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…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 DESCRIPTION	9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
		18	ev_io stdin_watcher;
		19	ev_timer timeout_watcher;
		20
		21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
		23	static void
		24	stdin_cb (EV_P_ ev_io *w, int revents)
		25	{
		26	puts ("stdin ready");
		27	// for one-shot events, one must manually stop the watcher
		28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
		33	}
		34
		35	// another callback, this time for a time-out
		36	static void
		37	timeout_cb (EV_P_ ev_timer *w, int revents)
		38	{
		39	puts ("timeout");
		40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
		42	}
		43
		44	int
		45	main (void)
		46	{
		47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = ev_default_loop (0);
		49
		50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
		52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		53	ev_io_start (loop, &stdin_watcher);
		54
		55	// initialise a timer watcher, then start it
		56	// simple non-repeating 5.5 second timeout
		57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		58	ev_timer_start (loop, &timeout_watcher);
		59
		60	// now wait for events to arrive
		61	ev_loop (loop, 0);
		62
		63	// unloop was called, so exit
		64	return 0;
		65	}
		66
		67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
10		84
11	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	87	these event sources and provide your program with events.
14		88
15	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	96	watcher.
23		97
24	=head1 FEATURES	98	=head2 FEATURES
25		99
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	103	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	104	with customised rescheduling (C<ev_periodic>), synchronous signals
		105	(C<ev_signal>), process status change events (C<ev_child>), and event
		106	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		107	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		108	file watchers (C<ev_stat>) and even limited support for fork events
		109	(C<ev_fork>).
		110
		111	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	112	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	113	for example).
33		114
34	=head1 CONVENTIONS	115	=head2 CONVENTIONS
35		116
36	Libev is very configurable. In this manual the default configuration	117	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	118	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	119	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	120	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	121	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 *>)	122	name C<loop> (which is always of type C<ev_loop *>) will not have
42	will not have this argument.	123	this argument.
43		124
44	=head1 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
45		126
46	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
48	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
50	to the double type in C.	131	aliases to the C<double> type in C. When you need to do any calculations
		132	on it, you should treat it as some floating point value. Unlike the name
		133	component C<stamp> might indicate, it is also used for time differences
		134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
		155
51		156
52	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
53		158
54	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
55	library in any way.	160	library in any way.
…		…
60		165
61	Returns the current time as libev would use it. Please note that the	166	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	167	C<ev_now> function is usually faster and also often returns the timestamp
63	you actually want to know.	168	you actually want to know.
64		169
		170	=item ev_sleep (ev_tstamp interval)
		171
		172	Sleep for the given interval: The current thread will be blocked until
		173	either it is interrupted or the given time interval has passed. Basically
		174	this is a sub-second-resolution C<sleep ()>.
		175
65	=item int ev_version_major ()	176	=item int ev_version_major ()
66		177
67	=item int ev_version_minor ()	178	=item int ev_version_minor ()
68		179
69	You can find out the major and minor version numbers of the library	180	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	181	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	182	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	183	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
73	version of the library your program was compiled against.	184	version of the library your program was compiled against.
74		185
		186	These version numbers refer to the ABI version of the library, not the
		187	release version.
		188
75	Usually, it's a good idea to terminate if the major versions mismatch,	189	Usually, it's a good idea to terminate if the major versions mismatch,
76	as this indicates an incompatible change. Minor versions are usually	190	as this indicates an incompatible change. Minor versions are usually
77	compatible to older versions, so a larger minor version alone is usually	191	compatible to older versions, so a larger minor version alone is usually
78	not a problem.	192	not a problem.
79		193
		194	Example: Make sure we haven't accidentally been linked against the wrong
		195	version.
		196
		197	assert (("libev version mismatch",
		198	ev_version_major () == EV_VERSION_MAJOR
		199	&& ev_version_minor () >= EV_VERSION_MINOR));
		200
		201	=item unsigned int ev_supported_backends ()
		202
		203	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		204	value) compiled into this binary of libev (independent of their
		205	availability on the system you are running on). See C<ev_default_loop> for
		206	a description of the set values.
		207
		208	Example: make sure we have the epoll method, because yeah this is cool and
		209	a must have and can we have a torrent of it please!!!11
		210
		211	assert (("sorry, no epoll, no sex",
		212	ev_supported_backends () & EVBACKEND_EPOLL));
		213
		214	=item unsigned int ev_recommended_backends ()
		215
		216	Return the set of all backends compiled into this binary of libev and also
		217	recommended for this platform. This set is often smaller than the one
		218	returned by C<ev_supported_backends>, as for example kqueue is broken on
		219	most BSDs and will not be auto-detected unless you explicitly request it
		220	(assuming you know what you are doing). This is the set of backends that
		221	libev will probe for if you specify no backends explicitly.
		222
		223	=item unsigned int ev_embeddable_backends ()
		224
		225	Returns the set of backends that are embeddable in other event loops. This
		226	is the theoretical, all-platform, value. To find which backends
		227	might be supported on the current system, you would need to look at
		228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		229	recommended ones.
		230
		231	See the description of C<ev_embed> watchers for more info.
		232
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
81		234
82	Sets the allocation function to use (the prototype is similar to the	235	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	236	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	237	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	238	when memory needs to be allocated (C<size != 0>), the library might abort
86	destructive action. The default is your system realloc function.	239	or take some potentially destructive action.
		240
		241	Since some systems (at least OpenBSD and Darwin) fail to implement
		242	correct C<realloc> semantics, libev will use a wrapper around the system
		243	C<realloc> and C<free> functions by default.
87		244
88	You could override this function in high-availability programs to, say,	245	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,	246	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.	247	or even to sleep a while and retry until some memory is available.
91		248
		249	Example: Replace the libev allocator with one that waits a bit and then
		250	retries (example requires a standards-compliant C<realloc>).
		251
		252	static void *
		253	persistent_realloc (void *ptr, size_t size)
		254	{
		255	for (;;)
		256	{
		257	void *newptr = realloc (ptr, size);
		258
		259	if (newptr)
		260	return newptr;
		261
		262	sleep (60);
		263	}
		264	}
		265
		266	...
		267	ev_set_allocator (persistent_realloc);
		268
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
93		270
94	Set the callback function to call on a retryable syscall error (such	271	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	272	as failed select, poll, epoll_wait). The message is a printable string
96	indicating the system call or subsystem causing the problem. If this	273	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	274	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	275	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	276	requested operation, or, if the condition doesn't go away, do bad stuff
100	(such as abort).	277	(such as abort).
101		278
		279	Example: This is basically the same thing that libev does internally, too.
		280
		281	static void
		282	fatal_error (const char *msg)
		283	{
		284	perror (msg);
		285	abort ();
		286	}
		287
		288	...
		289	ev_set_syserr_cb (fatal_error);
		290
102	=back	291	=back
103		292
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		294
106	An event loop is described by a C<struct ev_loop *>. The library knows two	295	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	296	is I<not> optional in this case, as there is also an C<ev_loop>
108	events, and dynamically created loops which do not.	297	I<function>).
109		298
110	If you use threads, a common model is to run the default event loop	299	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	300	supports signals and child events, and dynamically created loops which do
112	create, you also create another event loop. Libev itself does no locking	301	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		302
117	=over 4	303	=over 4
118		304
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		306
121	This will initialise the default event loop if it hasn't been initialised	307	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	308	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	309	false. If it already was initialised it simply returns it (and ignores the
124	flags).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		311
126	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
127	function.	313	function.
128		314
		315	Note that this function is I<not> thread-safe, so if you want to use it
		316	from multiple threads, you have to lock (note also that this is unlikely,
		317	as loops cannot be shared easily between threads anyway).
		318
		319	The default loop is the only loop that can handle C<ev_signal> and
		320	C<ev_child> watchers, and to do this, it always registers a handler
		321	for C<SIGCHLD>. If this is a problem for your application you can either
		322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		324	C<ev_default_init>.
		325
129	The flags argument can be used to specify special behaviour or specific	326	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).	327	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		328
132	It supports the following flags:	329	The following flags are supported:
133		330
134	=over 4	331	=over 4
135		332
136	=item C<EVFLAG_AUTO>	333	=item C<EVFLAG_AUTO>
137		334
138	The default flags value. Use this if you have no clue (it's the right	335	The default flags value. Use this if you have no clue (it's the right
139	thing, believe me).	336	thing, believe me).
140		337
141	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
142		339
143	If this flag bit is ored into the flag value (or the program runs setuid	340	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	341	or setgid) then libev will I<not> look at the environment variable
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	343	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	344	useful to try out specific backends to test their performance, or to work
148	around bugs.	345	around bugs.
149		346
		347	=item C<EVFLAG_FORKCHECK>
		348
		349	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		350	a fork, you can also make libev check for a fork in each iteration by
		351	enabling this flag.
		352
		353	This works by calling C<getpid ()> on every iteration of the loop,
		354	and thus this might slow down your event loop if you do a lot of loop
		355	iterations and little real work, but is usually not noticeable (on my
		356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		357	without a system call and thus I<very> fast, but my GNU/Linux system also has
		358	C<pthread_atfork> which is even faster).
		359
		360	The big advantage of this flag is that you can forget about fork (and
		361	forget about forgetting to tell libev about forking) when you use this
		362	flag.
		363
		364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		365	environment variable.
		366
150	=item C<EVMETHOD_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		368
152	This is your standard select(2) backend. Not I<completely> standard, as	369	This is your standard select(2) backend. Not I<completely> standard, as
153	libev tries to roll its own fd_set with no limits on the number of fds,	370	libev tries to roll its own fd_set with no limits on the number of fds,
154	but if that fails, expect a fairly low limit on the number of fds when	371	but if that fails, expect a fairly low limit on the number of fds when
155	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	372	using this backend. It doesn't scale too well (O(highest_fd)), but its
156	the fastest backend for a low number of fds.	373	usually the fastest backend for a low number of (low-numbered :) fds.
157		374
		375	To get good performance out of this backend you need a high amount of
		376	parallelism (most of the file descriptors should be busy). If you are
		377	writing a server, you should C<accept ()> in a loop to accept as many
		378	connections as possible during one iteration. You might also want to have
		379	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		380	readiness notifications you get per iteration.
		381
		382	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		383	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		384	C<exceptfds> set on that platform).
		385
158	=item C<EVMETHOD_POLL> (value 2, poll backend, available everywhere except on windows)	386	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
159		387
160	And this is your standard poll(2) backend. It's more complicated than	388	And this is your standard poll(2) backend. It's more complicated
161	select, but handles sparse fds better and has no artificial limit on the	389	than select, but handles sparse fds better and has no artificial
162	number of fds you can use (except it will slow down considerably with a	390	limit on the number of fds you can use (except it will slow down
163	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	391	considerably with a lot of inactive fds). It scales similarly to select,
		392	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		393	performance tips.
164		394
		395	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		396	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		397
165	=item C<EVMETHOD_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
166		399
167	For few fds, this backend is a bit little slower than poll and select,	400	For few fds, this backend is a bit little slower than poll and select,
168	but it scales phenomenally better. While poll and select usually scale like	401	but it scales phenomenally better. While poll and select usually scale
169	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	402	like O(total_fds) where n is the total number of fds (or the highest fd),
170	either O(1) or O(active_fds).	403	epoll scales either O(1) or O(active_fds).
171		404
		405	The epoll mechanism deserves honorable mention as the most misdesigned
		406	of the more advanced event mechanisms: mere annoyances include silently
		407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
		421
172	While stopping and starting an I/O watcher in the same iteration will	422	While stopping, setting and starting an I/O watcher in the same iteration
173	result in some caching, there is still a syscall per such incident	423	will result in some caching, there is still a system call per such
174	(because the fd could point to a different file description now), so its	424	incident (because the same I<file descriptor> could point to a different
175	best to avoid that. Also, dup()ed file descriptors might not work very	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
176	well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
		427	file descriptors.
177		428
		429	Best performance from this backend is achieved by not unregistering all
		430	watchers for a file descriptor until it has been closed, if possible,
		431	i.e. keep at least one watcher active per fd at all times. Stopping and
		432	starting a watcher (without re-setting it) also usually doesn't cause
		433	extra overhead. A fork can both result in spurious notifications as well
		434	as in libev having to destroy and recreate the epoll object, which can
		435	take considerable time and thus should be avoided.
		436
		437	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		438	faster than epoll for maybe up to a hundred file descriptors, depending on
		439	the usage. So sad.
		440
		441	While nominally embeddable in other event loops, this feature is broken in
		442	all kernel versions tested so far.
		443
		444	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		445	C<EVBACKEND_POLL>.
		446
178	=item C<EVMETHOD_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
179		448
180	Kqueue deserves special mention, as at the time of this writing, it	449	Kqueue deserves special mention, as at the time of this writing, it
181	was broken on all BSDs except NetBSD (usually it doesn't work with	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
182	anything but sockets and pipes, except on Darwin, where of course its	451	with anything but sockets and pipes, except on Darwin, where of course
183	completely useless). For this reason its not being "autodetected" unless	452	it's completely useless). Unlike epoll, however, whose brokenness
184	you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).	453	is by design, these kqueue bugs can (and eventually will) be fixed
		454	without API changes to existing programs. For this reason it's not being
		455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		457	system like NetBSD.
		458
		459	You still can embed kqueue into a normal poll or select backend and use it
		460	only for sockets (after having made sure that sockets work with kqueue on
		461	the target platform). See C<ev_embed> watchers for more info.
185		462
186	It scales in the same way as the epoll backend, but the interface to the	463	It scales in the same way as the epoll backend, but the interface to the
187	kernel is more efficient (which says nothing about its actual speed, of	464	kernel is more efficient (which says nothing about its actual speed, of
188	course). While starting and stopping an I/O watcher does not cause an	465	course). While stopping, setting and starting an I/O watcher does never
189	extra syscall as with epoll, it still adds up to four event changes per	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
190	incident, so its best to avoid that.	467	two event changes per incident. Support for C<fork ()> is very bad (but
		468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
191		470
		471	This backend usually performs well under most conditions.
		472
		473	While nominally embeddable in other event loops, this doesn't work
		474	everywhere, so you might need to test for this. And since it is broken
		475	almost everywhere, you should only use it when you have a lot of sockets
		476	(for which it usually works), by embedding it into another event loop
		477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		478	also broken on OS X)) and, did I mention it, using it only for sockets.
		479
		480	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		482	C<NOTE_EOF>.
		483
192	=item C<EVMETHOD_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
193		485
194	This is not implemented yet (and might never be).	486	This is not implemented yet (and might never be, unless you send me an
		487	implementation). According to reports, C</dev/poll> only supports sockets
		488	and is not embeddable, which would limit the usefulness of this backend
		489	immensely.
195		490
196	=item C<EVMETHOD_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
197		492
198	This uses the Solaris 10 port mechanism. As with everything on Solaris,	493	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
199	it's really slow, but it still scales very well (O(active_fds)).	494	it's really slow, but it still scales very well (O(active_fds)).
200		495
		496	Please note that Solaris event ports can deliver a lot of spurious
		497	notifications, so you need to use non-blocking I/O or other means to avoid
		498	blocking when no data (or space) is available.
		499
		500	While this backend scales well, it requires one system call per active
		501	file descriptor per loop iteration. For small and medium numbers of file
		502	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		503	might perform better.
		504
		505	On the positive side, with the exception of the spurious readiness
		506	notifications, this backend actually performed fully to specification
		507	in all tests and is fully embeddable, which is a rare feat among the
		508	OS-specific backends (I vastly prefer correctness over speed hacks).
		509
		510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		511	C<EVBACKEND_POLL>.
		512
201	=item C<EVMETHOD_ALL>	513	=item C<EVBACKEND_ALL>
202		514
203	Try all backends (even potentially broken ones that wouldn't be tried	515	Try all backends (even potentially broken ones that wouldn't be tried
204	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	516	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
205	C<EVMETHOD_ALL & ~EVMETHOD_KQUEUE>.	517	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		518
		519	It is definitely not recommended to use this flag.
206		520
207	=back	521	=back
208		522
209	If one or more of these are ored into the flags value, then only these	523	If one or more of these are or'ed into the flags value, then only these
210	backends will be tried (in the reverse order as given here). If none are	524	backends will be tried (in the reverse order as listed here). If none are
211	specified, most compiled-in backend will be tried, usually in reverse	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
212	order of their flag values :)	526
		527	Example: This is the most typical usage.
		528
		529	if (!ev_default_loop (0))
		530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		531
		532	Example: Restrict libev to the select and poll backends, and do not allow
		533	environment settings to be taken into account:
		534
		535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		536
		537	Example: Use whatever libev has to offer, but make sure that kqueue is
		538	used if available (warning, breaks stuff, best use only with your own
		539	private event loop and only if you know the OS supports your types of
		540	fds):
		541
		542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
213		543
214	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
215		545
216	Similar to C<ev_default_loop>, but always creates a new event loop that is	546	Similar to C<ev_default_loop>, but always creates a new event loop that is
217	always distinct from the default loop. Unlike the default loop, it cannot	547	always distinct from the default loop. Unlike the default loop, it cannot
218	handle signal and child watchers, and attempts to do so will be greeted by	548	handle signal and child watchers, and attempts to do so will be greeted by
219	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
220		550
		551	Note that this function I<is> thread-safe, and the recommended way to use
		552	libev with threads is indeed to create one loop per thread, and using the
		553	default loop in the "main" or "initial" thread.
		554
		555	Example: Try to create a event loop that uses epoll and nothing else.
		556
		557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		558	if (!epoller)
		559	fatal ("no epoll found here, maybe it hides under your chair");
		560
221	=item ev_default_destroy ()	561	=item ev_default_destroy ()
222		562
223	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
224	etc.). This stops all registered event watchers (by not touching them in	564	etc.). None of the active event watchers will be stopped in the normal
225	any way whatsoever, although you cannot rely on this :).	565	sense, so e.g. C<ev_is_active> might still return true. It is your
		566	responsibility to either stop all watchers cleanly yourself I<before>
		567	calling this function, or cope with the fact afterwards (which is usually
		568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		569	for example).
		570
		571	Note that certain global state, such as signal state (and installed signal
		572	handlers), will not be freed by this function, and related watchers (such
		573	as signal and child watchers) would need to be stopped manually.
		574
		575	In general it is not advisable to call this function except in the
		576	rare occasion where you really need to free e.g. the signal handling
		577	pipe fds. If you need dynamically allocated loops it is better to use
		578	C<ev_loop_new> and C<ev_loop_destroy>).
226		579
227	=item ev_loop_destroy (loop)	580	=item ev_loop_destroy (loop)
228		581
229	Like C<ev_default_destroy>, but destroys an event loop created by an	582	Like C<ev_default_destroy>, but destroys an event loop created by an
230	earlier call to C<ev_loop_new>.	583	earlier call to C<ev_loop_new>.
231		584
232	=item ev_default_fork ()	585	=item ev_default_fork ()
233		586
		587	This function sets a flag that causes subsequent C<ev_loop> iterations
234	This function reinitialises the kernel state for backends that have	588	to reinitialise the kernel state for backends that have one. Despite the
235	one. Despite the name, you can call it anytime, but it makes most sense	589	name, you can call it anytime, but it makes most sense after forking, in
236	after forking, in either the parent or child process (or both, but that	590	the child process (or both child and parent, but that again makes little
237	again makes little sense).	591	sense). You I<must> call it in the child before using any of the libev
		592	functions, and it will only take effect at the next C<ev_loop> iteration.
238		593
239	You I<must> call this function in the child process after forking if and	594	On the other hand, you only need to call this function in the child
240	only if you want to use the event library in both processes. If you just	595	process if and only if you want to use the event library in the child. If
241	fork+exec, you don't have to call it.	596	you just fork+exec, you don't have to call it at all.
242		597
243	The function itself is quite fast and it's usually not a problem to call	598	The function itself is quite fast and it's usually not a problem to call
244	it just in case after a fork. To make this easy, the function will fit in	599	it just in case after a fork. To make this easy, the function will fit in
245	quite nicely into a call to C<pthread_atfork>:	600	quite nicely into a call to C<pthread_atfork>:
246		601
…		…
248		603
249	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
250		605
251	Like C<ev_default_fork>, but acts on an event loop created by	606	Like C<ev_default_fork>, but acts on an event loop created by
252	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	607	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
253	after fork, and how you do this is entirely your own problem.	608	after fork that you want to re-use in the child, and how you do this is
		609	entirely your own problem.
254		610
		611	=item int ev_is_default_loop (loop)
		612
		613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
		615
		616	=item unsigned int ev_loop_count (loop)
		617
		618	Returns the count of loop iterations for the loop, which is identical to
		619	the number of times libev did poll for new events. It starts at C<0> and
		620	happily wraps around with enough iterations.
		621
		622	This value can sometimes be useful as a generation counter of sorts (it
		623	"ticks" the number of loop iterations), as it roughly corresponds with
		624	C<ev_prepare> and C<ev_check> calls.
		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
		637
255	=item unsigned int ev_method (loop)	638	=item unsigned int ev_backend (loop)
256		639
257	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
258	use.	641	use.
259		642
260	=item ev_tstamp ev_now (loop)	643	=item ev_tstamp ev_now (loop)
261		644
262	Returns the current "event loop time", which is the time the event loop	645	Returns the current "event loop time", which is the time the event loop
263	got events and started processing them. This timestamp does not change	646	received events and started processing them. This timestamp does not
264	as long as callbacks are being processed, and this is also the base time	647	change as long as callbacks are being processed, and this is also the base
265	used for relative timers. You can treat it as the timestamp of the event	648	time used for relative timers. You can treat it as the timestamp of the
266	occuring (or more correctly, the mainloop finding out about it).	649	event occurring (or more correctly, libev finding out about it).
