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…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_<type>
		16	ev_io stdin_watcher;
		17	ev_timer timeout_watcher;
		18
		19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
		21	static void
		22	stdin_cb (EV_P_ struct ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	struct ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://cvs.schmorp.de/libev/ev.html>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	108	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	117	to the C<double> type in C, and when you need to do any calculations on
		118	it, you should treat it as some floatingpoint value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
51		121
52	=head1 GLOBAL FUNCTIONS	122	=head1 GLOBAL FUNCTIONS
53		123
54	These functions can be called anytime, even before initialising the	124	These functions can be called anytime, even before initialising the
55	library in any way.	125	library in any way.
…		…
60		130
61	Returns the current time as libev would use it. Please note that the	131	Returns the current time as libev would use it. Please note that the
62	C<ev_now> function is usually faster and also often returns the timestamp	132	C<ev_now> function is usually faster and also often returns the timestamp
63	you actually want to know.	133	you actually want to know.
64		134
		135	=item ev_sleep (ev_tstamp interval)
		136
		137	Sleep for the given interval: The current thread will be blocked until
		138	either it is interrupted or the given time interval has passed. Basically
		139	this is a subsecond-resolution C<sleep ()>.
		140
65	=item int ev_version_major ()	141	=item int ev_version_major ()
66		142
67	=item int ev_version_minor ()	143	=item int ev_version_minor ()
68		144
69	You can find out the major and minor version numbers of the library	145	You can find out the major and minor ABI version numbers of the library
70	you linked against by calling the functions C<ev_version_major> and	146	you linked against by calling the functions C<ev_version_major> and
71	C<ev_version_minor>. If you want, you can compare against the global	147	C<ev_version_minor>. If you want, you can compare against the global
72	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	148	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
73	version of the library your program was compiled against.	149	version of the library your program was compiled against.
74		150
		151	These version numbers refer to the ABI version of the library, not the
		152	release version.
		153
75	Usually, it's a good idea to terminate if the major versions mismatch,	154	Usually, it's a good idea to terminate if the major versions mismatch,
76	as this indicates an incompatible change. Minor versions are usually	155	as this indicates an incompatible change. Minor versions are usually
77	compatible to older versions, so a larger minor version alone is usually	156	compatible to older versions, so a larger minor version alone is usually
78	not a problem.	157	not a problem.
79		158
		159	Example: Make sure we haven't accidentally been linked against the wrong
		160	version.
		161
		162	assert (("libev version mismatch",
		163	ev_version_major () == EV_VERSION_MAJOR
		164	&& ev_version_minor () >= EV_VERSION_MINOR));
		165
		166	=item unsigned int ev_supported_backends ()
		167
		168	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		169	value) compiled into this binary of libev (independent of their
		170	availability on the system you are running on). See C<ev_default_loop> for
		171	a description of the set values.
		172
		173	Example: make sure we have the epoll method, because yeah this is cool and
		174	a must have and can we have a torrent of it please!!!11
		175
		176	assert (("sorry, no epoll, no sex",
		177	ev_supported_backends () & EVBACKEND_EPOLL));
		178
		179	=item unsigned int ev_recommended_backends ()
		180
		181	Return the set of all backends compiled into this binary of libev and also
		182	recommended for this platform. This set is often smaller than the one
		183	returned by C<ev_supported_backends>, as for example kqueue is broken on
		184	most BSDs and will not be autodetected unless you explicitly request it
		185	(assuming you know what you are doing). This is the set of backends that
		186	libev will probe for if you specify no backends explicitly.
		187
		188	=item unsigned int ev_embeddable_backends ()
		189
		190	Returns the set of backends that are embeddable in other event loops. This
		191	is the theoretical, all-platform, value. To find which backends
		192	might be supported on the current system, you would need to look at
		193	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		194	recommended ones.
		195
		196	See the description of C<ev_embed> watchers for more info.
		197
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
81		199
82	Sets the allocation function to use (the prototype is similar to the	200	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	201	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
84	and free memory (no surprises here). If it returns zero when memory	202	used to allocate and free memory (no surprises here). If it returns zero
85	needs to be allocated, the library might abort or take some potentially	203	when memory needs to be allocated (C<size != 0>), the library might abort
86	destructive action. The default is your system realloc function.	204	or take some potentially destructive action.
		205
		206	Since some systems (at least OpenBSD and Darwin) fail to implement
		207	correct C<realloc> semantics, libev will use a wrapper around the system
		208	C<realloc> and C<free> functions by default.
87		209
88	You could override this function in high-availability programs to, say,	210	You could override this function in high-availability programs to, say,
89	free some memory if it cannot allocate memory, to use a special allocator,	211	free some memory if it cannot allocate memory, to use a special allocator,
90	or even to sleep a while and retry until some memory is available.	212	or even to sleep a while and retry until some memory is available.
		213
		214	Example: Replace the libev allocator with one that waits a bit and then
		215	retries (example requires a standards-compliant C<realloc>).
		216
		217	static void *
		218	persistent_realloc (void *ptr, size_t size)
		219	{
		220	for (;;)
		221	{
		222	void *newptr = realloc (ptr, size);
		223
		224	if (newptr)
		225	return newptr;
		226
		227	sleep (60);
		228	}
		229	}
		230
		231	...
		232	ev_set_allocator (persistent_realloc);
91		233
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	234	=item ev_set_syserr_cb (void (*cb)(const char *msg));
93		235
94	Set the callback function to call on a retryable syscall error (such	236	Set the callback function to call on a retryable syscall error (such
95	as failed select, poll, epoll_wait). The message is a printable string	237	as failed select, poll, epoll_wait). The message is a printable string
…		…
97	callback is set, then libev will expect it to remedy the sitution, no	239	callback is set, then libev will expect it to remedy the sitution, no
98	matter what, when it returns. That is, libev will generally retry the	240	matter what, when it returns. That is, libev will generally retry the
99	requested operation, or, if the condition doesn't go away, do bad stuff	241	requested operation, or, if the condition doesn't go away, do bad stuff
100	(such as abort).	242	(such as abort).
101		243
		244	Example: This is basically the same thing that libev does internally, too.
		245
		246	static void
		247	fatal_error (const char *msg)
		248	{
		249	perror (msg);
		250	abort ();
		251	}
		252
		253	...
		254	ev_set_syserr_cb (fatal_error);
		255
102	=back	256	=back
103		257
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	258	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		259
106	An event loop is described by a C<struct ev_loop *>. The library knows two	260	An event loop is described by a C<struct ev_loop *>. The library knows two
107	types of such loops, the I<default> loop, which supports signals and child	261	types of such loops, the I<default> loop, which supports signals and child
108	events, and dynamically created loops which do not.	262	events, and dynamically created loops which do not.
109		263
110	If you use threads, a common model is to run the default event loop
111	in your main thread (or in a separate thread) and for each thread you
112	create, you also create another event loop. Libev itself does no locking
113	whatsoever, so if you mix calls to the same event loop in different
114	threads, make sure you lock (this is usually a bad idea, though, even if
115	done correctly, because it's hideous and inefficient).
116
117	=over 4	264	=over 4
118		265
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	266	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		267
121	This will initialise the default event loop if it hasn't been initialised	268	This will initialise the default event loop if it hasn't been initialised
122	yet and return it. If the default loop could not be initialised, returns	269	yet and return it. If the default loop could not be initialised, returns
123	false. If it already was initialised it simply returns it (and ignores the	270	false. If it already was initialised it simply returns it (and ignores the
124	flags).	271	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		272
126	If you don't know what event loop to use, use the one returned from this	273	If you don't know what event loop to use, use the one returned from this
127	function.	274	function.
128		275
		276	Note that this function is I<not> thread-safe, so if you want to use it
		277	from multiple threads, you have to lock (note also that this is unlikely,
		278	as loops cannot bes hared easily between threads anyway).
		279
		280	The default loop is the only loop that can handle C<ev_signal> and
		281	C<ev_child> watchers, and to do this, it always registers a handler
		282	for C<SIGCHLD>. If this is a problem for your app you can either
		283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		284	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		285	C<ev_default_init>.
		286
129	The flags argument can be used to specify special behaviour or specific	287	The flags argument can be used to specify special behaviour or specific
130	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	288	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		289
132	It supports the following flags:	290	The following flags are supported:
133		291
134	=over 4	292	=over 4
135		293
136	=item C<EVFLAG_AUTO>	294	=item C<EVFLAG_AUTO>
137		295
…		…
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	304	override the flags completely if it is found in the environment. This is
147	useful to try out specific backends to test their performance, or to work	305	useful to try out specific backends to test their performance, or to work
148	around bugs.	306	around bugs.
149		307
		308	=item C<EVFLAG_FORKCHECK>
		309
		310	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		311	a fork, you can also make libev check for a fork in each iteration by
		312	enabling this flag.
		313
		314	This works by calling C<getpid ()> on every iteration of the loop,
		315	and thus this might slow down your event loop if you do a lot of loop
		316	iterations and little real work, but is usually not noticeable (on my
		317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		318	without a syscall and thus I<very> fast, but my GNU/Linux system also has
		319	C<pthread_atfork> which is even faster).
		320
		321	The big advantage of this flag is that you can forget about fork (and
		322	forget about forgetting to tell libev about forking) when you use this
		323	flag.
		324
		325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		326	environment variable.
		327
150	=item C<EVMETHOD_SELECT> (portable select backend)	328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		329
		330	This is your standard select(2) backend. Not I<completely> standard, as
		331	libev tries to roll its own fd_set with no limits on the number of fds,
		332	but if that fails, expect a fairly low limit on the number of fds when
		333	using this backend. It doesn't scale too well (O(highest_fd)), but its
		334	usually the fastest backend for a low number of (low-numbered :) fds.
		335
		336	To get good performance out of this backend you need a high amount of
		337	parallelity (most of the file descriptors should be busy). If you are
		338	writing a server, you should C<accept ()> in a loop to accept as many
		339	connections as possible during one iteration. You might also want to have
		340	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		341	readyness notifications you get per iteration.
		342
152	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
153		344
154	=item C<EVMETHOD_EPOLL> (linux only)	345	And this is your standard poll(2) backend. It's more complicated
		346	than select, but handles sparse fds better and has no artificial
		347	limit on the number of fds you can use (except it will slow down
		348	considerably with a lot of inactive fds). It scales similarly to select,
		349	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		350	performance tips.
155		351
156	=item C<EVMETHOD_KQUEUE> (some bsds only)	352	=item C<EVBACKEND_EPOLL> (value 4, Linux)
157		353
158	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	354	For few fds, this backend is a bit little slower than poll and select,
		355	but it scales phenomenally better. While poll and select usually scale
		356	like O(total_fds) where n is the total number of fds (or the highest fd),
		357	epoll scales either O(1) or O(active_fds). The epoll design has a number
		358	of shortcomings, such as silently dropping events in some hard-to-detect
		359	cases and requiring a syscall per fd change, no fork support and bad
		360	support for dup.
159		361
160	=item C<EVMETHOD_PORT> (solaris 10 only)	362	While stopping, setting and starting an I/O watcher in the same iteration
		363	will result in some caching, there is still a syscall per such incident
		364	(because the fd could point to a different file description now), so its
		365	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		366	very well if you register events for both fds.
		367
		368	Please note that epoll sometimes generates spurious notifications, so you
		369	need to use non-blocking I/O or other means to avoid blocking when no data
		370	(or space) is available.
		371
		372	Best performance from this backend is achieved by not unregistering all
		373	watchers for a file descriptor until it has been closed, if possible, i.e.
		374	keep at least one watcher active per fd at all times.
		375
		376	While nominally embeddeble in other event loops, this feature is broken in
		377	all kernel versions tested so far.
		378
		379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		380
		381	Kqueue deserves special mention, as at the time of this writing, it
		382	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		383	with anything but sockets and pipes, except on Darwin, where of course
		384	it's completely useless). For this reason it's not being "autodetected"
		385	unless you explicitly specify it explicitly in the flags (i.e. using
		386	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		387	system like NetBSD.
		388
		389	You still can embed kqueue into a normal poll or select backend and use it
		390	only for sockets (after having made sure that sockets work with kqueue on
		391	the target platform). See C<ev_embed> watchers for more info.
		392
		393	It scales in the same way as the epoll backend, but the interface to the
		394	kernel is more efficient (which says nothing about its actual speed, of
		395	course). While stopping, setting and starting an I/O watcher does never
		396	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
		397	two event changes per incident, support for C<fork ()> is very bad and it
		398	drops fds silently in similarly hard-to-detect cases.
		399
		400	This backend usually performs well under most conditions.
		401
		402	While nominally embeddable in other event loops, this doesn't work
		403	everywhere, so you might need to test for this. And since it is broken
		404	almost everywhere, you should only use it when you have a lot of sockets
		405	(for which it usually works), by embedding it into another event loop
		406	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		407	sockets.
		408
		409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		410
		411	This is not implemented yet (and might never be, unless you send me an
		412	implementation). According to reports, C</dev/poll> only supports sockets
		413	and is not embeddable, which would limit the usefulness of this backend
		414	immensely.
		415
		416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		417
		418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		419	it's really slow, but it still scales very well (O(active_fds)).
