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Revision 1.8 by root, Mon Nov 12 08:20:02 2007 UTC vs.
Revision 1.179 by root, Sat Sep 13 19:14:21 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, i.e.
		402	keep at least one watcher active per fd at all times.
		403
		404	While nominally embeddable in other event loops, this feature is broken in
		405	all kernel versions tested so far.
		406
		407	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		408	C<EVBACKEND_POLL>.
		409
		410	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		411
		412	Kqueue deserves special mention, as at the time of this writing, it
		413	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		414	with anything but sockets and pipes, except on Darwin, where of course
		415	it's completely useless). For this reason it's not being "auto-detected"
		416	unless you explicitly specify it explicitly in the flags (i.e. using
		417	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		418	system like NetBSD.
		419
		420	You still can embed kqueue into a normal poll or select backend and use it
		421	only for sockets (after having made sure that sockets work with kqueue on
		422	the target platform). See C<ev_embed> watchers for more info.
		423
		424	It scales in the same way as the epoll backend, but the interface to the
		425	kernel is more efficient (which says nothing about its actual speed, of
		426	course). While stopping, setting and starting an I/O watcher does never
		427	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		428	two event changes per incident, support for C<fork ()> is very bad and it
		429	drops fds silently in similarly hard-to-detect cases.
		430
		431	This backend usually performs well under most conditions.
		432
		433	While nominally embeddable in other event loops, this doesn't work
		434	everywhere, so you might need to test for this. And since it is broken
		435	almost everywhere, you should only use it when you have a lot of sockets
		436	(for which it usually works), by embedding it into another event loop
		437	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		438	sockets.
		439
		440	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		441	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		442	C<NOTE_EOF>.
		443
		444	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		445
		446	This is not implemented yet (and might never be, unless you send me an
		447	implementation). According to reports, C</dev/poll> only supports sockets
		448	and is not embeddable, which would limit the usefulness of this backend
		449	immensely.
		450
		451	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		452
		453	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		454	it's really slow, but it still scales very well (O(active_fds)).
		455
		456	Please note that Solaris event ports can deliver a lot of spurious
		457	notifications, so you need to use non-blocking I/O or other means to avoid
		458	blocking when no data (or space) is available.
		459
		460	While this backend scales well, it requires one system call per active
		461	file descriptor per loop iteration. For small and medium numbers of file
		462	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		463	might perform better.
		464
		465	On the positive side, ignoring the spurious readiness notifications, this
		466	backend actually performed to specification in all tests and is fully
		467	embeddable, which is a rare feat among the OS-specific backends.
		468
		469	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		470	C<EVBACKEND_POLL>.
		471
		472	=item C<EVBACKEND_ALL>
		473
		474	Try all backends (even potentially broken ones that wouldn't be tried
		475	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		476	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		477
		478	It is definitely not recommended to use this flag.
158		479
159	=back	480	=back
		481
		482	If one or more of these are or'ed into the flags value, then only these
		483	backends will be tried (in the reverse order as listed here). If none are
		484	specified, all backends in C<ev_recommended_backends ()> will be tried.
		485
		486	The most typical usage is like this:
		487
		488	if (!ev_default_loop (0))
		489	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		490
		491	Restrict libev to the select and poll backends, and do not allow
		492	environment settings to be taken into account:
		493
		494	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		495
		496	Use whatever libev has to offer, but make sure that kqueue is used if
		497	available (warning, breaks stuff, best use only with your own private
		498	event loop and only if you know the OS supports your types of fds):
		499
		500	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		501
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	502	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		503
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	504	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	505	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	506	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).	507	undefined behaviour (or a failed assertion if assertions are enabled).
167		508
		509	Note that this function I<is> thread-safe, and the recommended way to use
		510	libev with threads is indeed to create one loop per thread, and using the
		511	default loop in the "main" or "initial" thread.
		512
		513	Example: Try to create a event loop that uses epoll and nothing else.
		514
		515	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		516	if (!epoller)
		517	fatal ("no epoll found here, maybe it hides under your chair");
		518
168	=item ev_default_destroy ()	519	=item ev_default_destroy ()
169		520
170	Destroys the default loop again (frees all memory and kernel state	521	Destroys the default loop again (frees all memory and kernel state
171	etc.). This stops all registered event watchers (by not touching them in	522	etc.). None of the active event watchers will be stopped in the normal
172	any way whatsoever, although you cnanot rely on this :).	523	sense, so e.g. C<ev_is_active> might still return true. It is your
		524	responsibility to either stop all watchers cleanly yourself I<before>
		525	calling this function, or cope with the fact afterwards (which is usually
		526	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		527	for example).
		528
		529	Note that certain global state, such as signal state, will not be freed by
		530	this function, and related watchers (such as signal and child watchers)
		531	would need to be stopped manually.
		532
		533	In general it is not advisable to call this function except in the
		534	rare occasion where you really need to free e.g. the signal handling
		535	pipe fds. If you need dynamically allocated loops it is better to use
		536	C<ev_loop_new> and C<ev_loop_destroy>).
173		537
174	=item ev_loop_destroy (loop)	538	=item ev_loop_destroy (loop)
175		539
176	Like C<ev_default_destroy>, but destroys an event loop created by an	540	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	541	earlier call to C<ev_loop_new>.
178		542
179	=item ev_default_fork ()	543	=item ev_default_fork ()
180		544
		545	This function sets a flag that causes subsequent C<ev_loop> iterations
181	This function reinitialises the kernel state for backends that have	546	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	547	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	548	the child process (or both child and parent, but that again makes little
184	again makes little sense).	549	sense). You I<must> call it in the child before using any of the libev
		550	functions, and it will only take effect at the next C<ev_loop> iteration.
185		551
186	You I<must> call this function after forking if and only if you want to	552	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	553	process if and only if you want to use the event library in the child. If
188	have to call it.	554	you just fork+exec, you don't have to call it at all.
189		555
190	The function itself is quite fast and its usually not a problem to call	556	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	557	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>:	558	quite nicely into a call to C<pthread_atfork>:
193		559
194	pthread_atfork (0, 0, ev_default_fork);	560	pthread_atfork (0, 0, ev_default_fork);
195		561
…		…
197		563
198	Like C<ev_default_fork>, but acts on an event loop created by	564	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	565	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.	566	after fork, and how you do this is entirely your own problem.
201		567
		568	=item int ev_is_default_loop (loop)
		569
		570	Returns true when the given loop actually is the default loop, false otherwise.
		571
		572	=item unsigned int ev_loop_count (loop)
		573
		574	Returns the count of loop iterations for the loop, which is identical to
		575	the number of times libev did poll for new events. It starts at C<0> and
		576	happily wraps around with enough iterations.
		577
		578	This value can sometimes be useful as a generation counter of sorts (it
		579	"ticks" the number of loop iterations), as it roughly corresponds with
		580	C<ev_prepare> and C<ev_check> calls.
		581
202	=item unsigned int ev_method (loop)	582	=item unsigned int ev_backend (loop)
203		583
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	584	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	585	use.
206		586
207	=item ev_tstamp = ev_now (loop)	587	=item ev_tstamp ev_now (loop)
208		588
209	Returns the current "event loop time", which is the time the event loop	589	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	590	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	591	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	592	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).	593	event occurring (or more correctly, libev finding out about it).
		594
		595	=item ev_now_update (loop)
		596
		597	Establishes the current time by querying the kernel, updating the time
		598	returned by C<ev_now ()> in the progress. This is a costly operation and
		599	is usually done automatically within C<ev_loop ()>.
		600
		601	This function is rarely useful, but when some event callback runs for a
		602	very long time without entering the event loop, updating libev's idea of
		603	the current time is a good idea.
		604
		605	See also "The special problem of time updates" in the C<ev_timer> section.
214		606
215	=item ev_loop (loop, int flags)	607	=item ev_loop (loop, int flags)
216		608
217	Finally, this is it, the event handler. This function usually is called	609	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	610	after you initialised all your watchers and you want to start handling
219	events.	611	events.
220		612
221	If the flags argument is specified as 0, it will not return until either	613	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.	614	either no event watchers are active anymore or C<ev_unloop> was called.
		615
		616	Please note that an explicit C<ev_unloop> is usually better than
		617	relying on all watchers to be stopped when deciding when a program has
		618	finished (especially in interactive programs), but having a program that
		619	automatically loops as long as it has to and no longer by virtue of
		620	relying on its watchers stopping correctly is a thing of beauty.
223		621
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	622	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	623	those events and any outstanding ones, but will not block your process in
226	case there are no events.	624	case there are no events and will return after one iteration of the loop.
227		625
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	626	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	627	necessary) and will handle those and any outstanding ones. It will block
230	your process until at least one new event arrives.	628	your process until at least one new event arrives, and will return after
		629	one iteration of the loop. This is useful if you are waiting for some
		630	external event in conjunction with something not expressible using other
		631	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		632	usually a better approach for this kind of thing.
231		633
232	This flags value could be used to implement alternative looping	634	Here are the gory details of what C<ev_loop> does:
233	constructs, but the C<prepare> and C<check> watchers provide a better and	635
234	more generic mechanism.	636	- Before the first iteration, call any pending watchers.
		637	* If EVFLAG_FORKCHECK was used, check for a fork.
		638	- If a fork was detected (by any means), queue and call all fork watchers.
		639	- Queue and call all prepare watchers.
		640	- If we have been forked, detach and recreate the kernel state
		641	as to not disturb the other process.
		642	- Update the kernel state with all outstanding changes.
		643	- Update the "event loop time" (ev_now ()).
		644	- Calculate for how long to sleep or block, if at all
		645	(active idle watchers, EVLOOP_NONBLOCK or not having
		646	any active watchers at all will result in not sleeping).
		647	- Sleep if the I/O and timer collect interval say so.
		648	- Block the process, waiting for any events.
		649	- Queue all outstanding I/O (fd) events.
		650	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		651	- Queue all outstanding timers.
		652	- Queue all outstanding periodics.
		653	- Unless any events are pending now, queue all idle watchers.
		654	- Queue all check watchers.
		655	- Call all queued watchers in reverse order (i.e. check watchers first).
		656	Signals and child watchers are implemented as I/O watchers, and will
		657	be handled here by queueing them when their watcher gets executed.
		658	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		659	were used, or there are no active watchers, return, otherwise
		660	continue with step *.
		661
		662	Example: Queue some jobs and then loop until no events are outstanding
		663	anymore.
		664
		665	... queue jobs here, make sure they register event watchers as long
		666	... as they still have work to do (even an idle watcher will do..)
		667	ev_loop (my_loop, 0);
		668	... jobs done or somebody called unloop. yeah!
235		669
236	=item ev_unloop (loop, how)	670	=item ev_unloop (loop, how)
237		671
238	Can be used to make a call to C<ev_loop> return early. The C<how> argument	672	Can be used to make a call to C<ev_loop> return early (but only after it
		673	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>	674	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>	675	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
241	calls return.	676
		677	This "unloop state" will be cleared when entering C<ev_loop> again.
242		678
243	=item ev_ref (loop)	679	=item ev_ref (loop)
244		680
245	=item ev_unref (loop)	681	=item ev_unref (loop)
246		682
247	Ref/unref can be used to add or remove a refcount on the event loop: Every	683	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	684	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	685	count is nonzero, C<ev_loop> will not return on its own. If you have
250	starting, and ev_ref() before stopping it. Libev itself uses this for	686	a watcher you never unregister that should not keep C<ev_loop> from
251	example for its internal signal pipe: It is not visible to you as a user	687	returning, ev_unref() after starting, and ev_ref() before stopping it. For
252	and should not keep C<ev_loop> from exiting if the work is done. It is	688	example, libev itself uses this for its internal signal pipe: It is not
253	also an excellent way to do this for generic recurring timers or from	689	visible to the libev user and should not keep C<ev_loop> from exiting if
254	within third-party libraries. Just remember to unref after start and ref	690	no event watchers registered by it are active. It is also an excellent
255	before stop.	691	way to do this for generic recurring timers or from within third-party
		692	libraries. Just remember to I<unref after start> and I<ref before stop>
		693	(but only if the watcher wasn't active before, or was active before,
		694	respectively).
		695
		696	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		697	running when nothing else is active.
		698
		699	struct ev_signal exitsig;
		700	ev_signal_init (&exitsig, sig_cb, SIGINT);
		701	ev_signal_start (loop, &exitsig);
		702	evf_unref (loop);
		703
		704	Example: For some weird reason, unregister the above signal handler again.
		705
		706	ev_ref (loop);
		707	ev_signal_stop (loop, &exitsig);
		708
		709	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		710
		711	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		712
		713	These advanced functions influence the time that libev will spend waiting
		714	for events. Both time intervals are by default C<0>, meaning that libev
		715	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		716	latency.
		717
		718	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		719	allows libev to delay invocation of I/O and timer/periodic callbacks
		720	to increase efficiency of loop iterations (or to increase power-saving
		721	opportunities).
		722
		723	The background is that sometimes your program runs just fast enough to
		724	handle one (or very few) event(s) per loop iteration. While this makes
		725	the program responsive, it also wastes a lot of CPU time to poll for new
		726	events, especially with backends like C<select ()> which have a high
		727	overhead for the actual polling but can deliver many events at once.
		728
		729	By setting a higher I<io collect interval> you allow libev to spend more
		730	time collecting I/O events, so you can handle more events per iteration,
		731	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		732	C<ev_timer>) will be not affected. Setting this to a non-null value will
		733	introduce an additional C<ev_sleep ()> call into most loop iterations.
		734
		735	Likewise, by setting a higher I<timeout collect interval> you allow libev
		736	to spend more time collecting timeouts, at the expense of increased
		737	latency (the watcher callback will be called later). C<ev_io> watchers
		738	will not be affected. Setting this to a non-null value will not introduce
		739	any overhead in libev.
		740
		741	Many (busy) programs can usually benefit by setting the I/O collect
		742	interval to a value near C<0.1> or so, which is often enough for
		743	interactive servers (of course not for games), likewise for timeouts. It
		744	usually doesn't make much sense to set it to a lower value than C<0.01>,
		745	as this approaches the timing granularity of most systems.
		746
		747	Setting the I<timeout collect interval> can improve the opportunity for
		748	saving power, as the program will "bundle" timer callback invocations that
		749	are "near" in time together, by delaying some, thus reducing the number of
		750	times the process sleeps and wakes up again. Another useful technique to
		751	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		752	they fire on, say, one-second boundaries only.
		753
		754	=item ev_loop_verify (loop)
		755
		756	This function only does something when C<EV_VERIFY> support has been
		757	compiled in. It tries to go through all internal structures and checks
		758	them for validity. If anything is found to be inconsistent, it will print
		759	an error message to standard error and call C<abort ()>.
		760
		761	This can be used to catch bugs inside libev itself: under normal
		762	circumstances, this function will never abort as of course libev keeps its
		763	data structures consistent.
