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Revision 1.12 by root, Mon Nov 12 08:35:18 2007 UTC vs.
Revision 1.226 by root, Wed Mar 4 12:51:37 2009 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> (but C<poll> is of course
		466	also broken on OS X)) and, did I mention it, 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 cna 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 cna 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
313	The rceeived events usually include a single bit per event type received	869	The received events usually include a single bit per event type received
314	(you can receive multiple events at the same time). The possible bit masks	870	(you can receive multiple events at the same time). The possible bit masks
315	are:	871	are:
316		872
317	=over 4	873	=over 4
318		874
…		…
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 cna 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 cna 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 it	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 at, ev_tstamp interval, 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 other 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 cna 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>). The C<rpid> member	1884	the status word (use the macros from C<sys/wait.h> and see your systems
639	contains the pid of the process causing the status change.	1885	C<waitpid> documentation). The C<rpid> member contains the pid of the
		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).
640		1902
641	=back	1903	=back
642		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 usually 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
643	=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...
644		2160
645	Idle watchers trigger events when there are no other I/O or timer (or	2161	Idle watchers trigger events when no other events of the same or higher
646	periodic) events pending. That is, as long as your process is busy	2162	priority are pending (prepare, check and other idle watchers do not count
647	handling sockets or timeouts it will not be called. But when your process	2163	as receiving "events").
648	is idle all idle watchers are being called again and again - until	2164
		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
649	stopped, that is, or your process receives more events.	2169	iteration - until stopped, that is, or your process receives more events
		2170	and becomes busy again with higher priority stuff.
650		2171
651	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
652	active, the process will not block when waiting for new events.	2173	active, the process will not block when waiting for new events.
653		2174
654	Apart from keeping your process non-blocking (which is a useful	2175	Apart from keeping your process non-blocking (which is a useful
655	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
656	"pseudo-background processing", or delay processing stuff to after the	2177	"pseudo-background processing", or delay processing stuff to after the
657	event loop has handled all outstanding events.	2178	event loop has handled all outstanding events.
658		2179
		2180	=head3 Watcher-Specific Functions and Data Members
		2181
659	=over 4	2182	=over 4
660		2183
661	=item ev_idle_init (ev_signal *, callback)	2184	=item ev_idle_init (ev_idle *, callback)
662		2185
663	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
664	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,
665	believe me.	2188	believe me.
666		2189
667	=back	2190	=back
668		2191
669	=head2 prepare and check - your hooks into the event loop	2192	=head3 Examples
670		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
		2210	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
		2211
671	Prepare and check watchers usually (but not always) are used in	2212	Prepare and check watchers are usually (but not always) used in pairs:
672	tandom. Prepare watchers get invoked before the process blocks and check	2213	prepare watchers get invoked before the process blocks and check watchers
673	watchers afterwards.	2214	afterwards.
674		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
675	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
676	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
677	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).
678		2231
679	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
680	to be watched by the other library, registering C<ev_io> watchers for them	2233	need to be watched by the other library, registering C<ev_io> watchers
681	and starting an C<ev_timer> watcher for any timeouts (many libraries provide	2234	for them and starting an C<ev_timer> watcher for any timeouts (many
682	just this functionality). Then, in the check watcher you check for any	2235	libraries provide exactly this functionality). Then, in the check watcher,
683	events that occured (by making your callbacks set soem flags for example)	2236	you check for any events that occurred (by checking the pending status
684	and call back into the library.	2237	of all watchers and stopping them) and call back into the library. The
		2238	I/O and timer callbacks will never actually be called (but must be valid
		2239	nevertheless, because you never know, you know?).
685		2240
686	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
687	coroutines into libev programs, by yielding to other active coroutines	2242	coroutines into libev programs, by yielding to other active coroutines
688	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
689	are ready to run.	2244	are ready to run (it's actually more complicated: it only runs coroutines
		2245	with priority higher than or equal to the event loop and one coroutine
		2246	of lower priority, but only once, using idle watchers to keep the event
		2247	loop from blocking if lower-priority coroutines are active, thus mapping
		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
690		2263
691	=over 4	2264	=over 4
692		2265
693	=item ev_prepare_init (ev_prepare *, callback)	2266	=item ev_prepare_init (ev_prepare *, callback)
694		2267
695	=item ev_check_init (ev_check *, callback)	2268	=item ev_check_init (ev_check *, callback)
696		2269
697	Initialises and configures the prepare or check watcher - they have no	2270	Initialises and configures the prepare or check watcher - they have no
698	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>
699	macros, but using them is utterly, utterly pointless.	2272	macros, but using them is utterly, utterly, utterly and completely
		2273	pointless.
700		2274
701	=back	2275	=back
702		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
		2434	time there might be events pending in the embedded loop. The callback
		2435	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		2436	sweep and invoke their callbacks (the callback doesn't need to invoke the
		2437	C<ev_embed_sweep> function directly, it could also start an idle watcher
		2438	to give the embedded loop strictly lower priority for example).
		2439
		2440	You can also set the callback to C<0>, in which case the embed watcher
		2441	will automatically execute the embedded loop sweep whenever necessary.
		2442
		2443	Fork detection will be handled transparently while the C<ev_embed> watcher
		2444	is active, i.e., the embedded loop will automatically be forked when the
		2445	embedding loop forks. In other cases, the user is responsible for calling
		2446	C<ev_loop_fork> on the embedded loop.
		2447
		2448	Unfortunately, not all backends are embeddable: only the ones returned by
		2449	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2450	portable one.
		2451
		2452	So when you want to use this feature you will always have to be prepared
		2453	that you cannot get an embeddable loop. The recommended way to get around
		2454	this is to have a separate variables for your embeddable loop, try to
		2455	create it, and if that fails, use the normal loop for everything.
		2456
		2457	=head3 C<ev_embed> and fork
		2458
		2459	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2460	automatically be applied to the embedded loop as well, so no special
		2461	fork handling is required in that case. When the watcher is not running,
		2462	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2463	as applicable.
		2464
		2465	=head3 Watcher-Specific Functions and Data Members
		2466
		2467	=over 4
		2468
		2469	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2470
		2471	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2472
		2473	Configures the watcher to embed the given loop, which must be
		2474	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2475	invoked automatically, otherwise it is the responsibility of the callback
		2476	to invoke it (it will continue to be called until the sweep has been done,
		2477	if you do not want that, you need to temporarily stop the embed watcher).
		2478
		2479	=item ev_embed_sweep (loop, ev_embed *)
		2480
		2481	Make a single, non-blocking sweep over the embedded loop. This works
		2482	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2483	appropriate way for embedded loops.
		2484
		2485	=item struct ev_loop *other [read-only]
		2486
		2487	The embedded event loop.
		2488
		2489	=back
		2490
		2491	=head3 Examples
		2492
		2493	Example: Try to get an embeddable event loop and embed it into the default
		2494	event loop. If that is not possible, use the default loop. The default
		2495	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2496	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2497	used).
