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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 AND OTHER GLOBAL FUNCTIONS	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	117	to the C<double> type in C, and when you need to do any calculations on
		118	it, you should treat it as some floatingpoint value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 GLOBAL FUNCTIONS
		123
		124	These functions can be called anytime, even before initialising the
		125	library in any way.
51		126
52	=over 4	127	=over 4
53		128
54	=item ev_tstamp ev_time ()	129	=item ev_tstamp ev_time ()
55		130
56	Returns the current time as libev would use it.	131	Returns the current time as libev would use it. Please note that the
		132	C<ev_now> function is usually faster and also often returns the timestamp
		133	you actually want to know.
		134
		135	=item ev_sleep (ev_tstamp interval)
		136
		137	Sleep for the given interval: The current thread will be blocked until
		138	either it is interrupted or the given time interval has passed. Basically
		139	this is a subsecond-resolution C<sleep ()>.
57		140
58	=item int ev_version_major ()	141	=item int ev_version_major ()
59		142
60	=item int ev_version_minor ()	143	=item int ev_version_minor ()
61		144
62	You can find out the major and minor version numbers of the library	145	You can find out the major and minor ABI version numbers of the library
63	you linked against by calling the functions C<ev_version_major> and	146	you linked against by calling the functions C<ev_version_major> and
64	C<ev_version_minor>. If you want, you can compare against the global	147	C<ev_version_minor>. If you want, you can compare against the global
65	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	148	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	149	version of the library your program was compiled against.
67		150
		151	These version numbers refer to the ABI version of the library, not the
		152	release version.
		153
68	Usually, it's a good idea to terminate if the major versions mismatch,	154	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	155	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	156	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	157	not a problem.
72		158
		159	Example: Make sure we haven't accidentally been linked against the wrong
		160	version.
		161
		162	assert (("libev version mismatch",
		163	ev_version_major () == EV_VERSION_MAJOR
		164	&& ev_version_minor () >= EV_VERSION_MINOR));
		165
		166	=item unsigned int ev_supported_backends ()
		167
		168	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		169	value) compiled into this binary of libev (independent of their
		170	availability on the system you are running on). See C<ev_default_loop> for
		171	a description of the set values.
		172
		173	Example: make sure we have the epoll method, because yeah this is cool and
		174	a must have and can we have a torrent of it please!!!11
		175
		176	assert (("sorry, no epoll, no sex",
		177	ev_supported_backends () & EVBACKEND_EPOLL));
		178
		179	=item unsigned int ev_recommended_backends ()
		180
		181	Return the set of all backends compiled into this binary of libev and also
		182	recommended for this platform. This set is often smaller than the one
		183	returned by C<ev_supported_backends>, as for example kqueue is broken on
		184	most BSDs and will not be autodetected unless you explicitly request it
		185	(assuming you know what you are doing). This is the set of backends that
		186	libev will probe for if you specify no backends explicitly.
		187
		188	=item unsigned int ev_embeddable_backends ()
		189
		190	Returns the set of backends that are embeddable in other event loops. This
		191	is the theoretical, all-platform, value. To find which backends
		192	might be supported on the current system, you would need to look at
		193	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		194	recommended ones.
		195
		196	See the description of C<ev_embed> watchers for more info.
		197
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
74		199
75	Sets the allocation function to use (the prototype is similar to the	200	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	201	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
77	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
78	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
79	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.
80		209
81	You could override this function in high-availability programs to, say,	210	You could override this function in high-availability programs to, say,
82	free some memory if it cannot allocate memory, to use a special allocator,	211	free some memory if it cannot allocate memory, to use a special allocator,
83	or even to sleep a while and retry until some memory is available.	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);
84		233
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	234	=item ev_set_syserr_cb (void (*cb)(const char *msg));
86		235
87	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
88	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
…		…
90	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
91	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
92	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
93	(such as abort).	242	(such as abort).
94		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
95	=back	256	=back
96		257
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	258	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98		259
99	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
100	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
101	events, and dynamically created loops which do not.	262	events, and dynamically created loops which do not.
102		263
103	If you use threads, a common model is to run the default event loop
104	in your main thread (or in a separate thrad) and for each thread you
105	create, you also create another event loop. Libev itself does no locking
106	whatsoever, so if you mix calls to the same event loop in different
107	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because it's hideous and inefficient).
109
110	=over 4	264	=over 4
111		265
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	266	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		267
114	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
115	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
116	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
117	flags).	271	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		272
119	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
120	function.	274	function.
121		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
122	The flags argument can be used to specify special behaviour or specific	287	The flags argument can be used to specify special behaviour or specific
123	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	288	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		289
125	It supports the following flags:	290	The following flags are supported:
126		291
127	=over 4	292	=over 4
128		293
129	=item C<EVFLAG_AUTO>	294	=item C<EVFLAG_AUTO>
130		295
…		…
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	304	override the flags completely if it is found in the environment. This is
140	useful to try out specific backends to test their performance, or to work	305	useful to try out specific backends to test their performance, or to work
141	around bugs.	306	around bugs.
142		307
		308	=item C<EVFLAG_FORKCHECK>
		309
		310	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		311	a fork, you can also make libev check for a fork in each iteration by
		312	enabling this flag.
		313
		314	This works by calling C<getpid ()> on every iteration of the loop,
		315	and thus this might slow down your event loop if you do a lot of loop
		316	iterations and little real work, but is usually not noticeable (on my
		317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		318	without a syscall and thus I<very> fast, but my GNU/Linux system also has
		319	C<pthread_atfork> which is even faster).
		320
		321	The big advantage of this flag is that you can forget about fork (and
		322	forget about forgetting to tell libev about forking) when you use this
		323	flag.
		324
		325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		326	environment variable.
		327
143	=item C<EVMETHOD_SELECT> (portable select backend)	328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		329
		330	This is your standard select(2) backend. Not I<completely> standard, as
		331	libev tries to roll its own fd_set with no limits on the number of fds,
		332	but if that fails, expect a fairly low limit on the number of fds when
		333	using this backend. It doesn't scale too well (O(highest_fd)), but its
		334	usually the fastest backend for a low number of (low-numbered :) fds.
		335
		336	To get good performance out of this backend you need a high amount of
		337	parallelity (most of the file descriptors should be busy). If you are
		338	writing a server, you should C<accept ()> in a loop to accept as many
		339	connections as possible during one iteration. You might also want to have
		340	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		341	readiness notifications you get per iteration.
		342
145	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
146		344
147	=item C<EVMETHOD_EPOLL> (linux only)	345	And this is your standard poll(2) backend. It's more complicated
		346	than select, but handles sparse fds better and has no artificial
		347	limit on the number of fds you can use (except it will slow down
		348	considerably with a lot of inactive fds). It scales similarly to select,
		349	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		350	performance tips.
148		351
149	=item C<EVMETHOD_KQUEUE> (some bsds only)	352	=item C<EVBACKEND_EPOLL> (value 4, Linux)
150		353
151	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	354	For few fds, this backend is a bit little slower than poll and select,
		355	but it scales phenomenally better. While poll and select usually scale
		356	like O(total_fds) where n is the total number of fds (or the highest fd),
		357	epoll scales either O(1) or O(active_fds). The epoll design has a number
		358	of shortcomings, such as silently dropping events in some hard-to-detect
		359	cases and requiring a syscall per fd change, no fork support and bad
		360	support for dup.
152		361
153	=item C<EVMETHOD_PORT> (solaris 10 only)	362	While stopping, setting and starting an I/O watcher in the same iteration
		363	will result in some caching, there is still a syscall per such incident
		364	(because the fd could point to a different file description now), so its
		365	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		366	very well if you register events for both fds.
		367
		368	Please note that epoll sometimes generates spurious notifications, so you
		369	need to use non-blocking I/O or other means to avoid blocking when no data
		370	(or space) is available.
		371
		372	Best performance from this backend is achieved by not unregistering all
		373	watchers for a file descriptor until it has been closed, if possible, i.e.
		374	keep at least one watcher active per fd at all times.
		375
		376	While nominally embeddeble in other event loops, this feature is broken in
		377	all kernel versions tested so far.
		378
		379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		380
		381	Kqueue deserves special mention, as at the time of this writing, it
		382	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		383	with anything but sockets and pipes, except on Darwin, where of course
		384	it's completely useless). For this reason it's not being "autodetected"
		385	unless you explicitly specify it explicitly in the flags (i.e. using
		386	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		387	system like NetBSD.
		388
		389	You still can embed kqueue into a normal poll or select backend and use it
		390	only for sockets (after having made sure that sockets work with kqueue on
		391	the target platform). See C<ev_embed> watchers for more info.
		392
		393	It scales in the same way as the epoll backend, but the interface to the
		394	kernel is more efficient (which says nothing about its actual speed, of
		395	course). While stopping, setting and starting an I/O watcher does never
		396	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
		397	two event changes per incident, support for C<fork ()> is very bad and it
		398	drops fds silently in similarly hard-to-detect cases.
		399
		400	This backend usually performs well under most conditions.
		401
		402	While nominally embeddable in other event loops, this doesn't work
		403	everywhere, so you might need to test for this. And since it is broken
		404	almost everywhere, you should only use it when you have a lot of sockets
		405	(for which it usually works), by embedding it into another event loop
		406	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		407	sockets.
		408
		409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		410
		411	This is not implemented yet (and might never be, unless you send me an
		412	implementation). According to reports, C</dev/poll> only supports sockets
		413	and is not embeddable, which would limit the usefulness of this backend
		414	immensely.
		415
		416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		417
		418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		419	it's really slow, but it still scales very well (O(active_fds)).
		420
		421	Please note that solaris event ports can deliver a lot of spurious
		422	notifications, so you need to use non-blocking I/O or other means to avoid
		423	blocking when no data (or space) is available.
		424
		425	While this backend scales well, it requires one system call per active
		426	file descriptor per loop iteration. For small and medium numbers of file
		427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		428	might perform better.
		429
		430	On the positive side, ignoring the spurious 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
		434	=item C<EVBACKEND_ALL>
		435
		436	Try all backends (even potentially broken ones that wouldn't be tried
		437	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		438	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		439
		440	It is definitely not recommended to use this flag.
		441
		442	=back
154		443
155	If one or more of these are ored into the flags value, then only these	444	If one or more of these are ored into the flags value, then only these
156	backends will be tried (in the reverse order as given here). If one are	445	backends will be tried (in the reverse order as listed here). If none are
157	specified, any backend will do.	446	specified, all backends in C<ev_recommended_backends ()> will be tried.
158		447
159	=back	448	The most typical usage is like this:
		449
		450	if (!ev_default_loop (0))
		451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		452
		453	Restrict libev to the select and poll backends, and do not allow
		454	environment settings to be taken into account:
		455
		456	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		457
		458	Use whatever libev has to offer, but make sure that kqueue is used if
		459	available (warning, breaks stuff, best use only with your own private
		460	event loop and only if you know the OS supports your types of fds):
		461
		462	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		463
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	464	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		465
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	466	Similar to C<ev_default_loop>, but always creates a new event loop that is
164	always distinct from the default loop. Unlike the default loop, it cannot	467	always distinct from the default loop. Unlike the default loop, it cannot
165	handle signal and child watchers, and attempts to do so will be greeted by	468	handle signal and child watchers, and attempts to do so will be greeted by
166	undefined behaviour (or a failed assertion if assertions are enabled).	469	undefined behaviour (or a failed assertion if assertions are enabled).
167		470
		471	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
168	=item ev_default_destroy ()	481	=item ev_default_destroy ()
169		482
170	Destroys the default loop again (frees all memory and kernel state	483	Destroys the default loop again (frees all memory and kernel state
171	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
172	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>).
173		499
174	=item ev_loop_destroy (loop)	500	=item ev_loop_destroy (loop)
175		501
176	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
177	earlier call to C<ev_loop_new>.	503	earlier call to C<ev_loop_new>.
178		504
179	=item ev_default_fork ()	505	=item ev_default_fork ()
180		506
		507	This function sets a flag that causes subsequent C<ev_loop> iterations
181	This function reinitialises the kernel state for backends that have	508	to reinitialise the kernel state for backends that have one. Despite the
182	one. Despite the name, you can call it anytime, but it makes most sense	509	name, you can call it anytime, but it makes most sense after forking, in
183	after forking, in either the parent or child process (or both, but that	510	the child process (or both child and parent, but that again makes little
184	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.
185		513
186	You I<must> call this function after forking if and only if you want to	514	On the other hand, you only need to call this function in the child
187	use the event library in both processes. If you just fork+exec, you don't	515	process if and only if you want to use the event library in the child. If
188	have to call it.	516	you just fork+exec, you don't have to call it at all.
189		517
190	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
191	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
192	quite nicely into a call to C<pthread_atfork>:	520	quite nicely into a call to C<pthread_atfork>:
193		521
…		…
197		525
198	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
199	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
200	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.
201		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
202	=item unsigned int ev_method (loop)	544	=item unsigned int ev_backend (loop)
203		545
204	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
205	use.	547	use.
206		548
207	=item ev_tstamp ev_now (loop)	549	=item ev_tstamp ev_now (loop)
208		550
209	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
210	got events and started processing them. This timestamp does not change	552	received events and started processing them. This timestamp does not
211	as long as callbacks are being processed, and this is also the base time	553	change as long as callbacks are being processed, and this is also the base
212	used for relative timers. You can treat it as the timestamp of the event	554	time used for relative timers. You can treat it as the timestamp of the
213	occuring (or more correctly, the mainloop finding out about it).	555	event occurring (or more correctly, libev finding out about it).
214		556
215	=item ev_loop (loop, int flags)	557	=item ev_loop (loop, int flags)
216		558
217	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
218	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
219	events.	561	events.
220		562
221	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
222	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.
223		571
224	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
225	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
226	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.
227		575
228	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
229	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
230	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
231	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.
232		583
233	This flags value could be used to implement alternative looping	584	Here are the gory details of what C<ev_loop> does:
234	constructs, but the C<prepare> and C<check> watchers provide a better and	585
235	more generic mechanism.	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.
		589	- Queue and call all prepare watchers.
		590	- If we have been forked, recreate the kernel state.
		591	- Update the kernel state with all outstanding changes.
		592	- Update the "event loop time".
		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.
		597	- Block the process, waiting for any events.
		598	- Queue all outstanding I/O (fd) events.
		599	- Update the "event loop time" and do time jump handling.
		600	- Queue all outstanding timers.
		601	- Queue all outstanding periodics.
		602	- If no events are pending now, queue all idle watchers.
		603	- Queue all check watchers.
		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.
		607	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		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!
236		618
237	=item ev_unloop (loop, how)	619	=item ev_unloop (loop, how)
238		620
239	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
240	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
241	C<EVUNLOOP_ONCE>, 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
242	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.
243		627
244	=item ev_ref (loop)	628	=item ev_ref (loop)
245		629
246	=item ev_unref (loop)	630	=item ev_unref (loop)
247		631
…		…
252	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
253	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
254	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
255	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
256	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
257	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.
