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Revision 1.16 by root, Mon Nov 12 08:47:14 2007 UTC vs.
Revision 1.221 by root, Wed Dec 3 15:23:44 2008 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#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	}
8		66
9	=head1 DESCRIPTION	67	=head1 DESCRIPTION
10		68
		69	The newest version of this document is also available as an html-formatted
		70	web page you might find easier to navigate when reading it for the first
		71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		72
11	Libev is an event loop: you register interest in certain events (such as a	73	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	74	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	75	these event sources and provide your program with events.
14		76
15	To do this, it must take more or less complete control over your process	77	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	78	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	79	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	81	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	82	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	83	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	84	watcher.
23		85
24	=head1 FEATURES	86	=head2 FEATURES
25		87
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	88	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	89	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	90	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	91	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	92	with customised rescheduling (C<ev_periodic>), synchronous signals
		93	(C<ev_signal>), process status change events (C<ev_child>), and event
		94	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		95	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		96	file watchers (C<ev_stat>) and even limited support for fork events
		97	(C<ev_fork>).
		98
		99	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	100	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	101	for example).
33		102
34	=head1 CONVENTIONS	103	=head2 CONVENTIONS
35		104
36	Libev is very configurable. In this manual the default configuration	105	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	106	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	107	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	108	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	109	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 *>)	110	name C<loop> (which is always of type C<ev_loop *>) will not have
42	will not have this argument.	111	this argument.
43		112
44	=head1 TIME AND OTHER GLOBAL FUNCTIONS	113	=head2 TIME REPRESENTATION
45		114
46	Libev represents time as a single floating point number, representing the	115	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	116	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	117	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	118	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	119	to the C<double> type in C, and when you need to do any calculations on
		120	it, you should treat it as some floating point value. Unlike the name
		121	component C<stamp> might indicate, it is also used for time differences
		122	throughout libev.
		123
		124	=head1 ERROR HANDLING
		125
		126	Libev knows three classes of errors: operating system errors, usage errors
		127	and internal errors (bugs).
		128
		129	When libev catches an operating system error it cannot handle (for example
		130	a system call indicating a condition libev cannot fix), it calls the callback
		131	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		132	abort. The default is to print a diagnostic message and to call C<abort
		133	()>.
		134
		135	When libev detects a usage error such as a negative timer interval, then
		136	it will print a diagnostic message and abort (via the C<assert> mechanism,
		137	so C<NDEBUG> will disable this checking): these are programming errors in
		138	the libev caller and need to be fixed there.
		139
		140	Libev also has a few internal error-checking C<assert>ions, and also has
		141	extensive consistency checking code. These do not trigger under normal
		142	circumstances, as they indicate either a bug in libev or worse.
		143
		144
		145	=head1 GLOBAL FUNCTIONS
		146
		147	These functions can be called anytime, even before initialising the
		148	library in any way.
51		149
52	=over 4	150	=over 4
53		151
54	=item ev_tstamp ev_time ()	152	=item ev_tstamp ev_time ()
55		153
56	Returns the current time as libev would use it.	154	Returns the current time as libev would use it. Please note that the
		155	C<ev_now> function is usually faster and also often returns the timestamp
		156	you actually want to know.
		157
		158	=item ev_sleep (ev_tstamp interval)
		159
		160	Sleep for the given interval: The current thread will be blocked until
		161	either it is interrupted or the given time interval has passed. Basically
		162	this is a sub-second-resolution C<sleep ()>.
57		163
58	=item int ev_version_major ()	164	=item int ev_version_major ()
59		165
60	=item int ev_version_minor ()	166	=item int ev_version_minor ()
61		167
62	You can find out the major and minor version numbers of the library	168	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	169	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	170	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	171	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66	version of the library your program was compiled against.	172	version of the library your program was compiled against.
67		173
		174	These version numbers refer to the ABI version of the library, not the
		175	release version.
		176
68	Usually, it's a good idea to terminate if the major versions mismatch,	177	Usually, it's a good idea to terminate if the major versions mismatch,
69	as this indicates an incompatible change. Minor versions are usually	178	as this indicates an incompatible change. Minor versions are usually
70	compatible to older versions, so a larger minor version alone is usually	179	compatible to older versions, so a larger minor version alone is usually
71	not a problem.	180	not a problem.
72		181
		182	Example: Make sure we haven't accidentally been linked against the wrong
		183	version.
		184
		185	assert (("libev version mismatch",
		186	ev_version_major () == EV_VERSION_MAJOR
		187	&& ev_version_minor () >= EV_VERSION_MINOR));
		188
		189	=item unsigned int ev_supported_backends ()
		190
		191	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		192	value) compiled into this binary of libev (independent of their
		193	availability on the system you are running on). See C<ev_default_loop> for
		194	a description of the set values.
		195
		196	Example: make sure we have the epoll method, because yeah this is cool and
		197	a must have and can we have a torrent of it please!!!11
		198
		199	assert (("sorry, no epoll, no sex",
		200	ev_supported_backends () & EVBACKEND_EPOLL));
		201
		202	=item unsigned int ev_recommended_backends ()
		203
		204	Return the set of all backends compiled into this binary of libev and also
		205	recommended for this platform. This set is often smaller than the one
		206	returned by C<ev_supported_backends>, as for example kqueue is broken on
		207	most BSDs and will not be auto-detected unless you explicitly request it
		208	(assuming you know what you are doing). This is the set of backends that
		209	libev will probe for if you specify no backends explicitly.
		210
		211	=item unsigned int ev_embeddable_backends ()
		212
		213	Returns the set of backends that are embeddable in other event loops. This
		214	is the theoretical, all-platform, value. To find which backends
		215	might be supported on the current system, you would need to look at
		216	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		217	recommended ones.
		218
		219	See the description of C<ev_embed> watchers for more info.
		220
73	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	221	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
74		222
75	Sets the allocation function to use (the prototype is similar to the	223	Sets the allocation function to use (the prototype is similar - the
76	realloc C function, the semantics are identical). It is used to allocate	224	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	225	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	226	when memory needs to be allocated (C<size != 0>), the library might abort
79	destructive action. The default is your system realloc function.	227	or take some potentially destructive action.
		228
		229	Since some systems (at least OpenBSD and Darwin) fail to implement
		230	correct C<realloc> semantics, libev will use a wrapper around the system
		231	C<realloc> and C<free> functions by default.
80		232
81	You could override this function in high-availability programs to, say,	233	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,	234	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.	235	or even to sleep a while and retry until some memory is available.
84		236
		237	Example: Replace the libev allocator with one that waits a bit and then
		238	retries (example requires a standards-compliant C<realloc>).
		239
		240	static void *
		241	persistent_realloc (void *ptr, size_t size)
		242	{
		243	for (;;)
		244	{
		245	void *newptr = realloc (ptr, size);
		246
		247	if (newptr)
		248	return newptr;
		249
		250	sleep (60);
		251	}
		252	}
		253
		254	...
		255	ev_set_allocator (persistent_realloc);
		256
85	=item ev_set_syserr_cb (void (*cb)(const char *msg));	257	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
86		258
87	Set the callback function to call on a retryable syscall error (such	259	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	260	as failed select, poll, epoll_wait). The message is a printable string
89	indicating the system call or subsystem causing the problem. If this	261	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	262	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	263	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	264	requested operation, or, if the condition doesn't go away, do bad stuff
93	(such as abort).	265	(such as abort).
94		266
		267	Example: This is basically the same thing that libev does internally, too.
		268
		269	static void
		270	fatal_error (const char *msg)
		271	{
		272	perror (msg);
		273	abort ();
		274	}
		275
		276	...
		277	ev_set_syserr_cb (fatal_error);
		278
95	=back	279	=back
96		280
97	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	281	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
98		282
99	An event loop is described by a C<struct ev_loop *>. The library knows two	283	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	284	is I<not> optional in this case, as there is also an C<ev_loop>
101	events, and dynamically created loops which do not.	285	I<function>).
102		286
103	If you use threads, a common model is to run the default event loop	287	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	288	supports signals and child events, and dynamically created loops which do
105	create, you also create another event loop. Libev itself does no locking	289	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		290
110	=over 4	291	=over 4
111		292
112	=item struct ev_loop *ev_default_loop (unsigned int flags)	293	=item struct ev_loop *ev_default_loop (unsigned int flags)
113		294
114	This will initialise the default event loop if it hasn't been initialised	295	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	296	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	297	false. If it already was initialised it simply returns it (and ignores the
117	flags).	298	flags. If that is troubling you, check C<ev_backend ()> afterwards).
118		299
119	If you don't know what event loop to use, use the one returned from this	300	If you don't know what event loop to use, use the one returned from this
120	function.	301	function.
121		302
		303	Note that this function is I<not> thread-safe, so if you want to use it
		304	from multiple threads, you have to lock (note also that this is unlikely,
		305	as loops cannot be shared easily between threads anyway).
		306
		307	The default loop is the only loop that can handle C<ev_signal> and
		308	C<ev_child> watchers, and to do this, it always registers a handler
		309	for C<SIGCHLD>. If this is a problem for your application you can either
		310	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		311	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		312	C<ev_default_init>.
		313
122	The flags argument can be used to specify special behaviour or specific	314	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).	315	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
124		316
125	It supports the following flags:	317	The following flags are supported:
126		318
127	=over 4	319	=over 4
128		320
129	=item C<EVFLAG_AUTO>	321	=item C<EVFLAG_AUTO>
130		322
131	The default flags value. Use this if you have no clue (it's the right	323	The default flags value. Use this if you have no clue (it's the right
132	thing, believe me).	324	thing, believe me).
133		325
134	=item C<EVFLAG_NOENV>	326	=item C<EVFLAG_NOENV>
135		327
136	If this flag bit is ored into the flag value (or the program runs setuid	328	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	329	or setgid) then libev will I<not> look at the environment variable
138	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	330	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139	override the flags completely if it is found in the environment. This is	331	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	332	useful to try out specific backends to test their performance, or to work
141	around bugs.	333	around bugs.
142		334
		335	=item C<EVFLAG_FORKCHECK>
		336
		337	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		338	a fork, you can also make libev check for a fork in each iteration by
		339	enabling this flag.
		340
		341	This works by calling C<getpid ()> on every iteration of the loop,
		342	and thus this might slow down your event loop if you do a lot of loop
		343	iterations and little real work, but is usually not noticeable (on my
		344	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		345	without a system call and thus I<very> fast, but my GNU/Linux system also has
		346	C<pthread_atfork> which is even faster).
		347
		348	The big advantage of this flag is that you can forget about fork (and
		349	forget about forgetting to tell libev about forking) when you use this
		350	flag.
		351
		352	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		353	environment variable.
		354
143	=item C<EVMETHOD_SELECT> (portable select backend)	355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
144		356
		357	This is your standard select(2) backend. Not I<completely> standard, as
		358	libev tries to roll its own fd_set with no limits on the number of fds,
		359	but if that fails, expect a fairly low limit on the number of fds when
		360	using this backend. It doesn't scale too well (O(highest_fd)), but its
		361	usually the fastest backend for a low number of (low-numbered :) fds.
		362
		363	To get good performance out of this backend you need a high amount of
		364	parallelism (most of the file descriptors should be busy). If you are
		365	writing a server, you should C<accept ()> in a loop to accept as many
		366	connections as possible during one iteration. You might also want to have
		367	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		368	readiness notifications you get per iteration.
		369
		370	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		371	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		372	C<exceptfds> set on that platform).
		373
145	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	374	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
146		375
147	=item C<EVMETHOD_EPOLL> (linux only)	376	And this is your standard poll(2) backend. It's more complicated
		377	than select, but handles sparse fds better and has no artificial
		378	limit on the number of fds you can use (except it will slow down
		379	considerably with a lot of inactive fds). It scales similarly to select,
		380	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		381	performance tips.
148		382
149	=item C<EVMETHOD_KQUEUE> (some bsds only)	383	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		384	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
150		385
151	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	386	=item C<EVBACKEND_EPOLL> (value 4, Linux)
152		387
153	=item C<EVMETHOD_PORT> (solaris 10 only)	388	For few fds, this backend is a bit little slower than poll and select,
		389	but it scales phenomenally better. While poll and select usually scale
		390	like O(total_fds) where n is the total number of fds (or the highest fd),
		391	epoll scales either O(1) or O(active_fds).
154		392
155	If one or more of these are ored into the flags value, then only these	393	The epoll mechanism deserves honorable mention as the most misdesigned
156	backends will be tried (in the reverse order as given here). If one are	394	of the more advanced event mechanisms: mere annoyances include silently
157	specified, any backend will do.	395	dropping file descriptors, requiring a system call per change per file
		396	descriptor (and unnecessary guessing of parameters), problems with dup and
		397	so on. The biggest issue is fork races, however - if a program forks then
		398	I<both> parent and child process have to recreate the epoll set, which can
		399	take considerable time (one syscall per file descriptor) and is of course
		400	hard to detect.
		401
		402	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		403	of course I<doesn't>, and epoll just loves to report events for totally
		404	I<different> file descriptors (even already closed ones, so one cannot
		405	even remove them from the set) than registered in the set (especially
		406	on SMP systems). Libev tries to counter these spurious notifications by
		407	employing an additional generation counter and comparing that against the
		408	events to filter out spurious ones, recreating the set when required.
		409
		410	While stopping, setting and starting an I/O watcher in the same iteration
		411	will result in some caching, there is still a system call per such
		412	incident (because the same I<file descriptor> could point to a different
		413	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
		414	file descriptors might not work very well if you register events for both
		415	file descriptors.
		416
		417	Best performance from this backend is achieved by not unregistering all
		418	watchers for a file descriptor until it has been closed, if possible,
		419	i.e. keep at least one watcher active per fd at all times. Stopping and
		420	starting a watcher (without re-setting it) also usually doesn't cause
		421	extra overhead. A fork can both result in spurious notifications as well
		422	as in libev having to destroy and recreate the epoll object, which can
		423	take considerable time and thus should be avoided.
		424
		425	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		426	faster than epoll for maybe up to a hundred file descriptors, depending on
		427	the usage. So sad.
		428
		429	While nominally embeddable in other event loops, this feature is broken in
		430	all kernel versions tested so far.
		431
		432	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		433	C<EVBACKEND_POLL>.
		434
		435	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		436
		437	Kqueue deserves special mention, as at the time of this writing, it
		438	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		439	with anything but sockets and pipes, except on Darwin, where of course
		440	it's completely useless). Unlike epoll, however, whose brokenness
		441	is by design, these kqueue bugs can (and eventually will) be fixed
		442	without API changes to existing programs. For this reason it's not being
		443	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		444	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		445	system like NetBSD.
		446
		447	You still can embed kqueue into a normal poll or select backend and use it
		448	only for sockets (after having made sure that sockets work with kqueue on
		449	the target platform). See C<ev_embed> watchers for more info.
		450
		451	It scales in the same way as the epoll backend, but the interface to the
		452	kernel is more efficient (which says nothing about its actual speed, of
		453	course). While stopping, setting and starting an I/O watcher does never
		454	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		455	two event changes per incident. Support for C<fork ()> is very bad (but
		456	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		457	cases
		458
		459	This backend usually performs well under most conditions.
		460
		461	While nominally embeddable in other event loops, this doesn't work
		462	everywhere, so you might need to test for this. And since it is broken
		463	almost everywhere, you should only use it when you have a lot of sockets
		464	(for which it usually works), by embedding it into another event loop
		465	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
		466	using it only for sockets.
		467
		468	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		469	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		470	C<NOTE_EOF>.
		471
		472	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		473
		474	This is not implemented yet (and might never be, unless you send me an
		475	implementation). According to reports, C</dev/poll> only supports sockets
		476	and is not embeddable, which would limit the usefulness of this backend
		477	immensely.
		478
		479	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		480
		481	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		482	it's really slow, but it still scales very well (O(active_fds)).
		483
		484	Please note that Solaris event ports can deliver a lot of spurious
		485	notifications, so you need to use non-blocking I/O or other means to avoid
		486	blocking when no data (or space) is available.
		487
		488	While this backend scales well, it requires one system call per active
		489	file descriptor per loop iteration. For small and medium numbers of file
		490	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		491	might perform better.
		492
		493	On the positive side, with the exception of the spurious readiness
		494	notifications, this backend actually performed fully to specification
		495	in all tests and is fully embeddable, which is a rare feat among the
		496	OS-specific backends (I vastly prefer correctness over speed hacks).
		497
		498	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		499	C<EVBACKEND_POLL>.
		500
		501	=item C<EVBACKEND_ALL>
		502
		503	Try all backends (even potentially broken ones that wouldn't be tried
		504	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		505	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		506
		507	It is definitely not recommended to use this flag.
158		508
159	=back	509	=back
		510
		511	If one or more of these are or'ed into the flags value, then only these
		512	backends will be tried (in the reverse order as listed here). If none are
		513	specified, all backends in C<ev_recommended_backends ()> will be tried.
		514
		515	Example: This is the most typical usage.
		516
		517	if (!ev_default_loop (0))
		518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		519
		520	Example: Restrict libev to the select and poll backends, and do not allow
		521	environment settings to be taken into account:
		522
		523	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		524
		525	Example: Use whatever libev has to offer, but make sure that kqueue is
		526	used if available (warning, breaks stuff, best use only with your own
		527	private event loop and only if you know the OS supports your types of
		528	fds):
		529
		530	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
160		531
161	=item struct ev_loop *ev_loop_new (unsigned int flags)	532	=item struct ev_loop *ev_loop_new (unsigned int flags)
162		533
163	Similar to C<ev_default_loop>, but always creates a new event loop that is	534	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	535	always distinct from the default loop. Unlike the default loop, it cannot
165	handle signal and child watchers, and attempts to do so will be greeted by	536	handle signal and child watchers, and attempts to do so will be greeted by
166	undefined behaviour (or a failed assertion if assertions are enabled).	537	undefined behaviour (or a failed assertion if assertions are enabled).
