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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	// a single header file is required
		12	#include <ev.h>
		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_<type>
		16	ev_io stdin_watcher;
		17	ev_timer timeout_watcher;
		18
		19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
		21	static void
		22	stdin_cb (EV_P_ struct ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	struct ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://cvs.schmorp.de/libev/ev.html>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	108	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	117	to the C<double> type in C, and when you need to do any calculations on
		118	it, you should treat it as some floatingpoint value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 GLOBAL FUNCTIONS
		123
		124	These functions can be called anytime, even before initialising the
		125	library in any way.
51		126
52	=over 4	127	=over 4
53		128
54	=item ev_tstamp ev_time ()	129	=item ev_tstamp ev_time ()
55		130
56	Returns the current time as libev would use it.	131	Returns the current time as libev would use it. Please note that the
		132	C<ev_now> function is usually faster and also often returns the timestamp
		133	you actually want to know.
		134
		135	=item ev_sleep (ev_tstamp interval)
		136
		137	Sleep for the given interval: The current thread will be blocked until
		138	either it is interrupted or the given time interval has passed. Basically
		139	this is a subsecond-resolution C<sleep ()>.
57		140
58	=item int ev_version_major ()	141	=item int ev_version_major ()
59		142
60	=item int ev_version_minor ()	143	=item int ev_version_minor ()
61		144
62	You can find out the major and minor version numbers of the library	145	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	146	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	147	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	148	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	149	version of the library your program was compiled against.
67		150
		151	These version numbers refer to the ABI version of the library, not the
		152	release version.
		153
68	Usually, it's a good idea to terminate if the major versions mismatch,	154	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	155	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	156	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	157	not a problem.
72		158
		159	Example: Make sure we haven't accidentally been linked against the wrong
		160	version.
		161
		162	assert (("libev version mismatch",
		163	ev_version_major () == EV_VERSION_MAJOR
		164	&& ev_version_minor () >= EV_VERSION_MINOR));
		165
		166	=item unsigned int ev_supported_backends ()
		167
		168	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		169	value) compiled into this binary of libev (independent of their
		170	availability on the system you are running on). See C<ev_default_loop> for
		171	a description of the set values.
		172
		173	Example: make sure we have the epoll method, because yeah this is cool and
		174	a must have and can we have a torrent of it please!!!11
		175
		176	assert (("sorry, no epoll, no sex",
		177	ev_supported_backends () & EVBACKEND_EPOLL));
		178
		179	=item unsigned int ev_recommended_backends ()
		180
		181	Return the set of all backends compiled into this binary of libev and also
		182	recommended for this platform. This set is often smaller than the one
		183	returned by C<ev_supported_backends>, as for example kqueue is broken on
		184	most BSDs and will not be autodetected unless you explicitly request it
		185	(assuming you know what you are doing). This is the set of backends that
		186	libev will probe for if you specify no backends explicitly.
		187
		188	=item unsigned int ev_embeddable_backends ()
		189
		190	Returns the set of backends that are embeddable in other event loops. This
		191	is the theoretical, all-platform, value. To find which backends
		192	might be supported on the current system, you would need to look at
		193	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		194	recommended ones.
		195
		196	See the description of C<ev_embed> watchers for more info.
		197
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
74		199
75	Sets the allocation function to use (the prototype is similar to the	200	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	201	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	202	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	203	memory needs to be allocated, the library might abort or take some
79	destructive action. The default is your system realloc function.	204	potentially destructive action. The default is your system realloc
		205	function.
80		206
81	You could override this function in high-availability programs to, say,	207	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,	208	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.	209	or even to sleep a while and retry until some memory is available.
		210
		211	Example: Replace the libev allocator with one that waits a bit and then
		212	retries).
		213
		214	static void *
		215	persistent_realloc (void *ptr, size_t size)
		216	{
		217	for (;;)
		218	{
		219	void *newptr = realloc (ptr, size);
		220
		221	if (newptr)
		222	return newptr;
		223
		224	sleep (60);
		225	}
		226	}
		227
		228	...
		229	ev_set_allocator (persistent_realloc);
84		230
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	231	=item ev_set_syserr_cb (void (*cb)(const char *msg));
86		232
87	Set the callback function to call on a retryable syscall error (such	233	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	234	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	236	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	237	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	238	requested operation, or, if the condition doesn't go away, do bad stuff
93	(such as abort).	239	(such as abort).
94		240
		241	Example: This is basically the same thing that libev does internally, too.
		242
		243	static void
		244	fatal_error (const char *msg)
		245	{
		246	perror (msg);
		247	abort ();
		248	}
		249
		250	...
		251	ev_set_syserr_cb (fatal_error);
		252
95	=back	253	=back
96		254
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	255	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98		256
99	An event loop is described by a C<struct ev_loop *>. The library knows two	257	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	258	types of such loops, the I<default> loop, which supports signals and child
101	events, and dynamically created loops which do not.	259	events, and dynamically created loops which do not.
102		260
103	If you use threads, a common model is to run the default event loop	261	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	262	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	263	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	264	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	265	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because it's hideous and inefficient).	266	done correctly, because it's hideous and inefficient).
109		267
…		…
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	270	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		271
114	This will initialise the default event loop if it hasn't been initialised	272	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	273	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	274	false. If it already was initialised it simply returns it (and ignores the
117	flags).	275	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		276
119	If you don't know what event loop to use, use the one returned from this	277	If you don't know what event loop to use, use the one returned from this
120	function.	278	function.
121		279
		280	The default loop is the only loop that can handle C<ev_signal> and
		281	C<ev_child> watchers, and to do this, it always registers a handler
		282	for C<SIGCHLD>. If this is a problem for your app you can either
		283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		284	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		285	C<ev_default_init>.
		286
122	The flags argument can be used to specify special behaviour or specific	287	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).	288	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		289
125	It supports the following flags:	290	The following flags are supported:
126		291
127	=over 4	292	=over 4
128		293
129	=item C<EVFLAG_AUTO>	294	=item C<EVFLAG_AUTO>
130		295
…		…
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	304	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	305	useful to try out specific backends to test their performance, or to work
141	around bugs.	306	around bugs.
142		307
		308	=item C<EVFLAG_FORKCHECK>
		309
		310	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		311	a fork, you can also make libev check for a fork in each iteration by
		312	enabling this flag.
		313
		314	This works by calling C<getpid ()> on every iteration of the loop,
		315	and thus this might slow down your event loop if you do a lot of loop
		316	iterations and little real work, but is usually not noticeable (on my
		317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		318	without a syscall and thus I<very> fast, but my GNU/Linux system also has
		319	C<pthread_atfork> which is even faster).
		320
		321	The big advantage of this flag is that you can forget about fork (and
		322	forget about forgetting to tell libev about forking) when you use this
		323	flag.
		324
		325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		326	environment variable.
		327
143	=item C<EVMETHOD_SELECT> (portable select backend)	328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		329
		330	This is your standard select(2) backend. Not I<completely> standard, as
		331	libev tries to roll its own fd_set with no limits on the number of fds,
		332	but if that fails, expect a fairly low limit on the number of fds when
		333	using this backend. It doesn't scale too well (O(highest_fd)), but its
		334	usually the fastest backend for a low number of (low-numbered :) fds.
		335
		336	To get good performance out of this backend you need a high amount of
		337	parallelity (most of the file descriptors should be busy). If you are
		338	writing a server, you should C<accept ()> in a loop to accept as many
		339	connections as possible during one iteration. You might also want to have
		340	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		341	readyness notifications you get per iteration.
		342
145	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
146		344
147	=item C<EVMETHOD_EPOLL> (linux only)	345	And this is your standard poll(2) backend. It's more complicated
		346	than select, but handles sparse fds better and has no artificial
		347	limit on the number of fds you can use (except it will slow down
		348	considerably with a lot of inactive fds). It scales similarly to select,
		349	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		350	performance tips.
148		351
149	=item C<EVMETHOD_KQUEUE> (some bsds only)	352	=item C<EVBACKEND_EPOLL> (value 4, Linux)
150		353
151	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	354	For few fds, this backend is a bit little slower than poll and select,
		355	but it scales phenomenally better. While poll and select usually scale
		356	like O(total_fds) where n is the total number of fds (or the highest fd),
		357	epoll scales either O(1) or O(active_fds). The epoll design has a number
		358	of shortcomings, such as silently dropping events in some hard-to-detect
		359	cases and rewiring a syscall per fd change, no fork support and bad
		360	support for dup.
152		361
153	=item C<EVMETHOD_PORT> (solaris 10 only)	362	While stopping, setting and starting an I/O watcher in the same iteration
		363	will result in some caching, there is still a syscall per such incident
		364	(because the fd could point to a different file description now), so its
		365	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		366	very well if you register events for both fds.
		367
		368	Please note that epoll sometimes generates spurious notifications, so you
		369	need to use non-blocking I/O or other means to avoid blocking when no data
		370	(or space) is available.
		371
		372	Best performance from this backend is achieved by not unregistering all
		373	watchers for a file descriptor until it has been closed, if possible, i.e.
		374	keep at least one watcher active per fd at all times.
		375
		376	While nominally embeddeble in other event loops, this feature is broken in
		377	all kernel versions tested so far.
		378
		379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		380
		381	Kqueue deserves special mention, as at the time of this writing, it
		382	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		383	with anything but sockets and pipes, except on Darwin, where of course
		384	it's completely useless). For this reason it's not being "autodetected"
		385	unless you explicitly specify it explicitly in the flags (i.e. using
		386	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		387	system like NetBSD.
		388
		389	You still can embed kqueue into a normal poll or select backend and use it
		390	only for sockets (after having made sure that sockets work with kqueue on
		391	the target platform). See C<ev_embed> watchers for more info.
		392
		393	It scales in the same way as the epoll backend, but the interface to the
		394	kernel is more efficient (which says nothing about its actual speed, of
		395	course). While stopping, setting and starting an I/O watcher does never
		396	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
		397	two event changes per incident, support for C<fork ()> is very bad and it
		398	drops fds silently in similarly hard-to-detect cases.
		399
		400	This backend usually performs well under most conditions.
		401
		402	While nominally embeddable in other event loops, this doesn't work
		403	everywhere, so you might need to test for this. And since it is broken
		404	almost everywhere, you should only use it when you have a lot of sockets
		405	(for which it usually works), by embedding it into another event loop
		406	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		407	sockets.
		408
		409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		410
		411	This is not implemented yet (and might never be, unless you send me an
		412	implementation). According to reports, C</dev/poll> only supports sockets
		413	and is not embeddable, which would limit the usefulness of this backend
		414	immensely.
		415
		416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		417
		418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		419	it's really slow, but it still scales very well (O(active_fds)).
		420
		421	Please note that solaris event ports can deliver a lot of spurious
		422	notifications, so you need to use non-blocking I/O or other means to avoid
		423	blocking when no data (or space) is available.
		424
		425	While this backend scales well, it requires one system call per active
		426	file descriptor per loop iteration. For small and medium numbers of file
		427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		428	might perform better.
		429
		430	On the positive side, ignoring the spurious readyness notifications, this
		431	backend actually performed to specification in all tests and is fully
		432	embeddable, which is a rare feat among the OS-specific backends.
		433
		434	=item C<EVBACKEND_ALL>
		435
		436	Try all backends (even potentially broken ones that wouldn't be tried
		437	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		438	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		439
		440	It is definitely not recommended to use this flag.
		441
		442	=back
154		443
155	If one or more of these are ored into the flags value, then only these	444	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	445	backends will be tried (in the reverse order as listed here). If none are
157	specified, any backend will do.	446	specified, all backends in C<ev_recommended_backends ()> will be tried.
158		447
159	=back	448	The most typical usage is like this:
		449
		450	if (!ev_default_loop (0))
		451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		452
		453	Restrict libev to the select and poll backends, and do not allow
		454	environment settings to be taken into account:
		455
		456	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		457
		458	Use whatever libev has to offer, but make sure that kqueue is used if
		459	available (warning, breaks stuff, best use only with your own private
		460	event loop and only if you know the OS supports your types of fds):
		461
		462	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		463
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	464	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		465
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	466	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	467	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	468	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).	469	undefined behaviour (or a failed assertion if assertions are enabled).
167		470
		471	Example: Try to create a event loop that uses epoll and nothing else.
		472
		473	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		474	if (!epoller)
		475	fatal ("no epoll found here, maybe it hides under your chair");
		476
168	=item ev_default_destroy ()	477	=item ev_default_destroy ()
169		478
170	Destroys the default loop again (frees all memory and kernel state	479	Destroys the default loop again (frees all memory and kernel state
171	etc.). This stops all registered event watchers (by not touching them in	480	etc.). None of the active event watchers will be stopped in the normal
172	any way whatsoever, although you cannot rely on this :).	481	sense, so e.g. C<ev_is_active> might still return true. It is your
		482	responsibility to either stop all watchers cleanly yoursef I<before>
		483	calling this function, or cope with the fact afterwards (which is usually
		484	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		485	for example).
		486
		487	Note that certain global state, such as signal state, will not be freed by
		488	this function, and related watchers (such as signal and child watchers)
		489	would need to be stopped manually.
		490
		491	In general it is not advisable to call this function except in the
		492	rare occasion where you really need to free e.g. the signal handling
		493	pipe fds. If you need dynamically allocated loops it is better to use
		494	C<ev_loop_new> and C<ev_loop_destroy>).
173		495
174	=item ev_loop_destroy (loop)	496	=item ev_loop_destroy (loop)
175		497
176	Like C<ev_default_destroy>, but destroys an event loop created by an	498	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	499	earlier call to C<ev_loop_new>.
178		500
179	=item ev_default_fork ()	501	=item ev_default_fork ()
180		502
		503	This function sets a flag that causes subsequent C<ev_loop> iterations
181	This function reinitialises the kernel state for backends that have	504	to reinitialise the kernel state for backends that have one. Despite the
182	one. Despite the name, you can call it anytime, but it makes most sense	505	name, you can call it anytime, but it makes most sense after forking, in
183	after forking, in either the parent or child process (or both, but that	506	the child process (or both child and parent, but that again makes little
184	again makes little sense).	507	sense). You I<must> call it in the child before using any of the libev
		508	functions, and it will only take effect at the next C<ev_loop> iteration.
