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Revision 1.325 by root, Sun Oct 24 19:44:08 2010 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 DESCRIPTION	9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
		18	ev_io stdin_watcher;
		19	ev_timer timeout_watcher;
		20
		21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
		23	static void
		24	stdin_cb (EV_P_ ev_io *w, int revents)
		25	{
		26	puts ("stdin ready");
		27	// for one-shot events, one must manually stop the watcher
		28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_run's to stop iterating
		32	ev_break (EV_A_ EVBREAK_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_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_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;
		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_run (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	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
10		84
11	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	87	these event sources and provide your program with events.
14		88
15	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	96	watcher.
23		97
24	=head1 FEATURES	98	=head2 FEATURES
25		99
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
		104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
		105	timers (C<ev_timer>), absolute timers with customised rescheduling
		106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
29	events (related to SIGCHLD), and event watchers dealing with the event	107	change events (C<ev_child>), and event watchers dealing with the event
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
		109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
		111
		112	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	114	for example).
33		115
34	=head1 CONVENTIONS	116	=head2 CONVENTIONS
35		117
36	Libev is very configurable. In this manual the default configuration	118	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	119	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	120	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	121	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	122	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	124	this argument.
43		125
44	=head1 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
45		127
46	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (in practice
48	the beginning of 1970, details are complicated, don't ask). This type is	130	somewhere near the beginning of 1970, details are complicated, don't
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	ask). This type is called C<ev_tstamp>, which is what you should use
50	to the C<double> type in C, and when you need to do any calculations on	132	too. It usually aliases to the C<double> type in C. When you need to do
51	it, you should treat it as such.	133	any calculations on it, you should treat it as some floating point value.
		134
		135	Unlike the name component C<stamp> might indicate, it is also used for
		136	time differences (e.g. delays) throughout libev.
		137
		138	=head1 ERROR HANDLING
		139
		140	Libev knows three classes of errors: operating system errors, usage errors
		141	and internal errors (bugs).
		142
		143	When libev catches an operating system error it cannot handle (for example
		144	a system call indicating a condition libev cannot fix), it calls the callback
		145	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		146	abort. The default is to print a diagnostic message and to call C<abort
		147	()>.
		148
		149	When libev detects a usage error such as a negative timer interval, then
		150	it will print a diagnostic message and abort (via the C<assert> mechanism,
		151	so C<NDEBUG> will disable this checking): these are programming errors in
		152	the libev caller and need to be fixed there.
		153
		154	Libev also has a few internal error-checking C<assert>ions, and also has
		155	extensive consistency checking code. These do not trigger under normal
		156	circumstances, as they indicate either a bug in libev or worse.
52		157
53		158
54	=head1 GLOBAL FUNCTIONS	159	=head1 GLOBAL FUNCTIONS
55		160
56	These functions can be called anytime, even before initialising the	161	These functions can be called anytime, even before initialising the
…		…
60		165
61	=item ev_tstamp ev_time ()	166	=item ev_tstamp ev_time ()
62		167
63	Returns the current time as libev would use it. Please note that the	168	Returns the current time as libev would use it. Please note that the
64	C<ev_now> function is usually faster and also often returns the timestamp	169	C<ev_now> function is usually faster and also often returns the timestamp
65	you actually want to know.	170	you actually want to know. Also interesting is the combination of
		171	C<ev_update_now> and C<ev_now>.
		172
		173	=item ev_sleep (ev_tstamp interval)
		174
		175	Sleep for the given interval: The current thread will be blocked until
		176	either it is interrupted or the given time interval has passed. Basically
		177	this is a sub-second-resolution C<sleep ()>.
66		178
67	=item int ev_version_major ()	179	=item int ev_version_major ()
68		180
69	=item int ev_version_minor ()	181	=item int ev_version_minor ()
70		182
71	You can find out the major and minor version numbers of the library	183	You can find out the major and minor ABI version numbers of the library
72	you linked against by calling the functions C<ev_version_major> and	184	you linked against by calling the functions C<ev_version_major> and
73	C<ev_version_minor>. If you want, you can compare against the global	185	C<ev_version_minor>. If you want, you can compare against the global
74	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	186	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
75	version of the library your program was compiled against.	187	version of the library your program was compiled against.
76		188
		189	These version numbers refer to the ABI version of the library, not the
		190	release version.
		191
77	Usually, it's a good idea to terminate if the major versions mismatch,	192	Usually, it's a good idea to terminate if the major versions mismatch,
78	as this indicates an incompatible change. Minor versions are usually	193	as this indicates an incompatible change. Minor versions are usually
79	compatible to older versions, so a larger minor version alone is usually	194	compatible to older versions, so a larger minor version alone is usually
80	not a problem.	195	not a problem.
81		196
82	Example: make sure we haven't accidentally been linked against the wrong	197	Example: Make sure we haven't accidentally been linked against the wrong
83	version:	198	version (note, however, that this will not detect other ABI mismatches,
		199	such as LFS or reentrancy).
84		200
85	assert (("libev version mismatch",	201	assert (("libev version mismatch",
86	ev_version_major () == EV_VERSION_MAJOR	202	ev_version_major () == EV_VERSION_MAJOR
87	&& ev_version_minor () >= EV_VERSION_MINOR));	203	&& ev_version_minor () >= EV_VERSION_MINOR));
88		204
89	=item unsigned int ev_supported_backends ()	205	=item unsigned int ev_supported_backends ()
90		206
91	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	207	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
92	value) compiled into this binary of libev (independent of their	208	value) compiled into this binary of libev (independent of their
…		…
94	a description of the set values.	210	a description of the set values.
95		211
96	Example: make sure we have the epoll method, because yeah this is cool and	212	Example: make sure we have the epoll method, because yeah this is cool and
97	a must have and can we have a torrent of it please!!!11	213	a must have and can we have a torrent of it please!!!11
98		214
99	assert (("sorry, no epoll, no sex",	215	assert (("sorry, no epoll, no sex",
100	ev_supported_backends () & EVBACKEND_EPOLL));	216	ev_supported_backends () & EVBACKEND_EPOLL));
101		217
102	=item unsigned int ev_recommended_backends ()	218	=item unsigned int ev_recommended_backends ()
103		219
104	Return the set of all backends compiled into this binary of libev and also	220	Return the set of all backends compiled into this binary of libev and
105	recommended for this platform. This set is often smaller than the one	221	also recommended for this platform, meaning it will work for most file
		222	descriptor types. This set is often smaller than the one returned by
106	returned by C<ev_supported_backends>, as for example kqueue is broken on	223	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
107	most BSDs and will not be autodetected unless you explicitly request it	224	and will not be auto-detected unless you explicitly request it (assuming
108	(assuming you know what you are doing). This is the set of backends that	225	you know what you are doing). This is the set of backends that libev will
109	libev will probe for if you specify no backends explicitly.	226	probe for if you specify no backends explicitly.
110		227
111	=item unsigned int ev_embeddable_backends ()	228	=item unsigned int ev_embeddable_backends ()
112		229
113	Returns the set of backends that are embeddable in other event loops. This	230	Returns the set of backends that are embeddable in other event loops. This
114	is the theoretical, all-platform, value. To find which backends	231	value is platform-specific but can include backends not available on the
115	might be supported on the current system, you would need to look at	232	current system. To find which embeddable backends might be supported on
116	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	233	the current system, you would need to look at C<ev_embeddable_backends ()
117	recommended ones.	234	& ev_supported_backends ()>, likewise for recommended ones.
118		235
119	See the description of C<ev_embed> watchers for more info.	236	See the description of C<ev_embed> watchers for more info.
120		237
121	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	238	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
122		239
123	Sets the allocation function to use (the prototype is similar to the	240	Sets the allocation function to use (the prototype is similar - the
124	realloc C function, the semantics are identical). It is used to allocate	241	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
125	and free memory (no surprises here). If it returns zero when memory	242	used to allocate and free memory (no surprises here). If it returns zero
126	needs to be allocated, the library might abort or take some potentially	243	when memory needs to be allocated (C<size != 0>), the library might abort
127	destructive action. The default is your system realloc function.	244	or take some potentially destructive action.
		245
		246	Since some systems (at least OpenBSD and Darwin) fail to implement
		247	correct C<realloc> semantics, libev will use a wrapper around the system
		248	C<realloc> and C<free> functions by default.
128		249
129	You could override this function in high-availability programs to, say,	250	You could override this function in high-availability programs to, say,
130	free some memory if it cannot allocate memory, to use a special allocator,	251	free some memory if it cannot allocate memory, to use a special allocator,
131	or even to sleep a while and retry until some memory is available.	252	or even to sleep a while and retry until some memory is available.
132		253
133	Example: replace the libev allocator with one that waits a bit and then	254	Example: Replace the libev allocator with one that waits a bit and then
134	retries: better than mine).	255	retries (example requires a standards-compliant C<realloc>).
135		256
136	static void *	257	static void *
137	persistent_realloc (void *ptr, long size)	258	persistent_realloc (void *ptr, size_t size)
138	{	259	{
139	for (;;)	260	for (;;)
140	{	261	{
141	void *newptr = realloc (ptr, size);	262	void *newptr = realloc (ptr, size);
142		263
…		…
148	}	269	}
149		270
150	...	271	...
151	ev_set_allocator (persistent_realloc);	272	ev_set_allocator (persistent_realloc);
152		273
153	=item ev_set_syserr_cb (void (*cb)(const char *msg));	274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
154		275
155	Set the callback function to call on a retryable syscall error (such	276	Set the callback function to call on a retryable system call error (such
156	as failed select, poll, epoll_wait). The message is a printable string	277	as failed select, poll, epoll_wait). The message is a printable string
157	indicating the system call or subsystem causing the problem. If this	278	indicating the system call or subsystem causing the problem. If this
158	callback is set, then libev will expect it to remedy the sitution, no	279	callback is set, then libev will expect it to remedy the situation, no
159	matter what, when it returns. That is, libev will generally retry the	280	matter what, when it returns. That is, libev will generally retry the
160	requested operation, or, if the condition doesn't go away, do bad stuff	281	requested operation, or, if the condition doesn't go away, do bad stuff
161	(such as abort).	282	(such as abort).
162		283
163	Example: do the same thing as libev does internally:	284	Example: This is basically the same thing that libev does internally, too.
164		285
165	static void	286	static void
166	fatal_error (const char *msg)	287	fatal_error (const char *msg)
167	{	288	{
168	perror (msg);	289	perror (msg);
…		…
172	...	293	...
173	ev_set_syserr_cb (fatal_error);	294	ev_set_syserr_cb (fatal_error);
174		295
175	=back	296	=back
176		297
177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	298	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
178		299
179	An event loop is described by a C<struct ev_loop *>. The library knows two	300	An event loop is described by a C<struct ev_loop *> (the C<struct> is
180	types of such loops, the I<default> loop, which supports signals and child	301	I<not> optional in this case unless libev 3 compatibility is disabled, as
181	events, and dynamically created loops which do not.	302	libev 3 had an C<ev_loop> function colliding with the struct name).
182		303
183	If you use threads, a common model is to run the default event loop	304	The library knows two types of such loops, the I<default> loop, which
184	in your main thread (or in a separate thread) and for each thread you	305	supports signals and child events, and dynamically created event loops
185	create, you also create another event loop. Libev itself does no locking	306	which do not.
186	whatsoever, so if you mix calls to the same event loop in different
187	threads, make sure you lock (this is usually a bad idea, though, even if
188	done correctly, because it's hideous and inefficient).
189		307
190	=over 4	308	=over 4
191		309
192	=item struct ev_loop *ev_default_loop (unsigned int flags)	310	=item struct ev_loop *ev_default_loop (unsigned int flags)
193		311
194	This will initialise the default event loop if it hasn't been initialised	312	This returns the "default" event loop object, which is what you should
195	yet and return it. If the default loop could not be initialised, returns	313	normally use when you just need "the event loop". Event loop objects and
196	false. If it already was initialised it simply returns it (and ignores the	314	the C<flags> parameter are described in more detail in the entry for
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	315	C<ev_loop_new>.
		316
		317	If the default loop is already initialised then this function simply
		318	returns it (and ignores the flags. If that is troubling you, check
		319	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		320	flags, which should almost always be C<0>, unless the caller is also the
		321	one calling C<ev_run> or otherwise qualifies as "the main program".
198		322
199	If you don't know what event loop to use, use the one returned from this	323	If you don't know what event loop to use, use the one returned from this
200	function.	324	function (or via the C<EV_DEFAULT> macro).
		325
		326	Note that this function is I<not> thread-safe, so if you want to use it
		327	from multiple threads, you have to employ some kind of mutex (note also
		328	that this case is unlikely, as loops cannot be shared easily between
		329	threads anyway).
		330
		331	The default loop is the only loop that can handle C<ev_child> watchers,
		332	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		333	a problem for your application you can either create a dynamic loop with
		334	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		335	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
		336
		337	Example: This is the most typical usage.
		338
		339	if (!ev_default_loop (0))
		340	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		341
		342	Example: Restrict libev to the select and poll backends, and do not allow
		343	environment settings to be taken into account:
		344
		345	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		346
		347	=item struct ev_loop *ev_loop_new (unsigned int flags)
		348
		349	This will create and initialise a new event loop object. If the loop
		350	could not be initialised, returns false.
		351
		352	Note that this function I<is> thread-safe, and one common way to use
		353	libev with threads is indeed to create one loop per thread, and using the
		354	default loop in the "main" or "initial" thread.
201		355
202	The flags argument can be used to specify special behaviour or specific	356	The flags argument can be used to specify special behaviour or specific
203	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	357	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		358
205	The following flags are supported:	359	The following flags are supported:
…		…
211	The default flags value. Use this if you have no clue (it's the right	365	The default flags value. Use this if you have no clue (it's the right
212	thing, believe me).	366	thing, believe me).
213		367
214	=item C<EVFLAG_NOENV>	368	=item C<EVFLAG_NOENV>
215		369
216	If this flag bit is ored into the flag value (or the program runs setuid	370	If this flag bit is or'ed into the flag value (or the program runs setuid
217	or setgid) then libev will I<not> look at the environment variable	371	or setgid) then libev will I<not> look at the environment variable
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	372	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	373	override the flags completely if it is found in the environment. This is
220	useful to try out specific backends to test their performance, or to work	374	useful to try out specific backends to test their performance, or to work
221	around bugs.	375	around bugs.
222		376
		377	=item C<EVFLAG_FORKCHECK>
		378
		379	Instead of calling C<ev_loop_fork> manually after a fork, you can also
		380	make libev check for a fork in each iteration by enabling this flag.
		381
		382	This works by calling C<getpid ()> on every iteration of the loop,
		383	and thus this might slow down your event loop if you do a lot of loop
		384	iterations and little real work, but is usually not noticeable (on my
		385	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		386	without a system call and thus I<very> fast, but my GNU/Linux system also has
		387	C<pthread_atfork> which is even faster).
		388
		389	The big advantage of this flag is that you can forget about fork (and
		390	forget about forgetting to tell libev about forking) when you use this
		391	flag.
		392
		393	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		394	environment variable.
		395
		396	=item C<EVFLAG_NOINOTIFY>
		397
		398	When this flag is specified, then libev will not attempt to use the
		399	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		400	testing, this flag can be useful to conserve inotify file descriptors, as
		401	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		402
		403	=item C<EVFLAG_SIGNALFD>
		404
		405	When this flag is specified, then libev will attempt to use the
		406	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		407	delivers signals synchronously, which makes it both faster and might make
		408	it possible to get the queued signal data. It can also simplify signal
		409	handling with threads, as long as you properly block signals in your
		410	threads that are not interested in handling them.
		411
		412	Signalfd will not be used by default as this changes your signal mask, and
		413	there are a lot of shoddy libraries and programs (glib's threadpool for
		414	example) that can't properly initialise their signal masks.
		415
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	416	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		417
225	This is your standard select(2) backend. Not I<completely> standard, as	418	This is your standard select(2) backend. Not I<completely> standard, as
226	libev tries to roll its own fd_set with no limits on the number of fds,	419	libev tries to roll its own fd_set with no limits on the number of fds,
227	but if that fails, expect a fairly low limit on the number of fds when	420	but if that fails, expect a fairly low limit on the number of fds when
228	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	421	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	422	usually the fastest backend for a low number of (low-numbered :) fds.
		423
		424	To get good performance out of this backend you need a high amount of
		425	parallelism (most of the file descriptors should be busy). If you are
		426	writing a server, you should C<accept ()> in a loop to accept as many
		427	connections as possible during one iteration. You might also want to have
		428	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		429	readiness notifications you get per iteration.
		430
		431	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		432	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		433	C<exceptfds> set on that platform).
230		434
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	435	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		436
233	And this is your standard poll(2) backend. It's more complicated than	437	And this is your standard poll(2) backend. It's more complicated
234	select, but handles sparse fds better and has no artificial limit on the	438	than select, but handles sparse fds better and has no artificial
235	number of fds you can use (except it will slow down considerably with a	439	limit on the number of fds you can use (except it will slow down
236	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	440	considerably with a lot of inactive fds). It scales similarly to select,
		441	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		442	performance tips.
		443
		444	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		445	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
237		446
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	447	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		448
		449	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		450	kernels).
		451
240	For few fds, this backend is a bit little slower than poll and select,	452	For few fds, this backend is a bit little slower than poll and select,
241	but it scales phenomenally better. While poll and select usually scale like	453	but it scales phenomenally better. While poll and select usually scale
242	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	454	like O(total_fds) where n is the total number of fds (or the highest fd),
243	either O(1) or O(active_fds).	455	epoll scales either O(1) or O(active_fds).
244		456
		457	The epoll mechanism deserves honorable mention as the most misdesigned
		458	of the more advanced event mechanisms: mere annoyances include silently
		459	dropping file descriptors, requiring a system call per change per file
		460	descriptor (and unnecessary guessing of parameters), problems with dup and
		461	so on. The biggest issue is fork races, however - if a program forks then
		462	I<both> parent and child process have to recreate the epoll set, which can
		463	take considerable time (one syscall per file descriptor) and is of course
		464	hard to detect.
		465
		466	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		467	of course I<doesn't>, and epoll just loves to report events for totally
		468	I<different> file descriptors (even already closed ones, so one cannot
		469	even remove them from the set) than registered in the set (especially
		470	on SMP systems). Libev tries to counter these spurious notifications by
		471	employing an additional generation counter and comparing that against the
		472	events to filter out spurious ones, recreating the set when required. Last
		473	not least, it also refuses to work with some file descriptors which work
		474	perfectly fine with C<select> (files, many character devices...).
		475
245	While stopping and starting an I/O watcher in the same iteration will	476	While stopping, setting and starting an I/O watcher in the same iteration
246	result in some caching, there is still a syscall per such incident	477	will result in some caching, there is still a system call per such
247	(because the fd could point to a different file description now), so its	478	incident (because the same I<file descriptor> could point to a different
248	best to avoid that. Also, dup()ed file descriptors might not work very	479	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
249	well if you register events for both fds.	480	file descriptors might not work very well if you register events for both
		481	file descriptors.
250		482
251	Please note that epoll sometimes generates spurious notifications, so you	483	Best performance from this backend is achieved by not unregistering all
252	need to use non-blocking I/O or other means to avoid blocking when no data	484	watchers for a file descriptor until it has been closed, if possible,
253	(or space) is available.	485	i.e. keep at least one watcher active per fd at all times. Stopping and
		486	starting a watcher (without re-setting it) also usually doesn't cause
		487	extra overhead. A fork can both result in spurious notifications as well
		488	as in libev having to destroy and recreate the epoll object, which can
		489	take considerable time and thus should be avoided.
		490
		491	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		492	faster than epoll for maybe up to a hundred file descriptors, depending on
		493	the usage. So sad.
		494
		495	While nominally embeddable in other event loops, this feature is broken in
		496	all kernel versions tested so far.
		497
		498	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		499	C<EVBACKEND_POLL>.
254		500
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	501	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		502
257	Kqueue deserves special mention, as at the time of this writing, it	503	Kqueue deserves special mention, as at the time of this writing, it
258	was broken on all BSDs except NetBSD (usually it doesn't work with	504	was broken on all BSDs except NetBSD (usually it doesn't work reliably
259	anything but sockets and pipes, except on Darwin, where of course its	505	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	506	it's completely useless). Unlike epoll, however, whose brokenness
		507	is by design, these kqueue bugs can (and eventually will) be fixed
		508	without API changes to existing programs. For this reason it's not being
261	unless you explicitly specify it explicitly in the flags (i.e. using	509	"auto-detected" unless you explicitly specify it in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	510	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		511	system like NetBSD.
		512
		513	You still can embed kqueue into a normal poll or select backend and use it
		514	only for sockets (after having made sure that sockets work with kqueue on
		515	the target platform). See C<ev_embed> watchers for more info.
263		516
264	It scales in the same way as the epoll backend, but the interface to the	517	It scales in the same way as the epoll backend, but the interface to the
265	kernel is more efficient (which says nothing about its actual speed, of	518	kernel is more efficient (which says nothing about its actual speed, of
266	course). While starting and stopping an I/O watcher does not cause an	519	course). While stopping, setting and starting an I/O watcher does never
267	extra syscall as with epoll, it still adds up to four event changes per	520	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	521	two event changes per incident. Support for C<fork ()> is very bad (but
		522	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		523	cases
		524
		525	This backend usually performs well under most conditions.
		526
		527	While nominally embeddable in other event loops, this doesn't work
		528	everywhere, so you might need to test for this. And since it is broken
		529	almost everywhere, you should only use it when you have a lot of sockets
		530	(for which it usually works), by embedding it into another event loop
		531	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		532	also broken on OS X)) and, did I mention it, using it only for sockets.
		533
		534	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		535	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		536	C<NOTE_EOF>.
269		537
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	538	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		539
272	This is not implemented yet (and might never be).	540	This is not implemented yet (and might never be, unless you send me an
		541	implementation). According to reports, C</dev/poll> only supports sockets
		542	and is not embeddable, which would limit the usefulness of this backend
		543	immensely.
273		544
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	545	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		546
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	547	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
277	it's really slow, but it still scales very well (O(active_fds)).	548	it's really slow, but it still scales very well (O(active_fds)).
278		549
279	Please note that solaris ports can result in a lot of spurious	550	Please note that Solaris event ports can deliver a lot of spurious
280	notifications, so you need to use non-blocking I/O or other means to avoid	551	notifications, so you need to use non-blocking I/O or other means to avoid
281	blocking when no data (or space) is available.	552	blocking when no data (or space) is available.
		553
		554	While this backend scales well, it requires one system call per active
		555	file descriptor per loop iteration. For small and medium numbers of file
		556	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		557	might perform better.
		558
		559	On the positive side, with the exception of the spurious readiness
		560	notifications, this backend actually performed fully to specification
		561	in all tests and is fully embeddable, which is a rare feat among the
		562	OS-specific backends (I vastly prefer correctness over speed hacks).
		563
		564	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		565	C<EVBACKEND_POLL>.
282		566
283	=item C<EVBACKEND_ALL>	567	=item C<EVBACKEND_ALL>
284		568
285	Try all backends (even potentially broken ones that wouldn't be tried	569	Try all backends (even potentially broken ones that wouldn't be tried
286	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	570	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	571	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		572
		573	It is definitely not recommended to use this flag.
		574
289	=back	575	=back
290		576
291	If one or more of these are ored into the flags value, then only these	577	If one or more of the backend flags are or'ed into the flags value,
292	backends will be tried (in the reverse order as given here). If none are	578	then only these backends will be tried (in the reverse order as listed
293	specified, most compiled-in backend will be tried, usually in reverse	579	here). If none are specified, all backends in C<ev_recommended_backends
294	order of their flag values :)	580	()> will be tried.
295		581
296	The most typical usage is like this:
297
298	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
300
301	Restrict libev to the select and poll backends, and do not allow
302	environment settings to be taken into account:
303
304	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
305
306	Use whatever libev has to offer, but make sure that kqueue is used if
307	available (warning, breaks stuff, best use only with your own private
308	event loop and only if you know the OS supports your types of fds):
309
310	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
311
312	=item struct ev_loop *ev_loop_new (unsigned int flags)
313
314	Similar to C<ev_default_loop>, but always creates a new event loop that is
315	always distinct from the default loop. Unlike the default loop, it cannot
316	handle signal and child watchers, and attempts to do so will be greeted by
317	undefined behaviour (or a failed assertion if assertions are enabled).
318
319	Example: try to create a event loop that uses epoll and nothing else.	582	Example: Try to create a event loop that uses epoll and nothing else.
320		583
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	584	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	585	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	586	fatal ("no epoll found here, maybe it hides under your chair");
324		587
325	=item ev_default_destroy ()	588	Example: Use whatever libev has to offer, but make sure that kqueue is
		589	used if available.
326		590
327	Destroys the default loop again (frees all memory and kernel state	591	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
328	etc.). This stops all registered event watchers (by not touching them in
329	any way whatsoever, although you cannot rely on this :).
330		592
331	=item ev_loop_destroy (loop)	593	=item ev_loop_destroy (loop)
332		594
333	Like C<ev_default_destroy>, but destroys an event loop created by an	595	Destroys an event loop object (frees all memory and kernel state
334	earlier call to C<ev_loop_new>.	596	etc.). None of the active event watchers will be stopped in the normal
		597	sense, so e.g. C<ev_is_active> might still return true. It is your
		598	responsibility to either stop all watchers cleanly yourself I<before>
		599	calling this function, or cope with the fact afterwards (which is usually
		600	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		601	for example).
335		602
336	=item ev_default_fork ()	603	Note that certain global state, such as signal state (and installed signal
		604	handlers), will not be freed by this function, and related watchers (such
		605	as signal and child watchers) would need to be stopped manually.
