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Revision 1.121 by root, Mon Jan 28 12:13:54 2008 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	=head2 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
…		…
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	=head2 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	=head2 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
265	The default loop is the only loop that can handle C<ev_signal> and	319	The default loop is the only loop that can handle C<ev_signal> and
266	C<ev_child> watchers, and to do this, it always registers a handler	320	C<ev_child> watchers, and to do this, it always registers a handler
267	for C<SIGCHLD>. If this is a problem for your app you can either	321	for C<SIGCHLD>. If this is a problem for your application you can either
268	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
269	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
270	C<ev_default_init>.	324	C<ev_default_init>.
271		325
272	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
…		…
281	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
282	thing, believe me).	336	thing, believe me).
283		337
284	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
285		339
286	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
287	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
288	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
289	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
290	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
291	around bugs.	345	around bugs.
…		…
297	enabling this flag.	351	enabling this flag.
298		352
299	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,
300	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
301	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
302	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
303	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
304	C<pthread_atfork> which is even faster).	358	C<pthread_atfork> which is even faster).
305		359
306	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
307	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
308	flag.	362	flag.
309		363
310	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>
311	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.
312		381
313	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	382	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
314		383
315	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
316	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,
317	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
318	using this backend. It doesn't scale too well (O(highest_fd)), but its	387	using this backend. It doesn't scale too well (O(highest_fd)), but its
319	usually the fastest backend for a low number of (low-numbered :) fds.	388	usually the fastest backend for a low number of (low-numbered :) fds.
320		389
321	To get good performance out of this backend you need a high amount of	390	To get good performance out of this backend you need a high amount of
322	parallelity (most of the file descriptors should be busy). If you are	391	parallelism (most of the file descriptors should be busy). If you are
323	writing a server, you should C<accept ()> in a loop to accept as many	392	writing a server, you should C<accept ()> in a loop to accept as many
324	connections as possible during one iteration. You might also want to have	393	connections as possible during one iteration. You might also want to have
325	a look at C<ev_set_io_collect_interval ()> to increase the amount of	394	a look at C<ev_set_io_collect_interval ()> to increase the amount of
326	readyness notifications you get per iteration.	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).
327		400
328	=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)
329		402
330	And this is your standard poll(2) backend. It's more complicated	403	And this is your standard poll(2) backend. It's more complicated
331	than select, but handles sparse fds better and has no artificial	404	than select, but handles sparse fds better and has no artificial
332	limit on the number of fds you can use (except it will slow down	405	limit on the number of fds you can use (except it will slow down
333	considerably with a lot of inactive fds). It scales similarly to select,	406	considerably with a lot of inactive fds). It scales similarly to select,
334	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	407	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
335	performance tips.	408	performance tips.
336		409
		410	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		411	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		412
337	=item C<EVBACKEND_EPOLL> (value 4, Linux)	413	=item C<EVBACKEND_EPOLL> (value 4, Linux)
338		414
339	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,
340	but it scales phenomenally better. While poll and select usually scale	416	but it scales phenomenally better. While poll and select usually scale
341	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),
342	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).
343	of shortcomings, such as silently dropping events in some hard-to-detect	419
344	cases and rewiring a syscall per fd change, no fork support and bad	420	The epoll mechanism deserves honorable mention as the most misdesigned
345	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.
346		436
347	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
348	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
349	(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
350	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
351	very well if you register events for both fds.	441	file descriptors might not work very well if you register events for both
352		442	file descriptors.
353	Please note that epoll sometimes generates spurious notifications, so you
354	need to use non-blocking I/O or other means to avoid blocking when no data
355	(or space) is available.
356		443
357	Best performance from this backend is achieved by not unregistering all	444	Best performance from this backend is achieved by not unregistering all
358	watchers for a file descriptor until it has been closed, if possible, i.e.	445	watchers for a file descriptor until it has been closed, if possible,
359	keep at least one watcher active per fd at all times.	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.
360		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
361	While nominally embeddeble in other event loops, this feature is broken in	456	While nominally embeddable in other event loops, this feature is broken in
362	all kernel versions tested so far.	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>.
363		461
364	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	462	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
365		463
366	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
367	was broken on all BSDs except NetBSD (usually it doesn't work reliably	465	was broken on all BSDs except NetBSD (usually it doesn't work reliably
368	with anything but sockets and pipes, except on Darwin, where of course	466	with anything but sockets and pipes, except on Darwin, where of course
369	it's completely useless). For this reason it's not being "autodetected"	467	it's completely useless). Unlike epoll, however, whose brokenness
		468	is by design, these kqueue bugs can (and eventually will) be fixed
		469	without API changes to existing programs. For this reason it's not being
370	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
371	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)
372	system like NetBSD.	472	system like NetBSD.
373		473
374	You still can embed kqueue into a normal poll or select backend and use it	474	You still can embed kqueue into a normal poll or select backend and use it
375	only for sockets (after having made sure that sockets work with kqueue on	475	only for sockets (after having made sure that sockets work with kqueue on
376	the target platform). See C<ev_embed> watchers for more info.	476	the target platform). See C<ev_embed> watchers for more info.
377		477
378	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
379	kernel is more efficient (which says nothing about its actual speed, of	479	kernel is more efficient (which says nothing about its actual speed, of
380	course). While stopping, setting and starting an I/O watcher does never	480	course). While stopping, setting and starting an I/O watcher does never
381	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	481	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
382	two event changes per incident, support for C<fork ()> is very bad and it	482	two event changes per incident. Support for C<fork ()> is very bad (but
383	drops fds silently in similarly hard-to-detect cases.	483	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		484	cases
384		485
385	This backend usually performs well under most conditions.	486	This backend usually performs well under most conditions.
386		487
387	While nominally embeddable in other event loops, this doesn't work	488	While nominally embeddable in other event loops, this doesn't work
388	everywhere, so you might need to test for this. And since it is broken	489	everywhere, so you might need to test for this. And since it is broken
389	almost everywhere, you should only use it when you have a lot of sockets	490	almost everywhere, you should only use it when you have a lot of sockets
390	(for which it usually works), by embedding it into another event loop	491	(for which it usually works), by embedding it into another event loop
391	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	492	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
392	sockets.	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>.
393		498
394	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	499	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
395		500
396	This is not implemented yet (and might never be, unless you send me an	501	This is not implemented yet (and might never be, unless you send me an
397	implementation). According to reports, C</dev/poll> only supports sockets	502	implementation). According to reports, C</dev/poll> only supports sockets
…		…
401	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	506	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
402		507
403	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,
404	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)).
405		510
406	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
407	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
408	blocking when no data (or space) is available.	513	blocking when no data (or space) is available.
409		514
410	While this backend scales well, it requires one system call per active	515	While this backend scales well, it requires one system call per active
411	file descriptor per loop iteration. For small and medium numbers of file	516	file descriptor per loop iteration. For small and medium numbers of file
412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	517	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
413	might perform better.	518	might perform better.
414		519
415	On the positive side, ignoring the spurious readyness notifications, this	520	On the positive side, with the exception of the spurious readiness
416	backend actually performed to specification in all tests and is fully	521	notifications, this backend actually performed fully to specification
417	embeddable, which is a rare feat among the OS-specific backends.	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>.
418		527
419	=item C<EVBACKEND_ALL>	528	=item C<EVBACKEND_ALL>
420		529
421	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
422	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
…		…
424		533
425	It is definitely not recommended to use this flag.	534	It is definitely not recommended to use this flag.
426		535
427	=back	536	=back
428		537
429	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,
430	backends will be tried (in the reverse order as listed here). If none are	539	then only these backends will be tried (in the reverse order as listed
431	specified, all backends in C<ev_recommended_backends ()> will be tried.	540	here). If none are specified, all backends in C<ev_recommended_backends
		541	()> will be tried.
432		542
433	The most typical usage is like this:	543	Example: This is the most typical usage.
434		544
435	if (!ev_default_loop (0))	545	if (!ev_default_loop (0))
436	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	546	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
437		547
438	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
439	environment settings to be taken into account:	549	environment settings to be taken into account:
440		550
441	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	551	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
442		552
443	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
444	available (warning, breaks stuff, best use only with your own private	554	used if available (warning, breaks stuff, best use only with your own
445	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):
446		557
447	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	558	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
448		559
449	=item struct ev_loop *ev_loop_new (unsigned int flags)	560	=item struct ev_loop *ev_loop_new (unsigned int flags)
450		561
451	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
452	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
453	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
454	undefined behaviour (or a failed assertion if assertions are enabled).	565	undefined behaviour (or a failed assertion if assertions are enabled).
455		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
456	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.
457		572
458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	573	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
459	if (!epoller)	574	if (!epoller)
460	fatal ("no epoll found here, maybe it hides under your chair");	575	fatal ("no epoll found here, maybe it hides under your chair");
461		576
462	=item ev_default_destroy ()	577	=item ev_default_destroy ()
463		578
464	Destroys the default loop again (frees all memory and kernel state	579	Destroys the default loop again (frees all memory and kernel state
465	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
466	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
467	responsibility to either stop all watchers cleanly yoursef I<before>	582	responsibility to either stop all watchers cleanly yourself I<before>
468	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
469	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
470	for example).	585	for example).
471		586
472	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
473	this function, and related watchers (such as signal and child watchers)	588	handlers), will not be freed by this function, and related watchers (such
474	would need to be stopped manually.	589	as signal and child watchers) would need to be stopped manually.
475		590
476	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
477	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
478	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
479	C<ev_loop_new> and C<ev_loop_destroy>).	594	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
504		619
505	=item ev_loop_fork (loop)	620	=item ev_loop_fork (loop)
506		621
507	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
508	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
509	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.
510		631
511	=item unsigned int ev_loop_count (loop)	632	=item unsigned int ev_loop_count (loop)
512		633
513	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
514	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
515	happily wraps around with enough iterations.	636	happily wraps around with enough iterations.
516		637
517	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
518	"ticks" the number of loop iterations), as it roughly corresponds with	639	"ticks" the number of loop iterations), as it roughly corresponds with
519	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.
520		653
521	=item unsigned int ev_backend (loop)	654	=item unsigned int ev_backend (loop)
522		655
523	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
524	use.	657	use.
…		…
529	received events and started processing them. This timestamp does not	662	received events and started processing them. This timestamp does not
530	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
531	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
532	event occurring (or more correctly, libev finding out about it).	665	event occurring (or more correctly, libev finding out about it).
533		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
534	=item ev_loop (loop, int flags)	705	=item ev_loop (loop, int flags)
535		706
536	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
537	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
538	events.	709	events.
…		…
540	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
541	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.
542		713
543	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
544	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
545	finished (especially in interactive programs), but having a program that	716	finished (especially in interactive programs), but having a program
546	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
547	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.
548		720
549	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
550	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
551	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.
552		725
553	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
554	neccessary) and will handle those and any outstanding ones. It will block	727	necessary) and will handle those and any already outstanding ones. It
555	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
556	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
557	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
558	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
559	usually a better approach for this kind of thing.	736	usually a better approach for this kind of thing.
560		737
561	Here are the gory details of what C<ev_loop> does:	738	Here are the gory details of what C<ev_loop> does:
562		739
563	- Before the first iteration, call any pending watchers.	740	- Before the first iteration, call any pending watchers.
564	* If EVFLAG_FORKCHECK was used, check for a fork.	741	* If EVFLAG_FORKCHECK was used, check for a fork.
565	- If a fork was detected, queue and call all fork watchers.	742	- If a fork was detected (by any means), queue and call all fork watchers.
566	- Queue and call all prepare watchers.	743	- Queue and call all prepare watchers.
567	- 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.
568	- Update the kernel state with all outstanding changes.	746	- Update the kernel state with all outstanding changes.
569	- Update the "event loop time".	747	- Update the "event loop time" (ev_now ()).
570	- Calculate for how long to sleep or block, if at all	748	- Calculate for how long to sleep or block, if at all
571	(active idle watchers, EVLOOP_NONBLOCK or not having	749	(active idle watchers, EVLOOP_NONBLOCK or not having
572	any active watchers at all will result in not sleeping).	750	any active watchers at all will result in not sleeping).