		420
		421	Please note that solaris event ports can deliver a lot of spurious
		422	notifications, so you need to use non-blocking I/O or other means to avoid
		423	blocking when no data (or space) is available.
		424
		425	While this backend scales well, it requires one system call per active
		426	file descriptor per loop iteration. For small and medium numbers of file
		427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		428	might perform better.
		429
		430	On the positive side, ignoring the spurious readyness notifications, this
		431	backend actually performed to specification in all tests and is fully
		432	embeddable, which is a rare feat among the OS-specific backends.
		433
		434	=item C<EVBACKEND_ALL>
		435
		436	Try all backends (even potentially broken ones that wouldn't be tried
		437	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		438	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		439
		440	It is definitely not recommended to use this flag.
		441
		442	=back
161		443
162	If one or more of these are ored into the flags value, then only these	444	If one or more of these are ored into the flags value, then only these
163	backends will be tried (in the reverse order as given here). If one are	445	backends will be tried (in the reverse order as listed here). If none are
164	specified, any backend will do.	446	specified, all backends in C<ev_recommended_backends ()> will be tried.
165		447
166	=back	448	The most typical usage is like this:
		449
		450	if (!ev_default_loop (0))
		451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		452
		453	Restrict libev to the select and poll backends, and do not allow
		454	environment settings to be taken into account:
		455
		456	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		457
		458	Use whatever libev has to offer, but make sure that kqueue is used if
		459	available (warning, breaks stuff, best use only with your own private
		460	event loop and only if you know the OS supports your types of fds):
		461
		462	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
167		463
168	=item struct ev_loop *ev_loop_new (unsigned int flags)	464	=item struct ev_loop *ev_loop_new (unsigned int flags)
169		465
170	Similar to C<ev_default_loop>, but always creates a new event loop that is	466	Similar to C<ev_default_loop>, but always creates a new event loop that is
171	always distinct from the default loop. Unlike the default loop, it cannot	467	always distinct from the default loop. Unlike the default loop, it cannot
172	handle signal and child watchers, and attempts to do so will be greeted by	468	handle signal and child watchers, and attempts to do so will be greeted by
173	undefined behaviour (or a failed assertion if assertions are enabled).	469	undefined behaviour (or a failed assertion if assertions are enabled).
174		470
		471	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
175	=item ev_default_destroy ()	481	=item ev_default_destroy ()
176		482
177	Destroys the default loop again (frees all memory and kernel state	483	Destroys the default loop again (frees all memory and kernel state
178	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
179	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>).
180		499
181	=item ev_loop_destroy (loop)	500	=item ev_loop_destroy (loop)
182		501
183	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
184	earlier call to C<ev_loop_new>.	503	earlier call to C<ev_loop_new>.
185		504
186	=item ev_default_fork ()	505	=item ev_default_fork ()
187		506
		507	This function sets a flag that causes subsequent C<ev_loop> iterations
188	This function reinitialises the kernel state for backends that have	508	to reinitialise the kernel state for backends that have one. Despite the
189	one. Despite the name, you can call it anytime, but it makes most sense	509	name, you can call it anytime, but it makes most sense after forking, in
190	after forking, in either the parent or child process (or both, but that	510	the child process (or both child and parent, but that again makes little
191	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.
192		513
193	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
194	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
195	have to call it.	516	you just fork+exec, you don't have to call it at all.
196		517
197	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
198	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
199	quite nicely into a call to C<pthread_atfork>:	520	quite nicely into a call to C<pthread_atfork>:
200		521
…		…
204		525
205	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
206	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
207	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.
208		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
209	=item unsigned int ev_method (loop)	544	=item unsigned int ev_backend (loop)
210		545
211	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
212	use.	547	use.
213		548
214	=item ev_tstamp ev_now (loop)	549	=item ev_tstamp ev_now (loop)
215		550
216	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
217	got events and started processing them. This timestamp does not change	552	received events and started processing them. This timestamp does not
218	as long as callbacks are being processed, and this is also the base time	553	change as long as callbacks are being processed, and this is also the base
219	used for relative timers. You can treat it as the timestamp of the event	554	time used for relative timers. You can treat it as the timestamp of the
220	occuring (or more correctly, the mainloop finding out about it).	555	event occurring (or more correctly, libev finding out about it).
221		556
222	=item ev_loop (loop, int flags)	557	=item ev_loop (loop, int flags)
223		558
224	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
225	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
226	events.	561	events.
227		562
228	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
229	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.
230		571
231	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
232	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
233	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.
234		575
235	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
236	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
237	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
238	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.
239		583
240	This flags value could be used to implement alternative looping
241	constructs, but the C<prepare> and C<check> watchers provide a better and
242	more generic mechanism.
243
244	Here are the gory details of what ev_loop does:	584	Here are the gory details of what C<ev_loop> does:
245		585
246	1. If there are no active watchers (reference count is zero), return.	586	- Before the first iteration, call any pending watchers.
		587	* If EVFLAG_FORKCHECK was used, check for a fork.
		588	- If a fork was detected, queue and call all fork watchers.
247	2. Queue and immediately call all prepare watchers.	589	- Queue and call all prepare watchers.
248	3. If we have been forked, recreate the kernel state.	590	- If we have been forked, recreate the kernel state.
249	4. Update the kernel state with all outstanding changes.	591	- Update the kernel state with all outstanding changes.
250	5. Update the "event loop time".	592	- Update the "event loop time".
251	6. Calculate for how long to block.	593	- Calculate for how long to sleep or block, if at all
		594	(active idle watchers, EVLOOP_NONBLOCK or not having
		595	any active watchers at all will result in not sleeping).
		596	- Sleep if the I/O and timer collect interval say so.
252	7. Block the process, waiting for events.	597	- Block the process, waiting for any events.
		598	- Queue all outstanding I/O (fd) events.
253	8. Update the "event loop time" and do time jump handling.	599	- Update the "event loop time" and do time jump handling.
254	9. Queue all outstanding timers.	600	- Queue all outstanding timers.
255	10. Queue all outstanding periodics.	601	- Queue all outstanding periodics.
256	11. If no events are pending now, queue all idle watchers.	602	- If no events are pending now, queue all idle watchers.
257	12. Queue all check watchers.	603	- Queue all check watchers.
258	13. Call all queued watchers in reverse order (i.e. check watchers first).	604	- Call all queued watchers in reverse order (i.e. check watchers first).
		605	Signals and child watchers are implemented as I/O watchers, and will
		606	be handled here by queueing them when their watcher gets executed.
259	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	607	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
260	was used, return, otherwise continue with step #1.	608	were used, or there are no active watchers, return, otherwise
		609	continue with step *.
		610
		611	Example: Queue some jobs and then loop until no events are outstanding
		612	anymore.
		613
		614	... queue jobs here, make sure they register event watchers as long
		615	... as they still have work to do (even an idle watcher will do..)
		616	ev_loop (my_loop, 0);
		617	... jobs done. yeah!
261		618
262	=item ev_unloop (loop, how)	619	=item ev_unloop (loop, how)
263		620
264	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
265	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
266	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	623	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
267	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.
268		627
269	=item ev_ref (loop)	628	=item ev_ref (loop)
270		629
271	=item ev_unref (loop)	630	=item ev_unref (loop)
272		631
…		…
277	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
278	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
279	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
280	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
281	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
282	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.
283		693
284	=back	694	=back
		695
285		696
286	=head1 ANATOMY OF A WATCHER	697	=head1 ANATOMY OF A WATCHER
287		698
288	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
289	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
…		…
322	*) >>), 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
323	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	734	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
324		735
325	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
326	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
327	reinitialise it or call its set method.	738	reinitialise it or call its C<set> macro.
328
329	You can check whether an event is active by calling the C<ev_is_active
330	(watcher *)> macro. To see whether an event is outstanding (but the
331	callback for it has not been called yet) you can use the C<ev_is_pending
332	(watcher *)> macro.
333		739
334	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
335	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
336	third argument.	742	third argument.
337		743
…		…
361	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.
362		768
363	=item C<EV_CHILD>	769	=item C<EV_CHILD>
364		770
365	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.
366		776
367	=item C<EV_IDLE>	777	=item C<EV_IDLE>
368		778
369	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.
370		780
…		…
378	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
379	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
380	(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
381	C<ev_loop> from blocking).	791	C<ev_loop> from blocking).
382		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
383	=item C<EV_ERROR>	806	=item C<EV_ERROR>
384		807
385	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
386	happen because the watcher could not be properly started because libev	809	happen because the watcher could not be properly started because libev
387	ran out of memory, a file descriptor was found to be closed or any other	810	ran out of memory, a file descriptor was found to be closed or any other
…		…
393	your callbacks is well-written it can just attempt the operation and cope	816	your callbacks is well-written it can just attempt the operation and cope
394	with the error from read() or write(). This will not work in multithreaded	817	with the error from read() or write(). This will not work in multithreaded
395	programs, though, so beware.	818	programs, though, so beware.
396		819
397	=back	820	=back
		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
398		941
399	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	942	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
400		943
401	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
402	and read at any time, libev will completely ignore it. This can be used	945	and read at any time, libev will completely ignore it. This can be used
…		…
420	{	963	{
421	struct my_io *w = (struct my_io *)w_;	964	struct my_io *w = (struct my_io *)w_;
422	...	965	...
423	}	966	}
424		967
425	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
426	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	}
427		999
428		1000
429	=head1 WATCHER TYPES	1001	=head1 WATCHER TYPES
430		1002
431	This section describes each watcher in detail, but will not repeat	1003	This section describes each watcher in detail, but will not repeat
432	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.
433		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
434	=head2 C<ev_io> - is this file descriptor readable or writable	1017	=head2 C<ev_io> - is this file descriptor readable or writable?
435		1018
436	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
437	in each iteration of the event loop (This behaviour is called	1020	in each iteration of the event loop, or, more precisely, when reading
438	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
439	condition persists. Remember you can stop the watcher if you don't want to	1022	some data. This behaviour is called level-triggering because you keep
440	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.
441		1026
442	In general you can register as many read and/or write event watchers per	1027	In general you can register as many read and/or write event watchers per
443	fd as you want (as long as you don't confuse yourself). Setting all file	1028	fd as you want (as long as you don't confuse yourself). Setting all file
444	descriptors to non-blocking mode is also usually a good idea (but not	1029	descriptors to non-blocking mode is also usually a good idea (but not
445	required if you know what you are doing).	1030	required if you know what you are doing).
446		1031
447	You have to be careful with dup'ed file descriptors, though. Some backends
448	(the linux epoll backend is a notable example) cannot handle dup'ed file
449	descriptors correctly if you register interest in two or more fds pointing
450	to the same underlying file/socket etc. description (that is, they share
451	the same underlying "file open").
452
453	If you must do this, then force the use of a known-to-be-good backend	1032	If you must do this, then force the use of a known-to-be-good backend
454	(at the time of this writing, this includes only EVMETHOD_SELECT and	1033	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
455	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" readyness 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
456		1108
457	=over 4	1109	=over 4
458		1110
459	=item ev_io_init (ev_io *, callback, int fd, int events)	1111	=item ev_io_init (ev_io *, callback, int fd, int events)
460		1112
461	=item ev_io_set (ev_io *, int fd, int events)	1113	=item ev_io_set (ev_io *, int fd, int events)
462		1114
463	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
464	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
465	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.
466		1126
467	=back	1127	=back
468		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
469	=head2 C<ev_timer> - relative and optionally recurring timeouts	1150	=head2 C<ev_timer> - relative and optionally repeating timeouts
470		1151
471	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
472	given time, and optionally repeating in regular intervals after that.	1153	given time, and optionally repeating in regular intervals after that.
473		1154
474	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
475	times out after an hour and you reset your system clock to last years	1156	times out after an hour and you reset your system clock to last years
476	time, it will still time out after (roughly) and hour. "Roughly" because	1157	time, it will still time out after (roughly) and hour. "Roughly" because
477	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the
478	monotonic clock option helps a lot here).	1159	monotonic clock option helps a lot here).
479		1160
480	The relative timeouts are calculated relative to the C<ev_now ()>	1161	The relative timeouts are calculated relative to the C<ev_now ()>
481	time. This is usually the right thing as this timestamp refers to the time	1162	time. This is usually the right thing as this timestamp refers to the time
482	of the event triggering whatever timeout you are modifying/starting. If	1163	of the event triggering whatever timeout you are modifying/starting. If
483	you suspect event processing to be delayed and you *need* to base the timeout	1164	you suspect event processing to be delayed and you I<need> to base the timeout
484	on the current time, use something like this to adjust for this:	1165	on the current time, use something like this to adjust for this:
485		1166
486	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1168
		1169	The callback is guarenteed to be invoked only when 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
487		1174
488	=over 4	1175	=over 4
489		1176
490	=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)
491		1178
…		…
500	configure a timer to trigger every 10 seconds, then it will trigger at	1187	configure a timer to trigger every 10 seconds, then it will trigger at
501	exactly 10 second intervals. If, however, your program cannot keep up with	1188	exactly 10 second intervals. If, however, your program cannot keep up with
502	the timer (because it takes longer than those 10 seconds to do stuff) the	1189	the timer (because it takes longer than those 10 seconds to do stuff) the
503	timer will not fire more than once per event loop iteration.	1190	timer will not fire more than once per event loop iteration.
