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Revision 1.248 by root, Wed Jul 8 04:14:34 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
56		84
57	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occuring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	87	these event sources and provide your program with events.
60		88
61	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	96	watcher.
69		97
70	=head1 FEATURES	98	=head2 FEATURES
71		99
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
82		110
83	It also is quite fast (see this	111	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	112	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	113	for example).
86		114
87	=head1 CONVENTIONS	115	=head2 CONVENTIONS
88		116
89	Libev is very configurable. In this manual the default configuration will	117	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	118	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	119	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	120	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	121	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	122	name C<loop> (which is always of type C<ev_loop *>) will not have
		123	this argument.
95		124
96	=head1 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
97		126
98	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
100	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
102	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
103	it, you should treat it as such.	132	on it, you should treat it as some floating point value. Unlike the name
		133	component C<stamp> might indicate, it is also used for time differences
		134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
		155
104		156
105	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
106		158
107	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
108	library in any way.	160	library in any way.
…		…
113		165
114	Returns the current time as libev would use it. Please note that the	166	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	167	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	168	you actually want to know.
117		169
		170	=item ev_sleep (ev_tstamp interval)
		171
		172	Sleep for the given interval: The current thread will be blocked until
		173	either it is interrupted or the given time interval has passed. Basically
		174	this is a sub-second-resolution C<sleep ()>.
		175
118	=item int ev_version_major ()	176	=item int ev_version_major ()
119		177
120	=item int ev_version_minor ()	178	=item int ev_version_minor ()
121		179
122	You can find out the major and minor API/ABI version numbers of the library	180	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	181	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	182	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	183	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	184	version of the library your program was compiled against.
127		185
128	These version numbers refer to the API and ABI version of the library, not	186	These version numbers refer to the ABI version of the library, not the
129	the release version.	187	release version.
130		188
131	Usually, it's a good idea to terminate if the major versions mismatch,	189	Usually, it's a good idea to terminate if the major versions mismatch,
132	as this indicates an incompatible change. Minor versions are usually	190	as this indicates an incompatible change. Minor versions are usually
133	compatible to older versions, so a larger minor version alone is usually	191	compatible to older versions, so a larger minor version alone is usually
134	not a problem.	192	not a problem.
135		193
136	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
137	version.	195	version.
138		196
139	assert (("libev version mismatch",	197	assert (("libev version mismatch",
140	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
141	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
142		200
143	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
144		202
145	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_*>
146	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
148	a description of the set values.	206	a description of the set values.
149		207
150	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
151	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
152		210
153	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
154	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
155		213
156	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
157		215
158	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
159	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
160	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
161	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
162	(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
163	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
164		222
165	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
166		224
…		…
170	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
171	recommended ones.	229	recommended ones.
172		230
173	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
174		232
175	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
176		234
177	Sets the allocation function to use (the prototype is similar - the	235	Sets the allocation function to use (the prototype is similar - the
178	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
179	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
180	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
181	potentially destructive action. The default is your system realloc	239	or take some potentially destructive action.
182	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.
183		244
184	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
185	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,
186	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.
187		248
188	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
189	retries).	250	retries (example requires a standards-compliant C<realloc>).
190		251
191	static void *	252	static void *
192	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
193	{	254	{
194	for (;;)	255	for (;;)
…		…
203	}	264	}
204		265
205	...	266	...
206	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
207		268
208	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
209		270
210	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
211	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
212	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
213	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
214	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
215	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
216	(such as abort).	277	(such as abort).
217		278
218	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.
…		…
229		290
230	=back	291	=back
231		292
232	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
233		294
234	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>
235	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>
236	events, and dynamically created loops which do not.	297	I<function>).
237		298
238	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
239	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
240	create, you also create another event loop. Libev itself does no locking	301	not.
241	whatsoever, so if you mix calls to the same event loop in different
242	threads, make sure you lock (this is usually a bad idea, though, even if
243	done correctly, because it's hideous and inefficient).
244		302
245	=over 4	303	=over 4
246		304
247	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
248		306
…		…
252	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
253		311
254	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
255	function.	313	function.
256		314
		315	Note that this function is I<not> thread-safe, so if you want to use it
		316	from multiple threads, you have to lock (note also that this is unlikely,
		317	as loops cannot be shared easily between threads anyway).
		318
		319	The default loop is the only loop that can handle C<ev_signal> and
		320	C<ev_child> watchers, and to do this, it always registers a handler
		321	for C<SIGCHLD>. If this is a problem for your application you can either
		322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		324	C<ev_default_init>.
		325
257	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
258	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	327	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
259		328
260	The following flags are supported:	329	The following flags are supported:
261		330
…		…
266	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
267	thing, believe me).	336	thing, believe me).
268		337
269	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
270		339
271	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
272	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
273	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
274	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
275	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
276	around bugs.	345	around bugs.
…		…
282	enabling this flag.	351	enabling this flag.
283		352
284	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,
285	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
286	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
287	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
288	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
289	C<pthread_atfork> which is even faster).	358	C<pthread_atfork> which is even faster).
290		359
291	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
292	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
293	flag.	362	flag.
294		363
295	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>
296	environment variable.	365	environment variable.
297		366
298	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
299		368
300	This is your standard select(2) backend. Not I<completely> standard, as	369	This is your standard select(2) backend. Not I<completely> standard, as
301	libev tries to roll its own fd_set with no limits on the number of fds,	370	libev tries to roll its own fd_set with no limits on the number of fds,
302	but if that fails, expect a fairly low limit on the number of fds when	371	but if that fails, expect a fairly low limit on the number of fds when
303	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	372	using this backend. It doesn't scale too well (O(highest_fd)), but its
304	the fastest backend for a low number of fds.	373	usually the fastest backend for a low number of (low-numbered :) fds.
		374
		375	To get good performance out of this backend you need a high amount of
		376	parallelism (most of the file descriptors should be busy). If you are
		377	writing a server, you should C<accept ()> in a loop to accept as many
		378	connections as possible during one iteration. You might also want to have
		379	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		380	readiness notifications you get per iteration.
		381
		382	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		383	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		384	C<exceptfds> set on that platform).
305		385
306	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	386	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
307		387
308	And this is your standard poll(2) backend. It's more complicated than	388	And this is your standard poll(2) backend. It's more complicated
309	select, but handles sparse fds better and has no artificial limit on the	389	than select, but handles sparse fds better and has no artificial
310	number of fds you can use (except it will slow down considerably with a	390	limit on the number of fds you can use (except it will slow down
311	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	391	considerably with a lot of inactive fds). It scales similarly to select,
		392	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		393	performance tips.
		394
		395	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		396	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
312		397
313	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
314		399
315	For few fds, this backend is a bit little slower than poll and select,	400	For few fds, this backend is a bit little slower than poll and select,
316	but it scales phenomenally better. While poll and select usually scale like	401	but it scales phenomenally better. While poll and select usually scale
317	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	402	like O(total_fds) where n is the total number of fds (or the highest fd),
318	either O(1) or O(active_fds).	403	epoll scales either O(1) or O(active_fds).
319		404
		405	The epoll mechanism deserves honorable mention as the most misdesigned
		406	of the more advanced event mechanisms: mere annoyances include silently
		407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
		421
320	While stopping and starting an I/O watcher in the same iteration will	422	While stopping, setting and starting an I/O watcher in the same iteration
321	result in some caching, there is still a syscall per such incident	423	will result in some caching, there is still a system call per such
322	(because the fd could point to a different file description now), so its	424	incident (because the same I<file descriptor> could point to a different
323	best to avoid that. Also, dup()ed file descriptors might not work very	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
324	well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
		427	file descriptors.
325		428
326	Please note that epoll sometimes generates spurious notifications, so you	429	Best performance from this backend is achieved by not unregistering all
327	need to use non-blocking I/O or other means to avoid blocking when no data	430	watchers for a file descriptor until it has been closed, if possible,
328	(or space) is available.	431	i.e. keep at least one watcher active per fd at all times. Stopping and
		432	starting a watcher (without re-setting it) also usually doesn't cause
		433	extra overhead. A fork can both result in spurious notifications as well
		434	as in libev having to destroy and recreate the epoll object, which can
		435	take considerable time and thus should be avoided.
		436
		437	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		438	faster than epoll for maybe up to a hundred file descriptors, depending on
		439	the usage. So sad.
		440
		441	While nominally embeddable in other event loops, this feature is broken in
		442	all kernel versions tested so far.
		443
		444	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		445	C<EVBACKEND_POLL>.
329		446
330	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
331		448
332	Kqueue deserves special mention, as at the time of this writing, it	449	Kqueue deserves special mention, as at the time of this writing, it
333	was broken on all BSDs except NetBSD (usually it doesn't work with	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
334	anything but sockets and pipes, except on Darwin, where of course its	451	with anything but sockets and pipes, except on Darwin, where of course
335	completely useless). For this reason its not being "autodetected"	452	it's completely useless). Unlike epoll, however, whose brokenness
		453	is by design, these kqueue bugs can (and eventually will) be fixed
		454	without API changes to existing programs. For this reason it's not being
336	unless you explicitly specify it explicitly in the flags (i.e. using	455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
337	C<EVBACKEND_KQUEUE>).	456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		457	system like NetBSD.
		458
		459	You still can embed kqueue into a normal poll or select backend and use it
		460	only for sockets (after having made sure that sockets work with kqueue on
		461	the target platform). See C<ev_embed> watchers for more info.
338		462
339	It scales in the same way as the epoll backend, but the interface to the	463	It scales in the same way as the epoll backend, but the interface to the
340	kernel is more efficient (which says nothing about its actual speed, of	464	kernel is more efficient (which says nothing about its actual speed, of
341	course). While starting and stopping an I/O watcher does not cause an	465	course). While stopping, setting and starting an I/O watcher does never
342	extra syscall as with epoll, it still adds up to four event changes per	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
343	incident, so its best to avoid that.	467	two event changes per incident. Support for C<fork ()> is very bad (but
		468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
		470
		471	This backend usually performs well under most conditions.
		472
		473	While nominally embeddable in other event loops, this doesn't work
		474	everywhere, so you might need to test for this. And since it is broken
		475	almost everywhere, you should only use it when you have a lot of sockets
		476	(for which it usually works), by embedding it into another event loop
		477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		478	also broken on OS X)) and, did I mention it, using it only for sockets.
		479
		480	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		482	C<NOTE_EOF>.
344		483
345	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
346		485
347	This is not implemented yet (and might never be).	486	This is not implemented yet (and might never be, unless you send me an
		487	implementation). According to reports, C</dev/poll> only supports sockets
		488	and is not embeddable, which would limit the usefulness of this backend
		489	immensely.
348		490
349	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
350		492
351	This uses the Solaris 10 port mechanism. As with everything on Solaris,	493	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
352	it's really slow, but it still scales very well (O(active_fds)).	494	it's really slow, but it still scales very well (O(active_fds)).
353		495
354	Please note that solaris ports can result in a lot of spurious	496	Please note that Solaris event ports can deliver a lot of spurious
355	notifications, so you need to use non-blocking I/O or other means to avoid	497	notifications, so you need to use non-blocking I/O or other means to avoid
356	blocking when no data (or space) is available.	498	blocking when no data (or space) is available.
		499
		500	While this backend scales well, it requires one system call per active
		501	file descriptor per loop iteration. For small and medium numbers of file
		502	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		503	might perform better.
		504
		505	On the positive side, with the exception of the spurious readiness
		506	notifications, this backend actually performed fully to specification
		507	in all tests and is fully embeddable, which is a rare feat among the
		508	OS-specific backends (I vastly prefer correctness over speed hacks).
		509
		510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		511	C<EVBACKEND_POLL>.
357		512
358	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
359		514
360	Try all backends (even potentially broken ones that wouldn't be tried	515	Try all backends (even potentially broken ones that wouldn't be tried
361	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	516	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
362	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	517	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
363		518
		519	It is definitely not recommended to use this flag.
		520
364	=back	521	=back
365		522
366	If one or more of these are ored into the flags value, then only these	523	If one or more of these are or'ed into the flags value, then only these
367	backends will be tried (in the reverse order as given here). If none are	524	backends will be tried (in the reverse order as listed here). If none are
368	specified, most compiled-in backend will be tried, usually in reverse	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
369	order of their flag values :)
370		526
371	The most typical usage is like this:	527	Example: This is the most typical usage.
372		528
373	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
374	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
375		531
376	Restrict libev to the select and poll backends, and do not allow	532	Example: Restrict libev to the select and poll backends, and do not allow
377	environment settings to be taken into account:	533	environment settings to be taken into account:
378		534
379	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
380		536
381	Use whatever libev has to offer, but make sure that kqueue is used if	537	Example: Use whatever libev has to offer, but make sure that kqueue is
382	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
383	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
384		541
385	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
386		543
387	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
388		545
389	Similar to C<ev_default_loop>, but always creates a new event loop that is	546	Similar to C<ev_default_loop>, but always creates a new event loop that is
390	always distinct from the default loop. Unlike the default loop, it cannot	547	always distinct from the default loop. Unlike the default loop, it cannot
391	handle signal and child watchers, and attempts to do so will be greeted by	548	handle signal and child watchers, and attempts to do so will be greeted by
392	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
393		550
		551	Note that this function I<is> thread-safe, and the recommended way to use
		552	libev with threads is indeed to create one loop per thread, and using the
		553	default loop in the "main" or "initial" thread.
		554
394	Example: Try to create a event loop that uses epoll and nothing else.	555	Example: Try to create a event loop that uses epoll and nothing else.
395		556
396	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
397	if (!epoller)	558	if (!epoller)
398	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
399		560
400	=item ev_default_destroy ()	561	=item ev_default_destroy ()
401		562
402	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
403	etc.). None of the active event watchers will be stopped in the normal	564	etc.). None of the active event watchers will be stopped in the normal
404	sense, so e.g. C<ev_is_active> might still return true. It is your	565	sense, so e.g. C<ev_is_active> might still return true. It is your
405	responsibility to either stop all watchers cleanly yoursef I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
406	calling this function, or cope with the fact afterwards (which is usually	567	calling this function, or cope with the fact afterwards (which is usually
407	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
408	for example).	569	for example).
		570
		571	Note that certain global state, such as signal state (and installed signal
		572	handlers), will not be freed by this function, and related watchers (such
		573	as signal and child watchers) would need to be stopped manually.
		574
		575	In general it is not advisable to call this function except in the
		576	rare occasion where you really need to free e.g. the signal handling
		577	pipe fds. If you need dynamically allocated loops it is better to use
		578	C<ev_loop_new> and C<ev_loop_destroy>).
409		579
410	=item ev_loop_destroy (loop)	580	=item ev_loop_destroy (loop)
411		581
412	Like C<ev_default_destroy>, but destroys an event loop created by an	582	Like C<ev_default_destroy>, but destroys an event loop created by an
413	earlier call to C<ev_loop_new>.	583	earlier call to C<ev_loop_new>.
414		584
415	=item ev_default_fork ()	585	=item ev_default_fork ()
416		586
		587	This function sets a flag that causes subsequent C<ev_loop> iterations
417	This function reinitialises the kernel state for backends that have	588	to reinitialise the kernel state for backends that have one. Despite the
418	one. Despite the name, you can call it anytime, but it makes most sense	589	name, you can call it anytime, but it makes most sense after forking, in
419	after forking, in either the parent or child process (or both, but that	590	the child process (or both child and parent, but that again makes little
420	again makes little sense).	591	sense). You I<must> call it in the child before using any of the libev
		592	functions, and it will only take effect at the next C<ev_loop> iteration.
421		593
422	You I<must> call this function in the child process after forking if and	594	On the other hand, you only need to call this function in the child
423	only if you want to use the event library in both processes. If you just	595	process if and only if you want to use the event library in the child. If
424	fork+exec, you don't have to call it.	596	you just fork+exec, you don't have to call it at all.
425		597
426	The function itself is quite fast and it's usually not a problem to call	598	The function itself is quite fast and it's usually not a problem to call
427	it just in case after a fork. To make this easy, the function will fit in	599	it just in case after a fork. To make this easy, the function will fit in
428	quite nicely into a call to C<pthread_atfork>:	600	quite nicely into a call to C<pthread_atfork>:
429		601
430	pthread_atfork (0, 0, ev_default_fork);	602	pthread_atfork (0, 0, ev_default_fork);
431		603
432	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
433	without calling this function, so if you force one of those backends you
434	do not need to care.
435
436	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
437		605
438	Like C<ev_default_fork>, but acts on an event loop created by	606	Like C<ev_default_fork>, but acts on an event loop created by
439	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	607	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
440	after fork, and how you do this is entirely your own problem.	608	after fork that you want to re-use in the child, and how you do this is
		609	entirely your own problem.
		610
		611	=item int ev_is_default_loop (loop)
		612
		613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
441		615
442	=item unsigned int ev_loop_count (loop)	616	=item unsigned int ev_loop_count (loop)
443		617
444	Returns the count of loop iterations for the loop, which is identical to	618	Returns the count of loop iterations for the loop, which is identical to
445	the number of times libev did poll for new events. It starts at C<0> and	619	the number of times libev did poll for new events. It starts at C<0> and
446	happily wraps around with enough iterations.	620	happily wraps around with enough iterations.
447		621
448	This value can sometimes be useful as a generation counter of sorts (it	622	This value can sometimes be useful as a generation counter of sorts (it
449	"ticks" the number of loop iterations), as it roughly corresponds with	623	"ticks" the number of loop iterations), as it roughly corresponds with
450	C<ev_prepare> and C<ev_check> calls.	624	C<ev_prepare> and C<ev_check> calls.
		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
451		637
452	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
453		639
454	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
455	use.	641	use.
…		…
458		644
459	Returns the current "event loop time", which is the time the event loop	645	Returns the current "event loop time", which is the time the event loop
460	received events and started processing them. This timestamp does not	646	received events and started processing them. This timestamp does not
461	change as long as callbacks are being processed, and this is also the base	647	change as long as callbacks are being processed, and this is also the base
462	time used for relative timers. You can treat it as the timestamp of the	648	time used for relative timers. You can treat it as the timestamp of the
463	event occuring (or more correctly, libev finding out about it).	649	event occurring (or more correctly, libev finding out about it).
		650
		651	=item ev_now_update (loop)
		652
		653	Establishes the current time by querying the kernel, updating the time
		654	returned by C<ev_now ()> in the progress. This is a costly operation and
		655	is usually done automatically within C<ev_loop ()>.
		656
		657	This function is rarely useful, but when some event callback runs for a
		658	very long time without entering the event loop, updating libev's idea of
		659	the current time is a good idea.
		660
		661	See also L<The special problem of time updates> in the C<ev_timer> section.
		662
		663	=item ev_suspend (loop)
		664
		665	=item ev_resume (loop)
		666
		667	These two functions suspend and resume a loop, for use when the loop is
		668	not used for a while and timeouts should not be processed.
		669
		670	A typical use case would be an interactive program such as a game: When
		671	the user presses C<^Z> to suspend the game and resumes it an hour later it
		672	would be best to handle timeouts as if no time had actually passed while
		673	the program was suspended. This can be achieved by calling C<ev_suspend>
		674	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		675	C<ev_resume> directly afterwards to resume timer processing.
		676
		677	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		678	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		679	will be rescheduled (that is, they will lose any events that would have
		680	occured while suspended).
		681
		682	After calling C<ev_suspend> you B<must not> call I<any> function on the
		683	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		684	without a previous call to C<ev_suspend>.
		685
		686	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		687	event loop time (see C<ev_now_update>).
464		688
465	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
466		690
467	Finally, this is it, the event handler. This function usually is called	691	Finally, this is it, the event handler. This function usually is called
468	after you initialised all your watchers and you want to start handling	692	after you initialised all your watchers and you want to start handling
…		…
471	If the flags argument is specified as C<0>, it will not return until	695	If the flags argument is specified as C<0>, it will not return until
472	either no event watchers are active anymore or C<ev_unloop> was called.	696	either no event watchers are active anymore or C<ev_unloop> was called.
473		697
474	Please note that an explicit C<ev_unloop> is usually better than	698	Please note that an explicit C<ev_unloop> is usually better than
475	relying on all watchers to be stopped when deciding when a program has	699	relying on all watchers to be stopped when deciding when a program has
476	finished (especially in interactive programs), but having a program that	700	finished (especially in interactive programs), but having a program
477	automatically loops as long as it has to and no longer by virtue of	701	that automatically loops as long as it has to and no longer by virtue
478	relying on its watchers stopping correctly is a thing of beauty.	702	of relying on its watchers stopping correctly, that is truly a thing of
		703	beauty.
479		704
480	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	705	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
481	those events and any outstanding ones, but will not block your process in	706	those events and any already outstanding ones, but will not block your
482	case there are no events and will return after one iteration of the loop.	707	process in case there are no events and will return after one iteration of
		708	the loop.
483		709
484	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	710	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
485	neccessary) and will handle those and any outstanding ones. It will block	711	necessary) and will handle those and any already outstanding ones. It
486	your process until at least one new event arrives, and will return after	712	will block your process until at least one new event arrives (which could
487	one iteration of the loop. This is useful if you are waiting for some	713	be an event internal to libev itself, so there is no guarantee that a
488	external event in conjunction with something not expressible using other	714	user-registered callback will be called), and will return after one
		715	iteration of the loop.
		716
		717	This is useful if you are waiting for some external event in conjunction
		718	with something not expressible using other libev watchers (i.e. "roll your
489	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	719	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
490	usually a better approach for this kind of thing.	720	usually a better approach for this kind of thing.
491		721
492	Here are the gory details of what C<ev_loop> does:	722	Here are the gory details of what C<ev_loop> does:
493		723
494	- Before the first iteration, call any pending watchers.	724	- Before the first iteration, call any pending watchers.
495	* If there are no active watchers (reference count is zero), return.	725	* If EVFLAG_FORKCHECK was used, check for a fork.
496	- Queue all prepare watchers and then call all outstanding watchers.	726	- If a fork was detected (by any means), queue and call all fork watchers.
		727	- Queue and call all prepare watchers.
497	- If we have been forked, recreate the kernel state.	728	- If we have been forked, detach and recreate the kernel state
		729	as to not disturb the other process.
498	- Update the kernel state with all outstanding changes.	730	- Update the kernel state with all outstanding changes.
499	- Update the "event loop time".	731	- Update the "event loop time" (ev_now ()).
500	- Calculate for how long to block.	732	- Calculate for how long to sleep or block, if at all
		733	(active idle watchers, EVLOOP_NONBLOCK or not having
		734	any active watchers at all will result in not sleeping).
		735	- Sleep if the I/O and timer collect interval say so.
501	- Block the process, waiting for any events.	736	- Block the process, waiting for any events.
502	- Queue all outstanding I/O (fd) events.	737	- Queue all outstanding I/O (fd) events.
503	- Update the "event loop time" and do time jump handling.	738	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
504	- Queue all outstanding timers.	739	- Queue all expired timers.
505	- Queue all outstanding periodics.	740	- Queue all expired periodics.
506	- If no events are pending now, queue all idle watchers.	741	- Unless any events are pending now, queue all idle watchers.
507	- Queue all check watchers.	742	- Queue all check watchers.
508	- Call all queued watchers in reverse order (i.e. check watchers first).	743	- Call all queued watchers in reverse order (i.e. check watchers first).
509	Signals and child watchers are implemented as I/O watchers, and will	744	Signals and child watchers are implemented as I/O watchers, and will
510	be handled here by queueing them when their watcher gets executed.	745	be handled here by queueing them when their watcher gets executed.
