ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.14 by root, Mon Nov 12 08:45:49 2007 UTC vs.
Revision 1.297 by root, Tue Jun 29 11:49:02 2010 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		8
9	=head1 DESCRIPTION	9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
		18	ev_io stdin_watcher;
		19	ev_timer timeout_watcher;
		20
		21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
		23	static void
		24	stdin_cb (EV_P_ ev_io *w, int revents)
		25	{
		26	puts ("stdin ready");
		27	// for one-shot events, one must manually stop the watcher
		28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
		33	}
		34
		35	// another callback, this time for a time-out
		36	static void
		37	timeout_cb (EV_P_ ev_timer *w, int revents)
		38	{
		39	puts ("timeout");
		40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
		42	}
		43
		44	int
		45	main (void)
		46	{
		47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = ev_default_loop (0);
		49
		50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
		52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		53	ev_io_start (loop, &stdin_watcher);
		54
		55	// initialise a timer watcher, then start it
		56	// simple non-repeating 5.5 second timeout
		57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		58	ev_timer_start (loop, &timeout_watcher);
		59
		60	// now wait for events to arrive
		61	ev_loop (loop, 0);
		62
		63	// unloop was called, so exit
		64	return 0;
		65	}
		66
		67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
10		84
11	Libev is an event loop: you register interest in certain events (such as a	85	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	86	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	87	these event sources and provide your program with events.
14		88
15	To do this, it must take more or less complete control over your process	89	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	90	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	94	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	95	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	96	watcher.
23		97
24	=head1 FEATURES	98	=head2 FEATURES
25		99
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
		104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
		105	timers (C<ev_timer>), absolute timers with customised rescheduling
		106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
29	events (related to SIGCHLD), and event watchers dealing with the event	107	change events (C<ev_child>), and event watchers dealing with the event
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
		109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
		111
		112	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	114	for example).
33		115
34	=head1 CONVENTIONS	116	=head2 CONVENTIONS
35		117
36	Libev is very configurable. In this manual the default configuration	118	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	119	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	120	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	121	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	122	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 *>)	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	124	this argument.
43		125
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	126	=head2 TIME REPRESENTATION
45		127
46	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (in practise
48	the beginning of 1970, details are complicated, don't ask). This type is	130	somewhere near the beginning of 1970, details are complicated, don't
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	ask). This type is called C<ev_tstamp>, which is what you should use
50	to the double type in C.	132	too. It usually aliases to the C<double> type in C. When you need to do
		133	any calculations on it, you should treat it as some floating point value.
		134
		135	Unlike the name component C<stamp> might indicate, it is also used for
		136	time differences (e.g. delays) throughout libev.
		137
		138	=head1 ERROR HANDLING
		139
		140	Libev knows three classes of errors: operating system errors, usage errors
		141	and internal errors (bugs).
		142
		143	When libev catches an operating system error it cannot handle (for example
		144	a system call indicating a condition libev cannot fix), it calls the callback
		145	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		146	abort. The default is to print a diagnostic message and to call C<abort
		147	()>.
		148
		149	When libev detects a usage error such as a negative timer interval, then
		150	it will print a diagnostic message and abort (via the C<assert> mechanism,
		151	so C<NDEBUG> will disable this checking): these are programming errors in
		152	the libev caller and need to be fixed there.
		153
		154	Libev also has a few internal error-checking C<assert>ions, and also has
		155	extensive consistency checking code. These do not trigger under normal
		156	circumstances, as they indicate either a bug in libev or worse.
		157
		158
		159	=head1 GLOBAL FUNCTIONS
		160
		161	These functions can be called anytime, even before initialising the
		162	library in any way.
51		163
52	=over 4	164	=over 4
53		165
54	=item ev_tstamp ev_time ()	166	=item ev_tstamp ev_time ()
55		167
56	Returns the current time as libev would use it.	168	Returns the current time as libev would use it. Please note that the
		169	C<ev_now> function is usually faster and also often returns the timestamp
		170	you actually want to know.
		171
		172	=item ev_sleep (ev_tstamp interval)
		173
		174	Sleep for the given interval: The current thread will be blocked until
		175	either it is interrupted or the given time interval has passed. Basically
		176	this is a sub-second-resolution C<sleep ()>.
57		177
58	=item int ev_version_major ()	178	=item int ev_version_major ()
59		179
60	=item int ev_version_minor ()	180	=item int ev_version_minor ()
61		181
62	You can find out the major and minor version numbers of the library	182	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	183	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	184	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	185	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	186	version of the library your program was compiled against.
67		187
		188	These version numbers refer to the ABI version of the library, not the
		189	release version.
		190
68	Usually, it's a good idea to terminate if the major versions mismatch,	191	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	192	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	193	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	194	not a problem.
72		195
		196	Example: Make sure we haven't accidentally been linked against the wrong
		197	version (note, however, that this will not detect ABI mismatches :).
		198
		199	assert (("libev version mismatch",
		200	ev_version_major () == EV_VERSION_MAJOR
		201	&& ev_version_minor () >= EV_VERSION_MINOR));
		202
		203	=item unsigned int ev_supported_backends ()
		204
		205	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		206	value) compiled into this binary of libev (independent of their
		207	availability on the system you are running on). See C<ev_default_loop> for
		208	a description of the set values.
		209
		210	Example: make sure we have the epoll method, because yeah this is cool and
		211	a must have and can we have a torrent of it please!!!11
		212
		213	assert (("sorry, no epoll, no sex",
		214	ev_supported_backends () & EVBACKEND_EPOLL));
		215
		216	=item unsigned int ev_recommended_backends ()
		217
		218	Return the set of all backends compiled into this binary of libev and also
		219	recommended for this platform. This set is often smaller than the one
		220	returned by C<ev_supported_backends>, as for example kqueue is broken on
		221	most BSDs and will not be auto-detected unless you explicitly request it
		222	(assuming you know what you are doing). This is the set of backends that
		223	libev will probe for if you specify no backends explicitly.
		224
		225	=item unsigned int ev_embeddable_backends ()
		226
		227	Returns the set of backends that are embeddable in other event loops. This
		228	is the theoretical, all-platform, value. To find which backends
		229	might be supported on the current system, you would need to look at
		230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		231	recommended ones.
		232
		233	See the description of C<ev_embed> watchers for more info.
		234
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
74		236
75	Sets the allocation function to use (the prototype is similar to the	237	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	238	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	239	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	240	when memory needs to be allocated (C<size != 0>), the library might abort
79	destructive action. The default is your system realloc function.	241	or take some potentially destructive action.
		242
		243	Since some systems (at least OpenBSD and Darwin) fail to implement
		244	correct C<realloc> semantics, libev will use a wrapper around the system
		245	C<realloc> and C<free> functions by default.
80		246
81	You could override this function in high-availability programs to, say,	247	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,	248	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.	249	or even to sleep a while and retry until some memory is available.
84		250
		251	Example: Replace the libev allocator with one that waits a bit and then
		252	retries (example requires a standards-compliant C<realloc>).
		253
		254	static void *
		255	persistent_realloc (void *ptr, size_t size)
		256	{
		257	for (;;)
		258	{
		259	void *newptr = realloc (ptr, size);
		260
		261	if (newptr)
		262	return newptr;
		263
		264	sleep (60);
		265	}
		266	}
		267
		268	...
		269	ev_set_allocator (persistent_realloc);
		270
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
86		272
87	Set the callback function to call on a retryable syscall error (such	273	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	274	as failed select, poll, epoll_wait). The message is a printable string
89	indicating the system call or subsystem causing the problem. If this	275	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	276	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	277	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	278	requested operation, or, if the condition doesn't go away, do bad stuff
93	(such as abort).	279	(such as abort).
94		280
		281	Example: This is basically the same thing that libev does internally, too.
		282
		283	static void
		284	fatal_error (const char *msg)
		285	{
		286	perror (msg);
		287	abort ();
		288	}
		289
		290	...
		291	ev_set_syserr_cb (fatal_error);
		292
95	=back	293	=back
96		294
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98		296
99	An event loop is described by a C<struct ev_loop *>. The library knows two	297	An event loop is described by a C<struct ev_loop *> (the C<struct>
100	types of such loops, the I<default> loop, which supports signals and child	298	is I<not> optional in this case, as there is also an C<ev_loop>
101	events, and dynamically created loops which do not.	299	I<function>).
102		300
103	If you use threads, a common model is to run the default event loop	301	The library knows two types of such loops, the I<default> loop, which
104	in your main thread (or in a separate thrad) and for each thread you	302	supports signals and child events, and dynamically created loops which do
105	create, you also create another event loop. Libev itself does no locking	303	not.
106	whatsoever, so if you mix calls to the same event loop in different
107	threads, make sure you lock (this is usually a bad idea, though, even if
108	done correctly, because it's hideous and inefficient).
109		304
110	=over 4	305	=over 4
111		306
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	307	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		308
114	This will initialise the default event loop if it hasn't been initialised	309	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	310	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	311	false. If it already was initialised it simply returns it (and ignores the
117	flags).	312	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		313
119	If you don't know what event loop to use, use the one returned from this	314	If you don't know what event loop to use, use the one returned from this
120	function.	315	function.
121		316
		317	Note that this function is I<not> thread-safe, so if you want to use it
		318	from multiple threads, you have to lock (note also that this is unlikely,
		319	as loops cannot be shared easily between threads anyway).
		320
		321	The default loop is the only loop that can handle C<ev_signal> and
		322	C<ev_child> watchers, and to do this, it always registers a handler
		323	for C<SIGCHLD>. If this is a problem for your application you can either
		324	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		325	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		326	C<ev_default_init>.
		327
122	The flags argument can be used to specify special behaviour or specific	328	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).	329	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		330
125	It supports the following flags:	331	The following flags are supported:
126		332
127	=over 4	333	=over 4
128		334
129	=item C<EVFLAG_AUTO>	335	=item C<EVFLAG_AUTO>
130		336
131	The default flags value. Use this if you have no clue (it's the right	337	The default flags value. Use this if you have no clue (it's the right
132	thing, believe me).	338	thing, believe me).
133		339
134	=item C<EVFLAG_NOENV>	340	=item C<EVFLAG_NOENV>
135		341
136	If this flag bit is ored into the flag value (or the program runs setuid	342	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	343	or setgid) then libev will I<not> look at the environment variable
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	344	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	345	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	346	useful to try out specific backends to test their performance, or to work
141	around bugs.	347	around bugs.
142		348
		349	=item C<EVFLAG_FORKCHECK>
		350
		351	Instead of calling C<ev_loop_fork> manually after a fork, you can also
		352	make libev check for a fork in each iteration by enabling this flag.
		353
		354	This works by calling C<getpid ()> on every iteration of the loop,
		355	and thus this might slow down your event loop if you do a lot of loop
		356	iterations and little real work, but is usually not noticeable (on my
		357	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		358	without a system call and thus I<very> fast, but my GNU/Linux system also has
		359	C<pthread_atfork> which is even faster).
		360
		361	The big advantage of this flag is that you can forget about fork (and
		362	forget about forgetting to tell libev about forking) when you use this
		363	flag.
		364
		365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		366	environment variable.
		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_SIGNALFD>
		376
		377	When this flag is specified, then libev will attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		379	delivers signals synchronously, which makes it both faster and might make
		380	it possible to get the queued signal data. It can also simplify signal
		381	handling with threads, as long as you properly block signals in your
		382	threads that are not interested in handling them.
		383
		384	Signalfd will not be used by default as this changes your signal mask, and
		385	there are a lot of shoddy libraries and programs (glib's threadpool for
		386	example) that can't properly initialise their signal masks.
		387
143	=item C<EVMETHOD_SELECT> (portable select backend)	388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		389
		390	This is your standard select(2) backend. Not I<completely> standard, as
		391	libev tries to roll its own fd_set with no limits on the number of fds,
		392	but if that fails, expect a fairly low limit on the number of fds when
		393	using this backend. It doesn't scale too well (O(highest_fd)), but its
		394	usually the fastest backend for a low number of (low-numbered :) fds.
		395
		396	To get good performance out of this backend you need a high amount of
		397	parallelism (most of the file descriptors should be busy). If you are
		398	writing a server, you should C<accept ()> in a loop to accept as many
		399	connections as possible during one iteration. You might also want to have
		400	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		401	readiness notifications you get per iteration.
		402
		403	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		404	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		405	C<exceptfds> set on that platform).
		406
145	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	407	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
146		408
147	=item C<EVMETHOD_EPOLL> (linux only)	409	And this is your standard poll(2) backend. It's more complicated
		410	than select, but handles sparse fds better and has no artificial
		411	limit on the number of fds you can use (except it will slow down
		412	considerably with a lot of inactive fds). It scales similarly to select,
		413	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		414	performance tips.
148		415
149	=item C<EVMETHOD_KQUEUE> (some bsds only)	416	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		417	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
150		418
151	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	419	=item C<EVBACKEND_EPOLL> (value 4, Linux)
152		420
153	=item C<EVMETHOD_PORT> (solaris 10 only)	421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		422	kernels).
154		423
155	If one or more of these are ored into the flags value, then only these	424	For few fds, this backend is a bit little slower than poll and select,
156	backends will be tried (in the reverse order as given here). If one are	425	but it scales phenomenally better. While poll and select usually scale
157	specified, any backend will do.	426	like O(total_fds) where n is the total number of fds (or the highest fd),
		427	epoll scales either O(1) or O(active_fds).
		428
		429	The epoll mechanism deserves honorable mention as the most misdesigned
		430	of the more advanced event mechanisms: mere annoyances include silently
		431	dropping file descriptors, requiring a system call per change per file
		432	descriptor (and unnecessary guessing of parameters), problems with dup and
		433	so on. The biggest issue is fork races, however - if a program forks then
		434	I<both> parent and child process have to recreate the epoll set, which can
		435	take considerable time (one syscall per file descriptor) and is of course
		436	hard to detect.
		437
		438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		439	of course I<doesn't>, and epoll just loves to report events for totally
		440	I<different> file descriptors (even already closed ones, so one cannot
		441	even remove them from the set) than registered in the set (especially
		442	on SMP systems). Libev tries to counter these spurious notifications by
		443	employing an additional generation counter and comparing that against the
		444	events to filter out spurious ones, recreating the set when required.
		445
		446	While stopping, setting and starting an I/O watcher in the same iteration
		447	will result in some caching, there is still a system call per such
		448	incident (because the same I<file descriptor> could point to a different
		449	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
		450	file descriptors might not work very well if you register events for both
		451	file descriptors.
		452
		453	Best performance from this backend is achieved by not unregistering all
		454	watchers for a file descriptor until it has been closed, if possible,
		455	i.e. keep at least one watcher active per fd at all times. Stopping and
		456	starting a watcher (without re-setting it) also usually doesn't cause
		457	extra overhead. A fork can both result in spurious notifications as well
		458	as in libev having to destroy and recreate the epoll object, which can
		459	take considerable time and thus should be avoided.
		460
		461	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		462	faster than epoll for maybe up to a hundred file descriptors, depending on
		463	the usage. So sad.
		464
		465	While nominally embeddable in other event loops, this feature is broken in
		466	all kernel versions tested so far.
		467
		468	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		469	C<EVBACKEND_POLL>.
		470
		471	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		472
		473	Kqueue deserves special mention, as at the time of this writing, it
		474	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		475	with anything but sockets and pipes, except on Darwin, where of course
		476	it's completely useless). Unlike epoll, however, whose brokenness
		477	is by design, these kqueue bugs can (and eventually will) be fixed
		478	without API changes to existing programs. For this reason it's not being
		479	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		480	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		481	system like NetBSD.
		482
		483	You still can embed kqueue into a normal poll or select backend and use it
		484	only for sockets (after having made sure that sockets work with kqueue on
		485	the target platform). See C<ev_embed> watchers for more info.
		486
		487	It scales in the same way as the epoll backend, but the interface to the
		488	kernel is more efficient (which says nothing about its actual speed, of
		489	course). While stopping, setting and starting an I/O watcher does never
		490	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		491	two event changes per incident. Support for C<fork ()> is very bad (but
		492	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		493	cases
		494
		495	This backend usually performs well under most conditions.
		496
		497	While nominally embeddable in other event loops, this doesn't work
		498	everywhere, so you might need to test for this. And since it is broken
		499	almost everywhere, you should only use it when you have a lot of sockets
		500	(for which it usually works), by embedding it into another event loop
		501	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		502	also broken on OS X)) and, did I mention it, using it only for sockets.
		503
		504	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		505	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		506	C<NOTE_EOF>.
		507
		508	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		509
		510	This is not implemented yet (and might never be, unless you send me an
		511	implementation). According to reports, C</dev/poll> only supports sockets
		512	and is not embeddable, which would limit the usefulness of this backend
		513	immensely.
		514
		515	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		516
		517	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		518	it's really slow, but it still scales very well (O(active_fds)).
		519
		520	Please note that Solaris event ports can deliver a lot of spurious
		521	notifications, so you need to use non-blocking I/O or other means to avoid
		522	blocking when no data (or space) is available.
		523
		524	While this backend scales well, it requires one system call per active
		525	file descriptor per loop iteration. For small and medium numbers of file
		526	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		527	might perform better.
		528
		529	On the positive side, with the exception of the spurious readiness
		530	notifications, this backend actually performed fully to specification
		531	in all tests and is fully embeddable, which is a rare feat among the
		532	OS-specific backends (I vastly prefer correctness over speed hacks).
		533
		534	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		535	C<EVBACKEND_POLL>.
		536
		537	=item C<EVBACKEND_ALL>
		538
		539	Try all backends (even potentially broken ones that wouldn't be tried
		540	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		541	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		542
		543	It is definitely not recommended to use this flag.
158		544
159	=back	545	=back
160		546
		547	If one or more of the backend flags are or'ed into the flags value,
		548	then only these backends will be tried (in the reverse order as listed
		549	here). If none are specified, all backends in C<ev_recommended_backends
		550	()> will be tried.
		551
		552	Example: This is the most typical usage.
		553
		554	if (!ev_default_loop (0))
		555	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		556
		557	Example: Restrict libev to the select and poll backends, and do not allow
		558	environment settings to be taken into account:
		559
		560	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		561
		562	Example: Use whatever libev has to offer, but make sure that kqueue is
		563	used if available (warning, breaks stuff, best use only with your own
		564	private event loop and only if you know the OS supports your types of
		565	fds):
		566
		567	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
		568
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	569	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		570
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	571	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	572	always distinct from the default loop.
165	handle signal and child watchers, and attempts to do so will be greeted by	573
166	undefined behaviour (or a failed assertion if assertions are enabled).	574	Note that this function I<is> thread-safe, and one common way to use
		575	libev with threads is indeed to create one loop per thread, and using the
		576	default loop in the "main" or "initial" thread.
		577
		578	Example: Try to create a event loop that uses epoll and nothing else.
		579
		580	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		581	if (!epoller)
		582	fatal ("no epoll found here, maybe it hides under your chair");
167		583
168	=item ev_default_destroy ()	584	=item ev_default_destroy ()
169		585
170	Destroys the default loop again (frees all memory and kernel state	586	Destroys the default loop (frees all memory and kernel state etc.). None
171	etc.). This stops all registered event watchers (by not touching them in	587	of the active event watchers will be stopped in the normal sense, so
172	any way whatsoever, although you cannot rely on this :).	588	e.g. C<ev_is_active> might still return true. It is your responsibility to
		589	either stop all watchers cleanly yourself I<before> calling this function,
		590	or cope with the fact afterwards (which is usually the easiest thing, you
		591	can just ignore the watchers and/or C<free ()> them for example).
		592
		593	Note that certain global state, such as signal state (and installed signal
		594	handlers), will not be freed by this function, and related watchers (such
		595	as signal and child watchers) would need to be stopped manually.
		596
		597	In general it is not advisable to call this function except in the
		598	rare occasion where you really need to free e.g. the signal handling
		599	pipe fds. If you need dynamically allocated loops it is better to use
		600	C<ev_loop_new> and C<ev_loop_destroy>.
173		601
174	=item ev_loop_destroy (loop)	602	=item ev_loop_destroy (loop)
175		603
176	Like C<ev_default_destroy>, but destroys an event loop created by an	604	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	605	earlier call to C<ev_loop_new>.
178		606
179	=item ev_default_fork ()	607	=item ev_default_fork ()
180		608
		609	This function sets a flag that causes subsequent C<ev_loop> iterations
181	This function reinitialises the kernel state for backends that have	610	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	611	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	612	the child process (or both child and parent, but that again makes little
184	again makes little sense).	613	sense). You I<must> call it in the child before using any of the libev
		614	functions, and it will only take effect at the next C<ev_loop> iteration.
185		615
186	You I<must> call this function after forking if and only if you want to	616	Again, you I<have> to call it on I<any> loop that you want to re-use after
187	use the event library in both processes. If you just fork+exec, you don't	617	a fork, I<even if you do not plan to use the loop in the parent>. This is
188	have to call it.	618	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		619	during fork.
		620
		621	On the other hand, you only need to call this function in the child
		622	process if and only if you want to use the event loop in the child. If you
		623	just fork+exec or create a new loop in the child, you don't have to call
		624	it at all.
189		625
190	The function itself is quite fast and it's usually not a problem to call	626	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	627	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>:	628	quite nicely into a call to C<pthread_atfork>:
193		629
…		…
195		631
196	=item ev_loop_fork (loop)	632	=item ev_loop_fork (loop)
197		633
198	Like C<ev_default_fork>, but acts on an event loop created by	634	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	635	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.	636	after fork that you want to re-use in the child, and how you keep track of
		637	them is entirely your own problem.
201		638
		639	=item int ev_is_default_loop (loop)
		640
		641	Returns true when the given loop is, in fact, the default loop, and false
		642	otherwise.
		643
		644	=item unsigned int ev_iteration (loop)
		645
		646	Returns the current iteration count for the loop, which is identical to
		647	the number of times libev did poll for new events. It starts at C<0> and
		648	happily wraps around with enough iterations.
		649
		650	This value can sometimes be useful as a generation counter of sorts (it
		651	"ticks" the number of loop iterations), as it roughly corresponds with
		652	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		653	prepare and check phases.
		654
202	=item unsigned int ev_method (loop)	655	=item unsigned int ev_depth (loop)
203		656
		657	Returns the number of times C<ev_loop> was entered minus the number of
		658	times C<ev_loop> was exited, in other words, the recursion depth.
		659
		660	Outside C<ev_loop>, this number is zero. In a callback, this number is
		661	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		662	in which case it is higher.
		663
		664	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		665	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		666	ungentleman behaviour unless it's really convenient.
		667
		668	=item unsigned int ev_backend (loop)
		669
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	670	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	671	use.