258		693
259	=back	694	=back
		695
260		696
261	=head1 ANATOMY OF A WATCHER	697	=head1 ANATOMY OF A WATCHER
262		698
263	A watcher is a structure that you create and register to record your	699	A watcher is a structure that you create and register to record your
264	interest in some event. For instance, if you want to wait for STDIN to	700	interest in some event. For instance, if you want to wait for STDIN to
…		…
297	*) >>), and you can stop watching for events at any time by calling the	733	*) >>), and you can stop watching for events at any time by calling the
298	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	734	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
299		735
300	As long as your watcher is active (has been started but not stopped) you	736	As long as your watcher is active (has been started but not stopped) you
301	must not touch the values stored in it. Most specifically you must never	737	must not touch the values stored in it. Most specifically you must never
302	reinitialise it or call its set method.	738	reinitialise it or call its C<set> macro.
303
304	You cna check whether an event is active by calling the C<ev_is_active
305	(watcher *)> macro. To see whether an event is outstanding (but the
306	callback for it has not been called yet) you cna use the C<ev_is_pending
307	(watcher *)> macro.
308		739
309	Each and every callback receives the event loop pointer as first, the	740	Each and every callback receives the event loop pointer as first, the
310	registered watcher structure as second, and a bitset of received events as	741	registered watcher structure as second, and a bitset of received events as
311	third argument.	742	third argument.
312		743
313	The rceeived events usually include a single bit per event type received	744	The received events usually include a single bit per event type received
314	(you can receive multiple events at the same time). The possible bit masks	745	(you can receive multiple events at the same time). The possible bit masks
315	are:	746	are:
316		747
317	=over 4	748	=over 4
318		749
…		…
336	The signal specified in the C<ev_signal> watcher has been received by a thread.	767	The signal specified in the C<ev_signal> watcher has been received by a thread.
337		768
338	=item C<EV_CHILD>	769	=item C<EV_CHILD>
339		770
340	The pid specified in the C<ev_child> watcher has received a status change.	771	The pid specified in the C<ev_child> watcher has received a status change.
		772
		773	=item C<EV_STAT>
		774
		775	The path specified in the C<ev_stat> watcher changed its attributes somehow.
341		776
342	=item C<EV_IDLE>	777	=item C<EV_IDLE>
343		778
344	The C<ev_idle> watcher has determined that you have nothing better to do.	779	The C<ev_idle> watcher has determined that you have nothing better to do.
345		780
…		…
353	received events. Callbacks of both watcher types can start and stop as	788	received events. Callbacks of both watcher types can start and stop as
354	many watchers as they want, and all of them will be taken into account	789	many watchers as they want, and all of them will be taken into account
355	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	790	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
356	C<ev_loop> from blocking).	791	C<ev_loop> from blocking).
357		792
		793	=item C<EV_EMBED>
		794
		795	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		796
		797	=item C<EV_FORK>
		798
		799	The event loop has been resumed in the child process after fork (see
		800	C<ev_fork>).
		801
		802	=item C<EV_ASYNC>
		803
		804	The given async watcher has been asynchronously notified (see C<ev_async>).
		805
358	=item C<EV_ERROR>	806	=item C<EV_ERROR>
359		807
360	An unspecified error has occured, the watcher has been stopped. This might	808	An unspecified error has occured, the watcher has been stopped. This might
361	happen because the watcher could not be properly started because libev	809	happen because the watcher could not be properly started because libev
362	ran out of memory, a file descriptor was found to be closed or any other	810	ran out of memory, a file descriptor was found to be closed or any other
…		…
369	with the error from read() or write(). This will not work in multithreaded	817	with the error from read() or write(). This will not work in multithreaded
370	programs, though, so beware.	818	programs, though, so beware.
371		819
372	=back	820	=back
373		821
		822	=head2 GENERIC WATCHER FUNCTIONS
		823
		824	In the following description, C<TYPE> stands for the watcher type,
		825	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		826
		827	=over 4
		828
		829	=item C<ev_init> (ev_TYPE *watcher, callback)
		830
		831	This macro initialises the generic portion of a watcher. The contents
		832	of the watcher object can be arbitrary (so C<malloc> will do). Only
		833	the generic parts of the watcher are initialised, you I<need> to call
		834	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		835	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		836	which rolls both calls into one.
		837
		838	You can reinitialise a watcher at any time as long as it has been stopped
		839	(or never started) and there are no pending events outstanding.
		840
		841	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		842	int revents)>.
		843
		844	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		845
		846	This macro initialises the type-specific parts of a watcher. You need to
		847	call C<ev_init> at least once before you call this macro, but you can
		848	call C<ev_TYPE_set> any number of times. You must not, however, call this
		849	macro on a watcher that is active (it can be pending, however, which is a
		850	difference to the C<ev_init> macro).
		851
		852	Although some watcher types do not have type-specific arguments
		853	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		854
		855	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		856
		857	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		858	calls into a single call. This is the most convinient method to initialise
		859	a watcher. The same limitations apply, of course.
		860
		861	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		862
		863	Starts (activates) the given watcher. Only active watchers will receive
		864	events. If the watcher is already active nothing will happen.
		865
		866	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		867
		868	Stops the given watcher again (if active) and clears the pending
		869	status. It is possible that stopped watchers are pending (for example,
		870	non-repeating timers are being stopped when they become pending), but
		871	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		872	you want to free or reuse the memory used by the watcher it is therefore a
		873	good idea to always call its C<ev_TYPE_stop> function.
		874
		875	=item bool ev_is_active (ev_TYPE *watcher)
		876
		877	Returns a true value iff the watcher is active (i.e. it has been started
		878	and not yet been stopped). As long as a watcher is active you must not modify
		879	it.
		880
		881	=item bool ev_is_pending (ev_TYPE *watcher)
		882
		883	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		884	events but its callback has not yet been invoked). As long as a watcher
		885	is pending (but not active) you must not call an init function on it (but
		886	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		887	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		888	it).
		889
		890	=item callback ev_cb (ev_TYPE *watcher)
		891
		892	Returns the callback currently set on the watcher.
		893
		894	=item ev_cb_set (ev_TYPE *watcher, callback)
		895
		896	Change the callback. You can change the callback at virtually any time
		897	(modulo threads).
		898
		899	=item ev_set_priority (ev_TYPE *watcher, priority)
		900
		901	=item int ev_priority (ev_TYPE *watcher)
		902
		903	Set and query the priority of the watcher. The priority is a small
		904	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		905	(default: C<-2>). Pending watchers with higher priority will be invoked
		906	before watchers with lower priority, but priority will not keep watchers
		907	from being executed (except for C<ev_idle> watchers).
		908
		909	This means that priorities are I<only> used for ordering callback
		910	invocation after new events have been received. This is useful, for
		911	example, to reduce latency after idling, or more often, to bind two
		912	watchers on the same event and make sure one is called first.
		913
		914	If you need to suppress invocation when higher priority events are pending
		915	you need to look at C<ev_idle> watchers, which provide this functionality.
		916
		917	You I<must not> change the priority of a watcher as long as it is active or
		918	pending.
		919
		920	The default priority used by watchers when no priority has been set is
		921	always C<0>, which is supposed to not be too high and not be too low :).
		922
		923	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		924	fine, as long as you do not mind that the priority value you query might
		925	or might not have been adjusted to be within valid range.
		926
		927	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		928
		929	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		930	C<loop> nor C<revents> need to be valid as long as the watcher callback
		931	can deal with that fact.
		932
		933	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		934
		935	If the watcher is pending, this function returns clears its pending status
		936	and returns its C<revents> bitset (as if its callback was invoked). If the
		937	watcher isn't pending it does nothing and returns C<0>.
		938
		939	=back
		940
		941
374	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	942	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
375		943
376	Each watcher has, by default, a member C<void *data> that you can change	944	Each watcher has, by default, a member C<void *data> that you can change
377	and read at any time, libev will completely ignore it. This cna be used	945	and read at any time, libev will completely ignore it. This can be used
378	to associate arbitrary data with your watcher. If you need more data and	946	to associate arbitrary data with your watcher. If you need more data and
379	don't want to allocate memory and store a pointer to it in that data	947	don't want to allocate memory and store a pointer to it in that data
380	member, you can also "subclass" the watcher type and provide your own	948	member, you can also "subclass" the watcher type and provide your own
381	data:	949	data:
382		950
…		…
395	{	963	{
396	struct my_io *w = (struct my_io *)w_;	964	struct my_io *w = (struct my_io *)w_;
397	...	965	...
398	}	966	}
399		967
400	More interesting and less C-conformant ways of catsing your callback type	968	More interesting and less C-conformant ways of casting your callback type
401	have been omitted....	969	instead have been omitted.
		970
		971	Another common scenario is having some data structure with multiple
		972	watchers:
		973
		974	struct my_biggy
		975	{
		976	int some_data;
		977	ev_timer t1;
		978	ev_timer t2;
		979	}
		980
		981	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		982	you need to use C<offsetof>:
		983
		984	#include <stddef.h>
		985
		986	static void
		987	t1_cb (EV_P_ struct ev_timer *w, int revents)
		988	{
		989	struct my_biggy big = (struct my_biggy *
		990	(((char *)w) - offsetof (struct my_biggy, t1));
		991	}
		992
		993	static void
		994	t2_cb (EV_P_ struct ev_timer *w, int revents)
		995	{
		996	struct my_biggy big = (struct my_biggy *
		997	(((char *)w) - offsetof (struct my_biggy, t2));
		998	}
402		999
403		1000
404	=head1 WATCHER TYPES	1001	=head1 WATCHER TYPES
405		1002
406	This section describes each watcher in detail, but will not repeat	1003	This section describes each watcher in detail, but will not repeat
407	information given in the last section.	1004	information given in the last section. Any initialisation/set macros,
		1005	functions and members specific to the watcher type are explained.
408		1006
		1007	Members are additionally marked with either I<[read-only]>, meaning that,
		1008	while the watcher is active, you can look at the member and expect some
		1009	sensible content, but you must not modify it (you can modify it while the
		1010	watcher is stopped to your hearts content), or I<[read-write]>, which
		1011	means you can expect it to have some sensible content while the watcher
		1012	is active, but you can also modify it. Modifying it may not do something
		1013	sensible or take immediate effect (or do anything at all), but libev will
		1014	not crash or malfunction in any way.
		1015
		1016
409	=head2 C<ev_io> - is this file descriptor readable or writable	1017	=head2 C<ev_io> - is this file descriptor readable or writable?
410		1018
411	I/O watchers check whether a file descriptor is readable or writable	1019	I/O watchers check whether a file descriptor is readable or writable
412	in each iteration of the event loop (This behaviour is called	1020	in each iteration of the event loop, or, more precisely, when reading
413	level-triggering because you keep receiving events as long as the	1021	would not block the process and writing would at least be able to write
414	condition persists. Remember you cna stop the watcher if you don't want to	1022	some data. This behaviour is called level-triggering because you keep
415	act on the event and neither want to receive future events).	1023	receiving events as long as the condition persists. Remember you can stop
		1024	the watcher if you don't want to act on the event and neither want to
		1025	receive future events.
416		1026
417	In general you can register as many read and/or write event watchers oer	1027	In general you can register as many read and/or write event watchers per
418	fd as you want (as long as you don't confuse yourself). Setting all file	1028	fd as you want (as long as you don't confuse yourself). Setting all file
419	descriptors to non-blocking mode is also usually a good idea (but not	1029	descriptors to non-blocking mode is also usually a good idea (but not
420	required if you know what you are doing).	1030	required if you know what you are doing).
421		1031
422	You have to be careful with dup'ed file descriptors, though. Some backends
423	(the linux epoll backend is a notable example) cannot handle dup'ed file
424	descriptors correctly if you register interest in two or more fds pointing
425	to the same file/socket etc. description.
426
427	If you must do this, then force the use of a known-to-be-good backend	1032	If you must do this, then force the use of a known-to-be-good backend
428	(at the time of this writing, this includes only EVMETHOD_SELECT and	1033	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
429	EVMETHOD_POLL).	1034	C<EVBACKEND_POLL>).
		1035
		1036	Another thing you have to watch out for is that it is quite easy to
		1037	receive "spurious" readiness notifications, that is your callback might
		1038	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1039	because there is no data. Not only are some backends known to create a
		1040	lot of those (for example solaris ports), it is very easy to get into
		1041	this situation even with a relatively standard program structure. Thus
		1042	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1043	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1044
		1045	If you cannot run the fd in non-blocking mode (for example you should not
		1046	play around with an Xlib connection), then you have to seperately re-test
		1047	whether a file descriptor is really ready with a known-to-be good interface
		1048	such as poll (fortunately in our Xlib example, Xlib already does this on
		1049	its own, so its quite safe to use).
		1050
		1051	=head3 The special problem of disappearing file descriptors
		1052
		1053	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1054	descriptor (either by calling C<close> explicitly or by any other means,
		1055	such as C<dup>). The reason is that you register interest in some file
		1056	descriptor, but when it goes away, the operating system will silently drop
		1057	this interest. If another file descriptor with the same number then is
		1058	registered with libev, there is no efficient way to see that this is, in
		1059	fact, a different file descriptor.
		1060
		1061	To avoid having to explicitly tell libev about such cases, libev follows
		1062	the following policy: Each time C<ev_io_set> is being called, libev
		1063	will assume that this is potentially a new file descriptor, otherwise
		1064	it is assumed that the file descriptor stays the same. That means that
		1065	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1066	descriptor even if the file descriptor number itself did not change.
		1067
		1068	This is how one would do it normally anyway, the important point is that
		1069	the libev application should not optimise around libev but should leave
		1070	optimisations to libev.
		1071
		1072	=head3 The special problem of dup'ed file descriptors
		1073
		1074	Some backends (e.g. epoll), cannot register events for file descriptors,
		1075	but only events for the underlying file descriptions. That means when you
		1076	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1077	events for them, only one file descriptor might actually receive events.
		1078
		1079	There is no workaround possible except not registering events
		1080	for potentially C<dup ()>'ed file descriptors, or to resort to
		1081	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1082
		1083	=head3 The special problem of fork
		1084
		1085	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1086	useless behaviour. Libev fully supports fork, but needs to be told about
		1087	it in the child.
		1088
		1089	To support fork in your programs, you either have to call
		1090	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1091	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1092	C<EVBACKEND_POLL>.
		1093
		1094	=head3 The special problem of SIGPIPE
		1095
		1096	While not really specific to libev, it is easy to forget about SIGPIPE:
		1097	when reading from a pipe whose other end has been closed, your program
		1098	gets send a SIGPIPE, which, by default, aborts your program. For most
		1099	programs this is sensible behaviour, for daemons, this is usually
		1100	undesirable.
		1101
		1102	So when you encounter spurious, unexplained daemon exits, make sure you
		1103	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1104	somewhere, as that would have given you a big clue).