		650
		651	=item ev_now_update (loop)
		652
		653	Establishes the current time by querying the kernel, updating the time
		654	returned by C<ev_now ()> in the progress. This is a costly operation and
		655	is usually done automatically within C<ev_loop ()>.
		656
		657	This function is rarely useful, but when some event callback runs for a
		658	very long time without entering the event loop, updating libev's idea of
		659	the current time is a good idea.
		660
		661	See also L<The special problem of time updates> in the C<ev_timer> section.
		662
		663	=item ev_suspend (loop)
		664
		665	=item ev_resume (loop)
		666
		667	These two functions suspend and resume a loop, for use when the loop is
		668	not used for a while and timeouts should not be processed.
		669
		670	A typical use case would be an interactive program such as a game: When
		671	the user presses C<^Z> to suspend the game and resumes it an hour later it
		672	would be best to handle timeouts as if no time had actually passed while
		673	the program was suspended. This can be achieved by calling C<ev_suspend>
		674	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		675	C<ev_resume> directly afterwards to resume timer processing.
		676
		677	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		678	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		679	will be rescheduled (that is, they will lose any events that would have
		680	occured while suspended).
		681
		682	After calling C<ev_suspend> you B<must not> call I<any> function on the
		683	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		684	without a previous call to C<ev_suspend>.
		685
		686	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		687	event loop time (see C<ev_now_update>).
267		688
268	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
269		690
270	Finally, this is it, the event handler. This function usually is called	691	Finally, this is it, the event handler. This function usually is called
271	after you initialised all your watchers and you want to start handling	692	after you initialised all your watchers and you want to start handling
272	events.	693	events.
273		694
274	If the flags argument is specified as 0, it will not return until either	695	If the flags argument is specified as C<0>, it will not return until
275	no event watchers are active anymore or C<ev_unloop> was called.	696	either no event watchers are active anymore or C<ev_unloop> was called.
		697
		698	Please note that an explicit C<ev_unloop> is usually better than
		699	relying on all watchers to be stopped when deciding when a program has
		700	finished (especially in interactive programs), but having a program
		701	that automatically loops as long as it has to and no longer by virtue
		702	of relying on its watchers stopping correctly, that is truly a thing of
		703	beauty.
276		704
277	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	705	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
278	those events and any outstanding ones, but will not block your process in	706	those events and any already outstanding ones, but will not block your
279	case there are no events and will return after one iteration of the loop.	707	process in case there are no events and will return after one iteration of
		708	the loop.
280		709
281	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	710	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
282	neccessary) and will handle those and any outstanding ones. It will block	711	necessary) and will handle those and any already outstanding ones. It
283	your process until at least one new event arrives, and will return after	712	will block your process until at least one new event arrives (which could
		713	be an event internal to libev itself, so there is no guarantee that a
		714	user-registered callback will be called), and will return after one
284	one iteration of the loop.	715	iteration of the loop.
285		716
286	This flags value could be used to implement alternative looping	717	This is useful if you are waiting for some external event in conjunction
287	constructs, but the C<prepare> and C<check> watchers provide a better and	718	with something not expressible using other libev watchers (i.e. "roll your
288	more generic mechanism.	719	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		720	usually a better approach for this kind of thing.
289		721
290	Here are the gory details of what ev_loop does:	722	Here are the gory details of what C<ev_loop> does:
291		723
292	1. If there are no active watchers (reference count is zero), return.	724	- Before the first iteration, call any pending watchers.
		725	* If EVFLAG_FORKCHECK was used, check for a fork.
		726	- If a fork was detected (by any means), queue and call all fork watchers.
293	2. Queue and immediately call all prepare watchers.	727	- Queue and call all prepare watchers.
294	3. If we have been forked, recreate the kernel state.	728	- If we have been forked, detach and recreate the kernel state
		729	as to not disturb the other process.
295	4. Update the kernel state with all outstanding changes.	730	- Update the kernel state with all outstanding changes.
296	5. Update the "event loop time".	731	- Update the "event loop time" (ev_now ()).
297	6. Calculate for how long to block.	732	- Calculate for how long to sleep or block, if at all
		733	(active idle watchers, EVLOOP_NONBLOCK or not having
		734	any active watchers at all will result in not sleeping).
		735	- Sleep if the I/O and timer collect interval say so.
298	7. Block the process, waiting for events.	736	- Block the process, waiting for any events.
		737	- Queue all outstanding I/O (fd) events.
299	8. Update the "event loop time" and do time jump handling.	738	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
300	9. Queue all outstanding timers.	739	- Queue all expired timers.
301	10. Queue all outstanding periodics.	740	- Queue all expired periodics.
302	11. If no events are pending now, queue all idle watchers.	741	- Unless any events are pending now, queue all idle watchers.
303	12. Queue all check watchers.	742	- Queue all check watchers.
304	13. Call all queued watchers in reverse order (i.e. check watchers first).	743	- Call all queued watchers in reverse order (i.e. check watchers first).
		744	Signals and child watchers are implemented as I/O watchers, and will
		745	be handled here by queueing them when their watcher gets executed.
305	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	746	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
306	was used, return, otherwise continue with step #1.	747	were used, or there are no active watchers, return, otherwise
		748	continue with step *.
		749
		750	Example: Queue some jobs and then loop until no events are outstanding
		751	anymore.
		752
		753	... queue jobs here, make sure they register event watchers as long
		754	... as they still have work to do (even an idle watcher will do..)
		755	ev_loop (my_loop, 0);
		756	... jobs done or somebody called unloop. yeah!
307		757
308	=item ev_unloop (loop, how)	758	=item ev_unloop (loop, how)
309		759
310	Can be used to make a call to C<ev_loop> return early (but only after it	760	Can be used to make a call to C<ev_loop> return early (but only after it
311	has processed all outstanding events). The C<how> argument must be either	761	has processed all outstanding events). The C<how> argument must be either
312	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	762	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
313	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	763	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
314		764
		765	This "unloop state" will be cleared when entering C<ev_loop> again.
		766
		767	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		768
315	=item ev_ref (loop)	769	=item ev_ref (loop)
316		770
317	=item ev_unref (loop)	771	=item ev_unref (loop)
318		772
319	Ref/unref can be used to add or remove a reference count on the event	773	Ref/unref can be used to add or remove a reference count on the event
320	loop: Every watcher keeps one reference, and as long as the reference	774	loop: Every watcher keeps one reference, and as long as the reference
321	count is nonzero, C<ev_loop> will not return on its own. If you have	775	count is nonzero, C<ev_loop> will not return on its own.
		776
322	a watcher you never unregister that should not keep C<ev_loop> from	777	If you have a watcher you never unregister that should not keep C<ev_loop>
323	returning, ev_unref() after starting, and ev_ref() before stopping it. For	778	from returning, call ev_unref() after starting, and ev_ref() before
		779	stopping it.
		780
324	example, libev itself uses this for its internal signal pipe: It is not	781	As an example, libev itself uses this for its internal signal pipe: It
325	visible to the libev user and should not keep C<ev_loop> from exiting if	782	is not visible to the libev user and should not keep C<ev_loop> from
326	no event watchers registered by it are active. It is also an excellent	783	exiting if no event watchers registered by it are active. It is also an
327	way to do this for generic recurring timers or from within third-party	784	excellent way to do this for generic recurring timers or from within
328	libraries. Just remember to I<unref after start> and I<ref before stop>.	785	third-party libraries. Just remember to I<unref after start> and I<ref
		786	before stop> (but only if the watcher wasn't active before, or was active
		787	before, respectively. Note also that libev might stop watchers itself
		788	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		789	in the callback).
		790
		791	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		792	running when nothing else is active.
		793
		794	ev_signal exitsig;
		795	ev_signal_init (&exitsig, sig_cb, SIGINT);
		796	ev_signal_start (loop, &exitsig);
		797	evf_unref (loop);
		798
		799	Example: For some weird reason, unregister the above signal handler again.
		800
		801	ev_ref (loop);
		802	ev_signal_stop (loop, &exitsig);
		803
		804	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		805
		806	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		807
		808	These advanced functions influence the time that libev will spend waiting
		809	for events. Both time intervals are by default C<0>, meaning that libev
		810	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		811	latency.
		812
		813	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		814	allows libev to delay invocation of I/O and timer/periodic callbacks
		815	to increase efficiency of loop iterations (or to increase power-saving
		816	opportunities).
		817
		818	The idea is that sometimes your program runs just fast enough to handle
		819	one (or very few) event(s) per loop iteration. While this makes the
		820	program responsive, it also wastes a lot of CPU time to poll for new
		821	events, especially with backends like C<select ()> which have a high
		822	overhead for the actual polling but can deliver many events at once.
		823
		824	By setting a higher I<io collect interval> you allow libev to spend more
		825	time collecting I/O events, so you can handle more events per iteration,
		826	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		827	C<ev_timer>) will be not affected. Setting this to a non-null value will
		828	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		829	sleep time ensures that libev will not poll for I/O events more often then
		830	once per this interval, on average.
		831
		832	Likewise, by setting a higher I<timeout collect interval> you allow libev
		833	to spend more time collecting timeouts, at the expense of increased
		834	latency/jitter/inexactness (the watcher callback will be called
		835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		836	value will not introduce any overhead in libev.
		837
		838	Many (busy) programs can usually benefit by setting the I/O collect
		839	interval to a value near C<0.1> or so, which is often enough for
		840	interactive servers (of course not for games), likewise for timeouts. It
		841	usually doesn't make much sense to set it to a lower value than C<0.01>,
		842	as this approaches the timing granularity of most systems. Note that if
		843	you do transactions with the outside world and you can't increase the
		844	parallelity, then this setting will limit your transaction rate (if you
		845	need to poll once per transaction and the I/O collect interval is 0.01,
		846	then you can't do more than 100 transations per second).
		847
		848	Setting the I<timeout collect interval> can improve the opportunity for
		849	saving power, as the program will "bundle" timer callback invocations that
		850	are "near" in time together, by delaying some, thus reducing the number of
		851	times the process sleeps and wakes up again. Another useful technique to
		852	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		853	they fire on, say, one-second boundaries only.
		854
		855	Example: we only need 0.1s timeout granularity, and we wish not to poll
		856	more often than 100 times per second:
		857
		858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		860
		861	=item ev_invoke_pending (loop)
		862
		863	This call will simply invoke all pending watchers while resetting their
		864	pending state. Normally, C<ev_loop> does this automatically when required,
		865	but when overriding the invoke callback this call comes handy.
		866
		867	=item int ev_pending_count (loop)
		868
		869	Returns the number of pending watchers - zero indicates that no watchers
		870	are pending.
		871
		872	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		873
		874	This overrides the invoke pending functionality of the loop: Instead of
		875	invoking all pending watchers when there are any, C<ev_loop> will call
		876	this callback instead. This is useful, for example, when you want to
		877	invoke the actual watchers inside another context (another thread etc.).
		878
		879	If you want to reset the callback, use C<ev_invoke_pending> as new
		880	callback.
		881
		882	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		883
		884	Sometimes you want to share the same loop between multiple threads. This
		885	can be done relatively simply by putting mutex_lock/unlock calls around
		886	each call to a libev function.
		887
		888	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		889	wait for it to return. One way around this is to wake up the loop via
		890	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		891	and I<acquire> callbacks on the loop.
		892
		893	When set, then C<release> will be called just before the thread is
		894	suspended waiting for new events, and C<acquire> is called just
		895	afterwards.
		896
		897	Ideally, C<release> will just call your mutex_unlock function, and
		898	C<acquire> will just call the mutex_lock function again.
		899
		900	While event loop modifications are allowed between invocations of
		901	C<release> and C<acquire> (that's their only purpose after all), no
		902	modifications done will affect the event loop, i.e. adding watchers will
		903	have no effect on the set of file descriptors being watched, or the time
		904	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		905	to take note of any changes you made.
		906
		907	In theory, threads executing C<ev_loop> will be async-cancel safe between
		908	invocations of C<release> and C<acquire>.
		909
		910	See also the locking example in the C<THREADS> section later in this
		911	document.
		912
		913	=item ev_set_userdata (loop, void *data)
		914
		915	=item ev_userdata (loop)
		916
		917	Set and retrieve a single C<void *> associated with a loop. When
		918	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		919	C<0.>
		920
		921	These two functions can be used to associate arbitrary data with a loop,
		922	and are intended solely for the C<invoke_pending_cb>, C<release> and
		923	C<acquire> callbacks described above, but of course can be (ab-)used for
		924	any other purpose as well.
		925
		926	=item ev_loop_verify (loop)
		927
		928	This function only does something when C<EV_VERIFY> support has been
		929	compiled in, which is the default for non-minimal builds. It tries to go
		930	through all internal structures and checks them for validity. If anything
		931	is found to be inconsistent, it will print an error message to standard
		932	error and call C<abort ()>.
		933
		934	This can be used to catch bugs inside libev itself: under normal
		935	circumstances, this function will never abort as of course libev keeps its
		936	data structures consistent.
329		937
330	=back	938	=back
331		939
		940
332	=head1 ANATOMY OF A WATCHER	941	=head1 ANATOMY OF A WATCHER
		942
		943	In the following description, uppercase C<TYPE> in names stands for the
		944	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		945	watchers and C<ev_io_start> for I/O watchers.
333		946
334	A watcher is a structure that you create and register to record your	947	A watcher is a structure that you create and register to record your
335	interest in some event. For instance, if you want to wait for STDIN to	948	interest in some event. For instance, if you want to wait for STDIN to
336	become readable, you would create an C<ev_io> watcher for that:	949	become readable, you would create an C<ev_io> watcher for that:
337		950
338	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	951	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
339	{	952	{
340	ev_io_stop (w);	953	ev_io_stop (w);
341	ev_unloop (loop, EVUNLOOP_ALL);	954	ev_unloop (loop, EVUNLOOP_ALL);
342	}	955	}
343		956
344	struct ev_loop *loop = ev_default_loop (0);	957	struct ev_loop *loop = ev_default_loop (0);
		958
345	struct ev_io stdin_watcher;	959	ev_io stdin_watcher;
		960
346	ev_init (&stdin_watcher, my_cb);	961	ev_init (&stdin_watcher, my_cb);
347	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	962	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
348	ev_io_start (loop, &stdin_watcher);	963	ev_io_start (loop, &stdin_watcher);
		964
349	ev_loop (loop, 0);	965	ev_loop (loop, 0);
350		966
351	As you can see, you are responsible for allocating the memory for your	967	As you can see, you are responsible for allocating the memory for your
352	watcher structures (and it is usually a bad idea to do this on the stack,	968	watcher structures (and it is I<usually> a bad idea to do this on the
353	although this can sometimes be quite valid).	969	stack).
		970
		971	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		972	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
354		973
355	Each watcher structure must be initialised by a call to C<ev_init	974	Each watcher structure must be initialised by a call to C<ev_init
356	(watcher *, callback)>, which expects a callback to be provided. This	975	(watcher *, callback)>, which expects a callback to be provided. This
357	callback gets invoked each time the event occurs (or, in the case of io	976	callback gets invoked each time the event occurs (or, in the case of I/O
358	watchers, each time the event loop detects that the file descriptor given	977	watchers, each time the event loop detects that the file descriptor given
359	is readable and/or writable).	978	is readable and/or writable).
360		979
361	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	980	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
362	with arguments specific to this watcher type. There is also a macro	981	macro to configure it, with arguments specific to the watcher type. There
363	to combine initialisation and setting in one call: C<< ev_<type>_init	982	is also a macro to combine initialisation and setting in one call: C<<
364	(watcher *, callback, ...) >>.	983	ev_TYPE_init (watcher *, callback, ...) >>.
365		984
366	To make the watcher actually watch out for events, you have to start it	985	To make the watcher actually watch out for events, you have to start it
367	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	986	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
368	*) >>), and you can stop watching for events at any time by calling the	987	*) >>), and you can stop watching for events at any time by calling the
369	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	988	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
370		989
371	As long as your watcher is active (has been started but not stopped) you	990	As long as your watcher is active (has been started but not stopped) you
372	must not touch the values stored in it. Most specifically you must never	991	must not touch the values stored in it. Most specifically you must never
373	reinitialise it or call its set method.	992	reinitialise it or call its C<ev_TYPE_set> macro.
374
375	You can check whether an event is active by calling the C<ev_is_active
376	(watcher *)> macro. To see whether an event is outstanding (but the
377	callback for it has not been called yet) you can use the C<ev_is_pending
378	(watcher *)> macro.
379		993
380	Each and every callback receives the event loop pointer as first, the	994	Each and every callback receives the event loop pointer as first, the
381	registered watcher structure as second, and a bitset of received events as	995	registered watcher structure as second, and a bitset of received events as
382	third argument.	996	third argument.
383		997
…		…
407	The signal specified in the C<ev_signal> watcher has been received by a thread.	1021	The signal specified in the C<ev_signal> watcher has been received by a thread.
408		1022
409	=item C<EV_CHILD>	1023	=item C<EV_CHILD>
410		1024
411	The pid specified in the C<ev_child> watcher has received a status change.	1025	The pid specified in the C<ev_child> watcher has received a status change.
		1026
		1027	=item C<EV_STAT>
		1028
		1029	The path specified in the C<ev_stat> watcher changed its attributes somehow.
412		1030
413	=item C<EV_IDLE>	1031	=item C<EV_IDLE>
414		1032
415	The C<ev_idle> watcher has determined that you have nothing better to do.	1033	The C<ev_idle> watcher has determined that you have nothing better to do.
416		1034
…		…
424	received events. Callbacks of both watcher types can start and stop as	1042	received events. Callbacks of both watcher types can start and stop as
425	many watchers as they want, and all of them will be taken into account	1043	many watchers as they want, and all of them will be taken into account
426	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1044	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
427	C<ev_loop> from blocking).	1045	C<ev_loop> from blocking).
428		1046
		1047	=item C<EV_EMBED>
		1048
		1049	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1050
		1051	=item C<EV_FORK>
		1052
		1053	The event loop has been resumed in the child process after fork (see
		1054	C<ev_fork>).
		1055
		1056	=item C<EV_ASYNC>
		1057
		1058	The given async watcher has been asynchronously notified (see C<ev_async>).
		1059
		1060	=item C<EV_CUSTOM>
		1061
		1062	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1063	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1064
429	=item C<EV_ERROR>	1065	=item C<EV_ERROR>
430		1066
431	An unspecified error has occured, the watcher has been stopped. This might	1067	An unspecified error has occurred, the watcher has been stopped. This might
432	happen because the watcher could not be properly started because libev	1068	happen because the watcher could not be properly started because libev
433	ran out of memory, a file descriptor was found to be closed or any other	1069	ran out of memory, a file descriptor was found to be closed or any other
		1070	problem. Libev considers these application bugs.
		1071
434	problem. You best act on it by reporting the problem and somehow coping	1072	You best act on it by reporting the problem and somehow coping with the
435	with the watcher being stopped.	1073	watcher being stopped. Note that well-written programs should not receive
		1074	an error ever, so when your watcher receives it, this usually indicates a
		1075	bug in your program.
436		1076
437	Libev will usually signal a few "dummy" events together with an error,	1077	Libev will usually signal a few "dummy" events together with an error, for
438	for example it might indicate that a fd is readable or writable, and if	1078	example it might indicate that a fd is readable or writable, and if your
439	your callbacks is well-written it can just attempt the operation and cope	1079	callbacks is well-written it can just attempt the operation and cope with
440	with the error from read() or write(). This will not work in multithreaded	1080	the error from read() or write(). This will not work in multi-threaded
441	programs, though, so beware.	1081	programs, though, as the fd could already be closed and reused for another
		1082	thing, so beware.
442		1083
443	=back	1084	=back
444		1085
		1086	=head2 GENERIC WATCHER FUNCTIONS
		1087
		1088	=over 4
		1089
		1090	=item C<ev_init> (ev_TYPE *watcher, callback)
		1091
		1092	This macro initialises the generic portion of a watcher. The contents
		1093	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1094	the generic parts of the watcher are initialised, you I<need> to call
		1095	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1096	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1097	which rolls both calls into one.
		1098
		1099	You can reinitialise a watcher at any time as long as it has been stopped
		1100	(or never started) and there are no pending events outstanding.
		1101
		1102	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1103	int revents)>.
		1104
		1105	Example: Initialise an C<ev_io> watcher in two steps.
		1106
		1107	ev_io w;
		1108	ev_init (&w, my_cb);
		1109	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1110
		1111	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		1112
		1113	This macro initialises the type-specific parts of a watcher. You need to
		1114	call C<ev_init> at least once before you call this macro, but you can
		1115	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1116	macro on a watcher that is active (it can be pending, however, which is a
		1117	difference to the C<ev_init> macro).
		1118
		1119	Although some watcher types do not have type-specific arguments
		1120	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1121
		1122	See C<ev_init>, above, for an example.
		1123
		1124	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1125
		1126	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1127	calls into a single call. This is the most convenient method to initialise
		1128	a watcher. The same limitations apply, of course.
		1129
		1130	Example: Initialise and set an C<ev_io> watcher in one step.
		1131
		1132	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1133
		1134	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		1135
		1136	Starts (activates) the given watcher. Only active watchers will receive
		1137	events. If the watcher is already active nothing will happen.
