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Revision 1.54 by root, Tue Nov 27 20:26:51 2007 UTC vs.
Revision 1.316 by root, Fri Oct 22 09:34:01 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 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	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);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_run to stop iterating
		41	ev_break (EV_A_ EVBREAK_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_run (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	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
52		84
53	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
54	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
55	these event sources and provide your program with events.	87	these event sources and provide your program with events.
56		88
57	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
58	(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
59	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
61	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
62	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
63	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
64	watcher.	96	watcher.
65		97
66	=head1 FEATURES	98	=head2 FEATURES
67		99
68	Libev supports C<select>, C<poll>, the linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
69	bsd-specific C<kqueue> and the solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
70	for file descriptor events (C<ev_io>), relative timers (C<ev_timer>),	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
71	absolute timers with customised rescheduling (C<ev_periodic>), synchronous	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
72	signals (C<ev_signal>), process status change events (C<ev_child>), and	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
73	event watchers dealing with the event loop mechanism itself (C<ev_idle>,	105	timers (C<ev_timer>), absolute timers with customised rescheduling
74	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
75	file watchers (C<ev_stat>) and even limited support for fork events	107	change events (C<ev_child>), and event watchers dealing with the event
76	(C<ev_fork>).	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>).
77		111
78	It also is quite fast (see this	112	It also is quite fast (see this
79	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
80	for example).	114	for example).
81		115
82	=head1 CONVENTIONS	116	=head2 CONVENTIONS
83		117
84	Libev is very configurable. In this manual the default configuration will	118	Libev is very configurable. In this manual the default (and most common)
85	be described, which supports multiple event loops. For more info about	119	configuration will be described, which supports multiple event loops. For
86	various configuration options please have a look at B<EMBED> section in	120	more info about various configuration options please have a look at
87	this manual. If libev was configured without support for multiple event	121	B<EMBED> section in this manual. If libev was configured without support
88	loops, then all functions taking an initial argument of name C<loop>	122	for multiple event loops, then all functions taking an initial argument of
89	(which is always of type C<struct ev_loop *>) will not have this argument.	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		124	this argument.
90		125
91	=head1 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
92		127
93	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
94	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (in practise
95	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
96	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
97	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
98	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.
		157
99		158
100	=head1 GLOBAL FUNCTIONS	159	=head1 GLOBAL FUNCTIONS
101		160
102	These functions can be called anytime, even before initialising the	161	These functions can be called anytime, even before initialising the
103	library in any way.	162	library in any way.
…		…
108		167
109	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
110	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
111	you actually want to know.	170	you actually want to know.
112		171
		172	=item ev_sleep (ev_tstamp interval)
		173
		174	Sleep for the given interval: The current thread will be blocked until
		175	either it is interrupted or the given time interval has passed. Basically
		176	this is a sub-second-resolution C<sleep ()>.
		177
113	=item int ev_version_major ()	178	=item int ev_version_major ()
114		179
115	=item int ev_version_minor ()	180	=item int ev_version_minor ()
116		181
117	You can find out the major and minor version numbers of the library	182	You can find out the major and minor ABI version numbers of the library
118	you linked against by calling the functions C<ev_version_major> and	183	you linked against by calling the functions C<ev_version_major> and
119	C<ev_version_minor>. If you want, you can compare against the global	184	C<ev_version_minor>. If you want, you can compare against the global
120	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	185	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
121	version of the library your program was compiled against.	186	version of the library your program was compiled against.
122		187
		188	These version numbers refer to the ABI version of the library, not the
		189	release version.
		190
123	Usually, it's a good idea to terminate if the major versions mismatch,	191	Usually, it's a good idea to terminate if the major versions mismatch,
124	as this indicates an incompatible change. Minor versions are usually	192	as this indicates an incompatible change. Minor versions are usually
125	compatible to older versions, so a larger minor version alone is usually	193	compatible to older versions, so a larger minor version alone is usually
126	not a problem.	194	not a problem.
127		195
128	Example: Make sure we haven't accidentally been linked against the wrong	196	Example: Make sure we haven't accidentally been linked against the wrong
129	version.	197	version (note, however, that this will not detect ABI mismatches :).
130		198
131	assert (("libev version mismatch",	199	assert (("libev version mismatch",
132	ev_version_major () == EV_VERSION_MAJOR	200	ev_version_major () == EV_VERSION_MAJOR
133	&& ev_version_minor () >= EV_VERSION_MINOR));	201	&& ev_version_minor () >= EV_VERSION_MINOR));
134		202
135	=item unsigned int ev_supported_backends ()	203	=item unsigned int ev_supported_backends ()
136		204
137	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	205	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
138	value) compiled into this binary of libev (independent of their	206	value) compiled into this binary of libev (independent of their
…		…
140	a description of the set values.	208	a description of the set values.
141		209
142	Example: make sure we have the epoll method, because yeah this is cool and	210	Example: make sure we have the epoll method, because yeah this is cool and
143	a must have and can we have a torrent of it please!!!11	211	a must have and can we have a torrent of it please!!!11
144		212
145	assert (("sorry, no epoll, no sex",	213	assert (("sorry, no epoll, no sex",
146	ev_supported_backends () & EVBACKEND_EPOLL));	214	ev_supported_backends () & EVBACKEND_EPOLL));
147		215
148	=item unsigned int ev_recommended_backends ()	216	=item unsigned int ev_recommended_backends ()
149		217
150	Return the set of all backends compiled into this binary of libev and also	218	Return the set of all backends compiled into this binary of libev and also
151	recommended for this platform. This set is often smaller than the one	219	recommended for this platform. This set is often smaller than the one
152	returned by C<ev_supported_backends>, as for example kqueue is broken on	220	returned by C<ev_supported_backends>, as for example kqueue is broken on
153	most BSDs and will not be autodetected unless you explicitly request it	221	most BSDs and will not be auto-detected unless you explicitly request it
154	(assuming you know what you are doing). This is the set of backends that	222	(assuming you know what you are doing). This is the set of backends that
155	libev will probe for if you specify no backends explicitly.	223	libev will probe for if you specify no backends explicitly.
156		224
157	=item unsigned int ev_embeddable_backends ()	225	=item unsigned int ev_embeddable_backends ()
158		226
…		…
162	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
163	recommended ones.	231	recommended ones.
164		232
165	See the description of C<ev_embed> watchers for more info.	233	See the description of C<ev_embed> watchers for more info.
166		234
167	=item ev_set_allocator (void *(*cb)(void *ptr, size_t size))	235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
168		236
169	Sets the allocation function to use (the prototype and semantics are	237	Sets the allocation function to use (the prototype is similar - the
170	identical to the realloc C function). It is used to allocate and free	238	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
171	memory (no surprises here). If it returns zero when memory needs to be	239	used to allocate and free memory (no surprises here). If it returns zero
172	allocated, the library might abort or take some potentially destructive	240	when memory needs to be allocated (C<size != 0>), the library might abort
173	action. The default is your system realloc function.	241	or take some potentially destructive action.
		242
		243	Since some systems (at least OpenBSD and Darwin) fail to implement
		244	correct C<realloc> semantics, libev will use a wrapper around the system
		245	C<realloc> and C<free> functions by default.
174		246
175	You could override this function in high-availability programs to, say,	247	You could override this function in high-availability programs to, say,
176	free some memory if it cannot allocate memory, to use a special allocator,	248	free some memory if it cannot allocate memory, to use a special allocator,
177	or even to sleep a while and retry until some memory is available.	249	or even to sleep a while and retry until some memory is available.
178		250
179	Example: Replace the libev allocator with one that waits a bit and then	251	Example: Replace the libev allocator with one that waits a bit and then
180	retries).	252	retries (example requires a standards-compliant C<realloc>).
181		253
182	static void *	254	static void *
183	persistent_realloc (void *ptr, size_t size)	255	persistent_realloc (void *ptr, size_t size)
184	{	256	{
185	for (;;)	257	for (;;)
…		…
194	}	266	}
195		267
196	...	268	...
197	ev_set_allocator (persistent_realloc);	269	ev_set_allocator (persistent_realloc);
198		270
199	=item ev_set_syserr_cb (void (*cb)(const char *msg));	271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
200		272
201	Set the callback function to call on a retryable syscall error (such	273	Set the callback function to call on a retryable system call error (such
202	as failed select, poll, epoll_wait). The message is a printable string	274	as failed select, poll, epoll_wait). The message is a printable string
203	indicating the system call or subsystem causing the problem. If this	275	indicating the system call or subsystem causing the problem. If this
204	callback is set, then libev will expect it to remedy the sitution, no	276	callback is set, then libev will expect it to remedy the situation, no
205	matter what, when it returns. That is, libev will generally retry the	277	matter what, when it returns. That is, libev will generally retry the
206	requested operation, or, if the condition doesn't go away, do bad stuff	278	requested operation, or, if the condition doesn't go away, do bad stuff
207	(such as abort).	279	(such as abort).
208		280
209	Example: This is basically the same thing that libev does internally, too.	281	Example: This is basically the same thing that libev does internally, too.
…		…
220		292
221	=back	293	=back
222		294
223	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
224		296
225	An event loop is described by a C<struct ev_loop *>. The library knows two	297	An event loop is described by a C<struct ev_loop *> (the C<struct> is
226	types of such loops, the I<default> loop, which supports signals and child	298	I<not> optional in this case unless libev 3 compatibility is disabled, as
227	events, and dynamically created loops which do not.	299	libev 3 had an C<ev_loop> function colliding with the struct name).
228		300
229	If you use threads, a common model is to run the default event loop	301	The library knows two types of such loops, the I<default> loop, which
230	in your main thread (or in a separate thread) and for each thread you	302	supports signals and child events, and dynamically created event loops
231	create, you also create another event loop. Libev itself does no locking	303	which do not.
232	whatsoever, so if you mix calls to the same event loop in different
233	threads, make sure you lock (this is usually a bad idea, though, even if
234	done correctly, because it's hideous and inefficient).
235		304
236	=over 4	305	=over 4
237		306
238	=item struct ev_loop *ev_default_loop (unsigned int flags)	307	=item struct ev_loop *ev_default_loop (unsigned int flags)
239		308
…		…
243	flags. If that is troubling you, check C<ev_backend ()> afterwards).	312	flags. If that is troubling you, check C<ev_backend ()> afterwards).
244		313
245	If you don't know what event loop to use, use the one returned from this	314	If you don't know what event loop to use, use the one returned from this
246	function.	315	function.
247		316
		317	Note that this function is I<not> thread-safe, so if you want to use it
		318	from multiple threads, you have to lock (note also that this is unlikely,
		319	as loops cannot be shared easily between threads anyway).
		320
		321	The default loop is the only loop that can handle C<ev_signal> and
		322	C<ev_child> watchers, and to do this, it always registers a handler
		323	for C<SIGCHLD>. If this is a problem for your application you can either
		324	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		325	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		326	C<ev_default_init>.
		327
248	The flags argument can be used to specify special behaviour or specific	328	The flags argument can be used to specify special behaviour or specific
249	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	329	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
250		330
251	The following flags are supported:	331	The following flags are supported:
252		332
…		…
257	The default flags value. Use this if you have no clue (it's the right	337	The default flags value. Use this if you have no clue (it's the right
258	thing, believe me).	338	thing, believe me).
259		339
260	=item C<EVFLAG_NOENV>	340	=item C<EVFLAG_NOENV>
261		341
262	If this flag bit is ored into the flag value (or the program runs setuid	342	If this flag bit is or'ed into the flag value (or the program runs setuid
263	or setgid) then libev will I<not> look at the environment variable	343	or setgid) then libev will I<not> look at the environment variable
264	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	344	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
265	override the flags completely if it is found in the environment. This is	345	override the flags completely if it is found in the environment. This is
266	useful to try out specific backends to test their performance, or to work	346	useful to try out specific backends to test their performance, or to work
267	around bugs.	347	around bugs.
268		348
		349	=item C<EVFLAG_FORKCHECK>
		350
		351	Instead of calling C<ev_loop_fork> manually after a fork, you can also
		352	make libev check for a fork in each iteration by enabling this flag.
		353
		354	This works by calling C<getpid ()> on every iteration of the loop,
		355	and thus this might slow down your event loop if you do a lot of loop
		356	iterations and little real work, but is usually not noticeable (on my
		357	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		358	without a system call and thus I<very> fast, but my GNU/Linux system also has
		359	C<pthread_atfork> which is even faster).
		360
		361	The big advantage of this flag is that you can forget about fork (and
		362	forget about forgetting to tell libev about forking) when you use this
		363	flag.
		364
		365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		366	environment variable.
		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_SIGNALFD>
		376
		377	When this flag is specified, then libev will attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		379	delivers signals synchronously, which makes it both faster and might make
		380	it possible to get the queued signal data. It can also simplify signal
		381	handling with threads, as long as you properly block signals in your
		382	threads that are not interested in handling them.
		383
		384	Signalfd will not be used by default as this changes your signal mask, and
		385	there are a lot of shoddy libraries and programs (glib's threadpool for
		386	example) that can't properly initialise their signal masks.
		387
269	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
270		389
271	This is your standard select(2) backend. Not I<completely> standard, as	390	This is your standard select(2) backend. Not I<completely> standard, as
272	libev tries to roll its own fd_set with no limits on the number of fds,	391	libev tries to roll its own fd_set with no limits on the number of fds,
273	but if that fails, expect a fairly low limit on the number of fds when	392	but if that fails, expect a fairly low limit on the number of fds when
274	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	393	using this backend. It doesn't scale too well (O(highest_fd)), but its
275	the fastest backend for a low number of fds.	394	usually the fastest backend for a low number of (low-numbered :) fds.
		395
		396	To get good performance out of this backend you need a high amount of
		397	parallelism (most of the file descriptors should be busy). If you are
		398	writing a server, you should C<accept ()> in a loop to accept as many
		399	connections as possible during one iteration. You might also want to have
		400	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		401	readiness notifications you get per iteration.
		402
		403	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		404	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		405	C<exceptfds> set on that platform).
276		406
277	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	407	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
278		408
279	And this is your standard poll(2) backend. It's more complicated than	409	And this is your standard poll(2) backend. It's more complicated
280	select, but handles sparse fds better and has no artificial limit on the	410	than select, but handles sparse fds better and has no artificial
281	number of fds you can use (except it will slow down considerably with a	411	limit on the number of fds you can use (except it will slow down
282	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	412	considerably with a lot of inactive fds). It scales similarly to select,
		413	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		414	performance tips.
		415
		416	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		417	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
283		418
284	=item C<EVBACKEND_EPOLL> (value 4, Linux)	419	=item C<EVBACKEND_EPOLL> (value 4, Linux)
285		420
		421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		422	kernels).
		423
286	For few fds, this backend is a bit little slower than poll and select,	424	For few fds, this backend is a bit little slower than poll and select,
287	but it scales phenomenally better. While poll and select usually scale like	425	but it scales phenomenally better. While poll and select usually scale
288	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	426	like O(total_fds) where n is the total number of fds (or the highest fd),
289	either O(1) or O(active_fds).	427	epoll scales either O(1) or O(active_fds).
290		428
		429	The epoll mechanism deserves honorable mention as the most misdesigned
		430	of the more advanced event mechanisms: mere annoyances include silently
		431	dropping file descriptors, requiring a system call per change per file
		432	descriptor (and unnecessary guessing of parameters), problems with dup and
		433	so on. The biggest issue is fork races, however - if a program forks then
		434	I<both> parent and child process have to recreate the epoll set, which can
		435	take considerable time (one syscall per file descriptor) and is of course
		436	hard to detect.
		437
		438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		439	of course I<doesn't>, and epoll just loves to report events for totally
		440	I<different> file descriptors (even already closed ones, so one cannot
		441	even remove them from the set) than registered in the set (especially
		442	on SMP systems). Libev tries to counter these spurious notifications by
		443	employing an additional generation counter and comparing that against the
		444	events to filter out spurious ones, recreating the set when required. Last
		445	not least, it also refuses to work with some file descriptors which work
		446	perfectly fine with C<select> (files, many character devices...).
		447
291	While stopping and starting an I/O watcher in the same iteration will	448	While stopping, setting and starting an I/O watcher in the same iteration
292	result in some caching, there is still a syscall per such incident	449	will result in some caching, there is still a system call per such
293	(because the fd could point to a different file description now), so its	450	incident (because the same I<file descriptor> could point to a different
294	best to avoid that. Also, dup()ed file descriptors might not work very	451	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
295	well if you register events for both fds.	452	file descriptors might not work very well if you register events for both
		453	file descriptors.
296		454
297	Please note that epoll sometimes generates spurious notifications, so you	455	Best performance from this backend is achieved by not unregistering all
298	need to use non-blocking I/O or other means to avoid blocking when no data	456	watchers for a file descriptor until it has been closed, if possible,
299	(or space) is available.	457	i.e. keep at least one watcher active per fd at all times. Stopping and
		458	starting a watcher (without re-setting it) also usually doesn't cause
		459	extra overhead. A fork can both result in spurious notifications as well
		460	as in libev having to destroy and recreate the epoll object, which can
		461	take considerable time and thus should be avoided.
		462
		463	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		464	faster than epoll for maybe up to a hundred file descriptors, depending on
		465	the usage. So sad.
		466
		467	While nominally embeddable in other event loops, this feature is broken in
		468	all kernel versions tested so far.
		469
		470	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		471	C<EVBACKEND_POLL>.
300		472
301	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	473	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
302		474
303	Kqueue deserves special mention, as at the time of this writing, it	475	Kqueue deserves special mention, as at the time of this writing, it
304	was broken on all BSDs except NetBSD (usually it doesn't work with	476	was broken on all BSDs except NetBSD (usually it doesn't work reliably
305	anything but sockets and pipes, except on Darwin, where of course its	477	with anything but sockets and pipes, except on Darwin, where of course
306	completely useless). For this reason its not being "autodetected"	478	it's completely useless). Unlike epoll, however, whose brokenness
		479	is by design, these kqueue bugs can (and eventually will) be fixed
		480	without API changes to existing programs. For this reason it's not being
307	unless you explicitly specify it explicitly in the flags (i.e. using	481	"auto-detected" unless you explicitly specify it in the flags (i.e. using
308	C<EVBACKEND_KQUEUE>).	482	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		483	system like NetBSD.
		484
		485	You still can embed kqueue into a normal poll or select backend and use it
		486	only for sockets (after having made sure that sockets work with kqueue on
		487	the target platform). See C<ev_embed> watchers for more info.
309		488
310	It scales in the same way as the epoll backend, but the interface to the	489	It scales in the same way as the epoll backend, but the interface to the
311	kernel is more efficient (which says nothing about its actual speed, of	490	kernel is more efficient (which says nothing about its actual speed, of
312	course). While starting and stopping an I/O watcher does not cause an	491	course). While stopping, setting and starting an I/O watcher does never
313	extra syscall as with epoll, it still adds up to four event changes per	492	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
314	incident, so its best to avoid that.	493	two event changes per incident. Support for C<fork ()> is very bad (but
		494	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		495	cases
		496
		497	This backend usually performs well under most conditions.
		498
		499	While nominally embeddable in other event loops, this doesn't work
		500	everywhere, so you might need to test for this. And since it is broken
		501	almost everywhere, you should only use it when you have a lot of sockets
		502	(for which it usually works), by embedding it into another event loop
		503	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		504	also broken on OS X)) and, did I mention it, using it only for sockets.
		505
		506	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		507	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		508	C<NOTE_EOF>.
315		509
316	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	510	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
317		511
318	This is not implemented yet (and might never be).	512	This is not implemented yet (and might never be, unless you send me an
		513	implementation). According to reports, C</dev/poll> only supports sockets
		514	and is not embeddable, which would limit the usefulness of this backend
		515	immensely.
319		516
320	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	517	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
321		518
322	This uses the Solaris 10 port mechanism. As with everything on Solaris,	519	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
323	it's really slow, but it still scales very well (O(active_fds)).	520	it's really slow, but it still scales very well (O(active_fds)).
324		521
325	Please note that solaris ports can result in a lot of spurious	522	Please note that Solaris event ports can deliver a lot of spurious
326	notifications, so you need to use non-blocking I/O or other means to avoid	523	notifications, so you need to use non-blocking I/O or other means to avoid
327	blocking when no data (or space) is available.	524	blocking when no data (or space) is available.
		525
		526	While this backend scales well, it requires one system call per active
		527	file descriptor per loop iteration. For small and medium numbers of file
		528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		529	might perform better.
		530
		531	On the positive side, with the exception of the spurious readiness
		532	notifications, this backend actually performed fully to specification
		533	in all tests and is fully embeddable, which is a rare feat among the
		534	OS-specific backends (I vastly prefer correctness over speed hacks).
		535
		536	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		537	C<EVBACKEND_POLL>.
328		538
329	=item C<EVBACKEND_ALL>	539	=item C<EVBACKEND_ALL>
330		540
331	Try all backends (even potentially broken ones that wouldn't be tried	541	Try all backends (even potentially broken ones that wouldn't be tried
332	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	542	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
333	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	543	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
334		544
		545	It is definitely not recommended to use this flag.
		546
335	=back	547	=back
336		548
337	If one or more of these are ored into the flags value, then only these	549	If one or more of the backend flags are or'ed into the flags value,
338	backends will be tried (in the reverse order as given here). If none are	550	then only these backends will be tried (in the reverse order as listed
339	specified, most compiled-in backend will be tried, usually in reverse	551	here). If none are specified, all backends in C<ev_recommended_backends
340	order of their flag values :)	552	()> will be tried.
341		553
342	The most typical usage is like this:	554	Example: This is the most typical usage.
343		555
344	if (!ev_default_loop (0))	556	if (!ev_default_loop (0))
345	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	557	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
346		558
347	Restrict libev to the select and poll backends, and do not allow	559	Example: Restrict libev to the select and poll backends, and do not allow
348	environment settings to be taken into account:	560	environment settings to be taken into account:
349		561
350	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	562	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
351		563
352	Use whatever libev has to offer, but make sure that kqueue is used if	564	Example: Use whatever libev has to offer, but make sure that kqueue is
353	available (warning, breaks stuff, best use only with your own private	565	used if available (warning, breaks stuff, best use only with your own
354	event loop and only if you know the OS supports your types of fds):	566	private event loop and only if you know the OS supports your types of
		567	fds):
355		568
356	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	569	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
357		570
358	=item struct ev_loop *ev_loop_new (unsigned int flags)	571	=item struct ev_loop *ev_loop_new (unsigned int flags)
359		572
360	Similar to C<ev_default_loop>, but always creates a new event loop that is	573	Similar to C<ev_default_loop>, but always creates a new event loop that is
361	always distinct from the default loop. Unlike the default loop, it cannot	574	always distinct from the default loop.
362	handle signal and child watchers, and attempts to do so will be greeted by	575
363	undefined behaviour (or a failed assertion if assertions are enabled).	576	Note that this function I<is> thread-safe, and one common way to use
		577	libev with threads is indeed to create one loop per thread, and using the
		578	default loop in the "main" or "initial" thread.
364		579
365	Example: Try to create a event loop that uses epoll and nothing else.	580	Example: Try to create a event loop that uses epoll and nothing else.
366		581
367	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
368	if (!epoller)	583	if (!epoller)
369	fatal ("no epoll found here, maybe it hides under your chair");	584	fatal ("no epoll found here, maybe it hides under your chair");
370		585
371	=item ev_default_destroy ()	586	=item ev_default_destroy ()
372		587
373	Destroys the default loop again (frees all memory and kernel state	588	Destroys the default loop (frees all memory and kernel state etc.). None
374	etc.). None of the active event watchers will be stopped in the normal	589	of the active event watchers will be stopped in the normal sense, so
375	sense, so e.g. C<ev_is_active> might still return true. It is your	590	e.g. C<ev_is_active> might still return true. It is your responsibility to
376	responsibility to either stop all watchers cleanly yoursef I<before>	591	either stop all watchers cleanly yourself I<before> calling this function,
377	calling this function, or cope with the fact afterwards (which is usually	592	or cope with the fact afterwards (which is usually the easiest thing, you
378	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	593	can just ignore the watchers and/or C<free ()> them for example).
379	for example).	594
		595	Note that certain global state, such as signal state (and installed signal
		596	handlers), will not be freed by this function, and related watchers (such
		597	as signal and child watchers) would need to be stopped manually.
		598
		599	In general it is not advisable to call this function except in the
		600	rare occasion where you really need to free e.g. the signal handling
		601	pipe fds. If you need dynamically allocated loops it is better to use
		602	C<ev_loop_new> and C<ev_loop_destroy>.
380		603
381	=item ev_loop_destroy (loop)	604	=item ev_loop_destroy (loop)
382		605
383	Like C<ev_default_destroy>, but destroys an event loop created by an	606	Like C<ev_default_destroy>, but destroys an event loop created by an
384	earlier call to C<ev_loop_new>.	607	earlier call to C<ev_loop_new>.
385		608
386	=item ev_default_fork ()	609	=item ev_default_fork ()
387		610
		611	This function sets a flag that causes subsequent C<ev_run> iterations
388	This function reinitialises the kernel state for backends that have	612	to reinitialise the kernel state for backends that have one. Despite the
389	one. Despite the name, you can call it anytime, but it makes most sense	613	name, you can call it anytime, but it makes most sense after forking, in
390	after forking, in either the parent or child process (or both, but that	614	the child process (or both child and parent, but that again makes little
391	again makes little sense).	615	sense). You I<must> call it in the child before using any of the libev
		616	functions, and it will only take effect at the next C<ev_run> iteration.
392		617
393	You I<must> call this function in the child process after forking if and	618	Again, you I<have> to call it on I<any> loop that you want to re-use after
394	only if you want to use the event library in both processes. If you just	619	a fork, I<even if you do not plan to use the loop in the parent>. This is
395	fork+exec, you don't have to call it.	620	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		621	during fork.
		622
		623	On the other hand, you only need to call this function in the child
		624	process if and only if you want to use the event loop in the child. If
		625	you just fork+exec or create a new loop in the child, you don't have to
		626	call it at all (in fact, C<epoll> is so badly broken that it makes a
		627	difference, but libev will usually detect this case on its own and do a
		628	costly reset of the backend).
396		629
397	The function itself is quite fast and it's usually not a problem to call	630	The function itself is quite fast and it's usually not a problem to call
398	it just in case after a fork. To make this easy, the function will fit in	631	it just in case after a fork. To make this easy, the function will fit in
399	quite nicely into a call to C<pthread_atfork>:	632	quite nicely into a call to C<pthread_atfork>:
400		633
401	pthread_atfork (0, 0, ev_default_fork);	634	pthread_atfork (0, 0, ev_default_fork);
402		635
403	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
404	without calling this function, so if you force one of those backends you
405	do not need to care.
406
407	=item ev_loop_fork (loop)	636	=item ev_loop_fork (loop)
408		637
409	Like C<ev_default_fork>, but acts on an event loop created by	638	Like C<ev_default_fork>, but acts on an event loop created by
410	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	639	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
411	after fork, and how you do this is entirely your own problem.	640	after fork that you want to re-use in the child, and how you keep track of
		641	them is entirely your own problem.
		642
		643	=item int ev_is_default_loop (loop)
		644
		645	Returns true when the given loop is, in fact, the default loop, and false
		646	otherwise.
		647
		648	=item unsigned int ev_iteration (loop)
		649
		650	Returns the current iteration count for the event loop, which is identical
		651	to the number of times libev did poll for new events. It starts at C<0>
		652	and happily wraps around with enough iterations.
		653
		654	This value can sometimes be useful as a generation counter of sorts (it
		655	"ticks" the number of loop iterations), as it roughly corresponds with
		656	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		657	prepare and check phases.
		658
		659	=item unsigned int ev_depth (loop)
		660
		661	Returns the number of times C<ev_run> was entered minus the number of
		662	times C<ev_run> was exited, in other words, the recursion depth.
