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Revision 1.57 by root, Wed Nov 28 11:27:29 2007 UTC vs.
Revision 1.247 by root, Wed Jul 8 02:46:05 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
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
52		84
53	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
54	file descriptor being readable or a timeout occuring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
55	these event sources and provide your program with events.	87	these event sources and provide your program with events.
56		88
57	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
58	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
59	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
61	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
62	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
63	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
64	watcher.	96	watcher.
65		97
66	=head1 FEATURES	98	=head2 FEATURES
67		99
68	Libev supports C<select>, C<poll>, the linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
69	bsd-specific C<kqueue> and the solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
70	for file descriptor events (C<ev_io>), relative timers (C<ev_timer>),	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		103	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
71	absolute timers with customised rescheduling (C<ev_periodic>), synchronous	104	with customised rescheduling (C<ev_periodic>), synchronous signals
72	signals (C<ev_signal>), process status change events (C<ev_child>), and	105	(C<ev_signal>), process status change events (C<ev_child>), and event
73	event watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	watchers dealing with the event loop mechanism itself (C<ev_idle>,
74	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
75	file watchers (C<ev_stat>) and even limited support for fork events	108	file watchers (C<ev_stat>) and even limited support for fork events
76	(C<ev_fork>).	109	(C<ev_fork>).
77		110
78	It also is quite fast (see this	111	It also is quite fast (see this
79	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
80	for example).	113	for example).
81		114
82	=head1 CONVENTIONS	115	=head2 CONVENTIONS
83		116
84	Libev is very configurable. In this manual the default configuration will	117	Libev is very configurable. In this manual the default (and most common)
85	be described, which supports multiple event loops. For more info about	118	configuration will be described, which supports multiple event loops. For
86	various configuration options please have a look at B<EMBED> section in	119	more info about various configuration options please have a look at
87	this manual. If libev was configured without support for multiple event	120	B<EMBED> section in this manual. If libev was configured without support
88	loops, then all functions taking an initial argument of name C<loop>	121	for multiple event loops, then all functions taking an initial argument of
89	(which is always of type C<struct ev_loop *>) will not have this argument.	122	name C<loop> (which is always of type C<ev_loop *>) will not have
		123	this argument.
90		124
91	=head1 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
92		126
93	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
94	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
95	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
96	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
97	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
98	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
99		156
100	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
101		158
102	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
103	library in any way.	160	library in any way.
…		…
108		165
109	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
110	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
111	you actually want to know.	168	you actually want to know.
112		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
113	=item int ev_version_major ()	176	=item int ev_version_major ()
114		177
115	=item int ev_version_minor ()	178	=item int ev_version_minor ()
116		179
117	You can find out the major and minor version numbers of the library	180	You can find out the major and minor ABI version numbers of the library
118	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
119	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
120	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
121	version of the library your program was compiled against.	184	version of the library your program was compiled against.
122		185
		186	These version numbers refer to the ABI version of the library, not the
		187	release version.
		188
123	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,
124	as this indicates an incompatible change. Minor versions are usually	190	as this indicates an incompatible change. Minor versions are usually
125	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
126	not a problem.	192	not a problem.
127		193
128	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
129	version.	195	version.
130		196
131	assert (("libev version mismatch",	197	assert (("libev version mismatch",
132	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
133	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
134		200
135	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
136		202
137	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_*>
138	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
140	a description of the set values.	206	a description of the set values.
141		207
142	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
143	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
144		210
145	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
146	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
147		213
148	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
149		215
150	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
151	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
152	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
153	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
154	(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
155	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
156		222
157	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
158		224
…		…
162	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
163	recommended ones.	229	recommended ones.
164		230
165	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
166		232
167	=item ev_set_allocator (void *(*cb)(void *ptr, size_t size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
168		234
169	Sets the allocation function to use (the prototype and semantics are	235	Sets the allocation function to use (the prototype is similar - the
170	identical to the realloc C function). It is used to allocate and free	236	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
171	memory (no surprises here). If it returns zero when memory needs to be	237	used to allocate and free memory (no surprises here). If it returns zero
172	allocated, the library might abort or take some potentially destructive	238	when memory needs to be allocated (C<size != 0>), the library might abort
173	action. The default is your system realloc function.	239	or take some potentially destructive action.
		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.
174		244
175	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
176	free some memory if it cannot allocate memory, to use a special allocator,	246	free some memory if it cannot allocate memory, to use a special allocator,
177	or even to sleep a while and retry until some memory is available.	247	or even to sleep a while and retry until some memory is available.
178		248
179	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
180	retries).	250	retries (example requires a standards-compliant C<realloc>).
181		251
182	static void *	252	static void *
183	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
184	{	254	{
185	for (;;)	255	for (;;)
…		…
194	}	264	}
195		265
196	...	266	...
197	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
198		268
199	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
200		270
201	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
202	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
203	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
204	callback is set, then libev will expect it to remedy the sitution, no	274	callback is set, then libev will expect it to remedy the situation, no
205	matter what, when it returns. That is, libev will generally retry the	275	matter what, when it returns. That is, libev will generally retry the
206	requested operation, or, if the condition doesn't go away, do bad stuff	276	requested operation, or, if the condition doesn't go away, do bad stuff
207	(such as abort).	277	(such as abort).
208		278
209	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.
…		…
220		290
221	=back	291	=back
222		292
223	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
224		294
225	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>
226	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>
227	events, and dynamically created loops which do not.	297	I<function>).
228		298
229	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
230	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
231	create, you also create another event loop. Libev itself does no locking	301	not.
232	whatsoever, so if you mix calls to the same event loop in different
233	threads, make sure you lock (this is usually a bad idea, though, even if
234	done correctly, because it's hideous and inefficient).
235		302
236	=over 4	303	=over 4
237		304
238	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
239		306
…		…
243	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
244		311
245	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
246	function.	313	function.
247		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
248	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
249	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>).
250		328
251	The following flags are supported:	329	The following flags are supported:
252		330
…		…
257	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
258	thing, believe me).	336	thing, believe me).
259		337
260	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
261		339
262	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
263	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
264	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
265	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
266	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
267	around bugs.	345	around bugs.
268		346
		347	=item C<EVFLAG_FORKCHECK>
		348
		349	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		350	a fork, you can also make libev check for a fork in each iteration by
		351	enabling this flag.
		352
		353	This works by calling C<getpid ()> on every iteration of the loop,
		354	and thus this might slow down your event loop if you do a lot of loop
		355	iterations and little real work, but is usually not noticeable (on my
		356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		357	without a system call and thus I<very> fast, but my GNU/Linux system also has
		358	C<pthread_atfork> which is even faster).
		359
		360	The big advantage of this flag is that you can forget about fork (and
		361	forget about forgetting to tell libev about forking) when you use this
		362	flag.
		363
		364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		365	environment variable.
		366
269	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
270		368
271	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
272	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,
273	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
274	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
275	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).
276		385
277	=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)
278		387
279	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
280	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
281	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
282	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>.
283		397
284	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
285		399
286	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,
287	but it scales phenomenally better. While poll and select usually scale like	401	but it scales phenomenally better. While poll and select usually scale
288	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	402	like O(total_fds) where n is the total number of fds (or the highest fd),
289	either O(1) or O(active_fds).	403	epoll scales either O(1) or O(active_fds).
290		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
291	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
292	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
293	(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
294	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
295	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.
296		428
297	Please note that epoll sometimes generates spurious notifications, so you	429	Best performance from this backend is achieved by not unregistering all
298	need to use non-blocking I/O or other means to avoid blocking when no data	430	watchers for a file descriptor until it has been closed, if possible,
299	(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>.
300		446
301	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
302		448
303	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
304	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
305	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
306	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
307	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
308	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.
309		462
310	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
311	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
312	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
313	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
314	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>.
315		483
316	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
317		485
318	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.
319		490
320	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
321		492
322	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,
323	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)).
324		495
325	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
326	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
327	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>.
328		512
329	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
330		514
331	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
332	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
333	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	517	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
334		518
		519	It is definitely not recommended to use this flag.
		520
335	=back	521	=back
336		522
337	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
338	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
339	specified, most compiled-in backend will be tried, usually in reverse	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
340	order of their flag values :)
341		526
342	The most typical usage is like this:	527	Example: This is the most typical usage.
343		528
344	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
345	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
346		531
347	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
348	environment settings to be taken into account:	533	environment settings to be taken into account:
349		534
350	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
351		536
352	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
353	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
354	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
355		541
356	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
357		543
358	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
359		545
360	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
361	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
362	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
363	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
364		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
365	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.
366		556
367	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
368	if (!epoller)	558	if (!epoller)
369	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
370		560
371	=item ev_default_destroy ()	561	=item ev_default_destroy ()
372		562
373	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
374	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
375	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
376	responsibility to either stop all watchers cleanly yoursef I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
377	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
378	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
379	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>).
380		579
381	=item ev_loop_destroy (loop)	580	=item ev_loop_destroy (loop)
382		581
383	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
384	earlier call to C<ev_loop_new>.	583	earlier call to C<ev_loop_new>.
385		584
386	=item ev_default_fork ()	585	=item ev_default_fork ()
387		586
		587	This function sets a flag that causes subsequent C<ev_loop> iterations
388	This function reinitialises the kernel state for backends that have	588	to reinitialise the kernel state for backends that have one. Despite the
389	one. Despite the name, you can call it anytime, but it makes most sense	589	name, you can call it anytime, but it makes most sense after forking, in
390	after forking, in either the parent or child process (or both, but that	590	the child process (or both child and parent, but that again makes little
391	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.
392		593
393	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
394	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
395	fork+exec, you don't have to call it.	596	you just fork+exec, you don't have to call it at all.
396		597
397	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
398	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
399	quite nicely into a call to C<pthread_atfork>:	600	quite nicely into a call to C<pthread_atfork>:
400		601
401	pthread_atfork (0, 0, ev_default_fork);	602	pthread_atfork (0, 0, ev_default_fork);
402		603
403	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
404	without calling this function, so if you force one of those backends you
405	do not need to care.
406
407	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
408		605
409	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
410	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
411	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.
		615
		616	=item unsigned int ev_loop_count (loop)
		617
		618	Returns the count of loop iterations for the loop, which is identical to
		619	the number of times libev did poll for new events. It starts at C<0> and
		620	happily wraps around with enough iterations.
		621
		622	This value can sometimes be useful as a generation counter of sorts (it
		623	"ticks" the number of loop iterations), as it roughly corresponds with
		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.
412		637
413	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
414		639
415	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
416	use.	641	use.
…		…
419		644
420	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
421	received events and started processing them. This timestamp does not	646	received events and started processing them. This timestamp does not
422	change as long as callbacks are being processed, and this is also the base	647	change as long as callbacks are being processed, and this is also the base
423	time used for relative timers. You can treat it as the timestamp of the	648	time used for relative timers. You can treat it as the timestamp of the
424	event occuring (or more correctly, libev finding out about it).	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>).
425		688
426	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
427		690
428	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
429	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
…		…
432	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
433	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.
434		697
435	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
436	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
437	finished (especially in interactive programs), but having a program that	700	finished (especially in interactive programs), but having a program
438	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
439	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.
440		704
441	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
442	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
443	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.
444		709
445	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
446	neccessary) and will handle those and any outstanding ones. It will block	711	necessary) and will handle those and any already outstanding ones. It
447	your process until at least one new event arrives, and will return after	712	will block your process until at least one new event arrives (which could
448	one iteration of the loop. This is useful if you are waiting for some	713	be an event internal to libev itself, so there is no guarantee that a
449	external event in conjunction with something not expressible using other	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
450	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
451	usually a better approach for this kind of thing.	720	usually a better approach for this kind of thing.
452		721
453	Here are the gory details of what C<ev_loop> does:	722	Here are the gory details of what C<ev_loop> does:
454		723
455	* If there are no active watchers (reference count is zero), return.	724	- Before the first iteration, call any pending watchers.
456	- Queue prepare watchers and then call all outstanding watchers.	725	* If EVFLAG_FORKCHECK was used, check for a fork.
		726	- If a fork was detected (by any means), queue and call all fork watchers.
		727	- Queue and call all prepare watchers.
457	- 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.
458	- Update the kernel state with all outstanding changes.	730	- Update the kernel state with all outstanding changes.
459	- Update the "event loop time".	731	- Update the "event loop time" (ev_now ()).
460	- 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.
461	- Block the process, waiting for any events.	736	- Block the process, waiting for any events.
462	- Queue all outstanding I/O (fd) events.	737	- Queue all outstanding I/O (fd) events.
463	- Update the "event loop time" and do time jump handling.	738	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
464	- Queue all outstanding timers.	739	- Queue all expired timers.
465	- Queue all outstanding periodics.	740	- Queue all expired periodics.
466	- If no events are pending now, queue all idle watchers.	741	- Unless any events are pending now, queue all idle watchers.
467	- Queue all check watchers.	742	- Queue all check watchers.
468	- 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).
469	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
470	be handled here by queueing them when their watcher gets executed.	745	be handled here by queueing them when their watcher gets executed.
471	- 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
472	were used, return, otherwise continue with step *.	747	were used, or there are no active watchers, return, otherwise
		748	continue with step *.
473		749
474	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
475	anymore.	751	anymore.
476		752
477	... queue jobs here, make sure they register event watchers as long	753	... queue jobs here, make sure they register event watchers as long
478	... as they still have work to do (even an idle watcher will do..)	754	... as they still have work to do (even an idle watcher will do..)
479	ev_loop (my_loop, 0);	755	ev_loop (my_loop, 0);
480	... jobs done. yeah!	756	... jobs done or somebody called unloop. yeah!
481		757
482	=item ev_unloop (loop, how)	758	=item ev_unloop (loop, how)
483		759
484	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
485	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
486	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
487	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.
488		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
489	=item ev_ref (loop)	769	=item ev_ref (loop)
490		770
491	=item ev_unref (loop)	771	=item ev_unref (loop)
492		772
493	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
494	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
495	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
496	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>
497	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
498	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
499	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
500	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
501	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
502	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).
503		790
504	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>
505	running when nothing else is active.	792	running when nothing else is active.
506		793
507	struct ev_signal exitsig;	794	ev_signal exitsig;
508	ev_signal_init (&exitsig, sig_cb, SIGINT);	795	ev_signal_init (&exitsig, sig_cb, SIGINT);
509	ev_signal_start (loop, &exitsig);	796	ev_signal_start (loop, &exitsig);
510	evf_unref (loop);	797	evf_unref (loop);
511		798
512	Example: For some weird reason, unregister the above signal handler again.	799	Example: For some weird reason, unregister the above signal handler again.
513		800
514	ev_ref (loop);	801	ev_ref (loop);
515	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.
516		872
517	=back	873	=back
518		874
519		875
520	=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.
521		881
522	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
523	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
524	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:
525		885
526	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)
527	{	887	{
528	ev_io_stop (w);	888	ev_io_stop (w);
529	ev_unloop (loop, EVUNLOOP_ALL);	889	ev_unloop (loop, EVUNLOOP_ALL);
530	}	890	}
531		891
532	struct ev_loop *loop = ev_default_loop (0);	892	struct ev_loop *loop = ev_default_loop (0);
		893
533	struct ev_io stdin_watcher;	894	ev_io stdin_watcher;
		895
534	ev_init (&stdin_watcher, my_cb);	896	ev_init (&stdin_watcher, my_cb);
535	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	897	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
536	ev_io_start (loop, &stdin_watcher);	898	ev_io_start (loop, &stdin_watcher);
		899
537	ev_loop (loop, 0);	900	ev_loop (loop, 0);
538		901
539	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
540	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
541	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).
542		908
543	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
544	(watcher *, callback)>, which expects a callback to be provided. This	910	(watcher *, callback)>, which expects a callback to be provided. This
545	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
546	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
547	is readable and/or writable).	913	is readable and/or writable).
548		914
549	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 *, ...) >>
550	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
551	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<<
552	(watcher *, callback, ...) >>.	918	ev_TYPE_init (watcher *, callback, ...) >>.
553		919
554	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
555	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
556	*) >>), 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
557	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	923	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
558		924
559	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
560	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
561	reinitialise it or call its C<set> macro.	927	reinitialise it or call its C<ev_TYPE_set> macro.
562		928
563	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
564	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
565	third argument.	931	third argument.
566		932
…		…
620	=item C<EV_FORK>	986	=item C<EV_FORK>
621		987
622	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
623	C<ev_fork>).	989	C<ev_fork>).
624		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
625	=item C<EV_ERROR>	1000	=item C<EV_ERROR>
626		1001
627	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
628	happen because the watcher could not be properly started because libev	1003	happen because the watcher could not be properly started because libev
629	ran out of memory, a file descriptor was found to be closed or any other	1004	ran out of memory, a file descriptor was found to be closed or any other
		1005	problem. Libev considers these application bugs.
		1006
630	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
631	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.
632		1011
633	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
634	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
635	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
636	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
637	programs, though, so beware.	1016	programs, though, as the fd could already be closed and reused for another
		1017	thing, so beware.
638		1018
639	=back	1019	=back
640		1020
641	=head2 GENERIC WATCHER FUNCTIONS	1021	=head2 GENERIC WATCHER FUNCTIONS
642
643	In the following description, C<TYPE> stands for the watcher type,
644	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
645		1022
646	=over 4	1023	=over 4
647		1024
648	=item C<ev_init> (ev_TYPE *watcher, callback)	1025	=item C<ev_init> (ev_TYPE *watcher, callback)
649		1026
…		…
655	which rolls both calls into one.	1032	which rolls both calls into one.
656		1033
657	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
658	(or never started) and there are no pending events outstanding.	1035	(or never started) and there are no pending events outstanding.
