		2640	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2641	than enough. If you need to manage thousands of children you might want to
		2642	increase this value (I<must> be a power of two).
		2643
		2644	=item EV_INOTIFY_HASHSIZE
		2645
		2646	C<ev_stat> watchers use a small hash table to distribute workload by
		2647	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2648	usually more than enough. If you need to manage thousands of C<ev_stat>
		2649	watchers you might want to increase this value (I<must> be a power of
		2650	two).
		2651
		2652	=item EV_COMMON
		2653
		2654	By default, all watchers have a C<void *data> member. By redefining
		2655	this macro to a something else you can include more and other types of
		2656	members. You have to define it each time you include one of the files,
		2657	though, and it must be identical each time.
		2658
		2659	For example, the perl EV module uses something like this:
		2660
		2661	#define EV_COMMON \
		2662	SV *self; /* contains this struct */ \
		2663	SV *cb_sv, *fh /* note no trailing ";" */
		2664
		2665	=item EV_CB_DECLARE (type)
		2666
		2667	=item EV_CB_INVOKE (watcher, revents)
		2668
		2669	=item ev_set_cb (ev, cb)
		2670
		2671	Can be used to change the callback member declaration in each watcher,
		2672	and the way callbacks are invoked and set. Must expand to a struct member
		2673	definition and a statement, respectively. See the F<ev.h> header file for
		2674	their default definitions. One possible use for overriding these is to
		2675	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2676	method calls instead of plain function calls in C++.
		2677
		2678	=head2 EXPORTED API SYMBOLS
		2679
		2680	If you need to re-export the API (e.g. via a dll) and you need a list of
		2681	exported symbols, you can use the provided F<Symbol.*> files which list
		2682	all public symbols, one per line:
		2683
		2684	Symbols.ev for libev proper
		2685	Symbols.event for the libevent emulation
		2686
		2687	This can also be used to rename all public symbols to avoid clashes with
		2688	multiple versions of libev linked together (which is obviously bad in
		2689	itself, but sometimes it is inconvinient to avoid this).
		2690
		2691	A sed command like this will create wrapper C<#define>'s that you need to
		2692	include before including F<ev.h>:
		2693
		2694	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		2695
		2696	This would create a file F<wrap.h> which essentially looks like this:
		2697
		2698	#define ev_backend myprefix_ev_backend
		2699	#define ev_check_start myprefix_ev_check_start
		2700	#define ev_check_stop myprefix_ev_check_stop
		2701	...
		2702
		2703	=head2 EXAMPLES
		2704
		2705	For a real-world example of a program the includes libev
		2706	verbatim, you can have a look at the EV perl module
		2707	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2708	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2709	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2710	will be compiled. It is pretty complex because it provides its own header
		2711	file.
		2712
		2713	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2714	that everybody includes and which overrides some configure choices:
		2715
		2716	#define EV_MINIMAL 1
		2717	#define EV_USE_POLL 0
		2718	#define EV_MULTIPLICITY 0
		2719	#define EV_PERIODIC_ENABLE 0
		2720	#define EV_STAT_ENABLE 0
		2721	#define EV_FORK_ENABLE 0
		2722	#define EV_CONFIG_H <config.h>
		2723	#define EV_MINPRI 0
		2724	#define EV_MAXPRI 0
		2725
		2726	#include "ev++.h"
		2727
		2728	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		2729
		2730	#include "ev_cpp.h"
		2731	#include "ev.c"
		2732
		2733
		2734	=head1 COMPLEXITIES
		2735
		2736	In this section the complexities of (many of) the algorithms used inside
		2737	libev will be explained. For complexity discussions about backends see the
		2738	documentation for C<ev_default_init>.
		2739
		2740	All of the following are about amortised time: If an array needs to be
		2741	extended, libev needs to realloc and move the whole array, but this
		2742	happens asymptotically never with higher number of elements, so O(1) might
		2743	mean it might do a lengthy realloc operation in rare cases, but on average
		2744	it is much faster and asymptotically approaches constant time.
		2745
		2746	=over 4
		2747
		2748	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		2749
		2750	This means that, when you have a watcher that triggers in one hour and
		2751	there are 100 watchers that would trigger before that then inserting will
		2752	have to skip roughly seven (C<ld 100>) of these watchers.
