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Revision 1.74 by root, Sat Dec 8 14:12:08 2007 UTC vs.
Revision 1.260 by root, Sun Jul 19 21:18:03 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		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_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_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_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_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_loop (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
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
56		84
57	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
58	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
59	these event sources and provide your program with events.	87	these event sources and provide your program with events.
60		88
61	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
62	(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
63	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
65	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
66	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
67	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
68	watcher.	96	watcher.
69		97
70	=head1 FEATURES	98	=head2 FEATURES
71		99
72	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
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
82		110
83	It also is quite fast (see this	111	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	112	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	113	for example).
86		114
87	=head1 CONVENTIONS	115	=head2 CONVENTIONS
88		116
89	Libev is very configurable. In this manual the default configuration will	117	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	118	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	119	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	120	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	121	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	122	name C<loop> (which is always of type C<ev_loop *>) will not have
		123	this argument.
95		124
96	=head1 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
97		126
98	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
100	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
102	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
103	it, you should treat it as such.	132	on it, you should treat it as some floating point value. Unlike the name
		133	component C<stamp> might indicate, it is also used for time differences
		134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
		155
104		156
105	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
106		158
107	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
108	library in any way.	160	library in any way.
…		…
113		165
114	Returns the current time as libev would use it. Please note that the	166	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	167	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	168	you actually want to know.
117		169
		170	=item ev_sleep (ev_tstamp interval)
		171
		172	Sleep for the given interval: The current thread will be blocked until
		173	either it is interrupted or the given time interval has passed. Basically
		174	this is a sub-second-resolution C<sleep ()>.
		175
118	=item int ev_version_major ()	176	=item int ev_version_major ()
119		177
120	=item int ev_version_minor ()	178	=item int ev_version_minor ()
121		179
122	You can find out the major and minor version numbers of the library	180	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	181	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	182	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	183	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	184	version of the library your program was compiled against.
127		185
		186	These version numbers refer to the ABI version of the library, not the
		187	release version.
		188
128	Usually, it's a good idea to terminate if the major versions mismatch,	189	Usually, it's a good idea to terminate if the major versions mismatch,
129	as this indicates an incompatible change. Minor versions are usually	190	as this indicates an incompatible change. Minor versions are usually
130	compatible to older versions, so a larger minor version alone is usually	191	compatible to older versions, so a larger minor version alone is usually
131	not a problem.	192	not a problem.
132		193
133	Example: Make sure we haven't accidentally been linked against the wrong	194	Example: Make sure we haven't accidentally been linked against the wrong
134	version.	195	version.
135		196
136	assert (("libev version mismatch",	197	assert (("libev version mismatch",
137	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
138	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
139		200
140	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
141		202
142	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	203	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
143	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
145	a description of the set values.	206	a description of the set values.
146		207
147	Example: make sure we have the epoll method, because yeah this is cool and	208	Example: make sure we have the epoll method, because yeah this is cool and
148	a must have and can we have a torrent of it please!!!11	209	a must have and can we have a torrent of it please!!!11
149		210
150	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
151	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
152		213
153	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
154		215
155	Return the set of all backends compiled into this binary of libev and also	216	Return the set of all backends compiled into this binary of libev and also
156	recommended for this platform. This set is often smaller than the one	217	recommended for this platform. This set is often smaller than the one
157	returned by C<ev_supported_backends>, as for example kqueue is broken on	218	returned by C<ev_supported_backends>, as for example kqueue is broken on
158	most BSDs and will not be autodetected unless you explicitly request it	219	most BSDs and will not be auto-detected unless you explicitly request it
159	(assuming you know what you are doing). This is the set of backends that	220	(assuming you know what you are doing). This is the set of backends that
160	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
161		222
162	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
163		224
…		…
167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
168	recommended ones.	229	recommended ones.
169		230
170	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
171		232
172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
173		234
174	Sets the allocation function to use (the prototype is similar - the	235	Sets the allocation function to use (the prototype is similar - the
175	semantics is identical - to the realloc C function). It is used to	236	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
176	allocate and free memory (no surprises here). If it returns zero when	237	used to allocate and free memory (no surprises here). If it returns zero
177	memory needs to be allocated, the library might abort or take some	238	when memory needs to be allocated (C<size != 0>), the library might abort
178	potentially destructive action. The default is your system realloc	239	or take some potentially destructive action.
179	function.	240
		241	Since some systems (at least OpenBSD and Darwin) fail to implement
		242	correct C<realloc> semantics, libev will use a wrapper around the system
		243	C<realloc> and C<free> functions by default.
180		244
181	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
182	free some memory if it cannot allocate memory, to use a special allocator,	246	free some memory if it cannot allocate memory, to use a special allocator,
183	or even to sleep a while and retry until some memory is available.	247	or even to sleep a while and retry until some memory is available.
184		248
185	Example: Replace the libev allocator with one that waits a bit and then	249	Example: Replace the libev allocator with one that waits a bit and then
186	retries).	250	retries (example requires a standards-compliant C<realloc>).
187		251
188	static void *	252	static void *
189	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
190	{	254	{
191	for (;;)	255	for (;;)
…		…
200	}	264	}
201		265
202	...	266	...
203	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
204		268
205	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
206		270
207	Set the callback function to call on a retryable syscall error (such	271	Set the callback function to call on a retryable system call error (such
208	as failed select, poll, epoll_wait). The message is a printable string	272	as failed select, poll, epoll_wait). The message is a printable string
209	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
210	callback is set, then libev will expect it to remedy the sitution, no	274	callback is set, then libev will expect it to remedy the situation, no
211	matter what, when it returns. That is, libev will generally retry the	275	matter what, when it returns. That is, libev will generally retry the
212	requested operation, or, if the condition doesn't go away, do bad stuff	276	requested operation, or, if the condition doesn't go away, do bad stuff
213	(such as abort).	277	(such as abort).
214		278
215	Example: This is basically the same thing that libev does internally, too.	279	Example: This is basically the same thing that libev does internally, too.
…		…
226		290
227	=back	291	=back
228		292
229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
230		294
231	An event loop is described by a C<struct ev_loop *>. The library knows two	295	An event loop is described by a C<struct ev_loop *> (the C<struct>
232	types of such loops, the I<default> loop, which supports signals and child	296	is I<not> optional in this case, as there is also an C<ev_loop>
233	events, and dynamically created loops which do not.	297	I<function>).
234		298
235	If you use threads, a common model is to run the default event loop	299	The library knows two types of such loops, the I<default> loop, which
236	in your main thread (or in a separate thread) and for each thread you	300	supports signals and child events, and dynamically created loops which do
237	create, you also create another event loop. Libev itself does no locking	301	not.
238	whatsoever, so if you mix calls to the same event loop in different
239	threads, make sure you lock (this is usually a bad idea, though, even if
240	done correctly, because it's hideous and inefficient).
241		302
242	=over 4	303	=over 4
243		304
244	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
245		306
…		…
249	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
250		311
251	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
252	function.	313	function.
253		314
		315	Note that this function is I<not> thread-safe, so if you want to use it
		316	from multiple threads, you have to lock (note also that this is unlikely,
		317	as loops cannot be shared easily between threads anyway).
		318
		319	The default loop is the only loop that can handle C<ev_signal> and
		320	C<ev_child> watchers, and to do this, it always registers a handler
		321	for C<SIGCHLD>. If this is a problem for your application you can either
		322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		324	C<ev_default_init>.
		325
254	The flags argument can be used to specify special behaviour or specific	326	The flags argument can be used to specify special behaviour or specific
255	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	327	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
256		328
257	The following flags are supported:	329	The following flags are supported:
258		330
…		…
263	The default flags value. Use this if you have no clue (it's the right	335	The default flags value. Use this if you have no clue (it's the right
264	thing, believe me).	336	thing, believe me).
265		337
266	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
267		339
268	If this flag bit is ored into the flag value (or the program runs setuid	340	If this flag bit is or'ed into the flag value (or the program runs setuid
269	or setgid) then libev will I<not> look at the environment variable	341	or setgid) then libev will I<not> look at the environment variable
270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
271	override the flags completely if it is found in the environment. This is	343	override the flags completely if it is found in the environment. This is
272	useful to try out specific backends to test their performance, or to work	344	useful to try out specific backends to test their performance, or to work
273	around bugs.	345	around bugs.
…		…
279	enabling this flag.	351	enabling this flag.
280		352
281	This works by calling C<getpid ()> on every iteration of the loop,	353	This works by calling C<getpid ()> on every iteration of the loop,
282	and thus this might slow down your event loop if you do a lot of loop	354	and thus this might slow down your event loop if you do a lot of loop
283	iterations and little real work, but is usually not noticeable (on my	355	iterations and little real work, but is usually not noticeable (on my
284	Linux system for example, C<getpid> is actually a simple 5-insn sequence	356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
285	without a syscall and thus I<very> fast, but my Linux system also has	357	without a system call and thus I<very> fast, but my GNU/Linux system also has
286	C<pthread_atfork> which is even faster).	358	C<pthread_atfork> which is even faster).
287		359
288	The big advantage of this flag is that you can forget about fork (and	360	The big advantage of this flag is that you can forget about fork (and
289	forget about forgetting to tell libev about forking) when you use this	361	forget about forgetting to tell libev about forking) when you use this
290	flag.	362	flag.
291		363
292	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
293	environment variable.	365	environment variable.
		366
		367	=item C<EVFLAG_NOINOTIFY>
		368
		369	When this flag is specified, then libev will not attempt to use the
		370	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		371	testing, this flag can be useful to conserve inotify file descriptors, as
		372	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		373
		374	=item C<EVFLAG_NOSIGNALFD>
		375
		376	When this flag is specified, then libev will not attempt to use the
		377	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		378	probably only useful to work around any bugs in libev. Consequently, this
		379	flag might go away once the signalfd functionality is considered stable,
		380	so it's useful mostly in environment variables and not in program code.
294		381
295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	382	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
296		383
297	This is your standard select(2) backend. Not I<completely> standard, as	384	This is your standard select(2) backend. Not I<completely> standard, as
298	libev tries to roll its own fd_set with no limits on the number of fds,	385	libev tries to roll its own fd_set with no limits on the number of fds,
299	but if that fails, expect a fairly low limit on the number of fds when	386	but if that fails, expect a fairly low limit on the number of fds when
300	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	387	using this backend. It doesn't scale too well (O(highest_fd)), but its
301	the fastest backend for a low number of fds.	388	usually the fastest backend for a low number of (low-numbered :) fds.
		389
		390	To get good performance out of this backend you need a high amount of
		391	parallelism (most of the file descriptors should be busy). If you are
		392	writing a server, you should C<accept ()> in a loop to accept as many
		393	connections as possible during one iteration. You might also want to have
		394	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		395	readiness notifications you get per iteration.
		396
		397	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		398	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		399	C<exceptfds> set on that platform).
302		400
303	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	401	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
304		402
305	And this is your standard poll(2) backend. It's more complicated than	403	And this is your standard poll(2) backend. It's more complicated
306	select, but handles sparse fds better and has no artificial limit on the	404	than select, but handles sparse fds better and has no artificial
307	number of fds you can use (except it will slow down considerably with a	405	limit on the number of fds you can use (except it will slow down
308	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	406	considerably with a lot of inactive fds). It scales similarly to select,
		407	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		408	performance tips.
		409
		410	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		411	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
309		412
310	=item C<EVBACKEND_EPOLL> (value 4, Linux)	413	=item C<EVBACKEND_EPOLL> (value 4, Linux)
311		414
312	For few fds, this backend is a bit little slower than poll and select,	415	For few fds, this backend is a bit little slower than poll and select,
313	but it scales phenomenally better. While poll and select usually scale like	416	but it scales phenomenally better. While poll and select usually scale
314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	417	like O(total_fds) where n is the total number of fds (or the highest fd),
315	either O(1) or O(active_fds).	418	epoll scales either O(1) or O(active_fds).
316		419
		420	The epoll mechanism deserves honorable mention as the most misdesigned
		421	of the more advanced event mechanisms: mere annoyances include silently
		422	dropping file descriptors, requiring a system call per change per file
		423	descriptor (and unnecessary guessing of parameters), problems with dup and
		424	so on. The biggest issue is fork races, however - if a program forks then
		425	I<both> parent and child process have to recreate the epoll set, which can
		426	take considerable time (one syscall per file descriptor) and is of course
		427	hard to detect.
		428
		429	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		430	of course I<doesn't>, and epoll just loves to report events for totally
		431	I<different> file descriptors (even already closed ones, so one cannot
		432	even remove them from the set) than registered in the set (especially
		433	on SMP systems). Libev tries to counter these spurious notifications by
		434	employing an additional generation counter and comparing that against the
		435	events to filter out spurious ones, recreating the set when required.
		436
317	While stopping and starting an I/O watcher in the same iteration will	437	While stopping, setting and starting an I/O watcher in the same iteration
318	result in some caching, there is still a syscall per such incident	438	will result in some caching, there is still a system call per such
319	(because the fd could point to a different file description now), so its	439	incident (because the same I<file descriptor> could point to a different
320	best to avoid that. Also, dup()ed file descriptors might not work very	440	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
321	well if you register events for both fds.	441	file descriptors might not work very well if you register events for both
		442	file descriptors.
322		443
323	Please note that epoll sometimes generates spurious notifications, so you	444	Best performance from this backend is achieved by not unregistering all
324	need to use non-blocking I/O or other means to avoid blocking when no data	445	watchers for a file descriptor until it has been closed, if possible,
325	(or space) is available.	446	i.e. keep at least one watcher active per fd at all times. Stopping and
		447	starting a watcher (without re-setting it) also usually doesn't cause
		448	extra overhead. A fork can both result in spurious notifications as well
		449	as in libev having to destroy and recreate the epoll object, which can
		450	take considerable time and thus should be avoided.
		451
		452	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		453	faster than epoll for maybe up to a hundred file descriptors, depending on
		454	the usage. So sad.
		455
		456	While nominally embeddable in other event loops, this feature is broken in
		457	all kernel versions tested so far.
		458
		459	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		460	C<EVBACKEND_POLL>.
326		461
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	462	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		463
329	Kqueue deserves special mention, as at the time of this writing, it	464	Kqueue deserves special mention, as at the time of this writing, it
330	was broken on all BSDs except NetBSD (usually it doesn't work with	465	was broken on all BSDs except NetBSD (usually it doesn't work reliably
331	anything but sockets and pipes, except on Darwin, where of course its	466	with anything but sockets and pipes, except on Darwin, where of course
332	completely useless). For this reason its not being "autodetected"	467	it's completely useless). Unlike epoll, however, whose brokenness
		468	is by design, these kqueue bugs can (and eventually will) be fixed
		469	without API changes to existing programs. For this reason it's not being
333	unless you explicitly specify it explicitly in the flags (i.e. using	470	"auto-detected" unless you explicitly specify it in the flags (i.e. using
334	C<EVBACKEND_KQUEUE>).	471	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		472	system like NetBSD.
		473
		474	You still can embed kqueue into a normal poll or select backend and use it
		475	only for sockets (after having made sure that sockets work with kqueue on
		476	the target platform). See C<ev_embed> watchers for more info.
335		477
336	It scales in the same way as the epoll backend, but the interface to the	478	It scales in the same way as the epoll backend, but the interface to the
337	kernel is more efficient (which says nothing about its actual speed, of	479	kernel is more efficient (which says nothing about its actual speed, of
338	course). While starting and stopping an I/O watcher does not cause an	480	course). While stopping, setting and starting an I/O watcher does never
339	extra syscall as with epoll, it still adds up to four event changes per	481	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
340	incident, so its best to avoid that.	482	two event changes per incident. Support for C<fork ()> is very bad (but
		483	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		484	cases
		485
		486	This backend usually performs well under most conditions.
		487
		488	While nominally embeddable in other event loops, this doesn't work
		489	everywhere, so you might need to test for this. And since it is broken
		490	almost everywhere, you should only use it when you have a lot of sockets
		491	(for which it usually works), by embedding it into another event loop
		492	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		493	also broken on OS X)) and, did I mention it, using it only for sockets.
		494
		495	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		496	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		497	C<NOTE_EOF>.
341		498
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	499	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		500
344	This is not implemented yet (and might never be).	501	This is not implemented yet (and might never be, unless you send me an
		502	implementation). According to reports, C</dev/poll> only supports sockets
		503	and is not embeddable, which would limit the usefulness of this backend
		504	immensely.
345		505
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	506	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		507
348	This uses the Solaris 10 port mechanism. As with everything on Solaris,	508	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
349	it's really slow, but it still scales very well (O(active_fds)).	509	it's really slow, but it still scales very well (O(active_fds)).
350		510
351	Please note that solaris ports can result in a lot of spurious	511	Please note that Solaris event ports can deliver a lot of spurious
352	notifications, so you need to use non-blocking I/O or other means to avoid	512	notifications, so you need to use non-blocking I/O or other means to avoid
353	blocking when no data (or space) is available.	513	blocking when no data (or space) is available.
		514
		515	While this backend scales well, it requires one system call per active
		516	file descriptor per loop iteration. For small and medium numbers of file
		517	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		518	might perform better.
		519
		520	On the positive side, with the exception of the spurious readiness
		521	notifications, this backend actually performed fully to specification
		522	in all tests and is fully embeddable, which is a rare feat among the
		523	OS-specific backends (I vastly prefer correctness over speed hacks).
		524
		525	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		526	C<EVBACKEND_POLL>.
354		527
355	=item C<EVBACKEND_ALL>	528	=item C<EVBACKEND_ALL>
356		529
357	Try all backends (even potentially broken ones that wouldn't be tried	530	Try all backends (even potentially broken ones that wouldn't be tried
358	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	531	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	532	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		533
		534	It is definitely not recommended to use this flag.
		535
361	=back	536	=back
362		537
363	If one or more of these are ored into the flags value, then only these	538	If one or more of the backend flags are or'ed into the flags value,
364	backends will be tried (in the reverse order as given here). If none are	539	then only these backends will be tried (in the reverse order as listed
365	specified, most compiled-in backend will be tried, usually in reverse	540	here). If none are specified, all backends in C<ev_recommended_backends
366	order of their flag values :)	541	()> will be tried.
367		542
368	The most typical usage is like this:	543	Example: This is the most typical usage.
369		544
370	if (!ev_default_loop (0))	545	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	546	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372		547
373	Restrict libev to the select and poll backends, and do not allow	548	Example: Restrict libev to the select and poll backends, and do not allow
374	environment settings to be taken into account:	549	environment settings to be taken into account:
375		550
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	551	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377		552
378	Use whatever libev has to offer, but make sure that kqueue is used if	553	Example: Use whatever libev has to offer, but make sure that kqueue is
379	available (warning, breaks stuff, best use only with your own private	554	used if available (warning, breaks stuff, best use only with your own
380	event loop and only if you know the OS supports your types of fds):	555	private event loop and only if you know the OS supports your types of
		556	fds):
381		557
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	558	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383		559
384	=item struct ev_loop *ev_loop_new (unsigned int flags)	560	=item struct ev_loop *ev_loop_new (unsigned int flags)
385		561
386	Similar to C<ev_default_loop>, but always creates a new event loop that is	562	Similar to C<ev_default_loop>, but always creates a new event loop that is
387	always distinct from the default loop. Unlike the default loop, it cannot	563	always distinct from the default loop. Unlike the default loop, it cannot
388	handle signal and child watchers, and attempts to do so will be greeted by	564	handle signal and child watchers, and attempts to do so will be greeted by
389	undefined behaviour (or a failed assertion if assertions are enabled).	565	undefined behaviour (or a failed assertion if assertions are enabled).
390		566
		567	Note that this function I<is> thread-safe, and the recommended way to use
		568	libev with threads is indeed to create one loop per thread, and using the
		569	default loop in the "main" or "initial" thread.
		570
391	Example: Try to create a event loop that uses epoll and nothing else.	571	Example: Try to create a event loop that uses epoll and nothing else.
392		572
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	573	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	574	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	575	fatal ("no epoll found here, maybe it hides under your chair");
396		576
397	=item ev_default_destroy ()	577	=item ev_default_destroy ()
398		578
399	Destroys the default loop again (frees all memory and kernel state	579	Destroys the default loop again (frees all memory and kernel state
400	etc.). None of the active event watchers will be stopped in the normal	580	etc.). None of the active event watchers will be stopped in the normal
401	sense, so e.g. C<ev_is_active> might still return true. It is your	581	sense, so e.g. C<ev_is_active> might still return true. It is your
402	responsibility to either stop all watchers cleanly yoursef I<before>	582	responsibility to either stop all watchers cleanly yourself I<before>
403	calling this function, or cope with the fact afterwards (which is usually	583	calling this function, or cope with the fact afterwards (which is usually
404	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	584	the easiest thing, you can just ignore the watchers and/or C<free ()> them
405	for example).	585	for example).
		586
		587	Note that certain global state, such as signal state (and installed signal
		588	handlers), will not be freed by this function, and related watchers (such
		589	as signal and child watchers) would need to be stopped manually.
		590
		591	In general it is not advisable to call this function except in the
		592	rare occasion where you really need to free e.g. the signal handling
		593	pipe fds. If you need dynamically allocated loops it is better to use
		594	C<ev_loop_new> and C<ev_loop_destroy>).
406		595
407	=item ev_loop_destroy (loop)	596	=item ev_loop_destroy (loop)
408		597
409	Like C<ev_default_destroy>, but destroys an event loop created by an	598	Like C<ev_default_destroy>, but destroys an event loop created by an
410	earlier call to C<ev_loop_new>.	599	earlier call to C<ev_loop_new>.
411		600
412	=item ev_default_fork ()	601	=item ev_default_fork ()
413		602
		603	This function sets a flag that causes subsequent C<ev_loop> iterations
414	This function reinitialises the kernel state for backends that have	604	to reinitialise the kernel state for backends that have one. Despite the
415	one. Despite the name, you can call it anytime, but it makes most sense	605	name, you can call it anytime, but it makes most sense after forking, in
416	after forking, in either the parent or child process (or both, but that	606	the child process (or both child and parent, but that again makes little
417	again makes little sense).	607	sense). You I<must> call it in the child before using any of the libev
		608	functions, and it will only take effect at the next C<ev_loop> iteration.
418		609
419	You I<must> call this function in the child process after forking if and	610	On the other hand, you only need to call this function in the child
420	only if you want to use the event library in both processes. If you just	611	process if and only if you want to use the event library in the child. If
421	fork+exec, you don't have to call it.	612	you just fork+exec, you don't have to call it at all.
422		613
423	The function itself is quite fast and it's usually not a problem to call	614	The function itself is quite fast and it's usually not a problem to call
424	it just in case after a fork. To make this easy, the function will fit in	615	it just in case after a fork. To make this easy, the function will fit in
425	quite nicely into a call to C<pthread_atfork>:	616	quite nicely into a call to C<pthread_atfork>:
426		617
427	pthread_atfork (0, 0, ev_default_fork);	618	pthread_atfork (0, 0, ev_default_fork);
428		619
429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
430	without calling this function, so if you force one of those backends you
431	do not need to care.
432
433	=item ev_loop_fork (loop)	620	=item ev_loop_fork (loop)
434		621
435	Like C<ev_default_fork>, but acts on an event loop created by	622	Like C<ev_default_fork>, but acts on an event loop created by
436	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	623	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
437	after fork, and how you do this is entirely your own problem.	624	after fork that you want to re-use in the child, and how you do this is
		625	entirely your own problem.
		626
		627	=item int ev_is_default_loop (loop)
		628
		629	Returns true when the given loop is, in fact, the default loop, and false
		630	otherwise.
438		631
439	=item unsigned int ev_loop_count (loop)	632	=item unsigned int ev_loop_count (loop)
440		633
441	Returns the count of loop iterations for the loop, which is identical to	634	Returns the count of loop iterations for the loop, which is identical to
442	the number of times libev did poll for new events. It starts at C<0> and	635	the number of times libev did poll for new events. It starts at C<0> and
443	happily wraps around with enough iterations.	636	happily wraps around with enough iterations.
444		637
445	This value can sometimes be useful as a generation counter of sorts (it	638	This value can sometimes be useful as a generation counter of sorts (it
446	"ticks" the number of loop iterations), as it roughly corresponds with	639	"ticks" the number of loop iterations), as it roughly corresponds with
447	C<ev_prepare> and C<ev_check> calls.	640	C<ev_prepare> and C<ev_check> calls.
		641
		642	=item unsigned int ev_loop_depth (loop)
		643
		644	Returns the number of times C<ev_loop> was entered minus the number of
		645	times C<ev_loop> was exited, in other words, the recursion depth.
		646
		647	Outside C<ev_loop>, this number is zero. In a callback, this number is
		648	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		649	in which case it is higher.
		650
		651	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		652	etc.), doesn't count as exit.
448		653
449	=item unsigned int ev_backend (loop)	654	=item unsigned int ev_backend (loop)
450		655
451	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	656	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
452	use.	657	use.
…		…
455		660
456	Returns the current "event loop time", which is the time the event loop	661	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	662	received events and started processing them. This timestamp does not
458	change as long as callbacks are being processed, and this is also the base	663	change as long as callbacks are being processed, and this is also the base
459	time used for relative timers. You can treat it as the timestamp of the	664	time used for relative timers. You can treat it as the timestamp of the
460	event occuring (or more correctly, libev finding out about it).	665	event occurring (or more correctly, libev finding out about it).