337		606
		607	This function is normally used on loop objects allocated by
		608	C<ev_loop_new>, but it can also be used on the default loop returned by
		609	C<ev_default_loop>, in which case it is not thread-safe.
		610
		611	Note that it is not advisable to call this function on the default loop
		612	except in the rare occasion where you really need to free it's resources.
		613	If you need dynamically allocated loops it is better to use C<ev_loop_new>
		614	and C<ev_loop_destroy>.
		615
		616	=item ev_loop_fork (loop)
		617
		618	This function sets a flag that causes subsequent C<ev_run> iterations to
338	This function reinitialises the kernel state for backends that have	619	reinitialise the kernel state for backends that have one. Despite the
339	one. Despite the name, you can call it anytime, but it makes most sense	620	name, you can call it anytime, but it makes most sense after forking, in
340	after forking, in either the parent or child process (or both, but that	621	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
341	again makes little sense).	622	child before resuming or calling C<ev_run>.
342		623
343	You I<must> call this function in the child process after forking if and	624	Again, you I<have> to call it on I<any> loop that you want to re-use after
344	only if you want to use the event library in both processes. If you just	625	a fork, I<even if you do not plan to use the loop in the parent>. This is
345	fork+exec, you don't have to call it.	626	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		627	during fork.
		628
		629	On the other hand, you only need to call this function in the child
		630	process if and only if you want to use the event loop in the child. If
		631	you just fork+exec or create a new loop in the child, you don't have to
		632	call it at all (in fact, C<epoll> is so badly broken that it makes a
		633	difference, but libev will usually detect this case on its own and do a
		634	costly reset of the backend).
346		635
347	The function itself is quite fast and it's usually not a problem to call	636	The function itself is quite fast and it's usually not a problem to call
348	it just in case after a fork. To make this easy, the function will fit in	637	it just in case after a fork.
349	quite nicely into a call to C<pthread_atfork>:
350		638
		639	Example: Automate calling C<ev_loop_fork> on the default loop when
		640	using pthreads.
		641
		642	static void
		643	post_fork_child (void)
		644	{
		645	ev_loop_fork (EV_DEFAULT);
		646	}
		647
		648	...
351	pthread_atfork (0, 0, ev_default_fork);	649	pthread_atfork (0, 0, post_fork_child);
352		650
353	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	651	=item int ev_is_default_loop (loop)
354	without calling this function, so if you force one of those backends you
355	do not need to care.
356		652
357	=item ev_loop_fork (loop)	653	Returns true when the given loop is, in fact, the default loop, and false
		654	otherwise.
358		655
359	Like C<ev_default_fork>, but acts on an event loop created by	656	=item unsigned int ev_iteration (loop)
360	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	657
361	after fork, and how you do this is entirely your own problem.	658	Returns the current iteration count for the event loop, which is identical
		659	to the number of times libev did poll for new events. It starts at C<0>
		660	and happily wraps around with enough iterations.
		661
		662	This value can sometimes be useful as a generation counter of sorts (it
		663	"ticks" the number of loop iterations), as it roughly corresponds with
		664	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		665	prepare and check phases.
		666
		667	=item unsigned int ev_depth (loop)
		668
		669	Returns the number of times C<ev_run> was entered minus the number of
		670	times C<ev_run> was exited, in other words, the recursion depth.
		671
		672	Outside C<ev_run>, this number is zero. In a callback, this number is
		673	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		674	in which case it is higher.
		675
		676	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
		677	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		678	ungentleman-like behaviour unless it's really convenient.
362		679
363	=item unsigned int ev_backend (loop)	680	=item unsigned int ev_backend (loop)
364		681
365	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	682	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
366	use.	683	use.
…		…
369		686
370	Returns the current "event loop time", which is the time the event loop	687	Returns the current "event loop time", which is the time the event loop
371	received events and started processing them. This timestamp does not	688	received events and started processing them. This timestamp does not
372	change as long as callbacks are being processed, and this is also the base	689	change as long as callbacks are being processed, and this is also the base
373	time used for relative timers. You can treat it as the timestamp of the	690	time used for relative timers. You can treat it as the timestamp of the
374	event occuring (or more correctly, libev finding out about it).	691	event occurring (or more correctly, libev finding out about it).
375		692
		693	=item ev_now_update (loop)
		694
		695	Establishes the current time by querying the kernel, updating the time
		696	returned by C<ev_now ()> in the progress. This is a costly operation and
		697	is usually done automatically within C<ev_run ()>.
		698
		699	This function is rarely useful, but when some event callback runs for a
		700	very long time without entering the event loop, updating libev's idea of
		701	the current time is a good idea.
		702
		703	See also L<The special problem of time updates> in the C<ev_timer> section.
		704
		705	=item ev_suspend (loop)
		706
		707	=item ev_resume (loop)
		708
		709	These two functions suspend and resume an event loop, for use when the
		710	loop is not used for a while and timeouts should not be processed.
		711
		712	A typical use case would be an interactive program such as a game: When
		713	the user presses C<^Z> to suspend the game and resumes it an hour later it
		714	would be best to handle timeouts as if no time had actually passed while
		715	the program was suspended. This can be achieved by calling C<ev_suspend>
		716	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		717	C<ev_resume> directly afterwards to resume timer processing.
		718
		719	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		720	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		721	will be rescheduled (that is, they will lose any events that would have
		722	occurred while suspended).
		723
		724	After calling C<ev_suspend> you B<must not> call I<any> function on the
		725	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		726	without a previous call to C<ev_suspend>.
		727
		728	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		729	event loop time (see C<ev_now_update>).
		730
376	=item ev_loop (loop, int flags)	731	=item ev_run (loop, int flags)
377		732
378	Finally, this is it, the event handler. This function usually is called	733	Finally, this is it, the event handler. This function usually is called
379	after you initialised all your watchers and you want to start handling	734	after you have initialised all your watchers and you want to start
380	events.	735	handling events. It will ask the operating system for any new events, call
		736	the watcher callbacks, an then repeat the whole process indefinitely: This
		737	is why event loops are called I<loops>.
381		738
382	If the flags argument is specified as C<0>, it will not return until	739	If the flags argument is specified as C<0>, it will keep handling events
383	either no event watchers are active anymore or C<ev_unloop> was called.	740	until either no event watchers are active anymore or C<ev_break> was
		741	called.
384		742
385	Please note that an explicit C<ev_unloop> is usually better than	743	Please note that an explicit C<ev_break> is usually better than
386	relying on all watchers to be stopped when deciding when a program has	744	relying on all watchers to be stopped when deciding when a program has
387	finished (especially in interactive programs), but having a program that	745	finished (especially in interactive programs), but having a program
388	automatically loops as long as it has to and no longer by virtue of	746	that automatically loops as long as it has to and no longer by virtue
389	relying on its watchers stopping correctly is a thing of beauty.	747	of relying on its watchers stopping correctly, that is truly a thing of
		748	beauty.
390		749
391	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	750	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
392	those events and any outstanding ones, but will not block your process in	751	those events and any already outstanding ones, but will not wait and
393	case there are no events and will return after one iteration of the loop.	752	block your process in case there are no events and will return after one
		753	iteration of the loop. This is sometimes useful to poll and handle new
		754	events while doing lengthy calculations, to keep the program responsive.
394		755
395	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	756	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
396	neccessary) and will handle those and any outstanding ones. It will block	757	necessary) and will handle those and any already outstanding ones. It
397	your process until at least one new event arrives, and will return after	758	will block your process until at least one new event arrives (which could
398	one iteration of the loop. This is useful if you are waiting for some	759	be an event internal to libev itself, so there is no guarantee that a
399	external event in conjunction with something not expressible using other	760	user-registered callback will be called), and will return after one
		761	iteration of the loop.
		762
		763	This is useful if you are waiting for some external event in conjunction
		764	with something not expressible using other libev watchers (i.e. "roll your
400	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	765	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
401	usually a better approach for this kind of thing.	766	usually a better approach for this kind of thing.
402		767
403	Here are the gory details of what C<ev_loop> does:	768	Here are the gory details of what C<ev_run> does:
404		769
405	* If there are no active watchers (reference count is zero), return.	770	- Increment loop depth.
406	- Queue prepare watchers and then call all outstanding watchers.	771	- Reset the ev_break status.
		772	- Before the first iteration, call any pending watchers.
		773	LOOP:
		774	- If EVFLAG_FORKCHECK was used, check for a fork.
		775	- If a fork was detected (by any means), queue and call all fork watchers.
		776	- Queue and call all prepare watchers.
		777	- If ev_break was called, goto FINISH.
407	- If we have been forked, recreate the kernel state.	778	- If we have been forked, detach and recreate the kernel state
		779	as to not disturb the other process.
408	- Update the kernel state with all outstanding changes.	780	- Update the kernel state with all outstanding changes.
409	- Update the "event loop time".	781	- Update the "event loop time" (ev_now ()).
410	- Calculate for how long to block.	782	- Calculate for how long to sleep or block, if at all
		783	(active idle watchers, EVRUN_NOWAIT or not having
		784	any active watchers at all will result in not sleeping).
		785	- Sleep if the I/O and timer collect interval say so.
		786	- Increment loop iteration counter.
411	- Block the process, waiting for any events.	787	- Block the process, waiting for any events.
412	- Queue all outstanding I/O (fd) events.	788	- Queue all outstanding I/O (fd) events.
413	- Update the "event loop time" and do time jump handling.	789	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
414	- Queue all outstanding timers.	790	- Queue all expired timers.
415	- Queue all outstanding periodics.	791	- Queue all expired periodics.
416	- If no events are pending now, queue all idle watchers.	792	- Queue all idle watchers with priority higher than that of pending events.
417	- Queue all check watchers.	793	- Queue all check watchers.
418	- Call all queued watchers in reverse order (i.e. check watchers first).	794	- Call all queued watchers in reverse order (i.e. check watchers first).
419	Signals and child watchers are implemented as I/O watchers, and will	795	Signals and child watchers are implemented as I/O watchers, and will
420	be handled here by queueing them when their watcher gets executed.	796	be handled here by queueing them when their watcher gets executed.
421	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	797	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
422	were used, return, otherwise continue with step *.	798	were used, or there are no active watchers, goto FINISH, otherwise
		799	continue with step LOOP.
		800	FINISH:
		801	- Reset the ev_break status iff it was EVBREAK_ONE.
		802	- Decrement the loop depth.
		803	- Return.
423		804
424	Example: queue some jobs and then loop until no events are outsanding	805	Example: Queue some jobs and then loop until no events are outstanding
425	anymore.	806	anymore.
426		807
427	... queue jobs here, make sure they register event watchers as long	808	... queue jobs here, make sure they register event watchers as long
428	... as they still have work to do (even an idle watcher will do..)	809	... as they still have work to do (even an idle watcher will do..)
429	ev_loop (my_loop, 0);	810	ev_run (my_loop, 0);
430	... jobs done. yeah!	811	... jobs done or somebody called unloop. yeah!
431		812
432	=item ev_unloop (loop, how)	813	=item ev_break (loop, how)
433		814
434	Can be used to make a call to C<ev_loop> return early (but only after it	815	Can be used to make a call to C<ev_run> return early (but only after it
435	has processed all outstanding events). The C<how> argument must be either	816	has processed all outstanding events). The C<how> argument must be either
436	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	817	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
437	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	818	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		819
		820	This "unloop state" will be cleared when entering C<ev_run> again.
		821
		822	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##
438		823
439	=item ev_ref (loop)	824	=item ev_ref (loop)
440		825
441	=item ev_unref (loop)	826	=item ev_unref (loop)
442		827
443	Ref/unref can be used to add or remove a reference count on the event	828	Ref/unref can be used to add or remove a reference count on the event
444	loop: Every watcher keeps one reference, and as long as the reference	829	loop: Every watcher keeps one reference, and as long as the reference
445	count is nonzero, C<ev_loop> will not return on its own. If you have	830	count is nonzero, C<ev_run> will not return on its own.
446	a watcher you never unregister that should not keep C<ev_loop> from	831
447	returning, ev_unref() after starting, and ev_ref() before stopping it. For	832	This is useful when you have a watcher that you never intend to
		833	unregister, but that nevertheless should not keep C<ev_run> from
		834	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		835	before stopping it.
		836
448	example, libev itself uses this for its internal signal pipe: It is not	837	As an example, libev itself uses this for its internal signal pipe: It
449	visible to the libev user and should not keep C<ev_loop> from exiting if	838	is not visible to the libev user and should not keep C<ev_run> from
450	no event watchers registered by it are active. It is also an excellent	839	exiting if no event watchers registered by it are active. It is also an
451	way to do this for generic recurring timers or from within third-party	840	excellent way to do this for generic recurring timers or from within
452	libraries. Just remember to I<unref after start> and I<ref before stop>.	841	third-party libraries. Just remember to I<unref after start> and I<ref
		842	before stop> (but only if the watcher wasn't active before, or was active
		843	before, respectively. Note also that libev might stop watchers itself
		844	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		845	in the callback).
453		846
454	Example: create a signal watcher, but keep it from keeping C<ev_loop>	847	Example: Create a signal watcher, but keep it from keeping C<ev_run>
455	running when nothing else is active.	848	running when nothing else is active.
456		849
457	struct dv_signal exitsig;	850	ev_signal exitsig;
458	ev_signal_init (&exitsig, sig_cb, SIGINT);	851	ev_signal_init (&exitsig, sig_cb, SIGINT);
459	ev_signal_start (myloop, &exitsig);	852	ev_signal_start (loop, &exitsig);
460	evf_unref (myloop);	853	evf_unref (loop);
461		854
462	Example: for some weird reason, unregister the above signal handler again.	855	Example: For some weird reason, unregister the above signal handler again.
463		856
464	ev_ref (myloop);	857	ev_ref (loop);
465	ev_signal_stop (myloop, &exitsig);	858	ev_signal_stop (loop, &exitsig);
		859
		860	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		861
		862	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		863
		864	These advanced functions influence the time that libev will spend waiting
		865	for events. Both time intervals are by default C<0>, meaning that libev
		866	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		867	latency.
		868
		869	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		870	allows libev to delay invocation of I/O and timer/periodic callbacks
		871	to increase efficiency of loop iterations (or to increase power-saving
		872	opportunities).
		873
		874	The idea is that sometimes your program runs just fast enough to handle
		875	one (or very few) event(s) per loop iteration. While this makes the
		876	program responsive, it also wastes a lot of CPU time to poll for new
		877	events, especially with backends like C<select ()> which have a high
		878	overhead for the actual polling but can deliver many events at once.
		879
		880	By setting a higher I<io collect interval> you allow libev to spend more
		881	time collecting I/O events, so you can handle more events per iteration,
		882	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		883	C<ev_timer>) will be not affected. Setting this to a non-null value will
		884	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		885	sleep time ensures that libev will not poll for I/O events more often then
		886	once per this interval, on average.
		887
		888	Likewise, by setting a higher I<timeout collect interval> you allow libev
		889	to spend more time collecting timeouts, at the expense of increased
		890	latency/jitter/inexactness (the watcher callback will be called
		891	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		892	value will not introduce any overhead in libev.
		893
		894	Many (busy) programs can usually benefit by setting the I/O collect
		895	interval to a value near C<0.1> or so, which is often enough for
		896	interactive servers (of course not for games), likewise for timeouts. It
		897	usually doesn't make much sense to set it to a lower value than C<0.01>,
		898	as this approaches the timing granularity of most systems. Note that if
		899	you do transactions with the outside world and you can't increase the
		900	parallelity, then this setting will limit your transaction rate (if you
		901	need to poll once per transaction and the I/O collect interval is 0.01,
		902	then you can't do more than 100 transactions per second).
		903
		904	Setting the I<timeout collect interval> can improve the opportunity for
		905	saving power, as the program will "bundle" timer callback invocations that
		906	are "near" in time together, by delaying some, thus reducing the number of
		907	times the process sleeps and wakes up again. Another useful technique to
		908	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		909	they fire on, say, one-second boundaries only.
		910
		911	Example: we only need 0.1s timeout granularity, and we wish not to poll
		912	more often than 100 times per second:
		913
		914	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		915	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		916
		917	=item ev_invoke_pending (loop)
		918
		919	This call will simply invoke all pending watchers while resetting their
		920	pending state. Normally, C<ev_run> does this automatically when required,
		921	but when overriding the invoke callback this call comes handy. This
		922	function can be invoked from a watcher - this can be useful for example
		923	when you want to do some lengthy calculation and want to pass further
		924	event handling to another thread (you still have to make sure only one
		925	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		926
		927	=item int ev_pending_count (loop)
		928
		929	Returns the number of pending watchers - zero indicates that no watchers
		930	are pending.
		931
		932	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		933
		934	This overrides the invoke pending functionality of the loop: Instead of
		935	invoking all pending watchers when there are any, C<ev_run> will call
		936	this callback instead. This is useful, for example, when you want to
		937	invoke the actual watchers inside another context (another thread etc.).
		938
		939	If you want to reset the callback, use C<ev_invoke_pending> as new
		940	callback.
		941
		942	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		943
		944	Sometimes you want to share the same loop between multiple threads. This
		945	can be done relatively simply by putting mutex_lock/unlock calls around
		946	each call to a libev function.
		947
		948	However, C<ev_run> can run an indefinite time, so it is not feasible
		949	to wait for it to return. One way around this is to wake up the event
		950	loop via C<ev_break> and C<av_async_send>, another way is to set these
		951	I<release> and I<acquire> callbacks on the loop.
		952
		953	When set, then C<release> will be called just before the thread is
		954	suspended waiting for new events, and C<acquire> is called just
		955	afterwards.
		956
		957	Ideally, C<release> will just call your mutex_unlock function, and
		958	C<acquire> will just call the mutex_lock function again.
		959
		960	While event loop modifications are allowed between invocations of
		961	C<release> and C<acquire> (that's their only purpose after all), no
		962	modifications done will affect the event loop, i.e. adding watchers will
		963	have no effect on the set of file descriptors being watched, or the time
		964	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		965	to take note of any changes you made.
		966
		967	In theory, threads executing C<ev_run> will be async-cancel safe between
		968	invocations of C<release> and C<acquire>.
		969
		970	See also the locking example in the C<THREADS> section later in this
		971	document.
		972
		973	=item ev_set_userdata (loop, void *data)
		974
		975	=item ev_userdata (loop)
		976
		977	Set and retrieve a single C<void *> associated with a loop. When
		978	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		979	C<0.>
		980
		981	These two functions can be used to associate arbitrary data with a loop,
		982	and are intended solely for the C<invoke_pending_cb>, C<release> and
		983	C<acquire> callbacks described above, but of course can be (ab-)used for
		984	any other purpose as well.
		985
		986	=item ev_verify (loop)
		987
		988	This function only does something when C<EV_VERIFY> support has been
		989	compiled in, which is the default for non-minimal builds. It tries to go
		990	through all internal structures and checks them for validity. If anything
		991	is found to be inconsistent, it will print an error message to standard
		992	error and call C<abort ()>.
		993
		994	This can be used to catch bugs inside libev itself: under normal
		995	circumstances, this function will never abort as of course libev keeps its
		996	data structures consistent.
466		997
467	=back	998	=back
468		999
		1000
469	=head1 ANATOMY OF A WATCHER	1001	=head1 ANATOMY OF A WATCHER
470		1002
		1003	In the following description, uppercase C<TYPE> in names stands for the
		1004	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		1005	watchers and C<ev_io_start> for I/O watchers.
		1006
471	A watcher is a structure that you create and register to record your	1007	A watcher is an opaque structure that you allocate and register to record
472	interest in some event. For instance, if you want to wait for STDIN to	1008	your interest in some event. To make a concrete example, imagine you want
473	become readable, you would create an C<ev_io> watcher for that:	1009	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1010	for that:
474		1011
475	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1012	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
476	{	1013	{
477	ev_io_stop (w);	1014	ev_io_stop (w);
478	ev_unloop (loop, EVUNLOOP_ALL);	1015	ev_break (loop, EVBREAK_ALL);
479	}	1016	}
480		1017
481	struct ev_loop *loop = ev_default_loop (0);	1018	struct ev_loop *loop = ev_default_loop (0);
		1019
482	struct ev_io stdin_watcher;	1020	ev_io stdin_watcher;
		1021
483	ev_init (&stdin_watcher, my_cb);	1022	ev_init (&stdin_watcher, my_cb);
484	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1023	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
485	ev_io_start (loop, &stdin_watcher);	1024	ev_io_start (loop, &stdin_watcher);
		1025
486	ev_loop (loop, 0);	1026	ev_run (loop, 0);
487		1027
488	As you can see, you are responsible for allocating the memory for your	1028	As you can see, you are responsible for allocating the memory for your
489	watcher structures (and it is usually a bad idea to do this on the stack,	1029	watcher structures (and it is I<usually> a bad idea to do this on the
490	although this can sometimes be quite valid).	1030	stack).
491		1031
		1032	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1033	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1034
492	Each watcher structure must be initialised by a call to C<ev_init	1035	Each watcher structure must be initialised by a call to C<ev_init (watcher
493	(watcher *, callback)>, which expects a callback to be provided. This	1036	*, callback)>, which expects a callback to be provided. This callback is
494	callback gets invoked each time the event occurs (or, in the case of io	1037	invoked each time the event occurs (or, in the case of I/O watchers, each
495	watchers, each time the event loop detects that the file descriptor given	1038	time the event loop detects that the file descriptor given is readable
496	is readable and/or writable).	1039	and/or writable).
497		1040
498	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1041	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
499	with arguments specific to this watcher type. There is also a macro	1042	macro to configure it, with arguments specific to the watcher type. There
500	to combine initialisation and setting in one call: C<< ev_<type>_init	1043	is also a macro to combine initialisation and setting in one call: C<<
501	(watcher *, callback, ...) >>.	1044	ev_TYPE_init (watcher *, callback, ...) >>.
502		1045
503	To make the watcher actually watch out for events, you have to start it	1046	To make the watcher actually watch out for events, you have to start it
504	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1047	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
505	*) >>), and you can stop watching for events at any time by calling the	1048	*) >>), and you can stop watching for events at any time by calling the
506	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1049	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
507		1050
508	As long as your watcher is active (has been started but not stopped) you	1051	As long as your watcher is active (has been started but not stopped) you
509	must not touch the values stored in it. Most specifically you must never	1052	must not touch the values stored in it. Most specifically you must never
510	reinitialise it or call its set macro.	1053	reinitialise it or call its C<ev_TYPE_set> macro.
511
512	You can check whether an event is active by calling the C<ev_is_active
513	(watcher *)> macro. To see whether an event is outstanding (but the
514	callback for it has not been called yet) you can use the C<ev_is_pending
515	(watcher *)> macro.
516		1054
517	Each and every callback receives the event loop pointer as first, the	1055	Each and every callback receives the event loop pointer as first, the
518	registered watcher structure as second, and a bitset of received events as	1056	registered watcher structure as second, and a bitset of received events as
519	third argument.	1057	third argument.
520		1058
…		…
529	=item C<EV_WRITE>	1067	=item C<EV_WRITE>
530		1068
531	The file descriptor in the C<ev_io> watcher has become readable and/or	1069	The file descriptor in the C<ev_io> watcher has become readable and/or
532	writable.	1070	writable.
533		1071
534	=item C<EV_TIMEOUT>	1072	=item C<EV_TIMER>
535		1073
536	The C<ev_timer> watcher has timed out.	1074	The C<ev_timer> watcher has timed out.
537		1075
538	=item C<EV_PERIODIC>	1076	=item C<EV_PERIODIC>
539		1077
…		…
545		1083
546	=item C<EV_CHILD>	1084	=item C<EV_CHILD>
547		1085
548	The pid specified in the C<ev_child> watcher has received a status change.	1086	The pid specified in the C<ev_child> watcher has received a status change.
549		1087
		1088	=item C<EV_STAT>
		1089
		1090	The path specified in the C<ev_stat> watcher changed its attributes somehow.
		1091
550	=item C<EV_IDLE>	1092	=item C<EV_IDLE>
551		1093
552	The C<ev_idle> watcher has determined that you have nothing better to do.	1094	The C<ev_idle> watcher has determined that you have nothing better to do.
553		1095
554	=item C<EV_PREPARE>	1096	=item C<EV_PREPARE>
555		1097
556	=item C<EV_CHECK>	1098	=item C<EV_CHECK>
557		1099
558	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1100	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
559	to gather new events, and all C<ev_check> watchers are invoked just after	1101	to gather new events, and all C<ev_check> watchers are invoked just after
560	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1102	C<ev_run> has gathered them, but before it invokes any callbacks for any
561	received events. Callbacks of both watcher types can start and stop as	1103	received events. Callbacks of both watcher types can start and stop as
562	many watchers as they want, and all of them will be taken into account	1104	many watchers as they want, and all of them will be taken into account
563	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1105	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
564	C<ev_loop> from blocking).	1106	C<ev_run> from blocking).
		1107
		1108	=item C<EV_EMBED>
		1109
		1110	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1111
		1112	=item C<EV_FORK>
		1113
		1114	The event loop has been resumed in the child process after fork (see
		1115	C<ev_fork>).
		1116
		1117	=item C<EV_CLEANUP>
		1118
		1119	The event loop is abotu to be destroyed (see C<ev_cleanup>).
		1120
		1121	=item C<EV_ASYNC>
		1122
		1123	The given async watcher has been asynchronously notified (see C<ev_async>).
		1124
		1125	=item C<EV_CUSTOM>
		1126
		1127	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1128	by libev users to signal watchers (e.g. via C<ev_feed_event>).