		2498
		2499	struct ev_loop *loop_hi = ev_default_init (0);
		2500	struct ev_loop *loop_lo = 0;
		2501	ev_embed embed;
		2502
		2503	// see if there is a chance of getting one that works
		2504	// (remember that a flags value of 0 means autodetection)
		2505	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2506	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2507	: 0;
		2508
		2509	// if we got one, then embed it, otherwise default to loop_hi
		2510	if (loop_lo)
		2511	{
		2512	ev_embed_init (&embed, 0, loop_lo);
		2513	ev_embed_start (loop_hi, &embed);
		2514	}
		2515	else
		2516	loop_lo = loop_hi;
		2517
		2518	Example: Check if kqueue is available but not recommended and create
		2519	a kqueue backend for use with sockets (which usually work with any
		2520	kqueue implementation). Store the kqueue/socket-only event loop in
		2521	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2522
		2523	struct ev_loop *loop = ev_default_init (0);
		2524	struct ev_loop *loop_socket = 0;
		2525	ev_embed embed;
		2526
		2527	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2528	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2529	{
		2530	ev_embed_init (&embed, 0, loop_socket);
		2531	ev_embed_start (loop, &embed);
		2532	}
		2533
		2534	if (!loop_socket)
		2535	loop_socket = loop;
		2536
		2537	// now use loop_socket for all sockets, and loop for everything else
		2538
		2539
		2540	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2541
		2542	Fork watchers are called when a C<fork ()> was detected (usually because
		2543	whoever is a good citizen cared to tell libev about it by calling
		2544	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2545	event loop blocks next and before C<ev_check> watchers are being called,
		2546	and only in the child after the fork. If whoever good citizen calling
		2547	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2548	handlers will be invoked, too, of course.
		2549
		2550	=head3 Watcher-Specific Functions and Data Members
		2551
		2552	=over 4
		2553
		2554	=item ev_fork_init (ev_signal *, callback)
		2555
		2556	Initialises and configures the fork watcher - it has no parameters of any
		2557	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2558	believe me.
		2559
		2560	=back
		2561
		2562
		2563	=head2 C<ev_async> - how to wake up another event loop
		2564
		2565	In general, you cannot use an C<ev_loop> from multiple threads or other
		2566	asynchronous sources such as signal handlers (as opposed to multiple event
		2567	loops - those are of course safe to use in different threads).
		2568
		2569	Sometimes, however, you need to wake up another event loop you do not
		2570	control, for example because it belongs to another thread. This is what
		2571	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2572	can signal it by calling C<ev_async_send>, which is thread- and signal
		2573	safe.
		2574
		2575	This functionality is very similar to C<ev_signal> watchers, as signals,
		2576	too, are asynchronous in nature, and signals, too, will be compressed
		2577	(i.e. the number of callback invocations may be less than the number of
		2578	C<ev_async_sent> calls).
		2579
		2580	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2581	just the default loop.
		2582
		2583	=head3 Queueing
		2584
		2585	C<ev_async> does not support queueing of data in any way. The reason
		2586	is that the author does not know of a simple (or any) algorithm for a
		2587	multiple-writer-single-reader queue that works in all cases and doesn't
		2588	need elaborate support such as pthreads.
		2589
		2590	That means that if you want to queue data, you have to provide your own
		2591	queue. But at least I can tell you how to implement locking around your
		2592	queue:
		2593
		2594	=over 4
		2595
		2596	=item queueing from a signal handler context
		2597
		2598	To implement race-free queueing, you simply add to the queue in the signal
		2599	handler but you block the signal handler in the watcher callback. Here is
		2600	an example that does that for some fictitious SIGUSR1 handler:
		2601
		2602	static ev_async mysig;
		2603
		2604	static void
		2605	sigusr1_handler (void)
		2606	{
		2607	sometype data;
		2608
		2609	// no locking etc.
		2610	queue_put (data);
		2611	ev_async_send (EV_DEFAULT_ &mysig);
		2612	}
		2613
		2614	static void
		2615	mysig_cb (EV_P_ ev_async *w, int revents)
		2616	{
		2617	sometype data;
		2618	sigset_t block, prev;
		2619
		2620	sigemptyset (&block);
		2621	sigaddset (&block, SIGUSR1);
		2622	sigprocmask (SIG_BLOCK, &block, &prev);
		2623
		2624	while (queue_get (&data))
		2625	process (data);
		2626
		2627	if (sigismember (&prev, SIGUSR1)
		2628	sigprocmask (SIG_UNBLOCK, &block, 0);
		2629	}
		2630
		2631	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2632	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2633	either...).
		2634
		2635	=item queueing from a thread context
		2636
		2637	The strategy for threads is different, as you cannot (easily) block
		2638	threads but you can easily preempt them, so to queue safely you need to
		2639	employ a traditional mutex lock, such as in this pthread example:
		2640
		2641	static ev_async mysig;
		2642	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2643
		2644	static void
		2645	otherthread (void)
		2646	{
		2647	// only need to lock the actual queueing operation
		2648	pthread_mutex_lock (&mymutex);
		2649	queue_put (data);
		2650	pthread_mutex_unlock (&mymutex);
		2651
		2652	ev_async_send (EV_DEFAULT_ &mysig);
		2653	}
		2654
		2655	static void
		2656	mysig_cb (EV_P_ ev_async *w, int revents)
		2657	{
		2658	pthread_mutex_lock (&mymutex);
		2659
		2660	while (queue_get (&data))
		2661	process (data);
		2662
		2663	pthread_mutex_unlock (&mymutex);
		2664	}
		2665
		2666	=back
		2667
		2668
		2669	=head3 Watcher-Specific Functions and Data Members
		2670
		2671	=over 4
		2672
		2673	=item ev_async_init (ev_async *, callback)
		2674
		2675	Initialises and configures the async watcher - it has no parameters of any
		2676	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2677	trust me.
		2678
		2679	=item ev_async_send (loop, ev_async *)
		2680
		2681	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2682	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2683	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2684	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2685	section below on what exactly this means).
		2686
		2687	This call incurs the overhead of a system call only once per loop iteration,
		2688	so while the overhead might be noticeable, it doesn't apply to repeated
		2689	calls to C<ev_async_send>.
		2690
		2691	=item bool = ev_async_pending (ev_async *)
		2692
		2693	Returns a non-zero value when C<ev_async_send> has been called on the
		2694	watcher but the event has not yet been processed (or even noted) by the
		2695	event loop.
		2696
		2697	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2698	the loop iterates next and checks for the watcher to have become active,
		2699	it will reset the flag again. C<ev_async_pending> can be used to very
		2700	quickly check whether invoking the loop might be a good idea.
		2701
		2702	Not that this does I<not> check whether the watcher itself is pending, only
		2703	whether it has been requested to make this watcher pending.
		2704
		2705	=back
		2706
		2707
703	=head1 OTHER FUNCTIONS	2708	=head1 OTHER FUNCTIONS
704		2709
705	There are some other fucntions of possible interest. Described. Here. Now.	2710	There are some other functions of possible interest. Described. Here. Now.
706		2711
707	=over 4	2712	=over 4
708		2713
709	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2714	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
710		2715
711	This function combines a simple timer and an I/O watcher, calls your	2716	This function combines a simple timer and an I/O watcher, calls your
712	callback on whichever event happens first and automatically stop both	2717	callback on whichever event happens first and automatically stops both
713	watchers. This is useful if you want to wait for a single event on an fd	2718	watchers. This is useful if you want to wait for a single event on an fd
714	or timeout without havign to allocate/configure/start/stop/free one or	2719	or timeout without having to allocate/configure/start/stop/free one or
715	more watchers yourself.	2720	more watchers yourself.
