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…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	#include <ev.h>
		12
		13	ev_io stdin_watcher;
		14	ev_timer timeout_watcher;
		15
		16	/* called when data readable on stdin */
		17	static void
		18	stdin_cb (EV_P_ struct ev_io *w, int revents)
		19	{
		20	/* puts ("stdin ready"); */
		21	ev_io_stop (EV_A_ w); /* just a syntax example */
		22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */
		23	}
		24
		25	static void
		26	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		27	{
		28	/* puts ("timeout"); */
		29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */
		30	}
		31
		32	int
		33	main (void)
		34	{
		35	struct ev_loop *loop = ev_default_loop (0);
		36
		37	/* initialise an io watcher, then start it */
		38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		39	ev_io_start (loop, &stdin_watcher);
		40
		41	/* simple non-repeating 5.5 second timeout */
		42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		43	ev_timer_start (loop, &timeout_watcher);
		44
		45	/* loop till timeout or data ready */
		46	ev_loop (loop, 0);
		47
		48	return 0;
		49	}
		50
9	=head1 DESCRIPTION	51	=head1 DESCRIPTION
10		52
		53	The newest version of this document is also available as a html-formatted
		54	web page you might find easier to navigate when reading it for the first
		55	time: L<http://cvs.schmorp.de/libev/ev.html>.
		56
11	Libev is an event loop: you register interest in certain events (such as a	57	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	58	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	59	these event sources and provide your program with events.
14		60
15	To do this, it must take more or less complete control over your process	61	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	62	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	63	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	65	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	66	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	67	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	68	watcher.
23		69
24	=head1 FEATURES	70	=head2 FEATURES
25		71
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	76	with customised rescheduling (C<ev_periodic>), synchronous signals
		77	(C<ev_signal>), process status change events (C<ev_child>), and event
		78	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		80	file watchers (C<ev_stat>) and even limited support for fork events
		81	(C<ev_fork>).
		82
		83	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	85	for example).
33		86
34	=head1 CONVENTIONS	87	=head2 CONVENTIONS
35		88
36	Libev is very configurable. In this manual the default configuration	89	Libev is very configurable. In this manual the default configuration will
37	will be described, which supports multiple event loops. For more info	90	be described, which supports multiple event loops. For more info about
38	about various configuration options please have a look at the file	91	various configuration options please have a look at B<EMBED> section in
39	F<README.embed> in the libev distribution. If libev was configured without	92	this manual. If libev was configured without support for multiple event
40	support for multiple event loops, then all functions taking an initial	93	loops, then all functions taking an initial argument of name C<loop>
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	94	(which is always of type C<struct ev_loop *>) will not have this argument.
42	will not have this argument.
43		95
44	=head1 TIME REPRESENTATION	96	=head2 TIME REPRESENTATION
45		97
46	Libev represents time as a single floating point number, representing the	98	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	99	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	100	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	101	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	102	to the C<double> type in C, and when you need to do any calculations on
		103	it, you should treat it as some floatingpoint value. Unlike the name
		104	component C<stamp> might indicate, it is also used for time differences
		105	throughout libev.
51		106
52	=head1 GLOBAL FUNCTIONS	107	=head1 GLOBAL FUNCTIONS
53		108
54	These functions can be called anytime, even before initialising the	109	These functions can be called anytime, even before initialising the
55	library in any way.	110	library in any way.
56		111
57	=over 4	112	=over 4
58		113
59	=item ev_tstamp ev_time ()	114	=item ev_tstamp ev_time ()
60		115
61	Returns the current time as libev would use it.	116	Returns the current time as libev would use it. Please note that the
		117	C<ev_now> function is usually faster and also often returns the timestamp
		118	you actually want to know.
		119
		120	=item ev_sleep (ev_tstamp interval)
		121
		122	Sleep for the given interval: The current thread will be blocked until
		123	either it is interrupted or the given time interval has passed. Basically
		124	this is a subsecond-resolution C<sleep ()>.
62		125
63	=item int ev_version_major ()	126	=item int ev_version_major ()
64		127
65	=item int ev_version_minor ()	128	=item int ev_version_minor ()
66		129
67	You can find out the major and minor version numbers of the library	130	You can find out the major and minor ABI version numbers of the library
68	you linked against by calling the functions C<ev_version_major> and	131	you linked against by calling the functions C<ev_version_major> and
69	C<ev_version_minor>. If you want, you can compare against the global	132	C<ev_version_minor>. If you want, you can compare against the global
70	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	133	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
71	version of the library your program was compiled against.	134	version of the library your program was compiled against.
72		135
		136	These version numbers refer to the ABI version of the library, not the
		137	release version.
		138
73	Usually, it's a good idea to terminate if the major versions mismatch,	139	Usually, it's a good idea to terminate if the major versions mismatch,
74	as this indicates an incompatible change. Minor versions are usually	140	as this indicates an incompatible change. Minor versions are usually
75	compatible to older versions, so a larger minor version alone is usually	141	compatible to older versions, so a larger minor version alone is usually
76	not a problem.	142	not a problem.
77		143
		144	Example: Make sure we haven't accidentally been linked against the wrong
		145	version.
		146
		147	assert (("libev version mismatch",
		148	ev_version_major () == EV_VERSION_MAJOR
		149	&& ev_version_minor () >= EV_VERSION_MINOR));
		150
		151	=item unsigned int ev_supported_backends ()
		152
		153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		154	value) compiled into this binary of libev (independent of their
		155	availability on the system you are running on). See C<ev_default_loop> for
		156	a description of the set values.
		157
		158	Example: make sure we have the epoll method, because yeah this is cool and
		159	a must have and can we have a torrent of it please!!!11
		160
		161	assert (("sorry, no epoll, no sex",
		162	ev_supported_backends () & EVBACKEND_EPOLL));
		163
		164	=item unsigned int ev_recommended_backends ()
		165
		166	Return the set of all backends compiled into this binary of libev and also
		167	recommended for this platform. This set is often smaller than the one
		168	returned by C<ev_supported_backends>, as for example kqueue is broken on
		169	most BSDs and will not be autodetected unless you explicitly request it
		170	(assuming you know what you are doing). This is the set of backends that
		171	libev will probe for if you specify no backends explicitly.
		172
		173	=item unsigned int ev_embeddable_backends ()
		174
		175	Returns the set of backends that are embeddable in other event loops. This
		176	is the theoretical, all-platform, value. To find which backends
		177	might be supported on the current system, you would need to look at
		178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		179	recommended ones.
		180
		181	See the description of C<ev_embed> watchers for more info.
		182
78	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
79		184
80	Sets the allocation function to use (the prototype is similar to the	185	Sets the allocation function to use (the prototype is similar - the
81	realloc C function, the semantics are identical). It is used to allocate	186	semantics is identical - to the realloc C function). It is used to
82	and free memory (no surprises here). If it returns zero when memory	187	allocate and free memory (no surprises here). If it returns zero when
83	needs to be allocated, the library might abort or take some potentially	188	memory needs to be allocated, the library might abort or take some
84	destructive action. The default is your system realloc function.	189	potentially destructive action. The default is your system realloc
		190	function.
85		191
86	You could override this function in high-availability programs to, say,	192	You could override this function in high-availability programs to, say,
87	free some memory if it cannot allocate memory, to use a special allocator,	193	free some memory if it cannot allocate memory, to use a special allocator,
88	or even to sleep a while and retry until some memory is available.	194	or even to sleep a while and retry until some memory is available.
		195
		196	Example: Replace the libev allocator with one that waits a bit and then
		197	retries).
		198
		199	static void *
		200	persistent_realloc (void *ptr, size_t size)
		201	{
		202	for (;;)
		203	{
		204	void *newptr = realloc (ptr, size);
		205
		206	if (newptr)
		207	return newptr;
		208
		209	sleep (60);
		210	}
		211	}
		212
		213	...
		214	ev_set_allocator (persistent_realloc);
89		215
90	=item ev_set_syserr_cb (void (*cb)(const char *msg));	216	=item ev_set_syserr_cb (void (*cb)(const char *msg));
91		217
92	Set the callback function to call on a retryable syscall error (such	218	Set the callback function to call on a retryable syscall error (such
93	as failed select, poll, epoll_wait). The message is a printable string	219	as failed select, poll, epoll_wait). The message is a printable string
…		…
95	callback is set, then libev will expect it to remedy the sitution, no	221	callback is set, then libev will expect it to remedy the sitution, no
96	matter what, when it returns. That is, libev will generally retry the	222	matter what, when it returns. That is, libev will generally retry the
97	requested operation, or, if the condition doesn't go away, do bad stuff	223	requested operation, or, if the condition doesn't go away, do bad stuff
98	(such as abort).	224	(such as abort).
99		225
		226	Example: This is basically the same thing that libev does internally, too.
		227
		228	static void
		229	fatal_error (const char *msg)
		230	{
		231	perror (msg);
		232	abort ();
		233	}
		234
		235	...
		236	ev_set_syserr_cb (fatal_error);
		237
100	=back	238	=back
101		239
102	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
103		241
104	An event loop is described by a C<struct ev_loop *>. The library knows two	242	An event loop is described by a C<struct ev_loop *>. The library knows two
…		…
117	=item struct ev_loop *ev_default_loop (unsigned int flags)	255	=item struct ev_loop *ev_default_loop (unsigned int flags)
118		256
119	This will initialise the default event loop if it hasn't been initialised	257	This will initialise the default event loop if it hasn't been initialised
120	yet and return it. If the default loop could not be initialised, returns	258	yet and return it. If the default loop could not be initialised, returns
121	false. If it already was initialised it simply returns it (and ignores the	259	false. If it already was initialised it simply returns it (and ignores the
122	flags).	260	flags. If that is troubling you, check C<ev_backend ()> afterwards).
123		261
124	If you don't know what event loop to use, use the one returned from this	262	If you don't know what event loop to use, use the one returned from this
125	function.	263	function.
126		264
127	The flags argument can be used to specify special behaviour or specific	265	The flags argument can be used to specify special behaviour or specific
128	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
129		267
130	It supports the following flags:	268	The following flags are supported:
131		269
132	=over 4	270	=over 4
133		271
134	=item C<EVFLAG_AUTO>	272	=item C<EVFLAG_AUTO>
135		273
…		…
143	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
144	override the flags completely if it is found in the environment. This is	282	override the flags completely if it is found in the environment. This is
145	useful to try out specific backends to test their performance, or to work	283	useful to try out specific backends to test their performance, or to work
146	around bugs.	284	around bugs.
147		285
		286	=item C<EVFLAG_FORKCHECK>
		287
		288	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		289	a fork, you can also make libev check for a fork in each iteration by
		290	enabling this flag.
		291
		292	This works by calling C<getpid ()> on every iteration of the loop,
		293	and thus this might slow down your event loop if you do a lot of loop
		294	iterations and little real work, but is usually not noticeable (on my
		295	Linux system for example, C<getpid> is actually a simple 5-insn sequence
		296	without a syscall and thus I<very> fast, but my Linux system also has
		297	C<pthread_atfork> which is even faster).
		298
		299	The big advantage of this flag is that you can forget about fork (and
		300	forget about forgetting to tell libev about forking) when you use this
		301	flag.
		302
		303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		304	environment variable.
		305
148	=item C<EVMETHOD_SELECT> (portable select backend)	306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
149		307
		308	This is your standard select(2) backend. Not I<completely> standard, as
		309	libev tries to roll its own fd_set with no limits on the number of fds,
		310	but if that fails, expect a fairly low limit on the number of fds when
		311	using this backend. It doesn't scale too well (O(highest_fd)), but its
		312	usually the fastest backend for a low number of (low-numbered :) fds.
		313
		314	To get good performance out of this backend you need a high amount of
		315	parallelity (most of the file descriptors should be busy). If you are
		316	writing a server, you should C<accept ()> in a loop to accept as many
		317	connections as possible during one iteration. You might also want to have
		318	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		319	readyness notifications you get per iteration.
		320
150	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
151		322
152	=item C<EVMETHOD_EPOLL> (linux only)	323	And this is your standard poll(2) backend. It's more complicated
		324	than select, but handles sparse fds better and has no artificial
		325	limit on the number of fds you can use (except it will slow down
		326	considerably with a lot of inactive fds). It scales similarly to select,
		327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		328	performance tips.
153		329
154	=item C<EVMETHOD_KQUEUE> (some bsds only)	330	=item C<EVBACKEND_EPOLL> (value 4, Linux)
155		331
156	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	332	For few fds, this backend is a bit little slower than poll and select,
		333	but it scales phenomenally better. While poll and select usually scale
		334	like O(total_fds) where n is the total number of fds (or the highest fd),
		335	epoll scales either O(1) or O(active_fds). The epoll design has a number
		336	of shortcomings, such as silently dropping events in some hard-to-detect
		337	cases and rewiring a syscall per fd change, no fork support and bad
		338	support for dup.
157		339
158	=item C<EVMETHOD_PORT> (solaris 10 only)	340	While stopping, setting and starting an I/O watcher in the same iteration
		341	will result in some caching, there is still a syscall per such incident
		342	(because the fd could point to a different file description now), so its
		343	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		344	very well if you register events for both fds.
		345
		346	Please note that epoll sometimes generates spurious notifications, so you
		347	need to use non-blocking I/O or other means to avoid blocking when no data
		348	(or space) is available.
		349
		350	Best performance from this backend is achieved by not unregistering all
		351	watchers for a file descriptor until it has been closed, if possible, i.e.