		663
		664	Outside C<ev_run>, this number is zero. In a callback, this number is
		665	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		666	in which case it is higher.
		667
		668	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
		669	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		670	ungentleman-like behaviour unless it's really convenient.
412		671
413	=item unsigned int ev_backend (loop)	672	=item unsigned int ev_backend (loop)
414		673
415	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	674	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
416	use.	675	use.
…		…
419		678
420	Returns the current "event loop time", which is the time the event loop	679	Returns the current "event loop time", which is the time the event loop
421	received events and started processing them. This timestamp does not	680	received events and started processing them. This timestamp does not
422	change as long as callbacks are being processed, and this is also the base	681	change as long as callbacks are being processed, and this is also the base
423	time used for relative timers. You can treat it as the timestamp of the	682	time used for relative timers. You can treat it as the timestamp of the
424	event occuring (or more correctly, libev finding out about it).	683	event occurring (or more correctly, libev finding out about it).
425		684
		685	=item ev_now_update (loop)
		686
		687	Establishes the current time by querying the kernel, updating the time
		688	returned by C<ev_now ()> in the progress. This is a costly operation and
		689	is usually done automatically within C<ev_run ()>.
		690
		691	This function is rarely useful, but when some event callback runs for a
		692	very long time without entering the event loop, updating libev's idea of
		693	the current time is a good idea.
		694
		695	See also L<The special problem of time updates> in the C<ev_timer> section.
		696
		697	=item ev_suspend (loop)
		698
		699	=item ev_resume (loop)
		700
		701	These two functions suspend and resume an event loop, for use when the
		702	loop is not used for a while and timeouts should not be processed.
		703
		704	A typical use case would be an interactive program such as a game: When
		705	the user presses C<^Z> to suspend the game and resumes it an hour later it
		706	would be best to handle timeouts as if no time had actually passed while
		707	the program was suspended. This can be achieved by calling C<ev_suspend>
		708	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		709	C<ev_resume> directly afterwards to resume timer processing.
		710
		711	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		712	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		713	will be rescheduled (that is, they will lose any events that would have
		714	occurred while suspended).
		715
		716	After calling C<ev_suspend> you B<must not> call I<any> function on the
		717	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		718	without a previous call to C<ev_suspend>.
		719
		720	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		721	event loop time (see C<ev_now_update>).
		722
426	=item ev_loop (loop, int flags)	723	=item ev_run (loop, int flags)
427		724
428	Finally, this is it, the event handler. This function usually is called	725	Finally, this is it, the event handler. This function usually is called
429	after you initialised all your watchers and you want to start handling	726	after you have initialised all your watchers and you want to start
430	events.	727	handling events. It will ask the operating system for any new events, call
		728	the watcher callbacks, an then repeat the whole process indefinitely: This
		729	is why event loops are called I<loops>.
431		730
432	If the flags argument is specified as C<0>, it will not return until	731	If the flags argument is specified as C<0>, it will keep handling events
433	either no event watchers are active anymore or C<ev_unloop> was called.	732	until either no event watchers are active anymore or C<ev_break> was
		733	called.
434		734
435	Please note that an explicit C<ev_unloop> is usually better than	735	Please note that an explicit C<ev_break> is usually better than
436	relying on all watchers to be stopped when deciding when a program has	736	relying on all watchers to be stopped when deciding when a program has
437	finished (especially in interactive programs), but having a program that	737	finished (especially in interactive programs), but having a program
438	automatically loops as long as it has to and no longer by virtue of	738	that automatically loops as long as it has to and no longer by virtue
439	relying on its watchers stopping correctly is a thing of beauty.	739	of relying on its watchers stopping correctly, that is truly a thing of
		740	beauty.
440		741
441	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	742	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
442	those events and any outstanding ones, but will not block your process in	743	those events and any already outstanding ones, but will not wait and
443	case there are no events and will return after one iteration of the loop.	744	block your process in case there are no events and will return after one
		745	iteration of the loop. This is sometimes useful to poll and handle new
		746	events while doing lengthy calculations, to keep the program responsive.
444		747
445	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	748	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
446	neccessary) and will handle those and any outstanding ones. It will block	749	necessary) and will handle those and any already outstanding ones. It
447	your process until at least one new event arrives, and will return after	750	will block your process until at least one new event arrives (which could
448	one iteration of the loop. This is useful if you are waiting for some	751	be an event internal to libev itself, so there is no guarantee that a
449	external event in conjunction with something not expressible using other	752	user-registered callback will be called), and will return after one
		753	iteration of the loop.
		754
		755	This is useful if you are waiting for some external event in conjunction
		756	with something not expressible using other libev watchers (i.e. "roll your
450	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	757	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
451	usually a better approach for this kind of thing.	758	usually a better approach for this kind of thing.
452		759
453	Here are the gory details of what C<ev_loop> does:	760	Here are the gory details of what C<ev_run> does:
454		761
455	* If there are no active watchers (reference count is zero), return.	762	- Increment loop depth.
456	- Queue prepare watchers and then call all outstanding watchers.	763	- Reset the ev_break status.
		764	- Before the first iteration, call any pending watchers.
		765	LOOP:
		766	- If EVFLAG_FORKCHECK was used, check for a fork.
		767	- If a fork was detected (by any means), queue and call all fork watchers.
		768	- Queue and call all prepare watchers.
		769	- If ev_break was called, goto FINISH.
457	- If we have been forked, recreate the kernel state.	770	- If we have been forked, detach and recreate the kernel state
		771	as to not disturb the other process.
458	- Update the kernel state with all outstanding changes.	772	- Update the kernel state with all outstanding changes.
459	- Update the "event loop time".	773	- Update the "event loop time" (ev_now ()).
460	- Calculate for how long to block.	774	- Calculate for how long to sleep or block, if at all
		775	(active idle watchers, EVRUN_NOWAIT or not having
		776	any active watchers at all will result in not sleeping).
		777	- Sleep if the I/O and timer collect interval say so.
		778	- Increment loop iteration counter.
461	- Block the process, waiting for any events.	779	- Block the process, waiting for any events.
462	- Queue all outstanding I/O (fd) events.	780	- Queue all outstanding I/O (fd) events.
463	- Update the "event loop time" and do time jump handling.	781	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
464	- Queue all outstanding timers.	782	- Queue all expired timers.
465	- Queue all outstanding periodics.	783	- Queue all expired periodics.
466	- If no events are pending now, queue all idle watchers.	784	- Queue all idle watchers with priority higher than that of pending events.
467	- Queue all check watchers.	785	- Queue all check watchers.
468	- Call all queued watchers in reverse order (i.e. check watchers first).	786	- Call all queued watchers in reverse order (i.e. check watchers first).
469	Signals and child watchers are implemented as I/O watchers, and will	787	Signals and child watchers are implemented as I/O watchers, and will
470	be handled here by queueing them when their watcher gets executed.	788	be handled here by queueing them when their watcher gets executed.
471	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	789	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
472	were used, return, otherwise continue with step *.	790	were used, or there are no active watchers, goto FINISH, otherwise
		791	continue with step LOOP.
		792	FINISH:
		793	- Reset the ev_break status iff it was EVBREAK_ONE.
		794	- Decrement the loop depth.
		795	- Return.
473		796
474	Example: Queue some jobs and then loop until no events are outsanding	797	Example: Queue some jobs and then loop until no events are outstanding
475	anymore.	798	anymore.
476		799
477	... queue jobs here, make sure they register event watchers as long	800	... queue jobs here, make sure they register event watchers as long
478	... as they still have work to do (even an idle watcher will do..)	801	... as they still have work to do (even an idle watcher will do..)
479	ev_loop (my_loop, 0);	802	ev_run (my_loop, 0);
480	... jobs done. yeah!	803	... jobs done or somebody called unloop. yeah!
481		804
482	=item ev_unloop (loop, how)	805	=item ev_break (loop, how)
483		806
484	Can be used to make a call to C<ev_loop> return early (but only after it	807	Can be used to make a call to C<ev_run> return early (but only after it
485	has processed all outstanding events). The C<how> argument must be either	808	has processed all outstanding events). The C<how> argument must be either
486	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	809	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
487	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	810	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
		811
		812	This "unloop state" will be cleared when entering C<ev_run> again.
		813
		814	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##
488		815
489	=item ev_ref (loop)	816	=item ev_ref (loop)
490		817
491	=item ev_unref (loop)	818	=item ev_unref (loop)
492		819
493	Ref/unref can be used to add or remove a reference count on the event	820	Ref/unref can be used to add or remove a reference count on the event
494	loop: Every watcher keeps one reference, and as long as the reference	821	loop: Every watcher keeps one reference, and as long as the reference
495	count is nonzero, C<ev_loop> will not return on its own. If you have	822	count is nonzero, C<ev_run> will not return on its own.
496	a watcher you never unregister that should not keep C<ev_loop> from	823
497	returning, ev_unref() after starting, and ev_ref() before stopping it. For	824	This is useful when you have a watcher that you never intend to
		825	unregister, but that nevertheless should not keep C<ev_run> from
		826	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		827	before stopping it.
		828
498	example, libev itself uses this for its internal signal pipe: It is not	829	As an example, libev itself uses this for its internal signal pipe: It
499	visible to the libev user and should not keep C<ev_loop> from exiting if	830	is not visible to the libev user and should not keep C<ev_run> from
500	no event watchers registered by it are active. It is also an excellent	831	exiting if no event watchers registered by it are active. It is also an
501	way to do this for generic recurring timers or from within third-party	832	excellent way to do this for generic recurring timers or from within
502	libraries. Just remember to I<unref after start> and I<ref before stop>.	833	third-party libraries. Just remember to I<unref after start> and I<ref
		834	before stop> (but only if the watcher wasn't active before, or was active
		835	before, respectively. Note also that libev might stop watchers itself
		836	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		837	in the callback).
503		838
504	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	839	Example: Create a signal watcher, but keep it from keeping C<ev_run>
505	running when nothing else is active.	840	running when nothing else is active.
506		841
507	struct ev_signal exitsig;	842	ev_signal exitsig;
508	ev_signal_init (&exitsig, sig_cb, SIGINT);	843	ev_signal_init (&exitsig, sig_cb, SIGINT);
509	ev_signal_start (loop, &exitsig);	844	ev_signal_start (loop, &exitsig);
510	evf_unref (loop);	845	evf_unref (loop);
511		846
512	Example: For some weird reason, unregister the above signal handler again.	847	Example: For some weird reason, unregister the above signal handler again.
513		848
514	ev_ref (loop);	849	ev_ref (loop);
515	ev_signal_stop (loop, &exitsig);	850	ev_signal_stop (loop, &exitsig);
		851
		852	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		853
		854	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		855
		856	These advanced functions influence the time that libev will spend waiting
		857	for events. Both time intervals are by default C<0>, meaning that libev
		858	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		859	latency.
		860
		861	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		862	allows libev to delay invocation of I/O and timer/periodic callbacks
		863	to increase efficiency of loop iterations (or to increase power-saving
		864	opportunities).
		865
		866	The idea is that sometimes your program runs just fast enough to handle
		867	one (or very few) event(s) per loop iteration. While this makes the
		868	program responsive, it also wastes a lot of CPU time to poll for new
		869	events, especially with backends like C<select ()> which have a high
		870	overhead for the actual polling but can deliver many events at once.
		871
		872	By setting a higher I<io collect interval> you allow libev to spend more
		873	time collecting I/O events, so you can handle more events per iteration,
		874	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		875	C<ev_timer>) will be not affected. Setting this to a non-null value will
		876	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		877	sleep time ensures that libev will not poll for I/O events more often then
		878	once per this interval, on average.
		879
		880	Likewise, by setting a higher I<timeout collect interval> you allow libev
		881	to spend more time collecting timeouts, at the expense of increased
		882	latency/jitter/inexactness (the watcher callback will be called
		883	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		884	value will not introduce any overhead in libev.
		885
		886	Many (busy) programs can usually benefit by setting the I/O collect
		887	interval to a value near C<0.1> or so, which is often enough for
		888	interactive servers (of course not for games), likewise for timeouts. It
		889	usually doesn't make much sense to set it to a lower value than C<0.01>,
		890	as this approaches the timing granularity of most systems. Note that if
		891	you do transactions with the outside world and you can't increase the
		892	parallelity, then this setting will limit your transaction rate (if you
		893	need to poll once per transaction and the I/O collect interval is 0.01,
		894	then you can't do more than 100 transactions per second).
		895
		896	Setting the I<timeout collect interval> can improve the opportunity for
		897	saving power, as the program will "bundle" timer callback invocations that
		898	are "near" in time together, by delaying some, thus reducing the number of
		899	times the process sleeps and wakes up again. Another useful technique to
		900	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		901	they fire on, say, one-second boundaries only.
		902
		903	Example: we only need 0.1s timeout granularity, and we wish not to poll
		904	more often than 100 times per second:
		905
		906	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		907	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		908
		909	=item ev_invoke_pending (loop)
		910
		911	This call will simply invoke all pending watchers while resetting their
		912	pending state. Normally, C<ev_run> does this automatically when required,
		913	but when overriding the invoke callback this call comes handy. This
		914	function can be invoked from a watcher - this can be useful for example
		915	when you want to do some lengthy calculation and want to pass further
		916	event handling to another thread (you still have to make sure only one
		917	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		918
		919	=item int ev_pending_count (loop)
		920
		921	Returns the number of pending watchers - zero indicates that no watchers
		922	are pending.
		923
		924	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		925
		926	This overrides the invoke pending functionality of the loop: Instead of
		927	invoking all pending watchers when there are any, C<ev_run> will call
		928	this callback instead. This is useful, for example, when you want to
		929	invoke the actual watchers inside another context (another thread etc.).
		930
		931	If you want to reset the callback, use C<ev_invoke_pending> as new
		932	callback.
		933
		934	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		935
		936	Sometimes you want to share the same loop between multiple threads. This
		937	can be done relatively simply by putting mutex_lock/unlock calls around
		938	each call to a libev function.
		939
		940	However, C<ev_run> can run an indefinite time, so it is not feasible
		941	to wait for it to return. One way around this is to wake up the event
		942	loop via C<ev_break> and C<av_async_send>, another way is to set these
		943	I<release> and I<acquire> callbacks on the loop.
		944
		945	When set, then C<release> will be called just before the thread is
		946	suspended waiting for new events, and C<acquire> is called just
		947	afterwards.
		948
		949	Ideally, C<release> will just call your mutex_unlock function, and
		950	C<acquire> will just call the mutex_lock function again.
		951
		952	While event loop modifications are allowed between invocations of
		953	C<release> and C<acquire> (that's their only purpose after all), no
		954	modifications done will affect the event loop, i.e. adding watchers will
		955	have no effect on the set of file descriptors being watched, or the time
		956	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		957	to take note of any changes you made.
		958
		959	In theory, threads executing C<ev_run> will be async-cancel safe between
		960	invocations of C<release> and C<acquire>.
		961
		962	See also the locking example in the C<THREADS> section later in this
		963	document.
		964
		965	=item ev_set_userdata (loop, void *data)
		966
		967	=item ev_userdata (loop)
		968
		969	Set and retrieve a single C<void *> associated with a loop. When
		970	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		971	C<0.>
		972
		973	These two functions can be used to associate arbitrary data with a loop,
		974	and are intended solely for the C<invoke_pending_cb>, C<release> and
		975	C<acquire> callbacks described above, but of course can be (ab-)used for
		976	any other purpose as well.
		977
		978	=item ev_verify (loop)
		979
		980	This function only does something when C<EV_VERIFY> support has been
		981	compiled in, which is the default for non-minimal builds. It tries to go
		982	through all internal structures and checks them for validity. If anything
		983	is found to be inconsistent, it will print an error message to standard
		984	error and call C<abort ()>.
		985
		986	This can be used to catch bugs inside libev itself: under normal
		987	circumstances, this function will never abort as of course libev keeps its
		988	data structures consistent.
516		989
517	=back	990	=back
518		991
519		992
520	=head1 ANATOMY OF A WATCHER	993	=head1 ANATOMY OF A WATCHER
521		994
		995	In the following description, uppercase C<TYPE> in names stands for the
		996	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		997	watchers and C<ev_io_start> for I/O watchers.
		998
522	A watcher is a structure that you create and register to record your	999	A watcher is an opaque structure that you allocate and register to record
523	interest in some event. For instance, if you want to wait for STDIN to	1000	your interest in some event. To make a concrete example, imagine you want
524	become readable, you would create an C<ev_io> watcher for that:	1001	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1002	for that:
525		1003
526	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1004	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
527	{	1005	{
528	ev_io_stop (w);	1006	ev_io_stop (w);
529	ev_unloop (loop, EVUNLOOP_ALL);	1007	ev_break (loop, EVBREAK_ALL);
530	}	1008	}
531		1009
532	struct ev_loop *loop = ev_default_loop (0);	1010	struct ev_loop *loop = ev_default_loop (0);
		1011
533	struct ev_io stdin_watcher;	1012	ev_io stdin_watcher;
		1013
534	ev_init (&stdin_watcher, my_cb);	1014	ev_init (&stdin_watcher, my_cb);
535	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1015	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
536	ev_io_start (loop, &stdin_watcher);	1016	ev_io_start (loop, &stdin_watcher);
		1017
537	ev_loop (loop, 0);	1018	ev_run (loop, 0);
538		1019
539	As you can see, you are responsible for allocating the memory for your	1020	As you can see, you are responsible for allocating the memory for your
540	watcher structures (and it is usually a bad idea to do this on the stack,	1021	watcher structures (and it is I<usually> a bad idea to do this on the
541	although this can sometimes be quite valid).	1022	stack).
542		1023
		1024	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1025	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1026
543	Each watcher structure must be initialised by a call to C<ev_init	1027	Each watcher structure must be initialised by a call to C<ev_init (watcher
544	(watcher *, callback)>, which expects a callback to be provided. This	1028	*, callback)>, which expects a callback to be provided. This callback is
545	callback gets invoked each time the event occurs (or, in the case of io	1029	invoked each time the event occurs (or, in the case of I/O watchers, each
546	watchers, each time the event loop detects that the file descriptor given	1030	time the event loop detects that the file descriptor given is readable
547	is readable and/or writable).	1031	and/or writable).
548		1032
549	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1033	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
550	with arguments specific to this watcher type. There is also a macro	1034	macro to configure it, with arguments specific to the watcher type. There
551	to combine initialisation and setting in one call: C<< ev_<type>_init	1035	is also a macro to combine initialisation and setting in one call: C<<
552	(watcher *, callback, ...) >>.	1036	ev_TYPE_init (watcher *, callback, ...) >>.
553		1037
554	To make the watcher actually watch out for events, you have to start it	1038	To make the watcher actually watch out for events, you have to start it
555	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1039	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
556	*) >>), and you can stop watching for events at any time by calling the	1040	*) >>), and you can stop watching for events at any time by calling the
557	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1041	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
558		1042
559	As long as your watcher is active (has been started but not stopped) you	1043	As long as your watcher is active (has been started but not stopped) you
560	must not touch the values stored in it. Most specifically you must never	1044	must not touch the values stored in it. Most specifically you must never
561	reinitialise it or call its C<set> macro.	1045	reinitialise it or call its C<ev_TYPE_set> macro.
562		1046
563	Each and every callback receives the event loop pointer as first, the	1047	Each and every callback receives the event loop pointer as first, the
564	registered watcher structure as second, and a bitset of received events as	1048	registered watcher structure as second, and a bitset of received events as
565	third argument.	1049	third argument.
566		1050
…		…
575	=item C<EV_WRITE>	1059	=item C<EV_WRITE>
576		1060
577	The file descriptor in the C<ev_io> watcher has become readable and/or	1061	The file descriptor in the C<ev_io> watcher has become readable and/or
578	writable.	1062	writable.
579		1063
580	=item C<EV_TIMEOUT>	1064	=item C<EV_TIMER>
581		1065
582	The C<ev_timer> watcher has timed out.	1066	The C<ev_timer> watcher has timed out.
583		1067
584	=item C<EV_PERIODIC>	1068	=item C<EV_PERIODIC>
585		1069
…		…
603		1087
604	=item C<EV_PREPARE>	1088	=item C<EV_PREPARE>
605		1089
606	=item C<EV_CHECK>	1090	=item C<EV_CHECK>
607		1091
608	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1092	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
609	to gather new events, and all C<ev_check> watchers are invoked just after	1093	to gather new events, and all C<ev_check> watchers are invoked just after
610	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1094	C<ev_run> has gathered them, but before it invokes any callbacks for any
611	received events. Callbacks of both watcher types can start and stop as	1095	received events. Callbacks of both watcher types can start and stop as
612	many watchers as they want, and all of them will be taken into account	1096	many watchers as they want, and all of them will be taken into account
613	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1097	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
614	C<ev_loop> from blocking).	1098	C<ev_run> from blocking).
615		1099
616	=item C<EV_EMBED>	1100	=item C<EV_EMBED>
617		1101
618	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1102	The embedded event loop specified in the C<ev_embed> watcher needs attention.
619		1103
620	=item C<EV_FORK>	1104	=item C<EV_FORK>
621		1105
622	The event loop has been resumed in the child process after fork (see	1106	The event loop has been resumed in the child process after fork (see
623	C<ev_fork>).	1107	C<ev_fork>).
624		1108
		1109	=item C<EV_ASYNC>
		1110
		1111	The given async watcher has been asynchronously notified (see C<ev_async>).
		1112
		1113	=item C<EV_CUSTOM>
		1114
		1115	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1116	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1117
625	=item C<EV_ERROR>	1118	=item C<EV_ERROR>
626		1119
627	An unspecified error has occured, the watcher has been stopped. This might	1120	An unspecified error has occurred, the watcher has been stopped. This might
628	happen because the watcher could not be properly started because libev	1121	happen because the watcher could not be properly started because libev
629	ran out of memory, a file descriptor was found to be closed or any other	1122	ran out of memory, a file descriptor was found to be closed or any other
		1123	problem. Libev considers these application bugs.
		1124
630	problem. You best act on it by reporting the problem and somehow coping	1125	You best act on it by reporting the problem and somehow coping with the
631	with the watcher being stopped.	1126	watcher being stopped. Note that well-written programs should not receive
		1127	an error ever, so when your watcher receives it, this usually indicates a
		1128	bug in your program.
632		1129
633	Libev will usually signal a few "dummy" events together with an error,	1130	Libev will usually signal a few "dummy" events together with an error, for
634	for example it might indicate that a fd is readable or writable, and if	1131	example it might indicate that a fd is readable or writable, and if your
635	your callbacks is well-written it can just attempt the operation and cope	1132	callbacks is well-written it can just attempt the operation and cope with
636	with the error from read() or write(). This will not work in multithreaded	1133	the error from read() or write(). This will not work in multi-threaded
637	programs, though, so beware.	1134	programs, though, as the fd could already be closed and reused for another
		1135	thing, so beware.
638		1136
639	=back	1137	=back
640		1138
		1139	=head2 WATCHER STATES
		1140
		1141	There are various watcher states mentioned throughout this manual -
		1142	active, pending and so on. In this section these states and the rules to
		1143	transition between them will be described in more detail - and while these
		1144	rules might look complicated, they usually do "the right thing".
		1145
		1146	=over 4
		1147
		1148	=item initialiased
		1149
		1150	Before a watcher can be registered with the event looop it has to be
		1151	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1152	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1153
		1154	In this state it is simply some block of memory that is suitable for use
		1155	in an event loop. It can be moved around, freed, reused etc. at will.
		1156
		1157	=item started/running/active
		1158
		1159	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1160	property of the event loop, and is actively waiting for events. While in
		1161	this state it cannot be accessed (except in a few documented ways), moved,
		1162	freed or anything else - the only legal thing is to keep a pointer to it,
		1163	and call libev functions on it that are documented to work on active watchers.
		1164
		1165	=item pending
		1166
		1167	If a watcher is active and libev determines that an event it is interested
		1168	in has occurred (such as a timer expiring), it will become pending. It will
		1169	stay in this pending state until either it is stopped or its callback is
		1170	about to be invoked, so it is not normally pending inside the watcher
		1171	callback.
		1172
		1173	The watcher might or might not be active while it is pending (for example,
		1174	an expired non-repeating timer can be pending but no longer active). If it
		1175	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1176	but it is still property of the event loop at this time, so cannot be
		1177	moved, freed or reused. And if it is active the rules described in the
		1178	previous item still apply.
		1179
		1180	It is also possible to feed an event on a watcher that is not active (e.g.
		1181	via C<ev_feed_event>), in which case it becomes pending without being
		1182	active.
		1183
		1184	=item stopped
		1185
		1186	A watcher can be stopped implicitly by libev (in which case it might still
		1187	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1188	latter will clear any pending state the watcher might be in, regardless
		1189	of whether it was active or not, so stopping a watcher explicitly before
		1190	freeing it is often a good idea.
		1191
		1192	While stopped (and not pending) the watcher is essentially in the
		1193	initialised state, that is it can be reused, moved, modified in any way
		1194	you wish.
		1195
		1196	=back
		1197
641	=head2 GENERIC WATCHER FUNCTIONS	1198	=head2 GENERIC WATCHER FUNCTIONS
642
643	In the following description, C<TYPE> stands for the watcher type,
644	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
645		1199
646	=over 4	1200	=over 4
647		1201
648	=item C<ev_init> (ev_TYPE *watcher, callback)	1202	=item C<ev_init> (ev_TYPE *watcher, callback)
649		1203
…		…
655	which rolls both calls into one.	1209	which rolls both calls into one.
656		1210
657	You can reinitialise a watcher at any time as long as it has been stopped	1211	You can reinitialise a watcher at any time as long as it has been stopped
658	(or never started) and there are no pending events outstanding.	1212	(or never started) and there are no pending events outstanding.
659		1213
660	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1214	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
661	int revents)>.	1215	int revents)>.
662		1216
		1217	Example: Initialise an C<ev_io> watcher in two steps.
		1218
		1219	ev_io w;
		1220	ev_init (&w, my_cb);
		1221	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1222
663	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1223	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
664		1224
665	This macro initialises the type-specific parts of a watcher. You need to	1225	This macro initialises the type-specific parts of a watcher. You need to
666	call C<ev_init> at least once before you call this macro, but you can	1226	call C<ev_init> at least once before you call this macro, but you can
667	call C<ev_TYPE_set> any number of times. You must not, however, call this	1227	call C<ev_TYPE_set> any number of times. You must not, however, call this
668	macro on a watcher that is active (it can be pending, however, which is a	1228	macro on a watcher that is active (it can be pending, however, which is a
669	difference to the C<ev_init> macro).	1229	difference to the C<ev_init> macro).
670		1230
671	Although some watcher types do not have type-specific arguments	1231	Although some watcher types do not have type-specific arguments
672	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1232	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
673		1233
		1234	See C<ev_init>, above, for an example.
		1235
674	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1236	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
675		1237
676	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1238	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
677	calls into a single call. This is the most convinient method to initialise	1239	calls into a single call. This is the most convenient method to initialise
678	a watcher. The same limitations apply, of course.	1240	a watcher. The same limitations apply, of course.
679		1241
		1242	Example: Initialise and set an C<ev_io> watcher in one step.
		1243
		1244	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1245
680	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1246	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
681		1247
682	Starts (activates) the given watcher. Only active watchers will receive	1248	Starts (activates) the given watcher. Only active watchers will receive
683	events. If the watcher is already active nothing will happen.	1249	events. If the watcher is already active nothing will happen.
684		1250
		1251	Example: Start the C<ev_io> watcher that is being abused as example in this
		1252	whole section.
		1253
		1254	ev_io_start (EV_DEFAULT_UC, &w);
		1255
685	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1256	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
686		1257
687	Stops the given watcher again (if active) and clears the pending	1258	Stops the given watcher if active, and clears the pending status (whether
		1259	the watcher was active or not).
