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Revision 1.8 by root, Mon Nov 12 08:20:02 2007 UTC vs.
Revision 1.183 by root, Tue Sep 23 08:37:38 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_ struct ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	struct ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
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<struct ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	117	to the C<double> type in C, and when you need to do any calculations on
		118	it, you should treat it as some 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))
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));
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 library knows two
100	types of such loops, the I<default> loop, which supports signals and child	282	types of such loops, the I<default> loop, which supports signals and child
101	events, and dynamically created loops which do not.	283	events, and dynamically created loops which do not.
102		284
103	If you use threads, a common model is to run the default event loop
104	in your main thread (or in a separate thrad) and for each thread you
105	create, you also create another event loop. Libev itself does no locking
106	whatsoever, so if you mix calls to the same event loop in different
107	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because its hideous and inefficient).
109
110	=over 4	285	=over 4
111		286
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	287	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		288
114	This will initialise the default event loop if it hasn't been initialised	289	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	290	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	291	false. If it already was initialised it simply returns it (and ignores the
117	flags).	292	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		293
119	If you don't know what event loop to use, use the one returned from this	294	If you don't know what event loop to use, use the one returned from this
120	function.	295	function.
121		296
		297	Note that this function is I<not> thread-safe, so if you want to use it
		298	from multiple threads, you have to lock (note also that this is unlikely,
		299	as loops cannot bes hared easily between threads anyway).
		300
		301	The default loop is the only loop that can handle C<ev_signal> and
		302	C<ev_child> watchers, and to do this, it always registers a handler
		303	for C<SIGCHLD>. If this is a problem for your application you can either
		304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		306	C<ev_default_init>.
		307
122	The flags argument can be used to specify special behaviour or specific	308	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).	309	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		310
125	It supports the following flags:	311	The following flags are supported:
126		312
127	=over 4	313	=over 4
128		314
129	=item EVFLAG_AUTO	315	=item C<EVFLAG_AUTO>
130		316
131	The default flags value. Use this if you have no clue (its the right	317	The default flags value. Use this if you have no clue (it's the right
132	thing, believe me).	318	thing, believe me).
133		319
134	=item EVFLAG_NOENV	320	=item C<EVFLAG_NOENV>
135		321
136	If this flag bit is ored into the flag value (or the program runs setuid	322	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	323	or setgid) then libev will I<not> look at the environment variable
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	325	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	326	useful to try out specific backends to test their performance, or to work
141	around bugs.	327	around bugs.
142		328
		329	=item C<EVFLAG_FORKCHECK>
		330
		331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		332	a fork, you can also make libev check for a fork in each iteration by
		333	enabling this flag.
		334
		335	This works by calling C<getpid ()> on every iteration of the loop,
		336	and thus this might slow down your event loop if you do a lot of loop
		337	iterations and little real work, but is usually not noticeable (on my
		338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		339	without a system call and thus I<very> fast, but my GNU/Linux system also has
		340	C<pthread_atfork> which is even faster).
		341
		342	The big advantage of this flag is that you can forget about fork (and
		343	forget about forgetting to tell libev about forking) when you use this
		344	flag.
		345
		346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		347	environment variable.
		348
143	=item EVMETHOD_SELECT portable select backend	349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		350
145	=item EVMETHOD_POLL poll backend (everywhere except windows)	351	This is your standard select(2) backend. Not I<completely> standard, as
		352	libev tries to roll its own fd_set with no limits on the number of fds,
		353	but if that fails, expect a fairly low limit on the number of fds when
		354	using this backend. It doesn't scale too well (O(highest_fd)), but its
		355	usually the fastest backend for a low number of (low-numbered :) fds.
146		356
147	=item EVMETHOD_EPOLL linux only	357	To get good performance out of this backend you need a high amount of
		358	parallelism (most of the file descriptors should be busy). If you are
		359	writing a server, you should C<accept ()> in a loop to accept as many
		360	connections as possible during one iteration. You might also want to have
		361	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		362	readiness notifications you get per iteration.
148		363
149	=item EVMETHOD_KQUEUE some bsds only	364	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		365	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		366	C<exceptfds> set on that platform).
150		367
151	=item EVMETHOD_DEVPOLL solaris 8 only	368	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
152		369
153	=item EVMETHOD_PORT solaris 10 only	370	And this is your standard poll(2) backend. It's more complicated
		371	than select, but handles sparse fds better and has no artificial
		372	limit on the number of fds you can use (except it will slow down
		373	considerably with a lot of inactive fds). It scales similarly to select,
		374	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		375	performance tips.
154		376
155	If one or more of these are ored into the flags value, then only these	377	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	378	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
157	specified, any backend will do.	379
		380	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		381
		382	For few fds, this backend is a bit little slower than poll and select,
		383	but it scales phenomenally better. While poll and select usually scale
		384	like O(total_fds) where n is the total number of fds (or the highest fd),
		385	epoll scales either O(1) or O(active_fds). The epoll design has a number
		386	of shortcomings, such as silently dropping events in some hard-to-detect
		387	cases and requiring a system call per fd change, no fork support and bad
		388	support for dup.
		389
		390	While stopping, setting and starting an I/O watcher in the same iteration
		391	will result in some caching, there is still a system call per such incident
		392	(because the fd could point to a different file description now), so its
		393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
		394	very well if you register events for both fds.
		395
		396	Please note that epoll sometimes generates spurious notifications, so you
		397	need to use non-blocking I/O or other means to avoid blocking when no data
		398	(or space) is available.
		399
		400	Best performance from this backend is achieved by not unregistering all
		401	watchers for a file descriptor until it has been closed, if possible,
		402	i.e. keep at least one watcher active per fd at all times. Stopping and
		403	starting a watcher (without re-setting it) also usually doesn't cause
		404	extra overhead.
		405
		406	While nominally embeddable in other event loops, this feature is broken in
		407	all kernel versions tested so far.
		408
		409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		410	C<EVBACKEND_POLL>.
		411
		412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		413
		414	Kqueue deserves special mention, as at the time of this writing, it was
		415	broken on all BSDs except NetBSD (usually it doesn't work reliably with
		416	anything but sockets and pipes, except on Darwin, where of course it's
		417	completely useless). For this reason it's not being "auto-detected" unless
		418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or
		419	libev was compiled on a known-to-be-good (-enough) system like NetBSD.
		420
		421	You still can embed kqueue into a normal poll or select backend and use it
		422	only for sockets (after having made sure that sockets work with kqueue on
		423	the target platform). See C<ev_embed> watchers for more info.
		424
		425	It scales in the same way as the epoll backend, but the interface to the
		426	kernel is more efficient (which says nothing about its actual speed, of
		427	course). While stopping, setting and starting an I/O watcher does never
		428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		429	two event changes per incident. Support for C<fork ()> is very bad and it
		430	drops fds silently in similarly hard-to-detect cases.
		431
		432	This backend usually performs well under most conditions.
		433
		434	While nominally embeddable in other event loops, this doesn't work
		435	everywhere, so you might need to test for this. And since it is broken
		436	almost everywhere, you should only use it when you have a lot of sockets
		437	(for which it usually works), by embedding it into another event loop
		438	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
		439	using it only for sockets.
		440
		441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		442	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		443	C<NOTE_EOF>.
		444
		445	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		446
		447	This is not implemented yet (and might never be, unless you send me an
		448	implementation). According to reports, C</dev/poll> only supports sockets
		449	and is not embeddable, which would limit the usefulness of this backend
		450	immensely.
		451
		452	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		453
		454	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		455	it's really slow, but it still scales very well (O(active_fds)).
		456
		457	Please note that Solaris event ports can deliver a lot of spurious
		458	notifications, so you need to use non-blocking I/O or other means to avoid
		459	blocking when no data (or space) is available.
		460
		461	While this backend scales well, it requires one system call per active
		462	file descriptor per loop iteration. For small and medium numbers of file
		463	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		464	might perform better.
		465
		466	On the positive side, with the exception of the spurious readiness
		467	notifications, this backend actually performed fully to specification
		468	in all tests and is fully embeddable, which is a rare feat among the
		469	OS-specific backends.
		470
		471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		472	C<EVBACKEND_POLL>.
		473
		474	=item C<EVBACKEND_ALL>
		475
		476	Try all backends (even potentially broken ones that wouldn't be tried
		477	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		478	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		479
		480	It is definitely not recommended to use this flag.
158		481
159	=back	482	=back
		483
		484	If one or more of these are or'ed into the flags value, then only these
		485	backends will be tried (in the reverse order as listed here). If none are
		486	specified, all backends in C<ev_recommended_backends ()> will be tried.
		487
		488	Example: This is the most typical usage.
		489
		490	if (!ev_default_loop (0))
		491	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		492
		493	Example: Restrict libev to the select and poll backends, and do not allow
		494	environment settings to be taken into account:
		495
		496	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		497
		498	Example: Use whatever libev has to offer, but make sure that kqueue is
		499	used if available (warning, breaks stuff, best use only with your own
		500	private event loop and only if you know the OS supports your types of
		501	fds):
		502
		503	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		504
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	505	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		506
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	507	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	508	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	509	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).	510	undefined behaviour (or a failed assertion if assertions are enabled).
167		511
		512	Note that this function I<is> thread-safe, and the recommended way to use
		513	libev with threads is indeed to create one loop per thread, and using the
		514	default loop in the "main" or "initial" thread.
		515
		516	Example: Try to create a event loop that uses epoll and nothing else.
		517
		518	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		519	if (!epoller)
		520	fatal ("no epoll found here, maybe it hides under your chair");
		521
168	=item ev_default_destroy ()	522	=item ev_default_destroy ()
169		523
170	Destroys the default loop again (frees all memory and kernel state	524	Destroys the default loop again (frees all memory and kernel state
171	etc.). This stops all registered event watchers (by not touching them in	525	etc.). None of the active event watchers will be stopped in the normal
172	any way whatsoever, although you cnanot rely on this :).	526	sense, so e.g. C<ev_is_active> might still return true. It is your
		527	responsibility to either stop all watchers cleanly yourself I<before>
		528	calling this function, or cope with the fact afterwards (which is usually
		529	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		530	for example).
		531
		532	Note that certain global state, such as signal state, will not be freed by
		533	this function, and related watchers (such as signal and child watchers)
		534	would need to be stopped manually.
		535
		536	In general it is not advisable to call this function except in the
		537	rare occasion where you really need to free e.g. the signal handling
		538	pipe fds. If you need dynamically allocated loops it is better to use
		539	C<ev_loop_new> and C<ev_loop_destroy>).
173		540
174	=item ev_loop_destroy (loop)	541	=item ev_loop_destroy (loop)
175		542
176	Like C<ev_default_destroy>, but destroys an event loop created by an	543	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	544	earlier call to C<ev_loop_new>.
178		545
179	=item ev_default_fork ()	546	=item ev_default_fork ()
180		547
		548	This function sets a flag that causes subsequent C<ev_loop> iterations
181	This function reinitialises the kernel state for backends that have	549	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	550	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	551	the child process (or both child and parent, but that again makes little
184	again makes little sense).	552	sense). You I<must> call it in the child before using any of the libev
		553	functions, and it will only take effect at the next C<ev_loop> iteration.
185		554
186	You I<must> call this function after forking if and only if you want to	555	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	556	process if and only if you want to use the event library in the child. If
188	have to call it.	557	you just fork+exec, you don't have to call it at all.
189		558
190	The function itself is quite fast and its usually not a problem to call	559	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	560	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>:	561	quite nicely into a call to C<pthread_atfork>:
193		562
194	pthread_atfork (0, 0, ev_default_fork);	563	pthread_atfork (0, 0, ev_default_fork);
195		564
196	=item ev_loop_fork (loop)	565	=item ev_loop_fork (loop)
197		566
198	Like C<ev_default_fork>, but acts on an event loop created by	567	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	568	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.	569	after fork that you want to re-use in the child, and how you do this is
		570	entirely your own problem.
201		571
		572	=item int ev_is_default_loop (loop)
		573
		574	Returns true when the given loop is, in fact, the default loop, and false
		575	otherwise.
		576
		577	=item unsigned int ev_loop_count (loop)
		578
		579	Returns the count of loop iterations for the loop, which is identical to
		580	the number of times libev did poll for new events. It starts at C<0> and
		581	happily wraps around with enough iterations.
		582
		583	This value can sometimes be useful as a generation counter of sorts (it
		584	"ticks" the number of loop iterations), as it roughly corresponds with
		585	C<ev_prepare> and C<ev_check> calls.
		586
202	=item unsigned int ev_method (loop)	587	=item unsigned int ev_backend (loop)
203		588
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	589	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	590	use.
206		591
207	=item ev_tstamp = ev_now (loop)	592	=item ev_tstamp ev_now (loop)
208		593
209	Returns the current "event loop time", which is the time the event loop	594	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	595	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	596	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	597	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).	598	event occurring (or more correctly, libev finding out about it).
		599
		600	=item ev_now_update (loop)
		601
		602	Establishes the current time by querying the kernel, updating the time
		603	returned by C<ev_now ()> in the progress. This is a costly operation and
		604	is usually done automatically within C<ev_loop ()>.
		605
		606	This function is rarely useful, but when some event callback runs for a
		607	very long time without entering the event loop, updating libev's idea of
		608	the current time is a good idea.
		609
		610	See also "The special problem of time updates" in the C<ev_timer> section.
214		611
215	=item ev_loop (loop, int flags)	612	=item ev_loop (loop, int flags)
216		613
217	Finally, this is it, the event handler. This function usually is called	614	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	615	after you initialised all your watchers and you want to start handling
219	events.	616	events.
220		617
221	If the flags argument is specified as 0, it will not return until either	618	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.	619	either no event watchers are active anymore or C<ev_unloop> was called.
		620
		621	Please note that an explicit C<ev_unloop> is usually better than
		622	relying on all watchers to be stopped when deciding when a program has
		623	finished (especially in interactive programs), but having a program
		624	that automatically loops as long as it has to and no longer by virtue
		625	of relying on its watchers stopping correctly, that is truly a thing of
		626	beauty.
223		627
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	628	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	629	those events and any already outstanding ones, but will not block your
226	case there are no events.	630	process in case there are no events and will return after one iteration of
		631	the loop.
227		632
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	633	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	634	necessary) and will handle those and any already outstanding ones. It
230	your process until at least one new event arrives.	635	will block your process until at least one new event arrives (which could
		636	be an event internal to libev itself, so there is no guarentee that a
		637	user-registered callback will be called), and will return after one
		638	iteration of the loop.
231		639
232	This flags value could be used to implement alternative looping	640	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	641	with something not expressible using other libev watchers (i.e. "roll your
234	more generic mechanism.	642	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		643	usually a better approach for this kind of thing.
		644
		645	Here are the gory details of what C<ev_loop> does:
		646
		647	- Before the first iteration, call any pending watchers.
		648	* If EVFLAG_FORKCHECK was used, check for a fork.
		649	- If a fork was detected (by any means), queue and call all fork watchers.
		650	- Queue and call all prepare watchers.
		651	- If we have been forked, detach and recreate the kernel state
		652	as to not disturb the other process.
		653	- Update the kernel state with all outstanding changes.
		654	- Update the "event loop time" (ev_now ()).
		655	- Calculate for how long to sleep or block, if at all
		656	(active idle watchers, EVLOOP_NONBLOCK or not having
		657	any active watchers at all will result in not sleeping).
		658	- Sleep if the I/O and timer collect interval say so.
		659	- Block the process, waiting for any events.
		660	- Queue all outstanding I/O (fd) events.
		661	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		662	- Queue all expired timers.
		663	- Queue all expired periodics.
		664	- Unless any events are pending now, queue all idle watchers.
		665	- Queue all check watchers.
		666	- Call all queued watchers in reverse order (i.e. check watchers first).