		666
		667	=item ev_now_update (loop)
		668
		669	Establishes the current time by querying the kernel, updating the time
		670	returned by C<ev_now ()> in the progress. This is a costly operation and
		671	is usually done automatically within C<ev_loop ()>.
		672
		673	This function is rarely useful, but when some event callback runs for a
		674	very long time without entering the event loop, updating libev's idea of
		675	the current time is a good idea.
		676
		677	See also L<The special problem of time updates> in the C<ev_timer> section.
		678
		679	=item ev_suspend (loop)
		680
		681	=item ev_resume (loop)
		682
		683	These two functions suspend and resume a loop, for use when the loop is
		684	not used for a while and timeouts should not be processed.
		685
		686	A typical use case would be an interactive program such as a game: When
		687	the user presses C<^Z> to suspend the game and resumes it an hour later it
		688	would be best to handle timeouts as if no time had actually passed while
		689	the program was suspended. This can be achieved by calling C<ev_suspend>
		690	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		691	C<ev_resume> directly afterwards to resume timer processing.
		692
		693	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		694	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		695	will be rescheduled (that is, they will lose any events that would have
		696	occured while suspended).
		697
		698	After calling C<ev_suspend> you B<must not> call I<any> function on the
		699	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		700	without a previous call to C<ev_suspend>.
		701
		702	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		703	event loop time (see C<ev_now_update>).
461		704
462	=item ev_loop (loop, int flags)	705	=item ev_loop (loop, int flags)
463		706
464	Finally, this is it, the event handler. This function usually is called	707	Finally, this is it, the event handler. This function usually is called
465	after you initialised all your watchers and you want to start handling	708	after you initialised all your watchers and you want to start handling
…		…
468	If the flags argument is specified as C<0>, it will not return until	711	If the flags argument is specified as C<0>, it will not return until
469	either no event watchers are active anymore or C<ev_unloop> was called.	712	either no event watchers are active anymore or C<ev_unloop> was called.
470		713
471	Please note that an explicit C<ev_unloop> is usually better than	714	Please note that an explicit C<ev_unloop> is usually better than
472	relying on all watchers to be stopped when deciding when a program has	715	relying on all watchers to be stopped when deciding when a program has
473	finished (especially in interactive programs), but having a program that	716	finished (especially in interactive programs), but having a program
474	automatically loops as long as it has to and no longer by virtue of	717	that automatically loops as long as it has to and no longer by virtue
475	relying on its watchers stopping correctly is a thing of beauty.	718	of relying on its watchers stopping correctly, that is truly a thing of
		719	beauty.
476		720
477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	721	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
478	those events and any outstanding ones, but will not block your process in	722	those events and any already outstanding ones, but will not block your
479	case there are no events and will return after one iteration of the loop.	723	process in case there are no events and will return after one iteration of
		724	the loop.
480		725
481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	726	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
482	neccessary) and will handle those and any outstanding ones. It will block	727	necessary) and will handle those and any already outstanding ones. It
483	your process until at least one new event arrives, and will return after	728	will block your process until at least one new event arrives (which could
484	one iteration of the loop. This is useful if you are waiting for some	729	be an event internal to libev itself, so there is no guarantee that a
485	external event in conjunction with something not expressible using other	730	user-registered callback will be called), and will return after one
		731	iteration of the loop.
		732
		733	This is useful if you are waiting for some external event in conjunction
		734	with something not expressible using other libev watchers (i.e. "roll your
486	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	735	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
487	usually a better approach for this kind of thing.	736	usually a better approach for this kind of thing.
488		737
489	Here are the gory details of what C<ev_loop> does:	738	Here are the gory details of what C<ev_loop> does:
490		739
491	* If there are no active watchers (reference count is zero), return.	740	- Before the first iteration, call any pending watchers.
492	- Queue prepare watchers and then call all outstanding watchers.	741	* If EVFLAG_FORKCHECK was used, check for a fork.
		742	- If a fork was detected (by any means), queue and call all fork watchers.
		743	- Queue and call all prepare watchers.
493	- If we have been forked, recreate the kernel state.	744	- If we have been forked, detach and recreate the kernel state
		745	as to not disturb the other process.
494	- Update the kernel state with all outstanding changes.	746	- Update the kernel state with all outstanding changes.
495	- Update the "event loop time".	747	- Update the "event loop time" (ev_now ()).
496	- Calculate for how long to block.	748	- Calculate for how long to sleep or block, if at all
		749	(active idle watchers, EVLOOP_NONBLOCK or not having
		750	any active watchers at all will result in not sleeping).
		751	- Sleep if the I/O and timer collect interval say so.
497	- Block the process, waiting for any events.	752	- Block the process, waiting for any events.
498	- Queue all outstanding I/O (fd) events.	753	- Queue all outstanding I/O (fd) events.
499	- Update the "event loop time" and do time jump handling.	754	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
500	- Queue all outstanding timers.	755	- Queue all expired timers.
501	- Queue all outstanding periodics.	756	- Queue all expired periodics.
502	- If no events are pending now, queue all idle watchers.	757	- Unless any events are pending now, queue all idle watchers.
503	- Queue all check watchers.	758	- Queue all check watchers.
504	- Call all queued watchers in reverse order (i.e. check watchers first).	759	- Call all queued watchers in reverse order (i.e. check watchers first).
505	Signals and child watchers are implemented as I/O watchers, and will	760	Signals and child watchers are implemented as I/O watchers, and will
506	be handled here by queueing them when their watcher gets executed.	761	be handled here by queueing them when their watcher gets executed.
507	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	762	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
508	were used, return, otherwise continue with step *.	763	were used, or there are no active watchers, return, otherwise
		764	continue with step *.
509		765
510	Example: Queue some jobs and then loop until no events are outsanding	766	Example: Queue some jobs and then loop until no events are outstanding
511	anymore.	767	anymore.
512		768
513	... queue jobs here, make sure they register event watchers as long	769	... queue jobs here, make sure they register event watchers as long
514	... as they still have work to do (even an idle watcher will do..)	770	... as they still have work to do (even an idle watcher will do..)
515	ev_loop (my_loop, 0);	771	ev_loop (my_loop, 0);
516	... jobs done. yeah!	772	... jobs done or somebody called unloop. yeah!
517		773
518	=item ev_unloop (loop, how)	774	=item ev_unloop (loop, how)
519		775
520	Can be used to make a call to C<ev_loop> return early (but only after it	776	Can be used to make a call to C<ev_loop> return early (but only after it
521	has processed all outstanding events). The C<how> argument must be either	777	has processed all outstanding events). The C<how> argument must be either
522	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	778	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
523	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	779	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
524		780
		781	This "unloop state" will be cleared when entering C<ev_loop> again.
		782
		783	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		784
525	=item ev_ref (loop)	785	=item ev_ref (loop)
526		786
527	=item ev_unref (loop)	787	=item ev_unref (loop)
528		788
529	Ref/unref can be used to add or remove a reference count on the event	789	Ref/unref can be used to add or remove a reference count on the event
530	loop: Every watcher keeps one reference, and as long as the reference	790	loop: Every watcher keeps one reference, and as long as the reference
531	count is nonzero, C<ev_loop> will not return on its own. If you have	791	count is nonzero, C<ev_loop> will not return on its own.
		792
532	a watcher you never unregister that should not keep C<ev_loop> from	793	If you have a watcher you never unregister that should not keep C<ev_loop>
533	returning, ev_unref() after starting, and ev_ref() before stopping it. For	794	from returning, call ev_unref() after starting, and ev_ref() before
		795	stopping it.
		796
534	example, libev itself uses this for its internal signal pipe: It is not	797	As an example, libev itself uses this for its internal signal pipe: It
535	visible to the libev user and should not keep C<ev_loop> from exiting if	798	is not visible to the libev user and should not keep C<ev_loop> from
536	no event watchers registered by it are active. It is also an excellent	799	exiting if no event watchers registered by it are active. It is also an
537	way to do this for generic recurring timers or from within third-party	800	excellent way to do this for generic recurring timers or from within
538	libraries. Just remember to I<unref after start> and I<ref before stop>.	801	third-party libraries. Just remember to I<unref after start> and I<ref
		802	before stop> (but only if the watcher wasn't active before, or was active
		803	before, respectively. Note also that libev might stop watchers itself
		804	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		805	in the callback).
539		806
540	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	807	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
541	running when nothing else is active.	808	running when nothing else is active.
542		809
543	struct ev_signal exitsig;	810	ev_signal exitsig;
544	ev_signal_init (&exitsig, sig_cb, SIGINT);	811	ev_signal_init (&exitsig, sig_cb, SIGINT);
545	ev_signal_start (loop, &exitsig);	812	ev_signal_start (loop, &exitsig);
546	evf_unref (loop);	813	evf_unref (loop);
547		814
548	Example: For some weird reason, unregister the above signal handler again.	815	Example: For some weird reason, unregister the above signal handler again.
549		816
550	ev_ref (loop);	817	ev_ref (loop);
551	ev_signal_stop (loop, &exitsig);	818	ev_signal_stop (loop, &exitsig);
		819
		820	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		821
		822	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		823
		824	These advanced functions influence the time that libev will spend waiting
		825	for events. Both time intervals are by default C<0>, meaning that libev
		826	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		827	latency.
		828
		829	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		830	allows libev to delay invocation of I/O and timer/periodic callbacks
		831	to increase efficiency of loop iterations (or to increase power-saving
		832	opportunities).
		833
		834	The idea is that sometimes your program runs just fast enough to handle
		835	one (or very few) event(s) per loop iteration. While this makes the
		836	program responsive, it also wastes a lot of CPU time to poll for new
		837	events, especially with backends like C<select ()> which have a high
		838	overhead for the actual polling but can deliver many events at once.
		839
		840	By setting a higher I<io collect interval> you allow libev to spend more
		841	time collecting I/O events, so you can handle more events per iteration,
		842	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		843	C<ev_timer>) will be not affected. Setting this to a non-null value will
		844	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		845	sleep time ensures that libev will not poll for I/O events more often then
		846	once per this interval, on average.
		847
		848	Likewise, by setting a higher I<timeout collect interval> you allow libev
		849	to spend more time collecting timeouts, at the expense of increased
		850	latency/jitter/inexactness (the watcher callback will be called
		851	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		852	value will not introduce any overhead in libev.
		853
		854	Many (busy) programs can usually benefit by setting the I/O collect
		855	interval to a value near C<0.1> or so, which is often enough for
		856	interactive servers (of course not for games), likewise for timeouts. It
		857	usually doesn't make much sense to set it to a lower value than C<0.01>,
		858	as this approaches the timing granularity of most systems. Note that if
		859	you do transactions with the outside world and you can't increase the
		860	parallelity, then this setting will limit your transaction rate (if you
		861	need to poll once per transaction and the I/O collect interval is 0.01,
		862	then you can't do more than 100 transations per second).
		863
		864	Setting the I<timeout collect interval> can improve the opportunity for
		865	saving power, as the program will "bundle" timer callback invocations that
		866	are "near" in time together, by delaying some, thus reducing the number of
		867	times the process sleeps and wakes up again. Another useful technique to
		868	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		869	they fire on, say, one-second boundaries only.
		870
		871	Example: we only need 0.1s timeout granularity, and we wish not to poll
		872	more often than 100 times per second:
		873
		874	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		875	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		876
		877	=item ev_invoke_pending (loop)
		878
		879	This call will simply invoke all pending watchers while resetting their
		880	pending state. Normally, C<ev_loop> does this automatically when required,
		881	but when overriding the invoke callback this call comes handy.
		882
		883	=item int ev_pending_count (loop)
		884
		885	Returns the number of pending watchers - zero indicates that no watchers
		886	are pending.
		887
		888	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		889
		890	This overrides the invoke pending functionality of the loop: Instead of
		891	invoking all pending watchers when there are any, C<ev_loop> will call
		892	this callback instead. This is useful, for example, when you want to
		893	invoke the actual watchers inside another context (another thread etc.).
		894
		895	If you want to reset the callback, use C<ev_invoke_pending> as new
		896	callback.
		897
		898	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		899
		900	Sometimes you want to share the same loop between multiple threads. This
		901	can be done relatively simply by putting mutex_lock/unlock calls around
		902	each call to a libev function.
		903
		904	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		905	wait for it to return. One way around this is to wake up the loop via
		906	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		907	and I<acquire> callbacks on the loop.
		908
		909	When set, then C<release> will be called just before the thread is
		910	suspended waiting for new events, and C<acquire> is called just
		911	afterwards.
		912
		913	Ideally, C<release> will just call your mutex_unlock function, and
		914	C<acquire> will just call the mutex_lock function again.
		915
		916	While event loop modifications are allowed between invocations of
		917	C<release> and C<acquire> (that's their only purpose after all), no
		918	modifications done will affect the event loop, i.e. adding watchers will
		919	have no effect on the set of file descriptors being watched, or the time
		920	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		921	to take note of any changes you made.
		922
		923	In theory, threads executing C<ev_loop> will be async-cancel safe between
		924	invocations of C<release> and C<acquire>.
		925
		926	See also the locking example in the C<THREADS> section later in this
		927	document.
		928
		929	=item ev_set_userdata (loop, void *data)
		930
		931	=item ev_userdata (loop)
		932
		933	Set and retrieve a single C<void *> associated with a loop. When
		934	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		935	C<0.>
		936
		937	These two functions can be used to associate arbitrary data with a loop,
		938	and are intended solely for the C<invoke_pending_cb>, C<release> and
		939	C<acquire> callbacks described above, but of course can be (ab-)used for
		940	any other purpose as well.
		941
		942	=item ev_loop_verify (loop)
		943
		944	This function only does something when C<EV_VERIFY> support has been
		945	compiled in, which is the default for non-minimal builds. It tries to go
		946	through all internal structures and checks them for validity. If anything
		947	is found to be inconsistent, it will print an error message to standard
		948	error and call C<abort ()>.
		949
		950	This can be used to catch bugs inside libev itself: under normal
		951	circumstances, this function will never abort as of course libev keeps its
		952	data structures consistent.
552		953
553	=back	954	=back
554		955
555		956
556	=head1 ANATOMY OF A WATCHER	957	=head1 ANATOMY OF A WATCHER
		958
		959	In the following description, uppercase C<TYPE> in names stands for the
		960	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		961	watchers and C<ev_io_start> for I/O watchers.
557		962
558	A watcher is a structure that you create and register to record your	963	A watcher is a structure that you create and register to record your
559	interest in some event. For instance, if you want to wait for STDIN to	964	interest in some event. For instance, if you want to wait for STDIN to
560	become readable, you would create an C<ev_io> watcher for that:	965	become readable, you would create an C<ev_io> watcher for that:
561		966
562	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	967	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
563	{	968	{
564	ev_io_stop (w);	969	ev_io_stop (w);
565	ev_unloop (loop, EVUNLOOP_ALL);	970	ev_unloop (loop, EVUNLOOP_ALL);
566	}	971	}
567		972
568	struct ev_loop *loop = ev_default_loop (0);	973	struct ev_loop *loop = ev_default_loop (0);
		974
569	struct ev_io stdin_watcher;	975	ev_io stdin_watcher;
		976
570	ev_init (&stdin_watcher, my_cb);	977	ev_init (&stdin_watcher, my_cb);
571	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	978	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
572	ev_io_start (loop, &stdin_watcher);	979	ev_io_start (loop, &stdin_watcher);
		980
573	ev_loop (loop, 0);	981	ev_loop (loop, 0);
574		982
575	As you can see, you are responsible for allocating the memory for your	983	As you can see, you are responsible for allocating the memory for your
576	watcher structures (and it is usually a bad idea to do this on the stack,	984	watcher structures (and it is I<usually> a bad idea to do this on the
577	although this can sometimes be quite valid).	985	stack).
		986
		987	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		988	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
578		989
579	Each watcher structure must be initialised by a call to C<ev_init	990	Each watcher structure must be initialised by a call to C<ev_init
580	(watcher *, callback)>, which expects a callback to be provided. This	991	(watcher *, callback)>, which expects a callback to be provided. This
581	callback gets invoked each time the event occurs (or, in the case of io	992	callback gets invoked each time the event occurs (or, in the case of I/O
582	watchers, each time the event loop detects that the file descriptor given	993	watchers, each time the event loop detects that the file descriptor given
583	is readable and/or writable).	994	is readable and/or writable).
584		995
585	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	996	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
586	with arguments specific to this watcher type. There is also a macro	997	macro to configure it, with arguments specific to the watcher type. There
587	to combine initialisation and setting in one call: C<< ev_<type>_init	998	is also a macro to combine initialisation and setting in one call: C<<
588	(watcher *, callback, ...) >>.	999	ev_TYPE_init (watcher *, callback, ...) >>.
589		1000
590	To make the watcher actually watch out for events, you have to start it	1001	To make the watcher actually watch out for events, you have to start it
591	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1002	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
592	*) >>), and you can stop watching for events at any time by calling the	1003	*) >>), and you can stop watching for events at any time by calling the
593	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1004	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
594		1005
595	As long as your watcher is active (has been started but not stopped) you	1006	As long as your watcher is active (has been started but not stopped) you
596	must not touch the values stored in it. Most specifically you must never	1007	must not touch the values stored in it. Most specifically you must never
597	reinitialise it or call its C<set> macro.	1008	reinitialise it or call its C<ev_TYPE_set> macro.
598		1009
599	Each and every callback receives the event loop pointer as first, the	1010	Each and every callback receives the event loop pointer as first, the
600	registered watcher structure as second, and a bitset of received events as	1011	registered watcher structure as second, and a bitset of received events as
601	third argument.	1012	third argument.
602		1013
…		…
656	=item C<EV_FORK>	1067	=item C<EV_FORK>
657		1068
658	The event loop has been resumed in the child process after fork (see	1069	The event loop has been resumed in the child process after fork (see
659	C<ev_fork>).	1070	C<ev_fork>).
660		1071
		1072	=item C<EV_ASYNC>
		1073
		1074	The given async watcher has been asynchronously notified (see C<ev_async>).
		1075
		1076	=item C<EV_CUSTOM>
		1077
		1078	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1079	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1080
661	=item C<EV_ERROR>	1081	=item C<EV_ERROR>
662		1082
663	An unspecified error has occured, the watcher has been stopped. This might	1083	An unspecified error has occurred, the watcher has been stopped. This might
664	happen because the watcher could not be properly started because libev	1084	happen because the watcher could not be properly started because libev
665	ran out of memory, a file descriptor was found to be closed or any other	1085	ran out of memory, a file descriptor was found to be closed or any other
		1086	problem. Libev considers these application bugs.
		1087
666	problem. You best act on it by reporting the problem and somehow coping	1088	You best act on it by reporting the problem and somehow coping with the
667	with the watcher being stopped.	1089	watcher being stopped. Note that well-written programs should not receive
		1090	an error ever, so when your watcher receives it, this usually indicates a
		1091	bug in your program.
668		1092
669	Libev will usually signal a few "dummy" events together with an error,	1093	Libev will usually signal a few "dummy" events together with an error, for
670	for example it might indicate that a fd is readable or writable, and if	1094	example it might indicate that a fd is readable or writable, and if your
671	your callbacks is well-written it can just attempt the operation and cope	1095	callbacks is well-written it can just attempt the operation and cope with
672	with the error from read() or write(). This will not work in multithreaded	1096	the error from read() or write(). This will not work in multi-threaded
673	programs, though, so beware.	1097	programs, though, as the fd could already be closed and reused for another
		1098	thing, so beware.
674		1099
675	=back	1100	=back
676		1101
677	=head2 GENERIC WATCHER FUNCTIONS	1102	=head2 GENERIC WATCHER FUNCTIONS
678
679	In the following description, C<TYPE> stands for the watcher type,
680	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
681		1103
682	=over 4	1104	=over 4
683		1105
684	=item C<ev_init> (ev_TYPE *watcher, callback)	1106	=item C<ev_init> (ev_TYPE *watcher, callback)
685		1107
…		…
691	which rolls both calls into one.	1113	which rolls both calls into one.
692		1114
693	You can reinitialise a watcher at any time as long as it has been stopped	1115	You can reinitialise a watcher at any time as long as it has been stopped
694	(or never started) and there are no pending events outstanding.	1116	(or never started) and there are no pending events outstanding.
695		1117
696	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1118	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
697	int revents)>.	1119	int revents)>.
		1120
		1121	Example: Initialise an C<ev_io> watcher in two steps.
		1122
		1123	ev_io w;
		1124	ev_init (&w, my_cb);
		1125	ev_io_set (&w, STDIN_FILENO, EV_READ);
698		1126
699	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1127	=item C<ev_TYPE_set> (ev_TYPE *, [args])
700		1128
701	This macro initialises the type-specific parts of a watcher. You need to	1129	This macro initialises the type-specific parts of a watcher. You need to
702	call C<ev_init> at least once before you call this macro, but you can	1130	call C<ev_init> at least once before you call this macro, but you can
…		…
705	difference to the C<ev_init> macro).	1133	difference to the C<ev_init> macro).
706		1134
707	Although some watcher types do not have type-specific arguments	1135	Although some watcher types do not have type-specific arguments
708	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1136	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
709		1137
		1138	See C<ev_init>, above, for an example.
		1139
710	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1140	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
711		1141
712	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1142	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
713	calls into a single call. This is the most convinient method to initialise	1143	calls into a single call. This is the most convenient method to initialise
714	a watcher. The same limitations apply, of course.	1144	a watcher. The same limitations apply, of course.
		1145
		1146	Example: Initialise and set an C<ev_io> watcher in one step.
		1147
		1148	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
715		1149
716	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1150	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
717		1151
718	Starts (activates) the given watcher. Only active watchers will receive	1152	Starts (activates) the given watcher. Only active watchers will receive
719	events. If the watcher is already active nothing will happen.	1153	events. If the watcher is already active nothing will happen.
720		1154
		1155	Example: Start the C<ev_io> watcher that is being abused as example in this
		1156	whole section.
		1157
		1158	ev_io_start (EV_DEFAULT_UC, &w);
		1159
721	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1160	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
722		1161
723	Stops the given watcher again (if active) and clears the pending	1162	Stops the given watcher if active, and clears the pending status (whether
		1163	the watcher was active or not).
		1164
724	status. It is possible that stopped watchers are pending (for example,	1165	It is possible that stopped watchers are pending - for example,
725	non-repeating timers are being stopped when they become pending), but	1166	non-repeating timers are being stopped when they become pending - but
726	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1167	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
727	you want to free or reuse the memory used by the watcher it is therefore a	1168	pending. If you want to free or reuse the memory used by the watcher it is
728	good idea to always call its C<ev_TYPE_stop> function.	1169	therefore a good idea to always call its C<ev_TYPE_stop> function.
729		1170
730	=item bool ev_is_active (ev_TYPE *watcher)	1171	=item bool ev_is_active (ev_TYPE *watcher)
731		1172
732	Returns a true value iff the watcher is active (i.e. it has been started	1173	Returns a true value iff the watcher is active (i.e. it has been started
733	and not yet been stopped). As long as a watcher is active you must not modify	1174	and not yet been stopped). As long as a watcher is active you must not modify
…		…
759	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1200	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
760	(default: C<-2>). Pending watchers with higher priority will be invoked	1201	(default: C<-2>). Pending watchers with higher priority will be invoked
761	before watchers with lower priority, but priority will not keep watchers	1202	before watchers with lower priority, but priority will not keep watchers
762	from being executed (except for C<ev_idle> watchers).	1203	from being executed (except for C<ev_idle> watchers).
763		1204
764	This means that priorities are I<only> used for ordering callback
765	invocation after new events have been received. This is useful, for
766	example, to reduce latency after idling, or more often, to bind two
767	watchers on the same event and make sure one is called first.
768
769	If you need to suppress invocation when higher priority events are pending	1205	If you need to suppress invocation when higher priority events are pending
770	you need to look at C<ev_idle> watchers, which provide this functionality.	1206	you need to look at C<ev_idle> watchers, which provide this functionality.
771		1207
772	You I<must not> change the priority of a watcher as long as it is active or	1208	You I<must not> change the priority of a watcher as long as it is active or
773	pending.	1209	pending.
774		1210
		1211	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1212	fine, as long as you do not mind that the priority value you query might
		1213	or might not have been clamped to the valid range.
		1214
775	The default priority used by watchers when no priority has been set is	1215	The default priority used by watchers when no priority has been set is
776	always C<0>, which is supposed to not be too high and not be too low :).	1216	always C<0>, which is supposed to not be too high and not be too low :).
777		1217
778	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1218	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
779	fine, as long as you do not mind that the priority value you query might	1219	priorities.
780	or might not have been adjusted to be within valid range.
781		1220
782	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1221	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
783		1222
784	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1223	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
785	C<loop> nor C<revents> need to be valid as long as the watcher callback	1224	C<loop> nor C<revents> need to be valid as long as the watcher callback
786	can deal with that fact.	1225	can deal with that fact, as both are simply passed through to the
		1226	callback.
787		1227
788	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1228	=item int ev_clear_pending (loop, ev_TYPE *watcher)
789		1229
790	If the watcher is pending, this function returns clears its pending status	1230	If the watcher is pending, this function clears its pending status and
791	and returns its C<revents> bitset (as if its callback was invoked). If the	1231	returns its C<revents> bitset (as if its callback was invoked). If the
792	watcher isn't pending it does nothing and returns C<0>.	1232	watcher isn't pending it does nothing and returns C<0>.