		1105
		1106
		1107	=head3 Watcher-Specific Functions
430		1108
431	=over 4	1109	=over 4
432		1110
433	=item ev_io_init (ev_io *, callback, int fd, int events)	1111	=item ev_io_init (ev_io *, callback, int fd, int events)
434		1112
435	=item ev_io_set (ev_io *, int fd, int events)	1113	=item ev_io_set (ev_io *, int fd, int events)
436		1114
437	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1115	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
438	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1116	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
439	EV_WRITE> to receive the given events.	1117	C<EV_READ | EV_WRITE> to receive the given events.
		1118
		1119	=item int fd [read-only]
		1120
		1121	The file descriptor being watched.
		1122
		1123	=item int events [read-only]
		1124
		1125	The events being watched.
440		1126
441	=back	1127	=back
442		1128
		1129	=head3 Examples
		1130
		1131	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1132	readable, but only once. Since it is likely line-buffered, you could
		1133	attempt to read a whole line in the callback.
		1134
		1135	static void
		1136	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1137	{
		1138	ev_io_stop (loop, w);
		1139	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1140	}
		1141
		1142	...
		1143	struct ev_loop *loop = ev_default_init (0);
		1144	struct ev_io stdin_readable;
		1145	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1146	ev_io_start (loop, &stdin_readable);
		1147	ev_loop (loop, 0);
		1148
		1149
443	=head2 C<ev_timer> - relative and optionally recurring timeouts	1150	=head2 C<ev_timer> - relative and optionally repeating timeouts
444		1151
445	Timer watchers are simple relative timers that generate an event after a	1152	Timer watchers are simple relative timers that generate an event after a
446	given time, and optionally repeating in regular intervals after that.	1153	given time, and optionally repeating in regular intervals after that.
447		1154
448	The timers are based on real time, that is, if you register an event that	1155	The timers are based on real time, that is, if you register an event that
449	times out after an hour and youreset your system clock to last years	1156	times out after an hour and you reset your system clock to january last
450	time, it will still time out after (roughly) and hour. "Roughly" because	1157	year, it will still time out after (roughly) and hour. "Roughly" because
451	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the
452	monotonic clock option helps a lot here).	1159	monotonic clock option helps a lot here).
453		1160
454	The relative timeouts are calculated relative to the C<ev_now ()>	1161	The relative timeouts are calculated relative to the C<ev_now ()>
455	time. This is usually the right thing as this timestamp refers to the time	1162	time. This is usually the right thing as this timestamp refers to the time
456	of the event triggering whatever timeout you are modifying/starting. If	1163	of the event triggering whatever timeout you are modifying/starting. If
457	you suspect event processing to be delayed and you *need* to base the timeout	1164	you suspect event processing to be delayed and you I<need> to base the timeout
458	ion the current time, use something like this to adjust for this:	1165	on the current time, use something like this to adjust for this:
459		1166
460	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
461		1168
		1169	The callback is guarenteed to be invoked only after its timeout has passed,
		1170	but if multiple timers become ready during the same loop iteration then
		1171	order of execution is undefined.
		1172
		1173	=head3 Watcher-Specific Functions and Data Members
		1174
462	=over 4	1175	=over 4
463		1176
464	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1177	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465		1178
466	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1179	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
467		1180
468	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1181	Configure the timer to trigger after C<after> seconds. If C<repeat>
469	C<0.>, then it will automatically be stopped. If it is positive, then the	1182	is C<0.>, then it will automatically be stopped once the timeout is
470	timer will automatically be configured to trigger again C<repeat> seconds	1183	reached. If it is positive, then the timer will automatically be
471	later, again, and again, until stopped manually.	1184	configured to trigger again C<repeat> seconds later, again, and again,
		1185	until stopped manually.
472		1186
473	The timer itself will do a best-effort at avoiding drift, that is, if you	1187	The timer itself will do a best-effort at avoiding drift, that is, if
474	configure a timer to trigger every 10 seconds, then it will trigger at	1188	you configure a timer to trigger every 10 seconds, then it will normally
475	exactly 10 second intervals. If, however, your program cannot keep up with	1189	trigger at exactly 10 second intervals. If, however, your program cannot
476	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1190	keep up with the timer (because it takes longer than those 10 seconds to
477	timer will not fire more than once per event loop iteration.	1191	do stuff) the timer will not fire more than once per event loop iteration.
478		1192
479	=item ev_timer_again (loop)	1193	=item ev_timer_again (loop, ev_timer *)
480		1194
481	This will act as if the timer timed out and restart it again if it is	1195	This will act as if the timer timed out and restart it again if it is
482	repeating. The exact semantics are:	1196	repeating. The exact semantics are:
483		1197
		1198	If the timer is pending, its pending status is cleared.
		1199
484	If the timer is started but nonrepeating, stop it.	1200	If the timer is started but nonrepeating, stop it (as if it timed out).
485		1201
486	If the timer is repeating, either start it if necessary (with the repeat	1202	If the timer is repeating, either start it if necessary (with the
487	value), or reset the running timer to the repeat value.	1203	C<repeat> value), or reset the running timer to the C<repeat> value.
488		1204
489	This sounds a bit complicated, but here is a useful and typical	1205	This sounds a bit complicated, but here is a useful and typical
490	example: Imagine you have a tcp connection and you want a so-called idle	1206	example: Imagine you have a tcp connection and you want a so-called idle
491	timeout, that is, you want to be called when there have been, say, 60	1207	timeout, that is, you want to be called when there have been, say, 60
492	seconds of inactivity on the socket. The easiest way to do this is to	1208	seconds of inactivity on the socket. The easiest way to do this is to
493	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1209	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
494	time you successfully read or write some data. If you go into an idle	1210	C<ev_timer_again> each time you successfully read or write some data. If
495	state where you do not expect data to travel on the socket, you can stop	1211	you go into an idle state where you do not expect data to travel on the
496	the timer, and again will automatically restart it if need be.	1212	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1213	automatically restart it if need be.
		1214
		1215	That means you can ignore the C<after> value and C<ev_timer_start>
		1216	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1217
		1218	ev_timer_init (timer, callback, 0., 5.);
		1219	ev_timer_again (loop, timer);
		1220	...
		1221	timer->again = 17.;
		1222	ev_timer_again (loop, timer);
		1223	...
		1224	timer->again = 10.;
		1225	ev_timer_again (loop, timer);
		1226
		1227	This is more slightly efficient then stopping/starting the timer each time
		1228	you want to modify its timeout value.
		1229
		1230	=item ev_tstamp repeat [read-write]
		1231
		1232	The current C<repeat> value. Will be used each time the watcher times out
		1233	or C<ev_timer_again> is called and determines the next timeout (if any),
		1234	which is also when any modifications are taken into account.
497		1235
498	=back	1236	=back
499		1237
		1238	=head3 Examples
		1239
		1240	Example: Create a timer that fires after 60 seconds.
		1241
		1242	static void
		1243	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1244	{
		1245	.. one minute over, w is actually stopped right here
		1246	}
		1247
		1248	struct ev_timer mytimer;
		1249	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1250	ev_timer_start (loop, &mytimer);
		1251
		1252	Example: Create a timeout timer that times out after 10 seconds of
		1253	inactivity.
		1254
		1255	static void
		1256	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1257	{
		1258	.. ten seconds without any activity
		1259	}
		1260
		1261	struct ev_timer mytimer;
		1262	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1263	ev_timer_again (&mytimer); /* start timer */
		1264	ev_loop (loop, 0);
		1265
		1266	// and in some piece of code that gets executed on any "activity":
		1267	// reset the timeout to start ticking again at 10 seconds
		1268	ev_timer_again (&mytimer);
		1269
		1270
500	=head2 C<ev_periodic> - to cron or not to cron it	1271	=head2 C<ev_periodic> - to cron or not to cron?
501		1272
502	Periodic watchers are also timers of a kind, but they are very versatile	1273	Periodic watchers are also timers of a kind, but they are very versatile
503	(and unfortunately a bit complex).	1274	(and unfortunately a bit complex).
504		1275
505	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1276	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
506	but on wallclock time (absolute time). You can tell a periodic watcher	1277	but on wallclock time (absolute time). You can tell a periodic watcher
507	to trigger "at" some specific point in time. For example, if you tell a	1278	to trigger after some specific point in time. For example, if you tell a
508	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1279	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
509	+ 10.>) and then reset your system clock to the last year, then it will	1280	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1281	clock to january of the previous year, then it will take more than year
510	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1282	to trigger the event (unlike an C<ev_timer>, which would still trigger
511	roughly 10 seconds later and of course not if you reset your system time	1283	roughly 10 seconds later as it uses a relative timeout).
512	again).
513		1284
514	They can also be used to implement vastly more complex timers, such as	1285	C<ev_periodic>s can also be used to implement vastly more complex timers,
515	triggering an event on eahc midnight, local time.	1286	such as triggering an event on each "midnight, local time", or other
		1287	complicated, rules.
		1288
		1289	As with timers, the callback is guarenteed to be invoked only when the
		1290	time (C<at>) has passed, but if multiple periodic timers become ready
		1291	during the same loop iteration then order of execution is undefined.
		1292
		1293	=head3 Watcher-Specific Functions and Data Members
516		1294
517	=over 4	1295	=over 4
518		1296
519	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1297	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
520		1298
521	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1299	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
522		1300
523	Lots of arguments, lets sort it out... There are basically three modes of	1301	Lots of arguments, lets sort it out... There are basically three modes of
524	operation, and we will explain them from simplest to complex:	1302	operation, and we will explain them from simplest to complex:
525		1303
526
527	=over 4	1304	=over 4
528		1305
529	=item * absolute timer (interval = reschedule_cb = 0)	1306	=item * absolute timer (at = time, interval = reschedule_cb = 0)
530		1307
531	In this configuration the watcher triggers an event at the wallclock time	1308	In this configuration the watcher triggers an event after the wallclock
532	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1309	time C<at> has passed and doesn't repeat. It will not adjust when a time
533	that is, if it is to be run at January 1st 2011 then it will run when the	1310	jump occurs, that is, if it is to be run at January 1st 2011 then it will
534	system time reaches or surpasses this time.	1311	run when the system time reaches or surpasses this time.
535		1312
536	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1313	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
537		1314
538	In this mode the watcher will always be scheduled to time out at the next	1315	In this mode the watcher will always be scheduled to time out at the next
539	C<at + N * interval> time (for some integer N) and then repeat, regardless	1316	C<at + N * interval> time (for some integer N, which can also be negative)
540	of any time jumps.	1317	and then repeat, regardless of any time jumps.
541		1318
542	This can be used to create timers that do not drift with respect to system	1319	This can be used to create timers that do not drift with respect to system
543	time:	1320	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1321	the hour:
544		1322
545	ev_periodic_set (&periodic, 0., 3600., 0);	1323	ev_periodic_set (&periodic, 0., 3600., 0);
546		1324
547	This doesn't mean there will always be 3600 seconds in between triggers,	1325	This doesn't mean there will always be 3600 seconds in between triggers,
548	but only that the the callback will be called when the system time shows a	1326	but only that the the callback will be called when the system time shows a
…		…
551		1329
552	Another way to think about it (for the mathematically inclined) is that	1330	Another way to think about it (for the mathematically inclined) is that
553	C<ev_periodic> will try to run the callback in this mode at the next possible	1331	C<ev_periodic> will try to run the callback in this mode at the next possible
554	time where C<time = at (mod interval)>, regardless of any time jumps.	1332	time where C<time = at (mod interval)>, regardless of any time jumps.
555		1333
		1334	For numerical stability it is preferable that the C<at> value is near
		1335	C<ev_now ()> (the current time), but there is no range requirement for
		1336	this value, and in fact is often specified as zero.
		1337
556	=item * manual reschedule mode (reschedule_cb = callback)	1338	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
557		1339
558	In this mode the values for C<interval> and C<at> are both being	1340	In this mode the values for C<interval> and C<at> are both being
559	ignored. Instead, each time the periodic watcher gets scheduled, the	1341	ignored. Instead, each time the periodic watcher gets scheduled, the
560	reschedule callback will be called with the watcher as first, and the	1342	reschedule callback will be called with the watcher as first, and the
561	current time as second argument.	1343	current time as second argument.
562		1344
563	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1345	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
564	periodic watcher, ever, or make any event loop modifications>. If you need	1346	ever, or make ANY event loop modifications whatsoever>.
		1347
565	to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.	1348	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1349	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1350	only event loop modification you are allowed to do).
566		1351
567	Also, I<< this callback must always return a time that is later than the
568	passed C<now> value >>. Not even C<now> itself will be ok.
569
570	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1352	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
571	ev_tstamp now)>, e.g.:	1353	*w, ev_tstamp now)>, e.g.:
572		1354
573	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1355	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
574	{	1356	{
575	return now + 60.;	1357	return now + 60.;
576	}	1358	}
…		…
578	It must return the next time to trigger, based on the passed time value	1360	It must return the next time to trigger, based on the passed time value
579	(that is, the lowest time value larger than to the second argument). It	1361	(that is, the lowest time value larger than to the second argument). It
580	will usually be called just before the callback will be triggered, but	1362	will usually be called just before the callback will be triggered, but
581	might be called at other times, too.	1363	might be called at other times, too.
582		1364
		1365	NOTE: I<< This callback must always return a time that is higher than or
		1366	equal to the passed C<now> value >>.
		1367
583	This can be used to create very complex timers, such as a timer that	1368	This can be used to create very complex timers, such as a timer that
584	triggers on each midnight, local time. To do this, you would calculate the	1369	triggers on "next midnight, local time". To do this, you would calculate the
585	next midnight after C<now> and return the timestamp value for this. How you do this	1370	next midnight after C<now> and return the timestamp value for this. How
586	is, again, up to you (but it is not trivial).	1371	you do this is, again, up to you (but it is not trivial, which is the main
		1372	reason I omitted it as an example).
587		1373
588	=back	1374	=back
589		1375
590	=item ev_periodic_again (loop, ev_periodic *)	1376	=item ev_periodic_again (loop, ev_periodic *)
591		1377
592	Simply stops and restarts the periodic watcher again. This is only useful	1378	Simply stops and restarts the periodic watcher again. This is only useful
593	when you changed some parameters or the reschedule callback would return	1379	when you changed some parameters or the reschedule callback would return
594	a different time than the last time it was called (e.g. in a crond like	1380	a different time than the last time it was called (e.g. in a crond like
595	program when the crontabs have changed).	1381	program when the crontabs have changed).
596		1382
		1383	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1384
		1385	When active, returns the absolute time that the watcher is supposed to
		1386	trigger next.
		1387
		1388	=item ev_tstamp offset [read-write]
		1389
		1390	When repeating, this contains the offset value, otherwise this is the
		1391	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1392
		1393	Can be modified any time, but changes only take effect when the periodic
		1394	timer fires or C<ev_periodic_again> is being called.