511	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	746	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
512	were used, return, otherwise continue with step *.	747	were used, or there are no active watchers, return, otherwise
		748	continue with step *.
513		749
514	Example: Queue some jobs and then loop until no events are outsanding	750	Example: Queue some jobs and then loop until no events are outstanding
515	anymore.	751	anymore.
516		752
517	... queue jobs here, make sure they register event watchers as long	753	... queue jobs here, make sure they register event watchers as long
518	... as they still have work to do (even an idle watcher will do..)	754	... as they still have work to do (even an idle watcher will do..)
519	ev_loop (my_loop, 0);	755	ev_loop (my_loop, 0);
520	... jobs done. yeah!	756	... jobs done or somebody called unloop. yeah!
521		757
522	=item ev_unloop (loop, how)	758	=item ev_unloop (loop, how)
523		759
524	Can be used to make a call to C<ev_loop> return early (but only after it	760	Can be used to make a call to C<ev_loop> return early (but only after it
525	has processed all outstanding events). The C<how> argument must be either	761	has processed all outstanding events). The C<how> argument must be either
526	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	762	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
527	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	763	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
528		764
		765	This "unloop state" will be cleared when entering C<ev_loop> again.
		766
		767	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		768
529	=item ev_ref (loop)	769	=item ev_ref (loop)
530		770
531	=item ev_unref (loop)	771	=item ev_unref (loop)
532		772
533	Ref/unref can be used to add or remove a reference count on the event	773	Ref/unref can be used to add or remove a reference count on the event
534	loop: Every watcher keeps one reference, and as long as the reference	774	loop: Every watcher keeps one reference, and as long as the reference
535	count is nonzero, C<ev_loop> will not return on its own. If you have	775	count is nonzero, C<ev_loop> will not return on its own.
		776
536	a watcher you never unregister that should not keep C<ev_loop> from	777	If you have a watcher you never unregister that should not keep C<ev_loop>
537	returning, ev_unref() after starting, and ev_ref() before stopping it. For	778	from returning, call ev_unref() after starting, and ev_ref() before
		779	stopping it.
		780
538	example, libev itself uses this for its internal signal pipe: It is not	781	As an example, libev itself uses this for its internal signal pipe: It
539	visible to the libev user and should not keep C<ev_loop> from exiting if	782	is not visible to the libev user and should not keep C<ev_loop> from
540	no event watchers registered by it are active. It is also an excellent	783	exiting if no event watchers registered by it are active. It is also an
541	way to do this for generic recurring timers or from within third-party	784	excellent way to do this for generic recurring timers or from within
542	libraries. Just remember to I<unref after start> and I<ref before stop>.	785	third-party libraries. Just remember to I<unref after start> and I<ref
		786	before stop> (but only if the watcher wasn't active before, or was active
		787	before, respectively. Note also that libev might stop watchers itself
		788	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		789	in the callback).
543		790
544	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	791	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
545	running when nothing else is active.	792	running when nothing else is active.
546		793
547	struct ev_signal exitsig;	794	ev_signal exitsig;
548	ev_signal_init (&exitsig, sig_cb, SIGINT);	795	ev_signal_init (&exitsig, sig_cb, SIGINT);
549	ev_signal_start (loop, &exitsig);	796	ev_signal_start (loop, &exitsig);
550	evf_unref (loop);	797	evf_unref (loop);
551		798
552	Example: For some weird reason, unregister the above signal handler again.	799	Example: For some weird reason, unregister the above signal handler again.
553		800
554	ev_ref (loop);	801	ev_ref (loop);
555	ev_signal_stop (loop, &exitsig);	802	ev_signal_stop (loop, &exitsig);
		803
		804	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		805
		806	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		807
		808	These advanced functions influence the time that libev will spend waiting
		809	for events. Both time intervals are by default C<0>, meaning that libev
		810	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		811	latency.
		812
		813	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		814	allows libev to delay invocation of I/O and timer/periodic callbacks
		815	to increase efficiency of loop iterations (or to increase power-saving
		816	opportunities).
		817
		818	The idea is that sometimes your program runs just fast enough to handle
		819	one (or very few) event(s) per loop iteration. While this makes the
		820	program responsive, it also wastes a lot of CPU time to poll for new
		821	events, especially with backends like C<select ()> which have a high
		822	overhead for the actual polling but can deliver many events at once.
		823
		824	By setting a higher I<io collect interval> you allow libev to spend more
		825	time collecting I/O events, so you can handle more events per iteration,
		826	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		827	C<ev_timer>) will be not affected. Setting this to a non-null value will
		828	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		829	sleep time ensures that libev will not poll for I/O events more often then
		830	once per this interval, on average.
		831
		832	Likewise, by setting a higher I<timeout collect interval> you allow libev
		833	to spend more time collecting timeouts, at the expense of increased
		834	latency/jitter/inexactness (the watcher callback will be called
		835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		836	value will not introduce any overhead in libev.
		837
		838	Many (busy) programs can usually benefit by setting the I/O collect
		839	interval to a value near C<0.1> or so, which is often enough for
		840	interactive servers (of course not for games), likewise for timeouts. It
		841	usually doesn't make much sense to set it to a lower value than C<0.01>,
		842	as this approaches the timing granularity of most systems. Note that if
		843	you do transactions with the outside world and you can't increase the
		844	parallelity, then this setting will limit your transaction rate (if you
		845	need to poll once per transaction and the I/O collect interval is 0.01,
		846	then you can't do more than 100 transations per second).
		847
		848	Setting the I<timeout collect interval> can improve the opportunity for
		849	saving power, as the program will "bundle" timer callback invocations that
		850	are "near" in time together, by delaying some, thus reducing the number of
		851	times the process sleeps and wakes up again. Another useful technique to
		852	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		853	they fire on, say, one-second boundaries only.
		854
		855	Example: we only need 0.1s timeout granularity, and we wish not to poll
		856	more often than 100 times per second:
		857
		858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		860
		861	=item ev_loop_verify (loop)
		862
		863	This function only does something when C<EV_VERIFY> support has been
		864	compiled in, which is the default for non-minimal builds. It tries to go
		865	through all internal structures and checks them for validity. If anything
		866	is found to be inconsistent, it will print an error message to standard
		867	error and call C<abort ()>.
		868
		869	This can be used to catch bugs inside libev itself: under normal
		870	circumstances, this function will never abort as of course libev keeps its
		871	data structures consistent.
556		872
557	=back	873	=back
558		874
559		875
560	=head1 ANATOMY OF A WATCHER	876	=head1 ANATOMY OF A WATCHER
		877
		878	In the following description, uppercase C<TYPE> in names stands for the
		879	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		880	watchers and C<ev_io_start> for I/O watchers.
561		881
562	A watcher is a structure that you create and register to record your	882	A watcher is a structure that you create and register to record your
563	interest in some event. For instance, if you want to wait for STDIN to	883	interest in some event. For instance, if you want to wait for STDIN to
564	become readable, you would create an C<ev_io> watcher for that:	884	become readable, you would create an C<ev_io> watcher for that:
565		885
566	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	886	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
567	{	887	{
568	ev_io_stop (w);	888	ev_io_stop (w);
569	ev_unloop (loop, EVUNLOOP_ALL);	889	ev_unloop (loop, EVUNLOOP_ALL);
570	}	890	}
571		891
572	struct ev_loop *loop = ev_default_loop (0);	892	struct ev_loop *loop = ev_default_loop (0);
		893
573	struct ev_io stdin_watcher;	894	ev_io stdin_watcher;
		895
574	ev_init (&stdin_watcher, my_cb);	896	ev_init (&stdin_watcher, my_cb);
575	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	897	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
576	ev_io_start (loop, &stdin_watcher);	898	ev_io_start (loop, &stdin_watcher);
		899
577	ev_loop (loop, 0);	900	ev_loop (loop, 0);
578		901
579	As you can see, you are responsible for allocating the memory for your	902	As you can see, you are responsible for allocating the memory for your
580	watcher structures (and it is usually a bad idea to do this on the stack,	903	watcher structures (and it is I<usually> a bad idea to do this on the
581	although this can sometimes be quite valid).	904	stack).
		905
		906	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		907	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
582		908
583	Each watcher structure must be initialised by a call to C<ev_init	909	Each watcher structure must be initialised by a call to C<ev_init
584	(watcher *, callback)>, which expects a callback to be provided. This	910	(watcher *, callback)>, which expects a callback to be provided. This
585	callback gets invoked each time the event occurs (or, in the case of io	911	callback gets invoked each time the event occurs (or, in the case of I/O
586	watchers, each time the event loop detects that the file descriptor given	912	watchers, each time the event loop detects that the file descriptor given
587	is readable and/or writable).	913	is readable and/or writable).
588		914
589	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	915	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
590	with arguments specific to this watcher type. There is also a macro	916	macro to configure it, with arguments specific to the watcher type. There
591	to combine initialisation and setting in one call: C<< ev_<type>_init	917	is also a macro to combine initialisation and setting in one call: C<<
592	(watcher *, callback, ...) >>.	918	ev_TYPE_init (watcher *, callback, ...) >>.
593		919
594	To make the watcher actually watch out for events, you have to start it	920	To make the watcher actually watch out for events, you have to start it
595	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	921	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
596	*) >>), and you can stop watching for events at any time by calling the	922	*) >>), and you can stop watching for events at any time by calling the
597	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	923	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
598		924
599	As long as your watcher is active (has been started but not stopped) you	925	As long as your watcher is active (has been started but not stopped) you
600	must not touch the values stored in it. Most specifically you must never	926	must not touch the values stored in it. Most specifically you must never
601	reinitialise it or call its C<set> macro.	927	reinitialise it or call its C<ev_TYPE_set> macro.
602		928
603	Each and every callback receives the event loop pointer as first, the	929	Each and every callback receives the event loop pointer as first, the
604	registered watcher structure as second, and a bitset of received events as	930	registered watcher structure as second, and a bitset of received events as
605	third argument.	931	third argument.
606		932
…		…
660	=item C<EV_FORK>	986	=item C<EV_FORK>
661		987
662	The event loop has been resumed in the child process after fork (see	988	The event loop has been resumed in the child process after fork (see
663	C<ev_fork>).	989	C<ev_fork>).
664		990
		991	=item C<EV_ASYNC>
		992
		993	The given async watcher has been asynchronously notified (see C<ev_async>).
		994
		995	=item C<EV_CUSTOM>
		996
		997	Not ever sent (or otherwise used) by libev itself, but can be freely used
		998	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		999
665	=item C<EV_ERROR>	1000	=item C<EV_ERROR>
666		1001
667	An unspecified error has occured, the watcher has been stopped. This might	1002	An unspecified error has occurred, the watcher has been stopped. This might
668	happen because the watcher could not be properly started because libev	1003	happen because the watcher could not be properly started because libev
669	ran out of memory, a file descriptor was found to be closed or any other	1004	ran out of memory, a file descriptor was found to be closed or any other
		1005	problem. Libev considers these application bugs.
		1006
670	problem. You best act on it by reporting the problem and somehow coping	1007	You best act on it by reporting the problem and somehow coping with the
671	with the watcher being stopped.	1008	watcher being stopped. Note that well-written programs should not receive
		1009	an error ever, so when your watcher receives it, this usually indicates a
		1010	bug in your program.
672		1011
673	Libev will usually signal a few "dummy" events together with an error,	1012	Libev will usually signal a few "dummy" events together with an error, for
674	for example it might indicate that a fd is readable or writable, and if	1013	example it might indicate that a fd is readable or writable, and if your
675	your callbacks is well-written it can just attempt the operation and cope	1014	callbacks is well-written it can just attempt the operation and cope with
676	with the error from read() or write(). This will not work in multithreaded	1015	the error from read() or write(). This will not work in multi-threaded
677	programs, though, so beware.	1016	programs, though, as the fd could already be closed and reused for another
		1017	thing, so beware.
678		1018
679	=back	1019	=back
680		1020
681	=head2 GENERIC WATCHER FUNCTIONS	1021	=head2 GENERIC WATCHER FUNCTIONS
682
683	In the following description, C<TYPE> stands for the watcher type,
684	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
685		1022
686	=over 4	1023	=over 4
687		1024
688	=item C<ev_init> (ev_TYPE *watcher, callback)	1025	=item C<ev_init> (ev_TYPE *watcher, callback)
689		1026
…		…
695	which rolls both calls into one.	1032	which rolls both calls into one.
696		1033
697	You can reinitialise a watcher at any time as long as it has been stopped	1034	You can reinitialise a watcher at any time as long as it has been stopped
698	(or never started) and there are no pending events outstanding.	1035	(or never started) and there are no pending events outstanding.
699		1036
700	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1037	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
701	int revents)>.	1038	int revents)>.
		1039
		1040	Example: Initialise an C<ev_io> watcher in two steps.
		1041
		1042	ev_io w;
		1043	ev_init (&w, my_cb);
		1044	ev_io_set (&w, STDIN_FILENO, EV_READ);
702		1045
703	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1046	=item C<ev_TYPE_set> (ev_TYPE *, [args])
704		1047
705	This macro initialises the type-specific parts of a watcher. You need to	1048	This macro initialises the type-specific parts of a watcher. You need to
706	call C<ev_init> at least once before you call this macro, but you can	1049	call C<ev_init> at least once before you call this macro, but you can
…		…
709	difference to the C<ev_init> macro).	1052	difference to the C<ev_init> macro).
710		1053
711	Although some watcher types do not have type-specific arguments	1054	Although some watcher types do not have type-specific arguments
712	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1055	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
713		1056
		1057	See C<ev_init>, above, for an example.
		1058
714	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1059	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
715		1060
716	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1061	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
717	calls into a single call. This is the most convinient method to initialise	1062	calls into a single call. This is the most convenient method to initialise
718	a watcher. The same limitations apply, of course.	1063	a watcher. The same limitations apply, of course.
		1064
		1065	Example: Initialise and set an C<ev_io> watcher in one step.
		1066
		1067	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
719		1068
720	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1069	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
721		1070
722	Starts (activates) the given watcher. Only active watchers will receive	1071	Starts (activates) the given watcher. Only active watchers will receive
723	events. If the watcher is already active nothing will happen.	1072	events. If the watcher is already active nothing will happen.
724		1073
		1074	Example: Start the C<ev_io> watcher that is being abused as example in this
		1075	whole section.
		1076
		1077	ev_io_start (EV_DEFAULT_UC, &w);
		1078
725	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1079	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
726		1080
727	Stops the given watcher again (if active) and clears the pending	1081	Stops the given watcher if active, and clears the pending status (whether
		1082	the watcher was active or not).
		1083
728	status. It is possible that stopped watchers are pending (for example,	1084	It is possible that stopped watchers are pending - for example,
729	non-repeating timers are being stopped when they become pending), but	1085	non-repeating timers are being stopped when they become pending - but
730	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1086	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
731	you want to free or reuse the memory used by the watcher it is therefore a	1087	pending. If you want to free or reuse the memory used by the watcher it is
732	good idea to always call its C<ev_TYPE_stop> function.	1088	therefore a good idea to always call its C<ev_TYPE_stop> function.
733		1089
734	=item bool ev_is_active (ev_TYPE *watcher)	1090	=item bool ev_is_active (ev_TYPE *watcher)
735		1091
736	Returns a true value iff the watcher is active (i.e. it has been started	1092	Returns a true value iff the watcher is active (i.e. it has been started
737	and not yet been stopped). As long as a watcher is active you must not modify	1093	and not yet been stopped). As long as a watcher is active you must not modify
…		…
763	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1119	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
764	(default: C<-2>). Pending watchers with higher priority will be invoked	1120	(default: C<-2>). Pending watchers with higher priority will be invoked
765	before watchers with lower priority, but priority will not keep watchers	1121	before watchers with lower priority, but priority will not keep watchers
766	from being executed (except for C<ev_idle> watchers).	1122	from being executed (except for C<ev_idle> watchers).
767		1123
768	This means that priorities are I<only> used for ordering callback
769	invocation after new events have been received. This is useful, for
770	example, to reduce latency after idling, or more often, to bind two
771	watchers on the same event and make sure one is called first.
772
773	If you need to suppress invocation when higher priority events are pending	1124	If you need to suppress invocation when higher priority events are pending
774	you need to look at C<ev_idle> watchers, which provide this functionality.	1125	you need to look at C<ev_idle> watchers, which provide this functionality.
775		1126
776	You I<must not> change the priority of a watcher as long as it is active or	1127	You I<must not> change the priority of a watcher as long as it is active or
777	pending.	1128	pending.
778		1129
		1130	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1131	fine, as long as you do not mind that the priority value you query might
		1132	or might not have been clamped to the valid range.
		1133
779	The default priority used by watchers when no priority has been set is	1134	The default priority used by watchers when no priority has been set is
780	always C<0>, which is supposed to not be too high and not be too low :).	1135	always C<0>, which is supposed to not be too high and not be too low :).
781		1136
782	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1137	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
783	fine, as long as you do not mind that the priority value you query might	1138	priorities.
784	or might not have been adjusted to be within valid range.
785		1139
786	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1140	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
787		1141
788	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1142	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
789	C<loop> nor C<revents> need to be valid as long as the watcher callback	1143	C<loop> nor C<revents> need to be valid as long as the watcher callback
790	can deal with that fact.	1144	can deal with that fact, as both are simply passed through to the
		1145	callback.
791		1146
792	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1147	=item int ev_clear_pending (loop, ev_TYPE *watcher)
793		1148
794	If the watcher is pending, this function returns clears its pending status	1149	If the watcher is pending, this function clears its pending status and
795	and returns its C<revents> bitset (as if its callback was invoked). If the	1150	returns its C<revents> bitset (as if its callback was invoked). If the
796	watcher isn't pending it does nothing and returns C<0>.	1151	watcher isn't pending it does nothing and returns C<0>.
797		1152
		1153	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1154	callback to be invoked, which can be accomplished with this function.
		1155
798	=back	1156	=back
799		1157
800		1158
801	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1159	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
802		1160
803	Each watcher has, by default, a member C<void *data> that you can change	1161	Each watcher has, by default, a member C<void *data> that you can change
804	and read at any time, libev will completely ignore it. This can be used	1162	and read at any time: libev will completely ignore it. This can be used
805	to associate arbitrary data with your watcher. If you need more data and	1163	to associate arbitrary data with your watcher. If you need more data and
806	don't want to allocate memory and store a pointer to it in that data	1164	don't want to allocate memory and store a pointer to it in that data
807	member, you can also "subclass" the watcher type and provide your own	1165	member, you can also "subclass" the watcher type and provide your own
808	data:	1166	data:
809		1167
810	struct my_io	1168	struct my_io
811	{	1169	{
812	struct ev_io io;	1170	ev_io io;
813	int otherfd;	1171	int otherfd;
814	void *somedata;	1172	void *somedata;
815	struct whatever *mostinteresting;	1173	struct whatever *mostinteresting;
816	}	1174	};
		1175
		1176	...
		1177	struct my_io w;
		1178	ev_io_init (&w.io, my_cb, fd, EV_READ);
817		1179
818	And since your callback will be called with a pointer to the watcher, you	1180	And since your callback will be called with a pointer to the watcher, you
819	can cast it back to your own type:	1181	can cast it back to your own type:
820		1182
821	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1183	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
822	{	1184	{
823	struct my_io *w = (struct my_io *)w_;	1185	struct my_io *w = (struct my_io *)w_;
824	...	1186	...
825	}	1187	}
826		1188
827	More interesting and less C-conformant ways of casting your callback type	1189	More interesting and less C-conformant ways of casting your callback type
828	instead have been omitted.	1190	instead have been omitted.
829		1191
830	Another common scenario is having some data structure with multiple	1192	Another common scenario is to use some data structure with multiple
831	watchers:	1193	embedded watchers:
832		1194
833	struct my_biggy	1195	struct my_biggy
834	{	1196	{
835	int some_data;	1197	int some_data;
836	ev_timer t1;	1198	ev_timer t1;
837	ev_timer t2;	1199	ev_timer t2;
838	}	1200	}
839		1201
840	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1202	In this case getting the pointer to C<my_biggy> is a bit more
841	you need to use C<offsetof>:	1203	complicated: Either you store the address of your C<my_biggy> struct
		1204	in the C<data> member of the watcher (for woozies), or you need to use
		1205	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1206	programmers):
842		1207
843	#include <stddef.h>	1208	#include <stddef.h>
844		1209
845	static void	1210	static void
846	t1_cb (EV_P_ struct ev_timer *w, int revents)	1211	t1_cb (EV_P_ ev_timer *w, int revents)
847	{	1212	{
848	struct my_biggy big = (struct my_biggy *	1213	struct my_biggy big = (struct my_biggy *)
849	(((char *)w) - offsetof (struct my_biggy, t1));	1214	(((char *)w) - offsetof (struct my_biggy, t1));
850	}	1215	}
851		1216
852	static void	1217	static void
853	t2_cb (EV_P_ struct ev_timer *w, int revents)	1218	t2_cb (EV_P_ ev_timer *w, int revents)
854	{	1219	{
855	struct my_biggy big = (struct my_biggy *	1220	struct my_biggy big = (struct my_biggy *)
856	(((char *)w) - offsetof (struct my_biggy, t2));	1221	(((char *)w) - offsetof (struct my_biggy, t2));
857	}	1222	}
		1223
		1224	=head2 WATCHER PRIORITY MODELS
		1225
		1226	Many event loops support I<watcher priorities>, which are usually small
		1227	integers that influence the ordering of event callback invocation
		1228	between watchers in some way, all else being equal.
		1229
		1230	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1231	description for the more technical details such as the actual priority
		1232	range.
		1233
		1234	There are two common ways how these these priorities are being interpreted
		1235	by event loops:
		1236
		1237	In the more common lock-out model, higher priorities "lock out" invocation
		1238	of lower priority watchers, which means as long as higher priority
		1239	watchers receive events, lower priority watchers are not being invoked.
		1240
		1241	The less common only-for-ordering model uses priorities solely to order
		1242	callback invocation within a single event loop iteration: Higher priority
		1243	watchers are invoked before lower priority ones, but they all get invoked
		1244	before polling for new events.
		1245
		1246	Libev uses the second (only-for-ordering) model for all its watchers
		1247	except for idle watchers (which use the lock-out model).
		1248
		1249	The rationale behind this is that implementing the lock-out model for
		1250	watchers is not well supported by most kernel interfaces, and most event
		1251	libraries will just poll for the same events again and again as long as
		1252	their callbacks have not been executed, which is very inefficient in the
		1253	common case of one high-priority watcher locking out a mass of lower
		1254	priority ones.
		1255
		1256	Static (ordering) priorities are most useful when you have two or more
		1257	watchers handling the same resource: a typical usage example is having an
		1258	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1259	timeouts. Under load, data might be received while the program handles
		1260	other jobs, but since timers normally get invoked first, the timeout
		1261	handler will be executed before checking for data. In that case, giving
		1262	the timer a lower priority than the I/O watcher ensures that I/O will be
		1263	handled first even under adverse conditions (which is usually, but not
		1264	always, what you want).
		1265
		1266	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1267	will only be executed when no same or higher priority watchers have
		1268	received events, they can be used to implement the "lock-out" model when
		1269	required.
		1270
		1271	For example, to emulate how many other event libraries handle priorities,
		1272	you can associate an C<ev_idle> watcher to each such watcher, and in
		1273	the normal watcher callback, you just start the idle watcher. The real
		1274	processing is done in the idle watcher callback. This causes libev to
		1275	continously poll and process kernel event data for the watcher, but when
		1276	the lock-out case is known to be rare (which in turn is rare :), this is
		1277	workable.