		352	keep at least one watcher active per fd at all times.
		353
		354	While nominally embeddeble in other event loops, this feature is broken in
		355	all kernel versions tested so far.
		356
		357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		358
		359	Kqueue deserves special mention, as at the time of this writing, it
		360	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		361	with anything but sockets and pipes, except on Darwin, where of course
		362	it's completely useless). For this reason it's not being "autodetected"
		363	unless you explicitly specify it explicitly in the flags (i.e. using
		364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		365	system like NetBSD.
		366
		367	You still can embed kqueue into a normal poll or select backend and use it
		368	only for sockets (after having made sure that sockets work with kqueue on
		369	the target platform). See C<ev_embed> watchers for more info.
		370
		371	It scales in the same way as the epoll backend, but the interface to the
		372	kernel is more efficient (which says nothing about its actual speed, of
		373	course). While stopping, setting and starting an I/O watcher does never
		374	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
		375	two event changes per incident, support for C<fork ()> is very bad and it
		376	drops fds silently in similarly hard-to-detect cases.
		377
		378	This backend usually performs well under most conditions.
		379
		380	While nominally embeddable in other event loops, this doesn't work
		381	everywhere, so you might need to test for this. And since it is broken
		382	almost everywhere, you should only use it when you have a lot of sockets
		383	(for which it usually works), by embedding it into another event loop
		384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		385	sockets.
		386
		387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		388
		389	This is not implemented yet (and might never be, unless you send me an
		390	implementation). According to reports, C</dev/poll> only supports sockets
		391	and is not embeddable, which would limit the usefulness of this backend
		392	immensely.
		393
		394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		395
		396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		397	it's really slow, but it still scales very well (O(active_fds)).
		398
		399	Please note that solaris event ports can deliver a lot of spurious
		400	notifications, so you need to use non-blocking I/O or other means to avoid
		401	blocking when no data (or space) is available.
		402
		403	While this backend scales well, it requires one system call per active
		404	file descriptor per loop iteration. For small and medium numbers of file
		405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		406	might perform better.
		407
		408	=item C<EVBACKEND_ALL>
		409
		410	Try all backends (even potentially broken ones that wouldn't be tried
		411	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		413
		414	It is definitely not recommended to use this flag.
		415
		416	=back
159		417
160	If one or more of these are ored into the flags value, then only these	418	If one or more of these are ored into the flags value, then only these
161	backends will be tried (in the reverse order as given here). If one are	419	backends will be tried (in the reverse order as given here). If none are
162	specified, any backend will do.	420	specified, most compiled-in backend will be tried, usually in reverse
		421	order of their flag values :)
163		422
164	=back	423	The most typical usage is like this:
		424
		425	if (!ev_default_loop (0))
		426	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		427
		428	Restrict libev to the select and poll backends, and do not allow
		429	environment settings to be taken into account:
		430
		431	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		432
		433	Use whatever libev has to offer, but make sure that kqueue is used if
		434	available (warning, breaks stuff, best use only with your own private
		435	event loop and only if you know the OS supports your types of fds):
		436
		437	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
165		438
166	=item struct ev_loop *ev_loop_new (unsigned int flags)	439	=item struct ev_loop *ev_loop_new (unsigned int flags)
167		440
168	Similar to C<ev_default_loop>, but always creates a new event loop that is	441	Similar to C<ev_default_loop>, but always creates a new event loop that is
169	always distinct from the default loop. Unlike the default loop, it cannot	442	always distinct from the default loop. Unlike the default loop, it cannot
170	handle signal and child watchers, and attempts to do so will be greeted by	443	handle signal and child watchers, and attempts to do so will be greeted by
171	undefined behaviour (or a failed assertion if assertions are enabled).	444	undefined behaviour (or a failed assertion if assertions are enabled).
172		445
		446	Example: Try to create a event loop that uses epoll and nothing else.
		447
		448	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		449	if (!epoller)
		450	fatal ("no epoll found here, maybe it hides under your chair");
		451
173	=item ev_default_destroy ()	452	=item ev_default_destroy ()
174		453
175	Destroys the default loop again (frees all memory and kernel state	454	Destroys the default loop again (frees all memory and kernel state
176	etc.). This stops all registered event watchers (by not touching them in	455	etc.). None of the active event watchers will be stopped in the normal
177	any way whatsoever, although you cannot rely on this :).	456	sense, so e.g. C<ev_is_active> might still return true. It is your
		457	responsibility to either stop all watchers cleanly yoursef I<before>
		458	calling this function, or cope with the fact afterwards (which is usually
		459	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		460	for example).
		461
		462	Note that certain global state, such as signal state, will not be freed by
		463	this function, and related watchers (such as signal and child watchers)
		464	would need to be stopped manually.
		465
		466	In general it is not advisable to call this function except in the
		467	rare occasion where you really need to free e.g. the signal handling
		468	pipe fds. If you need dynamically allocated loops it is better to use
		469	C<ev_loop_new> and C<ev_loop_destroy>).
178		470
179	=item ev_loop_destroy (loop)	471	=item ev_loop_destroy (loop)
180		472
181	Like C<ev_default_destroy>, but destroys an event loop created by an	473	Like C<ev_default_destroy>, but destroys an event loop created by an
182	earlier call to C<ev_loop_new>.	474	earlier call to C<ev_loop_new>.
…		…
186	This function reinitialises the kernel state for backends that have	478	This function reinitialises the kernel state for backends that have
187	one. Despite the name, you can call it anytime, but it makes most sense	479	one. Despite the name, you can call it anytime, but it makes most sense
188	after forking, in either the parent or child process (or both, but that	480	after forking, in either the parent or child process (or both, but that
189	again makes little sense).	481	again makes little sense).
190		482
191	You I<must> call this function after forking if and only if you want to	483	You I<must> call this function in the child process after forking if and
192	use the event library in both processes. If you just fork+exec, you don't	484	only if you want to use the event library in both processes. If you just
193	have to call it.	485	fork+exec, you don't have to call it.
194		486
195	The function itself is quite fast and it's usually not a problem to call	487	The function itself is quite fast and it's usually not a problem to call
196	it just in case after a fork. To make this easy, the function will fit in	488	it just in case after a fork. To make this easy, the function will fit in
197	quite nicely into a call to C<pthread_atfork>:	489	quite nicely into a call to C<pthread_atfork>:
198		490
199	pthread_atfork (0, 0, ev_default_fork);	491	pthread_atfork (0, 0, ev_default_fork);
200		492
		493	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
		494	without calling this function, so if you force one of those backends you
		495	do not need to care.
		496
201	=item ev_loop_fork (loop)	497	=item ev_loop_fork (loop)
202		498
203	Like C<ev_default_fork>, but acts on an event loop created by	499	Like C<ev_default_fork>, but acts on an event loop created by
204	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	500	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
205	after fork, and how you do this is entirely your own problem.	501	after fork, and how you do this is entirely your own problem.
206		502
		503	=item unsigned int ev_loop_count (loop)
		504
		505	Returns the count of loop iterations for the loop, which is identical to
		506	the number of times libev did poll for new events. It starts at C<0> and
		507	happily wraps around with enough iterations.
		508
		509	This value can sometimes be useful as a generation counter of sorts (it
		510	"ticks" the number of loop iterations), as it roughly corresponds with
		511	C<ev_prepare> and C<ev_check> calls.
		512
207	=item unsigned int ev_method (loop)	513	=item unsigned int ev_backend (loop)
208		514
209	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	515	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
210	use.	516	use.
211		517
212	=item ev_tstamp ev_now (loop)	518	=item ev_tstamp ev_now (loop)
213		519
214	Returns the current "event loop time", which is the time the event loop	520	Returns the current "event loop time", which is the time the event loop
215	got events and started processing them. This timestamp does not change	521	received events and started processing them. This timestamp does not
216	as long as callbacks are being processed, and this is also the base time	522	change as long as callbacks are being processed, and this is also the base
217	used for relative timers. You can treat it as the timestamp of the event	523	time used for relative timers. You can treat it as the timestamp of the
218	occuring (or more correctly, the mainloop finding out about it).	524	event occurring (or more correctly, libev finding out about it).
219		525
220	=item ev_loop (loop, int flags)	526	=item ev_loop (loop, int flags)
221		527
222	Finally, this is it, the event handler. This function usually is called	528	Finally, this is it, the event handler. This function usually is called
223	after you initialised all your watchers and you want to start handling	529	after you initialised all your watchers and you want to start handling
224	events.	530	events.
225		531
226	If the flags argument is specified as 0, it will not return until either	532	If the flags argument is specified as C<0>, it will not return until
227	no event watchers are active anymore or C<ev_unloop> was called.	533	either no event watchers are active anymore or C<ev_unloop> was called.
		534
		535	Please note that an explicit C<ev_unloop> is usually better than
		536	relying on all watchers to be stopped when deciding when a program has
		537	finished (especially in interactive programs), but having a program that
		538	automatically loops as long as it has to and no longer by virtue of
		539	relying on its watchers stopping correctly is a thing of beauty.
228		540
229	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	541	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
230	those events and any outstanding ones, but will not block your process in	542	those events and any outstanding ones, but will not block your process in
231	case there are no events and will return after one iteration of the loop.	543	case there are no events and will return after one iteration of the loop.
232		544
233	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	545	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
234	neccessary) and will handle those and any outstanding ones. It will block	546	neccessary) and will handle those and any outstanding ones. It will block
235	your process until at least one new event arrives, and will return after	547	your process until at least one new event arrives, and will return after
236	one iteration of the loop.	548	one iteration of the loop. This is useful if you are waiting for some
		549	external event in conjunction with something not expressible using other
		550	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		551	usually a better approach for this kind of thing.
237		552
238	This flags value could be used to implement alternative looping	553	Here are the gory details of what C<ev_loop> does:
239	constructs, but the C<prepare> and C<check> watchers provide a better and	554
240	more generic mechanism.	555	- Before the first iteration, call any pending watchers.
		556	* If there are no active watchers (reference count is zero), return.
		557	- Queue all prepare watchers and then call all outstanding watchers.
		558	- If we have been forked, recreate the kernel state.
		559	- Update the kernel state with all outstanding changes.
		560	- Update the "event loop time".
		561	- Calculate for how long to block.
		562	- Block the process, waiting for any events.
		563	- Queue all outstanding I/O (fd) events.
		564	- Update the "event loop time" and do time jump handling.
		565	- Queue all outstanding timers.
		566	- Queue all outstanding periodics.
		567	- If no events are pending now, queue all idle watchers.
		568	- Queue all check watchers.
		569	- Call all queued watchers in reverse order (i.e. check watchers first).
		570	Signals and child watchers are implemented as I/O watchers, and will
		571	be handled here by queueing them when their watcher gets executed.
		572	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		573	were used, return, otherwise continue with step *.
		574
		575	Example: Queue some jobs and then loop until no events are outsanding
		576	anymore.
		577
		578	... queue jobs here, make sure they register event watchers as long
		579	... as they still have work to do (even an idle watcher will do..)
		580	ev_loop (my_loop, 0);
		581	... jobs done. yeah!
241		582
242	=item ev_unloop (loop, how)	583	=item ev_unloop (loop, how)
243		584
244	Can be used to make a call to C<ev_loop> return early (but only after it	585	Can be used to make a call to C<ev_loop> return early (but only after it
245	has processed all outstanding events). The C<how> argument must be either	586	has processed all outstanding events). The C<how> argument must be either
246	C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or	587	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
247	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	588	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
248		589
249	=item ev_ref (loop)	590	=item ev_ref (loop)
250		591
251	=item ev_unref (loop)	592	=item ev_unref (loop)
…		…
259	visible to the libev user and should not keep C<ev_loop> from exiting if	600	visible to the libev user and should not keep C<ev_loop> from exiting if
260	no event watchers registered by it are active. It is also an excellent	601	no event watchers registered by it are active. It is also an excellent
261	way to do this for generic recurring timers or from within third-party	602	way to do this for generic recurring timers or from within third-party
262	libraries. Just remember to I<unref after start> and I<ref before stop>.	603	libraries. Just remember to I<unref after start> and I<ref before stop>.
263		604
		605	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		606	running when nothing else is active.
		607
		608	struct ev_signal exitsig;
		609	ev_signal_init (&exitsig, sig_cb, SIGINT);
		610	ev_signal_start (loop, &exitsig);
		611	evf_unref (loop);
		612
		613	Example: For some weird reason, unregister the above signal handler again.
		614
		615	ev_ref (loop);
		616	ev_signal_stop (loop, &exitsig);
		617
		618	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		619
		620	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		621
		622	These advanced functions influence the time that libev will spend waiting
		623	for events. Both are by default C<0>, meaning that libev will try to
		624	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		625
		626	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		627	allows libev to delay invocation of I/O and timer/periodic callbacks to
		628	increase efficiency of loop iterations.
		629
		630	The background is that sometimes your program runs just fast enough to
		631	handle one (or very few) event(s) per loop iteration. While this makes
		632	the program responsive, it also wastes a lot of CPU time to poll for new
		633	events, especially with backends like C<select ()> which have a high
		634	overhead for the actual polling but can deliver many events at once.
		635
		636	By setting a higher I<io collect interval> you allow libev to spend more
		637	time collecting I/O events, so you can handle more events per iteration,
		638	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		639	C<ev_timer>) will be not affected. Setting this to a non-null value will
		640	introduce an additional C<ev_sleep ()> call into most loop iterations.