		1260
688	status. It is possible that stopped watchers are pending (for example,	1261	It is possible that stopped watchers are pending - for example,
689	non-repeating timers are being stopped when they become pending), but	1262	non-repeating timers are being stopped when they become pending - but
690	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1263	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
691	you want to free or reuse the memory used by the watcher it is therefore a	1264	pending. If you want to free or reuse the memory used by the watcher it is
692	good idea to always call its C<ev_TYPE_stop> function.	1265	therefore a good idea to always call its C<ev_TYPE_stop> function.
693		1266
694	=item bool ev_is_active (ev_TYPE *watcher)	1267	=item bool ev_is_active (ev_TYPE *watcher)
695		1268
696	Returns a true value iff the watcher is active (i.e. it has been started	1269	Returns a true value iff the watcher is active (i.e. it has been started
697	and not yet been stopped). As long as a watcher is active you must not modify	1270	and not yet been stopped). As long as a watcher is active you must not modify
…		…
700	=item bool ev_is_pending (ev_TYPE *watcher)	1273	=item bool ev_is_pending (ev_TYPE *watcher)
701		1274
702	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1275	Returns a true value iff the watcher is pending, (i.e. it has outstanding
703	events but its callback has not yet been invoked). As long as a watcher	1276	events but its callback has not yet been invoked). As long as a watcher
704	is pending (but not active) you must not call an init function on it (but	1277	is pending (but not active) you must not call an init function on it (but
705	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1278	C<ev_TYPE_set> is safe), you must not change its priority, and you must
706	libev (e.g. you cnanot C<free ()> it).	1279	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1280	it).
707		1281
708	=item callback = ev_cb (ev_TYPE *watcher)	1282	=item callback ev_cb (ev_TYPE *watcher)
709		1283
710	Returns the callback currently set on the watcher.	1284	Returns the callback currently set on the watcher.
711		1285
712	=item ev_cb_set (ev_TYPE *watcher, callback)	1286	=item ev_cb_set (ev_TYPE *watcher, callback)
713		1287
714	Change the callback. You can change the callback at virtually any time	1288	Change the callback. You can change the callback at virtually any time
715	(modulo threads).	1289	(modulo threads).
716		1290
		1291	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1292
		1293	=item int ev_priority (ev_TYPE *watcher)
		1294
		1295	Set and query the priority of the watcher. The priority is a small
		1296	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1297	(default: C<-2>). Pending watchers with higher priority will be invoked
		1298	before watchers with lower priority, but priority will not keep watchers
		1299	from being executed (except for C<ev_idle> watchers).
		1300
		1301	If you need to suppress invocation when higher priority events are pending
		1302	you need to look at C<ev_idle> watchers, which provide this functionality.
		1303
		1304	You I<must not> change the priority of a watcher as long as it is active or
		1305	pending.
		1306
		1307	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1308	fine, as long as you do not mind that the priority value you query might
		1309	or might not have been clamped to the valid range.
		1310
		1311	The default priority used by watchers when no priority has been set is
		1312	always C<0>, which is supposed to not be too high and not be too low :).
		1313
		1314	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1315	priorities.
		1316
		1317	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1318
		1319	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1320	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1321	can deal with that fact, as both are simply passed through to the
		1322	callback.
		1323
		1324	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1325
		1326	If the watcher is pending, this function clears its pending status and
		1327	returns its C<revents> bitset (as if its callback was invoked). If the
		1328	watcher isn't pending it does nothing and returns C<0>.
		1329
		1330	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1331	callback to be invoked, which can be accomplished with this function.
		1332
		1333	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1334
		1335	Feeds the given event set into the event loop, as if the specified event
		1336	had happened for the specified watcher (which must be a pointer to an
		1337	initialised but not necessarily started event watcher). Obviously you must
		1338	not free the watcher as long as it has pending events.
		1339
		1340	Stopping the watcher, letting libev invoke it, or calling
		1341	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1342	not started in the first place.
		1343
		1344	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1345	functions that do not need a watcher.
		1346
717	=back	1347	=back
718		1348
719		1349
720	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1350	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
721		1351
722	Each watcher has, by default, a member C<void *data> that you can change	1352	Each watcher has, by default, a member C<void *data> that you can change
723	and read at any time, libev will completely ignore it. This can be used	1353	and read at any time: libev will completely ignore it. This can be used
724	to associate arbitrary data with your watcher. If you need more data and	1354	to associate arbitrary data with your watcher. If you need more data and
725	don't want to allocate memory and store a pointer to it in that data	1355	don't want to allocate memory and store a pointer to it in that data
726	member, you can also "subclass" the watcher type and provide your own	1356	member, you can also "subclass" the watcher type and provide your own
727	data:	1357	data:
728		1358
729	struct my_io	1359	struct my_io
730	{	1360	{
731	struct ev_io io;	1361	ev_io io;
732	int otherfd;	1362	int otherfd;
733	void *somedata;	1363	void *somedata;
734	struct whatever *mostinteresting;	1364	struct whatever *mostinteresting;
735	}	1365	};
		1366
		1367	...
		1368	struct my_io w;
		1369	ev_io_init (&w.io, my_cb, fd, EV_READ);
736		1370
737	And since your callback will be called with a pointer to the watcher, you	1371	And since your callback will be called with a pointer to the watcher, you
738	can cast it back to your own type:	1372	can cast it back to your own type:
739		1373
740	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1374	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
741	{	1375	{
742	struct my_io *w = (struct my_io *)w_;	1376	struct my_io *w = (struct my_io *)w_;
743	...	1377	...
744	}	1378	}
745		1379
746	More interesting and less C-conformant ways of catsing your callback type	1380	More interesting and less C-conformant ways of casting your callback type
747	have been omitted....	1381	instead have been omitted.
		1382
		1383	Another common scenario is to use some data structure with multiple
		1384	embedded watchers:
		1385
		1386	struct my_biggy
		1387	{
		1388	int some_data;
		1389	ev_timer t1;
		1390	ev_timer t2;
		1391	}
		1392
		1393	In this case getting the pointer to C<my_biggy> is a bit more
		1394	complicated: Either you store the address of your C<my_biggy> struct
		1395	in the C<data> member of the watcher (for woozies), or you need to use
		1396	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1397	programmers):
		1398
		1399	#include <stddef.h>
		1400
		1401	static void
		1402	t1_cb (EV_P_ ev_timer *w, int revents)
		1403	{
		1404	struct my_biggy big = (struct my_biggy *)
		1405	(((char *)w) - offsetof (struct my_biggy, t1));
		1406	}
		1407
		1408	static void
		1409	t2_cb (EV_P_ ev_timer *w, int revents)
		1410	{
		1411	struct my_biggy big = (struct my_biggy *)
		1412	(((char *)w) - offsetof (struct my_biggy, t2));
		1413	}
		1414
		1415	=head2 WATCHER PRIORITY MODELS
		1416
		1417	Many event loops support I<watcher priorities>, which are usually small
		1418	integers that influence the ordering of event callback invocation
		1419	between watchers in some way, all else being equal.
		1420
		1421	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1422	description for the more technical details such as the actual priority
		1423	range.
		1424
		1425	There are two common ways how these these priorities are being interpreted
		1426	by event loops:
		1427
		1428	In the more common lock-out model, higher priorities "lock out" invocation
		1429	of lower priority watchers, which means as long as higher priority
		1430	watchers receive events, lower priority watchers are not being invoked.
		1431
		1432	The less common only-for-ordering model uses priorities solely to order
		1433	callback invocation within a single event loop iteration: Higher priority
		1434	watchers are invoked before lower priority ones, but they all get invoked
		1435	before polling for new events.
		1436
		1437	Libev uses the second (only-for-ordering) model for all its watchers
		1438	except for idle watchers (which use the lock-out model).
		1439
		1440	The rationale behind this is that implementing the lock-out model for
		1441	watchers is not well supported by most kernel interfaces, and most event
		1442	libraries will just poll for the same events again and again as long as
		1443	their callbacks have not been executed, which is very inefficient in the
		1444	common case of one high-priority watcher locking out a mass of lower
		1445	priority ones.
		1446
		1447	Static (ordering) priorities are most useful when you have two or more
		1448	watchers handling the same resource: a typical usage example is having an
		1449	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1450	timeouts. Under load, data might be received while the program handles
		1451	other jobs, but since timers normally get invoked first, the timeout
		1452	handler will be executed before checking for data. In that case, giving
		1453	the timer a lower priority than the I/O watcher ensures that I/O will be
		1454	handled first even under adverse conditions (which is usually, but not
		1455	always, what you want).
		1456
		1457	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1458	will only be executed when no same or higher priority watchers have
		1459	received events, they can be used to implement the "lock-out" model when
		1460	required.
		1461
		1462	For example, to emulate how many other event libraries handle priorities,
		1463	you can associate an C<ev_idle> watcher to each such watcher, and in
		1464	the normal watcher callback, you just start the idle watcher. The real
		1465	processing is done in the idle watcher callback. This causes libev to
		1466	continuously poll and process kernel event data for the watcher, but when
		1467	the lock-out case is known to be rare (which in turn is rare :), this is
		1468	workable.
		1469
		1470	Usually, however, the lock-out model implemented that way will perform
		1471	miserably under the type of load it was designed to handle. In that case,
		1472	it might be preferable to stop the real watcher before starting the
		1473	idle watcher, so the kernel will not have to process the event in case
		1474	the actual processing will be delayed for considerable time.
		1475
		1476	Here is an example of an I/O watcher that should run at a strictly lower
		1477	priority than the default, and which should only process data when no
		1478	other events are pending:
		1479
		1480	ev_idle idle; // actual processing watcher
		1481	ev_io io; // actual event watcher
		1482
		1483	static void
		1484	io_cb (EV_P_ ev_io *w, int revents)
		1485	{
		1486	// stop the I/O watcher, we received the event, but
		1487	// are not yet ready to handle it.
		1488	ev_io_stop (EV_A_ w);
		1489
		1490	// start the idle watcher to handle the actual event.
		1491	// it will not be executed as long as other watchers
		1492	// with the default priority are receiving events.
		1493	ev_idle_start (EV_A_ &idle);
		1494	}
		1495
		1496	static void
		1497	idle_cb (EV_P_ ev_idle *w, int revents)
		1498	{
		1499	// actual processing
		1500	read (STDIN_FILENO, ...);
		1501
		1502	// have to start the I/O watcher again, as
		1503	// we have handled the event
		1504	ev_io_start (EV_P_ &io);
		1505	}
		1506
		1507	// initialisation
		1508	ev_idle_init (&idle, idle_cb);
		1509	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1510	ev_io_start (EV_DEFAULT_ &io);
		1511
		1512	In the "real" world, it might also be beneficial to start a timer, so that
		1513	low-priority connections can not be locked out forever under load. This
		1514	enables your program to keep a lower latency for important connections
		1515	during short periods of high load, while not completely locking out less
		1516	important ones.
748		1517
749		1518
750	=head1 WATCHER TYPES	1519	=head1 WATCHER TYPES
751		1520
752	This section describes each watcher in detail, but will not repeat	1521	This section describes each watcher in detail, but will not repeat
…		…
776	In general you can register as many read and/or write event watchers per	1545	In general you can register as many read and/or write event watchers per
777	fd as you want (as long as you don't confuse yourself). Setting all file	1546	fd as you want (as long as you don't confuse yourself). Setting all file
778	descriptors to non-blocking mode is also usually a good idea (but not	1547	descriptors to non-blocking mode is also usually a good idea (but not
779	required if you know what you are doing).	1548	required if you know what you are doing).
780		1549
781	You have to be careful with dup'ed file descriptors, though. Some backends	1550	If you cannot use non-blocking mode, then force the use of a
782	(the linux epoll backend is a notable example) cannot handle dup'ed file	1551	known-to-be-good backend (at the time of this writing, this includes only
783	descriptors correctly if you register interest in two or more fds pointing	1552	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
784	to the same underlying file/socket/etc. description (that is, they share	1553	descriptors for which non-blocking operation makes no sense (such as
785	the same underlying "file open").	1554	files) - libev doesn't guarantee any specific behaviour in that case.
786
787	If you must do this, then force the use of a known-to-be-good backend
788	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
789	C<EVBACKEND_POLL>).
790		1555
791	Another thing you have to watch out for is that it is quite easy to	1556	Another thing you have to watch out for is that it is quite easy to
792	receive "spurious" readyness notifications, that is your callback might	1557	receive "spurious" readiness notifications, that is your callback might
793	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1558	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
794	because there is no data. Not only are some backends known to create a	1559	because there is no data. Not only are some backends known to create a
795	lot of those (for example solaris ports), it is very easy to get into	1560	lot of those (for example Solaris ports), it is very easy to get into
796	this situation even with a relatively standard program structure. Thus	1561	this situation even with a relatively standard program structure. Thus
797	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1562	it is best to always use non-blocking I/O: An extra C<read>(2) returning
798	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1563	C<EAGAIN> is far preferable to a program hanging until some data arrives.
799		1564
800	If you cannot run the fd in non-blocking mode (for example you should not	1565	If you cannot run the fd in non-blocking mode (for example you should
801	play around with an Xlib connection), then you have to seperately re-test	1566	not play around with an Xlib connection), then you have to separately
802	wether a file descriptor is really ready with a known-to-be good interface	1567	re-test whether a file descriptor is really ready with a known-to-be good
803	such as poll (fortunately in our Xlib example, Xlib already does this on	1568	interface such as poll (fortunately in our Xlib example, Xlib already
804	its own, so its quite safe to use).	1569	does this on its own, so its quite safe to use). Some people additionally
		1570	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1571	indefinitely.
		1572
		1573	But really, best use non-blocking mode.
		1574
		1575	=head3 The special problem of disappearing file descriptors
		1576
		1577	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1578	descriptor (either due to calling C<close> explicitly or any other means,
		1579	such as C<dup2>). The reason is that you register interest in some file
		1580	descriptor, but when it goes away, the operating system will silently drop
		1581	this interest. If another file descriptor with the same number then is
		1582	registered with libev, there is no efficient way to see that this is, in
		1583	fact, a different file descriptor.
		1584
		1585	To avoid having to explicitly tell libev about such cases, libev follows
		1586	the following policy: Each time C<ev_io_set> is being called, libev
		1587	will assume that this is potentially a new file descriptor, otherwise
		1588	it is assumed that the file descriptor stays the same. That means that
		1589	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1590	descriptor even if the file descriptor number itself did not change.
		1591
		1592	This is how one would do it normally anyway, the important point is that
		1593	the libev application should not optimise around libev but should leave
		1594	optimisations to libev.
		1595
		1596	=head3 The special problem of dup'ed file descriptors
		1597
		1598	Some backends (e.g. epoll), cannot register events for file descriptors,
		1599	but only events for the underlying file descriptions. That means when you
		1600	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1601	events for them, only one file descriptor might actually receive events.
		1602
		1603	There is no workaround possible except not registering events
		1604	for potentially C<dup ()>'ed file descriptors, or to resort to
		1605	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1606
		1607	=head3 The special problem of fork
		1608
		1609	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1610	useless behaviour. Libev fully supports fork, but needs to be told about
		1611	it in the child.
		1612
		1613	To support fork in your programs, you either have to call
		1614	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1615	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1616	C<EVBACKEND_POLL>.
		1617
		1618	=head3 The special problem of SIGPIPE
		1619
		1620	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1621	when writing to a pipe whose other end has been closed, your program gets
		1622	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1623	this is sensible behaviour, for daemons, this is usually undesirable.
		1624
		1625	So when you encounter spurious, unexplained daemon exits, make sure you
		1626	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1627	somewhere, as that would have given you a big clue).
		1628
		1629	=head3 The special problem of accept()ing when you can't
		1630
		1631	Many implementations of the POSIX C<accept> function (for example,
		1632	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1633	connection from the pending queue in all error cases.
		1634
		1635	For example, larger servers often run out of file descriptors (because
		1636	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1637	rejecting the connection, leading to libev signalling readiness on
		1638	the next iteration again (the connection still exists after all), and
		1639	typically causing the program to loop at 100% CPU usage.
		1640
		1641	Unfortunately, the set of errors that cause this issue differs between
		1642	operating systems, there is usually little the app can do to remedy the
		1643	situation, and no known thread-safe method of removing the connection to
		1644	cope with overload is known (to me).
		1645
		1646	One of the easiest ways to handle this situation is to just ignore it
		1647	- when the program encounters an overload, it will just loop until the
		1648	situation is over. While this is a form of busy waiting, no OS offers an
		1649	event-based way to handle this situation, so it's the best one can do.
		1650
		1651	A better way to handle the situation is to log any errors other than
		1652	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1653	messages, and continue as usual, which at least gives the user an idea of
		1654	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1655	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1656	usage.
		1657
		1658	If your program is single-threaded, then you could also keep a dummy file
		1659	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1660	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1661	close that fd, and create a new dummy fd. This will gracefully refuse
		1662	clients under typical overload conditions.
		1663
		1664	The last way to handle it is to simply log the error and C<exit>, as
		1665	is often done with C<malloc> failures, but this results in an easy
		1666	opportunity for a DoS attack.
		1667
		1668	=head3 Watcher-Specific Functions
805		1669
806	=over 4	1670	=over 4
807		1671
808	=item ev_io_init (ev_io *, callback, int fd, int events)	1672	=item ev_io_init (ev_io *, callback, int fd, int events)
809		1673
810	=item ev_io_set (ev_io *, int fd, int events)	1674	=item ev_io_set (ev_io *, int fd, int events)
811		1675
812	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1676	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
813	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1677	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
814	C<EV_READ | EV_WRITE> to receive the given events.	1678	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
815		1679
816	=item int fd [read-only]	1680	=item int fd [read-only]
817		1681
818	The file descriptor being watched.	1682	The file descriptor being watched.
819		1683
820	=item int events [read-only]	1684	=item int events [read-only]
821		1685
822	The events being watched.	1686	The events being watched.
823		1687
824	=back	1688	=back
		1689
		1690	=head3 Examples
825		1691
826	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1692	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
827	readable, but only once. Since it is likely line-buffered, you could	1693	readable, but only once. Since it is likely line-buffered, you could
828	attempt to read a whole line in the callback.	1694	attempt to read a whole line in the callback.
829		1695
830	static void	1696	static void
831	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1697	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
832	{	1698	{
833	ev_io_stop (loop, w);	1699	ev_io_stop (loop, w);
834	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1700	.. read from stdin here (or from w->fd) and handle any I/O errors
835	}	1701	}
836		1702
837	...	1703	...
838	struct ev_loop *loop = ev_default_init (0);	1704	struct ev_loop *loop = ev_default_init (0);
839	struct ev_io stdin_readable;	1705	ev_io stdin_readable;
840	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1706	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
841	ev_io_start (loop, &stdin_readable);	1707	ev_io_start (loop, &stdin_readable);
842	ev_loop (loop, 0);	1708	ev_run (loop, 0);
843		1709
844		1710
845	=head2 C<ev_timer> - relative and optionally repeating timeouts	1711	=head2 C<ev_timer> - relative and optionally repeating timeouts
846		1712
847	Timer watchers are simple relative timers that generate an event after a	1713	Timer watchers are simple relative timers that generate an event after a
848	given time, and optionally repeating in regular intervals after that.	1714	given time, and optionally repeating in regular intervals after that.
849		1715
850	The timers are based on real time, that is, if you register an event that	1716	The timers are based on real time, that is, if you register an event that
851	times out after an hour and you reset your system clock to last years	1717	times out after an hour and you reset your system clock to January last
852	time, it will still time out after (roughly) and hour. "Roughly" because	1718	year, it will still time out after (roughly) one hour. "Roughly" because
853	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1719	detecting time jumps is hard, and some inaccuracies are unavoidable (the
854	monotonic clock option helps a lot here).	1720	monotonic clock option helps a lot here).
		1721
		1722	The callback is guaranteed to be invoked only I<after> its timeout has
		1723	passed (not I<at>, so on systems with very low-resolution clocks this
		1724	might introduce a small delay). If multiple timers become ready during the
		1725	same loop iteration then the ones with earlier time-out values are invoked
		1726	before ones of the same priority with later time-out values (but this is
		1727	no longer true when a callback calls C<ev_run> recursively).
		1728
		1729	=head3 Be smart about timeouts
		1730
		1731	Many real-world problems involve some kind of timeout, usually for error
		1732	recovery. A typical example is an HTTP request - if the other side hangs,
		1733	you want to raise some error after a while.
		1734
		1735	What follows are some ways to handle this problem, from obvious and
		1736	inefficient to smart and efficient.
		1737
		1738	In the following, a 60 second activity timeout is assumed - a timeout that
		1739	gets reset to 60 seconds each time there is activity (e.g. each time some
		1740	data or other life sign was received).
		1741
		1742	=over 4
		1743
		1744	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1745
		1746	This is the most obvious, but not the most simple way: In the beginning,
		1747	start the watcher:
		1748
		1749	ev_timer_init (timer, callback, 60., 0.);
		1750	ev_timer_start (loop, timer);
		1751
		1752	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1753	and start it again:
		1754
		1755	ev_timer_stop (loop, timer);
		1756	ev_timer_set (timer, 60., 0.);
		1757	ev_timer_start (loop, timer);
		1758
		1759	This is relatively simple to implement, but means that each time there is
		1760	some activity, libev will first have to remove the timer from its internal
		1761	data structure and then add it again. Libev tries to be fast, but it's
		1762	still not a constant-time operation.
		1763
		1764	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1765
		1766	This is the easiest way, and involves using C<ev_timer_again> instead of
		1767	C<ev_timer_start>.
		1768
		1769	To implement this, configure an C<ev_timer> with a C<repeat> value
		1770	of C<60> and then call C<ev_timer_again> at start and each time you
		1771	successfully read or write some data. If you go into an idle state where
		1772	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1773	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1774
		1775	That means you can ignore both the C<ev_timer_start> function and the
		1776	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1777	member and C<ev_timer_again>.
		1778
		1779	At start:
		1780
		1781	ev_init (timer, callback);
		1782	timer->repeat = 60.;
		1783	ev_timer_again (loop, timer);
		1784
		1785	Each time there is some activity:
		1786
		1787	ev_timer_again (loop, timer);
		1788
		1789	It is even possible to change the time-out on the fly, regardless of
		1790	whether the watcher is active or not:
		1791
		1792	timer->repeat = 30.;
		1793	ev_timer_again (loop, timer);
		1794
		1795	This is slightly more efficient then stopping/starting the timer each time
		1796	you want to modify its timeout value, as libev does not have to completely
		1797	remove and re-insert the timer from/into its internal data structure.
		1798
		1799	It is, however, even simpler than the "obvious" way to do it.
		1800
		1801	=item 3. Let the timer time out, but then re-arm it as required.
		1802
		1803	This method is more tricky, but usually most efficient: Most timeouts are
		1804	relatively long compared to the intervals between other activity - in
		1805	our example, within 60 seconds, there are usually many I/O events with
		1806	associated activity resets.
		1807
		1808	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1809	but remember the time of last activity, and check for a real timeout only
		1810	within the callback:
		1811
		1812	ev_tstamp last_activity; // time of last activity
		1813
		1814	static void
		1815	callback (EV_P_ ev_timer *w, int revents)
		1816	{
		1817	ev_tstamp now = ev_now (EV_A);
		1818	ev_tstamp timeout = last_activity + 60.;
		1819
		1820	// if last_activity + 60. is older than now, we did time out
		1821	if (timeout < now)
		1822	{
		1823	// timeout occurred, take action
		1824	}
		1825	else
		1826	{
		1827	// callback was invoked, but there was some activity, re-arm
		1828	// the watcher to fire in last_activity + 60, which is
		1829	// guaranteed to be in the future, so "again" is positive:
		1830	w->repeat = timeout - now;
		1831	ev_timer_again (EV_A_ w);
		1832	}
		1833	}
		1834
		1835	To summarise the callback: first calculate the real timeout (defined
		1836	as "60 seconds after the last activity"), then check if that time has
		1837	been reached, which means something I<did>, in fact, time out. Otherwise
		1838	the callback was invoked too early (C<timeout> is in the future), so
		1839	re-schedule the timer to fire at that future time, to see if maybe we have
		1840	a timeout then.
		1841
		1842	Note how C<ev_timer_again> is used, taking advantage of the
		1843	C<ev_timer_again> optimisation when the timer is already running.
		1844
		1845	This scheme causes more callback invocations (about one every 60 seconds
		1846	minus half the average time between activity), but virtually no calls to
		1847	libev to change the timeout.
		1848
		1849	To start the timer, simply initialise the watcher and set C<last_activity>
		1850	to the current time (meaning we just have some activity :), then call the
		1851	callback, which will "do the right thing" and start the timer:
		1852
		1853	ev_init (timer, callback);
		1854	last_activity = ev_now (loop);
		1855	callback (loop, timer, EV_TIMER);
		1856
		1857	And when there is some activity, simply store the current time in
		1858	C<last_activity>, no libev calls at all:
		1859
		1860	last_activity = ev_now (loop);
		1861
		1862	This technique is slightly more complex, but in most cases where the
		1863	time-out is unlikely to be triggered, much more efficient.
		1864
		1865	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1866	callback :) - just change the timeout and invoke the callback, which will
		1867	fix things for you.
		1868
		1869	=item 4. Wee, just use a double-linked list for your timeouts.
		1870
		1871	If there is not one request, but many thousands (millions...), all
		1872	employing some kind of timeout with the same timeout value, then one can
		1873	do even better:
		1874
		1875	When starting the timeout, calculate the timeout value and put the timeout
		1876	at the I<end> of the list.
		1877
		1878	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1879	the list is expected to fire (for example, using the technique #3).
		1880
		1881	When there is some activity, remove the timer from the list, recalculate
		1882	the timeout, append it to the end of the list again, and make sure to
		1883	update the C<ev_timer> if it was taken from the beginning of the list.
		1884
		1885	This way, one can manage an unlimited number of timeouts in O(1) time for
		1886	starting, stopping and updating the timers, at the expense of a major
		1887	complication, and having to use a constant timeout. The constant timeout
		1888	ensures that the list stays sorted.
		1889
		1890	=back
		1891
		1892	So which method the best?
		1893
		1894	Method #2 is a simple no-brain-required solution that is adequate in most
		1895	situations. Method #3 requires a bit more thinking, but handles many cases
		1896	better, and isn't very complicated either. In most case, choosing either
		1897	one is fine, with #3 being better in typical situations.
		1898
		1899	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1900	rather complicated, but extremely efficient, something that really pays
		1901	off after the first million or so of active timers, i.e. it's usually
		1902	overkill :)
		1903
		1904	=head3 The special problem of time updates
		1905
		1906	Establishing the current time is a costly operation (it usually takes at
		1907	least two system calls): EV therefore updates its idea of the current
		1908	time only before and after C<ev_run> collects new events, which causes a
		1909	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1910	lots of events in one iteration.
855		1911
856	The relative timeouts are calculated relative to the C<ev_now ()>	1912	The relative timeouts are calculated relative to the C<ev_now ()>
857	time. This is usually the right thing as this timestamp refers to the time	1913	time. This is usually the right thing as this timestamp refers to the time
858	of the event triggering whatever timeout you are modifying/starting. If	1914	of the event triggering whatever timeout you are modifying/starting. If
859	you suspect event processing to be delayed and you I<need> to base the timeout	1915	you suspect event processing to be delayed and you I<need> to base the
860	on the current time, use something like this to adjust for this:	1916	timeout on the current time, use something like this to adjust for this:
861		1917
862	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1918	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
863		1919
864	The callback is guarenteed to be invoked only when its timeout has passed,	1920	If the event loop is suspended for a long time, you can also force an
865	but if multiple timers become ready during the same loop iteration then	1921	update of the time returned by C<ev_now ()> by calling C<ev_now_update
866	order of execution is undefined.	1922	()>.