		667	Signals and child watchers are implemented as I/O watchers, and will
		668	be handled here by queueing them when their watcher gets executed.
		669	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		670	were used, or there are no active watchers, return, otherwise
		671	continue with step *.
		672
		673	Example: Queue some jobs and then loop until no events are outstanding
		674	anymore.
		675
		676	... queue jobs here, make sure they register event watchers as long
		677	... as they still have work to do (even an idle watcher will do..)
		678	ev_loop (my_loop, 0);
		679	... jobs done or somebody called unloop. yeah!
235		680
236	=item ev_unloop (loop, how)	681	=item ev_unloop (loop, how)
237		682
238	Can be used to make a call to C<ev_loop> return early. The C<how> argument	683	Can be used to make a call to C<ev_loop> return early (but only after it
		684	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>	685	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>	686	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
241	calls return.	687
		688	This "unloop state" will be cleared when entering C<ev_loop> again.
242		689
243	=item ev_ref (loop)	690	=item ev_ref (loop)
244		691
245	=item ev_unref (loop)	692	=item ev_unref (loop)
246		693
247	Ref/unref can be used to add or remove a refcount on the event loop: Every	694	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	695	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	696	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	697
251	example for its internal signal pipe: It is not visible to you as a user	698	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	699	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	700	stopping it.
254	within third-party libraries. Just remember to unref after start and ref	701
255	before stop.	702	As an example, libev itself uses this for its internal signal pipe: It is
		703	not visible to the libev user and should not keep C<ev_loop> from exiting
		704	if no event watchers registered by it are active. It is also an excellent
		705	way to do this for generic recurring timers or from within third-party
		706	libraries. Just remember to I<unref after start> and I<ref before stop>
		707	(but only if the watcher wasn't active before, or was active before,
		708	respectively).
		709
		710	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		711	running when nothing else is active.
		712
		713	struct ev_signal exitsig;
		714	ev_signal_init (&exitsig, sig_cb, SIGINT);
		715	ev_signal_start (loop, &exitsig);
		716	evf_unref (loop);
		717
		718	Example: For some weird reason, unregister the above signal handler again.
		719
		720	ev_ref (loop);
		721	ev_signal_stop (loop, &exitsig);
		722
		723	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		724
		725	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		726
		727	These advanced functions influence the time that libev will spend waiting
		728	for events. Both time intervals are by default C<0>, meaning that libev
		729	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		730	latency.
		731
		732	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		733	allows libev to delay invocation of I/O and timer/periodic callbacks
		734	to increase efficiency of loop iterations (or to increase power-saving
		735	opportunities).
		736
		737	The idea is that sometimes your program runs just fast enough to handle
		738	one (or very few) event(s) per loop iteration. While this makes the
		739	program responsive, it also wastes a lot of CPU time to poll for new
		740	events, especially with backends like C<select ()> which have a high
		741	overhead for the actual polling but can deliver many events at once.
		742
		743	By setting a higher I<io collect interval> you allow libev to spend more
		744	time collecting I/O events, so you can handle more events per iteration,
		745	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		746	C<ev_timer>) will be not affected. Setting this to a non-null value will
		747	introduce an additional C<ev_sleep ()> call into most loop iterations.
		748
		749	Likewise, by setting a higher I<timeout collect interval> you allow libev
		750	to spend more time collecting timeouts, at the expense of increased
		751	latency/jitter/inexactness (the watcher callback will be called
		752	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		753	value will not introduce any overhead in libev.
		754
		755	Many (busy) programs can usually benefit by setting the I/O collect
		756	interval to a value near C<0.1> or so, which is often enough for
		757	interactive servers (of course not for games), likewise for timeouts. It
		758	usually doesn't make much sense to set it to a lower value than C<0.01>,
		759	as this approaches the timing granularity of most systems.
		760
		761	Setting the I<timeout collect interval> can improve the opportunity for
		762	saving power, as the program will "bundle" timer callback invocations that
		763	are "near" in time together, by delaying some, thus reducing the number of
		764	times the process sleeps and wakes up again. Another useful technique to
		765	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		766	they fire on, say, one-second boundaries only.
		767
		768	=item ev_loop_verify (loop)
		769
		770	This function only does something when C<EV_VERIFY> support has been
		771	compiled in. which is the default for non-minimal builds. It tries to go
		772	through all internal structures and checks them for validity. If anything
		773	is found to be inconsistent, it will print an error message to standard
		774	error and call C<abort ()>.
		775
		776	This can be used to catch bugs inside libev itself: under normal
		777	circumstances, this function will never abort as of course libev keeps its
		778	data structures consistent.
256		779
257	=back	780	=back
		781
258		782
259	=head1 ANATOMY OF A WATCHER	783	=head1 ANATOMY OF A WATCHER
260		784
261	A watcher is a structure that you create and register to record your	785	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	786	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:	787	become readable, you would create an C<ev_io> watcher for that:
264		788
265	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	789	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
266	{	790	{
267	ev_io_stop (w);	791	ev_io_stop (w);
268	ev_unloop (loop, EVUNLOOP_ALL);	792	ev_unloop (loop, EVUNLOOP_ALL);
269	}	793	}
270		794
271	struct ev_loop *loop = ev_default_loop (0);	795	struct ev_loop *loop = ev_default_loop (0);
272	struct ev_io stdin_watcher;	796	struct ev_io stdin_watcher;
273	ev_init (&stdin_watcher, my_cb);	797	ev_init (&stdin_watcher, my_cb);
274	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	798	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
275	ev_io_start (loop, &stdin_watcher);	799	ev_io_start (loop, &stdin_watcher);
276	ev_loop (loop, 0);	800	ev_loop (loop, 0);
277		801
278	As you can see, you are responsible for allocating the memory for your	802	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,	803	watcher structures (and it is usually a bad idea to do this on the stack,
280	although this can sometimes be quite valid).	804	although this can sometimes be quite valid).
281		805
282	Each watcher structure must be initialised by a call to C<ev_init	806	Each watcher structure must be initialised by a call to C<ev_init
283	(watcher *, callback)>, which expects a callback to be provided. This	807	(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	808	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	809	watchers, each time the event loop detects that the file descriptor given
286	is readable and/or writable).	810	is readable and/or writable).
287		811
288	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	812	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro
289	with arguments specific to this watcher type. There is also a macro	813	with arguments specific to this watcher type. There is also a macro
…		…
295	*) >>), and you can stop watching for events at any time by calling the	819	*) >>), and you can stop watching for events at any time by calling the
296	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	820	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
297		821
298	As long as your watcher is active (has been started but not stopped) you	822	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	823	must not touch the values stored in it. Most specifically you must never
300	reinitialise it or call its set method.	824	reinitialise it or call its C<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		825
307	Each and every callback receives the event loop pointer as first, the	826	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	827	registered watcher structure as second, and a bitset of received events as
309	third argument.	828	third argument.
310		829
311	The rceeived events usually include a single bit per event type received	830	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	831	(you can receive multiple events at the same time). The possible bit masks
313	are:	832	are:
314		833
315	=over 4	834	=over 4
316		835
317	=item EV_READ	836	=item C<EV_READ>
318		837
319	=item EV_WRITE	838	=item C<EV_WRITE>
320		839
321	The file descriptor in the ev_io watcher has become readable and/or	840	The file descriptor in the C<ev_io> watcher has become readable and/or
322	writable.	841	writable.
323		842
324	=item EV_TIMEOUT	843	=item C<EV_TIMEOUT>
325		844
326	The ev_timer watcher has timed out.	845	The C<ev_timer> watcher has timed out.
327		846
328	=item EV_PERIODIC	847	=item C<EV_PERIODIC>
329		848
330	The ev_periodic watcher has timed out.	849	The C<ev_periodic> watcher has timed out.
331		850
332	=item EV_SIGNAL	851	=item C<EV_SIGNAL>
333		852
334	The signal specified in the ev_signal watcher has been received by a thread.	853	The signal specified in the C<ev_signal> watcher has been received by a thread.
335		854
336	=item EV_CHILD	855	=item C<EV_CHILD>
337		856
338	The pid specified in the ev_child watcher has received a status change.	857	The pid specified in the C<ev_child> watcher has received a status change.
339		858
		859	=item C<EV_STAT>
		860
		861	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		862
340	=item EV_IDLE	863	=item C<EV_IDLE>
341		864
342	The ev_idle watcher has determined that you have nothing better to do.	865	The C<ev_idle> watcher has determined that you have nothing better to do.
343		866
344	=item EV_PREPARE	867	=item C<EV_PREPARE>
345		868
346	=item EV_CHECK	869	=item C<EV_CHECK>
347		870
348	All ev_prepare watchers are invoked just I<before> C<ev_loop> starts	871	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	872	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	873	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	874	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	875	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	876	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
354	C<ev_loop> from blocking).	877	C<ev_loop> from blocking).
355		878
		879	=item C<EV_EMBED>
		880
		881	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		882
		883	=item C<EV_FORK>
		884
		885	The event loop has been resumed in the child process after fork (see
		886	C<ev_fork>).
		887
		888	=item C<EV_ASYNC>
		889
		890	The given async watcher has been asynchronously notified (see C<ev_async>).
		891
356	=item EV_ERROR	892	=item C<EV_ERROR>
357		893
358	An unspecified error has occured, the watcher has been stopped. This might	894	An unspecified error has occurred, the watcher has been stopped. This might
359	happen because the watcher could not be properly started because libev	895	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	896	ran out of memory, a file descriptor was found to be closed or any other
361	problem. You best act on it by reporting the problem and somehow coping	897	problem. You best act on it by reporting the problem and somehow coping
362	with the watcher being stopped.	898	with the watcher being stopped.
363		899
364	Libev will usually signal a few "dummy" events together with an error,	900	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	901	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	902	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	903	the error from read() or write(). This will not work in multi-threaded
368	programs, though, so beware.	904	programs, though, as the fd could already be closed and reused for another
		905	thing, so beware.
369		906
370	=back	907	=back
371		908
		909	=head2 GENERIC WATCHER FUNCTIONS
		910
		911	In the following description, C<TYPE> stands for the watcher type,
		912	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		913
		914	=over 4
		915
		916	=item C<ev_init> (ev_TYPE *watcher, callback)
		917
		918	This macro initialises the generic portion of a watcher. The contents
		919	of the watcher object can be arbitrary (so C<malloc> will do). Only
		920	the generic parts of the watcher are initialised, you I<need> to call
		921	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		922	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		923	which rolls both calls into one.
		924
		925	You can reinitialise a watcher at any time as long as it has been stopped
		926	(or never started) and there are no pending events outstanding.
		927
		928	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		929	int revents)>.
		930
		931	Example: Initialise an C<ev_io> watcher in two steps.
		932
		933	ev_io w;
		934	ev_init (&w, my_cb);
		935	ev_io_set (&w, STDIN_FILENO, EV_READ);
		936
		937	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		938
		939	This macro initialises the type-specific parts of a watcher. You need to
		940	call C<ev_init> at least once before you call this macro, but you can
		941	call C<ev_TYPE_set> any number of times. You must not, however, call this
		942	macro on a watcher that is active (it can be pending, however, which is a
		943	difference to the C<ev_init> macro).
		944
		945	Although some watcher types do not have type-specific arguments
		946	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		947
		948	See C<ev_init>, above, for an example.
		949
		950	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		951
		952	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		953	calls into a single call. This is the most convenient method to initialise
		954	a watcher. The same limitations apply, of course.
		955
		956	Example: Initialise and set an C<ev_io> watcher in one step.
		957
		958	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		959
		960	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		961
		962	Starts (activates) the given watcher. Only active watchers will receive
		963	events. If the watcher is already active nothing will happen.
		964
		965	Example: Start the C<ev_io> watcher that is being abused as example in this
		966	whole section.
		967
		968	ev_io_start (EV_DEFAULT_UC, &w);
		969
		970	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		971
		972	Stops the given watcher again (if active) and clears the pending
		973	status. It is possible that stopped watchers are pending (for example,
		974	non-repeating timers are being stopped when they become pending), but
		975	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		976	you want to free or reuse the memory used by the watcher it is therefore a
		977	good idea to always call its C<ev_TYPE_stop> function.
		978
		979	=item bool ev_is_active (ev_TYPE *watcher)
		980
		981	Returns a true value iff the watcher is active (i.e. it has been started
		982	and not yet been stopped). As long as a watcher is active you must not modify
		983	it.
		984
		985	=item bool ev_is_pending (ev_TYPE *watcher)
		986
		987	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		988	events but its callback has not yet been invoked). As long as a watcher
		989	is pending (but not active) you must not call an init function on it (but
		990	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		991	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		992	it).
		993
		994	=item callback ev_cb (ev_TYPE *watcher)
		995
		996	Returns the callback currently set on the watcher.
		997
		998	=item ev_cb_set (ev_TYPE *watcher, callback)
		999
		1000	Change the callback. You can change the callback at virtually any time
		1001	(modulo threads).
		1002
		1003	=item ev_set_priority (ev_TYPE *watcher, priority)
		1004
		1005	=item int ev_priority (ev_TYPE *watcher)
		1006
		1007	Set and query the priority of the watcher. The priority is a small
		1008	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1009	(default: C<-2>). Pending watchers with higher priority will be invoked
		1010	before watchers with lower priority, but priority will not keep watchers
		1011	from being executed (except for C<ev_idle> watchers).
		1012
		1013	This means that priorities are I<only> used for ordering callback
		1014	invocation after new events have been received. This is useful, for
		1015	example, to reduce latency after idling, or more often, to bind two
		1016	watchers on the same event and make sure one is called first.
		1017
		1018	If you need to suppress invocation when higher priority events are pending
		1019	you need to look at C<ev_idle> watchers, which provide this functionality.
		1020
		1021	You I<must not> change the priority of a watcher as long as it is active or
		1022	pending.
		1023
		1024	The default priority used by watchers when no priority has been set is
		1025	always C<0>, which is supposed to not be too high and not be too low :).
		1026
		1027	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1028	fine, as long as you do not mind that the priority value you query might
		1029	or might not have been adjusted to be within valid range.
		1030
		1031	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1032
		1033	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1034	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1035	can deal with that fact, as both are simply passed through to the
		1036	callback.
		1037
		1038	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1039
		1040	If the watcher is pending, this function clears its pending status and
		1041	returns its C<revents> bitset (as if its callback was invoked). If the
		1042	watcher isn't pending it does nothing and returns C<0>.
		1043
		1044	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1045	callback to be invoked, which can be accomplished with this function.
		1046
		1047	=back
		1048
		1049
372	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1050	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
373		1051
374	Each watcher has, by default, a member C<void *data> that you can change	1052	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	1053	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	1054	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	1055	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	1056	member, you can also "subclass" the watcher type and provide your own
379	data:	1057	data:
380		1058
381	struct my_io	1059	struct my_io
382	{	1060	{
383	struct ev_io io;	1061	struct ev_io io;
384	int otherfd;	1062	int otherfd;
385	void *somedata;	1063	void *somedata;
386	struct whatever *mostinteresting;	1064	struct whatever *mostinteresting;
387	}	1065	};
		1066
		1067	...
		1068	struct my_io w;
		1069	ev_io_init (&w.io, my_cb, fd, EV_READ);
388		1070
389	And since your callback will be called with a pointer to the watcher, you	1071	And since your callback will be called with a pointer to the watcher, you
390	can cast it back to your own type:	1072	can cast it back to your own type:
391		1073
392	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1074	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
393	{	1075	{
394	struct my_io *w = (struct my_io *)w_;	1076	struct my_io *w = (struct my_io *)w_;
395	...	1077	...
396	}	1078	}
397		1079
398	More interesting and less C-conformant ways of catsing your callback type	1080	More interesting and less C-conformant ways of casting your callback type
399	have been omitted....	1081	instead have been omitted.