659		1036
660	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,
661	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);
662		1045
663	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1046	=item C<ev_TYPE_set> (ev_TYPE *, [args])
664		1047
665	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
666	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
…		…
669	difference to the C<ev_init> macro).	1052	difference to the C<ev_init> macro).
670		1053
671	Although some watcher types do not have type-specific arguments	1054	Although some watcher types do not have type-specific arguments
672	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1055	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
673		1056
		1057	See C<ev_init>, above, for an example.
		1058
674	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1059	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
675		1060
676	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
677	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
678	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);
679		1068
680	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1069	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
681		1070
682	Starts (activates) the given watcher. Only active watchers will receive	1071	Starts (activates) the given watcher. Only active watchers will receive
683	events. If the watcher is already active nothing will happen.	1072	events. If the watcher is already active nothing will happen.
684		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
685	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1079	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
686		1080
687	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
688	status. It is possible that stopped watchers are pending (for example,	1084	It is possible that stopped watchers are pending - for example,
689	non-repeating timers are being stopped when they become pending), but	1085	non-repeating timers are being stopped when they become pending - but
690	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1086	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
691	you want to free or reuse the memory used by the watcher it is therefore a	1087	pending. If you want to free or reuse the memory used by the watcher it is
692	good idea to always call its C<ev_TYPE_stop> function.	1088	therefore a good idea to always call its C<ev_TYPE_stop> function.
693		1089
694	=item bool ev_is_active (ev_TYPE *watcher)	1090	=item bool ev_is_active (ev_TYPE *watcher)
695		1091
696	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
697	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
…		…
700	=item bool ev_is_pending (ev_TYPE *watcher)	1096	=item bool ev_is_pending (ev_TYPE *watcher)
701		1097
702	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1098	Returns a true value iff the watcher is pending, (i.e. it has outstanding
703	events but its callback has not yet been invoked). As long as a watcher	1099	events but its callback has not yet been invoked). As long as a watcher
704	is pending (but not active) you must not call an init function on it (but	1100	is pending (but not active) you must not call an init function on it (but
705	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1101	C<ev_TYPE_set> is safe), you must not change its priority, and you must
706	libev (e.g. you cnanot C<free ()> it).	1102	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1103	it).
707		1104
708	=item callback ev_cb (ev_TYPE *watcher)	1105	=item callback ev_cb (ev_TYPE *watcher)
709		1106
710	Returns the callback currently set on the watcher.	1107	Returns the callback currently set on the watcher.
711		1108
712	=item ev_cb_set (ev_TYPE *watcher, callback)	1109	=item ev_cb_set (ev_TYPE *watcher, callback)
713		1110
714	Change the callback. You can change the callback at virtually any time	1111	Change the callback. You can change the callback at virtually any time
715	(modulo threads).	1112	(modulo threads).
716		1113
		1114	=item ev_set_priority (ev_TYPE *watcher, priority)
		1115
		1116	=item int ev_priority (ev_TYPE *watcher)
		1117
		1118	Set and query the priority of the watcher. The priority is a small
		1119	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1120	(default: C<-2>). Pending watchers with higher priority will be invoked
		1121	before watchers with lower priority, but priority will not keep watchers
		1122	from being executed (except for C<ev_idle> watchers).
		1123
		1124	If you need to suppress invocation when higher priority events are pending
		1125	you need to look at C<ev_idle> watchers, which provide this functionality.
		1126
		1127	You I<must not> change the priority of a watcher as long as it is active or
		1128	pending.
		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
		1134	The default priority used by watchers when no priority has been set is
		1135	always C<0>, which is supposed to not be too high and not be too low :).
		1136
		1137	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1138	priorities.
		1139
		1140	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1141
		1142	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1143	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1144	can deal with that fact, as both are simply passed through to the
		1145	callback.
		1146
		1147	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1148
		1149	If the watcher is pending, this function clears its pending status and
		1150	returns its C<revents> bitset (as if its callback was invoked). If the
		1151	watcher isn't pending it does nothing and returns C<0>.
		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
717	=back	1156	=back
718		1157
719		1158
720	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1159	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
721		1160
722	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
723	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
724	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
725	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
726	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
727	data:	1166	data:
728		1167
729	struct my_io	1168	struct my_io
730	{	1169	{
731	struct ev_io io;	1170	ev_io io;
732	int otherfd;	1171	int otherfd;
733	void *somedata;	1172	void *somedata;
734	struct whatever *mostinteresting;	1173	struct whatever *mostinteresting;
735	}	1174	};
		1175
		1176	...
		1177	struct my_io w;
		1178	ev_io_init (&w.io, my_cb, fd, EV_READ);
736		1179
737	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
738	can cast it back to your own type:	1181	can cast it back to your own type:
739		1182
740	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)
741	{	1184	{
742	struct my_io *w = (struct my_io *)w_;	1185	struct my_io *w = (struct my_io *)w_;
743	...	1186	...
744	}	1187	}
745		1188
746	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
747	instead have been omitted.	1190	instead have been omitted.
748		1191
749	Another common scenario is having some data structure with multiple	1192	Another common scenario is to use some data structure with multiple
750	watchers:	1193	embedded watchers:
751		1194
752	struct my_biggy	1195	struct my_biggy
753	{	1196	{
754	int some_data;	1197	int some_data;
755	ev_timer t1;	1198	ev_timer t1;
756	ev_timer t2;	1199	ev_timer t2;
757	}	1200	}
758		1201
759	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
760	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):
761		1207
762	#include <stddef.h>	1208	#include <stddef.h>
763		1209
764	static void	1210	static void
765	t1_cb (EV_P_ struct ev_timer *w, int revents)	1211	t1_cb (EV_P_ ev_timer *w, int revents)
766	{	1212	{
767	struct my_biggy big = (struct my_biggy *	1213	struct my_biggy big = (struct my_biggy *)
768	(((char *)w) - offsetof (struct my_biggy, t1));	1214	(((char *)w) - offsetof (struct my_biggy, t1));
769	}	1215	}
770		1216
771	static void	1217	static void
772	t2_cb (EV_P_ struct ev_timer *w, int revents)	1218	t2_cb (EV_P_ ev_timer *w, int revents)
773	{	1219	{
774	struct my_biggy big = (struct my_biggy *	1220	struct my_biggy big = (struct my_biggy *)
775	(((char *)w) - offsetof (struct my_biggy, t2));	1221	(((char *)w) - offsetof (struct my_biggy, t2));
776	}	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.
777		1326
778		1327
779	=head1 WATCHER TYPES	1328	=head1 WATCHER TYPES
780		1329
781	This section describes each watcher in detail, but will not repeat	1330	This section describes each watcher in detail, but will not repeat
…		…
805	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
806	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
807	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
808	required if you know what you are doing).	1357	required if you know what you are doing).
809		1358
810	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
811	(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
812	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
813	to the same underlying file/socket/etc. description (that is, they share	1362	descriptors for which non-blocking operation makes no sense (such as
814	the same underlying "file open").	1363	files) - libev doesn't guarentee any specific behaviour in that case.
815
816	If you must do this, then force the use of a known-to-be-good backend
817	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
818	C<EVBACKEND_POLL>).
819		1364
820	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
821	receive "spurious" readyness notifications, that is your callback might	1366	receive "spurious" readiness notifications, that is your callback might
822	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
823	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
824	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
825	this situation even with a relatively standard program structure. Thus	1370	this situation even with a relatively standard program structure. Thus
826	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
827	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.
828		1373
829	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
830	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
831	wether 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
832	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
833	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
834		1440
835	=over 4	1441	=over 4
836		1442
837	=item ev_io_init (ev_io *, callback, int fd, int events)	1443	=item ev_io_init (ev_io *, callback, int fd, int events)
838		1444
839	=item ev_io_set (ev_io *, int fd, int events)	1445	=item ev_io_set (ev_io *, int fd, int events)
840		1446
841	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
842	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
843	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.
844		1450
845	=item int fd [read-only]	1451	=item int fd [read-only]
846		1452
847	The file descriptor being watched.	1453	The file descriptor being watched.
848		1454
849	=item int events [read-only]	1455	=item int events [read-only]
850		1456
851	The events being watched.	1457	The events being watched.
852		1458
853	=back	1459	=back
		1460
		1461	=head3 Examples
854		1462
855	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
856	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
857	attempt to read a whole line in the callback.	1465	attempt to read a whole line in the callback.
858		1466
859	static void	1467	static void
860	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)
861	{	1469	{
862	ev_io_stop (loop, w);	1470	ev_io_stop (loop, w);
863	.. 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
864	}	1472	}
865		1473
866	...	1474	...
867	struct ev_loop *loop = ev_default_init (0);	1475	struct ev_loop *loop = ev_default_init (0);
868	struct ev_io stdin_readable;	1476	ev_io stdin_readable;
869	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);
870	ev_io_start (loop, &stdin_readable);	1478	ev_io_start (loop, &stdin_readable);
871	ev_loop (loop, 0);	1479	ev_loop (loop, 0);
872		1480
873		1481
874	=head2 C<ev_timer> - relative and optionally repeating timeouts	1482	=head2 C<ev_timer> - relative and optionally repeating timeouts
875		1483
876	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
877	given time, and optionally repeating in regular intervals after that.	1485	given time, and optionally repeating in regular intervals after that.
878		1486
879	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
880	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
881	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
882	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1490	detecting time jumps is hard, and some inaccuracies are unavoidable (the
883	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 with later time-out values (but this is no longer true when a
		1498	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.
884		1682
885	The relative timeouts are calculated relative to the C<ev_now ()>	1683	The relative timeouts are calculated relative to the C<ev_now ()>
886	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
887	of the event triggering whatever timeout you are modifying/starting. If	1685	of the event triggering whatever timeout you are modifying/starting. If
888	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
889	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:
890		1688
891	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1689	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
892		1690
893	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
894	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
895	order of execution is undefined.	1693	()>.
		1694
		1695	=head3 Watcher-Specific Functions and Data Members
896		1696
897	=over 4	1697	=over 4
898		1698
899	=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)
900		1700
901	=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)
902		1702
903	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>
904	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
905	timer will automatically be configured to trigger again C<repeat> seconds	1705	reached. If it is positive, then the timer will automatically be
906	later, again, and again, until stopped manually.	1706	configured to trigger again C<repeat> seconds later, again, and again,
		1707	until stopped manually.
907		1708
908	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
909	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
910	exactly 10 second intervals. If, however, your program cannot keep up with	1711	trigger at exactly 10 second intervals. If, however, your program cannot
911	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
912	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.
913		1714
914	=item ev_timer_again (loop)	1715	=item ev_timer_again (loop, ev_timer *)
915		1716
916	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
917	repeating. The exact semantics are:	1718	repeating. The exact semantics are:
918		1719
		1720	If the timer is pending, its pending status is cleared.
		1721
919	If the timer is started but nonrepeating, stop it.	1722	If the timer is started but non-repeating, stop it (as if it timed out).
920		1723
921	If the timer is repeating, either start it if necessary (with the repeat	1724	If the timer is repeating, either start it if necessary (with the
922	value), or reset the running timer to the repeat value.	1725	C<repeat> value), or reset the running timer to the C<repeat> value.
923		1726
924	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
925	example: Imagine you have a tcp connection and you want a so-called	1728	usage example.
926	idle timeout, that is, you want to be called when there have been,
927	say, 60 seconds of inactivity on the socket. The easiest way to do
928	this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
929	C<ev_timer_again> each time you successfully read or write some data. If
930	you go into an idle state where you do not expect data to travel on the
931	socket, you can stop the timer, and again will automatically restart it if
932	need be.
933
934	You can also ignore the C<after> value and C<ev_timer_start> altogether
935	and only ever use the C<repeat> value:
936
937	ev_timer_init (timer, callback, 0., 5.);
938	ev_timer_again (loop, timer);
939	...
940	timer->again = 17.;
941	ev_timer_again (loop, timer);
942	...
943	timer->again = 10.;
944	ev_timer_again (loop, timer);
945
946	This is more efficient then stopping/starting the timer eahc time you want
947	to modify its timeout value.
948		1729
949	=item ev_tstamp repeat [read-write]	1730	=item ev_tstamp repeat [read-write]
950		1731
951	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
952	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),
953	which is also when any modifications are taken into account.	1734	which is also when any modifications are taken into account.
954		1735
955	=back	1736	=back
956		1737
		1738	=head3 Examples
		1739
957	Example: Create a timer that fires after 60 seconds.	1740	Example: Create a timer that fires after 60 seconds.
958		1741
959	static void	1742	static void
960	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)
961	{	1744	{
962	.. one minute over, w is actually stopped right here	1745	.. one minute over, w is actually stopped right here
963	}	1746	}
964		1747
965	struct ev_timer mytimer;	1748	ev_timer mytimer;
966	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1749	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
967	ev_timer_start (loop, &mytimer);	1750	ev_timer_start (loop, &mytimer);
968		1751
969	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
970	inactivity.	1753	inactivity.
971		1754
972	static void	1755	static void
973	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1756	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
974	{	1757	{
975	.. ten seconds without any activity	1758	.. ten seconds without any activity
976	}	1759	}
977		1760
978	struct ev_timer mytimer;	1761	ev_timer mytimer;
979	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 */
980	ev_timer_again (&mytimer); /* start timer */	1763	ev_timer_again (&mytimer); /* start timer */
981	ev_loop (loop, 0);	1764	ev_loop (loop, 0);
982		1765
983	// 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":
984	// reset the timeout to start ticking again at 10 seconds	1767	// reset the timeout to start ticking again at 10 seconds
985	ev_timer_again (&mytimer);	1768	ev_timer_again (&mytimer);
986		1769
987		1770
988	=head2 C<ev_periodic> - to cron or not to cron?	1771	=head2 C<ev_periodic> - to cron or not to cron?
989		1772
990	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
991	(and unfortunately a bit complex).	1774	(and unfortunately a bit complex).
992		1775
993	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
994	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
995	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
996	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
997	+ 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
998	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1781	wrist-watch).
999	roughly 10 seconds later and of course not if you reset your system time
1000	again).
1001		1782
1002	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
		1784	in time: for example, if you tell a periodic watcher to trigger "in 10
		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).
		1790
		1791	C<ev_periodic> watchers can also be used to implement vastly more complex
1003	triggering an event on eahc midnight, local time.	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.
1004		1795
1005	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
1006	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
1007	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
1008		1803
1009	=over 4	1804	=over 4
1010		1805
1011	=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)
1012		1807
1013	=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)
1014		1809
1015	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
1016	operation, and we will explain them from simplest to complex:	1811	operation, and we will explain them from simplest to most complex:
1017		1812
1018	=over 4	1813	=over 4
1019		1814
1020	=item * absolute timer (interval = reschedule_cb = 0)	1815	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1021		1816
1022	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
1023	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
1024	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
1025	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.
1026		1822
1027	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1823	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1028		1824
1029	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
1030	C<at + N * interval> time (for some integer N) and then repeat, regardless	1826	C<offset + N * interval> time (for some integer N, which can also be
1031	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.
1032		1829
1033	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
1034	time:	1831	system clock, for example, here is an C<ev_periodic> that triggers each
		1832	hour, on the hour (with respect to UTC):
1035		1833
1036	ev_periodic_set (&periodic, 0., 3600., 0);	1834	ev_periodic_set (&periodic, 0., 3600., 0);
1037		1835
1038	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,
1039	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
1040	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
1041	by 3600.	1839	by 3600.
1042		1840
1043	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
1044	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
1045	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.
1046		1844
		1845	For numerical stability it is preferable that the C<offset> value is near
		1846	C<ev_now ()> (the current time), but there is no range requirement for
		1847	this value, and in fact is often specified as zero.
		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
1047	=item * manual reschedule mode (reschedule_cb = callback)	1854	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1048		1855
1049	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
1050	ignored. Instead, each time the periodic watcher gets scheduled, the	1857	ignored. Instead, each time the periodic watcher gets scheduled, the
1051	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
1052	current time as second argument.	1859	current time as second argument.
1053		1860
1054	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,
1055	ever, or make any event loop modifications>. If you need to stop it,	1862	or make ANY other event loop modifications whatsoever, unless explicitly
1056	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1863	allowed by documentation here>.
1057	starting a prepare watcher).
1058		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
1059	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1869	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1060	ev_tstamp now)>, e.g.:	1870	*w, ev_tstamp now)>, e.g.:
1061		1871
		1872	static ev_tstamp
1062	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1873	my_rescheduler (ev_periodic *w, ev_tstamp now)
1063	{	1874	{
1064	return now + 60.;	1875	return now + 60.;
1065	}	1876	}
1066		1877
1067	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
1068	(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
1069	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
1070	might be called at other times, too.	1881	might be called at other times, too.
1071		1882
1072	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
1073	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1884	equal to the passed C<now> value >>.
1074		1885
1075	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
1076	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
1077	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
1078	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
1079	reason I omitted it as an example).	1890	reason I omitted it as an example).
1080		1891
1081	=back	1892	=back
…		…
1085	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
1086	when you changed some parameters or the reschedule callback would return	1897	when you changed some parameters or the reschedule callback would return
1087	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
1088	program when the crontabs have changed).	1899	program when the crontabs have changed).
1089		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
		1908	=item ev_tstamp offset [read-write]
		1909
		1910	When repeating, this contains the offset value, otherwise this is the
		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).
		1913
		1914	Can be modified any time, but changes only take effect when the periodic
		1915	timer fires or C<ev_periodic_again> is being called.
		1916
1090	=item ev_tstamp interval [read-write]	1917	=item ev_tstamp interval [read-write]
1091		1918
1092	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
1093	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
1094	called.	1921	called.
