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Revision 1.8 by root, Mon Nov 12 08:20:02 2007 UTC vs.
Revision 1.207 by root, Tue Oct 28 14:13:52 2008 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
		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_ 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_ 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	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	}
8		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	108	name C<loop> (which is always of type C<ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	117	to the C<double> type in C, and when you need to do any calculations on
		118	it, you should treat it as some floating point value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 ERROR HANDLING
		123
		124	Libev knows three classes of errors: operating system errors, usage errors
		125	and internal errors (bugs).
		126
		127	When libev catches an operating system error it cannot handle (for example
		128	a system call indicating a condition libev cannot fix), it calls the callback
		129	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		130	abort. The default is to print a diagnostic message and to call C<abort
		131	()>.
		132
		133	When libev detects a usage error such as a negative timer interval, then
		134	it will print a diagnostic message and abort (via the C<assert> mechanism,
		135	so C<NDEBUG> will disable this checking): these are programming errors in
		136	the libev caller and need to be fixed there.
		137
		138	Libev also has a few internal error-checking C<assert>ions, and also has
		139	extensive consistency checking code. These do not trigger under normal
		140	circumstances, as they indicate either a bug in libev or worse.
		141
		142
		143	=head1 GLOBAL FUNCTIONS
		144
		145	These functions can be called anytime, even before initialising the
		146	library in any way.
51		147
52	=over 4	148	=over 4
53		149
54	=item ev_tstamp ev_time ()	150	=item ev_tstamp ev_time ()
55		151
56	Returns the current time as libev would use it.	152	Returns the current time as libev would use it. Please note that the
		153	C<ev_now> function is usually faster and also often returns the timestamp
		154	you actually want to know.
		155
		156	=item ev_sleep (ev_tstamp interval)
		157
		158	Sleep for the given interval: The current thread will be blocked until
		159	either it is interrupted or the given time interval has passed. Basically
		160	this is a sub-second-resolution C<sleep ()>.
57		161
58	=item int ev_version_major ()	162	=item int ev_version_major ()
59		163
60	=item int ev_version_minor ()	164	=item int ev_version_minor ()
61		165
62	You can find out the major and minor version numbers of the library	166	You can find out the major and minor ABI version numbers of the library
63	you linked against by calling the functions C<ev_version_major> and	167	you linked against by calling the functions C<ev_version_major> and
64	C<ev_version_minor>. If you want, you can compare against the global	168	C<ev_version_minor>. If you want, you can compare against the global
65	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	169	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	170	version of the library your program was compiled against.
67		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
68	Usually, its a good idea to terminate if the major versions mismatch,	175	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	177	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	178	not a problem.
72		179
		180	Example: Make sure we haven't accidentally been linked against the wrong
		181	version.
		182
		183	assert (("libev version mismatch",
		184	ev_version_major () == EV_VERSION_MAJOR
		185	&& ev_version_minor () >= EV_VERSION_MINOR));
		186
		187	=item unsigned int ev_supported_backends ()
		188
		189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		190	value) compiled into this binary of libev (independent of their
		191	availability on the system you are running on). See C<ev_default_loop> for
		192	a description of the set values.
		193
		194	Example: make sure we have the epoll method, because yeah this is cool and
		195	a must have and can we have a torrent of it please!!!11
		196
		197	assert (("sorry, no epoll, no sex",
		198	ev_supported_backends () & EVBACKEND_EPOLL));
		199
		200	=item unsigned int ev_recommended_backends ()
		201
		202	Return the set of all backends compiled into this binary of libev and also
		203	recommended for this platform. This set is often smaller than the one
		204	returned by C<ev_supported_backends>, as for example kqueue is broken on
		205	most BSDs and will not be auto-detected unless you explicitly request it
		206	(assuming you know what you are doing). This is the set of backends that
		207	libev will probe for if you specify no backends explicitly.
		208
		209	=item unsigned int ev_embeddable_backends ()
		210
		211	Returns the set of backends that are embeddable in other event loops. This
		212	is the theoretical, all-platform, value. To find which backends
		213	might be supported on the current system, you would need to look at
		214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		215	recommended ones.
		216
		217	See the description of C<ev_embed> watchers for more info.
		218
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
74		220
75	Sets the allocation function to use (the prototype is similar to the	221	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
77	and free memory (no surprises here). If it returns zero when memory	223	used to allocate and free memory (no surprises here). If it returns zero
78	needs to be allocated, the library might abort or take some potentially	224	when memory needs to be allocated (C<size != 0>), the library might abort
79	destructive action. The default is your system realloc function.	225	or take some potentially destructive action.
		226
		227	Since some systems (at least OpenBSD and Darwin) fail to implement
		228	correct C<realloc> semantics, libev will use a wrapper around the system
		229	C<realloc> and C<free> functions by default.
80		230
81	You could override this function in high-availability programs to, say,	231	You could override this function in high-availability programs to, say,
82	free some memory if it cannot allocate memory, to use a special allocator,	232	free some memory if it cannot allocate memory, to use a special allocator,
83	or even to sleep a while and retry until some memory is available.	233	or even to sleep a while and retry until some memory is available.
84		234
		235	Example: Replace the libev allocator with one that waits a bit and then
		236	retries (example requires a standards-compliant C<realloc>).
		237
		238	static void *
		239	persistent_realloc (void *ptr, size_t size)
		240	{
		241	for (;;)
		242	{
		243	void *newptr = realloc (ptr, size);
		244
		245	if (newptr)
		246	return newptr;
		247
		248	sleep (60);
		249	}
		250	}
		251
		252	...
		253	ev_set_allocator (persistent_realloc);
		254
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
86		256
87	Set the callback function to call on a retryable syscall error (such	257	Set the callback function to call on a retryable system call error (such
88	as failed select, poll, epoll_wait). The message is a printable string	258	as failed select, poll, epoll_wait). The message is a printable string
89	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
90	callback is set, then libev will expect it to remedy the sitution, no	260	callback is set, then libev will expect it to remedy the situation, no
91	matter what, when it returns. That is, libev will generally retry the	261	matter what, when it returns. That is, libev will generally retry the
92	requested operation, or, if the condition doesn't go away, do bad stuff	262	requested operation, or, if the condition doesn't go away, do bad stuff
93	(such as abort).	263	(such as abort).
94		264
		265	Example: This is basically the same thing that libev does internally, too.
		266
		267	static void
		268	fatal_error (const char *msg)
		269	{
		270	perror (msg);
		271	abort ();
		272	}
		273
		274	...
		275	ev_set_syserr_cb (fatal_error);
		276
95	=back	277	=back
96		278
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98		280
99	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<struct ev_loop *> (the C<struct>
100	types of such loops, the I<default> loop, which supports signals and child	282	is I<not> optional in this case, as there is also an C<ev_loop>
101	events, and dynamically created loops which do not.	283	I<function>).
102		284
103	If you use threads, a common model is to run the default event loop	285	The library knows two types of such loops, the I<default> loop, which
104	in your main thread (or in a separate thrad) and for each thread you	286	supports signals and child events, and dynamically created loops which do
105	create, you also create another event loop. Libev itself does no locking	287	not.
106	whatsoever, so if you mix calls to the same event loop in different
107	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because its hideous and inefficient).
109		288
110	=over 4	289	=over 4
111		290
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	291	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		292
114	This will initialise the default event loop if it hasn't been initialised	293	This will initialise the default event loop if it hasn't been initialised
115	yet and return it. If the default loop could not be initialised, returns	294	yet and return it. If the default loop could not be initialised, returns
116	false. If it already was initialised it simply returns it (and ignores the	295	false. If it already was initialised it simply returns it (and ignores the
117	flags).	296	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		297
119	If you don't know what event loop to use, use the one returned from this	298	If you don't know what event loop to use, use the one returned from this
120	function.	299	function.
121		300
		301	Note that this function is I<not> thread-safe, so if you want to use it
		302	from multiple threads, you have to lock (note also that this is unlikely,
		303	as loops cannot bes hared easily between threads anyway).
		304
		305	The default loop is the only loop that can handle C<ev_signal> and
		306	C<ev_child> watchers, and to do this, it always registers a handler
		307	for C<SIGCHLD>. If this is a problem for your application you can either
		308	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		309	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		310	C<ev_default_init>.
		311
122	The flags argument can be used to specify special behaviour or specific	312	The flags argument can be used to specify special behaviour or specific
123	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	313	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		314
125	It supports the following flags:	315	The following flags are supported:
126		316
127	=over 4	317	=over 4
128		318
129	=item EVFLAG_AUTO	319	=item C<EVFLAG_AUTO>
130		320
131	The default flags value. Use this if you have no clue (its the right	321	The default flags value. Use this if you have no clue (it's the right
132	thing, believe me).	322	thing, believe me).
133		323
134	=item EVFLAG_NOENV	324	=item C<EVFLAG_NOENV>
135		325
136	If this flag bit is ored into the flag value (or the program runs setuid	326	If this flag bit is or'ed into the flag value (or the program runs setuid
137	or setgid) then libev will I<not> look at the environment variable	327	or setgid) then libev will I<not> look at the environment variable
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	328	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	329	override the flags completely if it is found in the environment. This is
140	useful to try out specific backends to test their performance, or to work	330	useful to try out specific backends to test their performance, or to work
141	around bugs.	331	around bugs.
142		332
		333	=item C<EVFLAG_FORKCHECK>
		334
		335	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		336	a fork, you can also make libev check for a fork in each iteration by
		337	enabling this flag.
		338
		339	This works by calling C<getpid ()> on every iteration of the loop,
		340	and thus this might slow down your event loop if you do a lot of loop
		341	iterations and little real work, but is usually not noticeable (on my
		342	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		343	without a system call and thus I<very> fast, but my GNU/Linux system also has
		344	C<pthread_atfork> which is even faster).
		345
		346	The big advantage of this flag is that you can forget about fork (and
		347	forget about forgetting to tell libev about forking) when you use this
		348	flag.
		349
		350	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		351	environment variable.
		352
143	=item EVMETHOD_SELECT portable select backend	353	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		354
145	=item EVMETHOD_POLL poll backend (everywhere except windows)	355	This is your standard select(2) backend. Not I<completely> standard, as
		356	libev tries to roll its own fd_set with no limits on the number of fds,
		357	but if that fails, expect a fairly low limit on the number of fds when
		358	using this backend. It doesn't scale too well (O(highest_fd)), but its
		359	usually the fastest backend for a low number of (low-numbered :) fds.
146		360
147	=item EVMETHOD_EPOLL linux only	361	To get good performance out of this backend you need a high amount of
		362	parallelism (most of the file descriptors should be busy). If you are
		363	writing a server, you should C<accept ()> in a loop to accept as many
		364	connections as possible during one iteration. You might also want to have
		365	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		366	readiness notifications you get per iteration.
148		367
149	=item EVMETHOD_KQUEUE some bsds only	368	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		369	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		370	C<exceptfds> set on that platform).
150		371
151	=item EVMETHOD_DEVPOLL solaris 8 only	372	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
152		373
153	=item EVMETHOD_PORT solaris 10 only	374	And this is your standard poll(2) backend. It's more complicated
		375	than select, but handles sparse fds better and has no artificial
		376	limit on the number of fds you can use (except it will slow down
		377	considerably with a lot of inactive fds). It scales similarly to select,
		378	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		379	performance tips.
154		380
155	If one or more of these are ored into the flags value, then only these	381	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
156	backends will be tried (in the reverse order as given here). If one are	382	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
157	specified, any backend will do.	383
		384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		385
		386	For few fds, this backend is a bit little slower than poll and select,
		387	but it scales phenomenally better. While poll and select usually scale
		388	like O(total_fds) where n is the total number of fds (or the highest fd),
		389	epoll scales either O(1) or O(active_fds).
		390
		391	The epoll syscalls are the most misdesigned of the more advanced event
		392	mechanisms: problems include silently dropping fds, requiring a system
		393	call per change per fd (and unnecessary guessing of parameters), problems
		394	with dup and so on. The biggest issue is fork races, however - if a
		395	program forks then I<both> parent and child process have to recreate the
		396	epoll set, which can take considerable time (one syscall per fd) and is of
		397	course hard to detect.
		398
		399	Epoll is also notoriously buggy - embedding epoll fds should work, but
		400	of course doesn't, and epoll just loves to report events for totally
		401	I<different> file descriptors (even already closed ones, so one cannot
		402	even remove them from the set) than registered in the set (especially
		403	on SMP systems). Libev tries to counter these spurious notifications by
		404	employing an additional generation counter and comparing that against the
		405	events to filter out spurious ones.
		406
		407	While stopping, setting and starting an I/O watcher in the same iteration
		408	will result in some caching, there is still a system call per such incident
		409	(because the fd could point to a different file description now), so its
		410	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		411	very well if you register events for both fds.
		412
		413	Best performance from this backend is achieved by not unregistering all
		414	watchers for a file descriptor until it has been closed, if possible,
		415	i.e. keep at least one watcher active per fd at all times. Stopping and
		416	starting a watcher (without re-setting it) also usually doesn't cause
		417	extra overhead. A fork can both result in spurious notifications as well
		418	as in libev having to destroy and recreate the epoll object, which can
		419	take considerable time and thus should be avoided.
		420
		421	While nominally embeddable in other event loops, this feature is broken in
		422	all kernel versions tested so far.
		423
		424	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		425	C<EVBACKEND_POLL>.
		426
		427	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		428
		429	Kqueue deserves special mention, as at the time of this writing, it was
		430	broken on all BSDs except NetBSD (usually it doesn't work reliably with
		431	anything but sockets and pipes, except on Darwin, where of course it's
		432	completely useless). For this reason it's not being "auto-detected" unless
		433	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or
		434	libev was compiled on a known-to-be-good (-enough) system like NetBSD.
		435
		436	You still can embed kqueue into a normal poll or select backend and use it
		437	only for sockets (after having made sure that sockets work with kqueue on
		438	the target platform). See C<ev_embed> watchers for more info.
		439
		440	It scales in the same way as the epoll backend, but the interface to the
		441	kernel is more efficient (which says nothing about its actual speed, of
		442	course). While stopping, setting and starting an I/O watcher does never
		443	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		444	two event changes per incident. Support for C<fork ()> is very bad (but
		445	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		446	cases
		447
		448	This backend usually performs well under most conditions.
		449
		450	While nominally embeddable in other event loops, this doesn't work
		451	everywhere, so you might need to test for this. And since it is broken
		452	almost everywhere, you should only use it when you have a lot of sockets
		453	(for which it usually works), by embedding it into another event loop
		454	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
		455	using it only for sockets.
		456
		457	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		458	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		459	C<NOTE_EOF>.
		460
		461	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		462
		463	This is not implemented yet (and might never be, unless you send me an
		464	implementation). According to reports, C</dev/poll> only supports sockets
		465	and is not embeddable, which would limit the usefulness of this backend
		466	immensely.
		467
		468	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		469
		470	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		471	it's really slow, but it still scales very well (O(active_fds)).
		472
		473	Please note that Solaris event ports can deliver a lot of spurious
		474	notifications, so you need to use non-blocking I/O or other means to avoid
		475	blocking when no data (or space) is available.
		476
		477	While this backend scales well, it requires one system call per active
		478	file descriptor per loop iteration. For small and medium numbers of file
		479	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		480	might perform better.
		481
		482	On the positive side, with the exception of the spurious readiness
		483	notifications, this backend actually performed fully to specification
		484	in all tests and is fully embeddable, which is a rare feat among the
		485	OS-specific backends (I vastly prefer correctness over speed hacks).
		486
		487	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		488	C<EVBACKEND_POLL>.
		489
		490	=item C<EVBACKEND_ALL>
		491
		492	Try all backends (even potentially broken ones that wouldn't be tried
		493	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		494	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		495
		496	It is definitely not recommended to use this flag.
158		497
159	=back	498	=back
		499
		500	If one or more of these are or'ed into the flags value, then only these
		501	backends will be tried (in the reverse order as listed here). If none are
		502	specified, all backends in C<ev_recommended_backends ()> will be tried.
		503
		504	Example: This is the most typical usage.
		505
		506	if (!ev_default_loop (0))
		507	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		508
		509	Example: Restrict libev to the select and poll backends, and do not allow
		510	environment settings to be taken into account:
		511
		512	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		513
		514	Example: Use whatever libev has to offer, but make sure that kqueue is
		515	used if available (warning, breaks stuff, best use only with your own
		516	private event loop and only if you know the OS supports your types of
		517	fds):
		518
		519	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		520
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	521	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		522
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	523	Similar to C<ev_default_loop>, but always creates a new event loop that is
164	always distinct from the default loop. Unlike the default loop, it cannot	524	always distinct from the default loop. Unlike the default loop, it cannot
165	handle signal and child watchers, and attempts to do so will be greeted by	525	handle signal and child watchers, and attempts to do so will be greeted by
166	undefined behaviour (or a failed assertion if assertions are enabled).	526	undefined behaviour (or a failed assertion if assertions are enabled).
167		527
		528	Note that this function I<is> thread-safe, and the recommended way to use
		529	libev with threads is indeed to create one loop per thread, and using the
		530	default loop in the "main" or "initial" thread.
		531
		532	Example: Try to create a event loop that uses epoll and nothing else.
		533
		534	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		535	if (!epoller)
		536	fatal ("no epoll found here, maybe it hides under your chair");
		537
168	=item ev_default_destroy ()	538	=item ev_default_destroy ()
169		539
170	Destroys the default loop again (frees all memory and kernel state	540	Destroys the default loop again (frees all memory and kernel state
171	etc.). This stops all registered event watchers (by not touching them in	541	etc.). None of the active event watchers will be stopped in the normal
172	any way whatsoever, although you cnanot rely on this :).	542	sense, so e.g. C<ev_is_active> might still return true. It is your
		543	responsibility to either stop all watchers cleanly yourself I<before>
		544	calling this function, or cope with the fact afterwards (which is usually
		545	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		546	for example).
		547
		548	Note that certain global state, such as signal state (and installed signal
		549	handlers), will not be freed by this function, and related watchers (such
		550	as signal and child watchers) would need to be stopped manually.
		551
		552	In general it is not advisable to call this function except in the
		553	rare occasion where you really need to free e.g. the signal handling
		554	pipe fds. If you need dynamically allocated loops it is better to use
		555	C<ev_loop_new> and C<ev_loop_destroy>).
173		556
174	=item ev_loop_destroy (loop)	557	=item ev_loop_destroy (loop)
175		558
176	Like C<ev_default_destroy>, but destroys an event loop created by an	559	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	560	earlier call to C<ev_loop_new>.
178		561
179	=item ev_default_fork ()	562	=item ev_default_fork ()
180		563
		564	This function sets a flag that causes subsequent C<ev_loop> iterations
181	This function reinitialises the kernel state for backends that have	565	to reinitialise the kernel state for backends that have one. Despite the
182	one. Despite the name, you can call it anytime, but it makes most sense	566	name, you can call it anytime, but it makes most sense after forking, in
183	after forking, in either the parent or child process (or both, but that	567	the child process (or both child and parent, but that again makes little
184	again makes little sense).	568	sense). You I<must> call it in the child before using any of the libev
		569	functions, and it will only take effect at the next C<ev_loop> iteration.