		641
		642	Likewise, by setting a higher I<timeout collect interval> you allow libev
		643	to spend more time collecting timeouts, at the expense of increased
		644	latency (the watcher callback will be called later). C<ev_io> watchers
		645	will not be affected. Setting this to a non-null value will not introduce
		646	any overhead in libev.
		647
		648	Many (busy) programs can usually benefit by setting the io collect
		649	interval to a value near C<0.1> or so, which is often enough for
		650	interactive servers (of course not for games), likewise for timeouts. It
		651	usually doesn't make much sense to set it to a lower value than C<0.01>,
		652	as this approsaches the timing granularity of most systems.
		653
264	=back	654	=back
		655
265		656
266	=head1 ANATOMY OF A WATCHER	657	=head1 ANATOMY OF A WATCHER
267		658
268	A watcher is a structure that you create and register to record your	659	A watcher is a structure that you create and register to record your
269	interest in some event. For instance, if you want to wait for STDIN to	660	interest in some event. For instance, if you want to wait for STDIN to
…		…
302	*) >>), and you can stop watching for events at any time by calling the	693	*) >>), and you can stop watching for events at any time by calling the
303	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	694	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
304		695
305	As long as your watcher is active (has been started but not stopped) you	696	As long as your watcher is active (has been started but not stopped) you
306	must not touch the values stored in it. Most specifically you must never	697	must not touch the values stored in it. Most specifically you must never
307	reinitialise it or call its set method.	698	reinitialise it or call its C<set> macro.
308
309	You can check whether an event is active by calling the C<ev_is_active
310	(watcher *)> macro. To see whether an event is outstanding (but the
311	callback for it has not been called yet) you can use the C<ev_is_pending
312	(watcher *)> macro.
313		699
314	Each and every callback receives the event loop pointer as first, the	700	Each and every callback receives the event loop pointer as first, the
315	registered watcher structure as second, and a bitset of received events as	701	registered watcher structure as second, and a bitset of received events as
316	third argument.	702	third argument.
317		703
…		…
341	The signal specified in the C<ev_signal> watcher has been received by a thread.	727	The signal specified in the C<ev_signal> watcher has been received by a thread.
342		728
343	=item C<EV_CHILD>	729	=item C<EV_CHILD>
344		730
345	The pid specified in the C<ev_child> watcher has received a status change.	731	The pid specified in the C<ev_child> watcher has received a status change.
		732
		733	=item C<EV_STAT>
		734
		735	The path specified in the C<ev_stat> watcher changed its attributes somehow.
346		736
347	=item C<EV_IDLE>	737	=item C<EV_IDLE>
348		738
349	The C<ev_idle> watcher has determined that you have nothing better to do.	739	The C<ev_idle> watcher has determined that you have nothing better to do.
350		740
…		…
358	received events. Callbacks of both watcher types can start and stop as	748	received events. Callbacks of both watcher types can start and stop as
359	many watchers as they want, and all of them will be taken into account	749	many watchers as they want, and all of them will be taken into account
360	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	750	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
361	C<ev_loop> from blocking).	751	C<ev_loop> from blocking).
362		752
		753	=item C<EV_EMBED>
		754
		755	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		756
		757	=item C<EV_FORK>
		758
		759	The event loop has been resumed in the child process after fork (see
		760	C<ev_fork>).
		761
363	=item C<EV_ERROR>	762	=item C<EV_ERROR>
364		763
365	An unspecified error has occured, the watcher has been stopped. This might	764	An unspecified error has occured, the watcher has been stopped. This might
366	happen because the watcher could not be properly started because libev	765	happen because the watcher could not be properly started because libev
367	ran out of memory, a file descriptor was found to be closed or any other	766	ran out of memory, a file descriptor was found to be closed or any other
…		…
373	your callbacks is well-written it can just attempt the operation and cope	772	your callbacks is well-written it can just attempt the operation and cope
374	with the error from read() or write(). This will not work in multithreaded	773	with the error from read() or write(). This will not work in multithreaded
375	programs, though, so beware.	774	programs, though, so beware.
376		775
377	=back	776	=back
		777
		778	=head2 GENERIC WATCHER FUNCTIONS
		779
		780	In the following description, C<TYPE> stands for the watcher type,
		781	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		782
		783	=over 4
		784
		785	=item C<ev_init> (ev_TYPE *watcher, callback)
		786
		787	This macro initialises the generic portion of a watcher. The contents
		788	of the watcher object can be arbitrary (so C<malloc> will do). Only
		789	the generic parts of the watcher are initialised, you I<need> to call
		790	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		791	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		792	which rolls both calls into one.
		793
		794	You can reinitialise a watcher at any time as long as it has been stopped
		795	(or never started) and there are no pending events outstanding.
		796
		797	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		798	int revents)>.
		799
		800	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		801
		802	This macro initialises the type-specific parts of a watcher. You need to
		803	call C<ev_init> at least once before you call this macro, but you can
		804	call C<ev_TYPE_set> any number of times. You must not, however, call this
		805	macro on a watcher that is active (it can be pending, however, which is a
		806	difference to the C<ev_init> macro).
		807
		808	Although some watcher types do not have type-specific arguments
		809	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		810
		811	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		812
		813	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		814	calls into a single call. This is the most convinient method to initialise
		815	a watcher. The same limitations apply, of course.
		816
		817	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		818
		819	Starts (activates) the given watcher. Only active watchers will receive
		820	events. If the watcher is already active nothing will happen.
		821
		822	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		823
		824	Stops the given watcher again (if active) and clears the pending
		825	status. It is possible that stopped watchers are pending (for example,
		826	non-repeating timers are being stopped when they become pending), but
		827	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		828	you want to free or reuse the memory used by the watcher it is therefore a
		829	good idea to always call its C<ev_TYPE_stop> function.
		830
		831	=item bool ev_is_active (ev_TYPE *watcher)
		832
		833	Returns a true value iff the watcher is active (i.e. it has been started
		834	and not yet been stopped). As long as a watcher is active you must not modify
		835	it.
		836
		837	=item bool ev_is_pending (ev_TYPE *watcher)
		838
		839	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		840	events but its callback has not yet been invoked). As long as a watcher
		841	is pending (but not active) you must not call an init function on it (but
		842	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		843	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		844	it).
		845
		846	=item callback ev_cb (ev_TYPE *watcher)
		847
		848	Returns the callback currently set on the watcher.
		849
		850	=item ev_cb_set (ev_TYPE *watcher, callback)
		851
		852	Change the callback. You can change the callback at virtually any time
		853	(modulo threads).
		854
		855	=item ev_set_priority (ev_TYPE *watcher, priority)
		856
		857	=item int ev_priority (ev_TYPE *watcher)
		858
		859	Set and query the priority of the watcher. The priority is a small
		860	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		861	(default: C<-2>). Pending watchers with higher priority will be invoked
		862	before watchers with lower priority, but priority will not keep watchers
		863	from being executed (except for C<ev_idle> watchers).
		864
		865	This means that priorities are I<only> used for ordering callback
		866	invocation after new events have been received. This is useful, for
		867	example, to reduce latency after idling, or more often, to bind two
		868	watchers on the same event and make sure one is called first.
		869
		870	If you need to suppress invocation when higher priority events are pending
		871	you need to look at C<ev_idle> watchers, which provide this functionality.
		872
		873	You I<must not> change the priority of a watcher as long as it is active or
		874	pending.
		875
		876	The default priority used by watchers when no priority has been set is
		877	always C<0>, which is supposed to not be too high and not be too low :).
		878
		879	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		880	fine, as long as you do not mind that the priority value you query might
		881	or might not have been adjusted to be within valid range.
		882
		883	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		884
		885	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		886	C<loop> nor C<revents> need to be valid as long as the watcher callback
		887	can deal with that fact.
		888
		889	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		890
		891	If the watcher is pending, this function returns clears its pending status
		892	and returns its C<revents> bitset (as if its callback was invoked). If the
		893	watcher isn't pending it does nothing and returns C<0>.
		894
		895	=back
		896
378		897
379	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	898	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
380		899
381	Each watcher has, by default, a member C<void *data> that you can change	900	Each watcher has, by default, a member C<void *data> that you can change
382	and read at any time, libev will completely ignore it. This can be used	901	and read at any time, libev will completely ignore it. This can be used
…		…
400	{	919	{
401	struct my_io *w = (struct my_io *)w_;	920	struct my_io *w = (struct my_io *)w_;
402	...	921	...
403	}	922	}
404		923
405	More interesting and less C-conformant ways of catsing your callback type	924	More interesting and less C-conformant ways of casting your callback type
406	have been omitted....	925	instead have been omitted.
		926
		927	Another common scenario is having some data structure with multiple
		928	watchers:
		929
		930	struct my_biggy
		931	{
		932	int some_data;
		933	ev_timer t1;
		934	ev_timer t2;
		935	}
		936
		937	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		938	you need to use C<offsetof>:
		939
		940	#include <stddef.h>
		941
		942	static void
		943	t1_cb (EV_P_ struct ev_timer *w, int revents)
		944	{
		945	struct my_biggy big = (struct my_biggy *
		946	(((char *)w) - offsetof (struct my_biggy, t1));
		947	}
		948
		949	static void
		950	t2_cb (EV_P_ struct ev_timer *w, int revents)
		951	{
		952	struct my_biggy big = (struct my_biggy *
		953	(((char *)w) - offsetof (struct my_biggy, t2));
		954	}
407		955
408		956
409	=head1 WATCHER TYPES	957	=head1 WATCHER TYPES
410		958
411	This section describes each watcher in detail, but will not repeat	959	This section describes each watcher in detail, but will not repeat
412	information given in the last section.	960	information given in the last section. Any initialisation/set macros,
		961	functions and members specific to the watcher type are explained.
413		962
		963	Members are additionally marked with either I<[read-only]>, meaning that,
		964	while the watcher is active, you can look at the member and expect some
		965	sensible content, but you must not modify it (you can modify it while the
		966	watcher is stopped to your hearts content), or I<[read-write]>, which
		967	means you can expect it to have some sensible content while the watcher
		968	is active, but you can also modify it. Modifying it may not do something
		969	sensible or take immediate effect (or do anything at all), but libev will
		970	not crash or malfunction in any way.
		971
		972
414	=head2 C<ev_io> - is this file descriptor readable or writable	973	=head2 C<ev_io> - is this file descriptor readable or writable?
415		974
416	I/O watchers check whether a file descriptor is readable or writable	975	I/O watchers check whether a file descriptor is readable or writable
417	in each iteration of the event loop (This behaviour is called	976	in each iteration of the event loop, or, more precisely, when reading
418	level-triggering because you keep receiving events as long as the	977	would not block the process and writing would at least be able to write
419	condition persists. Remember you can stop the watcher if you don't want to	978	some data. This behaviour is called level-triggering because you keep
420	act on the event and neither want to receive future events).	979	receiving events as long as the condition persists. Remember you can stop
		980	the watcher if you don't want to act on the event and neither want to
		981	receive future events.
421		982
422	In general you can register as many read and/or write event watchers oer	983	In general you can register as many read and/or write event watchers per
423	fd as you want (as long as you don't confuse yourself). Setting all file	984	fd as you want (as long as you don't confuse yourself). Setting all file
424	descriptors to non-blocking mode is also usually a good idea (but not	985	descriptors to non-blocking mode is also usually a good idea (but not
425	required if you know what you are doing).	986	required if you know what you are doing).
426		987
427	You have to be careful with dup'ed file descriptors, though. Some backends	988	You have to be careful with dup'ed file descriptors, though. Some backends
428	(the linux epoll backend is a notable example) cannot handle dup'ed file	989	(the linux epoll backend is a notable example) cannot handle dup'ed file
429	descriptors correctly if you register interest in two or more fds pointing	990	descriptors correctly if you register interest in two or more fds pointing
430	to the same file/socket etc. description.	991	to the same underlying file/socket/etc. description (that is, they share
		992	the same underlying "file open").
431		993
432	If you must do this, then force the use of a known-to-be-good backend	994	If you must do this, then force the use of a known-to-be-good backend
433	(at the time of this writing, this includes only EVMETHOD_SELECT and	995	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
434	EVMETHOD_POLL).	996	C<EVBACKEND_POLL>).
		997
		998	Another thing you have to watch out for is that it is quite easy to
		999	receive "spurious" readyness notifications, that is your callback might
		1000	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1001	because there is no data. Not only are some backends known to create a
		1002	lot of those (for example solaris ports), it is very easy to get into
		1003	this situation even with a relatively standard program structure. Thus
		1004	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1005	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1006
		1007	If you cannot run the fd in non-blocking mode (for example you should not
		1008	play around with an Xlib connection), then you have to seperately re-test
		1009	whether a file descriptor is really ready with a known-to-be good interface
		1010	such as poll (fortunately in our Xlib example, Xlib already does this on
		1011	its own, so its quite safe to use).
		1012
		1013	=head3 The special problem of disappearing file descriptors
		1014
		1015	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1016	descriptor (either by calling C<close> explicitly or by any other means,
		1017	such as C<dup>). The reason is that you register interest in some file
		1018	descriptor, but when it goes away, the operating system will silently drop
		1019	this interest. If another file descriptor with the same number then is
		1020	registered with libev, there is no efficient way to see that this is, in
		1021	fact, a different file descriptor.
		1022
		1023	To avoid having to explicitly tell libev about such cases, libev follows
		1024	the following policy: Each time C<ev_io_set> is being called, libev
		1025	will assume that this is potentially a new file descriptor, otherwise
		1026	it is assumed that the file descriptor stays the same. That means that
		1027	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1028	descriptor even if the file descriptor number itself did not change.
