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Revision 1.97 by root, Sat Dec 22 05:48:02 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 occurring), 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
…		…
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 some floatingpoint value. Unlike the name	132	on it, you should treat it as some floating point value. Unlike the name
104	component C<stamp> might indicate, it is also used for time differences	133	component C<stamp> might indicate, it is also used for time differences
105	throughout libev.	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
106		156
107	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
108		158
109	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
110	library in any way.	160	library in any way.
…		…
119		169
120	=item ev_sleep (ev_tstamp interval)	170	=item ev_sleep (ev_tstamp interval)
121		171
122	Sleep for the given interval: The current thread will be blocked until	172	Sleep for the given interval: The current thread will be blocked until
123	either it is interrupted or the given time interval has passed. Basically	173	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	174	this is a sub-second-resolution C<sleep ()>.
125		175
126	=item int ev_version_major ()	176	=item int ev_version_major ()
127		177
128	=item int ev_version_minor ()	178	=item int ev_version_minor ()
129		179
…		…
142	not a problem.	192	not a problem.
143		193
144	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
145	version.	195	version.
146		196
147	assert (("libev version mismatch",	197	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
150		200
151	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
152		202
153	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_*>
154	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	206	a description of the set values.
157		207
158	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
159	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
160		210
161	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
163		213
164	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
165		215
166	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
167	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
168	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
169	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
170	(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
171	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
172		222
173	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
174		224
…		…
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
179	recommended ones.	229	recommended ones.
180		230
181	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
182		232
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
184		234
185	Sets the allocation function to use (the prototype is similar - the	235	Sets the allocation function to use (the prototype is similar - the
186	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
187	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
188	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
189	potentially destructive action. The default is your system realloc	239	or take some potentially destructive action.
190	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.
191		244
192	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
193	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,
194	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.
195		248
196	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
197	retries).	250	retries (example requires a standards-compliant C<realloc>).
198		251
199	static void *	252	static void *
200	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
201	{	254	{
202	for (;;)	255	for (;;)
…		…
211	}	264	}
212		265
213	...	266	...
214	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
215		268
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
217		270
218	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
219	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
220	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
221	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
222	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
223	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
224	(such as abort).	277	(such as abort).
225		278
226	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.
…		…
237		290
238	=back	291	=back
239		292
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
241		294
242	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>
243	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>
244	events, and dynamically created loops which do not.	297	I<function>).
245		298
246	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
247	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
248	create, you also create another event loop. Libev itself does no locking	301	not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		302
253	=over 4	303	=over 4
254		304
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		306
…		…
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		311
262	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
263	function.	313	function.
264		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
265	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
266	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>).
267		328
268	The following flags are supported:	329	The following flags are supported:
269		330
…		…
274	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
275	thing, believe me).	336	thing, believe me).
276		337
277	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
278		339
279	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
280	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
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	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
283	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
284	around bugs.	345	around bugs.
…		…
290	enabling this flag.	351	enabling this flag.
291		352
292	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,
293	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
294	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
295	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
296	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
297	C<pthread_atfork> which is even faster).	358	C<pthread_atfork> which is even faster).
298		359
299	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
300	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
301	flag.	362	flag.
302		363
303	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>
304	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.
305		381
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	382	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		383
308	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
309	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,
310	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
311	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
312	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).
313		400
314	=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)
315		402
316	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
317	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
318	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
319	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>.
320		412
321	=item C<EVBACKEND_EPOLL> (value 4, Linux)	413	=item C<EVBACKEND_EPOLL> (value 4, Linux)
322		414
323	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,
324	but it scales phenomenally better. While poll and select usually scale	416	but it scales phenomenally better. While poll and select usually scale
325	like O(total_fds) where n is the total number of fds (or the highest fd),	417	like O(total_fds) where n is the total number of fds (or the highest fd),
326	epoll scales either O(1) or O(active_fds). The epoll design has a number	418	epoll scales either O(1) or O(active_fds).
327	of shortcomings, such as silently dropping events in some hard-to-detect	419
328	cases and rewiring a syscall per fd change, no fork support and bad	420	The epoll mechanism deserves honorable mention as the most misdesigned
329	support for dup:	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.
330		436
331	While stopping, setting and starting an I/O watcher in the same iteration	437	While stopping, setting and starting an I/O watcher in the same iteration
332	will 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
333	(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
334	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	440	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
335	very 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.
336		443
337	Please note that epoll sometimes generates spurious notifications, so you	444	Best performance from this backend is achieved by not unregistering all
338	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,
339	(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>.
340		461
341	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	462	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
342		463
343	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
344	was broken on I<all> BSDs (usually it doesn't work with anything but	465	was broken on all BSDs except NetBSD (usually it doesn't work reliably
345	sockets and pipes, except on Darwin, where of course it's completely	466	with anything but sockets and pipes, except on Darwin, where of course
346	useless. On NetBSD, it seems to work for all the FD types I tested, so it	467	it's completely useless). Unlike epoll, however, whose brokenness
347	is used by default there). For this reason it's not being "autodetected"	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
348	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
349	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	471	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
350	system like NetBSD.	472	system like NetBSD.
351		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.
		477
352	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
353	kernel is more efficient (which says nothing about its actual speed,	479	kernel is more efficient (which says nothing about its actual speed, of
354	of course). While stopping, setting and starting an I/O watcher does	480	course). While stopping, setting and starting an I/O watcher does never
355	never cause an extra syscall as with epoll, it still adds up to two event	481	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
356	changes per incident, support for C<fork ()> is very bad and it drops fds	482	two event changes per incident. Support for C<fork ()> is very bad (but
357	silently in similarly hard-to-detetc cases.	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>.
358		498
359	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	499	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
360		500
361	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.
362		505
363	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	506	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
364		507
365	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	508	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
366	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)).
367		510
368	Please note that solaris event ports can deliver a lot of spurious	511	Please note that Solaris event ports can deliver a lot of spurious
369	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
370	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>.
371		527
372	=item C<EVBACKEND_ALL>	528	=item C<EVBACKEND_ALL>
373		529
374	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
375	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
376	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	532	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
377		533
		534	It is definitely not recommended to use this flag.
		535
378	=back	536	=back
379		537
380	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,
381	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
382	specified, most compiled-in backend will be tried, usually in reverse	540	here). If none are specified, all backends in C<ev_recommended_backends
383	order of their flag values :)	541	()> will be tried.
384		542
385	The most typical usage is like this:	543	Example: This is the most typical usage.
386		544
387	if (!ev_default_loop (0))	545	if (!ev_default_loop (0))
388	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	546	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
389		547
390	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
391	environment settings to be taken into account:	549	environment settings to be taken into account:
392		550
393	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	551	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
394		552
395	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
396	available (warning, breaks stuff, best use only with your own private	554	used if available (warning, breaks stuff, best use only with your own
397	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):
398		557
399	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	558	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
400		559
401	=item struct ev_loop *ev_loop_new (unsigned int flags)	560	=item struct ev_loop *ev_loop_new (unsigned int flags)
402		561
403	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
404	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
405	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
406	undefined behaviour (or a failed assertion if assertions are enabled).	565	undefined behaviour (or a failed assertion if assertions are enabled).
407		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
408	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.
409		572
410	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	573	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
411	if (!epoller)	574	if (!epoller)
412	fatal ("no epoll found here, maybe it hides under your chair");	575	fatal ("no epoll found here, maybe it hides under your chair");
413		576
414	=item ev_default_destroy ()	577	=item ev_default_destroy ()
415		578
416	Destroys the default loop again (frees all memory and kernel state	579	Destroys the default loop again (frees all memory and kernel state
417	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
418	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
419	responsibility to either stop all watchers cleanly yoursef I<before>	582	responsibility to either stop all watchers cleanly yourself I<before>
420	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
421	the easiest thing, you can just ignore the watchers and/or C<free ()> them	584	the easiest thing, you can just ignore the watchers and/or C<free ()> them
422	for example).	585	for example).
423		586
424	Note that certain global state, such as signal state, will not be freed by	587	Note that certain global state, such as signal state (and installed signal
425	this function, and related watchers (such as signal and child watchers)	588	handlers), will not be freed by this function, and related watchers (such
426	would need to be stopped manually.	589	as signal and child watchers) would need to be stopped manually.
427		590
428	In general it is not advisable to call this function except in the	591	In general it is not advisable to call this function except in the
429	rare occasion where you really need to free e.g. the signal handling	592	rare occasion where you really need to free e.g. the signal handling
430	pipe fds. If you need dynamically allocated loops it is better to use	593	pipe fds. If you need dynamically allocated loops it is better to use
431	C<ev_loop_new> and C<ev_loop_destroy>).	594	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
435	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
436	earlier call to C<ev_loop_new>.	599	earlier call to C<ev_loop_new>.
437		600
438	=item ev_default_fork ()	601	=item ev_default_fork ()
439		602
		603	This function sets a flag that causes subsequent C<ev_loop> iterations
440	This function reinitialises the kernel state for backends that have	604	to reinitialise the kernel state for backends that have one. Despite the
441	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
442	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
443	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.
444		609
445	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
446	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
447	fork+exec, you don't have to call it.	612	you just fork+exec, you don't have to call it at all.
448		613
449	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
450	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
451	quite nicely into a call to C<pthread_atfork>:	616	quite nicely into a call to C<pthread_atfork>:
452		617
453	pthread_atfork (0, 0, ev_default_fork);	618	pthread_atfork (0, 0, ev_default_fork);
454		619
455	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
456	without calling this function, so if you force one of those backends you
457	do not need to care.
458
459	=item ev_loop_fork (loop)	620	=item ev_loop_fork (loop)
460		621
461	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
462	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
463	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.
464		631
465	=item unsigned int ev_loop_count (loop)	632	=item unsigned int ev_loop_count (loop)
466		633
467	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
468	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
469	happily wraps around with enough iterations.	636	happily wraps around with enough iterations.
470		637
471	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
472	"ticks" the number of loop iterations), as it roughly corresponds with	639	"ticks" the number of loop iterations), as it roughly corresponds with
473	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.
474		653
475	=item unsigned int ev_backend (loop)	654	=item unsigned int ev_backend (loop)
476		655
477	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
478	use.	657	use.
…		…
483	received events and started processing them. This timestamp does not	662	received events and started processing them. This timestamp does not
484	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
485	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
486	event occurring (or more correctly, libev finding out about it).	665	event occurring (or more correctly, libev finding out about it).
487		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>).
		704
488	=item ev_loop (loop, int flags)	705	=item ev_loop (loop, int flags)
489		706
490	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
491	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
492	events.	709	events.
…		…
494	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
495	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.
496		713
497	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
498	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
499	finished (especially in interactive programs), but having a program that	716	finished (especially in interactive programs), but having a program
500	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
501	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.
502		720
503	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
504	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
505	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.
506		725
507	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
508	neccessary) and will handle those and any outstanding ones. It will block	727	necessary) and will handle those and any already outstanding ones. It
509	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
510	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
511	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
512	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
513	usually a better approach for this kind of thing.	736	usually a better approach for this kind of thing.