793		1233
		1234	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1235	callback to be invoked, which can be accomplished with this function.
		1236
794	=back	1237	=back
795		1238
796		1239
797	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1240	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
798		1241
799	Each watcher has, by default, a member C<void *data> that you can change	1242	Each watcher has, by default, a member C<void *data> that you can change
800	and read at any time, libev will completely ignore it. This can be used	1243	and read at any time: libev will completely ignore it. This can be used
801	to associate arbitrary data with your watcher. If you need more data and	1244	to associate arbitrary data with your watcher. If you need more data and
802	don't want to allocate memory and store a pointer to it in that data	1245	don't want to allocate memory and store a pointer to it in that data
803	member, you can also "subclass" the watcher type and provide your own	1246	member, you can also "subclass" the watcher type and provide your own
804	data:	1247	data:
805		1248
806	struct my_io	1249	struct my_io
807	{	1250	{
808	struct ev_io io;	1251	ev_io io;
809	int otherfd;	1252	int otherfd;
810	void *somedata;	1253	void *somedata;
811	struct whatever *mostinteresting;	1254	struct whatever *mostinteresting;
812	}	1255	};
		1256
		1257	...
		1258	struct my_io w;
		1259	ev_io_init (&w.io, my_cb, fd, EV_READ);
813		1260
814	And since your callback will be called with a pointer to the watcher, you	1261	And since your callback will be called with a pointer to the watcher, you
815	can cast it back to your own type:	1262	can cast it back to your own type:
816		1263
817	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1264	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
818	{	1265	{
819	struct my_io *w = (struct my_io *)w_;	1266	struct my_io *w = (struct my_io *)w_;
820	...	1267	...
821	}	1268	}
822		1269
823	More interesting and less C-conformant ways of casting your callback type	1270	More interesting and less C-conformant ways of casting your callback type
824	instead have been omitted.	1271	instead have been omitted.
825		1272
826	Another common scenario is having some data structure with multiple	1273	Another common scenario is to use some data structure with multiple
827	watchers:	1274	embedded watchers:
828		1275
829	struct my_biggy	1276	struct my_biggy
830	{	1277	{
831	int some_data;	1278	int some_data;
832	ev_timer t1;	1279	ev_timer t1;
833	ev_timer t2;	1280	ev_timer t2;
834	}	1281	}
835		1282
836	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1283	In this case getting the pointer to C<my_biggy> is a bit more
837	you need to use C<offsetof>:	1284	complicated: Either you store the address of your C<my_biggy> struct
		1285	in the C<data> member of the watcher (for woozies), or you need to use
		1286	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1287	programmers):
838		1288
839	#include <stddef.h>	1289	#include <stddef.h>
840		1290
841	static void	1291	static void
842	t1_cb (EV_P_ struct ev_timer *w, int revents)	1292	t1_cb (EV_P_ ev_timer *w, int revents)
843	{	1293	{
844	struct my_biggy big = (struct my_biggy *	1294	struct my_biggy big = (struct my_biggy *)
845	(((char *)w) - offsetof (struct my_biggy, t1));	1295	(((char *)w) - offsetof (struct my_biggy, t1));
846	}	1296	}
847		1297
848	static void	1298	static void
849	t2_cb (EV_P_ struct ev_timer *w, int revents)	1299	t2_cb (EV_P_ ev_timer *w, int revents)
850	{	1300	{
851	struct my_biggy big = (struct my_biggy *	1301	struct my_biggy big = (struct my_biggy *)
852	(((char *)w) - offsetof (struct my_biggy, t2));	1302	(((char *)w) - offsetof (struct my_biggy, t2));
853	}	1303	}
		1304
		1305	=head2 WATCHER PRIORITY MODELS
		1306
		1307	Many event loops support I<watcher priorities>, which are usually small
		1308	integers that influence the ordering of event callback invocation
		1309	between watchers in some way, all else being equal.
		1310
		1311	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1312	description for the more technical details such as the actual priority
		1313	range.
		1314
		1315	There are two common ways how these these priorities are being interpreted
		1316	by event loops:
		1317
		1318	In the more common lock-out model, higher priorities "lock out" invocation
		1319	of lower priority watchers, which means as long as higher priority
		1320	watchers receive events, lower priority watchers are not being invoked.
		1321
		1322	The less common only-for-ordering model uses priorities solely to order
		1323	callback invocation within a single event loop iteration: Higher priority
		1324	watchers are invoked before lower priority ones, but they all get invoked
		1325	before polling for new events.
		1326
		1327	Libev uses the second (only-for-ordering) model for all its watchers
		1328	except for idle watchers (which use the lock-out model).
		1329
		1330	The rationale behind this is that implementing the lock-out model for
		1331	watchers is not well supported by most kernel interfaces, and most event
		1332	libraries will just poll for the same events again and again as long as
		1333	their callbacks have not been executed, which is very inefficient in the
		1334	common case of one high-priority watcher locking out a mass of lower
		1335	priority ones.
		1336
		1337	Static (ordering) priorities are most useful when you have two or more
		1338	watchers handling the same resource: a typical usage example is having an
		1339	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1340	timeouts. Under load, data might be received while the program handles
		1341	other jobs, but since timers normally get invoked first, the timeout
		1342	handler will be executed before checking for data. In that case, giving
		1343	the timer a lower priority than the I/O watcher ensures that I/O will be
		1344	handled first even under adverse conditions (which is usually, but not
		1345	always, what you want).
		1346
		1347	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1348	will only be executed when no same or higher priority watchers have
		1349	received events, they can be used to implement the "lock-out" model when
		1350	required.
		1351
		1352	For example, to emulate how many other event libraries handle priorities,
		1353	you can associate an C<ev_idle> watcher to each such watcher, and in
		1354	the normal watcher callback, you just start the idle watcher. The real
		1355	processing is done in the idle watcher callback. This causes libev to
		1356	continously poll and process kernel event data for the watcher, but when
		1357	the lock-out case is known to be rare (which in turn is rare :), this is
		1358	workable.
		1359
		1360	Usually, however, the lock-out model implemented that way will perform
		1361	miserably under the type of load it was designed to handle. In that case,
		1362	it might be preferable to stop the real watcher before starting the
		1363	idle watcher, so the kernel will not have to process the event in case
		1364	the actual processing will be delayed for considerable time.
		1365
		1366	Here is an example of an I/O watcher that should run at a strictly lower
		1367	priority than the default, and which should only process data when no
		1368	other events are pending:
		1369
		1370	ev_idle idle; // actual processing watcher
		1371	ev_io io; // actual event watcher
		1372
		1373	static void
		1374	io_cb (EV_P_ ev_io *w, int revents)
		1375	{
		1376	// stop the I/O watcher, we received the event, but
		1377	// are not yet ready to handle it.
		1378	ev_io_stop (EV_A_ w);
		1379
		1380	// start the idle watcher to ahndle the actual event.
		1381	// it will not be executed as long as other watchers
		1382	// with the default priority are receiving events.
		1383	ev_idle_start (EV_A_ &idle);
		1384	}
		1385
		1386	static void
		1387	idle_cb (EV_P_ ev_idle *w, int revents)
		1388	{
		1389	// actual processing
		1390	read (STDIN_FILENO, ...);
		1391
		1392	// have to start the I/O watcher again, as
		1393	// we have handled the event
		1394	ev_io_start (EV_P_ &io);
		1395	}
		1396
		1397	// initialisation
		1398	ev_idle_init (&idle, idle_cb);
		1399	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1400	ev_io_start (EV_DEFAULT_ &io);
		1401
		1402	In the "real" world, it might also be beneficial to start a timer, so that
		1403	low-priority connections can not be locked out forever under load. This
		1404	enables your program to keep a lower latency for important connections
		1405	during short periods of high load, while not completely locking out less
		1406	important ones.
854		1407
855		1408
856	=head1 WATCHER TYPES	1409	=head1 WATCHER TYPES
857		1410
858	This section describes each watcher in detail, but will not repeat	1411	This section describes each watcher in detail, but will not repeat
…		…
882	In general you can register as many read and/or write event watchers per	1435	In general you can register as many read and/or write event watchers per
883	fd as you want (as long as you don't confuse yourself). Setting all file	1436	fd as you want (as long as you don't confuse yourself). Setting all file
884	descriptors to non-blocking mode is also usually a good idea (but not	1437	descriptors to non-blocking mode is also usually a good idea (but not
885	required if you know what you are doing).	1438	required if you know what you are doing).
886		1439
887	You have to be careful with dup'ed file descriptors, though. Some backends	1440	If you cannot use non-blocking mode, then force the use of a
888	(the linux epoll backend is a notable example) cannot handle dup'ed file	1441	known-to-be-good backend (at the time of this writing, this includes only
889	descriptors correctly if you register interest in two or more fds pointing	1442	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
890	to the same underlying file/socket/etc. description (that is, they share	1443	descriptors for which non-blocking operation makes no sense (such as
891	the same underlying "file open").	1444	files) - libev doesn't guarentee any specific behaviour in that case.
892
893	If you must do this, then force the use of a known-to-be-good backend
894	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
895	C<EVBACKEND_POLL>).
896		1445
897	Another thing you have to watch out for is that it is quite easy to	1446	Another thing you have to watch out for is that it is quite easy to
898	receive "spurious" readyness notifications, that is your callback might	1447	receive "spurious" readiness notifications, that is your callback might
899	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1448	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
900	because there is no data. Not only are some backends known to create a	1449	because there is no data. Not only are some backends known to create a
901	lot of those (for example solaris ports), it is very easy to get into	1450	lot of those (for example Solaris ports), it is very easy to get into
902	this situation even with a relatively standard program structure. Thus	1451	this situation even with a relatively standard program structure. Thus
903	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1452	it is best to always use non-blocking I/O: An extra C<read>(2) returning
904	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1453	C<EAGAIN> is far preferable to a program hanging until some data arrives.
905		1454
906	If you cannot run the fd in non-blocking mode (for example you should not	1455	If you cannot run the fd in non-blocking mode (for example you should
907	play around with an Xlib connection), then you have to seperately re-test	1456	not play around with an Xlib connection), then you have to separately
908	whether a file descriptor is really ready with a known-to-be good interface	1457	re-test whether a file descriptor is really ready with a known-to-be good
909	such as poll (fortunately in our Xlib example, Xlib already does this on	1458	interface such as poll (fortunately in our Xlib example, Xlib already
910	its own, so its quite safe to use).	1459	does this on its own, so its quite safe to use). Some people additionally
		1460	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1461	indefinitely.
		1462
		1463	But really, best use non-blocking mode.
		1464
		1465	=head3 The special problem of disappearing file descriptors
		1466
		1467	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1468	descriptor (either due to calling C<close> explicitly or any other means,
		1469	such as C<dup2>). The reason is that you register interest in some file
		1470	descriptor, but when it goes away, the operating system will silently drop
		1471	this interest. If another file descriptor with the same number then is
		1472	registered with libev, there is no efficient way to see that this is, in
		1473	fact, a different file descriptor.
		1474
		1475	To avoid having to explicitly tell libev about such cases, libev follows
		1476	the following policy: Each time C<ev_io_set> is being called, libev
		1477	will assume that this is potentially a new file descriptor, otherwise
		1478	it is assumed that the file descriptor stays the same. That means that
		1479	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1480	descriptor even if the file descriptor number itself did not change.
		1481
		1482	This is how one would do it normally anyway, the important point is that
		1483	the libev application should not optimise around libev but should leave
		1484	optimisations to libev.
		1485
		1486	=head3 The special problem of dup'ed file descriptors
		1487
		1488	Some backends (e.g. epoll), cannot register events for file descriptors,
		1489	but only events for the underlying file descriptions. That means when you
		1490	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1491	events for them, only one file descriptor might actually receive events.
		1492
		1493	There is no workaround possible except not registering events
		1494	for potentially C<dup ()>'ed file descriptors, or to resort to
		1495	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1496
		1497	=head3 The special problem of fork
		1498
		1499	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1500	useless behaviour. Libev fully supports fork, but needs to be told about
		1501	it in the child.
		1502
		1503	To support fork in your programs, you either have to call
		1504	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1505	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1506	C<EVBACKEND_POLL>.
		1507
		1508	=head3 The special problem of SIGPIPE
		1509
		1510	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1511	when writing to a pipe whose other end has been closed, your program gets
		1512	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1513	this is sensible behaviour, for daemons, this is usually undesirable.
		1514
		1515	So when you encounter spurious, unexplained daemon exits, make sure you
		1516	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1517	somewhere, as that would have given you a big clue).
		1518
		1519
		1520	=head3 Watcher-Specific Functions
911		1521
912	=over 4	1522	=over 4
913		1523
914	=item ev_io_init (ev_io *, callback, int fd, int events)	1524	=item ev_io_init (ev_io *, callback, int fd, int events)
915		1525
916	=item ev_io_set (ev_io *, int fd, int events)	1526	=item ev_io_set (ev_io *, int fd, int events)
917		1527
918	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1528	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
919	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1529	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
920	C<EV_READ | EV_WRITE> to receive the given events.	1530	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
921		1531
922	=item int fd [read-only]	1532	=item int fd [read-only]
923		1533
924	The file descriptor being watched.	1534	The file descriptor being watched.
925		1535
926	=item int events [read-only]	1536	=item int events [read-only]
927		1537
928	The events being watched.	1538	The events being watched.
929		1539
930	=back	1540	=back
		1541
		1542	=head3 Examples
931		1543
932	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1544	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
933	readable, but only once. Since it is likely line-buffered, you could	1545	readable, but only once. Since it is likely line-buffered, you could
934	attempt to read a whole line in the callback.	1546	attempt to read a whole line in the callback.
935		1547
936	static void	1548	static void
937	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1549	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
938	{	1550	{
939	ev_io_stop (loop, w);	1551	ev_io_stop (loop, w);
940	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1552	.. read from stdin here (or from w->fd) and handle any I/O errors
941	}	1553	}
942		1554
943	...	1555	...
944	struct ev_loop *loop = ev_default_init (0);	1556	struct ev_loop *loop = ev_default_init (0);
945	struct ev_io stdin_readable;	1557	ev_io stdin_readable;
946	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1558	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
947	ev_io_start (loop, &stdin_readable);	1559	ev_io_start (loop, &stdin_readable);
948	ev_loop (loop, 0);	1560	ev_loop (loop, 0);
949		1561
950		1562
951	=head2 C<ev_timer> - relative and optionally repeating timeouts	1563	=head2 C<ev_timer> - relative and optionally repeating timeouts
952		1564
953	Timer watchers are simple relative timers that generate an event after a	1565	Timer watchers are simple relative timers that generate an event after a
954	given time, and optionally repeating in regular intervals after that.	1566	given time, and optionally repeating in regular intervals after that.
955		1567
956	The timers are based on real time, that is, if you register an event that	1568	The timers are based on real time, that is, if you register an event that
957	times out after an hour and you reset your system clock to last years	1569	times out after an hour and you reset your system clock to January last
958	time, it will still time out after (roughly) and hour. "Roughly" because	1570	year, it will still time out after (roughly) one hour. "Roughly" because
959	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1571	detecting time jumps is hard, and some inaccuracies are unavoidable (the
960	monotonic clock option helps a lot here).	1572	monotonic clock option helps a lot here).
		1573
		1574	The callback is guaranteed to be invoked only I<after> its timeout has
		1575	passed (not I<at>, so on systems with very low-resolution clocks this
		1576	might introduce a small delay). If multiple timers become ready during the
		1577	same loop iteration then the ones with earlier time-out values are invoked
		1578	before ones of the same priority with later time-out values (but this is
		1579	no longer true when a callback calls C<ev_loop> recursively).
		1580
		1581	=head3 Be smart about timeouts
		1582
		1583	Many real-world problems involve some kind of timeout, usually for error
		1584	recovery. A typical example is an HTTP request - if the other side hangs,
		1585	you want to raise some error after a while.
		1586
		1587	What follows are some ways to handle this problem, from obvious and
		1588	inefficient to smart and efficient.
		1589
		1590	In the following, a 60 second activity timeout is assumed - a timeout that
		1591	gets reset to 60 seconds each time there is activity (e.g. each time some
		1592	data or other life sign was received).
		1593
		1594	=over 4
		1595
		1596	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1597
		1598	This is the most obvious, but not the most simple way: In the beginning,
		1599	start the watcher:
		1600
		1601	ev_timer_init (timer, callback, 60., 0.);
		1602	ev_timer_start (loop, timer);
		1603
		1604	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1605	and start it again:
		1606
		1607	ev_timer_stop (loop, timer);
		1608	ev_timer_set (timer, 60., 0.);
		1609	ev_timer_start (loop, timer);
		1610
		1611	This is relatively simple to implement, but means that each time there is
		1612	some activity, libev will first have to remove the timer from its internal
		1613	data structure and then add it again. Libev tries to be fast, but it's
		1614	still not a constant-time operation.
		1615
		1616	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1617
		1618	This is the easiest way, and involves using C<ev_timer_again> instead of
		1619	C<ev_timer_start>.
		1620
		1621	To implement this, configure an C<ev_timer> with a C<repeat> value
		1622	of C<60> and then call C<ev_timer_again> at start and each time you
		1623	successfully read or write some data. If you go into an idle state where
		1624	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1625	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1626
		1627	That means you can ignore both the C<ev_timer_start> function and the
		1628	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1629	member and C<ev_timer_again>.
		1630
		1631	At start:
		1632
		1633	ev_init (timer, callback);
		1634	timer->repeat = 60.;
		1635	ev_timer_again (loop, timer);
		1636
		1637	Each time there is some activity:
		1638
		1639	ev_timer_again (loop, timer);
		1640
		1641	It is even possible to change the time-out on the fly, regardless of
		1642	whether the watcher is active or not:
		1643
		1644	timer->repeat = 30.;
		1645	ev_timer_again (loop, timer);
		1646
		1647	This is slightly more efficient then stopping/starting the timer each time
		1648	you want to modify its timeout value, as libev does not have to completely
		1649	remove and re-insert the timer from/into its internal data structure.
		1650
		1651	It is, however, even simpler than the "obvious" way to do it.
		1652
		1653	=item 3. Let the timer time out, but then re-arm it as required.
		1654
		1655	This method is more tricky, but usually most efficient: Most timeouts are
		1656	relatively long compared to the intervals between other activity - in
		1657	our example, within 60 seconds, there are usually many I/O events with
		1658	associated activity resets.
		1659
		1660	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1661	but remember the time of last activity, and check for a real timeout only
		1662	within the callback:
		1663
		1664	ev_tstamp last_activity; // time of last activity
		1665
		1666	static void
		1667	callback (EV_P_ ev_timer *w, int revents)
		1668	{
		1669	ev_tstamp now = ev_now (EV_A);
		1670	ev_tstamp timeout = last_activity + 60.;
		1671
		1672	// if last_activity + 60. is older than now, we did time out
		1673	if (timeout < now)
		1674	{
		1675	// timeout occured, take action
		1676	}
		1677	else
		1678	{
		1679	// callback was invoked, but there was some activity, re-arm
		1680	// the watcher to fire in last_activity + 60, which is
		1681	// guaranteed to be in the future, so "again" is positive:
		1682	w->repeat = timeout - now;
		1683	ev_timer_again (EV_A_ w);
		1684	}
		1685	}
		1686
		1687	To summarise the callback: first calculate the real timeout (defined
		1688	as "60 seconds after the last activity"), then check if that time has
		1689	been reached, which means something I<did>, in fact, time out. Otherwise
		1690	the callback was invoked too early (C<timeout> is in the future), so
		1691	re-schedule the timer to fire at that future time, to see if maybe we have
		1692	a timeout then.
		1693
		1694	Note how C<ev_timer_again> is used, taking advantage of the
		1695	C<ev_timer_again> optimisation when the timer is already running.
		1696
		1697	This scheme causes more callback invocations (about one every 60 seconds
		1698	minus half the average time between activity), but virtually no calls to
		1699	libev to change the timeout.
		1700
		1701	To start the timer, simply initialise the watcher and set C<last_activity>
		1702	to the current time (meaning we just have some activity :), then call the
		1703	callback, which will "do the right thing" and start the timer:
		1704
		1705	ev_init (timer, callback);
		1706	last_activity = ev_now (loop);
		1707	callback (loop, timer, EV_TIMEOUT);
		1708
		1709	And when there is some activity, simply store the current time in
		1710	C<last_activity>, no libev calls at all:
		1711
		1712	last_actiivty = ev_now (loop);
		1713
		1714	This technique is slightly more complex, but in most cases where the
		1715	time-out is unlikely to be triggered, much more efficient.
		1716
		1717	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1718	callback :) - just change the timeout and invoke the callback, which will
		1719	fix things for you.
		1720
		1721	=item 4. Wee, just use a double-linked list for your timeouts.
		1722
		1723	If there is not one request, but many thousands (millions...), all
		1724	employing some kind of timeout with the same timeout value, then one can
		1725	do even better:
		1726
		1727	When starting the timeout, calculate the timeout value and put the timeout
		1728	at the I<end> of the list.
		1729
		1730	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1731	the list is expected to fire (for example, using the technique #3).
		1732
		1733	When there is some activity, remove the timer from the list, recalculate
		1734	the timeout, append it to the end of the list again, and make sure to
		1735	update the C<ev_timer> if it was taken from the beginning of the list.
		1736
		1737	This way, one can manage an unlimited number of timeouts in O(1) time for
		1738	starting, stopping and updating the timers, at the expense of a major
		1739	complication, and having to use a constant timeout. The constant timeout
		1740	ensures that the list stays sorted.
		1741
		1742	=back
		1743
		1744	So which method the best?
		1745
		1746	Method #2 is a simple no-brain-required solution that is adequate in most
		1747	situations. Method #3 requires a bit more thinking, but handles many cases
		1748	better, and isn't very complicated either. In most case, choosing either
		1749	one is fine, with #3 being better in typical situations.
		1750
		1751	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1752	rather complicated, but extremely efficient, something that really pays
		1753	off after the first million or so of active timers, i.e. it's usually
		1754	overkill :)
		1755
		1756	=head3 The special problem of time updates
		1757
		1758	Establishing the current time is a costly operation (it usually takes at
		1759	least two system calls): EV therefore updates its idea of the current
		1760	time only before and after C<ev_loop> collects new events, which causes a
		1761	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1762	lots of events in one iteration.
961		1763
962	The relative timeouts are calculated relative to the C<ev_now ()>	1764	The relative timeouts are calculated relative to the C<ev_now ()>
963	time. This is usually the right thing as this timestamp refers to the time	1765	time. This is usually the right thing as this timestamp refers to the time
964	of the event triggering whatever timeout you are modifying/starting. If	1766	of the event triggering whatever timeout you are modifying/starting. If
965	you suspect event processing to be delayed and you I<need> to base the timeout	1767	you suspect event processing to be delayed and you I<need> to base the
966	on the current time, use something like this to adjust for this:	1768	timeout on the current time, use something like this to adjust for this:
967		1769
968	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1770	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
969		1771
970	The callback is guarenteed to be invoked only when its timeout has passed,	1772	If the event loop is suspended for a long time, you can also force an
971	but if multiple timers become ready during the same loop iteration then	1773	update of the time returned by C<ev_now ()> by calling C<ev_now_update
972	order of execution is undefined.	1774	()>.
		1775
		1776	=head3 The special problems of suspended animation
		1777
		1778	When you leave the server world it is quite customary to hit machines that
		1779	can suspend/hibernate - what happens to the clocks during such a suspend?
		1780
		1781	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1782	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1783	to run until the system is suspended, but they will not advance while the
		1784	system is suspended. That means, on resume, it will be as if the program
		1785	was frozen for a few seconds, but the suspend time will not be counted
		1786	towards C<ev_timer> when a monotonic clock source is used. The real time
		1787	clock advanced as expected, but if it is used as sole clocksource, then a
		1788	long suspend would be detected as a time jump by libev, and timers would
		1789	be adjusted accordingly.
		1790
		1791	I would not be surprised to see different behaviour in different between
		1792	operating systems, OS versions or even different hardware.
		1793
		1794	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1795	time jump in the monotonic clocks and the realtime clock. If the program
		1796	is suspended for a very long time, and monotonic clock sources are in use,
		1797	then you can expect C<ev_timer>s to expire as the full suspension time
		1798	will be counted towards the timers. When no monotonic clock source is in
		1799	use, then libev will again assume a timejump and adjust accordingly.
		1800
		1801	It might be beneficial for this latter case to call C<ev_suspend>
		1802	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1803	deterministic behaviour in this case (you can do nothing against
		1804	C<SIGSTOP>).
		1805
		1806	=head3 Watcher-Specific Functions and Data Members
973		1807
974	=over 4	1808	=over 4
975		1809
976	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1810	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
977		1811
978	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1812	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
979		1813
980	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1814	Configure the timer to trigger after C<after> seconds. If C<repeat>
981	C<0.>, then it will automatically be stopped. If it is positive, then the	1815	is C<0.>, then it will automatically be stopped once the timeout is
982	timer will automatically be configured to trigger again C<repeat> seconds	1816	reached. If it is positive, then the timer will automatically be
983	later, again, and again, until stopped manually.	1817	configured to trigger again C<repeat> seconds later, again, and again,
		1818	until stopped manually.