206		672
207	=item ev_tstamp ev_now (loop)	673	=item ev_tstamp ev_now (loop)
208		674
209	Returns the current "event loop time", which is the time the event loop	675	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	676	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	677	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	678	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).	679	event occurring (or more correctly, libev finding out about it).
		680
		681	=item ev_now_update (loop)
		682
		683	Establishes the current time by querying the kernel, updating the time
		684	returned by C<ev_now ()> in the progress. This is a costly operation and
		685	is usually done automatically within C<ev_loop ()>.
		686
		687	This function is rarely useful, but when some event callback runs for a
		688	very long time without entering the event loop, updating libev's idea of
		689	the current time is a good idea.
		690
		691	See also L<The special problem of time updates> in the C<ev_timer> section.
		692
		693	=item ev_suspend (loop)
		694
		695	=item ev_resume (loop)
		696
		697	These two functions suspend and resume a loop, for use when the loop is
		698	not used for a while and timeouts should not be processed.
		699
		700	A typical use case would be an interactive program such as a game: When
		701	the user presses C<^Z> to suspend the game and resumes it an hour later it
		702	would be best to handle timeouts as if no time had actually passed while
		703	the program was suspended. This can be achieved by calling C<ev_suspend>
		704	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		705	C<ev_resume> directly afterwards to resume timer processing.
		706
		707	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		708	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		709	will be rescheduled (that is, they will lose any events that would have
		710	occured while suspended).
		711
		712	After calling C<ev_suspend> you B<must not> call I<any> function on the
		713	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		714	without a previous call to C<ev_suspend>.
		715
		716	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		717	event loop time (see C<ev_now_update>).
214		718
215	=item ev_loop (loop, int flags)	719	=item ev_loop (loop, int flags)
216		720
217	Finally, this is it, the event handler. This function usually is called	721	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	722	after you have initialised all your watchers and you want to start
219	events.	723	handling events.
220		724
221	If the flags argument is specified as 0, it will not return until either	725	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.	726	either no event watchers are active anymore or C<ev_unloop> was called.
		727
		728	Please note that an explicit C<ev_unloop> is usually better than
		729	relying on all watchers to be stopped when deciding when a program has
		730	finished (especially in interactive programs), but having a program
		731	that automatically loops as long as it has to and no longer by virtue
		732	of relying on its watchers stopping correctly, that is truly a thing of
		733	beauty.
223		734
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	735	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	736	those events and any already outstanding ones, but will not block your
226	case there are no events and will return after one iteration of the loop.	737	process in case there are no events and will return after one iteration of
		738	the loop.
227		739
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	740	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	741	necessary) and will handle those and any already outstanding ones. It
230	your process until at least one new event arrives, and will return after	742	will block your process until at least one new event arrives (which could
		743	be an event internal to libev itself, so there is no guarantee that a
		744	user-registered callback will be called), and will return after one
231	one iteration of the loop.	745	iteration of the loop.
232		746
233	This flags value could be used to implement alternative looping	747	This is useful if you are waiting for some external event in conjunction
234	constructs, but the C<prepare> and C<check> watchers provide a better and	748	with something not expressible using other libev watchers (i.e. "roll your
235	more generic mechanism.	749	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		750	usually a better approach for this kind of thing.
		751
		752	Here are the gory details of what C<ev_loop> does:
		753
		754	- Before the first iteration, call any pending watchers.
		755	* If EVFLAG_FORKCHECK was used, check for a fork.
		756	- If a fork was detected (by any means), queue and call all fork watchers.
		757	- Queue and call all prepare watchers.
		758	- If we have been forked, detach and recreate the kernel state
		759	as to not disturb the other process.
		760	- Update the kernel state with all outstanding changes.
		761	- Update the "event loop time" (ev_now ()).
		762	- Calculate for how long to sleep or block, if at all
		763	(active idle watchers, EVLOOP_NONBLOCK or not having
		764	any active watchers at all will result in not sleeping).
		765	- Sleep if the I/O and timer collect interval say so.
		766	- Block the process, waiting for any events.
		767	- Queue all outstanding I/O (fd) events.
		768	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		769	- Queue all expired timers.
		770	- Queue all expired periodics.
		771	- Unless any events are pending now, queue all idle watchers.
		772	- Queue all check watchers.
		773	- Call all queued watchers in reverse order (i.e. check watchers first).
		774	Signals and child watchers are implemented as I/O watchers, and will
		775	be handled here by queueing them when their watcher gets executed.
		776	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		777	were used, or there are no active watchers, return, otherwise
		778	continue with step *.
		779
		780	Example: Queue some jobs and then loop until no events are outstanding
		781	anymore.
		782
		783	... queue jobs here, make sure they register event watchers as long
		784	... as they still have work to do (even an idle watcher will do..)
		785	ev_loop (my_loop, 0);
		786	... jobs done or somebody called unloop. yeah!
236		787
237	=item ev_unloop (loop, how)	788	=item ev_unloop (loop, how)
238		789
239	Can be used to make a call to C<ev_loop> return early (but only after it	790	Can be used to make a call to C<ev_loop> return early (but only after it
240	has processed all outstanding events). The C<how> argument must be either	791	has processed all outstanding events). The C<how> argument must be either
241	C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or	792	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
242	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	793	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		794
		795	This "unloop state" will be cleared when entering C<ev_loop> again.
		796
		797	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
243		798
244	=item ev_ref (loop)	799	=item ev_ref (loop)
245		800
246	=item ev_unref (loop)	801	=item ev_unref (loop)
247		802
248	Ref/unref can be used to add or remove a reference count on the event	803	Ref/unref can be used to add or remove a reference count on the event
249	loop: Every watcher keeps one reference, and as long as the reference	804	loop: Every watcher keeps one reference, and as long as the reference
250	count is nonzero, C<ev_loop> will not return on its own. If you have	805	count is nonzero, C<ev_loop> will not return on its own.
251	a watcher you never unregister that should not keep C<ev_loop> from	806
252	returning, ev_unref() after starting, and ev_ref() before stopping it. For	807	This is useful when you have a watcher that you never intend to
		808	unregister, but that nevertheless should not keep C<ev_loop> from
		809	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		810	before stopping it.
		811
253	example, libev itself uses this for its internal signal pipe: It is not	812	As an example, libev itself uses this for its internal signal pipe: It
254	visible to the libev user and should not keep C<ev_loop> from exiting if	813	is not visible to the libev user and should not keep C<ev_loop> from
255	no event watchers registered by it are active. It is also an excellent	814	exiting if no event watchers registered by it are active. It is also an
256	way to do this for generic recurring timers or from within third-party	815	excellent way to do this for generic recurring timers or from within
257	libraries. Just remember to I<unref after start> and I<ref before stop>.	816	third-party libraries. Just remember to I<unref after start> and I<ref
		817	before stop> (but only if the watcher wasn't active before, or was active
		818	before, respectively. Note also that libev might stop watchers itself
		819	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		820	in the callback).
		821
		822	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		823	running when nothing else is active.
		824
		825	ev_signal exitsig;
		826	ev_signal_init (&exitsig, sig_cb, SIGINT);
		827	ev_signal_start (loop, &exitsig);
		828	evf_unref (loop);
		829
		830	Example: For some weird reason, unregister the above signal handler again.
		831
		832	ev_ref (loop);
		833	ev_signal_stop (loop, &exitsig);
		834
		835	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		836
		837	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		838
		839	These advanced functions influence the time that libev will spend waiting
		840	for events. Both time intervals are by default C<0>, meaning that libev
		841	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		842	latency.
		843
		844	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		845	allows libev to delay invocation of I/O and timer/periodic callbacks
		846	to increase efficiency of loop iterations (or to increase power-saving
		847	opportunities).
		848
		849	The idea is that sometimes your program runs just fast enough to handle
		850	one (or very few) event(s) per loop iteration. While this makes the
		851	program responsive, it also wastes a lot of CPU time to poll for new
		852	events, especially with backends like C<select ()> which have a high
		853	overhead for the actual polling but can deliver many events at once.
		854
		855	By setting a higher I<io collect interval> you allow libev to spend more
		856	time collecting I/O events, so you can handle more events per iteration,
		857	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		858	C<ev_timer>) will be not affected. Setting this to a non-null value will
		859	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		860	sleep time ensures that libev will not poll for I/O events more often then
		861	once per this interval, on average.
		862
		863	Likewise, by setting a higher I<timeout collect interval> you allow libev
		864	to spend more time collecting timeouts, at the expense of increased
		865	latency/jitter/inexactness (the watcher callback will be called
		866	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		867	value will not introduce any overhead in libev.
		868
		869	Many (busy) programs can usually benefit by setting the I/O collect
		870	interval to a value near C<0.1> or so, which is often enough for
		871	interactive servers (of course not for games), likewise for timeouts. It
		872	usually doesn't make much sense to set it to a lower value than C<0.01>,
		873	as this approaches the timing granularity of most systems. Note that if
		874	you do transactions with the outside world and you can't increase the
		875	parallelity, then this setting will limit your transaction rate (if you
		876	need to poll once per transaction and the I/O collect interval is 0.01,
		877	then you can't do more than 100 transations per second).
		878
		879	Setting the I<timeout collect interval> can improve the opportunity for
		880	saving power, as the program will "bundle" timer callback invocations that
		881	are "near" in time together, by delaying some, thus reducing the number of
		882	times the process sleeps and wakes up again. Another useful technique to
		883	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		884	they fire on, say, one-second boundaries only.
		885
		886	Example: we only need 0.1s timeout granularity, and we wish not to poll
		887	more often than 100 times per second:
		888
		889	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		890	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		891
		892	=item ev_invoke_pending (loop)
		893
		894	This call will simply invoke all pending watchers while resetting their
		895	pending state. Normally, C<ev_loop> does this automatically when required,
		896	but when overriding the invoke callback this call comes handy.
		897
		898	=item int ev_pending_count (loop)
		899
		900	Returns the number of pending watchers - zero indicates that no watchers
		901	are pending.
		902
		903	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		904
		905	This overrides the invoke pending functionality of the loop: Instead of
		906	invoking all pending watchers when there are any, C<ev_loop> will call
		907	this callback instead. This is useful, for example, when you want to
		908	invoke the actual watchers inside another context (another thread etc.).
		909
		910	If you want to reset the callback, use C<ev_invoke_pending> as new
		911	callback.
		912
		913	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		914
		915	Sometimes you want to share the same loop between multiple threads. This
		916	can be done relatively simply by putting mutex_lock/unlock calls around
		917	each call to a libev function.
		918
		919	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		920	wait for it to return. One way around this is to wake up the loop via
		921	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		922	and I<acquire> callbacks on the loop.
		923
		924	When set, then C<release> will be called just before the thread is
		925	suspended waiting for new events, and C<acquire> is called just
		926	afterwards.
		927
		928	Ideally, C<release> will just call your mutex_unlock function, and
		929	C<acquire> will just call the mutex_lock function again.
		930
		931	While event loop modifications are allowed between invocations of
		932	C<release> and C<acquire> (that's their only purpose after all), no
		933	modifications done will affect the event loop, i.e. adding watchers will
		934	have no effect on the set of file descriptors being watched, or the time
		935	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		936	to take note of any changes you made.
		937
		938	In theory, threads executing C<ev_loop> will be async-cancel safe between
		939	invocations of C<release> and C<acquire>.
		940
		941	See also the locking example in the C<THREADS> section later in this
		942	document.
		943
		944	=item ev_set_userdata (loop, void *data)
		945
		946	=item ev_userdata (loop)
		947
		948	Set and retrieve a single C<void *> associated with a loop. When
		949	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		950	C<0.>
		951
		952	These two functions can be used to associate arbitrary data with a loop,
		953	and are intended solely for the C<invoke_pending_cb>, C<release> and
		954	C<acquire> callbacks described above, but of course can be (ab-)used for
		955	any other purpose as well.
		956
		957	=item ev_loop_verify (loop)
		958
		959	This function only does something when C<EV_VERIFY> support has been
		960	compiled in, which is the default for non-minimal builds. It tries to go
		961	through all internal structures and checks them for validity. If anything
		962	is found to be inconsistent, it will print an error message to standard
		963	error and call C<abort ()>.
		964
		965	This can be used to catch bugs inside libev itself: under normal
		966	circumstances, this function will never abort as of course libev keeps its
		967	data structures consistent.
258		968
259	=back	969	=back
260		970
		971
261	=head1 ANATOMY OF A WATCHER	972	=head1 ANATOMY OF A WATCHER
		973
		974	In the following description, uppercase C<TYPE> in names stands for the
		975	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		976	watchers and C<ev_io_start> for I/O watchers.
262		977
263	A watcher is a structure that you create and register to record your	978	A watcher is a structure that you create and register to record your
264	interest in some event. For instance, if you want to wait for STDIN to	979	interest in some event. For instance, if you want to wait for STDIN to
265	become readable, you would create an C<ev_io> watcher for that:	980	become readable, you would create an C<ev_io> watcher for that:
266		981
267	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	982	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
268	{	983	{
269	ev_io_stop (w);	984	ev_io_stop (w);
270	ev_unloop (loop, EVUNLOOP_ALL);	985	ev_unloop (loop, EVUNLOOP_ALL);
271	}	986	}
272		987
273	struct ev_loop *loop = ev_default_loop (0);	988	struct ev_loop *loop = ev_default_loop (0);
		989
274	struct ev_io stdin_watcher;	990	ev_io stdin_watcher;
		991
275	ev_init (&stdin_watcher, my_cb);	992	ev_init (&stdin_watcher, my_cb);
276	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	993	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
277	ev_io_start (loop, &stdin_watcher);	994	ev_io_start (loop, &stdin_watcher);
		995
278	ev_loop (loop, 0);	996	ev_loop (loop, 0);
279		997
280	As you can see, you are responsible for allocating the memory for your	998	As you can see, you are responsible for allocating the memory for your
281	watcher structures (and it is usually a bad idea to do this on the stack,	999	watcher structures (and it is I<usually> a bad idea to do this on the
282	although this can sometimes be quite valid).	1000	stack).
		1001
		1002	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1003	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
283		1004
284	Each watcher structure must be initialised by a call to C<ev_init	1005	Each watcher structure must be initialised by a call to C<ev_init
285	(watcher *, callback)>, which expects a callback to be provided. This	1006	(watcher *, callback)>, which expects a callback to be provided. This
286	callback gets invoked each time the event occurs (or, in the case of io	1007	callback gets invoked each time the event occurs (or, in the case of I/O
287	watchers, each time the event loop detects that the file descriptor given	1008	watchers, each time the event loop detects that the file descriptor given
288	is readable and/or writable).	1009	is readable and/or writable).
289		1010
290	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1011	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
291	with arguments specific to this watcher type. There is also a macro	1012	macro to configure it, with arguments specific to the watcher type. There
292	to combine initialisation and setting in one call: C<< ev_<type>_init	1013	is also a macro to combine initialisation and setting in one call: C<<
293	(watcher *, callback, ...) >>.	1014	ev_TYPE_init (watcher *, callback, ...) >>.
294		1015
295	To make the watcher actually watch out for events, you have to start it	1016	To make the watcher actually watch out for events, you have to start it
296	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1017	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
297	*) >>), and you can stop watching for events at any time by calling the	1018	*) >>), and you can stop watching for events at any time by calling the
298	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1019	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
299		1020
300	As long as your watcher is active (has been started but not stopped) you	1021	As long as your watcher is active (has been started but not stopped) you
301	must not touch the values stored in it. Most specifically you must never	1022	must not touch the values stored in it. Most specifically you must never
302	reinitialise it or call its set method.	1023	reinitialise it or call its C<ev_TYPE_set> macro.
303
304	You can check whether an event is active by calling the C<ev_is_active
305	(watcher *)> macro. To see whether an event is outstanding (but the
306	callback for it has not been called yet) you can use the C<ev_is_pending
307	(watcher *)> macro.
308		1024
309	Each and every callback receives the event loop pointer as first, the	1025	Each and every callback receives the event loop pointer as first, the
310	registered watcher structure as second, and a bitset of received events as	1026	registered watcher structure as second, and a bitset of received events as
311	third argument.	1027	third argument.
312		1028
…		…
321	=item C<EV_WRITE>	1037	=item C<EV_WRITE>
322		1038
323	The file descriptor in the C<ev_io> watcher has become readable and/or	1039	The file descriptor in the C<ev_io> watcher has become readable and/or
324	writable.	1040	writable.
325		1041
326	=item C<EV_TIMEOUT>	1042	=item C<EV_TIMER>
327		1043
328	The C<ev_timer> watcher has timed out.	1044	The C<ev_timer> watcher has timed out.
329		1045
330	=item C<EV_PERIODIC>	1046	=item C<EV_PERIODIC>
331		1047
…		…
336	The signal specified in the C<ev_signal> watcher has been received by a thread.	1052	The signal specified in the C<ev_signal> watcher has been received by a thread.
337		1053
338	=item C<EV_CHILD>	1054	=item C<EV_CHILD>
339		1055
340	The pid specified in the C<ev_child> watcher has received a status change.	1056	The pid specified in the C<ev_child> watcher has received a status change.
		1057
		1058	=item C<EV_STAT>
		1059
		1060	The path specified in the C<ev_stat> watcher changed its attributes somehow.
341		1061
342	=item C<EV_IDLE>	1062	=item C<EV_IDLE>
343		1063
344	The C<ev_idle> watcher has determined that you have nothing better to do.	1064	The C<ev_idle> watcher has determined that you have nothing better to do.
345		1065
…		…
353	received events. Callbacks of both watcher types can start and stop as	1073	received events. Callbacks of both watcher types can start and stop as
354	many watchers as they want, and all of them will be taken into account	1074	many watchers as they want, and all of them will be taken into account
355	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1075	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
356	C<ev_loop> from blocking).	1076	C<ev_loop> from blocking).
357		1077
		1078	=item C<EV_EMBED>
		1079
		1080	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1081
		1082	=item C<EV_FORK>
		1083
		1084	The event loop has been resumed in the child process after fork (see
		1085	C<ev_fork>).
		1086
		1087	=item C<EV_ASYNC>
		1088
		1089	The given async watcher has been asynchronously notified (see C<ev_async>).
		1090
		1091	=item C<EV_CUSTOM>
		1092
		1093	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1094	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1095
358	=item C<EV_ERROR>	1096	=item C<EV_ERROR>
359		1097
360	An unspecified error has occured, the watcher has been stopped. This might	1098	An unspecified error has occurred, the watcher has been stopped. This might
361	happen because the watcher could not be properly started because libev	1099	happen because the watcher could not be properly started because libev
362	ran out of memory, a file descriptor was found to be closed or any other	1100	ran out of memory, a file descriptor was found to be closed or any other
		1101	problem. Libev considers these application bugs.
		1102
363	problem. You best act on it by reporting the problem and somehow coping	1103	You best act on it by reporting the problem and somehow coping with the
364	with the watcher being stopped.	1104	watcher being stopped. Note that well-written programs should not receive
		1105	an error ever, so when your watcher receives it, this usually indicates a
		1106	bug in your program.
365		1107
366	Libev will usually signal a few "dummy" events together with an error,	1108	Libev will usually signal a few "dummy" events together with an error, for
367	for example it might indicate that a fd is readable or writable, and if	1109	example it might indicate that a fd is readable or writable, and if your
368	your callbacks is well-written it can just attempt the operation and cope	1110	callbacks is well-written it can just attempt the operation and cope with
369	with the error from read() or write(). This will not work in multithreaded	1111	the error from read() or write(). This will not work in multi-threaded
370	programs, though, so beware.	1112	programs, though, as the fd could already be closed and reused for another
		1113	thing, so beware.
371		1114
372	=back	1115	=back
373		1116
		1117	=head2 GENERIC WATCHER FUNCTIONS
		1118
		1119	=over 4
		1120
		1121	=item C<ev_init> (ev_TYPE *watcher, callback)
		1122
		1123	This macro initialises the generic portion of a watcher. The contents
		1124	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1125	the generic parts of the watcher are initialised, you I<need> to call
		1126	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1127	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1128	which rolls both calls into one.
		1129
		1130	You can reinitialise a watcher at any time as long as it has been stopped
		1131	(or never started) and there are no pending events outstanding.
		1132
		1133	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1134	int revents)>.
		1135
		1136	Example: Initialise an C<ev_io> watcher in two steps.
		1137
		1138	ev_io w;
		1139	ev_init (&w, my_cb);
		1140	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1141
		1142	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1143
		1144	This macro initialises the type-specific parts of a watcher. You need to
		1145	call C<ev_init> at least once before you call this macro, but you can
		1146	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1147	macro on a watcher that is active (it can be pending, however, which is a
		1148	difference to the C<ev_init> macro).
		1149
		1150	Although some watcher types do not have type-specific arguments
		1151	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1152
		1153	See C<ev_init>, above, for an example.
		1154
		1155	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1156
		1157	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1158	calls into a single call. This is the most convenient method to initialise
		1159	a watcher. The same limitations apply, of course.
		1160
		1161	Example: Initialise and set an C<ev_io> watcher in one step.
		1162
		1163	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1164
		1165	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1166
		1167	Starts (activates) the given watcher. Only active watchers will receive
		1168	events. If the watcher is already active nothing will happen.
		1169
		1170	Example: Start the C<ev_io> watcher that is being abused as example in this
		1171	whole section.
		1172
		1173	ev_io_start (EV_DEFAULT_UC, &w);
		1174
		1175	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1176
		1177	Stops the given watcher if active, and clears the pending status (whether
		1178	the watcher was active or not).
		1179
		1180	It is possible that stopped watchers are pending - for example,
		1181	non-repeating timers are being stopped when they become pending - but
		1182	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1183	pending. If you want to free or reuse the memory used by the watcher it is
		1184	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1185
		1186	=item bool ev_is_active (ev_TYPE *watcher)
		1187
		1188	Returns a true value iff the watcher is active (i.e. it has been started
		1189	and not yet been stopped). As long as a watcher is active you must not modify
		1190	it.
		1191
		1192	=item bool ev_is_pending (ev_TYPE *watcher)
		1193
		1194	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1195	events but its callback has not yet been invoked). As long as a watcher
		1196	is pending (but not active) you must not call an init function on it (but
		1197	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1198	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1199	it).
		1200
		1201	=item callback ev_cb (ev_TYPE *watcher)
		1202
		1203	Returns the callback currently set on the watcher.
		1204
		1205	=item ev_cb_set (ev_TYPE *watcher, callback)
		1206
		1207	Change the callback. You can change the callback at virtually any time
		1208	(modulo threads).