565		1129
566	=item C<EV_ERROR>	1130	=item C<EV_ERROR>
567		1131
568	An unspecified error has occured, the watcher has been stopped. This might	1132	An unspecified error has occurred, the watcher has been stopped. This might
569	happen because the watcher could not be properly started because libev	1133	happen because the watcher could not be properly started because libev
570	ran out of memory, a file descriptor was found to be closed or any other	1134	ran out of memory, a file descriptor was found to be closed or any other
		1135	problem. Libev considers these application bugs.
		1136
571	problem. You best act on it by reporting the problem and somehow coping	1137	You best act on it by reporting the problem and somehow coping with the
572	with the watcher being stopped.	1138	watcher being stopped. Note that well-written programs should not receive
		1139	an error ever, so when your watcher receives it, this usually indicates a
		1140	bug in your program.
573		1141
574	Libev will usually signal a few "dummy" events together with an error,	1142	Libev will usually signal a few "dummy" events together with an error, for
575	for example it might indicate that a fd is readable or writable, and if	1143	example it might indicate that a fd is readable or writable, and if your
576	your callbacks is well-written it can just attempt the operation and cope	1144	callbacks is well-written it can just attempt the operation and cope with
577	with the error from read() or write(). This will not work in multithreaded	1145	the error from read() or write(). This will not work in multi-threaded
578	programs, though, so beware.	1146	programs, though, as the fd could already be closed and reused for another
		1147	thing, so beware.
579		1148
580	=back	1149	=back
581		1150
		1151	=head2 WATCHER STATES
		1152
		1153	There are various watcher states mentioned throughout this manual -
		1154	active, pending and so on. In this section these states and the rules to
		1155	transition between them will be described in more detail - and while these
		1156	rules might look complicated, they usually do "the right thing".
		1157
		1158	=over 4
		1159
		1160	=item initialiased
		1161
		1162	Before a watcher can be registered with the event looop it has to be
		1163	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1164	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1165
		1166	In this state it is simply some block of memory that is suitable for use
		1167	in an event loop. It can be moved around, freed, reused etc. at will.
		1168
		1169	=item started/running/active
		1170
		1171	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1172	property of the event loop, and is actively waiting for events. While in
		1173	this state it cannot be accessed (except in a few documented ways), moved,
		1174	freed or anything else - the only legal thing is to keep a pointer to it,
		1175	and call libev functions on it that are documented to work on active watchers.
		1176
		1177	=item pending
		1178
		1179	If a watcher is active and libev determines that an event it is interested
		1180	in has occurred (such as a timer expiring), it will become pending. It will
		1181	stay in this pending state until either it is stopped or its callback is
		1182	about to be invoked, so it is not normally pending inside the watcher
		1183	callback.
		1184
		1185	The watcher might or might not be active while it is pending (for example,
		1186	an expired non-repeating timer can be pending but no longer active). If it
		1187	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1188	but it is still property of the event loop at this time, so cannot be
		1189	moved, freed or reused. And if it is active the rules described in the
		1190	previous item still apply.
		1191
		1192	It is also possible to feed an event on a watcher that is not active (e.g.
		1193	via C<ev_feed_event>), in which case it becomes pending without being
		1194	active.
		1195
		1196	=item stopped
		1197
		1198	A watcher can be stopped implicitly by libev (in which case it might still
		1199	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1200	latter will clear any pending state the watcher might be in, regardless
		1201	of whether it was active or not, so stopping a watcher explicitly before
		1202	freeing it is often a good idea.
		1203
		1204	While stopped (and not pending) the watcher is essentially in the
		1205	initialised state, that is it can be reused, moved, modified in any way
		1206	you wish.
		1207
		1208	=back
		1209
		1210	=head2 GENERIC WATCHER FUNCTIONS
		1211
		1212	=over 4
		1213
		1214	=item C<ev_init> (ev_TYPE *watcher, callback)
		1215
		1216	This macro initialises the generic portion of a watcher. The contents
		1217	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1218	the generic parts of the watcher are initialised, you I<need> to call
		1219	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1220	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1221	which rolls both calls into one.
		1222
		1223	You can reinitialise a watcher at any time as long as it has been stopped
		1224	(or never started) and there are no pending events outstanding.
		1225
		1226	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1227	int revents)>.
		1228
		1229	Example: Initialise an C<ev_io> watcher in two steps.
		1230
		1231	ev_io w;
		1232	ev_init (&w, my_cb);
		1233	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1234
		1235	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1236
		1237	This macro initialises the type-specific parts of a watcher. You need to
		1238	call C<ev_init> at least once before you call this macro, but you can
		1239	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1240	macro on a watcher that is active (it can be pending, however, which is a
		1241	difference to the C<ev_init> macro).
		1242
		1243	Although some watcher types do not have type-specific arguments
		1244	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1245
		1246	See C<ev_init>, above, for an example.
		1247
		1248	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1249
		1250	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1251	calls into a single call. This is the most convenient method to initialise
		1252	a watcher. The same limitations apply, of course.
		1253
		1254	Example: Initialise and set an C<ev_io> watcher in one step.
		1255
		1256	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1257
		1258	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1259
		1260	Starts (activates) the given watcher. Only active watchers will receive
		1261	events. If the watcher is already active nothing will happen.
		1262
		1263	Example: Start the C<ev_io> watcher that is being abused as example in this
		1264	whole section.
		1265
		1266	ev_io_start (EV_DEFAULT_UC, &w);
		1267
		1268	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1269
		1270	Stops the given watcher if active, and clears the pending status (whether
		1271	the watcher was active or not).
		1272
		1273	It is possible that stopped watchers are pending - for example,
		1274	non-repeating timers are being stopped when they become pending - but
		1275	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1276	pending. If you want to free or reuse the memory used by the watcher it is
		1277	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1278
		1279	=item bool ev_is_active (ev_TYPE *watcher)
		1280
		1281	Returns a true value iff the watcher is active (i.e. it has been started
		1282	and not yet been stopped). As long as a watcher is active you must not modify
		1283	it.
		1284
		1285	=item bool ev_is_pending (ev_TYPE *watcher)
		1286
		1287	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1288	events but its callback has not yet been invoked). As long as a watcher
		1289	is pending (but not active) you must not call an init function on it (but
		1290	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1291	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1292	it).
		1293
		1294	=item callback ev_cb (ev_TYPE *watcher)
		1295
		1296	Returns the callback currently set on the watcher.
		1297
		1298	=item ev_cb_set (ev_TYPE *watcher, callback)
		1299
		1300	Change the callback. You can change the callback at virtually any time
		1301	(modulo threads).
		1302
		1303	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1304
		1305	=item int ev_priority (ev_TYPE *watcher)
		1306
		1307	Set and query the priority of the watcher. The priority is a small
		1308	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1309	(default: C<-2>). Pending watchers with higher priority will be invoked
		1310	before watchers with lower priority, but priority will not keep watchers
		1311	from being executed (except for C<ev_idle> watchers).
		1312
		1313	If you need to suppress invocation when higher priority events are pending
		1314	you need to look at C<ev_idle> watchers, which provide this functionality.
		1315
		1316	You I<must not> change the priority of a watcher as long as it is active or
		1317	pending.
		1318
		1319	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1320	fine, as long as you do not mind that the priority value you query might
		1321	or might not have been clamped to the valid range.
		1322
		1323	The default priority used by watchers when no priority has been set is
		1324	always C<0>, which is supposed to not be too high and not be too low :).
		1325
		1326	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1327	priorities.
		1328
		1329	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1330
		1331	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1332	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1333	can deal with that fact, as both are simply passed through to the
		1334	callback.
		1335
		1336	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1337
		1338	If the watcher is pending, this function clears its pending status and
		1339	returns its C<revents> bitset (as if its callback was invoked). If the
		1340	watcher isn't pending it does nothing and returns C<0>.
		1341
		1342	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1343	callback to be invoked, which can be accomplished with this function.
		1344
		1345	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1346
		1347	Feeds the given event set into the event loop, as if the specified event
		1348	had happened for the specified watcher (which must be a pointer to an
		1349	initialised but not necessarily started event watcher). Obviously you must
		1350	not free the watcher as long as it has pending events.
		1351
		1352	Stopping the watcher, letting libev invoke it, or calling
		1353	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1354	not started in the first place.
		1355
		1356	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1357	functions that do not need a watcher.
		1358
		1359	=back
		1360
		1361
582	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
583		1363
584	Each watcher has, by default, a member C<void *data> that you can change	1364	Each watcher has, by default, a member C<void *data> that you can change
585	and read at any time, libev will completely ignore it. This can be used	1365	and read at any time: libev will completely ignore it. This can be used
586	to associate arbitrary data with your watcher. If you need more data and	1366	to associate arbitrary data with your watcher. If you need more data and
587	don't want to allocate memory and store a pointer to it in that data	1367	don't want to allocate memory and store a pointer to it in that data
588	member, you can also "subclass" the watcher type and provide your own	1368	member, you can also "subclass" the watcher type and provide your own
589	data:	1369	data:
590		1370
591	struct my_io	1371	struct my_io
592	{	1372	{
593	struct ev_io io;	1373	ev_io io;
594	int otherfd;	1374	int otherfd;
595	void *somedata;	1375	void *somedata;
596	struct whatever *mostinteresting;	1376	struct whatever *mostinteresting;
597	}	1377	};
		1378
		1379	...
		1380	struct my_io w;
		1381	ev_io_init (&w.io, my_cb, fd, EV_READ);
598		1382
599	And since your callback will be called with a pointer to the watcher, you	1383	And since your callback will be called with a pointer to the watcher, you
600	can cast it back to your own type:	1384	can cast it back to your own type:
601		1385
602	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1386	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
603	{	1387	{
604	struct my_io *w = (struct my_io *)w_;	1388	struct my_io *w = (struct my_io *)w_;
605	...	1389	...
606	}	1390	}
607		1391
608	More interesting and less C-conformant ways of catsing your callback type	1392	More interesting and less C-conformant ways of casting your callback type
609	have been omitted....	1393	instead have been omitted.
		1394
		1395	Another common scenario is to use some data structure with multiple
		1396	embedded watchers:
		1397
		1398	struct my_biggy
		1399	{
		1400	int some_data;
		1401	ev_timer t1;
		1402	ev_timer t2;
		1403	}
		1404
		1405	In this case getting the pointer to C<my_biggy> is a bit more
		1406	complicated: Either you store the address of your C<my_biggy> struct
		1407	in the C<data> member of the watcher (for woozies), or you need to use
		1408	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1409	programmers):
		1410
		1411	#include <stddef.h>
		1412
		1413	static void
		1414	t1_cb (EV_P_ ev_timer *w, int revents)
		1415	{
		1416	struct my_biggy big = (struct my_biggy *)
		1417	(((char *)w) - offsetof (struct my_biggy, t1));
		1418	}
		1419
		1420	static void
		1421	t2_cb (EV_P_ ev_timer *w, int revents)
		1422	{
		1423	struct my_biggy big = (struct my_biggy *)
		1424	(((char *)w) - offsetof (struct my_biggy, t2));
		1425	}
		1426
		1427	=head2 WATCHER PRIORITY MODELS
		1428
		1429	Many event loops support I<watcher priorities>, which are usually small
		1430	integers that influence the ordering of event callback invocation
		1431	between watchers in some way, all else being equal.
		1432
		1433	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1434	description for the more technical details such as the actual priority
		1435	range.
		1436
		1437	There are two common ways how these these priorities are being interpreted
		1438	by event loops:
		1439
		1440	In the more common lock-out model, higher priorities "lock out" invocation
		1441	of lower priority watchers, which means as long as higher priority
		1442	watchers receive events, lower priority watchers are not being invoked.
		1443
		1444	The less common only-for-ordering model uses priorities solely to order
		1445	callback invocation within a single event loop iteration: Higher priority
		1446	watchers are invoked before lower priority ones, but they all get invoked
		1447	before polling for new events.
		1448
		1449	Libev uses the second (only-for-ordering) model for all its watchers
		1450	except for idle watchers (which use the lock-out model).
		1451
		1452	The rationale behind this is that implementing the lock-out model for
		1453	watchers is not well supported by most kernel interfaces, and most event
		1454	libraries will just poll for the same events again and again as long as
		1455	their callbacks have not been executed, which is very inefficient in the
		1456	common case of one high-priority watcher locking out a mass of lower
		1457	priority ones.
		1458
		1459	Static (ordering) priorities are most useful when you have two or more
		1460	watchers handling the same resource: a typical usage example is having an
		1461	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1462	timeouts. Under load, data might be received while the program handles
		1463	other jobs, but since timers normally get invoked first, the timeout
		1464	handler will be executed before checking for data. In that case, giving
		1465	the timer a lower priority than the I/O watcher ensures that I/O will be
		1466	handled first even under adverse conditions (which is usually, but not
		1467	always, what you want).
		1468
		1469	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1470	will only be executed when no same or higher priority watchers have
		1471	received events, they can be used to implement the "lock-out" model when
		1472	required.
		1473
		1474	For example, to emulate how many other event libraries handle priorities,
		1475	you can associate an C<ev_idle> watcher to each such watcher, and in
		1476	the normal watcher callback, you just start the idle watcher. The real
		1477	processing is done in the idle watcher callback. This causes libev to
		1478	continuously poll and process kernel event data for the watcher, but when
		1479	the lock-out case is known to be rare (which in turn is rare :), this is
		1480	workable.
		1481
		1482	Usually, however, the lock-out model implemented that way will perform
		1483	miserably under the type of load it was designed to handle. In that case,
		1484	it might be preferable to stop the real watcher before starting the
		1485	idle watcher, so the kernel will not have to process the event in case
		1486	the actual processing will be delayed for considerable time.
		1487
		1488	Here is an example of an I/O watcher that should run at a strictly lower
		1489	priority than the default, and which should only process data when no
		1490	other events are pending:
		1491
		1492	ev_idle idle; // actual processing watcher
		1493	ev_io io; // actual event watcher
		1494
		1495	static void
		1496	io_cb (EV_P_ ev_io *w, int revents)
		1497	{
		1498	// stop the I/O watcher, we received the event, but
		1499	// are not yet ready to handle it.
		1500	ev_io_stop (EV_A_ w);
		1501
		1502	// start the idle watcher to handle the actual event.
		1503	// it will not be executed as long as other watchers
		1504	// with the default priority are receiving events.
		1505	ev_idle_start (EV_A_ &idle);
		1506	}
		1507
		1508	static void
		1509	idle_cb (EV_P_ ev_idle *w, int revents)
		1510	{
		1511	// actual processing
		1512	read (STDIN_FILENO, ...);
		1513
		1514	// have to start the I/O watcher again, as
		1515	// we have handled the event
		1516	ev_io_start (EV_P_ &io);
		1517	}
		1518
		1519	// initialisation
		1520	ev_idle_init (&idle, idle_cb);
		1521	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1522	ev_io_start (EV_DEFAULT_ &io);
		1523
		1524	In the "real" world, it might also be beneficial to start a timer, so that
		1525	low-priority connections can not be locked out forever under load. This
		1526	enables your program to keep a lower latency for important connections
		1527	during short periods of high load, while not completely locking out less
		1528	important ones.
610		1529
611		1530
612	=head1 WATCHER TYPES	1531	=head1 WATCHER TYPES
613		1532
614	This section describes each watcher in detail, but will not repeat	1533	This section describes each watcher in detail, but will not repeat
615	information given in the last section.	1534	information given in the last section. Any initialisation/set macros,
		1535	functions and members specific to the watcher type are explained.
616		1536
		1537	Members are additionally marked with either I<[read-only]>, meaning that,
		1538	while the watcher is active, you can look at the member and expect some
		1539	sensible content, but you must not modify it (you can modify it while the
		1540	watcher is stopped to your hearts content), or I<[read-write]>, which
		1541	means you can expect it to have some sensible content while the watcher
		1542	is active, but you can also modify it. Modifying it may not do something
		1543	sensible or take immediate effect (or do anything at all), but libev will
		1544	not crash or malfunction in any way.
617		1545
		1546
618	=head2 C<ev_io> - is this file descriptor readable or writable	1547	=head2 C<ev_io> - is this file descriptor readable or writable?
619		1548
620	I/O watchers check whether a file descriptor is readable or writable	1549	I/O watchers check whether a file descriptor is readable or writable
621	in each iteration of the event loop (This behaviour is called	1550	in each iteration of the event loop, or, more precisely, when reading
622	level-triggering because you keep receiving events as long as the	1551	would not block the process and writing would at least be able to write
623	condition persists. Remember you can stop the watcher if you don't want to	1552	some data. This behaviour is called level-triggering because you keep
624	act on the event and neither want to receive future events).	1553	receiving events as long as the condition persists. Remember you can stop
		1554	the watcher if you don't want to act on the event and neither want to
		1555	receive future events.
625		1556
626	In general you can register as many read and/or write event watchers per	1557	In general you can register as many read and/or write event watchers per
627	fd as you want (as long as you don't confuse yourself). Setting all file	1558	fd as you want (as long as you don't confuse yourself). Setting all file
628	descriptors to non-blocking mode is also usually a good idea (but not	1559	descriptors to non-blocking mode is also usually a good idea (but not
629	required if you know what you are doing).	1560	required if you know what you are doing).
630		1561
631	You have to be careful with dup'ed file descriptors, though. Some backends	1562	If you cannot use non-blocking mode, then force the use of a
632	(the linux epoll backend is a notable example) cannot handle dup'ed file	1563	known-to-be-good backend (at the time of this writing, this includes only
633	descriptors correctly if you register interest in two or more fds pointing	1564	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
634	to the same underlying file/socket etc. description (that is, they share	1565	descriptors for which non-blocking operation makes no sense (such as
635	the same underlying "file open").	1566	files) - libev doesn't guarantee any specific behaviour in that case.
636		1567
637	If you must do this, then force the use of a known-to-be-good backend	1568	Another thing you have to watch out for is that it is quite easy to
638	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1569	receive "spurious" readiness notifications, that is your callback might
		1570	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1571	because there is no data. Not only are some backends known to create a
		1572	lot of those (for example Solaris ports), it is very easy to get into
		1573	this situation even with a relatively standard program structure. Thus
		1574	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1575	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1576
		1577	If you cannot run the fd in non-blocking mode (for example you should
		1578	not play around with an Xlib connection), then you have to separately
		1579	re-test whether a file descriptor is really ready with a known-to-be good
		1580	interface such as poll (fortunately in our Xlib example, Xlib already
		1581	does this on its own, so its quite safe to use). Some people additionally
		1582	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1583	indefinitely.
		1584
		1585	But really, best use non-blocking mode.
		1586
		1587	=head3 The special problem of disappearing file descriptors
		1588
		1589	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1590	descriptor (either due to calling C<close> explicitly or any other means,
		1591	such as C<dup2>). The reason is that you register interest in some file
		1592	descriptor, but when it goes away, the operating system will silently drop
		1593	this interest. If another file descriptor with the same number then is
		1594	registered with libev, there is no efficient way to see that this is, in
		1595	fact, a different file descriptor.
		1596
		1597	To avoid having to explicitly tell libev about such cases, libev follows
		1598	the following policy: Each time C<ev_io_set> is being called, libev
		1599	will assume that this is potentially a new file descriptor, otherwise
		1600	it is assumed that the file descriptor stays the same. That means that
		1601	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1602	descriptor even if the file descriptor number itself did not change.
		1603
		1604	This is how one would do it normally anyway, the important point is that
		1605	the libev application should not optimise around libev but should leave
		1606	optimisations to libev.
		1607
		1608	=head3 The special problem of dup'ed file descriptors
		1609
		1610	Some backends (e.g. epoll), cannot register events for file descriptors,
		1611	but only events for the underlying file descriptions. That means when you
		1612	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1613	events for them, only one file descriptor might actually receive events.
		1614
		1615	There is no workaround possible except not registering events
		1616	for potentially C<dup ()>'ed file descriptors, or to resort to
		1617	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1618
		1619	=head3 The special problem of fork
		1620
		1621	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1622	useless behaviour. Libev fully supports fork, but needs to be told about
		1623	it in the child.
		1624
		1625	To support fork in your programs, you either have to call
		1626	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1627	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
639	C<EVBACKEND_POLL>).	1628	C<EVBACKEND_POLL>.
		1629
		1630	=head3 The special problem of SIGPIPE
		1631
		1632	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1633	when writing to a pipe whose other end has been closed, your program gets
		1634	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1635	this is sensible behaviour, for daemons, this is usually undesirable.
		1636
		1637	So when you encounter spurious, unexplained daemon exits, make sure you
		1638	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1639	somewhere, as that would have given you a big clue).
		1640
		1641	=head3 The special problem of accept()ing when you can't
		1642
		1643	Many implementations of the POSIX C<accept> function (for example,
		1644	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1645	connection from the pending queue in all error cases.
		1646
		1647	For example, larger servers often run out of file descriptors (because
		1648	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1649	rejecting the connection, leading to libev signalling readiness on
		1650	the next iteration again (the connection still exists after all), and
		1651	typically causing the program to loop at 100% CPU usage.
		1652
		1653	Unfortunately, the set of errors that cause this issue differs between
		1654	operating systems, there is usually little the app can do to remedy the
		1655	situation, and no known thread-safe method of removing the connection to
		1656	cope with overload is known (to me).
		1657
		1658	One of the easiest ways to handle this situation is to just ignore it
		1659	- when the program encounters an overload, it will just loop until the
		1660	situation is over. While this is a form of busy waiting, no OS offers an
		1661	event-based way to handle this situation, so it's the best one can do.
		1662
		1663	A better way to handle the situation is to log any errors other than
		1664	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1665	messages, and continue as usual, which at least gives the user an idea of
		1666	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1667	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1668	usage.
		1669
		1670	If your program is single-threaded, then you could also keep a dummy file
		1671	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1672	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1673	close that fd, and create a new dummy fd. This will gracefully refuse
		1674	clients under typical overload conditions.
		1675
		1676	The last way to handle it is to simply log the error and C<exit>, as
		1677	is often done with C<malloc> failures, but this results in an easy
		1678	opportunity for a DoS attack.
		1679
		1680	=head3 Watcher-Specific Functions
640		1681
641	=over 4	1682	=over 4
642		1683
643	=item ev_io_init (ev_io *, callback, int fd, int events)	1684	=item ev_io_init (ev_io *, callback, int fd, int events)
644		1685
645	=item ev_io_set (ev_io *, int fd, int events)	1686	=item ev_io_set (ev_io *, int fd, int events)
646		1687
647	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1688	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
648	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1689	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
649	EV_WRITE> to receive the given events.	1690	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
650		1691
651	Please note that most of the more scalable backend mechanisms (for example	1692	=item int fd [read-only]
652	epoll and solaris ports) can result in spurious readyness notifications	1693
653	for file descriptors, so you practically need to use non-blocking I/O (and	1694	The file descriptor being watched.
654	treat callback invocation as hint only), or retest separately with a safe	1695
655	interface before doing I/O (XLib can do this), or force the use of either	1696	=item int events [read-only]
656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this	1697
657	problem. Also note that it is quite easy to have your callback invoked	1698	The events being watched.
658	when the readyness condition is no longer valid even when employing
659	typical ways of handling events, so its a good idea to use non-blocking
660	I/O unconditionally.
661		1699
662	=back	1700	=back
663		1701
		1702	=head3 Examples
		1703
664	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1704	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
665	readable, but only once. Since it is likely line-buffered, you could	1705	readable, but only once. Since it is likely line-buffered, you could
666	attempt to read a whole line in the callback:	1706	attempt to read a whole line in the callback.
667		1707
668	static void	1708	static void
669	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1709	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
670	{	1710	{
671	ev_io_stop (loop, w);	1711	ev_io_stop (loop, w);
672	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1712	.. read from stdin here (or from w->fd) and handle any I/O errors
673	}	1713	}
674		1714
675	...	1715	...
676	struct ev_loop *loop = ev_default_init (0);	1716	struct ev_loop *loop = ev_default_init (0);
677	struct ev_io stdin_readable;	1717	ev_io stdin_readable;
678	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1718	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
679	ev_io_start (loop, &stdin_readable);	1719	ev_io_start (loop, &stdin_readable);
680	ev_loop (loop, 0);	1720	ev_run (loop, 0);
681		1721
682		1722
683	=head2 C<ev_timer> - relative and optionally recurring timeouts	1723	=head2 C<ev_timer> - relative and optionally repeating timeouts
684		1724
685	Timer watchers are simple relative timers that generate an event after a	1725	Timer watchers are simple relative timers that generate an event after a
686	given time, and optionally repeating in regular intervals after that.	1726	given time, and optionally repeating in regular intervals after that.
687		1727
688	The timers are based on real time, that is, if you register an event that	1728	The timers are based on real time, that is, if you register an event that
689	times out after an hour and you reset your system clock to last years	1729	times out after an hour and you reset your system clock to January last
690	time, it will still time out after (roughly) and hour. "Roughly" because	1730	year, it will still time out after (roughly) one hour. "Roughly" because
691	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1731	detecting time jumps is hard, and some inaccuracies are unavoidable (the
692	monotonic clock option helps a lot here).	1732	monotonic clock option helps a lot here).
		1733
		1734	The callback is guaranteed to be invoked only I<after> its timeout has
		1735	passed (not I<at>, so on systems with very low-resolution clocks this
		1736	might introduce a small delay). If multiple timers become ready during the
		1737	same loop iteration then the ones with earlier time-out values are invoked
		1738	before ones of the same priority with later time-out values (but this is
		1739	no longer true when a callback calls C<ev_run> recursively).