		1395
		1396	=item ev_tstamp interval [read-write]
		1397
		1398	The current interval value. Can be modified any time, but changes only
		1399	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1400	called.
		1401
		1402	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1403
		1404	The current reschedule callback, or C<0>, if this functionality is
		1405	switched off. Can be changed any time, but changes only take effect when
		1406	the periodic timer fires or C<ev_periodic_again> is being called.
		1407
597	=back	1408	=back
598		1409
		1410	=head3 Examples
		1411
		1412	Example: Call a callback every hour, or, more precisely, whenever the
		1413	system clock is divisible by 3600. The callback invocation times have
		1414	potentially a lot of jittering, but good long-term stability.
		1415
		1416	static void
		1417	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1418	{
		1419	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1420	}
		1421
		1422	struct ev_periodic hourly_tick;
		1423	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1424	ev_periodic_start (loop, &hourly_tick);
		1425
		1426	Example: The same as above, but use a reschedule callback to do it:
		1427
		1428	#include <math.h>
		1429
		1430	static ev_tstamp
		1431	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1432	{
		1433	return fmod (now, 3600.) + 3600.;
		1434	}
		1435
		1436	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1437
		1438	Example: Call a callback every hour, starting now:
		1439
		1440	struct ev_periodic hourly_tick;
		1441	ev_periodic_init (&hourly_tick, clock_cb,
		1442	fmod (ev_now (loop), 3600.), 3600., 0);
		1443	ev_periodic_start (loop, &hourly_tick);
		1444
		1445
599	=head2 C<ev_signal> - signal me when a signal gets signalled	1446	=head2 C<ev_signal> - signal me when a signal gets signalled!
600		1447
601	Signal watchers will trigger an event when the process receives a specific	1448	Signal watchers will trigger an event when the process receives a specific
602	signal one or more times. Even though signals are very asynchronous, libev	1449	signal one or more times. Even though signals are very asynchronous, libev
603	will try it's best to deliver signals synchronously, i.e. as part of the	1450	will try it's best to deliver signals synchronously, i.e. as part of the
604	normal event processing, like any other event.	1451	normal event processing, like any other event.
605		1452
606	You cna configure as many watchers as you like per signal. Only when the	1453	You can configure as many watchers as you like per signal. Only when the
607	first watcher gets started will libev actually register a signal watcher	1454	first watcher gets started will libev actually register a signal watcher
608	with the kernel (thus it coexists with your own signal handlers as long	1455	with the kernel (thus it coexists with your own signal handlers as long
609	as you don't register any with libev). Similarly, when the last signal	1456	as you don't register any with libev). Similarly, when the last signal
610	watcher for a signal is stopped libev will reset the signal handler to	1457	watcher for a signal is stopped libev will reset the signal handler to
611	SIG_DFL (regardless of what it was set to before).	1458	SIG_DFL (regardless of what it was set to before).
612		1459
		1460	If possible and supported, libev will install its handlers with
		1461	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
		1462	interrupted. If you have a problem with syscalls getting interrupted by
		1463	signals you can block all signals in an C<ev_check> watcher and unblock
		1464	them in an C<ev_prepare> watcher.
		1465
		1466	=head3 Watcher-Specific Functions and Data Members
		1467
613	=over 4	1468	=over 4
614		1469
615	=item ev_signal_init (ev_signal *, callback, int signum)	1470	=item ev_signal_init (ev_signal *, callback, int signum)
616		1471
617	=item ev_signal_set (ev_signal *, int signum)	1472	=item ev_signal_set (ev_signal *, int signum)
618		1473
619	Configures the watcher to trigger on the given signal number (usually one	1474	Configures the watcher to trigger on the given signal number (usually one
620	of the C<SIGxxx> constants).	1475	of the C<SIGxxx> constants).
621		1476
		1477	=item int signum [read-only]
		1478
		1479	The signal the watcher watches out for.
		1480
622	=back	1481	=back
623		1482
		1483	=head3 Examples
		1484
		1485	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1486
		1487	static void
		1488	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1489	{
		1490	ev_unloop (loop, EVUNLOOP_ALL);
		1491	}
		1492
		1493	struct ev_signal signal_watcher;
		1494	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1495	ev_signal_start (loop, &sigint_cb);
		1496
		1497
624	=head2 C<ev_child> - wait for pid status changes	1498	=head2 C<ev_child> - watch out for process status changes
625		1499
626	Child watchers trigger when your process receives a SIGCHLD in response to	1500	Child watchers trigger when your process receives a SIGCHLD in response to
627	some child status changes (most typically when a child of yours dies).	1501	some child status changes (most typically when a child of yours dies). It
		1502	is permissible to install a child watcher I<after> the child has been
		1503	forked (which implies it might have already exited), as long as the event
		1504	loop isn't entered (or is continued from a watcher).
		1505
		1506	Only the default event loop is capable of handling signals, and therefore
		1507	you can only rgeister child watchers in the default event loop.
		1508
		1509	=head3 Process Interaction
		1510
		1511	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1512	initialised. This is necessary to guarantee proper behaviour even if
		1513	the first child watcher is started after the child exits. The occurance
		1514	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1515	synchronously as part of the event loop processing. Libev always reaps all
		1516	children, even ones not watched.
		1517
		1518	=head3 Overriding the Built-In Processing
		1519
		1520	Libev offers no special support for overriding the built-in child
		1521	processing, but if your application collides with libev's default child
		1522	handler, you can override it easily by installing your own handler for
		1523	C<SIGCHLD> after initialising the default loop, and making sure the
		1524	default loop never gets destroyed. You are encouraged, however, to use an
		1525	event-based approach to child reaping and thus use libev's support for
		1526	that, so other libev users can use C<ev_child> watchers freely.
		1527
		1528	=head3 Watcher-Specific Functions and Data Members
628		1529
629	=over 4	1530	=over 4
630		1531
631	=item ev_child_init (ev_child *, callback, int pid)	1532	=item ev_child_init (ev_child *, callback, int pid, int trace)
632		1533
633	=item ev_child_set (ev_child *, int pid)	1534	=item ev_child_set (ev_child *, int pid, int trace)
634		1535
635	Configures the watcher to wait for status changes of process C<pid> (or	1536	Configures the watcher to wait for status changes of process C<pid> (or
636	I<any> process if C<pid> is specified as C<0>). The callback can look	1537	I<any> process if C<pid> is specified as C<0>). The callback can look
637	at the C<rstatus> member of the C<ev_child> watcher structure to see	1538	at the C<rstatus> member of the C<ev_child> watcher structure to see
638	the status word (use the macros from C<sys/wait.h>). The C<rpid> member	1539	the status word (use the macros from C<sys/wait.h> and see your systems
639	contains the pid of the process causing the status change.	1540	C<waitpid> documentation). The C<rpid> member contains the pid of the
		1541	process causing the status change. C<trace> must be either C<0> (only
		1542	activate the watcher when the process terminates) or C<1> (additionally
		1543	activate the watcher when the process is stopped or continued).
		1544
		1545	=item int pid [read-only]
		1546
		1547	The process id this watcher watches out for, or C<0>, meaning any process id.
		1548
		1549	=item int rpid [read-write]
		1550
		1551	The process id that detected a status change.
		1552
		1553	=item int rstatus [read-write]
		1554
		1555	The process exit/trace status caused by C<rpid> (see your systems
		1556	C<waitpid> and C<sys/wait.h> documentation for details).
640		1557
641	=back	1558	=back
642		1559
		1560	=head3 Examples
		1561
		1562	Example: C<fork()> a new process and install a child handler to wait for
		1563	its completion.
		1564
		1565	ev_child cw;
		1566
		1567	static void
		1568	child_cb (EV_P_ struct ev_child *w, int revents)
		1569	{
		1570	ev_child_stop (EV_A_ w);
		1571	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1572	}
		1573
		1574	pid_t pid = fork ();
		1575
		1576	if (pid < 0)
		1577	// error
		1578	else if (pid == 0)
		1579	{
		1580	// the forked child executes here
		1581	exit (1);
		1582	}
		1583	else
		1584	{
		1585	ev_child_init (&cw, child_cb, pid, 0);
		1586	ev_child_start (EV_DEFAULT_ &cw);
		1587	}
		1588
		1589
		1590	=head2 C<ev_stat> - did the file attributes just change?
		1591
		1592	This watches a filesystem path for attribute changes. That is, it calls
		1593	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1594	compared to the last time, invoking the callback if it did.
		1595
		1596	The path does not need to exist: changing from "path exists" to "path does
		1597	not exist" is a status change like any other. The condition "path does
		1598	not exist" is signified by the C<st_nlink> field being zero (which is
		1599	otherwise always forced to be at least one) and all the other fields of
		1600	the stat buffer having unspecified contents.
		1601
		1602	The path I<should> be absolute and I<must not> end in a slash. If it is
		1603	relative and your working directory changes, the behaviour is undefined.
		1604
		1605	Since there is no standard to do this, the portable implementation simply
		1606	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1607	can specify a recommended polling interval for this case. If you specify
		1608	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1609	unspecified default> value will be used (which you can expect to be around
		1610	five seconds, although this might change dynamically). Libev will also
		1611	impose a minimum interval which is currently around C<0.1>, but thats
		1612	usually overkill.
		1613
		1614	This watcher type is not meant for massive numbers of stat watchers,
		1615	as even with OS-supported change notifications, this can be
		1616	resource-intensive.
		1617
		1618	At the time of this writing, only the Linux inotify interface is
		1619	implemented (implementing kqueue support is left as an exercise for the
		1620	reader, note, however, that the author sees no way of implementing ev_stat
		1621	semantics with kqueue). Inotify will be used to give hints only and should
		1622	not change the semantics of C<ev_stat> watchers, which means that libev
		1623	sometimes needs to fall back to regular polling again even with inotify,
		1624	but changes are usually detected immediately, and if the file exists there
		1625	will be no polling.
		1626
		1627	=head3 ABI Issues (Largefile Support)
		1628
		1629	Libev by default (unless the user overrides this) uses the default
		1630	compilation environment, which means that on systems with optionally
		1631	disabled large file support, you get the 32 bit version of the stat
		1632	structure. When using the library from programs that change the ABI to
		1633	use 64 bit file offsets the programs will fail. In that case you have to
		1634	compile libev with the same flags to get binary compatibility. This is
		1635	obviously the case with any flags that change the ABI, but the problem is
		1636	most noticably with ev_stat and largefile support.
		1637
		1638	=head3 Inotify
		1639
		1640	When C<inotify (7)> support has been compiled into libev (generally only
		1641	available on Linux) and present at runtime, it will be used to speed up
		1642	change detection where possible. The inotify descriptor will be created lazily
		1643	when the first C<ev_stat> watcher is being started.
		1644
		1645	Inotify presence does not change the semantics of C<ev_stat> watchers
		1646	except that changes might be detected earlier, and in some cases, to avoid
		1647	making regular C<stat> calls. Even in the presence of inotify support
		1648	there are many cases where libev has to resort to regular C<stat> polling.
		1649
		1650	(There is no support for kqueue, as apparently it cannot be used to
		1651	implement this functionality, due to the requirement of having a file
		1652	descriptor open on the object at all times).
		1653
		1654	=head3 The special problem of stat time resolution
		1655
		1656	The C<stat ()> syscall only supports full-second resolution portably, and
		1657	even on systems where the resolution is higher, many filesystems still
		1658	only support whole seconds.
		1659
		1660	That means that, if the time is the only thing that changes, you can
		1661	easily miss updates: on the first update, C<ev_stat> detects a change and
		1662	calls your callback, which does something. When there is another update
		1663	within the same second, C<ev_stat> will be unable to detect it as the stat
		1664	data does not change.
		1665
		1666	The solution to this is to delay acting on a change for slightly more
		1667	than a second (or till slightly after the next full second boundary), using
		1668	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1669	ev_timer_again (loop, w)>).
		1670
		1671	The C<.02> offset is added to work around small timing inconsistencies
		1672	of some operating systems (where the second counter of the current time
		1673	might be be delayed. One such system is the Linux kernel, where a call to
		1674	C<gettimeofday> might return a timestamp with a full second later than
		1675	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1676	update file times then there will be a small window where the kernel uses
		1677	the previous second to update file times but libev might already execute
		1678	the timer callback).
		1679
		1680	=head3 Watcher-Specific Functions and Data Members
		1681
		1682	=over 4
		1683
		1684	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1685
		1686	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1687
		1688	Configures the watcher to wait for status changes of the given
		1689	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1690	be detected and should normally be specified as C<0> to let libev choose
		1691	a suitable value. The memory pointed to by C<path> must point to the same
		1692	path for as long as the watcher is active.
		1693
		1694	The callback will receive C<EV_STAT> when a change was detected, relative
		1695	to the attributes at the time the watcher was started (or the last change
		1696	was detected).
		1697
		1698	=item ev_stat_stat (loop, ev_stat *)
		1699
		1700	Updates the stat buffer immediately with new values. If you change the
		1701	watched path in your callback, you could call this function to avoid
		1702	detecting this change (while introducing a race condition if you are not
		1703	the only one changing the path). Can also be useful simply to find out the
		1704	new values.
		1705
		1706	=item ev_statdata attr [read-only]
		1707
		1708	The most-recently detected attributes of the file. Although the type is
		1709	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1710	suitable for your system, but you can only rely on the POSIX-standardised
		1711	members to be present. If the C<st_nlink> member is C<0>, then there was
		1712	some error while C<stat>ing the file.
		1713
		1714	=item ev_statdata prev [read-only]
		1715
		1716	The previous attributes of the file. The callback gets invoked whenever
		1717	C<prev> != C<attr>, or, more precisely, one or more of these members
		1718	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1719	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1720
		1721	=item ev_tstamp interval [read-only]
		1722
		1723	The specified interval.
		1724
		1725	=item const char *path [read-only]
		1726
		1727	The filesystem path that is being watched.
		1728
		1729	=back
		1730
		1731	=head3 Examples
		1732
		1733	Example: Watch C</etc/passwd> for attribute changes.
		1734
		1735	static void
		1736	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1737	{
		1738	/* /etc/passwd changed in some way */
		1739	if (w->attr.st_nlink)
		1740	{
		1741	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1742	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1743	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1744	}
		1745	else
		1746	/* you shalt not abuse printf for puts */
		1747	puts ("wow, /etc/passwd is not there, expect problems. "
		1748	"if this is windows, they already arrived\n");
		1749	}
		1750
		1751	...