514		737
515	Here are the gory details of what C<ev_loop> does:	738	Here are the gory details of what C<ev_loop> does:
516		739
517	- Before the first iteration, call any pending watchers.	740	- Before the first iteration, call any pending watchers.
518	* If there are no active watchers (reference count is zero), return.	741	* If EVFLAG_FORKCHECK was used, check for a fork.
519	- Queue all prepare watchers and then call all outstanding watchers.	742	- If a fork was detected (by any means), queue and call all fork watchers.
		743	- Queue and call all prepare watchers.
520	- 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.
521	- Update the kernel state with all outstanding changes.	746	- Update the kernel state with all outstanding changes.
522	- Update the "event loop time".	747	- Update the "event loop time" (ev_now ()).
523	- 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.
524	- Block the process, waiting for any events.	752	- Block the process, waiting for any events.
525	- Queue all outstanding I/O (fd) events.	753	- Queue all outstanding I/O (fd) events.
526	- Update the "event loop time" and do time jump handling.	754	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
527	- Queue all outstanding timers.	755	- Queue all expired timers.
528	- Queue all outstanding periodics.	756	- Queue all expired periodics.
529	- If no events are pending now, queue all idle watchers.	757	- Unless any events are pending now, queue all idle watchers.
530	- Queue all check watchers.	758	- Queue all check watchers.
531	- 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).
532	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
533	be handled here by queueing them when their watcher gets executed.	761	be handled here by queueing them when their watcher gets executed.
534	- 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
535	were used, return, otherwise continue with step *.	763	were used, or there are no active watchers, return, otherwise
		764	continue with step *.
536		765
537	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
538	anymore.	767	anymore.
539		768
540	... queue jobs here, make sure they register event watchers as long	769	... queue jobs here, make sure they register event watchers as long
541	... 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..)
542	ev_loop (my_loop, 0);	771	ev_loop (my_loop, 0);
543	... jobs done. yeah!	772	... jobs done or somebody called unloop. yeah!
544		773
545	=item ev_unloop (loop, how)	774	=item ev_unloop (loop, how)
546		775
547	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
548	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
549	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
550	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.
551		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
552	=item ev_ref (loop)	785	=item ev_ref (loop)
553		786
554	=item ev_unref (loop)	787	=item ev_unref (loop)
555		788
556	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
557	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
558	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
559	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>
560	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
561	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
562	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
563	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
564	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
565	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).
566		806
567	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>
568	running when nothing else is active.	808	running when nothing else is active.
569		809
570	struct ev_signal exitsig;	810	ev_signal exitsig;
571	ev_signal_init (&exitsig, sig_cb, SIGINT);	811	ev_signal_init (&exitsig, sig_cb, SIGINT);
572	ev_signal_start (loop, &exitsig);	812	ev_signal_start (loop, &exitsig);
573	evf_unref (loop);	813	evf_unref (loop);
574		814
575	Example: For some weird reason, unregister the above signal handler again.	815	Example: For some weird reason, unregister the above signal handler again.
576		816
577	ev_ref (loop);	817	ev_ref (loop);
578	ev_signal_stop (loop, &exitsig);	818	ev_signal_stop (loop, &exitsig);
579		819
580	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	820	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
581		821
582	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	822	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
583		823
584	These advanced functions influence the time that libev will spend waiting	824	These advanced functions influence the time that libev will spend waiting
585	for events. Both are by default C<0>, meaning that libev will try to	825	for events. Both time intervals are by default C<0>, meaning that libev
586	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	826	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		827	latency.
587		828
588	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	829	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
589	allows libev to delay invocation of I/O and timer/periodic callbacks to	830	allows libev to delay invocation of I/O and timer/periodic callbacks
590	increase efficiency of loop iterations.	831	to increase efficiency of loop iterations (or to increase power-saving
		832	opportunities).
591		833
592	The background is that sometimes your program runs just fast enough to	834	The idea is that sometimes your program runs just fast enough to handle
593	handle one (or very few) event(s) per loop iteration. While this makes	835	one (or very few) event(s) per loop iteration. While this makes the
594	the program responsive, it also wastes a lot of CPU time to poll for new	836	program responsive, it also wastes a lot of CPU time to poll for new
595	events, especially with backends like C<select ()> which have a high	837	events, especially with backends like C<select ()> which have a high
596	overhead for the actual polling but can deliver many events at once.	838	overhead for the actual polling but can deliver many events at once.
597		839
598	By setting a higher I<io collect interval> you allow libev to spend more	840	By setting a higher I<io collect interval> you allow libev to spend more
599	time collecting I/O events, so you can handle more events per iteration,	841	time collecting I/O events, so you can handle more events per iteration,
600	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	842	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
601	C<ev_timer>) will be not affected.	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.
602		847
603	Likewise, by setting a higher I<timeout collect interval> you allow libev	848	Likewise, by setting a higher I<timeout collect interval> you allow libev
604	to spend more time collecting timeouts, at the expense of increased	849	to spend more time collecting timeouts, at the expense of increased
605	latency (the watcher callback will be called later). C<ev_io> watchers	850	latency/jitter/inexactness (the watcher callback will be called
606	will not be affected.	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.
607		853
608	Many programs can usually benefit by setting the io collect interval to	854	Many (busy) programs can usually benefit by setting the I/O collect
609	a value near C<0.1> or so, which is often enough for interactive servers	855	interval to a value near C<0.1> or so, which is often enough for
610	(of course not for games), likewise for timeouts. It usually doesn't make	856	interactive servers (of course not for games), likewise for timeouts. It
611	much sense to set it to a lower value than C<0.01>, as this approsaches	857	usually doesn't make much sense to set it to a lower value than C<0.01>,
612	the timing granularity of most systems.	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.
613		953
614	=back	954	=back
615		955
616		956
617	=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.
618		962
619	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
620	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
621	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:
622		966
623	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)
624	{	968	{
625	ev_io_stop (w);	969	ev_io_stop (w);
626	ev_unloop (loop, EVUNLOOP_ALL);	970	ev_unloop (loop, EVUNLOOP_ALL);
627	}	971	}
628		972
629	struct ev_loop *loop = ev_default_loop (0);	973	struct ev_loop *loop = ev_default_loop (0);
		974
630	struct ev_io stdin_watcher;	975	ev_io stdin_watcher;
		976
631	ev_init (&stdin_watcher, my_cb);	977	ev_init (&stdin_watcher, my_cb);
632	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	978	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
633	ev_io_start (loop, &stdin_watcher);	979	ev_io_start (loop, &stdin_watcher);
		980
634	ev_loop (loop, 0);	981	ev_loop (loop, 0);
635		982
636	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
637	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
638	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).
639		989
640	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
641	(watcher *, callback)>, which expects a callback to be provided. This	991	(watcher *, callback)>, which expects a callback to be provided. This
642	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
643	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
644	is readable and/or writable).	994	is readable and/or writable).
645		995
646	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 *, ...) >>
647	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
648	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<<
649	(watcher *, callback, ...) >>.	999	ev_TYPE_init (watcher *, callback, ...) >>.
650		1000
651	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
652	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
653	*) >>), 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
654	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1004	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
655		1005
656	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
657	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
658	reinitialise it or call its C<set> macro.	1008	reinitialise it or call its C<ev_TYPE_set> macro.
659		1009
660	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
661	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
662	third argument.	1012	third argument.
663		1013
…		…
717	=item C<EV_FORK>	1067	=item C<EV_FORK>
718		1068
719	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
720	C<ev_fork>).	1070	C<ev_fork>).
721		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
722	=item C<EV_ERROR>	1081	=item C<EV_ERROR>
723		1082
724	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
725	happen because the watcher could not be properly started because libev	1084	happen because the watcher could not be properly started because libev
726	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
727	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
728	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.
729		1092
730	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
731	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
732	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
733	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
734	programs, though, so beware.	1097	programs, though, as the fd could already be closed and reused for another
		1098	thing, so beware.
735		1099
736	=back	1100	=back
737		1101
738	=head2 GENERIC WATCHER FUNCTIONS	1102	=head2 GENERIC WATCHER FUNCTIONS
739
740	In the following description, C<TYPE> stands for the watcher type,
741	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
742		1103
743	=over 4	1104	=over 4
744		1105
745	=item C<ev_init> (ev_TYPE *watcher, callback)	1106	=item C<ev_init> (ev_TYPE *watcher, callback)
746		1107
…		…
752	which rolls both calls into one.	1113	which rolls both calls into one.
753		1114
754	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
755	(or never started) and there are no pending events outstanding.	1116	(or never started) and there are no pending events outstanding.
756		1117
757	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,
758	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);
759		1126
760	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1127	=item C<ev_TYPE_set> (ev_TYPE *, [args])
761		1128
762	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
763	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
…		…
766	difference to the C<ev_init> macro).	1133	difference to the C<ev_init> macro).
767		1134
768	Although some watcher types do not have type-specific arguments	1135	Although some watcher types do not have type-specific arguments
769	(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.
770		1137
		1138	See C<ev_init>, above, for an example.
		1139
771	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1140	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
772		1141
773	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
774	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
775	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);
776		1149
777	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1150	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
778		1151
779	Starts (activates) the given watcher. Only active watchers will receive	1152	Starts (activates) the given watcher. Only active watchers will receive
780	events. If the watcher is already active nothing will happen.	1153	events. If the watcher is already active nothing will happen.
781		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
782	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1160	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
783		1161
784	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
785	status. It is possible that stopped watchers are pending (for example,	1165	It is possible that stopped watchers are pending - for example,
786	non-repeating timers are being stopped when they become pending), but	1166	non-repeating timers are being stopped when they become pending - but
787	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
788	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
789	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.
790		1170
791	=item bool ev_is_active (ev_TYPE *watcher)	1171	=item bool ev_is_active (ev_TYPE *watcher)
792		1172
793	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
794	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
…		…
820	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>
821	(default: C<-2>). Pending watchers with higher priority will be invoked	1201	(default: C<-2>). Pending watchers with higher priority will be invoked
822	before watchers with lower priority, but priority will not keep watchers	1202	before watchers with lower priority, but priority will not keep watchers
823	from being executed (except for C<ev_idle> watchers).	1203	from being executed (except for C<ev_idle> watchers).
824		1204
825	This means that priorities are I<only> used for ordering callback
826	invocation after new events have been received. This is useful, for
827	example, to reduce latency after idling, or more often, to bind two
828	watchers on the same event and make sure one is called first.
829
830	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
831	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.
832		1207
833	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
834	pending.	1209	pending.
835		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
836	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
837	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 :).
838		1217
839	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
840	fine, as long as you do not mind that the priority value you query might	1219	priorities.
841	or might not have been adjusted to be within valid range.
842		1220
843	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1221	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
844		1222
845	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
846	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
847	can deal with that fact.	1225	can deal with that fact, as both are simply passed through to the
		1226	callback.
848		1227
849	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1228	=item int ev_clear_pending (loop, ev_TYPE *watcher)
850		1229
851	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
852	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
853	watcher isn't pending it does nothing and returns C<0>.	1232	watcher isn't pending it does nothing and returns C<0>.