		1082
		1083	Another common scenario is to use some data structure with multiple
		1084	embedded watchers:
		1085
		1086	struct my_biggy
		1087	{
		1088	int some_data;
		1089	ev_timer t1;
		1090	ev_timer t2;
		1091	}
		1092
		1093	In this case getting the pointer to C<my_biggy> is a bit more
		1094	complicated: Either you store the address of your C<my_biggy> struct
		1095	in the C<data> member of the watcher (for woozies), or you need to use
		1096	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1097	programmers):
		1098
		1099	#include <stddef.h>
		1100
		1101	static void
		1102	t1_cb (EV_P_ struct ev_timer *w, int revents)
		1103	{
		1104	struct my_biggy big = (struct my_biggy *
		1105	(((char *)w) - offsetof (struct my_biggy, t1));
		1106	}
		1107
		1108	static void
		1109	t2_cb (EV_P_ struct ev_timer *w, int revents)
		1110	{
		1111	struct my_biggy big = (struct my_biggy *
		1112	(((char *)w) - offsetof (struct my_biggy, t2));
		1113	}
400		1114
401		1115
402	=head1 WATCHER TYPES	1116	=head1 WATCHER TYPES
403		1117
404	This section describes each watcher in detail, but will not repeat	1118	This section describes each watcher in detail, but will not repeat
405	information given in the last section.	1119	information given in the last section. Any initialisation/set macros,
		1120	functions and members specific to the watcher type are explained.
406		1121
		1122	Members are additionally marked with either I<[read-only]>, meaning that,
		1123	while the watcher is active, you can look at the member and expect some
		1124	sensible content, but you must not modify it (you can modify it while the
		1125	watcher is stopped to your hearts content), or I<[read-write]>, which
		1126	means you can expect it to have some sensible content while the watcher
		1127	is active, but you can also modify it. Modifying it may not do something
		1128	sensible or take immediate effect (or do anything at all), but libev will
		1129	not crash or malfunction in any way.
		1130
		1131
407	=head2 struct ev_io - is my file descriptor readable or writable	1132	=head2 C<ev_io> - is this file descriptor readable or writable?
408		1133
409	I/O watchers check whether a file descriptor is readable or writable	1134	I/O watchers check whether a file descriptor is readable or writable
410	in each iteration of the event loop (This behaviour is called	1135	in each iteration of the event loop, or, more precisely, when reading
411	level-triggering because you keep receiving events as long as the	1136	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	1137	some data. This behaviour is called level-triggering because you keep
413	act on the event and neither want to receive future events).	1138	receiving events as long as the condition persists. Remember you can stop
		1139	the watcher if you don't want to act on the event and neither want to
		1140	receive future events.
414		1141
415	In general you can register as many read and/or write event watchers oer	1142	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	1143	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	1144	descriptors to non-blocking mode is also usually a good idea (but not
418	required if you know what you are doing).	1145	required if you know what you are doing).
419		1146
420	You have to be careful with dup'ed file descriptors, though. Some backends	1147	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	1148	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	1149	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
423	to the same file/socket etc. description.
424		1150
425	If you must do this, then force the use of a known-to-be-good backend	1151	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	1152	receive "spurious" readiness notifications, that is your callback might
427	EVMETHOD_POLL).	1153	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1154	because there is no data. Not only are some backends known to create a
		1155	lot of those (for example Solaris ports), it is very easy to get into
		1156	this situation even with a relatively standard program structure. Thus
		1157	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1158	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1159
		1160	If you cannot run the fd in non-blocking mode (for example you should
		1161	not play around with an Xlib connection), then you have to separately
		1162	re-test whether a file descriptor is really ready with a known-to-be good
		1163	interface such as poll (fortunately in our Xlib example, Xlib already
		1164	does this on its own, so its quite safe to use). Some people additionally
		1165	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1166	indefinitely.
		1167
		1168	But really, best use non-blocking mode.
		1169
		1170	=head3 The special problem of disappearing file descriptors
		1171
		1172	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1173	descriptor (either due to calling C<close> explicitly or any other means,
		1174	such as C<dup2>). The reason is that you register interest in some file
		1175	descriptor, but when it goes away, the operating system will silently drop
		1176	this interest. If another file descriptor with the same number then is
		1177	registered with libev, there is no efficient way to see that this is, in
		1178	fact, a different file descriptor.
		1179
		1180	To avoid having to explicitly tell libev about such cases, libev follows
		1181	the following policy: Each time C<ev_io_set> is being called, libev
		1182	will assume that this is potentially a new file descriptor, otherwise
		1183	it is assumed that the file descriptor stays the same. That means that
		1184	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1185	descriptor even if the file descriptor number itself did not change.
		1186
		1187	This is how one would do it normally anyway, the important point is that
		1188	the libev application should not optimise around libev but should leave
		1189	optimisations to libev.
		1190
		1191	=head3 The special problem of dup'ed file descriptors
		1192
		1193	Some backends (e.g. epoll), cannot register events for file descriptors,
		1194	but only events for the underlying file descriptions. That means when you
		1195	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1196	events for them, only one file descriptor might actually receive events.
		1197
		1198	There is no workaround possible except not registering events
		1199	for potentially C<dup ()>'ed file descriptors, or to resort to
		1200	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1201
		1202	=head3 The special problem of fork
		1203
		1204	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1205	useless behaviour. Libev fully supports fork, but needs to be told about
		1206	it in the child.
		1207
		1208	To support fork in your programs, you either have to call
		1209	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1210	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1211	C<EVBACKEND_POLL>.
		1212
		1213	=head3 The special problem of SIGPIPE
		1214
		1215	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1216	when writing to a pipe whose other end has been closed, your program gets
		1217	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1218	this is sensible behaviour, for daemons, this is usually undesirable.
		1219
		1220	So when you encounter spurious, unexplained daemon exits, make sure you
		1221	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1222	somewhere, as that would have given you a big clue).
		1223
		1224
		1225	=head3 Watcher-Specific Functions
428		1226
429	=over 4	1227	=over 4
430		1228
431	=item ev_io_init (ev_io *, callback, int fd, int events)	1229	=item ev_io_init (ev_io *, callback, int fd, int events)
432		1230
433	=item ev_io_set (ev_io *, int fd, int events)	1231	=item ev_io_set (ev_io *, int fd, int events)
434		1232
435	Configures an ev_io watcher. The fd is the file descriptor to rceeive	1233	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 |	1234	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
437	EV_WRITE> to receive the given events.	1235	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1236
		1237	=item int fd [read-only]
		1238
		1239	The file descriptor being watched.
		1240
		1241	=item int events [read-only]
		1242
		1243	The events being watched.
438		1244
439	=back	1245	=back
440		1246
		1247	=head3 Examples
		1248
		1249	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1250	readable, but only once. Since it is likely line-buffered, you could
		1251	attempt to read a whole line in the callback.
		1252
		1253	static void
		1254	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1255	{
		1256	ev_io_stop (loop, w);
		1257	.. read from stdin here (or from w->fd) and handle any I/O errors
		1258	}
		1259
		1260	...
		1261	struct ev_loop *loop = ev_default_init (0);
		1262	struct ev_io stdin_readable;
		1263	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1264	ev_io_start (loop, &stdin_readable);
		1265	ev_loop (loop, 0);
		1266
		1267
441	=head2 struct ev_timer - relative and optionally recurring timeouts	1268	=head2 C<ev_timer> - relative and optionally repeating timeouts
442		1269
443	Timer watchers are simple relative timers that generate an event after a	1270	Timer watchers are simple relative timers that generate an event after a
444	given time, and optionally repeating in regular intervals after that.	1271	given time, and optionally repeating in regular intervals after that.
445		1272
446	The timers are based on real time, that is, if you register an event that	1273	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	1274	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	1275	year, it will still time out after (roughly) one hour. "Roughly" because
449	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1276	detecting time jumps is hard, and some inaccuracies are unavoidable (the
450	monotonic clock option helps a lot here).	1277	monotonic clock option helps a lot here).
451		1278
		1279	The callback is guaranteed to be invoked only I<after> its timeout has
		1280	passed, but if multiple timers become ready during the same loop iteration
		1281	then order of execution is undefined.
		1282
		1283	=head3 The special problem of time updates
		1284
		1285	Establishing the current time is a costly operation (it usually takes at
		1286	least two system calls): EV therefore updates its idea of the current
		1287	time only before and after C<ev_loop> collects new events, which causes a
		1288	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1289	lots of events in one iteration.
		1290
		1291	The relative timeouts are calculated relative to the C<ev_now ()>
		1292	time. This is usually the right thing as this timestamp refers to the time
		1293	of the event triggering whatever timeout you are modifying/starting. If
		1294	you suspect event processing to be delayed and you I<need> to base the
		1295	timeout on the current time, use something like this to adjust for this:
		1296
		1297	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1298
		1299	If the event loop is suspended for a long time, you can also force an
		1300	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		1301	()>.
		1302
		1303	=head3 Watcher-Specific Functions and Data Members
		1304
452	=over 4	1305	=over 4
453		1306
454	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1307	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
455		1308
456	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1309	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
457		1310
458	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1311	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	1312	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	1313	reached. If it is positive, then the timer will automatically be
461	later, again, and again, until stopped manually.	1314	configured to trigger again C<repeat> seconds later, again, and again,
		1315	until stopped manually.
462		1316
463	The timer itself will do a best-effort at avoiding drift, that is, if you	1317	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	1318	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	1319	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	1320	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.	1321	do stuff) the timer will not fire more than once per event loop iteration.
468		1322
469	=item ev_timer_again (loop)	1323	=item ev_timer_again (loop, ev_timer *)
470		1324
471	This will act as if the timer timed out and restart it again if it is	1325	This will act as if the timer timed out and restart it again if it is
472	repeating. The exact semantics are:	1326	repeating. The exact semantics are:
473		1327
		1328	If the timer is pending, its pending status is cleared.
		1329
474	If the timer is started but nonrepeating, stop it.	1330	If the timer is started but non-repeating, stop it (as if it timed out).
475		1331
476	If the timer is repeating, either start it if necessary (with the repeat	1332	If the timer is repeating, either start it if necessary (with the
477	value), or reset the running timer to the repeat value.	1333	C<repeat> value), or reset the running timer to the C<repeat> value.
478		1334
479	This sounds a bit complicated, but here is a useful and typical	1335	This sounds a bit complicated, but here is a useful and typical
480	example: Imagine you have a tcp connection and you want a so-called idle	1336	example: Imagine you have a TCP connection and you want a so-called idle
481	timeout, that is, you want to be called when there have been, say, 60	1337	timeout, that is, you want to be called when there have been, say, 60
482	seconds of inactivity on the socket. The easiest way to do this is to	1338	seconds of inactivity on the socket. The easiest way to do this is to
483	configure an ev_timer with after=repeat=60 and calling ev_timer_again each	1339	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
484	time you successfully read or write some data. If you go into an idle	1340	C<ev_timer_again> each time you successfully read or write some data. If
485	state where you do not expect data to travel on the socket, you can stop	1341	you go into an idle state where you do not expect data to travel on the
486	the timer, and again will automatically restart it if need be.	1342	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1343	automatically restart it if need be.
		1344
		1345	That means you can ignore the C<after> value and C<ev_timer_start>
		1346	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1347
		1348	ev_timer_init (timer, callback, 0., 5.);
		1349	ev_timer_again (loop, timer);
		1350	...
		1351	timer->again = 17.;
		1352	ev_timer_again (loop, timer);
		1353	...
		1354	timer->again = 10.;
		1355	ev_timer_again (loop, timer);
		1356
		1357	This is more slightly efficient then stopping/starting the timer each time
		1358	you want to modify its timeout value.
		1359
		1360	Note, however, that it is often even more efficient to remember the
		1361	time of the last activity and let the timer time-out naturally. In the
		1362	callback, you then check whether the time-out is real, or, if there was
		1363	some activity, you reschedule the watcher to time-out in "last_activity +
		1364	timeout - ev_now ()" seconds.
		1365
		1366	=item ev_tstamp repeat [read-write]
		1367
		1368	The current C<repeat> value. Will be used each time the watcher times out
		1369	or C<ev_timer_again> is called, and determines the next timeout (if any),
		1370	which is also when any modifications are taken into account.
487		1371
488	=back	1372	=back
489		1373
		1374	=head3 Examples
		1375
		1376	Example: Create a timer that fires after 60 seconds.
		1377
		1378	static void
		1379	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1380	{
		1381	.. one minute over, w is actually stopped right here
		1382	}
		1383
		1384	struct ev_timer mytimer;
		1385	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1386	ev_timer_start (loop, &mytimer);
		1387
		1388	Example: Create a timeout timer that times out after 10 seconds of
		1389	inactivity.
		1390
		1391	static void
		1392	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1393	{
		1394	.. ten seconds without any activity
		1395	}
		1396
		1397	struct ev_timer mytimer;
		1398	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1399	ev_timer_again (&mytimer); /* start timer */
		1400	ev_loop (loop, 0);
		1401
		1402	// and in some piece of code that gets executed on any "activity":
		1403	// reset the timeout to start ticking again at 10 seconds
		1404	ev_timer_again (&mytimer);
		1405
		1406
490	=head2 ev_periodic - to cron or not to cron it	1407	=head2 C<ev_periodic> - to cron or not to cron?
491		1408
492	Periodic watchers are also timers of a kind, but they are very versatile	1409	Periodic watchers are also timers of a kind, but they are very versatile
493	(and unfortunately a bit complex).	1410	(and unfortunately a bit complex).
494		1411
495	Unlike ev_timer's, they are not based on real time (or relative time)	1412	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	1413	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	1414	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 ()	1415	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	1416	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1417	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	1418	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	1419	roughly 10 seconds later as it uses a relative timeout).
502	again).
503		1420
504	They can also be used to implement vastly more complex timers, such as	1421	C<ev_periodic>s can also be used to implement vastly more complex timers,
505	triggering an event on eahc midnight, local time.	1422	such as triggering an event on each "midnight, local time", or other
		1423	complicated rules.
		1424
		1425	As with timers, the callback is guaranteed to be invoked only when the
		1426	time (C<at>) has passed, but if multiple periodic timers become ready
		1427	during the same loop iteration, then order of execution is undefined.
		1428
		1429	=head3 Watcher-Specific Functions and Data Members
506		1430
507	=over 4	1431	=over 4
508		1432
509	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1433	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
510		1434
511	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1435	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
512		1436
513	Lots of arguments, lets sort it out... There are basically three modes of	1437	Lots of arguments, lets sort it out... There are basically three modes of
514	operation, and we will explain them from simplest to complex:	1438	operation, and we will explain them from simplest to most complex:
515
516		1439
517	=over 4	1440	=over 4
518		1441
519	=item * absolute timer (interval = reschedule_cb = 0)	1442	=item * absolute timer (at = time, interval = reschedule_cb = 0)
520		1443
521	In this configuration the watcher triggers an event at the wallclock time	1444	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,	1445	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	1446	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.	1447	only run when the system clock reaches or surpasses this time.
525		1448
526	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1449	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
527		1450
528	In this mode the watcher will always be scheduled to time out at the next	1451	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	1452	C<at + N * interval> time (for some integer N, which can also be negative)
530	of any time jumps.	1453	and then repeat, regardless of any time jumps.
531		1454
532	This can be used to create timers that do not drift with respect to system	1455	This can be used to create timers that do not drift with respect to the
533	time:	1456	system clock, for example, here is a C<ev_periodic> that triggers each
		1457	hour, on the hour:
534		1458
535	ev_periodic_set (&periodic, 0., 3600., 0);	1459	ev_periodic_set (&periodic, 0., 3600., 0);
536		1460
537	This doesn't mean there will always be 3600 seconds in between triggers,	1461	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	1462	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	1463	full hour (UTC), or more correctly, when the system time is evenly divisible
540	by 3600.	1464	by 3600.