185		570
186	You I<must> call this function after forking if and only if you want to	571	On the other hand, you only need to call this function in the child
187	use the event library in both processes. If you just fork+exec, you don't	572	process if and only if you want to use the event library in the child. If
188	have to call it.	573	you just fork+exec, you don't have to call it at all.
189		574
190	The function itself is quite fast and its usually not a problem to call	575	The function itself is quite fast and it's usually not a problem to call
191	it just in case after a fork. To make this easy, the function will fit in	576	it just in case after a fork. To make this easy, the function will fit in
192	quite nicely into a call to C<pthread_atfork>:	577	quite nicely into a call to C<pthread_atfork>:
193		578
194	pthread_atfork (0, 0, ev_default_fork);	579	pthread_atfork (0, 0, ev_default_fork);
195		580
196	=item ev_loop_fork (loop)	581	=item ev_loop_fork (loop)
197		582
198	Like C<ev_default_fork>, but acts on an event loop created by	583	Like C<ev_default_fork>, but acts on an event loop created by
199	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	584	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
200	after fork, and how you do this is entirely your own problem.	585	after fork that you want to re-use in the child, and how you do this is
		586	entirely your own problem.
201		587
		588	=item int ev_is_default_loop (loop)
		589
		590	Returns true when the given loop is, in fact, the default loop, and false
		591	otherwise.
		592
		593	=item unsigned int ev_loop_count (loop)
		594
		595	Returns the count of loop iterations for the loop, which is identical to
		596	the number of times libev did poll for new events. It starts at C<0> and
		597	happily wraps around with enough iterations.
		598
		599	This value can sometimes be useful as a generation counter of sorts (it
		600	"ticks" the number of loop iterations), as it roughly corresponds with
		601	C<ev_prepare> and C<ev_check> calls.
		602
202	=item unsigned int ev_method (loop)	603	=item unsigned int ev_backend (loop)
203		604
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	605	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	606	use.
206		607
207	=item ev_tstamp = ev_now (loop)	608	=item ev_tstamp ev_now (loop)
208		609
209	Returns the current "event loop time", which is the time the event loop	610	Returns the current "event loop time", which is the time the event loop
210	got events and started processing them. This timestamp does not change	611	received events and started processing them. This timestamp does not
211	as long as callbacks are being processed, and this is also the base time	612	change as long as callbacks are being processed, and this is also the base
212	used for relative timers. You can treat it as the timestamp of the event	613	time used for relative timers. You can treat it as the timestamp of the
213	occuring (or more correctly, the mainloop finding out about it).	614	event occurring (or more correctly, libev finding out about it).
		615
		616	=item ev_now_update (loop)
		617
		618	Establishes the current time by querying the kernel, updating the time
		619	returned by C<ev_now ()> in the progress. This is a costly operation and
		620	is usually done automatically within C<ev_loop ()>.
		621
		622	This function is rarely useful, but when some event callback runs for a
		623	very long time without entering the event loop, updating libev's idea of
		624	the current time is a good idea.
		625
		626	See also "The special problem of time updates" in the C<ev_timer> section.
214		627
215	=item ev_loop (loop, int flags)	628	=item ev_loop (loop, int flags)
216		629
217	Finally, this is it, the event handler. This function usually is called	630	Finally, this is it, the event handler. This function usually is called
218	after you initialised all your watchers and you want to start handling	631	after you initialised all your watchers and you want to start handling
219	events.	632	events.
220		633
221	If the flags argument is specified as 0, it will not return until either	634	If the flags argument is specified as C<0>, it will not return until
222	no event watchers are active anymore or C<ev_unloop> was called.	635	either no event watchers are active anymore or C<ev_unloop> was called.
		636
		637	Please note that an explicit C<ev_unloop> is usually better than
		638	relying on all watchers to be stopped when deciding when a program has
		639	finished (especially in interactive programs), but having a program
		640	that automatically loops as long as it has to and no longer by virtue
		641	of relying on its watchers stopping correctly, that is truly a thing of
		642	beauty.
223		643
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	644	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
225	those events and any outstanding ones, but will not block your process in	645	those events and any already outstanding ones, but will not block your
226	case there are no events.	646	process in case there are no events and will return after one iteration of
		647	the loop.
227		648
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	649	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
229	neccessary) and will handle those and any outstanding ones. It will block	650	necessary) and will handle those and any already outstanding ones. It
230	your process until at least one new event arrives.	651	will block your process until at least one new event arrives (which could
		652	be an event internal to libev itself, so there is no guarentee that a
		653	user-registered callback will be called), and will return after one
		654	iteration of the loop.
231		655
232	This flags value could be used to implement alternative looping	656	This is useful if you are waiting for some external event in conjunction
233	constructs, but the C<prepare> and C<check> watchers provide a better and	657	with something not expressible using other libev watchers (i.e. "roll your
234	more generic mechanism.	658	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		659	usually a better approach for this kind of thing.
		660
		661	Here are the gory details of what C<ev_loop> does:
		662
		663	- Before the first iteration, call any pending watchers.
		664	* If EVFLAG_FORKCHECK was used, check for a fork.
		665	- If a fork was detected (by any means), queue and call all fork watchers.
		666	- Queue and call all prepare watchers.
		667	- If we have been forked, detach and recreate the kernel state
		668	as to not disturb the other process.
		669	- Update the kernel state with all outstanding changes.
		670	- Update the "event loop time" (ev_now ()).
		671	- Calculate for how long to sleep or block, if at all
		672	(active idle watchers, EVLOOP_NONBLOCK or not having
		673	any active watchers at all will result in not sleeping).
		674	- Sleep if the I/O and timer collect interval say so.
		675	- Block the process, waiting for any events.
		676	- Queue all outstanding I/O (fd) events.
		677	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		678	- Queue all expired timers.
		679	- Queue all expired periodics.
		680	- Unless any events are pending now, queue all idle watchers.
		681	- Queue all check watchers.
		682	- Call all queued watchers in reverse order (i.e. check watchers first).
		683	Signals and child watchers are implemented as I/O watchers, and will
		684	be handled here by queueing them when their watcher gets executed.
		685	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		686	were used, or there are no active watchers, return, otherwise
		687	continue with step *.
		688
		689	Example: Queue some jobs and then loop until no events are outstanding
		690	anymore.
		691
		692	... queue jobs here, make sure they register event watchers as long
		693	... as they still have work to do (even an idle watcher will do..)
		694	ev_loop (my_loop, 0);
		695	... jobs done or somebody called unloop. yeah!
235		696
236	=item ev_unloop (loop, how)	697	=item ev_unloop (loop, how)
237		698
238	Can be used to make a call to C<ev_loop> return early. The C<how> argument	699	Can be used to make a call to C<ev_loop> return early (but only after it
		700	has processed all outstanding events). The C<how> argument must be either
239	must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop>	701	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
240	call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop>	702	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
241	calls return.	703
		704	This "unloop state" will be cleared when entering C<ev_loop> again.
		705
		706	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
242		707
243	=item ev_ref (loop)	708	=item ev_ref (loop)
244		709
245	=item ev_unref (loop)	710	=item ev_unref (loop)
246		711
247	Ref/unref can be used to add or remove a refcount on the event loop: Every	712	Ref/unref can be used to add or remove a reference count on the event
248	watcher keeps one reference. If you have a long-runing watcher you never	713	loop: Every watcher keeps one reference, and as long as the reference
249	unregister that should not keep ev_loop from running, ev_unref() after	714	count is nonzero, C<ev_loop> will not return on its own.
250	starting, and ev_ref() before stopping it. Libev itself uses this for	715
251	example for its internal signal pipe: It is not visible to you as a user	716	If you have a watcher you never unregister that should not keep C<ev_loop>
252	and should not keep C<ev_loop> from exiting if the work is done. It is	717	from returning, call ev_unref() after starting, and ev_ref() before
253	also an excellent way to do this for generic recurring timers or from	718	stopping it.
254	within third-party libraries. Just remember to unref after start and ref	719
255	before stop.	720	As an example, libev itself uses this for its internal signal pipe: It is
		721	not visible to the libev user and should not keep C<ev_loop> from exiting
		722	if no event watchers registered by it are active. It is also an excellent
		723	way to do this for generic recurring timers or from within third-party
		724	libraries. Just remember to I<unref after start> and I<ref before stop>
		725	(but only if the watcher wasn't active before, or was active before,
		726	respectively).
		727
		728	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		729	running when nothing else is active.
		730
		731	ev_signal exitsig;
		732	ev_signal_init (&exitsig, sig_cb, SIGINT);
		733	ev_signal_start (loop, &exitsig);
		734	evf_unref (loop);
		735
		736	Example: For some weird reason, unregister the above signal handler again.
		737
		738	ev_ref (loop);
		739	ev_signal_stop (loop, &exitsig);
		740
		741	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		742
		743	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		744
		745	These advanced functions influence the time that libev will spend waiting
		746	for events. Both time intervals are by default C<0>, meaning that libev
		747	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		748	latency.
		749
		750	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		751	allows libev to delay invocation of I/O and timer/periodic callbacks
		752	to increase efficiency of loop iterations (or to increase power-saving
		753	opportunities).
		754
		755	The idea is that sometimes your program runs just fast enough to handle
		756	one (or very few) event(s) per loop iteration. While this makes the
		757	program responsive, it also wastes a lot of CPU time to poll for new
		758	events, especially with backends like C<select ()> which have a high
		759	overhead for the actual polling but can deliver many events at once.
		760
		761	By setting a higher I<io collect interval> you allow libev to spend more
		762	time collecting I/O events, so you can handle more events per iteration,
		763	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		764	C<ev_timer>) will be not affected. Setting this to a non-null value will
		765	introduce an additional C<ev_sleep ()> call into most loop iterations.
		766
		767	Likewise, by setting a higher I<timeout collect interval> you allow libev
		768	to spend more time collecting timeouts, at the expense of increased
		769	latency/jitter/inexactness (the watcher callback will be called
		770	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		771	value will not introduce any overhead in libev.
		772
		773	Many (busy) programs can usually benefit by setting the I/O collect
		774	interval to a value near C<0.1> or so, which is often enough for
		775	interactive servers (of course not for games), likewise for timeouts. It
		776	usually doesn't make much sense to set it to a lower value than C<0.01>,
		777	as this approaches the timing granularity of most systems.
		778
		779	Setting the I<timeout collect interval> can improve the opportunity for
		780	saving power, as the program will "bundle" timer callback invocations that
		781	are "near" in time together, by delaying some, thus reducing the number of
		782	times the process sleeps and wakes up again. Another useful technique to
		783	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		784	they fire on, say, one-second boundaries only.
		785
		786	=item ev_loop_verify (loop)
		787
		788	This function only does something when C<EV_VERIFY> support has been
		789	compiled in, which is the default for non-minimal builds. It tries to go
		790	through all internal structures and checks them for validity. If anything
		791	is found to be inconsistent, it will print an error message to standard
		792	error and call C<abort ()>.
		793
		794	This can be used to catch bugs inside libev itself: under normal
		795	circumstances, this function will never abort as of course libev keeps its
		796	data structures consistent.
256		797
257	=back	798	=back
258		799
		800
259	=head1 ANATOMY OF A WATCHER	801	=head1 ANATOMY OF A WATCHER
		802
		803	In the following description, uppercase C<TYPE> in names stands for the
		804	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		805	watchers and C<ev_io_start> for I/O watchers.
260		806
261	A watcher is a structure that you create and register to record your	807	A watcher is a structure that you create and register to record your
262	interest in some event. For instance, if you want to wait for STDIN to	808	interest in some event. For instance, if you want to wait for STDIN to
263	become readable, you would create an ev_io watcher for that:	809	become readable, you would create an C<ev_io> watcher for that:
264		810
265	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	811	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
266	{	812	{
267	ev_io_stop (w);	813	ev_io_stop (w);
268	ev_unloop (loop, EVUNLOOP_ALL);	814	ev_unloop (loop, EVUNLOOP_ALL);
269	}	815	}
270		816
271	struct ev_loop *loop = ev_default_loop (0);	817	struct ev_loop *loop = ev_default_loop (0);
		818
272	struct ev_io stdin_watcher;	819	ev_io stdin_watcher;
		820
273	ev_init (&stdin_watcher, my_cb);	821	ev_init (&stdin_watcher, my_cb);
274	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	822	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
275	ev_io_start (loop, &stdin_watcher);	823	ev_io_start (loop, &stdin_watcher);
		824
276	ev_loop (loop, 0);	825	ev_loop (loop, 0);
277		826
278	As you can see, you are responsible for allocating the memory for your	827	As you can see, you are responsible for allocating the memory for your
279	watcher structures (and it is usually a bad idea to do this on the stack,	828	watcher structures (and it is I<usually> a bad idea to do this on the
280	although this can sometimes be quite valid).	829	stack).
		830
		831	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		832	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
281		833
282	Each watcher structure must be initialised by a call to C<ev_init	834	Each watcher structure must be initialised by a call to C<ev_init
283	(watcher *, callback)>, which expects a callback to be provided. This	835	(watcher *, callback)>, which expects a callback to be provided. This
284	callback gets invoked each time the event occurs (or, in the case of io	836	callback gets invoked each time the event occurs (or, in the case of I/O
285	watchers, each time the event loop detects that the file descriptor given	837	watchers, each time the event loop detects that the file descriptor given
286	is readable and/or writable).	838	is readable and/or writable).
287		839
288	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	840	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
289	with arguments specific to this watcher type. There is also a macro	841	macro to configure it, with arguments specific to the watcher type. There
290	to combine initialisation and setting in one call: C<< ev_<type>_init	842	is also a macro to combine initialisation and setting in one call: C<<
291	(watcher *, callback, ...) >>.	843	ev_TYPE_init (watcher *, callback, ...) >>.
292		844
293	To make the watcher actually watch out for events, you have to start it	845	To make the watcher actually watch out for events, you have to start it
294	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	846	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
295	*) >>), and you can stop watching for events at any time by calling the	847	*) >>), and you can stop watching for events at any time by calling the
296	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	848	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
297		849
298	As long as your watcher is active (has been started but not stopped) you	850	As long as your watcher is active (has been started but not stopped) you
299	must not touch the values stored in it. Most specifically you must never	851	must not touch the values stored in it. Most specifically you must never
300	reinitialise it or call its set method.	852	reinitialise it or call its C<ev_TYPE_set> macro.
301
302	You cna check whether an event is active by calling the C<ev_is_active
303	(watcher *)> macro. To see whether an event is outstanding (but the
304	callback for it has not been called yet) you cna use the C<ev_is_pending
305	(watcher *)> macro.
306		853
307	Each and every callback receives the event loop pointer as first, the	854	Each and every callback receives the event loop pointer as first, the
308	registered watcher structure as second, and a bitset of received events as	855	registered watcher structure as second, and a bitset of received events as
309	third argument.	856	third argument.
310		857
311	The rceeived events usually include a single bit per event type received	858	The received events usually include a single bit per event type received
312	(you can receive multiple events at the same time). The possible bit masks	859	(you can receive multiple events at the same time). The possible bit masks
313	are:	860	are:
314		861
315	=over 4	862	=over 4
316		863
317	=item EV_READ	864	=item C<EV_READ>
318		865
319	=item EV_WRITE	866	=item C<EV_WRITE>
320		867
321	The file descriptor in the ev_io watcher has become readable and/or	868	The file descriptor in the C<ev_io> watcher has become readable and/or
322	writable.	869	writable.
323		870
324	=item EV_TIMEOUT	871	=item C<EV_TIMEOUT>
325		872
326	The ev_timer watcher has timed out.	873	The C<ev_timer> watcher has timed out.
327		874
328	=item EV_PERIODIC	875	=item C<EV_PERIODIC>
329		876
330	The ev_periodic watcher has timed out.	877	The C<ev_periodic> watcher has timed out.
331		878
332	=item EV_SIGNAL	879	=item C<EV_SIGNAL>
333		880
334	The signal specified in the ev_signal watcher has been received by a thread.	881	The signal specified in the C<ev_signal> watcher has been received by a thread.
335		882
336	=item EV_CHILD	883	=item C<EV_CHILD>
337		884
338	The pid specified in the ev_child watcher has received a status change.	885	The pid specified in the C<ev_child> watcher has received a status change.
339		886
		887	=item C<EV_STAT>
		888
		889	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		890
340	=item EV_IDLE	891	=item C<EV_IDLE>
341		892
342	The ev_idle watcher has determined that you have nothing better to do.	893	The C<ev_idle> watcher has determined that you have nothing better to do.
343		894
344	=item EV_PREPARE	895	=item C<EV_PREPARE>
345		896
346	=item EV_CHECK	897	=item C<EV_CHECK>
347		898
348	All ev_prepare watchers are invoked just I<before> C<ev_loop> starts	899	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
349	to gather new events, and all ev_check watchers are invoked just after	900	to gather new events, and all C<ev_check> watchers are invoked just after
350	C<ev_loop> has gathered them, but before it invokes any callbacks for any	901	C<ev_loop> has gathered them, but before it invokes any callbacks for any
351	received events. Callbacks of both watcher types can start and stop as	902	received events. Callbacks of both watcher types can start and stop as
352	many watchers as they want, and all of them will be taken into account	903	many watchers as they want, and all of them will be taken into account
353	(for example, a ev_prepare watcher might start an idle watcher to keep	904	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
354	C<ev_loop> from blocking).	905	C<ev_loop> from blocking).
355		906
		907	=item C<EV_EMBED>
		908
		909	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		910
		911	=item C<EV_FORK>
		912
		913	The event loop has been resumed in the child process after fork (see
		914	C<ev_fork>).
		915
		916	=item C<EV_ASYNC>
		917
		918	The given async watcher has been asynchronously notified (see C<ev_async>).
		919
356	=item EV_ERROR	920	=item C<EV_ERROR>
357		921
358	An unspecified error has occured, the watcher has been stopped. This might	922	An unspecified error has occurred, the watcher has been stopped. This might
359	happen because the watcher could not be properly started because libev	923	happen because the watcher could not be properly started because libev
360	ran out of memory, a file descriptor was found to be closed or any other	924	ran out of memory, a file descriptor was found to be closed or any other
		925	problem. Libev considers these application bugs.
		926
361	problem. You best act on it by reporting the problem and somehow coping	927	You best act on it by reporting the problem and somehow coping with the
362	with the watcher being stopped.	928	watcher being stopped. Note that well-written programs should not receive
		929	an error ever, so when your watcher receives it, this usually indicates a
		930	bug in your program.