573	- Sleep if the I/O and timer collect interval say so.	751	- Sleep if the I/O and timer collect interval say so.
574	- Block the process, waiting for any events.	752	- Block the process, waiting for any events.
575	- Queue all outstanding I/O (fd) events.	753	- Queue all outstanding I/O (fd) events.
576	- Update the "event loop time" and do time jump handling.	754	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
577	- Queue all outstanding timers.	755	- Queue all expired timers.
578	- Queue all outstanding periodics.	756	- Queue all expired periodics.
579	- If no events are pending now, queue all idle watchers.	757	- Unless any events are pending now, queue all idle watchers.
580	- Queue all check watchers.	758	- Queue all check watchers.
581	- 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).
582	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
583	be handled here by queueing them when their watcher gets executed.	761	be handled here by queueing them when their watcher gets executed.
584	- 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
…		…
589	anymore.	767	anymore.
590		768
591	... queue jobs here, make sure they register event watchers as long	769	... queue jobs here, make sure they register event watchers as long
592	... 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..)
593	ev_loop (my_loop, 0);	771	ev_loop (my_loop, 0);
594	... jobs done. yeah!	772	... jobs done or somebody called unloop. yeah!
595		773
596	=item ev_unloop (loop, how)	774	=item ev_unloop (loop, how)
597		775
598	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
599	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
600	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
601	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.
602		780
603	This "unloop state" will be cleared when entering C<ev_loop> again.	781	This "unloop state" will be cleared when entering C<ev_loop> again.
604		782
		783	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		784
605	=item ev_ref (loop)	785	=item ev_ref (loop)
606		786
607	=item ev_unref (loop)	787	=item ev_unref (loop)
608		788
609	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
610	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
611	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
612	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>
613	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
614	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
615	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
616	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
617	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
618	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
619	(but only if the watcher wasn't active before, or was active before,	802	before stop> (but only if the watcher wasn't active before, or was active
620	respectively).	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).
621		806
622	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>
623	running when nothing else is active.	808	running when nothing else is active.
624		809
625	struct ev_signal exitsig;	810	ev_signal exitsig;
626	ev_signal_init (&exitsig, sig_cb, SIGINT);	811	ev_signal_init (&exitsig, sig_cb, SIGINT);
627	ev_signal_start (loop, &exitsig);	812	ev_signal_start (loop, &exitsig);
628	evf_unref (loop);	813	evf_unref (loop);
629		814
630	Example: For some weird reason, unregister the above signal handler again.	815	Example: For some weird reason, unregister the above signal handler again.
631		816
632	ev_ref (loop);	817	ev_ref (loop);
633	ev_signal_stop (loop, &exitsig);	818	ev_signal_stop (loop, &exitsig);
634		819
635	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	820	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
636		821
637	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	822	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
638		823
639	These advanced functions influence the time that libev will spend waiting	824	These advanced functions influence the time that libev will spend waiting
640	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
641	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.
642		828
643	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>)
644	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
645	increase efficiency of loop iterations.	831	to increase efficiency of loop iterations (or to increase power-saving
		832	opportunities).
646		833
647	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
648	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
649	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
650	events, especially with backends like C<select ()> which have a high	837	events, especially with backends like C<select ()> which have a high
651	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.
652		839
653	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
654	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,
655	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
656	C<ev_timer>) will be not affected. Setting this to a non-null value will	843	C<ev_timer>) will be not affected. Setting this to a non-null value will
657	introduce an additional C<ev_sleep ()> call into most loop iterations.	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.
658		847
659	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
660	to spend more time collecting timeouts, at the expense of increased	849	to spend more time collecting timeouts, at the expense of increased
661	latency (the watcher callback will be called later). C<ev_io> watchers	850	latency/jitter/inexactness (the watcher callback will be called
662	will not be affected. Setting this to a non-null value will not introduce	851	later). C<ev_io> watchers will not be affected. Setting this to a non-null
663	any overhead in libev.	852	value will not introduce any overhead in libev.
664		853
665	Many (busy) programs can usually benefit by setting the io collect	854	Many (busy) programs can usually benefit by setting the I/O collect
666	interval to a value near C<0.1> or so, which is often enough for	855	interval to a value near C<0.1> or so, which is often enough for
667	interactive servers (of course not for games), likewise for timeouts. It	856	interactive servers (of course not for games), likewise for timeouts. It
668	usually doesn't make much sense to set it to a lower value than C<0.01>,	857	usually doesn't make much sense to set it to a lower value than C<0.01>,
669	as this approsaches 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.
670		953
671	=back	954	=back
672		955
673		956
674	=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.
675		962
676	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
677	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
678	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:
679		966
680	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)
681	{	968	{
682	ev_io_stop (w);	969	ev_io_stop (w);
683	ev_unloop (loop, EVUNLOOP_ALL);	970	ev_unloop (loop, EVUNLOOP_ALL);
684	}	971	}
685		972
686	struct ev_loop *loop = ev_default_loop (0);	973	struct ev_loop *loop = ev_default_loop (0);
		974
687	struct ev_io stdin_watcher;	975	ev_io stdin_watcher;
		976
688	ev_init (&stdin_watcher, my_cb);	977	ev_init (&stdin_watcher, my_cb);
689	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	978	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
690	ev_io_start (loop, &stdin_watcher);	979	ev_io_start (loop, &stdin_watcher);
		980
691	ev_loop (loop, 0);	981	ev_loop (loop, 0);
692		982
693	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
694	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
695	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).
696		989
697	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
698	(watcher *, callback)>, which expects a callback to be provided. This	991	(watcher *, callback)>, which expects a callback to be provided. This
699	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
700	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
701	is readable and/or writable).	994	is readable and/or writable).
702		995
703	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 *, ...) >>
704	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
705	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<<
706	(watcher *, callback, ...) >>.	999	ev_TYPE_init (watcher *, callback, ...) >>.
707		1000
708	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
709	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
710	*) >>), 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
711	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1004	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
712		1005
713	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
714	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
715	reinitialise it or call its C<set> macro.	1008	reinitialise it or call its C<ev_TYPE_set> macro.
716		1009
717	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
718	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
719	third argument.	1012	third argument.
720		1013
…		…
774	=item C<EV_FORK>	1067	=item C<EV_FORK>
775		1068
776	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
777	C<ev_fork>).	1070	C<ev_fork>).
778		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
779	=item C<EV_ERROR>	1081	=item C<EV_ERROR>
780		1082
781	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
782	happen because the watcher could not be properly started because libev	1084	happen because the watcher could not be properly started because libev
783	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
784	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
785	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.
786		1092
787	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
788	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
789	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
790	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
791	programs, though, so beware.	1097	programs, though, as the fd could already be closed and reused for another
		1098	thing, so beware.
792		1099
793	=back	1100	=back
794		1101
795	=head2 GENERIC WATCHER FUNCTIONS	1102	=head2 GENERIC WATCHER FUNCTIONS
796
797	In the following description, C<TYPE> stands for the watcher type,
798	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
799		1103
800	=over 4	1104	=over 4
801		1105
802	=item C<ev_init> (ev_TYPE *watcher, callback)	1106	=item C<ev_init> (ev_TYPE *watcher, callback)
803		1107
…		…
809	which rolls both calls into one.	1113	which rolls both calls into one.
810		1114
811	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
812	(or never started) and there are no pending events outstanding.	1116	(or never started) and there are no pending events outstanding.
813		1117
814	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,
815	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);
816		1126
817	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1127	=item C<ev_TYPE_set> (ev_TYPE *, [args])
818		1128
819	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
820	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
…		…
823	difference to the C<ev_init> macro).	1133	difference to the C<ev_init> macro).
824		1134
825	Although some watcher types do not have type-specific arguments	1135	Although some watcher types do not have type-specific arguments
826	(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.
827		1137
		1138	See C<ev_init>, above, for an example.
		1139
828	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1140	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
829		1141
830	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
831	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
832	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);
833		1149
834	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1150	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
835		1151
836	Starts (activates) the given watcher. Only active watchers will receive	1152	Starts (activates) the given watcher. Only active watchers will receive
837	events. If the watcher is already active nothing will happen.	1153	events. If the watcher is already active nothing will happen.
838		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
839	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1160	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
840		1161
841	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
842	status. It is possible that stopped watchers are pending (for example,	1165	It is possible that stopped watchers are pending - for example,
843	non-repeating timers are being stopped when they become pending), but	1166	non-repeating timers are being stopped when they become pending - but
844	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
845	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
846	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.
847		1170
848	=item bool ev_is_active (ev_TYPE *watcher)	1171	=item bool ev_is_active (ev_TYPE *watcher)
849		1172
850	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
851	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
…		…
877	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>
878	(default: C<-2>). Pending watchers with higher priority will be invoked	1201	(default: C<-2>). Pending watchers with higher priority will be invoked
879	before watchers with lower priority, but priority will not keep watchers	1202	before watchers with lower priority, but priority will not keep watchers
880	from being executed (except for C<ev_idle> watchers).	1203	from being executed (except for C<ev_idle> watchers).
881		1204
882	This means that priorities are I<only> used for ordering callback
883	invocation after new events have been received. This is useful, for
884	example, to reduce latency after idling, or more often, to bind two
885	watchers on the same event and make sure one is called first.
886
887	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
888	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.
889		1207
890	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
891	pending.	1209	pending.
892		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
893	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
894	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 :).
895		1217
896	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
897	fine, as long as you do not mind that the priority value you query might	1219	priorities.
898	or might not have been adjusted to be within valid range.
899		1220
900	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1221	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
901		1222
902	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
903	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
904	can deal with that fact.	1225	can deal with that fact, as both are simply passed through to the
		1226	callback.
905		1227
906	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1228	=item int ev_clear_pending (loop, ev_TYPE *watcher)
907		1229
908	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
909	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
910	watcher isn't pending it does nothing and returns C<0>.	1232	watcher isn't pending it does nothing and returns C<0>.
911		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
912	=back	1237	=back
913		1238
914		1239
915	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1240	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
916		1241
917	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
918	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
919	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
920	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
921	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
922	data:	1247	data:
923		1248
924	struct my_io	1249	struct my_io
925	{	1250	{
926	struct ev_io io;	1251	ev_io io;
927	int otherfd;	1252	int otherfd;
928	void *somedata;	1253	void *somedata;
929	struct whatever *mostinteresting;	1254	struct whatever *mostinteresting;
930	}	1255	};
		1256
		1257	...
		1258	struct my_io w;
		1259	ev_io_init (&w.io, my_cb, fd, EV_READ);
931		1260
932	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
933	can cast it back to your own type:	1262	can cast it back to your own type:
934		1263
935	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)
936	{	1265	{
937	struct my_io *w = (struct my_io *)w_;	1266	struct my_io *w = (struct my_io *)w_;
938	...	1267	...
939	}	1268	}
940		1269
941	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
942	instead have been omitted.	1271	instead have been omitted.
943		1272
944	Another common scenario is having some data structure with multiple	1273	Another common scenario is to use some data structure with multiple
945	watchers:	1274	embedded watchers:
946		1275
947	struct my_biggy	1276	struct my_biggy
948	{	1277	{
949	int some_data;	1278	int some_data;
950	ev_timer t1;	1279	ev_timer t1;
951	ev_timer t2;	1280	ev_timer t2;
952	}	1281	}
953		1282
954	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
955	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):
956		1288
957	#include <stddef.h>	1289	#include <stddef.h>
958		1290
959	static void	1291	static void
960	t1_cb (EV_P_ struct ev_timer *w, int revents)	1292	t1_cb (EV_P_ ev_timer *w, int revents)
961	{	1293	{
962	struct my_biggy big = (struct my_biggy *	1294	struct my_biggy big = (struct my_biggy *)
963	(((char *)w) - offsetof (struct my_biggy, t1));	1295	(((char *)w) - offsetof (struct my_biggy, t1));
964	}	1296	}
965		1297
966	static void	1298	static void
967	t2_cb (EV_P_ struct ev_timer *w, int revents)	1299	t2_cb (EV_P_ ev_timer *w, int revents)
968	{	1300	{
969	struct my_biggy big = (struct my_biggy *	1301	struct my_biggy big = (struct my_biggy *)
970	(((char *)w) - offsetof (struct my_biggy, t2));	1302	(((char *)w) - offsetof (struct my_biggy, t2));
971	}	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.