984		1819
985	The timer itself will do a best-effort at avoiding drift, that is, if you	1820	The timer itself will do a best-effort at avoiding drift, that is, if
986	configure a timer to trigger every 10 seconds, then it will trigger at	1821	you configure a timer to trigger every 10 seconds, then it will normally
987	exactly 10 second intervals. If, however, your program cannot keep up with	1822	trigger at exactly 10 second intervals. If, however, your program cannot
988	the timer (because it takes longer than those 10 seconds to do stuff) the	1823	keep up with the timer (because it takes longer than those 10 seconds to
989	timer will not fire more than once per event loop iteration.	1824	do stuff) the timer will not fire more than once per event loop iteration.
990		1825
991	=item ev_timer_again (loop)	1826	=item ev_timer_again (loop, ev_timer *)
992		1827
993	This will act as if the timer timed out and restart it again if it is	1828	This will act as if the timer timed out and restart it again if it is
994	repeating. The exact semantics are:	1829	repeating. The exact semantics are:
995		1830
996	If the timer is pending, its pending status is cleared.	1831	If the timer is pending, its pending status is cleared.
997		1832
998	If the timer is started but nonrepeating, stop it (as if it timed out).	1833	If the timer is started but non-repeating, stop it (as if it timed out).
999		1834
1000	If the timer is repeating, either start it if necessary (with the	1835	If the timer is repeating, either start it if necessary (with the
1001	C<repeat> value), or reset the running timer to the C<repeat> value.	1836	C<repeat> value), or reset the running timer to the C<repeat> value.
1002		1837
1003	This sounds a bit complicated, but here is a useful and typical	1838	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1004	example: Imagine you have a tcp connection and you want a so-called idle	1839	usage example.
1005	timeout, that is, you want to be called when there have been, say, 60
1006	seconds of inactivity on the socket. The easiest way to do this is to
1007	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1008	C<ev_timer_again> each time you successfully read or write some data. If
1009	you go into an idle state where you do not expect data to travel on the
1010	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1011	automatically restart it if need be.
1012		1840
1013	That means you can ignore the C<after> value and C<ev_timer_start>	1841	=item ev_timer_remaining (loop, ev_timer *)
1014	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1015		1842
1016	ev_timer_init (timer, callback, 0., 5.);	1843	Returns the remaining time until a timer fires. If the timer is active,
1017	ev_timer_again (loop, timer);	1844	then this time is relative to the current event loop time, otherwise it's
1018	...	1845	the timeout value currently configured.
1019	timer->again = 17.;
1020	ev_timer_again (loop, timer);
1021	...
1022	timer->again = 10.;
1023	ev_timer_again (loop, timer);
1024		1846
1025	This is more slightly efficient then stopping/starting the timer each time	1847	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1026	you want to modify its timeout value.	1848	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1849	will return C<4>. When the timer expires and is restarted, it will return
		1850	roughly C<7> (likely slightly less as callback invocation takes some time,
		1851	too), and so on.
1027		1852
1028	=item ev_tstamp repeat [read-write]	1853	=item ev_tstamp repeat [read-write]
1029		1854
1030	The current C<repeat> value. Will be used each time the watcher times out	1855	The current C<repeat> value. Will be used each time the watcher times out
1031	or C<ev_timer_again> is called and determines the next timeout (if any),	1856	or C<ev_timer_again> is called, and determines the next timeout (if any),
1032	which is also when any modifications are taken into account.	1857	which is also when any modifications are taken into account.
1033		1858
1034	=back	1859	=back
1035		1860
		1861	=head3 Examples
		1862
1036	Example: Create a timer that fires after 60 seconds.	1863	Example: Create a timer that fires after 60 seconds.
1037		1864
1038	static void	1865	static void
1039	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1866	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1040	{	1867	{
1041	.. one minute over, w is actually stopped right here	1868	.. one minute over, w is actually stopped right here
1042	}	1869	}
1043		1870
1044	struct ev_timer mytimer;	1871	ev_timer mytimer;
1045	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1872	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1046	ev_timer_start (loop, &mytimer);	1873	ev_timer_start (loop, &mytimer);
1047		1874
1048	Example: Create a timeout timer that times out after 10 seconds of	1875	Example: Create a timeout timer that times out after 10 seconds of
1049	inactivity.	1876	inactivity.
1050		1877
1051	static void	1878	static void
1052	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1879	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1053	{	1880	{
1054	.. ten seconds without any activity	1881	.. ten seconds without any activity
1055	}	1882	}
1056		1883
1057	struct ev_timer mytimer;	1884	ev_timer mytimer;
1058	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1885	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1059	ev_timer_again (&mytimer); /* start timer */	1886	ev_timer_again (&mytimer); /* start timer */
1060	ev_loop (loop, 0);	1887	ev_loop (loop, 0);
1061		1888
1062	// and in some piece of code that gets executed on any "activity":	1889	// and in some piece of code that gets executed on any "activity":
1063	// reset the timeout to start ticking again at 10 seconds	1890	// reset the timeout to start ticking again at 10 seconds
1064	ev_timer_again (&mytimer);	1891	ev_timer_again (&mytimer);
1065		1892
1066		1893
1067	=head2 C<ev_periodic> - to cron or not to cron?	1894	=head2 C<ev_periodic> - to cron or not to cron?
1068		1895
1069	Periodic watchers are also timers of a kind, but they are very versatile	1896	Periodic watchers are also timers of a kind, but they are very versatile
1070	(and unfortunately a bit complex).	1897	(and unfortunately a bit complex).
1071		1898
1072	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1899	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1073	but on wallclock time (absolute time). You can tell a periodic watcher	1900	relative time, the physical time that passes) but on wall clock time
1074	to trigger "at" some specific point in time. For example, if you tell a	1901	(absolute time, the thing you can read on your calender or clock). The
1075	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1902	difference is that wall clock time can run faster or slower than real
1076	+ 10.>) and then reset your system clock to the last year, then it will	1903	time, and time jumps are not uncommon (e.g. when you adjust your
1077	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1904	wrist-watch).
1078	roughly 10 seconds later and of course not if you reset your system time
1079	again).
1080		1905
1081	They can also be used to implement vastly more complex timers, such as	1906	You can tell a periodic watcher to trigger after some specific point
		1907	in time: for example, if you tell a periodic watcher to trigger "in 10
		1908	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1909	not a delay) and then reset your system clock to January of the previous
		1910	year, then it will take a year or more to trigger the event (unlike an
		1911	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1912	it, as it uses a relative timeout).
		1913
		1914	C<ev_periodic> watchers can also be used to implement vastly more complex
1082	triggering an event on eahc midnight, local time.	1915	timers, such as triggering an event on each "midnight, local time", or
		1916	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1917	those cannot react to time jumps.
1083		1918
1084	As with timers, the callback is guarenteed to be invoked only when the	1919	As with timers, the callback is guaranteed to be invoked only when the
1085	time (C<at>) has been passed, but if multiple periodic timers become ready	1920	point in time where it is supposed to trigger has passed. If multiple
1086	during the same loop iteration then order of execution is undefined.	1921	timers become ready during the same loop iteration then the ones with
		1922	earlier time-out values are invoked before ones with later time-out values
		1923	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1924
		1925	=head3 Watcher-Specific Functions and Data Members
1087		1926
1088	=over 4	1927	=over 4
1089		1928
1090	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1929	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1091		1930
1092	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1931	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1093		1932
1094	Lots of arguments, lets sort it out... There are basically three modes of	1933	Lots of arguments, let's sort it out... There are basically three modes of
1095	operation, and we will explain them from simplest to complex:	1934	operation, and we will explain them from simplest to most complex:
1096		1935
1097	=over 4	1936	=over 4
1098		1937
1099	=item * absolute timer (interval = reschedule_cb = 0)	1938	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1100		1939
1101	In this configuration the watcher triggers an event at the wallclock time	1940	In this configuration the watcher triggers an event after the wall clock
1102	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1941	time C<offset> has passed. It will not repeat and will not adjust when a
1103	that is, if it is to be run at January 1st 2011 then it will run when the	1942	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1104	system time reaches or surpasses this time.	1943	will be stopped and invoked when the system clock reaches or surpasses
		1944	this point in time.
1105		1945
1106	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1946	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1107		1947
1108	In this mode the watcher will always be scheduled to time out at the next	1948	In this mode the watcher will always be scheduled to time out at the next
1109	C<at + N * interval> time (for some integer N) and then repeat, regardless	1949	C<offset + N * interval> time (for some integer N, which can also be
1110	of any time jumps.	1950	negative) and then repeat, regardless of any time jumps. The C<offset>
		1951	argument is merely an offset into the C<interval> periods.
1111		1952
1112	This can be used to create timers that do not drift with respect to system	1953	This can be used to create timers that do not drift with respect to the
1113	time:	1954	system clock, for example, here is an C<ev_periodic> that triggers each
		1955	hour, on the hour (with respect to UTC):
1114		1956
1115	ev_periodic_set (&periodic, 0., 3600., 0);	1957	ev_periodic_set (&periodic, 0., 3600., 0);
1116		1958
1117	This doesn't mean there will always be 3600 seconds in between triggers,	1959	This doesn't mean there will always be 3600 seconds in between triggers,
1118	but only that the the callback will be called when the system time shows a	1960	but only that the callback will be called when the system time shows a
1119	full hour (UTC), or more correctly, when the system time is evenly divisible	1961	full hour (UTC), or more correctly, when the system time is evenly divisible
1120	by 3600.	1962	by 3600.
1121		1963
1122	Another way to think about it (for the mathematically inclined) is that	1964	Another way to think about it (for the mathematically inclined) is that
1123	C<ev_periodic> will try to run the callback in this mode at the next possible	1965	C<ev_periodic> will try to run the callback in this mode at the next possible
1124	time where C<time = at (mod interval)>, regardless of any time jumps.	1966	time where C<time = offset (mod interval)>, regardless of any time jumps.
1125		1967
		1968	For numerical stability it is preferable that the C<offset> value is near
		1969	C<ev_now ()> (the current time), but there is no range requirement for
		1970	this value, and in fact is often specified as zero.
		1971
		1972	Note also that there is an upper limit to how often a timer can fire (CPU
		1973	speed for example), so if C<interval> is very small then timing stability
		1974	will of course deteriorate. Libev itself tries to be exact to be about one
		1975	millisecond (if the OS supports it and the machine is fast enough).
		1976
1126	=item * manual reschedule mode (reschedule_cb = callback)	1977	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1127		1978
1128	In this mode the values for C<interval> and C<at> are both being	1979	In this mode the values for C<interval> and C<offset> are both being
1129	ignored. Instead, each time the periodic watcher gets scheduled, the	1980	ignored. Instead, each time the periodic watcher gets scheduled, the
1130	reschedule callback will be called with the watcher as first, and the	1981	reschedule callback will be called with the watcher as first, and the
1131	current time as second argument.	1982	current time as second argument.
1132		1983
1133	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1984	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1134	ever, or make any event loop modifications>. If you need to stop it,	1985	or make ANY other event loop modifications whatsoever, unless explicitly
1135	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1986	allowed by documentation here>.
1136	starting a prepare watcher).
1137		1987
		1988	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1989	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1990	only event loop modification you are allowed to do).
		1991
1138	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1992	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1139	ev_tstamp now)>, e.g.:	1993	*w, ev_tstamp now)>, e.g.:
1140		1994
		1995	static ev_tstamp
1141	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1996	my_rescheduler (ev_periodic *w, ev_tstamp now)
1142	{	1997	{
1143	return now + 60.;	1998	return now + 60.;
1144	}	1999	}
1145		2000
1146	It must return the next time to trigger, based on the passed time value	2001	It must return the next time to trigger, based on the passed time value
1147	(that is, the lowest time value larger than to the second argument). It	2002	(that is, the lowest time value larger than to the second argument). It
1148	will usually be called just before the callback will be triggered, but	2003	will usually be called just before the callback will be triggered, but
1149	might be called at other times, too.	2004	might be called at other times, too.
1150		2005
1151	NOTE: I<< This callback must always return a time that is later than the	2006	NOTE: I<< This callback must always return a time that is higher than or
1152	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2007	equal to the passed C<now> value >>.
1153		2008
1154	This can be used to create very complex timers, such as a timer that	2009	This can be used to create very complex timers, such as a timer that
1155	triggers on each midnight, local time. To do this, you would calculate the	2010	triggers on "next midnight, local time". To do this, you would calculate the
1156	next midnight after C<now> and return the timestamp value for this. How	2011	next midnight after C<now> and return the timestamp value for this. How
1157	you do this is, again, up to you (but it is not trivial, which is the main	2012	you do this is, again, up to you (but it is not trivial, which is the main
1158	reason I omitted it as an example).	2013	reason I omitted it as an example).
1159		2014
1160	=back	2015	=back
…		…
1164	Simply stops and restarts the periodic watcher again. This is only useful	2019	Simply stops and restarts the periodic watcher again. This is only useful
1165	when you changed some parameters or the reschedule callback would return	2020	when you changed some parameters or the reschedule callback would return
1166	a different time than the last time it was called (e.g. in a crond like	2021	a different time than the last time it was called (e.g. in a crond like
1167	program when the crontabs have changed).	2022	program when the crontabs have changed).
1168		2023
		2024	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2025
		2026	When active, returns the absolute time that the watcher is supposed
		2027	to trigger next. This is not the same as the C<offset> argument to
		2028	C<ev_periodic_set>, but indeed works even in interval and manual
		2029	rescheduling modes.
		2030
		2031	=item ev_tstamp offset [read-write]
		2032
		2033	When repeating, this contains the offset value, otherwise this is the
		2034	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2035	although libev might modify this value for better numerical stability).
		2036
		2037	Can be modified any time, but changes only take effect when the periodic
		2038	timer fires or C<ev_periodic_again> is being called.
		2039
1169	=item ev_tstamp interval [read-write]	2040	=item ev_tstamp interval [read-write]
1170		2041
1171	The current interval value. Can be modified any time, but changes only	2042	The current interval value. Can be modified any time, but changes only
1172	take effect when the periodic timer fires or C<ev_periodic_again> is being	2043	take effect when the periodic timer fires or C<ev_periodic_again> is being
1173	called.	2044	called.
1174		2045
1175	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2046	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1176		2047
1177	The current reschedule callback, or C<0>, if this functionality is	2048	The current reschedule callback, or C<0>, if this functionality is
1178	switched off. Can be changed any time, but changes only take effect when	2049	switched off. Can be changed any time, but changes only take effect when
1179	the periodic timer fires or C<ev_periodic_again> is being called.	2050	the periodic timer fires or C<ev_periodic_again> is being called.
1180		2051
1181	=back	2052	=back
1182		2053
		2054	=head3 Examples
		2055
1183	Example: Call a callback every hour, or, more precisely, whenever the	2056	Example: Call a callback every hour, or, more precisely, whenever the
1184	system clock is divisible by 3600. The callback invocation times have	2057	system time is divisible by 3600. The callback invocation times have
1185	potentially a lot of jittering, but good long-term stability.	2058	potentially a lot of jitter, but good long-term stability.
1186		2059
1187	static void	2060	static void
1188	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2061	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1189	{	2062	{
1190	... its now a full hour (UTC, or TAI or whatever your clock follows)	2063	... its now a full hour (UTC, or TAI or whatever your clock follows)
1191	}	2064	}
1192		2065
1193	struct ev_periodic hourly_tick;	2066	ev_periodic hourly_tick;
1194	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2067	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1195	ev_periodic_start (loop, &hourly_tick);	2068	ev_periodic_start (loop, &hourly_tick);
1196		2069
1197	Example: The same as above, but use a reschedule callback to do it:	2070	Example: The same as above, but use a reschedule callback to do it:
1198		2071
1199	#include <math.h>	2072	#include <math.h>
1200		2073
1201	static ev_tstamp	2074	static ev_tstamp
1202	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2075	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1203	{	2076	{
1204	return fmod (now, 3600.) + 3600.;	2077	return now + (3600. - fmod (now, 3600.));
1205	}	2078	}
1206		2079
1207	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2080	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1208		2081
1209	Example: Call a callback every hour, starting now:	2082	Example: Call a callback every hour, starting now:
1210		2083
1211	struct ev_periodic hourly_tick;	2084	ev_periodic hourly_tick;
1212	ev_periodic_init (&hourly_tick, clock_cb,	2085	ev_periodic_init (&hourly_tick, clock_cb,
1213	fmod (ev_now (loop), 3600.), 3600., 0);	2086	fmod (ev_now (loop), 3600.), 3600., 0);
1214	ev_periodic_start (loop, &hourly_tick);	2087	ev_periodic_start (loop, &hourly_tick);
1215		2088
1216		2089
1217	=head2 C<ev_signal> - signal me when a signal gets signalled!	2090	=head2 C<ev_signal> - signal me when a signal gets signalled!
1218		2091
1219	Signal watchers will trigger an event when the process receives a specific	2092	Signal watchers will trigger an event when the process receives a specific
1220	signal one or more times. Even though signals are very asynchronous, libev	2093	signal one or more times. Even though signals are very asynchronous, libev
1221	will try it's best to deliver signals synchronously, i.e. as part of the	2094	will try it's best to deliver signals synchronously, i.e. as part of the
1222	normal event processing, like any other event.	2095	normal event processing, like any other event.
1223		2096
		2097	If you want signals to be delivered truly asynchronously, just use
		2098	C<sigaction> as you would do without libev and forget about sharing
		2099	the signal. You can even use C<ev_async> from a signal handler to
		2100	synchronously wake up an event loop.
		2101
1224	You can configure as many watchers as you like per signal. Only when the	2102	You can configure as many watchers as you like for the same signal, but
		2103	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2104	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2105	C<SIGINT> in both the default loop and another loop at the same time. At
		2106	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2107
1225	first watcher gets started will libev actually register a signal watcher	2108	When the first watcher gets started will libev actually register something
1226	with the kernel (thus it coexists with your own signal handlers as long	2109	with the kernel (thus it coexists with your own signal handlers as long as
1227	as you don't register any with libev). Similarly, when the last signal	2110	you don't register any with libev for the same signal).
1228	watcher for a signal is stopped libev will reset the signal handler to	2111
1229	SIG_DFL (regardless of what it was set to before).	2112	Both the signal mask state (C<sigprocmask>) and the signal handler state
		2113	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2114	sotpping it again), that is, libev might or might not block the signal,
		2115	and might or might not set or restore the installed signal handler.
		2116
		2117	If possible and supported, libev will install its handlers with
		2118	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2119	not be unduly interrupted. If you have a problem with system calls getting
		2120	interrupted by signals you can block all signals in an C<ev_check> watcher
		2121	and unblock them in an C<ev_prepare> watcher.
		2122
		2123	=head3 Watcher-Specific Functions and Data Members
1230		2124
1231	=over 4	2125	=over 4
1232		2126
1233	=item ev_signal_init (ev_signal *, callback, int signum)	2127	=item ev_signal_init (ev_signal *, callback, int signum)
1234		2128
…		…
1241		2135
1242	The signal the watcher watches out for.	2136	The signal the watcher watches out for.
1243		2137
1244	=back	2138	=back
1245		2139
		2140	=head3 Examples
		2141
		2142	Example: Try to exit cleanly on SIGINT.
		2143
		2144	static void
		2145	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2146	{
		2147	ev_unloop (loop, EVUNLOOP_ALL);
		2148	}
		2149
		2150	ev_signal signal_watcher;
		2151	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2152	ev_signal_start (loop, &signal_watcher);
		2153
1246		2154
1247	=head2 C<ev_child> - watch out for process status changes	2155	=head2 C<ev_child> - watch out for process status changes
1248		2156
1249	Child watchers trigger when your process receives a SIGCHLD in response to	2157	Child watchers trigger when your process receives a SIGCHLD in response to
1250	some child status changes (most typically when a child of yours dies).	2158	some child status changes (most typically when a child of yours dies or
		2159	exits). It is permissible to install a child watcher I<after> the child
		2160	has been forked (which implies it might have already exited), as long
		2161	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2162	forking and then immediately registering a watcher for the child is fine,
		2163	but forking and registering a watcher a few event loop iterations later or
		2164	in the next callback invocation is not.
		2165
		2166	Only the default event loop is capable of handling signals, and therefore
		2167	you can only register child watchers in the default event loop.
		2168
		2169	Due to some design glitches inside libev, child watchers will always be
		2170	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2171	libev)
		2172
		2173	=head3 Process Interaction
		2174
		2175	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2176	initialised. This is necessary to guarantee proper behaviour even if the
		2177	first child watcher is started after the child exits. The occurrence
		2178	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2179	synchronously as part of the event loop processing. Libev always reaps all
		2180	children, even ones not watched.
		2181
		2182	=head3 Overriding the Built-In Processing
		2183
		2184	Libev offers no special support for overriding the built-in child
		2185	processing, but if your application collides with libev's default child
		2186	handler, you can override it easily by installing your own handler for
		2187	C<SIGCHLD> after initialising the default loop, and making sure the
		2188	default loop never gets destroyed. You are encouraged, however, to use an
		2189	event-based approach to child reaping and thus use libev's support for
		2190	that, so other libev users can use C<ev_child> watchers freely.
		2191
		2192	=head3 Stopping the Child Watcher
		2193
		2194	Currently, the child watcher never gets stopped, even when the
		2195	child terminates, so normally one needs to stop the watcher in the
		2196	callback. Future versions of libev might stop the watcher automatically
		2197	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2198	problem).
		2199
		2200	=head3 Watcher-Specific Functions and Data Members
1251		2201
1252	=over 4	2202	=over 4
1253		2203
1254	=item ev_child_init (ev_child *, callback, int pid)	2204	=item ev_child_init (ev_child *, callback, int pid, int trace)
1255		2205
1256	=item ev_child_set (ev_child *, int pid)	2206	=item ev_child_set (ev_child *, int pid, int trace)
1257		2207
1258	Configures the watcher to wait for status changes of process C<pid> (or	2208	Configures the watcher to wait for status changes of process C<pid> (or
1259	I<any> process if C<pid> is specified as C<0>). The callback can look	2209	I<any> process if C<pid> is specified as C<0>). The callback can look
1260	at the C<rstatus> member of the C<ev_child> watcher structure to see	2210	at the C<rstatus> member of the C<ev_child> watcher structure to see
1261	the status word (use the macros from C<sys/wait.h> and see your systems	2211	the status word (use the macros from C<sys/wait.h> and see your systems
1262	C<waitpid> documentation). The C<rpid> member contains the pid of the	2212	C<waitpid> documentation). The C<rpid> member contains the pid of the
1263	process causing the status change.	2213	process causing the status change. C<trace> must be either C<0> (only
		2214	activate the watcher when the process terminates) or C<1> (additionally
		2215	activate the watcher when the process is stopped or continued).
1264		2216
1265	=item int pid [read-only]	2217	=item int pid [read-only]
1266		2218
1267	The process id this watcher watches out for, or C<0>, meaning any process id.	2219	The process id this watcher watches out for, or C<0>, meaning any process id.
1268		2220
…		…
1275	The process exit/trace status caused by C<rpid> (see your systems	2227	The process exit/trace status caused by C<rpid> (see your systems
1276	C<waitpid> and C<sys/wait.h> documentation for details).	2228	C<waitpid> and C<sys/wait.h> documentation for details).
1277		2229
1278	=back	2230	=back
1279		2231
1280	Example: Try to exit cleanly on SIGINT and SIGTERM.	2232	=head3 Examples
1281		2233
		2234	Example: C<fork()> a new process and install a child handler to wait for
		2235	its completion.
		2236
		2237	ev_child cw;
		2238
1282	static void	2239	static void
1283	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2240	child_cb (EV_P_ ev_child *w, int revents)
1284	{	2241	{
1285	ev_unloop (loop, EVUNLOOP_ALL);	2242	ev_child_stop (EV_A_ w);
		2243	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1286	}	2244	}
1287		2245
1288	struct ev_signal signal_watcher;	2246	pid_t pid = fork ();
1289	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2247
1290	ev_signal_start (loop, &sigint_cb);	2248	if (pid < 0)
		2249	// error
		2250	else if (pid == 0)
		2251	{
		2252	// the forked child executes here
		2253	exit (1);
		2254	}
		2255	else
		2256	{
		2257	ev_child_init (&cw, child_cb, pid, 0);
		2258	ev_child_start (EV_DEFAULT_ &cw);
		2259	}
1291		2260
1292		2261
1293	=head2 C<ev_stat> - did the file attributes just change?	2262	=head2 C<ev_stat> - did the file attributes just change?
1294		2263
1295	This watches a filesystem path for attribute changes. That is, it calls	2264	This watches a file system path for attribute changes. That is, it calls
1296	C<stat> regularly (or when the OS says it changed) and sees if it changed	2265	C<stat> on that path in regular intervals (or when the OS says it changed)
1297	compared to the last time, invoking the callback if it did.	2266	and sees if it changed compared to the last time, invoking the callback if
		2267	it did.