		1138
		1139	Example: Start the C<ev_io> watcher that is being abused as example in this
		1140	whole section.
		1141
		1142	ev_io_start (EV_DEFAULT_UC, &w);
		1143
		1144	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		1145
		1146	Stops the given watcher if active, and clears the pending status (whether
		1147	the watcher was active or not).
		1148
		1149	It is possible that stopped watchers are pending - for example,
		1150	non-repeating timers are being stopped when they become pending - but
		1151	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1152	pending. If you want to free or reuse the memory used by the watcher it is
		1153	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1154
		1155	=item bool ev_is_active (ev_TYPE *watcher)
		1156
		1157	Returns a true value iff the watcher is active (i.e. it has been started
		1158	and not yet been stopped). As long as a watcher is active you must not modify
		1159	it.
		1160
		1161	=item bool ev_is_pending (ev_TYPE *watcher)
		1162
		1163	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1164	events but its callback has not yet been invoked). As long as a watcher
		1165	is pending (but not active) you must not call an init function on it (but
		1166	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1167	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1168	it).
		1169
		1170	=item callback ev_cb (ev_TYPE *watcher)
		1171
		1172	Returns the callback currently set on the watcher.
		1173
		1174	=item ev_cb_set (ev_TYPE *watcher, callback)
		1175
		1176	Change the callback. You can change the callback at virtually any time
		1177	(modulo threads).
		1178
		1179	=item ev_set_priority (ev_TYPE *watcher, priority)
		1180
		1181	=item int ev_priority (ev_TYPE *watcher)
		1182
		1183	Set and query the priority of the watcher. The priority is a small
		1184	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1185	(default: C<-2>). Pending watchers with higher priority will be invoked
		1186	before watchers with lower priority, but priority will not keep watchers
		1187	from being executed (except for C<ev_idle> watchers).
		1188
		1189	If you need to suppress invocation when higher priority events are pending
		1190	you need to look at C<ev_idle> watchers, which provide this functionality.
		1191
		1192	You I<must not> change the priority of a watcher as long as it is active or
		1193	pending.
		1194
		1195	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1196	fine, as long as you do not mind that the priority value you query might
		1197	or might not have been clamped to the valid range.
		1198
		1199	The default priority used by watchers when no priority has been set is
		1200	always C<0>, which is supposed to not be too high and not be too low :).
		1201
		1202	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1203	priorities.
		1204
		1205	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1206
		1207	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1208	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1209	can deal with that fact, as both are simply passed through to the
		1210	callback.
		1211
		1212	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1213
		1214	If the watcher is pending, this function clears its pending status and
		1215	returns its C<revents> bitset (as if its callback was invoked). If the
		1216	watcher isn't pending it does nothing and returns C<0>.
		1217
		1218	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1219	callback to be invoked, which can be accomplished with this function.
		1220
		1221	=back
		1222
		1223
445	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1224	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
446		1225
447	Each watcher has, by default, a member C<void *data> that you can change	1226	Each watcher has, by default, a member C<void *data> that you can change
448	and read at any time, libev will completely ignore it. This can be used	1227	and read at any time: libev will completely ignore it. This can be used
449	to associate arbitrary data with your watcher. If you need more data and	1228	to associate arbitrary data with your watcher. If you need more data and
450	don't want to allocate memory and store a pointer to it in that data	1229	don't want to allocate memory and store a pointer to it in that data
451	member, you can also "subclass" the watcher type and provide your own	1230	member, you can also "subclass" the watcher type and provide your own
452	data:	1231	data:
453		1232
454	struct my_io	1233	struct my_io
455	{	1234	{
456	struct ev_io io;	1235	ev_io io;
457	int otherfd;	1236	int otherfd;
458	void *somedata;	1237	void *somedata;
459	struct whatever *mostinteresting;	1238	struct whatever *mostinteresting;
460	}	1239	};
		1240
		1241	...
		1242	struct my_io w;
		1243	ev_io_init (&w.io, my_cb, fd, EV_READ);
461		1244
462	And since your callback will be called with a pointer to the watcher, you	1245	And since your callback will be called with a pointer to the watcher, you
463	can cast it back to your own type:	1246	can cast it back to your own type:
464		1247
465	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1248	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
466	{	1249	{
467	struct my_io *w = (struct my_io *)w_;	1250	struct my_io *w = (struct my_io *)w_;
468	...	1251	...
469	}	1252	}
470		1253
471	More interesting and less C-conformant ways of catsing your callback type	1254	More interesting and less C-conformant ways of casting your callback type
472	have been omitted....	1255	instead have been omitted.
		1256
		1257	Another common scenario is to use some data structure with multiple
		1258	embedded watchers:
		1259
		1260	struct my_biggy
		1261	{
		1262	int some_data;
		1263	ev_timer t1;
		1264	ev_timer t2;
		1265	}
		1266
		1267	In this case getting the pointer to C<my_biggy> is a bit more
		1268	complicated: Either you store the address of your C<my_biggy> struct
		1269	in the C<data> member of the watcher (for woozies), or you need to use
		1270	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1271	programmers):
		1272
		1273	#include <stddef.h>
		1274
		1275	static void
		1276	t1_cb (EV_P_ ev_timer *w, int revents)
		1277	{
		1278	struct my_biggy big = (struct my_biggy *)
		1279	(((char *)w) - offsetof (struct my_biggy, t1));
		1280	}
		1281
		1282	static void
		1283	t2_cb (EV_P_ ev_timer *w, int revents)
		1284	{
		1285	struct my_biggy big = (struct my_biggy *)
		1286	(((char *)w) - offsetof (struct my_biggy, t2));
		1287	}
		1288
		1289	=head2 WATCHER PRIORITY MODELS
		1290
		1291	Many event loops support I<watcher priorities>, which are usually small
		1292	integers that influence the ordering of event callback invocation
		1293	between watchers in some way, all else being equal.
		1294
		1295	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1296	description for the more technical details such as the actual priority
		1297	range.
		1298
		1299	There are two common ways how these these priorities are being interpreted
		1300	by event loops:
		1301
		1302	In the more common lock-out model, higher priorities "lock out" invocation
		1303	of lower priority watchers, which means as long as higher priority
		1304	watchers receive events, lower priority watchers are not being invoked.
		1305
		1306	The less common only-for-ordering model uses priorities solely to order
		1307	callback invocation within a single event loop iteration: Higher priority
		1308	watchers are invoked before lower priority ones, but they all get invoked
		1309	before polling for new events.
		1310
		1311	Libev uses the second (only-for-ordering) model for all its watchers
		1312	except for idle watchers (which use the lock-out model).
		1313
		1314	The rationale behind this is that implementing the lock-out model for
		1315	watchers is not well supported by most kernel interfaces, and most event
		1316	libraries will just poll for the same events again and again as long as
		1317	their callbacks have not been executed, which is very inefficient in the
		1318	common case of one high-priority watcher locking out a mass of lower
		1319	priority ones.
		1320
		1321	Static (ordering) priorities are most useful when you have two or more
		1322	watchers handling the same resource: a typical usage example is having an
		1323	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1324	timeouts. Under load, data might be received while the program handles
		1325	other jobs, but since timers normally get invoked first, the timeout
		1326	handler will be executed before checking for data. In that case, giving
		1327	the timer a lower priority than the I/O watcher ensures that I/O will be
		1328	handled first even under adverse conditions (which is usually, but not
		1329	always, what you want).
		1330
		1331	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1332	will only be executed when no same or higher priority watchers have
		1333	received events, they can be used to implement the "lock-out" model when
		1334	required.
		1335
		1336	For example, to emulate how many other event libraries handle priorities,
		1337	you can associate an C<ev_idle> watcher to each such watcher, and in
		1338	the normal watcher callback, you just start the idle watcher. The real
		1339	processing is done in the idle watcher callback. This causes libev to
		1340	continously poll and process kernel event data for the watcher, but when
		1341	the lock-out case is known to be rare (which in turn is rare :), this is
		1342	workable.
		1343
		1344	Usually, however, the lock-out model implemented that way will perform
		1345	miserably under the type of load it was designed to handle. In that case,
		1346	it might be preferable to stop the real watcher before starting the
		1347	idle watcher, so the kernel will not have to process the event in case
		1348	the actual processing will be delayed for considerable time.
		1349
		1350	Here is an example of an I/O watcher that should run at a strictly lower
		1351	priority than the default, and which should only process data when no
		1352	other events are pending:
		1353
		1354	ev_idle idle; // actual processing watcher
		1355	ev_io io; // actual event watcher
		1356
		1357	static void
		1358	io_cb (EV_P_ ev_io *w, int revents)
		1359	{
		1360	// stop the I/O watcher, we received the event, but
		1361	// are not yet ready to handle it.
		1362	ev_io_stop (EV_A_ w);
		1363
		1364	// start the idle watcher to ahndle the actual event.
		1365	// it will not be executed as long as other watchers
		1366	// with the default priority are receiving events.
		1367	ev_idle_start (EV_A_ &idle);
		1368	}
		1369
		1370	static void
		1371	idle_cb (EV_P_ ev_idle *w, int revents)
		1372	{
		1373	// actual processing
		1374	read (STDIN_FILENO, ...);
		1375
		1376	// have to start the I/O watcher again, as
		1377	// we have handled the event
		1378	ev_io_start (EV_P_ &io);
		1379	}
		1380
		1381	// initialisation
		1382	ev_idle_init (&idle, idle_cb);
		1383	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1384	ev_io_start (EV_DEFAULT_ &io);
		1385
		1386	In the "real" world, it might also be beneficial to start a timer, so that
		1387	low-priority connections can not be locked out forever under load. This
		1388	enables your program to keep a lower latency for important connections
		1389	during short periods of high load, while not completely locking out less
		1390	important ones.
473		1391
474		1392
475	=head1 WATCHER TYPES	1393	=head1 WATCHER TYPES
476		1394
477	This section describes each watcher in detail, but will not repeat	1395	This section describes each watcher in detail, but will not repeat
478	information given in the last section.	1396	information given in the last section. Any initialisation/set macros,
		1397	functions and members specific to the watcher type are explained.
479		1398
		1399	Members are additionally marked with either I<[read-only]>, meaning that,
		1400	while the watcher is active, you can look at the member and expect some
		1401	sensible content, but you must not modify it (you can modify it while the
		1402	watcher is stopped to your hearts content), or I<[read-write]>, which
		1403	means you can expect it to have some sensible content while the watcher
		1404	is active, but you can also modify it. Modifying it may not do something
		1405	sensible or take immediate effect (or do anything at all), but libev will
		1406	not crash or malfunction in any way.
		1407
		1408
480	=head2 C<ev_io> - is this file descriptor readable or writable	1409	=head2 C<ev_io> - is this file descriptor readable or writable?
481		1410
482	I/O watchers check whether a file descriptor is readable or writable	1411	I/O watchers check whether a file descriptor is readable or writable
483	in each iteration of the event loop (This behaviour is called	1412	in each iteration of the event loop, or, more precisely, when reading
484	level-triggering because you keep receiving events as long as the	1413	would not block the process and writing would at least be able to write
485	condition persists. Remember you can stop the watcher if you don't want to	1414	some data. This behaviour is called level-triggering because you keep
486	act on the event and neither want to receive future events).	1415	receiving events as long as the condition persists. Remember you can stop
		1416	the watcher if you don't want to act on the event and neither want to
		1417	receive future events.
487		1418
488	In general you can register as many read and/or write event watchers per	1419	In general you can register as many read and/or write event watchers per
489	fd as you want (as long as you don't confuse yourself). Setting all file	1420	fd as you want (as long as you don't confuse yourself). Setting all file
490	descriptors to non-blocking mode is also usually a good idea (but not	1421	descriptors to non-blocking mode is also usually a good idea (but not
491	required if you know what you are doing).	1422	required if you know what you are doing).
492		1423
493	You have to be careful with dup'ed file descriptors, though. Some backends	1424	If you cannot use non-blocking mode, then force the use of a
494	(the linux epoll backend is a notable example) cannot handle dup'ed file	1425	known-to-be-good backend (at the time of this writing, this includes only
495	descriptors correctly if you register interest in two or more fds pointing	1426	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
496	to the same underlying file/socket etc. description (that is, they share	1427	descriptors for which non-blocking operation makes no sense (such as
497	the same underlying "file open").	1428	files) - libev doesn't guarentee any specific behaviour in that case.
498		1429
499	If you must do this, then force the use of a known-to-be-good backend	1430	Another thing you have to watch out for is that it is quite easy to
500	(at the time of this writing, this includes only EVMETHOD_SELECT and	1431	receive "spurious" readiness notifications, that is your callback might
501	EVMETHOD_POLL).	1432	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1433	because there is no data. Not only are some backends known to create a
		1434	lot of those (for example Solaris ports), it is very easy to get into
		1435	this situation even with a relatively standard program structure. Thus
		1436	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1437	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1438
		1439	If you cannot run the fd in non-blocking mode (for example you should
		1440	not play around with an Xlib connection), then you have to separately
		1441	re-test whether a file descriptor is really ready with a known-to-be good
		1442	interface such as poll (fortunately in our Xlib example, Xlib already
		1443	does this on its own, so its quite safe to use). Some people additionally
		1444	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1445	indefinitely.
		1446
		1447	But really, best use non-blocking mode.
		1448
		1449	=head3 The special problem of disappearing file descriptors
		1450
		1451	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1452	descriptor (either due to calling C<close> explicitly or any other means,
		1453	such as C<dup2>). The reason is that you register interest in some file
		1454	descriptor, but when it goes away, the operating system will silently drop
		1455	this interest. If another file descriptor with the same number then is
		1456	registered with libev, there is no efficient way to see that this is, in
		1457	fact, a different file descriptor.
		1458
		1459	To avoid having to explicitly tell libev about such cases, libev follows
		1460	the following policy: Each time C<ev_io_set> is being called, libev
		1461	will assume that this is potentially a new file descriptor, otherwise
		1462	it is assumed that the file descriptor stays the same. That means that
		1463	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1464	descriptor even if the file descriptor number itself did not change.
		1465
		1466	This is how one would do it normally anyway, the important point is that
		1467	the libev application should not optimise around libev but should leave
		1468	optimisations to libev.
		1469
		1470	=head3 The special problem of dup'ed file descriptors
		1471
		1472	Some backends (e.g. epoll), cannot register events for file descriptors,
		1473	but only events for the underlying file descriptions. That means when you
		1474	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1475	events for them, only one file descriptor might actually receive events.
		1476
		1477	There is no workaround possible except not registering events
		1478	for potentially C<dup ()>'ed file descriptors, or to resort to
		1479	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1480
		1481	=head3 The special problem of fork
		1482
		1483	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1484	useless behaviour. Libev fully supports fork, but needs to be told about
		1485	it in the child.
		1486
		1487	To support fork in your programs, you either have to call
		1488	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1489	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1490	C<EVBACKEND_POLL>.
		1491
		1492	=head3 The special problem of SIGPIPE
		1493
		1494	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1495	when writing to a pipe whose other end has been closed, your program gets
		1496	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1497	this is sensible behaviour, for daemons, this is usually undesirable.
		1498
		1499	So when you encounter spurious, unexplained daemon exits, make sure you
		1500	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1501	somewhere, as that would have given you a big clue).
		1502
		1503
		1504	=head3 Watcher-Specific Functions
502		1505
503	=over 4	1506	=over 4
504		1507
505	=item ev_io_init (ev_io *, callback, int fd, int events)	1508	=item ev_io_init (ev_io *, callback, int fd, int events)
506		1509
507	=item ev_io_set (ev_io *, int fd, int events)	1510	=item ev_io_set (ev_io *, int fd, int events)
508		1511
509	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1512	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
510	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1513	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
511	EV_WRITE> to receive the given events.	1514	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1515
		1516	=item int fd [read-only]
		1517
		1518	The file descriptor being watched.
		1519
		1520	=item int events [read-only]
		1521
		1522	The events being watched.
512		1523
513	=back	1524	=back
514		1525
		1526	=head3 Examples
		1527
		1528	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1529	readable, but only once. Since it is likely line-buffered, you could
		1530	attempt to read a whole line in the callback.
		1531
		1532	static void
		1533	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1534	{
		1535	ev_io_stop (loop, w);
		1536	.. read from stdin here (or from w->fd) and handle any I/O errors
		1537	}
		1538
		1539	...
		1540	struct ev_loop *loop = ev_default_init (0);
		1541	ev_io stdin_readable;
		1542	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1543	ev_io_start (loop, &stdin_readable);
		1544	ev_loop (loop, 0);
		1545
		1546
515	=head2 C<ev_timer> - relative and optionally recurring timeouts	1547	=head2 C<ev_timer> - relative and optionally repeating timeouts
516		1548
517	Timer watchers are simple relative timers that generate an event after a	1549	Timer watchers are simple relative timers that generate an event after a
518	given time, and optionally repeating in regular intervals after that.	1550	given time, and optionally repeating in regular intervals after that.
519		1551
520	The timers are based on real time, that is, if you register an event that	1552	The timers are based on real time, that is, if you register an event that
521	times out after an hour and you reset your system clock to last years	1553	times out after an hour and you reset your system clock to January last
522	time, it will still time out after (roughly) and hour. "Roughly" because	1554	year, it will still time out after (roughly) one hour. "Roughly" because
523	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1555	detecting time jumps is hard, and some inaccuracies are unavoidable (the
524	monotonic clock option helps a lot here).	1556	monotonic clock option helps a lot here).
		1557
		1558	The callback is guaranteed to be invoked only I<after> its timeout has
		1559	passed (not I<at>, so on systems with very low-resolution clocks this
		1560	might introduce a small delay). If multiple timers become ready during the
		1561	same loop iteration then the ones with earlier time-out values are invoked
		1562	before ones of the same priority with later time-out values (but this is
		1563	no longer true when a callback calls C<ev_loop> recursively).
		1564
		1565	=head3 Be smart about timeouts
		1566
		1567	Many real-world problems involve some kind of timeout, usually for error
		1568	recovery. A typical example is an HTTP request - if the other side hangs,
		1569	you want to raise some error after a while.
		1570
		1571	What follows are some ways to handle this problem, from obvious and
		1572	inefficient to smart and efficient.
		1573
		1574	In the following, a 60 second activity timeout is assumed - a timeout that
		1575	gets reset to 60 seconds each time there is activity (e.g. each time some
		1576	data or other life sign was received).
		1577
		1578	=over 4
		1579
		1580	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1581
		1582	This is the most obvious, but not the most simple way: In the beginning,
		1583	start the watcher:
		1584
		1585	ev_timer_init (timer, callback, 60., 0.);
		1586	ev_timer_start (loop, timer);
		1587
		1588	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1589	and start it again:
		1590
		1591	ev_timer_stop (loop, timer);
		1592	ev_timer_set (timer, 60., 0.);
		1593	ev_timer_start (loop, timer);
		1594
		1595	This is relatively simple to implement, but means that each time there is
		1596	some activity, libev will first have to remove the timer from its internal
		1597	data structure and then add it again. Libev tries to be fast, but it's
		1598	still not a constant-time operation.
		1599
		1600	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1601
		1602	This is the easiest way, and involves using C<ev_timer_again> instead of
		1603	C<ev_timer_start>.
		1604
		1605	To implement this, configure an C<ev_timer> with a C<repeat> value
		1606	of C<60> and then call C<ev_timer_again> at start and each time you
		1607	successfully read or write some data. If you go into an idle state where
		1608	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1609	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1610
		1611	That means you can ignore both the C<ev_timer_start> function and the
		1612	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1613	member and C<ev_timer_again>.
		1614
		1615	At start:
		1616
		1617	ev_init (timer, callback);
		1618	timer->repeat = 60.;
		1619	ev_timer_again (loop, timer);
		1620
		1621	Each time there is some activity:
		1622
		1623	ev_timer_again (loop, timer);
		1624
		1625	It is even possible to change the time-out on the fly, regardless of
		1626	whether the watcher is active or not:
		1627
		1628	timer->repeat = 30.;
		1629	ev_timer_again (loop, timer);
		1630
		1631	This is slightly more efficient then stopping/starting the timer each time
		1632	you want to modify its timeout value, as libev does not have to completely
		1633	remove and re-insert the timer from/into its internal data structure.
		1634
		1635	It is, however, even simpler than the "obvious" way to do it.
		1636
		1637	=item 3. Let the timer time out, but then re-arm it as required.
		1638
		1639	This method is more tricky, but usually most efficient: Most timeouts are
		1640	relatively long compared to the intervals between other activity - in
		1641	our example, within 60 seconds, there are usually many I/O events with
		1642	associated activity resets.
		1643
		1644	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1645	but remember the time of last activity, and check for a real timeout only
		1646	within the callback:
		1647
		1648	ev_tstamp last_activity; // time of last activity
		1649
		1650	static void
		1651	callback (EV_P_ ev_timer *w, int revents)
		1652	{
		1653	ev_tstamp now = ev_now (EV_A);
		1654	ev_tstamp timeout = last_activity + 60.;
		1655
		1656	// if last_activity + 60. is older than now, we did time out
		1657	if (timeout < now)
		1658	{
		1659	// timeout occured, take action
		1660	}
		1661	else
		1662	{
		1663	// callback was invoked, but there was some activity, re-arm
		1664	// the watcher to fire in last_activity + 60, which is
		1665	// guaranteed to be in the future, so "again" is positive:
		1666	w->repeat = timeout - now;
		1667	ev_timer_again (EV_A_ w);
		1668	}
		1669	}
		1670
		1671	To summarise the callback: first calculate the real timeout (defined
		1672	as "60 seconds after the last activity"), then check if that time has
		1673	been reached, which means something I<did>, in fact, time out. Otherwise
		1674	the callback was invoked too early (C<timeout> is in the future), so
		1675	re-schedule the timer to fire at that future time, to see if maybe we have
		1676	a timeout then.