256		764
257	=back	765	=back
		766
258		767
259	=head1 ANATOMY OF A WATCHER	768	=head1 ANATOMY OF A WATCHER
260		769
261	A watcher is a structure that you create and register to record your	770	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	771	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:	772	become readable, you would create an C<ev_io> watcher for that:
264		773
265	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	774	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
266	{	775	{
267	ev_io_stop (w);	776	ev_io_stop (w);
268	ev_unloop (loop, EVUNLOOP_ALL);	777	ev_unloop (loop, EVUNLOOP_ALL);
269	}	778	}
270		779
271	struct ev_loop *loop = ev_default_loop (0);	780	struct ev_loop *loop = ev_default_loop (0);
272	struct ev_io stdin_watcher;	781	struct ev_io stdin_watcher;
273	ev_init (&stdin_watcher, my_cb);	782	ev_init (&stdin_watcher, my_cb);
274	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	783	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
275	ev_io_start (loop, &stdin_watcher);	784	ev_io_start (loop, &stdin_watcher);
276	ev_loop (loop, 0);	785	ev_loop (loop, 0);
277		786
278	As you can see, you are responsible for allocating the memory for your	787	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,	788	watcher structures (and it is usually a bad idea to do this on the stack,
280	although this can sometimes be quite valid).	789	although this can sometimes be quite valid).
281		790
282	Each watcher structure must be initialised by a call to C<ev_init	791	Each watcher structure must be initialised by a call to C<ev_init
283	(watcher *, callback)>, which expects a callback to be provided. This	792	(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	793	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	794	watchers, each time the event loop detects that the file descriptor given
286	is readable and/or writable).	795	is readable and/or writable).
287		796
288	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	797	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	798	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	804	*) >>), and you can stop watching for events at any time by calling the
296	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	805	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
297		806
298	As long as your watcher is active (has been started but not stopped) you	807	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	808	must not touch the values stored in it. Most specifically you must never
300	reinitialise it or call its set method.	809	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		810
307	Each and every callback receives the event loop pointer as first, the	811	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	812	registered watcher structure as second, and a bitset of received events as
309	third argument.	813	third argument.
310		814
311	The rceeived events usually include a single bit per event type received	815	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	816	(you can receive multiple events at the same time). The possible bit masks
313	are:	817	are:
314		818
315	=over 4	819	=over 4
316		820
317	=item EV_READ	821	=item C<EV_READ>
318		822
319	=item EV_WRITE	823	=item C<EV_WRITE>
320		824
321	The file descriptor in the ev_io watcher has become readable and/or	825	The file descriptor in the C<ev_io> watcher has become readable and/or
322	writable.	826	writable.
323		827
324	=item EV_TIMEOUT	828	=item C<EV_TIMEOUT>
325		829
326	The ev_timer watcher has timed out.	830	The C<ev_timer> watcher has timed out.
327		831
328	=item EV_PERIODIC	832	=item C<EV_PERIODIC>
329		833
330	The ev_periodic watcher has timed out.	834	The C<ev_periodic> watcher has timed out.
331		835
332	=item EV_SIGNAL	836	=item C<EV_SIGNAL>
333		837
334	The signal specified in the ev_signal watcher has been received by a thread.	838	The signal specified in the C<ev_signal> watcher has been received by a thread.
335		839
336	=item EV_CHILD	840	=item C<EV_CHILD>
337		841
338	The pid specified in the ev_child watcher has received a status change.	842	The pid specified in the C<ev_child> watcher has received a status change.
339		843
		844	=item C<EV_STAT>
		845
		846	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		847
340	=item EV_IDLE	848	=item C<EV_IDLE>
341		849
342	The ev_idle watcher has determined that you have nothing better to do.	850	The C<ev_idle> watcher has determined that you have nothing better to do.
343		851
344	=item EV_PREPARE	852	=item C<EV_PREPARE>
345		853
346	=item EV_CHECK	854	=item C<EV_CHECK>
347		855
348	All ev_prepare watchers are invoked just I<before> C<ev_loop> starts	856	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	857	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	858	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	859	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	860	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	861	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
354	C<ev_loop> from blocking).	862	C<ev_loop> from blocking).
355		863
		864	=item C<EV_EMBED>
		865
		866	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		867
		868	=item C<EV_FORK>
		869
		870	The event loop has been resumed in the child process after fork (see
		871	C<ev_fork>).
		872
		873	=item C<EV_ASYNC>
		874
		875	The given async watcher has been asynchronously notified (see C<ev_async>).
		876
356	=item EV_ERROR	877	=item C<EV_ERROR>
357		878
358	An unspecified error has occured, the watcher has been stopped. This might	879	An unspecified error has occurred, the watcher has been stopped. This might
359	happen because the watcher could not be properly started because libev	880	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	881	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	882	problem. You best act on it by reporting the problem and somehow coping
362	with the watcher being stopped.	883	with the watcher being stopped.
363		884
364	Libev will usually signal a few "dummy" events together with an error,	885	Libev will usually signal a few "dummy" events together with an error,
365	for example it might indicate that a fd is readable or writable, and if	886	for example it might indicate that a fd is readable or writable, and if
366	your callbacks is well-written it can just attempt the operation and cope	887	your callbacks is well-written it can just attempt the operation and cope
367	with the error from read() or write(). This will not work in multithreaded	888	with the error from read() or write(). This will not work in multi-threaded
368	programs, though, so beware.	889	programs, though, so beware.
369		890
370	=back	891	=back
371		892
		893	=head2 GENERIC WATCHER FUNCTIONS
		894
		895	In the following description, C<TYPE> stands for the watcher type,
		896	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		897
		898	=over 4
		899
		900	=item C<ev_init> (ev_TYPE *watcher, callback)
		901
		902	This macro initialises the generic portion of a watcher. The contents
		903	of the watcher object can be arbitrary (so C<malloc> will do). Only
		904	the generic parts of the watcher are initialised, you I<need> to call
		905	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		906	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		907	which rolls both calls into one.
		908
		909	You can reinitialise a watcher at any time as long as it has been stopped
		910	(or never started) and there are no pending events outstanding.
		911
		912	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		913	int revents)>.
		914
		915	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		916
		917	This macro initialises the type-specific parts of a watcher. You need to
		918	call C<ev_init> at least once before you call this macro, but you can
		919	call C<ev_TYPE_set> any number of times. You must not, however, call this
		920	macro on a watcher that is active (it can be pending, however, which is a
		921	difference to the C<ev_init> macro).
		922
		923	Although some watcher types do not have type-specific arguments
		924	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		925
		926	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		927
		928	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		929	calls into a single call. This is the most convenient method to initialise
		930	a watcher. The same limitations apply, of course.
		931
		932	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		933
		934	Starts (activates) the given watcher. Only active watchers will receive
		935	events. If the watcher is already active nothing will happen.
		936
		937	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		938
		939	Stops the given watcher again (if active) and clears the pending
		940	status. It is possible that stopped watchers are pending (for example,
		941	non-repeating timers are being stopped when they become pending), but
		942	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		943	you want to free or reuse the memory used by the watcher it is therefore a
		944	good idea to always call its C<ev_TYPE_stop> function.
		945
		946	=item bool ev_is_active (ev_TYPE *watcher)
		947
		948	Returns a true value iff the watcher is active (i.e. it has been started
		949	and not yet been stopped). As long as a watcher is active you must not modify
		950	it.
		951
		952	=item bool ev_is_pending (ev_TYPE *watcher)
		953
		954	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		955	events but its callback has not yet been invoked). As long as a watcher
		956	is pending (but not active) you must not call an init function on it (but
		957	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		958	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		959	it).
		960
		961	=item callback ev_cb (ev_TYPE *watcher)
		962
		963	Returns the callback currently set on the watcher.
		964
		965	=item ev_cb_set (ev_TYPE *watcher, callback)
		966
		967	Change the callback. You can change the callback at virtually any time
		968	(modulo threads).
		969
		970	=item ev_set_priority (ev_TYPE *watcher, priority)
		971
		972	=item int ev_priority (ev_TYPE *watcher)
		973
		974	Set and query the priority of the watcher. The priority is a small
		975	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		976	(default: C<-2>). Pending watchers with higher priority will be invoked
		977	before watchers with lower priority, but priority will not keep watchers
		978	from being executed (except for C<ev_idle> watchers).
		979
		980	This means that priorities are I<only> used for ordering callback
		981	invocation after new events have been received. This is useful, for
		982	example, to reduce latency after idling, or more often, to bind two
		983	watchers on the same event and make sure one is called first.
		984
		985	If you need to suppress invocation when higher priority events are pending
		986	you need to look at C<ev_idle> watchers, which provide this functionality.
		987
		988	You I<must not> change the priority of a watcher as long as it is active or
		989	pending.
		990
		991	The default priority used by watchers when no priority has been set is
		992	always C<0>, which is supposed to not be too high and not be too low :).
		993
		994	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		995	fine, as long as you do not mind that the priority value you query might
		996	or might not have been adjusted to be within valid range.
		997
		998	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		999
		1000	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1001	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1002	can deal with that fact.
		1003
		1004	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1005
		1006	If the watcher is pending, this function returns clears its pending status
		1007	and returns its C<revents> bitset (as if its callback was invoked). If the
		1008	watcher isn't pending it does nothing and returns C<0>.
		1009
		1010	=back
		1011
		1012
372	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1013	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
373		1014
374	Each watcher has, by default, a member C<void *data> that you can change	1015	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	1016	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	1017	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	1018	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	1019	member, you can also "subclass" the watcher type and provide your own
379	data:	1020	data:
380		1021
381	struct my_io	1022	struct my_io
382	{	1023	{
383	struct ev_io io;	1024	struct ev_io io;
384	int otherfd;	1025	int otherfd;
385	void *somedata;	1026	void *somedata;
386	struct whatever *mostinteresting;	1027	struct whatever *mostinteresting;
387	}	1028	};
		1029
		1030	...
		1031	struct my_io w;
		1032	ev_io_init (&w.io, my_cb, fd, EV_READ);
388		1033
389	And since your callback will be called with a pointer to the watcher, you	1034	And since your callback will be called with a pointer to the watcher, you
390	can cast it back to your own type:	1035	can cast it back to your own type:
391		1036
392	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1037	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
393	{	1038	{
394	struct my_io *w = (struct my_io *)w_;	1039	struct my_io *w = (struct my_io *)w_;
395	...	1040	...
396	}	1041	}
397		1042
398	More interesting and less C-conformant ways of catsing your callback type	1043	More interesting and less C-conformant ways of casting your callback type
399	have been omitted....	1044	instead have been omitted.
		1045
		1046	Another common scenario is to use some data structure with multiple
		1047	embedded watchers:
		1048
		1049	struct my_biggy
		1050	{
		1051	int some_data;
		1052	ev_timer t1;
		1053	ev_timer t2;
		1054	}
		1055
		1056	In this case getting the pointer to C<my_biggy> is a bit more
		1057	complicated: Either you store the address of your C<my_biggy> struct
		1058	in the C<data> member of the watcher, or you need to use some pointer
		1059	arithmetic using C<offsetof> inside your watchers:
		1060
		1061	#include <stddef.h>
		1062
		1063	static void
		1064	t1_cb (EV_P_ struct ev_timer *w, int revents)
		1065	{
		1066	struct my_biggy big = (struct my_biggy *
		1067	(((char *)w) - offsetof (struct my_biggy, t1));
		1068	}
		1069
		1070	static void
		1071	t2_cb (EV_P_ struct ev_timer *w, int revents)
		1072	{
		1073	struct my_biggy big = (struct my_biggy *
		1074	(((char *)w) - offsetof (struct my_biggy, t2));
		1075	}
400		1076
401		1077
402	=head1 WATCHER TYPES	1078	=head1 WATCHER TYPES
403		1079
404	This section describes each watcher in detail, but will not repeat	1080	This section describes each watcher in detail, but will not repeat
405	information given in the last section.	1081	information given in the last section. Any initialisation/set macros,
		1082	functions and members specific to the watcher type are explained.
406		1083
		1084	Members are additionally marked with either I<[read-only]>, meaning that,
		1085	while the watcher is active, you can look at the member and expect some
		1086	sensible content, but you must not modify it (you can modify it while the
		1087	watcher is stopped to your hearts content), or I<[read-write]>, which
		1088	means you can expect it to have some sensible content while the watcher
		1089	is active, but you can also modify it. Modifying it may not do something
		1090	sensible or take immediate effect (or do anything at all), but libev will
		1091	not crash or malfunction in any way.
		1092
		1093
407	=head2 struct ev_io - is my file descriptor readable or writable	1094	=head2 C<ev_io> - is this file descriptor readable or writable?
408		1095
409	I/O watchers check whether a file descriptor is readable or writable	1096	I/O watchers check whether a file descriptor is readable or writable
410	in each iteration of the event loop (This behaviour is called	1097	in each iteration of the event loop, or, more precisely, when reading
411	level-triggering because you keep receiving events as long as the	1098	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	1099	some data. This behaviour is called level-triggering because you keep
413	act on the event and neither want to receive future events).	1100	receiving events as long as the condition persists. Remember you can stop
		1101	the watcher if you don't want to act on the event and neither want to
		1102	receive future events.
414		1103
415	In general you can register as many read and/or write event watchers oer	1104	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	1105	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	1106	descriptors to non-blocking mode is also usually a good idea (but not
418	required if you know what you are doing).	1107	required if you know what you are doing).
419		1108
420	You have to be careful with dup'ed file descriptors, though. Some backends
421	(the linux epoll backend is a notable example) cannot handle dup'ed file
422	descriptors correctly if you register interest in two or more fds pointing
423	to the same file/socket etc. description.
424
425	If you must do this, then force the use of a known-to-be-good backend	1109	If you must do this, then force the use of a known-to-be-good backend
426	(at the time of this writing, this includes only EVMETHOD_SELECT and	1110	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
427	EVMETHOD_POLL).	1111	C<EVBACKEND_POLL>).
		1112
		1113	Another thing you have to watch out for is that it is quite easy to
		1114	receive "spurious" readiness notifications, that is your callback might
		1115	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1116	because there is no data. Not only are some backends known to create a
		1117	lot of those (for example Solaris ports), it is very easy to get into
		1118	this situation even with a relatively standard program structure. Thus
		1119	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1120	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1121
		1122	If you cannot run the fd in non-blocking mode (for example you should not
		1123	play around with an Xlib connection), then you have to separately re-test
		1124	whether a file descriptor is really ready with a known-to-be good interface
		1125	such as poll (fortunately in our Xlib example, Xlib already does this on
		1126	its own, so its quite safe to use).
		1127
		1128	=head3 The special problem of disappearing file descriptors
		1129
		1130	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1131	descriptor (either by calling C<close> explicitly or by any other means,
		1132	such as C<dup>). The reason is that you register interest in some file
		1133	descriptor, but when it goes away, the operating system will silently drop
		1134	this interest. If another file descriptor with the same number then is
		1135	registered with libev, there is no efficient way to see that this is, in
		1136	fact, a different file descriptor.