1298		2268
1299	The path does not need to exist: changing from "path exists" to "path does	2269	The path does not need to exist: changing from "path exists" to "path does
1300	not exist" is a status change like any other. The condition "path does	2270	not exist" is a status change like any other. The condition "path does not
1301	not exist" is signified by the C<st_nlink> field being zero (which is	2271	exist" (or more correctly "path cannot be stat'ed") is signified by the
1302	otherwise always forced to be at least one) and all the other fields of	2272	C<st_nlink> field being zero (which is otherwise always forced to be at
1303	the stat buffer having unspecified contents.	2273	least one) and all the other fields of the stat buffer having unspecified
		2274	contents.
1304		2275
1305	The path I<should> be absolute and I<must not> end in a slash. If it is	2276	The path I<must not> end in a slash or contain special components such as
		2277	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1306	relative and your working directory changes, the behaviour is undefined.	2278	your working directory changes, then the behaviour is undefined.
1307		2279
1308	Since there is no standard to do this, the portable implementation simply	2280	Since there is no portable change notification interface available, the
1309	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2281	portable implementation simply calls C<stat(2)> regularly on the path
1310	can specify a recommended polling interval for this case. If you specify	2282	to see if it changed somehow. You can specify a recommended polling
1311	a polling interval of C<0> (highly recommended!) then a I<suitable,	2283	interval for this case. If you specify a polling interval of C<0> (highly
1312	unspecified default> value will be used (which you can expect to be around	2284	recommended!) then a I<suitable, unspecified default> value will be used
1313	five seconds, although this might change dynamically). Libev will also	2285	(which you can expect to be around five seconds, although this might
1314	impose a minimum interval which is currently around C<0.1>, but thats	2286	change dynamically). Libev will also impose a minimum interval which is
1315	usually overkill.	2287	currently around C<0.1>, but that's usually overkill.
1316		2288
1317	This watcher type is not meant for massive numbers of stat watchers,	2289	This watcher type is not meant for massive numbers of stat watchers,
1318	as even with OS-supported change notifications, this can be	2290	as even with OS-supported change notifications, this can be
1319	resource-intensive.	2291	resource-intensive.
1320		2292
1321	At the time of this writing, only the Linux inotify interface is	2293	At the time of this writing, the only OS-specific interface implemented
1322	implemented (implementing kqueue support is left as an exercise for the	2294	is the Linux inotify interface (implementing kqueue support is left as an
1323	reader). Inotify will be used to give hints only and should not change the	2295	exercise for the reader. Note, however, that the author sees no way of
1324	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2296	implementing C<ev_stat> semantics with kqueue, except as a hint).
1325	to fall back to regular polling again even with inotify, but changes are	2297
1326	usually detected immediately, and if the file exists there will be no	2298	=head3 ABI Issues (Largefile Support)
1327	polling.	2299
		2300	Libev by default (unless the user overrides this) uses the default
		2301	compilation environment, which means that on systems with large file
		2302	support disabled by default, you get the 32 bit version of the stat
		2303	structure. When using the library from programs that change the ABI to
		2304	use 64 bit file offsets the programs will fail. In that case you have to
		2305	compile libev with the same flags to get binary compatibility. This is
		2306	obviously the case with any flags that change the ABI, but the problem is
		2307	most noticeably displayed with ev_stat and large file support.
		2308
		2309	The solution for this is to lobby your distribution maker to make large
		2310	file interfaces available by default (as e.g. FreeBSD does) and not
		2311	optional. Libev cannot simply switch on large file support because it has
		2312	to exchange stat structures with application programs compiled using the
		2313	default compilation environment.
		2314
		2315	=head3 Inotify and Kqueue
		2316
		2317	When C<inotify (7)> support has been compiled into libev and present at
		2318	runtime, it will be used to speed up change detection where possible. The
		2319	inotify descriptor will be created lazily when the first C<ev_stat>
		2320	watcher is being started.
		2321
		2322	Inotify presence does not change the semantics of C<ev_stat> watchers
		2323	except that changes might be detected earlier, and in some cases, to avoid
		2324	making regular C<stat> calls. Even in the presence of inotify support
		2325	there are many cases where libev has to resort to regular C<stat> polling,
		2326	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2327	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2328	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2329	xfs are fully working) libev usually gets away without polling.
		2330
		2331	There is no support for kqueue, as apparently it cannot be used to
		2332	implement this functionality, due to the requirement of having a file
		2333	descriptor open on the object at all times, and detecting renames, unlinks
		2334	etc. is difficult.
		2335
		2336	=head3 C<stat ()> is a synchronous operation
		2337
		2338	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2339	the process. The exception are C<ev_stat> watchers - those call C<stat
		2340	()>, which is a synchronous operation.
		2341
		2342	For local paths, this usually doesn't matter: unless the system is very
		2343	busy or the intervals between stat's are large, a stat call will be fast,
		2344	as the path data is usually in memory already (except when starting the
		2345	watcher).
		2346
		2347	For networked file systems, calling C<stat ()> can block an indefinite
		2348	time due to network issues, and even under good conditions, a stat call
		2349	often takes multiple milliseconds.
		2350
		2351	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2352	paths, although this is fully supported by libev.
		2353
		2354	=head3 The special problem of stat time resolution
		2355
		2356	The C<stat ()> system call only supports full-second resolution portably,
		2357	and even on systems where the resolution is higher, most file systems
		2358	still only support whole seconds.
		2359
		2360	That means that, if the time is the only thing that changes, you can
		2361	easily miss updates: on the first update, C<ev_stat> detects a change and
		2362	calls your callback, which does something. When there is another update
		2363	within the same second, C<ev_stat> will be unable to detect unless the
		2364	stat data does change in other ways (e.g. file size).
		2365
		2366	The solution to this is to delay acting on a change for slightly more
		2367	than a second (or till slightly after the next full second boundary), using
		2368	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2369	ev_timer_again (loop, w)>).
		2370
		2371	The C<.02> offset is added to work around small timing inconsistencies
		2372	of some operating systems (where the second counter of the current time
		2373	might be be delayed. One such system is the Linux kernel, where a call to
		2374	C<gettimeofday> might return a timestamp with a full second later than
		2375	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2376	update file times then there will be a small window where the kernel uses
		2377	the previous second to update file times but libev might already execute
		2378	the timer callback).
		2379
		2380	=head3 Watcher-Specific Functions and Data Members
1328		2381
1329	=over 4	2382	=over 4
1330		2383
1331	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2384	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1332		2385
…		…
1336	C<path>. The C<interval> is a hint on how quickly a change is expected to	2389	C<path>. The C<interval> is a hint on how quickly a change is expected to
1337	be detected and should normally be specified as C<0> to let libev choose	2390	be detected and should normally be specified as C<0> to let libev choose
1338	a suitable value. The memory pointed to by C<path> must point to the same	2391	a suitable value. The memory pointed to by C<path> must point to the same
1339	path for as long as the watcher is active.	2392	path for as long as the watcher is active.
1340		2393
1341	The callback will be receive C<EV_STAT> when a change was detected,	2394	The callback will receive an C<EV_STAT> event when a change was detected,
1342	relative to the attributes at the time the watcher was started (or the	2395	relative to the attributes at the time the watcher was started (or the
1343	last change was detected).	2396	last change was detected).
1344		2397
1345	=item ev_stat_stat (ev_stat *)	2398	=item ev_stat_stat (loop, ev_stat *)
1346		2399
1347	Updates the stat buffer immediately with new values. If you change the	2400	Updates the stat buffer immediately with new values. If you change the
1348	watched path in your callback, you could call this fucntion to avoid	2401	watched path in your callback, you could call this function to avoid
1349	detecting this change (while introducing a race condition). Can also be	2402	detecting this change (while introducing a race condition if you are not
1350	useful simply to find out the new values.	2403	the only one changing the path). Can also be useful simply to find out the
		2404	new values.
1351		2405
1352	=item ev_statdata attr [read-only]	2406	=item ev_statdata attr [read-only]
1353		2407
1354	The most-recently detected attributes of the file. Although the type is of	2408	The most-recently detected attributes of the file. Although the type is
1355	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2409	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1356	suitable for your system. If the C<st_nlink> member is C<0>, then there	2410	suitable for your system, but you can only rely on the POSIX-standardised
		2411	members to be present. If the C<st_nlink> member is C<0>, then there was
1357	was some error while C<stat>ing the file.	2412	some error while C<stat>ing the file.
1358		2413
1359	=item ev_statdata prev [read-only]	2414	=item ev_statdata prev [read-only]
1360		2415
1361	The previous attributes of the file. The callback gets invoked whenever	2416	The previous attributes of the file. The callback gets invoked whenever
1362	C<prev> != C<attr>.	2417	C<prev> != C<attr>, or, more precisely, one or more of these members
		2418	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2419	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1363		2420
1364	=item ev_tstamp interval [read-only]	2421	=item ev_tstamp interval [read-only]
1365		2422
1366	The specified interval.	2423	The specified interval.
1367		2424
1368	=item const char *path [read-only]	2425	=item const char *path [read-only]
1369		2426
1370	The filesystem path that is being watched.	2427	The file system path that is being watched.
1371		2428
1372	=back	2429	=back
1373		2430
		2431	=head3 Examples
		2432
1374	Example: Watch C</etc/passwd> for attribute changes.	2433	Example: Watch C</etc/passwd> for attribute changes.
1375		2434
1376	static void	2435	static void
1377	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2436	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1378	{	2437	{
1379	/* /etc/passwd changed in some way */	2438	/* /etc/passwd changed in some way */
1380	if (w->attr.st_nlink)	2439	if (w->attr.st_nlink)
1381	{	2440	{
1382	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2441	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1383	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2442	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1384	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2443	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1385	}	2444	}
1386	else	2445	else
1387	/* you shalt not abuse printf for puts */	2446	/* you shalt not abuse printf for puts */
1388	puts ("wow, /etc/passwd is not there, expect problems. "	2447	puts ("wow, /etc/passwd is not there, expect problems. "
1389	"if this is windows, they already arrived\n");	2448	"if this is windows, they already arrived\n");
1390	}	2449	}
1391		2450
1392	...	2451	...
1393	ev_stat passwd;	2452	ev_stat passwd;
1394		2453
1395	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2454	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1396	ev_stat_start (loop, &passwd);	2455	ev_stat_start (loop, &passwd);
		2456
		2457	Example: Like above, but additionally use a one-second delay so we do not
		2458	miss updates (however, frequent updates will delay processing, too, so
		2459	one might do the work both on C<ev_stat> callback invocation I<and> on
		2460	C<ev_timer> callback invocation).
		2461
		2462	static ev_stat passwd;
		2463	static ev_timer timer;
		2464
		2465	static void
		2466	timer_cb (EV_P_ ev_timer *w, int revents)
		2467	{
		2468	ev_timer_stop (EV_A_ w);
		2469
		2470	/* now it's one second after the most recent passwd change */
		2471	}
		2472
		2473	static void
		2474	stat_cb (EV_P_ ev_stat *w, int revents)
		2475	{
		2476	/* reset the one-second timer */
		2477	ev_timer_again (EV_A_ &timer);
		2478	}
		2479
		2480	...
		2481	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2482	ev_stat_start (loop, &passwd);
		2483	ev_timer_init (&timer, timer_cb, 0., 1.02);
1397		2484
1398		2485
1399	=head2 C<ev_idle> - when you've got nothing better to do...	2486	=head2 C<ev_idle> - when you've got nothing better to do...
1400		2487
1401	Idle watchers trigger events when no other events of the same or higher	2488	Idle watchers trigger events when no other events of the same or higher
1402	priority are pending (prepare, check and other idle watchers do not	2489	priority are pending (prepare, check and other idle watchers do not count
1403	count).	2490	as receiving "events").
1404		2491
1405	That is, as long as your process is busy handling sockets or timeouts	2492	That is, as long as your process is busy handling sockets or timeouts
1406	(or even signals, imagine) of the same or higher priority it will not be	2493	(or even signals, imagine) of the same or higher priority it will not be
1407	triggered. But when your process is idle (or only lower-priority watchers	2494	triggered. But when your process is idle (or only lower-priority watchers
1408	are pending), the idle watchers are being called once per event loop	2495	are pending), the idle watchers are being called once per event loop
…		…
1415	Apart from keeping your process non-blocking (which is a useful	2502	Apart from keeping your process non-blocking (which is a useful
1416	effect on its own sometimes), idle watchers are a good place to do	2503	effect on its own sometimes), idle watchers are a good place to do
1417	"pseudo-background processing", or delay processing stuff to after the	2504	"pseudo-background processing", or delay processing stuff to after the
1418	event loop has handled all outstanding events.	2505	event loop has handled all outstanding events.
1419		2506
		2507	=head3 Watcher-Specific Functions and Data Members
		2508
1420	=over 4	2509	=over 4
1421		2510
1422	=item ev_idle_init (ev_signal *, callback)	2511	=item ev_idle_init (ev_idle *, callback)
1423		2512
1424	Initialises and configures the idle watcher - it has no parameters of any	2513	Initialises and configures the idle watcher - it has no parameters of any
1425	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2514	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1426	believe me.	2515	believe me.
1427		2516
1428	=back	2517	=back
1429		2518
		2519	=head3 Examples
		2520
1430	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2521	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1431	callback, free it. Also, use no error checking, as usual.	2522	callback, free it. Also, use no error checking, as usual.
1432		2523
1433	static void	2524	static void
1434	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2525	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1435	{	2526	{
1436	free (w);	2527	free (w);
1437	// now do something you wanted to do when the program has	2528	// now do something you wanted to do when the program has
1438	// no longer asnything immediate to do.	2529	// no longer anything immediate to do.
1439	}	2530	}
1440		2531
1441	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2532	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1442	ev_idle_init (idle_watcher, idle_cb);	2533	ev_idle_init (idle_watcher, idle_cb);
1443	ev_idle_start (loop, idle_cb);	2534	ev_idle_start (loop, idle_watcher);
1444		2535
1445		2536
1446	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2537	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1447		2538
1448	Prepare and check watchers are usually (but not always) used in tandem:	2539	Prepare and check watchers are usually (but not always) used in pairs:
1449	prepare watchers get invoked before the process blocks and check watchers	2540	prepare watchers get invoked before the process blocks and check watchers
1450	afterwards.	2541	afterwards.
1451		2542
1452	You I<must not> call C<ev_loop> or similar functions that enter	2543	You I<must not> call C<ev_loop> or similar functions that enter
1453	the current event loop from either C<ev_prepare> or C<ev_check>	2544	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1456	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2547	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1457	C<ev_check> so if you have one watcher of each kind they will always be	2548	C<ev_check> so if you have one watcher of each kind they will always be
1458	called in pairs bracketing the blocking call.	2549	called in pairs bracketing the blocking call.
1459		2550
1460	Their main purpose is to integrate other event mechanisms into libev and	2551	Their main purpose is to integrate other event mechanisms into libev and
1461	their use is somewhat advanced. This could be used, for example, to track	2552	their use is somewhat advanced. They could be used, for example, to track
1462	variable changes, implement your own watchers, integrate net-snmp or a	2553	variable changes, implement your own watchers, integrate net-snmp or a
1463	coroutine library and lots more. They are also occasionally useful if	2554	coroutine library and lots more. They are also occasionally useful if
1464	you cache some data and want to flush it before blocking (for example,	2555	you cache some data and want to flush it before blocking (for example,
1465	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2556	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1466	watcher).	2557	watcher).
1467		2558
1468	This is done by examining in each prepare call which file descriptors need	2559	This is done by examining in each prepare call which file descriptors
1469	to be watched by the other library, registering C<ev_io> watchers for	2560	need to be watched by the other library, registering C<ev_io> watchers
1470	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2561	for them and starting an C<ev_timer> watcher for any timeouts (many
1471	provide just this functionality). Then, in the check watcher you check for	2562	libraries provide exactly this functionality). Then, in the check watcher,
1472	any events that occured (by checking the pending status of all watchers	2563	you check for any events that occurred (by checking the pending status
1473	and stopping them) and call back into the library. The I/O and timer	2564	of all watchers and stopping them) and call back into the library. The
1474	callbacks will never actually be called (but must be valid nevertheless,	2565	I/O and timer callbacks will never actually be called (but must be valid
1475	because you never know, you know?).	2566	nevertheless, because you never know, you know?).
1476		2567
1477	As another example, the Perl Coro module uses these hooks to integrate	2568	As another example, the Perl Coro module uses these hooks to integrate
1478	coroutines into libev programs, by yielding to other active coroutines	2569	coroutines into libev programs, by yielding to other active coroutines
1479	during each prepare and only letting the process block if no coroutines	2570	during each prepare and only letting the process block if no coroutines
1480	are ready to run (it's actually more complicated: it only runs coroutines	2571	are ready to run (it's actually more complicated: it only runs coroutines
1481	with priority higher than or equal to the event loop and one coroutine	2572	with priority higher than or equal to the event loop and one coroutine
1482	of lower priority, but only once, using idle watchers to keep the event	2573	of lower priority, but only once, using idle watchers to keep the event
1483	loop from blocking if lower-priority coroutines are active, thus mapping	2574	loop from blocking if lower-priority coroutines are active, thus mapping
1484	low-priority coroutines to idle/background tasks).	2575	low-priority coroutines to idle/background tasks).
1485		2576
		2577	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2578	priority, to ensure that they are being run before any other watchers
		2579	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2580
		2581	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2582	activate ("feed") events into libev. While libev fully supports this, they
		2583	might get executed before other C<ev_check> watchers did their job. As
		2584	C<ev_check> watchers are often used to embed other (non-libev) event
		2585	loops those other event loops might be in an unusable state until their
		2586	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2587	others).
		2588
		2589	=head3 Watcher-Specific Functions and Data Members
		2590
1486	=over 4	2591	=over 4
1487		2592
1488	=item ev_prepare_init (ev_prepare *, callback)	2593	=item ev_prepare_init (ev_prepare *, callback)
1489		2594
1490	=item ev_check_init (ev_check *, callback)	2595	=item ev_check_init (ev_check *, callback)
1491		2596
1492	Initialises and configures the prepare or check watcher - they have no	2597	Initialises and configures the prepare or check watcher - they have no
1493	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2598	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1494	macros, but using them is utterly, utterly and completely pointless.	2599	macros, but using them is utterly, utterly, utterly and completely
		2600	pointless.
1495		2601
1496	=back	2602	=back
1497		2603
1498	Example: To include a library such as adns, you would add IO watchers	2604	=head3 Examples
1499	and a timeout watcher in a prepare handler, as required by libadns, and	2605
		2606	There are a number of principal ways to embed other event loops or modules
		2607	into libev. Here are some ideas on how to include libadns into libev
		2608	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2609	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2610	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2611	Glib event loop).
		2612
		2613	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1500	in a check watcher, destroy them and call into libadns. What follows is	2614	and in a check watcher, destroy them and call into libadns. What follows
1501	pseudo-code only of course:	2615	is pseudo-code only of course. This requires you to either use a low
		2616	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2617	the callbacks for the IO/timeout watchers might not have been called yet.
1502		2618
1503	static ev_io iow [nfd];	2619	static ev_io iow [nfd];
1504	static ev_timer tw;	2620	static ev_timer tw;
1505		2621
1506	static void	2622	static void
1507	io_cb (ev_loop *loop, ev_io *w, int revents)	2623	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1508	{	2624	{
1509	// set the relevant poll flags
1510	// could also call adns_processreadable etc. here
1511	struct pollfd *fd = (struct pollfd *)w->data;
1512	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1513	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1514	}	2625	}
1515		2626
1516	// create io watchers for each fd and a timer before blocking	2627	// create io watchers for each fd and a timer before blocking
1517	static void	2628	static void
1518	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2629	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1519	{	2630	{
1520	int timeout = 3600000;	2631	int timeout = 3600000;
1521	struct pollfd fds [nfd];	2632	struct pollfd fds [nfd];
1522	// actual code will need to loop here and realloc etc.	2633	// actual code will need to loop here and realloc etc.
1523	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2634	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1524		2635
1525	/* the callback is illegal, but won't be called as we stop during check */	2636	/* the callback is illegal, but won't be called as we stop during check */
1526	ev_timer_init (&tw, 0, timeout * 1e-3);	2637	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1527	ev_timer_start (loop, &tw);	2638	ev_timer_start (loop, &tw);
1528		2639
1529	// create on ev_io per pollfd	2640	// create one ev_io per pollfd
1530	for (int i = 0; i < nfd; ++i)	2641	for (int i = 0; i < nfd; ++i)
1531	{	2642	{
1532	ev_io_init (iow + i, io_cb, fds [i].fd,	2643	ev_io_init (iow + i, io_cb, fds [i].fd,
1533	((fds [i].events & POLLIN ? EV_READ : 0)	2644	((fds [i].events & POLLIN ? EV_READ : 0)
1534	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2645	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1535		2646
1536	fds [i].revents = 0;	2647	fds [i].revents = 0;
1537	iow [i].data = fds + i;
1538	ev_io_start (loop, iow + i);	2648	ev_io_start (loop, iow + i);
1539	}	2649	}
1540	}	2650	}
1541		2651
1542	// stop all watchers after blocking	2652	// stop all watchers after blocking
1543	static void	2653	static void
1544	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2654	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1545	{	2655	{
1546	ev_timer_stop (loop, &tw);	2656	ev_timer_stop (loop, &tw);
1547		2657
1548	for (int i = 0; i < nfd; ++i)	2658	for (int i = 0; i < nfd; ++i)
		2659	{
		2660	// set the relevant poll flags
		2661	// could also call adns_processreadable etc. here
		2662	struct pollfd *fd = fds + i;
		2663	int revents = ev_clear_pending (iow + i);
		2664	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2665	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2666
		2667	// now stop the watcher
1549	ev_io_stop (loop, iow + i);	2668	ev_io_stop (loop, iow + i);
		2669	}
1550		2670
1551	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2671	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1552	}	2672	}
		2673
		2674	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2675	in the prepare watcher and would dispose of the check watcher.
		2676
		2677	Method 3: If the module to be embedded supports explicit event
		2678	notification (libadns does), you can also make use of the actual watcher
		2679	callbacks, and only destroy/create the watchers in the prepare watcher.
		2680
		2681	static void
		2682	timer_cb (EV_P_ ev_timer *w, int revents)
		2683	{
		2684	adns_state ads = (adns_state)w->data;
		2685	update_now (EV_A);
		2686
		2687	adns_processtimeouts (ads, &tv_now);
		2688	}
		2689
		2690	static void
		2691	io_cb (EV_P_ ev_io *w, int revents)
		2692	{
		2693	adns_state ads = (adns_state)w->data;
		2694	update_now (EV_A);
		2695
		2696	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2697	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2698	}
		2699
		2700	// do not ever call adns_afterpoll
		2701
		2702	Method 4: Do not use a prepare or check watcher because the module you
		2703	want to embed is not flexible enough to support it. Instead, you can
		2704	override their poll function. The drawback with this solution is that the
		2705	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2706	this approach, effectively embedding EV as a client into the horrible
		2707	libglib event loop.
		2708
		2709	static gint
		2710	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2711	{
		2712	int got_events = 0;
		2713
		2714	for (n = 0; n < nfds; ++n)
		2715	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2716
		2717	if (timeout >= 0)
		2718	// create/start timer
		2719
		2720	// poll
		2721	ev_loop (EV_A_ 0);
		2722
		2723	// stop timer again
		2724	if (timeout >= 0)
		2725	ev_timer_stop (EV_A_ &to);
		2726
		2727	// stop io watchers again - their callbacks should have set
		2728	for (n = 0; n < nfds; ++n)
		2729	ev_io_stop (EV_A_ iow [n]);
		2730
		2731	return got_events;
		2732	}
1553		2733
1554		2734
1555	=head2 C<ev_embed> - when one backend isn't enough...	2735	=head2 C<ev_embed> - when one backend isn't enough...
1556		2736
1557	This is a rather advanced watcher type that lets you embed one event loop	2737	This is a rather advanced watcher type that lets you embed one event loop
…		…
1563	prioritise I/O.	2743	prioritise I/O.
1564		2744
1565	As an example for a bug workaround, the kqueue backend might only support	2745	As an example for a bug workaround, the kqueue backend might only support
1566	sockets on some platform, so it is unusable as generic backend, but you	2746	sockets on some platform, so it is unusable as generic backend, but you
1567	still want to make use of it because you have many sockets and it scales	2747	still want to make use of it because you have many sockets and it scales
1568	so nicely. In this case, you would create a kqueue-based loop and embed it	2748	so nicely. In this case, you would create a kqueue-based loop and embed
1569	into your default loop (which might use e.g. poll). Overall operation will	2749	it into your default loop (which might use e.g. poll). Overall operation
1570	be a bit slower because first libev has to poll and then call kevent, but	2750	will be a bit slower because first libev has to call C<poll> and then
1571	at least you can use both at what they are best.	2751	C<kevent>, but at least you can use both mechanisms for what they are
		2752	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1572		2753
1573	As for prioritising I/O: rarely you have the case where some fds have	2754	As for prioritising I/O: under rare circumstances you have the case where
1574	to be watched and handled very quickly (with low latency), and even	2755	some fds have to be watched and handled very quickly (with low latency),
1575	priorities and idle watchers might have too much overhead. In this case	2756	and even priorities and idle watchers might have too much overhead. In
1576	you would put all the high priority stuff in one loop and all the rest in	2757	this case you would put all the high priority stuff in one loop and all
1577	a second one, and embed the second one in the first.	2758	the rest in a second one, and embed the second one in the first.