716		2721
717	If C<fd> is less than 0, then no I/O watcher will be started and events is	2722	If C<fd> is less than 0, then no I/O watcher will be started and the
718	ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and C<events> set	2723	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
719	will be craeted and started.	2724	the given C<fd> and C<events> set will be created and started.
720		2725
721	If C<timeout> is less than 0, then no timeout watcher will be	2726	If C<timeout> is less than 0, then no timeout watcher will be
722	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and repeat	2727	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
723	= 0) will be started.	2728	repeat = 0) will be started. C<0> is a valid timeout.
724		2729
725	The callback has the type C<void (*cb)(int revents, void *arg)> and	2730	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
726	gets passed an events set (normally a combination of C<EV_ERROR>, C<EV_READ>,	2731	passed an C<revents> set like normal event callbacks (a combination of
727	C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg> value passed to C<ev_once>:	2732	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
		2733	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2734	a timeout and an io event at the same time - you probably should give io
		2735	events precedence.
728		2736
		2737	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2738
729	static void stdin_ready (int revents, void *arg)	2739	static void stdin_ready (int revents, void *arg)
730	{	2740	{
731	if (revents & EV_TIMEOUT)
732	/* doh, nothing entered */
733	else if (revents & EV_READ)	2741	if (revents & EV_READ)
734	/* stdin might have data for us, joy! */	2742	/* stdin might have data for us, joy! */;
		2743	else if (revents & EV_TIMEOUT)
		2744	/* doh, nothing entered */;
735	}	2745	}
736		2746
737	ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);	2747	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
738		2748
739	=item ev_feed_event (loop, watcher, int events)	2749	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
740		2750
741	Feeds the given event set into the event loop, as if the specified event	2751	Feeds the given event set into the event loop, as if the specified event
742	has happened for the specified watcher (which must be a pointer to an	2752	had happened for the specified watcher (which must be a pointer to an
743	initialised but not necessarily active event watcher).	2753	initialised but not necessarily started event watcher).
744		2754
745	=item ev_feed_fd_event (loop, int fd, int revents)	2755	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
746		2756
747	Feed an event on the given fd, as if a file descriptor backend detected it.	2757	Feed an event on the given fd, as if a file descriptor backend detected
		2758	the given events it.
748		2759
749	=item ev_feed_signal_event (loop, int signum)	2760	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
750		2761
751	Feed an event as if the given signal occured (loop must be the default loop!).	2762	Feed an event as if the given signal occurred (C<loop> must be the default
		2763	loop!).
752		2764
753	=back	2765	=back
754		2766
		2767
		2768	=head1 LIBEVENT EMULATION
		2769
		2770	Libev offers a compatibility emulation layer for libevent. It cannot
		2771	emulate the internals of libevent, so here are some usage hints:
		2772
		2773	=over 4
		2774
		2775	=item * Use it by including <event.h>, as usual.
		2776
		2777	=item * The following members are fully supported: ev_base, ev_callback,
		2778	ev_arg, ev_fd, ev_res, ev_events.
		2779
		2780	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		2781	maintained by libev, it does not work exactly the same way as in libevent (consider
		2782	it a private API).
		2783
		2784	=item * Priorities are not currently supported. Initialising priorities
		2785	will fail and all watchers will have the same priority, even though there
		2786	is an ev_pri field.
		2787
		2788	=item * In libevent, the last base created gets the signals, in libev, the
		2789	first base created (== the default loop) gets the signals.
		2790
		2791	=item * Other members are not supported.
		2792
		2793	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		2794	to use the libev header file and library.
		2795
		2796	=back
		2797
		2798	=head1 C++ SUPPORT
		2799
		2800	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2801	you to use some convenience methods to start/stop watchers and also change
		2802	the callback model to a model using method callbacks on objects.
		2803
		2804	To use it,
		2805
		2806	#include <ev++.h>
		2807
		2808	This automatically includes F<ev.h> and puts all of its definitions (many
		2809	of them macros) into the global namespace. All C++ specific things are
		2810	put into the C<ev> namespace. It should support all the same embedding
		2811	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2812
		2813	Care has been taken to keep the overhead low. The only data member the C++
		2814	classes add (compared to plain C-style watchers) is the event loop pointer
		2815	that the watcher is associated with (or no additional members at all if
		2816	you disable C<EV_MULTIPLICITY> when embedding libev).
		2817
		2818	Currently, functions, and static and non-static member functions can be
		2819	used as callbacks. Other types should be easy to add as long as they only
		2820	need one additional pointer for context. If you need support for other
		2821	types of functors please contact the author (preferably after implementing
		2822	it).
		2823
		2824	Here is a list of things available in the C<ev> namespace:
		2825
		2826	=over 4
		2827
		2828	=item C<ev::READ>, C<ev::WRITE> etc.
		2829
		2830	These are just enum values with the same values as the C<EV_READ> etc.
		2831	macros from F<ev.h>.
		2832
		2833	=item C<ev::tstamp>, C<ev::now>
		2834
		2835	Aliases to the same types/functions as with the C<ev_> prefix.
		2836
		2837	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2838
		2839	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2840	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2841	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2842	defines by many implementations.
		2843
		2844	All of those classes have these methods:
		2845
		2846	=over 4
		2847
		2848	=item ev::TYPE::TYPE ()
		2849
		2850	=item ev::TYPE::TYPE (struct ev_loop *)
		2851
		2852	=item ev::TYPE::~TYPE
		2853
		2854	The constructor (optionally) takes an event loop to associate the watcher
		2855	with. If it is omitted, it will use C<EV_DEFAULT>.
		2856
		2857	The constructor calls C<ev_init> for you, which means you have to call the
		2858	C<set> method before starting it.
		2859
		2860	It will not set a callback, however: You have to call the templated C<set>
		2861	method to set a callback before you can start the watcher.
		2862
		2863	(The reason why you have to use a method is a limitation in C++ which does
		2864	not allow explicit template arguments for constructors).
		2865
		2866	The destructor automatically stops the watcher if it is active.
		2867
		2868	=item w->set<class, &class::method> (object *)
		2869
		2870	This method sets the callback method to call. The method has to have a
		2871	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2872	first argument and the C<revents> as second. The object must be given as
		2873	parameter and is stored in the C<data> member of the watcher.
		2874
		2875	This method synthesizes efficient thunking code to call your method from
		2876	the C callback that libev requires. If your compiler can inline your
		2877	callback (i.e. it is visible to it at the place of the C<set> call and
		2878	your compiler is good :), then the method will be fully inlined into the
		2879	thunking function, making it as fast as a direct C callback.
		2880
		2881	Example: simple class declaration and watcher initialisation
		2882
		2883	struct myclass
		2884	{
		2885	void io_cb (ev::io &w, int revents) { }
		2886	}
		2887
		2888	myclass obj;
		2889	ev::io iow;
		2890	iow.set <myclass, &myclass::io_cb> (&obj);
		2891
		2892	=item w->set (object *)
		2893
		2894	This is an B<experimental> feature that might go away in a future version.
		2895
		2896	This is a variation of a method callback - leaving out the method to call
		2897	will default the method to C<operator ()>, which makes it possible to use
		2898	functor objects without having to manually specify the C<operator ()> all
		2899	the time. Incidentally, you can then also leave out the template argument
		2900	list.
		2901
		2902	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		2903	int revents)>.
