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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 REPRESENTATION	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.
51		121
52	=head1 GLOBAL FUNCTIONS	122	=head1 GLOBAL FUNCTIONS
53		123
54	These functions can be called anytime, even before initialising the	124	These functions can be called anytime, even before initialising the
55	library in any way.	125	library in any way.
…		…
60		130
61	Returns the current time as libev would use it. Please note that the	131	Returns the current time as libev would use it. Please note that the
62	C<ev_now> function is usually faster and also often returns the timestamp	132	C<ev_now> function is usually faster and also often returns the timestamp
63	you actually want to know.	133	you actually want to know.
64		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 ()>.
		140
65	=item int ev_version_major ()	141	=item int ev_version_major ()
66		142
67	=item int ev_version_minor ()	143	=item int ev_version_minor ()
68		144
69	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
70	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
71	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
72	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
73	version of the library your program was compiled against.	149	version of the library your program was compiled against.
74		150
		151	These version numbers refer to the ABI version of the library, not the
		152	release version.
		153
75	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,
76	as this indicates an incompatible change. Minor versions are usually	155	as this indicates an incompatible change. Minor versions are usually
77	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
78	not a problem.	157	not a problem.
79		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
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
81		199
82	Sets the allocation function to use (the prototype is similar to the	200	Sets the allocation function to use (the prototype is similar - the
83	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
84	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
85	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
86	destructive action. The default is your system realloc function.	204	potentially destructive action. The default is your system realloc
		205	function.
87		206
88	You could override this function in high-availability programs to, say,	207	You could override this function in high-availability programs to, say,
89	free some memory if it cannot allocate memory, to use a special allocator,	208	free some memory if it cannot allocate memory, to use a special allocator,
90	or even to sleep a while and retry until some memory is available.	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);
91		230
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	231	=item ev_set_syserr_cb (void (*cb)(const char *msg));
93		232
94	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
95	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
…		…
97	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
98	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
99	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
100	(such as abort).	239	(such as abort).
101		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
102	=back	253	=back
103		254
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	255	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		256
106	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
…		…
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	270	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		271
121	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
122	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
123	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
124	flags).	275	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		276
126	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
127	function.	278	function.
128		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
129	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
130	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>).
131		289
132	It supports the following flags:	290	The following flags are supported:
133		291
134	=over 4	292	=over 4
135		293
136	=item C<EVFLAG_AUTO>	294	=item C<EVFLAG_AUTO>
137		295
…		…
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	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
147	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
148	around bugs.	306	around bugs.
149		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
150	=item C<EVMETHOD_SELECT> (portable select backend)	328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		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
152	=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)
153		344
154	=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.
155		351
156	=item C<EVMETHOD_KQUEUE> (some bsds only)	352	=item C<EVBACKEND_EPOLL> (value 4, Linux)
157		353
158	=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.
159		361
160	=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
161		443
162	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
163	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
164	specified, any backend will do.	446	specified, all backends in C<ev_recommended_backends ()> will be tried.
165		447
166	=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);
167		463
168	=item struct ev_loop *ev_loop_new (unsigned int flags)	464	=item struct ev_loop *ev_loop_new (unsigned int flags)
169		465
170	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
171	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
172	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
173	undefined behaviour (or a failed assertion if assertions are enabled).	469	undefined behaviour (or a failed assertion if assertions are enabled).
174		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
175	=item ev_default_destroy ()	477	=item ev_default_destroy ()
176		478
177	Destroys the default loop again (frees all memory and kernel state	479	Destroys the default loop again (frees all memory and kernel state
178	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
179	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>).
180		495
181	=item ev_loop_destroy (loop)	496	=item ev_loop_destroy (loop)
182		497
183	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
184	earlier call to C<ev_loop_new>.	499	earlier call to C<ev_loop_new>.
185		500
186	=item ev_default_fork ()	501	=item ev_default_fork ()
187		502
		503	This function sets a flag that causes subsequent C<ev_loop> iterations
188	This function reinitialises the kernel state for backends that have	504	to reinitialise the kernel state for backends that have one. Despite the
189	one. Despite the name, you can call it anytime, but it makes most sense	505	name, you can call it anytime, but it makes most sense after forking, in
190	after forking, in either the parent or child process (or both, but that	506	the child process (or both child and parent, but that again makes little
191	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.
192		509
193	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
194	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
195	have to call it.	512	you just fork+exec, you don't have to call it at all.
196		513
197	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
198	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
199	quite nicely into a call to C<pthread_atfork>:	516	quite nicely into a call to C<pthread_atfork>:
200		517
…		…
204		521
205	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
206	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
207	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.
208		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
209	=item unsigned int ev_method (loop)	540	=item unsigned int ev_backend (loop)
210		541
211	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
212	use.	543	use.
213		544
214	=item ev_tstamp ev_now (loop)	545	=item ev_tstamp ev_now (loop)
215		546
216	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
217	got events and started processing them. This timestamp does not change	548	received events and started processing them. This timestamp does not
218	as long as callbacks are being processed, and this is also the base time	549	change as long as callbacks are being processed, and this is also the base
219	used for relative timers. You can treat it as the timestamp of the event	550	time used for relative timers. You can treat it as the timestamp of the
220	occuring (or more correctly, the mainloop finding out about it).	551	event occurring (or more correctly, libev finding out about it).
221		552
222	=item ev_loop (loop, int flags)	553	=item ev_loop (loop, int flags)
223		554
224	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
225	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
226	events.	557	events.
227		558
228	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
229	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.
230		567
231	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
232	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
233	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.
234		571
235	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
236	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
237	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
238	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.
239		579
240	This flags value could be used to implement alternative looping
241	constructs, but the C<prepare> and C<check> watchers provide a better and
242	more generic mechanism.
243
244	Here are the gory details of what ev_loop does:	580	Here are the gory details of what C<ev_loop> does:
245		581
246	1. If there are no active watchers (reference count is zero), return.	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.
247	2. Queue and immediately call all prepare watchers.	585	- Queue and call all prepare watchers.
248	3. If we have been forked, recreate the kernel state.	586	- If we have been forked, recreate the kernel state.
249	4. Update the kernel state with all outstanding changes.	587	- Update the kernel state with all outstanding changes.
250	5. Update the "event loop time".	588	- Update the "event loop time".
251	6. Calculate for how long to block.	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.
252	7. Block the process, waiting for events.	593	- Block the process, waiting for any events.
		594	- Queue all outstanding I/O (fd) events.
253	8. Update the "event loop time" and do time jump handling.	595	- Update the "event loop time" and do time jump handling.
254	9. Queue all outstanding timers.	596	- Queue all outstanding timers.
255	10. Queue all outstanding periodics.	597	- Queue all outstanding periodics.
256	11. If no events are pending now, queue all idle watchers.	598	- If no events are pending now, queue all idle watchers.
257	12. Queue all check watchers.	599	- Queue all check watchers.
258	13. Call all queued watchers in reverse order (i.e. check watchers first).	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.
259	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	603	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
260	was used, return, otherwise continue with step #1.	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!
261		614
262	=item ev_unloop (loop, how)	615	=item ev_unloop (loop, how)
263		616
264	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
265	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
266	C<EVUNLOOP_ONE>, 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
267	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.
268		623
269	=item ev_ref (loop)	624	=item ev_ref (loop)
270		625
271	=item ev_unref (loop)	626	=item ev_unref (loop)
272		627
…		…
277	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
278	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
279	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
280	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
281	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
282	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.
283		689
284	=back	690	=back
		691
285		692
286	=head1 ANATOMY OF A WATCHER	693	=head1 ANATOMY OF A WATCHER
287		694
288	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
289	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
…		…
322	*) >>), 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
323	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	730	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
324		731
325	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
326	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
327	reinitialise it or call its set method.	734	reinitialise it or call its C<set> macro.
328
329	You can check whether an event is active by calling the C<ev_is_active
330	(watcher *)> macro. To see whether an event is outstanding (but the
331	callback for it has not been called yet) you can use the C<ev_is_pending
332	(watcher *)> macro.
333		735
334	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
335	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
336	third argument.	738	third argument.
337		739
…		…
361	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.
362		764
363	=item C<EV_CHILD>	765	=item C<EV_CHILD>
364		766
365	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.
366		772
367	=item C<EV_IDLE>	773	=item C<EV_IDLE>
368		774
369	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.
370		776
…		…
378	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
379	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
380	(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
381	C<ev_loop> from blocking).	787	C<ev_loop> from blocking).
382		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
383	=item C<EV_ERROR>	802	=item C<EV_ERROR>
384		803
385	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
386	happen because the watcher could not be properly started because libev	805	happen because the watcher could not be properly started because libev
387	ran out of memory, a file descriptor was found to be closed or any other	806	ran out of memory, a file descriptor was found to be closed or any other
…		…
393	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
394	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
395	programs, though, so beware.	814	programs, though, so beware.
396		815
397	=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
398		937
399	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	938	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
400		939
401	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
402	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
…		…
420	{	959	{
421	struct my_io *w = (struct my_io *)w_;	960	struct my_io *w = (struct my_io *)w_;
422	...	961	...
423	}	962	}
424		963
425	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
426	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	}
427		995
428		996
429	=head1 WATCHER TYPES	997	=head1 WATCHER TYPES
430		998
431	This section describes each watcher in detail, but will not repeat	999	This section describes each watcher in detail, but will not repeat
432	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.
433		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
434	=head2 C<ev_io> - is this file descriptor readable or writable	1013	=head2 C<ev_io> - is this file descriptor readable or writable?
435		1014
436	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
437	in each iteration of the event loop (This behaviour is called	1016	in each iteration of the event loop, or, more precisely, when reading
438	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
439	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
440	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.
441		1022
442	In general you can register as many read and/or write event watchers per	1023	In general you can register as many read and/or write event watchers per
443	fd as you want (as long as you don't confuse yourself). Setting all file	1024	fd as you want (as long as you don't confuse yourself). Setting all file
444	descriptors to non-blocking mode is also usually a good idea (but not	1025	descriptors to non-blocking mode is also usually a good idea (but not
445	required if you know what you are doing).	1026	required if you know what you are doing).
446		1027
447	You have to be careful with dup'ed file descriptors, though. Some backends
448	(the linux epoll backend is a notable example) cannot handle dup'ed file
449	descriptors correctly if you register interest in two or more fds pointing
450	to the same underlying file/socket etc. description (that is, they share
451	the same underlying "file open").
452
453	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
454	(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
455	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	=head3 The special problem of SIGPIPE
		1091
		1092	While not really specific to libev, it is easy to forget about SIGPIPE:
		1093	when reading from a pipe whose other end has been closed, your program
		1094	gets send a SIGPIPE, which, by default, aborts your program. For most
		1095	programs this is sensible behaviour, for daemons, this is usually
		1096	undesirable.
		1097
		1098	So when you encounter spurious, unexplained daemon exits, make sure you
		1099	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1100	somewhere, as that would have given you a big clue).