		1029
		1030	This is how one would do it normally anyway, the important point is that
		1031	the libev application should not optimise around libev but should leave
		1032	optimisations to libev.
		1033
		1034	=head3 The special problem of dup'ed file descriptors
		1035
		1036	Some backends (e.g. epoll), cannot register events for file descriptors,
		1037	but only events for the underlying file descriptions. That means when you
		1038	have C<dup ()>'ed file descriptors and register events for them, only one
		1039	file descriptor might actually receive events.
		1040
		1041	There is no workaround possible except not registering events
		1042	for potentially C<dup ()>'ed file descriptors, or to resort to
		1043	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1044
		1045	=head3 The special problem of fork
		1046
		1047	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1048	useless behaviour. Libev fully supports fork, but needs to be told about
		1049	it in the child.
		1050
		1051	To support fork in your programs, you either have to call
		1052	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1053	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1054	C<EVBACKEND_POLL>.
		1055
		1056
		1057	=head3 Watcher-Specific Functions
435		1058
436	=over 4	1059	=over 4
437		1060
438	=item ev_io_init (ev_io *, callback, int fd, int events)	1061	=item ev_io_init (ev_io *, callback, int fd, int events)
439		1062
440	=item ev_io_set (ev_io *, int fd, int events)	1063	=item ev_io_set (ev_io *, int fd, int events)
441		1064
442	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1065	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
443	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1066	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
444	EV_WRITE> to receive the given events.	1067	C<EV_READ | EV_WRITE> to receive the given events.
		1068
		1069	=item int fd [read-only]
		1070
		1071	The file descriptor being watched.
		1072
		1073	=item int events [read-only]
		1074
		1075	The events being watched.
445		1076
446	=back	1077	=back
447		1078
		1079	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1080	readable, but only once. Since it is likely line-buffered, you could
		1081	attempt to read a whole line in the callback.
		1082
		1083	static void
		1084	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1085	{
		1086	ev_io_stop (loop, w);
		1087	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1088	}
		1089
		1090	...
		1091	struct ev_loop *loop = ev_default_init (0);
		1092	struct ev_io stdin_readable;
		1093	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1094	ev_io_start (loop, &stdin_readable);
		1095	ev_loop (loop, 0);
		1096
		1097
448	=head2 C<ev_timer> - relative and optionally recurring timeouts	1098	=head2 C<ev_timer> - relative and optionally repeating timeouts
449		1099
450	Timer watchers are simple relative timers that generate an event after a	1100	Timer watchers are simple relative timers that generate an event after a
451	given time, and optionally repeating in regular intervals after that.	1101	given time, and optionally repeating in regular intervals after that.
452		1102
453	The timers are based on real time, that is, if you register an event that	1103	The timers are based on real time, that is, if you register an event that
454	times out after an hour and youreset your system clock to last years	1104	times out after an hour and you reset your system clock to last years
455	time, it will still time out after (roughly) and hour. "Roughly" because	1105	time, it will still time out after (roughly) and hour. "Roughly" because
456	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1106	detecting time jumps is hard, and some inaccuracies are unavoidable (the
457	monotonic clock option helps a lot here).	1107	monotonic clock option helps a lot here).
458		1108
459	The relative timeouts are calculated relative to the C<ev_now ()>	1109	The relative timeouts are calculated relative to the C<ev_now ()>
460	time. This is usually the right thing as this timestamp refers to the time	1110	time. This is usually the right thing as this timestamp refers to the time
461	of the event triggering whatever timeout you are modifying/starting. If	1111	of the event triggering whatever timeout you are modifying/starting. If
462	you suspect event processing to be delayed and you *need* to base the timeout	1112	you suspect event processing to be delayed and you I<need> to base the timeout
463	ion the current time, use something like this to adjust for this:	1113	on the current time, use something like this to adjust for this:
464		1114
465	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1115	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1116
		1117	The callback is guarenteed to be invoked only when its timeout has passed,
		1118	but if multiple timers become ready during the same loop iteration then
		1119	order of execution is undefined.
		1120
		1121	=head3 Watcher-Specific Functions and Data Members
466		1122
467	=over 4	1123	=over 4
468		1124
469	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1125	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
470		1126
…		…
476	later, again, and again, until stopped manually.	1132	later, again, and again, until stopped manually.
477		1133
478	The timer itself will do a best-effort at avoiding drift, that is, if you	1134	The timer itself will do a best-effort at avoiding drift, that is, if you
479	configure a timer to trigger every 10 seconds, then it will trigger at	1135	configure a timer to trigger every 10 seconds, then it will trigger at
480	exactly 10 second intervals. If, however, your program cannot keep up with	1136	exactly 10 second intervals. If, however, your program cannot keep up with
481	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1137	the timer (because it takes longer than those 10 seconds to do stuff) the
482	timer will not fire more than once per event loop iteration.	1138	timer will not fire more than once per event loop iteration.
483		1139
484	=item ev_timer_again (loop)	1140	=item ev_timer_again (loop)
485		1141
486	This will act as if the timer timed out and restart it again if it is	1142	This will act as if the timer timed out and restart it again if it is
487	repeating. The exact semantics are:	1143	repeating. The exact semantics are:
488		1144
		1145	If the timer is pending, its pending status is cleared.
		1146
489	If the timer is started but nonrepeating, stop it.	1147	If the timer is started but nonrepeating, stop it (as if it timed out).
490		1148
491	If the timer is repeating, either start it if necessary (with the repeat	1149	If the timer is repeating, either start it if necessary (with the
492	value), or reset the running timer to the repeat value.	1150	C<repeat> value), or reset the running timer to the C<repeat> value.
493		1151
494	This sounds a bit complicated, but here is a useful and typical	1152	This sounds a bit complicated, but here is a useful and typical
495	example: Imagine you have a tcp connection and you want a so-called idle	1153	example: Imagine you have a tcp connection and you want a so-called idle
496	timeout, that is, you want to be called when there have been, say, 60	1154	timeout, that is, you want to be called when there have been, say, 60
497	seconds of inactivity on the socket. The easiest way to do this is to	1155	seconds of inactivity on the socket. The easiest way to do this is to
498	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1156	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
499	time you successfully read or write some data. If you go into an idle	1157	C<ev_timer_again> each time you successfully read or write some data. If
500	state where you do not expect data to travel on the socket, you can stop	1158	you go into an idle state where you do not expect data to travel on the
501	the timer, and again will automatically restart it if need be.	1159	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1160	automatically restart it if need be.
		1161
		1162	That means you can ignore the C<after> value and C<ev_timer_start>
		1163	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1164
		1165	ev_timer_init (timer, callback, 0., 5.);
		1166	ev_timer_again (loop, timer);
		1167	...
		1168	timer->again = 17.;
		1169	ev_timer_again (loop, timer);
		1170	...
		1171	timer->again = 10.;
		1172	ev_timer_again (loop, timer);
		1173
		1174	This is more slightly efficient then stopping/starting the timer each time
		1175	you want to modify its timeout value.
		1176
		1177	=item ev_tstamp repeat [read-write]
		1178
		1179	The current C<repeat> value. Will be used each time the watcher times out
		1180	or C<ev_timer_again> is called and determines the next timeout (if any),
		1181	which is also when any modifications are taken into account.
502		1182
503	=back	1183	=back
504		1184
		1185	Example: Create a timer that fires after 60 seconds.
		1186
		1187	static void
		1188	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1189	{
		1190	.. one minute over, w is actually stopped right here
		1191	}
		1192
		1193	struct ev_timer mytimer;
		1194	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1195	ev_timer_start (loop, &mytimer);
		1196
		1197	Example: Create a timeout timer that times out after 10 seconds of
		1198	inactivity.
		1199
		1200	static void
		1201	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1202	{
		1203	.. ten seconds without any activity
		1204	}
		1205
		1206	struct ev_timer mytimer;
		1207	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1208	ev_timer_again (&mytimer); /* start timer */
		1209	ev_loop (loop, 0);
		1210
		1211	// and in some piece of code that gets executed on any "activity":
		1212	// reset the timeout to start ticking again at 10 seconds
		1213	ev_timer_again (&mytimer);
		1214
		1215
505	=head2 C<ev_periodic> - to cron or not to cron	1216	=head2 C<ev_periodic> - to cron or not to cron?
506		1217
507	Periodic watchers are also timers of a kind, but they are very versatile	1218	Periodic watchers are also timers of a kind, but they are very versatile
508	(and unfortunately a bit complex).	1219	(and unfortunately a bit complex).
509		1220
510	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1221	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
511	but on wallclock time (absolute time). You can tell a periodic watcher	1222	but on wallclock time (absolute time). You can tell a periodic watcher
512	to trigger "at" some specific point in time. For example, if you tell a	1223	to trigger "at" some specific point in time. For example, if you tell a
513	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1224	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
514	+ 10.>) and then reset your system clock to the last year, then it will	1225	+ 10.>) and then reset your system clock to the last year, then it will
515	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1226	take a year to trigger the event (unlike an C<ev_timer>, which would trigger
516	roughly 10 seconds later and of course not if you reset your system time	1227	roughly 10 seconds later).
517	again).
518		1228
519	They can also be used to implement vastly more complex timers, such as	1229	They can also be used to implement vastly more complex timers, such as
520	triggering an event on eahc midnight, local time.	1230	triggering an event on each midnight, local time or other, complicated,
		1231	rules.
		1232
		1233	As with timers, the callback is guarenteed to be invoked only when the
		1234	time (C<at>) has been passed, but if multiple periodic timers become ready
		1235	during the same loop iteration then order of execution is undefined.
		1236
		1237	=head3 Watcher-Specific Functions and Data Members
521		1238
522	=over 4	1239	=over 4
523		1240
524	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1241	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
525		1242
526	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1243	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
527		1244
528	Lots of arguments, lets sort it out... There are basically three modes of	1245	Lots of arguments, lets sort it out... There are basically three modes of
529	operation, and we will explain them from simplest to complex:	1246	operation, and we will explain them from simplest to complex:
530		1247
531
532	=over 4	1248	=over 4
533		1249
534	=item * absolute timer (interval = reschedule_cb = 0)	1250	=item * absolute timer (at = time, interval = reschedule_cb = 0)
535		1251
536	In this configuration the watcher triggers an event at the wallclock time	1252	In this configuration the watcher triggers an event at the wallclock time
537	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1253	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
538	that is, if it is to be run at January 1st 2011 then it will run when the	1254	that is, if it is to be run at January 1st 2011 then it will run when the
539	system time reaches or surpasses this time.	1255	system time reaches or surpasses this time.
540		1256
541	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1257	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
542		1258
543	In this mode the watcher will always be scheduled to time out at the next	1259	In this mode the watcher will always be scheduled to time out at the next
544	C<at + N * interval> time (for some integer N) and then repeat, regardless	1260	C<at + N * interval> time (for some integer N, which can also be negative)
545	of any time jumps.	1261	and then repeat, regardless of any time jumps.
546		1262
547	This can be used to create timers that do not drift with respect to system	1263	This can be used to create timers that do not drift with respect to system
548	time:	1264	time:
549		1265
550	ev_periodic_set (&periodic, 0., 3600., 0);	1266	ev_periodic_set (&periodic, 0., 3600., 0);
…		…
556		1272
557	Another way to think about it (for the mathematically inclined) is that	1273	Another way to think about it (for the mathematically inclined) is that
558	C<ev_periodic> will try to run the callback in this mode at the next possible	1274	C<ev_periodic> will try to run the callback in this mode at the next possible
559	time where C<time = at (mod interval)>, regardless of any time jumps.	1275	time where C<time = at (mod interval)>, regardless of any time jumps.
560		1276
		1277	For numerical stability it is preferable that the C<at> value is near
		1278	C<ev_now ()> (the current time), but there is no range requirement for
		1279	this value.
		1280
561	=item * manual reschedule mode (reschedule_cb = callback)	1281	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
562		1282
563	In this mode the values for C<interval> and C<at> are both being	1283	In this mode the values for C<interval> and C<at> are both being
564	ignored. Instead, each time the periodic watcher gets scheduled, the	1284	ignored. Instead, each time the periodic watcher gets scheduled, the
565	reschedule callback will be called with the watcher as first, and the	1285	reschedule callback will be called with the watcher as first, and the
566	current time as second argument.	1286	current time as second argument.
567		1287
568	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1288	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
569	ever, or make any event loop modifications>. If you need to stop it,	1289	ever, or make any event loop modifications>. If you need to stop it,
570	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1290	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
571	starting a prepare watcher).	1291	starting an C<ev_prepare> watcher, which is legal).
572		1292
573	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1293	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
574	ev_tstamp now)>, e.g.:	1294	ev_tstamp now)>, e.g.:
575		1295
576	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1296	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
…		…
582	(that is, the lowest time value larger than to the second argument). It	1302	(that is, the lowest time value larger than to the second argument). It
583	will usually be called just before the callback will be triggered, but	1303	will usually be called just before the callback will be triggered, but
584	might be called at other times, too.	1304	might be called at other times, too.
585		1305
586	NOTE: I<< This callback must always return a time that is later than the	1306	NOTE: I<< This callback must always return a time that is later than the
587	passed C<now> value >>. Not even C<now> itself will do, it must be larger.	1307	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
588		1308
589	This can be used to create very complex timers, such as a timer that	1309	This can be used to create very complex timers, such as a timer that
590	triggers on each midnight, local time. To do this, you would calculate the	1310	triggers on each midnight, local time. To do this, you would calculate the
591	next midnight after C<now> and return the timestamp value for this. How you do this	1311	next midnight after C<now> and return the timestamp value for this. How
592	is, again, up to you (but it is not trivial).	1312	you do this is, again, up to you (but it is not trivial, which is the main
		1313	reason I omitted it as an example).