363		931
364	Libev will usually signal a few "dummy" events together with an error,	932	Libev will usually signal a few "dummy" events together with an error, for
365	for example it might indicate that a fd is readable or writable, and if	933	example it might indicate that a fd is readable or writable, and if your
366	your callbacks is well-written it can just attempt the operation and cope	934	callbacks is well-written it can just attempt the operation and cope with
367	with the error from read() or write(). This will not work in multithreaded	935	the error from read() or write(). This will not work in multi-threaded
368	programs, though, so beware.	936	programs, though, as the fd could already be closed and reused for another
		937	thing, so beware.
369		938
370	=back	939	=back
371		940
		941	=head2 GENERIC WATCHER FUNCTIONS
		942
		943	=over 4
		944
		945	=item C<ev_init> (ev_TYPE *watcher, callback)
		946
		947	This macro initialises the generic portion of a watcher. The contents
		948	of the watcher object can be arbitrary (so C<malloc> will do). Only
		949	the generic parts of the watcher are initialised, you I<need> to call
		950	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		951	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		952	which rolls both calls into one.
		953
		954	You can reinitialise a watcher at any time as long as it has been stopped
		955	(or never started) and there are no pending events outstanding.
		956
		957	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		958	int revents)>.
		959
		960	Example: Initialise an C<ev_io> watcher in two steps.
		961
		962	ev_io w;
		963	ev_init (&w, my_cb);
		964	ev_io_set (&w, STDIN_FILENO, EV_READ);
		965
		966	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		967
		968	This macro initialises the type-specific parts of a watcher. You need to
		969	call C<ev_init> at least once before you call this macro, but you can
		970	call C<ev_TYPE_set> any number of times. You must not, however, call this
		971	macro on a watcher that is active (it can be pending, however, which is a
		972	difference to the C<ev_init> macro).
		973
		974	Although some watcher types do not have type-specific arguments
		975	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		976
		977	See C<ev_init>, above, for an example.
		978
		979	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		980
		981	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		982	calls into a single call. This is the most convenient method to initialise
		983	a watcher. The same limitations apply, of course.
		984
		985	Example: Initialise and set an C<ev_io> watcher in one step.
		986
		987	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		988
		989	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		990
		991	Starts (activates) the given watcher. Only active watchers will receive
		992	events. If the watcher is already active nothing will happen.
		993
		994	Example: Start the C<ev_io> watcher that is being abused as example in this
		995	whole section.
		996
		997	ev_io_start (EV_DEFAULT_UC, &w);
		998
		999	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		1000
		1001	Stops the given watcher if active, and clears the pending status (whether
		1002	the watcher was active or not).
		1003
		1004	It is possible that stopped watchers are pending - for example,
		1005	non-repeating timers are being stopped when they become pending - but
		1006	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1007	pending. If you want to free or reuse the memory used by the watcher it is
		1008	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1009
		1010	=item bool ev_is_active (ev_TYPE *watcher)
		1011
		1012	Returns a true value iff the watcher is active (i.e. it has been started
		1013	and not yet been stopped). As long as a watcher is active you must not modify
		1014	it.
		1015
		1016	=item bool ev_is_pending (ev_TYPE *watcher)
		1017
		1018	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1019	events but its callback has not yet been invoked). As long as a watcher
		1020	is pending (but not active) you must not call an init function on it (but
		1021	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1022	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1023	it).
		1024
		1025	=item callback ev_cb (ev_TYPE *watcher)
		1026
		1027	Returns the callback currently set on the watcher.
		1028
		1029	=item ev_cb_set (ev_TYPE *watcher, callback)
		1030
		1031	Change the callback. You can change the callback at virtually any time
		1032	(modulo threads).
		1033
		1034	=item ev_set_priority (ev_TYPE *watcher, priority)
		1035
		1036	=item int ev_priority (ev_TYPE *watcher)
		1037
		1038	Set and query the priority of the watcher. The priority is a small
		1039	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1040	(default: C<-2>). Pending watchers with higher priority will be invoked
		1041	before watchers with lower priority, but priority will not keep watchers
		1042	from being executed (except for C<ev_idle> watchers).
		1043
		1044	This means that priorities are I<only> used for ordering callback
		1045	invocation after new events have been received. This is useful, for
		1046	example, to reduce latency after idling, or more often, to bind two
		1047	watchers on the same event and make sure one is called first.
		1048
		1049	If you need to suppress invocation when higher priority events are pending
		1050	you need to look at C<ev_idle> watchers, which provide this functionality.
		1051
		1052	You I<must not> change the priority of a watcher as long as it is active or
		1053	pending.
		1054
		1055	The default priority used by watchers when no priority has been set is
		1056	always C<0>, which is supposed to not be too high and not be too low :).
		1057
		1058	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1059	fine, as long as you do not mind that the priority value you query might
		1060	or might not have been clamped to the valid range.
		1061
		1062	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1063
		1064	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1065	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1066	can deal with that fact, as both are simply passed through to the
		1067	callback.
		1068
		1069	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1070
		1071	If the watcher is pending, this function clears its pending status and
		1072	returns its C<revents> bitset (as if its callback was invoked). If the
		1073	watcher isn't pending it does nothing and returns C<0>.
		1074
		1075	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1076	callback to be invoked, which can be accomplished with this function.
		1077
		1078	=back
		1079
		1080
372	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1081	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
373		1082
374	Each watcher has, by default, a member C<void *data> that you can change	1083	Each watcher has, by default, a member C<void *data> that you can change
375	and read at any time, libev will completely ignore it. This cna be used	1084	and read at any time: libev will completely ignore it. This can be used
376	to associate arbitrary data with your watcher. If you need more data and	1085	to associate arbitrary data with your watcher. If you need more data and
377	don't want to allocate memory and store a pointer to it in that data	1086	don't want to allocate memory and store a pointer to it in that data
378	member, you can also "subclass" the watcher type and provide your own	1087	member, you can also "subclass" the watcher type and provide your own
379	data:	1088	data:
380		1089
381	struct my_io	1090	struct my_io
382	{	1091	{
383	struct ev_io io;	1092	ev_io io;
384	int otherfd;	1093	int otherfd;
385	void *somedata;	1094	void *somedata;
386	struct whatever *mostinteresting;	1095	struct whatever *mostinteresting;
387	}	1096	};
		1097
		1098	...
		1099	struct my_io w;
		1100	ev_io_init (&w.io, my_cb, fd, EV_READ);
388		1101
389	And since your callback will be called with a pointer to the watcher, you	1102	And since your callback will be called with a pointer to the watcher, you
390	can cast it back to your own type:	1103	can cast it back to your own type:
391		1104
392	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1105	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
393	{	1106	{
394	struct my_io *w = (struct my_io *)w_;	1107	struct my_io *w = (struct my_io *)w_;
395	...	1108	...
396	}	1109	}
397		1110
398	More interesting and less C-conformant ways of catsing your callback type	1111	More interesting and less C-conformant ways of casting your callback type
399	have been omitted....	1112	instead have been omitted.
		1113
		1114	Another common scenario is to use some data structure with multiple
		1115	embedded watchers:
		1116
		1117	struct my_biggy
		1118	{
		1119	int some_data;
		1120	ev_timer t1;
		1121	ev_timer t2;
		1122	}
		1123
		1124	In this case getting the pointer to C<my_biggy> is a bit more
		1125	complicated: Either you store the address of your C<my_biggy> struct
		1126	in the C<data> member of the watcher (for woozies), or you need to use
		1127	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1128	programmers):
		1129
		1130	#include <stddef.h>
		1131
		1132	static void
		1133	t1_cb (EV_P_ ev_timer *w, int revents)
		1134	{
		1135	struct my_biggy big = (struct my_biggy *
		1136	(((char *)w) - offsetof (struct my_biggy, t1));
		1137	}
		1138
		1139	static void
		1140	t2_cb (EV_P_ ev_timer *w, int revents)
		1141	{
		1142	struct my_biggy big = (struct my_biggy *
		1143	(((char *)w) - offsetof (struct my_biggy, t2));
		1144	}
400		1145
401		1146
402	=head1 WATCHER TYPES	1147	=head1 WATCHER TYPES
403		1148
404	This section describes each watcher in detail, but will not repeat	1149	This section describes each watcher in detail, but will not repeat
405	information given in the last section.	1150	information given in the last section. Any initialisation/set macros,
		1151	functions and members specific to the watcher type are explained.
406		1152
		1153	Members are additionally marked with either I<[read-only]>, meaning that,
		1154	while the watcher is active, you can look at the member and expect some
		1155	sensible content, but you must not modify it (you can modify it while the
		1156	watcher is stopped to your hearts content), or I<[read-write]>, which
		1157	means you can expect it to have some sensible content while the watcher
		1158	is active, but you can also modify it. Modifying it may not do something
		1159	sensible or take immediate effect (or do anything at all), but libev will
		1160	not crash or malfunction in any way.
		1161
		1162
407	=head2 struct ev_io - is my file descriptor readable or writable	1163	=head2 C<ev_io> - is this file descriptor readable or writable?
408		1164
409	I/O watchers check whether a file descriptor is readable or writable	1165	I/O watchers check whether a file descriptor is readable or writable
410	in each iteration of the event loop (This behaviour is called	1166	in each iteration of the event loop, or, more precisely, when reading
411	level-triggering because you keep receiving events as long as the	1167	would not block the process and writing would at least be able to write
412	condition persists. Remember you cna stop the watcher if you don't want to	1168	some data. This behaviour is called level-triggering because you keep
413	act on the event and neither want to receive future events).	1169	receiving events as long as the condition persists. Remember you can stop
		1170	the watcher if you don't want to act on the event and neither want to
		1171	receive future events.
414		1172
415	In general you can register as many read and/or write event watchers oer	1173	In general you can register as many read and/or write event watchers per
416	fd as you want (as long as you don't confuse yourself). Setting all file	1174	fd as you want (as long as you don't confuse yourself). Setting all file
417	descriptors to non-blocking mode is also usually a good idea (but not	1175	descriptors to non-blocking mode is also usually a good idea (but not
418	required if you know what you are doing).	1176	required if you know what you are doing).
419		1177
420	You have to be careful with dup'ed file descriptors, though. Some backends	1178	If you cannot use non-blocking mode, then force the use of a
421	(the linux epoll backend is a notable example) cannot handle dup'ed file	1179	known-to-be-good backend (at the time of this writing, this includes only
422	descriptors correctly if you register interest in two or more fds pointing	1180	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
423	to the same file/socket etc. description.
424		1181
425	If you must do this, then force the use of a known-to-be-good backend	1182	Another thing you have to watch out for is that it is quite easy to
426	(at the time of this writing, this includes only EVMETHOD_SELECT and	1183	receive "spurious" readiness notifications, that is your callback might
427	EVMETHOD_POLL).	1184	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1185	because there is no data. Not only are some backends known to create a
		1186	lot of those (for example Solaris ports), it is very easy to get into
		1187	this situation even with a relatively standard program structure. Thus
		1188	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1189	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1190
		1191	If you cannot run the fd in non-blocking mode (for example you should
		1192	not play around with an Xlib connection), then you have to separately
		1193	re-test whether a file descriptor is really ready with a known-to-be good
		1194	interface such as poll (fortunately in our Xlib example, Xlib already
		1195	does this on its own, so its quite safe to use). Some people additionally
		1196	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1197	indefinitely.
		1198
		1199	But really, best use non-blocking mode.
		1200
		1201	=head3 The special problem of disappearing file descriptors
		1202
		1203	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1204	descriptor (either due to calling C<close> explicitly or any other means,
		1205	such as C<dup2>). The reason is that you register interest in some file
		1206	descriptor, but when it goes away, the operating system will silently drop
		1207	this interest. If another file descriptor with the same number then is
		1208	registered with libev, there is no efficient way to see that this is, in
		1209	fact, a different file descriptor.
		1210
		1211	To avoid having to explicitly tell libev about such cases, libev follows
		1212	the following policy: Each time C<ev_io_set> is being called, libev
		1213	will assume that this is potentially a new file descriptor, otherwise
		1214	it is assumed that the file descriptor stays the same. That means that
		1215	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1216	descriptor even if the file descriptor number itself did not change.
		1217
		1218	This is how one would do it normally anyway, the important point is that
		1219	the libev application should not optimise around libev but should leave
		1220	optimisations to libev.
		1221
		1222	=head3 The special problem of dup'ed file descriptors
		1223
		1224	Some backends (e.g. epoll), cannot register events for file descriptors,
		1225	but only events for the underlying file descriptions. That means when you
		1226	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1227	events for them, only one file descriptor might actually receive events.
		1228
		1229	There is no workaround possible except not registering events
		1230	for potentially C<dup ()>'ed file descriptors, or to resort to
		1231	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1232
		1233	=head3 The special problem of fork
		1234
		1235	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1236	useless behaviour. Libev fully supports fork, but needs to be told about
		1237	it in the child.
		1238
		1239	To support fork in your programs, you either have to call
		1240	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1241	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1242	C<EVBACKEND_POLL>.
		1243
		1244	=head3 The special problem of SIGPIPE
		1245
		1246	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1247	when writing to a pipe whose other end has been closed, your program gets
		1248	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1249	this is sensible behaviour, for daemons, this is usually undesirable.
		1250
		1251	So when you encounter spurious, unexplained daemon exits, make sure you
		1252	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1253	somewhere, as that would have given you a big clue).
		1254
		1255
		1256	=head3 Watcher-Specific Functions
428		1257
429	=over 4	1258	=over 4
430		1259
431	=item ev_io_init (ev_io *, callback, int fd, int events)	1260	=item ev_io_init (ev_io *, callback, int fd, int events)
432		1261
433	=item ev_io_set (ev_io *, int fd, int events)	1262	=item ev_io_set (ev_io *, int fd, int events)
434		1263
435	Configures an ev_io watcher. The fd is the file descriptor to rceeive	1264	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
436	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1265	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
437	EV_WRITE> to receive the given events.	1266	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1267
		1268	=item int fd [read-only]
		1269
		1270	The file descriptor being watched.
		1271
		1272	=item int events [read-only]
		1273
		1274	The events being watched.
438		1275
439	=back	1276	=back
440		1277
		1278	=head3 Examples
		1279
		1280	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1281	readable, but only once. Since it is likely line-buffered, you could
		1282	attempt to read a whole line in the callback.
		1283
		1284	static void
		1285	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1286	{
		1287	ev_io_stop (loop, w);
		1288	.. read from stdin here (or from w->fd) and handle any I/O errors
		1289	}
		1290
		1291	...
		1292	struct ev_loop *loop = ev_default_init (0);
		1293	ev_io stdin_readable;
		1294	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1295	ev_io_start (loop, &stdin_readable);
		1296	ev_loop (loop, 0);
		1297
		1298
441	=head2 struct ev_timer - relative and optionally recurring timeouts	1299	=head2 C<ev_timer> - relative and optionally repeating timeouts
442		1300
443	Timer watchers are simple relative timers that generate an event after a	1301	Timer watchers are simple relative timers that generate an event after a
444	given time, and optionally repeating in regular intervals after that.	1302	given time, and optionally repeating in regular intervals after that.
445		1303
446	The timers are based on real time, that is, if you register an event that	1304	The timers are based on real time, that is, if you register an event that
447	times out after an hour and youreset your system clock to last years	1305	times out after an hour and you reset your system clock to January last
448	time, it will still time out after (roughly) and hour. "Roughly" because	1306	year, it will still time out after (roughly) one hour. "Roughly" because
449	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1307	detecting time jumps is hard, and some inaccuracies are unavoidable (the
450	monotonic clock option helps a lot here).	1308	monotonic clock option helps a lot here).
451		1309
		1310	The callback is guaranteed to be invoked only I<after> its timeout has
		1311	passed, but if multiple timers become ready during the same loop iteration
		1312	then order of execution is undefined.
		1313
		1314	=head3 Be smart about timeouts
		1315
		1316	Many real-world problems involve some kind of timeout, usually for error
		1317	recovery. A typical example is an HTTP request - if the other side hangs,
		1318	you want to raise some error after a while.
		1319
		1320	What follows are some ways to handle this problem, from obvious and
		1321	inefficient to smart and efficient.
		1322
		1323	In the following, a 60 second activity timeout is assumed - a timeout that
		1324	gets reset to 60 seconds each time there is activity (e.g. each time some
		1325	data or other life sign was received).
		1326
452	=over 4	1327	=over 4
453		1328
		1329	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1330
		1331	This is the most obvious, but not the most simple way: In the beginning,
		1332	start the watcher:
		1333
		1334	ev_timer_init (timer, callback, 60., 0.);
		1335	ev_timer_start (loop, timer);
		1336
		1337	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1338	and start it again:
		1339
		1340	ev_timer_stop (loop, timer);
		1341	ev_timer_set (timer, 60., 0.);
		1342	ev_timer_start (loop, timer);
		1343
		1344	This is relatively simple to implement, but means that each time there is
		1345	some activity, libev will first have to remove the timer from its internal
		1346	data structure and then add it again. Libev tries to be fast, but it's
		1347	still not a constant-time operation.
		1348
		1349	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1350
		1351	This is the easiest way, and involves using C<ev_timer_again> instead of
		1352	C<ev_timer_start>.
		1353
		1354	To implement this, configure an C<ev_timer> with a C<repeat> value
		1355	of C<60> and then call C<ev_timer_again> at start and each time you
		1356	successfully read or write some data. If you go into an idle state where
		1357	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1358	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1359
		1360	That means you can ignore both the C<ev_timer_start> function and the
		1361	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1362	member and C<ev_timer_again>.
		1363
		1364	At start:
		1365
		1366	ev_timer_init (timer, callback);
		1367	timer->repeat = 60.;
		1368	ev_timer_again (loop, timer);
		1369
		1370	Each time there is some activity:
		1371
		1372	ev_timer_again (loop, timer);
		1373
		1374	It is even possible to change the time-out on the fly, regardless of
		1375	whether the watcher is active or not:
		1376
		1377	timer->repeat = 30.;
		1378	ev_timer_again (loop, timer);
		1379
		1380	This is slightly more efficient then stopping/starting the timer each time
		1381	you want to modify its timeout value, as libev does not have to completely
		1382	remove and re-insert the timer from/into its internal data structure.
		1383
		1384	It is, however, even simpler than the "obvious" way to do it.
		1385
		1386	=item 3. Let the timer time out, but then re-arm it as required.
		1387
		1388	This method is more tricky, but usually most efficient: Most timeouts are
		1389	relatively long compared to the intervals between other activity - in
		1390	our example, within 60 seconds, there are usually many I/O events with
		1391	associated activity resets.
		1392
		1393	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1394	but remember the time of last activity, and check for a real timeout only
		1395	within the callback:
		1396
		1397	ev_tstamp last_activity; // time of last activity
		1398
		1399	static void
		1400	callback (EV_P_ ev_timer *w, int revents)
		1401	{
		1402	ev_tstamp now = ev_now (EV_A);
		1403	ev_tstamp timeout = last_activity + 60.;
		1404
		1405	// if last_activity + 60. is older than now, we did time out
		1406	if (timeout < now)
		1407	{
		1408	// timeout occured, take action
		1409	}
		1410	else
		1411	{
		1412	// callback was invoked, but there was some activity, re-arm
		1413	// the watcher to fire in last_activity + 60, which is
		1414	// guaranteed to be in the future, so "again" is positive:
		1415	w->again = timeout - now;
		1416	ev_timer_again (EV_A_ w);
		1417	}
		1418	}
		1419
		1420	To summarise the callback: first calculate the real timeout (defined
		1421	as "60 seconds after the last activity"), then check if that time has
		1422	been reached, which means something I<did>, in fact, time out. Otherwise
		1423	the callback was invoked too early (C<timeout> is in the future), so
		1424	re-schedule the timer to fire at that future time, to see if maybe we have
		1425	a timeout then.