1095		1922
1096	=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]
1097		1924
1098	The current reschedule callback, or C<0>, if this functionality is	1925	The current reschedule callback, or C<0>, if this functionality is
1099	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
1100	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.
1101		1928
1102	=back	1929	=back
1103		1930
		1931	=head3 Examples
		1932
1104	Example: Call a callback every hour, or, more precisely, whenever the	1933	Example: Call a callback every hour, or, more precisely, whenever the
1105	system clock is divisible by 3600. The callback invocation times have	1934	system time is divisible by 3600. The callback invocation times have
1106	potentially a lot of jittering, but good long-term stability.	1935	potentially a lot of jitter, but good long-term stability.
1107		1936
1108	static void	1937	static void
1109	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1938	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1110	{	1939	{
1111	... 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)
1112	}	1941	}
1113		1942
1114	struct ev_periodic hourly_tick;	1943	ev_periodic hourly_tick;
1115	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1944	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1116	ev_periodic_start (loop, &hourly_tick);	1945	ev_periodic_start (loop, &hourly_tick);
1117		1946
1118	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:
1119		1948
1120	#include <math.h>	1949	#include <math.h>
1121		1950
1122	static ev_tstamp	1951	static ev_tstamp
1123	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1952	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1124	{	1953	{
1125	return fmod (now, 3600.) + 3600.;	1954	return now + (3600. - fmod (now, 3600.));
1126	}	1955	}
1127		1956
1128	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);
1129		1958
1130	Example: Call a callback every hour, starting now:	1959	Example: Call a callback every hour, starting now:
1131		1960
1132	struct ev_periodic hourly_tick;	1961	ev_periodic hourly_tick;
1133	ev_periodic_init (&hourly_tick, clock_cb,	1962	ev_periodic_init (&hourly_tick, clock_cb,
1134	fmod (ev_now (loop), 3600.), 3600., 0);	1963	fmod (ev_now (loop), 3600.), 3600., 0);
1135	ev_periodic_start (loop, &hourly_tick);	1964	ev_periodic_start (loop, &hourly_tick);
1136		1965
1137		1966
1138	=head2 C<ev_signal> - signal me when a signal gets signalled!	1967	=head2 C<ev_signal> - signal me when a signal gets signalled!
1139		1968
1140	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
1141	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
1142	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
1143	normal event processing, like any other event.	1972	normal event processing, like any other event.
1144		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
1145	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
1146	first watcher gets started will libev actually register a signal watcher	1979	first watcher gets started will libev actually register a signal handler
1147	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
1148	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
1149	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
1150	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
1151		1992
1152	=over 4	1993	=over 4
1153		1994
1154	=item ev_signal_init (ev_signal *, callback, int signum)	1995	=item ev_signal_init (ev_signal *, callback, int signum)
1155		1996
…		…
1162		2003
1163	The signal the watcher watches out for.	2004	The signal the watcher watches out for.
1164		2005
1165	=back	2006	=back
1166		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
1167		2022
1168	=head2 C<ev_child> - watch out for process status changes	2023	=head2 C<ev_child> - watch out for process status changes
1169		2024
1170	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
1171	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	=head3 Process Interaction
		2038
		2039	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2040	initialised. This is necessary to guarantee proper behaviour even if
		2041	the first child watcher is started after the child exits. The occurrence
		2042	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2043	synchronously as part of the event loop processing. Libev always reaps all
		2044	children, even ones not watched.
		2045
		2046	=head3 Overriding the Built-In Processing
		2047
		2048	Libev offers no special support for overriding the built-in child
		2049	processing, but if your application collides with libev's default child
		2050	handler, you can override it easily by installing your own handler for
		2051	C<SIGCHLD> after initialising the default loop, and making sure the
		2052	default loop never gets destroyed. You are encouraged, however, to use an
		2053	event-based approach to child reaping and thus use libev's support for
		2054	that, so other libev users can use C<ev_child> watchers freely.
		2055
		2056	=head3 Stopping the Child Watcher
		2057
		2058	Currently, the child watcher never gets stopped, even when the
		2059	child terminates, so normally one needs to stop the watcher in the
		2060	callback. Future versions of libev might stop the watcher automatically
		2061	when a child exit is detected.
		2062
		2063	=head3 Watcher-Specific Functions and Data Members
1172		2064
1173	=over 4	2065	=over 4
1174		2066
1175	=item ev_child_init (ev_child *, callback, int pid)	2067	=item ev_child_init (ev_child *, callback, int pid, int trace)
1176		2068
1177	=item ev_child_set (ev_child *, int pid)	2069	=item ev_child_set (ev_child *, int pid, int trace)
1178		2070
1179	Configures the watcher to wait for status changes of process C<pid> (or	2071	Configures the watcher to wait for status changes of process C<pid> (or
1180	I<any> process if C<pid> is specified as C<0>). The callback can look	2072	I<any> process if C<pid> is specified as C<0>). The callback can look
1181	at the C<rstatus> member of the C<ev_child> watcher structure to see	2073	at the C<rstatus> member of the C<ev_child> watcher structure to see
1182	the status word (use the macros from C<sys/wait.h> and see your systems	2074	the status word (use the macros from C<sys/wait.h> and see your systems
1183	C<waitpid> documentation). The C<rpid> member contains the pid of the	2075	C<waitpid> documentation). The C<rpid> member contains the pid of the
1184	process causing the status change.	2076	process causing the status change. C<trace> must be either C<0> (only
		2077	activate the watcher when the process terminates) or C<1> (additionally
		2078	activate the watcher when the process is stopped or continued).
1185		2079
1186	=item int pid [read-only]	2080	=item int pid [read-only]
1187		2081
1188	The process id this watcher watches out for, or C<0>, meaning any process id.	2082	The process id this watcher watches out for, or C<0>, meaning any process id.
1189		2083
…		…
1196	The process exit/trace status caused by C<rpid> (see your systems	2090	The process exit/trace status caused by C<rpid> (see your systems
1197	C<waitpid> and C<sys/wait.h> documentation for details).	2091	C<waitpid> and C<sys/wait.h> documentation for details).
1198		2092
1199	=back	2093	=back
1200		2094
1201	Example: Try to exit cleanly on SIGINT and SIGTERM.	2095	=head3 Examples
1202		2096
		2097	Example: C<fork()> a new process and install a child handler to wait for
		2098	its completion.
		2099
		2100	ev_child cw;
		2101
1203	static void	2102	static void
1204	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2103	child_cb (EV_P_ ev_child *w, int revents)
1205	{	2104	{
1206	ev_unloop (loop, EVUNLOOP_ALL);	2105	ev_child_stop (EV_A_ w);
		2106	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1207	}	2107	}
1208		2108
1209	struct ev_signal signal_watcher;	2109	pid_t pid = fork ();
1210	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2110
1211	ev_signal_start (loop, &sigint_cb);	2111	if (pid < 0)
		2112	// error
		2113	else if (pid == 0)
		2114	{
		2115	// the forked child executes here
		2116	exit (1);
		2117	}
		2118	else
		2119	{
		2120	ev_child_init (&cw, child_cb, pid, 0);
		2121	ev_child_start (EV_DEFAULT_ &cw);
		2122	}
1212		2123
1213		2124
1214	=head2 C<ev_stat> - did the file attributes just change?	2125	=head2 C<ev_stat> - did the file attributes just change?
1215		2126
1216	This watches a filesystem path for attribute changes. That is, it calls	2127	This watches a file system path for attribute changes. That is, it calls
1217	C<stat> regularly (or when the OS says it changed) and sees if it changed	2128	C<stat> on that path in regular intervals (or when the OS says it changed)
1218	compared to the last time, invoking the callback if it did.	2129	and sees if it changed compared to the last time, invoking the callback if
		2130	it did.
1219		2131
1220	The path does not need to exist: changing from "path exists" to "path does	2132	The path does not need to exist: changing from "path exists" to "path does
1221	not exist" is a status change like any other. The condition "path does	2133	not exist" is a status change like any other. The condition "path does not
1222	not exist" is signified by the C<st_nlink> field being zero (which is	2134	exist" (or more correctly "path cannot be stat'ed") is signified by the
1223	otherwise always forced to be at least one) and all the other fields of	2135	C<st_nlink> field being zero (which is otherwise always forced to be at
1224	the stat buffer having unspecified contents.	2136	least one) and all the other fields of the stat buffer having unspecified
		2137	contents.
1225		2138
1226	Since there is no standard to do this, the portable implementation simply	2139	The path I<must not> end in a slash or contain special components such as
1227	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2140	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1228	can specify a recommended polling interval for this case. If you specify	2141	your working directory changes, then the behaviour is undefined.
1229	a polling interval of C<0> (highly recommended!) then a I<suitable,	2142
1230	unspecified default> value will be used (which you can expect to be around	2143	Since there is no portable change notification interface available, the
1231	five seconds, although this might change dynamically). Libev will also	2144	portable implementation simply calls C<stat(2)> regularly on the path
1232	impose a minimum interval which is currently around C<0.1>, but thats	2145	to see if it changed somehow. You can specify a recommended polling
1233	usually overkill.	2146	interval for this case. If you specify a polling interval of C<0> (highly
		2147	recommended!) then a I<suitable, unspecified default> value will be used
		2148	(which you can expect to be around five seconds, although this might
		2149	change dynamically). Libev will also impose a minimum interval which is
		2150	currently around C<0.1>, but that's usually overkill.
1234		2151
1235	This watcher type is not meant for massive numbers of stat watchers,	2152	This watcher type is not meant for massive numbers of stat watchers,
1236	as even with OS-supported change notifications, this can be	2153	as even with OS-supported change notifications, this can be
1237	resource-intensive.	2154	resource-intensive.
1238		2155
1239	At the time of this writing, only the Linux inotify interface is	2156	At the time of this writing, the only OS-specific interface implemented
1240	implemented (implementing kqueue support is left as an exercise for the	2157	is the Linux inotify interface (implementing kqueue support is left as an
1241	reader). Inotify will be used to give hints only and should not change the	2158	exercise for the reader. Note, however, that the author sees no way of
1242	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2159	implementing C<ev_stat> semantics with kqueue, except as a hint).
1243	to fall back to regular polling again even with inotify, but changes are	2160
1244	usually detected immediately, and if the file exists there will be no	2161	=head3 ABI Issues (Largefile Support)
1245	polling.	2162
		2163	Libev by default (unless the user overrides this) uses the default
		2164	compilation environment, which means that on systems with large file
		2165	support disabled by default, you get the 32 bit version of the stat
		2166	structure. When using the library from programs that change the ABI to
		2167	use 64 bit file offsets the programs will fail. In that case you have to
		2168	compile libev with the same flags to get binary compatibility. This is
		2169	obviously the case with any flags that change the ABI, but the problem is
		2170	most noticeably displayed with ev_stat and large file support.
		2171
		2172	The solution for this is to lobby your distribution maker to make large
		2173	file interfaces available by default (as e.g. FreeBSD does) and not
		2174	optional. Libev cannot simply switch on large file support because it has
		2175	to exchange stat structures with application programs compiled using the
		2176	default compilation environment.
		2177
		2178	=head3 Inotify and Kqueue
		2179
		2180	When C<inotify (7)> support has been compiled into libev and present at
		2181	runtime, it will be used to speed up change detection where possible. The
		2182	inotify descriptor will be created lazily when the first C<ev_stat>
		2183	watcher is being started.
		2184
		2185	Inotify presence does not change the semantics of C<ev_stat> watchers
		2186	except that changes might be detected earlier, and in some cases, to avoid
		2187	making regular C<stat> calls. Even in the presence of inotify support
		2188	there are many cases where libev has to resort to regular C<stat> polling,
		2189	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2190	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2191	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2192	xfs are fully working) libev usually gets away without polling.
		2193
		2194	There is no support for kqueue, as apparently it cannot be used to
		2195	implement this functionality, due to the requirement of having a file
		2196	descriptor open on the object at all times, and detecting renames, unlinks
		2197	etc. is difficult.
		2198
		2199	=head3 C<stat ()> is a synchronous operation
		2200
		2201	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2202	the process. The exception are C<ev_stat> watchers - those call C<stat
		2203	()>, which is a synchronous operation.
		2204
		2205	For local paths, this usually doesn't matter: unless the system is very
		2206	busy or the intervals between stat's are large, a stat call will be fast,
		2207	as the path data is usually in memory already (except when starting the
		2208	watcher).
		2209
		2210	For networked file systems, calling C<stat ()> can block an indefinite
		2211	time due to network issues, and even under good conditions, a stat call
		2212	often takes multiple milliseconds.
		2213
		2214	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2215	paths, although this is fully supported by libev.
		2216
		2217	=head3 The special problem of stat time resolution
		2218
		2219	The C<stat ()> system call only supports full-second resolution portably,
		2220	and even on systems where the resolution is higher, most file systems
		2221	still only support whole seconds.
		2222
		2223	That means that, if the time is the only thing that changes, you can
		2224	easily miss updates: on the first update, C<ev_stat> detects a change and
		2225	calls your callback, which does something. When there is another update
		2226	within the same second, C<ev_stat> will be unable to detect unless the
		2227	stat data does change in other ways (e.g. file size).
		2228
		2229	The solution to this is to delay acting on a change for slightly more
		2230	than a second (or till slightly after the next full second boundary), using
		2231	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2232	ev_timer_again (loop, w)>).
		2233
		2234	The C<.02> offset is added to work around small timing inconsistencies
		2235	of some operating systems (where the second counter of the current time
		2236	might be be delayed. One such system is the Linux kernel, where a call to
		2237	C<gettimeofday> might return a timestamp with a full second later than
		2238	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2239	update file times then there will be a small window where the kernel uses
		2240	the previous second to update file times but libev might already execute
		2241	the timer callback).
		2242
		2243	=head3 Watcher-Specific Functions and Data Members
1246		2244
1247	=over 4	2245	=over 4
1248		2246
1249	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2247	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1250		2248
…		…
1254	C<path>. The C<interval> is a hint on how quickly a change is expected to	2252	C<path>. The C<interval> is a hint on how quickly a change is expected to
1255	be detected and should normally be specified as C<0> to let libev choose	2253	be detected and should normally be specified as C<0> to let libev choose
1256	a suitable value. The memory pointed to by C<path> must point to the same	2254	a suitable value. The memory pointed to by C<path> must point to the same
1257	path for as long as the watcher is active.	2255	path for as long as the watcher is active.
1258		2256
1259	The callback will be receive C<EV_STAT> when a change was detected,	2257	The callback will receive an C<EV_STAT> event when a change was detected,
1260	relative to the attributes at the time the watcher was started (or the	2258	relative to the attributes at the time the watcher was started (or the
1261	last change was detected).	2259	last change was detected).
1262		2260
1263	=item ev_stat_stat (ev_stat *)	2261	=item ev_stat_stat (loop, ev_stat *)
1264		2262
1265	Updates the stat buffer immediately with new values. If you change the	2263	Updates the stat buffer immediately with new values. If you change the
1266	watched path in your callback, you could call this fucntion to avoid	2264	watched path in your callback, you could call this function to avoid
1267	detecting this change (while introducing a race condition). Can also be	2265	detecting this change (while introducing a race condition if you are not
1268	useful simply to find out the new values.	2266	the only one changing the path). Can also be useful simply to find out the
		2267	new values.
1269		2268
1270	=item ev_statdata attr [read-only]	2269	=item ev_statdata attr [read-only]
1271		2270
1272	The most-recently detected attributes of the file. Although the type is of	2271	The most-recently detected attributes of the file. Although the type is
1273	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2272	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1274	suitable for your system. If the C<st_nlink> member is C<0>, then there	2273	suitable for your system, but you can only rely on the POSIX-standardised
		2274	members to be present. If the C<st_nlink> member is C<0>, then there was
1275	was some error while C<stat>ing the file.	2275	some error while C<stat>ing the file.
1276		2276
1277	=item ev_statdata prev [read-only]	2277	=item ev_statdata prev [read-only]
1278		2278
1279	The previous attributes of the file. The callback gets invoked whenever	2279	The previous attributes of the file. The callback gets invoked whenever
1280	C<prev> != C<attr>.	2280	C<prev> != C<attr>, or, more precisely, one or more of these members
		2281	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2282	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1281		2283
1282	=item ev_tstamp interval [read-only]	2284	=item ev_tstamp interval [read-only]
1283		2285
1284	The specified interval.	2286	The specified interval.
1285		2287
1286	=item const char *path [read-only]	2288	=item const char *path [read-only]
1287		2289
1288	The filesystem path that is being watched.	2290	The file system path that is being watched.
1289		2291
1290	=back	2292	=back
1291		2293
		2294	=head3 Examples
		2295
1292	Example: Watch C</etc/passwd> for attribute changes.	2296	Example: Watch C</etc/passwd> for attribute changes.
1293		2297
1294	static void	2298	static void
1295	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2299	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1296	{	2300	{
1297	/* /etc/passwd changed in some way */	2301	/* /etc/passwd changed in some way */
1298	if (w->attr.st_nlink)	2302	if (w->attr.st_nlink)
1299	{	2303	{
1300	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2304	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1301	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2305	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1302	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2306	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1303	}	2307	}
1304	else	2308	else
1305	/* you shalt not abuse printf for puts */	2309	/* you shalt not abuse printf for puts */
1306	puts ("wow, /etc/passwd is not there, expect problems. "	2310	puts ("wow, /etc/passwd is not there, expect problems. "
1307	"if this is windows, they already arrived\n");	2311	"if this is windows, they already arrived\n");
1308	}	2312	}
1309		2313
1310	...	2314	...