		1752	ev_stat passwd;
		1753
		1754	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1755	ev_stat_start (loop, &passwd);
		1756
		1757	Example: Like above, but additionally use a one-second delay so we do not
		1758	miss updates (however, frequent updates will delay processing, too, so
		1759	one might do the work both on C<ev_stat> callback invocation I<and> on
		1760	C<ev_timer> callback invocation).
		1761
		1762	static ev_stat passwd;
		1763	static ev_timer timer;
		1764
		1765	static void
		1766	timer_cb (EV_P_ ev_timer *w, int revents)
		1767	{
		1768	ev_timer_stop (EV_A_ w);
		1769
		1770	/* now it's one second after the most recent passwd change */
		1771	}
		1772
		1773	static void
		1774	stat_cb (EV_P_ ev_stat *w, int revents)
		1775	{
		1776	/* reset the one-second timer */
		1777	ev_timer_again (EV_A_ &timer);
		1778	}
		1779
		1780	...
		1781	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1782	ev_stat_start (loop, &passwd);
		1783	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1784
		1785
643	=head2 C<ev_idle> - when you've got nothing better to do	1786	=head2 C<ev_idle> - when you've got nothing better to do...
644		1787
645	Idle watchers trigger events when there are no other I/O or timer (or	1788	Idle watchers trigger events when no other events of the same or higher
646	periodic) events pending. That is, as long as your process is busy	1789	priority are pending (prepare, check and other idle watchers do not
647	handling sockets or timeouts it will not be called. But when your process	1790	count).
648	is idle all idle watchers are being called again and again - until	1791
		1792	That is, as long as your process is busy handling sockets or timeouts
		1793	(or even signals, imagine) of the same or higher priority it will not be
		1794	triggered. But when your process is idle (or only lower-priority watchers
		1795	are pending), the idle watchers are being called once per event loop
649	stopped, that is, or your process receives more events.	1796	iteration - until stopped, that is, or your process receives more events
		1797	and becomes busy again with higher priority stuff.
650		1798
651	The most noteworthy effect is that as long as any idle watchers are	1799	The most noteworthy effect is that as long as any idle watchers are
652	active, the process will not block when waiting for new events.	1800	active, the process will not block when waiting for new events.
653		1801
654	Apart from keeping your process non-blocking (which is a useful	1802	Apart from keeping your process non-blocking (which is a useful
655	effect on its own sometimes), idle watchers are a good place to do	1803	effect on its own sometimes), idle watchers are a good place to do
656	"pseudo-background processing", or delay processing stuff to after the	1804	"pseudo-background processing", or delay processing stuff to after the
657	event loop has handled all outstanding events.	1805	event loop has handled all outstanding events.
658		1806
		1807	=head3 Watcher-Specific Functions and Data Members
		1808
659	=over 4	1809	=over 4
660		1810
661	=item ev_idle_init (ev_signal *, callback)	1811	=item ev_idle_init (ev_signal *, callback)
662		1812
663	Initialises and configures the idle watcher - it has no parameters of any	1813	Initialises and configures the idle watcher - it has no parameters of any
664	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1814	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
665	believe me.	1815	believe me.
666		1816
667	=back	1817	=back
668		1818
669	=head2 prepare and check - your hooks into the event loop	1819	=head3 Examples
670		1820
		1821	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1822	callback, free it. Also, use no error checking, as usual.
		1823
		1824	static void
		1825	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1826	{
		1827	free (w);
		1828	// now do something you wanted to do when the program has
		1829	// no longer anything immediate to do.
		1830	}
		1831
		1832	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1833	ev_idle_init (idle_watcher, idle_cb);
		1834	ev_idle_start (loop, idle_cb);
		1835
		1836
		1837	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		1838
671	Prepare and check watchers usually (but not always) are used in	1839	Prepare and check watchers are usually (but not always) used in tandem:
672	tandom. Prepare watchers get invoked before the process blocks and check	1840	prepare watchers get invoked before the process blocks and check watchers
673	watchers afterwards.	1841	afterwards.
674		1842
		1843	You I<must not> call C<ev_loop> or similar functions that enter
		1844	the current event loop from either C<ev_prepare> or C<ev_check>
		1845	watchers. Other loops than the current one are fine, however. The
		1846	rationale behind this is that you do not need to check for recursion in
		1847	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1848	C<ev_check> so if you have one watcher of each kind they will always be
		1849	called in pairs bracketing the blocking call.
		1850
675	Their main purpose is to integrate other event mechanisms into libev. This	1851	Their main purpose is to integrate other event mechanisms into libev and
676	could be used, for example, to track variable changes, implement your own	1852	their use is somewhat advanced. This could be used, for example, to track
677	watchers, integrate net-snmp or a coroutine library and lots more.	1853	variable changes, implement your own watchers, integrate net-snmp or a
		1854	coroutine library and lots more. They are also occasionally useful if
		1855	you cache some data and want to flush it before blocking (for example,
		1856	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1857	watcher).
678		1858
679	This is done by examining in each prepare call which file descriptors need	1859	This is done by examining in each prepare call which file descriptors need
680	to be watched by the other library, registering C<ev_io> watchers for them	1860	to be watched by the other library, registering C<ev_io> watchers for
681	and starting an C<ev_timer> watcher for any timeouts (many libraries provide	1861	them and starting an C<ev_timer> watcher for any timeouts (many libraries
682	just this functionality). Then, in the check watcher you check for any	1862	provide just this functionality). Then, in the check watcher you check for
683	events that occured (by making your callbacks set soem flags for example)	1863	any events that occured (by checking the pending status of all watchers
684	and call back into the library.	1864	and stopping them) and call back into the library. The I/O and timer
		1865	callbacks will never actually be called (but must be valid nevertheless,
		1866	because you never know, you know?).
685		1867
686	As another example, the perl Coro module uses these hooks to integrate	1868	As another example, the Perl Coro module uses these hooks to integrate
687	coroutines into libev programs, by yielding to other active coroutines	1869	coroutines into libev programs, by yielding to other active coroutines
688	during each prepare and only letting the process block if no coroutines	1870	during each prepare and only letting the process block if no coroutines
689	are ready to run.	1871	are ready to run (it's actually more complicated: it only runs coroutines
		1872	with priority higher than or equal to the event loop and one coroutine
		1873	of lower priority, but only once, using idle watchers to keep the event
		1874	loop from blocking if lower-priority coroutines are active, thus mapping
		1875	low-priority coroutines to idle/background tasks).
		1876
		1877	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1878	priority, to ensure that they are being run before any other watchers
		1879	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1880	too) should not activate ("feed") events into libev. While libev fully
		1881	supports this, they might get executed before other C<ev_check> watchers
		1882	did their job. As C<ev_check> watchers are often used to embed other
		1883	(non-libev) event loops those other event loops might be in an unusable
		1884	state until their C<ev_check> watcher ran (always remind yourself to
		1885	coexist peacefully with others).
		1886
		1887	=head3 Watcher-Specific Functions and Data Members
690		1888
691	=over 4	1889	=over 4
692		1890
693	=item ev_prepare_init (ev_prepare *, callback)	1891	=item ev_prepare_init (ev_prepare *, callback)
694		1892
695	=item ev_check_init (ev_check *, callback)	1893	=item ev_check_init (ev_check *, callback)
696		1894
697	Initialises and configures the prepare or check watcher - they have no	1895	Initialises and configures the prepare or check watcher - they have no
698	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1896	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
699	macros, but using them is utterly, utterly pointless.	1897	macros, but using them is utterly, utterly and completely pointless.
700		1898
701	=back	1899	=back
702		1900
		1901	=head3 Examples
		1902
		1903	There are a number of principal ways to embed other event loops or modules
		1904	into libev. Here are some ideas on how to include libadns into libev
		1905	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1906	use as a working example. Another Perl module named C<EV::Glib> embeds a
		1907	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		1908	Glib event loop).
		1909
		1910	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1911	and in a check watcher, destroy them and call into libadns. What follows
		1912	is pseudo-code only of course. This requires you to either use a low
		1913	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1914	the callbacks for the IO/timeout watchers might not have been called yet.
		1915
		1916	static ev_io iow [nfd];
		1917	static ev_timer tw;
		1918
		1919	static void
		1920	io_cb (ev_loop *loop, ev_io *w, int revents)
		1921	{
		1922	}
		1923
		1924	// create io watchers for each fd and a timer before blocking
		1925	static void
		1926	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1927	{
		1928	int timeout = 3600000;
		1929	struct pollfd fds [nfd];
		1930	// actual code will need to loop here and realloc etc.
		1931	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1932
		1933	/* the callback is illegal, but won't be called as we stop during check */
		1934	ev_timer_init (&tw, 0, timeout * 1e-3);
		1935	ev_timer_start (loop, &tw);
		1936
		1937	// create one ev_io per pollfd
		1938	for (int i = 0; i < nfd; ++i)
		1939	{
		1940	ev_io_init (iow + i, io_cb, fds [i].fd,
		1941	((fds [i].events & POLLIN ? EV_READ : 0)
		1942	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1943
		1944	fds [i].revents = 0;
		1945	ev_io_start (loop, iow + i);
		1946	}
		1947	}
		1948
		1949	// stop all watchers after blocking
		1950	static void
		1951	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1952	{
		1953	ev_timer_stop (loop, &tw);
		1954
		1955	for (int i = 0; i < nfd; ++i)
		1956	{
		1957	// set the relevant poll flags
		1958	// could also call adns_processreadable etc. here
		1959	struct pollfd *fd = fds + i;
		1960	int revents = ev_clear_pending (iow + i);
		1961	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1962	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1963
		1964	// now stop the watcher
		1965	ev_io_stop (loop, iow + i);
		1966	}
		1967
		1968	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1969	}
		1970
		1971	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1972	in the prepare watcher and would dispose of the check watcher.
		1973
		1974	Method 3: If the module to be embedded supports explicit event
		1975	notification (adns does), you can also make use of the actual watcher
		1976	callbacks, and only destroy/create the watchers in the prepare watcher.
		1977
		1978	static void
		1979	timer_cb (EV_P_ ev_timer *w, int revents)
		1980	{
		1981	adns_state ads = (adns_state)w->data;
		1982	update_now (EV_A);
		1983
		1984	adns_processtimeouts (ads, &tv_now);
		1985	}
		1986
		1987	static void
		1988	io_cb (EV_P_ ev_io *w, int revents)
		1989	{
		1990	adns_state ads = (adns_state)w->data;
		1991	update_now (EV_A);
		1992
		1993	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1994	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1995	}
		1996
		1997	// do not ever call adns_afterpoll
		1998
		1999	Method 4: Do not use a prepare or check watcher because the module you
		2000	want to embed is too inflexible to support it. Instead, youc na override
		2001	their poll function. The drawback with this solution is that the main
		2002	loop is now no longer controllable by EV. The C<Glib::EV> module does
		2003	this.
		2004
		2005	static gint
		2006	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2007	{
		2008	int got_events = 0;
		2009
		2010	for (n = 0; n < nfds; ++n)
		2011	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2012
		2013	if (timeout >= 0)
		2014	// create/start timer
		2015
		2016	// poll
		2017	ev_loop (EV_A_ 0);
		2018
		2019	// stop timer again
		2020	if (timeout >= 0)
		2021	ev_timer_stop (EV_A_ &to);
		2022
		2023	// stop io watchers again - their callbacks should have set
		2024	for (n = 0; n < nfds; ++n)
		2025	ev_io_stop (EV_A_ iow [n]);
		2026
		2027	return got_events;
		2028	}
		2029
		2030
		2031	=head2 C<ev_embed> - when one backend isn't enough...
		2032
		2033	This is a rather advanced watcher type that lets you embed one event loop
		2034	into another (currently only C<ev_io> events are supported in the embedded
		2035	loop, other types of watchers might be handled in a delayed or incorrect
		2036	fashion and must not be used).
		2037
		2038	There are primarily two reasons you would want that: work around bugs and
		2039	prioritise I/O.
		2040
		2041	As an example for a bug workaround, the kqueue backend might only support
		2042	sockets on some platform, so it is unusable as generic backend, but you
		2043	still want to make use of it because you have many sockets and it scales
		2044	so nicely. In this case, you would create a kqueue-based loop and embed it
		2045	into your default loop (which might use e.g. poll). Overall operation will
		2046	be a bit slower because first libev has to poll and then call kevent, but
		2047	at least you can use both at what they are best.
		2048
		2049	As for prioritising I/O: rarely you have the case where some fds have
		2050	to be watched and handled very quickly (with low latency), and even
		2051	priorities and idle watchers might have too much overhead. In this case
		2052	you would put all the high priority stuff in one loop and all the rest in
		2053	a second one, and embed the second one in the first.
		2054
		2055	As long as the watcher is active, the callback will be invoked every time
		2056	there might be events pending in the embedded loop. The callback must then
		2057	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2058	their callbacks (you could also start an idle watcher to give the embedded
		2059	loop strictly lower priority for example). You can also set the callback
		2060	to C<0>, in which case the embed watcher will automatically execute the
		2061	embedded loop sweep.
		2062
		2063	As long as the watcher is started it will automatically handle events. The
		2064	callback will be invoked whenever some events have been handled. You can
		2065	set the callback to C<0> to avoid having to specify one if you are not
		2066	interested in that.
		2067
		2068	Also, there have not currently been made special provisions for forking:
		2069	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2070	but you will also have to stop and restart any C<ev_embed> watchers
		2071	yourself.
		2072
		2073	Unfortunately, not all backends are embeddable, only the ones returned by
		2074	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2075	portable one.
		2076
		2077	So when you want to use this feature you will always have to be prepared
		2078	that you cannot get an embeddable loop. The recommended way to get around
		2079	this is to have a separate variables for your embeddable loop, try to
		2080	create it, and if that fails, use the normal loop for everything.
		2081
		2082	=head3 Watcher-Specific Functions and Data Members
		2083
		2084	=over 4
		2085
		2086	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2087
		2088	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2089
		2090	Configures the watcher to embed the given loop, which must be
		2091	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2092	invoked automatically, otherwise it is the responsibility of the callback
		2093	to invoke it (it will continue to be called until the sweep has been done,
		2094	if you do not want thta, you need to temporarily stop the embed watcher).
		2095
		2096	=item ev_embed_sweep (loop, ev_embed *)
		2097
		2098	Make a single, non-blocking sweep over the embedded loop. This works
		2099	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2100	apropriate way for embedded loops.
		2101
		2102	=item struct ev_loop *other [read-only]
		2103
		2104	The embedded event loop.
		2105
		2106	=back
		2107
		2108	=head3 Examples
		2109
		2110	Example: Try to get an embeddable event loop and embed it into the default
		2111	event loop. If that is not possible, use the default loop. The default
		2112	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		2113	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		2114	used).
