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…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_<type>
		16	ev_io stdin_watcher;
		17	ev_timer timeout_watcher;
		18
		19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
		21	static void
		22	stdin_cb (EV_P_ struct ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	struct ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	108	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	117	to the C<double> type in C, and when you need to do any calculations on
		118	it, you should treat it as some floatingpoint value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
51		121
52	=head1 GLOBAL FUNCTIONS	122	=head1 GLOBAL FUNCTIONS
53		123
54	These functions can be called anytime, even before initialising the	124	These functions can be called anytime, even before initialising the
55	library in any way.	125	library in any way.
…		…
60		130
61	Returns the current time as libev would use it. Please note that the	131	Returns the current time as libev would use it. Please note that the
62	C<ev_now> function is usually faster and also often returns the timestamp	132	C<ev_now> function is usually faster and also often returns the timestamp
63	you actually want to know.	133	you actually want to know.
64		134
		135	=item ev_sleep (ev_tstamp interval)
		136
		137	Sleep for the given interval: The current thread will be blocked until
		138	either it is interrupted or the given time interval has passed. Basically
		139	this is a subsecond-resolution C<sleep ()>.
		140
65	=item int ev_version_major ()	141	=item int ev_version_major ()
66		142
67	=item int ev_version_minor ()	143	=item int ev_version_minor ()
68		144
69	You can find out the major and minor version numbers of the library	145	You can find out the major and minor ABI version numbers of the library
70	you linked against by calling the functions C<ev_version_major> and	146	you linked against by calling the functions C<ev_version_major> and
71	C<ev_version_minor>. If you want, you can compare against the global	147	C<ev_version_minor>. If you want, you can compare against the global
72	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	148	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
73	version of the library your program was compiled against.	149	version of the library your program was compiled against.
74		150
		151	These version numbers refer to the ABI version of the library, not the
		152	release version.
		153
75	Usually, it's a good idea to terminate if the major versions mismatch,	154	Usually, it's a good idea to terminate if the major versions mismatch,
76	as this indicates an incompatible change. Minor versions are usually	155	as this indicates an incompatible change. Minor versions are usually
77	compatible to older versions, so a larger minor version alone is usually	156	compatible to older versions, so a larger minor version alone is usually
78	not a problem.	157	not a problem.
79		158
		159	Example: Make sure we haven't accidentally been linked against the wrong
		160	version.
		161
		162	assert (("libev version mismatch",
		163	ev_version_major () == EV_VERSION_MAJOR
		164	&& ev_version_minor () >= EV_VERSION_MINOR));
		165
		166	=item unsigned int ev_supported_backends ()
		167
		168	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		169	value) compiled into this binary of libev (independent of their
		170	availability on the system you are running on). See C<ev_default_loop> for
		171	a description of the set values.
		172
		173	Example: make sure we have the epoll method, because yeah this is cool and
		174	a must have and can we have a torrent of it please!!!11
		175
		176	assert (("sorry, no epoll, no sex",
		177	ev_supported_backends () & EVBACKEND_EPOLL));
		178
		179	=item unsigned int ev_recommended_backends ()
		180
		181	Return the set of all backends compiled into this binary of libev and also
		182	recommended for this platform. This set is often smaller than the one
		183	returned by C<ev_supported_backends>, as for example kqueue is broken on
		184	most BSDs and will not be autodetected unless you explicitly request it
		185	(assuming you know what you are doing). This is the set of backends that
		186	libev will probe for if you specify no backends explicitly.
		187
		188	=item unsigned int ev_embeddable_backends ()
		189
		190	Returns the set of backends that are embeddable in other event loops. This
		191	is the theoretical, all-platform, value. To find which backends
		192	might be supported on the current system, you would need to look at
		193	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		194	recommended ones.
		195
		196	See the description of C<ev_embed> watchers for more info.
		197
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
81		199
82	Sets the allocation function to use (the prototype is similar to the	200	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	201	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
84	and free memory (no surprises here). If it returns zero when memory	202	used to allocate and free memory (no surprises here). If it returns zero
85	needs to be allocated, the library might abort or take some potentially	203	when memory needs to be allocated (C<size != 0>), the library might abort
86	destructive action. The default is your system realloc function.	204	or take some potentially destructive action.
		205
		206	Since some systems (at least OpenBSD and Darwin) fail to implement
		207	correct C<realloc> semantics, libev will use a wrapper around the system
		208	C<realloc> and C<free> functions by default.
87		209
88	You could override this function in high-availability programs to, say,	210	You could override this function in high-availability programs to, say,
89	free some memory if it cannot allocate memory, to use a special allocator,	211	free some memory if it cannot allocate memory, to use a special allocator,
90	or even to sleep a while and retry until some memory is available.	212	or even to sleep a while and retry until some memory is available.
		213
		214	Example: Replace the libev allocator with one that waits a bit and then
		215	retries (example requires a standards-compliant C<realloc>).
		216
		217	static void *
		218	persistent_realloc (void *ptr, size_t size)
		219	{
		220	for (;;)
		221	{
		222	void *newptr = realloc (ptr, size);
		223
		224	if (newptr)
		225	return newptr;
		226
		227	sleep (60);
		228	}
		229	}
		230
		231	...
		232	ev_set_allocator (persistent_realloc);
91		233
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	234	=item ev_set_syserr_cb (void (*cb)(const char *msg));
93		235
94	Set the callback function to call on a retryable syscall error (such	236	Set the callback function to call on a retryable syscall error (such
95	as failed select, poll, epoll_wait). The message is a printable string	237	as failed select, poll, epoll_wait). The message is a printable string
…		…
97	callback is set, then libev will expect it to remedy the sitution, no	239	callback is set, then libev will expect it to remedy the sitution, no
98	matter what, when it returns. That is, libev will generally retry the	240	matter what, when it returns. That is, libev will generally retry the
99	requested operation, or, if the condition doesn't go away, do bad stuff	241	requested operation, or, if the condition doesn't go away, do bad stuff
100	(such as abort).	242	(such as abort).
101		243
		244	Example: This is basically the same thing that libev does internally, too.
		245
		246	static void
		247	fatal_error (const char *msg)
		248	{
		249	perror (msg);
		250	abort ();
		251	}
		252
		253	...
		254	ev_set_syserr_cb (fatal_error);
		255
102	=back	256	=back
103		257
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	258	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		259
106	An event loop is described by a C<struct ev_loop *>. The library knows two	260	An event loop is described by a C<struct ev_loop *>. The library knows two
107	types of such loops, the I<default> loop, which supports signals and child	261	types of such loops, the I<default> loop, which supports signals and child
108	events, and dynamically created loops which do not.	262	events, and dynamically created loops which do not.
109		263
110	If you use threads, a common model is to run the default event loop
111	in your main thread (or in a separate thread) and for each thread you
112	create, you also create another event loop. Libev itself does no locking
113	whatsoever, so if you mix calls to the same event loop in different
114	threads, make sure you lock (this is usually a bad idea, though, even if
115	done correctly, because it's hideous and inefficient).
116
117	=over 4	264	=over 4
118		265
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	266	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		267
121	This will initialise the default event loop if it hasn't been initialised	268	This will initialise the default event loop if it hasn't been initialised
122	yet and return it. If the default loop could not be initialised, returns	269	yet and return it. If the default loop could not be initialised, returns
123	false. If it already was initialised it simply returns it (and ignores the	270	false. If it already was initialised it simply returns it (and ignores the
124	flags).	271	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		272
126	If you don't know what event loop to use, use the one returned from this	273	If you don't know what event loop to use, use the one returned from this
127	function.	274	function.
128		275
		276	Note that this function is I<not> thread-safe, so if you want to use it
		277	from multiple threads, you have to lock (note also that this is unlikely,
		278	as loops cannot bes hared easily between threads anyway).
		279
		280	The default loop is the only loop that can handle C<ev_signal> and
		281	C<ev_child> watchers, and to do this, it always registers a handler
		282	for C<SIGCHLD>. If this is a problem for your app you can either
		283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		284	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		285	C<ev_default_init>.
		286
129	The flags argument can be used to specify special behaviour or specific	287	The flags argument can be used to specify special behaviour or specific
130	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	288	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		289
132	It supports the following flags:	290	The following flags are supported:
133		291
134	=over 4	292	=over 4
135		293
136	=item C<EVFLAG_AUTO>	294	=item C<EVFLAG_AUTO>
137		295
…		…
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	304	override the flags completely if it is found in the environment. This is
147	useful to try out specific backends to test their performance, or to work	305	useful to try out specific backends to test their performance, or to work
148	around bugs.	306	around bugs.
149		307
		308	=item C<EVFLAG_FORKCHECK>
		309
		310	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		311	a fork, you can also make libev check for a fork in each iteration by
		312	enabling this flag.
		313
		314	This works by calling C<getpid ()> on every iteration of the loop,
		315	and thus this might slow down your event loop if you do a lot of loop
		316	iterations and little real work, but is usually not noticeable (on my
		317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		318	without a syscall and thus I<very> fast, but my GNU/Linux system also has
		319	C<pthread_atfork> which is even faster).
		320
		321	The big advantage of this flag is that you can forget about fork (and
		322	forget about forgetting to tell libev about forking) when you use this
		323	flag.
		324
		325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		326	environment variable.
		327
150	=item C<EVMETHOD_SELECT> (value 1, portable select backend)	328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		329
152	This is your standard select(2) backend. Not I<completely> standard, as	330	This is your standard select(2) backend. Not I<completely> standard, as
153	libev tries to roll its own fd_set with no limits on the number of fds,	331	libev tries to roll its own fd_set with no limits on the number of fds,
154	but if that fails, expect a fairly low limit on the number of fds when	332	but if that fails, expect a fairly low limit on the number of fds when
155	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	333	using this backend. It doesn't scale too well (O(highest_fd)), but its
156	the fastest backend for a low number of fds.	334	usually the fastest backend for a low number of (low-numbered :) fds.
157		335
		336	To get good performance out of this backend you need a high amount of
		337	parallelity (most of the file descriptors should be busy). If you are
		338	writing a server, you should C<accept ()> in a loop to accept as many
		339	connections as possible during one iteration. You might also want to have
		340	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		341	readiness notifications you get per iteration.
		342
158	=item C<EVMETHOD_POLL> (value 2, poll backend, available everywhere except on windows)	343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
159		344
160	And this is your standard poll(2) backend. It's more complicated than	345	And this is your standard poll(2) backend. It's more complicated
161	select, but handles sparse fds better and has no artificial limit on the	346	than select, but handles sparse fds better and has no artificial
162	number of fds you can use (except it will slow down considerably with a	347	limit on the number of fds you can use (except it will slow down
163	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	348	considerably with a lot of inactive fds). It scales similarly to select,
		349	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		350	performance tips.
164		351
165	=item C<EVMETHOD_EPOLL> (value 4, Linux)	352	=item C<EVBACKEND_EPOLL> (value 4, Linux)
166		353
167	For few fds, this backend is a bit little slower than poll and select,	354	For few fds, this backend is a bit little slower than poll and select,
168	but it scales phenomenally better. While poll and select usually scale like	355	but it scales phenomenally better. While poll and select usually scale
169	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	356	like O(total_fds) where n is the total number of fds (or the highest fd),
170	either O(1) or O(active_fds).	357	epoll scales either O(1) or O(active_fds). The epoll design has a number
		358	of shortcomings, such as silently dropping events in some hard-to-detect
		359	cases and requiring a syscall per fd change, no fork support and bad
		360	support for dup.
171		361
172	While stopping and starting an I/O watcher in the same iteration will	362	While stopping, setting and starting an I/O watcher in the same iteration
173	result in some caching, there is still a syscall per such incident	363	will result in some caching, there is still a syscall per such incident
174	(because the fd could point to a different file description now), so its	364	(because the fd could point to a different file description now), so its
175	best to avoid that. Also, dup()ed file descriptors might not work very	365	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
176	well if you register events for both fds.	366	very well if you register events for both fds.
177		367
		368	Please note that epoll sometimes generates spurious notifications, so you
		369	need to use non-blocking I/O or other means to avoid blocking when no data
		370	(or space) is available.
		371
		372	Best performance from this backend is achieved by not unregistering all
		373	watchers for a file descriptor until it has been closed, if possible, i.e.
		374	keep at least one watcher active per fd at all times.
		375
		376	While nominally embeddeble in other event loops, this feature is broken in
		377	all kernel versions tested so far.
		378
178	=item C<EVMETHOD_KQUEUE> (value 8, most BSD clones)	379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
179		380
180	Kqueue deserves special mention, as at the time of this writing, it	381	Kqueue deserves special mention, as at the time of this writing, it
181	was broken on all BSDs except NetBSD (usually it doesn't work with	382	was broken on all BSDs except NetBSD (usually it doesn't work reliably
182	anything but sockets and pipes, except on Darwin, where of course its	383	with anything but sockets and pipes, except on Darwin, where of course
183	completely useless). For this reason its not being "autodetected" unless	384	it's completely useless). For this reason it's not being "autodetected"
184	you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).	385	unless you explicitly specify it explicitly in the flags (i.e. using
		386	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		387	system like NetBSD.
		388
		389	You still can embed kqueue into a normal poll or select backend and use it
		390	only for sockets (after having made sure that sockets work with kqueue on
		391	the target platform). See C<ev_embed> watchers for more info.
185		392
186	It scales in the same way as the epoll backend, but the interface to the	393	It scales in the same way as the epoll backend, but the interface to the
187	kernel is more efficient (which says nothing about its actual speed, of	394	kernel is more efficient (which says nothing about its actual speed, of
188	course). While starting and stopping an I/O watcher does not cause an	395	course). While stopping, setting and starting an I/O watcher does never
189	extra syscall as with epoll, it still adds up to four event changes per	396	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
190	incident, so its best to avoid that.	397	two event changes per incident, support for C<fork ()> is very bad and it
		398	drops fds silently in similarly hard-to-detect cases.
191		399
		400	This backend usually performs well under most conditions.
		401
		402	While nominally embeddable in other event loops, this doesn't work
		403	everywhere, so you might need to test for this. And since it is broken
		404	almost everywhere, you should only use it when you have a lot of sockets
		405	(for which it usually works), by embedding it into another event loop
		406	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		407	sockets.
		408
192	=item C<EVMETHOD_DEVPOLL> (value 16, Solaris 8)	409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
193		410
194	This is not implemented yet (and might never be).	411	This is not implemented yet (and might never be, unless you send me an
		412	implementation). According to reports, C</dev/poll> only supports sockets
		413	and is not embeddable, which would limit the usefulness of this backend
		414	immensely.
195		415
196	=item C<EVMETHOD_PORT> (value 32, Solaris 10)	416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
197		417
198	This uses the Solaris 10 port mechanism. As with everything on Solaris,	418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
199	it's really slow, but it still scales very well (O(active_fds)).	419	it's really slow, but it still scales very well (O(active_fds)).
200		420
		421	Please note that solaris event ports can deliver a lot of spurious
		422	notifications, so you need to use non-blocking I/O or other means to avoid
		423	blocking when no data (or space) is available.
		424
		425	While this backend scales well, it requires one system call per active
		426	file descriptor per loop iteration. For small and medium numbers of file
		427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		428	might perform better.
		429
		430	On the positive side, ignoring the spurious readiness notifications, this
		431	backend actually performed to specification in all tests and is fully
		432	embeddable, which is a rare feat among the OS-specific backends.
		433
201	=item C<EVMETHOD_ALL>	434	=item C<EVBACKEND_ALL>
202		435
203	Try all backends (even potentially broken ones that wouldn't be tried	436	Try all backends (even potentially broken ones that wouldn't be tried
204	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	437	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
205	C<EVMETHOD_ALL & ~EVMETHOD_KQUEUE>.	438	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		439
		440	It is definitely not recommended to use this flag.
206		441
207	=back	442	=back
208		443
209	If one or more of these are ored into the flags value, then only these	444	If one or more of these are ored into the flags value, then only these
210	backends will be tried (in the reverse order as given here). If none are	445	backends will be tried (in the reverse order as listed here). If none are
211	specified, most compiled-in backend will be tried, usually in reverse	446	specified, all backends in C<ev_recommended_backends ()> will be tried.