1311	ev_stat passwd;	2315	ev_stat passwd;
1312		2316
1313	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2317	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1314	ev_stat_start (loop, &passwd);	2318	ev_stat_start (loop, &passwd);
		2319
		2320	Example: Like above, but additionally use a one-second delay so we do not
		2321	miss updates (however, frequent updates will delay processing, too, so
		2322	one might do the work both on C<ev_stat> callback invocation I<and> on
		2323	C<ev_timer> callback invocation).
		2324
		2325	static ev_stat passwd;
		2326	static ev_timer timer;
		2327
		2328	static void
		2329	timer_cb (EV_P_ ev_timer *w, int revents)
		2330	{
		2331	ev_timer_stop (EV_A_ w);
		2332
		2333	/* now it's one second after the most recent passwd change */
		2334	}
		2335
		2336	static void
		2337	stat_cb (EV_P_ ev_stat *w, int revents)
		2338	{
		2339	/* reset the one-second timer */
		2340	ev_timer_again (EV_A_ &timer);
		2341	}
		2342
		2343	...
		2344	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2345	ev_stat_start (loop, &passwd);
		2346	ev_timer_init (&timer, timer_cb, 0., 1.02);
1315		2347
1316		2348
1317	=head2 C<ev_idle> - when you've got nothing better to do...	2349	=head2 C<ev_idle> - when you've got nothing better to do...
1318		2350
1319	Idle watchers trigger events when there are no other events are pending	2351	Idle watchers trigger events when no other events of the same or higher
1320	(prepare, check and other idle watchers do not count). That is, as long	2352	priority are pending (prepare, check and other idle watchers do not count
1321	as your process is busy handling sockets or timeouts (or even signals,	2353	as receiving "events").
1322	imagine) it will not be triggered. But when your process is idle all idle	2354
1323	watchers are being called again and again, once per event loop iteration -	2355	That is, as long as your process is busy handling sockets or timeouts
		2356	(or even signals, imagine) of the same or higher priority it will not be
		2357	triggered. But when your process is idle (or only lower-priority watchers
		2358	are pending), the idle watchers are being called once per event loop
1324	until stopped, that is, or your process receives more events and becomes	2359	iteration - until stopped, that is, or your process receives more events
1325	busy.	2360	and becomes busy again with higher priority stuff.
1326		2361
1327	The most noteworthy effect is that as long as any idle watchers are	2362	The most noteworthy effect is that as long as any idle watchers are
1328	active, the process will not block when waiting for new events.	2363	active, the process will not block when waiting for new events.
1329		2364
1330	Apart from keeping your process non-blocking (which is a useful	2365	Apart from keeping your process non-blocking (which is a useful
1331	effect on its own sometimes), idle watchers are a good place to do	2366	effect on its own sometimes), idle watchers are a good place to do
1332	"pseudo-background processing", or delay processing stuff to after the	2367	"pseudo-background processing", or delay processing stuff to after the
1333	event loop has handled all outstanding events.	2368	event loop has handled all outstanding events.
1334		2369
		2370	=head3 Watcher-Specific Functions and Data Members
		2371
1335	=over 4	2372	=over 4
1336		2373
1337	=item ev_idle_init (ev_signal *, callback)	2374	=item ev_idle_init (ev_idle *, callback)
1338		2375
1339	Initialises and configures the idle watcher - it has no parameters of any	2376	Initialises and configures the idle watcher - it has no parameters of any
1340	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2377	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1341	believe me.	2378	believe me.
1342		2379
1343	=back	2380	=back
1344		2381
		2382	=head3 Examples
		2383
1345	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2384	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1346	callback, free it. Also, use no error checking, as usual.	2385	callback, free it. Also, use no error checking, as usual.
1347		2386
1348	static void	2387	static void
1349	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2388	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1350	{	2389	{
1351	free (w);	2390	free (w);
1352	// now do something you wanted to do when the program has	2391	// now do something you wanted to do when the program has
1353	// no longer asnything immediate to do.	2392	// no longer anything immediate to do.
1354	}	2393	}
1355		2394
1356	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2395	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1357	ev_idle_init (idle_watcher, idle_cb);	2396	ev_idle_init (idle_watcher, idle_cb);
1358	ev_idle_start (loop, idle_cb);	2397	ev_idle_start (loop, idle_watcher);
1359		2398
1360		2399
1361	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2400	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1362		2401
1363	Prepare and check watchers are usually (but not always) used in tandem:	2402	Prepare and check watchers are usually (but not always) used in pairs:
1364	prepare watchers get invoked before the process blocks and check watchers	2403	prepare watchers get invoked before the process blocks and check watchers
1365	afterwards.	2404	afterwards.
1366		2405
1367	You I<must not> call C<ev_loop> or similar functions that enter	2406	You I<must not> call C<ev_loop> or similar functions that enter
1368	the current event loop from either C<ev_prepare> or C<ev_check>	2407	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1371	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2410	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1372	C<ev_check> so if you have one watcher of each kind they will always be	2411	C<ev_check> so if you have one watcher of each kind they will always be
1373	called in pairs bracketing the blocking call.	2412	called in pairs bracketing the blocking call.
1374		2413
1375	Their main purpose is to integrate other event mechanisms into libev and	2414	Their main purpose is to integrate other event mechanisms into libev and
1376	their use is somewhat advanced. This could be used, for example, to track	2415	their use is somewhat advanced. They could be used, for example, to track
1377	variable changes, implement your own watchers, integrate net-snmp or a	2416	variable changes, implement your own watchers, integrate net-snmp or a
1378	coroutine library and lots more. They are also occasionally useful if	2417	coroutine library and lots more. They are also occasionally useful if
1379	you cache some data and want to flush it before blocking (for example,	2418	you cache some data and want to flush it before blocking (for example,
1380	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2419	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1381	watcher).	2420	watcher).
1382		2421
1383	This is done by examining in each prepare call which file descriptors need	2422	This is done by examining in each prepare call which file descriptors
1384	to be watched by the other library, registering C<ev_io> watchers for	2423	need to be watched by the other library, registering C<ev_io> watchers
1385	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2424	for them and starting an C<ev_timer> watcher for any timeouts (many
1386	provide just this functionality). Then, in the check watcher you check for	2425	libraries provide exactly this functionality). Then, in the check watcher,
1387	any events that occured (by checking the pending status of all watchers	2426	you check for any events that occurred (by checking the pending status
1388	and stopping them) and call back into the library. The I/O and timer	2427	of all watchers and stopping them) and call back into the library. The
1389	callbacks will never actually be called (but must be valid nevertheless,	2428	I/O and timer callbacks will never actually be called (but must be valid
1390	because you never know, you know?).	2429	nevertheless, because you never know, you know?).
1391		2430
1392	As another example, the Perl Coro module uses these hooks to integrate	2431	As another example, the Perl Coro module uses these hooks to integrate
1393	coroutines into libev programs, by yielding to other active coroutines	2432	coroutines into libev programs, by yielding to other active coroutines
1394	during each prepare and only letting the process block if no coroutines	2433	during each prepare and only letting the process block if no coroutines
1395	are ready to run (it's actually more complicated: it only runs coroutines	2434	are ready to run (it's actually more complicated: it only runs coroutines
1396	with priority higher than or equal to the event loop and one coroutine	2435	with priority higher than or equal to the event loop and one coroutine
1397	of lower priority, but only once, using idle watchers to keep the event	2436	of lower priority, but only once, using idle watchers to keep the event
1398	loop from blocking if lower-priority coroutines are active, thus mapping	2437	loop from blocking if lower-priority coroutines are active, thus mapping
1399	low-priority coroutines to idle/background tasks).	2438	low-priority coroutines to idle/background tasks).
1400		2439
		2440	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2441	priority, to ensure that they are being run before any other watchers
		2442	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2443
		2444	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2445	activate ("feed") events into libev. While libev fully supports this, they
		2446	might get executed before other C<ev_check> watchers did their job. As
		2447	C<ev_check> watchers are often used to embed other (non-libev) event
		2448	loops those other event loops might be in an unusable state until their
		2449	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2450	others).
		2451
		2452	=head3 Watcher-Specific Functions and Data Members
		2453
1401	=over 4	2454	=over 4
1402		2455
1403	=item ev_prepare_init (ev_prepare *, callback)	2456	=item ev_prepare_init (ev_prepare *, callback)
1404		2457
1405	=item ev_check_init (ev_check *, callback)	2458	=item ev_check_init (ev_check *, callback)
1406		2459
1407	Initialises and configures the prepare or check watcher - they have no	2460	Initialises and configures the prepare or check watcher - they have no
1408	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2461	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1409	macros, but using them is utterly, utterly and completely pointless.	2462	macros, but using them is utterly, utterly, utterly and completely
		2463	pointless.
1410		2464
1411	=back	2465	=back
1412		2466
1413	Example: To include a library such as adns, you would add IO watchers	2467	=head3 Examples
1414	and a timeout watcher in a prepare handler, as required by libadns, and	2468
		2469	There are a number of principal ways to embed other event loops or modules
		2470	into libev. Here are some ideas on how to include libadns into libev
		2471	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2472	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2473	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2474	Glib event loop).
		2475
		2476	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1415	in a check watcher, destroy them and call into libadns. What follows is	2477	and in a check watcher, destroy them and call into libadns. What follows
1416	pseudo-code only of course:	2478	is pseudo-code only of course. This requires you to either use a low
		2479	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2480	the callbacks for the IO/timeout watchers might not have been called yet.
1417		2481
1418	static ev_io iow [nfd];	2482	static ev_io iow [nfd];
1419	static ev_timer tw;	2483	static ev_timer tw;
1420		2484
1421	static void	2485	static void
1422	io_cb (ev_loop *loop, ev_io *w, int revents)	2486	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1423	{	2487	{
1424	// set the relevant poll flags
1425	// could also call adns_processreadable etc. here
1426	struct pollfd *fd = (struct pollfd *)w->data;
1427	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1428	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1429	}	2488	}
1430		2489
1431	// create io watchers for each fd and a timer before blocking	2490	// create io watchers for each fd and a timer before blocking
1432	static void	2491	static void
1433	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2492	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1434	{	2493	{
1435	int timeout = 3600000;truct pollfd fds [nfd];	2494	int timeout = 3600000;
		2495	struct pollfd fds [nfd];
1436	// actual code will need to loop here and realloc etc.	2496	// actual code will need to loop here and realloc etc.
1437	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2497	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1438		2498
1439	/* the callback is illegal, but won't be called as we stop during check */	2499	/* the callback is illegal, but won't be called as we stop during check */
1440	ev_timer_init (&tw, 0, timeout * 1e-3);	2500	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1441	ev_timer_start (loop, &tw);	2501	ev_timer_start (loop, &tw);
1442		2502
1443	// create on ev_io per pollfd	2503	// create one ev_io per pollfd
1444	for (int i = 0; i < nfd; ++i)	2504	for (int i = 0; i < nfd; ++i)
1445	{	2505	{
1446	ev_io_init (iow + i, io_cb, fds [i].fd,	2506	ev_io_init (iow + i, io_cb, fds [i].fd,
1447	((fds [i].events & POLLIN ? EV_READ : 0)	2507	((fds [i].events & POLLIN ? EV_READ : 0)
1448	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2508	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1449		2509
1450	fds [i].revents = 0;	2510	fds [i].revents = 0;
1451	iow [i].data = fds + i;
1452	ev_io_start (loop, iow + i);	2511	ev_io_start (loop, iow + i);
1453	}	2512	}
1454	}	2513	}
1455		2514
1456	// stop all watchers after blocking	2515	// stop all watchers after blocking
1457	static void	2516	static void
1458	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2517	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1459	{	2518	{
1460	ev_timer_stop (loop, &tw);	2519	ev_timer_stop (loop, &tw);
1461		2520
1462	for (int i = 0; i < nfd; ++i)	2521	for (int i = 0; i < nfd; ++i)
		2522	{
		2523	// set the relevant poll flags
		2524	// could also call adns_processreadable etc. here
		2525	struct pollfd *fd = fds + i;
		2526	int revents = ev_clear_pending (iow + i);
		2527	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2528	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2529
		2530	// now stop the watcher
1463	ev_io_stop (loop, iow + i);	2531	ev_io_stop (loop, iow + i);
		2532	}
1464		2533
1465	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2534	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1466	}	2535	}
		2536
		2537	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2538	in the prepare watcher and would dispose of the check watcher.
		2539
		2540	Method 3: If the module to be embedded supports explicit event
		2541	notification (libadns does), you can also make use of the actual watcher
		2542	callbacks, and only destroy/create the watchers in the prepare watcher.
		2543
		2544	static void
		2545	timer_cb (EV_P_ ev_timer *w, int revents)
		2546	{
		2547	adns_state ads = (adns_state)w->data;
		2548	update_now (EV_A);
		2549
		2550	adns_processtimeouts (ads, &tv_now);
		2551	}
		2552
		2553	static void
		2554	io_cb (EV_P_ ev_io *w, int revents)
		2555	{
		2556	adns_state ads = (adns_state)w->data;
		2557	update_now (EV_A);
		2558
		2559	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2560	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2561	}
		2562
		2563	// do not ever call adns_afterpoll
		2564
		2565	Method 4: Do not use a prepare or check watcher because the module you
		2566	want to embed is not flexible enough to support it. Instead, you can
		2567	override their poll function. The drawback with this solution is that the
		2568	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2569	this approach, effectively embedding EV as a client into the horrible
		2570	libglib event loop.
		2571
		2572	static gint
		2573	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2574	{
		2575	int got_events = 0;
		2576
		2577	for (n = 0; n < nfds; ++n)
		2578	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2579
		2580	if (timeout >= 0)
		2581	// create/start timer
		2582
		2583	// poll
		2584	ev_loop (EV_A_ 0);
		2585
		2586	// stop timer again
		2587	if (timeout >= 0)
		2588	ev_timer_stop (EV_A_ &to);
		2589
		2590	// stop io watchers again - their callbacks should have set
		2591	for (n = 0; n < nfds; ++n)
		2592	ev_io_stop (EV_A_ iow [n]);
		2593
		2594	return got_events;
		2595	}
1467		2596
1468		2597
1469	=head2 C<ev_embed> - when one backend isn't enough...	2598	=head2 C<ev_embed> - when one backend isn't enough...
1470		2599
1471	This is a rather advanced watcher type that lets you embed one event loop	2600	This is a rather advanced watcher type that lets you embed one event loop
…		…
1477	prioritise I/O.	2606	prioritise I/O.
1478		2607
1479	As an example for a bug workaround, the kqueue backend might only support	2608	As an example for a bug workaround, the kqueue backend might only support
1480	sockets on some platform, so it is unusable as generic backend, but you	2609	sockets on some platform, so it is unusable as generic backend, but you
1481	still want to make use of it because you have many sockets and it scales	2610	still want to make use of it because you have many sockets and it scales
1482	so nicely. In this case, you would create a kqueue-based loop and embed it	2611	so nicely. In this case, you would create a kqueue-based loop and embed
1483	into your default loop (which might use e.g. poll). Overall operation will	2612	it into your default loop (which might use e.g. poll). Overall operation
1484	be a bit slower because first libev has to poll and then call kevent, but	2613	will be a bit slower because first libev has to call C<poll> and then
1485	at least you can use both at what they are best.	2614	C<kevent>, but at least you can use both mechanisms for what they are
		2615	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1486		2616
1487	As for prioritising I/O: rarely you have the case where some fds have	2617	As for prioritising I/O: under rare circumstances you have the case where
1488	to be watched and handled very quickly (with low latency), and even	2618	some fds have to be watched and handled very quickly (with low latency),
1489	priorities and idle watchers might have too much overhead. In this case	2619	and even priorities and idle watchers might have too much overhead. In
1490	you would put all the high priority stuff in one loop and all the rest in	2620	this case you would put all the high priority stuff in one loop and all
1491	a second one, and embed the second one in the first.	2621	the rest in a second one, and embed the second one in the first.
1492		2622
1493	As long as the watcher is active, the callback will be invoked every time	2623	As long as the watcher is active, the callback will be invoked every
1494	there might be events pending in the embedded loop. The callback must then	2624	time there might be events pending in the embedded loop. The callback
1495	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2625	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1496	their callbacks (you could also start an idle watcher to give the embedded	2626	sweep and invoke their callbacks (the callback doesn't need to invoke the
1497	loop strictly lower priority for example). You can also set the callback	2627	C<ev_embed_sweep> function directly, it could also start an idle watcher
1498	to C<0>, in which case the embed watcher will automatically execute the	2628	to give the embedded loop strictly lower priority for example).
1499	embedded loop sweep.
1500		2629
1501	As long as the watcher is started it will automatically handle events. The	2630	You can also set the callback to C<0>, in which case the embed watcher
1502	callback will be invoked whenever some events have been handled. You can	2631	will automatically execute the embedded loop sweep whenever necessary.
1503	set the callback to C<0> to avoid having to specify one if you are not
1504	interested in that.
1505		2632
1506	Also, there have not currently been made special provisions for forking:	2633	Fork detection will be handled transparently while the C<ev_embed> watcher
1507	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2634	is active, i.e., the embedded loop will automatically be forked when the
1508	but you will also have to stop and restart any C<ev_embed> watchers	2635	embedding loop forks. In other cases, the user is responsible for calling
1509	yourself.	2636	C<ev_loop_fork> on the embedded loop.
1510		2637
1511	Unfortunately, not all backends are embeddable, only the ones returned by	2638	Unfortunately, not all backends are embeddable: only the ones returned by
1512	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2639	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1513	portable one.	2640	portable one.