		1101
		1102
		1103	=head3 Watcher-Specific Functions
456		1104
457	=over 4	1105	=over 4
458		1106
459	=item ev_io_init (ev_io *, callback, int fd, int events)	1107	=item ev_io_init (ev_io *, callback, int fd, int events)
460		1108
461	=item ev_io_set (ev_io *, int fd, int events)	1109	=item ev_io_set (ev_io *, int fd, int events)
462		1110
463	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1111	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
464	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1112	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
465	EV_WRITE> to receive the given events.	1113	C<EV_READ | EV_WRITE> to receive the given events.
		1114
		1115	=item int fd [read-only]
		1116
		1117	The file descriptor being watched.
		1118
		1119	=item int events [read-only]
		1120
		1121	The events being watched.
466		1122
467	=back	1123	=back
468		1124
		1125	=head3 Examples
		1126
		1127	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1128	readable, but only once. Since it is likely line-buffered, you could
		1129	attempt to read a whole line in the callback.
		1130
		1131	static void
		1132	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1133	{
		1134	ev_io_stop (loop, w);
		1135	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1136	}
		1137
		1138	...
		1139	struct ev_loop *loop = ev_default_init (0);
		1140	struct ev_io stdin_readable;
		1141	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1142	ev_io_start (loop, &stdin_readable);
		1143	ev_loop (loop, 0);
		1144
		1145
469	=head2 C<ev_timer> - relative and optionally recurring timeouts	1146	=head2 C<ev_timer> - relative and optionally repeating timeouts
470		1147
471	Timer watchers are simple relative timers that generate an event after a	1148	Timer watchers are simple relative timers that generate an event after a
472	given time, and optionally repeating in regular intervals after that.	1149	given time, and optionally repeating in regular intervals after that.
473		1150
474	The timers are based on real time, that is, if you register an event that	1151	The timers are based on real time, that is, if you register an event that
475	times out after an hour and you reset your system clock to last years	1152	times out after an hour and you reset your system clock to last years
476	time, it will still time out after (roughly) and hour. "Roughly" because	1153	time, it will still time out after (roughly) and hour. "Roughly" because
477	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1154	detecting time jumps is hard, and some inaccuracies are unavoidable (the
478	monotonic clock option helps a lot here).	1155	monotonic clock option helps a lot here).
479		1156
480	The relative timeouts are calculated relative to the C<ev_now ()>	1157	The relative timeouts are calculated relative to the C<ev_now ()>
481	time. This is usually the right thing as this timestamp refers to the time	1158	time. This is usually the right thing as this timestamp refers to the time
482	of the event triggering whatever timeout you are modifying/starting. If	1159	of the event triggering whatever timeout you are modifying/starting. If
483	you suspect event processing to be delayed and you *need* to base the timeout	1160	you suspect event processing to be delayed and you I<need> to base the timeout
484	on the current time, use something like this to adjust for this:	1161	on the current time, use something like this to adjust for this:
485		1162
486	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1163	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1164
		1165	The callback is guarenteed to be invoked only when its timeout has passed,
		1166	but if multiple timers become ready during the same loop iteration then
		1167	order of execution is undefined.
		1168
		1169	=head3 Watcher-Specific Functions and Data Members
487		1170
488	=over 4	1171	=over 4
489		1172
490	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1173	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
491		1174
…		…
500	configure a timer to trigger every 10 seconds, then it will trigger at	1183	configure a timer to trigger every 10 seconds, then it will trigger at
501	exactly 10 second intervals. If, however, your program cannot keep up with	1184	exactly 10 second intervals. If, however, your program cannot keep up with
502	the timer (because it takes longer than those 10 seconds to do stuff) the	1185	the timer (because it takes longer than those 10 seconds to do stuff) the
503	timer will not fire more than once per event loop iteration.	1186	timer will not fire more than once per event loop iteration.
504		1187
505	=item ev_timer_again (loop)	1188	=item ev_timer_again (loop, ev_timer *)
506		1189
507	This will act as if the timer timed out and restart it again if it is	1190	This will act as if the timer timed out and restart it again if it is
508	repeating. The exact semantics are:	1191	repeating. The exact semantics are:
509		1192
		1193	If the timer is pending, its pending status is cleared.
		1194
510	If the timer is started but nonrepeating, stop it.	1195	If the timer is started but nonrepeating, stop it (as if it timed out).
511		1196
512	If the timer is repeating, either start it if necessary (with the repeat	1197	If the timer is repeating, either start it if necessary (with the
513	value), or reset the running timer to the repeat value.	1198	C<repeat> value), or reset the running timer to the C<repeat> value.
514		1199
515	This sounds a bit complicated, but here is a useful and typical	1200	This sounds a bit complicated, but here is a useful and typical
516	example: Imagine you have a tcp connection and you want a so-called idle	1201	example: Imagine you have a tcp connection and you want a so-called idle
517	timeout, that is, you want to be called when there have been, say, 60	1202	timeout, that is, you want to be called when there have been, say, 60
518	seconds of inactivity on the socket. The easiest way to do this is to	1203	seconds of inactivity on the socket. The easiest way to do this is to
519	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1204	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
520	time you successfully read or write some data. If you go into an idle	1205	C<ev_timer_again> each time you successfully read or write some data. If
521	state where you do not expect data to travel on the socket, you can stop	1206	you go into an idle state where you do not expect data to travel on the
522	the timer, and again will automatically restart it if need be.	1207	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1208	automatically restart it if need be.
		1209
		1210	That means you can ignore the C<after> value and C<ev_timer_start>
		1211	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1212
		1213	ev_timer_init (timer, callback, 0., 5.);
		1214	ev_timer_again (loop, timer);
		1215	...
		1216	timer->again = 17.;
		1217	ev_timer_again (loop, timer);
		1218	...
		1219	timer->again = 10.;
		1220	ev_timer_again (loop, timer);
		1221
		1222	This is more slightly efficient then stopping/starting the timer each time
		1223	you want to modify its timeout value.
		1224
		1225	=item ev_tstamp repeat [read-write]
		1226
		1227	The current C<repeat> value. Will be used each time the watcher times out
		1228	or C<ev_timer_again> is called and determines the next timeout (if any),
		1229	which is also when any modifications are taken into account.
523		1230
524	=back	1231	=back
525		1232
		1233	=head3 Examples
		1234
		1235	Example: Create a timer that fires after 60 seconds.
		1236
		1237	static void
		1238	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1239	{
		1240	.. one minute over, w is actually stopped right here
		1241	}
		1242
		1243	struct ev_timer mytimer;
		1244	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1245	ev_timer_start (loop, &mytimer);
		1246
		1247	Example: Create a timeout timer that times out after 10 seconds of
		1248	inactivity.
		1249
		1250	static void
		1251	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1252	{
		1253	.. ten seconds without any activity
		1254	}
		1255
		1256	struct ev_timer mytimer;
		1257	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1258	ev_timer_again (&mytimer); /* start timer */
		1259	ev_loop (loop, 0);
		1260
		1261	// and in some piece of code that gets executed on any "activity":
		1262	// reset the timeout to start ticking again at 10 seconds
		1263	ev_timer_again (&mytimer);
		1264
		1265
526	=head2 C<ev_periodic> - to cron or not to cron	1266	=head2 C<ev_periodic> - to cron or not to cron?
527		1267
528	Periodic watchers are also timers of a kind, but they are very versatile	1268	Periodic watchers are also timers of a kind, but they are very versatile
529	(and unfortunately a bit complex).	1269	(and unfortunately a bit complex).
530		1270
531	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1271	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
532	but on wallclock time (absolute time). You can tell a periodic watcher	1272	but on wallclock time (absolute time). You can tell a periodic watcher
533	to trigger "at" some specific point in time. For example, if you tell a	1273	to trigger "at" some specific point in time. For example, if you tell a
534	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1274	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
535	+ 10.>) and then reset your system clock to the last year, then it will	1275	+ 10.>) and then reset your system clock to the last year, then it will
536	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1276	take a year to trigger the event (unlike an C<ev_timer>, which would trigger
537	roughly 10 seconds later and of course not if you reset your system time	1277	roughly 10 seconds later).
538	again).
539		1278
540	They can also be used to implement vastly more complex timers, such as	1279	They can also be used to implement vastly more complex timers, such as
541	triggering an event on eahc midnight, local time.	1280	triggering an event on each midnight, local time or other, complicated,
		1281	rules.
		1282
		1283	As with timers, the callback is guarenteed to be invoked only when the
		1284	time (C<at>) has been passed, but if multiple periodic timers become ready
		1285	during the same loop iteration then order of execution is undefined.
		1286
		1287	=head3 Watcher-Specific Functions and Data Members
542		1288
543	=over 4	1289	=over 4
544		1290
545	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1291	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
546		1292
547	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1293	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
548		1294
549	Lots of arguments, lets sort it out... There are basically three modes of	1295	Lots of arguments, lets sort it out... There are basically three modes of
550	operation, and we will explain them from simplest to complex:	1296	operation, and we will explain them from simplest to complex:
551		1297
552
553	=over 4	1298	=over 4
554		1299
555	=item * absolute timer (interval = reschedule_cb = 0)	1300	=item * absolute timer (at = time, interval = reschedule_cb = 0)
556		1301
557	In this configuration the watcher triggers an event at the wallclock time	1302	In this configuration the watcher triggers an event at the wallclock time
558	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1303	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
559	that is, if it is to be run at January 1st 2011 then it will run when the	1304	that is, if it is to be run at January 1st 2011 then it will run when the
560	system time reaches or surpasses this time.	1305	system time reaches or surpasses this time.
561		1306
562	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1307	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
563		1308
564	In this mode the watcher will always be scheduled to time out at the next	1309	In this mode the watcher will always be scheduled to time out at the next
565	C<at + N * interval> time (for some integer N) and then repeat, regardless	1310	C<at + N * interval> time (for some integer N, which can also be negative)
566	of any time jumps.	1311	and then repeat, regardless of any time jumps.
567		1312
568	This can be used to create timers that do not drift with respect to system	1313	This can be used to create timers that do not drift with respect to system
569	time:	1314	time:
570		1315
571	ev_periodic_set (&periodic, 0., 3600., 0);	1316	ev_periodic_set (&periodic, 0., 3600., 0);
…		…
577		1322
578	Another way to think about it (for the mathematically inclined) is that	1323	Another way to think about it (for the mathematically inclined) is that
579	C<ev_periodic> will try to run the callback in this mode at the next possible	1324	C<ev_periodic> will try to run the callback in this mode at the next possible
580	time where C<time = at (mod interval)>, regardless of any time jumps.	1325	time where C<time = at (mod interval)>, regardless of any time jumps.
581		1326
		1327	For numerical stability it is preferable that the C<at> value is near
		1328	C<ev_now ()> (the current time), but there is no range requirement for
		1329	this value.