		1278
		1279	Usually, however, the lock-out model implemented that way will perform
		1280	miserably under the type of load it was designed to handle. In that case,
		1281	it might be preferable to stop the real watcher before starting the
		1282	idle watcher, so the kernel will not have to process the event in case
		1283	the actual processing will be delayed for considerable time.
		1284
		1285	Here is an example of an I/O watcher that should run at a strictly lower
		1286	priority than the default, and which should only process data when no
		1287	other events are pending:
		1288
		1289	ev_idle idle; // actual processing watcher
		1290	ev_io io; // actual event watcher
		1291
		1292	static void
		1293	io_cb (EV_P_ ev_io *w, int revents)
		1294	{
		1295	// stop the I/O watcher, we received the event, but
		1296	// are not yet ready to handle it.
		1297	ev_io_stop (EV_A_ w);
		1298
		1299	// start the idle watcher to ahndle the actual event.
		1300	// it will not be executed as long as other watchers
		1301	// with the default priority are receiving events.
		1302	ev_idle_start (EV_A_ &idle);
		1303	}
		1304
		1305	static void
		1306	idle_cb (EV_P_ ev_idle *w, int revents)
		1307	{
		1308	// actual processing
		1309	read (STDIN_FILENO, ...);
		1310
		1311	// have to start the I/O watcher again, as
		1312	// we have handled the event
		1313	ev_io_start (EV_P_ &io);
		1314	}
		1315
		1316	// initialisation
		1317	ev_idle_init (&idle, idle_cb);
		1318	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1319	ev_io_start (EV_DEFAULT_ &io);
		1320
		1321	In the "real" world, it might also be beneficial to start a timer, so that
		1322	low-priority connections can not be locked out forever under load. This
		1323	enables your program to keep a lower latency for important connections
		1324	during short periods of high load, while not completely locking out less
		1325	important ones.
858		1326
859		1327
860	=head1 WATCHER TYPES	1328	=head1 WATCHER TYPES
861		1329
862	This section describes each watcher in detail, but will not repeat	1330	This section describes each watcher in detail, but will not repeat
…		…
886	In general you can register as many read and/or write event watchers per	1354	In general you can register as many read and/or write event watchers per
887	fd as you want (as long as you don't confuse yourself). Setting all file	1355	fd as you want (as long as you don't confuse yourself). Setting all file
888	descriptors to non-blocking mode is also usually a good idea (but not	1356	descriptors to non-blocking mode is also usually a good idea (but not
889	required if you know what you are doing).	1357	required if you know what you are doing).
890		1358
891	You have to be careful with dup'ed file descriptors, though. Some backends	1359	If you cannot use non-blocking mode, then force the use of a
892	(the linux epoll backend is a notable example) cannot handle dup'ed file	1360	known-to-be-good backend (at the time of this writing, this includes only
893	descriptors correctly if you register interest in two or more fds pointing	1361	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
894	to the same underlying file/socket/etc. description (that is, they share	1362	descriptors for which non-blocking operation makes no sense (such as
895	the same underlying "file open").	1363	files) - libev doesn't guarentee any specific behaviour in that case.
896
897	If you must do this, then force the use of a known-to-be-good backend
898	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
899	C<EVBACKEND_POLL>).
900		1364
901	Another thing you have to watch out for is that it is quite easy to	1365	Another thing you have to watch out for is that it is quite easy to
902	receive "spurious" readyness notifications, that is your callback might	1366	receive "spurious" readiness notifications, that is your callback might
903	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1367	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
904	because there is no data. Not only are some backends known to create a	1368	because there is no data. Not only are some backends known to create a
905	lot of those (for example solaris ports), it is very easy to get into	1369	lot of those (for example Solaris ports), it is very easy to get into
906	this situation even with a relatively standard program structure. Thus	1370	this situation even with a relatively standard program structure. Thus
907	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1371	it is best to always use non-blocking I/O: An extra C<read>(2) returning
908	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1372	C<EAGAIN> is far preferable to a program hanging until some data arrives.
909		1373
910	If you cannot run the fd in non-blocking mode (for example you should not	1374	If you cannot run the fd in non-blocking mode (for example you should
911	play around with an Xlib connection), then you have to seperately re-test	1375	not play around with an Xlib connection), then you have to separately
912	whether a file descriptor is really ready with a known-to-be good interface	1376	re-test whether a file descriptor is really ready with a known-to-be good
913	such as poll (fortunately in our Xlib example, Xlib already does this on	1377	interface such as poll (fortunately in our Xlib example, Xlib already
914	its own, so its quite safe to use).	1378	does this on its own, so its quite safe to use). Some people additionally
		1379	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1380	indefinitely.
		1381
		1382	But really, best use non-blocking mode.
		1383
		1384	=head3 The special problem of disappearing file descriptors
		1385
		1386	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1387	descriptor (either due to calling C<close> explicitly or any other means,
		1388	such as C<dup2>). The reason is that you register interest in some file
		1389	descriptor, but when it goes away, the operating system will silently drop
		1390	this interest. If another file descriptor with the same number then is
		1391	registered with libev, there is no efficient way to see that this is, in
		1392	fact, a different file descriptor.
		1393
		1394	To avoid having to explicitly tell libev about such cases, libev follows
		1395	the following policy: Each time C<ev_io_set> is being called, libev
		1396	will assume that this is potentially a new file descriptor, otherwise
		1397	it is assumed that the file descriptor stays the same. That means that
		1398	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1399	descriptor even if the file descriptor number itself did not change.
		1400
		1401	This is how one would do it normally anyway, the important point is that
		1402	the libev application should not optimise around libev but should leave
		1403	optimisations to libev.
		1404
		1405	=head3 The special problem of dup'ed file descriptors
		1406
		1407	Some backends (e.g. epoll), cannot register events for file descriptors,
		1408	but only events for the underlying file descriptions. That means when you
		1409	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1410	events for them, only one file descriptor might actually receive events.
		1411
		1412	There is no workaround possible except not registering events
		1413	for potentially C<dup ()>'ed file descriptors, or to resort to
		1414	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1415
		1416	=head3 The special problem of fork
		1417
		1418	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1419	useless behaviour. Libev fully supports fork, but needs to be told about
		1420	it in the child.
		1421
		1422	To support fork in your programs, you either have to call
		1423	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1424	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1425	C<EVBACKEND_POLL>.
		1426
		1427	=head3 The special problem of SIGPIPE
		1428
		1429	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1430	when writing to a pipe whose other end has been closed, your program gets
		1431	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1432	this is sensible behaviour, for daemons, this is usually undesirable.
		1433
		1434	So when you encounter spurious, unexplained daemon exits, make sure you
		1435	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1436	somewhere, as that would have given you a big clue).
		1437
		1438
		1439	=head3 Watcher-Specific Functions
915		1440
916	=over 4	1441	=over 4
917		1442
918	=item ev_io_init (ev_io *, callback, int fd, int events)	1443	=item ev_io_init (ev_io *, callback, int fd, int events)
919		1444
920	=item ev_io_set (ev_io *, int fd, int events)	1445	=item ev_io_set (ev_io *, int fd, int events)
921		1446
922	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1447	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
923	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1448	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
924	C<EV_READ | EV_WRITE> to receive the given events.	1449	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
925		1450
926	=item int fd [read-only]	1451	=item int fd [read-only]
927		1452
928	The file descriptor being watched.	1453	The file descriptor being watched.
929		1454
930	=item int events [read-only]	1455	=item int events [read-only]
931		1456
932	The events being watched.	1457	The events being watched.
933		1458
934	=back	1459	=back
		1460
		1461	=head3 Examples
935		1462
936	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1463	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
937	readable, but only once. Since it is likely line-buffered, you could	1464	readable, but only once. Since it is likely line-buffered, you could
938	attempt to read a whole line in the callback.	1465	attempt to read a whole line in the callback.
939		1466
940	static void	1467	static void
941	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1468	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
942	{	1469	{
943	ev_io_stop (loop, w);	1470	ev_io_stop (loop, w);
944	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1471	.. read from stdin here (or from w->fd) and handle any I/O errors
945	}	1472	}
946		1473
947	...	1474	...
948	struct ev_loop *loop = ev_default_init (0);	1475	struct ev_loop *loop = ev_default_init (0);
949	struct ev_io stdin_readable;	1476	ev_io stdin_readable;
950	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1477	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
951	ev_io_start (loop, &stdin_readable);	1478	ev_io_start (loop, &stdin_readable);
952	ev_loop (loop, 0);	1479	ev_loop (loop, 0);
953		1480
954		1481
955	=head2 C<ev_timer> - relative and optionally repeating timeouts	1482	=head2 C<ev_timer> - relative and optionally repeating timeouts
956		1483
957	Timer watchers are simple relative timers that generate an event after a	1484	Timer watchers are simple relative timers that generate an event after a
958	given time, and optionally repeating in regular intervals after that.	1485	given time, and optionally repeating in regular intervals after that.
959		1486
960	The timers are based on real time, that is, if you register an event that	1487	The timers are based on real time, that is, if you register an event that
961	times out after an hour and you reset your system clock to last years	1488	times out after an hour and you reset your system clock to January last
962	time, it will still time out after (roughly) and hour. "Roughly" because	1489	year, it will still time out after (roughly) one hour. "Roughly" because
963	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1490	detecting time jumps is hard, and some inaccuracies are unavoidable (the
964	monotonic clock option helps a lot here).	1491	monotonic clock option helps a lot here).
		1492
		1493	The callback is guaranteed to be invoked only I<after> its timeout has
		1494	passed (not I<at>, so on systems with very low-resolution clocks this
		1495	might introduce a small delay). If multiple timers become ready during the
		1496	same loop iteration then the ones with earlier time-out values are invoked
		1497	before ones of the same priority with later time-out values (but this is
		1498	no longer true when a callback calls C<ev_loop> recursively).
		1499
		1500	=head3 Be smart about timeouts
		1501
		1502	Many real-world problems involve some kind of timeout, usually for error
		1503	recovery. A typical example is an HTTP request - if the other side hangs,
		1504	you want to raise some error after a while.
		1505
		1506	What follows are some ways to handle this problem, from obvious and
		1507	inefficient to smart and efficient.
		1508
		1509	In the following, a 60 second activity timeout is assumed - a timeout that
		1510	gets reset to 60 seconds each time there is activity (e.g. each time some
		1511	data or other life sign was received).
		1512
		1513	=over 4
		1514
		1515	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1516
		1517	This is the most obvious, but not the most simple way: In the beginning,
		1518	start the watcher:
		1519
		1520	ev_timer_init (timer, callback, 60., 0.);
		1521	ev_timer_start (loop, timer);
		1522
		1523	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1524	and start it again:
		1525
		1526	ev_timer_stop (loop, timer);
		1527	ev_timer_set (timer, 60., 0.);
		1528	ev_timer_start (loop, timer);
		1529
		1530	This is relatively simple to implement, but means that each time there is
		1531	some activity, libev will first have to remove the timer from its internal
		1532	data structure and then add it again. Libev tries to be fast, but it's
		1533	still not a constant-time operation.
		1534
		1535	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1536
		1537	This is the easiest way, and involves using C<ev_timer_again> instead of
		1538	C<ev_timer_start>.
		1539
		1540	To implement this, configure an C<ev_timer> with a C<repeat> value
		1541	of C<60> and then call C<ev_timer_again> at start and each time you
		1542	successfully read or write some data. If you go into an idle state where
		1543	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1544	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1545
		1546	That means you can ignore both the C<ev_timer_start> function and the
		1547	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1548	member and C<ev_timer_again>.
		1549
		1550	At start:
		1551
		1552	ev_init (timer, callback);
		1553	timer->repeat = 60.;
		1554	ev_timer_again (loop, timer);
		1555
		1556	Each time there is some activity:
		1557
		1558	ev_timer_again (loop, timer);
		1559
		1560	It is even possible to change the time-out on the fly, regardless of
		1561	whether the watcher is active or not:
		1562
		1563	timer->repeat = 30.;
		1564	ev_timer_again (loop, timer);
		1565
		1566	This is slightly more efficient then stopping/starting the timer each time
		1567	you want to modify its timeout value, as libev does not have to completely
		1568	remove and re-insert the timer from/into its internal data structure.
		1569
		1570	It is, however, even simpler than the "obvious" way to do it.
		1571
		1572	=item 3. Let the timer time out, but then re-arm it as required.
		1573
		1574	This method is more tricky, but usually most efficient: Most timeouts are
		1575	relatively long compared to the intervals between other activity - in
		1576	our example, within 60 seconds, there are usually many I/O events with
		1577	associated activity resets.
		1578
		1579	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1580	but remember the time of last activity, and check for a real timeout only
		1581	within the callback:
		1582
		1583	ev_tstamp last_activity; // time of last activity
		1584
		1585	static void
		1586	callback (EV_P_ ev_timer *w, int revents)
		1587	{
		1588	ev_tstamp now = ev_now (EV_A);
		1589	ev_tstamp timeout = last_activity + 60.;
		1590
		1591	// if last_activity + 60. is older than now, we did time out
		1592	if (timeout < now)
		1593	{
		1594	// timeout occured, take action
		1595	}
		1596	else
		1597	{
		1598	// callback was invoked, but there was some activity, re-arm
		1599	// the watcher to fire in last_activity + 60, which is
		1600	// guaranteed to be in the future, so "again" is positive:
		1601	w->repeat = timeout - now;
		1602	ev_timer_again (EV_A_ w);
		1603	}
		1604	}
		1605
		1606	To summarise the callback: first calculate the real timeout (defined
		1607	as "60 seconds after the last activity"), then check if that time has
		1608	been reached, which means something I<did>, in fact, time out. Otherwise
		1609	the callback was invoked too early (C<timeout> is in the future), so
		1610	re-schedule the timer to fire at that future time, to see if maybe we have
		1611	a timeout then.
		1612
		1613	Note how C<ev_timer_again> is used, taking advantage of the
		1614	C<ev_timer_again> optimisation when the timer is already running.
		1615
		1616	This scheme causes more callback invocations (about one every 60 seconds
		1617	minus half the average time between activity), but virtually no calls to
		1618	libev to change the timeout.
		1619
		1620	To start the timer, simply initialise the watcher and set C<last_activity>
		1621	to the current time (meaning we just have some activity :), then call the
		1622	callback, which will "do the right thing" and start the timer:
		1623
		1624	ev_init (timer, callback);
		1625	last_activity = ev_now (loop);
		1626	callback (loop, timer, EV_TIMEOUT);
		1627
		1628	And when there is some activity, simply store the current time in
		1629	C<last_activity>, no libev calls at all:
		1630
		1631	last_actiivty = ev_now (loop);
		1632
		1633	This technique is slightly more complex, but in most cases where the
		1634	time-out is unlikely to be triggered, much more efficient.
		1635
		1636	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1637	callback :) - just change the timeout and invoke the callback, which will
		1638	fix things for you.
		1639
		1640	=item 4. Wee, just use a double-linked list for your timeouts.
		1641
		1642	If there is not one request, but many thousands (millions...), all
		1643	employing some kind of timeout with the same timeout value, then one can
		1644	do even better:
		1645
		1646	When starting the timeout, calculate the timeout value and put the timeout
		1647	at the I<end> of the list.
		1648
		1649	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1650	the list is expected to fire (for example, using the technique #3).
		1651
		1652	When there is some activity, remove the timer from the list, recalculate
		1653	the timeout, append it to the end of the list again, and make sure to
		1654	update the C<ev_timer> if it was taken from the beginning of the list.
		1655
		1656	This way, one can manage an unlimited number of timeouts in O(1) time for
		1657	starting, stopping and updating the timers, at the expense of a major
		1658	complication, and having to use a constant timeout. The constant timeout
		1659	ensures that the list stays sorted.
		1660
		1661	=back
		1662
		1663	So which method the best?
		1664
		1665	Method #2 is a simple no-brain-required solution that is adequate in most
		1666	situations. Method #3 requires a bit more thinking, but handles many cases
		1667	better, and isn't very complicated either. In most case, choosing either
		1668	one is fine, with #3 being better in typical situations.
		1669
		1670	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1671	rather complicated, but extremely efficient, something that really pays
		1672	off after the first million or so of active timers, i.e. it's usually
		1673	overkill :)
		1674
		1675	=head3 The special problem of time updates
		1676
		1677	Establishing the current time is a costly operation (it usually takes at
		1678	least two system calls): EV therefore updates its idea of the current
		1679	time only before and after C<ev_loop> collects new events, which causes a
		1680	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1681	lots of events in one iteration.
965		1682
966	The relative timeouts are calculated relative to the C<ev_now ()>	1683	The relative timeouts are calculated relative to the C<ev_now ()>
967	time. This is usually the right thing as this timestamp refers to the time	1684	time. This is usually the right thing as this timestamp refers to the time
968	of the event triggering whatever timeout you are modifying/starting. If	1685	of the event triggering whatever timeout you are modifying/starting. If
969	you suspect event processing to be delayed and you I<need> to base the timeout	1686	you suspect event processing to be delayed and you I<need> to base the
970	on the current time, use something like this to adjust for this:	1687	timeout on the current time, use something like this to adjust for this:
971		1688
972	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1689	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
973		1690
974	The callback is guarenteed to be invoked only when its timeout has passed,	1691	If the event loop is suspended for a long time, you can also force an
975	but if multiple timers become ready during the same loop iteration then	1692	update of the time returned by C<ev_now ()> by calling C<ev_now_update
976	order of execution is undefined.	1693	()>.
		1694
		1695	=head3 Watcher-Specific Functions and Data Members
977		1696
978	=over 4	1697	=over 4
979		1698
980	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1699	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
981		1700
982	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1701	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
983		1702
984	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1703	Configure the timer to trigger after C<after> seconds. If C<repeat>
985	C<0.>, then it will automatically be stopped. If it is positive, then the	1704	is C<0.>, then it will automatically be stopped once the timeout is
986	timer will automatically be configured to trigger again C<repeat> seconds	1705	reached. If it is positive, then the timer will automatically be
987	later, again, and again, until stopped manually.	1706	configured to trigger again C<repeat> seconds later, again, and again,
		1707	until stopped manually.
988		1708
989	The timer itself will do a best-effort at avoiding drift, that is, if you	1709	The timer itself will do a best-effort at avoiding drift, that is, if
990	configure a timer to trigger every 10 seconds, then it will trigger at	1710	you configure a timer to trigger every 10 seconds, then it will normally
991	exactly 10 second intervals. If, however, your program cannot keep up with	1711	trigger at exactly 10 second intervals. If, however, your program cannot
992	the timer (because it takes longer than those 10 seconds to do stuff) the	1712	keep up with the timer (because it takes longer than those 10 seconds to
993	timer will not fire more than once per event loop iteration.	1713	do stuff) the timer will not fire more than once per event loop iteration.
994		1714
995	=item ev_timer_again (loop)	1715	=item ev_timer_again (loop, ev_timer *)
996		1716
997	This will act as if the timer timed out and restart it again if it is	1717	This will act as if the timer timed out and restart it again if it is
998	repeating. The exact semantics are:	1718	repeating. The exact semantics are:
999		1719
1000	If the timer is pending, its pending status is cleared.	1720	If the timer is pending, its pending status is cleared.
1001		1721
1002	If the timer is started but nonrepeating, stop it (as if it timed out).	1722	If the timer is started but non-repeating, stop it (as if it timed out).
1003		1723
1004	If the timer is repeating, either start it if necessary (with the	1724	If the timer is repeating, either start it if necessary (with the
1005	C<repeat> value), or reset the running timer to the C<repeat> value.	1725	C<repeat> value), or reset the running timer to the C<repeat> value.
1006		1726
1007	This sounds a bit complicated, but here is a useful and typical	1727	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1008	example: Imagine you have a tcp connection and you want a so-called idle	1728	usage example.
1009	timeout, that is, you want to be called when there have been, say, 60
1010	seconds of inactivity on the socket. The easiest way to do this is to
1011	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1012	C<ev_timer_again> each time you successfully read or write some data. If
1013	you go into an idle state where you do not expect data to travel on the
1014	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1015	automatically restart it if need be.
1016
1017	That means you can ignore the C<after> value and C<ev_timer_start>
1018	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1019
1020	ev_timer_init (timer, callback, 0., 5.);
1021	ev_timer_again (loop, timer);
1022	...
1023	timer->again = 17.;
1024	ev_timer_again (loop, timer);
1025	...
1026	timer->again = 10.;
1027	ev_timer_again (loop, timer);
1028
1029	This is more slightly efficient then stopping/starting the timer each time
1030	you want to modify its timeout value.
1031		1729
1032	=item ev_tstamp repeat [read-write]	1730	=item ev_tstamp repeat [read-write]
1033		1731
1034	The current C<repeat> value. Will be used each time the watcher times out	1732	The current C<repeat> value. Will be used each time the watcher times out
1035	or C<ev_timer_again> is called and determines the next timeout (if any),	1733	or C<ev_timer_again> is called, and determines the next timeout (if any),
1036	which is also when any modifications are taken into account.	1734	which is also when any modifications are taken into account.
1037		1735
1038	=back	1736	=back
1039		1737
		1738	=head3 Examples
		1739
1040	Example: Create a timer that fires after 60 seconds.	1740	Example: Create a timer that fires after 60 seconds.
1041		1741
1042	static void	1742	static void
1043	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1743	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1044	{	1744	{
1045	.. one minute over, w is actually stopped right here	1745	.. one minute over, w is actually stopped right here
1046	}	1746	}
1047		1747
1048	struct ev_timer mytimer;	1748	ev_timer mytimer;
1049	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1749	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1050	ev_timer_start (loop, &mytimer);	1750	ev_timer_start (loop, &mytimer);
1051		1751
1052	Example: Create a timeout timer that times out after 10 seconds of	1752	Example: Create a timeout timer that times out after 10 seconds of
1053	inactivity.	1753	inactivity.
1054		1754
1055	static void	1755	static void
1056	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1756	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1057	{	1757	{
1058	.. ten seconds without any activity	1758	.. ten seconds without any activity
1059	}	1759	}
1060		1760
1061	struct ev_timer mytimer;	1761	ev_timer mytimer;
1062	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1762	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1063	ev_timer_again (&mytimer); /* start timer */	1763	ev_timer_again (&mytimer); /* start timer */
1064	ev_loop (loop, 0);	1764	ev_loop (loop, 0);
1065		1765
1066	// and in some piece of code that gets executed on any "activity":	1766	// and in some piece of code that gets executed on any "activity":
1067	// reset the timeout to start ticking again at 10 seconds	1767	// reset the timeout to start ticking again at 10 seconds
1068	ev_timer_again (&mytimer);	1768	ev_timer_again (&mytimer);
1069		1769
1070		1770
1071	=head2 C<ev_periodic> - to cron or not to cron?	1771	=head2 C<ev_periodic> - to cron or not to cron?
1072		1772
1073	Periodic watchers are also timers of a kind, but they are very versatile	1773	Periodic watchers are also timers of a kind, but they are very versatile
1074	(and unfortunately a bit complex).	1774	(and unfortunately a bit complex).
1075		1775
1076	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1776	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1077	but on wallclock time (absolute time). You can tell a periodic watcher	1777	relative time, the physical time that passes) but on wall clock time
1078	to trigger "at" some specific point in time. For example, if you tell a	1778	(absolute time, the thing you can read on your calender or clock). The
1079	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1779	difference is that wall clock time can run faster or slower than real
1080	+ 10.>) and then reset your system clock to the last year, then it will	1780	time, and time jumps are not uncommon (e.g. when you adjust your
1081	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1781	wrist-watch).