		1209
		1210	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1211
		1212	=item int ev_priority (ev_TYPE *watcher)
		1213
		1214	Set and query the priority of the watcher. The priority is a small
		1215	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1216	(default: C<-2>). Pending watchers with higher priority will be invoked
		1217	before watchers with lower priority, but priority will not keep watchers
		1218	from being executed (except for C<ev_idle> watchers).
		1219
		1220	If you need to suppress invocation when higher priority events are pending
		1221	you need to look at C<ev_idle> watchers, which provide this functionality.
		1222
		1223	You I<must not> change the priority of a watcher as long as it is active or
		1224	pending.
		1225
		1226	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1227	fine, as long as you do not mind that the priority value you query might
		1228	or might not have been clamped to the valid range.
		1229
		1230	The default priority used by watchers when no priority has been set is
		1231	always C<0>, which is supposed to not be too high and not be too low :).
		1232
		1233	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1234	priorities.
		1235
		1236	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1237
		1238	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1239	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1240	can deal with that fact, as both are simply passed through to the
		1241	callback.
		1242
		1243	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1244
		1245	If the watcher is pending, this function clears its pending status and
		1246	returns its C<revents> bitset (as if its callback was invoked). If the
		1247	watcher isn't pending it does nothing and returns C<0>.
		1248
		1249	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1250	callback to be invoked, which can be accomplished with this function.
		1251
		1252	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1253
		1254	Feeds the given event set into the event loop, as if the specified event
		1255	had happened for the specified watcher (which must be a pointer to an
		1256	initialised but not necessarily started event watcher). Obviously you must
		1257	not free the watcher as long as it has pending events.
		1258
		1259	Stopping the watcher, letting libev invoke it, or calling
		1260	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1261	not started in the first place.
		1262
		1263	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1264	functions that do not need a watcher.
		1265
		1266	=back
		1267
		1268
374	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1269	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
375		1270
376	Each watcher has, by default, a member C<void *data> that you can change	1271	Each watcher has, by default, a member C<void *data> that you can change
377	and read at any time, libev will completely ignore it. This can be used	1272	and read at any time: libev will completely ignore it. This can be used
378	to associate arbitrary data with your watcher. If you need more data and	1273	to associate arbitrary data with your watcher. If you need more data and
379	don't want to allocate memory and store a pointer to it in that data	1274	don't want to allocate memory and store a pointer to it in that data
380	member, you can also "subclass" the watcher type and provide your own	1275	member, you can also "subclass" the watcher type and provide your own
381	data:	1276	data:
382		1277
383	struct my_io	1278	struct my_io
384	{	1279	{
385	struct ev_io io;	1280	ev_io io;
386	int otherfd;	1281	int otherfd;
387	void *somedata;	1282	void *somedata;
388	struct whatever *mostinteresting;	1283	struct whatever *mostinteresting;
389	}	1284	};
		1285
		1286	...
		1287	struct my_io w;
		1288	ev_io_init (&w.io, my_cb, fd, EV_READ);
390		1289
391	And since your callback will be called with a pointer to the watcher, you	1290	And since your callback will be called with a pointer to the watcher, you
392	can cast it back to your own type:	1291	can cast it back to your own type:
393		1292
394	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1293	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
395	{	1294	{
396	struct my_io *w = (struct my_io *)w_;	1295	struct my_io *w = (struct my_io *)w_;
397	...	1296	...
398	}	1297	}
399		1298
400	More interesting and less C-conformant ways of catsing your callback type	1299	More interesting and less C-conformant ways of casting your callback type
401	have been omitted....	1300	instead have been omitted.
		1301
		1302	Another common scenario is to use some data structure with multiple
		1303	embedded watchers:
		1304
		1305	struct my_biggy
		1306	{
		1307	int some_data;
		1308	ev_timer t1;
		1309	ev_timer t2;
		1310	}
		1311
		1312	In this case getting the pointer to C<my_biggy> is a bit more
		1313	complicated: Either you store the address of your C<my_biggy> struct
		1314	in the C<data> member of the watcher (for woozies), or you need to use
		1315	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1316	programmers):
		1317
		1318	#include <stddef.h>
		1319
		1320	static void
		1321	t1_cb (EV_P_ ev_timer *w, int revents)
		1322	{
		1323	struct my_biggy big = (struct my_biggy *)
		1324	(((char *)w) - offsetof (struct my_biggy, t1));
		1325	}
		1326
		1327	static void
		1328	t2_cb (EV_P_ ev_timer *w, int revents)
		1329	{
		1330	struct my_biggy big = (struct my_biggy *)
		1331	(((char *)w) - offsetof (struct my_biggy, t2));
		1332	}
		1333
		1334	=head2 WATCHER PRIORITY MODELS
		1335
		1336	Many event loops support I<watcher priorities>, which are usually small
		1337	integers that influence the ordering of event callback invocation
		1338	between watchers in some way, all else being equal.
		1339
		1340	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1341	description for the more technical details such as the actual priority
		1342	range.
		1343
		1344	There are two common ways how these these priorities are being interpreted
		1345	by event loops:
		1346
		1347	In the more common lock-out model, higher priorities "lock out" invocation
		1348	of lower priority watchers, which means as long as higher priority
		1349	watchers receive events, lower priority watchers are not being invoked.
		1350
		1351	The less common only-for-ordering model uses priorities solely to order
		1352	callback invocation within a single event loop iteration: Higher priority
		1353	watchers are invoked before lower priority ones, but they all get invoked
		1354	before polling for new events.
		1355
		1356	Libev uses the second (only-for-ordering) model for all its watchers
		1357	except for idle watchers (which use the lock-out model).
		1358
		1359	The rationale behind this is that implementing the lock-out model for
		1360	watchers is not well supported by most kernel interfaces, and most event
		1361	libraries will just poll for the same events again and again as long as
		1362	their callbacks have not been executed, which is very inefficient in the
		1363	common case of one high-priority watcher locking out a mass of lower
		1364	priority ones.
		1365
		1366	Static (ordering) priorities are most useful when you have two or more
		1367	watchers handling the same resource: a typical usage example is having an
		1368	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1369	timeouts. Under load, data might be received while the program handles
		1370	other jobs, but since timers normally get invoked first, the timeout
		1371	handler will be executed before checking for data. In that case, giving
		1372	the timer a lower priority than the I/O watcher ensures that I/O will be
		1373	handled first even under adverse conditions (which is usually, but not
		1374	always, what you want).
		1375
		1376	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1377	will only be executed when no same or higher priority watchers have
		1378	received events, they can be used to implement the "lock-out" model when
		1379	required.
		1380
		1381	For example, to emulate how many other event libraries handle priorities,
		1382	you can associate an C<ev_idle> watcher to each such watcher, and in
		1383	the normal watcher callback, you just start the idle watcher. The real
		1384	processing is done in the idle watcher callback. This causes libev to
		1385	continously poll and process kernel event data for the watcher, but when
		1386	the lock-out case is known to be rare (which in turn is rare :), this is
		1387	workable.
		1388
		1389	Usually, however, the lock-out model implemented that way will perform
		1390	miserably under the type of load it was designed to handle. In that case,
		1391	it might be preferable to stop the real watcher before starting the
		1392	idle watcher, so the kernel will not have to process the event in case
		1393	the actual processing will be delayed for considerable time.
		1394
		1395	Here is an example of an I/O watcher that should run at a strictly lower
		1396	priority than the default, and which should only process data when no
		1397	other events are pending:
		1398
		1399	ev_idle idle; // actual processing watcher
		1400	ev_io io; // actual event watcher
		1401
		1402	static void
		1403	io_cb (EV_P_ ev_io *w, int revents)
		1404	{
		1405	// stop the I/O watcher, we received the event, but
		1406	// are not yet ready to handle it.
		1407	ev_io_stop (EV_A_ w);
		1408
		1409	// start the idle watcher to handle the actual event.
		1410	// it will not be executed as long as other watchers
		1411	// with the default priority are receiving events.
		1412	ev_idle_start (EV_A_ &idle);
		1413	}
		1414
		1415	static void
		1416	idle_cb (EV_P_ ev_idle *w, int revents)
		1417	{
		1418	// actual processing
		1419	read (STDIN_FILENO, ...);
		1420
		1421	// have to start the I/O watcher again, as
		1422	// we have handled the event
		1423	ev_io_start (EV_P_ &io);
		1424	}
		1425
		1426	// initialisation
		1427	ev_idle_init (&idle, idle_cb);
		1428	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1429	ev_io_start (EV_DEFAULT_ &io);
		1430
		1431	In the "real" world, it might also be beneficial to start a timer, so that
		1432	low-priority connections can not be locked out forever under load. This
		1433	enables your program to keep a lower latency for important connections
		1434	during short periods of high load, while not completely locking out less
		1435	important ones.
402		1436
403		1437
404	=head1 WATCHER TYPES	1438	=head1 WATCHER TYPES
405		1439
406	This section describes each watcher in detail, but will not repeat	1440	This section describes each watcher in detail, but will not repeat
407	information given in the last section.	1441	information given in the last section. Any initialisation/set macros,
		1442	functions and members specific to the watcher type are explained.
408		1443
		1444	Members are additionally marked with either I<[read-only]>, meaning that,
		1445	while the watcher is active, you can look at the member and expect some
		1446	sensible content, but you must not modify it (you can modify it while the
		1447	watcher is stopped to your hearts content), or I<[read-write]>, which
		1448	means you can expect it to have some sensible content while the watcher
		1449	is active, but you can also modify it. Modifying it may not do something
		1450	sensible or take immediate effect (or do anything at all), but libev will
		1451	not crash or malfunction in any way.
		1452
		1453
409	=head2 C<ev_io> - is this file descriptor readable or writable	1454	=head2 C<ev_io> - is this file descriptor readable or writable?
410		1455
411	I/O watchers check whether a file descriptor is readable or writable	1456	I/O watchers check whether a file descriptor is readable or writable
412	in each iteration of the event loop (This behaviour is called	1457	in each iteration of the event loop, or, more precisely, when reading
413	level-triggering because you keep receiving events as long as the	1458	would not block the process and writing would at least be able to write
414	condition persists. Remember you can stop the watcher if you don't want to	1459	some data. This behaviour is called level-triggering because you keep
415	act on the event and neither want to receive future events).	1460	receiving events as long as the condition persists. Remember you can stop
		1461	the watcher if you don't want to act on the event and neither want to
		1462	receive future events.
416		1463
417	In general you can register as many read and/or write event watchers oer	1464	In general you can register as many read and/or write event watchers per
418	fd as you want (as long as you don't confuse yourself). Setting all file	1465	fd as you want (as long as you don't confuse yourself). Setting all file
419	descriptors to non-blocking mode is also usually a good idea (but not	1466	descriptors to non-blocking mode is also usually a good idea (but not
420	required if you know what you are doing).	1467	required if you know what you are doing).
421		1468
422	You have to be careful with dup'ed file descriptors, though. Some backends	1469	If you cannot use non-blocking mode, then force the use of a
423	(the linux epoll backend is a notable example) cannot handle dup'ed file	1470	known-to-be-good backend (at the time of this writing, this includes only
424	descriptors correctly if you register interest in two or more fds pointing	1471	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
425	to the same file/socket etc. description.	1472	descriptors for which non-blocking operation makes no sense (such as
		1473	files) - libev doesn't guarentee any specific behaviour in that case.
426		1474
427	If you must do this, then force the use of a known-to-be-good backend	1475	Another thing you have to watch out for is that it is quite easy to
428	(at the time of this writing, this includes only EVMETHOD_SELECT and	1476	receive "spurious" readiness notifications, that is your callback might
429	EVMETHOD_POLL).	1477	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1478	because there is no data. Not only are some backends known to create a
		1479	lot of those (for example Solaris ports), it is very easy to get into
		1480	this situation even with a relatively standard program structure. Thus
		1481	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1482	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1483
		1484	If you cannot run the fd in non-blocking mode (for example you should
		1485	not play around with an Xlib connection), then you have to separately
		1486	re-test whether a file descriptor is really ready with a known-to-be good
		1487	interface such as poll (fortunately in our Xlib example, Xlib already
		1488	does this on its own, so its quite safe to use). Some people additionally
		1489	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1490	indefinitely.
		1491
		1492	But really, best use non-blocking mode.
		1493
		1494	=head3 The special problem of disappearing file descriptors
		1495
		1496	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1497	descriptor (either due to calling C<close> explicitly or any other means,
		1498	such as C<dup2>). The reason is that you register interest in some file
		1499	descriptor, but when it goes away, the operating system will silently drop
		1500	this interest. If another file descriptor with the same number then is
		1501	registered with libev, there is no efficient way to see that this is, in
		1502	fact, a different file descriptor.
		1503
		1504	To avoid having to explicitly tell libev about such cases, libev follows
		1505	the following policy: Each time C<ev_io_set> is being called, libev
		1506	will assume that this is potentially a new file descriptor, otherwise
		1507	it is assumed that the file descriptor stays the same. That means that
		1508	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1509	descriptor even if the file descriptor number itself did not change.
		1510
		1511	This is how one would do it normally anyway, the important point is that
		1512	the libev application should not optimise around libev but should leave
		1513	optimisations to libev.
		1514
		1515	=head3 The special problem of dup'ed file descriptors
		1516
		1517	Some backends (e.g. epoll), cannot register events for file descriptors,
		1518	but only events for the underlying file descriptions. That means when you
		1519	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1520	events for them, only one file descriptor might actually receive events.
		1521
		1522	There is no workaround possible except not registering events
		1523	for potentially C<dup ()>'ed file descriptors, or to resort to
		1524	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1525
		1526	=head3 The special problem of fork
		1527
		1528	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1529	useless behaviour. Libev fully supports fork, but needs to be told about
		1530	it in the child.
		1531
		1532	To support fork in your programs, you either have to call
		1533	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1534	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1535	C<EVBACKEND_POLL>.
		1536
		1537	=head3 The special problem of SIGPIPE
		1538
		1539	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1540	when writing to a pipe whose other end has been closed, your program gets
		1541	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1542	this is sensible behaviour, for daemons, this is usually undesirable.
		1543
		1544	So when you encounter spurious, unexplained daemon exits, make sure you
		1545	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1546	somewhere, as that would have given you a big clue).
		1547
		1548	=head3 The special problem of accept()ing when you can't
		1549
		1550	Many implementations of the POSIX C<accept> function (for example,
		1551	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1552	connection from the pending queue in all error cases.
		1553
		1554	For example, larger servers often run out of file descriptors (because
		1555	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1556	rejecting the connection, leading to libev signalling readiness on
		1557	the next iteration again (the connection still exists after all), and
		1558	typically causing the program to loop at 100% CPU usage.
		1559
		1560	Unfortunately, the set of errors that cause this issue differs between
		1561	operating systems, there is usually little the app can do to remedy the
		1562	situation, and no known thread-safe method of removing the connection to
		1563	cope with overload is known (to me).
		1564
		1565	One of the easiest ways to handle this situation is to just ignore it
		1566	- when the program encounters an overload, it will just loop until the
		1567	situation is over. While this is a form of busy waiting, no OS offers an
		1568	event-based way to handle this situation, so it's the best one can do.
		1569
		1570	A better way to handle the situation is to log any errors other than
		1571	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1572	messages, and continue as usual, which at least gives the user an idea of
		1573	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1574	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1575	usage.
		1576
		1577	If your program is single-threaded, then you could also keep a dummy file
		1578	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1579	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1580	close that fd, and create a new dummy fd. This will gracefully refuse
		1581	clients under typical overload conditions.
		1582
		1583	The last way to handle it is to simply log the error and C<exit>, as
		1584	is often done with C<malloc> failures, but this results in an easy
		1585	opportunity for a DoS attack.
		1586
		1587	=head3 Watcher-Specific Functions
430		1588
431	=over 4	1589	=over 4
432		1590
433	=item ev_io_init (ev_io *, callback, int fd, int events)	1591	=item ev_io_init (ev_io *, callback, int fd, int events)
434		1592
435	=item ev_io_set (ev_io *, int fd, int events)	1593	=item ev_io_set (ev_io *, int fd, int events)
436		1594
437	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1595	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
438	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1596	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
439	EV_WRITE> to receive the given events.	1597	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1598
		1599	=item int fd [read-only]
		1600
		1601	The file descriptor being watched.
		1602
		1603	=item int events [read-only]
		1604
		1605	The events being watched.
440		1606
441	=back	1607	=back
442		1608
		1609	=head3 Examples
		1610
		1611	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1612	readable, but only once. Since it is likely line-buffered, you could
		1613	attempt to read a whole line in the callback.
		1614
		1615	static void
		1616	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1617	{
		1618	ev_io_stop (loop, w);
		1619	.. read from stdin here (or from w->fd) and handle any I/O errors
		1620	}
		1621
		1622	...
		1623	struct ev_loop *loop = ev_default_init (0);
		1624	ev_io stdin_readable;
		1625	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1626	ev_io_start (loop, &stdin_readable);
		1627	ev_loop (loop, 0);
		1628
		1629
443	=head2 C<ev_timer> - relative and optionally recurring timeouts	1630	=head2 C<ev_timer> - relative and optionally repeating timeouts
444		1631
445	Timer watchers are simple relative timers that generate an event after a	1632	Timer watchers are simple relative timers that generate an event after a
446	given time, and optionally repeating in regular intervals after that.	1633	given time, and optionally repeating in regular intervals after that.
447		1634
448	The timers are based on real time, that is, if you register an event that	1635	The timers are based on real time, that is, if you register an event that
449	times out after an hour and youreset your system clock to last years	1636	times out after an hour and you reset your system clock to January last
450	time, it will still time out after (roughly) and hour. "Roughly" because	1637	year, it will still time out after (roughly) one hour. "Roughly" because
451	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1638	detecting time jumps is hard, and some inaccuracies are unavoidable (the
452	monotonic clock option helps a lot here).	1639	monotonic clock option helps a lot here).
		1640
		1641	The callback is guaranteed to be invoked only I<after> its timeout has
		1642	passed (not I<at>, so on systems with very low-resolution clocks this
		1643	might introduce a small delay). If multiple timers become ready during the
		1644	same loop iteration then the ones with earlier time-out values are invoked
		1645	before ones of the same priority with later time-out values (but this is
		1646	no longer true when a callback calls C<ev_loop> recursively).
		1647
		1648	=head3 Be smart about timeouts
		1649
		1650	Many real-world problems involve some kind of timeout, usually for error
		1651	recovery. A typical example is an HTTP request - if the other side hangs,
		1652	you want to raise some error after a while.
		1653
		1654	What follows are some ways to handle this problem, from obvious and
		1655	inefficient to smart and efficient.
		1656
		1657	In the following, a 60 second activity timeout is assumed - a timeout that
		1658	gets reset to 60 seconds each time there is activity (e.g. each time some
		1659	data or other life sign was received).
		1660
		1661	=over 4
		1662
		1663	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1664
		1665	This is the most obvious, but not the most simple way: In the beginning,
		1666	start the watcher:
		1667
		1668	ev_timer_init (timer, callback, 60., 0.);
		1669	ev_timer_start (loop, timer);
		1670
		1671	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1672	and start it again:
		1673
		1674	ev_timer_stop (loop, timer);
		1675	ev_timer_set (timer, 60., 0.);
		1676	ev_timer_start (loop, timer);
		1677
		1678	This is relatively simple to implement, but means that each time there is
		1679	some activity, libev will first have to remove the timer from its internal
		1680	data structure and then add it again. Libev tries to be fast, but it's
		1681	still not a constant-time operation.
		1682
		1683	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1684
		1685	This is the easiest way, and involves using C<ev_timer_again> instead of
		1686	C<ev_timer_start>.
		1687
		1688	To implement this, configure an C<ev_timer> with a C<repeat> value
		1689	of C<60> and then call C<ev_timer_again> at start and each time you
		1690	successfully read or write some data. If you go into an idle state where
		1691	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1692	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1693
		1694	That means you can ignore both the C<ev_timer_start> function and the
		1695	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1696	member and C<ev_timer_again>.
		1697
		1698	At start:
		1699
		1700	ev_init (timer, callback);
		1701	timer->repeat = 60.;
		1702	ev_timer_again (loop, timer);
		1703
		1704	Each time there is some activity:
		1705
		1706	ev_timer_again (loop, timer);
		1707
		1708	It is even possible to change the time-out on the fly, regardless of
		1709	whether the watcher is active or not:
		1710
		1711	timer->repeat = 30.;
		1712	ev_timer_again (loop, timer);
		1713
		1714	This is slightly more efficient then stopping/starting the timer each time
		1715	you want to modify its timeout value, as libev does not have to completely
		1716	remove and re-insert the timer from/into its internal data structure.
		1717
		1718	It is, however, even simpler than the "obvious" way to do it.
		1719
		1720	=item 3. Let the timer time out, but then re-arm it as required.
		1721
		1722	This method is more tricky, but usually most efficient: Most timeouts are
		1723	relatively long compared to the intervals between other activity - in
		1724	our example, within 60 seconds, there are usually many I/O events with
		1725	associated activity resets.
		1726
		1727	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1728	but remember the time of last activity, and check for a real timeout only
		1729	within the callback:
		1730
		1731	ev_tstamp last_activity; // time of last activity
		1732
		1733	static void
		1734	callback (EV_P_ ev_timer *w, int revents)
		1735	{
		1736	ev_tstamp now = ev_now (EV_A);
		1737	ev_tstamp timeout = last_activity + 60.;
		1738
		1739	// if last_activity + 60. is older than now, we did time out
		1740	if (timeout < now)
		1741	{
		1742	// timeout occured, take action
		1743	}
		1744	else
		1745	{
		1746	// callback was invoked, but there was some activity, re-arm
		1747	// the watcher to fire in last_activity + 60, which is
		1748	// guaranteed to be in the future, so "again" is positive:
		1749	w->repeat = timeout - now;
		1750	ev_timer_again (EV_A_ w);
		1751	}
		1752	}
		1753
		1754	To summarise the callback: first calculate the real timeout (defined
		1755	as "60 seconds after the last activity"), then check if that time has
		1756	been reached, which means something I<did>, in fact, time out. Otherwise
		1757	the callback was invoked too early (C<timeout> is in the future), so
		1758	re-schedule the timer to fire at that future time, to see if maybe we have
		1759	a timeout then.
		1760
		1761	Note how C<ev_timer_again> is used, taking advantage of the
		1762	C<ev_timer_again> optimisation when the timer is already running.
		1763
		1764	This scheme causes more callback invocations (about one every 60 seconds
		1765	minus half the average time between activity), but virtually no calls to
		1766	libev to change the timeout.