		1330
582	=item * manual reschedule mode (reschedule_cb = callback)	1331	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
583		1332
584	In this mode the values for C<interval> and C<at> are both being	1333	In this mode the values for C<interval> and C<at> are both being
585	ignored. Instead, each time the periodic watcher gets scheduled, the	1334	ignored. Instead, each time the periodic watcher gets scheduled, the
586	reschedule callback will be called with the watcher as first, and the	1335	reschedule callback will be called with the watcher as first, and the
587	current time as second argument.	1336	current time as second argument.
588		1337
589	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1338	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
590	ever, or make any event loop modifications>. If you need to stop it,	1339	ever, or make any event loop modifications>. If you need to stop it,
591	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1340	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
592	starting a prepare watcher).	1341	starting an C<ev_prepare> watcher, which is legal).
593		1342
594	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1343	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
595	ev_tstamp now)>, e.g.:	1344	ev_tstamp now)>, e.g.:
596		1345
597	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1346	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
…		…
620	Simply stops and restarts the periodic watcher again. This is only useful	1369	Simply stops and restarts the periodic watcher again. This is only useful
621	when you changed some parameters or the reschedule callback would return	1370	when you changed some parameters or the reschedule callback would return
622	a different time than the last time it was called (e.g. in a crond like	1371	a different time than the last time it was called (e.g. in a crond like
623	program when the crontabs have changed).	1372	program when the crontabs have changed).
624		1373
		1374	=item ev_tstamp offset [read-write]
		1375
		1376	When repeating, this contains the offset value, otherwise this is the
		1377	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1378
		1379	Can be modified any time, but changes only take effect when the periodic
		1380	timer fires or C<ev_periodic_again> is being called.
		1381
		1382	=item ev_tstamp interval [read-write]
		1383
		1384	The current interval value. Can be modified any time, but changes only
		1385	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1386	called.
		1387
		1388	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1389
		1390	The current reschedule callback, or C<0>, if this functionality is
		1391	switched off. Can be changed any time, but changes only take effect when
		1392	the periodic timer fires or C<ev_periodic_again> is being called.
		1393
		1394	=item ev_tstamp at [read-only]
		1395
		1396	When active, contains the absolute time that the watcher is supposed to
		1397	trigger next.
		1398
625	=back	1399	=back
626		1400
		1401	=head3 Examples
		1402
		1403	Example: Call a callback every hour, or, more precisely, whenever the
		1404	system clock is divisible by 3600. The callback invocation times have
		1405	potentially a lot of jittering, but good long-term stability.
		1406
		1407	static void
		1408	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1409	{
		1410	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1411	}
		1412
		1413	struct ev_periodic hourly_tick;
		1414	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1415	ev_periodic_start (loop, &hourly_tick);
		1416
		1417	Example: The same as above, but use a reschedule callback to do it:
		1418
		1419	#include <math.h>
		1420
		1421	static ev_tstamp
		1422	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1423	{
		1424	return fmod (now, 3600.) + 3600.;
		1425	}
		1426
		1427	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1428
		1429	Example: Call a callback every hour, starting now:
		1430
		1431	struct ev_periodic hourly_tick;
		1432	ev_periodic_init (&hourly_tick, clock_cb,
		1433	fmod (ev_now (loop), 3600.), 3600., 0);
		1434	ev_periodic_start (loop, &hourly_tick);
		1435
		1436
627	=head2 C<ev_signal> - signal me when a signal gets signalled	1437	=head2 C<ev_signal> - signal me when a signal gets signalled!
628		1438
629	Signal watchers will trigger an event when the process receives a specific	1439	Signal watchers will trigger an event when the process receives a specific
630	signal one or more times. Even though signals are very asynchronous, libev	1440	signal one or more times. Even though signals are very asynchronous, libev
631	will try it's best to deliver signals synchronously, i.e. as part of the	1441	will try it's best to deliver signals synchronously, i.e. as part of the
632	normal event processing, like any other event.	1442	normal event processing, like any other event.
…		…
636	with the kernel (thus it coexists with your own signal handlers as long	1446	with the kernel (thus it coexists with your own signal handlers as long
637	as you don't register any with libev). Similarly, when the last signal	1447	as you don't register any with libev). Similarly, when the last signal
638	watcher for a signal is stopped libev will reset the signal handler to	1448	watcher for a signal is stopped libev will reset the signal handler to
639	SIG_DFL (regardless of what it was set to before).	1449	SIG_DFL (regardless of what it was set to before).
640		1450
		1451	If possible and supported, libev will install its handlers with
		1452	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
		1453	interrupted. If you have a problem with syscalls getting interrupted by
		1454	signals you can block all signals in an C<ev_check> watcher and unblock
		1455	them in an C<ev_prepare> watcher.
		1456
		1457	=head3 Watcher-Specific Functions and Data Members
		1458
641	=over 4	1459	=over 4
642		1460
643	=item ev_signal_init (ev_signal *, callback, int signum)	1461	=item ev_signal_init (ev_signal *, callback, int signum)
644		1462
645	=item ev_signal_set (ev_signal *, int signum)	1463	=item ev_signal_set (ev_signal *, int signum)
646		1464
647	Configures the watcher to trigger on the given signal number (usually one	1465	Configures the watcher to trigger on the given signal number (usually one
648	of the C<SIGxxx> constants).	1466	of the C<SIGxxx> constants).
649		1467
		1468	=item int signum [read-only]
		1469
		1470	The signal the watcher watches out for.
		1471
650	=back	1472	=back
651		1473
		1474	=head3 Examples
		1475
		1476	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1477
		1478	static void
		1479	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1480	{
		1481	ev_unloop (loop, EVUNLOOP_ALL);
		1482	}
		1483
		1484	struct ev_signal signal_watcher;
		1485	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1486	ev_signal_start (loop, &sigint_cb);
		1487
		1488
652	=head2 C<ev_child> - wait for pid status changes	1489	=head2 C<ev_child> - watch out for process status changes
653		1490
654	Child watchers trigger when your process receives a SIGCHLD in response to	1491	Child watchers trigger when your process receives a SIGCHLD in response to
655	some child status changes (most typically when a child of yours dies).	1492	some child status changes (most typically when a child of yours dies). It
		1493	is permissible to install a child watcher I<after> the child has been
		1494	forked (which implies it might have already exited), as long as the event
		1495	loop isn't entered (or is continued from a watcher).
		1496
		1497	Only the default event loop is capable of handling signals, and therefore
		1498	you can only rgeister child watchers in the default event loop.
		1499
		1500	=head3 Process Interaction
		1501
		1502	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1503	initialised. This is necessary to guarantee proper behaviour even if
		1504	the first child watcher is started after the child exits. The occurance
		1505	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1506	synchronously as part of the event loop processing. Libev always reaps all
		1507	children, even ones not watched.
		1508
		1509	=head3 Overriding the Built-In Processing
		1510
		1511	Libev offers no special support for overriding the built-in child
		1512	processing, but if your application collides with libev's default child
		1513	handler, you can override it easily by installing your own handler for
		1514	C<SIGCHLD> after initialising the default loop, and making sure the
		1515	default loop never gets destroyed. You are encouraged, however, to use an
		1516	event-based approach to child reaping and thus use libev's support for
		1517	that, so other libev users can use C<ev_child> watchers freely.
		1518
		1519	=head3 Watcher-Specific Functions and Data Members
656		1520
657	=over 4	1521	=over 4
658		1522
659	=item ev_child_init (ev_child *, callback, int pid)	1523	=item ev_child_init (ev_child *, callback, int pid, int trace)
660		1524
661	=item ev_child_set (ev_child *, int pid)	1525	=item ev_child_set (ev_child *, int pid, int trace)
662		1526
663	Configures the watcher to wait for status changes of process C<pid> (or	1527	Configures the watcher to wait for status changes of process C<pid> (or
664	I<any> process if C<pid> is specified as C<0>). The callback can look	1528	I<any> process if C<pid> is specified as C<0>). The callback can look
665	at the C<rstatus> member of the C<ev_child> watcher structure to see	1529	at the C<rstatus> member of the C<ev_child> watcher structure to see
666	the status word (use the macros from C<sys/wait.h> and see your systems	1530	the status word (use the macros from C<sys/wait.h> and see your systems
667	C<waitpid> documentation). The C<rpid> member contains the pid of the	1531	C<waitpid> documentation). The C<rpid> member contains the pid of the
668	process causing the status change.	1532	process causing the status change. C<trace> must be either C<0> (only
		1533	activate the watcher when the process terminates) or C<1> (additionally
		1534	activate the watcher when the process is stopped or continued).
		1535
		1536	=item int pid [read-only]
		1537
		1538	The process id this watcher watches out for, or C<0>, meaning any process id.
		1539
		1540	=item int rpid [read-write]
		1541
		1542	The process id that detected a status change.
		1543
		1544	=item int rstatus [read-write]
		1545
		1546	The process exit/trace status caused by C<rpid> (see your systems
		1547	C<waitpid> and C<sys/wait.h> documentation for details).
669		1548
670	=back	1549	=back
671		1550
		1551	=head3 Examples
		1552
		1553	Example: C<fork()> a new process and install a child handler to wait for
		1554	its completion.
		1555
		1556	ev_child cw;
		1557
		1558	static void
		1559	child_cb (EV_P_ struct ev_child *w, int revents)
		1560	{
		1561	ev_child_stop (EV_A_ w);
		1562	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1563	}
		1564
		1565	pid_t pid = fork ();
		1566
		1567	if (pid < 0)
		1568	// error
		1569	else if (pid == 0)
		1570	{
		1571	// the forked child executes here
		1572	exit (1);
		1573	}
		1574	else
		1575	{
		1576	ev_child_init (&cw, child_cb, pid, 0);
		1577	ev_child_start (EV_DEFAULT_ &cw);
		1578	}
		1579
		1580
		1581	=head2 C<ev_stat> - did the file attributes just change?
		1582
		1583	This watches a filesystem path for attribute changes. That is, it calls
		1584	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1585	compared to the last time, invoking the callback if it did.
		1586
		1587	The path does not need to exist: changing from "path exists" to "path does
		1588	not exist" is a status change like any other. The condition "path does
		1589	not exist" is signified by the C<st_nlink> field being zero (which is
		1590	otherwise always forced to be at least one) and all the other fields of
		1591	the stat buffer having unspecified contents.
		1592
		1593	The path I<should> be absolute and I<must not> end in a slash. If it is
		1594	relative and your working directory changes, the behaviour is undefined.
		1595
		1596	Since there is no standard to do this, the portable implementation simply
		1597	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1598	can specify a recommended polling interval for this case. If you specify
		1599	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1600	unspecified default> value will be used (which you can expect to be around
		1601	five seconds, although this might change dynamically). Libev will also
		1602	impose a minimum interval which is currently around C<0.1>, but thats
		1603	usually overkill.
		1604
		1605	This watcher type is not meant for massive numbers of stat watchers,
		1606	as even with OS-supported change notifications, this can be
		1607	resource-intensive.
		1608
		1609	At the time of this writing, only the Linux inotify interface is
		1610	implemented (implementing kqueue support is left as an exercise for the
		1611	reader). Inotify will be used to give hints only and should not change the
		1612	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1613	to fall back to regular polling again even with inotify, but changes are
		1614	usually detected immediately, and if the file exists there will be no
		1615	polling.