212	order of their flag values :)	447
		448	The most typical usage is like this:
		449
		450	if (!ev_default_loop (0))
		451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		452
		453	Restrict libev to the select and poll backends, and do not allow
		454	environment settings to be taken into account:
		455
		456	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		457
		458	Use whatever libev has to offer, but make sure that kqueue is used if
		459	available (warning, breaks stuff, best use only with your own private
		460	event loop and only if you know the OS supports your types of fds):
		461
		462	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
213		463
214	=item struct ev_loop *ev_loop_new (unsigned int flags)	464	=item struct ev_loop *ev_loop_new (unsigned int flags)
215		465
216	Similar to C<ev_default_loop>, but always creates a new event loop that is	466	Similar to C<ev_default_loop>, but always creates a new event loop that is
217	always distinct from the default loop. Unlike the default loop, it cannot	467	always distinct from the default loop. Unlike the default loop, it cannot
218	handle signal and child watchers, and attempts to do so will be greeted by	468	handle signal and child watchers, and attempts to do so will be greeted by
219	undefined behaviour (or a failed assertion if assertions are enabled).	469	undefined behaviour (or a failed assertion if assertions are enabled).
220		470
		471	Note that this function I<is> thread-safe, and the recommended way to use
		472	libev with threads is indeed to create one loop per thread, and using the
		473	default loop in the "main" or "initial" thread.
		474
		475	Example: Try to create a event loop that uses epoll and nothing else.
		476
		477	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		478	if (!epoller)
		479	fatal ("no epoll found here, maybe it hides under your chair");
		480
221	=item ev_default_destroy ()	481	=item ev_default_destroy ()
222		482
223	Destroys the default loop again (frees all memory and kernel state	483	Destroys the default loop again (frees all memory and kernel state
224	etc.). This stops all registered event watchers (by not touching them in	484	etc.). None of the active event watchers will be stopped in the normal
225	any way whatsoever, although you cannot rely on this :).	485	sense, so e.g. C<ev_is_active> might still return true. It is your
		486	responsibility to either stop all watchers cleanly yoursef I<before>
		487	calling this function, or cope with the fact afterwards (which is usually
		488	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		489	for example).
		490
		491	Note that certain global state, such as signal state, will not be freed by
		492	this function, and related watchers (such as signal and child watchers)
		493	would need to be stopped manually.
		494
		495	In general it is not advisable to call this function except in the
		496	rare occasion where you really need to free e.g. the signal handling
		497	pipe fds. If you need dynamically allocated loops it is better to use
		498	C<ev_loop_new> and C<ev_loop_destroy>).
226		499
227	=item ev_loop_destroy (loop)	500	=item ev_loop_destroy (loop)
228		501
229	Like C<ev_default_destroy>, but destroys an event loop created by an	502	Like C<ev_default_destroy>, but destroys an event loop created by an
230	earlier call to C<ev_loop_new>.	503	earlier call to C<ev_loop_new>.
231		504
232	=item ev_default_fork ()	505	=item ev_default_fork ()
233		506
		507	This function sets a flag that causes subsequent C<ev_loop> iterations
234	This function reinitialises the kernel state for backends that have	508	to reinitialise the kernel state for backends that have one. Despite the
235	one. Despite the name, you can call it anytime, but it makes most sense	509	name, you can call it anytime, but it makes most sense after forking, in
236	after forking, in either the parent or child process (or both, but that	510	the child process (or both child and parent, but that again makes little
237	again makes little sense).	511	sense). You I<must> call it in the child before using any of the libev
		512	functions, and it will only take effect at the next C<ev_loop> iteration.
238		513
239	You I<must> call this function in the child process after forking if and	514	On the other hand, you only need to call this function in the child
240	only if you want to use the event library in both processes. If you just	515	process if and only if you want to use the event library in the child. If
241	fork+exec, you don't have to call it.	516	you just fork+exec, you don't have to call it at all.
242		517
243	The function itself is quite fast and it's usually not a problem to call	518	The function itself is quite fast and it's usually not a problem to call
244	it just in case after a fork. To make this easy, the function will fit in	519	it just in case after a fork. To make this easy, the function will fit in
245	quite nicely into a call to C<pthread_atfork>:	520	quite nicely into a call to C<pthread_atfork>:
246		521
…		…
250		525
251	Like C<ev_default_fork>, but acts on an event loop created by	526	Like C<ev_default_fork>, but acts on an event loop created by
252	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	527	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
253	after fork, and how you do this is entirely your own problem.	528	after fork, and how you do this is entirely your own problem.
254		529
		530	=item int ev_is_default_loop (loop)
		531
		532	Returns true when the given loop actually is the default loop, false otherwise.
		533
		534	=item unsigned int ev_loop_count (loop)
		535
		536	Returns the count of loop iterations for the loop, which is identical to
		537	the number of times libev did poll for new events. It starts at C<0> and
		538	happily wraps around with enough iterations.
		539
		540	This value can sometimes be useful as a generation counter of sorts (it
		541	"ticks" the number of loop iterations), as it roughly corresponds with
		542	C<ev_prepare> and C<ev_check> calls.
		543
255	=item unsigned int ev_method (loop)	544	=item unsigned int ev_backend (loop)
256		545
257	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	546	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
258	use.	547	use.
259		548
260	=item ev_tstamp ev_now (loop)	549	=item ev_tstamp ev_now (loop)
261		550
262	Returns the current "event loop time", which is the time the event loop	551	Returns the current "event loop time", which is the time the event loop
263	got events and started processing them. This timestamp does not change	552	received events and started processing them. This timestamp does not
264	as long as callbacks are being processed, and this is also the base time	553	change as long as callbacks are being processed, and this is also the base
265	used for relative timers. You can treat it as the timestamp of the event	554	time used for relative timers. You can treat it as the timestamp of the
266	occuring (or more correctly, the mainloop finding out about it).	555	event occurring (or more correctly, libev finding out about it).
267		556
268	=item ev_loop (loop, int flags)	557	=item ev_loop (loop, int flags)
269		558
270	Finally, this is it, the event handler. This function usually is called	559	Finally, this is it, the event handler. This function usually is called
271	after you initialised all your watchers and you want to start handling	560	after you initialised all your watchers and you want to start handling
272	events.	561	events.
273		562
274	If the flags argument is specified as 0, it will not return until either	563	If the flags argument is specified as C<0>, it will not return until
275	no event watchers are active anymore or C<ev_unloop> was called.	564	either no event watchers are active anymore or C<ev_unloop> was called.
		565
		566	Please note that an explicit C<ev_unloop> is usually better than
		567	relying on all watchers to be stopped when deciding when a program has
		568	finished (especially in interactive programs), but having a program that
		569	automatically loops as long as it has to and no longer by virtue of
		570	relying on its watchers stopping correctly is a thing of beauty.
276		571
277	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	572	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
278	those events and any outstanding ones, but will not block your process in	573	those events and any outstanding ones, but will not block your process in
279	case there are no events and will return after one iteration of the loop.	574	case there are no events and will return after one iteration of the loop.
280		575
281	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	576	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
282	neccessary) and will handle those and any outstanding ones. It will block	577	neccessary) and will handle those and any outstanding ones. It will block
283	your process until at least one new event arrives, and will return after	578	your process until at least one new event arrives, and will return after
284	one iteration of the loop.	579	one iteration of the loop. This is useful if you are waiting for some
		580	external event in conjunction with something not expressible using other
		581	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		582	usually a better approach for this kind of thing.
285		583
286	This flags value could be used to implement alternative looping
287	constructs, but the C<prepare> and C<check> watchers provide a better and
288	more generic mechanism.
289
290	Here are the gory details of what ev_loop does:	584	Here are the gory details of what C<ev_loop> does:
291		585
292	1. If there are no active watchers (reference count is zero), return.	586	- Before the first iteration, call any pending watchers.
		587	* If EVFLAG_FORKCHECK was used, check for a fork.
		588	- If a fork was detected, queue and call all fork watchers.
293	2. Queue and immediately call all prepare watchers.	589	- Queue and call all prepare watchers.
294	3. If we have been forked, recreate the kernel state.	590	- If we have been forked, recreate the kernel state.
295	4. Update the kernel state with all outstanding changes.	591	- Update the kernel state with all outstanding changes.
296	5. Update the "event loop time".	592	- Update the "event loop time".
297	6. Calculate for how long to block.	593	- Calculate for how long to sleep or block, if at all
		594	(active idle watchers, EVLOOP_NONBLOCK or not having
		595	any active watchers at all will result in not sleeping).
		596	- Sleep if the I/O and timer collect interval say so.
298	7. Block the process, waiting for events.	597	- Block the process, waiting for any events.
		598	- Queue all outstanding I/O (fd) events.
299	8. Update the "event loop time" and do time jump handling.	599	- Update the "event loop time" and do time jump handling.
300	9. Queue all outstanding timers.	600	- Queue all outstanding timers.
301	10. Queue all outstanding periodics.	601	- Queue all outstanding periodics.
302	11. If no events are pending now, queue all idle watchers.	602	- If no events are pending now, queue all idle watchers.
303	12. Queue all check watchers.	603	- Queue all check watchers.
304	13. Call all queued watchers in reverse order (i.e. check watchers first).	604	- Call all queued watchers in reverse order (i.e. check watchers first).
		605	Signals and child watchers are implemented as I/O watchers, and will
		606	be handled here by queueing them when their watcher gets executed.
305	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	607	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
306	was used, return, otherwise continue with step #1.	608	were used, or there are no active watchers, return, otherwise
		609	continue with step *.
		610
		611	Example: Queue some jobs and then loop until no events are outstanding
		612	anymore.
		613
		614	... queue jobs here, make sure they register event watchers as long
		615	... as they still have work to do (even an idle watcher will do..)
		616	ev_loop (my_loop, 0);
		617	... jobs done. yeah!
307		618
308	=item ev_unloop (loop, how)	619	=item ev_unloop (loop, how)
309		620
310	Can be used to make a call to C<ev_loop> return early (but only after it	621	Can be used to make a call to C<ev_loop> return early (but only after it
311	has processed all outstanding events). The C<how> argument must be either	622	has processed all outstanding events). The C<how> argument must be either
312	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	623	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
313	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	624	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		625
		626	This "unloop state" will be cleared when entering C<ev_loop> again.
314		627
315	=item ev_ref (loop)	628	=item ev_ref (loop)
316		629
317	=item ev_unref (loop)	630	=item ev_unref (loop)
318		631
…		…
323	returning, ev_unref() after starting, and ev_ref() before stopping it. For	636	returning, ev_unref() after starting, and ev_ref() before stopping it. For
324	example, libev itself uses this for its internal signal pipe: It is not	637	example, libev itself uses this for its internal signal pipe: It is not
325	visible to the libev user and should not keep C<ev_loop> from exiting if	638	visible to the libev user and should not keep C<ev_loop> from exiting if
326	no event watchers registered by it are active. It is also an excellent	639	no event watchers registered by it are active. It is also an excellent
327	way to do this for generic recurring timers or from within third-party	640	way to do this for generic recurring timers or from within third-party
328	libraries. Just remember to I<unref after start> and I<ref before stop>.	641	libraries. Just remember to I<unref after start> and I<ref before stop>
		642	(but only if the watcher wasn't active before, or was active before,
		643	respectively).
		644
		645	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		646	running when nothing else is active.
		647
		648	struct ev_signal exitsig;
		649	ev_signal_init (&exitsig, sig_cb, SIGINT);
		650	ev_signal_start (loop, &exitsig);
		651	evf_unref (loop);
		652
		653	Example: For some weird reason, unregister the above signal handler again.
		654
		655	ev_ref (loop);
		656	ev_signal_stop (loop, &exitsig);
		657
		658	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		659
		660	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		661
		662	These advanced functions influence the time that libev will spend waiting
		663	for events. Both are by default C<0>, meaning that libev will try to
		664	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		665
		666	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		667	allows libev to delay invocation of I/O and timer/periodic callbacks to
		668	increase efficiency of loop iterations.
		669
		670	The background is that sometimes your program runs just fast enough to
		671	handle one (or very few) event(s) per loop iteration. While this makes
		672	the program responsive, it also wastes a lot of CPU time to poll for new
		673	events, especially with backends like C<select ()> which have a high
		674	overhead for the actual polling but can deliver many events at once.
		675
		676	By setting a higher I<io collect interval> you allow libev to spend more
		677	time collecting I/O events, so you can handle more events per iteration,
		678	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		679	C<ev_timer>) will be not affected. Setting this to a non-null value will
		680	introduce an additional C<ev_sleep ()> call into most loop iterations.
		681
		682	Likewise, by setting a higher I<timeout collect interval> you allow libev
		683	to spend more time collecting timeouts, at the expense of increased
		684	latency (the watcher callback will be called later). C<ev_io> watchers
		685	will not be affected. Setting this to a non-null value will not introduce
		686	any overhead in libev.
		687
		688	Many (busy) programs can usually benefit by setting the io collect
		689	interval to a value near C<0.1> or so, which is often enough for
		690	interactive servers (of course not for games), likewise for timeouts. It
		691	usually doesn't make much sense to set it to a lower value than C<0.01>,
		692	as this approsaches the timing granularity of most systems.
		693
		694	=item ev_loop_verify (loop)
		695
		696	This function only does something when C<EV_VERIFY> support has been
		697	compiled in. It tries to go through all internal structures and checks
		698	them for validity. If anything is found to be inconsistent, it will print
		699	an error message to standard error and call C<abort ()>.
		700
		701	This can be used to catch bugs inside libev itself: under normal
		702	circumstances, this function will never abort as of course libev keeps its
		703	data structures consistent.
329		704
330	=back	705	=back
		706
331		707
332	=head1 ANATOMY OF A WATCHER	708	=head1 ANATOMY OF A WATCHER
333		709
334	A watcher is a structure that you create and register to record your	710	A watcher is a structure that you create and register to record your
335	interest in some event. For instance, if you want to wait for STDIN to	711	interest in some event. For instance, if you want to wait for STDIN to
…		…
368	*) >>), and you can stop watching for events at any time by calling the	744	*) >>), and you can stop watching for events at any time by calling the
369	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	745	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
370		746
371	As long as your watcher is active (has been started but not stopped) you	747	As long as your watcher is active (has been started but not stopped) you
372	must not touch the values stored in it. Most specifically you must never	748	must not touch the values stored in it. Most specifically you must never
373	reinitialise it or call its set method.	749	reinitialise it or call its C<set> macro.
374
375	You can check whether an event is active by calling the C<ev_is_active
376	(watcher *)> macro. To see whether an event is outstanding (but the
377	callback for it has not been called yet) you can use the C<ev_is_pending
378	(watcher *)> macro.
379		750
380	Each and every callback receives the event loop pointer as first, the	751	Each and every callback receives the event loop pointer as first, the
381	registered watcher structure as second, and a bitset of received events as	752	registered watcher structure as second, and a bitset of received events as
382	third argument.	753	third argument.
383		754
…		…
407	The signal specified in the C<ev_signal> watcher has been received by a thread.	778	The signal specified in the C<ev_signal> watcher has been received by a thread.
408		779
409	=item C<EV_CHILD>	780	=item C<EV_CHILD>
410		781
411	The pid specified in the C<ev_child> watcher has received a status change.	782	The pid specified in the C<ev_child> watcher has received a status change.
		783
		784	=item C<EV_STAT>
		785
		786	The path specified in the C<ev_stat> watcher changed its attributes somehow.
412		787
413	=item C<EV_IDLE>	788	=item C<EV_IDLE>
414		789
415	The C<ev_idle> watcher has determined that you have nothing better to do.	790	The C<ev_idle> watcher has determined that you have nothing better to do.
416		791
…		…
424	received events. Callbacks of both watcher types can start and stop as	799	received events. Callbacks of both watcher types can start and stop as
425	many watchers as they want, and all of them will be taken into account	800	many watchers as they want, and all of them will be taken into account
426	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	801	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
427	C<ev_loop> from blocking).	802	C<ev_loop> from blocking).
428		803
		804	=item C<EV_EMBED>
		805
		806	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		807
		808	=item C<EV_FORK>
		809
		810	The event loop has been resumed in the child process after fork (see
		811	C<ev_fork>).
		812
		813	=item C<EV_ASYNC>
		814
		815	The given async watcher has been asynchronously notified (see C<ev_async>).
		816
429	=item C<EV_ERROR>	817	=item C<EV_ERROR>
430		818
431	An unspecified error has occured, the watcher has been stopped. This might	819	An unspecified error has occured, the watcher has been stopped. This might
432	happen because the watcher could not be properly started because libev	820	happen because the watcher could not be properly started because libev
433	ran out of memory, a file descriptor was found to be closed or any other	821	ran out of memory, a file descriptor was found to be closed or any other
…		…
439	your callbacks is well-written it can just attempt the operation and cope	827	your callbacks is well-written it can just attempt the operation and cope
440	with the error from read() or write(). This will not work in multithreaded	828	with the error from read() or write(). This will not work in multithreaded
441	programs, though, so beware.	829	programs, though, so beware.