		2115
		2116	struct ev_loop *loop_hi = ev_default_init (0);
		2117	struct ev_loop *loop_lo = 0;
		2118	struct ev_embed embed;
		2119
		2120	// see if there is a chance of getting one that works
		2121	// (remember that a flags value of 0 means autodetection)
		2122	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2123	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2124	: 0;
		2125
		2126	// if we got one, then embed it, otherwise default to loop_hi
		2127	if (loop_lo)
		2128	{
		2129	ev_embed_init (&embed, 0, loop_lo);
		2130	ev_embed_start (loop_hi, &embed);
		2131	}
		2132	else
		2133	loop_lo = loop_hi;
		2134
		2135	Example: Check if kqueue is available but not recommended and create
		2136	a kqueue backend for use with sockets (which usually work with any
		2137	kqueue implementation). Store the kqueue/socket-only event loop in
		2138	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2139
		2140	struct ev_loop *loop = ev_default_init (0);
		2141	struct ev_loop *loop_socket = 0;
		2142	struct ev_embed embed;
		2143
		2144	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2145	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2146	{
		2147	ev_embed_init (&embed, 0, loop_socket);
		2148	ev_embed_start (loop, &embed);
		2149	}
		2150
		2151	if (!loop_socket)
		2152	loop_socket = loop;
		2153
		2154	// now use loop_socket for all sockets, and loop for everything else
		2155
		2156
		2157	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2158
		2159	Fork watchers are called when a C<fork ()> was detected (usually because
		2160	whoever is a good citizen cared to tell libev about it by calling
		2161	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2162	event loop blocks next and before C<ev_check> watchers are being called,
		2163	and only in the child after the fork. If whoever good citizen calling
		2164	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2165	handlers will be invoked, too, of course.
		2166
		2167	=head3 Watcher-Specific Functions and Data Members
		2168
		2169	=over 4
		2170
		2171	=item ev_fork_init (ev_signal *, callback)
		2172
		2173	Initialises and configures the fork watcher - it has no parameters of any
		2174	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2175	believe me.
		2176
		2177	=back
		2178
		2179
		2180	=head2 C<ev_async> - how to wake up another event loop
		2181
		2182	In general, you cannot use an C<ev_loop> from multiple threads or other
		2183	asynchronous sources such as signal handlers (as opposed to multiple event
		2184	loops - those are of course safe to use in different threads).
		2185
		2186	Sometimes, however, you need to wake up another event loop you do not
		2187	control, for example because it belongs to another thread. This is what
		2188	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2189	can signal it by calling C<ev_async_send>, which is thread- and signal
		2190	safe.
		2191
		2192	This functionality is very similar to C<ev_signal> watchers, as signals,
		2193	too, are asynchronous in nature, and signals, too, will be compressed
		2194	(i.e. the number of callback invocations may be less than the number of
		2195	C<ev_async_sent> calls).
		2196
		2197	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2198	just the default loop.
		2199
		2200	=head3 Queueing
		2201
		2202	C<ev_async> does not support queueing of data in any way. The reason
		2203	is that the author does not know of a simple (or any) algorithm for a
		2204	multiple-writer-single-reader queue that works in all cases and doesn't
		2205	need elaborate support such as pthreads.
		2206
		2207	That means that if you want to queue data, you have to provide your own
		2208	queue. But at least I can tell you would implement locking around your
		2209	queue:
		2210
		2211	=over 4
		2212
		2213	=item queueing from a signal handler context
		2214
		2215	To implement race-free queueing, you simply add to the queue in the signal
		2216	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2217	some fictitiuous SIGUSR1 handler:
		2218
		2219	static ev_async mysig;
		2220
		2221	static void
		2222	sigusr1_handler (void)
		2223	{
		2224	sometype data;
		2225
		2226	// no locking etc.
		2227	queue_put (data);
		2228	ev_async_send (EV_DEFAULT_ &mysig);
		2229	}
		2230
		2231	static void
		2232	mysig_cb (EV_P_ ev_async *w, int revents)
		2233	{
		2234	sometype data;
		2235	sigset_t block, prev;
		2236
		2237	sigemptyset (&block);
		2238	sigaddset (&block, SIGUSR1);
		2239	sigprocmask (SIG_BLOCK, &block, &prev);
		2240
		2241	while (queue_get (&data))
		2242	process (data);
		2243
		2244	if (sigismember (&prev, SIGUSR1)
		2245	sigprocmask (SIG_UNBLOCK, &block, 0);
		2246	}
		2247
		2248	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2249	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2250	either...).
		2251
		2252	=item queueing from a thread context
		2253
		2254	The strategy for threads is different, as you cannot (easily) block
		2255	threads but you can easily preempt them, so to queue safely you need to
		2256	employ a traditional mutex lock, such as in this pthread example:
		2257
		2258	static ev_async mysig;
		2259	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2260
		2261	static void
		2262	otherthread (void)
		2263	{
		2264	// only need to lock the actual queueing operation
		2265	pthread_mutex_lock (&mymutex);
		2266	queue_put (data);
		2267	pthread_mutex_unlock (&mymutex);
		2268
		2269	ev_async_send (EV_DEFAULT_ &mysig);
		2270	}
		2271
		2272	static void
		2273	mysig_cb (EV_P_ ev_async *w, int revents)
		2274	{
		2275	pthread_mutex_lock (&mymutex);
		2276
		2277	while (queue_get (&data))
		2278	process (data);
		2279
		2280	pthread_mutex_unlock (&mymutex);
		2281	}
		2282
		2283	=back
		2284
		2285
		2286	=head3 Watcher-Specific Functions and Data Members
		2287
		2288	=over 4
		2289
		2290	=item ev_async_init (ev_async *, callback)
		2291
		2292	Initialises and configures the async watcher - it has no parameters of any
		2293	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2294	believe me.
		2295
		2296	=item ev_async_send (loop, ev_async *)
		2297
		2298	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2299	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2300	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2301	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2302	section below on what exactly this means).
		2303
		2304	This call incurs the overhead of a syscall only once per loop iteration,
		2305	so while the overhead might be noticable, it doesn't apply to repeated
		2306	calls to C<ev_async_send>.
		2307
		2308	=item bool = ev_async_pending (ev_async *)
		2309
		2310	Returns a non-zero value when C<ev_async_send> has been called on the
		2311	watcher but the event has not yet been processed (or even noted) by the
		2312	event loop.
		2313
		2314	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2315	the loop iterates next and checks for the watcher to have become active,
		2316	it will reset the flag again. C<ev_async_pending> can be used to very
		2317	quickly check wether invoking the loop might be a good idea.
		2318
		2319	Not that this does I<not> check wether the watcher itself is pending, only
		2320	wether it has been requested to make this watcher pending.
		2321
		2322	=back
		2323
		2324
703	=head1 OTHER FUNCTIONS	2325	=head1 OTHER FUNCTIONS
704		2326
705	There are some other fucntions of possible interest. Described. Here. Now.	2327	There are some other functions of possible interest. Described. Here. Now.
706		2328
707	=over 4	2329	=over 4
708		2330
709	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2331	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
710		2332
711	This function combines a simple timer and an I/O watcher, calls your	2333	This function combines a simple timer and an I/O watcher, calls your
712	callback on whichever event happens first and automatically stop both	2334	callback on whichever event happens first and automatically stop both
713	watchers. This is useful if you want to wait for a single event on an fd	2335	watchers. This is useful if you want to wait for a single event on an fd
714	or timeout without havign to allocate/configure/start/stop/free one or	2336	or timeout without having to allocate/configure/start/stop/free one or
715	more watchers yourself.	2337	more watchers yourself.
716		2338
717	If C<fd> is less than 0, then no I/O watcher will be started and events is	2339	If C<fd> is less than 0, then no I/O watcher will be started and events
718	ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and C<events> set	2340	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
719	will be craeted and started.	2341	C<events> set will be craeted and started.
720		2342
721	If C<timeout> is less than 0, then no timeout watcher will be	2343	If C<timeout> is less than 0, then no timeout watcher will be
722	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and repeat	2344	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
723	= 0) will be started.	2345	repeat = 0) will be started. While C<0> is a valid timeout, it is of
		2346	dubious value.
724		2347
725	The callback has the type C<void (*cb)(int revents, void *arg)> and	2348	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
726	gets passed an events set (normally a combination of C<EV_ERROR>, C<EV_READ>,	2349	passed an C<revents> set like normal event callbacks (a combination of
727	C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg> value passed to C<ev_once>:	2350	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
		2351	value passed to C<ev_once>:
728		2352
729	static void stdin_ready (int revents, void *arg)	2353	static void stdin_ready (int revents, void *arg)
730	{	2354	{
731	if (revents & EV_TIMEOUT)	2355	if (revents & EV_TIMEOUT)
732	/* doh, nothing entered */	2356	/* doh, nothing entered */;
733	else if (revents & EV_READ)	2357	else if (revents & EV_READ)
734	/* stdin might have data for us, joy! */	2358	/* stdin might have data for us, joy! */;
735	}	2359	}
736		2360
737	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	2361	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
738		2362
739	=item ev_feed_event (loop, watcher, int events)	2363	=item ev_feed_event (ev_loop *, watcher *, int revents)
740		2364
741	Feeds the given event set into the event loop, as if the specified event	2365	Feeds the given event set into the event loop, as if the specified event
742	has happened for the specified watcher (which must be a pointer to an	2366	had happened for the specified watcher (which must be a pointer to an
743	initialised but not necessarily active event watcher).	2367	initialised but not necessarily started event watcher).
744		2368
745	=item ev_feed_fd_event (loop, int fd, int revents)	2369	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
746		2370
747	Feed an event on the given fd, as if a file descriptor backend detected it.	2371	Feed an event on the given fd, as if a file descriptor backend detected
		2372	the given events it.
748		2373
749	=item ev_feed_signal_event (loop, int signum)	2374	=item ev_feed_signal_event (ev_loop *loop, int signum)
750		2375
751	Feed an event as if the given signal occured (loop must be the default loop!).	2376	Feed an event as if the given signal occured (C<loop> must be the default
		2377	loop!).
752		2378
753	=back	2379	=back
754		2380
		2381
		2382	=head1 LIBEVENT EMULATION
		2383
		2384	Libev offers a compatibility emulation layer for libevent. It cannot
		2385	emulate the internals of libevent, so here are some usage hints:
		2386
		2387	=over 4
		2388
		2389	=item * Use it by including <event.h>, as usual.
		2390
		2391	=item * The following members are fully supported: ev_base, ev_callback,
		2392	ev_arg, ev_fd, ev_res, ev_events.
		2393
		2394	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2395	maintained by libev, it does not work exactly the same way as in libevent (consider
		2396	it a private API).
		2397
		2398	=item * Priorities are not currently supported. Initialising priorities
		2399	will fail and all watchers will have the same priority, even though there
		2400	is an ev_pri field.
		2401
		2402	=item * In libevent, the last base created gets the signals, in libev, the
		2403	first base created (== the default loop) gets the signals.
		2404
		2405	=item * Other members are not supported.
		2406
		2407	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2408	to use the libev header file and library.
		2409
		2410	=back
		2411
		2412	=head1 C++ SUPPORT
		2413
		2414	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2415	you to use some convinience methods to start/stop watchers and also change
		2416	the callback model to a model using method callbacks on objects.
		2417
		2418	To use it,
		2419
		2420	#include <ev++.h>
		2421
		2422	This automatically includes F<ev.h> and puts all of its definitions (many
		2423	of them macros) into the global namespace. All C++ specific things are
		2424	put into the C<ev> namespace. It should support all the same embedding
		2425	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2426
		2427	Care has been taken to keep the overhead low. The only data member the C++
		2428	classes add (compared to plain C-style watchers) is the event loop pointer
		2429	that the watcher is associated with (or no additional members at all if
		2430	you disable C<EV_MULTIPLICITY> when embedding libev).
		2431
		2432	Currently, functions, and static and non-static member functions can be
		2433	used as callbacks. Other types should be easy to add as long as they only
		2434	need one additional pointer for context. If you need support for other
		2435	types of functors please contact the author (preferably after implementing
		2436	it).
		2437
		2438	Here is a list of things available in the C<ev> namespace:
		2439
		2440	=over 4
		2441
		2442	=item C<ev::READ>, C<ev::WRITE> etc.
		2443
		2444	These are just enum values with the same values as the C<EV_READ> etc.
		2445	macros from F<ev.h>.
		2446
		2447	=item C<ev::tstamp>, C<ev::now>
		2448
		2449	Aliases to the same types/functions as with the C<ev_> prefix.
		2450
		2451	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2452
		2453	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2454	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2455	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2456	defines by many implementations.
		2457
		2458	All of those classes have these methods:
		2459
		2460	=over 4
		2461
		2462	=item ev::TYPE::TYPE ()
		2463
		2464	=item ev::TYPE::TYPE (struct ev_loop *)
		2465
		2466	=item ev::TYPE::~TYPE
		2467
		2468	The constructor (optionally) takes an event loop to associate the watcher
		2469	with. If it is omitted, it will use C<EV_DEFAULT>.
		2470
		2471	The constructor calls C<ev_init> for you, which means you have to call the
		2472	C<set> method before starting it.
		2473
		2474	It will not set a callback, however: You have to call the templated C<set>
		2475	method to set a callback before you can start the watcher.
		2476
		2477	(The reason why you have to use a method is a limitation in C++ which does
		2478	not allow explicit template arguments for constructors).
		2479
		2480	The destructor automatically stops the watcher if it is active.
		2481
		2482	=item w->set<class, &class::method> (object *)
		2483
		2484	This method sets the callback method to call. The method has to have a
		2485	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2486	first argument and the C<revents> as second. The object must be given as
		2487	parameter and is stored in the C<data> member of the watcher.
		2488
		2489	This method synthesizes efficient thunking code to call your method from
		2490	the C callback that libev requires. If your compiler can inline your
		2491	callback (i.e. it is visible to it at the place of the C<set> call and
		2492	your compiler is good :), then the method will be fully inlined into the
		2493	thunking function, making it as fast as a direct C callback.
		2494
		2495	Example: simple class declaration and watcher initialisation
		2496
		2497	struct myclass
		2498	{
		2499	void io_cb (ev::io &w, int revents) { }
		2500	}
		2501
		2502	myclass obj;
		2503	ev::io iow;
		2504	iow.set <myclass, &myclass::io_cb> (&obj);
		2505
		2506	=item w->set<function> (void *data = 0)
		2507
		2508	Also sets a callback, but uses a static method or plain function as
		2509	callback. The optional C<data> argument will be stored in the watcher's
		2510	C<data> member and is free for you to use.
		2511
		2512	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2513
		2514	See the method-C<set> above for more details.
		2515
		2516	Example:
		2517
		2518	static void io_cb (ev::io &w, int revents) { }
		2519	iow.set <io_cb> ();
		2520
		2521	=item w->set (struct ev_loop *)
		2522
		2523	Associates a different C<struct ev_loop> with this watcher. You can only
		2524	do this when the watcher is inactive (and not pending either).
		2525
		2526	=item w->set ([args])
		2527
		2528	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2529	called at least once. Unlike the C counterpart, an active watcher gets
		2530	automatically stopped and restarted when reconfiguring it with this
		2531	method.
		2532
		2533	=item w->start ()
		2534
		2535	Starts the watcher. Note that there is no C<loop> argument, as the
		2536	constructor already stores the event loop.