185		509
186	You I<must> call this function after forking if and only if you want to	510	On the other hand, you only need to call this function in the child
187	use the event library in both processes. If you just fork+exec, you don't	511	process if and only if you want to use the event library in the child. If
188	have to call it.	512	you just fork+exec, you don't have to call it at all.
189		513
190	The function itself is quite fast and it's usually not a problem to call	514	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	515	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>:	516	quite nicely into a call to C<pthread_atfork>:
193		517
…		…
197		521
198	Like C<ev_default_fork>, but acts on an event loop created by	522	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	523	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.	524	after fork, and how you do this is entirely your own problem.
201		525
		526	=item int ev_is_default_loop (loop)
		527
		528	Returns true when the given loop actually is the default loop, false otherwise.
		529
		530	=item unsigned int ev_loop_count (loop)
		531
		532	Returns the count of loop iterations for the loop, which is identical to
		533	the number of times libev did poll for new events. It starts at C<0> and
		534	happily wraps around with enough iterations.
		535
		536	This value can sometimes be useful as a generation counter of sorts (it
		537	"ticks" the number of loop iterations), as it roughly corresponds with
		538	C<ev_prepare> and C<ev_check> calls.
		539
202	=item unsigned int ev_method (loop)	540	=item unsigned int ev_backend (loop)
203		541
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	542	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	543	use.
206		544
207	=item ev_tstamp ev_now (loop)	545	=item ev_tstamp ev_now (loop)
208		546
209	Returns the current "event loop time", which is the time the event loop	547	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	548	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	549	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	550	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).	551	event occurring (or more correctly, libev finding out about it).
214		552
215	=item ev_loop (loop, int flags)	553	=item ev_loop (loop, int flags)
216		554
217	Finally, this is it, the event handler. This function usually is called	555	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	556	after you initialised all your watchers and you want to start handling
219	events.	557	events.
220		558
221	If the flags argument is specified as 0, it will not return until either	559	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.	560	either no event watchers are active anymore or C<ev_unloop> was called.
		561
		562	Please note that an explicit C<ev_unloop> is usually better than
		563	relying on all watchers to be stopped when deciding when a program has
		564	finished (especially in interactive programs), but having a program that
		565	automatically loops as long as it has to and no longer by virtue of
		566	relying on its watchers stopping correctly is a thing of beauty.
223		567
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	568	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	569	those events and any outstanding ones, but will not block your process in
226	case there are no events and will return after one iteration of the loop.	570	case there are no events and will return after one iteration of the loop.
227		571
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	572	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	573	neccessary) and will handle those and any outstanding ones. It will block
230	your process until at least one new event arrives, and will return after	574	your process until at least one new event arrives, and will return after
231	one iteration of the loop.	575	one iteration of the loop. This is useful if you are waiting for some
		576	external event in conjunction with something not expressible using other
		577	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		578	usually a better approach for this kind of thing.
232		579
233	This flags value could be used to implement alternative looping	580	Here are the gory details of what C<ev_loop> does:
234	constructs, but the C<prepare> and C<check> watchers provide a better and	581
235	more generic mechanism.	582	- Before the first iteration, call any pending watchers.
		583	* If EVFLAG_FORKCHECK was used, check for a fork.
		584	- If a fork was detected, queue and call all fork watchers.
		585	- Queue and call all prepare watchers.
		586	- If we have been forked, recreate the kernel state.
		587	- Update the kernel state with all outstanding changes.
		588	- Update the "event loop time".
		589	- Calculate for how long to sleep or block, if at all
		590	(active idle watchers, EVLOOP_NONBLOCK or not having
		591	any active watchers at all will result in not sleeping).
		592	- Sleep if the I/O and timer collect interval say so.
		593	- Block the process, waiting for any events.
		594	- Queue all outstanding I/O (fd) events.
		595	- Update the "event loop time" and do time jump handling.
		596	- Queue all outstanding timers.
		597	- Queue all outstanding periodics.
		598	- If no events are pending now, queue all idle watchers.
		599	- Queue all check watchers.
		600	- Call all queued watchers in reverse order (i.e. check watchers first).
		601	Signals and child watchers are implemented as I/O watchers, and will
		602	be handled here by queueing them when their watcher gets executed.
		603	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		604	were used, or there are no active watchers, return, otherwise
		605	continue with step *.
		606
		607	Example: Queue some jobs and then loop until no events are outstanding
		608	anymore.
		609
		610	... queue jobs here, make sure they register event watchers as long
		611	... as they still have work to do (even an idle watcher will do..)
		612	ev_loop (my_loop, 0);
		613	... jobs done. yeah!
236		614
237	=item ev_unloop (loop, how)	615	=item ev_unloop (loop, how)
238		616
239	Can be used to make a call to C<ev_loop> return early (but only after it	617	Can be used to make a call to C<ev_loop> return early (but only after it
240	has processed all outstanding events). The C<how> argument must be either	618	has processed all outstanding events). The C<how> argument must be either
241	C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or	619	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
242	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	620	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		621
		622	This "unloop state" will be cleared when entering C<ev_loop> again.
243		623
244	=item ev_ref (loop)	624	=item ev_ref (loop)
245		625
246	=item ev_unref (loop)	626	=item ev_unref (loop)
247		627
…		…
252	returning, ev_unref() after starting, and ev_ref() before stopping it. For	632	returning, ev_unref() after starting, and ev_ref() before stopping it. For
253	example, libev itself uses this for its internal signal pipe: It is not	633	example, libev itself uses this for its internal signal pipe: It is not
254	visible to the libev user and should not keep C<ev_loop> from exiting if	634	visible to the libev user and should not keep C<ev_loop> from exiting if
255	no event watchers registered by it are active. It is also an excellent	635	no event watchers registered by it are active. It is also an excellent
256	way to do this for generic recurring timers or from within third-party	636	way to do this for generic recurring timers or from within third-party
257	libraries. Just remember to I<unref after start> and I<ref before stop>.	637	libraries. Just remember to I<unref after start> and I<ref before stop>
		638	(but only if the watcher wasn't active before, or was active before,
		639	respectively).
		640
		641	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		642	running when nothing else is active.
		643
		644	struct ev_signal exitsig;
		645	ev_signal_init (&exitsig, sig_cb, SIGINT);
		646	ev_signal_start (loop, &exitsig);
		647	evf_unref (loop);
		648
		649	Example: For some weird reason, unregister the above signal handler again.
		650
		651	ev_ref (loop);
		652	ev_signal_stop (loop, &exitsig);
		653
		654	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		655
		656	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		657
		658	These advanced functions influence the time that libev will spend waiting
		659	for events. Both are by default C<0>, meaning that libev will try to
		660	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		661
		662	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		663	allows libev to delay invocation of I/O and timer/periodic callbacks to
		664	increase efficiency of loop iterations.
		665
		666	The background is that sometimes your program runs just fast enough to
		667	handle one (or very few) event(s) per loop iteration. While this makes
		668	the program responsive, it also wastes a lot of CPU time to poll for new
		669	events, especially with backends like C<select ()> which have a high
		670	overhead for the actual polling but can deliver many events at once.
		671
		672	By setting a higher I<io collect interval> you allow libev to spend more
		673	time collecting I/O events, so you can handle more events per iteration,
		674	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		675	C<ev_timer>) will be not affected. Setting this to a non-null value will
		676	introduce an additional C<ev_sleep ()> call into most loop iterations.
		677
		678	Likewise, by setting a higher I<timeout collect interval> you allow libev
		679	to spend more time collecting timeouts, at the expense of increased
		680	latency (the watcher callback will be called later). C<ev_io> watchers
		681	will not be affected. Setting this to a non-null value will not introduce
		682	any overhead in libev.
		683
		684	Many (busy) programs can usually benefit by setting the io collect
		685	interval to a value near C<0.1> or so, which is often enough for
		686	interactive servers (of course not for games), likewise for timeouts. It
		687	usually doesn't make much sense to set it to a lower value than C<0.01>,
		688	as this approsaches the timing granularity of most systems.
258		689
259	=back	690	=back
		691
260		692
261	=head1 ANATOMY OF A WATCHER	693	=head1 ANATOMY OF A WATCHER
262		694
263	A watcher is a structure that you create and register to record your	695	A watcher is a structure that you create and register to record your
264	interest in some event. For instance, if you want to wait for STDIN to	696	interest in some event. For instance, if you want to wait for STDIN to
…		…
297	*) >>), and you can stop watching for events at any time by calling the	729	*) >>), and you can stop watching for events at any time by calling the
298	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	730	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
299		731
300	As long as your watcher is active (has been started but not stopped) you	732	As long as your watcher is active (has been started but not stopped) you
301	must not touch the values stored in it. Most specifically you must never	733	must not touch the values stored in it. Most specifically you must never
302	reinitialise it or call its set method.	734	reinitialise it or call its C<set> macro.
303
304	You can check whether an event is active by calling the C<ev_is_active
305	(watcher *)> macro. To see whether an event is outstanding (but the
306	callback for it has not been called yet) you can use the C<ev_is_pending
307	(watcher *)> macro.
308		735
309	Each and every callback receives the event loop pointer as first, the	736	Each and every callback receives the event loop pointer as first, the
310	registered watcher structure as second, and a bitset of received events as	737	registered watcher structure as second, and a bitset of received events as
311	third argument.	738	third argument.
312		739
…		…
336	The signal specified in the C<ev_signal> watcher has been received by a thread.	763	The signal specified in the C<ev_signal> watcher has been received by a thread.
337		764
338	=item C<EV_CHILD>	765	=item C<EV_CHILD>
339		766
340	The pid specified in the C<ev_child> watcher has received a status change.	767	The pid specified in the C<ev_child> watcher has received a status change.
		768
		769	=item C<EV_STAT>
		770
		771	The path specified in the C<ev_stat> watcher changed its attributes somehow.
341		772
342	=item C<EV_IDLE>	773	=item C<EV_IDLE>
343		774
344	The C<ev_idle> watcher has determined that you have nothing better to do.	775	The C<ev_idle> watcher has determined that you have nothing better to do.
345		776
…		…
353	received events. Callbacks of both watcher types can start and stop as	784	received events. Callbacks of both watcher types can start and stop as
354	many watchers as they want, and all of them will be taken into account	785	many watchers as they want, and all of them will be taken into account
355	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	786	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
356	C<ev_loop> from blocking).	787	C<ev_loop> from blocking).
357		788
		789	=item C<EV_EMBED>
		790
		791	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		792
		793	=item C<EV_FORK>
		794
		795	The event loop has been resumed in the child process after fork (see
		796	C<ev_fork>).
		797
		798	=item C<EV_ASYNC>
		799
		800	The given async watcher has been asynchronously notified (see C<ev_async>).
		801
358	=item C<EV_ERROR>	802	=item C<EV_ERROR>
359		803
360	An unspecified error has occured, the watcher has been stopped. This might	804	An unspecified error has occured, the watcher has been stopped. This might
361	happen because the watcher could not be properly started because libev	805	happen because the watcher could not be properly started because libev
362	ran out of memory, a file descriptor was found to be closed or any other	806	ran out of memory, a file descriptor was found to be closed or any other
…		…
368	your callbacks is well-written it can just attempt the operation and cope	812	your callbacks is well-written it can just attempt the operation and cope
369	with the error from read() or write(). This will not work in multithreaded	813	with the error from read() or write(). This will not work in multithreaded
370	programs, though, so beware.	814	programs, though, so beware.
371		815
372	=back	816	=back
		817
		818	=head2 GENERIC WATCHER FUNCTIONS
		819
		820	In the following description, C<TYPE> stands for the watcher type,
		821	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		822
		823	=over 4
		824
		825	=item C<ev_init> (ev_TYPE *watcher, callback)
		826
		827	This macro initialises the generic portion of a watcher. The contents
		828	of the watcher object can be arbitrary (so C<malloc> will do). Only
		829	the generic parts of the watcher are initialised, you I<need> to call
		830	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		831	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		832	which rolls both calls into one.
		833
		834	You can reinitialise a watcher at any time as long as it has been stopped
		835	(or never started) and there are no pending events outstanding.
		836
		837	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		838	int revents)>.
		839
		840	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		841
		842	This macro initialises the type-specific parts of a watcher. You need to
		843	call C<ev_init> at least once before you call this macro, but you can
		844	call C<ev_TYPE_set> any number of times. You must not, however, call this
		845	macro on a watcher that is active (it can be pending, however, which is a
		846	difference to the C<ev_init> macro).
		847
		848	Although some watcher types do not have type-specific arguments
		849	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		850
		851	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		852
		853	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		854	calls into a single call. This is the most convinient method to initialise
		855	a watcher. The same limitations apply, of course.
		856
		857	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		858
		859	Starts (activates) the given watcher. Only active watchers will receive
		860	events. If the watcher is already active nothing will happen.
		861
		862	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		863
		864	Stops the given watcher again (if active) and clears the pending
		865	status. It is possible that stopped watchers are pending (for example,
		866	non-repeating timers are being stopped when they become pending), but
		867	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		868	you want to free or reuse the memory used by the watcher it is therefore a
		869	good idea to always call its C<ev_TYPE_stop> function.
		870
		871	=item bool ev_is_active (ev_TYPE *watcher)
		872
		873	Returns a true value iff the watcher is active (i.e. it has been started
		874	and not yet been stopped). As long as a watcher is active you must not modify
		875	it.
		876
		877	=item bool ev_is_pending (ev_TYPE *watcher)
		878
		879	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		880	events but its callback has not yet been invoked). As long as a watcher
		881	is pending (but not active) you must not call an init function on it (but
		882	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		883	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		884	it).
		885
		886	=item callback ev_cb (ev_TYPE *watcher)
		887
		888	Returns the callback currently set on the watcher.
		889
		890	=item ev_cb_set (ev_TYPE *watcher, callback)
		891
		892	Change the callback. You can change the callback at virtually any time
		893	(modulo threads).
		894
		895	=item ev_set_priority (ev_TYPE *watcher, priority)
		896
		897	=item int ev_priority (ev_TYPE *watcher)
		898
		899	Set and query the priority of the watcher. The priority is a small
		900	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		901	(default: C<-2>). Pending watchers with higher priority will be invoked
		902	before watchers with lower priority, but priority will not keep watchers
		903	from being executed (except for C<ev_idle> watchers).
		904
		905	This means that priorities are I<only> used for ordering callback
		906	invocation after new events have been received. This is useful, for
		907	example, to reduce latency after idling, or more often, to bind two
		908	watchers on the same event and make sure one is called first.