		1740
		1741	=head3 Be smart about timeouts
		1742
		1743	Many real-world problems involve some kind of timeout, usually for error
		1744	recovery. A typical example is an HTTP request - if the other side hangs,
		1745	you want to raise some error after a while.
		1746
		1747	What follows are some ways to handle this problem, from obvious and
		1748	inefficient to smart and efficient.
		1749
		1750	In the following, a 60 second activity timeout is assumed - a timeout that
		1751	gets reset to 60 seconds each time there is activity (e.g. each time some
		1752	data or other life sign was received).
		1753
		1754	=over 4
		1755
		1756	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1757
		1758	This is the most obvious, but not the most simple way: In the beginning,
		1759	start the watcher:
		1760
		1761	ev_timer_init (timer, callback, 60., 0.);
		1762	ev_timer_start (loop, timer);
		1763
		1764	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1765	and start it again:
		1766
		1767	ev_timer_stop (loop, timer);
		1768	ev_timer_set (timer, 60., 0.);
		1769	ev_timer_start (loop, timer);
		1770
		1771	This is relatively simple to implement, but means that each time there is
		1772	some activity, libev will first have to remove the timer from its internal
		1773	data structure and then add it again. Libev tries to be fast, but it's
		1774	still not a constant-time operation.
		1775
		1776	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1777
		1778	This is the easiest way, and involves using C<ev_timer_again> instead of
		1779	C<ev_timer_start>.
		1780
		1781	To implement this, configure an C<ev_timer> with a C<repeat> value
		1782	of C<60> and then call C<ev_timer_again> at start and each time you
		1783	successfully read or write some data. If you go into an idle state where
		1784	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1785	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1786
		1787	That means you can ignore both the C<ev_timer_start> function and the
		1788	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1789	member and C<ev_timer_again>.
		1790
		1791	At start:
		1792
		1793	ev_init (timer, callback);
		1794	timer->repeat = 60.;
		1795	ev_timer_again (loop, timer);
		1796
		1797	Each time there is some activity:
		1798
		1799	ev_timer_again (loop, timer);
		1800
		1801	It is even possible to change the time-out on the fly, regardless of
		1802	whether the watcher is active or not:
		1803
		1804	timer->repeat = 30.;
		1805	ev_timer_again (loop, timer);
		1806
		1807	This is slightly more efficient then stopping/starting the timer each time
		1808	you want to modify its timeout value, as libev does not have to completely
		1809	remove and re-insert the timer from/into its internal data structure.
		1810
		1811	It is, however, even simpler than the "obvious" way to do it.
		1812
		1813	=item 3. Let the timer time out, but then re-arm it as required.
		1814
		1815	This method is more tricky, but usually most efficient: Most timeouts are
		1816	relatively long compared to the intervals between other activity - in
		1817	our example, within 60 seconds, there are usually many I/O events with
		1818	associated activity resets.
		1819
		1820	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1821	but remember the time of last activity, and check for a real timeout only
		1822	within the callback:
		1823
		1824	ev_tstamp last_activity; // time of last activity
		1825
		1826	static void
		1827	callback (EV_P_ ev_timer *w, int revents)
		1828	{
		1829	ev_tstamp now = ev_now (EV_A);
		1830	ev_tstamp timeout = last_activity + 60.;
		1831
		1832	// if last_activity + 60. is older than now, we did time out
		1833	if (timeout < now)
		1834	{
		1835	// timeout occurred, take action
		1836	}
		1837	else
		1838	{
		1839	// callback was invoked, but there was some activity, re-arm
		1840	// the watcher to fire in last_activity + 60, which is
		1841	// guaranteed to be in the future, so "again" is positive:
		1842	w->repeat = timeout - now;
		1843	ev_timer_again (EV_A_ w);
		1844	}
		1845	}
		1846
		1847	To summarise the callback: first calculate the real timeout (defined
		1848	as "60 seconds after the last activity"), then check if that time has
		1849	been reached, which means something I<did>, in fact, time out. Otherwise
		1850	the callback was invoked too early (C<timeout> is in the future), so
		1851	re-schedule the timer to fire at that future time, to see if maybe we have
		1852	a timeout then.
		1853
		1854	Note how C<ev_timer_again> is used, taking advantage of the
		1855	C<ev_timer_again> optimisation when the timer is already running.
		1856
		1857	This scheme causes more callback invocations (about one every 60 seconds
		1858	minus half the average time between activity), but virtually no calls to
		1859	libev to change the timeout.
		1860
		1861	To start the timer, simply initialise the watcher and set C<last_activity>
		1862	to the current time (meaning we just have some activity :), then call the
		1863	callback, which will "do the right thing" and start the timer:
		1864
		1865	ev_init (timer, callback);
		1866	last_activity = ev_now (loop);
		1867	callback (loop, timer, EV_TIMER);
		1868
		1869	And when there is some activity, simply store the current time in
		1870	C<last_activity>, no libev calls at all:
		1871
		1872	last_activity = ev_now (loop);
		1873
		1874	This technique is slightly more complex, but in most cases where the
		1875	time-out is unlikely to be triggered, much more efficient.
		1876
		1877	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1878	callback :) - just change the timeout and invoke the callback, which will
		1879	fix things for you.
		1880
		1881	=item 4. Wee, just use a double-linked list for your timeouts.
		1882
		1883	If there is not one request, but many thousands (millions...), all
		1884	employing some kind of timeout with the same timeout value, then one can
		1885	do even better:
		1886
		1887	When starting the timeout, calculate the timeout value and put the timeout
		1888	at the I<end> of the list.
		1889
		1890	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1891	the list is expected to fire (for example, using the technique #3).
		1892
		1893	When there is some activity, remove the timer from the list, recalculate
		1894	the timeout, append it to the end of the list again, and make sure to
		1895	update the C<ev_timer> if it was taken from the beginning of the list.
		1896
		1897	This way, one can manage an unlimited number of timeouts in O(1) time for
		1898	starting, stopping and updating the timers, at the expense of a major
		1899	complication, and having to use a constant timeout. The constant timeout
		1900	ensures that the list stays sorted.
		1901
		1902	=back
		1903
		1904	So which method the best?
		1905
		1906	Method #2 is a simple no-brain-required solution that is adequate in most
		1907	situations. Method #3 requires a bit more thinking, but handles many cases
		1908	better, and isn't very complicated either. In most case, choosing either
		1909	one is fine, with #3 being better in typical situations.
		1910
		1911	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1912	rather complicated, but extremely efficient, something that really pays
		1913	off after the first million or so of active timers, i.e. it's usually
		1914	overkill :)
		1915
		1916	=head3 The special problem of time updates
		1917
		1918	Establishing the current time is a costly operation (it usually takes at
		1919	least two system calls): EV therefore updates its idea of the current
		1920	time only before and after C<ev_run> collects new events, which causes a
		1921	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1922	lots of events in one iteration.
693		1923
694	The relative timeouts are calculated relative to the C<ev_now ()>	1924	The relative timeouts are calculated relative to the C<ev_now ()>
695	time. This is usually the right thing as this timestamp refers to the time	1925	time. This is usually the right thing as this timestamp refers to the time
696	of the event triggering whatever timeout you are modifying/starting. If	1926	of the event triggering whatever timeout you are modifying/starting. If
697	you suspect event processing to be delayed and you I<need> to base the timeout	1927	you suspect event processing to be delayed and you I<need> to base the
698	on the current time, use something like this to adjust for this:	1928	timeout on the current time, use something like this to adjust for this:
699		1929
700	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1930	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
701		1931
702	The callback is guarenteed to be invoked only when its timeout has passed,	1932	If the event loop is suspended for a long time, you can also force an
703	but if multiple timers become ready during the same loop iteration then	1933	update of the time returned by C<ev_now ()> by calling C<ev_now_update
704	order of execution is undefined.	1934	()>.
		1935
		1936	=head3 The special problems of suspended animation
		1937
		1938	When you leave the server world it is quite customary to hit machines that
		1939	can suspend/hibernate - what happens to the clocks during such a suspend?
		1940
		1941	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1942	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1943	to run until the system is suspended, but they will not advance while the
		1944	system is suspended. That means, on resume, it will be as if the program
		1945	was frozen for a few seconds, but the suspend time will not be counted
		1946	towards C<ev_timer> when a monotonic clock source is used. The real time
		1947	clock advanced as expected, but if it is used as sole clocksource, then a
		1948	long suspend would be detected as a time jump by libev, and timers would
		1949	be adjusted accordingly.
		1950
		1951	I would not be surprised to see different behaviour in different between
		1952	operating systems, OS versions or even different hardware.
		1953
		1954	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1955	time jump in the monotonic clocks and the realtime clock. If the program
		1956	is suspended for a very long time, and monotonic clock sources are in use,
		1957	then you can expect C<ev_timer>s to expire as the full suspension time
		1958	will be counted towards the timers. When no monotonic clock source is in
		1959	use, then libev will again assume a timejump and adjust accordingly.
		1960
		1961	It might be beneficial for this latter case to call C<ev_suspend>
		1962	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1963	deterministic behaviour in this case (you can do nothing against
		1964	C<SIGSTOP>).
		1965
		1966	=head3 Watcher-Specific Functions and Data Members
705		1967
706	=over 4	1968	=over 4
707		1969
708	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1970	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
709		1971
710	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1972	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
711		1973
712	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1974	Configure the timer to trigger after C<after> seconds. If C<repeat>
713	C<0.>, then it will automatically be stopped. If it is positive, then the	1975	is C<0.>, then it will automatically be stopped once the timeout is
714	timer will automatically be configured to trigger again C<repeat> seconds	1976	reached. If it is positive, then the timer will automatically be
715	later, again, and again, until stopped manually.	1977	configured to trigger again C<repeat> seconds later, again, and again,
		1978	until stopped manually.
716		1979
717	The timer itself will do a best-effort at avoiding drift, that is, if you	1980	The timer itself will do a best-effort at avoiding drift, that is, if
718	configure a timer to trigger every 10 seconds, then it will trigger at	1981	you configure a timer to trigger every 10 seconds, then it will normally
719	exactly 10 second intervals. If, however, your program cannot keep up with	1982	trigger at exactly 10 second intervals. If, however, your program cannot
720	the timer (because it takes longer than those 10 seconds to do stuff) the	1983	keep up with the timer (because it takes longer than those 10 seconds to
721	timer will not fire more than once per event loop iteration.	1984	do stuff) the timer will not fire more than once per event loop iteration.
722		1985
723	=item ev_timer_again (loop)	1986	=item ev_timer_again (loop, ev_timer *)
724		1987
725	This will act as if the timer timed out and restart it again if it is	1988	This will act as if the timer timed out and restart it again if it is
726	repeating. The exact semantics are:	1989	repeating. The exact semantics are:
727		1990
		1991	If the timer is pending, its pending status is cleared.
		1992
728	If the timer is started but nonrepeating, stop it.	1993	If the timer is started but non-repeating, stop it (as if it timed out).
729		1994
730	If the timer is repeating, either start it if necessary (with the repeat	1995	If the timer is repeating, either start it if necessary (with the
731	value), or reset the running timer to the repeat value.	1996	C<repeat> value), or reset the running timer to the C<repeat> value.
732		1997
733	This sounds a bit complicated, but here is a useful and typical	1998	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
734	example: Imagine you have a tcp connection and you want a so-called idle	1999	usage example.
735	timeout, that is, you want to be called when there have been, say, 60	2000
736	seconds of inactivity on the socket. The easiest way to do this is to	2001	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
737	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	2002
738	time you successfully read or write some data. If you go into an idle	2003	Returns the remaining time until a timer fires. If the timer is active,
739	state where you do not expect data to travel on the socket, you can stop	2004	then this time is relative to the current event loop time, otherwise it's
740	the timer, and again will automatically restart it if need be.	2005	the timeout value currently configured.
		2006
		2007	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2008	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2009	will return C<4>. When the timer expires and is restarted, it will return
		2010	roughly C<7> (likely slightly less as callback invocation takes some time,
		2011	too), and so on.
		2012
		2013	=item ev_tstamp repeat [read-write]
		2014
		2015	The current C<repeat> value. Will be used each time the watcher times out
		2016	or C<ev_timer_again> is called, and determines the next timeout (if any),
		2017	which is also when any modifications are taken into account.
741		2018
742	=back	2019	=back
743		2020
		2021	=head3 Examples
		2022
744	Example: create a timer that fires after 60 seconds.	2023	Example: Create a timer that fires after 60 seconds.
745		2024
746	static void	2025	static void
747	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2026	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
748	{	2027	{
749	.. one minute over, w is actually stopped right here	2028	.. one minute over, w is actually stopped right here
750	}	2029	}
751		2030
752	struct ev_timer mytimer;	2031	ev_timer mytimer;
753	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2032	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
754	ev_timer_start (loop, &mytimer);	2033	ev_timer_start (loop, &mytimer);
755		2034
756	Example: create a timeout timer that times out after 10 seconds of	2035	Example: Create a timeout timer that times out after 10 seconds of
757	inactivity.	2036	inactivity.
758		2037
759	static void	2038	static void
760	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2039	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
761	{	2040	{
762	.. ten seconds without any activity	2041	.. ten seconds without any activity
763	}	2042	}
764		2043
765	struct ev_timer mytimer;	2044	ev_timer mytimer;
766	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2045	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
767	ev_timer_again (&mytimer); /* start timer */	2046	ev_timer_again (&mytimer); /* start timer */
768	ev_loop (loop, 0);	2047	ev_run (loop, 0);
769		2048
770	// and in some piece of code that gets executed on any "activity":	2049	// and in some piece of code that gets executed on any "activity":
771	// reset the timeout to start ticking again at 10 seconds	2050	// reset the timeout to start ticking again at 10 seconds
772	ev_timer_again (&mytimer);	2051	ev_timer_again (&mytimer);
773		2052
774		2053
775	=head2 C<ev_periodic> - to cron or not to cron	2054	=head2 C<ev_periodic> - to cron or not to cron?
776		2055
777	Periodic watchers are also timers of a kind, but they are very versatile	2056	Periodic watchers are also timers of a kind, but they are very versatile
778	(and unfortunately a bit complex).	2057	(and unfortunately a bit complex).
779		2058
780	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2059	Unlike C<ev_timer>, periodic watchers are not based on real time (or
781	but on wallclock time (absolute time). You can tell a periodic watcher	2060	relative time, the physical time that passes) but on wall clock time
782	to trigger "at" some specific point in time. For example, if you tell a	2061	(absolute time, the thing you can read on your calender or clock). The
783	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	2062	difference is that wall clock time can run faster or slower than real
784	+ 10.>) and then reset your system clock to the last year, then it will	2063	time, and time jumps are not uncommon (e.g. when you adjust your
785	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2064	wrist-watch).
786	roughly 10 seconds later and of course not if you reset your system time
787	again).
788		2065
789	They can also be used to implement vastly more complex timers, such as	2066	You can tell a periodic watcher to trigger after some specific point
		2067	in time: for example, if you tell a periodic watcher to trigger "in 10
		2068	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2069	not a delay) and then reset your system clock to January of the previous
		2070	year, then it will take a year or more to trigger the event (unlike an
		2071	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2072	it, as it uses a relative timeout).
		2073
		2074	C<ev_periodic> watchers can also be used to implement vastly more complex
790	triggering an event on eahc midnight, local time.	2075	timers, such as triggering an event on each "midnight, local time", or
		2076	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2077	those cannot react to time jumps.
791		2078
792	As with timers, the callback is guarenteed to be invoked only when the	2079	As with timers, the callback is guaranteed to be invoked only when the
793	time (C<at>) has been passed, but if multiple periodic timers become ready	2080	point in time where it is supposed to trigger has passed. If multiple
794	during the same loop iteration then order of execution is undefined.	2081	timers become ready during the same loop iteration then the ones with
		2082	earlier time-out values are invoked before ones with later time-out values
		2083	(but this is no longer true when a callback calls C<ev_run> recursively).
		2084
		2085	=head3 Watcher-Specific Functions and Data Members
795		2086
796	=over 4	2087	=over 4
797		2088
798	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2089	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
799		2090
800	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2091	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
801		2092
802	Lots of arguments, lets sort it out... There are basically three modes of	2093	Lots of arguments, let's sort it out... There are basically three modes of
803	operation, and we will explain them from simplest to complex:	2094	operation, and we will explain them from simplest to most complex:
804		2095
805	=over 4	2096	=over 4
806		2097
807	=item * absolute timer (interval = reschedule_cb = 0)	2098	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
808		2099
809	In this configuration the watcher triggers an event at the wallclock time	2100	In this configuration the watcher triggers an event after the wall clock
810	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2101	time C<offset> has passed. It will not repeat and will not adjust when a
811	that is, if it is to be run at January 1st 2011 then it will run when the	2102	time jump occurs, that is, if it is to be run at January 1st 2011 then it
812	system time reaches or surpasses this time.	2103	will be stopped and invoked when the system clock reaches or surpasses
		2104	this point in time.
813		2105
814	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2106	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
815		2107
816	In this mode the watcher will always be scheduled to time out at the next	2108	In this mode the watcher will always be scheduled to time out at the next
817	C<at + N * interval> time (for some integer N) and then repeat, regardless	2109	C<offset + N * interval> time (for some integer N, which can also be
818	of any time jumps.	2110	negative) and then repeat, regardless of any time jumps. The C<offset>
		2111	argument is merely an offset into the C<interval> periods.
819		2112
820	This can be used to create timers that do not drift with respect to system	2113	This can be used to create timers that do not drift with respect to the
821	time:	2114	system clock, for example, here is an C<ev_periodic> that triggers each
		2115	hour, on the hour (with respect to UTC):
822		2116
823	ev_periodic_set (&periodic, 0., 3600., 0);	2117	ev_periodic_set (&periodic, 0., 3600., 0);
824		2118
825	This doesn't mean there will always be 3600 seconds in between triggers,	2119	This doesn't mean there will always be 3600 seconds in between triggers,
826	but only that the the callback will be called when the system time shows a	2120	but only that the callback will be called when the system time shows a
827	full hour (UTC), or more correctly, when the system time is evenly divisible	2121	full hour (UTC), or more correctly, when the system time is evenly divisible
828	by 3600.	2122	by 3600.
829		2123
830	Another way to think about it (for the mathematically inclined) is that	2124	Another way to think about it (for the mathematically inclined) is that
831	C<ev_periodic> will try to run the callback in this mode at the next possible	2125	C<ev_periodic> will try to run the callback in this mode at the next possible
832	time where C<time = at (mod interval)>, regardless of any time jumps.	2126	time where C<time = offset (mod interval)>, regardless of any time jumps.
833		2127
		2128	For numerical stability it is preferable that the C<offset> value is near
		2129	C<ev_now ()> (the current time), but there is no range requirement for
		2130	this value, and in fact is often specified as zero.
		2131
		2132	Note also that there is an upper limit to how often a timer can fire (CPU
		2133	speed for example), so if C<interval> is very small then timing stability
		2134	will of course deteriorate. Libev itself tries to be exact to be about one
		2135	millisecond (if the OS supports it and the machine is fast enough).
		2136
834	=item * manual reschedule mode (reschedule_cb = callback)	2137	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
835		2138
836	In this mode the values for C<interval> and C<at> are both being	2139	In this mode the values for C<interval> and C<offset> are both being
837	ignored. Instead, each time the periodic watcher gets scheduled, the	2140	ignored. Instead, each time the periodic watcher gets scheduled, the
838	reschedule callback will be called with the watcher as first, and the	2141	reschedule callback will be called with the watcher as first, and the
839	current time as second argument.	2142	current time as second argument.
840		2143
841	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2144	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
842	ever, or make any event loop modifications>. If you need to stop it,	2145	or make ANY other event loop modifications whatsoever, unless explicitly
843	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2146	allowed by documentation here>.
844	starting a prepare watcher).
845		2147
		2148	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2149	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2150	only event loop modification you are allowed to do).
		2151
846	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2152	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
847	ev_tstamp now)>, e.g.:	2153	*w, ev_tstamp now)>, e.g.:
848		2154
		2155	static ev_tstamp
849	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2156	my_rescheduler (ev_periodic *w, ev_tstamp now)
850	{	2157	{
851	return now + 60.;	2158	return now + 60.;
852	}	2159	}
853		2160
854	It must return the next time to trigger, based on the passed time value	2161	It must return the next time to trigger, based on the passed time value
855	(that is, the lowest time value larger than to the second argument). It	2162	(that is, the lowest time value larger than to the second argument). It
856	will usually be called just before the callback will be triggered, but	2163	will usually be called just before the callback will be triggered, but
857	might be called at other times, too.	2164	might be called at other times, too.
858		2165
859	NOTE: I<< This callback must always return a time that is later than the	2166	NOTE: I<< This callback must always return a time that is higher than or
860	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2167	equal to the passed C<now> value >>.
861		2168
862	This can be used to create very complex timers, such as a timer that	2169	This can be used to create very complex timers, such as a timer that
863	triggers on each midnight, local time. To do this, you would calculate the	2170	triggers on "next midnight, local time". To do this, you would calculate the
864	next midnight after C<now> and return the timestamp value for this. How	2171	next midnight after C<now> and return the timestamp value for this. How
865	you do this is, again, up to you (but it is not trivial, which is the main	2172	you do this is, again, up to you (but it is not trivial, which is the main
866	reason I omitted it as an example).	2173	reason I omitted it as an example).
867		2174
868	=back	2175	=back
…		…
872	Simply stops and restarts the periodic watcher again. This is only useful	2179	Simply stops and restarts the periodic watcher again. This is only useful
873	when you changed some parameters or the reschedule callback would return	2180	when you changed some parameters or the reschedule callback would return
874	a different time than the last time it was called (e.g. in a crond like	2181	a different time than the last time it was called (e.g. in a crond like
875	program when the crontabs have changed).	2182	program when the crontabs have changed).
876		2183
		2184	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2185
		2186	When active, returns the absolute time that the watcher is supposed
		2187	to trigger next. This is not the same as the C<offset> argument to
		2188	C<ev_periodic_set>, but indeed works even in interval and manual
		2189	rescheduling modes.
		2190
		2191	=item ev_tstamp offset [read-write]
		2192
		2193	When repeating, this contains the offset value, otherwise this is the
		2194	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2195	although libev might modify this value for better numerical stability).
		2196
		2197	Can be modified any time, but changes only take effect when the periodic
		2198	timer fires or C<ev_periodic_again> is being called.
		2199
		2200	=item ev_tstamp interval [read-write]
		2201
		2202	The current interval value. Can be modified any time, but changes only
		2203	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2204	called.
		2205
		2206	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2207
		2208	The current reschedule callback, or C<0>, if this functionality is
		2209	switched off. Can be changed any time, but changes only take effect when
		2210	the periodic timer fires or C<ev_periodic_again> is being called.
		2211
877	=back	2212	=back
878		2213
		2214	=head3 Examples
		2215
879	Example: call a callback every hour, or, more precisely, whenever the	2216	Example: Call a callback every hour, or, more precisely, whenever the
880	system clock is divisible by 3600. The callback invocation times have	2217	system time is divisible by 3600. The callback invocation times have
881	potentially a lot of jittering, but good long-term stability.	2218	potentially a lot of jitter, but good long-term stability.
882		2219
883	static void	2220	static void
884	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2221	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
885	{	2222	{
886	... its now a full hour (UTC, or TAI or whatever your clock follows)	2223	... its now a full hour (UTC, or TAI or whatever your clock follows)
887	}	2224	}
888		2225
889	struct ev_periodic hourly_tick;	2226	ev_periodic hourly_tick;
890	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2227	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
891	ev_periodic_start (loop, &hourly_tick);	2228	ev_periodic_start (loop, &hourly_tick);
892		2229
893	Example: the same as above, but use a reschedule callback to do it:	2230	Example: The same as above, but use a reschedule callback to do it:
894		2231
895	#include <math.h>	2232	#include <math.h>
896		2233
897	static ev_tstamp	2234	static ev_tstamp
898	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2235	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
899	{	2236	{
900	return fmod (now, 3600.) + 3600.;	2237	return now + (3600. - fmod (now, 3600.));
901	}	2238	}
902		2239
903	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2240	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
904		2241
905	Example: call a callback every hour, starting now:	2242	Example: Call a callback every hour, starting now:
906		2243
907	struct ev_periodic hourly_tick;	2244	ev_periodic hourly_tick;
908	ev_periodic_init (&hourly_tick, clock_cb,	2245	ev_periodic_init (&hourly_tick, clock_cb,
909	fmod (ev_now (loop), 3600.), 3600., 0);	2246	fmod (ev_now (loop), 3600.), 3600., 0);
910	ev_periodic_start (loop, &hourly_tick);	2247	ev_periodic_start (loop, &hourly_tick);
911		2248
912		2249
913	=head2 C<ev_signal> - signal me when a signal gets signalled	2250	=head2 C<ev_signal> - signal me when a signal gets signalled!
914		2251
915	Signal watchers will trigger an event when the process receives a specific	2252	Signal watchers will trigger an event when the process receives a specific
916	signal one or more times. Even though signals are very asynchronous, libev	2253	signal one or more times. Even though signals are very asynchronous, libev
917	will try it's best to deliver signals synchronously, i.e. as part of the	2254	will try it's best to deliver signals synchronously, i.e. as part of the
918	normal event processing, like any other event.	2255	normal event processing, like any other event.
919		2256
		2257	If you want signals to be delivered truly asynchronously, just use
		2258	C<sigaction> as you would do without libev and forget about sharing
		2259	the signal. You can even use C<ev_async> from a signal handler to
		2260	synchronously wake up an event loop.