		1767
		1768	To start the timer, simply initialise the watcher and set C<last_activity>
		1769	to the current time (meaning we just have some activity :), then call the
		1770	callback, which will "do the right thing" and start the timer:
		1771
		1772	ev_init (timer, callback);
		1773	last_activity = ev_now (loop);
		1774	callback (loop, timer, EV_TIMER);
		1775
		1776	And when there is some activity, simply store the current time in
		1777	C<last_activity>, no libev calls at all:
		1778
		1779	last_activity = ev_now (loop);
		1780
		1781	This technique is slightly more complex, but in most cases where the
		1782	time-out is unlikely to be triggered, much more efficient.
		1783
		1784	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1785	callback :) - just change the timeout and invoke the callback, which will
		1786	fix things for you.
		1787
		1788	=item 4. Wee, just use a double-linked list for your timeouts.
		1789
		1790	If there is not one request, but many thousands (millions...), all
		1791	employing some kind of timeout with the same timeout value, then one can
		1792	do even better:
		1793
		1794	When starting the timeout, calculate the timeout value and put the timeout
		1795	at the I<end> of the list.
		1796
		1797	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1798	the list is expected to fire (for example, using the technique #3).
		1799
		1800	When there is some activity, remove the timer from the list, recalculate
		1801	the timeout, append it to the end of the list again, and make sure to
		1802	update the C<ev_timer> if it was taken from the beginning of the list.
		1803
		1804	This way, one can manage an unlimited number of timeouts in O(1) time for
		1805	starting, stopping and updating the timers, at the expense of a major
		1806	complication, and having to use a constant timeout. The constant timeout
		1807	ensures that the list stays sorted.
		1808
		1809	=back
		1810
		1811	So which method the best?
		1812
		1813	Method #2 is a simple no-brain-required solution that is adequate in most
		1814	situations. Method #3 requires a bit more thinking, but handles many cases
		1815	better, and isn't very complicated either. In most case, choosing either
		1816	one is fine, with #3 being better in typical situations.
		1817
		1818	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1819	rather complicated, but extremely efficient, something that really pays
		1820	off after the first million or so of active timers, i.e. it's usually
		1821	overkill :)
		1822
		1823	=head3 The special problem of time updates
		1824
		1825	Establishing the current time is a costly operation (it usually takes at
		1826	least two system calls): EV therefore updates its idea of the current
		1827	time only before and after C<ev_loop> collects new events, which causes a
		1828	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1829	lots of events in one iteration.
453		1830
454	The relative timeouts are calculated relative to the C<ev_now ()>	1831	The relative timeouts are calculated relative to the C<ev_now ()>
455	time. This is usually the right thing as this timestamp refers to the time	1832	time. This is usually the right thing as this timestamp refers to the time
456	of the event triggering whatever timeout you are modifying/starting. If	1833	of the event triggering whatever timeout you are modifying/starting. If
457	you suspect event processing to be delayed and you *need* to base the timeout	1834	you suspect event processing to be delayed and you I<need> to base the
458	ion the current time, use something like this to adjust for this:	1835	timeout on the current time, use something like this to adjust for this:
459		1836
460	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1837	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
461		1838
		1839	If the event loop is suspended for a long time, you can also force an
		1840	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		1841	()>.
		1842
		1843	=head3 The special problems of suspended animation
		1844
		1845	When you leave the server world it is quite customary to hit machines that
		1846	can suspend/hibernate - what happens to the clocks during such a suspend?
		1847
		1848	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1849	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1850	to run until the system is suspended, but they will not advance while the
		1851	system is suspended. That means, on resume, it will be as if the program
		1852	was frozen for a few seconds, but the suspend time will not be counted
		1853	towards C<ev_timer> when a monotonic clock source is used. The real time
		1854	clock advanced as expected, but if it is used as sole clocksource, then a
		1855	long suspend would be detected as a time jump by libev, and timers would
		1856	be adjusted accordingly.
		1857
		1858	I would not be surprised to see different behaviour in different between
		1859	operating systems, OS versions or even different hardware.
		1860
		1861	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1862	time jump in the monotonic clocks and the realtime clock. If the program
		1863	is suspended for a very long time, and monotonic clock sources are in use,
		1864	then you can expect C<ev_timer>s to expire as the full suspension time
		1865	will be counted towards the timers. When no monotonic clock source is in
		1866	use, then libev will again assume a timejump and adjust accordingly.
		1867
		1868	It might be beneficial for this latter case to call C<ev_suspend>
		1869	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1870	deterministic behaviour in this case (you can do nothing against
		1871	C<SIGSTOP>).
		1872
		1873	=head3 Watcher-Specific Functions and Data Members
		1874
462	=over 4	1875	=over 4
463		1876
464	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1877	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465		1878
466	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1879	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
467		1880
468	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1881	Configure the timer to trigger after C<after> seconds. If C<repeat>
469	C<0.>, then it will automatically be stopped. If it is positive, then the	1882	is C<0.>, then it will automatically be stopped once the timeout is
470	timer will automatically be configured to trigger again C<repeat> seconds	1883	reached. If it is positive, then the timer will automatically be
471	later, again, and again, until stopped manually.	1884	configured to trigger again C<repeat> seconds later, again, and again,
		1885	until stopped manually.
472		1886
473	The timer itself will do a best-effort at avoiding drift, that is, if you	1887	The timer itself will do a best-effort at avoiding drift, that is, if
474	configure a timer to trigger every 10 seconds, then it will trigger at	1888	you configure a timer to trigger every 10 seconds, then it will normally
475	exactly 10 second intervals. If, however, your program cannot keep up with	1889	trigger at exactly 10 second intervals. If, however, your program cannot
476	the timer (ecause it takes longer than those 10 seconds to do stuff) the	1890	keep up with the timer (because it takes longer than those 10 seconds to
477	timer will not fire more than once per event loop iteration.	1891	do stuff) the timer will not fire more than once per event loop iteration.
478		1892
479	=item ev_timer_again (loop)	1893	=item ev_timer_again (loop, ev_timer *)
480		1894
481	This will act as if the timer timed out and restart it again if it is	1895	This will act as if the timer timed out and restart it again if it is
482	repeating. The exact semantics are:	1896	repeating. The exact semantics are:
483		1897
		1898	If the timer is pending, its pending status is cleared.
		1899
484	If the timer is started but nonrepeating, stop it.	1900	If the timer is started but non-repeating, stop it (as if it timed out).
485		1901
486	If the timer is repeating, either start it if necessary (with the repeat	1902	If the timer is repeating, either start it if necessary (with the
487	value), or reset the running timer to the repeat value.	1903	C<repeat> value), or reset the running timer to the C<repeat> value.
488		1904
489	This sounds a bit complicated, but here is a useful and typical	1905	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
490	example: Imagine you have a tcp connection and you want a so-called idle	1906	usage example.
491	timeout, that is, you want to be called when there have been, say, 60	1907
492	seconds of inactivity on the socket. The easiest way to do this is to	1908	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
493	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1909
494	time you successfully read or write some data. If you go into an idle	1910	Returns the remaining time until a timer fires. If the timer is active,
495	state where you do not expect data to travel on the socket, you can stop	1911	then this time is relative to the current event loop time, otherwise it's
496	the timer, and again will automatically restart it if need be.	1912	the timeout value currently configured.
		1913
		1914	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1915	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1916	will return C<4>. When the timer expires and is restarted, it will return
		1917	roughly C<7> (likely slightly less as callback invocation takes some time,
		1918	too), and so on.
		1919
		1920	=item ev_tstamp repeat [read-write]
		1921
		1922	The current C<repeat> value. Will be used each time the watcher times out
		1923	or C<ev_timer_again> is called, and determines the next timeout (if any),
		1924	which is also when any modifications are taken into account.
497		1925
498	=back	1926	=back
499		1927
		1928	=head3 Examples
		1929
		1930	Example: Create a timer that fires after 60 seconds.
		1931
		1932	static void
		1933	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1934	{
		1935	.. one minute over, w is actually stopped right here
		1936	}
		1937
		1938	ev_timer mytimer;
		1939	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1940	ev_timer_start (loop, &mytimer);
		1941
		1942	Example: Create a timeout timer that times out after 10 seconds of
		1943	inactivity.
		1944
		1945	static void
		1946	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1947	{
		1948	.. ten seconds without any activity
		1949	}
		1950
		1951	ev_timer mytimer;
		1952	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1953	ev_timer_again (&mytimer); /* start timer */
		1954	ev_loop (loop, 0);
		1955
		1956	// and in some piece of code that gets executed on any "activity":
		1957	// reset the timeout to start ticking again at 10 seconds
		1958	ev_timer_again (&mytimer);
		1959
		1960
500	=head2 C<ev_periodic> - to cron or not to cron	1961	=head2 C<ev_periodic> - to cron or not to cron?
501		1962
502	Periodic watchers are also timers of a kind, but they are very versatile	1963	Periodic watchers are also timers of a kind, but they are very versatile
503	(and unfortunately a bit complex).	1964	(and unfortunately a bit complex).
504		1965
505	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1966	Unlike C<ev_timer>, periodic watchers are not based on real time (or
506	but on wallclock time (absolute time). You can tell a periodic watcher	1967	relative time, the physical time that passes) but on wall clock time
507	to trigger "at" some specific point in time. For example, if you tell a	1968	(absolute time, the thing you can read on your calender or clock). The
508	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1969	difference is that wall clock time can run faster or slower than real
509	+ 10.>) and then reset your system clock to the last year, then it will	1970	time, and time jumps are not uncommon (e.g. when you adjust your
510	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1971	wrist-watch).
511	roughly 10 seconds later and of course not if you reset your system time
512	again).
513		1972
514	They can also be used to implement vastly more complex timers, such as	1973	You can tell a periodic watcher to trigger after some specific point
		1974	in time: for example, if you tell a periodic watcher to trigger "in 10
		1975	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1976	not a delay) and then reset your system clock to January of the previous
		1977	year, then it will take a year or more to trigger the event (unlike an
		1978	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1979	it, as it uses a relative timeout).
		1980
		1981	C<ev_periodic> watchers can also be used to implement vastly more complex
515	triggering an event on eahc midnight, local time.	1982	timers, such as triggering an event on each "midnight, local time", or
		1983	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1984	those cannot react to time jumps.
		1985
		1986	As with timers, the callback is guaranteed to be invoked only when the
		1987	point in time where it is supposed to trigger has passed. If multiple
		1988	timers become ready during the same loop iteration then the ones with
		1989	earlier time-out values are invoked before ones with later time-out values
		1990	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1991
		1992	=head3 Watcher-Specific Functions and Data Members
516		1993
517	=over 4	1994	=over 4
518		1995
519	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1996	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
520		1997
521	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1998	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
522		1999
523	Lots of arguments, lets sort it out... There are basically three modes of	2000	Lots of arguments, let's sort it out... There are basically three modes of
524	operation, and we will explain them from simplest to complex:	2001	operation, and we will explain them from simplest to most complex:
525
526		2002
527	=over 4	2003	=over 4
528		2004
529	=item * absolute timer (interval = reschedule_cb = 0)	2005	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
530		2006
531	In this configuration the watcher triggers an event at the wallclock time	2007	In this configuration the watcher triggers an event after the wall clock
532	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2008	time C<offset> has passed. It will not repeat and will not adjust when a
533	that is, if it is to be run at January 1st 2011 then it will run when the	2009	time jump occurs, that is, if it is to be run at January 1st 2011 then it
534	system time reaches or surpasses this time.	2010	will be stopped and invoked when the system clock reaches or surpasses
		2011	this point in time.
535		2012
536	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2013	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
537		2014
538	In this mode the watcher will always be scheduled to time out at the next	2015	In this mode the watcher will always be scheduled to time out at the next
539	C<at + N * interval> time (for some integer N) and then repeat, regardless	2016	C<offset + N * interval> time (for some integer N, which can also be
540	of any time jumps.	2017	negative) and then repeat, regardless of any time jumps. The C<offset>
		2018	argument is merely an offset into the C<interval> periods.
541		2019
542	This can be used to create timers that do not drift with respect to system	2020	This can be used to create timers that do not drift with respect to the
543	time:	2021	system clock, for example, here is an C<ev_periodic> that triggers each
		2022	hour, on the hour (with respect to UTC):
544		2023
545	ev_periodic_set (&periodic, 0., 3600., 0);	2024	ev_periodic_set (&periodic, 0., 3600., 0);
546		2025
547	This doesn't mean there will always be 3600 seconds in between triggers,	2026	This doesn't mean there will always be 3600 seconds in between triggers,
548	but only that the the callback will be called when the system time shows a	2027	but only that the callback will be called when the system time shows a
549	full hour (UTC), or more correctly, when the system time is evenly divisible	2028	full hour (UTC), or more correctly, when the system time is evenly divisible
550	by 3600.	2029	by 3600.
551		2030
552	Another way to think about it (for the mathematically inclined) is that	2031	Another way to think about it (for the mathematically inclined) is that
553	C<ev_periodic> will try to run the callback in this mode at the next possible	2032	C<ev_periodic> will try to run the callback in this mode at the next possible
554	time where C<time = at (mod interval)>, regardless of any time jumps.	2033	time where C<time = offset (mod interval)>, regardless of any time jumps.
555		2034
		2035	For numerical stability it is preferable that the C<offset> value is near
		2036	C<ev_now ()> (the current time), but there is no range requirement for
		2037	this value, and in fact is often specified as zero.
		2038
		2039	Note also that there is an upper limit to how often a timer can fire (CPU
		2040	speed for example), so if C<interval> is very small then timing stability
		2041	will of course deteriorate. Libev itself tries to be exact to be about one
		2042	millisecond (if the OS supports it and the machine is fast enough).
		2043
556	=item * manual reschedule mode (reschedule_cb = callback)	2044	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
557		2045
558	In this mode the values for C<interval> and C<at> are both being	2046	In this mode the values for C<interval> and C<offset> are both being
559	ignored. Instead, each time the periodic watcher gets scheduled, the	2047	ignored. Instead, each time the periodic watcher gets scheduled, the
560	reschedule callback will be called with the watcher as first, and the	2048	reschedule callback will be called with the watcher as first, and the
561	current time as second argument.	2049	current time as second argument.
562		2050
563	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	2051	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
564	periodic watcher, ever, or make any event loop modifications>. If you need	2052	or make ANY other event loop modifications whatsoever, unless explicitly
		2053	allowed by documentation here>.
		2054
565	to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.	2055	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2056	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2057	only event loop modification you are allowed to do).
566		2058
567	Also, I<< this callback must always return a time that is later than the
568	passed C<now> value >>. Not even C<now> itself will be ok.
569
570	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2059	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
571	ev_tstamp now)>, e.g.:	2060	*w, ev_tstamp now)>, e.g.:
572		2061
		2062	static ev_tstamp
573	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2063	my_rescheduler (ev_periodic *w, ev_tstamp now)
574	{	2064	{
575	return now + 60.;	2065	return now + 60.;
576	}	2066	}
577		2067
578	It must return the next time to trigger, based on the passed time value	2068	It must return the next time to trigger, based on the passed time value
579	(that is, the lowest time value larger than to the second argument). It	2069	(that is, the lowest time value larger than to the second argument). It
580	will usually be called just before the callback will be triggered, but	2070	will usually be called just before the callback will be triggered, but
581	might be called at other times, too.	2071	might be called at other times, too.
582		2072
		2073	NOTE: I<< This callback must always return a time that is higher than or
		2074	equal to the passed C<now> value >>.
		2075
583	This can be used to create very complex timers, such as a timer that	2076	This can be used to create very complex timers, such as a timer that
584	triggers on each midnight, local time. To do this, you would calculate the	2077	triggers on "next midnight, local time". To do this, you would calculate the
585	next midnight after C<now> and return the timestamp value for this. How you do this	2078	next midnight after C<now> and return the timestamp value for this. How
586	is, again, up to you (but it is not trivial).	2079	you do this is, again, up to you (but it is not trivial, which is the main
		2080	reason I omitted it as an example).
587		2081
588	=back	2082	=back
589		2083
590	=item ev_periodic_again (loop, ev_periodic *)	2084	=item ev_periodic_again (loop, ev_periodic *)
591		2085
592	Simply stops and restarts the periodic watcher again. This is only useful	2086	Simply stops and restarts the periodic watcher again. This is only useful
593	when you changed some parameters or the reschedule callback would return	2087	when you changed some parameters or the reschedule callback would return
594	a different time than the last time it was called (e.g. in a crond like	2088	a different time than the last time it was called (e.g. in a crond like
595	program when the crontabs have changed).	2089	program when the crontabs have changed).
596		2090
		2091	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2092
		2093	When active, returns the absolute time that the watcher is supposed
		2094	to trigger next. This is not the same as the C<offset> argument to
		2095	C<ev_periodic_set>, but indeed works even in interval and manual
		2096	rescheduling modes.
		2097
		2098	=item ev_tstamp offset [read-write]
		2099
		2100	When repeating, this contains the offset value, otherwise this is the
		2101	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2102	although libev might modify this value for better numerical stability).
		2103
		2104	Can be modified any time, but changes only take effect when the periodic
		2105	timer fires or C<ev_periodic_again> is being called.
		2106
		2107	=item ev_tstamp interval [read-write]
		2108
		2109	The current interval value. Can be modified any time, but changes only
		2110	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2111	called.
		2112
		2113	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2114
		2115	The current reschedule callback, or C<0>, if this functionality is
		2116	switched off. Can be changed any time, but changes only take effect when
		2117	the periodic timer fires or C<ev_periodic_again> is being called.
		2118
597	=back	2119	=back
598		2120
		2121	=head3 Examples
		2122
		2123	Example: Call a callback every hour, or, more precisely, whenever the
		2124	system time is divisible by 3600. The callback invocation times have
		2125	potentially a lot of jitter, but good long-term stability.
		2126
		2127	static void
		2128	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
		2129	{
		2130	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2131	}
		2132
		2133	ev_periodic hourly_tick;
		2134	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2135	ev_periodic_start (loop, &hourly_tick);
		2136
		2137	Example: The same as above, but use a reschedule callback to do it:
		2138
		2139	#include <math.h>
		2140
		2141	static ev_tstamp
		2142	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2143	{
		2144	return now + (3600. - fmod (now, 3600.));
		2145	}
		2146
		2147	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2148
		2149	Example: Call a callback every hour, starting now:
		2150
		2151	ev_periodic hourly_tick;
		2152	ev_periodic_init (&hourly_tick, clock_cb,
		2153	fmod (ev_now (loop), 3600.), 3600., 0);
		2154	ev_periodic_start (loop, &hourly_tick);
		2155
		2156
599	=head2 C<ev_signal> - signal me when a signal gets signalled	2157	=head2 C<ev_signal> - signal me when a signal gets signalled!
600		2158
601	Signal watchers will trigger an event when the process receives a specific	2159	Signal watchers will trigger an event when the process receives a specific
602	signal one or more times. Even though signals are very asynchronous, libev	2160	signal one or more times. Even though signals are very asynchronous, libev
603	will try it's best to deliver signals synchronously, i.e. as part of the	2161	will try it's best to deliver signals synchronously, i.e. as part of the
604	normal event processing, like any other event.	2162	normal event processing, like any other event.
605		2163
		2164	If you want signals to be delivered truly asynchronously, just use
		2165	C<sigaction> as you would do without libev and forget about sharing
		2166	the signal. You can even use C<ev_async> from a signal handler to
		2167	synchronously wake up an event loop.
		2168
606	You can configure as many watchers as you like per signal. Only when the	2169	You can configure as many watchers as you like for the same signal, but
		2170	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2171	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2172	C<SIGINT> in both the default loop and another loop at the same time. At
		2173	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2174
607	first watcher gets started will libev actually register a signal watcher	2175	When the first watcher gets started will libev actually register something
608	with the kernel (thus it coexists with your own signal handlers as long	2176	with the kernel (thus it coexists with your own signal handlers as long as
609	as you don't register any with libev). Similarly, when the last signal	2177	you don't register any with libev for the same signal).
610	watcher for a signal is stopped libev will reset the signal handler to	2178
611	SIG_DFL (regardless of what it was set to before).	2179	If possible and supported, libev will install its handlers with
		2180	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2181	not be unduly interrupted. If you have a problem with system calls getting
		2182	interrupted by signals you can block all signals in an C<ev_check> watcher
		2183	and unblock them in an C<ev_prepare> watcher.
		2184
		2185	=head3 The special problem of inheritance over fork/execve/pthread_create
		2186
		2187	Both the signal mask (C<sigprocmask>) and the signal disposition
		2188	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2189	stopping it again), that is, libev might or might not block the signal,
		2190	and might or might not set or restore the installed signal handler.
		2191
		2192	While this does not matter for the signal disposition (libev never
		2193	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2194	C<execve>), this matters for the signal mask: many programs do not expect
		2195	certain signals to be blocked.
		2196
		2197	This means that before calling C<exec> (from the child) you should reset
		2198	the signal mask to whatever "default" you expect (all clear is a good
		2199	choice usually).
		2200
		2201	The simplest way to ensure that the signal mask is reset in the child is
		2202	to install a fork handler with C<pthread_atfork> that resets it. That will
		2203	catch fork calls done by libraries (such as the libc) as well.
		2204
		2205	In current versions of libev, the signal will not be blocked indefinitely
		2206	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2207	the window of opportunity for problems, it will not go away, as libev
		2208	I<has> to modify the signal mask, at least temporarily.
		2209
		2210	So I can't stress this enough: I<If you do not reset your signal mask when
		2211	you expect it to be empty, you have a race condition in your code>. This
		2212	is not a libev-specific thing, this is true for most event libraries.
		2213
		2214	=head3 Watcher-Specific Functions and Data Members
612		2215
613	=over 4	2216	=over 4
614		2217
615	=item ev_signal_init (ev_signal *, callback, int signum)	2218	=item ev_signal_init (ev_signal *, callback, int signum)
616		2219
617	=item ev_signal_set (ev_signal *, int signum)	2220	=item ev_signal_set (ev_signal *, int signum)
618		2221
619	Configures the watcher to trigger on the given signal number (usually one	2222	Configures the watcher to trigger on the given signal number (usually one
620	of the C<SIGxxx> constants).	2223	of the C<SIGxxx> constants).
621		2224
		2225	=item int signum [read-only]
		2226
		2227	The signal the watcher watches out for.
		2228
622	=back	2229	=back
623		2230
		2231	=head3 Examples
		2232
		2233	Example: Try to exit cleanly on SIGINT.
		2234
		2235	static void
		2236	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2237	{
		2238	ev_unloop (loop, EVUNLOOP_ALL);
		2239	}
		2240
		2241	ev_signal signal_watcher;
		2242	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2243	ev_signal_start (loop, &signal_watcher);
		2244
		2245
624	=head2 C<ev_child> - wait for pid status changes	2246	=head2 C<ev_child> - watch out for process status changes
625		2247
626	Child watchers trigger when your process receives a SIGCHLD in response to	2248	Child watchers trigger when your process receives a SIGCHLD in response to
627	some child status changes (most typically when a child of yours dies).	2249	some child status changes (most typically when a child of yours dies or
		2250	exits). It is permissible to install a child watcher I<after> the child
		2251	has been forked (which implies it might have already exited), as long
		2252	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2253	forking and then immediately registering a watcher for the child is fine,
		2254	but forking and registering a watcher a few event loop iterations later or
		2255	in the next callback invocation is not.