1578		2759
1579	As long as the watcher is active, the callback will be invoked every time	2760	As long as the watcher is active, the callback will be invoked every
1580	there might be events pending in the embedded loop. The callback must then	2761	time there might be events pending in the embedded loop. The callback
1581	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2762	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1582	their callbacks (you could also start an idle watcher to give the embedded	2763	sweep and invoke their callbacks (the callback doesn't need to invoke the
1583	loop strictly lower priority for example). You can also set the callback	2764	C<ev_embed_sweep> function directly, it could also start an idle watcher
1584	to C<0>, in which case the embed watcher will automatically execute the	2765	to give the embedded loop strictly lower priority for example).
1585	embedded loop sweep.
1586		2766
1587	As long as the watcher is started it will automatically handle events. The	2767	You can also set the callback to C<0>, in which case the embed watcher
1588	callback will be invoked whenever some events have been handled. You can	2768	will automatically execute the embedded loop sweep whenever necessary.
1589	set the callback to C<0> to avoid having to specify one if you are not
1590	interested in that.
1591		2769
1592	Also, there have not currently been made special provisions for forking:	2770	Fork detection will be handled transparently while the C<ev_embed> watcher
1593	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2771	is active, i.e., the embedded loop will automatically be forked when the
1594	but you will also have to stop and restart any C<ev_embed> watchers	2772	embedding loop forks. In other cases, the user is responsible for calling
1595	yourself.	2773	C<ev_loop_fork> on the embedded loop.
1596		2774
1597	Unfortunately, not all backends are embeddable, only the ones returned by	2775	Unfortunately, not all backends are embeddable: only the ones returned by
1598	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2776	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1599	portable one.	2777	portable one.
1600		2778
1601	So when you want to use this feature you will always have to be prepared	2779	So when you want to use this feature you will always have to be prepared
1602	that you cannot get an embeddable loop. The recommended way to get around	2780	that you cannot get an embeddable loop. The recommended way to get around
1603	this is to have a separate variables for your embeddable loop, try to	2781	this is to have a separate variables for your embeddable loop, try to
1604	create it, and if that fails, use the normal loop for everything:	2782	create it, and if that fails, use the normal loop for everything.
1605		2783
1606	struct ev_loop *loop_hi = ev_default_init (0);	2784	=head3 C<ev_embed> and fork
1607	struct ev_loop *loop_lo = 0;
1608	struct ev_embed embed;
1609
1610	// see if there is a chance of getting one that works
1611	// (remember that a flags value of 0 means autodetection)
1612	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1613	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1614	: 0;
1615		2785
1616	// if we got one, then embed it, otherwise default to loop_hi	2786	While the C<ev_embed> watcher is running, forks in the embedding loop will
1617	if (loop_lo)	2787	automatically be applied to the embedded loop as well, so no special
1618	{	2788	fork handling is required in that case. When the watcher is not running,
1619	ev_embed_init (&embed, 0, loop_lo);	2789	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1620	ev_embed_start (loop_hi, &embed);	2790	as applicable.
1621	}	2791
1622	else	2792	=head3 Watcher-Specific Functions and Data Members
1623	loop_lo = loop_hi;
1624		2793
1625	=over 4	2794	=over 4
1626		2795
1627	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2796	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1628		2797
…		…
1630		2799
1631	Configures the watcher to embed the given loop, which must be	2800	Configures the watcher to embed the given loop, which must be
1632	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2801	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1633	invoked automatically, otherwise it is the responsibility of the callback	2802	invoked automatically, otherwise it is the responsibility of the callback
1634	to invoke it (it will continue to be called until the sweep has been done,	2803	to invoke it (it will continue to be called until the sweep has been done,
1635	if you do not want thta, you need to temporarily stop the embed watcher).	2804	if you do not want that, you need to temporarily stop the embed watcher).
1636		2805
1637	=item ev_embed_sweep (loop, ev_embed *)	2806	=item ev_embed_sweep (loop, ev_embed *)
1638		2807
1639	Make a single, non-blocking sweep over the embedded loop. This works	2808	Make a single, non-blocking sweep over the embedded loop. This works
1640	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2809	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1641	apropriate way for embedded loops.	2810	appropriate way for embedded loops.
1642		2811
1643	=item struct ev_loop *loop [read-only]	2812	=item struct ev_loop *other [read-only]
1644		2813
1645	The embedded event loop.	2814	The embedded event loop.
1646		2815
1647	=back	2816	=back
		2817
		2818	=head3 Examples
		2819
		2820	Example: Try to get an embeddable event loop and embed it into the default
		2821	event loop. If that is not possible, use the default loop. The default
		2822	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2823	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2824	used).
		2825
		2826	struct ev_loop *loop_hi = ev_default_init (0);
		2827	struct ev_loop *loop_lo = 0;
		2828	ev_embed embed;
		2829
		2830	// see if there is a chance of getting one that works
		2831	// (remember that a flags value of 0 means autodetection)
		2832	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2833	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2834	: 0;
		2835
		2836	// if we got one, then embed it, otherwise default to loop_hi
		2837	if (loop_lo)
		2838	{
		2839	ev_embed_init (&embed, 0, loop_lo);
		2840	ev_embed_start (loop_hi, &embed);
		2841	}
		2842	else
		2843	loop_lo = loop_hi;
		2844
		2845	Example: Check if kqueue is available but not recommended and create
		2846	a kqueue backend for use with sockets (which usually work with any
		2847	kqueue implementation). Store the kqueue/socket-only event loop in
		2848	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2849
		2850	struct ev_loop *loop = ev_default_init (0);
		2851	struct ev_loop *loop_socket = 0;
		2852	ev_embed embed;
		2853
		2854	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2855	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2856	{
		2857	ev_embed_init (&embed, 0, loop_socket);
		2858	ev_embed_start (loop, &embed);
		2859	}
		2860
		2861	if (!loop_socket)
		2862	loop_socket = loop;
		2863
		2864	// now use loop_socket for all sockets, and loop for everything else
1648		2865
1649		2866
1650	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2867	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1651		2868
1652	Fork watchers are called when a C<fork ()> was detected (usually because	2869	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1655	event loop blocks next and before C<ev_check> watchers are being called,	2872	event loop blocks next and before C<ev_check> watchers are being called,
1656	and only in the child after the fork. If whoever good citizen calling	2873	and only in the child after the fork. If whoever good citizen calling
1657	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2874	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1658	handlers will be invoked, too, of course.	2875	handlers will be invoked, too, of course.
1659		2876
		2877	=head3 The special problem of life after fork - how is it possible?
		2878
		2879	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2880	up/change the process environment, followed by a call to C<exec()>. This
		2881	sequence should be handled by libev without any problems.
		2882
		2883	This changes when the application actually wants to do event handling
		2884	in the child, or both parent in child, in effect "continuing" after the
		2885	fork.
		2886
		2887	The default mode of operation (for libev, with application help to detect
		2888	forks) is to duplicate all the state in the child, as would be expected
		2889	when I<either> the parent I<or> the child process continues.
		2890
		2891	When both processes want to continue using libev, then this is usually the
		2892	wrong result. In that case, usually one process (typically the parent) is
		2893	supposed to continue with all watchers in place as before, while the other
		2894	process typically wants to start fresh, i.e. without any active watchers.
		2895
		2896	The cleanest and most efficient way to achieve that with libev is to
		2897	simply create a new event loop, which of course will be "empty", and
		2898	use that for new watchers. This has the advantage of not touching more
		2899	memory than necessary, and thus avoiding the copy-on-write, and the
		2900	disadvantage of having to use multiple event loops (which do not support
		2901	signal watchers).
		2902
		2903	When this is not possible, or you want to use the default loop for
		2904	other reasons, then in the process that wants to start "fresh", call
		2905	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2906	the default loop will "orphan" (not stop) all registered watchers, so you
		2907	have to be careful not to execute code that modifies those watchers. Note
		2908	also that in that case, you have to re-register any signal watchers.
		2909
		2910	=head3 Watcher-Specific Functions and Data Members
		2911
1660	=over 4	2912	=over 4
1661		2913
1662	=item ev_fork_init (ev_signal *, callback)	2914	=item ev_fork_init (ev_signal *, callback)
1663		2915
1664	Initialises and configures the fork watcher - it has no parameters of any	2916	Initialises and configures the fork watcher - it has no parameters of any
…		…
1666	believe me.	2918	believe me.
1667		2919
1668	=back	2920	=back
1669		2921
1670		2922
		2923	=head2 C<ev_async> - how to wake up another event loop
		2924
		2925	In general, you cannot use an C<ev_loop> from multiple threads or other
		2926	asynchronous sources such as signal handlers (as opposed to multiple event
		2927	loops - those are of course safe to use in different threads).
		2928
		2929	Sometimes, however, you need to wake up another event loop you do not
		2930	control, for example because it belongs to another thread. This is what
		2931	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2932	can signal it by calling C<ev_async_send>, which is thread- and signal
		2933	safe.
		2934
		2935	This functionality is very similar to C<ev_signal> watchers, as signals,
		2936	too, are asynchronous in nature, and signals, too, will be compressed
		2937	(i.e. the number of callback invocations may be less than the number of
		2938	C<ev_async_sent> calls).
		2939
		2940	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2941	just the default loop.
		2942
		2943	=head3 Queueing
		2944
		2945	C<ev_async> does not support queueing of data in any way. The reason
		2946	is that the author does not know of a simple (or any) algorithm for a
		2947	multiple-writer-single-reader queue that works in all cases and doesn't
		2948	need elaborate support such as pthreads.
		2949
		2950	That means that if you want to queue data, you have to provide your own
		2951	queue. But at least I can tell you how to implement locking around your
		2952	queue:
		2953
		2954	=over 4
		2955
		2956	=item queueing from a signal handler context
		2957
		2958	To implement race-free queueing, you simply add to the queue in the signal
		2959	handler but you block the signal handler in the watcher callback. Here is
		2960	an example that does that for some fictitious SIGUSR1 handler:
		2961
		2962	static ev_async mysig;
		2963
		2964	static void
		2965	sigusr1_handler (void)
		2966	{
		2967	sometype data;
		2968
		2969	// no locking etc.
		2970	queue_put (data);
		2971	ev_async_send (EV_DEFAULT_ &mysig);
		2972	}
		2973
		2974	static void
		2975	mysig_cb (EV_P_ ev_async *w, int revents)
		2976	{
		2977	sometype data;
		2978	sigset_t block, prev;
		2979
		2980	sigemptyset (&block);
		2981	sigaddset (&block, SIGUSR1);
		2982	sigprocmask (SIG_BLOCK, &block, &prev);
		2983
		2984	while (queue_get (&data))
		2985	process (data);
		2986
		2987	if (sigismember (&prev, SIGUSR1)
		2988	sigprocmask (SIG_UNBLOCK, &block, 0);
		2989	}
		2990
		2991	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2992	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2993	either...).
		2994
		2995	=item queueing from a thread context
		2996
		2997	The strategy for threads is different, as you cannot (easily) block
		2998	threads but you can easily preempt them, so to queue safely you need to
		2999	employ a traditional mutex lock, such as in this pthread example:
		3000
		3001	static ev_async mysig;
		3002	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3003
		3004	static void
		3005	otherthread (void)
		3006	{
		3007	// only need to lock the actual queueing operation
		3008	pthread_mutex_lock (&mymutex);
		3009	queue_put (data);
		3010	pthread_mutex_unlock (&mymutex);
		3011
		3012	ev_async_send (EV_DEFAULT_ &mysig);
		3013	}
		3014
		3015	static void
		3016	mysig_cb (EV_P_ ev_async *w, int revents)
		3017	{
		3018	pthread_mutex_lock (&mymutex);
		3019
		3020	while (queue_get (&data))
		3021	process (data);
		3022
		3023	pthread_mutex_unlock (&mymutex);
		3024	}
		3025
		3026	=back
		3027
		3028
		3029	=head3 Watcher-Specific Functions and Data Members
		3030
		3031	=over 4
		3032
		3033	=item ev_async_init (ev_async *, callback)
		3034
		3035	Initialises and configures the async watcher - it has no parameters of any
		3036	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3037	trust me.
		3038
		3039	=item ev_async_send (loop, ev_async *)
		3040
		3041	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3042	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3043	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3044	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3045	section below on what exactly this means).
		3046
		3047	Note that, as with other watchers in libev, multiple events might get
		3048	compressed into a single callback invocation (another way to look at this
		3049	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3050	reset when the event loop detects that).
		3051
		3052	This call incurs the overhead of a system call only once per event loop
		3053	iteration, so while the overhead might be noticeable, it doesn't apply to
		3054	repeated calls to C<ev_async_send> for the same event loop.
		3055
		3056	=item bool = ev_async_pending (ev_async *)
		3057
		3058	Returns a non-zero value when C<ev_async_send> has been called on the
		3059	watcher but the event has not yet been processed (or even noted) by the
		3060	event loop.
		3061
		3062	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3063	the loop iterates next and checks for the watcher to have become active,
		3064	it will reset the flag again. C<ev_async_pending> can be used to very
		3065	quickly check whether invoking the loop might be a good idea.
		3066
		3067	Not that this does I<not> check whether the watcher itself is pending,
		3068	only whether it has been requested to make this watcher pending: there
		3069	is a time window between the event loop checking and resetting the async
		3070	notification, and the callback being invoked.
		3071
		3072	=back
		3073
		3074
1671	=head1 OTHER FUNCTIONS	3075	=head1 OTHER FUNCTIONS
1672		3076
1673	There are some other functions of possible interest. Described. Here. Now.	3077	There are some other functions of possible interest. Described. Here. Now.
1674		3078
1675	=over 4	3079	=over 4
1676		3080
1677	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3081	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1678		3082
1679	This function combines a simple timer and an I/O watcher, calls your	3083	This function combines a simple timer and an I/O watcher, calls your
1680	callback on whichever event happens first and automatically stop both	3084	callback on whichever event happens first and automatically stops both
1681	watchers. This is useful if you want to wait for a single event on an fd	3085	watchers. This is useful if you want to wait for a single event on an fd
1682	or timeout without having to allocate/configure/start/stop/free one or	3086	or timeout without having to allocate/configure/start/stop/free one or
1683	more watchers yourself.	3087	more watchers yourself.
1684		3088
1685	If C<fd> is less than 0, then no I/O watcher will be started and events	3089	If C<fd> is less than 0, then no I/O watcher will be started and the
1686	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3090	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1687	C<events> set will be craeted and started.	3091	the given C<fd> and C<events> set will be created and started.
1688		3092
1689	If C<timeout> is less than 0, then no timeout watcher will be	3093	If C<timeout> is less than 0, then no timeout watcher will be
1690	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3094	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1691	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3095	repeat = 0) will be started. C<0> is a valid timeout.
1692	dubious value.
1693		3096
1694	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3097	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1695	passed an C<revents> set like normal event callbacks (a combination of	3098	passed an C<revents> set like normal event callbacks (a combination of
1696	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3099	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1697	value passed to C<ev_once>:	3100	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3101	a timeout and an io event at the same time - you probably should give io
		3102	events precedence.
1698		3103
		3104	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3105
1699	static void stdin_ready (int revents, void *arg)	3106	static void stdin_ready (int revents, void *arg)
1700	{	3107	{
1701	if (revents & EV_TIMEOUT)
1702	/* doh, nothing entered */;
1703	else if (revents & EV_READ)	3108	if (revents & EV_READ)
1704	/* stdin might have data for us, joy! */;	3109	/* stdin might have data for us, joy! */;
		3110	else if (revents & EV_TIMEOUT)
		3111	/* doh, nothing entered */;
1705	}	3112	}
1706		3113
1707	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3114	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1708		3115
1709	=item ev_feed_event (ev_loop *, watcher *, int revents)	3116	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1710		3117
1711	Feeds the given event set into the event loop, as if the specified event	3118	Feeds the given event set into the event loop, as if the specified event
1712	had happened for the specified watcher (which must be a pointer to an	3119	had happened for the specified watcher (which must be a pointer to an
1713	initialised but not necessarily started event watcher).	3120	initialised but not necessarily started event watcher).
1714		3121
1715	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3122	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1716		3123
1717	Feed an event on the given fd, as if a file descriptor backend detected	3124	Feed an event on the given fd, as if a file descriptor backend detected
1718	the given events it.	3125	the given events it.
1719		3126
1720	=item ev_feed_signal_event (ev_loop *loop, int signum)	3127	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1721		3128
1722	Feed an event as if the given signal occured (C<loop> must be the default	3129	Feed an event as if the given signal occurred (C<loop> must be the default
1723	loop!).	3130	loop!).
1724		3131
1725	=back	3132	=back
1726		3133
1727		3134
…		…
1743		3150
1744	=item * Priorities are not currently supported. Initialising priorities	3151	=item * Priorities are not currently supported. Initialising priorities
1745	will fail and all watchers will have the same priority, even though there	3152	will fail and all watchers will have the same priority, even though there
1746	is an ev_pri field.	3153	is an ev_pri field.
1747		3154
		3155	=item * In libevent, the last base created gets the signals, in libev, the
		3156	first base created (== the default loop) gets the signals.
		3157
1748	=item * Other members are not supported.	3158	=item * Other members are not supported.
1749		3159
1750	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3160	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1751	to use the libev header file and library.	3161	to use the libev header file and library.
1752		3162
1753	=back	3163	=back
1754		3164
1755	=head1 C++ SUPPORT	3165	=head1 C++ SUPPORT
1756		3166
1757	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3167	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1758	you to use some convinience methods to start/stop watchers and also change	3168	you to use some convenience methods to start/stop watchers and also change
1759	the callback model to a model using method callbacks on objects.	3169	the callback model to a model using method callbacks on objects.
1760		3170
1761	To use it,	3171	To use it,
1762		3172
1763	#include <ev++.h>	3173	#include <ev++.h>
1764		3174
1765	This automatically includes F<ev.h> and puts all of its definitions (many	3175	This automatically includes F<ev.h> and puts all of its definitions (many
1766	of them macros) into the global namespace. All C++ specific things are	3176	of them macros) into the global namespace. All C++ specific things are
1767	put into the C<ev> namespace. It should support all the same embedding	3177	put into the C<ev> namespace. It should support all the same embedding
1768	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3178	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1835	your compiler is good :), then the method will be fully inlined into the	3245	your compiler is good :), then the method will be fully inlined into the
1836	thunking function, making it as fast as a direct C callback.	3246	thunking function, making it as fast as a direct C callback.
1837		3247
1838	Example: simple class declaration and watcher initialisation	3248	Example: simple class declaration and watcher initialisation
1839		3249
1840	struct myclass	3250	struct myclass
1841	{	3251	{
1842	void io_cb (ev::io &w, int revents) { }	3252	void io_cb (ev::io &w, int revents) { }
1843	}	3253	}
1844		3254
1845	myclass obj;	3255	myclass obj;
1846	ev::io iow;	3256	ev::io iow;
1847	iow.set <myclass, &myclass::io_cb> (&obj);	3257	iow.set <myclass, &myclass::io_cb> (&obj);
1848		3258
1849	=item w->set (void (*function)(watcher &w, int), void *data = 0)	3259	=item w->set (object *)
		3260
		3261	This is an B<experimental> feature that might go away in a future version.
		3262
		3263	This is a variation of a method callback - leaving out the method to call
		3264	will default the method to C<operator ()>, which makes it possible to use
		3265	functor objects without having to manually specify the C<operator ()> all
		3266	the time. Incidentally, you can then also leave out the template argument
		3267	list.
		3268
		3269	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3270	int revents)>.
		3271
		3272	See the method-C<set> above for more details.
		3273
		3274	Example: use a functor object as callback.
		3275
		3276	struct myfunctor
		3277	{
		3278	void operator() (ev::io &w, int revents)
		3279	{
		3280	...
		3281	}
		3282	}
		3283
		3284	myfunctor f;
		3285
		3286	ev::io w;
		3287	w.set (&f);
		3288
		3289	=item w->set<function> (void *data = 0)
1850		3290
1851	Also sets a callback, but uses a static method or plain function as	3291	Also sets a callback, but uses a static method or plain function as
1852	callback. The optional C<data> argument will be stored in the watcher's	3292	callback. The optional C<data> argument will be stored in the watcher's
1853	C<data> member and is free for you to use.	3293	C<data> member and is free for you to use.
1854		3294
		3295	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3296
1855	See the method-C<set> above for more details.	3297	See the method-C<set> above for more details.
		3298
		3299	Example: Use a plain function as callback.
		3300
		3301	static void io_cb (ev::io &w, int revents) { }
		3302	iow.set <io_cb> ();
1856		3303
1857	=item w->set (struct ev_loop *)	3304	=item w->set (struct ev_loop *)
1858		3305
1859	Associates a different C<struct ev_loop> with this watcher. You can only	3306	Associates a different C<struct ev_loop> with this watcher. You can only
1860	do this when the watcher is inactive (and not pending either).	3307	do this when the watcher is inactive (and not pending either).
1861		3308
1862	=item w->set ([args])	3309	=item w->set ([arguments])
1863		3310
1864	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3311	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1865	called at least once. Unlike the C counterpart, an active watcher gets	3312	called at least once. Unlike the C counterpart, an active watcher gets
1866	automatically stopped and restarted when reconfiguring it with this	3313	automatically stopped and restarted when reconfiguring it with this
1867	method.	3314	method.
1868		3315
1869	=item w->start ()	3316	=item w->start ()
…		…
1873		3320
1874	=item w->stop ()	3321	=item w->stop ()
1875		3322
1876	Stops the watcher if it is active. Again, no C<loop> argument.	3323	Stops the watcher if it is active. Again, no C<loop> argument.
1877		3324
1878	=item w->again () C<ev::timer>, C<ev::periodic> only	3325	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1879		3326
1880	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3327	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1881	C<ev_TYPE_again> function.	3328	C<ev_TYPE_again> function.
1882		3329
1883	=item w->sweep () C<ev::embed> only	3330	=item w->sweep () (C<ev::embed> only)
1884		3331
1885	Invokes C<ev_embed_sweep>.	3332	Invokes C<ev_embed_sweep>.
1886		3333
1887	=item w->update () C<ev::stat> only	3334	=item w->update () (C<ev::stat> only)
1888		3335
1889	Invokes C<ev_stat_stat>.	3336	Invokes C<ev_stat_stat>.
1890		3337
1891	=back	3338	=back
1892		3339
1893	=back	3340	=back
1894		3341
1895	Example: Define a class with an IO and idle watcher, start one of them in	3342	Example: Define a class with an IO and idle watcher, start one of them in
1896	the constructor.	3343	the constructor.
1897		3344
1898	class myclass	3345	class myclass
1899	{	3346	{
1900	ev_io io; void io_cb (ev::io &w, int revents);	3347	ev::io io ; void io_cb (ev::io &w, int revents);
1901	ev_idle idle void idle_cb (ev::idle &w, int revents);	3348	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1902		3349
1903	myclass ();	3350	myclass (int fd)
1904	}	3351	{
1905
1906	myclass::myclass (int fd)
1907	{
1908	io .set <myclass, &myclass::io_cb > (this);	3352	io .set <myclass, &myclass::io_cb > (this);
1909	idle.set <myclass, &myclass::idle_cb> (this);	3353	idle.set <myclass, &myclass::idle_cb> (this);
1910		3354
1911	io.start (fd, ev::READ);	3355	io.start (fd, ev::READ);
		3356	}
1912	}	3357	};
		3358
		3359
		3360	=head1 OTHER LANGUAGE BINDINGS
		3361
		3362	Libev does not offer other language bindings itself, but bindings for a
		3363	number of languages exist in the form of third-party packages. If you know
		3364	any interesting language binding in addition to the ones listed here, drop
		3365	me a note.
		3366
		3367	=over 4
		3368
		3369	=item Perl
		3370
		3371	The EV module implements the full libev API and is actually used to test
		3372	libev. EV is developed together with libev. Apart from the EV core module,
		3373	there are additional modules that implement libev-compatible interfaces
		3374	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3375	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3376	and C<EV::Glib>).
		3377
		3378	It can be found and installed via CPAN, its homepage is at
		3379	L<http://software.schmorp.de/pkg/EV>.
		3380
		3381	=item Python
		3382
		3383	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3384	seems to be quite complete and well-documented.
		3385
		3386	=item Ruby
		3387
		3388	Tony Arcieri has written a ruby extension that offers access to a subset
		3389	of the libev API and adds file handle abstractions, asynchronous DNS and
		3390	more on top of it. It can be found via gem servers. Its homepage is at
		3391	L<http://rev.rubyforge.org/>.
		3392
		3393	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3394	makes rev work even on mingw.
		3395
		3396	=item Haskell
		3397
		3398	A haskell binding to libev is available at
		3399	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3400
		3401	=item D
		3402
		3403	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3404	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3405
		3406	=item Ocaml
		3407
		3408	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3409	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3410
		3411	=back
1913		3412
1914		3413
1915	=head1 MACRO MAGIC	3414	=head1 MACRO MAGIC
1916		3415
1917	Libev can be compiled with a variety of options, the most fundemantal is	3416	Libev can be compiled with a variety of options, the most fundamental
1918	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3417	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1919	callbacks have an initial C<struct ev_loop *> argument.	3418	functions and callbacks have an initial C<struct ev_loop *> argument.