		2753
		2754	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		2755
		2756	That means that changing a timer costs less than removing/adding them
		2757	as only the relative motion in the event queue has to be paid for.
		2758
		2759	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
		2760
		2761	These just add the watcher into an array or at the head of a list.
		2762
		2763	=item Stopping check/prepare/idle watchers: O(1)
		2764
		2765	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		2766
		2767	These watchers are stored in lists then need to be walked to find the
		2768	correct watcher to remove. The lists are usually short (you don't usually
		2769	have many watchers waiting for the same fd or signal).
		2770
		2771	=item Finding the next timer in each loop iteration: O(1)
		2772
		2773	By virtue of using a binary heap, the next timer is always found at the
		2774	beginning of the storage array.
		2775
		2776	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		2777
		2778	A change means an I/O watcher gets started or stopped, which requires
		2779	libev to recalculate its status (and possibly tell the kernel, depending
		2780	on backend and wether C<ev_io_set> was used).
		2781
		2782	=item Activating one watcher (putting it into the pending state): O(1)
		2783
		2784	=item Priority handling: O(number_of_priorities)
		2785
		2786	Priorities are implemented by allocating some space for each
		2787	priority. When doing priority-based operations, libev usually has to
		2788	linearly search all the priorities, but starting/stopping and activating
		2789	watchers becomes O(1) w.r.t. prioritiy handling.
		2790
		2791	=back
		2792
		2793
		2794	=head1 Win32 platform limitations and workarounds
		2795
		2796	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		2797	requires, and its I/O model is fundamentally incompatible with the POSIX
		2798	model. Libev still offers limited functionality on this platform in
		2799	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		2800	descriptors. This only applies when using Win32 natively, not when using
		2801	e.g. cygwin.
		2802
		2803	There is no supported compilation method available on windows except
		2804	embedding it into other applications.
		2805
		2806	Due to the many, low, and arbitrary limits on the win32 platform and the
		2807	abysmal performance of winsockets, using a large number of sockets is not
		2808	recommended (and not reasonable). If your program needs to use more than
		2809	a hundred or so sockets, then likely it needs to use a totally different
		2810	implementation for windows, as libev offers the POSIX model, which cannot
		2811	be implemented efficiently on windows (microsoft monopoly games).
		2812
		2813	=over 4
		2814
		2815	=item The winsocket select function
		2816
		2817	The winsocket C<select> function doesn't follow POSIX in that it requires
		2818	socket I<handles> and not socket I<file descriptors>. This makes select
		2819	very inefficient, and also requires a mapping from file descriptors
		2820	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		2821	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		2822	symbols for more info.
		2823
		2824	The configuration for a "naked" win32 using the microsoft runtime
		2825	libraries and raw winsocket select is:
		2826
		2827	#define EV_USE_SELECT 1
		2828	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		2829
		2830	Note that winsockets handling of fd sets is O(n), so you can easily get a
		2831	complexity in the O(n²) range when using win32.
		2832
		2833	=item Limited number of file descriptors
		2834
		2835	Windows has numerous arbitrary (and low) limits on things. Early versions
		2836	of winsocket's select only supported waiting for a max. of C<64> handles
		2837	(probably owning to the fact that all windows kernels can only wait for
		2838	C<64> things at the same time internally; microsoft recommends spawning a
		2839	chain of threads and wait for 63 handles and the previous thread in each).
		2840
		2841	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		2842	to some high number (e.g. C<2048>) before compiling the winsocket select
		2843	call (which might be in libev or elsewhere, for example, perl does its own
		2844	select emulation on windows).
		2845
		2846	Another limit is the number of file descriptors in the microsoft runtime
		2847	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		2848	or something like this inside microsoft). You can increase this by calling
		2849	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		2850	arbitrary limit), but is broken in many versions of the microsoft runtime
		2851	libraries.
		2852
		2853	This might get you to about C<512> or C<2048> sockets (depending on
		2854	windows version and/or the phase of the moon). To get more, you need to
		2855	wrap all I/O functions and provide your own fd management, but the cost of
		2856	calling select (O(n²)) will likely make this unworkable.
		2857
		2858	=back
		2859
		2860
742	=head1 AUTHOR	2861	=head1 AUTHOR
743		2862
744	Marc Lehmann <libev@schmorp.de>.	2863	Marc Lehmann <libev@schmorp.de>.
745		2864

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