		1137
		1138	To avoid having to explicitly tell libev about such cases, libev follows
		1139	the following policy: Each time C<ev_io_set> is being called, libev
		1140	will assume that this is potentially a new file descriptor, otherwise
		1141	it is assumed that the file descriptor stays the same. That means that
		1142	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1143	descriptor even if the file descriptor number itself did not change.
		1144
		1145	This is how one would do it normally anyway, the important point is that
		1146	the libev application should not optimise around libev but should leave
		1147	optimisations to libev.
		1148
		1149	=head3 The special problem of dup'ed file descriptors
		1150
		1151	Some backends (e.g. epoll), cannot register events for file descriptors,
		1152	but only events for the underlying file descriptions. That means when you
		1153	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1154	events for them, only one file descriptor might actually receive events.
		1155
		1156	There is no workaround possible except not registering events
		1157	for potentially C<dup ()>'ed file descriptors, or to resort to
		1158	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1159
		1160	=head3 The special problem of fork
		1161
		1162	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1163	useless behaviour. Libev fully supports fork, but needs to be told about
		1164	it in the child.
		1165
		1166	To support fork in your programs, you either have to call
		1167	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1168	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1169	C<EVBACKEND_POLL>.
		1170
		1171	=head3 The special problem of SIGPIPE
		1172
		1173	While not really specific to libev, it is easy to forget about SIGPIPE:
		1174	when writing to a pipe whose other end has been closed, your program gets
		1175	send a SIGPIPE, which, by default, aborts your program. For most programs
		1176	this is sensible behaviour, for daemons, this is usually undesirable.
		1177
		1178	So when you encounter spurious, unexplained daemon exits, make sure you
		1179	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1180	somewhere, as that would have given you a big clue).
		1181
		1182
		1183	=head3 Watcher-Specific Functions
428		1184
429	=over 4	1185	=over 4
430		1186
431	=item ev_io_init (ev_io *, callback, int fd, int events)	1187	=item ev_io_init (ev_io *, callback, int fd, int events)
432		1188
433	=item ev_io_set (ev_io *, int fd, int events)	1189	=item ev_io_set (ev_io *, int fd, int events)
434		1190
435	Configures an ev_io watcher. The fd is the file descriptor to rceeive	1191	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 |	1192	receive events for and events is either C<EV_READ>, C<EV_WRITE> or
437	EV_WRITE> to receive the given events.	1193	C<EV_READ | EV_WRITE> to receive the given events.
		1194
		1195	=item int fd [read-only]
		1196
		1197	The file descriptor being watched.
		1198
		1199	=item int events [read-only]
		1200
		1201	The events being watched.
438		1202
439	=back	1203	=back
440		1204
		1205	=head3 Examples
		1206
		1207	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1208	readable, but only once. Since it is likely line-buffered, you could
		1209	attempt to read a whole line in the callback.
		1210
		1211	static void
		1212	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1213	{
		1214	ev_io_stop (loop, w);
		1215	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1216	}
		1217
		1218	...
		1219	struct ev_loop *loop = ev_default_init (0);
		1220	struct ev_io stdin_readable;
		1221	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1222	ev_io_start (loop, &stdin_readable);
		1223	ev_loop (loop, 0);
		1224
		1225
441	=head2 struct ev_timer - relative and optionally recurring timeouts	1226	=head2 C<ev_timer> - relative and optionally repeating timeouts
442		1227
443	Timer watchers are simple relative timers that generate an event after a	1228	Timer watchers are simple relative timers that generate an event after a
444	given time, and optionally repeating in regular intervals after that.	1229	given time, and optionally repeating in regular intervals after that.
445		1230
446	The timers are based on real time, that is, if you register an event that	1231	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	1232	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	1233	year, it will still time out after (roughly) and hour. "Roughly" because
449	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1234	detecting time jumps is hard, and some inaccuracies are unavoidable (the
450	monotonic clock option helps a lot here).	1235	monotonic clock option helps a lot here).
451		1236
		1237	The callback is guaranteed to be invoked only after its timeout has passed,
		1238	but if multiple timers become ready during the same loop iteration then
		1239	order of execution is undefined.
		1240
		1241	=head3 The special problem of time updates
		1242
		1243	Establishing the current time is a costly operation (it usually takes at
		1244	least two system calls): EV therefore updates its idea of the current
		1245	time only before and after C<ev_loop> polls for new events, which causes
		1246	a growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1247	lots of events.
		1248
		1249	The relative timeouts are calculated relative to the C<ev_now ()>
		1250	time. This is usually the right thing as this timestamp refers to the time
		1251	of the event triggering whatever timeout you are modifying/starting. If
		1252	you suspect event processing to be delayed and you I<need> to base the
		1253	timeout on the current time, use something like this to adjust for this:
		1254
		1255	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		1256
		1257	If the event loop is suspended for a long time, you can also force an
		1258	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		1259	()>.
		1260
		1261	=head3 Watcher-Specific Functions and Data Members
		1262
452	=over 4	1263	=over 4
453		1264
454	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1265	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
455		1266
456	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1267	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
457		1268
458	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1269	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	1270	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	1271	reached. If it is positive, then the timer will automatically be
461	later, again, and again, until stopped manually.	1272	configured to trigger again C<repeat> seconds later, again, and again,
		1273	until stopped manually.
462		1274
463	The timer itself will do a best-effort at avoiding drift, that is, if you	1275	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	1276	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	1277	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	1278	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.	1279	do stuff) the timer will not fire more than once per event loop iteration.
468		1280
469	=item ev_timer_again (loop)	1281	=item ev_timer_again (loop, ev_timer *)
470		1282
471	This will act as if the timer timed out and restart it again if it is	1283	This will act as if the timer timed out and restart it again if it is
472	repeating. The exact semantics are:	1284	repeating. The exact semantics are:
473		1285
		1286	If the timer is pending, its pending status is cleared.
		1287
474	If the timer is started but nonrepeating, stop it.	1288	If the timer is started but non-repeating, stop it (as if it timed out).
475		1289
476	If the timer is repeating, either start it if necessary (with the repeat	1290	If the timer is repeating, either start it if necessary (with the
477	value), or reset the running timer to the repeat value.	1291	C<repeat> value), or reset the running timer to the C<repeat> value.
478		1292
479	This sounds a bit complicated, but here is a useful and typical	1293	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	1294	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	1295	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	1296	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	1297	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	1298	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	1299	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.	1300	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1301	automatically restart it if need be.
		1302
		1303	That means you can ignore the C<after> value and C<ev_timer_start>
		1304	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1305
		1306	ev_timer_init (timer, callback, 0., 5.);
		1307	ev_timer_again (loop, timer);
		1308	...
		1309	timer->again = 17.;
		1310	ev_timer_again (loop, timer);
		1311	...
		1312	timer->again = 10.;
		1313	ev_timer_again (loop, timer);
		1314
		1315	This is more slightly efficient then stopping/starting the timer each time
		1316	you want to modify its timeout value.
		1317
		1318	=item ev_tstamp repeat [read-write]
		1319
		1320	The current C<repeat> value. Will be used each time the watcher times out
		1321	or C<ev_timer_again> is called and determines the next timeout (if any),
		1322	which is also when any modifications are taken into account.
487		1323
488	=back	1324	=back
489		1325
		1326	=head3 Examples
		1327
		1328	Example: Create a timer that fires after 60 seconds.
		1329
		1330	static void
		1331	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1332	{
		1333	.. one minute over, w is actually stopped right here
		1334	}
		1335
		1336	struct ev_timer mytimer;
		1337	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1338	ev_timer_start (loop, &mytimer);
		1339
		1340	Example: Create a timeout timer that times out after 10 seconds of
		1341	inactivity.
		1342
		1343	static void
		1344	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1345	{
		1346	.. ten seconds without any activity
		1347	}
		1348
		1349	struct ev_timer mytimer;
		1350	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1351	ev_timer_again (&mytimer); /* start timer */
		1352	ev_loop (loop, 0);
		1353
		1354	// and in some piece of code that gets executed on any "activity":
		1355	// reset the timeout to start ticking again at 10 seconds
		1356	ev_timer_again (&mytimer);
		1357
		1358
490	=head2 ev_periodic - to cron or not to cron it	1359	=head2 C<ev_periodic> - to cron or not to cron?
491		1360
492	Periodic watchers are also timers of a kind, but they are very versatile	1361	Periodic watchers are also timers of a kind, but they are very versatile
493	(and unfortunately a bit complex).	1362	(and unfortunately a bit complex).
494		1363
495	Unlike ev_timer's, they are not based on real time (or relative time)	1364	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	1365	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	1366	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 ()	1367	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	1368	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1369	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	1370	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	1371	roughly 10 seconds later as it uses a relative timeout).
502	again).
503		1372
504	They can also be used to implement vastly more complex timers, such as	1373	C<ev_periodic>s can also be used to implement vastly more complex timers,
505	triggering an event on eahc midnight, local time.	1374	such as triggering an event on each "midnight, local time", or other
		1375	complicated, rules.
		1376
		1377	As with timers, the callback is guaranteed to be invoked only when the
		1378	time (C<at>) has passed, but if multiple periodic timers become ready
		1379	during the same loop iteration then order of execution is undefined.
		1380
		1381	=head3 Watcher-Specific Functions and Data Members
506		1382
507	=over 4	1383	=over 4
508		1384
509	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1385	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
510		1386
511	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1387	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
512		1388
513	Lots of arguments, lets sort it out... There are basically three modes of	1389	Lots of arguments, lets sort it out... There are basically three modes of
514	operation, and we will explain them from simplest to complex:	1390	operation, and we will explain them from simplest to complex:
515		1391
516
517	=over 4	1392	=over 4
518		1393
519	=item * absolute timer (interval = reschedule_cb = 0)	1394	=item * absolute timer (at = time, interval = reschedule_cb = 0)
520		1395
521	In this configuration the watcher triggers an event at the wallclock time	1396	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,	1397	time C<at> has passed and doesn't repeat. It 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	1398	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.	1399	run when the system time reaches or surpasses this time.
525		1400
526	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1401	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
527		1402
528	In this mode the watcher will always be scheduled to time out at the next	1403	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	1404	C<at + N * interval> time (for some integer N, which can also be negative)
530	of any time jumps.	1405	and then repeat, regardless of any time jumps.
531		1406
532	This can be used to create timers that do not drift with respect to system	1407	This can be used to create timers that do not drift with respect to system
533	time:	1408	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1409	the hour:
534		1410
535	ev_periodic_set (&periodic, 0., 3600., 0);	1411	ev_periodic_set (&periodic, 0., 3600., 0);
536		1412
537	This doesn't mean there will always be 3600 seconds in between triggers,	1413	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	1414	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	1415	full hour (UTC), or more correctly, when the system time is evenly divisible
540	by 3600.	1416	by 3600.
541		1417
542	Another way to think about it (for the mathematically inclined) is that	1418	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	1419	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.	1420	time where C<time = at (mod interval)>, regardless of any time jumps.
545		1421
		1422	For numerical stability it is preferable that the C<at> value is near
		1423	C<ev_now ()> (the current time), but there is no range requirement for
		1424	this value, and in fact is often specified as zero.
		1425
		1426	Note also that there is an upper limit to how often a timer can fire (CPU
		1427	speed for example), so if C<interval> is very small then timing stability
		1428	will of course deteriorate. Libev itself tries to be exact to be about one
		1429	millisecond (if the OS supports it and the machine is fast enough).
		1430
546	=item * manual reschedule mode (reschedule_cb = callback)	1431	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
547		1432
548	In this mode the values for C<interval> and C<at> are both being	1433	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	1434	ignored. Instead, each time the periodic watcher gets scheduled, the
550	reschedule callback will be called with the watcher as first, and the	1435	reschedule callback will be called with the watcher as first, and the
551	current time as second argument.	1436	current time as second argument.
552		1437
553	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1438	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	1439	ever, or make ANY event loop modifications whatsoever>.
555	to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
556		1440
		1441	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1442	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1443	only event loop modification you are allowed to do).
		1444
557	Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1445	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
558	ev_tstamp now)>, e.g.:	1446	*w, ev_tstamp now)>, e.g.:
559		1447
560	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1448	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
561	{	1449	{
562	return now + 60.;	1450	return now + 60.;
563	}	1451	}
…		…
565	It must return the next time to trigger, based on the passed time value	1453	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	1454	(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	1455	will usually be called just before the callback will be triggered, but
568	might be called at other times, too.	1456	might be called at other times, too.
569		1457
		1458	NOTE: I<< This callback must always return a time that is higher than or
		1459	equal to the passed C<now> value >>.
		1460
570	This can be used to create very complex timers, such as a timer that	1461	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	1462	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	1463	next midnight after C<now> and return the timestamp value for this. How
573	is, again, up to you (but it is not trivial).	1464	you do this is, again, up to you (but it is not trivial, which is the main
		1465	reason I omitted it as an example).
574		1466
575	=back	1467	=back
576		1468
577	=item ev_periodic_again (loop, ev_periodic *)	1469	=item ev_periodic_again (loop, ev_periodic *)
578		1470
579	Simply stops and restarts the periodic watcher again. This is only useful	1471	Simply stops and restarts the periodic watcher again. This is only useful
580	when you changed some parameters or the reschedule callback would return	1472	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	1473	a different time than the last time it was called (e.g. in a crond like
582	program when the crontabs have changed).	1474	program when the crontabs have changed).
583		1475
		1476	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1477
		1478	When active, returns the absolute time that the watcher is supposed to
		1479	trigger next.
		1480
		1481	=item ev_tstamp offset [read-write]
		1482
		1483	When repeating, this contains the offset value, otherwise this is the
		1484	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1485
		1486	Can be modified any time, but changes only take effect when the periodic
		1487	timer fires or C<ev_periodic_again> is being called.
		1488
		1489	=item ev_tstamp interval [read-write]
		1490
		1491	The current interval value. Can be modified any time, but changes only
		1492	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1493	called.
		1494
		1495	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1496
		1497	The current reschedule callback, or C<0>, if this functionality is
		1498	switched off. Can be changed any time, but changes only take effect when
		1499	the periodic timer fires or C<ev_periodic_again> is being called.
		1500
584	=back	1501	=back
585		1502
		1503	=head3 Examples
		1504
		1505	Example: Call a callback every hour, or, more precisely, whenever the
		1506	system clock is divisible by 3600. The callback invocation times have
		1507	potentially a lot of jitter, but good long-term stability.