442		830
443	=back	831	=back
		832
		833	=head2 GENERIC WATCHER FUNCTIONS
		834
		835	In the following description, C<TYPE> stands for the watcher type,
		836	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		837
		838	=over 4
		839
		840	=item C<ev_init> (ev_TYPE *watcher, callback)
		841
		842	This macro initialises the generic portion of a watcher. The contents
		843	of the watcher object can be arbitrary (so C<malloc> will do). Only
		844	the generic parts of the watcher are initialised, you I<need> to call
		845	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		846	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		847	which rolls both calls into one.
		848
		849	You can reinitialise a watcher at any time as long as it has been stopped
		850	(or never started) and there are no pending events outstanding.
		851
		852	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		853	int revents)>.
		854
		855	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		856
		857	This macro initialises the type-specific parts of a watcher. You need to
		858	call C<ev_init> at least once before you call this macro, but you can
		859	call C<ev_TYPE_set> any number of times. You must not, however, call this
		860	macro on a watcher that is active (it can be pending, however, which is a
		861	difference to the C<ev_init> macro).
		862
		863	Although some watcher types do not have type-specific arguments
		864	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		865
		866	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		867
		868	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		869	calls into a single call. This is the most convinient method to initialise
		870	a watcher. The same limitations apply, of course.
		871
		872	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		873
		874	Starts (activates) the given watcher. Only active watchers will receive
		875	events. If the watcher is already active nothing will happen.
		876
		877	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		878
		879	Stops the given watcher again (if active) and clears the pending
		880	status. It is possible that stopped watchers are pending (for example,
		881	non-repeating timers are being stopped when they become pending), but
		882	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		883	you want to free or reuse the memory used by the watcher it is therefore a
		884	good idea to always call its C<ev_TYPE_stop> function.
		885
		886	=item bool ev_is_active (ev_TYPE *watcher)
		887
		888	Returns a true value iff the watcher is active (i.e. it has been started
		889	and not yet been stopped). As long as a watcher is active you must not modify
		890	it.
		891
		892	=item bool ev_is_pending (ev_TYPE *watcher)
		893
		894	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		895	events but its callback has not yet been invoked). As long as a watcher
		896	is pending (but not active) you must not call an init function on it (but
		897	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		898	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		899	it).
		900
		901	=item callback ev_cb (ev_TYPE *watcher)
		902
		903	Returns the callback currently set on the watcher.
		904
		905	=item ev_cb_set (ev_TYPE *watcher, callback)
		906
		907	Change the callback. You can change the callback at virtually any time
		908	(modulo threads).
		909
		910	=item ev_set_priority (ev_TYPE *watcher, priority)
		911
		912	=item int ev_priority (ev_TYPE *watcher)
		913
		914	Set and query the priority of the watcher. The priority is a small
		915	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		916	(default: C<-2>). Pending watchers with higher priority will be invoked
		917	before watchers with lower priority, but priority will not keep watchers
		918	from being executed (except for C<ev_idle> watchers).
		919
		920	This means that priorities are I<only> used for ordering callback
		921	invocation after new events have been received. This is useful, for
		922	example, to reduce latency after idling, or more often, to bind two
		923	watchers on the same event and make sure one is called first.
		924
		925	If you need to suppress invocation when higher priority events are pending
		926	you need to look at C<ev_idle> watchers, which provide this functionality.
		927
		928	You I<must not> change the priority of a watcher as long as it is active or
		929	pending.
		930
		931	The default priority used by watchers when no priority has been set is
		932	always C<0>, which is supposed to not be too high and not be too low :).
		933
		934	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		935	fine, as long as you do not mind that the priority value you query might
		936	or might not have been adjusted to be within valid range.
		937
		938	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		939
		940	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		941	C<loop> nor C<revents> need to be valid as long as the watcher callback
		942	can deal with that fact.
		943
		944	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		945
		946	If the watcher is pending, this function returns clears its pending status
		947	and returns its C<revents> bitset (as if its callback was invoked). If the
		948	watcher isn't pending it does nothing and returns C<0>.
		949
		950	=back
		951
444		952
445	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	953	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
446		954
447	Each watcher has, by default, a member C<void *data> that you can change	955	Each watcher has, by default, a member C<void *data> that you can change
448	and read at any time, libev will completely ignore it. This can be used	956	and read at any time, libev will completely ignore it. This can be used
…		…
466	{	974	{
467	struct my_io *w = (struct my_io *)w_;	975	struct my_io *w = (struct my_io *)w_;
468	...	976	...
469	}	977	}
470		978
471	More interesting and less C-conformant ways of catsing your callback type	979	More interesting and less C-conformant ways of casting your callback type
472	have been omitted....	980	instead have been omitted.
		981
		982	Another common scenario is having some data structure with multiple
		983	watchers:
		984
		985	struct my_biggy
		986	{
		987	int some_data;
		988	ev_timer t1;
		989	ev_timer t2;
		990	}
		991
		992	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		993	you need to use C<offsetof>:
		994
		995	#include <stddef.h>
		996
		997	static void
		998	t1_cb (EV_P_ struct ev_timer *w, int revents)
		999	{
		1000	struct my_biggy big = (struct my_biggy *
		1001	(((char *)w) - offsetof (struct my_biggy, t1));
		1002	}
		1003
		1004	static void
		1005	t2_cb (EV_P_ struct ev_timer *w, int revents)
		1006	{
		1007	struct my_biggy big = (struct my_biggy *
		1008	(((char *)w) - offsetof (struct my_biggy, t2));
		1009	}
473		1010
474		1011
475	=head1 WATCHER TYPES	1012	=head1 WATCHER TYPES
476		1013
477	This section describes each watcher in detail, but will not repeat	1014	This section describes each watcher in detail, but will not repeat
478	information given in the last section.	1015	information given in the last section. Any initialisation/set macros,
		1016	functions and members specific to the watcher type are explained.
479		1017
		1018	Members are additionally marked with either I<[read-only]>, meaning that,
		1019	while the watcher is active, you can look at the member and expect some
		1020	sensible content, but you must not modify it (you can modify it while the
		1021	watcher is stopped to your hearts content), or I<[read-write]>, which
		1022	means you can expect it to have some sensible content while the watcher
		1023	is active, but you can also modify it. Modifying it may not do something
		1024	sensible or take immediate effect (or do anything at all), but libev will
		1025	not crash or malfunction in any way.
		1026
		1027
480	=head2 C<ev_io> - is this file descriptor readable or writable	1028	=head2 C<ev_io> - is this file descriptor readable or writable?
481		1029
482	I/O watchers check whether a file descriptor is readable or writable	1030	I/O watchers check whether a file descriptor is readable or writable
483	in each iteration of the event loop (This behaviour is called	1031	in each iteration of the event loop, or, more precisely, when reading
484	level-triggering because you keep receiving events as long as the	1032	would not block the process and writing would at least be able to write
485	condition persists. Remember you can stop the watcher if you don't want to	1033	some data. This behaviour is called level-triggering because you keep
486	act on the event and neither want to receive future events).	1034	receiving events as long as the condition persists. Remember you can stop
		1035	the watcher if you don't want to act on the event and neither want to
		1036	receive future events.
487		1037
488	In general you can register as many read and/or write event watchers per	1038	In general you can register as many read and/or write event watchers per
489	fd as you want (as long as you don't confuse yourself). Setting all file	1039	fd as you want (as long as you don't confuse yourself). Setting all file
490	descriptors to non-blocking mode is also usually a good idea (but not	1040	descriptors to non-blocking mode is also usually a good idea (but not
491	required if you know what you are doing).	1041	required if you know what you are doing).
492		1042
493	You have to be careful with dup'ed file descriptors, though. Some backends
494	(the linux epoll backend is a notable example) cannot handle dup'ed file
495	descriptors correctly if you register interest in two or more fds pointing
496	to the same underlying file/socket etc. description (that is, they share
497	the same underlying "file open").
498
499	If you must do this, then force the use of a known-to-be-good backend	1043	If you must do this, then force the use of a known-to-be-good backend
500	(at the time of this writing, this includes only EVMETHOD_SELECT and	1044	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
501	EVMETHOD_POLL).	1045	C<EVBACKEND_POLL>).
		1046
		1047	Another thing you have to watch out for is that it is quite easy to
		1048	receive "spurious" readiness notifications, that is your callback might
		1049	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1050	because there is no data. Not only are some backends known to create a
		1051	lot of those (for example solaris ports), it is very easy to get into
		1052	this situation even with a relatively standard program structure. Thus
		1053	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1054	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1055
		1056	If you cannot run the fd in non-blocking mode (for example you should not
		1057	play around with an Xlib connection), then you have to seperately re-test
		1058	whether a file descriptor is really ready with a known-to-be good interface
		1059	such as poll (fortunately in our Xlib example, Xlib already does this on
		1060	its own, so its quite safe to use).
		1061
		1062	=head3 The special problem of disappearing file descriptors
		1063
		1064	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1065	descriptor (either by calling C<close> explicitly or by any other means,
		1066	such as C<dup>). The reason is that you register interest in some file
		1067	descriptor, but when it goes away, the operating system will silently drop
		1068	this interest. If another file descriptor with the same number then is
		1069	registered with libev, there is no efficient way to see that this is, in
		1070	fact, a different file descriptor.
		1071
		1072	To avoid having to explicitly tell libev about such cases, libev follows
		1073	the following policy: Each time C<ev_io_set> is being called, libev
		1074	will assume that this is potentially a new file descriptor, otherwise
		1075	it is assumed that the file descriptor stays the same. That means that
		1076	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1077	descriptor even if the file descriptor number itself did not change.
		1078
		1079	This is how one would do it normally anyway, the important point is that
		1080	the libev application should not optimise around libev but should leave
		1081	optimisations to libev.
		1082
		1083	=head3 The special problem of dup'ed file descriptors
		1084
		1085	Some backends (e.g. epoll), cannot register events for file descriptors,
		1086	but only events for the underlying file descriptions. That means when you
		1087	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1088	events for them, only one file descriptor might actually receive events.
		1089
		1090	There is no workaround possible except not registering events
		1091	for potentially C<dup ()>'ed file descriptors, or to resort to
		1092	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1093
		1094	=head3 The special problem of fork
		1095
		1096	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1097	useless behaviour. Libev fully supports fork, but needs to be told about
		1098	it in the child.
		1099
		1100	To support fork in your programs, you either have to call
		1101	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1102	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1103	C<EVBACKEND_POLL>.
		1104
		1105	=head3 The special problem of SIGPIPE
		1106
		1107	While not really specific to libev, it is easy to forget about SIGPIPE:
		1108	when reading from a pipe whose other end has been closed, your program
		1109	gets send a SIGPIPE, which, by default, aborts your program. For most
		1110	programs this is sensible behaviour, for daemons, this is usually
		1111	undesirable.
		1112
		1113	So when you encounter spurious, unexplained daemon exits, make sure you
		1114	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1115	somewhere, as that would have given you a big clue).
		1116
		1117
		1118	=head3 Watcher-Specific Functions
502		1119
503	=over 4	1120	=over 4
504		1121
505	=item ev_io_init (ev_io *, callback, int fd, int events)	1122	=item ev_io_init (ev_io *, callback, int fd, int events)
506		1123
507	=item ev_io_set (ev_io *, int fd, int events)	1124	=item ev_io_set (ev_io *, int fd, int events)
508		1125
509	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1126	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
510	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1127	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
511	EV_WRITE> to receive the given events.	1128	C<EV_READ | EV_WRITE> to receive the given events.
		1129
		1130	=item int fd [read-only]
		1131
		1132	The file descriptor being watched.
		1133
		1134	=item int events [read-only]
		1135
		1136	The events being watched.
512		1137
513	=back	1138	=back
514		1139
		1140	=head3 Examples
		1141
		1142	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1143	readable, but only once. Since it is likely line-buffered, you could
		1144	attempt to read a whole line in the callback.
		1145
		1146	static void
		1147	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1148	{
		1149	ev_io_stop (loop, w);
		1150	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1151	}
		1152
		1153	...
		1154	struct ev_loop *loop = ev_default_init (0);
		1155	struct ev_io stdin_readable;
		1156	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1157	ev_io_start (loop, &stdin_readable);
		1158	ev_loop (loop, 0);
		1159
		1160
515	=head2 C<ev_timer> - relative and optionally recurring timeouts	1161	=head2 C<ev_timer> - relative and optionally repeating timeouts
516		1162
517	Timer watchers are simple relative timers that generate an event after a	1163	Timer watchers are simple relative timers that generate an event after a
518	given time, and optionally repeating in regular intervals after that.	1164	given time, and optionally repeating in regular intervals after that.
519		1165
520	The timers are based on real time, that is, if you register an event that	1166	The timers are based on real time, that is, if you register an event that
521	times out after an hour and you reset your system clock to last years	1167	times out after an hour and you reset your system clock to january last
522	time, it will still time out after (roughly) and hour. "Roughly" because	1168	year, it will still time out after (roughly) and hour. "Roughly" because
523	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1169	detecting time jumps is hard, and some inaccuracies are unavoidable (the
524	monotonic clock option helps a lot here).	1170	monotonic clock option helps a lot here).
525		1171
526	The relative timeouts are calculated relative to the C<ev_now ()>	1172	The relative timeouts are calculated relative to the C<ev_now ()>
527	time. This is usually the right thing as this timestamp refers to the time	1173	time. This is usually the right thing as this timestamp refers to the time
…		…
529	you suspect event processing to be delayed and you I<need> to base the timeout	1175	you suspect event processing to be delayed and you I<need> to base the timeout
530	on the current time, use something like this to adjust for this:	1176	on the current time, use something like this to adjust for this:
531		1177
532	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1178	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
533		1179
534	The callback is guarenteed to be invoked only when its timeout has passed,	1180	The callback is guarenteed to be invoked only after its timeout has passed,
535	but if multiple timers become ready during the same loop iteration then	1181	but if multiple timers become ready during the same loop iteration then
536	order of execution is undefined.	1182	order of execution is undefined.
537		1183
		1184	=head3 Watcher-Specific Functions and Data Members
		1185
538	=over 4	1186	=over 4
539		1187
540	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1188	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
541		1189
542	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1190	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
543		1191
544	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1192	Configure the timer to trigger after C<after> seconds. If C<repeat>
545	C<0.>, then it will automatically be stopped. If it is positive, then the	1193	is C<0.>, then it will automatically be stopped once the timeout is
546	timer will automatically be configured to trigger again C<repeat> seconds	1194	reached. If it is positive, then the timer will automatically be
547	later, again, and again, until stopped manually.	1195	configured to trigger again C<repeat> seconds later, again, and again,
		1196	until stopped manually.
548		1197
549	The timer itself will do a best-effort at avoiding drift, that is, if you	1198	The timer itself will do a best-effort at avoiding drift, that is, if
550	configure a timer to trigger every 10 seconds, then it will trigger at	1199	you configure a timer to trigger every 10 seconds, then it will normally
551	exactly 10 second intervals. If, however, your program cannot keep up with	1200	trigger at exactly 10 second intervals. If, however, your program cannot
552	the timer (because it takes longer than those 10 seconds to do stuff) the	1201	keep up with the timer (because it takes longer than those 10 seconds to
553	timer will not fire more than once per event loop iteration.	1202	do stuff) the timer will not fire more than once per event loop iteration.
554		1203
555	=item ev_timer_again (loop)	1204	=item ev_timer_again (loop, ev_timer *)
556		1205
557	This will act as if the timer timed out and restart it again if it is	1206	This will act as if the timer timed out and restart it again if it is
558	repeating. The exact semantics are:	1207	repeating. The exact semantics are:
559		1208
		1209	If the timer is pending, its pending status is cleared.
		1210
560	If the timer is started but nonrepeating, stop it.	1211	If the timer is started but nonrepeating, stop it (as if it timed out).
561		1212
562	If the timer is repeating, either start it if necessary (with the repeat	1213	If the timer is repeating, either start it if necessary (with the
563	value), or reset the running timer to the repeat value.	1214	C<repeat> value), or reset the running timer to the C<repeat> value.