		1923
		1924	=head3 The special problems of suspended animation
		1925
		1926	When you leave the server world it is quite customary to hit machines that
		1927	can suspend/hibernate - what happens to the clocks during such a suspend?
		1928
		1929	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1930	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1931	to run until the system is suspended, but they will not advance while the
		1932	system is suspended. That means, on resume, it will be as if the program
		1933	was frozen for a few seconds, but the suspend time will not be counted
		1934	towards C<ev_timer> when a monotonic clock source is used. The real time
		1935	clock advanced as expected, but if it is used as sole clocksource, then a
		1936	long suspend would be detected as a time jump by libev, and timers would
		1937	be adjusted accordingly.
		1938
		1939	I would not be surprised to see different behaviour in different between
		1940	operating systems, OS versions or even different hardware.
		1941
		1942	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1943	time jump in the monotonic clocks and the realtime clock. If the program
		1944	is suspended for a very long time, and monotonic clock sources are in use,
		1945	then you can expect C<ev_timer>s to expire as the full suspension time
		1946	will be counted towards the timers. When no monotonic clock source is in
		1947	use, then libev will again assume a timejump and adjust accordingly.
		1948
		1949	It might be beneficial for this latter case to call C<ev_suspend>
		1950	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1951	deterministic behaviour in this case (you can do nothing against
		1952	C<SIGSTOP>).
		1953
		1954	=head3 Watcher-Specific Functions and Data Members
867		1955
868	=over 4	1956	=over 4
869		1957
870	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1958	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
871		1959
872	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1960	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
873		1961
874	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1962	Configure the timer to trigger after C<after> seconds. If C<repeat>
875	C<0.>, then it will automatically be stopped. If it is positive, then the	1963	is C<0.>, then it will automatically be stopped once the timeout is
876	timer will automatically be configured to trigger again C<repeat> seconds	1964	reached. If it is positive, then the timer will automatically be
877	later, again, and again, until stopped manually.	1965	configured to trigger again C<repeat> seconds later, again, and again,
		1966	until stopped manually.
878		1967
879	The timer itself will do a best-effort at avoiding drift, that is, if you	1968	The timer itself will do a best-effort at avoiding drift, that is, if
880	configure a timer to trigger every 10 seconds, then it will trigger at	1969	you configure a timer to trigger every 10 seconds, then it will normally
881	exactly 10 second intervals. If, however, your program cannot keep up with	1970	trigger at exactly 10 second intervals. If, however, your program cannot
882	the timer (because it takes longer than those 10 seconds to do stuff) the	1971	keep up with the timer (because it takes longer than those 10 seconds to
883	timer will not fire more than once per event loop iteration.	1972	do stuff) the timer will not fire more than once per event loop iteration.
884		1973
885	=item ev_timer_again (loop)	1974	=item ev_timer_again (loop, ev_timer *)
886		1975
887	This will act as if the timer timed out and restart it again if it is	1976	This will act as if the timer timed out and restart it again if it is
888	repeating. The exact semantics are:	1977	repeating. The exact semantics are:
889		1978
		1979	If the timer is pending, its pending status is cleared.
		1980
890	If the timer is started but nonrepeating, stop it.	1981	If the timer is started but non-repeating, stop it (as if it timed out).
891		1982
892	If the timer is repeating, either start it if necessary (with the repeat	1983	If the timer is repeating, either start it if necessary (with the
893	value), or reset the running timer to the repeat value.	1984	C<repeat> value), or reset the running timer to the C<repeat> value.
894		1985
895	This sounds a bit complicated, but here is a useful and typical	1986	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
896	example: Imagine you have a tcp connection and you want a so-called	1987	usage example.
897	idle timeout, that is, you want to be called when there have been,
898	say, 60 seconds of inactivity on the socket. The easiest way to do
899	this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
900	C<ev_timer_again> each time you successfully read or write some data. If
901	you go into an idle state where you do not expect data to travel on the
902	socket, you can stop the timer, and again will automatically restart it if
903	need be.
904		1988
905	You can also ignore the C<after> value and C<ev_timer_start> altogether	1989	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
906	and only ever use the C<repeat> value:
907		1990
908	ev_timer_init (timer, callback, 0., 5.);	1991	Returns the remaining time until a timer fires. If the timer is active,
909	ev_timer_again (loop, timer);	1992	then this time is relative to the current event loop time, otherwise it's
910	...	1993	the timeout value currently configured.
911	timer->again = 17.;
912	ev_timer_again (loop, timer);
913	...
914	timer->again = 10.;
915	ev_timer_again (loop, timer);
916		1994
917	This is more efficient then stopping/starting the timer eahc time you want	1995	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
918	to modify its timeout value.	1996	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1997	will return C<4>. When the timer expires and is restarted, it will return
		1998	roughly C<7> (likely slightly less as callback invocation takes some time,
		1999	too), and so on.
919		2000
920	=item ev_tstamp repeat [read-write]	2001	=item ev_tstamp repeat [read-write]
921		2002
922	The current C<repeat> value. Will be used each time the watcher times out	2003	The current C<repeat> value. Will be used each time the watcher times out
923	or C<ev_timer_again> is called and determines the next timeout (if any),	2004	or C<ev_timer_again> is called, and determines the next timeout (if any),
924	which is also when any modifications are taken into account.	2005	which is also when any modifications are taken into account.
925		2006
926	=back	2007	=back
927		2008
		2009	=head3 Examples
		2010
928	Example: Create a timer that fires after 60 seconds.	2011	Example: Create a timer that fires after 60 seconds.
929		2012
930	static void	2013	static void
931	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2014	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
932	{	2015	{
933	.. one minute over, w is actually stopped right here	2016	.. one minute over, w is actually stopped right here
934	}	2017	}
935		2018
936	struct ev_timer mytimer;	2019	ev_timer mytimer;
937	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2020	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
938	ev_timer_start (loop, &mytimer);	2021	ev_timer_start (loop, &mytimer);
939		2022
940	Example: Create a timeout timer that times out after 10 seconds of	2023	Example: Create a timeout timer that times out after 10 seconds of
941	inactivity.	2024	inactivity.
942		2025
943	static void	2026	static void
944	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2027	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
945	{	2028	{
946	.. ten seconds without any activity	2029	.. ten seconds without any activity
947	}	2030	}
948		2031
949	struct ev_timer mytimer;	2032	ev_timer mytimer;
950	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2033	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
951	ev_timer_again (&mytimer); /* start timer */	2034	ev_timer_again (&mytimer); /* start timer */
952	ev_loop (loop, 0);	2035	ev_run (loop, 0);
953		2036
954	// and in some piece of code that gets executed on any "activity":	2037	// and in some piece of code that gets executed on any "activity":
955	// reset the timeout to start ticking again at 10 seconds	2038	// reset the timeout to start ticking again at 10 seconds
956	ev_timer_again (&mytimer);	2039	ev_timer_again (&mytimer);
957		2040
958		2041
959	=head2 C<ev_periodic> - to cron or not to cron?	2042	=head2 C<ev_periodic> - to cron or not to cron?
960		2043
961	Periodic watchers are also timers of a kind, but they are very versatile	2044	Periodic watchers are also timers of a kind, but they are very versatile
962	(and unfortunately a bit complex).	2045	(and unfortunately a bit complex).
963		2046
964	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2047	Unlike C<ev_timer>, periodic watchers are not based on real time (or
965	but on wallclock time (absolute time). You can tell a periodic watcher	2048	relative time, the physical time that passes) but on wall clock time
966	to trigger "at" some specific point in time. For example, if you tell a	2049	(absolute time, the thing you can read on your calender or clock). The
967	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2050	difference is that wall clock time can run faster or slower than real
968	+ 10.>) and then reset your system clock to the last year, then it will	2051	time, and time jumps are not uncommon (e.g. when you adjust your
969	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2052	wrist-watch).
970	roughly 10 seconds later and of course not if you reset your system time
971	again).
972		2053
973	They can also be used to implement vastly more complex timers, such as	2054	You can tell a periodic watcher to trigger after some specific point
		2055	in time: for example, if you tell a periodic watcher to trigger "in 10
		2056	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2057	not a delay) and then reset your system clock to January of the previous
		2058	year, then it will take a year or more to trigger the event (unlike an
		2059	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2060	it, as it uses a relative timeout).
		2061
		2062	C<ev_periodic> watchers can also be used to implement vastly more complex
974	triggering an event on eahc midnight, local time.	2063	timers, such as triggering an event on each "midnight, local time", or
		2064	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2065	those cannot react to time jumps.
975		2066
976	As with timers, the callback is guarenteed to be invoked only when the	2067	As with timers, the callback is guaranteed to be invoked only when the
977	time (C<at>) has been passed, but if multiple periodic timers become ready	2068	point in time where it is supposed to trigger has passed. If multiple
978	during the same loop iteration then order of execution is undefined.	2069	timers become ready during the same loop iteration then the ones with
		2070	earlier time-out values are invoked before ones with later time-out values
		2071	(but this is no longer true when a callback calls C<ev_run> recursively).
		2072
		2073	=head3 Watcher-Specific Functions and Data Members
979		2074
980	=over 4	2075	=over 4
981		2076
982	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2077	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
983		2078
984	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2079	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
985		2080
986	Lots of arguments, lets sort it out... There are basically three modes of	2081	Lots of arguments, let's sort it out... There are basically three modes of
987	operation, and we will explain them from simplest to complex:	2082	operation, and we will explain them from simplest to most complex:
988		2083
989	=over 4	2084	=over 4
990		2085
991	=item * absolute timer (interval = reschedule_cb = 0)	2086	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
992		2087
993	In this configuration the watcher triggers an event at the wallclock time	2088	In this configuration the watcher triggers an event after the wall clock
994	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2089	time C<offset> has passed. It will not repeat and will not adjust when a
995	that is, if it is to be run at January 1st 2011 then it will run when the	2090	time jump occurs, that is, if it is to be run at January 1st 2011 then it
996	system time reaches or surpasses this time.	2091	will be stopped and invoked when the system clock reaches or surpasses
		2092	this point in time.
997		2093
998	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	2094	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
999		2095
1000	In this mode the watcher will always be scheduled to time out at the next	2096	In this mode the watcher will always be scheduled to time out at the next
1001	C<at + N * interval> time (for some integer N) and then repeat, regardless	2097	C<offset + N * interval> time (for some integer N, which can also be
1002	of any time jumps.	2098	negative) and then repeat, regardless of any time jumps. The C<offset>
		2099	argument is merely an offset into the C<interval> periods.
1003		2100
1004	This can be used to create timers that do not drift with respect to system	2101	This can be used to create timers that do not drift with respect to the
1005	time:	2102	system clock, for example, here is an C<ev_periodic> that triggers each
		2103	hour, on the hour (with respect to UTC):
1006		2104
1007	ev_periodic_set (&periodic, 0., 3600., 0);	2105	ev_periodic_set (&periodic, 0., 3600., 0);
1008		2106
1009	This doesn't mean there will always be 3600 seconds in between triggers,	2107	This doesn't mean there will always be 3600 seconds in between triggers,
1010	but only that the the callback will be called when the system time shows a	2108	but only that the callback will be called when the system time shows a
1011	full hour (UTC), or more correctly, when the system time is evenly divisible	2109	full hour (UTC), or more correctly, when the system time is evenly divisible
1012	by 3600.	2110	by 3600.
1013		2111
1014	Another way to think about it (for the mathematically inclined) is that	2112	Another way to think about it (for the mathematically inclined) is that
1015	C<ev_periodic> will try to run the callback in this mode at the next possible	2113	C<ev_periodic> will try to run the callback in this mode at the next possible
1016	time where C<time = at (mod interval)>, regardless of any time jumps.	2114	time where C<time = offset (mod interval)>, regardless of any time jumps.
1017		2115
		2116	For numerical stability it is preferable that the C<offset> value is near
		2117	C<ev_now ()> (the current time), but there is no range requirement for
		2118	this value, and in fact is often specified as zero.
		2119
		2120	Note also that there is an upper limit to how often a timer can fire (CPU
		2121	speed for example), so if C<interval> is very small then timing stability
		2122	will of course deteriorate. Libev itself tries to be exact to be about one
		2123	millisecond (if the OS supports it and the machine is fast enough).
		2124
1018	=item * manual reschedule mode (reschedule_cb = callback)	2125	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1019		2126
1020	In this mode the values for C<interval> and C<at> are both being	2127	In this mode the values for C<interval> and C<offset> are both being
1021	ignored. Instead, each time the periodic watcher gets scheduled, the	2128	ignored. Instead, each time the periodic watcher gets scheduled, the
1022	reschedule callback will be called with the watcher as first, and the	2129	reschedule callback will be called with the watcher as first, and the
1023	current time as second argument.	2130	current time as second argument.
1024		2131
1025	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2132	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1026	ever, or make any event loop modifications>. If you need to stop it,	2133	or make ANY other event loop modifications whatsoever, unless explicitly
1027	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2134	allowed by documentation here>.
1028	starting a prepare watcher).
1029		2135
		2136	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2137	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2138	only event loop modification you are allowed to do).
		2139
1030	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2140	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1031	ev_tstamp now)>, e.g.:	2141	*w, ev_tstamp now)>, e.g.:
1032		2142
		2143	static ev_tstamp
1033	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2144	my_rescheduler (ev_periodic *w, ev_tstamp now)
1034	{	2145	{
1035	return now + 60.;	2146	return now + 60.;
1036	}	2147	}
1037		2148
1038	It must return the next time to trigger, based on the passed time value	2149	It must return the next time to trigger, based on the passed time value
1039	(that is, the lowest time value larger than to the second argument). It	2150	(that is, the lowest time value larger than to the second argument). It
1040	will usually be called just before the callback will be triggered, but	2151	will usually be called just before the callback will be triggered, but
1041	might be called at other times, too.	2152	might be called at other times, too.
1042		2153
1043	NOTE: I<< This callback must always return a time that is later than the	2154	NOTE: I<< This callback must always return a time that is higher than or
1044	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2155	equal to the passed C<now> value >>.
1045		2156
1046	This can be used to create very complex timers, such as a timer that	2157	This can be used to create very complex timers, such as a timer that
1047	triggers on each midnight, local time. To do this, you would calculate the	2158	triggers on "next midnight, local time". To do this, you would calculate the
1048	next midnight after C<now> and return the timestamp value for this. How	2159	next midnight after C<now> and return the timestamp value for this. How
1049	you do this is, again, up to you (but it is not trivial, which is the main	2160	you do this is, again, up to you (but it is not trivial, which is the main
1050	reason I omitted it as an example).	2161	reason I omitted it as an example).
1051		2162
1052	=back	2163	=back
…		…
1056	Simply stops and restarts the periodic watcher again. This is only useful	2167	Simply stops and restarts the periodic watcher again. This is only useful
1057	when you changed some parameters or the reschedule callback would return	2168	when you changed some parameters or the reschedule callback would return
1058	a different time than the last time it was called (e.g. in a crond like	2169	a different time than the last time it was called (e.g. in a crond like
1059	program when the crontabs have changed).	2170	program when the crontabs have changed).
1060		2171
		2172	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2173
		2174	When active, returns the absolute time that the watcher is supposed
		2175	to trigger next. This is not the same as the C<offset> argument to
		2176	C<ev_periodic_set>, but indeed works even in interval and manual
		2177	rescheduling modes.
		2178
		2179	=item ev_tstamp offset [read-write]
		2180
		2181	When repeating, this contains the offset value, otherwise this is the
		2182	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2183	although libev might modify this value for better numerical stability).
		2184
		2185	Can be modified any time, but changes only take effect when the periodic
		2186	timer fires or C<ev_periodic_again> is being called.
		2187
1061	=item ev_tstamp interval [read-write]	2188	=item ev_tstamp interval [read-write]
1062		2189
1063	The current interval value. Can be modified any time, but changes only	2190	The current interval value. Can be modified any time, but changes only
1064	take effect when the periodic timer fires or C<ev_periodic_again> is being	2191	take effect when the periodic timer fires or C<ev_periodic_again> is being
1065	called.	2192	called.
1066		2193
1067	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2194	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1068		2195
1069	The current reschedule callback, or C<0>, if this functionality is	2196	The current reschedule callback, or C<0>, if this functionality is
1070	switched off. Can be changed any time, but changes only take effect when	2197	switched off. Can be changed any time, but changes only take effect when
1071	the periodic timer fires or C<ev_periodic_again> is being called.	2198	the periodic timer fires or C<ev_periodic_again> is being called.
1072		2199
1073	=back	2200	=back
1074		2201
		2202	=head3 Examples
		2203
1075	Example: Call a callback every hour, or, more precisely, whenever the	2204	Example: Call a callback every hour, or, more precisely, whenever the
1076	system clock is divisible by 3600. The callback invocation times have	2205	system time is divisible by 3600. The callback invocation times have
1077	potentially a lot of jittering, but good long-term stability.	2206	potentially a lot of jitter, but good long-term stability.
1078		2207
1079	static void	2208	static void
1080	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2209	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1081	{	2210	{
1082	... its now a full hour (UTC, or TAI or whatever your clock follows)	2211	... its now a full hour (UTC, or TAI or whatever your clock follows)
1083	}	2212	}
1084		2213
1085	struct ev_periodic hourly_tick;	2214	ev_periodic hourly_tick;
1086	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2215	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1087	ev_periodic_start (loop, &hourly_tick);	2216	ev_periodic_start (loop, &hourly_tick);
1088		2217
1089	Example: The same as above, but use a reschedule callback to do it:	2218	Example: The same as above, but use a reschedule callback to do it:
1090		2219
1091	#include <math.h>	2220	#include <math.h>
1092		2221
1093	static ev_tstamp	2222	static ev_tstamp
1094	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2223	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1095	{	2224	{
1096	return fmod (now, 3600.) + 3600.;	2225	return now + (3600. - fmod (now, 3600.));
1097	}	2226	}
1098		2227
1099	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2228	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1100		2229
1101	Example: Call a callback every hour, starting now:	2230	Example: Call a callback every hour, starting now:
1102		2231
1103	struct ev_periodic hourly_tick;	2232	ev_periodic hourly_tick;
1104	ev_periodic_init (&hourly_tick, clock_cb,	2233	ev_periodic_init (&hourly_tick, clock_cb,
1105	fmod (ev_now (loop), 3600.), 3600., 0);	2234	fmod (ev_now (loop), 3600.), 3600., 0);
1106	ev_periodic_start (loop, &hourly_tick);	2235	ev_periodic_start (loop, &hourly_tick);
1107		2236
1108		2237
1109	=head2 C<ev_signal> - signal me when a signal gets signalled!	2238	=head2 C<ev_signal> - signal me when a signal gets signalled!
1110		2239
1111	Signal watchers will trigger an event when the process receives a specific	2240	Signal watchers will trigger an event when the process receives a specific
1112	signal one or more times. Even though signals are very asynchronous, libev	2241	signal one or more times. Even though signals are very asynchronous, libev
1113	will try it's best to deliver signals synchronously, i.e. as part of the	2242	will try it's best to deliver signals synchronously, i.e. as part of the
1114	normal event processing, like any other event.	2243	normal event processing, like any other event.
1115		2244
		2245	If you want signals to be delivered truly asynchronously, just use
		2246	C<sigaction> as you would do without libev and forget about sharing
		2247	the signal. You can even use C<ev_async> from a signal handler to
		2248	synchronously wake up an event loop.
		2249
1116	You can configure as many watchers as you like per signal. Only when the	2250	You can configure as many watchers as you like for the same signal, but
		2251	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2252	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2253	C<SIGINT> in both the default loop and another loop at the same time. At
		2254	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2255
1117	first watcher gets started will libev actually register a signal watcher	2256	When the first watcher gets started will libev actually register something
1118	with the kernel (thus it coexists with your own signal handlers as long	2257	with the kernel (thus it coexists with your own signal handlers as long as
1119	as you don't register any with libev). Similarly, when the last signal	2258	you don't register any with libev for the same signal).
1120	watcher for a signal is stopped libev will reset the signal handler to	2259
1121	SIG_DFL (regardless of what it was set to before).	2260	If possible and supported, libev will install its handlers with
		2261	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2262	not be unduly interrupted. If you have a problem with system calls getting
		2263	interrupted by signals you can block all signals in an C<ev_check> watcher
		2264	and unblock them in an C<ev_prepare> watcher.
		2265
		2266	=head3 The special problem of inheritance over fork/execve/pthread_create
		2267
		2268	Both the signal mask (C<sigprocmask>) and the signal disposition
		2269	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2270	stopping it again), that is, libev might or might not block the signal,
		2271	and might or might not set or restore the installed signal handler.
		2272
		2273	While this does not matter for the signal disposition (libev never
		2274	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2275	C<execve>), this matters for the signal mask: many programs do not expect
		2276	certain signals to be blocked.
		2277
		2278	This means that before calling C<exec> (from the child) you should reset
		2279	the signal mask to whatever "default" you expect (all clear is a good
		2280	choice usually).
		2281
		2282	The simplest way to ensure that the signal mask is reset in the child is
		2283	to install a fork handler with C<pthread_atfork> that resets it. That will
		2284	catch fork calls done by libraries (such as the libc) as well.
		2285
		2286	In current versions of libev, the signal will not be blocked indefinitely
		2287	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2288	the window of opportunity for problems, it will not go away, as libev
		2289	I<has> to modify the signal mask, at least temporarily.
		2290
		2291	So I can't stress this enough: I<If you do not reset your signal mask when
		2292	you expect it to be empty, you have a race condition in your code>. This
		2293	is not a libev-specific thing, this is true for most event libraries.
		2294
		2295	=head3 Watcher-Specific Functions and Data Members
1122		2296
1123	=over 4	2297	=over 4
1124		2298
1125	=item ev_signal_init (ev_signal *, callback, int signum)	2299	=item ev_signal_init (ev_signal *, callback, int signum)
1126		2300
…		…
1133		2307
1134	The signal the watcher watches out for.	2308	The signal the watcher watches out for.
1135		2309
1136	=back	2310	=back
1137		2311
		2312	=head3 Examples
		2313
		2314	Example: Try to exit cleanly on SIGINT.
		2315
		2316	static void
		2317	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2318	{
		2319	ev_break (loop, EVBREAK_ALL);
		2320	}
		2321
		2322	ev_signal signal_watcher;
		2323	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2324	ev_signal_start (loop, &signal_watcher);
		2325
1138		2326
1139	=head2 C<ev_child> - watch out for process status changes	2327	=head2 C<ev_child> - watch out for process status changes
1140		2328
1141	Child watchers trigger when your process receives a SIGCHLD in response to	2329	Child watchers trigger when your process receives a SIGCHLD in response to
1142	some child status changes (most typically when a child of yours dies).	2330	some child status changes (most typically when a child of yours dies or
		2331	exits). It is permissible to install a child watcher I<after> the child
		2332	has been forked (which implies it might have already exited), as long
		2333	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2334	forking and then immediately registering a watcher for the child is fine,
		2335	but forking and registering a watcher a few event loop iterations later or
		2336	in the next callback invocation is not.
		2337
		2338	Only the default event loop is capable of handling signals, and therefore
		2339	you can only register child watchers in the default event loop.
		2340
		2341	Due to some design glitches inside libev, child watchers will always be
		2342	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2343	libev)
		2344
		2345	=head3 Process Interaction
		2346
		2347	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2348	initialised. This is necessary to guarantee proper behaviour even if the
		2349	first child watcher is started after the child exits. The occurrence
		2350	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2351	synchronously as part of the event loop processing. Libev always reaps all
		2352	children, even ones not watched.
		2353
		2354	=head3 Overriding the Built-In Processing
		2355
		2356	Libev offers no special support for overriding the built-in child
		2357	processing, but if your application collides with libev's default child
		2358	handler, you can override it easily by installing your own handler for
		2359	C<SIGCHLD> after initialising the default loop, and making sure the
		2360	default loop never gets destroyed. You are encouraged, however, to use an
		2361	event-based approach to child reaping and thus use libev's support for
		2362	that, so other libev users can use C<ev_child> watchers freely.
		2363
		2364	=head3 Stopping the Child Watcher
		2365
		2366	Currently, the child watcher never gets stopped, even when the
		2367	child terminates, so normally one needs to stop the watcher in the
		2368	callback. Future versions of libev might stop the watcher automatically
		2369	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2370	problem).
		2371
		2372	=head3 Watcher-Specific Functions and Data Members
1143		2373
1144	=over 4	2374	=over 4
1145		2375
1146	=item ev_child_init (ev_child *, callback, int pid)	2376	=item ev_child_init (ev_child *, callback, int pid, int trace)
1147		2377
1148	=item ev_child_set (ev_child *, int pid)	2378	=item ev_child_set (ev_child *, int pid, int trace)
1149		2379
1150	Configures the watcher to wait for status changes of process C<pid> (or	2380	Configures the watcher to wait for status changes of process C<pid> (or
1151	I<any> process if C<pid> is specified as C<0>). The callback can look	2381	I<any> process if C<pid> is specified as C<0>). The callback can look
1152	at the C<rstatus> member of the C<ev_child> watcher structure to see	2382	at the C<rstatus> member of the C<ev_child> watcher structure to see
1153	the status word (use the macros from C<sys/wait.h> and see your systems	2383	the status word (use the macros from C<sys/wait.h> and see your systems
1154	C<waitpid> documentation). The C<rpid> member contains the pid of the	2384	C<waitpid> documentation). The C<rpid> member contains the pid of the
1155	process causing the status change.	2385	process causing the status change. C<trace> must be either C<0> (only
		2386	activate the watcher when the process terminates) or C<1> (additionally
		2387	activate the watcher when the process is stopped or continued).
1156		2388
1157	=item int pid [read-only]	2389	=item int pid [read-only]
1158		2390
1159	The process id this watcher watches out for, or C<0>, meaning any process id.	2391	The process id this watcher watches out for, or C<0>, meaning any process id.
1160		2392
…		…
1167	The process exit/trace status caused by C<rpid> (see your systems	2399	The process exit/trace status caused by C<rpid> (see your systems
1168	C<waitpid> and C<sys/wait.h> documentation for details).	2400	C<waitpid> and C<sys/wait.h> documentation for details).
1169		2401
1170	=back	2402	=back
1171		2403
1172	Example: Try to exit cleanly on SIGINT and SIGTERM.	2404	=head3 Examples
1173		2405
		2406	Example: C<fork()> a new process and install a child handler to wait for
		2407	its completion.
		2408
		2409	ev_child cw;
		2410
1174	static void	2411	static void
1175	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2412	child_cb (EV_P_ ev_child *w, int revents)
1176	{	2413	{
1177	ev_unloop (loop, EVUNLOOP_ALL);	2414	ev_child_stop (EV_A_ w);
		2415	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1178	}	2416	}
1179		2417
1180	struct ev_signal signal_watcher;	2418	pid_t pid = fork ();
1181	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2419
1182	ev_signal_start (loop, &sigint_cb);	2420	if (pid < 0)
		2421	// error
		2422	else if (pid == 0)
		2423	{
		2424	// the forked child executes here
		2425	exit (1);
		2426	}
		2427	else
		2428	{
		2429	ev_child_init (&cw, child_cb, pid, 0);
		2430	ev_child_start (EV_DEFAULT_ &cw);
		2431	}
1183		2432
1184		2433
1185	=head2 C<ev_stat> - did the file attributes just change?	2434	=head2 C<ev_stat> - did the file attributes just change?
1186		2435
1187	This watches a filesystem path for attribute changes. That is, it calls	2436	This watches a file system path for attribute changes. That is, it calls
1188	C<stat> regularly (or when the OS says it changed) and sees if it changed	2437	C<stat> on that path in regular intervals (or when the OS says it changed)
1189	compared to the last time, invoking the callback if it did.	2438	and sees if it changed compared to the last time, invoking the callback if
		2439	it did.