		909
		910	If you need to suppress invocation when higher priority events are pending
		911	you need to look at C<ev_idle> watchers, which provide this functionality.
		912
		913	You I<must not> change the priority of a watcher as long as it is active or
		914	pending.
		915
		916	The default priority used by watchers when no priority has been set is
		917	always C<0>, which is supposed to not be too high and not be too low :).
		918
		919	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		920	fine, as long as you do not mind that the priority value you query might
		921	or might not have been adjusted to be within valid range.
		922
		923	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		924
		925	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		926	C<loop> nor C<revents> need to be valid as long as the watcher callback
		927	can deal with that fact.
		928
		929	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		930
		931	If the watcher is pending, this function returns clears its pending status
		932	and returns its C<revents> bitset (as if its callback was invoked). If the
		933	watcher isn't pending it does nothing and returns C<0>.
		934
		935	=back
		936
373		937
374	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	938	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
375		939
376	Each watcher has, by default, a member C<void *data> that you can change	940	Each watcher has, by default, a member C<void *data> that you can change
377	and read at any time, libev will completely ignore it. This can be used	941	and read at any time, libev will completely ignore it. This can be used
…		…
395	{	959	{
396	struct my_io *w = (struct my_io *)w_;	960	struct my_io *w = (struct my_io *)w_;
397	...	961	...
398	}	962	}
399		963
400	More interesting and less C-conformant ways of catsing your callback type	964	More interesting and less C-conformant ways of casting your callback type
401	have been omitted....	965	instead have been omitted.
		966
		967	Another common scenario is having some data structure with multiple
		968	watchers:
		969
		970	struct my_biggy
		971	{
		972	int some_data;
		973	ev_timer t1;
		974	ev_timer t2;
		975	}
		976
		977	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		978	you need to use C<offsetof>:
		979
		980	#include <stddef.h>
		981
		982	static void
		983	t1_cb (EV_P_ struct ev_timer *w, int revents)
		984	{
		985	struct my_biggy big = (struct my_biggy *
		986	(((char *)w) - offsetof (struct my_biggy, t1));
		987	}
		988
		989	static void
		990	t2_cb (EV_P_ struct ev_timer *w, int revents)
		991	{
		992	struct my_biggy big = (struct my_biggy *
		993	(((char *)w) - offsetof (struct my_biggy, t2));
		994	}
402		995
403		996
404	=head1 WATCHER TYPES	997	=head1 WATCHER TYPES
405		998
406	This section describes each watcher in detail, but will not repeat	999	This section describes each watcher in detail, but will not repeat
407	information given in the last section.	1000	information given in the last section. Any initialisation/set macros,
		1001	functions and members specific to the watcher type are explained.
408		1002
		1003	Members are additionally marked with either I<[read-only]>, meaning that,
		1004	while the watcher is active, you can look at the member and expect some
		1005	sensible content, but you must not modify it (you can modify it while the
		1006	watcher is stopped to your hearts content), or I<[read-write]>, which
		1007	means you can expect it to have some sensible content while the watcher
		1008	is active, but you can also modify it. Modifying it may not do something
		1009	sensible or take immediate effect (or do anything at all), but libev will
		1010	not crash or malfunction in any way.
		1011
		1012
409	=head2 C<ev_io> - is this file descriptor readable or writable	1013	=head2 C<ev_io> - is this file descriptor readable or writable?
410		1014
411	I/O watchers check whether a file descriptor is readable or writable	1015	I/O watchers check whether a file descriptor is readable or writable
412	in each iteration of the event loop (This behaviour is called	1016	in each iteration of the event loop, or, more precisely, when reading
413	level-triggering because you keep receiving events as long as the	1017	would not block the process and writing would at least be able to write
414	condition persists. Remember you can stop the watcher if you don't want to	1018	some data. This behaviour is called level-triggering because you keep
415	act on the event and neither want to receive future events).	1019	receiving events as long as the condition persists. Remember you can stop
		1020	the watcher if you don't want to act on the event and neither want to
		1021	receive future events.
416		1022
417	In general you can register as many read and/or write event watchers oer	1023	In general you can register as many read and/or write event watchers per
418	fd as you want (as long as you don't confuse yourself). Setting all file	1024	fd as you want (as long as you don't confuse yourself). Setting all file
419	descriptors to non-blocking mode is also usually a good idea (but not	1025	descriptors to non-blocking mode is also usually a good idea (but not
420	required if you know what you are doing).	1026	required if you know what you are doing).
421		1027
422	You have to be careful with dup'ed file descriptors, though. Some backends
423	(the linux epoll backend is a notable example) cannot handle dup'ed file
424	descriptors correctly if you register interest in two or more fds pointing
425	to the same file/socket etc. description.
426
427	If you must do this, then force the use of a known-to-be-good backend	1028	If you must do this, then force the use of a known-to-be-good backend
428	(at the time of this writing, this includes only EVMETHOD_SELECT and	1029	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
429	EVMETHOD_POLL).	1030	C<EVBACKEND_POLL>).
		1031
		1032	Another thing you have to watch out for is that it is quite easy to
		1033	receive "spurious" readyness notifications, that is your callback might
		1034	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1035	because there is no data. Not only are some backends known to create a
		1036	lot of those (for example solaris ports), it is very easy to get into
		1037	this situation even with a relatively standard program structure. Thus
		1038	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1039	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1040
		1041	If you cannot run the fd in non-blocking mode (for example you should not
		1042	play around with an Xlib connection), then you have to seperately re-test
		1043	whether a file descriptor is really ready with a known-to-be good interface
		1044	such as poll (fortunately in our Xlib example, Xlib already does this on
		1045	its own, so its quite safe to use).
		1046
		1047	=head3 The special problem of disappearing file descriptors
		1048
		1049	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1050	descriptor (either by calling C<close> explicitly or by any other means,
		1051	such as C<dup>). The reason is that you register interest in some file
		1052	descriptor, but when it goes away, the operating system will silently drop
		1053	this interest. If another file descriptor with the same number then is
		1054	registered with libev, there is no efficient way to see that this is, in
		1055	fact, a different file descriptor.
		1056
		1057	To avoid having to explicitly tell libev about such cases, libev follows
		1058	the following policy: Each time C<ev_io_set> is being called, libev
		1059	will assume that this is potentially a new file descriptor, otherwise
		1060	it is assumed that the file descriptor stays the same. That means that
		1061	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1062	descriptor even if the file descriptor number itself did not change.
		1063
		1064	This is how one would do it normally anyway, the important point is that
		1065	the libev application should not optimise around libev but should leave
		1066	optimisations to libev.
		1067
		1068	=head3 The special problem of dup'ed file descriptors
		1069
		1070	Some backends (e.g. epoll), cannot register events for file descriptors,
		1071	but only events for the underlying file descriptions. That means when you
		1072	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1073	events for them, only one file descriptor might actually receive events.
		1074
		1075	There is no workaround possible except not registering events
		1076	for potentially C<dup ()>'ed file descriptors, or to resort to
		1077	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1078
		1079	=head3 The special problem of fork
		1080
		1081	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1082	useless behaviour. Libev fully supports fork, but needs to be told about
		1083	it in the child.
		1084
		1085	To support fork in your programs, you either have to call
		1086	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1087	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1088	C<EVBACKEND_POLL>.
		1089
		1090
		1091	=head3 Watcher-Specific Functions
430		1092
431	=over 4	1093	=over 4
432		1094
433	=item ev_io_init (ev_io *, callback, int fd, int events)	1095	=item ev_io_init (ev_io *, callback, int fd, int events)
434		1096
435	=item ev_io_set (ev_io *, int fd, int events)	1097	=item ev_io_set (ev_io *, int fd, int events)
436		1098
437	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1099	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
438	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1100	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
439	EV_WRITE> to receive the given events.	1101	C<EV_READ | EV_WRITE> to receive the given events.
		1102
		1103	=item int fd [read-only]
		1104
		1105	The file descriptor being watched.
		1106
		1107	=item int events [read-only]
		1108
		1109	The events being watched.
440		1110
441	=back	1111	=back
442		1112
		1113	=head3 Examples
		1114
		1115	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1116	readable, but only once. Since it is likely line-buffered, you could
		1117	attempt to read a whole line in the callback.
		1118
		1119	static void
		1120	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1121	{
		1122	ev_io_stop (loop, w);
		1123	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1124	}
		1125
		1126	...
		1127	struct ev_loop *loop = ev_default_init (0);
		1128	struct ev_io stdin_readable;
		1129	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1130	ev_io_start (loop, &stdin_readable);
		1131	ev_loop (loop, 0);
		1132
		1133
443	=head2 C<ev_timer> - relative and optionally recurring timeouts	1134	=head2 C<ev_timer> - relative and optionally repeating timeouts
444		1135
445	Timer watchers are simple relative timers that generate an event after a	1136	Timer watchers are simple relative timers that generate an event after a
446	given time, and optionally repeating in regular intervals after that.	1137	given time, and optionally repeating in regular intervals after that.
447		1138
448	The timers are based on real time, that is, if you register an event that	1139	The timers are based on real time, that is, if you register an event that
449	times out after an hour and youreset your system clock to last years	1140	times out after an hour and you reset your system clock to last years
450	time, it will still time out after (roughly) and hour. "Roughly" because	1141	time, it will still time out after (roughly) and hour. "Roughly" because
451	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1142	detecting time jumps is hard, and some inaccuracies are unavoidable (the
452	monotonic clock option helps a lot here).	1143	monotonic clock option helps a lot here).
453		1144
454	The relative timeouts are calculated relative to the C<ev_now ()>	1145	The relative timeouts are calculated relative to the C<ev_now ()>
455	time. This is usually the right thing as this timestamp refers to the time	1146	time. This is usually the right thing as this timestamp refers to the time
456	of the event triggering whatever timeout you are modifying/starting. If	1147	of the event triggering whatever timeout you are modifying/starting. If
457	you suspect event processing to be delayed and you *need* to base the timeout	1148	you suspect event processing to be delayed and you I<need> to base the timeout
458	ion the current time, use something like this to adjust for this:	1149	on the current time, use something like this to adjust for this:
459		1150
460	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1151	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1152
		1153	The callback is guarenteed to be invoked only when its timeout has passed,
		1154	but if multiple timers become ready during the same loop iteration then
		1155	order of execution is undefined.
		1156
		1157	=head3 Watcher-Specific Functions and Data Members
461		1158
462	=over 4	1159	=over 4
463		1160
464	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1161	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465		1162
…		…
471	later, again, and again, until stopped manually.	1168	later, again, and again, until stopped manually.
472		1169
473	The timer itself will do a best-effort at avoiding drift, that is, if you	1170	The timer itself will do a best-effort at avoiding drift, that is, if you
474	configure a timer to trigger every 10 seconds, then it will trigger at	1171	configure a timer to trigger every 10 seconds, then it will trigger at
475	exactly 10 second intervals. If, however, your program cannot keep up with	1172	exactly 10 second intervals. If, however, your program cannot keep up with
476	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1173	the timer (because it takes longer than those 10 seconds to do stuff) the
477	timer will not fire more than once per event loop iteration.	1174	timer will not fire more than once per event loop iteration.
478		1175
479	=item ev_timer_again (loop)	1176	=item ev_timer_again (loop, ev_timer *)
480		1177
481	This will act as if the timer timed out and restart it again if it is	1178	This will act as if the timer timed out and restart it again if it is
482	repeating. The exact semantics are:	1179	repeating. The exact semantics are:
483		1180
		1181	If the timer is pending, its pending status is cleared.
		1182
484	If the timer is started but nonrepeating, stop it.	1183	If the timer is started but nonrepeating, stop it (as if it timed out).
485		1184
486	If the timer is repeating, either start it if necessary (with the repeat	1185	If the timer is repeating, either start it if necessary (with the
487	value), or reset the running timer to the repeat value.	1186	C<repeat> value), or reset the running timer to the C<repeat> value.
488		1187
489	This sounds a bit complicated, but here is a useful and typical	1188	This sounds a bit complicated, but here is a useful and typical
490	example: Imagine you have a tcp connection and you want a so-called idle	1189	example: Imagine you have a tcp connection and you want a so-called idle
491	timeout, that is, you want to be called when there have been, say, 60	1190	timeout, that is, you want to be called when there have been, say, 60
492	seconds of inactivity on the socket. The easiest way to do this is to	1191	seconds of inactivity on the socket. The easiest way to do this is to
493	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1192	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
494	time you successfully read or write some data. If you go into an idle	1193	C<ev_timer_again> each time you successfully read or write some data. If
495	state where you do not expect data to travel on the socket, you can stop	1194	you go into an idle state where you do not expect data to travel on the
496	the timer, and again will automatically restart it if need be.	1195	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1196	automatically restart it if need be.
		1197
		1198	That means you can ignore the C<after> value and C<ev_timer_start>
		1199	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1200
		1201	ev_timer_init (timer, callback, 0., 5.);
		1202	ev_timer_again (loop, timer);
		1203	...
		1204	timer->again = 17.;
		1205	ev_timer_again (loop, timer);
		1206	...
		1207	timer->again = 10.;
		1208	ev_timer_again (loop, timer);
		1209
		1210	This is more slightly efficient then stopping/starting the timer each time
		1211	you want to modify its timeout value.
		1212
		1213	=item ev_tstamp repeat [read-write]
		1214
		1215	The current C<repeat> value. Will be used each time the watcher times out
		1216	or C<ev_timer_again> is called and determines the next timeout (if any),
		1217	which is also when any modifications are taken into account.
497		1218
498	=back	1219	=back
499		1220
		1221	=head3 Examples
		1222
		1223	Example: Create a timer that fires after 60 seconds.
		1224
		1225	static void
		1226	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1227	{
		1228	.. one minute over, w is actually stopped right here
		1229	}
		1230
		1231	struct ev_timer mytimer;
		1232	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1233	ev_timer_start (loop, &mytimer);
		1234
		1235	Example: Create a timeout timer that times out after 10 seconds of
		1236	inactivity.