564		1215
565	This sounds a bit complicated, but here is a useful and typical	1216	This sounds a bit complicated, but here is a useful and typical
566	example: Imagine you have a tcp connection and you want a so-called idle	1217	example: Imagine you have a tcp connection and you want a so-called idle
567	timeout, that is, you want to be called when there have been, say, 60	1218	timeout, that is, you want to be called when there have been, say, 60
568	seconds of inactivity on the socket. The easiest way to do this is to	1219	seconds of inactivity on the socket. The easiest way to do this is to
569	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1220	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
570	time you successfully read or write some data. If you go into an idle	1221	C<ev_timer_again> each time you successfully read or write some data. If
571	state where you do not expect data to travel on the socket, you can stop	1222	you go into an idle state where you do not expect data to travel on the
572	the timer, and again will automatically restart it if need be.	1223	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1224	automatically restart it if need be.
		1225
		1226	That means you can ignore the C<after> value and C<ev_timer_start>
		1227	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1228
		1229	ev_timer_init (timer, callback, 0., 5.);
		1230	ev_timer_again (loop, timer);
		1231	...
		1232	timer->again = 17.;
		1233	ev_timer_again (loop, timer);
		1234	...
		1235	timer->again = 10.;
		1236	ev_timer_again (loop, timer);
		1237
		1238	This is more slightly efficient then stopping/starting the timer each time
		1239	you want to modify its timeout value.
		1240
		1241	=item ev_tstamp repeat [read-write]
		1242
		1243	The current C<repeat> value. Will be used each time the watcher times out
		1244	or C<ev_timer_again> is called and determines the next timeout (if any),
		1245	which is also when any modifications are taken into account.
573		1246
574	=back	1247	=back
575		1248
		1249	=head3 Examples
		1250
		1251	Example: Create a timer that fires after 60 seconds.
		1252
		1253	static void
		1254	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1255	{
		1256	.. one minute over, w is actually stopped right here
		1257	}
		1258
		1259	struct ev_timer mytimer;
		1260	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1261	ev_timer_start (loop, &mytimer);
		1262
		1263	Example: Create a timeout timer that times out after 10 seconds of
		1264	inactivity.
		1265
		1266	static void
		1267	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1268	{
		1269	.. ten seconds without any activity
		1270	}
		1271
		1272	struct ev_timer mytimer;
		1273	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1274	ev_timer_again (&mytimer); /* start timer */
		1275	ev_loop (loop, 0);
		1276
		1277	// and in some piece of code that gets executed on any "activity":
		1278	// reset the timeout to start ticking again at 10 seconds
		1279	ev_timer_again (&mytimer);
		1280
		1281
576	=head2 C<ev_periodic> - to cron or not to cron	1282	=head2 C<ev_periodic> - to cron or not to cron?
577		1283
578	Periodic watchers are also timers of a kind, but they are very versatile	1284	Periodic watchers are also timers of a kind, but they are very versatile
579	(and unfortunately a bit complex).	1285	(and unfortunately a bit complex).
580		1286
581	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1287	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
582	but on wallclock time (absolute time). You can tell a periodic watcher	1288	but on wallclock time (absolute time). You can tell a periodic watcher
583	to trigger "at" some specific point in time. For example, if you tell a	1289	to trigger after some specific point in time. For example, if you tell a
584	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1290	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
585	+ 10.>) and then reset your system clock to the last year, then it will	1291	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1292	clock to january of the previous year, then it will take more than year
586	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1293	to trigger the event (unlike an C<ev_timer>, which would still trigger
587	roughly 10 seconds later and of course not if you reset your system time	1294	roughly 10 seconds later as it uses a relative timeout).
588	again).
589		1295
590	They can also be used to implement vastly more complex timers, such as	1296	C<ev_periodic>s can also be used to implement vastly more complex timers,
591	triggering an event on eahc midnight, local time.	1297	such as triggering an event on each "midnight, local time", or other
		1298	complicated, rules.
592		1299
593	As with timers, the callback is guarenteed to be invoked only when the	1300	As with timers, the callback is guarenteed to be invoked only when the
594	time (C<at>) has been passed, but if multiple periodic timers become ready	1301	time (C<at>) has passed, but if multiple periodic timers become ready
595	during the same loop iteration then order of execution is undefined.	1302	during the same loop iteration then order of execution is undefined.
		1303
		1304	=head3 Watcher-Specific Functions and Data Members
596		1305
597	=over 4	1306	=over 4
598		1307
599	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1308	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
600		1309
…		…
603	Lots of arguments, lets sort it out... There are basically three modes of	1312	Lots of arguments, lets sort it out... There are basically three modes of
604	operation, and we will explain them from simplest to complex:	1313	operation, and we will explain them from simplest to complex:
605		1314
606	=over 4	1315	=over 4
607		1316
608	=item * absolute timer (interval = reschedule_cb = 0)	1317	=item * absolute timer (at = time, interval = reschedule_cb = 0)
609		1318
610	In this configuration the watcher triggers an event at the wallclock time	1319	In this configuration the watcher triggers an event after the wallclock
611	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1320	time C<at> has passed and doesn't repeat. It will not adjust when a time
612	that is, if it is to be run at January 1st 2011 then it will run when the	1321	jump occurs, that is, if it is to be run at January 1st 2011 then it will
613	system time reaches or surpasses this time.	1322	run when the system time reaches or surpasses this time.
614		1323
615	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1324	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
616		1325
617	In this mode the watcher will always be scheduled to time out at the next	1326	In this mode the watcher will always be scheduled to time out at the next
618	C<at + N * interval> time (for some integer N) and then repeat, regardless	1327	C<at + N * interval> time (for some integer N, which can also be negative)
619	of any time jumps.	1328	and then repeat, regardless of any time jumps.
620		1329
621	This can be used to create timers that do not drift with respect to system	1330	This can be used to create timers that do not drift with respect to system
622	time:	1331	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1332	the hour:
623		1333
624	ev_periodic_set (&periodic, 0., 3600., 0);	1334	ev_periodic_set (&periodic, 0., 3600., 0);
625		1335
626	This doesn't mean there will always be 3600 seconds in between triggers,	1336	This doesn't mean there will always be 3600 seconds in between triggers,
627	but only that the the callback will be called when the system time shows a	1337	but only that the the callback will be called when the system time shows a
…		…
630		1340
631	Another way to think about it (for the mathematically inclined) is that	1341	Another way to think about it (for the mathematically inclined) is that
632	C<ev_periodic> will try to run the callback in this mode at the next possible	1342	C<ev_periodic> will try to run the callback in this mode at the next possible
633	time where C<time = at (mod interval)>, regardless of any time jumps.	1343	time where C<time = at (mod interval)>, regardless of any time jumps.
634		1344
		1345	For numerical stability it is preferable that the C<at> value is near
		1346	C<ev_now ()> (the current time), but there is no range requirement for
		1347	this value, and in fact is often specified as zero.
		1348
		1349	Note also that there is an upper limit to how often a timer can fire (cpu
		1350	speed for example), so if C<interval> is very small then timing stability
		1351	will of course detoriate. Libev itself tries to be exact to be about one
		1352	millisecond (if the OS supports it and the machine is fast enough).
		1353
635	=item * manual reschedule mode (reschedule_cb = callback)	1354	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
636		1355
637	In this mode the values for C<interval> and C<at> are both being	1356	In this mode the values for C<interval> and C<at> are both being
638	ignored. Instead, each time the periodic watcher gets scheduled, the	1357	ignored. Instead, each time the periodic watcher gets scheduled, the
639	reschedule callback will be called with the watcher as first, and the	1358	reschedule callback will be called with the watcher as first, and the
640	current time as second argument.	1359	current time as second argument.
641		1360
642	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1361	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
643	ever, or make any event loop modifications>. If you need to stop it,	1362	ever, or make ANY event loop modifications whatsoever>.
644	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
645	starting a prepare watcher).
646		1363
		1364	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1365	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1366	only event loop modification you are allowed to do).
		1367
647	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1368	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
648	ev_tstamp now)>, e.g.:	1369	*w, ev_tstamp now)>, e.g.:
649		1370
650	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1371	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
651	{	1372	{
652	return now + 60.;	1373	return now + 60.;
653	}	1374	}
…		…
655	It must return the next time to trigger, based on the passed time value	1376	It must return the next time to trigger, based on the passed time value
656	(that is, the lowest time value larger than to the second argument). It	1377	(that is, the lowest time value larger than to the second argument). It
657	will usually be called just before the callback will be triggered, but	1378	will usually be called just before the callback will be triggered, but
658	might be called at other times, too.	1379	might be called at other times, too.
659		1380
660	NOTE: I<< This callback must always return a time that is later than the	1381	NOTE: I<< This callback must always return a time that is higher than or
661	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1382	equal to the passed C<now> value >>.
662		1383
663	This can be used to create very complex timers, such as a timer that	1384	This can be used to create very complex timers, such as a timer that
664	triggers on each midnight, local time. To do this, you would calculate the	1385	triggers on "next midnight, local time". To do this, you would calculate the
665	next midnight after C<now> and return the timestamp value for this. How	1386	next midnight after C<now> and return the timestamp value for this. How
666	you do this is, again, up to you (but it is not trivial, which is the main	1387	you do this is, again, up to you (but it is not trivial, which is the main
667	reason I omitted it as an example).	1388	reason I omitted it as an example).
668		1389
669	=back	1390	=back
…		…
673	Simply stops and restarts the periodic watcher again. This is only useful	1394	Simply stops and restarts the periodic watcher again. This is only useful
674	when you changed some parameters or the reschedule callback would return	1395	when you changed some parameters or the reschedule callback would return
675	a different time than the last time it was called (e.g. in a crond like	1396	a different time than the last time it was called (e.g. in a crond like
676	program when the crontabs have changed).	1397	program when the crontabs have changed).
677		1398
		1399	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1400
		1401	When active, returns the absolute time that the watcher is supposed to
		1402	trigger next.
		1403
		1404	=item ev_tstamp offset [read-write]
		1405
		1406	When repeating, this contains the offset value, otherwise this is the
		1407	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1408
		1409	Can be modified any time, but changes only take effect when the periodic
		1410	timer fires or C<ev_periodic_again> is being called.
		1411
		1412	=item ev_tstamp interval [read-write]
		1413
		1414	The current interval value. Can be modified any time, but changes only
		1415	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1416	called.
		1417
		1418	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1419
		1420	The current reschedule callback, or C<0>, if this functionality is
		1421	switched off. Can be changed any time, but changes only take effect when
		1422	the periodic timer fires or C<ev_periodic_again> is being called.
		1423
678	=back	1424	=back
679		1425
		1426	=head3 Examples
		1427
		1428	Example: Call a callback every hour, or, more precisely, whenever the
		1429	system clock is divisible by 3600. The callback invocation times have
		1430	potentially a lot of jittering, but good long-term stability.
		1431
		1432	static void
		1433	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1434	{
		1435	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1436	}
		1437
		1438	struct ev_periodic hourly_tick;
		1439	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1440	ev_periodic_start (loop, &hourly_tick);
		1441
		1442	Example: The same as above, but use a reschedule callback to do it:
		1443
		1444	#include <math.h>
		1445
		1446	static ev_tstamp
		1447	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1448	{
		1449	return fmod (now, 3600.) + 3600.;
		1450	}
		1451
		1452	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1453
		1454	Example: Call a callback every hour, starting now:
		1455
		1456	struct ev_periodic hourly_tick;
		1457	ev_periodic_init (&hourly_tick, clock_cb,
		1458	fmod (ev_now (loop), 3600.), 3600., 0);
		1459	ev_periodic_start (loop, &hourly_tick);
		1460
		1461
680	=head2 C<ev_signal> - signal me when a signal gets signalled	1462	=head2 C<ev_signal> - signal me when a signal gets signalled!
681		1463
682	Signal watchers will trigger an event when the process receives a specific	1464	Signal watchers will trigger an event when the process receives a specific
683	signal one or more times. Even though signals are very asynchronous, libev	1465	signal one or more times. Even though signals are very asynchronous, libev
684	will try it's best to deliver signals synchronously, i.e. as part of the	1466	will try it's best to deliver signals synchronously, i.e. as part of the
685	normal event processing, like any other event.	1467	normal event processing, like any other event.
…		…
689	with the kernel (thus it coexists with your own signal handlers as long	1471	with the kernel (thus it coexists with your own signal handlers as long
690	as you don't register any with libev). Similarly, when the last signal	1472	as you don't register any with libev). Similarly, when the last signal
691	watcher for a signal is stopped libev will reset the signal handler to	1473	watcher for a signal is stopped libev will reset the signal handler to
692	SIG_DFL (regardless of what it was set to before).	1474	SIG_DFL (regardless of what it was set to before).
693		1475
		1476	If possible and supported, libev will install its handlers with
		1477	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
		1478	interrupted. If you have a problem with syscalls getting interrupted by
		1479	signals you can block all signals in an C<ev_check> watcher and unblock
		1480	them in an C<ev_prepare> watcher.
		1481
		1482	=head3 Watcher-Specific Functions and Data Members
		1483
694	=over 4	1484	=over 4
695		1485
696	=item ev_signal_init (ev_signal *, callback, int signum)	1486	=item ev_signal_init (ev_signal *, callback, int signum)
697		1487
698	=item ev_signal_set (ev_signal *, int signum)	1488	=item ev_signal_set (ev_signal *, int signum)
699		1489
700	Configures the watcher to trigger on the given signal number (usually one	1490	Configures the watcher to trigger on the given signal number (usually one
701	of the C<SIGxxx> constants).	1491	of the C<SIGxxx> constants).
702		1492
		1493	=item int signum [read-only]
		1494
		1495	The signal the watcher watches out for.
		1496
703	=back	1497	=back
704		1498
		1499	=head3 Examples
		1500
		1501	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1502
		1503	static void
		1504	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1505	{
		1506	ev_unloop (loop, EVUNLOOP_ALL);
		1507	}
		1508
		1509	struct ev_signal signal_watcher;
		1510	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1511	ev_signal_start (loop, &sigint_cb);
		1512
		1513
705	=head2 C<ev_child> - wait for pid status changes	1514	=head2 C<ev_child> - watch out for process status changes
706		1515
707	Child watchers trigger when your process receives a SIGCHLD in response to	1516	Child watchers trigger when your process receives a SIGCHLD in response to
708	some child status changes (most typically when a child of yours dies).	1517	some child status changes (most typically when a child of yours dies). It
		1518	is permissible to install a child watcher I<after> the child has been
		1519	forked (which implies it might have already exited), as long as the event
		1520	loop isn't entered (or is continued from a watcher).
		1521
		1522	Only the default event loop is capable of handling signals, and therefore
		1523	you can only rgeister child watchers in the default event loop.
		1524
		1525	=head3 Process Interaction
		1526
		1527	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1528	initialised. This is necessary to guarantee proper behaviour even if
		1529	the first child watcher is started after the child exits. The occurance
		1530	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1531	synchronously as part of the event loop processing. Libev always reaps all
		1532	children, even ones not watched.
		1533
		1534	=head3 Overriding the Built-In Processing
		1535
		1536	Libev offers no special support for overriding the built-in child
		1537	processing, but if your application collides with libev's default child
		1538	handler, you can override it easily by installing your own handler for
		1539	C<SIGCHLD> after initialising the default loop, and making sure the
		1540	default loop never gets destroyed. You are encouraged, however, to use an
		1541	event-based approach to child reaping and thus use libev's support for
		1542	that, so other libev users can use C<ev_child> watchers freely.
		1543
		1544	=head3 Watcher-Specific Functions and Data Members
709		1545
710	=over 4	1546	=over 4
711		1547
712	=item ev_child_init (ev_child *, callback, int pid)	1548	=item ev_child_init (ev_child *, callback, int pid, int trace)
713		1549
714	=item ev_child_set (ev_child *, int pid)	1550	=item ev_child_set (ev_child *, int pid, int trace)
715		1551
716	Configures the watcher to wait for status changes of process C<pid> (or	1552	Configures the watcher to wait for status changes of process C<pid> (or
717	I<any> process if C<pid> is specified as C<0>). The callback can look	1553	I<any> process if C<pid> is specified as C<0>). The callback can look
718	at the C<rstatus> member of the C<ev_child> watcher structure to see	1554	at the C<rstatus> member of the C<ev_child> watcher structure to see
719	the status word (use the macros from C<sys/wait.h> and see your systems	1555	the status word (use the macros from C<sys/wait.h> and see your systems
720	C<waitpid> documentation). The C<rpid> member contains the pid of the	1556	C<waitpid> documentation). The C<rpid> member contains the pid of the
721	process causing the status change.	1557	process causing the status change. C<trace> must be either C<0> (only
		1558	activate the watcher when the process terminates) or C<1> (additionally
		1559	activate the watcher when the process is stopped or continued).