167		538
		539	Note that this function I<is> thread-safe, and the recommended way to use
		540	libev with threads is indeed to create one loop per thread, and using the
		541	default loop in the "main" or "initial" thread.
		542
		543	Example: Try to create a event loop that uses epoll and nothing else.
		544
		545	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		546	if (!epoller)
		547	fatal ("no epoll found here, maybe it hides under your chair");
		548
168	=item ev_default_destroy ()	549	=item ev_default_destroy ()
169		550
170	Destroys the default loop again (frees all memory and kernel state	551	Destroys the default loop again (frees all memory and kernel state
171	etc.). This stops all registered event watchers (by not touching them in	552	etc.). None of the active event watchers will be stopped in the normal
172	any way whatsoever, although you cannot rely on this :).	553	sense, so e.g. C<ev_is_active> might still return true. It is your
		554	responsibility to either stop all watchers cleanly yourself I<before>
		555	calling this function, or cope with the fact afterwards (which is usually
		556	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		557	for example).
		558
		559	Note that certain global state, such as signal state (and installed signal
		560	handlers), will not be freed by this function, and related watchers (such
		561	as signal and child watchers) would need to be stopped manually.
		562
		563	In general it is not advisable to call this function except in the
		564	rare occasion where you really need to free e.g. the signal handling
		565	pipe fds. If you need dynamically allocated loops it is better to use
		566	C<ev_loop_new> and C<ev_loop_destroy>).
173		567
174	=item ev_loop_destroy (loop)	568	=item ev_loop_destroy (loop)
175		569
176	Like C<ev_default_destroy>, but destroys an event loop created by an	570	Like C<ev_default_destroy>, but destroys an event loop created by an
177	earlier call to C<ev_loop_new>.	571	earlier call to C<ev_loop_new>.
178		572
179	=item ev_default_fork ()	573	=item ev_default_fork ()
180		574
		575	This function sets a flag that causes subsequent C<ev_loop> iterations
181	This function reinitialises the kernel state for backends that have	576	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	577	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	578	the child process (or both child and parent, but that again makes little
184	again makes little sense).	579	sense). You I<must> call it in the child before using any of the libev
		580	functions, and it will only take effect at the next C<ev_loop> iteration.
185		581
186	You I<must> call this function after forking if and only if you want to	582	On the other hand, you only need to call this function in the child
187	use the event library in both processes. If you just fork+exec, you don't	583	process if and only if you want to use the event library in the child. If
188	have to call it.	584	you just fork+exec, you don't have to call it at all.
189		585
190	The function itself is quite fast and it's usually not a problem to call	586	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	587	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>:	588	quite nicely into a call to C<pthread_atfork>:
193		589
…		…
195		591
196	=item ev_loop_fork (loop)	592	=item ev_loop_fork (loop)
197		593
198	Like C<ev_default_fork>, but acts on an event loop created by	594	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	595	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.	596	after fork that you want to re-use in the child, and how you do this is
		597	entirely your own problem.
201		598
		599	=item int ev_is_default_loop (loop)
		600
		601	Returns true when the given loop is, in fact, the default loop, and false
		602	otherwise.
		603
		604	=item unsigned int ev_loop_count (loop)
		605
		606	Returns the count of loop iterations for the loop, which is identical to
		607	the number of times libev did poll for new events. It starts at C<0> and
		608	happily wraps around with enough iterations.
		609
		610	This value can sometimes be useful as a generation counter of sorts (it
		611	"ticks" the number of loop iterations), as it roughly corresponds with
		612	C<ev_prepare> and C<ev_check> calls.
		613
202	=item unsigned int ev_method (loop)	614	=item unsigned int ev_backend (loop)
203		615
204	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	616	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
205	use.	617	use.
206		618
207	=item ev_tstamp ev_now (loop)	619	=item ev_tstamp ev_now (loop)
208		620
209	Returns the current "event loop time", which is the time the event loop	621	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	622	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	623	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	624	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).	625	event occurring (or more correctly, libev finding out about it).
		626
		627	=item ev_now_update (loop)
		628
		629	Establishes the current time by querying the kernel, updating the time
		630	returned by C<ev_now ()> in the progress. This is a costly operation and
		631	is usually done automatically within C<ev_loop ()>.
		632
		633	This function is rarely useful, but when some event callback runs for a
		634	very long time without entering the event loop, updating libev's idea of
		635	the current time is a good idea.
		636
		637	See also "The special problem of time updates" in the C<ev_timer> section.
214		638
215	=item ev_loop (loop, int flags)	639	=item ev_loop (loop, int flags)
216		640
217	Finally, this is it, the event handler. This function usually is called	641	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	642	after you initialised all your watchers and you want to start handling
219	events.	643	events.
220		644
221	If the flags argument is specified as 0, it will not return until either	645	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.	646	either no event watchers are active anymore or C<ev_unloop> was called.
		647
		648	Please note that an explicit C<ev_unloop> is usually better than
		649	relying on all watchers to be stopped when deciding when a program has
		650	finished (especially in interactive programs), but having a program
		651	that automatically loops as long as it has to and no longer by virtue
		652	of relying on its watchers stopping correctly, that is truly a thing of
		653	beauty.
223		654
224	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	655	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	656	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.	657	process in case there are no events and will return after one iteration of
		658	the loop.
227		659
228	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	660	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	661	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	662	will block your process until at least one new event arrives (which could
		663	be an event internal to libev itself, so there is no guarantee that a
		664	user-registered callback will be called), and will return after one
231	one iteration of the loop.	665	iteration of the loop.
232		666
233	This flags value could be used to implement alternative looping	667	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	668	with something not expressible using other libev watchers (i.e. "roll your
235	more generic mechanism.	669	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		670	usually a better approach for this kind of thing.
		671
		672	Here are the gory details of what C<ev_loop> does:
		673
		674	- Before the first iteration, call any pending watchers.
		675	* If EVFLAG_FORKCHECK was used, check for a fork.
		676	- If a fork was detected (by any means), queue and call all fork watchers.
		677	- Queue and call all prepare watchers.
		678	- If we have been forked, detach and recreate the kernel state
		679	as to not disturb the other process.
		680	- Update the kernel state with all outstanding changes.
		681	- Update the "event loop time" (ev_now ()).
		682	- Calculate for how long to sleep or block, if at all
		683	(active idle watchers, EVLOOP_NONBLOCK or not having
		684	any active watchers at all will result in not sleeping).
		685	- Sleep if the I/O and timer collect interval say so.
		686	- Block the process, waiting for any events.
		687	- Queue all outstanding I/O (fd) events.
		688	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
		689	- Queue all expired timers.
		690	- Queue all expired periodics.
		691	- Unless any events are pending now, queue all idle watchers.
		692	- Queue all check watchers.
		693	- Call all queued watchers in reverse order (i.e. check watchers first).
		694	Signals and child watchers are implemented as I/O watchers, and will
		695	be handled here by queueing them when their watcher gets executed.
		696	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		697	were used, or there are no active watchers, return, otherwise
		698	continue with step *.
		699
		700	Example: Queue some jobs and then loop until no events are outstanding
		701	anymore.
		702
		703	... queue jobs here, make sure they register event watchers as long
		704	... as they still have work to do (even an idle watcher will do..)
		705	ev_loop (my_loop, 0);
		706	... jobs done or somebody called unloop. yeah!
236		707
237	=item ev_unloop (loop, how)	708	=item ev_unloop (loop, how)
238		709
239	Can be used to make a call to C<ev_loop> return early (but only after it	710	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	711	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	712	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.	713	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		714
		715	This "unloop state" will be cleared when entering C<ev_loop> again.
		716
		717	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
243		718
244	=item ev_ref (loop)	719	=item ev_ref (loop)
245		720
246	=item ev_unref (loop)	721	=item ev_unref (loop)
247		722
248	Ref/unref can be used to add or remove a reference count on the event	723	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	724	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	725	count is nonzero, C<ev_loop> will not return on its own.
		726
251	a watcher you never unregister that should not keep C<ev_loop> from	727	If you have a watcher you never unregister that should not keep C<ev_loop>
252	returning, ev_unref() after starting, and ev_ref() before stopping it. For	728	from returning, call ev_unref() after starting, and ev_ref() before
		729	stopping it.
		730
253	example, libev itself uses this for its internal signal pipe: It is not	731	As an example, libev itself uses this for its internal signal pipe: It is
254	visible to the libev user and should not keep C<ev_loop> from exiting if	732	not visible to the libev user and should not keep C<ev_loop> from exiting
255	no event watchers registered by it are active. It is also an excellent	733	if no event watchers registered by it are active. It is also an excellent
256	way to do this for generic recurring timers or from within third-party	734	way to do this for generic recurring timers or from within third-party
257	libraries. Just remember to I<unref after start> and I<ref before stop>.	735	libraries. Just remember to I<unref after start> and I<ref before stop>
		736	(but only if the watcher wasn't active before, or was active before,
		737	respectively).
		738
		739	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		740	running when nothing else is active.
		741
		742	ev_signal exitsig;
		743	ev_signal_init (&exitsig, sig_cb, SIGINT);
		744	ev_signal_start (loop, &exitsig);
		745	evf_unref (loop);
		746
		747	Example: For some weird reason, unregister the above signal handler again.
		748
		749	ev_ref (loop);
		750	ev_signal_stop (loop, &exitsig);
		751
		752	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		753
		754	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		755
		756	These advanced functions influence the time that libev will spend waiting
		757	for events. Both time intervals are by default C<0>, meaning that libev
		758	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		759	latency.
		760
		761	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		762	allows libev to delay invocation of I/O and timer/periodic callbacks
		763	to increase efficiency of loop iterations (or to increase power-saving
		764	opportunities).
		765
		766	The idea is that sometimes your program runs just fast enough to handle
		767	one (or very few) event(s) per loop iteration. While this makes the
		768	program responsive, it also wastes a lot of CPU time to poll for new
		769	events, especially with backends like C<select ()> which have a high
		770	overhead for the actual polling but can deliver many events at once.
		771
		772	By setting a higher I<io collect interval> you allow libev to spend more
		773	time collecting I/O events, so you can handle more events per iteration,
		774	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		775	C<ev_timer>) will be not affected. Setting this to a non-null value will
		776	introduce an additional C<ev_sleep ()> call into most loop iterations.
		777
		778	Likewise, by setting a higher I<timeout collect interval> you allow libev
		779	to spend more time collecting timeouts, at the expense of increased
		780	latency/jitter/inexactness (the watcher callback will be called
		781	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		782	value will not introduce any overhead in libev.
		783
		784	Many (busy) programs can usually benefit by setting the I/O collect
		785	interval to a value near C<0.1> or so, which is often enough for
		786	interactive servers (of course not for games), likewise for timeouts. It
		787	usually doesn't make much sense to set it to a lower value than C<0.01>,
		788	as this approaches the timing granularity of most systems.
		789
		790	Setting the I<timeout collect interval> can improve the opportunity for
		791	saving power, as the program will "bundle" timer callback invocations that
		792	are "near" in time together, by delaying some, thus reducing the number of
		793	times the process sleeps and wakes up again. Another useful technique to
		794	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		795	they fire on, say, one-second boundaries only.
		796
		797	=item ev_loop_verify (loop)
		798
		799	This function only does something when C<EV_VERIFY> support has been
		800	compiled in, which is the default for non-minimal builds. It tries to go
		801	through all internal structures and checks them for validity. If anything
		802	is found to be inconsistent, it will print an error message to standard
		803	error and call C<abort ()>.
		804
		805	This can be used to catch bugs inside libev itself: under normal
		806	circumstances, this function will never abort as of course libev keeps its
		807	data structures consistent.
258		808
259	=back	809	=back
260		810
		811
261	=head1 ANATOMY OF A WATCHER	812	=head1 ANATOMY OF A WATCHER
		813
		814	In the following description, uppercase C<TYPE> in names stands for the
		815	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		816	watchers and C<ev_io_start> for I/O watchers.
262		817
263	A watcher is a structure that you create and register to record your	818	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	819	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:	820	become readable, you would create an C<ev_io> watcher for that:
266		821
267	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	822	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
268	{	823	{
269	ev_io_stop (w);	824	ev_io_stop (w);
270	ev_unloop (loop, EVUNLOOP_ALL);	825	ev_unloop (loop, EVUNLOOP_ALL);
271	}	826	}
272		827
273	struct ev_loop *loop = ev_default_loop (0);	828	struct ev_loop *loop = ev_default_loop (0);
		829
274	struct ev_io stdin_watcher;	830	ev_io stdin_watcher;
		831
275	ev_init (&stdin_watcher, my_cb);	832	ev_init (&stdin_watcher, my_cb);
276	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	833	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
277	ev_io_start (loop, &stdin_watcher);	834	ev_io_start (loop, &stdin_watcher);
		835
278	ev_loop (loop, 0);	836	ev_loop (loop, 0);
279		837
280	As you can see, you are responsible for allocating the memory for your	838	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,	839	watcher structures (and it is I<usually> a bad idea to do this on the
282	although this can sometimes be quite valid).	840	stack).
		841
		842	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		843	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
283		844
284	Each watcher structure must be initialised by a call to C<ev_init	845	Each watcher structure must be initialised by a call to C<ev_init
285	(watcher *, callback)>, which expects a callback to be provided. This	846	(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	847	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	848	watchers, each time the event loop detects that the file descriptor given
288	is readable and/or writable).	849	is readable and/or writable).
289		850
290	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	851	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	852	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	853	is also a macro to combine initialisation and setting in one call: C<<
293	(watcher *, callback, ...) >>.	854	ev_TYPE_init (watcher *, callback, ...) >>.
294		855
295	To make the watcher actually watch out for events, you have to start it	856	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	857	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	858	*) >>), and you can stop watching for events at any time by calling the
298	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	859	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
299		860
300	As long as your watcher is active (has been started but not stopped) you	861	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	862	must not touch the values stored in it. Most specifically you must never
302	reinitialise it or call its set method.	863	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		864
309	Each and every callback receives the event loop pointer as first, the	865	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	866	registered watcher structure as second, and a bitset of received events as
311	third argument.	867	third argument.
312		868
…		…
336	The signal specified in the C<ev_signal> watcher has been received by a thread.	892	The signal specified in the C<ev_signal> watcher has been received by a thread.
337		893
338	=item C<EV_CHILD>	894	=item C<EV_CHILD>
339		895
340	The pid specified in the C<ev_child> watcher has received a status change.	896	The pid specified in the C<ev_child> watcher has received a status change.
		897
		898	=item C<EV_STAT>
		899
		900	The path specified in the C<ev_stat> watcher changed its attributes somehow.
341		901
342	=item C<EV_IDLE>	902	=item C<EV_IDLE>
343		903
344	The C<ev_idle> watcher has determined that you have nothing better to do.	904	The C<ev_idle> watcher has determined that you have nothing better to do.
345		905
…		…
353	received events. Callbacks of both watcher types can start and stop as	913	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	914	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	915	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
356	C<ev_loop> from blocking).	916	C<ev_loop> from blocking).
357		917
		918	=item C<EV_EMBED>
		919
		920	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		921
		922	=item C<EV_FORK>
		923
		924	The event loop has been resumed in the child process after fork (see
		925	C<ev_fork>).
		926
		927	=item C<EV_ASYNC>
		928
		929	The given async watcher has been asynchronously notified (see C<ev_async>).
		930
358	=item C<EV_ERROR>	931	=item C<EV_ERROR>
359		932
360	An unspecified error has occured, the watcher has been stopped. This might	933	An unspecified error has occurred, the watcher has been stopped. This might
361	happen because the watcher could not be properly started because libev	934	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	935	ran out of memory, a file descriptor was found to be closed or any other
		936	problem. Libev considers these application bugs.
		937
363	problem. You best act on it by reporting the problem and somehow coping	938	You best act on it by reporting the problem and somehow coping with the
364	with the watcher being stopped.	939	watcher being stopped. Note that well-written programs should not receive
		940	an error ever, so when your watcher receives it, this usually indicates a
		941	bug in your program.
365		942
366	Libev will usually signal a few "dummy" events together with an error,	943	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	944	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	945	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	946	the error from read() or write(). This will not work in multi-threaded
370	programs, though, so beware.	947	programs, though, as the fd could already be closed and reused for another
		948	thing, so beware.
371		949
372	=back	950	=back
373		951
		952	=head2 GENERIC WATCHER FUNCTIONS
		953
		954	=over 4
		955
		956	=item C<ev_init> (ev_TYPE *watcher, callback)
		957
		958	This macro initialises the generic portion of a watcher. The contents
		959	of the watcher object can be arbitrary (so C<malloc> will do). Only
		960	the generic parts of the watcher are initialised, you I<need> to call
		961	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		962	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		963	which rolls both calls into one.
		964
		965	You can reinitialise a watcher at any time as long as it has been stopped
		966	(or never started) and there are no pending events outstanding.
		967
		968	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		969	int revents)>.
		970
		971	Example: Initialise an C<ev_io> watcher in two steps.
		972
		973	ev_io w;
		974	ev_init (&w, my_cb);
		975	ev_io_set (&w, STDIN_FILENO, EV_READ);
		976
		977	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		978
		979	This macro initialises the type-specific parts of a watcher. You need to
		980	call C<ev_init> at least once before you call this macro, but you can
		981	call C<ev_TYPE_set> any number of times. You must not, however, call this
		982	macro on a watcher that is active (it can be pending, however, which is a
		983	difference to the C<ev_init> macro).
		984
		985	Although some watcher types do not have type-specific arguments
		986	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		987
		988	See C<ev_init>, above, for an example.
		989
		990	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		991
		992	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		993	calls into a single call. This is the most convenient method to initialise
		994	a watcher. The same limitations apply, of course.
		995
		996	Example: Initialise and set an C<ev_io> watcher in one step.
		997
		998	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		999
		1000	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		1001
		1002	Starts (activates) the given watcher. Only active watchers will receive
		1003	events. If the watcher is already active nothing will happen.
		1004
		1005	Example: Start the C<ev_io> watcher that is being abused as example in this
		1006	whole section.