1082	roughly 10 seconds later).
1083		1782
1084	They can also be used to implement vastly more complex timers, such as	1783	You can tell a periodic watcher to trigger after some specific point
1085	triggering an event on each midnight, local time or other, complicated,	1784	in time: for example, if you tell a periodic watcher to trigger "in 10
1086	rules.	1785	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1786	not a delay) and then reset your system clock to January of the previous
		1787	year, then it will take a year or more to trigger the event (unlike an
		1788	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1789	it, as it uses a relative timeout).
1087		1790
		1791	C<ev_periodic> watchers can also be used to implement vastly more complex
		1792	timers, such as triggering an event on each "midnight, local time", or
		1793	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1794	those cannot react to time jumps.
		1795
1088	As with timers, the callback is guarenteed to be invoked only when the	1796	As with timers, the callback is guaranteed to be invoked only when the
1089	time (C<at>) has been passed, but if multiple periodic timers become ready	1797	point in time where it is supposed to trigger has passed. If multiple
1090	during the same loop iteration then order of execution is undefined.	1798	timers become ready during the same loop iteration then the ones with
		1799	earlier time-out values are invoked before ones with later time-out values
		1800	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1801
		1802	=head3 Watcher-Specific Functions and Data Members
1091		1803
1092	=over 4	1804	=over 4
1093		1805
1094	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1806	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1095		1807
1096	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1808	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1097		1809
1098	Lots of arguments, lets sort it out... There are basically three modes of	1810	Lots of arguments, let's sort it out... There are basically three modes of
1099	operation, and we will explain them from simplest to complex:	1811	operation, and we will explain them from simplest to most complex:
1100		1812
1101	=over 4	1813	=over 4
1102		1814
1103	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1815	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1104		1816
1105	In this configuration the watcher triggers an event at the wallclock time	1817	In this configuration the watcher triggers an event after the wall clock
1106	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1818	time C<offset> has passed. It will not repeat and will not adjust when a
1107	that is, if it is to be run at January 1st 2011 then it will run when the	1819	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1108	system time reaches or surpasses this time.	1820	will be stopped and invoked when the system clock reaches or surpasses
		1821	this point in time.
1109		1822
1110	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1823	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1111		1824
1112	In this mode the watcher will always be scheduled to time out at the next	1825	In this mode the watcher will always be scheduled to time out at the next
1113	C<at + N * interval> time (for some integer N, which can also be negative)	1826	C<offset + N * interval> time (for some integer N, which can also be
1114	and then repeat, regardless of any time jumps.	1827	negative) and then repeat, regardless of any time jumps. The C<offset>
		1828	argument is merely an offset into the C<interval> periods.
1115		1829
1116	This can be used to create timers that do not drift with respect to system	1830	This can be used to create timers that do not drift with respect to the
1117	time:	1831	system clock, for example, here is an C<ev_periodic> that triggers each
		1832	hour, on the hour (with respect to UTC):
1118		1833
1119	ev_periodic_set (&periodic, 0., 3600., 0);	1834	ev_periodic_set (&periodic, 0., 3600., 0);
1120		1835
1121	This doesn't mean there will always be 3600 seconds in between triggers,	1836	This doesn't mean there will always be 3600 seconds in between triggers,
1122	but only that the the callback will be called when the system time shows a	1837	but only that the callback will be called when the system time shows a
1123	full hour (UTC), or more correctly, when the system time is evenly divisible	1838	full hour (UTC), or more correctly, when the system time is evenly divisible
1124	by 3600.	1839	by 3600.
1125		1840
1126	Another way to think about it (for the mathematically inclined) is that	1841	Another way to think about it (for the mathematically inclined) is that
1127	C<ev_periodic> will try to run the callback in this mode at the next possible	1842	C<ev_periodic> will try to run the callback in this mode at the next possible
1128	time where C<time = at (mod interval)>, regardless of any time jumps.	1843	time where C<time = offset (mod interval)>, regardless of any time jumps.
1129		1844
1130	For numerical stability it is preferable that the C<at> value is near	1845	For numerical stability it is preferable that the C<offset> value is near
1131	C<ev_now ()> (the current time), but there is no range requirement for	1846	C<ev_now ()> (the current time), but there is no range requirement for
1132	this value.	1847	this value, and in fact is often specified as zero.
1133		1848
		1849	Note also that there is an upper limit to how often a timer can fire (CPU
		1850	speed for example), so if C<interval> is very small then timing stability
		1851	will of course deteriorate. Libev itself tries to be exact to be about one
		1852	millisecond (if the OS supports it and the machine is fast enough).
		1853
1134	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1854	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1135		1855
1136	In this mode the values for C<interval> and C<at> are both being	1856	In this mode the values for C<interval> and C<offset> are both being
1137	ignored. Instead, each time the periodic watcher gets scheduled, the	1857	ignored. Instead, each time the periodic watcher gets scheduled, the
1138	reschedule callback will be called with the watcher as first, and the	1858	reschedule callback will be called with the watcher as first, and the
1139	current time as second argument.	1859	current time as second argument.
1140		1860
1141	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1861	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1142	ever, or make any event loop modifications>. If you need to stop it,	1862	or make ANY other event loop modifications whatsoever, unless explicitly
1143	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1863	allowed by documentation here>.
1144	starting an C<ev_prepare> watcher, which is legal).
1145		1864
		1865	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1866	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1867	only event loop modification you are allowed to do).
		1868
1146	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1869	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1147	ev_tstamp now)>, e.g.:	1870	*w, ev_tstamp now)>, e.g.:
1148		1871
		1872	static ev_tstamp
1149	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1873	my_rescheduler (ev_periodic *w, ev_tstamp now)
1150	{	1874	{
1151	return now + 60.;	1875	return now + 60.;
1152	}	1876	}
1153		1877
1154	It must return the next time to trigger, based on the passed time value	1878	It must return the next time to trigger, based on the passed time value
1155	(that is, the lowest time value larger than to the second argument). It	1879	(that is, the lowest time value larger than to the second argument). It
1156	will usually be called just before the callback will be triggered, but	1880	will usually be called just before the callback will be triggered, but
1157	might be called at other times, too.	1881	might be called at other times, too.
1158		1882
1159	NOTE: I<< This callback must always return a time that is later than the	1883	NOTE: I<< This callback must always return a time that is higher than or
1160	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1884	equal to the passed C<now> value >>.
1161		1885
1162	This can be used to create very complex timers, such as a timer that	1886	This can be used to create very complex timers, such as a timer that
1163	triggers on each midnight, local time. To do this, you would calculate the	1887	triggers on "next midnight, local time". To do this, you would calculate the
1164	next midnight after C<now> and return the timestamp value for this. How	1888	next midnight after C<now> and return the timestamp value for this. How
1165	you do this is, again, up to you (but it is not trivial, which is the main	1889	you do this is, again, up to you (but it is not trivial, which is the main
1166	reason I omitted it as an example).	1890	reason I omitted it as an example).
1167		1891
1168	=back	1892	=back
…		…
1172	Simply stops and restarts the periodic watcher again. This is only useful	1896	Simply stops and restarts the periodic watcher again. This is only useful
1173	when you changed some parameters or the reschedule callback would return	1897	when you changed some parameters or the reschedule callback would return
1174	a different time than the last time it was called (e.g. in a crond like	1898	a different time than the last time it was called (e.g. in a crond like
1175	program when the crontabs have changed).	1899	program when the crontabs have changed).
1176		1900
		1901	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1902
		1903	When active, returns the absolute time that the watcher is supposed
		1904	to trigger next. This is not the same as the C<offset> argument to
		1905	C<ev_periodic_set>, but indeed works even in interval and manual
		1906	rescheduling modes.
		1907
1177	=item ev_tstamp offset [read-write]	1908	=item ev_tstamp offset [read-write]
1178		1909
1179	When repeating, this contains the offset value, otherwise this is the	1910	When repeating, this contains the offset value, otherwise this is the
1180	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1911	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1912	although libev might modify this value for better numerical stability).
1181		1913
1182	Can be modified any time, but changes only take effect when the periodic	1914	Can be modified any time, but changes only take effect when the periodic
1183	timer fires or C<ev_periodic_again> is being called.	1915	timer fires or C<ev_periodic_again> is being called.
1184		1916
1185	=item ev_tstamp interval [read-write]	1917	=item ev_tstamp interval [read-write]
1186		1918
1187	The current interval value. Can be modified any time, but changes only	1919	The current interval value. Can be modified any time, but changes only
1188	take effect when the periodic timer fires or C<ev_periodic_again> is being	1920	take effect when the periodic timer fires or C<ev_periodic_again> is being
1189	called.	1921	called.
1190		1922
1191	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1923	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1192		1924
1193	The current reschedule callback, or C<0>, if this functionality is	1925	The current reschedule callback, or C<0>, if this functionality is
1194	switched off. Can be changed any time, but changes only take effect when	1926	switched off. Can be changed any time, but changes only take effect when
1195	the periodic timer fires or C<ev_periodic_again> is being called.	1927	the periodic timer fires or C<ev_periodic_again> is being called.
1196		1928
1197	=back	1929	=back
1198		1930
		1931	=head3 Examples
		1932
1199	Example: Call a callback every hour, or, more precisely, whenever the	1933	Example: Call a callback every hour, or, more precisely, whenever the
1200	system clock is divisible by 3600. The callback invocation times have	1934	system time is divisible by 3600. The callback invocation times have
1201	potentially a lot of jittering, but good long-term stability.	1935	potentially a lot of jitter, but good long-term stability.
1202		1936
1203	static void	1937	static void
1204	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1938	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1205	{	1939	{
1206	... its now a full hour (UTC, or TAI or whatever your clock follows)	1940	... its now a full hour (UTC, or TAI or whatever your clock follows)
1207	}	1941	}
1208		1942
1209	struct ev_periodic hourly_tick;	1943	ev_periodic hourly_tick;
1210	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1944	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1211	ev_periodic_start (loop, &hourly_tick);	1945	ev_periodic_start (loop, &hourly_tick);
1212		1946
1213	Example: The same as above, but use a reschedule callback to do it:	1947	Example: The same as above, but use a reschedule callback to do it:
1214		1948
1215	#include <math.h>	1949	#include <math.h>
1216		1950
1217	static ev_tstamp	1951	static ev_tstamp
1218	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1952	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1219	{	1953	{
1220	return fmod (now, 3600.) + 3600.;	1954	return now + (3600. - fmod (now, 3600.));
1221	}	1955	}
1222		1956
1223	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1957	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1224		1958
1225	Example: Call a callback every hour, starting now:	1959	Example: Call a callback every hour, starting now:
1226		1960
1227	struct ev_periodic hourly_tick;	1961	ev_periodic hourly_tick;
1228	ev_periodic_init (&hourly_tick, clock_cb,	1962	ev_periodic_init (&hourly_tick, clock_cb,
1229	fmod (ev_now (loop), 3600.), 3600., 0);	1963	fmod (ev_now (loop), 3600.), 3600., 0);
1230	ev_periodic_start (loop, &hourly_tick);	1964	ev_periodic_start (loop, &hourly_tick);
1231		1965
1232		1966
1233	=head2 C<ev_signal> - signal me when a signal gets signalled!	1967	=head2 C<ev_signal> - signal me when a signal gets signalled!
1234		1968
1235	Signal watchers will trigger an event when the process receives a specific	1969	Signal watchers will trigger an event when the process receives a specific
1236	signal one or more times. Even though signals are very asynchronous, libev	1970	signal one or more times. Even though signals are very asynchronous, libev
1237	will try it's best to deliver signals synchronously, i.e. as part of the	1971	will try it's best to deliver signals synchronously, i.e. as part of the
1238	normal event processing, like any other event.	1972	normal event processing, like any other event.
1239		1973
		1974	If you want signals asynchronously, just use C<sigaction> as you would
		1975	do without libev and forget about sharing the signal. You can even use
		1976	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1977
1240	You can configure as many watchers as you like per signal. Only when the	1978	You can configure as many watchers as you like per signal. Only when the
1241	first watcher gets started will libev actually register a signal watcher	1979	first watcher gets started will libev actually register a signal handler
1242	with the kernel (thus it coexists with your own signal handlers as long	1980	with the kernel (thus it coexists with your own signal handlers as long as
1243	as you don't register any with libev). Similarly, when the last signal	1981	you don't register any with libev for the same signal). Similarly, when
1244	watcher for a signal is stopped libev will reset the signal handler to	1982	the last signal watcher for a signal is stopped, libev will reset the
1245	SIG_DFL (regardless of what it was set to before).	1983	signal handler to SIG_DFL (regardless of what it was set to before).
		1984
		1985	If possible and supported, libev will install its handlers with
		1986	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1987	interrupted. If you have a problem with system calls getting interrupted by
		1988	signals you can block all signals in an C<ev_check> watcher and unblock
		1989	them in an C<ev_prepare> watcher.
		1990
		1991	=head3 Watcher-Specific Functions and Data Members
1246		1992
1247	=over 4	1993	=over 4
1248		1994
1249	=item ev_signal_init (ev_signal *, callback, int signum)	1995	=item ev_signal_init (ev_signal *, callback, int signum)
1250		1996
…		…
1257		2003
1258	The signal the watcher watches out for.	2004	The signal the watcher watches out for.
1259		2005
1260	=back	2006	=back
1261		2007
		2008	=head3 Examples
		2009
		2010	Example: Try to exit cleanly on SIGINT.
		2011
		2012	static void
		2013	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2014	{
		2015	ev_unloop (loop, EVUNLOOP_ALL);
		2016	}
		2017
		2018	ev_signal signal_watcher;
		2019	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2020	ev_signal_start (loop, &signal_watcher);
		2021
1262		2022
1263	=head2 C<ev_child> - watch out for process status changes	2023	=head2 C<ev_child> - watch out for process status changes
1264		2024
1265	Child watchers trigger when your process receives a SIGCHLD in response to	2025	Child watchers trigger when your process receives a SIGCHLD in response to
1266	some child status changes (most typically when a child of yours dies).	2026	some child status changes (most typically when a child of yours dies or
		2027	exits). It is permissible to install a child watcher I<after> the child
		2028	has been forked (which implies it might have already exited), as long
		2029	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2030	forking and then immediately registering a watcher for the child is fine,
		2031	but forking and registering a watcher a few event loop iterations later or
		2032	in the next callback invocation is not.
		2033
		2034	Only the default event loop is capable of handling signals, and therefore
		2035	you can only register child watchers in the default event loop.
		2036
		2037	Due to some design glitches inside libev, child watchers will always be
		2038	handled at maximum priority (their priority is set to EV_MAXPRI by libev)
		2039
		2040	=head3 Process Interaction
		2041
		2042	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2043	initialised. This is necessary to guarantee proper behaviour even if
		2044	the first child watcher is started after the child exits. The occurrence
		2045	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2046	synchronously as part of the event loop processing. Libev always reaps all
		2047	children, even ones not watched.
		2048
		2049	=head3 Overriding the Built-In Processing
		2050
		2051	Libev offers no special support for overriding the built-in child
		2052	processing, but if your application collides with libev's default child
		2053	handler, you can override it easily by installing your own handler for
		2054	C<SIGCHLD> after initialising the default loop, and making sure the
		2055	default loop never gets destroyed. You are encouraged, however, to use an
		2056	event-based approach to child reaping and thus use libev's support for
		2057	that, so other libev users can use C<ev_child> watchers freely.
		2058
		2059	=head3 Stopping the Child Watcher
		2060
		2061	Currently, the child watcher never gets stopped, even when the
		2062	child terminates, so normally one needs to stop the watcher in the
		2063	callback. Future versions of libev might stop the watcher automatically
		2064	when a child exit is detected.
		2065
		2066	=head3 Watcher-Specific Functions and Data Members
1267		2067
1268	=over 4	2068	=over 4
1269		2069
1270	=item ev_child_init (ev_child *, callback, int pid)	2070	=item ev_child_init (ev_child *, callback, int pid, int trace)
1271		2071
1272	=item ev_child_set (ev_child *, int pid)	2072	=item ev_child_set (ev_child *, int pid, int trace)
1273		2073
1274	Configures the watcher to wait for status changes of process C<pid> (or	2074	Configures the watcher to wait for status changes of process C<pid> (or
1275	I<any> process if C<pid> is specified as C<0>). The callback can look	2075	I<any> process if C<pid> is specified as C<0>). The callback can look
1276	at the C<rstatus> member of the C<ev_child> watcher structure to see	2076	at the C<rstatus> member of the C<ev_child> watcher structure to see
1277	the status word (use the macros from C<sys/wait.h> and see your systems	2077	the status word (use the macros from C<sys/wait.h> and see your systems
1278	C<waitpid> documentation). The C<rpid> member contains the pid of the	2078	C<waitpid> documentation). The C<rpid> member contains the pid of the
1279	process causing the status change.	2079	process causing the status change. C<trace> must be either C<0> (only
		2080	activate the watcher when the process terminates) or C<1> (additionally
		2081	activate the watcher when the process is stopped or continued).
1280		2082
1281	=item int pid [read-only]	2083	=item int pid [read-only]
1282		2084
1283	The process id this watcher watches out for, or C<0>, meaning any process id.	2085	The process id this watcher watches out for, or C<0>, meaning any process id.
1284		2086
…		…
1291	The process exit/trace status caused by C<rpid> (see your systems	2093	The process exit/trace status caused by C<rpid> (see your systems
1292	C<waitpid> and C<sys/wait.h> documentation for details).	2094	C<waitpid> and C<sys/wait.h> documentation for details).
1293		2095
1294	=back	2096	=back
1295		2097
1296	Example: Try to exit cleanly on SIGINT and SIGTERM.	2098	=head3 Examples
1297		2099
		2100	Example: C<fork()> a new process and install a child handler to wait for
		2101	its completion.
		2102
		2103	ev_child cw;
		2104
1298	static void	2105	static void
1299	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2106	child_cb (EV_P_ ev_child *w, int revents)
1300	{	2107	{
1301	ev_unloop (loop, EVUNLOOP_ALL);	2108	ev_child_stop (EV_A_ w);
		2109	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1302	}	2110	}
1303		2111
1304	struct ev_signal signal_watcher;	2112	pid_t pid = fork ();
1305	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2113
1306	ev_signal_start (loop, &sigint_cb);	2114	if (pid < 0)
		2115	// error
		2116	else if (pid == 0)
		2117	{
		2118	// the forked child executes here
		2119	exit (1);
		2120	}
		2121	else
		2122	{
		2123	ev_child_init (&cw, child_cb, pid, 0);
		2124	ev_child_start (EV_DEFAULT_ &cw);
		2125	}
1307		2126
1308		2127
1309	=head2 C<ev_stat> - did the file attributes just change?	2128	=head2 C<ev_stat> - did the file attributes just change?
1310		2129
1311	This watches a filesystem path for attribute changes. That is, it calls	2130	This watches a file system path for attribute changes. That is, it calls
1312	C<stat> regularly (or when the OS says it changed) and sees if it changed	2131	C<stat> on that path in regular intervals (or when the OS says it changed)
1313	compared to the last time, invoking the callback if it did.	2132	and sees if it changed compared to the last time, invoking the callback if
		2133	it did.
1314		2134
1315	The path does not need to exist: changing from "path exists" to "path does	2135	The path does not need to exist: changing from "path exists" to "path does
1316	not exist" is a status change like any other. The condition "path does	2136	not exist" is a status change like any other. The condition "path does not
1317	not exist" is signified by the C<st_nlink> field being zero (which is	2137	exist" (or more correctly "path cannot be stat'ed") is signified by the
1318	otherwise always forced to be at least one) and all the other fields of	2138	C<st_nlink> field being zero (which is otherwise always forced to be at
1319	the stat buffer having unspecified contents.	2139	least one) and all the other fields of the stat buffer having unspecified
		2140	contents.
1320		2141
1321	The path I<should> be absolute and I<must not> end in a slash. If it is	2142	The path I<must not> end in a slash or contain special components such as
		2143	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1322	relative and your working directory changes, the behaviour is undefined.	2144	your working directory changes, then the behaviour is undefined.
1323		2145
1324	Since there is no standard to do this, the portable implementation simply	2146	Since there is no portable change notification interface available, the
1325	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2147	portable implementation simply calls C<stat(2)> regularly on the path
1326	can specify a recommended polling interval for this case. If you specify	2148	to see if it changed somehow. You can specify a recommended polling
1327	a polling interval of C<0> (highly recommended!) then a I<suitable,	2149	interval for this case. If you specify a polling interval of C<0> (highly
1328	unspecified default> value will be used (which you can expect to be around	2150	recommended!) then a I<suitable, unspecified default> value will be used
1329	five seconds, although this might change dynamically). Libev will also	2151	(which you can expect to be around five seconds, although this might
1330	impose a minimum interval which is currently around C<0.1>, but thats	2152	change dynamically). Libev will also impose a minimum interval which is
1331	usually overkill.	2153	currently around C<0.1>, but that's usually overkill.
1332		2154
1333	This watcher type is not meant for massive numbers of stat watchers,	2155	This watcher type is not meant for massive numbers of stat watchers,
1334	as even with OS-supported change notifications, this can be	2156	as even with OS-supported change notifications, this can be
1335	resource-intensive.	2157	resource-intensive.
1336		2158
1337	At the time of this writing, only the Linux inotify interface is	2159	At the time of this writing, the only OS-specific interface implemented
1338	implemented (implementing kqueue support is left as an exercise for the	2160	is the Linux inotify interface (implementing kqueue support is left as an
1339	reader). Inotify will be used to give hints only and should not change the	2161	exercise for the reader. Note, however, that the author sees no way of
1340	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2162	implementing C<ev_stat> semantics with kqueue, except as a hint).
1341	to fall back to regular polling again even with inotify, but changes are	2163
1342	usually detected immediately, and if the file exists there will be no	2164	=head3 ABI Issues (Largefile Support)
1343	polling.	2165
		2166	Libev by default (unless the user overrides this) uses the default
		2167	compilation environment, which means that on systems with large file
		2168	support disabled by default, you get the 32 bit version of the stat
		2169	structure. When using the library from programs that change the ABI to
		2170	use 64 bit file offsets the programs will fail. In that case you have to
		2171	compile libev with the same flags to get binary compatibility. This is
		2172	obviously the case with any flags that change the ABI, but the problem is
		2173	most noticeably displayed with ev_stat and large file support.
		2174
		2175	The solution for this is to lobby your distribution maker to make large
		2176	file interfaces available by default (as e.g. FreeBSD does) and not
		2177	optional. Libev cannot simply switch on large file support because it has
		2178	to exchange stat structures with application programs compiled using the
		2179	default compilation environment.
		2180
		2181	=head3 Inotify and Kqueue
		2182
		2183	When C<inotify (7)> support has been compiled into libev and present at
		2184	runtime, it will be used to speed up change detection where possible. The
		2185	inotify descriptor will be created lazily when the first C<ev_stat>
		2186	watcher is being started.
		2187
		2188	Inotify presence does not change the semantics of C<ev_stat> watchers
		2189	except that changes might be detected earlier, and in some cases, to avoid
		2190	making regular C<stat> calls. Even in the presence of inotify support
		2191	there are many cases where libev has to resort to regular C<stat> polling,
		2192	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2193	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2194	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2195	xfs are fully working) libev usually gets away without polling.