		1237
		1238	static void
		1239	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1240	{
		1241	.. ten seconds without any activity
		1242	}
		1243
		1244	struct ev_timer mytimer;
		1245	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1246	ev_timer_again (&mytimer); /* start timer */
		1247	ev_loop (loop, 0);
		1248
		1249	// and in some piece of code that gets executed on any "activity":
		1250	// reset the timeout to start ticking again at 10 seconds
		1251	ev_timer_again (&mytimer);
		1252
		1253
500	=head2 C<ev_periodic> - to cron or not to cron	1254	=head2 C<ev_periodic> - to cron or not to cron?
501		1255
502	Periodic watchers are also timers of a kind, but they are very versatile	1256	Periodic watchers are also timers of a kind, but they are very versatile
503	(and unfortunately a bit complex).	1257	(and unfortunately a bit complex).
504		1258
505	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1259	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
506	but on wallclock time (absolute time). You can tell a periodic watcher	1260	but on wallclock time (absolute time). You can tell a periodic watcher
507	to trigger "at" some specific point in time. For example, if you tell a	1261	to trigger "at" some specific point in time. For example, if you tell a
508	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1262	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
509	+ 10.>) and then reset your system clock to the last year, then it will	1263	+ 10.>) and then reset your system clock to the last year, then it will
510	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1264	take a year to trigger the event (unlike an C<ev_timer>, which would trigger
511	roughly 10 seconds later and of course not if you reset your system time	1265	roughly 10 seconds later).
512	again).
513		1266
514	They can also be used to implement vastly more complex timers, such as	1267	They can also be used to implement vastly more complex timers, such as
515	triggering an event on eahc midnight, local time.	1268	triggering an event on each midnight, local time or other, complicated,
		1269	rules.
		1270
		1271	As with timers, the callback is guarenteed to be invoked only when the
		1272	time (C<at>) has been passed, but if multiple periodic timers become ready
		1273	during the same loop iteration then order of execution is undefined.
		1274
		1275	=head3 Watcher-Specific Functions and Data Members
516		1276
517	=over 4	1277	=over 4
518		1278
519	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1279	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
520		1280
521	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1281	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
522		1282
523	Lots of arguments, lets sort it out... There are basically three modes of	1283	Lots of arguments, lets sort it out... There are basically three modes of
524	operation, and we will explain them from simplest to complex:	1284	operation, and we will explain them from simplest to complex:
525		1285
526
527	=over 4	1286	=over 4
528		1287
529	=item * absolute timer (interval = reschedule_cb = 0)	1288	=item * absolute timer (at = time, interval = reschedule_cb = 0)
530		1289
531	In this configuration the watcher triggers an event at the wallclock time	1290	In this configuration the watcher triggers an event at the wallclock time
532	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1291	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
533	that is, if it is to be run at January 1st 2011 then it will run when the	1292	that is, if it is to be run at January 1st 2011 then it will run when the
534	system time reaches or surpasses this time.	1293	system time reaches or surpasses this time.
535		1294
536	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1295	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
537		1296
538	In this mode the watcher will always be scheduled to time out at the next	1297	In this mode the watcher will always be scheduled to time out at the next
539	C<at + N * interval> time (for some integer N) and then repeat, regardless	1298	C<at + N * interval> time (for some integer N, which can also be negative)
540	of any time jumps.	1299	and then repeat, regardless of any time jumps.
541		1300
542	This can be used to create timers that do not drift with respect to system	1301	This can be used to create timers that do not drift with respect to system
543	time:	1302	time:
544		1303
545	ev_periodic_set (&periodic, 0., 3600., 0);	1304	ev_periodic_set (&periodic, 0., 3600., 0);
…		…
551		1310
552	Another way to think about it (for the mathematically inclined) is that	1311	Another way to think about it (for the mathematically inclined) is that
553	C<ev_periodic> will try to run the callback in this mode at the next possible	1312	C<ev_periodic> will try to run the callback in this mode at the next possible
554	time where C<time = at (mod interval)>, regardless of any time jumps.	1313	time where C<time = at (mod interval)>, regardless of any time jumps.
555		1314
		1315	For numerical stability it is preferable that the C<at> value is near
		1316	C<ev_now ()> (the current time), but there is no range requirement for
		1317	this value.
		1318
556	=item * manual reschedule mode (reschedule_cb = callback)	1319	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
557		1320
558	In this mode the values for C<interval> and C<at> are both being	1321	In this mode the values for C<interval> and C<at> are both being
559	ignored. Instead, each time the periodic watcher gets scheduled, the	1322	ignored. Instead, each time the periodic watcher gets scheduled, the
560	reschedule callback will be called with the watcher as first, and the	1323	reschedule callback will be called with the watcher as first, and the
561	current time as second argument.	1324	current time as second argument.
562		1325
563	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1326	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
564	periodic watcher, ever, or make any event loop modifications>. If you need	1327	ever, or make any event loop modifications>. If you need to stop it,
565	to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.	1328	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
566		1329	starting an C<ev_prepare> watcher, which is legal).
567	Also, I<< this callback must always return a time that is later than the
568	passed C<now> value >>. Not even C<now> itself will be ok.
569		1330
570	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1331	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
571	ev_tstamp now)>, e.g.:	1332	ev_tstamp now)>, e.g.:
572		1333
573	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1334	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
…		…
578	It must return the next time to trigger, based on the passed time value	1339	It must return the next time to trigger, based on the passed time value
579	(that is, the lowest time value larger than to the second argument). It	1340	(that is, the lowest time value larger than to the second argument). It
580	will usually be called just before the callback will be triggered, but	1341	will usually be called just before the callback will be triggered, but
581	might be called at other times, too.	1342	might be called at other times, too.
582		1343
		1344	NOTE: I<< This callback must always return a time that is later than the
		1345	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
		1346
583	This can be used to create very complex timers, such as a timer that	1347	This can be used to create very complex timers, such as a timer that
584	triggers on each midnight, local time. To do this, you would calculate the	1348	triggers on each midnight, local time. To do this, you would calculate the
585	next midnight after C<now> and return the timestamp value for this. How you do this	1349	next midnight after C<now> and return the timestamp value for this. How
586	is, again, up to you (but it is not trivial).	1350	you do this is, again, up to you (but it is not trivial, which is the main
		1351	reason I omitted it as an example).
587		1352
588	=back	1353	=back
589		1354
590	=item ev_periodic_again (loop, ev_periodic *)	1355	=item ev_periodic_again (loop, ev_periodic *)
591		1356
592	Simply stops and restarts the periodic watcher again. This is only useful	1357	Simply stops and restarts the periodic watcher again. This is only useful
593	when you changed some parameters or the reschedule callback would return	1358	when you changed some parameters or the reschedule callback would return
594	a different time than the last time it was called (e.g. in a crond like	1359	a different time than the last time it was called (e.g. in a crond like
595	program when the crontabs have changed).	1360	program when the crontabs have changed).
596		1361
		1362	=item ev_tstamp offset [read-write]
		1363
		1364	When repeating, this contains the offset value, otherwise this is the
		1365	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1366
		1367	Can be modified any time, but changes only take effect when the periodic
		1368	timer fires or C<ev_periodic_again> is being called.
		1369
		1370	=item ev_tstamp interval [read-write]
		1371
		1372	The current interval value. Can be modified any time, but changes only
		1373	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1374	called.
		1375
		1376	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1377
		1378	The current reschedule callback, or C<0>, if this functionality is
		1379	switched off. Can be changed any time, but changes only take effect when
		1380	the periodic timer fires or C<ev_periodic_again> is being called.
		1381
		1382	=item ev_tstamp at [read-only]
		1383
		1384	When active, contains the absolute time that the watcher is supposed to
		1385	trigger next.
		1386
597	=back	1387	=back
598		1388
		1389	=head3 Examples
		1390
		1391	Example: Call a callback every hour, or, more precisely, whenever the
		1392	system clock is divisible by 3600. The callback invocation times have
		1393	potentially a lot of jittering, but good long-term stability.
		1394
		1395	static void
		1396	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1397	{
		1398	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1399	}
		1400
		1401	struct ev_periodic hourly_tick;
		1402	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1403	ev_periodic_start (loop, &hourly_tick);
		1404
		1405	Example: The same as above, but use a reschedule callback to do it:
		1406
		1407	#include <math.h>
		1408
		1409	static ev_tstamp
		1410	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1411	{
		1412	return fmod (now, 3600.) + 3600.;
		1413	}
		1414
		1415	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1416
		1417	Example: Call a callback every hour, starting now:
		1418
		1419	struct ev_periodic hourly_tick;
		1420	ev_periodic_init (&hourly_tick, clock_cb,
		1421	fmod (ev_now (loop), 3600.), 3600., 0);
		1422	ev_periodic_start (loop, &hourly_tick);
		1423
		1424
599	=head2 C<ev_signal> - signal me when a signal gets signalled	1425	=head2 C<ev_signal> - signal me when a signal gets signalled!
600		1426
601	Signal watchers will trigger an event when the process receives a specific	1427	Signal watchers will trigger an event when the process receives a specific
602	signal one or more times. Even though signals are very asynchronous, libev	1428	signal one or more times. Even though signals are very asynchronous, libev
603	will try it's best to deliver signals synchronously, i.e. as part of the	1429	will try it's best to deliver signals synchronously, i.e. as part of the
604	normal event processing, like any other event.	1430	normal event processing, like any other event.
…		…
608	with the kernel (thus it coexists with your own signal handlers as long	1434	with the kernel (thus it coexists with your own signal handlers as long
609	as you don't register any with libev). Similarly, when the last signal	1435	as you don't register any with libev). Similarly, when the last signal
610	watcher for a signal is stopped libev will reset the signal handler to	1436	watcher for a signal is stopped libev will reset the signal handler to
611	SIG_DFL (regardless of what it was set to before).	1437	SIG_DFL (regardless of what it was set to before).
612		1438
		1439	If possible and supported, libev will install its handlers with
		1440	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
		1441	interrupted. If you have a problem with syscalls getting interrupted by
		1442	signals you can block all signals in an C<ev_check> watcher and unblock
		1443	them in an C<ev_prepare> watcher.
		1444
		1445	=head3 Watcher-Specific Functions and Data Members
		1446
613	=over 4	1447	=over 4
614		1448
615	=item ev_signal_init (ev_signal *, callback, int signum)	1449	=item ev_signal_init (ev_signal *, callback, int signum)
616		1450
617	=item ev_signal_set (ev_signal *, int signum)	1451	=item ev_signal_set (ev_signal *, int signum)
618		1452
619	Configures the watcher to trigger on the given signal number (usually one	1453	Configures the watcher to trigger on the given signal number (usually one
620	of the C<SIGxxx> constants).	1454	of the C<SIGxxx> constants).
621		1455
		1456	=item int signum [read-only]
		1457
		1458	The signal the watcher watches out for.
		1459
622	=back	1460	=back
623		1461
		1462	=head3 Examples
		1463
		1464	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1465
		1466	static void
		1467	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1468	{
		1469	ev_unloop (loop, EVUNLOOP_ALL);
		1470	}
		1471
		1472	struct ev_signal signal_watcher;
		1473	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1474	ev_signal_start (loop, &sigint_cb);
		1475
		1476
624	=head2 C<ev_child> - wait for pid status changes	1477	=head2 C<ev_child> - watch out for process status changes
625		1478
626	Child watchers trigger when your process receives a SIGCHLD in response to	1479	Child watchers trigger when your process receives a SIGCHLD in response to
627	some child status changes (most typically when a child of yours dies).	1480	some child status changes (most typically when a child of yours dies). It
		1481	is permissible to install a child watcher I<after> the child has been
		1482	forked (which implies it might have already exited), as long as the event
		1483	loop isn't entered (or is continued from a watcher).
		1484
		1485	Only the default event loop is capable of handling signals, and therefore
		1486	you can only rgeister child watchers in the default event loop.
		1487
		1488	=head3 Process Interaction
		1489
		1490	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1491	initialised. This is necessary to guarantee proper behaviour even if
		1492	the first child watcher is started after the child exits. The occurance
		1493	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1494	synchronously as part of the event loop processing. Libev always reaps all
		1495	children, even ones not watched.
		1496
		1497	=head3 Overriding the Built-In Processing
		1498
		1499	Libev offers no special support for overriding the built-in child
		1500	processing, but if your application collides with libev's default child
		1501	handler, you can override it easily by installing your own handler for
		1502	C<SIGCHLD> after initialising the default loop, and making sure the
		1503	default loop never gets destroyed. You are encouraged, however, to use an
		1504	event-based approach to child reaping and thus use libev's support for
		1505	that, so other libev users can use C<ev_child> watchers freely.
		1506
		1507	=head3 Watcher-Specific Functions and Data Members
628		1508
629	=over 4	1509	=over 4
630		1510
631	=item ev_child_init (ev_child *, callback, int pid)	1511	=item ev_child_init (ev_child *, callback, int pid, int trace)
632		1512
633	=item ev_child_set (ev_child *, int pid)	1513	=item ev_child_set (ev_child *, int pid, int trace)
634		1514
635	Configures the watcher to wait for status changes of process C<pid> (or	1515	Configures the watcher to wait for status changes of process C<pid> (or
636	I<any> process if C<pid> is specified as C<0>). The callback can look	1516	I<any> process if C<pid> is specified as C<0>). The callback can look
637	at the C<rstatus> member of the C<ev_child> watcher structure to see	1517	at the C<rstatus> member of the C<ev_child> watcher structure to see
638	the status word (use the macros from C<sys/wait.h> and see your systems	1518	the status word (use the macros from C<sys/wait.h> and see your systems
639	C<waitpid> documentation). The C<rpid> member contains the pid of the	1519	C<waitpid> documentation). The C<rpid> member contains the pid of the
640	process causing the status change.	1520	process causing the status change. C<trace> must be either C<0> (only
		1521	activate the watcher when the process terminates) or C<1> (additionally
		1522	activate the watcher when the process is stopped or continued).
		1523
		1524	=item int pid [read-only]
		1525
		1526	The process id this watcher watches out for, or C<0>, meaning any process id.
		1527
		1528	=item int rpid [read-write]
		1529
		1530	The process id that detected a status change.
		1531
		1532	=item int rstatus [read-write]
		1533
		1534	The process exit/trace status caused by C<rpid> (see your systems
		1535	C<waitpid> and C<sys/wait.h> documentation for details).
641		1536
642	=back	1537	=back
643		1538
		1539	=head3 Examples
		1540
		1541	Example: C<fork()> a new process and install a child handler to wait for
		1542	its completion.