504		1191
505	=item ev_timer_again (loop)	1192	=item ev_timer_again (loop, ev_timer *)
506		1193
507	This will act as if the timer timed out and restart it again if it is	1194	This will act as if the timer timed out and restart it again if it is
508	repeating. The exact semantics are:	1195	repeating. The exact semantics are:
509		1196
		1197	If the timer is pending, its pending status is cleared.
		1198
510	If the timer is started but nonrepeating, stop it.	1199	If the timer is started but nonrepeating, stop it (as if it timed out).
511		1200
512	If the timer is repeating, either start it if necessary (with the repeat	1201	If the timer is repeating, either start it if necessary (with the
513	value), or reset the running timer to the repeat value.	1202	C<repeat> value), or reset the running timer to the C<repeat> value.
514		1203
515	This sounds a bit complicated, but here is a useful and typical	1204	This sounds a bit complicated, but here is a useful and typical
516	example: Imagine you have a tcp connection and you want a so-called idle	1205	example: Imagine you have a tcp connection and you want a so-called idle
517	timeout, that is, you want to be called when there have been, say, 60	1206	timeout, that is, you want to be called when there have been, say, 60
518	seconds of inactivity on the socket. The easiest way to do this is to	1207	seconds of inactivity on the socket. The easiest way to do this is to
519	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1208	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
520	time you successfully read or write some data. If you go into an idle	1209	C<ev_timer_again> each time you successfully read or write some data. If
521	state where you do not expect data to travel on the socket, you can stop	1210	you go into an idle state where you do not expect data to travel on the
522	the timer, and again will automatically restart it if need be.	1211	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1212	automatically restart it if need be.
		1213
		1214	That means you can ignore the C<after> value and C<ev_timer_start>
		1215	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1216
		1217	ev_timer_init (timer, callback, 0., 5.);
		1218	ev_timer_again (loop, timer);
		1219	...
		1220	timer->again = 17.;
		1221	ev_timer_again (loop, timer);
		1222	...
		1223	timer->again = 10.;
		1224	ev_timer_again (loop, timer);
		1225
		1226	This is more slightly efficient then stopping/starting the timer each time
		1227	you want to modify its timeout value.
		1228
		1229	=item ev_tstamp repeat [read-write]
		1230
		1231	The current C<repeat> value. Will be used each time the watcher times out
		1232	or C<ev_timer_again> is called and determines the next timeout (if any),
		1233	which is also when any modifications are taken into account.
523		1234
524	=back	1235	=back
525		1236
		1237	=head3 Examples
		1238
		1239	Example: Create a timer that fires after 60 seconds.
		1240
		1241	static void
		1242	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1243	{
		1244	.. one minute over, w is actually stopped right here
		1245	}
		1246
		1247	struct ev_timer mytimer;
		1248	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1249	ev_timer_start (loop, &mytimer);
		1250
		1251	Example: Create a timeout timer that times out after 10 seconds of
		1252	inactivity.
		1253
		1254	static void
		1255	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1256	{
		1257	.. ten seconds without any activity
		1258	}
		1259
		1260	struct ev_timer mytimer;
		1261	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1262	ev_timer_again (&mytimer); /* start timer */
		1263	ev_loop (loop, 0);
		1264
		1265	// and in some piece of code that gets executed on any "activity":
		1266	// reset the timeout to start ticking again at 10 seconds
		1267	ev_timer_again (&mytimer);
		1268
		1269
526	=head2 C<ev_periodic> - to cron or not to cron	1270	=head2 C<ev_periodic> - to cron or not to cron?
527		1271
528	Periodic watchers are also timers of a kind, but they are very versatile	1272	Periodic watchers are also timers of a kind, but they are very versatile
529	(and unfortunately a bit complex).	1273	(and unfortunately a bit complex).
530		1274
531	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1275	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
532	but on wallclock time (absolute time). You can tell a periodic watcher	1276	but on wallclock time (absolute time). You can tell a periodic watcher
533	to trigger "at" some specific point in time. For example, if you tell a	1277	to trigger "at" some specific point in time. For example, if you tell a
534	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1278	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
535	+ 10.>) and then reset your system clock to the last year, then it will	1279	+ 10.>) and then reset your system clock to the last year, then it will
536	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1280	take a year to trigger the event (unlike an C<ev_timer>, which would trigger
537	roughly 10 seconds later and of course not if you reset your system time	1281	roughly 10 seconds later).
538	again).
539		1282
540	They can also be used to implement vastly more complex timers, such as	1283	They can also be used to implement vastly more complex timers, such as
541	triggering an event on eahc midnight, local time.	1284	triggering an event on each midnight, local time or other, complicated,
		1285	rules.
		1286
		1287	As with timers, the callback is guarenteed to be invoked only when the
		1288	time (C<at>) has been passed, but if multiple periodic timers become ready
		1289	during the same loop iteration then order of execution is undefined.
		1290
		1291	=head3 Watcher-Specific Functions and Data Members
542		1292
543	=over 4	1293	=over 4
544		1294
545	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1295	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
546		1296
547	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1297	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
548		1298
549	Lots of arguments, lets sort it out... There are basically three modes of	1299	Lots of arguments, lets sort it out... There are basically three modes of
550	operation, and we will explain them from simplest to complex:	1300	operation, and we will explain them from simplest to complex:
551		1301
552
553	=over 4	1302	=over 4
554		1303
555	=item * absolute timer (interval = reschedule_cb = 0)	1304	=item * absolute timer (at = time, interval = reschedule_cb = 0)
556		1305
557	In this configuration the watcher triggers an event at the wallclock time	1306	In this configuration the watcher triggers an event at the wallclock time
558	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1307	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
559	that is, if it is to be run at January 1st 2011 then it will run when the	1308	that is, if it is to be run at January 1st 2011 then it will run when the
560	system time reaches or surpasses this time.	1309	system time reaches or surpasses this time.
561		1310
562	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1311	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
563		1312
564	In this mode the watcher will always be scheduled to time out at the next	1313	In this mode the watcher will always be scheduled to time out at the next
565	C<at + N * interval> time (for some integer N) and then repeat, regardless	1314	C<at + N * interval> time (for some integer N, which can also be negative)
566	of any time jumps.	1315	and then repeat, regardless of any time jumps.
567		1316
568	This can be used to create timers that do not drift with respect to system	1317	This can be used to create timers that do not drift with respect to system
569	time:	1318	time:
570		1319
571	ev_periodic_set (&periodic, 0., 3600., 0);	1320	ev_periodic_set (&periodic, 0., 3600., 0);
…		…
577		1326
578	Another way to think about it (for the mathematically inclined) is that	1327	Another way to think about it (for the mathematically inclined) is that
579	C<ev_periodic> will try to run the callback in this mode at the next possible	1328	C<ev_periodic> will try to run the callback in this mode at the next possible
580	time where C<time = at (mod interval)>, regardless of any time jumps.	1329	time where C<time = at (mod interval)>, regardless of any time jumps.
581		1330
		1331	For numerical stability it is preferable that the C<at> value is near
		1332	C<ev_now ()> (the current time), but there is no range requirement for
		1333	this value.
		1334
582	=item * manual reschedule mode (reschedule_cb = callback)	1335	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
583		1336
584	In this mode the values for C<interval> and C<at> are both being	1337	In this mode the values for C<interval> and C<at> are both being
585	ignored. Instead, each time the periodic watcher gets scheduled, the	1338	ignored. Instead, each time the periodic watcher gets scheduled, the
586	reschedule callback will be called with the watcher as first, and the	1339	reschedule callback will be called with the watcher as first, and the
587	current time as second argument.	1340	current time as second argument.
588		1341
589	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1342	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
590	ever, or make any event loop modifications>. If you need to stop it,	1343	ever, or make any event loop modifications>. If you need to stop it,
591	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1344	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
592	starting a prepare watcher).	1345	starting an C<ev_prepare> watcher, which is legal).
593		1346
594	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1347	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
595	ev_tstamp now)>, e.g.:	1348	ev_tstamp now)>, e.g.:
596		1349
597	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1350	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
…		…
620	Simply stops and restarts the periodic watcher again. This is only useful	1373	Simply stops and restarts the periodic watcher again. This is only useful
621	when you changed some parameters or the reschedule callback would return	1374	when you changed some parameters or the reschedule callback would return
622	a different time than the last time it was called (e.g. in a crond like	1375	a different time than the last time it was called (e.g. in a crond like
623	program when the crontabs have changed).	1376	program when the crontabs have changed).
624		1377
		1378	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1379
		1380	When active, returns the absolute time that the watcher is supposed to
		1381	trigger next.
		1382
		1383	=item ev_tstamp offset [read-write]
		1384
		1385	When repeating, this contains the offset value, otherwise this is the
		1386	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1387
		1388	Can be modified any time, but changes only take effect when the periodic
		1389	timer fires or C<ev_periodic_again> is being called.
		1390
		1391	=item ev_tstamp interval [read-write]
		1392
		1393	The current interval value. Can be modified any time, but changes only
		1394	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1395	called.
		1396
		1397	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1398
		1399	The current reschedule callback, or C<0>, if this functionality is
		1400	switched off. Can be changed any time, but changes only take effect when
		1401	the periodic timer fires or C<ev_periodic_again> is being called.
		1402
625	=back	1403	=back
626		1404
		1405	=head3 Examples
		1406
		1407	Example: Call a callback every hour, or, more precisely, whenever the
		1408	system clock is divisible by 3600. The callback invocation times have
		1409	potentially a lot of jittering, but good long-term stability.
		1410
		1411	static void
		1412	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1413	{
		1414	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1415	}
		1416
		1417	struct ev_periodic hourly_tick;
		1418	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1419	ev_periodic_start (loop, &hourly_tick);
		1420
		1421	Example: The same as above, but use a reschedule callback to do it:
		1422
		1423	#include <math.h>
		1424
		1425	static ev_tstamp
		1426	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1427	{
		1428	return fmod (now, 3600.) + 3600.;
		1429	}
		1430
		1431	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1432
		1433	Example: Call a callback every hour, starting now:
		1434
		1435	struct ev_periodic hourly_tick;
		1436	ev_periodic_init (&hourly_tick, clock_cb,
		1437	fmod (ev_now (loop), 3600.), 3600., 0);
		1438	ev_periodic_start (loop, &hourly_tick);
		1439
		1440
627	=head2 C<ev_signal> - signal me when a signal gets signalled	1441	=head2 C<ev_signal> - signal me when a signal gets signalled!
628		1442
629	Signal watchers will trigger an event when the process receives a specific	1443	Signal watchers will trigger an event when the process receives a specific
630	signal one or more times. Even though signals are very asynchronous, libev	1444	signal one or more times. Even though signals are very asynchronous, libev
631	will try it's best to deliver signals synchronously, i.e. as part of the	1445	will try it's best to deliver signals synchronously, i.e. as part of the
632	normal event processing, like any other event.	1446	normal event processing, like any other event.
…		…
636	with the kernel (thus it coexists with your own signal handlers as long	1450	with the kernel (thus it coexists with your own signal handlers as long
637	as you don't register any with libev). Similarly, when the last signal	1451	as you don't register any with libev). Similarly, when the last signal
638	watcher for a signal is stopped libev will reset the signal handler to	1452	watcher for a signal is stopped libev will reset the signal handler to
639	SIG_DFL (regardless of what it was set to before).	1453	SIG_DFL (regardless of what it was set to before).
640		1454
		1455	If possible and supported, libev will install its handlers with
		1456	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
		1457	interrupted. If you have a problem with syscalls getting interrupted by
		1458	signals you can block all signals in an C<ev_check> watcher and unblock
		1459	them in an C<ev_prepare> watcher.
		1460
		1461	=head3 Watcher-Specific Functions and Data Members
		1462
641	=over 4	1463	=over 4
642		1464
643	=item ev_signal_init (ev_signal *, callback, int signum)	1465	=item ev_signal_init (ev_signal *, callback, int signum)
644		1466
645	=item ev_signal_set (ev_signal *, int signum)	1467	=item ev_signal_set (ev_signal *, int signum)
646		1468
647	Configures the watcher to trigger on the given signal number (usually one	1469	Configures the watcher to trigger on the given signal number (usually one
648	of the C<SIGxxx> constants).	1470	of the C<SIGxxx> constants).
649		1471
		1472	=item int signum [read-only]
		1473
		1474	The signal the watcher watches out for.
		1475
650	=back	1476	=back
651		1477
		1478	=head3 Examples
		1479
		1480	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1481
		1482	static void
		1483	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1484	{
		1485	ev_unloop (loop, EVUNLOOP_ALL);
		1486	}
		1487
		1488	struct ev_signal signal_watcher;
		1489	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1490	ev_signal_start (loop, &sigint_cb);
		1491
		1492
652	=head2 C<ev_child> - wait for pid status changes	1493	=head2 C<ev_child> - watch out for process status changes
653		1494
654	Child watchers trigger when your process receives a SIGCHLD in response to	1495	Child watchers trigger when your process receives a SIGCHLD in response to
655	some child status changes (most typically when a child of yours dies).	1496	some child status changes (most typically when a child of yours dies). It
		1497	is permissible to install a child watcher I<after> the child has been
		1498	forked (which implies it might have already exited), as long as the event
		1499	loop isn't entered (or is continued from a watcher).