		1616
		1617	=head3 ABI Issues (Largefile Support)
		1618
		1619	Libev by default (unless the user overrides this) uses the default
		1620	compilation environment, which means that on systems with optionally
		1621	disabled large file support, you get the 32 bit version of the stat
		1622	structure. When using the library from programs that change the ABI to
		1623	use 64 bit file offsets the programs will fail. In that case you have to
		1624	compile libev with the same flags to get binary compatibility. This is
		1625	obviously the case with any flags that change the ABI, but the problem is
		1626	most noticably with ev_stat and largefile support.
		1627
		1628	=head3 Inotify
		1629
		1630	When C<inotify (7)> support has been compiled into libev (generally only
		1631	available on Linux) and present at runtime, it will be used to speed up
		1632	change detection where possible. The inotify descriptor will be created lazily
		1633	when the first C<ev_stat> watcher is being started.
		1634
		1635	Inotify presense does not change the semantics of C<ev_stat> watchers
		1636	except that changes might be detected earlier, and in some cases, to avoid
		1637	making regular C<stat> calls. Even in the presense of inotify support
		1638	there are many cases where libev has to resort to regular C<stat> polling.
		1639
		1640	(There is no support for kqueue, as apparently it cannot be used to
		1641	implement this functionality, due to the requirement of having a file
		1642	descriptor open on the object at all times).
		1643
		1644	=head3 The special problem of stat time resolution
		1645
		1646	The C<stat ()> syscall only supports full-second resolution portably, and
		1647	even on systems where the resolution is higher, many filesystems still
		1648	only support whole seconds.
		1649
		1650	That means that, if the time is the only thing that changes, you might
		1651	miss updates: on the first update, C<ev_stat> detects a change and calls
		1652	your callback, which does something. When there is another update within
		1653	the same second, C<ev_stat> will be unable to detect it.
		1654
		1655	The solution to this is to delay acting on a change for a second (or till
		1656	the next second boundary), using a roughly one-second delay C<ev_timer>
		1657	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1658	is added to work around small timing inconsistencies of some operating
		1659	systems.
		1660
		1661	=head3 Watcher-Specific Functions and Data Members
		1662
		1663	=over 4
		1664
		1665	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1666
		1667	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1668
		1669	Configures the watcher to wait for status changes of the given
		1670	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1671	be detected and should normally be specified as C<0> to let libev choose
		1672	a suitable value. The memory pointed to by C<path> must point to the same
		1673	path for as long as the watcher is active.
		1674
		1675	The callback will be receive C<EV_STAT> when a change was detected,
		1676	relative to the attributes at the time the watcher was started (or the
		1677	last change was detected).
		1678
		1679	=item ev_stat_stat (loop, ev_stat *)
		1680
		1681	Updates the stat buffer immediately with new values. If you change the
		1682	watched path in your callback, you could call this fucntion to avoid
		1683	detecting this change (while introducing a race condition). Can also be
		1684	useful simply to find out the new values.
		1685
		1686	=item ev_statdata attr [read-only]
		1687
		1688	The most-recently detected attributes of the file. Although the type is of
		1689	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1690	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1691	was some error while C<stat>ing the file.
		1692
		1693	=item ev_statdata prev [read-only]
		1694
		1695	The previous attributes of the file. The callback gets invoked whenever
		1696	C<prev> != C<attr>.
		1697
		1698	=item ev_tstamp interval [read-only]
		1699
		1700	The specified interval.
		1701
		1702	=item const char *path [read-only]
		1703
		1704	The filesystem path that is being watched.
		1705
		1706	=back
		1707
		1708	=head3 Examples
		1709
		1710	Example: Watch C</etc/passwd> for attribute changes.
		1711
		1712	static void
		1713	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1714	{
		1715	/* /etc/passwd changed in some way */
		1716	if (w->attr.st_nlink)
		1717	{
		1718	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1719	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1720	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1721	}
		1722	else
		1723	/* you shalt not abuse printf for puts */
		1724	puts ("wow, /etc/passwd is not there, expect problems. "
		1725	"if this is windows, they already arrived\n");
		1726	}
		1727
		1728	...
		1729	ev_stat passwd;
		1730
		1731	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1732	ev_stat_start (loop, &passwd);
		1733
		1734	Example: Like above, but additionally use a one-second delay so we do not
		1735	miss updates (however, frequent updates will delay processing, too, so
		1736	one might do the work both on C<ev_stat> callback invocation I<and> on
		1737	C<ev_timer> callback invocation).
		1738
		1739	static ev_stat passwd;
		1740	static ev_timer timer;
		1741
		1742	static void
		1743	timer_cb (EV_P_ ev_timer *w, int revents)
		1744	{
		1745	ev_timer_stop (EV_A_ w);
		1746
		1747	/* now it's one second after the most recent passwd change */
		1748	}
		1749
		1750	static void
		1751	stat_cb (EV_P_ ev_stat *w, int revents)
		1752	{
		1753	/* reset the one-second timer */
		1754	ev_timer_again (EV_A_ &timer);
		1755	}
		1756
		1757	...
		1758	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1759	ev_stat_start (loop, &passwd);
		1760	ev_timer_init (&timer, timer_cb, 0., 1.01);
		1761
		1762
672	=head2 C<ev_idle> - when you've got nothing better to do	1763	=head2 C<ev_idle> - when you've got nothing better to do...
673		1764
674	Idle watchers trigger events when there are no other events are pending	1765	Idle watchers trigger events when no other events of the same or higher
675	(prepare, check and other idle watchers do not count). That is, as long	1766	priority are pending (prepare, check and other idle watchers do not
676	as your process is busy handling sockets or timeouts (or even signals,	1767	count).
677	imagine) it will not be triggered. But when your process is idle all idle	1768
678	watchers are being called again and again, once per event loop iteration -	1769	That is, as long as your process is busy handling sockets or timeouts
		1770	(or even signals, imagine) of the same or higher priority it will not be
		1771	triggered. But when your process is idle (or only lower-priority watchers
		1772	are pending), the idle watchers are being called once per event loop
679	until stopped, that is, or your process receives more events and becomes	1773	iteration - until stopped, that is, or your process receives more events
680	busy.	1774	and becomes busy again with higher priority stuff.
681		1775
682	The most noteworthy effect is that as long as any idle watchers are	1776	The most noteworthy effect is that as long as any idle watchers are
683	active, the process will not block when waiting for new events.	1777	active, the process will not block when waiting for new events.
684		1778
685	Apart from keeping your process non-blocking (which is a useful	1779	Apart from keeping your process non-blocking (which is a useful
686	effect on its own sometimes), idle watchers are a good place to do	1780	effect on its own sometimes), idle watchers are a good place to do
687	"pseudo-background processing", or delay processing stuff to after the	1781	"pseudo-background processing", or delay processing stuff to after the
688	event loop has handled all outstanding events.	1782	event loop has handled all outstanding events.
689		1783
		1784	=head3 Watcher-Specific Functions and Data Members
		1785
690	=over 4	1786	=over 4
691		1787
692	=item ev_idle_init (ev_signal *, callback)	1788	=item ev_idle_init (ev_signal *, callback)
693		1789
694	Initialises and configures the idle watcher - it has no parameters of any	1790	Initialises and configures the idle watcher - it has no parameters of any
695	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1791	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
696	believe me.	1792	believe me.
697		1793
698	=back	1794	=back
699		1795
		1796	=head3 Examples
		1797
		1798	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1799	callback, free it. Also, use no error checking, as usual.
		1800
		1801	static void
		1802	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1803	{
		1804	free (w);
		1805	// now do something you wanted to do when the program has
		1806	// no longer anything immediate to do.
		1807	}
		1808
		1809	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1810	ev_idle_init (idle_watcher, idle_cb);
		1811	ev_idle_start (loop, idle_cb);
		1812
		1813
700	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1814	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
701		1815
702	Prepare and check watchers are usually (but not always) used in tandem:	1816	Prepare and check watchers are usually (but not always) used in tandem:
703	prepare watchers get invoked before the process blocks and check watchers	1817	prepare watchers get invoked before the process blocks and check watchers
704	afterwards.	1818	afterwards.
705		1819
		1820	You I<must not> call C<ev_loop> or similar functions that enter
		1821	the current event loop from either C<ev_prepare> or C<ev_check>
		1822	watchers. Other loops than the current one are fine, however. The
		1823	rationale behind this is that you do not need to check for recursion in
		1824	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1825	C<ev_check> so if you have one watcher of each kind they will always be
		1826	called in pairs bracketing the blocking call.
		1827
706	Their main purpose is to integrate other event mechanisms into libev. This	1828	Their main purpose is to integrate other event mechanisms into libev and
707	could be used, for example, to track variable changes, implement your own	1829	their use is somewhat advanced. This could be used, for example, to track
708	watchers, integrate net-snmp or a coroutine library and lots more.	1830	variable changes, implement your own watchers, integrate net-snmp or a
		1831	coroutine library and lots more. They are also occasionally useful if
		1832	you cache some data and want to flush it before blocking (for example,
		1833	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1834	watcher).
709		1835
710	This is done by examining in each prepare call which file descriptors need	1836	This is done by examining in each prepare call which file descriptors need
711	to be watched by the other library, registering C<ev_io> watchers for	1837	to be watched by the other library, registering C<ev_io> watchers for
712	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1838	them and starting an C<ev_timer> watcher for any timeouts (many libraries
713	provide just this functionality). Then, in the check watcher you check for	1839	provide just this functionality). Then, in the check watcher you check for
…		…
723	with priority higher than or equal to the event loop and one coroutine	1849	with priority higher than or equal to the event loop and one coroutine
724	of lower priority, but only once, using idle watchers to keep the event	1850	of lower priority, but only once, using idle watchers to keep the event
725	loop from blocking if lower-priority coroutines are active, thus mapping	1851	loop from blocking if lower-priority coroutines are active, thus mapping
726	low-priority coroutines to idle/background tasks).	1852	low-priority coroutines to idle/background tasks).
727		1853
		1854	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1855	priority, to ensure that they are being run before any other watchers
		1856	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1857	too) should not activate ("feed") events into libev. While libev fully
		1858	supports this, they will be called before other C<ev_check> watchers
		1859	did their job. As C<ev_check> watchers are often used to embed other
		1860	(non-libev) event loops those other event loops might be in an unusable
		1861	state until their C<ev_check> watcher ran (always remind yourself to
		1862	coexist peacefully with others).
		1863
		1864	=head3 Watcher-Specific Functions and Data Members
		1865
728	=over 4	1866	=over 4
729		1867
730	=item ev_prepare_init (ev_prepare *, callback)	1868	=item ev_prepare_init (ev_prepare *, callback)
731		1869
732	=item ev_check_init (ev_check *, callback)	1870	=item ev_check_init (ev_check *, callback)
…		…
734	Initialises and configures the prepare or check watcher - they have no	1872	Initialises and configures the prepare or check watcher - they have no
735	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1873	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
736	macros, but using them is utterly, utterly and completely pointless.	1874	macros, but using them is utterly, utterly and completely pointless.