		2537
		2538	=item w->stop ()
		2539
		2540	Stops the watcher if it is active. Again, no C<loop> argument.
		2541
		2542	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2543
		2544	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2545	C<ev_TYPE_again> function.
		2546
		2547	=item w->sweep () (C<ev::embed> only)
		2548
		2549	Invokes C<ev_embed_sweep>.
		2550
		2551	=item w->update () (C<ev::stat> only)
		2552
		2553	Invokes C<ev_stat_stat>.
		2554
		2555	=back
		2556
		2557	=back
		2558
		2559	Example: Define a class with an IO and idle watcher, start one of them in
		2560	the constructor.
		2561
		2562	class myclass
		2563	{
		2564	ev::io io; void io_cb (ev::io &w, int revents);
		2565	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2566
		2567	myclass (int fd)
		2568	{
		2569	io .set <myclass, &myclass::io_cb > (this);
		2570	idle.set <myclass, &myclass::idle_cb> (this);
		2571
		2572	io.start (fd, ev::READ);
		2573	}
		2574	};
		2575
		2576
		2577	=head1 OTHER LANGUAGE BINDINGS
		2578
		2579	Libev does not offer other language bindings itself, but bindings for a
		2580	numbe rof languages exist in the form of third-party packages. If you know
		2581	any interesting language binding in addition to the ones listed here, drop
		2582	me a note.
		2583
		2584	=over 4
		2585
		2586	=item Perl
		2587
		2588	The EV module implements the full libev API and is actually used to test
		2589	libev. EV is developed together with libev. Apart from the EV core module,
		2590	there are additional modules that implement libev-compatible interfaces
		2591	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2592	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2593
		2594	It can be found and installed via CPAN, its homepage is found at
		2595	L<http://software.schmorp.de/pkg/EV>.
		2596
		2597	=item Ruby
		2598
		2599	Tony Arcieri has written a ruby extension that offers access to a subset
		2600	of the libev API and adds filehandle abstractions, asynchronous DNS and
		2601	more on top of it. It can be found via gem servers. Its homepage is at
		2602	L<http://rev.rubyforge.org/>.
		2603
		2604	=item D
		2605
		2606	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2607	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2608
		2609	=back
		2610
		2611
		2612	=head1 MACRO MAGIC
		2613
		2614	Libev can be compiled with a variety of options, the most fundamantal
		2615	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2616	functions and callbacks have an initial C<struct ev_loop *> argument.
		2617
		2618	To make it easier to write programs that cope with either variant, the
		2619	following macros are defined:
		2620
		2621	=over 4
		2622
		2623	=item C<EV_A>, C<EV_A_>
		2624
		2625	This provides the loop I<argument> for functions, if one is required ("ev
		2626	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2627	C<EV_A_> is used when other arguments are following. Example:
		2628
		2629	ev_unref (EV_A);
		2630	ev_timer_add (EV_A_ watcher);
		2631	ev_loop (EV_A_ 0);
		2632
		2633	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2634	which is often provided by the following macro.
		2635
		2636	=item C<EV_P>, C<EV_P_>
		2637
		2638	This provides the loop I<parameter> for functions, if one is required ("ev
		2639	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2640	C<EV_P_> is used when other parameters are following. Example:
		2641
		2642	// this is how ev_unref is being declared
		2643	static void ev_unref (EV_P);
		2644
		2645	// this is how you can declare your typical callback
		2646	static void cb (EV_P_ ev_timer *w, int revents)
		2647
		2648	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2649	suitable for use with C<EV_A>.
		2650
		2651	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2652
		2653	Similar to the other two macros, this gives you the value of the default
		2654	loop, if multiple loops are supported ("ev loop default").
		2655
		2656	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2657
		2658	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2659	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2660	is undefined when the default loop has not been initialised by a previous
		2661	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2662
		2663	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2664	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2665
		2666	=back
		2667
		2668	Example: Declare and initialise a check watcher, utilising the above
		2669	macros so it will work regardless of whether multiple loops are supported
		2670	or not.
		2671
		2672	static void
		2673	check_cb (EV_P_ ev_timer *w, int revents)
		2674	{
		2675	ev_check_stop (EV_A_ w);
		2676	}
		2677
		2678	ev_check check;
		2679	ev_check_init (&check, check_cb);
		2680	ev_check_start (EV_DEFAULT_ &check);
		2681	ev_loop (EV_DEFAULT_ 0);
		2682
		2683	=head1 EMBEDDING
		2684
		2685	Libev can (and often is) directly embedded into host
		2686	applications. Examples of applications that embed it include the Deliantra
		2687	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2688	and rxvt-unicode.
		2689
		2690	The goal is to enable you to just copy the necessary files into your
		2691	source directory without having to change even a single line in them, so
		2692	you can easily upgrade by simply copying (or having a checked-out copy of
		2693	libev somewhere in your source tree).
		2694
		2695	=head2 FILESETS
		2696
		2697	Depending on what features you need you need to include one or more sets of files
		2698	in your app.
		2699
		2700	=head3 CORE EVENT LOOP
		2701
		2702	To include only the libev core (all the C<ev_*> functions), with manual
		2703	configuration (no autoconf):
		2704
		2705	#define EV_STANDALONE 1
		2706	#include "ev.c"
		2707
		2708	This will automatically include F<ev.h>, too, and should be done in a
		2709	single C source file only to provide the function implementations. To use
		2710	it, do the same for F<ev.h> in all files wishing to use this API (best
		2711	done by writing a wrapper around F<ev.h> that you can include instead and
		2712	where you can put other configuration options):
		2713
		2714	#define EV_STANDALONE 1
		2715	#include "ev.h"
		2716
		2717	Both header files and implementation files can be compiled with a C++
		2718	compiler (at least, thats a stated goal, and breakage will be treated
		2719	as a bug).
		2720
		2721	You need the following files in your source tree, or in a directory
		2722	in your include path (e.g. in libev/ when using -Ilibev):
		2723
		2724	ev.h
		2725	ev.c
		2726	ev_vars.h
		2727	ev_wrap.h
		2728
		2729	ev_win32.c required on win32 platforms only
		2730
		2731	ev_select.c only when select backend is enabled (which is enabled by default)
		2732	ev_poll.c only when poll backend is enabled (disabled by default)
		2733	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2734	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2735	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2736
		2737	F<ev.c> includes the backend files directly when enabled, so you only need
		2738	to compile this single file.
		2739
		2740	=head3 LIBEVENT COMPATIBILITY API
		2741
		2742	To include the libevent compatibility API, also include:
		2743
		2744	#include "event.c"
		2745
		2746	in the file including F<ev.c>, and:
		2747
		2748	#include "event.h"
		2749
		2750	in the files that want to use the libevent API. This also includes F<ev.h>.
		2751
		2752	You need the following additional files for this:
		2753
		2754	event.h
		2755	event.c
		2756
		2757	=head3 AUTOCONF SUPPORT
		2758
		2759	Instead of using C<EV_STANDALONE=1> and providing your config in
		2760	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2761	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2762	include F<config.h> and configure itself accordingly.
		2763
		2764	For this of course you need the m4 file:
		2765
		2766	libev.m4
		2767
		2768	=head2 PREPROCESSOR SYMBOLS/MACROS
		2769
		2770	Libev can be configured via a variety of preprocessor symbols you have to
		2771	define before including any of its files. The default in the absense of
		2772	autoconf is noted for every option.
		2773
		2774	=over 4
		2775
		2776	=item EV_STANDALONE
		2777
		2778	Must always be C<1> if you do not use autoconf configuration, which
		2779	keeps libev from including F<config.h>, and it also defines dummy
		2780	implementations for some libevent functions (such as logging, which is not
		2781	supported). It will also not define any of the structs usually found in
		2782	F<event.h> that are not directly supported by the libev core alone.
		2783
		2784	=item EV_USE_MONOTONIC
		2785
		2786	If defined to be C<1>, libev will try to detect the availability of the
		2787	monotonic clock option at both compiletime and runtime. Otherwise no use
		2788	of the monotonic clock option will be attempted. If you enable this, you
		2789	usually have to link against librt or something similar. Enabling it when
		2790	the functionality isn't available is safe, though, although you have
		2791	to make sure you link against any libraries where the C<clock_gettime>
		2792	function is hiding in (often F<-lrt>).
		2793
		2794	=item EV_USE_REALTIME
		2795
		2796	If defined to be C<1>, libev will try to detect the availability of the
		2797	realtime clock option at compiletime (and assume its availability at
		2798	runtime if successful). Otherwise no use of the realtime clock option will
		2799	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2800	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2801	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2802
		2803	=item EV_USE_NANOSLEEP
		2804
		2805	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2806	and will use it for delays. Otherwise it will use C<select ()>.
		2807
		2808	=item EV_USE_EVENTFD
		2809
		2810	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2811	available and will probe for kernel support at runtime. This will improve
		2812	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2813	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2814	2.7 or newer, otherwise disabled.
		2815
		2816	=item EV_USE_SELECT
		2817
		2818	If undefined or defined to be C<1>, libev will compile in support for the
		2819	C<select>(2) backend. No attempt at autodetection will be done: if no
		2820	other method takes over, select will be it. Otherwise the select backend
		2821	will not be compiled in.
		2822
		2823	=item EV_SELECT_USE_FD_SET
		2824
		2825	If defined to C<1>, then the select backend will use the system C<fd_set>
		2826	structure. This is useful if libev doesn't compile due to a missing
		2827	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2828	exotic systems. This usually limits the range of file descriptors to some
		2829	low limit such as 1024 or might have other limitations (winsocket only
		2830	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2831	influence the size of the C<fd_set> used.
		2832
		2833	=item EV_SELECT_IS_WINSOCKET
		2834
		2835	When defined to C<1>, the select backend will assume that
		2836	select/socket/connect etc. don't understand file descriptors but
		2837	wants osf handles on win32 (this is the case when the select to
		2838	be used is the winsock select). This means that it will call
		2839	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2840	it is assumed that all these functions actually work on fds, even
		2841	on win32. Should not be defined on non-win32 platforms.
		2842
		2843	=item EV_FD_TO_WIN32_HANDLE
		2844
		2845	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2846	file descriptors to socket handles. When not defining this symbol (the
		2847	default), then libev will call C<_get_osfhandle>, which is usually
		2848	correct. In some cases, programs use their own file descriptor management,
		2849	in which case they can provide this function to map fds to socket handles.
		2850
		2851	=item EV_USE_POLL
		2852
		2853	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2854	backend. Otherwise it will be enabled on non-win32 platforms. It
		2855	takes precedence over select.
		2856
		2857	=item EV_USE_EPOLL
		2858
		2859	If defined to be C<1>, libev will compile in support for the Linux
		2860	C<epoll>(7) backend. Its availability will be detected at runtime,
		2861	otherwise another method will be used as fallback. This is the preferred
		2862	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2863	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2864
		2865	=item EV_USE_KQUEUE
		2866
		2867	If defined to be C<1>, libev will compile in support for the BSD style
		2868	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2869	otherwise another method will be used as fallback. This is the preferred
		2870	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2871	supports some types of fds correctly (the only platform we found that
		2872	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2873	not be used unless explicitly requested. The best way to use it is to find
		2874	out whether kqueue supports your type of fd properly and use an embedded
		2875	kqueue loop.
		2876
		2877	=item EV_USE_PORT
		2878
		2879	If defined to be C<1>, libev will compile in support for the Solaris
		2880	10 port style backend. Its availability will be detected at runtime,
		2881	otherwise another method will be used as fallback. This is the preferred
		2882	backend for Solaris 10 systems.
		2883
		2884	=item EV_USE_DEVPOLL
		2885
		2886	reserved for future expansion, works like the USE symbols above.
		2887
		2888	=item EV_USE_INOTIFY
		2889
		2890	If defined to be C<1>, libev will compile in support for the Linux inotify
		2891	interface to speed up C<ev_stat> watchers. Its actual availability will
		2892	be detected at runtime. If undefined, it will be enabled if the headers
		2893	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2894
		2895	=item EV_ATOMIC_T
		2896
		2897	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2898	access is atomic with respect to other threads or signal contexts. No such
		2899	type is easily found in the C language, so you can provide your own type
		2900	that you know is safe for your purposes. It is used both for signal handler "locking"
		2901	as well as for signal and thread safety in C<ev_async> watchers.
		2902
		2903	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2904	(from F<signal.h>), which is usually good enough on most platforms.
		2905
		2906	=item EV_H
		2907
		2908	The name of the F<ev.h> header file used to include it. The default if
		2909	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2910	used to virtually rename the F<ev.h> header file in case of conflicts.
		2911
		2912	=item EV_CONFIG_H
		2913
		2914	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2915	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2916	C<EV_H>, above.
		2917
		2918	=item EV_EVENT_H
		2919
		2920	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2921	of how the F<event.h> header can be found, the default is C<"event.h">.
		2922
		2923	=item EV_PROTOTYPES
		2924
		2925	If defined to be C<0>, then F<ev.h> will not define any function
		2926	prototypes, but still define all the structs and other symbols. This is
		2927	occasionally useful if you want to provide your own wrapper functions
		2928	around libev functions.
		2929
		2930	=item EV_MULTIPLICITY
		2931
		2932	If undefined or defined to C<1>, then all event-loop-specific functions
		2933	will have the C<struct ev_loop *> as first argument, and you can create
		2934	additional independent event loops. Otherwise there will be no support
		2935	for multiple event loops and there is no first event loop pointer
		2936	argument. Instead, all functions act on the single default loop.
		2937
		2938	=item EV_MINPRI
		2939
		2940	=item EV_MAXPRI
		2941
		2942	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2943	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2944	provide for more priorities by overriding those symbols (usually defined
		2945	to be C<-2> and C<2>, respectively).
		2946
		2947	When doing priority-based operations, libev usually has to linearly search
		2948	all the priorities, so having many of them (hundreds) uses a lot of space
		2949	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2950	fine.
		2951
		2952	If your embedding app does not need any priorities, defining these both to
		2953	C<0> will save some memory and cpu.
		2954
		2955	=item EV_PERIODIC_ENABLE
		2956
		2957	If undefined or defined to be C<1>, then periodic timers are supported. If
		2958	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2959	code.
		2960
		2961	=item EV_IDLE_ENABLE
		2962
		2963	If undefined or defined to be C<1>, then idle watchers are supported. If
		2964	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2965	code.
		2966
		2967	=item EV_EMBED_ENABLE
		2968
		2969	If undefined or defined to be C<1>, then embed watchers are supported. If
		2970	defined to be C<0>, then they are not.
		2971
		2972	=item EV_STAT_ENABLE
		2973
		2974	If undefined or defined to be C<1>, then stat watchers are supported. If
		2975	defined to be C<0>, then they are not.
		2976
		2977	=item EV_FORK_ENABLE
		2978
		2979	If undefined or defined to be C<1>, then fork watchers are supported. If
		2980	defined to be C<0>, then they are not.