		1560
		1561	=item int pid [read-only]
		1562
		1563	The process id this watcher watches out for, or C<0>, meaning any process id.
		1564
		1565	=item int rpid [read-write]
		1566
		1567	The process id that detected a status change.
		1568
		1569	=item int rstatus [read-write]
		1570
		1571	The process exit/trace status caused by C<rpid> (see your systems
		1572	C<waitpid> and C<sys/wait.h> documentation for details).
722		1573
723	=back	1574	=back
724		1575
		1576	=head3 Examples
		1577
		1578	Example: C<fork()> a new process and install a child handler to wait for
		1579	its completion.
		1580
		1581	ev_child cw;
		1582
		1583	static void
		1584	child_cb (EV_P_ struct ev_child *w, int revents)
		1585	{
		1586	ev_child_stop (EV_A_ w);
		1587	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1588	}
		1589
		1590	pid_t pid = fork ();
		1591
		1592	if (pid < 0)
		1593	// error
		1594	else if (pid == 0)
		1595	{
		1596	// the forked child executes here
		1597	exit (1);
		1598	}
		1599	else
		1600	{
		1601	ev_child_init (&cw, child_cb, pid, 0);
		1602	ev_child_start (EV_DEFAULT_ &cw);
		1603	}
		1604
		1605
		1606	=head2 C<ev_stat> - did the file attributes just change?
		1607
		1608	This watches a filesystem path for attribute changes. That is, it calls
		1609	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1610	compared to the last time, invoking the callback if it did.
		1611
		1612	The path does not need to exist: changing from "path exists" to "path does
		1613	not exist" is a status change like any other. The condition "path does
		1614	not exist" is signified by the C<st_nlink> field being zero (which is
		1615	otherwise always forced to be at least one) and all the other fields of
		1616	the stat buffer having unspecified contents.
		1617
		1618	The path I<should> be absolute and I<must not> end in a slash. If it is
		1619	relative and your working directory changes, the behaviour is undefined.
		1620
		1621	Since there is no standard to do this, the portable implementation simply
		1622	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1623	can specify a recommended polling interval for this case. If you specify
		1624	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1625	unspecified default> value will be used (which you can expect to be around
		1626	five seconds, although this might change dynamically). Libev will also
		1627	impose a minimum interval which is currently around C<0.1>, but thats
		1628	usually overkill.
		1629
		1630	This watcher type is not meant for massive numbers of stat watchers,
		1631	as even with OS-supported change notifications, this can be
		1632	resource-intensive.
		1633
		1634	At the time of this writing, only the Linux inotify interface is
		1635	implemented (implementing kqueue support is left as an exercise for the
		1636	reader, note, however, that the author sees no way of implementing ev_stat
		1637	semantics with kqueue). Inotify will be used to give hints only and should
		1638	not change the semantics of C<ev_stat> watchers, which means that libev
		1639	sometimes needs to fall back to regular polling again even with inotify,
		1640	but changes are usually detected immediately, and if the file exists there
		1641	will be no polling.
		1642
		1643	=head3 ABI Issues (Largefile Support)
		1644
		1645	Libev by default (unless the user overrides this) uses the default
		1646	compilation environment, which means that on systems with optionally
		1647	disabled large file support, you get the 32 bit version of the stat
		1648	structure. When using the library from programs that change the ABI to
		1649	use 64 bit file offsets the programs will fail. In that case you have to
		1650	compile libev with the same flags to get binary compatibility. This is
		1651	obviously the case with any flags that change the ABI, but the problem is
		1652	most noticably with ev_stat and largefile support.
		1653
		1654	=head3 Inotify
		1655
		1656	When C<inotify (7)> support has been compiled into libev (generally only
		1657	available on Linux) and present at runtime, it will be used to speed up
		1658	change detection where possible. The inotify descriptor will be created lazily
		1659	when the first C<ev_stat> watcher is being started.
		1660
		1661	Inotify presence does not change the semantics of C<ev_stat> watchers
		1662	except that changes might be detected earlier, and in some cases, to avoid
		1663	making regular C<stat> calls. Even in the presence of inotify support
		1664	there are many cases where libev has to resort to regular C<stat> polling.
		1665
		1666	(There is no support for kqueue, as apparently it cannot be used to
		1667	implement this functionality, due to the requirement of having a file
		1668	descriptor open on the object at all times).
		1669
		1670	=head3 The special problem of stat time resolution
		1671
		1672	The C<stat ()> syscall only supports full-second resolution portably, and
		1673	even on systems where the resolution is higher, many filesystems still
		1674	only support whole seconds.
		1675
		1676	That means that, if the time is the only thing that changes, you can
		1677	easily miss updates: on the first update, C<ev_stat> detects a change and
		1678	calls your callback, which does something. When there is another update
		1679	within the same second, C<ev_stat> will be unable to detect it as the stat
		1680	data does not change.
		1681
		1682	The solution to this is to delay acting on a change for slightly more
		1683	than a second (or till slightly after the next full second boundary), using
		1684	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1685	ev_timer_again (loop, w)>).
		1686
		1687	The C<.02> offset is added to work around small timing inconsistencies
		1688	of some operating systems (where the second counter of the current time
		1689	might be be delayed. One such system is the Linux kernel, where a call to
		1690	C<gettimeofday> might return a timestamp with a full second later than
		1691	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1692	update file times then there will be a small window where the kernel uses
		1693	the previous second to update file times but libev might already execute
		1694	the timer callback).
		1695
		1696	=head3 Watcher-Specific Functions and Data Members
		1697
		1698	=over 4
		1699
		1700	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1701
		1702	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1703
		1704	Configures the watcher to wait for status changes of the given
		1705	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1706	be detected and should normally be specified as C<0> to let libev choose
		1707	a suitable value. The memory pointed to by C<path> must point to the same
		1708	path for as long as the watcher is active.
		1709
		1710	The callback will receive C<EV_STAT> when a change was detected, relative
		1711	to the attributes at the time the watcher was started (or the last change
		1712	was detected).
		1713
		1714	=item ev_stat_stat (loop, ev_stat *)
		1715
		1716	Updates the stat buffer immediately with new values. If you change the
		1717	watched path in your callback, you could call this function to avoid
		1718	detecting this change (while introducing a race condition if you are not
		1719	the only one changing the path). Can also be useful simply to find out the
		1720	new values.
		1721
		1722	=item ev_statdata attr [read-only]
		1723
		1724	The most-recently detected attributes of the file. Although the type is
		1725	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1726	suitable for your system, but you can only rely on the POSIX-standardised
		1727	members to be present. If the C<st_nlink> member is C<0>, then there was
		1728	some error while C<stat>ing the file.
		1729
		1730	=item ev_statdata prev [read-only]
		1731
		1732	The previous attributes of the file. The callback gets invoked whenever
		1733	C<prev> != C<attr>, or, more precisely, one or more of these members
		1734	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1735	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1736
		1737	=item ev_tstamp interval [read-only]
		1738
		1739	The specified interval.
		1740
		1741	=item const char *path [read-only]
		1742
		1743	The filesystem path that is being watched.
		1744
		1745	=back
		1746
		1747	=head3 Examples
		1748
		1749	Example: Watch C</etc/passwd> for attribute changes.
		1750
		1751	static void
		1752	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1753	{
		1754	/* /etc/passwd changed in some way */
		1755	if (w->attr.st_nlink)
		1756	{
		1757	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1758	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1759	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1760	}
		1761	else
		1762	/* you shalt not abuse printf for puts */
		1763	puts ("wow, /etc/passwd is not there, expect problems. "
		1764	"if this is windows, they already arrived\n");
		1765	}
		1766
		1767	...
		1768	ev_stat passwd;
		1769
		1770	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1771	ev_stat_start (loop, &passwd);
		1772
		1773	Example: Like above, but additionally use a one-second delay so we do not
		1774	miss updates (however, frequent updates will delay processing, too, so
		1775	one might do the work both on C<ev_stat> callback invocation I<and> on
		1776	C<ev_timer> callback invocation).
		1777
		1778	static ev_stat passwd;
		1779	static ev_timer timer;
		1780
		1781	static void
		1782	timer_cb (EV_P_ ev_timer *w, int revents)
		1783	{
		1784	ev_timer_stop (EV_A_ w);
		1785
		1786	/* now it's one second after the most recent passwd change */
		1787	}
		1788
		1789	static void
		1790	stat_cb (EV_P_ ev_stat *w, int revents)
		1791	{
		1792	/* reset the one-second timer */
		1793	ev_timer_again (EV_A_ &timer);
		1794	}
		1795
		1796	...
		1797	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1798	ev_stat_start (loop, &passwd);
		1799	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1800
		1801
725	=head2 C<ev_idle> - when you've got nothing better to do	1802	=head2 C<ev_idle> - when you've got nothing better to do...
726		1803
727	Idle watchers trigger events when there are no other events are pending	1804	Idle watchers trigger events when no other events of the same or higher
728	(prepare, check and other idle watchers do not count). That is, as long	1805	priority are pending (prepare, check and other idle watchers do not
729	as your process is busy handling sockets or timeouts (or even signals,	1806	count).
730	imagine) it will not be triggered. But when your process is idle all idle	1807
731	watchers are being called again and again, once per event loop iteration -	1808	That is, as long as your process is busy handling sockets or timeouts
		1809	(or even signals, imagine) of the same or higher priority it will not be
		1810	triggered. But when your process is idle (or only lower-priority watchers
		1811	are pending), the idle watchers are being called once per event loop
732	until stopped, that is, or your process receives more events and becomes	1812	iteration - until stopped, that is, or your process receives more events
733	busy.	1813	and becomes busy again with higher priority stuff.
734		1814
735	The most noteworthy effect is that as long as any idle watchers are	1815	The most noteworthy effect is that as long as any idle watchers are
736	active, the process will not block when waiting for new events.	1816	active, the process will not block when waiting for new events.
737		1817
738	Apart from keeping your process non-blocking (which is a useful	1818	Apart from keeping your process non-blocking (which is a useful
739	effect on its own sometimes), idle watchers are a good place to do	1819	effect on its own sometimes), idle watchers are a good place to do
740	"pseudo-background processing", or delay processing stuff to after the	1820	"pseudo-background processing", or delay processing stuff to after the
741	event loop has handled all outstanding events.	1821	event loop has handled all outstanding events.
742		1822
		1823	=head3 Watcher-Specific Functions and Data Members
		1824
743	=over 4	1825	=over 4
744		1826
745	=item ev_idle_init (ev_signal *, callback)	1827	=item ev_idle_init (ev_signal *, callback)
746		1828
747	Initialises and configures the idle watcher - it has no parameters of any	1829	Initialises and configures the idle watcher - it has no parameters of any
748	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1830	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
749	believe me.	1831	believe me.
750		1832
751	=back	1833	=back
752		1834
		1835	=head3 Examples
		1836
		1837	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1838	callback, free it. Also, use no error checking, as usual.
		1839
		1840	static void
		1841	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1842	{
		1843	free (w);
		1844	// now do something you wanted to do when the program has
		1845	// no longer anything immediate to do.
		1846	}
		1847
		1848	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1849	ev_idle_init (idle_watcher, idle_cb);
		1850	ev_idle_start (loop, idle_cb);
		1851
		1852
753	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1853	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
754		1854
755	Prepare and check watchers are usually (but not always) used in tandem:	1855	Prepare and check watchers are usually (but not always) used in tandem:
756	prepare watchers get invoked before the process blocks and check watchers	1856	prepare watchers get invoked before the process blocks and check watchers
757	afterwards.	1857	afterwards.
758		1858
		1859	You I<must not> call C<ev_loop> or similar functions that enter
		1860	the current event loop from either C<ev_prepare> or C<ev_check>
		1861	watchers. Other loops than the current one are fine, however. The
		1862	rationale behind this is that you do not need to check for recursion in
		1863	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1864	C<ev_check> so if you have one watcher of each kind they will always be
		1865	called in pairs bracketing the blocking call.
		1866
759	Their main purpose is to integrate other event mechanisms into libev. This	1867	Their main purpose is to integrate other event mechanisms into libev and
760	could be used, for example, to track variable changes, implement your own	1868	their use is somewhat advanced. This could be used, for example, to track
761	watchers, integrate net-snmp or a coroutine library and lots more.	1869	variable changes, implement your own watchers, integrate net-snmp or a
		1870	coroutine library and lots more. They are also occasionally useful if
		1871	you cache some data and want to flush it before blocking (for example,
		1872	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1873	watcher).
762		1874
763	This is done by examining in each prepare call which file descriptors need	1875	This is done by examining in each prepare call which file descriptors need
764	to be watched by the other library, registering C<ev_io> watchers for	1876	to be watched by the other library, registering C<ev_io> watchers for
765	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1877	them and starting an C<ev_timer> watcher for any timeouts (many libraries
766	provide just this functionality). Then, in the check watcher you check for	1878	provide just this functionality). Then, in the check watcher you check for
…		…
776	with priority higher than or equal to the event loop and one coroutine	1888	with priority higher than or equal to the event loop and one coroutine
777	of lower priority, but only once, using idle watchers to keep the event	1889	of lower priority, but only once, using idle watchers to keep the event
778	loop from blocking if lower-priority coroutines are active, thus mapping	1890	loop from blocking if lower-priority coroutines are active, thus mapping
779	low-priority coroutines to idle/background tasks).	1891	low-priority coroutines to idle/background tasks).
780		1892
		1893	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1894	priority, to ensure that they are being run before any other watchers
		1895	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1896	too) should not activate ("feed") events into libev. While libev fully
		1897	supports this, they might get executed before other C<ev_check> watchers
		1898	did their job. As C<ev_check> watchers are often used to embed other
		1899	(non-libev) event loops those other event loops might be in an unusable
		1900	state until their C<ev_check> watcher ran (always remind yourself to
		1901	coexist peacefully with others).
		1902
		1903	=head3 Watcher-Specific Functions and Data Members
		1904
781	=over 4	1905	=over 4
782		1906
783	=item ev_prepare_init (ev_prepare *, callback)	1907	=item ev_prepare_init (ev_prepare *, callback)
784		1908
785	=item ev_check_init (ev_check *, callback)	1909	=item ev_check_init (ev_check *, callback)
…		…
787	Initialises and configures the prepare or check watcher - they have no	1911	Initialises and configures the prepare or check watcher - they have no
788	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1912	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
789	macros, but using them is utterly, utterly and completely pointless.	1913	macros, but using them is utterly, utterly and completely pointless.
790		1914
791	=back	1915	=back
		1916
		1917	=head3 Examples
		1918
		1919	There are a number of principal ways to embed other event loops or modules
		1920	into libev. Here are some ideas on how to include libadns into libev
		1921	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1922	use as a working example. Another Perl module named C<EV::Glib> embeds a
		1923	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		1924	Glib event loop).
		1925
		1926	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1927	and in a check watcher, destroy them and call into libadns. What follows
		1928	is pseudo-code only of course. This requires you to either use a low
		1929	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1930	the callbacks for the IO/timeout watchers might not have been called yet.
		1931
		1932	static ev_io iow [nfd];
		1933	static ev_timer tw;
		1934
		1935	static void
		1936	io_cb (ev_loop *loop, ev_io *w, int revents)
		1937	{
		1938	}
		1939
		1940	// create io watchers for each fd and a timer before blocking
		1941	static void
		1942	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1943	{
		1944	int timeout = 3600000;
		1945	struct pollfd fds [nfd];
		1946	// actual code will need to loop here and realloc etc.
		1947	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1948
		1949	/* the callback is illegal, but won't be called as we stop during check */
		1950	ev_timer_init (&tw, 0, timeout * 1e-3);
		1951	ev_timer_start (loop, &tw);
		1952
		1953	// create one ev_io per pollfd
		1954	for (int i = 0; i < nfd; ++i)
		1955	{
		1956	ev_io_init (iow + i, io_cb, fds [i].fd,
		1957	((fds [i].events & POLLIN ? EV_READ : 0)
		1958	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1959
		1960	fds [i].revents = 0;
		1961	ev_io_start (loop, iow + i);
		1962	}
		1963	}
		1964
		1965	// stop all watchers after blocking
		1966	static void
		1967	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1968	{
		1969	ev_timer_stop (loop, &tw);
		1970
		1971	for (int i = 0; i < nfd; ++i)
		1972	{
		1973	// set the relevant poll flags
		1974	// could also call adns_processreadable etc. here
		1975	struct pollfd *fd = fds + i;
		1976	int revents = ev_clear_pending (iow + i);
		1977	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1978	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1979
		1980	// now stop the watcher
		1981	ev_io_stop (loop, iow + i);
		1982	}
		1983
		1984	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1985	}
		1986
		1987	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1988	in the prepare watcher and would dispose of the check watcher.