737		1875
738	=back	1876	=back
		1877
		1878	=head3 Examples
		1879
		1880	There are a number of principal ways to embed other event loops or modules
		1881	into libev. Here are some ideas on how to include libadns into libev
		1882	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1883	use for an actually working example. Another Perl module named C<EV::Glib>
		1884	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
		1885	into the Glib event loop).
		1886
		1887	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1888	and in a check watcher, destroy them and call into libadns. What follows
		1889	is pseudo-code only of course. This requires you to either use a low
		1890	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1891	the callbacks for the IO/timeout watchers might not have been called yet.
		1892
		1893	static ev_io iow [nfd];
		1894	static ev_timer tw;
		1895
		1896	static void
		1897	io_cb (ev_loop *loop, ev_io *w, int revents)
		1898	{
		1899	}
		1900
		1901	// create io watchers for each fd and a timer before blocking
		1902	static void
		1903	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1904	{
		1905	int timeout = 3600000;
		1906	struct pollfd fds [nfd];
		1907	// actual code will need to loop here and realloc etc.
		1908	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1909
		1910	/* the callback is illegal, but won't be called as we stop during check */
		1911	ev_timer_init (&tw, 0, timeout * 1e-3);
		1912	ev_timer_start (loop, &tw);
		1913
		1914	// create one ev_io per pollfd
		1915	for (int i = 0; i < nfd; ++i)
		1916	{
		1917	ev_io_init (iow + i, io_cb, fds [i].fd,
		1918	((fds [i].events & POLLIN ? EV_READ : 0)
		1919	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1920
		1921	fds [i].revents = 0;
		1922	ev_io_start (loop, iow + i);
		1923	}
		1924	}
		1925
		1926	// stop all watchers after blocking
		1927	static void
		1928	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1929	{
		1930	ev_timer_stop (loop, &tw);
		1931
		1932	for (int i = 0; i < nfd; ++i)
		1933	{
		1934	// set the relevant poll flags
		1935	// could also call adns_processreadable etc. here
		1936	struct pollfd *fd = fds + i;
		1937	int revents = ev_clear_pending (iow + i);
		1938	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1939	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1940
		1941	// now stop the watcher
		1942	ev_io_stop (loop, iow + i);
		1943	}
		1944
		1945	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1946	}
		1947
		1948	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1949	in the prepare watcher and would dispose of the check watcher.
		1950
		1951	Method 3: If the module to be embedded supports explicit event
		1952	notification (adns does), you can also make use of the actual watcher
		1953	callbacks, and only destroy/create the watchers in the prepare watcher.
		1954
		1955	static void
		1956	timer_cb (EV_P_ ev_timer *w, int revents)
		1957	{
		1958	adns_state ads = (adns_state)w->data;
		1959	update_now (EV_A);
		1960
		1961	adns_processtimeouts (ads, &tv_now);
		1962	}
		1963
		1964	static void
		1965	io_cb (EV_P_ ev_io *w, int revents)
		1966	{
		1967	adns_state ads = (adns_state)w->data;
		1968	update_now (EV_A);
		1969
		1970	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1971	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1972	}
		1973
		1974	// do not ever call adns_afterpoll
		1975
		1976	Method 4: Do not use a prepare or check watcher because the module you
		1977	want to embed is too inflexible to support it. Instead, youc na override
		1978	their poll function. The drawback with this solution is that the main
		1979	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1980	this.
		1981
		1982	static gint
		1983	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		1984	{
		1985	int got_events = 0;
		1986
		1987	for (n = 0; n < nfds; ++n)
		1988	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		1989
		1990	if (timeout >= 0)
		1991	// create/start timer
		1992
		1993	// poll
		1994	ev_loop (EV_A_ 0);
		1995
		1996	// stop timer again
		1997	if (timeout >= 0)
		1998	ev_timer_stop (EV_A_ &to);
		1999
		2000	// stop io watchers again - their callbacks should have set
		2001	for (n = 0; n < nfds; ++n)
		2002	ev_io_stop (EV_A_ iow [n]);
		2003
		2004	return got_events;
		2005	}
		2006
		2007
		2008	=head2 C<ev_embed> - when one backend isn't enough...
		2009
		2010	This is a rather advanced watcher type that lets you embed one event loop
		2011	into another (currently only C<ev_io> events are supported in the embedded
		2012	loop, other types of watchers might be handled in a delayed or incorrect
		2013	fashion and must not be used).
		2014
		2015	There are primarily two reasons you would want that: work around bugs and
		2016	prioritise I/O.
		2017
		2018	As an example for a bug workaround, the kqueue backend might only support
		2019	sockets on some platform, so it is unusable as generic backend, but you
		2020	still want to make use of it because you have many sockets and it scales
		2021	so nicely. In this case, you would create a kqueue-based loop and embed it
		2022	into your default loop (which might use e.g. poll). Overall operation will
		2023	be a bit slower because first libev has to poll and then call kevent, but
		2024	at least you can use both at what they are best.
		2025
		2026	As for prioritising I/O: rarely you have the case where some fds have
		2027	to be watched and handled very quickly (with low latency), and even
		2028	priorities and idle watchers might have too much overhead. In this case
		2029	you would put all the high priority stuff in one loop and all the rest in
		2030	a second one, and embed the second one in the first.
		2031
		2032	As long as the watcher is active, the callback will be invoked every time
		2033	there might be events pending in the embedded loop. The callback must then
		2034	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2035	their callbacks (you could also start an idle watcher to give the embedded
		2036	loop strictly lower priority for example). You can also set the callback
		2037	to C<0>, in which case the embed watcher will automatically execute the
		2038	embedded loop sweep.
		2039
		2040	As long as the watcher is started it will automatically handle events. The
		2041	callback will be invoked whenever some events have been handled. You can
		2042	set the callback to C<0> to avoid having to specify one if you are not
		2043	interested in that.
		2044
		2045	Also, there have not currently been made special provisions for forking:
		2046	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2047	but you will also have to stop and restart any C<ev_embed> watchers
		2048	yourself.
		2049
		2050	Unfortunately, not all backends are embeddable, only the ones returned by
		2051	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2052	portable one.
		2053
		2054	So when you want to use this feature you will always have to be prepared
		2055	that you cannot get an embeddable loop. The recommended way to get around
		2056	this is to have a separate variables for your embeddable loop, try to
		2057	create it, and if that fails, use the normal loop for everything.
		2058
		2059	=head3 Watcher-Specific Functions and Data Members
		2060
		2061	=over 4
		2062
		2063	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2064
		2065	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2066
		2067	Configures the watcher to embed the given loop, which must be
		2068	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2069	invoked automatically, otherwise it is the responsibility of the callback
		2070	to invoke it (it will continue to be called until the sweep has been done,
		2071	if you do not want thta, you need to temporarily stop the embed watcher).
		2072
		2073	=item ev_embed_sweep (loop, ev_embed *)
		2074
		2075	Make a single, non-blocking sweep over the embedded loop. This works
		2076	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2077	apropriate way for embedded loops.
		2078
		2079	=item struct ev_loop *other [read-only]
		2080
		2081	The embedded event loop.
		2082
		2083	=back
		2084
		2085	=head3 Examples
		2086
		2087	Example: Try to get an embeddable event loop and embed it into the default
		2088	event loop. If that is not possible, use the default loop. The default
		2089	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		2090	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		2091	used).
		2092
		2093	struct ev_loop *loop_hi = ev_default_init (0);
		2094	struct ev_loop *loop_lo = 0;
		2095	struct ev_embed embed;
		2096
		2097	// see if there is a chance of getting one that works
		2098	// (remember that a flags value of 0 means autodetection)
		2099	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2100	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2101	: 0;
		2102
		2103	// if we got one, then embed it, otherwise default to loop_hi
		2104	if (loop_lo)
		2105	{
		2106	ev_embed_init (&embed, 0, loop_lo);
		2107	ev_embed_start (loop_hi, &embed);
		2108	}
		2109	else
		2110	loop_lo = loop_hi;
		2111
		2112	Example: Check if kqueue is available but not recommended and create
		2113	a kqueue backend for use with sockets (which usually work with any
		2114	kqueue implementation). Store the kqueue/socket-only event loop in
		2115	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2116
		2117	struct ev_loop *loop = ev_default_init (0);
		2118	struct ev_loop *loop_socket = 0;
		2119	struct ev_embed embed;
		2120
		2121	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2122	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2123	{
		2124	ev_embed_init (&embed, 0, loop_socket);
		2125	ev_embed_start (loop, &embed);
		2126	}
		2127
		2128	if (!loop_socket)
		2129	loop_socket = loop;
		2130
		2131	// now use loop_socket for all sockets, and loop for everything else
		2132
		2133
		2134	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2135
		2136	Fork watchers are called when a C<fork ()> was detected (usually because
		2137	whoever is a good citizen cared to tell libev about it by calling
		2138	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2139	event loop blocks next and before C<ev_check> watchers are being called,
		2140	and only in the child after the fork. If whoever good citizen calling
		2141	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2142	handlers will be invoked, too, of course.
		2143
		2144	=head3 Watcher-Specific Functions and Data Members
		2145
		2146	=over 4
		2147
		2148	=item ev_fork_init (ev_signal *, callback)
		2149
		2150	Initialises and configures the fork watcher - it has no parameters of any
		2151	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2152	believe me.
		2153
		2154	=back
		2155
		2156
		2157	=head2 C<ev_async> - how to wake up another event loop
		2158
		2159	In general, you cannot use an C<ev_loop> from multiple threads or other
		2160	asynchronous sources such as signal handlers (as opposed to multiple event
		2161	loops - those are of course safe to use in different threads).
		2162
		2163	Sometimes, however, you need to wake up another event loop you do not
		2164	control, for example because it belongs to another thread. This is what
		2165	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2166	can signal it by calling C<ev_async_send>, which is thread- and signal
		2167	safe.
		2168
		2169	This functionality is very similar to C<ev_signal> watchers, as signals,
		2170	too, are asynchronous in nature, and signals, too, will be compressed
		2171	(i.e. the number of callback invocations may be less than the number of
		2172	C<ev_async_sent> calls).
		2173
		2174	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2175	just the default loop.
		2176
		2177	=head3 Queueing
		2178
		2179	C<ev_async> does not support queueing of data in any way. The reason
		2180	is that the author does not know of a simple (or any) algorithm for a
		2181	multiple-writer-single-reader queue that works in all cases and doesn't
		2182	need elaborate support such as pthreads.
		2183
		2184	That means that if you want to queue data, you have to provide your own
		2185	queue. But at least I can tell you would implement locking around your
		2186	queue:
		2187
		2188	=over 4
		2189
		2190	=item queueing from a signal handler context
		2191
		2192	To implement race-free queueing, you simply add to the queue in the signal
		2193	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2194	some fictitiuous SIGUSR1 handler:
		2195
		2196	static ev_async mysig;
		2197
		2198	static void
		2199	sigusr1_handler (void)
		2200	{
		2201	sometype data;
		2202
		2203	// no locking etc.