		1508
		1509	static void
		1510	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1511	{
		1512	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1513	}
		1514
		1515	struct ev_periodic hourly_tick;
		1516	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1517	ev_periodic_start (loop, &hourly_tick);
		1518
		1519	Example: The same as above, but use a reschedule callback to do it:
		1520
		1521	#include <math.h>
		1522
		1523	static ev_tstamp
		1524	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1525	{
		1526	return fmod (now, 3600.) + 3600.;
		1527	}
		1528
		1529	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1530
		1531	Example: Call a callback every hour, starting now:
		1532
		1533	struct ev_periodic hourly_tick;
		1534	ev_periodic_init (&hourly_tick, clock_cb,
		1535	fmod (ev_now (loop), 3600.), 3600., 0);
		1536	ev_periodic_start (loop, &hourly_tick);
		1537
		1538
586	=head2 ev_signal - signal me when a signal gets signalled	1539	=head2 C<ev_signal> - signal me when a signal gets signalled!
587		1540
588	Signal watchers will trigger an event when the process receives a specific	1541	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	1542	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	1543	will try it's best to deliver signals synchronously, i.e. as part of the
591	normal event processing, like any other event.	1544	normal event processing, like any other event.
592		1545
593	You cna configure as many watchers as you like per signal. Only when the	1546	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	1547	first watcher gets started will libev actually register a signal watcher
595	with the kernel (thus it coexists with your own signal handlers as long	1548	with the kernel (thus it coexists with your own signal handlers as long
596	as you don't register any with libev). Similarly, when the last signal	1549	as you don't register any with libev). Similarly, when the last signal
597	watcher for a signal is stopped libev will reset the signal handler to	1550	watcher for a signal is stopped libev will reset the signal handler to
598	SIG_DFL (regardless of what it was set to before).	1551	SIG_DFL (regardless of what it was set to before).
599		1552
		1553	If possible and supported, libev will install its handlers with
		1554	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1555	interrupted. If you have a problem with system calls getting interrupted by
		1556	signals you can block all signals in an C<ev_check> watcher and unblock
		1557	them in an C<ev_prepare> watcher.
		1558
		1559	=head3 Watcher-Specific Functions and Data Members
		1560
600	=over 4	1561	=over 4
601		1562
602	=item ev_signal_init (ev_signal *, callback, int signum)	1563	=item ev_signal_init (ev_signal *, callback, int signum)
603		1564
604	=item ev_signal_set (ev_signal *, int signum)	1565	=item ev_signal_set (ev_signal *, int signum)
605		1566
606	Configures the watcher to trigger on the given signal number (usually one	1567	Configures the watcher to trigger on the given signal number (usually one
607	of the C<SIGxxx> constants).	1568	of the C<SIGxxx> constants).
608		1569
		1570	=item int signum [read-only]
		1571
		1572	The signal the watcher watches out for.
		1573
609	=back	1574	=back
610		1575
		1576	=head3 Examples
		1577
		1578	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1579
		1580	static void
		1581	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1582	{
		1583	ev_unloop (loop, EVUNLOOP_ALL);
		1584	}
		1585
		1586	struct ev_signal signal_watcher;
		1587	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1588	ev_signal_start (loop, &sigint_cb);
		1589
		1590
611	=head2 ev_child - wait for pid status changes	1591	=head2 C<ev_child> - watch out for process status changes
612		1592
613	Child watchers trigger when your process receives a SIGCHLD in response to	1593	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).	1594	some child status changes (most typically when a child of yours dies). It
		1595	is permissible to install a child watcher I<after> the child has been
		1596	forked (which implies it might have already exited), as long as the event
		1597	loop isn't entered (or is continued from a watcher).
		1598
		1599	Only the default event loop is capable of handling signals, and therefore
		1600	you can only register child watchers in the default event loop.
		1601
		1602	=head3 Process Interaction
		1603
		1604	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1605	initialised. This is necessary to guarantee proper behaviour even if
		1606	the first child watcher is started after the child exits. The occurrence
		1607	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1608	synchronously as part of the event loop processing. Libev always reaps all
		1609	children, even ones not watched.
		1610
		1611	=head3 Overriding the Built-In Processing
		1612
		1613	Libev offers no special support for overriding the built-in child
		1614	processing, but if your application collides with libev's default child
		1615	handler, you can override it easily by installing your own handler for
		1616	C<SIGCHLD> after initialising the default loop, and making sure the
		1617	default loop never gets destroyed. You are encouraged, however, to use an
		1618	event-based approach to child reaping and thus use libev's support for
		1619	that, so other libev users can use C<ev_child> watchers freely.
		1620
		1621	=head3 Stopping the Child Watcher
		1622
		1623	Currently, the child watcher never gets stopped, even when the
		1624	child terminates, so normally one needs to stop the watcher in the
		1625	callback. Future versions of libev might stop the watcher automatically
		1626	when a child exit is detected.
		1627
		1628	=head3 Watcher-Specific Functions and Data Members
615		1629
616	=over 4	1630	=over 4
617		1631
618	=item ev_child_init (ev_child *, callback, int pid)	1632	=item ev_child_init (ev_child *, callback, int pid, int trace)
619		1633
620	=item ev_child_set (ev_child *, int pid)	1634	=item ev_child_set (ev_child *, int pid, int trace)
621		1635
622	Configures the watcher to wait for status changes of process C<pid> (or	1636	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	1637	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	1638	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	1639	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.	1640	C<waitpid> documentation). The C<rpid> member contains the pid of the
		1641	process causing the status change. C<trace> must be either C<0> (only
		1642	activate the watcher when the process terminates) or C<1> (additionally
		1643	activate the watcher when the process is stopped or continued).
		1644
		1645	=item int pid [read-only]
		1646
		1647	The process id this watcher watches out for, or C<0>, meaning any process id.
		1648
		1649	=item int rpid [read-write]
		1650
		1651	The process id that detected a status change.
		1652
		1653	=item int rstatus [read-write]
		1654
		1655	The process exit/trace status caused by C<rpid> (see your systems
		1656	C<waitpid> and C<sys/wait.h> documentation for details).
627		1657
628	=back	1658	=back
629		1659
		1660	=head3 Examples
		1661
		1662	Example: C<fork()> a new process and install a child handler to wait for
		1663	its completion.
		1664
		1665	ev_child cw;
		1666
		1667	static void
		1668	child_cb (EV_P_ struct ev_child *w, int revents)
		1669	{
		1670	ev_child_stop (EV_A_ w);
		1671	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1672	}
		1673
		1674	pid_t pid = fork ();
		1675
		1676	if (pid < 0)
		1677	// error
		1678	else if (pid == 0)
		1679	{
		1680	// the forked child executes here
		1681	exit (1);
		1682	}
		1683	else
		1684	{
		1685	ev_child_init (&cw, child_cb, pid, 0);
		1686	ev_child_start (EV_DEFAULT_ &cw);
		1687	}
		1688
		1689
		1690	=head2 C<ev_stat> - did the file attributes just change?
		1691
		1692	This watches a file system path for attribute changes. That is, it calls
		1693	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1694	compared to the last time, invoking the callback if it did.
		1695
		1696	The path does not need to exist: changing from "path exists" to "path does
		1697	not exist" is a status change like any other. The condition "path does
		1698	not exist" is signified by the C<st_nlink> field being zero (which is
		1699	otherwise always forced to be at least one) and all the other fields of
		1700	the stat buffer having unspecified contents.
		1701
		1702	The path I<should> be absolute and I<must not> end in a slash. If it is
		1703	relative and your working directory changes, the behaviour is undefined.
		1704
		1705	Since there is no standard to do this, the portable implementation simply
		1706	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1707	can specify a recommended polling interval for this case. If you specify
		1708	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1709	unspecified default> value will be used (which you can expect to be around
		1710	five seconds, although this might change dynamically). Libev will also
		1711	impose a minimum interval which is currently around C<0.1>, but thats
		1712	usually overkill.
		1713
		1714	This watcher type is not meant for massive numbers of stat watchers,
		1715	as even with OS-supported change notifications, this can be
		1716	resource-intensive.
		1717
		1718	At the time of this writing, only the Linux inotify interface is
		1719	implemented (implementing kqueue support is left as an exercise for the
		1720	reader, note, however, that the author sees no way of implementing ev_stat
		1721	semantics with kqueue). Inotify will be used to give hints only and should
		1722	not change the semantics of C<ev_stat> watchers, which means that libev
		1723	sometimes needs to fall back to regular polling again even with inotify,
		1724	but changes are usually detected immediately, and if the file exists there
		1725	will be no polling.
		1726
		1727	=head3 ABI Issues (Largefile Support)
		1728
		1729	Libev by default (unless the user overrides this) uses the default
		1730	compilation environment, which means that on systems with large file
		1731	support disabled by default, you get the 32 bit version of the stat
		1732	structure. When using the library from programs that change the ABI to
		1733	use 64 bit file offsets the programs will fail. In that case you have to
		1734	compile libev with the same flags to get binary compatibility. This is
		1735	obviously the case with any flags that change the ABI, but the problem is
		1736	most noticeably disabled with ev_stat and large file support.
		1737
		1738	The solution for this is to lobby your distribution maker to make large
		1739	file interfaces available by default (as e.g. FreeBSD does) and not
		1740	optional. Libev cannot simply switch on large file support because it has
		1741	to exchange stat structures with application programs compiled using the
		1742	default compilation environment.
		1743
		1744	=head3 Inotify
		1745
		1746	When C<inotify (7)> support has been compiled into libev (generally only
		1747	available on Linux) and present at runtime, it will be used to speed up
		1748	change detection where possible. The inotify descriptor will be created lazily
		1749	when the first C<ev_stat> watcher is being started.
		1750
		1751	Inotify presence does not change the semantics of C<ev_stat> watchers
		1752	except that changes might be detected earlier, and in some cases, to avoid
		1753	making regular C<stat> calls. Even in the presence of inotify support
		1754	there are many cases where libev has to resort to regular C<stat> polling.
		1755
		1756	(There is no support for kqueue, as apparently it cannot be used to
		1757	implement this functionality, due to the requirement of having a file
		1758	descriptor open on the object at all times).
		1759
		1760	=head3 The special problem of stat time resolution
		1761
		1762	The C<stat ()> system call only supports full-second resolution portably, and
		1763	even on systems where the resolution is higher, many file systems still
		1764	only support whole seconds.
		1765
		1766	That means that, if the time is the only thing that changes, you can
		1767	easily miss updates: on the first update, C<ev_stat> detects a change and
		1768	calls your callback, which does something. When there is another update
		1769	within the same second, C<ev_stat> will be unable to detect it as the stat
		1770	data does not change.
		1771
		1772	The solution to this is to delay acting on a change for slightly more
		1773	than a second (or till slightly after the next full second boundary), using
		1774	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1775	ev_timer_again (loop, w)>).
		1776
		1777	The C<.02> offset is added to work around small timing inconsistencies
		1778	of some operating systems (where the second counter of the current time
		1779	might be be delayed. One such system is the Linux kernel, where a call to
		1780	C<gettimeofday> might return a timestamp with a full second later than
		1781	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1782	update file times then there will be a small window where the kernel uses
		1783	the previous second to update file times but libev might already execute
		1784	the timer callback).
		1785
		1786	=head3 Watcher-Specific Functions and Data Members
		1787
		1788	=over 4
		1789
		1790	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1791
		1792	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1793
		1794	Configures the watcher to wait for status changes of the given
		1795	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1796	be detected and should normally be specified as C<0> to let libev choose
		1797	a suitable value. The memory pointed to by C<path> must point to the same
		1798	path for as long as the watcher is active.
		1799
		1800	The callback will receive C<EV_STAT> when a change was detected, relative
		1801	to the attributes at the time the watcher was started (or the last change
		1802	was detected).
		1803
		1804	=item ev_stat_stat (loop, ev_stat *)
		1805
		1806	Updates the stat buffer immediately with new values. If you change the
		1807	watched path in your callback, you could call this function to avoid
		1808	detecting this change (while introducing a race condition if you are not
		1809	the only one changing the path). Can also be useful simply to find out the
		1810	new values.
		1811
		1812	=item ev_statdata attr [read-only]
		1813
		1814	The most-recently detected attributes of the file. Although the type is
		1815	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1816	suitable for your system, but you can only rely on the POSIX-standardised
		1817	members to be present. If the C<st_nlink> member is C<0>, then there was
		1818	some error while C<stat>ing the file.
		1819
		1820	=item ev_statdata prev [read-only]
		1821
		1822	The previous attributes of the file. The callback gets invoked whenever
		1823	C<prev> != C<attr>, or, more precisely, one or more of these members
		1824	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1825	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1826
		1827	=item ev_tstamp interval [read-only]
		1828
		1829	The specified interval.
		1830
		1831	=item const char *path [read-only]
		1832
		1833	The file system path that is being watched.
		1834
		1835	=back
		1836
		1837	=head3 Examples
		1838
		1839	Example: Watch C</etc/passwd> for attribute changes.
		1840
		1841	static void
		1842	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1843	{
		1844	/* /etc/passwd changed in some way */
		1845	if (w->attr.st_nlink)
		1846	{
		1847	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1848	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1849	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1850	}
		1851	else
		1852	/* you shalt not abuse printf for puts */
		1853	puts ("wow, /etc/passwd is not there, expect problems. "
		1854	"if this is windows, they already arrived\n");
		1855	}
		1856
		1857	...
		1858	ev_stat passwd;
		1859
		1860	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1861	ev_stat_start (loop, &passwd);
		1862
		1863	Example: Like above, but additionally use a one-second delay so we do not
		1864	miss updates (however, frequent updates will delay processing, too, so
		1865	one might do the work both on C<ev_stat> callback invocation I<and> on
		1866	C<ev_timer> callback invocation).
		1867
		1868	static ev_stat passwd;
		1869	static ev_timer timer;
		1870
		1871	static void
		1872	timer_cb (EV_P_ ev_timer *w, int revents)
		1873	{
		1874	ev_timer_stop (EV_A_ w);
		1875
		1876	/* now it's one second after the most recent passwd change */
		1877	}
		1878
		1879	static void
		1880	stat_cb (EV_P_ ev_stat *w, int revents)
		1881	{
		1882	/* reset the one-second timer */
		1883	ev_timer_again (EV_A_ &timer);
		1884	}
		1885
		1886	...
		1887	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1888	ev_stat_start (loop, &passwd);
		1889	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1890
		1891
630	=head2 ev_idle - when you've got nothing better to do	1892	=head2 C<ev_idle> - when you've got nothing better to do...
631		1893
632	Idle watchers trigger events when there are no other I/O or timer (or	1894	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	1895	priority are pending (prepare, check and other idle watchers do not
634	handling sockets or timeouts it will not be called. But when your process	1896	count).
635	is idle all idle watchers are being called again and again - until	1897
		1898	That is, as long as your process is busy handling sockets or timeouts
		1899	(or even signals, imagine) of the same or higher priority it will not be
		1900	triggered. But when your process is idle (or only lower-priority watchers
		1901	are pending), the idle watchers are being called once per event loop
636	stopped, that is, or your process receives more events.	1902	iteration - until stopped, that is, or your process receives more events
		1903	and becomes busy again with higher priority stuff.
637		1904
638	The most noteworthy effect is that as long as any idle watchers are	1905	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.	1906	active, the process will not block when waiting for new events.