		1426
		1427	Note how C<ev_timer_again> is used, taking advantage of the
		1428	C<ev_timer_again> optimisation when the timer is already running.
		1429
		1430	This scheme causes more callback invocations (about one every 60 seconds
		1431	minus half the average time between activity), but virtually no calls to
		1432	libev to change the timeout.
		1433
		1434	To start the timer, simply initialise the watcher and set C<last_activity>
		1435	to the current time (meaning we just have some activity :), then call the
		1436	callback, which will "do the right thing" and start the timer:
		1437
		1438	ev_timer_init (timer, callback);
		1439	last_activity = ev_now (loop);
		1440	callback (loop, timer, EV_TIMEOUT);
		1441
		1442	And when there is some activity, simply store the current time in
		1443	C<last_activity>, no libev calls at all:
		1444
		1445	last_actiivty = ev_now (loop);
		1446
		1447	This technique is slightly more complex, but in most cases where the
		1448	time-out is unlikely to be triggered, much more efficient.
		1449
		1450	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1451	callback :) - just change the timeout and invoke the callback, which will
		1452	fix things for you.
		1453
		1454	=item 4. Wee, just use a double-linked list for your timeouts.
		1455
		1456	If there is not one request, but many thousands (millions...), all
		1457	employing some kind of timeout with the same timeout value, then one can
		1458	do even better:
		1459
		1460	When starting the timeout, calculate the timeout value and put the timeout
		1461	at the I<end> of the list.
		1462
		1463	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1464	the list is expected to fire (for example, using the technique #3).
		1465
		1466	When there is some activity, remove the timer from the list, recalculate
		1467	the timeout, append it to the end of the list again, and make sure to
		1468	update the C<ev_timer> if it was taken from the beginning of the list.
		1469
		1470	This way, one can manage an unlimited number of timeouts in O(1) time for
		1471	starting, stopping and updating the timers, at the expense of a major
		1472	complication, and having to use a constant timeout. The constant timeout
		1473	ensures that the list stays sorted.
		1474
		1475	=back
		1476
		1477	So which method the best?
		1478
		1479	Method #2 is a simple no-brain-required solution that is adequate in most
		1480	situations. Method #3 requires a bit more thinking, but handles many cases
		1481	better, and isn't very complicated either. In most case, choosing either
		1482	one is fine, with #3 being better in typical situations.
		1483
		1484	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1485	rather complicated, but extremely efficient, something that really pays
		1486	off after the first million or so of active timers, i.e. it's usually
		1487	overkill :)
		1488
		1489	=head3 The special problem of time updates
		1490
		1491	Establishing the current time is a costly operation (it usually takes at
		1492	least two system calls): EV therefore updates its idea of the current
		1493	time only before and after C<ev_loop> collects new events, which causes a
		1494	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1495	lots of events in one iteration.
		1496
		1497	The relative timeouts are calculated relative to the C<ev_now ()>
		1498	time. This is usually the right thing as this timestamp refers to the time
		1499	of the event triggering whatever timeout you are modifying/starting. If
		1500	you suspect event processing to be delayed and you I<need> to base the
		1501	timeout on the current time, use something like this to adjust for this:
		1502
		1503	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1504
		1505	If the event loop is suspended for a long time, you can also force an
		1506	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		1507	()>.
		1508
		1509	=head3 Watcher-Specific Functions and Data Members
		1510
		1511	=over 4
		1512
454	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1513	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
455		1514
456	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1515	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
457		1516
458	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1517	Configure the timer to trigger after C<after> seconds. If C<repeat>
459	C<0.>, then it will automatically be stopped. If it is positive, then the	1518	is C<0.>, then it will automatically be stopped once the timeout is
460	timer will automatically be configured to trigger again C<repeat> seconds	1519	reached. If it is positive, then the timer will automatically be
461	later, again, and again, until stopped manually.	1520	configured to trigger again C<repeat> seconds later, again, and again,
		1521	until stopped manually.
462		1522
463	The timer itself will do a best-effort at avoiding drift, that is, if you	1523	The timer itself will do a best-effort at avoiding drift, that is, if
464	configure a timer to trigger every 10 seconds, then it will trigger at	1524	you configure a timer to trigger every 10 seconds, then it will normally
465	exactly 10 second intervals. If, however, your program cannot keep up with	1525	trigger at exactly 10 second intervals. If, however, your program cannot
466	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1526	keep up with the timer (because it takes longer than those 10 seconds to
467	timer will not fire more than once per event loop iteration.	1527	do stuff) the timer will not fire more than once per event loop iteration.
468		1528
469	=item ev_timer_again (loop)	1529	=item ev_timer_again (loop, ev_timer *)
470		1530
471	This will act as if the timer timed out and restart it again if it is	1531	This will act as if the timer timed out and restart it again if it is
472	repeating. The exact semantics are:	1532	repeating. The exact semantics are:
473		1533
		1534	If the timer is pending, its pending status is cleared.
		1535
474	If the timer is started but nonrepeating, stop it.	1536	If the timer is started but non-repeating, stop it (as if it timed out).
475		1537
476	If the timer is repeating, either start it if necessary (with the repeat	1538	If the timer is repeating, either start it if necessary (with the
477	value), or reset the running timer to the repeat value.	1539	C<repeat> value), or reset the running timer to the C<repeat> value.
478		1540
479	This sounds a bit complicated, but here is a useful and typical	1541	This sounds a bit complicated, see "Be smart about timeouts", above, for a
480	example: Imagine you have a tcp connection and you want a so-called idle	1542	usage example.
481	timeout, that is, you want to be called when there have been, say, 60	1543
482	seconds of inactivity on the socket. The easiest way to do this is to	1544	=item ev_tstamp repeat [read-write]
483	configure an ev_timer with after=repeat=60 and calling ev_timer_again each	1545
484	time you successfully read or write some data. If you go into an idle	1546	The current C<repeat> value. Will be used each time the watcher times out
485	state where you do not expect data to travel on the socket, you can stop	1547	or C<ev_timer_again> is called, and determines the next timeout (if any),
486	the timer, and again will automatically restart it if need be.	1548	which is also when any modifications are taken into account.
487		1549
488	=back	1550	=back
489		1551
		1552	=head3 Examples
		1553
		1554	Example: Create a timer that fires after 60 seconds.
		1555
		1556	static void
		1557	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1558	{
		1559	.. one minute over, w is actually stopped right here
		1560	}
		1561
		1562	ev_timer mytimer;
		1563	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1564	ev_timer_start (loop, &mytimer);
		1565
		1566	Example: Create a timeout timer that times out after 10 seconds of
		1567	inactivity.
		1568
		1569	static void
		1570	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1571	{
		1572	.. ten seconds without any activity
		1573	}
		1574
		1575	ev_timer mytimer;
		1576	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1577	ev_timer_again (&mytimer); /* start timer */
		1578	ev_loop (loop, 0);
		1579
		1580	// and in some piece of code that gets executed on any "activity":
		1581	// reset the timeout to start ticking again at 10 seconds
		1582	ev_timer_again (&mytimer);
		1583
		1584
490	=head2 ev_periodic - to cron or not to cron it	1585	=head2 C<ev_periodic> - to cron or not to cron?
491		1586
492	Periodic watchers are also timers of a kind, but they are very versatile	1587	Periodic watchers are also timers of a kind, but they are very versatile
493	(and unfortunately a bit complex).	1588	(and unfortunately a bit complex).
494		1589
495	Unlike ev_timer's, they are not based on real time (or relative time)	1590	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
496	but on wallclock time (absolute time). You can tell a periodic watcher	1591	but on wall clock time (absolute time). You can tell a periodic watcher
497	to trigger "at" some specific point in time. For example, if you tell a	1592	to trigger after some specific point in time. For example, if you tell a
498	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1593	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
499	+ 10.>) and then reset your system clock to the last year, then it will	1594	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1595	clock to January of the previous year, then it will take more than year
500	take a year to trigger the event (unlike an ev_timer, which would trigger	1596	to trigger the event (unlike an C<ev_timer>, which would still trigger
501	roughly 10 seconds later and of course not if you reset your system time	1597	roughly 10 seconds later as it uses a relative timeout).
502	again).
503		1598
504	They can also be used to implement vastly more complex timers, such as	1599	C<ev_periodic>s can also be used to implement vastly more complex timers,
505	triggering an event on eahc midnight, local time.	1600	such as triggering an event on each "midnight, local time", or other
		1601	complicated rules.
		1602
		1603	As with timers, the callback is guaranteed to be invoked only when the
		1604	time (C<at>) has passed, but if multiple periodic timers become ready
		1605	during the same loop iteration, then order of execution is undefined.
		1606
		1607	=head3 Watcher-Specific Functions and Data Members
506		1608
507	=over 4	1609	=over 4
508		1610
509	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1611	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
510		1612
511	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1613	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
512		1614
513	Lots of arguments, lets sort it out... There are basically three modes of	1615	Lots of arguments, lets sort it out... There are basically three modes of
514	operation, and we will explain them from simplest to complex:	1616	operation, and we will explain them from simplest to most complex:
515
516		1617
517	=over 4	1618	=over 4
518		1619
519	=item * absolute timer (interval = reschedule_cb = 0)	1620	=item * absolute timer (at = time, interval = reschedule_cb = 0)
520		1621
521	In this configuration the watcher triggers an event at the wallclock time	1622	In this configuration the watcher triggers an event after the wall clock
522	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1623	time C<at> has passed. It will not repeat and will not adjust when a time
523	that is, if it is to be run at January 1st 2011 then it will run when the	1624	jump occurs, that is, if it is to be run at January 1st 2011 then it will
524	system time reaches or surpasses this time.	1625	only run when the system clock reaches or surpasses this time.
525		1626
526	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1627	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
527		1628
528	In this mode the watcher will always be scheduled to time out at the next	1629	In this mode the watcher will always be scheduled to time out at the next
529	C<at + N * interval> time (for some integer N) and then repeat, regardless	1630	C<at + N * interval> time (for some integer N, which can also be negative)
530	of any time jumps.	1631	and then repeat, regardless of any time jumps.
531		1632
532	This can be used to create timers that do not drift with respect to system	1633	This can be used to create timers that do not drift with respect to the
533	time:	1634	system clock, for example, here is a C<ev_periodic> that triggers each
		1635	hour, on the hour:
534		1636
535	ev_periodic_set (&periodic, 0., 3600., 0);	1637	ev_periodic_set (&periodic, 0., 3600., 0);
536		1638
537	This doesn't mean there will always be 3600 seconds in between triggers,	1639	This doesn't mean there will always be 3600 seconds in between triggers,
538	but only that the the callback will be called when the system time shows a	1640	but only that the callback will be called when the system time shows a
539	full hour (UTC), or more correct, when the system time is evenly divisible	1641	full hour (UTC), or more correctly, when the system time is evenly divisible
540	by 3600.	1642	by 3600.
541		1643
542	Another way to think about it (for the mathematically inclined) is that	1644	Another way to think about it (for the mathematically inclined) is that
543	ev_periodic will try to run the callback in this mode at the next possible	1645	C<ev_periodic> will try to run the callback in this mode at the next possible
544	time where C<time = at (mod interval)>, regardless of any time jumps.	1646	time where C<time = at (mod interval)>, regardless of any time jumps.
545		1647
		1648	For numerical stability it is preferable that the C<at> value is near
		1649	C<ev_now ()> (the current time), but there is no range requirement for
		1650	this value, and in fact is often specified as zero.
		1651
		1652	Note also that there is an upper limit to how often a timer can fire (CPU
		1653	speed for example), so if C<interval> is very small then timing stability
		1654	will of course deteriorate. Libev itself tries to be exact to be about one
		1655	millisecond (if the OS supports it and the machine is fast enough).
		1656
546	=item * manual reschedule mode (reschedule_cb = callback)	1657	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
547		1658
548	In this mode the values for C<interval> and C<at> are both being	1659	In this mode the values for C<interval> and C<at> are both being
549	ignored. Instead, each time the periodic watcher gets scheduled, the	1660	ignored. Instead, each time the periodic watcher gets scheduled, the
550	reschedule callback will be called with the watcher as first, and the	1661	reschedule callback will be called with the watcher as first, and the
551	current time as second argument.	1662	current time as second argument.
552		1663
553	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1664	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
554	periodic watcher, ever, or make any event loop modificstions>. If you need	1665	ever, or make ANY event loop modifications whatsoever>.
555	to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
556		1666
		1667	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1668	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1669	only event loop modification you are allowed to do).
		1670
557	Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1671	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
558	ev_tstamp now)>, e.g.:	1672	*w, ev_tstamp now)>, e.g.:
559		1673
		1674	static ev_tstamp
560	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1675	my_rescheduler (ev_periodic *w, ev_tstamp now)
561	{	1676	{
562	return now + 60.;	1677	return now + 60.;
563	}	1678	}
564		1679
565	It must return the next time to trigger, based on the passed time value	1680	It must return the next time to trigger, based on the passed time value
566	(that is, the lowest time value larger than to the second argument). It	1681	(that is, the lowest time value larger than to the second argument). It
567	will usually be called just before the callback will be triggered, but	1682	will usually be called just before the callback will be triggered, but
568	might be called at other times, too.	1683	might be called at other times, too.
569		1684
		1685	NOTE: I<< This callback must always return a time that is higher than or
		1686	equal to the passed C<now> value >>.
		1687
570	This can be used to create very complex timers, such as a timer that	1688	This can be used to create very complex timers, such as a timer that
571	triggers on each midnight, local time. To do this, you would calculate the	1689	triggers on "next midnight, local time". To do this, you would calculate the
572	next midnight after C<now> and return the timestamp value for this. How you do this	1690	next midnight after C<now> and return the timestamp value for this. How
573	is, again, up to you (but it is not trivial).	1691	you do this is, again, up to you (but it is not trivial, which is the main
		1692	reason I omitted it as an example).
574		1693
575	=back	1694	=back
576		1695
577	=item ev_periodic_again (loop, ev_periodic *)	1696	=item ev_periodic_again (loop, ev_periodic *)
578		1697
579	Simply stops and restarts the periodic watcher again. This is only useful	1698	Simply stops and restarts the periodic watcher again. This is only useful
580	when you changed some parameters or the reschedule callback would return	1699	when you changed some parameters or the reschedule callback would return
581	a different time than the last time it was called (e.g. in a crond like	1700	a different time than the last time it was called (e.g. in a crond like
582	program when the crontabs have changed).	1701	program when the crontabs have changed).
583		1702
		1703	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1704
		1705	When active, returns the absolute time that the watcher is supposed to
		1706	trigger next.
		1707
		1708	=item ev_tstamp offset [read-write]
		1709
		1710	When repeating, this contains the offset value, otherwise this is the
		1711	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1712
		1713	Can be modified any time, but changes only take effect when the periodic
		1714	timer fires or C<ev_periodic_again> is being called.
		1715
		1716	=item ev_tstamp interval [read-write]
		1717
		1718	The current interval value. Can be modified any time, but changes only
		1719	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1720	called.
		1721
		1722	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		1723
		1724	The current reschedule callback, or C<0>, if this functionality is
		1725	switched off. Can be changed any time, but changes only take effect when
		1726	the periodic timer fires or C<ev_periodic_again> is being called.
		1727
584	=back	1728	=back
585		1729
		1730	=head3 Examples
		1731
		1732	Example: Call a callback every hour, or, more precisely, whenever the
		1733	system time is divisible by 3600. The callback invocation times have
		1734	potentially a lot of jitter, but good long-term stability.
		1735
		1736	static void
		1737	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
		1738	{
		1739	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1740	}
		1741
		1742	ev_periodic hourly_tick;
		1743	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1744	ev_periodic_start (loop, &hourly_tick);
		1745
		1746	Example: The same as above, but use a reschedule callback to do it:
		1747
		1748	#include <math.h>
		1749
		1750	static ev_tstamp
		1751	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		1752	{
		1753	return now + (3600. - fmod (now, 3600.));
		1754	}
		1755
		1756	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1757
		1758	Example: Call a callback every hour, starting now:
		1759
		1760	ev_periodic hourly_tick;
		1761	ev_periodic_init (&hourly_tick, clock_cb,
		1762	fmod (ev_now (loop), 3600.), 3600., 0);
		1763	ev_periodic_start (loop, &hourly_tick);
		1764
		1765
586	=head2 ev_signal - signal me when a signal gets signalled	1766	=head2 C<ev_signal> - signal me when a signal gets signalled!
587		1767
588	Signal watchers will trigger an event when the process receives a specific	1768	Signal watchers will trigger an event when the process receives a specific
589	signal one or more times. Even though signals are very asynchronous, libev	1769	signal one or more times. Even though signals are very asynchronous, libev
590	will try its best to deliver signals synchronously, i.e. as part of the	1770	will try it's best to deliver signals synchronously, i.e. as part of the
591	normal event processing, like any other event.	1771	normal event processing, like any other event.
592		1772
		1773	If you want signals asynchronously, just use C<sigaction> as you would
		1774	do without libev and forget about sharing the signal. You can even use
		1775	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1776
593	You cna configure as many watchers as you like per signal. Only when the	1777	You can configure as many watchers as you like per signal. Only when the
594	first watcher gets started will libev actually register a signal watcher	1778	first watcher gets started will libev actually register a signal handler
595	with the kernel (thus it coexists with your own signal handlers as long	1779	with the kernel (thus it coexists with your own signal handlers as long as
596	as you don't register any with libev). Similarly, when the last signal	1780	you don't register any with libev for the same signal). Similarly, when
597	watcher for a signal is stopped libev will reset the signal handler to	1781	the last signal watcher for a signal is stopped, libev will reset the
598	SIG_DFL (regardless of what it was set to before).	1782	signal handler to SIG_DFL (regardless of what it was set to before).
		1783
		1784	If possible and supported, libev will install its handlers with
		1785	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1786	interrupted. If you have a problem with system calls getting interrupted by
		1787	signals you can block all signals in an C<ev_check> watcher and unblock
		1788	them in an C<ev_prepare> watcher.
		1789
		1790	=head3 Watcher-Specific Functions and Data Members
599		1791
600	=over 4	1792	=over 4
601		1793
602	=item ev_signal_init (ev_signal *, callback, int signum)	1794	=item ev_signal_init (ev_signal *, callback, int signum)
603		1795
604	=item ev_signal_set (ev_signal *, int signum)	1796	=item ev_signal_set (ev_signal *, int signum)
605		1797
606	Configures the watcher to trigger on the given signal number (usually one	1798	Configures the watcher to trigger on the given signal number (usually one
607	of the C<SIGxxx> constants).	1799	of the C<SIGxxx> constants).