		2904
		2905	See the method-C<set> above for more details.
		2906
		2907	Example: use a functor object as callback.
		2908
		2909	struct myfunctor
		2910	{
		2911	void operator() (ev::io &w, int revents)
		2912	{
		2913	...
		2914	}
		2915	}
		2916
		2917	myfunctor f;
		2918
		2919	ev::io w;
		2920	w.set (&f);
		2921
		2922	=item w->set<function> (void *data = 0)
		2923
		2924	Also sets a callback, but uses a static method or plain function as
		2925	callback. The optional C<data> argument will be stored in the watcher's
		2926	C<data> member and is free for you to use.
		2927
		2928	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2929
		2930	See the method-C<set> above for more details.
		2931
		2932	Example: Use a plain function as callback.
		2933
		2934	static void io_cb (ev::io &w, int revents) { }
		2935	iow.set <io_cb> ();
		2936
		2937	=item w->set (struct ev_loop *)
		2938
		2939	Associates a different C<struct ev_loop> with this watcher. You can only
		2940	do this when the watcher is inactive (and not pending either).
		2941
		2942	=item w->set ([arguments])
		2943
		2944	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2945	called at least once. Unlike the C counterpart, an active watcher gets
		2946	automatically stopped and restarted when reconfiguring it with this
		2947	method.
		2948
		2949	=item w->start ()
		2950
		2951	Starts the watcher. Note that there is no C<loop> argument, as the
		2952	constructor already stores the event loop.
		2953
		2954	=item w->stop ()
		2955
		2956	Stops the watcher if it is active. Again, no C<loop> argument.
		2957
		2958	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2959
		2960	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2961	C<ev_TYPE_again> function.
		2962
		2963	=item w->sweep () (C<ev::embed> only)
		2964
		2965	Invokes C<ev_embed_sweep>.
		2966
		2967	=item w->update () (C<ev::stat> only)
		2968
		2969	Invokes C<ev_stat_stat>.
		2970
		2971	=back
		2972
		2973	=back
		2974
		2975	Example: Define a class with an IO and idle watcher, start one of them in
		2976	the constructor.
		2977
		2978	class myclass
		2979	{
		2980	ev::io io ; void io_cb (ev::io &w, int revents);
		2981	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		2982
		2983	myclass (int fd)
		2984	{
		2985	io .set <myclass, &myclass::io_cb > (this);
		2986	idle.set <myclass, &myclass::idle_cb> (this);
		2987
		2988	io.start (fd, ev::READ);
		2989	}
		2990	};
		2991
		2992
		2993	=head1 OTHER LANGUAGE BINDINGS
		2994
		2995	Libev does not offer other language bindings itself, but bindings for a
		2996	number of languages exist in the form of third-party packages. If you know
		2997	any interesting language binding in addition to the ones listed here, drop
		2998	me a note.
		2999
		3000	=over 4
		3001
		3002	=item Perl
		3003
		3004	The EV module implements the full libev API and is actually used to test
		3005	libev. EV is developed together with libev. Apart from the EV core module,
		3006	there are additional modules that implement libev-compatible interfaces
		3007	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3008	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3009	and C<EV::Glib>).
		3010
		3011	It can be found and installed via CPAN, its homepage is at
		3012	L<http://software.schmorp.de/pkg/EV>.
		3013
		3014	=item Python
		3015
		3016	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3017	seems to be quite complete and well-documented. Note, however, that the
		3018	patch they require for libev is outright dangerous as it breaks the ABI
		3019	for everybody else, and therefore, should never be applied in an installed
		3020	libev (if python requires an incompatible ABI then it needs to embed
		3021	libev).
		3022
		3023	=item Ruby
		3024
		3025	Tony Arcieri has written a ruby extension that offers access to a subset
		3026	of the libev API and adds file handle abstractions, asynchronous DNS and
		3027	more on top of it. It can be found via gem servers. Its homepage is at
		3028	L<http://rev.rubyforge.org/>.
		3029
		3030	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3031	makes rev work even on mingw.
		3032
		3033	=item D
		3034
		3035	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3036	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3037
		3038	=item Ocaml
		3039
		3040	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3041	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3042
		3043	=back
		3044
		3045
		3046	=head1 MACRO MAGIC
		3047
		3048	Libev can be compiled with a variety of options, the most fundamental
		3049	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3050	functions and callbacks have an initial C<struct ev_loop *> argument.
		3051
		3052	To make it easier to write programs that cope with either variant, the
		3053	following macros are defined:
		3054
		3055	=over 4
		3056
		3057	=item C<EV_A>, C<EV_A_>
		3058
		3059	This provides the loop I<argument> for functions, if one is required ("ev
		3060	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3061	C<EV_A_> is used when other arguments are following. Example:
		3062
		3063	ev_unref (EV_A);
		3064	ev_timer_add (EV_A_ watcher);
		3065	ev_loop (EV_A_ 0);
		3066
		3067	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3068	which is often provided by the following macro.
		3069
		3070	=item C<EV_P>, C<EV_P_>
		3071
		3072	This provides the loop I<parameter> for functions, if one is required ("ev
		3073	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3074	C<EV_P_> is used when other parameters are following. Example:
		3075
		3076	// this is how ev_unref is being declared
		3077	static void ev_unref (EV_P);
		3078
		3079	// this is how you can declare your typical callback
		3080	static void cb (EV_P_ ev_timer *w, int revents)
		3081
		3082	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3083	suitable for use with C<EV_A>.
		3084
		3085	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3086
		3087	Similar to the other two macros, this gives you the value of the default
		3088	loop, if multiple loops are supported ("ev loop default").
		3089
		3090	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3091
		3092	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3093	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3094	is undefined when the default loop has not been initialised by a previous
		3095	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3096
		3097	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3098	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3099
		3100	=back
		3101
		3102	Example: Declare and initialise a check watcher, utilising the above
		3103	macros so it will work regardless of whether multiple loops are supported
		3104	or not.
		3105
		3106	static void
		3107	check_cb (EV_P_ ev_timer *w, int revents)
		3108	{
		3109	ev_check_stop (EV_A_ w);
		3110	}
		3111
		3112	ev_check check;
		3113	ev_check_init (&check, check_cb);
		3114	ev_check_start (EV_DEFAULT_ &check);
		3115	ev_loop (EV_DEFAULT_ 0);
		3116
		3117	=head1 EMBEDDING
		3118
		3119	Libev can (and often is) directly embedded into host
		3120	applications. Examples of applications that embed it include the Deliantra
		3121	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3122	and rxvt-unicode.
		3123
		3124	The goal is to enable you to just copy the necessary files into your
		3125	source directory without having to change even a single line in them, so
		3126	you can easily upgrade by simply copying (or having a checked-out copy of
		3127	libev somewhere in your source tree).
		3128
		3129	=head2 FILESETS
		3130
		3131	Depending on what features you need you need to include one or more sets of files
		3132	in your application.
		3133
		3134	=head3 CORE EVENT LOOP
		3135
		3136	To include only the libev core (all the C<ev_*> functions), with manual
		3137	configuration (no autoconf):
		3138
		3139	#define EV_STANDALONE 1
		3140	#include "ev.c"
		3141
		3142	This will automatically include F<ev.h>, too, and should be done in a
		3143	single C source file only to provide the function implementations. To use
		3144	it, do the same for F<ev.h> in all files wishing to use this API (best
		3145	done by writing a wrapper around F<ev.h> that you can include instead and
		3146	where you can put other configuration options):
		3147
		3148	#define EV_STANDALONE 1
		3149	#include "ev.h"
		3150
		3151	Both header files and implementation files can be compiled with a C++
		3152	compiler (at least, that's a stated goal, and breakage will be treated
		3153	as a bug).
