ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.74 by root, Sat Dec 8 14:12:08 2007 UTC vs.
Revision 1.239 by root, Tue Apr 21 14:14:19 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
56		84
57	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occuring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	87	these event sources and provide your program with events.
60		88
61	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	96	watcher.
69		97
70	=head1 FEATURES	98	=head2 FEATURES
71		99
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
82		110
83	It also is quite fast (see this	111	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	112	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	113	for example).
86		114
87	=head1 CONVENTIONS	115	=head2 CONVENTIONS
88		116
89	Libev is very configurable. In this manual the default configuration will	117	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	118	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	119	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	120	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	121	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	122	name C<loop> (which is always of type C<ev_loop *>) will not have
		123	this argument.
95		124
96	=head1 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
97		126
98	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
100	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
102	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
103	it, you should treat it as such.	132	on it, you should treat it as some floating point value. Unlike the name
		133	component C<stamp> might indicate, it is also used for time differences
		134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
		155
104		156
105	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
106		158
107	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
108	library in any way.	160	library in any way.
…		…
113		165
114	Returns the current time as libev would use it. Please note that the	166	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	167	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	168	you actually want to know.
117		169
		170	=item ev_sleep (ev_tstamp interval)
		171
		172	Sleep for the given interval: The current thread will be blocked until
		173	either it is interrupted or the given time interval has passed. Basically
		174	this is a sub-second-resolution C<sleep ()>.
		175
118	=item int ev_version_major ()	176	=item int ev_version_major ()
119		177
120	=item int ev_version_minor ()	178	=item int ev_version_minor ()
121		179
122	You can find out the major and minor version numbers of the library	180	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	181	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	182	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	183	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	184	version of the library your program was compiled against.
127		185
		186	These version numbers refer to the ABI version of the library, not the
		187	release version.
		188
128	Usually, it's a good idea to terminate if the major versions mismatch,	189	Usually, it's a good idea to terminate if the major versions mismatch,
129	as this indicates an incompatible change. Minor versions are usually	190	as this indicates an incompatible change. Minor versions are usually
130	compatible to older versions, so a larger minor version alone is usually	191	compatible to older versions, so a larger minor version alone is usually
131	not a problem.	192	not a problem.
132		193
133	Example: Make sure we haven't accidentally been linked against the wrong	194	Example: Make sure we haven't accidentally been linked against the wrong
134	version.	195	version.
135		196
136	assert (("libev version mismatch",	197	assert (("libev version mismatch",
137	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
138	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
139		200
140	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
141		202
142	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	203	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
143	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
145	a description of the set values.	206	a description of the set values.
146		207
147	Example: make sure we have the epoll method, because yeah this is cool and	208	Example: make sure we have the epoll method, because yeah this is cool and
148	a must have and can we have a torrent of it please!!!11	209	a must have and can we have a torrent of it please!!!11
149		210
150	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
151	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
152		213
153	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
154		215
155	Return the set of all backends compiled into this binary of libev and also	216	Return the set of all backends compiled into this binary of libev and also
156	recommended for this platform. This set is often smaller than the one	217	recommended for this platform. This set is often smaller than the one
157	returned by C<ev_supported_backends>, as for example kqueue is broken on	218	returned by C<ev_supported_backends>, as for example kqueue is broken on
158	most BSDs and will not be autodetected unless you explicitly request it	219	most BSDs and will not be auto-detected unless you explicitly request it
159	(assuming you know what you are doing). This is the set of backends that	220	(assuming you know what you are doing). This is the set of backends that
160	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
161		222
162	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
163		224
…		…
167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
168	recommended ones.	229	recommended ones.
169		230
170	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
171		232
172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
173		234
174	Sets the allocation function to use (the prototype is similar - the	235	Sets the allocation function to use (the prototype is similar - the
175	semantics is identical - to the realloc C function). It is used to	236	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
176	allocate and free memory (no surprises here). If it returns zero when	237	used to allocate and free memory (no surprises here). If it returns zero
177	memory needs to be allocated, the library might abort or take some	238	when memory needs to be allocated (C<size != 0>), the library might abort
178	potentially destructive action. The default is your system realloc	239	or take some potentially destructive action.
179	function.	240
		241	Since some systems (at least OpenBSD and Darwin) fail to implement
		242	correct C<realloc> semantics, libev will use a wrapper around the system
		243	C<realloc> and C<free> functions by default.
180		244
181	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
182	free some memory if it cannot allocate memory, to use a special allocator,	246	free some memory if it cannot allocate memory, to use a special allocator,
183	or even to sleep a while and retry until some memory is available.	247	or even to sleep a while and retry until some memory is available.
184		248
185	Example: Replace the libev allocator with one that waits a bit and then	249	Example: Replace the libev allocator with one that waits a bit and then
186	retries).	250	retries (example requires a standards-compliant C<realloc>).
187		251
188	static void *	252	static void *
189	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
190	{	254	{
191	for (;;)	255	for (;;)
…		…
200	}	264	}
201		265
202	...	266	...
203	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
204		268
205	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
206		270
207	Set the callback function to call on a retryable syscall error (such	271	Set the callback function to call on a retryable system call error (such
208	as failed select, poll, epoll_wait). The message is a printable string	272	as failed select, poll, epoll_wait). The message is a printable string
209	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
210	callback is set, then libev will expect it to remedy the sitution, no	274	callback is set, then libev will expect it to remedy the situation, no
211	matter what, when it returns. That is, libev will generally retry the	275	matter what, when it returns. That is, libev will generally retry the
212	requested operation, or, if the condition doesn't go away, do bad stuff	276	requested operation, or, if the condition doesn't go away, do bad stuff
213	(such as abort).	277	(such as abort).
214		278
215	Example: This is basically the same thing that libev does internally, too.	279	Example: This is basically the same thing that libev does internally, too.
…		…
226		290
227	=back	291	=back
228		292
229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
230		294
231	An event loop is described by a C<struct ev_loop *>. The library knows two	295	An event loop is described by a C<struct ev_loop *> (the C<struct>
232	types of such loops, the I<default> loop, which supports signals and child	296	is I<not> optional in this case, as there is also an C<ev_loop>
233	events, and dynamically created loops which do not.	297	I<function>).
234		298
235	If you use threads, a common model is to run the default event loop	299	The library knows two types of such loops, the I<default> loop, which
236	in your main thread (or in a separate thread) and for each thread you	300	supports signals and child events, and dynamically created loops which do
237	create, you also create another event loop. Libev itself does no locking	301	not.
238	whatsoever, so if you mix calls to the same event loop in different
239	threads, make sure you lock (this is usually a bad idea, though, even if
240	done correctly, because it's hideous and inefficient).
241		302
242	=over 4	303	=over 4
243		304
244	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
245		306
…		…
249	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
250		311
251	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
252	function.	313	function.
253		314
		315	Note that this function is I<not> thread-safe, so if you want to use it
		316	from multiple threads, you have to lock (note also that this is unlikely,
		317	as loops cannot be shared easily between threads anyway).
		318
		319	The default loop is the only loop that can handle C<ev_signal> and
		320	C<ev_child> watchers, and to do this, it always registers a handler
		321	for C<SIGCHLD>. If this is a problem for your application you can either
		322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		324	C<ev_default_init>.
		325
254	The flags argument can be used to specify special behaviour or specific	326	The flags argument can be used to specify special behaviour or specific
255	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	327	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
256		328
257	The following flags are supported:	329	The following flags are supported:
258		330
…		…
263	The default flags value. Use this if you have no clue (it's the right	335	The default flags value. Use this if you have no clue (it's the right
264	thing, believe me).	336	thing, believe me).
265		337
266	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
267		339
268	If this flag bit is ored into the flag value (or the program runs setuid	340	If this flag bit is or'ed into the flag value (or the program runs setuid
269	or setgid) then libev will I<not> look at the environment variable	341	or setgid) then libev will I<not> look at the environment variable
270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
271	override the flags completely if it is found in the environment. This is	343	override the flags completely if it is found in the environment. This is
272	useful to try out specific backends to test their performance, or to work	344	useful to try out specific backends to test their performance, or to work
273	around bugs.	345	around bugs.
…		…
279	enabling this flag.	351	enabling this flag.
280		352
281	This works by calling C<getpid ()> on every iteration of the loop,	353	This works by calling C<getpid ()> on every iteration of the loop,
282	and thus this might slow down your event loop if you do a lot of loop	354	and thus this might slow down your event loop if you do a lot of loop
283	iterations and little real work, but is usually not noticeable (on my	355	iterations and little real work, but is usually not noticeable (on my
284	Linux system for example, C<getpid> is actually a simple 5-insn sequence	356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
285	without a syscall and thus I<very> fast, but my Linux system also has	357	without a system call and thus I<very> fast, but my GNU/Linux system also has
286	C<pthread_atfork> which is even faster).	358	C<pthread_atfork> which is even faster).
287		359
288	The big advantage of this flag is that you can forget about fork (and	360	The big advantage of this flag is that you can forget about fork (and
289	forget about forgetting to tell libev about forking) when you use this	361	forget about forgetting to tell libev about forking) when you use this
290	flag.	362	flag.
291		363
292	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
293	environment variable.	365	environment variable.
294		366
295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
296		368
297	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
298	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,
299	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
300	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
301	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).
302		385
303	=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)
304		387
305	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
306	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
307	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
308	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>.
309		397
310	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
311		399
312	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,
313	but it scales phenomenally better. While poll and select usually scale like	401	but it scales phenomenally better. While poll and select usually scale
314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	402	like O(total_fds) where n is the total number of fds (or the highest fd),
315	either O(1) or O(active_fds).	403	epoll scales either O(1) or O(active_fds).
316		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
317	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
318	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
319	(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
320	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
321	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.
322		428
323	Please note that epoll sometimes generates spurious notifications, so you	429	Best performance from this backend is achieved by not unregistering all
324	need to use non-blocking I/O or other means to avoid blocking when no data	430	watchers for a file descriptor until it has been closed, if possible,
325	(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>.
326		446
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		448
329	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
330	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
331	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
332	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
333	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
334	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.
335		462
336	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
337	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
338	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
339	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
340	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>.
341		483
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		485
344	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.
345		490
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		492
348	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,
349	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)).
350		495
351	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
352	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
353	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>.
354		512
355	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
356		514
357	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
358	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
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	517	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		518
		519	It is definitely not recommended to use this flag.
		520
361	=back	521	=back
362		522
363	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
364	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
365	specified, most compiled-in backend will be tried, usually in reverse	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
366	order of their flag values :)
367		526
368	The most typical usage is like this:	527	Example: This is the most typical usage.
369		528
370	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372		531
373	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
374	environment settings to be taken into account:	533	environment settings to be taken into account:
375		534
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377		536
378	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
379	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
380	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
381		541
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383		543
384	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
385		545
386	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
387	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
388	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
389	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
390		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
391	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.
392		556
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	558	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
396		560
397	=item ev_default_destroy ()	561	=item ev_default_destroy ()
398		562
399	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
400	etc.). None of the active event watchers will be stopped in the normal	564	etc.). None of the active event watchers will be stopped in the normal
401	sense, so e.g. C<ev_is_active> might still return true. It is your	565	sense, so e.g. C<ev_is_active> might still return true. It is your
402	responsibility to either stop all watchers cleanly yoursef I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
403	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
404	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
405	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>).
406		579
407	=item ev_loop_destroy (loop)	580	=item ev_loop_destroy (loop)
408		581
409	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
410	earlier call to C<ev_loop_new>.	583	earlier call to C<ev_loop_new>.
411		584
412	=item ev_default_fork ()	585	=item ev_default_fork ()
413		586
		587	This function sets a flag that causes subsequent C<ev_loop> iterations
414	This function reinitialises the kernel state for backends that have	588	to reinitialise the kernel state for backends that have one. Despite the
415	one. Despite the name, you can call it anytime, but it makes most sense	589	name, you can call it anytime, but it makes most sense after forking, in
416	after forking, in either the parent or child process (or both, but that	590	the child process (or both child and parent, but that again makes little
417	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.
418		593
419	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
420	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
421	fork+exec, you don't have to call it.	596	you just fork+exec, you don't have to call it at all.
422		597
423	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
424	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
425	quite nicely into a call to C<pthread_atfork>:	600	quite nicely into a call to C<pthread_atfork>:
426		601
427	pthread_atfork (0, 0, ev_default_fork);	602	pthread_atfork (0, 0, ev_default_fork);
428		603
429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
430	without calling this function, so if you force one of those backends you
431	do not need to care.
432
433	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
434		605
435	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
436	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
437	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.
438		615
439	=item unsigned int ev_loop_count (loop)	616	=item unsigned int ev_loop_count (loop)
440		617
441	Returns the count of loop iterations for the loop, which is identical to	618	Returns the count of loop iterations for the loop, which is identical to
442	the number of times libev did poll for new events. It starts at C<0> and	619	the number of times libev did poll for new events. It starts at C<0> and
…		…
455		632
456	Returns the current "event loop time", which is the time the event loop	633	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	634	received events and started processing them. This timestamp does not
458	change as long as callbacks are being processed, and this is also the base	635	change as long as callbacks are being processed, and this is also the base
459	time used for relative timers. You can treat it as the timestamp of the	636	time used for relative timers. You can treat it as the timestamp of the
460	event occuring (or more correctly, libev finding out about it).	637	event occurring (or more correctly, libev finding out about it).
		638
		639	=item ev_now_update (loop)
		640
		641	Establishes the current time by querying the kernel, updating the time
		642	returned by C<ev_now ()> in the progress. This is a costly operation and
		643	is usually done automatically within C<ev_loop ()>.
		644
		645	This function is rarely useful, but when some event callback runs for a
		646	very long time without entering the event loop, updating libev's idea of
		647	the current time is a good idea.
		648
		649	See also L<The special problem of time updates> in the C<ev_timer> section.
		650
		651	=item ev_suspend (loop)
		652
		653	=item ev_resume (loop)
		654
		655	These two functions suspend and resume a loop, for use when the loop is
		656	not used for a while and timeouts should not be processed.
		657
		658	A typical use case would be an interactive program such as a game: When
		659	the user presses C<^Z> to suspend the game and resumes it an hour later it
		660	would be best to handle timeouts as if no time had actually passed while
		661	the program was suspended. This can be achieved by calling C<ev_suspend>
		662	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		663	C<ev_resume> directly afterwards to resume timer processing.
		664
		665	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		666	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		667	will be rescheduled (that is, they will lose any events that would have
		668	occured while suspended).
		669
		670	After calling C<ev_suspend> you B<must not> call I<any> function on the
		671	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		672	without a previous call to C<ev_suspend>.
		673
		674	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		675	event loop time (see C<ev_now_update>).
461		676
462	=item ev_loop (loop, int flags)	677	=item ev_loop (loop, int flags)
463		678
464	Finally, this is it, the event handler. This function usually is called	679	Finally, this is it, the event handler. This function usually is called
465	after you initialised all your watchers and you want to start handling	680	after you initialised all your watchers and you want to start handling
…		…
468	If the flags argument is specified as C<0>, it will not return until	683	If the flags argument is specified as C<0>, it will not return until
469	either no event watchers are active anymore or C<ev_unloop> was called.	684	either no event watchers are active anymore or C<ev_unloop> was called.
470		685
471	Please note that an explicit C<ev_unloop> is usually better than	686	Please note that an explicit C<ev_unloop> is usually better than
472	relying on all watchers to be stopped when deciding when a program has	687	relying on all watchers to be stopped when deciding when a program has
473	finished (especially in interactive programs), but having a program that	688	finished (especially in interactive programs), but having a program
474	automatically loops as long as it has to and no longer by virtue of	689	that automatically loops as long as it has to and no longer by virtue
475	relying on its watchers stopping correctly is a thing of beauty.	690	of relying on its watchers stopping correctly, that is truly a thing of
		691	beauty.
476		692
477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	693	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
478	those events and any outstanding ones, but will not block your process in	694	those events and any already outstanding ones, but will not block your
479	case there are no events and will return after one iteration of the loop.	695	process in case there are no events and will return after one iteration of
		696	the loop.
480		697
481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	698	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
482	neccessary) and will handle those and any outstanding ones. It will block	699	necessary) and will handle those and any already outstanding ones. It
483	your process until at least one new event arrives, and will return after	700	will block your process until at least one new event arrives (which could
484	one iteration of the loop. This is useful if you are waiting for some	701	be an event internal to libev itself, so there is no guarantee that a
485	external event in conjunction with something not expressible using other	702	user-registered callback will be called), and will return after one
		703	iteration of the loop.
		704
		705	This is useful if you are waiting for some external event in conjunction
		706	with something not expressible using other libev watchers (i.e. "roll your
486	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	707	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
487	usually a better approach for this kind of thing.	708	usually a better approach for this kind of thing.
488		709
489	Here are the gory details of what C<ev_loop> does:	710	Here are the gory details of what C<ev_loop> does:
490		711
491	* If there are no active watchers (reference count is zero), return.	712	- Before the first iteration, call any pending watchers.
492	- Queue prepare watchers and then call all outstanding watchers.	713	* If EVFLAG_FORKCHECK was used, check for a fork.
		714	- If a fork was detected (by any means), queue and call all fork watchers.