854		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
855	=back	1237	=back
856		1238
857		1239
858	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1240	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
859		1241
860	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
861	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
862	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
863	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
864	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
865	data:	1247	data:
866		1248
867	struct my_io	1249	struct my_io
868	{	1250	{
869	struct ev_io io;	1251	ev_io io;
870	int otherfd;	1252	int otherfd;
871	void *somedata;	1253	void *somedata;
872	struct whatever *mostinteresting;	1254	struct whatever *mostinteresting;
873	}	1255	};
		1256
		1257	...
		1258	struct my_io w;
		1259	ev_io_init (&w.io, my_cb, fd, EV_READ);
874		1260
875	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
876	can cast it back to your own type:	1262	can cast it back to your own type:
877		1263
878	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)
879	{	1265	{
880	struct my_io *w = (struct my_io *)w_;	1266	struct my_io *w = (struct my_io *)w_;
881	...	1267	...
882	}	1268	}
883		1269
884	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
885	instead have been omitted.	1271	instead have been omitted.
886		1272
887	Another common scenario is having some data structure with multiple	1273	Another common scenario is to use some data structure with multiple
888	watchers:	1274	embedded watchers:
889		1275
890	struct my_biggy	1276	struct my_biggy
891	{	1277	{
892	int some_data;	1278	int some_data;
893	ev_timer t1;	1279	ev_timer t1;
894	ev_timer t2;	1280	ev_timer t2;
895	}	1281	}
896		1282
897	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
898	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):
899		1288
900	#include <stddef.h>	1289	#include <stddef.h>
901		1290
902	static void	1291	static void
903	t1_cb (EV_P_ struct ev_timer *w, int revents)	1292	t1_cb (EV_P_ ev_timer *w, int revents)
904	{	1293	{
905	struct my_biggy big = (struct my_biggy *	1294	struct my_biggy big = (struct my_biggy *)
906	(((char *)w) - offsetof (struct my_biggy, t1));	1295	(((char *)w) - offsetof (struct my_biggy, t1));
907	}	1296	}
908		1297
909	static void	1298	static void
910	t2_cb (EV_P_ struct ev_timer *w, int revents)	1299	t2_cb (EV_P_ ev_timer *w, int revents)
911	{	1300	{
912	struct my_biggy big = (struct my_biggy *	1301	struct my_biggy big = (struct my_biggy *)
913	(((char *)w) - offsetof (struct my_biggy, t2));	1302	(((char *)w) - offsetof (struct my_biggy, t2));
914	}	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.
915		1407
916		1408
917	=head1 WATCHER TYPES	1409	=head1 WATCHER TYPES
918		1410
919	This section describes each watcher in detail, but will not repeat	1411	This section describes each watcher in detail, but will not repeat
…		…
943	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
944	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
945	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
946	required if you know what you are doing).	1438	required if you know what you are doing).
947		1439
948	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
949	(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
950	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
951	to the same underlying file/socket/etc. description (that is, they share	1443	descriptors for which non-blocking operation makes no sense (such as
952	the same underlying "file open").	1444	files) - libev doesn't guarentee any specific behaviour in that case.
953
954	If you must do this, then force the use of a known-to-be-good backend
955	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
956	C<EVBACKEND_POLL>).
957		1445
958	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
959	receive "spurious" readyness notifications, that is your callback might	1447	receive "spurious" readiness notifications, that is your callback might
960	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
961	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
962	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
963	this situation even with a relatively standard program structure. Thus	1451	this situation even with a relatively standard program structure. Thus
964	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
965	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.
966		1454
967	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
968	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
969	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
970	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
971	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.
972		1464
973	=head3 The special problem of disappearing file descriptors	1465	=head3 The special problem of disappearing file descriptors
974		1466
975	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1467	Some backends (e.g. kqueue, epoll) need to be told about closing a file
976	descriptor (either by calling C<close> explicitly or by any other means,	1468	descriptor (either due to calling C<close> explicitly or any other means,
977	such as C<dup>). The reason is that you register interest in some file	1469	such as C<dup2>). The reason is that you register interest in some file
978	descriptor, but when it goes away, the operating system will silently drop	1470	descriptor, but when it goes away, the operating system will silently drop
979	this interest. If another file descriptor with the same number then is	1471	this interest. If another file descriptor with the same number then is
980	registered with libev, there is no efficient way to see that this is, in	1472	registered with libev, there is no efficient way to see that this is, in
981	fact, a different file descriptor.	1473	fact, a different file descriptor.
982		1474
…		…
992	optimisations to libev.	1484	optimisations to libev.
993		1485
994	=head3 The special problem of dup'ed file descriptors	1486	=head3 The special problem of dup'ed file descriptors
995		1487
996	Some backends (e.g. epoll), cannot register events for file descriptors,	1488	Some backends (e.g. epoll), cannot register events for file descriptors,
997	but only events for the underlying file descriptions. That menas when you	1489	but only events for the underlying file descriptions. That means when you
998	have C<dup ()>'ed file descriptors and register events for them, only one	1490	have C<dup ()>'ed file descriptors or weirder constellations, and register
999	file descriptor might actually receive events.	1491	events for them, only one file descriptor might actually receive events.
1000		1492
1001	There is no workaorund possible except not registering events	1493	There is no workaround possible except not registering events
1002	for potentially C<dup ()>'ed file descriptors or to resort to	1494	for potentially C<dup ()>'ed file descriptors, or to resort to
1003	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1495	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1004		1496
1005	=head3 The special problem of fork	1497	=head3 The special problem of fork
1006		1498
1007	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1499	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
…		…
1011	To support fork in your programs, you either have to call	1503	To support fork in your programs, you either have to call
1012	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1504	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1013	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1505	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1014	C<EVBACKEND_POLL>.	1506	C<EVBACKEND_POLL>.
1015		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
1016		1519
1017	=head3 Watcher-Specific Functions	1520	=head3 Watcher-Specific Functions
1018		1521
1019	=over 4	1522	=over 4
1020		1523
1021	=item ev_io_init (ev_io *, callback, int fd, int events)	1524	=item ev_io_init (ev_io *, callback, int fd, int events)
1022		1525
1023	=item ev_io_set (ev_io *, int fd, int events)	1526	=item ev_io_set (ev_io *, int fd, int events)
1024		1527
1025	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
1026	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
1027	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.
1028		1531
1029	=item int fd [read-only]	1532	=item int fd [read-only]
1030		1533
1031	The file descriptor being watched.	1534	The file descriptor being watched.
1032		1535
1033	=item int events [read-only]	1536	=item int events [read-only]
1034		1537
1035	The events being watched.	1538	The events being watched.
1036		1539
1037	=back	1540	=back
		1541
		1542	=head3 Examples
1038		1543
1039	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
1040	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
1041	attempt to read a whole line in the callback.	1546	attempt to read a whole line in the callback.
1042		1547
1043	static void	1548	static void
1044	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)
1045	{	1550	{
1046	ev_io_stop (loop, w);	1551	ev_io_stop (loop, w);
1047	.. 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
1048	}	1553	}
1049		1554
1050	...	1555	...
1051	struct ev_loop *loop = ev_default_init (0);	1556	struct ev_loop *loop = ev_default_init (0);
1052	struct ev_io stdin_readable;	1557	ev_io stdin_readable;
1053	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);
1054	ev_io_start (loop, &stdin_readable);	1559	ev_io_start (loop, &stdin_readable);
1055	ev_loop (loop, 0);	1560	ev_loop (loop, 0);
1056		1561
1057		1562
1058	=head2 C<ev_timer> - relative and optionally repeating timeouts	1563	=head2 C<ev_timer> - relative and optionally repeating timeouts
1059		1564
1060	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
1061	given time, and optionally repeating in regular intervals after that.	1566	given time, and optionally repeating in regular intervals after that.
1062		1567
1063	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
1064	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
1065	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
1066	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1571	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1067	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.
1068		1763
1069	The relative timeouts are calculated relative to the C<ev_now ()>	1764	The relative timeouts are calculated relative to the C<ev_now ()>
1070	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
1071	of the event triggering whatever timeout you are modifying/starting. If	1766	of the event triggering whatever timeout you are modifying/starting. If
1072	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
1073	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:
1074		1769
1075	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1770	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1076		1771
1077	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
1078	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
1079	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>).
1080		1805
1081	=head3 Watcher-Specific Functions and Data Members	1806	=head3 Watcher-Specific Functions and Data Members
1082		1807
1083	=over 4	1808	=over 4
1084		1809
1085	=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)
1086		1811
1087	=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)
1088		1813
1089	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>
1090	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
1091	timer will automatically be configured to trigger again C<repeat> seconds	1816	reached. If it is positive, then the timer will automatically be
1092	later, again, and again, until stopped manually.	1817	configured to trigger again C<repeat> seconds later, again, and again,
		1818	until stopped manually.
1093		1819
1094	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
1095	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
1096	exactly 10 second intervals. If, however, your program cannot keep up with	1822	trigger at exactly 10 second intervals. If, however, your program cannot
1097	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
1098	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.
1099		1825
1100	=item ev_timer_again (loop)	1826	=item ev_timer_again (loop, ev_timer *)
1101		1827
1102	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
1103	repeating. The exact semantics are:	1829	repeating. The exact semantics are:
1104		1830
1105	If the timer is pending, its pending status is cleared.	1831	If the timer is pending, its pending status is cleared.
1106		1832
1107	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).
1108		1834
1109	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
1110	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.
1111		1837
1112	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
1113	example: Imagine you have a tcp connection and you want a so-called idle	1839	usage example.
1114	timeout, that is, you want to be called when there have been, say, 60
1115	seconds of inactivity on the socket. The easiest way to do this is to
1116	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1117	C<ev_timer_again> each time you successfully read or write some data. If
1118	you go into an idle state where you do not expect data to travel on the
1119	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1120	automatically restart it if need be.
1121		1840
1122	That means you can ignore the C<after> value and C<ev_timer_start>	1841	=item ev_timer_remaining (loop, ev_timer *)
1123	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1124		1842
1125	ev_timer_init (timer, callback, 0., 5.);	1843	Returns the remaining time until a timer fires. If the timer is active,
1126	ev_timer_again (loop, timer);	1844	then this time is relative to the current event loop time, otherwise it's
1127	...	1845	the timeout value currently configured.
1128	timer->again = 17.;
1129	ev_timer_again (loop, timer);
1130	...
1131	timer->again = 10.;
1132	ev_timer_again (loop, timer);
1133		1846
1134	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
1135	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.
1136		1852
1137	=item ev_tstamp repeat [read-write]	1853	=item ev_tstamp repeat [read-write]
1138		1854
1139	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
1140	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),
1141	which is also when any modifications are taken into account.	1857	which is also when any modifications are taken into account.