		2261
920	You can configure as many watchers as you like per signal. Only when the	2262	You can configure as many watchers as you like for the same signal, but
		2263	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2264	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2265	C<SIGINT> in both the default loop and another loop at the same time. At
		2266	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2267
921	first watcher gets started will libev actually register a signal watcher	2268	When the first watcher gets started will libev actually register something
922	with the kernel (thus it coexists with your own signal handlers as long	2269	with the kernel (thus it coexists with your own signal handlers as long as
923	as you don't register any with libev). Similarly, when the last signal	2270	you don't register any with libev for the same signal).
924	watcher for a signal is stopped libev will reset the signal handler to	2271
925	SIG_DFL (regardless of what it was set to before).	2272	If possible and supported, libev will install its handlers with
		2273	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2274	not be unduly interrupted. If you have a problem with system calls getting
		2275	interrupted by signals you can block all signals in an C<ev_check> watcher
		2276	and unblock them in an C<ev_prepare> watcher.
		2277
		2278	=head3 The special problem of inheritance over fork/execve/pthread_create
		2279
		2280	Both the signal mask (C<sigprocmask>) and the signal disposition
		2281	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2282	stopping it again), that is, libev might or might not block the signal,
		2283	and might or might not set or restore the installed signal handler.
		2284
		2285	While this does not matter for the signal disposition (libev never
		2286	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2287	C<execve>), this matters for the signal mask: many programs do not expect
		2288	certain signals to be blocked.
		2289
		2290	This means that before calling C<exec> (from the child) you should reset
		2291	the signal mask to whatever "default" you expect (all clear is a good
		2292	choice usually).
		2293
		2294	The simplest way to ensure that the signal mask is reset in the child is
		2295	to install a fork handler with C<pthread_atfork> that resets it. That will
		2296	catch fork calls done by libraries (such as the libc) as well.
		2297
		2298	In current versions of libev, the signal will not be blocked indefinitely
		2299	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2300	the window of opportunity for problems, it will not go away, as libev
		2301	I<has> to modify the signal mask, at least temporarily.
		2302
		2303	So I can't stress this enough: I<If you do not reset your signal mask when
		2304	you expect it to be empty, you have a race condition in your code>. This
		2305	is not a libev-specific thing, this is true for most event libraries.
		2306
		2307	=head3 Watcher-Specific Functions and Data Members
926		2308
927	=over 4	2309	=over 4
928		2310
929	=item ev_signal_init (ev_signal *, callback, int signum)	2311	=item ev_signal_init (ev_signal *, callback, int signum)
930		2312
931	=item ev_signal_set (ev_signal *, int signum)	2313	=item ev_signal_set (ev_signal *, int signum)
932		2314
933	Configures the watcher to trigger on the given signal number (usually one	2315	Configures the watcher to trigger on the given signal number (usually one
934	of the C<SIGxxx> constants).	2316	of the C<SIGxxx> constants).
935		2317
		2318	=item int signum [read-only]
		2319
		2320	The signal the watcher watches out for.
		2321
936	=back	2322	=back
937		2323
		2324	=head3 Examples
938		2325
		2326	Example: Try to exit cleanly on SIGINT.
		2327
		2328	static void
		2329	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2330	{
		2331	ev_break (loop, EVBREAK_ALL);
		2332	}
		2333
		2334	ev_signal signal_watcher;
		2335	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2336	ev_signal_start (loop, &signal_watcher);
		2337
		2338
939	=head2 C<ev_child> - wait for pid status changes	2339	=head2 C<ev_child> - watch out for process status changes
940		2340
941	Child watchers trigger when your process receives a SIGCHLD in response to	2341	Child watchers trigger when your process receives a SIGCHLD in response to
942	some child status changes (most typically when a child of yours dies).	2342	some child status changes (most typically when a child of yours dies or
		2343	exits). It is permissible to install a child watcher I<after> the child
		2344	has been forked (which implies it might have already exited), as long
		2345	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2346	forking and then immediately registering a watcher for the child is fine,
		2347	but forking and registering a watcher a few event loop iterations later or
		2348	in the next callback invocation is not.
		2349
		2350	Only the default event loop is capable of handling signals, and therefore
		2351	you can only register child watchers in the default event loop.
		2352
		2353	Due to some design glitches inside libev, child watchers will always be
		2354	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2355	libev)
		2356
		2357	=head3 Process Interaction
		2358
		2359	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2360	initialised. This is necessary to guarantee proper behaviour even if the
		2361	first child watcher is started after the child exits. The occurrence
		2362	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2363	synchronously as part of the event loop processing. Libev always reaps all
		2364	children, even ones not watched.
		2365
		2366	=head3 Overriding the Built-In Processing
		2367
		2368	Libev offers no special support for overriding the built-in child
		2369	processing, but if your application collides with libev's default child
		2370	handler, you can override it easily by installing your own handler for
		2371	C<SIGCHLD> after initialising the default loop, and making sure the
		2372	default loop never gets destroyed. You are encouraged, however, to use an
		2373	event-based approach to child reaping and thus use libev's support for
		2374	that, so other libev users can use C<ev_child> watchers freely.
		2375
		2376	=head3 Stopping the Child Watcher
		2377
		2378	Currently, the child watcher never gets stopped, even when the
		2379	child terminates, so normally one needs to stop the watcher in the
		2380	callback. Future versions of libev might stop the watcher automatically
		2381	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2382	problem).
		2383
		2384	=head3 Watcher-Specific Functions and Data Members
943		2385
944	=over 4	2386	=over 4
945		2387
946	=item ev_child_init (ev_child *, callback, int pid)	2388	=item ev_child_init (ev_child *, callback, int pid, int trace)
947		2389
948	=item ev_child_set (ev_child *, int pid)	2390	=item ev_child_set (ev_child *, int pid, int trace)
949		2391
950	Configures the watcher to wait for status changes of process C<pid> (or	2392	Configures the watcher to wait for status changes of process C<pid> (or
951	I<any> process if C<pid> is specified as C<0>). The callback can look	2393	I<any> process if C<pid> is specified as C<0>). The callback can look
952	at the C<rstatus> member of the C<ev_child> watcher structure to see	2394	at the C<rstatus> member of the C<ev_child> watcher structure to see
953	the status word (use the macros from C<sys/wait.h> and see your systems	2395	the status word (use the macros from C<sys/wait.h> and see your systems
954	C<waitpid> documentation). The C<rpid> member contains the pid of the	2396	C<waitpid> documentation). The C<rpid> member contains the pid of the
955	process causing the status change.	2397	process causing the status change. C<trace> must be either C<0> (only
		2398	activate the watcher when the process terminates) or C<1> (additionally
		2399	activate the watcher when the process is stopped or continued).
		2400
		2401	=item int pid [read-only]
		2402
		2403	The process id this watcher watches out for, or C<0>, meaning any process id.
		2404
		2405	=item int rpid [read-write]
		2406
		2407	The process id that detected a status change.
		2408
		2409	=item int rstatus [read-write]
		2410
		2411	The process exit/trace status caused by C<rpid> (see your systems
		2412	C<waitpid> and C<sys/wait.h> documentation for details).
956		2413
957	=back	2414	=back
958		2415
959	Example: try to exit cleanly on SIGINT and SIGTERM.	2416	=head3 Examples
960		2417
		2418	Example: C<fork()> a new process and install a child handler to wait for
		2419	its completion.
		2420
		2421	ev_child cw;
		2422
961	static void	2423	static void
962	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2424	child_cb (EV_P_ ev_child *w, int revents)
963	{	2425	{
964	ev_unloop (loop, EVUNLOOP_ALL);	2426	ev_child_stop (EV_A_ w);
		2427	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
965	}	2428	}
966		2429
967	struct ev_signal signal_watcher;	2430	pid_t pid = fork ();
968	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
969	ev_signal_start (loop, &sigint_cb);
970		2431
		2432	if (pid < 0)
		2433	// error
		2434	else if (pid == 0)
		2435	{
		2436	// the forked child executes here
		2437	exit (1);
		2438	}
		2439	else
		2440	{
		2441	ev_child_init (&cw, child_cb, pid, 0);
		2442	ev_child_start (EV_DEFAULT_ &cw);
		2443	}
971		2444
		2445
		2446	=head2 C<ev_stat> - did the file attributes just change?
		2447
		2448	This watches a file system path for attribute changes. That is, it calls
		2449	C<stat> on that path in regular intervals (or when the OS says it changed)
		2450	and sees if it changed compared to the last time, invoking the callback if
		2451	it did.
		2452
		2453	The path does not need to exist: changing from "path exists" to "path does
		2454	not exist" is a status change like any other. The condition "path does not
		2455	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2456	C<st_nlink> field being zero (which is otherwise always forced to be at
		2457	least one) and all the other fields of the stat buffer having unspecified
		2458	contents.
		2459
		2460	The path I<must not> end in a slash or contain special components such as
		2461	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2462	your working directory changes, then the behaviour is undefined.
		2463
		2464	Since there is no portable change notification interface available, the
		2465	portable implementation simply calls C<stat(2)> regularly on the path
		2466	to see if it changed somehow. You can specify a recommended polling
		2467	interval for this case. If you specify a polling interval of C<0> (highly
		2468	recommended!) then a I<suitable, unspecified default> value will be used
		2469	(which you can expect to be around five seconds, although this might
		2470	change dynamically). Libev will also impose a minimum interval which is
		2471	currently around C<0.1>, but that's usually overkill.
		2472
		2473	This watcher type is not meant for massive numbers of stat watchers,
		2474	as even with OS-supported change notifications, this can be
		2475	resource-intensive.
		2476
		2477	At the time of this writing, the only OS-specific interface implemented
		2478	is the Linux inotify interface (implementing kqueue support is left as an
		2479	exercise for the reader. Note, however, that the author sees no way of
		2480	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2481
		2482	=head3 ABI Issues (Largefile Support)
		2483
		2484	Libev by default (unless the user overrides this) uses the default
		2485	compilation environment, which means that on systems with large file
		2486	support disabled by default, you get the 32 bit version of the stat
		2487	structure. When using the library from programs that change the ABI to
		2488	use 64 bit file offsets the programs will fail. In that case you have to
		2489	compile libev with the same flags to get binary compatibility. This is
		2490	obviously the case with any flags that change the ABI, but the problem is
		2491	most noticeably displayed with ev_stat and large file support.
		2492
		2493	The solution for this is to lobby your distribution maker to make large
		2494	file interfaces available by default (as e.g. FreeBSD does) and not
		2495	optional. Libev cannot simply switch on large file support because it has
		2496	to exchange stat structures with application programs compiled using the
		2497	default compilation environment.
		2498
		2499	=head3 Inotify and Kqueue
		2500
		2501	When C<inotify (7)> support has been compiled into libev and present at
		2502	runtime, it will be used to speed up change detection where possible. The
		2503	inotify descriptor will be created lazily when the first C<ev_stat>
		2504	watcher is being started.
		2505
		2506	Inotify presence does not change the semantics of C<ev_stat> watchers
		2507	except that changes might be detected earlier, and in some cases, to avoid
		2508	making regular C<stat> calls. Even in the presence of inotify support
		2509	there are many cases where libev has to resort to regular C<stat> polling,
		2510	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2511	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2512	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2513	xfs are fully working) libev usually gets away without polling.
		2514
		2515	There is no support for kqueue, as apparently it cannot be used to
		2516	implement this functionality, due to the requirement of having a file
		2517	descriptor open on the object at all times, and detecting renames, unlinks
		2518	etc. is difficult.
		2519
		2520	=head3 C<stat ()> is a synchronous operation
		2521
		2522	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2523	the process. The exception are C<ev_stat> watchers - those call C<stat
		2524	()>, which is a synchronous operation.
		2525
		2526	For local paths, this usually doesn't matter: unless the system is very
		2527	busy or the intervals between stat's are large, a stat call will be fast,
		2528	as the path data is usually in memory already (except when starting the
		2529	watcher).
		2530
		2531	For networked file systems, calling C<stat ()> can block an indefinite
		2532	time due to network issues, and even under good conditions, a stat call
		2533	often takes multiple milliseconds.
		2534
		2535	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2536	paths, although this is fully supported by libev.
		2537
		2538	=head3 The special problem of stat time resolution
		2539
		2540	The C<stat ()> system call only supports full-second resolution portably,
		2541	and even on systems where the resolution is higher, most file systems
		2542	still only support whole seconds.
		2543
		2544	That means that, if the time is the only thing that changes, you can
		2545	easily miss updates: on the first update, C<ev_stat> detects a change and
		2546	calls your callback, which does something. When there is another update
		2547	within the same second, C<ev_stat> will be unable to detect unless the
		2548	stat data does change in other ways (e.g. file size).
		2549
		2550	The solution to this is to delay acting on a change for slightly more
		2551	than a second (or till slightly after the next full second boundary), using
		2552	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2553	ev_timer_again (loop, w)>).
		2554
		2555	The C<.02> offset is added to work around small timing inconsistencies
		2556	of some operating systems (where the second counter of the current time
		2557	might be be delayed. One such system is the Linux kernel, where a call to
		2558	C<gettimeofday> might return a timestamp with a full second later than
		2559	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2560	update file times then there will be a small window where the kernel uses
		2561	the previous second to update file times but libev might already execute
		2562	the timer callback).
		2563
		2564	=head3 Watcher-Specific Functions and Data Members
		2565
		2566	=over 4
		2567
		2568	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2569
		2570	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2571
		2572	Configures the watcher to wait for status changes of the given
		2573	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2574	be detected and should normally be specified as C<0> to let libev choose
		2575	a suitable value. The memory pointed to by C<path> must point to the same
		2576	path for as long as the watcher is active.
		2577
		2578	The callback will receive an C<EV_STAT> event when a change was detected,
		2579	relative to the attributes at the time the watcher was started (or the
		2580	last change was detected).
		2581
		2582	=item ev_stat_stat (loop, ev_stat *)
		2583
		2584	Updates the stat buffer immediately with new values. If you change the
		2585	watched path in your callback, you could call this function to avoid
		2586	detecting this change (while introducing a race condition if you are not
		2587	the only one changing the path). Can also be useful simply to find out the
		2588	new values.
		2589
		2590	=item ev_statdata attr [read-only]
		2591
		2592	The most-recently detected attributes of the file. Although the type is
		2593	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2594	suitable for your system, but you can only rely on the POSIX-standardised
		2595	members to be present. If the C<st_nlink> member is C<0>, then there was
		2596	some error while C<stat>ing the file.
		2597
		2598	=item ev_statdata prev [read-only]
		2599
		2600	The previous attributes of the file. The callback gets invoked whenever
		2601	C<prev> != C<attr>, or, more precisely, one or more of these members
		2602	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2603	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2604
		2605	=item ev_tstamp interval [read-only]
		2606
		2607	The specified interval.
		2608
		2609	=item const char *path [read-only]
		2610
		2611	The file system path that is being watched.
		2612
		2613	=back
		2614
		2615	=head3 Examples
		2616
		2617	Example: Watch C</etc/passwd> for attribute changes.
		2618
		2619	static void
		2620	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2621	{
		2622	/* /etc/passwd changed in some way */
		2623	if (w->attr.st_nlink)
		2624	{
		2625	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2626	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2627	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2628	}
		2629	else
		2630	/* you shalt not abuse printf for puts */
		2631	puts ("wow, /etc/passwd is not there, expect problems. "
		2632	"if this is windows, they already arrived\n");
		2633	}
		2634
		2635	...
		2636	ev_stat passwd;
		2637
		2638	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2639	ev_stat_start (loop, &passwd);
		2640
		2641	Example: Like above, but additionally use a one-second delay so we do not
		2642	miss updates (however, frequent updates will delay processing, too, so
		2643	one might do the work both on C<ev_stat> callback invocation I<and> on
		2644	C<ev_timer> callback invocation).
		2645
		2646	static ev_stat passwd;
		2647	static ev_timer timer;
		2648
		2649	static void
		2650	timer_cb (EV_P_ ev_timer *w, int revents)
		2651	{
		2652	ev_timer_stop (EV_A_ w);
		2653
		2654	/* now it's one second after the most recent passwd change */
		2655	}
		2656
		2657	static void
		2658	stat_cb (EV_P_ ev_stat *w, int revents)
		2659	{
		2660	/* reset the one-second timer */
		2661	ev_timer_again (EV_A_ &timer);
		2662	}
		2663
		2664	...
		2665	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2666	ev_stat_start (loop, &passwd);
		2667	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2668
		2669
972	=head2 C<ev_idle> - when you've got nothing better to do	2670	=head2 C<ev_idle> - when you've got nothing better to do...
973		2671
974	Idle watchers trigger events when there are no other events are pending	2672	Idle watchers trigger events when no other events of the same or higher
975	(prepare, check and other idle watchers do not count). That is, as long	2673	priority are pending (prepare, check and other idle watchers do not count
976	as your process is busy handling sockets or timeouts (or even signals,	2674	as receiving "events").
977	imagine) it will not be triggered. But when your process is idle all idle	2675
978	watchers are being called again and again, once per event loop iteration -	2676	That is, as long as your process is busy handling sockets or timeouts
		2677	(or even signals, imagine) of the same or higher priority it will not be
		2678	triggered. But when your process is idle (or only lower-priority watchers
		2679	are pending), the idle watchers are being called once per event loop
979	until stopped, that is, or your process receives more events and becomes	2680	iteration - until stopped, that is, or your process receives more events
980	busy.	2681	and becomes busy again with higher priority stuff.
981		2682
982	The most noteworthy effect is that as long as any idle watchers are	2683	The most noteworthy effect is that as long as any idle watchers are
983	active, the process will not block when waiting for new events.	2684	active, the process will not block when waiting for new events.
984		2685
985	Apart from keeping your process non-blocking (which is a useful	2686	Apart from keeping your process non-blocking (which is a useful
986	effect on its own sometimes), idle watchers are a good place to do	2687	effect on its own sometimes), idle watchers are a good place to do
987	"pseudo-background processing", or delay processing stuff to after the	2688	"pseudo-background processing", or delay processing stuff to after the
988	event loop has handled all outstanding events.	2689	event loop has handled all outstanding events.
989		2690
		2691	=head3 Watcher-Specific Functions and Data Members
		2692
990	=over 4	2693	=over 4
991		2694
992	=item ev_idle_init (ev_signal *, callback)	2695	=item ev_idle_init (ev_idle *, callback)
993		2696
994	Initialises and configures the idle watcher - it has no parameters of any	2697	Initialises and configures the idle watcher - it has no parameters of any
995	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2698	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
996	believe me.	2699	believe me.
997		2700
998	=back	2701	=back
999		2702
		2703	=head3 Examples
		2704
1000	Example: dynamically allocate an C<ev_idle>, start it, and in the	2705	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1001	callback, free it. Alos, use no error checking, as usual.	2706	callback, free it. Also, use no error checking, as usual.
1002		2707
1003	static void	2708	static void
1004	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2709	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1005	{	2710	{
1006	free (w);	2711	free (w);
1007	// now do something you wanted to do when the program has	2712	// now do something you wanted to do when the program has
1008	// no longer asnything immediate to do.	2713	// no longer anything immediate to do.
1009	}	2714	}
1010		2715
1011	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2716	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1012	ev_idle_init (idle_watcher, idle_cb);	2717	ev_idle_init (idle_watcher, idle_cb);
1013	ev_idle_start (loop, idle_cb);	2718	ev_idle_start (loop, idle_watcher);
1014		2719
1015		2720
1016	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2721	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1017		2722
1018	Prepare and check watchers are usually (but not always) used in tandem:	2723	Prepare and check watchers are usually (but not always) used in pairs:
1019	prepare watchers get invoked before the process blocks and check watchers	2724	prepare watchers get invoked before the process blocks and check watchers
1020	afterwards.	2725	afterwards.
1021		2726
		2727	You I<must not> call C<ev_run> or similar functions that enter
		2728	the current event loop from either C<ev_prepare> or C<ev_check>
		2729	watchers. Other loops than the current one are fine, however. The
		2730	rationale behind this is that you do not need to check for recursion in
		2731	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2732	C<ev_check> so if you have one watcher of each kind they will always be
		2733	called in pairs bracketing the blocking call.
		2734
1022	Their main purpose is to integrate other event mechanisms into libev and	2735	Their main purpose is to integrate other event mechanisms into libev and
1023	their use is somewhat advanced. This could be used, for example, to track	2736	their use is somewhat advanced. They could be used, for example, to track
1024	variable changes, implement your own watchers, integrate net-snmp or a	2737	variable changes, implement your own watchers, integrate net-snmp or a
1025	coroutine library and lots more.	2738	coroutine library and lots more. They are also occasionally useful if
		2739	you cache some data and want to flush it before blocking (for example,
		2740	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2741	watcher).
1026		2742
1027	This is done by examining in each prepare call which file descriptors need	2743	This is done by examining in each prepare call which file descriptors
1028	to be watched by the other library, registering C<ev_io> watchers for	2744	need to be watched by the other library, registering C<ev_io> watchers
1029	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2745	for them and starting an C<ev_timer> watcher for any timeouts (many
1030	provide just this functionality). Then, in the check watcher you check for	2746	libraries provide exactly this functionality). Then, in the check watcher,
1031	any events that occured (by checking the pending status of all watchers	2747	you check for any events that occurred (by checking the pending status
1032	and stopping them) and call back into the library. The I/O and timer	2748	of all watchers and stopping them) and call back into the library. The
1033	callbacks will never actually be called (but must be valid nevertheless,	2749	I/O and timer callbacks will never actually be called (but must be valid
1034	because you never know, you know?).	2750	nevertheless, because you never know, you know?).
1035		2751
1036	As another example, the Perl Coro module uses these hooks to integrate	2752	As another example, the Perl Coro module uses these hooks to integrate
1037	coroutines into libev programs, by yielding to other active coroutines	2753	coroutines into libev programs, by yielding to other active coroutines
1038	during each prepare and only letting the process block if no coroutines	2754	during each prepare and only letting the process block if no coroutines
1039	are ready to run (it's actually more complicated: it only runs coroutines	2755	are ready to run (it's actually more complicated: it only runs coroutines
1040	with priority higher than or equal to the event loop and one coroutine	2756	with priority higher than or equal to the event loop and one coroutine
1041	of lower priority, but only once, using idle watchers to keep the event	2757	of lower priority, but only once, using idle watchers to keep the event
1042	loop from blocking if lower-priority coroutines are active, thus mapping	2758	loop from blocking if lower-priority coroutines are active, thus mapping
1043	low-priority coroutines to idle/background tasks).	2759	low-priority coroutines to idle/background tasks).
1044		2760
		2761	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2762	priority, to ensure that they are being run before any other watchers
		2763	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2764
		2765	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2766	activate ("feed") events into libev. While libev fully supports this, they
		2767	might get executed before other C<ev_check> watchers did their job. As
		2768	C<ev_check> watchers are often used to embed other (non-libev) event
		2769	loops those other event loops might be in an unusable state until their
		2770	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2771	others).
		2772
		2773	=head3 Watcher-Specific Functions and Data Members
		2774
1045	=over 4	2775	=over 4
1046		2776
1047	=item ev_prepare_init (ev_prepare *, callback)	2777	=item ev_prepare_init (ev_prepare *, callback)
1048		2778
1049	=item ev_check_init (ev_check *, callback)	2779	=item ev_check_init (ev_check *, callback)
1050		2780
1051	Initialises and configures the prepare or check watcher - they have no	2781	Initialises and configures the prepare or check watcher - they have no
1052	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2782	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1053	macros, but using them is utterly, utterly and completely pointless.	2783	macros, but using them is utterly, utterly, utterly and completely
		2784	pointless.
1054		2785
1055	=back	2786	=back
1056		2787
1057	Example: *TODO*.	2788	=head3 Examples
1058		2789
		2790	There are a number of principal ways to embed other event loops or modules
		2791	into libev. Here are some ideas on how to include libadns into libev
		2792	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2793	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2794	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2795	Glib event loop).
1059		2796
		2797	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2798	and in a check watcher, destroy them and call into libadns. What follows
		2799	is pseudo-code only of course. This requires you to either use a low
		2800	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2801	the callbacks for the IO/timeout watchers might not have been called yet.
		2802
		2803	static ev_io iow [nfd];
		2804	static ev_timer tw;
		2805
		2806	static void
		2807	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2808	{
		2809	}
		2810
		2811	// create io watchers for each fd and a timer before blocking
		2812	static void
		2813	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2814	{
		2815	int timeout = 3600000;
		2816	struct pollfd fds [nfd];
		2817	// actual code will need to loop here and realloc etc.
		2818	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2819
		2820	/* the callback is illegal, but won't be called as we stop during check */
		2821	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		2822	ev_timer_start (loop, &tw);
		2823
		2824	// create one ev_io per pollfd
		2825	for (int i = 0; i < nfd; ++i)
		2826	{
		2827	ev_io_init (iow + i, io_cb, fds [i].fd,
		2828	((fds [i].events & POLLIN ? EV_READ : 0)
		2829	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2830
		2831	fds [i].revents = 0;
		2832	ev_io_start (loop, iow + i);
		2833	}
		2834	}
		2835
		2836	// stop all watchers after blocking
		2837	static void
		2838	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2839	{
		2840	ev_timer_stop (loop, &tw);
		2841
		2842	for (int i = 0; i < nfd; ++i)
		2843	{
		2844	// set the relevant poll flags
		2845	// could also call adns_processreadable etc. here
		2846	struct pollfd *fd = fds + i;
		2847	int revents = ev_clear_pending (iow + i);
		2848	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2849	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2850
		2851	// now stop the watcher
		2852	ev_io_stop (loop, iow + i);
		2853	}
		2854
		2855	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2856	}
		2857
		2858	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2859	in the prepare watcher and would dispose of the check watcher.