1514		2641
1515	So when you want to use this feature you will always have to be prepared	2642	So when you want to use this feature you will always have to be prepared
1516	that you cannot get an embeddable loop. The recommended way to get around	2643	that you cannot get an embeddable loop. The recommended way to get around
1517	this is to have a separate variables for your embeddable loop, try to	2644	this is to have a separate variables for your embeddable loop, try to
1518	create it, and if that fails, use the normal loop for everything:	2645	create it, and if that fails, use the normal loop for everything.
1519		2646
1520	struct ev_loop *loop_hi = ev_default_init (0);	2647	=head3 C<ev_embed> and fork
1521	struct ev_loop *loop_lo = 0;
1522	struct ev_embed embed;
1523
1524	// see if there is a chance of getting one that works
1525	// (remember that a flags value of 0 means autodetection)
1526	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1527	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1528	: 0;
1529		2648
1530	// if we got one, then embed it, otherwise default to loop_hi	2649	While the C<ev_embed> watcher is running, forks in the embedding loop will
1531	if (loop_lo)	2650	automatically be applied to the embedded loop as well, so no special
1532	{	2651	fork handling is required in that case. When the watcher is not running,
1533	ev_embed_init (&embed, 0, loop_lo);	2652	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1534	ev_embed_start (loop_hi, &embed);	2653	as applicable.
1535	}	2654
1536	else	2655	=head3 Watcher-Specific Functions and Data Members
1537	loop_lo = loop_hi;
1538		2656
1539	=over 4	2657	=over 4
1540		2658
1541	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2659	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1542		2660
…		…
1544		2662
1545	Configures the watcher to embed the given loop, which must be	2663	Configures the watcher to embed the given loop, which must be
1546	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2664	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1547	invoked automatically, otherwise it is the responsibility of the callback	2665	invoked automatically, otherwise it is the responsibility of the callback
1548	to invoke it (it will continue to be called until the sweep has been done,	2666	to invoke it (it will continue to be called until the sweep has been done,
1549	if you do not want thta, you need to temporarily stop the embed watcher).	2667	if you do not want that, you need to temporarily stop the embed watcher).
1550		2668
1551	=item ev_embed_sweep (loop, ev_embed *)	2669	=item ev_embed_sweep (loop, ev_embed *)
1552		2670
1553	Make a single, non-blocking sweep over the embedded loop. This works	2671	Make a single, non-blocking sweep over the embedded loop. This works
1554	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2672	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1555	apropriate way for embedded loops.	2673	appropriate way for embedded loops.
1556		2674
1557	=item struct ev_loop *loop [read-only]	2675	=item struct ev_loop *other [read-only]
1558		2676
1559	The embedded event loop.	2677	The embedded event loop.
1560		2678
1561	=back	2679	=back
		2680
		2681	=head3 Examples
		2682
		2683	Example: Try to get an embeddable event loop and embed it into the default
		2684	event loop. If that is not possible, use the default loop. The default
		2685	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2686	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2687	used).
		2688
		2689	struct ev_loop *loop_hi = ev_default_init (0);
		2690	struct ev_loop *loop_lo = 0;
		2691	ev_embed embed;
		2692
		2693	// see if there is a chance of getting one that works
		2694	// (remember that a flags value of 0 means autodetection)
		2695	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2696	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2697	: 0;
		2698
		2699	// if we got one, then embed it, otherwise default to loop_hi
		2700	if (loop_lo)
		2701	{
		2702	ev_embed_init (&embed, 0, loop_lo);
		2703	ev_embed_start (loop_hi, &embed);
		2704	}
		2705	else
		2706	loop_lo = loop_hi;
		2707
		2708	Example: Check if kqueue is available but not recommended and create
		2709	a kqueue backend for use with sockets (which usually work with any
		2710	kqueue implementation). Store the kqueue/socket-only event loop in
		2711	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2712
		2713	struct ev_loop *loop = ev_default_init (0);
		2714	struct ev_loop *loop_socket = 0;
		2715	ev_embed embed;
		2716
		2717	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2718	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2719	{
		2720	ev_embed_init (&embed, 0, loop_socket);
		2721	ev_embed_start (loop, &embed);
		2722	}
		2723
		2724	if (!loop_socket)
		2725	loop_socket = loop;
		2726
		2727	// now use loop_socket for all sockets, and loop for everything else
1562		2728
1563		2729
1564	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2730	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1565		2731
1566	Fork watchers are called when a C<fork ()> was detected (usually because	2732	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1569	event loop blocks next and before C<ev_check> watchers are being called,	2735	event loop blocks next and before C<ev_check> watchers are being called,
1570	and only in the child after the fork. If whoever good citizen calling	2736	and only in the child after the fork. If whoever good citizen calling
1571	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2737	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1572	handlers will be invoked, too, of course.	2738	handlers will be invoked, too, of course.
1573		2739
		2740	=head3 The special problem of life after fork - how is it possible?
		2741
		2742	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2743	up/change the process environment, followed by a call to C<exec()>. This
		2744	sequence should be handled by libev without any problems.
		2745
		2746	This changes when the application actually wants to do event handling
		2747	in the child, or both parent in child, in effect "continuing" after the
		2748	fork.
		2749
		2750	The default mode of operation (for libev, with application help to detect
		2751	forks) is to duplicate all the state in the child, as would be expected
		2752	when I<either> the parent I<or> the child process continues.
		2753
		2754	When both processes want to continue using libev, then this is usually the
		2755	wrong result. In that case, usually one process (typically the parent) is
		2756	supposed to continue with all watchers in place as before, while the other
		2757	process typically wants to start fresh, i.e. without any active watchers.
		2758
		2759	The cleanest and most efficient way to achieve that with libev is to
		2760	simply create a new event loop, which of course will be "empty", and
		2761	use that for new watchers. This has the advantage of not touching more
		2762	memory than necessary, and thus avoiding the copy-on-write, and the
		2763	disadvantage of having to use multiple event loops (which do not support
		2764	signal watchers).
		2765
		2766	When this is not possible, or you want to use the default loop for
		2767	other reasons, then in the process that wants to start "fresh", call
		2768	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2769	the default loop will "orphan" (not stop) all registered watchers, so you
		2770	have to be careful not to execute code that modifies those watchers. Note
		2771	also that in that case, you have to re-register any signal watchers.
		2772
		2773	=head3 Watcher-Specific Functions and Data Members
		2774
1574	=over 4	2775	=over 4
1575		2776
1576	=item ev_fork_init (ev_signal *, callback)	2777	=item ev_fork_init (ev_signal *, callback)
1577		2778
1578	Initialises and configures the fork watcher - it has no parameters of any	2779	Initialises and configures the fork watcher - it has no parameters of any
…		…
1580	believe me.	2781	believe me.
1581		2782
1582	=back	2783	=back
1583		2784
1584		2785
		2786	=head2 C<ev_async> - how to wake up another event loop
		2787
		2788	In general, you cannot use an C<ev_loop> from multiple threads or other
		2789	asynchronous sources such as signal handlers (as opposed to multiple event
		2790	loops - those are of course safe to use in different threads).
		2791
		2792	Sometimes, however, you need to wake up another event loop you do not
		2793	control, for example because it belongs to another thread. This is what
		2794	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2795	can signal it by calling C<ev_async_send>, which is thread- and signal
		2796	safe.
		2797
		2798	This functionality is very similar to C<ev_signal> watchers, as signals,
		2799	too, are asynchronous in nature, and signals, too, will be compressed
		2800	(i.e. the number of callback invocations may be less than the number of
		2801	C<ev_async_sent> calls).
		2802
		2803	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2804	just the default loop.
		2805
		2806	=head3 Queueing
		2807
		2808	C<ev_async> does not support queueing of data in any way. The reason
		2809	is that the author does not know of a simple (or any) algorithm for a
		2810	multiple-writer-single-reader queue that works in all cases and doesn't
		2811	need elaborate support such as pthreads.
		2812
		2813	That means that if you want to queue data, you have to provide your own
		2814	queue. But at least I can tell you how to implement locking around your
		2815	queue:
		2816
		2817	=over 4
		2818
		2819	=item queueing from a signal handler context
		2820
		2821	To implement race-free queueing, you simply add to the queue in the signal
		2822	handler but you block the signal handler in the watcher callback. Here is
		2823	an example that does that for some fictitious SIGUSR1 handler:
		2824
		2825	static ev_async mysig;
		2826
		2827	static void
		2828	sigusr1_handler (void)
		2829	{
		2830	sometype data;
		2831
		2832	// no locking etc.
		2833	queue_put (data);
		2834	ev_async_send (EV_DEFAULT_ &mysig);
		2835	}
		2836
		2837	static void
		2838	mysig_cb (EV_P_ ev_async *w, int revents)
		2839	{
		2840	sometype data;
		2841	sigset_t block, prev;
		2842
		2843	sigemptyset (&block);
		2844	sigaddset (&block, SIGUSR1);
		2845	sigprocmask (SIG_BLOCK, &block, &prev);
		2846
		2847	while (queue_get (&data))
		2848	process (data);
		2849
		2850	if (sigismember (&prev, SIGUSR1)
		2851	sigprocmask (SIG_UNBLOCK, &block, 0);
		2852	}
		2853
		2854	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2855	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2856	either...).
		2857
		2858	=item queueing from a thread context
		2859
		2860	The strategy for threads is different, as you cannot (easily) block
		2861	threads but you can easily preempt them, so to queue safely you need to
		2862	employ a traditional mutex lock, such as in this pthread example:
		2863
		2864	static ev_async mysig;
		2865	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2866
		2867	static void
		2868	otherthread (void)
		2869	{
		2870	// only need to lock the actual queueing operation
		2871	pthread_mutex_lock (&mymutex);
		2872	queue_put (data);
		2873	pthread_mutex_unlock (&mymutex);
		2874
		2875	ev_async_send (EV_DEFAULT_ &mysig);
		2876	}
		2877
		2878	static void
		2879	mysig_cb (EV_P_ ev_async *w, int revents)
		2880	{
		2881	pthread_mutex_lock (&mymutex);
		2882
		2883	while (queue_get (&data))
		2884	process (data);
		2885
		2886	pthread_mutex_unlock (&mymutex);
		2887	}
		2888
		2889	=back
		2890
		2891
		2892	=head3 Watcher-Specific Functions and Data Members
		2893
		2894	=over 4
		2895
		2896	=item ev_async_init (ev_async *, callback)
		2897
		2898	Initialises and configures the async watcher - it has no parameters of any
		2899	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2900	trust me.
		2901
		2902	=item ev_async_send (loop, ev_async *)
		2903
		2904	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2905	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2906	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2907	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2908	section below on what exactly this means).
		2909
		2910	Note that, as with other watchers in libev, multiple events might get
		2911	compressed into a single callback invocation (another way to look at this
		2912	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2913	reset when the event loop detects that).
		2914
		2915	This call incurs the overhead of a system call only once per event loop
		2916	iteration, so while the overhead might be noticeable, it doesn't apply to
		2917	repeated calls to C<ev_async_send> for the same event loop.
		2918
		2919	=item bool = ev_async_pending (ev_async *)
		2920
		2921	Returns a non-zero value when C<ev_async_send> has been called on the
		2922	watcher but the event has not yet been processed (or even noted) by the
		2923	event loop.
		2924
		2925	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2926	the loop iterates next and checks for the watcher to have become active,
		2927	it will reset the flag again. C<ev_async_pending> can be used to very
		2928	quickly check whether invoking the loop might be a good idea.
		2929
		2930	Not that this does I<not> check whether the watcher itself is pending,
		2931	only whether it has been requested to make this watcher pending: there
		2932	is a time window between the event loop checking and resetting the async
		2933	notification, and the callback being invoked.
		2934
		2935	=back
		2936
		2937
1585	=head1 OTHER FUNCTIONS	2938	=head1 OTHER FUNCTIONS
1586		2939
1587	There are some other functions of possible interest. Described. Here. Now.	2940	There are some other functions of possible interest. Described. Here. Now.
1588		2941
1589	=over 4	2942	=over 4
1590		2943
1591	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2944	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1592		2945
1593	This function combines a simple timer and an I/O watcher, calls your	2946	This function combines a simple timer and an I/O watcher, calls your
1594	callback on whichever event happens first and automatically stop both	2947	callback on whichever event happens first and automatically stops both
1595	watchers. This is useful if you want to wait for a single event on an fd	2948	watchers. This is useful if you want to wait for a single event on an fd
1596	or timeout without having to allocate/configure/start/stop/free one or	2949	or timeout without having to allocate/configure/start/stop/free one or
1597	more watchers yourself.	2950	more watchers yourself.
1598		2951
1599	If C<fd> is less than 0, then no I/O watcher will be started and events	2952	If C<fd> is less than 0, then no I/O watcher will be started and the
1600	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2953	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1601	C<events> set will be craeted and started.	2954	the given C<fd> and C<events> set will be created and started.
1602		2955
1603	If C<timeout> is less than 0, then no timeout watcher will be	2956	If C<timeout> is less than 0, then no timeout watcher will be
1604	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2957	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1605	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2958	repeat = 0) will be started. C<0> is a valid timeout.
1606	dubious value.
1607		2959
1608	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2960	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1609	passed an C<revents> set like normal event callbacks (a combination of	2961	passed an C<revents> set like normal event callbacks (a combination of
1610	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2962	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1611	value passed to C<ev_once>:	2963	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2964	a timeout and an io event at the same time - you probably should give io
		2965	events precedence.
1612		2966
		2967	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2968
1613	static void stdin_ready (int revents, void *arg)	2969	static void stdin_ready (int revents, void *arg)
1614	{	2970	{
1615	if (revents & EV_TIMEOUT)
1616	/* doh, nothing entered */;
1617	else if (revents & EV_READ)	2971	if (revents & EV_READ)
1618	/* stdin might have data for us, joy! */;	2972	/* stdin might have data for us, joy! */;
		2973	else if (revents & EV_TIMEOUT)
		2974	/* doh, nothing entered */;
1619	}	2975	}
1620		2976
1621	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2977	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1622		2978
1623	=item ev_feed_event (ev_loop *, watcher *, int revents)	2979	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1624		2980
1625	Feeds the given event set into the event loop, as if the specified event	2981	Feeds the given event set into the event loop, as if the specified event
1626	had happened for the specified watcher (which must be a pointer to an	2982	had happened for the specified watcher (which must be a pointer to an
1627	initialised but not necessarily started event watcher).	2983	initialised but not necessarily started event watcher).
1628		2984
1629	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2985	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1630		2986
1631	Feed an event on the given fd, as if a file descriptor backend detected	2987	Feed an event on the given fd, as if a file descriptor backend detected
1632	the given events it.	2988	the given events it.
1633		2989
1634	=item ev_feed_signal_event (ev_loop *loop, int signum)	2990	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1635		2991
1636	Feed an event as if the given signal occured (C<loop> must be the default	2992	Feed an event as if the given signal occurred (C<loop> must be the default
1637	loop!).	2993	loop!).
1638		2994
1639	=back	2995	=back
1640		2996
1641		2997
…		…
1657		3013
1658	=item * Priorities are not currently supported. Initialising priorities	3014	=item * Priorities are not currently supported. Initialising priorities
1659	will fail and all watchers will have the same priority, even though there	3015	will fail and all watchers will have the same priority, even though there
1660	is an ev_pri field.	3016	is an ev_pri field.
1661		3017
		3018	=item * In libevent, the last base created gets the signals, in libev, the
		3019	first base created (== the default loop) gets the signals.
		3020
1662	=item * Other members are not supported.	3021	=item * Other members are not supported.
1663		3022
1664	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3023	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1665	to use the libev header file and library.	3024	to use the libev header file and library.
1666		3025
1667	=back	3026	=back
1668		3027
1669	=head1 C++ SUPPORT	3028	=head1 C++ SUPPORT
1670		3029
1671	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3030	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1672	you to use some convinience methods to start/stop watchers and also change	3031	you to use some convenience methods to start/stop watchers and also change
1673	the callback model to a model using method callbacks on objects.	3032	the callback model to a model using method callbacks on objects.
1674		3033
1675	To use it,	3034	To use it,
1676		3035
1677	#include <ev++.h>	3036	#include <ev++.h>
1678		3037
1679	(it is not installed by default). This automatically includes F<ev.h>	3038	This automatically includes F<ev.h> and puts all of its definitions (many
1680	and puts all of its definitions (many of them macros) into the global	3039	of them macros) into the global namespace. All C++ specific things are
1681	namespace. All C++ specific things are put into the C<ev> namespace.	3040	put into the C<ev> namespace. It should support all the same embedding
		3041	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1682		3042
1683	It should support all the same embedding options as F<ev.h>, most notably	3043	Care has been taken to keep the overhead low. The only data member the C++
1684	C<EV_MULTIPLICITY>.	3044	classes add (compared to plain C-style watchers) is the event loop pointer
		3045	that the watcher is associated with (or no additional members at all if
		3046	you disable C<EV_MULTIPLICITY> when embedding libev).
		3047
		3048	Currently, functions, and static and non-static member functions can be
		3049	used as callbacks. Other types should be easy to add as long as they only
		3050	need one additional pointer for context. If you need support for other
		3051	types of functors please contact the author (preferably after implementing
		3052	it).
1685		3053
1686	Here is a list of things available in the C<ev> namespace:	3054	Here is a list of things available in the C<ev> namespace:
1687		3055
1688	=over 4	3056	=over 4
1689		3057
…		…
1705		3073
1706	All of those classes have these methods:	3074	All of those classes have these methods:
1707		3075
1708	=over 4	3076	=over 4
1709		3077
1710	=item ev::TYPE::TYPE (object *, object::method *)	3078	=item ev::TYPE::TYPE ()
1711		3079
1712	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	3080	=item ev::TYPE::TYPE (struct ev_loop *)
1713		3081
1714	=item ev::TYPE::~TYPE	3082	=item ev::TYPE::~TYPE
1715		3083
1716	The constructor takes a pointer to an object and a method pointer to	3084	The constructor (optionally) takes an event loop to associate the watcher
1717	the event handler callback to call in this class. The constructor calls	3085	with. If it is omitted, it will use C<EV_DEFAULT>.