		2256
		2257	Only the default event loop is capable of handling signals, and therefore
		2258	you can only register child watchers in the default event loop.
		2259
		2260	Due to some design glitches inside libev, child watchers will always be
		2261	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2262	libev)
		2263
		2264	=head3 Process Interaction
		2265
		2266	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2267	initialised. This is necessary to guarantee proper behaviour even if the
		2268	first child watcher is started after the child exits. The occurrence
		2269	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2270	synchronously as part of the event loop processing. Libev always reaps all
		2271	children, even ones not watched.
		2272
		2273	=head3 Overriding the Built-In Processing
		2274
		2275	Libev offers no special support for overriding the built-in child
		2276	processing, but if your application collides with libev's default child
		2277	handler, you can override it easily by installing your own handler for
		2278	C<SIGCHLD> after initialising the default loop, and making sure the
		2279	default loop never gets destroyed. You are encouraged, however, to use an
		2280	event-based approach to child reaping and thus use libev's support for
		2281	that, so other libev users can use C<ev_child> watchers freely.
		2282
		2283	=head3 Stopping the Child Watcher
		2284
		2285	Currently, the child watcher never gets stopped, even when the
		2286	child terminates, so normally one needs to stop the watcher in the
		2287	callback. Future versions of libev might stop the watcher automatically
		2288	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2289	problem).
		2290
		2291	=head3 Watcher-Specific Functions and Data Members
628		2292
629	=over 4	2293	=over 4
630		2294
631	=item ev_child_init (ev_child *, callback, int pid)	2295	=item ev_child_init (ev_child *, callback, int pid, int trace)
632		2296
633	=item ev_child_set (ev_child *, int pid)	2297	=item ev_child_set (ev_child *, int pid, int trace)
634		2298
635	Configures the watcher to wait for status changes of process C<pid> (or	2299	Configures the watcher to wait for status changes of process C<pid> (or
636	I<any> process if C<pid> is specified as C<0>). The callback can look	2300	I<any> process if C<pid> is specified as C<0>). The callback can look
637	at the C<rstatus> member of the C<ev_child> watcher structure to see	2301	at the C<rstatus> member of the C<ev_child> watcher structure to see
638	the status word (use the macros from C<sys/wait.h> and see your systems	2302	the status word (use the macros from C<sys/wait.h> and see your systems
639	C<waitpid> documentation). The C<rpid> member contains the pid of the	2303	C<waitpid> documentation). The C<rpid> member contains the pid of the
640	process causing the status change.	2304	process causing the status change. C<trace> must be either C<0> (only
		2305	activate the watcher when the process terminates) or C<1> (additionally
		2306	activate the watcher when the process is stopped or continued).
		2307
		2308	=item int pid [read-only]
		2309
		2310	The process id this watcher watches out for, or C<0>, meaning any process id.
		2311
		2312	=item int rpid [read-write]
		2313
		2314	The process id that detected a status change.
		2315
		2316	=item int rstatus [read-write]
		2317
		2318	The process exit/trace status caused by C<rpid> (see your systems
		2319	C<waitpid> and C<sys/wait.h> documentation for details).
641		2320
642	=back	2321	=back
643		2322
		2323	=head3 Examples
		2324
		2325	Example: C<fork()> a new process and install a child handler to wait for
		2326	its completion.
		2327
		2328	ev_child cw;
		2329
		2330	static void
		2331	child_cb (EV_P_ ev_child *w, int revents)
		2332	{
		2333	ev_child_stop (EV_A_ w);
		2334	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2335	}
		2336
		2337	pid_t pid = fork ();
		2338
		2339	if (pid < 0)
		2340	// error
		2341	else if (pid == 0)
		2342	{
		2343	// the forked child executes here
		2344	exit (1);
		2345	}
		2346	else
		2347	{
		2348	ev_child_init (&cw, child_cb, pid, 0);
		2349	ev_child_start (EV_DEFAULT_ &cw);
		2350	}
		2351
		2352
		2353	=head2 C<ev_stat> - did the file attributes just change?
		2354
		2355	This watches a file system path for attribute changes. That is, it calls
		2356	C<stat> on that path in regular intervals (or when the OS says it changed)
		2357	and sees if it changed compared to the last time, invoking the callback if
		2358	it did.
		2359
		2360	The path does not need to exist: changing from "path exists" to "path does
		2361	not exist" is a status change like any other. The condition "path does not
		2362	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2363	C<st_nlink> field being zero (which is otherwise always forced to be at
		2364	least one) and all the other fields of the stat buffer having unspecified
		2365	contents.
		2366
		2367	The path I<must not> end in a slash or contain special components such as
		2368	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2369	your working directory changes, then the behaviour is undefined.
		2370
		2371	Since there is no portable change notification interface available, the
		2372	portable implementation simply calls C<stat(2)> regularly on the path
		2373	to see if it changed somehow. You can specify a recommended polling
		2374	interval for this case. If you specify a polling interval of C<0> (highly
		2375	recommended!) then a I<suitable, unspecified default> value will be used
		2376	(which you can expect to be around five seconds, although this might
		2377	change dynamically). Libev will also impose a minimum interval which is
		2378	currently around C<0.1>, but that's usually overkill.
		2379
		2380	This watcher type is not meant for massive numbers of stat watchers,
		2381	as even with OS-supported change notifications, this can be
		2382	resource-intensive.
		2383
		2384	At the time of this writing, the only OS-specific interface implemented
		2385	is the Linux inotify interface (implementing kqueue support is left as an
		2386	exercise for the reader. Note, however, that the author sees no way of
		2387	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2388
		2389	=head3 ABI Issues (Largefile Support)
		2390
		2391	Libev by default (unless the user overrides this) uses the default
		2392	compilation environment, which means that on systems with large file
		2393	support disabled by default, you get the 32 bit version of the stat
		2394	structure. When using the library from programs that change the ABI to
		2395	use 64 bit file offsets the programs will fail. In that case you have to
		2396	compile libev with the same flags to get binary compatibility. This is
		2397	obviously the case with any flags that change the ABI, but the problem is
		2398	most noticeably displayed with ev_stat and large file support.
		2399
		2400	The solution for this is to lobby your distribution maker to make large
		2401	file interfaces available by default (as e.g. FreeBSD does) and not
		2402	optional. Libev cannot simply switch on large file support because it has
		2403	to exchange stat structures with application programs compiled using the
		2404	default compilation environment.
		2405
		2406	=head3 Inotify and Kqueue
		2407
		2408	When C<inotify (7)> support has been compiled into libev and present at
		2409	runtime, it will be used to speed up change detection where possible. The
		2410	inotify descriptor will be created lazily when the first C<ev_stat>
		2411	watcher is being started.
		2412
		2413	Inotify presence does not change the semantics of C<ev_stat> watchers
		2414	except that changes might be detected earlier, and in some cases, to avoid
		2415	making regular C<stat> calls. Even in the presence of inotify support
		2416	there are many cases where libev has to resort to regular C<stat> polling,
		2417	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2418	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2419	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2420	xfs are fully working) libev usually gets away without polling.
		2421
		2422	There is no support for kqueue, as apparently it cannot be used to
		2423	implement this functionality, due to the requirement of having a file
		2424	descriptor open on the object at all times, and detecting renames, unlinks
		2425	etc. is difficult.
		2426
		2427	=head3 C<stat ()> is a synchronous operation
		2428
		2429	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2430	the process. The exception are C<ev_stat> watchers - those call C<stat
		2431	()>, which is a synchronous operation.
		2432
		2433	For local paths, this usually doesn't matter: unless the system is very
		2434	busy or the intervals between stat's are large, a stat call will be fast,
		2435	as the path data is usually in memory already (except when starting the
		2436	watcher).
		2437
		2438	For networked file systems, calling C<stat ()> can block an indefinite
		2439	time due to network issues, and even under good conditions, a stat call
		2440	often takes multiple milliseconds.
		2441
		2442	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2443	paths, although this is fully supported by libev.
		2444
		2445	=head3 The special problem of stat time resolution
		2446
		2447	The C<stat ()> system call only supports full-second resolution portably,
		2448	and even on systems where the resolution is higher, most file systems
		2449	still only support whole seconds.
		2450
		2451	That means that, if the time is the only thing that changes, you can
		2452	easily miss updates: on the first update, C<ev_stat> detects a change and
		2453	calls your callback, which does something. When there is another update
		2454	within the same second, C<ev_stat> will be unable to detect unless the
		2455	stat data does change in other ways (e.g. file size).
		2456
		2457	The solution to this is to delay acting on a change for slightly more
		2458	than a second (or till slightly after the next full second boundary), using
		2459	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2460	ev_timer_again (loop, w)>).
		2461
		2462	The C<.02> offset is added to work around small timing inconsistencies
		2463	of some operating systems (where the second counter of the current time
		2464	might be be delayed. One such system is the Linux kernel, where a call to
		2465	C<gettimeofday> might return a timestamp with a full second later than
		2466	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2467	update file times then there will be a small window where the kernel uses
		2468	the previous second to update file times but libev might already execute
		2469	the timer callback).
		2470
		2471	=head3 Watcher-Specific Functions and Data Members
		2472
		2473	=over 4
		2474
		2475	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2476
		2477	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2478
		2479	Configures the watcher to wait for status changes of the given
		2480	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2481	be detected and should normally be specified as C<0> to let libev choose
		2482	a suitable value. The memory pointed to by C<path> must point to the same
		2483	path for as long as the watcher is active.
		2484
		2485	The callback will receive an C<EV_STAT> event when a change was detected,
		2486	relative to the attributes at the time the watcher was started (or the
		2487	last change was detected).
		2488
		2489	=item ev_stat_stat (loop, ev_stat *)
		2490
		2491	Updates the stat buffer immediately with new values. If you change the
		2492	watched path in your callback, you could call this function to avoid
		2493	detecting this change (while introducing a race condition if you are not
		2494	the only one changing the path). Can also be useful simply to find out the
		2495	new values.
		2496
		2497	=item ev_statdata attr [read-only]
		2498
		2499	The most-recently detected attributes of the file. Although the type is
		2500	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2501	suitable for your system, but you can only rely on the POSIX-standardised
		2502	members to be present. If the C<st_nlink> member is C<0>, then there was
		2503	some error while C<stat>ing the file.
		2504
		2505	=item ev_statdata prev [read-only]
		2506
		2507	The previous attributes of the file. The callback gets invoked whenever
		2508	C<prev> != C<attr>, or, more precisely, one or more of these members
		2509	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2510	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2511
		2512	=item ev_tstamp interval [read-only]
		2513
		2514	The specified interval.
		2515
		2516	=item const char *path [read-only]
		2517
		2518	The file system path that is being watched.
		2519
		2520	=back
		2521
		2522	=head3 Examples
		2523
		2524	Example: Watch C</etc/passwd> for attribute changes.
		2525
		2526	static void
		2527	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2528	{
		2529	/* /etc/passwd changed in some way */
		2530	if (w->attr.st_nlink)
		2531	{
		2532	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2533	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2534	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2535	}
		2536	else
		2537	/* you shalt not abuse printf for puts */
		2538	puts ("wow, /etc/passwd is not there, expect problems. "
		2539	"if this is windows, they already arrived\n");
		2540	}
		2541
		2542	...
		2543	ev_stat passwd;
		2544
		2545	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2546	ev_stat_start (loop, &passwd);
		2547
		2548	Example: Like above, but additionally use a one-second delay so we do not
		2549	miss updates (however, frequent updates will delay processing, too, so
		2550	one might do the work both on C<ev_stat> callback invocation I<and> on
		2551	C<ev_timer> callback invocation).
		2552
		2553	static ev_stat passwd;
		2554	static ev_timer timer;
		2555
		2556	static void
		2557	timer_cb (EV_P_ ev_timer *w, int revents)
		2558	{
		2559	ev_timer_stop (EV_A_ w);
		2560
		2561	/* now it's one second after the most recent passwd change */
		2562	}
		2563
		2564	static void
		2565	stat_cb (EV_P_ ev_stat *w, int revents)
		2566	{
		2567	/* reset the one-second timer */
		2568	ev_timer_again (EV_A_ &timer);
		2569	}
		2570
		2571	...
		2572	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2573	ev_stat_start (loop, &passwd);
		2574	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2575
		2576
644	=head2 C<ev_idle> - when you've got nothing better to do	2577	=head2 C<ev_idle> - when you've got nothing better to do...
645		2578
646	Idle watchers trigger events when there are no other events are pending	2579	Idle watchers trigger events when no other events of the same or higher
647	(prepare, check and other idle watchers do not count). That is, as long	2580	priority are pending (prepare, check and other idle watchers do not count
648	as your process is busy handling sockets or timeouts (or even signals,	2581	as receiving "events").
649	imagine) it will not be triggered. But when your process is idle all idle	2582
650	watchers are being called again and again, once per event loop iteration -	2583	That is, as long as your process is busy handling sockets or timeouts
		2584	(or even signals, imagine) of the same or higher priority it will not be
		2585	triggered. But when your process is idle (or only lower-priority watchers
		2586	are pending), the idle watchers are being called once per event loop
651	until stopped, that is, or your process receives more events and becomes	2587	iteration - until stopped, that is, or your process receives more events
652	busy.	2588	and becomes busy again with higher priority stuff.
653		2589
654	The most noteworthy effect is that as long as any idle watchers are	2590	The most noteworthy effect is that as long as any idle watchers are
655	active, the process will not block when waiting for new events.	2591	active, the process will not block when waiting for new events.
656		2592
657	Apart from keeping your process non-blocking (which is a useful	2593	Apart from keeping your process non-blocking (which is a useful
658	effect on its own sometimes), idle watchers are a good place to do	2594	effect on its own sometimes), idle watchers are a good place to do
659	"pseudo-background processing", or delay processing stuff to after the	2595	"pseudo-background processing", or delay processing stuff to after the
660	event loop has handled all outstanding events.	2596	event loop has handled all outstanding events.
661		2597
		2598	=head3 Watcher-Specific Functions and Data Members
		2599
662	=over 4	2600	=over 4
663		2601
664	=item ev_idle_init (ev_signal *, callback)	2602	=item ev_idle_init (ev_idle *, callback)
665		2603
666	Initialises and configures the idle watcher - it has no parameters of any	2604	Initialises and configures the idle watcher - it has no parameters of any
667	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2605	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
668	believe me.	2606	believe me.
669		2607
670	=back	2608	=back
671		2609
672	=head2 prepare and check - your hooks into the event loop	2610	=head3 Examples
673		2611
		2612	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2613	callback, free it. Also, use no error checking, as usual.
		2614
		2615	static void
		2616	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2617	{
		2618	free (w);
		2619	// now do something you wanted to do when the program has
		2620	// no longer anything immediate to do.
		2621	}
		2622
		2623	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2624	ev_idle_init (idle_watcher, idle_cb);
		2625	ev_idle_start (loop, idle_watcher);
		2626
		2627
		2628	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		2629
674	Prepare and check watchers are usually (but not always) used in tandem:	2630	Prepare and check watchers are usually (but not always) used in pairs:
675	Prepare watchers get invoked before the process blocks and check watchers	2631	prepare watchers get invoked before the process blocks and check watchers
676	afterwards.	2632	afterwards.
677		2633
		2634	You I<must not> call C<ev_loop> or similar functions that enter
		2635	the current event loop from either C<ev_prepare> or C<ev_check>
		2636	watchers. Other loops than the current one are fine, however. The
		2637	rationale behind this is that you do not need to check for recursion in
		2638	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2639	C<ev_check> so if you have one watcher of each kind they will always be
		2640	called in pairs bracketing the blocking call.
		2641
678	Their main purpose is to integrate other event mechanisms into libev. This	2642	Their main purpose is to integrate other event mechanisms into libev and
679	could be used, for example, to track variable changes, implement your own	2643	their use is somewhat advanced. They could be used, for example, to track
680	watchers, integrate net-snmp or a coroutine library and lots more.	2644	variable changes, implement your own watchers, integrate net-snmp or a
		2645	coroutine library and lots more. They are also occasionally useful if
		2646	you cache some data and want to flush it before blocking (for example,
		2647	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2648	watcher).
681		2649
682	This is done by examining in each prepare call which file descriptors need	2650	This is done by examining in each prepare call which file descriptors
683	to be watched by the other library, registering C<ev_io> watchers for	2651	need to be watched by the other library, registering C<ev_io> watchers
684	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2652	for them and starting an C<ev_timer> watcher for any timeouts (many
685	provide just this functionality). Then, in the check watcher you check for	2653	libraries provide exactly this functionality). Then, in the check watcher,
686	any events that occured (by checking the pending status of all watchers	2654	you check for any events that occurred (by checking the pending status
687	and stopping them) and call back into the library. The I/O and timer	2655	of all watchers and stopping them) and call back into the library. The
688	callbacks will never actually be called (but must be valid neverthelles,	2656	I/O and timer callbacks will never actually be called (but must be valid
689	because you never know, you know?).	2657	nevertheless, because you never know, you know?).
690		2658
691	As another example, the Perl Coro module uses these hooks to integrate	2659	As another example, the Perl Coro module uses these hooks to integrate
692	coroutines into libev programs, by yielding to other active coroutines	2660	coroutines into libev programs, by yielding to other active coroutines
693	during each prepare and only letting the process block if no coroutines	2661	during each prepare and only letting the process block if no coroutines
694	are ready to run (its actually more complicated, it only runs coroutines	2662	are ready to run (it's actually more complicated: it only runs coroutines
695	with priority higher than the event loop and one lower priority once,	2663	with priority higher than or equal to the event loop and one coroutine
696	using idle watchers to keep the event loop from blocking if lower-priority	2664	of lower priority, but only once, using idle watchers to keep the event
697	coroutines exist, thus mapping low-priority coroutines to idle/background	2665	loop from blocking if lower-priority coroutines are active, thus mapping
698	tasks).	2666	low-priority coroutines to idle/background tasks).
		2667
		2668	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2669	priority, to ensure that they are being run before any other watchers
		2670	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2671
		2672	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2673	activate ("feed") events into libev. While libev fully supports this, they
		2674	might get executed before other C<ev_check> watchers did their job. As
		2675	C<ev_check> watchers are often used to embed other (non-libev) event
		2676	loops those other event loops might be in an unusable state until their
		2677	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2678	others).
		2679
		2680	=head3 Watcher-Specific Functions and Data Members
699		2681
700	=over 4	2682	=over 4
701		2683
702	=item ev_prepare_init (ev_prepare *, callback)	2684	=item ev_prepare_init (ev_prepare *, callback)
703		2685
704	=item ev_check_init (ev_check *, callback)	2686	=item ev_check_init (ev_check *, callback)
705		2687
706	Initialises and configures the prepare or check watcher - they have no	2688	Initialises and configures the prepare or check watcher - they have no
707	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2689	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
708	macros, but using them is utterly, utterly and completely pointless.	2690	macros, but using them is utterly, utterly, utterly and completely
		2691	pointless.
709		2692
710	=back	2693	=back
711		2694
		2695	=head3 Examples
		2696
		2697	There are a number of principal ways to embed other event loops or modules
		2698	into libev. Here are some ideas on how to include libadns into libev
		2699	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2700	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2701	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2702	Glib event loop).
		2703
		2704	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2705	and in a check watcher, destroy them and call into libadns. What follows
		2706	is pseudo-code only of course. This requires you to either use a low
		2707	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2708	the callbacks for the IO/timeout watchers might not have been called yet.
		2709
		2710	static ev_io iow [nfd];
		2711	static ev_timer tw;
		2712
		2713	static void
		2714	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2715	{
		2716	}
		2717
		2718	// create io watchers for each fd and a timer before blocking
		2719	static void
		2720	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2721	{
		2722	int timeout = 3600000;
		2723	struct pollfd fds [nfd];
		2724	// actual code will need to loop here and realloc etc.
		2725	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2726
		2727	/* the callback is illegal, but won't be called as we stop during check */
		2728	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		2729	ev_timer_start (loop, &tw);
		2730
		2731	// create one ev_io per pollfd
		2732	for (int i = 0; i < nfd; ++i)
		2733	{
		2734	ev_io_init (iow + i, io_cb, fds [i].fd,
		2735	((fds [i].events & POLLIN ? EV_READ : 0)
		2736	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2737
		2738	fds [i].revents = 0;
		2739	ev_io_start (loop, iow + i);
		2740	}
		2741	}
		2742
		2743	// stop all watchers after blocking
		2744	static void
		2745	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2746	{
		2747	ev_timer_stop (loop, &tw);
		2748
		2749	for (int i = 0; i < nfd; ++i)
		2750	{
		2751	// set the relevant poll flags
		2752	// could also call adns_processreadable etc. here
		2753	struct pollfd *fd = fds + i;
		2754	int revents = ev_clear_pending (iow + i);
		2755	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2756	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2757
		2758	// now stop the watcher
		2759	ev_io_stop (loop, iow + i);
		2760	}
		2761
		2762	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2763	}
		2764
		2765	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2766	in the prepare watcher and would dispose of the check watcher.
		2767
		2768	Method 3: If the module to be embedded supports explicit event
		2769	notification (libadns does), you can also make use of the actual watcher
		2770	callbacks, and only destroy/create the watchers in the prepare watcher.
		2771
		2772	static void
		2773	timer_cb (EV_P_ ev_timer *w, int revents)
		2774	{
		2775	adns_state ads = (adns_state)w->data;
		2776	update_now (EV_A);
		2777
		2778	adns_processtimeouts (ads, &tv_now);
		2779	}
		2780
		2781	static void
		2782	io_cb (EV_P_ ev_io *w, int revents)
		2783	{
		2784	adns_state ads = (adns_state)w->data;
		2785	update_now (EV_A);
		2786
		2787	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2788	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2789	}
		2790
		2791	// do not ever call adns_afterpoll
		2792
		2793	Method 4: Do not use a prepare or check watcher because the module you
		2794	want to embed is not flexible enough to support it. Instead, you can
		2795	override their poll function. The drawback with this solution is that the
		2796	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2797	this approach, effectively embedding EV as a client into the horrible
		2798	libglib event loop.