1920		3419
1921	To make it easier to write programs that cope with either variant, the	3420	To make it easier to write programs that cope with either variant, the
1922	following macros are defined:	3421	following macros are defined:
1923		3422
1924	=over 4	3423	=over 4
…		…
1927		3426
1928	This provides the loop I<argument> for functions, if one is required ("ev	3427	This provides the loop I<argument> for functions, if one is required ("ev
1929	loop argument"). The C<EV_A> form is used when this is the sole argument,	3428	loop argument"). The C<EV_A> form is used when this is the sole argument,
1930	C<EV_A_> is used when other arguments are following. Example:	3429	C<EV_A_> is used when other arguments are following. Example:
1931		3430
1932	ev_unref (EV_A);	3431	ev_unref (EV_A);
1933	ev_timer_add (EV_A_ watcher);	3432	ev_timer_add (EV_A_ watcher);
1934	ev_loop (EV_A_ 0);	3433	ev_loop (EV_A_ 0);
1935		3434
1936	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3435	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1937	which is often provided by the following macro.	3436	which is often provided by the following macro.
1938		3437
1939	=item C<EV_P>, C<EV_P_>	3438	=item C<EV_P>, C<EV_P_>
1940		3439
1941	This provides the loop I<parameter> for functions, if one is required ("ev	3440	This provides the loop I<parameter> for functions, if one is required ("ev
1942	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3441	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1943	C<EV_P_> is used when other parameters are following. Example:	3442	C<EV_P_> is used when other parameters are following. Example:
1944		3443
1945	// this is how ev_unref is being declared	3444	// this is how ev_unref is being declared
1946	static void ev_unref (EV_P);	3445	static void ev_unref (EV_P);
1947		3446
1948	// this is how you can declare your typical callback	3447	// this is how you can declare your typical callback
1949	static void cb (EV_P_ ev_timer *w, int revents)	3448	static void cb (EV_P_ ev_timer *w, int revents)
1950		3449
1951	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3450	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1952	suitable for use with C<EV_A>.	3451	suitable for use with C<EV_A>.
1953		3452
1954	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3453	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1955		3454
1956	Similar to the other two macros, this gives you the value of the default	3455	Similar to the other two macros, this gives you the value of the default
1957	loop, if multiple loops are supported ("ev loop default").	3456	loop, if multiple loops are supported ("ev loop default").
		3457
		3458	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3459
		3460	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3461	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3462	is undefined when the default loop has not been initialised by a previous
		3463	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3464
		3465	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3466	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
1958		3467
1959	=back	3468	=back
1960		3469
1961	Example: Declare and initialise a check watcher, utilising the above	3470	Example: Declare and initialise a check watcher, utilising the above
1962	macros so it will work regardless of whether multiple loops are supported	3471	macros so it will work regardless of whether multiple loops are supported
1963	or not.	3472	or not.
1964		3473
1965	static void	3474	static void
1966	check_cb (EV_P_ ev_timer *w, int revents)	3475	check_cb (EV_P_ ev_timer *w, int revents)
1967	{	3476	{
1968	ev_check_stop (EV_A_ w);	3477	ev_check_stop (EV_A_ w);
1969	}	3478	}
1970		3479
1971	ev_check check;	3480	ev_check check;
1972	ev_check_init (&check, check_cb);	3481	ev_check_init (&check, check_cb);
1973	ev_check_start (EV_DEFAULT_ &check);	3482	ev_check_start (EV_DEFAULT_ &check);
1974	ev_loop (EV_DEFAULT_ 0);	3483	ev_loop (EV_DEFAULT_ 0);
1975		3484
1976	=head1 EMBEDDING	3485	=head1 EMBEDDING
1977		3486
1978	Libev can (and often is) directly embedded into host	3487	Libev can (and often is) directly embedded into host
1979	applications. Examples of applications that embed it include the Deliantra	3488	applications. Examples of applications that embed it include the Deliantra
1980	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3489	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1981	and rxvt-unicode.	3490	and rxvt-unicode.
1982		3491
1983	The goal is to enable you to just copy the neecssary files into your	3492	The goal is to enable you to just copy the necessary files into your
1984	source directory without having to change even a single line in them, so	3493	source directory without having to change even a single line in them, so
1985	you can easily upgrade by simply copying (or having a checked-out copy of	3494	you can easily upgrade by simply copying (or having a checked-out copy of
1986	libev somewhere in your source tree).	3495	libev somewhere in your source tree).
1987		3496
1988	=head2 FILESETS	3497	=head2 FILESETS
1989		3498
1990	Depending on what features you need you need to include one or more sets of files	3499	Depending on what features you need you need to include one or more sets of files
1991	in your app.	3500	in your application.
1992		3501
1993	=head3 CORE EVENT LOOP	3502	=head3 CORE EVENT LOOP
1994		3503
1995	To include only the libev core (all the C<ev_*> functions), with manual	3504	To include only the libev core (all the C<ev_*> functions), with manual
1996	configuration (no autoconf):	3505	configuration (no autoconf):
1997		3506
1998	#define EV_STANDALONE 1	3507	#define EV_STANDALONE 1
1999	#include "ev.c"	3508	#include "ev.c"
2000		3509
2001	This will automatically include F<ev.h>, too, and should be done in a	3510	This will automatically include F<ev.h>, too, and should be done in a
2002	single C source file only to provide the function implementations. To use	3511	single C source file only to provide the function implementations. To use
2003	it, do the same for F<ev.h> in all files wishing to use this API (best	3512	it, do the same for F<ev.h> in all files wishing to use this API (best
2004	done by writing a wrapper around F<ev.h> that you can include instead and	3513	done by writing a wrapper around F<ev.h> that you can include instead and
2005	where you can put other configuration options):	3514	where you can put other configuration options):
2006		3515
2007	#define EV_STANDALONE 1	3516	#define EV_STANDALONE 1
2008	#include "ev.h"	3517	#include "ev.h"
2009		3518
2010	Both header files and implementation files can be compiled with a C++	3519	Both header files and implementation files can be compiled with a C++
2011	compiler (at least, thats a stated goal, and breakage will be treated	3520	compiler (at least, that's a stated goal, and breakage will be treated
2012	as a bug).	3521	as a bug).
2013		3522
2014	You need the following files in your source tree, or in a directory	3523	You need the following files in your source tree, or in a directory
2015	in your include path (e.g. in libev/ when using -Ilibev):	3524	in your include path (e.g. in libev/ when using -Ilibev):
2016		3525
2017	ev.h	3526	ev.h
2018	ev.c	3527	ev.c
2019	ev_vars.h	3528	ev_vars.h
2020	ev_wrap.h	3529	ev_wrap.h
2021		3530
2022	ev_win32.c required on win32 platforms only	3531	ev_win32.c required on win32 platforms only
2023		3532
2024	ev_select.c only when select backend is enabled (which is enabled by default)	3533	ev_select.c only when select backend is enabled (which is enabled by default)
2025	ev_poll.c only when poll backend is enabled (disabled by default)	3534	ev_poll.c only when poll backend is enabled (disabled by default)
2026	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3535	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2027	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3536	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2028	ev_port.c only when the solaris port backend is enabled (disabled by default)	3537	ev_port.c only when the solaris port backend is enabled (disabled by default)
2029		3538
2030	F<ev.c> includes the backend files directly when enabled, so you only need	3539	F<ev.c> includes the backend files directly when enabled, so you only need
2031	to compile this single file.	3540	to compile this single file.
2032		3541
2033	=head3 LIBEVENT COMPATIBILITY API	3542	=head3 LIBEVENT COMPATIBILITY API
2034		3543
2035	To include the libevent compatibility API, also include:	3544	To include the libevent compatibility API, also include:
2036		3545
2037	#include "event.c"	3546	#include "event.c"
2038		3547
2039	in the file including F<ev.c>, and:	3548	in the file including F<ev.c>, and:
2040		3549
2041	#include "event.h"	3550	#include "event.h"
2042		3551
2043	in the files that want to use the libevent API. This also includes F<ev.h>.	3552	in the files that want to use the libevent API. This also includes F<ev.h>.
2044		3553
2045	You need the following additional files for this:	3554	You need the following additional files for this:
2046		3555
2047	event.h	3556	event.h
2048	event.c	3557	event.c
2049		3558
2050	=head3 AUTOCONF SUPPORT	3559	=head3 AUTOCONF SUPPORT
2051		3560
2052	Instead of using C<EV_STANDALONE=1> and providing your config in	3561	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2053	whatever way you want, you can also C<m4_include([libev.m4])> in your	3562	whatever way you want, you can also C<m4_include([libev.m4])> in your
2054	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3563	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2055	include F<config.h> and configure itself accordingly.	3564	include F<config.h> and configure itself accordingly.
2056		3565
2057	For this of course you need the m4 file:	3566	For this of course you need the m4 file:
2058		3567
2059	libev.m4	3568	libev.m4
2060		3569
2061	=head2 PREPROCESSOR SYMBOLS/MACROS	3570	=head2 PREPROCESSOR SYMBOLS/MACROS
2062		3571
2063	Libev can be configured via a variety of preprocessor symbols you have to define	3572	Libev can be configured via a variety of preprocessor symbols you have to
2064	before including any of its files. The default is not to build for multiplicity	3573	define before including any of its files. The default in the absence of
2065	and only include the select backend.	3574	autoconf is documented for every option.
2066		3575
2067	=over 4	3576	=over 4
2068		3577
2069	=item EV_STANDALONE	3578	=item EV_STANDALONE
2070		3579
…		…
2072	keeps libev from including F<config.h>, and it also defines dummy	3581	keeps libev from including F<config.h>, and it also defines dummy
2073	implementations for some libevent functions (such as logging, which is not	3582	implementations for some libevent functions (such as logging, which is not
2074	supported). It will also not define any of the structs usually found in	3583	supported). It will also not define any of the structs usually found in
2075	F<event.h> that are not directly supported by the libev core alone.	3584	F<event.h> that are not directly supported by the libev core alone.
2076		3585
		3586	In stanbdalone mode, libev will still try to automatically deduce the
		3587	configuration, but has to be more conservative.
		3588
2077	=item EV_USE_MONOTONIC	3589	=item EV_USE_MONOTONIC
2078		3590
2079	If defined to be C<1>, libev will try to detect the availability of the	3591	If defined to be C<1>, libev will try to detect the availability of the
2080	monotonic clock option at both compiletime and runtime. Otherwise no use	3592	monotonic clock option at both compile time and runtime. Otherwise no
2081	of the monotonic clock option will be attempted. If you enable this, you	3593	use of the monotonic clock option will be attempted. If you enable this,
2082	usually have to link against librt or something similar. Enabling it when	3594	you usually have to link against librt or something similar. Enabling it
2083	the functionality isn't available is safe, though, althoguh you have	3595	when the functionality isn't available is safe, though, although you have
2084	to make sure you link against any libraries where the C<clock_gettime>	3596	to make sure you link against any libraries where the C<clock_gettime>
2085	function is hiding in (often F<-lrt>).	3597	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2086		3598
2087	=item EV_USE_REALTIME	3599	=item EV_USE_REALTIME
2088		3600
2089	If defined to be C<1>, libev will try to detect the availability of the	3601	If defined to be C<1>, libev will try to detect the availability of the
2090	realtime clock option at compiletime (and assume its availability at	3602	real-time clock option at compile time (and assume its availability
2091	runtime if successful). Otherwise no use of the realtime clock option will	3603	at runtime if successful). Otherwise no use of the real-time clock
2092	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3604	option will be attempted. This effectively replaces C<gettimeofday>
2093	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3605	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2094	in the description of C<EV_USE_MONOTONIC>, though.	3606	correctness. See the note about libraries in the description of
		3607	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3608	C<EV_USE_CLOCK_SYSCALL>.
		3609
		3610	=item EV_USE_CLOCK_SYSCALL
		3611
		3612	If defined to be C<1>, libev will try to use a direct syscall instead
		3613	of calling the system-provided C<clock_gettime> function. This option
		3614	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3615	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3616	programs needlessly. Using a direct syscall is slightly slower (in
		3617	theory), because no optimised vdso implementation can be used, but avoids
		3618	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3619	higher, as it simplifies linking (no need for C<-lrt>).
		3620
		3621	=item EV_USE_NANOSLEEP
		3622
		3623	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3624	and will use it for delays. Otherwise it will use C<select ()>.
		3625
		3626	=item EV_USE_EVENTFD
		3627
		3628	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3629	available and will probe for kernel support at runtime. This will improve
		3630	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3631	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3632	2.7 or newer, otherwise disabled.
2095		3633
2096	=item EV_USE_SELECT	3634	=item EV_USE_SELECT
2097		3635
2098	If undefined or defined to be C<1>, libev will compile in support for the	3636	If undefined or defined to be C<1>, libev will compile in support for the
2099	C<select>(2) backend. No attempt at autodetection will be done: if no	3637	C<select>(2) backend. No attempt at auto-detection will be done: if no
2100	other method takes over, select will be it. Otherwise the select backend	3638	other method takes over, select will be it. Otherwise the select backend
2101	will not be compiled in.	3639	will not be compiled in.
2102		3640
2103	=item EV_SELECT_USE_FD_SET	3641	=item EV_SELECT_USE_FD_SET
2104		3642
2105	If defined to C<1>, then the select backend will use the system C<fd_set>	3643	If defined to C<1>, then the select backend will use the system C<fd_set>
2106	structure. This is useful if libev doesn't compile due to a missing	3644	structure. This is useful if libev doesn't compile due to a missing
2107	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3645	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2108	exotic systems. This usually limits the range of file descriptors to some	3646	on exotic systems. This usually limits the range of file descriptors to
2109	low limit such as 1024 or might have other limitations (winsocket only	3647	some low limit such as 1024 or might have other limitations (winsocket
2110	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3648	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2111	influence the size of the C<fd_set> used.	3649	configures the maximum size of the C<fd_set>.
2112		3650
2113	=item EV_SELECT_IS_WINSOCKET	3651	=item EV_SELECT_IS_WINSOCKET
2114		3652
2115	When defined to C<1>, the select backend will assume that	3653	When defined to C<1>, the select backend will assume that
2116	select/socket/connect etc. don't understand file descriptors but	3654	select/socket/connect etc. don't understand file descriptors but
…		…
2118	be used is the winsock select). This means that it will call	3656	be used is the winsock select). This means that it will call
2119	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3657	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2120	it is assumed that all these functions actually work on fds, even	3658	it is assumed that all these functions actually work on fds, even
2121	on win32. Should not be defined on non-win32 platforms.	3659	on win32. Should not be defined on non-win32 platforms.
2122		3660
		3661	=item EV_FD_TO_WIN32_HANDLE
		3662
		3663	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3664	file descriptors to socket handles. When not defining this symbol (the
		3665	default), then libev will call C<_get_osfhandle>, which is usually
		3666	correct. In some cases, programs use their own file descriptor management,
		3667	in which case they can provide this function to map fds to socket handles.
		3668
2123	=item EV_USE_POLL	3669	=item EV_USE_POLL
2124		3670
2125	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3671	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2126	backend. Otherwise it will be enabled on non-win32 platforms. It	3672	backend. Otherwise it will be enabled on non-win32 platforms. It
2127	takes precedence over select.	3673	takes precedence over select.
2128		3674
2129	=item EV_USE_EPOLL	3675	=item EV_USE_EPOLL
2130		3676
2131	If defined to be C<1>, libev will compile in support for the Linux	3677	If defined to be C<1>, libev will compile in support for the Linux
2132	C<epoll>(7) backend. Its availability will be detected at runtime,	3678	C<epoll>(7) backend. Its availability will be detected at runtime,
2133	otherwise another method will be used as fallback. This is the	3679	otherwise another method will be used as fallback. This is the preferred
2134	preferred backend for GNU/Linux systems.	3680	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3681	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2135		3682
2136	=item EV_USE_KQUEUE	3683	=item EV_USE_KQUEUE
2137		3684
2138	If defined to be C<1>, libev will compile in support for the BSD style	3685	If defined to be C<1>, libev will compile in support for the BSD style
2139	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3686	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2152	otherwise another method will be used as fallback. This is the preferred	3699	otherwise another method will be used as fallback. This is the preferred
2153	backend for Solaris 10 systems.	3700	backend for Solaris 10 systems.
2154		3701
2155	=item EV_USE_DEVPOLL	3702	=item EV_USE_DEVPOLL
2156		3703
2157	reserved for future expansion, works like the USE symbols above.	3704	Reserved for future expansion, works like the USE symbols above.
2158		3705
2159	=item EV_USE_INOTIFY	3706	=item EV_USE_INOTIFY
2160		3707
2161	If defined to be C<1>, libev will compile in support for the Linux inotify	3708	If defined to be C<1>, libev will compile in support for the Linux inotify
2162	interface to speed up C<ev_stat> watchers. Its actual availability will	3709	interface to speed up C<ev_stat> watchers. Its actual availability will
2163	be detected at runtime.	3710	be detected at runtime. If undefined, it will be enabled if the headers
		3711	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3712
		3713	=item EV_ATOMIC_T
		3714
		3715	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3716	access is atomic with respect to other threads or signal contexts. No such
		3717	type is easily found in the C language, so you can provide your own type
		3718	that you know is safe for your purposes. It is used both for signal handler "locking"
		3719	as well as for signal and thread safety in C<ev_async> watchers.
		3720
		3721	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3722	(from F<signal.h>), which is usually good enough on most platforms.
2164		3723
2165	=item EV_H	3724	=item EV_H
2166		3725
2167	The name of the F<ev.h> header file used to include it. The default if	3726	The name of the F<ev.h> header file used to include it. The default if
2168	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3727	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2169	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3728	used to virtually rename the F<ev.h> header file in case of conflicts.
2170		3729
2171	=item EV_CONFIG_H	3730	=item EV_CONFIG_H
2172		3731
2173	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3732	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2174	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3733	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2175	C<EV_H>, above.	3734	C<EV_H>, above.
2176		3735
2177	=item EV_EVENT_H	3736	=item EV_EVENT_H
2178		3737
2179	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3738	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2180	of how the F<event.h> header can be found.	3739	of how the F<event.h> header can be found, the default is C<"event.h">.
2181		3740
2182	=item EV_PROTOTYPES	3741	=item EV_PROTOTYPES
2183		3742
2184	If defined to be C<0>, then F<ev.h> will not define any function	3743	If defined to be C<0>, then F<ev.h> will not define any function
2185	prototypes, but still define all the structs and other symbols. This is	3744	prototypes, but still define all the structs and other symbols. This is
…		…
2206	When doing priority-based operations, libev usually has to linearly search	3765	When doing priority-based operations, libev usually has to linearly search
2207	all the priorities, so having many of them (hundreds) uses a lot of space	3766	all the priorities, so having many of them (hundreds) uses a lot of space
2208	and time, so using the defaults of five priorities (-2 .. +2) is usually	3767	and time, so using the defaults of five priorities (-2 .. +2) is usually
2209	fine.	3768	fine.
2210		3769
2211	If your embedding app does not need any priorities, defining these both to	3770	If your embedding application does not need any priorities, defining these
2212	C<0> will save some memory and cpu.	3771	both to C<0> will save some memory and CPU.
2213		3772
2214	=item EV_PERIODIC_ENABLE	3773	=item EV_PERIODIC_ENABLE
2215		3774
2216	If undefined or defined to be C<1>, then periodic timers are supported. If	3775	If undefined or defined to be C<1>, then periodic timers are supported. If
2217	defined to be C<0>, then they are not. Disabling them saves a few kB of	3776	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2224	code.	3783	code.
2225		3784
2226	=item EV_EMBED_ENABLE	3785	=item EV_EMBED_ENABLE
2227		3786
2228	If undefined or defined to be C<1>, then embed watchers are supported. If	3787	If undefined or defined to be C<1>, then embed watchers are supported. If
2229	defined to be C<0>, then they are not.	3788	defined to be C<0>, then they are not. Embed watchers rely on most other
		3789	watcher types, which therefore must not be disabled.
2230		3790
2231	=item EV_STAT_ENABLE	3791	=item EV_STAT_ENABLE
2232		3792
2233	If undefined or defined to be C<1>, then stat watchers are supported. If	3793	If undefined or defined to be C<1>, then stat watchers are supported. If
2234	defined to be C<0>, then they are not.	3794	defined to be C<0>, then they are not.
…		…
2236	=item EV_FORK_ENABLE	3796	=item EV_FORK_ENABLE
2237		3797
2238	If undefined or defined to be C<1>, then fork watchers are supported. If	3798	If undefined or defined to be C<1>, then fork watchers are supported. If
2239	defined to be C<0>, then they are not.	3799	defined to be C<0>, then they are not.
2240		3800
		3801	=item EV_ASYNC_ENABLE
		3802
		3803	If undefined or defined to be C<1>, then async watchers are supported. If
		3804	defined to be C<0>, then they are not.
		3805
2241	=item EV_MINIMAL	3806	=item EV_MINIMAL
2242		3807
2243	If you need to shave off some kilobytes of code at the expense of some	3808	If you need to shave off some kilobytes of code at the expense of some
2244	speed, define this symbol to C<1>. Currently only used for gcc to override	3809	speed (but with the full API), define this symbol to C<1>. Currently this
2245	some inlining decisions, saves roughly 30% codesize of amd64.	3810	is used to override some inlining decisions, saves roughly 30% code size
		3811	on amd64. It also selects a much smaller 2-heap for timer management over
		3812	the default 4-heap.
		3813
		3814	You can save even more by disabling watcher types you do not need
		3815	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3816	(C<-DNDEBUG>) will usually reduce code size a lot.
		3817
		3818	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3819	provide a bare-bones event library. See C<ev.h> for details on what parts
		3820	of the API are still available, and do not complain if this subset changes
		3821	over time.
		3822
		3823	=item EV_NSIG
		3824
		3825	The highest supported signal number, +1 (or, the number of
		3826	signals): Normally, libev tries to deduce the maximum number of signals
		3827	automatically, but sometimes this fails, in which case it can be
		3828	specified. Also, using a lower number than detected (C<32> should be
		3829	good for about any system in existance) can save some memory, as libev
		3830	statically allocates some 12-24 bytes per signal number.
2246		3831
2247	=item EV_PID_HASHSIZE	3832	=item EV_PID_HASHSIZE
2248		3833
2249	C<ev_child> watchers use a small hash table to distribute workload by	3834	C<ev_child> watchers use a small hash table to distribute workload by
2250	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3835	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2251	than enough. If you need to manage thousands of children you might want to	3836	than enough. If you need to manage thousands of children you might want to
2252	increase this value (I<must> be a power of two).	3837	increase this value (I<must> be a power of two).
2253		3838
2254	=item EV_INOTIFY_HASHSIZE	3839	=item EV_INOTIFY_HASHSIZE
2255		3840
2256	C<ev_staz> watchers use a small hash table to distribute workload by	3841	C<ev_stat> watchers use a small hash table to distribute workload by
2257	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3842	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2258	usually more than enough. If you need to manage thousands of C<ev_stat>	3843	usually more than enough. If you need to manage thousands of C<ev_stat>
2259	watchers you might want to increase this value (I<must> be a power of	3844	watchers you might want to increase this value (I<must> be a power of
2260	two).	3845	two).
2261		3846
		3847	=item EV_USE_4HEAP
		3848
		3849	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3850	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3851	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3852	faster performance with many (thousands) of watchers.
		3853
		3854	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3855	(disabled).
		3856
		3857	=item EV_HEAP_CACHE_AT
		3858
		3859	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3860	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3861	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3862	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3863	but avoids random read accesses on heap changes. This improves performance
		3864	noticeably with many (hundreds) of watchers.
		3865
		3866	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3867	(disabled).
		3868
		3869	=item EV_VERIFY
		3870
		3871	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3872	be done: If set to C<0>, no internal verification code will be compiled
		3873	in. If set to C<1>, then verification code will be compiled in, but not
		3874	called. If set to C<2>, then the internal verification code will be
		3875	called once per loop, which can slow down libev. If set to C<3>, then the
		3876	verification code will be called very frequently, which will slow down
		3877	libev considerably.
		3878
		3879	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3880	C<0>.
		3881
2262	=item EV_COMMON	3882	=item EV_COMMON
2263		3883
2264	By default, all watchers have a C<void *data> member. By redefining	3884	By default, all watchers have a C<void *data> member. By redefining
2265	this macro to a something else you can include more and other types of	3885	this macro to a something else you can include more and other types of
2266	members. You have to define it each time you include one of the files,	3886	members. You have to define it each time you include one of the files,
2267	though, and it must be identical each time.	3887	though, and it must be identical each time.
2268		3888
2269	For example, the perl EV module uses something like this:	3889	For example, the perl EV module uses something like this:
2270		3890
2271	#define EV_COMMON \	3891	#define EV_COMMON \
2272	SV *self; /* contains this struct */ \	3892	SV *self; /* contains this struct */ \
2273	SV *cb_sv, *fh /* note no trailing ";" */	3893	SV *cb_sv, *fh /* note no trailing ";" */
2274		3894
2275	=item EV_CB_DECLARE (type)	3895	=item EV_CB_DECLARE (type)
2276		3896
2277	=item EV_CB_INVOKE (watcher, revents)	3897	=item EV_CB_INVOKE (watcher, revents)
2278		3898
2279	=item ev_set_cb (ev, cb)	3899	=item ev_set_cb (ev, cb)
2280		3900
2281	Can be used to change the callback member declaration in each watcher,	3901	Can be used to change the callback member declaration in each watcher,
2282	and the way callbacks are invoked and set. Must expand to a struct member	3902	and the way callbacks are invoked and set. Must expand to a struct member
2283	definition and a statement, respectively. See the F<ev.v> header file for	3903	definition and a statement, respectively. See the F<ev.h> header file for
2284	their default definitions. One possible use for overriding these is to	3904	their default definitions. One possible use for overriding these is to
2285	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3905	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2286	method calls instead of plain function calls in C++.	3906	method calls instead of plain function calls in C++.