		1500
		1501	Only the default event loop is capable of handling signals, and therefore
		1502	you can only rgeister child watchers in the default event loop.
		1503
		1504	=head3 Process Interaction
		1505
		1506	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1507	initialised. This is necessary to guarantee proper behaviour even if
		1508	the first child watcher is started after the child exits. The occurance
		1509	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1510	synchronously as part of the event loop processing. Libev always reaps all
		1511	children, even ones not watched.
		1512
		1513	=head3 Overriding the Built-In Processing
		1514
		1515	Libev offers no special support for overriding the built-in child
		1516	processing, but if your application collides with libev's default child
		1517	handler, you can override it easily by installing your own handler for
		1518	C<SIGCHLD> after initialising the default loop, and making sure the
		1519	default loop never gets destroyed. You are encouraged, however, to use an
		1520	event-based approach to child reaping and thus use libev's support for
		1521	that, so other libev users can use C<ev_child> watchers freely.
		1522
		1523	=head3 Watcher-Specific Functions and Data Members
656		1524
657	=over 4	1525	=over 4
658		1526
659	=item ev_child_init (ev_child *, callback, int pid)	1527	=item ev_child_init (ev_child *, callback, int pid, int trace)
660		1528
661	=item ev_child_set (ev_child *, int pid)	1529	=item ev_child_set (ev_child *, int pid, int trace)
662		1530
663	Configures the watcher to wait for status changes of process C<pid> (or	1531	Configures the watcher to wait for status changes of process C<pid> (or
664	I<any> process if C<pid> is specified as C<0>). The callback can look	1532	I<any> process if C<pid> is specified as C<0>). The callback can look
665	at the C<rstatus> member of the C<ev_child> watcher structure to see	1533	at the C<rstatus> member of the C<ev_child> watcher structure to see
666	the status word (use the macros from C<sys/wait.h> and see your systems	1534	the status word (use the macros from C<sys/wait.h> and see your systems
667	C<waitpid> documentation). The C<rpid> member contains the pid of the	1535	C<waitpid> documentation). The C<rpid> member contains the pid of the
668	process causing the status change.	1536	process causing the status change. C<trace> must be either C<0> (only
		1537	activate the watcher when the process terminates) or C<1> (additionally
		1538	activate the watcher when the process is stopped or continued).
		1539
		1540	=item int pid [read-only]
		1541
		1542	The process id this watcher watches out for, or C<0>, meaning any process id.
		1543
		1544	=item int rpid [read-write]
		1545
		1546	The process id that detected a status change.
		1547
		1548	=item int rstatus [read-write]
		1549
		1550	The process exit/trace status caused by C<rpid> (see your systems
		1551	C<waitpid> and C<sys/wait.h> documentation for details).
669		1552
670	=back	1553	=back
671		1554
		1555	=head3 Examples
		1556
		1557	Example: C<fork()> a new process and install a child handler to wait for
		1558	its completion.
		1559
		1560	ev_child cw;
		1561
		1562	static void
		1563	child_cb (EV_P_ struct ev_child *w, int revents)
		1564	{
		1565	ev_child_stop (EV_A_ w);
		1566	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1567	}
		1568
		1569	pid_t pid = fork ();
		1570
		1571	if (pid < 0)
		1572	// error
		1573	else if (pid == 0)
		1574	{
		1575	// the forked child executes here
		1576	exit (1);
		1577	}
		1578	else
		1579	{
		1580	ev_child_init (&cw, child_cb, pid, 0);
		1581	ev_child_start (EV_DEFAULT_ &cw);
		1582	}
		1583
		1584
		1585	=head2 C<ev_stat> - did the file attributes just change?
		1586
		1587	This watches a filesystem path for attribute changes. That is, it calls
		1588	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1589	compared to the last time, invoking the callback if it did.
		1590
		1591	The path does not need to exist: changing from "path exists" to "path does
		1592	not exist" is a status change like any other. The condition "path does
		1593	not exist" is signified by the C<st_nlink> field being zero (which is
		1594	otherwise always forced to be at least one) and all the other fields of
		1595	the stat buffer having unspecified contents.
		1596
		1597	The path I<should> be absolute and I<must not> end in a slash. If it is
		1598	relative and your working directory changes, the behaviour is undefined.
		1599
		1600	Since there is no standard to do this, the portable implementation simply
		1601	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1602	can specify a recommended polling interval for this case. If you specify
		1603	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1604	unspecified default> value will be used (which you can expect to be around
		1605	five seconds, although this might change dynamically). Libev will also
		1606	impose a minimum interval which is currently around C<0.1>, but thats
		1607	usually overkill.
		1608
		1609	This watcher type is not meant for massive numbers of stat watchers,
		1610	as even with OS-supported change notifications, this can be
		1611	resource-intensive.
		1612
		1613	At the time of this writing, only the Linux inotify interface is
		1614	implemented (implementing kqueue support is left as an exercise for the
		1615	reader, note, however, that the author sees no way of implementing ev_stat
		1616	semantics with kqueue). Inotify will be used to give hints only and should
		1617	not change the semantics of C<ev_stat> watchers, which means that libev
		1618	sometimes needs to fall back to regular polling again even with inotify,
		1619	but changes are usually detected immediately, and if the file exists there
		1620	will be no polling.
		1621
		1622	=head3 ABI Issues (Largefile Support)
		1623
		1624	Libev by default (unless the user overrides this) uses the default
		1625	compilation environment, which means that on systems with optionally
		1626	disabled large file support, you get the 32 bit version of the stat
		1627	structure. When using the library from programs that change the ABI to
		1628	use 64 bit file offsets the programs will fail. In that case you have to
		1629	compile libev with the same flags to get binary compatibility. This is
		1630	obviously the case with any flags that change the ABI, but the problem is
		1631	most noticably with ev_stat and largefile support.
		1632
		1633	=head3 Inotify
		1634
		1635	When C<inotify (7)> support has been compiled into libev (generally only
		1636	available on Linux) and present at runtime, it will be used to speed up
		1637	change detection where possible. The inotify descriptor will be created lazily
		1638	when the first C<ev_stat> watcher is being started.
		1639
		1640	Inotify presence does not change the semantics of C<ev_stat> watchers
		1641	except that changes might be detected earlier, and in some cases, to avoid
		1642	making regular C<stat> calls. Even in the presence of inotify support
		1643	there are many cases where libev has to resort to regular C<stat> polling.
		1644
		1645	(There is no support for kqueue, as apparently it cannot be used to
		1646	implement this functionality, due to the requirement of having a file
		1647	descriptor open on the object at all times).
		1648
		1649	=head3 The special problem of stat time resolution
		1650
		1651	The C<stat ()> syscall only supports full-second resolution portably, and
		1652	even on systems where the resolution is higher, many filesystems still
		1653	only support whole seconds.
		1654
		1655	That means that, if the time is the only thing that changes, you can
		1656	easily miss updates: on the first update, C<ev_stat> detects a change and
		1657	calls your callback, which does something. When there is another update
		1658	within the same second, C<ev_stat> will be unable to detect it as the stat
		1659	data does not change.
		1660
		1661	The solution to this is to delay acting on a change for slightly more
		1662	than second (or till slightly after the next full second boundary), using
		1663	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1664	ev_timer_again (loop, w)>).
		1665
		1666	The C<.02> offset is added to work around small timing inconsistencies
		1667	of some operating systems (where the second counter of the current time
		1668	might be be delayed. One such system is the Linux kernel, where a call to
		1669	C<gettimeofday> might return a timestamp with a full second later than
		1670	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1671	update file times then there will be a small window where the kernel uses
		1672	the previous second to update file times but libev might already execute
		1673	the timer callback).
		1674
		1675	=head3 Watcher-Specific Functions and Data Members
		1676
		1677	=over 4
		1678
		1679	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1680
		1681	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1682
		1683	Configures the watcher to wait for status changes of the given
		1684	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1685	be detected and should normally be specified as C<0> to let libev choose
		1686	a suitable value. The memory pointed to by C<path> must point to the same
		1687	path for as long as the watcher is active.
		1688
		1689	The callback will receive C<EV_STAT> when a change was detected, relative
		1690	to the attributes at the time the watcher was started (or the last change
		1691	was detected).
		1692
		1693	=item ev_stat_stat (loop, ev_stat *)
		1694
		1695	Updates the stat buffer immediately with new values. If you change the
		1696	watched path in your callback, you could call this function to avoid
		1697	detecting this change (while introducing a race condition if you are not
		1698	the only one changing the path). Can also be useful simply to find out the
		1699	new values.
		1700
		1701	=item ev_statdata attr [read-only]
		1702
		1703	The most-recently detected attributes of the file. Although the type is
		1704	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1705	suitable for your system, but you can only rely on the POSIX-standardised
		1706	members to be present. If the C<st_nlink> member is C<0>, then there was
		1707	some error while C<stat>ing the file.
		1708
		1709	=item ev_statdata prev [read-only]
		1710
		1711	The previous attributes of the file. The callback gets invoked whenever
		1712	C<prev> != C<attr>, or, more precisely, one or more of these members
		1713	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1714	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1715
		1716	=item ev_tstamp interval [read-only]
		1717
		1718	The specified interval.
		1719
		1720	=item const char *path [read-only]
		1721
		1722	The filesystem path that is being watched.
		1723
		1724	=back
		1725
		1726	=head3 Examples
		1727
		1728	Example: Watch C</etc/passwd> for attribute changes.
		1729
		1730	static void
		1731	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1732	{
		1733	/* /etc/passwd changed in some way */
		1734	if (w->attr.st_nlink)
		1735	{
		1736	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1737	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1738	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1739	}
		1740	else
		1741	/* you shalt not abuse printf for puts */
		1742	puts ("wow, /etc/passwd is not there, expect problems. "
		1743	"if this is windows, they already arrived\n");
		1744	}
		1745
		1746	...
		1747	ev_stat passwd;
		1748
		1749	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1750	ev_stat_start (loop, &passwd);
		1751
		1752	Example: Like above, but additionally use a one-second delay so we do not
		1753	miss updates (however, frequent updates will delay processing, too, so
		1754	one might do the work both on C<ev_stat> callback invocation I<and> on
		1755	C<ev_timer> callback invocation).
		1756
		1757	static ev_stat passwd;
		1758	static ev_timer timer;
		1759
		1760	static void
		1761	timer_cb (EV_P_ ev_timer *w, int revents)
		1762	{
		1763	ev_timer_stop (EV_A_ w);
		1764
		1765	/* now it's one second after the most recent passwd change */
		1766	}
		1767
		1768	static void
		1769	stat_cb (EV_P_ ev_stat *w, int revents)
		1770	{
		1771	/* reset the one-second timer */
		1772	ev_timer_again (EV_A_ &timer);
		1773	}
		1774
		1775	...
		1776	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1777	ev_stat_start (loop, &passwd);
		1778	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1779
		1780
672	=head2 C<ev_idle> - when you've got nothing better to do	1781	=head2 C<ev_idle> - when you've got nothing better to do...
673		1782
674	Idle watchers trigger events when there are no other events are pending	1783	Idle watchers trigger events when no other events of the same or higher
675	(prepare, check and other idle watchers do not count). That is, as long	1784	priority are pending (prepare, check and other idle watchers do not
676	as your process is busy handling sockets or timeouts (or even signals,	1785	count).
677	imagine) it will not be triggered. But when your process is idle all idle	1786
678	watchers are being called again and again, once per event loop iteration -	1787	That is, as long as your process is busy handling sockets or timeouts
		1788	(or even signals, imagine) of the same or higher priority it will not be
		1789	triggered. But when your process is idle (or only lower-priority watchers
		1790	are pending), the idle watchers are being called once per event loop
679	until stopped, that is, or your process receives more events and becomes	1791	iteration - until stopped, that is, or your process receives more events
680	busy.	1792	and becomes busy again with higher priority stuff.
681		1793
682	The most noteworthy effect is that as long as any idle watchers are	1794	The most noteworthy effect is that as long as any idle watchers are
683	active, the process will not block when waiting for new events.	1795	active, the process will not block when waiting for new events.
684		1796
685	Apart from keeping your process non-blocking (which is a useful	1797	Apart from keeping your process non-blocking (which is a useful
686	effect on its own sometimes), idle watchers are a good place to do	1798	effect on its own sometimes), idle watchers are a good place to do
687	"pseudo-background processing", or delay processing stuff to after the	1799	"pseudo-background processing", or delay processing stuff to after the
688	event loop has handled all outstanding events.	1800	event loop has handled all outstanding events.
689		1801
		1802	=head3 Watcher-Specific Functions and Data Members
		1803
690	=over 4	1804	=over 4
691		1805
692	=item ev_idle_init (ev_signal *, callback)	1806	=item ev_idle_init (ev_signal *, callback)
693		1807
694	Initialises and configures the idle watcher - it has no parameters of any	1808	Initialises and configures the idle watcher - it has no parameters of any
695	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1809	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
696	believe me.	1810	believe me.
697		1811
698	=back	1812	=back
699		1813
		1814	=head3 Examples
		1815
		1816	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1817	callback, free it. Also, use no error checking, as usual.