		1677
		1678	Note how C<ev_timer_again> is used, taking advantage of the
		1679	C<ev_timer_again> optimisation when the timer is already running.
		1680
		1681	This scheme causes more callback invocations (about one every 60 seconds
		1682	minus half the average time between activity), but virtually no calls to
		1683	libev to change the timeout.
		1684
		1685	To start the timer, simply initialise the watcher and set C<last_activity>
		1686	to the current time (meaning we just have some activity :), then call the
		1687	callback, which will "do the right thing" and start the timer:
		1688
		1689	ev_init (timer, callback);
		1690	last_activity = ev_now (loop);
		1691	callback (loop, timer, EV_TIMEOUT);
		1692
		1693	And when there is some activity, simply store the current time in
		1694	C<last_activity>, no libev calls at all:
		1695
		1696	last_actiivty = ev_now (loop);
		1697
		1698	This technique is slightly more complex, but in most cases where the
		1699	time-out is unlikely to be triggered, much more efficient.
		1700
		1701	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1702	callback :) - just change the timeout and invoke the callback, which will
		1703	fix things for you.
		1704
		1705	=item 4. Wee, just use a double-linked list for your timeouts.
		1706
		1707	If there is not one request, but many thousands (millions...), all
		1708	employing some kind of timeout with the same timeout value, then one can
		1709	do even better:
		1710
		1711	When starting the timeout, calculate the timeout value and put the timeout
		1712	at the I<end> of the list.
		1713
		1714	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1715	the list is expected to fire (for example, using the technique #3).
		1716
		1717	When there is some activity, remove the timer from the list, recalculate
		1718	the timeout, append it to the end of the list again, and make sure to
		1719	update the C<ev_timer> if it was taken from the beginning of the list.
		1720
		1721	This way, one can manage an unlimited number of timeouts in O(1) time for
		1722	starting, stopping and updating the timers, at the expense of a major
		1723	complication, and having to use a constant timeout. The constant timeout
		1724	ensures that the list stays sorted.
		1725
		1726	=back
		1727
		1728	So which method the best?
		1729
		1730	Method #2 is a simple no-brain-required solution that is adequate in most
		1731	situations. Method #3 requires a bit more thinking, but handles many cases
		1732	better, and isn't very complicated either. In most case, choosing either
		1733	one is fine, with #3 being better in typical situations.
		1734
		1735	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1736	rather complicated, but extremely efficient, something that really pays
		1737	off after the first million or so of active timers, i.e. it's usually
		1738	overkill :)
		1739
		1740	=head3 The special problem of time updates
		1741
		1742	Establishing the current time is a costly operation (it usually takes at
		1743	least two system calls): EV therefore updates its idea of the current
		1744	time only before and after C<ev_loop> collects new events, which causes a
		1745	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1746	lots of events in one iteration.
525		1747
526	The relative timeouts are calculated relative to the C<ev_now ()>	1748	The relative timeouts are calculated relative to the C<ev_now ()>
527	time. This is usually the right thing as this timestamp refers to the time	1749	time. This is usually the right thing as this timestamp refers to the time
528	of the event triggering whatever timeout you are modifying/starting. If	1750	of the event triggering whatever timeout you are modifying/starting. If
529	you suspect event processing to be delayed and you I<need> to base the timeout	1751	you suspect event processing to be delayed and you I<need> to base the
530	on the current time, use something like this to adjust for this:	1752	timeout on the current time, use something like this to adjust for this:
531		1753
532	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1754	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
533		1755
534	The callback is guarenteed to be invoked only when its timeout has passed,	1756	If the event loop is suspended for a long time, you can also force an
535	but if multiple timers become ready during the same loop iteration then	1757	update of the time returned by C<ev_now ()> by calling C<ev_now_update
536	order of execution is undefined.	1758	()>.
		1759
		1760	=head3 Watcher-Specific Functions and Data Members
537		1761
538	=over 4	1762	=over 4
539		1763
540	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1764	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
541		1765
542	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1766	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
543		1767
544	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1768	Configure the timer to trigger after C<after> seconds. If C<repeat>
545	C<0.>, then it will automatically be stopped. If it is positive, then the	1769	is C<0.>, then it will automatically be stopped once the timeout is
546	timer will automatically be configured to trigger again C<repeat> seconds	1770	reached. If it is positive, then the timer will automatically be
547	later, again, and again, until stopped manually.	1771	configured to trigger again C<repeat> seconds later, again, and again,
		1772	until stopped manually.
548		1773
549	The timer itself will do a best-effort at avoiding drift, that is, if you	1774	The timer itself will do a best-effort at avoiding drift, that is, if
550	configure a timer to trigger every 10 seconds, then it will trigger at	1775	you configure a timer to trigger every 10 seconds, then it will normally
551	exactly 10 second intervals. If, however, your program cannot keep up with	1776	trigger at exactly 10 second intervals. If, however, your program cannot
552	the timer (because it takes longer than those 10 seconds to do stuff) the	1777	keep up with the timer (because it takes longer than those 10 seconds to
553	timer will not fire more than once per event loop iteration.	1778	do stuff) the timer will not fire more than once per event loop iteration.
554		1779
555	=item ev_timer_again (loop)	1780	=item ev_timer_again (loop, ev_timer *)
556		1781
557	This will act as if the timer timed out and restart it again if it is	1782	This will act as if the timer timed out and restart it again if it is
558	repeating. The exact semantics are:	1783	repeating. The exact semantics are:
559		1784
		1785	If the timer is pending, its pending status is cleared.
		1786
560	If the timer is started but nonrepeating, stop it.	1787	If the timer is started but non-repeating, stop it (as if it timed out).
561		1788
562	If the timer is repeating, either start it if necessary (with the repeat	1789	If the timer is repeating, either start it if necessary (with the
563	value), or reset the running timer to the repeat value.	1790	C<repeat> value), or reset the running timer to the C<repeat> value.
564		1791
565	This sounds a bit complicated, but here is a useful and typical	1792	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
566	example: Imagine you have a tcp connection and you want a so-called idle	1793	usage example.
567	timeout, that is, you want to be called when there have been, say, 60	1794
568	seconds of inactivity on the socket. The easiest way to do this is to	1795	=item ev_tstamp repeat [read-write]
569	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1796
570	time you successfully read or write some data. If you go into an idle	1797	The current C<repeat> value. Will be used each time the watcher times out
571	state where you do not expect data to travel on the socket, you can stop	1798	or C<ev_timer_again> is called, and determines the next timeout (if any),
572	the timer, and again will automatically restart it if need be.	1799	which is also when any modifications are taken into account.
573		1800
574	=back	1801	=back
575		1802
		1803	=head3 Examples
		1804
		1805	Example: Create a timer that fires after 60 seconds.
		1806
		1807	static void
		1808	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1809	{
		1810	.. one minute over, w is actually stopped right here
		1811	}
		1812
		1813	ev_timer mytimer;
		1814	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1815	ev_timer_start (loop, &mytimer);
		1816
		1817	Example: Create a timeout timer that times out after 10 seconds of
		1818	inactivity.
		1819
		1820	static void
		1821	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1822	{
		1823	.. ten seconds without any activity
		1824	}
		1825
		1826	ev_timer mytimer;
		1827	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1828	ev_timer_again (&mytimer); /* start timer */
		1829	ev_loop (loop, 0);
		1830
		1831	// and in some piece of code that gets executed on any "activity":
		1832	// reset the timeout to start ticking again at 10 seconds
		1833	ev_timer_again (&mytimer);
		1834
		1835
576	=head2 C<ev_periodic> - to cron or not to cron	1836	=head2 C<ev_periodic> - to cron or not to cron?
577		1837
578	Periodic watchers are also timers of a kind, but they are very versatile	1838	Periodic watchers are also timers of a kind, but they are very versatile
579	(and unfortunately a bit complex).	1839	(and unfortunately a bit complex).
580		1840
581	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1841	Unlike C<ev_timer>, periodic watchers are not based on real time (or
582	but on wallclock time (absolute time). You can tell a periodic watcher	1842	relative time, the physical time that passes) but on wall clock time
583	to trigger "at" some specific point in time. For example, if you tell a	1843	(absolute time, the thing you can read on your calender or clock). The
584	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1844	difference is that wall clock time can run faster or slower than real
585	+ 10.>) and then reset your system clock to the last year, then it will	1845	time, and time jumps are not uncommon (e.g. when you adjust your
586	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1846	wrist-watch).
587	roughly 10 seconds later and of course not if you reset your system time
588	again).
589		1847
590	They can also be used to implement vastly more complex timers, such as	1848	You can tell a periodic watcher to trigger after some specific point
		1849	in time: for example, if you tell a periodic watcher to trigger "in 10
		1850	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1851	not a delay) and then reset your system clock to January of the previous
		1852	year, then it will take a year or more to trigger the event (unlike an
		1853	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1854	it, as it uses a relative timeout).
		1855
		1856	C<ev_periodic> watchers can also be used to implement vastly more complex
591	triggering an event on eahc midnight, local time.	1857	timers, such as triggering an event on each "midnight, local time", or
		1858	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1859	those cannot react to time jumps.
592		1860
593	As with timers, the callback is guarenteed to be invoked only when the	1861	As with timers, the callback is guaranteed to be invoked only when the
594	time (C<at>) has been passed, but if multiple periodic timers become ready	1862	point in time where it is supposed to trigger has passed. If multiple
595	during the same loop iteration then order of execution is undefined.	1863	timers become ready during the same loop iteration then the ones with
		1864	earlier time-out values are invoked before ones with later time-out values
		1865	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1866
		1867	=head3 Watcher-Specific Functions and Data Members
596		1868
597	=over 4	1869	=over 4
598		1870
599	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1871	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
600		1872
601	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1873	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
602		1874
603	Lots of arguments, lets sort it out... There are basically three modes of	1875	Lots of arguments, let's sort it out... There are basically three modes of
604	operation, and we will explain them from simplest to complex:	1876	operation, and we will explain them from simplest to most complex:
605		1877
606	=over 4	1878	=over 4
607		1879
608	=item * absolute timer (interval = reschedule_cb = 0)	1880	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
609		1881
610	In this configuration the watcher triggers an event at the wallclock time	1882	In this configuration the watcher triggers an event after the wall clock
611	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1883	time C<offset> has passed. It will not repeat and will not adjust when a
612	that is, if it is to be run at January 1st 2011 then it will run when the	1884	time jump occurs, that is, if it is to be run at January 1st 2011 then it
613	system time reaches or surpasses this time.	1885	will be stopped and invoked when the system clock reaches or surpasses
		1886	this point in time.
614		1887
615	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1888	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
616		1889
617	In this mode the watcher will always be scheduled to time out at the next	1890	In this mode the watcher will always be scheduled to time out at the next
618	C<at + N * interval> time (for some integer N) and then repeat, regardless	1891	C<offset + N * interval> time (for some integer N, which can also be
619	of any time jumps.	1892	negative) and then repeat, regardless of any time jumps. The C<offset>
		1893	argument is merely an offset into the C<interval> periods.
620		1894
621	This can be used to create timers that do not drift with respect to system	1895	This can be used to create timers that do not drift with respect to the
622	time:	1896	system clock, for example, here is an C<ev_periodic> that triggers each
		1897	hour, on the hour (with respect to UTC):
623		1898
624	ev_periodic_set (&periodic, 0., 3600., 0);	1899	ev_periodic_set (&periodic, 0., 3600., 0);
625		1900
626	This doesn't mean there will always be 3600 seconds in between triggers,	1901	This doesn't mean there will always be 3600 seconds in between triggers,
627	but only that the the callback will be called when the system time shows a	1902	but only that the callback will be called when the system time shows a
628	full hour (UTC), or more correctly, when the system time is evenly divisible	1903	full hour (UTC), or more correctly, when the system time is evenly divisible
629	by 3600.	1904	by 3600.
630		1905
631	Another way to think about it (for the mathematically inclined) is that	1906	Another way to think about it (for the mathematically inclined) is that
632	C<ev_periodic> will try to run the callback in this mode at the next possible	1907	C<ev_periodic> will try to run the callback in this mode at the next possible
633	time where C<time = at (mod interval)>, regardless of any time jumps.	1908	time where C<time = offset (mod interval)>, regardless of any time jumps.
634		1909
		1910	For numerical stability it is preferable that the C<offset> value is near
		1911	C<ev_now ()> (the current time), but there is no range requirement for
		1912	this value, and in fact is often specified as zero.
		1913
		1914	Note also that there is an upper limit to how often a timer can fire (CPU
		1915	speed for example), so if C<interval> is very small then timing stability
		1916	will of course deteriorate. Libev itself tries to be exact to be about one
		1917	millisecond (if the OS supports it and the machine is fast enough).
		1918
635	=item * manual reschedule mode (reschedule_cb = callback)	1919	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
636		1920
637	In this mode the values for C<interval> and C<at> are both being	1921	In this mode the values for C<interval> and C<offset> are both being
638	ignored. Instead, each time the periodic watcher gets scheduled, the	1922	ignored. Instead, each time the periodic watcher gets scheduled, the
639	reschedule callback will be called with the watcher as first, and the	1923	reschedule callback will be called with the watcher as first, and the
640	current time as second argument.	1924	current time as second argument.
641		1925
642	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1926	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
643	ever, or make any event loop modifications>. If you need to stop it,	1927	or make ANY other event loop modifications whatsoever, unless explicitly
644	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1928	allowed by documentation here>.
645	starting a prepare watcher).
646		1929
		1930	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1931	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1932	only event loop modification you are allowed to do).
		1933
647	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1934	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
648	ev_tstamp now)>, e.g.:	1935	*w, ev_tstamp now)>, e.g.:
649		1936
		1937	static ev_tstamp
650	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1938	my_rescheduler (ev_periodic *w, ev_tstamp now)
651	{	1939	{
652	return now + 60.;	1940	return now + 60.;
653	}	1941	}
654		1942
655	It must return the next time to trigger, based on the passed time value	1943	It must return the next time to trigger, based on the passed time value
656	(that is, the lowest time value larger than to the second argument). It	1944	(that is, the lowest time value larger than to the second argument). It
657	will usually be called just before the callback will be triggered, but	1945	will usually be called just before the callback will be triggered, but
658	might be called at other times, too.	1946	might be called at other times, too.
659		1947
660	NOTE: I<< This callback must always return a time that is later than the	1948	NOTE: I<< This callback must always return a time that is higher than or
661	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1949	equal to the passed C<now> value >>.
662		1950
663	This can be used to create very complex timers, such as a timer that	1951	This can be used to create very complex timers, such as a timer that
664	triggers on each midnight, local time. To do this, you would calculate the	1952	triggers on "next midnight, local time". To do this, you would calculate the
665	next midnight after C<now> and return the timestamp value for this. How	1953	next midnight after C<now> and return the timestamp value for this. How
666	you do this is, again, up to you (but it is not trivial, which is the main	1954	you do this is, again, up to you (but it is not trivial, which is the main
667	reason I omitted it as an example).	1955	reason I omitted it as an example).
668		1956
669	=back	1957	=back
…		…
673	Simply stops and restarts the periodic watcher again. This is only useful	1961	Simply stops and restarts the periodic watcher again. This is only useful
674	when you changed some parameters or the reschedule callback would return	1962	when you changed some parameters or the reschedule callback would return
675	a different time than the last time it was called (e.g. in a crond like	1963	a different time than the last time it was called (e.g. in a crond like
676	program when the crontabs have changed).	1964	program when the crontabs have changed).
677		1965
		1966	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1967
		1968	When active, returns the absolute time that the watcher is supposed
		1969	to trigger next. This is not the same as the C<offset> argument to
		1970	C<ev_periodic_set>, but indeed works even in interval and manual
		1971	rescheduling modes.
		1972
		1973	=item ev_tstamp offset [read-write]
		1974
		1975	When repeating, this contains the offset value, otherwise this is the
		1976	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1977	although libev might modify this value for better numerical stability).
		1978
		1979	Can be modified any time, but changes only take effect when the periodic
		1980	timer fires or C<ev_periodic_again> is being called.
		1981
		1982	=item ev_tstamp interval [read-write]
		1983
		1984	The current interval value. Can be modified any time, but changes only
		1985	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1986	called.
		1987
		1988	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		1989
		1990	The current reschedule callback, or C<0>, if this functionality is
		1991	switched off. Can be changed any time, but changes only take effect when
		1992	the periodic timer fires or C<ev_periodic_again> is being called.
		1993
678	=back	1994	=back
679		1995
		1996	=head3 Examples
		1997
		1998	Example: Call a callback every hour, or, more precisely, whenever the
		1999	system time is divisible by 3600. The callback invocation times have
		2000	potentially a lot of jitter, but good long-term stability.
		2001
		2002	static void
		2003	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
		2004	{
		2005	... its now a full hour (UTC, or TAI or whatever your clock follows)
		2006	}
		2007
		2008	ev_periodic hourly_tick;
		2009	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		2010	ev_periodic_start (loop, &hourly_tick);
		2011
		2012	Example: The same as above, but use a reschedule callback to do it:
		2013
		2014	#include <math.h>
		2015
		2016	static ev_tstamp
		2017	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		2018	{
		2019	return now + (3600. - fmod (now, 3600.));
		2020	}
		2021
		2022	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		2023
		2024	Example: Call a callback every hour, starting now:
		2025
		2026	ev_periodic hourly_tick;
		2027	ev_periodic_init (&hourly_tick, clock_cb,
		2028	fmod (ev_now (loop), 3600.), 3600., 0);
		2029	ev_periodic_start (loop, &hourly_tick);
		2030
		2031
680	=head2 C<ev_signal> - signal me when a signal gets signalled	2032	=head2 C<ev_signal> - signal me when a signal gets signalled!
681		2033
682	Signal watchers will trigger an event when the process receives a specific	2034	Signal watchers will trigger an event when the process receives a specific
683	signal one or more times. Even though signals are very asynchronous, libev	2035	signal one or more times. Even though signals are very asynchronous, libev
684	will try it's best to deliver signals synchronously, i.e. as part of the	2036	will try it's best to deliver signals synchronously, i.e. as part of the
685	normal event processing, like any other event.	2037	normal event processing, like any other event.
686		2038
		2039	If you want signals asynchronously, just use C<sigaction> as you would
		2040	do without libev and forget about sharing the signal. You can even use
		2041	C<ev_async> from a signal handler to synchronously wake up an event loop.
		2042
687	You can configure as many watchers as you like per signal. Only when the	2043	You can configure as many watchers as you like per signal. Only when the
688	first watcher gets started will libev actually register a signal watcher	2044	first watcher gets started will libev actually register a signal handler
689	with the kernel (thus it coexists with your own signal handlers as long	2045	with the kernel (thus it coexists with your own signal handlers as long as
690	as you don't register any with libev). Similarly, when the last signal	2046	you don't register any with libev for the same signal). Similarly, when
691	watcher for a signal is stopped libev will reset the signal handler to	2047	the last signal watcher for a signal is stopped, libev will reset the
692	SIG_DFL (regardless of what it was set to before).	2048	signal handler to SIG_DFL (regardless of what it was set to before).
		2049
		2050	If possible and supported, libev will install its handlers with
		2051	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		2052	interrupted. If you have a problem with system calls getting interrupted by
		2053	signals you can block all signals in an C<ev_check> watcher and unblock
		2054	them in an C<ev_prepare> watcher.
		2055
		2056	=head3 Watcher-Specific Functions and Data Members
693		2057
694	=over 4	2058	=over 4
695		2059
696	=item ev_signal_init (ev_signal *, callback, int signum)	2060	=item ev_signal_init (ev_signal *, callback, int signum)
697		2061
698	=item ev_signal_set (ev_signal *, int signum)	2062	=item ev_signal_set (ev_signal *, int signum)
699		2063
700	Configures the watcher to trigger on the given signal number (usually one	2064	Configures the watcher to trigger on the given signal number (usually one
701	of the C<SIGxxx> constants).	2065	of the C<SIGxxx> constants).
702		2066
		2067	=item int signum [read-only]
		2068
		2069	The signal the watcher watches out for.
		2070
703	=back	2071	=back
704		2072
		2073	=head3 Examples
		2074
		2075	Example: Try to exit cleanly on SIGINT.
		2076
		2077	static void
		2078	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2079	{
		2080	ev_unloop (loop, EVUNLOOP_ALL);
		2081	}
		2082
		2083	ev_signal signal_watcher;
		2084	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2085	ev_signal_start (loop, &signal_watcher);
		2086
		2087
705	=head2 C<ev_child> - wait for pid status changes	2088	=head2 C<ev_child> - watch out for process status changes
706		2089
707	Child watchers trigger when your process receives a SIGCHLD in response to	2090	Child watchers trigger when your process receives a SIGCHLD in response to
708	some child status changes (most typically when a child of yours dies).	2091	some child status changes (most typically when a child of yours dies or
		2092	exits). It is permissible to install a child watcher I<after> the child
		2093	has been forked (which implies it might have already exited), as long
		2094	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2095	forking and then immediately registering a watcher for the child is fine,
		2096	but forking and registering a watcher a few event loop iterations later or
		2097	in the next callback invocation is not.