		2204	queue_put (data);
		2205	ev_async_send (EV_DEFAULT_ &mysig);
		2206	}
		2207
		2208	static void
		2209	mysig_cb (EV_P_ ev_async *w, int revents)
		2210	{
		2211	sometype data;
		2212	sigset_t block, prev;
		2213
		2214	sigemptyset (&block);
		2215	sigaddset (&block, SIGUSR1);
		2216	sigprocmask (SIG_BLOCK, &block, &prev);
		2217
		2218	while (queue_get (&data))
		2219	process (data);
		2220
		2221	if (sigismember (&prev, SIGUSR1)
		2222	sigprocmask (SIG_UNBLOCK, &block, 0);
		2223	}
		2224
		2225	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2226	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2227	either...).
		2228
		2229	=item queueing from a thread context
		2230
		2231	The strategy for threads is different, as you cannot (easily) block
		2232	threads but you can easily preempt them, so to queue safely you need to
		2233	employ a traditional mutex lock, such as in this pthread example:
		2234
		2235	static ev_async mysig;
		2236	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2237
		2238	static void
		2239	otherthread (void)
		2240	{
		2241	// only need to lock the actual queueing operation
		2242	pthread_mutex_lock (&mymutex);
		2243	queue_put (data);
		2244	pthread_mutex_unlock (&mymutex);
		2245
		2246	ev_async_send (EV_DEFAULT_ &mysig);
		2247	}
		2248
		2249	static void
		2250	mysig_cb (EV_P_ ev_async *w, int revents)
		2251	{
		2252	pthread_mutex_lock (&mymutex);
		2253
		2254	while (queue_get (&data))
		2255	process (data);
		2256
		2257	pthread_mutex_unlock (&mymutex);
		2258	}
		2259
		2260	=back
		2261
		2262
		2263	=head3 Watcher-Specific Functions and Data Members
		2264
		2265	=over 4
		2266
		2267	=item ev_async_init (ev_async *, callback)
		2268
		2269	Initialises and configures the async watcher - it has no parameters of any
		2270	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2271	believe me.
		2272
		2273	=item ev_async_send (loop, ev_async *)
		2274
		2275	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2276	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2277	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2278	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2279	section below on what exactly this means).
		2280
		2281	This call incurs the overhead of a syscall only once per loop iteration,
		2282	so while the overhead might be noticable, it doesn't apply to repeated
		2283	calls to C<ev_async_send>.
		2284
		2285	=back
		2286
739		2287
740	=head1 OTHER FUNCTIONS	2288	=head1 OTHER FUNCTIONS
741		2289
742	There are some other functions of possible interest. Described. Here. Now.	2290	There are some other functions of possible interest. Described. Here. Now.
743		2291
…		…
773	/* stdin might have data for us, joy! */;	2321	/* stdin might have data for us, joy! */;
774	}	2322	}
775		2323
776	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2324	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
777		2325
778	=item ev_feed_event (loop, watcher, int events)	2326	=item ev_feed_event (ev_loop *, watcher *, int revents)
779		2327
780	Feeds the given event set into the event loop, as if the specified event	2328	Feeds the given event set into the event loop, as if the specified event
781	had happened for the specified watcher (which must be a pointer to an	2329	had happened for the specified watcher (which must be a pointer to an
782	initialised but not necessarily started event watcher).	2330	initialised but not necessarily started event watcher).
783		2331
784	=item ev_feed_fd_event (loop, int fd, int revents)	2332	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
785		2333
786	Feed an event on the given fd, as if a file descriptor backend detected	2334	Feed an event on the given fd, as if a file descriptor backend detected
787	the given events it.	2335	the given events it.
788		2336
789	=item ev_feed_signal_event (loop, int signum)	2337	=item ev_feed_signal_event (ev_loop *loop, int signum)
790		2338
791	Feed an event as if the given signal occured (loop must be the default loop!).	2339	Feed an event as if the given signal occured (C<loop> must be the default
		2340	loop!).
792		2341
793	=back	2342	=back
		2343
794		2344
795	=head1 LIBEVENT EMULATION	2345	=head1 LIBEVENT EMULATION
796		2346
797	Libev offers a compatibility emulation layer for libevent. It cannot	2347	Libev offers a compatibility emulation layer for libevent. It cannot
798	emulate the internals of libevent, so here are some usage hints:	2348	emulate the internals of libevent, so here are some usage hints:
…		…
819		2369
820	=back	2370	=back
821		2371
822	=head1 C++ SUPPORT	2372	=head1 C++ SUPPORT
823		2373
824	TBD.	2374	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2375	you to use some convinience methods to start/stop watchers and also change
		2376	the callback model to a model using method callbacks on objects.
		2377
		2378	To use it,
		2379
		2380	#include <ev++.h>
		2381
		2382	This automatically includes F<ev.h> and puts all of its definitions (many
		2383	of them macros) into the global namespace. All C++ specific things are
		2384	put into the C<ev> namespace. It should support all the same embedding
		2385	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2386
		2387	Care has been taken to keep the overhead low. The only data member the C++
		2388	classes add (compared to plain C-style watchers) is the event loop pointer
		2389	that the watcher is associated with (or no additional members at all if
		2390	you disable C<EV_MULTIPLICITY> when embedding libev).
		2391
		2392	Currently, functions, and static and non-static member functions can be
		2393	used as callbacks. Other types should be easy to add as long as they only
		2394	need one additional pointer for context. If you need support for other
		2395	types of functors please contact the author (preferably after implementing
		2396	it).
		2397
		2398	Here is a list of things available in the C<ev> namespace:
		2399
		2400	=over 4
		2401
		2402	=item C<ev::READ>, C<ev::WRITE> etc.
		2403
		2404	These are just enum values with the same values as the C<EV_READ> etc.
		2405	macros from F<ev.h>.
		2406
		2407	=item C<ev::tstamp>, C<ev::now>
		2408
		2409	Aliases to the same types/functions as with the C<ev_> prefix.
		2410
		2411	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2412
		2413	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2414	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2415	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2416	defines by many implementations.
		2417
		2418	All of those classes have these methods:
		2419
		2420	=over 4
		2421
		2422	=item ev::TYPE::TYPE ()
		2423
		2424	=item ev::TYPE::TYPE (struct ev_loop *)
		2425
		2426	=item ev::TYPE::~TYPE
		2427
		2428	The constructor (optionally) takes an event loop to associate the watcher
		2429	with. If it is omitted, it will use C<EV_DEFAULT>.
		2430
		2431	The constructor calls C<ev_init> for you, which means you have to call the
		2432	C<set> method before starting it.
		2433
		2434	It will not set a callback, however: You have to call the templated C<set>
		2435	method to set a callback before you can start the watcher.
		2436
		2437	(The reason why you have to use a method is a limitation in C++ which does
		2438	not allow explicit template arguments for constructors).
		2439
		2440	The destructor automatically stops the watcher if it is active.
		2441
		2442	=item w->set<class, &class::method> (object *)
		2443
		2444	This method sets the callback method to call. The method has to have a
		2445	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2446	first argument and the C<revents> as second. The object must be given as
		2447	parameter and is stored in the C<data> member of the watcher.
		2448
		2449	This method synthesizes efficient thunking code to call your method from
		2450	the C callback that libev requires. If your compiler can inline your
		2451	callback (i.e. it is visible to it at the place of the C<set> call and
		2452	your compiler is good :), then the method will be fully inlined into the
		2453	thunking function, making it as fast as a direct C callback.
		2454
		2455	Example: simple class declaration and watcher initialisation
		2456
		2457	struct myclass
		2458	{
		2459	void io_cb (ev::io &w, int revents) { }
		2460	}
		2461
		2462	myclass obj;
		2463	ev::io iow;
		2464	iow.set <myclass, &myclass::io_cb> (&obj);
		2465
		2466	=item w->set<function> (void *data = 0)
		2467
		2468	Also sets a callback, but uses a static method or plain function as
		2469	callback. The optional C<data> argument will be stored in the watcher's
		2470	C<data> member and is free for you to use.
		2471
		2472	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2473
		2474	See the method-C<set> above for more details.
		2475
		2476	Example:
		2477
		2478	static void io_cb (ev::io &w, int revents) { }
		2479	iow.set <io_cb> ();
		2480
		2481	=item w->set (struct ev_loop *)
		2482
		2483	Associates a different C<struct ev_loop> with this watcher. You can only
		2484	do this when the watcher is inactive (and not pending either).
		2485
		2486	=item w->set ([args])
		2487
		2488	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2489	called at least once. Unlike the C counterpart, an active watcher gets
		2490	automatically stopped and restarted when reconfiguring it with this
		2491	method.
		2492
		2493	=item w->start ()
		2494
		2495	Starts the watcher. Note that there is no C<loop> argument, as the
		2496	constructor already stores the event loop.
		2497
		2498	=item w->stop ()
		2499
		2500	Stops the watcher if it is active. Again, no C<loop> argument.
		2501
		2502	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2503
		2504	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2505	C<ev_TYPE_again> function.
		2506
		2507	=item w->sweep () (C<ev::embed> only)
		2508
		2509	Invokes C<ev_embed_sweep>.
		2510
		2511	=item w->update () (C<ev::stat> only)
		2512
		2513	Invokes C<ev_stat_stat>.
		2514
		2515	=back
		2516
		2517	=back
		2518
		2519	Example: Define a class with an IO and idle watcher, start one of them in
		2520	the constructor.
		2521
		2522	class myclass
		2523	{
		2524	ev::io io; void io_cb (ev::io &w, int revents);
		2525	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2526
		2527	myclass (int fd)
		2528	{
		2529	io .set <myclass, &myclass::io_cb > (this);
		2530	idle.set <myclass, &myclass::idle_cb> (this);
		2531
		2532	io.start (fd, ev::READ);
		2533	}
		2534	};
		2535
		2536
		2537	=head1 OTHER LANGUAGE BINDINGS
		2538
		2539	Libev does not offer other language bindings itself, but bindings for a
		2540	numbe rof languages exist in the form of third-party packages. If you know
		2541	any interesting language binding in addition to the ones listed here, drop
		2542	me a note.
		2543
		2544	=over 4
		2545
		2546	=item Perl
		2547
		2548	The EV module implements the full libev API and is actually used to test
		2549	libev. EV is developed together with libev. Apart from the EV core module,
		2550	there are additional modules that implement libev-compatible interfaces
		2551	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2552	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2553
		2554	It can be found and installed via CPAN, its homepage is found at
		2555	L<http://software.schmorp.de/pkg/EV>.
		2556
		2557	=item Ruby
		2558
		2559	Tony Arcieri has written a ruby extension that offers access to a subset
		2560	of the libev API and adds filehandle abstractions, asynchronous DNS and
		2561	more on top of it. It can be found via gem servers. Its homepage is at
		2562	L<http://rev.rubyforge.org/>.
		2563
		2564	=item D
		2565
		2566	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2567	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2568
		2569	=back
		2570
		2571
		2572	=head1 MACRO MAGIC
		2573
		2574	Libev can be compiled with a variety of options, the most fundamantal
		2575	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2576	functions and callbacks have an initial C<struct ev_loop *> argument.