		2860
		2861	Method 3: If the module to be embedded supports explicit event
		2862	notification (libadns does), you can also make use of the actual watcher
		2863	callbacks, and only destroy/create the watchers in the prepare watcher.
		2864
		2865	static void
		2866	timer_cb (EV_P_ ev_timer *w, int revents)
		2867	{
		2868	adns_state ads = (adns_state)w->data;
		2869	update_now (EV_A);
		2870
		2871	adns_processtimeouts (ads, &tv_now);
		2872	}
		2873
		2874	static void
		2875	io_cb (EV_P_ ev_io *w, int revents)
		2876	{
		2877	adns_state ads = (adns_state)w->data;
		2878	update_now (EV_A);
		2879
		2880	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2881	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2882	}
		2883
		2884	// do not ever call adns_afterpoll
		2885
		2886	Method 4: Do not use a prepare or check watcher because the module you
		2887	want to embed is not flexible enough to support it. Instead, you can
		2888	override their poll function. The drawback with this solution is that the
		2889	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2890	this approach, effectively embedding EV as a client into the horrible
		2891	libglib event loop.
		2892
		2893	static gint
		2894	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2895	{
		2896	int got_events = 0;
		2897
		2898	for (n = 0; n < nfds; ++n)
		2899	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2900
		2901	if (timeout >= 0)
		2902	// create/start timer
		2903
		2904	// poll
		2905	ev_run (EV_A_ 0);
		2906
		2907	// stop timer again
		2908	if (timeout >= 0)
		2909	ev_timer_stop (EV_A_ &to);
		2910
		2911	// stop io watchers again - their callbacks should have set
		2912	for (n = 0; n < nfds; ++n)
		2913	ev_io_stop (EV_A_ iow [n]);
		2914
		2915	return got_events;
		2916	}
		2917
		2918
1060	=head2 C<ev_embed> - when one backend isn't enough	2919	=head2 C<ev_embed> - when one backend isn't enough...
1061		2920
1062	This is a rather advanced watcher type that lets you embed one event loop	2921	This is a rather advanced watcher type that lets you embed one event loop
1063	into another.	2922	into another (currently only C<ev_io> events are supported in the embedded
		2923	loop, other types of watchers might be handled in a delayed or incorrect
		2924	fashion and must not be used).
1064		2925
1065	There are primarily two reasons you would want that: work around bugs and	2926	There are primarily two reasons you would want that: work around bugs and
1066	prioritise I/O.	2927	prioritise I/O.
1067		2928
1068	As an example for a bug workaround, the kqueue backend might only support	2929	As an example for a bug workaround, the kqueue backend might only support
1069	sockets on some platform, so it is unusable as generic backend, but you	2930	sockets on some platform, so it is unusable as generic backend, but you
1070	still want to make use of it because you have many sockets and it scales	2931	still want to make use of it because you have many sockets and it scales
1071	so nicely. In this case, you would create a kqueue-based loop and embed it	2932	so nicely. In this case, you would create a kqueue-based loop and embed
1072	into your default loop (which might use e.g. poll). Overall operation will	2933	it into your default loop (which might use e.g. poll). Overall operation
1073	be a bit slower because first libev has to poll and then call kevent, but	2934	will be a bit slower because first libev has to call C<poll> and then
1074	at least you can use both at what they are best.	2935	C<kevent>, but at least you can use both mechanisms for what they are
		2936	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1075		2937
1076	As for prioritising I/O: rarely you have the case where some fds have	2938	As for prioritising I/O: under rare circumstances you have the case where
1077	to be watched and handled very quickly (with low latency), and even	2939	some fds have to be watched and handled very quickly (with low latency),
1078	priorities and idle watchers might have too much overhead. In this case	2940	and even priorities and idle watchers might have too much overhead. In
1079	you would put all the high priority stuff in one loop and all the rest in	2941	this case you would put all the high priority stuff in one loop and all
1080	a second one, and embed the second one in the first.	2942	the rest in a second one, and embed the second one in the first.
1081		2943
1082	As long as the watcher is started it will automatically handle events. The	2944	As long as the watcher is active, the callback will be invoked every
1083	callback will be invoked whenever some events have been handled. You can	2945	time there might be events pending in the embedded loop. The callback
1084	set the callback to C<0> to avoid having to specify one if you are not	2946	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1085	interested in that.	2947	sweep and invoke their callbacks (the callback doesn't need to invoke the
		2948	C<ev_embed_sweep> function directly, it could also start an idle watcher
		2949	to give the embedded loop strictly lower priority for example).
1086		2950
1087	Also, there have not currently been made special provisions for forking:	2951	You can also set the callback to C<0>, in which case the embed watcher
1088	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2952	will automatically execute the embedded loop sweep whenever necessary.
1089	but you will also have to stop and restart any C<ev_embed> watchers
1090	yourself.
1091		2953
		2954	Fork detection will be handled transparently while the C<ev_embed> watcher
		2955	is active, i.e., the embedded loop will automatically be forked when the
		2956	embedding loop forks. In other cases, the user is responsible for calling
		2957	C<ev_loop_fork> on the embedded loop.
		2958
1092	Unfortunately, not all backends are embeddable, only the ones returned by	2959	Unfortunately, not all backends are embeddable: only the ones returned by
1093	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2960	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1094	portable one.	2961	portable one.
1095		2962
1096	So when you want to use this feature you will always have to be prepared	2963	So when you want to use this feature you will always have to be prepared
1097	that you cannot get an embeddable loop. The recommended way to get around	2964	that you cannot get an embeddable loop. The recommended way to get around
1098	this is to have a separate variables for your embeddable loop, try to	2965	this is to have a separate variables for your embeddable loop, try to
1099	create it, and if that fails, use the normal loop for everything:	2966	create it, and if that fails, use the normal loop for everything.
1100		2967
1101	struct ev_loop *loop_hi = ev_default_init (0);	2968	=head3 C<ev_embed> and fork
1102	struct ev_loop *loop_lo = 0;
1103	struct ev_embed embed;
1104
1105	// see if there is a chance of getting one that works
1106	// (remember that a flags value of 0 means autodetection)
1107	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1108	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1109	: 0;
1110		2969
1111	// if we got one, then embed it, otherwise default to loop_hi	2970	While the C<ev_embed> watcher is running, forks in the embedding loop will
1112	if (loop_lo)	2971	automatically be applied to the embedded loop as well, so no special
1113	{	2972	fork handling is required in that case. When the watcher is not running,
1114	ev_embed_init (&embed, 0, loop_lo);	2973	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1115	ev_embed_start (loop_hi, &embed);	2974	as applicable.
1116	}	2975
1117	else	2976	=head3 Watcher-Specific Functions and Data Members
1118	loop_lo = loop_hi;
1119		2977
1120	=over 4	2978	=over 4
1121		2979
1122	=item ev_embed_init (ev_embed *, callback, struct ev_loop *loop)	2980	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1123		2981
1124	=item ev_embed_set (ev_embed *, callback, struct ev_loop *loop)	2982	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
1125		2983
1126	Configures the watcher to embed the given loop, which must be embeddable.	2984	Configures the watcher to embed the given loop, which must be
		2985	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2986	invoked automatically, otherwise it is the responsibility of the callback
		2987	to invoke it (it will continue to be called until the sweep has been done,
		2988	if you do not want that, you need to temporarily stop the embed watcher).
		2989
		2990	=item ev_embed_sweep (loop, ev_embed *)
		2991
		2992	Make a single, non-blocking sweep over the embedded loop. This works
		2993	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
		2994	appropriate way for embedded loops.
		2995
		2996	=item struct ev_loop *other [read-only]
		2997
		2998	The embedded event loop.
1127		2999
1128	=back	3000	=back
1129		3001
		3002	=head3 Examples
		3003
		3004	Example: Try to get an embeddable event loop and embed it into the default
		3005	event loop. If that is not possible, use the default loop. The default
		3006	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3007	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3008	used).
		3009
		3010	struct ev_loop *loop_hi = ev_default_init (0);
		3011	struct ev_loop *loop_lo = 0;
		3012	ev_embed embed;
		3013
		3014	// see if there is a chance of getting one that works
		3015	// (remember that a flags value of 0 means autodetection)
		3016	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3017	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3018	: 0;
		3019
		3020	// if we got one, then embed it, otherwise default to loop_hi
		3021	if (loop_lo)
		3022	{
		3023	ev_embed_init (&embed, 0, loop_lo);
		3024	ev_embed_start (loop_hi, &embed);
		3025	}
		3026	else
		3027	loop_lo = loop_hi;
		3028
		3029	Example: Check if kqueue is available but not recommended and create
		3030	a kqueue backend for use with sockets (which usually work with any
		3031	kqueue implementation). Store the kqueue/socket-only event loop in
		3032	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3033
		3034	struct ev_loop *loop = ev_default_init (0);
		3035	struct ev_loop *loop_socket = 0;
		3036	ev_embed embed;
		3037
		3038	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3039	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3040	{
		3041	ev_embed_init (&embed, 0, loop_socket);
		3042	ev_embed_start (loop, &embed);
		3043	}
		3044
		3045	if (!loop_socket)
		3046	loop_socket = loop;
		3047
		3048	// now use loop_socket for all sockets, and loop for everything else
		3049
		3050
		3051	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		3052
		3053	Fork watchers are called when a C<fork ()> was detected (usually because
		3054	whoever is a good citizen cared to tell libev about it by calling
		3055	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		3056	event loop blocks next and before C<ev_check> watchers are being called,
		3057	and only in the child after the fork. If whoever good citizen calling
		3058	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		3059	handlers will be invoked, too, of course.
		3060
		3061	=head3 The special problem of life after fork - how is it possible?
		3062
		3063	Most uses of C<fork()> consist of forking, then some simple calls to set
		3064	up/change the process environment, followed by a call to C<exec()>. This
		3065	sequence should be handled by libev without any problems.
		3066
		3067	This changes when the application actually wants to do event handling
		3068	in the child, or both parent in child, in effect "continuing" after the
		3069	fork.
		3070
		3071	The default mode of operation (for libev, with application help to detect
		3072	forks) is to duplicate all the state in the child, as would be expected
		3073	when I<either> the parent I<or> the child process continues.
		3074
		3075	When both processes want to continue using libev, then this is usually the
		3076	wrong result. In that case, usually one process (typically the parent) is
		3077	supposed to continue with all watchers in place as before, while the other
		3078	process typically wants to start fresh, i.e. without any active watchers.
		3079
		3080	The cleanest and most efficient way to achieve that with libev is to
		3081	simply create a new event loop, which of course will be "empty", and
		3082	use that for new watchers. This has the advantage of not touching more
		3083	memory than necessary, and thus avoiding the copy-on-write, and the
		3084	disadvantage of having to use multiple event loops (which do not support
		3085	signal watchers).
		3086
		3087	When this is not possible, or you want to use the default loop for
		3088	other reasons, then in the process that wants to start "fresh", call
		3089	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3090	Destroying the default loop will "orphan" (not stop) all registered
		3091	watchers, so you have to be careful not to execute code that modifies
		3092	those watchers. Note also that in that case, you have to re-register any
		3093	signal watchers.
		3094
		3095	=head3 Watcher-Specific Functions and Data Members
		3096
		3097	=over 4
		3098
		3099	=item ev_fork_init (ev_fork *, callback)
		3100
		3101	Initialises and configures the fork watcher - it has no parameters of any
		3102	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		3103	believe me.
		3104
		3105	=back
		3106
		3107
		3108	=head2 C<ev_cleanup> - even the best things end
		3109
		3110	Cleanup watchers are called just before the event loop they are registered
		3111	with is being destroyed.
		3112
		3113	While there is no guarantee that the event loop gets destroyed, cleanup
		3114	watchers provide a convenient method to install cleanup watchers for your
		3115	program, worker threads and so on - you just to make sure to destroy the
		3116	loop when you want them to be invoked.
		3117
		3118	=head3 Watcher-Specific Functions and Data Members
		3119
		3120	=over 4
		3121
		3122	=item ev_cleanup_init (ev_cleanup *, callback)
		3123
		3124	Initialises and configures the cleanup watcher - it has no parameters of
		3125	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3126	pointless, believe me.
		3127
		3128	=back
		3129
		3130	Example: Register an atexit handler to destroy the default loop, so any
		3131	cleanup functions are called.
		3132
		3133	static void
		3134	program_exits (void)
		3135	{
		3136	ev_loop_destroy (EV_DEFAULT_UC);
		3137	}
		3138
		3139	...
		3140	atexit (program_exits);
		3141
		3142
		3143	=head2 C<ev_async> - how to wake up an event loop
		3144
		3145	In general, you cannot use an C<ev_run> from multiple threads or other
		3146	asynchronous sources such as signal handlers (as opposed to multiple event
		3147	loops - those are of course safe to use in different threads).
		3148
		3149	Sometimes, however, you need to wake up an event loop you do not control,
		3150	for example because it belongs to another thread. This is what C<ev_async>
		3151	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3152	it by calling C<ev_async_send>, which is thread- and signal safe.
		3153
		3154	This functionality is very similar to C<ev_signal> watchers, as signals,
		3155	too, are asynchronous in nature, and signals, too, will be compressed
		3156	(i.e. the number of callback invocations may be less than the number of
		3157	C<ev_async_sent> calls).
		3158
		3159	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3160	just the default loop.
		3161
		3162	=head3 Queueing
		3163
		3164	C<ev_async> does not support queueing of data in any way. The reason
		3165	is that the author does not know of a simple (or any) algorithm for a
		3166	multiple-writer-single-reader queue that works in all cases and doesn't
		3167	need elaborate support such as pthreads or unportable memory access
		3168	semantics.
		3169
		3170	That means that if you want to queue data, you have to provide your own
		3171	queue. But at least I can tell you how to implement locking around your
		3172	queue:
		3173
		3174	=over 4
		3175
		3176	=item queueing from a signal handler context
		3177
		3178	To implement race-free queueing, you simply add to the queue in the signal
		3179	handler but you block the signal handler in the watcher callback. Here is
		3180	an example that does that for some fictitious SIGUSR1 handler:
		3181
		3182	static ev_async mysig;
		3183
		3184	static void
		3185	sigusr1_handler (void)
		3186	{
		3187	sometype data;
		3188
		3189	// no locking etc.
		3190	queue_put (data);
		3191	ev_async_send (EV_DEFAULT_ &mysig);
		3192	}
		3193
		3194	static void
		3195	mysig_cb (EV_P_ ev_async *w, int revents)
		3196	{
		3197	sometype data;
		3198	sigset_t block, prev;
		3199
		3200	sigemptyset (&block);
		3201	sigaddset (&block, SIGUSR1);
		3202	sigprocmask (SIG_BLOCK, &block, &prev);
		3203
		3204	while (queue_get (&data))
		3205	process (data);
		3206
		3207	if (sigismember (&prev, SIGUSR1)
		3208	sigprocmask (SIG_UNBLOCK, &block, 0);
		3209	}
		3210
		3211	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3212	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3213	either...).
		3214
		3215	=item queueing from a thread context
		3216
		3217	The strategy for threads is different, as you cannot (easily) block
		3218	threads but you can easily preempt them, so to queue safely you need to
		3219	employ a traditional mutex lock, such as in this pthread example:
		3220
		3221	static ev_async mysig;
		3222	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3223
		3224	static void
		3225	otherthread (void)
		3226	{
		3227	// only need to lock the actual queueing operation
		3228	pthread_mutex_lock (&mymutex);
		3229	queue_put (data);
		3230	pthread_mutex_unlock (&mymutex);
		3231
		3232	ev_async_send (EV_DEFAULT_ &mysig);
		3233	}
		3234
		3235	static void
		3236	mysig_cb (EV_P_ ev_async *w, int revents)
		3237	{
		3238	pthread_mutex_lock (&mymutex);
		3239
		3240	while (queue_get (&data))
		3241	process (data);
		3242
		3243	pthread_mutex_unlock (&mymutex);
		3244	}
		3245
		3246	=back
		3247
		3248
		3249	=head3 Watcher-Specific Functions and Data Members
		3250
		3251	=over 4
		3252
		3253	=item ev_async_init (ev_async *, callback)
		3254
		3255	Initialises and configures the async watcher - it has no parameters of any
		3256	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3257	trust me.
		3258
		3259	=item ev_async_send (loop, ev_async *)
		3260
		3261	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3262	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3263	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3264	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3265	section below on what exactly this means).
		3266
		3267	Note that, as with other watchers in libev, multiple events might get
		3268	compressed into a single callback invocation (another way to look at this
		3269	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3270	reset when the event loop detects that).
		3271
		3272	This call incurs the overhead of a system call only once per event loop
		3273	iteration, so while the overhead might be noticeable, it doesn't apply to
		3274	repeated calls to C<ev_async_send> for the same event loop.
		3275
		3276	=item bool = ev_async_pending (ev_async *)
		3277
		3278	Returns a non-zero value when C<ev_async_send> has been called on the
		3279	watcher but the event has not yet been processed (or even noted) by the
		3280	event loop.
		3281
		3282	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3283	the loop iterates next and checks for the watcher to have become active,
		3284	it will reset the flag again. C<ev_async_pending> can be used to very
		3285	quickly check whether invoking the loop might be a good idea.
		3286
		3287	Not that this does I<not> check whether the watcher itself is pending,
		3288	only whether it has been requested to make this watcher pending: there
		3289	is a time window between the event loop checking and resetting the async
		3290	notification, and the callback being invoked.
		3291
		3292	=back
		3293
1130		3294
1131	=head1 OTHER FUNCTIONS	3295	=head1 OTHER FUNCTIONS
1132		3296
1133	There are some other functions of possible interest. Described. Here. Now.	3297	There are some other functions of possible interest. Described. Here. Now.
1134		3298
1135	=over 4	3299	=over 4
1136		3300
1137	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3301	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1138		3302
1139	This function combines a simple timer and an I/O watcher, calls your	3303	This function combines a simple timer and an I/O watcher, calls your
1140	callback on whichever event happens first and automatically stop both	3304	callback on whichever event happens first and automatically stops both
1141	watchers. This is useful if you want to wait for a single event on an fd	3305	watchers. This is useful if you want to wait for a single event on an fd
1142	or timeout without having to allocate/configure/start/stop/free one or	3306	or timeout without having to allocate/configure/start/stop/free one or
1143	more watchers yourself.	3307	more watchers yourself.
1144		3308
1145	If C<fd> is less than 0, then no I/O watcher will be started and events	3309	If C<fd> is less than 0, then no I/O watcher will be started and the
1146	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3310	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1147	C<events> set will be craeted and started.	3311	the given C<fd> and C<events> set will be created and started.
1148		3312
1149	If C<timeout> is less than 0, then no timeout watcher will be	3313	If C<timeout> is less than 0, then no timeout watcher will be
1150	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3314	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1151	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3315	repeat = 0) will be started. C<0> is a valid timeout.
1152	dubious value.
1153		3316
1154	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3317	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1155	passed an C<revents> set like normal event callbacks (a combination of	3318	passed an C<revents> set like normal event callbacks (a combination of
1156	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3319	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1157	value passed to C<ev_once>:	3320	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3321	a timeout and an io event at the same time - you probably should give io
		3322	events precedence.
1158		3323
		3324	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3325
1159	static void stdin_ready (int revents, void *arg)	3326	static void stdin_ready (int revents, void *arg)
1160	{	3327	{
1161	if (revents & EV_TIMEOUT)
1162	/* doh, nothing entered */;
1163	else if (revents & EV_READ)	3328	if (revents & EV_READ)
1164	/* stdin might have data for us, joy! */;	3329	/* stdin might have data for us, joy! */;
		3330	else if (revents & EV_TIMER)
		3331	/* doh, nothing entered */;
1165	}	3332	}
1166		3333
1167	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3334	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1168
1169	=item ev_feed_event (loop, watcher, int events)
1170
1171	Feeds the given event set into the event loop, as if the specified event
1172	had happened for the specified watcher (which must be a pointer to an
1173	initialised but not necessarily started event watcher).
1174		3335
1175	=item ev_feed_fd_event (loop, int fd, int revents)	3336	=item ev_feed_fd_event (loop, int fd, int revents)
1176		3337
1177	Feed an event on the given fd, as if a file descriptor backend detected	3338	Feed an event on the given fd, as if a file descriptor backend detected
1178	the given events it.	3339	the given events it.
1179		3340
1180	=item ev_feed_signal_event (loop, int signum)	3341	=item ev_feed_signal_event (loop, int signum)
1181		3342
1182	Feed an event as if the given signal occured (loop must be the default loop!).	3343	Feed an event as if the given signal occurred (C<loop> must be the default
		3344	loop!).
1183		3345
1184	=back	3346	=back
1185		3347
1186		3348
1187	=head1 LIBEVENT EMULATION	3349	=head1 LIBEVENT EMULATION
…		…
1202		3364
1203	=item * Priorities are not currently supported. Initialising priorities	3365	=item * Priorities are not currently supported. Initialising priorities
1204	will fail and all watchers will have the same priority, even though there	3366	will fail and all watchers will have the same priority, even though there
1205	is an ev_pri field.	3367	is an ev_pri field.
1206		3368
		3369	=item * In libevent, the last base created gets the signals, in libev, the
		3370	first base created (== the default loop) gets the signals.
		3371
1207	=item * Other members are not supported.	3372	=item * Other members are not supported.
1208		3373
1209	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3374	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1210	to use the libev header file and library.	3375	to use the libev header file and library.
1211		3376
1212	=back	3377	=back
1213		3378
1214	=head1 C++ SUPPORT	3379	=head1 C++ SUPPORT
1215		3380
1216	TBD.	3381	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3382	you to use some convenience methods to start/stop watchers and also change
		3383	the callback model to a model using method callbacks on objects.
		3384
		3385	To use it,
		3386
		3387	#include <ev++.h>
		3388
		3389	This automatically includes F<ev.h> and puts all of its definitions (many
		3390	of them macros) into the global namespace. All C++ specific things are
		3391	put into the C<ev> namespace. It should support all the same embedding
		3392	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3393
		3394	Care has been taken to keep the overhead low. The only data member the C++
		3395	classes add (compared to plain C-style watchers) is the event loop pointer
		3396	that the watcher is associated with (or no additional members at all if
		3397	you disable C<EV_MULTIPLICITY> when embedding libev).
		3398
		3399	Currently, functions, and static and non-static member functions can be
		3400	used as callbacks. Other types should be easy to add as long as they only
		3401	need one additional pointer for context. If you need support for other
		3402	types of functors please contact the author (preferably after implementing
		3403	it).
		3404
		3405	Here is a list of things available in the C<ev> namespace:
		3406
		3407	=over 4
		3408
		3409	=item C<ev::READ>, C<ev::WRITE> etc.
		3410
		3411	These are just enum values with the same values as the C<EV_READ> etc.
		3412	macros from F<ev.h>.
		3413
		3414	=item C<ev::tstamp>, C<ev::now>
		3415
		3416	Aliases to the same types/functions as with the C<ev_> prefix.
		3417
		3418	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		3419
		3420	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		3421	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		3422	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3423	defines by many implementations.
		3424
		3425	All of those classes have these methods:
		3426
		3427	=over 4
		3428
		3429	=item ev::TYPE::TYPE ()
		3430
		3431	=item ev::TYPE::TYPE (loop)
		3432
		3433	=item ev::TYPE::~TYPE
		3434
		3435	The constructor (optionally) takes an event loop to associate the watcher
		3436	with. If it is omitted, it will use C<EV_DEFAULT>.
		3437
		3438	The constructor calls C<ev_init> for you, which means you have to call the
		3439	C<set> method before starting it.
		3440
		3441	It will not set a callback, however: You have to call the templated C<set>
		3442	method to set a callback before you can start the watcher.
		3443
		3444	(The reason why you have to use a method is a limitation in C++ which does
		3445	not allow explicit template arguments for constructors).
		3446
		3447	The destructor automatically stops the watcher if it is active.
		3448
		3449	=item w->set<class, &class::method> (object *)
		3450
		3451	This method sets the callback method to call. The method has to have a
		3452	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3453	first argument and the C<revents> as second. The object must be given as
		3454	parameter and is stored in the C<data> member of the watcher.
		3455
		3456	This method synthesizes efficient thunking code to call your method from
		3457	the C callback that libev requires. If your compiler can inline your
		3458	callback (i.e. it is visible to it at the place of the C<set> call and
		3459	your compiler is good :), then the method will be fully inlined into the
		3460	thunking function, making it as fast as a direct C callback.
		3461
		3462	Example: simple class declaration and watcher initialisation
		3463
		3464	struct myclass
		3465	{
		3466	void io_cb (ev::io &w, int revents) { }
		3467	}
		3468
		3469	myclass obj;
		3470	ev::io iow;
		3471	iow.set <myclass, &myclass::io_cb> (&obj);
		3472
		3473	=item w->set (object *)
		3474
		3475	This is a variation of a method callback - leaving out the method to call
		3476	will default the method to C<operator ()>, which makes it possible to use
		3477	functor objects without having to manually specify the C<operator ()> all
		3478	the time. Incidentally, you can then also leave out the template argument
		3479	list.
		3480
		3481	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3482	int revents)>.
		3483
		3484	See the method-C<set> above for more details.
		3485
		3486	Example: use a functor object as callback.
		3487
		3488	struct myfunctor
		3489	{
		3490	void operator() (ev::io &w, int revents)
		3491	{
		3492	...