		2098
		2099	Only the default event loop is capable of handling signals, and therefore
		2100	you can only register child watchers in the default event loop.
		2101
		2102	Due to some design glitches inside libev, child watchers will always be
		2103	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2104	libev)
		2105
		2106	=head3 Process Interaction
		2107
		2108	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2109	initialised. This is necessary to guarantee proper behaviour even if
		2110	the first child watcher is started after the child exits. The occurrence
		2111	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2112	synchronously as part of the event loop processing. Libev always reaps all
		2113	children, even ones not watched.
		2114
		2115	=head3 Overriding the Built-In Processing
		2116
		2117	Libev offers no special support for overriding the built-in child
		2118	processing, but if your application collides with libev's default child
		2119	handler, you can override it easily by installing your own handler for
		2120	C<SIGCHLD> after initialising the default loop, and making sure the
		2121	default loop never gets destroyed. You are encouraged, however, to use an
		2122	event-based approach to child reaping and thus use libev's support for
		2123	that, so other libev users can use C<ev_child> watchers freely.
		2124
		2125	=head3 Stopping the Child Watcher
		2126
		2127	Currently, the child watcher never gets stopped, even when the
		2128	child terminates, so normally one needs to stop the watcher in the
		2129	callback. Future versions of libev might stop the watcher automatically
		2130	when a child exit is detected.
		2131
		2132	=head3 Watcher-Specific Functions and Data Members
709		2133
710	=over 4	2134	=over 4
711		2135
712	=item ev_child_init (ev_child *, callback, int pid)	2136	=item ev_child_init (ev_child *, callback, int pid, int trace)
713		2137
714	=item ev_child_set (ev_child *, int pid)	2138	=item ev_child_set (ev_child *, int pid, int trace)
715		2139
716	Configures the watcher to wait for status changes of process C<pid> (or	2140	Configures the watcher to wait for status changes of process C<pid> (or
717	I<any> process if C<pid> is specified as C<0>). The callback can look	2141	I<any> process if C<pid> is specified as C<0>). The callback can look
718	at the C<rstatus> member of the C<ev_child> watcher structure to see	2142	at the C<rstatus> member of the C<ev_child> watcher structure to see
719	the status word (use the macros from C<sys/wait.h> and see your systems	2143	the status word (use the macros from C<sys/wait.h> and see your systems
720	C<waitpid> documentation). The C<rpid> member contains the pid of the	2144	C<waitpid> documentation). The C<rpid> member contains the pid of the
721	process causing the status change.	2145	process causing the status change. C<trace> must be either C<0> (only
		2146	activate the watcher when the process terminates) or C<1> (additionally
		2147	activate the watcher when the process is stopped or continued).
		2148
		2149	=item int pid [read-only]
		2150
		2151	The process id this watcher watches out for, or C<0>, meaning any process id.
		2152
		2153	=item int rpid [read-write]
		2154
		2155	The process id that detected a status change.
		2156
		2157	=item int rstatus [read-write]
		2158
		2159	The process exit/trace status caused by C<rpid> (see your systems
		2160	C<waitpid> and C<sys/wait.h> documentation for details).
722		2161
723	=back	2162	=back
724		2163
		2164	=head3 Examples
		2165
		2166	Example: C<fork()> a new process and install a child handler to wait for
		2167	its completion.
		2168
		2169	ev_child cw;
		2170
		2171	static void
		2172	child_cb (EV_P_ ev_child *w, int revents)
		2173	{
		2174	ev_child_stop (EV_A_ w);
		2175	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2176	}
		2177
		2178	pid_t pid = fork ();
		2179
		2180	if (pid < 0)
		2181	// error
		2182	else if (pid == 0)
		2183	{
		2184	// the forked child executes here
		2185	exit (1);
		2186	}
		2187	else
		2188	{
		2189	ev_child_init (&cw, child_cb, pid, 0);
		2190	ev_child_start (EV_DEFAULT_ &cw);
		2191	}
		2192
		2193
		2194	=head2 C<ev_stat> - did the file attributes just change?
		2195
		2196	This watches a file system path for attribute changes. That is, it calls
		2197	C<stat> on that path in regular intervals (or when the OS says it changed)
		2198	and sees if it changed compared to the last time, invoking the callback if
		2199	it did.
		2200
		2201	The path does not need to exist: changing from "path exists" to "path does
		2202	not exist" is a status change like any other. The condition "path does not
		2203	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2204	C<st_nlink> field being zero (which is otherwise always forced to be at
		2205	least one) and all the other fields of the stat buffer having unspecified
		2206	contents.
		2207
		2208	The path I<must not> end in a slash or contain special components such as
		2209	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2210	your working directory changes, then the behaviour is undefined.
		2211
		2212	Since there is no portable change notification interface available, the
		2213	portable implementation simply calls C<stat(2)> regularly on the path
		2214	to see if it changed somehow. You can specify a recommended polling
		2215	interval for this case. If you specify a polling interval of C<0> (highly
		2216	recommended!) then a I<suitable, unspecified default> value will be used
		2217	(which you can expect to be around five seconds, although this might
		2218	change dynamically). Libev will also impose a minimum interval which is
		2219	currently around C<0.1>, but that's usually overkill.
		2220
		2221	This watcher type is not meant for massive numbers of stat watchers,
		2222	as even with OS-supported change notifications, this can be
		2223	resource-intensive.
		2224
		2225	At the time of this writing, the only OS-specific interface implemented
		2226	is the Linux inotify interface (implementing kqueue support is left as an
		2227	exercise for the reader. Note, however, that the author sees no way of
		2228	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2229
		2230	=head3 ABI Issues (Largefile Support)
		2231
		2232	Libev by default (unless the user overrides this) uses the default
		2233	compilation environment, which means that on systems with large file
		2234	support disabled by default, you get the 32 bit version of the stat
		2235	structure. When using the library from programs that change the ABI to
		2236	use 64 bit file offsets the programs will fail. In that case you have to
		2237	compile libev with the same flags to get binary compatibility. This is
		2238	obviously the case with any flags that change the ABI, but the problem is
		2239	most noticeably displayed with ev_stat and large file support.
		2240
		2241	The solution for this is to lobby your distribution maker to make large
		2242	file interfaces available by default (as e.g. FreeBSD does) and not
		2243	optional. Libev cannot simply switch on large file support because it has
		2244	to exchange stat structures with application programs compiled using the
		2245	default compilation environment.
		2246
		2247	=head3 Inotify and Kqueue
		2248
		2249	When C<inotify (7)> support has been compiled into libev and present at
		2250	runtime, it will be used to speed up change detection where possible. The
		2251	inotify descriptor will be created lazily when the first C<ev_stat>
		2252	watcher is being started.
		2253
		2254	Inotify presence does not change the semantics of C<ev_stat> watchers
		2255	except that changes might be detected earlier, and in some cases, to avoid
		2256	making regular C<stat> calls. Even in the presence of inotify support
		2257	there are many cases where libev has to resort to regular C<stat> polling,
		2258	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2259	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2260	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2261	xfs are fully working) libev usually gets away without polling.
		2262
		2263	There is no support for kqueue, as apparently it cannot be used to
		2264	implement this functionality, due to the requirement of having a file
		2265	descriptor open on the object at all times, and detecting renames, unlinks
		2266	etc. is difficult.
		2267
		2268	=head3 C<stat ()> is a synchronous operation
		2269
		2270	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2271	the process. The exception are C<ev_stat> watchers - those call C<stat
		2272	()>, which is a synchronous operation.
		2273
		2274	For local paths, this usually doesn't matter: unless the system is very
		2275	busy or the intervals between stat's are large, a stat call will be fast,
		2276	as the path data is usually in memory already (except when starting the
		2277	watcher).
		2278
		2279	For networked file systems, calling C<stat ()> can block an indefinite
		2280	time due to network issues, and even under good conditions, a stat call
		2281	often takes multiple milliseconds.
		2282
		2283	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2284	paths, although this is fully supported by libev.
		2285
		2286	=head3 The special problem of stat time resolution
		2287
		2288	The C<stat ()> system call only supports full-second resolution portably,
		2289	and even on systems where the resolution is higher, most file systems
		2290	still only support whole seconds.
		2291
		2292	That means that, if the time is the only thing that changes, you can
		2293	easily miss updates: on the first update, C<ev_stat> detects a change and
		2294	calls your callback, which does something. When there is another update
		2295	within the same second, C<ev_stat> will be unable to detect unless the
		2296	stat data does change in other ways (e.g. file size).
		2297
		2298	The solution to this is to delay acting on a change for slightly more
		2299	than a second (or till slightly after the next full second boundary), using
		2300	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2301	ev_timer_again (loop, w)>).
		2302
		2303	The C<.02> offset is added to work around small timing inconsistencies
		2304	of some operating systems (where the second counter of the current time
		2305	might be be delayed. One such system is the Linux kernel, where a call to
		2306	C<gettimeofday> might return a timestamp with a full second later than
		2307	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2308	update file times then there will be a small window where the kernel uses
		2309	the previous second to update file times but libev might already execute
		2310	the timer callback).
		2311
		2312	=head3 Watcher-Specific Functions and Data Members
		2313
		2314	=over 4
		2315
		2316	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2317
		2318	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2319
		2320	Configures the watcher to wait for status changes of the given
		2321	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2322	be detected and should normally be specified as C<0> to let libev choose
		2323	a suitable value. The memory pointed to by C<path> must point to the same
		2324	path for as long as the watcher is active.
		2325
		2326	The callback will receive an C<EV_STAT> event when a change was detected,
		2327	relative to the attributes at the time the watcher was started (or the
		2328	last change was detected).
		2329
		2330	=item ev_stat_stat (loop, ev_stat *)
		2331
		2332	Updates the stat buffer immediately with new values. If you change the
		2333	watched path in your callback, you could call this function to avoid
		2334	detecting this change (while introducing a race condition if you are not
		2335	the only one changing the path). Can also be useful simply to find out the
		2336	new values.
		2337
		2338	=item ev_statdata attr [read-only]
		2339
		2340	The most-recently detected attributes of the file. Although the type is
		2341	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2342	suitable for your system, but you can only rely on the POSIX-standardised
		2343	members to be present. If the C<st_nlink> member is C<0>, then there was
		2344	some error while C<stat>ing the file.
		2345
		2346	=item ev_statdata prev [read-only]
		2347
		2348	The previous attributes of the file. The callback gets invoked whenever
		2349	C<prev> != C<attr>, or, more precisely, one or more of these members
		2350	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2351	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2352
		2353	=item ev_tstamp interval [read-only]
		2354
		2355	The specified interval.
		2356
		2357	=item const char *path [read-only]
		2358
		2359	The file system path that is being watched.
		2360
		2361	=back
		2362
		2363	=head3 Examples
		2364
		2365	Example: Watch C</etc/passwd> for attribute changes.
		2366
		2367	static void
		2368	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2369	{
		2370	/* /etc/passwd changed in some way */
		2371	if (w->attr.st_nlink)
		2372	{
		2373	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2374	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2375	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2376	}
		2377	else
		2378	/* you shalt not abuse printf for puts */
		2379	puts ("wow, /etc/passwd is not there, expect problems. "
		2380	"if this is windows, they already arrived\n");
		2381	}
		2382
		2383	...
		2384	ev_stat passwd;
		2385
		2386	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2387	ev_stat_start (loop, &passwd);
		2388
		2389	Example: Like above, but additionally use a one-second delay so we do not
		2390	miss updates (however, frequent updates will delay processing, too, so
		2391	one might do the work both on C<ev_stat> callback invocation I<and> on
		2392	C<ev_timer> callback invocation).
		2393
		2394	static ev_stat passwd;
		2395	static ev_timer timer;
		2396
		2397	static void
		2398	timer_cb (EV_P_ ev_timer *w, int revents)
		2399	{
		2400	ev_timer_stop (EV_A_ w);
		2401
		2402	/* now it's one second after the most recent passwd change */
		2403	}
		2404
		2405	static void
		2406	stat_cb (EV_P_ ev_stat *w, int revents)
		2407	{
		2408	/* reset the one-second timer */
		2409	ev_timer_again (EV_A_ &timer);
		2410	}
		2411
		2412	...
		2413	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2414	ev_stat_start (loop, &passwd);
		2415	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2416
		2417
725	=head2 C<ev_idle> - when you've got nothing better to do	2418	=head2 C<ev_idle> - when you've got nothing better to do...
726		2419
727	Idle watchers trigger events when there are no other events are pending	2420	Idle watchers trigger events when no other events of the same or higher
728	(prepare, check and other idle watchers do not count). That is, as long	2421	priority are pending (prepare, check and other idle watchers do not count
729	as your process is busy handling sockets or timeouts (or even signals,	2422	as receiving "events").
730	imagine) it will not be triggered. But when your process is idle all idle	2423
731	watchers are being called again and again, once per event loop iteration -	2424	That is, as long as your process is busy handling sockets or timeouts
		2425	(or even signals, imagine) of the same or higher priority it will not be
		2426	triggered. But when your process is idle (or only lower-priority watchers
		2427	are pending), the idle watchers are being called once per event loop
732	until stopped, that is, or your process receives more events and becomes	2428	iteration - until stopped, that is, or your process receives more events
733	busy.	2429	and becomes busy again with higher priority stuff.
734		2430
735	The most noteworthy effect is that as long as any idle watchers are	2431	The most noteworthy effect is that as long as any idle watchers are
736	active, the process will not block when waiting for new events.	2432	active, the process will not block when waiting for new events.
737		2433
738	Apart from keeping your process non-blocking (which is a useful	2434	Apart from keeping your process non-blocking (which is a useful
739	effect on its own sometimes), idle watchers are a good place to do	2435	effect on its own sometimes), idle watchers are a good place to do
740	"pseudo-background processing", or delay processing stuff to after the	2436	"pseudo-background processing", or delay processing stuff to after the
741	event loop has handled all outstanding events.	2437	event loop has handled all outstanding events.
742		2438
		2439	=head3 Watcher-Specific Functions and Data Members
		2440
743	=over 4	2441	=over 4
744		2442
745	=item ev_idle_init (ev_signal *, callback)	2443	=item ev_idle_init (ev_idle *, callback)
746		2444
747	Initialises and configures the idle watcher - it has no parameters of any	2445	Initialises and configures the idle watcher - it has no parameters of any
748	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2446	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
749	believe me.	2447	believe me.
750		2448
751	=back	2449	=back
752		2450
		2451	=head3 Examples
		2452
		2453	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2454	callback, free it. Also, use no error checking, as usual.
		2455
		2456	static void
		2457	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2458	{
		2459	free (w);
		2460	// now do something you wanted to do when the program has
		2461	// no longer anything immediate to do.
		2462	}
		2463
		2464	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2465	ev_idle_init (idle_watcher, idle_cb);
		2466	ev_idle_start (loop, idle_watcher);
		2467
		2468
753	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2469	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
754		2470
755	Prepare and check watchers are usually (but not always) used in tandem:	2471	Prepare and check watchers are usually (but not always) used in pairs:
756	prepare watchers get invoked before the process blocks and check watchers	2472	prepare watchers get invoked before the process blocks and check watchers
757	afterwards.	2473	afterwards.
758		2474
		2475	You I<must not> call C<ev_loop> or similar functions that enter
		2476	the current event loop from either C<ev_prepare> or C<ev_check>
		2477	watchers. Other loops than the current one are fine, however. The
		2478	rationale behind this is that you do not need to check for recursion in
		2479	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2480	C<ev_check> so if you have one watcher of each kind they will always be
		2481	called in pairs bracketing the blocking call.
		2482
759	Their main purpose is to integrate other event mechanisms into libev. This	2483	Their main purpose is to integrate other event mechanisms into libev and
760	could be used, for example, to track variable changes, implement your own	2484	their use is somewhat advanced. They could be used, for example, to track
761	watchers, integrate net-snmp or a coroutine library and lots more.	2485	variable changes, implement your own watchers, integrate net-snmp or a
		2486	coroutine library and lots more. They are also occasionally useful if
		2487	you cache some data and want to flush it before blocking (for example,
		2488	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2489	watcher).
762		2490
763	This is done by examining in each prepare call which file descriptors need	2491	This is done by examining in each prepare call which file descriptors
764	to be watched by the other library, registering C<ev_io> watchers for	2492	need to be watched by the other library, registering C<ev_io> watchers
765	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2493	for them and starting an C<ev_timer> watcher for any timeouts (many
766	provide just this functionality). Then, in the check watcher you check for	2494	libraries provide exactly this functionality). Then, in the check watcher,
767	any events that occured (by checking the pending status of all watchers	2495	you check for any events that occurred (by checking the pending status
768	and stopping them) and call back into the library. The I/O and timer	2496	of all watchers and stopping them) and call back into the library. The
769	callbacks will never actually be called (but must be valid nevertheless,	2497	I/O and timer callbacks will never actually be called (but must be valid
770	because you never know, you know?).	2498	nevertheless, because you never know, you know?).
771		2499
772	As another example, the Perl Coro module uses these hooks to integrate	2500	As another example, the Perl Coro module uses these hooks to integrate
773	coroutines into libev programs, by yielding to other active coroutines	2501	coroutines into libev programs, by yielding to other active coroutines
774	during each prepare and only letting the process block if no coroutines	2502	during each prepare and only letting the process block if no coroutines
775	are ready to run (it's actually more complicated: it only runs coroutines	2503	are ready to run (it's actually more complicated: it only runs coroutines
776	with priority higher than or equal to the event loop and one coroutine	2504	with priority higher than or equal to the event loop and one coroutine
777	of lower priority, but only once, using idle watchers to keep the event	2505	of lower priority, but only once, using idle watchers to keep the event
778	loop from blocking if lower-priority coroutines are active, thus mapping	2506	loop from blocking if lower-priority coroutines are active, thus mapping
779	low-priority coroutines to idle/background tasks).	2507	low-priority coroutines to idle/background tasks).
780		2508
		2509	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2510	priority, to ensure that they are being run before any other watchers
		2511	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2512
		2513	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2514	activate ("feed") events into libev. While libev fully supports this, they
		2515	might get executed before other C<ev_check> watchers did their job. As
		2516	C<ev_check> watchers are often used to embed other (non-libev) event
		2517	loops those other event loops might be in an unusable state until their
		2518	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2519	others).
		2520
		2521	=head3 Watcher-Specific Functions and Data Members
		2522
781	=over 4	2523	=over 4
782		2524
783	=item ev_prepare_init (ev_prepare *, callback)	2525	=item ev_prepare_init (ev_prepare *, callback)
784		2526
785	=item ev_check_init (ev_check *, callback)	2527	=item ev_check_init (ev_check *, callback)
786		2528
787	Initialises and configures the prepare or check watcher - they have no	2529	Initialises and configures the prepare or check watcher - they have no
788	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2530	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
789	macros, but using them is utterly, utterly and completely pointless.	2531	macros, but using them is utterly, utterly, utterly and completely
		2532	pointless.
790		2533
791	=back	2534	=back
792		2535
		2536	=head3 Examples
		2537
		2538	There are a number of principal ways to embed other event loops or modules
		2539	into libev. Here are some ideas on how to include libadns into libev
		2540	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2541	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2542	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2543	Glib event loop).
		2544
		2545	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2546	and in a check watcher, destroy them and call into libadns. What follows
		2547	is pseudo-code only of course. This requires you to either use a low
		2548	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2549	the callbacks for the IO/timeout watchers might not have been called yet.
		2550
		2551	static ev_io iow [nfd];
		2552	static ev_timer tw;
		2553
		2554	static void
		2555	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2556	{
		2557	}
		2558
		2559	// create io watchers for each fd and a timer before blocking
		2560	static void
		2561	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2562	{
		2563	int timeout = 3600000;
		2564	struct pollfd fds [nfd];
		2565	// actual code will need to loop here and realloc etc.
		2566	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2567
		2568	/* the callback is illegal, but won't be called as we stop during check */
		2569	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		2570	ev_timer_start (loop, &tw);
		2571
		2572	// create one ev_io per pollfd
		2573	for (int i = 0; i < nfd; ++i)
		2574	{
		2575	ev_io_init (iow + i, io_cb, fds [i].fd,
		2576	((fds [i].events & POLLIN ? EV_READ : 0)
		2577	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2578
		2579	fds [i].revents = 0;
		2580	ev_io_start (loop, iow + i);
		2581	}
		2582	}
		2583
		2584	// stop all watchers after blocking
		2585	static void
		2586	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2587	{
		2588	ev_timer_stop (loop, &tw);
		2589
		2590	for (int i = 0; i < nfd; ++i)
		2591	{
		2592	// set the relevant poll flags
		2593	// could also call adns_processreadable etc. here
		2594	struct pollfd *fd = fds + i;
		2595	int revents = ev_clear_pending (iow + i);
		2596	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2597	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2598
		2599	// now stop the watcher
		2600	ev_io_stop (loop, iow + i);
		2601	}
		2602
		2603	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2604	}
		2605
		2606	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2607	in the prepare watcher and would dispose of the check watcher.
		2608
		2609	Method 3: If the module to be embedded supports explicit event
		2610	notification (libadns does), you can also make use of the actual watcher
		2611	callbacks, and only destroy/create the watchers in the prepare watcher.