541		1465
542	Another way to think about it (for the mathematically inclined) is that	1466	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	1467	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.	1468	time where C<time = at (mod interval)>, regardless of any time jumps.
545		1469
		1470	For numerical stability it is preferable that the C<at> value is near
		1471	C<ev_now ()> (the current time), but there is no range requirement for
		1472	this value, and in fact is often specified as zero.
		1473
		1474	Note also that there is an upper limit to how often a timer can fire (CPU
		1475	speed for example), so if C<interval> is very small then timing stability
		1476	will of course deteriorate. Libev itself tries to be exact to be about one
		1477	millisecond (if the OS supports it and the machine is fast enough).
		1478
546	=item * manual reschedule mode (reschedule_cb = callback)	1479	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
547		1480
548	In this mode the values for C<interval> and C<at> are both being	1481	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	1482	ignored. Instead, each time the periodic watcher gets scheduled, the
550	reschedule callback will be called with the watcher as first, and the	1483	reschedule callback will be called with the watcher as first, and the
551	current time as second argument.	1484	current time as second argument.
552		1485
553	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1486	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	1487	ever, or make ANY event loop modifications whatsoever>.
555	to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
556		1488
		1489	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1490	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1491	only event loop modification you are allowed to do).
		1492
557	Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1493	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
558	ev_tstamp now)>, e.g.:	1494	*w, ev_tstamp now)>, e.g.:
559		1495
560	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1496	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
561	{	1497	{
562	return now + 60.;	1498	return now + 60.;
563	}	1499	}
…		…
565	It must return the next time to trigger, based on the passed time value	1501	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	1502	(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	1503	will usually be called just before the callback will be triggered, but
568	might be called at other times, too.	1504	might be called at other times, too.
569		1505
		1506	NOTE: I<< This callback must always return a time that is higher than or
		1507	equal to the passed C<now> value >>.
		1508
570	This can be used to create very complex timers, such as a timer that	1509	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	1510	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	1511	next midnight after C<now> and return the timestamp value for this. How
573	is, again, up to you (but it is not trivial).	1512	you do this is, again, up to you (but it is not trivial, which is the main
		1513	reason I omitted it as an example).
574		1514
575	=back	1515	=back
576		1516
577	=item ev_periodic_again (loop, ev_periodic *)	1517	=item ev_periodic_again (loop, ev_periodic *)
578		1518
579	Simply stops and restarts the periodic watcher again. This is only useful	1519	Simply stops and restarts the periodic watcher again. This is only useful
580	when you changed some parameters or the reschedule callback would return	1520	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	1521	a different time than the last time it was called (e.g. in a crond like
582	program when the crontabs have changed).	1522	program when the crontabs have changed).
583		1523
		1524	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1525
		1526	When active, returns the absolute time that the watcher is supposed to
		1527	trigger next.
		1528
		1529	=item ev_tstamp offset [read-write]
		1530
		1531	When repeating, this contains the offset value, otherwise this is the
		1532	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1533
		1534	Can be modified any time, but changes only take effect when the periodic
		1535	timer fires or C<ev_periodic_again> is being called.
		1536
		1537	=item ev_tstamp interval [read-write]
		1538
		1539	The current interval value. Can be modified any time, but changes only
		1540	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1541	called.
		1542
		1543	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1544
		1545	The current reschedule callback, or C<0>, if this functionality is
		1546	switched off. Can be changed any time, but changes only take effect when
		1547	the periodic timer fires or C<ev_periodic_again> is being called.
		1548
584	=back	1549	=back
585		1550
		1551	=head3 Examples
		1552
		1553	Example: Call a callback every hour, or, more precisely, whenever the
		1554	system time is divisible by 3600. The callback invocation times have
		1555	potentially a lot of jitter, but good long-term stability.
		1556
		1557	static void
		1558	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1559	{
		1560	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1561	}
		1562
		1563	struct ev_periodic hourly_tick;
		1564	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1565	ev_periodic_start (loop, &hourly_tick);
		1566
		1567	Example: The same as above, but use a reschedule callback to do it:
		1568
		1569	#include <math.h>
		1570
		1571	static ev_tstamp
		1572	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1573	{
		1574	return now + (3600. - fmod (now, 3600.));
		1575	}
		1576
		1577	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1578
		1579	Example: Call a callback every hour, starting now:
		1580
		1581	struct ev_periodic hourly_tick;
		1582	ev_periodic_init (&hourly_tick, clock_cb,
		1583	fmod (ev_now (loop), 3600.), 3600., 0);
		1584	ev_periodic_start (loop, &hourly_tick);
		1585
		1586
586	=head2 ev_signal - signal me when a signal gets signalled	1587	=head2 C<ev_signal> - signal me when a signal gets signalled!
587		1588
588	Signal watchers will trigger an event when the process receives a specific	1589	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	1590	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	1591	will try it's best to deliver signals synchronously, i.e. as part of the
591	normal event processing, like any other event.	1592	normal event processing, like any other event.
592		1593
		1594	If you want signals asynchronously, just use C<sigaction> as you would
		1595	do without libev and forget about sharing the signal. You can even use
		1596	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1597
593	You cna configure as many watchers as you like per signal. Only when the	1598	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	1599	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	1600	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	1601	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	1602	the last signal watcher for a signal is stopped, libev will reset the
598	SIG_DFL (regardless of what it was set to before).	1603	signal handler to SIG_DFL (regardless of what it was set to before).
		1604
		1605	If possible and supported, libev will install its handlers with
		1606	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1607	interrupted. If you have a problem with system calls getting interrupted by
		1608	signals you can block all signals in an C<ev_check> watcher and unblock
		1609	them in an C<ev_prepare> watcher.
		1610
		1611	=head3 Watcher-Specific Functions and Data Members
599		1612
600	=over 4	1613	=over 4
601		1614
602	=item ev_signal_init (ev_signal *, callback, int signum)	1615	=item ev_signal_init (ev_signal *, callback, int signum)
603		1616
604	=item ev_signal_set (ev_signal *, int signum)	1617	=item ev_signal_set (ev_signal *, int signum)
605		1618
606	Configures the watcher to trigger on the given signal number (usually one	1619	Configures the watcher to trigger on the given signal number (usually one
607	of the C<SIGxxx> constants).	1620	of the C<SIGxxx> constants).
608		1621
		1622	=item int signum [read-only]
		1623
		1624	The signal the watcher watches out for.
		1625
609	=back	1626	=back
610		1627
		1628	=head3 Examples
		1629
		1630	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1631
		1632	static void
		1633	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1634	{
		1635	ev_unloop (loop, EVUNLOOP_ALL);
		1636	}
		1637
		1638	struct ev_signal signal_watcher;
		1639	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1640	ev_signal_start (loop, &sigint_cb);
		1641
		1642
611	=head2 ev_child - wait for pid status changes	1643	=head2 C<ev_child> - watch out for process status changes
612		1644
613	Child watchers trigger when your process receives a SIGCHLD in response to	1645	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).	1646	some child status changes (most typically when a child of yours dies or
		1647	exits). It is permissible to install a child watcher I<after> the child
		1648	has been forked (which implies it might have already exited), as long
		1649	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1650	forking and then immediately registering a watcher for the child is fine,
		1651	but forking and registering a watcher a few event loop iterations later is
		1652	not.
		1653
		1654	Only the default event loop is capable of handling signals, and therefore
		1655	you can only register child watchers in the default event loop.
		1656
		1657	=head3 Process Interaction
		1658
		1659	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1660	initialised. This is necessary to guarantee proper behaviour even if
		1661	the first child watcher is started after the child exits. The occurrence
		1662	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1663	synchronously as part of the event loop processing. Libev always reaps all
		1664	children, even ones not watched.
		1665
		1666	=head3 Overriding the Built-In Processing
		1667
		1668	Libev offers no special support for overriding the built-in child
		1669	processing, but if your application collides with libev's default child
		1670	handler, you can override it easily by installing your own handler for
		1671	C<SIGCHLD> after initialising the default loop, and making sure the
		1672	default loop never gets destroyed. You are encouraged, however, to use an
		1673	event-based approach to child reaping and thus use libev's support for
		1674	that, so other libev users can use C<ev_child> watchers freely.
		1675
		1676	=head3 Stopping the Child Watcher
		1677
		1678	Currently, the child watcher never gets stopped, even when the
		1679	child terminates, so normally one needs to stop the watcher in the
		1680	callback. Future versions of libev might stop the watcher automatically
		1681	when a child exit is detected.
		1682
		1683	=head3 Watcher-Specific Functions and Data Members
615		1684
616	=over 4	1685	=over 4
617		1686
618	=item ev_child_init (ev_child *, callback, int pid)	1687	=item ev_child_init (ev_child *, callback, int pid, int trace)
619		1688
620	=item ev_child_set (ev_child *, int pid)	1689	=item ev_child_set (ev_child *, int pid, int trace)
621		1690
622	Configures the watcher to wait for status changes of process C<pid> (or	1691	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	1692	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	1693	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	1694	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.	1695	C<waitpid> documentation). The C<rpid> member contains the pid of the
		1696	process causing the status change. C<trace> must be either C<0> (only
		1697	activate the watcher when the process terminates) or C<1> (additionally
		1698	activate the watcher when the process is stopped or continued).
		1699
		1700	=item int pid [read-only]
		1701
		1702	The process id this watcher watches out for, or C<0>, meaning any process id.
		1703
		1704	=item int rpid [read-write]
		1705
		1706	The process id that detected a status change.
		1707
		1708	=item int rstatus [read-write]
		1709
		1710	The process exit/trace status caused by C<rpid> (see your systems
		1711	C<waitpid> and C<sys/wait.h> documentation for details).
627		1712
628	=back	1713	=back
629		1714
		1715	=head3 Examples
		1716
		1717	Example: C<fork()> a new process and install a child handler to wait for
		1718	its completion.
		1719
		1720	ev_child cw;
		1721
		1722	static void
		1723	child_cb (EV_P_ struct ev_child *w, int revents)
		1724	{
		1725	ev_child_stop (EV_A_ w);
		1726	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1727	}
		1728
		1729	pid_t pid = fork ();
		1730
		1731	if (pid < 0)
		1732	// error
		1733	else if (pid == 0)
		1734	{
		1735	// the forked child executes here
		1736	exit (1);
		1737	}
		1738	else
		1739	{
		1740	ev_child_init (&cw, child_cb, pid, 0);
		1741	ev_child_start (EV_DEFAULT_ &cw);
		1742	}
		1743
		1744
		1745	=head2 C<ev_stat> - did the file attributes just change?
		1746
		1747	This watches a file system path for attribute changes. That is, it calls
		1748	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1749	compared to the last time, invoking the callback if it did.
		1750
		1751	The path does not need to exist: changing from "path exists" to "path does
		1752	not exist" is a status change like any other. The condition "path does
		1753	not exist" is signified by the C<st_nlink> field being zero (which is
		1754	otherwise always forced to be at least one) and all the other fields of
		1755	the stat buffer having unspecified contents.
		1756
		1757	The path I<should> be absolute and I<must not> end in a slash. If it is
		1758	relative and your working directory changes, the behaviour is undefined.
		1759
		1760	Since there is no standard kernel interface to do this, the portable
		1761	implementation simply calls C<stat (2)> regularly on the path to see if
		1762	it changed somehow. You can specify a recommended polling interval for
		1763	this case. If you specify a polling interval of C<0> (highly recommended!)
		1764	then a I<suitable, unspecified default> value will be used (which
		1765	you can expect to be around five seconds, although this might change
		1766	dynamically). Libev will also impose a minimum interval which is currently
		1767	around C<0.1>, but thats usually overkill.
		1768
		1769	This watcher type is not meant for massive numbers of stat watchers,
		1770	as even with OS-supported change notifications, this can be
		1771	resource-intensive.
		1772
		1773	At the time of this writing, the only OS-specific interface implemented
		1774	is the Linux inotify interface (implementing kqueue support is left as
		1775	an exercise for the reader. Note, however, that the author sees no way
		1776	of implementing C<ev_stat> semantics with kqueue).
		1777
		1778	=head3 ABI Issues (Largefile Support)
		1779
		1780	Libev by default (unless the user overrides this) uses the default
		1781	compilation environment, which means that on systems with large file
		1782	support disabled by default, you get the 32 bit version of the stat
		1783	structure. When using the library from programs that change the ABI to
		1784	use 64 bit file offsets the programs will fail. In that case you have to
		1785	compile libev with the same flags to get binary compatibility. This is
		1786	obviously the case with any flags that change the ABI, but the problem is
		1787	most noticeably disabled with ev_stat and large file support.
		1788
		1789	The solution for this is to lobby your distribution maker to make large
		1790	file interfaces available by default (as e.g. FreeBSD does) and not
		1791	optional. Libev cannot simply switch on large file support because it has
		1792	to exchange stat structures with application programs compiled using the
		1793	default compilation environment.
		1794
		1795	=head3 Inotify and Kqueue
		1796
		1797	When C<inotify (7)> support has been compiled into libev (generally only
		1798	available with Linux) and present at runtime, it will be used to speed up
		1799	change detection where possible. The inotify descriptor will be created lazily
		1800	when the first C<ev_stat> watcher is being started.
		1801
		1802	Inotify presence does not change the semantics of C<ev_stat> watchers
		1803	except that changes might be detected earlier, and in some cases, to avoid
		1804	making regular C<stat> calls. Even in the presence of inotify support
		1805	there are many cases where libev has to resort to regular C<stat> polling,
		1806	but as long as the path exists, libev usually gets away without polling.
		1807
		1808	There is no support for kqueue, as apparently it cannot be used to
		1809	implement this functionality, due to the requirement of having a file
		1810	descriptor open on the object at all times, and detecting renames, unlinks
		1811	etc. is difficult.
		1812
		1813	=head3 The special problem of stat time resolution
		1814
		1815	The C<stat ()> system call only supports full-second resolution portably, and
		1816	even on systems where the resolution is higher, most file systems still
		1817	only support whole seconds.
		1818
		1819	That means that, if the time is the only thing that changes, you can
		1820	easily miss updates: on the first update, C<ev_stat> detects a change and
		1821	calls your callback, which does something. When there is another update
		1822	within the same second, C<ev_stat> will be unable to detect unless the
		1823	stat data does change in other ways (e.g. file size).
		1824
		1825	The solution to this is to delay acting on a change for slightly more
		1826	than a second (or till slightly after the next full second boundary), using
		1827	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1828	ev_timer_again (loop, w)>).
		1829
		1830	The C<.02> offset is added to work around small timing inconsistencies
		1831	of some operating systems (where the second counter of the current time
		1832	might be be delayed. One such system is the Linux kernel, where a call to
		1833	C<gettimeofday> might return a timestamp with a full second later than
		1834	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1835	update file times then there will be a small window where the kernel uses
		1836	the previous second to update file times but libev might already execute
		1837	the timer callback).
		1838
		1839	=head3 Watcher-Specific Functions and Data Members
		1840
		1841	=over 4
		1842
		1843	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1844
		1845	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1846
		1847	Configures the watcher to wait for status changes of the given
		1848	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1849	be detected and should normally be specified as C<0> to let libev choose
		1850	a suitable value. The memory pointed to by C<path> must point to the same
		1851	path for as long as the watcher is active.
		1852
		1853	The callback will receive an C<EV_STAT> event when a change was detected,
		1854	relative to the attributes at the time the watcher was started (or the
		1855	last change was detected).
		1856
		1857	=item ev_stat_stat (loop, ev_stat *)
		1858
		1859	Updates the stat buffer immediately with new values. If you change the
		1860	watched path in your callback, you could call this function to avoid
		1861	detecting this change (while introducing a race condition if you are not
		1862	the only one changing the path). Can also be useful simply to find out the
		1863	new values.