640		1907
641	Apart from keeping your process non-blocking (which is a useful	1908	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	1909	effect on its own sometimes), idle watchers are a good place to do
643	"pseudo-background processing", or delay processing stuff to after the	1910	"pseudo-background processing", or delay processing stuff to after the
644	event loop has handled all outstanding events.	1911	event loop has handled all outstanding events.
645		1912
		1913	=head3 Watcher-Specific Functions and Data Members
		1914
646	=over 4	1915	=over 4
647		1916
648	=item ev_idle_init (ev_signal *, callback)	1917	=item ev_idle_init (ev_signal *, callback)
649		1918
650	Initialises and configures the idle watcher - it has no parameters of any	1919	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,	1920	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
652	believe me.	1921	believe me.
653		1922
654	=back	1923	=back
655		1924
656	=head2 prepare and check - your hooks into the event loop	1925	=head3 Examples
657		1926
		1927	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1928	callback, free it. Also, use no error checking, as usual.
		1929
		1930	static void
		1931	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1932	{
		1933	free (w);
		1934	// now do something you wanted to do when the program has
		1935	// no longer anything immediate to do.
		1936	}
		1937
		1938	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1939	ev_idle_init (idle_watcher, idle_cb);
		1940	ev_idle_start (loop, idle_cb);
		1941
		1942
		1943	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		1944
658	Prepare and check watchers usually (but not always) are used in	1945	Prepare and check watchers are usually (but not always) used in tandem:
659	tandom. Prepare watchers get invoked before the process blocks and check	1946	prepare watchers get invoked before the process blocks and check watchers
660	watchers afterwards.	1947	afterwards.
661		1948
		1949	You I<must not> call C<ev_loop> or similar functions that enter
		1950	the current event loop from either C<ev_prepare> or C<ev_check>
		1951	watchers. Other loops than the current one are fine, however. The
		1952	rationale behind this is that you do not need to check for recursion in
		1953	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1954	C<ev_check> so if you have one watcher of each kind they will always be
		1955	called in pairs bracketing the blocking call.
		1956
662	Their main purpose is to integrate other event mechanisms into libev. This	1957	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	1958	their use is somewhat advanced. This could be used, for example, to track
664	watchers, integrate net-snmp or a coroutine library and lots more.	1959	variable changes, implement your own watchers, integrate net-snmp or a
		1960	coroutine library and lots more. They are also occasionally useful if
		1961	you cache some data and want to flush it before blocking (for example,
		1962	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1963	watcher).
665		1964
666	This is done by examining in each prepare call which file descriptors need	1965	This is done by examining in each prepare call which file descriptors need
667	to be watched by the other library, registering ev_io watchers for them	1966	to be watched by the other library, registering C<ev_io> watchers for
668	and starting an ev_timer watcher for any timeouts (many libraries provide	1967	them and starting an C<ev_timer> watcher for any timeouts (many libraries
669	just this functionality). Then, in the check watcher you check for any	1968	provide just this functionality). Then, in the check watcher you check for
670	events that occured (by making your callbacks set soem flags for example)	1969	any events that occurred (by checking the pending status of all watchers
671	and call back into the library.	1970	and stopping them) and call back into the library. The I/O and timer
		1971	callbacks will never actually be called (but must be valid nevertheless,
		1972	because you never know, you know?).
672		1973
673	As another example, the perl Coro module uses these hooks to integrate	1974	As another example, the Perl Coro module uses these hooks to integrate
674	coroutines into libev programs, by yielding to other active coroutines	1975	coroutines into libev programs, by yielding to other active coroutines
675	during each prepare and only letting the process block if no coroutines	1976	during each prepare and only letting the process block if no coroutines
676	are ready to run.	1977	are ready to run (it's actually more complicated: it only runs coroutines
		1978	with priority higher than or equal to the event loop and one coroutine
		1979	of lower priority, but only once, using idle watchers to keep the event
		1980	loop from blocking if lower-priority coroutines are active, thus mapping
		1981	low-priority coroutines to idle/background tasks).
		1982
		1983	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1984	priority, to ensure that they are being run before any other watchers
		1985	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1986	too) should not activate ("feed") events into libev. While libev fully
		1987	supports this, they might get executed before other C<ev_check> watchers
		1988	did their job. As C<ev_check> watchers are often used to embed other
		1989	(non-libev) event loops those other event loops might be in an unusable
		1990	state until their C<ev_check> watcher ran (always remind yourself to
		1991	coexist peacefully with others).
		1992
		1993	=head3 Watcher-Specific Functions and Data Members
677		1994
678	=over 4	1995	=over 4
679		1996
680	=item ev_prepare_init (ev_prepare *, callback)	1997	=item ev_prepare_init (ev_prepare *, callback)
681		1998
682	=item ev_check_init (ev_check *, callback)	1999	=item ev_check_init (ev_check *, callback)
683		2000
684	Initialises and configures the prepare or check watcher - they have no	2001	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>	2002	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
686	macros, but using them is utterly, utterly pointless.	2003	macros, but using them is utterly, utterly and completely pointless.
687		2004
688	=back	2005	=back
689		2006
		2007	=head3 Examples
		2008
		2009	There are a number of principal ways to embed other event loops or modules
		2010	into libev. Here are some ideas on how to include libadns into libev
		2011	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2012	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2013	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2014	Glib event loop).
		2015
		2016	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2017	and in a check watcher, destroy them and call into libadns. What follows
		2018	is pseudo-code only of course. This requires you to either use a low
		2019	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2020	the callbacks for the IO/timeout watchers might not have been called yet.
		2021
		2022	static ev_io iow [nfd];
		2023	static ev_timer tw;
		2024
		2025	static void
		2026	io_cb (ev_loop *loop, ev_io *w, int revents)
		2027	{
		2028	}
		2029
		2030	// create io watchers for each fd and a timer before blocking
		2031	static void
		2032	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		2033	{
		2034	int timeout = 3600000;
		2035	struct pollfd fds [nfd];
		2036	// actual code will need to loop here and realloc etc.
		2037	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2038
		2039	/* the callback is illegal, but won't be called as we stop during check */
		2040	ev_timer_init (&tw, 0, timeout * 1e-3);
		2041	ev_timer_start (loop, &tw);
		2042
		2043	// create one ev_io per pollfd
		2044	for (int i = 0; i < nfd; ++i)
		2045	{
		2046	ev_io_init (iow + i, io_cb, fds [i].fd,
		2047	((fds [i].events & POLLIN ? EV_READ : 0)
		2048	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2049
		2050	fds [i].revents = 0;
		2051	ev_io_start (loop, iow + i);
		2052	}
		2053	}
		2054
		2055	// stop all watchers after blocking
		2056	static void
		2057	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		2058	{
		2059	ev_timer_stop (loop, &tw);
		2060
		2061	for (int i = 0; i < nfd; ++i)
		2062	{
		2063	// set the relevant poll flags
		2064	// could also call adns_processreadable etc. here
		2065	struct pollfd *fd = fds + i;
		2066	int revents = ev_clear_pending (iow + i);
		2067	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2068	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2069
		2070	// now stop the watcher
		2071	ev_io_stop (loop, iow + i);
		2072	}
		2073
		2074	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2075	}
		2076
		2077	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2078	in the prepare watcher and would dispose of the check watcher.
		2079
		2080	Method 3: If the module to be embedded supports explicit event
		2081	notification (libadns does), you can also make use of the actual watcher
		2082	callbacks, and only destroy/create the watchers in the prepare watcher.
		2083
		2084	static void
		2085	timer_cb (EV_P_ ev_timer *w, int revents)
		2086	{
		2087	adns_state ads = (adns_state)w->data;
		2088	update_now (EV_A);
		2089
		2090	adns_processtimeouts (ads, &tv_now);
		2091	}
		2092
		2093	static void
		2094	io_cb (EV_P_ ev_io *w, int revents)
		2095	{
		2096	adns_state ads = (adns_state)w->data;
		2097	update_now (EV_A);
		2098
		2099	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2100	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2101	}
		2102
		2103	// do not ever call adns_afterpoll
		2104
		2105	Method 4: Do not use a prepare or check watcher because the module you
		2106	want to embed is too inflexible to support it. Instead, you can override
		2107	their poll function. The drawback with this solution is that the main
		2108	loop is now no longer controllable by EV. The C<Glib::EV> module does
		2109	this.
		2110
		2111	static gint
		2112	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2113	{
		2114	int got_events = 0;
		2115
		2116	for (n = 0; n < nfds; ++n)
		2117	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2118
		2119	if (timeout >= 0)
		2120	// create/start timer
		2121
		2122	// poll
		2123	ev_loop (EV_A_ 0);
		2124
		2125	// stop timer again
		2126	if (timeout >= 0)
		2127	ev_timer_stop (EV_A_ &to);
		2128
		2129	// stop io watchers again - their callbacks should have set
		2130	for (n = 0; n < nfds; ++n)
		2131	ev_io_stop (EV_A_ iow [n]);
		2132
		2133	return got_events;
		2134	}
		2135
		2136
		2137	=head2 C<ev_embed> - when one backend isn't enough...
		2138
		2139	This is a rather advanced watcher type that lets you embed one event loop
		2140	into another (currently only C<ev_io> events are supported in the embedded
		2141	loop, other types of watchers might be handled in a delayed or incorrect
		2142	fashion and must not be used).
		2143
		2144	There are primarily two reasons you would want that: work around bugs and
		2145	prioritise I/O.
		2146
		2147	As an example for a bug workaround, the kqueue backend might only support
		2148	sockets on some platform, so it is unusable as generic backend, but you
		2149	still want to make use of it because you have many sockets and it scales
		2150	so nicely. In this case, you would create a kqueue-based loop and embed it
		2151	into your default loop (which might use e.g. poll). Overall operation will
		2152	be a bit slower because first libev has to poll and then call kevent, but
		2153	at least you can use both at what they are best.
		2154
		2155	As for prioritising I/O: rarely you have the case where some fds have
		2156	to be watched and handled very quickly (with low latency), and even
		2157	priorities and idle watchers might have too much overhead. In this case
		2158	you would put all the high priority stuff in one loop and all the rest in
		2159	a second one, and embed the second one in the first.
		2160
		2161	As long as the watcher is active, the callback will be invoked every time
		2162	there might be events pending in the embedded loop. The callback must then
		2163	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2164	their callbacks (you could also start an idle watcher to give the embedded
		2165	loop strictly lower priority for example). You can also set the callback
		2166	to C<0>, in which case the embed watcher will automatically execute the
		2167	embedded loop sweep.
		2168
		2169	As long as the watcher is started it will automatically handle events. The
		2170	callback will be invoked whenever some events have been handled. You can
		2171	set the callback to C<0> to avoid having to specify one if you are not
		2172	interested in that.
		2173
		2174	Also, there have not currently been made special provisions for forking:
		2175	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2176	but you will also have to stop and restart any C<ev_embed> watchers
		2177	yourself.
		2178
		2179	Unfortunately, not all backends are embeddable, only the ones returned by
		2180	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2181	portable one.
		2182
		2183	So when you want to use this feature you will always have to be prepared
		2184	that you cannot get an embeddable loop. The recommended way to get around
		2185	this is to have a separate variables for your embeddable loop, try to
		2186	create it, and if that fails, use the normal loop for everything.
		2187
		2188	=head3 Watcher-Specific Functions and Data Members
		2189
		2190	=over 4
		2191
		2192	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2193
		2194	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2195
		2196	Configures the watcher to embed the given loop, which must be
		2197	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2198	invoked automatically, otherwise it is the responsibility of the callback
		2199	to invoke it (it will continue to be called until the sweep has been done,
		2200	if you do not want that, you need to temporarily stop the embed watcher).
		2201
		2202	=item ev_embed_sweep (loop, ev_embed *)
		2203
		2204	Make a single, non-blocking sweep over the embedded loop. This works
		2205	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2206	appropriate way for embedded loops.
		2207
		2208	=item struct ev_loop *other [read-only]
		2209
		2210	The embedded event loop.
		2211
		2212	=back
		2213
		2214	=head3 Examples
		2215
		2216	Example: Try to get an embeddable event loop and embed it into the default
		2217	event loop. If that is not possible, use the default loop. The default
		2218	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2219	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2220	used).
		2221
		2222	struct ev_loop *loop_hi = ev_default_init (0);
		2223	struct ev_loop *loop_lo = 0;
		2224	struct ev_embed embed;
		2225
		2226	// see if there is a chance of getting one that works
		2227	// (remember that a flags value of 0 means autodetection)
		2228	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2229	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2230	: 0;
		2231
		2232	// if we got one, then embed it, otherwise default to loop_hi
		2233	if (loop_lo)
		2234	{
		2235	ev_embed_init (&embed, 0, loop_lo);
		2236	ev_embed_start (loop_hi, &embed);
		2237	}
		2238	else
		2239	loop_lo = loop_hi;
		2240
		2241	Example: Check if kqueue is available but not recommended and create
		2242	a kqueue backend for use with sockets (which usually work with any
		2243	kqueue implementation). Store the kqueue/socket-only event loop in
		2244	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2245
		2246	struct ev_loop *loop = ev_default_init (0);
		2247	struct ev_loop *loop_socket = 0;
		2248	struct ev_embed embed;
		2249
		2250	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2251	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2252	{
		2253	ev_embed_init (&embed, 0, loop_socket);
		2254	ev_embed_start (loop, &embed);
		2255	}
		2256
		2257	if (!loop_socket)
		2258	loop_socket = loop;
		2259
		2260	// now use loop_socket for all sockets, and loop for everything else
		2261
		2262
		2263	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2264
		2265	Fork watchers are called when a C<fork ()> was detected (usually because
		2266	whoever is a good citizen cared to tell libev about it by calling
		2267	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2268	event loop blocks next and before C<ev_check> watchers are being called,
		2269	and only in the child after the fork. If whoever good citizen calling
		2270	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2271	handlers will be invoked, too, of course.
		2272
		2273	=head3 Watcher-Specific Functions and Data Members
		2274
		2275	=over 4
		2276
		2277	=item ev_fork_init (ev_signal *, callback)
		2278
		2279	Initialises and configures the fork watcher - it has no parameters of any
		2280	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2281	believe me.
		2282
		2283	=back
		2284
		2285
		2286	=head2 C<ev_async> - how to wake up another event loop
		2287
		2288	In general, you cannot use an C<ev_loop> from multiple threads or other
		2289	asynchronous sources such as signal handlers (as opposed to multiple event
		2290	loops - those are of course safe to use in different threads).
		2291
		2292	Sometimes, however, you need to wake up another event loop you do not
		2293	control, for example because it belongs to another thread. This is what
		2294	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2295	can signal it by calling C<ev_async_send>, which is thread- and signal
		2296	safe.
		2297
		2298	This functionality is very similar to C<ev_signal> watchers, as signals,
		2299	too, are asynchronous in nature, and signals, too, will be compressed
		2300	(i.e. the number of callback invocations may be less than the number of
		2301	C<ev_async_sent> calls).
		2302
		2303	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2304	just the default loop.