		2799
		2800	static gint
		2801	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2802	{
		2803	int got_events = 0;
		2804
		2805	for (n = 0; n < nfds; ++n)
		2806	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2807
		2808	if (timeout >= 0)
		2809	// create/start timer
		2810
		2811	// poll
		2812	ev_loop (EV_A_ 0);
		2813
		2814	// stop timer again
		2815	if (timeout >= 0)
		2816	ev_timer_stop (EV_A_ &to);
		2817
		2818	// stop io watchers again - their callbacks should have set
		2819	for (n = 0; n < nfds; ++n)
		2820	ev_io_stop (EV_A_ iow [n]);
		2821
		2822	return got_events;
		2823	}
		2824
		2825
		2826	=head2 C<ev_embed> - when one backend isn't enough...
		2827
		2828	This is a rather advanced watcher type that lets you embed one event loop
		2829	into another (currently only C<ev_io> events are supported in the embedded
		2830	loop, other types of watchers might be handled in a delayed or incorrect
		2831	fashion and must not be used).
		2832
		2833	There are primarily two reasons you would want that: work around bugs and
		2834	prioritise I/O.
		2835
		2836	As an example for a bug workaround, the kqueue backend might only support
		2837	sockets on some platform, so it is unusable as generic backend, but you
		2838	still want to make use of it because you have many sockets and it scales
		2839	so nicely. In this case, you would create a kqueue-based loop and embed
		2840	it into your default loop (which might use e.g. poll). Overall operation
		2841	will be a bit slower because first libev has to call C<poll> and then
		2842	C<kevent>, but at least you can use both mechanisms for what they are
		2843	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2844
		2845	As for prioritising I/O: under rare circumstances you have the case where
		2846	some fds have to be watched and handled very quickly (with low latency),
		2847	and even priorities and idle watchers might have too much overhead. In
		2848	this case you would put all the high priority stuff in one loop and all
		2849	the rest in a second one, and embed the second one in the first.
		2850
		2851	As long as the watcher is active, the callback will be invoked every
		2852	time there might be events pending in the embedded loop. The callback
		2853	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		2854	sweep and invoke their callbacks (the callback doesn't need to invoke the
		2855	C<ev_embed_sweep> function directly, it could also start an idle watcher
		2856	to give the embedded loop strictly lower priority for example).
		2857
		2858	You can also set the callback to C<0>, in which case the embed watcher
		2859	will automatically execute the embedded loop sweep whenever necessary.
		2860
		2861	Fork detection will be handled transparently while the C<ev_embed> watcher
		2862	is active, i.e., the embedded loop will automatically be forked when the
		2863	embedding loop forks. In other cases, the user is responsible for calling
		2864	C<ev_loop_fork> on the embedded loop.
		2865
		2866	Unfortunately, not all backends are embeddable: only the ones returned by
		2867	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2868	portable one.
		2869
		2870	So when you want to use this feature you will always have to be prepared
		2871	that you cannot get an embeddable loop. The recommended way to get around
		2872	this is to have a separate variables for your embeddable loop, try to
		2873	create it, and if that fails, use the normal loop for everything.
		2874
		2875	=head3 C<ev_embed> and fork
		2876
		2877	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2878	automatically be applied to the embedded loop as well, so no special
		2879	fork handling is required in that case. When the watcher is not running,
		2880	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2881	as applicable.
		2882
		2883	=head3 Watcher-Specific Functions and Data Members
		2884
		2885	=over 4
		2886
		2887	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2888
		2889	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2890
		2891	Configures the watcher to embed the given loop, which must be
		2892	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2893	invoked automatically, otherwise it is the responsibility of the callback
		2894	to invoke it (it will continue to be called until the sweep has been done,
		2895	if you do not want that, you need to temporarily stop the embed watcher).
		2896
		2897	=item ev_embed_sweep (loop, ev_embed *)
		2898
		2899	Make a single, non-blocking sweep over the embedded loop. This works
		2900	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2901	appropriate way for embedded loops.
		2902
		2903	=item struct ev_loop *other [read-only]
		2904
		2905	The embedded event loop.
		2906
		2907	=back
		2908
		2909	=head3 Examples
		2910
		2911	Example: Try to get an embeddable event loop and embed it into the default
		2912	event loop. If that is not possible, use the default loop. The default
		2913	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2914	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2915	used).
		2916
		2917	struct ev_loop *loop_hi = ev_default_init (0);
		2918	struct ev_loop *loop_lo = 0;
		2919	ev_embed embed;
		2920
		2921	// see if there is a chance of getting one that works
		2922	// (remember that a flags value of 0 means autodetection)
		2923	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2924	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2925	: 0;
		2926
		2927	// if we got one, then embed it, otherwise default to loop_hi
		2928	if (loop_lo)
		2929	{
		2930	ev_embed_init (&embed, 0, loop_lo);
		2931	ev_embed_start (loop_hi, &embed);
		2932	}
		2933	else
		2934	loop_lo = loop_hi;
		2935
		2936	Example: Check if kqueue is available but not recommended and create
		2937	a kqueue backend for use with sockets (which usually work with any
		2938	kqueue implementation). Store the kqueue/socket-only event loop in
		2939	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2940
		2941	struct ev_loop *loop = ev_default_init (0);
		2942	struct ev_loop *loop_socket = 0;
		2943	ev_embed embed;
		2944
		2945	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2946	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2947	{
		2948	ev_embed_init (&embed, 0, loop_socket);
		2949	ev_embed_start (loop, &embed);
		2950	}
		2951
		2952	if (!loop_socket)
		2953	loop_socket = loop;
		2954
		2955	// now use loop_socket for all sockets, and loop for everything else
		2956
		2957
		2958	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2959
		2960	Fork watchers are called when a C<fork ()> was detected (usually because
		2961	whoever is a good citizen cared to tell libev about it by calling
		2962	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2963	event loop blocks next and before C<ev_check> watchers are being called,
		2964	and only in the child after the fork. If whoever good citizen calling
		2965	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2966	handlers will be invoked, too, of course.
		2967
		2968	=head3 The special problem of life after fork - how is it possible?
		2969
		2970	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2971	up/change the process environment, followed by a call to C<exec()>. This
		2972	sequence should be handled by libev without any problems.
		2973
		2974	This changes when the application actually wants to do event handling
		2975	in the child, or both parent in child, in effect "continuing" after the
		2976	fork.
		2977
		2978	The default mode of operation (for libev, with application help to detect
		2979	forks) is to duplicate all the state in the child, as would be expected
		2980	when I<either> the parent I<or> the child process continues.
		2981
		2982	When both processes want to continue using libev, then this is usually the
		2983	wrong result. In that case, usually one process (typically the parent) is
		2984	supposed to continue with all watchers in place as before, while the other
		2985	process typically wants to start fresh, i.e. without any active watchers.
		2986
		2987	The cleanest and most efficient way to achieve that with libev is to
		2988	simply create a new event loop, which of course will be "empty", and
		2989	use that for new watchers. This has the advantage of not touching more
		2990	memory than necessary, and thus avoiding the copy-on-write, and the
		2991	disadvantage of having to use multiple event loops (which do not support
		2992	signal watchers).
		2993
		2994	When this is not possible, or you want to use the default loop for
		2995	other reasons, then in the process that wants to start "fresh", call
		2996	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2997	the default loop will "orphan" (not stop) all registered watchers, so you
		2998	have to be careful not to execute code that modifies those watchers. Note
		2999	also that in that case, you have to re-register any signal watchers.
		3000
		3001	=head3 Watcher-Specific Functions and Data Members
		3002
		3003	=over 4
		3004
		3005	=item ev_fork_init (ev_signal *, callback)
		3006
		3007	Initialises and configures the fork watcher - it has no parameters of any
		3008	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3009	believe me.
		3010
		3011	=back
		3012
		3013
		3014	=head2 C<ev_async> - how to wake up another event loop
		3015
		3016	In general, you cannot use an C<ev_loop> from multiple threads or other
		3017	asynchronous sources such as signal handlers (as opposed to multiple event
		3018	loops - those are of course safe to use in different threads).
		3019
		3020	Sometimes, however, you need to wake up another event loop you do not
		3021	control, for example because it belongs to another thread. This is what
		3022	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		3023	can signal it by calling C<ev_async_send>, which is thread- and signal
		3024	safe.
		3025
		3026	This functionality is very similar to C<ev_signal> watchers, as signals,
		3027	too, are asynchronous in nature, and signals, too, will be compressed
		3028	(i.e. the number of callback invocations may be less than the number of
		3029	C<ev_async_sent> calls).
		3030
		3031	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3032	just the default loop.
		3033
		3034	=head3 Queueing
		3035
		3036	C<ev_async> does not support queueing of data in any way. The reason
		3037	is that the author does not know of a simple (or any) algorithm for a
		3038	multiple-writer-single-reader queue that works in all cases and doesn't
		3039	need elaborate support such as pthreads or unportable memory access
		3040	semantics.
		3041
		3042	That means that if you want to queue data, you have to provide your own
		3043	queue. But at least I can tell you how to implement locking around your
		3044	queue:
		3045
		3046	=over 4
		3047
		3048	=item queueing from a signal handler context
		3049
		3050	To implement race-free queueing, you simply add to the queue in the signal
		3051	handler but you block the signal handler in the watcher callback. Here is
		3052	an example that does that for some fictitious SIGUSR1 handler:
		3053
		3054	static ev_async mysig;
		3055
		3056	static void
		3057	sigusr1_handler (void)
		3058	{
		3059	sometype data;
		3060
		3061	// no locking etc.
		3062	queue_put (data);
		3063	ev_async_send (EV_DEFAULT_ &mysig);
		3064	}
		3065
		3066	static void
		3067	mysig_cb (EV_P_ ev_async *w, int revents)
		3068	{
		3069	sometype data;
		3070	sigset_t block, prev;
		3071
		3072	sigemptyset (&block);
		3073	sigaddset (&block, SIGUSR1);
		3074	sigprocmask (SIG_BLOCK, &block, &prev);
		3075
		3076	while (queue_get (&data))
		3077	process (data);
		3078
		3079	if (sigismember (&prev, SIGUSR1)
		3080	sigprocmask (SIG_UNBLOCK, &block, 0);
		3081	}
		3082
		3083	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3084	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3085	either...).
		3086
		3087	=item queueing from a thread context
		3088
		3089	The strategy for threads is different, as you cannot (easily) block
		3090	threads but you can easily preempt them, so to queue safely you need to
		3091	employ a traditional mutex lock, such as in this pthread example:
		3092
		3093	static ev_async mysig;
		3094	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3095
		3096	static void
		3097	otherthread (void)
		3098	{
		3099	// only need to lock the actual queueing operation
		3100	pthread_mutex_lock (&mymutex);
		3101	queue_put (data);
		3102	pthread_mutex_unlock (&mymutex);
		3103
		3104	ev_async_send (EV_DEFAULT_ &mysig);
		3105	}
		3106
		3107	static void
		3108	mysig_cb (EV_P_ ev_async *w, int revents)
		3109	{
		3110	pthread_mutex_lock (&mymutex);
		3111
		3112	while (queue_get (&data))
		3113	process (data);
		3114
		3115	pthread_mutex_unlock (&mymutex);
		3116	}
		3117
		3118	=back
		3119
		3120
		3121	=head3 Watcher-Specific Functions and Data Members
		3122
		3123	=over 4
		3124
		3125	=item ev_async_init (ev_async *, callback)
		3126
		3127	Initialises and configures the async watcher - it has no parameters of any
		3128	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3129	trust me.
		3130
		3131	=item ev_async_send (loop, ev_async *)
		3132
		3133	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3134	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3135	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3136	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3137	section below on what exactly this means).
		3138
		3139	Note that, as with other watchers in libev, multiple events might get
		3140	compressed into a single callback invocation (another way to look at this
		3141	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3142	reset when the event loop detects that).
		3143
		3144	This call incurs the overhead of a system call only once per event loop
		3145	iteration, so while the overhead might be noticeable, it doesn't apply to
		3146	repeated calls to C<ev_async_send> for the same event loop.
		3147
		3148	=item bool = ev_async_pending (ev_async *)
		3149
		3150	Returns a non-zero value when C<ev_async_send> has been called on the
		3151	watcher but the event has not yet been processed (or even noted) by the
		3152	event loop.
		3153
		3154	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3155	the loop iterates next and checks for the watcher to have become active,
		3156	it will reset the flag again. C<ev_async_pending> can be used to very
		3157	quickly check whether invoking the loop might be a good idea.
		3158
		3159	Not that this does I<not> check whether the watcher itself is pending,
		3160	only whether it has been requested to make this watcher pending: there
		3161	is a time window between the event loop checking and resetting the async
		3162	notification, and the callback being invoked.
		3163
		3164	=back
		3165
		3166
712	=head1 OTHER FUNCTIONS	3167	=head1 OTHER FUNCTIONS
713		3168
714	There are some other functions of possible interest. Described. Here. Now.	3169	There are some other functions of possible interest. Described. Here. Now.
715		3170
716	=over 4	3171	=over 4
717		3172
718	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3173	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
719		3174
720	This function combines a simple timer and an I/O watcher, calls your	3175	This function combines a simple timer and an I/O watcher, calls your
721	callback on whichever event happens first and automatically stop both	3176	callback on whichever event happens first and automatically stops both
722	watchers. This is useful if you want to wait for a single event on an fd	3177	watchers. This is useful if you want to wait for a single event on an fd
723	or timeout without havign to allocate/configure/start/stop/free one or	3178	or timeout without having to allocate/configure/start/stop/free one or
724	more watchers yourself.	3179	more watchers yourself.
725		3180
726	If C<fd> is less than 0, then no I/O watcher will be started and events	3181	If C<fd> is less than 0, then no I/O watcher will be started and the
727	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3182	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
728	C<events> set will be craeted and started.	3183	the given C<fd> and C<events> set will be created and started.
729		3184
730	If C<timeout> is less than 0, then no timeout watcher will be	3185	If C<timeout> is less than 0, then no timeout watcher will be
731	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3186	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
732	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3187	repeat = 0) will be started. C<0> is a valid timeout.
733	dubious value.
734		3188
735	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3189	The callback has the type C<void (*cb)(int revents, void *arg)> and is
736	passed an events set like normal event callbacks (with a combination of	3190	passed an C<revents> set like normal event callbacks (a combination of
737	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3191	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
738	value passed to C<ev_once>:	3192	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3193	a timeout and an io event at the same time - you probably should give io
		3194	events precedence.
739		3195
		3196	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3197
740	static void stdin_ready (int revents, void *arg)	3198	static void stdin_ready (int revents, void *arg)
741	{	3199	{
742	if (revents & EV_TIMEOUT)
743	/* doh, nothing entered */;
744	else if (revents & EV_READ)	3200	if (revents & EV_READ)
745	/* stdin might have data for us, joy! */;	3201	/* stdin might have data for us, joy! */;
		3202	else if (revents & EV_TIMER)
		3203	/* doh, nothing entered */;
746	}	3204	}
747		3205
748	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3206	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
749
750	=item ev_feed_event (loop, watcher, int events)
751
752	Feeds the given event set into the event loop, as if the specified event
753	had happened for the specified watcher (which must be a pointer to an
754	initialised but not necessarily started event watcher).
755		3207
756	=item ev_feed_fd_event (loop, int fd, int revents)	3208	=item ev_feed_fd_event (loop, int fd, int revents)
757		3209
758	Feed an event on the given fd, as if a file descriptor backend detected	3210	Feed an event on the given fd, as if a file descriptor backend detected
759	the given events it.	3211	the given events it.
760		3212
761	=item ev_feed_signal_event (loop, int signum)	3213	=item ev_feed_signal_event (loop, int signum)
762		3214
763	Feed an event as if the given signal occured (loop must be the default loop!).	3215	Feed an event as if the given signal occurred (C<loop> must be the default
		3216	loop!).
764		3217
765	=back	3218	=back
766		3219
		3220
		3221	=head1 LIBEVENT EMULATION
		3222
		3223	Libev offers a compatibility emulation layer for libevent. It cannot
		3224	emulate the internals of libevent, so here are some usage hints:
		3225
		3226	=over 4
		3227
		3228	=item * Use it by including <event.h>, as usual.
		3229
		3230	=item * The following members are fully supported: ev_base, ev_callback,
		3231	ev_arg, ev_fd, ev_res, ev_events.
		3232
		3233	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		3234	maintained by libev, it does not work exactly the same way as in libevent (consider
		3235	it a private API).
		3236
		3237	=item * Priorities are not currently supported. Initialising priorities
		3238	will fail and all watchers will have the same priority, even though there
		3239	is an ev_pri field.
		3240
		3241	=item * In libevent, the last base created gets the signals, in libev, the
		3242	first base created (== the default loop) gets the signals.
		3243
		3244	=item * Other members are not supported.
		3245
		3246	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		3247	to use the libev header file and library.
		3248
		3249	=back
		3250
		3251	=head1 C++ SUPPORT
		3252
		3253	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3254	you to use some convenience methods to start/stop watchers and also change
		3255	the callback model to a model using method callbacks on objects.
		3256
		3257	To use it,
		3258
		3259	#include <ev++.h>
		3260
		3261	This automatically includes F<ev.h> and puts all of its definitions (many
		3262	of them macros) into the global namespace. All C++ specific things are
		3263	put into the C<ev> namespace. It should support all the same embedding
		3264	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3265
		3266	Care has been taken to keep the overhead low. The only data member the C++
		3267	classes add (compared to plain C-style watchers) is the event loop pointer
		3268	that the watcher is associated with (or no additional members at all if
		3269	you disable C<EV_MULTIPLICITY> when embedding libev).
		3270
		3271	Currently, functions, and static and non-static member functions can be
		3272	used as callbacks. Other types should be easy to add as long as they only
		3273	need one additional pointer for context. If you need support for other
		3274	types of functors please contact the author (preferably after implementing
		3275	it).
		3276
		3277	Here is a list of things available in the C<ev> namespace:
		3278
		3279	=over 4
		3280
		3281	=item C<ev::READ>, C<ev::WRITE> etc.
		3282
		3283	These are just enum values with the same values as the C<EV_READ> etc.
		3284	macros from F<ev.h>.
		3285
		3286	=item C<ev::tstamp>, C<ev::now>
		3287
		3288	Aliases to the same types/functions as with the C<ev_> prefix.
		3289
		3290	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		3291
		3292	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		3293	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		3294	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3295	defines by many implementations.
		3296
		3297	All of those classes have these methods:
		3298
		3299	=over 4
		3300
		3301	=item ev::TYPE::TYPE ()
		3302
		3303	=item ev::TYPE::TYPE (loop)
		3304
		3305	=item ev::TYPE::~TYPE
		3306
		3307	The constructor (optionally) takes an event loop to associate the watcher
		3308	with. If it is omitted, it will use C<EV_DEFAULT>.
		3309
		3310	The constructor calls C<ev_init> for you, which means you have to call the
		3311	C<set> method before starting it.
		3312
		3313	It will not set a callback, however: You have to call the templated C<set>
		3314	method to set a callback before you can start the watcher.
		3315
		3316	(The reason why you have to use a method is a limitation in C++ which does
		3317	not allow explicit template arguments for constructors).
		3318
		3319	The destructor automatically stops the watcher if it is active.
		3320
		3321	=item w->set<class, &class::method> (object *)
		3322
		3323	This method sets the callback method to call. The method has to have a
		3324	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3325	first argument and the C<revents> as second. The object must be given as
		3326	parameter and is stored in the C<data> member of the watcher.
		3327
		3328	This method synthesizes efficient thunking code to call your method from
		3329	the C callback that libev requires. If your compiler can inline your
		3330	callback (i.e. it is visible to it at the place of the C<set> call and
		3331	your compiler is good :), then the method will be fully inlined into the
		3332	thunking function, making it as fast as a direct C callback.
		3333
		3334	Example: simple class declaration and watcher initialisation
		3335
		3336	struct myclass
		3337	{
		3338	void io_cb (ev::io &w, int revents) { }
		3339	}
		3340
		3341	myclass obj;
		3342	ev::io iow;
		3343	iow.set <myclass, &myclass::io_cb> (&obj);
		3344
		3345	=item w->set (object *)
		3346
		3347	This is a variation of a method callback - leaving out the method to call
		3348	will default the method to C<operator ()>, which makes it possible to use
		3349	functor objects without having to manually specify the C<operator ()> all
		3350	the time. Incidentally, you can then also leave out the template argument
		3351	list.
		3352
		3353	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3354	int revents)>.
		3355
		3356	See the method-C<set> above for more details.
		3357
		3358	Example: use a functor object as callback.
		3359
		3360	struct myfunctor
		3361	{
		3362	void operator() (ev::io &w, int revents)
		3363	{
		3364	...
		3365	}
		3366	}
		3367
		3368	myfunctor f;
		3369
		3370	ev::io w;
		3371	w.set (&f);
		3372
		3373	=item w->set<function> (void *data = 0)
		3374
		3375	Also sets a callback, but uses a static method or plain function as
		3376	callback. The optional C<data> argument will be stored in the watcher's
		3377	C<data> member and is free for you to use.
		3378
		3379	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3380
		3381	See the method-C<set> above for more details.
		3382
		3383	Example: Use a plain function as callback.
		3384
		3385	static void io_cb (ev::io &w, int revents) { }
		3386	iow.set <io_cb> ();
		3387
		3388	=item w->set (loop)
		3389
		3390	Associates a different C<struct ev_loop> with this watcher. You can only
		3391	do this when the watcher is inactive (and not pending either).
		3392
		3393	=item w->set ([arguments])
		3394
		3395	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		3396	called at least once. Unlike the C counterpart, an active watcher gets
		3397	automatically stopped and restarted when reconfiguring it with this
		3398	method.
		3399
		3400	=item w->start ()
		3401
		3402	Starts the watcher. Note that there is no C<loop> argument, as the
		3403	constructor already stores the event loop.
		3404
		3405	=item w->stop ()
		3406
		3407	Stops the watcher if it is active. Again, no C<loop> argument.
		3408
		3409	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		3410
		3411	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		3412	C<ev_TYPE_again> function.
		3413
		3414	=item w->sweep () (C<ev::embed> only)
		3415
		3416	Invokes C<ev_embed_sweep>.
		3417
		3418	=item w->update () (C<ev::stat> only)
		3419
		3420	Invokes C<ev_stat_stat>.
		3421
		3422	=back
		3423
		3424	=back
		3425
		3426	Example: Define a class with an IO and idle watcher, start one of them in
		3427	the constructor.