972		1407
973		1408
974	=head1 WATCHER TYPES	1409	=head1 WATCHER TYPES
975		1410
976	This section describes each watcher in detail, but will not repeat	1411	This section describes each watcher in detail, but will not repeat
…		…
1000	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
1001	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
1002	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
1003	required if you know what you are doing).	1438	required if you know what you are doing).
1004		1439
1005	If you must do this, then force the use of a known-to-be-good backend	1440	If you cannot use non-blocking mode, then force the use of a
1006	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1441	known-to-be-good backend (at the time of this writing, this includes only
1007	C<EVBACKEND_POLL>).	1442	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1443	descriptors for which non-blocking operation makes no sense (such as
		1444	files) - libev doesn't guarentee any specific behaviour in that case.
1008		1445
1009	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
1010	receive "spurious" readyness notifications, that is your callback might	1447	receive "spurious" readiness notifications, that is your callback might
1011	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
1012	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
1013	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
1014	this situation even with a relatively standard program structure. Thus	1451	this situation even with a relatively standard program structure. Thus
1015	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
1016	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.
1017		1454
1018	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
1019	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
1020	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
1021	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
1022	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.
1023		1464
1024	=head3 The special problem of disappearing file descriptors	1465	=head3 The special problem of disappearing file descriptors
1025		1466
1026	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
1027	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,
1028	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
1029	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
1030	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
1031	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
1032	fact, a different file descriptor.	1473	fact, a different file descriptor.
1033		1474
…		…
1062	To support fork in your programs, you either have to call	1503	To support fork in your programs, you either have to call
1063	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,
1064	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1505	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1065	C<EVBACKEND_POLL>.	1506	C<EVBACKEND_POLL>.
1066		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
1067		1519
1068	=head3 Watcher-Specific Functions	1520	=head3 Watcher-Specific Functions
1069		1521
1070	=over 4	1522	=over 4
1071		1523
1072	=item ev_io_init (ev_io *, callback, int fd, int events)	1524	=item ev_io_init (ev_io *, callback, int fd, int events)
1073		1525
1074	=item ev_io_set (ev_io *, int fd, int events)	1526	=item ev_io_set (ev_io *, int fd, int events)
1075		1527
1076	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
1077	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
1078	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.
1079		1531
1080	=item int fd [read-only]	1532	=item int fd [read-only]
1081		1533
1082	The file descriptor being watched.	1534	The file descriptor being watched.
1083		1535
…		…
1091		1543
1092	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
1093	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
1094	attempt to read a whole line in the callback.	1546	attempt to read a whole line in the callback.
1095		1547
1096	static void	1548	static void
1097	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)
1098	{	1550	{
1099	ev_io_stop (loop, w);	1551	ev_io_stop (loop, w);
1100	.. 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
1101	}	1553	}
1102		1554
1103	...	1555	...
1104	struct ev_loop *loop = ev_default_init (0);	1556	struct ev_loop *loop = ev_default_init (0);
1105	struct ev_io stdin_readable;	1557	ev_io stdin_readable;
1106	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);
1107	ev_io_start (loop, &stdin_readable);	1559	ev_io_start (loop, &stdin_readable);
1108	ev_loop (loop, 0);	1560	ev_loop (loop, 0);
1109		1561
1110		1562
1111	=head2 C<ev_timer> - relative and optionally repeating timeouts	1563	=head2 C<ev_timer> - relative and optionally repeating timeouts
1112		1564
1113	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
1114	given time, and optionally repeating in regular intervals after that.	1566	given time, and optionally repeating in regular intervals after that.
1115		1567
1116	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
1117	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
1118	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
1119	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1571	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1120	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.
1121		1763
1122	The relative timeouts are calculated relative to the C<ev_now ()>	1764	The relative timeouts are calculated relative to the C<ev_now ()>
1123	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
1124	of the event triggering whatever timeout you are modifying/starting. If	1766	of the event triggering whatever timeout you are modifying/starting. If
1125	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
1126	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:
1127		1769
1128	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1770	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1129		1771
1130	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
1131	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
1132	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>).
1133		1805
1134	=head3 Watcher-Specific Functions and Data Members	1806	=head3 Watcher-Specific Functions and Data Members
1135		1807
1136	=over 4	1808	=over 4
1137		1809
1138	=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)
1139		1811
1140	=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)
1141		1813
1142	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>
1143	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
1144	timer will automatically be configured to trigger again C<repeat> seconds	1816	reached. If it is positive, then the timer will automatically be
1145	later, again, and again, until stopped manually.	1817	configured to trigger again C<repeat> seconds later, again, and again,
		1818	until stopped manually.
1146		1819
1147	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
1148	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
1149	exactly 10 second intervals. If, however, your program cannot keep up with	1822	trigger at exactly 10 second intervals. If, however, your program cannot
1150	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
1151	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.
1152		1825
1153	=item ev_timer_again (loop)	1826	=item ev_timer_again (loop, ev_timer *)
1154		1827
1155	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
1156	repeating. The exact semantics are:	1829	repeating. The exact semantics are:
1157		1830
1158	If the timer is pending, its pending status is cleared.	1831	If the timer is pending, its pending status is cleared.
1159		1832
1160	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).
1161		1834
1162	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
1163	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.
1164		1837
1165	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
1166	example: Imagine you have a tcp connection and you want a so-called idle	1839	usage example.
1167	timeout, that is, you want to be called when there have been, say, 60
1168	seconds of inactivity on the socket. The easiest way to do this is to
1169	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1170	C<ev_timer_again> each time you successfully read or write some data. If
1171	you go into an idle state where you do not expect data to travel on the
1172	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1173	automatically restart it if need be.
1174		1840
1175	That means you can ignore the C<after> value and C<ev_timer_start>	1841	=item ev_timer_remaining (loop, ev_timer *)
1176	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1177		1842
1178	ev_timer_init (timer, callback, 0., 5.);	1843	Returns the remaining time until a timer fires. If the timer is active,
1179	ev_timer_again (loop, timer);	1844	then this time is relative to the current event loop time, otherwise it's
1180	...	1845	the timeout value currently configured.
1181	timer->again = 17.;
1182	ev_timer_again (loop, timer);
1183	...
1184	timer->again = 10.;
1185	ev_timer_again (loop, timer);
1186		1846
1187	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
1188	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.
1189		1852
1190	=item ev_tstamp repeat [read-write]	1853	=item ev_tstamp repeat [read-write]
1191		1854
1192	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
1193	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),
1194	which is also when any modifications are taken into account.	1857	which is also when any modifications are taken into account.
1195		1858
1196	=back	1859	=back
1197		1860
1198	=head3 Examples	1861	=head3 Examples
1199		1862
1200	Example: Create a timer that fires after 60 seconds.	1863	Example: Create a timer that fires after 60 seconds.
1201		1864
1202	static void	1865	static void
1203	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)
1204	{	1867	{
1205	.. one minute over, w is actually stopped right here	1868	.. one minute over, w is actually stopped right here
1206	}	1869	}
1207		1870
1208	struct ev_timer mytimer;	1871	ev_timer mytimer;
1209	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1872	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1210	ev_timer_start (loop, &mytimer);	1873	ev_timer_start (loop, &mytimer);
1211		1874
1212	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
1213	inactivity.	1876	inactivity.
1214		1877
1215	static void	1878	static void
1216	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1879	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1217	{	1880	{
1218	.. ten seconds without any activity	1881	.. ten seconds without any activity
1219	}	1882	}
1220		1883
1221	struct ev_timer mytimer;	1884	ev_timer mytimer;
1222	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 */
1223	ev_timer_again (&mytimer); /* start timer */	1886	ev_timer_again (&mytimer); /* start timer */
1224	ev_loop (loop, 0);	1887	ev_loop (loop, 0);
1225		1888
1226	// 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":
1227	// reset the timeout to start ticking again at 10 seconds	1890	// reset the timeout to start ticking again at 10 seconds
1228	ev_timer_again (&mytimer);	1891	ev_timer_again (&mytimer);
1229		1892
1230		1893
1231	=head2 C<ev_periodic> - to cron or not to cron?	1894	=head2 C<ev_periodic> - to cron or not to cron?
1232		1895
1233	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
1234	(and unfortunately a bit complex).	1897	(and unfortunately a bit complex).
1235		1898
1236	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
1237	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
1238	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
1239	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
1240	+ 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
1241	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1904	wrist-watch).
1242	roughly 10 seconds later).
1243		1905
1244	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
1245	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
1246	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).
1247		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
1248	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
1249	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
1250	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).
1251		1924
1252	=head3 Watcher-Specific Functions and Data Members	1925	=head3 Watcher-Specific Functions and Data Members
1253		1926
1254	=over 4	1927	=over 4
1255		1928
1256	=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)
1257		1930
1258	=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)
1259		1932
1260	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
1261	operation, and we will explain them from simplest to complex:	1934	operation, and we will explain them from simplest to most complex:
1262		1935
1263	=over 4	1936	=over 4
1264		1937
1265	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1938	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1266		1939
1267	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
1268	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
1269	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
1270	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.
1271		1945
1272	=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)
1273		1947
1274	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
1275	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
1276	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.
1277		1952
1278	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
1279	time:	1954	system clock, for example, here is an C<ev_periodic> that triggers each
		1955	hour, on the hour (with respect to UTC):
1280		1956
1281	ev_periodic_set (&periodic, 0., 3600., 0);	1957	ev_periodic_set (&periodic, 0., 3600., 0);
1282		1958
1283	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,
1284	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
1285	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
1286	by 3600.	1962	by 3600.
1287		1963
1288	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
1289	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
1290	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.
1291		1967
1292	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
1293	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
1294	this value.	1970	this value, and in fact is often specified as zero.
1295		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
1296	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1977	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1297		1978
1298	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
1299	ignored. Instead, each time the periodic watcher gets scheduled, the	1980	ignored. Instead, each time the periodic watcher gets scheduled, the
1300	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
1301	current time as second argument.	1982	current time as second argument.
1302		1983
1303	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,
1304	ever, or make any event loop modifications>. If you need to stop it,	1985	or make ANY other event loop modifications whatsoever, unless explicitly
1305	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1986	allowed by documentation here>.
1306	starting an C<ev_prepare> watcher, which is legal).
1307		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
1308	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1992	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1309	ev_tstamp now)>, e.g.:	1993	*w, ev_tstamp now)>, e.g.:
1310		1994
		1995	static ev_tstamp
1311	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1996	my_rescheduler (ev_periodic *w, ev_tstamp now)
1312	{	1997	{
1313	return now + 60.;	1998	return now + 60.;
1314	}	1999	}
1315		2000
1316	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
1317	(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
1318	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
1319	might be called at other times, too.	2004	might be called at other times, too.
1320		2005
1321	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
1322	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2007	equal to the passed C<now> value >>.
1323		2008
1324	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
1325	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
1326	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
1327	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
1328	reason I omitted it as an example).	2013	reason I omitted it as an example).
1329		2014
1330	=back	2015	=back
…		…
1334	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
1335	when you changed some parameters or the reschedule callback would return	2020	when you changed some parameters or the reschedule callback would return
1336	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
1337	program when the crontabs have changed).	2022	program when the crontabs have changed).
1338		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
1339	=item ev_tstamp offset [read-write]	2031	=item ev_tstamp offset [read-write]
1340		2032
1341	When repeating, this contains the offset value, otherwise this is the	2033	When repeating, this contains the offset value, otherwise this is the
1342	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).
1343		2036
1344	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
1345	timer fires or C<ev_periodic_again> is being called.	2038	timer fires or C<ev_periodic_again> is being called.