		2577
		2578	To make it easier to write programs that cope with either variant, the
		2579	following macros are defined:
		2580
		2581	=over 4
		2582
		2583	=item C<EV_A>, C<EV_A_>
		2584
		2585	This provides the loop I<argument> for functions, if one is required ("ev
		2586	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2587	C<EV_A_> is used when other arguments are following. Example:
		2588
		2589	ev_unref (EV_A);
		2590	ev_timer_add (EV_A_ watcher);
		2591	ev_loop (EV_A_ 0);
		2592
		2593	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2594	which is often provided by the following macro.
		2595
		2596	=item C<EV_P>, C<EV_P_>
		2597
		2598	This provides the loop I<parameter> for functions, if one is required ("ev
		2599	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2600	C<EV_P_> is used when other parameters are following. Example:
		2601
		2602	// this is how ev_unref is being declared
		2603	static void ev_unref (EV_P);
		2604
		2605	// this is how you can declare your typical callback
		2606	static void cb (EV_P_ ev_timer *w, int revents)
		2607
		2608	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2609	suitable for use with C<EV_A>.
		2610
		2611	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2612
		2613	Similar to the other two macros, this gives you the value of the default
		2614	loop, if multiple loops are supported ("ev loop default").
		2615
		2616	=back
		2617
		2618	Example: Declare and initialise a check watcher, utilising the above
		2619	macros so it will work regardless of whether multiple loops are supported
		2620	or not.
		2621
		2622	static void
		2623	check_cb (EV_P_ ev_timer *w, int revents)
		2624	{
		2625	ev_check_stop (EV_A_ w);
		2626	}
		2627
		2628	ev_check check;
		2629	ev_check_init (&check, check_cb);
		2630	ev_check_start (EV_DEFAULT_ &check);
		2631	ev_loop (EV_DEFAULT_ 0);
		2632
		2633	=head1 EMBEDDING
		2634
		2635	Libev can (and often is) directly embedded into host
		2636	applications. Examples of applications that embed it include the Deliantra
		2637	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2638	and rxvt-unicode.
		2639
		2640	The goal is to enable you to just copy the necessary files into your
		2641	source directory without having to change even a single line in them, so
		2642	you can easily upgrade by simply copying (or having a checked-out copy of
		2643	libev somewhere in your source tree).
		2644
		2645	=head2 FILESETS
		2646
		2647	Depending on what features you need you need to include one or more sets of files
		2648	in your app.
		2649
		2650	=head3 CORE EVENT LOOP
		2651
		2652	To include only the libev core (all the C<ev_*> functions), with manual
		2653	configuration (no autoconf):
		2654
		2655	#define EV_STANDALONE 1
		2656	#include "ev.c"
		2657
		2658	This will automatically include F<ev.h>, too, and should be done in a
		2659	single C source file only to provide the function implementations. To use
		2660	it, do the same for F<ev.h> in all files wishing to use this API (best
		2661	done by writing a wrapper around F<ev.h> that you can include instead and
		2662	where you can put other configuration options):
		2663
		2664	#define EV_STANDALONE 1
		2665	#include "ev.h"
		2666
		2667	Both header files and implementation files can be compiled with a C++
		2668	compiler (at least, thats a stated goal, and breakage will be treated
		2669	as a bug).
		2670
		2671	You need the following files in your source tree, or in a directory
		2672	in your include path (e.g. in libev/ when using -Ilibev):
		2673
		2674	ev.h
		2675	ev.c
		2676	ev_vars.h
		2677	ev_wrap.h
		2678
		2679	ev_win32.c required on win32 platforms only
		2680
		2681	ev_select.c only when select backend is enabled (which is enabled by default)
		2682	ev_poll.c only when poll backend is enabled (disabled by default)
		2683	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2684	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2685	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2686
		2687	F<ev.c> includes the backend files directly when enabled, so you only need
		2688	to compile this single file.
		2689
		2690	=head3 LIBEVENT COMPATIBILITY API
		2691
		2692	To include the libevent compatibility API, also include:
		2693
		2694	#include "event.c"
		2695
		2696	in the file including F<ev.c>, and:
		2697
		2698	#include "event.h"
		2699
		2700	in the files that want to use the libevent API. This also includes F<ev.h>.
		2701
		2702	You need the following additional files for this:
		2703
		2704	event.h
		2705	event.c
		2706
		2707	=head3 AUTOCONF SUPPORT
		2708
		2709	Instead of using C<EV_STANDALONE=1> and providing your config in
		2710	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2711	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2712	include F<config.h> and configure itself accordingly.
		2713
		2714	For this of course you need the m4 file:
		2715
		2716	libev.m4
		2717
		2718	=head2 PREPROCESSOR SYMBOLS/MACROS
		2719
		2720	Libev can be configured via a variety of preprocessor symbols you have to define
		2721	before including any of its files. The default is not to build for multiplicity
		2722	and only include the select backend.
		2723
		2724	=over 4
		2725
		2726	=item EV_STANDALONE
		2727
		2728	Must always be C<1> if you do not use autoconf configuration, which
		2729	keeps libev from including F<config.h>, and it also defines dummy
		2730	implementations for some libevent functions (such as logging, which is not
		2731	supported). It will also not define any of the structs usually found in
		2732	F<event.h> that are not directly supported by the libev core alone.
		2733
		2734	=item EV_USE_MONOTONIC
		2735
		2736	If defined to be C<1>, libev will try to detect the availability of the
		2737	monotonic clock option at both compiletime and runtime. Otherwise no use
		2738	of the monotonic clock option will be attempted. If you enable this, you
		2739	usually have to link against librt or something similar. Enabling it when
		2740	the functionality isn't available is safe, though, although you have
		2741	to make sure you link against any libraries where the C<clock_gettime>
		2742	function is hiding in (often F<-lrt>).
		2743
		2744	=item EV_USE_REALTIME
		2745
		2746	If defined to be C<1>, libev will try to detect the availability of the
		2747	realtime clock option at compiletime (and assume its availability at
		2748	runtime if successful). Otherwise no use of the realtime clock option will
		2749	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2750	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2751	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2752
		2753	=item EV_USE_NANOSLEEP
		2754
		2755	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2756	and will use it for delays. Otherwise it will use C<select ()>.
		2757
		2758	=item EV_USE_SELECT
		2759
		2760	If undefined or defined to be C<1>, libev will compile in support for the
		2761	C<select>(2) backend. No attempt at autodetection will be done: if no
		2762	other method takes over, select will be it. Otherwise the select backend
		2763	will not be compiled in.
		2764
		2765	=item EV_SELECT_USE_FD_SET
		2766
		2767	If defined to C<1>, then the select backend will use the system C<fd_set>
		2768	structure. This is useful if libev doesn't compile due to a missing
		2769	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2770	exotic systems. This usually limits the range of file descriptors to some
		2771	low limit such as 1024 or might have other limitations (winsocket only
		2772	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2773	influence the size of the C<fd_set> used.
		2774
		2775	=item EV_SELECT_IS_WINSOCKET
		2776
		2777	When defined to C<1>, the select backend will assume that
		2778	select/socket/connect etc. don't understand file descriptors but
		2779	wants osf handles on win32 (this is the case when the select to
		2780	be used is the winsock select). This means that it will call
		2781	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2782	it is assumed that all these functions actually work on fds, even
		2783	on win32. Should not be defined on non-win32 platforms.
		2784
		2785	=item EV_FD_TO_WIN32_HANDLE
		2786
		2787	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2788	file descriptors to socket handles. When not defining this symbol (the
		2789	default), then libev will call C<_get_osfhandle>, which is usually
		2790	correct. In some cases, programs use their own file descriptor management,
		2791	in which case they can provide this function to map fds to socket handles.
		2792
		2793	=item EV_USE_POLL
		2794
		2795	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2796	backend. Otherwise it will be enabled on non-win32 platforms. It
		2797	takes precedence over select.
		2798
		2799	=item EV_USE_EPOLL
		2800
		2801	If defined to be C<1>, libev will compile in support for the Linux
		2802	C<epoll>(7) backend. Its availability will be detected at runtime,
		2803	otherwise another method will be used as fallback. This is the
		2804	preferred backend for GNU/Linux systems.
		2805
		2806	=item EV_USE_KQUEUE
		2807
		2808	If defined to be C<1>, libev will compile in support for the BSD style
		2809	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2810	otherwise another method will be used as fallback. This is the preferred
		2811	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2812	supports some types of fds correctly (the only platform we found that
		2813	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2814	not be used unless explicitly requested. The best way to use it is to find
		2815	out whether kqueue supports your type of fd properly and use an embedded
		2816	kqueue loop.
		2817
		2818	=item EV_USE_PORT
		2819
		2820	If defined to be C<1>, libev will compile in support for the Solaris
		2821	10 port style backend. Its availability will be detected at runtime,
		2822	otherwise another method will be used as fallback. This is the preferred
		2823	backend for Solaris 10 systems.
		2824
		2825	=item EV_USE_DEVPOLL
		2826
		2827	reserved for future expansion, works like the USE symbols above.
		2828
		2829	=item EV_USE_INOTIFY
		2830
		2831	If defined to be C<1>, libev will compile in support for the Linux inotify
		2832	interface to speed up C<ev_stat> watchers. Its actual availability will
		2833	be detected at runtime.
		2834
		2835	=item EV_ATOMIC_T
		2836
		2837	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2838	access is atomic with respect to other threads or signal contexts. No such
		2839	type is easily found in the C language, so you can provide your own type
		2840	that you know is safe for your purposes. It is used both for signal handler "locking"
		2841	as well as for signal and thread safety in C<ev_async> watchers.
		2842
		2843	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2844	(from F<signal.h>), which is usually good enough on most platforms.
		2845
		2846	=item EV_H
		2847
		2848	The name of the F<ev.h> header file used to include it. The default if
		2849	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2850	used to virtually rename the F<ev.h> header file in case of conflicts.
		2851
		2852	=item EV_CONFIG_H
		2853
		2854	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2855	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2856	C<EV_H>, above.
		2857
		2858	=item EV_EVENT_H
		2859
		2860	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2861	of how the F<event.h> header can be found, the default is C<"event.h">.
		2862
		2863	=item EV_PROTOTYPES
		2864
		2865	If defined to be C<0>, then F<ev.h> will not define any function
		2866	prototypes, but still define all the structs and other symbols. This is
		2867	occasionally useful if you want to provide your own wrapper functions
		2868	around libev functions.