		1989
		1990	Method 3: If the module to be embedded supports explicit event
		1991	notification (adns does), you can also make use of the actual watcher
		1992	callbacks, and only destroy/create the watchers in the prepare watcher.
		1993
		1994	static void
		1995	timer_cb (EV_P_ ev_timer *w, int revents)
		1996	{
		1997	adns_state ads = (adns_state)w->data;
		1998	update_now (EV_A);
		1999
		2000	adns_processtimeouts (ads, &tv_now);
		2001	}
		2002
		2003	static void
		2004	io_cb (EV_P_ ev_io *w, int revents)
		2005	{
		2006	adns_state ads = (adns_state)w->data;
		2007	update_now (EV_A);
		2008
		2009	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2010	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2011	}
		2012
		2013	// do not ever call adns_afterpoll
		2014
		2015	Method 4: Do not use a prepare or check watcher because the module you
		2016	want to embed is too inflexible to support it. Instead, youc na override
		2017	their poll function. The drawback with this solution is that the main
		2018	loop is now no longer controllable by EV. The C<Glib::EV> module does
		2019	this.
		2020
		2021	static gint
		2022	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2023	{
		2024	int got_events = 0;
		2025
		2026	for (n = 0; n < nfds; ++n)
		2027	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2028
		2029	if (timeout >= 0)
		2030	// create/start timer
		2031
		2032	// poll
		2033	ev_loop (EV_A_ 0);
		2034
		2035	// stop timer again
		2036	if (timeout >= 0)
		2037	ev_timer_stop (EV_A_ &to);
		2038
		2039	// stop io watchers again - their callbacks should have set
		2040	for (n = 0; n < nfds; ++n)
		2041	ev_io_stop (EV_A_ iow [n]);
		2042
		2043	return got_events;
		2044	}
		2045
		2046
		2047	=head2 C<ev_embed> - when one backend isn't enough...
		2048
		2049	This is a rather advanced watcher type that lets you embed one event loop
		2050	into another (currently only C<ev_io> events are supported in the embedded
		2051	loop, other types of watchers might be handled in a delayed or incorrect
		2052	fashion and must not be used).
		2053
		2054	There are primarily two reasons you would want that: work around bugs and
		2055	prioritise I/O.
		2056
		2057	As an example for a bug workaround, the kqueue backend might only support
		2058	sockets on some platform, so it is unusable as generic backend, but you
		2059	still want to make use of it because you have many sockets and it scales
		2060	so nicely. In this case, you would create a kqueue-based loop and embed it
		2061	into your default loop (which might use e.g. poll). Overall operation will
		2062	be a bit slower because first libev has to poll and then call kevent, but
		2063	at least you can use both at what they are best.
		2064
		2065	As for prioritising I/O: rarely you have the case where some fds have
		2066	to be watched and handled very quickly (with low latency), and even
		2067	priorities and idle watchers might have too much overhead. In this case
		2068	you would put all the high priority stuff in one loop and all the rest in
		2069	a second one, and embed the second one in the first.
		2070
		2071	As long as the watcher is active, the callback will be invoked every time
		2072	there might be events pending in the embedded loop. The callback must then
		2073	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2074	their callbacks (you could also start an idle watcher to give the embedded
		2075	loop strictly lower priority for example). You can also set the callback
		2076	to C<0>, in which case the embed watcher will automatically execute the
		2077	embedded loop sweep.
		2078
		2079	As long as the watcher is started it will automatically handle events. The
		2080	callback will be invoked whenever some events have been handled. You can
		2081	set the callback to C<0> to avoid having to specify one if you are not
		2082	interested in that.
		2083
		2084	Also, there have not currently been made special provisions for forking:
		2085	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2086	but you will also have to stop and restart any C<ev_embed> watchers
		2087	yourself.
		2088
		2089	Unfortunately, not all backends are embeddable, only the ones returned by
		2090	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2091	portable one.
		2092
		2093	So when you want to use this feature you will always have to be prepared
		2094	that you cannot get an embeddable loop. The recommended way to get around
		2095	this is to have a separate variables for your embeddable loop, try to
		2096	create it, and if that fails, use the normal loop for everything.
		2097
		2098	=head3 Watcher-Specific Functions and Data Members
		2099
		2100	=over 4
		2101
		2102	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2103
		2104	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2105
		2106	Configures the watcher to embed the given loop, which must be
		2107	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2108	invoked automatically, otherwise it is the responsibility of the callback
		2109	to invoke it (it will continue to be called until the sweep has been done,
		2110	if you do not want thta, you need to temporarily stop the embed watcher).
		2111
		2112	=item ev_embed_sweep (loop, ev_embed *)
		2113
		2114	Make a single, non-blocking sweep over the embedded loop. This works
		2115	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2116	apropriate way for embedded loops.
		2117
		2118	=item struct ev_loop *other [read-only]
		2119
		2120	The embedded event loop.
		2121
		2122	=back
		2123
		2124	=head3 Examples
		2125
		2126	Example: Try to get an embeddable event loop and embed it into the default
		2127	event loop. If that is not possible, use the default loop. The default
		2128	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		2129	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		2130	used).
		2131
		2132	struct ev_loop *loop_hi = ev_default_init (0);
		2133	struct ev_loop *loop_lo = 0;
		2134	struct ev_embed embed;
		2135
		2136	// see if there is a chance of getting one that works
		2137	// (remember that a flags value of 0 means autodetection)
		2138	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2139	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2140	: 0;
		2141
		2142	// if we got one, then embed it, otherwise default to loop_hi
		2143	if (loop_lo)
		2144	{
		2145	ev_embed_init (&embed, 0, loop_lo);
		2146	ev_embed_start (loop_hi, &embed);
		2147	}
		2148	else
		2149	loop_lo = loop_hi;
		2150
		2151	Example: Check if kqueue is available but not recommended and create
		2152	a kqueue backend for use with sockets (which usually work with any
		2153	kqueue implementation). Store the kqueue/socket-only event loop in
		2154	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2155
		2156	struct ev_loop *loop = ev_default_init (0);
		2157	struct ev_loop *loop_socket = 0;
		2158	struct ev_embed embed;
		2159
		2160	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2161	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2162	{
		2163	ev_embed_init (&embed, 0, loop_socket);
		2164	ev_embed_start (loop, &embed);
		2165	}
		2166
		2167	if (!loop_socket)
		2168	loop_socket = loop;
		2169
		2170	// now use loop_socket for all sockets, and loop for everything else
		2171
		2172
		2173	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2174
		2175	Fork watchers are called when a C<fork ()> was detected (usually because
		2176	whoever is a good citizen cared to tell libev about it by calling
		2177	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2178	event loop blocks next and before C<ev_check> watchers are being called,
		2179	and only in the child after the fork. If whoever good citizen calling
		2180	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2181	handlers will be invoked, too, of course.
		2182
		2183	=head3 Watcher-Specific Functions and Data Members
		2184
		2185	=over 4
		2186
		2187	=item ev_fork_init (ev_signal *, callback)
		2188
		2189	Initialises and configures the fork watcher - it has no parameters of any
		2190	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2191	believe me.
		2192
		2193	=back
		2194
		2195
		2196	=head2 C<ev_async> - how to wake up another event loop
		2197
		2198	In general, you cannot use an C<ev_loop> from multiple threads or other
		2199	asynchronous sources such as signal handlers (as opposed to multiple event
		2200	loops - those are of course safe to use in different threads).
		2201
		2202	Sometimes, however, you need to wake up another event loop you do not
		2203	control, for example because it belongs to another thread. This is what
		2204	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2205	can signal it by calling C<ev_async_send>, which is thread- and signal
		2206	safe.
		2207
		2208	This functionality is very similar to C<ev_signal> watchers, as signals,
		2209	too, are asynchronous in nature, and signals, too, will be compressed
		2210	(i.e. the number of callback invocations may be less than the number of
		2211	C<ev_async_sent> calls).
		2212
		2213	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2214	just the default loop.
		2215
		2216	=head3 Queueing
		2217
		2218	C<ev_async> does not support queueing of data in any way. The reason
		2219	is that the author does not know of a simple (or any) algorithm for a
		2220	multiple-writer-single-reader queue that works in all cases and doesn't
		2221	need elaborate support such as pthreads.
		2222
		2223	That means that if you want to queue data, you have to provide your own
		2224	queue. But at least I can tell you would implement locking around your
		2225	queue:
		2226
		2227	=over 4
		2228
		2229	=item queueing from a signal handler context
		2230
		2231	To implement race-free queueing, you simply add to the queue in the signal
		2232	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2233	some fictitiuous SIGUSR1 handler:
		2234
		2235	static ev_async mysig;
		2236
		2237	static void
		2238	sigusr1_handler (void)
		2239	{
		2240	sometype data;
		2241
		2242	// no locking etc.
		2243	queue_put (data);
		2244	ev_async_send (EV_DEFAULT_ &mysig);
		2245	}
		2246
		2247	static void
		2248	mysig_cb (EV_P_ ev_async *w, int revents)
		2249	{
		2250	sometype data;
		2251	sigset_t block, prev;
		2252
		2253	sigemptyset (&block);
		2254	sigaddset (&block, SIGUSR1);
		2255	sigprocmask (SIG_BLOCK, &block, &prev);
		2256
		2257	while (queue_get (&data))
		2258	process (data);
		2259
		2260	if (sigismember (&prev, SIGUSR1)
		2261	sigprocmask (SIG_UNBLOCK, &block, 0);
		2262	}
		2263
		2264	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2265	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2266	either...).
		2267
		2268	=item queueing from a thread context
		2269
		2270	The strategy for threads is different, as you cannot (easily) block
		2271	threads but you can easily preempt them, so to queue safely you need to
		2272	employ a traditional mutex lock, such as in this pthread example:
		2273
		2274	static ev_async mysig;
		2275	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2276
		2277	static void
		2278	otherthread (void)
		2279	{
		2280	// only need to lock the actual queueing operation
		2281	pthread_mutex_lock (&mymutex);
		2282	queue_put (data);
		2283	pthread_mutex_unlock (&mymutex);
		2284
		2285	ev_async_send (EV_DEFAULT_ &mysig);
		2286	}
		2287
		2288	static void
		2289	mysig_cb (EV_P_ ev_async *w, int revents)
		2290	{
		2291	pthread_mutex_lock (&mymutex);
		2292
		2293	while (queue_get (&data))
		2294	process (data);
		2295
		2296	pthread_mutex_unlock (&mymutex);
		2297	}
		2298
		2299	=back
		2300
		2301
		2302	=head3 Watcher-Specific Functions and Data Members
		2303
		2304	=over 4
		2305
		2306	=item ev_async_init (ev_async *, callback)
		2307
		2308	Initialises and configures the async watcher - it has no parameters of any
		2309	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2310	believe me.
		2311
		2312	=item ev_async_send (loop, ev_async *)
		2313
		2314	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2315	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2316	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2317	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2318	section below on what exactly this means).
		2319
		2320	This call incurs the overhead of a syscall only once per loop iteration,
		2321	so while the overhead might be noticable, it doesn't apply to repeated
		2322	calls to C<ev_async_send>.
		2323
		2324	=item bool = ev_async_pending (ev_async *)
		2325
		2326	Returns a non-zero value when C<ev_async_send> has been called on the
		2327	watcher but the event has not yet been processed (or even noted) by the
		2328	event loop.
		2329
		2330	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2331	the loop iterates next and checks for the watcher to have become active,
		2332	it will reset the flag again. C<ev_async_pending> can be used to very
		2333	quickly check wether invoking the loop might be a good idea.
		2334
		2335	Not that this does I<not> check wether the watcher itself is pending, only
		2336	wether it has been requested to make this watcher pending.
		2337
		2338	=back
		2339
792		2340
793	=head1 OTHER FUNCTIONS	2341	=head1 OTHER FUNCTIONS
794		2342
795	There are some other functions of possible interest. Described. Here. Now.	2343	There are some other functions of possible interest. Described. Here. Now.
796		2344
…		…
826	/* stdin might have data for us, joy! */;	2374	/* stdin might have data for us, joy! */;
827	}	2375	}
828		2376
829	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2377	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
830		2378
831	=item ev_feed_event (loop, watcher, int events)	2379	=item ev_feed_event (ev_loop *, watcher *, int revents)
832		2380
833	Feeds the given event set into the event loop, as if the specified event	2381	Feeds the given event set into the event loop, as if the specified event
834	had happened for the specified watcher (which must be a pointer to an	2382	had happened for the specified watcher (which must be a pointer to an
835	initialised but not necessarily started event watcher).	2383	initialised but not necessarily started event watcher).
836		2384
837	=item ev_feed_fd_event (loop, int fd, int revents)	2385	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
838		2386
839	Feed an event on the given fd, as if a file descriptor backend detected	2387	Feed an event on the given fd, as if a file descriptor backend detected
840	the given events it.	2388	the given events it.
841		2389
842	=item ev_feed_signal_event (loop, int signum)	2390	=item ev_feed_signal_event (ev_loop *loop, int signum)
843		2391
844	Feed an event as if the given signal occured (loop must be the default loop!).	2392	Feed an event as if the given signal occured (C<loop> must be the default
		2393	loop!).
845		2394
846	=back	2395	=back
		2396
847		2397
848	=head1 LIBEVENT EMULATION	2398	=head1 LIBEVENT EMULATION
849		2399
850	Libev offers a compatibility emulation layer for libevent. It cannot	2400	Libev offers a compatibility emulation layer for libevent. It cannot
851	emulate the internals of libevent, so here are some usage hints:	2401	emulate the internals of libevent, so here are some usage hints:
…		…
863		2413
864	=item * Priorities are not currently supported. Initialising priorities	2414	=item * Priorities are not currently supported. Initialising priorities
865	will fail and all watchers will have the same priority, even though there	2415	will fail and all watchers will have the same priority, even though there
866	is an ev_pri field.	2416	is an ev_pri field.
867		2417
		2418	=item * In libevent, the last base created gets the signals, in libev, the
		2419	first base created (== the default loop) gets the signals.
		2420
868	=item * Other members are not supported.	2421	=item * Other members are not supported.
869		2422
870	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2423	=item * The libev emulation is I<not> ABI compatible to libevent, you need
871	to use the libev header file and library.	2424	to use the libev header file and library.
872		2425
873	=back	2426	=back
874		2427
875	=head1 C++ SUPPORT	2428	=head1 C++ SUPPORT
876		2429
877	TBD.	2430	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2431	you to use some convinience methods to start/stop watchers and also change
		2432	the callback model to a model using method callbacks on objects.
		2433
		2434	To use it,
		2435
		2436	#include <ev++.h>
		2437
		2438	This automatically includes F<ev.h> and puts all of its definitions (many
		2439	of them macros) into the global namespace. All C++ specific things are
		2440	put into the C<ev> namespace. It should support all the same embedding
		2441	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2442
		2443	Care has been taken to keep the overhead low. The only data member the C++
		2444	classes add (compared to plain C-style watchers) is the event loop pointer
		2445	that the watcher is associated with (or no additional members at all if
		2446	you disable C<EV_MULTIPLICITY> when embedding libev).
		2447
		2448	Currently, functions, and static and non-static member functions can be
		2449	used as callbacks. Other types should be easy to add as long as they only
		2450	need one additional pointer for context. If you need support for other
		2451	types of functors please contact the author (preferably after implementing
		2452	it).
		2453
		2454	Here is a list of things available in the C<ev> namespace:
		2455
		2456	=over 4
		2457
		2458	=item C<ev::READ>, C<ev::WRITE> etc.
		2459
		2460	These are just enum values with the same values as the C<EV_READ> etc.
		2461	macros from F<ev.h>.
		2462
		2463	=item C<ev::tstamp>, C<ev::now>
		2464
		2465	Aliases to the same types/functions as with the C<ev_> prefix.
		2466
		2467	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2468
		2469	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2470	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2471	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2472	defines by many implementations.