		2196
		2197	There is no support for kqueue, as apparently it cannot be used to
		2198	implement this functionality, due to the requirement of having a file
		2199	descriptor open on the object at all times, and detecting renames, unlinks
		2200	etc. is difficult.
		2201
		2202	=head3 C<stat ()> is a synchronous operation
		2203
		2204	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2205	the process. The exception are C<ev_stat> watchers - those call C<stat
		2206	()>, which is a synchronous operation.
		2207
		2208	For local paths, this usually doesn't matter: unless the system is very
		2209	busy or the intervals between stat's are large, a stat call will be fast,
		2210	as the path data is usually in memory already (except when starting the
		2211	watcher).
		2212
		2213	For networked file systems, calling C<stat ()> can block an indefinite
		2214	time due to network issues, and even under good conditions, a stat call
		2215	often takes multiple milliseconds.
		2216
		2217	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2218	paths, although this is fully supported by libev.
		2219
		2220	=head3 The special problem of stat time resolution
		2221
		2222	The C<stat ()> system call only supports full-second resolution portably,
		2223	and even on systems where the resolution is higher, most file systems
		2224	still only support whole seconds.
		2225
		2226	That means that, if the time is the only thing that changes, you can
		2227	easily miss updates: on the first update, C<ev_stat> detects a change and
		2228	calls your callback, which does something. When there is another update
		2229	within the same second, C<ev_stat> will be unable to detect unless the
		2230	stat data does change in other ways (e.g. file size).
		2231
		2232	The solution to this is to delay acting on a change for slightly more
		2233	than a second (or till slightly after the next full second boundary), using
		2234	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2235	ev_timer_again (loop, w)>).
		2236
		2237	The C<.02> offset is added to work around small timing inconsistencies
		2238	of some operating systems (where the second counter of the current time
		2239	might be be delayed. One such system is the Linux kernel, where a call to
		2240	C<gettimeofday> might return a timestamp with a full second later than
		2241	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2242	update file times then there will be a small window where the kernel uses
		2243	the previous second to update file times but libev might already execute
		2244	the timer callback).
		2245
		2246	=head3 Watcher-Specific Functions and Data Members
1344		2247
1345	=over 4	2248	=over 4
1346		2249
1347	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2250	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1348		2251
…		…
1352	C<path>. The C<interval> is a hint on how quickly a change is expected to	2255	C<path>. The C<interval> is a hint on how quickly a change is expected to
1353	be detected and should normally be specified as C<0> to let libev choose	2256	be detected and should normally be specified as C<0> to let libev choose
1354	a suitable value. The memory pointed to by C<path> must point to the same	2257	a suitable value. The memory pointed to by C<path> must point to the same
1355	path for as long as the watcher is active.	2258	path for as long as the watcher is active.
1356		2259
1357	The callback will be receive C<EV_STAT> when a change was detected,	2260	The callback will receive an C<EV_STAT> event when a change was detected,
1358	relative to the attributes at the time the watcher was started (or the	2261	relative to the attributes at the time the watcher was started (or the
1359	last change was detected).	2262	last change was detected).
1360		2263
1361	=item ev_stat_stat (ev_stat *)	2264	=item ev_stat_stat (loop, ev_stat *)
1362		2265
1363	Updates the stat buffer immediately with new values. If you change the	2266	Updates the stat buffer immediately with new values. If you change the
1364	watched path in your callback, you could call this fucntion to avoid	2267	watched path in your callback, you could call this function to avoid
1365	detecting this change (while introducing a race condition). Can also be	2268	detecting this change (while introducing a race condition if you are not
1366	useful simply to find out the new values.	2269	the only one changing the path). Can also be useful simply to find out the
		2270	new values.
1367		2271
1368	=item ev_statdata attr [read-only]	2272	=item ev_statdata attr [read-only]
1369		2273
1370	The most-recently detected attributes of the file. Although the type is of	2274	The most-recently detected attributes of the file. Although the type is
1371	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2275	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1372	suitable for your system. If the C<st_nlink> member is C<0>, then there	2276	suitable for your system, but you can only rely on the POSIX-standardised
		2277	members to be present. If the C<st_nlink> member is C<0>, then there was
1373	was some error while C<stat>ing the file.	2278	some error while C<stat>ing the file.
1374		2279
1375	=item ev_statdata prev [read-only]	2280	=item ev_statdata prev [read-only]
1376		2281
1377	The previous attributes of the file. The callback gets invoked whenever	2282	The previous attributes of the file. The callback gets invoked whenever
1378	C<prev> != C<attr>.	2283	C<prev> != C<attr>, or, more precisely, one or more of these members
		2284	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2285	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1379		2286
1380	=item ev_tstamp interval [read-only]	2287	=item ev_tstamp interval [read-only]
1381		2288
1382	The specified interval.	2289	The specified interval.
1383		2290
1384	=item const char *path [read-only]	2291	=item const char *path [read-only]
1385		2292
1386	The filesystem path that is being watched.	2293	The file system path that is being watched.
1387		2294
1388	=back	2295	=back
1389		2296
		2297	=head3 Examples
		2298
1390	Example: Watch C</etc/passwd> for attribute changes.	2299	Example: Watch C</etc/passwd> for attribute changes.
1391		2300
1392	static void	2301	static void
1393	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2302	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1394	{	2303	{
1395	/* /etc/passwd changed in some way */	2304	/* /etc/passwd changed in some way */
1396	if (w->attr.st_nlink)	2305	if (w->attr.st_nlink)
1397	{	2306	{
1398	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2307	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1399	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2308	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1400	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2309	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1401	}	2310	}
1402	else	2311	else
1403	/* you shalt not abuse printf for puts */	2312	/* you shalt not abuse printf for puts */
1404	puts ("wow, /etc/passwd is not there, expect problems. "	2313	puts ("wow, /etc/passwd is not there, expect problems. "
1405	"if this is windows, they already arrived\n");	2314	"if this is windows, they already arrived\n");
1406	}	2315	}
1407		2316
1408	...	2317	...
1409	ev_stat passwd;	2318	ev_stat passwd;
1410		2319
1411	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2320	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1412	ev_stat_start (loop, &passwd);	2321	ev_stat_start (loop, &passwd);
		2322
		2323	Example: Like above, but additionally use a one-second delay so we do not
		2324	miss updates (however, frequent updates will delay processing, too, so
		2325	one might do the work both on C<ev_stat> callback invocation I<and> on
		2326	C<ev_timer> callback invocation).
		2327
		2328	static ev_stat passwd;
		2329	static ev_timer timer;
		2330
		2331	static void
		2332	timer_cb (EV_P_ ev_timer *w, int revents)
		2333	{
		2334	ev_timer_stop (EV_A_ w);
		2335
		2336	/* now it's one second after the most recent passwd change */
		2337	}
		2338
		2339	static void
		2340	stat_cb (EV_P_ ev_stat *w, int revents)
		2341	{
		2342	/* reset the one-second timer */
		2343	ev_timer_again (EV_A_ &timer);
		2344	}
		2345
		2346	...
		2347	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2348	ev_stat_start (loop, &passwd);
		2349	ev_timer_init (&timer, timer_cb, 0., 1.02);
1413		2350
1414		2351
1415	=head2 C<ev_idle> - when you've got nothing better to do...	2352	=head2 C<ev_idle> - when you've got nothing better to do...
1416		2353
1417	Idle watchers trigger events when no other events of the same or higher	2354	Idle watchers trigger events when no other events of the same or higher
1418	priority are pending (prepare, check and other idle watchers do not	2355	priority are pending (prepare, check and other idle watchers do not count
1419	count).	2356	as receiving "events").
1420		2357
1421	That is, as long as your process is busy handling sockets or timeouts	2358	That is, as long as your process is busy handling sockets or timeouts
1422	(or even signals, imagine) of the same or higher priority it will not be	2359	(or even signals, imagine) of the same or higher priority it will not be
1423	triggered. But when your process is idle (or only lower-priority watchers	2360	triggered. But when your process is idle (or only lower-priority watchers
1424	are pending), the idle watchers are being called once per event loop	2361	are pending), the idle watchers are being called once per event loop
…		…
1431	Apart from keeping your process non-blocking (which is a useful	2368	Apart from keeping your process non-blocking (which is a useful
1432	effect on its own sometimes), idle watchers are a good place to do	2369	effect on its own sometimes), idle watchers are a good place to do
1433	"pseudo-background processing", or delay processing stuff to after the	2370	"pseudo-background processing", or delay processing stuff to after the
1434	event loop has handled all outstanding events.	2371	event loop has handled all outstanding events.
1435		2372
		2373	=head3 Watcher-Specific Functions and Data Members
		2374
1436	=over 4	2375	=over 4
1437		2376
1438	=item ev_idle_init (ev_signal *, callback)	2377	=item ev_idle_init (ev_idle *, callback)
1439		2378
1440	Initialises and configures the idle watcher - it has no parameters of any	2379	Initialises and configures the idle watcher - it has no parameters of any
1441	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2380	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1442	believe me.	2381	believe me.
1443		2382
1444	=back	2383	=back
1445		2384
		2385	=head3 Examples
		2386
1446	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2387	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1447	callback, free it. Also, use no error checking, as usual.	2388	callback, free it. Also, use no error checking, as usual.
1448		2389
1449	static void	2390	static void
1450	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2391	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1451	{	2392	{
1452	free (w);	2393	free (w);
1453	// now do something you wanted to do when the program has	2394	// now do something you wanted to do when the program has
1454	// no longer asnything immediate to do.	2395	// no longer anything immediate to do.
1455	}	2396	}
1456		2397
1457	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2398	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1458	ev_idle_init (idle_watcher, idle_cb);	2399	ev_idle_init (idle_watcher, idle_cb);
1459	ev_idle_start (loop, idle_cb);	2400	ev_idle_start (loop, idle_watcher);
1460		2401
1461		2402
1462	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2403	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1463		2404
1464	Prepare and check watchers are usually (but not always) used in tandem:	2405	Prepare and check watchers are usually (but not always) used in pairs:
1465	prepare watchers get invoked before the process blocks and check watchers	2406	prepare watchers get invoked before the process blocks and check watchers
1466	afterwards.	2407	afterwards.
1467		2408
1468	You I<must not> call C<ev_loop> or similar functions that enter	2409	You I<must not> call C<ev_loop> or similar functions that enter
1469	the current event loop from either C<ev_prepare> or C<ev_check>	2410	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1472	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2413	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1473	C<ev_check> so if you have one watcher of each kind they will always be	2414	C<ev_check> so if you have one watcher of each kind they will always be
1474	called in pairs bracketing the blocking call.	2415	called in pairs bracketing the blocking call.
1475		2416
1476	Their main purpose is to integrate other event mechanisms into libev and	2417	Their main purpose is to integrate other event mechanisms into libev and
1477	their use is somewhat advanced. This could be used, for example, to track	2418	their use is somewhat advanced. They could be used, for example, to track
1478	variable changes, implement your own watchers, integrate net-snmp or a	2419	variable changes, implement your own watchers, integrate net-snmp or a
1479	coroutine library and lots more. They are also occasionally useful if	2420	coroutine library and lots more. They are also occasionally useful if
1480	you cache some data and want to flush it before blocking (for example,	2421	you cache some data and want to flush it before blocking (for example,
1481	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2422	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1482	watcher).	2423	watcher).
1483		2424
1484	This is done by examining in each prepare call which file descriptors need	2425	This is done by examining in each prepare call which file descriptors
1485	to be watched by the other library, registering C<ev_io> watchers for	2426	need to be watched by the other library, registering C<ev_io> watchers
1486	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2427	for them and starting an C<ev_timer> watcher for any timeouts (many
1487	provide just this functionality). Then, in the check watcher you check for	2428	libraries provide exactly this functionality). Then, in the check watcher,
1488	any events that occured (by checking the pending status of all watchers	2429	you check for any events that occurred (by checking the pending status
1489	and stopping them) and call back into the library. The I/O and timer	2430	of all watchers and stopping them) and call back into the library. The
1490	callbacks will never actually be called (but must be valid nevertheless,	2431	I/O and timer callbacks will never actually be called (but must be valid
1491	because you never know, you know?).	2432	nevertheless, because you never know, you know?).
1492		2433
1493	As another example, the Perl Coro module uses these hooks to integrate	2434	As another example, the Perl Coro module uses these hooks to integrate
1494	coroutines into libev programs, by yielding to other active coroutines	2435	coroutines into libev programs, by yielding to other active coroutines
1495	during each prepare and only letting the process block if no coroutines	2436	during each prepare and only letting the process block if no coroutines
1496	are ready to run (it's actually more complicated: it only runs coroutines	2437	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1499	loop from blocking if lower-priority coroutines are active, thus mapping	2440	loop from blocking if lower-priority coroutines are active, thus mapping
1500	low-priority coroutines to idle/background tasks).	2441	low-priority coroutines to idle/background tasks).
1501		2442
1502	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2443	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1503	priority, to ensure that they are being run before any other watchers	2444	priority, to ensure that they are being run before any other watchers
		2445	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2446
1504	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2447	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1505	too) should not activate ("feed") events into libev. While libev fully	2448	activate ("feed") events into libev. While libev fully supports this, they
1506	supports this, they will be called before other C<ev_check> watchers did	2449	might get executed before other C<ev_check> watchers did their job. As
1507	their job. As C<ev_check> watchers are often used to embed other event	2450	C<ev_check> watchers are often used to embed other (non-libev) event
1508	loops those other event loops might be in an unusable state until their	2451	loops those other event loops might be in an unusable state until their
1509	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2452	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1510	others).	2453	others).
1511		2454
		2455	=head3 Watcher-Specific Functions and Data Members
		2456
1512	=over 4	2457	=over 4
1513		2458
1514	=item ev_prepare_init (ev_prepare *, callback)	2459	=item ev_prepare_init (ev_prepare *, callback)
1515		2460
1516	=item ev_check_init (ev_check *, callback)	2461	=item ev_check_init (ev_check *, callback)
1517		2462
1518	Initialises and configures the prepare or check watcher - they have no	2463	Initialises and configures the prepare or check watcher - they have no
1519	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2464	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1520	macros, but using them is utterly, utterly and completely pointless.	2465	macros, but using them is utterly, utterly, utterly and completely
		2466	pointless.
1521		2467
1522	=back	2468	=back
		2469
		2470	=head3 Examples
1523		2471
1524	There are a number of principal ways to embed other event loops or modules	2472	There are a number of principal ways to embed other event loops or modules
1525	into libev. Here are some ideas on how to include libadns into libev	2473	into libev. Here are some ideas on how to include libadns into libev
1526	(there is a Perl module named C<EV::ADNS> that does this, which you could	2474	(there is a Perl module named C<EV::ADNS> that does this, which you could
1527	use for an actually working example. Another Perl module named C<EV::Glib>	2475	use as a working example. Another Perl module named C<EV::Glib> embeds a
1528	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2476	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1529	into the Glib event loop).	2477	Glib event loop).
1530		2478
1531	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2479	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1532	and in a check watcher, destroy them and call into libadns. What follows	2480	and in a check watcher, destroy them and call into libadns. What follows
1533	is pseudo-code only of course. This requires you to either use a low	2481	is pseudo-code only of course. This requires you to either use a low
1534	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2482	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1535	the callbacks for the IO/timeout watchers might not have been called yet.	2483	the callbacks for the IO/timeout watchers might not have been called yet.
1536		2484
1537	static ev_io iow [nfd];	2485	static ev_io iow [nfd];
1538	static ev_timer tw;	2486	static ev_timer tw;
1539		2487
1540	static void	2488	static void
1541	io_cb (ev_loop *loop, ev_io *w, int revents)	2489	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1542	{	2490	{
1543	}	2491	}
1544		2492
1545	// create io watchers for each fd and a timer before blocking	2493	// create io watchers for each fd and a timer before blocking
1546	static void	2494	static void
1547	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2495	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1548	{	2496	{
1549	int timeout = 3600000;	2497	int timeout = 3600000;
1550	struct pollfd fds [nfd];	2498	struct pollfd fds [nfd];
1551	// actual code will need to loop here and realloc etc.	2499	// actual code will need to loop here and realloc etc.
1552	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2500	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1553		2501
1554	/* the callback is illegal, but won't be called as we stop during check */	2502	/* the callback is illegal, but won't be called as we stop during check */
1555	ev_timer_init (&tw, 0, timeout * 1e-3);	2503	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1556	ev_timer_start (loop, &tw);	2504	ev_timer_start (loop, &tw);
1557		2505
1558	// create one ev_io per pollfd	2506	// create one ev_io per pollfd
1559	for (int i = 0; i < nfd; ++i)	2507	for (int i = 0; i < nfd; ++i)
1560	{	2508	{
1561	ev_io_init (iow + i, io_cb, fds [i].fd,	2509	ev_io_init (iow + i, io_cb, fds [i].fd,
1562	((fds [i].events & POLLIN ? EV_READ : 0)	2510	((fds [i].events & POLLIN ? EV_READ : 0)
1563	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2511	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1564		2512
1565	fds [i].revents = 0;	2513	fds [i].revents = 0;
1566	ev_io_start (loop, iow + i);	2514	ev_io_start (loop, iow + i);
1567	}	2515	}
1568	}	2516	}
1569		2517
1570	// stop all watchers after blocking	2518	// stop all watchers after blocking
1571	static void	2519	static void
1572	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2520	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1573	{	2521	{
1574	ev_timer_stop (loop, &tw);	2522	ev_timer_stop (loop, &tw);
1575		2523
1576	for (int i = 0; i < nfd; ++i)	2524	for (int i = 0; i < nfd; ++i)
1577	{	2525	{
1578	// set the relevant poll flags	2526	// set the relevant poll flags
1579	// could also call adns_processreadable etc. here	2527	// could also call adns_processreadable etc. here
1580	struct pollfd *fd = fds + i;	2528	struct pollfd *fd = fds + i;
1581	int revents = ev_clear_pending (iow + i);	2529	int revents = ev_clear_pending (iow + i);
1582	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2530	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1583	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2531	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1584		2532
1585	// now stop the watcher	2533	// now stop the watcher
1586	ev_io_stop (loop, iow + i);	2534	ev_io_stop (loop, iow + i);
1587	}	2535	}
1588		2536
1589	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2537	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1590	}	2538	}
1591		2539
1592	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2540	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1593	in the prepare watcher and would dispose of the check watcher.	2541	in the prepare watcher and would dispose of the check watcher.
1594		2542
1595	Method 3: If the module to be embedded supports explicit event	2543	Method 3: If the module to be embedded supports explicit event
1596	notification (adns does), you can also make use of the actual watcher	2544	notification (libadns does), you can also make use of the actual watcher
1597	callbacks, and only destroy/create the watchers in the prepare watcher.	2545	callbacks, and only destroy/create the watchers in the prepare watcher.
1598		2546
1599	static void	2547	static void
1600	timer_cb (EV_P_ ev_timer *w, int revents)	2548	timer_cb (EV_P_ ev_timer *w, int revents)
1601	{	2549	{
1602	adns_state ads = (adns_state)w->data;	2550	adns_state ads = (adns_state)w->data;
1603	update_now (EV_A);	2551	update_now (EV_A);
1604		2552
1605	adns_processtimeouts (ads, &tv_now);	2553	adns_processtimeouts (ads, &tv_now);
1606	}	2554	}
1607		2555
1608	static void	2556	static void
1609	io_cb (EV_P_ ev_io *w, int revents)	2557	io_cb (EV_P_ ev_io *w, int revents)
1610	{	2558	{
1611	adns_state ads = (adns_state)w->data;	2559	adns_state ads = (adns_state)w->data;
1612	update_now (EV_A);	2560	update_now (EV_A);
1613		2561
1614	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2562	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1615	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2563	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1616	}	2564	}
1617		2565
1618	// do not ever call adns_afterpoll	2566	// do not ever call adns_afterpoll
1619		2567
1620	Method 4: Do not use a prepare or check watcher because the module you	2568	Method 4: Do not use a prepare or check watcher because the module you
1621	want to embed is too inflexible to support it. Instead, youc na override	2569	want to embed is not flexible enough to support it. Instead, you can
1622	their poll function. The drawback with this solution is that the main	2570	override their poll function. The drawback with this solution is that the
1623	loop is now no longer controllable by EV. The C<Glib::EV> module does	2571	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1624	this.	2572	this approach, effectively embedding EV as a client into the horrible
		2573	libglib event loop.
1625		2574
1626	static gint	2575	static gint
1627	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2576	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1628	{	2577	{
1629	int got_events = 0;	2578	int got_events = 0;
1630		2579
1631	for (n = 0; n < nfds; ++n)	2580	for (n = 0; n < nfds; ++n)
1632	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2581	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1633		2582
1634	if (timeout >= 0)	2583	if (timeout >= 0)
1635	// create/start timer	2584	// create/start timer
1636		2585
1637	// poll	2586	// poll
1638	ev_loop (EV_A_ 0);	2587	ev_loop (EV_A_ 0);
1639		2588
1640	// stop timer again	2589	// stop timer again
1641	if (timeout >= 0)	2590	if (timeout >= 0)
1642	ev_timer_stop (EV_A_ &to);	2591	ev_timer_stop (EV_A_ &to);
1643		2592
1644	// stop io watchers again - their callbacks should have set	2593	// stop io watchers again - their callbacks should have set
1645	for (n = 0; n < nfds; ++n)	2594	for (n = 0; n < nfds; ++n)
1646	ev_io_stop (EV_A_ iow [n]);	2595	ev_io_stop (EV_A_ iow [n]);
1647		2596
1648	return got_events;	2597	return got_events;
1649	}	2598	}
1650		2599
1651		2600
1652	=head2 C<ev_embed> - when one backend isn't enough...	2601	=head2 C<ev_embed> - when one backend isn't enough...
1653		2602
1654	This is a rather advanced watcher type that lets you embed one event loop	2603	This is a rather advanced watcher type that lets you embed one event loop
…		…
1660	prioritise I/O.	2609	prioritise I/O.
1661		2610
1662	As an example for a bug workaround, the kqueue backend might only support	2611	As an example for a bug workaround, the kqueue backend might only support
1663	sockets on some platform, so it is unusable as generic backend, but you	2612	sockets on some platform, so it is unusable as generic backend, but you
1664	still want to make use of it because you have many sockets and it scales	2613	still want to make use of it because you have many sockets and it scales
1665	so nicely. In this case, you would create a kqueue-based loop and embed it	2614	so nicely. In this case, you would create a kqueue-based loop and embed
1666	into your default loop (which might use e.g. poll). Overall operation will	2615	it into your default loop (which might use e.g. poll). Overall operation
1667	be a bit slower because first libev has to poll and then call kevent, but	2616	will be a bit slower because first libev has to call C<poll> and then
1668	at least you can use both at what they are best.	2617	C<kevent>, but at least you can use both mechanisms for what they are
		2618	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1669		2619
1670	As for prioritising I/O: rarely you have the case where some fds have	2620	As for prioritising I/O: under rare circumstances you have the case where
1671	to be watched and handled very quickly (with low latency), and even	2621	some fds have to be watched and handled very quickly (with low latency),
1672	priorities and idle watchers might have too much overhead. In this case	2622	and even priorities and idle watchers might have too much overhead. In
1673	you would put all the high priority stuff in one loop and all the rest in	2623	this case you would put all the high priority stuff in one loop and all
1674	a second one, and embed the second one in the first.	2624	the rest in a second one, and embed the second one in the first.