		2981
		2982	=item EV_ASYNC_ENABLE
		2983
		2984	If undefined or defined to be C<1>, then async watchers are supported. If
		2985	defined to be C<0>, then they are not.
		2986
		2987	=item EV_MINIMAL
		2988
		2989	If you need to shave off some kilobytes of code at the expense of some
		2990	speed, define this symbol to C<1>. Currently this is used to override some
		2991	inlining decisions, saves roughly 30% codesize of amd64. It also selects a
		2992	much smaller 2-heap for timer management over the default 4-heap.
		2993
		2994	=item EV_PID_HASHSIZE
		2995
		2996	C<ev_child> watchers use a small hash table to distribute workload by
		2997	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2998	than enough. If you need to manage thousands of children you might want to
		2999	increase this value (I<must> be a power of two).
		3000
		3001	=item EV_INOTIFY_HASHSIZE
		3002
		3003	C<ev_stat> watchers use a small hash table to distribute workload by
		3004	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3005	usually more than enough. If you need to manage thousands of C<ev_stat>
		3006	watchers you might want to increase this value (I<must> be a power of
		3007	two).
		3008
		3009	=item EV_USE_4HEAP
		3010
		3011	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3012	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3013	to C<1>. The 4-heap uses more complicated (longer) code but has
		3014	noticably faster performance with many (thousands) of watchers.
		3015
		3016	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3017	(disabled).
		3018
		3019	=item EV_HEAP_CACHE_AT
		3020
		3021	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3022	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3023	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3024	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3025	but avoids random read accesses on heap changes. This improves performance
		3026	noticably with with many (hundreds) of watchers.
		3027
		3028	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3029	(disabled).
		3030
		3031	=item EV_COMMON
		3032
		3033	By default, all watchers have a C<void *data> member. By redefining
		3034	this macro to a something else you can include more and other types of
		3035	members. You have to define it each time you include one of the files,
		3036	though, and it must be identical each time.
		3037
		3038	For example, the perl EV module uses something like this:
		3039
		3040	#define EV_COMMON \
		3041	SV *self; /* contains this struct */ \
		3042	SV *cb_sv, *fh /* note no trailing ";" */
		3043
		3044	=item EV_CB_DECLARE (type)
		3045
		3046	=item EV_CB_INVOKE (watcher, revents)
		3047
		3048	=item ev_set_cb (ev, cb)
		3049
		3050	Can be used to change the callback member declaration in each watcher,
		3051	and the way callbacks are invoked and set. Must expand to a struct member
		3052	definition and a statement, respectively. See the F<ev.h> header file for
		3053	their default definitions. One possible use for overriding these is to
		3054	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3055	method calls instead of plain function calls in C++.
		3056
		3057	=head2 EXPORTED API SYMBOLS
		3058
		3059	If you need to re-export the API (e.g. via a dll) and you need a list of
		3060	exported symbols, you can use the provided F<Symbol.*> files which list
		3061	all public symbols, one per line:
		3062
		3063	Symbols.ev for libev proper
		3064	Symbols.event for the libevent emulation
		3065
		3066	This can also be used to rename all public symbols to avoid clashes with
		3067	multiple versions of libev linked together (which is obviously bad in
		3068	itself, but sometimes it is inconvinient to avoid this).
		3069
		3070	A sed command like this will create wrapper C<#define>'s that you need to
		3071	include before including F<ev.h>:
		3072
		3073	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3074
		3075	This would create a file F<wrap.h> which essentially looks like this:
		3076
		3077	#define ev_backend myprefix_ev_backend
		3078	#define ev_check_start myprefix_ev_check_start
		3079	#define ev_check_stop myprefix_ev_check_stop
		3080	...
		3081
		3082	=head2 EXAMPLES
		3083
		3084	For a real-world example of a program the includes libev
		3085	verbatim, you can have a look at the EV perl module
		3086	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3087	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3088	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3089	will be compiled. It is pretty complex because it provides its own header
		3090	file.
		3091
		3092	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3093	that everybody includes and which overrides some configure choices:
		3094
		3095	#define EV_MINIMAL 1
		3096	#define EV_USE_POLL 0
		3097	#define EV_MULTIPLICITY 0
		3098	#define EV_PERIODIC_ENABLE 0
		3099	#define EV_STAT_ENABLE 0
		3100	#define EV_FORK_ENABLE 0
		3101	#define EV_CONFIG_H <config.h>
		3102	#define EV_MINPRI 0
		3103	#define EV_MAXPRI 0
		3104
		3105	#include "ev++.h"
		3106
		3107	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3108
		3109	#include "ev_cpp.h"
		3110	#include "ev.c"
		3111
		3112
		3113	=head1 THREADS AND COROUTINES
		3114
		3115	=head2 THREADS
		3116
		3117	Libev itself is completely threadsafe, but it uses no locking. This
		3118	means that you can use as many loops as you want in parallel, as long as
		3119	only one thread ever calls into one libev function with the same loop
		3120	parameter.
		3121
		3122	Or put differently: calls with different loop parameters can be done in
		3123	parallel from multiple threads, calls with the same loop parameter must be
		3124	done serially (but can be done from different threads, as long as only one
		3125	thread ever is inside a call at any point in time, e.g. by using a mutex
		3126	per loop).
		3127
		3128	If you want to know which design is best for your problem, then I cannot
		3129	help you but by giving some generic advice:
		3130
		3131	=over 4
		3132
		3133	=item * most applications have a main thread: use the default libev loop
		3134	in that thread, or create a seperate thread running only the default loop.
		3135
		3136	This helps integrating other libraries or software modules that use libev
		3137	themselves and don't care/know about threading.
		3138
		3139	=item * one loop per thread is usually a good model.
		3140
		3141	Doing this is almost never wrong, sometimes a better-performance model
		3142	exists, but it is always a good start.
		3143
		3144	=item * other models exist, such as the leader/follower pattern, where one
		3145	loop is handed through multiple threads in a kind of round-robbin fashion.
		3146
		3147	Chosing a model is hard - look around, learn, know that usually you cna do
		3148	better than you currently do :-)
		3149
		3150	=item * often you need to talk to some other thread which blocks in the
		3151	event loop - C<ev_async> watchers can be used to wake them up from other
		3152	threads safely (or from signal contexts...).
		3153
		3154	=back
		3155
		3156	=head2 COROUTINES
		3157
		3158	Libev is much more accomodating to coroutines ("cooperative threads"):
		3159	libev fully supports nesting calls to it's functions from different
		3160	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3161	different coroutines and switch freely between both coroutines running the
		3162	loop, as long as you don't confuse yourself). The only exception is that
		3163	you must not do this from C<ev_periodic> reschedule callbacks.
		3164
		3165	Care has been invested into making sure that libev does not keep local
		3166	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3167	switches.
		3168
		3169
		3170	=head1 COMPLEXITIES
		3171
		3172	In this section the complexities of (many of) the algorithms used inside
		3173	libev will be explained. For complexity discussions about backends see the
		3174	documentation for C<ev_default_init>.
		3175
		3176	All of the following are about amortised time: If an array needs to be
		3177	extended, libev needs to realloc and move the whole array, but this
		3178	happens asymptotically never with higher number of elements, so O(1) might
		3179	mean it might do a lengthy realloc operation in rare cases, but on average
		3180	it is much faster and asymptotically approaches constant time.
		3181
		3182	=over 4
		3183
		3184	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3185
		3186	This means that, when you have a watcher that triggers in one hour and
		3187	there are 100 watchers that would trigger before that then inserting will
		3188	have to skip roughly seven (C<ld 100>) of these watchers.
		3189
		3190	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3191
		3192	That means that changing a timer costs less than removing/adding them
		3193	as only the relative motion in the event queue has to be paid for.
		3194
		3195	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3196
		3197	These just add the watcher into an array or at the head of a list.
		3198
		3199	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3200
		3201	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3202
		3203	These watchers are stored in lists then need to be walked to find the
		3204	correct watcher to remove. The lists are usually short (you don't usually
		3205	have many watchers waiting for the same fd or signal).
		3206
		3207	=item Finding the next timer in each loop iteration: O(1)
		3208
		3209	By virtue of using a binary or 4-heap, the next timer is always found at a
		3210	fixed position in the storage array.
		3211
		3212	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3213
		3214	A change means an I/O watcher gets started or stopped, which requires
		3215	libev to recalculate its status (and possibly tell the kernel, depending
		3216	on backend and wether C<ev_io_set> was used).
		3217
		3218	=item Activating one watcher (putting it into the pending state): O(1)
		3219
		3220	=item Priority handling: O(number_of_priorities)
		3221
		3222	Priorities are implemented by allocating some space for each
		3223	priority. When doing priority-based operations, libev usually has to
		3224	linearly search all the priorities, but starting/stopping and activating
		3225	watchers becomes O(1) w.r.t. priority handling.
		3226
		3227	=item Sending an ev_async: O(1)
		3228
		3229	=item Processing ev_async_send: O(number_of_async_watchers)
		3230
		3231	=item Processing signals: O(max_signal_number)
		3232
		3233	Sending involves a syscall I<iff> there were no other C<ev_async_send>
		3234	calls in the current loop iteration. Checking for async and signal events
		3235	involves iterating over all running async watchers or all signal numbers.
		3236
		3237	=back
		3238
		3239
		3240	=head1 Win32 platform limitations and workarounds
		3241
		3242	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3243	requires, and its I/O model is fundamentally incompatible with the POSIX
		3244	model. Libev still offers limited functionality on this platform in
		3245	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3246	descriptors. This only applies when using Win32 natively, not when using
		3247	e.g. cygwin.
		3248
		3249	Lifting these limitations would basically require the full
		3250	re-implementation of the I/O system. If you are into these kinds of
		3251	things, then note that glib does exactly that for you in a very portable
		3252	way (note also that glib is the slowest event library known to man).
		3253
		3254	There is no supported compilation method available on windows except
		3255	embedding it into other applications.
		3256
		3257	Due to the many, low, and arbitrary limits on the win32 platform and
		3258	the abysmal performance of winsockets, using a large number of sockets
		3259	is not recommended (and not reasonable). If your program needs to use
		3260	more than a hundred or so sockets, then likely it needs to use a totally
		3261	different implementation for windows, as libev offers the POSIX readiness
		3262	notification model, which cannot be implemented efficiently on windows
		3263	(microsoft monopoly games).
		3264
		3265	=over 4
		3266
		3267	=item The winsocket select function
		3268
		3269	The winsocket C<select> function doesn't follow POSIX in that it requires
		3270	socket I<handles> and not socket I<file descriptors>. This makes select
		3271	very inefficient, and also requires a mapping from file descriptors
		3272	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		3273	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		3274	symbols for more info.
		3275
		3276	The configuration for a "naked" win32 using the microsoft runtime
		3277	libraries and raw winsocket select is:
		3278
		3279	#define EV_USE_SELECT 1
		3280	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3281
		3282	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3283	complexity in the O(n²) range when using win32.
		3284
		3285	=item Limited number of file descriptors
		3286
		3287	Windows has numerous arbitrary (and low) limits on things.
		3288
		3289	Early versions of winsocket's select only supported waiting for a maximum
		3290	of C<64> handles (probably owning to the fact that all windows kernels
		3291	can only wait for C<64> things at the same time internally; microsoft
		3292	recommends spawning a chain of threads and wait for 63 handles and the
		3293	previous thread in each. Great).
		3294
		3295	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3296	to some high number (e.g. C<2048>) before compiling the winsocket select
		3297	call (which might be in libev or elsewhere, for example, perl does its own
		3298	select emulation on windows).
		3299
		3300	Another limit is the number of file descriptors in the microsoft runtime
		3301	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3302	or something like this inside microsoft). You can increase this by calling
		3303	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3304	arbitrary limit), but is broken in many versions of the microsoft runtime
		3305	libraries.
		3306
		3307	This might get you to about C<512> or C<2048> sockets (depending on
		3308	windows version and/or the phase of the moon). To get more, you need to
		3309	wrap all I/O functions and provide your own fd management, but the cost of
		3310	calling select (O(n²)) will likely make this unworkable.
		3311
		3312	=back
		3313
		3314
		3315	=head1 PORTABILITY REQUIREMENTS
		3316
		3317	In addition to a working ISO-C implementation, libev relies on a few
		3318	additional extensions:
		3319
		3320	=over 4
		3321
		3322	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3323
		3324	The type C<sig_atomic_t volatile> (or whatever is defined as
		3325	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3326	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3327	believed to be sufficiently portable.
		3328
		3329	=item C<sigprocmask> must work in a threaded environment
		3330
		3331	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3332	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3333	pthread implementations will either allow C<sigprocmask> in the "main
		3334	thread" or will block signals process-wide, both behaviours would
		3335	be compatible with libev. Interaction between C<sigprocmask> and
		3336	C<pthread_sigmask> could complicate things, however.
		3337
		3338	The most portable way to handle signals is to block signals in all threads
		3339	except the initial one, and run the default loop in the initial thread as
		3340	well.
		3341
		3342	=item C<long> must be large enough for common memory allocation sizes
		3343
		3344	To improve portability and simplify using libev, libev uses C<long>
		3345	internally instead of C<size_t> when allocating its data structures. On
		3346	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3347	is still at least 31 bits everywhere, which is enough for hundreds of
		3348	millions of watchers.
		3349
		3350	=item C<double> must hold a time value in seconds with enough accuracy
		3351
		3352	The type C<double> is used to represent timestamps. It is required to
		3353	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3354	enough for at least into the year 4000. This requirement is fulfilled by
		3355	implementations implementing IEEE 754 (basically all existing ones).
		3356
		3357	=back
		3358
		3359	If you know of other additional requirements drop me a note.
		3360
		3361
		3362	=head1 VALGRIND
		3363
		3364	Valgrind has a special section here because it is a popular tool that is
		3365	highly useful, but valgrind reports are very hard to interpret.
		3366
		3367	If you think you found a bug (memory leak, uninitialised data access etc.)
		3368	in libev, then check twice: If valgrind reports something like:
		3369
		3370	==2274== definitely lost: 0 bytes in 0 blocks.
		3371	==2274== possibly lost: 0 bytes in 0 blocks.
		3372	==2274== still reachable: 256 bytes in 1 blocks.
		3373
		3374	then there is no memory leak. Similarly, under some circumstances,
		3375	valgrind might report kernel bugs as if it were a bug in libev, or it
		3376	might be confused (it is a very good tool, but only a tool).
		3377
		3378	If you are unsure about something, feel free to contact the mailing list
		3379	with the full valgrind report and an explanation on why you think this is
		3380	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3381	no bug" answer and take the chance of learning how to interpret valgrind
		3382	properly.
		3383
		3384	If you need, for some reason, empty reports from valgrind for your project
		3385	I suggest using suppression lists.
		3386
		3387
755	=head1 AUTHOR	3388	=head1 AUTHOR
756		3389
757	Marc Lehmann <libev@schmorp.de>.	3390	Marc Lehmann <libev@schmorp.de>.
758		3391

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