1190		2440
1191	The path does not need to exist: changing from "path exists" to "path does	2441	The path does not need to exist: changing from "path exists" to "path does
1192	not exist" is a status change like any other. The condition "path does	2442	not exist" is a status change like any other. The condition "path does not
1193	not exist" is signified by the C<st_nlink> field being zero (which is	2443	exist" (or more correctly "path cannot be stat'ed") is signified by the
1194	otherwise always forced to be at least one) and all the other fields of	2444	C<st_nlink> field being zero (which is otherwise always forced to be at
1195	the stat buffer having unspecified contents.	2445	least one) and all the other fields of the stat buffer having unspecified
		2446	contents.
1196		2447
1197	Since there is no standard to do this, the portable implementation simply	2448	The path I<must not> end in a slash or contain special components such as
1198	calls C<stat (2)> regulalry on the path to see if it changed somehow. You	2449	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1199	can specify a recommended polling interval for this case. If you specify	2450	your working directory changes, then the behaviour is undefined.
1200	a polling interval of C<0> (highly recommended!) then a I<suitable,	2451
1201	unspecified default> value will be used (which you can expect to be around	2452	Since there is no portable change notification interface available, the
1202	five seconds, although this might change dynamically). Libev will also	2453	portable implementation simply calls C<stat(2)> regularly on the path
1203	impose a minimum interval which is currently around C<0.1>, but thats	2454	to see if it changed somehow. You can specify a recommended polling
1204	usually overkill.	2455	interval for this case. If you specify a polling interval of C<0> (highly
		2456	recommended!) then a I<suitable, unspecified default> value will be used
		2457	(which you can expect to be around five seconds, although this might
		2458	change dynamically). Libev will also impose a minimum interval which is
		2459	currently around C<0.1>, but that's usually overkill.
1205		2460
1206	This watcher type is not meant for massive numbers of stat watchers,	2461	This watcher type is not meant for massive numbers of stat watchers,
1207	as even with OS-supported change notifications, this can be	2462	as even with OS-supported change notifications, this can be
1208	resource-intensive.	2463	resource-intensive.
1209		2464
1210	At the time of this writing, no specific OS backends are implemented, but	2465	At the time of this writing, the only OS-specific interface implemented
1211	if demand increases, at least a kqueue and inotify backend will be added.	2466	is the Linux inotify interface (implementing kqueue support is left as an
		2467	exercise for the reader. Note, however, that the author sees no way of
		2468	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2469
		2470	=head3 ABI Issues (Largefile Support)
		2471
		2472	Libev by default (unless the user overrides this) uses the default
		2473	compilation environment, which means that on systems with large file
		2474	support disabled by default, you get the 32 bit version of the stat
		2475	structure. When using the library from programs that change the ABI to
		2476	use 64 bit file offsets the programs will fail. In that case you have to
		2477	compile libev with the same flags to get binary compatibility. This is
		2478	obviously the case with any flags that change the ABI, but the problem is
		2479	most noticeably displayed with ev_stat and large file support.
		2480
		2481	The solution for this is to lobby your distribution maker to make large
		2482	file interfaces available by default (as e.g. FreeBSD does) and not
		2483	optional. Libev cannot simply switch on large file support because it has
		2484	to exchange stat structures with application programs compiled using the
		2485	default compilation environment.
		2486
		2487	=head3 Inotify and Kqueue
		2488
		2489	When C<inotify (7)> support has been compiled into libev and present at
		2490	runtime, it will be used to speed up change detection where possible. The
		2491	inotify descriptor will be created lazily when the first C<ev_stat>
		2492	watcher is being started.
		2493
		2494	Inotify presence does not change the semantics of C<ev_stat> watchers
		2495	except that changes might be detected earlier, and in some cases, to avoid
		2496	making regular C<stat> calls. Even in the presence of inotify support
		2497	there are many cases where libev has to resort to regular C<stat> polling,
		2498	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2499	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2500	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2501	xfs are fully working) libev usually gets away without polling.
		2502
		2503	There is no support for kqueue, as apparently it cannot be used to
		2504	implement this functionality, due to the requirement of having a file
		2505	descriptor open on the object at all times, and detecting renames, unlinks
		2506	etc. is difficult.
		2507
		2508	=head3 C<stat ()> is a synchronous operation
		2509
		2510	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2511	the process. The exception are C<ev_stat> watchers - those call C<stat
		2512	()>, which is a synchronous operation.
		2513
		2514	For local paths, this usually doesn't matter: unless the system is very
		2515	busy or the intervals between stat's are large, a stat call will be fast,
		2516	as the path data is usually in memory already (except when starting the
		2517	watcher).
		2518
		2519	For networked file systems, calling C<stat ()> can block an indefinite
		2520	time due to network issues, and even under good conditions, a stat call
		2521	often takes multiple milliseconds.
		2522
		2523	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2524	paths, although this is fully supported by libev.
		2525
		2526	=head3 The special problem of stat time resolution
		2527
		2528	The C<stat ()> system call only supports full-second resolution portably,
		2529	and even on systems where the resolution is higher, most file systems
		2530	still only support whole seconds.
		2531
		2532	That means that, if the time is the only thing that changes, you can
		2533	easily miss updates: on the first update, C<ev_stat> detects a change and
		2534	calls your callback, which does something. When there is another update
		2535	within the same second, C<ev_stat> will be unable to detect unless the
		2536	stat data does change in other ways (e.g. file size).
		2537
		2538	The solution to this is to delay acting on a change for slightly more
		2539	than a second (or till slightly after the next full second boundary), using
		2540	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2541	ev_timer_again (loop, w)>).
		2542
		2543	The C<.02> offset is added to work around small timing inconsistencies
		2544	of some operating systems (where the second counter of the current time
		2545	might be be delayed. One such system is the Linux kernel, where a call to
		2546	C<gettimeofday> might return a timestamp with a full second later than
		2547	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2548	update file times then there will be a small window where the kernel uses
		2549	the previous second to update file times but libev might already execute
		2550	the timer callback).
		2551
		2552	=head3 Watcher-Specific Functions and Data Members
1212		2553
1213	=over 4	2554	=over 4
1214		2555
1215	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2556	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1216		2557
…		…
1220	C<path>. The C<interval> is a hint on how quickly a change is expected to	2561	C<path>. The C<interval> is a hint on how quickly a change is expected to
1221	be detected and should normally be specified as C<0> to let libev choose	2562	be detected and should normally be specified as C<0> to let libev choose
1222	a suitable value. The memory pointed to by C<path> must point to the same	2563	a suitable value. The memory pointed to by C<path> must point to the same
1223	path for as long as the watcher is active.	2564	path for as long as the watcher is active.
1224		2565
1225	The callback will be receive C<EV_STAT> when a change was detected,	2566	The callback will receive an C<EV_STAT> event when a change was detected,
1226	relative to the attributes at the time the watcher was started (or the	2567	relative to the attributes at the time the watcher was started (or the
1227	last change was detected).	2568	last change was detected).
1228		2569
1229	=item ev_stat_stat (ev_stat *)	2570	=item ev_stat_stat (loop, ev_stat *)
1230		2571
1231	Updates the stat buffer immediately with new values. If you change the	2572	Updates the stat buffer immediately with new values. If you change the
1232	watched path in your callback, you could call this fucntion to avoid	2573	watched path in your callback, you could call this function to avoid
1233	detecting this change (while introducing a race condition). Can also be	2574	detecting this change (while introducing a race condition if you are not
1234	useful simply to find out the new values.	2575	the only one changing the path). Can also be useful simply to find out the
		2576	new values.
1235		2577
1236	=item ev_statdata attr [read-only]	2578	=item ev_statdata attr [read-only]
1237		2579
1238	The most-recently detected attributes of the file. Although the type is of	2580	The most-recently detected attributes of the file. Although the type is
1239	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2581	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1240	suitable for your system. If the C<st_nlink> member is C<0>, then there	2582	suitable for your system, but you can only rely on the POSIX-standardised
		2583	members to be present. If the C<st_nlink> member is C<0>, then there was
1241	was some error while C<stat>ing the file.	2584	some error while C<stat>ing the file.
1242		2585
1243	=item ev_statdata prev [read-only]	2586	=item ev_statdata prev [read-only]
1244		2587
1245	The previous attributes of the file. The callback gets invoked whenever	2588	The previous attributes of the file. The callback gets invoked whenever
1246	C<prev> != C<attr>.	2589	C<prev> != C<attr>, or, more precisely, one or more of these members
		2590	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2591	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1247		2592
1248	=item ev_tstamp interval [read-only]	2593	=item ev_tstamp interval [read-only]
1249		2594
1250	The specified interval.	2595	The specified interval.
1251		2596
1252	=item const char *path [read-only]	2597	=item const char *path [read-only]
1253		2598
1254	The filesystem path that is being watched.	2599	The file system path that is being watched.
1255		2600
1256	=back	2601	=back
1257		2602
		2603	=head3 Examples
		2604
1258	Example: Watch C</etc/passwd> for attribute changes.	2605	Example: Watch C</etc/passwd> for attribute changes.
1259		2606
1260	static void	2607	static void
1261	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2608	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1262	{	2609	{
1263	/* /etc/passwd changed in some way */	2610	/* /etc/passwd changed in some way */
1264	if (w->attr.st_nlink)	2611	if (w->attr.st_nlink)
1265	{	2612	{
1266	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2613	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1267	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2614	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1268	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2615	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1269	}	2616	}
1270	else	2617	else
1271	/* you shalt not abuse printf for puts */	2618	/* you shalt not abuse printf for puts */
1272	puts ("wow, /etc/passwd is not there, expect problems. "	2619	puts ("wow, /etc/passwd is not there, expect problems. "
1273	"if this is windows, they already arrived\n");	2620	"if this is windows, they already arrived\n");
1274	}	2621	}
1275		2622
1276	...	2623	...
1277	ev_stat passwd;	2624	ev_stat passwd;
1278		2625
1279	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2626	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1280	ev_stat_start (loop, &passwd);	2627	ev_stat_start (loop, &passwd);
		2628
		2629	Example: Like above, but additionally use a one-second delay so we do not
		2630	miss updates (however, frequent updates will delay processing, too, so
		2631	one might do the work both on C<ev_stat> callback invocation I<and> on
		2632	C<ev_timer> callback invocation).
		2633
		2634	static ev_stat passwd;
		2635	static ev_timer timer;
		2636
		2637	static void
		2638	timer_cb (EV_P_ ev_timer *w, int revents)
		2639	{
		2640	ev_timer_stop (EV_A_ w);
		2641
		2642	/* now it's one second after the most recent passwd change */
		2643	}
		2644
		2645	static void
		2646	stat_cb (EV_P_ ev_stat *w, int revents)
		2647	{
		2648	/* reset the one-second timer */
		2649	ev_timer_again (EV_A_ &timer);
		2650	}
		2651
		2652	...
		2653	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2654	ev_stat_start (loop, &passwd);
		2655	ev_timer_init (&timer, timer_cb, 0., 1.02);
1281		2656
1282		2657
1283	=head2 C<ev_idle> - when you've got nothing better to do...	2658	=head2 C<ev_idle> - when you've got nothing better to do...
1284		2659
1285	Idle watchers trigger events when there are no other events are pending	2660	Idle watchers trigger events when no other events of the same or higher
1286	(prepare, check and other idle watchers do not count). That is, as long	2661	priority are pending (prepare, check and other idle watchers do not count
1287	as your process is busy handling sockets or timeouts (or even signals,	2662	as receiving "events").
1288	imagine) it will not be triggered. But when your process is idle all idle	2663
1289	watchers are being called again and again, once per event loop iteration -	2664	That is, as long as your process is busy handling sockets or timeouts
		2665	(or even signals, imagine) of the same or higher priority it will not be
		2666	triggered. But when your process is idle (or only lower-priority watchers
		2667	are pending), the idle watchers are being called once per event loop
1290	until stopped, that is, or your process receives more events and becomes	2668	iteration - until stopped, that is, or your process receives more events
1291	busy.	2669	and becomes busy again with higher priority stuff.
1292		2670
1293	The most noteworthy effect is that as long as any idle watchers are	2671	The most noteworthy effect is that as long as any idle watchers are
1294	active, the process will not block when waiting for new events.	2672	active, the process will not block when waiting for new events.
1295		2673
1296	Apart from keeping your process non-blocking (which is a useful	2674	Apart from keeping your process non-blocking (which is a useful
1297	effect on its own sometimes), idle watchers are a good place to do	2675	effect on its own sometimes), idle watchers are a good place to do
1298	"pseudo-background processing", or delay processing stuff to after the	2676	"pseudo-background processing", or delay processing stuff to after the
1299	event loop has handled all outstanding events.	2677	event loop has handled all outstanding events.
1300		2678
		2679	=head3 Watcher-Specific Functions and Data Members
		2680
1301	=over 4	2681	=over 4
1302		2682
1303	=item ev_idle_init (ev_signal *, callback)	2683	=item ev_idle_init (ev_idle *, callback)
1304		2684
1305	Initialises and configures the idle watcher - it has no parameters of any	2685	Initialises and configures the idle watcher - it has no parameters of any
1306	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2686	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1307	believe me.	2687	believe me.
1308		2688
1309	=back	2689	=back
1310		2690
		2691	=head3 Examples
		2692
1311	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2693	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1312	callback, free it. Also, use no error checking, as usual.	2694	callback, free it. Also, use no error checking, as usual.
1313		2695
1314	static void	2696	static void
1315	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2697	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1316	{	2698	{
1317	free (w);	2699	free (w);
1318	// now do something you wanted to do when the program has	2700	// now do something you wanted to do when the program has
1319	// no longer asnything immediate to do.	2701	// no longer anything immediate to do.
1320	}	2702	}
1321		2703
1322	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2704	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1323	ev_idle_init (idle_watcher, idle_cb);	2705	ev_idle_init (idle_watcher, idle_cb);
1324	ev_idle_start (loop, idle_cb);	2706	ev_idle_start (loop, idle_watcher);
1325		2707
1326		2708
1327	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2709	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1328		2710
1329	Prepare and check watchers are usually (but not always) used in tandem:	2711	Prepare and check watchers are usually (but not always) used in pairs:
1330	prepare watchers get invoked before the process blocks and check watchers	2712	prepare watchers get invoked before the process blocks and check watchers
1331	afterwards.	2713	afterwards.
1332		2714
1333	You I<must not> call C<ev_loop> or similar functions that enter	2715	You I<must not> call C<ev_run> or similar functions that enter
1334	the current event loop from either C<ev_prepare> or C<ev_check>	2716	the current event loop from either C<ev_prepare> or C<ev_check>
1335	watchers. Other loops than the current one are fine, however. The	2717	watchers. Other loops than the current one are fine, however. The
1336	rationale behind this is that you do not need to check for recursion in	2718	rationale behind this is that you do not need to check for recursion in
1337	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2719	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1338	C<ev_check> so if you have one watcher of each kind they will always be	2720	C<ev_check> so if you have one watcher of each kind they will always be
1339	called in pairs bracketing the blocking call.	2721	called in pairs bracketing the blocking call.
1340		2722
1341	Their main purpose is to integrate other event mechanisms into libev and	2723	Their main purpose is to integrate other event mechanisms into libev and
1342	their use is somewhat advanced. This could be used, for example, to track	2724	their use is somewhat advanced. They could be used, for example, to track
1343	variable changes, implement your own watchers, integrate net-snmp or a	2725	variable changes, implement your own watchers, integrate net-snmp or a
1344	coroutine library and lots more. They are also occasionally useful if	2726	coroutine library and lots more. They are also occasionally useful if
1345	you cache some data and want to flush it before blocking (for example,	2727	you cache some data and want to flush it before blocking (for example,
1346	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2728	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1347	watcher).	2729	watcher).
1348		2730
1349	This is done by examining in each prepare call which file descriptors need	2731	This is done by examining in each prepare call which file descriptors
1350	to be watched by the other library, registering C<ev_io> watchers for	2732	need to be watched by the other library, registering C<ev_io> watchers
1351	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2733	for them and starting an C<ev_timer> watcher for any timeouts (many
1352	provide just this functionality). Then, in the check watcher you check for	2734	libraries provide exactly this functionality). Then, in the check watcher,
1353	any events that occured (by checking the pending status of all watchers	2735	you check for any events that occurred (by checking the pending status
1354	and stopping them) and call back into the library. The I/O and timer	2736	of all watchers and stopping them) and call back into the library. The
1355	callbacks will never actually be called (but must be valid nevertheless,	2737	I/O and timer callbacks will never actually be called (but must be valid
1356	because you never know, you know?).	2738	nevertheless, because you never know, you know?).
1357		2739
1358	As another example, the Perl Coro module uses these hooks to integrate	2740	As another example, the Perl Coro module uses these hooks to integrate
1359	coroutines into libev programs, by yielding to other active coroutines	2741	coroutines into libev programs, by yielding to other active coroutines
1360	during each prepare and only letting the process block if no coroutines	2742	during each prepare and only letting the process block if no coroutines
1361	are ready to run (it's actually more complicated: it only runs coroutines	2743	are ready to run (it's actually more complicated: it only runs coroutines
1362	with priority higher than or equal to the event loop and one coroutine	2744	with priority higher than or equal to the event loop and one coroutine
1363	of lower priority, but only once, using idle watchers to keep the event	2745	of lower priority, but only once, using idle watchers to keep the event
1364	loop from blocking if lower-priority coroutines are active, thus mapping	2746	loop from blocking if lower-priority coroutines are active, thus mapping
1365	low-priority coroutines to idle/background tasks).	2747	low-priority coroutines to idle/background tasks).
1366		2748
		2749	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2750	priority, to ensure that they are being run before any other watchers
		2751	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2752
		2753	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2754	activate ("feed") events into libev. While libev fully supports this, they
		2755	might get executed before other C<ev_check> watchers did their job. As
		2756	C<ev_check> watchers are often used to embed other (non-libev) event
		2757	loops those other event loops might be in an unusable state until their
		2758	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2759	others).
		2760
		2761	=head3 Watcher-Specific Functions and Data Members
		2762
1367	=over 4	2763	=over 4
1368		2764
1369	=item ev_prepare_init (ev_prepare *, callback)	2765	=item ev_prepare_init (ev_prepare *, callback)
1370		2766
1371	=item ev_check_init (ev_check *, callback)	2767	=item ev_check_init (ev_check *, callback)
1372		2768
1373	Initialises and configures the prepare or check watcher - they have no	2769	Initialises and configures the prepare or check watcher - they have no
1374	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2770	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1375	macros, but using them is utterly, utterly and completely pointless.	2771	macros, but using them is utterly, utterly, utterly and completely
		2772	pointless.
1376		2773
1377	=back	2774	=back
1378		2775
1379	Example: To include a library such as adns, you would add IO watchers	2776	=head3 Examples
1380	and a timeout watcher in a prepare handler, as required by libadns, and	2777
		2778	There are a number of principal ways to embed other event loops or modules
		2779	into libev. Here are some ideas on how to include libadns into libev
		2780	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2781	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2782	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2783	Glib event loop).
		2784
		2785	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1381	in a check watcher, destroy them and call into libadns. What follows is	2786	and in a check watcher, destroy them and call into libadns. What follows
1382	pseudo-code only of course:	2787	is pseudo-code only of course. This requires you to either use a low
		2788	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2789	the callbacks for the IO/timeout watchers might not have been called yet.
1383		2790
1384	static ev_io iow [nfd];	2791	static ev_io iow [nfd];
1385	static ev_timer tw;	2792	static ev_timer tw;
1386		2793
1387	static void	2794	static void
1388	io_cb (ev_loop *loop, ev_io *w, int revents)	2795	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1389	{	2796	{
1390	// set the relevant poll flags
1391	// could also call adns_processreadable etc. here
1392	struct pollfd *fd = (struct pollfd *)w->data;
1393	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1394	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1395	}	2797	}
1396		2798
1397	// create io watchers for each fd and a timer before blocking	2799	// create io watchers for each fd and a timer before blocking
1398	static void	2800	static void
1399	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2801	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1400	{	2802	{
1401	int timeout = 3600000;truct pollfd fds [nfd];	2803	int timeout = 3600000;
		2804	struct pollfd fds [nfd];
1402	// actual code will need to loop here and realloc etc.	2805	// actual code will need to loop here and realloc etc.
1403	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2806	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1404		2807
1405	/* the callback is illegal, but won't be called as we stop during check */	2808	/* the callback is illegal, but won't be called as we stop during check */
1406	ev_timer_init (&tw, 0, timeout * 1e-3);	2809	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1407	ev_timer_start (loop, &tw);	2810	ev_timer_start (loop, &tw);
1408		2811
1409	// create on ev_io per pollfd	2812	// create one ev_io per pollfd
1410	for (int i = 0; i < nfd; ++i)	2813	for (int i = 0; i < nfd; ++i)
1411	{	2814	{
1412	ev_io_init (iow + i, io_cb, fds [i].fd,	2815	ev_io_init (iow + i, io_cb, fds [i].fd,
1413	((fds [i].events & POLLIN ? EV_READ : 0)	2816	((fds [i].events & POLLIN ? EV_READ : 0)
1414	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2817	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1415		2818
1416	fds [i].revents = 0;	2819	fds [i].revents = 0;
1417	iow [i].data = fds + i;
1418	ev_io_start (loop, iow + i);	2820	ev_io_start (loop, iow + i);
1419	}	2821	}
1420	}	2822	}
1421		2823
1422	// stop all watchers after blocking	2824	// stop all watchers after blocking
1423	static void	2825	static void
1424	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2826	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1425	{	2827	{
1426	ev_timer_stop (loop, &tw);	2828	ev_timer_stop (loop, &tw);
1427		2829
1428	for (int i = 0; i < nfd; ++i)	2830	for (int i = 0; i < nfd; ++i)
		2831	{
		2832	// set the relevant poll flags
		2833	// could also call adns_processreadable etc. here
		2834	struct pollfd *fd = fds + i;
		2835	int revents = ev_clear_pending (iow + i);
		2836	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2837	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2838
		2839	// now stop the watcher
1429	ev_io_stop (loop, iow + i);	2840	ev_io_stop (loop, iow + i);
		2841	}
1430		2842
1431	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2843	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1432	}	2844	}
		2845
		2846	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2847	in the prepare watcher and would dispose of the check watcher.
		2848
		2849	Method 3: If the module to be embedded supports explicit event
		2850	notification (libadns does), you can also make use of the actual watcher
		2851	callbacks, and only destroy/create the watchers in the prepare watcher.
		2852
		2853	static void
		2854	timer_cb (EV_P_ ev_timer *w, int revents)
		2855	{
		2856	adns_state ads = (adns_state)w->data;
		2857	update_now (EV_A);
		2858
		2859	adns_processtimeouts (ads, &tv_now);
		2860	}
		2861
		2862	static void
		2863	io_cb (EV_P_ ev_io *w, int revents)
		2864	{
		2865	adns_state ads = (adns_state)w->data;
		2866	update_now (EV_A);
		2867
		2868	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2869	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2870	}
		2871
		2872	// do not ever call adns_afterpoll
		2873
		2874	Method 4: Do not use a prepare or check watcher because the module you
		2875	want to embed is not flexible enough to support it. Instead, you can
		2876	override their poll function. The drawback with this solution is that the
		2877	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2878	this approach, effectively embedding EV as a client into the horrible
		2879	libglib event loop.
		2880
		2881	static gint
		2882	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2883	{
		2884	int got_events = 0;
		2885
		2886	for (n = 0; n < nfds; ++n)
		2887	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2888
		2889	if (timeout >= 0)
		2890	// create/start timer
		2891
		2892	// poll
		2893	ev_run (EV_A_ 0);
		2894
		2895	// stop timer again
		2896	if (timeout >= 0)
		2897	ev_timer_stop (EV_A_ &to);
		2898
		2899	// stop io watchers again - their callbacks should have set
		2900	for (n = 0; n < nfds; ++n)
		2901	ev_io_stop (EV_A_ iow [n]);
		2902
		2903	return got_events;
		2904	}
1433		2905
1434		2906
1435	=head2 C<ev_embed> - when one backend isn't enough...	2907	=head2 C<ev_embed> - when one backend isn't enough...
1436		2908
1437	This is a rather advanced watcher type that lets you embed one event loop	2909	This is a rather advanced watcher type that lets you embed one event loop
…		…
1443	prioritise I/O.	2915	prioritise I/O.
1444		2916
1445	As an example for a bug workaround, the kqueue backend might only support	2917	As an example for a bug workaround, the kqueue backend might only support
1446	sockets on some platform, so it is unusable as generic backend, but you	2918	sockets on some platform, so it is unusable as generic backend, but you
1447	still want to make use of it because you have many sockets and it scales	2919	still want to make use of it because you have many sockets and it scales
1448	so nicely. In this case, you would create a kqueue-based loop and embed it	2920	so nicely. In this case, you would create a kqueue-based loop and embed
1449	into your default loop (which might use e.g. poll). Overall operation will	2921	it into your default loop (which might use e.g. poll). Overall operation
1450	be a bit slower because first libev has to poll and then call kevent, but	2922	will be a bit slower because first libev has to call C<poll> and then
1451	at least you can use both at what they are best.	2923	C<kevent>, but at least you can use both mechanisms for what they are
		2924	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1452		2925
1453	As for prioritising I/O: rarely you have the case where some fds have	2926	As for prioritising I/O: under rare circumstances you have the case where
1454	to be watched and handled very quickly (with low latency), and even	2927	some fds have to be watched and handled very quickly (with low latency),
1455	priorities and idle watchers might have too much overhead. In this case	2928	and even priorities and idle watchers might have too much overhead. In
1456	you would put all the high priority stuff in one loop and all the rest in	2929	this case you would put all the high priority stuff in one loop and all
1457	a second one, and embed the second one in the first.	2930	the rest in a second one, and embed the second one in the first.
1458		2931
1459	As long as the watcher is active, the callback will be invoked every time	2932	As long as the watcher is active, the callback will be invoked every
1460	there might be events pending in the embedded loop. The callback must then	2933	time there might be events pending in the embedded loop. The callback
1461	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2934	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1462	their callbacks (you could also start an idle watcher to give the embedded	2935	sweep and invoke their callbacks (the callback doesn't need to invoke the
1463	loop strictly lower priority for example). You can also set the callback	2936	C<ev_embed_sweep> function directly, it could also start an idle watcher
1464	to C<0>, in which case the embed watcher will automatically execute the	2937	to give the embedded loop strictly lower priority for example).
1465	embedded loop sweep.
1466		2938
1467	As long as the watcher is started it will automatically handle events. The	2939	You can also set the callback to C<0>, in which case the embed watcher
1468	callback will be invoked whenever some events have been handled. You can	2940	will automatically execute the embedded loop sweep whenever necessary.
1469	set the callback to C<0> to avoid having to specify one if you are not
1470	interested in that.
1471		2941
1472	Also, there have not currently been made special provisions for forking:	2942	Fork detection will be handled transparently while the C<ev_embed> watcher
1473	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2943	is active, i.e., the embedded loop will automatically be forked when the
1474	but you will also have to stop and restart any C<ev_embed> watchers	2944	embedding loop forks. In other cases, the user is responsible for calling
1475	yourself.	2945	C<ev_loop_fork> on the embedded loop.
1476		2946
1477	Unfortunately, not all backends are embeddable, only the ones returned by	2947	Unfortunately, not all backends are embeddable: only the ones returned by
1478	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2948	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1479	portable one.	2949	portable one.