		1864
		1865	=item ev_statdata attr [read-only]
		1866
		1867	The most-recently detected attributes of the file. Although the type is
		1868	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1869	suitable for your system, but you can only rely on the POSIX-standardised
		1870	members to be present. If the C<st_nlink> member is C<0>, then there was
		1871	some error while C<stat>ing the file.
		1872
		1873	=item ev_statdata prev [read-only]
		1874
		1875	The previous attributes of the file. The callback gets invoked whenever
		1876	C<prev> != C<attr>, or, more precisely, one or more of these members
		1877	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1878	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1879
		1880	=item ev_tstamp interval [read-only]
		1881
		1882	The specified interval.
		1883
		1884	=item const char *path [read-only]
		1885
		1886	The file system path that is being watched.
		1887
		1888	=back
		1889
		1890	=head3 Examples
		1891
		1892	Example: Watch C</etc/passwd> for attribute changes.
		1893
		1894	static void
		1895	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1896	{
		1897	/* /etc/passwd changed in some way */
		1898	if (w->attr.st_nlink)
		1899	{
		1900	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1901	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1902	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1903	}
		1904	else
		1905	/* you shalt not abuse printf for puts */
		1906	puts ("wow, /etc/passwd is not there, expect problems. "
		1907	"if this is windows, they already arrived\n");
		1908	}
		1909
		1910	...
		1911	ev_stat passwd;
		1912
		1913	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1914	ev_stat_start (loop, &passwd);
		1915
		1916	Example: Like above, but additionally use a one-second delay so we do not
		1917	miss updates (however, frequent updates will delay processing, too, so
		1918	one might do the work both on C<ev_stat> callback invocation I<and> on
		1919	C<ev_timer> callback invocation).
		1920
		1921	static ev_stat passwd;
		1922	static ev_timer timer;
		1923
		1924	static void
		1925	timer_cb (EV_P_ ev_timer *w, int revents)
		1926	{
		1927	ev_timer_stop (EV_A_ w);
		1928
		1929	/* now it's one second after the most recent passwd change */
		1930	}
		1931
		1932	static void
		1933	stat_cb (EV_P_ ev_stat *w, int revents)
		1934	{
		1935	/* reset the one-second timer */
		1936	ev_timer_again (EV_A_ &timer);
		1937	}
		1938
		1939	...
		1940	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1941	ev_stat_start (loop, &passwd);
		1942	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1943
		1944
630	=head2 ev_idle - when you've got nothing better to do	1945	=head2 C<ev_idle> - when you've got nothing better to do...
631		1946
632	Idle watchers trigger events when there are no other I/O or timer (or	1947	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	1948	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	1949	as receiving "events").
635	is idle all idle watchers are being called again and again - until	1950
		1951	That is, as long as your process is busy handling sockets or timeouts
		1952	(or even signals, imagine) of the same or higher priority it will not be
		1953	triggered. But when your process is idle (or only lower-priority watchers
		1954	are pending), the idle watchers are being called once per event loop
636	stopped, that is, or your process receives more events.	1955	iteration - until stopped, that is, or your process receives more events
		1956	and becomes busy again with higher priority stuff.
637		1957
638	The most noteworthy effect is that as long as any idle watchers are	1958	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.	1959	active, the process will not block when waiting for new events.
640		1960
641	Apart from keeping your process non-blocking (which is a useful	1961	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	1962	effect on its own sometimes), idle watchers are a good place to do
643	"pseudo-background processing", or delay processing stuff to after the	1963	"pseudo-background processing", or delay processing stuff to after the
644	event loop has handled all outstanding events.	1964	event loop has handled all outstanding events.
645		1965
		1966	=head3 Watcher-Specific Functions and Data Members
		1967
646	=over 4	1968	=over 4
647		1969
648	=item ev_idle_init (ev_signal *, callback)	1970	=item ev_idle_init (ev_signal *, callback)
649		1971
650	Initialises and configures the idle watcher - it has no parameters of any	1972	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,	1973	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
652	believe me.	1974	believe me.
653		1975
654	=back	1976	=back
655		1977
656	=head2 prepare and check - your hooks into the event loop	1978	=head3 Examples
657		1979
		1980	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1981	callback, free it. Also, use no error checking, as usual.
		1982
		1983	static void
		1984	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1985	{
		1986	free (w);
		1987	// now do something you wanted to do when the program has
		1988	// no longer anything immediate to do.
		1989	}
		1990
		1991	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1992	ev_idle_init (idle_watcher, idle_cb);
		1993	ev_idle_start (loop, idle_cb);
		1994
		1995
		1996	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		1997
658	Prepare and check watchers usually (but not always) are used in	1998	Prepare and check watchers are usually (but not always) used in pairs:
659	tandom. Prepare watchers get invoked before the process blocks and check	1999	prepare watchers get invoked before the process blocks and check watchers
660	watchers afterwards.	2000	afterwards.
661		2001
		2002	You I<must not> call C<ev_loop> or similar functions that enter
		2003	the current event loop from either C<ev_prepare> or C<ev_check>
		2004	watchers. Other loops than the current one are fine, however. The
		2005	rationale behind this is that you do not need to check for recursion in
		2006	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2007	C<ev_check> so if you have one watcher of each kind they will always be
		2008	called in pairs bracketing the blocking call.
		2009
662	Their main purpose is to integrate other event mechanisms into libev. This	2010	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	2011	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.	2012	variable changes, implement your own watchers, integrate net-snmp or a
		2013	coroutine library and lots more. They are also occasionally useful if
		2014	you cache some data and want to flush it before blocking (for example,
		2015	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2016	watcher).
665		2017
666	This is done by examining in each prepare call which file descriptors need	2018	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	2019	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	2020	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	2021	libraries provide exactly this functionality). Then, in the check watcher,
670	events that occured (by making your callbacks set soem flags for example)	2022	you check for any events that occurred (by checking the pending status
671	and call back into the library.	2023	of all watchers and stopping them) and call back into the library. The
		2024	I/O and timer callbacks will never actually be called (but must be valid
		2025	nevertheless, because you never know, you know?).
672		2026
673	As another example, the perl Coro module uses these hooks to integrate	2027	As another example, the Perl Coro module uses these hooks to integrate
674	coroutines into libev programs, by yielding to other active coroutines	2028	coroutines into libev programs, by yielding to other active coroutines
675	during each prepare and only letting the process block if no coroutines	2029	during each prepare and only letting the process block if no coroutines
676	are ready to run.	2030	are ready to run (it's actually more complicated: it only runs coroutines
		2031	with priority higher than or equal to the event loop and one coroutine
		2032	of lower priority, but only once, using idle watchers to keep the event
		2033	loop from blocking if lower-priority coroutines are active, thus mapping
		2034	low-priority coroutines to idle/background tasks).
		2035
		2036	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2037	priority, to ensure that they are being run before any other watchers
		2038	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2039
		2040	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2041	activate ("feed") events into libev. While libev fully supports this, they
		2042	might get executed before other C<ev_check> watchers did their job. As
		2043	C<ev_check> watchers are often used to embed other (non-libev) event
		2044	loops those other event loops might be in an unusable state until their
		2045	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2046	others).
		2047
		2048	=head3 Watcher-Specific Functions and Data Members
677		2049
678	=over 4	2050	=over 4
679		2051
680	=item ev_prepare_init (ev_prepare *, callback)	2052	=item ev_prepare_init (ev_prepare *, callback)
681		2053
682	=item ev_check_init (ev_check *, callback)	2054	=item ev_check_init (ev_check *, callback)
683		2055
684	Initialises and configures the prepare or check watcher - they have no	2056	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>	2057	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
686	macros, but using them is utterly, utterly pointless.	2058	macros, but using them is utterly, utterly, utterly and completely
		2059	pointless.
687		2060
688	=back	2061	=back
689		2062
		2063	=head3 Examples
		2064
		2065	There are a number of principal ways to embed other event loops or modules
		2066	into libev. Here are some ideas on how to include libadns into libev
		2067	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2068	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2069	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2070	Glib event loop).
		2071
		2072	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2073	and in a check watcher, destroy them and call into libadns. What follows
		2074	is pseudo-code only of course. This requires you to either use a low
		2075	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2076	the callbacks for the IO/timeout watchers might not have been called yet.
		2077
		2078	static ev_io iow [nfd];
		2079	static ev_timer tw;
		2080
		2081	static void
		2082	io_cb (ev_loop *loop, ev_io *w, int revents)
		2083	{
		2084	}
		2085
		2086	// create io watchers for each fd and a timer before blocking
		2087	static void
		2088	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		2089	{
		2090	int timeout = 3600000;
		2091	struct pollfd fds [nfd];
		2092	// actual code will need to loop here and realloc etc.
		2093	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2094
		2095	/* the callback is illegal, but won't be called as we stop during check */
		2096	ev_timer_init (&tw, 0, timeout * 1e-3);
		2097	ev_timer_start (loop, &tw);
		2098
		2099	// create one ev_io per pollfd
		2100	for (int i = 0; i < nfd; ++i)
		2101	{
		2102	ev_io_init (iow + i, io_cb, fds [i].fd,
		2103	((fds [i].events & POLLIN ? EV_READ : 0)
		2104	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2105
		2106	fds [i].revents = 0;
		2107	ev_io_start (loop, iow + i);
		2108	}
		2109	}
		2110
		2111	// stop all watchers after blocking
		2112	static void
		2113	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		2114	{
		2115	ev_timer_stop (loop, &tw);
		2116
		2117	for (int i = 0; i < nfd; ++i)
		2118	{
		2119	// set the relevant poll flags
		2120	// could also call adns_processreadable etc. here
		2121	struct pollfd *fd = fds + i;
		2122	int revents = ev_clear_pending (iow + i);
		2123	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2124	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2125
		2126	// now stop the watcher
		2127	ev_io_stop (loop, iow + i);
		2128	}
		2129
		2130	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2131	}
		2132
		2133	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2134	in the prepare watcher and would dispose of the check watcher.
		2135
		2136	Method 3: If the module to be embedded supports explicit event
		2137	notification (libadns does), you can also make use of the actual watcher
		2138	callbacks, and only destroy/create the watchers in the prepare watcher.
		2139
		2140	static void
		2141	timer_cb (EV_P_ ev_timer *w, int revents)
		2142	{
		2143	adns_state ads = (adns_state)w->data;
		2144	update_now (EV_A);
		2145
		2146	adns_processtimeouts (ads, &tv_now);
		2147	}
		2148
		2149	static void
		2150	io_cb (EV_P_ ev_io *w, int revents)
		2151	{
		2152	adns_state ads = (adns_state)w->data;
		2153	update_now (EV_A);
		2154
		2155	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2156	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2157	}
		2158
		2159	// do not ever call adns_afterpoll
		2160
		2161	Method 4: Do not use a prepare or check watcher because the module you
		2162	want to embed is not flexible enough to support it. Instead, you can
		2163	override their poll function. The drawback with this solution is that the
		2164	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2165	this approach, effectively embedding EV as a client into the horrible
		2166	libglib event loop.
		2167
		2168	static gint
		2169	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2170	{
		2171	int got_events = 0;
		2172
		2173	for (n = 0; n < nfds; ++n)
		2174	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2175
		2176	if (timeout >= 0)
		2177	// create/start timer
		2178
		2179	// poll
		2180	ev_loop (EV_A_ 0);
		2181
		2182	// stop timer again
		2183	if (timeout >= 0)
		2184	ev_timer_stop (EV_A_ &to);
		2185
		2186	// stop io watchers again - their callbacks should have set
		2187	for (n = 0; n < nfds; ++n)
		2188	ev_io_stop (EV_A_ iow [n]);
		2189
		2190	return got_events;
		2191	}
		2192
		2193
		2194	=head2 C<ev_embed> - when one backend isn't enough...
		2195
		2196	This is a rather advanced watcher type that lets you embed one event loop
		2197	into another (currently only C<ev_io> events are supported in the embedded
		2198	loop, other types of watchers might be handled in a delayed or incorrect
		2199	fashion and must not be used).
		2200
		2201	There are primarily two reasons you would want that: work around bugs and
		2202	prioritise I/O.
		2203
		2204	As an example for a bug workaround, the kqueue backend might only support
		2205	sockets on some platform, so it is unusable as generic backend, but you
		2206	still want to make use of it because you have many sockets and it scales
		2207	so nicely. In this case, you would create a kqueue-based loop and embed
		2208	it into your default loop (which might use e.g. poll). Overall operation
		2209	will be a bit slower because first libev has to call C<poll> and then
		2210	C<kevent>, but at least you can use both mechanisms for what they are
		2211	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2212
		2213	As for prioritising I/O: under rare circumstances you have the case where
		2214	some fds have to be watched and handled very quickly (with low latency),
		2215	and even priorities and idle watchers might have too much overhead. In
		2216	this case you would put all the high priority stuff in one loop and all
		2217	the rest in a second one, and embed the second one in the first.
		2218
		2219	As long as the watcher is active, the callback will be invoked every time
		2220	there might be events pending in the embedded loop. The callback must then
		2221	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2222	their callbacks (you could also start an idle watcher to give the embedded
		2223	loop strictly lower priority for example). You can also set the callback
		2224	to C<0>, in which case the embed watcher will automatically execute the
		2225	embedded loop sweep.
		2226
		2227	As long as the watcher is started it will automatically handle events. The
		2228	callback will be invoked whenever some events have been handled. You can
		2229	set the callback to C<0> to avoid having to specify one if you are not
		2230	interested in that.
		2231
		2232	Also, there have not currently been made special provisions for forking:
		2233	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2234	but you will also have to stop and restart any C<ev_embed> watchers
		2235	yourself - but you can use a fork watcher to handle this automatically,
		2236	and future versions of libev might do just that.
		2237
		2238	Unfortunately, not all backends are embeddable, only the ones returned by
		2239	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2240	portable one.
		2241
		2242	So when you want to use this feature you will always have to be prepared
		2243	that you cannot get an embeddable loop. The recommended way to get around
		2244	this is to have a separate variables for your embeddable loop, try to
		2245	create it, and if that fails, use the normal loop for everything.
		2246
		2247	=head3 Watcher-Specific Functions and Data Members
		2248
		2249	=over 4
		2250
		2251	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2252
		2253	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2254
		2255	Configures the watcher to embed the given loop, which must be
		2256	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2257	invoked automatically, otherwise it is the responsibility of the callback
		2258	to invoke it (it will continue to be called until the sweep has been done,
		2259	if you do not want that, you need to temporarily stop the embed watcher).
		2260
		2261	=item ev_embed_sweep (loop, ev_embed *)
		2262
		2263	Make a single, non-blocking sweep over the embedded loop. This works
		2264	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2265	appropriate way for embedded loops.
		2266
		2267	=item struct ev_loop *other [read-only]
		2268
		2269	The embedded event loop.
		2270
		2271	=back
		2272
		2273	=head3 Examples
		2274
		2275	Example: Try to get an embeddable event loop and embed it into the default
		2276	event loop. If that is not possible, use the default loop. The default
		2277	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2278	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2279	used).