		1543
		1544	ev_child cw;
		1545
		1546	static void
		1547	child_cb (EV_P_ struct ev_child *w, int revents)
		1548	{
		1549	ev_child_stop (EV_A_ w);
		1550	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1551	}
		1552
		1553	pid_t pid = fork ();
		1554
		1555	if (pid < 0)
		1556	// error
		1557	else if (pid == 0)
		1558	{
		1559	// the forked child executes here
		1560	exit (1);
		1561	}
		1562	else
		1563	{
		1564	ev_child_init (&cw, child_cb, pid, 0);
		1565	ev_child_start (EV_DEFAULT_ &cw);
		1566	}
		1567
		1568
		1569	=head2 C<ev_stat> - did the file attributes just change?
		1570
		1571	This watches a filesystem path for attribute changes. That is, it calls
		1572	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1573	compared to the last time, invoking the callback if it did.
		1574
		1575	The path does not need to exist: changing from "path exists" to "path does
		1576	not exist" is a status change like any other. The condition "path does
		1577	not exist" is signified by the C<st_nlink> field being zero (which is
		1578	otherwise always forced to be at least one) and all the other fields of
		1579	the stat buffer having unspecified contents.
		1580
		1581	The path I<should> be absolute and I<must not> end in a slash. If it is
		1582	relative and your working directory changes, the behaviour is undefined.
		1583
		1584	Since there is no standard to do this, the portable implementation simply
		1585	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1586	can specify a recommended polling interval for this case. If you specify
		1587	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1588	unspecified default> value will be used (which you can expect to be around
		1589	five seconds, although this might change dynamically). Libev will also
		1590	impose a minimum interval which is currently around C<0.1>, but thats
		1591	usually overkill.
		1592
		1593	This watcher type is not meant for massive numbers of stat watchers,
		1594	as even with OS-supported change notifications, this can be
		1595	resource-intensive.
		1596
		1597	At the time of this writing, only the Linux inotify interface is
		1598	implemented (implementing kqueue support is left as an exercise for the
		1599	reader). Inotify will be used to give hints only and should not change the
		1600	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1601	to fall back to regular polling again even with inotify, but changes are
		1602	usually detected immediately, and if the file exists there will be no
		1603	polling.
		1604
		1605	=head3 Inotify
		1606
		1607	When C<inotify (7)> support has been compiled into libev (generally only
		1608	available on Linux) and present at runtime, it will be used to speed up
		1609	change detection where possible. The inotify descriptor will be created lazily
		1610	when the first C<ev_stat> watcher is being started.
		1611
		1612	Inotify presense does not change the semantics of C<ev_stat> watchers
		1613	except that changes might be detected earlier, and in some cases, to avoid
		1614	making regular C<stat> calls. Even in the presense of inotify support
		1615	there are many cases where libev has to resort to regular C<stat> polling.
		1616
		1617	(There is no support for kqueue, as apparently it cannot be used to
		1618	implement this functionality, due to the requirement of having a file
		1619	descriptor open on the object at all times).
		1620
		1621	=head3 The special problem of stat time resolution
		1622
		1623	The C<stat ()> syscall only supports full-second resolution portably, and
		1624	even on systems where the resolution is higher, many filesystems still
		1625	only support whole seconds.
		1626
		1627	That means that, if the time is the only thing that changes, you might
		1628	miss updates: on the first update, C<ev_stat> detects a change and calls
		1629	your callback, which does something. When there is another update within
		1630	the same second, C<ev_stat> will be unable to detect it.
		1631
		1632	The solution to this is to delay acting on a change for a second (or till
		1633	the next second boundary), using a roughly one-second delay C<ev_timer>
		1634	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1635	is added to work around small timing inconsistencies of some operating
		1636	systems.
		1637
		1638	=head3 Watcher-Specific Functions and Data Members
		1639
		1640	=over 4
		1641
		1642	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1643
		1644	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1645
		1646	Configures the watcher to wait for status changes of the given
		1647	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1648	be detected and should normally be specified as C<0> to let libev choose
		1649	a suitable value. The memory pointed to by C<path> must point to the same
		1650	path for as long as the watcher is active.
		1651
		1652	The callback will be receive C<EV_STAT> when a change was detected,
		1653	relative to the attributes at the time the watcher was started (or the
		1654	last change was detected).
		1655
		1656	=item ev_stat_stat (loop, ev_stat *)
		1657
		1658	Updates the stat buffer immediately with new values. If you change the
		1659	watched path in your callback, you could call this fucntion to avoid
		1660	detecting this change (while introducing a race condition). Can also be
		1661	useful simply to find out the new values.
		1662
		1663	=item ev_statdata attr [read-only]
		1664
		1665	The most-recently detected attributes of the file. Although the type is of
		1666	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1667	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1668	was some error while C<stat>ing the file.
		1669
		1670	=item ev_statdata prev [read-only]
		1671
		1672	The previous attributes of the file. The callback gets invoked whenever
		1673	C<prev> != C<attr>.
		1674
		1675	=item ev_tstamp interval [read-only]
		1676
		1677	The specified interval.
		1678
		1679	=item const char *path [read-only]
		1680
		1681	The filesystem path that is being watched.
		1682
		1683	=back
		1684
		1685	=head3 Examples
		1686
		1687	Example: Watch C</etc/passwd> for attribute changes.
		1688
		1689	static void
		1690	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1691	{
		1692	/* /etc/passwd changed in some way */
		1693	if (w->attr.st_nlink)
		1694	{
		1695	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1696	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1697	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1698	}
		1699	else
		1700	/* you shalt not abuse printf for puts */
		1701	puts ("wow, /etc/passwd is not there, expect problems. "
		1702	"if this is windows, they already arrived\n");
		1703	}
		1704
		1705	...
		1706	ev_stat passwd;
		1707
		1708	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1709	ev_stat_start (loop, &passwd);
		1710
		1711	Example: Like above, but additionally use a one-second delay so we do not
		1712	miss updates (however, frequent updates will delay processing, too, so
		1713	one might do the work both on C<ev_stat> callback invocation I<and> on
		1714	C<ev_timer> callback invocation).
		1715
		1716	static ev_stat passwd;
		1717	static ev_timer timer;
		1718
		1719	static void
		1720	timer_cb (EV_P_ ev_timer *w, int revents)
		1721	{
		1722	ev_timer_stop (EV_A_ w);
		1723
		1724	/* now it's one second after the most recent passwd change */
		1725	}
		1726
		1727	static void
		1728	stat_cb (EV_P_ ev_stat *w, int revents)
		1729	{
		1730	/* reset the one-second timer */
		1731	ev_timer_again (EV_A_ &timer);
		1732	}
		1733
		1734	...
		1735	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1736	ev_stat_start (loop, &passwd);
		1737	ev_timer_init (&timer, timer_cb, 0., 1.01);
		1738
		1739
644	=head2 C<ev_idle> - when you've got nothing better to do	1740	=head2 C<ev_idle> - when you've got nothing better to do...
645		1741
646	Idle watchers trigger events when there are no other events are pending	1742	Idle watchers trigger events when no other events of the same or higher
647	(prepare, check and other idle watchers do not count). That is, as long	1743	priority are pending (prepare, check and other idle watchers do not
648	as your process is busy handling sockets or timeouts (or even signals,	1744	count).
649	imagine) it will not be triggered. But when your process is idle all idle	1745
650	watchers are being called again and again, once per event loop iteration -	1746	That is, as long as your process is busy handling sockets or timeouts
		1747	(or even signals, imagine) of the same or higher priority it will not be
		1748	triggered. But when your process is idle (or only lower-priority watchers
		1749	are pending), the idle watchers are being called once per event loop
651	until stopped, that is, or your process receives more events and becomes	1750	iteration - until stopped, that is, or your process receives more events
652	busy.	1751	and becomes busy again with higher priority stuff.
653		1752
654	The most noteworthy effect is that as long as any idle watchers are	1753	The most noteworthy effect is that as long as any idle watchers are
655	active, the process will not block when waiting for new events.	1754	active, the process will not block when waiting for new events.
656		1755
657	Apart from keeping your process non-blocking (which is a useful	1756	Apart from keeping your process non-blocking (which is a useful
658	effect on its own sometimes), idle watchers are a good place to do	1757	effect on its own sometimes), idle watchers are a good place to do
659	"pseudo-background processing", or delay processing stuff to after the	1758	"pseudo-background processing", or delay processing stuff to after the
660	event loop has handled all outstanding events.	1759	event loop has handled all outstanding events.
661		1760
		1761	=head3 Watcher-Specific Functions and Data Members
		1762
662	=over 4	1763	=over 4
663		1764
664	=item ev_idle_init (ev_signal *, callback)	1765	=item ev_idle_init (ev_signal *, callback)
665		1766
666	Initialises and configures the idle watcher - it has no parameters of any	1767	Initialises and configures the idle watcher - it has no parameters of any
667	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1768	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
668	believe me.	1769	believe me.
669		1770
670	=back	1771	=back
671		1772
		1773	=head3 Examples
		1774
		1775	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1776	callback, free it. Also, use no error checking, as usual.
		1777
		1778	static void
		1779	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1780	{
		1781	free (w);
		1782	// now do something you wanted to do when the program has
		1783	// no longer anything immediate to do.
		1784	}
		1785
		1786	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1787	ev_idle_init (idle_watcher, idle_cb);
		1788	ev_idle_start (loop, idle_cb);
		1789
		1790
672	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1791	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
673		1792
674	Prepare and check watchers are usually (but not always) used in tandem:	1793	Prepare and check watchers are usually (but not always) used in tandem:
675	Prepare watchers get invoked before the process blocks and check watchers	1794	prepare watchers get invoked before the process blocks and check watchers
676	afterwards.	1795	afterwards.
677		1796
		1797	You I<must not> call C<ev_loop> or similar functions that enter
		1798	the current event loop from either C<ev_prepare> or C<ev_check>
		1799	watchers. Other loops than the current one are fine, however. The
		1800	rationale behind this is that you do not need to check for recursion in
		1801	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1802	C<ev_check> so if you have one watcher of each kind they will always be
		1803	called in pairs bracketing the blocking call.
		1804
678	Their main purpose is to integrate other event mechanisms into libev. This	1805	Their main purpose is to integrate other event mechanisms into libev and
679	could be used, for example, to track variable changes, implement your own	1806	their use is somewhat advanced. This could be used, for example, to track
680	watchers, integrate net-snmp or a coroutine library and lots more.	1807	variable changes, implement your own watchers, integrate net-snmp or a
		1808	coroutine library and lots more. They are also occasionally useful if
		1809	you cache some data and want to flush it before blocking (for example,
		1810	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1811	watcher).
681		1812
682	This is done by examining in each prepare call which file descriptors need	1813	This is done by examining in each prepare call which file descriptors need
683	to be watched by the other library, registering C<ev_io> watchers for	1814	to be watched by the other library, registering C<ev_io> watchers for
684	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1815	them and starting an C<ev_timer> watcher for any timeouts (many libraries
685	provide just this functionality). Then, in the check watcher you check for	1816	provide just this functionality). Then, in the check watcher you check for
686	any events that occured (by checking the pending status of all watchers	1817	any events that occured (by checking the pending status of all watchers
687	and stopping them) and call back into the library. The I/O and timer	1818	and stopping them) and call back into the library. The I/O and timer
688	callbacks will never actually be called (but must be valid neverthelles,	1819	callbacks will never actually be called (but must be valid nevertheless,
689	because you never know, you know?).	1820	because you never know, you know?).
690		1821
691	As another example, the Perl Coro module uses these hooks to integrate	1822	As another example, the Perl Coro module uses these hooks to integrate
692	coroutines into libev programs, by yielding to other active coroutines	1823	coroutines into libev programs, by yielding to other active coroutines
693	during each prepare and only letting the process block if no coroutines	1824	during each prepare and only letting the process block if no coroutines
694	are ready to run (its actually more complicated, it only runs coroutines	1825	are ready to run (it's actually more complicated: it only runs coroutines
695	with priority higher than the event loop and one lower priority once,	1826	with priority higher than or equal to the event loop and one coroutine
696	using idle watchers to keep the event loop from blocking if lower-priority	1827	of lower priority, but only once, using idle watchers to keep the event
697	coroutines exist, thus mapping low-priority coroutines to idle/background	1828	loop from blocking if lower-priority coroutines are active, thus mapping
698	tasks).	1829	low-priority coroutines to idle/background tasks).
		1830
		1831	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1832	priority, to ensure that they are being run before any other watchers
		1833	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1834	too) should not activate ("feed") events into libev. While libev fully
		1835	supports this, they will be called before other C<ev_check> watchers
		1836	did their job. As C<ev_check> watchers are often used to embed other
		1837	(non-libev) event loops those other event loops might be in an unusable
		1838	state until their C<ev_check> watcher ran (always remind yourself to
		1839	coexist peacefully with others).
		1840
		1841	=head3 Watcher-Specific Functions and Data Members
699		1842
700	=over 4	1843	=over 4
701		1844
702	=item ev_prepare_init (ev_prepare *, callback)	1845	=item ev_prepare_init (ev_prepare *, callback)
703		1846
…		…
707	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1850	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
708	macros, but using them is utterly, utterly and completely pointless.	1851	macros, but using them is utterly, utterly and completely pointless.
709		1852
710	=back	1853	=back
711		1854
		1855	=head3 Examples
		1856
		1857	There are a number of principal ways to embed other event loops or modules
		1858	into libev. Here are some ideas on how to include libadns into libev
		1859	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1860	use for an actually working example. Another Perl module named C<EV::Glib>
		1861	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
		1862	into the Glib event loop).
		1863
		1864	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1865	and in a check watcher, destroy them and call into libadns. What follows
		1866	is pseudo-code only of course. This requires you to either use a low
		1867	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1868	the callbacks for the IO/timeout watchers might not have been called yet.
		1869
		1870	static ev_io iow [nfd];
		1871	static ev_timer tw;
		1872
		1873	static void
		1874	io_cb (ev_loop *loop, ev_io *w, int revents)
		1875	{
		1876	}
		1877
		1878	// create io watchers for each fd and a timer before blocking
		1879	static void
		1880	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1881	{
		1882	int timeout = 3600000;
		1883	struct pollfd fds [nfd];
		1884	// actual code will need to loop here and realloc etc.