		2473
		2474	All of those classes have these methods:
		2475
		2476	=over 4
		2477
		2478	=item ev::TYPE::TYPE ()
		2479
		2480	=item ev::TYPE::TYPE (struct ev_loop *)
		2481
		2482	=item ev::TYPE::~TYPE
		2483
		2484	The constructor (optionally) takes an event loop to associate the watcher
		2485	with. If it is omitted, it will use C<EV_DEFAULT>.
		2486
		2487	The constructor calls C<ev_init> for you, which means you have to call the
		2488	C<set> method before starting it.
		2489
		2490	It will not set a callback, however: You have to call the templated C<set>
		2491	method to set a callback before you can start the watcher.
		2492
		2493	(The reason why you have to use a method is a limitation in C++ which does
		2494	not allow explicit template arguments for constructors).
		2495
		2496	The destructor automatically stops the watcher if it is active.
		2497
		2498	=item w->set<class, &class::method> (object *)
		2499
		2500	This method sets the callback method to call. The method has to have a
		2501	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2502	first argument and the C<revents> as second. The object must be given as
		2503	parameter and is stored in the C<data> member of the watcher.
		2504
		2505	This method synthesizes efficient thunking code to call your method from
		2506	the C callback that libev requires. If your compiler can inline your
		2507	callback (i.e. it is visible to it at the place of the C<set> call and
		2508	your compiler is good :), then the method will be fully inlined into the
		2509	thunking function, making it as fast as a direct C callback.
		2510
		2511	Example: simple class declaration and watcher initialisation
		2512
		2513	struct myclass
		2514	{
		2515	void io_cb (ev::io &w, int revents) { }
		2516	}
		2517
		2518	myclass obj;
		2519	ev::io iow;
		2520	iow.set <myclass, &myclass::io_cb> (&obj);
		2521
		2522	=item w->set<function> (void *data = 0)
		2523
		2524	Also sets a callback, but uses a static method or plain function as
		2525	callback. The optional C<data> argument will be stored in the watcher's
		2526	C<data> member and is free for you to use.
		2527
		2528	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2529
		2530	See the method-C<set> above for more details.
		2531
		2532	Example:
		2533
		2534	static void io_cb (ev::io &w, int revents) { }
		2535	iow.set <io_cb> ();
		2536
		2537	=item w->set (struct ev_loop *)
		2538
		2539	Associates a different C<struct ev_loop> with this watcher. You can only
		2540	do this when the watcher is inactive (and not pending either).
		2541
		2542	=item w->set ([args])
		2543
		2544	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2545	called at least once. Unlike the C counterpart, an active watcher gets
		2546	automatically stopped and restarted when reconfiguring it with this
		2547	method.
		2548
		2549	=item w->start ()
		2550
		2551	Starts the watcher. Note that there is no C<loop> argument, as the
		2552	constructor already stores the event loop.
		2553
		2554	=item w->stop ()
		2555
		2556	Stops the watcher if it is active. Again, no C<loop> argument.
		2557
		2558	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2559
		2560	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2561	C<ev_TYPE_again> function.
		2562
		2563	=item w->sweep () (C<ev::embed> only)
		2564
		2565	Invokes C<ev_embed_sweep>.
		2566
		2567	=item w->update () (C<ev::stat> only)
		2568
		2569	Invokes C<ev_stat_stat>.
		2570
		2571	=back
		2572
		2573	=back
		2574
		2575	Example: Define a class with an IO and idle watcher, start one of them in
		2576	the constructor.
		2577
		2578	class myclass
		2579	{
		2580	ev::io io; void io_cb (ev::io &w, int revents);
		2581	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2582
		2583	myclass (int fd)
		2584	{
		2585	io .set <myclass, &myclass::io_cb > (this);
		2586	idle.set <myclass, &myclass::idle_cb> (this);
		2587
		2588	io.start (fd, ev::READ);
		2589	}
		2590	};
		2591
		2592
		2593	=head1 OTHER LANGUAGE BINDINGS
		2594
		2595	Libev does not offer other language bindings itself, but bindings for a
		2596	numbe rof languages exist in the form of third-party packages. If you know
		2597	any interesting language binding in addition to the ones listed here, drop
		2598	me a note.
		2599
		2600	=over 4
		2601
		2602	=item Perl
		2603
		2604	The EV module implements the full libev API and is actually used to test
		2605	libev. EV is developed together with libev. Apart from the EV core module,
		2606	there are additional modules that implement libev-compatible interfaces
		2607	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2608	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2609
		2610	It can be found and installed via CPAN, its homepage is found at
		2611	L<http://software.schmorp.de/pkg/EV>.
		2612
		2613	=item Ruby
		2614
		2615	Tony Arcieri has written a ruby extension that offers access to a subset
		2616	of the libev API and adds filehandle abstractions, asynchronous DNS and
		2617	more on top of it. It can be found via gem servers. Its homepage is at
		2618	L<http://rev.rubyforge.org/>.
		2619
		2620	=item D
		2621
		2622	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2623	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2624
		2625	=back
		2626
		2627
		2628	=head1 MACRO MAGIC
		2629
		2630	Libev can be compiled with a variety of options, the most fundamantal
		2631	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2632	functions and callbacks have an initial C<struct ev_loop *> argument.
		2633
		2634	To make it easier to write programs that cope with either variant, the
		2635	following macros are defined:
		2636
		2637	=over 4
		2638
		2639	=item C<EV_A>, C<EV_A_>
		2640
		2641	This provides the loop I<argument> for functions, if one is required ("ev
		2642	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2643	C<EV_A_> is used when other arguments are following. Example:
		2644
		2645	ev_unref (EV_A);
		2646	ev_timer_add (EV_A_ watcher);
		2647	ev_loop (EV_A_ 0);
		2648
		2649	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2650	which is often provided by the following macro.
		2651
		2652	=item C<EV_P>, C<EV_P_>
		2653
		2654	This provides the loop I<parameter> for functions, if one is required ("ev
		2655	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2656	C<EV_P_> is used when other parameters are following. Example:
		2657
		2658	// this is how ev_unref is being declared
		2659	static void ev_unref (EV_P);
		2660
		2661	// this is how you can declare your typical callback
		2662	static void cb (EV_P_ ev_timer *w, int revents)
		2663
		2664	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2665	suitable for use with C<EV_A>.
		2666
		2667	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2668
		2669	Similar to the other two macros, this gives you the value of the default
		2670	loop, if multiple loops are supported ("ev loop default").
		2671
		2672	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2673
		2674	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2675	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2676	is undefined when the default loop has not been initialised by a previous
		2677	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2678
		2679	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2680	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2681
		2682	=back
		2683
		2684	Example: Declare and initialise a check watcher, utilising the above
		2685	macros so it will work regardless of whether multiple loops are supported
		2686	or not.
		2687
		2688	static void
		2689	check_cb (EV_P_ ev_timer *w, int revents)
		2690	{
		2691	ev_check_stop (EV_A_ w);
		2692	}
		2693
		2694	ev_check check;
		2695	ev_check_init (&check, check_cb);
		2696	ev_check_start (EV_DEFAULT_ &check);
		2697	ev_loop (EV_DEFAULT_ 0);
		2698
		2699	=head1 EMBEDDING
		2700
		2701	Libev can (and often is) directly embedded into host
		2702	applications. Examples of applications that embed it include the Deliantra
		2703	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2704	and rxvt-unicode.
		2705
		2706	The goal is to enable you to just copy the necessary files into your
		2707	source directory without having to change even a single line in them, so
		2708	you can easily upgrade by simply copying (or having a checked-out copy of
		2709	libev somewhere in your source tree).
		2710
		2711	=head2 FILESETS
		2712
		2713	Depending on what features you need you need to include one or more sets of files
		2714	in your app.
		2715
		2716	=head3 CORE EVENT LOOP
		2717
		2718	To include only the libev core (all the C<ev_*> functions), with manual
		2719	configuration (no autoconf):
		2720
		2721	#define EV_STANDALONE 1
		2722	#include "ev.c"
		2723
		2724	This will automatically include F<ev.h>, too, and should be done in a
		2725	single C source file only to provide the function implementations. To use
		2726	it, do the same for F<ev.h> in all files wishing to use this API (best
		2727	done by writing a wrapper around F<ev.h> that you can include instead and
		2728	where you can put other configuration options):
		2729
		2730	#define EV_STANDALONE 1
		2731	#include "ev.h"
		2732
		2733	Both header files and implementation files can be compiled with a C++
		2734	compiler (at least, thats a stated goal, and breakage will be treated
		2735	as a bug).
		2736
		2737	You need the following files in your source tree, or in a directory
		2738	in your include path (e.g. in libev/ when using -Ilibev):
		2739
		2740	ev.h
		2741	ev.c
		2742	ev_vars.h
		2743	ev_wrap.h
		2744
		2745	ev_win32.c required on win32 platforms only
		2746
		2747	ev_select.c only when select backend is enabled (which is enabled by default)
		2748	ev_poll.c only when poll backend is enabled (disabled by default)
		2749	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2750	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2751	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2752
		2753	F<ev.c> includes the backend files directly when enabled, so you only need
		2754	to compile this single file.
		2755
		2756	=head3 LIBEVENT COMPATIBILITY API
		2757
		2758	To include the libevent compatibility API, also include:
		2759
		2760	#include "event.c"
		2761
		2762	in the file including F<ev.c>, and:
		2763
		2764	#include "event.h"
		2765
		2766	in the files that want to use the libevent API. This also includes F<ev.h>.
		2767
		2768	You need the following additional files for this:
		2769
		2770	event.h
		2771	event.c
		2772
		2773	=head3 AUTOCONF SUPPORT
		2774
		2775	Instead of using C<EV_STANDALONE=1> and providing your config in
		2776	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2777	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2778	include F<config.h> and configure itself accordingly.
		2779
		2780	For this of course you need the m4 file:
		2781
		2782	libev.m4
		2783
		2784	=head2 PREPROCESSOR SYMBOLS/MACROS
		2785
		2786	Libev can be configured via a variety of preprocessor symbols you have to
		2787	define before including any of its files. The default in the absense of
		2788	autoconf is noted for every option.
		2789
		2790	=over 4
		2791
		2792	=item EV_STANDALONE
		2793
		2794	Must always be C<1> if you do not use autoconf configuration, which
		2795	keeps libev from including F<config.h>, and it also defines dummy
		2796	implementations for some libevent functions (such as logging, which is not
		2797	supported). It will also not define any of the structs usually found in
		2798	F<event.h> that are not directly supported by the libev core alone.
		2799
		2800	=item EV_USE_MONOTONIC
		2801
		2802	If defined to be C<1>, libev will try to detect the availability of the
		2803	monotonic clock option at both compiletime and runtime. Otherwise no use
		2804	of the monotonic clock option will be attempted. If you enable this, you
		2805	usually have to link against librt or something similar. Enabling it when
		2806	the functionality isn't available is safe, though, although you have
		2807	to make sure you link against any libraries where the C<clock_gettime>
		2808	function is hiding in (often F<-lrt>).
		2809
		2810	=item EV_USE_REALTIME
		2811
		2812	If defined to be C<1>, libev will try to detect the availability of the
		2813	realtime clock option at compiletime (and assume its availability at
		2814	runtime if successful). Otherwise no use of the realtime clock option will
		2815	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2816	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2817	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2818
		2819	=item EV_USE_NANOSLEEP
		2820
		2821	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2822	and will use it for delays. Otherwise it will use C<select ()>.
		2823
		2824	=item EV_USE_EVENTFD
		2825
		2826	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2827	available and will probe for kernel support at runtime. This will improve
		2828	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2829	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2830	2.7 or newer, otherwise disabled.
		2831
		2832	=item EV_USE_SELECT
		2833
		2834	If undefined or defined to be C<1>, libev will compile in support for the
		2835	C<select>(2) backend. No attempt at autodetection will be done: if no
		2836	other method takes over, select will be it. Otherwise the select backend
		2837	will not be compiled in.
		2838
		2839	=item EV_SELECT_USE_FD_SET
		2840
		2841	If defined to C<1>, then the select backend will use the system C<fd_set>
		2842	structure. This is useful if libev doesn't compile due to a missing
		2843	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2844	exotic systems. This usually limits the range of file descriptors to some
		2845	low limit such as 1024 or might have other limitations (winsocket only
		2846	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2847	influence the size of the C<fd_set> used.
		2848
		2849	=item EV_SELECT_IS_WINSOCKET
		2850
		2851	When defined to C<1>, the select backend will assume that
		2852	select/socket/connect etc. don't understand file descriptors but
		2853	wants osf handles on win32 (this is the case when the select to
		2854	be used is the winsock select). This means that it will call
		2855	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2856	it is assumed that all these functions actually work on fds, even
		2857	on win32. Should not be defined on non-win32 platforms.
		2858
		2859	=item EV_FD_TO_WIN32_HANDLE
		2860
		2861	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2862	file descriptors to socket handles. When not defining this symbol (the
		2863	default), then libev will call C<_get_osfhandle>, which is usually
		2864	correct. In some cases, programs use their own file descriptor management,
		2865	in which case they can provide this function to map fds to socket handles.
		2866
		2867	=item EV_USE_POLL
		2868
		2869	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2870	backend. Otherwise it will be enabled on non-win32 platforms. It
		2871	takes precedence over select.
		2872
		2873	=item EV_USE_EPOLL
		2874
		2875	If defined to be C<1>, libev will compile in support for the Linux
		2876	C<epoll>(7) backend. Its availability will be detected at runtime,
		2877	otherwise another method will be used as fallback. This is the preferred
		2878	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2879	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2880
		2881	=item EV_USE_KQUEUE
		2882
		2883	If defined to be C<1>, libev will compile in support for the BSD style
		2884	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2885	otherwise another method will be used as fallback. This is the preferred
		2886	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2887	supports some types of fds correctly (the only platform we found that
		2888	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2889	not be used unless explicitly requested. The best way to use it is to find
		2890	out whether kqueue supports your type of fd properly and use an embedded
		2891	kqueue loop.
		2892
		2893	=item EV_USE_PORT
		2894
		2895	If defined to be C<1>, libev will compile in support for the Solaris
		2896	10 port style backend. Its availability will be detected at runtime,
		2897	otherwise another method will be used as fallback. This is the preferred
		2898	backend for Solaris 10 systems.
		2899
		2900	=item EV_USE_DEVPOLL
		2901
		2902	reserved for future expansion, works like the USE symbols above.
		2903
		2904	=item EV_USE_INOTIFY
		2905
		2906	If defined to be C<1>, libev will compile in support for the Linux inotify
		2907	interface to speed up C<ev_stat> watchers. Its actual availability will
		2908	be detected at runtime. If undefined, it will be enabled if the headers
		2909	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2910
		2911	=item EV_ATOMIC_T
		2912
		2913	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2914	access is atomic with respect to other threads or signal contexts. No such
		2915	type is easily found in the C language, so you can provide your own type
		2916	that you know is safe for your purposes. It is used both for signal handler "locking"
		2917	as well as for signal and thread safety in C<ev_async> watchers.
		2918
		2919	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2920	(from F<signal.h>), which is usually good enough on most platforms.
		2921
		2922	=item EV_H
		2923
		2924	The name of the F<ev.h> header file used to include it. The default if
		2925	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2926	used to virtually rename the F<ev.h> header file in case of conflicts.
		2927
		2928	=item EV_CONFIG_H
		2929
		2930	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2931	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2932	C<EV_H>, above.
		2933
		2934	=item EV_EVENT_H
		2935
		2936	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2937	of how the F<event.h> header can be found, the default is C<"event.h">.
		2938
		2939	=item EV_PROTOTYPES
		2940
		2941	If defined to be C<0>, then F<ev.h> will not define any function
		2942	prototypes, but still define all the structs and other symbols. This is
		2943	occasionally useful if you want to provide your own wrapper functions
		2944	around libev functions.
		2945
		2946	=item EV_MULTIPLICITY
		2947
		2948	If undefined or defined to C<1>, then all event-loop-specific functions
		2949	will have the C<struct ev_loop *> as first argument, and you can create
		2950	additional independent event loops. Otherwise there will be no support
		2951	for multiple event loops and there is no first event loop pointer
		2952	argument. Instead, all functions act on the single default loop.
		2953
		2954	=item EV_MINPRI
		2955
		2956	=item EV_MAXPRI
		2957
		2958	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2959	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2960	provide for more priorities by overriding those symbols (usually defined
		2961	to be C<-2> and C<2>, respectively).
		2962
		2963	When doing priority-based operations, libev usually has to linearly search
		2964	all the priorities, so having many of them (hundreds) uses a lot of space
		2965	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2966	fine.