1142		1858
1143	=back	1859	=back
1144		1860
		1861	=head3 Examples
		1862
1145	Example: Create a timer that fires after 60 seconds.	1863	Example: Create a timer that fires after 60 seconds.
1146		1864
1147	static void	1865	static void
1148	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)
1149	{	1867	{
1150	.. one minute over, w is actually stopped right here	1868	.. one minute over, w is actually stopped right here
1151	}	1869	}
1152		1870
1153	struct ev_timer mytimer;	1871	ev_timer mytimer;
1154	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1872	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1155	ev_timer_start (loop, &mytimer);	1873	ev_timer_start (loop, &mytimer);
1156		1874
1157	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
1158	inactivity.	1876	inactivity.
1159		1877
1160	static void	1878	static void
1161	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1879	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1162	{	1880	{
1163	.. ten seconds without any activity	1881	.. ten seconds without any activity
1164	}	1882	}
1165		1883
1166	struct ev_timer mytimer;	1884	ev_timer mytimer;
1167	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 */
1168	ev_timer_again (&mytimer); /* start timer */	1886	ev_timer_again (&mytimer); /* start timer */
1169	ev_loop (loop, 0);	1887	ev_loop (loop, 0);
1170		1888
1171	// 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":
1172	// reset the timeout to start ticking again at 10 seconds	1890	// reset the timeout to start ticking again at 10 seconds
1173	ev_timer_again (&mytimer);	1891	ev_timer_again (&mytimer);
1174		1892
1175		1893
1176	=head2 C<ev_periodic> - to cron or not to cron?	1894	=head2 C<ev_periodic> - to cron or not to cron?
1177		1895
1178	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
1179	(and unfortunately a bit complex).	1897	(and unfortunately a bit complex).
1180		1898
1181	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
1182	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
1183	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
1184	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
1185	+ 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
1186	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1904	wrist-watch).
1187	roughly 10 seconds later).
1188		1905
1189	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
1190	triggering an event on each midnight, local time or other, complicated,	1907	in time: for example, if you tell a periodic watcher to trigger "in 10
1191	rules.	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).
1192		1913
		1914	C<ev_periodic> watchers can also be used to implement vastly more complex
		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.
		1918
1193	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
1194	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
1195	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).
1196		1924
1197	=head3 Watcher-Specific Functions and Data Members	1925	=head3 Watcher-Specific Functions and Data Members
1198		1926
1199	=over 4	1927	=over 4
1200		1928
1201	=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)
1202		1930
1203	=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)
1204		1932
1205	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
1206	operation, and we will explain them from simplest to complex:	1934	operation, and we will explain them from simplest to most complex:
1207		1935
1208	=over 4	1936	=over 4
1209		1937
1210	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1938	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1211		1939
1212	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
1213	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
1214	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
1215	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.
1216		1945
1217	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1946	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1218		1947
1219	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
1220	C<at + N * interval> time (for some integer N, which can also be negative)	1949	C<offset + N * interval> time (for some integer N, which can also be
1221	and then repeat, regardless 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.
1222		1952
1223	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
1224	time:	1954	system clock, for example, here is an C<ev_periodic> that triggers each
		1955	hour, on the hour (with respect to UTC):
1225		1956
1226	ev_periodic_set (&periodic, 0., 3600., 0);	1957	ev_periodic_set (&periodic, 0., 3600., 0);
1227		1958
1228	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,
1229	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
1230	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
1231	by 3600.	1962	by 3600.
1232		1963
1233	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
1234	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
1235	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.
1236		1967
1237	For numerical stability it is preferable that the C<at> value is near	1968	For numerical stability it is preferable that the C<offset> value is near
1238	C<ev_now ()> (the current time), but there is no range requirement for	1969	C<ev_now ()> (the current time), but there is no range requirement for
1239	this value.	1970	this value, and in fact is often specified as zero.
1240		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
1241	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1977	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1242		1978
1243	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
1244	ignored. Instead, each time the periodic watcher gets scheduled, the	1980	ignored. Instead, each time the periodic watcher gets scheduled, the
1245	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
1246	current time as second argument.	1982	current time as second argument.
1247		1983
1248	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,
1249	ever, or make any event loop modifications>. If you need to stop it,	1985	or make ANY other event loop modifications whatsoever, unless explicitly
1250	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1986	allowed by documentation here>.
1251	starting an C<ev_prepare> watcher, which is legal).
1252		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
1253	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1992	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1254	ev_tstamp now)>, e.g.:	1993	*w, ev_tstamp now)>, e.g.:
1255		1994
		1995	static ev_tstamp
1256	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1996	my_rescheduler (ev_periodic *w, ev_tstamp now)
1257	{	1997	{
1258	return now + 60.;	1998	return now + 60.;
1259	}	1999	}
1260		2000
1261	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
1262	(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
1263	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
1264	might be called at other times, too.	2004	might be called at other times, too.
1265		2005
1266	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
1267	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2007	equal to the passed C<now> value >>.
1268		2008
1269	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
1270	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
1271	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
1272	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
1273	reason I omitted it as an example).	2013	reason I omitted it as an example).
1274		2014
1275	=back	2015	=back
…		…
1279	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
1280	when you changed some parameters or the reschedule callback would return	2020	when you changed some parameters or the reschedule callback would return
1281	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
1282	program when the crontabs have changed).	2022	program when the crontabs have changed).
1283		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
1284	=item ev_tstamp offset [read-write]	2031	=item ev_tstamp offset [read-write]
1285		2032
1286	When repeating, this contains the offset value, otherwise this is the	2033	When repeating, this contains the offset value, otherwise this is the
1287	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	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).
1288		2036
1289	Can be modified any time, but changes only take effect when the periodic	2037	Can be modified any time, but changes only take effect when the periodic
1290	timer fires or C<ev_periodic_again> is being called.	2038	timer fires or C<ev_periodic_again> is being called.
1291		2039
1292	=item ev_tstamp interval [read-write]	2040	=item ev_tstamp interval [read-write]
1293		2041
1294	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
1295	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
1296	called.	2044	called.
1297		2045
1298	=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]
1299		2047
1300	The current reschedule callback, or C<0>, if this functionality is	2048	The current reschedule callback, or C<0>, if this functionality is
1301	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
1302	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.
1303		2051
1304	=item ev_tstamp at [read-only]
1305
1306	When active, contains the absolute time that the watcher is supposed to
1307	trigger next.
1308
1309	=back	2052	=back
1310		2053
		2054	=head3 Examples
		2055
1311	Example: Call a callback every hour, or, more precisely, whenever the	2056	Example: Call a callback every hour, or, more precisely, whenever the
1312	system clock is divisible by 3600. The callback invocation times have	2057	system time is divisible by 3600. The callback invocation times have
1313	potentially a lot of jittering, but good long-term stability.	2058	potentially a lot of jitter, but good long-term stability.
1314		2059
1315	static void	2060	static void
1316	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2061	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1317	{	2062	{
1318	... 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)
1319	}	2064	}
1320		2065
1321	struct ev_periodic hourly_tick;	2066	ev_periodic hourly_tick;
1322	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2067	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1323	ev_periodic_start (loop, &hourly_tick);	2068	ev_periodic_start (loop, &hourly_tick);
1324		2069
1325	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:
1326		2071
1327	#include <math.h>	2072	#include <math.h>
1328		2073
1329	static ev_tstamp	2074	static ev_tstamp
1330	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2075	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1331	{	2076	{
1332	return fmod (now, 3600.) + 3600.;	2077	return now + (3600. - fmod (now, 3600.));
1333	}	2078	}
1334		2079
1335	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);
1336		2081
1337	Example: Call a callback every hour, starting now:	2082	Example: Call a callback every hour, starting now:
1338		2083
1339	struct ev_periodic hourly_tick;	2084	ev_periodic hourly_tick;
1340	ev_periodic_init (&hourly_tick, clock_cb,	2085	ev_periodic_init (&hourly_tick, clock_cb,
1341	fmod (ev_now (loop), 3600.), 3600., 0);	2086	fmod (ev_now (loop), 3600.), 3600., 0);
1342	ev_periodic_start (loop, &hourly_tick);	2087	ev_periodic_start (loop, &hourly_tick);
1343		2088
1344		2089
1345	=head2 C<ev_signal> - signal me when a signal gets signalled!	2090	=head2 C<ev_signal> - signal me when a signal gets signalled!
1346		2091
1347	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
1348	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
1349	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
1350	normal event processing, like any other event.	2095	normal event processing, like any other event.
1351		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
1352	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
1353	first watcher gets started will libev actually register a signal watcher	2108	When the first watcher gets started will libev actually register something
1354	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
1355	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).
1356	watcher for a signal is stopped libev will reset the signal handler to	2111
1357	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.
1358		2122
1359	=head3 Watcher-Specific Functions and Data Members	2123	=head3 Watcher-Specific Functions and Data Members
1360		2124
1361	=over 4	2125	=over 4
1362		2126
…		…
1371		2135
1372	The signal the watcher watches out for.	2136	The signal the watcher watches out for.
1373		2137
1374	=back	2138	=back
1375		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
1376		2154
1377	=head2 C<ev_child> - watch out for process status changes	2155	=head2 C<ev_child> - watch out for process status changes
1378		2156
1379	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
1380	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).
1381		2199
1382	=head3 Watcher-Specific Functions and Data Members	2200	=head3 Watcher-Specific Functions and Data Members
1383		2201
1384	=over 4	2202	=over 4
1385		2203
1386	=item ev_child_init (ev_child *, callback, int pid)	2204	=item ev_child_init (ev_child *, callback, int pid, int trace)
1387		2205
1388	=item ev_child_set (ev_child *, int pid)	2206	=item ev_child_set (ev_child *, int pid, int trace)
1389		2207
1390	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
1391	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
1392	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
1393	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
1394	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
1395	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).
1396		2216
1397	=item int pid [read-only]	2217	=item int pid [read-only]
1398		2218
1399	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.
1400		2220
…		…
1407	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
1408	C<waitpid> and C<sys/wait.h> documentation for details).	2228	C<waitpid> and C<sys/wait.h> documentation for details).
1409		2229
1410	=back	2230	=back
1411		2231
1412	Example: Try to exit cleanly on SIGINT and SIGTERM.	2232	=head3 Examples
1413		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
1414	static void	2239	static void
1415	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2240	child_cb (EV_P_ ev_child *w, int revents)
1416	{	2241	{
1417	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);
1418	}	2244	}
1419		2245
1420	struct ev_signal signal_watcher;	2246	pid_t pid = fork ();
1421	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2247
1422	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	}
1423		2260
1424		2261
1425	=head2 C<ev_stat> - did the file attributes just change?	2262	=head2 C<ev_stat> - did the file attributes just change?
1426		2263
1427	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
1428	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)
1429	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.
1430		2268
1431	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
1432	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
1433	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
1434	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
1435	the stat buffer having unspecified contents.	2273	least one) and all the other fields of the stat buffer having unspecified
		2274	contents.
1436		2275
1437	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
1438	relative and your working directory changes, the behaviour is undefined.	2278	your working directory changes, then the behaviour is undefined.