		2612
		2613	static void
		2614	timer_cb (EV_P_ ev_timer *w, int revents)
		2615	{
		2616	adns_state ads = (adns_state)w->data;
		2617	update_now (EV_A);
		2618
		2619	adns_processtimeouts (ads, &tv_now);
		2620	}
		2621
		2622	static void
		2623	io_cb (EV_P_ ev_io *w, int revents)
		2624	{
		2625	adns_state ads = (adns_state)w->data;
		2626	update_now (EV_A);
		2627
		2628	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2629	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2630	}
		2631
		2632	// do not ever call adns_afterpoll
		2633
		2634	Method 4: Do not use a prepare or check watcher because the module you
		2635	want to embed is not flexible enough to support it. Instead, you can
		2636	override their poll function. The drawback with this solution is that the
		2637	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2638	this approach, effectively embedding EV as a client into the horrible
		2639	libglib event loop.
		2640
		2641	static gint
		2642	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2643	{
		2644	int got_events = 0;
		2645
		2646	for (n = 0; n < nfds; ++n)
		2647	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2648
		2649	if (timeout >= 0)
		2650	// create/start timer
		2651
		2652	// poll
		2653	ev_loop (EV_A_ 0);
		2654
		2655	// stop timer again
		2656	if (timeout >= 0)
		2657	ev_timer_stop (EV_A_ &to);
		2658
		2659	// stop io watchers again - their callbacks should have set
		2660	for (n = 0; n < nfds; ++n)
		2661	ev_io_stop (EV_A_ iow [n]);
		2662
		2663	return got_events;
		2664	}
		2665
		2666
		2667	=head2 C<ev_embed> - when one backend isn't enough...
		2668
		2669	This is a rather advanced watcher type that lets you embed one event loop
		2670	into another (currently only C<ev_io> events are supported in the embedded
		2671	loop, other types of watchers might be handled in a delayed or incorrect
		2672	fashion and must not be used).
		2673
		2674	There are primarily two reasons you would want that: work around bugs and
		2675	prioritise I/O.
		2676
		2677	As an example for a bug workaround, the kqueue backend might only support
		2678	sockets on some platform, so it is unusable as generic backend, but you
		2679	still want to make use of it because you have many sockets and it scales
		2680	so nicely. In this case, you would create a kqueue-based loop and embed
		2681	it into your default loop (which might use e.g. poll). Overall operation
		2682	will be a bit slower because first libev has to call C<poll> and then
		2683	C<kevent>, but at least you can use both mechanisms for what they are
		2684	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2685
		2686	As for prioritising I/O: under rare circumstances you have the case where
		2687	some fds have to be watched and handled very quickly (with low latency),
		2688	and even priorities and idle watchers might have too much overhead. In
		2689	this case you would put all the high priority stuff in one loop and all
		2690	the rest in a second one, and embed the second one in the first.
		2691
		2692	As long as the watcher is active, the callback will be invoked every
		2693	time there might be events pending in the embedded loop. The callback
		2694	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		2695	sweep and invoke their callbacks (the callback doesn't need to invoke the
		2696	C<ev_embed_sweep> function directly, it could also start an idle watcher
		2697	to give the embedded loop strictly lower priority for example).
		2698
		2699	You can also set the callback to C<0>, in which case the embed watcher
		2700	will automatically execute the embedded loop sweep whenever necessary.
		2701
		2702	Fork detection will be handled transparently while the C<ev_embed> watcher
		2703	is active, i.e., the embedded loop will automatically be forked when the
		2704	embedding loop forks. In other cases, the user is responsible for calling
		2705	C<ev_loop_fork> on the embedded loop.
		2706
		2707	Unfortunately, not all backends are embeddable: only the ones returned by
		2708	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2709	portable one.
		2710
		2711	So when you want to use this feature you will always have to be prepared
		2712	that you cannot get an embeddable loop. The recommended way to get around
		2713	this is to have a separate variables for your embeddable loop, try to
		2714	create it, and if that fails, use the normal loop for everything.
		2715
		2716	=head3 C<ev_embed> and fork
		2717
		2718	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2719	automatically be applied to the embedded loop as well, so no special
		2720	fork handling is required in that case. When the watcher is not running,
		2721	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2722	as applicable.
		2723
		2724	=head3 Watcher-Specific Functions and Data Members
		2725
		2726	=over 4
		2727
		2728	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2729
		2730	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2731
		2732	Configures the watcher to embed the given loop, which must be
		2733	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2734	invoked automatically, otherwise it is the responsibility of the callback
		2735	to invoke it (it will continue to be called until the sweep has been done,
		2736	if you do not want that, you need to temporarily stop the embed watcher).
		2737
		2738	=item ev_embed_sweep (loop, ev_embed *)
		2739
		2740	Make a single, non-blocking sweep over the embedded loop. This works
		2741	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2742	appropriate way for embedded loops.
		2743
		2744	=item struct ev_loop *other [read-only]
		2745
		2746	The embedded event loop.
		2747
		2748	=back
		2749
		2750	=head3 Examples
		2751
		2752	Example: Try to get an embeddable event loop and embed it into the default
		2753	event loop. If that is not possible, use the default loop. The default
		2754	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2755	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2756	used).
		2757
		2758	struct ev_loop *loop_hi = ev_default_init (0);
		2759	struct ev_loop *loop_lo = 0;
		2760	ev_embed embed;
		2761
		2762	// see if there is a chance of getting one that works
		2763	// (remember that a flags value of 0 means autodetection)
		2764	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2765	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2766	: 0;
		2767
		2768	// if we got one, then embed it, otherwise default to loop_hi
		2769	if (loop_lo)
		2770	{
		2771	ev_embed_init (&embed, 0, loop_lo);
		2772	ev_embed_start (loop_hi, &embed);
		2773	}
		2774	else
		2775	loop_lo = loop_hi;
		2776
		2777	Example: Check if kqueue is available but not recommended and create
		2778	a kqueue backend for use with sockets (which usually work with any
		2779	kqueue implementation). Store the kqueue/socket-only event loop in
		2780	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2781
		2782	struct ev_loop *loop = ev_default_init (0);
		2783	struct ev_loop *loop_socket = 0;
		2784	ev_embed embed;
		2785
		2786	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2787	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2788	{
		2789	ev_embed_init (&embed, 0, loop_socket);
		2790	ev_embed_start (loop, &embed);
		2791	}
		2792
		2793	if (!loop_socket)
		2794	loop_socket = loop;
		2795
		2796	// now use loop_socket for all sockets, and loop for everything else
		2797
		2798
		2799	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2800
		2801	Fork watchers are called when a C<fork ()> was detected (usually because
		2802	whoever is a good citizen cared to tell libev about it by calling
		2803	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2804	event loop blocks next and before C<ev_check> watchers are being called,
		2805	and only in the child after the fork. If whoever good citizen calling
		2806	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2807	handlers will be invoked, too, of course.
		2808
		2809	=head3 The special problem of life after fork - how is it possible?
		2810
		2811	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2812	up/change the process environment, followed by a call to C<exec()>. This
		2813	sequence should be handled by libev without any problems.
		2814
		2815	This changes when the application actually wants to do event handling
		2816	in the child, or both parent in child, in effect "continuing" after the
		2817	fork.
		2818
		2819	The default mode of operation (for libev, with application help to detect
		2820	forks) is to duplicate all the state in the child, as would be expected
		2821	when I<either> the parent I<or> the child process continues.
		2822
		2823	When both processes want to continue using libev, then this is usually the
		2824	wrong result. In that case, usually one process (typically the parent) is
		2825	supposed to continue with all watchers in place as before, while the other
		2826	process typically wants to start fresh, i.e. without any active watchers.
		2827
		2828	The cleanest and most efficient way to achieve that with libev is to
		2829	simply create a new event loop, which of course will be "empty", and
		2830	use that for new watchers. This has the advantage of not touching more
		2831	memory than necessary, and thus avoiding the copy-on-write, and the
		2832	disadvantage of having to use multiple event loops (which do not support
		2833	signal watchers).
		2834
		2835	When this is not possible, or you want to use the default loop for
		2836	other reasons, then in the process that wants to start "fresh", call
		2837	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2838	the default loop will "orphan" (not stop) all registered watchers, so you
		2839	have to be careful not to execute code that modifies those watchers. Note
		2840	also that in that case, you have to re-register any signal watchers.
		2841
		2842	=head3 Watcher-Specific Functions and Data Members
		2843
		2844	=over 4
		2845
		2846	=item ev_fork_init (ev_signal *, callback)
		2847
		2848	Initialises and configures the fork watcher - it has no parameters of any
		2849	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2850	believe me.
		2851
		2852	=back
		2853
		2854
		2855	=head2 C<ev_async> - how to wake up another event loop
		2856
		2857	In general, you cannot use an C<ev_loop> from multiple threads or other
		2858	asynchronous sources such as signal handlers (as opposed to multiple event
		2859	loops - those are of course safe to use in different threads).
		2860
		2861	Sometimes, however, you need to wake up another event loop you do not
		2862	control, for example because it belongs to another thread. This is what
		2863	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2864	can signal it by calling C<ev_async_send>, which is thread- and signal
		2865	safe.
		2866
		2867	This functionality is very similar to C<ev_signal> watchers, as signals,
		2868	too, are asynchronous in nature, and signals, too, will be compressed
		2869	(i.e. the number of callback invocations may be less than the number of
		2870	C<ev_async_sent> calls).
		2871
		2872	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2873	just the default loop.
		2874
		2875	=head3 Queueing
		2876
		2877	C<ev_async> does not support queueing of data in any way. The reason
		2878	is that the author does not know of a simple (or any) algorithm for a
		2879	multiple-writer-single-reader queue that works in all cases and doesn't
		2880	need elaborate support such as pthreads.
		2881
		2882	That means that if you want to queue data, you have to provide your own
		2883	queue. But at least I can tell you how to implement locking around your
		2884	queue:
		2885
		2886	=over 4
		2887
		2888	=item queueing from a signal handler context
		2889
		2890	To implement race-free queueing, you simply add to the queue in the signal
		2891	handler but you block the signal handler in the watcher callback. Here is
		2892	an example that does that for some fictitious SIGUSR1 handler:
		2893
		2894	static ev_async mysig;
		2895
		2896	static void
		2897	sigusr1_handler (void)
		2898	{
		2899	sometype data;
		2900
		2901	// no locking etc.
		2902	queue_put (data);
		2903	ev_async_send (EV_DEFAULT_ &mysig);
		2904	}
		2905
		2906	static void
		2907	mysig_cb (EV_P_ ev_async *w, int revents)
		2908	{
		2909	sometype data;
		2910	sigset_t block, prev;
		2911
		2912	sigemptyset (&block);
		2913	sigaddset (&block, SIGUSR1);
		2914	sigprocmask (SIG_BLOCK, &block, &prev);
		2915
		2916	while (queue_get (&data))
		2917	process (data);
		2918
		2919	if (sigismember (&prev, SIGUSR1)
		2920	sigprocmask (SIG_UNBLOCK, &block, 0);
		2921	}
		2922
		2923	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2924	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2925	either...).
		2926
		2927	=item queueing from a thread context
		2928
		2929	The strategy for threads is different, as you cannot (easily) block
		2930	threads but you can easily preempt them, so to queue safely you need to
		2931	employ a traditional mutex lock, such as in this pthread example:
		2932
		2933	static ev_async mysig;
		2934	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2935
		2936	static void
		2937	otherthread (void)
		2938	{
		2939	// only need to lock the actual queueing operation
		2940	pthread_mutex_lock (&mymutex);
		2941	queue_put (data);
		2942	pthread_mutex_unlock (&mymutex);
		2943
		2944	ev_async_send (EV_DEFAULT_ &mysig);
		2945	}
		2946
		2947	static void
		2948	mysig_cb (EV_P_ ev_async *w, int revents)
		2949	{
		2950	pthread_mutex_lock (&mymutex);
		2951
		2952	while (queue_get (&data))
		2953	process (data);
		2954
		2955	pthread_mutex_unlock (&mymutex);
		2956	}
		2957
		2958	=back
		2959
		2960
		2961	=head3 Watcher-Specific Functions and Data Members
		2962
		2963	=over 4
		2964
		2965	=item ev_async_init (ev_async *, callback)
		2966
		2967	Initialises and configures the async watcher - it has no parameters of any
		2968	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2969	trust me.
		2970
		2971	=item ev_async_send (loop, ev_async *)
		2972
		2973	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2974	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2975	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2976	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2977	section below on what exactly this means).
		2978
		2979	Note that, as with other watchers in libev, multiple events might get
		2980	compressed into a single callback invocation (another way to look at this
		2981	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2982	reset when the event loop detects that).
		2983
		2984	This call incurs the overhead of a system call only once per event loop
		2985	iteration, so while the overhead might be noticeable, it doesn't apply to
		2986	repeated calls to C<ev_async_send> for the same event loop.
		2987
		2988	=item bool = ev_async_pending (ev_async *)
		2989
		2990	Returns a non-zero value when C<ev_async_send> has been called on the
		2991	watcher but the event has not yet been processed (or even noted) by the
		2992	event loop.
		2993
		2994	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2995	the loop iterates next and checks for the watcher to have become active,
		2996	it will reset the flag again. C<ev_async_pending> can be used to very
		2997	quickly check whether invoking the loop might be a good idea.
		2998
		2999	Not that this does I<not> check whether the watcher itself is pending,
		3000	only whether it has been requested to make this watcher pending: there
		3001	is a time window between the event loop checking and resetting the async
		3002	notification, and the callback being invoked.
		3003
		3004	=back
		3005
		3006
793	=head1 OTHER FUNCTIONS	3007	=head1 OTHER FUNCTIONS
794		3008
795	There are some other functions of possible interest. Described. Here. Now.	3009	There are some other functions of possible interest. Described. Here. Now.
796		3010
797	=over 4	3011	=over 4
798		3012
799	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3013	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
800		3014
801	This function combines a simple timer and an I/O watcher, calls your	3015	This function combines a simple timer and an I/O watcher, calls your
802	callback on whichever event happens first and automatically stop both	3016	callback on whichever event happens first and automatically stops both
803	watchers. This is useful if you want to wait for a single event on an fd	3017	watchers. This is useful if you want to wait for a single event on an fd
804	or timeout without having to allocate/configure/start/stop/free one or	3018	or timeout without having to allocate/configure/start/stop/free one or
805	more watchers yourself.	3019	more watchers yourself.
806		3020
807	If C<fd> is less than 0, then no I/O watcher will be started and events	3021	If C<fd> is less than 0, then no I/O watcher will be started and the
808	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3022	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
809	C<events> set will be craeted and started.	3023	the given C<fd> and C<events> set will be created and started.
810		3024
811	If C<timeout> is less than 0, then no timeout watcher will be	3025	If C<timeout> is less than 0, then no timeout watcher will be
812	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3026	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
813	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3027	repeat = 0) will be started. C<0> is a valid timeout.
814	dubious value.
815		3028
816	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3029	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
817	passed an C<revents> set like normal event callbacks (a combination of	3030	passed an C<revents> set like normal event callbacks (a combination of
818	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3031	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
819	value passed to C<ev_once>:	3032	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3033	a timeout and an io event at the same time - you probably should give io
		3034	events precedence.
820		3035
		3036	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3037
821	static void stdin_ready (int revents, void *arg)	3038	static void stdin_ready (int revents, void *arg)
822	{	3039	{
823	if (revents & EV_TIMEOUT)
824	/* doh, nothing entered */;
825	else if (revents & EV_READ)	3040	if (revents & EV_READ)
826	/* stdin might have data for us, joy! */;	3041	/* stdin might have data for us, joy! */;
		3042	else if (revents & EV_TIMEOUT)
		3043	/* doh, nothing entered */;
827	}	3044	}
828		3045
829	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3046	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
830		3047
831	=item ev_feed_event (loop, watcher, int events)	3048	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
832		3049
833	Feeds the given event set into the event loop, as if the specified event	3050	Feeds the given event set into the event loop, as if the specified event
834	had happened for the specified watcher (which must be a pointer to an	3051	had happened for the specified watcher (which must be a pointer to an
835	initialised but not necessarily started event watcher).	3052	initialised but not necessarily started event watcher).
836		3053
837	=item ev_feed_fd_event (loop, int fd, int revents)	3054	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
838		3055
839	Feed an event on the given fd, as if a file descriptor backend detected	3056	Feed an event on the given fd, as if a file descriptor backend detected
840	the given events it.	3057	the given events it.
841		3058
842	=item ev_feed_signal_event (loop, int signum)	3059	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
843		3060
844	Feed an event as if the given signal occured (loop must be the default loop!).	3061	Feed an event as if the given signal occurred (C<loop> must be the default
		3062	loop!).
845		3063
846	=back	3064	=back
		3065
847		3066
848	=head1 LIBEVENT EMULATION	3067	=head1 LIBEVENT EMULATION
849		3068
850	Libev offers a compatibility emulation layer for libevent. It cannot	3069	Libev offers a compatibility emulation layer for libevent. It cannot
851	emulate the internals of libevent, so here are some usage hints:	3070	emulate the internals of libevent, so here are some usage hints:
…		…
863		3082
864	=item * Priorities are not currently supported. Initialising priorities	3083	=item * Priorities are not currently supported. Initialising priorities
865	will fail and all watchers will have the same priority, even though there	3084	will fail and all watchers will have the same priority, even though there
866	is an ev_pri field.	3085	is an ev_pri field.
867		3086
		3087	=item * In libevent, the last base created gets the signals, in libev, the
		3088	first base created (== the default loop) gets the signals.
		3089
868	=item * Other members are not supported.	3090	=item * Other members are not supported.
869		3091
870	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3092	=item * The libev emulation is I<not> ABI compatible to libevent, you need
871	to use the libev header file and library.	3093	to use the libev header file and library.
872		3094
873	=back	3095	=back
874		3096
875	=head1 C++ SUPPORT	3097	=head1 C++ SUPPORT
876		3098
877	TBD.	3099	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3100	you to use some convenience methods to start/stop watchers and also change
		3101	the callback model to a model using method callbacks on objects.
		3102
		3103	To use it,
		3104
		3105	#include <ev++.h>
		3106
		3107	This automatically includes F<ev.h> and puts all of its definitions (many
		3108	of them macros) into the global namespace. All C++ specific things are
		3109	put into the C<ev> namespace. It should support all the same embedding
		3110	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3111
		3112	Care has been taken to keep the overhead low. The only data member the C++
		3113	classes add (compared to plain C-style watchers) is the event loop pointer
		3114	that the watcher is associated with (or no additional members at all if
		3115	you disable C<EV_MULTIPLICITY> when embedding libev).
		3116
		3117	Currently, functions, and static and non-static member functions can be
		3118	used as callbacks. Other types should be easy to add as long as they only
		3119	need one additional pointer for context. If you need support for other
		3120	types of functors please contact the author (preferably after implementing
		3121	it).
		3122
		3123	Here is a list of things available in the C<ev> namespace:
		3124
		3125	=over 4
		3126
		3127	=item C<ev::READ>, C<ev::WRITE> etc.
		3128
		3129	These are just enum values with the same values as the C<EV_READ> etc.
		3130	macros from F<ev.h>.
		3131
		3132	=item C<ev::tstamp>, C<ev::now>
		3133
		3134	Aliases to the same types/functions as with the C<ev_> prefix.
		3135
		3136	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		3137
		3138	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		3139	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		3140	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3141	defines by many implementations.
		3142
		3143	All of those classes have these methods:
		3144
		3145	=over 4
		3146
		3147	=item ev::TYPE::TYPE ()
		3148
		3149	=item ev::TYPE::TYPE (struct ev_loop *)
		3150
		3151	=item ev::TYPE::~TYPE
		3152
		3153	The constructor (optionally) takes an event loop to associate the watcher
		3154	with. If it is omitted, it will use C<EV_DEFAULT>.
		3155
		3156	The constructor calls C<ev_init> for you, which means you have to call the
		3157	C<set> method before starting it.
		3158
		3159	It will not set a callback, however: You have to call the templated C<set>
		3160	method to set a callback before you can start the watcher.
		3161
		3162	(The reason why you have to use a method is a limitation in C++ which does
		3163	not allow explicit template arguments for constructors).
		3164
		3165	The destructor automatically stops the watcher if it is active.
		3166
		3167	=item w->set<class, &class::method> (object *)
		3168
		3169	This method sets the callback method to call. The method has to have a
		3170	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3171	first argument and the C<revents> as second. The object must be given as
		3172	parameter and is stored in the C<data> member of the watcher.
		3173
		3174	This method synthesizes efficient thunking code to call your method from
		3175	the C callback that libev requires. If your compiler can inline your
		3176	callback (i.e. it is visible to it at the place of the C<set> call and
		3177	your compiler is good :), then the method will be fully inlined into the
		3178	thunking function, making it as fast as a direct C callback.
		3179
		3180	Example: simple class declaration and watcher initialisation
		3181
		3182	struct myclass
		3183	{
		3184	void io_cb (ev::io &w, int revents) { }
		3185	}
		3186
		3187	myclass obj;
		3188	ev::io iow;
		3189	iow.set <myclass, &myclass::io_cb> (&obj);
		3190
		3191	=item w->set (object *)
		3192
		3193	This is an B<experimental> feature that might go away in a future version.
		3194
		3195	This is a variation of a method callback - leaving out the method to call
		3196	will default the method to C<operator ()>, which makes it possible to use
		3197	functor objects without having to manually specify the C<operator ()> all
		3198	the time. Incidentally, you can then also leave out the template argument
		3199	list.
		3200
		3201	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3202	int revents)>.