		1818
		1819	static void
		1820	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1821	{
		1822	free (w);
		1823	// now do something you wanted to do when the program has
		1824	// no longer anything immediate to do.
		1825	}
		1826
		1827	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1828	ev_idle_init (idle_watcher, idle_cb);
		1829	ev_idle_start (loop, idle_cb);
		1830
		1831
700	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1832	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
701		1833
702	Prepare and check watchers are usually (but not always) used in tandem:	1834	Prepare and check watchers are usually (but not always) used in tandem:
703	prepare watchers get invoked before the process blocks and check watchers	1835	prepare watchers get invoked before the process blocks and check watchers
704	afterwards.	1836	afterwards.
705		1837
		1838	You I<must not> call C<ev_loop> or similar functions that enter
		1839	the current event loop from either C<ev_prepare> or C<ev_check>
		1840	watchers. Other loops than the current one are fine, however. The
		1841	rationale behind this is that you do not need to check for recursion in
		1842	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1843	C<ev_check> so if you have one watcher of each kind they will always be
		1844	called in pairs bracketing the blocking call.
		1845
706	Their main purpose is to integrate other event mechanisms into libev. This	1846	Their main purpose is to integrate other event mechanisms into libev and
707	could be used, for example, to track variable changes, implement your own	1847	their use is somewhat advanced. This could be used, for example, to track
708	watchers, integrate net-snmp or a coroutine library and lots more.	1848	variable changes, implement your own watchers, integrate net-snmp or a
		1849	coroutine library and lots more. They are also occasionally useful if
		1850	you cache some data and want to flush it before blocking (for example,
		1851	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1852	watcher).
709		1853
710	This is done by examining in each prepare call which file descriptors need	1854	This is done by examining in each prepare call which file descriptors need
711	to be watched by the other library, registering C<ev_io> watchers for	1855	to be watched by the other library, registering C<ev_io> watchers for
712	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1856	them and starting an C<ev_timer> watcher for any timeouts (many libraries
713	provide just this functionality). Then, in the check watcher you check for	1857	provide just this functionality). Then, in the check watcher you check for
…		…
723	with priority higher than or equal to the event loop and one coroutine	1867	with priority higher than or equal to the event loop and one coroutine
724	of lower priority, but only once, using idle watchers to keep the event	1868	of lower priority, but only once, using idle watchers to keep the event
725	loop from blocking if lower-priority coroutines are active, thus mapping	1869	loop from blocking if lower-priority coroutines are active, thus mapping
726	low-priority coroutines to idle/background tasks).	1870	low-priority coroutines to idle/background tasks).
727		1871
		1872	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1873	priority, to ensure that they are being run before any other watchers
		1874	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1875	too) should not activate ("feed") events into libev. While libev fully
		1876	supports this, they might get executed before other C<ev_check> watchers
		1877	did their job. As C<ev_check> watchers are often used to embed other
		1878	(non-libev) event loops those other event loops might be in an unusable
		1879	state until their C<ev_check> watcher ran (always remind yourself to
		1880	coexist peacefully with others).
		1881
		1882	=head3 Watcher-Specific Functions and Data Members
		1883
728	=over 4	1884	=over 4
729		1885
730	=item ev_prepare_init (ev_prepare *, callback)	1886	=item ev_prepare_init (ev_prepare *, callback)
731		1887
732	=item ev_check_init (ev_check *, callback)	1888	=item ev_check_init (ev_check *, callback)
…		…
734	Initialises and configures the prepare or check watcher - they have no	1890	Initialises and configures the prepare or check watcher - they have no
735	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1891	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
736	macros, but using them is utterly, utterly and completely pointless.	1892	macros, but using them is utterly, utterly and completely pointless.
737		1893
738	=back	1894	=back
		1895
		1896	=head3 Examples
		1897
		1898	There are a number of principal ways to embed other event loops or modules
		1899	into libev. Here are some ideas on how to include libadns into libev
		1900	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1901	use as a working example. Another Perl module named C<EV::Glib> embeds a
		1902	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		1903	Glib event loop).
		1904
		1905	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1906	and in a check watcher, destroy them and call into libadns. What follows
		1907	is pseudo-code only of course. This requires you to either use a low
		1908	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1909	the callbacks for the IO/timeout watchers might not have been called yet.
		1910
		1911	static ev_io iow [nfd];
		1912	static ev_timer tw;
		1913
		1914	static void
		1915	io_cb (ev_loop *loop, ev_io *w, int revents)
		1916	{
		1917	}
		1918
		1919	// create io watchers for each fd and a timer before blocking
		1920	static void
		1921	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1922	{
		1923	int timeout = 3600000;
		1924	struct pollfd fds [nfd];
		1925	// actual code will need to loop here and realloc etc.
		1926	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1927
		1928	/* the callback is illegal, but won't be called as we stop during check */
		1929	ev_timer_init (&tw, 0, timeout * 1e-3);
		1930	ev_timer_start (loop, &tw);
		1931
		1932	// create one ev_io per pollfd
		1933	for (int i = 0; i < nfd; ++i)
		1934	{
		1935	ev_io_init (iow + i, io_cb, fds [i].fd,
		1936	((fds [i].events & POLLIN ? EV_READ : 0)
		1937	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1938
		1939	fds [i].revents = 0;
		1940	ev_io_start (loop, iow + i);
		1941	}
		1942	}
		1943
		1944	// stop all watchers after blocking
		1945	static void
		1946	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1947	{
		1948	ev_timer_stop (loop, &tw);
		1949
		1950	for (int i = 0; i < nfd; ++i)
		1951	{
		1952	// set the relevant poll flags
		1953	// could also call adns_processreadable etc. here
		1954	struct pollfd *fd = fds + i;
		1955	int revents = ev_clear_pending (iow + i);
		1956	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1957	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1958
		1959	// now stop the watcher
		1960	ev_io_stop (loop, iow + i);
		1961	}
		1962
		1963	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1964	}
		1965
		1966	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1967	in the prepare watcher and would dispose of the check watcher.
		1968
		1969	Method 3: If the module to be embedded supports explicit event
		1970	notification (adns does), you can also make use of the actual watcher
		1971	callbacks, and only destroy/create the watchers in the prepare watcher.
		1972
		1973	static void
		1974	timer_cb (EV_P_ ev_timer *w, int revents)
		1975	{
		1976	adns_state ads = (adns_state)w->data;
		1977	update_now (EV_A);
		1978
		1979	adns_processtimeouts (ads, &tv_now);
		1980	}
		1981
		1982	static void
		1983	io_cb (EV_P_ ev_io *w, int revents)
		1984	{
		1985	adns_state ads = (adns_state)w->data;
		1986	update_now (EV_A);
		1987
		1988	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1989	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1990	}
		1991
		1992	// do not ever call adns_afterpoll
		1993
		1994	Method 4: Do not use a prepare or check watcher because the module you
		1995	want to embed is too inflexible to support it. Instead, youc na override
		1996	their poll function. The drawback with this solution is that the main
		1997	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1998	this.
		1999
		2000	static gint
		2001	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2002	{
		2003	int got_events = 0;
		2004
		2005	for (n = 0; n < nfds; ++n)
		2006	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2007
		2008	if (timeout >= 0)
		2009	// create/start timer
		2010
		2011	// poll
		2012	ev_loop (EV_A_ 0);
		2013
		2014	// stop timer again
		2015	if (timeout >= 0)
		2016	ev_timer_stop (EV_A_ &to);
		2017
		2018	// stop io watchers again - their callbacks should have set
		2019	for (n = 0; n < nfds; ++n)
		2020	ev_io_stop (EV_A_ iow [n]);
		2021
		2022	return got_events;
		2023	}
		2024
		2025
		2026	=head2 C<ev_embed> - when one backend isn't enough...
		2027
		2028	This is a rather advanced watcher type that lets you embed one event loop
		2029	into another (currently only C<ev_io> events are supported in the embedded
		2030	loop, other types of watchers might be handled in a delayed or incorrect
		2031	fashion and must not be used).
		2032
		2033	There are primarily two reasons you would want that: work around bugs and
		2034	prioritise I/O.
		2035
		2036	As an example for a bug workaround, the kqueue backend might only support
		2037	sockets on some platform, so it is unusable as generic backend, but you
		2038	still want to make use of it because you have many sockets and it scales
		2039	so nicely. In this case, you would create a kqueue-based loop and embed it
		2040	into your default loop (which might use e.g. poll). Overall operation will
		2041	be a bit slower because first libev has to poll and then call kevent, but
		2042	at least you can use both at what they are best.
		2043
		2044	As for prioritising I/O: rarely you have the case where some fds have
		2045	to be watched and handled very quickly (with low latency), and even
		2046	priorities and idle watchers might have too much overhead. In this case
		2047	you would put all the high priority stuff in one loop and all the rest in
		2048	a second one, and embed the second one in the first.
		2049
		2050	As long as the watcher is active, the callback will be invoked every time
		2051	there might be events pending in the embedded loop. The callback must then
		2052	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2053	their callbacks (you could also start an idle watcher to give the embedded
		2054	loop strictly lower priority for example). You can also set the callback
		2055	to C<0>, in which case the embed watcher will automatically execute the
		2056	embedded loop sweep.
		2057
		2058	As long as the watcher is started it will automatically handle events. The
		2059	callback will be invoked whenever some events have been handled. You can
		2060	set the callback to C<0> to avoid having to specify one if you are not
		2061	interested in that.
		2062
		2063	Also, there have not currently been made special provisions for forking:
		2064	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2065	but you will also have to stop and restart any C<ev_embed> watchers
		2066	yourself.
		2067
		2068	Unfortunately, not all backends are embeddable, only the ones returned by
		2069	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2070	portable one.
		2071
		2072	So when you want to use this feature you will always have to be prepared
		2073	that you cannot get an embeddable loop. The recommended way to get around
		2074	this is to have a separate variables for your embeddable loop, try to
		2075	create it, and if that fails, use the normal loop for everything.
		2076
		2077	=head3 Watcher-Specific Functions and Data Members
		2078
		2079	=over 4
		2080
		2081	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2082
		2083	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2084
		2085	Configures the watcher to embed the given loop, which must be
		2086	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2087	invoked automatically, otherwise it is the responsibility of the callback
		2088	to invoke it (it will continue to be called until the sweep has been done,
		2089	if you do not want thta, you need to temporarily stop the embed watcher).
		2090
		2091	=item ev_embed_sweep (loop, ev_embed *)
		2092
		2093	Make a single, non-blocking sweep over the embedded loop. This works
		2094	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2095	apropriate way for embedded loops.
		2096
		2097	=item struct ev_loop *other [read-only]
		2098
		2099	The embedded event loop.
		2100
		2101	=back
		2102
		2103	=head3 Examples
		2104
		2105	Example: Try to get an embeddable event loop and embed it into the default
		2106	event loop. If that is not possible, use the default loop. The default
		2107	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		2108	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		2109	used).
		2110
		2111	struct ev_loop *loop_hi = ev_default_init (0);
		2112	struct ev_loop *loop_lo = 0;
		2113	struct ev_embed embed;
		2114
		2115	// see if there is a chance of getting one that works
		2116	// (remember that a flags value of 0 means autodetection)
		2117	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2118	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2119	: 0;
		2120
		2121	// if we got one, then embed it, otherwise default to loop_hi
		2122	if (loop_lo)
		2123	{
		2124	ev_embed_init (&embed, 0, loop_lo);
		2125	ev_embed_start (loop_hi, &embed);
		2126	}
		2127	else
		2128	loop_lo = loop_hi;
		2129
		2130	Example: Check if kqueue is available but not recommended and create
		2131	a kqueue backend for use with sockets (which usually work with any
		2132	kqueue implementation). Store the kqueue/socket-only event loop in
		2133	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2134
		2135	struct ev_loop *loop = ev_default_init (0);
		2136	struct ev_loop *loop_socket = 0;
		2137	struct ev_embed embed;
		2138
		2139	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2140	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2141	{
		2142	ev_embed_init (&embed, 0, loop_socket);
		2143	ev_embed_start (loop, &embed);
		2144	}
		2145
		2146	if (!loop_socket)
		2147	loop_socket = loop;
		2148
		2149	// now use loop_socket for all sockets, and loop for everything else
		2150
		2151
		2152	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2153
		2154	Fork watchers are called when a C<fork ()> was detected (usually because
		2155	whoever is a good citizen cared to tell libev about it by calling
		2156	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2157	event loop blocks next and before C<ev_check> watchers are being called,
		2158	and only in the child after the fork. If whoever good citizen calling
		2159	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2160	handlers will be invoked, too, of course.
		2161
		2162	=head3 Watcher-Specific Functions and Data Members
		2163
		2164	=over 4
		2165
		2166	=item ev_fork_init (ev_signal *, callback)
		2167
		2168	Initialises and configures the fork watcher - it has no parameters of any
		2169	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2170	believe me.
		2171
		2172	=back
		2173
		2174
		2175	=head2 C<ev_async> - how to wake up another event loop
		2176
		2177	In general, you cannot use an C<ev_loop> from multiple threads or other
		2178	asynchronous sources such as signal handlers (as opposed to multiple event
		2179	loops - those are of course safe to use in different threads).