1480		2950
1481	So when you want to use this feature you will always have to be prepared	2951	So when you want to use this feature you will always have to be prepared
1482	that you cannot get an embeddable loop. The recommended way to get around	2952	that you cannot get an embeddable loop. The recommended way to get around
1483	this is to have a separate variables for your embeddable loop, try to	2953	this is to have a separate variables for your embeddable loop, try to
1484	create it, and if that fails, use the normal loop for everything:	2954	create it, and if that fails, use the normal loop for everything.
1485		2955
1486	struct ev_loop *loop_hi = ev_default_init (0);	2956	=head3 C<ev_embed> and fork
1487	struct ev_loop *loop_lo = 0;
1488	struct ev_embed embed;
1489
1490	// see if there is a chance of getting one that works
1491	// (remember that a flags value of 0 means autodetection)
1492	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1493	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1494	: 0;
1495		2957
1496	// if we got one, then embed it, otherwise default to loop_hi	2958	While the C<ev_embed> watcher is running, forks in the embedding loop will
1497	if (loop_lo)	2959	automatically be applied to the embedded loop as well, so no special
1498	{	2960	fork handling is required in that case. When the watcher is not running,
1499	ev_embed_init (&embed, 0, loop_lo);	2961	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1500	ev_embed_start (loop_hi, &embed);	2962	as applicable.
1501	}	2963
1502	else	2964	=head3 Watcher-Specific Functions and Data Members
1503	loop_lo = loop_hi;
1504		2965
1505	=over 4	2966	=over 4
1506		2967
1507	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2968	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1508		2969
…		…
1510		2971
1511	Configures the watcher to embed the given loop, which must be	2972	Configures the watcher to embed the given loop, which must be
1512	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2973	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1513	invoked automatically, otherwise it is the responsibility of the callback	2974	invoked automatically, otherwise it is the responsibility of the callback
1514	to invoke it (it will continue to be called until the sweep has been done,	2975	to invoke it (it will continue to be called until the sweep has been done,
1515	if you do not want thta, you need to temporarily stop the embed watcher).	2976	if you do not want that, you need to temporarily stop the embed watcher).
1516		2977
1517	=item ev_embed_sweep (loop, ev_embed *)	2978	=item ev_embed_sweep (loop, ev_embed *)
1518		2979
1519	Make a single, non-blocking sweep over the embedded loop. This works	2980	Make a single, non-blocking sweep over the embedded loop. This works
1520	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2981	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1521	apropriate way for embedded loops.	2982	appropriate way for embedded loops.
1522		2983
1523	=item struct ev_loop *loop [read-only]	2984	=item struct ev_loop *other [read-only]
1524		2985
1525	The embedded event loop.	2986	The embedded event loop.
1526		2987
1527	=back	2988	=back
		2989
		2990	=head3 Examples
		2991
		2992	Example: Try to get an embeddable event loop and embed it into the default
		2993	event loop. If that is not possible, use the default loop. The default
		2994	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2995	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2996	used).
		2997
		2998	struct ev_loop *loop_hi = ev_default_init (0);
		2999	struct ev_loop *loop_lo = 0;
		3000	ev_embed embed;
		3001
		3002	// see if there is a chance of getting one that works
		3003	// (remember that a flags value of 0 means autodetection)
		3004	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3005	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3006	: 0;
		3007
		3008	// if we got one, then embed it, otherwise default to loop_hi
		3009	if (loop_lo)
		3010	{
		3011	ev_embed_init (&embed, 0, loop_lo);
		3012	ev_embed_start (loop_hi, &embed);
		3013	}
		3014	else
		3015	loop_lo = loop_hi;
		3016
		3017	Example: Check if kqueue is available but not recommended and create
		3018	a kqueue backend for use with sockets (which usually work with any
		3019	kqueue implementation). Store the kqueue/socket-only event loop in
		3020	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3021
		3022	struct ev_loop *loop = ev_default_init (0);
		3023	struct ev_loop *loop_socket = 0;
		3024	ev_embed embed;
		3025
		3026	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3027	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3028	{
		3029	ev_embed_init (&embed, 0, loop_socket);
		3030	ev_embed_start (loop, &embed);
		3031	}
		3032
		3033	if (!loop_socket)
		3034	loop_socket = loop;
		3035
		3036	// now use loop_socket for all sockets, and loop for everything else
1528		3037
1529		3038
1530	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3039	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1531		3040
1532	Fork watchers are called when a C<fork ()> was detected (usually because	3041	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1535	event loop blocks next and before C<ev_check> watchers are being called,	3044	event loop blocks next and before C<ev_check> watchers are being called,
1536	and only in the child after the fork. If whoever good citizen calling	3045	and only in the child after the fork. If whoever good citizen calling
1537	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3046	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1538	handlers will be invoked, too, of course.	3047	handlers will be invoked, too, of course.
1539		3048
		3049	=head3 The special problem of life after fork - how is it possible?
		3050
		3051	Most uses of C<fork()> consist of forking, then some simple calls to set
		3052	up/change the process environment, followed by a call to C<exec()>. This
		3053	sequence should be handled by libev without any problems.
		3054
		3055	This changes when the application actually wants to do event handling
		3056	in the child, or both parent in child, in effect "continuing" after the
		3057	fork.
		3058
		3059	The default mode of operation (for libev, with application help to detect
		3060	forks) is to duplicate all the state in the child, as would be expected
		3061	when I<either> the parent I<or> the child process continues.
		3062
		3063	When both processes want to continue using libev, then this is usually the
		3064	wrong result. In that case, usually one process (typically the parent) is
		3065	supposed to continue with all watchers in place as before, while the other
		3066	process typically wants to start fresh, i.e. without any active watchers.
		3067
		3068	The cleanest and most efficient way to achieve that with libev is to
		3069	simply create a new event loop, which of course will be "empty", and
		3070	use that for new watchers. This has the advantage of not touching more
		3071	memory than necessary, and thus avoiding the copy-on-write, and the
		3072	disadvantage of having to use multiple event loops (which do not support
		3073	signal watchers).
		3074
		3075	When this is not possible, or you want to use the default loop for
		3076	other reasons, then in the process that wants to start "fresh", call
		3077	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		3078	the default loop will "orphan" (not stop) all registered watchers, so you
		3079	have to be careful not to execute code that modifies those watchers. Note
		3080	also that in that case, you have to re-register any signal watchers.
		3081
		3082	=head3 Watcher-Specific Functions and Data Members
		3083
1540	=over 4	3084	=over 4
1541		3085
1542	=item ev_fork_init (ev_signal *, callback)	3086	=item ev_fork_init (ev_signal *, callback)
1543		3087
1544	Initialises and configures the fork watcher - it has no parameters of any	3088	Initialises and configures the fork watcher - it has no parameters of any
…		…
1546	believe me.	3090	believe me.
1547		3091
1548	=back	3092	=back
1549		3093
1550		3094
		3095	=head2 C<ev_async> - how to wake up an event loop
		3096
		3097	In general, you cannot use an C<ev_run> from multiple threads or other
		3098	asynchronous sources such as signal handlers (as opposed to multiple event
		3099	loops - those are of course safe to use in different threads).
		3100
		3101	Sometimes, however, you need to wake up an event loop you do not control,
		3102	for example because it belongs to another thread. This is what C<ev_async>
		3103	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3104	it by calling C<ev_async_send>, which is thread- and signal safe.
		3105
		3106	This functionality is very similar to C<ev_signal> watchers, as signals,
		3107	too, are asynchronous in nature, and signals, too, will be compressed
		3108	(i.e. the number of callback invocations may be less than the number of
		3109	C<ev_async_sent> calls).
		3110
		3111	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3112	just the default loop.
		3113
		3114	=head3 Queueing
		3115
		3116	C<ev_async> does not support queueing of data in any way. The reason
		3117	is that the author does not know of a simple (or any) algorithm for a
		3118	multiple-writer-single-reader queue that works in all cases and doesn't
		3119	need elaborate support such as pthreads or unportable memory access
		3120	semantics.
		3121
		3122	That means that if you want to queue data, you have to provide your own
		3123	queue. But at least I can tell you how to implement locking around your
		3124	queue:
		3125
		3126	=over 4
		3127
		3128	=item queueing from a signal handler context
		3129
		3130	To implement race-free queueing, you simply add to the queue in the signal
		3131	handler but you block the signal handler in the watcher callback. Here is
		3132	an example that does that for some fictitious SIGUSR1 handler:
		3133
		3134	static ev_async mysig;
		3135
		3136	static void
		3137	sigusr1_handler (void)
		3138	{
		3139	sometype data;
		3140
		3141	// no locking etc.
		3142	queue_put (data);
		3143	ev_async_send (EV_DEFAULT_ &mysig);
		3144	}
		3145
		3146	static void
		3147	mysig_cb (EV_P_ ev_async *w, int revents)
		3148	{
		3149	sometype data;
		3150	sigset_t block, prev;
		3151
		3152	sigemptyset (&block);
		3153	sigaddset (&block, SIGUSR1);
		3154	sigprocmask (SIG_BLOCK, &block, &prev);
		3155
		3156	while (queue_get (&data))
		3157	process (data);
		3158
		3159	if (sigismember (&prev, SIGUSR1)
		3160	sigprocmask (SIG_UNBLOCK, &block, 0);
		3161	}
		3162
		3163	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3164	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3165	either...).
		3166
		3167	=item queueing from a thread context
		3168
		3169	The strategy for threads is different, as you cannot (easily) block
		3170	threads but you can easily preempt them, so to queue safely you need to
		3171	employ a traditional mutex lock, such as in this pthread example:
		3172
		3173	static ev_async mysig;
		3174	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3175
		3176	static void
		3177	otherthread (void)
		3178	{
		3179	// only need to lock the actual queueing operation
		3180	pthread_mutex_lock (&mymutex);
		3181	queue_put (data);
		3182	pthread_mutex_unlock (&mymutex);
		3183
		3184	ev_async_send (EV_DEFAULT_ &mysig);
		3185	}
		3186
		3187	static void
		3188	mysig_cb (EV_P_ ev_async *w, int revents)
		3189	{
		3190	pthread_mutex_lock (&mymutex);
		3191
		3192	while (queue_get (&data))
		3193	process (data);
		3194
		3195	pthread_mutex_unlock (&mymutex);
		3196	}
		3197
		3198	=back
		3199
		3200
		3201	=head3 Watcher-Specific Functions and Data Members
		3202
		3203	=over 4
		3204
		3205	=item ev_async_init (ev_async *, callback)
		3206
		3207	Initialises and configures the async watcher - it has no parameters of any
		3208	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3209	trust me.
		3210
		3211	=item ev_async_send (loop, ev_async *)
		3212
		3213	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3214	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3215	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3216	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3217	section below on what exactly this means).
		3218
		3219	Note that, as with other watchers in libev, multiple events might get
		3220	compressed into a single callback invocation (another way to look at this
		3221	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3222	reset when the event loop detects that).
		3223
		3224	This call incurs the overhead of a system call only once per event loop
		3225	iteration, so while the overhead might be noticeable, it doesn't apply to
		3226	repeated calls to C<ev_async_send> for the same event loop.
		3227
		3228	=item bool = ev_async_pending (ev_async *)
		3229
		3230	Returns a non-zero value when C<ev_async_send> has been called on the
		3231	watcher but the event has not yet been processed (or even noted) by the
		3232	event loop.
		3233
		3234	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3235	the loop iterates next and checks for the watcher to have become active,
		3236	it will reset the flag again. C<ev_async_pending> can be used to very
		3237	quickly check whether invoking the loop might be a good idea.
		3238
		3239	Not that this does I<not> check whether the watcher itself is pending,
		3240	only whether it has been requested to make this watcher pending: there
		3241	is a time window between the event loop checking and resetting the async
		3242	notification, and the callback being invoked.
		3243
		3244	=back
		3245
		3246
1551	=head1 OTHER FUNCTIONS	3247	=head1 OTHER FUNCTIONS
1552		3248
1553	There are some other functions of possible interest. Described. Here. Now.	3249	There are some other functions of possible interest. Described. Here. Now.
1554		3250
1555	=over 4	3251	=over 4
1556		3252
1557	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3253	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1558		3254
1559	This function combines a simple timer and an I/O watcher, calls your	3255	This function combines a simple timer and an I/O watcher, calls your
1560	callback on whichever event happens first and automatically stop both	3256	callback on whichever event happens first and automatically stops both
1561	watchers. This is useful if you want to wait for a single event on an fd	3257	watchers. This is useful if you want to wait for a single event on an fd
1562	or timeout without having to allocate/configure/start/stop/free one or	3258	or timeout without having to allocate/configure/start/stop/free one or
1563	more watchers yourself.	3259	more watchers yourself.
1564		3260
1565	If C<fd> is less than 0, then no I/O watcher will be started and events	3261	If C<fd> is less than 0, then no I/O watcher will be started and the
1566	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3262	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1567	C<events> set will be craeted and started.	3263	the given C<fd> and C<events> set will be created and started.
1568		3264
1569	If C<timeout> is less than 0, then no timeout watcher will be	3265	If C<timeout> is less than 0, then no timeout watcher will be
1570	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3266	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1571	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3267	repeat = 0) will be started. C<0> is a valid timeout.
1572	dubious value.
1573		3268
1574	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3269	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1575	passed an C<revents> set like normal event callbacks (a combination of	3270	passed an C<revents> set like normal event callbacks (a combination of
1576	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3271	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1577	value passed to C<ev_once>:	3272	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3273	a timeout and an io event at the same time - you probably should give io
		3274	events precedence.
1578		3275
		3276	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3277
1579	static void stdin_ready (int revents, void *arg)	3278	static void stdin_ready (int revents, void *arg)
1580	{	3279	{
1581	if (revents & EV_TIMEOUT)
1582	/* doh, nothing entered */;
1583	else if (revents & EV_READ)	3280	if (revents & EV_READ)
1584	/* stdin might have data for us, joy! */;	3281	/* stdin might have data for us, joy! */;
		3282	else if (revents & EV_TIMER)
		3283	/* doh, nothing entered */;
1585	}	3284	}
1586		3285
1587	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3286	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1588		3287
1589	=item ev_feed_event (ev_loop *, watcher *, int revents)
1590
1591	Feeds the given event set into the event loop, as if the specified event
1592	had happened for the specified watcher (which must be a pointer to an
1593	initialised but not necessarily started event watcher).
1594
1595	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3288	=item ev_feed_fd_event (loop, int fd, int revents)
1596		3289
1597	Feed an event on the given fd, as if a file descriptor backend detected	3290	Feed an event on the given fd, as if a file descriptor backend detected
1598	the given events it.	3291	the given events it.
1599		3292
1600	=item ev_feed_signal_event (ev_loop *loop, int signum)	3293	=item ev_feed_signal_event (loop, int signum)
1601		3294
1602	Feed an event as if the given signal occured (C<loop> must be the default	3295	Feed an event as if the given signal occurred (C<loop> must be the default
1603	loop!).	3296	loop!).
1604		3297
1605	=back	3298	=back
1606		3299
1607		3300
…		…
1623		3316
1624	=item * Priorities are not currently supported. Initialising priorities	3317	=item * Priorities are not currently supported. Initialising priorities
1625	will fail and all watchers will have the same priority, even though there	3318	will fail and all watchers will have the same priority, even though there
1626	is an ev_pri field.	3319	is an ev_pri field.
1627		3320
		3321	=item * In libevent, the last base created gets the signals, in libev, the
		3322	first base created (== the default loop) gets the signals.
		3323
1628	=item * Other members are not supported.	3324	=item * Other members are not supported.
1629		3325
1630	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3326	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1631	to use the libev header file and library.	3327	to use the libev header file and library.
1632		3328
1633	=back	3329	=back
1634		3330
1635	=head1 C++ SUPPORT	3331	=head1 C++ SUPPORT
1636		3332
1637	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3333	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1638	you to use some convinience methods to start/stop watchers and also change	3334	you to use some convenience methods to start/stop watchers and also change
1639	the callback model to a model using method callbacks on objects.	3335	the callback model to a model using method callbacks on objects.
1640		3336
1641	To use it,	3337	To use it,
1642		3338
1643	#include <ev++.h>	3339	#include <ev++.h>
1644		3340
1645	(it is not installed by default). This automatically includes F<ev.h>	3341	This automatically includes F<ev.h> and puts all of its definitions (many
1646	and puts all of its definitions (many of them macros) into the global	3342	of them macros) into the global namespace. All C++ specific things are
1647	namespace. All C++ specific things are put into the C<ev> namespace.	3343	put into the C<ev> namespace. It should support all the same embedding
		3344	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1648		3345
1649	It should support all the same embedding options as F<ev.h>, most notably	3346	Care has been taken to keep the overhead low. The only data member the C++
1650	C<EV_MULTIPLICITY>.	3347	classes add (compared to plain C-style watchers) is the event loop pointer
		3348	that the watcher is associated with (or no additional members at all if
		3349	you disable C<EV_MULTIPLICITY> when embedding libev).
		3350
		3351	Currently, functions, and static and non-static member functions can be
		3352	used as callbacks. Other types should be easy to add as long as they only
		3353	need one additional pointer for context. If you need support for other
		3354	types of functors please contact the author (preferably after implementing
		3355	it).
1651		3356
1652	Here is a list of things available in the C<ev> namespace:	3357	Here is a list of things available in the C<ev> namespace:
1653		3358
1654	=over 4	3359	=over 4
1655		3360
…		…
1671		3376
1672	All of those classes have these methods:	3377	All of those classes have these methods:
1673		3378
1674	=over 4	3379	=over 4
1675		3380
1676	=item ev::TYPE::TYPE (object *, object::method *)	3381	=item ev::TYPE::TYPE ()
1677		3382
1678	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	3383	=item ev::TYPE::TYPE (loop)
1679		3384
1680	=item ev::TYPE::~TYPE	3385	=item ev::TYPE::~TYPE
1681		3386
1682	The constructor takes a pointer to an object and a method pointer to	3387	The constructor (optionally) takes an event loop to associate the watcher
1683	the event handler callback to call in this class. The constructor calls	3388	with. If it is omitted, it will use C<EV_DEFAULT>.
1684	C<ev_init> for you, which means you have to call the C<set> method	3389
1685	before starting it. If you do not specify a loop then the constructor	3390	The constructor calls C<ev_init> for you, which means you have to call the
1686	automatically associates the default loop with this watcher.	3391	C<set> method before starting it.
		3392
		3393	It will not set a callback, however: You have to call the templated C<set>
		3394	method to set a callback before you can start the watcher.
		3395
		3396	(The reason why you have to use a method is a limitation in C++ which does
		3397	not allow explicit template arguments for constructors).
1687		3398
1688	The destructor automatically stops the watcher if it is active.	3399	The destructor automatically stops the watcher if it is active.
1689		3400
		3401	=item w->set<class, &class::method> (object *)
		3402
		3403	This method sets the callback method to call. The method has to have a
		3404	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3405	first argument and the C<revents> as second. The object must be given as
		3406	parameter and is stored in the C<data> member of the watcher.
		3407
		3408	This method synthesizes efficient thunking code to call your method from
		3409	the C callback that libev requires. If your compiler can inline your
		3410	callback (i.e. it is visible to it at the place of the C<set> call and
		3411	your compiler is good :), then the method will be fully inlined into the
		3412	thunking function, making it as fast as a direct C callback.
		3413
		3414	Example: simple class declaration and watcher initialisation
		3415
		3416	struct myclass
		3417	{
		3418	void io_cb (ev::io &w, int revents) { }
		3419	}
		3420
		3421	myclass obj;
		3422	ev::io iow;
		3423	iow.set <myclass, &myclass::io_cb> (&obj);
		3424
		3425	=item w->set (object *)
		3426
		3427	This is a variation of a method callback - leaving out the method to call
		3428	will default the method to C<operator ()>, which makes it possible to use
		3429	functor objects without having to manually specify the C<operator ()> all
		3430	the time. Incidentally, you can then also leave out the template argument
		3431	list.
		3432
		3433	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3434	int revents)>.
		3435
		3436	See the method-C<set> above for more details.
		3437
		3438	Example: use a functor object as callback.
		3439
		3440	struct myfunctor
		3441	{
		3442	void operator() (ev::io &w, int revents)
		3443	{
		3444	...
		3445	}
		3446	}
		3447
		3448	myfunctor f;
		3449
		3450	ev::io w;
		3451	w.set (&f);
		3452
		3453	=item w->set<function> (void *data = 0)
		3454
		3455	Also sets a callback, but uses a static method or plain function as
		3456	callback. The optional C<data> argument will be stored in the watcher's
		3457	C<data> member and is free for you to use.
		3458
		3459	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3460
		3461	See the method-C<set> above for more details.
		3462
		3463	Example: Use a plain function as callback.
		3464
		3465	static void io_cb (ev::io &w, int revents) { }
		3466	iow.set <io_cb> ();
		3467
1690	=item w->set (struct ev_loop *)	3468	=item w->set (loop)
1691		3469
1692	Associates a different C<struct ev_loop> with this watcher. You can only	3470	Associates a different C<struct ev_loop> with this watcher. You can only
1693	do this when the watcher is inactive (and not pending either).	3471	do this when the watcher is inactive (and not pending either).
1694		3472
1695	=item w->set ([args])	3473	=item w->set ([arguments])
1696		3474
1697	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3475	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
1698	called at least once. Unlike the C counterpart, an active watcher gets	3476	method or a suitable start method must be called at least once. Unlike the
1699	automatically stopped and restarted.	3477	C counterpart, an active watcher gets automatically stopped and restarted
		3478	when reconfiguring it with this method.
1700		3479
1701	=item w->start ()	3480	=item w->start ()
1702		3481
1703	Starts the watcher. Note that there is no C<loop> argument as the	3482	Starts the watcher. Note that there is no C<loop> argument, as the
1704	constructor already takes the loop.	3483	constructor already stores the event loop.
		3484
		3485	=item w->start ([arguments])
		3486
		3487	Instead of calling C<set> and C<start> methods separately, it is often
		3488	convenient to wrap them in one call. Uses the same type of arguments as
		3489	the configure C<set> method of the watcher.
1705		3490
1706	=item w->stop ()	3491	=item w->stop ()
1707		3492
1708	Stops the watcher if it is active. Again, no C<loop> argument.	3493	Stops the watcher if it is active. Again, no C<loop> argument.
1709		3494
1710	=item w->again () C<ev::timer>, C<ev::periodic> only	3495	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1711		3496
1712	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3497	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1713	C<ev_TYPE_again> function.	3498	C<ev_TYPE_again> function.
1714		3499
1715	=item w->sweep () C<ev::embed> only	3500	=item w->sweep () (C<ev::embed> only)
1716		3501
1717	Invokes C<ev_embed_sweep>.	3502	Invokes C<ev_embed_sweep>.
1718		3503
1719	=item w->update () C<ev::stat> only	3504	=item w->update () (C<ev::stat> only)
1720		3505
1721	Invokes C<ev_stat_stat>.	3506	Invokes C<ev_stat_stat>.
1722		3507
1723	=back	3508	=back
1724		3509
1725	=back	3510	=back
1726		3511
1727	Example: Define a class with an IO and idle watcher, start one of them in	3512	Example: Define a class with two I/O and idle watchers, start the I/O
1728	the constructor.	3513	watchers in the constructor.
1729		3514
1730	class myclass	3515	class myclass
1731	{	3516	{
1732	ev_io io; void io_cb (ev::io &w, int revents);	3517	ev::io io ; void io_cb (ev::io &w, int revents);
		3518	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
1733	ev_idle idle void idle_cb (ev::idle &w, int revents);	3519	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1734		3520
1735	myclass ();	3521	myclass (int fd)
		3522	{
		3523	io .set <myclass, &myclass::io_cb > (this);
		3524	io2 .set <myclass, &myclass::io2_cb > (this);
		3525	idle.set <myclass, &myclass::idle_cb> (this);
		3526
		3527	io.set (fd, ev::WRITE); // configure the watcher
		3528	io.start (); // start it whenever convenient
		3529
		3530	io2.start (fd, ev::READ); // set + start in one call
		3531	}
1736	}	3532	};
1737		3533
1738	myclass::myclass (int fd)	3534
1739	: io (this, &myclass::io_cb),	3535	=head1 OTHER LANGUAGE BINDINGS
1740	idle (this, &myclass::idle_cb)	3536
1741	{	3537	Libev does not offer other language bindings itself, but bindings for a
1742	io.start (fd, ev::READ);	3538	number of languages exist in the form of third-party packages. If you know
1743	}	3539	any interesting language binding in addition to the ones listed here, drop
		3540	me a note.
		3541
		3542	=over 4
		3543
		3544	=item Perl
		3545
		3546	The EV module implements the full libev API and is actually used to test
		3547	libev. EV is developed together with libev. Apart from the EV core module,
		3548	there are additional modules that implement libev-compatible interfaces
		3549	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3550	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3551	and C<EV::Glib>).
		3552
		3553	It can be found and installed via CPAN, its homepage is at
		3554	L<http://software.schmorp.de/pkg/EV>.
		3555
		3556	=item Python
		3557
		3558	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3559	seems to be quite complete and well-documented.
		3560
		3561	=item Ruby
		3562
		3563	Tony Arcieri has written a ruby extension that offers access to a subset
		3564	of the libev API and adds file handle abstractions, asynchronous DNS and
		3565	more on top of it. It can be found via gem servers. Its homepage is at
		3566	L<http://rev.rubyforge.org/>.
		3567
		3568	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3569	makes rev work even on mingw.
		3570
		3571	=item Haskell
		3572
		3573	A haskell binding to libev is available at
		3574	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3575
		3576	=item D
		3577
		3578	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3579	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3580
		3581	=item Ocaml
		3582
		3583	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3584	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3585
		3586	=item Lua
		3587
		3588	Brian Maher has written a partial interface to libev for lua (at the
		3589	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3590	L<http://github.com/brimworks/lua-ev>.
		3591
		3592	=back
1744		3593
1745		3594
1746	=head1 MACRO MAGIC	3595	=head1 MACRO MAGIC
1747		3596
1748	Libev can be compiled with a variety of options, the most fundemantal is	3597	Libev can be compiled with a variety of options, the most fundamental
1749	C<EV_MULTIPLICITY>. This option determines wether (most) functions and	3598	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1750	callbacks have an initial C<struct ev_loop *> argument.	3599	functions and callbacks have an initial C<struct ev_loop *> argument.
1751		3600
1752	To make it easier to write programs that cope with either variant, the	3601	To make it easier to write programs that cope with either variant, the
1753	following macros are defined:	3602	following macros are defined:
1754		3603
1755	=over 4	3604	=over 4
…		…
1758		3607
1759	This provides the loop I<argument> for functions, if one is required ("ev	3608	This provides the loop I<argument> for functions, if one is required ("ev
1760	loop argument"). The C<EV_A> form is used when this is the sole argument,	3609	loop argument"). The C<EV_A> form is used when this is the sole argument,
1761	C<EV_A_> is used when other arguments are following. Example:	3610	C<EV_A_> is used when other arguments are following. Example:
1762		3611
1763	ev_unref (EV_A);	3612	ev_unref (EV_A);
1764	ev_timer_add (EV_A_ watcher);	3613	ev_timer_add (EV_A_ watcher);
1765	ev_loop (EV_A_ 0);	3614	ev_run (EV_A_ 0);
1766		3615
1767	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3616	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1768	which is often provided by the following macro.	3617	which is often provided by the following macro.
1769		3618
1770	=item C<EV_P>, C<EV_P_>	3619	=item C<EV_P>, C<EV_P_>
1771		3620
1772	This provides the loop I<parameter> for functions, if one is required ("ev	3621	This provides the loop I<parameter> for functions, if one is required ("ev
1773	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3622	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1774	C<EV_P_> is used when other parameters are following. Example:	3623	C<EV_P_> is used when other parameters are following. Example:
1775		3624
1776	// this is how ev_unref is being declared	3625	// this is how ev_unref is being declared
1777	static void ev_unref (EV_P);	3626	static void ev_unref (EV_P);
1778		3627
1779	// this is how you can declare your typical callback	3628	// this is how you can declare your typical callback
1780	static void cb (EV_P_ ev_timer *w, int revents)	3629	static void cb (EV_P_ ev_timer *w, int revents)
1781		3630
1782	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3631	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1783	suitable for use with C<EV_A>.	3632	suitable for use with C<EV_A>.