1439		2279
1440	Since there is no standard to do this, the portable implementation simply	2280	Since there is no portable change notification interface available, the
1441	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
1442	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
1443	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
1444	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
1445	five seconds, although this might change dynamically). Libev will also	2285	(which you can expect to be around five seconds, although this might
1446	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
1447	usually overkill.	2287	currently around C<0.1>, but that's usually overkill.
1448		2288
1449	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,
1450	as even with OS-supported change notifications, this can be	2290	as even with OS-supported change notifications, this can be
1451	resource-intensive.	2291	resource-intensive.
1452		2292
1453	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
1454	implemented (implementing kqueue support is left as an exercise for the	2294	is the Linux inotify interface (implementing kqueue support is left as an
1455	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
1456	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2296	implementing C<ev_stat> semantics with kqueue, except as a hint).
1457	to fall back to regular polling again even with inotify, but changes are	2297
1458	usually detected immediately, and if the file exists there will be no	2298	=head3 ABI Issues (Largefile Support)
1459	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).
1460		2379
1461	=head3 Watcher-Specific Functions and Data Members	2380	=head3 Watcher-Specific Functions and Data Members
1462		2381
1463	=over 4	2382	=over 4
1464		2383
…		…
1470	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
1471	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
1472	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
1473	path for as long as the watcher is active.	2392	path for as long as the watcher is active.
1474		2393
1475	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,
1476	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
1477	last change was detected).	2396	last change was detected).
1478		2397
1479	=item ev_stat_stat (ev_stat *)	2398	=item ev_stat_stat (loop, ev_stat *)
1480		2399
1481	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
1482	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
1483	detecting this change (while introducing a race condition). Can also be	2402	detecting this change (while introducing a race condition if you are not
1484	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.
1485		2405
1486	=item ev_statdata attr [read-only]	2406	=item ev_statdata attr [read-only]
1487		2407
1488	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
1489	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
1490	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
1491	was some error while C<stat>ing the file.	2412	some error while C<stat>ing the file.
1492		2413
1493	=item ev_statdata prev [read-only]	2414	=item ev_statdata prev [read-only]
1494		2415
1495	The previous attributes of the file. The callback gets invoked whenever	2416	The previous attributes of the file. The callback gets invoked whenever
1496	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>.
1497		2420
1498	=item ev_tstamp interval [read-only]	2421	=item ev_tstamp interval [read-only]
1499		2422
1500	The specified interval.	2423	The specified interval.
1501		2424
1502	=item const char *path [read-only]	2425	=item const char *path [read-only]
1503		2426
1504	The filesystem path that is being watched.	2427	The file system path that is being watched.
1505		2428
1506	=back	2429	=back
1507		2430
		2431	=head3 Examples
		2432
1508	Example: Watch C</etc/passwd> for attribute changes.	2433	Example: Watch C</etc/passwd> for attribute changes.
1509		2434
1510	static void	2435	static void
1511	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2436	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1512	{	2437	{
1513	/* /etc/passwd changed in some way */	2438	/* /etc/passwd changed in some way */
1514	if (w->attr.st_nlink)	2439	if (w->attr.st_nlink)
1515	{	2440	{
1516	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2441	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1517	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2442	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1518	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2443	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1519	}	2444	}
1520	else	2445	else
1521	/* you shalt not abuse printf for puts */	2446	/* you shalt not abuse printf for puts */
1522	puts ("wow, /etc/passwd is not there, expect problems. "	2447	puts ("wow, /etc/passwd is not there, expect problems. "
1523	"if this is windows, they already arrived\n");	2448	"if this is windows, they already arrived\n");
1524	}	2449	}
1525		2450
1526	...	2451	...
1527	ev_stat passwd;	2452	ev_stat passwd;
1528		2453
1529	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2454	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1530	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);
1531		2484
1532		2485
1533	=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...
1534		2487
1535	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
1536	priority are pending (prepare, check and other idle watchers do not	2489	priority are pending (prepare, check and other idle watchers do not count
1537	count).	2490	as receiving "events").
1538		2491
1539	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
1540	(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
1541	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
1542	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
…		…
1553		2506
1554	=head3 Watcher-Specific Functions and Data Members	2507	=head3 Watcher-Specific Functions and Data Members
1555		2508
1556	=over 4	2509	=over 4
1557		2510
1558	=item ev_idle_init (ev_signal *, callback)	2511	=item ev_idle_init (ev_idle *, callback)
1559		2512
1560	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
1561	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,
1562	believe me.	2515	believe me.
1563		2516
1564	=back	2517	=back
1565		2518
		2519	=head3 Examples
		2520
1566	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
1567	callback, free it. Also, use no error checking, as usual.	2522	callback, free it. Also, use no error checking, as usual.
1568		2523
1569	static void	2524	static void
1570	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2525	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1571	{	2526	{
1572	free (w);	2527	free (w);
1573	// now do something you wanted to do when the program has	2528	// now do something you wanted to do when the program has
1574	// no longer asnything immediate to do.	2529	// no longer anything immediate to do.
1575	}	2530	}
1576		2531
1577	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2532	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1578	ev_idle_init (idle_watcher, idle_cb);	2533	ev_idle_init (idle_watcher, idle_cb);
1579	ev_idle_start (loop, idle_cb);	2534	ev_idle_start (loop, idle_watcher);
1580		2535
1581		2536
1582	=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!
1583		2538
1584	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:
1585	prepare watchers get invoked before the process blocks and check watchers	2540	prepare watchers get invoked before the process blocks and check watchers
1586	afterwards.	2541	afterwards.
1587		2542
1588	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
1589	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>
…		…
1592	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,
1593	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
1594	called in pairs bracketing the blocking call.	2549	called in pairs bracketing the blocking call.
1595		2550
1596	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
1597	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
1598	variable changes, implement your own watchers, integrate net-snmp or a	2553	variable changes, implement your own watchers, integrate net-snmp or a
1599	coroutine library and lots more. They are also occasionally useful if	2554	coroutine library and lots more. They are also occasionally useful if
1600	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,
1601	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>
1602	watcher).	2557	watcher).
1603		2558
1604	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
1605	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
1606	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
1607	provide just this functionality). Then, in the check watcher you check for	2562	libraries provide exactly this functionality). Then, in the check watcher,
1608	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
1609	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
1610	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
1611	because you never know, you know?).	2566	nevertheless, because you never know, you know?).
1612		2567
1613	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
1614	coroutines into libev programs, by yielding to other active coroutines	2569	coroutines into libev programs, by yielding to other active coroutines
1615	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
1616	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
…		…
1619	loop from blocking if lower-priority coroutines are active, thus mapping	2574	loop from blocking if lower-priority coroutines are active, thus mapping
1620	low-priority coroutines to idle/background tasks).	2575	low-priority coroutines to idle/background tasks).
1621		2576
1622	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2577	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1623	priority, to ensure that they are being run before any other watchers	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
1624	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2581	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1625	too) should not activate ("feed") events into libev. While libev fully	2582	activate ("feed") events into libev. While libev fully supports this, they
1626	supports this, they will be called before other C<ev_check> watchers did	2583	might get executed before other C<ev_check> watchers did their job. As
1627	their job. As C<ev_check> watchers are often used to embed other event	2584	C<ev_check> watchers are often used to embed other (non-libev) event
1628	loops those other event loops might be in an unusable state until their	2585	loops those other event loops might be in an unusable state until their
1629	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2586	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1630	others).	2587	others).
1631		2588
1632	=head3 Watcher-Specific Functions and Data Members	2589	=head3 Watcher-Specific Functions and Data Members
…		…
1637		2594
1638	=item ev_check_init (ev_check *, callback)	2595	=item ev_check_init (ev_check *, callback)
1639		2596
1640	Initialises and configures the prepare or check watcher - they have no	2597	Initialises and configures the prepare or check watcher - they have no
1641	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>
1642	macros, but using them is utterly, utterly and completely pointless.	2599	macros, but using them is utterly, utterly, utterly and completely
		2600	pointless.
1643		2601
1644	=back	2602	=back
		2603
		2604	=head3 Examples
1645		2605
1646	There are a number of principal ways to embed other event loops or modules	2606	There are a number of principal ways to embed other event loops or modules
1647	into libev. Here are some ideas on how to include libadns into libev	2607	into libev. Here are some ideas on how to include libadns into libev
1648	(there is a Perl module named C<EV::ADNS> that does this, which you could	2608	(there is a Perl module named C<EV::ADNS> that does this, which you could
1649	use for an actually working example. Another Perl module named C<EV::Glib>	2609	use as a working example. Another Perl module named C<EV::Glib> embeds a
1650	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2610	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1651	into the Glib event loop).	2611	Glib event loop).
1652		2612
1653	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2613	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1654	and in a check watcher, destroy them and call into libadns. What follows	2614	and in a check watcher, destroy them and call into libadns. What follows
1655	is pseudo-code only of course. This requires you to either use a low	2615	is pseudo-code only of course. This requires you to either use a low
1656	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2616	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1657	the callbacks for the IO/timeout watchers might not have been called yet.	2617	the callbacks for the IO/timeout watchers might not have been called yet.
1658		2618
1659	static ev_io iow [nfd];	2619	static ev_io iow [nfd];
1660	static ev_timer tw;	2620	static ev_timer tw;
1661		2621
1662	static void	2622	static void
1663	io_cb (ev_loop *loop, ev_io *w, int revents)	2623	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1664	{	2624	{
1665	}	2625	}
1666		2626
1667	// create io watchers for each fd and a timer before blocking	2627	// create io watchers for each fd and a timer before blocking
1668	static void	2628	static void
1669	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2629	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1670	{	2630	{
1671	int timeout = 3600000;	2631	int timeout = 3600000;
1672	struct pollfd fds [nfd];	2632	struct pollfd fds [nfd];
1673	// actual code will need to loop here and realloc etc.	2633	// actual code will need to loop here and realloc etc.
1674	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2634	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1675		2635
1676	/* 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 */
1677	ev_timer_init (&tw, 0, timeout * 1e-3);	2637	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1678	ev_timer_start (loop, &tw);	2638	ev_timer_start (loop, &tw);
1679		2639
1680	// create one ev_io per pollfd	2640	// create one ev_io per pollfd
1681	for (int i = 0; i < nfd; ++i)	2641	for (int i = 0; i < nfd; ++i)
1682	{	2642	{
1683	ev_io_init (iow + i, io_cb, fds [i].fd,	2643	ev_io_init (iow + i, io_cb, fds [i].fd,
1684	((fds [i].events & POLLIN ? EV_READ : 0)	2644	((fds [i].events & POLLIN ? EV_READ : 0)
1685	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2645	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1686		2646
1687	fds [i].revents = 0;	2647	fds [i].revents = 0;
1688	ev_io_start (loop, iow + i);	2648	ev_io_start (loop, iow + i);
1689	}	2649	}
1690	}	2650	}
1691		2651
1692	// stop all watchers after blocking	2652	// stop all watchers after blocking
1693	static void	2653	static void
1694	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2654	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1695	{	2655	{
1696	ev_timer_stop (loop, &tw);	2656	ev_timer_stop (loop, &tw);
1697		2657
1698	for (int i = 0; i < nfd; ++i)	2658	for (int i = 0; i < nfd; ++i)
1699	{	2659	{
1700	// set the relevant poll flags	2660	// set the relevant poll flags
1701	// could also call adns_processreadable etc. here	2661	// could also call adns_processreadable etc. here
1702	struct pollfd *fd = fds + i;	2662	struct pollfd *fd = fds + i;
1703	int revents = ev_clear_pending (iow + i);	2663	int revents = ev_clear_pending (iow + i);
1704	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2664	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1705	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2665	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1706		2666
1707	// now stop the watcher	2667	// now stop the watcher
1708	ev_io_stop (loop, iow + i);	2668	ev_io_stop (loop, iow + i);
1709	}	2669	}
1710		2670
1711	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2671	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1712	}	2672	}
1713		2673
1714	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2674	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1715	in the prepare watcher and would dispose of the check watcher.	2675	in the prepare watcher and would dispose of the check watcher.