		1007
		1008	ev_io_start (EV_DEFAULT_UC, &w);
		1009
		1010	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		1011
		1012	Stops the given watcher if active, and clears the pending status (whether
		1013	the watcher was active or not).
		1014
		1015	It is possible that stopped watchers are pending - for example,
		1016	non-repeating timers are being stopped when they become pending - but
		1017	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1018	pending. If you want to free or reuse the memory used by the watcher it is
		1019	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1020
		1021	=item bool ev_is_active (ev_TYPE *watcher)
		1022
		1023	Returns a true value iff the watcher is active (i.e. it has been started
		1024	and not yet been stopped). As long as a watcher is active you must not modify
		1025	it.
		1026
		1027	=item bool ev_is_pending (ev_TYPE *watcher)
		1028
		1029	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1030	events but its callback has not yet been invoked). As long as a watcher
		1031	is pending (but not active) you must not call an init function on it (but
		1032	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1033	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1034	it).
		1035
		1036	=item callback ev_cb (ev_TYPE *watcher)
		1037
		1038	Returns the callback currently set on the watcher.
		1039
		1040	=item ev_cb_set (ev_TYPE *watcher, callback)
		1041
		1042	Change the callback. You can change the callback at virtually any time
		1043	(modulo threads).
		1044
		1045	=item ev_set_priority (ev_TYPE *watcher, priority)
		1046
		1047	=item int ev_priority (ev_TYPE *watcher)
		1048
		1049	Set and query the priority of the watcher. The priority is a small
		1050	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1051	(default: C<-2>). Pending watchers with higher priority will be invoked
		1052	before watchers with lower priority, but priority will not keep watchers
		1053	from being executed (except for C<ev_idle> watchers).
		1054
		1055	This means that priorities are I<only> used for ordering callback
		1056	invocation after new events have been received. This is useful, for
		1057	example, to reduce latency after idling, or more often, to bind two
		1058	watchers on the same event and make sure one is called first.
		1059
		1060	If you need to suppress invocation when higher priority events are pending
		1061	you need to look at C<ev_idle> watchers, which provide this functionality.
		1062
		1063	You I<must not> change the priority of a watcher as long as it is active or
		1064	pending.
		1065
		1066	The default priority used by watchers when no priority has been set is
		1067	always C<0>, which is supposed to not be too high and not be too low :).
		1068
		1069	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1070	fine, as long as you do not mind that the priority value you query might
		1071	or might not have been clamped to the valid range.
		1072
		1073	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1074
		1075	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1076	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1077	can deal with that fact, as both are simply passed through to the
		1078	callback.
		1079
		1080	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1081
		1082	If the watcher is pending, this function clears its pending status and
		1083	returns its C<revents> bitset (as if its callback was invoked). If the
		1084	watcher isn't pending it does nothing and returns C<0>.
		1085
		1086	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1087	callback to be invoked, which can be accomplished with this function.
		1088
		1089	=back
		1090
		1091
374	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1092	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
375		1093
376	Each watcher has, by default, a member C<void *data> that you can change	1094	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	1095	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	1096	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	1097	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	1098	member, you can also "subclass" the watcher type and provide your own
381	data:	1099	data:
382		1100
383	struct my_io	1101	struct my_io
384	{	1102	{
385	struct ev_io io;	1103	ev_io io;
386	int otherfd;	1104	int otherfd;
387	void *somedata;	1105	void *somedata;
388	struct whatever *mostinteresting;	1106	struct whatever *mostinteresting;
389	}	1107	};
		1108
		1109	...
		1110	struct my_io w;
		1111	ev_io_init (&w.io, my_cb, fd, EV_READ);
390		1112
391	And since your callback will be called with a pointer to the watcher, you	1113	And since your callback will be called with a pointer to the watcher, you
392	can cast it back to your own type:	1114	can cast it back to your own type:
393		1115
394	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1116	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
395	{	1117	{
396	struct my_io *w = (struct my_io *)w_;	1118	struct my_io *w = (struct my_io *)w_;
397	...	1119	...
398	}	1120	}
399		1121
400	More interesting and less C-conformant ways of catsing your callback type	1122	More interesting and less C-conformant ways of casting your callback type
401	have been omitted....	1123	instead have been omitted.
		1124
		1125	Another common scenario is to use some data structure with multiple
		1126	embedded watchers:
		1127
		1128	struct my_biggy
		1129	{
		1130	int some_data;
		1131	ev_timer t1;
		1132	ev_timer t2;
		1133	}
		1134
		1135	In this case getting the pointer to C<my_biggy> is a bit more
		1136	complicated: Either you store the address of your C<my_biggy> struct
		1137	in the C<data> member of the watcher (for woozies), or you need to use
		1138	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1139	programmers):
		1140
		1141	#include <stddef.h>
		1142
		1143	static void
		1144	t1_cb (EV_P_ ev_timer *w, int revents)
		1145	{
		1146	struct my_biggy big = (struct my_biggy *
		1147	(((char *)w) - offsetof (struct my_biggy, t1));
		1148	}
		1149
		1150	static void
		1151	t2_cb (EV_P_ ev_timer *w, int revents)
		1152	{
		1153	struct my_biggy big = (struct my_biggy *
		1154	(((char *)w) - offsetof (struct my_biggy, t2));
		1155	}
402		1156
403		1157
404	=head1 WATCHER TYPES	1158	=head1 WATCHER TYPES
405		1159
406	This section describes each watcher in detail, but will not repeat	1160	This section describes each watcher in detail, but will not repeat
407	information given in the last section.	1161	information given in the last section. Any initialisation/set macros,
		1162	functions and members specific to the watcher type are explained.
408		1163
		1164	Members are additionally marked with either I<[read-only]>, meaning that,
		1165	while the watcher is active, you can look at the member and expect some
		1166	sensible content, but you must not modify it (you can modify it while the
		1167	watcher is stopped to your hearts content), or I<[read-write]>, which
		1168	means you can expect it to have some sensible content while the watcher
		1169	is active, but you can also modify it. Modifying it may not do something
		1170	sensible or take immediate effect (or do anything at all), but libev will
		1171	not crash or malfunction in any way.
		1172
		1173
409	=head2 C<ev_io> - is this file descriptor readable or writable	1174	=head2 C<ev_io> - is this file descriptor readable or writable?
410		1175
411	I/O watchers check whether a file descriptor is readable or writable	1176	I/O watchers check whether a file descriptor is readable or writable
412	in each iteration of the event loop (This behaviour is called	1177	in each iteration of the event loop, or, more precisely, when reading
413	level-triggering because you keep receiving events as long as the	1178	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	1179	some data. This behaviour is called level-triggering because you keep
415	act on the event and neither want to receive future events).	1180	receiving events as long as the condition persists. Remember you can stop
		1181	the watcher if you don't want to act on the event and neither want to
		1182	receive future events.
416		1183
417	In general you can register as many read and/or write event watchers oer	1184	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	1185	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	1186	descriptors to non-blocking mode is also usually a good idea (but not
420	required if you know what you are doing).	1187	required if you know what you are doing).
421		1188
422	You have to be careful with dup'ed file descriptors, though. Some backends	1189	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	1190	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	1191	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
425	to the same file/socket etc. description.
426		1192
427	If you must do this, then force the use of a known-to-be-good backend	1193	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	1194	receive "spurious" readiness notifications, that is your callback might
429	EVMETHOD_POLL).	1195	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1196	because there is no data. Not only are some backends known to create a
		1197	lot of those (for example Solaris ports), it is very easy to get into
		1198	this situation even with a relatively standard program structure. Thus
		1199	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1200	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1201
		1202	If you cannot run the fd in non-blocking mode (for example you should
		1203	not play around with an Xlib connection), then you have to separately
		1204	re-test whether a file descriptor is really ready with a known-to-be good
		1205	interface such as poll (fortunately in our Xlib example, Xlib already
		1206	does this on its own, so its quite safe to use). Some people additionally
		1207	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1208	indefinitely.
		1209
		1210	But really, best use non-blocking mode.
		1211
		1212	=head3 The special problem of disappearing file descriptors
		1213
		1214	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1215	descriptor (either due to calling C<close> explicitly or any other means,
		1216	such as C<dup2>). The reason is that you register interest in some file
		1217	descriptor, but when it goes away, the operating system will silently drop
		1218	this interest. If another file descriptor with the same number then is
		1219	registered with libev, there is no efficient way to see that this is, in
		1220	fact, a different file descriptor.
		1221
		1222	To avoid having to explicitly tell libev about such cases, libev follows
		1223	the following policy: Each time C<ev_io_set> is being called, libev
		1224	will assume that this is potentially a new file descriptor, otherwise
		1225	it is assumed that the file descriptor stays the same. That means that
		1226	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1227	descriptor even if the file descriptor number itself did not change.
		1228
		1229	This is how one would do it normally anyway, the important point is that
		1230	the libev application should not optimise around libev but should leave
		1231	optimisations to libev.
		1232
		1233	=head3 The special problem of dup'ed file descriptors
		1234
		1235	Some backends (e.g. epoll), cannot register events for file descriptors,
		1236	but only events for the underlying file descriptions. That means when you
		1237	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1238	events for them, only one file descriptor might actually receive events.
		1239
		1240	There is no workaround possible except not registering events
		1241	for potentially C<dup ()>'ed file descriptors, or to resort to
		1242	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1243
		1244	=head3 The special problem of fork
		1245
		1246	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1247	useless behaviour. Libev fully supports fork, but needs to be told about
		1248	it in the child.
		1249
		1250	To support fork in your programs, you either have to call
		1251	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1252	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1253	C<EVBACKEND_POLL>.
		1254
		1255	=head3 The special problem of SIGPIPE
		1256
		1257	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1258	when writing to a pipe whose other end has been closed, your program gets
		1259	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1260	this is sensible behaviour, for daemons, this is usually undesirable.
		1261
		1262	So when you encounter spurious, unexplained daemon exits, make sure you
		1263	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1264	somewhere, as that would have given you a big clue).
		1265
		1266
		1267	=head3 Watcher-Specific Functions
430		1268
431	=over 4	1269	=over 4
432		1270
433	=item ev_io_init (ev_io *, callback, int fd, int events)	1271	=item ev_io_init (ev_io *, callback, int fd, int events)
434		1272
435	=item ev_io_set (ev_io *, int fd, int events)	1273	=item ev_io_set (ev_io *, int fd, int events)
436		1274
437	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1275	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 |	1276	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
439	EV_WRITE> to receive the given events.	1277	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1278
		1279	=item int fd [read-only]
		1280
		1281	The file descriptor being watched.
		1282
		1283	=item int events [read-only]
		1284
		1285	The events being watched.
440		1286
441	=back	1287	=back
442		1288
		1289	=head3 Examples
		1290
		1291	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1292	readable, but only once. Since it is likely line-buffered, you could
		1293	attempt to read a whole line in the callback.
		1294
		1295	static void
		1296	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1297	{
		1298	ev_io_stop (loop, w);
		1299	.. read from stdin here (or from w->fd) and handle any I/O errors
		1300	}
		1301
		1302	...
		1303	struct ev_loop *loop = ev_default_init (0);
		1304	ev_io stdin_readable;
		1305	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1306	ev_io_start (loop, &stdin_readable);
		1307	ev_loop (loop, 0);
		1308
		1309
443	=head2 C<ev_timer> - relative and optionally recurring timeouts	1310	=head2 C<ev_timer> - relative and optionally repeating timeouts
444		1311
445	Timer watchers are simple relative timers that generate an event after a	1312	Timer watchers are simple relative timers that generate an event after a
446	given time, and optionally repeating in regular intervals after that.	1313	given time, and optionally repeating in regular intervals after that.
447		1314
448	The timers are based on real time, that is, if you register an event that	1315	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	1316	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	1317	year, it will still time out after (roughly) one hour. "Roughly" because
451	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1318	detecting time jumps is hard, and some inaccuracies are unavoidable (the
452	monotonic clock option helps a lot here).	1319	monotonic clock option helps a lot here).
		1320
		1321	The callback is guaranteed to be invoked only I<after> its timeout has
		1322	passed, but if multiple timers become ready during the same loop iteration
		1323	then order of execution is undefined.
		1324
		1325	=head3 Be smart about timeouts
		1326
		1327	Many real-world problems involve some kind of timeout, usually for error
		1328	recovery. A typical example is an HTTP request - if the other side hangs,
		1329	you want to raise some error after a while.
		1330
		1331	What follows are some ways to handle this problem, from obvious and
		1332	inefficient to smart and efficient.
		1333
		1334	In the following, a 60 second activity timeout is assumed - a timeout that
		1335	gets reset to 60 seconds each time there is activity (e.g. each time some
		1336	data or other life sign was received).
		1337
		1338	=over 4
		1339
		1340	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1341
		1342	This is the most obvious, but not the most simple way: In the beginning,
		1343	start the watcher:
		1344
		1345	ev_timer_init (timer, callback, 60., 0.);
		1346	ev_timer_start (loop, timer);
		1347
		1348	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1349	and start it again:
		1350
		1351	ev_timer_stop (loop, timer);
		1352	ev_timer_set (timer, 60., 0.);
		1353	ev_timer_start (loop, timer);
		1354
		1355	This is relatively simple to implement, but means that each time there is
		1356	some activity, libev will first have to remove the timer from its internal
		1357	data structure and then add it again. Libev tries to be fast, but it's
		1358	still not a constant-time operation.
		1359
		1360	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1361
		1362	This is the easiest way, and involves using C<ev_timer_again> instead of
		1363	C<ev_timer_start>.
		1364
		1365	To implement this, configure an C<ev_timer> with a C<repeat> value
		1366	of C<60> and then call C<ev_timer_again> at start and each time you
		1367	successfully read or write some data. If you go into an idle state where
		1368	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1369	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1370
		1371	That means you can ignore both the C<ev_timer_start> function and the
		1372	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1373	member and C<ev_timer_again>.
		1374
		1375	At start:
		1376
		1377	ev_timer_init (timer, callback);
		1378	timer->repeat = 60.;
		1379	ev_timer_again (loop, timer);
		1380
		1381	Each time there is some activity:
		1382
		1383	ev_timer_again (loop, timer);
		1384
		1385	It is even possible to change the time-out on the fly, regardless of
		1386	whether the watcher is active or not:
		1387
		1388	timer->repeat = 30.;
		1389	ev_timer_again (loop, timer);
		1390
		1391	This is slightly more efficient then stopping/starting the timer each time
		1392	you want to modify its timeout value, as libev does not have to completely
		1393	remove and re-insert the timer from/into its internal data structure.
		1394
		1395	It is, however, even simpler than the "obvious" way to do it.
		1396
		1397	=item 3. Let the timer time out, but then re-arm it as required.
		1398
		1399	This method is more tricky, but usually most efficient: Most timeouts are
		1400	relatively long compared to the intervals between other activity - in
		1401	our example, within 60 seconds, there are usually many I/O events with
		1402	associated activity resets.
		1403
		1404	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1405	but remember the time of last activity, and check for a real timeout only
		1406	within the callback:
		1407
		1408	ev_tstamp last_activity; // time of last activity
		1409
		1410	static void
		1411	callback (EV_P_ ev_timer *w, int revents)
		1412	{
		1413	ev_tstamp now = ev_now (EV_A);
		1414	ev_tstamp timeout = last_activity + 60.;
		1415
		1416	// if last_activity + 60. is older than now, we did time out
		1417	if (timeout < now)
		1418	{
		1419	// timeout occured, take action
		1420	}
		1421	else
		1422	{
		1423	// callback was invoked, but there was some activity, re-arm
		1424	// the watcher to fire in last_activity + 60, which is
		1425	// guaranteed to be in the future, so "again" is positive:
		1426	w->repeat = timeout - now;
		1427	ev_timer_again (EV_A_ w);
		1428	}
		1429	}
		1430
		1431	To summarise the callback: first calculate the real timeout (defined
		1432	as "60 seconds after the last activity"), then check if that time has
		1433	been reached, which means something I<did>, in fact, time out. Otherwise
		1434	the callback was invoked too early (C<timeout> is in the future), so
		1435	re-schedule the timer to fire at that future time, to see if maybe we have
		1436	a timeout then.
		1437
		1438	Note how C<ev_timer_again> is used, taking advantage of the
		1439	C<ev_timer_again> optimisation when the timer is already running.
		1440
		1441	This scheme causes more callback invocations (about one every 60 seconds
		1442	minus half the average time between activity), but virtually no calls to
		1443	libev to change the timeout.
		1444
		1445	To start the timer, simply initialise the watcher and set C<last_activity>
		1446	to the current time (meaning we just have some activity :), then call the
		1447	callback, which will "do the right thing" and start the timer:
		1448
		1449	ev_timer_init (timer, callback);
		1450	last_activity = ev_now (loop);
		1451	callback (loop, timer, EV_TIMEOUT);
		1452
		1453	And when there is some activity, simply store the current time in
		1454	C<last_activity>, no libev calls at all:
		1455
		1456	last_actiivty = ev_now (loop);
		1457
		1458	This technique is slightly more complex, but in most cases where the
		1459	time-out is unlikely to be triggered, much more efficient.
		1460
		1461	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1462	callback :) - just change the timeout and invoke the callback, which will
		1463	fix things for you.
		1464
		1465	=item 4. Wee, just use a double-linked list for your timeouts.
		1466
		1467	If there is not one request, but many thousands (millions...), all
		1468	employing some kind of timeout with the same timeout value, then one can
		1469	do even better:
		1470
		1471	When starting the timeout, calculate the timeout value and put the timeout
		1472	at the I<end> of the list.
		1473
		1474	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1475	the list is expected to fire (for example, using the technique #3).
		1476
		1477	When there is some activity, remove the timer from the list, recalculate
		1478	the timeout, append it to the end of the list again, and make sure to
		1479	update the C<ev_timer> if it was taken from the beginning of the list.