1718	C<ev_init> for you, which means you have to call the C<set> method	3086
1719	before starting it. If you do not specify a loop then the constructor	3087	The constructor calls C<ev_init> for you, which means you have to call the
1720	automatically associates the default loop with this watcher.	3088	C<set> method before starting it.
		3089
		3090	It will not set a callback, however: You have to call the templated C<set>
		3091	method to set a callback before you can start the watcher.
		3092
		3093	(The reason why you have to use a method is a limitation in C++ which does
		3094	not allow explicit template arguments for constructors).
1721		3095
1722	The destructor automatically stops the watcher if it is active.	3096	The destructor automatically stops the watcher if it is active.
		3097
		3098	=item w->set<class, &class::method> (object *)
		3099
		3100	This method sets the callback method to call. The method has to have a
		3101	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3102	first argument and the C<revents> as second. The object must be given as
		3103	parameter and is stored in the C<data> member of the watcher.
		3104
		3105	This method synthesizes efficient thunking code to call your method from
		3106	the C callback that libev requires. If your compiler can inline your
		3107	callback (i.e. it is visible to it at the place of the C<set> call and
		3108	your compiler is good :), then the method will be fully inlined into the
		3109	thunking function, making it as fast as a direct C callback.
		3110
		3111	Example: simple class declaration and watcher initialisation
		3112
		3113	struct myclass
		3114	{
		3115	void io_cb (ev::io &w, int revents) { }
		3116	}
		3117
		3118	myclass obj;
		3119	ev::io iow;
		3120	iow.set <myclass, &myclass::io_cb> (&obj);
		3121
		3122	=item w->set (object *)
		3123
		3124	This is an B<experimental> feature that might go away in a future version.
		3125
		3126	This is a variation of a method callback - leaving out the method to call
		3127	will default the method to C<operator ()>, which makes it possible to use
		3128	functor objects without having to manually specify the C<operator ()> all
		3129	the time. Incidentally, you can then also leave out the template argument
		3130	list.
		3131
		3132	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3133	int revents)>.
		3134
		3135	See the method-C<set> above for more details.
		3136
		3137	Example: use a functor object as callback.
		3138
		3139	struct myfunctor
		3140	{
		3141	void operator() (ev::io &w, int revents)
		3142	{
		3143	...
		3144	}
		3145	}
		3146
		3147	myfunctor f;
		3148
		3149	ev::io w;
		3150	w.set (&f);
		3151
		3152	=item w->set<function> (void *data = 0)
		3153
		3154	Also sets a callback, but uses a static method or plain function as
		3155	callback. The optional C<data> argument will be stored in the watcher's
		3156	C<data> member and is free for you to use.
		3157
		3158	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3159
		3160	See the method-C<set> above for more details.
		3161
		3162	Example: Use a plain function as callback.
		3163
		3164	static void io_cb (ev::io &w, int revents) { }
		3165	iow.set <io_cb> ();
1723		3166
1724	=item w->set (struct ev_loop *)	3167	=item w->set (struct ev_loop *)
1725		3168
1726	Associates a different C<struct ev_loop> with this watcher. You can only	3169	Associates a different C<struct ev_loop> with this watcher. You can only
1727	do this when the watcher is inactive (and not pending either).	3170	do this when the watcher is inactive (and not pending either).
1728		3171
1729	=item w->set ([args])	3172	=item w->set ([arguments])
1730		3173
1731	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3174	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1732	called at least once. Unlike the C counterpart, an active watcher gets	3175	called at least once. Unlike the C counterpart, an active watcher gets
1733	automatically stopped and restarted.	3176	automatically stopped and restarted when reconfiguring it with this
		3177	method.
1734		3178
1735	=item w->start ()	3179	=item w->start ()
1736		3180
1737	Starts the watcher. Note that there is no C<loop> argument as the	3181	Starts the watcher. Note that there is no C<loop> argument, as the
1738	constructor already takes the loop.	3182	constructor already stores the event loop.
1739		3183
1740	=item w->stop ()	3184	=item w->stop ()
1741		3185
1742	Stops the watcher if it is active. Again, no C<loop> argument.	3186	Stops the watcher if it is active. Again, no C<loop> argument.
1743		3187
1744	=item w->again () C<ev::timer>, C<ev::periodic> only	3188	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1745		3189
1746	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3190	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1747	C<ev_TYPE_again> function.	3191	C<ev_TYPE_again> function.
1748		3192
1749	=item w->sweep () C<ev::embed> only	3193	=item w->sweep () (C<ev::embed> only)
1750		3194
1751	Invokes C<ev_embed_sweep>.	3195	Invokes C<ev_embed_sweep>.
1752		3196
1753	=item w->update () C<ev::stat> only	3197	=item w->update () (C<ev::stat> only)
1754		3198
1755	Invokes C<ev_stat_stat>.	3199	Invokes C<ev_stat_stat>.
1756		3200
1757	=back	3201	=back
1758		3202
1759	=back	3203	=back
1760		3204
1761	Example: Define a class with an IO and idle watcher, start one of them in	3205	Example: Define a class with an IO and idle watcher, start one of them in
1762	the constructor.	3206	the constructor.
1763		3207
1764	class myclass	3208	class myclass
1765	{	3209	{
1766	ev_io io; void io_cb (ev::io &w, int revents);	3210	ev::io io ; void io_cb (ev::io &w, int revents);
1767	ev_idle idle void idle_cb (ev::idle &w, int revents);	3211	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1768		3212
1769	myclass ();	3213	myclass (int fd)
1770	}	3214	{
		3215	io .set <myclass, &myclass::io_cb > (this);
		3216	idle.set <myclass, &myclass::idle_cb> (this);
1771		3217
1772	myclass::myclass (int fd)
1773	: io (this, &myclass::io_cb),
1774	idle (this, &myclass::idle_cb)
1775	{
1776	io.start (fd, ev::READ);	3218	io.start (fd, ev::READ);
		3219	}
1777	}	3220	};
		3221
		3222
		3223	=head1 OTHER LANGUAGE BINDINGS
		3224
		3225	Libev does not offer other language bindings itself, but bindings for a
		3226	number of languages exist in the form of third-party packages. If you know
		3227	any interesting language binding in addition to the ones listed here, drop
		3228	me a note.
		3229
		3230	=over 4
		3231
		3232	=item Perl
		3233
		3234	The EV module implements the full libev API and is actually used to test
		3235	libev. EV is developed together with libev. Apart from the EV core module,
		3236	there are additional modules that implement libev-compatible interfaces
		3237	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3238	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3239	and C<EV::Glib>).
		3240
		3241	It can be found and installed via CPAN, its homepage is at
		3242	L<http://software.schmorp.de/pkg/EV>.
		3243
		3244	=item Python
		3245
		3246	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3247	seems to be quite complete and well-documented.
		3248
		3249	=item Ruby
		3250
		3251	Tony Arcieri has written a ruby extension that offers access to a subset
		3252	of the libev API and adds file handle abstractions, asynchronous DNS and
		3253	more on top of it. It can be found via gem servers. Its homepage is at
		3254	L<http://rev.rubyforge.org/>.
		3255
		3256	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3257	makes rev work even on mingw.
		3258
		3259	=item Haskell
		3260
		3261	A haskell binding to libev is available at
		3262	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3263
		3264	=item D
		3265
		3266	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3267	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3268
		3269	=item Ocaml
		3270
		3271	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3272	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3273
		3274	=back
1778		3275
1779		3276
1780	=head1 MACRO MAGIC	3277	=head1 MACRO MAGIC
1781		3278
1782	Libev can be compiled with a variety of options, the most fundemantal is	3279	Libev can be compiled with a variety of options, the most fundamental
1783	C<EV_MULTIPLICITY>. This option determines wether (most) functions and	3280	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1784	callbacks have an initial C<struct ev_loop *> argument.	3281	functions and callbacks have an initial C<struct ev_loop *> argument.
1785		3282
1786	To make it easier to write programs that cope with either variant, the	3283	To make it easier to write programs that cope with either variant, the
1787	following macros are defined:	3284	following macros are defined:
1788		3285
1789	=over 4	3286	=over 4
…		…
1792		3289
1793	This provides the loop I<argument> for functions, if one is required ("ev	3290	This provides the loop I<argument> for functions, if one is required ("ev
1794	loop argument"). The C<EV_A> form is used when this is the sole argument,	3291	loop argument"). The C<EV_A> form is used when this is the sole argument,
1795	C<EV_A_> is used when other arguments are following. Example:	3292	C<EV_A_> is used when other arguments are following. Example:
1796		3293
1797	ev_unref (EV_A);	3294	ev_unref (EV_A);
1798	ev_timer_add (EV_A_ watcher);	3295	ev_timer_add (EV_A_ watcher);
1799	ev_loop (EV_A_ 0);	3296	ev_loop (EV_A_ 0);
1800		3297
1801	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3298	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1802	which is often provided by the following macro.	3299	which is often provided by the following macro.
1803		3300
1804	=item C<EV_P>, C<EV_P_>	3301	=item C<EV_P>, C<EV_P_>
1805		3302
1806	This provides the loop I<parameter> for functions, if one is required ("ev	3303	This provides the loop I<parameter> for functions, if one is required ("ev
1807	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3304	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1808	C<EV_P_> is used when other parameters are following. Example:	3305	C<EV_P_> is used when other parameters are following. Example:
1809		3306
1810	// this is how ev_unref is being declared	3307	// this is how ev_unref is being declared
1811	static void ev_unref (EV_P);	3308	static void ev_unref (EV_P);
1812		3309
1813	// this is how you can declare your typical callback	3310	// this is how you can declare your typical callback
1814	static void cb (EV_P_ ev_timer *w, int revents)	3311	static void cb (EV_P_ ev_timer *w, int revents)
1815		3312
1816	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3313	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1817	suitable for use with C<EV_A>.	3314	suitable for use with C<EV_A>.
1818		3315
1819	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3316	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1820		3317
1821	Similar to the other two macros, this gives you the value of the default	3318	Similar to the other two macros, this gives you the value of the default
1822	loop, if multiple loops are supported ("ev loop default").	3319	loop, if multiple loops are supported ("ev loop default").
1823		3320
		3321	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3322
		3323	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3324	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3325	is undefined when the default loop has not been initialised by a previous
		3326	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3327
		3328	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3329	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3330
1824	=back	3331	=back
1825		3332
1826	Example: Declare and initialise a check watcher, working regardless of	3333	Example: Declare and initialise a check watcher, utilising the above
1827	wether multiple loops are supported or not.	3334	macros so it will work regardless of whether multiple loops are supported
		3335	or not.
1828		3336
1829	static void	3337	static void
1830	check_cb (EV_P_ ev_timer *w, int revents)	3338	check_cb (EV_P_ ev_timer *w, int revents)
1831	{	3339	{
1832	ev_check_stop (EV_A_ w);	3340	ev_check_stop (EV_A_ w);
1833	}	3341	}
1834		3342
1835	ev_check check;	3343	ev_check check;
1836	ev_check_init (&check, check_cb);	3344	ev_check_init (&check, check_cb);
1837	ev_check_start (EV_DEFAULT_ &check);	3345	ev_check_start (EV_DEFAULT_ &check);
1838	ev_loop (EV_DEFAULT_ 0);	3346	ev_loop (EV_DEFAULT_ 0);
1839
1840		3347
1841	=head1 EMBEDDING	3348	=head1 EMBEDDING
1842		3349
1843	Libev can (and often is) directly embedded into host	3350	Libev can (and often is) directly embedded into host
1844	applications. Examples of applications that embed it include the Deliantra	3351	applications. Examples of applications that embed it include the Deliantra
1845	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3352	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1846	and rxvt-unicode.	3353	and rxvt-unicode.
1847		3354
1848	The goal is to enable you to just copy the neecssary files into your	3355	The goal is to enable you to just copy the necessary files into your
1849	source directory without having to change even a single line in them, so	3356	source directory without having to change even a single line in them, so
1850	you can easily upgrade by simply copying (or having a checked-out copy of	3357	you can easily upgrade by simply copying (or having a checked-out copy of
1851	libev somewhere in your source tree).	3358	libev somewhere in your source tree).
1852		3359
1853	=head2 FILESETS	3360	=head2 FILESETS
1854		3361
1855	Depending on what features you need you need to include one or more sets of files	3362	Depending on what features you need you need to include one or more sets of files
1856	in your app.	3363	in your application.
1857		3364
1858	=head3 CORE EVENT LOOP	3365	=head3 CORE EVENT LOOP
1859		3366
1860	To include only the libev core (all the C<ev_*> functions), with manual	3367	To include only the libev core (all the C<ev_*> functions), with manual
1861	configuration (no autoconf):	3368	configuration (no autoconf):
1862		3369
1863	#define EV_STANDALONE 1	3370	#define EV_STANDALONE 1
1864	#include "ev.c"	3371	#include "ev.c"
1865		3372
1866	This will automatically include F<ev.h>, too, and should be done in a	3373	This will automatically include F<ev.h>, too, and should be done in a
1867	single C source file only to provide the function implementations. To use	3374	single C source file only to provide the function implementations. To use
1868	it, do the same for F<ev.h> in all files wishing to use this API (best	3375	it, do the same for F<ev.h> in all files wishing to use this API (best
1869	done by writing a wrapper around F<ev.h> that you can include instead and	3376	done by writing a wrapper around F<ev.h> that you can include instead and
1870	where you can put other configuration options):	3377	where you can put other configuration options):
1871		3378
1872	#define EV_STANDALONE 1	3379	#define EV_STANDALONE 1
1873	#include "ev.h"	3380	#include "ev.h"
1874		3381
1875	Both header files and implementation files can be compiled with a C++	3382	Both header files and implementation files can be compiled with a C++
1876	compiler (at least, thats a stated goal, and breakage will be treated	3383	compiler (at least, that's a stated goal, and breakage will be treated
1877	as a bug).	3384	as a bug).
1878		3385
1879	You need the following files in your source tree, or in a directory	3386	You need the following files in your source tree, or in a directory
1880	in your include path (e.g. in libev/ when using -Ilibev):	3387	in your include path (e.g. in libev/ when using -Ilibev):
1881		3388
1882	ev.h	3389	ev.h
1883	ev.c	3390	ev.c
1884	ev_vars.h	3391	ev_vars.h
1885	ev_wrap.h	3392	ev_wrap.h
1886		3393
1887	ev_win32.c required on win32 platforms only	3394	ev_win32.c required on win32 platforms only
1888		3395
1889	ev_select.c only when select backend is enabled (which is by default)	3396	ev_select.c only when select backend is enabled (which is enabled by default)
1890	ev_poll.c only when poll backend is enabled (disabled by default)	3397	ev_poll.c only when poll backend is enabled (disabled by default)
1891	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3398	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1892	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3399	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1893	ev_port.c only when the solaris port backend is enabled (disabled by default)	3400	ev_port.c only when the solaris port backend is enabled (disabled by default)
1894		3401
1895	F<ev.c> includes the backend files directly when enabled, so you only need	3402	F<ev.c> includes the backend files directly when enabled, so you only need
1896	to compile this single file.	3403	to compile this single file.
1897		3404
1898	=head3 LIBEVENT COMPATIBILITY API	3405	=head3 LIBEVENT COMPATIBILITY API
1899		3406
1900	To include the libevent compatibility API, also include:	3407	To include the libevent compatibility API, also include:
1901		3408
1902	#include "event.c"	3409	#include "event.c"
1903		3410
1904	in the file including F<ev.c>, and:	3411	in the file including F<ev.c>, and:
1905		3412
1906	#include "event.h"	3413	#include "event.h"
1907		3414
1908	in the files that want to use the libevent API. This also includes F<ev.h>.	3415	in the files that want to use the libevent API. This also includes F<ev.h>.
1909		3416
1910	You need the following additional files for this:	3417	You need the following additional files for this:
1911		3418
1912	event.h	3419	event.h
1913	event.c	3420	event.c
1914		3421
1915	=head3 AUTOCONF SUPPORT	3422	=head3 AUTOCONF SUPPORT
1916		3423
1917	Instead of using C<EV_STANDALONE=1> and providing your config in	3424	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1918	whatever way you want, you can also C<m4_include([libev.m4])> in your	3425	whatever way you want, you can also C<m4_include([libev.m4])> in your
1919	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3426	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1920	include F<config.h> and configure itself accordingly.	3427	include F<config.h> and configure itself accordingly.
1921		3428
1922	For this of course you need the m4 file:	3429	For this of course you need the m4 file:
1923		3430
1924	libev.m4	3431	libev.m4
1925		3432
1926	=head2 PREPROCESSOR SYMBOLS/MACROS	3433	=head2 PREPROCESSOR SYMBOLS/MACROS
1927		3434
1928	Libev can be configured via a variety of preprocessor symbols you have to define	3435	Libev can be configured via a variety of preprocessor symbols you have to
1929	before including any of its files. The default is not to build for multiplicity	3436	define before including any of its files. The default in the absence of
1930	and only include the select backend.	3437	autoconf is documented for every option.
1931		3438
1932	=over 4	3439	=over 4
1933		3440
1934	=item EV_STANDALONE	3441	=item EV_STANDALONE
1935		3442
…		…
1937	keeps libev from including F<config.h>, and it also defines dummy	3444	keeps libev from including F<config.h>, and it also defines dummy
1938	implementations for some libevent functions (such as logging, which is not	3445	implementations for some libevent functions (such as logging, which is not
1939	supported). It will also not define any of the structs usually found in	3446	supported). It will also not define any of the structs usually found in
1940	F<event.h> that are not directly supported by the libev core alone.	3447	F<event.h> that are not directly supported by the libev core alone.