		715	- Queue and call all prepare watchers.
493	- If we have been forked, recreate the kernel state.	716	- If we have been forked, detach and recreate the kernel state
		717	as to not disturb the other process.
494	- Update the kernel state with all outstanding changes.	718	- Update the kernel state with all outstanding changes.
495	- Update the "event loop time".	719	- Update the "event loop time" (ev_now ()).
496	- Calculate for how long to block.	720	- Calculate for how long to sleep or block, if at all
		721	(active idle watchers, EVLOOP_NONBLOCK or not having
		722	any active watchers at all will result in not sleeping).
		723	- Sleep if the I/O and timer collect interval say so.
497	- Block the process, waiting for any events.	724	- Block the process, waiting for any events.
498	- Queue all outstanding I/O (fd) events.	725	- Queue all outstanding I/O (fd) events.
499	- Update the "event loop time" and do time jump handling.	726	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
500	- Queue all outstanding timers.	727	- Queue all expired timers.
501	- Queue all outstanding periodics.	728	- Queue all expired periodics.
502	- If no events are pending now, queue all idle watchers.	729	- Unless any events are pending now, queue all idle watchers.
503	- Queue all check watchers.	730	- Queue all check watchers.
504	- Call all queued watchers in reverse order (i.e. check watchers first).	731	- Call all queued watchers in reverse order (i.e. check watchers first).
505	Signals and child watchers are implemented as I/O watchers, and will	732	Signals and child watchers are implemented as I/O watchers, and will
506	be handled here by queueing them when their watcher gets executed.	733	be handled here by queueing them when their watcher gets executed.
507	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	734	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
508	were used, return, otherwise continue with step *.	735	were used, or there are no active watchers, return, otherwise
		736	continue with step *.
509		737
510	Example: Queue some jobs and then loop until no events are outsanding	738	Example: Queue some jobs and then loop until no events are outstanding
511	anymore.	739	anymore.
512		740
513	... queue jobs here, make sure they register event watchers as long	741	... queue jobs here, make sure they register event watchers as long
514	... as they still have work to do (even an idle watcher will do..)	742	... as they still have work to do (even an idle watcher will do..)
515	ev_loop (my_loop, 0);	743	ev_loop (my_loop, 0);
516	... jobs done. yeah!	744	... jobs done or somebody called unloop. yeah!
517		745
518	=item ev_unloop (loop, how)	746	=item ev_unloop (loop, how)
519		747
520	Can be used to make a call to C<ev_loop> return early (but only after it	748	Can be used to make a call to C<ev_loop> return early (but only after it
521	has processed all outstanding events). The C<how> argument must be either	749	has processed all outstanding events). The C<how> argument must be either
522	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	750	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
523	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	751	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
524		752
		753	This "unloop state" will be cleared when entering C<ev_loop> again.
		754
		755	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		756
525	=item ev_ref (loop)	757	=item ev_ref (loop)
526		758
527	=item ev_unref (loop)	759	=item ev_unref (loop)
528		760
529	Ref/unref can be used to add or remove a reference count on the event	761	Ref/unref can be used to add or remove a reference count on the event
530	loop: Every watcher keeps one reference, and as long as the reference	762	loop: Every watcher keeps one reference, and as long as the reference
531	count is nonzero, C<ev_loop> will not return on its own. If you have	763	count is nonzero, C<ev_loop> will not return on its own.
		764
532	a watcher you never unregister that should not keep C<ev_loop> from	765	If you have a watcher you never unregister that should not keep C<ev_loop>
533	returning, ev_unref() after starting, and ev_ref() before stopping it. For	766	from returning, call ev_unref() after starting, and ev_ref() before
		767	stopping it.
		768
534	example, libev itself uses this for its internal signal pipe: It is not	769	As an example, libev itself uses this for its internal signal pipe: It
535	visible to the libev user and should not keep C<ev_loop> from exiting if	770	is not visible to the libev user and should not keep C<ev_loop> from
536	no event watchers registered by it are active. It is also an excellent	771	exiting if no event watchers registered by it are active. It is also an
537	way to do this for generic recurring timers or from within third-party	772	excellent way to do this for generic recurring timers or from within
538	libraries. Just remember to I<unref after start> and I<ref before stop>.	773	third-party libraries. Just remember to I<unref after start> and I<ref
		774	before stop> (but only if the watcher wasn't active before, or was active
		775	before, respectively. Note also that libev might stop watchers itself
		776	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		777	in the callback).
539		778
540	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	779	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
541	running when nothing else is active.	780	running when nothing else is active.
542		781
543	struct ev_signal exitsig;	782	ev_signal exitsig;
544	ev_signal_init (&exitsig, sig_cb, SIGINT);	783	ev_signal_init (&exitsig, sig_cb, SIGINT);
545	ev_signal_start (loop, &exitsig);	784	ev_signal_start (loop, &exitsig);
546	evf_unref (loop);	785	evf_unref (loop);
547		786
548	Example: For some weird reason, unregister the above signal handler again.	787	Example: For some weird reason, unregister the above signal handler again.
549		788
550	ev_ref (loop);	789	ev_ref (loop);
551	ev_signal_stop (loop, &exitsig);	790	ev_signal_stop (loop, &exitsig);
		791
		792	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		793
		794	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		795
		796	These advanced functions influence the time that libev will spend waiting
		797	for events. Both time intervals are by default C<0>, meaning that libev
		798	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		799	latency.
		800
		801	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		802	allows libev to delay invocation of I/O and timer/periodic callbacks
		803	to increase efficiency of loop iterations (or to increase power-saving
		804	opportunities).
		805
		806	The idea is that sometimes your program runs just fast enough to handle
		807	one (or very few) event(s) per loop iteration. While this makes the
		808	program responsive, it also wastes a lot of CPU time to poll for new
		809	events, especially with backends like C<select ()> which have a high
		810	overhead for the actual polling but can deliver many events at once.
		811
		812	By setting a higher I<io collect interval> you allow libev to spend more
		813	time collecting I/O events, so you can handle more events per iteration,
		814	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		815	C<ev_timer>) will be not affected. Setting this to a non-null value will
		816	introduce an additional C<ev_sleep ()> call into most loop iterations.
		817
		818	Likewise, by setting a higher I<timeout collect interval> you allow libev
		819	to spend more time collecting timeouts, at the expense of increased
		820	latency/jitter/inexactness (the watcher callback will be called
		821	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		822	value will not introduce any overhead in libev.
		823
		824	Many (busy) programs can usually benefit by setting the I/O collect
		825	interval to a value near C<0.1> or so, which is often enough for
		826	interactive servers (of course not for games), likewise for timeouts. It
		827	usually doesn't make much sense to set it to a lower value than C<0.01>,
		828	as this approaches the timing granularity of most systems.
		829
		830	Setting the I<timeout collect interval> can improve the opportunity for
		831	saving power, as the program will "bundle" timer callback invocations that
		832	are "near" in time together, by delaying some, thus reducing the number of
		833	times the process sleeps and wakes up again. Another useful technique to
		834	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		835	they fire on, say, one-second boundaries only.
		836
		837	=item ev_loop_verify (loop)
		838
		839	This function only does something when C<EV_VERIFY> support has been
		840	compiled in, which is the default for non-minimal builds. It tries to go
		841	through all internal structures and checks them for validity. If anything
		842	is found to be inconsistent, it will print an error message to standard
		843	error and call C<abort ()>.
		844
		845	This can be used to catch bugs inside libev itself: under normal
		846	circumstances, this function will never abort as of course libev keeps its
		847	data structures consistent.
552		848
553	=back	849	=back
554		850
555		851
556	=head1 ANATOMY OF A WATCHER	852	=head1 ANATOMY OF A WATCHER
		853
		854	In the following description, uppercase C<TYPE> in names stands for the
		855	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		856	watchers and C<ev_io_start> for I/O watchers.
557		857
558	A watcher is a structure that you create and register to record your	858	A watcher is a structure that you create and register to record your
559	interest in some event. For instance, if you want to wait for STDIN to	859	interest in some event. For instance, if you want to wait for STDIN to
560	become readable, you would create an C<ev_io> watcher for that:	860	become readable, you would create an C<ev_io> watcher for that:
561		861
562	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	862	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
563	{	863	{
564	ev_io_stop (w);	864	ev_io_stop (w);
565	ev_unloop (loop, EVUNLOOP_ALL);	865	ev_unloop (loop, EVUNLOOP_ALL);
566	}	866	}
567		867
568	struct ev_loop *loop = ev_default_loop (0);	868	struct ev_loop *loop = ev_default_loop (0);
		869
569	struct ev_io stdin_watcher;	870	ev_io stdin_watcher;
		871
570	ev_init (&stdin_watcher, my_cb);	872	ev_init (&stdin_watcher, my_cb);
571	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	873	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
572	ev_io_start (loop, &stdin_watcher);	874	ev_io_start (loop, &stdin_watcher);
		875
573	ev_loop (loop, 0);	876	ev_loop (loop, 0);
574		877
575	As you can see, you are responsible for allocating the memory for your	878	As you can see, you are responsible for allocating the memory for your
576	watcher structures (and it is usually a bad idea to do this on the stack,	879	watcher structures (and it is I<usually> a bad idea to do this on the
577	although this can sometimes be quite valid).	880	stack).
		881
		882	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		883	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
578		884
579	Each watcher structure must be initialised by a call to C<ev_init	885	Each watcher structure must be initialised by a call to C<ev_init
580	(watcher *, callback)>, which expects a callback to be provided. This	886	(watcher *, callback)>, which expects a callback to be provided. This
581	callback gets invoked each time the event occurs (or, in the case of io	887	callback gets invoked each time the event occurs (or, in the case of I/O
582	watchers, each time the event loop detects that the file descriptor given	888	watchers, each time the event loop detects that the file descriptor given
583	is readable and/or writable).	889	is readable and/or writable).
584		890
585	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	891	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
586	with arguments specific to this watcher type. There is also a macro	892	macro to configure it, with arguments specific to the watcher type. There
587	to combine initialisation and setting in one call: C<< ev_<type>_init	893	is also a macro to combine initialisation and setting in one call: C<<
588	(watcher *, callback, ...) >>.	894	ev_TYPE_init (watcher *, callback, ...) >>.
589		895
590	To make the watcher actually watch out for events, you have to start it	896	To make the watcher actually watch out for events, you have to start it
591	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	897	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
592	*) >>), and you can stop watching for events at any time by calling the	898	*) >>), and you can stop watching for events at any time by calling the
593	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	899	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
594		900
595	As long as your watcher is active (has been started but not stopped) you	901	As long as your watcher is active (has been started but not stopped) you
596	must not touch the values stored in it. Most specifically you must never	902	must not touch the values stored in it. Most specifically you must never
597	reinitialise it or call its C<set> macro.	903	reinitialise it or call its C<ev_TYPE_set> macro.
598		904
599	Each and every callback receives the event loop pointer as first, the	905	Each and every callback receives the event loop pointer as first, the
600	registered watcher structure as second, and a bitset of received events as	906	registered watcher structure as second, and a bitset of received events as
601	third argument.	907	third argument.
602		908
…		…
656	=item C<EV_FORK>	962	=item C<EV_FORK>
657		963
658	The event loop has been resumed in the child process after fork (see	964	The event loop has been resumed in the child process after fork (see
659	C<ev_fork>).	965	C<ev_fork>).
660		966
		967	=item C<EV_ASYNC>
		968
		969	The given async watcher has been asynchronously notified (see C<ev_async>).
		970
		971	=item C<EV_CUSTOM>
		972
		973	Not ever sent (or otherwise used) by libev itself, but can be freely used
		974	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		975
661	=item C<EV_ERROR>	976	=item C<EV_ERROR>
662		977
663	An unspecified error has occured, the watcher has been stopped. This might	978	An unspecified error has occurred, the watcher has been stopped. This might
664	happen because the watcher could not be properly started because libev	979	happen because the watcher could not be properly started because libev
665	ran out of memory, a file descriptor was found to be closed or any other	980	ran out of memory, a file descriptor was found to be closed or any other
		981	problem. Libev considers these application bugs.
		982
666	problem. You best act on it by reporting the problem and somehow coping	983	You best act on it by reporting the problem and somehow coping with the
667	with the watcher being stopped.	984	watcher being stopped. Note that well-written programs should not receive
		985	an error ever, so when your watcher receives it, this usually indicates a
		986	bug in your program.
668		987
669	Libev will usually signal a few "dummy" events together with an error,	988	Libev will usually signal a few "dummy" events together with an error, for
670	for example it might indicate that a fd is readable or writable, and if	989	example it might indicate that a fd is readable or writable, and if your
671	your callbacks is well-written it can just attempt the operation and cope	990	callbacks is well-written it can just attempt the operation and cope with
672	with the error from read() or write(). This will not work in multithreaded	991	the error from read() or write(). This will not work in multi-threaded
673	programs, though, so beware.	992	programs, though, as the fd could already be closed and reused for another
		993	thing, so beware.
674		994
675	=back	995	=back
676		996
677	=head2 GENERIC WATCHER FUNCTIONS	997	=head2 GENERIC WATCHER FUNCTIONS
678
679	In the following description, C<TYPE> stands for the watcher type,
680	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
681		998
682	=over 4	999	=over 4
683		1000
684	=item C<ev_init> (ev_TYPE *watcher, callback)	1001	=item C<ev_init> (ev_TYPE *watcher, callback)
685		1002
…		…
691	which rolls both calls into one.	1008	which rolls both calls into one.
692		1009
693	You can reinitialise a watcher at any time as long as it has been stopped	1010	You can reinitialise a watcher at any time as long as it has been stopped
694	(or never started) and there are no pending events outstanding.	1011	(or never started) and there are no pending events outstanding.
695		1012
696	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1013	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
697	int revents)>.	1014	int revents)>.
		1015
		1016	Example: Initialise an C<ev_io> watcher in two steps.
		1017
		1018	ev_io w;
		1019	ev_init (&w, my_cb);
		1020	ev_io_set (&w, STDIN_FILENO, EV_READ);
698		1021
699	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1022	=item C<ev_TYPE_set> (ev_TYPE *, [args])
700		1023
701	This macro initialises the type-specific parts of a watcher. You need to	1024	This macro initialises the type-specific parts of a watcher. You need to
702	call C<ev_init> at least once before you call this macro, but you can	1025	call C<ev_init> at least once before you call this macro, but you can
…		…
705	difference to the C<ev_init> macro).	1028	difference to the C<ev_init> macro).
706		1029
707	Although some watcher types do not have type-specific arguments	1030	Although some watcher types do not have type-specific arguments
708	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1031	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
709		1032
		1033	See C<ev_init>, above, for an example.
		1034
710	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1035	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
711		1036
712	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1037	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
713	calls into a single call. This is the most convinient method to initialise	1038	calls into a single call. This is the most convenient method to initialise
714	a watcher. The same limitations apply, of course.	1039	a watcher. The same limitations apply, of course.
		1040
		1041	Example: Initialise and set an C<ev_io> watcher in one step.
		1042
		1043	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
715		1044
716	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1045	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
717		1046
718	Starts (activates) the given watcher. Only active watchers will receive	1047	Starts (activates) the given watcher. Only active watchers will receive
719	events. If the watcher is already active nothing will happen.	1048	events. If the watcher is already active nothing will happen.
720		1049
		1050	Example: Start the C<ev_io> watcher that is being abused as example in this
		1051	whole section.
		1052
		1053	ev_io_start (EV_DEFAULT_UC, &w);
		1054
721	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1055	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
722		1056
723	Stops the given watcher again (if active) and clears the pending	1057	Stops the given watcher if active, and clears the pending status (whether
		1058	the watcher was active or not).
		1059
724	status. It is possible that stopped watchers are pending (for example,	1060	It is possible that stopped watchers are pending - for example,
725	non-repeating timers are being stopped when they become pending), but	1061	non-repeating timers are being stopped when they become pending - but
726	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1062	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
727	you want to free or reuse the memory used by the watcher it is therefore a	1063	pending. If you want to free or reuse the memory used by the watcher it is
728	good idea to always call its C<ev_TYPE_stop> function.	1064	therefore a good idea to always call its C<ev_TYPE_stop> function.
729		1065
730	=item bool ev_is_active (ev_TYPE *watcher)	1066	=item bool ev_is_active (ev_TYPE *watcher)
731		1067
732	Returns a true value iff the watcher is active (i.e. it has been started	1068	Returns a true value iff the watcher is active (i.e. it has been started
733	and not yet been stopped). As long as a watcher is active you must not modify	1069	and not yet been stopped). As long as a watcher is active you must not modify
…		…
759	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1095	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
760	(default: C<-2>). Pending watchers with higher priority will be invoked	1096	(default: C<-2>). Pending watchers with higher priority will be invoked
761	before watchers with lower priority, but priority will not keep watchers	1097	before watchers with lower priority, but priority will not keep watchers
762	from being executed (except for C<ev_idle> watchers).	1098	from being executed (except for C<ev_idle> watchers).
763		1099
764	This means that priorities are I<only> used for ordering callback
765	invocation after new events have been received. This is useful, for
766	example, to reduce latency after idling, or more often, to bind two
767	watchers on the same event and make sure one is called first.