		2280
		2281	struct ev_loop *loop_hi = ev_default_init (0);
		2282	struct ev_loop *loop_lo = 0;
		2283	struct ev_embed embed;
		2284
		2285	// see if there is a chance of getting one that works
		2286	// (remember that a flags value of 0 means autodetection)
		2287	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2288	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2289	: 0;
		2290
		2291	// if we got one, then embed it, otherwise default to loop_hi
		2292	if (loop_lo)
		2293	{
		2294	ev_embed_init (&embed, 0, loop_lo);
		2295	ev_embed_start (loop_hi, &embed);
		2296	}
		2297	else
		2298	loop_lo = loop_hi;
		2299
		2300	Example: Check if kqueue is available but not recommended and create
		2301	a kqueue backend for use with sockets (which usually work with any
		2302	kqueue implementation). Store the kqueue/socket-only event loop in
		2303	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2304
		2305	struct ev_loop *loop = ev_default_init (0);
		2306	struct ev_loop *loop_socket = 0;
		2307	struct ev_embed embed;
		2308
		2309	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2310	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2311	{
		2312	ev_embed_init (&embed, 0, loop_socket);
		2313	ev_embed_start (loop, &embed);
		2314	}
		2315
		2316	if (!loop_socket)
		2317	loop_socket = loop;
		2318
		2319	// now use loop_socket for all sockets, and loop for everything else
		2320
		2321
		2322	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2323
		2324	Fork watchers are called when a C<fork ()> was detected (usually because
		2325	whoever is a good citizen cared to tell libev about it by calling
		2326	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2327	event loop blocks next and before C<ev_check> watchers are being called,
		2328	and only in the child after the fork. If whoever good citizen calling
		2329	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2330	handlers will be invoked, too, of course.
		2331
		2332	=head3 Watcher-Specific Functions and Data Members
		2333
		2334	=over 4
		2335
		2336	=item ev_fork_init (ev_signal *, callback)
		2337
		2338	Initialises and configures the fork watcher - it has no parameters of any
		2339	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2340	believe me.
		2341
		2342	=back
		2343
		2344
		2345	=head2 C<ev_async> - how to wake up another event loop
		2346
		2347	In general, you cannot use an C<ev_loop> from multiple threads or other
		2348	asynchronous sources such as signal handlers (as opposed to multiple event
		2349	loops - those are of course safe to use in different threads).
		2350
		2351	Sometimes, however, you need to wake up another event loop you do not
		2352	control, for example because it belongs to another thread. This is what
		2353	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2354	can signal it by calling C<ev_async_send>, which is thread- and signal
		2355	safe.
		2356
		2357	This functionality is very similar to C<ev_signal> watchers, as signals,
		2358	too, are asynchronous in nature, and signals, too, will be compressed
		2359	(i.e. the number of callback invocations may be less than the number of
		2360	C<ev_async_sent> calls).
		2361
		2362	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2363	just the default loop.
		2364
		2365	=head3 Queueing
		2366
		2367	C<ev_async> does not support queueing of data in any way. The reason
		2368	is that the author does not know of a simple (or any) algorithm for a
		2369	multiple-writer-single-reader queue that works in all cases and doesn't
		2370	need elaborate support such as pthreads.
		2371
		2372	That means that if you want to queue data, you have to provide your own
		2373	queue. But at least I can tell you would implement locking around your
		2374	queue:
		2375
		2376	=over 4
		2377
		2378	=item queueing from a signal handler context
		2379
		2380	To implement race-free queueing, you simply add to the queue in the signal
		2381	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2382	some fictitious SIGUSR1 handler:
		2383
		2384	static ev_async mysig;
		2385
		2386	static void
		2387	sigusr1_handler (void)
		2388	{
		2389	sometype data;
		2390
		2391	// no locking etc.
		2392	queue_put (data);
		2393	ev_async_send (EV_DEFAULT_ &mysig);
		2394	}
		2395
		2396	static void
		2397	mysig_cb (EV_P_ ev_async *w, int revents)
		2398	{
		2399	sometype data;
		2400	sigset_t block, prev;
		2401
		2402	sigemptyset (&block);
		2403	sigaddset (&block, SIGUSR1);
		2404	sigprocmask (SIG_BLOCK, &block, &prev);
		2405
		2406	while (queue_get (&data))
		2407	process (data);
		2408
		2409	if (sigismember (&prev, SIGUSR1)
		2410	sigprocmask (SIG_UNBLOCK, &block, 0);
		2411	}
		2412
		2413	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2414	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2415	either...).
		2416
		2417	=item queueing from a thread context
		2418
		2419	The strategy for threads is different, as you cannot (easily) block
		2420	threads but you can easily preempt them, so to queue safely you need to
		2421	employ a traditional mutex lock, such as in this pthread example:
		2422
		2423	static ev_async mysig;
		2424	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2425
		2426	static void
		2427	otherthread (void)
		2428	{
		2429	// only need to lock the actual queueing operation
		2430	pthread_mutex_lock (&mymutex);
		2431	queue_put (data);
		2432	pthread_mutex_unlock (&mymutex);
		2433
		2434	ev_async_send (EV_DEFAULT_ &mysig);
		2435	}
		2436
		2437	static void
		2438	mysig_cb (EV_P_ ev_async *w, int revents)
		2439	{
		2440	pthread_mutex_lock (&mymutex);
		2441
		2442	while (queue_get (&data))
		2443	process (data);
		2444
		2445	pthread_mutex_unlock (&mymutex);
		2446	}
		2447
		2448	=back
		2449
		2450
		2451	=head3 Watcher-Specific Functions and Data Members
		2452
		2453	=over 4
		2454
		2455	=item ev_async_init (ev_async *, callback)
		2456
		2457	Initialises and configures the async watcher - it has no parameters of any
		2458	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2459	believe me.
		2460
		2461	=item ev_async_send (loop, ev_async *)
		2462
		2463	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2464	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2465	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2466	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2467	section below on what exactly this means).
		2468
		2469	This call incurs the overhead of a system call only once per loop iteration,
		2470	so while the overhead might be noticeable, it doesn't apply to repeated
		2471	calls to C<ev_async_send>.
		2472
		2473	=item bool = ev_async_pending (ev_async *)
		2474
		2475	Returns a non-zero value when C<ev_async_send> has been called on the
		2476	watcher but the event has not yet been processed (or even noted) by the
		2477	event loop.
		2478
		2479	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2480	the loop iterates next and checks for the watcher to have become active,
		2481	it will reset the flag again. C<ev_async_pending> can be used to very
		2482	quickly check whether invoking the loop might be a good idea.
		2483
		2484	Not that this does I<not> check whether the watcher itself is pending, only
		2485	whether it has been requested to make this watcher pending.
		2486
		2487	=back
		2488
		2489
690	=head1 OTHER FUNCTIONS	2490	=head1 OTHER FUNCTIONS
691		2491
692	There are some other fucntions of possible interest. Described. Here. Now.	2492	There are some other functions of possible interest. Described. Here. Now.
693		2493
694	=over 4	2494	=over 4
695		2495
696	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2496	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
697		2497
698	This function combines a simple timer and an I/O watcher, calls your	2498	This function combines a simple timer and an I/O watcher, calls your
699	callback on whichever event happens first and automatically stop both	2499	callback on whichever event happens first and automatically stop both
700	watchers. This is useful if you want to wait for a single event on an fd	2500	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	2501	or timeout without having to allocate/configure/start/stop/free one or
702	more watchers yourself.	2502	more watchers yourself.
703		2503
704	If C<fd> is less than 0, then no I/O watcher will be started and events is	2504	If C<fd> is less than 0, then no I/O watcher will be started and events
705	ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set	2505	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
706	will be craeted and started.	2506	C<events> set will be created and started.
707		2507
708	If C<timeout> is less than 0, then no timeout watcher will be	2508	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	2509	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
710	= 0) will be started.	2510	repeat = 0) will be started. While C<0> is a valid timeout, it is of
		2511	dubious value.
711		2512
712	The callback has the type C<void (*cb)(int revents, void *arg)> and	2513	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,	2514	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>:	2515	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
		2516	value passed to C<ev_once>:
715		2517
716	static void stdin_ready (int revents, void *arg)	2518	static void stdin_ready (int revents, void *arg)
717	{	2519	{
718	if (revents & EV_TIMEOUT)	2520	if (revents & EV_TIMEOUT)
719	/* doh, nothing entered */	2521	/* doh, nothing entered */;
720	else if (revents & EV_READ)	2522	else if (revents & EV_READ)
721	/* stdin might have data for us, joy! */	2523	/* stdin might have data for us, joy! */;
722	}	2524	}
723		2525
724	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	2526	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
725		2527
726	=item ev_feed_event (loop, watcher, int events)	2528	=item ev_feed_event (ev_loop *, watcher *, int revents)
727		2529
728	Feeds the given event set into the event loop, as if the specified event	2530	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	2531	had happened for the specified watcher (which must be a pointer to an
730	initialised but not necessarily active event watcher).	2532	initialised but not necessarily started event watcher).
731		2533
732	=item ev_feed_fd_event (loop, int fd, int revents)	2534	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
733		2535
734	Feed an event on the given fd, as if a file descriptor backend detected it.	2536	Feed an event on the given fd, as if a file descriptor backend detected
		2537	the given events it.
735		2538
736	=item ev_feed_signal_event (loop, int signum)	2539	=item ev_feed_signal_event (ev_loop *loop, int signum)
737		2540
738	Feed an event as if the given signal occured (loop must be the default loop!).	2541	Feed an event as if the given signal occurred (C<loop> must be the default
		2542	loop!).
739		2543
740	=back	2544	=back
741		2545
		2546
		2547	=head1 LIBEVENT EMULATION
		2548
		2549	Libev offers a compatibility emulation layer for libevent. It cannot
		2550	emulate the internals of libevent, so here are some usage hints:
		2551
		2552	=over 4
		2553
		2554	=item * Use it by including <event.h>, as usual.
		2555
		2556	=item * The following members are fully supported: ev_base, ev_callback,
		2557	ev_arg, ev_fd, ev_res, ev_events.
		2558
		2559	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2560	maintained by libev, it does not work exactly the same way as in libevent (consider
		2561	it a private API).
		2562
		2563	=item * Priorities are not currently supported. Initialising priorities
		2564	will fail and all watchers will have the same priority, even though there
		2565	is an ev_pri field.
		2566
		2567	=item * In libevent, the last base created gets the signals, in libev, the
		2568	first base created (== the default loop) gets the signals.
		2569
		2570	=item * Other members are not supported.
		2571
		2572	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2573	to use the libev header file and library.
		2574
		2575	=back
		2576
		2577	=head1 C++ SUPPORT
		2578
		2579	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2580	you to use some convenience methods to start/stop watchers and also change
		2581	the callback model to a model using method callbacks on objects.
		2582
		2583	To use it,
		2584
		2585	#include <ev++.h>
		2586
		2587	This automatically includes F<ev.h> and puts all of its definitions (many
		2588	of them macros) into the global namespace. All C++ specific things are
		2589	put into the C<ev> namespace. It should support all the same embedding
		2590	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2591
		2592	Care has been taken to keep the overhead low. The only data member the C++
		2593	classes add (compared to plain C-style watchers) is the event loop pointer
		2594	that the watcher is associated with (or no additional members at all if
		2595	you disable C<EV_MULTIPLICITY> when embedding libev).
		2596
		2597	Currently, functions, and static and non-static member functions can be
		2598	used as callbacks. Other types should be easy to add as long as they only
		2599	need one additional pointer for context. If you need support for other
		2600	types of functors please contact the author (preferably after implementing
		2601	it).
		2602
		2603	Here is a list of things available in the C<ev> namespace:
		2604
		2605	=over 4
		2606
		2607	=item C<ev::READ>, C<ev::WRITE> etc.
		2608
		2609	These are just enum values with the same values as the C<EV_READ> etc.
		2610	macros from F<ev.h>.
		2611
		2612	=item C<ev::tstamp>, C<ev::now>
		2613
		2614	Aliases to the same types/functions as with the C<ev_> prefix.
		2615
		2616	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2617
		2618	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2619	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2620	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2621	defines by many implementations.
		2622
		2623	All of those classes have these methods:
		2624
		2625	=over 4
		2626
		2627	=item ev::TYPE::TYPE ()
		2628
		2629	=item ev::TYPE::TYPE (struct ev_loop *)
		2630
		2631	=item ev::TYPE::~TYPE
		2632
		2633	The constructor (optionally) takes an event loop to associate the watcher
		2634	with. If it is omitted, it will use C<EV_DEFAULT>.
		2635
		2636	The constructor calls C<ev_init> for you, which means you have to call the
		2637	C<set> method before starting it.
		2638
		2639	It will not set a callback, however: You have to call the templated C<set>
		2640	method to set a callback before you can start the watcher.
		2641
		2642	(The reason why you have to use a method is a limitation in C++ which does
		2643	not allow explicit template arguments for constructors).
		2644
		2645	The destructor automatically stops the watcher if it is active.
		2646
		2647	=item w->set<class, &class::method> (object *)
		2648
		2649	This method sets the callback method to call. The method has to have a
		2650	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2651	first argument and the C<revents> as second. The object must be given as
		2652	parameter and is stored in the C<data> member of the watcher.
		2653
		2654	This method synthesizes efficient thunking code to call your method from
		2655	the C callback that libev requires. If your compiler can inline your
		2656	callback (i.e. it is visible to it at the place of the C<set> call and
		2657	your compiler is good :), then the method will be fully inlined into the
		2658	thunking function, making it as fast as a direct C callback.
		2659
		2660	Example: simple class declaration and watcher initialisation
		2661
		2662	struct myclass
		2663	{
		2664	void io_cb (ev::io &w, int revents) { }
		2665	}
		2666
		2667	myclass obj;
		2668	ev::io iow;
		2669	iow.set <myclass, &myclass::io_cb> (&obj);
		2670
		2671	=item w->set<function> (void *data = 0)
		2672
		2673	Also sets a callback, but uses a static method or plain function as
		2674	callback. The optional C<data> argument will be stored in the watcher's
		2675	C<data> member and is free for you to use.
		2676
		2677	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2678
		2679	See the method-C<set> above for more details.
		2680
		2681	Example:
		2682
		2683	static void io_cb (ev::io &w, int revents) { }
		2684	iow.set <io_cb> ();
		2685
		2686	=item w->set (struct ev_loop *)
		2687
		2688	Associates a different C<struct ev_loop> with this watcher. You can only
		2689	do this when the watcher is inactive (and not pending either).
		2690
		2691	=item w->set ([arguments])
		2692
		2693	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2694	called at least once. Unlike the C counterpart, an active watcher gets
		2695	automatically stopped and restarted when reconfiguring it with this
		2696	method.
		2697
		2698	=item w->start ()
		2699
		2700	Starts the watcher. Note that there is no C<loop> argument, as the
		2701	constructor already stores the event loop.
		2702
		2703	=item w->stop ()
		2704
		2705	Stops the watcher if it is active. Again, no C<loop> argument.
		2706
		2707	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2708
		2709	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2710	C<ev_TYPE_again> function.
		2711
		2712	=item w->sweep () (C<ev::embed> only)
		2713
		2714	Invokes C<ev_embed_sweep>.
		2715
		2716	=item w->update () (C<ev::stat> only)
		2717
		2718	Invokes C<ev_stat_stat>.
		2719
		2720	=back
		2721
		2722	=back
		2723
		2724	Example: Define a class with an IO and idle watcher, start one of them in
		2725	the constructor.
		2726
		2727	class myclass
		2728	{
		2729	ev::io io; void io_cb (ev::io &w, int revents);
		2730	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2731
		2732	myclass (int fd)
		2733	{
		2734	io .set <myclass, &myclass::io_cb > (this);
		2735	idle.set <myclass, &myclass::idle_cb> (this);
		2736
		2737	io.start (fd, ev::READ);
		2738	}
		2739	};
		2740
		2741
		2742	=head1 OTHER LANGUAGE BINDINGS
		2743
		2744	Libev does not offer other language bindings itself, but bindings for a
		2745	number of languages exist in the form of third-party packages. If you know
		2746	any interesting language binding in addition to the ones listed here, drop
		2747	me a note.
		2748
		2749	=over 4
		2750
		2751	=item Perl
		2752
		2753	The EV module implements the full libev API and is actually used to test
		2754	libev. EV is developed together with libev. Apart from the EV core module,
		2755	there are additional modules that implement libev-compatible interfaces
		2756	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2757	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2758
		2759	It can be found and installed via CPAN, its homepage is at
		2760	L<http://software.schmorp.de/pkg/EV>.
		2761
		2762	=item Python
		2763
		2764	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2765	seems to be quite complete and well-documented. Note, however, that the
		2766	patch they require for libev is outright dangerous as it breaks the ABI
		2767	for everybody else, and therefore, should never be applied in an installed
		2768	libev (if python requires an incompatible ABI then it needs to embed
		2769	libev).