608		1800
		1801	=item int signum [read-only]
		1802
		1803	The signal the watcher watches out for.
		1804
609	=back	1805	=back
610		1806
		1807	=head3 Examples
		1808
		1809	Example: Try to exit cleanly on SIGINT.
		1810
		1811	static void
		1812	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1813	{
		1814	ev_unloop (loop, EVUNLOOP_ALL);
		1815	}
		1816
		1817	ev_signal signal_watcher;
		1818	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1819	ev_signal_start (loop, &signal_watcher);
		1820
		1821
611	=head2 ev_child - wait for pid status changes	1822	=head2 C<ev_child> - watch out for process status changes
612		1823
613	Child watchers trigger when your process receives a SIGCHLD in response to	1824	Child watchers trigger when your process receives a SIGCHLD in response to
614	some child status changes (most typically when a child of yours dies).	1825	some child status changes (most typically when a child of yours dies or
		1826	exits). It is permissible to install a child watcher I<after> the child
		1827	has been forked (which implies it might have already exited), as long
		1828	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1829	forking and then immediately registering a watcher for the child is fine,
		1830	but forking and registering a watcher a few event loop iterations later is
		1831	not.
		1832
		1833	Only the default event loop is capable of handling signals, and therefore
		1834	you can only register child watchers in the default event loop.
		1835
		1836	=head3 Process Interaction
		1837
		1838	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1839	initialised. This is necessary to guarantee proper behaviour even if
		1840	the first child watcher is started after the child exits. The occurrence
		1841	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1842	synchronously as part of the event loop processing. Libev always reaps all
		1843	children, even ones not watched.
		1844
		1845	=head3 Overriding the Built-In Processing
		1846
		1847	Libev offers no special support for overriding the built-in child
		1848	processing, but if your application collides with libev's default child
		1849	handler, you can override it easily by installing your own handler for
		1850	C<SIGCHLD> after initialising the default loop, and making sure the
		1851	default loop never gets destroyed. You are encouraged, however, to use an
		1852	event-based approach to child reaping and thus use libev's support for
		1853	that, so other libev users can use C<ev_child> watchers freely.
		1854
		1855	=head3 Stopping the Child Watcher
		1856
		1857	Currently, the child watcher never gets stopped, even when the
		1858	child terminates, so normally one needs to stop the watcher in the
		1859	callback. Future versions of libev might stop the watcher automatically
		1860	when a child exit is detected.
		1861
		1862	=head3 Watcher-Specific Functions and Data Members
615		1863
616	=over 4	1864	=over 4
617		1865
618	=item ev_child_init (ev_child *, callback, int pid)	1866	=item ev_child_init (ev_child *, callback, int pid, int trace)
619		1867
620	=item ev_child_set (ev_child *, int pid)	1868	=item ev_child_set (ev_child *, int pid, int trace)
621		1869
622	Configures the watcher to wait for status changes of process C<pid> (or	1870	Configures the watcher to wait for status changes of process C<pid> (or
623	I<any> process if C<pid> is specified as C<0>). The callback can look	1871	I<any> process if C<pid> is specified as C<0>). The callback can look
624	at the C<rstatus> member of the C<ev_child> watcher structure to see	1872	at the C<rstatus> member of the C<ev_child> watcher structure to see
625	the status word (use the macros from C<sys/wait.h>). The C<rpid> member	1873	the status word (use the macros from C<sys/wait.h> and see your systems
626	contains the pid of the process causing the status change.	1874	C<waitpid> documentation). The C<rpid> member contains the pid of the
		1875	process causing the status change. C<trace> must be either C<0> (only
		1876	activate the watcher when the process terminates) or C<1> (additionally
		1877	activate the watcher when the process is stopped or continued).
		1878
		1879	=item int pid [read-only]
		1880
		1881	The process id this watcher watches out for, or C<0>, meaning any process id.
		1882
		1883	=item int rpid [read-write]
		1884
		1885	The process id that detected a status change.
		1886
		1887	=item int rstatus [read-write]
		1888
		1889	The process exit/trace status caused by C<rpid> (see your systems
		1890	C<waitpid> and C<sys/wait.h> documentation for details).
627		1891
628	=back	1892	=back
629		1893
		1894	=head3 Examples
		1895
		1896	Example: C<fork()> a new process and install a child handler to wait for
		1897	its completion.
		1898
		1899	ev_child cw;
		1900
		1901	static void
		1902	child_cb (EV_P_ ev_child *w, int revents)
		1903	{
		1904	ev_child_stop (EV_A_ w);
		1905	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1906	}
		1907
		1908	pid_t pid = fork ();
		1909
		1910	if (pid < 0)
		1911	// error
		1912	else if (pid == 0)
		1913	{
		1914	// the forked child executes here
		1915	exit (1);
		1916	}
		1917	else
		1918	{
		1919	ev_child_init (&cw, child_cb, pid, 0);
		1920	ev_child_start (EV_DEFAULT_ &cw);
		1921	}
		1922
		1923
		1924	=head2 C<ev_stat> - did the file attributes just change?
		1925
		1926	This watches a file system path for attribute changes. That is, it calls
		1927	C<stat> on that path in regular intervals (or when the OS says it changed)
		1928	and sees if it changed compared to the last time, invoking the callback if
		1929	it did.
		1930
		1931	The path does not need to exist: changing from "path exists" to "path does
		1932	not exist" is a status change like any other. The condition "path does
		1933	not exist" is signified by the C<st_nlink> field being zero (which is
		1934	otherwise always forced to be at least one) and all the other fields of
		1935	the stat buffer having unspecified contents.
		1936
		1937	The path I<must not> end in a slash or contain special components such as
		1938	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		1939	your working directory changes, then the behaviour is undefined.
		1940
		1941	Since there is no portable change notification interface available, the
		1942	portable implementation simply calls C<stat(2)> regularly on the path
		1943	to see if it changed somehow. You can specify a recommended polling
		1944	interval for this case. If you specify a polling interval of C<0> (highly
		1945	recommended!) then a I<suitable, unspecified default> value will be used
		1946	(which you can expect to be around five seconds, although this might
		1947	change dynamically). Libev will also impose a minimum interval which is
		1948	currently around C<0.1>, but thats usually overkill.
		1949
		1950	This watcher type is not meant for massive numbers of stat watchers,
		1951	as even with OS-supported change notifications, this can be
		1952	resource-intensive.
		1953
		1954	At the time of this writing, the only OS-specific interface implemented
		1955	is the Linux inotify interface (implementing kqueue support is left as
		1956	an exercise for the reader. Note, however, that the author sees no way
		1957	of implementing C<ev_stat> semantics with kqueue).
		1958
		1959	=head3 ABI Issues (Largefile Support)
		1960
		1961	Libev by default (unless the user overrides this) uses the default
		1962	compilation environment, which means that on systems with large file
		1963	support disabled by default, you get the 32 bit version of the stat
		1964	structure. When using the library from programs that change the ABI to
		1965	use 64 bit file offsets the programs will fail. In that case you have to
		1966	compile libev with the same flags to get binary compatibility. This is
		1967	obviously the case with any flags that change the ABI, but the problem is
		1968	most noticeably displayed with ev_stat and large file support.
		1969
		1970	The solution for this is to lobby your distribution maker to make large
		1971	file interfaces available by default (as e.g. FreeBSD does) and not
		1972	optional. Libev cannot simply switch on large file support because it has
		1973	to exchange stat structures with application programs compiled using the
		1974	default compilation environment.
		1975
		1976	=head3 Inotify and Kqueue
		1977
		1978	When C<inotify (7)> support has been compiled into libev (generally
		1979	only available with Linux 2.6.25 or above due to bugs in earlier
		1980	implementations) and present at runtime, it will be used to speed up
		1981	change detection where possible. The inotify descriptor will be created
		1982	lazily when the first C<ev_stat> watcher is being started.
		1983
		1984	Inotify presence does not change the semantics of C<ev_stat> watchers
		1985	except that changes might be detected earlier, and in some cases, to avoid
		1986	making regular C<stat> calls. Even in the presence of inotify support
		1987	there are many cases where libev has to resort to regular C<stat> polling,
		1988	but as long as the path exists, libev usually gets away without polling.
		1989
		1990	There is no support for kqueue, as apparently it cannot be used to
		1991	implement this functionality, due to the requirement of having a file
		1992	descriptor open on the object at all times, and detecting renames, unlinks
		1993	etc. is difficult.
		1994
		1995	=head3 The special problem of stat time resolution
		1996
		1997	The C<stat ()> system call only supports full-second resolution portably,
		1998	and even on systems where the resolution is higher, most file systems
		1999	still only support whole seconds.
		2000
		2001	That means that, if the time is the only thing that changes, you can
		2002	easily miss updates: on the first update, C<ev_stat> detects a change and
		2003	calls your callback, which does something. When there is another update
		2004	within the same second, C<ev_stat> will be unable to detect unless the
		2005	stat data does change in other ways (e.g. file size).
		2006
		2007	The solution to this is to delay acting on a change for slightly more
		2008	than a second (or till slightly after the next full second boundary), using
		2009	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2010	ev_timer_again (loop, w)>).
		2011
		2012	The C<.02> offset is added to work around small timing inconsistencies
		2013	of some operating systems (where the second counter of the current time
		2014	might be be delayed. One such system is the Linux kernel, where a call to
		2015	C<gettimeofday> might return a timestamp with a full second later than
		2016	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2017	update file times then there will be a small window where the kernel uses
		2018	the previous second to update file times but libev might already execute
		2019	the timer callback).
		2020
		2021	=head3 Watcher-Specific Functions and Data Members
		2022
		2023	=over 4
		2024
		2025	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2026
		2027	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2028
		2029	Configures the watcher to wait for status changes of the given
		2030	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2031	be detected and should normally be specified as C<0> to let libev choose
		2032	a suitable value. The memory pointed to by C<path> must point to the same
		2033	path for as long as the watcher is active.
		2034
		2035	The callback will receive an C<EV_STAT> event when a change was detected,
		2036	relative to the attributes at the time the watcher was started (or the
		2037	last change was detected).
		2038
		2039	=item ev_stat_stat (loop, ev_stat *)
		2040
		2041	Updates the stat buffer immediately with new values. If you change the
		2042	watched path in your callback, you could call this function to avoid
		2043	detecting this change (while introducing a race condition if you are not
		2044	the only one changing the path). Can also be useful simply to find out the
		2045	new values.
		2046
		2047	=item ev_statdata attr [read-only]
		2048
		2049	The most-recently detected attributes of the file. Although the type is
		2050	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2051	suitable for your system, but you can only rely on the POSIX-standardised
		2052	members to be present. If the C<st_nlink> member is C<0>, then there was
		2053	some error while C<stat>ing the file.
		2054
		2055	=item ev_statdata prev [read-only]
		2056
		2057	The previous attributes of the file. The callback gets invoked whenever
		2058	C<prev> != C<attr>, or, more precisely, one or more of these members
		2059	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2060	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2061
		2062	=item ev_tstamp interval [read-only]
		2063
		2064	The specified interval.
		2065
		2066	=item const char *path [read-only]
		2067
		2068	The file system path that is being watched.
		2069
		2070	=back
		2071
		2072	=head3 Examples
		2073
		2074	Example: Watch C</etc/passwd> for attribute changes.
		2075
		2076	static void
		2077	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2078	{
		2079	/* /etc/passwd changed in some way */
		2080	if (w->attr.st_nlink)
		2081	{
		2082	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2083	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2084	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2085	}
		2086	else
		2087	/* you shalt not abuse printf for puts */
		2088	puts ("wow, /etc/passwd is not there, expect problems. "
		2089	"if this is windows, they already arrived\n");
		2090	}
		2091
		2092	...
		2093	ev_stat passwd;
		2094
		2095	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2096	ev_stat_start (loop, &passwd);
		2097
		2098	Example: Like above, but additionally use a one-second delay so we do not
		2099	miss updates (however, frequent updates will delay processing, too, so
		2100	one might do the work both on C<ev_stat> callback invocation I<and> on
		2101	C<ev_timer> callback invocation).
		2102
		2103	static ev_stat passwd;
		2104	static ev_timer timer;
		2105
		2106	static void
		2107	timer_cb (EV_P_ ev_timer *w, int revents)
		2108	{
		2109	ev_timer_stop (EV_A_ w);
		2110
		2111	/* now it's one second after the most recent passwd change */
		2112	}
		2113
		2114	static void
		2115	stat_cb (EV_P_ ev_stat *w, int revents)
		2116	{
		2117	/* reset the one-second timer */
		2118	ev_timer_again (EV_A_ &timer);
		2119	}
		2120
		2121	...
		2122	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2123	ev_stat_start (loop, &passwd);
		2124	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2125
		2126
630	=head2 ev_idle - when you've got nothing better to do	2127	=head2 C<ev_idle> - when you've got nothing better to do...
631		2128
632	Idle watchers trigger events when there are no other I/O or timer (or	2129	Idle watchers trigger events when no other events of the same or higher
633	periodic) events pending. That is, as long as your process is busy	2130	priority are pending (prepare, check and other idle watchers do not count
634	handling sockets or timeouts it will not be called. But when your process	2131	as receiving "events").
635	is idle all idle watchers are being called again and again - until	2132
		2133	That is, as long as your process is busy handling sockets or timeouts
		2134	(or even signals, imagine) of the same or higher priority it will not be
		2135	triggered. But when your process is idle (or only lower-priority watchers
		2136	are pending), the idle watchers are being called once per event loop
636	stopped, that is, or your process receives more events.	2137	iteration - until stopped, that is, or your process receives more events
		2138	and becomes busy again with higher priority stuff.
637		2139
638	The most noteworthy effect is that as long as any idle watchers are	2140	The most noteworthy effect is that as long as any idle watchers are
639	active, the process will not block when waiting for new events.	2141	active, the process will not block when waiting for new events.
640		2142
641	Apart from keeping your process non-blocking (which is a useful	2143	Apart from keeping your process non-blocking (which is a useful
642	effect on its own sometimes), idle watchers are a good place to do	2144	effect on its own sometimes), idle watchers are a good place to do
643	"pseudo-background processing", or delay processing stuff to after the	2145	"pseudo-background processing", or delay processing stuff to after the
644	event loop has handled all outstanding events.	2146	event loop has handled all outstanding events.
645		2147
		2148	=head3 Watcher-Specific Functions and Data Members
		2149
646	=over 4	2150	=over 4
647		2151
648	=item ev_idle_init (ev_signal *, callback)	2152	=item ev_idle_init (ev_signal *, callback)
649		2153
650	Initialises and configures the idle watcher - it has no parameters of any	2154	Initialises and configures the idle watcher - it has no parameters of any
651	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2155	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
652	believe me.	2156	believe me.
653		2157
654	=back	2158	=back
655		2159
656	=head2 prepare and check - your hooks into the event loop	2160	=head3 Examples
657		2161
		2162	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2163	callback, free it. Also, use no error checking, as usual.
		2164
		2165	static void
		2166	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2167	{
		2168	free (w);
		2169	// now do something you wanted to do when the program has
		2170	// no longer anything immediate to do.
		2171	}
		2172
		2173	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2174	ev_idle_init (idle_watcher, idle_cb);
		2175	ev_idle_start (loop, idle_cb);
		2176
		2177
		2178	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		2179
658	Prepare and check watchers usually (but not always) are used in	2180	Prepare and check watchers are usually (but not always) used in pairs:
659	tandom. Prepare watchers get invoked before the process blocks and check	2181	prepare watchers get invoked before the process blocks and check watchers
660	watchers afterwards.	2182	afterwards.
661		2183
		2184	You I<must not> call C<ev_loop> or similar functions that enter
		2185	the current event loop from either C<ev_prepare> or C<ev_check>
		2186	watchers. Other loops than the current one are fine, however. The
		2187	rationale behind this is that you do not need to check for recursion in
		2188	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2189	C<ev_check> so if you have one watcher of each kind they will always be
		2190	called in pairs bracketing the blocking call.
		2191
662	Their main purpose is to integrate other event mechanisms into libev. This	2192	Their main purpose is to integrate other event mechanisms into libev and
663	could be used, for example, to track variable changes, implement your own	2193	their use is somewhat advanced. They could be used, for example, to track
664	watchers, integrate net-snmp or a coroutine library and lots more.	2194	variable changes, implement your own watchers, integrate net-snmp or a
		2195	coroutine library and lots more. They are also occasionally useful if
		2196	you cache some data and want to flush it before blocking (for example,
		2197	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2198	watcher).
665		2199
666	This is done by examining in each prepare call which file descriptors need	2200	This is done by examining in each prepare call which file descriptors
667	to be watched by the other library, registering ev_io watchers for them	2201	need to be watched by the other library, registering C<ev_io> watchers
668	and starting an ev_timer watcher for any timeouts (many libraries provide	2202	for them and starting an C<ev_timer> watcher for any timeouts (many
669	just this functionality). Then, in the check watcher you check for any	2203	libraries provide exactly this functionality). Then, in the check watcher,
670	events that occured (by making your callbacks set soem flags for example)	2204	you check for any events that occurred (by checking the pending status
671	and call back into the library.	2205	of all watchers and stopping them) and call back into the library. The
		2206	I/O and timer callbacks will never actually be called (but must be valid
		2207	nevertheless, because you never know, you know?).
672		2208
673	As another example, the perl Coro module uses these hooks to integrate	2209	As another example, the Perl Coro module uses these hooks to integrate
674	coroutines into libev programs, by yielding to other active coroutines	2210	coroutines into libev programs, by yielding to other active coroutines
675	during each prepare and only letting the process block if no coroutines	2211	during each prepare and only letting the process block if no coroutines
676	are ready to run.	2212	are ready to run (it's actually more complicated: it only runs coroutines
		2213	with priority higher than or equal to the event loop and one coroutine
		2214	of lower priority, but only once, using idle watchers to keep the event
		2215	loop from blocking if lower-priority coroutines are active, thus mapping
		2216	low-priority coroutines to idle/background tasks).
		2217
		2218	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2219	priority, to ensure that they are being run before any other watchers
		2220	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2221
		2222	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2223	activate ("feed") events into libev. While libev fully supports this, they
		2224	might get executed before other C<ev_check> watchers did their job. As
		2225	C<ev_check> watchers are often used to embed other (non-libev) event
		2226	loops those other event loops might be in an unusable state until their
		2227	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2228	others).
		2229
		2230	=head3 Watcher-Specific Functions and Data Members
677		2231
678	=over 4	2232	=over 4
679		2233
680	=item ev_prepare_init (ev_prepare *, callback)	2234	=item ev_prepare_init (ev_prepare *, callback)
681		2235
682	=item ev_check_init (ev_check *, callback)	2236	=item ev_check_init (ev_check *, callback)
683		2237
684	Initialises and configures the prepare or check watcher - they have no	2238	Initialises and configures the prepare or check watcher - they have no
685	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2239	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
686	macros, but using them is utterly, utterly pointless.	2240	macros, but using them is utterly, utterly, utterly and completely
		2241	pointless.