1675		2625
1676	As long as the watcher is active, the callback will be invoked every time	2626	As long as the watcher is active, the callback will be invoked every
1677	there might be events pending in the embedded loop. The callback must then	2627	time there might be events pending in the embedded loop. The callback
1678	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2628	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1679	their callbacks (you could also start an idle watcher to give the embedded	2629	sweep and invoke their callbacks (the callback doesn't need to invoke the
1680	loop strictly lower priority for example). You can also set the callback	2630	C<ev_embed_sweep> function directly, it could also start an idle watcher
1681	to C<0>, in which case the embed watcher will automatically execute the	2631	to give the embedded loop strictly lower priority for example).
1682	embedded loop sweep.
1683		2632
1684	As long as the watcher is started it will automatically handle events. The	2633	You can also set the callback to C<0>, in which case the embed watcher
1685	callback will be invoked whenever some events have been handled. You can	2634	will automatically execute the embedded loop sweep whenever necessary.
1686	set the callback to C<0> to avoid having to specify one if you are not
1687	interested in that.
1688		2635
1689	Also, there have not currently been made special provisions for forking:	2636	Fork detection will be handled transparently while the C<ev_embed> watcher
1690	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2637	is active, i.e., the embedded loop will automatically be forked when the
1691	but you will also have to stop and restart any C<ev_embed> watchers	2638	embedding loop forks. In other cases, the user is responsible for calling
1692	yourself.	2639	C<ev_loop_fork> on the embedded loop.
1693		2640
1694	Unfortunately, not all backends are embeddable, only the ones returned by	2641	Unfortunately, not all backends are embeddable: only the ones returned by
1695	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2642	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1696	portable one.	2643	portable one.
1697		2644
1698	So when you want to use this feature you will always have to be prepared	2645	So when you want to use this feature you will always have to be prepared
1699	that you cannot get an embeddable loop. The recommended way to get around	2646	that you cannot get an embeddable loop. The recommended way to get around
1700	this is to have a separate variables for your embeddable loop, try to	2647	this is to have a separate variables for your embeddable loop, try to
1701	create it, and if that fails, use the normal loop for everything:	2648	create it, and if that fails, use the normal loop for everything.
1702		2649
1703	struct ev_loop *loop_hi = ev_default_init (0);	2650	=head3 C<ev_embed> and fork
1704	struct ev_loop *loop_lo = 0;
1705	struct ev_embed embed;
1706
1707	// see if there is a chance of getting one that works
1708	// (remember that a flags value of 0 means autodetection)
1709	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1710	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1711	: 0;
1712		2651
1713	// if we got one, then embed it, otherwise default to loop_hi	2652	While the C<ev_embed> watcher is running, forks in the embedding loop will
1714	if (loop_lo)	2653	automatically be applied to the embedded loop as well, so no special
1715	{	2654	fork handling is required in that case. When the watcher is not running,
1716	ev_embed_init (&embed, 0, loop_lo);	2655	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1717	ev_embed_start (loop_hi, &embed);	2656	as applicable.
1718	}	2657
1719	else	2658	=head3 Watcher-Specific Functions and Data Members
1720	loop_lo = loop_hi;
1721		2659
1722	=over 4	2660	=over 4
1723		2661
1724	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2662	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1725		2663
…		…
1727		2665
1728	Configures the watcher to embed the given loop, which must be	2666	Configures the watcher to embed the given loop, which must be
1729	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2667	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1730	invoked automatically, otherwise it is the responsibility of the callback	2668	invoked automatically, otherwise it is the responsibility of the callback
1731	to invoke it (it will continue to be called until the sweep has been done,	2669	to invoke it (it will continue to be called until the sweep has been done,
1732	if you do not want thta, you need to temporarily stop the embed watcher).	2670	if you do not want that, you need to temporarily stop the embed watcher).
1733		2671
1734	=item ev_embed_sweep (loop, ev_embed *)	2672	=item ev_embed_sweep (loop, ev_embed *)
1735		2673
1736	Make a single, non-blocking sweep over the embedded loop. This works	2674	Make a single, non-blocking sweep over the embedded loop. This works
1737	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2675	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1738	apropriate way for embedded loops.	2676	appropriate way for embedded loops.
1739		2677
1740	=item struct ev_loop *loop [read-only]	2678	=item struct ev_loop *other [read-only]
1741		2679
1742	The embedded event loop.	2680	The embedded event loop.
1743		2681
1744	=back	2682	=back
		2683
		2684	=head3 Examples
		2685
		2686	Example: Try to get an embeddable event loop and embed it into the default
		2687	event loop. If that is not possible, use the default loop. The default
		2688	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2689	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2690	used).
		2691
		2692	struct ev_loop *loop_hi = ev_default_init (0);
		2693	struct ev_loop *loop_lo = 0;
		2694	ev_embed embed;
		2695
		2696	// see if there is a chance of getting one that works
		2697	// (remember that a flags value of 0 means autodetection)
		2698	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2699	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2700	: 0;
		2701
		2702	// if we got one, then embed it, otherwise default to loop_hi
		2703	if (loop_lo)
		2704	{
		2705	ev_embed_init (&embed, 0, loop_lo);
		2706	ev_embed_start (loop_hi, &embed);
		2707	}
		2708	else
		2709	loop_lo = loop_hi;
		2710
		2711	Example: Check if kqueue is available but not recommended and create
		2712	a kqueue backend for use with sockets (which usually work with any
		2713	kqueue implementation). Store the kqueue/socket-only event loop in
		2714	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2715
		2716	struct ev_loop *loop = ev_default_init (0);
		2717	struct ev_loop *loop_socket = 0;
		2718	ev_embed embed;
		2719
		2720	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2721	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2722	{
		2723	ev_embed_init (&embed, 0, loop_socket);
		2724	ev_embed_start (loop, &embed);
		2725	}
		2726
		2727	if (!loop_socket)
		2728	loop_socket = loop;
		2729
		2730	// now use loop_socket for all sockets, and loop for everything else
1745		2731
1746		2732
1747	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2733	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1748		2734
1749	Fork watchers are called when a C<fork ()> was detected (usually because	2735	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1752	event loop blocks next and before C<ev_check> watchers are being called,	2738	event loop blocks next and before C<ev_check> watchers are being called,
1753	and only in the child after the fork. If whoever good citizen calling	2739	and only in the child after the fork. If whoever good citizen calling
1754	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2740	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1755	handlers will be invoked, too, of course.	2741	handlers will be invoked, too, of course.
1756		2742
		2743	=head3 The special problem of life after fork - how is it possible?
		2744
		2745	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2746	up/change the process environment, followed by a call to C<exec()>. This
		2747	sequence should be handled by libev without any problems.
		2748
		2749	This changes when the application actually wants to do event handling
		2750	in the child, or both parent in child, in effect "continuing" after the
		2751	fork.
		2752
		2753	The default mode of operation (for libev, with application help to detect
		2754	forks) is to duplicate all the state in the child, as would be expected
		2755	when I<either> the parent I<or> the child process continues.
		2756
		2757	When both processes want to continue using libev, then this is usually the
		2758	wrong result. In that case, usually one process (typically the parent) is
		2759	supposed to continue with all watchers in place as before, while the other
		2760	process typically wants to start fresh, i.e. without any active watchers.
		2761
		2762	The cleanest and most efficient way to achieve that with libev is to
		2763	simply create a new event loop, which of course will be "empty", and
		2764	use that for new watchers. This has the advantage of not touching more
		2765	memory than necessary, and thus avoiding the copy-on-write, and the
		2766	disadvantage of having to use multiple event loops (which do not support
		2767	signal watchers).
		2768
		2769	When this is not possible, or you want to use the default loop for
		2770	other reasons, then in the process that wants to start "fresh", call
		2771	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2772	the default loop will "orphan" (not stop) all registered watchers, so you
		2773	have to be careful not to execute code that modifies those watchers. Note
		2774	also that in that case, you have to re-register any signal watchers.
		2775
		2776	=head3 Watcher-Specific Functions and Data Members
		2777
1757	=over 4	2778	=over 4
1758		2779
1759	=item ev_fork_init (ev_signal *, callback)	2780	=item ev_fork_init (ev_signal *, callback)
1760		2781
1761	Initialises and configures the fork watcher - it has no parameters of any	2782	Initialises and configures the fork watcher - it has no parameters of any
…		…
1763	believe me.	2784	believe me.
1764		2785
1765	=back	2786	=back
1766		2787
1767		2788
		2789	=head2 C<ev_async> - how to wake up another event loop
		2790
		2791	In general, you cannot use an C<ev_loop> from multiple threads or other
		2792	asynchronous sources such as signal handlers (as opposed to multiple event
		2793	loops - those are of course safe to use in different threads).
		2794
		2795	Sometimes, however, you need to wake up another event loop you do not
		2796	control, for example because it belongs to another thread. This is what
		2797	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2798	can signal it by calling C<ev_async_send>, which is thread- and signal
		2799	safe.
		2800
		2801	This functionality is very similar to C<ev_signal> watchers, as signals,
		2802	too, are asynchronous in nature, and signals, too, will be compressed
		2803	(i.e. the number of callback invocations may be less than the number of
		2804	C<ev_async_sent> calls).
		2805
		2806	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2807	just the default loop.
		2808
		2809	=head3 Queueing
		2810
		2811	C<ev_async> does not support queueing of data in any way. The reason
		2812	is that the author does not know of a simple (or any) algorithm for a
		2813	multiple-writer-single-reader queue that works in all cases and doesn't
		2814	need elaborate support such as pthreads.
		2815
		2816	That means that if you want to queue data, you have to provide your own
		2817	queue. But at least I can tell you how to implement locking around your
		2818	queue:
		2819
		2820	=over 4
		2821
		2822	=item queueing from a signal handler context
		2823
		2824	To implement race-free queueing, you simply add to the queue in the signal
		2825	handler but you block the signal handler in the watcher callback. Here is
		2826	an example that does that for some fictitious SIGUSR1 handler:
		2827
		2828	static ev_async mysig;
		2829
		2830	static void
		2831	sigusr1_handler (void)
		2832	{
		2833	sometype data;
		2834
		2835	// no locking etc.
		2836	queue_put (data);
		2837	ev_async_send (EV_DEFAULT_ &mysig);
		2838	}
		2839
		2840	static void
		2841	mysig_cb (EV_P_ ev_async *w, int revents)
		2842	{
		2843	sometype data;
		2844	sigset_t block, prev;
		2845
		2846	sigemptyset (&block);
		2847	sigaddset (&block, SIGUSR1);
		2848	sigprocmask (SIG_BLOCK, &block, &prev);
		2849
		2850	while (queue_get (&data))
		2851	process (data);
		2852
		2853	if (sigismember (&prev, SIGUSR1)
		2854	sigprocmask (SIG_UNBLOCK, &block, 0);
		2855	}
		2856
		2857	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2858	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2859	either...).
		2860
		2861	=item queueing from a thread context
		2862
		2863	The strategy for threads is different, as you cannot (easily) block
		2864	threads but you can easily preempt them, so to queue safely you need to
		2865	employ a traditional mutex lock, such as in this pthread example:
		2866
		2867	static ev_async mysig;
		2868	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2869
		2870	static void
		2871	otherthread (void)
		2872	{
		2873	// only need to lock the actual queueing operation
		2874	pthread_mutex_lock (&mymutex);
		2875	queue_put (data);
		2876	pthread_mutex_unlock (&mymutex);
		2877
		2878	ev_async_send (EV_DEFAULT_ &mysig);
		2879	}
		2880
		2881	static void
		2882	mysig_cb (EV_P_ ev_async *w, int revents)
		2883	{
		2884	pthread_mutex_lock (&mymutex);
		2885
		2886	while (queue_get (&data))
		2887	process (data);
		2888
		2889	pthread_mutex_unlock (&mymutex);
		2890	}
		2891
		2892	=back
		2893
		2894
		2895	=head3 Watcher-Specific Functions and Data Members
		2896
		2897	=over 4
		2898
		2899	=item ev_async_init (ev_async *, callback)
		2900
		2901	Initialises and configures the async watcher - it has no parameters of any
		2902	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2903	trust me.
		2904
		2905	=item ev_async_send (loop, ev_async *)
		2906
		2907	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2908	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2909	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2910	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2911	section below on what exactly this means).
		2912
		2913	Note that, as with other watchers in libev, multiple events might get
		2914	compressed into a single callback invocation (another way to look at this
		2915	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2916	reset when the event loop detects that).
		2917
		2918	This call incurs the overhead of a system call only once per event loop
		2919	iteration, so while the overhead might be noticeable, it doesn't apply to
		2920	repeated calls to C<ev_async_send> for the same event loop.
		2921
		2922	=item bool = ev_async_pending (ev_async *)
		2923
		2924	Returns a non-zero value when C<ev_async_send> has been called on the
		2925	watcher but the event has not yet been processed (or even noted) by the
		2926	event loop.
		2927
		2928	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2929	the loop iterates next and checks for the watcher to have become active,
		2930	it will reset the flag again. C<ev_async_pending> can be used to very
		2931	quickly check whether invoking the loop might be a good idea.
		2932
		2933	Not that this does I<not> check whether the watcher itself is pending,
		2934	only whether it has been requested to make this watcher pending: there
		2935	is a time window between the event loop checking and resetting the async
		2936	notification, and the callback being invoked.
		2937
		2938	=back
		2939
		2940
1768	=head1 OTHER FUNCTIONS	2941	=head1 OTHER FUNCTIONS
1769		2942
1770	There are some other functions of possible interest. Described. Here. Now.	2943	There are some other functions of possible interest. Described. Here. Now.
1771		2944
1772	=over 4	2945	=over 4
1773		2946
1774	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2947	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1775		2948
1776	This function combines a simple timer and an I/O watcher, calls your	2949	This function combines a simple timer and an I/O watcher, calls your
1777	callback on whichever event happens first and automatically stop both	2950	callback on whichever event happens first and automatically stops both
1778	watchers. This is useful if you want to wait for a single event on an fd	2951	watchers. This is useful if you want to wait for a single event on an fd
1779	or timeout without having to allocate/configure/start/stop/free one or	2952	or timeout without having to allocate/configure/start/stop/free one or
1780	more watchers yourself.	2953	more watchers yourself.
1781		2954
1782	If C<fd> is less than 0, then no I/O watcher will be started and events	2955	If C<fd> is less than 0, then no I/O watcher will be started and the
1783	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2956	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1784	C<events> set will be craeted and started.	2957	the given C<fd> and C<events> set will be created and started.
1785		2958
1786	If C<timeout> is less than 0, then no timeout watcher will be	2959	If C<timeout> is less than 0, then no timeout watcher will be
1787	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2960	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1788	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2961	repeat = 0) will be started. C<0> is a valid timeout.
1789	dubious value.
1790		2962
1791	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2963	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1792	passed an C<revents> set like normal event callbacks (a combination of	2964	passed an C<revents> set like normal event callbacks (a combination of
1793	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2965	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1794	value passed to C<ev_once>:	2966	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2967	a timeout and an io event at the same time - you probably should give io
		2968	events precedence.
1795		2969
		2970	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2971
1796	static void stdin_ready (int revents, void *arg)	2972	static void stdin_ready (int revents, void *arg)
1797	{	2973	{
1798	if (revents & EV_TIMEOUT)
1799	/* doh, nothing entered */;
1800	else if (revents & EV_READ)	2974	if (revents & EV_READ)
1801	/* stdin might have data for us, joy! */;	2975	/* stdin might have data for us, joy! */;
		2976	else if (revents & EV_TIMEOUT)
		2977	/* doh, nothing entered */;
1802	}	2978	}
1803		2979
1804	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2980	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1805		2981
1806	=item ev_feed_event (ev_loop *, watcher *, int revents)	2982	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1807		2983
1808	Feeds the given event set into the event loop, as if the specified event	2984	Feeds the given event set into the event loop, as if the specified event
1809	had happened for the specified watcher (which must be a pointer to an	2985	had happened for the specified watcher (which must be a pointer to an
1810	initialised but not necessarily started event watcher).	2986	initialised but not necessarily started event watcher).
1811		2987
1812	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2988	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1813		2989
1814	Feed an event on the given fd, as if a file descriptor backend detected	2990	Feed an event on the given fd, as if a file descriptor backend detected
1815	the given events it.	2991	the given events it.
1816		2992
1817	=item ev_feed_signal_event (ev_loop *loop, int signum)	2993	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1818		2994
1819	Feed an event as if the given signal occured (C<loop> must be the default	2995	Feed an event as if the given signal occurred (C<loop> must be the default
1820	loop!).	2996	loop!).
1821		2997
1822	=back	2998	=back
1823		2999
1824		3000
…		…
1840		3016
1841	=item * Priorities are not currently supported. Initialising priorities	3017	=item * Priorities are not currently supported. Initialising priorities
1842	will fail and all watchers will have the same priority, even though there	3018	will fail and all watchers will have the same priority, even though there
1843	is an ev_pri field.	3019	is an ev_pri field.
1844		3020
		3021	=item * In libevent, the last base created gets the signals, in libev, the
		3022	first base created (== the default loop) gets the signals.
		3023
1845	=item * Other members are not supported.	3024	=item * Other members are not supported.
1846		3025
1847	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3026	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1848	to use the libev header file and library.	3027	to use the libev header file and library.
1849		3028
1850	=back	3029	=back
1851		3030
1852	=head1 C++ SUPPORT	3031	=head1 C++ SUPPORT
1853		3032
1854	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3033	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1855	you to use some convinience methods to start/stop watchers and also change	3034	you to use some convenience methods to start/stop watchers and also change
1856	the callback model to a model using method callbacks on objects.	3035	the callback model to a model using method callbacks on objects.
1857		3036
1858	To use it,	3037	To use it,
1859		3038
1860	#include <ev++.h>	3039	#include <ev++.h>
1861		3040
1862	This automatically includes F<ev.h> and puts all of its definitions (many	3041	This automatically includes F<ev.h> and puts all of its definitions (many
1863	of them macros) into the global namespace. All C++ specific things are	3042	of them macros) into the global namespace. All C++ specific things are
1864	put into the C<ev> namespace. It should support all the same embedding	3043	put into the C<ev> namespace. It should support all the same embedding
1865	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3044	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1932	your compiler is good :), then the method will be fully inlined into the	3111	your compiler is good :), then the method will be fully inlined into the
1933	thunking function, making it as fast as a direct C callback.	3112	thunking function, making it as fast as a direct C callback.
1934		3113
1935	Example: simple class declaration and watcher initialisation	3114	Example: simple class declaration and watcher initialisation
1936		3115
1937	struct myclass	3116	struct myclass
1938	{	3117	{
1939	void io_cb (ev::io &w, int revents) { }	3118	void io_cb (ev::io &w, int revents) { }
1940	}	3119	}
1941		3120
1942	myclass obj;	3121	myclass obj;
1943	ev::io iow;	3122	ev::io iow;
1944	iow.set <myclass, &myclass::io_cb> (&obj);	3123	iow.set <myclass, &myclass::io_cb> (&obj);
		3124
		3125	=item w->set (object *)
		3126
		3127	This is an B<experimental> feature that might go away in a future version.
		3128
		3129	This is a variation of a method callback - leaving out the method to call
		3130	will default the method to C<operator ()>, which makes it possible to use
		3131	functor objects without having to manually specify the C<operator ()> all
		3132	the time. Incidentally, you can then also leave out the template argument
		3133	list.
		3134
		3135	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3136	int revents)>.
		3137
		3138	See the method-C<set> above for more details.
		3139
		3140	Example: use a functor object as callback.
		3141
		3142	struct myfunctor
		3143	{
		3144	void operator() (ev::io &w, int revents)
		3145	{
		3146	...
		3147	}
		3148	}
		3149
		3150	myfunctor f;
		3151
		3152	ev::io w;
		3153	w.set (&f);
1945		3154
1946	=item w->set<function> (void *data = 0)	3155	=item w->set<function> (void *data = 0)
1947		3156
1948	Also sets a callback, but uses a static method or plain function as	3157	Also sets a callback, but uses a static method or plain function as
1949	callback. The optional C<data> argument will be stored in the watcher's	3158	callback. The optional C<data> argument will be stored in the watcher's
…		…
1951		3160
1952	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3161	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1953		3162
1954	See the method-C<set> above for more details.	3163	See the method-C<set> above for more details.
1955		3164
1956	Example:	3165	Example: Use a plain function as callback.
1957		3166
1958	static void io_cb (ev::io &w, int revents) { }	3167	static void io_cb (ev::io &w, int revents) { }
1959	iow.set <io_cb> ();	3168	iow.set <io_cb> ();
1960		3169
1961	=item w->set (struct ev_loop *)	3170	=item w->set (struct ev_loop *)
1962		3171
1963	Associates a different C<struct ev_loop> with this watcher. You can only	3172	Associates a different C<struct ev_loop> with this watcher. You can only
1964	do this when the watcher is inactive (and not pending either).	3173	do this when the watcher is inactive (and not pending either).
1965		3174
1966	=item w->set ([args])	3175	=item w->set ([arguments])
1967		3176
1968	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3177	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1969	called at least once. Unlike the C counterpart, an active watcher gets	3178	called at least once. Unlike the C counterpart, an active watcher gets
1970	automatically stopped and restarted when reconfiguring it with this	3179	automatically stopped and restarted when reconfiguring it with this
1971	method.	3180	method.
1972		3181
1973	=item w->start ()	3182	=item w->start ()
…		…
1977		3186
1978	=item w->stop ()	3187	=item w->stop ()
1979		3188
1980	Stops the watcher if it is active. Again, no C<loop> argument.	3189	Stops the watcher if it is active. Again, no C<loop> argument.
1981		3190
1982	=item w->again () C<ev::timer>, C<ev::periodic> only	3191	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1983		3192
1984	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3193	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1985	C<ev_TYPE_again> function.	3194	C<ev_TYPE_again> function.
1986		3195
1987	=item w->sweep () C<ev::embed> only	3196	=item w->sweep () (C<ev::embed> only)
1988		3197
1989	Invokes C<ev_embed_sweep>.	3198	Invokes C<ev_embed_sweep>.
1990		3199
1991	=item w->update () C<ev::stat> only	3200	=item w->update () (C<ev::stat> only)
1992		3201
1993	Invokes C<ev_stat_stat>.	3202	Invokes C<ev_stat_stat>.
1994		3203
1995	=back	3204	=back
1996		3205
1997	=back	3206	=back
1998		3207
1999	Example: Define a class with an IO and idle watcher, start one of them in	3208	Example: Define a class with an IO and idle watcher, start one of them in
2000	the constructor.	3209	the constructor.
2001		3210
2002	class myclass	3211	class myclass
2003	{	3212	{
2004	ev_io io; void io_cb (ev::io &w, int revents);	3213	ev::io io ; void io_cb (ev::io &w, int revents);
2005	ev_idle idle void idle_cb (ev::idle &w, int revents);	3214	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2006		3215
2007	myclass ();	3216	myclass (int fd)
2008	}	3217	{
2009
2010	myclass::myclass (int fd)
2011	{
2012	io .set <myclass, &myclass::io_cb > (this);	3218	io .set <myclass, &myclass::io_cb > (this);
2013	idle.set <myclass, &myclass::idle_cb> (this);	3219	idle.set <myclass, &myclass::idle_cb> (this);
2014		3220
2015	io.start (fd, ev::READ);	3221	io.start (fd, ev::READ);
		3222	}
2016	}	3223	};
		3224
		3225
		3226	=head1 OTHER LANGUAGE BINDINGS
		3227
		3228	Libev does not offer other language bindings itself, but bindings for a
		3229	number of languages exist in the form of third-party packages. If you know
		3230	any interesting language binding in addition to the ones listed here, drop
		3231	me a note.