		3428
		3429	class myclass
		3430	{
		3431	ev::io io ; void io_cb (ev::io &w, int revents);
		3432	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3433
		3434	myclass (int fd)
		3435	{
		3436	io .set <myclass, &myclass::io_cb > (this);
		3437	idle.set <myclass, &myclass::idle_cb> (this);
		3438
		3439	io.start (fd, ev::READ);
		3440	}
		3441	};
		3442
		3443
		3444	=head1 OTHER LANGUAGE BINDINGS
		3445
		3446	Libev does not offer other language bindings itself, but bindings for a
		3447	number of languages exist in the form of third-party packages. If you know
		3448	any interesting language binding in addition to the ones listed here, drop
		3449	me a note.
		3450
		3451	=over 4
		3452
		3453	=item Perl
		3454
		3455	The EV module implements the full libev API and is actually used to test
		3456	libev. EV is developed together with libev. Apart from the EV core module,
		3457	there are additional modules that implement libev-compatible interfaces
		3458	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3459	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3460	and C<EV::Glib>).
		3461
		3462	It can be found and installed via CPAN, its homepage is at
		3463	L<http://software.schmorp.de/pkg/EV>.
		3464
		3465	=item Python
		3466
		3467	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3468	seems to be quite complete and well-documented.
		3469
		3470	=item Ruby
		3471
		3472	Tony Arcieri has written a ruby extension that offers access to a subset
		3473	of the libev API and adds file handle abstractions, asynchronous DNS and
		3474	more on top of it. It can be found via gem servers. Its homepage is at
		3475	L<http://rev.rubyforge.org/>.
		3476
		3477	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3478	makes rev work even on mingw.
		3479
		3480	=item Haskell
		3481
		3482	A haskell binding to libev is available at
		3483	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3484
		3485	=item D
		3486
		3487	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3488	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3489
		3490	=item Ocaml
		3491
		3492	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3493	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3494
		3495	=item Lua
		3496
		3497	Brian Maher has written a partial interface to libev for lua (at the
		3498	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3499	L<http://github.com/brimworks/lua-ev>.
		3500
		3501	=back
		3502
		3503
		3504	=head1 MACRO MAGIC
		3505
		3506	Libev can be compiled with a variety of options, the most fundamental
		3507	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3508	functions and callbacks have an initial C<struct ev_loop *> argument.
		3509
		3510	To make it easier to write programs that cope with either variant, the
		3511	following macros are defined:
		3512
		3513	=over 4
		3514
		3515	=item C<EV_A>, C<EV_A_>
		3516
		3517	This provides the loop I<argument> for functions, if one is required ("ev
		3518	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3519	C<EV_A_> is used when other arguments are following. Example:
		3520
		3521	ev_unref (EV_A);
		3522	ev_timer_add (EV_A_ watcher);
		3523	ev_loop (EV_A_ 0);
		3524
		3525	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3526	which is often provided by the following macro.
		3527
		3528	=item C<EV_P>, C<EV_P_>
		3529
		3530	This provides the loop I<parameter> for functions, if one is required ("ev
		3531	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3532	C<EV_P_> is used when other parameters are following. Example:
		3533
		3534	// this is how ev_unref is being declared
		3535	static void ev_unref (EV_P);
		3536
		3537	// this is how you can declare your typical callback
		3538	static void cb (EV_P_ ev_timer *w, int revents)
		3539
		3540	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3541	suitable for use with C<EV_A>.
		3542
		3543	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3544
		3545	Similar to the other two macros, this gives you the value of the default
		3546	loop, if multiple loops are supported ("ev loop default").
		3547
		3548	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3549
		3550	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3551	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3552	is undefined when the default loop has not been initialised by a previous
		3553	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3554
		3555	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3556	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3557
		3558	=back
		3559
		3560	Example: Declare and initialise a check watcher, utilising the above
		3561	macros so it will work regardless of whether multiple loops are supported
		3562	or not.
		3563
		3564	static void
		3565	check_cb (EV_P_ ev_timer *w, int revents)
		3566	{
		3567	ev_check_stop (EV_A_ w);
		3568	}
		3569
		3570	ev_check check;
		3571	ev_check_init (&check, check_cb);
		3572	ev_check_start (EV_DEFAULT_ &check);
		3573	ev_loop (EV_DEFAULT_ 0);
		3574
		3575	=head1 EMBEDDING
		3576
		3577	Libev can (and often is) directly embedded into host
		3578	applications. Examples of applications that embed it include the Deliantra
		3579	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3580	and rxvt-unicode.
		3581
		3582	The goal is to enable you to just copy the necessary files into your
		3583	source directory without having to change even a single line in them, so
		3584	you can easily upgrade by simply copying (or having a checked-out copy of
		3585	libev somewhere in your source tree).
		3586
		3587	=head2 FILESETS
		3588
		3589	Depending on what features you need you need to include one or more sets of files
		3590	in your application.
		3591
		3592	=head3 CORE EVENT LOOP
		3593
		3594	To include only the libev core (all the C<ev_*> functions), with manual
		3595	configuration (no autoconf):
		3596
		3597	#define EV_STANDALONE 1
		3598	#include "ev.c"
		3599
		3600	This will automatically include F<ev.h>, too, and should be done in a
		3601	single C source file only to provide the function implementations. To use
		3602	it, do the same for F<ev.h> in all files wishing to use this API (best
		3603	done by writing a wrapper around F<ev.h> that you can include instead and
		3604	where you can put other configuration options):
		3605
		3606	#define EV_STANDALONE 1
		3607	#include "ev.h"
		3608
		3609	Both header files and implementation files can be compiled with a C++
		3610	compiler (at least, that's a stated goal, and breakage will be treated
		3611	as a bug).
		3612
		3613	You need the following files in your source tree, or in a directory
		3614	in your include path (e.g. in libev/ when using -Ilibev):
		3615
		3616	ev.h
		3617	ev.c
		3618	ev_vars.h
		3619	ev_wrap.h
		3620
		3621	ev_win32.c required on win32 platforms only
		3622
		3623	ev_select.c only when select backend is enabled (which is enabled by default)
		3624	ev_poll.c only when poll backend is enabled (disabled by default)
		3625	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3626	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3627	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3628
		3629	F<ev.c> includes the backend files directly when enabled, so you only need
		3630	to compile this single file.
		3631
		3632	=head3 LIBEVENT COMPATIBILITY API
		3633
		3634	To include the libevent compatibility API, also include:
		3635
		3636	#include "event.c"
		3637
		3638	in the file including F<ev.c>, and:
		3639
		3640	#include "event.h"
		3641
		3642	in the files that want to use the libevent API. This also includes F<ev.h>.
		3643
		3644	You need the following additional files for this:
		3645
		3646	event.h
		3647	event.c
		3648
		3649	=head3 AUTOCONF SUPPORT
		3650
		3651	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3652	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3653	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3654	include F<config.h> and configure itself accordingly.
		3655
		3656	For this of course you need the m4 file:
		3657
		3658	libev.m4
		3659
		3660	=head2 PREPROCESSOR SYMBOLS/MACROS
		3661
		3662	Libev can be configured via a variety of preprocessor symbols you have to
		3663	define before including (or compiling) any of its files. The default in
		3664	the absence of autoconf is documented for every option.
		3665
		3666	Symbols marked with "(h)" do not change the ABI, and can have different
		3667	values when compiling libev vs. including F<ev.h>, so it is permissible
		3668	to redefine them before including F<ev.h> without breaking compatibility
		3669	to a compiled library. All other symbols change the ABI, which means all
		3670	users of libev and the libev code itself must be compiled with compatible
		3671	settings.
		3672
		3673	=over 4
		3674
		3675	=item EV_STANDALONE (h)
		3676
		3677	Must always be C<1> if you do not use autoconf configuration, which
		3678	keeps libev from including F<config.h>, and it also defines dummy
		3679	implementations for some libevent functions (such as logging, which is not
		3680	supported). It will also not define any of the structs usually found in
		3681	F<event.h> that are not directly supported by the libev core alone.
		3682
		3683	In standalone mode, libev will still try to automatically deduce the
		3684	configuration, but has to be more conservative.
		3685
		3686	=item EV_USE_MONOTONIC
		3687
		3688	If defined to be C<1>, libev will try to detect the availability of the
		3689	monotonic clock option at both compile time and runtime. Otherwise no
		3690	use of the monotonic clock option will be attempted. If you enable this,
		3691	you usually have to link against librt or something similar. Enabling it
		3692	when the functionality isn't available is safe, though, although you have
		3693	to make sure you link against any libraries where the C<clock_gettime>
		3694	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3695
		3696	=item EV_USE_REALTIME
		3697
		3698	If defined to be C<1>, libev will try to detect the availability of the
		3699	real-time clock option at compile time (and assume its availability
		3700	at runtime if successful). Otherwise no use of the real-time clock
		3701	option will be attempted. This effectively replaces C<gettimeofday>
		3702	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		3703	correctness. See the note about libraries in the description of
		3704	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3705	C<EV_USE_CLOCK_SYSCALL>.
		3706
		3707	=item EV_USE_CLOCK_SYSCALL
		3708
		3709	If defined to be C<1>, libev will try to use a direct syscall instead
		3710	of calling the system-provided C<clock_gettime> function. This option
		3711	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3712	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3713	programs needlessly. Using a direct syscall is slightly slower (in
		3714	theory), because no optimised vdso implementation can be used, but avoids
		3715	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3716	higher, as it simplifies linking (no need for C<-lrt>).
		3717
		3718	=item EV_USE_NANOSLEEP
		3719
		3720	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3721	and will use it for delays. Otherwise it will use C<select ()>.
		3722
		3723	=item EV_USE_EVENTFD
		3724
		3725	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3726	available and will probe for kernel support at runtime. This will improve
		3727	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3728	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3729	2.7 or newer, otherwise disabled.
		3730
		3731	=item EV_USE_SELECT
		3732
		3733	If undefined or defined to be C<1>, libev will compile in support for the
		3734	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3735	other method takes over, select will be it. Otherwise the select backend
		3736	will not be compiled in.
		3737
		3738	=item EV_SELECT_USE_FD_SET
		3739
		3740	If defined to C<1>, then the select backend will use the system C<fd_set>
		3741	structure. This is useful if libev doesn't compile due to a missing
		3742	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		3743	on exotic systems. This usually limits the range of file descriptors to
		3744	some low limit such as 1024 or might have other limitations (winsocket
		3745	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		3746	configures the maximum size of the C<fd_set>.
		3747
		3748	=item EV_SELECT_IS_WINSOCKET
		3749
		3750	When defined to C<1>, the select backend will assume that
		3751	select/socket/connect etc. don't understand file descriptors but
		3752	wants osf handles on win32 (this is the case when the select to
		3753	be used is the winsock select). This means that it will call
		3754	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3755	it is assumed that all these functions actually work on fds, even
		3756	on win32. Should not be defined on non-win32 platforms.
		3757
		3758	=item EV_FD_TO_WIN32_HANDLE(fd)
		3759
		3760	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3761	file descriptors to socket handles. When not defining this symbol (the
		3762	default), then libev will call C<_get_osfhandle>, which is usually
		3763	correct. In some cases, programs use their own file descriptor management,
		3764	in which case they can provide this function to map fds to socket handles.
		3765
		3766	=item EV_WIN32_HANDLE_TO_FD(handle)
		3767
		3768	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3769	using the standard C<_open_osfhandle> function. For programs implementing
		3770	their own fd to handle mapping, overwriting this function makes it easier
		3771	to do so. This can be done by defining this macro to an appropriate value.
		3772
		3773	=item EV_WIN32_CLOSE_FD(fd)
		3774
		3775	If programs implement their own fd to handle mapping on win32, then this
		3776	macro can be used to override the C<close> function, useful to unregister
		3777	file descriptors again. Note that the replacement function has to close
		3778	the underlying OS handle.
		3779
		3780	=item EV_USE_POLL
		3781
		3782	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3783	backend. Otherwise it will be enabled on non-win32 platforms. It
		3784	takes precedence over select.
		3785
		3786	=item EV_USE_EPOLL
		3787
		3788	If defined to be C<1>, libev will compile in support for the Linux
		3789	C<epoll>(7) backend. Its availability will be detected at runtime,
		3790	otherwise another method will be used as fallback. This is the preferred
		3791	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3792	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3793
		3794	=item EV_USE_KQUEUE
		3795
		3796	If defined to be C<1>, libev will compile in support for the BSD style
		3797	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3798	otherwise another method will be used as fallback. This is the preferred
		3799	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3800	supports some types of fds correctly (the only platform we found that
		3801	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3802	not be used unless explicitly requested. The best way to use it is to find
		3803	out whether kqueue supports your type of fd properly and use an embedded
		3804	kqueue loop.
		3805
		3806	=item EV_USE_PORT
		3807
		3808	If defined to be C<1>, libev will compile in support for the Solaris
		3809	10 port style backend. Its availability will be detected at runtime,
		3810	otherwise another method will be used as fallback. This is the preferred
		3811	backend for Solaris 10 systems.
		3812
		3813	=item EV_USE_DEVPOLL
		3814
		3815	Reserved for future expansion, works like the USE symbols above.
		3816
		3817	=item EV_USE_INOTIFY
		3818
		3819	If defined to be C<1>, libev will compile in support for the Linux inotify
		3820	interface to speed up C<ev_stat> watchers. Its actual availability will
		3821	be detected at runtime. If undefined, it will be enabled if the headers
		3822	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3823
		3824	=item EV_ATOMIC_T
		3825
		3826	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3827	access is atomic with respect to other threads or signal contexts. No such
		3828	type is easily found in the C language, so you can provide your own type
		3829	that you know is safe for your purposes. It is used both for signal handler "locking"
		3830	as well as for signal and thread safety in C<ev_async> watchers.
		3831
		3832	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3833	(from F<signal.h>), which is usually good enough on most platforms.
		3834
		3835	=item EV_H (h)
		3836
		3837	The name of the F<ev.h> header file used to include it. The default if
		3838	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3839	used to virtually rename the F<ev.h> header file in case of conflicts.
		3840
		3841	=item EV_CONFIG_H (h)
		3842
		3843	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3844	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3845	C<EV_H>, above.
		3846
		3847	=item EV_EVENT_H (h)
		3848
		3849	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3850	of how the F<event.h> header can be found, the default is C<"event.h">.
		3851
		3852	=item EV_PROTOTYPES (h)
		3853
		3854	If defined to be C<0>, then F<ev.h> will not define any function
		3855	prototypes, but still define all the structs and other symbols. This is
		3856	occasionally useful if you want to provide your own wrapper functions
		3857	around libev functions.
		3858
		3859	=item EV_MULTIPLICITY
		3860
		3861	If undefined or defined to C<1>, then all event-loop-specific functions
		3862	will have the C<struct ev_loop *> as first argument, and you can create
		3863	additional independent event loops. Otherwise there will be no support
		3864	for multiple event loops and there is no first event loop pointer
		3865	argument. Instead, all functions act on the single default loop.
		3866
		3867	=item EV_MINPRI
		3868
		3869	=item EV_MAXPRI
		3870
		3871	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3872	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3873	provide for more priorities by overriding those symbols (usually defined
		3874	to be C<-2> and C<2>, respectively).
		3875
		3876	When doing priority-based operations, libev usually has to linearly search
		3877	all the priorities, so having many of them (hundreds) uses a lot of space
		3878	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3879	fine.
		3880
		3881	If your embedding application does not need any priorities, defining these
		3882	both to C<0> will save some memory and CPU.
		3883
		3884	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3885	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3886	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		3887
		3888	If undefined or defined to be C<1> (and the platform supports it), then
		3889	the respective watcher type is supported. If defined to be C<0>, then it
		3890	is not. Disabling watcher types mainly saves codesize.
		3891
		3892	=item EV_FEATURES
		3893
		3894	If you need to shave off some kilobytes of code at the expense of some
		3895	speed (but with the full API), you can define this symbol to request
		3896	certain subsets of functionality. The default is to enable all features
		3897	that can be enabled on the platform.
		3898
		3899	A typical way to use this symbol is to define it to C<0> (or to a bitset
		3900	with some broad features you want) and then selectively re-enable
		3901	additional parts you want, for example if you want everything minimal,
		3902	but multiple event loop support, async and child watchers and the poll
		3903	backend, use this:
		3904
		3905	#define EV_FEATURES 0
		3906	#define EV_MULTIPLICITY 1
		3907	#define EV_USE_POLL 1
		3908	#define EV_CHILD_ENABLE 1
		3909	#define EV_ASYNC_ENABLE 1
		3910
		3911	The actual value is a bitset, it can be a combination of the following
		3912	values:
		3913
		3914	=over 4
		3915
		3916	=item C<1> - faster/larger code
		3917
		3918	Use larger code to speed up some operations.
		3919
		3920	Currently this is used to override some inlining decisions (enlarging the roughly
		3921	30% code size on amd64.
		3922
		3923	When optimising for size, use of compiler flags such as C<-Os> with
		3924	gcc recommended, as well as C<-DNDEBUG>, as libev contains a number of
		3925	assertions.
		3926
		3927	=item C<2> - faster/larger data structures
		3928
		3929	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		3930	hash table sizes and so on. This will usually further increase codesize
		3931	and can additionally have an effect on the size of data structures at
		3932	runtime.
		3933
		3934	=item C<4> - full API configuration
		3935
		3936	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		3937	enables multiplicity (C<EV_MULTIPLICITY>=1).
		3938
		3939	=item C<8> - full API
		3940
		3941	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		3942	details on which parts of the API are still available without this
		3943	feature, and do not complain if this subset changes over time.
		3944
		3945	=item C<16> - enable all optional watcher types
		3946
		3947	Enables all optional watcher types. If you want to selectively enable
		3948	only some watcher types other than I/O and timers (e.g. prepare,
		3949	embed, async, child...) you can enable them manually by defining
		3950	C<EV_watchertype_ENABLE> to C<1> instead.
		3951
		3952	=item C<32> - enable all backends
		3953
		3954	This enables all backends - without this feature, you need to enable at
		3955	least one backend manually (C<EV_USE_SELECT> is a good choice).
		3956
		3957	=item C<64> - enable OS-specific "helper" APIs
		3958
		3959	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		3960	default.
		3961
		3962	=back
		3963
		3964	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		3965	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		3966	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		3967	watchers, timers and monotonic clock support.
		3968
		3969	With an intelligent-enough linker (gcc+binutils are intelligent enough
		3970	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		3971	your program might be left out as well - a binary starting a timer and an
		3972	I/O watcher then might come out at only 5Kb.
		3973
		3974	=item EV_AVOID_STDIO
		3975
		3976	If this is set to C<1> at compiletime, then libev will avoid using stdio
		3977	functions (printf, scanf, perror etc.). This will increase the codesize
		3978	somewhat, but if your program doesn't otherwise depend on stdio and your
		3979	libc allows it, this avoids linking in the stdio library which is quite
		3980	big.
		3981
		3982	Note that error messages might become less precise when this option is
		3983	enabled.
		3984
		3985	=item EV_NSIG
		3986
		3987	The highest supported signal number, +1 (or, the number of
		3988	signals): Normally, libev tries to deduce the maximum number of signals
		3989	automatically, but sometimes this fails, in which case it can be
		3990	specified. Also, using a lower number than detected (C<32> should be
		3991	good for about any system in existance) can save some memory, as libev
		3992	statically allocates some 12-24 bytes per signal number.
		3993
		3994	=item EV_PID_HASHSIZE
		3995
		3996	C<ev_child> watchers use a small hash table to distribute workload by
		3997	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		3998	usually more than enough. If you need to manage thousands of children you
		3999	might want to increase this value (I<must> be a power of two).
		4000
		4001	=item EV_INOTIFY_HASHSIZE
		4002
		4003	C<ev_stat> watchers use a small hash table to distribute workload by
		4004	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4005	disabled), usually more than enough. If you need to manage thousands of
		4006	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4007	power of two).
		4008
		4009	=item EV_USE_4HEAP
		4010
		4011	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4012	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4013	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4014	faster performance with many (thousands) of watchers.
		4015
		4016	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4017	will be C<0>.
		4018
		4019	=item EV_HEAP_CACHE_AT
		4020
		4021	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4022	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4023	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4024	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4025	but avoids random read accesses on heap changes. This improves performance
		4026	noticeably with many (hundreds) of watchers.
		4027
		4028	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4029	will be C<0>.
		4030
		4031	=item EV_VERIFY
		4032
		4033	Controls how much internal verification (see C<ev_loop_verify ()>) will
		4034	be done: If set to C<0>, no internal verification code will be compiled
		4035	in. If set to C<1>, then verification code will be compiled in, but not
		4036	called. If set to C<2>, then the internal verification code will be
		4037	called once per loop, which can slow down libev. If set to C<3>, then the
		4038	verification code will be called very frequently, which will slow down
		4039	libev considerably.
		4040
		4041	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4042	will be C<0>.
		4043
		4044	=item EV_COMMON
		4045
		4046	By default, all watchers have a C<void *data> member. By redefining
		4047	this macro to a something else you can include more and other types of
		4048	members. You have to define it each time you include one of the files,
		4049	though, and it must be identical each time.
		4050
		4051	For example, the perl EV module uses something like this:
		4052
		4053	#define EV_COMMON \
		4054	SV *self; /* contains this struct */ \
		4055	SV *cb_sv, *fh /* note no trailing ";" */
		4056
		4057	=item EV_CB_DECLARE (type)
		4058
		4059	=item EV_CB_INVOKE (watcher, revents)
		4060
		4061	=item ev_set_cb (ev, cb)
		4062
		4063	Can be used to change the callback member declaration in each watcher,
		4064	and the way callbacks are invoked and set. Must expand to a struct member
		4065	definition and a statement, respectively. See the F<ev.h> header file for
		4066	their default definitions. One possible use for overriding these is to
		4067	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		4068	method calls instead of plain function calls in C++.
		4069
		4070	=back
		4071
		4072	=head2 EXPORTED API SYMBOLS
		4073
		4074	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4075	exported symbols, you can use the provided F<Symbol.*> files which list
		4076	all public symbols, one per line:
		4077
		4078	Symbols.ev for libev proper
		4079	Symbols.event for the libevent emulation
		4080
		4081	This can also be used to rename all public symbols to avoid clashes with
		4082	multiple versions of libev linked together (which is obviously bad in
		4083	itself, but sometimes it is inconvenient to avoid this).
		4084
		4085	A sed command like this will create wrapper C<#define>'s that you need to
		4086	include before including F<ev.h>:
		4087
		4088	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4089
		4090	This would create a file F<wrap.h> which essentially looks like this:
		4091
		4092	#define ev_backend myprefix_ev_backend
		4093	#define ev_check_start myprefix_ev_check_start
		4094	#define ev_check_stop myprefix_ev_check_stop
		4095	...
		4096
		4097	=head2 EXAMPLES
		4098
		4099	For a real-world example of a program the includes libev
		4100	verbatim, you can have a look at the EV perl module
		4101	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		4102	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		4103	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		4104	will be compiled. It is pretty complex because it provides its own header
		4105	file.