687		2242
688	=back	2243	=back
689		2244
		2245	=head3 Examples
		2246
		2247	There are a number of principal ways to embed other event loops or modules
		2248	into libev. Here are some ideas on how to include libadns into libev
		2249	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2250	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2251	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2252	Glib event loop).
		2253
		2254	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2255	and in a check watcher, destroy them and call into libadns. What follows
		2256	is pseudo-code only of course. This requires you to either use a low
		2257	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2258	the callbacks for the IO/timeout watchers might not have been called yet.
		2259
		2260	static ev_io iow [nfd];
		2261	static ev_timer tw;
		2262
		2263	static void
		2264	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2265	{
		2266	}
		2267
		2268	// create io watchers for each fd and a timer before blocking
		2269	static void
		2270	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2271	{
		2272	int timeout = 3600000;
		2273	struct pollfd fds [nfd];
		2274	// actual code will need to loop here and realloc etc.
		2275	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2276
		2277	/* the callback is illegal, but won't be called as we stop during check */
		2278	ev_timer_init (&tw, 0, timeout * 1e-3);
		2279	ev_timer_start (loop, &tw);
		2280
		2281	// create one ev_io per pollfd
		2282	for (int i = 0; i < nfd; ++i)
		2283	{
		2284	ev_io_init (iow + i, io_cb, fds [i].fd,
		2285	((fds [i].events & POLLIN ? EV_READ : 0)
		2286	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2287
		2288	fds [i].revents = 0;
		2289	ev_io_start (loop, iow + i);
		2290	}
		2291	}
		2292
		2293	// stop all watchers after blocking
		2294	static void
		2295	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2296	{
		2297	ev_timer_stop (loop, &tw);
		2298
		2299	for (int i = 0; i < nfd; ++i)
		2300	{
		2301	// set the relevant poll flags
		2302	// could also call adns_processreadable etc. here
		2303	struct pollfd *fd = fds + i;
		2304	int revents = ev_clear_pending (iow + i);
		2305	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2306	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2307
		2308	// now stop the watcher
		2309	ev_io_stop (loop, iow + i);
		2310	}
		2311
		2312	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2313	}
		2314
		2315	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2316	in the prepare watcher and would dispose of the check watcher.
		2317
		2318	Method 3: If the module to be embedded supports explicit event
		2319	notification (libadns does), you can also make use of the actual watcher
		2320	callbacks, and only destroy/create the watchers in the prepare watcher.
		2321
		2322	static void
		2323	timer_cb (EV_P_ ev_timer *w, int revents)
		2324	{
		2325	adns_state ads = (adns_state)w->data;
		2326	update_now (EV_A);
		2327
		2328	adns_processtimeouts (ads, &tv_now);
		2329	}
		2330
		2331	static void
		2332	io_cb (EV_P_ ev_io *w, int revents)
		2333	{
		2334	adns_state ads = (adns_state)w->data;
		2335	update_now (EV_A);
		2336
		2337	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2338	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2339	}
		2340
		2341	// do not ever call adns_afterpoll
		2342
		2343	Method 4: Do not use a prepare or check watcher because the module you
		2344	want to embed is not flexible enough to support it. Instead, you can
		2345	override their poll function. The drawback with this solution is that the
		2346	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2347	this approach, effectively embedding EV as a client into the horrible
		2348	libglib event loop.
		2349
		2350	static gint
		2351	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2352	{
		2353	int got_events = 0;
		2354
		2355	for (n = 0; n < nfds; ++n)
		2356	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2357
		2358	if (timeout >= 0)
		2359	// create/start timer
		2360
		2361	// poll
		2362	ev_loop (EV_A_ 0);
		2363
		2364	// stop timer again
		2365	if (timeout >= 0)
		2366	ev_timer_stop (EV_A_ &to);
		2367
		2368	// stop io watchers again - their callbacks should have set
		2369	for (n = 0; n < nfds; ++n)
		2370	ev_io_stop (EV_A_ iow [n]);
		2371
		2372	return got_events;
		2373	}
		2374
		2375
		2376	=head2 C<ev_embed> - when one backend isn't enough...
		2377
		2378	This is a rather advanced watcher type that lets you embed one event loop
		2379	into another (currently only C<ev_io> events are supported in the embedded
		2380	loop, other types of watchers might be handled in a delayed or incorrect
		2381	fashion and must not be used).
		2382
		2383	There are primarily two reasons you would want that: work around bugs and
		2384	prioritise I/O.
		2385
		2386	As an example for a bug workaround, the kqueue backend might only support
		2387	sockets on some platform, so it is unusable as generic backend, but you
		2388	still want to make use of it because you have many sockets and it scales
		2389	so nicely. In this case, you would create a kqueue-based loop and embed
		2390	it into your default loop (which might use e.g. poll). Overall operation
		2391	will be a bit slower because first libev has to call C<poll> and then
		2392	C<kevent>, but at least you can use both mechanisms for what they are
		2393	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2394
		2395	As for prioritising I/O: under rare circumstances you have the case where
		2396	some fds have to be watched and handled very quickly (with low latency),
		2397	and even priorities and idle watchers might have too much overhead. In
		2398	this case you would put all the high priority stuff in one loop and all
		2399	the rest in a second one, and embed the second one in the first.
		2400
		2401	As long as the watcher is active, the callback will be invoked every time
		2402	there might be events pending in the embedded loop. The callback must then
		2403	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2404	their callbacks (you could also start an idle watcher to give the embedded
		2405	loop strictly lower priority for example). You can also set the callback
		2406	to C<0>, in which case the embed watcher will automatically execute the
		2407	embedded loop sweep.
		2408
		2409	As long as the watcher is started it will automatically handle events. The
		2410	callback will be invoked whenever some events have been handled. You can
		2411	set the callback to C<0> to avoid having to specify one if you are not
		2412	interested in that.
		2413
		2414	Also, there have not currently been made special provisions for forking:
		2415	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2416	but you will also have to stop and restart any C<ev_embed> watchers
		2417	yourself - but you can use a fork watcher to handle this automatically,
		2418	and future versions of libev might do just that.
		2419
		2420	Unfortunately, not all backends are embeddable: only the ones returned by
		2421	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2422	portable one.
		2423
		2424	So when you want to use this feature you will always have to be prepared
		2425	that you cannot get an embeddable loop. The recommended way to get around
		2426	this is to have a separate variables for your embeddable loop, try to
		2427	create it, and if that fails, use the normal loop for everything.
		2428
		2429	=head3 C<ev_embed> and fork
		2430
		2431	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2432	automatically be applied to the embedded loop as well, so no special
		2433	fork handling is required in that case. When the watcher is not running,
		2434	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2435	as applicable.
		2436
		2437	=head3 Watcher-Specific Functions and Data Members
		2438
		2439	=over 4
		2440
		2441	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2442
		2443	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2444
		2445	Configures the watcher to embed the given loop, which must be
		2446	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2447	invoked automatically, otherwise it is the responsibility of the callback
		2448	to invoke it (it will continue to be called until the sweep has been done,
		2449	if you do not want that, you need to temporarily stop the embed watcher).
		2450
		2451	=item ev_embed_sweep (loop, ev_embed *)
		2452
		2453	Make a single, non-blocking sweep over the embedded loop. This works
		2454	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2455	appropriate way for embedded loops.
		2456
		2457	=item struct ev_loop *other [read-only]
		2458
		2459	The embedded event loop.
		2460
		2461	=back
		2462
		2463	=head3 Examples
		2464
		2465	Example: Try to get an embeddable event loop and embed it into the default
		2466	event loop. If that is not possible, use the default loop. The default
		2467	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2468	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2469	used).
		2470
		2471	struct ev_loop *loop_hi = ev_default_init (0);
		2472	struct ev_loop *loop_lo = 0;
		2473	ev_embed embed;
		2474
		2475	// see if there is a chance of getting one that works
		2476	// (remember that a flags value of 0 means autodetection)
		2477	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2478	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2479	: 0;
		2480
		2481	// if we got one, then embed it, otherwise default to loop_hi
		2482	if (loop_lo)
		2483	{
		2484	ev_embed_init (&embed, 0, loop_lo);
		2485	ev_embed_start (loop_hi, &embed);
		2486	}
		2487	else
		2488	loop_lo = loop_hi;
		2489
		2490	Example: Check if kqueue is available but not recommended and create
		2491	a kqueue backend for use with sockets (which usually work with any
		2492	kqueue implementation). Store the kqueue/socket-only event loop in
		2493	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2494
		2495	struct ev_loop *loop = ev_default_init (0);
		2496	struct ev_loop *loop_socket = 0;
		2497	ev_embed embed;
		2498
		2499	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2500	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2501	{
		2502	ev_embed_init (&embed, 0, loop_socket);
		2503	ev_embed_start (loop, &embed);
		2504	}
		2505
		2506	if (!loop_socket)
		2507	loop_socket = loop;
		2508
		2509	// now use loop_socket for all sockets, and loop for everything else
		2510
		2511
		2512	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2513
		2514	Fork watchers are called when a C<fork ()> was detected (usually because
		2515	whoever is a good citizen cared to tell libev about it by calling
		2516	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2517	event loop blocks next and before C<ev_check> watchers are being called,
		2518	and only in the child after the fork. If whoever good citizen calling
		2519	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2520	handlers will be invoked, too, of course.
		2521
		2522	=head3 Watcher-Specific Functions and Data Members
		2523
		2524	=over 4
		2525
		2526	=item ev_fork_init (ev_signal *, callback)
		2527
		2528	Initialises and configures the fork watcher - it has no parameters of any
		2529	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2530	believe me.
		2531
		2532	=back
		2533
		2534
		2535	=head2 C<ev_async> - how to wake up another event loop
		2536
		2537	In general, you cannot use an C<ev_loop> from multiple threads or other
		2538	asynchronous sources such as signal handlers (as opposed to multiple event
		2539	loops - those are of course safe to use in different threads).
		2540
		2541	Sometimes, however, you need to wake up another event loop you do not
		2542	control, for example because it belongs to another thread. This is what
		2543	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2544	can signal it by calling C<ev_async_send>, which is thread- and signal
		2545	safe.
		2546
		2547	This functionality is very similar to C<ev_signal> watchers, as signals,
		2548	too, are asynchronous in nature, and signals, too, will be compressed
		2549	(i.e. the number of callback invocations may be less than the number of
		2550	C<ev_async_sent> calls).
		2551
		2552	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2553	just the default loop.
		2554
		2555	=head3 Queueing
		2556
		2557	C<ev_async> does not support queueing of data in any way. The reason
		2558	is that the author does not know of a simple (or any) algorithm for a
		2559	multiple-writer-single-reader queue that works in all cases and doesn't
		2560	need elaborate support such as pthreads.
		2561
		2562	That means that if you want to queue data, you have to provide your own
		2563	queue. But at least I can tell you how to implement locking around your
		2564	queue:
		2565
		2566	=over 4
		2567
		2568	=item queueing from a signal handler context
		2569
		2570	To implement race-free queueing, you simply add to the queue in the signal
		2571	handler but you block the signal handler in the watcher callback. Here is
		2572	an example that does that for some fictitious SIGUSR1 handler:
		2573
		2574	static ev_async mysig;
		2575
		2576	static void
		2577	sigusr1_handler (void)
		2578	{
		2579	sometype data;
		2580
		2581	// no locking etc.
		2582	queue_put (data);
		2583	ev_async_send (EV_DEFAULT_ &mysig);
		2584	}
		2585
		2586	static void
		2587	mysig_cb (EV_P_ ev_async *w, int revents)
		2588	{
		2589	sometype data;
		2590	sigset_t block, prev;
		2591
		2592	sigemptyset (&block);
		2593	sigaddset (&block, SIGUSR1);
		2594	sigprocmask (SIG_BLOCK, &block, &prev);
		2595
		2596	while (queue_get (&data))
		2597	process (data);
		2598
		2599	if (sigismember (&prev, SIGUSR1)
		2600	sigprocmask (SIG_UNBLOCK, &block, 0);
		2601	}
		2602
		2603	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2604	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2605	either...).
		2606
		2607	=item queueing from a thread context
		2608
		2609	The strategy for threads is different, as you cannot (easily) block
		2610	threads but you can easily preempt them, so to queue safely you need to
		2611	employ a traditional mutex lock, such as in this pthread example:
		2612
		2613	static ev_async mysig;
		2614	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2615
		2616	static void
		2617	otherthread (void)
		2618	{
		2619	// only need to lock the actual queueing operation
		2620	pthread_mutex_lock (&mymutex);
		2621	queue_put (data);
		2622	pthread_mutex_unlock (&mymutex);
		2623
		2624	ev_async_send (EV_DEFAULT_ &mysig);
		2625	}
		2626
		2627	static void
		2628	mysig_cb (EV_P_ ev_async *w, int revents)
		2629	{
		2630	pthread_mutex_lock (&mymutex);
		2631
		2632	while (queue_get (&data))
		2633	process (data);
		2634
		2635	pthread_mutex_unlock (&mymutex);
		2636	}
		2637
		2638	=back
		2639
		2640
		2641	=head3 Watcher-Specific Functions and Data Members
		2642
		2643	=over 4
		2644
		2645	=item ev_async_init (ev_async *, callback)
		2646
		2647	Initialises and configures the async watcher - it has no parameters of any
		2648	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2649	trust me.
		2650
		2651	=item ev_async_send (loop, ev_async *)
		2652
		2653	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2654	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2655	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2656	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2657	section below on what exactly this means).
		2658
		2659	This call incurs the overhead of a system call only once per loop iteration,
		2660	so while the overhead might be noticeable, it doesn't apply to repeated
		2661	calls to C<ev_async_send>.
		2662
		2663	=item bool = ev_async_pending (ev_async *)
		2664
		2665	Returns a non-zero value when C<ev_async_send> has been called on the
		2666	watcher but the event has not yet been processed (or even noted) by the
		2667	event loop.
		2668
		2669	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2670	the loop iterates next and checks for the watcher to have become active,
		2671	it will reset the flag again. C<ev_async_pending> can be used to very
		2672	quickly check whether invoking the loop might be a good idea.
		2673
		2674	Not that this does I<not> check whether the watcher itself is pending, only
		2675	whether it has been requested to make this watcher pending.
		2676
		2677	=back
		2678
		2679
690	=head1 OTHER FUNCTIONS	2680	=head1 OTHER FUNCTIONS
691		2681
692	There are some other fucntions of possible interest. Described. Here. Now.	2682	There are some other functions of possible interest. Described. Here. Now.
693		2683
694	=over 4	2684	=over 4
695		2685
696	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2686	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
697		2687
698	This function combines a simple timer and an I/O watcher, calls your	2688	This function combines a simple timer and an I/O watcher, calls your
699	callback on whichever event happens first and automatically stop both	2689	callback on whichever event happens first and automatically stops both
700	watchers. This is useful if you want to wait for a single event on an fd	2690	watchers. This is useful if you want to wait for a single event on an fd
701	or timeout without havign to allocate/configure/start/stop/free one or	2691	or timeout without having to allocate/configure/start/stop/free one or
702	more watchers yourself.	2692	more watchers yourself.
703		2693
704	If C<fd> is less than 0, then no I/O watcher will be started and events is	2694	If C<fd> is less than 0, then no I/O watcher will be started and the
705	ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set	2695	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
706	will be craeted and started.	2696	the given C<fd> and C<events> set will be created and started.
707		2697
708	If C<timeout> is less than 0, then no timeout watcher will be	2698	If C<timeout> is less than 0, then no timeout watcher will be
709	started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat	2699	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
710	= 0) will be started.	2700	repeat = 0) will be started. C<0> is a valid timeout.
711		2701
712	The callback has the type C<void (*cb)(int revents, void *arg)> and	2702	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
713	gets passed an events set (normally a combination of EV_ERROR, EV_READ,	2703	passed an C<revents> set like normal event callbacks (a combination of
714	EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>:	2704	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
		2705	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2706	a timeout and an io event at the same time - you probably should give io
		2707	events precedence.
715		2708
		2709	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2710
716	static void stdin_ready (int revents, void *arg)	2711	static void stdin_ready (int revents, void *arg)
717	{	2712	{
718	if (revents & EV_TIMEOUT)
719	/* doh, nothing entered */
720	else if (revents & EV_READ)	2713	if (revents & EV_READ)
721	/* stdin might have data for us, joy! */	2714	/* stdin might have data for us, joy! */;
		2715	else if (revents & EV_TIMEOUT)
		2716	/* doh, nothing entered */;
722	}	2717	}
723		2718
724	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	2719	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
725		2720
726	=item ev_feed_event (loop, watcher, int events)	2721	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
727		2722
728	Feeds the given event set into the event loop, as if the specified event	2723	Feeds the given event set into the event loop, as if the specified event
729	has happened for the specified watcher (which must be a pointer to an	2724	had happened for the specified watcher (which must be a pointer to an
730	initialised but not necessarily active event watcher).	2725	initialised but not necessarily started event watcher).
731		2726
732	=item ev_feed_fd_event (loop, int fd, int revents)	2727	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
733		2728
734	Feed an event on the given fd, as if a file descriptor backend detected it.	2729	Feed an event on the given fd, as if a file descriptor backend detected
		2730	the given events it.
735		2731
736	=item ev_feed_signal_event (loop, int signum)	2732	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
737		2733
738	Feed an event as if the given signal occured (loop must be the default loop!).	2734	Feed an event as if the given signal occurred (C<loop> must be the default
		2735	loop!).
739		2736
740	=back	2737	=back
741		2738
		2739
		2740	=head1 LIBEVENT EMULATION
		2741
		2742	Libev offers a compatibility emulation layer for libevent. It cannot
		2743	emulate the internals of libevent, so here are some usage hints:
		2744
		2745	=over 4
		2746
		2747	=item * Use it by including <event.h>, as usual.
		2748
		2749	=item * The following members are fully supported: ev_base, ev_callback,
		2750	ev_arg, ev_fd, ev_res, ev_events.
		2751
		2752	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2753	maintained by libev, it does not work exactly the same way as in libevent (consider
		2754	it a private API).
		2755
		2756	=item * Priorities are not currently supported. Initialising priorities
		2757	will fail and all watchers will have the same priority, even though there
		2758	is an ev_pri field.
		2759
		2760	=item * In libevent, the last base created gets the signals, in libev, the
		2761	first base created (== the default loop) gets the signals.
		2762
		2763	=item * Other members are not supported.
		2764
		2765	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2766	to use the libev header file and library.
		2767
		2768	=back
		2769
		2770	=head1 C++ SUPPORT
		2771
		2772	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2773	you to use some convenience methods to start/stop watchers and also change
		2774	the callback model to a model using method callbacks on objects.