1346		2039
1347	=item ev_tstamp interval [read-write]	2040	=item ev_tstamp interval [read-write]
1348		2041
1349	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
1350	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
1351	called.	2044	called.
1352		2045
1353	=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]
1354		2047
1355	The current reschedule callback, or C<0>, if this functionality is	2048	The current reschedule callback, or C<0>, if this functionality is
1356	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
1357	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.
1358		2051
1359	=item ev_tstamp at [read-only]
1360
1361	When active, contains the absolute time that the watcher is supposed to
1362	trigger next.
1363
1364	=back	2052	=back
1365		2053
1366	=head3 Examples	2054	=head3 Examples
1367		2055
1368	Example: Call a callback every hour, or, more precisely, whenever the	2056	Example: Call a callback every hour, or, more precisely, whenever the
1369	system clock is divisible by 3600. The callback invocation times have	2057	system time is divisible by 3600. The callback invocation times have
1370	potentially a lot of jittering, but good long-term stability.	2058	potentially a lot of jitter, but good long-term stability.
1371		2059
1372	static void	2060	static void
1373	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2061	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1374	{	2062	{
1375	... 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)
1376	}	2064	}
1377		2065
1378	struct ev_periodic hourly_tick;	2066	ev_periodic hourly_tick;
1379	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2067	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1380	ev_periodic_start (loop, &hourly_tick);	2068	ev_periodic_start (loop, &hourly_tick);
1381		2069
1382	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:
1383		2071
1384	#include <math.h>	2072	#include <math.h>
1385		2073
1386	static ev_tstamp	2074	static ev_tstamp
1387	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2075	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1388	{	2076	{
1389	return fmod (now, 3600.) + 3600.;	2077	return now + (3600. - fmod (now, 3600.));
1390	}	2078	}
1391		2079
1392	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);
1393		2081
1394	Example: Call a callback every hour, starting now:	2082	Example: Call a callback every hour, starting now:
1395		2083
1396	struct ev_periodic hourly_tick;	2084	ev_periodic hourly_tick;
1397	ev_periodic_init (&hourly_tick, clock_cb,	2085	ev_periodic_init (&hourly_tick, clock_cb,
1398	fmod (ev_now (loop), 3600.), 3600., 0);	2086	fmod (ev_now (loop), 3600.), 3600., 0);
1399	ev_periodic_start (loop, &hourly_tick);	2087	ev_periodic_start (loop, &hourly_tick);
1400		2088
1401		2089
1402	=head2 C<ev_signal> - signal me when a signal gets signalled!	2090	=head2 C<ev_signal> - signal me when a signal gets signalled!
1403		2091
1404	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
1405	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
1406	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
1407	normal event processing, like any other event.	2095	normal event processing, like any other event.
1408		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
1409	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
1410	first watcher gets started will libev actually register a signal watcher	2108	When the first watcher gets started will libev actually register something
1411	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
1412	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).
1413	watcher for a signal is stopped libev will reset the signal handler to	2111
1414	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.
1415		2122
1416	=head3 Watcher-Specific Functions and Data Members	2123	=head3 Watcher-Specific Functions and Data Members
1417		2124
1418	=over 4	2125	=over 4
1419		2126
…		…
1428		2135
1429	The signal the watcher watches out for.	2136	The signal the watcher watches out for.
1430		2137
1431	=back	2138	=back
1432		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
1433		2154
1434	=head2 C<ev_child> - watch out for process status changes	2155	=head2 C<ev_child> - watch out for process status changes
1435		2156
1436	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
1437	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).
1438		2199
1439	=head3 Watcher-Specific Functions and Data Members	2200	=head3 Watcher-Specific Functions and Data Members
1440		2201
1441	=over 4	2202	=over 4
1442		2203
…		…
1468		2229
1469	=back	2230	=back
1470		2231
1471	=head3 Examples	2232	=head3 Examples
1472		2233
1473	Example: Try to exit cleanly on SIGINT and SIGTERM.	2234	Example: C<fork()> a new process and install a child handler to wait for
		2235	its completion.
1474		2236
		2237	ev_child cw;
		2238
1475	static void	2239	static void
1476	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2240	child_cb (EV_P_ ev_child *w, int revents)
1477	{	2241	{
1478	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);
1479	}	2244	}
1480		2245
1481	struct ev_signal signal_watcher;	2246	pid_t pid = fork ();
1482	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2247
1483	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	}
1484		2260
1485		2261
1486	=head2 C<ev_stat> - did the file attributes just change?	2262	=head2 C<ev_stat> - did the file attributes just change?
1487		2263
1488	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
1489	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)
1490	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.
1491		2268
1492	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
1493	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
1494	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
1495	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
1496	the stat buffer having unspecified contents.	2273	least one) and all the other fields of the stat buffer having unspecified
		2274	contents.
1497		2275
1498	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
1499	relative and your working directory changes, the behaviour is undefined.	2278	your working directory changes, then the behaviour is undefined.
1500		2279
1501	Since there is no standard to do this, the portable implementation simply	2280	Since there is no portable change notification interface available, the
1502	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
1503	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
1504	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
1505	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
1506	five seconds, although this might change dynamically). Libev will also	2285	(which you can expect to be around five seconds, although this might
1507	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
1508	usually overkill.	2287	currently around C<0.1>, but that's usually overkill.
1509		2288
1510	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,
1511	as even with OS-supported change notifications, this can be	2290	as even with OS-supported change notifications, this can be
1512	resource-intensive.	2291	resource-intensive.
1513		2292
1514	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
1515	implemented (implementing kqueue support is left as an exercise for the	2294	is the Linux inotify interface (implementing kqueue support is left as an
1516	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
1517	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2296	implementing C<ev_stat> semantics with kqueue, except as a hint).
1518	to fall back to regular polling again even with inotify, but changes are
1519	usually detected immediately, and if the file exists there will be no
1520	polling.
1521		2297
1522	=head3 Inotify	2298	=head3 ABI Issues (Largefile Support)
1523		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
1524	When C<inotify (7)> support has been compiled into libev (generally only	2317	When C<inotify (7)> support has been compiled into libev and present at
1525	available on Linux) and present at runtime, it will be used to speed up	2318	runtime, it will be used to speed up change detection where possible. The
1526	change detection where possible. The inotify descriptor will be created lazily	2319	inotify descriptor will be created lazily when the first C<ev_stat>
1527	when the first C<ev_stat> watcher is being started.	2320	watcher is being started.
1528		2321
1529	Inotify presense does not change the semantics of C<ev_stat> watchers	2322	Inotify presence does not change the semantics of C<ev_stat> watchers
1530	except that changes might be detected earlier, and in some cases, to avoid	2323	except that changes might be detected earlier, and in some cases, to avoid
1531	making regular C<stat> calls. Even in the presense of inotify support	2324	making regular C<stat> calls. Even in the presence of inotify support
1532	there are many cases where libev has to resort to regular C<stat> polling.	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.
1533		2330
1534	(There is no support for kqueue, as apparently it cannot be used to	2331	There is no support for kqueue, as apparently it cannot be used to
1535	implement this functionality, due to the requirement of having a file	2332	implement this functionality, due to the requirement of having a file
1536	descriptor open on the object at all times).	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.
1537		2353
1538	=head3 The special problem of stat time resolution	2354	=head3 The special problem of stat time resolution
1539		2355
1540	The C<stat ()> syscall only supports full-second resolution portably, and	2356	The C<stat ()> system call only supports full-second resolution portably,
1541	even on systems where the resolution is higher, many filesystems still	2357	and even on systems where the resolution is higher, most file systems
1542	only support whole seconds.	2358	still only support whole seconds.
1543		2359
1544	That means that, if the time is the only thing that changes, you might	2360	That means that, if the time is the only thing that changes, you can
1545	miss updates: on the first update, C<ev_stat> detects a change and calls	2361	easily miss updates: on the first update, C<ev_stat> detects a change and
1546	your callback, which does something. When there is another update within	2362	calls your callback, which does something. When there is another update
1547	the same second, C<ev_stat> will be unable to detect it.	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).
1548		2365
1549	The solution to this is to delay acting on a change for a second (or till	2366	The solution to this is to delay acting on a change for slightly more
1550	the next second boundary), using a roughly one-second delay C<ev_timer>	2367	than a second (or till slightly after the next full second boundary), using
1551	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2368	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1552	is added to work around small timing inconsistencies of some operating	2369	ev_timer_again (loop, w)>).
1553	systems.	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).
1554		2379
1555	=head3 Watcher-Specific Functions and Data Members	2380	=head3 Watcher-Specific Functions and Data Members
1556		2381
1557	=over 4	2382	=over 4
1558		2383
…		…
1564	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
1565	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
1566	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
1567	path for as long as the watcher is active.	2392	path for as long as the watcher is active.
1568		2393
1569	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,
1570	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
1571	last change was detected).	2396	last change was detected).
1572		2397
1573	=item ev_stat_stat (ev_stat *)	2398	=item ev_stat_stat (loop, ev_stat *)
1574		2399
1575	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
1576	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
1577	detecting this change (while introducing a race condition). Can also be	2402	detecting this change (while introducing a race condition if you are not
1578	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.
1579		2405
1580	=item ev_statdata attr [read-only]	2406	=item ev_statdata attr [read-only]
1581		2407
1582	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
1583	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
1584	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
1585	was some error while C<stat>ing the file.	2412	some error while C<stat>ing the file.
1586		2413
1587	=item ev_statdata prev [read-only]	2414	=item ev_statdata prev [read-only]
1588		2415
1589	The previous attributes of the file. The callback gets invoked whenever	2416	The previous attributes of the file. The callback gets invoked whenever
1590	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>.
1591		2420
1592	=item ev_tstamp interval [read-only]	2421	=item ev_tstamp interval [read-only]
1593		2422
1594	The specified interval.	2423	The specified interval.
1595		2424
1596	=item const char *path [read-only]	2425	=item const char *path [read-only]
1597		2426
1598	The filesystem path that is being watched.	2427	The file system path that is being watched.
1599		2428
1600	=back	2429	=back
1601		2430
1602	=head3 Examples	2431	=head3 Examples
1603		2432
1604	Example: Watch C</etc/passwd> for attribute changes.	2433	Example: Watch C</etc/passwd> for attribute changes.
1605		2434
1606	static void	2435	static void
1607	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2436	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1608	{	2437	{
1609	/* /etc/passwd changed in some way */	2438	/* /etc/passwd changed in some way */
1610	if (w->attr.st_nlink)	2439	if (w->attr.st_nlink)
1611	{	2440	{
1612	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2441	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1613	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2442	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1614	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2443	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1615	}	2444	}
1616	else	2445	else
1617	/* you shalt not abuse printf for puts */	2446	/* you shalt not abuse printf for puts */
1618	puts ("wow, /etc/passwd is not there, expect problems. "	2447	puts ("wow, /etc/passwd is not there, expect problems. "
1619	"if this is windows, they already arrived\n");	2448	"if this is windows, they already arrived\n");
1620	}	2449	}
1621		2450
1622	...	2451	...
1623	ev_stat passwd;	2452	ev_stat passwd;
1624		2453
1625	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2454	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1626	ev_stat_start (loop, &passwd);	2455	ev_stat_start (loop, &passwd);
1627		2456
1628	Example: Like above, but additionally use a one-second delay so we do not	2457	Example: Like above, but additionally use a one-second delay so we do not
1629	miss updates (however, frequent updates will delay processing, too, so	2458	miss updates (however, frequent updates will delay processing, too, so
1630	one might do the work both on C<ev_stat> callback invocation I<and> on	2459	one might do the work both on C<ev_stat> callback invocation I<and> on
1631	C<ev_timer> callback invocation).	2460	C<ev_timer> callback invocation).
1632		2461
1633	static ev_stat passwd;	2462	static ev_stat passwd;
1634	static ev_timer timer;	2463	static ev_timer timer;
1635		2464
1636	static void	2465	static void
1637	timer_cb (EV_P_ ev_timer *w, int revents)	2466	timer_cb (EV_P_ ev_timer *w, int revents)
1638	{	2467	{
1639	ev_timer_stop (EV_A_ w);	2468	ev_timer_stop (EV_A_ w);
1640		2469
1641	/* now it's one second after the most recent passwd change */	2470	/* now it's one second after the most recent passwd change */
1642	}	2471	}
1643		2472
1644	static void	2473	static void
1645	stat_cb (EV_P_ ev_stat *w, int revents)	2474	stat_cb (EV_P_ ev_stat *w, int revents)
1646	{	2475	{
1647	/* reset the one-second timer */	2476	/* reset the one-second timer */
1648	ev_timer_again (EV_A_ &timer);	2477	ev_timer_again (EV_A_ &timer);
1649	}	2478	}
1650		2479
1651	...	2480	...