		3203
		3204	See the method-C<set> above for more details.
		3205
		3206	Example: use a functor object as callback.
		3207
		3208	struct myfunctor
		3209	{
		3210	void operator() (ev::io &w, int revents)
		3211	{
		3212	...
		3213	}
		3214	}
		3215
		3216	myfunctor f;
		3217
		3218	ev::io w;
		3219	w.set (&f);
		3220
		3221	=item w->set<function> (void *data = 0)
		3222
		3223	Also sets a callback, but uses a static method or plain function as
		3224	callback. The optional C<data> argument will be stored in the watcher's
		3225	C<data> member and is free for you to use.
		3226
		3227	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3228
		3229	See the method-C<set> above for more details.
		3230
		3231	Example: Use a plain function as callback.
		3232
		3233	static void io_cb (ev::io &w, int revents) { }
		3234	iow.set <io_cb> ();
		3235
		3236	=item w->set (struct ev_loop *)
		3237
		3238	Associates a different C<struct ev_loop> with this watcher. You can only
		3239	do this when the watcher is inactive (and not pending either).
		3240
		3241	=item w->set ([arguments])
		3242
		3243	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		3244	called at least once. Unlike the C counterpart, an active watcher gets
		3245	automatically stopped and restarted when reconfiguring it with this
		3246	method.
		3247
		3248	=item w->start ()
		3249
		3250	Starts the watcher. Note that there is no C<loop> argument, as the
		3251	constructor already stores the event loop.
		3252
		3253	=item w->stop ()
		3254
		3255	Stops the watcher if it is active. Again, no C<loop> argument.
		3256
		3257	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		3258
		3259	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		3260	C<ev_TYPE_again> function.
		3261
		3262	=item w->sweep () (C<ev::embed> only)
		3263
		3264	Invokes C<ev_embed_sweep>.
		3265
		3266	=item w->update () (C<ev::stat> only)
		3267
		3268	Invokes C<ev_stat_stat>.
		3269
		3270	=back
		3271
		3272	=back
		3273
		3274	Example: Define a class with an IO and idle watcher, start one of them in
		3275	the constructor.
		3276
		3277	class myclass
		3278	{
		3279	ev::io io ; void io_cb (ev::io &w, int revents);
		3280	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3281
		3282	myclass (int fd)
		3283	{
		3284	io .set <myclass, &myclass::io_cb > (this);
		3285	idle.set <myclass, &myclass::idle_cb> (this);
		3286
		3287	io.start (fd, ev::READ);
		3288	}
		3289	};
		3290
		3291
		3292	=head1 OTHER LANGUAGE BINDINGS
		3293
		3294	Libev does not offer other language bindings itself, but bindings for a
		3295	number of languages exist in the form of third-party packages. If you know
		3296	any interesting language binding in addition to the ones listed here, drop
		3297	me a note.
		3298
		3299	=over 4
		3300
		3301	=item Perl
		3302
		3303	The EV module implements the full libev API and is actually used to test
		3304	libev. EV is developed together with libev. Apart from the EV core module,
		3305	there are additional modules that implement libev-compatible interfaces
		3306	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3307	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3308	and C<EV::Glib>).
		3309
		3310	It can be found and installed via CPAN, its homepage is at
		3311	L<http://software.schmorp.de/pkg/EV>.
		3312
		3313	=item Python
		3314
		3315	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3316	seems to be quite complete and well-documented.
		3317
		3318	=item Ruby
		3319
		3320	Tony Arcieri has written a ruby extension that offers access to a subset
		3321	of the libev API and adds file handle abstractions, asynchronous DNS and
		3322	more on top of it. It can be found via gem servers. Its homepage is at
		3323	L<http://rev.rubyforge.org/>.
		3324
		3325	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3326	makes rev work even on mingw.
		3327
		3328	=item Haskell
		3329
		3330	A haskell binding to libev is available at
		3331	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3332
		3333	=item D
		3334
		3335	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3336	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3337
		3338	=item Ocaml
		3339
		3340	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3341	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3342
		3343	=back
		3344
		3345
		3346	=head1 MACRO MAGIC
		3347
		3348	Libev can be compiled with a variety of options, the most fundamental
		3349	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3350	functions and callbacks have an initial C<struct ev_loop *> argument.
		3351
		3352	To make it easier to write programs that cope with either variant, the
		3353	following macros are defined:
		3354
		3355	=over 4
		3356
		3357	=item C<EV_A>, C<EV_A_>
		3358
		3359	This provides the loop I<argument> for functions, if one is required ("ev
		3360	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3361	C<EV_A_> is used when other arguments are following. Example:
		3362
		3363	ev_unref (EV_A);
		3364	ev_timer_add (EV_A_ watcher);
		3365	ev_loop (EV_A_ 0);
		3366
		3367	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3368	which is often provided by the following macro.
		3369
		3370	=item C<EV_P>, C<EV_P_>
		3371
		3372	This provides the loop I<parameter> for functions, if one is required ("ev
		3373	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3374	C<EV_P_> is used when other parameters are following. Example:
		3375
		3376	// this is how ev_unref is being declared
		3377	static void ev_unref (EV_P);
		3378
		3379	// this is how you can declare your typical callback
		3380	static void cb (EV_P_ ev_timer *w, int revents)
		3381
		3382	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3383	suitable for use with C<EV_A>.
		3384
		3385	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3386
		3387	Similar to the other two macros, this gives you the value of the default
		3388	loop, if multiple loops are supported ("ev loop default").
		3389
		3390	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3391
		3392	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3393	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3394	is undefined when the default loop has not been initialised by a previous
		3395	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3396
		3397	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3398	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3399
		3400	=back
		3401
		3402	Example: Declare and initialise a check watcher, utilising the above
		3403	macros so it will work regardless of whether multiple loops are supported
		3404	or not.
		3405
		3406	static void
		3407	check_cb (EV_P_ ev_timer *w, int revents)
		3408	{
		3409	ev_check_stop (EV_A_ w);
		3410	}
		3411
		3412	ev_check check;
		3413	ev_check_init (&check, check_cb);
		3414	ev_check_start (EV_DEFAULT_ &check);
		3415	ev_loop (EV_DEFAULT_ 0);
		3416
		3417	=head1 EMBEDDING
		3418
		3419	Libev can (and often is) directly embedded into host
		3420	applications. Examples of applications that embed it include the Deliantra
		3421	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3422	and rxvt-unicode.
		3423
		3424	The goal is to enable you to just copy the necessary files into your
		3425	source directory without having to change even a single line in them, so
		3426	you can easily upgrade by simply copying (or having a checked-out copy of
		3427	libev somewhere in your source tree).
		3428
		3429	=head2 FILESETS
		3430
		3431	Depending on what features you need you need to include one or more sets of files
		3432	in your application.
		3433
		3434	=head3 CORE EVENT LOOP
		3435
		3436	To include only the libev core (all the C<ev_*> functions), with manual
		3437	configuration (no autoconf):
		3438
		3439	#define EV_STANDALONE 1
		3440	#include "ev.c"
		3441
		3442	This will automatically include F<ev.h>, too, and should be done in a
		3443	single C source file only to provide the function implementations. To use
		3444	it, do the same for F<ev.h> in all files wishing to use this API (best
		3445	done by writing a wrapper around F<ev.h> that you can include instead and
		3446	where you can put other configuration options):
		3447
		3448	#define EV_STANDALONE 1
		3449	#include "ev.h"
		3450
		3451	Both header files and implementation files can be compiled with a C++
		3452	compiler (at least, that's a stated goal, and breakage will be treated
		3453	as a bug).
		3454
		3455	You need the following files in your source tree, or in a directory
		3456	in your include path (e.g. in libev/ when using -Ilibev):
		3457
		3458	ev.h
		3459	ev.c
		3460	ev_vars.h
		3461	ev_wrap.h
		3462
		3463	ev_win32.c required on win32 platforms only
		3464
		3465	ev_select.c only when select backend is enabled (which is enabled by default)
		3466	ev_poll.c only when poll backend is enabled (disabled by default)
		3467	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3468	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3469	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3470
		3471	F<ev.c> includes the backend files directly when enabled, so you only need
		3472	to compile this single file.
		3473
		3474	=head3 LIBEVENT COMPATIBILITY API
		3475
		3476	To include the libevent compatibility API, also include:
		3477
		3478	#include "event.c"
		3479
		3480	in the file including F<ev.c>, and:
		3481
		3482	#include "event.h"
		3483
		3484	in the files that want to use the libevent API. This also includes F<ev.h>.
		3485
		3486	You need the following additional files for this:
		3487
		3488	event.h
		3489	event.c
		3490
		3491	=head3 AUTOCONF SUPPORT
		3492
		3493	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3494	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3495	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3496	include F<config.h> and configure itself accordingly.
		3497
		3498	For this of course you need the m4 file:
		3499
		3500	libev.m4
		3501
		3502	=head2 PREPROCESSOR SYMBOLS/MACROS
		3503
		3504	Libev can be configured via a variety of preprocessor symbols you have to
		3505	define before including any of its files. The default in the absence of
		3506	autoconf is documented for every option.
		3507
		3508	=over 4
		3509
		3510	=item EV_STANDALONE
		3511
		3512	Must always be C<1> if you do not use autoconf configuration, which
		3513	keeps libev from including F<config.h>, and it also defines dummy
		3514	implementations for some libevent functions (such as logging, which is not
		3515	supported). It will also not define any of the structs usually found in
		3516	F<event.h> that are not directly supported by the libev core alone.
		3517
		3518	In stanbdalone mode, libev will still try to automatically deduce the
		3519	configuration, but has to be more conservative.
		3520
		3521	=item EV_USE_MONOTONIC
		3522
		3523	If defined to be C<1>, libev will try to detect the availability of the
		3524	monotonic clock option at both compile time and runtime. Otherwise no
		3525	use of the monotonic clock option will be attempted. If you enable this,
		3526	you usually have to link against librt or something similar. Enabling it
		3527	when the functionality isn't available is safe, though, although you have
		3528	to make sure you link against any libraries where the C<clock_gettime>
		3529	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3530
		3531	=item EV_USE_REALTIME
		3532
		3533	If defined to be C<1>, libev will try to detect the availability of the
		3534	real-time clock option at compile time (and assume its availability
		3535	at runtime if successful). Otherwise no use of the real-time clock
		3536	option will be attempted. This effectively replaces C<gettimeofday>
		3537	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		3538	correctness. See the note about libraries in the description of
		3539	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3540	C<EV_USE_CLOCK_SYSCALL>.
		3541
		3542	=item EV_USE_CLOCK_SYSCALL
		3543
		3544	If defined to be C<1>, libev will try to use a direct syscall instead
		3545	of calling the system-provided C<clock_gettime> function. This option
		3546	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3547	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3548	programs needlessly. Using a direct syscall is slightly slower (in
		3549	theory), because no optimised vdso implementation can be used, but avoids
		3550	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3551	higher, as it simplifies linking (no need for C<-lrt>).
		3552
		3553	=item EV_USE_NANOSLEEP
		3554
		3555	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3556	and will use it for delays. Otherwise it will use C<select ()>.
		3557
		3558	=item EV_USE_EVENTFD
		3559
		3560	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3561	available and will probe for kernel support at runtime. This will improve
		3562	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3563	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3564	2.7 or newer, otherwise disabled.
		3565
		3566	=item EV_USE_SELECT
		3567
		3568	If undefined or defined to be C<1>, libev will compile in support for the
		3569	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3570	other method takes over, select will be it. Otherwise the select backend
		3571	will not be compiled in.
		3572
		3573	=item EV_SELECT_USE_FD_SET
		3574
		3575	If defined to C<1>, then the select backend will use the system C<fd_set>
		3576	structure. This is useful if libev doesn't compile due to a missing
		3577	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		3578	on exotic systems. This usually limits the range of file descriptors to
		3579	some low limit such as 1024 or might have other limitations (winsocket
		3580	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		3581	configures the maximum size of the C<fd_set>.
		3582
		3583	=item EV_SELECT_IS_WINSOCKET
		3584
		3585	When defined to C<1>, the select backend will assume that
		3586	select/socket/connect etc. don't understand file descriptors but
		3587	wants osf handles on win32 (this is the case when the select to
		3588	be used is the winsock select). This means that it will call
		3589	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3590	it is assumed that all these functions actually work on fds, even
		3591	on win32. Should not be defined on non-win32 platforms.
		3592
		3593	=item EV_FD_TO_WIN32_HANDLE
		3594
		3595	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3596	file descriptors to socket handles. When not defining this symbol (the
		3597	default), then libev will call C<_get_osfhandle>, which is usually
		3598	correct. In some cases, programs use their own file descriptor management,
		3599	in which case they can provide this function to map fds to socket handles.
		3600
		3601	=item EV_USE_POLL
		3602
		3603	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3604	backend. Otherwise it will be enabled on non-win32 platforms. It
		3605	takes precedence over select.
		3606
		3607	=item EV_USE_EPOLL
		3608
		3609	If defined to be C<1>, libev will compile in support for the Linux
		3610	C<epoll>(7) backend. Its availability will be detected at runtime,
		3611	otherwise another method will be used as fallback. This is the preferred
		3612	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3613	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3614
		3615	=item EV_USE_KQUEUE
		3616
		3617	If defined to be C<1>, libev will compile in support for the BSD style
		3618	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3619	otherwise another method will be used as fallback. This is the preferred
		3620	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3621	supports some types of fds correctly (the only platform we found that
		3622	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3623	not be used unless explicitly requested. The best way to use it is to find
		3624	out whether kqueue supports your type of fd properly and use an embedded
		3625	kqueue loop.
		3626
		3627	=item EV_USE_PORT
		3628
		3629	If defined to be C<1>, libev will compile in support for the Solaris
		3630	10 port style backend. Its availability will be detected at runtime,
		3631	otherwise another method will be used as fallback. This is the preferred
		3632	backend for Solaris 10 systems.
		3633
		3634	=item EV_USE_DEVPOLL
		3635
		3636	Reserved for future expansion, works like the USE symbols above.
		3637
		3638	=item EV_USE_INOTIFY
		3639
		3640	If defined to be C<1>, libev will compile in support for the Linux inotify
		3641	interface to speed up C<ev_stat> watchers. Its actual availability will
		3642	be detected at runtime. If undefined, it will be enabled if the headers
		3643	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3644
		3645	=item EV_ATOMIC_T
		3646
		3647	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3648	access is atomic with respect to other threads or signal contexts. No such
		3649	type is easily found in the C language, so you can provide your own type
		3650	that you know is safe for your purposes. It is used both for signal handler "locking"
		3651	as well as for signal and thread safety in C<ev_async> watchers.
		3652
		3653	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3654	(from F<signal.h>), which is usually good enough on most platforms.
		3655
		3656	=item EV_H
		3657
		3658	The name of the F<ev.h> header file used to include it. The default if
		3659	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3660	used to virtually rename the F<ev.h> header file in case of conflicts.
		3661
		3662	=item EV_CONFIG_H
		3663
		3664	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3665	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3666	C<EV_H>, above.
		3667
		3668	=item EV_EVENT_H
		3669
		3670	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3671	of how the F<event.h> header can be found, the default is C<"event.h">.
		3672
		3673	=item EV_PROTOTYPES
		3674
		3675	If defined to be C<0>, then F<ev.h> will not define any function
		3676	prototypes, but still define all the structs and other symbols. This is
		3677	occasionally useful if you want to provide your own wrapper functions
		3678	around libev functions.
		3679
		3680	=item EV_MULTIPLICITY
		3681
		3682	If undefined or defined to C<1>, then all event-loop-specific functions
		3683	will have the C<struct ev_loop *> as first argument, and you can create
		3684	additional independent event loops. Otherwise there will be no support
		3685	for multiple event loops and there is no first event loop pointer
		3686	argument. Instead, all functions act on the single default loop.
		3687
		3688	=item EV_MINPRI
		3689
		3690	=item EV_MAXPRI
		3691
		3692	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3693	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3694	provide for more priorities by overriding those symbols (usually defined
		3695	to be C<-2> and C<2>, respectively).
		3696
		3697	When doing priority-based operations, libev usually has to linearly search
		3698	all the priorities, so having many of them (hundreds) uses a lot of space
		3699	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3700	fine.
		3701
		3702	If your embedding application does not need any priorities, defining these
		3703	both to C<0> will save some memory and CPU.
		3704
		3705	=item EV_PERIODIC_ENABLE
		3706
		3707	If undefined or defined to be C<1>, then periodic timers are supported. If
		3708	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3709	code.
		3710
		3711	=item EV_IDLE_ENABLE
		3712
		3713	If undefined or defined to be C<1>, then idle watchers are supported. If
		3714	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3715	code.
		3716
		3717	=item EV_EMBED_ENABLE
		3718
		3719	If undefined or defined to be C<1>, then embed watchers are supported. If
		3720	defined to be C<0>, then they are not. Embed watchers rely on most other
		3721	watcher types, which therefore must not be disabled.
		3722
		3723	=item EV_STAT_ENABLE
		3724
		3725	If undefined or defined to be C<1>, then stat watchers are supported. If
		3726	defined to be C<0>, then they are not.
		3727
		3728	=item EV_FORK_ENABLE
		3729
		3730	If undefined or defined to be C<1>, then fork watchers are supported. If
		3731	defined to be C<0>, then they are not.
		3732
		3733	=item EV_ASYNC_ENABLE
		3734
		3735	If undefined or defined to be C<1>, then async watchers are supported. If
		3736	defined to be C<0>, then they are not.
		3737
		3738	=item EV_MINIMAL
		3739
		3740	If you need to shave off some kilobytes of code at the expense of some
		3741	speed (but with the full API), define this symbol to C<1>. Currently this
		3742	is used to override some inlining decisions, saves roughly 30% code size
		3743	on amd64. It also selects a much smaller 2-heap for timer management over
		3744	the default 4-heap.
		3745
		3746	You can save even more by disabling watcher types you do not need
		3747	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3748	(C<-DNDEBUG>) will usually reduce code size a lot.
		3749
		3750	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3751	provide a bare-bones event library. See C<ev.h> for details on what parts
		3752	of the API are still available, and do not complain if this subset changes
		3753	over time.
		3754
		3755	=item EV_PID_HASHSIZE
		3756
		3757	C<ev_child> watchers use a small hash table to distribute workload by
		3758	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3759	than enough. If you need to manage thousands of children you might want to
		3760	increase this value (I<must> be a power of two).
		3761
		3762	=item EV_INOTIFY_HASHSIZE
		3763
		3764	C<ev_stat> watchers use a small hash table to distribute workload by
		3765	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3766	usually more than enough. If you need to manage thousands of C<ev_stat>
		3767	watchers you might want to increase this value (I<must> be a power of
		3768	two).
		3769
		3770	=item EV_USE_4HEAP
		3771
		3772	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3773	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3774	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3775	faster performance with many (thousands) of watchers.
		3776
		3777	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3778	(disabled).
		3779
		3780	=item EV_HEAP_CACHE_AT
		3781
		3782	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3783	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3784	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3785	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3786	but avoids random read accesses on heap changes. This improves performance
		3787	noticeably with many (hundreds) of watchers.
		3788
		3789	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3790	(disabled).
		3791
		3792	=item EV_VERIFY
		3793
		3794	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3795	be done: If set to C<0>, no internal verification code will be compiled
		3796	in. If set to C<1>, then verification code will be compiled in, but not
		3797	called. If set to C<2>, then the internal verification code will be
		3798	called once per loop, which can slow down libev. If set to C<3>, then the
		3799	verification code will be called very frequently, which will slow down
		3800	libev considerably.
		3801
		3802	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3803	C<0>.
		3804
		3805	=item EV_COMMON
		3806
		3807	By default, all watchers have a C<void *data> member. By redefining
		3808	this macro to a something else you can include more and other types of
		3809	members. You have to define it each time you include one of the files,
		3810	though, and it must be identical each time.
		3811
		3812	For example, the perl EV module uses something like this:
		3813
		3814	#define EV_COMMON \
		3815	SV *self; /* contains this struct */ \
		3816	SV *cb_sv, *fh /* note no trailing ";" */
		3817
		3818	=item EV_CB_DECLARE (type)
		3819
		3820	=item EV_CB_INVOKE (watcher, revents)
		3821
		3822	=item ev_set_cb (ev, cb)
		3823
		3824	Can be used to change the callback member declaration in each watcher,
		3825	and the way callbacks are invoked and set. Must expand to a struct member
		3826	definition and a statement, respectively. See the F<ev.h> header file for
		3827	their default definitions. One possible use for overriding these is to
		3828	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3829	method calls instead of plain function calls in C++.
		3830
		3831	=back
		3832
		3833	=head2 EXPORTED API SYMBOLS
		3834
		3835	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3836	exported symbols, you can use the provided F<Symbol.*> files which list
		3837	all public symbols, one per line:
		3838
		3839	Symbols.ev for libev proper
		3840	Symbols.event for the libevent emulation
		3841
		3842	This can also be used to rename all public symbols to avoid clashes with
		3843	multiple versions of libev linked together (which is obviously bad in
		3844	itself, but sometimes it is inconvenient to avoid this).
		3845
		3846	A sed command like this will create wrapper C<#define>'s that you need to
		3847	include before including F<ev.h>:
		3848
		3849	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3850
		3851	This would create a file F<wrap.h> which essentially looks like this:
		3852
		3853	#define ev_backend myprefix_ev_backend
		3854	#define ev_check_start myprefix_ev_check_start
		3855	#define ev_check_stop myprefix_ev_check_stop
		3856	...