768
769	If you need to suppress invocation when higher priority events are pending	1100	If you need to suppress invocation when higher priority events are pending
770	you need to look at C<ev_idle> watchers, which provide this functionality.	1101	you need to look at C<ev_idle> watchers, which provide this functionality.
771		1102
772	You I<must not> change the priority of a watcher as long as it is active or	1103	You I<must not> change the priority of a watcher as long as it is active or
773	pending.	1104	pending.
774		1105
		1106	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1107	fine, as long as you do not mind that the priority value you query might
		1108	or might not have been clamped to the valid range.
		1109
775	The default priority used by watchers when no priority has been set is	1110	The default priority used by watchers when no priority has been set is
776	always C<0>, which is supposed to not be too high and not be too low :).	1111	always C<0>, which is supposed to not be too high and not be too low :).
777		1112
778	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1113	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
779	fine, as long as you do not mind that the priority value you query might	1114	priorities.
780	or might not have been adjusted to be within valid range.
781		1115
782	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1116	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
783		1117
784	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1118	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
785	C<loop> nor C<revents> need to be valid as long as the watcher callback	1119	C<loop> nor C<revents> need to be valid as long as the watcher callback
786	can deal with that fact.	1120	can deal with that fact, as both are simply passed through to the
		1121	callback.
787		1122
788	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1123	=item int ev_clear_pending (loop, ev_TYPE *watcher)
789		1124
790	If the watcher is pending, this function returns clears its pending status	1125	If the watcher is pending, this function clears its pending status and
791	and returns its C<revents> bitset (as if its callback was invoked). If the	1126	returns its C<revents> bitset (as if its callback was invoked). If the
792	watcher isn't pending it does nothing and returns C<0>.	1127	watcher isn't pending it does nothing and returns C<0>.
793		1128
		1129	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1130	callback to be invoked, which can be accomplished with this function.
		1131
794	=back	1132	=back
795		1133
796		1134
797	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1135	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
798		1136
799	Each watcher has, by default, a member C<void *data> that you can change	1137	Each watcher has, by default, a member C<void *data> that you can change
800	and read at any time, libev will completely ignore it. This can be used	1138	and read at any time: libev will completely ignore it. This can be used
801	to associate arbitrary data with your watcher. If you need more data and	1139	to associate arbitrary data with your watcher. If you need more data and
802	don't want to allocate memory and store a pointer to it in that data	1140	don't want to allocate memory and store a pointer to it in that data
803	member, you can also "subclass" the watcher type and provide your own	1141	member, you can also "subclass" the watcher type and provide your own
804	data:	1142	data:
805		1143
806	struct my_io	1144	struct my_io
807	{	1145	{
808	struct ev_io io;	1146	ev_io io;
809	int otherfd;	1147	int otherfd;
810	void *somedata;	1148	void *somedata;
811	struct whatever *mostinteresting;	1149	struct whatever *mostinteresting;
812	}	1150	};
		1151
		1152	...
		1153	struct my_io w;
		1154	ev_io_init (&w.io, my_cb, fd, EV_READ);
813		1155
814	And since your callback will be called with a pointer to the watcher, you	1156	And since your callback will be called with a pointer to the watcher, you
815	can cast it back to your own type:	1157	can cast it back to your own type:
816		1158
817	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1159	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
818	{	1160	{
819	struct my_io *w = (struct my_io *)w_;	1161	struct my_io *w = (struct my_io *)w_;
820	...	1162	...
821	}	1163	}
822		1164
823	More interesting and less C-conformant ways of casting your callback type	1165	More interesting and less C-conformant ways of casting your callback type
824	instead have been omitted.	1166	instead have been omitted.
825		1167
826	Another common scenario is having some data structure with multiple	1168	Another common scenario is to use some data structure with multiple
827	watchers:	1169	embedded watchers:
828		1170
829	struct my_biggy	1171	struct my_biggy
830	{	1172	{
831	int some_data;	1173	int some_data;
832	ev_timer t1;	1174	ev_timer t1;
833	ev_timer t2;	1175	ev_timer t2;
834	}	1176	}
835		1177
836	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1178	In this case getting the pointer to C<my_biggy> is a bit more
837	you need to use C<offsetof>:	1179	complicated: Either you store the address of your C<my_biggy> struct
		1180	in the C<data> member of the watcher (for woozies), or you need to use
		1181	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1182	programmers):
838		1183
839	#include <stddef.h>	1184	#include <stddef.h>
840		1185
841	static void	1186	static void
842	t1_cb (EV_P_ struct ev_timer *w, int revents)	1187	t1_cb (EV_P_ ev_timer *w, int revents)
843	{	1188	{
844	struct my_biggy big = (struct my_biggy *	1189	struct my_biggy big = (struct my_biggy *
845	(((char *)w) - offsetof (struct my_biggy, t1));	1190	(((char *)w) - offsetof (struct my_biggy, t1));
846	}	1191	}
847		1192
848	static void	1193	static void
849	t2_cb (EV_P_ struct ev_timer *w, int revents)	1194	t2_cb (EV_P_ ev_timer *w, int revents)
850	{	1195	{
851	struct my_biggy big = (struct my_biggy *	1196	struct my_biggy big = (struct my_biggy *
852	(((char *)w) - offsetof (struct my_biggy, t2));	1197	(((char *)w) - offsetof (struct my_biggy, t2));
853	}	1198	}
		1199
		1200	=head2 WATCHER PRIORITY MODELS
		1201
		1202	Many event loops support I<watcher priorities>, which are usually small
		1203	integers that influence the ordering of event callback invocation
		1204	between watchers in some way, all else being equal.
		1205
		1206	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1207	description for the more technical details such as the actual priority
		1208	range.
		1209
		1210	There are two common ways how these these priorities are being interpreted
		1211	by event loops:
		1212
		1213	In the more common lock-out model, higher priorities "lock out" invocation
		1214	of lower priority watchers, which means as long as higher priority
		1215	watchers receive events, lower priority watchers are not being invoked.
		1216
		1217	The less common only-for-ordering model uses priorities solely to order
		1218	callback invocation within a single event loop iteration: Higher priority
		1219	watchers are invoked before lower priority ones, but they all get invoked
		1220	before polling for new events.
		1221
		1222	Libev uses the second (only-for-ordering) model for all its watchers
		1223	except for idle watchers (which use the lock-out model).
		1224
		1225	The rationale behind this is that implementing the lock-out model for
		1226	watchers is not well supported by most kernel interfaces, and most event
		1227	libraries will just poll for the same events again and again as long as
		1228	their callbacks have not been executed, which is very inefficient in the
		1229	common case of one high-priority watcher locking out a mass of lower
		1230	priority ones.
		1231
		1232	Static (ordering) priorities are most useful when you have two or more
		1233	watchers handling the same resource: a typical usage example is having an
		1234	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1235	timeouts. Under load, data might be received while the program handles
		1236	other jobs, but since timers normally get invoked first, the timeout
		1237	handler will be executed before checking for data. In that case, giving
		1238	the timer a lower priority than the I/O watcher ensures that I/O will be
		1239	handled first even under adverse conditions (which is usually, but not
		1240	always, what you want).
		1241
		1242	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1243	will only be executed when no same or higher priority watchers have
		1244	received events, they can be used to implement the "lock-out" model when
		1245	required.
		1246
		1247	For example, to emulate how many other event libraries handle priorities,
		1248	you can associate an C<ev_idle> watcher to each such watcher, and in
		1249	the normal watcher callback, you just start the idle watcher. The real
		1250	processing is done in the idle watcher callback. This causes libev to
		1251	continously poll and process kernel event data for the watcher, but when
		1252	the lock-out case is known to be rare (which in turn is rare :), this is
		1253	workable.
		1254
		1255	Usually, however, the lock-out model implemented that way will perform
		1256	miserably under the type of load it was designed to handle. In that case,
		1257	it might be preferable to stop the real watcher before starting the
		1258	idle watcher, so the kernel will not have to process the event in case
		1259	the actual processing will be delayed for considerable time.
		1260
		1261	Here is an example of an I/O watcher that should run at a strictly lower
		1262	priority than the default, and which should only process data when no
		1263	other events are pending:
		1264
		1265	ev_idle idle; // actual processing watcher
		1266	ev_io io; // actual event watcher
		1267
		1268	static void
		1269	io_cb (EV_P_ ev_io *w, int revents)
		1270	{
		1271	// stop the I/O watcher, we received the event, but
		1272	// are not yet ready to handle it.
		1273	ev_io_stop (EV_A_ w);
		1274
		1275	// start the idle watcher to ahndle the actual event.
		1276	// it will not be executed as long as other watchers
		1277	// with the default priority are receiving events.
		1278	ev_idle_start (EV_A_ &idle);
		1279	}
		1280
		1281	static void
		1282	idle-cb (EV_P_ ev_idle *w, int revents)
		1283	{
		1284	// actual processing
		1285	read (STDIN_FILENO, ...);
		1286
		1287	// have to start the I/O watcher again, as
		1288	// we have handled the event
		1289	ev_io_start (EV_P_ &io);
		1290	}
		1291
		1292	// initialisation
		1293	ev_idle_init (&idle, idle_cb);
		1294	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1295	ev_io_start (EV_DEFAULT_ &io);
		1296
		1297	In the "real" world, it might also be beneficial to start a timer, so that
		1298	low-priority connections can not be locked out forever under load. This
		1299	enables your program to keep a lower latency for important connections
		1300	during short periods of high load, while not completely locking out less
		1301	important ones.
854		1302
855		1303
856	=head1 WATCHER TYPES	1304	=head1 WATCHER TYPES
857		1305
858	This section describes each watcher in detail, but will not repeat	1306	This section describes each watcher in detail, but will not repeat
…		…
882	In general you can register as many read and/or write event watchers per	1330	In general you can register as many read and/or write event watchers per
883	fd as you want (as long as you don't confuse yourself). Setting all file	1331	fd as you want (as long as you don't confuse yourself). Setting all file
884	descriptors to non-blocking mode is also usually a good idea (but not	1332	descriptors to non-blocking mode is also usually a good idea (but not
885	required if you know what you are doing).	1333	required if you know what you are doing).
886		1334
887	You have to be careful with dup'ed file descriptors, though. Some backends	1335	If you cannot use non-blocking mode, then force the use of a
888	(the linux epoll backend is a notable example) cannot handle dup'ed file	1336	known-to-be-good backend (at the time of this writing, this includes only
889	descriptors correctly if you register interest in two or more fds pointing	1337	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
890	to the same underlying file/socket/etc. description (that is, they share	1338	descriptors for which non-blocking operation makes no sense (such as
891	the same underlying "file open").	1339	files) - libev doesn't guarentee any specific behaviour in that case.
892
893	If you must do this, then force the use of a known-to-be-good backend
894	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
895	C<EVBACKEND_POLL>).
896		1340
897	Another thing you have to watch out for is that it is quite easy to	1341	Another thing you have to watch out for is that it is quite easy to
898	receive "spurious" readyness notifications, that is your callback might	1342	receive "spurious" readiness notifications, that is your callback might
899	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1343	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
900	because there is no data. Not only are some backends known to create a	1344	because there is no data. Not only are some backends known to create a
901	lot of those (for example solaris ports), it is very easy to get into	1345	lot of those (for example Solaris ports), it is very easy to get into
902	this situation even with a relatively standard program structure. Thus	1346	this situation even with a relatively standard program structure. Thus
903	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1347	it is best to always use non-blocking I/O: An extra C<read>(2) returning
904	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1348	C<EAGAIN> is far preferable to a program hanging until some data arrives.
905		1349
906	If you cannot run the fd in non-blocking mode (for example you should not	1350	If you cannot run the fd in non-blocking mode (for example you should
907	play around with an Xlib connection), then you have to seperately re-test	1351	not play around with an Xlib connection), then you have to separately
908	whether a file descriptor is really ready with a known-to-be good interface	1352	re-test whether a file descriptor is really ready with a known-to-be good
909	such as poll (fortunately in our Xlib example, Xlib already does this on	1353	interface such as poll (fortunately in our Xlib example, Xlib already
910	its own, so its quite safe to use).	1354	does this on its own, so its quite safe to use). Some people additionally
		1355	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1356	indefinitely.
		1357
		1358	But really, best use non-blocking mode.
		1359
		1360	=head3 The special problem of disappearing file descriptors
		1361
		1362	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1363	descriptor (either due to calling C<close> explicitly or any other means,
		1364	such as C<dup2>). The reason is that you register interest in some file
		1365	descriptor, but when it goes away, the operating system will silently drop
		1366	this interest. If another file descriptor with the same number then is
		1367	registered with libev, there is no efficient way to see that this is, in
		1368	fact, a different file descriptor.
		1369
		1370	To avoid having to explicitly tell libev about such cases, libev follows
		1371	the following policy: Each time C<ev_io_set> is being called, libev
		1372	will assume that this is potentially a new file descriptor, otherwise
		1373	it is assumed that the file descriptor stays the same. That means that
		1374	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1375	descriptor even if the file descriptor number itself did not change.
		1376
		1377	This is how one would do it normally anyway, the important point is that
		1378	the libev application should not optimise around libev but should leave
		1379	optimisations to libev.
		1380
		1381	=head3 The special problem of dup'ed file descriptors
		1382
		1383	Some backends (e.g. epoll), cannot register events for file descriptors,
		1384	but only events for the underlying file descriptions. That means when you
		1385	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1386	events for them, only one file descriptor might actually receive events.
		1387
		1388	There is no workaround possible except not registering events
		1389	for potentially C<dup ()>'ed file descriptors, or to resort to
		1390	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1391
		1392	=head3 The special problem of fork
		1393
		1394	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1395	useless behaviour. Libev fully supports fork, but needs to be told about
		1396	it in the child.
		1397
		1398	To support fork in your programs, you either have to call
		1399	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1400	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1401	C<EVBACKEND_POLL>.
		1402
		1403	=head3 The special problem of SIGPIPE
		1404
		1405	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1406	when writing to a pipe whose other end has been closed, your program gets
		1407	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1408	this is sensible behaviour, for daemons, this is usually undesirable.
		1409
		1410	So when you encounter spurious, unexplained daemon exits, make sure you
		1411	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1412	somewhere, as that would have given you a big clue).
		1413
		1414
		1415	=head3 Watcher-Specific Functions
911		1416
912	=over 4	1417	=over 4
913		1418
914	=item ev_io_init (ev_io *, callback, int fd, int events)	1419	=item ev_io_init (ev_io *, callback, int fd, int events)
915		1420
916	=item ev_io_set (ev_io *, int fd, int events)	1421	=item ev_io_set (ev_io *, int fd, int events)
917		1422
918	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1423	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
919	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1424	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
920	C<EV_READ | EV_WRITE> to receive the given events.	1425	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
921		1426
922	=item int fd [read-only]	1427	=item int fd [read-only]
923		1428
924	The file descriptor being watched.	1429	The file descriptor being watched.
925		1430
926	=item int events [read-only]	1431	=item int events [read-only]
927		1432
928	The events being watched.	1433	The events being watched.
929		1434
930	=back	1435	=back
		1436
		1437	=head3 Examples
931		1438
932	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1439	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
933	readable, but only once. Since it is likely line-buffered, you could	1440	readable, but only once. Since it is likely line-buffered, you could
934	attempt to read a whole line in the callback.	1441	attempt to read a whole line in the callback.
935		1442
936	static void	1443	static void
937	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1444	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
938	{	1445	{
939	ev_io_stop (loop, w);	1446	ev_io_stop (loop, w);
940	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1447	.. read from stdin here (or from w->fd) and handle any I/O errors
941	}	1448	}
942		1449
943	...	1450	...
944	struct ev_loop *loop = ev_default_init (0);	1451	struct ev_loop *loop = ev_default_init (0);
945	struct ev_io stdin_readable;	1452	ev_io stdin_readable;
946	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1453	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
947	ev_io_start (loop, &stdin_readable);	1454	ev_io_start (loop, &stdin_readable);
948	ev_loop (loop, 0);	1455	ev_loop (loop, 0);
949		1456
950		1457
951	=head2 C<ev_timer> - relative and optionally repeating timeouts	1458	=head2 C<ev_timer> - relative and optionally repeating timeouts
952		1459
953	Timer watchers are simple relative timers that generate an event after a	1460	Timer watchers are simple relative timers that generate an event after a
954	given time, and optionally repeating in regular intervals after that.	1461	given time, and optionally repeating in regular intervals after that.
955		1462
956	The timers are based on real time, that is, if you register an event that	1463	The timers are based on real time, that is, if you register an event that
957	times out after an hour and you reset your system clock to last years	1464	times out after an hour and you reset your system clock to January last
958	time, it will still time out after (roughly) and hour. "Roughly" because	1465	year, it will still time out after (roughly) one hour. "Roughly" because
959	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1466	detecting time jumps is hard, and some inaccuracies are unavoidable (the
960	monotonic clock option helps a lot here).	1467	monotonic clock option helps a lot here).