		2180
		2181	Sometimes, however, you need to wake up another event loop you do not
		2182	control, for example because it belongs to another thread. This is what
		2183	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2184	can signal it by calling C<ev_async_send>, which is thread- and signal
		2185	safe.
		2186
		2187	This functionality is very similar to C<ev_signal> watchers, as signals,
		2188	too, are asynchronous in nature, and signals, too, will be compressed
		2189	(i.e. the number of callback invocations may be less than the number of
		2190	C<ev_async_sent> calls).
		2191
		2192	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2193	just the default loop.
		2194
		2195	=head3 Queueing
		2196
		2197	C<ev_async> does not support queueing of data in any way. The reason
		2198	is that the author does not know of a simple (or any) algorithm for a
		2199	multiple-writer-single-reader queue that works in all cases and doesn't
		2200	need elaborate support such as pthreads.
		2201
		2202	That means that if you want to queue data, you have to provide your own
		2203	queue. But at least I can tell you would implement locking around your
		2204	queue:
		2205
		2206	=over 4
		2207
		2208	=item queueing from a signal handler context
		2209
		2210	To implement race-free queueing, you simply add to the queue in the signal
		2211	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2212	some fictitiuous SIGUSR1 handler:
		2213
		2214	static ev_async mysig;
		2215
		2216	static void
		2217	sigusr1_handler (void)
		2218	{
		2219	sometype data;
		2220
		2221	// no locking etc.
		2222	queue_put (data);
		2223	ev_async_send (EV_DEFAULT_ &mysig);
		2224	}
		2225
		2226	static void
		2227	mysig_cb (EV_P_ ev_async *w, int revents)
		2228	{
		2229	sometype data;
		2230	sigset_t block, prev;
		2231
		2232	sigemptyset (&block);
		2233	sigaddset (&block, SIGUSR1);
		2234	sigprocmask (SIG_BLOCK, &block, &prev);
		2235
		2236	while (queue_get (&data))
		2237	process (data);
		2238
		2239	if (sigismember (&prev, SIGUSR1)
		2240	sigprocmask (SIG_UNBLOCK, &block, 0);
		2241	}
		2242
		2243	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2244	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2245	either...).
		2246
		2247	=item queueing from a thread context
		2248
		2249	The strategy for threads is different, as you cannot (easily) block
		2250	threads but you can easily preempt them, so to queue safely you need to
		2251	employ a traditional mutex lock, such as in this pthread example:
		2252
		2253	static ev_async mysig;
		2254	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2255
		2256	static void
		2257	otherthread (void)
		2258	{
		2259	// only need to lock the actual queueing operation
		2260	pthread_mutex_lock (&mymutex);
		2261	queue_put (data);
		2262	pthread_mutex_unlock (&mymutex);
		2263
		2264	ev_async_send (EV_DEFAULT_ &mysig);
		2265	}
		2266
		2267	static void
		2268	mysig_cb (EV_P_ ev_async *w, int revents)
		2269	{
		2270	pthread_mutex_lock (&mymutex);
		2271
		2272	while (queue_get (&data))
		2273	process (data);
		2274
		2275	pthread_mutex_unlock (&mymutex);
		2276	}
		2277
		2278	=back
		2279
		2280
		2281	=head3 Watcher-Specific Functions and Data Members
		2282
		2283	=over 4
		2284
		2285	=item ev_async_init (ev_async *, callback)
		2286
		2287	Initialises and configures the async watcher - it has no parameters of any
		2288	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2289	believe me.
		2290
		2291	=item ev_async_send (loop, ev_async *)
		2292
		2293	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2294	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2295	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2296	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2297	section below on what exactly this means).
		2298
		2299	This call incurs the overhead of a syscall only once per loop iteration,
		2300	so while the overhead might be noticable, it doesn't apply to repeated
		2301	calls to C<ev_async_send>.
		2302
		2303	=item bool = ev_async_pending (ev_async *)
		2304
		2305	Returns a non-zero value when C<ev_async_send> has been called on the
		2306	watcher but the event has not yet been processed (or even noted) by the
		2307	event loop.
		2308
		2309	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2310	the loop iterates next and checks for the watcher to have become active,
		2311	it will reset the flag again. C<ev_async_pending> can be used to very
		2312	quickly check wether invoking the loop might be a good idea.
		2313
		2314	Not that this does I<not> check wether the watcher itself is pending, only
		2315	wether it has been requested to make this watcher pending.
		2316
		2317	=back
		2318
739		2319
740	=head1 OTHER FUNCTIONS	2320	=head1 OTHER FUNCTIONS
741		2321
742	There are some other functions of possible interest. Described. Here. Now.	2322	There are some other functions of possible interest. Described. Here. Now.
743		2323
…		…
773	/* stdin might have data for us, joy! */;	2353	/* stdin might have data for us, joy! */;
774	}	2354	}
775		2355
776	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2356	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
777		2357
778	=item ev_feed_event (loop, watcher, int events)	2358	=item ev_feed_event (ev_loop *, watcher *, int revents)
779		2359
780	Feeds the given event set into the event loop, as if the specified event	2360	Feeds the given event set into the event loop, as if the specified event
781	had happened for the specified watcher (which must be a pointer to an	2361	had happened for the specified watcher (which must be a pointer to an
782	initialised but not necessarily started event watcher).	2362	initialised but not necessarily started event watcher).
783		2363
784	=item ev_feed_fd_event (loop, int fd, int revents)	2364	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
785		2365
786	Feed an event on the given fd, as if a file descriptor backend detected	2366	Feed an event on the given fd, as if a file descriptor backend detected
787	the given events it.	2367	the given events it.
788		2368
789	=item ev_feed_signal_event (loop, int signum)	2369	=item ev_feed_signal_event (ev_loop *loop, int signum)
790		2370
791	Feed an event as if the given signal occured (loop must be the default loop!).	2371	Feed an event as if the given signal occured (C<loop> must be the default
		2372	loop!).
792		2373
793	=back	2374	=back
		2375
794		2376
795	=head1 LIBEVENT EMULATION	2377	=head1 LIBEVENT EMULATION
796		2378
797	Libev offers a compatibility emulation layer for libevent. It cannot	2379	Libev offers a compatibility emulation layer for libevent. It cannot
798	emulate the internals of libevent, so here are some usage hints:	2380	emulate the internals of libevent, so here are some usage hints:
…		…
810		2392
811	=item * Priorities are not currently supported. Initialising priorities	2393	=item * Priorities are not currently supported. Initialising priorities
812	will fail and all watchers will have the same priority, even though there	2394	will fail and all watchers will have the same priority, even though there
813	is an ev_pri field.	2395	is an ev_pri field.
814		2396
		2397	=item * In libevent, the last base created gets the signals, in libev, the
		2398	first base created (== the default loop) gets the signals.
		2399
815	=item * Other members are not supported.	2400	=item * Other members are not supported.
816		2401
817	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2402	=item * The libev emulation is I<not> ABI compatible to libevent, you need
818	to use the libev header file and library.	2403	to use the libev header file and library.
819		2404
820	=back	2405	=back
821		2406
822	=head1 C++ SUPPORT	2407	=head1 C++ SUPPORT
823		2408
824	TBD.	2409	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2410	you to use some convinience methods to start/stop watchers and also change
		2411	the callback model to a model using method callbacks on objects.
		2412
		2413	To use it,
		2414
		2415	#include <ev++.h>
		2416
		2417	This automatically includes F<ev.h> and puts all of its definitions (many
		2418	of them macros) into the global namespace. All C++ specific things are
		2419	put into the C<ev> namespace. It should support all the same embedding
		2420	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2421
		2422	Care has been taken to keep the overhead low. The only data member the C++
		2423	classes add (compared to plain C-style watchers) is the event loop pointer
		2424	that the watcher is associated with (or no additional members at all if
		2425	you disable C<EV_MULTIPLICITY> when embedding libev).
		2426
		2427	Currently, functions, and static and non-static member functions can be
		2428	used as callbacks. Other types should be easy to add as long as they only
		2429	need one additional pointer for context. If you need support for other
		2430	types of functors please contact the author (preferably after implementing
		2431	it).
		2432
		2433	Here is a list of things available in the C<ev> namespace:
		2434
		2435	=over 4
		2436
		2437	=item C<ev::READ>, C<ev::WRITE> etc.
		2438
		2439	These are just enum values with the same values as the C<EV_READ> etc.
		2440	macros from F<ev.h>.
		2441
		2442	=item C<ev::tstamp>, C<ev::now>
		2443
		2444	Aliases to the same types/functions as with the C<ev_> prefix.
		2445
		2446	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2447
		2448	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2449	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2450	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2451	defines by many implementations.
		2452
		2453	All of those classes have these methods:
		2454
		2455	=over 4
		2456
		2457	=item ev::TYPE::TYPE ()
		2458
		2459	=item ev::TYPE::TYPE (struct ev_loop *)
		2460
		2461	=item ev::TYPE::~TYPE
		2462
		2463	The constructor (optionally) takes an event loop to associate the watcher
		2464	with. If it is omitted, it will use C<EV_DEFAULT>.
		2465
		2466	The constructor calls C<ev_init> for you, which means you have to call the
		2467	C<set> method before starting it.
		2468
		2469	It will not set a callback, however: You have to call the templated C<set>
		2470	method to set a callback before you can start the watcher.
		2471
		2472	(The reason why you have to use a method is a limitation in C++ which does
		2473	not allow explicit template arguments for constructors).
		2474
		2475	The destructor automatically stops the watcher if it is active.
		2476
		2477	=item w->set<class, &class::method> (object *)
		2478
		2479	This method sets the callback method to call. The method has to have a
		2480	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2481	first argument and the C<revents> as second. The object must be given as
		2482	parameter and is stored in the C<data> member of the watcher.
		2483
		2484	This method synthesizes efficient thunking code to call your method from
		2485	the C callback that libev requires. If your compiler can inline your
		2486	callback (i.e. it is visible to it at the place of the C<set> call and
		2487	your compiler is good :), then the method will be fully inlined into the
		2488	thunking function, making it as fast as a direct C callback.
		2489
		2490	Example: simple class declaration and watcher initialisation
		2491
		2492	struct myclass
		2493	{
		2494	void io_cb (ev::io &w, int revents) { }
		2495	}
		2496
		2497	myclass obj;
		2498	ev::io iow;
		2499	iow.set <myclass, &myclass::io_cb> (&obj);
		2500
		2501	=item w->set<function> (void *data = 0)
		2502
		2503	Also sets a callback, but uses a static method or plain function as
		2504	callback. The optional C<data> argument will be stored in the watcher's
		2505	C<data> member and is free for you to use.
		2506
		2507	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2508
		2509	See the method-C<set> above for more details.
		2510
		2511	Example:
		2512
		2513	static void io_cb (ev::io &w, int revents) { }
		2514	iow.set <io_cb> ();
		2515
		2516	=item w->set (struct ev_loop *)
		2517
		2518	Associates a different C<struct ev_loop> with this watcher. You can only
		2519	do this when the watcher is inactive (and not pending either).
		2520
		2521	=item w->set ([args])
		2522
		2523	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2524	called at least once. Unlike the C counterpart, an active watcher gets
		2525	automatically stopped and restarted when reconfiguring it with this
		2526	method.
		2527
		2528	=item w->start ()
		2529
		2530	Starts the watcher. Note that there is no C<loop> argument, as the
		2531	constructor already stores the event loop.
		2532
		2533	=item w->stop ()
		2534
		2535	Stops the watcher if it is active. Again, no C<loop> argument.
		2536
		2537	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2538
		2539	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2540	C<ev_TYPE_again> function.
		2541
		2542	=item w->sweep () (C<ev::embed> only)
		2543
		2544	Invokes C<ev_embed_sweep>.
		2545
		2546	=item w->update () (C<ev::stat> only)
		2547
		2548	Invokes C<ev_stat_stat>.
		2549
		2550	=back
		2551
		2552	=back
		2553
		2554	Example: Define a class with an IO and idle watcher, start one of them in
		2555	the constructor.
		2556
		2557	class myclass
		2558	{
		2559	ev::io io; void io_cb (ev::io &w, int revents);
		2560	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2561
		2562	myclass (int fd)
		2563	{
		2564	io .set <myclass, &myclass::io_cb > (this);
		2565	idle.set <myclass, &myclass::idle_cb> (this);
		2566
		2567	io.start (fd, ev::READ);
		2568	}
		2569	};
		2570
		2571
		2572	=head1 OTHER LANGUAGE BINDINGS
		2573
		2574	Libev does not offer other language bindings itself, but bindings for a
		2575	numbe rof languages exist in the form of third-party packages. If you know
		2576	any interesting language binding in addition to the ones listed here, drop
		2577	me a note.