		1480
		1481	This way, one can manage an unlimited number of timeouts in O(1) time for
		1482	starting, stopping and updating the timers, at the expense of a major
		1483	complication, and having to use a constant timeout. The constant timeout
		1484	ensures that the list stays sorted.
		1485
		1486	=back
		1487
		1488	So which method the best?
		1489
		1490	Method #2 is a simple no-brain-required solution that is adequate in most
		1491	situations. Method #3 requires a bit more thinking, but handles many cases
		1492	better, and isn't very complicated either. In most case, choosing either
		1493	one is fine, with #3 being better in typical situations.
		1494
		1495	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1496	rather complicated, but extremely efficient, something that really pays
		1497	off after the first million or so of active timers, i.e. it's usually
		1498	overkill :)
		1499
		1500	=head3 The special problem of time updates
		1501
		1502	Establishing the current time is a costly operation (it usually takes at
		1503	least two system calls): EV therefore updates its idea of the current
		1504	time only before and after C<ev_loop> collects new events, which causes a
		1505	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1506	lots of events in one iteration.
453		1507
454	The relative timeouts are calculated relative to the C<ev_now ()>	1508	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	1509	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	1510	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	1511	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:	1512	timeout on the current time, use something like this to adjust for this:
459		1513
460	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1514	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
461		1515
		1516	If the event loop is suspended for a long time, you can also force an
		1517	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		1518	()>.
		1519
		1520	=head3 Watcher-Specific Functions and Data Members
		1521
462	=over 4	1522	=over 4
463		1523
464	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1524	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
465		1525
466	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1526	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
467		1527
468	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1528	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	1529	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	1530	reached. If it is positive, then the timer will automatically be
471	later, again, and again, until stopped manually.	1531	configured to trigger again C<repeat> seconds later, again, and again,
		1532	until stopped manually.
472		1533
473	The timer itself will do a best-effort at avoiding drift, that is, if you	1534	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	1535	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	1536	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	1537	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.	1538	do stuff) the timer will not fire more than once per event loop iteration.
478		1539
479	=item ev_timer_again (loop)	1540	=item ev_timer_again (loop, ev_timer *)
480		1541
481	This will act as if the timer timed out and restart it again if it is	1542	This will act as if the timer timed out and restart it again if it is
482	repeating. The exact semantics are:	1543	repeating. The exact semantics are:
483		1544
		1545	If the timer is pending, its pending status is cleared.
		1546
484	If the timer is started but nonrepeating, stop it.	1547	If the timer is started but non-repeating, stop it (as if it timed out).
485		1548
486	If the timer is repeating, either start it if necessary (with the repeat	1549	If the timer is repeating, either start it if necessary (with the
487	value), or reset the running timer to the repeat value.	1550	C<repeat> value), or reset the running timer to the C<repeat> value.
488		1551
489	This sounds a bit complicated, but here is a useful and typical	1552	This sounds a bit complicated, see "Be smart about timeouts", above, for a
490	example: Imagine you have a tcp connection and you want a so-called idle	1553	usage example.
491	timeout, that is, you want to be called when there have been, say, 60	1554
492	seconds of inactivity on the socket. The easiest way to do this is to	1555	=item ev_tstamp repeat [read-write]
493	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1556
494	time you successfully read or write some data. If you go into an idle	1557	The current C<repeat> value. Will be used each time the watcher times out
495	state where you do not expect data to travel on the socket, you can stop	1558	or C<ev_timer_again> is called, and determines the next timeout (if any),
496	the timer, and again will automatically restart it if need be.	1559	which is also when any modifications are taken into account.
497		1560
498	=back	1561	=back
499		1562
		1563	=head3 Examples
		1564
		1565	Example: Create a timer that fires after 60 seconds.
		1566
		1567	static void
		1568	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1569	{
		1570	.. one minute over, w is actually stopped right here
		1571	}
		1572
		1573	ev_timer mytimer;
		1574	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1575	ev_timer_start (loop, &mytimer);
		1576
		1577	Example: Create a timeout timer that times out after 10 seconds of
		1578	inactivity.
		1579
		1580	static void
		1581	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1582	{
		1583	.. ten seconds without any activity
		1584	}
		1585
		1586	ev_timer mytimer;
		1587	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1588	ev_timer_again (&mytimer); /* start timer */
		1589	ev_loop (loop, 0);
		1590
		1591	// and in some piece of code that gets executed on any "activity":
		1592	// reset the timeout to start ticking again at 10 seconds
		1593	ev_timer_again (&mytimer);
		1594
		1595
500	=head2 C<ev_periodic> - to cron or not to cron	1596	=head2 C<ev_periodic> - to cron or not to cron?
501		1597
502	Periodic watchers are also timers of a kind, but they are very versatile	1598	Periodic watchers are also timers of a kind, but they are very versatile
503	(and unfortunately a bit complex).	1599	(and unfortunately a bit complex).
504		1600
505	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1601	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
506	but on wallclock time (absolute time). You can tell a periodic watcher	1602	but on wall clock time (absolute time). You can tell a periodic watcher
507	to trigger "at" some specific point in time. For example, if you tell a	1603	to trigger after some specific point in time. For example, if you tell a
508	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1604	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
509	+ 10.>) and then reset your system clock to the last year, then it will	1605	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1606	clock to January of the previous year, then it will take more than year
510	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1607	to trigger the event (unlike an C<ev_timer>, which would still trigger
511	roughly 10 seconds later and of course not if you reset your system time	1608	roughly 10 seconds later as it uses a relative timeout).
512	again).
513		1609
514	They can also be used to implement vastly more complex timers, such as	1610	C<ev_periodic>s can also be used to implement vastly more complex timers,
515	triggering an event on eahc midnight, local time.	1611	such as triggering an event on each "midnight, local time", or other
		1612	complicated rules.
		1613
		1614	As with timers, the callback is guaranteed to be invoked only when the
		1615	time (C<at>) has passed, but if multiple periodic timers become ready
		1616	during the same loop iteration, then order of execution is undefined.
		1617
		1618	=head3 Watcher-Specific Functions and Data Members
516		1619
517	=over 4	1620	=over 4
518		1621
519	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1622	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
520		1623
521	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1624	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
522		1625
523	Lots of arguments, lets sort it out... There are basically three modes of	1626	Lots of arguments, lets sort it out... There are basically three modes of
524	operation, and we will explain them from simplest to complex:	1627	operation, and we will explain them from simplest to most complex:
525
526		1628
527	=over 4	1629	=over 4
528		1630
529	=item * absolute timer (interval = reschedule_cb = 0)	1631	=item * absolute timer (at = time, interval = reschedule_cb = 0)
530		1632
531	In this configuration the watcher triggers an event at the wallclock time	1633	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,	1634	time C<at> has passed. It will not repeat and will not adjust when a time
533	that is, if it is to be run at January 1st 2011 then it will run when the	1635	jump occurs, that is, if it is to be run at January 1st 2011 then it will
534	system time reaches or surpasses this time.	1636	only run when the system clock reaches or surpasses this time.
535		1637
536	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1638	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
537		1639
538	In this mode the watcher will always be scheduled to time out at the next	1640	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	1641	C<at + N * interval> time (for some integer N, which can also be negative)
540	of any time jumps.	1642	and then repeat, regardless of any time jumps.
541		1643
542	This can be used to create timers that do not drift with respect to system	1644	This can be used to create timers that do not drift with respect to the
543	time:	1645	system clock, for example, here is a C<ev_periodic> that triggers each
		1646	hour, on the hour:
544		1647
545	ev_periodic_set (&periodic, 0., 3600., 0);	1648	ev_periodic_set (&periodic, 0., 3600., 0);
546		1649
547	This doesn't mean there will always be 3600 seconds in between triggers,	1650	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	1651	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	1652	full hour (UTC), or more correctly, when the system time is evenly divisible
550	by 3600.	1653	by 3600.
551		1654
552	Another way to think about it (for the mathematically inclined) is that	1655	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	1656	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.	1657	time where C<time = at (mod interval)>, regardless of any time jumps.
555		1658
		1659	For numerical stability it is preferable that the C<at> value is near
		1660	C<ev_now ()> (the current time), but there is no range requirement for
		1661	this value, and in fact is often specified as zero.
		1662
		1663	Note also that there is an upper limit to how often a timer can fire (CPU
		1664	speed for example), so if C<interval> is very small then timing stability
		1665	will of course deteriorate. Libev itself tries to be exact to be about one
		1666	millisecond (if the OS supports it and the machine is fast enough).
		1667
556	=item * manual reschedule mode (reschedule_cb = callback)	1668	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
557		1669
558	In this mode the values for C<interval> and C<at> are both being	1670	In this mode the values for C<interval> and C<at> are both being
559	ignored. Instead, each time the periodic watcher gets scheduled, the	1671	ignored. Instead, each time the periodic watcher gets scheduled, the
560	reschedule callback will be called with the watcher as first, and the	1672	reschedule callback will be called with the watcher as first, and the
561	current time as second argument.	1673	current time as second argument.
562		1674
563	NOTE: I<This callback MUST NOT stop or destroy the periodic or any other	1675	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
564	periodic watcher, ever, or make any event loop modifications>. If you need	1676	ever, or make ANY event loop modifications whatsoever>.
		1677
565	to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.	1678	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1679	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1680	only event loop modification you are allowed to do).
566		1681
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,	1682	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
571	ev_tstamp now)>, e.g.:	1683	*w, ev_tstamp now)>, e.g.:
572		1684
		1685	static ev_tstamp
573	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1686	my_rescheduler (ev_periodic *w, ev_tstamp now)
574	{	1687	{
575	return now + 60.;	1688	return now + 60.;
576	}	1689	}
577		1690
578	It must return the next time to trigger, based on the passed time value	1691	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	1692	(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	1693	will usually be called just before the callback will be triggered, but
581	might be called at other times, too.	1694	might be called at other times, too.
582		1695
		1696	NOTE: I<< This callback must always return a time that is higher than or
		1697	equal to the passed C<now> value >>.
		1698
583	This can be used to create very complex timers, such as a timer that	1699	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	1700	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	1701	next midnight after C<now> and return the timestamp value for this. How
586	is, again, up to you (but it is not trivial).	1702	you do this is, again, up to you (but it is not trivial, which is the main
		1703	reason I omitted it as an example).
587		1704
588	=back	1705	=back
589		1706
590	=item ev_periodic_again (loop, ev_periodic *)	1707	=item ev_periodic_again (loop, ev_periodic *)
591		1708
592	Simply stops and restarts the periodic watcher again. This is only useful	1709	Simply stops and restarts the periodic watcher again. This is only useful
593	when you changed some parameters or the reschedule callback would return	1710	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	1711	a different time than the last time it was called (e.g. in a crond like
595	program when the crontabs have changed).	1712	program when the crontabs have changed).
596		1713
		1714	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1715
		1716	When active, returns the absolute time that the watcher is supposed to
		1717	trigger next.
		1718
		1719	=item ev_tstamp offset [read-write]
		1720
		1721	When repeating, this contains the offset value, otherwise this is the
		1722	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1723
		1724	Can be modified any time, but changes only take effect when the periodic
		1725	timer fires or C<ev_periodic_again> is being called.
		1726
		1727	=item ev_tstamp interval [read-write]
		1728
		1729	The current interval value. Can be modified any time, but changes only
		1730	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1731	called.
		1732
		1733	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		1734
		1735	The current reschedule callback, or C<0>, if this functionality is
		1736	switched off. Can be changed any time, but changes only take effect when
		1737	the periodic timer fires or C<ev_periodic_again> is being called.
		1738
597	=back	1739	=back
598		1740
		1741	=head3 Examples
		1742
		1743	Example: Call a callback every hour, or, more precisely, whenever the
		1744	system time is divisible by 3600. The callback invocation times have
		1745	potentially a lot of jitter, but good long-term stability.
		1746
		1747	static void
		1748	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
		1749	{
		1750	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1751	}
		1752
		1753	ev_periodic hourly_tick;
		1754	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1755	ev_periodic_start (loop, &hourly_tick);
		1756
		1757	Example: The same as above, but use a reschedule callback to do it:
		1758
		1759	#include <math.h>
		1760
		1761	static ev_tstamp
		1762	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		1763	{
		1764	return now + (3600. - fmod (now, 3600.));
		1765	}
		1766
		1767	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1768
		1769	Example: Call a callback every hour, starting now:
		1770
		1771	ev_periodic hourly_tick;
		1772	ev_periodic_init (&hourly_tick, clock_cb,
		1773	fmod (ev_now (loop), 3600.), 3600., 0);
		1774	ev_periodic_start (loop, &hourly_tick);
		1775
		1776
599	=head2 C<ev_signal> - signal me when a signal gets signalled	1777	=head2 C<ev_signal> - signal me when a signal gets signalled!
600		1778
601	Signal watchers will trigger an event when the process receives a specific	1779	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	1780	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	1781	will try it's best to deliver signals synchronously, i.e. as part of the
604	normal event processing, like any other event.	1782	normal event processing, like any other event.
605		1783
		1784	If you want signals asynchronously, just use C<sigaction> as you would
		1785	do without libev and forget about sharing the signal. You can even use
		1786	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1787
606	You can configure as many watchers as you like per signal. Only when the	1788	You can configure as many watchers as you like per signal. Only when the
607	first watcher gets started will libev actually register a signal watcher	1789	first watcher gets started will libev actually register a signal handler
608	with the kernel (thus it coexists with your own signal handlers as long	1790	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	1791	you don't register any with libev for the same signal). Similarly, when
610	watcher for a signal is stopped libev will reset the signal handler to	1792	the last signal watcher for a signal is stopped, libev will reset the
611	SIG_DFL (regardless of what it was set to before).	1793	signal handler to SIG_DFL (regardless of what it was set to before).
		1794
		1795	If possible and supported, libev will install its handlers with
		1796	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1797	interrupted. If you have a problem with system calls getting interrupted by
		1798	signals you can block all signals in an C<ev_check> watcher and unblock
		1799	them in an C<ev_prepare> watcher.
		1800
		1801	=head3 Watcher-Specific Functions and Data Members
612		1802
613	=over 4	1803	=over 4
614		1804
615	=item ev_signal_init (ev_signal *, callback, int signum)	1805	=item ev_signal_init (ev_signal *, callback, int signum)
616		1806
617	=item ev_signal_set (ev_signal *, int signum)	1807	=item ev_signal_set (ev_signal *, int signum)
618		1808
619	Configures the watcher to trigger on the given signal number (usually one	1809	Configures the watcher to trigger on the given signal number (usually one
620	of the C<SIGxxx> constants).	1810	of the C<SIGxxx> constants).
621		1811
		1812	=item int signum [read-only]
		1813
		1814	The signal the watcher watches out for.
		1815
622	=back	1816	=back
623		1817
		1818	=head3 Examples
		1819
		1820	Example: Try to exit cleanly on SIGINT.
		1821
		1822	static void
		1823	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1824	{
		1825	ev_unloop (loop, EVUNLOOP_ALL);
		1826	}
		1827
		1828	ev_signal signal_watcher;
		1829	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1830	ev_signal_start (loop, &signal_watcher);
		1831
		1832
624	=head2 C<ev_child> - wait for pid status changes	1833	=head2 C<ev_child> - watch out for process status changes
625		1834
626	Child watchers trigger when your process receives a SIGCHLD in response to	1835	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).	1836	some child status changes (most typically when a child of yours dies or
		1837	exits). It is permissible to install a child watcher I<after> the child
		1838	has been forked (which implies it might have already exited), as long
		1839	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1840	forking and then immediately registering a watcher for the child is fine,
		1841	but forking and registering a watcher a few event loop iterations later is
		1842	not.
		1843
		1844	Only the default event loop is capable of handling signals, and therefore
		1845	you can only register child watchers in the default event loop.
		1846
		1847	=head3 Process Interaction
		1848
		1849	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1850	initialised. This is necessary to guarantee proper behaviour even if
		1851	the first child watcher is started after the child exits. The occurrence
		1852	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1853	synchronously as part of the event loop processing. Libev always reaps all
		1854	children, even ones not watched.
		1855
		1856	=head3 Overriding the Built-In Processing
		1857
		1858	Libev offers no special support for overriding the built-in child
		1859	processing, but if your application collides with libev's default child
		1860	handler, you can override it easily by installing your own handler for
		1861	C<SIGCHLD> after initialising the default loop, and making sure the
		1862	default loop never gets destroyed. You are encouraged, however, to use an
		1863	event-based approach to child reaping and thus use libev's support for
		1864	that, so other libev users can use C<ev_child> watchers freely.
		1865
		1866	=head3 Stopping the Child Watcher
		1867
		1868	Currently, the child watcher never gets stopped, even when the
		1869	child terminates, so normally one needs to stop the watcher in the
		1870	callback. Future versions of libev might stop the watcher automatically
		1871	when a child exit is detected.
		1872
		1873	=head3 Watcher-Specific Functions and Data Members
628		1874
629	=over 4	1875	=over 4
630		1876
631	=item ev_child_init (ev_child *, callback, int pid)	1877	=item ev_child_init (ev_child *, callback, int pid, int trace)
632		1878
633	=item ev_child_set (ev_child *, int pid)	1879	=item ev_child_set (ev_child *, int pid, int trace)
634		1880
635	Configures the watcher to wait for status changes of process C<pid> (or	1881	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	1882	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	1883	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	1884	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	1885	C<waitpid> documentation). The C<rpid> member contains the pid of the
640	process causing the status change.	1886	process causing the status change. C<trace> must be either C<0> (only
		1887	activate the watcher when the process terminates) or C<1> (additionally
		1888	activate the watcher when the process is stopped or continued).
		1889
		1890	=item int pid [read-only]
		1891
		1892	The process id this watcher watches out for, or C<0>, meaning any process id.
		1893
		1894	=item int rpid [read-write]
		1895
		1896	The process id that detected a status change.
		1897
		1898	=item int rstatus [read-write]
		1899
		1900	The process exit/trace status caused by C<rpid> (see your systems
		1901	C<waitpid> and C<sys/wait.h> documentation for details).
641		1902
642	=back	1903	=back
643		1904
		1905	=head3 Examples
		1906
		1907	Example: C<fork()> a new process and install a child handler to wait for
		1908	its completion.