		2305
		2306	=head3 Queueing
		2307
		2308	C<ev_async> does not support queueing of data in any way. The reason
		2309	is that the author does not know of a simple (or any) algorithm for a
		2310	multiple-writer-single-reader queue that works in all cases and doesn't
		2311	need elaborate support such as pthreads.
		2312
		2313	That means that if you want to queue data, you have to provide your own
		2314	queue. But at least I can tell you would implement locking around your
		2315	queue:
		2316
		2317	=over 4
		2318
		2319	=item queueing from a signal handler context
		2320
		2321	To implement race-free queueing, you simply add to the queue in the signal
		2322	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2323	some fictitious SIGUSR1 handler:
		2324
		2325	static ev_async mysig;
		2326
		2327	static void
		2328	sigusr1_handler (void)
		2329	{
		2330	sometype data;
		2331
		2332	// no locking etc.
		2333	queue_put (data);
		2334	ev_async_send (EV_DEFAULT_ &mysig);
		2335	}
		2336
		2337	static void
		2338	mysig_cb (EV_P_ ev_async *w, int revents)
		2339	{
		2340	sometype data;
		2341	sigset_t block, prev;
		2342
		2343	sigemptyset (&block);
		2344	sigaddset (&block, SIGUSR1);
		2345	sigprocmask (SIG_BLOCK, &block, &prev);
		2346
		2347	while (queue_get (&data))
		2348	process (data);
		2349
		2350	if (sigismember (&prev, SIGUSR1)
		2351	sigprocmask (SIG_UNBLOCK, &block, 0);
		2352	}
		2353
		2354	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2355	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2356	either...).
		2357
		2358	=item queueing from a thread context
		2359
		2360	The strategy for threads is different, as you cannot (easily) block
		2361	threads but you can easily preempt them, so to queue safely you need to
		2362	employ a traditional mutex lock, such as in this pthread example:
		2363
		2364	static ev_async mysig;
		2365	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2366
		2367	static void
		2368	otherthread (void)
		2369	{
		2370	// only need to lock the actual queueing operation
		2371	pthread_mutex_lock (&mymutex);
		2372	queue_put (data);
		2373	pthread_mutex_unlock (&mymutex);
		2374
		2375	ev_async_send (EV_DEFAULT_ &mysig);
		2376	}
		2377
		2378	static void
		2379	mysig_cb (EV_P_ ev_async *w, int revents)
		2380	{
		2381	pthread_mutex_lock (&mymutex);
		2382
		2383	while (queue_get (&data))
		2384	process (data);
		2385
		2386	pthread_mutex_unlock (&mymutex);
		2387	}
		2388
		2389	=back
		2390
		2391
		2392	=head3 Watcher-Specific Functions and Data Members
		2393
		2394	=over 4
		2395
		2396	=item ev_async_init (ev_async *, callback)
		2397
		2398	Initialises and configures the async watcher - it has no parameters of any
		2399	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2400	believe me.
		2401
		2402	=item ev_async_send (loop, ev_async *)
		2403
		2404	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2405	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2406	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2407	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2408	section below on what exactly this means).
		2409
		2410	This call incurs the overhead of a system call only once per loop iteration,
		2411	so while the overhead might be noticeable, it doesn't apply to repeated
		2412	calls to C<ev_async_send>.
		2413
		2414	=item bool = ev_async_pending (ev_async *)
		2415
		2416	Returns a non-zero value when C<ev_async_send> has been called on the
		2417	watcher but the event has not yet been processed (or even noted) by the
		2418	event loop.
		2419
		2420	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2421	the loop iterates next and checks for the watcher to have become active,
		2422	it will reset the flag again. C<ev_async_pending> can be used to very
		2423	quickly check whether invoking the loop might be a good idea.
		2424
		2425	Not that this does I<not> check whether the watcher itself is pending, only
		2426	whether it has been requested to make this watcher pending.
		2427
		2428	=back
		2429
		2430
690	=head1 OTHER FUNCTIONS	2431	=head1 OTHER FUNCTIONS
691		2432
692	There are some other fucntions of possible interest. Described. Here. Now.	2433	There are some other functions of possible interest. Described. Here. Now.
693		2434
694	=over 4	2435	=over 4
695		2436
696	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2437	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
697		2438
698	This function combines a simple timer and an I/O watcher, calls your	2439	This function combines a simple timer and an I/O watcher, calls your
699	callback on whichever event happens first and automatically stop both	2440	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	2441	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	2442	or timeout without having to allocate/configure/start/stop/free one or
702	more watchers yourself.	2443	more watchers yourself.
703		2444
704	If C<fd> is less than 0, then no I/O watcher will be started and events is	2445	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	2446	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
706	will be craeted and started.	2447	C<events> set will be created and started.
707		2448
708	If C<timeout> is less than 0, then no timeout watcher will be	2449	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	2450	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
710	= 0) will be started.	2451	repeat = 0) will be started. While C<0> is a valid timeout, it is of
		2452	dubious value.
711		2453
712	The callback has the type C<void (*cb)(int revents, void *arg)> and	2454	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,	2455	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>:	2456	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
		2457	value passed to C<ev_once>:
715		2458
716	static void stdin_ready (int revents, void *arg)	2459	static void stdin_ready (int revents, void *arg)
717	{	2460	{
718	if (revents & EV_TIMEOUT)	2461	if (revents & EV_TIMEOUT)
719	/* doh, nothing entered */	2462	/* doh, nothing entered */;
720	else if (revents & EV_READ)	2463	else if (revents & EV_READ)
721	/* stdin might have data for us, joy! */	2464	/* stdin might have data for us, joy! */;
722	}	2465	}
723		2466
724	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	2467	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
725		2468
726	=item ev_feed_event (loop, watcher, int events)	2469	=item ev_feed_event (ev_loop *, watcher *, int revents)
727		2470
728	Feeds the given event set into the event loop, as if the specified event	2471	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	2472	had happened for the specified watcher (which must be a pointer to an
730	initialised but not necessarily active event watcher).	2473	initialised but not necessarily started event watcher).
731		2474
732	=item ev_feed_fd_event (loop, int fd, int revents)	2475	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
733		2476
734	Feed an event on the given fd, as if a file descriptor backend detected it.	2477	Feed an event on the given fd, as if a file descriptor backend detected
		2478	the given events it.
735		2479
736	=item ev_feed_signal_event (loop, int signum)	2480	=item ev_feed_signal_event (ev_loop *loop, int signum)
737		2481
738	Feed an event as if the given signal occured (loop must be the default loop!).	2482	Feed an event as if the given signal occurred (C<loop> must be the default
		2483	loop!).
739		2484
740	=back	2485	=back
741		2486
		2487
		2488	=head1 LIBEVENT EMULATION
		2489
		2490	Libev offers a compatibility emulation layer for libevent. It cannot
		2491	emulate the internals of libevent, so here are some usage hints:
		2492
		2493	=over 4
		2494
		2495	=item * Use it by including <event.h>, as usual.
		2496
		2497	=item * The following members are fully supported: ev_base, ev_callback,
		2498	ev_arg, ev_fd, ev_res, ev_events.
		2499
		2500	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2501	maintained by libev, it does not work exactly the same way as in libevent (consider
		2502	it a private API).
		2503
		2504	=item * Priorities are not currently supported. Initialising priorities
		2505	will fail and all watchers will have the same priority, even though there
		2506	is an ev_pri field.
		2507
		2508	=item * In libevent, the last base created gets the signals, in libev, the
		2509	first base created (== the default loop) gets the signals.
		2510
		2511	=item * Other members are not supported.
		2512
		2513	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2514	to use the libev header file and library.
		2515
		2516	=back
		2517
		2518	=head1 C++ SUPPORT
		2519
		2520	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2521	you to use some convenience methods to start/stop watchers and also change
		2522	the callback model to a model using method callbacks on objects.
		2523
		2524	To use it,
		2525
		2526	#include <ev++.h>
		2527
		2528	This automatically includes F<ev.h> and puts all of its definitions (many
		2529	of them macros) into the global namespace. All C++ specific things are
		2530	put into the C<ev> namespace. It should support all the same embedding
		2531	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2532
		2533	Care has been taken to keep the overhead low. The only data member the C++
		2534	classes add (compared to plain C-style watchers) is the event loop pointer
		2535	that the watcher is associated with (or no additional members at all if
		2536	you disable C<EV_MULTIPLICITY> when embedding libev).
		2537
		2538	Currently, functions, and static and non-static member functions can be
		2539	used as callbacks. Other types should be easy to add as long as they only
		2540	need one additional pointer for context. If you need support for other
		2541	types of functors please contact the author (preferably after implementing
		2542	it).
		2543
		2544	Here is a list of things available in the C<ev> namespace:
		2545
		2546	=over 4
		2547
		2548	=item C<ev::READ>, C<ev::WRITE> etc.
		2549
		2550	These are just enum values with the same values as the C<EV_READ> etc.
		2551	macros from F<ev.h>.
		2552
		2553	=item C<ev::tstamp>, C<ev::now>
		2554
		2555	Aliases to the same types/functions as with the C<ev_> prefix.
		2556
		2557	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2558
		2559	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2560	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2561	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2562	defines by many implementations.
		2563
		2564	All of those classes have these methods:
		2565
		2566	=over 4
		2567
		2568	=item ev::TYPE::TYPE ()
		2569
		2570	=item ev::TYPE::TYPE (struct ev_loop *)
		2571
		2572	=item ev::TYPE::~TYPE
		2573
		2574	The constructor (optionally) takes an event loop to associate the watcher
		2575	with. If it is omitted, it will use C<EV_DEFAULT>.
		2576
		2577	The constructor calls C<ev_init> for you, which means you have to call the
		2578	C<set> method before starting it.
		2579
		2580	It will not set a callback, however: You have to call the templated C<set>
		2581	method to set a callback before you can start the watcher.
		2582
		2583	(The reason why you have to use a method is a limitation in C++ which does
		2584	not allow explicit template arguments for constructors).
		2585
		2586	The destructor automatically stops the watcher if it is active.
		2587
		2588	=item w->set<class, &class::method> (object *)
		2589
		2590	This method sets the callback method to call. The method has to have a
		2591	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2592	first argument and the C<revents> as second. The object must be given as
		2593	parameter and is stored in the C<data> member of the watcher.
		2594
		2595	This method synthesizes efficient thunking code to call your method from
		2596	the C callback that libev requires. If your compiler can inline your
		2597	callback (i.e. it is visible to it at the place of the C<set> call and
		2598	your compiler is good :), then the method will be fully inlined into the
		2599	thunking function, making it as fast as a direct C callback.
		2600
		2601	Example: simple class declaration and watcher initialisation
		2602
		2603	struct myclass
		2604	{
		2605	void io_cb (ev::io &w, int revents) { }
		2606	}
		2607
		2608	myclass obj;
		2609	ev::io iow;
		2610	iow.set <myclass, &myclass::io_cb> (&obj);
		2611
		2612	=item w->set<function> (void *data = 0)
		2613
		2614	Also sets a callback, but uses a static method or plain function as
		2615	callback. The optional C<data> argument will be stored in the watcher's
		2616	C<data> member and is free for you to use.
		2617
		2618	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2619
		2620	See the method-C<set> above for more details.
		2621
		2622	Example:
		2623
		2624	static void io_cb (ev::io &w, int revents) { }
		2625	iow.set <io_cb> ();
		2626
		2627	=item w->set (struct ev_loop *)
		2628
		2629	Associates a different C<struct ev_loop> with this watcher. You can only
		2630	do this when the watcher is inactive (and not pending either).
		2631
		2632	=item w->set ([arguments])
		2633
		2634	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2635	called at least once. Unlike the C counterpart, an active watcher gets
		2636	automatically stopped and restarted when reconfiguring it with this
		2637	method.
		2638
		2639	=item w->start ()
		2640
		2641	Starts the watcher. Note that there is no C<loop> argument, as the
		2642	constructor already stores the event loop.
		2643
		2644	=item w->stop ()
		2645
		2646	Stops the watcher if it is active. Again, no C<loop> argument.
		2647
		2648	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2649
		2650	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2651	C<ev_TYPE_again> function.
		2652
		2653	=item w->sweep () (C<ev::embed> only)
		2654
		2655	Invokes C<ev_embed_sweep>.
		2656
		2657	=item w->update () (C<ev::stat> only)
		2658
		2659	Invokes C<ev_stat_stat>.
		2660
		2661	=back
		2662
		2663	=back
		2664
		2665	Example: Define a class with an IO and idle watcher, start one of them in
		2666	the constructor.
		2667
		2668	class myclass
		2669	{
		2670	ev::io io; void io_cb (ev::io &w, int revents);
		2671	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2672
		2673	myclass (int fd)
		2674	{
		2675	io .set <myclass, &myclass::io_cb > (this);
		2676	idle.set <myclass, &myclass::idle_cb> (this);
		2677
		2678	io.start (fd, ev::READ);
		2679	}
		2680	};
		2681
		2682
		2683	=head1 OTHER LANGUAGE BINDINGS
		2684
		2685	Libev does not offer other language bindings itself, but bindings for a
		2686	number of languages exist in the form of third-party packages. If you know
		2687	any interesting language binding in addition to the ones listed here, drop
		2688	me a note.
		2689
		2690	=over 4
		2691
		2692	=item Perl
		2693
		2694	The EV module implements the full libev API and is actually used to test
		2695	libev. EV is developed together with libev. Apart from the EV core module,
		2696	there are additional modules that implement libev-compatible interfaces
		2697	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2698	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2699
		2700	It can be found and installed via CPAN, its homepage is at
		2701	L<http://software.schmorp.de/pkg/EV>.
		2702
		2703	=item Python
		2704
		2705	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2706	seems to be quite complete and well-documented. Note, however, that the
		2707	patch they require for libev is outright dangerous as it breaks the ABI
		2708	for everybody else, and therefore, should never be applied in an installed
		2709	libev (if python requires an incompatible ABI then it needs to embed
		2710	libev).
		2711
		2712	=item Ruby
		2713
		2714	Tony Arcieri has written a ruby extension that offers access to a subset
		2715	of the libev API and adds file handle abstractions, asynchronous DNS and
		2716	more on top of it. It can be found via gem servers. Its homepage is at
		2717	L<http://rev.rubyforge.org/>.
		2718
		2719	=item D
		2720
		2721	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2722	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2723
		2724	=back
		2725
		2726
		2727	=head1 MACRO MAGIC
		2728
		2729	Libev can be compiled with a variety of options, the most fundamental
		2730	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2731	functions and callbacks have an initial C<struct ev_loop *> argument.