1941		3448
		3449	In stanbdalone mode, libev will still try to automatically deduce the
		3450	configuration, but has to be more conservative.
		3451
1942	=item EV_USE_MONOTONIC	3452	=item EV_USE_MONOTONIC
1943		3453
1944	If defined to be C<1>, libev will try to detect the availability of the	3454	If defined to be C<1>, libev will try to detect the availability of the
1945	monotonic clock option at both compiletime and runtime. Otherwise no use	3455	monotonic clock option at both compile time and runtime. Otherwise no
1946	of the monotonic clock option will be attempted. If you enable this, you	3456	use of the monotonic clock option will be attempted. If you enable this,
1947	usually have to link against librt or something similar. Enabling it when	3457	you usually have to link against librt or something similar. Enabling it
1948	the functionality isn't available is safe, though, althoguh you have	3458	when the functionality isn't available is safe, though, although you have
1949	to make sure you link against any libraries where the C<clock_gettime>	3459	to make sure you link against any libraries where the C<clock_gettime>
1950	function is hiding in (often F<-lrt>).	3460	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
1951		3461
1952	=item EV_USE_REALTIME	3462	=item EV_USE_REALTIME
1953		3463
1954	If defined to be C<1>, libev will try to detect the availability of the	3464	If defined to be C<1>, libev will try to detect the availability of the
1955	realtime clock option at compiletime (and assume its availability at	3465	real-time clock option at compile time (and assume its availability
1956	runtime if successful). Otherwise no use of the realtime clock option will	3466	at runtime if successful). Otherwise no use of the real-time clock
1957	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3467	option will be attempted. This effectively replaces C<gettimeofday>
1958	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3468	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
1959	in the description of C<EV_USE_MONOTONIC>, though.	3469	correctness. See the note about libraries in the description of
		3470	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3471	C<EV_USE_CLOCK_SYSCALL>.
		3472
		3473	=item EV_USE_CLOCK_SYSCALL
		3474
		3475	If defined to be C<1>, libev will try to use a direct syscall instead
		3476	of calling the system-provided C<clock_gettime> function. This option
		3477	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3478	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3479	programs needlessly. Using a direct syscall is slightly slower (in
		3480	theory), because no optimised vdso implementation can be used, but avoids
		3481	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3482	higher, as it simplifies linking (no need for C<-lrt>).
		3483
		3484	=item EV_USE_NANOSLEEP
		3485
		3486	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3487	and will use it for delays. Otherwise it will use C<select ()>.
		3488
		3489	=item EV_USE_EVENTFD
		3490
		3491	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3492	available and will probe for kernel support at runtime. This will improve
		3493	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3494	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3495	2.7 or newer, otherwise disabled.
1960		3496
1961	=item EV_USE_SELECT	3497	=item EV_USE_SELECT
1962		3498
1963	If undefined or defined to be C<1>, libev will compile in support for the	3499	If undefined or defined to be C<1>, libev will compile in support for the
1964	C<select>(2) backend. No attempt at autodetection will be done: if no	3500	C<select>(2) backend. No attempt at auto-detection will be done: if no
1965	other method takes over, select will be it. Otherwise the select backend	3501	other method takes over, select will be it. Otherwise the select backend
1966	will not be compiled in.	3502	will not be compiled in.
1967		3503
1968	=item EV_SELECT_USE_FD_SET	3504	=item EV_SELECT_USE_FD_SET
1969		3505
1970	If defined to C<1>, then the select backend will use the system C<fd_set>	3506	If defined to C<1>, then the select backend will use the system C<fd_set>
1971	structure. This is useful if libev doesn't compile due to a missing	3507	structure. This is useful if libev doesn't compile due to a missing
1972	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3508	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
1973	exotic systems. This usually limits the range of file descriptors to some	3509	on exotic systems. This usually limits the range of file descriptors to
1974	low limit such as 1024 or might have other limitations (winsocket only	3510	some low limit such as 1024 or might have other limitations (winsocket
1975	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3511	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
1976	influence the size of the C<fd_set> used.	3512	configures the maximum size of the C<fd_set>.
1977		3513
1978	=item EV_SELECT_IS_WINSOCKET	3514	=item EV_SELECT_IS_WINSOCKET
1979		3515
1980	When defined to C<1>, the select backend will assume that	3516	When defined to C<1>, the select backend will assume that
1981	select/socket/connect etc. don't understand file descriptors but	3517	select/socket/connect etc. don't understand file descriptors but
…		…
1983	be used is the winsock select). This means that it will call	3519	be used is the winsock select). This means that it will call
1984	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3520	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1985	it is assumed that all these functions actually work on fds, even	3521	it is assumed that all these functions actually work on fds, even
1986	on win32. Should not be defined on non-win32 platforms.	3522	on win32. Should not be defined on non-win32 platforms.
1987		3523
		3524	=item EV_FD_TO_WIN32_HANDLE
		3525
		3526	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3527	file descriptors to socket handles. When not defining this symbol (the
		3528	default), then libev will call C<_get_osfhandle>, which is usually
		3529	correct. In some cases, programs use their own file descriptor management,
		3530	in which case they can provide this function to map fds to socket handles.
		3531
1988	=item EV_USE_POLL	3532	=item EV_USE_POLL
1989		3533
1990	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3534	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1991	backend. Otherwise it will be enabled on non-win32 platforms. It	3535	backend. Otherwise it will be enabled on non-win32 platforms. It
1992	takes precedence over select.	3536	takes precedence over select.
1993		3537
1994	=item EV_USE_EPOLL	3538	=item EV_USE_EPOLL
1995		3539
1996	If defined to be C<1>, libev will compile in support for the Linux	3540	If defined to be C<1>, libev will compile in support for the Linux
1997	C<epoll>(7) backend. Its availability will be detected at runtime,	3541	C<epoll>(7) backend. Its availability will be detected at runtime,
1998	otherwise another method will be used as fallback. This is the	3542	otherwise another method will be used as fallback. This is the preferred
1999	preferred backend for GNU/Linux systems.	3543	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3544	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2000		3545
2001	=item EV_USE_KQUEUE	3546	=item EV_USE_KQUEUE
2002		3547
2003	If defined to be C<1>, libev will compile in support for the BSD style	3548	If defined to be C<1>, libev will compile in support for the BSD style
2004	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3549	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2017	otherwise another method will be used as fallback. This is the preferred	3562	otherwise another method will be used as fallback. This is the preferred
2018	backend for Solaris 10 systems.	3563	backend for Solaris 10 systems.
2019		3564
2020	=item EV_USE_DEVPOLL	3565	=item EV_USE_DEVPOLL
2021		3566
2022	reserved for future expansion, works like the USE symbols above.	3567	Reserved for future expansion, works like the USE symbols above.
2023		3568
2024	=item EV_USE_INOTIFY	3569	=item EV_USE_INOTIFY
2025		3570
2026	If defined to be C<1>, libev will compile in support for the Linux inotify	3571	If defined to be C<1>, libev will compile in support for the Linux inotify
2027	interface to speed up C<ev_stat> watchers. Its actual availability will	3572	interface to speed up C<ev_stat> watchers. Its actual availability will
2028	be detected at runtime.	3573	be detected at runtime. If undefined, it will be enabled if the headers
		3574	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3575
		3576	=item EV_ATOMIC_T
		3577
		3578	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3579	access is atomic with respect to other threads or signal contexts. No such
		3580	type is easily found in the C language, so you can provide your own type
		3581	that you know is safe for your purposes. It is used both for signal handler "locking"
		3582	as well as for signal and thread safety in C<ev_async> watchers.
		3583
		3584	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3585	(from F<signal.h>), which is usually good enough on most platforms.
2029		3586
2030	=item EV_H	3587	=item EV_H
2031		3588
2032	The name of the F<ev.h> header file used to include it. The default if	3589	The name of the F<ev.h> header file used to include it. The default if
2033	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3590	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2034	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3591	used to virtually rename the F<ev.h> header file in case of conflicts.
2035		3592
2036	=item EV_CONFIG_H	3593	=item EV_CONFIG_H
2037		3594
2038	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3595	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2039	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3596	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2040	C<EV_H>, above.	3597	C<EV_H>, above.
2041		3598
2042	=item EV_EVENT_H	3599	=item EV_EVENT_H
2043		3600
2044	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3601	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2045	of how the F<event.h> header can be found.	3602	of how the F<event.h> header can be found, the default is C<"event.h">.
2046		3603
2047	=item EV_PROTOTYPES	3604	=item EV_PROTOTYPES
2048		3605
2049	If defined to be C<0>, then F<ev.h> will not define any function	3606	If defined to be C<0>, then F<ev.h> will not define any function
2050	prototypes, but still define all the structs and other symbols. This is	3607	prototypes, but still define all the structs and other symbols. This is
…		…
2057	will have the C<struct ev_loop *> as first argument, and you can create	3614	will have the C<struct ev_loop *> as first argument, and you can create
2058	additional independent event loops. Otherwise there will be no support	3615	additional independent event loops. Otherwise there will be no support
2059	for multiple event loops and there is no first event loop pointer	3616	for multiple event loops and there is no first event loop pointer
2060	argument. Instead, all functions act on the single default loop.	3617	argument. Instead, all functions act on the single default loop.
2061		3618
		3619	=item EV_MINPRI
		3620
		3621	=item EV_MAXPRI
		3622
		3623	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3624	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3625	provide for more priorities by overriding those symbols (usually defined
		3626	to be C<-2> and C<2>, respectively).
		3627
		3628	When doing priority-based operations, libev usually has to linearly search
		3629	all the priorities, so having many of them (hundreds) uses a lot of space
		3630	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3631	fine.
		3632
		3633	If your embedding application does not need any priorities, defining these
		3634	both to C<0> will save some memory and CPU.
		3635
2062	=item EV_PERIODIC_ENABLE	3636	=item EV_PERIODIC_ENABLE
2063		3637
2064	If undefined or defined to be C<1>, then periodic timers are supported. If	3638	If undefined or defined to be C<1>, then periodic timers are supported. If
2065	defined to be C<0>, then they are not. Disabling them saves a few kB of	3639	defined to be C<0>, then they are not. Disabling them saves a few kB of
2066	code.	3640	code.
2067		3641
		3642	=item EV_IDLE_ENABLE
		3643
		3644	If undefined or defined to be C<1>, then idle watchers are supported. If
		3645	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3646	code.
		3647
2068	=item EV_EMBED_ENABLE	3648	=item EV_EMBED_ENABLE
2069		3649
2070	If undefined or defined to be C<1>, then embed watchers are supported. If	3650	If undefined or defined to be C<1>, then embed watchers are supported. If
2071	defined to be C<0>, then they are not.	3651	defined to be C<0>, then they are not. Embed watchers rely on most other
		3652	watcher types, which therefore must not be disabled.
2072		3653
2073	=item EV_STAT_ENABLE	3654	=item EV_STAT_ENABLE
2074		3655
2075	If undefined or defined to be C<1>, then stat watchers are supported. If	3656	If undefined or defined to be C<1>, then stat watchers are supported. If
2076	defined to be C<0>, then they are not.	3657	defined to be C<0>, then they are not.
…		…
2078	=item EV_FORK_ENABLE	3659	=item EV_FORK_ENABLE
2079		3660
2080	If undefined or defined to be C<1>, then fork watchers are supported. If	3661	If undefined or defined to be C<1>, then fork watchers are supported. If
2081	defined to be C<0>, then they are not.	3662	defined to be C<0>, then they are not.
2082		3663
		3664	=item EV_ASYNC_ENABLE
		3665
		3666	If undefined or defined to be C<1>, then async watchers are supported. If
		3667	defined to be C<0>, then they are not.
		3668
2083	=item EV_MINIMAL	3669	=item EV_MINIMAL
2084		3670
2085	If you need to shave off some kilobytes of code at the expense of some	3671	If you need to shave off some kilobytes of code at the expense of some
2086	speed, define this symbol to C<1>. Currently only used for gcc to override	3672	speed, define this symbol to C<1>. Currently this is used to override some
2087	some inlining decisions, saves roughly 30% codesize of amd64.	3673	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3674	much smaller 2-heap for timer management over the default 4-heap.
2088		3675
2089	=item EV_PID_HASHSIZE	3676	=item EV_PID_HASHSIZE
2090		3677
2091	C<ev_child> watchers use a small hash table to distribute workload by	3678	C<ev_child> watchers use a small hash table to distribute workload by
2092	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3679	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2093	than enough. If you need to manage thousands of children you might want to	3680	than enough. If you need to manage thousands of children you might want to
2094	increase this value (I<must> be a power of two).	3681	increase this value (I<must> be a power of two).
2095		3682
2096	=item EV_INOTIFY_HASHSIZE	3683	=item EV_INOTIFY_HASHSIZE
2097		3684
2098	C<ev_staz> watchers use a small hash table to distribute workload by	3685	C<ev_stat> watchers use a small hash table to distribute workload by
2099	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3686	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2100	usually more than enough. If you need to manage thousands of C<ev_stat>	3687	usually more than enough. If you need to manage thousands of C<ev_stat>
2101	watchers you might want to increase this value (I<must> be a power of	3688	watchers you might want to increase this value (I<must> be a power of
2102	two).	3689	two).
2103		3690
		3691	=item EV_USE_4HEAP
		3692
		3693	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3694	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3695	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3696	faster performance with many (thousands) of watchers.
		3697
		3698	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3699	(disabled).
		3700
		3701	=item EV_HEAP_CACHE_AT
		3702
		3703	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3704	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3705	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3706	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3707	but avoids random read accesses on heap changes. This improves performance
		3708	noticeably with many (hundreds) of watchers.
		3709
		3710	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3711	(disabled).
		3712
		3713	=item EV_VERIFY
		3714
		3715	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3716	be done: If set to C<0>, no internal verification code will be compiled
		3717	in. If set to C<1>, then verification code will be compiled in, but not
		3718	called. If set to C<2>, then the internal verification code will be
		3719	called once per loop, which can slow down libev. If set to C<3>, then the
		3720	verification code will be called very frequently, which will slow down
		3721	libev considerably.
		3722
		3723	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3724	C<0>.
		3725
2104	=item EV_COMMON	3726	=item EV_COMMON
2105		3727
2106	By default, all watchers have a C<void *data> member. By redefining	3728	By default, all watchers have a C<void *data> member. By redefining
2107	this macro to a something else you can include more and other types of	3729	this macro to a something else you can include more and other types of
2108	members. You have to define it each time you include one of the files,	3730	members. You have to define it each time you include one of the files,
2109	though, and it must be identical each time.	3731	though, and it must be identical each time.
2110		3732
2111	For example, the perl EV module uses something like this:	3733	For example, the perl EV module uses something like this:
2112		3734
2113	#define EV_COMMON \	3735	#define EV_COMMON \
2114	SV *self; /* contains this struct */ \	3736	SV *self; /* contains this struct */ \
2115	SV *cb_sv, *fh /* note no trailing ";" */	3737	SV *cb_sv, *fh /* note no trailing ";" */
2116		3738
2117	=item EV_CB_DECLARE (type)	3739	=item EV_CB_DECLARE (type)
2118		3740
2119	=item EV_CB_INVOKE (watcher, revents)	3741	=item EV_CB_INVOKE (watcher, revents)
2120		3742
2121	=item ev_set_cb (ev, cb)	3743	=item ev_set_cb (ev, cb)
2122		3744
2123	Can be used to change the callback member declaration in each watcher,	3745	Can be used to change the callback member declaration in each watcher,
2124	and the way callbacks are invoked and set. Must expand to a struct member	3746	and the way callbacks are invoked and set. Must expand to a struct member
2125	definition and a statement, respectively. See the F<ev.v> header file for	3747	definition and a statement, respectively. See the F<ev.h> header file for
2126	their default definitions. One possible use for overriding these is to	3748	their default definitions. One possible use for overriding these is to
2127	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3749	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2128	method calls instead of plain function calls in C++.	3750	method calls instead of plain function calls in C++.
		3751
		3752	=back
		3753
		3754	=head2 EXPORTED API SYMBOLS
		3755
		3756	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3757	exported symbols, you can use the provided F<Symbol.*> files which list
		3758	all public symbols, one per line:
		3759
		3760	Symbols.ev for libev proper
		3761	Symbols.event for the libevent emulation
		3762
		3763	This can also be used to rename all public symbols to avoid clashes with
		3764	multiple versions of libev linked together (which is obviously bad in
		3765	itself, but sometimes it is inconvenient to avoid this).
		3766
		3767	A sed command like this will create wrapper C<#define>'s that you need to
		3768	include before including F<ev.h>:
		3769
		3770	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3771
		3772	This would create a file F<wrap.h> which essentially looks like this:
		3773
		3774	#define ev_backend myprefix_ev_backend
		3775	#define ev_check_start myprefix_ev_check_start
		3776	#define ev_check_stop myprefix_ev_check_stop
		3777	...
2129		3778
2130	=head2 EXAMPLES	3779	=head2 EXAMPLES
2131		3780
2132	For a real-world example of a program the includes libev	3781	For a real-world example of a program the includes libev
2133	verbatim, you can have a look at the EV perl module	3782	verbatim, you can have a look at the EV perl module
…		…
2136	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	3785	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
2137	will be compiled. It is pretty complex because it provides its own header	3786	will be compiled. It is pretty complex because it provides its own header
2138	file.	3787	file.