		2775
		2776	To use it,
		2777
		2778	#include <ev++.h>
		2779
		2780	This automatically includes F<ev.h> and puts all of its definitions (many
		2781	of them macros) into the global namespace. All C++ specific things are
		2782	put into the C<ev> namespace. It should support all the same embedding
		2783	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2784
		2785	Care has been taken to keep the overhead low. The only data member the C++
		2786	classes add (compared to plain C-style watchers) is the event loop pointer
		2787	that the watcher is associated with (or no additional members at all if
		2788	you disable C<EV_MULTIPLICITY> when embedding libev).
		2789
		2790	Currently, functions, and static and non-static member functions can be
		2791	used as callbacks. Other types should be easy to add as long as they only
		2792	need one additional pointer for context. If you need support for other
		2793	types of functors please contact the author (preferably after implementing
		2794	it).
		2795
		2796	Here is a list of things available in the C<ev> namespace:
		2797
		2798	=over 4
		2799
		2800	=item C<ev::READ>, C<ev::WRITE> etc.
		2801
		2802	These are just enum values with the same values as the C<EV_READ> etc.
		2803	macros from F<ev.h>.
		2804
		2805	=item C<ev::tstamp>, C<ev::now>
		2806
		2807	Aliases to the same types/functions as with the C<ev_> prefix.
		2808
		2809	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2810
		2811	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2812	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2813	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2814	defines by many implementations.
		2815
		2816	All of those classes have these methods:
		2817
		2818	=over 4
		2819
		2820	=item ev::TYPE::TYPE ()
		2821
		2822	=item ev::TYPE::TYPE (struct ev_loop *)
		2823
		2824	=item ev::TYPE::~TYPE
		2825
		2826	The constructor (optionally) takes an event loop to associate the watcher
		2827	with. If it is omitted, it will use C<EV_DEFAULT>.
		2828
		2829	The constructor calls C<ev_init> for you, which means you have to call the
		2830	C<set> method before starting it.
		2831
		2832	It will not set a callback, however: You have to call the templated C<set>
		2833	method to set a callback before you can start the watcher.
		2834
		2835	(The reason why you have to use a method is a limitation in C++ which does
		2836	not allow explicit template arguments for constructors).
		2837
		2838	The destructor automatically stops the watcher if it is active.
		2839
		2840	=item w->set<class, &class::method> (object *)
		2841
		2842	This method sets the callback method to call. The method has to have a
		2843	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2844	first argument and the C<revents> as second. The object must be given as
		2845	parameter and is stored in the C<data> member of the watcher.
		2846
		2847	This method synthesizes efficient thunking code to call your method from
		2848	the C callback that libev requires. If your compiler can inline your
		2849	callback (i.e. it is visible to it at the place of the C<set> call and
		2850	your compiler is good :), then the method will be fully inlined into the
		2851	thunking function, making it as fast as a direct C callback.
		2852
		2853	Example: simple class declaration and watcher initialisation
		2854
		2855	struct myclass
		2856	{
		2857	void io_cb (ev::io &w, int revents) { }
		2858	}
		2859
		2860	myclass obj;
		2861	ev::io iow;
		2862	iow.set <myclass, &myclass::io_cb> (&obj);
		2863
		2864	=item w->set<function> (void *data = 0)
		2865
		2866	Also sets a callback, but uses a static method or plain function as
		2867	callback. The optional C<data> argument will be stored in the watcher's
		2868	C<data> member and is free for you to use.
		2869
		2870	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2871
		2872	See the method-C<set> above for more details.
		2873
		2874	Example: Use a plain function as callback.
		2875
		2876	static void io_cb (ev::io &w, int revents) { }
		2877	iow.set <io_cb> ();
		2878
		2879	=item w->set (struct ev_loop *)
		2880
		2881	Associates a different C<struct ev_loop> with this watcher. You can only
		2882	do this when the watcher is inactive (and not pending either).
		2883
		2884	=item w->set ([arguments])
		2885
		2886	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2887	called at least once. Unlike the C counterpart, an active watcher gets
		2888	automatically stopped and restarted when reconfiguring it with this
		2889	method.
		2890
		2891	=item w->start ()
		2892
		2893	Starts the watcher. Note that there is no C<loop> argument, as the
		2894	constructor already stores the event loop.
		2895
		2896	=item w->stop ()
		2897
		2898	Stops the watcher if it is active. Again, no C<loop> argument.
		2899
		2900	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2901
		2902	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2903	C<ev_TYPE_again> function.
		2904
		2905	=item w->sweep () (C<ev::embed> only)
		2906
		2907	Invokes C<ev_embed_sweep>.
		2908
		2909	=item w->update () (C<ev::stat> only)
		2910
		2911	Invokes C<ev_stat_stat>.
		2912
		2913	=back
		2914
		2915	=back
		2916
		2917	Example: Define a class with an IO and idle watcher, start one of them in
		2918	the constructor.
		2919
		2920	class myclass
		2921	{
		2922	ev::io io ; void io_cb (ev::io &w, int revents);
		2923	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		2924
		2925	myclass (int fd)
		2926	{
		2927	io .set <myclass, &myclass::io_cb > (this);
		2928	idle.set <myclass, &myclass::idle_cb> (this);
		2929
		2930	io.start (fd, ev::READ);
		2931	}
		2932	};
		2933
		2934
		2935	=head1 OTHER LANGUAGE BINDINGS
		2936
		2937	Libev does not offer other language bindings itself, but bindings for a
		2938	number of languages exist in the form of third-party packages. If you know
		2939	any interesting language binding in addition to the ones listed here, drop
		2940	me a note.
		2941
		2942	=over 4
		2943
		2944	=item Perl
		2945
		2946	The EV module implements the full libev API and is actually used to test
		2947	libev. EV is developed together with libev. Apart from the EV core module,
		2948	there are additional modules that implement libev-compatible interfaces
		2949	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2950	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2951	and C<EV::Glib>).
		2952
		2953	It can be found and installed via CPAN, its homepage is at
		2954	L<http://software.schmorp.de/pkg/EV>.
		2955
		2956	=item Python
		2957
		2958	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2959	seems to be quite complete and well-documented. Note, however, that the
		2960	patch they require for libev is outright dangerous as it breaks the ABI
		2961	for everybody else, and therefore, should never be applied in an installed
		2962	libev (if python requires an incompatible ABI then it needs to embed
		2963	libev).
		2964
		2965	=item Ruby
		2966
		2967	Tony Arcieri has written a ruby extension that offers access to a subset
		2968	of the libev API and adds file handle abstractions, asynchronous DNS and
		2969	more on top of it. It can be found via gem servers. Its homepage is at
		2970	L<http://rev.rubyforge.org/>.
		2971
		2972	=item D
		2973
		2974	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2975	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2976
		2977	=item Ocaml
		2978
		2979	Erkki Seppala has written Ocaml bindings for libev, to be found at
		2980	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		2981
		2982	=back
		2983
		2984
		2985	=head1 MACRO MAGIC
		2986
		2987	Libev can be compiled with a variety of options, the most fundamental
		2988	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2989	functions and callbacks have an initial C<struct ev_loop *> argument.
		2990
		2991	To make it easier to write programs that cope with either variant, the
		2992	following macros are defined:
		2993
		2994	=over 4
		2995
		2996	=item C<EV_A>, C<EV_A_>
		2997
		2998	This provides the loop I<argument> for functions, if one is required ("ev
		2999	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3000	C<EV_A_> is used when other arguments are following. Example:
		3001
		3002	ev_unref (EV_A);
		3003	ev_timer_add (EV_A_ watcher);
		3004	ev_loop (EV_A_ 0);
		3005
		3006	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3007	which is often provided by the following macro.
		3008
		3009	=item C<EV_P>, C<EV_P_>
		3010
		3011	This provides the loop I<parameter> for functions, if one is required ("ev
		3012	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3013	C<EV_P_> is used when other parameters are following. Example:
		3014
		3015	// this is how ev_unref is being declared
		3016	static void ev_unref (EV_P);
		3017
		3018	// this is how you can declare your typical callback
		3019	static void cb (EV_P_ ev_timer *w, int revents)
		3020
		3021	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3022	suitable for use with C<EV_A>.
		3023
		3024	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3025
		3026	Similar to the other two macros, this gives you the value of the default
		3027	loop, if multiple loops are supported ("ev loop default").
		3028
		3029	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3030
		3031	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3032	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3033	is undefined when the default loop has not been initialised by a previous
		3034	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3035
		3036	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3037	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3038
		3039	=back
		3040
		3041	Example: Declare and initialise a check watcher, utilising the above
		3042	macros so it will work regardless of whether multiple loops are supported
		3043	or not.
		3044
		3045	static void
		3046	check_cb (EV_P_ ev_timer *w, int revents)
		3047	{
		3048	ev_check_stop (EV_A_ w);
		3049	}
		3050
		3051	ev_check check;
		3052	ev_check_init (&check, check_cb);
		3053	ev_check_start (EV_DEFAULT_ &check);
		3054	ev_loop (EV_DEFAULT_ 0);
		3055
		3056	=head1 EMBEDDING
		3057
		3058	Libev can (and often is) directly embedded into host
		3059	applications. Examples of applications that embed it include the Deliantra
		3060	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3061	and rxvt-unicode.
		3062
		3063	The goal is to enable you to just copy the necessary files into your
		3064	source directory without having to change even a single line in them, so
		3065	you can easily upgrade by simply copying (or having a checked-out copy of
		3066	libev somewhere in your source tree).
		3067
		3068	=head2 FILESETS
		3069
		3070	Depending on what features you need you need to include one or more sets of files
		3071	in your application.
		3072
		3073	=head3 CORE EVENT LOOP
		3074
		3075	To include only the libev core (all the C<ev_*> functions), with manual
		3076	configuration (no autoconf):
		3077
		3078	#define EV_STANDALONE 1
		3079	#include "ev.c"
		3080
		3081	This will automatically include F<ev.h>, too, and should be done in a
		3082	single C source file only to provide the function implementations. To use
		3083	it, do the same for F<ev.h> in all files wishing to use this API (best
		3084	done by writing a wrapper around F<ev.h> that you can include instead and
		3085	where you can put other configuration options):
		3086
		3087	#define EV_STANDALONE 1
		3088	#include "ev.h"
		3089
		3090	Both header files and implementation files can be compiled with a C++
		3091	compiler (at least, thats a stated goal, and breakage will be treated
		3092	as a bug).
		3093
		3094	You need the following files in your source tree, or in a directory
		3095	in your include path (e.g. in libev/ when using -Ilibev):
		3096
		3097	ev.h
		3098	ev.c
		3099	ev_vars.h
		3100	ev_wrap.h
		3101
		3102	ev_win32.c required on win32 platforms only
		3103
		3104	ev_select.c only when select backend is enabled (which is enabled by default)
		3105	ev_poll.c only when poll backend is enabled (disabled by default)
		3106	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3107	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3108	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3109
		3110	F<ev.c> includes the backend files directly when enabled, so you only need
		3111	to compile this single file.
		3112
		3113	=head3 LIBEVENT COMPATIBILITY API
		3114
		3115	To include the libevent compatibility API, also include:
		3116
		3117	#include "event.c"
		3118
		3119	in the file including F<ev.c>, and:
		3120
		3121	#include "event.h"
		3122
		3123	in the files that want to use the libevent API. This also includes F<ev.h>.
		3124
		3125	You need the following additional files for this:
		3126
		3127	event.h
		3128	event.c
		3129
		3130	=head3 AUTOCONF SUPPORT
		3131
		3132	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3133	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3134	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3135	include F<config.h> and configure itself accordingly.
		3136
		3137	For this of course you need the m4 file:
		3138
		3139	libev.m4
		3140
		3141	=head2 PREPROCESSOR SYMBOLS/MACROS
		3142
		3143	Libev can be configured via a variety of preprocessor symbols you have to
		3144	define before including any of its files. The default in the absence of
		3145	autoconf is documented for every option.
		3146
		3147	=over 4
		3148
		3149	=item EV_STANDALONE
		3150
		3151	Must always be C<1> if you do not use autoconf configuration, which
		3152	keeps libev from including F<config.h>, and it also defines dummy
		3153	implementations for some libevent functions (such as logging, which is not
		3154	supported). It will also not define any of the structs usually found in
		3155	F<event.h> that are not directly supported by the libev core alone.
		3156
		3157	=item EV_USE_MONOTONIC
		3158
		3159	If defined to be C<1>, libev will try to detect the availability of the
		3160	monotonic clock option at both compile time and runtime. Otherwise no use
		3161	of the monotonic clock option will be attempted. If you enable this, you
		3162	usually have to link against librt or something similar. Enabling it when
		3163	the functionality isn't available is safe, though, although you have
		3164	to make sure you link against any libraries where the C<clock_gettime>
		3165	function is hiding in (often F<-lrt>).
		3166
		3167	=item EV_USE_REALTIME
		3168
		3169	If defined to be C<1>, libev will try to detect the availability of the
		3170	real-time clock option at compile time (and assume its availability at
		3171	runtime if successful). Otherwise no use of the real-time clock option will
		3172	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		3173	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		3174	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		3175
		3176	=item EV_USE_NANOSLEEP
		3177
		3178	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3179	and will use it for delays. Otherwise it will use C<select ()>.
		3180
		3181	=item EV_USE_EVENTFD
		3182
		3183	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3184	available and will probe for kernel support at runtime. This will improve
		3185	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3186	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3187	2.7 or newer, otherwise disabled.
		3188
		3189	=item EV_USE_SELECT
		3190
		3191	If undefined or defined to be C<1>, libev will compile in support for the
		3192	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3193	other method takes over, select will be it. Otherwise the select backend
		3194	will not be compiled in.
		3195
		3196	=item EV_SELECT_USE_FD_SET
		3197
		3198	If defined to C<1>, then the select backend will use the system C<fd_set>
		3199	structure. This is useful if libev doesn't compile due to a missing
		3200	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		3201	exotic systems. This usually limits the range of file descriptors to some
		3202	low limit such as 1024 or might have other limitations (winsocket only
		3203	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		3204	influence the size of the C<fd_set> used.
		3205
		3206	=item EV_SELECT_IS_WINSOCKET
		3207
		3208	When defined to C<1>, the select backend will assume that
		3209	select/socket/connect etc. don't understand file descriptors but
		3210	wants osf handles on win32 (this is the case when the select to
		3211	be used is the winsock select). This means that it will call
		3212	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3213	it is assumed that all these functions actually work on fds, even
		3214	on win32. Should not be defined on non-win32 platforms.
		3215
		3216	=item EV_FD_TO_WIN32_HANDLE
		3217
		3218	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3219	file descriptors to socket handles. When not defining this symbol (the
		3220	default), then libev will call C<_get_osfhandle>, which is usually
		3221	correct. In some cases, programs use their own file descriptor management,
		3222	in which case they can provide this function to map fds to socket handles.
		3223
		3224	=item EV_USE_POLL
		3225
		3226	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3227	backend. Otherwise it will be enabled on non-win32 platforms. It
		3228	takes precedence over select.
		3229
		3230	=item EV_USE_EPOLL
		3231
		3232	If defined to be C<1>, libev will compile in support for the Linux
		3233	C<epoll>(7) backend. Its availability will be detected at runtime,
		3234	otherwise another method will be used as fallback. This is the preferred
		3235	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3236	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3237
		3238	=item EV_USE_KQUEUE
		3239
		3240	If defined to be C<1>, libev will compile in support for the BSD style
		3241	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3242	otherwise another method will be used as fallback. This is the preferred
		3243	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3244	supports some types of fds correctly (the only platform we found that
		3245	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3246	not be used unless explicitly requested. The best way to use it is to find
		3247	out whether kqueue supports your type of fd properly and use an embedded
		3248	kqueue loop.
		3249
		3250	=item EV_USE_PORT
		3251
		3252	If defined to be C<1>, libev will compile in support for the Solaris
		3253	10 port style backend. Its availability will be detected at runtime,
		3254	otherwise another method will be used as fallback. This is the preferred
		3255	backend for Solaris 10 systems.
		3256
		3257	=item EV_USE_DEVPOLL
		3258
		3259	Reserved for future expansion, works like the USE symbols above.
		3260
		3261	=item EV_USE_INOTIFY
		3262
		3263	If defined to be C<1>, libev will compile in support for the Linux inotify
		3264	interface to speed up C<ev_stat> watchers. Its actual availability will
		3265	be detected at runtime. If undefined, it will be enabled if the headers
		3266	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3267
		3268	=item EV_ATOMIC_T
		3269
		3270	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3271	access is atomic with respect to other threads or signal contexts. No such
		3272	type is easily found in the C language, so you can provide your own type
		3273	that you know is safe for your purposes. It is used both for signal handler "locking"
		3274	as well as for signal and thread safety in C<ev_async> watchers.
		3275
		3276	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3277	(from F<signal.h>), which is usually good enough on most platforms.
		3278
		3279	=item EV_H
		3280
		3281	The name of the F<ev.h> header file used to include it. The default if
		3282	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3283	used to virtually rename the F<ev.h> header file in case of conflicts.
		3284
		3285	=item EV_CONFIG_H
		3286
		3287	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3288	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3289	C<EV_H>, above.
		3290
		3291	=item EV_EVENT_H
		3292
		3293	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3294	of how the F<event.h> header can be found, the default is C<"event.h">.
		3295
		3296	=item EV_PROTOTYPES
		3297
		3298	If defined to be C<0>, then F<ev.h> will not define any function
		3299	prototypes, but still define all the structs and other symbols. This is
		3300	occasionally useful if you want to provide your own wrapper functions
		3301	around libev functions.
		3302
		3303	=item EV_MULTIPLICITY
		3304
		3305	If undefined or defined to C<1>, then all event-loop-specific functions
		3306	will have the C<struct ev_loop *> as first argument, and you can create
		3307	additional independent event loops. Otherwise there will be no support
		3308	for multiple event loops and there is no first event loop pointer
		3309	argument. Instead, all functions act on the single default loop.
		3310
		3311	=item EV_MINPRI
		3312
		3313	=item EV_MAXPRI
		3314
		3315	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3316	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3317	provide for more priorities by overriding those symbols (usually defined
		3318	to be C<-2> and C<2>, respectively).
		3319
		3320	When doing priority-based operations, libev usually has to linearly search
		3321	all the priorities, so having many of them (hundreds) uses a lot of space
		3322	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3323	fine.
		3324
		3325	If your embedding application does not need any priorities, defining these
		3326	both to C<0> will save some memory and CPU.
		3327
		3328	=item EV_PERIODIC_ENABLE
		3329
		3330	If undefined or defined to be C<1>, then periodic timers are supported. If
		3331	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3332	code.
		3333
		3334	=item EV_IDLE_ENABLE
		3335
		3336	If undefined or defined to be C<1>, then idle watchers are supported. If
		3337	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3338	code.
		3339
		3340	=item EV_EMBED_ENABLE
		3341
		3342	If undefined or defined to be C<1>, then embed watchers are supported. If
		3343	defined to be C<0>, then they are not. Embed watchers rely on most other
		3344	watcher types, which therefore must not be disabled.