		2967
		2968	If your embedding app does not need any priorities, defining these both to
		2969	C<0> will save some memory and cpu.
		2970
		2971	=item EV_PERIODIC_ENABLE
		2972
		2973	If undefined or defined to be C<1>, then periodic timers are supported. If
		2974	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2975	code.
		2976
		2977	=item EV_IDLE_ENABLE
		2978
		2979	If undefined or defined to be C<1>, then idle watchers are supported. If
		2980	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2981	code.
		2982
		2983	=item EV_EMBED_ENABLE
		2984
		2985	If undefined or defined to be C<1>, then embed watchers are supported. If
		2986	defined to be C<0>, then they are not.
		2987
		2988	=item EV_STAT_ENABLE
		2989
		2990	If undefined or defined to be C<1>, then stat watchers are supported. If
		2991	defined to be C<0>, then they are not.
		2992
		2993	=item EV_FORK_ENABLE
		2994
		2995	If undefined or defined to be C<1>, then fork watchers are supported. If
		2996	defined to be C<0>, then they are not.
		2997
		2998	=item EV_ASYNC_ENABLE
		2999
		3000	If undefined or defined to be C<1>, then async watchers are supported. If
		3001	defined to be C<0>, then they are not.
		3002
		3003	=item EV_MINIMAL
		3004
		3005	If you need to shave off some kilobytes of code at the expense of some
		3006	speed, define this symbol to C<1>. Currently this is used to override some
		3007	inlining decisions, saves roughly 30% codesize of amd64. It also selects a
		3008	much smaller 2-heap for timer management over the default 4-heap.
		3009
		3010	=item EV_PID_HASHSIZE
		3011
		3012	C<ev_child> watchers use a small hash table to distribute workload by
		3013	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3014	than enough. If you need to manage thousands of children you might want to
		3015	increase this value (I<must> be a power of two).
		3016
		3017	=item EV_INOTIFY_HASHSIZE
		3018
		3019	C<ev_stat> watchers use a small hash table to distribute workload by
		3020	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3021	usually more than enough. If you need to manage thousands of C<ev_stat>
		3022	watchers you might want to increase this value (I<must> be a power of
		3023	two).
		3024
		3025	=item EV_USE_4HEAP
		3026
		3027	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3028	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3029	to C<1>. The 4-heap uses more complicated (longer) code but has
		3030	noticably faster performance with many (thousands) of watchers.
		3031
		3032	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3033	(disabled).
		3034
		3035	=item EV_HEAP_CACHE_AT
		3036
		3037	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3038	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3039	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3040	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3041	but avoids random read accesses on heap changes. This improves performance
		3042	noticably with with many (hundreds) of watchers.
		3043
		3044	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3045	(disabled).
		3046
		3047	=item EV_VERIFY
		3048
		3049	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3050	be done: If set to C<0>, no internal verification code will be compiled
		3051	in. If set to C<1>, then verification code will be compiled in, but not
		3052	called. If set to C<2>, then the internal verification code will be
		3053	called once per loop, which can slow down libev. If set to C<3>, then the
		3054	verification code will be called very frequently, which will slow down
		3055	libev considerably.
		3056
		3057	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3058	C<0.>
		3059
		3060	=item EV_COMMON
		3061
		3062	By default, all watchers have a C<void *data> member. By redefining
		3063	this macro to a something else you can include more and other types of
		3064	members. You have to define it each time you include one of the files,
		3065	though, and it must be identical each time.
		3066
		3067	For example, the perl EV module uses something like this:
		3068
		3069	#define EV_COMMON \
		3070	SV *self; /* contains this struct */ \
		3071	SV *cb_sv, *fh /* note no trailing ";" */
		3072
		3073	=item EV_CB_DECLARE (type)
		3074
		3075	=item EV_CB_INVOKE (watcher, revents)
		3076
		3077	=item ev_set_cb (ev, cb)
		3078
		3079	Can be used to change the callback member declaration in each watcher,
		3080	and the way callbacks are invoked and set. Must expand to a struct member
		3081	definition and a statement, respectively. See the F<ev.h> header file for
		3082	their default definitions. One possible use for overriding these is to
		3083	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3084	method calls instead of plain function calls in C++.
		3085
		3086	=head2 EXPORTED API SYMBOLS
		3087
		3088	If you need to re-export the API (e.g. via a dll) and you need a list of
		3089	exported symbols, you can use the provided F<Symbol.*> files which list
		3090	all public symbols, one per line:
		3091
		3092	Symbols.ev for libev proper
		3093	Symbols.event for the libevent emulation
		3094
		3095	This can also be used to rename all public symbols to avoid clashes with
		3096	multiple versions of libev linked together (which is obviously bad in
		3097	itself, but sometimes it is inconvinient to avoid this).
		3098
		3099	A sed command like this will create wrapper C<#define>'s that you need to
		3100	include before including F<ev.h>:
		3101
		3102	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3103
		3104	This would create a file F<wrap.h> which essentially looks like this:
		3105
		3106	#define ev_backend myprefix_ev_backend
		3107	#define ev_check_start myprefix_ev_check_start
		3108	#define ev_check_stop myprefix_ev_check_stop
		3109	...
		3110
		3111	=head2 EXAMPLES
		3112
		3113	For a real-world example of a program the includes libev
		3114	verbatim, you can have a look at the EV perl module
		3115	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3116	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3117	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3118	will be compiled. It is pretty complex because it provides its own header
		3119	file.
		3120
		3121	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3122	that everybody includes and which overrides some configure choices:
		3123
		3124	#define EV_MINIMAL 1
		3125	#define EV_USE_POLL 0
		3126	#define EV_MULTIPLICITY 0
		3127	#define EV_PERIODIC_ENABLE 0
		3128	#define EV_STAT_ENABLE 0
		3129	#define EV_FORK_ENABLE 0
		3130	#define EV_CONFIG_H <config.h>
		3131	#define EV_MINPRI 0
		3132	#define EV_MAXPRI 0
		3133
		3134	#include "ev++.h"
		3135
		3136	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3137
		3138	#include "ev_cpp.h"
		3139	#include "ev.c"
		3140
		3141
		3142	=head1 THREADS AND COROUTINES
		3143
		3144	=head2 THREADS
		3145
		3146	Libev itself is completely threadsafe, but it uses no locking. This
		3147	means that you can use as many loops as you want in parallel, as long as
		3148	only one thread ever calls into one libev function with the same loop
		3149	parameter.
		3150
		3151	Or put differently: calls with different loop parameters can be done in
		3152	parallel from multiple threads, calls with the same loop parameter must be
		3153	done serially (but can be done from different threads, as long as only one
		3154	thread ever is inside a call at any point in time, e.g. by using a mutex
		3155	per loop).
		3156
		3157	If you want to know which design is best for your problem, then I cannot
		3158	help you but by giving some generic advice:
		3159
		3160	=over 4
		3161
		3162	=item * most applications have a main thread: use the default libev loop
		3163	in that thread, or create a seperate thread running only the default loop.
		3164
		3165	This helps integrating other libraries or software modules that use libev
		3166	themselves and don't care/know about threading.
		3167
		3168	=item * one loop per thread is usually a good model.
		3169
		3170	Doing this is almost never wrong, sometimes a better-performance model
		3171	exists, but it is always a good start.
		3172
		3173	=item * other models exist, such as the leader/follower pattern, where one
		3174	loop is handed through multiple threads in a kind of round-robbin fashion.
		3175
		3176	Chosing a model is hard - look around, learn, know that usually you cna do
		3177	better than you currently do :-)
		3178
		3179	=item * often you need to talk to some other thread which blocks in the
		3180	event loop - C<ev_async> watchers can be used to wake them up from other
		3181	threads safely (or from signal contexts...).
		3182
		3183	=back
		3184
		3185	=head2 COROUTINES
		3186
		3187	Libev is much more accomodating to coroutines ("cooperative threads"):
		3188	libev fully supports nesting calls to it's functions from different
		3189	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3190	different coroutines and switch freely between both coroutines running the
		3191	loop, as long as you don't confuse yourself). The only exception is that
		3192	you must not do this from C<ev_periodic> reschedule callbacks.
		3193
		3194	Care has been invested into making sure that libev does not keep local
		3195	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3196	switches.
		3197
		3198
		3199	=head1 COMPLEXITIES
		3200
		3201	In this section the complexities of (many of) the algorithms used inside
		3202	libev will be explained. For complexity discussions about backends see the
		3203	documentation for C<ev_default_init>.
		3204
		3205	All of the following are about amortised time: If an array needs to be
		3206	extended, libev needs to realloc and move the whole array, but this
		3207	happens asymptotically never with higher number of elements, so O(1) might
		3208	mean it might do a lengthy realloc operation in rare cases, but on average
		3209	it is much faster and asymptotically approaches constant time.
		3210
		3211	=over 4
		3212
		3213	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3214
		3215	This means that, when you have a watcher that triggers in one hour and
		3216	there are 100 watchers that would trigger before that then inserting will
		3217	have to skip roughly seven (C<ld 100>) of these watchers.
		3218
		3219	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3220
		3221	That means that changing a timer costs less than removing/adding them
		3222	as only the relative motion in the event queue has to be paid for.
		3223
		3224	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3225
		3226	These just add the watcher into an array or at the head of a list.
		3227
		3228	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3229
		3230	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3231
		3232	These watchers are stored in lists then need to be walked to find the
		3233	correct watcher to remove. The lists are usually short (you don't usually
		3234	have many watchers waiting for the same fd or signal).
		3235
		3236	=item Finding the next timer in each loop iteration: O(1)
		3237
		3238	By virtue of using a binary or 4-heap, the next timer is always found at a
		3239	fixed position in the storage array.
		3240
		3241	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3242
		3243	A change means an I/O watcher gets started or stopped, which requires
		3244	libev to recalculate its status (and possibly tell the kernel, depending
		3245	on backend and wether C<ev_io_set> was used).
		3246
		3247	=item Activating one watcher (putting it into the pending state): O(1)
		3248
		3249	=item Priority handling: O(number_of_priorities)
		3250
		3251	Priorities are implemented by allocating some space for each
		3252	priority. When doing priority-based operations, libev usually has to
		3253	linearly search all the priorities, but starting/stopping and activating
		3254	watchers becomes O(1) w.r.t. priority handling.
		3255
		3256	=item Sending an ev_async: O(1)
		3257
		3258	=item Processing ev_async_send: O(number_of_async_watchers)
		3259
		3260	=item Processing signals: O(max_signal_number)
		3261
		3262	Sending involves a syscall I<iff> there were no other C<ev_async_send>
		3263	calls in the current loop iteration. Checking for async and signal events
		3264	involves iterating over all running async watchers or all signal numbers.
		3265
		3266	=back
		3267
		3268
		3269	=head1 Win32 platform limitations and workarounds
		3270
		3271	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3272	requires, and its I/O model is fundamentally incompatible with the POSIX
		3273	model. Libev still offers limited functionality on this platform in
		3274	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3275	descriptors. This only applies when using Win32 natively, not when using
		3276	e.g. cygwin.
		3277
		3278	Lifting these limitations would basically require the full
		3279	re-implementation of the I/O system. If you are into these kinds of
		3280	things, then note that glib does exactly that for you in a very portable
		3281	way (note also that glib is the slowest event library known to man).
		3282
		3283	There is no supported compilation method available on windows except
		3284	embedding it into other applications.
		3285
		3286	Due to the many, low, and arbitrary limits on the win32 platform and
		3287	the abysmal performance of winsockets, using a large number of sockets
		3288	is not recommended (and not reasonable). If your program needs to use
		3289	more than a hundred or so sockets, then likely it needs to use a totally
		3290	different implementation for windows, as libev offers the POSIX readiness
		3291	notification model, which cannot be implemented efficiently on windows
		3292	(microsoft monopoly games).
		3293
		3294	=over 4
		3295
		3296	=item The winsocket select function
		3297
		3298	The winsocket C<select> function doesn't follow POSIX in that it requires
		3299	socket I<handles> and not socket I<file descriptors>. This makes select
		3300	very inefficient, and also requires a mapping from file descriptors
		3301	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		3302	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		3303	symbols for more info.
		3304
		3305	The configuration for a "naked" win32 using the microsoft runtime
		3306	libraries and raw winsocket select is:
		3307
		3308	#define EV_USE_SELECT 1
		3309	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3310
		3311	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3312	complexity in the O(n²) range when using win32.
		3313
		3314	=item Limited number of file descriptors
		3315
		3316	Windows has numerous arbitrary (and low) limits on things.
		3317
		3318	Early versions of winsocket's select only supported waiting for a maximum
		3319	of C<64> handles (probably owning to the fact that all windows kernels
		3320	can only wait for C<64> things at the same time internally; microsoft
		3321	recommends spawning a chain of threads and wait for 63 handles and the
		3322	previous thread in each. Great).
		3323
		3324	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3325	to some high number (e.g. C<2048>) before compiling the winsocket select
		3326	call (which might be in libev or elsewhere, for example, perl does its own
		3327	select emulation on windows).
		3328
		3329	Another limit is the number of file descriptors in the microsoft runtime
		3330	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3331	or something like this inside microsoft). You can increase this by calling
		3332	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3333	arbitrary limit), but is broken in many versions of the microsoft runtime
		3334	libraries.
		3335
		3336	This might get you to about C<512> or C<2048> sockets (depending on
		3337	windows version and/or the phase of the moon). To get more, you need to
		3338	wrap all I/O functions and provide your own fd management, but the cost of
		3339	calling select (O(n²)) will likely make this unworkable.
		3340
		3341	=back
		3342
		3343
		3344	=head1 PORTABILITY REQUIREMENTS
		3345
		3346	In addition to a working ISO-C implementation, libev relies on a few
		3347	additional extensions:
		3348
		3349	=over 4
		3350
		3351	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3352
		3353	The type C<sig_atomic_t volatile> (or whatever is defined as
		3354	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3355	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3356	believed to be sufficiently portable.
		3357
		3358	=item C<sigprocmask> must work in a threaded environment
		3359
		3360	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3361	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3362	pthread implementations will either allow C<sigprocmask> in the "main
		3363	thread" or will block signals process-wide, both behaviours would
		3364	be compatible with libev. Interaction between C<sigprocmask> and
		3365	C<pthread_sigmask> could complicate things, however.
		3366
		3367	The most portable way to handle signals is to block signals in all threads
		3368	except the initial one, and run the default loop in the initial thread as
		3369	well.
		3370
		3371	=item C<long> must be large enough for common memory allocation sizes
		3372
		3373	To improve portability and simplify using libev, libev uses C<long>
		3374	internally instead of C<size_t> when allocating its data structures. On
		3375	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3376	is still at least 31 bits everywhere, which is enough for hundreds of
		3377	millions of watchers.
		3378
		3379	=item C<double> must hold a time value in seconds with enough accuracy
		3380
		3381	The type C<double> is used to represent timestamps. It is required to
		3382	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3383	enough for at least into the year 4000. This requirement is fulfilled by
		3384	implementations implementing IEEE 754 (basically all existing ones).
		3385
		3386	=back
		3387
		3388	If you know of other additional requirements drop me a note.
		3389
		3390
		3391	=head1 VALGRIND
		3392
		3393	Valgrind has a special section here because it is a popular tool that is
		3394	highly useful, but valgrind reports are very hard to interpret.
		3395
		3396	If you think you found a bug (memory leak, uninitialised data access etc.)
		3397	in libev, then check twice: If valgrind reports something like:
		3398
		3399	==2274== definitely lost: 0 bytes in 0 blocks.
		3400	==2274== possibly lost: 0 bytes in 0 blocks.
		3401	==2274== still reachable: 256 bytes in 1 blocks.
		3402
		3403	then there is no memory leak. Similarly, under some circumstances,
		3404	valgrind might report kernel bugs as if it were a bug in libev, or it
		3405	might be confused (it is a very good tool, but only a tool).
		3406
		3407	If you are unsure about something, feel free to contact the mailing list
		3408	with the full valgrind report and an explanation on why you think this is
		3409	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3410	no bug" answer and take the chance of learning how to interpret valgrind
		3411	properly.
		3412
		3413	If you need, for some reason, empty reports from valgrind for your project
		3414	I suggest using suppression lists.
		3415
878		3416
879	=head1 AUTHOR	3417	=head1 AUTHOR
880		3418
881	Marc Lehmann <libev@schmorp.de>.	3419	Marc Lehmann <libev@schmorp.de>.
882		3420

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