		1909
		1910	ev_child cw;
		1911
		1912	static void
		1913	child_cb (EV_P_ ev_child *w, int revents)
		1914	{
		1915	ev_child_stop (EV_A_ w);
		1916	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1917	}
		1918
		1919	pid_t pid = fork ();
		1920
		1921	if (pid < 0)
		1922	// error
		1923	else if (pid == 0)
		1924	{
		1925	// the forked child executes here
		1926	exit (1);
		1927	}
		1928	else
		1929	{
		1930	ev_child_init (&cw, child_cb, pid, 0);
		1931	ev_child_start (EV_DEFAULT_ &cw);
		1932	}
		1933
		1934
		1935	=head2 C<ev_stat> - did the file attributes just change?
		1936
		1937	This watches a file system path for attribute changes. That is, it calls
		1938	C<stat> on that path in regular intervals (or when the OS says it changed)
		1939	and sees if it changed compared to the last time, invoking the callback if
		1940	it did.
		1941
		1942	The path does not need to exist: changing from "path exists" to "path does
		1943	not exist" is a status change like any other. The condition "path does not
		1944	exist" (or more correctly "path cannot be stat'ed") is signified by the
		1945	C<st_nlink> field being zero (which is otherwise always forced to be at
		1946	least one) and all the other fields of the stat buffer having unspecified
		1947	contents.
		1948
		1949	The path I<must not> end in a slash or contain special components such as
		1950	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		1951	your working directory changes, then the behaviour is undefined.
		1952
		1953	Since there is no portable change notification interface available, the
		1954	portable implementation simply calls C<stat(2)> regularly on the path
		1955	to see if it changed somehow. You can specify a recommended polling
		1956	interval for this case. If you specify a polling interval of C<0> (highly
		1957	recommended!) then a I<suitable, unspecified default> value will be used
		1958	(which you can expect to be around five seconds, although this might
		1959	change dynamically). Libev will also impose a minimum interval which is
		1960	currently around C<0.1>, but that's usually overkill.
		1961
		1962	This watcher type is not meant for massive numbers of stat watchers,
		1963	as even with OS-supported change notifications, this can be
		1964	resource-intensive.
		1965
		1966	At the time of this writing, the only OS-specific interface implemented
		1967	is the Linux inotify interface (implementing kqueue support is left as an
		1968	exercise for the reader. Note, however, that the author sees no way of
		1969	implementing C<ev_stat> semantics with kqueue, except as a hint).
		1970
		1971	=head3 ABI Issues (Largefile Support)
		1972
		1973	Libev by default (unless the user overrides this) uses the default
		1974	compilation environment, which means that on systems with large file
		1975	support disabled by default, you get the 32 bit version of the stat
		1976	structure. When using the library from programs that change the ABI to
		1977	use 64 bit file offsets the programs will fail. In that case you have to
		1978	compile libev with the same flags to get binary compatibility. This is
		1979	obviously the case with any flags that change the ABI, but the problem is
		1980	most noticeably displayed with ev_stat and large file support.
		1981
		1982	The solution for this is to lobby your distribution maker to make large
		1983	file interfaces available by default (as e.g. FreeBSD does) and not
		1984	optional. Libev cannot simply switch on large file support because it has
		1985	to exchange stat structures with application programs compiled using the
		1986	default compilation environment.
		1987
		1988	=head3 Inotify and Kqueue
		1989
		1990	When C<inotify (7)> support has been compiled into libev and present at
		1991	runtime, it will be used to speed up change detection where possible. The
		1992	inotify descriptor will be created lazily when the first C<ev_stat>
		1993	watcher is being started.
		1994
		1995	Inotify presence does not change the semantics of C<ev_stat> watchers
		1996	except that changes might be detected earlier, and in some cases, to avoid
		1997	making regular C<stat> calls. Even in the presence of inotify support
		1998	there are many cases where libev has to resort to regular C<stat> polling,
		1999	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2000	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2001	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2002	xfs are fully working) libev usually gets away without polling.
		2003
		2004	There is no support for kqueue, as apparently it cannot be used to
		2005	implement this functionality, due to the requirement of having a file
		2006	descriptor open on the object at all times, and detecting renames, unlinks
		2007	etc. is difficult.
		2008
		2009	=head3 C<stat ()> is a synchronous operation
		2010
		2011	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2012	the process. The exception are C<ev_stat> watchers - those call C<stat
		2013	()>, which is a synchronous operation.
		2014
		2015	For local paths, this usually doesn't matter: unless the system is very
		2016	busy or the intervals between stat's are large, a stat call will be fast,
		2017	as the path data is suually in memory already (except when starting the
		2018	watcher).
		2019
		2020	For networked file systems, calling C<stat ()> can block an indefinite
		2021	time due to network issues, and even under good conditions, a stat call
		2022	often takes multiple milliseconds.
		2023
		2024	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2025	paths, although this is fully supported by libev.
		2026
		2027	=head3 The special problem of stat time resolution
		2028
		2029	The C<stat ()> system call only supports full-second resolution portably,
		2030	and even on systems where the resolution is higher, most file systems
		2031	still only support whole seconds.
		2032
		2033	That means that, if the time is the only thing that changes, you can
		2034	easily miss updates: on the first update, C<ev_stat> detects a change and
		2035	calls your callback, which does something. When there is another update
		2036	within the same second, C<ev_stat> will be unable to detect unless the
		2037	stat data does change in other ways (e.g. file size).
		2038
		2039	The solution to this is to delay acting on a change for slightly more
		2040	than a second (or till slightly after the next full second boundary), using
		2041	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2042	ev_timer_again (loop, w)>).
		2043
		2044	The C<.02> offset is added to work around small timing inconsistencies
		2045	of some operating systems (where the second counter of the current time
		2046	might be be delayed. One such system is the Linux kernel, where a call to
		2047	C<gettimeofday> might return a timestamp with a full second later than
		2048	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2049	update file times then there will be a small window where the kernel uses
		2050	the previous second to update file times but libev might already execute
		2051	the timer callback).
		2052
		2053	=head3 Watcher-Specific Functions and Data Members
		2054
		2055	=over 4
		2056
		2057	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2058
		2059	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2060
		2061	Configures the watcher to wait for status changes of the given
		2062	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2063	be detected and should normally be specified as C<0> to let libev choose
		2064	a suitable value. The memory pointed to by C<path> must point to the same
		2065	path for as long as the watcher is active.
		2066
		2067	The callback will receive an C<EV_STAT> event when a change was detected,
		2068	relative to the attributes at the time the watcher was started (or the
		2069	last change was detected).
		2070
		2071	=item ev_stat_stat (loop, ev_stat *)
		2072
		2073	Updates the stat buffer immediately with new values. If you change the
		2074	watched path in your callback, you could call this function to avoid
		2075	detecting this change (while introducing a race condition if you are not
		2076	the only one changing the path). Can also be useful simply to find out the
		2077	new values.
		2078
		2079	=item ev_statdata attr [read-only]
		2080
		2081	The most-recently detected attributes of the file. Although the type is
		2082	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2083	suitable for your system, but you can only rely on the POSIX-standardised
		2084	members to be present. If the C<st_nlink> member is C<0>, then there was
		2085	some error while C<stat>ing the file.
		2086
		2087	=item ev_statdata prev [read-only]
		2088
		2089	The previous attributes of the file. The callback gets invoked whenever
		2090	C<prev> != C<attr>, or, more precisely, one or more of these members
		2091	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2092	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2093
		2094	=item ev_tstamp interval [read-only]
		2095
		2096	The specified interval.
		2097
		2098	=item const char *path [read-only]
		2099
		2100	The file system path that is being watched.
		2101
		2102	=back
		2103
		2104	=head3 Examples
		2105
		2106	Example: Watch C</etc/passwd> for attribute changes.
		2107
		2108	static void
		2109	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2110	{
		2111	/* /etc/passwd changed in some way */
		2112	if (w->attr.st_nlink)
		2113	{
		2114	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2115	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2116	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2117	}
		2118	else
		2119	/* you shalt not abuse printf for puts */
		2120	puts ("wow, /etc/passwd is not there, expect problems. "
		2121	"if this is windows, they already arrived\n");
		2122	}
		2123
		2124	...
		2125	ev_stat passwd;
		2126
		2127	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2128	ev_stat_start (loop, &passwd);
		2129
		2130	Example: Like above, but additionally use a one-second delay so we do not
		2131	miss updates (however, frequent updates will delay processing, too, so
		2132	one might do the work both on C<ev_stat> callback invocation I<and> on
		2133	C<ev_timer> callback invocation).
		2134
		2135	static ev_stat passwd;
		2136	static ev_timer timer;
		2137
		2138	static void
		2139	timer_cb (EV_P_ ev_timer *w, int revents)
		2140	{
		2141	ev_timer_stop (EV_A_ w);
		2142
		2143	/* now it's one second after the most recent passwd change */
		2144	}
		2145
		2146	static void
		2147	stat_cb (EV_P_ ev_stat *w, int revents)
		2148	{
		2149	/* reset the one-second timer */
		2150	ev_timer_again (EV_A_ &timer);
		2151	}
		2152
		2153	...
		2154	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2155	ev_stat_start (loop, &passwd);
		2156	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2157
		2158
644	=head2 C<ev_idle> - when you've got nothing better to do	2159	=head2 C<ev_idle> - when you've got nothing better to do...
645		2160
646	Idle watchers trigger events when there are no other events are pending	2161	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	2162	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,	2163	as receiving "events").
649	imagine) it will not be triggered. But when your process is idle all idle	2164
650	watchers are being called again and again, once per event loop iteration -	2165	That is, as long as your process is busy handling sockets or timeouts
		2166	(or even signals, imagine) of the same or higher priority it will not be
		2167	triggered. But when your process is idle (or only lower-priority watchers
		2168	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	2169	iteration - until stopped, that is, or your process receives more events
652	busy.	2170	and becomes busy again with higher priority stuff.
653		2171
654	The most noteworthy effect is that as long as any idle watchers are	2172	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.	2173	active, the process will not block when waiting for new events.
656		2174
657	Apart from keeping your process non-blocking (which is a useful	2175	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	2176	effect on its own sometimes), idle watchers are a good place to do
659	"pseudo-background processing", or delay processing stuff to after the	2177	"pseudo-background processing", or delay processing stuff to after the
660	event loop has handled all outstanding events.	2178	event loop has handled all outstanding events.
661		2179
		2180	=head3 Watcher-Specific Functions and Data Members
		2181
662	=over 4	2182	=over 4
663		2183
664	=item ev_idle_init (ev_signal *, callback)	2184	=item ev_idle_init (ev_signal *, callback)
665		2185
666	Initialises and configures the idle watcher - it has no parameters of any	2186	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,	2187	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
668	believe me.	2188	believe me.
669		2189
670	=back	2190	=back
671		2191
		2192	=head3 Examples
		2193
		2194	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2195	callback, free it. Also, use no error checking, as usual.
		2196
		2197	static void
		2198	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2199	{
		2200	free (w);
		2201	// now do something you wanted to do when the program has
		2202	// no longer anything immediate to do.
		2203	}
		2204
		2205	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2206	ev_idle_init (idle_watcher, idle_cb);
		2207	ev_idle_start (loop, idle_cb);
		2208
		2209
672	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2210	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
673		2211
674	Prepare and check watchers are usually (but not always) used in tandem:	2212	Prepare and check watchers are usually (but not always) used in pairs:
675	Prepare watchers get invoked before the process blocks and check watchers	2213	prepare watchers get invoked before the process blocks and check watchers
676	afterwards.	2214	afterwards.
677		2215
		2216	You I<must not> call C<ev_loop> or similar functions that enter
		2217	the current event loop from either C<ev_prepare> or C<ev_check>
		2218	watchers. Other loops than the current one are fine, however. The
		2219	rationale behind this is that you do not need to check for recursion in
		2220	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2221	C<ev_check> so if you have one watcher of each kind they will always be
		2222	called in pairs bracketing the blocking call.
		2223
678	Their main purpose is to integrate other event mechanisms into libev. This	2224	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	2225	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.	2226	variable changes, implement your own watchers, integrate net-snmp or a
		2227	coroutine library and lots more. They are also occasionally useful if
		2228	you cache some data and want to flush it before blocking (for example,
		2229	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2230	watcher).
681		2231
682	This is done by examining in each prepare call which file descriptors need	2232	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	2233	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	2234	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	2235	libraries provide exactly this functionality). Then, in the check watcher,
686	any events that occured (by checking the pending status of all watchers	2236	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	2237	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,	2238	I/O and timer callbacks will never actually be called (but must be valid
689	because you never know, you know?).	2239	nevertheless, because you never know, you know?).
690		2240
691	As another example, the Perl Coro module uses these hooks to integrate	2241	As another example, the Perl Coro module uses these hooks to integrate
692	coroutines into libev programs, by yielding to other active coroutines	2242	coroutines into libev programs, by yielding to other active coroutines
693	during each prepare and only letting the process block if no coroutines	2243	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	2244	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,	2245	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	2246	of lower priority, but only once, using idle watchers to keep the event
697	coroutines exist, thus mapping low-priority coroutines to idle/background	2247	loop from blocking if lower-priority coroutines are active, thus mapping
698	tasks).	2248	low-priority coroutines to idle/background tasks).
		2249
		2250	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2251	priority, to ensure that they are being run before any other watchers
		2252	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2253
		2254	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2255	activate ("feed") events into libev. While libev fully supports this, they
		2256	might get executed before other C<ev_check> watchers did their job. As
		2257	C<ev_check> watchers are often used to embed other (non-libev) event
		2258	loops those other event loops might be in an unusable state until their
		2259	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2260	others).
		2261
		2262	=head3 Watcher-Specific Functions and Data Members
699		2263
700	=over 4	2264	=over 4
701		2265
702	=item ev_prepare_init (ev_prepare *, callback)	2266	=item ev_prepare_init (ev_prepare *, callback)
703		2267
704	=item ev_check_init (ev_check *, callback)	2268	=item ev_check_init (ev_check *, callback)
705		2269
706	Initialises and configures the prepare or check watcher - they have no	2270	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>	2271	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.	2272	macros, but using them is utterly, utterly, utterly and completely
		2273	pointless.
709		2274
710	=back	2275	=back
711		2276
		2277	=head3 Examples
		2278
		2279	There are a number of principal ways to embed other event loops or modules
		2280	into libev. Here are some ideas on how to include libadns into libev
		2281	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2282	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2283	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2284	Glib event loop).
		2285
		2286	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2287	and in a check watcher, destroy them and call into libadns. What follows
		2288	is pseudo-code only of course. This requires you to either use a low
		2289	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2290	the callbacks for the IO/timeout watchers might not have been called yet.
		2291
		2292	static ev_io iow [nfd];
		2293	static ev_timer tw;
		2294
		2295	static void
		2296	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2297	{
		2298	}
		2299
		2300	// create io watchers for each fd and a timer before blocking
		2301	static void
		2302	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2303	{
		2304	int timeout = 3600000;
		2305	struct pollfd fds [nfd];
		2306	// actual code will need to loop here and realloc etc.
		2307	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2308
		2309	/* the callback is illegal, but won't be called as we stop during check */
		2310	ev_timer_init (&tw, 0, timeout * 1e-3);
		2311	ev_timer_start (loop, &tw);
		2312
		2313	// create one ev_io per pollfd
		2314	for (int i = 0; i < nfd; ++i)
		2315	{
		2316	ev_io_init (iow + i, io_cb, fds [i].fd,
		2317	((fds [i].events & POLLIN ? EV_READ : 0)
		2318	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2319
		2320	fds [i].revents = 0;
		2321	ev_io_start (loop, iow + i);
		2322	}
		2323	}
		2324
		2325	// stop all watchers after blocking
		2326	static void
		2327	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2328	{
		2329	ev_timer_stop (loop, &tw);
		2330
		2331	for (int i = 0; i < nfd; ++i)
		2332	{
		2333	// set the relevant poll flags
		2334	// could also call adns_processreadable etc. here
		2335	struct pollfd *fd = fds + i;
		2336	int revents = ev_clear_pending (iow + i);
		2337	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2338	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2339
		2340	// now stop the watcher
		2341	ev_io_stop (loop, iow + i);
		2342	}
		2343
		2344	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2345	}
		2346
		2347	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2348	in the prepare watcher and would dispose of the check watcher.
		2349
		2350	Method 3: If the module to be embedded supports explicit event
		2351	notification (libadns does), you can also make use of the actual watcher
		2352	callbacks, and only destroy/create the watchers in the prepare watcher.
		2353
		2354	static void
		2355	timer_cb (EV_P_ ev_timer *w, int revents)
		2356	{
		2357	adns_state ads = (adns_state)w->data;
		2358	update_now (EV_A);
		2359
		2360	adns_processtimeouts (ads, &tv_now);
		2361	}
		2362
		2363	static void
		2364	io_cb (EV_P_ ev_io *w, int revents)
		2365	{
		2366	adns_state ads = (adns_state)w->data;
		2367	update_now (EV_A);
		2368
		2369	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2370	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2371	}
		2372
		2373	// do not ever call adns_afterpoll
		2374
		2375	Method 4: Do not use a prepare or check watcher because the module you
		2376	want to embed is not flexible enough to support it. Instead, you can
		2377	override their poll function. The drawback with this solution is that the
		2378	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2379	this approach, effectively embedding EV as a client into the horrible
		2380	libglib event loop.
		2381
		2382	static gint
		2383	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2384	{
		2385	int got_events = 0;
		2386
		2387	for (n = 0; n < nfds; ++n)
		2388	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2389
		2390	if (timeout >= 0)
		2391	// create/start timer
		2392
		2393	// poll
		2394	ev_loop (EV_A_ 0);
		2395
		2396	// stop timer again
		2397	if (timeout >= 0)
		2398	ev_timer_stop (EV_A_ &to);
		2399
		2400	// stop io watchers again - their callbacks should have set
		2401	for (n = 0; n < nfds; ++n)
		2402	ev_io_stop (EV_A_ iow [n]);
		2403
		2404	return got_events;
		2405	}
		2406
		2407
		2408	=head2 C<ev_embed> - when one backend isn't enough...