1784		3633
1785	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3634	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1786		3635
1787	Similar to the other two macros, this gives you the value of the default	3636	Similar to the other two macros, this gives you the value of the default
1788	loop, if multiple loops are supported ("ev loop default").	3637	loop, if multiple loops are supported ("ev loop default").
1789		3638
		3639	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3640
		3641	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3642	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3643	is undefined when the default loop has not been initialised by a previous
		3644	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3645
		3646	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3647	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3648
1790	=back	3649	=back
1791		3650
1792	Example: Declare and initialise a check watcher, working regardless of	3651	Example: Declare and initialise a check watcher, utilising the above
1793	wether multiple loops are supported or not.	3652	macros so it will work regardless of whether multiple loops are supported
		3653	or not.
1794		3654
1795	static void	3655	static void
1796	check_cb (EV_P_ ev_timer *w, int revents)	3656	check_cb (EV_P_ ev_timer *w, int revents)
1797	{	3657	{
1798	ev_check_stop (EV_A_ w);	3658	ev_check_stop (EV_A_ w);
1799	}	3659	}
1800		3660
1801	ev_check check;	3661	ev_check check;
1802	ev_check_init (&check, check_cb);	3662	ev_check_init (&check, check_cb);
1803	ev_check_start (EV_DEFAULT_ &check);	3663	ev_check_start (EV_DEFAULT_ &check);
1804	ev_loop (EV_DEFAULT_ 0);	3664	ev_run (EV_DEFAULT_ 0);
1805
1806		3665
1807	=head1 EMBEDDING	3666	=head1 EMBEDDING
1808		3667
1809	Libev can (and often is) directly embedded into host	3668	Libev can (and often is) directly embedded into host
1810	applications. Examples of applications that embed it include the Deliantra	3669	applications. Examples of applications that embed it include the Deliantra
1811	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3670	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1812	and rxvt-unicode.	3671	and rxvt-unicode.
1813		3672
1814	The goal is to enable you to just copy the neecssary files into your	3673	The goal is to enable you to just copy the necessary files into your
1815	source directory without having to change even a single line in them, so	3674	source directory without having to change even a single line in them, so
1816	you can easily upgrade by simply copying (or having a checked-out copy of	3675	you can easily upgrade by simply copying (or having a checked-out copy of
1817	libev somewhere in your source tree).	3676	libev somewhere in your source tree).
1818		3677
1819	=head2 FILESETS	3678	=head2 FILESETS
1820		3679
1821	Depending on what features you need you need to include one or more sets of files	3680	Depending on what features you need you need to include one or more sets of files
1822	in your app.	3681	in your application.
1823		3682
1824	=head3 CORE EVENT LOOP	3683	=head3 CORE EVENT LOOP
1825		3684
1826	To include only the libev core (all the C<ev_*> functions), with manual	3685	To include only the libev core (all the C<ev_*> functions), with manual
1827	configuration (no autoconf):	3686	configuration (no autoconf):
1828		3687
1829	#define EV_STANDALONE 1	3688	#define EV_STANDALONE 1
1830	#include "ev.c"	3689	#include "ev.c"
1831		3690
1832	This will automatically include F<ev.h>, too, and should be done in a	3691	This will automatically include F<ev.h>, too, and should be done in a
1833	single C source file only to provide the function implementations. To use	3692	single C source file only to provide the function implementations. To use
1834	it, do the same for F<ev.h> in all files wishing to use this API (best	3693	it, do the same for F<ev.h> in all files wishing to use this API (best
1835	done by writing a wrapper around F<ev.h> that you can include instead and	3694	done by writing a wrapper around F<ev.h> that you can include instead and
1836	where you can put other configuration options):	3695	where you can put other configuration options):
1837		3696
1838	#define EV_STANDALONE 1	3697	#define EV_STANDALONE 1
1839	#include "ev.h"	3698	#include "ev.h"
1840		3699
1841	Both header files and implementation files can be compiled with a C++	3700	Both header files and implementation files can be compiled with a C++
1842	compiler (at least, thats a stated goal, and breakage will be treated	3701	compiler (at least, that's a stated goal, and breakage will be treated
1843	as a bug).	3702	as a bug).
1844		3703
1845	You need the following files in your source tree, or in a directory	3704	You need the following files in your source tree, or in a directory
1846	in your include path (e.g. in libev/ when using -Ilibev):	3705	in your include path (e.g. in libev/ when using -Ilibev):
1847		3706
1848	ev.h	3707	ev.h
1849	ev.c	3708	ev.c
1850	ev_vars.h	3709	ev_vars.h
1851	ev_wrap.h	3710	ev_wrap.h
1852		3711
1853	ev_win32.c required on win32 platforms only	3712	ev_win32.c required on win32 platforms only
1854		3713
1855	ev_select.c only when select backend is enabled (which is by default)	3714	ev_select.c only when select backend is enabled (which is enabled by default)
1856	ev_poll.c only when poll backend is enabled (disabled by default)	3715	ev_poll.c only when poll backend is enabled (disabled by default)
1857	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3716	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1858	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3717	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1859	ev_port.c only when the solaris port backend is enabled (disabled by default)	3718	ev_port.c only when the solaris port backend is enabled (disabled by default)
1860		3719
1861	F<ev.c> includes the backend files directly when enabled, so you only need	3720	F<ev.c> includes the backend files directly when enabled, so you only need
1862	to compile this single file.	3721	to compile this single file.
1863		3722
1864	=head3 LIBEVENT COMPATIBILITY API	3723	=head3 LIBEVENT COMPATIBILITY API
1865		3724
1866	To include the libevent compatibility API, also include:	3725	To include the libevent compatibility API, also include:
1867		3726
1868	#include "event.c"	3727	#include "event.c"
1869		3728
1870	in the file including F<ev.c>, and:	3729	in the file including F<ev.c>, and:
1871		3730
1872	#include "event.h"	3731	#include "event.h"
1873		3732
1874	in the files that want to use the libevent API. This also includes F<ev.h>.	3733	in the files that want to use the libevent API. This also includes F<ev.h>.
1875		3734
1876	You need the following additional files for this:	3735	You need the following additional files for this:
1877		3736
1878	event.h	3737	event.h
1879	event.c	3738	event.c
1880		3739
1881	=head3 AUTOCONF SUPPORT	3740	=head3 AUTOCONF SUPPORT
1882		3741
1883	Instead of using C<EV_STANDALONE=1> and providing your config in	3742	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1884	whatever way you want, you can also C<m4_include([libev.m4])> in your	3743	whatever way you want, you can also C<m4_include([libev.m4])> in your
1885	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3744	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1886	include F<config.h> and configure itself accordingly.	3745	include F<config.h> and configure itself accordingly.
1887		3746
1888	For this of course you need the m4 file:	3747	For this of course you need the m4 file:
1889		3748
1890	libev.m4	3749	libev.m4
1891		3750
1892	=head2 PREPROCESSOR SYMBOLS/MACROS	3751	=head2 PREPROCESSOR SYMBOLS/MACROS
1893		3752
1894	Libev can be configured via a variety of preprocessor symbols you have to define	3753	Libev can be configured via a variety of preprocessor symbols you have to
1895	before including any of its files. The default is not to build for multiplicity	3754	define before including (or compiling) any of its files. The default in
1896	and only include the select backend.	3755	the absence of autoconf is documented for every option.
		3756
		3757	Symbols marked with "(h)" do not change the ABI, and can have different
		3758	values when compiling libev vs. including F<ev.h>, so it is permissible
		3759	to redefine them before including F<ev.h> without breaking compatibility
		3760	to a compiled library. All other symbols change the ABI, which means all
		3761	users of libev and the libev code itself must be compiled with compatible
		3762	settings.
1897		3763
1898	=over 4	3764	=over 4
1899		3765
		3766	=item EV_COMPAT3 (h)
		3767
		3768	Backwards compatibility is a major concern for libev. This is why this
		3769	release of libev comes with wrappers for the functions and symbols that
		3770	have been renamed between libev version 3 and 4.
		3771
		3772	You can disable these wrappers (to test compatibility with future
		3773	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3774	sources. This has the additional advantage that you can drop the C<struct>
		3775	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3776	typedef in that case.
		3777
		3778	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3779	and in some even more future version the compatibility code will be
		3780	removed completely.
		3781
1900	=item EV_STANDALONE	3782	=item EV_STANDALONE (h)
1901		3783
1902	Must always be C<1> if you do not use autoconf configuration, which	3784	Must always be C<1> if you do not use autoconf configuration, which
1903	keeps libev from including F<config.h>, and it also defines dummy	3785	keeps libev from including F<config.h>, and it also defines dummy
1904	implementations for some libevent functions (such as logging, which is not	3786	implementations for some libevent functions (such as logging, which is not
1905	supported). It will also not define any of the structs usually found in	3787	supported). It will also not define any of the structs usually found in
1906	F<event.h> that are not directly supported by the libev core alone.	3788	F<event.h> that are not directly supported by the libev core alone.
1907		3789
		3790	In standalone mode, libev will still try to automatically deduce the
		3791	configuration, but has to be more conservative.
		3792
1908	=item EV_USE_MONOTONIC	3793	=item EV_USE_MONOTONIC
1909		3794
1910	If defined to be C<1>, libev will try to detect the availability of the	3795	If defined to be C<1>, libev will try to detect the availability of the
1911	monotonic clock option at both compiletime and runtime. Otherwise no use	3796	monotonic clock option at both compile time and runtime. Otherwise no
1912	of the monotonic clock option will be attempted. If you enable this, you	3797	use of the monotonic clock option will be attempted. If you enable this,
1913	usually have to link against librt or something similar. Enabling it when	3798	you usually have to link against librt or something similar. Enabling it
1914	the functionality isn't available is safe, though, althoguh you have	3799	when the functionality isn't available is safe, though, although you have
1915	to make sure you link against any libraries where the C<clock_gettime>	3800	to make sure you link against any libraries where the C<clock_gettime>
1916	function is hiding in (often F<-lrt>).	3801	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
1917		3802
1918	=item EV_USE_REALTIME	3803	=item EV_USE_REALTIME
1919		3804
1920	If defined to be C<1>, libev will try to detect the availability of the	3805	If defined to be C<1>, libev will try to detect the availability of the
1921	realtime clock option at compiletime (and assume its availability at	3806	real-time clock option at compile time (and assume its availability
1922	runtime if successful). Otherwise no use of the realtime clock option will	3807	at runtime if successful). Otherwise no use of the real-time clock
1923	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3808	option will be attempted. This effectively replaces C<gettimeofday>
1924	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3809	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
1925	in the description of C<EV_USE_MONOTONIC>, though.	3810	correctness. See the note about libraries in the description of
		3811	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3812	C<EV_USE_CLOCK_SYSCALL>.
		3813
		3814	=item EV_USE_CLOCK_SYSCALL
		3815
		3816	If defined to be C<1>, libev will try to use a direct syscall instead
		3817	of calling the system-provided C<clock_gettime> function. This option
		3818	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3819	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3820	programs needlessly. Using a direct syscall is slightly slower (in
		3821	theory), because no optimised vdso implementation can be used, but avoids
		3822	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3823	higher, as it simplifies linking (no need for C<-lrt>).
		3824
		3825	=item EV_USE_NANOSLEEP
		3826
		3827	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3828	and will use it for delays. Otherwise it will use C<select ()>.
		3829
		3830	=item EV_USE_EVENTFD
		3831
		3832	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3833	available and will probe for kernel support at runtime. This will improve
		3834	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3835	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3836	2.7 or newer, otherwise disabled.
1926		3837
1927	=item EV_USE_SELECT	3838	=item EV_USE_SELECT
1928		3839
1929	If undefined or defined to be C<1>, libev will compile in support for the	3840	If undefined or defined to be C<1>, libev will compile in support for the
1930	C<select>(2) backend. No attempt at autodetection will be done: if no	3841	C<select>(2) backend. No attempt at auto-detection will be done: if no
1931	other method takes over, select will be it. Otherwise the select backend	3842	other method takes over, select will be it. Otherwise the select backend
1932	will not be compiled in.	3843	will not be compiled in.
1933		3844
1934	=item EV_SELECT_USE_FD_SET	3845	=item EV_SELECT_USE_FD_SET
1935		3846
1936	If defined to C<1>, then the select backend will use the system C<fd_set>	3847	If defined to C<1>, then the select backend will use the system C<fd_set>
1937	structure. This is useful if libev doesn't compile due to a missing	3848	structure. This is useful if libev doesn't compile due to a missing
1938	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3849	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
1939	exotic systems. This usually limits the range of file descriptors to some	3850	on exotic systems. This usually limits the range of file descriptors to
1940	low limit such as 1024 or might have other limitations (winsocket only	3851	some low limit such as 1024 or might have other limitations (winsocket
1941	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3852	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
1942	influence the size of the C<fd_set> used.	3853	configures the maximum size of the C<fd_set>.
1943		3854
1944	=item EV_SELECT_IS_WINSOCKET	3855	=item EV_SELECT_IS_WINSOCKET
1945		3856
1946	When defined to C<1>, the select backend will assume that	3857	When defined to C<1>, the select backend will assume that
1947	select/socket/connect etc. don't understand file descriptors but	3858	select/socket/connect etc. don't understand file descriptors but
…		…
1949	be used is the winsock select). This means that it will call	3860	be used is the winsock select). This means that it will call
1950	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3861	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1951	it is assumed that all these functions actually work on fds, even	3862	it is assumed that all these functions actually work on fds, even
1952	on win32. Should not be defined on non-win32 platforms.	3863	on win32. Should not be defined on non-win32 platforms.
1953		3864
		3865	=item EV_FD_TO_WIN32_HANDLE(fd)
		3866
		3867	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3868	file descriptors to socket handles. When not defining this symbol (the
		3869	default), then libev will call C<_get_osfhandle>, which is usually
		3870	correct. In some cases, programs use their own file descriptor management,
		3871	in which case they can provide this function to map fds to socket handles.
		3872
		3873	=item EV_WIN32_HANDLE_TO_FD(handle)
		3874
		3875	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3876	using the standard C<_open_osfhandle> function. For programs implementing
		3877	their own fd to handle mapping, overwriting this function makes it easier
		3878	to do so. This can be done by defining this macro to an appropriate value.
		3879
		3880	=item EV_WIN32_CLOSE_FD(fd)
		3881
		3882	If programs implement their own fd to handle mapping on win32, then this
		3883	macro can be used to override the C<close> function, useful to unregister
		3884	file descriptors again. Note that the replacement function has to close
		3885	the underlying OS handle.
		3886
1954	=item EV_USE_POLL	3887	=item EV_USE_POLL
1955		3888
1956	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3889	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1957	backend. Otherwise it will be enabled on non-win32 platforms. It	3890	backend. Otherwise it will be enabled on non-win32 platforms. It
1958	takes precedence over select.	3891	takes precedence over select.
1959		3892
1960	=item EV_USE_EPOLL	3893	=item EV_USE_EPOLL
1961		3894
1962	If defined to be C<1>, libev will compile in support for the Linux	3895	If defined to be C<1>, libev will compile in support for the Linux
1963	C<epoll>(7) backend. Its availability will be detected at runtime,	3896	C<epoll>(7) backend. Its availability will be detected at runtime,
1964	otherwise another method will be used as fallback. This is the	3897	otherwise another method will be used as fallback. This is the preferred
1965	preferred backend for GNU/Linux systems.	3898	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3899	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1966		3900
1967	=item EV_USE_KQUEUE	3901	=item EV_USE_KQUEUE
1968		3902
1969	If defined to be C<1>, libev will compile in support for the BSD style	3903	If defined to be C<1>, libev will compile in support for the BSD style
1970	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3904	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
1983	otherwise another method will be used as fallback. This is the preferred	3917	otherwise another method will be used as fallback. This is the preferred
1984	backend for Solaris 10 systems.	3918	backend for Solaris 10 systems.
1985		3919
1986	=item EV_USE_DEVPOLL	3920	=item EV_USE_DEVPOLL
1987		3921
1988	reserved for future expansion, works like the USE symbols above.	3922	Reserved for future expansion, works like the USE symbols above.
1989		3923
		3924	=item EV_USE_INOTIFY
		3925
		3926	If defined to be C<1>, libev will compile in support for the Linux inotify
		3927	interface to speed up C<ev_stat> watchers. Its actual availability will
		3928	be detected at runtime. If undefined, it will be enabled if the headers
		3929	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3930
		3931	=item EV_ATOMIC_T
		3932
		3933	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3934	access is atomic with respect to other threads or signal contexts. No such
		3935	type is easily found in the C language, so you can provide your own type
		3936	that you know is safe for your purposes. It is used both for signal handler "locking"
		3937	as well as for signal and thread safety in C<ev_async> watchers.
		3938
		3939	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3940	(from F<signal.h>), which is usually good enough on most platforms.
		3941
1990	=item EV_H	3942	=item EV_H (h)
1991		3943
1992	The name of the F<ev.h> header file used to include it. The default if	3944	The name of the F<ev.h> header file used to include it. The default if
1993	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3945	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
1994	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3946	used to virtually rename the F<ev.h> header file in case of conflicts.
1995		3947
1996	=item EV_CONFIG_H	3948	=item EV_CONFIG_H (h)
1997		3949
1998	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3950	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
1999	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3951	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2000	C<EV_H>, above.	3952	C<EV_H>, above.
2001		3953
2002	=item EV_EVENT_H	3954	=item EV_EVENT_H (h)
2003		3955
2004	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3956	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2005	of how the F<event.h> header can be found.	3957	of how the F<event.h> header can be found, the default is C<"event.h">.
2006		3958
2007	=item EV_PROTOTYPES	3959	=item EV_PROTOTYPES (h)
2008		3960
2009	If defined to be C<0>, then F<ev.h> will not define any function	3961	If defined to be C<0>, then F<ev.h> will not define any function
2010	prototypes, but still define all the structs and other symbols. This is	3962	prototypes, but still define all the structs and other symbols. This is
2011	occasionally useful if you want to provide your own wrapper functions	3963	occasionally useful if you want to provide your own wrapper functions
2012	around libev functions.	3964	around libev functions.
…		…
2017	will have the C<struct ev_loop *> as first argument, and you can create	3969	will have the C<struct ev_loop *> as first argument, and you can create
2018	additional independent event loops. Otherwise there will be no support	3970	additional independent event loops. Otherwise there will be no support
2019	for multiple event loops and there is no first event loop pointer	3971	for multiple event loops and there is no first event loop pointer
2020	argument. Instead, all functions act on the single default loop.	3972	argument. Instead, all functions act on the single default loop.
2021		3973
2022	=item EV_PERIODIC_ENABLE
2023
2024	If undefined or defined to be C<1>, then periodic timers are supported. If
2025	defined to be C<0>, then they are not. Disabling them saves a few kB of
2026	code.
2027
2028	=item EV_EMBED_ENABLE
2029
2030	If undefined or defined to be C<1>, then embed watchers are supported. If
2031	defined to be C<0>, then they are not.
2032
2033	=item EV_STAT_ENABLE
2034
2035	If undefined or defined to be C<1>, then stat watchers are supported. If
2036	defined to be C<0>, then they are not.
2037
2038	=item EV_FORK_ENABLE
2039
2040	If undefined or defined to be C<1>, then fork watchers are supported. If
2041	defined to be C<0>, then they are not.
2042
2043	=item EV_MINIMAL	3974	=item EV_MINPRI
		3975
		3976	=item EV_MAXPRI
		3977
		3978	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3979	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3980	provide for more priorities by overriding those symbols (usually defined
		3981	to be C<-2> and C<2>, respectively).
		3982
		3983	When doing priority-based operations, libev usually has to linearly search
		3984	all the priorities, so having many of them (hundreds) uses a lot of space
		3985	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3986	fine.
		3987
		3988	If your embedding application does not need any priorities, defining these
		3989	both to C<0> will save some memory and CPU.
		3990
		3991	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3992	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3993	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
		3994
		3995	If undefined or defined to be C<1> (and the platform supports it), then
		3996	the respective watcher type is supported. If defined to be C<0>, then it
		3997	is not. Disabling watcher types mainly saves code size.
		3998
		3999	=item EV_FEATURES
2044		4000
2045	If you need to shave off some kilobytes of code at the expense of some	4001	If you need to shave off some kilobytes of code at the expense of some
2046	speed, define this symbol to C<1>. Currently only used for gcc to override	4002	speed (but with the full API), you can define this symbol to request
2047	some inlining decisions, saves roughly 30% codesize of amd64.	4003	certain subsets of functionality. The default is to enable all features
		4004	that can be enabled on the platform.
		4005
		4006	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4007	with some broad features you want) and then selectively re-enable
		4008	additional parts you want, for example if you want everything minimal,
		4009	but multiple event loop support, async and child watchers and the poll
		4010	backend, use this:
		4011
		4012	#define EV_FEATURES 0
		4013	#define EV_MULTIPLICITY 1
		4014	#define EV_USE_POLL 1
		4015	#define EV_CHILD_ENABLE 1
		4016	#define EV_ASYNC_ENABLE 1
		4017
		4018	The actual value is a bitset, it can be a combination of the following
		4019	values:
		4020
		4021	=over 4
		4022
		4023	=item C<1> - faster/larger code
		4024
		4025	Use larger code to speed up some operations.
		4026
		4027	Currently this is used to override some inlining decisions (enlarging the
		4028	code size by roughly 30% on amd64).
		4029
		4030	When optimising for size, use of compiler flags such as C<-Os> with
		4031	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4032	assertions.
		4033
		4034	=item C<2> - faster/larger data structures
		4035
		4036	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4037	hash table sizes and so on. This will usually further increase code size
		4038	and can additionally have an effect on the size of data structures at
		4039	runtime.
		4040
		4041	=item C<4> - full API configuration
		4042
		4043	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4044	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4045
		4046	=item C<8> - full API
		4047
		4048	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4049	details on which parts of the API are still available without this
		4050	feature, and do not complain if this subset changes over time.
		4051
		4052	=item C<16> - enable all optional watcher types
		4053
		4054	Enables all optional watcher types. If you want to selectively enable
		4055	only some watcher types other than I/O and timers (e.g. prepare,
		4056	embed, async, child...) you can enable them manually by defining
		4057	C<EV_watchertype_ENABLE> to C<1> instead.
		4058
		4059	=item C<32> - enable all backends
		4060
		4061	This enables all backends - without this feature, you need to enable at
		4062	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4063
		4064	=item C<64> - enable OS-specific "helper" APIs
		4065
		4066	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4067	default.
		4068
		4069	=back
		4070
		4071	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4072	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4073	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4074	watchers, timers and monotonic clock support.
		4075
		4076	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4077	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4078	your program might be left out as well - a binary starting a timer and an
		4079	I/O watcher then might come out at only 5Kb.
		4080
		4081	=item EV_AVOID_STDIO
		4082
		4083	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4084	functions (printf, scanf, perror etc.). This will increase the code size
		4085	somewhat, but if your program doesn't otherwise depend on stdio and your
		4086	libc allows it, this avoids linking in the stdio library which is quite
		4087	big.
		4088
		4089	Note that error messages might become less precise when this option is
		4090	enabled.
		4091
		4092	=item EV_NSIG
		4093
		4094	The highest supported signal number, +1 (or, the number of
		4095	signals): Normally, libev tries to deduce the maximum number of signals
		4096	automatically, but sometimes this fails, in which case it can be
		4097	specified. Also, using a lower number than detected (C<32> should be
		4098	good for about any system in existence) can save some memory, as libev
		4099	statically allocates some 12-24 bytes per signal number.
2048		4100
2049	=item EV_PID_HASHSIZE	4101	=item EV_PID_HASHSIZE
2050		4102
2051	C<ev_child> watchers use a small hash table to distribute workload by	4103	C<ev_child> watchers use a small hash table to distribute workload by
2052	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4104	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2053	than enough. If you need to manage thousands of children you might want to	4105	usually more than enough. If you need to manage thousands of children you
2054	increase this value.	4106	might want to increase this value (I<must> be a power of two).
		4107
		4108	=item EV_INOTIFY_HASHSIZE
		4109
		4110	C<ev_stat> watchers use a small hash table to distribute workload by
		4111	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
		4112	disabled), usually more than enough. If you need to manage thousands of
		4113	C<ev_stat> watchers you might want to increase this value (I<must> be a
		4114	power of two).
		4115
		4116	=item EV_USE_4HEAP
		4117
		4118	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4119	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4120	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4121	faster performance with many (thousands) of watchers.
		4122
		4123	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4124	will be C<0>.
		4125
		4126	=item EV_HEAP_CACHE_AT
		4127
		4128	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4129	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4130	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4131	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4132	but avoids random read accesses on heap changes. This improves performance
		4133	noticeably with many (hundreds) of watchers.
		4134
		4135	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4136	will be C<0>.
		4137
		4138	=item EV_VERIFY
		4139
		4140	Controls how much internal verification (see C<ev_verify ()>) will
		4141	be done: If set to C<0>, no internal verification code will be compiled
		4142	in. If set to C<1>, then verification code will be compiled in, but not
		4143	called. If set to C<2>, then the internal verification code will be
		4144	called once per loop, which can slow down libev. If set to C<3>, then the
		4145	verification code will be called very frequently, which will slow down
		4146	libev considerably.
		4147
		4148	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4149	will be C<0>.
2055		4150
2056	=item EV_COMMON	4151	=item EV_COMMON
2057		4152
2058	By default, all watchers have a C<void *data> member. By redefining	4153	By default, all watchers have a C<void *data> member. By redefining
2059	this macro to a something else you can include more and other types of	4154	this macro to something else you can include more and other types of
2060	members. You have to define it each time you include one of the files,	4155	members. You have to define it each time you include one of the files,
2061	though, and it must be identical each time.	4156	though, and it must be identical each time.
2062		4157
2063	For example, the perl EV module uses something like this:	4158	For example, the perl EV module uses something like this:
2064		4159
2065	#define EV_COMMON \	4160	#define EV_COMMON \
2066	SV *self; /* contains this struct */ \	4161	SV *self; /* contains this struct */ \
2067	SV *cb_sv, *fh /* note no trailing ";" */	4162	SV *cb_sv, *fh /* note no trailing ";" */
2068		4163
2069	=item EV_CB_DECLARE (type)	4164	=item EV_CB_DECLARE (type)
2070		4165
2071	=item EV_CB_INVOKE (watcher, revents)	4166	=item EV_CB_INVOKE (watcher, revents)
2072		4167
2073	=item ev_set_cb (ev, cb)	4168	=item ev_set_cb (ev, cb)
2074		4169
2075	Can be used to change the callback member declaration in each watcher,	4170	Can be used to change the callback member declaration in each watcher,
2076	and the way callbacks are invoked and set. Must expand to a struct member	4171	and the way callbacks are invoked and set. Must expand to a struct member
2077	definition and a statement, respectively. See the F<ev.v> header file for	4172	definition and a statement, respectively. See the F<ev.h> header file for
2078	their default definitions. One possible use for overriding these is to	4173	their default definitions. One possible use for overriding these is to
2079	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4174	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2080	method calls instead of plain function calls in C++.	4175	method calls instead of plain function calls in C++.
		4176
		4177	=back
		4178
		4179	=head2 EXPORTED API SYMBOLS
		4180
		4181	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4182	exported symbols, you can use the provided F<Symbol.*> files which list
		4183	all public symbols, one per line:
		4184
		4185	Symbols.ev for libev proper
		4186	Symbols.event for the libevent emulation
		4187
		4188	This can also be used to rename all public symbols to avoid clashes with
		4189	multiple versions of libev linked together (which is obviously bad in
		4190	itself, but sometimes it is inconvenient to avoid this).