		1885	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1886
		1887	/* the callback is illegal, but won't be called as we stop during check */
		1888	ev_timer_init (&tw, 0, timeout * 1e-3);
		1889	ev_timer_start (loop, &tw);
		1890
		1891	// create one ev_io per pollfd
		1892	for (int i = 0; i < nfd; ++i)
		1893	{
		1894	ev_io_init (iow + i, io_cb, fds [i].fd,
		1895	((fds [i].events & POLLIN ? EV_READ : 0)
		1896	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1897
		1898	fds [i].revents = 0;
		1899	ev_io_start (loop, iow + i);
		1900	}
		1901	}
		1902
		1903	// stop all watchers after blocking
		1904	static void
		1905	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1906	{
		1907	ev_timer_stop (loop, &tw);
		1908
		1909	for (int i = 0; i < nfd; ++i)
		1910	{
		1911	// set the relevant poll flags
		1912	// could also call adns_processreadable etc. here
		1913	struct pollfd *fd = fds + i;
		1914	int revents = ev_clear_pending (iow + i);
		1915	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1916	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1917
		1918	// now stop the watcher
		1919	ev_io_stop (loop, iow + i);
		1920	}
		1921
		1922	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1923	}
		1924
		1925	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1926	in the prepare watcher and would dispose of the check watcher.
		1927
		1928	Method 3: If the module to be embedded supports explicit event
		1929	notification (adns does), you can also make use of the actual watcher
		1930	callbacks, and only destroy/create the watchers in the prepare watcher.
		1931
		1932	static void
		1933	timer_cb (EV_P_ ev_timer *w, int revents)
		1934	{
		1935	adns_state ads = (adns_state)w->data;
		1936	update_now (EV_A);
		1937
		1938	adns_processtimeouts (ads, &tv_now);
		1939	}
		1940
		1941	static void
		1942	io_cb (EV_P_ ev_io *w, int revents)
		1943	{
		1944	adns_state ads = (adns_state)w->data;
		1945	update_now (EV_A);
		1946
		1947	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1948	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1949	}
		1950
		1951	// do not ever call adns_afterpoll
		1952
		1953	Method 4: Do not use a prepare or check watcher because the module you
		1954	want to embed is too inflexible to support it. Instead, youc na override
		1955	their poll function. The drawback with this solution is that the main
		1956	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1957	this.
		1958
		1959	static gint
		1960	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		1961	{
		1962	int got_events = 0;
		1963
		1964	for (n = 0; n < nfds; ++n)
		1965	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		1966
		1967	if (timeout >= 0)
		1968	// create/start timer
		1969
		1970	// poll
		1971	ev_loop (EV_A_ 0);
		1972
		1973	// stop timer again
		1974	if (timeout >= 0)
		1975	ev_timer_stop (EV_A_ &to);
		1976
		1977	// stop io watchers again - their callbacks should have set
		1978	for (n = 0; n < nfds; ++n)
		1979	ev_io_stop (EV_A_ iow [n]);
		1980
		1981	return got_events;
		1982	}
		1983
		1984
		1985	=head2 C<ev_embed> - when one backend isn't enough...
		1986
		1987	This is a rather advanced watcher type that lets you embed one event loop
		1988	into another (currently only C<ev_io> events are supported in the embedded
		1989	loop, other types of watchers might be handled in a delayed or incorrect
		1990	fashion and must not be used).
		1991
		1992	There are primarily two reasons you would want that: work around bugs and
		1993	prioritise I/O.
		1994
		1995	As an example for a bug workaround, the kqueue backend might only support
		1996	sockets on some platform, so it is unusable as generic backend, but you
		1997	still want to make use of it because you have many sockets and it scales
		1998	so nicely. In this case, you would create a kqueue-based loop and embed it
		1999	into your default loop (which might use e.g. poll). Overall operation will
		2000	be a bit slower because first libev has to poll and then call kevent, but
		2001	at least you can use both at what they are best.
		2002
		2003	As for prioritising I/O: rarely you have the case where some fds have
		2004	to be watched and handled very quickly (with low latency), and even
		2005	priorities and idle watchers might have too much overhead. In this case
		2006	you would put all the high priority stuff in one loop and all the rest in
		2007	a second one, and embed the second one in the first.
		2008
		2009	As long as the watcher is active, the callback will be invoked every time
		2010	there might be events pending in the embedded loop. The callback must then
		2011	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2012	their callbacks (you could also start an idle watcher to give the embedded
		2013	loop strictly lower priority for example). You can also set the callback
		2014	to C<0>, in which case the embed watcher will automatically execute the
		2015	embedded loop sweep.
		2016
		2017	As long as the watcher is started it will automatically handle events. The
		2018	callback will be invoked whenever some events have been handled. You can
		2019	set the callback to C<0> to avoid having to specify one if you are not
		2020	interested in that.
		2021
		2022	Also, there have not currently been made special provisions for forking:
		2023	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2024	but you will also have to stop and restart any C<ev_embed> watchers
		2025	yourself.
		2026
		2027	Unfortunately, not all backends are embeddable, only the ones returned by
		2028	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2029	portable one.
		2030
		2031	So when you want to use this feature you will always have to be prepared
		2032	that you cannot get an embeddable loop. The recommended way to get around
		2033	this is to have a separate variables for your embeddable loop, try to
		2034	create it, and if that fails, use the normal loop for everything.
		2035
		2036	=head3 Watcher-Specific Functions and Data Members
		2037
		2038	=over 4
		2039
		2040	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2041
		2042	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2043
		2044	Configures the watcher to embed the given loop, which must be
		2045	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2046	invoked automatically, otherwise it is the responsibility of the callback
		2047	to invoke it (it will continue to be called until the sweep has been done,
		2048	if you do not want thta, you need to temporarily stop the embed watcher).
		2049
		2050	=item ev_embed_sweep (loop, ev_embed *)
		2051
		2052	Make a single, non-blocking sweep over the embedded loop. This works
		2053	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2054	apropriate way for embedded loops.
		2055
		2056	=item struct ev_loop *other [read-only]
		2057
		2058	The embedded event loop.
		2059
		2060	=back
		2061
		2062	=head3 Examples
		2063
		2064	Example: Try to get an embeddable event loop and embed it into the default
		2065	event loop. If that is not possible, use the default loop. The default
		2066	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		2067	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		2068	used).
		2069
		2070	struct ev_loop *loop_hi = ev_default_init (0);
		2071	struct ev_loop *loop_lo = 0;
		2072	struct ev_embed embed;
		2073
		2074	// see if there is a chance of getting one that works
		2075	// (remember that a flags value of 0 means autodetection)
		2076	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2077	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2078	: 0;
		2079
		2080	// if we got one, then embed it, otherwise default to loop_hi
		2081	if (loop_lo)
		2082	{
		2083	ev_embed_init (&embed, 0, loop_lo);
		2084	ev_embed_start (loop_hi, &embed);
		2085	}
		2086	else
		2087	loop_lo = loop_hi;
		2088
		2089	Example: Check if kqueue is available but not recommended and create
		2090	a kqueue backend for use with sockets (which usually work with any
		2091	kqueue implementation). Store the kqueue/socket-only event loop in
		2092	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2093
		2094	struct ev_loop *loop = ev_default_init (0);
		2095	struct ev_loop *loop_socket = 0;
		2096	struct ev_embed embed;
		2097
		2098	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2099	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2100	{
		2101	ev_embed_init (&embed, 0, loop_socket);
		2102	ev_embed_start (loop, &embed);
		2103	}
		2104
		2105	if (!loop_socket)
		2106	loop_socket = loop;
		2107
		2108	// now use loop_socket for all sockets, and loop for everything else
		2109
		2110
		2111	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2112
		2113	Fork watchers are called when a C<fork ()> was detected (usually because
		2114	whoever is a good citizen cared to tell libev about it by calling
		2115	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2116	event loop blocks next and before C<ev_check> watchers are being called,
		2117	and only in the child after the fork. If whoever good citizen calling
		2118	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2119	handlers will be invoked, too, of course.
		2120
		2121	=head3 Watcher-Specific Functions and Data Members
		2122
		2123	=over 4
		2124
		2125	=item ev_fork_init (ev_signal *, callback)
		2126
		2127	Initialises and configures the fork watcher - it has no parameters of any
		2128	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2129	believe me.
		2130
		2131	=back
		2132
		2133
		2134	=head2 C<ev_async> - how to wake up another event loop
		2135
		2136	In general, you cannot use an C<ev_loop> from multiple threads or other
		2137	asynchronous sources such as signal handlers (as opposed to multiple event
		2138	loops - those are of course safe to use in different threads).
		2139
		2140	Sometimes, however, you need to wake up another event loop you do not
		2141	control, for example because it belongs to another thread. This is what
		2142	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2143	can signal it by calling C<ev_async_send>, which is thread- and signal
		2144	safe.
		2145
		2146	This functionality is very similar to C<ev_signal> watchers, as signals,
		2147	too, are asynchronous in nature, and signals, too, will be compressed
		2148	(i.e. the number of callback invocations may be less than the number of
		2149	C<ev_async_sent> calls).
		2150
		2151	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2152	just the default loop.
		2153
		2154	=head3 Queueing
		2155
		2156	C<ev_async> does not support queueing of data in any way. The reason
		2157	is that the author does not know of a simple (or any) algorithm for a
		2158	multiple-writer-single-reader queue that works in all cases and doesn't
		2159	need elaborate support such as pthreads.
		2160
		2161	That means that if you want to queue data, you have to provide your own
		2162	queue. But at least I can tell you would implement locking around your
		2163	queue:
		2164
		2165	=over 4
		2166
		2167	=item queueing from a signal handler context
		2168
		2169	To implement race-free queueing, you simply add to the queue in the signal
		2170	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2171	some fictitiuous SIGUSR1 handler:
		2172
		2173	static ev_async mysig;
		2174
		2175	static void
		2176	sigusr1_handler (void)
		2177	{
		2178	sometype data;
		2179
		2180	// no locking etc.
		2181	queue_put (data);
		2182	ev_async_send (EV_DEFAULT_ &mysig);
		2183	}
		2184
		2185	static void
		2186	mysig_cb (EV_P_ ev_async *w, int revents)
		2187	{
		2188	sometype data;
		2189	sigset_t block, prev;
		2190
		2191	sigemptyset (&block);
		2192	sigaddset (&block, SIGUSR1);
		2193	sigprocmask (SIG_BLOCK, &block, &prev);
		2194
		2195	while (queue_get (&data))
		2196	process (data);
		2197
		2198	if (sigismember (&prev, SIGUSR1)
		2199	sigprocmask (SIG_UNBLOCK, &block, 0);
		2200	}
		2201
		2202	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2203	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2204	either...).
		2205
		2206	=item queueing from a thread context
		2207
		2208	The strategy for threads is different, as you cannot (easily) block
		2209	threads but you can easily preempt them, so to queue safely you need to
		2210	employ a traditional mutex lock, such as in this pthread example:
		2211
		2212	static ev_async mysig;
		2213	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2214
		2215	static void
		2216	otherthread (void)
		2217	{
		2218	// only need to lock the actual queueing operation
		2219	pthread_mutex_lock (&mymutex);
		2220	queue_put (data);
		2221	pthread_mutex_unlock (&mymutex);
		2222
		2223	ev_async_send (EV_DEFAULT_ &mysig);
		2224	}
		2225
		2226	static void
		2227	mysig_cb (EV_P_ ev_async *w, int revents)
		2228	{
		2229	pthread_mutex_lock (&mymutex);
		2230
		2231	while (queue_get (&data))
		2232	process (data);
		2233
		2234	pthread_mutex_unlock (&mymutex);
		2235	}
		2236
		2237	=back
		2238
		2239
		2240	=head3 Watcher-Specific Functions and Data Members
		2241
		2242	=over 4
		2243
		2244	=item ev_async_init (ev_async *, callback)
		2245
		2246	Initialises and configures the async watcher - it has no parameters of any
		2247	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2248	believe me.
		2249
		2250	=item ev_async_send (loop, ev_async *)
		2251
		2252	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2253	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2254	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2255	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2256	section below on what exactly this means).
		2257
		2258	This call incurs the overhead of a syscall only once per loop iteration,
		2259	so while the overhead might be noticable, it doesn't apply to repeated
		2260	calls to C<ev_async_send>.
		2261
		2262	=back
		2263
		2264
712	=head1 OTHER FUNCTIONS	2265	=head1 OTHER FUNCTIONS
713		2266
714	There are some other functions of possible interest. Described. Here. Now.	2267	There are some other functions of possible interest. Described. Here. Now.
715		2268
716	=over 4	2269	=over 4
…		…
718	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2271	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
719		2272
720	This function combines a simple timer and an I/O watcher, calls your	2273	This function combines a simple timer and an I/O watcher, calls your
721	callback on whichever event happens first and automatically stop both	2274	callback on whichever event happens first and automatically stop both
722	watchers. This is useful if you want to wait for a single event on an fd	2275	watchers. This is useful if you want to wait for a single event on an fd
723	or timeout without havign to allocate/configure/start/stop/free one or	2276	or timeout without having to allocate/configure/start/stop/free one or
724	more watchers yourself.	2277	more watchers yourself.
725		2278
726	If C<fd> is less than 0, then no I/O watcher will be started and events	2279	If C<fd> is less than 0, then no I/O watcher will be started and events
727	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2280	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
728	C<events> set will be craeted and started.	2281	C<events> set will be craeted and started.
…		…
731	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2284	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
732	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2285	repeat = 0) will be started. While C<0> is a valid timeout, it is of
733	dubious value.	2286	dubious value.
734		2287
735	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2288	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
736	passed an events set like normal event callbacks (with a combination of	2289	passed an C<revents> set like normal event callbacks (a combination of
737	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2290	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
738	value passed to C<ev_once>:	2291	value passed to C<ev_once>:
739		2292
740	static void stdin_ready (int revents, void *arg)	2293	static void stdin_ready (int revents, void *arg)
741	{	2294	{
…		…
745	/* stdin might have data for us, joy! */;	2298	/* stdin might have data for us, joy! */;
746	}	2299	}
747		2300
748	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2301	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
749		2302
750	=item ev_feed_event (loop, watcher, int events)	2303	=item ev_feed_event (ev_loop *, watcher *, int revents)
751		2304
752	Feeds the given event set into the event loop, as if the specified event	2305	Feeds the given event set into the event loop, as if the specified event
753	had happened for the specified watcher (which must be a pointer to an	2306	had happened for the specified watcher (which must be a pointer to an
754	initialised but not necessarily started event watcher).	2307	initialised but not necessarily started event watcher).