		3493	}
		3494	}
		3495
		3496	myfunctor f;
		3497
		3498	ev::io w;
		3499	w.set (&f);
		3500
		3501	=item w->set<function> (void *data = 0)
		3502
		3503	Also sets a callback, but uses a static method or plain function as
		3504	callback. The optional C<data> argument will be stored in the watcher's
		3505	C<data> member and is free for you to use.
		3506
		3507	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3508
		3509	See the method-C<set> above for more details.
		3510
		3511	Example: Use a plain function as callback.
		3512
		3513	static void io_cb (ev::io &w, int revents) { }
		3514	iow.set <io_cb> ();
		3515
		3516	=item w->set (loop)
		3517
		3518	Associates a different C<struct ev_loop> with this watcher. You can only
		3519	do this when the watcher is inactive (and not pending either).
		3520
		3521	=item w->set ([arguments])
		3522
		3523	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
		3524	method or a suitable start method must be called at least once. Unlike the
		3525	C counterpart, an active watcher gets automatically stopped and restarted
		3526	when reconfiguring it with this method.
		3527
		3528	=item w->start ()
		3529
		3530	Starts the watcher. Note that there is no C<loop> argument, as the
		3531	constructor already stores the event loop.
		3532
		3533	=item w->start ([arguments])
		3534
		3535	Instead of calling C<set> and C<start> methods separately, it is often
		3536	convenient to wrap them in one call. Uses the same type of arguments as
		3537	the configure C<set> method of the watcher.
		3538
		3539	=item w->stop ()
		3540
		3541	Stops the watcher if it is active. Again, no C<loop> argument.
		3542
		3543	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		3544
		3545	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		3546	C<ev_TYPE_again> function.
		3547
		3548	=item w->sweep () (C<ev::embed> only)
		3549
		3550	Invokes C<ev_embed_sweep>.
		3551
		3552	=item w->update () (C<ev::stat> only)
		3553
		3554	Invokes C<ev_stat_stat>.
		3555
		3556	=back
		3557
		3558	=back
		3559
		3560	Example: Define a class with two I/O and idle watchers, start the I/O
		3561	watchers in the constructor.
		3562
		3563	class myclass
		3564	{
		3565	ev::io io ; void io_cb (ev::io &w, int revents);
		3566	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
		3567	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3568
		3569	myclass (int fd)
		3570	{
		3571	io .set <myclass, &myclass::io_cb > (this);
		3572	io2 .set <myclass, &myclass::io2_cb > (this);
		3573	idle.set <myclass, &myclass::idle_cb> (this);
		3574
		3575	io.set (fd, ev::WRITE); // configure the watcher
		3576	io.start (); // start it whenever convenient
		3577
		3578	io2.start (fd, ev::READ); // set + start in one call
		3579	}
		3580	};
		3581
		3582
		3583	=head1 OTHER LANGUAGE BINDINGS
		3584
		3585	Libev does not offer other language bindings itself, but bindings for a
		3586	number of languages exist in the form of third-party packages. If you know
		3587	any interesting language binding in addition to the ones listed here, drop
		3588	me a note.
		3589
		3590	=over 4
		3591
		3592	=item Perl
		3593
		3594	The EV module implements the full libev API and is actually used to test
		3595	libev. EV is developed together with libev. Apart from the EV core module,
		3596	there are additional modules that implement libev-compatible interfaces
		3597	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3598	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3599	and C<EV::Glib>).
		3600
		3601	It can be found and installed via CPAN, its homepage is at
		3602	L<http://software.schmorp.de/pkg/EV>.
		3603
		3604	=item Python
		3605
		3606	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3607	seems to be quite complete and well-documented.
		3608
		3609	=item Ruby
		3610
		3611	Tony Arcieri has written a ruby extension that offers access to a subset
		3612	of the libev API and adds file handle abstractions, asynchronous DNS and
		3613	more on top of it. It can be found via gem servers. Its homepage is at
		3614	L<http://rev.rubyforge.org/>.
		3615
		3616	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3617	makes rev work even on mingw.
		3618
		3619	=item Haskell
		3620
		3621	A haskell binding to libev is available at
		3622	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3623
		3624	=item D
		3625
		3626	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3627	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3628
		3629	=item Ocaml
		3630
		3631	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3632	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3633
		3634	=item Lua
		3635
		3636	Brian Maher has written a partial interface to libev for lua (at the
		3637	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3638	L<http://github.com/brimworks/lua-ev>.
		3639
		3640	=back
		3641
		3642
		3643	=head1 MACRO MAGIC
		3644
		3645	Libev can be compiled with a variety of options, the most fundamental
		3646	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3647	functions and callbacks have an initial C<struct ev_loop *> argument.
		3648
		3649	To make it easier to write programs that cope with either variant, the
		3650	following macros are defined:
		3651
		3652	=over 4
		3653
		3654	=item C<EV_A>, C<EV_A_>
		3655
		3656	This provides the loop I<argument> for functions, if one is required ("ev
		3657	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3658	C<EV_A_> is used when other arguments are following. Example:
		3659
		3660	ev_unref (EV_A);
		3661	ev_timer_add (EV_A_ watcher);
		3662	ev_run (EV_A_ 0);
		3663
		3664	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3665	which is often provided by the following macro.
		3666
		3667	=item C<EV_P>, C<EV_P_>
		3668
		3669	This provides the loop I<parameter> for functions, if one is required ("ev
		3670	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3671	C<EV_P_> is used when other parameters are following. Example:
		3672
		3673	// this is how ev_unref is being declared
		3674	static void ev_unref (EV_P);
		3675
		3676	// this is how you can declare your typical callback
		3677	static void cb (EV_P_ ev_timer *w, int revents)
		3678
		3679	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3680	suitable for use with C<EV_A>.
		3681
		3682	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3683
		3684	Similar to the other two macros, this gives you the value of the default
		3685	loop, if multiple loops are supported ("ev loop default").
		3686
		3687	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3688
		3689	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3690	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3691	is undefined when the default loop has not been initialised by a previous
		3692	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3693
		3694	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3695	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3696
		3697	=back
		3698
		3699	Example: Declare and initialise a check watcher, utilising the above
		3700	macros so it will work regardless of whether multiple loops are supported
		3701	or not.
		3702
		3703	static void
		3704	check_cb (EV_P_ ev_timer *w, int revents)
		3705	{
		3706	ev_check_stop (EV_A_ w);
		3707	}
		3708
		3709	ev_check check;
		3710	ev_check_init (&check, check_cb);
		3711	ev_check_start (EV_DEFAULT_ &check);
		3712	ev_run (EV_DEFAULT_ 0);
		3713
		3714	=head1 EMBEDDING
		3715
		3716	Libev can (and often is) directly embedded into host
		3717	applications. Examples of applications that embed it include the Deliantra
		3718	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3719	and rxvt-unicode.
		3720
		3721	The goal is to enable you to just copy the necessary files into your
		3722	source directory without having to change even a single line in them, so
		3723	you can easily upgrade by simply copying (or having a checked-out copy of
		3724	libev somewhere in your source tree).
		3725
		3726	=head2 FILESETS
		3727
		3728	Depending on what features you need you need to include one or more sets of files
		3729	in your application.
		3730
		3731	=head3 CORE EVENT LOOP
		3732
		3733	To include only the libev core (all the C<ev_*> functions), with manual
		3734	configuration (no autoconf):
		3735
		3736	#define EV_STANDALONE 1
		3737	#include "ev.c"
		3738
		3739	This will automatically include F<ev.h>, too, and should be done in a
		3740	single C source file only to provide the function implementations. To use
		3741	it, do the same for F<ev.h> in all files wishing to use this API (best
		3742	done by writing a wrapper around F<ev.h> that you can include instead and
		3743	where you can put other configuration options):
		3744
		3745	#define EV_STANDALONE 1
		3746	#include "ev.h"
		3747
		3748	Both header files and implementation files can be compiled with a C++
		3749	compiler (at least, that's a stated goal, and breakage will be treated
		3750	as a bug).
		3751
		3752	You need the following files in your source tree, or in a directory
		3753	in your include path (e.g. in libev/ when using -Ilibev):
		3754
		3755	ev.h
		3756	ev.c
		3757	ev_vars.h
		3758	ev_wrap.h
		3759
		3760	ev_win32.c required on win32 platforms only
		3761
		3762	ev_select.c only when select backend is enabled (which is enabled by default)
		3763	ev_poll.c only when poll backend is enabled (disabled by default)
		3764	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3765	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3766	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3767
		3768	F<ev.c> includes the backend files directly when enabled, so you only need
		3769	to compile this single file.
		3770
		3771	=head3 LIBEVENT COMPATIBILITY API
		3772
		3773	To include the libevent compatibility API, also include:
		3774
		3775	#include "event.c"
		3776
		3777	in the file including F<ev.c>, and:
		3778
		3779	#include "event.h"
		3780
		3781	in the files that want to use the libevent API. This also includes F<ev.h>.
		3782
		3783	You need the following additional files for this:
		3784
		3785	event.h
		3786	event.c
		3787
		3788	=head3 AUTOCONF SUPPORT
		3789
		3790	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3791	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3792	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3793	include F<config.h> and configure itself accordingly.
		3794
		3795	For this of course you need the m4 file:
		3796
		3797	libev.m4
		3798
		3799	=head2 PREPROCESSOR SYMBOLS/MACROS
		3800
		3801	Libev can be configured via a variety of preprocessor symbols you have to
		3802	define before including (or compiling) any of its files. The default in
		3803	the absence of autoconf is documented for every option.
		3804
		3805	Symbols marked with "(h)" do not change the ABI, and can have different
		3806	values when compiling libev vs. including F<ev.h>, so it is permissible
		3807	to redefine them before including F<ev.h> without breaking compatibility
		3808	to a compiled library. All other symbols change the ABI, which means all
		3809	users of libev and the libev code itself must be compiled with compatible
		3810	settings.
		3811
		3812	=over 4
		3813
		3814	=item EV_COMPAT3 (h)
		3815
		3816	Backwards compatibility is a major concern for libev. This is why this
		3817	release of libev comes with wrappers for the functions and symbols that
		3818	have been renamed between libev version 3 and 4.
		3819
		3820	You can disable these wrappers (to test compatibility with future
		3821	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3822	sources. This has the additional advantage that you can drop the C<struct>
		3823	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3824	typedef in that case.
		3825
		3826	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3827	and in some even more future version the compatibility code will be
		3828	removed completely.
		3829
		3830	=item EV_STANDALONE (h)
		3831
		3832	Must always be C<1> if you do not use autoconf configuration, which
		3833	keeps libev from including F<config.h>, and it also defines dummy
		3834	implementations for some libevent functions (such as logging, which is not
		3835	supported). It will also not define any of the structs usually found in
		3836	F<event.h> that are not directly supported by the libev core alone.
		3837
		3838	In standalone mode, libev will still try to automatically deduce the
		3839	configuration, but has to be more conservative.
		3840
		3841	=item EV_USE_MONOTONIC
		3842
		3843	If defined to be C<1>, libev will try to detect the availability of the
		3844	monotonic clock option at both compile time and runtime. Otherwise no
		3845	use of the monotonic clock option will be attempted. If you enable this,
		3846	you usually have to link against librt or something similar. Enabling it
		3847	when the functionality isn't available is safe, though, although you have
		3848	to make sure you link against any libraries where the C<clock_gettime>
		3849	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3850
		3851	=item EV_USE_REALTIME
		3852
		3853	If defined to be C<1>, libev will try to detect the availability of the
		3854	real-time clock option at compile time (and assume its availability
		3855	at runtime if successful). Otherwise no use of the real-time clock
		3856	option will be attempted. This effectively replaces C<gettimeofday>
		3857	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		3858	correctness. See the note about libraries in the description of
		3859	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3860	C<EV_USE_CLOCK_SYSCALL>.
		3861
		3862	=item EV_USE_CLOCK_SYSCALL
		3863
		3864	If defined to be C<1>, libev will try to use a direct syscall instead
		3865	of calling the system-provided C<clock_gettime> function. This option
		3866	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3867	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3868	programs needlessly. Using a direct syscall is slightly slower (in
		3869	theory), because no optimised vdso implementation can be used, but avoids
		3870	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3871	higher, as it simplifies linking (no need for C<-lrt>).
		3872
		3873	=item EV_USE_NANOSLEEP
		3874
		3875	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3876	and will use it for delays. Otherwise it will use C<select ()>.
		3877
		3878	=item EV_USE_EVENTFD
		3879
		3880	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3881	available and will probe for kernel support at runtime. This will improve
		3882	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3883	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3884	2.7 or newer, otherwise disabled.
		3885
		3886	=item EV_USE_SELECT
		3887
		3888	If undefined or defined to be C<1>, libev will compile in support for the
		3889	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3890	other method takes over, select will be it. Otherwise the select backend
		3891	will not be compiled in.
		3892
		3893	=item EV_SELECT_USE_FD_SET
		3894
		3895	If defined to C<1>, then the select backend will use the system C<fd_set>
		3896	structure. This is useful if libev doesn't compile due to a missing
		3897	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		3898	on exotic systems. This usually limits the range of file descriptors to
		3899	some low limit such as 1024 or might have other limitations (winsocket
		3900	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		3901	configures the maximum size of the C<fd_set>.
		3902
		3903	=item EV_SELECT_IS_WINSOCKET
		3904
		3905	When defined to C<1>, the select backend will assume that
		3906	select/socket/connect etc. don't understand file descriptors but
		3907	wants osf handles on win32 (this is the case when the select to
		3908	be used is the winsock select). This means that it will call
		3909	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3910	it is assumed that all these functions actually work on fds, even
		3911	on win32. Should not be defined on non-win32 platforms.
		3912
		3913	=item EV_FD_TO_WIN32_HANDLE(fd)
		3914
		3915	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3916	file descriptors to socket handles. When not defining this symbol (the
		3917	default), then libev will call C<_get_osfhandle>, which is usually
		3918	correct. In some cases, programs use their own file descriptor management,
		3919	in which case they can provide this function to map fds to socket handles.
		3920
		3921	=item EV_WIN32_HANDLE_TO_FD(handle)
		3922
		3923	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3924	using the standard C<_open_osfhandle> function. For programs implementing
		3925	their own fd to handle mapping, overwriting this function makes it easier
		3926	to do so. This can be done by defining this macro to an appropriate value.
		3927
		3928	=item EV_WIN32_CLOSE_FD(fd)
		3929
		3930	If programs implement their own fd to handle mapping on win32, then this
		3931	macro can be used to override the C<close> function, useful to unregister
		3932	file descriptors again. Note that the replacement function has to close
		3933	the underlying OS handle.
		3934
		3935	=item EV_USE_POLL
		3936
		3937	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3938	backend. Otherwise it will be enabled on non-win32 platforms. It
		3939	takes precedence over select.
		3940
		3941	=item EV_USE_EPOLL
		3942
		3943	If defined to be C<1>, libev will compile in support for the Linux
		3944	C<epoll>(7) backend. Its availability will be detected at runtime,
		3945	otherwise another method will be used as fallback. This is the preferred
		3946	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3947	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3948
		3949	=item EV_USE_KQUEUE
		3950
		3951	If defined to be C<1>, libev will compile in support for the BSD style
		3952	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3953	otherwise another method will be used as fallback. This is the preferred
		3954	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3955	supports some types of fds correctly (the only platform we found that
		3956	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3957	not be used unless explicitly requested. The best way to use it is to find
		3958	out whether kqueue supports your type of fd properly and use an embedded
		3959	kqueue loop.
		3960
		3961	=item EV_USE_PORT
		3962
		3963	If defined to be C<1>, libev will compile in support for the Solaris
		3964	10 port style backend. Its availability will be detected at runtime,
		3965	otherwise another method will be used as fallback. This is the preferred
		3966	backend for Solaris 10 systems.
		3967
		3968	=item EV_USE_DEVPOLL
		3969
		3970	Reserved for future expansion, works like the USE symbols above.
		3971
		3972	=item EV_USE_INOTIFY
		3973
		3974	If defined to be C<1>, libev will compile in support for the Linux inotify
		3975	interface to speed up C<ev_stat> watchers. Its actual availability will
		3976	be detected at runtime. If undefined, it will be enabled if the headers
		3977	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3978
		3979	=item EV_ATOMIC_T
		3980
		3981	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3982	access is atomic with respect to other threads or signal contexts. No such
		3983	type is easily found in the C language, so you can provide your own type
		3984	that you know is safe for your purposes. It is used both for signal handler "locking"
		3985	as well as for signal and thread safety in C<ev_async> watchers.
		3986
		3987	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3988	(from F<signal.h>), which is usually good enough on most platforms.
		3989
		3990	=item EV_H (h)
		3991
		3992	The name of the F<ev.h> header file used to include it. The default if
		3993	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3994	used to virtually rename the F<ev.h> header file in case of conflicts.
		3995
		3996	=item EV_CONFIG_H (h)
		3997
		3998	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3999	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		4000	C<EV_H>, above.
		4001
		4002	=item EV_EVENT_H (h)
		4003
		4004	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		4005	of how the F<event.h> header can be found, the default is C<"event.h">.
		4006
		4007	=item EV_PROTOTYPES (h)
		4008
		4009	If defined to be C<0>, then F<ev.h> will not define any function
		4010	prototypes, but still define all the structs and other symbols. This is
		4011	occasionally useful if you want to provide your own wrapper functions
		4012	around libev functions.
		4013
		4014	=item EV_MULTIPLICITY
		4015
		4016	If undefined or defined to C<1>, then all event-loop-specific functions
		4017	will have the C<struct ev_loop *> as first argument, and you can create
		4018	additional independent event loops. Otherwise there will be no support
		4019	for multiple event loops and there is no first event loop pointer
		4020	argument. Instead, all functions act on the single default loop.
		4021
		4022	=item EV_MINPRI
		4023
		4024	=item EV_MAXPRI
		4025
		4026	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		4027	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		4028	provide for more priorities by overriding those symbols (usually defined
		4029	to be C<-2> and C<2>, respectively).
		4030
		4031	When doing priority-based operations, libev usually has to linearly search
		4032	all the priorities, so having many of them (hundreds) uses a lot of space
		4033	and time, so using the defaults of five priorities (-2 .. +2) is usually
		4034	fine.
		4035
		4036	If your embedding application does not need any priorities, defining these
		4037	both to C<0> will save some memory and CPU.
		4038
		4039	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4040	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4041	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		4042
		4043	If undefined or defined to be C<1> (and the platform supports it), then
		4044	the respective watcher type is supported. If defined to be C<0>, then it
		4045	is not. Disabling watcher types mainly saves code size.
		4046
		4047	=item EV_FEATURES
		4048
		4049	If you need to shave off some kilobytes of code at the expense of some
		4050	speed (but with the full API), you can define this symbol to request
		4051	certain subsets of functionality. The default is to enable all features
		4052	that can be enabled on the platform.
		4053
		4054	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4055	with some broad features you want) and then selectively re-enable
		4056	additional parts you want, for example if you want everything minimal,
		4057	but multiple event loop support, async and child watchers and the poll
		4058	backend, use this:
		4059
		4060	#define EV_FEATURES 0
		4061	#define EV_MULTIPLICITY 1
		4062	#define EV_USE_POLL 1
		4063	#define EV_CHILD_ENABLE 1
		4064	#define EV_ASYNC_ENABLE 1
		4065
		4066	The actual value is a bitset, it can be a combination of the following
		4067	values:
		4068
		4069	=over 4
		4070
		4071	=item C<1> - faster/larger code
		4072
		4073	Use larger code to speed up some operations.
		4074
		4075	Currently this is used to override some inlining decisions (enlarging the
		4076	code size by roughly 30% on amd64).
		4077
		4078	When optimising for size, use of compiler flags such as C<-Os> with
		4079	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4080	assertions.
		4081
		4082	=item C<2> - faster/larger data structures
		4083
		4084	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4085	hash table sizes and so on. This will usually further increase code size
		4086	and can additionally have an effect on the size of data structures at
		4087	runtime.
		4088
		4089	=item C<4> - full API configuration
		4090
		4091	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4092	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4093
		4094	=item C<8> - full API
		4095
		4096	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4097	details on which parts of the API are still available without this
		4098	feature, and do not complain if this subset changes over time.
		4099
		4100	=item C<16> - enable all optional watcher types
		4101
		4102	Enables all optional watcher types. If you want to selectively enable
		4103	only some watcher types other than I/O and timers (e.g. prepare,
		4104	embed, async, child...) you can enable them manually by defining
		4105	C<EV_watchertype_ENABLE> to C<1> instead.
		4106
		4107	=item C<32> - enable all backends
		4108
		4109	This enables all backends - without this feature, you need to enable at
		4110	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4111
		4112	=item C<64> - enable OS-specific "helper" APIs
		4113
		4114	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4115	default.
		4116
		4117	=back
		4118
		4119	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4120	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4121	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4122	watchers, timers and monotonic clock support.
		4123
		4124	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4125	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4126	your program might be left out as well - a binary starting a timer and an
		4127	I/O watcher then might come out at only 5Kb.
		4128
		4129	=item EV_AVOID_STDIO
		4130
		4131	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4132	functions (printf, scanf, perror etc.). This will increase the code size
		4133	somewhat, but if your program doesn't otherwise depend on stdio and your
		4134	libc allows it, this avoids linking in the stdio library which is quite
		4135	big.
		4136
		4137	Note that error messages might become less precise when this option is
		4138	enabled.
		4139
		4140	=item EV_NSIG
		4141
		4142	The highest supported signal number, +1 (or, the number of
		4143	signals): Normally, libev tries to deduce the maximum number of signals
		4144	automatically, but sometimes this fails, in which case it can be
		4145	specified. Also, using a lower number than detected (C<32> should be
		4146	good for about any system in existence) can save some memory, as libev
		4147	statically allocates some 12-24 bytes per signal number.
		4148
		4149	=item EV_PID_HASHSIZE
		4150
		4151	C<ev_child> watchers use a small hash table to distribute workload by
		4152	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
		4153	usually more than enough. If you need to manage thousands of children you
		4154	might want to increase this value (I<must> be a power of two).
		4155
		4156	=item EV_INOTIFY_HASHSIZE
		4157
		4158	C<ev_stat> watchers use a small hash table to distribute workload by
		4159	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4160	disabled), usually more than enough. If you need to manage thousands of
		4161	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4162	power of two).
		4163
		4164	=item EV_USE_4HEAP
		4165
		4166	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4167	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4168	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4169	faster performance with many (thousands) of watchers.
		4170
		4171	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4172	will be C<0>.
		4173
		4174	=item EV_HEAP_CACHE_AT
		4175
		4176	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4177	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4178	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4179	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4180	but avoids random read accesses on heap changes. This improves performance
		4181	noticeably with many (hundreds) of watchers.
		4182
		4183	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4184	will be C<0>.
		4185
		4186	=item EV_VERIFY
		4187
		4188	Controls how much internal verification (see C<ev_verify ()>) will
		4189	be done: If set to C<0>, no internal verification code will be compiled
		4190	in. If set to C<1>, then verification code will be compiled in, but not
		4191	called. If set to C<2>, then the internal verification code will be
		4192	called once per loop, which can slow down libev. If set to C<3>, then the
		4193	verification code will be called very frequently, which will slow down
		4194	libev considerably.
		4195
		4196	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4197	will be C<0>.
		4198
		4199	=item EV_COMMON
		4200
		4201	By default, all watchers have a C<void *data> member. By redefining
		4202	this macro to something else you can include more and other types of
		4203	members. You have to define it each time you include one of the files,
		4204	though, and it must be identical each time.
		4205
		4206	For example, the perl EV module uses something like this:
		4207
		4208	#define EV_COMMON \
		4209	SV *self; /* contains this struct */ \
		4210	SV *cb_sv, *fh /* note no trailing ";" */
		4211
		4212	=item EV_CB_DECLARE (type)
		4213
		4214	=item EV_CB_INVOKE (watcher, revents)
		4215
		4216	=item ev_set_cb (ev, cb)
		4217
		4218	Can be used to change the callback member declaration in each watcher,
		4219	and the way callbacks are invoked and set. Must expand to a struct member
		4220	definition and a statement, respectively. See the F<ev.h> header file for
		4221	their default definitions. One possible use for overriding these is to
		4222	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		4223	method calls instead of plain function calls in C++.
		4224
		4225	=back
		4226
		4227	=head2 EXPORTED API SYMBOLS
		4228
		4229	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4230	exported symbols, you can use the provided F<Symbol.*> files which list
		4231	all public symbols, one per line:
		4232
		4233	Symbols.ev for libev proper
		4234	Symbols.event for the libevent emulation
		4235
		4236	This can also be used to rename all public symbols to avoid clashes with
		4237	multiple versions of libev linked together (which is obviously bad in
		4238	itself, but sometimes it is inconvenient to avoid this).
		4239
		4240	A sed command like this will create wrapper C<#define>'s that you need to
		4241	include before including F<ev.h>:
		4242
		4243	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4244
		4245	This would create a file F<wrap.h> which essentially looks like this:
		4246
		4247	#define ev_backend myprefix_ev_backend
		4248	#define ev_check_start myprefix_ev_check_start
		4249	#define ev_check_stop myprefix_ev_check_stop
		4250	...
		4251
		4252	=head2 EXAMPLES
		4253
		4254	For a real-world example of a program the includes libev
		4255	verbatim, you can have a look at the EV perl module
		4256	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		4257	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		4258	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		4259	will be compiled. It is pretty complex because it provides its own header
		4260	file.