		3154
		3155	You need the following files in your source tree, or in a directory
		3156	in your include path (e.g. in libev/ when using -Ilibev):
		3157
		3158	ev.h
		3159	ev.c
		3160	ev_vars.h
		3161	ev_wrap.h
		3162
		3163	ev_win32.c required on win32 platforms only
		3164
		3165	ev_select.c only when select backend is enabled (which is enabled by default)
		3166	ev_poll.c only when poll backend is enabled (disabled by default)
		3167	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3168	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3169	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3170
		3171	F<ev.c> includes the backend files directly when enabled, so you only need
		3172	to compile this single file.
		3173
		3174	=head3 LIBEVENT COMPATIBILITY API
		3175
		3176	To include the libevent compatibility API, also include:
		3177
		3178	#include "event.c"
		3179
		3180	in the file including F<ev.c>, and:
		3181
		3182	#include "event.h"
		3183
		3184	in the files that want to use the libevent API. This also includes F<ev.h>.
		3185
		3186	You need the following additional files for this:
		3187
		3188	event.h
		3189	event.c
		3190
		3191	=head3 AUTOCONF SUPPORT
		3192
		3193	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3194	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3195	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3196	include F<config.h> and configure itself accordingly.
		3197
		3198	For this of course you need the m4 file:
		3199
		3200	libev.m4
		3201
		3202	=head2 PREPROCESSOR SYMBOLS/MACROS
		3203
		3204	Libev can be configured via a variety of preprocessor symbols you have to
		3205	define before including any of its files. The default in the absence of
		3206	autoconf is documented for every option.
		3207
		3208	=over 4
		3209
		3210	=item EV_STANDALONE
		3211
		3212	Must always be C<1> if you do not use autoconf configuration, which
		3213	keeps libev from including F<config.h>, and it also defines dummy
		3214	implementations for some libevent functions (such as logging, which is not
		3215	supported). It will also not define any of the structs usually found in
		3216	F<event.h> that are not directly supported by the libev core alone.
		3217
		3218	In stanbdalone mode, libev will still try to automatically deduce the
		3219	configuration, but has to be more conservative.
		3220
		3221	=item EV_USE_MONOTONIC
		3222
		3223	If defined to be C<1>, libev will try to detect the availability of the
		3224	monotonic clock option at both compile time and runtime. Otherwise no
		3225	use of the monotonic clock option will be attempted. If you enable this,
		3226	you usually have to link against librt or something similar. Enabling it
		3227	when the functionality isn't available is safe, though, although you have
		3228	to make sure you link against any libraries where the C<clock_gettime>
		3229	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3230
		3231	=item EV_USE_REALTIME
		3232
		3233	If defined to be C<1>, libev will try to detect the availability of the
		3234	real-time clock option at compile time (and assume its availability
		3235	at runtime if successful). Otherwise no use of the real-time clock
		3236	option will be attempted. This effectively replaces C<gettimeofday>
		3237	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		3238	correctness. See the note about libraries in the description of
		3239	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3240	C<EV_USE_CLOCK_SYSCALL>.
		3241
		3242	=item EV_USE_CLOCK_SYSCALL
		3243
		3244	If defined to be C<1>, libev will try to use a direct syscall instead
		3245	of calling the system-provided C<clock_gettime> function. This option
		3246	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3247	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3248	programs needlessly. Using a direct syscall is slightly slower (in
		3249	theory), because no optimised vdso implementation can be used, but avoids
		3250	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3251	higher, as it simplifies linking (no need for C<-lrt>).
		3252
		3253	=item EV_USE_NANOSLEEP
		3254
		3255	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3256	and will use it for delays. Otherwise it will use C<select ()>.
		3257
		3258	=item EV_USE_EVENTFD
		3259
		3260	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3261	available and will probe for kernel support at runtime. This will improve
		3262	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3263	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3264	2.7 or newer, otherwise disabled.
		3265
		3266	=item EV_USE_SELECT
		3267
		3268	If undefined or defined to be C<1>, libev will compile in support for the
		3269	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3270	other method takes over, select will be it. Otherwise the select backend
		3271	will not be compiled in.
		3272
		3273	=item EV_SELECT_USE_FD_SET
		3274
		3275	If defined to C<1>, then the select backend will use the system C<fd_set>
		3276	structure. This is useful if libev doesn't compile due to a missing
		3277	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		3278	on exotic systems. This usually limits the range of file descriptors to
		3279	some low limit such as 1024 or might have other limitations (winsocket
		3280	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		3281	configures the maximum size of the C<fd_set>.
		3282
		3283	=item EV_SELECT_IS_WINSOCKET
		3284
		3285	When defined to C<1>, the select backend will assume that
		3286	select/socket/connect etc. don't understand file descriptors but
		3287	wants osf handles on win32 (this is the case when the select to
		3288	be used is the winsock select). This means that it will call
		3289	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3290	it is assumed that all these functions actually work on fds, even
		3291	on win32. Should not be defined on non-win32 platforms.
		3292
		3293	=item EV_FD_TO_WIN32_HANDLE
		3294
		3295	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3296	file descriptors to socket handles. When not defining this symbol (the
		3297	default), then libev will call C<_get_osfhandle>, which is usually
		3298	correct. In some cases, programs use their own file descriptor management,
		3299	in which case they can provide this function to map fds to socket handles.
		3300
		3301	=item EV_USE_POLL
		3302
		3303	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3304	backend. Otherwise it will be enabled on non-win32 platforms. It
		3305	takes precedence over select.
		3306
		3307	=item EV_USE_EPOLL
		3308
		3309	If defined to be C<1>, libev will compile in support for the Linux
		3310	C<epoll>(7) backend. Its availability will be detected at runtime,
		3311	otherwise another method will be used as fallback. This is the preferred
		3312	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3313	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3314
		3315	=item EV_USE_KQUEUE
		3316
		3317	If defined to be C<1>, libev will compile in support for the BSD style
		3318	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3319	otherwise another method will be used as fallback. This is the preferred
		3320	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3321	supports some types of fds correctly (the only platform we found that
		3322	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3323	not be used unless explicitly requested. The best way to use it is to find
		3324	out whether kqueue supports your type of fd properly and use an embedded
		3325	kqueue loop.
		3326
		3327	=item EV_USE_PORT
		3328
		3329	If defined to be C<1>, libev will compile in support for the Solaris
		3330	10 port style backend. Its availability will be detected at runtime,
		3331	otherwise another method will be used as fallback. This is the preferred
		3332	backend for Solaris 10 systems.
		3333
		3334	=item EV_USE_DEVPOLL
		3335
		3336	Reserved for future expansion, works like the USE symbols above.
		3337
		3338	=item EV_USE_INOTIFY
		3339
		3340	If defined to be C<1>, libev will compile in support for the Linux inotify
		3341	interface to speed up C<ev_stat> watchers. Its actual availability will
		3342	be detected at runtime. If undefined, it will be enabled if the headers
		3343	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3344
		3345	=item EV_ATOMIC_T
		3346
		3347	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3348	access is atomic with respect to other threads or signal contexts. No such
		3349	type is easily found in the C language, so you can provide your own type
		3350	that you know is safe for your purposes. It is used both for signal handler "locking"
		3351	as well as for signal and thread safety in C<ev_async> watchers.
		3352
		3353	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3354	(from F<signal.h>), which is usually good enough on most platforms.
		3355
		3356	=item EV_H
		3357
		3358	The name of the F<ev.h> header file used to include it. The default if
		3359	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3360	used to virtually rename the F<ev.h> header file in case of conflicts.
		3361
		3362	=item EV_CONFIG_H
		3363
		3364	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3365	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3366	C<EV_H>, above.
		3367
		3368	=item EV_EVENT_H
		3369
		3370	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3371	of how the F<event.h> header can be found, the default is C<"event.h">.
		3372
		3373	=item EV_PROTOTYPES
		3374
		3375	If defined to be C<0>, then F<ev.h> will not define any function
		3376	prototypes, but still define all the structs and other symbols. This is
		3377	occasionally useful if you want to provide your own wrapper functions
		3378	around libev functions.
		3379
		3380	=item EV_MULTIPLICITY
		3381
		3382	If undefined or defined to C<1>, then all event-loop-specific functions
		3383	will have the C<struct ev_loop *> as first argument, and you can create
		3384	additional independent event loops. Otherwise there will be no support
		3385	for multiple event loops and there is no first event loop pointer
		3386	argument. Instead, all functions act on the single default loop.
		3387
		3388	=item EV_MINPRI
		3389
		3390	=item EV_MAXPRI
		3391
		3392	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3393	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3394	provide for more priorities by overriding those symbols (usually defined
		3395	to be C<-2> and C<2>, respectively).
		3396
		3397	When doing priority-based operations, libev usually has to linearly search
		3398	all the priorities, so having many of them (hundreds) uses a lot of space
		3399	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3400	fine.
		3401
		3402	If your embedding application does not need any priorities, defining these
		3403	both to C<0> will save some memory and CPU.
		3404
		3405	=item EV_PERIODIC_ENABLE
		3406
		3407	If undefined or defined to be C<1>, then periodic timers are supported. If
		3408	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3409	code.
		3410
		3411	=item EV_IDLE_ENABLE
		3412
		3413	If undefined or defined to be C<1>, then idle watchers are supported. If
		3414	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3415	code.
		3416
		3417	=item EV_EMBED_ENABLE
		3418
		3419	If undefined or defined to be C<1>, then embed watchers are supported. If
		3420	defined to be C<0>, then they are not. Embed watchers rely on most other
		3421	watcher types, which therefore must not be disabled.
		3422
		3423	=item EV_STAT_ENABLE
		3424
		3425	If undefined or defined to be C<1>, then stat watchers are supported. If
		3426	defined to be C<0>, then they are not.
		3427
		3428	=item EV_FORK_ENABLE
		3429
		3430	If undefined or defined to be C<1>, then fork watchers are supported. If
		3431	defined to be C<0>, then they are not.
		3432
		3433	=item EV_ASYNC_ENABLE
		3434
		3435	If undefined or defined to be C<1>, then async watchers are supported. If
		3436	defined to be C<0>, then they are not.
		3437
		3438	=item EV_MINIMAL
		3439
		3440	If you need to shave off some kilobytes of code at the expense of some
		3441	speed, define this symbol to C<1>. Currently this is used to override some
		3442	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3443	much smaller 2-heap for timer management over the default 4-heap.
		3444
		3445	=item EV_PID_HASHSIZE
		3446
		3447	C<ev_child> watchers use a small hash table to distribute workload by
		3448	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3449	than enough. If you need to manage thousands of children you might want to
		3450	increase this value (I<must> be a power of two).
		3451
		3452	=item EV_INOTIFY_HASHSIZE
		3453
		3454	C<ev_stat> watchers use a small hash table to distribute workload by
		3455	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3456	usually more than enough. If you need to manage thousands of C<ev_stat>
		3457	watchers you might want to increase this value (I<must> be a power of
		3458	two).
		3459
		3460	=item EV_USE_4HEAP
		3461
		3462	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3463	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3464	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3465	faster performance with many (thousands) of watchers.
		3466
		3467	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3468	(disabled).
		3469
		3470	=item EV_HEAP_CACHE_AT
		3471
		3472	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3473	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3474	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3475	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3476	but avoids random read accesses on heap changes. This improves performance
		3477	noticeably with many (hundreds) of watchers.
		3478
		3479	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3480	(disabled).
		3481
		3482	=item EV_VERIFY
		3483
		3484	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3485	be done: If set to C<0>, no internal verification code will be compiled
		3486	in. If set to C<1>, then verification code will be compiled in, but not
		3487	called. If set to C<2>, then the internal verification code will be
		3488	called once per loop, which can slow down libev. If set to C<3>, then the
		3489	verification code will be called very frequently, which will slow down
		3490	libev considerably.
		3491
		3492	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3493	C<0>.
		3494
		3495	=item EV_COMMON
		3496
		3497	By default, all watchers have a C<void *data> member. By redefining
		3498	this macro to a something else you can include more and other types of
		3499	members. You have to define it each time you include one of the files,
		3500	though, and it must be identical each time.
		3501
		3502	For example, the perl EV module uses something like this:
		3503
		3504	#define EV_COMMON \
		3505	SV *self; /* contains this struct */ \
		3506	SV *cb_sv, *fh /* note no trailing ";" */
		3507
		3508	=item EV_CB_DECLARE (type)
		3509
		3510	=item EV_CB_INVOKE (watcher, revents)
		3511
		3512	=item ev_set_cb (ev, cb)
		3513
		3514	Can be used to change the callback member declaration in each watcher,
		3515	and the way callbacks are invoked and set. Must expand to a struct member
		3516	definition and a statement, respectively. See the F<ev.h> header file for
		3517	their default definitions. One possible use for overriding these is to
		3518	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3519	method calls instead of plain function calls in C++.
		3520
		3521	=back
		3522
		3523	=head2 EXPORTED API SYMBOLS
		3524
		3525	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3526	exported symbols, you can use the provided F<Symbol.*> files which list
		3527	all public symbols, one per line:
		3528
		3529	Symbols.ev for libev proper
		3530	Symbols.event for the libevent emulation
		3531
		3532	This can also be used to rename all public symbols to avoid clashes with
		3533	multiple versions of libev linked together (which is obviously bad in
		3534	itself, but sometimes it is inconvenient to avoid this).
		3535
		3536	A sed command like this will create wrapper C<#define>'s that you need to
		3537	include before including F<ev.h>:
		3538
		3539	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3540
		3541	This would create a file F<wrap.h> which essentially looks like this:
		3542
		3543	#define ev_backend myprefix_ev_backend
		3544	#define ev_check_start myprefix_ev_check_start
		3545	#define ev_check_stop myprefix_ev_check_stop
		3546	...
		3547
		3548	=head2 EXAMPLES
		3549
		3550	For a real-world example of a program the includes libev
		3551	verbatim, you can have a look at the EV perl module
		3552	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3553	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3554	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3555	will be compiled. It is pretty complex because it provides its own header
		3556	file.
		3557
		3558	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3559	that everybody includes and which overrides some configure choices:
		3560
		3561	#define EV_MINIMAL 1
		3562	#define EV_USE_POLL 0
		3563	#define EV_MULTIPLICITY 0
		3564	#define EV_PERIODIC_ENABLE 0
		3565	#define EV_STAT_ENABLE 0
		3566	#define EV_FORK_ENABLE 0
		3567	#define EV_CONFIG_H <config.h>
		3568	#define EV_MINPRI 0
		3569	#define EV_MAXPRI 0
		3570
		3571	#include "ev++.h"
		3572
		3573	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3574
		3575	#include "ev_cpp.h"
		3576	#include "ev.c"
		3577
		3578	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3579
		3580	=head2 THREADS AND COROUTINES
		3581
		3582	=head3 THREADS
		3583
		3584	All libev functions are reentrant and thread-safe unless explicitly
		3585	documented otherwise, but libev implements no locking itself. This means
		3586	that you can use as many loops as you want in parallel, as long as there
		3587	are no concurrent calls into any libev function with the same loop
		3588	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3589	of course): libev guarantees that different event loops share no data
		3590	structures that need any locking.
		3591
		3592	Or to put it differently: calls with different loop parameters can be done
		3593	concurrently from multiple threads, calls with the same loop parameter
		3594	must be done serially (but can be done from different threads, as long as
		3595	only one thread ever is inside a call at any point in time, e.g. by using
		3596	a mutex per loop).
		3597
		3598	Specifically to support threads (and signal handlers), libev implements
		3599	so-called C<ev_async> watchers, which allow some limited form of
		3600	concurrency on the same event loop, namely waking it up "from the
		3601	outside".
		3602
		3603	If you want to know which design (one loop, locking, or multiple loops
		3604	without or something else still) is best for your problem, then I cannot
		3605	help you, but here is some generic advice:
		3606
		3607	=over 4
		3608
		3609	=item * most applications have a main thread: use the default libev loop
		3610	in that thread, or create a separate thread running only the default loop.
		3611
		3612	This helps integrating other libraries or software modules that use libev
		3613	themselves and don't care/know about threading.
		3614
		3615	=item * one loop per thread is usually a good model.
		3616
		3617	Doing this is almost never wrong, sometimes a better-performance model
		3618	exists, but it is always a good start.
		3619
		3620	=item * other models exist, such as the leader/follower pattern, where one
		3621	loop is handed through multiple threads in a kind of round-robin fashion.
		3622
		3623	Choosing a model is hard - look around, learn, know that usually you can do
		3624	better than you currently do :-)
		3625
		3626	=item * often you need to talk to some other thread which blocks in the
		3627	event loop.
		3628
		3629	C<ev_async> watchers can be used to wake them up from other threads safely
		3630	(or from signal contexts...).
		3631
		3632	An example use would be to communicate signals or other events that only
		3633	work in the default loop by registering the signal watcher with the
		3634	default loop and triggering an C<ev_async> watcher from the default loop
		3635	watcher callback into the event loop interested in the signal.
		3636
		3637	=back
		3638
		3639	=head3 COROUTINES
		3640
		3641	Libev is very accommodating to coroutines ("cooperative threads"):
		3642	libev fully supports nesting calls to its functions from different
		3643	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3644	different coroutines, and switch freely between both coroutines running the
		3645	loop, as long as you don't confuse yourself). The only exception is that
		3646	you must not do this from C<ev_periodic> reschedule callbacks.
		3647
		3648	Care has been taken to ensure that libev does not keep local state inside
		3649	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3650	they do not call any callbacks.
		3651
		3652	=head2 COMPILER WARNINGS
		3653
		3654	Depending on your compiler and compiler settings, you might get no or a
		3655	lot of warnings when compiling libev code. Some people are apparently
		3656	scared by this.
		3657
		3658	However, these are unavoidable for many reasons. For one, each compiler
		3659	has different warnings, and each user has different tastes regarding
		3660	warning options. "Warn-free" code therefore cannot be a goal except when
		3661	targeting a specific compiler and compiler-version.
		3662
		3663	Another reason is that some compiler warnings require elaborate
		3664	workarounds, or other changes to the code that make it less clear and less
		3665	maintainable.
		3666
		3667	And of course, some compiler warnings are just plain stupid, or simply
		3668	wrong (because they don't actually warn about the condition their message
		3669	seems to warn about). For example, certain older gcc versions had some
		3670	warnings that resulted an extreme number of false positives. These have
		3671	been fixed, but some people still insist on making code warn-free with
		3672	such buggy versions.
		3673
		3674	While libev is written to generate as few warnings as possible,
		3675	"warn-free" code is not a goal, and it is recommended not to build libev
		3676	with any compiler warnings enabled unless you are prepared to cope with
		3677	them (e.g. by ignoring them). Remember that warnings are just that:
		3678	warnings, not errors, or proof of bugs.
		3679
		3680
		3681	=head2 VALGRIND
		3682
		3683	Valgrind has a special section here because it is a popular tool that is
		3684	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3685
		3686	If you think you found a bug (memory leak, uninitialised data access etc.)
		3687	in libev, then check twice: If valgrind reports something like:
		3688
		3689	==2274== definitely lost: 0 bytes in 0 blocks.
		3690	==2274== possibly lost: 0 bytes in 0 blocks.
		3691	==2274== still reachable: 256 bytes in 1 blocks.
		3692
		3693	Then there is no memory leak, just as memory accounted to global variables
		3694	is not a memleak - the memory is still being referenced, and didn't leak.
		3695
		3696	Similarly, under some circumstances, valgrind might report kernel bugs
		3697	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3698	although an acceptable workaround has been found here), or it might be
		3699	confused.
		3700
		3701	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3702	make it into some kind of religion.
		3703
		3704	If you are unsure about something, feel free to contact the mailing list
		3705	with the full valgrind report and an explanation on why you think this
		3706	is a bug in libev (best check the archives, too :). However, don't be
		3707	annoyed when you get a brisk "this is no bug" answer and take the chance
		3708	of learning how to interpret valgrind properly.
		3709
		3710	If you need, for some reason, empty reports from valgrind for your project
		3711	I suggest using suppression lists.
		3712
		3713
		3714	=head1 PORTABILITY NOTES
		3715
		3716	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3717
		3718	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3719	requires, and its I/O model is fundamentally incompatible with the POSIX
		3720	model. Libev still offers limited functionality on this platform in
		3721	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3722	descriptors. This only applies when using Win32 natively, not when using
		3723	e.g. cygwin.
		3724
		3725	Lifting these limitations would basically require the full
		3726	re-implementation of the I/O system. If you are into these kinds of
		3727	things, then note that glib does exactly that for you in a very portable
		3728	way (note also that glib is the slowest event library known to man).
		3729
		3730	There is no supported compilation method available on windows except
		3731	embedding it into other applications.
		3732
		3733	Not a libev limitation but worth mentioning: windows apparently doesn't
		3734	accept large writes: instead of resulting in a partial write, windows will
		3735	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3736	so make sure you only write small amounts into your sockets (less than a
		3737	megabyte seems safe, but this apparently depends on the amount of memory
		3738	available).