593		1314
594	=back	1315	=back
595		1316
596	=item ev_periodic_again (loop, ev_periodic *)	1317	=item ev_periodic_again (loop, ev_periodic *)
597		1318
598	Simply stops and restarts the periodic watcher again. This is only useful	1319	Simply stops and restarts the periodic watcher again. This is only useful
599	when you changed some parameters or the reschedule callback would return	1320	when you changed some parameters or the reschedule callback would return
600	a different time than the last time it was called (e.g. in a crond like	1321	a different time than the last time it was called (e.g. in a crond like
601	program when the crontabs have changed).	1322	program when the crontabs have changed).
602		1323
		1324	=item ev_tstamp offset [read-write]
		1325
		1326	When repeating, this contains the offset value, otherwise this is the
		1327	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1328
		1329	Can be modified any time, but changes only take effect when the periodic
		1330	timer fires or C<ev_periodic_again> is being called.
		1331
		1332	=item ev_tstamp interval [read-write]
		1333
		1334	The current interval value. Can be modified any time, but changes only
		1335	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1336	called.
		1337
		1338	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1339
		1340	The current reschedule callback, or C<0>, if this functionality is
		1341	switched off. Can be changed any time, but changes only take effect when
		1342	the periodic timer fires or C<ev_periodic_again> is being called.
		1343
		1344	=item ev_tstamp at [read-only]
		1345
		1346	When active, contains the absolute time that the watcher is supposed to
		1347	trigger next.
		1348
603	=back	1349	=back
604		1350
		1351	Example: Call a callback every hour, or, more precisely, whenever the
		1352	system clock is divisible by 3600. The callback invocation times have
		1353	potentially a lot of jittering, but good long-term stability.
		1354
		1355	static void
		1356	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1357	{
		1358	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1359	}
		1360
		1361	struct ev_periodic hourly_tick;
		1362	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1363	ev_periodic_start (loop, &hourly_tick);
		1364
		1365	Example: The same as above, but use a reschedule callback to do it:
		1366
		1367	#include <math.h>
		1368
		1369	static ev_tstamp
		1370	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1371	{
		1372	return fmod (now, 3600.) + 3600.;
		1373	}
		1374
		1375	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1376
		1377	Example: Call a callback every hour, starting now:
		1378
		1379	struct ev_periodic hourly_tick;
		1380	ev_periodic_init (&hourly_tick, clock_cb,
		1381	fmod (ev_now (loop), 3600.), 3600., 0);
		1382	ev_periodic_start (loop, &hourly_tick);
		1383
		1384
605	=head2 C<ev_signal> - signal me when a signal gets signalled	1385	=head2 C<ev_signal> - signal me when a signal gets signalled!
606		1386
607	Signal watchers will trigger an event when the process receives a specific	1387	Signal watchers will trigger an event when the process receives a specific
608	signal one or more times. Even though signals are very asynchronous, libev	1388	signal one or more times. Even though signals are very asynchronous, libev
609	will try it's best to deliver signals synchronously, i.e. as part of the	1389	will try it's best to deliver signals synchronously, i.e. as part of the
610	normal event processing, like any other event.	1390	normal event processing, like any other event.
…		…
614	with the kernel (thus it coexists with your own signal handlers as long	1394	with the kernel (thus it coexists with your own signal handlers as long
615	as you don't register any with libev). Similarly, when the last signal	1395	as you don't register any with libev). Similarly, when the last signal
616	watcher for a signal is stopped libev will reset the signal handler to	1396	watcher for a signal is stopped libev will reset the signal handler to
617	SIG_DFL (regardless of what it was set to before).	1397	SIG_DFL (regardless of what it was set to before).
618		1398
		1399	=head3 Watcher-Specific Functions and Data Members
		1400
619	=over 4	1401	=over 4
620		1402
621	=item ev_signal_init (ev_signal *, callback, int signum)	1403	=item ev_signal_init (ev_signal *, callback, int signum)
622		1404
623	=item ev_signal_set (ev_signal *, int signum)	1405	=item ev_signal_set (ev_signal *, int signum)
624		1406
625	Configures the watcher to trigger on the given signal number (usually one	1407	Configures the watcher to trigger on the given signal number (usually one
626	of the C<SIGxxx> constants).	1408	of the C<SIGxxx> constants).
627		1409
		1410	=item int signum [read-only]
		1411
		1412	The signal the watcher watches out for.
		1413
628	=back	1414	=back
629		1415
		1416
630	=head2 C<ev_child> - wait for pid status changes	1417	=head2 C<ev_child> - watch out for process status changes
631		1418
632	Child watchers trigger when your process receives a SIGCHLD in response to	1419	Child watchers trigger when your process receives a SIGCHLD in response to
633	some child status changes (most typically when a child of yours dies).	1420	some child status changes (most typically when a child of yours dies).
		1421
		1422	=head3 Watcher-Specific Functions and Data Members
634		1423
635	=over 4	1424	=over 4
636		1425
637	=item ev_child_init (ev_child *, callback, int pid)	1426	=item ev_child_init (ev_child *, callback, int pid)
638		1427
…		…
643	at the C<rstatus> member of the C<ev_child> watcher structure to see	1432	at the C<rstatus> member of the C<ev_child> watcher structure to see
644	the status word (use the macros from C<sys/wait.h> and see your systems	1433	the status word (use the macros from C<sys/wait.h> and see your systems
645	C<waitpid> documentation). The C<rpid> member contains the pid of the	1434	C<waitpid> documentation). The C<rpid> member contains the pid of the
646	process causing the status change.	1435	process causing the status change.
647		1436
		1437	=item int pid [read-only]
		1438
		1439	The process id this watcher watches out for, or C<0>, meaning any process id.
		1440
		1441	=item int rpid [read-write]
		1442
		1443	The process id that detected a status change.
		1444
		1445	=item int rstatus [read-write]
		1446
		1447	The process exit/trace status caused by C<rpid> (see your systems
		1448	C<waitpid> and C<sys/wait.h> documentation for details).
		1449
648	=back	1450	=back
649		1451
		1452	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1453
		1454	static void
		1455	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1456	{
		1457	ev_unloop (loop, EVUNLOOP_ALL);
		1458	}
		1459
		1460	struct ev_signal signal_watcher;
		1461	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1462	ev_signal_start (loop, &sigint_cb);
		1463
		1464
		1465	=head2 C<ev_stat> - did the file attributes just change?
		1466
		1467	This watches a filesystem path for attribute changes. That is, it calls
		1468	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1469	compared to the last time, invoking the callback if it did.
		1470
		1471	The path does not need to exist: changing from "path exists" to "path does
		1472	not exist" is a status change like any other. The condition "path does
		1473	not exist" is signified by the C<st_nlink> field being zero (which is
		1474	otherwise always forced to be at least one) and all the other fields of
		1475	the stat buffer having unspecified contents.
		1476
		1477	The path I<should> be absolute and I<must not> end in a slash. If it is
		1478	relative and your working directory changes, the behaviour is undefined.
		1479
		1480	Since there is no standard to do this, the portable implementation simply
		1481	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1482	can specify a recommended polling interval for this case. If you specify
		1483	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1484	unspecified default> value will be used (which you can expect to be around
		1485	five seconds, although this might change dynamically). Libev will also
		1486	impose a minimum interval which is currently around C<0.1>, but thats
		1487	usually overkill.
		1488
		1489	This watcher type is not meant for massive numbers of stat watchers,
		1490	as even with OS-supported change notifications, this can be
		1491	resource-intensive.
		1492
		1493	At the time of this writing, only the Linux inotify interface is
		1494	implemented (implementing kqueue support is left as an exercise for the
		1495	reader). Inotify will be used to give hints only and should not change the
		1496	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1497	to fall back to regular polling again even with inotify, but changes are
		1498	usually detected immediately, and if the file exists there will be no
		1499	polling.
		1500
		1501	=head3 The special problem of stat time resolution
		1502
		1503	The C<stat ()> syscall only supports full-second resolution portably, and
		1504	even on systems where the resolution is higher, many filesystems still
		1505	only support whole seconds.
		1506
		1507	That means that, if the time is the only thing that changes, you might
		1508	miss updates: on the first update, C<ev_stat> detects a change and calls
		1509	your callback, which does something. When there is another update within
		1510	the same second, C<ev_stat> will be unable to detect it.
		1511
		1512	The solution to this is to delay acting on a change for a second (or till
		1513	the next second boundary), using a roughly one-second delay C<ev_timer>
		1514	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1515	is added to work around small timing inconsistencies of some operating
		1516	systems.
		1517
		1518	=head3 Watcher-Specific Functions and Data Members
		1519
		1520	=over 4
		1521
		1522	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1523
		1524	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1525
		1526	Configures the watcher to wait for status changes of the given
		1527	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1528	be detected and should normally be specified as C<0> to let libev choose
		1529	a suitable value. The memory pointed to by C<path> must point to the same
		1530	path for as long as the watcher is active.
		1531
		1532	The callback will be receive C<EV_STAT> when a change was detected,
		1533	relative to the attributes at the time the watcher was started (or the
		1534	last change was detected).
		1535
		1536	=item ev_stat_stat (ev_stat *)
		1537
		1538	Updates the stat buffer immediately with new values. If you change the
		1539	watched path in your callback, you could call this fucntion to avoid
		1540	detecting this change (while introducing a race condition). Can also be
		1541	useful simply to find out the new values.
		1542
		1543	=item ev_statdata attr [read-only]
		1544
		1545	The most-recently detected attributes of the file. Although the type is of
		1546	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1547	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1548	was some error while C<stat>ing the file.
		1549
		1550	=item ev_statdata prev [read-only]
		1551
		1552	The previous attributes of the file. The callback gets invoked whenever
		1553	C<prev> != C<attr>.
		1554
		1555	=item ev_tstamp interval [read-only]
		1556
		1557	The specified interval.
		1558
		1559	=item const char *path [read-only]
		1560
		1561	The filesystem path that is being watched.
		1562
		1563	=back
		1564
		1565	Example: Watch C</etc/passwd> for attribute changes.
		1566
		1567	static void
		1568	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1569	{
		1570	/* /etc/passwd changed in some way */
		1571	if (w->attr.st_nlink)
		1572	{
		1573	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1574	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1575	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1576	}
		1577	else
		1578	/* you shalt not abuse printf for puts */
		1579	puts ("wow, /etc/passwd is not there, expect problems. "
		1580	"if this is windows, they already arrived\n");
		1581	}
		1582
		1583	...
		1584	ev_stat passwd;
		1585
		1586	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1587	ev_stat_start (loop, &passwd);
		1588
		1589	Example: Like above, but additionally use a one-second delay so we do not
		1590	miss updates (however, frequent updates will delay processing, too, so
		1591	one might do the work both on C<ev_stat> callback invocation I<and> on
		1592	C<ev_timer> callback invocation).
		1593
		1594	static ev_stat passwd;
		1595	static ev_timer timer;
		1596
		1597	static void
		1598	timer_cb (EV_P_ ev_timer *w, int revents)
		1599	{
		1600	ev_timer_stop (EV_A_ w);
		1601
		1602	/* now it's one second after the most recent passwd change */
		1603	}
		1604
		1605	static void
		1606	stat_cb (EV_P_ ev_stat *w, int revents)
		1607	{
		1608	/* reset the one-second timer */
		1609	ev_timer_again (EV_A_ &timer);
		1610	}
		1611
		1612	...
		1613	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1614	ev_stat_start (loop, &passwd);
		1615	ev_timer_init (&timer, timer_cb, 0., 1.01);
		1616
		1617
650	=head2 C<ev_idle> - when you've got nothing better to do	1618	=head2 C<ev_idle> - when you've got nothing better to do...
651		1619
652	Idle watchers trigger events when there are no other events are pending	1620	Idle watchers trigger events when no other events of the same or higher
653	(prepare, check and other idle watchers do not count). That is, as long	1621	priority are pending (prepare, check and other idle watchers do not
654	as your process is busy handling sockets or timeouts (or even signals,	1622	count).
655	imagine) it will not be triggered. But when your process is idle all idle	1623
656	watchers are being called again and again, once per event loop iteration -	1624	That is, as long as your process is busy handling sockets or timeouts
		1625	(or even signals, imagine) of the same or higher priority it will not be
		1626	triggered. But when your process is idle (or only lower-priority watchers
		1627	are pending), the idle watchers are being called once per event loop
657	until stopped, that is, or your process receives more events and becomes	1628	iteration - until stopped, that is, or your process receives more events
658	busy.	1629	and becomes busy again with higher priority stuff.
659		1630
660	The most noteworthy effect is that as long as any idle watchers are	1631	The most noteworthy effect is that as long as any idle watchers are
661	active, the process will not block when waiting for new events.	1632	active, the process will not block when waiting for new events.
662		1633
663	Apart from keeping your process non-blocking (which is a useful	1634	Apart from keeping your process non-blocking (which is a useful
664	effect on its own sometimes), idle watchers are a good place to do	1635	effect on its own sometimes), idle watchers are a good place to do
665	"pseudo-background processing", or delay processing stuff to after the	1636	"pseudo-background processing", or delay processing stuff to after the
666	event loop has handled all outstanding events.	1637	event loop has handled all outstanding events.