755		2308
756	=item ev_feed_fd_event (loop, int fd, int revents)	2309	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
757		2310
758	Feed an event on the given fd, as if a file descriptor backend detected	2311	Feed an event on the given fd, as if a file descriptor backend detected
759	the given events it.	2312	the given events it.
760		2313
761	=item ev_feed_signal_event (loop, int signum)	2314	=item ev_feed_signal_event (ev_loop *loop, int signum)
762		2315
763	Feed an event as if the given signal occured (loop must be the default loop!).	2316	Feed an event as if the given signal occured (C<loop> must be the default
		2317	loop!).
764		2318
765	=back	2319	=back
766		2320
		2321
		2322	=head1 LIBEVENT EMULATION
		2323
		2324	Libev offers a compatibility emulation layer for libevent. It cannot
		2325	emulate the internals of libevent, so here are some usage hints:
		2326
		2327	=over 4
		2328
		2329	=item * Use it by including <event.h>, as usual.
		2330
		2331	=item * The following members are fully supported: ev_base, ev_callback,
		2332	ev_arg, ev_fd, ev_res, ev_events.
		2333
		2334	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2335	maintained by libev, it does not work exactly the same way as in libevent (consider
		2336	it a private API).
		2337
		2338	=item * Priorities are not currently supported. Initialising priorities
		2339	will fail and all watchers will have the same priority, even though there
		2340	is an ev_pri field.
		2341
		2342	=item * Other members are not supported.
		2343
		2344	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2345	to use the libev header file and library.
		2346
		2347	=back
		2348
		2349	=head1 C++ SUPPORT
		2350
		2351	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2352	you to use some convinience methods to start/stop watchers and also change
		2353	the callback model to a model using method callbacks on objects.
		2354
		2355	To use it,
		2356
		2357	#include <ev++.h>
		2358
		2359	This automatically includes F<ev.h> and puts all of its definitions (many
		2360	of them macros) into the global namespace. All C++ specific things are
		2361	put into the C<ev> namespace. It should support all the same embedding
		2362	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2363
		2364	Care has been taken to keep the overhead low. The only data member the C++
		2365	classes add (compared to plain C-style watchers) is the event loop pointer
		2366	that the watcher is associated with (or no additional members at all if
		2367	you disable C<EV_MULTIPLICITY> when embedding libev).
		2368
		2369	Currently, functions, and static and non-static member functions can be
		2370	used as callbacks. Other types should be easy to add as long as they only
		2371	need one additional pointer for context. If you need support for other
		2372	types of functors please contact the author (preferably after implementing
		2373	it).
		2374
		2375	Here is a list of things available in the C<ev> namespace:
		2376
		2377	=over 4
		2378
		2379	=item C<ev::READ>, C<ev::WRITE> etc.
		2380
		2381	These are just enum values with the same values as the C<EV_READ> etc.
		2382	macros from F<ev.h>.
		2383
		2384	=item C<ev::tstamp>, C<ev::now>
		2385
		2386	Aliases to the same types/functions as with the C<ev_> prefix.
		2387
		2388	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2389
		2390	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2391	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2392	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2393	defines by many implementations.
		2394
		2395	All of those classes have these methods:
		2396
		2397	=over 4
		2398
		2399	=item ev::TYPE::TYPE ()
		2400
		2401	=item ev::TYPE::TYPE (struct ev_loop *)
		2402
		2403	=item ev::TYPE::~TYPE
		2404
		2405	The constructor (optionally) takes an event loop to associate the watcher
		2406	with. If it is omitted, it will use C<EV_DEFAULT>.
		2407
		2408	The constructor calls C<ev_init> for you, which means you have to call the
		2409	C<set> method before starting it.
		2410
		2411	It will not set a callback, however: You have to call the templated C<set>
		2412	method to set a callback before you can start the watcher.
		2413
		2414	(The reason why you have to use a method is a limitation in C++ which does
		2415	not allow explicit template arguments for constructors).
		2416
		2417	The destructor automatically stops the watcher if it is active.
		2418
		2419	=item w->set<class, &class::method> (object *)
		2420
		2421	This method sets the callback method to call. The method has to have a
		2422	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2423	first argument and the C<revents> as second. The object must be given as
		2424	parameter and is stored in the C<data> member of the watcher.
		2425
		2426	This method synthesizes efficient thunking code to call your method from
		2427	the C callback that libev requires. If your compiler can inline your
		2428	callback (i.e. it is visible to it at the place of the C<set> call and
		2429	your compiler is good :), then the method will be fully inlined into the
		2430	thunking function, making it as fast as a direct C callback.
		2431
		2432	Example: simple class declaration and watcher initialisation
		2433
		2434	struct myclass
		2435	{
		2436	void io_cb (ev::io &w, int revents) { }
		2437	}
		2438
		2439	myclass obj;
		2440	ev::io iow;
		2441	iow.set <myclass, &myclass::io_cb> (&obj);
		2442
		2443	=item w->set<function> (void *data = 0)
		2444
		2445	Also sets a callback, but uses a static method or plain function as
		2446	callback. The optional C<data> argument will be stored in the watcher's
		2447	C<data> member and is free for you to use.
		2448
		2449	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2450
		2451	See the method-C<set> above for more details.
		2452
		2453	Example:
		2454
		2455	static void io_cb (ev::io &w, int revents) { }
		2456	iow.set <io_cb> ();
		2457
		2458	=item w->set (struct ev_loop *)
		2459
		2460	Associates a different C<struct ev_loop> with this watcher. You can only
		2461	do this when the watcher is inactive (and not pending either).
		2462
		2463	=item w->set ([args])
		2464
		2465	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2466	called at least once. Unlike the C counterpart, an active watcher gets
		2467	automatically stopped and restarted when reconfiguring it with this
		2468	method.
		2469
		2470	=item w->start ()
		2471
		2472	Starts the watcher. Note that there is no C<loop> argument, as the
		2473	constructor already stores the event loop.
		2474
		2475	=item w->stop ()
		2476
		2477	Stops the watcher if it is active. Again, no C<loop> argument.
		2478
		2479	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2480
		2481	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2482	C<ev_TYPE_again> function.
		2483
		2484	=item w->sweep () (C<ev::embed> only)
		2485
		2486	Invokes C<ev_embed_sweep>.
		2487
		2488	=item w->update () (C<ev::stat> only)
		2489
		2490	Invokes C<ev_stat_stat>.
		2491
		2492	=back
		2493
		2494	=back
		2495
		2496	Example: Define a class with an IO and idle watcher, start one of them in
		2497	the constructor.
		2498
		2499	class myclass
		2500	{
		2501	ev::io io; void io_cb (ev::io &w, int revents);
		2502	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2503
		2504	myclass (int fd)
		2505	{
		2506	io .set <myclass, &myclass::io_cb > (this);
		2507	idle.set <myclass, &myclass::idle_cb> (this);
		2508
		2509	io.start (fd, ev::READ);
		2510	}
		2511	};
		2512
		2513
		2514	=head1 MACRO MAGIC
		2515
		2516	Libev can be compiled with a variety of options, the most fundamantal
		2517	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2518	functions and callbacks have an initial C<struct ev_loop *> argument.
		2519
		2520	To make it easier to write programs that cope with either variant, the
		2521	following macros are defined:
		2522
		2523	=over 4
		2524
		2525	=item C<EV_A>, C<EV_A_>
		2526
		2527	This provides the loop I<argument> for functions, if one is required ("ev
		2528	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2529	C<EV_A_> is used when other arguments are following. Example:
		2530
		2531	ev_unref (EV_A);
		2532	ev_timer_add (EV_A_ watcher);
		2533	ev_loop (EV_A_ 0);
		2534
		2535	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2536	which is often provided by the following macro.
		2537
		2538	=item C<EV_P>, C<EV_P_>
		2539
		2540	This provides the loop I<parameter> for functions, if one is required ("ev
		2541	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2542	C<EV_P_> is used when other parameters are following. Example:
		2543
		2544	// this is how ev_unref is being declared
		2545	static void ev_unref (EV_P);
		2546
		2547	// this is how you can declare your typical callback
		2548	static void cb (EV_P_ ev_timer *w, int revents)
		2549
		2550	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2551	suitable for use with C<EV_A>.
		2552
		2553	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2554
		2555	Similar to the other two macros, this gives you the value of the default
		2556	loop, if multiple loops are supported ("ev loop default").
		2557
		2558	=back
		2559
		2560	Example: Declare and initialise a check watcher, utilising the above
		2561	macros so it will work regardless of whether multiple loops are supported
		2562	or not.
		2563
		2564	static void
		2565	check_cb (EV_P_ ev_timer *w, int revents)
		2566	{
		2567	ev_check_stop (EV_A_ w);
		2568	}
		2569
		2570	ev_check check;
		2571	ev_check_init (&check, check_cb);
		2572	ev_check_start (EV_DEFAULT_ &check);
		2573	ev_loop (EV_DEFAULT_ 0);
		2574
		2575	=head1 EMBEDDING
		2576
		2577	Libev can (and often is) directly embedded into host
		2578	applications. Examples of applications that embed it include the Deliantra
		2579	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2580	and rxvt-unicode.
		2581
		2582	The goal is to enable you to just copy the necessary files into your
		2583	source directory without having to change even a single line in them, so
		2584	you can easily upgrade by simply copying (or having a checked-out copy of
		2585	libev somewhere in your source tree).
		2586
		2587	=head2 FILESETS
		2588
		2589	Depending on what features you need you need to include one or more sets of files
		2590	in your app.
		2591
		2592	=head3 CORE EVENT LOOP
		2593
		2594	To include only the libev core (all the C<ev_*> functions), with manual
		2595	configuration (no autoconf):
		2596
		2597	#define EV_STANDALONE 1
		2598	#include "ev.c"
		2599
		2600	This will automatically include F<ev.h>, too, and should be done in a
		2601	single C source file only to provide the function implementations. To use
		2602	it, do the same for F<ev.h> in all files wishing to use this API (best
		2603	done by writing a wrapper around F<ev.h> that you can include instead and
		2604	where you can put other configuration options):
		2605
		2606	#define EV_STANDALONE 1
		2607	#include "ev.h"
		2608
		2609	Both header files and implementation files can be compiled with a C++
		2610	compiler (at least, thats a stated goal, and breakage will be treated
		2611	as a bug).
		2612
		2613	You need the following files in your source tree, or in a directory
		2614	in your include path (e.g. in libev/ when using -Ilibev):
		2615
		2616	ev.h
		2617	ev.c
		2618	ev_vars.h
		2619	ev_wrap.h
		2620
		2621	ev_win32.c required on win32 platforms only
		2622
		2623	ev_select.c only when select backend is enabled (which is enabled by default)
		2624	ev_poll.c only when poll backend is enabled (disabled by default)
		2625	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2626	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2627	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2628
		2629	F<ev.c> includes the backend files directly when enabled, so you only need
		2630	to compile this single file.
		2631
		2632	=head3 LIBEVENT COMPATIBILITY API
		2633
		2634	To include the libevent compatibility API, also include:
		2635
		2636	#include "event.c"
		2637
		2638	in the file including F<ev.c>, and:
		2639
		2640	#include "event.h"
		2641
		2642	in the files that want to use the libevent API. This also includes F<ev.h>.
		2643
		2644	You need the following additional files for this:
		2645
		2646	event.h
		2647	event.c
		2648
		2649	=head3 AUTOCONF SUPPORT
		2650
		2651	Instead of using C<EV_STANDALONE=1> and providing your config in
		2652	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2653	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2654	include F<config.h> and configure itself accordingly.
		2655
		2656	For this of course you need the m4 file:
		2657
		2658	libev.m4
		2659
		2660	=head2 PREPROCESSOR SYMBOLS/MACROS
		2661
		2662	Libev can be configured via a variety of preprocessor symbols you have to define
		2663	before including any of its files. The default is not to build for multiplicity
		2664	and only include the select backend.
		2665
		2666	=over 4
		2667
		2668	=item EV_STANDALONE
		2669
		2670	Must always be C<1> if you do not use autoconf configuration, which
		2671	keeps libev from including F<config.h>, and it also defines dummy
		2672	implementations for some libevent functions (such as logging, which is not
		2673	supported). It will also not define any of the structs usually found in
		2674	F<event.h> that are not directly supported by the libev core alone.
		2675
		2676	=item EV_USE_MONOTONIC
		2677
		2678	If defined to be C<1>, libev will try to detect the availability of the
		2679	monotonic clock option at both compiletime and runtime. Otherwise no use
		2680	of the monotonic clock option will be attempted. If you enable this, you
		2681	usually have to link against librt or something similar. Enabling it when
		2682	the functionality isn't available is safe, though, although you have
		2683	to make sure you link against any libraries where the C<clock_gettime>
		2684	function is hiding in (often F<-lrt>).
		2685
		2686	=item EV_USE_REALTIME
		2687
		2688	If defined to be C<1>, libev will try to detect the availability of the
		2689	realtime clock option at compiletime (and assume its availability at
		2690	runtime if successful). Otherwise no use of the realtime clock option will
		2691	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2692	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2693	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2694
		2695	=item EV_USE_NANOSLEEP
		2696
		2697	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2698	and will use it for delays. Otherwise it will use C<select ()>.
		2699
		2700	=item EV_USE_SELECT
		2701
		2702	If undefined or defined to be C<1>, libev will compile in support for the
		2703	C<select>(2) backend. No attempt at autodetection will be done: if no
		2704	other method takes over, select will be it. Otherwise the select backend
		2705	will not be compiled in.
		2706
		2707	=item EV_SELECT_USE_FD_SET
		2708
		2709	If defined to C<1>, then the select backend will use the system C<fd_set>
		2710	structure. This is useful if libev doesn't compile due to a missing
		2711	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2712	exotic systems. This usually limits the range of file descriptors to some
		2713	low limit such as 1024 or might have other limitations (winsocket only
		2714	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2715	influence the size of the C<fd_set> used.
		2716
		2717	=item EV_SELECT_IS_WINSOCKET
		2718
		2719	When defined to C<1>, the select backend will assume that
		2720	select/socket/connect etc. don't understand file descriptors but
		2721	wants osf handles on win32 (this is the case when the select to
		2722	be used is the winsock select). This means that it will call
		2723	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2724	it is assumed that all these functions actually work on fds, even
		2725	on win32. Should not be defined on non-win32 platforms.