		1468
		1469	The callback is guaranteed to be invoked only I<after> its timeout has
		1470	passed. If multiple timers become ready during the same loop iteration
		1471	then the ones with earlier time-out values are invoked before ones with
		1472	later time-out values (but this is no longer true when a callback calls
		1473	C<ev_loop> recursively).
		1474
		1475	=head3 Be smart about timeouts
		1476
		1477	Many real-world problems involve some kind of timeout, usually for error
		1478	recovery. A typical example is an HTTP request - if the other side hangs,
		1479	you want to raise some error after a while.
		1480
		1481	What follows are some ways to handle this problem, from obvious and
		1482	inefficient to smart and efficient.
		1483
		1484	In the following, a 60 second activity timeout is assumed - a timeout that
		1485	gets reset to 60 seconds each time there is activity (e.g. each time some
		1486	data or other life sign was received).
		1487
		1488	=over 4
		1489
		1490	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1491
		1492	This is the most obvious, but not the most simple way: In the beginning,
		1493	start the watcher:
		1494
		1495	ev_timer_init (timer, callback, 60., 0.);
		1496	ev_timer_start (loop, timer);
		1497
		1498	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1499	and start it again:
		1500
		1501	ev_timer_stop (loop, timer);
		1502	ev_timer_set (timer, 60., 0.);
		1503	ev_timer_start (loop, timer);
		1504
		1505	This is relatively simple to implement, but means that each time there is
		1506	some activity, libev will first have to remove the timer from its internal
		1507	data structure and then add it again. Libev tries to be fast, but it's
		1508	still not a constant-time operation.
		1509
		1510	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1511
		1512	This is the easiest way, and involves using C<ev_timer_again> instead of
		1513	C<ev_timer_start>.
		1514
		1515	To implement this, configure an C<ev_timer> with a C<repeat> value
		1516	of C<60> and then call C<ev_timer_again> at start and each time you
		1517	successfully read or write some data. If you go into an idle state where
		1518	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1519	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1520
		1521	That means you can ignore both the C<ev_timer_start> function and the
		1522	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1523	member and C<ev_timer_again>.
		1524
		1525	At start:
		1526
		1527	ev_timer_init (timer, callback);
		1528	timer->repeat = 60.;
		1529	ev_timer_again (loop, timer);
		1530
		1531	Each time there is some activity:
		1532
		1533	ev_timer_again (loop, timer);
		1534
		1535	It is even possible to change the time-out on the fly, regardless of
		1536	whether the watcher is active or not:
		1537
		1538	timer->repeat = 30.;
		1539	ev_timer_again (loop, timer);
		1540
		1541	This is slightly more efficient then stopping/starting the timer each time
		1542	you want to modify its timeout value, as libev does not have to completely
		1543	remove and re-insert the timer from/into its internal data structure.
		1544
		1545	It is, however, even simpler than the "obvious" way to do it.
		1546
		1547	=item 3. Let the timer time out, but then re-arm it as required.
		1548
		1549	This method is more tricky, but usually most efficient: Most timeouts are
		1550	relatively long compared to the intervals between other activity - in
		1551	our example, within 60 seconds, there are usually many I/O events with
		1552	associated activity resets.
		1553
		1554	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1555	but remember the time of last activity, and check for a real timeout only
		1556	within the callback:
		1557
		1558	ev_tstamp last_activity; // time of last activity
		1559
		1560	static void
		1561	callback (EV_P_ ev_timer *w, int revents)
		1562	{
		1563	ev_tstamp now = ev_now (EV_A);
		1564	ev_tstamp timeout = last_activity + 60.;
		1565
		1566	// if last_activity + 60. is older than now, we did time out
		1567	if (timeout < now)
		1568	{
		1569	// timeout occured, take action
		1570	}
		1571	else
		1572	{
		1573	// callback was invoked, but there was some activity, re-arm
		1574	// the watcher to fire in last_activity + 60, which is
		1575	// guaranteed to be in the future, so "again" is positive:
		1576	w->repeat = timeout - now;
		1577	ev_timer_again (EV_A_ w);
		1578	}
		1579	}
		1580
		1581	To summarise the callback: first calculate the real timeout (defined
		1582	as "60 seconds after the last activity"), then check if that time has
		1583	been reached, which means something I<did>, in fact, time out. Otherwise
		1584	the callback was invoked too early (C<timeout> is in the future), so
		1585	re-schedule the timer to fire at that future time, to see if maybe we have
		1586	a timeout then.
		1587
		1588	Note how C<ev_timer_again> is used, taking advantage of the
		1589	C<ev_timer_again> optimisation when the timer is already running.
		1590
		1591	This scheme causes more callback invocations (about one every 60 seconds
		1592	minus half the average time between activity), but virtually no calls to
		1593	libev to change the timeout.
		1594
		1595	To start the timer, simply initialise the watcher and set C<last_activity>
		1596	to the current time (meaning we just have some activity :), then call the
		1597	callback, which will "do the right thing" and start the timer:
		1598
		1599	ev_timer_init (timer, callback);
		1600	last_activity = ev_now (loop);
		1601	callback (loop, timer, EV_TIMEOUT);
		1602
		1603	And when there is some activity, simply store the current time in
		1604	C<last_activity>, no libev calls at all:
		1605
		1606	last_actiivty = ev_now (loop);
		1607
		1608	This technique is slightly more complex, but in most cases where the
		1609	time-out is unlikely to be triggered, much more efficient.
		1610
		1611	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1612	callback :) - just change the timeout and invoke the callback, which will
		1613	fix things for you.
		1614
		1615	=item 4. Wee, just use a double-linked list for your timeouts.
		1616
		1617	If there is not one request, but many thousands (millions...), all
		1618	employing some kind of timeout with the same timeout value, then one can
		1619	do even better:
		1620
		1621	When starting the timeout, calculate the timeout value and put the timeout
		1622	at the I<end> of the list.
		1623
		1624	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1625	the list is expected to fire (for example, using the technique #3).
		1626
		1627	When there is some activity, remove the timer from the list, recalculate
		1628	the timeout, append it to the end of the list again, and make sure to
		1629	update the C<ev_timer> if it was taken from the beginning of the list.
		1630
		1631	This way, one can manage an unlimited number of timeouts in O(1) time for
		1632	starting, stopping and updating the timers, at the expense of a major
		1633	complication, and having to use a constant timeout. The constant timeout
		1634	ensures that the list stays sorted.
		1635
		1636	=back
		1637
		1638	So which method the best?
		1639
		1640	Method #2 is a simple no-brain-required solution that is adequate in most
		1641	situations. Method #3 requires a bit more thinking, but handles many cases
		1642	better, and isn't very complicated either. In most case, choosing either
		1643	one is fine, with #3 being better in typical situations.
		1644
		1645	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1646	rather complicated, but extremely efficient, something that really pays
		1647	off after the first million or so of active timers, i.e. it's usually
		1648	overkill :)
		1649
		1650	=head3 The special problem of time updates
		1651
		1652	Establishing the current time is a costly operation (it usually takes at
		1653	least two system calls): EV therefore updates its idea of the current
		1654	time only before and after C<ev_loop> collects new events, which causes a
		1655	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1656	lots of events in one iteration.
961		1657
962	The relative timeouts are calculated relative to the C<ev_now ()>	1658	The relative timeouts are calculated relative to the C<ev_now ()>
963	time. This is usually the right thing as this timestamp refers to the time	1659	time. This is usually the right thing as this timestamp refers to the time
964	of the event triggering whatever timeout you are modifying/starting. If	1660	of the event triggering whatever timeout you are modifying/starting. If
965	you suspect event processing to be delayed and you I<need> to base the timeout	1661	you suspect event processing to be delayed and you I<need> to base the
966	on the current time, use something like this to adjust for this:	1662	timeout on the current time, use something like this to adjust for this:
967		1663
968	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1664	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
969		1665
970	The callback is guarenteed to be invoked only when its timeout has passed,	1666	If the event loop is suspended for a long time, you can also force an
971	but if multiple timers become ready during the same loop iteration then	1667	update of the time returned by C<ev_now ()> by calling C<ev_now_update
972	order of execution is undefined.	1668	()>.
		1669
		1670	=head3 Watcher-Specific Functions and Data Members
973		1671
974	=over 4	1672	=over 4
975		1673
976	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1674	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
977		1675
978	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1676	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
979		1677
980	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1678	Configure the timer to trigger after C<after> seconds. If C<repeat>
981	C<0.>, then it will automatically be stopped. If it is positive, then the	1679	is C<0.>, then it will automatically be stopped once the timeout is
982	timer will automatically be configured to trigger again C<repeat> seconds	1680	reached. If it is positive, then the timer will automatically be
983	later, again, and again, until stopped manually.	1681	configured to trigger again C<repeat> seconds later, again, and again,
		1682	until stopped manually.
984		1683
985	The timer itself will do a best-effort at avoiding drift, that is, if you	1684	The timer itself will do a best-effort at avoiding drift, that is, if
986	configure a timer to trigger every 10 seconds, then it will trigger at	1685	you configure a timer to trigger every 10 seconds, then it will normally
987	exactly 10 second intervals. If, however, your program cannot keep up with	1686	trigger at exactly 10 second intervals. If, however, your program cannot
988	the timer (because it takes longer than those 10 seconds to do stuff) the	1687	keep up with the timer (because it takes longer than those 10 seconds to
989	timer will not fire more than once per event loop iteration.	1688	do stuff) the timer will not fire more than once per event loop iteration.
990		1689
991	=item ev_timer_again (loop)	1690	=item ev_timer_again (loop, ev_timer *)
992		1691
993	This will act as if the timer timed out and restart it again if it is	1692	This will act as if the timer timed out and restart it again if it is
994	repeating. The exact semantics are:	1693	repeating. The exact semantics are:
995		1694
996	If the timer is pending, its pending status is cleared.	1695	If the timer is pending, its pending status is cleared.
997		1696
998	If the timer is started but nonrepeating, stop it (as if it timed out).	1697	If the timer is started but non-repeating, stop it (as if it timed out).
999		1698
1000	If the timer is repeating, either start it if necessary (with the	1699	If the timer is repeating, either start it if necessary (with the
1001	C<repeat> value), or reset the running timer to the C<repeat> value.	1700	C<repeat> value), or reset the running timer to the C<repeat> value.
1002		1701
1003	This sounds a bit complicated, but here is a useful and typical	1702	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1004	example: Imagine you have a tcp connection and you want a so-called idle	1703	usage example.
1005	timeout, that is, you want to be called when there have been, say, 60
1006	seconds of inactivity on the socket. The easiest way to do this is to
1007	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1008	C<ev_timer_again> each time you successfully read or write some data. If
1009	you go into an idle state where you do not expect data to travel on the
1010	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1011	automatically restart it if need be.
1012
1013	That means you can ignore the C<after> value and C<ev_timer_start>
1014	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1015
1016	ev_timer_init (timer, callback, 0., 5.);
1017	ev_timer_again (loop, timer);
1018	...
1019	timer->again = 17.;
1020	ev_timer_again (loop, timer);
1021	...
1022	timer->again = 10.;
1023	ev_timer_again (loop, timer);
1024
1025	This is more slightly efficient then stopping/starting the timer each time
1026	you want to modify its timeout value.
1027		1704
1028	=item ev_tstamp repeat [read-write]	1705	=item ev_tstamp repeat [read-write]
1029		1706
1030	The current C<repeat> value. Will be used each time the watcher times out	1707	The current C<repeat> value. Will be used each time the watcher times out
1031	or C<ev_timer_again> is called and determines the next timeout (if any),	1708	or C<ev_timer_again> is called, and determines the next timeout (if any),
1032	which is also when any modifications are taken into account.	1709	which is also when any modifications are taken into account.
1033		1710
1034	=back	1711	=back
1035		1712
		1713	=head3 Examples
		1714
1036	Example: Create a timer that fires after 60 seconds.	1715	Example: Create a timer that fires after 60 seconds.
1037		1716
1038	static void	1717	static void
1039	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1718	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1040	{	1719	{
1041	.. one minute over, w is actually stopped right here	1720	.. one minute over, w is actually stopped right here
1042	}	1721	}
1043		1722
1044	struct ev_timer mytimer;	1723	ev_timer mytimer;
1045	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1724	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1046	ev_timer_start (loop, &mytimer);	1725	ev_timer_start (loop, &mytimer);
1047		1726
1048	Example: Create a timeout timer that times out after 10 seconds of	1727	Example: Create a timeout timer that times out after 10 seconds of
1049	inactivity.	1728	inactivity.
1050		1729
1051	static void	1730	static void
1052	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1731	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1053	{	1732	{
1054	.. ten seconds without any activity	1733	.. ten seconds without any activity
1055	}	1734	}
1056		1735
1057	struct ev_timer mytimer;	1736	ev_timer mytimer;
1058	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1737	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1059	ev_timer_again (&mytimer); /* start timer */	1738	ev_timer_again (&mytimer); /* start timer */
1060	ev_loop (loop, 0);	1739	ev_loop (loop, 0);
1061		1740
1062	// and in some piece of code that gets executed on any "activity":	1741	// and in some piece of code that gets executed on any "activity":
1063	// reset the timeout to start ticking again at 10 seconds	1742	// reset the timeout to start ticking again at 10 seconds
1064	ev_timer_again (&mytimer);	1743	ev_timer_again (&mytimer);
1065		1744
1066		1745
1067	=head2 C<ev_periodic> - to cron or not to cron?	1746	=head2 C<ev_periodic> - to cron or not to cron?
1068		1747
1069	Periodic watchers are also timers of a kind, but they are very versatile	1748	Periodic watchers are also timers of a kind, but they are very versatile
1070	(and unfortunately a bit complex).	1749	(and unfortunately a bit complex).
1071		1750
1072	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1751	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1073	but on wallclock time (absolute time). You can tell a periodic watcher	1752	relative time, the physical time that passes) but on wall clock time
1074	to trigger "at" some specific point in time. For example, if you tell a	1753	(absolute time, the thing you can read on your calender or clock). The
1075	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1754	difference is that wall clock time can run faster or slower than real
1076	+ 10.>) and then reset your system clock to the last year, then it will	1755	time, and time jumps are not uncommon (e.g. when you adjust your
1077	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1756	wrist-watch).
1078	roughly 10 seconds later and of course not if you reset your system time
1079	again).
1080		1757
1081	They can also be used to implement vastly more complex timers, such as	1758	You can tell a periodic watcher to trigger after some specific point
		1759	in time: for example, if you tell a periodic watcher to trigger "in 10
		1760	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1761	not a delay) and then reset your system clock to January of the previous
		1762	year, then it will take a year or more to trigger the event (unlike an
		1763	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1764	it, as it uses a relative timeout).
		1765
		1766	C<ev_periodic> watchers can also be used to implement vastly more complex
1082	triggering an event on eahc midnight, local time.	1767	timers, such as triggering an event on each "midnight, local time", or
		1768	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1769	those cannot react to time jumps.
1083		1770
1084	As with timers, the callback is guarenteed to be invoked only when the	1771	As with timers, the callback is guaranteed to be invoked only when the
1085	time (C<at>) has been passed, but if multiple periodic timers become ready	1772	point in time where it is supposed to trigger has passed. If multiple
1086	during the same loop iteration then order of execution is undefined.	1773	timers become ready during the same loop iteration then the ones with
		1774	earlier time-out values are invoked before ones with later time-out values
		1775	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1776
		1777	=head3 Watcher-Specific Functions and Data Members
1087		1778
1088	=over 4	1779	=over 4
1089		1780
1090	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1781	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1091		1782
1092	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1783	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1093		1784
1094	Lots of arguments, lets sort it out... There are basically three modes of	1785	Lots of arguments, let's sort it out... There are basically three modes of
1095	operation, and we will explain them from simplest to complex:	1786	operation, and we will explain them from simplest to most complex:
1096		1787
1097	=over 4	1788	=over 4
1098		1789
1099	=item * absolute timer (interval = reschedule_cb = 0)	1790	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1100		1791
1101	In this configuration the watcher triggers an event at the wallclock time	1792	In this configuration the watcher triggers an event after the wall clock
1102	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1793	time C<offset> has passed. It will not repeat and will not adjust when a
1103	that is, if it is to be run at January 1st 2011 then it will run when the	1794	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1104	system time reaches or surpasses this time.	1795	will be stopped and invoked when the system clock reaches or surpasses
		1796	this point in time.
1105		1797
1106	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1798	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1107		1799
1108	In this mode the watcher will always be scheduled to time out at the next	1800	In this mode the watcher will always be scheduled to time out at the next
1109	C<at + N * interval> time (for some integer N) and then repeat, regardless	1801	C<offset + N * interval> time (for some integer N, which can also be
1110	of any time jumps.	1802	negative) and then repeat, regardless of any time jumps. The C<offset>
		1803	argument is merely an offset into the C<interval> periods.
1111		1804
1112	This can be used to create timers that do not drift with respect to system	1805	This can be used to create timers that do not drift with respect to the
1113	time:	1806	system clock, for example, here is an C<ev_periodic> that triggers each
		1807	hour, on the hour (with respect to UTC):
1114		1808
1115	ev_periodic_set (&periodic, 0., 3600., 0);	1809	ev_periodic_set (&periodic, 0., 3600., 0);
1116		1810
1117	This doesn't mean there will always be 3600 seconds in between triggers,	1811	This doesn't mean there will always be 3600 seconds in between triggers,
1118	but only that the the callback will be called when the system time shows a	1812	but only that the callback will be called when the system time shows a
1119	full hour (UTC), or more correctly, when the system time is evenly divisible	1813	full hour (UTC), or more correctly, when the system time is evenly divisible
1120	by 3600.	1814	by 3600.