		4191
		4192	A sed command like this will create wrapper C<#define>'s that you need to
		4193	include before including F<ev.h>:
		4194
		4195	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4196
		4197	This would create a file F<wrap.h> which essentially looks like this:
		4198
		4199	#define ev_backend myprefix_ev_backend
		4200	#define ev_check_start myprefix_ev_check_start
		4201	#define ev_check_stop myprefix_ev_check_stop
		4202	...
2081		4203
2082	=head2 EXAMPLES	4204	=head2 EXAMPLES
2083		4205
2084	For a real-world example of a program the includes libev	4206	For a real-world example of a program the includes libev
2085	verbatim, you can have a look at the EV perl module	4207	verbatim, you can have a look at the EV perl module
…		…
2088	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	4210	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
2089	will be compiled. It is pretty complex because it provides its own header	4211	will be compiled. It is pretty complex because it provides its own header
2090	file.	4212	file.
2091		4213
2092	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4214	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2093	that everybody includes and which overrides some autoconf choices:	4215	that everybody includes and which overrides some configure choices:
2094		4216
		4217	#define EV_FEATURES 8
		4218	#define EV_USE_SELECT 1
		4219	#define EV_PREPARE_ENABLE 1
		4220	#define EV_IDLE_ENABLE 1
		4221	#define EV_SIGNAL_ENABLE 1
		4222	#define EV_CHILD_ENABLE 1
2095	#define EV_USE_POLL 0	4223	#define EV_USE_STDEXCEPT 0
2096	#define EV_MULTIPLICITY 0
2097	#define EV_PERIODICS 0
2098	#define EV_CONFIG_H <config.h>	4224	#define EV_CONFIG_H <config.h>
2099		4225
2100	#include "ev++.h"	4226	#include "ev++.h"
2101		4227
2102	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4228	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2103		4229
2104	#include "ev_cpp.h"	4230	#include "ev_cpp.h"
2105	#include "ev.c"	4231	#include "ev.c"
2106		4232
		4233	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2107		4234
		4235	=head2 THREADS AND COROUTINES
		4236
		4237	=head3 THREADS
		4238
		4239	All libev functions are reentrant and thread-safe unless explicitly
		4240	documented otherwise, but libev implements no locking itself. This means
		4241	that you can use as many loops as you want in parallel, as long as there
		4242	are no concurrent calls into any libev function with the same loop
		4243	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4244	of course): libev guarantees that different event loops share no data
		4245	structures that need any locking.
		4246
		4247	Or to put it differently: calls with different loop parameters can be done
		4248	concurrently from multiple threads, calls with the same loop parameter
		4249	must be done serially (but can be done from different threads, as long as
		4250	only one thread ever is inside a call at any point in time, e.g. by using
		4251	a mutex per loop).
		4252
		4253	Specifically to support threads (and signal handlers), libev implements
		4254	so-called C<ev_async> watchers, which allow some limited form of
		4255	concurrency on the same event loop, namely waking it up "from the
		4256	outside".
		4257
		4258	If you want to know which design (one loop, locking, or multiple loops
		4259	without or something else still) is best for your problem, then I cannot
		4260	help you, but here is some generic advice:
		4261
		4262	=over 4
		4263
		4264	=item * most applications have a main thread: use the default libev loop
		4265	in that thread, or create a separate thread running only the default loop.
		4266
		4267	This helps integrating other libraries or software modules that use libev
		4268	themselves and don't care/know about threading.
		4269
		4270	=item * one loop per thread is usually a good model.
		4271
		4272	Doing this is almost never wrong, sometimes a better-performance model
		4273	exists, but it is always a good start.
		4274
		4275	=item * other models exist, such as the leader/follower pattern, where one
		4276	loop is handed through multiple threads in a kind of round-robin fashion.
		4277
		4278	Choosing a model is hard - look around, learn, know that usually you can do
		4279	better than you currently do :-)
		4280
		4281	=item * often you need to talk to some other thread which blocks in the
		4282	event loop.
		4283
		4284	C<ev_async> watchers can be used to wake them up from other threads safely
		4285	(or from signal contexts...).
		4286
		4287	An example use would be to communicate signals or other events that only
		4288	work in the default loop by registering the signal watcher with the
		4289	default loop and triggering an C<ev_async> watcher from the default loop
		4290	watcher callback into the event loop interested in the signal.
		4291
		4292	=back
		4293
		4294	=head4 THREAD LOCKING EXAMPLE
		4295
		4296	Here is a fictitious example of how to run an event loop in a different
		4297	thread than where callbacks are being invoked and watchers are
		4298	created/added/removed.
		4299
		4300	For a real-world example, see the C<EV::Loop::Async> perl module,
		4301	which uses exactly this technique (which is suited for many high-level
		4302	languages).
		4303
		4304	The example uses a pthread mutex to protect the loop data, a condition
		4305	variable to wait for callback invocations, an async watcher to notify the
		4306	event loop thread and an unspecified mechanism to wake up the main thread.
		4307
		4308	First, you need to associate some data with the event loop:
		4309
		4310	typedef struct {
		4311	mutex_t lock; /* global loop lock */
		4312	ev_async async_w;
		4313	thread_t tid;
		4314	cond_t invoke_cv;
		4315	} userdata;
		4316
		4317	void prepare_loop (EV_P)
		4318	{
		4319	// for simplicity, we use a static userdata struct.
		4320	static userdata u;
		4321
		4322	ev_async_init (&u->async_w, async_cb);
		4323	ev_async_start (EV_A_ &u->async_w);
		4324
		4325	pthread_mutex_init (&u->lock, 0);
		4326	pthread_cond_init (&u->invoke_cv, 0);
		4327
		4328	// now associate this with the loop
		4329	ev_set_userdata (EV_A_ u);
		4330	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4331	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4332
		4333	// then create the thread running ev_loop
		4334	pthread_create (&u->tid, 0, l_run, EV_A);
		4335	}
		4336
		4337	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4338	solely to wake up the event loop so it takes notice of any new watchers
		4339	that might have been added:
		4340
		4341	static void
		4342	async_cb (EV_P_ ev_async *w, int revents)
		4343	{
		4344	// just used for the side effects
		4345	}
		4346
		4347	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4348	protecting the loop data, respectively.
		4349
		4350	static void
		4351	l_release (EV_P)
		4352	{
		4353	userdata *u = ev_userdata (EV_A);
		4354	pthread_mutex_unlock (&u->lock);
		4355	}
		4356
		4357	static void
		4358	l_acquire (EV_P)
		4359	{
		4360	userdata *u = ev_userdata (EV_A);
		4361	pthread_mutex_lock (&u->lock);
		4362	}
		4363
		4364	The event loop thread first acquires the mutex, and then jumps straight
		4365	into C<ev_run>:
		4366
		4367	void *
		4368	l_run (void *thr_arg)
		4369	{
		4370	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4371
		4372	l_acquire (EV_A);
		4373	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4374	ev_run (EV_A_ 0);
		4375	l_release (EV_A);
		4376
		4377	return 0;
		4378	}
		4379
		4380	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4381	signal the main thread via some unspecified mechanism (signals? pipe
		4382	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4383	have been called (in a while loop because a) spurious wakeups are possible
		4384	and b) skipping inter-thread-communication when there are no pending
		4385	watchers is very beneficial):
		4386
		4387	static void
		4388	l_invoke (EV_P)
		4389	{
		4390	userdata *u = ev_userdata (EV_A);
		4391
		4392	while (ev_pending_count (EV_A))
		4393	{
		4394	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4395	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4396	}
		4397	}
		4398
		4399	Now, whenever the main thread gets told to invoke pending watchers, it
		4400	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4401	thread to continue:
		4402
		4403	static void
		4404	real_invoke_pending (EV_P)
		4405	{
		4406	userdata *u = ev_userdata (EV_A);
		4407
		4408	pthread_mutex_lock (&u->lock);
		4409	ev_invoke_pending (EV_A);
		4410	pthread_cond_signal (&u->invoke_cv);
		4411	pthread_mutex_unlock (&u->lock);
		4412	}
		4413
		4414	Whenever you want to start/stop a watcher or do other modifications to an
		4415	event loop, you will now have to lock:
		4416
		4417	ev_timer timeout_watcher;
		4418	userdata *u = ev_userdata (EV_A);
		4419
		4420	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4421
		4422	pthread_mutex_lock (&u->lock);
		4423	ev_timer_start (EV_A_ &timeout_watcher);
		4424	ev_async_send (EV_A_ &u->async_w);
		4425	pthread_mutex_unlock (&u->lock);
		4426
		4427	Note that sending the C<ev_async> watcher is required because otherwise
		4428	an event loop currently blocking in the kernel will have no knowledge
		4429	about the newly added timer. By waking up the loop it will pick up any new
		4430	watchers in the next event loop iteration.
		4431
		4432	=head3 COROUTINES
		4433
		4434	Libev is very accommodating to coroutines ("cooperative threads"):
		4435	libev fully supports nesting calls to its functions from different
		4436	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4437	different coroutines, and switch freely between both coroutines running
		4438	the loop, as long as you don't confuse yourself). The only exception is
		4439	that you must not do this from C<ev_periodic> reschedule callbacks.
		4440
		4441	Care has been taken to ensure that libev does not keep local state inside
		4442	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4443	they do not call any callbacks.
		4444
		4445	=head2 COMPILER WARNINGS
		4446
		4447	Depending on your compiler and compiler settings, you might get no or a
		4448	lot of warnings when compiling libev code. Some people are apparently
		4449	scared by this.
		4450
		4451	However, these are unavoidable for many reasons. For one, each compiler
		4452	has different warnings, and each user has different tastes regarding
		4453	warning options. "Warn-free" code therefore cannot be a goal except when
		4454	targeting a specific compiler and compiler-version.
		4455
		4456	Another reason is that some compiler warnings require elaborate
		4457	workarounds, or other changes to the code that make it less clear and less
		4458	maintainable.
		4459
		4460	And of course, some compiler warnings are just plain stupid, or simply
		4461	wrong (because they don't actually warn about the condition their message
		4462	seems to warn about). For example, certain older gcc versions had some
		4463	warnings that resulted in an extreme number of false positives. These have
		4464	been fixed, but some people still insist on making code warn-free with
		4465	such buggy versions.
		4466
		4467	While libev is written to generate as few warnings as possible,
		4468	"warn-free" code is not a goal, and it is recommended not to build libev
		4469	with any compiler warnings enabled unless you are prepared to cope with
		4470	them (e.g. by ignoring them). Remember that warnings are just that:
		4471	warnings, not errors, or proof of bugs.
		4472
		4473
		4474	=head2 VALGRIND
		4475
		4476	Valgrind has a special section here because it is a popular tool that is
		4477	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4478
		4479	If you think you found a bug (memory leak, uninitialised data access etc.)
		4480	in libev, then check twice: If valgrind reports something like:
		4481
		4482	==2274== definitely lost: 0 bytes in 0 blocks.
		4483	==2274== possibly lost: 0 bytes in 0 blocks.
		4484	==2274== still reachable: 256 bytes in 1 blocks.
		4485
		4486	Then there is no memory leak, just as memory accounted to global variables
		4487	is not a memleak - the memory is still being referenced, and didn't leak.
		4488
		4489	Similarly, under some circumstances, valgrind might report kernel bugs
		4490	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4491	although an acceptable workaround has been found here), or it might be
		4492	confused.
		4493
		4494	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4495	make it into some kind of religion.
		4496
		4497	If you are unsure about something, feel free to contact the mailing list
		4498	with the full valgrind report and an explanation on why you think this
		4499	is a bug in libev (best check the archives, too :). However, don't be
		4500	annoyed when you get a brisk "this is no bug" answer and take the chance
		4501	of learning how to interpret valgrind properly.
		4502
		4503	If you need, for some reason, empty reports from valgrind for your project
		4504	I suggest using suppression lists.
		4505
		4506
		4507	=head1 PORTABILITY NOTES
		4508
		4509	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4510
		4511	GNU/Linux is the only common platform that supports 64 bit file/large file
		4512	interfaces but I<disables> them by default.
		4513
		4514	That means that libev compiled in the default environment doesn't support
		4515	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4516
		4517	Unfortunately, many programs try to work around this GNU/Linux issue
		4518	by enabling the large file API, which makes them incompatible with the
		4519	standard libev compiled for their system.
		4520
		4521	Likewise, libev cannot enable the large file API itself as this would
		4522	suddenly make it incompatible to the default compile time environment,
		4523	i.e. all programs not using special compile switches.
		4524
		4525	=head2 OS/X AND DARWIN BUGS
		4526
		4527	The whole thing is a bug if you ask me - basically any system interface
		4528	you touch is broken, whether it is locales, poll, kqueue or even the
		4529	OpenGL drivers.
		4530
		4531	=head3 C<kqueue> is buggy
		4532
		4533	The kqueue syscall is broken in all known versions - most versions support
		4534	only sockets, many support pipes.
		4535
		4536	Libev tries to work around this by not using C<kqueue> by default on this
		4537	rotten platform, but of course you can still ask for it when creating a
		4538	loop - embedding a socket-only kqueue loop into a select-based one is
		4539	probably going to work well.
		4540
		4541	=head3 C<poll> is buggy
		4542
		4543	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4544	implementation by something calling C<kqueue> internally around the 10.5.6
		4545	release, so now C<kqueue> I<and> C<poll> are broken.
		4546
		4547	Libev tries to work around this by not using C<poll> by default on
		4548	this rotten platform, but of course you can still ask for it when creating
		4549	a loop.
		4550
		4551	=head3 C<select> is buggy
		4552
		4553	All that's left is C<select>, and of course Apple found a way to fuck this
		4554	one up as well: On OS/X, C<select> actively limits the number of file
		4555	descriptors you can pass in to 1024 - your program suddenly crashes when
		4556	you use more.
		4557
		4558	There is an undocumented "workaround" for this - defining
		4559	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4560	work on OS/X.
		4561
		4562	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4563
		4564	=head3 C<errno> reentrancy
		4565
		4566	The default compile environment on Solaris is unfortunately so
		4567	thread-unsafe that you can't even use components/libraries compiled
		4568	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4569	defined by default. A valid, if stupid, implementation choice.
		4570
		4571	If you want to use libev in threaded environments you have to make sure
		4572	it's compiled with C<_REENTRANT> defined.
		4573
		4574	=head3 Event port backend
		4575
		4576	The scalable event interface for Solaris is called "event
		4577	ports". Unfortunately, this mechanism is very buggy in all major
		4578	releases. If you run into high CPU usage, your program freezes or you get
		4579	a large number of spurious wakeups, make sure you have all the relevant
		4580	and latest kernel patches applied. No, I don't know which ones, but there
		4581	are multiple ones to apply, and afterwards, event ports actually work
		4582	great.
		4583
		4584	If you can't get it to work, you can try running the program by setting
		4585	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4586	C<select> backends.
		4587
		4588	=head2 AIX POLL BUG
		4589
		4590	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4591	this by trying to avoid the poll backend altogether (i.e. it's not even
		4592	compiled in), which normally isn't a big problem as C<select> works fine
		4593	with large bitsets on AIX, and AIX is dead anyway.
		4594
		4595	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4596
		4597	=head3 General issues
		4598
		4599	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4600	requires, and its I/O model is fundamentally incompatible with the POSIX
		4601	model. Libev still offers limited functionality on this platform in
		4602	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4603	descriptors. This only applies when using Win32 natively, not when using
		4604	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4605	as every compielr comes with a slightly differently broken/incompatible
		4606	environment.
		4607
		4608	Lifting these limitations would basically require the full
		4609	re-implementation of the I/O system. If you are into this kind of thing,
		4610	then note that glib does exactly that for you in a very portable way (note
		4611	also that glib is the slowest event library known to man).
		4612
		4613	There is no supported compilation method available on windows except
		4614	embedding it into other applications.
		4615
		4616	Sensible signal handling is officially unsupported by Microsoft - libev
		4617	tries its best, but under most conditions, signals will simply not work.
		4618
		4619	Not a libev limitation but worth mentioning: windows apparently doesn't
		4620	accept large writes: instead of resulting in a partial write, windows will
		4621	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4622	so make sure you only write small amounts into your sockets (less than a
		4623	megabyte seems safe, but this apparently depends on the amount of memory
		4624	available).
		4625
		4626	Due to the many, low, and arbitrary limits on the win32 platform and
		4627	the abysmal performance of winsockets, using a large number of sockets
		4628	is not recommended (and not reasonable). If your program needs to use
		4629	more than a hundred or so sockets, then likely it needs to use a totally
		4630	different implementation for windows, as libev offers the POSIX readiness
		4631	notification model, which cannot be implemented efficiently on windows
		4632	(due to Microsoft monopoly games).
		4633
		4634	A typical way to use libev under windows is to embed it (see the embedding
		4635	section for details) and use the following F<evwrap.h> header file instead
		4636	of F<ev.h>:
		4637
		4638	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4639	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4640
		4641	#include "ev.h"
		4642
		4643	And compile the following F<evwrap.c> file into your project (make sure
		4644	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4645
		4646	#include "evwrap.h"
		4647	#include "ev.c"
		4648
		4649	=head3 The winsocket C<select> function
		4650
		4651	The winsocket C<select> function doesn't follow POSIX in that it
		4652	requires socket I<handles> and not socket I<file descriptors> (it is
		4653	also extremely buggy). This makes select very inefficient, and also
		4654	requires a mapping from file descriptors to socket handles (the Microsoft
		4655	C runtime provides the function C<_open_osfhandle> for this). See the
		4656	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4657	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4658
		4659	The configuration for a "naked" win32 using the Microsoft runtime
		4660	libraries and raw winsocket select is:
		4661
		4662	#define EV_USE_SELECT 1
		4663	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4664
		4665	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4666	complexity in the O(n²) range when using win32.
		4667
		4668	=head3 Limited number of file descriptors
		4669
		4670	Windows has numerous arbitrary (and low) limits on things.
		4671
		4672	Early versions of winsocket's select only supported waiting for a maximum
		4673	of C<64> handles (probably owning to the fact that all windows kernels
		4674	can only wait for C<64> things at the same time internally; Microsoft
		4675	recommends spawning a chain of threads and wait for 63 handles and the
		4676	previous thread in each. Sounds great!).
		4677
		4678	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4679	to some high number (e.g. C<2048>) before compiling the winsocket select
		4680	call (which might be in libev or elsewhere, for example, perl and many
		4681	other interpreters do their own select emulation on windows).
		4682
		4683	Another limit is the number of file descriptors in the Microsoft runtime
		4684	libraries, which by default is C<64> (there must be a hidden I<64>
		4685	fetish or something like this inside Microsoft). You can increase this
		4686	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4687	(another arbitrary limit), but is broken in many versions of the Microsoft
		4688	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4689	(depending on windows version and/or the phase of the moon). To get more,
		4690	you need to wrap all I/O functions and provide your own fd management, but
		4691	the cost of calling select (O(n²)) will likely make this unworkable.
		4692
		4693	=head2 PORTABILITY REQUIREMENTS
		4694
		4695	In addition to a working ISO-C implementation and of course the
		4696	backend-specific APIs, libev relies on a few additional extensions:
		4697
		4698	=over 4
		4699
		4700	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4701	calling conventions regardless of C<ev_watcher_type *>.
		4702
		4703	Libev assumes not only that all watcher pointers have the same internal
		4704	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4705	assumes that the same (machine) code can be used to call any watcher
		4706	callback: The watcher callbacks have different type signatures, but libev
		4707	calls them using an C<ev_watcher *> internally.
		4708
		4709	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4710
		4711	The type C<sig_atomic_t volatile> (or whatever is defined as
		4712	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4713	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4714	believed to be sufficiently portable.
		4715
		4716	=item C<sigprocmask> must work in a threaded environment
		4717
		4718	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4719	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4720	pthread implementations will either allow C<sigprocmask> in the "main
		4721	thread" or will block signals process-wide, both behaviours would
		4722	be compatible with libev. Interaction between C<sigprocmask> and
		4723	C<pthread_sigmask> could complicate things, however.
		4724
		4725	The most portable way to handle signals is to block signals in all threads
		4726	except the initial one, and run the default loop in the initial thread as
		4727	well.
		4728
		4729	=item C<long> must be large enough for common memory allocation sizes
		4730
		4731	To improve portability and simplify its API, libev uses C<long> internally
		4732	instead of C<size_t> when allocating its data structures. On non-POSIX
		4733	systems (Microsoft...) this might be unexpectedly low, but is still at
		4734	least 31 bits everywhere, which is enough for hundreds of millions of
		4735	watchers.
		4736
		4737	=item C<double> must hold a time value in seconds with enough accuracy
		4738
		4739	The type C<double> is used to represent timestamps. It is required to
		4740	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4741	good enough for at least into the year 4000 with millisecond accuracy
		4742	(the design goal for libev). This requirement is overfulfilled by
		4743	implementations using IEEE 754, which is basically all existing ones. With
		4744	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4745
		4746	=back
		4747
		4748	If you know of other additional requirements drop me a note.
		4749
		4750
2108	=head1 COMPLEXITIES	4751	=head1 ALGORITHMIC COMPLEXITIES
2109		4752
2110	In this section the complexities of (many of) the algorithms used inside	4753	In this section the complexities of (many of) the algorithms used inside
2111	libev will be explained. For complexity discussions about backends see the	4754	libev will be documented. For complexity discussions about backends see
2112	documentation for C<ev_default_init>.	4755	the documentation for C<ev_default_init>.
		4756
		4757	All of the following are about amortised time: If an array needs to be
		4758	extended, libev needs to realloc and move the whole array, but this
		4759	happens asymptotically rarer with higher number of elements, so O(1) might
		4760	mean that libev does a lengthy realloc operation in rare cases, but on
		4761	average it is much faster and asymptotically approaches constant time.
2113		4762
2114	=over 4	4763	=over 4
2115		4764
2116	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4765	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2117		4766
		4767	This means that, when you have a watcher that triggers in one hour and
		4768	there are 100 watchers that would trigger before that, then inserting will
		4769	have to skip roughly seven (C<ld 100>) of these watchers.
		4770
2118	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4771	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2119		4772
		4773	That means that changing a timer costs less than removing/adding them,
		4774	as only the relative motion in the event queue has to be paid for.
		4775
2120	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4776	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2121		4777
		4778	These just add the watcher into an array or at the head of a list.
		4779
2122	=item Stopping check/prepare/idle watchers: O(1)	4780	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2123		4781
2124	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))	4782	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2125		4783
		4784	These watchers are stored in lists, so they need to be walked to find the
		4785	correct watcher to remove. The lists are usually short (you don't usually
		4786	have many watchers waiting for the same fd or signal: one is typical, two
		4787	is rare).
		4788
2126	=item Finding the next timer per loop iteration: O(1)	4789	=item Finding the next timer in each loop iteration: O(1)
		4790
		4791	By virtue of using a binary or 4-heap, the next timer is always found at a
		4792	fixed position in the storage array.
2127		4793
2128	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4794	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2129		4795
2130	=item Activating one watcher: O(1)	4796	A change means an I/O watcher gets started or stopped, which requires
		4797	libev to recalculate its status (and possibly tell the kernel, depending
		4798	on backend and whether C<ev_io_set> was used).
		4799
		4800	=item Activating one watcher (putting it into the pending state): O(1)
		4801
		4802	=item Priority handling: O(number_of_priorities)
		4803
		4804	Priorities are implemented by allocating some space for each
		4805	priority. When doing priority-based operations, libev usually has to
		4806	linearly search all the priorities, but starting/stopping and activating
		4807	watchers becomes O(1) with respect to priority handling.
		4808
		4809	=item Sending an ev_async: O(1)
		4810
		4811	=item Processing ev_async_send: O(number_of_async_watchers)
		4812
		4813	=item Processing signals: O(max_signal_number)
		4814
		4815	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4816	calls in the current loop iteration. Checking for async and signal events
		4817	involves iterating over all running async watchers or all signal numbers.
2131		4818
2132	=back	4819	=back
2133		4820
2134		4821
		4822	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4823
		4824	The major version 4 introduced some minor incompatible changes to the API.
		4825
		4826	At the moment, the C<ev.h> header file tries to implement superficial
		4827	compatibility, so most programs should still compile. Those might be
		4828	removed in later versions of libev, so better update early than late.
		4829
		4830	=over 4
		4831
		4832	=item function/symbol renames
		4833
		4834	A number of functions and symbols have been renamed:
		4835
		4836	ev_loop => ev_run
		4837	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4838	EVLOOP_ONESHOT => EVRUN_ONCE
		4839
		4840	ev_unloop => ev_break
		4841	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4842	EVUNLOOP_ONE => EVBREAK_ONE
		4843	EVUNLOOP_ALL => EVBREAK_ALL
		4844
		4845	EV_TIMEOUT => EV_TIMER
		4846
		4847	ev_loop_count => ev_iteration
		4848	ev_loop_depth => ev_depth
		4849	ev_loop_verify => ev_verify
		4850
		4851	Most functions working on C<struct ev_loop> objects don't have an
		4852	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4853	associated constants have been renamed to not collide with the C<struct
		4854	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4855	as all other watcher types. Note that C<ev_loop_fork> is still called
		4856	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4857	typedef.
		4858
		4859	=item C<EV_COMPAT3> backwards compatibility mechanism
		4860
		4861	The backward compatibility mechanism can be controlled by
		4862	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4863	section.
		4864
		4865	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4866
		4867	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4868	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4869	and work, but the library code will of course be larger.
		4870
		4871	=back
		4872
		4873
		4874	=head1 GLOSSARY
		4875
		4876	=over 4
		4877
		4878	=item active
		4879
		4880	A watcher is active as long as it has been started and not yet stopped.
		4881	See L<WATCHER STATES> for details.
		4882
		4883	=item application
		4884
		4885	In this document, an application is whatever is using libev.
		4886
		4887	=item backend
		4888
		4889	The part of the code dealing with the operating system interfaces.
		4890
		4891	=item callback
		4892
		4893	The address of a function that is called when some event has been
		4894	detected. Callbacks are being passed the event loop, the watcher that
		4895	received the event, and the actual event bitset.
		4896
		4897	=item callback/watcher invocation
		4898
		4899	The act of calling the callback associated with a watcher.
		4900
		4901	=item event
		4902
		4903	A change of state of some external event, such as data now being available
		4904	for reading on a file descriptor, time having passed or simply not having
		4905	any other events happening anymore.
		4906
		4907	In libev, events are represented as single bits (such as C<EV_READ> or
		4908	C<EV_TIMER>).
		4909
		4910	=item event library
		4911
		4912	A software package implementing an event model and loop.
		4913
		4914	=item event loop
		4915
		4916	An entity that handles and processes external events and converts them
		4917	into callback invocations.
		4918
		4919	=item event model
		4920
		4921	The model used to describe how an event loop handles and processes
		4922	watchers and events.
		4923
		4924	=item pending
		4925
		4926	A watcher is pending as soon as the corresponding event has been
		4927	detected. See L<WATCHER STATES> for details.
		4928
		4929	=item real time
		4930
		4931	The physical time that is observed. It is apparently strictly monotonic :)
		4932
		4933	=item wall-clock time
		4934
		4935	The time and date as shown on clocks. Unlike real time, it can actually
		4936	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4937	clock.
		4938
		4939	=item watcher
		4940
		4941	A data structure that describes interest in certain events. Watchers need
		4942	to be started (attached to an event loop) before they can receive events.
		4943
		4944	=back
		4945
2135	=head1 AUTHOR	4946	=head1 AUTHOR
2136		4947
2137	Marc Lehmann <libev@schmorp.de>.	4948	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2138		4949

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