		3232
		3233	=over 4
		3234
		3235	=item Perl
		3236
		3237	The EV module implements the full libev API and is actually used to test
		3238	libev. EV is developed together with libev. Apart from the EV core module,
		3239	there are additional modules that implement libev-compatible interfaces
		3240	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3241	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3242	and C<EV::Glib>).
		3243
		3244	It can be found and installed via CPAN, its homepage is at
		3245	L<http://software.schmorp.de/pkg/EV>.
		3246
		3247	=item Python
		3248
		3249	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3250	seems to be quite complete and well-documented.
		3251
		3252	=item Ruby
		3253
		3254	Tony Arcieri has written a ruby extension that offers access to a subset
		3255	of the libev API and adds file handle abstractions, asynchronous DNS and
		3256	more on top of it. It can be found via gem servers. Its homepage is at
		3257	L<http://rev.rubyforge.org/>.
		3258
		3259	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3260	makes rev work even on mingw.
		3261
		3262	=item Haskell
		3263
		3264	A haskell binding to libev is available at
		3265	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3266
		3267	=item D
		3268
		3269	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3270	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3271
		3272	=item Ocaml
		3273
		3274	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3275	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3276
		3277	=back
2017		3278
2018		3279
2019	=head1 MACRO MAGIC	3280	=head1 MACRO MAGIC
2020		3281
2021	Libev can be compiled with a variety of options, the most fundemantal is	3282	Libev can be compiled with a variety of options, the most fundamental
2022	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3283	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2023	callbacks have an initial C<struct ev_loop *> argument.	3284	functions and callbacks have an initial C<struct ev_loop *> argument.
2024		3285
2025	To make it easier to write programs that cope with either variant, the	3286	To make it easier to write programs that cope with either variant, the
2026	following macros are defined:	3287	following macros are defined:
2027		3288
2028	=over 4	3289	=over 4
…		…
2031		3292
2032	This provides the loop I<argument> for functions, if one is required ("ev	3293	This provides the loop I<argument> for functions, if one is required ("ev
2033	loop argument"). The C<EV_A> form is used when this is the sole argument,	3294	loop argument"). The C<EV_A> form is used when this is the sole argument,
2034	C<EV_A_> is used when other arguments are following. Example:	3295	C<EV_A_> is used when other arguments are following. Example:
2035		3296
2036	ev_unref (EV_A);	3297	ev_unref (EV_A);
2037	ev_timer_add (EV_A_ watcher);	3298	ev_timer_add (EV_A_ watcher);
2038	ev_loop (EV_A_ 0);	3299	ev_loop (EV_A_ 0);
2039		3300
2040	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3301	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2041	which is often provided by the following macro.	3302	which is often provided by the following macro.
2042		3303
2043	=item C<EV_P>, C<EV_P_>	3304	=item C<EV_P>, C<EV_P_>
2044		3305
2045	This provides the loop I<parameter> for functions, if one is required ("ev	3306	This provides the loop I<parameter> for functions, if one is required ("ev
2046	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3307	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2047	C<EV_P_> is used when other parameters are following. Example:	3308	C<EV_P_> is used when other parameters are following. Example:
2048		3309
2049	// this is how ev_unref is being declared	3310	// this is how ev_unref is being declared
2050	static void ev_unref (EV_P);	3311	static void ev_unref (EV_P);
2051		3312
2052	// this is how you can declare your typical callback	3313	// this is how you can declare your typical callback
2053	static void cb (EV_P_ ev_timer *w, int revents)	3314	static void cb (EV_P_ ev_timer *w, int revents)
2054		3315
2055	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3316	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2056	suitable for use with C<EV_A>.	3317	suitable for use with C<EV_A>.
2057		3318
2058	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3319	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2059		3320
2060	Similar to the other two macros, this gives you the value of the default	3321	Similar to the other two macros, this gives you the value of the default
2061	loop, if multiple loops are supported ("ev loop default").	3322	loop, if multiple loops are supported ("ev loop default").
		3323
		3324	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3325
		3326	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3327	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3328	is undefined when the default loop has not been initialised by a previous
		3329	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3330
		3331	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3332	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2062		3333
2063	=back	3334	=back
2064		3335
2065	Example: Declare and initialise a check watcher, utilising the above	3336	Example: Declare and initialise a check watcher, utilising the above
2066	macros so it will work regardless of whether multiple loops are supported	3337	macros so it will work regardless of whether multiple loops are supported
2067	or not.	3338	or not.
2068		3339
2069	static void	3340	static void
2070	check_cb (EV_P_ ev_timer *w, int revents)	3341	check_cb (EV_P_ ev_timer *w, int revents)
2071	{	3342	{
2072	ev_check_stop (EV_A_ w);	3343	ev_check_stop (EV_A_ w);
2073	}	3344	}
2074		3345
2075	ev_check check;	3346	ev_check check;
2076	ev_check_init (&check, check_cb);	3347	ev_check_init (&check, check_cb);
2077	ev_check_start (EV_DEFAULT_ &check);	3348	ev_check_start (EV_DEFAULT_ &check);
2078	ev_loop (EV_DEFAULT_ 0);	3349	ev_loop (EV_DEFAULT_ 0);
2079		3350
2080	=head1 EMBEDDING	3351	=head1 EMBEDDING
2081		3352
2082	Libev can (and often is) directly embedded into host	3353	Libev can (and often is) directly embedded into host
2083	applications. Examples of applications that embed it include the Deliantra	3354	applications. Examples of applications that embed it include the Deliantra
2084	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3355	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2085	and rxvt-unicode.	3356	and rxvt-unicode.
2086		3357
2087	The goal is to enable you to just copy the neecssary files into your	3358	The goal is to enable you to just copy the necessary files into your
2088	source directory without having to change even a single line in them, so	3359	source directory without having to change even a single line in them, so
2089	you can easily upgrade by simply copying (or having a checked-out copy of	3360	you can easily upgrade by simply copying (or having a checked-out copy of
2090	libev somewhere in your source tree).	3361	libev somewhere in your source tree).
2091		3362
2092	=head2 FILESETS	3363	=head2 FILESETS
2093		3364
2094	Depending on what features you need you need to include one or more sets of files	3365	Depending on what features you need you need to include one or more sets of files
2095	in your app.	3366	in your application.
2096		3367
2097	=head3 CORE EVENT LOOP	3368	=head3 CORE EVENT LOOP
2098		3369
2099	To include only the libev core (all the C<ev_*> functions), with manual	3370	To include only the libev core (all the C<ev_*> functions), with manual
2100	configuration (no autoconf):	3371	configuration (no autoconf):
2101		3372
2102	#define EV_STANDALONE 1	3373	#define EV_STANDALONE 1
2103	#include "ev.c"	3374	#include "ev.c"
2104		3375
2105	This will automatically include F<ev.h>, too, and should be done in a	3376	This will automatically include F<ev.h>, too, and should be done in a
2106	single C source file only to provide the function implementations. To use	3377	single C source file only to provide the function implementations. To use
2107	it, do the same for F<ev.h> in all files wishing to use this API (best	3378	it, do the same for F<ev.h> in all files wishing to use this API (best
2108	done by writing a wrapper around F<ev.h> that you can include instead and	3379	done by writing a wrapper around F<ev.h> that you can include instead and
2109	where you can put other configuration options):	3380	where you can put other configuration options):
2110		3381
2111	#define EV_STANDALONE 1	3382	#define EV_STANDALONE 1
2112	#include "ev.h"	3383	#include "ev.h"
2113		3384
2114	Both header files and implementation files can be compiled with a C++	3385	Both header files and implementation files can be compiled with a C++
2115	compiler (at least, thats a stated goal, and breakage will be treated	3386	compiler (at least, that's a stated goal, and breakage will be treated
2116	as a bug).	3387	as a bug).
2117		3388
2118	You need the following files in your source tree, or in a directory	3389	You need the following files in your source tree, or in a directory
2119	in your include path (e.g. in libev/ when using -Ilibev):	3390	in your include path (e.g. in libev/ when using -Ilibev):
2120		3391
2121	ev.h	3392	ev.h
2122	ev.c	3393	ev.c
2123	ev_vars.h	3394	ev_vars.h
2124	ev_wrap.h	3395	ev_wrap.h
2125		3396
2126	ev_win32.c required on win32 platforms only	3397	ev_win32.c required on win32 platforms only
2127		3398
2128	ev_select.c only when select backend is enabled (which is enabled by default)	3399	ev_select.c only when select backend is enabled (which is enabled by default)
2129	ev_poll.c only when poll backend is enabled (disabled by default)	3400	ev_poll.c only when poll backend is enabled (disabled by default)
2130	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3401	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2131	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3402	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2132	ev_port.c only when the solaris port backend is enabled (disabled by default)	3403	ev_port.c only when the solaris port backend is enabled (disabled by default)
2133		3404
2134	F<ev.c> includes the backend files directly when enabled, so you only need	3405	F<ev.c> includes the backend files directly when enabled, so you only need
2135	to compile this single file.	3406	to compile this single file.
2136		3407
2137	=head3 LIBEVENT COMPATIBILITY API	3408	=head3 LIBEVENT COMPATIBILITY API
2138		3409
2139	To include the libevent compatibility API, also include:	3410	To include the libevent compatibility API, also include:
2140		3411
2141	#include "event.c"	3412	#include "event.c"
2142		3413
2143	in the file including F<ev.c>, and:	3414	in the file including F<ev.c>, and:
2144		3415
2145	#include "event.h"	3416	#include "event.h"
2146		3417
2147	in the files that want to use the libevent API. This also includes F<ev.h>.	3418	in the files that want to use the libevent API. This also includes F<ev.h>.
2148		3419
2149	You need the following additional files for this:	3420	You need the following additional files for this:
2150		3421
2151	event.h	3422	event.h
2152	event.c	3423	event.c
2153		3424
2154	=head3 AUTOCONF SUPPORT	3425	=head3 AUTOCONF SUPPORT
2155		3426
2156	Instead of using C<EV_STANDALONE=1> and providing your config in	3427	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2157	whatever way you want, you can also C<m4_include([libev.m4])> in your	3428	whatever way you want, you can also C<m4_include([libev.m4])> in your
2158	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3429	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2159	include F<config.h> and configure itself accordingly.	3430	include F<config.h> and configure itself accordingly.
2160		3431
2161	For this of course you need the m4 file:	3432	For this of course you need the m4 file:
2162		3433
2163	libev.m4	3434	libev.m4
2164		3435
2165	=head2 PREPROCESSOR SYMBOLS/MACROS	3436	=head2 PREPROCESSOR SYMBOLS/MACROS
2166		3437
2167	Libev can be configured via a variety of preprocessor symbols you have to define	3438	Libev can be configured via a variety of preprocessor symbols you have to
2168	before including any of its files. The default is not to build for multiplicity	3439	define before including any of its files. The default in the absence of
2169	and only include the select backend.	3440	autoconf is documented for every option.
2170		3441
2171	=over 4	3442	=over 4
2172		3443
2173	=item EV_STANDALONE	3444	=item EV_STANDALONE
2174		3445
…		…
2176	keeps libev from including F<config.h>, and it also defines dummy	3447	keeps libev from including F<config.h>, and it also defines dummy
2177	implementations for some libevent functions (such as logging, which is not	3448	implementations for some libevent functions (such as logging, which is not
2178	supported). It will also not define any of the structs usually found in	3449	supported). It will also not define any of the structs usually found in
2179	F<event.h> that are not directly supported by the libev core alone.	3450	F<event.h> that are not directly supported by the libev core alone.
2180		3451
		3452	In stanbdalone mode, libev will still try to automatically deduce the
		3453	configuration, but has to be more conservative.
		3454
2181	=item EV_USE_MONOTONIC	3455	=item EV_USE_MONOTONIC
2182		3456
2183	If defined to be C<1>, libev will try to detect the availability of the	3457	If defined to be C<1>, libev will try to detect the availability of the
2184	monotonic clock option at both compiletime and runtime. Otherwise no use	3458	monotonic clock option at both compile time and runtime. Otherwise no
2185	of the monotonic clock option will be attempted. If you enable this, you	3459	use of the monotonic clock option will be attempted. If you enable this,
2186	usually have to link against librt or something similar. Enabling it when	3460	you usually have to link against librt or something similar. Enabling it
2187	the functionality isn't available is safe, though, althoguh you have	3461	when the functionality isn't available is safe, though, although you have
2188	to make sure you link against any libraries where the C<clock_gettime>	3462	to make sure you link against any libraries where the C<clock_gettime>
2189	function is hiding in (often F<-lrt>).	3463	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2190		3464
2191	=item EV_USE_REALTIME	3465	=item EV_USE_REALTIME
2192		3466
2193	If defined to be C<1>, libev will try to detect the availability of the	3467	If defined to be C<1>, libev will try to detect the availability of the
2194	realtime clock option at compiletime (and assume its availability at	3468	real-time clock option at compile time (and assume its availability
2195	runtime if successful). Otherwise no use of the realtime clock option will	3469	at runtime if successful). Otherwise no use of the real-time clock
2196	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3470	option will be attempted. This effectively replaces C<gettimeofday>
2197	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3471	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2198	in the description of C<EV_USE_MONOTONIC>, though.	3472	correctness. See the note about libraries in the description of
		3473	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3474	C<EV_USE_CLOCK_SYSCALL>.
		3475
		3476	=item EV_USE_CLOCK_SYSCALL
		3477
		3478	If defined to be C<1>, libev will try to use a direct syscall instead
		3479	of calling the system-provided C<clock_gettime> function. This option
		3480	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3481	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3482	programs needlessly. Using a direct syscall is slightly slower (in
		3483	theory), because no optimised vdso implementation can be used, but avoids
		3484	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3485	higher, as it simplifies linking (no need for C<-lrt>).
		3486
		3487	=item EV_USE_NANOSLEEP
		3488
		3489	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3490	and will use it for delays. Otherwise it will use C<select ()>.
		3491
		3492	=item EV_USE_EVENTFD
		3493
		3494	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3495	available and will probe for kernel support at runtime. This will improve
		3496	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3497	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3498	2.7 or newer, otherwise disabled.
2199		3499
2200	=item EV_USE_SELECT	3500	=item EV_USE_SELECT
2201		3501
2202	If undefined or defined to be C<1>, libev will compile in support for the	3502	If undefined or defined to be C<1>, libev will compile in support for the
2203	C<select>(2) backend. No attempt at autodetection will be done: if no	3503	C<select>(2) backend. No attempt at auto-detection will be done: if no
2204	other method takes over, select will be it. Otherwise the select backend	3504	other method takes over, select will be it. Otherwise the select backend
2205	will not be compiled in.	3505	will not be compiled in.
2206		3506
2207	=item EV_SELECT_USE_FD_SET	3507	=item EV_SELECT_USE_FD_SET
2208		3508
2209	If defined to C<1>, then the select backend will use the system C<fd_set>	3509	If defined to C<1>, then the select backend will use the system C<fd_set>
2210	structure. This is useful if libev doesn't compile due to a missing	3510	structure. This is useful if libev doesn't compile due to a missing
2211	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3511	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2212	exotic systems. This usually limits the range of file descriptors to some	3512	on exotic systems. This usually limits the range of file descriptors to
2213	low limit such as 1024 or might have other limitations (winsocket only	3513	some low limit such as 1024 or might have other limitations (winsocket
2214	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3514	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2215	influence the size of the C<fd_set> used.	3515	configures the maximum size of the C<fd_set>.
2216		3516
2217	=item EV_SELECT_IS_WINSOCKET	3517	=item EV_SELECT_IS_WINSOCKET
2218		3518
2219	When defined to C<1>, the select backend will assume that	3519	When defined to C<1>, the select backend will assume that
2220	select/socket/connect etc. don't understand file descriptors but	3520	select/socket/connect etc. don't understand file descriptors but
…		…
2222	be used is the winsock select). This means that it will call	3522	be used is the winsock select). This means that it will call
2223	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3523	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2224	it is assumed that all these functions actually work on fds, even	3524	it is assumed that all these functions actually work on fds, even
2225	on win32. Should not be defined on non-win32 platforms.	3525	on win32. Should not be defined on non-win32 platforms.
2226		3526
		3527	=item EV_FD_TO_WIN32_HANDLE
		3528
		3529	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3530	file descriptors to socket handles. When not defining this symbol (the
		3531	default), then libev will call C<_get_osfhandle>, which is usually
		3532	correct. In some cases, programs use their own file descriptor management,
		3533	in which case they can provide this function to map fds to socket handles.
		3534
2227	=item EV_USE_POLL	3535	=item EV_USE_POLL
2228		3536
2229	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3537	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2230	backend. Otherwise it will be enabled on non-win32 platforms. It	3538	backend. Otherwise it will be enabled on non-win32 platforms. It
2231	takes precedence over select.	3539	takes precedence over select.
2232		3540
2233	=item EV_USE_EPOLL	3541	=item EV_USE_EPOLL
2234		3542
2235	If defined to be C<1>, libev will compile in support for the Linux	3543	If defined to be C<1>, libev will compile in support for the Linux
2236	C<epoll>(7) backend. Its availability will be detected at runtime,	3544	C<epoll>(7) backend. Its availability will be detected at runtime,
2237	otherwise another method will be used as fallback. This is the	3545	otherwise another method will be used as fallback. This is the preferred
2238	preferred backend for GNU/Linux systems.	3546	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3547	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2239		3548
2240	=item EV_USE_KQUEUE	3549	=item EV_USE_KQUEUE
2241		3550
2242	If defined to be C<1>, libev will compile in support for the BSD style	3551	If defined to be C<1>, libev will compile in support for the BSD style
2243	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3552	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2256	otherwise another method will be used as fallback. This is the preferred	3565	otherwise another method will be used as fallback. This is the preferred
2257	backend for Solaris 10 systems.	3566	backend for Solaris 10 systems.
2258		3567
2259	=item EV_USE_DEVPOLL	3568	=item EV_USE_DEVPOLL
2260		3569
2261	reserved for future expansion, works like the USE symbols above.	3570	Reserved for future expansion, works like the USE symbols above.
2262		3571
2263	=item EV_USE_INOTIFY	3572	=item EV_USE_INOTIFY
2264		3573
2265	If defined to be C<1>, libev will compile in support for the Linux inotify	3574	If defined to be C<1>, libev will compile in support for the Linux inotify
2266	interface to speed up C<ev_stat> watchers. Its actual availability will	3575	interface to speed up C<ev_stat> watchers. Its actual availability will
2267	be detected at runtime.	3576	be detected at runtime. If undefined, it will be enabled if the headers
		3577	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3578
		3579	=item EV_ATOMIC_T
		3580
		3581	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3582	access is atomic with respect to other threads or signal contexts. No such
		3583	type is easily found in the C language, so you can provide your own type
		3584	that you know is safe for your purposes. It is used both for signal handler "locking"
		3585	as well as for signal and thread safety in C<ev_async> watchers.
		3586
		3587	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3588	(from F<signal.h>), which is usually good enough on most platforms.
2268		3589
2269	=item EV_H	3590	=item EV_H
2270		3591
2271	The name of the F<ev.h> header file used to include it. The default if	3592	The name of the F<ev.h> header file used to include it. The default if
2272	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3593	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2273	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3594	used to virtually rename the F<ev.h> header file in case of conflicts.
2274		3595
2275	=item EV_CONFIG_H	3596	=item EV_CONFIG_H
2276		3597
2277	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3598	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2278	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3599	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2279	C<EV_H>, above.	3600	C<EV_H>, above.
2280		3601
2281	=item EV_EVENT_H	3602	=item EV_EVENT_H
2282		3603
2283	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3604	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2284	of how the F<event.h> header can be found.	3605	of how the F<event.h> header can be found, the default is C<"event.h">.
2285		3606
2286	=item EV_PROTOTYPES	3607	=item EV_PROTOTYPES
2287		3608
2288	If defined to be C<0>, then F<ev.h> will not define any function	3609	If defined to be C<0>, then F<ev.h> will not define any function
2289	prototypes, but still define all the structs and other symbols. This is	3610	prototypes, but still define all the structs and other symbols. This is
…		…
2310	When doing priority-based operations, libev usually has to linearly search	3631	When doing priority-based operations, libev usually has to linearly search
2311	all the priorities, so having many of them (hundreds) uses a lot of space	3632	all the priorities, so having many of them (hundreds) uses a lot of space
2312	and time, so using the defaults of five priorities (-2 .. +2) is usually	3633	and time, so using the defaults of five priorities (-2 .. +2) is usually
2313	fine.	3634	fine.
2314		3635
2315	If your embedding app does not need any priorities, defining these both to	3636	If your embedding application does not need any priorities, defining these
2316	C<0> will save some memory and cpu.	3637	both to C<0> will save some memory and CPU.
2317		3638
2318	=item EV_PERIODIC_ENABLE	3639	=item EV_PERIODIC_ENABLE
2319		3640
2320	If undefined or defined to be C<1>, then periodic timers are supported. If	3641	If undefined or defined to be C<1>, then periodic timers are supported. If
2321	defined to be C<0>, then they are not. Disabling them saves a few kB of	3642	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2328	code.	3649	code.
2329		3650
2330	=item EV_EMBED_ENABLE	3651	=item EV_EMBED_ENABLE
2331		3652
2332	If undefined or defined to be C<1>, then embed watchers are supported. If	3653	If undefined or defined to be C<1>, then embed watchers are supported. If
2333	defined to be C<0>, then they are not.	3654	defined to be C<0>, then they are not. Embed watchers rely on most other
		3655	watcher types, which therefore must not be disabled.
2334		3656
2335	=item EV_STAT_ENABLE	3657	=item EV_STAT_ENABLE
2336		3658
2337	If undefined or defined to be C<1>, then stat watchers are supported. If	3659	If undefined or defined to be C<1>, then stat watchers are supported. If
2338	defined to be C<0>, then they are not.	3660	defined to be C<0>, then they are not.
…		…
2340	=item EV_FORK_ENABLE	3662	=item EV_FORK_ENABLE
2341		3663
2342	If undefined or defined to be C<1>, then fork watchers are supported. If	3664	If undefined or defined to be C<1>, then fork watchers are supported. If
2343	defined to be C<0>, then they are not.	3665	defined to be C<0>, then they are not.
2344		3666
		3667	=item EV_ASYNC_ENABLE
		3668
		3669	If undefined or defined to be C<1>, then async watchers are supported. If
		3670	defined to be C<0>, then they are not.
		3671
2345	=item EV_MINIMAL	3672	=item EV_MINIMAL
2346		3673
2347	If you need to shave off some kilobytes of code at the expense of some	3674	If you need to shave off some kilobytes of code at the expense of some
2348	speed, define this symbol to C<1>. Currently only used for gcc to override	3675	speed, define this symbol to C<1>. Currently this is used to override some
2349	some inlining decisions, saves roughly 30% codesize of amd64.	3676	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3677	much smaller 2-heap for timer management over the default 4-heap.
2350		3678
2351	=item EV_PID_HASHSIZE	3679	=item EV_PID_HASHSIZE
2352		3680
2353	C<ev_child> watchers use a small hash table to distribute workload by	3681	C<ev_child> watchers use a small hash table to distribute workload by
2354	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3682	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2355	than enough. If you need to manage thousands of children you might want to	3683	than enough. If you need to manage thousands of children you might want to
2356	increase this value (I<must> be a power of two).	3684	increase this value (I<must> be a power of two).