1121		1815
1122	Another way to think about it (for the mathematically inclined) is that	1816	Another way to think about it (for the mathematically inclined) is that
1123	C<ev_periodic> will try to run the callback in this mode at the next possible	1817	C<ev_periodic> will try to run the callback in this mode at the next possible
1124	time where C<time = at (mod interval)>, regardless of any time jumps.	1818	time where C<time = offset (mod interval)>, regardless of any time jumps.
1125		1819
		1820	For numerical stability it is preferable that the C<offset> value is near
		1821	C<ev_now ()> (the current time), but there is no range requirement for
		1822	this value, and in fact is often specified as zero.
		1823
		1824	Note also that there is an upper limit to how often a timer can fire (CPU
		1825	speed for example), so if C<interval> is very small then timing stability
		1826	will of course deteriorate. Libev itself tries to be exact to be about one
		1827	millisecond (if the OS supports it and the machine is fast enough).
		1828
1126	=item * manual reschedule mode (reschedule_cb = callback)	1829	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1127		1830
1128	In this mode the values for C<interval> and C<at> are both being	1831	In this mode the values for C<interval> and C<offset> are both being
1129	ignored. Instead, each time the periodic watcher gets scheduled, the	1832	ignored. Instead, each time the periodic watcher gets scheduled, the
1130	reschedule callback will be called with the watcher as first, and the	1833	reschedule callback will be called with the watcher as first, and the
1131	current time as second argument.	1834	current time as second argument.
1132		1835
1133	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1836	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1134	ever, or make any event loop modifications>. If you need to stop it,	1837	or make ANY other event loop modifications whatsoever, unless explicitly
1135	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1838	allowed by documentation here>.
1136	starting a prepare watcher).
1137		1839
		1840	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1841	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1842	only event loop modification you are allowed to do).
		1843
1138	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1844	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1139	ev_tstamp now)>, e.g.:	1845	*w, ev_tstamp now)>, e.g.:
1140		1846
		1847	static ev_tstamp
1141	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1848	my_rescheduler (ev_periodic *w, ev_tstamp now)
1142	{	1849	{
1143	return now + 60.;	1850	return now + 60.;
1144	}	1851	}
1145		1852
1146	It must return the next time to trigger, based on the passed time value	1853	It must return the next time to trigger, based on the passed time value
1147	(that is, the lowest time value larger than to the second argument). It	1854	(that is, the lowest time value larger than to the second argument). It
1148	will usually be called just before the callback will be triggered, but	1855	will usually be called just before the callback will be triggered, but
1149	might be called at other times, too.	1856	might be called at other times, too.
1150		1857
1151	NOTE: I<< This callback must always return a time that is later than the	1858	NOTE: I<< This callback must always return a time that is higher than or
1152	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1859	equal to the passed C<now> value >>.
1153		1860
1154	This can be used to create very complex timers, such as a timer that	1861	This can be used to create very complex timers, such as a timer that
1155	triggers on each midnight, local time. To do this, you would calculate the	1862	triggers on "next midnight, local time". To do this, you would calculate the
1156	next midnight after C<now> and return the timestamp value for this. How	1863	next midnight after C<now> and return the timestamp value for this. How
1157	you do this is, again, up to you (but it is not trivial, which is the main	1864	you do this is, again, up to you (but it is not trivial, which is the main
1158	reason I omitted it as an example).	1865	reason I omitted it as an example).
1159		1866
1160	=back	1867	=back
…		…
1164	Simply stops and restarts the periodic watcher again. This is only useful	1871	Simply stops and restarts the periodic watcher again. This is only useful
1165	when you changed some parameters or the reschedule callback would return	1872	when you changed some parameters or the reschedule callback would return
1166	a different time than the last time it was called (e.g. in a crond like	1873	a different time than the last time it was called (e.g. in a crond like
1167	program when the crontabs have changed).	1874	program when the crontabs have changed).
1168		1875
		1876	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1877
		1878	When active, returns the absolute time that the watcher is supposed
		1879	to trigger next. This is not the same as the C<offset> argument to
		1880	C<ev_periodic_set>, but indeed works even in interval and manual
		1881	rescheduling modes.
		1882
		1883	=item ev_tstamp offset [read-write]
		1884
		1885	When repeating, this contains the offset value, otherwise this is the
		1886	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1887	although libev might modify this value for better numerical stability).
		1888
		1889	Can be modified any time, but changes only take effect when the periodic
		1890	timer fires or C<ev_periodic_again> is being called.
		1891
1169	=item ev_tstamp interval [read-write]	1892	=item ev_tstamp interval [read-write]
1170		1893
1171	The current interval value. Can be modified any time, but changes only	1894	The current interval value. Can be modified any time, but changes only
1172	take effect when the periodic timer fires or C<ev_periodic_again> is being	1895	take effect when the periodic timer fires or C<ev_periodic_again> is being
1173	called.	1896	called.
1174		1897
1175	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1898	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1176		1899
1177	The current reschedule callback, or C<0>, if this functionality is	1900	The current reschedule callback, or C<0>, if this functionality is
1178	switched off. Can be changed any time, but changes only take effect when	1901	switched off. Can be changed any time, but changes only take effect when
1179	the periodic timer fires or C<ev_periodic_again> is being called.	1902	the periodic timer fires or C<ev_periodic_again> is being called.
1180		1903
1181	=back	1904	=back
1182		1905
		1906	=head3 Examples
		1907
1183	Example: Call a callback every hour, or, more precisely, whenever the	1908	Example: Call a callback every hour, or, more precisely, whenever the
1184	system clock is divisible by 3600. The callback invocation times have	1909	system time is divisible by 3600. The callback invocation times have
1185	potentially a lot of jittering, but good long-term stability.	1910	potentially a lot of jitter, but good long-term stability.
1186		1911
1187	static void	1912	static void
1188	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1913	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1189	{	1914	{
1190	... its now a full hour (UTC, or TAI or whatever your clock follows)	1915	... its now a full hour (UTC, or TAI or whatever your clock follows)
1191	}	1916	}
1192		1917
1193	struct ev_periodic hourly_tick;	1918	ev_periodic hourly_tick;
1194	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1919	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1195	ev_periodic_start (loop, &hourly_tick);	1920	ev_periodic_start (loop, &hourly_tick);
1196		1921
1197	Example: The same as above, but use a reschedule callback to do it:	1922	Example: The same as above, but use a reschedule callback to do it:
1198		1923
1199	#include <math.h>	1924	#include <math.h>
1200		1925
1201	static ev_tstamp	1926	static ev_tstamp
1202	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1927	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1203	{	1928	{
1204	return fmod (now, 3600.) + 3600.;	1929	return now + (3600. - fmod (now, 3600.));
1205	}	1930	}
1206		1931
1207	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1932	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1208		1933
1209	Example: Call a callback every hour, starting now:	1934	Example: Call a callback every hour, starting now:
1210		1935
1211	struct ev_periodic hourly_tick;	1936	ev_periodic hourly_tick;
1212	ev_periodic_init (&hourly_tick, clock_cb,	1937	ev_periodic_init (&hourly_tick, clock_cb,
1213	fmod (ev_now (loop), 3600.), 3600., 0);	1938	fmod (ev_now (loop), 3600.), 3600., 0);
1214	ev_periodic_start (loop, &hourly_tick);	1939	ev_periodic_start (loop, &hourly_tick);
1215		1940
1216		1941
1217	=head2 C<ev_signal> - signal me when a signal gets signalled!	1942	=head2 C<ev_signal> - signal me when a signal gets signalled!
1218		1943
1219	Signal watchers will trigger an event when the process receives a specific	1944	Signal watchers will trigger an event when the process receives a specific
1220	signal one or more times. Even though signals are very asynchronous, libev	1945	signal one or more times. Even though signals are very asynchronous, libev
1221	will try it's best to deliver signals synchronously, i.e. as part of the	1946	will try it's best to deliver signals synchronously, i.e. as part of the
1222	normal event processing, like any other event.	1947	normal event processing, like any other event.
1223		1948
		1949	If you want signals asynchronously, just use C<sigaction> as you would
		1950	do without libev and forget about sharing the signal. You can even use
		1951	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1952
1224	You can configure as many watchers as you like per signal. Only when the	1953	You can configure as many watchers as you like per signal. Only when the
1225	first watcher gets started will libev actually register a signal watcher	1954	first watcher gets started will libev actually register a signal handler
1226	with the kernel (thus it coexists with your own signal handlers as long	1955	with the kernel (thus it coexists with your own signal handlers as long as
1227	as you don't register any with libev). Similarly, when the last signal	1956	you don't register any with libev for the same signal). Similarly, when
1228	watcher for a signal is stopped libev will reset the signal handler to	1957	the last signal watcher for a signal is stopped, libev will reset the
1229	SIG_DFL (regardless of what it was set to before).	1958	signal handler to SIG_DFL (regardless of what it was set to before).
		1959
		1960	If possible and supported, libev will install its handlers with
		1961	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1962	interrupted. If you have a problem with system calls getting interrupted by
		1963	signals you can block all signals in an C<ev_check> watcher and unblock
		1964	them in an C<ev_prepare> watcher.
		1965
		1966	=head3 Watcher-Specific Functions and Data Members
1230		1967
1231	=over 4	1968	=over 4
1232		1969
1233	=item ev_signal_init (ev_signal *, callback, int signum)	1970	=item ev_signal_init (ev_signal *, callback, int signum)
1234		1971
…		…
1241		1978
1242	The signal the watcher watches out for.	1979	The signal the watcher watches out for.
1243		1980
1244	=back	1981	=back
1245		1982
		1983	=head3 Examples
		1984
		1985	Example: Try to exit cleanly on SIGINT.
		1986
		1987	static void
		1988	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1989	{
		1990	ev_unloop (loop, EVUNLOOP_ALL);
		1991	}
		1992
		1993	ev_signal signal_watcher;
		1994	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1995	ev_signal_start (loop, &signal_watcher);
		1996
1246		1997
1247	=head2 C<ev_child> - watch out for process status changes	1998	=head2 C<ev_child> - watch out for process status changes
1248		1999
1249	Child watchers trigger when your process receives a SIGCHLD in response to	2000	Child watchers trigger when your process receives a SIGCHLD in response to
1250	some child status changes (most typically when a child of yours dies).	2001	some child status changes (most typically when a child of yours dies or
		2002	exits). It is permissible to install a child watcher I<after> the child
		2003	has been forked (which implies it might have already exited), as long
		2004	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2005	forking and then immediately registering a watcher for the child is fine,
		2006	but forking and registering a watcher a few event loop iterations later is
		2007	not.
		2008
		2009	Only the default event loop is capable of handling signals, and therefore
		2010	you can only register child watchers in the default event loop.
		2011
		2012	=head3 Process Interaction
		2013
		2014	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2015	initialised. This is necessary to guarantee proper behaviour even if
		2016	the first child watcher is started after the child exits. The occurrence
		2017	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2018	synchronously as part of the event loop processing. Libev always reaps all
		2019	children, even ones not watched.
		2020
		2021	=head3 Overriding the Built-In Processing
		2022
		2023	Libev offers no special support for overriding the built-in child
		2024	processing, but if your application collides with libev's default child
		2025	handler, you can override it easily by installing your own handler for
		2026	C<SIGCHLD> after initialising the default loop, and making sure the
		2027	default loop never gets destroyed. You are encouraged, however, to use an
		2028	event-based approach to child reaping and thus use libev's support for
		2029	that, so other libev users can use C<ev_child> watchers freely.
		2030
		2031	=head3 Stopping the Child Watcher
		2032
		2033	Currently, the child watcher never gets stopped, even when the
		2034	child terminates, so normally one needs to stop the watcher in the
		2035	callback. Future versions of libev might stop the watcher automatically
		2036	when a child exit is detected.
		2037
		2038	=head3 Watcher-Specific Functions and Data Members
1251		2039
1252	=over 4	2040	=over 4
1253		2041
1254	=item ev_child_init (ev_child *, callback, int pid)	2042	=item ev_child_init (ev_child *, callback, int pid, int trace)
1255		2043
1256	=item ev_child_set (ev_child *, int pid)	2044	=item ev_child_set (ev_child *, int pid, int trace)
1257		2045
1258	Configures the watcher to wait for status changes of process C<pid> (or	2046	Configures the watcher to wait for status changes of process C<pid> (or
1259	I<any> process if C<pid> is specified as C<0>). The callback can look	2047	I<any> process if C<pid> is specified as C<0>). The callback can look
1260	at the C<rstatus> member of the C<ev_child> watcher structure to see	2048	at the C<rstatus> member of the C<ev_child> watcher structure to see
1261	the status word (use the macros from C<sys/wait.h> and see your systems	2049	the status word (use the macros from C<sys/wait.h> and see your systems
1262	C<waitpid> documentation). The C<rpid> member contains the pid of the	2050	C<waitpid> documentation). The C<rpid> member contains the pid of the
1263	process causing the status change.	2051	process causing the status change. C<trace> must be either C<0> (only
		2052	activate the watcher when the process terminates) or C<1> (additionally
		2053	activate the watcher when the process is stopped or continued).
1264		2054
1265	=item int pid [read-only]	2055	=item int pid [read-only]
1266		2056
1267	The process id this watcher watches out for, or C<0>, meaning any process id.	2057	The process id this watcher watches out for, or C<0>, meaning any process id.
1268		2058
…		…
1275	The process exit/trace status caused by C<rpid> (see your systems	2065	The process exit/trace status caused by C<rpid> (see your systems
1276	C<waitpid> and C<sys/wait.h> documentation for details).	2066	C<waitpid> and C<sys/wait.h> documentation for details).
1277		2067
1278	=back	2068	=back
1279		2069
1280	Example: Try to exit cleanly on SIGINT and SIGTERM.	2070	=head3 Examples
1281		2071
		2072	Example: C<fork()> a new process and install a child handler to wait for
		2073	its completion.
		2074
		2075	ev_child cw;
		2076
1282	static void	2077	static void
1283	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2078	child_cb (EV_P_ ev_child *w, int revents)
1284	{	2079	{
1285	ev_unloop (loop, EVUNLOOP_ALL);	2080	ev_child_stop (EV_A_ w);
		2081	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1286	}	2082	}
1287		2083
1288	struct ev_signal signal_watcher;	2084	pid_t pid = fork ();
1289	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2085
1290	ev_signal_start (loop, &sigint_cb);	2086	if (pid < 0)
		2087	// error
		2088	else if (pid == 0)
		2089	{
		2090	// the forked child executes here
		2091	exit (1);
		2092	}
		2093	else
		2094	{
		2095	ev_child_init (&cw, child_cb, pid, 0);
		2096	ev_child_start (EV_DEFAULT_ &cw);
		2097	}
1291		2098
1292		2099
1293	=head2 C<ev_stat> - did the file attributes just change?	2100	=head2 C<ev_stat> - did the file attributes just change?
1294		2101
1295	This watches a filesystem path for attribute changes. That is, it calls	2102	This watches a file system path for attribute changes. That is, it calls
1296	C<stat> regularly (or when the OS says it changed) and sees if it changed	2103	C<stat> on that path in regular intervals (or when the OS says it changed)
1297	compared to the last time, invoking the callback if it did.	2104	and sees if it changed compared to the last time, invoking the callback if
		2105	it did.
1298		2106
1299	The path does not need to exist: changing from "path exists" to "path does	2107	The path does not need to exist: changing from "path exists" to "path does
1300	not exist" is a status change like any other. The condition "path does	2108	not exist" is a status change like any other. The condition "path does not
1301	not exist" is signified by the C<st_nlink> field being zero (which is	2109	exist" (or more correctly "path cannot be stat'ed") is signified by the
1302	otherwise always forced to be at least one) and all the other fields of	2110	C<st_nlink> field being zero (which is otherwise always forced to be at
1303	the stat buffer having unspecified contents.	2111	least one) and all the other fields of the stat buffer having unspecified
		2112	contents.
1304		2113
1305	The path I<should> be absolute and I<must not> end in a slash. If it is	2114	The path I<must not> end in a slash or contain special components such as
		2115	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1306	relative and your working directory changes, the behaviour is undefined.	2116	your working directory changes, then the behaviour is undefined.
1307		2117
1308	Since there is no standard to do this, the portable implementation simply	2118	Since there is no portable change notification interface available, the
1309	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2119	portable implementation simply calls C<stat(2)> regularly on the path
1310	can specify a recommended polling interval for this case. If you specify	2120	to see if it changed somehow. You can specify a recommended polling
1311	a polling interval of C<0> (highly recommended!) then a I<suitable,	2121	interval for this case. If you specify a polling interval of C<0> (highly
1312	unspecified default> value will be used (which you can expect to be around	2122	recommended!) then a I<suitable, unspecified default> value will be used
1313	five seconds, although this might change dynamically). Libev will also	2123	(which you can expect to be around five seconds, although this might
1314	impose a minimum interval which is currently around C<0.1>, but thats	2124	change dynamically). Libev will also impose a minimum interval which is
1315	usually overkill.	2125	currently around C<0.1>, but that's usually overkill.