1652	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2481	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1653	ev_stat_start (loop, &passwd);	2482	ev_stat_start (loop, &passwd);
1654	ev_timer_init (&timer, timer_cb, 0., 1.01);	2483	ev_timer_init (&timer, timer_cb, 0., 1.02);
1655		2484
1656		2485
1657	=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...
1658		2487
1659	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
1660	priority are pending (prepare, check and other idle watchers do not	2489	priority are pending (prepare, check and other idle watchers do not count
1661	count).	2490	as receiving "events").
1662		2491
1663	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
1664	(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
1665	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
1666	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
…		…
1677		2506
1678	=head3 Watcher-Specific Functions and Data Members	2507	=head3 Watcher-Specific Functions and Data Members
1679		2508
1680	=over 4	2509	=over 4
1681		2510
1682	=item ev_idle_init (ev_signal *, callback)	2511	=item ev_idle_init (ev_idle *, callback)
1683		2512
1684	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
1685	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,
1686	believe me.	2515	believe me.
1687		2516
…		…
1690	=head3 Examples	2519	=head3 Examples
1691		2520
1692	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
1693	callback, free it. Also, use no error checking, as usual.	2522	callback, free it. Also, use no error checking, as usual.
1694		2523
1695	static void	2524	static void
1696	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2525	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1697	{	2526	{
1698	free (w);	2527	free (w);
1699	// now do something you wanted to do when the program has	2528	// now do something you wanted to do when the program has
1700	// no longer anything immediate to do.	2529	// no longer anything immediate to do.
1701	}	2530	}
1702		2531
1703	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2532	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1704	ev_idle_init (idle_watcher, idle_cb);	2533	ev_idle_init (idle_watcher, idle_cb);
1705	ev_idle_start (loop, idle_cb);	2534	ev_idle_start (loop, idle_watcher);
1706		2535
1707		2536
1708	=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!
1709		2538
1710	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:
1711	prepare watchers get invoked before the process blocks and check watchers	2540	prepare watchers get invoked before the process blocks and check watchers
1712	afterwards.	2541	afterwards.
1713		2542
1714	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
1715	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>
…		…
1718	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,
1719	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
1720	called in pairs bracketing the blocking call.	2549	called in pairs bracketing the blocking call.
1721		2550
1722	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
1723	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
1724	variable changes, implement your own watchers, integrate net-snmp or a	2553	variable changes, implement your own watchers, integrate net-snmp or a
1725	coroutine library and lots more. They are also occasionally useful if	2554	coroutine library and lots more. They are also occasionally useful if
1726	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,
1727	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>
1728	watcher).	2557	watcher).
1729		2558
1730	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
1731	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
1732	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
1733	provide just this functionality). Then, in the check watcher you check for	2562	libraries provide exactly this functionality). Then, in the check watcher,
1734	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
1735	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
1736	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
1737	because you never know, you know?).	2566	nevertheless, because you never know, you know?).
1738		2567
1739	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
1740	coroutines into libev programs, by yielding to other active coroutines	2569	coroutines into libev programs, by yielding to other active coroutines
1741	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
1742	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
…		…
1745	loop from blocking if lower-priority coroutines are active, thus mapping	2574	loop from blocking if lower-priority coroutines are active, thus mapping
1746	low-priority coroutines to idle/background tasks).	2575	low-priority coroutines to idle/background tasks).
1747		2576
1748	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>)
1749	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
1750	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
1751	too) should not activate ("feed") events into libev. While libev fully	2582	activate ("feed") events into libev. While libev fully supports this, they
1752	supports this, they will be called before other C<ev_check> watchers	2583	might get executed before other C<ev_check> watchers did their job. As
1753	did their job. As C<ev_check> watchers are often used to embed other	2584	C<ev_check> watchers are often used to embed other (non-libev) event
1754	(non-libev) event loops those other event loops might be in an unusable	2585	loops those other event loops might be in an unusable state until their
1755	state until their C<ev_check> watcher ran (always remind yourself to	2586	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1756	coexist peacefully with others).	2587	others).
1757		2588
1758	=head3 Watcher-Specific Functions and Data Members	2589	=head3 Watcher-Specific Functions and Data Members
1759		2590
1760	=over 4	2591	=over 4
1761		2592
…		…
1763		2594
1764	=item ev_check_init (ev_check *, callback)	2595	=item ev_check_init (ev_check *, callback)
1765		2596
1766	Initialises and configures the prepare or check watcher - they have no	2597	Initialises and configures the prepare or check watcher - they have no
1767	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>
1768	macros, but using them is utterly, utterly and completely pointless.	2599	macros, but using them is utterly, utterly, utterly and completely
		2600	pointless.
1769		2601
1770	=back	2602	=back
1771		2603
1772	=head3 Examples	2604	=head3 Examples
1773		2605
1774	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
1775	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
1776	(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
1777	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
1778	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
1779	into the Glib event loop).	2611	Glib event loop).
1780		2612
1781	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,
1782	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
1783	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
1784	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
1785	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.
1786		2618
1787	static ev_io iow [nfd];	2619	static ev_io iow [nfd];
1788	static ev_timer tw;	2620	static ev_timer tw;
1789		2621
1790	static void	2622	static void
1791	io_cb (ev_loop *loop, ev_io *w, int revents)	2623	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1792	{	2624	{
1793	}	2625	}
1794		2626
1795	// create io watchers for each fd and a timer before blocking	2627	// create io watchers for each fd and a timer before blocking
1796	static void	2628	static void
1797	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2629	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1798	{	2630	{
1799	int timeout = 3600000;	2631	int timeout = 3600000;
1800	struct pollfd fds [nfd];	2632	struct pollfd fds [nfd];
1801	// actual code will need to loop here and realloc etc.	2633	// actual code will need to loop here and realloc etc.
1802	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2634	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1803		2635
1804	/* 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 */
1805	ev_timer_init (&tw, 0, timeout * 1e-3);	2637	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1806	ev_timer_start (loop, &tw);	2638	ev_timer_start (loop, &tw);
1807		2639
1808	// create one ev_io per pollfd	2640	// create one ev_io per pollfd
1809	for (int i = 0; i < nfd; ++i)	2641	for (int i = 0; i < nfd; ++i)
1810	{	2642	{
1811	ev_io_init (iow + i, io_cb, fds [i].fd,	2643	ev_io_init (iow + i, io_cb, fds [i].fd,
1812	((fds [i].events & POLLIN ? EV_READ : 0)	2644	((fds [i].events & POLLIN ? EV_READ : 0)
1813	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2645	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1814		2646
1815	fds [i].revents = 0;	2647	fds [i].revents = 0;
1816	ev_io_start (loop, iow + i);	2648	ev_io_start (loop, iow + i);
1817	}	2649	}
1818	}	2650	}
1819		2651
1820	// stop all watchers after blocking	2652	// stop all watchers after blocking
1821	static void	2653	static void
1822	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2654	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1823	{	2655	{
1824	ev_timer_stop (loop, &tw);	2656	ev_timer_stop (loop, &tw);
1825		2657
1826	for (int i = 0; i < nfd; ++i)	2658	for (int i = 0; i < nfd; ++i)
1827	{	2659	{
1828	// set the relevant poll flags	2660	// set the relevant poll flags
1829	// could also call adns_processreadable etc. here	2661	// could also call adns_processreadable etc. here
1830	struct pollfd *fd = fds + i;	2662	struct pollfd *fd = fds + i;
1831	int revents = ev_clear_pending (iow + i);	2663	int revents = ev_clear_pending (iow + i);
1832	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2664	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1833	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2665	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1834		2666
1835	// now stop the watcher	2667	// now stop the watcher
1836	ev_io_stop (loop, iow + i);	2668	ev_io_stop (loop, iow + i);
1837	}	2669	}
1838		2670
1839	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2671	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1840	}	2672	}
1841		2673
1842	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>
1843	in the prepare watcher and would dispose of the check watcher.	2675	in the prepare watcher and would dispose of the check watcher.
1844		2676
1845	Method 3: If the module to be embedded supports explicit event	2677	Method 3: If the module to be embedded supports explicit event
1846	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
1847	callbacks, and only destroy/create the watchers in the prepare watcher.	2679	callbacks, and only destroy/create the watchers in the prepare watcher.
1848		2680
1849	static void	2681	static void
1850	timer_cb (EV_P_ ev_timer *w, int revents)	2682	timer_cb (EV_P_ ev_timer *w, int revents)
1851	{	2683	{
1852	adns_state ads = (adns_state)w->data;	2684	adns_state ads = (adns_state)w->data;
1853	update_now (EV_A);	2685	update_now (EV_A);
1854		2686
1855	adns_processtimeouts (ads, &tv_now);	2687	adns_processtimeouts (ads, &tv_now);
1856	}	2688	}
1857		2689
1858	static void	2690	static void
1859	io_cb (EV_P_ ev_io *w, int revents)	2691	io_cb (EV_P_ ev_io *w, int revents)
1860	{	2692	{
1861	adns_state ads = (adns_state)w->data;	2693	adns_state ads = (adns_state)w->data;
1862	update_now (EV_A);	2694	update_now (EV_A);
1863		2695
1864	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2696	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1865	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2697	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1866	}	2698	}
1867		2699
1868	// do not ever call adns_afterpoll	2700	// do not ever call adns_afterpoll
1869		2701
1870	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
1871	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
1872	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
1873	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
1874	this.	2706	this approach, effectively embedding EV as a client into the horrible
		2707	libglib event loop.
1875		2708
1876	static gint	2709	static gint
1877	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2710	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1878	{	2711	{
1879	int got_events = 0;	2712	int got_events = 0;
1880		2713
1881	for (n = 0; n < nfds; ++n)	2714	for (n = 0; n < nfds; ++n)
1882	// 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
1883		2716
1884	if (timeout >= 0)	2717	if (timeout >= 0)
1885	// create/start timer	2718	// create/start timer
1886		2719
1887	// poll	2720	// poll
1888	ev_loop (EV_A_ 0);	2721	ev_loop (EV_A_ 0);
1889		2722
1890	// stop timer again	2723	// stop timer again
1891	if (timeout >= 0)	2724	if (timeout >= 0)
1892	ev_timer_stop (EV_A_ &to);	2725	ev_timer_stop (EV_A_ &to);
1893		2726
1894	// stop io watchers again - their callbacks should have set	2727	// stop io watchers again - their callbacks should have set
1895	for (n = 0; n < nfds; ++n)	2728	for (n = 0; n < nfds; ++n)
1896	ev_io_stop (EV_A_ iow [n]);	2729	ev_io_stop (EV_A_ iow [n]);
1897		2730
1898	return got_events;	2731	return got_events;
1899	}	2732	}
1900		2733
1901		2734
1902	=head2 C<ev_embed> - when one backend isn't enough...	2735	=head2 C<ev_embed> - when one backend isn't enough...
1903		2736
1904	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
…		…
1910	prioritise I/O.	2743	prioritise I/O.
1911		2744
1912	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
1913	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
1914	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
1915	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
1916	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
1917	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
1918	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 :)
1919		2753
1920	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
1921	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),
1922	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
1923	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
1924	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.