		4261
		4262	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		4263	that everybody includes and which overrides some configure choices:
		4264
		4265	#define EV_FEATURES 8
		4266	#define EV_USE_SELECT 1
		4267	#define EV_PREPARE_ENABLE 1
		4268	#define EV_IDLE_ENABLE 1
		4269	#define EV_SIGNAL_ENABLE 1
		4270	#define EV_CHILD_ENABLE 1
		4271	#define EV_USE_STDEXCEPT 0
		4272	#define EV_CONFIG_H <config.h>
		4273
		4274	#include "ev++.h"
		4275
		4276	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		4277
		4278	#include "ev_cpp.h"
		4279	#include "ev.c"
		4280
		4281	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		4282
		4283	=head2 THREADS AND COROUTINES
		4284
		4285	=head3 THREADS
		4286
		4287	All libev functions are reentrant and thread-safe unless explicitly
		4288	documented otherwise, but libev implements no locking itself. This means
		4289	that you can use as many loops as you want in parallel, as long as there
		4290	are no concurrent calls into any libev function with the same loop
		4291	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4292	of course): libev guarantees that different event loops share no data
		4293	structures that need any locking.
		4294
		4295	Or to put it differently: calls with different loop parameters can be done
		4296	concurrently from multiple threads, calls with the same loop parameter
		4297	must be done serially (but can be done from different threads, as long as
		4298	only one thread ever is inside a call at any point in time, e.g. by using
		4299	a mutex per loop).
		4300
		4301	Specifically to support threads (and signal handlers), libev implements
		4302	so-called C<ev_async> watchers, which allow some limited form of
		4303	concurrency on the same event loop, namely waking it up "from the
		4304	outside".
		4305
		4306	If you want to know which design (one loop, locking, or multiple loops
		4307	without or something else still) is best for your problem, then I cannot
		4308	help you, but here is some generic advice:
		4309
		4310	=over 4
		4311
		4312	=item * most applications have a main thread: use the default libev loop
		4313	in that thread, or create a separate thread running only the default loop.
		4314
		4315	This helps integrating other libraries or software modules that use libev
		4316	themselves and don't care/know about threading.
		4317
		4318	=item * one loop per thread is usually a good model.
		4319
		4320	Doing this is almost never wrong, sometimes a better-performance model
		4321	exists, but it is always a good start.
		4322
		4323	=item * other models exist, such as the leader/follower pattern, where one
		4324	loop is handed through multiple threads in a kind of round-robin fashion.
		4325
		4326	Choosing a model is hard - look around, learn, know that usually you can do
		4327	better than you currently do :-)
		4328
		4329	=item * often you need to talk to some other thread which blocks in the
		4330	event loop.
		4331
		4332	C<ev_async> watchers can be used to wake them up from other threads safely
		4333	(or from signal contexts...).
		4334
		4335	An example use would be to communicate signals or other events that only
		4336	work in the default loop by registering the signal watcher with the
		4337	default loop and triggering an C<ev_async> watcher from the default loop
		4338	watcher callback into the event loop interested in the signal.
		4339
		4340	=back
		4341
		4342	=head4 THREAD LOCKING EXAMPLE
		4343
		4344	Here is a fictitious example of how to run an event loop in a different
		4345	thread than where callbacks are being invoked and watchers are
		4346	created/added/removed.
		4347
		4348	For a real-world example, see the C<EV::Loop::Async> perl module,
		4349	which uses exactly this technique (which is suited for many high-level
		4350	languages).
		4351
		4352	The example uses a pthread mutex to protect the loop data, a condition
		4353	variable to wait for callback invocations, an async watcher to notify the
		4354	event loop thread and an unspecified mechanism to wake up the main thread.
		4355
		4356	First, you need to associate some data with the event loop:
		4357
		4358	typedef struct {
		4359	mutex_t lock; /* global loop lock */
		4360	ev_async async_w;
		4361	thread_t tid;
		4362	cond_t invoke_cv;
		4363	} userdata;
		4364
		4365	void prepare_loop (EV_P)
		4366	{
		4367	// for simplicity, we use a static userdata struct.
		4368	static userdata u;
		4369
		4370	ev_async_init (&u->async_w, async_cb);
		4371	ev_async_start (EV_A_ &u->async_w);
		4372
		4373	pthread_mutex_init (&u->lock, 0);
		4374	pthread_cond_init (&u->invoke_cv, 0);
		4375
		4376	// now associate this with the loop
		4377	ev_set_userdata (EV_A_ u);
		4378	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4379	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4380
		4381	// then create the thread running ev_loop
		4382	pthread_create (&u->tid, 0, l_run, EV_A);
		4383	}
		4384
		4385	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4386	solely to wake up the event loop so it takes notice of any new watchers
		4387	that might have been added:
		4388
		4389	static void
		4390	async_cb (EV_P_ ev_async *w, int revents)
		4391	{
		4392	// just used for the side effects
		4393	}
		4394
		4395	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4396	protecting the loop data, respectively.
		4397
		4398	static void
		4399	l_release (EV_P)
		4400	{
		4401	userdata *u = ev_userdata (EV_A);
		4402	pthread_mutex_unlock (&u->lock);
		4403	}
		4404
		4405	static void
		4406	l_acquire (EV_P)
		4407	{
		4408	userdata *u = ev_userdata (EV_A);
		4409	pthread_mutex_lock (&u->lock);
		4410	}
		4411
		4412	The event loop thread first acquires the mutex, and then jumps straight
		4413	into C<ev_run>:
		4414
		4415	void *
		4416	l_run (void *thr_arg)
		4417	{
		4418	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4419
		4420	l_acquire (EV_A);
		4421	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4422	ev_run (EV_A_ 0);
		4423	l_release (EV_A);
		4424
		4425	return 0;
		4426	}
		4427
		4428	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4429	signal the main thread via some unspecified mechanism (signals? pipe
		4430	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4431	have been called (in a while loop because a) spurious wakeups are possible
		4432	and b) skipping inter-thread-communication when there are no pending
		4433	watchers is very beneficial):
		4434
		4435	static void
		4436	l_invoke (EV_P)
		4437	{
		4438	userdata *u = ev_userdata (EV_A);
		4439
		4440	while (ev_pending_count (EV_A))
		4441	{
		4442	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4443	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4444	}
		4445	}
		4446
		4447	Now, whenever the main thread gets told to invoke pending watchers, it
		4448	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4449	thread to continue:
		4450
		4451	static void
		4452	real_invoke_pending (EV_P)
		4453	{
		4454	userdata *u = ev_userdata (EV_A);
		4455
		4456	pthread_mutex_lock (&u->lock);
		4457	ev_invoke_pending (EV_A);
		4458	pthread_cond_signal (&u->invoke_cv);
		4459	pthread_mutex_unlock (&u->lock);
		4460	}
		4461
		4462	Whenever you want to start/stop a watcher or do other modifications to an
		4463	event loop, you will now have to lock:
		4464
		4465	ev_timer timeout_watcher;
		4466	userdata *u = ev_userdata (EV_A);
		4467
		4468	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4469
		4470	pthread_mutex_lock (&u->lock);
		4471	ev_timer_start (EV_A_ &timeout_watcher);
		4472	ev_async_send (EV_A_ &u->async_w);
		4473	pthread_mutex_unlock (&u->lock);
		4474
		4475	Note that sending the C<ev_async> watcher is required because otherwise
		4476	an event loop currently blocking in the kernel will have no knowledge
		4477	about the newly added timer. By waking up the loop it will pick up any new
		4478	watchers in the next event loop iteration.
		4479
		4480	=head3 COROUTINES
		4481
		4482	Libev is very accommodating to coroutines ("cooperative threads"):
		4483	libev fully supports nesting calls to its functions from different
		4484	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4485	different coroutines, and switch freely between both coroutines running
		4486	the loop, as long as you don't confuse yourself). The only exception is
		4487	that you must not do this from C<ev_periodic> reschedule callbacks.
		4488
		4489	Care has been taken to ensure that libev does not keep local state inside
		4490	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4491	they do not call any callbacks.
		4492
		4493	=head2 COMPILER WARNINGS
		4494
		4495	Depending on your compiler and compiler settings, you might get no or a
		4496	lot of warnings when compiling libev code. Some people are apparently
		4497	scared by this.
		4498
		4499	However, these are unavoidable for many reasons. For one, each compiler
		4500	has different warnings, and each user has different tastes regarding
		4501	warning options. "Warn-free" code therefore cannot be a goal except when
		4502	targeting a specific compiler and compiler-version.
		4503
		4504	Another reason is that some compiler warnings require elaborate
		4505	workarounds, or other changes to the code that make it less clear and less
		4506	maintainable.
		4507
		4508	And of course, some compiler warnings are just plain stupid, or simply
		4509	wrong (because they don't actually warn about the condition their message
		4510	seems to warn about). For example, certain older gcc versions had some
		4511	warnings that resulted in an extreme number of false positives. These have
		4512	been fixed, but some people still insist on making code warn-free with
		4513	such buggy versions.
		4514
		4515	While libev is written to generate as few warnings as possible,
		4516	"warn-free" code is not a goal, and it is recommended not to build libev
		4517	with any compiler warnings enabled unless you are prepared to cope with
		4518	them (e.g. by ignoring them). Remember that warnings are just that:
		4519	warnings, not errors, or proof of bugs.
		4520
		4521
		4522	=head2 VALGRIND
		4523
		4524	Valgrind has a special section here because it is a popular tool that is
		4525	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4526
		4527	If you think you found a bug (memory leak, uninitialised data access etc.)
		4528	in libev, then check twice: If valgrind reports something like:
		4529
		4530	==2274== definitely lost: 0 bytes in 0 blocks.
		4531	==2274== possibly lost: 0 bytes in 0 blocks.
		4532	==2274== still reachable: 256 bytes in 1 blocks.
		4533
		4534	Then there is no memory leak, just as memory accounted to global variables
		4535	is not a memleak - the memory is still being referenced, and didn't leak.
		4536
		4537	Similarly, under some circumstances, valgrind might report kernel bugs
		4538	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4539	although an acceptable workaround has been found here), or it might be
		4540	confused.
		4541
		4542	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4543	make it into some kind of religion.
		4544
		4545	If you are unsure about something, feel free to contact the mailing list
		4546	with the full valgrind report and an explanation on why you think this
		4547	is a bug in libev (best check the archives, too :). However, don't be
		4548	annoyed when you get a brisk "this is no bug" answer and take the chance
		4549	of learning how to interpret valgrind properly.
		4550
		4551	If you need, for some reason, empty reports from valgrind for your project
		4552	I suggest using suppression lists.
		4553
		4554
		4555	=head1 PORTABILITY NOTES
		4556
		4557	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4558
		4559	GNU/Linux is the only common platform that supports 64 bit file/large file
		4560	interfaces but I<disables> them by default.
		4561
		4562	That means that libev compiled in the default environment doesn't support
		4563	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4564
		4565	Unfortunately, many programs try to work around this GNU/Linux issue
		4566	by enabling the large file API, which makes them incompatible with the
		4567	standard libev compiled for their system.
		4568
		4569	Likewise, libev cannot enable the large file API itself as this would
		4570	suddenly make it incompatible to the default compile time environment,
		4571	i.e. all programs not using special compile switches.
		4572
		4573	=head2 OS/X AND DARWIN BUGS
		4574
		4575	The whole thing is a bug if you ask me - basically any system interface
		4576	you touch is broken, whether it is locales, poll, kqueue or even the
		4577	OpenGL drivers.
		4578
		4579	=head3 C<kqueue> is buggy
		4580
		4581	The kqueue syscall is broken in all known versions - most versions support
		4582	only sockets, many support pipes.
		4583
		4584	Libev tries to work around this by not using C<kqueue> by default on this
		4585	rotten platform, but of course you can still ask for it when creating a
		4586	loop - embedding a socket-only kqueue loop into a select-based one is
		4587	probably going to work well.
		4588
		4589	=head3 C<poll> is buggy
		4590
		4591	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4592	implementation by something calling C<kqueue> internally around the 10.5.6
		4593	release, so now C<kqueue> I<and> C<poll> are broken.
		4594
		4595	Libev tries to work around this by not using C<poll> by default on
		4596	this rotten platform, but of course you can still ask for it when creating
		4597	a loop.
		4598
		4599	=head3 C<select> is buggy
		4600
		4601	All that's left is C<select>, and of course Apple found a way to fuck this
		4602	one up as well: On OS/X, C<select> actively limits the number of file
		4603	descriptors you can pass in to 1024 - your program suddenly crashes when
		4604	you use more.
		4605
		4606	There is an undocumented "workaround" for this - defining
		4607	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4608	work on OS/X.
		4609
		4610	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4611
		4612	=head3 C<errno> reentrancy
		4613
		4614	The default compile environment on Solaris is unfortunately so
		4615	thread-unsafe that you can't even use components/libraries compiled
		4616	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4617	defined by default. A valid, if stupid, implementation choice.
		4618
		4619	If you want to use libev in threaded environments you have to make sure
		4620	it's compiled with C<_REENTRANT> defined.
		4621
		4622	=head3 Event port backend
		4623
		4624	The scalable event interface for Solaris is called "event
		4625	ports". Unfortunately, this mechanism is very buggy in all major
		4626	releases. If you run into high CPU usage, your program freezes or you get
		4627	a large number of spurious wakeups, make sure you have all the relevant
		4628	and latest kernel patches applied. No, I don't know which ones, but there
		4629	are multiple ones to apply, and afterwards, event ports actually work
		4630	great.
		4631
		4632	If you can't get it to work, you can try running the program by setting
		4633	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4634	C<select> backends.
		4635
		4636	=head2 AIX POLL BUG
		4637
		4638	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4639	this by trying to avoid the poll backend altogether (i.e. it's not even
		4640	compiled in), which normally isn't a big problem as C<select> works fine
		4641	with large bitsets on AIX, and AIX is dead anyway.
		4642
		4643	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4644
		4645	=head3 General issues
		4646
		4647	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4648	requires, and its I/O model is fundamentally incompatible with the POSIX
		4649	model. Libev still offers limited functionality on this platform in
		4650	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4651	descriptors. This only applies when using Win32 natively, not when using
		4652	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4653	as every compielr comes with a slightly differently broken/incompatible
		4654	environment.
		4655
		4656	Lifting these limitations would basically require the full
		4657	re-implementation of the I/O system. If you are into this kind of thing,
		4658	then note that glib does exactly that for you in a very portable way (note
		4659	also that glib is the slowest event library known to man).
		4660
		4661	There is no supported compilation method available on windows except
		4662	embedding it into other applications.
		4663
		4664	Sensible signal handling is officially unsupported by Microsoft - libev
		4665	tries its best, but under most conditions, signals will simply not work.
		4666
		4667	Not a libev limitation but worth mentioning: windows apparently doesn't
		4668	accept large writes: instead of resulting in a partial write, windows will
		4669	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4670	so make sure you only write small amounts into your sockets (less than a
		4671	megabyte seems safe, but this apparently depends on the amount of memory
		4672	available).
		4673
		4674	Due to the many, low, and arbitrary limits on the win32 platform and
		4675	the abysmal performance of winsockets, using a large number of sockets
		4676	is not recommended (and not reasonable). If your program needs to use
		4677	more than a hundred or so sockets, then likely it needs to use a totally
		4678	different implementation for windows, as libev offers the POSIX readiness
		4679	notification model, which cannot be implemented efficiently on windows
		4680	(due to Microsoft monopoly games).
		4681
		4682	A typical way to use libev under windows is to embed it (see the embedding
		4683	section for details) and use the following F<evwrap.h> header file instead
		4684	of F<ev.h>:
		4685
		4686	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4687	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4688
		4689	#include "ev.h"
		4690
		4691	And compile the following F<evwrap.c> file into your project (make sure
		4692	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4693
		4694	#include "evwrap.h"
		4695	#include "ev.c"
		4696
		4697	=head3 The winsocket C<select> function
		4698
		4699	The winsocket C<select> function doesn't follow POSIX in that it
		4700	requires socket I<handles> and not socket I<file descriptors> (it is
		4701	also extremely buggy). This makes select very inefficient, and also
		4702	requires a mapping from file descriptors to socket handles (the Microsoft
		4703	C runtime provides the function C<_open_osfhandle> for this). See the
		4704	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4705	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4706
		4707	The configuration for a "naked" win32 using the Microsoft runtime
		4708	libraries and raw winsocket select is:
		4709
		4710	#define EV_USE_SELECT 1
		4711	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4712
		4713	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4714	complexity in the O(n²) range when using win32.
		4715
		4716	=head3 Limited number of file descriptors
		4717
		4718	Windows has numerous arbitrary (and low) limits on things.
		4719
		4720	Early versions of winsocket's select only supported waiting for a maximum
		4721	of C<64> handles (probably owning to the fact that all windows kernels
		4722	can only wait for C<64> things at the same time internally; Microsoft
		4723	recommends spawning a chain of threads and wait for 63 handles and the
		4724	previous thread in each. Sounds great!).
		4725
		4726	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4727	to some high number (e.g. C<2048>) before compiling the winsocket select
		4728	call (which might be in libev or elsewhere, for example, perl and many
		4729	other interpreters do their own select emulation on windows).
		4730
		4731	Another limit is the number of file descriptors in the Microsoft runtime
		4732	libraries, which by default is C<64> (there must be a hidden I<64>
		4733	fetish or something like this inside Microsoft). You can increase this
		4734	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4735	(another arbitrary limit), but is broken in many versions of the Microsoft
		4736	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4737	(depending on windows version and/or the phase of the moon). To get more,
		4738	you need to wrap all I/O functions and provide your own fd management, but
		4739	the cost of calling select (O(n²)) will likely make this unworkable.
		4740
		4741	=head2 PORTABILITY REQUIREMENTS
		4742
		4743	In addition to a working ISO-C implementation and of course the
		4744	backend-specific APIs, libev relies on a few additional extensions:
		4745
		4746	=over 4
		4747
		4748	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4749	calling conventions regardless of C<ev_watcher_type *>.
		4750
		4751	Libev assumes not only that all watcher pointers have the same internal
		4752	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4753	assumes that the same (machine) code can be used to call any watcher
		4754	callback: The watcher callbacks have different type signatures, but libev
		4755	calls them using an C<ev_watcher *> internally.
		4756
		4757	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4758
		4759	The type C<sig_atomic_t volatile> (or whatever is defined as
		4760	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4761	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4762	believed to be sufficiently portable.
		4763
		4764	=item C<sigprocmask> must work in a threaded environment
		4765
		4766	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4767	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4768	pthread implementations will either allow C<sigprocmask> in the "main
		4769	thread" or will block signals process-wide, both behaviours would
		4770	be compatible with libev. Interaction between C<sigprocmask> and
		4771	C<pthread_sigmask> could complicate things, however.
		4772
		4773	The most portable way to handle signals is to block signals in all threads
		4774	except the initial one, and run the default loop in the initial thread as
		4775	well.
		4776
		4777	=item C<long> must be large enough for common memory allocation sizes
		4778
		4779	To improve portability and simplify its API, libev uses C<long> internally
		4780	instead of C<size_t> when allocating its data structures. On non-POSIX
		4781	systems (Microsoft...) this might be unexpectedly low, but is still at
		4782	least 31 bits everywhere, which is enough for hundreds of millions of
		4783	watchers.
		4784
		4785	=item C<double> must hold a time value in seconds with enough accuracy
		4786
		4787	The type C<double> is used to represent timestamps. It is required to
		4788	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4789	good enough for at least into the year 4000 with millisecond accuracy
		4790	(the design goal for libev). This requirement is overfulfilled by
		4791	implementations using IEEE 754, which is basically all existing ones. With
		4792	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4793
		4794	=back
		4795
		4796	If you know of other additional requirements drop me a note.
		4797
		4798
		4799	=head1 ALGORITHMIC COMPLEXITIES
		4800
		4801	In this section the complexities of (many of) the algorithms used inside
		4802	libev will be documented. For complexity discussions about backends see
		4803	the documentation for C<ev_default_init>.
		4804
		4805	All of the following are about amortised time: If an array needs to be
		4806	extended, libev needs to realloc and move the whole array, but this
		4807	happens asymptotically rarer with higher number of elements, so O(1) might
		4808	mean that libev does a lengthy realloc operation in rare cases, but on
		4809	average it is much faster and asymptotically approaches constant time.
		4810
		4811	=over 4
		4812
		4813	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4814
		4815	This means that, when you have a watcher that triggers in one hour and
		4816	there are 100 watchers that would trigger before that, then inserting will
		4817	have to skip roughly seven (C<ld 100>) of these watchers.
		4818
		4819	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4820
		4821	That means that changing a timer costs less than removing/adding them,
		4822	as only the relative motion in the event queue has to be paid for.
		4823
		4824	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4825
		4826	These just add the watcher into an array or at the head of a list.
		4827
		4828	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4829
		4830	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4831
		4832	These watchers are stored in lists, so they need to be walked to find the
		4833	correct watcher to remove. The lists are usually short (you don't usually
		4834	have many watchers waiting for the same fd or signal: one is typical, two
		4835	is rare).
		4836
		4837	=item Finding the next timer in each loop iteration: O(1)
		4838
		4839	By virtue of using a binary or 4-heap, the next timer is always found at a
		4840	fixed position in the storage array.
		4841
		4842	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4843
		4844	A change means an I/O watcher gets started or stopped, which requires
		4845	libev to recalculate its status (and possibly tell the kernel, depending
		4846	on backend and whether C<ev_io_set> was used).
		4847
		4848	=item Activating one watcher (putting it into the pending state): O(1)
		4849
		4850	=item Priority handling: O(number_of_priorities)
		4851
		4852	Priorities are implemented by allocating some space for each
		4853	priority. When doing priority-based operations, libev usually has to
		4854	linearly search all the priorities, but starting/stopping and activating
		4855	watchers becomes O(1) with respect to priority handling.
		4856
		4857	=item Sending an ev_async: O(1)
		4858
		4859	=item Processing ev_async_send: O(number_of_async_watchers)
		4860
		4861	=item Processing signals: O(max_signal_number)
		4862
		4863	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4864	calls in the current loop iteration. Checking for async and signal events
		4865	involves iterating over all running async watchers or all signal numbers.
		4866
		4867	=back
		4868
		4869
		4870	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4871
		4872	The major version 4 introduced some minor incompatible changes to the API.
		4873
		4874	At the moment, the C<ev.h> header file tries to implement superficial
		4875	compatibility, so most programs should still compile. Those might be
		4876	removed in later versions of libev, so better update early than late.
		4877
		4878	=over 4
		4879
		4880	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		4881
		4882	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		4883
		4884	ev_loop_destroy (EV_DEFAULT_UC);
		4885	ev_loop_fork (EV_DEFAULT);
		4886
		4887	=item function/symbol renames
		4888
		4889	A number of functions and symbols have been renamed:
		4890
		4891	ev_loop => ev_run
		4892	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4893	EVLOOP_ONESHOT => EVRUN_ONCE
		4894
		4895	ev_unloop => ev_break
		4896	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4897	EVUNLOOP_ONE => EVBREAK_ONE
		4898	EVUNLOOP_ALL => EVBREAK_ALL
		4899
		4900	EV_TIMEOUT => EV_TIMER
		4901
		4902	ev_loop_count => ev_iteration
		4903	ev_loop_depth => ev_depth
		4904	ev_loop_verify => ev_verify
		4905
		4906	Most functions working on C<struct ev_loop> objects don't have an
		4907	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4908	associated constants have been renamed to not collide with the C<struct
		4909	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4910	as all other watcher types. Note that C<ev_loop_fork> is still called
		4911	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4912	typedef.
		4913
		4914	=item C<EV_COMPAT3> backwards compatibility mechanism
		4915
		4916	The backward compatibility mechanism can be controlled by
		4917	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4918	section.
		4919
		4920	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4921
		4922	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4923	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4924	and work, but the library code will of course be larger.
		4925
		4926	=back
		4927
		4928
		4929	=head1 GLOSSARY
		4930
		4931	=over 4
		4932
		4933	=item active
		4934
		4935	A watcher is active as long as it has been started and not yet stopped.
		4936	See L<WATCHER STATES> for details.
		4937
		4938	=item application
		4939
		4940	In this document, an application is whatever is using libev.
		4941
		4942	=item backend
		4943
		4944	The part of the code dealing with the operating system interfaces.
		4945
		4946	=item callback
		4947
		4948	The address of a function that is called when some event has been
		4949	detected. Callbacks are being passed the event loop, the watcher that
		4950	received the event, and the actual event bitset.
		4951
		4952	=item callback/watcher invocation
		4953
		4954	The act of calling the callback associated with a watcher.
		4955
		4956	=item event
		4957
		4958	A change of state of some external event, such as data now being available
		4959	for reading on a file descriptor, time having passed or simply not having
		4960	any other events happening anymore.
		4961
		4962	In libev, events are represented as single bits (such as C<EV_READ> or
		4963	C<EV_TIMER>).
		4964
		4965	=item event library
		4966
		4967	A software package implementing an event model and loop.
		4968
		4969	=item event loop
		4970
		4971	An entity that handles and processes external events and converts them
		4972	into callback invocations.
		4973
		4974	=item event model
		4975
		4976	The model used to describe how an event loop handles and processes
		4977	watchers and events.
		4978
		4979	=item pending
		4980
		4981	A watcher is pending as soon as the corresponding event has been
		4982	detected. See L<WATCHER STATES> for details.
		4983
		4984	=item real time
		4985
		4986	The physical time that is observed. It is apparently strictly monotonic :)
		4987
		4988	=item wall-clock time
		4989
		4990	The time and date as shown on clocks. Unlike real time, it can actually
		4991	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4992	clock.
		4993
		4994	=item watcher
		4995
		4996	A data structure that describes interest in certain events. Watchers need
		4997	to be started (attached to an event loop) before they can receive events.
		4998
		4999	=back
1217		5000
1218	=head1 AUTHOR	5001	=head1 AUTHOR
1219		5002
1220	Marc Lehmann <libev@schmorp.de>.	5003	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
1221		5004

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