		2869
		2870	=item EV_MULTIPLICITY
		2871
		2872	If undefined or defined to C<1>, then all event-loop-specific functions
		2873	will have the C<struct ev_loop *> as first argument, and you can create
		2874	additional independent event loops. Otherwise there will be no support
		2875	for multiple event loops and there is no first event loop pointer
		2876	argument. Instead, all functions act on the single default loop.
		2877
		2878	=item EV_MINPRI
		2879
		2880	=item EV_MAXPRI
		2881
		2882	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2883	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2884	provide for more priorities by overriding those symbols (usually defined
		2885	to be C<-2> and C<2>, respectively).
		2886
		2887	When doing priority-based operations, libev usually has to linearly search
		2888	all the priorities, so having many of them (hundreds) uses a lot of space
		2889	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2890	fine.
		2891
		2892	If your embedding app does not need any priorities, defining these both to
		2893	C<0> will save some memory and cpu.
		2894
		2895	=item EV_PERIODIC_ENABLE
		2896
		2897	If undefined or defined to be C<1>, then periodic timers are supported. If
		2898	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2899	code.
		2900
		2901	=item EV_IDLE_ENABLE
		2902
		2903	If undefined or defined to be C<1>, then idle watchers are supported. If
		2904	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2905	code.
		2906
		2907	=item EV_EMBED_ENABLE
		2908
		2909	If undefined or defined to be C<1>, then embed watchers are supported. If
		2910	defined to be C<0>, then they are not.
		2911
		2912	=item EV_STAT_ENABLE
		2913
		2914	If undefined or defined to be C<1>, then stat watchers are supported. If
		2915	defined to be C<0>, then they are not.
		2916
		2917	=item EV_FORK_ENABLE
		2918
		2919	If undefined or defined to be C<1>, then fork watchers are supported. If
		2920	defined to be C<0>, then they are not.
		2921
		2922	=item EV_ASYNC_ENABLE
		2923
		2924	If undefined or defined to be C<1>, then async watchers are supported. If
		2925	defined to be C<0>, then they are not.
		2926
		2927	=item EV_MINIMAL
		2928
		2929	If you need to shave off some kilobytes of code at the expense of some
		2930	speed, define this symbol to C<1>. Currently only used for gcc to override
		2931	some inlining decisions, saves roughly 30% codesize of amd64.
		2932
		2933	=item EV_PID_HASHSIZE
		2934
		2935	C<ev_child> watchers use a small hash table to distribute workload by
		2936	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2937	than enough. If you need to manage thousands of children you might want to
		2938	increase this value (I<must> be a power of two).
		2939
		2940	=item EV_INOTIFY_HASHSIZE
		2941
		2942	C<ev_stat> watchers use a small hash table to distribute workload by
		2943	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2944	usually more than enough. If you need to manage thousands of C<ev_stat>
		2945	watchers you might want to increase this value (I<must> be a power of
		2946	two).
		2947
		2948	=item EV_COMMON
		2949
		2950	By default, all watchers have a C<void *data> member. By redefining
		2951	this macro to a something else you can include more and other types of
		2952	members. You have to define it each time you include one of the files,
		2953	though, and it must be identical each time.
		2954
		2955	For example, the perl EV module uses something like this:
		2956
		2957	#define EV_COMMON \
		2958	SV *self; /* contains this struct */ \
		2959	SV *cb_sv, *fh /* note no trailing ";" */
		2960
		2961	=item EV_CB_DECLARE (type)
		2962
		2963	=item EV_CB_INVOKE (watcher, revents)
		2964
		2965	=item ev_set_cb (ev, cb)
		2966
		2967	Can be used to change the callback member declaration in each watcher,
		2968	and the way callbacks are invoked and set. Must expand to a struct member
		2969	definition and a statement, respectively. See the F<ev.h> header file for
		2970	their default definitions. One possible use for overriding these is to
		2971	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2972	method calls instead of plain function calls in C++.
		2973
		2974	=head2 EXPORTED API SYMBOLS
		2975
		2976	If you need to re-export the API (e.g. via a dll) and you need a list of
		2977	exported symbols, you can use the provided F<Symbol.*> files which list
		2978	all public symbols, one per line:
		2979
		2980	Symbols.ev for libev proper
		2981	Symbols.event for the libevent emulation
		2982
		2983	This can also be used to rename all public symbols to avoid clashes with
		2984	multiple versions of libev linked together (which is obviously bad in
		2985	itself, but sometimes it is inconvinient to avoid this).
		2986
		2987	A sed command like this will create wrapper C<#define>'s that you need to
		2988	include before including F<ev.h>:
		2989
		2990	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		2991
		2992	This would create a file F<wrap.h> which essentially looks like this:
		2993
		2994	#define ev_backend myprefix_ev_backend
		2995	#define ev_check_start myprefix_ev_check_start
		2996	#define ev_check_stop myprefix_ev_check_stop
		2997	...
		2998
		2999	=head2 EXAMPLES
		3000
		3001	For a real-world example of a program the includes libev
		3002	verbatim, you can have a look at the EV perl module
		3003	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3004	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3005	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3006	will be compiled. It is pretty complex because it provides its own header
		3007	file.
		3008
		3009	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3010	that everybody includes and which overrides some configure choices:
		3011
		3012	#define EV_MINIMAL 1
		3013	#define EV_USE_POLL 0
		3014	#define EV_MULTIPLICITY 0
		3015	#define EV_PERIODIC_ENABLE 0
		3016	#define EV_STAT_ENABLE 0
		3017	#define EV_FORK_ENABLE 0
		3018	#define EV_CONFIG_H <config.h>
		3019	#define EV_MINPRI 0
		3020	#define EV_MAXPRI 0
		3021
		3022	#include "ev++.h"
		3023
		3024	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3025
		3026	#include "ev_cpp.h"
		3027	#include "ev.c"
		3028
		3029
		3030	=head1 COMPLEXITIES
		3031
		3032	In this section the complexities of (many of) the algorithms used inside
		3033	libev will be explained. For complexity discussions about backends see the
		3034	documentation for C<ev_default_init>.
		3035
		3036	All of the following are about amortised time: If an array needs to be
		3037	extended, libev needs to realloc and move the whole array, but this
		3038	happens asymptotically never with higher number of elements, so O(1) might
		3039	mean it might do a lengthy realloc operation in rare cases, but on average
		3040	it is much faster and asymptotically approaches constant time.
		3041
		3042	=over 4
		3043
		3044	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3045
		3046	This means that, when you have a watcher that triggers in one hour and
		3047	there are 100 watchers that would trigger before that then inserting will
		3048	have to skip roughly seven (C<ld 100>) of these watchers.
		3049
		3050	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3051
		3052	That means that changing a timer costs less than removing/adding them
		3053	as only the relative motion in the event queue has to be paid for.
		3054
		3055	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3056
		3057	These just add the watcher into an array or at the head of a list.
		3058
		3059	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3060
		3061	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3062
		3063	These watchers are stored in lists then need to be walked to find the
		3064	correct watcher to remove. The lists are usually short (you don't usually
		3065	have many watchers waiting for the same fd or signal).
		3066
		3067	=item Finding the next timer in each loop iteration: O(1)
		3068
		3069	By virtue of using a binary heap, the next timer is always found at the
		3070	beginning of the storage array.
		3071
		3072	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3073
		3074	A change means an I/O watcher gets started or stopped, which requires
		3075	libev to recalculate its status (and possibly tell the kernel, depending
		3076	on backend and wether C<ev_io_set> was used).
		3077
		3078	=item Activating one watcher (putting it into the pending state): O(1)
		3079
		3080	=item Priority handling: O(number_of_priorities)
		3081
		3082	Priorities are implemented by allocating some space for each
		3083	priority. When doing priority-based operations, libev usually has to
		3084	linearly search all the priorities, but starting/stopping and activating
		3085	watchers becomes O(1) w.r.t. priority handling.
		3086
		3087	=item Sending an ev_async: O(1)
		3088
		3089	=item Processing ev_async_send: O(number_of_async_watchers)
		3090
		3091	=item Processing signals: O(max_signal_number)
		3092
		3093	Sending involves a syscall I<iff> there were no other C<ev_async_send>
		3094	calls in the current loop iteration. Checking for async and signal events
		3095	involves iterating over all running async watchers or all signal numbers.
		3096
		3097	=back
		3098
		3099
		3100	=head1 Win32 platform limitations and workarounds
		3101
		3102	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3103	requires, and its I/O model is fundamentally incompatible with the POSIX
		3104	model. Libev still offers limited functionality on this platform in
		3105	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3106	descriptors. This only applies when using Win32 natively, not when using
		3107	e.g. cygwin.
		3108
		3109	There is no supported compilation method available on windows except
		3110	embedding it into other applications.
		3111
		3112	Due to the many, low, and arbitrary limits on the win32 platform and the
		3113	abysmal performance of winsockets, using a large number of sockets is not
		3114	recommended (and not reasonable). If your program needs to use more than
		3115	a hundred or so sockets, then likely it needs to use a totally different
		3116	implementation for windows, as libev offers the POSIX model, which cannot
		3117	be implemented efficiently on windows (microsoft monopoly games).
		3118
		3119	=over 4
		3120
		3121	=item The winsocket select function
		3122
		3123	The winsocket C<select> function doesn't follow POSIX in that it requires
		3124	socket I<handles> and not socket I<file descriptors>. This makes select
		3125	very inefficient, and also requires a mapping from file descriptors
		3126	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		3127	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		3128	symbols for more info.
		3129
		3130	The configuration for a "naked" win32 using the microsoft runtime
		3131	libraries and raw winsocket select is:
		3132
		3133	#define EV_USE_SELECT 1
		3134	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3135
		3136	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3137	complexity in the O(n²) range when using win32.
		3138
		3139	=item Limited number of file descriptors
		3140
		3141	Windows has numerous arbitrary (and low) limits on things. Early versions
		3142	of winsocket's select only supported waiting for a max. of C<64> handles
		3143	(probably owning to the fact that all windows kernels can only wait for
		3144	C<64> things at the same time internally; microsoft recommends spawning a
		3145	chain of threads and wait for 63 handles and the previous thread in each).
		3146
		3147	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3148	to some high number (e.g. C<2048>) before compiling the winsocket select
		3149	call (which might be in libev or elsewhere, for example, perl does its own
		3150	select emulation on windows).
		3151
		3152	Another limit is the number of file descriptors in the microsoft runtime
		3153	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3154	or something like this inside microsoft). You can increase this by calling
		3155	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3156	arbitrary limit), but is broken in many versions of the microsoft runtime
		3157	libraries.
		3158
		3159	This might get you to about C<512> or C<2048> sockets (depending on
		3160	windows version and/or the phase of the moon). To get more, you need to
		3161	wrap all I/O functions and provide your own fd management, but the cost of
		3162	calling select (O(n²)) will likely make this unworkable.
		3163
		3164	=back
		3165
825		3166
826	=head1 AUTHOR	3167	=head1 AUTHOR
827		3168
828	Marc Lehmann <libev@schmorp.de>.	3169	Marc Lehmann <libev@schmorp.de>.
829		3170

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