1925		2759
1926	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
1927	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
1928	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
1929	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
1930	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
1931	to C<0>, in which case the embed watcher will automatically execute the	2765	to give the embedded loop strictly lower priority for example).
1932	embedded loop sweep.
1933		2766
1934	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
1935	callback will be invoked whenever some events have been handled. You can	2768	will automatically execute the embedded loop sweep whenever necessary.
1936	set the callback to C<0> to avoid having to specify one if you are not
1937	interested in that.
1938		2769
1939	Also, there have not currently been made special provisions for forking:	2770	Fork detection will be handled transparently while the C<ev_embed> watcher
1940	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
1941	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
1942	yourself.	2773	C<ev_loop_fork> on the embedded loop.
1943		2774
1944	Unfortunately, not all backends are embeddable, only the ones returned by	2775	Unfortunately, not all backends are embeddable: only the ones returned by
1945	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2776	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1946	portable one.	2777	portable one.
1947		2778
1948	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
1949	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
1950	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
1951	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.
1952		2783
		2784	=head3 C<ev_embed> and fork
		2785
		2786	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2787	automatically be applied to the embedded loop as well, so no special
		2788	fork handling is required in that case. When the watcher is not running,
		2789	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2790	as applicable.
		2791
1953	=head3 Watcher-Specific Functions and Data Members	2792	=head3 Watcher-Specific Functions and Data Members
1954		2793
1955	=over 4	2794	=over 4
1956		2795
1957	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2796	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
1960		2799
1961	Configures the watcher to embed the given loop, which must be	2800	Configures the watcher to embed the given loop, which must be
1962	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
1963	invoked automatically, otherwise it is the responsibility of the callback	2802	invoked automatically, otherwise it is the responsibility of the callback
1964	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,
1965	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).
1966		2805
1967	=item ev_embed_sweep (loop, ev_embed *)	2806	=item ev_embed_sweep (loop, ev_embed *)
1968		2807
1969	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
1970	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
1971	apropriate way for embedded loops.	2810	appropriate way for embedded loops.
1972		2811
1973	=item struct ev_loop *other [read-only]	2812	=item struct ev_loop *other [read-only]
1974		2813
1975	The embedded event loop.	2814	The embedded event loop.
1976		2815
…		…
1978		2817
1979	=head3 Examples	2818	=head3 Examples
1980		2819
1981	Example: Try to get an embeddable event loop and embed it into the default	2820	Example: Try to get an embeddable event loop and embed it into the default
1982	event loop. If that is not possible, use the default loop. The default	2821	event loop. If that is not possible, use the default loop. The default
1983	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	2822	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1984	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	2823	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1985	used).	2824	used).
1986		2825
1987	struct ev_loop *loop_hi = ev_default_init (0);	2826	struct ev_loop *loop_hi = ev_default_init (0);
1988	struct ev_loop *loop_lo = 0;	2827	struct ev_loop *loop_lo = 0;
1989	struct ev_embed embed;	2828	ev_embed embed;
1990		2829
1991	// see if there is a chance of getting one that works	2830	// see if there is a chance of getting one that works
1992	// (remember that a flags value of 0 means autodetection)	2831	// (remember that a flags value of 0 means autodetection)
1993	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2832	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1994	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2833	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1995	: 0;	2834	: 0;
1996		2835
1997	// if we got one, then embed it, otherwise default to loop_hi	2836	// if we got one, then embed it, otherwise default to loop_hi
1998	if (loop_lo)	2837	if (loop_lo)
1999	{	2838	{
2000	ev_embed_init (&embed, 0, loop_lo);	2839	ev_embed_init (&embed, 0, loop_lo);
2001	ev_embed_start (loop_hi, &embed);	2840	ev_embed_start (loop_hi, &embed);
2002	}	2841	}
2003	else	2842	else
2004	loop_lo = loop_hi;	2843	loop_lo = loop_hi;
2005		2844
2006	Example: Check if kqueue is available but not recommended and create	2845	Example: Check if kqueue is available but not recommended and create
2007	a kqueue backend for use with sockets (which usually work with any	2846	a kqueue backend for use with sockets (which usually work with any
2008	kqueue implementation). Store the kqueue/socket-only event loop in	2847	kqueue implementation). Store the kqueue/socket-only event loop in
2009	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2848	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2010		2849
2011	struct ev_loop *loop = ev_default_init (0);	2850	struct ev_loop *loop = ev_default_init (0);
2012	struct ev_loop *loop_socket = 0;	2851	struct ev_loop *loop_socket = 0;
2013	struct ev_embed embed;	2852	ev_embed embed;
2014		2853
2015	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2854	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2016	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2855	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2017	{	2856	{
2018	ev_embed_init (&embed, 0, loop_socket);	2857	ev_embed_init (&embed, 0, loop_socket);
2019	ev_embed_start (loop, &embed);	2858	ev_embed_start (loop, &embed);
2020	}	2859	}
2021		2860
2022	if (!loop_socket)	2861	if (!loop_socket)
2023	loop_socket = loop;	2862	loop_socket = loop;
2024		2863
2025	// now use loop_socket for all sockets, and loop for everything else	2864	// now use loop_socket for all sockets, and loop for everything else
2026		2865
2027		2866
2028	=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
2029		2868
2030	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
…		…
2033	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,
2034	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
2035	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
2036	handlers will be invoked, too, of course.	2875	handlers will be invoked, too, of course.
2037		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
2038	=head3 Watcher-Specific Functions and Data Members	2910	=head3 Watcher-Specific Functions and Data Members
2039		2911
2040	=over 4	2912	=over 4
2041		2913
2042	=item ev_fork_init (ev_signal *, callback)	2914	=item ev_fork_init (ev_signal *, callback)
…		…
2046	believe me.	2918	believe me.
2047		2919
2048	=back	2920	=back
2049		2921
2050		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
2051	=head1 OTHER FUNCTIONS	3075	=head1 OTHER FUNCTIONS
2052		3076
2053	There are some other functions of possible interest. Described. Here. Now.	3077	There are some other functions of possible interest. Described. Here. Now.
2054		3078
2055	=over 4	3079	=over 4
2056		3080
2057	=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)
2058		3082
2059	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
2060	callback on whichever event happens first and automatically stop both	3084	callback on whichever event happens first and automatically stops both
2061	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
2062	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
2063	more watchers yourself.	3087	more watchers yourself.
2064		3088
2065	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
2066	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
2067	C<events> set will be craeted and started.	3091	the given C<fd> and C<events> set will be created and started.
2068		3092
2069	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
2070	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
2071	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.
2072	dubious value.
2073		3096
2074	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
2075	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
2076	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>
2077	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.
2078		3103
		3104	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3105
2079	static void stdin_ready (int revents, void *arg)	3106	static void stdin_ready (int revents, void *arg)
2080	{	3107	{
2081	if (revents & EV_TIMEOUT)
2082	/* doh, nothing entered */;
2083	else if (revents & EV_READ)	3108	if (revents & EV_READ)
2084	/* 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 */;
2085	}	3112	}
2086		3113
2087	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3114	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2088		3115
2089	=item ev_feed_event (ev_loop *, watcher *, int revents)	3116	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2090		3117
2091	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
2092	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
2093	initialised but not necessarily started event watcher).	3120	initialised but not necessarily started event watcher).
2094		3121
2095	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3122	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2096		3123
2097	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
2098	the given events it.	3125	the given events it.
2099		3126
2100	=item ev_feed_signal_event (ev_loop *loop, int signum)	3127	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2101		3128
2102	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
2103	loop!).	3130	loop!).
2104		3131
2105	=back	3132	=back
2106		3133
2107		3134
…		…
2123		3150
2124	=item * Priorities are not currently supported. Initialising priorities	3151	=item * Priorities are not currently supported. Initialising priorities
2125	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
2126	is an ev_pri field.	3153	is an ev_pri field.
2127		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
2128	=item * Other members are not supported.	3158	=item * Other members are not supported.
2129		3159
2130	=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
2131	to use the libev header file and library.	3161	to use the libev header file and library.
2132		3162
2133	=back	3163	=back
2134		3164
2135	=head1 C++ SUPPORT	3165	=head1 C++ SUPPORT
2136		3166
2137	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
2138	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
2139	the callback model to a model using method callbacks on objects.	3169	the callback model to a model using method callbacks on objects.
2140		3170
2141	To use it,	3171	To use it,
2142		3172
2143	#include <ev++.h>	3173	#include <ev++.h>
2144		3174
2145	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
2146	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
2147	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
2148	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3178	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2215	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
2216	thunking function, making it as fast as a direct C callback.	3246	thunking function, making it as fast as a direct C callback.
2217		3247
2218	Example: simple class declaration and watcher initialisation	3248	Example: simple class declaration and watcher initialisation
2219		3249
2220	struct myclass	3250	struct myclass
2221	{	3251	{
2222	void io_cb (ev::io &w, int revents) { }	3252	void io_cb (ev::io &w, int revents) { }
2223	}	3253	}
2224		3254
2225	myclass obj;	3255	myclass obj;
2226	ev::io iow;	3256	ev::io iow;
2227	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);
2228		3288
2229	=item w->set<function> (void *data = 0)	3289	=item w->set<function> (void *data = 0)
2230		3290
2231	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
2232	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
…		…
2234		3294
2235	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)>.
2236		3296
2237	See the method-C<set> above for more details.	3297	See the method-C<set> above for more details.
2238		3298
2239	Example:	3299	Example: Use a plain function as callback.
2240		3300
2241	static void io_cb (ev::io &w, int revents) { }	3301	static void io_cb (ev::io &w, int revents) { }
2242	iow.set <io_cb> ();	3302	iow.set <io_cb> ();
2243		3303
2244	=item w->set (struct ev_loop *)	3304	=item w->set (struct ev_loop *)
2245		3305
2246	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
2247	do this when the watcher is inactive (and not pending either).	3307	do this when the watcher is inactive (and not pending either).
2248		3308
2249	=item w->set ([args])	3309	=item w->set ([arguments])
2250		3310
2251	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
2252	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
2253	automatically stopped and restarted when reconfiguring it with this	3313	automatically stopped and restarted when reconfiguring it with this
2254	method.	3314	method.
2255		3315
2256	=item w->start ()	3316	=item w->start ()
…		…
2280	=back	3340	=back
2281		3341
2282	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
2283	the constructor.	3343	the constructor.
2284		3344
2285	class myclass	3345	class myclass
2286	{	3346	{
2287	ev::io io; void io_cb (ev::io &w, int revents);	3347	ev::io io ; void io_cb (ev::io &w, int revents);
2288	ev:idle idle void idle_cb (ev::idle &w, int revents);	3348	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2289		3349
2290	myclass (int fd)	3350	myclass (int fd)
2291	{	3351	{
2292	io .set <myclass, &myclass::io_cb > (this);	3352	io .set <myclass, &myclass::io_cb > (this);
2293	idle.set <myclass, &myclass::idle_cb> (this);	3353	idle.set <myclass, &myclass::idle_cb> (this);
2294		3354
2295	io.start (fd, ev::READ);	3355	io.start (fd, ev::READ);
2296	}	3356	}
2297	};	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
2298		3412
2299		3413
2300	=head1 MACRO MAGIC	3414	=head1 MACRO MAGIC
2301		3415
2302	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
2303	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3417	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2304	functions and callbacks have an initial C<struct ev_loop *> argument.	3418	functions and callbacks have an initial C<struct ev_loop *> argument.
2305		3419
2306	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
2307	following macros are defined:	3421	following macros are defined:
…		…
2312		3426
2313	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
2314	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,
2315	C<EV_A_> is used when other arguments are following. Example:	3429	C<EV_A_> is used when other arguments are following. Example:
2316		3430
2317	ev_unref (EV_A);	3431	ev_unref (EV_A);
2318	ev_timer_add (EV_A_ watcher);	3432	ev_timer_add (EV_A_ watcher);
2319	ev_loop (EV_A_ 0);	3433	ev_loop (EV_A_ 0);
2320		3434
2321	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,
2322	which is often provided by the following macro.	3436	which is often provided by the following macro.