		2770
		2771	=item Ruby
		2772
		2773	Tony Arcieri has written a ruby extension that offers access to a subset
		2774	of the libev API and adds file handle abstractions, asynchronous DNS and
		2775	more on top of it. It can be found via gem servers. Its homepage is at
		2776	L<http://rev.rubyforge.org/>.
		2777
		2778	=item D
		2779
		2780	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2781	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2782
		2783	=back
		2784
		2785
		2786	=head1 MACRO MAGIC
		2787
		2788	Libev can be compiled with a variety of options, the most fundamental
		2789	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2790	functions and callbacks have an initial C<struct ev_loop *> argument.
		2791
		2792	To make it easier to write programs that cope with either variant, the
		2793	following macros are defined:
		2794
		2795	=over 4
		2796
		2797	=item C<EV_A>, C<EV_A_>
		2798
		2799	This provides the loop I<argument> for functions, if one is required ("ev
		2800	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2801	C<EV_A_> is used when other arguments are following. Example:
		2802
		2803	ev_unref (EV_A);
		2804	ev_timer_add (EV_A_ watcher);
		2805	ev_loop (EV_A_ 0);
		2806
		2807	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2808	which is often provided by the following macro.
		2809
		2810	=item C<EV_P>, C<EV_P_>
		2811
		2812	This provides the loop I<parameter> for functions, if one is required ("ev
		2813	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2814	C<EV_P_> is used when other parameters are following. Example:
		2815
		2816	// this is how ev_unref is being declared
		2817	static void ev_unref (EV_P);
		2818
		2819	// this is how you can declare your typical callback
		2820	static void cb (EV_P_ ev_timer *w, int revents)
		2821
		2822	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2823	suitable for use with C<EV_A>.
		2824
		2825	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2826
		2827	Similar to the other two macros, this gives you the value of the default
		2828	loop, if multiple loops are supported ("ev loop default").
		2829
		2830	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2831
		2832	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2833	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2834	is undefined when the default loop has not been initialised by a previous
		2835	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2836
		2837	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2838	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2839
		2840	=back
		2841
		2842	Example: Declare and initialise a check watcher, utilising the above
		2843	macros so it will work regardless of whether multiple loops are supported
		2844	or not.
		2845
		2846	static void
		2847	check_cb (EV_P_ ev_timer *w, int revents)
		2848	{
		2849	ev_check_stop (EV_A_ w);
		2850	}
		2851
		2852	ev_check check;
		2853	ev_check_init (&check, check_cb);
		2854	ev_check_start (EV_DEFAULT_ &check);
		2855	ev_loop (EV_DEFAULT_ 0);
		2856
		2857	=head1 EMBEDDING
		2858
		2859	Libev can (and often is) directly embedded into host
		2860	applications. Examples of applications that embed it include the Deliantra
		2861	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2862	and rxvt-unicode.
		2863
		2864	The goal is to enable you to just copy the necessary files into your
		2865	source directory without having to change even a single line in them, so
		2866	you can easily upgrade by simply copying (or having a checked-out copy of
		2867	libev somewhere in your source tree).
		2868
		2869	=head2 FILESETS
		2870
		2871	Depending on what features you need you need to include one or more sets of files
		2872	in your application.
		2873
		2874	=head3 CORE EVENT LOOP
		2875
		2876	To include only the libev core (all the C<ev_*> functions), with manual
		2877	configuration (no autoconf):
		2878
		2879	#define EV_STANDALONE 1
		2880	#include "ev.c"
		2881
		2882	This will automatically include F<ev.h>, too, and should be done in a
		2883	single C source file only to provide the function implementations. To use
		2884	it, do the same for F<ev.h> in all files wishing to use this API (best
		2885	done by writing a wrapper around F<ev.h> that you can include instead and
		2886	where you can put other configuration options):
		2887
		2888	#define EV_STANDALONE 1
		2889	#include "ev.h"
		2890
		2891	Both header files and implementation files can be compiled with a C++
		2892	compiler (at least, thats a stated goal, and breakage will be treated
		2893	as a bug).
		2894
		2895	You need the following files in your source tree, or in a directory
		2896	in your include path (e.g. in libev/ when using -Ilibev):
		2897
		2898	ev.h
		2899	ev.c
		2900	ev_vars.h
		2901	ev_wrap.h
		2902
		2903	ev_win32.c required on win32 platforms only
		2904
		2905	ev_select.c only when select backend is enabled (which is enabled by default)
		2906	ev_poll.c only when poll backend is enabled (disabled by default)
		2907	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2908	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2909	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2910
		2911	F<ev.c> includes the backend files directly when enabled, so you only need
		2912	to compile this single file.
		2913
		2914	=head3 LIBEVENT COMPATIBILITY API
		2915
		2916	To include the libevent compatibility API, also include:
		2917
		2918	#include "event.c"
		2919
		2920	in the file including F<ev.c>, and:
		2921
		2922	#include "event.h"
		2923
		2924	in the files that want to use the libevent API. This also includes F<ev.h>.
		2925
		2926	You need the following additional files for this:
		2927
		2928	event.h
		2929	event.c
		2930
		2931	=head3 AUTOCONF SUPPORT
		2932
		2933	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		2934	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2935	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2936	include F<config.h> and configure itself accordingly.
		2937
		2938	For this of course you need the m4 file:
		2939
		2940	libev.m4
		2941
		2942	=head2 PREPROCESSOR SYMBOLS/MACROS
		2943
		2944	Libev can be configured via a variety of preprocessor symbols you have to
		2945	define before including any of its files. The default in the absence of
		2946	autoconf is noted for every option.
		2947
		2948	=over 4
		2949
		2950	=item EV_STANDALONE
		2951
		2952	Must always be C<1> if you do not use autoconf configuration, which
		2953	keeps libev from including F<config.h>, and it also defines dummy
		2954	implementations for some libevent functions (such as logging, which is not
		2955	supported). It will also not define any of the structs usually found in
		2956	F<event.h> that are not directly supported by the libev core alone.
		2957
		2958	=item EV_USE_MONOTONIC
		2959
		2960	If defined to be C<1>, libev will try to detect the availability of the
		2961	monotonic clock option at both compile time and runtime. Otherwise no use
		2962	of the monotonic clock option will be attempted. If you enable this, you
		2963	usually have to link against librt or something similar. Enabling it when
		2964	the functionality isn't available is safe, though, although you have
		2965	to make sure you link against any libraries where the C<clock_gettime>
		2966	function is hiding in (often F<-lrt>).
		2967
		2968	=item EV_USE_REALTIME
		2969
		2970	If defined to be C<1>, libev will try to detect the availability of the
		2971	real-time clock option at compile time (and assume its availability at
		2972	runtime if successful). Otherwise no use of the real-time clock option will
		2973	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2974	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2975	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2976
		2977	=item EV_USE_NANOSLEEP
		2978
		2979	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2980	and will use it for delays. Otherwise it will use C<select ()>.
		2981
		2982	=item EV_USE_EVENTFD
		2983
		2984	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2985	available and will probe for kernel support at runtime. This will improve
		2986	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2987	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2988	2.7 or newer, otherwise disabled.
		2989
		2990	=item EV_USE_SELECT
		2991
		2992	If undefined or defined to be C<1>, libev will compile in support for the
		2993	C<select>(2) backend. No attempt at auto-detection will be done: if no
		2994	other method takes over, select will be it. Otherwise the select backend
		2995	will not be compiled in.
		2996
		2997	=item EV_SELECT_USE_FD_SET
		2998
		2999	If defined to C<1>, then the select backend will use the system C<fd_set>
		3000	structure. This is useful if libev doesn't compile due to a missing
		3001	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		3002	exotic systems. This usually limits the range of file descriptors to some
		3003	low limit such as 1024 or might have other limitations (winsocket only
		3004	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		3005	influence the size of the C<fd_set> used.
		3006
		3007	=item EV_SELECT_IS_WINSOCKET
		3008
		3009	When defined to C<1>, the select backend will assume that
		3010	select/socket/connect etc. don't understand file descriptors but
		3011	wants osf handles on win32 (this is the case when the select to
		3012	be used is the winsock select). This means that it will call
		3013	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3014	it is assumed that all these functions actually work on fds, even
		3015	on win32. Should not be defined on non-win32 platforms.
		3016
		3017	=item EV_FD_TO_WIN32_HANDLE
		3018
		3019	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3020	file descriptors to socket handles. When not defining this symbol (the
		3021	default), then libev will call C<_get_osfhandle>, which is usually
		3022	correct. In some cases, programs use their own file descriptor management,
		3023	in which case they can provide this function to map fds to socket handles.
		3024
		3025	=item EV_USE_POLL
		3026
		3027	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3028	backend. Otherwise it will be enabled on non-win32 platforms. It
		3029	takes precedence over select.
		3030
		3031	=item EV_USE_EPOLL
		3032
		3033	If defined to be C<1>, libev will compile in support for the Linux
		3034	C<epoll>(7) backend. Its availability will be detected at runtime,
		3035	otherwise another method will be used as fallback. This is the preferred
		3036	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3037	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3038
		3039	=item EV_USE_KQUEUE
		3040
		3041	If defined to be C<1>, libev will compile in support for the BSD style
		3042	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3043	otherwise another method will be used as fallback. This is the preferred
		3044	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3045	supports some types of fds correctly (the only platform we found that
		3046	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3047	not be used unless explicitly requested. The best way to use it is to find
		3048	out whether kqueue supports your type of fd properly and use an embedded
		3049	kqueue loop.
		3050
		3051	=item EV_USE_PORT
		3052
		3053	If defined to be C<1>, libev will compile in support for the Solaris
		3054	10 port style backend. Its availability will be detected at runtime,
		3055	otherwise another method will be used as fallback. This is the preferred
		3056	backend for Solaris 10 systems.
		3057
		3058	=item EV_USE_DEVPOLL
		3059
		3060	Reserved for future expansion, works like the USE symbols above.
		3061
		3062	=item EV_USE_INOTIFY
		3063
		3064	If defined to be C<1>, libev will compile in support for the Linux inotify
		3065	interface to speed up C<ev_stat> watchers. Its actual availability will
		3066	be detected at runtime. If undefined, it will be enabled if the headers
		3067	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3068
		3069	=item EV_ATOMIC_T
		3070
		3071	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3072	access is atomic with respect to other threads or signal contexts. No such
		3073	type is easily found in the C language, so you can provide your own type
		3074	that you know is safe for your purposes. It is used both for signal handler "locking"
		3075	as well as for signal and thread safety in C<ev_async> watchers.
		3076
		3077	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3078	(from F<signal.h>), which is usually good enough on most platforms.
		3079
		3080	=item EV_H
		3081
		3082	The name of the F<ev.h> header file used to include it. The default if
		3083	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3084	used to virtually rename the F<ev.h> header file in case of conflicts.
		3085
		3086	=item EV_CONFIG_H
		3087
		3088	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3089	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3090	C<EV_H>, above.
		3091
		3092	=item EV_EVENT_H
		3093
		3094	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3095	of how the F<event.h> header can be found, the default is C<"event.h">.
		3096
		3097	=item EV_PROTOTYPES
		3098
		3099	If defined to be C<0>, then F<ev.h> will not define any function
		3100	prototypes, but still define all the structs and other symbols. This is
		3101	occasionally useful if you want to provide your own wrapper functions
		3102	around libev functions.
		3103
		3104	=item EV_MULTIPLICITY
		3105
		3106	If undefined or defined to C<1>, then all event-loop-specific functions
		3107	will have the C<struct ev_loop *> as first argument, and you can create
		3108	additional independent event loops. Otherwise there will be no support
		3109	for multiple event loops and there is no first event loop pointer
		3110	argument. Instead, all functions act on the single default loop.
		3111
		3112	=item EV_MINPRI
		3113
		3114	=item EV_MAXPRI
		3115
		3116	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3117	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3118	provide for more priorities by overriding those symbols (usually defined
		3119	to be C<-2> and C<2>, respectively).
		3120
		3121	When doing priority-based operations, libev usually has to linearly search
		3122	all the priorities, so having many of them (hundreds) uses a lot of space
		3123	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3124	fine.
		3125
		3126	If your embedding application does not need any priorities, defining these both to
		3127	C<0> will save some memory and CPU.
		3128
		3129	=item EV_PERIODIC_ENABLE
		3130
		3131	If undefined or defined to be C<1>, then periodic timers are supported. If
		3132	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3133	code.
		3134
		3135	=item EV_IDLE_ENABLE
		3136
		3137	If undefined or defined to be C<1>, then idle watchers are supported. If
		3138	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3139	code.
		3140
		3141	=item EV_EMBED_ENABLE
		3142
		3143	If undefined or defined to be C<1>, then embed watchers are supported. If
		3144	defined to be C<0>, then they are not.
		3145
		3146	=item EV_STAT_ENABLE
		3147
		3148	If undefined or defined to be C<1>, then stat watchers are supported. If
		3149	defined to be C<0>, then they are not.
		3150
		3151	=item EV_FORK_ENABLE
		3152
		3153	If undefined or defined to be C<1>, then fork watchers are supported. If
		3154	defined to be C<0>, then they are not.
		3155
		3156	=item EV_ASYNC_ENABLE
		3157
		3158	If undefined or defined to be C<1>, then async watchers are supported. If
		3159	defined to be C<0>, then they are not.
		3160
		3161	=item EV_MINIMAL
		3162
		3163	If you need to shave off some kilobytes of code at the expense of some
		3164	speed, define this symbol to C<1>. Currently this is used to override some
		3165	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3166	much smaller 2-heap for timer management over the default 4-heap.
		3167
		3168	=item EV_PID_HASHSIZE
		3169
		3170	C<ev_child> watchers use a small hash table to distribute workload by
		3171	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3172	than enough. If you need to manage thousands of children you might want to
		3173	increase this value (I<must> be a power of two).
		3174
		3175	=item EV_INOTIFY_HASHSIZE
		3176
		3177	C<ev_stat> watchers use a small hash table to distribute workload by
		3178	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3179	usually more than enough. If you need to manage thousands of C<ev_stat>
		3180	watchers you might want to increase this value (I<must> be a power of
		3181	two).
		3182
		3183	=item EV_USE_4HEAP
		3184
		3185	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3186	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3187	to C<1>. The 4-heap uses more complicated (longer) code but has
		3188	noticeably faster performance with many (thousands) of watchers.
		3189
		3190	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3191	(disabled).
		3192
		3193	=item EV_HEAP_CACHE_AT
		3194
		3195	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3196	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3197	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3198	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3199	but avoids random read accesses on heap changes. This improves performance
		3200	noticeably with with many (hundreds) of watchers.
		3201
		3202	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3203	(disabled).
		3204
		3205	=item EV_VERIFY
		3206
		3207	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3208	be done: If set to C<0>, no internal verification code will be compiled
		3209	in. If set to C<1>, then verification code will be compiled in, but not
		3210	called. If set to C<2>, then the internal verification code will be
		3211	called once per loop, which can slow down libev. If set to C<3>, then the
		3212	verification code will be called very frequently, which will slow down
		3213	libev considerably.
		3214
		3215	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3216	C<0.>
		3217
		3218	=item EV_COMMON
		3219
		3220	By default, all watchers have a C<void *data> member. By redefining
		3221	this macro to a something else you can include more and other types of
		3222	members. You have to define it each time you include one of the files,
		3223	though, and it must be identical each time.