2357		3685
2358	=item EV_INOTIFY_HASHSIZE	3686	=item EV_INOTIFY_HASHSIZE
2359		3687
2360	C<ev_staz> watchers use a small hash table to distribute workload by	3688	C<ev_stat> watchers use a small hash table to distribute workload by
2361	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3689	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2362	usually more than enough. If you need to manage thousands of C<ev_stat>	3690	usually more than enough. If you need to manage thousands of C<ev_stat>
2363	watchers you might want to increase this value (I<must> be a power of	3691	watchers you might want to increase this value (I<must> be a power of
2364	two).	3692	two).
2365		3693
		3694	=item EV_USE_4HEAP
		3695
		3696	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3697	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3698	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3699	faster performance with many (thousands) of watchers.
		3700
		3701	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3702	(disabled).
		3703
		3704	=item EV_HEAP_CACHE_AT
		3705
		3706	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3707	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3708	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3709	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3710	but avoids random read accesses on heap changes. This improves performance
		3711	noticeably with many (hundreds) of watchers.
		3712
		3713	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3714	(disabled).
		3715
		3716	=item EV_VERIFY
		3717
		3718	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3719	be done: If set to C<0>, no internal verification code will be compiled
		3720	in. If set to C<1>, then verification code will be compiled in, but not
		3721	called. If set to C<2>, then the internal verification code will be
		3722	called once per loop, which can slow down libev. If set to C<3>, then the
		3723	verification code will be called very frequently, which will slow down
		3724	libev considerably.
		3725
		3726	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3727	C<0>.
		3728
2366	=item EV_COMMON	3729	=item EV_COMMON
2367		3730
2368	By default, all watchers have a C<void *data> member. By redefining	3731	By default, all watchers have a C<void *data> member. By redefining
2369	this macro to a something else you can include more and other types of	3732	this macro to a something else you can include more and other types of
2370	members. You have to define it each time you include one of the files,	3733	members. You have to define it each time you include one of the files,
2371	though, and it must be identical each time.	3734	though, and it must be identical each time.
2372		3735
2373	For example, the perl EV module uses something like this:	3736	For example, the perl EV module uses something like this:
2374		3737
2375	#define EV_COMMON \	3738	#define EV_COMMON \
2376	SV *self; /* contains this struct */ \	3739	SV *self; /* contains this struct */ \
2377	SV *cb_sv, *fh /* note no trailing ";" */	3740	SV *cb_sv, *fh /* note no trailing ";" */
2378		3741
2379	=item EV_CB_DECLARE (type)	3742	=item EV_CB_DECLARE (type)
2380		3743
2381	=item EV_CB_INVOKE (watcher, revents)	3744	=item EV_CB_INVOKE (watcher, revents)
2382		3745
2383	=item ev_set_cb (ev, cb)	3746	=item ev_set_cb (ev, cb)
2384		3747
2385	Can be used to change the callback member declaration in each watcher,	3748	Can be used to change the callback member declaration in each watcher,
2386	and the way callbacks are invoked and set. Must expand to a struct member	3749	and the way callbacks are invoked and set. Must expand to a struct member
2387	definition and a statement, respectively. See the F<ev.v> header file for	3750	definition and a statement, respectively. See the F<ev.h> header file for
2388	their default definitions. One possible use for overriding these is to	3751	their default definitions. One possible use for overriding these is to
2389	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3752	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2390	method calls instead of plain function calls in C++.	3753	method calls instead of plain function calls in C++.
		3754
		3755	=back
		3756
		3757	=head2 EXPORTED API SYMBOLS
		3758
		3759	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3760	exported symbols, you can use the provided F<Symbol.*> files which list
		3761	all public symbols, one per line:
		3762
		3763	Symbols.ev for libev proper
		3764	Symbols.event for the libevent emulation
		3765
		3766	This can also be used to rename all public symbols to avoid clashes with
		3767	multiple versions of libev linked together (which is obviously bad in
		3768	itself, but sometimes it is inconvenient to avoid this).
		3769
		3770	A sed command like this will create wrapper C<#define>'s that you need to
		3771	include before including F<ev.h>:
		3772
		3773	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3774
		3775	This would create a file F<wrap.h> which essentially looks like this:
		3776
		3777	#define ev_backend myprefix_ev_backend
		3778	#define ev_check_start myprefix_ev_check_start
		3779	#define ev_check_stop myprefix_ev_check_stop
		3780	...
2391		3781
2392	=head2 EXAMPLES	3782	=head2 EXAMPLES
2393		3783
2394	For a real-world example of a program the includes libev	3784	For a real-world example of a program the includes libev
2395	verbatim, you can have a look at the EV perl module	3785	verbatim, you can have a look at the EV perl module
…		…
2400	file.	3790	file.
2401		3791
2402	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3792	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2403	that everybody includes and which overrides some configure choices:	3793	that everybody includes and which overrides some configure choices:
2404		3794
2405	#define EV_MINIMAL 1	3795	#define EV_MINIMAL 1
2406	#define EV_USE_POLL 0	3796	#define EV_USE_POLL 0
2407	#define EV_MULTIPLICITY 0	3797	#define EV_MULTIPLICITY 0
2408	#define EV_PERIODIC_ENABLE 0	3798	#define EV_PERIODIC_ENABLE 0
2409	#define EV_STAT_ENABLE 0	3799	#define EV_STAT_ENABLE 0
2410	#define EV_FORK_ENABLE 0	3800	#define EV_FORK_ENABLE 0
2411	#define EV_CONFIG_H <config.h>	3801	#define EV_CONFIG_H <config.h>
2412	#define EV_MINPRI 0	3802	#define EV_MINPRI 0
2413	#define EV_MAXPRI 0	3803	#define EV_MAXPRI 0
2414		3804
2415	#include "ev++.h"	3805	#include "ev++.h"
2416		3806
2417	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3807	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2418		3808
2419	#include "ev_cpp.h"	3809	#include "ev_cpp.h"
2420	#include "ev.c"	3810	#include "ev.c"
2421		3811
		3812	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2422		3813
		3814	=head2 THREADS AND COROUTINES
		3815
		3816	=head3 THREADS
		3817
		3818	All libev functions are reentrant and thread-safe unless explicitly
		3819	documented otherwise, but libev implements no locking itself. This means
		3820	that you can use as many loops as you want in parallel, as long as there
		3821	are no concurrent calls into any libev function with the same loop
		3822	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3823	of course): libev guarantees that different event loops share no data
		3824	structures that need any locking.
		3825
		3826	Or to put it differently: calls with different loop parameters can be done
		3827	concurrently from multiple threads, calls with the same loop parameter
		3828	must be done serially (but can be done from different threads, as long as
		3829	only one thread ever is inside a call at any point in time, e.g. by using
		3830	a mutex per loop).
		3831
		3832	Specifically to support threads (and signal handlers), libev implements
		3833	so-called C<ev_async> watchers, which allow some limited form of
		3834	concurrency on the same event loop, namely waking it up "from the
		3835	outside".
		3836
		3837	If you want to know which design (one loop, locking, or multiple loops
		3838	without or something else still) is best for your problem, then I cannot
		3839	help you, but here is some generic advice:
		3840
		3841	=over 4
		3842
		3843	=item * most applications have a main thread: use the default libev loop
		3844	in that thread, or create a separate thread running only the default loop.
		3845
		3846	This helps integrating other libraries or software modules that use libev
		3847	themselves and don't care/know about threading.
		3848
		3849	=item * one loop per thread is usually a good model.
		3850
		3851	Doing this is almost never wrong, sometimes a better-performance model
		3852	exists, but it is always a good start.
		3853
		3854	=item * other models exist, such as the leader/follower pattern, where one
		3855	loop is handed through multiple threads in a kind of round-robin fashion.
		3856
		3857	Choosing a model is hard - look around, learn, know that usually you can do
		3858	better than you currently do :-)
		3859
		3860	=item * often you need to talk to some other thread which blocks in the
		3861	event loop.
		3862
		3863	C<ev_async> watchers can be used to wake them up from other threads safely
		3864	(or from signal contexts...).
		3865
		3866	An example use would be to communicate signals or other events that only
		3867	work in the default loop by registering the signal watcher with the
		3868	default loop and triggering an C<ev_async> watcher from the default loop
		3869	watcher callback into the event loop interested in the signal.
		3870
		3871	=back
		3872
		3873	=head3 COROUTINES
		3874
		3875	Libev is very accommodating to coroutines ("cooperative threads"):
		3876	libev fully supports nesting calls to its functions from different
		3877	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3878	different coroutines, and switch freely between both coroutines running the
		3879	loop, as long as you don't confuse yourself). The only exception is that
		3880	you must not do this from C<ev_periodic> reschedule callbacks.
		3881
		3882	Care has been taken to ensure that libev does not keep local state inside
		3883	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3884	they do not call any callbacks.
		3885
		3886	=head2 COMPILER WARNINGS
		3887
		3888	Depending on your compiler and compiler settings, you might get no or a
		3889	lot of warnings when compiling libev code. Some people are apparently
		3890	scared by this.
		3891
		3892	However, these are unavoidable for many reasons. For one, each compiler
		3893	has different warnings, and each user has different tastes regarding
		3894	warning options. "Warn-free" code therefore cannot be a goal except when
		3895	targeting a specific compiler and compiler-version.
		3896
		3897	Another reason is that some compiler warnings require elaborate
		3898	workarounds, or other changes to the code that make it less clear and less
		3899	maintainable.
		3900
		3901	And of course, some compiler warnings are just plain stupid, or simply
		3902	wrong (because they don't actually warn about the condition their message
		3903	seems to warn about). For example, certain older gcc versions had some
		3904	warnings that resulted an extreme number of false positives. These have
		3905	been fixed, but some people still insist on making code warn-free with
		3906	such buggy versions.
		3907
		3908	While libev is written to generate as few warnings as possible,
		3909	"warn-free" code is not a goal, and it is recommended not to build libev
		3910	with any compiler warnings enabled unless you are prepared to cope with
		3911	them (e.g. by ignoring them). Remember that warnings are just that:
		3912	warnings, not errors, or proof of bugs.
		3913
		3914
		3915	=head2 VALGRIND
		3916
		3917	Valgrind has a special section here because it is a popular tool that is
		3918	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3919
		3920	If you think you found a bug (memory leak, uninitialised data access etc.)
		3921	in libev, then check twice: If valgrind reports something like:
		3922
		3923	==2274== definitely lost: 0 bytes in 0 blocks.
		3924	==2274== possibly lost: 0 bytes in 0 blocks.
		3925	==2274== still reachable: 256 bytes in 1 blocks.
		3926
		3927	Then there is no memory leak, just as memory accounted to global variables
		3928	is not a memleak - the memory is still being referenced, and didn't leak.
		3929
		3930	Similarly, under some circumstances, valgrind might report kernel bugs
		3931	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3932	although an acceptable workaround has been found here), or it might be
		3933	confused.
		3934
		3935	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3936	make it into some kind of religion.
		3937
		3938	If you are unsure about something, feel free to contact the mailing list
		3939	with the full valgrind report and an explanation on why you think this
		3940	is a bug in libev (best check the archives, too :). However, don't be
		3941	annoyed when you get a brisk "this is no bug" answer and take the chance
		3942	of learning how to interpret valgrind properly.
		3943
		3944	If you need, for some reason, empty reports from valgrind for your project
		3945	I suggest using suppression lists.
		3946
		3947
		3948	=head1 PORTABILITY NOTES
		3949
		3950	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3951
		3952	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3953	requires, and its I/O model is fundamentally incompatible with the POSIX
		3954	model. Libev still offers limited functionality on this platform in
		3955	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3956	descriptors. This only applies when using Win32 natively, not when using
		3957	e.g. cygwin.
		3958
		3959	Lifting these limitations would basically require the full
		3960	re-implementation of the I/O system. If you are into these kinds of
		3961	things, then note that glib does exactly that for you in a very portable
		3962	way (note also that glib is the slowest event library known to man).
		3963
		3964	There is no supported compilation method available on windows except
		3965	embedding it into other applications.
		3966
		3967	Sensible signal handling is officially unsupported by Microsoft - libev
		3968	tries its best, but under most conditions, signals will simply not work.
		3969
		3970	Not a libev limitation but worth mentioning: windows apparently doesn't
		3971	accept large writes: instead of resulting in a partial write, windows will
		3972	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3973	so make sure you only write small amounts into your sockets (less than a
		3974	megabyte seems safe, but this apparently depends on the amount of memory
		3975	available).
		3976
		3977	Due to the many, low, and arbitrary limits on the win32 platform and
		3978	the abysmal performance of winsockets, using a large number of sockets
		3979	is not recommended (and not reasonable). If your program needs to use
		3980	more than a hundred or so sockets, then likely it needs to use a totally
		3981	different implementation for windows, as libev offers the POSIX readiness
		3982	notification model, which cannot be implemented efficiently on windows
		3983	(due to Microsoft monopoly games).
		3984
		3985	A typical way to use libev under windows is to embed it (see the embedding
		3986	section for details) and use the following F<evwrap.h> header file instead
		3987	of F<ev.h>:
		3988
		3989	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3990	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3991
		3992	#include "ev.h"
		3993
		3994	And compile the following F<evwrap.c> file into your project (make sure
		3995	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3996
		3997	#include "evwrap.h"
		3998	#include "ev.c"
		3999
		4000	=over 4
		4001
		4002	=item The winsocket select function
		4003
		4004	The winsocket C<select> function doesn't follow POSIX in that it
		4005	requires socket I<handles> and not socket I<file descriptors> (it is
		4006	also extremely buggy). This makes select very inefficient, and also
		4007	requires a mapping from file descriptors to socket handles (the Microsoft
		4008	C runtime provides the function C<_open_osfhandle> for this). See the
		4009	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4010	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4011
		4012	The configuration for a "naked" win32 using the Microsoft runtime
		4013	libraries and raw winsocket select is:
		4014
		4015	#define EV_USE_SELECT 1
		4016	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4017
		4018	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4019	complexity in the O(n²) range when using win32.
		4020
		4021	=item Limited number of file descriptors
		4022
		4023	Windows has numerous arbitrary (and low) limits on things.
		4024
		4025	Early versions of winsocket's select only supported waiting for a maximum
		4026	of C<64> handles (probably owning to the fact that all windows kernels
		4027	can only wait for C<64> things at the same time internally; Microsoft
		4028	recommends spawning a chain of threads and wait for 63 handles and the
		4029	previous thread in each. Sounds great!).
		4030
		4031	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4032	to some high number (e.g. C<2048>) before compiling the winsocket select
		4033	call (which might be in libev or elsewhere, for example, perl and many
		4034	other interpreters do their own select emulation on windows).
		4035
		4036	Another limit is the number of file descriptors in the Microsoft runtime
		4037	libraries, which by default is C<64> (there must be a hidden I<64>
		4038	fetish or something like this inside Microsoft). You can increase this
		4039	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4040	(another arbitrary limit), but is broken in many versions of the Microsoft
		4041	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4042	(depending on windows version and/or the phase of the moon). To get more,
		4043	you need to wrap all I/O functions and provide your own fd management, but
		4044	the cost of calling select (O(n²)) will likely make this unworkable.
		4045
		4046	=back
		4047
		4048	=head2 PORTABILITY REQUIREMENTS
		4049
		4050	In addition to a working ISO-C implementation and of course the
		4051	backend-specific APIs, libev relies on a few additional extensions:
		4052
		4053	=over 4
		4054
		4055	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4056	calling conventions regardless of C<ev_watcher_type *>.
		4057
		4058	Libev assumes not only that all watcher pointers have the same internal
		4059	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4060	assumes that the same (machine) code can be used to call any watcher
		4061	callback: The watcher callbacks have different type signatures, but libev
		4062	calls them using an C<ev_watcher *> internally.
		4063
		4064	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4065
		4066	The type C<sig_atomic_t volatile> (or whatever is defined as
		4067	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4068	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4069	believed to be sufficiently portable.
		4070
		4071	=item C<sigprocmask> must work in a threaded environment
		4072
		4073	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4074	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4075	pthread implementations will either allow C<sigprocmask> in the "main
		4076	thread" or will block signals process-wide, both behaviours would
		4077	be compatible with libev. Interaction between C<sigprocmask> and
		4078	C<pthread_sigmask> could complicate things, however.
		4079
		4080	The most portable way to handle signals is to block signals in all threads
		4081	except the initial one, and run the default loop in the initial thread as
		4082	well.
		4083
		4084	=item C<long> must be large enough for common memory allocation sizes
		4085
		4086	To improve portability and simplify its API, libev uses C<long> internally
		4087	instead of C<size_t> when allocating its data structures. On non-POSIX
		4088	systems (Microsoft...) this might be unexpectedly low, but is still at
		4089	least 31 bits everywhere, which is enough for hundreds of millions of
		4090	watchers.
		4091
		4092	=item C<double> must hold a time value in seconds with enough accuracy
		4093
		4094	The type C<double> is used to represent timestamps. It is required to
		4095	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4096	enough for at least into the year 4000. This requirement is fulfilled by
		4097	implementations implementing IEEE 754, which is basically all existing
		4098	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4099	2200.
		4100
		4101	=back
		4102
		4103	If you know of other additional requirements drop me a note.
		4104
		4105
2423	=head1 COMPLEXITIES	4106	=head1 ALGORITHMIC COMPLEXITIES
2424		4107
2425	In this section the complexities of (many of) the algorithms used inside	4108	In this section the complexities of (many of) the algorithms used inside
2426	libev will be explained. For complexity discussions about backends see the	4109	libev will be documented. For complexity discussions about backends see
2427	documentation for C<ev_default_init>.	4110	the documentation for C<ev_default_init>.
2428		4111
2429	All of the following are about amortised time: If an array needs to be	4112	All of the following are about amortised time: If an array needs to be
2430	extended, libev needs to realloc and move the whole array, but this	4113	extended, libev needs to realloc and move the whole array, but this
2431	happens asymptotically never with higher number of elements, so O(1) might	4114	happens asymptotically rarer with higher number of elements, so O(1) might
2432	mean it might do a lengthy realloc operation in rare cases, but on average	4115	mean that libev does a lengthy realloc operation in rare cases, but on
2433	it is much faster and asymptotically approaches constant time.	4116	average it is much faster and asymptotically approaches constant time.
2434		4117
2435	=over 4	4118	=over 4
2436		4119
2437	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4120	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2438		4121
2439	This means that, when you have a watcher that triggers in one hour and	4122	This means that, when you have a watcher that triggers in one hour and
2440	there are 100 watchers that would trigger before that then inserting will	4123	there are 100 watchers that would trigger before that, then inserting will
2441	have to skip those 100 watchers.	4124	have to skip roughly seven (C<ld 100>) of these watchers.
2442		4125
2443	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4126	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2444		4127
2445	That means that for changing a timer costs less than removing/adding them	4128	That means that changing a timer costs less than removing/adding them,
2446	as only the relative motion in the event queue has to be paid for.	4129	as only the relative motion in the event queue has to be paid for.
2447		4130
2448	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4131	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2449		4132
2450	These just add the watcher into an array or at the head of a list.	4133	These just add the watcher into an array or at the head of a list.
		4134
2451	=item Stopping check/prepare/idle watchers: O(1)	4135	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2452		4136
2453	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4137	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2454		4138
2455	These watchers are stored in lists then need to be walked to find the	4139	These watchers are stored in lists, so they need to be walked to find the
2456	correct watcher to remove. The lists are usually short (you don't usually	4140	correct watcher to remove. The lists are usually short (you don't usually
2457	have many watchers waiting for the same fd or signal).	4141	have many watchers waiting for the same fd or signal: one is typical, two
		4142	is rare).
2458		4143
2459	=item Finding the next timer per loop iteration: O(1)	4144	=item Finding the next timer in each loop iteration: O(1)
		4145
		4146	By virtue of using a binary or 4-heap, the next timer is always found at a
		4147	fixed position in the storage array.
2460		4148
2461	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4149	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2462		4150
2463	A change means an I/O watcher gets started or stopped, which requires	4151	A change means an I/O watcher gets started or stopped, which requires
2464	libev to recalculate its status (and possibly tell the kernel).	4152	libev to recalculate its status (and possibly tell the kernel, depending
		4153	on backend and whether C<ev_io_set> was used).
2465		4154
2466	=item Activating one watcher: O(1)	4155	=item Activating one watcher (putting it into the pending state): O(1)
2467		4156
2468	=item Priority handling: O(number_of_priorities)	4157	=item Priority handling: O(number_of_priorities)
2469		4158
2470	Priorities are implemented by allocating some space for each	4159	Priorities are implemented by allocating some space for each
2471	priority. When doing priority-based operations, libev usually has to	4160	priority. When doing priority-based operations, libev usually has to
2472	linearly search all the priorities.	4161	linearly search all the priorities, but starting/stopping and activating
		4162	watchers becomes O(1) with respect to priority handling.
		4163
		4164	=item Sending an ev_async: O(1)
		4165
		4166	=item Processing ev_async_send: O(number_of_async_watchers)
		4167
		4168	=item Processing signals: O(max_signal_number)
		4169
		4170	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4171	calls in the current loop iteration. Checking for async and signal events
		4172	involves iterating over all running async watchers or all signal numbers.
2473		4173
2474	=back	4174	=back
2475		4175
2476		4176
		4177	=head1 GLOSSARY
		4178
		4179	=over 4
		4180
		4181	=item active
		4182
		4183	A watcher is active as long as it has been started (has been attached to
		4184	an event loop) but not yet stopped (disassociated from the event loop).
		4185
		4186	=item application
		4187
		4188	In this document, an application is whatever is using libev.
		4189
		4190	=item callback
		4191
		4192	The address of a function that is called when some event has been
		4193	detected. Callbacks are being passed the event loop, the watcher that
		4194	received the event, and the actual event bitset.
		4195
		4196	=item callback invocation
		4197
		4198	The act of calling the callback associated with a watcher.
		4199
		4200	=item event
		4201
		4202	A change of state of some external event, such as data now being available
		4203	for reading on a file descriptor, time having passed or simply not having
		4204	any other events happening anymore.
		4205
		4206	In libev, events are represented as single bits (such as C<EV_READ> or
		4207	C<EV_TIMEOUT>).
		4208
		4209	=item event library
		4210
		4211	A software package implementing an event model and loop.
		4212
		4213	=item event loop
		4214
		4215	An entity that handles and processes external events and converts them
		4216	into callback invocations.
		4217
		4218	=item event model
		4219
		4220	The model used to describe how an event loop handles and processes
		4221	watchers and events.
		4222
		4223	=item pending
		4224
		4225	A watcher is pending as soon as the corresponding event has been detected,
		4226	and stops being pending as soon as the watcher will be invoked or its
		4227	pending status is explicitly cleared by the application.
		4228
		4229	A watcher can be pending, but not active. Stopping a watcher also clears
		4230	its pending status.
		4231
		4232	=item real time
		4233
		4234	The physical time that is observed. It is apparently strictly monotonic :)
		4235
		4236	=item wall-clock time
		4237
		4238	The time and date as shown on clocks. Unlike real time, it can actually
		4239	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4240	clock.
		4241
		4242	=item watcher
		4243
		4244	A data structure that describes interest in certain events. Watchers need
		4245	to be started (attached to an event loop) before they can receive events.
		4246
		4247	=item watcher invocation
		4248
		4249	The act of calling the callback associated with a watcher.
		4250
		4251	=back
		4252
2477	=head1 AUTHOR	4253	=head1 AUTHOR
2478		4254
2479	Marc Lehmann <libev@schmorp.de>.	4255	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2480		4256

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