		2409
		2410	This is a rather advanced watcher type that lets you embed one event loop
		2411	into another (currently only C<ev_io> events are supported in the embedded
		2412	loop, other types of watchers might be handled in a delayed or incorrect
		2413	fashion and must not be used).
		2414
		2415	There are primarily two reasons you would want that: work around bugs and
		2416	prioritise I/O.
		2417
		2418	As an example for a bug workaround, the kqueue backend might only support
		2419	sockets on some platform, so it is unusable as generic backend, but you
		2420	still want to make use of it because you have many sockets and it scales
		2421	so nicely. In this case, you would create a kqueue-based loop and embed
		2422	it into your default loop (which might use e.g. poll). Overall operation
		2423	will be a bit slower because first libev has to call C<poll> and then
		2424	C<kevent>, but at least you can use both mechanisms for what they are
		2425	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2426
		2427	As for prioritising I/O: under rare circumstances you have the case where
		2428	some fds have to be watched and handled very quickly (with low latency),
		2429	and even priorities and idle watchers might have too much overhead. In
		2430	this case you would put all the high priority stuff in one loop and all
		2431	the rest in a second one, and embed the second one in the first.
		2432
		2433	As long as the watcher is active, the callback will be invoked every time
		2434	there might be events pending in the embedded loop. The callback must then
		2435	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2436	their callbacks (you could also start an idle watcher to give the embedded
		2437	loop strictly lower priority for example). You can also set the callback
		2438	to C<0>, in which case the embed watcher will automatically execute the
		2439	embedded loop sweep.
		2440
		2441	As long as the watcher is started it will automatically handle events. The
		2442	callback will be invoked whenever some events have been handled. You can
		2443	set the callback to C<0> to avoid having to specify one if you are not
		2444	interested in that.
		2445
		2446	Also, there have not currently been made special provisions for forking:
		2447	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2448	but you will also have to stop and restart any C<ev_embed> watchers
		2449	yourself - but you can use a fork watcher to handle this automatically,
		2450	and future versions of libev might do just that.
		2451
		2452	Unfortunately, not all backends are embeddable: only the ones returned by
		2453	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2454	portable one.
		2455
		2456	So when you want to use this feature you will always have to be prepared
		2457	that you cannot get an embeddable loop. The recommended way to get around
		2458	this is to have a separate variables for your embeddable loop, try to
		2459	create it, and if that fails, use the normal loop for everything.
		2460
		2461	=head3 C<ev_embed> and fork
		2462
		2463	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2464	automatically be applied to the embedded loop as well, so no special
		2465	fork handling is required in that case. When the watcher is not running,
		2466	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2467	as applicable.
		2468
		2469	=head3 Watcher-Specific Functions and Data Members
		2470
		2471	=over 4
		2472
		2473	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2474
		2475	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2476
		2477	Configures the watcher to embed the given loop, which must be
		2478	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2479	invoked automatically, otherwise it is the responsibility of the callback
		2480	to invoke it (it will continue to be called until the sweep has been done,
		2481	if you do not want that, you need to temporarily stop the embed watcher).
		2482
		2483	=item ev_embed_sweep (loop, ev_embed *)
		2484
		2485	Make a single, non-blocking sweep over the embedded loop. This works
		2486	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2487	appropriate way for embedded loops.
		2488
		2489	=item struct ev_loop *other [read-only]
		2490
		2491	The embedded event loop.
		2492
		2493	=back
		2494
		2495	=head3 Examples
		2496
		2497	Example: Try to get an embeddable event loop and embed it into the default
		2498	event loop. If that is not possible, use the default loop. The default
		2499	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2500	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2501	used).
		2502
		2503	struct ev_loop *loop_hi = ev_default_init (0);
		2504	struct ev_loop *loop_lo = 0;
		2505	ev_embed embed;
		2506
		2507	// see if there is a chance of getting one that works
		2508	// (remember that a flags value of 0 means autodetection)
		2509	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2510	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2511	: 0;
		2512
		2513	// if we got one, then embed it, otherwise default to loop_hi
		2514	if (loop_lo)
		2515	{
		2516	ev_embed_init (&embed, 0, loop_lo);
		2517	ev_embed_start (loop_hi, &embed);
		2518	}
		2519	else
		2520	loop_lo = loop_hi;
		2521
		2522	Example: Check if kqueue is available but not recommended and create
		2523	a kqueue backend for use with sockets (which usually work with any
		2524	kqueue implementation). Store the kqueue/socket-only event loop in
		2525	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2526
		2527	struct ev_loop *loop = ev_default_init (0);
		2528	struct ev_loop *loop_socket = 0;
		2529	ev_embed embed;
		2530
		2531	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2532	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2533	{
		2534	ev_embed_init (&embed, 0, loop_socket);
		2535	ev_embed_start (loop, &embed);
		2536	}
		2537
		2538	if (!loop_socket)
		2539	loop_socket = loop;
		2540
		2541	// now use loop_socket for all sockets, and loop for everything else
		2542
		2543
		2544	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2545
		2546	Fork watchers are called when a C<fork ()> was detected (usually because
		2547	whoever is a good citizen cared to tell libev about it by calling
		2548	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2549	event loop blocks next and before C<ev_check> watchers are being called,
		2550	and only in the child after the fork. If whoever good citizen calling
		2551	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2552	handlers will be invoked, too, of course.
		2553
		2554	=head3 Watcher-Specific Functions and Data Members
		2555
		2556	=over 4
		2557
		2558	=item ev_fork_init (ev_signal *, callback)
		2559
		2560	Initialises and configures the fork watcher - it has no parameters of any
		2561	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2562	believe me.
		2563
		2564	=back
		2565
		2566
		2567	=head2 C<ev_async> - how to wake up another event loop
		2568
		2569	In general, you cannot use an C<ev_loop> from multiple threads or other
		2570	asynchronous sources such as signal handlers (as opposed to multiple event
		2571	loops - those are of course safe to use in different threads).
		2572
		2573	Sometimes, however, you need to wake up another event loop you do not
		2574	control, for example because it belongs to another thread. This is what
		2575	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2576	can signal it by calling C<ev_async_send>, which is thread- and signal
		2577	safe.
		2578
		2579	This functionality is very similar to C<ev_signal> watchers, as signals,
		2580	too, are asynchronous in nature, and signals, too, will be compressed
		2581	(i.e. the number of callback invocations may be less than the number of
		2582	C<ev_async_sent> calls).
		2583
		2584	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2585	just the default loop.
		2586
		2587	=head3 Queueing
		2588
		2589	C<ev_async> does not support queueing of data in any way. The reason
		2590	is that the author does not know of a simple (or any) algorithm for a
		2591	multiple-writer-single-reader queue that works in all cases and doesn't
		2592	need elaborate support such as pthreads.
		2593
		2594	That means that if you want to queue data, you have to provide your own
		2595	queue. But at least I can tell you how to implement locking around your
		2596	queue:
		2597
		2598	=over 4
		2599
		2600	=item queueing from a signal handler context
		2601
		2602	To implement race-free queueing, you simply add to the queue in the signal
		2603	handler but you block the signal handler in the watcher callback. Here is
		2604	an example that does that for some fictitious SIGUSR1 handler:
		2605
		2606	static ev_async mysig;
		2607
		2608	static void
		2609	sigusr1_handler (void)
		2610	{
		2611	sometype data;
		2612
		2613	// no locking etc.
		2614	queue_put (data);
		2615	ev_async_send (EV_DEFAULT_ &mysig);
		2616	}
		2617
		2618	static void
		2619	mysig_cb (EV_P_ ev_async *w, int revents)
		2620	{
		2621	sometype data;
		2622	sigset_t block, prev;
		2623
		2624	sigemptyset (&block);
		2625	sigaddset (&block, SIGUSR1);
		2626	sigprocmask (SIG_BLOCK, &block, &prev);
		2627
		2628	while (queue_get (&data))
		2629	process (data);
		2630
		2631	if (sigismember (&prev, SIGUSR1)
		2632	sigprocmask (SIG_UNBLOCK, &block, 0);
		2633	}
		2634
		2635	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2636	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2637	either...).
		2638
		2639	=item queueing from a thread context
		2640
		2641	The strategy for threads is different, as you cannot (easily) block
		2642	threads but you can easily preempt them, so to queue safely you need to
		2643	employ a traditional mutex lock, such as in this pthread example:
		2644
		2645	static ev_async mysig;
		2646	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2647
		2648	static void
		2649	otherthread (void)
		2650	{
		2651	// only need to lock the actual queueing operation
		2652	pthread_mutex_lock (&mymutex);
		2653	queue_put (data);
		2654	pthread_mutex_unlock (&mymutex);
		2655
		2656	ev_async_send (EV_DEFAULT_ &mysig);
		2657	}
		2658
		2659	static void
		2660	mysig_cb (EV_P_ ev_async *w, int revents)
		2661	{
		2662	pthread_mutex_lock (&mymutex);
		2663
		2664	while (queue_get (&data))
		2665	process (data);
		2666
		2667	pthread_mutex_unlock (&mymutex);
		2668	}
		2669
		2670	=back
		2671
		2672
		2673	=head3 Watcher-Specific Functions and Data Members
		2674
		2675	=over 4
		2676
		2677	=item ev_async_init (ev_async *, callback)
		2678
		2679	Initialises and configures the async watcher - it has no parameters of any
		2680	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2681	trust me.
		2682
		2683	=item ev_async_send (loop, ev_async *)
		2684
		2685	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2686	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2687	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2688	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2689	section below on what exactly this means).
		2690
		2691	This call incurs the overhead of a system call only once per loop iteration,
		2692	so while the overhead might be noticeable, it doesn't apply to repeated
		2693	calls to C<ev_async_send>.
		2694
		2695	=item bool = ev_async_pending (ev_async *)
		2696
		2697	Returns a non-zero value when C<ev_async_send> has been called on the
		2698	watcher but the event has not yet been processed (or even noted) by the
		2699	event loop.
		2700
		2701	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2702	the loop iterates next and checks for the watcher to have become active,
		2703	it will reset the flag again. C<ev_async_pending> can be used to very
		2704	quickly check whether invoking the loop might be a good idea.
		2705
		2706	Not that this does I<not> check whether the watcher itself is pending, only
		2707	whether it has been requested to make this watcher pending.
		2708
		2709	=back
		2710
		2711
712	=head1 OTHER FUNCTIONS	2712	=head1 OTHER FUNCTIONS
713		2713
714	There are some other functions of possible interest. Described. Here. Now.	2714	There are some other functions of possible interest. Described. Here. Now.
715		2715
716	=over 4	2716	=over 4
717		2717
718	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2718	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
719		2719
720	This function combines a simple timer and an I/O watcher, calls your	2720	This function combines a simple timer and an I/O watcher, calls your
721	callback on whichever event happens first and automatically stop both	2721	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	2722	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	2723	or timeout without having to allocate/configure/start/stop/free one or
724	more watchers yourself.	2724	more watchers yourself.
725		2725
726	If C<fd> is less than 0, then no I/O watcher will be started and events	2726	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	2727	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
728	C<events> set will be craeted and started.	2728	the given C<fd> and C<events> set will be created and started.
729		2729
730	If C<timeout> is less than 0, then no timeout watcher will be	2730	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	2731	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	2732	repeat = 0) will be started. C<0> is a valid timeout.
733	dubious value.
734		2733
735	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2734	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
736	passed an events set like normal event callbacks (with a combination of	2735	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>	2736	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
738	value passed to C<ev_once>:	2737	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2738	a timeout and an io event at the same time - you probably should give io
		2739	events precedence.
739		2740
		2741	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2742
740	static void stdin_ready (int revents, void *arg)	2743	static void stdin_ready (int revents, void *arg)
741	{	2744	{
742	if (revents & EV_TIMEOUT)
743	/* doh, nothing entered */;
744	else if (revents & EV_READ)	2745	if (revents & EV_READ)
745	/* stdin might have data for us, joy! */;	2746	/* stdin might have data for us, joy! */;
		2747	else if (revents & EV_TIMEOUT)
		2748	/* doh, nothing entered */;
746	}	2749	}
747		2750
748	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2751	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
749		2752
750	=item ev_feed_event (loop, watcher, int events)	2753	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
751		2754
752	Feeds the given event set into the event loop, as if the specified event	2755	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	2756	had happened for the specified watcher (which must be a pointer to an
754	initialised but not necessarily started event watcher).	2757	initialised but not necessarily started event watcher).
755		2758
756	=item ev_feed_fd_event (loop, int fd, int revents)	2759	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
757		2760
758	Feed an event on the given fd, as if a file descriptor backend detected	2761	Feed an event on the given fd, as if a file descriptor backend detected
759	the given events it.	2762	the given events it.
760		2763
761	=item ev_feed_signal_event (loop, int signum)	2764	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
762		2765
763	Feed an event as if the given signal occured (loop must be the default loop!).	2766	Feed an event as if the given signal occurred (C<loop> must be the default
		2767	loop!).
764		2768
765	=back	2769	=back
766		2770
		2771
		2772	=head1 LIBEVENT EMULATION
		2773
		2774	Libev offers a compatibility emulation layer for libevent. It cannot
		2775	emulate the internals of libevent, so here are some usage hints:
		2776
		2777	=over 4
		2778
		2779	=item * Use it by including <event.h>, as usual.
		2780
		2781	=item * The following members are fully supported: ev_base, ev_callback,
		2782	ev_arg, ev_fd, ev_res, ev_events.
		2783
		2784	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2785	maintained by libev, it does not work exactly the same way as in libevent (consider
		2786	it a private API).
		2787
		2788	=item * Priorities are not currently supported. Initialising priorities
		2789	will fail and all watchers will have the same priority, even though there
		2790	is an ev_pri field.
		2791
		2792	=item * In libevent, the last base created gets the signals, in libev, the
		2793	first base created (== the default loop) gets the signals.
		2794
		2795	=item * Other members are not supported.
		2796
		2797	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2798	to use the libev header file and library.
		2799
		2800	=back
		2801
		2802	=head1 C++ SUPPORT
		2803
		2804	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2805	you to use some convenience methods to start/stop watchers and also change
		2806	the callback model to a model using method callbacks on objects.
		2807
		2808	To use it,
		2809
		2810	#include <ev++.h>
		2811
		2812	This automatically includes F<ev.h> and puts all of its definitions (many
		2813	of them macros) into the global namespace. All C++ specific things are
		2814	put into the C<ev> namespace. It should support all the same embedding
		2815	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2816
		2817	Care has been taken to keep the overhead low. The only data member the C++
		2818	classes add (compared to plain C-style watchers) is the event loop pointer
		2819	that the watcher is associated with (or no additional members at all if
		2820	you disable C<EV_MULTIPLICITY> when embedding libev).
		2821
		2822	Currently, functions, and static and non-static member functions can be
		2823	used as callbacks. Other types should be easy to add as long as they only
		2824	need one additional pointer for context. If you need support for other
		2825	types of functors please contact the author (preferably after implementing
		2826	it).
		2827
		2828	Here is a list of things available in the C<ev> namespace:
		2829
		2830	=over 4
		2831
		2832	=item C<ev::READ>, C<ev::WRITE> etc.
		2833
		2834	These are just enum values with the same values as the C<EV_READ> etc.
		2835	macros from F<ev.h>.
		2836
		2837	=item C<ev::tstamp>, C<ev::now>
		2838
		2839	Aliases to the same types/functions as with the C<ev_> prefix.
		2840
		2841	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2842
		2843	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2844	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2845	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2846	defines by many implementations.
		2847
		2848	All of those classes have these methods:
		2849
		2850	=over 4
		2851
		2852	=item ev::TYPE::TYPE ()
		2853
		2854	=item ev::TYPE::TYPE (struct ev_loop *)
		2855
		2856	=item ev::TYPE::~TYPE
		2857
		2858	The constructor (optionally) takes an event loop to associate the watcher
		2859	with. If it is omitted, it will use C<EV_DEFAULT>.
		2860
		2861	The constructor calls C<ev_init> for you, which means you have to call the
		2862	C<set> method before starting it.
		2863
		2864	It will not set a callback, however: You have to call the templated C<set>
		2865	method to set a callback before you can start the watcher.
		2866
		2867	(The reason why you have to use a method is a limitation in C++ which does
		2868	not allow explicit template arguments for constructors).
		2869
		2870	The destructor automatically stops the watcher if it is active.
		2871
		2872	=item w->set<class, &class::method> (object *)
		2873
		2874	This method sets the callback method to call. The method has to have a
		2875	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2876	first argument and the C<revents> as second. The object must be given as
		2877	parameter and is stored in the C<data> member of the watcher.
		2878
		2879	This method synthesizes efficient thunking code to call your method from
		2880	the C callback that libev requires. If your compiler can inline your
		2881	callback (i.e. it is visible to it at the place of the C<set> call and
		2882	your compiler is good :), then the method will be fully inlined into the
		2883	thunking function, making it as fast as a direct C callback.
		2884
		2885	Example: simple class declaration and watcher initialisation
		2886
		2887	struct myclass
		2888	{
		2889	void io_cb (ev::io &w, int revents) { }
		2890	}
		2891
		2892	myclass obj;
		2893	ev::io iow;
		2894	iow.set <myclass, &myclass::io_cb> (&obj);
		2895
		2896	=item w->set (object *)
		2897
		2898	This is an B<experimental> feature that might go away in a future version.
		2899
		2900	This is a variation of a method callback - leaving out the method to call
		2901	will default the method to C<operator ()>, which makes it possible to use
		2902	functor objects without having to manually specify the C<operator ()> all
		2903	the time. Incidentally, you can then also leave out the template argument
		2904	list.