1716		2676
1717	Method 3: If the module to be embedded supports explicit event	2677	Method 3: If the module to be embedded supports explicit event
1718	notification (adns does), you can also make use of the actual watcher	2678	notification (libadns does), you can also make use of the actual watcher
1719	callbacks, and only destroy/create the watchers in the prepare watcher.	2679	callbacks, and only destroy/create the watchers in the prepare watcher.
1720		2680
1721	static void	2681	static void
1722	timer_cb (EV_P_ ev_timer *w, int revents)	2682	timer_cb (EV_P_ ev_timer *w, int revents)
1723	{	2683	{
1724	adns_state ads = (adns_state)w->data;	2684	adns_state ads = (adns_state)w->data;
1725	update_now (EV_A);	2685	update_now (EV_A);
1726		2686
1727	adns_processtimeouts (ads, &tv_now);	2687	adns_processtimeouts (ads, &tv_now);
1728	}	2688	}
1729		2689
1730	static void	2690	static void
1731	io_cb (EV_P_ ev_io *w, int revents)	2691	io_cb (EV_P_ ev_io *w, int revents)
1732	{	2692	{
1733	adns_state ads = (adns_state)w->data;	2693	adns_state ads = (adns_state)w->data;
1734	update_now (EV_A);	2694	update_now (EV_A);
1735		2695
1736	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2696	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1737	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2697	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1738	}	2698	}
1739		2699
1740	// do not ever call adns_afterpoll	2700	// do not ever call adns_afterpoll
1741		2701
1742	Method 4: Do not use a prepare or check watcher because the module you	2702	Method 4: Do not use a prepare or check watcher because the module you
1743	want to embed is too inflexible to support it. Instead, youc na override	2703	want to embed is not flexible enough to support it. Instead, you can
1744	their poll function. The drawback with this solution is that the main	2704	override their poll function. The drawback with this solution is that the
1745	loop is now no longer controllable by EV. The C<Glib::EV> module does	2705	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1746	this.	2706	this approach, effectively embedding EV as a client into the horrible
		2707	libglib event loop.
1747		2708
1748	static gint	2709	static gint
1749	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2710	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1750	{	2711	{
1751	int got_events = 0;	2712	int got_events = 0;
1752		2713
1753	for (n = 0; n < nfds; ++n)	2714	for (n = 0; n < nfds; ++n)
1754	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2715	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1755		2716
1756	if (timeout >= 0)	2717	if (timeout >= 0)
1757	// create/start timer	2718	// create/start timer
1758		2719
1759	// poll	2720	// poll
1760	ev_loop (EV_A_ 0);	2721	ev_loop (EV_A_ 0);
1761		2722
1762	// stop timer again	2723	// stop timer again
1763	if (timeout >= 0)	2724	if (timeout >= 0)
1764	ev_timer_stop (EV_A_ &to);	2725	ev_timer_stop (EV_A_ &to);
1765		2726
1766	// stop io watchers again - their callbacks should have set	2727	// stop io watchers again - their callbacks should have set
1767	for (n = 0; n < nfds; ++n)	2728	for (n = 0; n < nfds; ++n)
1768	ev_io_stop (EV_A_ iow [n]);	2729	ev_io_stop (EV_A_ iow [n]);
1769		2730
1770	return got_events;	2731	return got_events;
1771	}	2732	}
1772		2733
1773		2734
1774	=head2 C<ev_embed> - when one backend isn't enough...	2735	=head2 C<ev_embed> - when one backend isn't enough...
1775		2736
1776	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
1777	into another (currently only C<ev_io> events are supported in the embedded	2738	into another (currently only C<ev_io> events are supported in the embedded
1778	loop, other types of watchers might be handled in a delayed or incorrect	2739	loop, other types of watchers might be handled in a delayed or incorrect
1779	fashion and must not be used). (See portability notes, below).	2740	fashion and must not be used).
1780		2741
1781	There are primarily two reasons you would want that: work around bugs and	2742	There are primarily two reasons you would want that: work around bugs and
1782	prioritise I/O.	2743	prioritise I/O.
1783		2744
1784	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
1785	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
1786	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
1787	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
1788	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
1789	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
1790	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 :)
1791		2753
1792	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
1793	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),
1794	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
1795	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
1796	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.
1797		2759
1798	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
1799	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
1800	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
1801	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
1802	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
1803	to C<0>, in which case the embed watcher will automatically execute the	2765	to give the embedded loop strictly lower priority for example).
1804	embedded loop sweep.
1805		2766
1806	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
1807	callback will be invoked whenever some events have been handled. You can	2768	will automatically execute the embedded loop sweep whenever necessary.
1808	set the callback to C<0> to avoid having to specify one if you are not
1809	interested in that.
1810		2769
1811	Also, there have not currently been made special provisions for forking:	2770	Fork detection will be handled transparently while the C<ev_embed> watcher
1812	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
1813	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
1814	yourself.	2773	C<ev_loop_fork> on the embedded loop.
1815		2774
1816	Unfortunately, not all backends are embeddable, only the ones returned by	2775	Unfortunately, not all backends are embeddable: only the ones returned by
1817	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2776	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1818	portable one.	2777	portable one.
1819		2778
1820	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
1821	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
1822	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
1823	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.
1824		2783
1825	struct ev_loop *loop_hi = ev_default_init (0);	2784	=head3 C<ev_embed> and fork
1826	struct ev_loop *loop_lo = 0;
1827	struct ev_embed embed;
1828
1829	// see if there is a chance of getting one that works
1830	// (remember that a flags value of 0 means autodetection)
1831	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1832	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1833	: 0;
1834		2785
1835	// 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
1836	if (loop_lo)	2787	automatically be applied to the embedded loop as well, so no special
1837	{	2788	fork handling is required in that case. When the watcher is not running,
1838	ev_embed_init (&embed, 0, loop_lo);	2789	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1839	ev_embed_start (loop_hi, &embed);	2790	as applicable.
1840	}
1841	else
1842	loop_lo = loop_hi;
1843
1844	=head2 Portability notes
1845
1846	Kqueue is nominally embeddable, but this is broken on all BSDs that I
1847	tried, in various ways. Usually the embedded event loop will simply never
1848	receive events, sometimes it will only trigger a few times, sometimes in a
1849	loop. Epoll is also nominally embeddable, but many Linux kernel versions
1850	will always eport the epoll fd as ready, even when no events are pending.
1851
1852	While libev allows embedding these backends (they are contained in
1853	C<ev_embeddable_backends ()>), take extreme care that it will actually
1854	work.
1855
1856	When in doubt, create a dynamic event loop forced to use sockets (this
1857	usually works) and possibly another thread and a pipe or so to report to
1858	your main event loop.
1859		2791
1860	=head3 Watcher-Specific Functions and Data Members	2792	=head3 Watcher-Specific Functions and Data Members
1861		2793
1862	=over 4	2794	=over 4
1863		2795
…		…
1867		2799
1868	Configures the watcher to embed the given loop, which must be	2800	Configures the watcher to embed the given loop, which must be
1869	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
1870	invoked automatically, otherwise it is the responsibility of the callback	2802	invoked automatically, otherwise it is the responsibility of the callback
1871	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,
1872	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).
1873		2805
1874	=item ev_embed_sweep (loop, ev_embed *)	2806	=item ev_embed_sweep (loop, ev_embed *)
1875		2807
1876	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
1877	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
1878	apropriate way for embedded loops.	2810	appropriate way for embedded loops.
1879		2811
1880	=item struct ev_loop *other [read-only]	2812	=item struct ev_loop *other [read-only]
1881		2813
1882	The embedded event loop.	2814	The embedded event loop.
1883		2815
1884	=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
1885		2865
1886		2866
1887	=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
1888		2868
1889	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
…		…
1892	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,
1893	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
1894	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
1895	handlers will be invoked, too, of course.	2875	handlers will be invoked, too, of course.
1896		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
1897	=head3 Watcher-Specific Functions and Data Members	2910	=head3 Watcher-Specific Functions and Data Members
1898		2911
1899	=over 4	2912	=over 4
1900		2913
1901	=item ev_fork_init (ev_signal *, callback)	2914	=item ev_fork_init (ev_signal *, callback)
…		…
1905	believe me.	2918	believe me.
1906		2919
1907	=back	2920	=back
1908		2921
1909		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
1910	=head1 OTHER FUNCTIONS	3075	=head1 OTHER FUNCTIONS
1911		3076
1912	There are some other functions of possible interest. Described. Here. Now.	3077	There are some other functions of possible interest. Described. Here. Now.
1913		3078
1914	=over 4	3079	=over 4
1915		3080
1916	=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)
1917		3082
1918	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
1919	callback on whichever event happens first and automatically stop both	3084	callback on whichever event happens first and automatically stops both
1920	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
1921	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
1922	more watchers yourself.	3087	more watchers yourself.
1923		3088
1924	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
1925	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
1926	C<events> set will be craeted and started.	3091	the given C<fd> and C<events> set will be created and started.
1927		3092
1928	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
1929	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
1930	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.
1931	dubious value.
1932		3096
1933	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
1934	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
1935	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>
1936	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.
1937		3103
		3104	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3105
1938	static void stdin_ready (int revents, void *arg)	3106	static void stdin_ready (int revents, void *arg)
1939	{	3107	{
1940	if (revents & EV_TIMEOUT)
1941	/* doh, nothing entered */;
1942	else if (revents & EV_READ)	3108	if (revents & EV_READ)
1943	/* 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 */;
1944	}	3112	}
1945		3113
1946	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3114	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1947		3115
1948	=item ev_feed_event (ev_loop *, watcher *, int revents)	3116	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1949		3117
1950	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
1951	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
1952	initialised but not necessarily started event watcher).	3120	initialised but not necessarily started event watcher).
1953		3121
1954	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3122	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1955		3123
1956	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
1957	the given events it.	3125	the given events it.
1958		3126
1959	=item ev_feed_signal_event (ev_loop *loop, int signum)	3127	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1960		3128
1961	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
1962	loop!).	3130	loop!).