		4106
		4107	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		4108	that everybody includes and which overrides some configure choices:
		4109
		4110	#define EV_FEATURES 8
		4111	#define EV_USE_SELECT 1
		4112	#define EV_PREPARE_ENABLE 1
		4113	#define EV_IDLE_ENABLE 1
		4114	#define EV_SIGNAL_ENABLE 1
		4115	#define EV_CHILD_ENABLE 1
		4116	#define EV_USE_STDEXCEPT 0
		4117	#define EV_CONFIG_H <config.h>
		4118
		4119	#include "ev++.h"
		4120
		4121	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		4122
		4123	#include "ev_cpp.h"
		4124	#include "ev.c"
		4125
		4126	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		4127
		4128	=head2 THREADS AND COROUTINES
		4129
		4130	=head3 THREADS
		4131
		4132	All libev functions are reentrant and thread-safe unless explicitly
		4133	documented otherwise, but libev implements no locking itself. This means
		4134	that you can use as many loops as you want in parallel, as long as there
		4135	are no concurrent calls into any libev function with the same loop
		4136	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4137	of course): libev guarantees that different event loops share no data
		4138	structures that need any locking.
		4139
		4140	Or to put it differently: calls with different loop parameters can be done
		4141	concurrently from multiple threads, calls with the same loop parameter
		4142	must be done serially (but can be done from different threads, as long as
		4143	only one thread ever is inside a call at any point in time, e.g. by using
		4144	a mutex per loop).
		4145
		4146	Specifically to support threads (and signal handlers), libev implements
		4147	so-called C<ev_async> watchers, which allow some limited form of
		4148	concurrency on the same event loop, namely waking it up "from the
		4149	outside".
		4150
		4151	If you want to know which design (one loop, locking, or multiple loops
		4152	without or something else still) is best for your problem, then I cannot
		4153	help you, but here is some generic advice:
		4154
		4155	=over 4
		4156
		4157	=item * most applications have a main thread: use the default libev loop
		4158	in that thread, or create a separate thread running only the default loop.
		4159
		4160	This helps integrating other libraries or software modules that use libev
		4161	themselves and don't care/know about threading.
		4162
		4163	=item * one loop per thread is usually a good model.
		4164
		4165	Doing this is almost never wrong, sometimes a better-performance model
		4166	exists, but it is always a good start.
		4167
		4168	=item * other models exist, such as the leader/follower pattern, where one
		4169	loop is handed through multiple threads in a kind of round-robin fashion.
		4170
		4171	Choosing a model is hard - look around, learn, know that usually you can do
		4172	better than you currently do :-)
		4173
		4174	=item * often you need to talk to some other thread which blocks in the
		4175	event loop.
		4176
		4177	C<ev_async> watchers can be used to wake them up from other threads safely
		4178	(or from signal contexts...).
		4179
		4180	An example use would be to communicate signals or other events that only
		4181	work in the default loop by registering the signal watcher with the
		4182	default loop and triggering an C<ev_async> watcher from the default loop
		4183	watcher callback into the event loop interested in the signal.
		4184
		4185	=back
		4186
		4187	=head4 THREAD LOCKING EXAMPLE
		4188
		4189	Here is a fictitious example of how to run an event loop in a different
		4190	thread than where callbacks are being invoked and watchers are
		4191	created/added/removed.
		4192
		4193	For a real-world example, see the C<EV::Loop::Async> perl module,
		4194	which uses exactly this technique (which is suited for many high-level
		4195	languages).
		4196
		4197	The example uses a pthread mutex to protect the loop data, a condition
		4198	variable to wait for callback invocations, an async watcher to notify the
		4199	event loop thread and an unspecified mechanism to wake up the main thread.
		4200
		4201	First, you need to associate some data with the event loop:
		4202
		4203	typedef struct {
		4204	mutex_t lock; /* global loop lock */
		4205	ev_async async_w;
		4206	thread_t tid;
		4207	cond_t invoke_cv;
		4208	} userdata;
		4209
		4210	void prepare_loop (EV_P)
		4211	{
		4212	// for simplicity, we use a static userdata struct.
		4213	static userdata u;
		4214
		4215	ev_async_init (&u->async_w, async_cb);
		4216	ev_async_start (EV_A_ &u->async_w);
		4217
		4218	pthread_mutex_init (&u->lock, 0);
		4219	pthread_cond_init (&u->invoke_cv, 0);
		4220
		4221	// now associate this with the loop
		4222	ev_set_userdata (EV_A_ u);
		4223	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4224	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4225
		4226	// then create the thread running ev_loop
		4227	pthread_create (&u->tid, 0, l_run, EV_A);
		4228	}
		4229
		4230	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4231	solely to wake up the event loop so it takes notice of any new watchers
		4232	that might have been added:
		4233
		4234	static void
		4235	async_cb (EV_P_ ev_async *w, int revents)
		4236	{
		4237	// just used for the side effects
		4238	}
		4239
		4240	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4241	protecting the loop data, respectively.
		4242
		4243	static void
		4244	l_release (EV_P)
		4245	{
		4246	userdata *u = ev_userdata (EV_A);
		4247	pthread_mutex_unlock (&u->lock);
		4248	}
		4249
		4250	static void
		4251	l_acquire (EV_P)
		4252	{
		4253	userdata *u = ev_userdata (EV_A);
		4254	pthread_mutex_lock (&u->lock);
		4255	}
		4256
		4257	The event loop thread first acquires the mutex, and then jumps straight
		4258	into C<ev_loop>:
		4259
		4260	void *
		4261	l_run (void *thr_arg)
		4262	{
		4263	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4264
		4265	l_acquire (EV_A);
		4266	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4267	ev_loop (EV_A_ 0);
		4268	l_release (EV_A);
		4269
		4270	return 0;
		4271	}
		4272
		4273	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4274	signal the main thread via some unspecified mechanism (signals? pipe
		4275	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4276	have been called (in a while loop because a) spurious wakeups are possible
		4277	and b) skipping inter-thread-communication when there are no pending
		4278	watchers is very beneficial):
		4279
		4280	static void
		4281	l_invoke (EV_P)
		4282	{
		4283	userdata *u = ev_userdata (EV_A);
		4284
		4285	while (ev_pending_count (EV_A))
		4286	{
		4287	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4288	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4289	}
		4290	}
		4291
		4292	Now, whenever the main thread gets told to invoke pending watchers, it
		4293	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4294	thread to continue:
		4295
		4296	static void
		4297	real_invoke_pending (EV_P)
		4298	{
		4299	userdata *u = ev_userdata (EV_A);
		4300
		4301	pthread_mutex_lock (&u->lock);
		4302	ev_invoke_pending (EV_A);
		4303	pthread_cond_signal (&u->invoke_cv);
		4304	pthread_mutex_unlock (&u->lock);
		4305	}
		4306
		4307	Whenever you want to start/stop a watcher or do other modifications to an
		4308	event loop, you will now have to lock:
		4309
		4310	ev_timer timeout_watcher;
		4311	userdata *u = ev_userdata (EV_A);
		4312
		4313	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4314
		4315	pthread_mutex_lock (&u->lock);
		4316	ev_timer_start (EV_A_ &timeout_watcher);
		4317	ev_async_send (EV_A_ &u->async_w);
		4318	pthread_mutex_unlock (&u->lock);
		4319
		4320	Note that sending the C<ev_async> watcher is required because otherwise
		4321	an event loop currently blocking in the kernel will have no knowledge
		4322	about the newly added timer. By waking up the loop it will pick up any new
		4323	watchers in the next event loop iteration.
		4324
		4325	=head3 COROUTINES
		4326
		4327	Libev is very accommodating to coroutines ("cooperative threads"):
		4328	libev fully supports nesting calls to its functions from different
		4329	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4330	different coroutines, and switch freely between both coroutines running
		4331	the loop, as long as you don't confuse yourself). The only exception is
		4332	that you must not do this from C<ev_periodic> reschedule callbacks.
		4333
		4334	Care has been taken to ensure that libev does not keep local state inside
		4335	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4336	they do not call any callbacks.
		4337
		4338	=head2 COMPILER WARNINGS
		4339
		4340	Depending on your compiler and compiler settings, you might get no or a
		4341	lot of warnings when compiling libev code. Some people are apparently
		4342	scared by this.
		4343
		4344	However, these are unavoidable for many reasons. For one, each compiler
		4345	has different warnings, and each user has different tastes regarding
		4346	warning options. "Warn-free" code therefore cannot be a goal except when
		4347	targeting a specific compiler and compiler-version.
		4348
		4349	Another reason is that some compiler warnings require elaborate
		4350	workarounds, or other changes to the code that make it less clear and less
		4351	maintainable.
		4352
		4353	And of course, some compiler warnings are just plain stupid, or simply
		4354	wrong (because they don't actually warn about the condition their message
		4355	seems to warn about). For example, certain older gcc versions had some
		4356	warnings that resulted an extreme number of false positives. These have
		4357	been fixed, but some people still insist on making code warn-free with
		4358	such buggy versions.
		4359
		4360	While libev is written to generate as few warnings as possible,
		4361	"warn-free" code is not a goal, and it is recommended not to build libev
		4362	with any compiler warnings enabled unless you are prepared to cope with
		4363	them (e.g. by ignoring them). Remember that warnings are just that:
		4364	warnings, not errors, or proof of bugs.
		4365
		4366
		4367	=head2 VALGRIND
		4368
		4369	Valgrind has a special section here because it is a popular tool that is
		4370	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4371
		4372	If you think you found a bug (memory leak, uninitialised data access etc.)
		4373	in libev, then check twice: If valgrind reports something like:
		4374
		4375	==2274== definitely lost: 0 bytes in 0 blocks.
		4376	==2274== possibly lost: 0 bytes in 0 blocks.
		4377	==2274== still reachable: 256 bytes in 1 blocks.
		4378
		4379	Then there is no memory leak, just as memory accounted to global variables
		4380	is not a memleak - the memory is still being referenced, and didn't leak.
		4381
		4382	Similarly, under some circumstances, valgrind might report kernel bugs
		4383	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4384	although an acceptable workaround has been found here), or it might be
		4385	confused.
		4386
		4387	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4388	make it into some kind of religion.
		4389
		4390	If you are unsure about something, feel free to contact the mailing list
		4391	with the full valgrind report and an explanation on why you think this
		4392	is a bug in libev (best check the archives, too :). However, don't be
		4393	annoyed when you get a brisk "this is no bug" answer and take the chance
		4394	of learning how to interpret valgrind properly.
		4395
		4396	If you need, for some reason, empty reports from valgrind for your project
		4397	I suggest using suppression lists.
		4398
		4399
		4400	=head1 PORTABILITY NOTES
		4401
		4402	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4403
		4404	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4405	requires, and its I/O model is fundamentally incompatible with the POSIX
		4406	model. Libev still offers limited functionality on this platform in
		4407	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4408	descriptors. This only applies when using Win32 natively, not when using
		4409	e.g. cygwin.
		4410
		4411	Lifting these limitations would basically require the full
		4412	re-implementation of the I/O system. If you are into these kinds of
		4413	things, then note that glib does exactly that for you in a very portable
		4414	way (note also that glib is the slowest event library known to man).
		4415
		4416	There is no supported compilation method available on windows except
		4417	embedding it into other applications.
		4418
		4419	Sensible signal handling is officially unsupported by Microsoft - libev
		4420	tries its best, but under most conditions, signals will simply not work.
		4421
		4422	Not a libev limitation but worth mentioning: windows apparently doesn't
		4423	accept large writes: instead of resulting in a partial write, windows will
		4424	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4425	so make sure you only write small amounts into your sockets (less than a
		4426	megabyte seems safe, but this apparently depends on the amount of memory
		4427	available).
		4428
		4429	Due to the many, low, and arbitrary limits on the win32 platform and
		4430	the abysmal performance of winsockets, using a large number of sockets
		4431	is not recommended (and not reasonable). If your program needs to use
		4432	more than a hundred or so sockets, then likely it needs to use a totally
		4433	different implementation for windows, as libev offers the POSIX readiness
		4434	notification model, which cannot be implemented efficiently on windows
		4435	(due to Microsoft monopoly games).
		4436
		4437	A typical way to use libev under windows is to embed it (see the embedding
		4438	section for details) and use the following F<evwrap.h> header file instead
		4439	of F<ev.h>:
		4440
		4441	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4442	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4443
		4444	#include "ev.h"
		4445
		4446	And compile the following F<evwrap.c> file into your project (make sure
		4447	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4448
		4449	#include "evwrap.h"
		4450	#include "ev.c"
		4451
		4452	=over 4
		4453
		4454	=item The winsocket select function
		4455
		4456	The winsocket C<select> function doesn't follow POSIX in that it
		4457	requires socket I<handles> and not socket I<file descriptors> (it is
		4458	also extremely buggy). This makes select very inefficient, and also
		4459	requires a mapping from file descriptors to socket handles (the Microsoft
		4460	C runtime provides the function C<_open_osfhandle> for this). See the
		4461	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4462	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4463
		4464	The configuration for a "naked" win32 using the Microsoft runtime
		4465	libraries and raw winsocket select is:
		4466
		4467	#define EV_USE_SELECT 1
		4468	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4469
		4470	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4471	complexity in the O(n²) range when using win32.
		4472
		4473	=item Limited number of file descriptors
		4474
		4475	Windows has numerous arbitrary (and low) limits on things.
		4476
		4477	Early versions of winsocket's select only supported waiting for a maximum
		4478	of C<64> handles (probably owning to the fact that all windows kernels
		4479	can only wait for C<64> things at the same time internally; Microsoft
		4480	recommends spawning a chain of threads and wait for 63 handles and the
		4481	previous thread in each. Sounds great!).
		4482
		4483	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4484	to some high number (e.g. C<2048>) before compiling the winsocket select
		4485	call (which might be in libev or elsewhere, for example, perl and many
		4486	other interpreters do their own select emulation on windows).
		4487
		4488	Another limit is the number of file descriptors in the Microsoft runtime
		4489	libraries, which by default is C<64> (there must be a hidden I<64>
		4490	fetish or something like this inside Microsoft). You can increase this
		4491	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4492	(another arbitrary limit), but is broken in many versions of the Microsoft
		4493	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4494	(depending on windows version and/or the phase of the moon). To get more,
		4495	you need to wrap all I/O functions and provide your own fd management, but
		4496	the cost of calling select (O(n²)) will likely make this unworkable.
		4497
		4498	=back
		4499
		4500	=head2 PORTABILITY REQUIREMENTS
		4501
		4502	In addition to a working ISO-C implementation and of course the
		4503	backend-specific APIs, libev relies on a few additional extensions:
		4504
		4505	=over 4
		4506
		4507	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4508	calling conventions regardless of C<ev_watcher_type *>.
		4509
		4510	Libev assumes not only that all watcher pointers have the same internal
		4511	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4512	assumes that the same (machine) code can be used to call any watcher
		4513	callback: The watcher callbacks have different type signatures, but libev
		4514	calls them using an C<ev_watcher *> internally.
		4515
		4516	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4517
		4518	The type C<sig_atomic_t volatile> (or whatever is defined as
		4519	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4520	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4521	believed to be sufficiently portable.
		4522
		4523	=item C<sigprocmask> must work in a threaded environment
		4524
		4525	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4526	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4527	pthread implementations will either allow C<sigprocmask> in the "main
		4528	thread" or will block signals process-wide, both behaviours would
		4529	be compatible with libev. Interaction between C<sigprocmask> and
		4530	C<pthread_sigmask> could complicate things, however.
		4531
		4532	The most portable way to handle signals is to block signals in all threads
		4533	except the initial one, and run the default loop in the initial thread as
		4534	well.
		4535
		4536	=item C<long> must be large enough for common memory allocation sizes
		4537
		4538	To improve portability and simplify its API, libev uses C<long> internally
		4539	instead of C<size_t> when allocating its data structures. On non-POSIX
		4540	systems (Microsoft...) this might be unexpectedly low, but is still at
		4541	least 31 bits everywhere, which is enough for hundreds of millions of
		4542	watchers.
		4543
		4544	=item C<double> must hold a time value in seconds with enough accuracy
		4545
		4546	The type C<double> is used to represent timestamps. It is required to
		4547	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4548	enough for at least into the year 4000. This requirement is fulfilled by
		4549	implementations implementing IEEE 754, which is basically all existing
		4550	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4551	2200.
		4552
		4553	=back
		4554
		4555	If you know of other additional requirements drop me a note.
		4556
		4557
		4558	=head1 ALGORITHMIC COMPLEXITIES
		4559
		4560	In this section the complexities of (many of) the algorithms used inside
		4561	libev will be documented. For complexity discussions about backends see
		4562	the documentation for C<ev_default_init>.
		4563
		4564	All of the following are about amortised time: If an array needs to be
		4565	extended, libev needs to realloc and move the whole array, but this
		4566	happens asymptotically rarer with higher number of elements, so O(1) might
		4567	mean that libev does a lengthy realloc operation in rare cases, but on
		4568	average it is much faster and asymptotically approaches constant time.
		4569
		4570	=over 4
		4571
		4572	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4573
		4574	This means that, when you have a watcher that triggers in one hour and
		4575	there are 100 watchers that would trigger before that, then inserting will
		4576	have to skip roughly seven (C<ld 100>) of these watchers.
		4577
		4578	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4579
		4580	That means that changing a timer costs less than removing/adding them,
		4581	as only the relative motion in the event queue has to be paid for.
		4582
		4583	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4584
		4585	These just add the watcher into an array or at the head of a list.
		4586
		4587	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4588
		4589	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4590
		4591	These watchers are stored in lists, so they need to be walked to find the
		4592	correct watcher to remove. The lists are usually short (you don't usually
		4593	have many watchers waiting for the same fd or signal: one is typical, two
		4594	is rare).
		4595
		4596	=item Finding the next timer in each loop iteration: O(1)
		4597
		4598	By virtue of using a binary or 4-heap, the next timer is always found at a
		4599	fixed position in the storage array.
		4600
		4601	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4602
		4603	A change means an I/O watcher gets started or stopped, which requires
		4604	libev to recalculate its status (and possibly tell the kernel, depending
		4605	on backend and whether C<ev_io_set> was used).
		4606
		4607	=item Activating one watcher (putting it into the pending state): O(1)
		4608
		4609	=item Priority handling: O(number_of_priorities)
		4610
		4611	Priorities are implemented by allocating some space for each
		4612	priority. When doing priority-based operations, libev usually has to
		4613	linearly search all the priorities, but starting/stopping and activating
		4614	watchers becomes O(1) with respect to priority handling.
		4615
		4616	=item Sending an ev_async: O(1)
		4617
		4618	=item Processing ev_async_send: O(number_of_async_watchers)
		4619
		4620	=item Processing signals: O(max_signal_number)
		4621
		4622	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4623	calls in the current loop iteration. Checking for async and signal events
		4624	involves iterating over all running async watchers or all signal numbers.
		4625
		4626	=back
		4627
		4628
		4629	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4630
		4631	The major version 4 introduced some minor incompatible changes to the API.
		4632
		4633	At the moment, the C<ev.h> header file tries to implement superficial
		4634	compatibility, so most programs should still compile. Those might be
		4635	removed in later versions of libev, so better update early than late.
		4636
		4637	=over 4
		4638
		4639	=item C<ev_loop_count> renamed to C<ev_iteration>
		4640
		4641	=item C<ev_loop_depth> renamed to C<ev_depth>
		4642
		4643	=item C<ev_loop_verify> renamed to C<ev_verify>
		4644
		4645	Most functions working on C<struct ev_loop> objects don't have an
		4646	C<ev_loop_> prefix, so it was removed. Note that C<ev_loop_fork> is
		4647	still called C<ev_loop_fork> because it would otherwise clash with the
		4648	C<ev_fork> typedef.
		4649
		4650	=item C<EV_TIMEOUT> renamed to C<EV_TIMER> in C<revents>
		4651
		4652	This is a simple rename - all other watcher types use their name
		4653	as revents flag, and now C<ev_timer> does, too.
		4654
		4655	Both C<EV_TIMER> and C<EV_TIMEOUT> symbols were present in 3.x versions
		4656	and continue to be present for the forseeable future, so this is mostly a
		4657	documentation change.
		4658
		4659	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4660
		4661	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4662	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4663	and work, but the library code will of course be larger.
		4664
		4665	=back
		4666
		4667
		4668	=head1 GLOSSARY
		4669
		4670	=over 4
		4671
		4672	=item active
		4673
		4674	A watcher is active as long as it has been started (has been attached to
		4675	an event loop) but not yet stopped (disassociated from the event loop).
		4676
		4677	=item application
		4678
		4679	In this document, an application is whatever is using libev.
		4680
		4681	=item callback
		4682
		4683	The address of a function that is called when some event has been
		4684	detected. Callbacks are being passed the event loop, the watcher that
		4685	received the event, and the actual event bitset.
		4686
		4687	=item callback invocation
		4688
		4689	The act of calling the callback associated with a watcher.
		4690
		4691	=item event
		4692
		4693	A change of state of some external event, such as data now being available
		4694	for reading on a file descriptor, time having passed or simply not having
		4695	any other events happening anymore.
		4696
		4697	In libev, events are represented as single bits (such as C<EV_READ> or
		4698	C<EV_TIMER>).
		4699
		4700	=item event library
		4701
		4702	A software package implementing an event model and loop.
		4703
		4704	=item event loop
		4705
		4706	An entity that handles and processes external events and converts them
		4707	into callback invocations.
		4708
		4709	=item event model
		4710
		4711	The model used to describe how an event loop handles and processes
		4712	watchers and events.
		4713
		4714	=item pending
		4715
		4716	A watcher is pending as soon as the corresponding event has been detected,
		4717	and stops being pending as soon as the watcher will be invoked or its
		4718	pending status is explicitly cleared by the application.
		4719
		4720	A watcher can be pending, but not active. Stopping a watcher also clears
		4721	its pending status.
		4722
		4723	=item real time
		4724
		4725	The physical time that is observed. It is apparently strictly monotonic :)
		4726
		4727	=item wall-clock time
		4728
		4729	The time and date as shown on clocks. Unlike real time, it can actually
		4730	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4731	clock.
		4732
		4733	=item watcher
		4734
		4735	A data structure that describes interest in certain events. Watchers need
		4736	to be started (attached to an event loop) before they can receive events.
		4737
		4738	=item watcher invocation
		4739
		4740	The act of calling the callback associated with a watcher.
		4741
		4742	=back
		4743
767	=head1 AUTHOR	4744	=head1 AUTHOR
768		4745
769	Marc Lehmann <libev@schmorp.de>.	4746	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
770		4747

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines