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Revision 1.27 by root, Wed Nov 14 05:02:07 2007 UTC vs.
Revision 1.212 by root, Mon Nov 3 15:13:53 2008 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_TYPE
		16	ev_io stdin_watcher;
		17	ev_timer timeout_watcher;
		18
		19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
		21	static void
		22	stdin_cb (EV_P_ ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
8		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	108	name C<loop> (which is always of type C<ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	117	to the C<double> type in C, and when you need to do any calculations on
		118	it, you should treat it as some floating point value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 ERROR HANDLING
		123
		124	Libev knows three classes of errors: operating system errors, usage errors
		125	and internal errors (bugs).
		126
		127	When libev catches an operating system error it cannot handle (for example
		128	a system call indicating a condition libev cannot fix), it calls the callback
		129	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		130	abort. The default is to print a diagnostic message and to call C<abort
		131	()>.
		132
		133	When libev detects a usage error such as a negative timer interval, then
		134	it will print a diagnostic message and abort (via the C<assert> mechanism,
		135	so C<NDEBUG> will disable this checking): these are programming errors in
		136	the libev caller and need to be fixed there.
		137
		138	Libev also has a few internal error-checking C<assert>ions, and also has
		139	extensive consistency checking code. These do not trigger under normal
		140	circumstances, as they indicate either a bug in libev or worse.
		141
51		142
52	=head1 GLOBAL FUNCTIONS	143	=head1 GLOBAL FUNCTIONS
53		144
54	These functions can be called anytime, even before initialising the	145	These functions can be called anytime, even before initialising the
55	library in any way.	146	library in any way.
…		…
60		151
61	Returns the current time as libev would use it. Please note that the	152	Returns the current time as libev would use it. Please note that the
62	C<ev_now> function is usually faster and also often returns the timestamp	153	C<ev_now> function is usually faster and also often returns the timestamp
63	you actually want to know.	154	you actually want to know.
64		155
		156	=item ev_sleep (ev_tstamp interval)
		157
		158	Sleep for the given interval: The current thread will be blocked until
		159	either it is interrupted or the given time interval has passed. Basically
		160	this is a sub-second-resolution C<sleep ()>.
		161
65	=item int ev_version_major ()	162	=item int ev_version_major ()
66		163
67	=item int ev_version_minor ()	164	=item int ev_version_minor ()
68		165
69	You can find out the major and minor version numbers of the library	166	You can find out the major and minor ABI version numbers of the library
70	you linked against by calling the functions C<ev_version_major> and	167	you linked against by calling the functions C<ev_version_major> and
71	C<ev_version_minor>. If you want, you can compare against the global	168	C<ev_version_minor>. If you want, you can compare against the global
72	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	169	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
73	version of the library your program was compiled against.	170	version of the library your program was compiled against.
74		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
75	Usually, it's a good idea to terminate if the major versions mismatch,	175	Usually, it's a good idea to terminate if the major versions mismatch,
76	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
77	compatible to older versions, so a larger minor version alone is usually	177	compatible to older versions, so a larger minor version alone is usually
78	not a problem.	178	not a problem.
79		179
		180	Example: Make sure we haven't accidentally been linked against the wrong
		181	version.
		182
		183	assert (("libev version mismatch",
		184	ev_version_major () == EV_VERSION_MAJOR
		185	&& ev_version_minor () >= EV_VERSION_MINOR));
		186
		187	=item unsigned int ev_supported_backends ()
		188
		189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		190	value) compiled into this binary of libev (independent of their
		191	availability on the system you are running on). See C<ev_default_loop> for
		192	a description of the set values.
		193
		194	Example: make sure we have the epoll method, because yeah this is cool and
		195	a must have and can we have a torrent of it please!!!11
		196
		197	assert (("sorry, no epoll, no sex",
		198	ev_supported_backends () & EVBACKEND_EPOLL));
		199
		200	=item unsigned int ev_recommended_backends ()
		201
		202	Return the set of all backends compiled into this binary of libev and also
		203	recommended for this platform. This set is often smaller than the one
		204	returned by C<ev_supported_backends>, as for example kqueue is broken on
		205	most BSDs and will not be auto-detected unless you explicitly request it
		206	(assuming you know what you are doing). This is the set of backends that
		207	libev will probe for if you specify no backends explicitly.
		208
		209	=item unsigned int ev_embeddable_backends ()
		210
		211	Returns the set of backends that are embeddable in other event loops. This
		212	is the theoretical, all-platform, value. To find which backends
		213	might be supported on the current system, you would need to look at
		214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		215	recommended ones.
		216
		217	See the description of C<ev_embed> watchers for more info.
		218
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
81		220
82	Sets the allocation function to use (the prototype is similar to the	221	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
84	and free memory (no surprises here). If it returns zero when memory	223	used to allocate and free memory (no surprises here). If it returns zero
85	needs to be allocated, the library might abort or take some potentially	224	when memory needs to be allocated (C<size != 0>), the library might abort
86	destructive action. The default is your system realloc function.	225	or take some potentially destructive action.
		226
		227	Since some systems (at least OpenBSD and Darwin) fail to implement
		228	correct C<realloc> semantics, libev will use a wrapper around the system
		229	C<realloc> and C<free> functions by default.
87		230
88	You could override this function in high-availability programs to, say,	231	You could override this function in high-availability programs to, say,
89	free some memory if it cannot allocate memory, to use a special allocator,	232	free some memory if it cannot allocate memory, to use a special allocator,
90	or even to sleep a while and retry until some memory is available.	233	or even to sleep a while and retry until some memory is available.
91		234
		235	Example: Replace the libev allocator with one that waits a bit and then
		236	retries (example requires a standards-compliant C<realloc>).
		237
		238	static void *
		239	persistent_realloc (void *ptr, size_t size)
		240	{
		241	for (;;)
		242	{
		243	void *newptr = realloc (ptr, size);
		244
		245	if (newptr)
		246	return newptr;
		247
		248	sleep (60);
		249	}
		250	}
		251
		252	...
		253	ev_set_allocator (persistent_realloc);
		254
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
93		256
94	Set the callback function to call on a retryable syscall error (such	257	Set the callback function to call on a retryable system call error (such
95	as failed select, poll, epoll_wait). The message is a printable string	258	as failed select, poll, epoll_wait). The message is a printable string
96	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
97	callback is set, then libev will expect it to remedy the sitution, no	260	callback is set, then libev will expect it to remedy the situation, no
98	matter what, when it returns. That is, libev will generally retry the	261	matter what, when it returns. That is, libev will generally retry the
99	requested operation, or, if the condition doesn't go away, do bad stuff	262	requested operation, or, if the condition doesn't go away, do bad stuff
100	(such as abort).	263	(such as abort).
101		264
		265	Example: This is basically the same thing that libev does internally, too.
		266
		267	static void
		268	fatal_error (const char *msg)
		269	{
		270	perror (msg);
		271	abort ();
		272	}
		273
		274	...
		275	ev_set_syserr_cb (fatal_error);
		276
102	=back	277	=back
103		278
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		280
106	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<struct ev_loop *> (the C<struct>
107	types of such loops, the I<default> loop, which supports signals and child	282	is I<not> optional in this case, as there is also an C<ev_loop>
108	events, and dynamically created loops which do not.	283	I<function>).
109		284
110	If you use threads, a common model is to run the default event loop	285	The library knows two types of such loops, the I<default> loop, which
111	in your main thread (or in a separate thread) and for each thread you	286	supports signals and child events, and dynamically created loops which do
112	create, you also create another event loop. Libev itself does no locking	287	not.
113	whatsoever, so if you mix calls to the same event loop in different
114	threads, make sure you lock (this is usually a bad idea, though, even if
115	done correctly, because it's hideous and inefficient).
116		288
117	=over 4	289	=over 4
118		290
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	291	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		292
121	This will initialise the default event loop if it hasn't been initialised	293	This will initialise the default event loop if it hasn't been initialised
122	yet and return it. If the default loop could not be initialised, returns	294	yet and return it. If the default loop could not be initialised, returns
123	false. If it already was initialised it simply returns it (and ignores the	295	false. If it already was initialised it simply returns it (and ignores the
124	flags).	296	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		297
126	If you don't know what event loop to use, use the one returned from this	298	If you don't know what event loop to use, use the one returned from this
127	function.	299	function.
128		300
		301	Note that this function is I<not> thread-safe, so if you want to use it
		302	from multiple threads, you have to lock (note also that this is unlikely,
		303	as loops cannot be shared easily between threads anyway).
		304
		305	The default loop is the only loop that can handle C<ev_signal> and
		306	C<ev_child> watchers, and to do this, it always registers a handler
		307	for C<SIGCHLD>. If this is a problem for your application you can either
		308	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		309	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		310	C<ev_default_init>.
		311
129	The flags argument can be used to specify special behaviour or specific	312	The flags argument can be used to specify special behaviour or specific
130	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	313	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		314
132	It supports the following flags:	315	The following flags are supported:
133		316
134	=over 4	317	=over 4
135		318
136	=item C<EVFLAG_AUTO>	319	=item C<EVFLAG_AUTO>
137		320
138	The default flags value. Use this if you have no clue (it's the right	321	The default flags value. Use this if you have no clue (it's the right
139	thing, believe me).	322	thing, believe me).
140		323
141	=item C<EVFLAG_NOENV>	324	=item C<EVFLAG_NOENV>
142		325
143	If this flag bit is ored into the flag value (or the program runs setuid	326	If this flag bit is or'ed into the flag value (or the program runs setuid
144	or setgid) then libev will I<not> look at the environment variable	327	or setgid) then libev will I<not> look at the environment variable
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	328	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	329	override the flags completely if it is found in the environment. This is
147	useful to try out specific backends to test their performance, or to work	330	useful to try out specific backends to test their performance, or to work
148	around bugs.	331	around bugs.
149		332
		333	=item C<EVFLAG_FORKCHECK>
		334
		335	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		336	a fork, you can also make libev check for a fork in each iteration by
		337	enabling this flag.
		338
		339	This works by calling C<getpid ()> on every iteration of the loop,
		340	and thus this might slow down your event loop if you do a lot of loop
		341	iterations and little real work, but is usually not noticeable (on my
		342	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		343	without a system call and thus I<very> fast, but my GNU/Linux system also has
		344	C<pthread_atfork> which is even faster).
		345
		346	The big advantage of this flag is that you can forget about fork (and
		347	forget about forgetting to tell libev about forking) when you use this
		348	flag.
		349
		350	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		351	environment variable.
		352
150	=item C<EVMETHOD_SELECT> (portable select backend)	353	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		354
		355	This is your standard select(2) backend. Not I<completely> standard, as
		356	libev tries to roll its own fd_set with no limits on the number of fds,
		357	but if that fails, expect a fairly low limit on the number of fds when
		358	using this backend. It doesn't scale too well (O(highest_fd)), but its
		359	usually the fastest backend for a low number of (low-numbered :) fds.
		360
		361	To get good performance out of this backend you need a high amount of
		362	parallelism (most of the file descriptors should be busy). If you are
		363	writing a server, you should C<accept ()> in a loop to accept as many
		364	connections as possible during one iteration. You might also want to have
		365	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		366	readiness notifications you get per iteration.
		367
		368	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		369	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		370	C<exceptfds> set on that platform).
		371
152	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	372	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
153		373
154	=item C<EVMETHOD_EPOLL> (linux only)	374	And this is your standard poll(2) backend. It's more complicated
		375	than select, but handles sparse fds better and has no artificial
		376	limit on the number of fds you can use (except it will slow down
		377	considerably with a lot of inactive fds). It scales similarly to select,
		378	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		379	performance tips.
155		380
156	=item C<EVMETHOD_KQUEUE> (some bsds only)	381	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		382	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
157		383
158	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
159		385
160	=item C<EVMETHOD_PORT> (solaris 10 only)	386	For few fds, this backend is a bit little slower than poll and select,
		387	but it scales phenomenally better. While poll and select usually scale
		388	like O(total_fds) where n is the total number of fds (or the highest fd),
		389	epoll scales either O(1) or O(active_fds).
161		390
162	If one or more of these are ored into the flags value, then only these	391	The epoll mechanism deserves honorable mention as the most misdesigned
163	backends will be tried (in the reverse order as given here). If one are	392	of the more advanced event mechanisms: mere annoyances include silently
164	specified, any backend will do.	393	dropping file descriptors, requiring a system call per change per file
		394	descriptor (and unnecessary guessing of parameters), problems with dup and
		395	so on. The biggest issue is fork races, however - if a program forks then
		396	I<both> parent and child process have to recreate the epoll set, which can
		397	take considerable time (one syscall per file descriptor) and is of course
		398	hard to detect.
		399
		400	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		401	of course I<doesn't>, and epoll just loves to report events for totally
		402	I<different> file descriptors (even already closed ones, so one cannot
		403	even remove them from the set) than registered in the set (especially
		404	on SMP systems). Libev tries to counter these spurious notifications by
		405	employing an additional generation counter and comparing that against the
		406	events to filter out spurious ones, recreating the set when required.
		407
		408	While stopping, setting and starting an I/O watcher in the same iteration
		409	will result in some caching, there is still a system call per such
		410	incident (because the same I<file descriptor> could point to a different
		411	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
		412	file descriptors might not work very well if you register events for both
		413	file descriptors.
		414
		415	Best performance from this backend is achieved by not unregistering all
		416	watchers for a file descriptor until it has been closed, if possible,
		417	i.e. keep at least one watcher active per fd at all times. Stopping and
		418	starting a watcher (without re-setting it) also usually doesn't cause
		419	extra overhead. A fork can both result in spurious notifications as well
		420	as in libev having to destroy and recreate the epoll object, which can
		421	take considerable time and thus should be avoided.
		422
		423	While nominally embeddable in other event loops, this feature is broken in
		424	all kernel versions tested so far.
		425
		426	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		427	C<EVBACKEND_POLL>.
		428
		429	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		430
		431	Kqueue deserves special mention, as at the time of this writing, it
		432	was broken on all BSDs except NetBSD (usually it doesn't work reliably
		433	with anything but sockets and pipes, except on Darwin, where of course
		434	it's completely useless). Unlike epoll, however, whose brokenness
		435	is by design, these kqueue bugs can (and eventually will) be fixed
		436	without API changes to existing programs. For this reason it's not being
		437	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		438	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		439	system like NetBSD.
		440
		441	You still can embed kqueue into a normal poll or select backend and use it
		442	only for sockets (after having made sure that sockets work with kqueue on
		443	the target platform). See C<ev_embed> watchers for more info.
		444
		445	It scales in the same way as the epoll backend, but the interface to the
		446	kernel is more efficient (which says nothing about its actual speed, of
		447	course). While stopping, setting and starting an I/O watcher does never
		448	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
		449	two event changes per incident. Support for C<fork ()> is very bad (but
		450	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		451	cases
		452
		453	This backend usually performs well under most conditions.
		454
		455	While nominally embeddable in other event loops, this doesn't work
		456	everywhere, so you might need to test for this. And since it is broken
		457	almost everywhere, you should only use it when you have a lot of sockets
		458	(for which it usually works), by embedding it into another event loop
		459	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
		460	using it only for sockets.
		461
		462	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		463	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		464	C<NOTE_EOF>.
		465
		466	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		467
		468	This is not implemented yet (and might never be, unless you send me an
		469	implementation). According to reports, C</dev/poll> only supports sockets
		470	and is not embeddable, which would limit the usefulness of this backend
		471	immensely.
		472
		473	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		474
		475	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
		476	it's really slow, but it still scales very well (O(active_fds)).
		477
		478	Please note that Solaris event ports can deliver a lot of spurious
		479	notifications, so you need to use non-blocking I/O or other means to avoid
		480	blocking when no data (or space) is available.
		481
		482	While this backend scales well, it requires one system call per active
		483	file descriptor per loop iteration. For small and medium numbers of file
		484	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		485	might perform better.
		486
		487	On the positive side, with the exception of the spurious readiness
		488	notifications, this backend actually performed fully to specification
		489	in all tests and is fully embeddable, which is a rare feat among the
		490	OS-specific backends (I vastly prefer correctness over speed hacks).
		491
		492	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		493	C<EVBACKEND_POLL>.
		494
		495	=item C<EVBACKEND_ALL>
		496
		497	Try all backends (even potentially broken ones that wouldn't be tried
		498	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		499	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		500
		501	It is definitely not recommended to use this flag.
165		502
166	=back	503	=back
		504
		505	If one or more of these are or'ed into the flags value, then only these
		506	backends will be tried (in the reverse order as listed here). If none are
		507	specified, all backends in C<ev_recommended_backends ()> will be tried.
		508
		509	Example: This is the most typical usage.
		510
		511	if (!ev_default_loop (0))
		512	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		513
		514	Example: Restrict libev to the select and poll backends, and do not allow
		515	environment settings to be taken into account:
		516
		517	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		518
		519	Example: Use whatever libev has to offer, but make sure that kqueue is
		520	used if available (warning, breaks stuff, best use only with your own
		521	private event loop and only if you know the OS supports your types of
		522	fds):
		523
		524	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
167		525
168	=item struct ev_loop *ev_loop_new (unsigned int flags)	526	=item struct ev_loop *ev_loop_new (unsigned int flags)
169		527
170	Similar to C<ev_default_loop>, but always creates a new event loop that is	528	Similar to C<ev_default_loop>, but always creates a new event loop that is
171	always distinct from the default loop. Unlike the default loop, it cannot	529	always distinct from the default loop. Unlike the default loop, it cannot
172	handle signal and child watchers, and attempts to do so will be greeted by	530	handle signal and child watchers, and attempts to do so will be greeted by
173	undefined behaviour (or a failed assertion if assertions are enabled).	531	undefined behaviour (or a failed assertion if assertions are enabled).
174		532
		533	Note that this function I<is> thread-safe, and the recommended way to use
		534	libev with threads is indeed to create one loop per thread, and using the
		535	default loop in the "main" or "initial" thread.
		536
		537	Example: Try to create a event loop that uses epoll and nothing else.
		538
		539	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		540	if (!epoller)
		541	fatal ("no epoll found here, maybe it hides under your chair");
		542
175	=item ev_default_destroy ()	543	=item ev_default_destroy ()
176		544
177	Destroys the default loop again (frees all memory and kernel state	545	Destroys the default loop again (frees all memory and kernel state
178	etc.). This stops all registered event watchers (by not touching them in	546	etc.). None of the active event watchers will be stopped in the normal
179	any way whatsoever, although you cannot rely on this :).	547	sense, so e.g. C<ev_is_active> might still return true. It is your
		548	responsibility to either stop all watchers cleanly yourself I<before>
		549	calling this function, or cope with the fact afterwards (which is usually
		550	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		551	for example).
		552
		553	Note that certain global state, such as signal state (and installed signal
		554	handlers), will not be freed by this function, and related watchers (such
		555	as signal and child watchers) would need to be stopped manually.
		556
		557	In general it is not advisable to call this function except in the
		558	rare occasion where you really need to free e.g. the signal handling
		559	pipe fds. If you need dynamically allocated loops it is better to use
		560	C<ev_loop_new> and C<ev_loop_destroy>).
180		561
181	=item ev_loop_destroy (loop)	562	=item ev_loop_destroy (loop)
182		563
183	Like C<ev_default_destroy>, but destroys an event loop created by an	564	Like C<ev_default_destroy>, but destroys an event loop created by an
184	earlier call to C<ev_loop_new>.	565	earlier call to C<ev_loop_new>.
185		566
186	=item ev_default_fork ()	567	=item ev_default_fork ()
187		568
		569	This function sets a flag that causes subsequent C<ev_loop> iterations
188	This function reinitialises the kernel state for backends that have	570	to reinitialise the kernel state for backends that have one. Despite the
189	one. Despite the name, you can call it anytime, but it makes most sense	571	name, you can call it anytime, but it makes most sense after forking, in
190	after forking, in either the parent or child process (or both, but that	572	the child process (or both child and parent, but that again makes little
191	again makes little sense).	573	sense). You I<must> call it in the child before using any of the libev
		574	functions, and it will only take effect at the next C<ev_loop> iteration.
192		575
193	You I<must> call this function after forking if and only if you want to	576	On the other hand, you only need to call this function in the child
194	use the event library in both processes. If you just fork+exec, you don't	577	process if and only if you want to use the event library in the child. If
195	have to call it.	578	you just fork+exec, you don't have to call it at all.
196		579
197	The function itself is quite fast and it's usually not a problem to call	580	The function itself is quite fast and it's usually not a problem to call
198	it just in case after a fork. To make this easy, the function will fit in	581	it just in case after a fork. To make this easy, the function will fit in
199	quite nicely into a call to C<pthread_atfork>:	582	quite nicely into a call to C<pthread_atfork>:
200		583
…		…
202		585
203	=item ev_loop_fork (loop)	586	=item ev_loop_fork (loop)
204		587
205	Like C<ev_default_fork>, but acts on an event loop created by	588	Like C<ev_default_fork>, but acts on an event loop created by
206	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	589	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
207	after fork, and how you do this is entirely your own problem.	590	after fork that you want to re-use in the child, and how you do this is
		591	entirely your own problem.
208		592
		593	=item int ev_is_default_loop (loop)
		594
		595	Returns true when the given loop is, in fact, the default loop, and false
		596	otherwise.
		597
		598	=item unsigned int ev_loop_count (loop)
		599
		600	Returns the count of loop iterations for the loop, which is identical to
		601	the number of times libev did poll for new events. It starts at C<0> and
		602	happily wraps around with enough iterations.
		603
		604	This value can sometimes be useful as a generation counter of sorts (it
		605	"ticks" the number of loop iterations), as it roughly corresponds with
		606	C<ev_prepare> and C<ev_check> calls.
		607
209	=item unsigned int ev_method (loop)	608	=item unsigned int ev_backend (loop)
210		609
211	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	610	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
212	use.	611	use.
213		612
214	=item ev_tstamp ev_now (loop)	613	=item ev_tstamp ev_now (loop)
215		614
216	Returns the current "event loop time", which is the time the event loop	615	Returns the current "event loop time", which is the time the event loop
217	got events and started processing them. This timestamp does not change	616	received events and started processing them. This timestamp does not
218	as long as callbacks are being processed, and this is also the base time	617	change as long as callbacks are being processed, and this is also the base
219	used for relative timers. You can treat it as the timestamp of the event	618	time used for relative timers. You can treat it as the timestamp of the
220	occuring (or more correctly, the mainloop finding out about it).	619	event occurring (or more correctly, libev finding out about it).
		620
		621	=item ev_now_update (loop)
		622
		623	Establishes the current time by querying the kernel, updating the time
		624	returned by C<ev_now ()> in the progress. This is a costly operation and
		625	is usually done automatically within C<ev_loop ()>.
		626
		627	This function is rarely useful, but when some event callback runs for a
		628	very long time without entering the event loop, updating libev's idea of
		629	the current time is a good idea.
		630
		631	See also "The special problem of time updates" in the C<ev_timer> section.
221		632
222	=item ev_loop (loop, int flags)	633	=item ev_loop (loop, int flags)
223		634
224	Finally, this is it, the event handler. This function usually is called	635	Finally, this is it, the event handler. This function usually is called
225	after you initialised all your watchers and you want to start handling	636	after you initialised all your watchers and you want to start handling
226	events.	637	events.
227		638
228	If the flags argument is specified as 0, it will not return until either	639	If the flags argument is specified as C<0>, it will not return until
229	no event watchers are active anymore or C<ev_unloop> was called.	640	either no event watchers are active anymore or C<ev_unloop> was called.
		641
		642	Please note that an explicit C<ev_unloop> is usually better than
		643	relying on all watchers to be stopped when deciding when a program has
		644	finished (especially in interactive programs), but having a program
		645	that automatically loops as long as it has to and no longer by virtue
		646	of relying on its watchers stopping correctly, that is truly a thing of
		647	beauty.
230		648
231	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	649	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
232	those events and any outstanding ones, but will not block your process in	650	those events and any already outstanding ones, but will not block your
233	case there are no events and will return after one iteration of the loop.	651	process in case there are no events and will return after one iteration of
		652	the loop.
234		653
235	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	654	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
236	neccessary) and will handle those and any outstanding ones. It will block	655	necessary) and will handle those and any already outstanding ones. It
237	your process until at least one new event arrives, and will return after	656	will block your process until at least one new event arrives (which could
		657	be an event internal to libev itself, so there is no guarantee that a
		658	user-registered callback will be called), and will return after one
238	one iteration of the loop.	659	iteration of the loop.
239		660
240	This flags value could be used to implement alternative looping	661	This is useful if you are waiting for some external event in conjunction
241	constructs, but the C<prepare> and C<check> watchers provide a better and	662	with something not expressible using other libev watchers (i.e. "roll your
242	more generic mechanism.	663	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		664	usually a better approach for this kind of thing.
243		665
244	Here are the gory details of what ev_loop does:	666	Here are the gory details of what C<ev_loop> does:
245		667
246	1. If there are no active watchers (reference count is zero), return.	668	- Before the first iteration, call any pending watchers.
		669	* If EVFLAG_FORKCHECK was used, check for a fork.
		670	- If a fork was detected (by any means), queue and call all fork watchers.
247	2. Queue and immediately call all prepare watchers.	671	- Queue and call all prepare watchers.
248	3. If we have been forked, recreate the kernel state.	672	- If we have been forked, detach and recreate the kernel state
		673	as to not disturb the other process.
249	4. Update the kernel state with all outstanding changes.	674	- Update the kernel state with all outstanding changes.
250	5. Update the "event loop time".	675	- Update the "event loop time" (ev_now ()).
251	6. Calculate for how long to block.	676	- Calculate for how long to sleep or block, if at all
		677	(active idle watchers, EVLOOP_NONBLOCK or not having
		678	any active watchers at all will result in not sleeping).
		679	- Sleep if the I/O and timer collect interval say so.
252	7. Block the process, waiting for events.	680	- Block the process, waiting for any events.
		681	- Queue all outstanding I/O (fd) events.
253	8. Update the "event loop time" and do time jump handling.	682	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
254	9. Queue all outstanding timers.	683	- Queue all expired timers.
255	10. Queue all outstanding periodics.	684	- Queue all expired periodics.
256	11. If no events are pending now, queue all idle watchers.	685	- Unless any events are pending now, queue all idle watchers.
257	12. Queue all check watchers.	686	- Queue all check watchers.
258	13. Call all queued watchers in reverse order (i.e. check watchers first).	687	- Call all queued watchers in reverse order (i.e. check watchers first).
		688	Signals and child watchers are implemented as I/O watchers, and will
		689	be handled here by queueing them when their watcher gets executed.
259	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	690	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
260	was used, return, otherwise continue with step #1.	691	were used, or there are no active watchers, return, otherwise
		692	continue with step *.
		693
		694	Example: Queue some jobs and then loop until no events are outstanding
		695	anymore.
		696
		697	... queue jobs here, make sure they register event watchers as long
		698	... as they still have work to do (even an idle watcher will do..)
		699	ev_loop (my_loop, 0);
		700	... jobs done or somebody called unloop. yeah!
261		701
262	=item ev_unloop (loop, how)	702	=item ev_unloop (loop, how)
263		703
264	Can be used to make a call to C<ev_loop> return early (but only after it	704	Can be used to make a call to C<ev_loop> return early (but only after it
265	has processed all outstanding events). The C<how> argument must be either	705	has processed all outstanding events). The C<how> argument must be either
266	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	706	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
267	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	707	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
268		708
		709	This "unloop state" will be cleared when entering C<ev_loop> again.
		710
		711	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		712
269	=item ev_ref (loop)	713	=item ev_ref (loop)
270		714
271	=item ev_unref (loop)	715	=item ev_unref (loop)
272		716
273	Ref/unref can be used to add or remove a reference count on the event	717	Ref/unref can be used to add or remove a reference count on the event
274	loop: Every watcher keeps one reference, and as long as the reference	718	loop: Every watcher keeps one reference, and as long as the reference
275	count is nonzero, C<ev_loop> will not return on its own. If you have	719	count is nonzero, C<ev_loop> will not return on its own.
		720
276	a watcher you never unregister that should not keep C<ev_loop> from	721	If you have a watcher you never unregister that should not keep C<ev_loop>
277	returning, ev_unref() after starting, and ev_ref() before stopping it. For	722	from returning, call ev_unref() after starting, and ev_ref() before
		723	stopping it.
		724
278	example, libev itself uses this for its internal signal pipe: It is not	725	As an example, libev itself uses this for its internal signal pipe: It is
279	visible to the libev user and should not keep C<ev_loop> from exiting if	726	not visible to the libev user and should not keep C<ev_loop> from exiting
280	no event watchers registered by it are active. It is also an excellent	727	if no event watchers registered by it are active. It is also an excellent
281	way to do this for generic recurring timers or from within third-party	728	way to do this for generic recurring timers or from within third-party
282	libraries. Just remember to I<unref after start> and I<ref before stop>.	729	libraries. Just remember to I<unref after start> and I<ref before stop>
		730	(but only if the watcher wasn't active before, or was active before,
		731	respectively).
		732
		733	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		734	running when nothing else is active.
		735
		736	ev_signal exitsig;
		737	ev_signal_init (&exitsig, sig_cb, SIGINT);
		738	ev_signal_start (loop, &exitsig);
		739	evf_unref (loop);
		740
		741	Example: For some weird reason, unregister the above signal handler again.
		742
		743	ev_ref (loop);
		744	ev_signal_stop (loop, &exitsig);
		745
		746	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		747
		748	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		749
		750	These advanced functions influence the time that libev will spend waiting
		751	for events. Both time intervals are by default C<0>, meaning that libev
		752	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		753	latency.
		754
		755	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		756	allows libev to delay invocation of I/O and timer/periodic callbacks
		757	to increase efficiency of loop iterations (or to increase power-saving
		758	opportunities).
		759
		760	The idea is that sometimes your program runs just fast enough to handle
		761	one (or very few) event(s) per loop iteration. While this makes the
		762	program responsive, it also wastes a lot of CPU time to poll for new
		763	events, especially with backends like C<select ()> which have a high
		764	overhead for the actual polling but can deliver many events at once.
		765
		766	By setting a higher I<io collect interval> you allow libev to spend more
		767	time collecting I/O events, so you can handle more events per iteration,
		768	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		769	C<ev_timer>) will be not affected. Setting this to a non-null value will
		770	introduce an additional C<ev_sleep ()> call into most loop iterations.
		771
		772	Likewise, by setting a higher I<timeout collect interval> you allow libev
		773	to spend more time collecting timeouts, at the expense of increased
		774	latency/jitter/inexactness (the watcher callback will be called
		775	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		776	value will not introduce any overhead in libev.
		777
		778	Many (busy) programs can usually benefit by setting the I/O collect
		779	interval to a value near C<0.1> or so, which is often enough for
		780	interactive servers (of course not for games), likewise for timeouts. It
		781	usually doesn't make much sense to set it to a lower value than C<0.01>,
		782	as this approaches the timing granularity of most systems.
		783
		784	Setting the I<timeout collect interval> can improve the opportunity for
		785	saving power, as the program will "bundle" timer callback invocations that
		786	are "near" in time together, by delaying some, thus reducing the number of
		787	times the process sleeps and wakes up again. Another useful technique to
		788	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		789	they fire on, say, one-second boundaries only.
		790
		791	=item ev_loop_verify (loop)
		792
		793	This function only does something when C<EV_VERIFY> support has been
		794	compiled in, which is the default for non-minimal builds. It tries to go
		795	through all internal structures and checks them for validity. If anything
		796	is found to be inconsistent, it will print an error message to standard
		797	error and call C<abort ()>.
		798
		799	This can be used to catch bugs inside libev itself: under normal
		800	circumstances, this function will never abort as of course libev keeps its
		801	data structures consistent.
283		802
284	=back	803	=back
285		804
		805
286	=head1 ANATOMY OF A WATCHER	806	=head1 ANATOMY OF A WATCHER
		807
		808	In the following description, uppercase C<TYPE> in names stands for the
		809	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		810	watchers and C<ev_io_start> for I/O watchers.
287		811
288	A watcher is a structure that you create and register to record your	812	A watcher is a structure that you create and register to record your
289	interest in some event. For instance, if you want to wait for STDIN to	813	interest in some event. For instance, if you want to wait for STDIN to
290	become readable, you would create an C<ev_io> watcher for that:	814	become readable, you would create an C<ev_io> watcher for that:
291		815
292	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	816	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
293	{	817	{
294	ev_io_stop (w);	818	ev_io_stop (w);
295	ev_unloop (loop, EVUNLOOP_ALL);	819	ev_unloop (loop, EVUNLOOP_ALL);
296	}	820	}
297		821
298	struct ev_loop *loop = ev_default_loop (0);	822	struct ev_loop *loop = ev_default_loop (0);
		823
299	struct ev_io stdin_watcher;	824	ev_io stdin_watcher;
		825
300	ev_init (&stdin_watcher, my_cb);	826	ev_init (&stdin_watcher, my_cb);
301	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	827	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
302	ev_io_start (loop, &stdin_watcher);	828	ev_io_start (loop, &stdin_watcher);
		829
303	ev_loop (loop, 0);	830	ev_loop (loop, 0);
304		831
305	As you can see, you are responsible for allocating the memory for your	832	As you can see, you are responsible for allocating the memory for your
306	watcher structures (and it is usually a bad idea to do this on the stack,	833	watcher structures (and it is I<usually> a bad idea to do this on the
307	although this can sometimes be quite valid).	834	stack).
		835
		836	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		837	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
308		838
309	Each watcher structure must be initialised by a call to C<ev_init	839	Each watcher structure must be initialised by a call to C<ev_init
310	(watcher *, callback)>, which expects a callback to be provided. This	840	(watcher *, callback)>, which expects a callback to be provided. This
311	callback gets invoked each time the event occurs (or, in the case of io	841	callback gets invoked each time the event occurs (or, in the case of I/O
312	watchers, each time the event loop detects that the file descriptor given	842	watchers, each time the event loop detects that the file descriptor given
313	is readable and/or writable).	843	is readable and/or writable).
314		844
315	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	845	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
316	with arguments specific to this watcher type. There is also a macro	846	macro to configure it, with arguments specific to the watcher type. There
317	to combine initialisation and setting in one call: C<< ev_<type>_init	847	is also a macro to combine initialisation and setting in one call: C<<
318	(watcher *, callback, ...) >>.	848	ev_TYPE_init (watcher *, callback, ...) >>.
319		849
320	To make the watcher actually watch out for events, you have to start it	850	To make the watcher actually watch out for events, you have to start it
321	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	851	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
322	*) >>), and you can stop watching for events at any time by calling the	852	*) >>), and you can stop watching for events at any time by calling the
323	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	853	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
324		854
325	As long as your watcher is active (has been started but not stopped) you	855	As long as your watcher is active (has been started but not stopped) you
326	must not touch the values stored in it. Most specifically you must never	856	must not touch the values stored in it. Most specifically you must never
327	reinitialise it or call its set method.	857	reinitialise it or call its C<ev_TYPE_set> macro.
328
329	You can check whether an event is active by calling the C<ev_is_active
330	(watcher *)> macro. To see whether an event is outstanding (but the
331	callback for it has not been called yet) you can use the C<ev_is_pending
332	(watcher *)> macro.
333		858
334	Each and every callback receives the event loop pointer as first, the	859	Each and every callback receives the event loop pointer as first, the
335	registered watcher structure as second, and a bitset of received events as	860	registered watcher structure as second, and a bitset of received events as
336	third argument.	861	third argument.
337		862
…		…
361	The signal specified in the C<ev_signal> watcher has been received by a thread.	886	The signal specified in the C<ev_signal> watcher has been received by a thread.
362		887
363	=item C<EV_CHILD>	888	=item C<EV_CHILD>
364		889
365	The pid specified in the C<ev_child> watcher has received a status change.	890	The pid specified in the C<ev_child> watcher has received a status change.
		891
		892	=item C<EV_STAT>
		893
		894	The path specified in the C<ev_stat> watcher changed its attributes somehow.
366		895
367	=item C<EV_IDLE>	896	=item C<EV_IDLE>
368		897
369	The C<ev_idle> watcher has determined that you have nothing better to do.	898	The C<ev_idle> watcher has determined that you have nothing better to do.
370		899
…		…
378	received events. Callbacks of both watcher types can start and stop as	907	received events. Callbacks of both watcher types can start and stop as
379	many watchers as they want, and all of them will be taken into account	908	many watchers as they want, and all of them will be taken into account
380	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	909	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
381	C<ev_loop> from blocking).	910	C<ev_loop> from blocking).
382		911
		912	=item C<EV_EMBED>
		913
		914	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		915
		916	=item C<EV_FORK>
		917
		918	The event loop has been resumed in the child process after fork (see
		919	C<ev_fork>).
		920
		921	=item C<EV_ASYNC>
		922
		923	The given async watcher has been asynchronously notified (see C<ev_async>).
		924
383	=item C<EV_ERROR>	925	=item C<EV_ERROR>
384		926
385	An unspecified error has occured, the watcher has been stopped. This might	927	An unspecified error has occurred, the watcher has been stopped. This might
386	happen because the watcher could not be properly started because libev	928	happen because the watcher could not be properly started because libev
387	ran out of memory, a file descriptor was found to be closed or any other	929	ran out of memory, a file descriptor was found to be closed or any other
		930	problem. Libev considers these application bugs.
		931
388	problem. You best act on it by reporting the problem and somehow coping	932	You best act on it by reporting the problem and somehow coping with the
389	with the watcher being stopped.	933	watcher being stopped. Note that well-written programs should not receive
		934	an error ever, so when your watcher receives it, this usually indicates a
		935	bug in your program.
390		936
391	Libev will usually signal a few "dummy" events together with an error,	937	Libev will usually signal a few "dummy" events together with an error, for
392	for example it might indicate that a fd is readable or writable, and if	938	example it might indicate that a fd is readable or writable, and if your
393	your callbacks is well-written it can just attempt the operation and cope	939	callbacks is well-written it can just attempt the operation and cope with
394	with the error from read() or write(). This will not work in multithreaded	940	the error from read() or write(). This will not work in multi-threaded
395	programs, though, so beware.	941	programs, though, as the fd could already be closed and reused for another
		942	thing, so beware.
396		943
397	=back	944	=back
398		945
		946	=head2 GENERIC WATCHER FUNCTIONS
		947
		948	=over 4
		949
		950	=item C<ev_init> (ev_TYPE *watcher, callback)
		951
		952	This macro initialises the generic portion of a watcher. The contents
		953	of the watcher object can be arbitrary (so C<malloc> will do). Only
		954	the generic parts of the watcher are initialised, you I<need> to call
		955	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		956	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		957	which rolls both calls into one.
		958
		959	You can reinitialise a watcher at any time as long as it has been stopped
		960	(or never started) and there are no pending events outstanding.
		961
		962	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		963	int revents)>.
		964
		965	Example: Initialise an C<ev_io> watcher in two steps.
		966
		967	ev_io w;
		968	ev_init (&w, my_cb);
		969	ev_io_set (&w, STDIN_FILENO, EV_READ);
		970
		971	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		972
		973	This macro initialises the type-specific parts of a watcher. You need to
		974	call C<ev_init> at least once before you call this macro, but you can
		975	call C<ev_TYPE_set> any number of times. You must not, however, call this
		976	macro on a watcher that is active (it can be pending, however, which is a
		977	difference to the C<ev_init> macro).
		978
		979	Although some watcher types do not have type-specific arguments
		980	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		981
		982	See C<ev_init>, above, for an example.
		983
		984	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		985
		986	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		987	calls into a single call. This is the most convenient method to initialise
		988	a watcher. The same limitations apply, of course.
		989
		990	Example: Initialise and set an C<ev_io> watcher in one step.
		991
		992	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		993
		994	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		995
		996	Starts (activates) the given watcher. Only active watchers will receive
		997	events. If the watcher is already active nothing will happen.
		998
		999	Example: Start the C<ev_io> watcher that is being abused as example in this
		1000	whole section.
		1001
		1002	ev_io_start (EV_DEFAULT_UC, &w);
		1003
		1004	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		1005
		1006	Stops the given watcher if active, and clears the pending status (whether
		1007	the watcher was active or not).
		1008
		1009	It is possible that stopped watchers are pending - for example,
		1010	non-repeating timers are being stopped when they become pending - but
		1011	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1012	pending. If you want to free or reuse the memory used by the watcher it is
		1013	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1014
		1015	=item bool ev_is_active (ev_TYPE *watcher)
		1016
		1017	Returns a true value iff the watcher is active (i.e. it has been started
		1018	and not yet been stopped). As long as a watcher is active you must not modify
		1019	it.
		1020
		1021	=item bool ev_is_pending (ev_TYPE *watcher)
		1022
		1023	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1024	events but its callback has not yet been invoked). As long as a watcher
		1025	is pending (but not active) you must not call an init function on it (but
		1026	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1027	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1028	it).
		1029
		1030	=item callback ev_cb (ev_TYPE *watcher)
		1031
		1032	Returns the callback currently set on the watcher.
		1033
		1034	=item ev_cb_set (ev_TYPE *watcher, callback)
		1035
		1036	Change the callback. You can change the callback at virtually any time
		1037	(modulo threads).
		1038
		1039	=item ev_set_priority (ev_TYPE *watcher, priority)
		1040
		1041	=item int ev_priority (ev_TYPE *watcher)
		1042
		1043	Set and query the priority of the watcher. The priority is a small
		1044	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1045	(default: C<-2>). Pending watchers with higher priority will be invoked
		1046	before watchers with lower priority, but priority will not keep watchers
		1047	from being executed (except for C<ev_idle> watchers).
		1048
		1049	This means that priorities are I<only> used for ordering callback
		1050	invocation after new events have been received. This is useful, for
		1051	example, to reduce latency after idling, or more often, to bind two
		1052	watchers on the same event and make sure one is called first.
		1053
		1054	If you need to suppress invocation when higher priority events are pending
		1055	you need to look at C<ev_idle> watchers, which provide this functionality.
		1056
		1057	You I<must not> change the priority of a watcher as long as it is active or
		1058	pending.
		1059
		1060	The default priority used by watchers when no priority has been set is
		1061	always C<0>, which is supposed to not be too high and not be too low :).
		1062
		1063	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1064	fine, as long as you do not mind that the priority value you query might
		1065	or might not have been clamped to the valid range.
		1066
		1067	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1068
		1069	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1070	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1071	can deal with that fact, as both are simply passed through to the
		1072	callback.
		1073
		1074	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1075
		1076	If the watcher is pending, this function clears its pending status and
		1077	returns its C<revents> bitset (as if its callback was invoked). If the
		1078	watcher isn't pending it does nothing and returns C<0>.
		1079
		1080	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1081	callback to be invoked, which can be accomplished with this function.
		1082
		1083	=back
		1084
		1085
399	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1086	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
400		1087
401	Each watcher has, by default, a member C<void *data> that you can change	1088	Each watcher has, by default, a member C<void *data> that you can change
402	and read at any time, libev will completely ignore it. This can be used	1089	and read at any time: libev will completely ignore it. This can be used
403	to associate arbitrary data with your watcher. If you need more data and	1090	to associate arbitrary data with your watcher. If you need more data and
404	don't want to allocate memory and store a pointer to it in that data	1091	don't want to allocate memory and store a pointer to it in that data
405	member, you can also "subclass" the watcher type and provide your own	1092	member, you can also "subclass" the watcher type and provide your own
406	data:	1093	data:
407		1094
408	struct my_io	1095	struct my_io
409	{	1096	{
410	struct ev_io io;	1097	ev_io io;
411	int otherfd;	1098	int otherfd;
412	void *somedata;	1099	void *somedata;
413	struct whatever *mostinteresting;	1100	struct whatever *mostinteresting;
414	}	1101	};
		1102
		1103	...
		1104	struct my_io w;
		1105	ev_io_init (&w.io, my_cb, fd, EV_READ);
415		1106
416	And since your callback will be called with a pointer to the watcher, you	1107	And since your callback will be called with a pointer to the watcher, you
417	can cast it back to your own type:	1108	can cast it back to your own type:
418		1109
419	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1110	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
420	{	1111	{
421	struct my_io *w = (struct my_io *)w_;	1112	struct my_io *w = (struct my_io *)w_;
422	...	1113	...
423	}	1114	}
424		1115
425	More interesting and less C-conformant ways of catsing your callback type	1116	More interesting and less C-conformant ways of casting your callback type
426	have been omitted....	1117	instead have been omitted.
		1118
		1119	Another common scenario is to use some data structure with multiple
		1120	embedded watchers:
		1121
		1122	struct my_biggy
		1123	{
		1124	int some_data;
		1125	ev_timer t1;
		1126	ev_timer t2;
		1127	}
		1128
		1129	In this case getting the pointer to C<my_biggy> is a bit more
		1130	complicated: Either you store the address of your C<my_biggy> struct
		1131	in the C<data> member of the watcher (for woozies), or you need to use
		1132	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1133	programmers):
		1134
		1135	#include <stddef.h>
		1136
		1137	static void
		1138	t1_cb (EV_P_ ev_timer *w, int revents)
		1139	{
		1140	struct my_biggy big = (struct my_biggy *
		1141	(((char *)w) - offsetof (struct my_biggy, t1));
		1142	}
		1143
		1144	static void
		1145	t2_cb (EV_P_ ev_timer *w, int revents)
		1146	{
		1147	struct my_biggy big = (struct my_biggy *
		1148	(((char *)w) - offsetof (struct my_biggy, t2));
		1149	}
427		1150
428		1151
429	=head1 WATCHER TYPES	1152	=head1 WATCHER TYPES
430		1153
431	This section describes each watcher in detail, but will not repeat	1154	This section describes each watcher in detail, but will not repeat
432	information given in the last section.	1155	information given in the last section. Any initialisation/set macros,
		1156	functions and members specific to the watcher type are explained.
433		1157
		1158	Members are additionally marked with either I<[read-only]>, meaning that,
		1159	while the watcher is active, you can look at the member and expect some
		1160	sensible content, but you must not modify it (you can modify it while the
		1161	watcher is stopped to your hearts content), or I<[read-write]>, which
		1162	means you can expect it to have some sensible content while the watcher
		1163	is active, but you can also modify it. Modifying it may not do something
		1164	sensible or take immediate effect (or do anything at all), but libev will
		1165	not crash or malfunction in any way.
		1166
		1167
434	=head2 C<ev_io> - is this file descriptor readable or writable	1168	=head2 C<ev_io> - is this file descriptor readable or writable?
435		1169
436	I/O watchers check whether a file descriptor is readable or writable	1170	I/O watchers check whether a file descriptor is readable or writable
437	in each iteration of the event loop (This behaviour is called	1171	in each iteration of the event loop, or, more precisely, when reading
438	level-triggering because you keep receiving events as long as the	1172	would not block the process and writing would at least be able to write
439	condition persists. Remember you can stop the watcher if you don't want to	1173	some data. This behaviour is called level-triggering because you keep
440	act on the event and neither want to receive future events).	1174	receiving events as long as the condition persists. Remember you can stop
		1175	the watcher if you don't want to act on the event and neither want to
		1176	receive future events.
441		1177
442	In general you can register as many read and/or write event watchers per	1178	In general you can register as many read and/or write event watchers per
443	fd as you want (as long as you don't confuse yourself). Setting all file	1179	fd as you want (as long as you don't confuse yourself). Setting all file
444	descriptors to non-blocking mode is also usually a good idea (but not	1180	descriptors to non-blocking mode is also usually a good idea (but not
445	required if you know what you are doing).	1181	required if you know what you are doing).
446		1182
447	You have to be careful with dup'ed file descriptors, though. Some backends	1183	If you cannot use non-blocking mode, then force the use of a
448	(the linux epoll backend is a notable example) cannot handle dup'ed file	1184	known-to-be-good backend (at the time of this writing, this includes only
449	descriptors correctly if you register interest in two or more fds pointing	1185	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
450	to the same underlying file/socket etc. description (that is, they share
451	the same underlying "file open").
452		1186
453	If you must do this, then force the use of a known-to-be-good backend	1187	Another thing you have to watch out for is that it is quite easy to
454	(at the time of this writing, this includes only EVMETHOD_SELECT and	1188	receive "spurious" readiness notifications, that is your callback might
455	EVMETHOD_POLL).	1189	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1190	because there is no data. Not only are some backends known to create a
		1191	lot of those (for example Solaris ports), it is very easy to get into
		1192	this situation even with a relatively standard program structure. Thus
		1193	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1194	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1195
		1196	If you cannot run the fd in non-blocking mode (for example you should
		1197	not play around with an Xlib connection), then you have to separately
		1198	re-test whether a file descriptor is really ready with a known-to-be good
		1199	interface such as poll (fortunately in our Xlib example, Xlib already
		1200	does this on its own, so its quite safe to use). Some people additionally
		1201	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1202	indefinitely.
		1203
		1204	But really, best use non-blocking mode.
		1205
		1206	=head3 The special problem of disappearing file descriptors
		1207
		1208	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1209	descriptor (either due to calling C<close> explicitly or any other means,
		1210	such as C<dup2>). The reason is that you register interest in some file
		1211	descriptor, but when it goes away, the operating system will silently drop
		1212	this interest. If another file descriptor with the same number then is
		1213	registered with libev, there is no efficient way to see that this is, in
		1214	fact, a different file descriptor.
		1215
		1216	To avoid having to explicitly tell libev about such cases, libev follows
		1217	the following policy: Each time C<ev_io_set> is being called, libev
		1218	will assume that this is potentially a new file descriptor, otherwise
		1219	it is assumed that the file descriptor stays the same. That means that
		1220	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1221	descriptor even if the file descriptor number itself did not change.
		1222
		1223	This is how one would do it normally anyway, the important point is that
		1224	the libev application should not optimise around libev but should leave
		1225	optimisations to libev.
		1226
		1227	=head3 The special problem of dup'ed file descriptors
		1228
		1229	Some backends (e.g. epoll), cannot register events for file descriptors,
		1230	but only events for the underlying file descriptions. That means when you
		1231	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1232	events for them, only one file descriptor might actually receive events.
		1233
		1234	There is no workaround possible except not registering events
		1235	for potentially C<dup ()>'ed file descriptors, or to resort to
		1236	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1237
		1238	=head3 The special problem of fork
		1239
		1240	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1241	useless behaviour. Libev fully supports fork, but needs to be told about
		1242	it in the child.
		1243
		1244	To support fork in your programs, you either have to call
		1245	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1246	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1247	C<EVBACKEND_POLL>.
		1248
		1249	=head3 The special problem of SIGPIPE
		1250
		1251	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1252	when writing to a pipe whose other end has been closed, your program gets
		1253	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1254	this is sensible behaviour, for daemons, this is usually undesirable.
		1255
		1256	So when you encounter spurious, unexplained daemon exits, make sure you
		1257	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1258	somewhere, as that would have given you a big clue).
		1259
		1260
		1261	=head3 Watcher-Specific Functions
456		1262
457	=over 4	1263	=over 4
458		1264
459	=item ev_io_init (ev_io *, callback, int fd, int events)	1265	=item ev_io_init (ev_io *, callback, int fd, int events)
460		1266
461	=item ev_io_set (ev_io *, int fd, int events)	1267	=item ev_io_set (ev_io *, int fd, int events)
462		1268
463	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1269	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
464	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1270	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
465	EV_WRITE> to receive the given events.	1271	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1272
		1273	=item int fd [read-only]
		1274
		1275	The file descriptor being watched.
		1276
		1277	=item int events [read-only]
		1278
		1279	The events being watched.
466		1280
467	=back	1281	=back
468		1282
		1283	=head3 Examples
		1284
		1285	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1286	readable, but only once. Since it is likely line-buffered, you could
		1287	attempt to read a whole line in the callback.
		1288
		1289	static void
		1290	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1291	{
		1292	ev_io_stop (loop, w);
		1293	.. read from stdin here (or from w->fd) and handle any I/O errors
		1294	}
		1295
		1296	...
		1297	struct ev_loop *loop = ev_default_init (0);
		1298	ev_io stdin_readable;
		1299	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1300	ev_io_start (loop, &stdin_readable);
		1301	ev_loop (loop, 0);
		1302
		1303
469	=head2 C<ev_timer> - relative and optionally recurring timeouts	1304	=head2 C<ev_timer> - relative and optionally repeating timeouts
470		1305
471	Timer watchers are simple relative timers that generate an event after a	1306	Timer watchers are simple relative timers that generate an event after a
472	given time, and optionally repeating in regular intervals after that.	1307	given time, and optionally repeating in regular intervals after that.
473		1308
474	The timers are based on real time, that is, if you register an event that	1309	The timers are based on real time, that is, if you register an event that
475	times out after an hour and you reset your system clock to last years	1310	times out after an hour and you reset your system clock to January last
476	time, it will still time out after (roughly) and hour. "Roughly" because	1311	year, it will still time out after (roughly) one hour. "Roughly" because
477	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	1312	detecting time jumps is hard, and some inaccuracies are unavoidable (the
478	monotonic clock option helps a lot here).	1313	monotonic clock option helps a lot here).
		1314
		1315	The callback is guaranteed to be invoked only I<after> its timeout has
		1316	passed, but if multiple timers become ready during the same loop iteration
		1317	then order of execution is undefined.
		1318
		1319	=head3 Be smart about timeouts
		1320
		1321	Many real-world problems involve some kind of timeout, usually for error
		1322	recovery. A typical example is an HTTP request - if the other side hangs,
		1323	you want to raise some error after a while.
		1324
		1325	What follows are some ways to handle this problem, from obvious and
		1326	inefficient to smart and efficient.
		1327
		1328	In the following, a 60 second activity timeout is assumed - a timeout that
		1329	gets reset to 60 seconds each time there is activity (e.g. each time some
		1330	data or other life sign was received).
		1331
		1332	=over 4
		1333
		1334	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1335
		1336	This is the most obvious, but not the most simple way: In the beginning,
		1337	start the watcher:
		1338
		1339	ev_timer_init (timer, callback, 60., 0.);
		1340	ev_timer_start (loop, timer);
		1341
		1342	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1343	and start it again:
		1344
		1345	ev_timer_stop (loop, timer);
		1346	ev_timer_set (timer, 60., 0.);
		1347	ev_timer_start (loop, timer);
		1348
		1349	This is relatively simple to implement, but means that each time there is
		1350	some activity, libev will first have to remove the timer from its internal
		1351	data structure and then add it again. Libev tries to be fast, but it's
		1352	still not a constant-time operation.
		1353
		1354	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1355
		1356	This is the easiest way, and involves using C<ev_timer_again> instead of
		1357	C<ev_timer_start>.
		1358
		1359	To implement this, configure an C<ev_timer> with a C<repeat> value
		1360	of C<60> and then call C<ev_timer_again> at start and each time you
		1361	successfully read or write some data. If you go into an idle state where
		1362	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1363	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1364
		1365	That means you can ignore both the C<ev_timer_start> function and the
		1366	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1367	member and C<ev_timer_again>.
		1368
		1369	At start:
		1370
		1371	ev_timer_init (timer, callback);
		1372	timer->repeat = 60.;
		1373	ev_timer_again (loop, timer);
		1374
		1375	Each time there is some activity:
		1376
		1377	ev_timer_again (loop, timer);
		1378
		1379	It is even possible to change the time-out on the fly, regardless of
		1380	whether the watcher is active or not:
		1381
		1382	timer->repeat = 30.;
		1383	ev_timer_again (loop, timer);
		1384
		1385	This is slightly more efficient then stopping/starting the timer each time
		1386	you want to modify its timeout value, as libev does not have to completely
		1387	remove and re-insert the timer from/into its internal data structure.
		1388
		1389	It is, however, even simpler than the "obvious" way to do it.
		1390
		1391	=item 3. Let the timer time out, but then re-arm it as required.
		1392
		1393	This method is more tricky, but usually most efficient: Most timeouts are
		1394	relatively long compared to the intervals between other activity - in
		1395	our example, within 60 seconds, there are usually many I/O events with
		1396	associated activity resets.
		1397
		1398	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1399	but remember the time of last activity, and check for a real timeout only
		1400	within the callback:
		1401
		1402	ev_tstamp last_activity; // time of last activity
		1403
		1404	static void
		1405	callback (EV_P_ ev_timer *w, int revents)
		1406	{
		1407	ev_tstamp now = ev_now (EV_A);
		1408	ev_tstamp timeout = last_activity + 60.;
		1409
		1410	// if last_activity + 60. is older than now, we did time out
		1411	if (timeout < now)
		1412	{
		1413	// timeout occured, take action
		1414	}
		1415	else
		1416	{
		1417	// callback was invoked, but there was some activity, re-arm
		1418	// the watcher to fire in last_activity + 60, which is
		1419	// guaranteed to be in the future, so "again" is positive:
		1420	w->again = timeout - now;
		1421	ev_timer_again (EV_A_ w);
		1422	}
		1423	}
		1424
		1425	To summarise the callback: first calculate the real timeout (defined
		1426	as "60 seconds after the last activity"), then check if that time has
		1427	been reached, which means something I<did>, in fact, time out. Otherwise
		1428	the callback was invoked too early (C<timeout> is in the future), so
		1429	re-schedule the timer to fire at that future time, to see if maybe we have
		1430	a timeout then.
		1431
		1432	Note how C<ev_timer_again> is used, taking advantage of the
		1433	C<ev_timer_again> optimisation when the timer is already running.
		1434
		1435	This scheme causes more callback invocations (about one every 60 seconds
		1436	minus half the average time between activity), but virtually no calls to
		1437	libev to change the timeout.
		1438
		1439	To start the timer, simply initialise the watcher and set C<last_activity>
		1440	to the current time (meaning we just have some activity :), then call the
		1441	callback, which will "do the right thing" and start the timer:
		1442
		1443	ev_timer_init (timer, callback);
		1444	last_activity = ev_now (loop);
		1445	callback (loop, timer, EV_TIMEOUT);
		1446
		1447	And when there is some activity, simply store the current time in
		1448	C<last_activity>, no libev calls at all:
		1449
		1450	last_actiivty = ev_now (loop);
		1451
		1452	This technique is slightly more complex, but in most cases where the
		1453	time-out is unlikely to be triggered, much more efficient.
		1454
		1455	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1456	callback :) - just change the timeout and invoke the callback, which will
		1457	fix things for you.
		1458
		1459	=item 4. Wee, just use a double-linked list for your timeouts.
		1460
		1461	If there is not one request, but many thousands (millions...), all
		1462	employing some kind of timeout with the same timeout value, then one can
		1463	do even better:
		1464
		1465	When starting the timeout, calculate the timeout value and put the timeout
		1466	at the I<end> of the list.
		1467
		1468	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1469	the list is expected to fire (for example, using the technique #3).
		1470
		1471	When there is some activity, remove the timer from the list, recalculate
		1472	the timeout, append it to the end of the list again, and make sure to
		1473	update the C<ev_timer> if it was taken from the beginning of the list.
		1474
		1475	This way, one can manage an unlimited number of timeouts in O(1) time for
		1476	starting, stopping and updating the timers, at the expense of a major
		1477	complication, and having to use a constant timeout. The constant timeout
		1478	ensures that the list stays sorted.
		1479
		1480	=back
		1481
		1482	So which method the best?
		1483
		1484	Method #2 is a simple no-brain-required solution that is adequate in most
		1485	situations. Method #3 requires a bit more thinking, but handles many cases
		1486	better, and isn't very complicated either. In most case, choosing either
		1487	one is fine, with #3 being better in typical situations.
		1488
		1489	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1490	rather complicated, but extremely efficient, something that really pays
		1491	off after the first million or so of active timers, i.e. it's usually
		1492	overkill :)
		1493
		1494	=head3 The special problem of time updates
		1495
		1496	Establishing the current time is a costly operation (it usually takes at
		1497	least two system calls): EV therefore updates its idea of the current
		1498	time only before and after C<ev_loop> collects new events, which causes a
		1499	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1500	lots of events in one iteration.
479		1501
480	The relative timeouts are calculated relative to the C<ev_now ()>	1502	The relative timeouts are calculated relative to the C<ev_now ()>
481	time. This is usually the right thing as this timestamp refers to the time	1503	time. This is usually the right thing as this timestamp refers to the time
482	of the event triggering whatever timeout you are modifying/starting. If	1504	of the event triggering whatever timeout you are modifying/starting. If
483	you suspect event processing to be delayed and you *need* to base the timeout	1505	you suspect event processing to be delayed and you I<need> to base the
484	on the current time, use something like this to adjust for this:	1506	timeout on the current time, use something like this to adjust for this:
485		1507
486	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1508	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
487		1509
		1510	If the event loop is suspended for a long time, you can also force an
		1511	update of the time returned by C<ev_now ()> by calling C<ev_now_update
		1512	()>.
		1513
		1514	=head3 Watcher-Specific Functions and Data Members
		1515
488	=over 4	1516	=over 4
489		1517
490	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1518	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
491		1519
492	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1520	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
493		1521
494	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1522	Configure the timer to trigger after C<after> seconds. If C<repeat>
495	C<0.>, then it will automatically be stopped. If it is positive, then the	1523	is C<0.>, then it will automatically be stopped once the timeout is
496	timer will automatically be configured to trigger again C<repeat> seconds	1524	reached. If it is positive, then the timer will automatically be
497	later, again, and again, until stopped manually.	1525	configured to trigger again C<repeat> seconds later, again, and again,
		1526	until stopped manually.
498		1527
499	The timer itself will do a best-effort at avoiding drift, that is, if you	1528	The timer itself will do a best-effort at avoiding drift, that is, if
500	configure a timer to trigger every 10 seconds, then it will trigger at	1529	you configure a timer to trigger every 10 seconds, then it will normally
501	exactly 10 second intervals. If, however, your program cannot keep up with	1530	trigger at exactly 10 second intervals. If, however, your program cannot
502	the timer (because it takes longer than those 10 seconds to do stuff) the	1531	keep up with the timer (because it takes longer than those 10 seconds to
503	timer will not fire more than once per event loop iteration.	1532	do stuff) the timer will not fire more than once per event loop iteration.
504		1533
505	=item ev_timer_again (loop)	1534	=item ev_timer_again (loop, ev_timer *)
506		1535
507	This will act as if the timer timed out and restart it again if it is	1536	This will act as if the timer timed out and restart it again if it is
508	repeating. The exact semantics are:	1537	repeating. The exact semantics are:
509		1538
		1539	If the timer is pending, its pending status is cleared.
		1540
510	If the timer is started but nonrepeating, stop it.	1541	If the timer is started but non-repeating, stop it (as if it timed out).
511		1542
512	If the timer is repeating, either start it if necessary (with the repeat	1543	If the timer is repeating, either start it if necessary (with the
513	value), or reset the running timer to the repeat value.	1544	C<repeat> value), or reset the running timer to the C<repeat> value.
514		1545
515	This sounds a bit complicated, but here is a useful and typical	1546	This sounds a bit complicated, see "Be smart about timeouts", above, for a
516	example: Imagine you have a tcp connection and you want a so-called idle	1547	usage example.
517	timeout, that is, you want to be called when there have been, say, 60	1548
518	seconds of inactivity on the socket. The easiest way to do this is to	1549	=item ev_tstamp repeat [read-write]
519	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1550
520	time you successfully read or write some data. If you go into an idle	1551	The current C<repeat> value. Will be used each time the watcher times out
521	state where you do not expect data to travel on the socket, you can stop	1552	or C<ev_timer_again> is called, and determines the next timeout (if any),
522	the timer, and again will automatically restart it if need be.	1553	which is also when any modifications are taken into account.
523		1554
524	=back	1555	=back
525		1556
		1557	=head3 Examples
		1558
		1559	Example: Create a timer that fires after 60 seconds.
		1560
		1561	static void
		1562	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1563	{
		1564	.. one minute over, w is actually stopped right here
		1565	}
		1566
		1567	ev_timer mytimer;
		1568	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1569	ev_timer_start (loop, &mytimer);
		1570
		1571	Example: Create a timeout timer that times out after 10 seconds of
		1572	inactivity.
		1573
		1574	static void
		1575	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1576	{
		1577	.. ten seconds without any activity
		1578	}
		1579
		1580	ev_timer mytimer;
		1581	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1582	ev_timer_again (&mytimer); /* start timer */
		1583	ev_loop (loop, 0);
		1584
		1585	// and in some piece of code that gets executed on any "activity":
		1586	// reset the timeout to start ticking again at 10 seconds
		1587	ev_timer_again (&mytimer);
		1588
		1589
526	=head2 C<ev_periodic> - to cron or not to cron	1590	=head2 C<ev_periodic> - to cron or not to cron?
527		1591
528	Periodic watchers are also timers of a kind, but they are very versatile	1592	Periodic watchers are also timers of a kind, but they are very versatile
529	(and unfortunately a bit complex).	1593	(and unfortunately a bit complex).
530		1594
531	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1595	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
532	but on wallclock time (absolute time). You can tell a periodic watcher	1596	but on wall clock time (absolute time). You can tell a periodic watcher
533	to trigger "at" some specific point in time. For example, if you tell a	1597	to trigger after some specific point in time. For example, if you tell a
534	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1598	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
535	+ 10.>) and then reset your system clock to the last year, then it will	1599	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1600	clock to January of the previous year, then it will take more than year
536	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1601	to trigger the event (unlike an C<ev_timer>, which would still trigger
537	roughly 10 seconds later and of course not if you reset your system time	1602	roughly 10 seconds later as it uses a relative timeout).
538	again).
539		1603
540	They can also be used to implement vastly more complex timers, such as	1604	C<ev_periodic>s can also be used to implement vastly more complex timers,
541	triggering an event on eahc midnight, local time.	1605	such as triggering an event on each "midnight, local time", or other
		1606	complicated rules.
		1607
		1608	As with timers, the callback is guaranteed to be invoked only when the
		1609	time (C<at>) has passed, but if multiple periodic timers become ready
		1610	during the same loop iteration, then order of execution is undefined.
		1611
		1612	=head3 Watcher-Specific Functions and Data Members
542		1613
543	=over 4	1614	=over 4
544		1615
545	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1616	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
546		1617
547	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1618	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
548		1619
549	Lots of arguments, lets sort it out... There are basically three modes of	1620	Lots of arguments, lets sort it out... There are basically three modes of
550	operation, and we will explain them from simplest to complex:	1621	operation, and we will explain them from simplest to most complex:
551
552		1622
553	=over 4	1623	=over 4
554		1624
555	=item * absolute timer (interval = reschedule_cb = 0)	1625	=item * absolute timer (at = time, interval = reschedule_cb = 0)
556		1626
557	In this configuration the watcher triggers an event at the wallclock time	1627	In this configuration the watcher triggers an event after the wall clock
558	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1628	time C<at> has passed. It will not repeat and will not adjust when a time
559	that is, if it is to be run at January 1st 2011 then it will run when the	1629	jump occurs, that is, if it is to be run at January 1st 2011 then it will
560	system time reaches or surpasses this time.	1630	only run when the system clock reaches or surpasses this time.
561		1631
562	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1632	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
563		1633
564	In this mode the watcher will always be scheduled to time out at the next	1634	In this mode the watcher will always be scheduled to time out at the next
565	C<at + N * interval> time (for some integer N) and then repeat, regardless	1635	C<at + N * interval> time (for some integer N, which can also be negative)
566	of any time jumps.	1636	and then repeat, regardless of any time jumps.
567		1637
568	This can be used to create timers that do not drift with respect to system	1638	This can be used to create timers that do not drift with respect to the
569	time:	1639	system clock, for example, here is a C<ev_periodic> that triggers each
		1640	hour, on the hour:
570		1641
571	ev_periodic_set (&periodic, 0., 3600., 0);	1642	ev_periodic_set (&periodic, 0., 3600., 0);
572		1643
573	This doesn't mean there will always be 3600 seconds in between triggers,	1644	This doesn't mean there will always be 3600 seconds in between triggers,
574	but only that the the callback will be called when the system time shows a	1645	but only that the callback will be called when the system time shows a
575	full hour (UTC), or more correctly, when the system time is evenly divisible	1646	full hour (UTC), or more correctly, when the system time is evenly divisible
576	by 3600.	1647	by 3600.
577		1648
578	Another way to think about it (for the mathematically inclined) is that	1649	Another way to think about it (for the mathematically inclined) is that
579	C<ev_periodic> will try to run the callback in this mode at the next possible	1650	C<ev_periodic> will try to run the callback in this mode at the next possible
580	time where C<time = at (mod interval)>, regardless of any time jumps.	1651	time where C<time = at (mod interval)>, regardless of any time jumps.
581		1652
		1653	For numerical stability it is preferable that the C<at> value is near
		1654	C<ev_now ()> (the current time), but there is no range requirement for
		1655	this value, and in fact is often specified as zero.
		1656
		1657	Note also that there is an upper limit to how often a timer can fire (CPU
		1658	speed for example), so if C<interval> is very small then timing stability
		1659	will of course deteriorate. Libev itself tries to be exact to be about one
		1660	millisecond (if the OS supports it and the machine is fast enough).
		1661
582	=item * manual reschedule mode (reschedule_cb = callback)	1662	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
583		1663
584	In this mode the values for C<interval> and C<at> are both being	1664	In this mode the values for C<interval> and C<at> are both being
585	ignored. Instead, each time the periodic watcher gets scheduled, the	1665	ignored. Instead, each time the periodic watcher gets scheduled, the
586	reschedule callback will be called with the watcher as first, and the	1666	reschedule callback will be called with the watcher as first, and the
587	current time as second argument.	1667	current time as second argument.
588		1668
589	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1669	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
590	ever, or make any event loop modifications>. If you need to stop it,	1670	ever, or make ANY event loop modifications whatsoever>.
591	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
592	starting a prepare watcher).
593		1671
		1672	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1673	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1674	only event loop modification you are allowed to do).
		1675
594	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1676	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
595	ev_tstamp now)>, e.g.:	1677	*w, ev_tstamp now)>, e.g.:
596		1678
		1679	static ev_tstamp
597	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1680	my_rescheduler (ev_periodic *w, ev_tstamp now)
598	{	1681	{
599	return now + 60.;	1682	return now + 60.;
600	}	1683	}
601		1684
602	It must return the next time to trigger, based on the passed time value	1685	It must return the next time to trigger, based on the passed time value
603	(that is, the lowest time value larger than to the second argument). It	1686	(that is, the lowest time value larger than to the second argument). It
604	will usually be called just before the callback will be triggered, but	1687	will usually be called just before the callback will be triggered, but
605	might be called at other times, too.	1688	might be called at other times, too.
606		1689
607	NOTE: I<< This callback must always return a time that is later than the	1690	NOTE: I<< This callback must always return a time that is higher than or
608	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1691	equal to the passed C<now> value >>.
609		1692
610	This can be used to create very complex timers, such as a timer that	1693	This can be used to create very complex timers, such as a timer that
611	triggers on each midnight, local time. To do this, you would calculate the	1694	triggers on "next midnight, local time". To do this, you would calculate the
612	next midnight after C<now> and return the timestamp value for this. How	1695	next midnight after C<now> and return the timestamp value for this. How
613	you do this is, again, up to you (but it is not trivial, which is the main	1696	you do this is, again, up to you (but it is not trivial, which is the main
614	reason I omitted it as an example).	1697	reason I omitted it as an example).
615		1698
616	=back	1699	=back
…		…
620	Simply stops and restarts the periodic watcher again. This is only useful	1703	Simply stops and restarts the periodic watcher again. This is only useful
621	when you changed some parameters or the reschedule callback would return	1704	when you changed some parameters or the reschedule callback would return
622	a different time than the last time it was called (e.g. in a crond like	1705	a different time than the last time it was called (e.g. in a crond like
623	program when the crontabs have changed).	1706	program when the crontabs have changed).
624		1707
		1708	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1709
		1710	When active, returns the absolute time that the watcher is supposed to
		1711	trigger next.
		1712
		1713	=item ev_tstamp offset [read-write]
		1714
		1715	When repeating, this contains the offset value, otherwise this is the
		1716	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1717
		1718	Can be modified any time, but changes only take effect when the periodic
		1719	timer fires or C<ev_periodic_again> is being called.
		1720
		1721	=item ev_tstamp interval [read-write]
		1722
		1723	The current interval value. Can be modified any time, but changes only
		1724	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1725	called.
		1726
		1727	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		1728
		1729	The current reschedule callback, or C<0>, if this functionality is
		1730	switched off. Can be changed any time, but changes only take effect when
		1731	the periodic timer fires or C<ev_periodic_again> is being called.
		1732
625	=back	1733	=back
626		1734
		1735	=head3 Examples
		1736
		1737	Example: Call a callback every hour, or, more precisely, whenever the
		1738	system time is divisible by 3600. The callback invocation times have
		1739	potentially a lot of jitter, but good long-term stability.
		1740
		1741	static void
		1742	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
		1743	{
		1744	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1745	}
		1746
		1747	ev_periodic hourly_tick;
		1748	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1749	ev_periodic_start (loop, &hourly_tick);
		1750
		1751	Example: The same as above, but use a reschedule callback to do it:
		1752
		1753	#include <math.h>
		1754
		1755	static ev_tstamp
		1756	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		1757	{
		1758	return now + (3600. - fmod (now, 3600.));
		1759	}
		1760
		1761	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1762
		1763	Example: Call a callback every hour, starting now:
		1764
		1765	ev_periodic hourly_tick;
		1766	ev_periodic_init (&hourly_tick, clock_cb,
		1767	fmod (ev_now (loop), 3600.), 3600., 0);
		1768	ev_periodic_start (loop, &hourly_tick);
		1769
		1770
627	=head2 C<ev_signal> - signal me when a signal gets signalled	1771	=head2 C<ev_signal> - signal me when a signal gets signalled!
628		1772
629	Signal watchers will trigger an event when the process receives a specific	1773	Signal watchers will trigger an event when the process receives a specific
630	signal one or more times. Even though signals are very asynchronous, libev	1774	signal one or more times. Even though signals are very asynchronous, libev
631	will try it's best to deliver signals synchronously, i.e. as part of the	1775	will try it's best to deliver signals synchronously, i.e. as part of the
632	normal event processing, like any other event.	1776	normal event processing, like any other event.
633		1777
		1778	If you want signals asynchronously, just use C<sigaction> as you would
		1779	do without libev and forget about sharing the signal. You can even use
		1780	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1781
634	You can configure as many watchers as you like per signal. Only when the	1782	You can configure as many watchers as you like per signal. Only when the
635	first watcher gets started will libev actually register a signal watcher	1783	first watcher gets started will libev actually register a signal handler
636	with the kernel (thus it coexists with your own signal handlers as long	1784	with the kernel (thus it coexists with your own signal handlers as long as
637	as you don't register any with libev). Similarly, when the last signal	1785	you don't register any with libev for the same signal). Similarly, when
638	watcher for a signal is stopped libev will reset the signal handler to	1786	the last signal watcher for a signal is stopped, libev will reset the
639	SIG_DFL (regardless of what it was set to before).	1787	signal handler to SIG_DFL (regardless of what it was set to before).
		1788
		1789	If possible and supported, libev will install its handlers with
		1790	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1791	interrupted. If you have a problem with system calls getting interrupted by
		1792	signals you can block all signals in an C<ev_check> watcher and unblock
		1793	them in an C<ev_prepare> watcher.
		1794
		1795	=head3 Watcher-Specific Functions and Data Members
640		1796
641	=over 4	1797	=over 4
642		1798
643	=item ev_signal_init (ev_signal *, callback, int signum)	1799	=item ev_signal_init (ev_signal *, callback, int signum)
644		1800
645	=item ev_signal_set (ev_signal *, int signum)	1801	=item ev_signal_set (ev_signal *, int signum)
646		1802
647	Configures the watcher to trigger on the given signal number (usually one	1803	Configures the watcher to trigger on the given signal number (usually one
648	of the C<SIGxxx> constants).	1804	of the C<SIGxxx> constants).
649		1805
		1806	=item int signum [read-only]
		1807
		1808	The signal the watcher watches out for.
		1809
650	=back	1810	=back
651		1811
		1812	=head3 Examples
		1813
		1814	Example: Try to exit cleanly on SIGINT.
		1815
		1816	static void
		1817	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1818	{
		1819	ev_unloop (loop, EVUNLOOP_ALL);
		1820	}
		1821
		1822	ev_signal signal_watcher;
		1823	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1824	ev_signal_start (loop, &signal_watcher);
		1825
		1826
652	=head2 C<ev_child> - wait for pid status changes	1827	=head2 C<ev_child> - watch out for process status changes
653		1828
654	Child watchers trigger when your process receives a SIGCHLD in response to	1829	Child watchers trigger when your process receives a SIGCHLD in response to
655	some child status changes (most typically when a child of yours dies).	1830	some child status changes (most typically when a child of yours dies or
		1831	exits). It is permissible to install a child watcher I<after> the child
		1832	has been forked (which implies it might have already exited), as long
		1833	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1834	forking and then immediately registering a watcher for the child is fine,
		1835	but forking and registering a watcher a few event loop iterations later is
		1836	not.
		1837
		1838	Only the default event loop is capable of handling signals, and therefore
		1839	you can only register child watchers in the default event loop.
		1840
		1841	=head3 Process Interaction
		1842
		1843	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1844	initialised. This is necessary to guarantee proper behaviour even if
		1845	the first child watcher is started after the child exits. The occurrence
		1846	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1847	synchronously as part of the event loop processing. Libev always reaps all
		1848	children, even ones not watched.
		1849
		1850	=head3 Overriding the Built-In Processing
		1851
		1852	Libev offers no special support for overriding the built-in child
		1853	processing, but if your application collides with libev's default child
		1854	handler, you can override it easily by installing your own handler for
		1855	C<SIGCHLD> after initialising the default loop, and making sure the
		1856	default loop never gets destroyed. You are encouraged, however, to use an
		1857	event-based approach to child reaping and thus use libev's support for
		1858	that, so other libev users can use C<ev_child> watchers freely.
		1859
		1860	=head3 Stopping the Child Watcher
		1861
		1862	Currently, the child watcher never gets stopped, even when the
		1863	child terminates, so normally one needs to stop the watcher in the
		1864	callback. Future versions of libev might stop the watcher automatically
		1865	when a child exit is detected.
		1866
		1867	=head3 Watcher-Specific Functions and Data Members
656		1868
657	=over 4	1869	=over 4
658		1870
659	=item ev_child_init (ev_child *, callback, int pid)	1871	=item ev_child_init (ev_child *, callback, int pid, int trace)
660		1872
661	=item ev_child_set (ev_child *, int pid)	1873	=item ev_child_set (ev_child *, int pid, int trace)
662		1874
663	Configures the watcher to wait for status changes of process C<pid> (or	1875	Configures the watcher to wait for status changes of process C<pid> (or
664	I<any> process if C<pid> is specified as C<0>). The callback can look	1876	I<any> process if C<pid> is specified as C<0>). The callback can look
665	at the C<rstatus> member of the C<ev_child> watcher structure to see	1877	at the C<rstatus> member of the C<ev_child> watcher structure to see
666	the status word (use the macros from C<sys/wait.h> and see your systems	1878	the status word (use the macros from C<sys/wait.h> and see your systems
667	C<waitpid> documentation). The C<rpid> member contains the pid of the	1879	C<waitpid> documentation). The C<rpid> member contains the pid of the
668	process causing the status change.	1880	process causing the status change. C<trace> must be either C<0> (only
		1881	activate the watcher when the process terminates) or C<1> (additionally
		1882	activate the watcher when the process is stopped or continued).
		1883
		1884	=item int pid [read-only]
		1885
		1886	The process id this watcher watches out for, or C<0>, meaning any process id.
		1887
		1888	=item int rpid [read-write]
		1889
		1890	The process id that detected a status change.
		1891
		1892	=item int rstatus [read-write]
		1893
		1894	The process exit/trace status caused by C<rpid> (see your systems
		1895	C<waitpid> and C<sys/wait.h> documentation for details).
669		1896
670	=back	1897	=back
671		1898
		1899	=head3 Examples
		1900
		1901	Example: C<fork()> a new process and install a child handler to wait for
		1902	its completion.
		1903
		1904	ev_child cw;
		1905
		1906	static void
		1907	child_cb (EV_P_ ev_child *w, int revents)
		1908	{
		1909	ev_child_stop (EV_A_ w);
		1910	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1911	}
		1912
		1913	pid_t pid = fork ();
		1914
		1915	if (pid < 0)
		1916	// error
		1917	else if (pid == 0)
		1918	{
		1919	// the forked child executes here
		1920	exit (1);
		1921	}
		1922	else
		1923	{
		1924	ev_child_init (&cw, child_cb, pid, 0);
		1925	ev_child_start (EV_DEFAULT_ &cw);
		1926	}
		1927
		1928
		1929	=head2 C<ev_stat> - did the file attributes just change?
		1930
		1931	This watches a file system path for attribute changes. That is, it calls
		1932	C<stat> on that path in regular intervals (or when the OS says it changed)
		1933	and sees if it changed compared to the last time, invoking the callback if
		1934	it did.
		1935
		1936	The path does not need to exist: changing from "path exists" to "path does
		1937	not exist" is a status change like any other. The condition "path does not
		1938	exist" (or more correctly "path cannot be stat'ed") is signified by the
		1939	C<st_nlink> field being zero (which is otherwise always forced to be at
		1940	least one) and all the other fields of the stat buffer having unspecified
		1941	contents.
		1942
		1943	The path I<must not> end in a slash or contain special components such as
		1944	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		1945	your working directory changes, then the behaviour is undefined.
		1946
		1947	Since there is no portable change notification interface available, the
		1948	portable implementation simply calls C<stat(2)> regularly on the path
		1949	to see if it changed somehow. You can specify a recommended polling
		1950	interval for this case. If you specify a polling interval of C<0> (highly
		1951	recommended!) then a I<suitable, unspecified default> value will be used
		1952	(which you can expect to be around five seconds, although this might
		1953	change dynamically). Libev will also impose a minimum interval which is
		1954	currently around C<0.1>, but that's usually overkill.
		1955
		1956	This watcher type is not meant for massive numbers of stat watchers,
		1957	as even with OS-supported change notifications, this can be
		1958	resource-intensive.
		1959
		1960	At the time of this writing, the only OS-specific interface implemented
		1961	is the Linux inotify interface (implementing kqueue support is left as an
		1962	exercise for the reader. Note, however, that the author sees no way of
		1963	implementing C<ev_stat> semantics with kqueue, except as a hint).
		1964
		1965	=head3 ABI Issues (Largefile Support)
		1966
		1967	Libev by default (unless the user overrides this) uses the default
		1968	compilation environment, which means that on systems with large file
		1969	support disabled by default, you get the 32 bit version of the stat
		1970	structure. When using the library from programs that change the ABI to
		1971	use 64 bit file offsets the programs will fail. In that case you have to
		1972	compile libev with the same flags to get binary compatibility. This is
		1973	obviously the case with any flags that change the ABI, but the problem is
		1974	most noticeably displayed with ev_stat and large file support.
		1975
		1976	The solution for this is to lobby your distribution maker to make large
		1977	file interfaces available by default (as e.g. FreeBSD does) and not
		1978	optional. Libev cannot simply switch on large file support because it has
		1979	to exchange stat structures with application programs compiled using the
		1980	default compilation environment.
		1981
		1982	=head3 Inotify and Kqueue
		1983
		1984	When C<inotify (7)> support has been compiled into libev and present at
		1985	runtime, it will be used to speed up change detection where possible. The
		1986	inotify descriptor will be created lazily when the first C<ev_stat>
		1987	watcher is being started.
		1988
		1989	Inotify presence does not change the semantics of C<ev_stat> watchers
		1990	except that changes might be detected earlier, and in some cases, to avoid
		1991	making regular C<stat> calls. Even in the presence of inotify support
		1992	there are many cases where libev has to resort to regular C<stat> polling,
		1993	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		1994	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		1995	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		1996	xfs are fully working) libev usually gets away without polling.
		1997
		1998	There is no support for kqueue, as apparently it cannot be used to
		1999	implement this functionality, due to the requirement of having a file
		2000	descriptor open on the object at all times, and detecting renames, unlinks
		2001	etc. is difficult.
		2002
		2003	=head3 C<stat ()> is a synchronous operation
		2004
		2005	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2006	the process. The exception are C<ev_stat> watchers - those call C<stat
		2007	()>, which is a synchronous operation.
		2008
		2009	For local paths, this usually doesn't matter: unless the system is very
		2010	busy or the intervals between stat's are large, a stat call will be fast,
		2011	as the path data is suually in memory already (except when starting the
		2012	watcher).
		2013
		2014	For networked file systems, calling C<stat ()> can block an indefinite
		2015	time due to network issues, and even under good conditions, a stat call
		2016	often takes multiple milliseconds.
		2017
		2018	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2019	paths, although this is fully supported by libev.
		2020
		2021	=head3 The special problem of stat time resolution
		2022
		2023	The C<stat ()> system call only supports full-second resolution portably,
		2024	and even on systems where the resolution is higher, most file systems
		2025	still only support whole seconds.
		2026
		2027	That means that, if the time is the only thing that changes, you can
		2028	easily miss updates: on the first update, C<ev_stat> detects a change and
		2029	calls your callback, which does something. When there is another update
		2030	within the same second, C<ev_stat> will be unable to detect unless the
		2031	stat data does change in other ways (e.g. file size).
		2032
		2033	The solution to this is to delay acting on a change for slightly more
		2034	than a second (or till slightly after the next full second boundary), using
		2035	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2036	ev_timer_again (loop, w)>).
		2037
		2038	The C<.02> offset is added to work around small timing inconsistencies
		2039	of some operating systems (where the second counter of the current time
		2040	might be be delayed. One such system is the Linux kernel, where a call to
		2041	C<gettimeofday> might return a timestamp with a full second later than
		2042	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2043	update file times then there will be a small window where the kernel uses
		2044	the previous second to update file times but libev might already execute
		2045	the timer callback).
		2046
		2047	=head3 Watcher-Specific Functions and Data Members
		2048
		2049	=over 4
		2050
		2051	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2052
		2053	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2054
		2055	Configures the watcher to wait for status changes of the given
		2056	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2057	be detected and should normally be specified as C<0> to let libev choose
		2058	a suitable value. The memory pointed to by C<path> must point to the same
		2059	path for as long as the watcher is active.
		2060
		2061	The callback will receive an C<EV_STAT> event when a change was detected,
		2062	relative to the attributes at the time the watcher was started (or the
		2063	last change was detected).
		2064
		2065	=item ev_stat_stat (loop, ev_stat *)
		2066
		2067	Updates the stat buffer immediately with new values. If you change the
		2068	watched path in your callback, you could call this function to avoid
		2069	detecting this change (while introducing a race condition if you are not
		2070	the only one changing the path). Can also be useful simply to find out the
		2071	new values.
		2072
		2073	=item ev_statdata attr [read-only]
		2074
		2075	The most-recently detected attributes of the file. Although the type is
		2076	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2077	suitable for your system, but you can only rely on the POSIX-standardised
		2078	members to be present. If the C<st_nlink> member is C<0>, then there was
		2079	some error while C<stat>ing the file.
		2080
		2081	=item ev_statdata prev [read-only]
		2082
		2083	The previous attributes of the file. The callback gets invoked whenever
		2084	C<prev> != C<attr>, or, more precisely, one or more of these members
		2085	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2086	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2087
		2088	=item ev_tstamp interval [read-only]
		2089
		2090	The specified interval.
		2091
		2092	=item const char *path [read-only]
		2093
		2094	The file system path that is being watched.
		2095
		2096	=back
		2097
		2098	=head3 Examples
		2099
		2100	Example: Watch C</etc/passwd> for attribute changes.
		2101
		2102	static void
		2103	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2104	{
		2105	/* /etc/passwd changed in some way */
		2106	if (w->attr.st_nlink)
		2107	{
		2108	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2109	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2110	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2111	}
		2112	else
		2113	/* you shalt not abuse printf for puts */
		2114	puts ("wow, /etc/passwd is not there, expect problems. "
		2115	"if this is windows, they already arrived\n");
		2116	}
		2117
		2118	...
		2119	ev_stat passwd;
		2120
		2121	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2122	ev_stat_start (loop, &passwd);
		2123
		2124	Example: Like above, but additionally use a one-second delay so we do not
		2125	miss updates (however, frequent updates will delay processing, too, so
		2126	one might do the work both on C<ev_stat> callback invocation I<and> on
		2127	C<ev_timer> callback invocation).
		2128
		2129	static ev_stat passwd;
		2130	static ev_timer timer;
		2131
		2132	static void
		2133	timer_cb (EV_P_ ev_timer *w, int revents)
		2134	{
		2135	ev_timer_stop (EV_A_ w);
		2136
		2137	/* now it's one second after the most recent passwd change */
		2138	}
		2139
		2140	static void
		2141	stat_cb (EV_P_ ev_stat *w, int revents)
		2142	{
		2143	/* reset the one-second timer */
		2144	ev_timer_again (EV_A_ &timer);
		2145	}
		2146
		2147	...
		2148	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2149	ev_stat_start (loop, &passwd);
		2150	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2151
		2152
672	=head2 C<ev_idle> - when you've got nothing better to do	2153	=head2 C<ev_idle> - when you've got nothing better to do...
673		2154
674	Idle watchers trigger events when there are no other events are pending	2155	Idle watchers trigger events when no other events of the same or higher
675	(prepare, check and other idle watchers do not count). That is, as long	2156	priority are pending (prepare, check and other idle watchers do not count
676	as your process is busy handling sockets or timeouts (or even signals,	2157	as receiving "events").
677	imagine) it will not be triggered. But when your process is idle all idle	2158
678	watchers are being called again and again, once per event loop iteration -	2159	That is, as long as your process is busy handling sockets or timeouts
		2160	(or even signals, imagine) of the same or higher priority it will not be
		2161	triggered. But when your process is idle (or only lower-priority watchers
		2162	are pending), the idle watchers are being called once per event loop
679	until stopped, that is, or your process receives more events and becomes	2163	iteration - until stopped, that is, or your process receives more events
680	busy.	2164	and becomes busy again with higher priority stuff.
681		2165
682	The most noteworthy effect is that as long as any idle watchers are	2166	The most noteworthy effect is that as long as any idle watchers are
683	active, the process will not block when waiting for new events.	2167	active, the process will not block when waiting for new events.
684		2168
685	Apart from keeping your process non-blocking (which is a useful	2169	Apart from keeping your process non-blocking (which is a useful
686	effect on its own sometimes), idle watchers are a good place to do	2170	effect on its own sometimes), idle watchers are a good place to do
687	"pseudo-background processing", or delay processing stuff to after the	2171	"pseudo-background processing", or delay processing stuff to after the
688	event loop has handled all outstanding events.	2172	event loop has handled all outstanding events.
689		2173
		2174	=head3 Watcher-Specific Functions and Data Members
		2175
690	=over 4	2176	=over 4
691		2177
692	=item ev_idle_init (ev_signal *, callback)	2178	=item ev_idle_init (ev_signal *, callback)
693		2179
694	Initialises and configures the idle watcher - it has no parameters of any	2180	Initialises and configures the idle watcher - it has no parameters of any
695	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2181	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
696	believe me.	2182	believe me.
697		2183
698	=back	2184	=back
699		2185
		2186	=head3 Examples
		2187
		2188	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2189	callback, free it. Also, use no error checking, as usual.
		2190
		2191	static void
		2192	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2193	{
		2194	free (w);
		2195	// now do something you wanted to do when the program has
		2196	// no longer anything immediate to do.
		2197	}
		2198
		2199	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2200	ev_idle_init (idle_watcher, idle_cb);
		2201	ev_idle_start (loop, idle_cb);
		2202
		2203
700	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2204	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
701		2205
702	Prepare and check watchers are usually (but not always) used in tandem:	2206	Prepare and check watchers are usually (but not always) used in pairs:
703	prepare watchers get invoked before the process blocks and check watchers	2207	prepare watchers get invoked before the process blocks and check watchers
704	afterwards.	2208	afterwards.
705		2209
		2210	You I<must not> call C<ev_loop> or similar functions that enter
		2211	the current event loop from either C<ev_prepare> or C<ev_check>
		2212	watchers. Other loops than the current one are fine, however. The
		2213	rationale behind this is that you do not need to check for recursion in
		2214	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2215	C<ev_check> so if you have one watcher of each kind they will always be
		2216	called in pairs bracketing the blocking call.
		2217
706	Their main purpose is to integrate other event mechanisms into libev. This	2218	Their main purpose is to integrate other event mechanisms into libev and
707	could be used, for example, to track variable changes, implement your own	2219	their use is somewhat advanced. They could be used, for example, to track
708	watchers, integrate net-snmp or a coroutine library and lots more.	2220	variable changes, implement your own watchers, integrate net-snmp or a
		2221	coroutine library and lots more. They are also occasionally useful if
		2222	you cache some data and want to flush it before blocking (for example,
		2223	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2224	watcher).
709		2225
710	This is done by examining in each prepare call which file descriptors need	2226	This is done by examining in each prepare call which file descriptors
711	to be watched by the other library, registering C<ev_io> watchers for	2227	need to be watched by the other library, registering C<ev_io> watchers
712	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2228	for them and starting an C<ev_timer> watcher for any timeouts (many
713	provide just this functionality). Then, in the check watcher you check for	2229	libraries provide exactly this functionality). Then, in the check watcher,
714	any events that occured (by checking the pending status of all watchers	2230	you check for any events that occurred (by checking the pending status
715	and stopping them) and call back into the library. The I/O and timer	2231	of all watchers and stopping them) and call back into the library. The
716	callbacks will never actually be called (but must be valid nevertheless,	2232	I/O and timer callbacks will never actually be called (but must be valid
717	because you never know, you know?).	2233	nevertheless, because you never know, you know?).
718		2234
719	As another example, the Perl Coro module uses these hooks to integrate	2235	As another example, the Perl Coro module uses these hooks to integrate
720	coroutines into libev programs, by yielding to other active coroutines	2236	coroutines into libev programs, by yielding to other active coroutines
721	during each prepare and only letting the process block if no coroutines	2237	during each prepare and only letting the process block if no coroutines
722	are ready to run (it's actually more complicated: it only runs coroutines	2238	are ready to run (it's actually more complicated: it only runs coroutines
723	with priority higher than or equal to the event loop and one coroutine	2239	with priority higher than or equal to the event loop and one coroutine
724	of lower priority, but only once, using idle watchers to keep the event	2240	of lower priority, but only once, using idle watchers to keep the event
725	loop from blocking if lower-priority coroutines are active, thus mapping	2241	loop from blocking if lower-priority coroutines are active, thus mapping
726	low-priority coroutines to idle/background tasks).	2242	low-priority coroutines to idle/background tasks).
727		2243
		2244	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2245	priority, to ensure that they are being run before any other watchers
		2246	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2247
		2248	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2249	activate ("feed") events into libev. While libev fully supports this, they
		2250	might get executed before other C<ev_check> watchers did their job. As
		2251	C<ev_check> watchers are often used to embed other (non-libev) event
		2252	loops those other event loops might be in an unusable state until their
		2253	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2254	others).
		2255
		2256	=head3 Watcher-Specific Functions and Data Members
		2257
728	=over 4	2258	=over 4
729		2259
730	=item ev_prepare_init (ev_prepare *, callback)	2260	=item ev_prepare_init (ev_prepare *, callback)
731		2261
732	=item ev_check_init (ev_check *, callback)	2262	=item ev_check_init (ev_check *, callback)
733		2263
734	Initialises and configures the prepare or check watcher - they have no	2264	Initialises and configures the prepare or check watcher - they have no
735	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2265	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
736	macros, but using them is utterly, utterly and completely pointless.	2266	macros, but using them is utterly, utterly, utterly and completely
		2267	pointless.
737		2268
738	=back	2269	=back
739		2270
		2271	=head3 Examples
		2272
		2273	There are a number of principal ways to embed other event loops or modules
		2274	into libev. Here are some ideas on how to include libadns into libev
		2275	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2276	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2277	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2278	Glib event loop).
		2279
		2280	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2281	and in a check watcher, destroy them and call into libadns. What follows
		2282	is pseudo-code only of course. This requires you to either use a low
		2283	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2284	the callbacks for the IO/timeout watchers might not have been called yet.
		2285
		2286	static ev_io iow [nfd];
		2287	static ev_timer tw;
		2288
		2289	static void
		2290	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2291	{
		2292	}
		2293
		2294	// create io watchers for each fd and a timer before blocking
		2295	static void
		2296	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2297	{
		2298	int timeout = 3600000;
		2299	struct pollfd fds [nfd];
		2300	// actual code will need to loop here and realloc etc.
		2301	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2302
		2303	/* the callback is illegal, but won't be called as we stop during check */
		2304	ev_timer_init (&tw, 0, timeout * 1e-3);
		2305	ev_timer_start (loop, &tw);
		2306
		2307	// create one ev_io per pollfd
		2308	for (int i = 0; i < nfd; ++i)
		2309	{
		2310	ev_io_init (iow + i, io_cb, fds [i].fd,
		2311	((fds [i].events & POLLIN ? EV_READ : 0)
		2312	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2313
		2314	fds [i].revents = 0;
		2315	ev_io_start (loop, iow + i);
		2316	}
		2317	}
		2318
		2319	// stop all watchers after blocking
		2320	static void
		2321	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2322	{
		2323	ev_timer_stop (loop, &tw);
		2324
		2325	for (int i = 0; i < nfd; ++i)
		2326	{
		2327	// set the relevant poll flags
		2328	// could also call adns_processreadable etc. here
		2329	struct pollfd *fd = fds + i;
		2330	int revents = ev_clear_pending (iow + i);
		2331	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2332	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2333
		2334	// now stop the watcher
		2335	ev_io_stop (loop, iow + i);
		2336	}
		2337
		2338	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2339	}
		2340
		2341	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2342	in the prepare watcher and would dispose of the check watcher.
		2343
		2344	Method 3: If the module to be embedded supports explicit event
		2345	notification (libadns does), you can also make use of the actual watcher
		2346	callbacks, and only destroy/create the watchers in the prepare watcher.
		2347
		2348	static void
		2349	timer_cb (EV_P_ ev_timer *w, int revents)
		2350	{
		2351	adns_state ads = (adns_state)w->data;
		2352	update_now (EV_A);
		2353
		2354	adns_processtimeouts (ads, &tv_now);
		2355	}
		2356
		2357	static void
		2358	io_cb (EV_P_ ev_io *w, int revents)
		2359	{
		2360	adns_state ads = (adns_state)w->data;
		2361	update_now (EV_A);
		2362
		2363	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2364	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2365	}
		2366
		2367	// do not ever call adns_afterpoll
		2368
		2369	Method 4: Do not use a prepare or check watcher because the module you
		2370	want to embed is not flexible enough to support it. Instead, you can
		2371	override their poll function. The drawback with this solution is that the
		2372	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2373	this approach, effectively embedding EV as a client into the horrible
		2374	libglib event loop.
		2375
		2376	static gint
		2377	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2378	{
		2379	int got_events = 0;
		2380
		2381	for (n = 0; n < nfds; ++n)
		2382	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2383
		2384	if (timeout >= 0)
		2385	// create/start timer
		2386
		2387	// poll
		2388	ev_loop (EV_A_ 0);
		2389
		2390	// stop timer again
		2391	if (timeout >= 0)
		2392	ev_timer_stop (EV_A_ &to);
		2393
		2394	// stop io watchers again - their callbacks should have set
		2395	for (n = 0; n < nfds; ++n)
		2396	ev_io_stop (EV_A_ iow [n]);
		2397
		2398	return got_events;
		2399	}
		2400
		2401
		2402	=head2 C<ev_embed> - when one backend isn't enough...
		2403
		2404	This is a rather advanced watcher type that lets you embed one event loop
		2405	into another (currently only C<ev_io> events are supported in the embedded
		2406	loop, other types of watchers might be handled in a delayed or incorrect
		2407	fashion and must not be used).
		2408
		2409	There are primarily two reasons you would want that: work around bugs and
		2410	prioritise I/O.
		2411
		2412	As an example for a bug workaround, the kqueue backend might only support
		2413	sockets on some platform, so it is unusable as generic backend, but you
		2414	still want to make use of it because you have many sockets and it scales
		2415	so nicely. In this case, you would create a kqueue-based loop and embed
		2416	it into your default loop (which might use e.g. poll). Overall operation
		2417	will be a bit slower because first libev has to call C<poll> and then
		2418	C<kevent>, but at least you can use both mechanisms for what they are
		2419	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2420
		2421	As for prioritising I/O: under rare circumstances you have the case where
		2422	some fds have to be watched and handled very quickly (with low latency),
		2423	and even priorities and idle watchers might have too much overhead. In
		2424	this case you would put all the high priority stuff in one loop and all
		2425	the rest in a second one, and embed the second one in the first.
		2426
		2427	As long as the watcher is active, the callback will be invoked every time
		2428	there might be events pending in the embedded loop. The callback must then
		2429	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2430	their callbacks (you could also start an idle watcher to give the embedded
		2431	loop strictly lower priority for example). You can also set the callback
		2432	to C<0>, in which case the embed watcher will automatically execute the
		2433	embedded loop sweep.
		2434
		2435	As long as the watcher is started it will automatically handle events. The
		2436	callback will be invoked whenever some events have been handled. You can
		2437	set the callback to C<0> to avoid having to specify one if you are not
		2438	interested in that.
		2439
		2440	Also, there have not currently been made special provisions for forking:
		2441	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2442	but you will also have to stop and restart any C<ev_embed> watchers
		2443	yourself - but you can use a fork watcher to handle this automatically,
		2444	and future versions of libev might do just that.
		2445
		2446	Unfortunately, not all backends are embeddable: only the ones returned by
		2447	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2448	portable one.
		2449
		2450	So when you want to use this feature you will always have to be prepared
		2451	that you cannot get an embeddable loop. The recommended way to get around
		2452	this is to have a separate variables for your embeddable loop, try to
		2453	create it, and if that fails, use the normal loop for everything.
		2454
		2455	=head3 C<ev_embed> and fork
		2456
		2457	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2458	automatically be applied to the embedded loop as well, so no special
		2459	fork handling is required in that case. When the watcher is not running,
		2460	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2461	as applicable.
		2462
		2463	=head3 Watcher-Specific Functions and Data Members
		2464
		2465	=over 4
		2466
		2467	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2468
		2469	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2470
		2471	Configures the watcher to embed the given loop, which must be
		2472	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2473	invoked automatically, otherwise it is the responsibility of the callback
		2474	to invoke it (it will continue to be called until the sweep has been done,
		2475	if you do not want that, you need to temporarily stop the embed watcher).
		2476
		2477	=item ev_embed_sweep (loop, ev_embed *)
		2478
		2479	Make a single, non-blocking sweep over the embedded loop. This works
		2480	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2481	appropriate way for embedded loops.
		2482
		2483	=item struct ev_loop *other [read-only]
		2484
		2485	The embedded event loop.
		2486
		2487	=back
		2488
		2489	=head3 Examples
		2490
		2491	Example: Try to get an embeddable event loop and embed it into the default
		2492	event loop. If that is not possible, use the default loop. The default
		2493	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2494	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2495	used).
		2496
		2497	struct ev_loop *loop_hi = ev_default_init (0);
		2498	struct ev_loop *loop_lo = 0;
		2499	ev_embed embed;
		2500
		2501	// see if there is a chance of getting one that works
		2502	// (remember that a flags value of 0 means autodetection)
		2503	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2504	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2505	: 0;
		2506
		2507	// if we got one, then embed it, otherwise default to loop_hi
		2508	if (loop_lo)
		2509	{
		2510	ev_embed_init (&embed, 0, loop_lo);
		2511	ev_embed_start (loop_hi, &embed);
		2512	}
		2513	else
		2514	loop_lo = loop_hi;
		2515
		2516	Example: Check if kqueue is available but not recommended and create
		2517	a kqueue backend for use with sockets (which usually work with any
		2518	kqueue implementation). Store the kqueue/socket-only event loop in
		2519	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2520
		2521	struct ev_loop *loop = ev_default_init (0);
		2522	struct ev_loop *loop_socket = 0;
		2523	ev_embed embed;
		2524
		2525	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2526	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2527	{
		2528	ev_embed_init (&embed, 0, loop_socket);
		2529	ev_embed_start (loop, &embed);
		2530	}
		2531
		2532	if (!loop_socket)
		2533	loop_socket = loop;
		2534
		2535	// now use loop_socket for all sockets, and loop for everything else
		2536
		2537
		2538	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2539
		2540	Fork watchers are called when a C<fork ()> was detected (usually because
		2541	whoever is a good citizen cared to tell libev about it by calling
		2542	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2543	event loop blocks next and before C<ev_check> watchers are being called,
		2544	and only in the child after the fork. If whoever good citizen calling
		2545	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2546	handlers will be invoked, too, of course.
		2547
		2548	=head3 Watcher-Specific Functions and Data Members
		2549
		2550	=over 4
		2551
		2552	=item ev_fork_init (ev_signal *, callback)
		2553
		2554	Initialises and configures the fork watcher - it has no parameters of any
		2555	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2556	believe me.
		2557
		2558	=back
		2559
		2560
		2561	=head2 C<ev_async> - how to wake up another event loop
		2562
		2563	In general, you cannot use an C<ev_loop> from multiple threads or other
		2564	asynchronous sources such as signal handlers (as opposed to multiple event
		2565	loops - those are of course safe to use in different threads).
		2566
		2567	Sometimes, however, you need to wake up another event loop you do not
		2568	control, for example because it belongs to another thread. This is what
		2569	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2570	can signal it by calling C<ev_async_send>, which is thread- and signal
		2571	safe.
		2572
		2573	This functionality is very similar to C<ev_signal> watchers, as signals,
		2574	too, are asynchronous in nature, and signals, too, will be compressed
		2575	(i.e. the number of callback invocations may be less than the number of
		2576	C<ev_async_sent> calls).
		2577
		2578	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2579	just the default loop.
		2580
		2581	=head3 Queueing
		2582
		2583	C<ev_async> does not support queueing of data in any way. The reason
		2584	is that the author does not know of a simple (or any) algorithm for a
		2585	multiple-writer-single-reader queue that works in all cases and doesn't
		2586	need elaborate support such as pthreads.
		2587
		2588	That means that if you want to queue data, you have to provide your own
		2589	queue. But at least I can tell you how to implement locking around your
		2590	queue:
		2591
		2592	=over 4
		2593
		2594	=item queueing from a signal handler context
		2595
		2596	To implement race-free queueing, you simply add to the queue in the signal
		2597	handler but you block the signal handler in the watcher callback. Here is
		2598	an example that does that for some fictitious SIGUSR1 handler:
		2599
		2600	static ev_async mysig;
		2601
		2602	static void
		2603	sigusr1_handler (void)
		2604	{
		2605	sometype data;
		2606
		2607	// no locking etc.
		2608	queue_put (data);
		2609	ev_async_send (EV_DEFAULT_ &mysig);
		2610	}
		2611
		2612	static void
		2613	mysig_cb (EV_P_ ev_async *w, int revents)
		2614	{
		2615	sometype data;
		2616	sigset_t block, prev;
		2617
		2618	sigemptyset (&block);
		2619	sigaddset (&block, SIGUSR1);
		2620	sigprocmask (SIG_BLOCK, &block, &prev);
		2621
		2622	while (queue_get (&data))
		2623	process (data);
		2624
		2625	if (sigismember (&prev, SIGUSR1)
		2626	sigprocmask (SIG_UNBLOCK, &block, 0);
		2627	}
		2628
		2629	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2630	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2631	either...).
		2632
		2633	=item queueing from a thread context
		2634
		2635	The strategy for threads is different, as you cannot (easily) block
		2636	threads but you can easily preempt them, so to queue safely you need to
		2637	employ a traditional mutex lock, such as in this pthread example:
		2638
		2639	static ev_async mysig;
		2640	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2641
		2642	static void
		2643	otherthread (void)
		2644	{
		2645	// only need to lock the actual queueing operation
		2646	pthread_mutex_lock (&mymutex);
		2647	queue_put (data);
		2648	pthread_mutex_unlock (&mymutex);
		2649
		2650	ev_async_send (EV_DEFAULT_ &mysig);
		2651	}
		2652
		2653	static void
		2654	mysig_cb (EV_P_ ev_async *w, int revents)
		2655	{
		2656	pthread_mutex_lock (&mymutex);
		2657
		2658	while (queue_get (&data))
		2659	process (data);
		2660
		2661	pthread_mutex_unlock (&mymutex);
		2662	}
		2663
		2664	=back
		2665
		2666
		2667	=head3 Watcher-Specific Functions and Data Members
		2668
		2669	=over 4
		2670
		2671	=item ev_async_init (ev_async *, callback)
		2672
		2673	Initialises and configures the async watcher - it has no parameters of any
		2674	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2675	trust me.
		2676
		2677	=item ev_async_send (loop, ev_async *)
		2678
		2679	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2680	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2681	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2682	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2683	section below on what exactly this means).
		2684
		2685	This call incurs the overhead of a system call only once per loop iteration,
		2686	so while the overhead might be noticeable, it doesn't apply to repeated
		2687	calls to C<ev_async_send>.
		2688
		2689	=item bool = ev_async_pending (ev_async *)
		2690
		2691	Returns a non-zero value when C<ev_async_send> has been called on the
		2692	watcher but the event has not yet been processed (or even noted) by the
		2693	event loop.
		2694
		2695	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2696	the loop iterates next and checks for the watcher to have become active,
		2697	it will reset the flag again. C<ev_async_pending> can be used to very
		2698	quickly check whether invoking the loop might be a good idea.
		2699
		2700	Not that this does I<not> check whether the watcher itself is pending, only
		2701	whether it has been requested to make this watcher pending.
		2702
		2703	=back
		2704
		2705
740	=head1 OTHER FUNCTIONS	2706	=head1 OTHER FUNCTIONS
741		2707
742	There are some other functions of possible interest. Described. Here. Now.	2708	There are some other functions of possible interest. Described. Here. Now.
743		2709
744	=over 4	2710	=over 4
745		2711
746	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2712	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
747		2713
748	This function combines a simple timer and an I/O watcher, calls your	2714	This function combines a simple timer and an I/O watcher, calls your
749	callback on whichever event happens first and automatically stop both	2715	callback on whichever event happens first and automatically stops both
750	watchers. This is useful if you want to wait for a single event on an fd	2716	watchers. This is useful if you want to wait for a single event on an fd
751	or timeout without having to allocate/configure/start/stop/free one or	2717	or timeout without having to allocate/configure/start/stop/free one or
752	more watchers yourself.	2718	more watchers yourself.
753		2719
754	If C<fd> is less than 0, then no I/O watcher will be started and events	2720	If C<fd> is less than 0, then no I/O watcher will be started and the
755	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2721	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
756	C<events> set will be craeted and started.	2722	the given C<fd> and C<events> set will be created and started.
757		2723
758	If C<timeout> is less than 0, then no timeout watcher will be	2724	If C<timeout> is less than 0, then no timeout watcher will be
759	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2725	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
760	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2726	repeat = 0) will be started. C<0> is a valid timeout.
761	dubious value.
762		2727
763	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2728	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
764	passed an C<revents> set like normal event callbacks (a combination of	2729	passed an C<revents> set like normal event callbacks (a combination of
765	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2730	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
766	value passed to C<ev_once>:	2731	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2732	a timeout and an io event at the same time - you probably should give io
		2733	events precedence.
767		2734
		2735	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2736
768	static void stdin_ready (int revents, void *arg)	2737	static void stdin_ready (int revents, void *arg)
769	{	2738	{
770	if (revents & EV_TIMEOUT)
771	/* doh, nothing entered */;
772	else if (revents & EV_READ)	2739	if (revents & EV_READ)
773	/* stdin might have data for us, joy! */;	2740	/* stdin might have data for us, joy! */;
		2741	else if (revents & EV_TIMEOUT)
		2742	/* doh, nothing entered */;
774	}	2743	}
775		2744
776	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2745	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
777		2746
778	=item ev_feed_event (loop, watcher, int events)	2747	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
779		2748
780	Feeds the given event set into the event loop, as if the specified event	2749	Feeds the given event set into the event loop, as if the specified event
781	had happened for the specified watcher (which must be a pointer to an	2750	had happened for the specified watcher (which must be a pointer to an
782	initialised but not necessarily started event watcher).	2751	initialised but not necessarily started event watcher).
783		2752
784	=item ev_feed_fd_event (loop, int fd, int revents)	2753	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
785		2754
786	Feed an event on the given fd, as if a file descriptor backend detected	2755	Feed an event on the given fd, as if a file descriptor backend detected
787	the given events it.	2756	the given events it.
788		2757
789	=item ev_feed_signal_event (loop, int signum)	2758	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
790		2759
791	Feed an event as if the given signal occured (loop must be the default loop!).	2760	Feed an event as if the given signal occurred (C<loop> must be the default
		2761	loop!).
792		2762
793	=back	2763	=back
		2764
794		2765
795	=head1 LIBEVENT EMULATION	2766	=head1 LIBEVENT EMULATION
796		2767
797	Libev offers a compatibility emulation layer for libevent. It cannot	2768	Libev offers a compatibility emulation layer for libevent. It cannot
798	emulate the internals of libevent, so here are some usage hints:	2769	emulate the internals of libevent, so here are some usage hints:
…		…
810		2781
811	=item * Priorities are not currently supported. Initialising priorities	2782	=item * Priorities are not currently supported. Initialising priorities
812	will fail and all watchers will have the same priority, even though there	2783	will fail and all watchers will have the same priority, even though there
813	is an ev_pri field.	2784	is an ev_pri field.
814		2785
		2786	=item * In libevent, the last base created gets the signals, in libev, the
		2787	first base created (== the default loop) gets the signals.
		2788
815	=item * Other members are not supported.	2789	=item * Other members are not supported.
816		2790
817	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2791	=item * The libev emulation is I<not> ABI compatible to libevent, you need
818	to use the libev header file and library.	2792	to use the libev header file and library.
819		2793
820	=back	2794	=back
821		2795
822	=head1 C++ SUPPORT	2796	=head1 C++ SUPPORT
823		2797
824	TBD.	2798	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2799	you to use some convenience methods to start/stop watchers and also change
		2800	the callback model to a model using method callbacks on objects.
		2801
		2802	To use it,
		2803
		2804	#include <ev++.h>
		2805
		2806	This automatically includes F<ev.h> and puts all of its definitions (many
		2807	of them macros) into the global namespace. All C++ specific things are
		2808	put into the C<ev> namespace. It should support all the same embedding
		2809	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2810
		2811	Care has been taken to keep the overhead low. The only data member the C++
		2812	classes add (compared to plain C-style watchers) is the event loop pointer
		2813	that the watcher is associated with (or no additional members at all if
		2814	you disable C<EV_MULTIPLICITY> when embedding libev).
		2815
		2816	Currently, functions, and static and non-static member functions can be
		2817	used as callbacks. Other types should be easy to add as long as they only
		2818	need one additional pointer for context. If you need support for other
		2819	types of functors please contact the author (preferably after implementing
		2820	it).
		2821
		2822	Here is a list of things available in the C<ev> namespace:
		2823
		2824	=over 4
		2825
		2826	=item C<ev::READ>, C<ev::WRITE> etc.
		2827
		2828	These are just enum values with the same values as the C<EV_READ> etc.
		2829	macros from F<ev.h>.
		2830
		2831	=item C<ev::tstamp>, C<ev::now>
		2832
		2833	Aliases to the same types/functions as with the C<ev_> prefix.
		2834
		2835	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2836
		2837	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2838	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2839	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2840	defines by many implementations.
		2841
		2842	All of those classes have these methods:
		2843
		2844	=over 4
		2845
		2846	=item ev::TYPE::TYPE ()
		2847
		2848	=item ev::TYPE::TYPE (struct ev_loop *)
		2849
		2850	=item ev::TYPE::~TYPE
		2851
		2852	The constructor (optionally) takes an event loop to associate the watcher
		2853	with. If it is omitted, it will use C<EV_DEFAULT>.
		2854
		2855	The constructor calls C<ev_init> for you, which means you have to call the
		2856	C<set> method before starting it.
		2857
		2858	It will not set a callback, however: You have to call the templated C<set>
		2859	method to set a callback before you can start the watcher.
		2860
		2861	(The reason why you have to use a method is a limitation in C++ which does
		2862	not allow explicit template arguments for constructors).
		2863
		2864	The destructor automatically stops the watcher if it is active.
		2865
		2866	=item w->set<class, &class::method> (object *)
		2867
		2868	This method sets the callback method to call. The method has to have a
		2869	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2870	first argument and the C<revents> as second. The object must be given as
		2871	parameter and is stored in the C<data> member of the watcher.
		2872
		2873	This method synthesizes efficient thunking code to call your method from
		2874	the C callback that libev requires. If your compiler can inline your
		2875	callback (i.e. it is visible to it at the place of the C<set> call and
		2876	your compiler is good :), then the method will be fully inlined into the
		2877	thunking function, making it as fast as a direct C callback.
		2878
		2879	Example: simple class declaration and watcher initialisation
		2880
		2881	struct myclass
		2882	{
		2883	void io_cb (ev::io &w, int revents) { }
		2884	}
		2885
		2886	myclass obj;
		2887	ev::io iow;
		2888	iow.set <myclass, &myclass::io_cb> (&obj);
		2889
		2890	=item w->set<function> (void *data = 0)
		2891
		2892	Also sets a callback, but uses a static method or plain function as
		2893	callback. The optional C<data> argument will be stored in the watcher's
		2894	C<data> member and is free for you to use.
		2895
		2896	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2897
		2898	See the method-C<set> above for more details.
		2899
		2900	Example: Use a plain function as callback.
		2901
		2902	static void io_cb (ev::io &w, int revents) { }
		2903	iow.set <io_cb> ();
		2904
		2905	=item w->set (struct ev_loop *)
		2906
		2907	Associates a different C<struct ev_loop> with this watcher. You can only
		2908	do this when the watcher is inactive (and not pending either).
		2909
		2910	=item w->set ([arguments])
		2911
		2912	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2913	called at least once. Unlike the C counterpart, an active watcher gets
		2914	automatically stopped and restarted when reconfiguring it with this
		2915	method.
		2916
		2917	=item w->start ()
		2918
		2919	Starts the watcher. Note that there is no C<loop> argument, as the
		2920	constructor already stores the event loop.
		2921
		2922	=item w->stop ()
		2923
		2924	Stops the watcher if it is active. Again, no C<loop> argument.
		2925
		2926	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2927
		2928	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2929	C<ev_TYPE_again> function.
		2930
		2931	=item w->sweep () (C<ev::embed> only)
		2932
		2933	Invokes C<ev_embed_sweep>.
		2934
		2935	=item w->update () (C<ev::stat> only)
		2936
		2937	Invokes C<ev_stat_stat>.
		2938
		2939	=back
		2940
		2941	=back
		2942
		2943	Example: Define a class with an IO and idle watcher, start one of them in
		2944	the constructor.
		2945
		2946	class myclass
		2947	{
		2948	ev::io io ; void io_cb (ev::io &w, int revents);
		2949	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		2950
		2951	myclass (int fd)
		2952	{
		2953	io .set <myclass, &myclass::io_cb > (this);
		2954	idle.set <myclass, &myclass::idle_cb> (this);
		2955
		2956	io.start (fd, ev::READ);
		2957	}
		2958	};
		2959
		2960
		2961	=head1 OTHER LANGUAGE BINDINGS
		2962
		2963	Libev does not offer other language bindings itself, but bindings for a
		2964	number of languages exist in the form of third-party packages. If you know
		2965	any interesting language binding in addition to the ones listed here, drop
		2966	me a note.
		2967
		2968	=over 4
		2969
		2970	=item Perl
		2971
		2972	The EV module implements the full libev API and is actually used to test
		2973	libev. EV is developed together with libev. Apart from the EV core module,
		2974	there are additional modules that implement libev-compatible interfaces
		2975	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2976	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2977	and C<EV::Glib>).
		2978
		2979	It can be found and installed via CPAN, its homepage is at
		2980	L<http://software.schmorp.de/pkg/EV>.
		2981
		2982	=item Python
		2983
		2984	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2985	seems to be quite complete and well-documented. Note, however, that the
		2986	patch they require for libev is outright dangerous as it breaks the ABI
		2987	for everybody else, and therefore, should never be applied in an installed
		2988	libev (if python requires an incompatible ABI then it needs to embed
		2989	libev).
		2990
		2991	=item Ruby
		2992
		2993	Tony Arcieri has written a ruby extension that offers access to a subset
		2994	of the libev API and adds file handle abstractions, asynchronous DNS and
		2995	more on top of it. It can be found via gem servers. Its homepage is at
		2996	L<http://rev.rubyforge.org/>.
		2997
		2998	=item D
		2999
		3000	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3001	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3002
		3003	=item Ocaml
		3004
		3005	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3006	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3007
		3008	=back
		3009
		3010
		3011	=head1 MACRO MAGIC
		3012
		3013	Libev can be compiled with a variety of options, the most fundamental
		3014	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3015	functions and callbacks have an initial C<struct ev_loop *> argument.
		3016
		3017	To make it easier to write programs that cope with either variant, the
		3018	following macros are defined:
		3019
		3020	=over 4
		3021
		3022	=item C<EV_A>, C<EV_A_>
		3023
		3024	This provides the loop I<argument> for functions, if one is required ("ev
		3025	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3026	C<EV_A_> is used when other arguments are following. Example:
		3027
		3028	ev_unref (EV_A);
		3029	ev_timer_add (EV_A_ watcher);
		3030	ev_loop (EV_A_ 0);
		3031
		3032	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3033	which is often provided by the following macro.
		3034
		3035	=item C<EV_P>, C<EV_P_>
		3036
		3037	This provides the loop I<parameter> for functions, if one is required ("ev
		3038	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3039	C<EV_P_> is used when other parameters are following. Example:
		3040
		3041	// this is how ev_unref is being declared
		3042	static void ev_unref (EV_P);
		3043
		3044	// this is how you can declare your typical callback
		3045	static void cb (EV_P_ ev_timer *w, int revents)
		3046
		3047	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3048	suitable for use with C<EV_A>.
		3049
		3050	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3051
		3052	Similar to the other two macros, this gives you the value of the default
		3053	loop, if multiple loops are supported ("ev loop default").
		3054
		3055	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3056
		3057	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3058	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3059	is undefined when the default loop has not been initialised by a previous
		3060	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3061
		3062	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3063	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3064
		3065	=back
		3066
		3067	Example: Declare and initialise a check watcher, utilising the above
		3068	macros so it will work regardless of whether multiple loops are supported
		3069	or not.
		3070
		3071	static void
		3072	check_cb (EV_P_ ev_timer *w, int revents)
		3073	{
		3074	ev_check_stop (EV_A_ w);
		3075	}
		3076
		3077	ev_check check;
		3078	ev_check_init (&check, check_cb);
		3079	ev_check_start (EV_DEFAULT_ &check);
		3080	ev_loop (EV_DEFAULT_ 0);
		3081
		3082	=head1 EMBEDDING
		3083
		3084	Libev can (and often is) directly embedded into host
		3085	applications. Examples of applications that embed it include the Deliantra
		3086	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3087	and rxvt-unicode.
		3088
		3089	The goal is to enable you to just copy the necessary files into your
		3090	source directory without having to change even a single line in them, so
		3091	you can easily upgrade by simply copying (or having a checked-out copy of
		3092	libev somewhere in your source tree).
		3093
		3094	=head2 FILESETS
		3095
		3096	Depending on what features you need you need to include one or more sets of files
		3097	in your application.
		3098
		3099	=head3 CORE EVENT LOOP
		3100
		3101	To include only the libev core (all the C<ev_*> functions), with manual
		3102	configuration (no autoconf):
		3103
		3104	#define EV_STANDALONE 1
		3105	#include "ev.c"
		3106
		3107	This will automatically include F<ev.h>, too, and should be done in a
		3108	single C source file only to provide the function implementations. To use
		3109	it, do the same for F<ev.h> in all files wishing to use this API (best
		3110	done by writing a wrapper around F<ev.h> that you can include instead and
		3111	where you can put other configuration options):
		3112
		3113	#define EV_STANDALONE 1
		3114	#include "ev.h"
		3115
		3116	Both header files and implementation files can be compiled with a C++
		3117	compiler (at least, that's a stated goal, and breakage will be treated
		3118	as a bug).
		3119
		3120	You need the following files in your source tree, or in a directory
		3121	in your include path (e.g. in libev/ when using -Ilibev):
		3122
		3123	ev.h
		3124	ev.c
		3125	ev_vars.h
		3126	ev_wrap.h
		3127
		3128	ev_win32.c required on win32 platforms only
		3129
		3130	ev_select.c only when select backend is enabled (which is enabled by default)
		3131	ev_poll.c only when poll backend is enabled (disabled by default)
		3132	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3133	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3134	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3135
		3136	F<ev.c> includes the backend files directly when enabled, so you only need
		3137	to compile this single file.
		3138
		3139	=head3 LIBEVENT COMPATIBILITY API
		3140
		3141	To include the libevent compatibility API, also include:
		3142
		3143	#include "event.c"
		3144
		3145	in the file including F<ev.c>, and:
		3146
		3147	#include "event.h"
		3148
		3149	in the files that want to use the libevent API. This also includes F<ev.h>.
		3150
		3151	You need the following additional files for this:
		3152
		3153	event.h
		3154	event.c
		3155
		3156	=head3 AUTOCONF SUPPORT
		3157
		3158	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3159	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3160	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3161	include F<config.h> and configure itself accordingly.
		3162
		3163	For this of course you need the m4 file:
		3164
		3165	libev.m4
		3166
		3167	=head2 PREPROCESSOR SYMBOLS/MACROS
		3168
		3169	Libev can be configured via a variety of preprocessor symbols you have to
		3170	define before including any of its files. The default in the absence of
		3171	autoconf is documented for every option.
		3172
		3173	=over 4
		3174
		3175	=item EV_STANDALONE
		3176
		3177	Must always be C<1> if you do not use autoconf configuration, which
		3178	keeps libev from including F<config.h>, and it also defines dummy
		3179	implementations for some libevent functions (such as logging, which is not
		3180	supported). It will also not define any of the structs usually found in
		3181	F<event.h> that are not directly supported by the libev core alone.
		3182
		3183	=item EV_USE_MONOTONIC
		3184
		3185	If defined to be C<1>, libev will try to detect the availability of the
		3186	monotonic clock option at both compile time and runtime. Otherwise no use
		3187	of the monotonic clock option will be attempted. If you enable this, you
		3188	usually have to link against librt or something similar. Enabling it when
		3189	the functionality isn't available is safe, though, although you have
		3190	to make sure you link against any libraries where the C<clock_gettime>
		3191	function is hiding in (often F<-lrt>).
		3192
		3193	=item EV_USE_REALTIME
		3194
		3195	If defined to be C<1>, libev will try to detect the availability of the
		3196	real-time clock option at compile time (and assume its availability at
		3197	runtime if successful). Otherwise no use of the real-time clock option will
		3198	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		3199	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		3200	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		3201
		3202	=item EV_USE_NANOSLEEP
		3203
		3204	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3205	and will use it for delays. Otherwise it will use C<select ()>.
		3206
		3207	=item EV_USE_EVENTFD
		3208
		3209	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3210	available and will probe for kernel support at runtime. This will improve
		3211	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3212	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3213	2.7 or newer, otherwise disabled.
		3214
		3215	=item EV_USE_SELECT
		3216
		3217	If undefined or defined to be C<1>, libev will compile in support for the
		3218	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3219	other method takes over, select will be it. Otherwise the select backend
		3220	will not be compiled in.
		3221
		3222	=item EV_SELECT_USE_FD_SET
		3223
		3224	If defined to C<1>, then the select backend will use the system C<fd_set>
		3225	structure. This is useful if libev doesn't compile due to a missing
		3226	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		3227	exotic systems. This usually limits the range of file descriptors to some
		3228	low limit such as 1024 or might have other limitations (winsocket only
		3229	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		3230	influence the size of the C<fd_set> used.
		3231
		3232	=item EV_SELECT_IS_WINSOCKET
		3233
		3234	When defined to C<1>, the select backend will assume that
		3235	select/socket/connect etc. don't understand file descriptors but
		3236	wants osf handles on win32 (this is the case when the select to
		3237	be used is the winsock select). This means that it will call
		3238	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3239	it is assumed that all these functions actually work on fds, even
		3240	on win32. Should not be defined on non-win32 platforms.
		3241
		3242	=item EV_FD_TO_WIN32_HANDLE
		3243
		3244	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3245	file descriptors to socket handles. When not defining this symbol (the
		3246	default), then libev will call C<_get_osfhandle>, which is usually
		3247	correct. In some cases, programs use their own file descriptor management,
		3248	in which case they can provide this function to map fds to socket handles.
		3249
		3250	=item EV_USE_POLL
		3251
		3252	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3253	backend. Otherwise it will be enabled on non-win32 platforms. It
		3254	takes precedence over select.
		3255
		3256	=item EV_USE_EPOLL
		3257
		3258	If defined to be C<1>, libev will compile in support for the Linux
		3259	C<epoll>(7) backend. Its availability will be detected at runtime,
		3260	otherwise another method will be used as fallback. This is the preferred
		3261	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3262	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3263
		3264	=item EV_USE_KQUEUE
		3265
		3266	If defined to be C<1>, libev will compile in support for the BSD style
		3267	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3268	otherwise another method will be used as fallback. This is the preferred
		3269	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3270	supports some types of fds correctly (the only platform we found that
		3271	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3272	not be used unless explicitly requested. The best way to use it is to find
		3273	out whether kqueue supports your type of fd properly and use an embedded
		3274	kqueue loop.
		3275
		3276	=item EV_USE_PORT
		3277
		3278	If defined to be C<1>, libev will compile in support for the Solaris
		3279	10 port style backend. Its availability will be detected at runtime,
		3280	otherwise another method will be used as fallback. This is the preferred
		3281	backend for Solaris 10 systems.
		3282
		3283	=item EV_USE_DEVPOLL
		3284
		3285	Reserved for future expansion, works like the USE symbols above.
		3286
		3287	=item EV_USE_INOTIFY
		3288
		3289	If defined to be C<1>, libev will compile in support for the Linux inotify
		3290	interface to speed up C<ev_stat> watchers. Its actual availability will
		3291	be detected at runtime. If undefined, it will be enabled if the headers
		3292	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3293
		3294	=item EV_ATOMIC_T
		3295
		3296	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3297	access is atomic with respect to other threads or signal contexts. No such
		3298	type is easily found in the C language, so you can provide your own type
		3299	that you know is safe for your purposes. It is used both for signal handler "locking"
		3300	as well as for signal and thread safety in C<ev_async> watchers.
		3301
		3302	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3303	(from F<signal.h>), which is usually good enough on most platforms.
		3304
		3305	=item EV_H
		3306
		3307	The name of the F<ev.h> header file used to include it. The default if
		3308	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3309	used to virtually rename the F<ev.h> header file in case of conflicts.
		3310
		3311	=item EV_CONFIG_H
		3312
		3313	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3314	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3315	C<EV_H>, above.
		3316
		3317	=item EV_EVENT_H
		3318
		3319	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3320	of how the F<event.h> header can be found, the default is C<"event.h">.
		3321
		3322	=item EV_PROTOTYPES
		3323
		3324	If defined to be C<0>, then F<ev.h> will not define any function
		3325	prototypes, but still define all the structs and other symbols. This is
		3326	occasionally useful if you want to provide your own wrapper functions
		3327	around libev functions.
		3328
		3329	=item EV_MULTIPLICITY
		3330
		3331	If undefined or defined to C<1>, then all event-loop-specific functions
		3332	will have the C<struct ev_loop *> as first argument, and you can create
		3333	additional independent event loops. Otherwise there will be no support
		3334	for multiple event loops and there is no first event loop pointer
		3335	argument. Instead, all functions act on the single default loop.
		3336
		3337	=item EV_MINPRI
		3338
		3339	=item EV_MAXPRI
		3340
		3341	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3342	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3343	provide for more priorities by overriding those symbols (usually defined
		3344	to be C<-2> and C<2>, respectively).
		3345
		3346	When doing priority-based operations, libev usually has to linearly search
		3347	all the priorities, so having many of them (hundreds) uses a lot of space
		3348	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3349	fine.
		3350
		3351	If your embedding application does not need any priorities, defining these
		3352	both to C<0> will save some memory and CPU.
		3353
		3354	=item EV_PERIODIC_ENABLE
		3355
		3356	If undefined or defined to be C<1>, then periodic timers are supported. If
		3357	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3358	code.
		3359
		3360	=item EV_IDLE_ENABLE
		3361
		3362	If undefined or defined to be C<1>, then idle watchers are supported. If
		3363	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3364	code.
		3365
		3366	=item EV_EMBED_ENABLE
		3367
		3368	If undefined or defined to be C<1>, then embed watchers are supported. If
		3369	defined to be C<0>, then they are not. Embed watchers rely on most other
		3370	watcher types, which therefore must not be disabled.
		3371
		3372	=item EV_STAT_ENABLE
		3373
		3374	If undefined or defined to be C<1>, then stat watchers are supported. If
		3375	defined to be C<0>, then they are not.
		3376
		3377	=item EV_FORK_ENABLE
		3378
		3379	If undefined or defined to be C<1>, then fork watchers are supported. If
		3380	defined to be C<0>, then they are not.
		3381
		3382	=item EV_ASYNC_ENABLE
		3383
		3384	If undefined or defined to be C<1>, then async watchers are supported. If
		3385	defined to be C<0>, then they are not.
		3386
		3387	=item EV_MINIMAL
		3388
		3389	If you need to shave off some kilobytes of code at the expense of some
		3390	speed, define this symbol to C<1>. Currently this is used to override some
		3391	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3392	much smaller 2-heap for timer management over the default 4-heap.
		3393
		3394	=item EV_PID_HASHSIZE
		3395
		3396	C<ev_child> watchers use a small hash table to distribute workload by
		3397	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3398	than enough. If you need to manage thousands of children you might want to
		3399	increase this value (I<must> be a power of two).
		3400
		3401	=item EV_INOTIFY_HASHSIZE
		3402
		3403	C<ev_stat> watchers use a small hash table to distribute workload by
		3404	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3405	usually more than enough. If you need to manage thousands of C<ev_stat>
		3406	watchers you might want to increase this value (I<must> be a power of
		3407	two).
		3408
		3409	=item EV_USE_4HEAP
		3410
		3411	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3412	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3413	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3414	faster performance with many (thousands) of watchers.
		3415
		3416	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3417	(disabled).
		3418
		3419	=item EV_HEAP_CACHE_AT
		3420
		3421	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3422	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3423	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3424	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3425	but avoids random read accesses on heap changes. This improves performance
		3426	noticeably with many (hundreds) of watchers.
		3427
		3428	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3429	(disabled).
		3430
		3431	=item EV_VERIFY
		3432
		3433	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3434	be done: If set to C<0>, no internal verification code will be compiled
		3435	in. If set to C<1>, then verification code will be compiled in, but not
		3436	called. If set to C<2>, then the internal verification code will be
		3437	called once per loop, which can slow down libev. If set to C<3>, then the
		3438	verification code will be called very frequently, which will slow down
		3439	libev considerably.
		3440
		3441	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3442	C<0>.
		3443
		3444	=item EV_COMMON
		3445
		3446	By default, all watchers have a C<void *data> member. By redefining
		3447	this macro to a something else you can include more and other types of
		3448	members. You have to define it each time you include one of the files,
		3449	though, and it must be identical each time.
		3450
		3451	For example, the perl EV module uses something like this:
		3452
		3453	#define EV_COMMON \
		3454	SV *self; /* contains this struct */ \
		3455	SV *cb_sv, *fh /* note no trailing ";" */
		3456
		3457	=item EV_CB_DECLARE (type)
		3458
		3459	=item EV_CB_INVOKE (watcher, revents)
		3460
		3461	=item ev_set_cb (ev, cb)
		3462
		3463	Can be used to change the callback member declaration in each watcher,
		3464	and the way callbacks are invoked and set. Must expand to a struct member
		3465	definition and a statement, respectively. See the F<ev.h> header file for
		3466	their default definitions. One possible use for overriding these is to
		3467	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3468	method calls instead of plain function calls in C++.
		3469
		3470	=back
		3471
		3472	=head2 EXPORTED API SYMBOLS
		3473
		3474	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3475	exported symbols, you can use the provided F<Symbol.*> files which list
		3476	all public symbols, one per line:
		3477
		3478	Symbols.ev for libev proper
		3479	Symbols.event for the libevent emulation
		3480
		3481	This can also be used to rename all public symbols to avoid clashes with
		3482	multiple versions of libev linked together (which is obviously bad in
		3483	itself, but sometimes it is inconvenient to avoid this).
		3484
		3485	A sed command like this will create wrapper C<#define>'s that you need to
		3486	include before including F<ev.h>:
		3487
		3488	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3489
		3490	This would create a file F<wrap.h> which essentially looks like this:
		3491
		3492	#define ev_backend myprefix_ev_backend
		3493	#define ev_check_start myprefix_ev_check_start
		3494	#define ev_check_stop myprefix_ev_check_stop
		3495	...
		3496
		3497	=head2 EXAMPLES
		3498
		3499	For a real-world example of a program the includes libev
		3500	verbatim, you can have a look at the EV perl module
		3501	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3502	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3503	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3504	will be compiled. It is pretty complex because it provides its own header
		3505	file.
		3506
		3507	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3508	that everybody includes and which overrides some configure choices:
		3509
		3510	#define EV_MINIMAL 1
		3511	#define EV_USE_POLL 0
		3512	#define EV_MULTIPLICITY 0
		3513	#define EV_PERIODIC_ENABLE 0
		3514	#define EV_STAT_ENABLE 0
		3515	#define EV_FORK_ENABLE 0
		3516	#define EV_CONFIG_H <config.h>
		3517	#define EV_MINPRI 0
		3518	#define EV_MAXPRI 0
		3519
		3520	#include "ev++.h"
		3521
		3522	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3523
		3524	#include "ev_cpp.h"
		3525	#include "ev.c"
		3526
		3527	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3528
		3529	=head2 THREADS AND COROUTINES
		3530
		3531	=head3 THREADS
		3532
		3533	All libev functions are reentrant and thread-safe unless explicitly
		3534	documented otherwise, but libev implements no locking itself. This means
		3535	that you can use as many loops as you want in parallel, as long as there
		3536	are no concurrent calls into any libev function with the same loop
		3537	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3538	of course): libev guarantees that different event loops share no data
		3539	structures that need any locking.
		3540
		3541	Or to put it differently: calls with different loop parameters can be done
		3542	concurrently from multiple threads, calls with the same loop parameter
		3543	must be done serially (but can be done from different threads, as long as
		3544	only one thread ever is inside a call at any point in time, e.g. by using
		3545	a mutex per loop).
		3546
		3547	Specifically to support threads (and signal handlers), libev implements
		3548	so-called C<ev_async> watchers, which allow some limited form of
		3549	concurrency on the same event loop, namely waking it up "from the
		3550	outside".
		3551
		3552	If you want to know which design (one loop, locking, or multiple loops
		3553	without or something else still) is best for your problem, then I cannot
		3554	help you, but here is some generic advice:
		3555
		3556	=over 4
		3557
		3558	=item * most applications have a main thread: use the default libev loop
		3559	in that thread, or create a separate thread running only the default loop.
		3560
		3561	This helps integrating other libraries or software modules that use libev
		3562	themselves and don't care/know about threading.
		3563
		3564	=item * one loop per thread is usually a good model.
		3565
		3566	Doing this is almost never wrong, sometimes a better-performance model
		3567	exists, but it is always a good start.
		3568
		3569	=item * other models exist, such as the leader/follower pattern, where one
		3570	loop is handed through multiple threads in a kind of round-robin fashion.
		3571
		3572	Choosing a model is hard - look around, learn, know that usually you can do
		3573	better than you currently do :-)
		3574
		3575	=item * often you need to talk to some other thread which blocks in the
		3576	event loop.
		3577
		3578	C<ev_async> watchers can be used to wake them up from other threads safely
		3579	(or from signal contexts...).
		3580
		3581	An example use would be to communicate signals or other events that only
		3582	work in the default loop by registering the signal watcher with the
		3583	default loop and triggering an C<ev_async> watcher from the default loop
		3584	watcher callback into the event loop interested in the signal.
		3585
		3586	=back
		3587
		3588	=head3 COROUTINES
		3589
		3590	Libev is very accommodating to coroutines ("cooperative threads"):
		3591	libev fully supports nesting calls to its functions from different
		3592	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3593	different coroutines, and switch freely between both coroutines running the
		3594	loop, as long as you don't confuse yourself). The only exception is that
		3595	you must not do this from C<ev_periodic> reschedule callbacks.
		3596
		3597	Care has been taken to ensure that libev does not keep local state inside
		3598	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3599	they do not call any callbacks.
		3600
		3601	=head2 COMPILER WARNINGS
		3602
		3603	Depending on your compiler and compiler settings, you might get no or a
		3604	lot of warnings when compiling libev code. Some people are apparently
		3605	scared by this.
		3606
		3607	However, these are unavoidable for many reasons. For one, each compiler
		3608	has different warnings, and each user has different tastes regarding
		3609	warning options. "Warn-free" code therefore cannot be a goal except when
		3610	targeting a specific compiler and compiler-version.
		3611
		3612	Another reason is that some compiler warnings require elaborate
		3613	workarounds, or other changes to the code that make it less clear and less
		3614	maintainable.
		3615
		3616	And of course, some compiler warnings are just plain stupid, or simply
		3617	wrong (because they don't actually warn about the condition their message
		3618	seems to warn about). For example, certain older gcc versions had some
		3619	warnings that resulted an extreme number of false positives. These have
		3620	been fixed, but some people still insist on making code warn-free with
		3621	such buggy versions.
		3622
		3623	While libev is written to generate as few warnings as possible,
		3624	"warn-free" code is not a goal, and it is recommended not to build libev
		3625	with any compiler warnings enabled unless you are prepared to cope with
		3626	them (e.g. by ignoring them). Remember that warnings are just that:
		3627	warnings, not errors, or proof of bugs.
		3628
		3629
		3630	=head2 VALGRIND
		3631
		3632	Valgrind has a special section here because it is a popular tool that is
		3633	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3634
		3635	If you think you found a bug (memory leak, uninitialised data access etc.)
		3636	in libev, then check twice: If valgrind reports something like:
		3637
		3638	==2274== definitely lost: 0 bytes in 0 blocks.
		3639	==2274== possibly lost: 0 bytes in 0 blocks.
		3640	==2274== still reachable: 256 bytes in 1 blocks.
		3641
		3642	Then there is no memory leak, just as memory accounted to global variables
		3643	is not a memleak - the memory is still being referenced, and didn't leak.
		3644
		3645	Similarly, under some circumstances, valgrind might report kernel bugs
		3646	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3647	although an acceptable workaround has been found here), or it might be
		3648	confused.
		3649
		3650	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3651	make it into some kind of religion.
		3652
		3653	If you are unsure about something, feel free to contact the mailing list
		3654	with the full valgrind report and an explanation on why you think this
		3655	is a bug in libev (best check the archives, too :). However, don't be
		3656	annoyed when you get a brisk "this is no bug" answer and take the chance
		3657	of learning how to interpret valgrind properly.
		3658
		3659	If you need, for some reason, empty reports from valgrind for your project
		3660	I suggest using suppression lists.
		3661
		3662
		3663	=head1 PORTABILITY NOTES
		3664
		3665	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3666
		3667	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3668	requires, and its I/O model is fundamentally incompatible with the POSIX
		3669	model. Libev still offers limited functionality on this platform in
		3670	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3671	descriptors. This only applies when using Win32 natively, not when using
		3672	e.g. cygwin.
		3673
		3674	Lifting these limitations would basically require the full
		3675	re-implementation of the I/O system. If you are into these kinds of
		3676	things, then note that glib does exactly that for you in a very portable
		3677	way (note also that glib is the slowest event library known to man).
		3678
		3679	There is no supported compilation method available on windows except
		3680	embedding it into other applications.
		3681
		3682	Not a libev limitation but worth mentioning: windows apparently doesn't
		3683	accept large writes: instead of resulting in a partial write, windows will
		3684	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3685	so make sure you only write small amounts into your sockets (less than a
		3686	megabyte seems safe, but this apparently depends on the amount of memory
		3687	available).
		3688
		3689	Due to the many, low, and arbitrary limits on the win32 platform and
		3690	the abysmal performance of winsockets, using a large number of sockets
		3691	is not recommended (and not reasonable). If your program needs to use
		3692	more than a hundred or so sockets, then likely it needs to use a totally
		3693	different implementation for windows, as libev offers the POSIX readiness
		3694	notification model, which cannot be implemented efficiently on windows
		3695	(Microsoft monopoly games).
		3696
		3697	A typical way to use libev under windows is to embed it (see the embedding
		3698	section for details) and use the following F<evwrap.h> header file instead
		3699	of F<ev.h>:
		3700
		3701	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3702	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3703
		3704	#include "ev.h"
		3705
		3706	And compile the following F<evwrap.c> file into your project (make sure
		3707	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3708
		3709	#include "evwrap.h"
		3710	#include "ev.c"
		3711
		3712	=over 4
		3713
		3714	=item The winsocket select function
		3715
		3716	The winsocket C<select> function doesn't follow POSIX in that it
		3717	requires socket I<handles> and not socket I<file descriptors> (it is
		3718	also extremely buggy). This makes select very inefficient, and also
		3719	requires a mapping from file descriptors to socket handles (the Microsoft
		3720	C runtime provides the function C<_open_osfhandle> for this). See the
		3721	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3722	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3723
		3724	The configuration for a "naked" win32 using the Microsoft runtime
		3725	libraries and raw winsocket select is:
		3726
		3727	#define EV_USE_SELECT 1
		3728	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3729
		3730	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3731	complexity in the O(n²) range when using win32.
		3732
		3733	=item Limited number of file descriptors
		3734
		3735	Windows has numerous arbitrary (and low) limits on things.
		3736
		3737	Early versions of winsocket's select only supported waiting for a maximum
		3738	of C<64> handles (probably owning to the fact that all windows kernels
		3739	can only wait for C<64> things at the same time internally; Microsoft
		3740	recommends spawning a chain of threads and wait for 63 handles and the
		3741	previous thread in each. Great).
		3742
		3743	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3744	to some high number (e.g. C<2048>) before compiling the winsocket select
		3745	call (which might be in libev or elsewhere, for example, perl does its own
		3746	select emulation on windows).
		3747
		3748	Another limit is the number of file descriptors in the Microsoft runtime
		3749	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3750	or something like this inside Microsoft). You can increase this by calling
		3751	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3752	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3753	libraries.
		3754
		3755	This might get you to about C<512> or C<2048> sockets (depending on
		3756	windows version and/or the phase of the moon). To get more, you need to
		3757	wrap all I/O functions and provide your own fd management, but the cost of
		3758	calling select (O(n²)) will likely make this unworkable.
		3759
		3760	=back
		3761
		3762	=head2 PORTABILITY REQUIREMENTS
		3763
		3764	In addition to a working ISO-C implementation and of course the
		3765	backend-specific APIs, libev relies on a few additional extensions:
		3766
		3767	=over 4
		3768
		3769	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3770	calling conventions regardless of C<ev_watcher_type *>.
		3771
		3772	Libev assumes not only that all watcher pointers have the same internal
		3773	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3774	assumes that the same (machine) code can be used to call any watcher
		3775	callback: The watcher callbacks have different type signatures, but libev
		3776	calls them using an C<ev_watcher *> internally.
		3777
		3778	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3779
		3780	The type C<sig_atomic_t volatile> (or whatever is defined as
		3781	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3782	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3783	believed to be sufficiently portable.
		3784
		3785	=item C<sigprocmask> must work in a threaded environment
		3786
		3787	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3788	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3789	pthread implementations will either allow C<sigprocmask> in the "main
		3790	thread" or will block signals process-wide, both behaviours would
		3791	be compatible with libev. Interaction between C<sigprocmask> and
		3792	C<pthread_sigmask> could complicate things, however.
		3793
		3794	The most portable way to handle signals is to block signals in all threads
		3795	except the initial one, and run the default loop in the initial thread as
		3796	well.
		3797
		3798	=item C<long> must be large enough for common memory allocation sizes
		3799
		3800	To improve portability and simplify its API, libev uses C<long> internally
		3801	instead of C<size_t> when allocating its data structures. On non-POSIX
		3802	systems (Microsoft...) this might be unexpectedly low, but is still at
		3803	least 31 bits everywhere, which is enough for hundreds of millions of
		3804	watchers.
		3805
		3806	=item C<double> must hold a time value in seconds with enough accuracy
		3807
		3808	The type C<double> is used to represent timestamps. It is required to
		3809	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3810	enough for at least into the year 4000. This requirement is fulfilled by
		3811	implementations implementing IEEE 754 (basically all existing ones).
		3812
		3813	=back
		3814
		3815	If you know of other additional requirements drop me a note.
		3816
		3817
		3818	=head1 ALGORITHMIC COMPLEXITIES
		3819
		3820	In this section the complexities of (many of) the algorithms used inside
		3821	libev will be documented. For complexity discussions about backends see
		3822	the documentation for C<ev_default_init>.
		3823
		3824	All of the following are about amortised time: If an array needs to be
		3825	extended, libev needs to realloc and move the whole array, but this
		3826	happens asymptotically rarer with higher number of elements, so O(1) might
		3827	mean that libev does a lengthy realloc operation in rare cases, but on
		3828	average it is much faster and asymptotically approaches constant time.
		3829
		3830	=over 4
		3831
		3832	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3833
		3834	This means that, when you have a watcher that triggers in one hour and
		3835	there are 100 watchers that would trigger before that, then inserting will
		3836	have to skip roughly seven (C<ld 100>) of these watchers.
		3837
		3838	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3839
		3840	That means that changing a timer costs less than removing/adding them,
		3841	as only the relative motion in the event queue has to be paid for.
		3842
		3843	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3844
		3845	These just add the watcher into an array or at the head of a list.
		3846
		3847	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3848
		3849	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3850
		3851	These watchers are stored in lists, so they need to be walked to find the
		3852	correct watcher to remove. The lists are usually short (you don't usually
		3853	have many watchers waiting for the same fd or signal: one is typical, two
		3854	is rare).
		3855
		3856	=item Finding the next timer in each loop iteration: O(1)
		3857
		3858	By virtue of using a binary or 4-heap, the next timer is always found at a
		3859	fixed position in the storage array.
		3860
		3861	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3862
		3863	A change means an I/O watcher gets started or stopped, which requires
		3864	libev to recalculate its status (and possibly tell the kernel, depending
		3865	on backend and whether C<ev_io_set> was used).
		3866
		3867	=item Activating one watcher (putting it into the pending state): O(1)
		3868
		3869	=item Priority handling: O(number_of_priorities)
		3870
		3871	Priorities are implemented by allocating some space for each
		3872	priority. When doing priority-based operations, libev usually has to
		3873	linearly search all the priorities, but starting/stopping and activating
		3874	watchers becomes O(1) with respect to priority handling.
		3875
		3876	=item Sending an ev_async: O(1)
		3877
		3878	=item Processing ev_async_send: O(number_of_async_watchers)
		3879
		3880	=item Processing signals: O(max_signal_number)
		3881
		3882	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3883	calls in the current loop iteration. Checking for async and signal events
		3884	involves iterating over all running async watchers or all signal numbers.
		3885
		3886	=back
		3887
825		3888
826	=head1 AUTHOR	3889	=head1 AUTHOR
827		3890
828	Marc Lehmann <libev@schmorp.de>.	3891	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
829		3892

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