		3857
		3858	=head2 EXAMPLES
		3859
		3860	For a real-world example of a program the includes libev
		3861	verbatim, you can have a look at the EV perl module
		3862	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3863	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3864	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3865	will be compiled. It is pretty complex because it provides its own header
		3866	file.
		3867
		3868	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3869	that everybody includes and which overrides some configure choices:
		3870
		3871	#define EV_MINIMAL 1
		3872	#define EV_USE_POLL 0
		3873	#define EV_MULTIPLICITY 0
		3874	#define EV_PERIODIC_ENABLE 0
		3875	#define EV_STAT_ENABLE 0
		3876	#define EV_FORK_ENABLE 0
		3877	#define EV_CONFIG_H <config.h>
		3878	#define EV_MINPRI 0
		3879	#define EV_MAXPRI 0
		3880
		3881	#include "ev++.h"
		3882
		3883	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3884
		3885	#include "ev_cpp.h"
		3886	#include "ev.c"
		3887
		3888	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3889
		3890	=head2 THREADS AND COROUTINES
		3891
		3892	=head3 THREADS
		3893
		3894	All libev functions are reentrant and thread-safe unless explicitly
		3895	documented otherwise, but libev implements no locking itself. This means
		3896	that you can use as many loops as you want in parallel, as long as there
		3897	are no concurrent calls into any libev function with the same loop
		3898	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3899	of course): libev guarantees that different event loops share no data
		3900	structures that need any locking.
		3901
		3902	Or to put it differently: calls with different loop parameters can be done
		3903	concurrently from multiple threads, calls with the same loop parameter
		3904	must be done serially (but can be done from different threads, as long as
		3905	only one thread ever is inside a call at any point in time, e.g. by using
		3906	a mutex per loop).
		3907
		3908	Specifically to support threads (and signal handlers), libev implements
		3909	so-called C<ev_async> watchers, which allow some limited form of
		3910	concurrency on the same event loop, namely waking it up "from the
		3911	outside".
		3912
		3913	If you want to know which design (one loop, locking, or multiple loops
		3914	without or something else still) is best for your problem, then I cannot
		3915	help you, but here is some generic advice:
		3916
		3917	=over 4
		3918
		3919	=item * most applications have a main thread: use the default libev loop
		3920	in that thread, or create a separate thread running only the default loop.
		3921
		3922	This helps integrating other libraries or software modules that use libev
		3923	themselves and don't care/know about threading.
		3924
		3925	=item * one loop per thread is usually a good model.
		3926
		3927	Doing this is almost never wrong, sometimes a better-performance model
		3928	exists, but it is always a good start.
		3929
		3930	=item * other models exist, such as the leader/follower pattern, where one
		3931	loop is handed through multiple threads in a kind of round-robin fashion.
		3932
		3933	Choosing a model is hard - look around, learn, know that usually you can do
		3934	better than you currently do :-)
		3935
		3936	=item * often you need to talk to some other thread which blocks in the
		3937	event loop.
		3938
		3939	C<ev_async> watchers can be used to wake them up from other threads safely
		3940	(or from signal contexts...).
		3941
		3942	An example use would be to communicate signals or other events that only
		3943	work in the default loop by registering the signal watcher with the
		3944	default loop and triggering an C<ev_async> watcher from the default loop
		3945	watcher callback into the event loop interested in the signal.
		3946
		3947	=back
		3948
		3949	=head4 THREAD LOCKING EXAMPLE
		3950
		3951	Here is a fictitious example of how to run an event loop in a different
		3952	thread than where callbacks are being invoked and watchers are
		3953	created/added/removed.
		3954
		3955	For a real-world example, see the C<EV::Loop::Async> perl module,
		3956	which uses exactly this technique (which is suited for many high-level
		3957	languages).
		3958
		3959	The example uses a pthread mutex to protect the loop data, a condition
		3960	variable to wait for callback invocations, an async watcher to notify the
		3961	event loop thread and an unspecified mechanism to wake up the main thread.
		3962
		3963	First, you need to associate some data with the event loop:
		3964
		3965	typedef struct {
		3966	mutex_t lock; /* global loop lock */
		3967	ev_async async_w;
		3968	thread_t tid;
		3969	cond_t invoke_cv;
		3970	} userdata;
		3971
		3972	void prepare_loop (EV_P)
		3973	{
		3974	// for simplicity, we use a static userdata struct.
		3975	static userdata u;
		3976
		3977	ev_async_init (&u->async_w, async_cb);
		3978	ev_async_start (EV_A_ &u->async_w);
		3979
		3980	pthread_mutex_init (&u->lock, 0);
		3981	pthread_cond_init (&u->invoke_cv, 0);
		3982
		3983	// now associate this with the loop
		3984	ev_set_userdata (EV_A_ u);
		3985	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3986	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3987
		3988	// then create the thread running ev_loop
		3989	pthread_create (&u->tid, 0, l_run, EV_A);
		3990	}
		3991
		3992	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3993	solely to wake up the event loop so it takes notice of any new watchers
		3994	that might have been added:
		3995
		3996	static void
		3997	async_cb (EV_P_ ev_async *w, int revents)
		3998	{
		3999	// just used for the side effects
		4000	}
		4001
		4002	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4003	protecting the loop data, respectively.
		4004
		4005	static void
		4006	l_release (EV_P)
		4007	{
		4008	userdata *u = ev_userdata (EV_A);
		4009	pthread_mutex_unlock (&u->lock);
		4010	}
		4011
		4012	static void
		4013	l_acquire (EV_P)
		4014	{
		4015	userdata *u = ev_userdata (EV_A);
		4016	pthread_mutex_lock (&u->lock);
		4017	}
		4018
		4019	The event loop thread first acquires the mutex, and then jumps straight
		4020	into C<ev_loop>:
		4021
		4022	void *
		4023	l_run (void *thr_arg)
		4024	{
		4025	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4026
		4027	l_acquire (EV_A);
		4028	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4029	ev_loop (EV_A_ 0);
		4030	l_release (EV_A);
		4031
		4032	return 0;
		4033	}
		4034
		4035	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4036	signal the main thread via some unspecified mechanism (signals? pipe
		4037	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4038	have been called (in a while loop because a) spurious wakeups are possible
		4039	and b) skipping inter-thread-communication when there are no pending
		4040	watchers is very beneficial):
		4041
		4042	static void
		4043	l_invoke (EV_P)
		4044	{
		4045	userdata *u = ev_userdata (EV_A);
		4046
		4047	while (ev_pending_count (EV_A))
		4048	{
		4049	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4050	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4051	}
		4052	}
		4053
		4054	Now, whenever the main thread gets told to invoke pending watchers, it
		4055	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4056	thread to continue:
		4057
		4058	static void
		4059	real_invoke_pending (EV_P)
		4060	{
		4061	userdata *u = ev_userdata (EV_A);
		4062
		4063	pthread_mutex_lock (&u->lock);
		4064	ev_invoke_pending (EV_A);
		4065	pthread_cond_signal (&u->invoke_cv);
		4066	pthread_mutex_unlock (&u->lock);
		4067	}
		4068
		4069	Whenever you want to start/stop a watcher or do other modifications to an
		4070	event loop, you will now have to lock:
		4071
		4072	ev_timer timeout_watcher;
		4073	userdata *u = ev_userdata (EV_A);
		4074
		4075	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4076
		4077	pthread_mutex_lock (&u->lock);
		4078	ev_timer_start (EV_A_ &timeout_watcher);
		4079	ev_async_send (EV_A_ &u->async_w);
		4080	pthread_mutex_unlock (&u->lock);
		4081
		4082	Note that sending the C<ev_async> watcher is required because otherwise
		4083	an event loop currently blocking in the kernel will have no knowledge
		4084	about the newly added timer. By waking up the loop it will pick up any new
		4085	watchers in the next event loop iteration.
		4086
		4087	=head3 COROUTINES
		4088
		4089	Libev is very accommodating to coroutines ("cooperative threads"):
		4090	libev fully supports nesting calls to its functions from different
		4091	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4092	different coroutines, and switch freely between both coroutines running
		4093	the loop, as long as you don't confuse yourself). The only exception is
		4094	that you must not do this from C<ev_periodic> reschedule callbacks.
		4095
		4096	Care has been taken to ensure that libev does not keep local state inside
		4097	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4098	they do not call any callbacks.
		4099
		4100	=head2 COMPILER WARNINGS
		4101
		4102	Depending on your compiler and compiler settings, you might get no or a
		4103	lot of warnings when compiling libev code. Some people are apparently
		4104	scared by this.
		4105
		4106	However, these are unavoidable for many reasons. For one, each compiler
		4107	has different warnings, and each user has different tastes regarding
		4108	warning options. "Warn-free" code therefore cannot be a goal except when
		4109	targeting a specific compiler and compiler-version.
		4110
		4111	Another reason is that some compiler warnings require elaborate
		4112	workarounds, or other changes to the code that make it less clear and less
		4113	maintainable.
		4114
		4115	And of course, some compiler warnings are just plain stupid, or simply
		4116	wrong (because they don't actually warn about the condition their message
		4117	seems to warn about). For example, certain older gcc versions had some
		4118	warnings that resulted an extreme number of false positives. These have
		4119	been fixed, but some people still insist on making code warn-free with
		4120	such buggy versions.
		4121
		4122	While libev is written to generate as few warnings as possible,
		4123	"warn-free" code is not a goal, and it is recommended not to build libev
		4124	with any compiler warnings enabled unless you are prepared to cope with
		4125	them (e.g. by ignoring them). Remember that warnings are just that:
		4126	warnings, not errors, or proof of bugs.
		4127
		4128
		4129	=head2 VALGRIND
		4130
		4131	Valgrind has a special section here because it is a popular tool that is
		4132	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4133
		4134	If you think you found a bug (memory leak, uninitialised data access etc.)
		4135	in libev, then check twice: If valgrind reports something like:
		4136
		4137	==2274== definitely lost: 0 bytes in 0 blocks.
		4138	==2274== possibly lost: 0 bytes in 0 blocks.
		4139	==2274== still reachable: 256 bytes in 1 blocks.
		4140
		4141	Then there is no memory leak, just as memory accounted to global variables
		4142	is not a memleak - the memory is still being referenced, and didn't leak.
		4143
		4144	Similarly, under some circumstances, valgrind might report kernel bugs
		4145	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4146	although an acceptable workaround has been found here), or it might be
		4147	confused.
		4148
		4149	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4150	make it into some kind of religion.
		4151
		4152	If you are unsure about something, feel free to contact the mailing list
		4153	with the full valgrind report and an explanation on why you think this
		4154	is a bug in libev (best check the archives, too :). However, don't be
		4155	annoyed when you get a brisk "this is no bug" answer and take the chance
		4156	of learning how to interpret valgrind properly.
		4157
		4158	If you need, for some reason, empty reports from valgrind for your project
		4159	I suggest using suppression lists.
		4160
		4161
		4162	=head1 PORTABILITY NOTES
		4163
		4164	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4165
		4166	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4167	requires, and its I/O model is fundamentally incompatible with the POSIX
		4168	model. Libev still offers limited functionality on this platform in
		4169	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4170	descriptors. This only applies when using Win32 natively, not when using
		4171	e.g. cygwin.
		4172
		4173	Lifting these limitations would basically require the full
		4174	re-implementation of the I/O system. If you are into these kinds of
		4175	things, then note that glib does exactly that for you in a very portable
		4176	way (note also that glib is the slowest event library known to man).
		4177
		4178	There is no supported compilation method available on windows except
		4179	embedding it into other applications.
		4180
		4181	Sensible signal handling is officially unsupported by Microsoft - libev
		4182	tries its best, but under most conditions, signals will simply not work.
		4183
		4184	Not a libev limitation but worth mentioning: windows apparently doesn't
		4185	accept large writes: instead of resulting in a partial write, windows will
		4186	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4187	so make sure you only write small amounts into your sockets (less than a
		4188	megabyte seems safe, but this apparently depends on the amount of memory
		4189	available).
		4190
		4191	Due to the many, low, and arbitrary limits on the win32 platform and
		4192	the abysmal performance of winsockets, using a large number of sockets
		4193	is not recommended (and not reasonable). If your program needs to use
		4194	more than a hundred or so sockets, then likely it needs to use a totally
		4195	different implementation for windows, as libev offers the POSIX readiness
		4196	notification model, which cannot be implemented efficiently on windows
		4197	(due to Microsoft monopoly games).
		4198
		4199	A typical way to use libev under windows is to embed it (see the embedding
		4200	section for details) and use the following F<evwrap.h> header file instead
		4201	of F<ev.h>:
		4202
		4203	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4204	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4205
		4206	#include "ev.h"
		4207
		4208	And compile the following F<evwrap.c> file into your project (make sure
		4209	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4210
		4211	#include "evwrap.h"
		4212	#include "ev.c"
		4213
		4214	=over 4
		4215
		4216	=item The winsocket select function
		4217
		4218	The winsocket C<select> function doesn't follow POSIX in that it
		4219	requires socket I<handles> and not socket I<file descriptors> (it is
		4220	also extremely buggy). This makes select very inefficient, and also
		4221	requires a mapping from file descriptors to socket handles (the Microsoft
		4222	C runtime provides the function C<_open_osfhandle> for this). See the
		4223	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4224	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4225
		4226	The configuration for a "naked" win32 using the Microsoft runtime
		4227	libraries and raw winsocket select is:
		4228
		4229	#define EV_USE_SELECT 1
		4230	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4231
		4232	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4233	complexity in the O(n²) range when using win32.
		4234
		4235	=item Limited number of file descriptors
		4236
		4237	Windows has numerous arbitrary (and low) limits on things.
		4238
		4239	Early versions of winsocket's select only supported waiting for a maximum
		4240	of C<64> handles (probably owning to the fact that all windows kernels
		4241	can only wait for C<64> things at the same time internally; Microsoft
		4242	recommends spawning a chain of threads and wait for 63 handles and the
		4243	previous thread in each. Sounds great!).
		4244
		4245	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4246	to some high number (e.g. C<2048>) before compiling the winsocket select
		4247	call (which might be in libev or elsewhere, for example, perl and many
		4248	other interpreters do their own select emulation on windows).
		4249
		4250	Another limit is the number of file descriptors in the Microsoft runtime
		4251	libraries, which by default is C<64> (there must be a hidden I<64>
		4252	fetish or something like this inside Microsoft). You can increase this
		4253	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4254	(another arbitrary limit), but is broken in many versions of the Microsoft
		4255	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4256	(depending on windows version and/or the phase of the moon). To get more,
		4257	you need to wrap all I/O functions and provide your own fd management, but
		4258	the cost of calling select (O(n²)) will likely make this unworkable.
		4259
		4260	=back
		4261
		4262	=head2 PORTABILITY REQUIREMENTS
		4263
		4264	In addition to a working ISO-C implementation and of course the
		4265	backend-specific APIs, libev relies on a few additional extensions:
		4266
		4267	=over 4
		4268
		4269	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4270	calling conventions regardless of C<ev_watcher_type *>.
		4271
		4272	Libev assumes not only that all watcher pointers have the same internal
		4273	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4274	assumes that the same (machine) code can be used to call any watcher
		4275	callback: The watcher callbacks have different type signatures, but libev
		4276	calls them using an C<ev_watcher *> internally.
		4277
		4278	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4279
		4280	The type C<sig_atomic_t volatile> (or whatever is defined as
		4281	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4282	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4283	believed to be sufficiently portable.
		4284
		4285	=item C<sigprocmask> must work in a threaded environment
		4286
		4287	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4288	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4289	pthread implementations will either allow C<sigprocmask> in the "main
		4290	thread" or will block signals process-wide, both behaviours would
		4291	be compatible with libev. Interaction between C<sigprocmask> and
		4292	C<pthread_sigmask> could complicate things, however.
		4293
		4294	The most portable way to handle signals is to block signals in all threads
		4295	except the initial one, and run the default loop in the initial thread as
		4296	well.
		4297
		4298	=item C<long> must be large enough for common memory allocation sizes
		4299
		4300	To improve portability and simplify its API, libev uses C<long> internally
		4301	instead of C<size_t> when allocating its data structures. On non-POSIX
		4302	systems (Microsoft...) this might be unexpectedly low, but is still at
		4303	least 31 bits everywhere, which is enough for hundreds of millions of
		4304	watchers.
		4305
		4306	=item C<double> must hold a time value in seconds with enough accuracy
		4307
		4308	The type C<double> is used to represent timestamps. It is required to
		4309	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4310	enough for at least into the year 4000. This requirement is fulfilled by
		4311	implementations implementing IEEE 754, which is basically all existing
		4312	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4313	2200.
		4314
		4315	=back
		4316
		4317	If you know of other additional requirements drop me a note.
		4318
		4319
		4320	=head1 ALGORITHMIC COMPLEXITIES
		4321
		4322	In this section the complexities of (many of) the algorithms used inside
		4323	libev will be documented. For complexity discussions about backends see
		4324	the documentation for C<ev_default_init>.
		4325
		4326	All of the following are about amortised time: If an array needs to be
		4327	extended, libev needs to realloc and move the whole array, but this
		4328	happens asymptotically rarer with higher number of elements, so O(1) might
		4329	mean that libev does a lengthy realloc operation in rare cases, but on
		4330	average it is much faster and asymptotically approaches constant time.
		4331
		4332	=over 4
		4333
		4334	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4335
		4336	This means that, when you have a watcher that triggers in one hour and
		4337	there are 100 watchers that would trigger before that, then inserting will
		4338	have to skip roughly seven (C<ld 100>) of these watchers.
		4339
		4340	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4341
		4342	That means that changing a timer costs less than removing/adding them,
		4343	as only the relative motion in the event queue has to be paid for.
		4344
		4345	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4346
		4347	These just add the watcher into an array or at the head of a list.
		4348
		4349	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4350
		4351	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4352
		4353	These watchers are stored in lists, so they need to be walked to find the
		4354	correct watcher to remove. The lists are usually short (you don't usually
		4355	have many watchers waiting for the same fd or signal: one is typical, two
		4356	is rare).
		4357
		4358	=item Finding the next timer in each loop iteration: O(1)
		4359
		4360	By virtue of using a binary or 4-heap, the next timer is always found at a
		4361	fixed position in the storage array.
		4362
		4363	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4364
		4365	A change means an I/O watcher gets started or stopped, which requires
		4366	libev to recalculate its status (and possibly tell the kernel, depending
		4367	on backend and whether C<ev_io_set> was used).
		4368
		4369	=item Activating one watcher (putting it into the pending state): O(1)
		4370
		4371	=item Priority handling: O(number_of_priorities)
		4372
		4373	Priorities are implemented by allocating some space for each
		4374	priority. When doing priority-based operations, libev usually has to
		4375	linearly search all the priorities, but starting/stopping and activating
		4376	watchers becomes O(1) with respect to priority handling.
		4377
		4378	=item Sending an ev_async: O(1)
		4379
		4380	=item Processing ev_async_send: O(number_of_async_watchers)
		4381
		4382	=item Processing signals: O(max_signal_number)
		4383
		4384	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4385	calls in the current loop iteration. Checking for async and signal events
		4386	involves iterating over all running async watchers or all signal numbers.
		4387
		4388	=back
		4389
		4390
		4391	=head1 GLOSSARY
		4392
		4393	=over 4
		4394
		4395	=item active
		4396
		4397	A watcher is active as long as it has been started (has been attached to
		4398	an event loop) but not yet stopped (disassociated from the event loop).
		4399
		4400	=item application
		4401
		4402	In this document, an application is whatever is using libev.
		4403
		4404	=item callback
		4405
		4406	The address of a function that is called when some event has been
		4407	detected. Callbacks are being passed the event loop, the watcher that
		4408	received the event, and the actual event bitset.
		4409
		4410	=item callback invocation
		4411
		4412	The act of calling the callback associated with a watcher.
		4413
		4414	=item event
		4415
		4416	A change of state of some external event, such as data now being available
		4417	for reading on a file descriptor, time having passed or simply not having
		4418	any other events happening anymore.
		4419
		4420	In libev, events are represented as single bits (such as C<EV_READ> or
		4421	C<EV_TIMEOUT>).
		4422
		4423	=item event library
		4424
		4425	A software package implementing an event model and loop.
		4426
		4427	=item event loop
		4428
		4429	An entity that handles and processes external events and converts them
		4430	into callback invocations.
		4431
		4432	=item event model
		4433
		4434	The model used to describe how an event loop handles and processes
		4435	watchers and events.
		4436
		4437	=item pending
		4438
		4439	A watcher is pending as soon as the corresponding event has been detected,
		4440	and stops being pending as soon as the watcher will be invoked or its
		4441	pending status is explicitly cleared by the application.
		4442
		4443	A watcher can be pending, but not active. Stopping a watcher also clears
		4444	its pending status.
		4445
		4446	=item real time
		4447
		4448	The physical time that is observed. It is apparently strictly monotonic :)
		4449
		4450	=item wall-clock time
		4451
		4452	The time and date as shown on clocks. Unlike real time, it can actually
		4453	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4454	clock.
		4455
		4456	=item watcher
		4457
		4458	A data structure that describes interest in certain events. Watchers need
		4459	to be started (attached to an event loop) before they can receive events.
		4460
		4461	=item watcher invocation
		4462
		4463	The act of calling the callback associated with a watcher.
		4464
		4465	=back
878		4466
879	=head1 AUTHOR	4467	=head1 AUTHOR
880		4468
881	Marc Lehmann <libev@schmorp.de>.	4469	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
882		4470

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