		3739
		3740	Due to the many, low, and arbitrary limits on the win32 platform and
		3741	the abysmal performance of winsockets, using a large number of sockets
		3742	is not recommended (and not reasonable). If your program needs to use
		3743	more than a hundred or so sockets, then likely it needs to use a totally
		3744	different implementation for windows, as libev offers the POSIX readiness
		3745	notification model, which cannot be implemented efficiently on windows
		3746	(Microsoft monopoly games).
		3747
		3748	A typical way to use libev under windows is to embed it (see the embedding
		3749	section for details) and use the following F<evwrap.h> header file instead
		3750	of F<ev.h>:
		3751
		3752	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3753	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3754
		3755	#include "ev.h"
		3756
		3757	And compile the following F<evwrap.c> file into your project (make sure
		3758	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3759
		3760	#include "evwrap.h"
		3761	#include "ev.c"
		3762
		3763	=over 4
		3764
		3765	=item The winsocket select function
		3766
		3767	The winsocket C<select> function doesn't follow POSIX in that it
		3768	requires socket I<handles> and not socket I<file descriptors> (it is
		3769	also extremely buggy). This makes select very inefficient, and also
		3770	requires a mapping from file descriptors to socket handles (the Microsoft
		3771	C runtime provides the function C<_open_osfhandle> for this). See the
		3772	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3773	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3774
		3775	The configuration for a "naked" win32 using the Microsoft runtime
		3776	libraries and raw winsocket select is:
		3777
		3778	#define EV_USE_SELECT 1
		3779	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3780
		3781	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3782	complexity in the O(n²) range when using win32.
		3783
		3784	=item Limited number of file descriptors
		3785
		3786	Windows has numerous arbitrary (and low) limits on things.
		3787
		3788	Early versions of winsocket's select only supported waiting for a maximum
		3789	of C<64> handles (probably owning to the fact that all windows kernels
		3790	can only wait for C<64> things at the same time internally; Microsoft
		3791	recommends spawning a chain of threads and wait for 63 handles and the
		3792	previous thread in each. Great).
		3793
		3794	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3795	to some high number (e.g. C<2048>) before compiling the winsocket select
		3796	call (which might be in libev or elsewhere, for example, perl does its own
		3797	select emulation on windows).
		3798
		3799	Another limit is the number of file descriptors in the Microsoft runtime
		3800	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3801	or something like this inside Microsoft). You can increase this by calling
		3802	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3803	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3804	libraries.
		3805
		3806	This might get you to about C<512> or C<2048> sockets (depending on
		3807	windows version and/or the phase of the moon). To get more, you need to
		3808	wrap all I/O functions and provide your own fd management, but the cost of
		3809	calling select (O(n²)) will likely make this unworkable.
		3810
		3811	=back
		3812
		3813	=head2 PORTABILITY REQUIREMENTS
		3814
		3815	In addition to a working ISO-C implementation and of course the
		3816	backend-specific APIs, libev relies on a few additional extensions:
		3817
		3818	=over 4
		3819
		3820	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3821	calling conventions regardless of C<ev_watcher_type *>.
		3822
		3823	Libev assumes not only that all watcher pointers have the same internal
		3824	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3825	assumes that the same (machine) code can be used to call any watcher
		3826	callback: The watcher callbacks have different type signatures, but libev
		3827	calls them using an C<ev_watcher *> internally.
		3828
		3829	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3830
		3831	The type C<sig_atomic_t volatile> (or whatever is defined as
		3832	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3833	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3834	believed to be sufficiently portable.
		3835
		3836	=item C<sigprocmask> must work in a threaded environment
		3837
		3838	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3839	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3840	pthread implementations will either allow C<sigprocmask> in the "main
		3841	thread" or will block signals process-wide, both behaviours would
		3842	be compatible with libev. Interaction between C<sigprocmask> and
		3843	C<pthread_sigmask> could complicate things, however.
		3844
		3845	The most portable way to handle signals is to block signals in all threads
		3846	except the initial one, and run the default loop in the initial thread as
		3847	well.
		3848
		3849	=item C<long> must be large enough for common memory allocation sizes
		3850
		3851	To improve portability and simplify its API, libev uses C<long> internally
		3852	instead of C<size_t> when allocating its data structures. On non-POSIX
		3853	systems (Microsoft...) this might be unexpectedly low, but is still at
		3854	least 31 bits everywhere, which is enough for hundreds of millions of
		3855	watchers.
		3856
		3857	=item C<double> must hold a time value in seconds with enough accuracy
		3858
		3859	The type C<double> is used to represent timestamps. It is required to
		3860	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3861	enough for at least into the year 4000. This requirement is fulfilled by
		3862	implementations implementing IEEE 754 (basically all existing ones).
		3863
		3864	=back
		3865
		3866	If you know of other additional requirements drop me a note.
		3867
		3868
		3869	=head1 ALGORITHMIC COMPLEXITIES
		3870
		3871	In this section the complexities of (many of) the algorithms used inside
		3872	libev will be documented. For complexity discussions about backends see
		3873	the documentation for C<ev_default_init>.
		3874
		3875	All of the following are about amortised time: If an array needs to be
		3876	extended, libev needs to realloc and move the whole array, but this
		3877	happens asymptotically rarer with higher number of elements, so O(1) might
		3878	mean that libev does a lengthy realloc operation in rare cases, but on
		3879	average it is much faster and asymptotically approaches constant time.
		3880
		3881	=over 4
		3882
		3883	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3884
		3885	This means that, when you have a watcher that triggers in one hour and
		3886	there are 100 watchers that would trigger before that, then inserting will
		3887	have to skip roughly seven (C<ld 100>) of these watchers.
		3888
		3889	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3890
		3891	That means that changing a timer costs less than removing/adding them,
		3892	as only the relative motion in the event queue has to be paid for.
		3893
		3894	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3895
		3896	These just add the watcher into an array or at the head of a list.
		3897
		3898	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3899
		3900	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3901
		3902	These watchers are stored in lists, so they need to be walked to find the
		3903	correct watcher to remove. The lists are usually short (you don't usually
		3904	have many watchers waiting for the same fd or signal: one is typical, two
		3905	is rare).
		3906
		3907	=item Finding the next timer in each loop iteration: O(1)
		3908
		3909	By virtue of using a binary or 4-heap, the next timer is always found at a
		3910	fixed position in the storage array.
		3911
		3912	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3913
		3914	A change means an I/O watcher gets started or stopped, which requires
		3915	libev to recalculate its status (and possibly tell the kernel, depending
		3916	on backend and whether C<ev_io_set> was used).
		3917
		3918	=item Activating one watcher (putting it into the pending state): O(1)
		3919
		3920	=item Priority handling: O(number_of_priorities)
		3921
		3922	Priorities are implemented by allocating some space for each
		3923	priority. When doing priority-based operations, libev usually has to
		3924	linearly search all the priorities, but starting/stopping and activating
		3925	watchers becomes O(1) with respect to priority handling.
		3926
		3927	=item Sending an ev_async: O(1)
		3928
		3929	=item Processing ev_async_send: O(number_of_async_watchers)
		3930
		3931	=item Processing signals: O(max_signal_number)
		3932
		3933	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3934	calls in the current loop iteration. Checking for async and signal events
		3935	involves iterating over all running async watchers or all signal numbers.
		3936
		3937	=back
		3938
		3939
755	=head1 AUTHOR	3940	=head1 AUTHOR
756		3941
757	Marc Lehmann <libev@schmorp.de>.	3942	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
758		3943

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