		3907
		3908	=back
		3909
		3910	=head2 EXPORTED API SYMBOLS
		3911
		3912	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3913	exported symbols, you can use the provided F<Symbol.*> files which list
		3914	all public symbols, one per line:
		3915
		3916	Symbols.ev for libev proper
		3917	Symbols.event for the libevent emulation
		3918
		3919	This can also be used to rename all public symbols to avoid clashes with
		3920	multiple versions of libev linked together (which is obviously bad in
		3921	itself, but sometimes it is inconvenient to avoid this).
		3922
		3923	A sed command like this will create wrapper C<#define>'s that you need to
		3924	include before including F<ev.h>:
		3925
		3926	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3927
		3928	This would create a file F<wrap.h> which essentially looks like this:
		3929
		3930	#define ev_backend myprefix_ev_backend
		3931	#define ev_check_start myprefix_ev_check_start
		3932	#define ev_check_stop myprefix_ev_check_stop
		3933	...
2287		3934
2288	=head2 EXAMPLES	3935	=head2 EXAMPLES
2289		3936
2290	For a real-world example of a program the includes libev	3937	For a real-world example of a program the includes libev
2291	verbatim, you can have a look at the EV perl module	3938	verbatim, you can have a look at the EV perl module
…		…
2296	file.	3943	file.
2297		3944
2298	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3945	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2299	that everybody includes and which overrides some configure choices:	3946	that everybody includes and which overrides some configure choices:
2300		3947
2301	#define EV_MINIMAL 1	3948	#define EV_MINIMAL 1
2302	#define EV_USE_POLL 0	3949	#define EV_USE_POLL 0
2303	#define EV_MULTIPLICITY 0	3950	#define EV_MULTIPLICITY 0
2304	#define EV_PERIODIC_ENABLE 0	3951	#define EV_PERIODIC_ENABLE 0
2305	#define EV_STAT_ENABLE 0	3952	#define EV_STAT_ENABLE 0
2306	#define EV_FORK_ENABLE 0	3953	#define EV_FORK_ENABLE 0
2307	#define EV_CONFIG_H <config.h>	3954	#define EV_CONFIG_H <config.h>
2308	#define EV_MINPRI 0	3955	#define EV_MINPRI 0
2309	#define EV_MAXPRI 0	3956	#define EV_MAXPRI 0
2310		3957
2311	#include "ev++.h"	3958	#include "ev++.h"
2312		3959
2313	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3960	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2314		3961
2315	#include "ev_cpp.h"	3962	#include "ev_cpp.h"
2316	#include "ev.c"	3963	#include "ev.c"
2317		3964
		3965	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2318		3966
		3967	=head2 THREADS AND COROUTINES
		3968
		3969	=head3 THREADS
		3970
		3971	All libev functions are reentrant and thread-safe unless explicitly
		3972	documented otherwise, but libev implements no locking itself. This means
		3973	that you can use as many loops as you want in parallel, as long as there
		3974	are no concurrent calls into any libev function with the same loop
		3975	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3976	of course): libev guarantees that different event loops share no data
		3977	structures that need any locking.
		3978
		3979	Or to put it differently: calls with different loop parameters can be done
		3980	concurrently from multiple threads, calls with the same loop parameter
		3981	must be done serially (but can be done from different threads, as long as
		3982	only one thread ever is inside a call at any point in time, e.g. by using
		3983	a mutex per loop).
		3984
		3985	Specifically to support threads (and signal handlers), libev implements
		3986	so-called C<ev_async> watchers, which allow some limited form of
		3987	concurrency on the same event loop, namely waking it up "from the
		3988	outside".
		3989
		3990	If you want to know which design (one loop, locking, or multiple loops
		3991	without or something else still) is best for your problem, then I cannot
		3992	help you, but here is some generic advice:
		3993
		3994	=over 4
		3995
		3996	=item * most applications have a main thread: use the default libev loop
		3997	in that thread, or create a separate thread running only the default loop.
		3998
		3999	This helps integrating other libraries or software modules that use libev
		4000	themselves and don't care/know about threading.
		4001
		4002	=item * one loop per thread is usually a good model.
		4003
		4004	Doing this is almost never wrong, sometimes a better-performance model
		4005	exists, but it is always a good start.
		4006
		4007	=item * other models exist, such as the leader/follower pattern, where one
		4008	loop is handed through multiple threads in a kind of round-robin fashion.
		4009
		4010	Choosing a model is hard - look around, learn, know that usually you can do
		4011	better than you currently do :-)
		4012
		4013	=item * often you need to talk to some other thread which blocks in the
		4014	event loop.
		4015
		4016	C<ev_async> watchers can be used to wake them up from other threads safely
		4017	(or from signal contexts...).
		4018
		4019	An example use would be to communicate signals or other events that only
		4020	work in the default loop by registering the signal watcher with the
		4021	default loop and triggering an C<ev_async> watcher from the default loop
		4022	watcher callback into the event loop interested in the signal.
		4023
		4024	=back
		4025
		4026	=head4 THREAD LOCKING EXAMPLE
		4027
		4028	Here is a fictitious example of how to run an event loop in a different
		4029	thread than where callbacks are being invoked and watchers are
		4030	created/added/removed.
		4031
		4032	For a real-world example, see the C<EV::Loop::Async> perl module,
		4033	which uses exactly this technique (which is suited for many high-level
		4034	languages).
		4035
		4036	The example uses a pthread mutex to protect the loop data, a condition
		4037	variable to wait for callback invocations, an async watcher to notify the
		4038	event loop thread and an unspecified mechanism to wake up the main thread.
		4039
		4040	First, you need to associate some data with the event loop:
		4041
		4042	typedef struct {
		4043	mutex_t lock; /* global loop lock */
		4044	ev_async async_w;
		4045	thread_t tid;
		4046	cond_t invoke_cv;
		4047	} userdata;
		4048
		4049	void prepare_loop (EV_P)
		4050	{
		4051	// for simplicity, we use a static userdata struct.
		4052	static userdata u;
		4053
		4054	ev_async_init (&u->async_w, async_cb);
		4055	ev_async_start (EV_A_ &u->async_w);
		4056
		4057	pthread_mutex_init (&u->lock, 0);
		4058	pthread_cond_init (&u->invoke_cv, 0);
		4059
		4060	// now associate this with the loop
		4061	ev_set_userdata (EV_A_ u);
		4062	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4063	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4064
		4065	// then create the thread running ev_loop
		4066	pthread_create (&u->tid, 0, l_run, EV_A);
		4067	}
		4068
		4069	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4070	solely to wake up the event loop so it takes notice of any new watchers
		4071	that might have been added:
		4072
		4073	static void
		4074	async_cb (EV_P_ ev_async *w, int revents)
		4075	{
		4076	// just used for the side effects
		4077	}
		4078
		4079	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4080	protecting the loop data, respectively.
		4081
		4082	static void
		4083	l_release (EV_P)
		4084	{
		4085	userdata *u = ev_userdata (EV_A);
		4086	pthread_mutex_unlock (&u->lock);
		4087	}
		4088
		4089	static void
		4090	l_acquire (EV_P)
		4091	{
		4092	userdata *u = ev_userdata (EV_A);
		4093	pthread_mutex_lock (&u->lock);
		4094	}
		4095
		4096	The event loop thread first acquires the mutex, and then jumps straight
		4097	into C<ev_loop>:
		4098
		4099	void *
		4100	l_run (void *thr_arg)
		4101	{
		4102	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4103
		4104	l_acquire (EV_A);
		4105	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4106	ev_loop (EV_A_ 0);
		4107	l_release (EV_A);
		4108
		4109	return 0;
		4110	}
		4111
		4112	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4113	signal the main thread via some unspecified mechanism (signals? pipe
		4114	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4115	have been called (in a while loop because a) spurious wakeups are possible
		4116	and b) skipping inter-thread-communication when there are no pending
		4117	watchers is very beneficial):
		4118
		4119	static void
		4120	l_invoke (EV_P)
		4121	{
		4122	userdata *u = ev_userdata (EV_A);
		4123
		4124	while (ev_pending_count (EV_A))
		4125	{
		4126	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4127	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4128	}
		4129	}
		4130
		4131	Now, whenever the main thread gets told to invoke pending watchers, it
		4132	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4133	thread to continue:
		4134
		4135	static void
		4136	real_invoke_pending (EV_P)
		4137	{
		4138	userdata *u = ev_userdata (EV_A);
		4139
		4140	pthread_mutex_lock (&u->lock);
		4141	ev_invoke_pending (EV_A);
		4142	pthread_cond_signal (&u->invoke_cv);
		4143	pthread_mutex_unlock (&u->lock);
		4144	}
		4145
		4146	Whenever you want to start/stop a watcher or do other modifications to an
		4147	event loop, you will now have to lock:
		4148
		4149	ev_timer timeout_watcher;
		4150	userdata *u = ev_userdata (EV_A);
		4151
		4152	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4153
		4154	pthread_mutex_lock (&u->lock);
		4155	ev_timer_start (EV_A_ &timeout_watcher);
		4156	ev_async_send (EV_A_ &u->async_w);
		4157	pthread_mutex_unlock (&u->lock);
		4158
		4159	Note that sending the C<ev_async> watcher is required because otherwise
		4160	an event loop currently blocking in the kernel will have no knowledge
		4161	about the newly added timer. By waking up the loop it will pick up any new
		4162	watchers in the next event loop iteration.
		4163
		4164	=head3 COROUTINES
		4165
		4166	Libev is very accommodating to coroutines ("cooperative threads"):
		4167	libev fully supports nesting calls to its functions from different
		4168	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4169	different coroutines, and switch freely between both coroutines running
		4170	the loop, as long as you don't confuse yourself). The only exception is
		4171	that you must not do this from C<ev_periodic> reschedule callbacks.
		4172
		4173	Care has been taken to ensure that libev does not keep local state inside
		4174	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4175	they do not call any callbacks.
		4176
		4177	=head2 COMPILER WARNINGS
		4178
		4179	Depending on your compiler and compiler settings, you might get no or a
		4180	lot of warnings when compiling libev code. Some people are apparently
		4181	scared by this.
		4182
		4183	However, these are unavoidable for many reasons. For one, each compiler
		4184	has different warnings, and each user has different tastes regarding
		4185	warning options. "Warn-free" code therefore cannot be a goal except when
		4186	targeting a specific compiler and compiler-version.
		4187
		4188	Another reason is that some compiler warnings require elaborate
		4189	workarounds, or other changes to the code that make it less clear and less
		4190	maintainable.
		4191
		4192	And of course, some compiler warnings are just plain stupid, or simply
		4193	wrong (because they don't actually warn about the condition their message
		4194	seems to warn about). For example, certain older gcc versions had some
		4195	warnings that resulted an extreme number of false positives. These have
		4196	been fixed, but some people still insist on making code warn-free with
		4197	such buggy versions.
		4198
		4199	While libev is written to generate as few warnings as possible,
		4200	"warn-free" code is not a goal, and it is recommended not to build libev
		4201	with any compiler warnings enabled unless you are prepared to cope with
		4202	them (e.g. by ignoring them). Remember that warnings are just that:
		4203	warnings, not errors, or proof of bugs.
		4204
		4205
		4206	=head2 VALGRIND
		4207
		4208	Valgrind has a special section here because it is a popular tool that is
		4209	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4210
		4211	If you think you found a bug (memory leak, uninitialised data access etc.)
		4212	in libev, then check twice: If valgrind reports something like:
		4213
		4214	==2274== definitely lost: 0 bytes in 0 blocks.
		4215	==2274== possibly lost: 0 bytes in 0 blocks.
		4216	==2274== still reachable: 256 bytes in 1 blocks.
		4217
		4218	Then there is no memory leak, just as memory accounted to global variables
		4219	is not a memleak - the memory is still being referenced, and didn't leak.
		4220
		4221	Similarly, under some circumstances, valgrind might report kernel bugs
		4222	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4223	although an acceptable workaround has been found here), or it might be
		4224	confused.
		4225
		4226	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4227	make it into some kind of religion.
		4228
		4229	If you are unsure about something, feel free to contact the mailing list
		4230	with the full valgrind report and an explanation on why you think this
		4231	is a bug in libev (best check the archives, too :). However, don't be
		4232	annoyed when you get a brisk "this is no bug" answer and take the chance
		4233	of learning how to interpret valgrind properly.
		4234
		4235	If you need, for some reason, empty reports from valgrind for your project
		4236	I suggest using suppression lists.
		4237
		4238
		4239	=head1 PORTABILITY NOTES
		4240
		4241	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4242
		4243	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4244	requires, and its I/O model is fundamentally incompatible with the POSIX
		4245	model. Libev still offers limited functionality on this platform in
		4246	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4247	descriptors. This only applies when using Win32 natively, not when using
		4248	e.g. cygwin.
		4249
		4250	Lifting these limitations would basically require the full
		4251	re-implementation of the I/O system. If you are into these kinds of
		4252	things, then note that glib does exactly that for you in a very portable
		4253	way (note also that glib is the slowest event library known to man).
		4254
		4255	There is no supported compilation method available on windows except
		4256	embedding it into other applications.
		4257
		4258	Sensible signal handling is officially unsupported by Microsoft - libev
		4259	tries its best, but under most conditions, signals will simply not work.
		4260
		4261	Not a libev limitation but worth mentioning: windows apparently doesn't
		4262	accept large writes: instead of resulting in a partial write, windows will
		4263	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4264	so make sure you only write small amounts into your sockets (less than a
		4265	megabyte seems safe, but this apparently depends on the amount of memory
		4266	available).
		4267
		4268	Due to the many, low, and arbitrary limits on the win32 platform and
		4269	the abysmal performance of winsockets, using a large number of sockets
		4270	is not recommended (and not reasonable). If your program needs to use
		4271	more than a hundred or so sockets, then likely it needs to use a totally
		4272	different implementation for windows, as libev offers the POSIX readiness
		4273	notification model, which cannot be implemented efficiently on windows
		4274	(due to Microsoft monopoly games).
		4275
		4276	A typical way to use libev under windows is to embed it (see the embedding
		4277	section for details) and use the following F<evwrap.h> header file instead
		4278	of F<ev.h>:
		4279
		4280	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4281	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4282
		4283	#include "ev.h"
		4284
		4285	And compile the following F<evwrap.c> file into your project (make sure
		4286	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4287
		4288	#include "evwrap.h"
		4289	#include "ev.c"
		4290
		4291	=over 4
		4292
		4293	=item The winsocket select function
		4294
		4295	The winsocket C<select> function doesn't follow POSIX in that it
		4296	requires socket I<handles> and not socket I<file descriptors> (it is
		4297	also extremely buggy). This makes select very inefficient, and also
		4298	requires a mapping from file descriptors to socket handles (the Microsoft
		4299	C runtime provides the function C<_open_osfhandle> for this). See the
		4300	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4301	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4302
		4303	The configuration for a "naked" win32 using the Microsoft runtime
		4304	libraries and raw winsocket select is:
		4305
		4306	#define EV_USE_SELECT 1
		4307	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4308
		4309	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4310	complexity in the O(n²) range when using win32.
		4311
		4312	=item Limited number of file descriptors
		4313
		4314	Windows has numerous arbitrary (and low) limits on things.
		4315
		4316	Early versions of winsocket's select only supported waiting for a maximum
		4317	of C<64> handles (probably owning to the fact that all windows kernels
		4318	can only wait for C<64> things at the same time internally; Microsoft
		4319	recommends spawning a chain of threads and wait for 63 handles and the
		4320	previous thread in each. Sounds great!).
		4321
		4322	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4323	to some high number (e.g. C<2048>) before compiling the winsocket select
		4324	call (which might be in libev or elsewhere, for example, perl and many
		4325	other interpreters do their own select emulation on windows).
		4326
		4327	Another limit is the number of file descriptors in the Microsoft runtime
		4328	libraries, which by default is C<64> (there must be a hidden I<64>
		4329	fetish or something like this inside Microsoft). You can increase this
		4330	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4331	(another arbitrary limit), but is broken in many versions of the Microsoft
		4332	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4333	(depending on windows version and/or the phase of the moon). To get more,
		4334	you need to wrap all I/O functions and provide your own fd management, but
		4335	the cost of calling select (O(n²)) will likely make this unworkable.
		4336
		4337	=back
		4338
		4339	=head2 PORTABILITY REQUIREMENTS
		4340
		4341	In addition to a working ISO-C implementation and of course the
		4342	backend-specific APIs, libev relies on a few additional extensions:
		4343
		4344	=over 4
		4345
		4346	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4347	calling conventions regardless of C<ev_watcher_type *>.
		4348
		4349	Libev assumes not only that all watcher pointers have the same internal
		4350	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4351	assumes that the same (machine) code can be used to call any watcher
		4352	callback: The watcher callbacks have different type signatures, but libev
		4353	calls them using an C<ev_watcher *> internally.
		4354
		4355	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4356
		4357	The type C<sig_atomic_t volatile> (or whatever is defined as
		4358	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4359	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4360	believed to be sufficiently portable.
		4361
		4362	=item C<sigprocmask> must work in a threaded environment
		4363
		4364	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4365	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4366	pthread implementations will either allow C<sigprocmask> in the "main
		4367	thread" or will block signals process-wide, both behaviours would
		4368	be compatible with libev. Interaction between C<sigprocmask> and
		4369	C<pthread_sigmask> could complicate things, however.
		4370
		4371	The most portable way to handle signals is to block signals in all threads
		4372	except the initial one, and run the default loop in the initial thread as
		4373	well.
		4374
		4375	=item C<long> must be large enough for common memory allocation sizes
		4376
		4377	To improve portability and simplify its API, libev uses C<long> internally
		4378	instead of C<size_t> when allocating its data structures. On non-POSIX
		4379	systems (Microsoft...) this might be unexpectedly low, but is still at
		4380	least 31 bits everywhere, which is enough for hundreds of millions of
		4381	watchers.
		4382
		4383	=item C<double> must hold a time value in seconds with enough accuracy
		4384
		4385	The type C<double> is used to represent timestamps. It is required to
		4386	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4387	enough for at least into the year 4000. This requirement is fulfilled by
		4388	implementations implementing IEEE 754, which is basically all existing
		4389	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4390	2200.
		4391
		4392	=back
		4393
		4394	If you know of other additional requirements drop me a note.
		4395
		4396
2319	=head1 COMPLEXITIES	4397	=head1 ALGORITHMIC COMPLEXITIES
2320		4398
2321	In this section the complexities of (many of) the algorithms used inside	4399	In this section the complexities of (many of) the algorithms used inside
2322	libev will be explained. For complexity discussions about backends see the	4400	libev will be documented. For complexity discussions about backends see
2323	documentation for C<ev_default_init>.	4401	the documentation for C<ev_default_init>.
2324		4402
2325	All of the following are about amortised time: If an array needs to be	4403	All of the following are about amortised time: If an array needs to be
2326	extended, libev needs to realloc and move the whole array, but this	4404	extended, libev needs to realloc and move the whole array, but this
2327	happens asymptotically never with higher number of elements, so O(1) might	4405	happens asymptotically rarer with higher number of elements, so O(1) might
2328	mean it might do a lengthy realloc operation in rare cases, but on average	4406	mean that libev does a lengthy realloc operation in rare cases, but on
2329	it is much faster and asymptotically approaches constant time.	4407	average it is much faster and asymptotically approaches constant time.
2330		4408
2331	=over 4	4409	=over 4
2332		4410
2333	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4411	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2334		4412
2335	This means that, when you have a watcher that triggers in one hour and	4413	This means that, when you have a watcher that triggers in one hour and
2336	there are 100 watchers that would trigger before that then inserting will	4414	there are 100 watchers that would trigger before that, then inserting will
2337	have to skip those 100 watchers.	4415	have to skip roughly seven (C<ld 100>) of these watchers.
2338		4416
2339	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4417	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2340		4418
2341	That means that for changing a timer costs less than removing/adding them	4419	That means that changing a timer costs less than removing/adding them,
2342	as only the relative motion in the event queue has to be paid for.	4420	as only the relative motion in the event queue has to be paid for.
2343		4421
2344	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4422	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2345		4423
2346	These just add the watcher into an array or at the head of a list.	4424	These just add the watcher into an array or at the head of a list.
		4425
2347	=item Stopping check/prepare/idle watchers: O(1)	4426	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2348		4427
2349	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4428	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2350		4429
2351	These watchers are stored in lists then need to be walked to find the	4430	These watchers are stored in lists, so they need to be walked to find the
2352	correct watcher to remove. The lists are usually short (you don't usually	4431	correct watcher to remove. The lists are usually short (you don't usually
2353	have many watchers waiting for the same fd or signal).	4432	have many watchers waiting for the same fd or signal: one is typical, two
		4433	is rare).
2354		4434
2355	=item Finding the next timer per loop iteration: O(1)	4435	=item Finding the next timer in each loop iteration: O(1)
		4436
		4437	By virtue of using a binary or 4-heap, the next timer is always found at a
		4438	fixed position in the storage array.
2356		4439
2357	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4440	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2358		4441
2359	A change means an I/O watcher gets started or stopped, which requires	4442	A change means an I/O watcher gets started or stopped, which requires
2360	libev to recalculate its status (and possibly tell the kernel).	4443	libev to recalculate its status (and possibly tell the kernel, depending
		4444	on backend and whether C<ev_io_set> was used).
2361		4445
2362	=item Activating one watcher: O(1)	4446	=item Activating one watcher (putting it into the pending state): O(1)
2363		4447
2364	=item Priority handling: O(number_of_priorities)	4448	=item Priority handling: O(number_of_priorities)
2365		4449
2366	Priorities are implemented by allocating some space for each	4450	Priorities are implemented by allocating some space for each
2367	priority. When doing priority-based operations, libev usually has to	4451	priority. When doing priority-based operations, libev usually has to
2368	linearly search all the priorities.	4452	linearly search all the priorities, but starting/stopping and activating
		4453	watchers becomes O(1) with respect to priority handling.
		4454
		4455	=item Sending an ev_async: O(1)
		4456
		4457	=item Processing ev_async_send: O(number_of_async_watchers)
		4458
		4459	=item Processing signals: O(max_signal_number)
		4460
		4461	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4462	calls in the current loop iteration. Checking for async and signal events
		4463	involves iterating over all running async watchers or all signal numbers.
2369		4464
2370	=back	4465	=back
2371		4466
2372		4467
		4468	=head1 GLOSSARY
		4469
		4470	=over 4
		4471
		4472	=item active
		4473
		4474	A watcher is active as long as it has been started (has been attached to
		4475	an event loop) but not yet stopped (disassociated from the event loop).
		4476
		4477	=item application
		4478
		4479	In this document, an application is whatever is using libev.
		4480
		4481	=item callback
		4482
		4483	The address of a function that is called when some event has been
		4484	detected. Callbacks are being passed the event loop, the watcher that
		4485	received the event, and the actual event bitset.
		4486
		4487	=item callback invocation
		4488
		4489	The act of calling the callback associated with a watcher.
		4490
		4491	=item event
		4492
		4493	A change of state of some external event, such as data now being available
		4494	for reading on a file descriptor, time having passed or simply not having
		4495	any other events happening anymore.
		4496
		4497	In libev, events are represented as single bits (such as C<EV_READ> or
		4498	C<EV_TIMEOUT>).
		4499
		4500	=item event library
		4501
		4502	A software package implementing an event model and loop.
		4503
		4504	=item event loop
		4505
		4506	An entity that handles and processes external events and converts them
		4507	into callback invocations.
		4508
		4509	=item event model
		4510
		4511	The model used to describe how an event loop handles and processes
		4512	watchers and events.
		4513
		4514	=item pending
		4515
		4516	A watcher is pending as soon as the corresponding event has been detected,
		4517	and stops being pending as soon as the watcher will be invoked or its
		4518	pending status is explicitly cleared by the application.
		4519
		4520	A watcher can be pending, but not active. Stopping a watcher also clears
		4521	its pending status.
		4522
		4523	=item real time
		4524
		4525	The physical time that is observed. It is apparently strictly monotonic :)
		4526
		4527	=item wall-clock time
		4528
		4529	The time and date as shown on clocks. Unlike real time, it can actually
		4530	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4531	clock.
		4532
		4533	=item watcher
		4534
		4535	A data structure that describes interest in certain events. Watchers need
		4536	to be started (attached to an event loop) before they can receive events.
		4537
		4538	=item watcher invocation
		4539
		4540	The act of calling the callback associated with a watcher.
		4541
		4542	=back
		4543
2373	=head1 AUTHOR	4544	=head1 AUTHOR
2374		4545
2375	Marc Lehmann <libev@schmorp.de>.	4546	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2376		4547

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