		2578
		2579	=over 4
		2580
		2581	=item Perl
		2582
		2583	The EV module implements the full libev API and is actually used to test
		2584	libev. EV is developed together with libev. Apart from the EV core module,
		2585	there are additional modules that implement libev-compatible interfaces
		2586	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2587	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2588
		2589	It can be found and installed via CPAN, its homepage is found at
		2590	L<http://software.schmorp.de/pkg/EV>.
		2591
		2592	=item Ruby
		2593
		2594	Tony Arcieri has written a ruby extension that offers access to a subset
		2595	of the libev API and adds filehandle abstractions, asynchronous DNS and
		2596	more on top of it. It can be found via gem servers. Its homepage is at
		2597	L<http://rev.rubyforge.org/>.
		2598
		2599	=item D
		2600
		2601	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2602	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2603
		2604	=back
		2605
		2606
		2607	=head1 MACRO MAGIC
		2608
		2609	Libev can be compiled with a variety of options, the most fundamantal
		2610	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2611	functions and callbacks have an initial C<struct ev_loop *> argument.
		2612
		2613	To make it easier to write programs that cope with either variant, the
		2614	following macros are defined:
		2615
		2616	=over 4
		2617
		2618	=item C<EV_A>, C<EV_A_>
		2619
		2620	This provides the loop I<argument> for functions, if one is required ("ev
		2621	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2622	C<EV_A_> is used when other arguments are following. Example:
		2623
		2624	ev_unref (EV_A);
		2625	ev_timer_add (EV_A_ watcher);
		2626	ev_loop (EV_A_ 0);
		2627
		2628	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2629	which is often provided by the following macro.
		2630
		2631	=item C<EV_P>, C<EV_P_>
		2632
		2633	This provides the loop I<parameter> for functions, if one is required ("ev
		2634	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2635	C<EV_P_> is used when other parameters are following. Example:
		2636
		2637	// this is how ev_unref is being declared
		2638	static void ev_unref (EV_P);
		2639
		2640	// this is how you can declare your typical callback
		2641	static void cb (EV_P_ ev_timer *w, int revents)
		2642
		2643	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2644	suitable for use with C<EV_A>.
		2645
		2646	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2647
		2648	Similar to the other two macros, this gives you the value of the default
		2649	loop, if multiple loops are supported ("ev loop default").
		2650
		2651	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2652
		2653	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2654	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2655	is undefined when the default loop has not been initialised by a previous
		2656	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2657
		2658	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2659	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2660
		2661	=back
		2662
		2663	Example: Declare and initialise a check watcher, utilising the above
		2664	macros so it will work regardless of whether multiple loops are supported
		2665	or not.
		2666
		2667	static void
		2668	check_cb (EV_P_ ev_timer *w, int revents)
		2669	{
		2670	ev_check_stop (EV_A_ w);
		2671	}
		2672
		2673	ev_check check;
		2674	ev_check_init (&check, check_cb);
		2675	ev_check_start (EV_DEFAULT_ &check);
		2676	ev_loop (EV_DEFAULT_ 0);
		2677
		2678	=head1 EMBEDDING
		2679
		2680	Libev can (and often is) directly embedded into host
		2681	applications. Examples of applications that embed it include the Deliantra
		2682	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2683	and rxvt-unicode.
		2684
		2685	The goal is to enable you to just copy the necessary files into your
		2686	source directory without having to change even a single line in them, so
		2687	you can easily upgrade by simply copying (or having a checked-out copy of
		2688	libev somewhere in your source tree).
		2689
		2690	=head2 FILESETS
		2691
		2692	Depending on what features you need you need to include one or more sets of files
		2693	in your app.
		2694
		2695	=head3 CORE EVENT LOOP
		2696
		2697	To include only the libev core (all the C<ev_*> functions), with manual
		2698	configuration (no autoconf):
		2699
		2700	#define EV_STANDALONE 1
		2701	#include "ev.c"
		2702
		2703	This will automatically include F<ev.h>, too, and should be done in a
		2704	single C source file only to provide the function implementations. To use
		2705	it, do the same for F<ev.h> in all files wishing to use this API (best
		2706	done by writing a wrapper around F<ev.h> that you can include instead and
		2707	where you can put other configuration options):
		2708
		2709	#define EV_STANDALONE 1
		2710	#include "ev.h"
		2711
		2712	Both header files and implementation files can be compiled with a C++
		2713	compiler (at least, thats a stated goal, and breakage will be treated
		2714	as a bug).
		2715
		2716	You need the following files in your source tree, or in a directory
		2717	in your include path (e.g. in libev/ when using -Ilibev):
		2718
		2719	ev.h
		2720	ev.c
		2721	ev_vars.h
		2722	ev_wrap.h
		2723
		2724	ev_win32.c required on win32 platforms only
		2725
		2726	ev_select.c only when select backend is enabled (which is enabled by default)
		2727	ev_poll.c only when poll backend is enabled (disabled by default)
		2728	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2729	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2730	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2731
		2732	F<ev.c> includes the backend files directly when enabled, so you only need
		2733	to compile this single file.
		2734
		2735	=head3 LIBEVENT COMPATIBILITY API
		2736
		2737	To include the libevent compatibility API, also include:
		2738
		2739	#include "event.c"
		2740
		2741	in the file including F<ev.c>, and:
		2742
		2743	#include "event.h"
		2744
		2745	in the files that want to use the libevent API. This also includes F<ev.h>.
		2746
		2747	You need the following additional files for this:
		2748
		2749	event.h
		2750	event.c
		2751
		2752	=head3 AUTOCONF SUPPORT
		2753
		2754	Instead of using C<EV_STANDALONE=1> and providing your config in
		2755	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2756	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2757	include F<config.h> and configure itself accordingly.
		2758
		2759	For this of course you need the m4 file:
		2760
		2761	libev.m4
		2762
		2763	=head2 PREPROCESSOR SYMBOLS/MACROS
		2764
		2765	Libev can be configured via a variety of preprocessor symbols you have to
		2766	define before including any of its files. The default in the absense of
		2767	autoconf is noted for every option.
		2768
		2769	=over 4
		2770
		2771	=item EV_STANDALONE
		2772
		2773	Must always be C<1> if you do not use autoconf configuration, which
		2774	keeps libev from including F<config.h>, and it also defines dummy
		2775	implementations for some libevent functions (such as logging, which is not
		2776	supported). It will also not define any of the structs usually found in
		2777	F<event.h> that are not directly supported by the libev core alone.
		2778
		2779	=item EV_USE_MONOTONIC
		2780
		2781	If defined to be C<1>, libev will try to detect the availability of the
		2782	monotonic clock option at both compiletime and runtime. Otherwise no use
		2783	of the monotonic clock option will be attempted. If you enable this, you
		2784	usually have to link against librt or something similar. Enabling it when
		2785	the functionality isn't available is safe, though, although you have
		2786	to make sure you link against any libraries where the C<clock_gettime>
		2787	function is hiding in (often F<-lrt>).
		2788
		2789	=item EV_USE_REALTIME
		2790
		2791	If defined to be C<1>, libev will try to detect the availability of the
		2792	realtime clock option at compiletime (and assume its availability at
		2793	runtime if successful). Otherwise no use of the realtime clock option will
		2794	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2795	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2796	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2797
		2798	=item EV_USE_NANOSLEEP
		2799
		2800	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2801	and will use it for delays. Otherwise it will use C<select ()>.
		2802
		2803	=item EV_USE_EVENTFD
		2804
		2805	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2806	available and will probe for kernel support at runtime. This will improve
		2807	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2808	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2809	2.7 or newer, otherwise disabled.
		2810
		2811	=item EV_USE_SELECT
		2812
		2813	If undefined or defined to be C<1>, libev will compile in support for the
		2814	C<select>(2) backend. No attempt at autodetection will be done: if no
		2815	other method takes over, select will be it. Otherwise the select backend
		2816	will not be compiled in.
		2817
		2818	=item EV_SELECT_USE_FD_SET
		2819
		2820	If defined to C<1>, then the select backend will use the system C<fd_set>
		2821	structure. This is useful if libev doesn't compile due to a missing
		2822	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2823	exotic systems. This usually limits the range of file descriptors to some
		2824	low limit such as 1024 or might have other limitations (winsocket only
		2825	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2826	influence the size of the C<fd_set> used.
		2827
		2828	=item EV_SELECT_IS_WINSOCKET
		2829
		2830	When defined to C<1>, the select backend will assume that
		2831	select/socket/connect etc. don't understand file descriptors but
		2832	wants osf handles on win32 (this is the case when the select to
		2833	be used is the winsock select). This means that it will call
		2834	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2835	it is assumed that all these functions actually work on fds, even
		2836	on win32. Should not be defined on non-win32 platforms.
		2837
		2838	=item EV_FD_TO_WIN32_HANDLE
		2839
		2840	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2841	file descriptors to socket handles. When not defining this symbol (the
		2842	default), then libev will call C<_get_osfhandle>, which is usually
		2843	correct. In some cases, programs use their own file descriptor management,
		2844	in which case they can provide this function to map fds to socket handles.
		2845
		2846	=item EV_USE_POLL
		2847
		2848	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2849	backend. Otherwise it will be enabled on non-win32 platforms. It
		2850	takes precedence over select.
		2851
		2852	=item EV_USE_EPOLL
		2853
		2854	If defined to be C<1>, libev will compile in support for the Linux
		2855	C<epoll>(7) backend. Its availability will be detected at runtime,
		2856	otherwise another method will be used as fallback. This is the preferred
		2857	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2858	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2859
		2860	=item EV_USE_KQUEUE
		2861
		2862	If defined to be C<1>, libev will compile in support for the BSD style
		2863	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2864	otherwise another method will be used as fallback. This is the preferred
		2865	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2866	supports some types of fds correctly (the only platform we found that
		2867	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2868	not be used unless explicitly requested. The best way to use it is to find
		2869	out whether kqueue supports your type of fd properly and use an embedded
		2870	kqueue loop.
		2871
		2872	=item EV_USE_PORT
		2873
		2874	If defined to be C<1>, libev will compile in support for the Solaris
		2875	10 port style backend. Its availability will be detected at runtime,
		2876	otherwise another method will be used as fallback. This is the preferred
		2877	backend for Solaris 10 systems.
		2878
		2879	=item EV_USE_DEVPOLL
		2880
		2881	reserved for future expansion, works like the USE symbols above.
		2882
		2883	=item EV_USE_INOTIFY
		2884
		2885	If defined to be C<1>, libev will compile in support for the Linux inotify
		2886	interface to speed up C<ev_stat> watchers. Its actual availability will
		2887	be detected at runtime. If undefined, it will be enabled if the headers
		2888	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2889
		2890	=item EV_ATOMIC_T
		2891
		2892	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2893	access is atomic with respect to other threads or signal contexts. No such
		2894	type is easily found in the C language, so you can provide your own type
		2895	that you know is safe for your purposes. It is used both for signal handler "locking"
		2896	as well as for signal and thread safety in C<ev_async> watchers.
		2897
		2898	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2899	(from F<signal.h>), which is usually good enough on most platforms.
		2900
		2901	=item EV_H
		2902
		2903	The name of the F<ev.h> header file used to include it. The default if
		2904	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2905	used to virtually rename the F<ev.h> header file in case of conflicts.
		2906
		2907	=item EV_CONFIG_H
		2908
		2909	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2910	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2911	C<EV_H>, above.
		2912
		2913	=item EV_EVENT_H
		2914
		2915	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2916	of how the F<event.h> header can be found, the default is C<"event.h">.
		2917
		2918	=item EV_PROTOTYPES
		2919
		2920	If defined to be C<0>, then F<ev.h> will not define any function
		2921	prototypes, but still define all the structs and other symbols. This is
		2922	occasionally useful if you want to provide your own wrapper functions
		2923	around libev functions.
		2924
		2925	=item EV_MULTIPLICITY
		2926
		2927	If undefined or defined to C<1>, then all event-loop-specific functions
		2928	will have the C<struct ev_loop *> as first argument, and you can create
		2929	additional independent event loops. Otherwise there will be no support
		2930	for multiple event loops and there is no first event loop pointer
		2931	argument. Instead, all functions act on the single default loop.
		2932
		2933	=item EV_MINPRI
		2934
		2935	=item EV_MAXPRI
		2936
		2937	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2938	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2939	provide for more priorities by overriding those symbols (usually defined
		2940	to be C<-2> and C<2>, respectively).
		2941
		2942	When doing priority-based operations, libev usually has to linearly search
		2943	all the priorities, so having many of them (hundreds) uses a lot of space
		2944	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2945	fine.
		2946
		2947	If your embedding app does not need any priorities, defining these both to
		2948	C<0> will save some memory and cpu.
		2949
		2950	=item EV_PERIODIC_ENABLE
		2951
		2952	If undefined or defined to be C<1>, then periodic timers are supported. If
		2953	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2954	code.
		2955
		2956	=item EV_IDLE_ENABLE
		2957
		2958	If undefined or defined to be C<1>, then idle watchers are supported. If
		2959	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2960	code.
		2961
		2962	=item EV_EMBED_ENABLE
		2963
		2964	If undefined or defined to be C<1>, then embed watchers are supported. If
		2965	defined to be C<0>, then they are not.
		2966
		2967	=item EV_STAT_ENABLE
		2968
		2969	If undefined or defined to be C<1>, then stat watchers are supported. If
		2970	defined to be C<0>, then they are not.
		2971
		2972	=item EV_FORK_ENABLE
		2973
		2974	If undefined or defined to be C<1>, then fork watchers are supported. If
		2975	defined to be C<0>, then they are not.