		3224
		3225	For example, the perl EV module uses something like this:
		3226
		3227	#define EV_COMMON \
		3228	SV *self; /* contains this struct */ \
		3229	SV *cb_sv, *fh /* note no trailing ";" */
		3230
		3231	=item EV_CB_DECLARE (type)
		3232
		3233	=item EV_CB_INVOKE (watcher, revents)
		3234
		3235	=item ev_set_cb (ev, cb)
		3236
		3237	Can be used to change the callback member declaration in each watcher,
		3238	and the way callbacks are invoked and set. Must expand to a struct member
		3239	definition and a statement, respectively. See the F<ev.h> header file for
		3240	their default definitions. One possible use for overriding these is to
		3241	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3242	method calls instead of plain function calls in C++.
		3243
		3244	=head2 EXPORTED API SYMBOLS
		3245
		3246	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3247	exported symbols, you can use the provided F<Symbol.*> files which list
		3248	all public symbols, one per line:
		3249
		3250	Symbols.ev for libev proper
		3251	Symbols.event for the libevent emulation
		3252
		3253	This can also be used to rename all public symbols to avoid clashes with
		3254	multiple versions of libev linked together (which is obviously bad in
		3255	itself, but sometimes it is inconvenient to avoid this).
		3256
		3257	A sed command like this will create wrapper C<#define>'s that you need to
		3258	include before including F<ev.h>:
		3259
		3260	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3261
		3262	This would create a file F<wrap.h> which essentially looks like this:
		3263
		3264	#define ev_backend myprefix_ev_backend
		3265	#define ev_check_start myprefix_ev_check_start
		3266	#define ev_check_stop myprefix_ev_check_stop
		3267	...
		3268
		3269	=head2 EXAMPLES
		3270
		3271	For a real-world example of a program the includes libev
		3272	verbatim, you can have a look at the EV perl module
		3273	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3274	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3275	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3276	will be compiled. It is pretty complex because it provides its own header
		3277	file.
		3278
		3279	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3280	that everybody includes and which overrides some configure choices:
		3281
		3282	#define EV_MINIMAL 1
		3283	#define EV_USE_POLL 0
		3284	#define EV_MULTIPLICITY 0
		3285	#define EV_PERIODIC_ENABLE 0
		3286	#define EV_STAT_ENABLE 0
		3287	#define EV_FORK_ENABLE 0
		3288	#define EV_CONFIG_H <config.h>
		3289	#define EV_MINPRI 0
		3290	#define EV_MAXPRI 0
		3291
		3292	#include "ev++.h"
		3293
		3294	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3295
		3296	#include "ev_cpp.h"
		3297	#include "ev.c"
		3298
		3299
		3300	=head1 THREADS AND COROUTINES
		3301
		3302	=head2 THREADS
		3303
		3304	Libev itself is thread-safe (unless the opposite is specifically
		3305	documented for a function), but it uses no locking itself. This means that
		3306	you can use as many loops as you want in parallel, as long as only one
		3307	thread ever calls into one libev function with the same loop parameter:
		3308	libev guarentees that different event loops share no data structures that
		3309	need locking.
		3310
		3311	Or to put it differently: calls with different loop parameters can be done
		3312	concurrently from multiple threads, calls with the same loop parameter
		3313	must be done serially (but can be done from different threads, as long as
		3314	only one thread ever is inside a call at any point in time, e.g. by using
		3315	a mutex per loop).
		3316
		3317	Specifically to support threads (and signal handlers), libev implements
		3318	so-called C<ev_async> watchers, which allow some limited form of
		3319	concurrency on the same event loop.
		3320
		3321	If you want to know which design (one loop, locking, or multiple loops
		3322	without or something else still) is best for your problem, then I cannot
		3323	help you. I can give some generic advice however:
		3324
		3325	=over 4
		3326
		3327	=item * most applications have a main thread: use the default libev loop
		3328	in that thread, or create a separate thread running only the default loop.
		3329
		3330	This helps integrating other libraries or software modules that use libev
		3331	themselves and don't care/know about threading.
		3332
		3333	=item * one loop per thread is usually a good model.
		3334
		3335	Doing this is almost never wrong, sometimes a better-performance model
		3336	exists, but it is always a good start.
		3337
		3338	=item * other models exist, such as the leader/follower pattern, where one
		3339	loop is handed through multiple threads in a kind of round-robin fashion.
		3340
		3341	Choosing a model is hard - look around, learn, know that usually you can do
		3342	better than you currently do :-)
		3343
		3344	=item * often you need to talk to some other thread which blocks in the
		3345	event loop.
		3346
		3347	C<ev_async> watchers can be used to wake them up from other threads safely
		3348	(or from signal contexts...).
		3349
		3350	An example use would be to communicate signals or other events that only
		3351	work in the default loop by registering the signal watcher with the
		3352	default loop and triggering an C<ev_async> watcher from the default loop
		3353	watcher callback into the event loop interested in the signal.
		3354
		3355	=back
		3356
		3357	=head2 COROUTINES
		3358
		3359	Libev is much more accommodating to coroutines ("cooperative threads"):
		3360	libev fully supports nesting calls to it's functions from different
		3361	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3362	different coroutines and switch freely between both coroutines running the
		3363	loop, as long as you don't confuse yourself). The only exception is that
		3364	you must not do this from C<ev_periodic> reschedule callbacks.
		3365
		3366	Care has been taken to ensure that libev does not keep local state inside
		3367	C<ev_loop>, and other calls do not usually allow coroutine switches.
		3368
		3369
		3370	=head1 COMPLEXITIES
		3371
		3372	In this section the complexities of (many of) the algorithms used inside
		3373	libev will be explained. For complexity discussions about backends see the
		3374	documentation for C<ev_default_init>.
		3375
		3376	All of the following are about amortised time: If an array needs to be
		3377	extended, libev needs to realloc and move the whole array, but this
		3378	happens asymptotically never with higher number of elements, so O(1) might
		3379	mean it might do a lengthy realloc operation in rare cases, but on average
		3380	it is much faster and asymptotically approaches constant time.
		3381
		3382	=over 4
		3383
		3384	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3385
		3386	This means that, when you have a watcher that triggers in one hour and
		3387	there are 100 watchers that would trigger before that then inserting will
		3388	have to skip roughly seven (C<ld 100>) of these watchers.
		3389
		3390	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3391
		3392	That means that changing a timer costs less than removing/adding them
		3393	as only the relative motion in the event queue has to be paid for.
		3394
		3395	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3396
		3397	These just add the watcher into an array or at the head of a list.
		3398
		3399	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3400
		3401	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3402
		3403	These watchers are stored in lists then need to be walked to find the
		3404	correct watcher to remove. The lists are usually short (you don't usually
		3405	have many watchers waiting for the same fd or signal).
		3406
		3407	=item Finding the next timer in each loop iteration: O(1)
		3408
		3409	By virtue of using a binary or 4-heap, the next timer is always found at a
		3410	fixed position in the storage array.
		3411
		3412	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3413
		3414	A change means an I/O watcher gets started or stopped, which requires
		3415	libev to recalculate its status (and possibly tell the kernel, depending
		3416	on backend and whether C<ev_io_set> was used).
		3417
		3418	=item Activating one watcher (putting it into the pending state): O(1)
		3419
		3420	=item Priority handling: O(number_of_priorities)
		3421
		3422	Priorities are implemented by allocating some space for each
		3423	priority. When doing priority-based operations, libev usually has to
		3424	linearly search all the priorities, but starting/stopping and activating
		3425	watchers becomes O(1) w.r.t. priority handling.
		3426
		3427	=item Sending an ev_async: O(1)
		3428
		3429	=item Processing ev_async_send: O(number_of_async_watchers)
		3430
		3431	=item Processing signals: O(max_signal_number)
		3432
		3433	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3434	calls in the current loop iteration. Checking for async and signal events
		3435	involves iterating over all running async watchers or all signal numbers.
		3436
		3437	=back
		3438
		3439
		3440	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3441
		3442	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3443	requires, and its I/O model is fundamentally incompatible with the POSIX
		3444	model. Libev still offers limited functionality on this platform in
		3445	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3446	descriptors. This only applies when using Win32 natively, not when using
		3447	e.g. cygwin.
		3448
		3449	Lifting these limitations would basically require the full
		3450	re-implementation of the I/O system. If you are into these kinds of
		3451	things, then note that glib does exactly that for you in a very portable
		3452	way (note also that glib is the slowest event library known to man).
		3453
		3454	There is no supported compilation method available on windows except
		3455	embedding it into other applications.
		3456
		3457	Not a libev limitation but worth mentioning: windows apparently doesn't
		3458	accept large writes: instead of resulting in a partial write, windows will
		3459	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3460	so make sure you only write small amounts into your sockets (less than a
		3461	megabyte seems safe, but thsi apparently depends on the amount of memory
		3462	available).
		3463
		3464	Due to the many, low, and arbitrary limits on the win32 platform and
		3465	the abysmal performance of winsockets, using a large number of sockets
		3466	is not recommended (and not reasonable). If your program needs to use
		3467	more than a hundred or so sockets, then likely it needs to use a totally
		3468	different implementation for windows, as libev offers the POSIX readiness
		3469	notification model, which cannot be implemented efficiently on windows
		3470	(Microsoft monopoly games).
		3471
		3472	A typical way to use libev under windows is to embed it (see the embedding
		3473	section for details) and use the following F<evwrap.h> header file instead
		3474	of F<ev.h>:
		3475
		3476	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3477	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3478
		3479	#include "ev.h"
		3480
		3481	And compile the following F<evwrap.c> file into your project (make sure
		3482	you do I<not> compile the F<ev.c> or any other embedded soruce files!):
		3483
		3484	#include "evwrap.h"
		3485	#include "ev.c"
		3486
		3487	=over 4
		3488
		3489	=item The winsocket select function
		3490
		3491	The winsocket C<select> function doesn't follow POSIX in that it
		3492	requires socket I<handles> and not socket I<file descriptors> (it is
		3493	also extremely buggy). This makes select very inefficient, and also
		3494	requires a mapping from file descriptors to socket handles (the Microsoft
		3495	C runtime provides the function C<_open_osfhandle> for this). See the
		3496	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3497	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3498
		3499	The configuration for a "naked" win32 using the Microsoft runtime
		3500	libraries and raw winsocket select is:
		3501
		3502	#define EV_USE_SELECT 1
		3503	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3504
		3505	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3506	complexity in the O(n²) range when using win32.
		3507
		3508	=item Limited number of file descriptors
		3509
		3510	Windows has numerous arbitrary (and low) limits on things.
		3511
		3512	Early versions of winsocket's select only supported waiting for a maximum
		3513	of C<64> handles (probably owning to the fact that all windows kernels
		3514	can only wait for C<64> things at the same time internally; Microsoft
		3515	recommends spawning a chain of threads and wait for 63 handles and the
		3516	previous thread in each. Great).
		3517
		3518	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3519	to some high number (e.g. C<2048>) before compiling the winsocket select
		3520	call (which might be in libev or elsewhere, for example, perl does its own
		3521	select emulation on windows).
		3522
		3523	Another limit is the number of file descriptors in the Microsoft runtime
		3524	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3525	or something like this inside Microsoft). You can increase this by calling
		3526	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3527	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3528	libraries.
		3529
		3530	This might get you to about C<512> or C<2048> sockets (depending on
		3531	windows version and/or the phase of the moon). To get more, you need to
		3532	wrap all I/O functions and provide your own fd management, but the cost of
		3533	calling select (O(n²)) will likely make this unworkable.
		3534
		3535	=back
		3536
		3537
		3538	=head1 PORTABILITY REQUIREMENTS
		3539
		3540	In addition to a working ISO-C implementation, libev relies on a few
		3541	additional extensions:
		3542
		3543	=over 4
		3544
		3545	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3546	calling conventions regardless of C<ev_watcher_type *>.
		3547
		3548	Libev assumes not only that all watcher pointers have the same internal
		3549	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3550	assumes that the same (machine) code can be used to call any watcher
		3551	callback: The watcher callbacks have different type signatures, but libev
		3552	calls them using an C<ev_watcher *> internally.
		3553
		3554	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3555
		3556	The type C<sig_atomic_t volatile> (or whatever is defined as
		3557	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3558	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3559	believed to be sufficiently portable.
		3560
		3561	=item C<sigprocmask> must work in a threaded environment
		3562
		3563	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3564	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3565	pthread implementations will either allow C<sigprocmask> in the "main
		3566	thread" or will block signals process-wide, both behaviours would
		3567	be compatible with libev. Interaction between C<sigprocmask> and
		3568	C<pthread_sigmask> could complicate things, however.
		3569
		3570	The most portable way to handle signals is to block signals in all threads
		3571	except the initial one, and run the default loop in the initial thread as
		3572	well.
		3573
		3574	=item C<long> must be large enough for common memory allocation sizes
		3575
		3576	To improve portability and simplify using libev, libev uses C<long>
		3577	internally instead of C<size_t> when allocating its data structures. On
		3578	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3579	is still at least 31 bits everywhere, which is enough for hundreds of
		3580	millions of watchers.
		3581
		3582	=item C<double> must hold a time value in seconds with enough accuracy
		3583
		3584	The type C<double> is used to represent timestamps. It is required to
		3585	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3586	enough for at least into the year 4000. This requirement is fulfilled by
		3587	implementations implementing IEEE 754 (basically all existing ones).
		3588
		3589	=back
		3590
		3591	If you know of other additional requirements drop me a note.
		3592
		3593
		3594	=head1 COMPILER WARNINGS
		3595
		3596	Depending on your compiler and compiler settings, you might get no or a
		3597	lot of warnings when compiling libev code. Some people are apparently
		3598	scared by this.
		3599
		3600	However, these are unavoidable for many reasons. For one, each compiler
		3601	has different warnings, and each user has different tastes regarding
		3602	warning options. "Warn-free" code therefore cannot be a goal except when
		3603	targeting a specific compiler and compiler-version.
		3604
		3605	Another reason is that some compiler warnings require elaborate
		3606	workarounds, or other changes to the code that make it less clear and less
		3607	maintainable.
		3608
		3609	And of course, some compiler warnings are just plain stupid, or simply
		3610	wrong (because they don't actually warn about the condition their message
		3611	seems to warn about).
		3612
		3613	While libev is written to generate as few warnings as possible,
		3614	"warn-free" code is not a goal, and it is recommended not to build libev
		3615	with any compiler warnings enabled unless you are prepared to cope with
		3616	them (e.g. by ignoring them). Remember that warnings are just that:
		3617	warnings, not errors, or proof of bugs.
		3618
		3619
		3620	=head1 VALGRIND
		3621
		3622	Valgrind has a special section here because it is a popular tool that is
		3623	highly useful, but valgrind reports are very hard to interpret.
		3624
		3625	If you think you found a bug (memory leak, uninitialised data access etc.)
		3626	in libev, then check twice: If valgrind reports something like:
		3627
		3628	==2274== definitely lost: 0 bytes in 0 blocks.
		3629	==2274== possibly lost: 0 bytes in 0 blocks.
		3630	==2274== still reachable: 256 bytes in 1 blocks.
		3631
		3632	Then there is no memory leak. Similarly, under some circumstances,
		3633	valgrind might report kernel bugs as if it were a bug in libev, or it
		3634	might be confused (it is a very good tool, but only a tool).
		3635
		3636	If you are unsure about something, feel free to contact the mailing list
		3637	with the full valgrind report and an explanation on why you think this is
		3638	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3639	no bug" answer and take the chance of learning how to interpret valgrind
		3640	properly.
		3641
		3642	If you need, for some reason, empty reports from valgrind for your project
		3643	I suggest using suppression lists.
		3644
		3645
742	=head1 AUTHOR	3646	=head1 AUTHOR
743		3647
744	Marc Lehmann <libev@schmorp.de>.	3648	Marc Lehmann <libev@schmorp.de>.
745		3649

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