		2726
		2727	=item EV_FD_TO_WIN32_HANDLE
		2728
		2729	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2730	file descriptors to socket handles. When not defining this symbol (the
		2731	default), then libev will call C<_get_osfhandle>, which is usually
		2732	correct. In some cases, programs use their own file descriptor management,
		2733	in which case they can provide this function to map fds to socket handles.
		2734
		2735	=item EV_USE_POLL
		2736
		2737	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2738	backend. Otherwise it will be enabled on non-win32 platforms. It
		2739	takes precedence over select.
		2740
		2741	=item EV_USE_EPOLL
		2742
		2743	If defined to be C<1>, libev will compile in support for the Linux
		2744	C<epoll>(7) backend. Its availability will be detected at runtime,
		2745	otherwise another method will be used as fallback. This is the
		2746	preferred backend for GNU/Linux systems.
		2747
		2748	=item EV_USE_KQUEUE
		2749
		2750	If defined to be C<1>, libev will compile in support for the BSD style
		2751	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2752	otherwise another method will be used as fallback. This is the preferred
		2753	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2754	supports some types of fds correctly (the only platform we found that
		2755	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2756	not be used unless explicitly requested. The best way to use it is to find
		2757	out whether kqueue supports your type of fd properly and use an embedded
		2758	kqueue loop.
		2759
		2760	=item EV_USE_PORT
		2761
		2762	If defined to be C<1>, libev will compile in support for the Solaris
		2763	10 port style backend. Its availability will be detected at runtime,
		2764	otherwise another method will be used as fallback. This is the preferred
		2765	backend for Solaris 10 systems.
		2766
		2767	=item EV_USE_DEVPOLL
		2768
		2769	reserved for future expansion, works like the USE symbols above.
		2770
		2771	=item EV_USE_INOTIFY
		2772
		2773	If defined to be C<1>, libev will compile in support for the Linux inotify
		2774	interface to speed up C<ev_stat> watchers. Its actual availability will
		2775	be detected at runtime.
		2776
		2777	=item EV_ATOMIC_T
		2778
		2779	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2780	access is atomic with respect to other threads or signal contexts. No such
		2781	type is easily found in the C language, so you can provide your own type
		2782	that you know is safe for your purposes. It is used both for signal handler "locking"
		2783	as well as for signal and thread safety in C<ev_async> watchers.
		2784
		2785	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2786	(from F<signal.h>), which is usually good enough on most platforms.
		2787
		2788	=item EV_H
		2789
		2790	The name of the F<ev.h> header file used to include it. The default if
		2791	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2792	used to virtually rename the F<ev.h> header file in case of conflicts.
		2793
		2794	=item EV_CONFIG_H
		2795
		2796	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2797	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2798	C<EV_H>, above.
		2799
		2800	=item EV_EVENT_H
		2801
		2802	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2803	of how the F<event.h> header can be found, the default is C<"event.h">.
		2804
		2805	=item EV_PROTOTYPES
		2806
		2807	If defined to be C<0>, then F<ev.h> will not define any function
		2808	prototypes, but still define all the structs and other symbols. This is
		2809	occasionally useful if you want to provide your own wrapper functions
		2810	around libev functions.
		2811
		2812	=item EV_MULTIPLICITY
		2813
		2814	If undefined or defined to C<1>, then all event-loop-specific functions
		2815	will have the C<struct ev_loop *> as first argument, and you can create
		2816	additional independent event loops. Otherwise there will be no support
		2817	for multiple event loops and there is no first event loop pointer
		2818	argument. Instead, all functions act on the single default loop.
		2819
		2820	=item EV_MINPRI
		2821
		2822	=item EV_MAXPRI
		2823
		2824	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2825	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2826	provide for more priorities by overriding those symbols (usually defined
		2827	to be C<-2> and C<2>, respectively).
		2828
		2829	When doing priority-based operations, libev usually has to linearly search
		2830	all the priorities, so having many of them (hundreds) uses a lot of space
		2831	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2832	fine.
		2833
		2834	If your embedding app does not need any priorities, defining these both to
		2835	C<0> will save some memory and cpu.
		2836
		2837	=item EV_PERIODIC_ENABLE
		2838
		2839	If undefined or defined to be C<1>, then periodic timers are supported. If
		2840	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2841	code.
		2842
		2843	=item EV_IDLE_ENABLE
		2844
		2845	If undefined or defined to be C<1>, then idle watchers are supported. If
		2846	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2847	code.
		2848
		2849	=item EV_EMBED_ENABLE
		2850
		2851	If undefined or defined to be C<1>, then embed watchers are supported. If
		2852	defined to be C<0>, then they are not.
		2853
		2854	=item EV_STAT_ENABLE
		2855
		2856	If undefined or defined to be C<1>, then stat watchers are supported. If
		2857	defined to be C<0>, then they are not.
		2858
		2859	=item EV_FORK_ENABLE
		2860
		2861	If undefined or defined to be C<1>, then fork watchers are supported. If
		2862	defined to be C<0>, then they are not.
		2863
		2864	=item EV_ASYNC_ENABLE
		2865
		2866	If undefined or defined to be C<1>, then async watchers are supported. If
		2867	defined to be C<0>, then they are not.
		2868
		2869	=item EV_MINIMAL
		2870
		2871	If you need to shave off some kilobytes of code at the expense of some
		2872	speed, define this symbol to C<1>. Currently only used for gcc to override
		2873	some inlining decisions, saves roughly 30% codesize of amd64.
		2874
		2875	=item EV_PID_HASHSIZE
		2876
		2877	C<ev_child> watchers use a small hash table to distribute workload by
		2878	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2879	than enough. If you need to manage thousands of children you might want to
		2880	increase this value (I<must> be a power of two).
		2881
		2882	=item EV_INOTIFY_HASHSIZE
		2883
		2884	C<ev_stat> watchers use a small hash table to distribute workload by
		2885	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2886	usually more than enough. If you need to manage thousands of C<ev_stat>
		2887	watchers you might want to increase this value (I<must> be a power of
		2888	two).
		2889
		2890	=item EV_COMMON
		2891
		2892	By default, all watchers have a C<void *data> member. By redefining
		2893	this macro to a something else you can include more and other types of
		2894	members. You have to define it each time you include one of the files,
		2895	though, and it must be identical each time.
		2896
		2897	For example, the perl EV module uses something like this:
		2898
		2899	#define EV_COMMON \
		2900	SV *self; /* contains this struct */ \
		2901	SV *cb_sv, *fh /* note no trailing ";" */
		2902
		2903	=item EV_CB_DECLARE (type)
		2904
		2905	=item EV_CB_INVOKE (watcher, revents)
		2906
		2907	=item ev_set_cb (ev, cb)
		2908
		2909	Can be used to change the callback member declaration in each watcher,
		2910	and the way callbacks are invoked and set. Must expand to a struct member
		2911	definition and a statement, respectively. See the F<ev.h> header file for
		2912	their default definitions. One possible use for overriding these is to
		2913	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2914	method calls instead of plain function calls in C++.
		2915
		2916	=head2 EXPORTED API SYMBOLS
		2917
		2918	If you need to re-export the API (e.g. via a dll) and you need a list of
		2919	exported symbols, you can use the provided F<Symbol.*> files which list
		2920	all public symbols, one per line:
		2921
		2922	Symbols.ev for libev proper
		2923	Symbols.event for the libevent emulation
		2924
		2925	This can also be used to rename all public symbols to avoid clashes with
		2926	multiple versions of libev linked together (which is obviously bad in
		2927	itself, but sometimes it is inconvinient to avoid this).
		2928
		2929	A sed command like this will create wrapper C<#define>'s that you need to
		2930	include before including F<ev.h>:
		2931
		2932	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		2933
		2934	This would create a file F<wrap.h> which essentially looks like this:
		2935
		2936	#define ev_backend myprefix_ev_backend
		2937	#define ev_check_start myprefix_ev_check_start
		2938	#define ev_check_stop myprefix_ev_check_stop
		2939	...
		2940
		2941	=head2 EXAMPLES
		2942
		2943	For a real-world example of a program the includes libev
		2944	verbatim, you can have a look at the EV perl module
		2945	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2946	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2947	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2948	will be compiled. It is pretty complex because it provides its own header
		2949	file.
		2950
		2951	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2952	that everybody includes and which overrides some configure choices:
		2953
		2954	#define EV_MINIMAL 1
		2955	#define EV_USE_POLL 0
		2956	#define EV_MULTIPLICITY 0
		2957	#define EV_PERIODIC_ENABLE 0
		2958	#define EV_STAT_ENABLE 0
		2959	#define EV_FORK_ENABLE 0
		2960	#define EV_CONFIG_H <config.h>
		2961	#define EV_MINPRI 0
		2962	#define EV_MAXPRI 0
		2963
		2964	#include "ev++.h"
		2965
		2966	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		2967
		2968	#include "ev_cpp.h"
		2969	#include "ev.c"
		2970
		2971
		2972	=head1 COMPLEXITIES
		2973
		2974	In this section the complexities of (many of) the algorithms used inside
		2975	libev will be explained. For complexity discussions about backends see the
		2976	documentation for C<ev_default_init>.
		2977
		2978	All of the following are about amortised time: If an array needs to be
		2979	extended, libev needs to realloc and move the whole array, but this
		2980	happens asymptotically never with higher number of elements, so O(1) might
		2981	mean it might do a lengthy realloc operation in rare cases, but on average
		2982	it is much faster and asymptotically approaches constant time.
		2983
		2984	=over 4
		2985
		2986	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		2987
		2988	This means that, when you have a watcher that triggers in one hour and
		2989	there are 100 watchers that would trigger before that then inserting will
		2990	have to skip roughly seven (C<ld 100>) of these watchers.
		2991
		2992	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		2993
		2994	That means that changing a timer costs less than removing/adding them
		2995	as only the relative motion in the event queue has to be paid for.
		2996
		2997	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		2998
		2999	These just add the watcher into an array or at the head of a list.
		3000
		3001	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3002
		3003	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3004
		3005	These watchers are stored in lists then need to be walked to find the
		3006	correct watcher to remove. The lists are usually short (you don't usually
		3007	have many watchers waiting for the same fd or signal).
		3008
		3009	=item Finding the next timer in each loop iteration: O(1)
		3010
		3011	By virtue of using a binary heap, the next timer is always found at the
		3012	beginning of the storage array.
		3013
		3014	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3015
		3016	A change means an I/O watcher gets started or stopped, which requires
		3017	libev to recalculate its status (and possibly tell the kernel, depending
		3018	on backend and wether C<ev_io_set> was used).
		3019
		3020	=item Activating one watcher (putting it into the pending state): O(1)
		3021
		3022	=item Priority handling: O(number_of_priorities)
		3023
		3024	Priorities are implemented by allocating some space for each
		3025	priority. When doing priority-based operations, libev usually has to
		3026	linearly search all the priorities, but starting/stopping and activating
		3027	watchers becomes O(1) w.r.t. priority handling.
		3028
		3029	=item Sending an ev_async: O(1)
		3030
		3031	=item Processing ev_async_send: O(number_of_async_watchers)
		3032
		3033	=item Processing signals: O(max_signal_number)
		3034
		3035	Sending involves a syscall I<iff> there were no other C<ev_async_send>
		3036	calls in the current loop iteration. Checking for async and signal events
		3037	involves iterating over all running async watchers or all signal numbers.
		3038
		3039	=back
		3040
		3041
		3042	=head1 Win32 platform limitations and workarounds
		3043
		3044	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3045	requires, and its I/O model is fundamentally incompatible with the POSIX
		3046	model. Libev still offers limited functionality on this platform in
		3047	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3048	descriptors. This only applies when using Win32 natively, not when using
		3049	e.g. cygwin.
		3050
		3051	There is no supported compilation method available on windows except
		3052	embedding it into other applications.
		3053
		3054	Due to the many, low, and arbitrary limits on the win32 platform and the
		3055	abysmal performance of winsockets, using a large number of sockets is not
		3056	recommended (and not reasonable). If your program needs to use more than
		3057	a hundred or so sockets, then likely it needs to use a totally different
		3058	implementation for windows, as libev offers the POSIX model, which cannot
		3059	be implemented efficiently on windows (microsoft monopoly games).
		3060
		3061	=over 4
		3062
		3063	=item The winsocket select function
		3064
		3065	The winsocket C<select> function doesn't follow POSIX in that it requires
		3066	socket I<handles> and not socket I<file descriptors>. This makes select
		3067	very inefficient, and also requires a mapping from file descriptors
		3068	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		3069	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		3070	symbols for more info.
		3071
		3072	The configuration for a "naked" win32 using the microsoft runtime
		3073	libraries and raw winsocket select is:
		3074
		3075	#define EV_USE_SELECT 1
		3076	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3077
		3078	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3079	complexity in the O(n²) range when using win32.
		3080
		3081	=item Limited number of file descriptors
		3082
		3083	Windows has numerous arbitrary (and low) limits on things. Early versions
		3084	of winsocket's select only supported waiting for a max. of C<64> handles
		3085	(probably owning to the fact that all windows kernels can only wait for
		3086	C<64> things at the same time internally; microsoft recommends spawning a
		3087	chain of threads and wait for 63 handles and the previous thread in each).
		3088
		3089	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3090	to some high number (e.g. C<2048>) before compiling the winsocket select
		3091	call (which might be in libev or elsewhere, for example, perl does its own
		3092	select emulation on windows).
		3093
		3094	Another limit is the number of file descriptors in the microsoft runtime
		3095	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3096	or something like this inside microsoft). You can increase this by calling
		3097	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3098	arbitrary limit), but is broken in many versions of the microsoft runtime
		3099	libraries.
		3100
		3101	This might get you to about C<512> or C<2048> sockets (depending on
		3102	windows version and/or the phase of the moon). To get more, you need to
		3103	wrap all I/O functions and provide your own fd management, but the cost of
		3104	calling select (O(n²)) will likely make this unworkable.
		3105
		3106	=back
		3107
		3108
767	=head1 AUTHOR	3109	=head1 AUTHOR
768		3110
769	Marc Lehmann <libev@schmorp.de>.	3111	Marc Lehmann <libev@schmorp.de>.
770		3112

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