		2732
		2733	To make it easier to write programs that cope with either variant, the
		2734	following macros are defined:
		2735
		2736	=over 4
		2737
		2738	=item C<EV_A>, C<EV_A_>
		2739
		2740	This provides the loop I<argument> for functions, if one is required ("ev
		2741	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2742	C<EV_A_> is used when other arguments are following. Example:
		2743
		2744	ev_unref (EV_A);
		2745	ev_timer_add (EV_A_ watcher);
		2746	ev_loop (EV_A_ 0);
		2747
		2748	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2749	which is often provided by the following macro.
		2750
		2751	=item C<EV_P>, C<EV_P_>
		2752
		2753	This provides the loop I<parameter> for functions, if one is required ("ev
		2754	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2755	C<EV_P_> is used when other parameters are following. Example:
		2756
		2757	// this is how ev_unref is being declared
		2758	static void ev_unref (EV_P);
		2759
		2760	// this is how you can declare your typical callback
		2761	static void cb (EV_P_ ev_timer *w, int revents)
		2762
		2763	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2764	suitable for use with C<EV_A>.
		2765
		2766	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2767
		2768	Similar to the other two macros, this gives you the value of the default
		2769	loop, if multiple loops are supported ("ev loop default").
		2770
		2771	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2772
		2773	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2774	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2775	is undefined when the default loop has not been initialised by a previous
		2776	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2777
		2778	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2779	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2780
		2781	=back
		2782
		2783	Example: Declare and initialise a check watcher, utilising the above
		2784	macros so it will work regardless of whether multiple loops are supported
		2785	or not.
		2786
		2787	static void
		2788	check_cb (EV_P_ ev_timer *w, int revents)
		2789	{
		2790	ev_check_stop (EV_A_ w);
		2791	}
		2792
		2793	ev_check check;
		2794	ev_check_init (&check, check_cb);
		2795	ev_check_start (EV_DEFAULT_ &check);
		2796	ev_loop (EV_DEFAULT_ 0);
		2797
		2798	=head1 EMBEDDING
		2799
		2800	Libev can (and often is) directly embedded into host
		2801	applications. Examples of applications that embed it include the Deliantra
		2802	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2803	and rxvt-unicode.
		2804
		2805	The goal is to enable you to just copy the necessary files into your
		2806	source directory without having to change even a single line in them, so
		2807	you can easily upgrade by simply copying (or having a checked-out copy of
		2808	libev somewhere in your source tree).
		2809
		2810	=head2 FILESETS
		2811
		2812	Depending on what features you need you need to include one or more sets of files
		2813	in your application.
		2814
		2815	=head3 CORE EVENT LOOP
		2816
		2817	To include only the libev core (all the C<ev_*> functions), with manual
		2818	configuration (no autoconf):
		2819
		2820	#define EV_STANDALONE 1
		2821	#include "ev.c"
		2822
		2823	This will automatically include F<ev.h>, too, and should be done in a
		2824	single C source file only to provide the function implementations. To use
		2825	it, do the same for F<ev.h> in all files wishing to use this API (best
		2826	done by writing a wrapper around F<ev.h> that you can include instead and
		2827	where you can put other configuration options):
		2828
		2829	#define EV_STANDALONE 1
		2830	#include "ev.h"
		2831
		2832	Both header files and implementation files can be compiled with a C++
		2833	compiler (at least, thats a stated goal, and breakage will be treated
		2834	as a bug).
		2835
		2836	You need the following files in your source tree, or in a directory
		2837	in your include path (e.g. in libev/ when using -Ilibev):
		2838
		2839	ev.h
		2840	ev.c
		2841	ev_vars.h
		2842	ev_wrap.h
		2843
		2844	ev_win32.c required on win32 platforms only
		2845
		2846	ev_select.c only when select backend is enabled (which is enabled by default)
		2847	ev_poll.c only when poll backend is enabled (disabled by default)
		2848	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2849	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2850	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2851
		2852	F<ev.c> includes the backend files directly when enabled, so you only need
		2853	to compile this single file.
		2854
		2855	=head3 LIBEVENT COMPATIBILITY API
		2856
		2857	To include the libevent compatibility API, also include:
		2858
		2859	#include "event.c"
		2860
		2861	in the file including F<ev.c>, and:
		2862
		2863	#include "event.h"
		2864
		2865	in the files that want to use the libevent API. This also includes F<ev.h>.
		2866
		2867	You need the following additional files for this:
		2868
		2869	event.h
		2870	event.c
		2871
		2872	=head3 AUTOCONF SUPPORT
		2873
		2874	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		2875	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2876	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2877	include F<config.h> and configure itself accordingly.
		2878
		2879	For this of course you need the m4 file:
		2880
		2881	libev.m4
		2882
		2883	=head2 PREPROCESSOR SYMBOLS/MACROS
		2884
		2885	Libev can be configured via a variety of preprocessor symbols you have to
		2886	define before including any of its files. The default in the absence of
		2887	autoconf is noted for every option.
		2888
		2889	=over 4
		2890
		2891	=item EV_STANDALONE
		2892
		2893	Must always be C<1> if you do not use autoconf configuration, which
		2894	keeps libev from including F<config.h>, and it also defines dummy
		2895	implementations for some libevent functions (such as logging, which is not
		2896	supported). It will also not define any of the structs usually found in
		2897	F<event.h> that are not directly supported by the libev core alone.
		2898
		2899	=item EV_USE_MONOTONIC
		2900
		2901	If defined to be C<1>, libev will try to detect the availability of the
		2902	monotonic clock option at both compile time and runtime. Otherwise no use
		2903	of the monotonic clock option will be attempted. If you enable this, you
		2904	usually have to link against librt or something similar. Enabling it when
		2905	the functionality isn't available is safe, though, although you have
		2906	to make sure you link against any libraries where the C<clock_gettime>
		2907	function is hiding in (often F<-lrt>).
		2908
		2909	=item EV_USE_REALTIME
		2910
		2911	If defined to be C<1>, libev will try to detect the availability of the
		2912	real-time clock option at compile time (and assume its availability at
		2913	runtime if successful). Otherwise no use of the real-time clock option will
		2914	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2915	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2916	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2917
		2918	=item EV_USE_NANOSLEEP
		2919
		2920	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2921	and will use it for delays. Otherwise it will use C<select ()>.
		2922
		2923	=item EV_USE_EVENTFD
		2924
		2925	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2926	available and will probe for kernel support at runtime. This will improve
		2927	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2928	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2929	2.7 or newer, otherwise disabled.
		2930
		2931	=item EV_USE_SELECT
		2932
		2933	If undefined or defined to be C<1>, libev will compile in support for the
		2934	C<select>(2) backend. No attempt at auto-detection will be done: if no
		2935	other method takes over, select will be it. Otherwise the select backend
		2936	will not be compiled in.
		2937
		2938	=item EV_SELECT_USE_FD_SET
		2939
		2940	If defined to C<1>, then the select backend will use the system C<fd_set>
		2941	structure. This is useful if libev doesn't compile due to a missing
		2942	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		2943	exotic systems. This usually limits the range of file descriptors to some
		2944	low limit such as 1024 or might have other limitations (winsocket only
		2945	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2946	influence the size of the C<fd_set> used.
		2947
		2948	=item EV_SELECT_IS_WINSOCKET
		2949
		2950	When defined to C<1>, the select backend will assume that
		2951	select/socket/connect etc. don't understand file descriptors but
		2952	wants osf handles on win32 (this is the case when the select to
		2953	be used is the winsock select). This means that it will call
		2954	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2955	it is assumed that all these functions actually work on fds, even
		2956	on win32. Should not be defined on non-win32 platforms.
		2957
		2958	=item EV_FD_TO_WIN32_HANDLE
		2959
		2960	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2961	file descriptors to socket handles. When not defining this symbol (the
		2962	default), then libev will call C<_get_osfhandle>, which is usually
		2963	correct. In some cases, programs use their own file descriptor management,
		2964	in which case they can provide this function to map fds to socket handles.
		2965
		2966	=item EV_USE_POLL
		2967
		2968	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2969	backend. Otherwise it will be enabled on non-win32 platforms. It
		2970	takes precedence over select.
		2971
		2972	=item EV_USE_EPOLL
		2973
		2974	If defined to be C<1>, libev will compile in support for the Linux
		2975	C<epoll>(7) backend. Its availability will be detected at runtime,
		2976	otherwise another method will be used as fallback. This is the preferred
		2977	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2978	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2979
		2980	=item EV_USE_KQUEUE
		2981
		2982	If defined to be C<1>, libev will compile in support for the BSD style
		2983	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2984	otherwise another method will be used as fallback. This is the preferred
		2985	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2986	supports some types of fds correctly (the only platform we found that
		2987	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2988	not be used unless explicitly requested. The best way to use it is to find
		2989	out whether kqueue supports your type of fd properly and use an embedded
		2990	kqueue loop.
		2991
		2992	=item EV_USE_PORT
		2993
		2994	If defined to be C<1>, libev will compile in support for the Solaris
		2995	10 port style backend. Its availability will be detected at runtime,
		2996	otherwise another method will be used as fallback. This is the preferred
		2997	backend for Solaris 10 systems.
		2998
		2999	=item EV_USE_DEVPOLL
		3000
		3001	Reserved for future expansion, works like the USE symbols above.
		3002
		3003	=item EV_USE_INOTIFY
		3004
		3005	If defined to be C<1>, libev will compile in support for the Linux inotify
		3006	interface to speed up C<ev_stat> watchers. Its actual availability will
		3007	be detected at runtime. If undefined, it will be enabled if the headers
		3008	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3009
		3010	=item EV_ATOMIC_T
		3011
		3012	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3013	access is atomic with respect to other threads or signal contexts. No such
		3014	type is easily found in the C language, so you can provide your own type
		3015	that you know is safe for your purposes. It is used both for signal handler "locking"
		3016	as well as for signal and thread safety in C<ev_async> watchers.
		3017
		3018	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3019	(from F<signal.h>), which is usually good enough on most platforms.
		3020
		3021	=item EV_H
		3022
		3023	The name of the F<ev.h> header file used to include it. The default if
		3024	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3025	used to virtually rename the F<ev.h> header file in case of conflicts.
		3026
		3027	=item EV_CONFIG_H
		3028
		3029	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3030	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3031	C<EV_H>, above.
		3032
		3033	=item EV_EVENT_H
		3034
		3035	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3036	of how the F<event.h> header can be found, the default is C<"event.h">.
		3037
		3038	=item EV_PROTOTYPES
		3039
		3040	If defined to be C<0>, then F<ev.h> will not define any function
		3041	prototypes, but still define all the structs and other symbols. This is
		3042	occasionally useful if you want to provide your own wrapper functions
		3043	around libev functions.
		3044
		3045	=item EV_MULTIPLICITY
		3046
		3047	If undefined or defined to C<1>, then all event-loop-specific functions
		3048	will have the C<struct ev_loop *> as first argument, and you can create
		3049	additional independent event loops. Otherwise there will be no support
		3050	for multiple event loops and there is no first event loop pointer
		3051	argument. Instead, all functions act on the single default loop.
		3052
		3053	=item EV_MINPRI
		3054
		3055	=item EV_MAXPRI
		3056
		3057	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3058	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3059	provide for more priorities by overriding those symbols (usually defined
		3060	to be C<-2> and C<2>, respectively).
		3061
		3062	When doing priority-based operations, libev usually has to linearly search
		3063	all the priorities, so having many of them (hundreds) uses a lot of space
		3064	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3065	fine.
		3066
		3067	If your embedding application does not need any priorities, defining these both to
		3068	C<0> will save some memory and CPU.
		3069
		3070	=item EV_PERIODIC_ENABLE
		3071
		3072	If undefined or defined to be C<1>, then periodic timers are supported. If
		3073	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3074	code.
		3075
		3076	=item EV_IDLE_ENABLE
		3077
		3078	If undefined or defined to be C<1>, then idle watchers are supported. If
		3079	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3080	code.
		3081
		3082	=item EV_EMBED_ENABLE
		3083
		3084	If undefined or defined to be C<1>, then embed watchers are supported. If
		3085	defined to be C<0>, then they are not.
		3086
		3087	=item EV_STAT_ENABLE
		3088
		3089	If undefined or defined to be C<1>, then stat watchers are supported. If
		3090	defined to be C<0>, then they are not.
		3091
		3092	=item EV_FORK_ENABLE
		3093
		3094	If undefined or defined to be C<1>, then fork watchers are supported. If
		3095	defined to be C<0>, then they are not.
		3096
		3097	=item EV_ASYNC_ENABLE
		3098
		3099	If undefined or defined to be C<1>, then async watchers are supported. If
		3100	defined to be C<0>, then they are not.
		3101
		3102	=item EV_MINIMAL
		3103
		3104	If you need to shave off some kilobytes of code at the expense of some
		3105	speed, define this symbol to C<1>. Currently this is used to override some
		3106	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3107	much smaller 2-heap for timer management over the default 4-heap.
		3108
		3109	=item EV_PID_HASHSIZE
		3110
		3111	C<ev_child> watchers use a small hash table to distribute workload by
		3112	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3113	than enough. If you need to manage thousands of children you might want to
		3114	increase this value (I<must> be a power of two).
		3115
		3116	=item EV_INOTIFY_HASHSIZE
		3117
		3118	C<ev_stat> watchers use a small hash table to distribute workload by
		3119	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3120	usually more than enough. If you need to manage thousands of C<ev_stat>
		3121	watchers you might want to increase this value (I<must> be a power of
		3122	two).
		3123
		3124	=item EV_USE_4HEAP
		3125
		3126	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3127	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3128	to C<1>. The 4-heap uses more complicated (longer) code but has
		3129	noticeably faster performance with many (thousands) of watchers.
		3130
		3131	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3132	(disabled).
		3133
		3134	=item EV_HEAP_CACHE_AT
		3135
		3136	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3137	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3138	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3139	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3140	but avoids random read accesses on heap changes. This improves performance
		3141	noticeably with with many (hundreds) of watchers.
		3142
		3143	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3144	(disabled).
		3145
		3146	=item EV_VERIFY
		3147
		3148	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3149	be done: If set to C<0>, no internal verification code will be compiled
		3150	in. If set to C<1>, then verification code will be compiled in, but not
		3151	called. If set to C<2>, then the internal verification code will be
		3152	called once per loop, which can slow down libev. If set to C<3>, then the
		3153	verification code will be called very frequently, which will slow down
		3154	libev considerably.
		3155
		3156	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3157	C<0.>
		3158
		3159	=item EV_COMMON
		3160
		3161	By default, all watchers have a C<void *data> member. By redefining
		3162	this macro to a something else you can include more and other types of
		3163	members. You have to define it each time you include one of the files,
		3164	though, and it must be identical each time.
		3165
		3166	For example, the perl EV module uses something like this:
		3167
		3168	#define EV_COMMON \
		3169	SV *self; /* contains this struct */ \
		3170	SV *cb_sv, *fh /* note no trailing ";" */
		3171
		3172	=item EV_CB_DECLARE (type)
		3173
		3174	=item EV_CB_INVOKE (watcher, revents)
		3175
		3176	=item ev_set_cb (ev, cb)
		3177
		3178	Can be used to change the callback member declaration in each watcher,
		3179	and the way callbacks are invoked and set. Must expand to a struct member
		3180	definition and a statement, respectively. See the F<ev.h> header file for
		3181	their default definitions. One possible use for overriding these is to
		3182	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3183	method calls instead of plain function calls in C++.