2323		3437
2324	=item C<EV_P>, C<EV_P_>	3438	=item C<EV_P>, C<EV_P_>
2325		3439
2326	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
2327	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,
2328	C<EV_P_> is used when other parameters are following. Example:	3442	C<EV_P_> is used when other parameters are following. Example:
2329		3443
2330	// this is how ev_unref is being declared	3444	// this is how ev_unref is being declared
2331	static void ev_unref (EV_P);	3445	static void ev_unref (EV_P);
2332		3446
2333	// this is how you can declare your typical callback	3447	// this is how you can declare your typical callback
2334	static void cb (EV_P_ ev_timer *w, int revents)	3448	static void cb (EV_P_ ev_timer *w, int revents)
2335		3449
2336	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
2337	suitable for use with C<EV_A>.	3451	suitable for use with C<EV_A>.
2338		3452
2339	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3453	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2340		3454
2341	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
2342	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.
2343		3467
2344	=back	3468	=back
2345		3469
2346	Example: Declare and initialise a check watcher, utilising the above	3470	Example: Declare and initialise a check watcher, utilising the above
2347	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
2348	or not.	3472	or not.
2349		3473
2350	static void	3474	static void
2351	check_cb (EV_P_ ev_timer *w, int revents)	3475	check_cb (EV_P_ ev_timer *w, int revents)
2352	{	3476	{
2353	ev_check_stop (EV_A_ w);	3477	ev_check_stop (EV_A_ w);
2354	}	3478	}
2355		3479
2356	ev_check check;	3480	ev_check check;
2357	ev_check_init (&check, check_cb);	3481	ev_check_init (&check, check_cb);
2358	ev_check_start (EV_DEFAULT_ &check);	3482	ev_check_start (EV_DEFAULT_ &check);
2359	ev_loop (EV_DEFAULT_ 0);	3483	ev_loop (EV_DEFAULT_ 0);
2360		3484
2361	=head1 EMBEDDING	3485	=head1 EMBEDDING
2362		3486
2363	Libev can (and often is) directly embedded into host	3487	Libev can (and often is) directly embedded into host
2364	applications. Examples of applications that embed it include the Deliantra	3488	applications. Examples of applications that embed it include the Deliantra
…		…
2371	libev somewhere in your source tree).	3495	libev somewhere in your source tree).
2372		3496
2373	=head2 FILESETS	3497	=head2 FILESETS
2374		3498
2375	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
2376	in your app.	3500	in your application.
2377		3501
2378	=head3 CORE EVENT LOOP	3502	=head3 CORE EVENT LOOP
2379		3503
2380	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
2381	configuration (no autoconf):	3505	configuration (no autoconf):
2382		3506
2383	#define EV_STANDALONE 1	3507	#define EV_STANDALONE 1
2384	#include "ev.c"	3508	#include "ev.c"
2385		3509
2386	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
2387	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
2388	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
2389	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
2390	where you can put other configuration options):	3514	where you can put other configuration options):
2391		3515
2392	#define EV_STANDALONE 1	3516	#define EV_STANDALONE 1
2393	#include "ev.h"	3517	#include "ev.h"
2394		3518
2395	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++
2396	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
2397	as a bug).	3521	as a bug).
2398		3522
2399	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
2400	in your include path (e.g. in libev/ when using -Ilibev):	3524	in your include path (e.g. in libev/ when using -Ilibev):
2401		3525
2402	ev.h	3526	ev.h
2403	ev.c	3527	ev.c
2404	ev_vars.h	3528	ev_vars.h
2405	ev_wrap.h	3529	ev_wrap.h
2406		3530
2407	ev_win32.c required on win32 platforms only	3531	ev_win32.c required on win32 platforms only
2408		3532
2409	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)
2410	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)
2411	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)
2412	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)
2413	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)
2414		3538
2415	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
2416	to compile this single file.	3540	to compile this single file.
2417		3541
2418	=head3 LIBEVENT COMPATIBILITY API	3542	=head3 LIBEVENT COMPATIBILITY API
2419		3543
2420	To include the libevent compatibility API, also include:	3544	To include the libevent compatibility API, also include:
2421		3545
2422	#include "event.c"	3546	#include "event.c"
2423		3547
2424	in the file including F<ev.c>, and:	3548	in the file including F<ev.c>, and:
2425		3549
2426	#include "event.h"	3550	#include "event.h"
2427		3551
2428	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>.
2429		3553
2430	You need the following additional files for this:	3554	You need the following additional files for this:
2431		3555
2432	event.h	3556	event.h
2433	event.c	3557	event.c
2434		3558
2435	=head3 AUTOCONF SUPPORT	3559	=head3 AUTOCONF SUPPORT
2436		3560
2437	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
2438	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
2439	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
2440	include F<config.h> and configure itself accordingly.	3564	include F<config.h> and configure itself accordingly.
2441		3565
2442	For this of course you need the m4 file:	3566	For this of course you need the m4 file:
2443		3567
2444	libev.m4	3568	libev.m4
2445		3569
2446	=head2 PREPROCESSOR SYMBOLS/MACROS	3570	=head2 PREPROCESSOR SYMBOLS/MACROS
2447		3571
2448	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
2449	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
2450	and only include the select backend.	3574	autoconf is documented for every option.
2451		3575
2452	=over 4	3576	=over 4
2453		3577
2454	=item EV_STANDALONE	3578	=item EV_STANDALONE
2455		3579
…		…
2457	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
2458	implementations for some libevent functions (such as logging, which is not	3582	implementations for some libevent functions (such as logging, which is not
2459	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
2460	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.
2461		3585
		3586	In stanbdalone mode, libev will still try to automatically deduce the
		3587	configuration, but has to be more conservative.
		3588
2462	=item EV_USE_MONOTONIC	3589	=item EV_USE_MONOTONIC
2463		3590
2464	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
2465	monotonic clock option at both compiletime and runtime. Otherwise no use	3592	monotonic clock option at both compile time and runtime. Otherwise no
2466	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,
2467	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
2468	the functionality isn't available is safe, though, although you have	3595	when the functionality isn't available is safe, though, although you have
2469	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>
2470	function is hiding in (often F<-lrt>).	3597	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2471		3598
2472	=item EV_USE_REALTIME	3599	=item EV_USE_REALTIME
2473		3600
2474	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
2475	realtime clock option at compiletime (and assume its availability at	3602	real-time clock option at compile time (and assume its availability
2476	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
2477	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3604	option will be attempted. This effectively replaces C<gettimeofday>
2478	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3605	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2479	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>).
2480		3620
2481	=item EV_USE_NANOSLEEP	3621	=item EV_USE_NANOSLEEP
2482		3622
2483	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
2484	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 ()>.
2485		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
2486	=item EV_USE_SELECT	3634	=item EV_USE_SELECT
2487		3635
2488	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
2489	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
2490	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
2491	will not be compiled in.	3639	will not be compiled in.
2492		3640
2493	=item EV_SELECT_USE_FD_SET	3641	=item EV_SELECT_USE_FD_SET
2494		3642
2495	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>
2496	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
2497	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
2498	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
2499	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
2500	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,
2501	influence the size of the C<fd_set> used.	3649	configures the maximum size of the C<fd_set>.
2502		3650
2503	=item EV_SELECT_IS_WINSOCKET	3651	=item EV_SELECT_IS_WINSOCKET
2504		3652
2505	When defined to C<1>, the select backend will assume that	3653	When defined to C<1>, the select backend will assume that
2506	select/socket/connect etc. don't understand file descriptors but	3654	select/socket/connect etc. don't understand file descriptors but
…		…
2526		3674
2527	=item EV_USE_EPOLL	3675	=item EV_USE_EPOLL
2528		3676
2529	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
2530	C<epoll>(7) backend. Its availability will be detected at runtime,	3678	C<epoll>(7) backend. Its availability will be detected at runtime,
2531	otherwise another method will be used as fallback. This is the	3679	otherwise another method will be used as fallback. This is the preferred
2532	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.
2533		3682
2534	=item EV_USE_KQUEUE	3683	=item EV_USE_KQUEUE
2535		3684
2536	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
2537	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,
…		…
2550	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
2551	backend for Solaris 10 systems.	3700	backend for Solaris 10 systems.
2552		3701
2553	=item EV_USE_DEVPOLL	3702	=item EV_USE_DEVPOLL
2554		3703
2555	reserved for future expansion, works like the USE symbols above.	3704	Reserved for future expansion, works like the USE symbols above.
2556		3705
2557	=item EV_USE_INOTIFY	3706	=item EV_USE_INOTIFY
2558		3707
2559	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
2560	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
2561	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.
2562		3723
2563	=item EV_H	3724	=item EV_H
2564		3725
2565	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
2566	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	3727	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
2604	When doing priority-based operations, libev usually has to linearly search	3765	When doing priority-based operations, libev usually has to linearly search
2605	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
2606	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
2607	fine.	3768	fine.
2608		3769
2609	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
2610	C<0> will save some memory and cpu.	3771	both to C<0> will save some memory and CPU.
2611		3772
2612	=item EV_PERIODIC_ENABLE	3773	=item EV_PERIODIC_ENABLE
2613		3774
2614	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
2615	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
…		…
2622	code.	3783	code.
2623		3784
2624	=item EV_EMBED_ENABLE	3785	=item EV_EMBED_ENABLE
2625		3786
2626	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
2627	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.
2628		3790
2629	=item EV_STAT_ENABLE	3791	=item EV_STAT_ENABLE
2630		3792
2631	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
2632	defined to be C<0>, then they are not.	3794	defined to be C<0>, then they are not.
…		…
2634	=item EV_FORK_ENABLE	3796	=item EV_FORK_ENABLE
2635		3797
2636	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
2637	defined to be C<0>, then they are not.	3799	defined to be C<0>, then they are not.
2638		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
2639	=item EV_MINIMAL	3806	=item EV_MINIMAL
2640		3807
2641	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
2642	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
2643	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.
2644		3831
2645	=item EV_PID_HASHSIZE	3832	=item EV_PID_HASHSIZE
2646		3833
2647	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
2648	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
…		…
2655	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>),
2656	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>
2657	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
2658	two).	3845	two).
2659		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
2660	=item EV_COMMON	3882	=item EV_COMMON
2661		3883
2662	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
2663	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
2664	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,
2665	though, and it must be identical each time.	3887	though, and it must be identical each time.
2666		3888
2667	For example, the perl EV module uses something like this:	3889	For example, the perl EV module uses something like this:
2668		3890
2669	#define EV_COMMON \	3891	#define EV_COMMON \
2670	SV *self; /* contains this struct */ \	3892	SV *self; /* contains this struct */ \
2671	SV *cb_sv, *fh /* note no trailing ";" */	3893	SV *cb_sv, *fh /* note no trailing ";" */
2672		3894
2673	=item EV_CB_DECLARE (type)	3895	=item EV_CB_DECLARE (type)
2674		3896
2675	=item EV_CB_INVOKE (watcher, revents)	3897	=item EV_CB_INVOKE (watcher, revents)
2676		3898
…		…
2681	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
2682	their default definitions. One possible use for overriding these is to	3904	their default definitions. One possible use for overriding these is to
2683	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
2684	method calls instead of plain function calls in C++.	3906	method calls instead of plain function calls in C++.
2685		3907
		3908	=back
		3909
2686	=head2 EXPORTED API SYMBOLS	3910	=head2 EXPORTED API SYMBOLS
2687		3911
2688	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
2689	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
2690	all public symbols, one per line:	3914	all public symbols, one per line:
2691		3915
2692	Symbols.ev for libev proper	3916	Symbols.ev for libev proper
2693	Symbols.event for the libevent emulation	3917	Symbols.event for the libevent emulation
2694		3918
2695	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
2696	multiple versions of libev linked together (which is obviously bad in	3920	multiple versions of libev linked together (which is obviously bad in
2697	itself, but sometimes it is inconvinient to avoid this).	3921	itself, but sometimes it is inconvenient to avoid this).