1316		2126
1317	This watcher type is not meant for massive numbers of stat watchers,	2127	This watcher type is not meant for massive numbers of stat watchers,
1318	as even with OS-supported change notifications, this can be	2128	as even with OS-supported change notifications, this can be
1319	resource-intensive.	2129	resource-intensive.
1320		2130
1321	At the time of this writing, only the Linux inotify interface is	2131	At the time of this writing, the only OS-specific interface implemented
1322	implemented (implementing kqueue support is left as an exercise for the	2132	is the Linux inotify interface (implementing kqueue support is left as an
1323	reader). Inotify will be used to give hints only and should not change the	2133	exercise for the reader. Note, however, that the author sees no way of
1324	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2134	implementing C<ev_stat> semantics with kqueue, except as a hint).
1325	to fall back to regular polling again even with inotify, but changes are	2135
1326	usually detected immediately, and if the file exists there will be no	2136	=head3 ABI Issues (Largefile Support)
1327	polling.	2137
		2138	Libev by default (unless the user overrides this) uses the default
		2139	compilation environment, which means that on systems with large file
		2140	support disabled by default, you get the 32 bit version of the stat
		2141	structure. When using the library from programs that change the ABI to
		2142	use 64 bit file offsets the programs will fail. In that case you have to
		2143	compile libev with the same flags to get binary compatibility. This is
		2144	obviously the case with any flags that change the ABI, but the problem is
		2145	most noticeably displayed with ev_stat and large file support.
		2146
		2147	The solution for this is to lobby your distribution maker to make large
		2148	file interfaces available by default (as e.g. FreeBSD does) and not
		2149	optional. Libev cannot simply switch on large file support because it has
		2150	to exchange stat structures with application programs compiled using the
		2151	default compilation environment.
		2152
		2153	=head3 Inotify and Kqueue
		2154
		2155	When C<inotify (7)> support has been compiled into libev and present at
		2156	runtime, it will be used to speed up change detection where possible. The
		2157	inotify descriptor will be created lazily when the first C<ev_stat>
		2158	watcher is being started.
		2159
		2160	Inotify presence does not change the semantics of C<ev_stat> watchers
		2161	except that changes might be detected earlier, and in some cases, to avoid
		2162	making regular C<stat> calls. Even in the presence of inotify support
		2163	there are many cases where libev has to resort to regular C<stat> polling,
		2164	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2165	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2166	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2167	xfs are fully working) libev usually gets away without polling.
		2168
		2169	There is no support for kqueue, as apparently it cannot be used to
		2170	implement this functionality, due to the requirement of having a file
		2171	descriptor open on the object at all times, and detecting renames, unlinks
		2172	etc. is difficult.
		2173
		2174	=head3 C<stat ()> is a synchronous operation
		2175
		2176	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2177	the process. The exception are C<ev_stat> watchers - those call C<stat
		2178	()>, which is a synchronous operation.
		2179
		2180	For local paths, this usually doesn't matter: unless the system is very
		2181	busy or the intervals between stat's are large, a stat call will be fast,
		2182	as the path data is usually in memory already (except when starting the
		2183	watcher).
		2184
		2185	For networked file systems, calling C<stat ()> can block an indefinite
		2186	time due to network issues, and even under good conditions, a stat call
		2187	often takes multiple milliseconds.
		2188
		2189	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2190	paths, although this is fully supported by libev.
		2191
		2192	=head3 The special problem of stat time resolution
		2193
		2194	The C<stat ()> system call only supports full-second resolution portably,
		2195	and even on systems where the resolution is higher, most file systems
		2196	still only support whole seconds.
		2197
		2198	That means that, if the time is the only thing that changes, you can
		2199	easily miss updates: on the first update, C<ev_stat> detects a change and
		2200	calls your callback, which does something. When there is another update
		2201	within the same second, C<ev_stat> will be unable to detect unless the
		2202	stat data does change in other ways (e.g. file size).
		2203
		2204	The solution to this is to delay acting on a change for slightly more
		2205	than a second (or till slightly after the next full second boundary), using
		2206	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2207	ev_timer_again (loop, w)>).
		2208
		2209	The C<.02> offset is added to work around small timing inconsistencies
		2210	of some operating systems (where the second counter of the current time
		2211	might be be delayed. One such system is the Linux kernel, where a call to
		2212	C<gettimeofday> might return a timestamp with a full second later than
		2213	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2214	update file times then there will be a small window where the kernel uses
		2215	the previous second to update file times but libev might already execute
		2216	the timer callback).
		2217
		2218	=head3 Watcher-Specific Functions and Data Members
1328		2219
1329	=over 4	2220	=over 4
1330		2221
1331	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2222	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1332		2223
…		…
1336	C<path>. The C<interval> is a hint on how quickly a change is expected to	2227	C<path>. The C<interval> is a hint on how quickly a change is expected to
1337	be detected and should normally be specified as C<0> to let libev choose	2228	be detected and should normally be specified as C<0> to let libev choose
1338	a suitable value. The memory pointed to by C<path> must point to the same	2229	a suitable value. The memory pointed to by C<path> must point to the same
1339	path for as long as the watcher is active.	2230	path for as long as the watcher is active.
1340		2231
1341	The callback will be receive C<EV_STAT> when a change was detected,	2232	The callback will receive an C<EV_STAT> event when a change was detected,
1342	relative to the attributes at the time the watcher was started (or the	2233	relative to the attributes at the time the watcher was started (or the
1343	last change was detected).	2234	last change was detected).
1344		2235
1345	=item ev_stat_stat (ev_stat *)	2236	=item ev_stat_stat (loop, ev_stat *)
1346		2237
1347	Updates the stat buffer immediately with new values. If you change the	2238	Updates the stat buffer immediately with new values. If you change the
1348	watched path in your callback, you could call this fucntion to avoid	2239	watched path in your callback, you could call this function to avoid
1349	detecting this change (while introducing a race condition). Can also be	2240	detecting this change (while introducing a race condition if you are not
1350	useful simply to find out the new values.	2241	the only one changing the path). Can also be useful simply to find out the
		2242	new values.
1351		2243
1352	=item ev_statdata attr [read-only]	2244	=item ev_statdata attr [read-only]
1353		2245
1354	The most-recently detected attributes of the file. Although the type is of	2246	The most-recently detected attributes of the file. Although the type is
1355	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2247	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1356	suitable for your system. If the C<st_nlink> member is C<0>, then there	2248	suitable for your system, but you can only rely on the POSIX-standardised
		2249	members to be present. If the C<st_nlink> member is C<0>, then there was
1357	was some error while C<stat>ing the file.	2250	some error while C<stat>ing the file.
1358		2251
1359	=item ev_statdata prev [read-only]	2252	=item ev_statdata prev [read-only]
1360		2253
1361	The previous attributes of the file. The callback gets invoked whenever	2254	The previous attributes of the file. The callback gets invoked whenever
1362	C<prev> != C<attr>.	2255	C<prev> != C<attr>, or, more precisely, one or more of these members
		2256	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2257	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1363		2258
1364	=item ev_tstamp interval [read-only]	2259	=item ev_tstamp interval [read-only]
1365		2260
1366	The specified interval.	2261	The specified interval.
1367		2262
1368	=item const char *path [read-only]	2263	=item const char *path [read-only]
1369		2264
1370	The filesystem path that is being watched.	2265	The file system path that is being watched.
1371		2266
1372	=back	2267	=back
1373		2268
		2269	=head3 Examples
		2270
1374	Example: Watch C</etc/passwd> for attribute changes.	2271	Example: Watch C</etc/passwd> for attribute changes.
1375		2272
1376	static void	2273	static void
1377	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2274	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1378	{	2275	{
1379	/* /etc/passwd changed in some way */	2276	/* /etc/passwd changed in some way */
1380	if (w->attr.st_nlink)	2277	if (w->attr.st_nlink)
1381	{	2278	{
1382	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2279	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1383	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2280	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1384	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2281	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1385	}	2282	}
1386	else	2283	else
1387	/* you shalt not abuse printf for puts */	2284	/* you shalt not abuse printf for puts */
1388	puts ("wow, /etc/passwd is not there, expect problems. "	2285	puts ("wow, /etc/passwd is not there, expect problems. "
1389	"if this is windows, they already arrived\n");	2286	"if this is windows, they already arrived\n");
1390	}	2287	}
1391		2288
1392	...	2289	...
1393	ev_stat passwd;	2290	ev_stat passwd;
1394		2291
1395	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2292	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1396	ev_stat_start (loop, &passwd);	2293	ev_stat_start (loop, &passwd);
		2294
		2295	Example: Like above, but additionally use a one-second delay so we do not
		2296	miss updates (however, frequent updates will delay processing, too, so
		2297	one might do the work both on C<ev_stat> callback invocation I<and> on
		2298	C<ev_timer> callback invocation).
		2299
		2300	static ev_stat passwd;
		2301	static ev_timer timer;
		2302
		2303	static void
		2304	timer_cb (EV_P_ ev_timer *w, int revents)
		2305	{
		2306	ev_timer_stop (EV_A_ w);
		2307
		2308	/* now it's one second after the most recent passwd change */
		2309	}
		2310
		2311	static void
		2312	stat_cb (EV_P_ ev_stat *w, int revents)
		2313	{
		2314	/* reset the one-second timer */
		2315	ev_timer_again (EV_A_ &timer);
		2316	}
		2317
		2318	...
		2319	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2320	ev_stat_start (loop, &passwd);
		2321	ev_timer_init (&timer, timer_cb, 0., 1.02);
1397		2322
1398		2323
1399	=head2 C<ev_idle> - when you've got nothing better to do...	2324	=head2 C<ev_idle> - when you've got nothing better to do...
1400		2325
1401	Idle watchers trigger events when no other events of the same or higher	2326	Idle watchers trigger events when no other events of the same or higher
1402	priority are pending (prepare, check and other idle watchers do not	2327	priority are pending (prepare, check and other idle watchers do not count
1403	count).	2328	as receiving "events").
1404		2329
1405	That is, as long as your process is busy handling sockets or timeouts	2330	That is, as long as your process is busy handling sockets or timeouts
1406	(or even signals, imagine) of the same or higher priority it will not be	2331	(or even signals, imagine) of the same or higher priority it will not be
1407	triggered. But when your process is idle (or only lower-priority watchers	2332	triggered. But when your process is idle (or only lower-priority watchers
1408	are pending), the idle watchers are being called once per event loop	2333	are pending), the idle watchers are being called once per event loop
…		…
1415	Apart from keeping your process non-blocking (which is a useful	2340	Apart from keeping your process non-blocking (which is a useful
1416	effect on its own sometimes), idle watchers are a good place to do	2341	effect on its own sometimes), idle watchers are a good place to do
1417	"pseudo-background processing", or delay processing stuff to after the	2342	"pseudo-background processing", or delay processing stuff to after the
1418	event loop has handled all outstanding events.	2343	event loop has handled all outstanding events.
1419		2344
		2345	=head3 Watcher-Specific Functions and Data Members
		2346
1420	=over 4	2347	=over 4
1421		2348
1422	=item ev_idle_init (ev_signal *, callback)	2349	=item ev_idle_init (ev_idle *, callback)
1423		2350
1424	Initialises and configures the idle watcher - it has no parameters of any	2351	Initialises and configures the idle watcher - it has no parameters of any
1425	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2352	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1426	believe me.	2353	believe me.
1427		2354
1428	=back	2355	=back
1429		2356
		2357	=head3 Examples
		2358
1430	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2359	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1431	callback, free it. Also, use no error checking, as usual.	2360	callback, free it. Also, use no error checking, as usual.
1432		2361
1433	static void	2362	static void
1434	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2363	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1435	{	2364	{
1436	free (w);	2365	free (w);
1437	// now do something you wanted to do when the program has	2366	// now do something you wanted to do when the program has
1438	// no longer asnything immediate to do.	2367	// no longer anything immediate to do.
1439	}	2368	}
1440		2369
1441	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2370	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1442	ev_idle_init (idle_watcher, idle_cb);	2371	ev_idle_init (idle_watcher, idle_cb);
1443	ev_idle_start (loop, idle_cb);	2372	ev_idle_start (loop, idle_cb);
1444		2373
1445		2374
1446	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2375	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1447		2376
1448	Prepare and check watchers are usually (but not always) used in tandem:	2377	Prepare and check watchers are usually (but not always) used in pairs:
1449	prepare watchers get invoked before the process blocks and check watchers	2378	prepare watchers get invoked before the process blocks and check watchers
1450	afterwards.	2379	afterwards.
1451		2380
1452	You I<must not> call C<ev_loop> or similar functions that enter	2381	You I<must not> call C<ev_loop> or similar functions that enter
1453	the current event loop from either C<ev_prepare> or C<ev_check>	2382	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1456	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2385	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1457	C<ev_check> so if you have one watcher of each kind they will always be	2386	C<ev_check> so if you have one watcher of each kind they will always be
1458	called in pairs bracketing the blocking call.	2387	called in pairs bracketing the blocking call.
1459		2388
1460	Their main purpose is to integrate other event mechanisms into libev and	2389	Their main purpose is to integrate other event mechanisms into libev and
1461	their use is somewhat advanced. This could be used, for example, to track	2390	their use is somewhat advanced. They could be used, for example, to track
1462	variable changes, implement your own watchers, integrate net-snmp or a	2391	variable changes, implement your own watchers, integrate net-snmp or a
1463	coroutine library and lots more. They are also occasionally useful if	2392	coroutine library and lots more. They are also occasionally useful if
1464	you cache some data and want to flush it before blocking (for example,	2393	you cache some data and want to flush it before blocking (for example,
1465	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2394	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1466	watcher).	2395	watcher).
1467		2396
1468	This is done by examining in each prepare call which file descriptors need	2397	This is done by examining in each prepare call which file descriptors
1469	to be watched by the other library, registering C<ev_io> watchers for	2398	need to be watched by the other library, registering C<ev_io> watchers
1470	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2399	for them and starting an C<ev_timer> watcher for any timeouts (many
1471	provide just this functionality). Then, in the check watcher you check for	2400	libraries provide exactly this functionality). Then, in the check watcher,
1472	any events that occured (by checking the pending status of all watchers	2401	you check for any events that occurred (by checking the pending status
1473	and stopping them) and call back into the library. The I/O and timer	2402	of all watchers and stopping them) and call back into the library. The
1474	callbacks will never actually be called (but must be valid nevertheless,	2403	I/O and timer callbacks will never actually be called (but must be valid
1475	because you never know, you know?).	2404	nevertheless, because you never know, you know?).
1476		2405
1477	As another example, the Perl Coro module uses these hooks to integrate	2406	As another example, the Perl Coro module uses these hooks to integrate
1478	coroutines into libev programs, by yielding to other active coroutines	2407	coroutines into libev programs, by yielding to other active coroutines
1479	during each prepare and only letting the process block if no coroutines	2408	during each prepare and only letting the process block if no coroutines
1480	are ready to run (it's actually more complicated: it only runs coroutines	2409	are ready to run (it's actually more complicated: it only runs coroutines
1481	with priority higher than or equal to the event loop and one coroutine	2410	with priority higher than or equal to the event loop and one coroutine
1482	of lower priority, but only once, using idle watchers to keep the event	2411	of lower priority, but only once, using idle watchers to keep the event
1483	loop from blocking if lower-priority coroutines are active, thus mapping	2412	loop from blocking if lower-priority coroutines are active, thus mapping
1484	low-priority coroutines to idle/background tasks).	2413	low-priority coroutines to idle/background tasks).
1485		2414
		2415	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2416	priority, to ensure that they are being run before any other watchers
		2417	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2418
		2419	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2420	activate ("feed") events into libev. While libev fully supports this, they
		2421	might get executed before other C<ev_check> watchers did their job. As
		2422	C<ev_check> watchers are often used to embed other (non-libev) event
		2423	loops those other event loops might be in an unusable state until their
		2424	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2425	others).
		2426
		2427	=head3 Watcher-Specific Functions and Data Members
		2428
1486	=over 4	2429	=over 4
1487		2430
1488	=item ev_prepare_init (ev_prepare *, callback)	2431	=item ev_prepare_init (ev_prepare *, callback)
1489		2432
1490	=item ev_check_init (ev_check *, callback)	2433	=item ev_check_init (ev_check *, callback)
1491		2434
1492	Initialises and configures the prepare or check watcher - they have no	2435	Initialises and configures the prepare or check watcher - they have no
1493	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2436	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1494	macros, but using them is utterly, utterly and completely pointless.	2437	macros, but using them is utterly, utterly, utterly and completely
		2438	pointless.
1495		2439
1496	=back	2440	=back
1497		2441
1498	Example: To include a library such as adns, you would add IO watchers	2442	=head3 Examples
1499	and a timeout watcher in a prepare handler, as required by libadns, and	2443
		2444	There are a number of principal ways to embed other event loops or modules
		2445	into libev. Here are some ideas on how to include libadns into libev
		2446	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2447	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2448	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2449	Glib event loop).