2139		3788
2140	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3789	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2141	that everybody includes and which overrides some autoconf choices:	3790	that everybody includes and which overrides some configure choices:
2142		3791
		3792	#define EV_MINIMAL 1
2143	#define EV_USE_POLL 0	3793	#define EV_USE_POLL 0
2144	#define EV_MULTIPLICITY 0	3794	#define EV_MULTIPLICITY 0
2145	#define EV_PERIODICS 0	3795	#define EV_PERIODIC_ENABLE 0
		3796	#define EV_STAT_ENABLE 0
		3797	#define EV_FORK_ENABLE 0
2146	#define EV_CONFIG_H <config.h>	3798	#define EV_CONFIG_H <config.h>
		3799	#define EV_MINPRI 0
		3800	#define EV_MAXPRI 0
2147		3801
2148	#include "ev++.h"	3802	#include "ev++.h"
2149		3803
2150	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3804	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2151		3805
2152	#include "ev_cpp.h"	3806	#include "ev_cpp.h"
2153	#include "ev.c"	3807	#include "ev.c"
2154		3808
		3809	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2155		3810
		3811	=head2 THREADS AND COROUTINES
		3812
		3813	=head3 THREADS
		3814
		3815	All libev functions are reentrant and thread-safe unless explicitly
		3816	documented otherwise, but libev implements no locking itself. This means
		3817	that you can use as many loops as you want in parallel, as long as there
		3818	are no concurrent calls into any libev function with the same loop
		3819	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3820	of course): libev guarantees that different event loops share no data
		3821	structures that need any locking.
		3822
		3823	Or to put it differently: calls with different loop parameters can be done
		3824	concurrently from multiple threads, calls with the same loop parameter
		3825	must be done serially (but can be done from different threads, as long as
		3826	only one thread ever is inside a call at any point in time, e.g. by using
		3827	a mutex per loop).
		3828
		3829	Specifically to support threads (and signal handlers), libev implements
		3830	so-called C<ev_async> watchers, which allow some limited form of
		3831	concurrency on the same event loop, namely waking it up "from the
		3832	outside".
		3833
		3834	If you want to know which design (one loop, locking, or multiple loops
		3835	without or something else still) is best for your problem, then I cannot
		3836	help you, but here is some generic advice:
		3837
		3838	=over 4
		3839
		3840	=item * most applications have a main thread: use the default libev loop
		3841	in that thread, or create a separate thread running only the default loop.
		3842
		3843	This helps integrating other libraries or software modules that use libev
		3844	themselves and don't care/know about threading.
		3845
		3846	=item * one loop per thread is usually a good model.
		3847
		3848	Doing this is almost never wrong, sometimes a better-performance model
		3849	exists, but it is always a good start.
		3850
		3851	=item * other models exist, such as the leader/follower pattern, where one
		3852	loop is handed through multiple threads in a kind of round-robin fashion.
		3853
		3854	Choosing a model is hard - look around, learn, know that usually you can do
		3855	better than you currently do :-)
		3856
		3857	=item * often you need to talk to some other thread which blocks in the
		3858	event loop.
		3859
		3860	C<ev_async> watchers can be used to wake them up from other threads safely
		3861	(or from signal contexts...).
		3862
		3863	An example use would be to communicate signals or other events that only
		3864	work in the default loop by registering the signal watcher with the
		3865	default loop and triggering an C<ev_async> watcher from the default loop
		3866	watcher callback into the event loop interested in the signal.
		3867
		3868	=back
		3869
		3870	=head3 COROUTINES
		3871
		3872	Libev is very accommodating to coroutines ("cooperative threads"):
		3873	libev fully supports nesting calls to its functions from different
		3874	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3875	different coroutines, and switch freely between both coroutines running the
		3876	loop, as long as you don't confuse yourself). The only exception is that
		3877	you must not do this from C<ev_periodic> reschedule callbacks.
		3878
		3879	Care has been taken to ensure that libev does not keep local state inside
		3880	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3881	they do not call any callbacks.
		3882
		3883	=head2 COMPILER WARNINGS
		3884
		3885	Depending on your compiler and compiler settings, you might get no or a
		3886	lot of warnings when compiling libev code. Some people are apparently
		3887	scared by this.
		3888
		3889	However, these are unavoidable for many reasons. For one, each compiler
		3890	has different warnings, and each user has different tastes regarding
		3891	warning options. "Warn-free" code therefore cannot be a goal except when
		3892	targeting a specific compiler and compiler-version.
		3893
		3894	Another reason is that some compiler warnings require elaborate
		3895	workarounds, or other changes to the code that make it less clear and less
		3896	maintainable.
		3897
		3898	And of course, some compiler warnings are just plain stupid, or simply
		3899	wrong (because they don't actually warn about the condition their message
		3900	seems to warn about). For example, certain older gcc versions had some
		3901	warnings that resulted an extreme number of false positives. These have
		3902	been fixed, but some people still insist on making code warn-free with
		3903	such buggy versions.
		3904
		3905	While libev is written to generate as few warnings as possible,
		3906	"warn-free" code is not a goal, and it is recommended not to build libev
		3907	with any compiler warnings enabled unless you are prepared to cope with
		3908	them (e.g. by ignoring them). Remember that warnings are just that:
		3909	warnings, not errors, or proof of bugs.
		3910
		3911
		3912	=head2 VALGRIND
		3913
		3914	Valgrind has a special section here because it is a popular tool that is
		3915	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3916
		3917	If you think you found a bug (memory leak, uninitialised data access etc.)
		3918	in libev, then check twice: If valgrind reports something like:
		3919
		3920	==2274== definitely lost: 0 bytes in 0 blocks.
		3921	==2274== possibly lost: 0 bytes in 0 blocks.
		3922	==2274== still reachable: 256 bytes in 1 blocks.
		3923
		3924	Then there is no memory leak, just as memory accounted to global variables
		3925	is not a memleak - the memory is still being referenced, and didn't leak.
		3926
		3927	Similarly, under some circumstances, valgrind might report kernel bugs
		3928	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3929	although an acceptable workaround has been found here), or it might be
		3930	confused.
		3931
		3932	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3933	make it into some kind of religion.
		3934
		3935	If you are unsure about something, feel free to contact the mailing list
		3936	with the full valgrind report and an explanation on why you think this
		3937	is a bug in libev (best check the archives, too :). However, don't be
		3938	annoyed when you get a brisk "this is no bug" answer and take the chance
		3939	of learning how to interpret valgrind properly.
		3940
		3941	If you need, for some reason, empty reports from valgrind for your project
		3942	I suggest using suppression lists.
		3943
		3944
		3945	=head1 PORTABILITY NOTES
		3946
		3947	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3948
		3949	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3950	requires, and its I/O model is fundamentally incompatible with the POSIX
		3951	model. Libev still offers limited functionality on this platform in
		3952	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3953	descriptors. This only applies when using Win32 natively, not when using
		3954	e.g. cygwin.
		3955
		3956	Lifting these limitations would basically require the full
		3957	re-implementation of the I/O system. If you are into these kinds of
		3958	things, then note that glib does exactly that for you in a very portable
		3959	way (note also that glib is the slowest event library known to man).
		3960
		3961	There is no supported compilation method available on windows except
		3962	embedding it into other applications.
		3963
		3964	Sensible signal handling is officially unsupported by Microsoft - libev
		3965	tries its best, but under most conditions, signals will simply not work.
		3966
		3967	Not a libev limitation but worth mentioning: windows apparently doesn't
		3968	accept large writes: instead of resulting in a partial write, windows will
		3969	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3970	so make sure you only write small amounts into your sockets (less than a
		3971	megabyte seems safe, but this apparently depends on the amount of memory
		3972	available).
		3973
		3974	Due to the many, low, and arbitrary limits on the win32 platform and
		3975	the abysmal performance of winsockets, using a large number of sockets
		3976	is not recommended (and not reasonable). If your program needs to use
		3977	more than a hundred or so sockets, then likely it needs to use a totally
		3978	different implementation for windows, as libev offers the POSIX readiness
		3979	notification model, which cannot be implemented efficiently on windows
		3980	(due to Microsoft monopoly games).
		3981
		3982	A typical way to use libev under windows is to embed it (see the embedding
		3983	section for details) and use the following F<evwrap.h> header file instead
		3984	of F<ev.h>:
		3985
		3986	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3987	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3988
		3989	#include "ev.h"
		3990
		3991	And compile the following F<evwrap.c> file into your project (make sure
		3992	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3993
		3994	#include "evwrap.h"
		3995	#include "ev.c"
		3996
		3997	=over 4
		3998
		3999	=item The winsocket select function
		4000
		4001	The winsocket C<select> function doesn't follow POSIX in that it
		4002	requires socket I<handles> and not socket I<file descriptors> (it is
		4003	also extremely buggy). This makes select very inefficient, and also
		4004	requires a mapping from file descriptors to socket handles (the Microsoft
		4005	C runtime provides the function C<_open_osfhandle> for this). See the
		4006	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4007	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4008
		4009	The configuration for a "naked" win32 using the Microsoft runtime
		4010	libraries and raw winsocket select is:
		4011
		4012	#define EV_USE_SELECT 1
		4013	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4014
		4015	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4016	complexity in the O(n²) range when using win32.
		4017
		4018	=item Limited number of file descriptors
		4019
		4020	Windows has numerous arbitrary (and low) limits on things.
		4021
		4022	Early versions of winsocket's select only supported waiting for a maximum
		4023	of C<64> handles (probably owning to the fact that all windows kernels
		4024	can only wait for C<64> things at the same time internally; Microsoft
		4025	recommends spawning a chain of threads and wait for 63 handles and the
		4026	previous thread in each. Sounds great!).
		4027
		4028	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4029	to some high number (e.g. C<2048>) before compiling the winsocket select
		4030	call (which might be in libev or elsewhere, for example, perl and many
		4031	other interpreters do their own select emulation on windows).
		4032
		4033	Another limit is the number of file descriptors in the Microsoft runtime
		4034	libraries, which by default is C<64> (there must be a hidden I<64>
		4035	fetish or something like this inside Microsoft). You can increase this
		4036	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4037	(another arbitrary limit), but is broken in many versions of the Microsoft
		4038	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4039	(depending on windows version and/or the phase of the moon). To get more,
		4040	you need to wrap all I/O functions and provide your own fd management, but
		4041	the cost of calling select (O(n²)) will likely make this unworkable.
		4042
		4043	=back
		4044
		4045	=head2 PORTABILITY REQUIREMENTS
		4046
		4047	In addition to a working ISO-C implementation and of course the
		4048	backend-specific APIs, libev relies on a few additional extensions:
		4049
		4050	=over 4
		4051
		4052	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4053	calling conventions regardless of C<ev_watcher_type *>.
		4054
		4055	Libev assumes not only that all watcher pointers have the same internal
		4056	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4057	assumes that the same (machine) code can be used to call any watcher
		4058	callback: The watcher callbacks have different type signatures, but libev
		4059	calls them using an C<ev_watcher *> internally.
		4060
		4061	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4062
		4063	The type C<sig_atomic_t volatile> (or whatever is defined as
		4064	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4065	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4066	believed to be sufficiently portable.
		4067
		4068	=item C<sigprocmask> must work in a threaded environment
		4069
		4070	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4071	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4072	pthread implementations will either allow C<sigprocmask> in the "main
		4073	thread" or will block signals process-wide, both behaviours would
		4074	be compatible with libev. Interaction between C<sigprocmask> and
		4075	C<pthread_sigmask> could complicate things, however.
		4076
		4077	The most portable way to handle signals is to block signals in all threads
		4078	except the initial one, and run the default loop in the initial thread as
		4079	well.
		4080
		4081	=item C<long> must be large enough for common memory allocation sizes
		4082
		4083	To improve portability and simplify its API, libev uses C<long> internally
		4084	instead of C<size_t> when allocating its data structures. On non-POSIX
		4085	systems (Microsoft...) this might be unexpectedly low, but is still at
		4086	least 31 bits everywhere, which is enough for hundreds of millions of
		4087	watchers.
		4088
		4089	=item C<double> must hold a time value in seconds with enough accuracy
		4090
		4091	The type C<double> is used to represent timestamps. It is required to
		4092	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4093	enough for at least into the year 4000. This requirement is fulfilled by
		4094	implementations implementing IEEE 754, which is basically all existing
		4095	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4096	2200.
		4097
		4098	=back
		4099
		4100	If you know of other additional requirements drop me a note.
		4101
		4102
2156	=head1 COMPLEXITIES	4103	=head1 ALGORITHMIC COMPLEXITIES
2157		4104
2158	In this section the complexities of (many of) the algorithms used inside	4105	In this section the complexities of (many of) the algorithms used inside
2159	libev will be explained. For complexity discussions about backends see the	4106	libev will be documented. For complexity discussions about backends see
2160	documentation for C<ev_default_init>.	4107	the documentation for C<ev_default_init>.
		4108
		4109	All of the following are about amortised time: If an array needs to be
		4110	extended, libev needs to realloc and move the whole array, but this
		4111	happens asymptotically rarer with higher number of elements, so O(1) might
		4112	mean that libev does a lengthy realloc operation in rare cases, but on
		4113	average it is much faster and asymptotically approaches constant time.
2161		4114
2162	=over 4	4115	=over 4
2163		4116
2164	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4117	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2165		4118
		4119	This means that, when you have a watcher that triggers in one hour and
		4120	there are 100 watchers that would trigger before that, then inserting will
		4121	have to skip roughly seven (C<ld 100>) of these watchers.
		4122
2166	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4123	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2167		4124
		4125	That means that changing a timer costs less than removing/adding them,
		4126	as only the relative motion in the event queue has to be paid for.
		4127
2168	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4128	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2169		4129
		4130	These just add the watcher into an array or at the head of a list.
		4131
2170	=item Stopping check/prepare/idle watchers: O(1)	4132	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2171		4133
2172	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4134	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2173		4135
		4136	These watchers are stored in lists, so they need to be walked to find the
		4137	correct watcher to remove. The lists are usually short (you don't usually
		4138	have many watchers waiting for the same fd or signal: one is typical, two
		4139	is rare).
		4140
2174	=item Finding the next timer per loop iteration: O(1)	4141	=item Finding the next timer in each loop iteration: O(1)
		4142
		4143	By virtue of using a binary or 4-heap, the next timer is always found at a
		4144	fixed position in the storage array.
2175		4145
2176	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4146	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2177		4147
2178	=item Activating one watcher: O(1)	4148	A change means an I/O watcher gets started or stopped, which requires
		4149	libev to recalculate its status (and possibly tell the kernel, depending
		4150	on backend and whether C<ev_io_set> was used).
		4151
		4152	=item Activating one watcher (putting it into the pending state): O(1)
		4153
		4154	=item Priority handling: O(number_of_priorities)
		4155
		4156	Priorities are implemented by allocating some space for each
		4157	priority. When doing priority-based operations, libev usually has to
		4158	linearly search all the priorities, but starting/stopping and activating
		4159	watchers becomes O(1) with respect to priority handling.
		4160
		4161	=item Sending an ev_async: O(1)
		4162
		4163	=item Processing ev_async_send: O(number_of_async_watchers)
		4164
		4165	=item Processing signals: O(max_signal_number)
		4166
		4167	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4168	calls in the current loop iteration. Checking for async and signal events
		4169	involves iterating over all running async watchers or all signal numbers.
2179		4170
2180	=back	4171	=back
2181		4172
2182		4173
		4174	=head1 GLOSSARY
		4175
		4176	=over 4
		4177
		4178	=item active
		4179
		4180	A watcher is active as long as it has been started (has been attached to
		4181	an event loop) but not yet stopped (disassociated from the event loop).
		4182
		4183	=item application
		4184
		4185	In this document, an application is whatever is using libev.
		4186
		4187	=item callback
		4188
		4189	The address of a function that is called when some event has been
		4190	detected. Callbacks are being passed the event loop, the watcher that
		4191	received the event, and the actual event bitset.
		4192
		4193	=item callback invocation
		4194
		4195	The act of calling the callback associated with a watcher.
		4196
		4197	=item event
		4198
		4199	A change of state of some external event, such as data now being available
		4200	for reading on a file descriptor, time having passed or simply not having
		4201	any other events happening anymore.
		4202
		4203	In libev, events are represented as single bits (such as C<EV_READ> or
		4204	C<EV_TIMEOUT>).
		4205
		4206	=item event library
		4207
		4208	A software package implementing an event model and loop.
		4209
		4210	=item event loop
		4211
		4212	An entity that handles and processes external events and converts them
		4213	into callback invocations.
		4214
		4215	=item event model
		4216
		4217	The model used to describe how an event loop handles and processes
		4218	watchers and events.
		4219
		4220	=item pending
		4221
		4222	A watcher is pending as soon as the corresponding event has been detected,
		4223	and stops being pending as soon as the watcher will be invoked or its
		4224	pending status is explicitly cleared by the application.
		4225
		4226	A watcher can be pending, but not active. Stopping a watcher also clears
		4227	its pending status.
		4228
		4229	=item real time
		4230
		4231	The physical time that is observed. It is apparently strictly monotonic :)
		4232
		4233	=item wall-clock time
		4234
		4235	The time and date as shown on clocks. Unlike real time, it can actually
		4236	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4237	clock.
		4238
		4239	=item watcher
		4240
		4241	A data structure that describes interest in certain events. Watchers need
		4242	to be started (attached to an event loop) before they can receive events.
		4243
		4244	=item watcher invocation
		4245
		4246	The act of calling the callback associated with a watcher.
		4247
		4248	=back
		4249
2183	=head1 AUTHOR	4250	=head1 AUTHOR
2184		4251
2185	Marc Lehmann <libev@schmorp.de>.	4252	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2186		4253

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