667		1638
		1639	=head3 Watcher-Specific Functions and Data Members
		1640
668	=over 4	1641	=over 4
669		1642
670	=item ev_idle_init (ev_signal *, callback)	1643	=item ev_idle_init (ev_signal *, callback)
671		1644
672	Initialises and configures the idle watcher - it has no parameters of any	1645	Initialises and configures the idle watcher - it has no parameters of any
673	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1646	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
674	believe me.	1647	believe me.
675		1648
676	=back	1649	=back
677		1650
		1651	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1652	callback, free it. Also, use no error checking, as usual.
		1653
		1654	static void
		1655	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1656	{
		1657	free (w);
		1658	// now do something you wanted to do when the program has
		1659	// no longer asnything immediate to do.
		1660	}
		1661
		1662	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1663	ev_idle_init (idle_watcher, idle_cb);
		1664	ev_idle_start (loop, idle_cb);
		1665
		1666
678	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1667	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
679		1668
680	Prepare and check watchers are usually (but not always) used in tandem:	1669	Prepare and check watchers are usually (but not always) used in tandem:
681	Prepare watchers get invoked before the process blocks and check watchers	1670	prepare watchers get invoked before the process blocks and check watchers
682	afterwards.	1671	afterwards.
683		1672
		1673	You I<must not> call C<ev_loop> or similar functions that enter
		1674	the current event loop from either C<ev_prepare> or C<ev_check>
		1675	watchers. Other loops than the current one are fine, however. The
		1676	rationale behind this is that you do not need to check for recursion in
		1677	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1678	C<ev_check> so if you have one watcher of each kind they will always be
		1679	called in pairs bracketing the blocking call.
		1680
684	Their main purpose is to integrate other event mechanisms into libev. This	1681	Their main purpose is to integrate other event mechanisms into libev and
685	could be used, for example, to track variable changes, implement your own	1682	their use is somewhat advanced. This could be used, for example, to track
686	watchers, integrate net-snmp or a coroutine library and lots more.	1683	variable changes, implement your own watchers, integrate net-snmp or a
		1684	coroutine library and lots more. They are also occasionally useful if
		1685	you cache some data and want to flush it before blocking (for example,
		1686	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1687	watcher).
687		1688
688	This is done by examining in each prepare call which file descriptors need	1689	This is done by examining in each prepare call which file descriptors need
689	to be watched by the other library, registering C<ev_io> watchers for	1690	to be watched by the other library, registering C<ev_io> watchers for
690	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1691	them and starting an C<ev_timer> watcher for any timeouts (many libraries
691	provide just this functionality). Then, in the check watcher you check for	1692	provide just this functionality). Then, in the check watcher you check for
692	any events that occured (by checking the pending status of all watchers	1693	any events that occured (by checking the pending status of all watchers
693	and stopping them) and call back into the library. The I/O and timer	1694	and stopping them) and call back into the library. The I/O and timer
694	callbacks will never actually be called (but must be valid neverthelles,	1695	callbacks will never actually be called (but must be valid nevertheless,
695	because you never know, you know?).	1696	because you never know, you know?).
696		1697
697	As another example, the Perl Coro module uses these hooks to integrate	1698	As another example, the Perl Coro module uses these hooks to integrate
698	coroutines into libev programs, by yielding to other active coroutines	1699	coroutines into libev programs, by yielding to other active coroutines
699	during each prepare and only letting the process block if no coroutines	1700	during each prepare and only letting the process block if no coroutines
700	are ready to run (its actually more complicated, it only runs coroutines	1701	are ready to run (it's actually more complicated: it only runs coroutines
701	with priority higher than the event loop and one lower priority once,	1702	with priority higher than or equal to the event loop and one coroutine
702	using idle watchers to keep the event loop from blocking if lower-priority	1703	of lower priority, but only once, using idle watchers to keep the event
703	coroutines exist, thus mapping low-priority coroutines to idle/background	1704	loop from blocking if lower-priority coroutines are active, thus mapping
704	tasks).	1705	low-priority coroutines to idle/background tasks).
		1706
		1707	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1708	priority, to ensure that they are being run before any other watchers
		1709	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1710	too) should not activate ("feed") events into libev. While libev fully
		1711	supports this, they will be called before other C<ev_check> watchers
		1712	did their job. As C<ev_check> watchers are often used to embed other
		1713	(non-libev) event loops those other event loops might be in an unusable
		1714	state until their C<ev_check> watcher ran (always remind yourself to
		1715	coexist peacefully with others).
		1716
		1717	=head3 Watcher-Specific Functions and Data Members
705		1718
706	=over 4	1719	=over 4
707		1720
708	=item ev_prepare_init (ev_prepare *, callback)	1721	=item ev_prepare_init (ev_prepare *, callback)
709		1722
…		…
713	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1726	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
714	macros, but using them is utterly, utterly and completely pointless.	1727	macros, but using them is utterly, utterly and completely pointless.
715		1728
716	=back	1729	=back
717		1730
		1731	There are a number of principal ways to embed other event loops or modules
		1732	into libev. Here are some ideas on how to include libadns into libev
		1733	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1734	use for an actually working example. Another Perl module named C<EV::Glib>
		1735	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
		1736	into the Glib event loop).
		1737
		1738	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1739	and in a check watcher, destroy them and call into libadns. What follows
		1740	is pseudo-code only of course. This requires you to either use a low
		1741	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1742	the callbacks for the IO/timeout watchers might not have been called yet.
		1743
		1744	static ev_io iow [nfd];
		1745	static ev_timer tw;
		1746
		1747	static void
		1748	io_cb (ev_loop *loop, ev_io *w, int revents)
		1749	{
		1750	}
		1751
		1752	// create io watchers for each fd and a timer before blocking
		1753	static void
		1754	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1755	{
		1756	int timeout = 3600000;
		1757	struct pollfd fds [nfd];
		1758	// actual code will need to loop here and realloc etc.
		1759	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1760
		1761	/* the callback is illegal, but won't be called as we stop during check */
		1762	ev_timer_init (&tw, 0, timeout * 1e-3);
		1763	ev_timer_start (loop, &tw);
		1764
		1765	// create one ev_io per pollfd
		1766	for (int i = 0; i < nfd; ++i)
		1767	{
		1768	ev_io_init (iow + i, io_cb, fds [i].fd,
		1769	((fds [i].events & POLLIN ? EV_READ : 0)
		1770	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1771
		1772	fds [i].revents = 0;
		1773	ev_io_start (loop, iow + i);
		1774	}
		1775	}
		1776
		1777	// stop all watchers after blocking
		1778	static void
		1779	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1780	{
		1781	ev_timer_stop (loop, &tw);
		1782
		1783	for (int i = 0; i < nfd; ++i)
		1784	{
		1785	// set the relevant poll flags
		1786	// could also call adns_processreadable etc. here
		1787	struct pollfd *fd = fds + i;
		1788	int revents = ev_clear_pending (iow + i);
		1789	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1790	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1791
		1792	// now stop the watcher
		1793	ev_io_stop (loop, iow + i);
		1794	}
		1795
		1796	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1797	}
		1798
		1799	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1800	in the prepare watcher and would dispose of the check watcher.
		1801
		1802	Method 3: If the module to be embedded supports explicit event
		1803	notification (adns does), you can also make use of the actual watcher
		1804	callbacks, and only destroy/create the watchers in the prepare watcher.
		1805
		1806	static void
		1807	timer_cb (EV_P_ ev_timer *w, int revents)
		1808	{
		1809	adns_state ads = (adns_state)w->data;
		1810	update_now (EV_A);
		1811
		1812	adns_processtimeouts (ads, &tv_now);
		1813	}
		1814
		1815	static void
		1816	io_cb (EV_P_ ev_io *w, int revents)
		1817	{
		1818	adns_state ads = (adns_state)w->data;
		1819	update_now (EV_A);
		1820
		1821	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1822	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1823	}
		1824
		1825	// do not ever call adns_afterpoll
		1826
		1827	Method 4: Do not use a prepare or check watcher because the module you
		1828	want to embed is too inflexible to support it. Instead, youc na override
		1829	their poll function. The drawback with this solution is that the main
		1830	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1831	this.
		1832
		1833	static gint
		1834	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		1835	{
		1836	int got_events = 0;
		1837
		1838	for (n = 0; n < nfds; ++n)
		1839	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		1840
		1841	if (timeout >= 0)
		1842	// create/start timer
		1843
		1844	// poll
		1845	ev_loop (EV_A_ 0);
		1846
		1847	// stop timer again
		1848	if (timeout >= 0)
		1849	ev_timer_stop (EV_A_ &to);
		1850
		1851	// stop io watchers again - their callbacks should have set
		1852	for (n = 0; n < nfds; ++n)
		1853	ev_io_stop (EV_A_ iow [n]);
		1854
		1855	return got_events;
		1856	}
		1857
		1858
		1859	=head2 C<ev_embed> - when one backend isn't enough...
		1860
		1861	This is a rather advanced watcher type that lets you embed one event loop
		1862	into another (currently only C<ev_io> events are supported in the embedded
		1863	loop, other types of watchers might be handled in a delayed or incorrect
		1864	fashion and must not be used).
		1865
		1866	There are primarily two reasons you would want that: work around bugs and
		1867	prioritise I/O.
		1868
		1869	As an example for a bug workaround, the kqueue backend might only support
		1870	sockets on some platform, so it is unusable as generic backend, but you
		1871	still want to make use of it because you have many sockets and it scales
		1872	so nicely. In this case, you would create a kqueue-based loop and embed it
		1873	into your default loop (which might use e.g. poll). Overall operation will
		1874	be a bit slower because first libev has to poll and then call kevent, but
		1875	at least you can use both at what they are best.
		1876
		1877	As for prioritising I/O: rarely you have the case where some fds have
		1878	to be watched and handled very quickly (with low latency), and even
		1879	priorities and idle watchers might have too much overhead. In this case
		1880	you would put all the high priority stuff in one loop and all the rest in
		1881	a second one, and embed the second one in the first.
		1882
		1883	As long as the watcher is active, the callback will be invoked every time
		1884	there might be events pending in the embedded loop. The callback must then
		1885	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		1886	their callbacks (you could also start an idle watcher to give the embedded
		1887	loop strictly lower priority for example). You can also set the callback
		1888	to C<0>, in which case the embed watcher will automatically execute the
		1889	embedded loop sweep.
		1890
		1891	As long as the watcher is started it will automatically handle events. The
		1892	callback will be invoked whenever some events have been handled. You can
		1893	set the callback to C<0> to avoid having to specify one if you are not
		1894	interested in that.
		1895
		1896	Also, there have not currently been made special provisions for forking:
		1897	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1898	but you will also have to stop and restart any C<ev_embed> watchers
		1899	yourself.
		1900
		1901	Unfortunately, not all backends are embeddable, only the ones returned by
		1902	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1903	portable one.
		1904
		1905	So when you want to use this feature you will always have to be prepared
		1906	that you cannot get an embeddable loop. The recommended way to get around
		1907	this is to have a separate variables for your embeddable loop, try to
		1908	create it, and if that fails, use the normal loop for everything:
		1909
		1910	struct ev_loop *loop_hi = ev_default_init (0);
		1911	struct ev_loop *loop_lo = 0;
		1912	struct ev_embed embed;
		1913
		1914	// see if there is a chance of getting one that works
		1915	// (remember that a flags value of 0 means autodetection)
		1916	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		1917	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		1918	: 0;
		1919
		1920	// if we got one, then embed it, otherwise default to loop_hi
		1921	if (loop_lo)
		1922	{
		1923	ev_embed_init (&embed, 0, loop_lo);
		1924	ev_embed_start (loop_hi, &embed);
		1925	}
		1926	else
		1927	loop_lo = loop_hi;
		1928
		1929	=head3 Watcher-Specific Functions and Data Members
		1930
		1931	=over 4
		1932
		1933	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		1934
		1935	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		1936
		1937	Configures the watcher to embed the given loop, which must be
		1938	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1939	invoked automatically, otherwise it is the responsibility of the callback
		1940	to invoke it (it will continue to be called until the sweep has been done,
		1941	if you do not want thta, you need to temporarily stop the embed watcher).
		1942
		1943	=item ev_embed_sweep (loop, ev_embed *)
		1944
		1945	Make a single, non-blocking sweep over the embedded loop. This works
		1946	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1947	apropriate way for embedded loops.
		1948
		1949	=item struct ev_loop *other [read-only]
		1950
		1951	The embedded event loop.
		1952
		1953	=back
		1954
		1955
		1956	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		1957
		1958	Fork watchers are called when a C<fork ()> was detected (usually because
		1959	whoever is a good citizen cared to tell libev about it by calling
		1960	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		1961	event loop blocks next and before C<ev_check> watchers are being called,
		1962	and only in the child after the fork. If whoever good citizen calling
		1963	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		1964	handlers will be invoked, too, of course.
		1965
		1966	=head3 Watcher-Specific Functions and Data Members
		1967
		1968	=over 4
		1969
		1970	=item ev_fork_init (ev_signal *, callback)
		1971
		1972	Initialises and configures the fork watcher - it has no parameters of any
		1973	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		1974	believe me.
		1975
		1976	=back
		1977
		1978
718	=head1 OTHER FUNCTIONS	1979	=head1 OTHER FUNCTIONS
719		1980
720	There are some other functions of possible interest. Described. Here. Now.	1981	There are some other functions of possible interest. Described. Here. Now.