1963		3131
1964	=back	3132	=back
1965		3133
1966		3134
…		…
1982		3150
1983	=item * Priorities are not currently supported. Initialising priorities	3151	=item * Priorities are not currently supported. Initialising priorities
1984	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
1985	is an ev_pri field.	3153	is an ev_pri field.
1986		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
1987	=item * Other members are not supported.	3158	=item * Other members are not supported.
1988		3159
1989	=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
1990	to use the libev header file and library.	3161	to use the libev header file and library.
1991		3162
1992	=back	3163	=back
1993		3164
1994	=head1 C++ SUPPORT	3165	=head1 C++ SUPPORT
1995		3166
1996	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
1997	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
1998	the callback model to a model using method callbacks on objects.	3169	the callback model to a model using method callbacks on objects.
1999		3170
2000	To use it,	3171	To use it,
2001		3172
2002	#include <ev++.h>	3173	#include <ev++.h>
2003		3174
2004	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
2005	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
2006	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
2007	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3178	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2074	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
2075	thunking function, making it as fast as a direct C callback.	3246	thunking function, making it as fast as a direct C callback.
2076		3247
2077	Example: simple class declaration and watcher initialisation	3248	Example: simple class declaration and watcher initialisation
2078		3249
2079	struct myclass	3250	struct myclass
2080	{	3251	{
2081	void io_cb (ev::io &w, int revents) { }	3252	void io_cb (ev::io &w, int revents) { }
2082	}	3253	}
2083		3254
2084	myclass obj;	3255	myclass obj;
2085	ev::io iow;	3256	ev::io iow;
2086	iow.set <myclass, &myclass::io_cb> (&obj);	3257	iow.set <myclass, &myclass::io_cb> (&obj);
		3258
		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);
2087		3288
2088	=item w->set<function> (void *data = 0)	3289	=item w->set<function> (void *data = 0)
2089		3290
2090	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
2091	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
…		…
2093		3294
2094	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3295	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2095		3296
2096	See the method-C<set> above for more details.	3297	See the method-C<set> above for more details.
2097		3298
2098	Example:	3299	Example: Use a plain function as callback.
2099		3300
2100	static void io_cb (ev::io &w, int revents) { }	3301	static void io_cb (ev::io &w, int revents) { }
2101	iow.set <io_cb> ();	3302	iow.set <io_cb> ();
2102		3303
2103	=item w->set (struct ev_loop *)	3304	=item w->set (struct ev_loop *)
2104		3305
2105	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
2106	do this when the watcher is inactive (and not pending either).	3307	do this when the watcher is inactive (and not pending either).
2107		3308
2108	=item w->set ([args])	3309	=item w->set ([arguments])
2109		3310
2110	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
2111	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
2112	automatically stopped and restarted when reconfiguring it with this	3313	automatically stopped and restarted when reconfiguring it with this
2113	method.	3314	method.
2114		3315
2115	=item w->start ()	3316	=item w->start ()
…		…
2139	=back	3340	=back
2140		3341
2141	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
2142	the constructor.	3343	the constructor.
2143		3344
2144	class myclass	3345	class myclass
2145	{	3346	{
2146	ev_io io; void io_cb (ev::io &w, int revents);	3347	ev::io io ; void io_cb (ev::io &w, int revents);
2147	ev_idle idle void idle_cb (ev::idle &w, int revents);	3348	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2148		3349
2149	myclass ();	3350	myclass (int fd)
2150	}	3351	{
2151
2152	myclass::myclass (int fd)
2153	{
2154	io .set <myclass, &myclass::io_cb > (this);	3352	io .set <myclass, &myclass::io_cb > (this);
2155	idle.set <myclass, &myclass::idle_cb> (this);	3353	idle.set <myclass, &myclass::idle_cb> (this);
2156		3354
2157	io.start (fd, ev::READ);	3355	io.start (fd, ev::READ);
		3356	}
2158	}	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
2159		3412
2160		3413
2161	=head1 MACRO MAGIC	3414	=head1 MACRO MAGIC
2162		3415
2163	Libev can be compiled with a variety of options, the most fundamantal	3416	Libev can be compiled with a variety of options, the most fundamental
2164	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3417	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2165	functions and callbacks have an initial C<struct ev_loop *> argument.	3418	functions and callbacks have an initial C<struct ev_loop *> argument.
2166		3419
2167	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
2168	following macros are defined:	3421	following macros are defined:
…		…
2173		3426
2174	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
2175	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,
2176	C<EV_A_> is used when other arguments are following. Example:	3429	C<EV_A_> is used when other arguments are following. Example:
2177		3430
2178	ev_unref (EV_A);	3431	ev_unref (EV_A);
2179	ev_timer_add (EV_A_ watcher);	3432	ev_timer_add (EV_A_ watcher);
2180	ev_loop (EV_A_ 0);	3433	ev_loop (EV_A_ 0);
2181		3434
2182	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,
2183	which is often provided by the following macro.	3436	which is often provided by the following macro.
2184		3437
2185	=item C<EV_P>, C<EV_P_>	3438	=item C<EV_P>, C<EV_P_>
2186		3439
2187	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
2188	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,
2189	C<EV_P_> is used when other parameters are following. Example:	3442	C<EV_P_> is used when other parameters are following. Example:
2190		3443
2191	// this is how ev_unref is being declared	3444	// this is how ev_unref is being declared
2192	static void ev_unref (EV_P);	3445	static void ev_unref (EV_P);
2193		3446
2194	// this is how you can declare your typical callback	3447	// this is how you can declare your typical callback
2195	static void cb (EV_P_ ev_timer *w, int revents)	3448	static void cb (EV_P_ ev_timer *w, int revents)
2196		3449
2197	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
2198	suitable for use with C<EV_A>.	3451	suitable for use with C<EV_A>.
2199		3452
2200	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3453	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2201		3454
2202	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
2203	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.
2204		3467
2205	=back	3468	=back
2206		3469
2207	Example: Declare and initialise a check watcher, utilising the above	3470	Example: Declare and initialise a check watcher, utilising the above
2208	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
2209	or not.	3472	or not.
2210		3473
2211	static void	3474	static void
2212	check_cb (EV_P_ ev_timer *w, int revents)	3475	check_cb (EV_P_ ev_timer *w, int revents)
2213	{	3476	{
2214	ev_check_stop (EV_A_ w);	3477	ev_check_stop (EV_A_ w);
2215	}	3478	}
2216		3479
2217	ev_check check;	3480	ev_check check;
2218	ev_check_init (&check, check_cb);	3481	ev_check_init (&check, check_cb);
2219	ev_check_start (EV_DEFAULT_ &check);	3482	ev_check_start (EV_DEFAULT_ &check);
2220	ev_loop (EV_DEFAULT_ 0);	3483	ev_loop (EV_DEFAULT_ 0);
2221		3484
2222	=head1 EMBEDDING	3485	=head1 EMBEDDING
2223		3486
2224	Libev can (and often is) directly embedded into host	3487	Libev can (and often is) directly embedded into host
2225	applications. Examples of applications that embed it include the Deliantra	3488	applications. Examples of applications that embed it include the Deliantra
…		…
2232	libev somewhere in your source tree).	3495	libev somewhere in your source tree).
2233		3496
2234	=head2 FILESETS	3497	=head2 FILESETS
2235		3498
2236	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
2237	in your app.	3500	in your application.
2238		3501
2239	=head3 CORE EVENT LOOP	3502	=head3 CORE EVENT LOOP
2240		3503
2241	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
2242	configuration (no autoconf):	3505	configuration (no autoconf):
2243		3506
2244	#define EV_STANDALONE 1	3507	#define EV_STANDALONE 1
2245	#include "ev.c"	3508	#include "ev.c"
2246		3509
2247	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
2248	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
2249	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
2250	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
2251	where you can put other configuration options):	3514	where you can put other configuration options):
2252		3515
2253	#define EV_STANDALONE 1	3516	#define EV_STANDALONE 1
2254	#include "ev.h"	3517	#include "ev.h"
2255		3518
2256	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++
2257	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
2258	as a bug).	3521	as a bug).
2259		3522
2260	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
2261	in your include path (e.g. in libev/ when using -Ilibev):	3524	in your include path (e.g. in libev/ when using -Ilibev):
2262		3525
2263	ev.h	3526	ev.h
2264	ev.c	3527	ev.c
2265	ev_vars.h	3528	ev_vars.h
2266	ev_wrap.h	3529	ev_wrap.h
2267		3530
2268	ev_win32.c required on win32 platforms only	3531	ev_win32.c required on win32 platforms only
2269		3532
2270	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)
2271	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)
2272	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)
2273	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)
2274	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)
2275		3538
2276	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
2277	to compile this single file.	3540	to compile this single file.
2278		3541
2279	=head3 LIBEVENT COMPATIBILITY API	3542	=head3 LIBEVENT COMPATIBILITY API
2280		3543
2281	To include the libevent compatibility API, also include:	3544	To include the libevent compatibility API, also include:
2282		3545
2283	#include "event.c"	3546	#include "event.c"
2284		3547
2285	in the file including F<ev.c>, and:	3548	in the file including F<ev.c>, and:
2286		3549
2287	#include "event.h"	3550	#include "event.h"
2288		3551
2289	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>.
2290		3553
2291	You need the following additional files for this:	3554	You need the following additional files for this:
2292		3555
2293	event.h	3556	event.h
2294	event.c	3557	event.c
2295		3558
2296	=head3 AUTOCONF SUPPORT	3559	=head3 AUTOCONF SUPPORT
2297		3560
2298	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
2299	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
2300	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
2301	include F<config.h> and configure itself accordingly.	3564	include F<config.h> and configure itself accordingly.
2302		3565
2303	For this of course you need the m4 file:	3566	For this of course you need the m4 file:
2304		3567
2305	libev.m4	3568	libev.m4
2306		3569
2307	=head2 PREPROCESSOR SYMBOLS/MACROS	3570	=head2 PREPROCESSOR SYMBOLS/MACROS
2308		3571
2309	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
2310	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
2311	and only include the select backend.	3574	autoconf is documented for every option.
2312		3575
2313	=over 4	3576	=over 4
2314		3577
2315	=item EV_STANDALONE	3578	=item EV_STANDALONE
2316		3579
…		…
2318	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
2319	implementations for some libevent functions (such as logging, which is not	3582	implementations for some libevent functions (such as logging, which is not
2320	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
2321	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.
2322		3585
		3586	In stanbdalone mode, libev will still try to automatically deduce the
		3587	configuration, but has to be more conservative.
		3588
2323	=item EV_USE_MONOTONIC	3589	=item EV_USE_MONOTONIC
2324		3590
2325	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
2326	monotonic clock option at both compiletime and runtime. Otherwise no use	3592	monotonic clock option at both compile time and runtime. Otherwise no
2327	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,
2328	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
2329	the functionality isn't available is safe, though, although you have	3595	when the functionality isn't available is safe, though, although you have
2330	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>
2331	function is hiding in (often F<-lrt>).	3597	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2332		3598
2333	=item EV_USE_REALTIME	3599	=item EV_USE_REALTIME
2334		3600
2335	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
2336	realtime clock option at compiletime (and assume its availability at	3602	real-time clock option at compile time (and assume its availability
2337	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
2338	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3604	option will be attempted. This effectively replaces C<gettimeofday>
2339	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3605	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2340	note about libraries 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>).