		2450
		2451	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1500	in a check watcher, destroy them and call into libadns. What follows is	2452	and in a check watcher, destroy them and call into libadns. What follows
1501	pseudo-code only of course:	2453	is pseudo-code only of course. This requires you to either use a low
		2454	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2455	the callbacks for the IO/timeout watchers might not have been called yet.
1502		2456
1503	static ev_io iow [nfd];	2457	static ev_io iow [nfd];
1504	static ev_timer tw;	2458	static ev_timer tw;
1505		2459
1506	static void	2460	static void
1507	io_cb (ev_loop *loop, ev_io *w, int revents)	2461	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1508	{	2462	{
1509	// set the relevant poll flags
1510	// could also call adns_processreadable etc. here
1511	struct pollfd *fd = (struct pollfd *)w->data;
1512	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1513	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1514	}	2463	}
1515		2464
1516	// create io watchers for each fd and a timer before blocking	2465	// create io watchers for each fd and a timer before blocking
1517	static void	2466	static void
1518	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2467	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1519	{	2468	{
1520	int timeout = 3600000;	2469	int timeout = 3600000;
1521	struct pollfd fds [nfd];	2470	struct pollfd fds [nfd];
1522	// actual code will need to loop here and realloc etc.	2471	// actual code will need to loop here and realloc etc.
1523	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2472	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1524		2473
1525	/* the callback is illegal, but won't be called as we stop during check */	2474	/* the callback is illegal, but won't be called as we stop during check */
1526	ev_timer_init (&tw, 0, timeout * 1e-3);	2475	ev_timer_init (&tw, 0, timeout * 1e-3);
1527	ev_timer_start (loop, &tw);	2476	ev_timer_start (loop, &tw);
1528		2477
1529	// create on ev_io per pollfd	2478	// create one ev_io per pollfd
1530	for (int i = 0; i < nfd; ++i)	2479	for (int i = 0; i < nfd; ++i)
1531	{	2480	{
1532	ev_io_init (iow + i, io_cb, fds [i].fd,	2481	ev_io_init (iow + i, io_cb, fds [i].fd,
1533	((fds [i].events & POLLIN ? EV_READ : 0)	2482	((fds [i].events & POLLIN ? EV_READ : 0)
1534	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2483	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1535		2484
1536	fds [i].revents = 0;	2485	fds [i].revents = 0;
1537	iow [i].data = fds + i;
1538	ev_io_start (loop, iow + i);	2486	ev_io_start (loop, iow + i);
1539	}	2487	}
1540	}	2488	}
1541		2489
1542	// stop all watchers after blocking	2490	// stop all watchers after blocking
1543	static void	2491	static void
1544	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2492	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1545	{	2493	{
1546	ev_timer_stop (loop, &tw);	2494	ev_timer_stop (loop, &tw);
1547		2495
1548	for (int i = 0; i < nfd; ++i)	2496	for (int i = 0; i < nfd; ++i)
		2497	{
		2498	// set the relevant poll flags
		2499	// could also call adns_processreadable etc. here
		2500	struct pollfd *fd = fds + i;
		2501	int revents = ev_clear_pending (iow + i);
		2502	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2503	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2504
		2505	// now stop the watcher
1549	ev_io_stop (loop, iow + i);	2506	ev_io_stop (loop, iow + i);
		2507	}
1550		2508
1551	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2509	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1552	}	2510	}
		2511
		2512	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2513	in the prepare watcher and would dispose of the check watcher.
		2514
		2515	Method 3: If the module to be embedded supports explicit event
		2516	notification (libadns does), you can also make use of the actual watcher
		2517	callbacks, and only destroy/create the watchers in the prepare watcher.
		2518
		2519	static void
		2520	timer_cb (EV_P_ ev_timer *w, int revents)
		2521	{
		2522	adns_state ads = (adns_state)w->data;
		2523	update_now (EV_A);
		2524
		2525	adns_processtimeouts (ads, &tv_now);
		2526	}
		2527
		2528	static void
		2529	io_cb (EV_P_ ev_io *w, int revents)
		2530	{
		2531	adns_state ads = (adns_state)w->data;
		2532	update_now (EV_A);
		2533
		2534	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2535	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2536	}
		2537
		2538	// do not ever call adns_afterpoll
		2539
		2540	Method 4: Do not use a prepare or check watcher because the module you
		2541	want to embed is not flexible enough to support it. Instead, you can
		2542	override their poll function. The drawback with this solution is that the
		2543	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2544	this approach, effectively embedding EV as a client into the horrible
		2545	libglib event loop.
		2546
		2547	static gint
		2548	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2549	{
		2550	int got_events = 0;
		2551
		2552	for (n = 0; n < nfds; ++n)
		2553	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2554
		2555	if (timeout >= 0)
		2556	// create/start timer
		2557
		2558	// poll
		2559	ev_loop (EV_A_ 0);
		2560
		2561	// stop timer again
		2562	if (timeout >= 0)
		2563	ev_timer_stop (EV_A_ &to);
		2564
		2565	// stop io watchers again - their callbacks should have set
		2566	for (n = 0; n < nfds; ++n)
		2567	ev_io_stop (EV_A_ iow [n]);
		2568
		2569	return got_events;
		2570	}
1553		2571
1554		2572
1555	=head2 C<ev_embed> - when one backend isn't enough...	2573	=head2 C<ev_embed> - when one backend isn't enough...
1556		2574
1557	This is a rather advanced watcher type that lets you embed one event loop	2575	This is a rather advanced watcher type that lets you embed one event loop
…		…
1563	prioritise I/O.	2581	prioritise I/O.
1564		2582
1565	As an example for a bug workaround, the kqueue backend might only support	2583	As an example for a bug workaround, the kqueue backend might only support
1566	sockets on some platform, so it is unusable as generic backend, but you	2584	sockets on some platform, so it is unusable as generic backend, but you
1567	still want to make use of it because you have many sockets and it scales	2585	still want to make use of it because you have many sockets and it scales
1568	so nicely. In this case, you would create a kqueue-based loop and embed it	2586	so nicely. In this case, you would create a kqueue-based loop and embed
1569	into your default loop (which might use e.g. poll). Overall operation will	2587	it into your default loop (which might use e.g. poll). Overall operation
1570	be a bit slower because first libev has to poll and then call kevent, but	2588	will be a bit slower because first libev has to call C<poll> and then
1571	at least you can use both at what they are best.	2589	C<kevent>, but at least you can use both mechanisms for what they are
		2590	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1572		2591
1573	As for prioritising I/O: rarely you have the case where some fds have	2592	As for prioritising I/O: under rare circumstances you have the case where
1574	to be watched and handled very quickly (with low latency), and even	2593	some fds have to be watched and handled very quickly (with low latency),
1575	priorities and idle watchers might have too much overhead. In this case	2594	and even priorities and idle watchers might have too much overhead. In
1576	you would put all the high priority stuff in one loop and all the rest in	2595	this case you would put all the high priority stuff in one loop and all
1577	a second one, and embed the second one in the first.	2596	the rest in a second one, and embed the second one in the first.
1578		2597
1579	As long as the watcher is active, the callback will be invoked every time	2598	As long as the watcher is active, the callback will be invoked every
1580	there might be events pending in the embedded loop. The callback must then	2599	time there might be events pending in the embedded loop. The callback
1581	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2600	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1582	their callbacks (you could also start an idle watcher to give the embedded	2601	sweep and invoke their callbacks (the callback doesn't need to invoke the
1583	loop strictly lower priority for example). You can also set the callback	2602	C<ev_embed_sweep> function directly, it could also start an idle watcher
1584	to C<0>, in which case the embed watcher will automatically execute the	2603	to give the embedded loop strictly lower priority for example).
1585	embedded loop sweep.
1586		2604
1587	As long as the watcher is started it will automatically handle events. The	2605	You can also set the callback to C<0>, in which case the embed watcher
1588	callback will be invoked whenever some events have been handled. You can	2606	will automatically execute the embedded loop sweep whenever necessary.
1589	set the callback to C<0> to avoid having to specify one if you are not
1590	interested in that.
1591		2607
1592	Also, there have not currently been made special provisions for forking:	2608	Fork detection will be handled transparently while the C<ev_embed> watcher
1593	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2609	is active, i.e., the embedded loop will automatically be forked when the
1594	but you will also have to stop and restart any C<ev_embed> watchers	2610	embedding loop forks. In other cases, the user is responsible for calling
1595	yourself.	2611	C<ev_loop_fork> on the embedded loop.
1596		2612
1597	Unfortunately, not all backends are embeddable, only the ones returned by	2613	Unfortunately, not all backends are embeddable: only the ones returned by
1598	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2614	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1599	portable one.	2615	portable one.
1600		2616
1601	So when you want to use this feature you will always have to be prepared	2617	So when you want to use this feature you will always have to be prepared
1602	that you cannot get an embeddable loop. The recommended way to get around	2618	that you cannot get an embeddable loop. The recommended way to get around
1603	this is to have a separate variables for your embeddable loop, try to	2619	this is to have a separate variables for your embeddable loop, try to
1604	create it, and if that fails, use the normal loop for everything:	2620	create it, and if that fails, use the normal loop for everything.
1605		2621
1606	struct ev_loop *loop_hi = ev_default_init (0);	2622	=head3 C<ev_embed> and fork
1607	struct ev_loop *loop_lo = 0;
1608	struct ev_embed embed;
1609
1610	// see if there is a chance of getting one that works
1611	// (remember that a flags value of 0 means autodetection)
1612	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1613	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1614	: 0;
1615		2623
1616	// if we got one, then embed it, otherwise default to loop_hi	2624	While the C<ev_embed> watcher is running, forks in the embedding loop will
1617	if (loop_lo)	2625	automatically be applied to the embedded loop as well, so no special
1618	{	2626	fork handling is required in that case. When the watcher is not running,
1619	ev_embed_init (&embed, 0, loop_lo);	2627	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1620	ev_embed_start (loop_hi, &embed);	2628	as applicable.
1621	}	2629
1622	else	2630	=head3 Watcher-Specific Functions and Data Members
1623	loop_lo = loop_hi;
1624		2631
1625	=over 4	2632	=over 4
1626		2633
1627	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2634	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1628		2635
…		…
1630		2637
1631	Configures the watcher to embed the given loop, which must be	2638	Configures the watcher to embed the given loop, which must be
1632	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2639	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1633	invoked automatically, otherwise it is the responsibility of the callback	2640	invoked automatically, otherwise it is the responsibility of the callback
1634	to invoke it (it will continue to be called until the sweep has been done,	2641	to invoke it (it will continue to be called until the sweep has been done,
1635	if you do not want thta, you need to temporarily stop the embed watcher).	2642	if you do not want that, you need to temporarily stop the embed watcher).
1636		2643
1637	=item ev_embed_sweep (loop, ev_embed *)	2644	=item ev_embed_sweep (loop, ev_embed *)
1638		2645
1639	Make a single, non-blocking sweep over the embedded loop. This works	2646	Make a single, non-blocking sweep over the embedded loop. This works
1640	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2647	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1641	apropriate way for embedded loops.	2648	appropriate way for embedded loops.
1642		2649
1643	=item struct ev_loop *loop [read-only]	2650	=item struct ev_loop *other [read-only]
1644		2651
1645	The embedded event loop.	2652	The embedded event loop.
1646		2653
1647	=back	2654	=back
		2655
		2656	=head3 Examples
		2657
		2658	Example: Try to get an embeddable event loop and embed it into the default
		2659	event loop. If that is not possible, use the default loop. The default
		2660	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2661	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2662	used).
		2663
		2664	struct ev_loop *loop_hi = ev_default_init (0);
		2665	struct ev_loop *loop_lo = 0;
		2666	ev_embed embed;
		2667
		2668	// see if there is a chance of getting one that works
		2669	// (remember that a flags value of 0 means autodetection)
		2670	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2671	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2672	: 0;
		2673
		2674	// if we got one, then embed it, otherwise default to loop_hi
		2675	if (loop_lo)
		2676	{
		2677	ev_embed_init (&embed, 0, loop_lo);
		2678	ev_embed_start (loop_hi, &embed);
		2679	}
		2680	else
		2681	loop_lo = loop_hi;
		2682
		2683	Example: Check if kqueue is available but not recommended and create
		2684	a kqueue backend for use with sockets (which usually work with any
		2685	kqueue implementation). Store the kqueue/socket-only event loop in
		2686	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2687
		2688	struct ev_loop *loop = ev_default_init (0);
		2689	struct ev_loop *loop_socket = 0;
		2690	ev_embed embed;
		2691
		2692	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2693	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2694	{
		2695	ev_embed_init (&embed, 0, loop_socket);
		2696	ev_embed_start (loop, &embed);
		2697	}
		2698
		2699	if (!loop_socket)
		2700	loop_socket = loop;
		2701
		2702	// now use loop_socket for all sockets, and loop for everything else
1648		2703
1649		2704
1650	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2705	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1651		2706
1652	Fork watchers are called when a C<fork ()> was detected (usually because	2707	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1655	event loop blocks next and before C<ev_check> watchers are being called,	2710	event loop blocks next and before C<ev_check> watchers are being called,
1656	and only in the child after the fork. If whoever good citizen calling	2711	and only in the child after the fork. If whoever good citizen calling
1657	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2712	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1658	handlers will be invoked, too, of course.	2713	handlers will be invoked, too, of course.
1659		2714
		2715	=head3 The special problem of life after fork - how is it possible?
		2716
		2717	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2718	up/change the process environment, followed by a call to C<exec()>. This
		2719	sequence should be handled by libev without any problems.
		2720
		2721	This changes when the application actually wants to do event handling
		2722	in the child, or both parent in child, in effect "continuing" after the
		2723	fork.
		2724
		2725	The default mode of operation (for libev, with application help to detect
		2726	forks) is to duplicate all the state in the child, as would be expected
		2727	when I<either> the parent I<or> the child process continues.
		2728
		2729	When both processes want to continue using libev, then this is usually the
		2730	wrong result. In that case, usually one process (typically the parent) is
		2731	supposed to continue with all watchers in place as before, while the other
		2732	process typically wants to start fresh, i.e. without any active watchers.
		2733
		2734	The cleanest and most efficient way to achieve that with libev is to
		2735	simply create a new event loop, which of course will be "empty", and
		2736	use that for new watchers. This has the advantage of not touching more
		2737	memory than necessary, and thus avoiding the copy-on-write, and the
		2738	disadvantage of having to use multiple event loops (which do not support
		2739	signal watchers).
		2740
		2741	When this is not possible, or you want to use the default loop for
		2742	other reasons, then in the process that wants to start "fresh", call
		2743	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2744	the default loop will "orphan" (not stop) all registered watchers, so you
		2745	have to be careful not to execute code that modifies those watchers. Note
		2746	also that in that case, you have to re-register any signal watchers.
		2747
		2748	=head3 Watcher-Specific Functions and Data Members
		2749
1660	=over 4	2750	=over 4
1661		2751
1662	=item ev_fork_init (ev_signal *, callback)	2752	=item ev_fork_init (ev_signal *, callback)
1663		2753
1664	Initialises and configures the fork watcher - it has no parameters of any	2754	Initialises and configures the fork watcher - it has no parameters of any
…		…
1666	believe me.	2756	believe me.
1667		2757
1668	=back	2758	=back
1669		2759
1670		2760
		2761	=head2 C<ev_async> - how to wake up another event loop
		2762
		2763	In general, you cannot use an C<ev_loop> from multiple threads or other
		2764	asynchronous sources such as signal handlers (as opposed to multiple event
		2765	loops - those are of course safe to use in different threads).
		2766
		2767	Sometimes, however, you need to wake up another event loop you do not
		2768	control, for example because it belongs to another thread. This is what
		2769	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2770	can signal it by calling C<ev_async_send>, which is thread- and signal
		2771	safe.
		2772
		2773	This functionality is very similar to C<ev_signal> watchers, as signals,
		2774	too, are asynchronous in nature, and signals, too, will be compressed
		2775	(i.e. the number of callback invocations may be less than the number of
		2776	C<ev_async_sent> calls).
		2777
		2778	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2779	just the default loop.
		2780
		2781	=head3 Queueing
		2782
		2783	C<ev_async> does not support queueing of data in any way. The reason
		2784	is that the author does not know of a simple (or any) algorithm for a
		2785	multiple-writer-single-reader queue that works in all cases and doesn't
		2786	need elaborate support such as pthreads.
		2787
		2788	That means that if you want to queue data, you have to provide your own
		2789	queue. But at least I can tell you how to implement locking around your
		2790	queue:
		2791
		2792	=over 4
		2793
		2794	=item queueing from a signal handler context
		2795
		2796	To implement race-free queueing, you simply add to the queue in the signal
		2797	handler but you block the signal handler in the watcher callback. Here is
		2798	an example that does that for some fictitious SIGUSR1 handler:
		2799
		2800	static ev_async mysig;
		2801
		2802	static void
		2803	sigusr1_handler (void)
		2804	{
		2805	sometype data;
		2806
		2807	// no locking etc.