2698		3922
2699	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
2700	include before including F<ev.h>:	3924	include before including F<ev.h>:
2701		3925
2702	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3926	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2719	file.	3943	file.
2720		3944
2721	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
2722	that everybody includes and which overrides some configure choices:	3946	that everybody includes and which overrides some configure choices:
2723		3947
2724	#define EV_MINIMAL 1	3948	#define EV_MINIMAL 1
2725	#define EV_USE_POLL 0	3949	#define EV_USE_POLL 0
2726	#define EV_MULTIPLICITY 0	3950	#define EV_MULTIPLICITY 0
2727	#define EV_PERIODIC_ENABLE 0	3951	#define EV_PERIODIC_ENABLE 0
2728	#define EV_STAT_ENABLE 0	3952	#define EV_STAT_ENABLE 0
2729	#define EV_FORK_ENABLE 0	3953	#define EV_FORK_ENABLE 0
2730	#define EV_CONFIG_H <config.h>	3954	#define EV_CONFIG_H <config.h>
2731	#define EV_MINPRI 0	3955	#define EV_MINPRI 0
2732	#define EV_MAXPRI 0	3956	#define EV_MAXPRI 0
2733		3957
2734	#include "ev++.h"	3958	#include "ev++.h"
2735		3959
2736	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:
2737		3961
2738	#include "ev_cpp.h"	3962	#include "ev_cpp.h"
2739	#include "ev.c"	3963	#include "ev.c"
2740		3964
		3965	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2741		3966
2742	=head1 COMPLEXITIES	3967	=head2 THREADS AND COROUTINES
2743		3968
2744	In this section the complexities of (many of) the algorithms used inside	3969	=head3 THREADS
2745	libev will be explained. For complexity discussions about backends see the
2746	documentation for C<ev_default_init>.
2747		3970
2748	All of the following are about amortised time: If an array needs to be	3971	All libev functions are reentrant and thread-safe unless explicitly
2749	extended, libev needs to realloc and move the whole array, but this	3972	documented otherwise, but libev implements no locking itself. This means
2750	happens asymptotically never with higher number of elements, so O(1) might	3973	that you can use as many loops as you want in parallel, as long as there
2751	mean it might do a lengthy realloc operation in rare cases, but on average	3974	are no concurrent calls into any libev function with the same loop
2752	it is much faster and asymptotically approaches constant time.	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:
2753		3993
2754	=over 4	3994	=over 4
2755		3995
2756	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	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.
2757		3998
2758	This means that, when you have a watcher that triggers in one hour and	3999	This helps integrating other libraries or software modules that use libev
2759	there are 100 watchers that would trigger before that then inserting will	4000	themselves and don't care/know about threading.
2760	have to skip roughly seven (C<ld 100>) of these watchers.
2761		4001
2762	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4002	=item * one loop per thread is usually a good model.
2763		4003
2764	That means that changing a timer costs less than removing/adding them	4004	Doing this is almost never wrong, sometimes a better-performance model
2765	as only the relative motion in the event queue has to be paid for.	4005	exists, but it is always a good start.
2766		4006
2767	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	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.
2768		4009
2769	These just add the watcher into an array or at the head of a list.	4010	Choosing a model is hard - look around, learn, know that usually you can do
		4011	better than you currently do :-)
2770		4012
2771	=item Stopping check/prepare/idle watchers: O(1)	4013	=item * often you need to talk to some other thread which blocks in the
		4014	event loop.
2772		4015
2773	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4016	C<ev_async> watchers can be used to wake them up from other threads safely
		4017	(or from signal contexts...).
2774		4018
2775	These watchers are stored in lists then need to be walked to find the	4019	An example use would be to communicate signals or other events that only
2776	correct watcher to remove. The lists are usually short (you don't usually	4020	work in the default loop by registering the signal watcher with the
2777	have many watchers waiting for the same fd or signal).	4021	default loop and triggering an C<ev_async> watcher from the default loop
2778		4022	watcher callback into the event loop interested in the signal.
2779	=item Finding the next timer in each loop iteration: O(1)
2780
2781	By virtue of using a binary heap, the next timer is always found at the
2782	beginning of the storage array.
2783
2784	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2785
2786	A change means an I/O watcher gets started or stopped, which requires
2787	libev to recalculate its status (and possibly tell the kernel, depending
2788	on backend and wether C<ev_io_set> was used).
2789
2790	=item Activating one watcher (putting it into the pending state): O(1)
2791
2792	=item Priority handling: O(number_of_priorities)
2793
2794	Priorities are implemented by allocating some space for each
2795	priority. When doing priority-based operations, libev usually has to
2796	linearly search all the priorities, but starting/stopping and activating
2797	watchers becomes O(1) w.r.t. prioritiy handling.
2798		4023
2799	=back	4024	=back
2800		4025
		4026	=head4 THREAD LOCKING EXAMPLE
2801		4027
2802	=head1 Win32 platform limitations and workarounds	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
2803		4242
2804	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4243	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2805	requires, and its I/O model is fundamentally incompatible with the POSIX	4244	requires, and its I/O model is fundamentally incompatible with the POSIX
2806	model. Libev still offers limited functionality on this platform in	4245	model. Libev still offers limited functionality on this platform in
2807	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4246	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2808	descriptors. This only applies when using Win32 natively, not when using	4247	descriptors. This only applies when using Win32 natively, not when using
2809	e.g. cygwin.	4248	e.g. cygwin.
2810		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
2811	There is no supported compilation method available on windows except	4255	There is no supported compilation method available on windows except
2812	embedding it into other applications.	4256	embedding it into other applications.
2813		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
2814	Due to the many, low, and arbitrary limits on the win32 platform and the	4268	Due to the many, low, and arbitrary limits on the win32 platform and
2815	abysmal performance of winsockets, using a large number of sockets is not	4269	the abysmal performance of winsockets, using a large number of sockets
2816	recommended (and not reasonable). If your program needs to use more than	4270	is not recommended (and not reasonable). If your program needs to use
2817	a hundred or so sockets, then likely it needs to use a totally different	4271	more than a hundred or so sockets, then likely it needs to use a totally
2818	implementation for windows, as libev offers the POSIX model, which cannot	4272	different implementation for windows, as libev offers the POSIX readiness
2819	be implemented efficiently on windows (microsoft monopoly games).	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"
2820		4290
2821	=over 4	4291	=over 4
2822		4292
2823	=item The winsocket select function	4293	=item The winsocket select function
2824		4294
2825	The winsocket C<select> function doesn't follow POSIX in that it requires	4295	The winsocket C<select> function doesn't follow POSIX in that it
2826	socket I<handles> and not socket I<file descriptors>. This makes select	4296	requires socket I<handles> and not socket I<file descriptors> (it is
2827	very inefficient, and also requires a mapping from file descriptors	4297	also extremely buggy). This makes select very inefficient, and also
2828	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4298	requires a mapping from file descriptors to socket handles (the Microsoft
2829	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4299	C runtime provides the function C<_open_osfhandle> for this). See the
2830	symbols for more info.	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.
2831		4302
2832	The configuration for a "naked" win32 using the microsoft runtime	4303	The configuration for a "naked" win32 using the Microsoft runtime
2833	libraries and raw winsocket select is:	4304	libraries and raw winsocket select is:
2834		4305
2835	#define EV_USE_SELECT 1	4306	#define EV_USE_SELECT 1
2836	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4307	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2837		4308
2838	Note that winsockets handling of fd sets is O(n), so you can easily get a	4309	Note that winsockets handling of fd sets is O(n), so you can easily get a
2839	complexity in the O(n²) range when using win32.	4310	complexity in the O(n²) range when using win32.
2840		4311
2841	=item Limited number of file descriptors	4312	=item Limited number of file descriptors
2842		4313
2843	Windows has numerous arbitrary (and low) limits on things. Early versions	4314	Windows has numerous arbitrary (and low) limits on things.
2844	of winsocket's select only supported waiting for a max. of C<64> handles	4315
		4316	Early versions of winsocket's select only supported waiting for a maximum
2845	(probably owning to the fact that all windows kernels can only wait for	4317	of C<64> handles (probably owning to the fact that all windows kernels
2846	C<64> things at the same time internally; microsoft recommends spawning a	4318	can only wait for C<64> things at the same time internally; Microsoft
2847	chain of threads and wait for 63 handles and the previous thread in each).	4319	recommends spawning a chain of threads and wait for 63 handles and the
		4320	previous thread in each. Sounds great!).
2848		4321
2849	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4322	Newer versions support more handles, but you need to define C<FD_SETSIZE>
2850	to some high number (e.g. C<2048>) before compiling the winsocket select	4323	to some high number (e.g. C<2048>) before compiling the winsocket select
2851	call (which might be in libev or elsewhere, for example, perl does its own	4324	call (which might be in libev or elsewhere, for example, perl and many
2852	select emulation on windows).	4325	other interpreters do their own select emulation on windows).
2853		4326
2854	Another limit is the number of file descriptors in the microsoft runtime	4327	Another limit is the number of file descriptors in the Microsoft runtime
2855	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4328	libraries, which by default is C<64> (there must be a hidden I<64>
2856	or something like this inside microsoft). You can increase this by calling	4329	fetish or something like this inside Microsoft). You can increase this
2857	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4330	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
2858	arbitrary limit), but is broken in many versions of the microsoft runtime	4331	(another arbitrary limit), but is broken in many versions of the Microsoft
2859	libraries.
2860
2861	This might get you to about C<512> or C<2048> sockets (depending on	4332	runtime libraries. This might get you to about C<512> or C<2048> sockets
2862	windows version and/or the phase of the moon). To get more, you need to	4333	(depending on windows version and/or the phase of the moon). To get more,
2863	wrap all I/O functions and provide your own fd management, but the cost of	4334	you need to wrap all I/O functions and provide your own fd management, but
2864	calling select (O(n²)) will likely make this unworkable.	4335	the cost of calling select (O(n²)) will likely make this unworkable.
2865		4336
2866	=back	4337	=back
2867		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
		4397	=head1 ALGORITHMIC COMPLEXITIES
		4398
		4399	In this section the complexities of (many of) the algorithms used inside
		4400	libev will be documented. For complexity discussions about backends see
		4401	the documentation for C<ev_default_init>.
		4402
		4403	All of the following are about amortised time: If an array needs to be
		4404	extended, libev needs to realloc and move the whole array, but this
		4405	happens asymptotically rarer with higher number of elements, so O(1) might
		4406	mean that libev does a lengthy realloc operation in rare cases, but on
		4407	average it is much faster and asymptotically approaches constant time.
		4408
		4409	=over 4
		4410
		4411	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4412
		4413	This means that, when you have a watcher that triggers in one hour and
		4414	there are 100 watchers that would trigger before that, then inserting will
		4415	have to skip roughly seven (C<ld 100>) of these watchers.
		4416
		4417	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4418
		4419	That means that changing a timer costs less than removing/adding them,
		4420	as only the relative motion in the event queue has to be paid for.
		4421
		4422	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4423
		4424	These just add the watcher into an array or at the head of a list.
		4425
		4426	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4427
		4428	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4429
		4430	These watchers are stored in lists, so they need to be walked to find the
		4431	correct watcher to remove. The lists are usually short (you don't usually
		4432	have many watchers waiting for the same fd or signal: one is typical, two
		4433	is rare).
		4434
		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.
		4439
		4440	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4441
		4442	A change means an I/O watcher gets started or stopped, which requires
		4443	libev to recalculate its status (and possibly tell the kernel, depending
		4444	on backend and whether C<ev_io_set> was used).
		4445
		4446	=item Activating one watcher (putting it into the pending state): O(1)
		4447
		4448	=item Priority handling: O(number_of_priorities)
		4449
		4450	Priorities are implemented by allocating some space for each
		4451	priority. When doing priority-based operations, libev usually has to
		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.
		4464
		4465	=back
		4466
		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
2868		4543
2869	=head1 AUTHOR	4544	=head1 AUTHOR
2870		4545
2871	Marc Lehmann <libev@schmorp.de>.	4546	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2872		4547

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