2341		3620
2342	=item EV_USE_NANOSLEEP	3621	=item EV_USE_NANOSLEEP
2343		3622
2344	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3623	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2345	and will use it for delays. Otherwise it will use C<select ()>.	3624	and will use it for delays. Otherwise it will use C<select ()>.
2346		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.
		3633
2347	=item EV_USE_SELECT	3634	=item EV_USE_SELECT
2348		3635
2349	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
2350	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
2351	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
2352	will not be compiled in.	3639	will not be compiled in.
2353		3640
2354	=item EV_SELECT_USE_FD_SET	3641	=item EV_SELECT_USE_FD_SET
2355		3642
2356	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>
2357	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
2358	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
2359	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
2360	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
2361	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,
2362	influence the size of the C<fd_set> used.	3649	configures the maximum size of the C<fd_set>.
2363		3650
2364	=item EV_SELECT_IS_WINSOCKET	3651	=item EV_SELECT_IS_WINSOCKET
2365		3652
2366	When defined to C<1>, the select backend will assume that	3653	When defined to C<1>, the select backend will assume that
2367	select/socket/connect etc. don't understand file descriptors but	3654	select/socket/connect etc. don't understand file descriptors but
…		…
2369	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
2370	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,
2371	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
2372	on win32. Should not be defined on non-win32 platforms.	3659	on win32. Should not be defined on non-win32 platforms.
2373		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
2374	=item EV_USE_POLL	3669	=item EV_USE_POLL
2375		3670
2376	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)
2377	backend. Otherwise it will be enabled on non-win32 platforms. It	3672	backend. Otherwise it will be enabled on non-win32 platforms. It
2378	takes precedence over select.	3673	takes precedence over select.
2379		3674
2380	=item EV_USE_EPOLL	3675	=item EV_USE_EPOLL
2381		3676
2382	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
2383	C<epoll>(7) backend. Its availability will be detected at runtime,	3678	C<epoll>(7) backend. Its availability will be detected at runtime,
2384	otherwise another method will be used as fallback. This is the	3679	otherwise another method will be used as fallback. This is the preferred
2385	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.
2386		3682
2387	=item EV_USE_KQUEUE	3683	=item EV_USE_KQUEUE
2388		3684
2389	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
2390	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,
…		…
2403	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
2404	backend for Solaris 10 systems.	3700	backend for Solaris 10 systems.
2405		3701
2406	=item EV_USE_DEVPOLL	3702	=item EV_USE_DEVPOLL
2407		3703
2408	reserved for future expansion, works like the USE symbols above.	3704	Reserved for future expansion, works like the USE symbols above.
2409		3705
2410	=item EV_USE_INOTIFY	3706	=item EV_USE_INOTIFY
2411		3707
2412	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
2413	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
2414	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.
2415		3723
2416	=item EV_H	3724	=item EV_H
2417		3725
2418	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
2419	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
2420	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.
2421		3729
2422	=item EV_CONFIG_H	3730	=item EV_CONFIG_H
2423		3731
2424	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
2425	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
2426	C<EV_H>, above.	3734	C<EV_H>, above.
2427		3735
2428	=item EV_EVENT_H	3736	=item EV_EVENT_H
2429		3737
2430	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
2431	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">.
2432		3740
2433	=item EV_PROTOTYPES	3741	=item EV_PROTOTYPES
2434		3742
2435	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
2436	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
…		…
2457	When doing priority-based operations, libev usually has to linearly search	3765	When doing priority-based operations, libev usually has to linearly search
2458	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
2459	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
2460	fine.	3768	fine.
2461		3769
2462	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
2463	C<0> will save some memory and cpu.	3771	both to C<0> will save some memory and CPU.
2464		3772
2465	=item EV_PERIODIC_ENABLE	3773	=item EV_PERIODIC_ENABLE
2466		3774
2467	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
2468	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
…		…
2475	code.	3783	code.
2476		3784
2477	=item EV_EMBED_ENABLE	3785	=item EV_EMBED_ENABLE
2478		3786
2479	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
2480	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.
2481		3790
2482	=item EV_STAT_ENABLE	3791	=item EV_STAT_ENABLE
2483		3792
2484	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
2485	defined to be C<0>, then they are not.	3794	defined to be C<0>, then they are not.
…		…
2487	=item EV_FORK_ENABLE	3796	=item EV_FORK_ENABLE
2488		3797
2489	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
2490	defined to be C<0>, then they are not.	3799	defined to be C<0>, then they are not.
2491		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
2492	=item EV_MINIMAL	3806	=item EV_MINIMAL
2493		3807
2494	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
2495	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
2496	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.
2497		3831
2498	=item EV_PID_HASHSIZE	3832	=item EV_PID_HASHSIZE
2499		3833
2500	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
2501	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
2502	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
2503	increase this value (I<must> be a power of two).	3837	increase this value (I<must> be a power of two).
2504		3838
2505	=item EV_INOTIFY_HASHSIZE	3839	=item EV_INOTIFY_HASHSIZE
2506		3840
2507	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
2508	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>),
2509	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>
2510	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
2511	two).	3845	two).
2512		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
2513	=item EV_COMMON	3882	=item EV_COMMON
2514		3883
2515	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
2516	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
2517	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,
2518	though, and it must be identical each time.	3887	though, and it must be identical each time.
2519		3888
2520	For example, the perl EV module uses something like this:	3889	For example, the perl EV module uses something like this:
2521		3890
2522	#define EV_COMMON \	3891	#define EV_COMMON \
2523	SV *self; /* contains this struct */ \	3892	SV *self; /* contains this struct */ \
2524	SV *cb_sv, *fh /* note no trailing ";" */	3893	SV *cb_sv, *fh /* note no trailing ";" */
2525		3894
2526	=item EV_CB_DECLARE (type)	3895	=item EV_CB_DECLARE (type)
2527		3896
2528	=item EV_CB_INVOKE (watcher, revents)	3897	=item EV_CB_INVOKE (watcher, revents)
2529		3898
…		…
2534	definition and a statement, respectively. See the F<ev.h> header file for	3903	definition and a statement, respectively. See the F<ev.h> header file for
2535	their default definitions. One possible use for overriding these is to	3904	their default definitions. One possible use for overriding these is to
2536	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
2537	method calls instead of plain function calls in C++.	3906	method calls instead of plain function calls in C++.
2538		3907
		3908	=back
		3909
2539	=head2 EXPORTED API SYMBOLS	3910	=head2 EXPORTED API SYMBOLS
2540		3911
2541	If you need to re-export the API (e.g. via a dll) and you need a list of	3912	If you need to re-export the API (e.g. via a DLL) and you need a list of
2542	exported symbols, you can use the provided F<Symbol.*> files which list	3913	exported symbols, you can use the provided F<Symbol.*> files which list
2543	all public symbols, one per line:	3914	all public symbols, one per line:
2544		3915
2545	Symbols.ev for libev proper	3916	Symbols.ev for libev proper
2546	Symbols.event for the libevent emulation	3917	Symbols.event for the libevent emulation
2547		3918
2548	This can also be used to rename all public symbols to avoid clashes with	3919	This can also be used to rename all public symbols to avoid clashes with
2549	multiple versions of libev linked together (which is obviously bad in	3920	multiple versions of libev linked together (which is obviously bad in
2550	itself, but sometimes it is inconvinient to avoid this).	3921	itself, but sometimes it is inconvenient to avoid this).
2551		3922
2552	A sed command like this will create wrapper C<#define>'s that you need to	3923	A sed command like this will create wrapper C<#define>'s that you need to
2553	include before including F<ev.h>:	3924	include before including F<ev.h>:
2554		3925
2555	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3926	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2572	file.	3943	file.
2573		3944
2574	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
2575	that everybody includes and which overrides some configure choices:	3946	that everybody includes and which overrides some configure choices:
2576		3947
2577	#define EV_MINIMAL 1	3948	#define EV_MINIMAL 1
2578	#define EV_USE_POLL 0	3949	#define EV_USE_POLL 0
2579	#define EV_MULTIPLICITY 0	3950	#define EV_MULTIPLICITY 0
2580	#define EV_PERIODIC_ENABLE 0	3951	#define EV_PERIODIC_ENABLE 0
2581	#define EV_STAT_ENABLE 0	3952	#define EV_STAT_ENABLE 0
2582	#define EV_FORK_ENABLE 0	3953	#define EV_FORK_ENABLE 0
2583	#define EV_CONFIG_H <config.h>	3954	#define EV_CONFIG_H <config.h>
2584	#define EV_MINPRI 0	3955	#define EV_MINPRI 0
2585	#define EV_MAXPRI 0	3956	#define EV_MAXPRI 0
2586		3957
2587	#include "ev++.h"	3958	#include "ev++.h"
2588		3959
2589	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:
2590		3961
2591	#include "ev_cpp.h"	3962	#include "ev_cpp.h"
2592	#include "ev.c"	3963	#include "ev.c"
2593		3964
		3965	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2594		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
2595	=head1 COMPLEXITIES	4397	=head1 ALGORITHMIC COMPLEXITIES
2596		4398
2597	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
2598	libev will be explained. For complexity discussions about backends see the	4400	libev will be documented. For complexity discussions about backends see
2599	documentation for C<ev_default_init>.	4401	the documentation for C<ev_default_init>.
2600		4402
2601	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
2602	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
2603	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
2604	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
2605	it is much faster and asymptotically approaches constant time.	4407	average it is much faster and asymptotically approaches constant time.
2606		4408
2607	=over 4	4409	=over 4
2608		4410
2609	=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)
2610		4412
2611	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
2612	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
2613	have to skip those 100 watchers.	4415	have to skip roughly seven (C<ld 100>) of these watchers.
2614		4416
2615	=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)
2616		4418
2617	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,
2618	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.
2619		4421
2620	=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)
2621		4423
2622	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
2623	=item Stopping check/prepare/idle watchers: O(1)	4426	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2624		4427
2625	=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))
2626		4429
2627	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
2628	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
2629	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).
2630		4434
2631	=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.
2632		4439
2633	=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)
2634		4441
2635	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
2636	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).
2637		4445
2638	=item Activating one watcher: O(1)	4446	=item Activating one watcher (putting it into the pending state): O(1)
2639		4447
2640	=item Priority handling: O(number_of_priorities)	4448	=item Priority handling: O(number_of_priorities)
2641		4449
2642	Priorities are implemented by allocating some space for each	4450	Priorities are implemented by allocating some space for each
2643	priority. When doing priority-based operations, libev usually has to	4451	priority. When doing priority-based operations, libev usually has to
2644	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.
2645		4464
2646	=back	4465	=back
2647		4466
2648		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
2649	=head1 AUTHOR	4544	=head1 AUTHOR
2650		4545
2651	Marc Lehmann <libev@schmorp.de>.	4546	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2652		4547

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