		2905
		2906	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		2907	int revents)>.
		2908
		2909	See the method-C<set> above for more details.
		2910
		2911	Example: use a functor object as callback.
		2912
		2913	struct myfunctor
		2914	{
		2915	void operator() (ev::io &w, int revents)
		2916	{
		2917	...
		2918	}
		2919	}
		2920
		2921	myfunctor f;
		2922
		2923	ev::io w;
		2924	w.set (&f);
		2925
		2926	=item w->set<function> (void *data = 0)
		2927
		2928	Also sets a callback, but uses a static method or plain function as
		2929	callback. The optional C<data> argument will be stored in the watcher's
		2930	C<data> member and is free for you to use.
		2931
		2932	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2933
		2934	See the method-C<set> above for more details.
		2935
		2936	Example: Use a plain function as callback.
		2937
		2938	static void io_cb (ev::io &w, int revents) { }
		2939	iow.set <io_cb> ();
		2940
		2941	=item w->set (struct ev_loop *)
		2942
		2943	Associates a different C<struct ev_loop> with this watcher. You can only
		2944	do this when the watcher is inactive (and not pending either).
		2945
		2946	=item w->set ([arguments])
		2947
		2948	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2949	called at least once. Unlike the C counterpart, an active watcher gets
		2950	automatically stopped and restarted when reconfiguring it with this
		2951	method.
		2952
		2953	=item w->start ()
		2954
		2955	Starts the watcher. Note that there is no C<loop> argument, as the
		2956	constructor already stores the event loop.
		2957
		2958	=item w->stop ()
		2959
		2960	Stops the watcher if it is active. Again, no C<loop> argument.
		2961
		2962	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2963
		2964	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2965	C<ev_TYPE_again> function.
		2966
		2967	=item w->sweep () (C<ev::embed> only)
		2968
		2969	Invokes C<ev_embed_sweep>.
		2970
		2971	=item w->update () (C<ev::stat> only)
		2972
		2973	Invokes C<ev_stat_stat>.
		2974
		2975	=back
		2976
		2977	=back
		2978
		2979	Example: Define a class with an IO and idle watcher, start one of them in
		2980	the constructor.
		2981
		2982	class myclass
		2983	{
		2984	ev::io io ; void io_cb (ev::io &w, int revents);
		2985	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		2986
		2987	myclass (int fd)
		2988	{
		2989	io .set <myclass, &myclass::io_cb > (this);
		2990	idle.set <myclass, &myclass::idle_cb> (this);
		2991
		2992	io.start (fd, ev::READ);
		2993	}
		2994	};
		2995
		2996
		2997	=head1 OTHER LANGUAGE BINDINGS
		2998
		2999	Libev does not offer other language bindings itself, but bindings for a
		3000	number of languages exist in the form of third-party packages. If you know
		3001	any interesting language binding in addition to the ones listed here, drop
		3002	me a note.
		3003
		3004	=over 4
		3005
		3006	=item Perl
		3007
		3008	The EV module implements the full libev API and is actually used to test
		3009	libev. EV is developed together with libev. Apart from the EV core module,
		3010	there are additional modules that implement libev-compatible interfaces
		3011	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3012	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3013	and C<EV::Glib>).
		3014
		3015	It can be found and installed via CPAN, its homepage is at
		3016	L<http://software.schmorp.de/pkg/EV>.
		3017
		3018	=item Python
		3019
		3020	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3021	seems to be quite complete and well-documented. Note, however, that the
		3022	patch they require for libev is outright dangerous as it breaks the ABI
		3023	for everybody else, and therefore, should never be applied in an installed
		3024	libev (if python requires an incompatible ABI then it needs to embed
		3025	libev).
		3026
		3027	=item Ruby
		3028
		3029	Tony Arcieri has written a ruby extension that offers access to a subset
		3030	of the libev API and adds file handle abstractions, asynchronous DNS and
		3031	more on top of it. It can be found via gem servers. Its homepage is at
		3032	L<http://rev.rubyforge.org/>.
		3033
		3034	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3035	makes rev work even on mingw.
		3036
		3037	=item D
		3038
		3039	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3040	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3041
		3042	=item Ocaml
		3043
		3044	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3045	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3046
		3047	=back
		3048
		3049
		3050	=head1 MACRO MAGIC
		3051
		3052	Libev can be compiled with a variety of options, the most fundamental
		3053	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3054	functions and callbacks have an initial C<struct ev_loop *> argument.
		3055
		3056	To make it easier to write programs that cope with either variant, the
		3057	following macros are defined:
		3058
		3059	=over 4
		3060
		3061	=item C<EV_A>, C<EV_A_>
		3062
		3063	This provides the loop I<argument> for functions, if one is required ("ev
		3064	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3065	C<EV_A_> is used when other arguments are following. Example:
		3066
		3067	ev_unref (EV_A);
		3068	ev_timer_add (EV_A_ watcher);
		3069	ev_loop (EV_A_ 0);
		3070
		3071	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3072	which is often provided by the following macro.
		3073
		3074	=item C<EV_P>, C<EV_P_>
		3075
		3076	This provides the loop I<parameter> for functions, if one is required ("ev
		3077	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3078	C<EV_P_> is used when other parameters are following. Example:
		3079
		3080	// this is how ev_unref is being declared
		3081	static void ev_unref (EV_P);
		3082
		3083	// this is how you can declare your typical callback
		3084	static void cb (EV_P_ ev_timer *w, int revents)
		3085
		3086	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3087	suitable for use with C<EV_A>.
		3088
		3089	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3090
		3091	Similar to the other two macros, this gives you the value of the default
		3092	loop, if multiple loops are supported ("ev loop default").
		3093
		3094	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3095
		3096	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3097	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3098	is undefined when the default loop has not been initialised by a previous
		3099	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3100
		3101	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3102	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3103
		3104	=back
		3105
		3106	Example: Declare and initialise a check watcher, utilising the above
		3107	macros so it will work regardless of whether multiple loops are supported
		3108	or not.
		3109
		3110	static void
		3111	check_cb (EV_P_ ev_timer *w, int revents)
		3112	{
		3113	ev_check_stop (EV_A_ w);
		3114	}
		3115
		3116	ev_check check;
		3117	ev_check_init (&check, check_cb);
		3118	ev_check_start (EV_DEFAULT_ &check);
		3119	ev_loop (EV_DEFAULT_ 0);
		3120
		3121	=head1 EMBEDDING
		3122
		3123	Libev can (and often is) directly embedded into host
		3124	applications. Examples of applications that embed it include the Deliantra
		3125	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3126	and rxvt-unicode.
		3127
		3128	The goal is to enable you to just copy the necessary files into your
		3129	source directory without having to change even a single line in them, so
		3130	you can easily upgrade by simply copying (or having a checked-out copy of
		3131	libev somewhere in your source tree).
		3132
		3133	=head2 FILESETS
		3134
		3135	Depending on what features you need you need to include one or more sets of files
		3136	in your application.
		3137
		3138	=head3 CORE EVENT LOOP
		3139
		3140	To include only the libev core (all the C<ev_*> functions), with manual
		3141	configuration (no autoconf):
		3142
		3143	#define EV_STANDALONE 1
		3144	#include "ev.c"
		3145
		3146	This will automatically include F<ev.h>, too, and should be done in a
		3147	single C source file only to provide the function implementations. To use
		3148	it, do the same for F<ev.h> in all files wishing to use this API (best
		3149	done by writing a wrapper around F<ev.h> that you can include instead and
		3150	where you can put other configuration options):
		3151
		3152	#define EV_STANDALONE 1
		3153	#include "ev.h"
		3154
		3155	Both header files and implementation files can be compiled with a C++
		3156	compiler (at least, that's a stated goal, and breakage will be treated
		3157	as a bug).
		3158
		3159	You need the following files in your source tree, or in a directory
		3160	in your include path (e.g. in libev/ when using -Ilibev):
		3161
		3162	ev.h
		3163	ev.c
		3164	ev_vars.h
		3165	ev_wrap.h
		3166
		3167	ev_win32.c required on win32 platforms only
		3168
		3169	ev_select.c only when select backend is enabled (which is enabled by default)
		3170	ev_poll.c only when poll backend is enabled (disabled by default)
		3171	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3172	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3173	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3174
		3175	F<ev.c> includes the backend files directly when enabled, so you only need
		3176	to compile this single file.
		3177
		3178	=head3 LIBEVENT COMPATIBILITY API
		3179
		3180	To include the libevent compatibility API, also include:
		3181
		3182	#include "event.c"
		3183
		3184	in the file including F<ev.c>, and:
		3185
		3186	#include "event.h"
		3187
		3188	in the files that want to use the libevent API. This also includes F<ev.h>.
		3189
		3190	You need the following additional files for this:
		3191
		3192	event.h
		3193	event.c
		3194
		3195	=head3 AUTOCONF SUPPORT
		3196
		3197	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3198	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3199	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3200	include F<config.h> and configure itself accordingly.
		3201
		3202	For this of course you need the m4 file:
		3203
		3204	libev.m4
		3205
		3206	=head2 PREPROCESSOR SYMBOLS/MACROS
		3207
		3208	Libev can be configured via a variety of preprocessor symbols you have to
		3209	define before including any of its files. The default in the absence of
		3210	autoconf is documented for every option.
		3211
		3212	=over 4
		3213
		3214	=item EV_STANDALONE
		3215
		3216	Must always be C<1> if you do not use autoconf configuration, which
		3217	keeps libev from including F<config.h>, and it also defines dummy
		3218	implementations for some libevent functions (such as logging, which is not
		3219	supported). It will also not define any of the structs usually found in
		3220	F<event.h> that are not directly supported by the libev core alone.
		3221
		3222	In stanbdalone mode, libev will still try to automatically deduce the
		3223	configuration, but has to be more conservative.
		3224
		3225	=item EV_USE_MONOTONIC
		3226
		3227	If defined to be C<1>, libev will try to detect the availability of the
		3228	monotonic clock option at both compile time and runtime. Otherwise no
		3229	use of the monotonic clock option will be attempted. If you enable this,
		3230	you usually have to link against librt or something similar. Enabling it
		3231	when the functionality isn't available is safe, though, although you have
		3232	to make sure you link against any libraries where the C<clock_gettime>
		3233	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3234
		3235	=item EV_USE_REALTIME
		3236
		3237	If defined to be C<1>, libev will try to detect the availability of the
		3238	real-time clock option at compile time (and assume its availability at
		3239	runtime if successful). Otherwise no use of the real-time clock option will
		3240	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		3241	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		3242	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		3243
		3244	=item EV_USE_CLOCK_SYSCALL
		3245
		3246	If defined to be C<1>, libev will try to use a direct syscall instead
		3247	of calling the system-provided C<clock_gettime> function. This option
		3248	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3249	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3250	programs needlessly. Using a direct syscall is slightly slower (in
		3251	theory), because no optimised vdso implementation can be used, but avoids
		3252	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3253	higher, as it simplifies linking (no need for C<-lrt>).
		3254
		3255	=item EV_USE_NANOSLEEP
		3256
		3257	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3258	and will use it for delays. Otherwise it will use C<select ()>.
		3259
		3260	=item EV_USE_EVENTFD
		3261
		3262	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3263	available and will probe for kernel support at runtime. This will improve
		3264	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3265	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3266	2.7 or newer, otherwise disabled.
		3267
		3268	=item EV_USE_SELECT
		3269
		3270	If undefined or defined to be C<1>, libev will compile in support for the
		3271	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3272	other method takes over, select will be it. Otherwise the select backend
		3273	will not be compiled in.
		3274
		3275	=item EV_SELECT_USE_FD_SET
		3276
		3277	If defined to C<1>, then the select backend will use the system C<fd_set>
		3278	structure. This is useful if libev doesn't compile due to a missing
		3279	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		3280	on exotic systems. This usually limits the range of file descriptors to
		3281	some low limit such as 1024 or might have other limitations (winsocket
		3282	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		3283	configures the maximum size of the C<fd_set>.
		3284
		3285	=item EV_SELECT_IS_WINSOCKET
		3286
		3287	When defined to C<1>, the select backend will assume that
		3288	select/socket/connect etc. don't understand file descriptors but
		3289	wants osf handles on win32 (this is the case when the select to
		3290	be used is the winsock select). This means that it will call
		3291	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3292	it is assumed that all these functions actually work on fds, even
		3293	on win32. Should not be defined on non-win32 platforms.
		3294
		3295	=item EV_FD_TO_WIN32_HANDLE
		3296
		3297	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3298	file descriptors to socket handles. When not defining this symbol (the
		3299	default), then libev will call C<_get_osfhandle>, which is usually
		3300	correct. In some cases, programs use their own file descriptor management,
		3301	in which case they can provide this function to map fds to socket handles.
		3302
		3303	=item EV_USE_POLL
		3304
		3305	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3306	backend. Otherwise it will be enabled on non-win32 platforms. It
		3307	takes precedence over select.
		3308
		3309	=item EV_USE_EPOLL
		3310
		3311	If defined to be C<1>, libev will compile in support for the Linux
		3312	C<epoll>(7) backend. Its availability will be detected at runtime,
		3313	otherwise another method will be used as fallback. This is the preferred
		3314	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3315	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3316
		3317	=item EV_USE_KQUEUE
		3318
		3319	If defined to be C<1>, libev will compile in support for the BSD style
		3320	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3321	otherwise another method will be used as fallback. This is the preferred
		3322	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3323	supports some types of fds correctly (the only platform we found that
		3324	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3325	not be used unless explicitly requested. The best way to use it is to find
		3326	out whether kqueue supports your type of fd properly and use an embedded
		3327	kqueue loop.
		3328
		3329	=item EV_USE_PORT
		3330
		3331	If defined to be C<1>, libev will compile in support for the Solaris
		3332	10 port style backend. Its availability will be detected at runtime,
		3333	otherwise another method will be used as fallback. This is the preferred
		3334	backend for Solaris 10 systems.
		3335
		3336	=item EV_USE_DEVPOLL
		3337
		3338	Reserved for future expansion, works like the USE symbols above.
		3339
		3340	=item EV_USE_INOTIFY
		3341
		3342	If defined to be C<1>, libev will compile in support for the Linux inotify
		3343	interface to speed up C<ev_stat> watchers. Its actual availability will
		3344	be detected at runtime. If undefined, it will be enabled if the headers
		3345	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3346
		3347	=item EV_ATOMIC_T
		3348
		3349	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3350	access is atomic with respect to other threads or signal contexts. No such
		3351	type is easily found in the C language, so you can provide your own type
		3352	that you know is safe for your purposes. It is used both for signal handler "locking"
		3353	as well as for signal and thread safety in C<ev_async> watchers.
		3354
		3355	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3356	(from F<signal.h>), which is usually good enough on most platforms.
		3357
		3358	=item EV_H
		3359
		3360	The name of the F<ev.h> header file used to include it. The default if
		3361	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3362	used to virtually rename the F<ev.h> header file in case of conflicts.
		3363
		3364	=item EV_CONFIG_H
		3365
		3366	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3367	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3368	C<EV_H>, above.
		3369
		3370	=item EV_EVENT_H
		3371
		3372	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3373	of how the F<event.h> header can be found, the default is C<"event.h">.
		3374
		3375	=item EV_PROTOTYPES
		3376
		3377	If defined to be C<0>, then F<ev.h> will not define any function
		3378	prototypes, but still define all the structs and other symbols. This is
		3379	occasionally useful if you want to provide your own wrapper functions
		3380	around libev functions.
		3381
		3382	=item EV_MULTIPLICITY
		3383
		3384	If undefined or defined to C<1>, then all event-loop-specific functions
		3385	will have the C<struct ev_loop *> as first argument, and you can create
		3386	additional independent event loops. Otherwise there will be no support
		3387	for multiple event loops and there is no first event loop pointer
		3388	argument. Instead, all functions act on the single default loop.
		3389
		3390	=item EV_MINPRI
		3391
		3392	=item EV_MAXPRI
		3393
		3394	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3395	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3396	provide for more priorities by overriding those symbols (usually defined
		3397	to be C<-2> and C<2>, respectively).
		3398
		3399	When doing priority-based operations, libev usually has to linearly search
		3400	all the priorities, so having many of them (hundreds) uses a lot of space
		3401	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3402	fine.
		3403
		3404	If your embedding application does not need any priorities, defining these
		3405	both to C<0> will save some memory and CPU.
		3406
		3407	=item EV_PERIODIC_ENABLE
		3408
		3409	If undefined or defined to be C<1>, then periodic timers are supported. If
		3410	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3411	code.
		3412
		3413	=item EV_IDLE_ENABLE
		3414
		3415	If undefined or defined to be C<1>, then idle watchers are supported. If
		3416	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3417	code.
		3418
		3419	=item EV_EMBED_ENABLE
		3420
		3421	If undefined or defined to be C<1>, then embed watchers are supported. If
		3422	defined to be C<0>, then they are not. Embed watchers rely on most other
		3423	watcher types, which therefore must not be disabled.
		3424
		3425	=item EV_STAT_ENABLE
		3426
		3427	If undefined or defined to be C<1>, then stat watchers are supported. If
		3428	defined to be C<0>, then they are not.
		3429
		3430	=item EV_FORK_ENABLE
		3431
		3432	If undefined or defined to be C<1>, then fork watchers are supported. If
		3433	defined to be C<0>, then they are not.
		3434
		3435	=item EV_ASYNC_ENABLE
		3436
		3437	If undefined or defined to be C<1>, then async watchers are supported. If
		3438	defined to be C<0>, then they are not.
		3439
		3440	=item EV_MINIMAL
		3441
		3442	If you need to shave off some kilobytes of code at the expense of some
		3443	speed, define this symbol to C<1>. Currently this is used to override some
		3444	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3445	much smaller 2-heap for timer management over the default 4-heap.
		3446
		3447	=item EV_PID_HASHSIZE
		3448
		3449	C<ev_child> watchers use a small hash table to distribute workload by
		3450	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3451	than enough. If you need to manage thousands of children you might want to
		3452	increase this value (I<must> be a power of two).