		3345
		3346	=item EV_STAT_ENABLE
		3347
		3348	If undefined or defined to be C<1>, then stat watchers are supported. If
		3349	defined to be C<0>, then they are not.
		3350
		3351	=item EV_FORK_ENABLE
		3352
		3353	If undefined or defined to be C<1>, then fork watchers are supported. If
		3354	defined to be C<0>, then they are not.
		3355
		3356	=item EV_ASYNC_ENABLE
		3357
		3358	If undefined or defined to be C<1>, then async watchers are supported. If
		3359	defined to be C<0>, then they are not.
		3360
		3361	=item EV_MINIMAL
		3362
		3363	If you need to shave off some kilobytes of code at the expense of some
		3364	speed, define this symbol to C<1>. Currently this is used to override some
		3365	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3366	much smaller 2-heap for timer management over the default 4-heap.
		3367
		3368	=item EV_PID_HASHSIZE
		3369
		3370	C<ev_child> watchers use a small hash table to distribute workload by
		3371	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3372	than enough. If you need to manage thousands of children you might want to
		3373	increase this value (I<must> be a power of two).
		3374
		3375	=item EV_INOTIFY_HASHSIZE
		3376
		3377	C<ev_stat> watchers use a small hash table to distribute workload by
		3378	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3379	usually more than enough. If you need to manage thousands of C<ev_stat>
		3380	watchers you might want to increase this value (I<must> be a power of
		3381	two).
		3382
		3383	=item EV_USE_4HEAP
		3384
		3385	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3386	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3387	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3388	faster performance with many (thousands) of watchers.
		3389
		3390	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3391	(disabled).
		3392
		3393	=item EV_HEAP_CACHE_AT
		3394
		3395	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3396	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3397	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3398	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3399	but avoids random read accesses on heap changes. This improves performance
		3400	noticeably with many (hundreds) of watchers.
		3401
		3402	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3403	(disabled).
		3404
		3405	=item EV_VERIFY
		3406
		3407	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3408	be done: If set to C<0>, no internal verification code will be compiled
		3409	in. If set to C<1>, then verification code will be compiled in, but not
		3410	called. If set to C<2>, then the internal verification code will be
		3411	called once per loop, which can slow down libev. If set to C<3>, then the
		3412	verification code will be called very frequently, which will slow down
		3413	libev considerably.
		3414
		3415	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3416	C<0>.
		3417
		3418	=item EV_COMMON
		3419
		3420	By default, all watchers have a C<void *data> member. By redefining
		3421	this macro to a something else you can include more and other types of
		3422	members. You have to define it each time you include one of the files,
		3423	though, and it must be identical each time.
		3424
		3425	For example, the perl EV module uses something like this:
		3426
		3427	#define EV_COMMON \
		3428	SV *self; /* contains this struct */ \
		3429	SV *cb_sv, *fh /* note no trailing ";" */
		3430
		3431	=item EV_CB_DECLARE (type)
		3432
		3433	=item EV_CB_INVOKE (watcher, revents)
		3434
		3435	=item ev_set_cb (ev, cb)
		3436
		3437	Can be used to change the callback member declaration in each watcher,
		3438	and the way callbacks are invoked and set. Must expand to a struct member
		3439	definition and a statement, respectively. See the F<ev.h> header file for
		3440	their default definitions. One possible use for overriding these is to
		3441	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3442	method calls instead of plain function calls in C++.
		3443
		3444	=back
		3445
		3446	=head2 EXPORTED API SYMBOLS
		3447
		3448	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3449	exported symbols, you can use the provided F<Symbol.*> files which list
		3450	all public symbols, one per line:
		3451
		3452	Symbols.ev for libev proper
		3453	Symbols.event for the libevent emulation
		3454
		3455	This can also be used to rename all public symbols to avoid clashes with
		3456	multiple versions of libev linked together (which is obviously bad in
		3457	itself, but sometimes it is inconvenient to avoid this).
		3458
		3459	A sed command like this will create wrapper C<#define>'s that you need to
		3460	include before including F<ev.h>:
		3461
		3462	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3463
		3464	This would create a file F<wrap.h> which essentially looks like this:
		3465
		3466	#define ev_backend myprefix_ev_backend
		3467	#define ev_check_start myprefix_ev_check_start
		3468	#define ev_check_stop myprefix_ev_check_stop
		3469	...
		3470
		3471	=head2 EXAMPLES
		3472
		3473	For a real-world example of a program the includes libev
		3474	verbatim, you can have a look at the EV perl module
		3475	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3476	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3477	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3478	will be compiled. It is pretty complex because it provides its own header
		3479	file.
		3480
		3481	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3482	that everybody includes and which overrides some configure choices:
		3483
		3484	#define EV_MINIMAL 1
		3485	#define EV_USE_POLL 0
		3486	#define EV_MULTIPLICITY 0
		3487	#define EV_PERIODIC_ENABLE 0
		3488	#define EV_STAT_ENABLE 0
		3489	#define EV_FORK_ENABLE 0
		3490	#define EV_CONFIG_H <config.h>
		3491	#define EV_MINPRI 0
		3492	#define EV_MAXPRI 0
		3493
		3494	#include "ev++.h"
		3495
		3496	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3497
		3498	#include "ev_cpp.h"
		3499	#include "ev.c"
		3500
		3501	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3502
		3503	=head2 THREADS AND COROUTINES
		3504
		3505	=head3 THREADS
		3506
		3507	All libev functions are reentrant and thread-safe unless explicitly
		3508	documented otherwise, but libev implements no locking itself. This means
		3509	that you can use as many loops as you want in parallel, as long as there
		3510	are no concurrent calls into any libev function with the same loop
		3511	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3512	of course): libev guarantees that different event loops share no data
		3513	structures that need any locking.
		3514
		3515	Or to put it differently: calls with different loop parameters can be done
		3516	concurrently from multiple threads, calls with the same loop parameter
		3517	must be done serially (but can be done from different threads, as long as
		3518	only one thread ever is inside a call at any point in time, e.g. by using
		3519	a mutex per loop).
		3520
		3521	Specifically to support threads (and signal handlers), libev implements
		3522	so-called C<ev_async> watchers, which allow some limited form of
		3523	concurrency on the same event loop, namely waking it up "from the
		3524	outside".
		3525
		3526	If you want to know which design (one loop, locking, or multiple loops
		3527	without or something else still) is best for your problem, then I cannot
		3528	help you, but here is some generic advice:
		3529
		3530	=over 4
		3531
		3532	=item * most applications have a main thread: use the default libev loop
		3533	in that thread, or create a separate thread running only the default loop.
		3534
		3535	This helps integrating other libraries or software modules that use libev
		3536	themselves and don't care/know about threading.
		3537
		3538	=item * one loop per thread is usually a good model.
		3539
		3540	Doing this is almost never wrong, sometimes a better-performance model
		3541	exists, but it is always a good start.
		3542
		3543	=item * other models exist, such as the leader/follower pattern, where one
		3544	loop is handed through multiple threads in a kind of round-robin fashion.
		3545
		3546	Choosing a model is hard - look around, learn, know that usually you can do
		3547	better than you currently do :-)
		3548
		3549	=item * often you need to talk to some other thread which blocks in the
		3550	event loop.
		3551
		3552	C<ev_async> watchers can be used to wake them up from other threads safely
		3553	(or from signal contexts...).
		3554
		3555	An example use would be to communicate signals or other events that only
		3556	work in the default loop by registering the signal watcher with the
		3557	default loop and triggering an C<ev_async> watcher from the default loop
		3558	watcher callback into the event loop interested in the signal.
		3559
		3560	=back
		3561
		3562	=head3 COROUTINES
		3563
		3564	Libev is very accommodating to coroutines ("cooperative threads"):
		3565	libev fully supports nesting calls to its functions from different
		3566	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3567	different coroutines, and switch freely between both coroutines running the
		3568	loop, as long as you don't confuse yourself). The only exception is that
		3569	you must not do this from C<ev_periodic> reschedule callbacks.
		3570
		3571	Care has been taken to ensure that libev does not keep local state inside
		3572	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3573	they do not clal any callbacks.
		3574
		3575	=head2 COMPILER WARNINGS
		3576
		3577	Depending on your compiler and compiler settings, you might get no or a
		3578	lot of warnings when compiling libev code. Some people are apparently
		3579	scared by this.
		3580
		3581	However, these are unavoidable for many reasons. For one, each compiler
		3582	has different warnings, and each user has different tastes regarding
		3583	warning options. "Warn-free" code therefore cannot be a goal except when
		3584	targeting a specific compiler and compiler-version.
		3585
		3586	Another reason is that some compiler warnings require elaborate
		3587	workarounds, or other changes to the code that make it less clear and less
		3588	maintainable.
		3589
		3590	And of course, some compiler warnings are just plain stupid, or simply
		3591	wrong (because they don't actually warn about the condition their message
		3592	seems to warn about). For example, certain older gcc versions had some
		3593	warnings that resulted an extreme number of false positives. These have
		3594	been fixed, but some people still insist on making code warn-free with
		3595	such buggy versions.
		3596
		3597	While libev is written to generate as few warnings as possible,
		3598	"warn-free" code is not a goal, and it is recommended not to build libev
		3599	with any compiler warnings enabled unless you are prepared to cope with
		3600	them (e.g. by ignoring them). Remember that warnings are just that:
		3601	warnings, not errors, or proof of bugs.
		3602
		3603
		3604	=head2 VALGRIND
		3605
		3606	Valgrind has a special section here because it is a popular tool that is
		3607	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3608
		3609	If you think you found a bug (memory leak, uninitialised data access etc.)
		3610	in libev, then check twice: If valgrind reports something like:
		3611
		3612	==2274== definitely lost: 0 bytes in 0 blocks.
		3613	==2274== possibly lost: 0 bytes in 0 blocks.
		3614	==2274== still reachable: 256 bytes in 1 blocks.
		3615
		3616	Then there is no memory leak, just as memory accounted to global variables
		3617	is not a memleak - the memory is still being refernced, and didn't leak.
		3618
		3619	Similarly, under some circumstances, valgrind might report kernel bugs
		3620	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3621	although an acceptable workaround has been found here), or it might be
		3622	confused.
		3623
		3624	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3625	make it into some kind of religion.
		3626
		3627	If you are unsure about something, feel free to contact the mailing list
		3628	with the full valgrind report and an explanation on why you think this
		3629	is a bug in libev (best check the archives, too :). However, don't be
		3630	annoyed when you get a brisk "this is no bug" answer and take the chance
		3631	of learning how to interpret valgrind properly.
		3632
		3633	If you need, for some reason, empty reports from valgrind for your project
		3634	I suggest using suppression lists.
		3635
		3636
		3637	=head1 PORTABILITY NOTES
		3638
		3639	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3640
		3641	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3642	requires, and its I/O model is fundamentally incompatible with the POSIX
		3643	model. Libev still offers limited functionality on this platform in
		3644	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3645	descriptors. This only applies when using Win32 natively, not when using
		3646	e.g. cygwin.
		3647
		3648	Lifting these limitations would basically require the full
		3649	re-implementation of the I/O system. If you are into these kinds of
		3650	things, then note that glib does exactly that for you in a very portable
		3651	way (note also that glib is the slowest event library known to man).
		3652
		3653	There is no supported compilation method available on windows except
		3654	embedding it into other applications.
		3655
		3656	Not a libev limitation but worth mentioning: windows apparently doesn't
		3657	accept large writes: instead of resulting in a partial write, windows will
		3658	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3659	so make sure you only write small amounts into your sockets (less than a
		3660	megabyte seems safe, but this apparently depends on the amount of memory
		3661	available).
		3662
		3663	Due to the many, low, and arbitrary limits on the win32 platform and
		3664	the abysmal performance of winsockets, using a large number of sockets
		3665	is not recommended (and not reasonable). If your program needs to use
		3666	more than a hundred or so sockets, then likely it needs to use a totally
		3667	different implementation for windows, as libev offers the POSIX readiness
		3668	notification model, which cannot be implemented efficiently on windows
		3669	(Microsoft monopoly games).
		3670
		3671	A typical way to use libev under windows is to embed it (see the embedding
		3672	section for details) and use the following F<evwrap.h> header file instead
		3673	of F<ev.h>:
		3674
		3675	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3676	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3677
		3678	#include "ev.h"
		3679
		3680	And compile the following F<evwrap.c> file into your project (make sure
		3681	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3682
		3683	#include "evwrap.h"
		3684	#include "ev.c"
		3685
		3686	=over 4
		3687
		3688	=item The winsocket select function
		3689
		3690	The winsocket C<select> function doesn't follow POSIX in that it
		3691	requires socket I<handles> and not socket I<file descriptors> (it is
		3692	also extremely buggy). This makes select very inefficient, and also
		3693	requires a mapping from file descriptors to socket handles (the Microsoft
		3694	C runtime provides the function C<_open_osfhandle> for this). See the
		3695	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3696	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3697
		3698	The configuration for a "naked" win32 using the Microsoft runtime
		3699	libraries and raw winsocket select is:
		3700
		3701	#define EV_USE_SELECT 1
		3702	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3703
		3704	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3705	complexity in the O(n²) range when using win32.
		3706
		3707	=item Limited number of file descriptors
		3708
		3709	Windows has numerous arbitrary (and low) limits on things.
		3710
		3711	Early versions of winsocket's select only supported waiting for a maximum
		3712	of C<64> handles (probably owning to the fact that all windows kernels
		3713	can only wait for C<64> things at the same time internally; Microsoft
		3714	recommends spawning a chain of threads and wait for 63 handles and the
		3715	previous thread in each. Great).
		3716
		3717	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3718	to some high number (e.g. C<2048>) before compiling the winsocket select
		3719	call (which might be in libev or elsewhere, for example, perl does its own
		3720	select emulation on windows).
		3721
		3722	Another limit is the number of file descriptors in the Microsoft runtime
		3723	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3724	or something like this inside Microsoft). You can increase this by calling
		3725	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3726	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3727	libraries.
		3728
		3729	This might get you to about C<512> or C<2048> sockets (depending on
		3730	windows version and/or the phase of the moon). To get more, you need to
		3731	wrap all I/O functions and provide your own fd management, but the cost of
		3732	calling select (O(n²)) will likely make this unworkable.
		3733
		3734	=back
		3735
		3736	=head2 PORTABILITY REQUIREMENTS
		3737
		3738	In addition to a working ISO-C implementation and of course the
		3739	backend-specific APIs, libev relies on a few additional extensions:
		3740
		3741	=over 4
		3742
		3743	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3744	calling conventions regardless of C<ev_watcher_type *>.
		3745
		3746	Libev assumes not only that all watcher pointers have the same internal
		3747	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3748	assumes that the same (machine) code can be used to call any watcher
		3749	callback: The watcher callbacks have different type signatures, but libev
		3750	calls them using an C<ev_watcher *> internally.
		3751
		3752	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3753
		3754	The type C<sig_atomic_t volatile> (or whatever is defined as
		3755	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3756	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3757	believed to be sufficiently portable.
		3758
		3759	=item C<sigprocmask> must work in a threaded environment
		3760
		3761	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3762	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3763	pthread implementations will either allow C<sigprocmask> in the "main
		3764	thread" or will block signals process-wide, both behaviours would
		3765	be compatible with libev. Interaction between C<sigprocmask> and
		3766	C<pthread_sigmask> could complicate things, however.
		3767
		3768	The most portable way to handle signals is to block signals in all threads
		3769	except the initial one, and run the default loop in the initial thread as
		3770	well.
		3771
		3772	=item C<long> must be large enough for common memory allocation sizes
		3773
		3774	To improve portability and simplify its API, libev uses C<long> internally
		3775	instead of C<size_t> when allocating its data structures. On non-POSIX
		3776	systems (Microsoft...) this might be unexpectedly low, but is still at
		3777	least 31 bits everywhere, which is enough for hundreds of millions of
		3778	watchers.
		3779
		3780	=item C<double> must hold a time value in seconds with enough accuracy
		3781
		3782	The type C<double> is used to represent timestamps. It is required to
		3783	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3784	enough for at least into the year 4000. This requirement is fulfilled by
		3785	implementations implementing IEEE 754 (basically all existing ones).
		3786
		3787	=back
		3788
		3789	If you know of other additional requirements drop me a note.
		3790
		3791
		3792	=head1 ALGORITHMIC COMPLEXITIES
		3793
		3794	In this section the complexities of (many of) the algorithms used inside
		3795	libev will be documented. For complexity discussions about backends see
		3796	the documentation for C<ev_default_init>.
		3797
		3798	All of the following are about amortised time: If an array needs to be
		3799	extended, libev needs to realloc and move the whole array, but this
		3800	happens asymptotically rarer with higher number of elements, so O(1) might
		3801	mean that libev does a lengthy realloc operation in rare cases, but on
		3802	average it is much faster and asymptotically approaches constant time.
		3803
		3804	=over 4
		3805
		3806	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3807
		3808	This means that, when you have a watcher that triggers in one hour and
		3809	there are 100 watchers that would trigger before that, then inserting will
		3810	have to skip roughly seven (C<ld 100>) of these watchers.
		3811
		3812	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3813
		3814	That means that changing a timer costs less than removing/adding them,
		3815	as only the relative motion in the event queue has to be paid for.
		3816
		3817	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3818
		3819	These just add the watcher into an array or at the head of a list.
		3820
		3821	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3822
		3823	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3824
		3825	These watchers are stored in lists, so they need to be walked to find the
		3826	correct watcher to remove. The lists are usually short (you don't usually
		3827	have many watchers waiting for the same fd or signal: one is typical, two
		3828	is rare).
		3829
		3830	=item Finding the next timer in each loop iteration: O(1)
		3831
		3832	By virtue of using a binary or 4-heap, the next timer is always found at a
		3833	fixed position in the storage array.
		3834
		3835	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3836
		3837	A change means an I/O watcher gets started or stopped, which requires
		3838	libev to recalculate its status (and possibly tell the kernel, depending
		3839	on backend and whether C<ev_io_set> was used).
		3840
		3841	=item Activating one watcher (putting it into the pending state): O(1)
		3842
		3843	=item Priority handling: O(number_of_priorities)
		3844
		3845	Priorities are implemented by allocating some space for each
		3846	priority. When doing priority-based operations, libev usually has to
		3847	linearly search all the priorities, but starting/stopping and activating
		3848	watchers becomes O(1) with respect to priority handling.
		3849
		3850	=item Sending an ev_async: O(1)
		3851
		3852	=item Processing ev_async_send: O(number_of_async_watchers)
		3853
		3854	=item Processing signals: O(max_signal_number)
		3855
		3856	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3857	calls in the current loop iteration. Checking for async and signal events
		3858	involves iterating over all running async watchers or all signal numbers.
		3859
		3860	=back
		3861
		3862
742	=head1 AUTHOR	3863	=head1 AUTHOR
743		3864
744	Marc Lehmann <libev@schmorp.de>.	3865	Marc Lehmann <libev@schmorp.de>.
745		3866

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