721		1982
722	=over 4	1983	=over 4
…		…
724	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	1985	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
725		1986
726	This function combines a simple timer and an I/O watcher, calls your	1987	This function combines a simple timer and an I/O watcher, calls your
727	callback on whichever event happens first and automatically stop both	1988	callback on whichever event happens first and automatically stop both
728	watchers. This is useful if you want to wait for a single event on an fd	1989	watchers. This is useful if you want to wait for a single event on an fd
729	or timeout without havign to allocate/configure/start/stop/free one or	1990	or timeout without having to allocate/configure/start/stop/free one or
730	more watchers yourself.	1991	more watchers yourself.
731		1992
732	If C<fd> is less than 0, then no I/O watcher will be started and events	1993	If C<fd> is less than 0, then no I/O watcher will be started and events
733	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	1994	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
734	C<events> set will be craeted and started.	1995	C<events> set will be craeted and started.
…		…
737	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	1998	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
738	repeat = 0) will be started. While C<0> is a valid timeout, it is of	1999	repeat = 0) will be started. While C<0> is a valid timeout, it is of
739	dubious value.	2000	dubious value.
740		2001
741	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2002	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
742	passed an events set like normal event callbacks (with a combination of	2003	passed an C<revents> set like normal event callbacks (a combination of
743	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2004	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
744	value passed to C<ev_once>:	2005	value passed to C<ev_once>:
745		2006
746	static void stdin_ready (int revents, void *arg)	2007	static void stdin_ready (int revents, void *arg)
747	{	2008	{
…		…
751	/* stdin might have data for us, joy! */;	2012	/* stdin might have data for us, joy! */;
752	}	2013	}
753		2014
754	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2015	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
755		2016
756	=item ev_feed_event (loop, watcher, int events)	2017	=item ev_feed_event (ev_loop *, watcher *, int revents)
757		2018
758	Feeds the given event set into the event loop, as if the specified event	2019	Feeds the given event set into the event loop, as if the specified event
759	had happened for the specified watcher (which must be a pointer to an	2020	had happened for the specified watcher (which must be a pointer to an
760	initialised but not necessarily started event watcher).	2021	initialised but not necessarily started event watcher).
761		2022
762	=item ev_feed_fd_event (loop, int fd, int revents)	2023	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
763		2024
764	Feed an event on the given fd, as if a file descriptor backend detected	2025	Feed an event on the given fd, as if a file descriptor backend detected
765	the given events it.	2026	the given events it.
766		2027
767	=item ev_feed_signal_event (loop, int signum)	2028	=item ev_feed_signal_event (ev_loop *loop, int signum)
768		2029
769	Feed an event as if the given signal occured (loop must be the default loop!).	2030	Feed an event as if the given signal occured (C<loop> must be the default
		2031	loop!).
770		2032
771	=back	2033	=back
772		2034
		2035
		2036	=head1 LIBEVENT EMULATION
		2037
		2038	Libev offers a compatibility emulation layer for libevent. It cannot
		2039	emulate the internals of libevent, so here are some usage hints:
		2040
		2041	=over 4
		2042
		2043	=item * Use it by including <event.h>, as usual.
		2044
		2045	=item * The following members are fully supported: ev_base, ev_callback,
		2046	ev_arg, ev_fd, ev_res, ev_events.
		2047
		2048	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2049	maintained by libev, it does not work exactly the same way as in libevent (consider
		2050	it a private API).
		2051
		2052	=item * Priorities are not currently supported. Initialising priorities
		2053	will fail and all watchers will have the same priority, even though there
		2054	is an ev_pri field.
		2055
		2056	=item * Other members are not supported.
		2057
		2058	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2059	to use the libev header file and library.
		2060
		2061	=back
		2062
		2063	=head1 C++ SUPPORT
		2064
		2065	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2066	you to use some convinience methods to start/stop watchers and also change
		2067	the callback model to a model using method callbacks on objects.
		2068
		2069	To use it,
		2070
		2071	#include <ev++.h>
		2072
		2073	This automatically includes F<ev.h> and puts all of its definitions (many
		2074	of them macros) into the global namespace. All C++ specific things are
		2075	put into the C<ev> namespace. It should support all the same embedding
		2076	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2077
		2078	Care has been taken to keep the overhead low. The only data member the C++
		2079	classes add (compared to plain C-style watchers) is the event loop pointer
		2080	that the watcher is associated with (or no additional members at all if
		2081	you disable C<EV_MULTIPLICITY> when embedding libev).
		2082
		2083	Currently, functions, and static and non-static member functions can be
		2084	used as callbacks. Other types should be easy to add as long as they only
		2085	need one additional pointer for context. If you need support for other
		2086	types of functors please contact the author (preferably after implementing
		2087	it).
		2088
		2089	Here is a list of things available in the C<ev> namespace:
		2090
		2091	=over 4
		2092
		2093	=item C<ev::READ>, C<ev::WRITE> etc.
		2094
		2095	These are just enum values with the same values as the C<EV_READ> etc.
		2096	macros from F<ev.h>.
		2097
		2098	=item C<ev::tstamp>, C<ev::now>
		2099
		2100	Aliases to the same types/functions as with the C<ev_> prefix.
		2101
		2102	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2103
		2104	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2105	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2106	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2107	defines by many implementations.
		2108
		2109	All of those classes have these methods:
		2110
		2111	=over 4
		2112
		2113	=item ev::TYPE::TYPE ()
		2114
		2115	=item ev::TYPE::TYPE (struct ev_loop *)
		2116
		2117	=item ev::TYPE::~TYPE
		2118
		2119	The constructor (optionally) takes an event loop to associate the watcher
		2120	with. If it is omitted, it will use C<EV_DEFAULT>.
		2121
		2122	The constructor calls C<ev_init> for you, which means you have to call the
		2123	C<set> method before starting it.
		2124
		2125	It will not set a callback, however: You have to call the templated C<set>
		2126	method to set a callback before you can start the watcher.
		2127
		2128	(The reason why you have to use a method is a limitation in C++ which does
		2129	not allow explicit template arguments for constructors).
		2130
		2131	The destructor automatically stops the watcher if it is active.
		2132
		2133	=item w->set<class, &class::method> (object *)
		2134
		2135	This method sets the callback method to call. The method has to have a
		2136	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2137	first argument and the C<revents> as second. The object must be given as
		2138	parameter and is stored in the C<data> member of the watcher.
		2139
		2140	This method synthesizes efficient thunking code to call your method from
		2141	the C callback that libev requires. If your compiler can inline your
		2142	callback (i.e. it is visible to it at the place of the C<set> call and
		2143	your compiler is good :), then the method will be fully inlined into the
		2144	thunking function, making it as fast as a direct C callback.
		2145
		2146	Example: simple class declaration and watcher initialisation
		2147
		2148	struct myclass
		2149	{
		2150	void io_cb (ev::io &w, int revents) { }
		2151	}
		2152
		2153	myclass obj;
		2154	ev::io iow;
		2155	iow.set <myclass, &myclass::io_cb> (&obj);
		2156
		2157	=item w->set<function> (void *data = 0)
		2158
		2159	Also sets a callback, but uses a static method or plain function as
		2160	callback. The optional C<data> argument will be stored in the watcher's
		2161	C<data> member and is free for you to use.
		2162
		2163	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2164
		2165	See the method-C<set> above for more details.
		2166
		2167	Example:
		2168
		2169	static void io_cb (ev::io &w, int revents) { }
		2170	iow.set <io_cb> ();
		2171
		2172	=item w->set (struct ev_loop *)
		2173
		2174	Associates a different C<struct ev_loop> with this watcher. You can only
		2175	do this when the watcher is inactive (and not pending either).
		2176
		2177	=item w->set ([args])
		2178
		2179	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2180	called at least once. Unlike the C counterpart, an active watcher gets
		2181	automatically stopped and restarted when reconfiguring it with this
		2182	method.
		2183
		2184	=item w->start ()
		2185
		2186	Starts the watcher. Note that there is no C<loop> argument, as the
		2187	constructor already stores the event loop.
		2188
		2189	=item w->stop ()
		2190
		2191	Stops the watcher if it is active. Again, no C<loop> argument.
		2192
		2193	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2194
		2195	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2196	C<ev_TYPE_again> function.
		2197
		2198	=item w->sweep () (C<ev::embed> only)
		2199
		2200	Invokes C<ev_embed_sweep>.
		2201
		2202	=item w->update () (C<ev::stat> only)
		2203
		2204	Invokes C<ev_stat_stat>.
		2205
		2206	=back
		2207
		2208	=back
		2209
		2210	Example: Define a class with an IO and idle watcher, start one of them in
		2211	the constructor.
		2212
		2213	class myclass
		2214	{
		2215	ev_io io; void io_cb (ev::io &w, int revents);
		2216	ev_idle idle void idle_cb (ev::idle &w, int revents);
		2217
		2218	myclass ();
		2219	}
		2220
		2221	myclass::myclass (int fd)
		2222	{
		2223	io .set <myclass, &myclass::io_cb > (this);
		2224	idle.set <myclass, &myclass::idle_cb> (this);
		2225
		2226	io.start (fd, ev::READ);
		2227	}
		2228
		2229
		2230	=head1 MACRO MAGIC
		2231
		2232	Libev can be compiled with a variety of options, the most fundamantal
		2233	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2234	functions and callbacks have an initial C<struct ev_loop *> argument.
		2235
		2236	To make it easier to write programs that cope with either variant, the
		2237	following macros are defined:
		2238
		2239	=over 4
		2240
		2241	=item C<EV_A>, C<EV_A_>
		2242
		2243	This provides the loop I<argument> for functions, if one is required ("ev
		2244	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2245	C<EV_A_> is used when other arguments are following. Example:
		2246
		2247	ev_unref (EV_A);
		2248	ev_timer_add (EV_A_ watcher);
		2249	ev_loop (EV_A_ 0);
		2250
		2251	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2252	which is often provided by the following macro.
		2253
		2254	=item C<EV_P>, C<EV_P_>
		2255
		2256	This provides the loop I<parameter> for functions, if one is required ("ev
		2257	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2258	C<EV_P_> is used when other parameters are following. Example:
		2259
		2260	// this is how ev_unref is being declared
		2261	static void ev_unref (EV_P);
		2262
		2263	// this is how you can declare your typical callback
		2264	static void cb (EV_P_ ev_timer *w, int revents)
		2265
		2266	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2267	suitable for use with C<EV_A>.
		2268
		2269	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2270
		2271	Similar to the other two macros, this gives you the value of the default
		2272	loop, if multiple loops are supported ("ev loop default").
		2273
		2274	=back
		2275
		2276	Example: Declare and initialise a check watcher, utilising the above
		2277	macros so it will work regardless of whether multiple loops are supported
		2278	or not.
		2279
		2280	static void
		2281	check_cb (EV_P_ ev_timer *w, int revents)
		2282	{
		2283	ev_check_stop (EV_A_ w);
		2284	}
		2285
		2286	ev_check check;
		2287	ev_check_init (&check, check_cb);
		2288	ev_check_start (EV_DEFAULT_ &check);
		2289	ev_loop (EV_DEFAULT_ 0);
		2290
		2291	=head1 EMBEDDING
		2292
		2293	Libev can (and often is) directly embedded into host
		2294	applications. Examples of applications that embed it include the Deliantra
		2295	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2296	and rxvt-unicode.
		2297
		2298	The goal is to enable you to just copy the necessary files into your
		2299	source directory without having to change even a single line in them, so
		2300	you can easily upgrade by simply copying (or having a checked-out copy of
		2301	libev somewhere in your source tree).
		2302
		2303	=head2 FILESETS
		2304
		2305	Depending on what features you need you need to include one or more sets of files
		2306	in your app.
		2307
		2308	=head3 CORE EVENT LOOP
		2309
		2310	To include only the libev core (all the C<ev_*> functions), with manual
		2311	configuration (no autoconf):
		2312
		2313	#define EV_STANDALONE 1
		2314	#include "ev.c"
		2315
		2316	This will automatically include F<ev.h>, too, and should be done in a
		2317	single C source file only to provide the function implementations. To use
		2318	it, do the same for F<ev.h> in all files wishing to use this API (best
		2319	done by writing a wrapper around F<ev.h> that you can include instead and
		2320	where you can put other configuration options):
		2321
		2322	#define EV_STANDALONE 1
		2323	#include "ev.h"
		2324
		2325	Both header files and implementation files can be compiled with a C++
		2326	compiler (at least, thats a stated goal, and breakage will be treated
		2327	as a bug).
		2328
		2329	You need the following files in your source tree, or in a directory
		2330	in your include path (e.g. in libev/ when using -Ilibev):
		2331
		2332	ev.h
		2333	ev.c
		2334	ev_vars.h
		2335	ev_wrap.h
		2336
		2337	ev_win32.c required on win32 platforms only
		2338
		2339	ev_select.c only when select backend is enabled (which is enabled by default)
		2340	ev_poll.c only when poll backend is enabled (disabled by default)
		2341	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2342	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2343	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2344
		2345	F<ev.c> includes the backend files directly when enabled, so you only need
		2346	to compile this single file.
		2347
		2348	=head3 LIBEVENT COMPATIBILITY API
		2349
		2350	To include the libevent compatibility API, also include:
		2351
		2352	#include "event.c"
		2353
		2354	in the file including F<ev.c>, and:
		2355
		2356	#include "event.h"
		2357
		2358	in the files that want to use the libevent API. This also includes F<ev.h>.