		3453
		3454	=item EV_INOTIFY_HASHSIZE
		3455
		3456	C<ev_stat> watchers use a small hash table to distribute workload by
		3457	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3458	usually more than enough. If you need to manage thousands of C<ev_stat>
		3459	watchers you might want to increase this value (I<must> be a power of
		3460	two).
		3461
		3462	=item EV_USE_4HEAP
		3463
		3464	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3465	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3466	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3467	faster performance with many (thousands) of watchers.
		3468
		3469	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3470	(disabled).
		3471
		3472	=item EV_HEAP_CACHE_AT
		3473
		3474	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3475	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3476	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3477	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3478	but avoids random read accesses on heap changes. This improves performance
		3479	noticeably with many (hundreds) of watchers.
		3480
		3481	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3482	(disabled).
		3483
		3484	=item EV_VERIFY
		3485
		3486	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3487	be done: If set to C<0>, no internal verification code will be compiled
		3488	in. If set to C<1>, then verification code will be compiled in, but not
		3489	called. If set to C<2>, then the internal verification code will be
		3490	called once per loop, which can slow down libev. If set to C<3>, then the
		3491	verification code will be called very frequently, which will slow down
		3492	libev considerably.
		3493
		3494	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3495	C<0>.
		3496
		3497	=item EV_COMMON
		3498
		3499	By default, all watchers have a C<void *data> member. By redefining
		3500	this macro to a something else you can include more and other types of
		3501	members. You have to define it each time you include one of the files,
		3502	though, and it must be identical each time.
		3503
		3504	For example, the perl EV module uses something like this:
		3505
		3506	#define EV_COMMON \
		3507	SV *self; /* contains this struct */ \
		3508	SV *cb_sv, *fh /* note no trailing ";" */
		3509
		3510	=item EV_CB_DECLARE (type)
		3511
		3512	=item EV_CB_INVOKE (watcher, revents)
		3513
		3514	=item ev_set_cb (ev, cb)
		3515
		3516	Can be used to change the callback member declaration in each watcher,
		3517	and the way callbacks are invoked and set. Must expand to a struct member
		3518	definition and a statement, respectively. See the F<ev.h> header file for
		3519	their default definitions. One possible use for overriding these is to
		3520	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3521	method calls instead of plain function calls in C++.
		3522
		3523	=back
		3524
		3525	=head2 EXPORTED API SYMBOLS
		3526
		3527	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3528	exported symbols, you can use the provided F<Symbol.*> files which list
		3529	all public symbols, one per line:
		3530
		3531	Symbols.ev for libev proper
		3532	Symbols.event for the libevent emulation
		3533
		3534	This can also be used to rename all public symbols to avoid clashes with
		3535	multiple versions of libev linked together (which is obviously bad in
		3536	itself, but sometimes it is inconvenient to avoid this).
		3537
		3538	A sed command like this will create wrapper C<#define>'s that you need to
		3539	include before including F<ev.h>:
		3540
		3541	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3542
		3543	This would create a file F<wrap.h> which essentially looks like this:
		3544
		3545	#define ev_backend myprefix_ev_backend
		3546	#define ev_check_start myprefix_ev_check_start
		3547	#define ev_check_stop myprefix_ev_check_stop
		3548	...
		3549
		3550	=head2 EXAMPLES
		3551
		3552	For a real-world example of a program the includes libev
		3553	verbatim, you can have a look at the EV perl module
		3554	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3555	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3556	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3557	will be compiled. It is pretty complex because it provides its own header
		3558	file.
		3559
		3560	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3561	that everybody includes and which overrides some configure choices:
		3562
		3563	#define EV_MINIMAL 1
		3564	#define EV_USE_POLL 0
		3565	#define EV_MULTIPLICITY 0
		3566	#define EV_PERIODIC_ENABLE 0
		3567	#define EV_STAT_ENABLE 0
		3568	#define EV_FORK_ENABLE 0
		3569	#define EV_CONFIG_H <config.h>
		3570	#define EV_MINPRI 0
		3571	#define EV_MAXPRI 0
		3572
		3573	#include "ev++.h"
		3574
		3575	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3576
		3577	#include "ev_cpp.h"
		3578	#include "ev.c"
		3579
		3580	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3581
		3582	=head2 THREADS AND COROUTINES
		3583
		3584	=head3 THREADS
		3585
		3586	All libev functions are reentrant and thread-safe unless explicitly
		3587	documented otherwise, but libev implements no locking itself. This means
		3588	that you can use as many loops as you want in parallel, as long as there
		3589	are no concurrent calls into any libev function with the same loop
		3590	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3591	of course): libev guarantees that different event loops share no data
		3592	structures that need any locking.
		3593
		3594	Or to put it differently: calls with different loop parameters can be done
		3595	concurrently from multiple threads, calls with the same loop parameter
		3596	must be done serially (but can be done from different threads, as long as
		3597	only one thread ever is inside a call at any point in time, e.g. by using
		3598	a mutex per loop).
		3599
		3600	Specifically to support threads (and signal handlers), libev implements
		3601	so-called C<ev_async> watchers, which allow some limited form of
		3602	concurrency on the same event loop, namely waking it up "from the
		3603	outside".
		3604
		3605	If you want to know which design (one loop, locking, or multiple loops
		3606	without or something else still) is best for your problem, then I cannot
		3607	help you, but here is some generic advice:
		3608
		3609	=over 4
		3610
		3611	=item * most applications have a main thread: use the default libev loop
		3612	in that thread, or create a separate thread running only the default loop.
		3613
		3614	This helps integrating other libraries or software modules that use libev
		3615	themselves and don't care/know about threading.
		3616
		3617	=item * one loop per thread is usually a good model.
		3618
		3619	Doing this is almost never wrong, sometimes a better-performance model
		3620	exists, but it is always a good start.
		3621
		3622	=item * other models exist, such as the leader/follower pattern, where one
		3623	loop is handed through multiple threads in a kind of round-robin fashion.
		3624
		3625	Choosing a model is hard - look around, learn, know that usually you can do
		3626	better than you currently do :-)
		3627
		3628	=item * often you need to talk to some other thread which blocks in the
		3629	event loop.
		3630
		3631	C<ev_async> watchers can be used to wake them up from other threads safely
		3632	(or from signal contexts...).
		3633
		3634	An example use would be to communicate signals or other events that only
		3635	work in the default loop by registering the signal watcher with the
		3636	default loop and triggering an C<ev_async> watcher from the default loop
		3637	watcher callback into the event loop interested in the signal.
		3638
		3639	=back
		3640
		3641	=head3 COROUTINES
		3642
		3643	Libev is very accommodating to coroutines ("cooperative threads"):
		3644	libev fully supports nesting calls to its functions from different
		3645	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3646	different coroutines, and switch freely between both coroutines running the
		3647	loop, as long as you don't confuse yourself). The only exception is that
		3648	you must not do this from C<ev_periodic> reschedule callbacks.
		3649
		3650	Care has been taken to ensure that libev does not keep local state inside
		3651	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3652	they do not call any callbacks.
		3653
		3654	=head2 COMPILER WARNINGS
		3655
		3656	Depending on your compiler and compiler settings, you might get no or a
		3657	lot of warnings when compiling libev code. Some people are apparently
		3658	scared by this.
		3659
		3660	However, these are unavoidable for many reasons. For one, each compiler
		3661	has different warnings, and each user has different tastes regarding
		3662	warning options. "Warn-free" code therefore cannot be a goal except when
		3663	targeting a specific compiler and compiler-version.
		3664
		3665	Another reason is that some compiler warnings require elaborate
		3666	workarounds, or other changes to the code that make it less clear and less
		3667	maintainable.
		3668
		3669	And of course, some compiler warnings are just plain stupid, or simply
		3670	wrong (because they don't actually warn about the condition their message
		3671	seems to warn about). For example, certain older gcc versions had some
		3672	warnings that resulted an extreme number of false positives. These have
		3673	been fixed, but some people still insist on making code warn-free with
		3674	such buggy versions.
		3675
		3676	While libev is written to generate as few warnings as possible,
		3677	"warn-free" code is not a goal, and it is recommended not to build libev
		3678	with any compiler warnings enabled unless you are prepared to cope with
		3679	them (e.g. by ignoring them). Remember that warnings are just that:
		3680	warnings, not errors, or proof of bugs.
		3681
		3682
		3683	=head2 VALGRIND
		3684
		3685	Valgrind has a special section here because it is a popular tool that is
		3686	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3687
		3688	If you think you found a bug (memory leak, uninitialised data access etc.)
		3689	in libev, then check twice: If valgrind reports something like:
		3690
		3691	==2274== definitely lost: 0 bytes in 0 blocks.
		3692	==2274== possibly lost: 0 bytes in 0 blocks.
		3693	==2274== still reachable: 256 bytes in 1 blocks.
		3694
		3695	Then there is no memory leak, just as memory accounted to global variables
		3696	is not a memleak - the memory is still being referenced, and didn't leak.
		3697
		3698	Similarly, under some circumstances, valgrind might report kernel bugs
		3699	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3700	although an acceptable workaround has been found here), or it might be
		3701	confused.
		3702
		3703	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3704	make it into some kind of religion.
		3705
		3706	If you are unsure about something, feel free to contact the mailing list
		3707	with the full valgrind report and an explanation on why you think this
		3708	is a bug in libev (best check the archives, too :). However, don't be
		3709	annoyed when you get a brisk "this is no bug" answer and take the chance
		3710	of learning how to interpret valgrind properly.
		3711
		3712	If you need, for some reason, empty reports from valgrind for your project
		3713	I suggest using suppression lists.
		3714
		3715
		3716	=head1 PORTABILITY NOTES
		3717
		3718	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3719
		3720	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3721	requires, and its I/O model is fundamentally incompatible with the POSIX
		3722	model. Libev still offers limited functionality on this platform in
		3723	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3724	descriptors. This only applies when using Win32 natively, not when using
		3725	e.g. cygwin.
		3726
		3727	Lifting these limitations would basically require the full
		3728	re-implementation of the I/O system. If you are into these kinds of
		3729	things, then note that glib does exactly that for you in a very portable
		3730	way (note also that glib is the slowest event library known to man).
		3731
		3732	There is no supported compilation method available on windows except
		3733	embedding it into other applications.
		3734
		3735	Not a libev limitation but worth mentioning: windows apparently doesn't
		3736	accept large writes: instead of resulting in a partial write, windows will
		3737	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3738	so make sure you only write small amounts into your sockets (less than a
		3739	megabyte seems safe, but this apparently depends on the amount of memory
		3740	available).
		3741
		3742	Due to the many, low, and arbitrary limits on the win32 platform and
		3743	the abysmal performance of winsockets, using a large number of sockets
		3744	is not recommended (and not reasonable). If your program needs to use
		3745	more than a hundred or so sockets, then likely it needs to use a totally
		3746	different implementation for windows, as libev offers the POSIX readiness
		3747	notification model, which cannot be implemented efficiently on windows
		3748	(Microsoft monopoly games).
		3749
		3750	A typical way to use libev under windows is to embed it (see the embedding
		3751	section for details) and use the following F<evwrap.h> header file instead
		3752	of F<ev.h>:
		3753
		3754	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3755	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3756
		3757	#include "ev.h"
		3758
		3759	And compile the following F<evwrap.c> file into your project (make sure
		3760	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3761
		3762	#include "evwrap.h"
		3763	#include "ev.c"
		3764
		3765	=over 4
		3766
		3767	=item The winsocket select function
		3768
		3769	The winsocket C<select> function doesn't follow POSIX in that it
		3770	requires socket I<handles> and not socket I<file descriptors> (it is
		3771	also extremely buggy). This makes select very inefficient, and also
		3772	requires a mapping from file descriptors to socket handles (the Microsoft
		3773	C runtime provides the function C<_open_osfhandle> for this). See the
		3774	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3775	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3776
		3777	The configuration for a "naked" win32 using the Microsoft runtime
		3778	libraries and raw winsocket select is:
		3779
		3780	#define EV_USE_SELECT 1
		3781	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3782
		3783	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3784	complexity in the O(n²) range when using win32.
		3785
		3786	=item Limited number of file descriptors
		3787
		3788	Windows has numerous arbitrary (and low) limits on things.
		3789
		3790	Early versions of winsocket's select only supported waiting for a maximum
		3791	of C<64> handles (probably owning to the fact that all windows kernels
		3792	can only wait for C<64> things at the same time internally; Microsoft
		3793	recommends spawning a chain of threads and wait for 63 handles and the
		3794	previous thread in each. Great).
		3795
		3796	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3797	to some high number (e.g. C<2048>) before compiling the winsocket select
		3798	call (which might be in libev or elsewhere, for example, perl does its own
		3799	select emulation on windows).
		3800
		3801	Another limit is the number of file descriptors in the Microsoft runtime
		3802	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3803	or something like this inside Microsoft). You can increase this by calling
		3804	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3805	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3806	libraries.
		3807
		3808	This might get you to about C<512> or C<2048> sockets (depending on
		3809	windows version and/or the phase of the moon). To get more, you need to
		3810	wrap all I/O functions and provide your own fd management, but the cost of
		3811	calling select (O(n²)) will likely make this unworkable.
		3812
		3813	=back
		3814
		3815	=head2 PORTABILITY REQUIREMENTS
		3816
		3817	In addition to a working ISO-C implementation and of course the
		3818	backend-specific APIs, libev relies on a few additional extensions:
		3819
		3820	=over 4
		3821
		3822	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3823	calling conventions regardless of C<ev_watcher_type *>.
		3824
		3825	Libev assumes not only that all watcher pointers have the same internal
		3826	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3827	assumes that the same (machine) code can be used to call any watcher
		3828	callback: The watcher callbacks have different type signatures, but libev
		3829	calls them using an C<ev_watcher *> internally.
		3830
		3831	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3832
		3833	The type C<sig_atomic_t volatile> (or whatever is defined as
		3834	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3835	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3836	believed to be sufficiently portable.
		3837
		3838	=item C<sigprocmask> must work in a threaded environment
		3839
		3840	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3841	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3842	pthread implementations will either allow C<sigprocmask> in the "main
		3843	thread" or will block signals process-wide, both behaviours would
		3844	be compatible with libev. Interaction between C<sigprocmask> and
		3845	C<pthread_sigmask> could complicate things, however.
		3846
		3847	The most portable way to handle signals is to block signals in all threads
		3848	except the initial one, and run the default loop in the initial thread as
		3849	well.
		3850
		3851	=item C<long> must be large enough for common memory allocation sizes
		3852
		3853	To improve portability and simplify its API, libev uses C<long> internally
		3854	instead of C<size_t> when allocating its data structures. On non-POSIX
		3855	systems (Microsoft...) this might be unexpectedly low, but is still at
		3856	least 31 bits everywhere, which is enough for hundreds of millions of
		3857	watchers.
		3858
		3859	=item C<double> must hold a time value in seconds with enough accuracy
		3860
		3861	The type C<double> is used to represent timestamps. It is required to
		3862	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3863	enough for at least into the year 4000. This requirement is fulfilled by
		3864	implementations implementing IEEE 754 (basically all existing ones).
		3865
		3866	=back
		3867
		3868	If you know of other additional requirements drop me a note.
		3869
		3870
		3871	=head1 ALGORITHMIC COMPLEXITIES
		3872
		3873	In this section the complexities of (many of) the algorithms used inside
		3874	libev will be documented. For complexity discussions about backends see
		3875	the documentation for C<ev_default_init>.
		3876
		3877	All of the following are about amortised time: If an array needs to be
		3878	extended, libev needs to realloc and move the whole array, but this
		3879	happens asymptotically rarer with higher number of elements, so O(1) might
		3880	mean that libev does a lengthy realloc operation in rare cases, but on
		3881	average it is much faster and asymptotically approaches constant time.
		3882
		3883	=over 4
		3884
		3885	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3886
		3887	This means that, when you have a watcher that triggers in one hour and
		3888	there are 100 watchers that would trigger before that, then inserting will
		3889	have to skip roughly seven (C<ld 100>) of these watchers.
		3890
		3891	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3892
		3893	That means that changing a timer costs less than removing/adding them,
		3894	as only the relative motion in the event queue has to be paid for.
		3895
		3896	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3897
		3898	These just add the watcher into an array or at the head of a list.
		3899
		3900	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3901
		3902	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3903
		3904	These watchers are stored in lists, so they need to be walked to find the
		3905	correct watcher to remove. The lists are usually short (you don't usually
		3906	have many watchers waiting for the same fd or signal: one is typical, two
		3907	is rare).
		3908
		3909	=item Finding the next timer in each loop iteration: O(1)
		3910
		3911	By virtue of using a binary or 4-heap, the next timer is always found at a
		3912	fixed position in the storage array.
		3913
		3914	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3915
		3916	A change means an I/O watcher gets started or stopped, which requires
		3917	libev to recalculate its status (and possibly tell the kernel, depending
		3918	on backend and whether C<ev_io_set> was used).
		3919
		3920	=item Activating one watcher (putting it into the pending state): O(1)
		3921
		3922	=item Priority handling: O(number_of_priorities)
		3923
		3924	Priorities are implemented by allocating some space for each
		3925	priority. When doing priority-based operations, libev usually has to
		3926	linearly search all the priorities, but starting/stopping and activating
		3927	watchers becomes O(1) with respect to priority handling.
		3928
		3929	=item Sending an ev_async: O(1)
		3930
		3931	=item Processing ev_async_send: O(number_of_async_watchers)
		3932
		3933	=item Processing signals: O(max_signal_number)
		3934
		3935	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3936	calls in the current loop iteration. Checking for async and signal events
		3937	involves iterating over all running async watchers or all signal numbers.
		3938
		3939	=back
		3940
		3941
767	=head1 AUTHOR	3942	=head1 AUTHOR
768		3943
769	Marc Lehmann <libev@schmorp.de>.	3944	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
770		3945

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