		3184
		3185	=head2 EXPORTED API SYMBOLS
		3186
		3187	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3188	exported symbols, you can use the provided F<Symbol.*> files which list
		3189	all public symbols, one per line:
		3190
		3191	Symbols.ev for libev proper
		3192	Symbols.event for the libevent emulation
		3193
		3194	This can also be used to rename all public symbols to avoid clashes with
		3195	multiple versions of libev linked together (which is obviously bad in
		3196	itself, but sometimes it is inconvenient to avoid this).
		3197
		3198	A sed command like this will create wrapper C<#define>'s that you need to
		3199	include before including F<ev.h>:
		3200
		3201	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3202
		3203	This would create a file F<wrap.h> which essentially looks like this:
		3204
		3205	#define ev_backend myprefix_ev_backend
		3206	#define ev_check_start myprefix_ev_check_start
		3207	#define ev_check_stop myprefix_ev_check_stop
		3208	...
		3209
		3210	=head2 EXAMPLES
		3211
		3212	For a real-world example of a program the includes libev
		3213	verbatim, you can have a look at the EV perl module
		3214	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3215	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3216	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3217	will be compiled. It is pretty complex because it provides its own header
		3218	file.
		3219
		3220	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3221	that everybody includes and which overrides some configure choices:
		3222
		3223	#define EV_MINIMAL 1
		3224	#define EV_USE_POLL 0
		3225	#define EV_MULTIPLICITY 0
		3226	#define EV_PERIODIC_ENABLE 0
		3227	#define EV_STAT_ENABLE 0
		3228	#define EV_FORK_ENABLE 0
		3229	#define EV_CONFIG_H <config.h>
		3230	#define EV_MINPRI 0
		3231	#define EV_MAXPRI 0
		3232
		3233	#include "ev++.h"
		3234
		3235	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3236
		3237	#include "ev_cpp.h"
		3238	#include "ev.c"
		3239
		3240
		3241	=head1 THREADS AND COROUTINES
		3242
		3243	=head2 THREADS
		3244
		3245	Libev itself is completely thread-safe, but it uses no locking. This
		3246	means that you can use as many loops as you want in parallel, as long as
		3247	only one thread ever calls into one libev function with the same loop
		3248	parameter.
		3249
		3250	Or put differently: calls with different loop parameters can be done in
		3251	parallel from multiple threads, calls with the same loop parameter must be
		3252	done serially (but can be done from different threads, as long as only one
		3253	thread ever is inside a call at any point in time, e.g. by using a mutex
		3254	per loop).
		3255
		3256	If you want to know which design (one loop, locking, or multiple loops
		3257	without or something else still) is best for your problem, then I cannot
		3258	help you. I can give some generic advice however:
		3259
		3260	=over 4
		3261
		3262	=item * most applications have a main thread: use the default libev loop
		3263	in that thread, or create a separate thread running only the default loop.
		3264
		3265	This helps integrating other libraries or software modules that use libev
		3266	themselves and don't care/know about threading.
		3267
		3268	=item * one loop per thread is usually a good model.
		3269
		3270	Doing this is almost never wrong, sometimes a better-performance model
		3271	exists, but it is always a good start.
		3272
		3273	=item * other models exist, such as the leader/follower pattern, where one
		3274	loop is handed through multiple threads in a kind of round-robin fashion.
		3275
		3276	Choosing a model is hard - look around, learn, know that usually you can do
		3277	better than you currently do :-)
		3278
		3279	=item * often you need to talk to some other thread which blocks in the
		3280	event loop - C<ev_async> watchers can be used to wake them up from other
		3281	threads safely (or from signal contexts...).
		3282
		3283	=back
		3284
		3285	=head2 COROUTINES
		3286
		3287	Libev is much more accommodating to coroutines ("cooperative threads"):
		3288	libev fully supports nesting calls to it's functions from different
		3289	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3290	different coroutines and switch freely between both coroutines running the
		3291	loop, as long as you don't confuse yourself). The only exception is that
		3292	you must not do this from C<ev_periodic> reschedule callbacks.
		3293
		3294	Care has been invested into making sure that libev does not keep local
		3295	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3296	switches.
		3297
		3298
		3299	=head1 COMPLEXITIES
		3300
		3301	In this section the complexities of (many of) the algorithms used inside
		3302	libev will be explained. For complexity discussions about backends see the
		3303	documentation for C<ev_default_init>.
		3304
		3305	All of the following are about amortised time: If an array needs to be
		3306	extended, libev needs to realloc and move the whole array, but this
		3307	happens asymptotically never with higher number of elements, so O(1) might
		3308	mean it might do a lengthy realloc operation in rare cases, but on average
		3309	it is much faster and asymptotically approaches constant time.
		3310
		3311	=over 4
		3312
		3313	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3314
		3315	This means that, when you have a watcher that triggers in one hour and
		3316	there are 100 watchers that would trigger before that then inserting will
		3317	have to skip roughly seven (C<ld 100>) of these watchers.
		3318
		3319	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3320
		3321	That means that changing a timer costs less than removing/adding them
		3322	as only the relative motion in the event queue has to be paid for.
		3323
		3324	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3325
		3326	These just add the watcher into an array or at the head of a list.
		3327
		3328	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3329
		3330	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3331
		3332	These watchers are stored in lists then need to be walked to find the
		3333	correct watcher to remove. The lists are usually short (you don't usually
		3334	have many watchers waiting for the same fd or signal).
		3335
		3336	=item Finding the next timer in each loop iteration: O(1)
		3337
		3338	By virtue of using a binary or 4-heap, the next timer is always found at a
		3339	fixed position in the storage array.
		3340
		3341	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3342
		3343	A change means an I/O watcher gets started or stopped, which requires
		3344	libev to recalculate its status (and possibly tell the kernel, depending
		3345	on backend and whether C<ev_io_set> was used).
		3346
		3347	=item Activating one watcher (putting it into the pending state): O(1)
		3348
		3349	=item Priority handling: O(number_of_priorities)
		3350
		3351	Priorities are implemented by allocating some space for each
		3352	priority. When doing priority-based operations, libev usually has to
		3353	linearly search all the priorities, but starting/stopping and activating
		3354	watchers becomes O(1) w.r.t. priority handling.
		3355
		3356	=item Sending an ev_async: O(1)
		3357
		3358	=item Processing ev_async_send: O(number_of_async_watchers)
		3359
		3360	=item Processing signals: O(max_signal_number)
		3361
		3362	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3363	calls in the current loop iteration. Checking for async and signal events
		3364	involves iterating over all running async watchers or all signal numbers.
		3365
		3366	=back
		3367
		3368
		3369	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3370
		3371	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3372	requires, and its I/O model is fundamentally incompatible with the POSIX
		3373	model. Libev still offers limited functionality on this platform in
		3374	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3375	descriptors. This only applies when using Win32 natively, not when using
		3376	e.g. cygwin.
		3377
		3378	Lifting these limitations would basically require the full
		3379	re-implementation of the I/O system. If you are into these kinds of
		3380	things, then note that glib does exactly that for you in a very portable
		3381	way (note also that glib is the slowest event library known to man).
		3382
		3383	There is no supported compilation method available on windows except
		3384	embedding it into other applications.
		3385
		3386	Not a libev limitation but worth mentioning: windows apparently doesn't
		3387	accept large writes: instead of resulting in a partial write, windows will
		3388	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3389	so make sure you only write small amounts into your sockets (less than a
		3390	megabyte seems safe, but thsi apparently depends on the amount of memory
		3391	available).
		3392
		3393	Due to the many, low, and arbitrary limits on the win32 platform and
		3394	the abysmal performance of winsockets, using a large number of sockets
		3395	is not recommended (and not reasonable). If your program needs to use
		3396	more than a hundred or so sockets, then likely it needs to use a totally
		3397	different implementation for windows, as libev offers the POSIX readiness
		3398	notification model, which cannot be implemented efficiently on windows
		3399	(Microsoft monopoly games).
		3400
		3401	A typical way to use libev under windows is to embed it (see the embedding
		3402	section for details) and use the following F<evwrap.h> header file instead
		3403	of F<ev.h>:
		3404
		3405	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3406	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3407
		3408	#include "ev.h"
		3409
		3410	And compile the following F<evwrap.c> file into your project (make sure
		3411	you do I<not> compile the F<ev.c> or any other embedded soruce files!):
		3412
		3413	#include "evwrap.h"
		3414	#include "ev.c"
		3415
		3416	=over 4
		3417
		3418	=item The winsocket select function
		3419
		3420	The winsocket C<select> function doesn't follow POSIX in that it
		3421	requires socket I<handles> and not socket I<file descriptors> (it is
		3422	also extremely buggy). This makes select very inefficient, and also
		3423	requires a mapping from file descriptors to socket handles (the Microsoft
		3424	C runtime provides the function C<_open_osfhandle> for this). See the
		3425	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3426	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3427
		3428	The configuration for a "naked" win32 using the Microsoft runtime
		3429	libraries and raw winsocket select is:
		3430
		3431	#define EV_USE_SELECT 1
		3432	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3433
		3434	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3435	complexity in the O(n²) range when using win32.
		3436
		3437	=item Limited number of file descriptors
		3438
		3439	Windows has numerous arbitrary (and low) limits on things.
		3440
		3441	Early versions of winsocket's select only supported waiting for a maximum
		3442	of C<64> handles (probably owning to the fact that all windows kernels
		3443	can only wait for C<64> things at the same time internally; Microsoft
		3444	recommends spawning a chain of threads and wait for 63 handles and the
		3445	previous thread in each. Great).
		3446
		3447	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3448	to some high number (e.g. C<2048>) before compiling the winsocket select
		3449	call (which might be in libev or elsewhere, for example, perl does its own
		3450	select emulation on windows).
		3451
		3452	Another limit is the number of file descriptors in the Microsoft runtime
		3453	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3454	or something like this inside Microsoft). You can increase this by calling
		3455	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3456	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3457	libraries.
		3458
		3459	This might get you to about C<512> or C<2048> sockets (depending on
		3460	windows version and/or the phase of the moon). To get more, you need to
		3461	wrap all I/O functions and provide your own fd management, but the cost of
		3462	calling select (O(n²)) will likely make this unworkable.
		3463
		3464	=back
		3465
		3466
		3467	=head1 PORTABILITY REQUIREMENTS
		3468
		3469	In addition to a working ISO-C implementation, libev relies on a few
		3470	additional extensions:
		3471
		3472	=over 4
		3473
		3474	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3475	calling conventions regardless of C<ev_watcher_type *>.
		3476
		3477	Libev assumes not only that all watcher pointers have the same internal
		3478	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3479	assumes that the same (machine) code can be used to call any watcher
		3480	callback: The watcher callbacks have different type signatures, but libev
		3481	calls them using an C<ev_watcher *> internally.
		3482
		3483	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3484
		3485	The type C<sig_atomic_t volatile> (or whatever is defined as
		3486	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3487	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3488	believed to be sufficiently portable.
		3489
		3490	=item C<sigprocmask> must work in a threaded environment
		3491
		3492	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3493	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3494	pthread implementations will either allow C<sigprocmask> in the "main
		3495	thread" or will block signals process-wide, both behaviours would
		3496	be compatible with libev. Interaction between C<sigprocmask> and
		3497	C<pthread_sigmask> could complicate things, however.
		3498
		3499	The most portable way to handle signals is to block signals in all threads
		3500	except the initial one, and run the default loop in the initial thread as
		3501	well.
		3502
		3503	=item C<long> must be large enough for common memory allocation sizes
		3504
		3505	To improve portability and simplify using libev, libev uses C<long>
		3506	internally instead of C<size_t> when allocating its data structures. On
		3507	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3508	is still at least 31 bits everywhere, which is enough for hundreds of
		3509	millions of watchers.
		3510
		3511	=item C<double> must hold a time value in seconds with enough accuracy
		3512
		3513	The type C<double> is used to represent timestamps. It is required to
		3514	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3515	enough for at least into the year 4000. This requirement is fulfilled by
		3516	implementations implementing IEEE 754 (basically all existing ones).
		3517
		3518	=back
		3519
		3520	If you know of other additional requirements drop me a note.
		3521
		3522
		3523	=head1 COMPILER WARNINGS
		3524
		3525	Depending on your compiler and compiler settings, you might get no or a
		3526	lot of warnings when compiling libev code. Some people are apparently
		3527	scared by this.
		3528
		3529	However, these are unavoidable for many reasons. For one, each compiler
		3530	has different warnings, and each user has different tastes regarding
		3531	warning options. "Warn-free" code therefore cannot be a goal except when
		3532	targeting a specific compiler and compiler-version.
		3533
		3534	Another reason is that some compiler warnings require elaborate
		3535	workarounds, or other changes to the code that make it less clear and less
		3536	maintainable.
		3537
		3538	And of course, some compiler warnings are just plain stupid, or simply
		3539	wrong (because they don't actually warn about the condition their message
		3540	seems to warn about).
		3541
		3542	While libev is written to generate as few warnings as possible,
		3543	"warn-free" code is not a goal, and it is recommended not to build libev
		3544	with any compiler warnings enabled unless you are prepared to cope with
		3545	them (e.g. by ignoring them). Remember that warnings are just that:
		3546	warnings, not errors, or proof of bugs.
		3547
		3548
		3549	=head1 VALGRIND
		3550
		3551	Valgrind has a special section here because it is a popular tool that is
		3552	highly useful, but valgrind reports are very hard to interpret.
		3553
		3554	If you think you found a bug (memory leak, uninitialised data access etc.)
		3555	in libev, then check twice: If valgrind reports something like:
		3556
		3557	==2274== definitely lost: 0 bytes in 0 blocks.
		3558	==2274== possibly lost: 0 bytes in 0 blocks.
		3559	==2274== still reachable: 256 bytes in 1 blocks.
		3560
		3561	Then there is no memory leak. Similarly, under some circumstances,
		3562	valgrind might report kernel bugs as if it were a bug in libev, or it
		3563	might be confused (it is a very good tool, but only a tool).
		3564
		3565	If you are unsure about something, feel free to contact the mailing list
		3566	with the full valgrind report and an explanation on why you think this is
		3567	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3568	no bug" answer and take the chance of learning how to interpret valgrind
		3569	properly.
		3570
		3571	If you need, for some reason, empty reports from valgrind for your project
		3572	I suggest using suppression lists.
		3573
		3574
742	=head1 AUTHOR	3575	=head1 AUTHOR
743		3576
744	Marc Lehmann <libev@schmorp.de>.	3577	Marc Lehmann <libev@schmorp.de>.
745		3578

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