		2359
		2360	You need the following additional files for this:
		2361
		2362	event.h
		2363	event.c
		2364
		2365	=head3 AUTOCONF SUPPORT
		2366
		2367	Instead of using C<EV_STANDALONE=1> and providing your config in
		2368	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2369	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2370	include F<config.h> and configure itself accordingly.
		2371
		2372	For this of course you need the m4 file:
		2373
		2374	libev.m4
		2375
		2376	=head2 PREPROCESSOR SYMBOLS/MACROS
		2377
		2378	Libev can be configured via a variety of preprocessor symbols you have to define
		2379	before including any of its files. The default is not to build for multiplicity
		2380	and only include the select backend.
		2381
		2382	=over 4
		2383
		2384	=item EV_STANDALONE
		2385
		2386	Must always be C<1> if you do not use autoconf configuration, which
		2387	keeps libev from including F<config.h>, and it also defines dummy
		2388	implementations for some libevent functions (such as logging, which is not
		2389	supported). It will also not define any of the structs usually found in
		2390	F<event.h> that are not directly supported by the libev core alone.
		2391
		2392	=item EV_USE_MONOTONIC
		2393
		2394	If defined to be C<1>, libev will try to detect the availability of the
		2395	monotonic clock option at both compiletime and runtime. Otherwise no use
		2396	of the monotonic clock option will be attempted. If you enable this, you
		2397	usually have to link against librt or something similar. Enabling it when
		2398	the functionality isn't available is safe, though, although you have
		2399	to make sure you link against any libraries where the C<clock_gettime>
		2400	function is hiding in (often F<-lrt>).
		2401
		2402	=item EV_USE_REALTIME
		2403
		2404	If defined to be C<1>, libev will try to detect the availability of the
		2405	realtime clock option at compiletime (and assume its availability at
		2406	runtime if successful). Otherwise no use of the realtime clock option will
		2407	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2408	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2409	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2410
		2411	=item EV_USE_NANOSLEEP
		2412
		2413	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2414	and will use it for delays. Otherwise it will use C<select ()>.
		2415
		2416	=item EV_USE_SELECT
		2417
		2418	If undefined or defined to be C<1>, libev will compile in support for the
		2419	C<select>(2) backend. No attempt at autodetection will be done: if no
		2420	other method takes over, select will be it. Otherwise the select backend
		2421	will not be compiled in.
		2422
		2423	=item EV_SELECT_USE_FD_SET
		2424
		2425	If defined to C<1>, then the select backend will use the system C<fd_set>
		2426	structure. This is useful if libev doesn't compile due to a missing
		2427	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2428	exotic systems. This usually limits the range of file descriptors to some
		2429	low limit such as 1024 or might have other limitations (winsocket only
		2430	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2431	influence the size of the C<fd_set> used.
		2432
		2433	=item EV_SELECT_IS_WINSOCKET
		2434
		2435	When defined to C<1>, the select backend will assume that
		2436	select/socket/connect etc. don't understand file descriptors but
		2437	wants osf handles on win32 (this is the case when the select to
		2438	be used is the winsock select). This means that it will call
		2439	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2440	it is assumed that all these functions actually work on fds, even
		2441	on win32. Should not be defined on non-win32 platforms.
		2442
		2443	=item EV_USE_POLL
		2444
		2445	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2446	backend. Otherwise it will be enabled on non-win32 platforms. It
		2447	takes precedence over select.
		2448
		2449	=item EV_USE_EPOLL
		2450
		2451	If defined to be C<1>, libev will compile in support for the Linux
		2452	C<epoll>(7) backend. Its availability will be detected at runtime,
		2453	otherwise another method will be used as fallback. This is the
		2454	preferred backend for GNU/Linux systems.
		2455
		2456	=item EV_USE_KQUEUE
		2457
		2458	If defined to be C<1>, libev will compile in support for the BSD style
		2459	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2460	otherwise another method will be used as fallback. This is the preferred
		2461	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2462	supports some types of fds correctly (the only platform we found that
		2463	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2464	not be used unless explicitly requested. The best way to use it is to find
		2465	out whether kqueue supports your type of fd properly and use an embedded
		2466	kqueue loop.
		2467
		2468	=item EV_USE_PORT
		2469
		2470	If defined to be C<1>, libev will compile in support for the Solaris
		2471	10 port style backend. Its availability will be detected at runtime,
		2472	otherwise another method will be used as fallback. This is the preferred
		2473	backend for Solaris 10 systems.
		2474
		2475	=item EV_USE_DEVPOLL
		2476
		2477	reserved for future expansion, works like the USE symbols above.
		2478
		2479	=item EV_USE_INOTIFY
		2480
		2481	If defined to be C<1>, libev will compile in support for the Linux inotify
		2482	interface to speed up C<ev_stat> watchers. Its actual availability will
		2483	be detected at runtime.
		2484
		2485	=item EV_H
		2486
		2487	The name of the F<ev.h> header file used to include it. The default if
		2488	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
		2489	can be used to virtually rename the F<ev.h> header file in case of conflicts.
		2490
		2491	=item EV_CONFIG_H
		2492
		2493	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2494	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2495	C<EV_H>, above.
		2496
		2497	=item EV_EVENT_H
		2498
		2499	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2500	of how the F<event.h> header can be found.
		2501
		2502	=item EV_PROTOTYPES
		2503
		2504	If defined to be C<0>, then F<ev.h> will not define any function
		2505	prototypes, but still define all the structs and other symbols. This is
		2506	occasionally useful if you want to provide your own wrapper functions
		2507	around libev functions.
		2508
		2509	=item EV_MULTIPLICITY
		2510
		2511	If undefined or defined to C<1>, then all event-loop-specific functions
		2512	will have the C<struct ev_loop *> as first argument, and you can create
		2513	additional independent event loops. Otherwise there will be no support
		2514	for multiple event loops and there is no first event loop pointer
		2515	argument. Instead, all functions act on the single default loop.
		2516
		2517	=item EV_MINPRI
		2518
		2519	=item EV_MAXPRI
		2520
		2521	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2522	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2523	provide for more priorities by overriding those symbols (usually defined
		2524	to be C<-2> and C<2>, respectively).
		2525
		2526	When doing priority-based operations, libev usually has to linearly search
		2527	all the priorities, so having many of them (hundreds) uses a lot of space
		2528	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2529	fine.
		2530
		2531	If your embedding app does not need any priorities, defining these both to
		2532	C<0> will save some memory and cpu.
		2533
		2534	=item EV_PERIODIC_ENABLE
		2535
		2536	If undefined or defined to be C<1>, then periodic timers are supported. If
		2537	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2538	code.
		2539
		2540	=item EV_IDLE_ENABLE
		2541
		2542	If undefined or defined to be C<1>, then idle watchers are supported. If
		2543	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2544	code.
		2545
		2546	=item EV_EMBED_ENABLE
		2547
		2548	If undefined or defined to be C<1>, then embed watchers are supported. If
		2549	defined to be C<0>, then they are not.
		2550
		2551	=item EV_STAT_ENABLE
		2552
		2553	If undefined or defined to be C<1>, then stat watchers are supported. If
		2554	defined to be C<0>, then they are not.
		2555
		2556	=item EV_FORK_ENABLE
		2557
		2558	If undefined or defined to be C<1>, then fork watchers are supported. If
		2559	defined to be C<0>, then they are not.
		2560
		2561	=item EV_MINIMAL
		2562
		2563	If you need to shave off some kilobytes of code at the expense of some
		2564	speed, define this symbol to C<1>. Currently only used for gcc to override
		2565	some inlining decisions, saves roughly 30% codesize of amd64.
		2566
		2567	=item EV_PID_HASHSIZE
		2568
		2569	C<ev_child> watchers use a small hash table to distribute workload by
		2570	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2571	than enough. If you need to manage thousands of children you might want to
		2572	increase this value (I<must> be a power of two).
		2573
		2574	=item EV_INOTIFY_HASHSIZE
		2575
		2576	C<ev_stat> watchers use a small hash table to distribute workload by
		2577	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2578	usually more than enough. If you need to manage thousands of C<ev_stat>
		2579	watchers you might want to increase this value (I<must> be a power of
		2580	two).
		2581
		2582	=item EV_COMMON
		2583
		2584	By default, all watchers have a C<void *data> member. By redefining
		2585	this macro to a something else you can include more and other types of
		2586	members. You have to define it each time you include one of the files,
		2587	though, and it must be identical each time.
		2588
		2589	For example, the perl EV module uses something like this:
		2590
		2591	#define EV_COMMON \
		2592	SV *self; /* contains this struct */ \
		2593	SV *cb_sv, *fh /* note no trailing ";" */
		2594
		2595	=item EV_CB_DECLARE (type)
		2596
		2597	=item EV_CB_INVOKE (watcher, revents)
		2598
		2599	=item ev_set_cb (ev, cb)
		2600
		2601	Can be used to change the callback member declaration in each watcher,
		2602	and the way callbacks are invoked and set. Must expand to a struct member
		2603	definition and a statement, respectively. See the F<ev.h> header file for
		2604	their default definitions. One possible use for overriding these is to
		2605	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2606	method calls instead of plain function calls in C++.
		2607
		2608	=head2 EXPORTED API SYMBOLS
		2609
		2610	If you need to re-export the API (e.g. via a dll) and you need a list of
		2611	exported symbols, you can use the provided F<Symbol.*> files which list
		2612	all public symbols, one per line:
		2613
		2614	Symbols.ev for libev proper
		2615	Symbols.event for the libevent emulation
		2616
		2617	This can also be used to rename all public symbols to avoid clashes with
		2618	multiple versions of libev linked together (which is obviously bad in
		2619	itself, but sometimes it is inconvinient to avoid this).
		2620
		2621	A sed command like this will create wrapper C<#define>'s that you need to
		2622	include before including F<ev.h>:
		2623
		2624	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		2625
		2626	This would create a file F<wrap.h> which essentially looks like this:
		2627
		2628	#define ev_backend myprefix_ev_backend
		2629	#define ev_check_start myprefix_ev_check_start
		2630	#define ev_check_stop myprefix_ev_check_stop
		2631	...
		2632
		2633	=head2 EXAMPLES
		2634
		2635	For a real-world example of a program the includes libev
		2636	verbatim, you can have a look at the EV perl module
		2637	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2638	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2639	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2640	will be compiled. It is pretty complex because it provides its own header
		2641	file.
		2642
		2643	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2644	that everybody includes and which overrides some configure choices:
		2645
		2646	#define EV_MINIMAL 1
		2647	#define EV_USE_POLL 0
		2648	#define EV_MULTIPLICITY 0
		2649	#define EV_PERIODIC_ENABLE 0
		2650	#define EV_STAT_ENABLE 0
		2651	#define EV_FORK_ENABLE 0
		2652	#define EV_CONFIG_H <config.h>
		2653	#define EV_MINPRI 0
		2654	#define EV_MAXPRI 0
		2655
		2656	#include "ev++.h"
		2657
		2658	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		2659
		2660	#include "ev_cpp.h"
		2661	#include "ev.c"
		2662
		2663
		2664	=head1 COMPLEXITIES
		2665
		2666	In this section the complexities of (many of) the algorithms used inside
		2667	libev will be explained. For complexity discussions about backends see the
		2668	documentation for C<ev_default_init>.
		2669
		2670	All of the following are about amortised time: If an array needs to be
		2671	extended, libev needs to realloc and move the whole array, but this
		2672	happens asymptotically never with higher number of elements, so O(1) might
		2673	mean it might do a lengthy realloc operation in rare cases, but on average
		2674	it is much faster and asymptotically approaches constant time.
		2675
		2676	=over 4
		2677
		2678	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		2679
		2680	This means that, when you have a watcher that triggers in one hour and
		2681	there are 100 watchers that would trigger before that then inserting will
		2682	have to skip roughly seven (C<ld 100>) of these watchers.
		2683
		2684	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		2685
		2686	That means that changing a timer costs less than removing/adding them
		2687	as only the relative motion in the event queue has to be paid for.
		2688
		2689	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
		2690
		2691	These just add the watcher into an array or at the head of a list.
		2692
		2693	=item Stopping check/prepare/idle watchers: O(1)
		2694
		2695	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		2696
		2697	These watchers are stored in lists then need to be walked to find the
		2698	correct watcher to remove. The lists are usually short (you don't usually
		2699	have many watchers waiting for the same fd or signal).
		2700
		2701	=item Finding the next timer in each loop iteration: O(1)
		2702
		2703	By virtue of using a binary heap, the next timer is always found at the
		2704	beginning of the storage array.
		2705
		2706	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		2707
		2708	A change means an I/O watcher gets started or stopped, which requires
		2709	libev to recalculate its status (and possibly tell the kernel, depending
		2710	on backend and wether C<ev_io_set> was used).
		2711
		2712	=item Activating one watcher (putting it into the pending state): O(1)
		2713
		2714	=item Priority handling: O(number_of_priorities)
		2715
		2716	Priorities are implemented by allocating some space for each
		2717	priority. When doing priority-based operations, libev usually has to
		2718	linearly search all the priorities, but starting/stopping and activating
		2719	watchers becomes O(1) w.r.t. prioritiy handling.
		2720
		2721	=back
		2722
		2723
773	=head1 AUTHOR	2724	=head1 AUTHOR
774		2725
775	Marc Lehmann <libev@schmorp.de>.	2726	Marc Lehmann <libev@schmorp.de>.
776		2727

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