		2976
		2977	=item EV_ASYNC_ENABLE
		2978
		2979	If undefined or defined to be C<1>, then async watchers are supported. If
		2980	defined to be C<0>, then they are not.
		2981
		2982	=item EV_MINIMAL
		2983
		2984	If you need to shave off some kilobytes of code at the expense of some
		2985	speed, define this symbol to C<1>. Currently only used for gcc to override
		2986	some inlining decisions, saves roughly 30% codesize of amd64.
		2987
		2988	=item EV_PID_HASHSIZE
		2989
		2990	C<ev_child> watchers use a small hash table to distribute workload by
		2991	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2992	than enough. If you need to manage thousands of children you might want to
		2993	increase this value (I<must> be a power of two).
		2994
		2995	=item EV_INOTIFY_HASHSIZE
		2996
		2997	C<ev_stat> watchers use a small hash table to distribute workload by
		2998	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2999	usually more than enough. If you need to manage thousands of C<ev_stat>
		3000	watchers you might want to increase this value (I<must> be a power of
		3001	two).
		3002
		3003	=item EV_COMMON
		3004
		3005	By default, all watchers have a C<void *data> member. By redefining
		3006	this macro to a something else you can include more and other types of
		3007	members. You have to define it each time you include one of the files,
		3008	though, and it must be identical each time.
		3009
		3010	For example, the perl EV module uses something like this:
		3011
		3012	#define EV_COMMON \
		3013	SV *self; /* contains this struct */ \
		3014	SV *cb_sv, *fh /* note no trailing ";" */
		3015
		3016	=item EV_CB_DECLARE (type)
		3017
		3018	=item EV_CB_INVOKE (watcher, revents)
		3019
		3020	=item ev_set_cb (ev, cb)
		3021
		3022	Can be used to change the callback member declaration in each watcher,
		3023	and the way callbacks are invoked and set. Must expand to a struct member
		3024	definition and a statement, respectively. See the F<ev.h> header file for
		3025	their default definitions. One possible use for overriding these is to
		3026	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3027	method calls instead of plain function calls in C++.
		3028
		3029	=head2 EXPORTED API SYMBOLS
		3030
		3031	If you need to re-export the API (e.g. via a dll) and you need a list of
		3032	exported symbols, you can use the provided F<Symbol.*> files which list
		3033	all public symbols, one per line:
		3034
		3035	Symbols.ev for libev proper
		3036	Symbols.event for the libevent emulation
		3037
		3038	This can also be used to rename all public symbols to avoid clashes with
		3039	multiple versions of libev linked together (which is obviously bad in
		3040	itself, but sometimes it is inconvinient to avoid this).
		3041
		3042	A sed command like this will create wrapper C<#define>'s that you need to
		3043	include before including F<ev.h>:
		3044
		3045	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3046
		3047	This would create a file F<wrap.h> which essentially looks like this:
		3048
		3049	#define ev_backend myprefix_ev_backend
		3050	#define ev_check_start myprefix_ev_check_start
		3051	#define ev_check_stop myprefix_ev_check_stop
		3052	...
		3053
		3054	=head2 EXAMPLES
		3055
		3056	For a real-world example of a program the includes libev
		3057	verbatim, you can have a look at the EV perl module
		3058	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3059	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3060	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3061	will be compiled. It is pretty complex because it provides its own header
		3062	file.
		3063
		3064	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3065	that everybody includes and which overrides some configure choices:
		3066
		3067	#define EV_MINIMAL 1
		3068	#define EV_USE_POLL 0
		3069	#define EV_MULTIPLICITY 0
		3070	#define EV_PERIODIC_ENABLE 0
		3071	#define EV_STAT_ENABLE 0
		3072	#define EV_FORK_ENABLE 0
		3073	#define EV_CONFIG_H <config.h>
		3074	#define EV_MINPRI 0
		3075	#define EV_MAXPRI 0
		3076
		3077	#include "ev++.h"
		3078
		3079	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3080
		3081	#include "ev_cpp.h"
		3082	#include "ev.c"
		3083
		3084
		3085	=head1 THREADS AND COROUTINES
		3086
		3087	=head2 THREADS
		3088
		3089	Libev itself is completely threadsafe, but it uses no locking. This
		3090	means that you can use as many loops as you want in parallel, as long as
		3091	only one thread ever calls into one libev function with the same loop
		3092	parameter.
		3093
		3094	Or put differently: calls with different loop parameters can be done in
		3095	parallel from multiple threads, calls with the same loop parameter must be
		3096	done serially (but can be done from different threads, as long as only one
		3097	thread ever is inside a call at any point in time, e.g. by using a mutex
		3098	per loop).
		3099
		3100	If you want to know which design is best for your problem, then I cannot
		3101	help you but by giving some generic advice:
		3102
		3103	=over 4
		3104
		3105	=item * most applications have a main thread: use the default libev loop
		3106	in that thread, or create a seperate thread running only the default loop.
		3107
		3108	This helps integrating other libraries or software modules that use libev
		3109	themselves and don't care/know about threading.
		3110
		3111	=item * one loop per thread is usually a good model.
		3112
		3113	Doing this is almost never wrong, sometimes a better-performance model
		3114	exists, but it is always a good start.
		3115
		3116	=item * other models exist, such as the leader/follower pattern, where one
		3117	loop is handed through multiple threads in a kind of round-robbin fashion.
		3118
		3119	Chosing a model is hard - look around, learn, know that usually you cna do
		3120	better than you currently do :-)
		3121
		3122	=item * often you need to talk to some other thread which blocks in the
		3123	event loop - C<ev_async> watchers can be used to wake them up from other
		3124	threads safely (or from signal contexts...).
		3125
		3126	=back
		3127
		3128	=head2 COROUTINES
		3129
		3130	Libev is much more accomodating to coroutines ("cooperative threads"):
		3131	libev fully supports nesting calls to it's functions from different
		3132	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3133	different coroutines and switch freely between both coroutines running the
		3134	loop, as long as you don't confuse yourself). The only exception is that
		3135	you must not do this from C<ev_periodic> reschedule callbacks.
		3136
		3137	Care has been invested into making sure that libev does not keep local
		3138	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3139	switches.
		3140
		3141
		3142	=head1 COMPLEXITIES
		3143
		3144	In this section the complexities of (many of) the algorithms used inside
		3145	libev will be explained. For complexity discussions about backends see the
		3146	documentation for C<ev_default_init>.
		3147
		3148	All of the following are about amortised time: If an array needs to be
		3149	extended, libev needs to realloc and move the whole array, but this
		3150	happens asymptotically never with higher number of elements, so O(1) might
		3151	mean it might do a lengthy realloc operation in rare cases, but on average
		3152	it is much faster and asymptotically approaches constant time.
		3153
		3154	=over 4
		3155
		3156	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3157
		3158	This means that, when you have a watcher that triggers in one hour and
		3159	there are 100 watchers that would trigger before that then inserting will
		3160	have to skip roughly seven (C<ld 100>) of these watchers.
		3161
		3162	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3163
		3164	That means that changing a timer costs less than removing/adding them
		3165	as only the relative motion in the event queue has to be paid for.
		3166
		3167	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3168
		3169	These just add the watcher into an array or at the head of a list.
		3170
		3171	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3172
		3173	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3174
		3175	These watchers are stored in lists then need to be walked to find the
		3176	correct watcher to remove. The lists are usually short (you don't usually
		3177	have many watchers waiting for the same fd or signal).
		3178
		3179	=item Finding the next timer in each loop iteration: O(1)
		3180
		3181	By virtue of using a binary heap, the next timer is always found at the
		3182	beginning of the storage array.
		3183
		3184	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3185
		3186	A change means an I/O watcher gets started or stopped, which requires
		3187	libev to recalculate its status (and possibly tell the kernel, depending
		3188	on backend and wether C<ev_io_set> was used).
		3189
		3190	=item Activating one watcher (putting it into the pending state): O(1)
		3191
		3192	=item Priority handling: O(number_of_priorities)
		3193
		3194	Priorities are implemented by allocating some space for each
		3195	priority. When doing priority-based operations, libev usually has to
		3196	linearly search all the priorities, but starting/stopping and activating
		3197	watchers becomes O(1) w.r.t. priority handling.
		3198
		3199	=item Sending an ev_async: O(1)
		3200
		3201	=item Processing ev_async_send: O(number_of_async_watchers)
		3202
		3203	=item Processing signals: O(max_signal_number)
		3204
		3205	Sending involves a syscall I<iff> there were no other C<ev_async_send>
		3206	calls in the current loop iteration. Checking for async and signal events
		3207	involves iterating over all running async watchers or all signal numbers.
		3208
		3209	=back
		3210
		3211
		3212	=head1 Win32 platform limitations and workarounds
		3213
		3214	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3215	requires, and its I/O model is fundamentally incompatible with the POSIX
		3216	model. Libev still offers limited functionality on this platform in
		3217	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3218	descriptors. This only applies when using Win32 natively, not when using
		3219	e.g. cygwin.
		3220
		3221	Lifting these limitations would basically require the full
		3222	re-implementation of the I/O system. If you are into these kinds of
		3223	things, then note that glib does exactly that for you in a very portable
		3224	way (note also that glib is the slowest event library known to man).
		3225
		3226	There is no supported compilation method available on windows except
		3227	embedding it into other applications.
		3228
		3229	Due to the many, low, and arbitrary limits on the win32 platform and
		3230	the abysmal performance of winsockets, using a large number of sockets
		3231	is not recommended (and not reasonable). If your program needs to use
		3232	more than a hundred or so sockets, then likely it needs to use a totally
		3233	different implementation for windows, as libev offers the POSIX readyness
		3234	notification model, which cannot be implemented efficiently on windows
		3235	(microsoft monopoly games).
		3236
		3237	=over 4
		3238
		3239	=item The winsocket select function
		3240
		3241	The winsocket C<select> function doesn't follow POSIX in that it requires
		3242	socket I<handles> and not socket I<file descriptors>. This makes select
		3243	very inefficient, and also requires a mapping from file descriptors
		3244	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		3245	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		3246	symbols for more info.
		3247
		3248	The configuration for a "naked" win32 using the microsoft runtime
		3249	libraries and raw winsocket select is:
		3250
		3251	#define EV_USE_SELECT 1
		3252	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3253
		3254	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3255	complexity in the O(n²) range when using win32.
		3256
		3257	=item Limited number of file descriptors
		3258
		3259	Windows has numerous arbitrary (and low) limits on things.
		3260
		3261	Early versions of winsocket's select only supported waiting for a maximum
		3262	of C<64> handles (probably owning to the fact that all windows kernels
		3263	can only wait for C<64> things at the same time internally; microsoft
		3264	recommends spawning a chain of threads and wait for 63 handles and the
		3265	previous thread in each. Great).
		3266
		3267	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3268	to some high number (e.g. C<2048>) before compiling the winsocket select
		3269	call (which might be in libev or elsewhere, for example, perl does its own
		3270	select emulation on windows).
		3271
		3272	Another limit is the number of file descriptors in the microsoft runtime
		3273	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3274	or something like this inside microsoft). You can increase this by calling
		3275	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3276	arbitrary limit), but is broken in many versions of the microsoft runtime
		3277	libraries.
		3278
		3279	This might get you to about C<512> or C<2048> sockets (depending on
		3280	windows version and/or the phase of the moon). To get more, you need to
		3281	wrap all I/O functions and provide your own fd management, but the cost of
		3282	calling select (O(n²)) will likely make this unworkable.
		3283
		3284	=back
		3285
		3286
		3287	=head1 PORTABILITY REQUIREMENTS
		3288
		3289	In addition to a working ISO-C implementation, libev relies on a few
		3290	additional extensions:
		3291
		3292	=over 4
		3293
		3294	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3295
		3296	The type C<sig_atomic_t volatile> (or whatever is defined as
		3297	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3298	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3299	believed to be sufficiently portable.
		3300
		3301	=item C<sigprocmask> must work in a threaded environment
		3302
		3303	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3304	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3305	pthread implementations will either allow C<sigprocmask> in the "main
		3306	thread" or will block signals process-wide, both behaviours would
		3307	be compatible with libev. Interaction between C<sigprocmask> and
		3308	C<pthread_sigmask> could complicate things, however.
		3309
		3310	The most portable way to handle signals is to block signals in all threads
		3311	except the initial one, and run the default loop in the initial thread as
		3312	well.
		3313
		3314	=item C<long> must be large enough for common memory allocation sizes
		3315
		3316	To improve portability and simplify using libev, libev uses C<long>
		3317	internally instead of C<size_t> when allocating its data structures. On
		3318	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3319	is still at least 31 bits everywhere, which is enough for hundreds of
		3320	millions of watchers.
		3321
		3322	=item C<double> must hold a time value in seconds with enough accuracy
		3323
		3324	The type C<double> is used to represent timestamps. It is required to
		3325	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3326	enough for at least into the year 4000. This requirement is fulfilled by
		3327	implementations implementing IEEE 754 (basically all existing ones).
		3328
		3329	=back
		3330
		3331	If you know of other additional requirements drop me a note.
		3332
825		3333
826	=head1 AUTHOR	3334	=head1 AUTHOR
827		3335
828	Marc Lehmann <libev@schmorp.de>.	3336	Marc Lehmann <libev@schmorp.de>.
829		3337

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