		2808	queue_put (data);
		2809	ev_async_send (EV_DEFAULT_ &mysig);
		2810	}
		2811
		2812	static void
		2813	mysig_cb (EV_P_ ev_async *w, int revents)
		2814	{
		2815	sometype data;
		2816	sigset_t block, prev;
		2817
		2818	sigemptyset (&block);
		2819	sigaddset (&block, SIGUSR1);
		2820	sigprocmask (SIG_BLOCK, &block, &prev);
		2821
		2822	while (queue_get (&data))
		2823	process (data);
		2824
		2825	if (sigismember (&prev, SIGUSR1)
		2826	sigprocmask (SIG_UNBLOCK, &block, 0);
		2827	}
		2828
		2829	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2830	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2831	either...).
		2832
		2833	=item queueing from a thread context
		2834
		2835	The strategy for threads is different, as you cannot (easily) block
		2836	threads but you can easily preempt them, so to queue safely you need to
		2837	employ a traditional mutex lock, such as in this pthread example:
		2838
		2839	static ev_async mysig;
		2840	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2841
		2842	static void
		2843	otherthread (void)
		2844	{
		2845	// only need to lock the actual queueing operation
		2846	pthread_mutex_lock (&mymutex);
		2847	queue_put (data);
		2848	pthread_mutex_unlock (&mymutex);
		2849
		2850	ev_async_send (EV_DEFAULT_ &mysig);
		2851	}
		2852
		2853	static void
		2854	mysig_cb (EV_P_ ev_async *w, int revents)
		2855	{
		2856	pthread_mutex_lock (&mymutex);
		2857
		2858	while (queue_get (&data))
		2859	process (data);
		2860
		2861	pthread_mutex_unlock (&mymutex);
		2862	}
		2863
		2864	=back
		2865
		2866
		2867	=head3 Watcher-Specific Functions and Data Members
		2868
		2869	=over 4
		2870
		2871	=item ev_async_init (ev_async *, callback)
		2872
		2873	Initialises and configures the async watcher - it has no parameters of any
		2874	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2875	trust me.
		2876
		2877	=item ev_async_send (loop, ev_async *)
		2878
		2879	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2880	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2881	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2882	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2883	section below on what exactly this means).
		2884
		2885	Note that, as with other watchers in libev, multiple events might get
		2886	compressed into a single callback invocation (another way to look at this
		2887	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2888	reset when the event loop detects that).
		2889
		2890	This call incurs the overhead of a system call only once per event loop
		2891	iteration, so while the overhead might be noticeable, it doesn't apply to
		2892	repeated calls to C<ev_async_send> for the same event loop.
		2893
		2894	=item bool = ev_async_pending (ev_async *)
		2895
		2896	Returns a non-zero value when C<ev_async_send> has been called on the
		2897	watcher but the event has not yet been processed (or even noted) by the
		2898	event loop.
		2899
		2900	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2901	the loop iterates next and checks for the watcher to have become active,
		2902	it will reset the flag again. C<ev_async_pending> can be used to very
		2903	quickly check whether invoking the loop might be a good idea.
		2904
		2905	Not that this does I<not> check whether the watcher itself is pending,
		2906	only whether it has been requested to make this watcher pending: there
		2907	is a time window between the event loop checking and resetting the async
		2908	notification, and the callback being invoked.
		2909
		2910	=back
		2911
		2912
1671	=head1 OTHER FUNCTIONS	2913	=head1 OTHER FUNCTIONS
1672		2914
1673	There are some other functions of possible interest. Described. Here. Now.	2915	There are some other functions of possible interest. Described. Here. Now.
1674		2916
1675	=over 4	2917	=over 4
1676		2918
1677	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2919	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1678		2920
1679	This function combines a simple timer and an I/O watcher, calls your	2921	This function combines a simple timer and an I/O watcher, calls your
1680	callback on whichever event happens first and automatically stop both	2922	callback on whichever event happens first and automatically stops both
1681	watchers. This is useful if you want to wait for a single event on an fd	2923	watchers. This is useful if you want to wait for a single event on an fd
1682	or timeout without having to allocate/configure/start/stop/free one or	2924	or timeout without having to allocate/configure/start/stop/free one or
1683	more watchers yourself.	2925	more watchers yourself.
1684		2926
1685	If C<fd> is less than 0, then no I/O watcher will be started and events	2927	If C<fd> is less than 0, then no I/O watcher will be started and the
1686	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2928	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1687	C<events> set will be craeted and started.	2929	the given C<fd> and C<events> set will be created and started.
1688		2930
1689	If C<timeout> is less than 0, then no timeout watcher will be	2931	If C<timeout> is less than 0, then no timeout watcher will be
1690	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2932	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1691	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2933	repeat = 0) will be started. C<0> is a valid timeout.
1692	dubious value.
1693		2934
1694	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2935	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1695	passed an C<revents> set like normal event callbacks (a combination of	2936	passed an C<revents> set like normal event callbacks (a combination of
1696	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2937	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1697	value passed to C<ev_once>:	2938	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2939	a timeout and an io event at the same time - you probably should give io
		2940	events precedence.
1698		2941
		2942	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2943
1699	static void stdin_ready (int revents, void *arg)	2944	static void stdin_ready (int revents, void *arg)
1700	{	2945	{
1701	if (revents & EV_TIMEOUT)
1702	/* doh, nothing entered */;
1703	else if (revents & EV_READ)	2946	if (revents & EV_READ)
1704	/* stdin might have data for us, joy! */;	2947	/* stdin might have data for us, joy! */;
		2948	else if (revents & EV_TIMEOUT)
		2949	/* doh, nothing entered */;
1705	}	2950	}
1706		2951
1707	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2952	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1708		2953
1709	=item ev_feed_event (ev_loop *, watcher *, int revents)	2954	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1710		2955
1711	Feeds the given event set into the event loop, as if the specified event	2956	Feeds the given event set into the event loop, as if the specified event
1712	had happened for the specified watcher (which must be a pointer to an	2957	had happened for the specified watcher (which must be a pointer to an
1713	initialised but not necessarily started event watcher).	2958	initialised but not necessarily started event watcher).
1714		2959
1715	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2960	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1716		2961
1717	Feed an event on the given fd, as if a file descriptor backend detected	2962	Feed an event on the given fd, as if a file descriptor backend detected
1718	the given events it.	2963	the given events it.
1719		2964
1720	=item ev_feed_signal_event (ev_loop *loop, int signum)	2965	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1721		2966
1722	Feed an event as if the given signal occured (C<loop> must be the default	2967	Feed an event as if the given signal occurred (C<loop> must be the default
1723	loop!).	2968	loop!).
1724		2969
1725	=back	2970	=back
1726		2971
1727		2972
…		…
1743		2988
1744	=item * Priorities are not currently supported. Initialising priorities	2989	=item * Priorities are not currently supported. Initialising priorities
1745	will fail and all watchers will have the same priority, even though there	2990	will fail and all watchers will have the same priority, even though there
1746	is an ev_pri field.	2991	is an ev_pri field.
1747		2992
		2993	=item * In libevent, the last base created gets the signals, in libev, the
		2994	first base created (== the default loop) gets the signals.
		2995
1748	=item * Other members are not supported.	2996	=item * Other members are not supported.
1749		2997
1750	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2998	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1751	to use the libev header file and library.	2999	to use the libev header file and library.
1752		3000
1753	=back	3001	=back
1754		3002
1755	=head1 C++ SUPPORT	3003	=head1 C++ SUPPORT
1756		3004
1757	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3005	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1758	you to use some convinience methods to start/stop watchers and also change	3006	you to use some convenience methods to start/stop watchers and also change
1759	the callback model to a model using method callbacks on objects.	3007	the callback model to a model using method callbacks on objects.
1760		3008
1761	To use it,	3009	To use it,
1762		3010
1763	#include <ev++.h>	3011	#include <ev++.h>
1764		3012
1765	This automatically includes F<ev.h> and puts all of its definitions (many	3013	This automatically includes F<ev.h> and puts all of its definitions (many
1766	of them macros) into the global namespace. All C++ specific things are	3014	of them macros) into the global namespace. All C++ specific things are
1767	put into the C<ev> namespace. It should support all the same embedding	3015	put into the C<ev> namespace. It should support all the same embedding
1768	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3016	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1835	your compiler is good :), then the method will be fully inlined into the	3083	your compiler is good :), then the method will be fully inlined into the
1836	thunking function, making it as fast as a direct C callback.	3084	thunking function, making it as fast as a direct C callback.
1837		3085
1838	Example: simple class declaration and watcher initialisation	3086	Example: simple class declaration and watcher initialisation
1839		3087
1840	struct myclass	3088	struct myclass
1841	{	3089	{
1842	void io_cb (ev::io &w, int revents) { }	3090	void io_cb (ev::io &w, int revents) { }
1843	}	3091	}
1844		3092
1845	myclass obj;	3093	myclass obj;
1846	ev::io iow;	3094	ev::io iow;
1847	iow.set <myclass, &myclass::io_cb> (&obj);	3095	iow.set <myclass, &myclass::io_cb> (&obj);
1848		3096
1849	=item w->set (void (*function)(watcher &w, int), void *data = 0)	3097	=item w->set (object *)
		3098
		3099	This is an B<experimental> feature that might go away in a future version.
		3100
		3101	This is a variation of a method callback - leaving out the method to call
		3102	will default the method to C<operator ()>, which makes it possible to use
		3103	functor objects without having to manually specify the C<operator ()> all
		3104	the time. Incidentally, you can then also leave out the template argument
		3105	list.
		3106
		3107	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3108	int revents)>.
		3109
		3110	See the method-C<set> above for more details.
		3111
		3112	Example: use a functor object as callback.
		3113
		3114	struct myfunctor
		3115	{
		3116	void operator() (ev::io &w, int revents)
		3117	{
		3118	...
		3119	}
		3120	}
		3121
		3122	myfunctor f;
		3123
		3124	ev::io w;
		3125	w.set (&f);
		3126
		3127	=item w->set<function> (void *data = 0)
1850		3128
1851	Also sets a callback, but uses a static method or plain function as	3129	Also sets a callback, but uses a static method or plain function as
1852	callback. The optional C<data> argument will be stored in the watcher's	3130	callback. The optional C<data> argument will be stored in the watcher's
1853	C<data> member and is free for you to use.	3131	C<data> member and is free for you to use.
1854		3132
		3133	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3134
1855	See the method-C<set> above for more details.	3135	See the method-C<set> above for more details.
		3136
		3137	Example: Use a plain function as callback.
		3138
		3139	static void io_cb (ev::io &w, int revents) { }
		3140	iow.set <io_cb> ();
1856		3141
1857	=item w->set (struct ev_loop *)	3142	=item w->set (struct ev_loop *)
1858		3143
1859	Associates a different C<struct ev_loop> with this watcher. You can only	3144	Associates a different C<struct ev_loop> with this watcher. You can only
1860	do this when the watcher is inactive (and not pending either).	3145	do this when the watcher is inactive (and not pending either).
1861		3146
1862	=item w->set ([args])	3147	=item w->set ([arguments])
1863		3148
1864	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3149	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1865	called at least once. Unlike the C counterpart, an active watcher gets	3150	called at least once. Unlike the C counterpart, an active watcher gets
1866	automatically stopped and restarted when reconfiguring it with this	3151	automatically stopped and restarted when reconfiguring it with this
1867	method.	3152	method.
1868		3153
1869	=item w->start ()	3154	=item w->start ()
…		…
1873		3158
1874	=item w->stop ()	3159	=item w->stop ()
1875		3160
1876	Stops the watcher if it is active. Again, no C<loop> argument.	3161	Stops the watcher if it is active. Again, no C<loop> argument.
1877		3162
1878	=item w->again () C<ev::timer>, C<ev::periodic> only	3163	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1879		3164
1880	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3165	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1881	C<ev_TYPE_again> function.	3166	C<ev_TYPE_again> function.
1882		3167
1883	=item w->sweep () C<ev::embed> only	3168	=item w->sweep () (C<ev::embed> only)
1884		3169
1885	Invokes C<ev_embed_sweep>.	3170	Invokes C<ev_embed_sweep>.
1886		3171
1887	=item w->update () C<ev::stat> only	3172	=item w->update () (C<ev::stat> only)
1888		3173
1889	Invokes C<ev_stat_stat>.	3174	Invokes C<ev_stat_stat>.
1890		3175
1891	=back	3176	=back
1892		3177
1893	=back	3178	=back
1894		3179
1895	Example: Define a class with an IO and idle watcher, start one of them in	3180	Example: Define a class with an IO and idle watcher, start one of them in
1896	the constructor.	3181	the constructor.
1897		3182
1898	class myclass	3183	class myclass
1899	{	3184	{
1900	ev_io io; void io_cb (ev::io &w, int revents);	3185	ev::io io ; void io_cb (ev::io &w, int revents);
1901	ev_idle idle void idle_cb (ev::idle &w, int revents);	3186	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1902		3187
1903	myclass ();	3188	myclass (int fd)
1904	}	3189	{
1905
1906	myclass::myclass (int fd)
1907	{
1908	io .set <myclass, &myclass::io_cb > (this);	3190	io .set <myclass, &myclass::io_cb > (this);
1909	idle.set <myclass, &myclass::idle_cb> (this);	3191	idle.set <myclass, &myclass::idle_cb> (this);
1910		3192
1911	io.start (fd, ev::READ);	3193	io.start (fd, ev::READ);
		3194	}
1912	}	3195	};
		3196
		3197
		3198	=head1 OTHER LANGUAGE BINDINGS
		3199
		3200	Libev does not offer other language bindings itself, but bindings for a
		3201	number of languages exist in the form of third-party packages. If you know
		3202	any interesting language binding in addition to the ones listed here, drop
		3203	me a note.
		3204
		3205	=over 4
		3206
		3207	=item Perl
		3208
		3209	The EV module implements the full libev API and is actually used to test
		3210	libev. EV is developed together with libev. Apart from the EV core module,
		3211	there are additional modules that implement libev-compatible interfaces
		3212	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3213	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3214	and C<EV::Glib>).
		3215
		3216	It can be found and installed via CPAN, its homepage is at
		3217	L<http://software.schmorp.de/pkg/EV>.
		3218
		3219	=item Python
		3220
		3221	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3222	seems to be quite complete and well-documented.
		3223
		3224	=item Ruby
		3225
		3226	Tony Arcieri has written a ruby extension that offers access to a subset
		3227	of the libev API and adds file handle abstractions, asynchronous DNS and
		3228	more on top of it. It can be found via gem servers. Its homepage is at
		3229	L<http://rev.rubyforge.org/>.
		3230
		3231	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3232	makes rev work even on mingw.
		3233
		3234	=item Haskell
		3235
		3236	A haskell binding to libev is available at
		3237	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3238
		3239	=item D
		3240
		3241	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3242	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3243
		3244	=item Ocaml
		3245
		3246	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3247	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3248
		3249	=back
1913		3250
1914		3251
1915	=head1 MACRO MAGIC	3252	=head1 MACRO MAGIC
1916		3253
1917	Libev can be compiled with a variety of options, the most fundemantal is	3254	Libev can be compiled with a variety of options, the most fundamental
1918	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3255	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1919	callbacks have an initial C<struct ev_loop *> argument.	3256	functions and callbacks have an initial C<struct ev_loop *> argument.
1920		3257
1921	To make it easier to write programs that cope with either variant, the	3258	To make it easier to write programs that cope with either variant, the
1922	following macros are defined:	3259	following macros are defined:
1923		3260
1924	=over 4	3261	=over 4
…		…
1927		3264
1928	This provides the loop I<argument> for functions, if one is required ("ev	3265	This provides the loop I<argument> for functions, if one is required ("ev
1929	loop argument"). The C<EV_A> form is used when this is the sole argument,	3266	loop argument"). The C<EV_A> form is used when this is the sole argument,
1930	C<EV_A_> is used when other arguments are following. Example:	3267	C<EV_A_> is used when other arguments are following. Example:
1931		3268
1932	ev_unref (EV_A);	3269	ev_unref (EV_A);
1933	ev_timer_add (EV_A_ watcher);	3270	ev_timer_add (EV_A_ watcher);
1934	ev_loop (EV_A_ 0);	3271	ev_loop (EV_A_ 0);
1935		3272
1936	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3273	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1937	which is often provided by the following macro.	3274	which is often provided by the following macro.
1938		3275
1939	=item C<EV_P>, C<EV_P_>	3276	=item C<EV_P>, C<EV_P_>
1940		3277
1941	This provides the loop I<parameter> for functions, if one is required ("ev	3278	This provides the loop I<parameter> for functions, if one is required ("ev
1942	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3279	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1943	C<EV_P_> is used when other parameters are following. Example:	3280	C<EV_P_> is used when other parameters are following. Example:
1944		3281
1945	// this is how ev_unref is being declared	3282	// this is how ev_unref is being declared
1946	static void ev_unref (EV_P);	3283	static void ev_unref (EV_P);
1947		3284
1948	// this is how you can declare your typical callback	3285	// this is how you can declare your typical callback
1949	static void cb (EV_P_ ev_timer *w, int revents)	3286	static void cb (EV_P_ ev_timer *w, int revents)
1950		3287
1951	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3288	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1952	suitable for use with C<EV_A>.	3289	suitable for use with C<EV_A>.
1953		3290
1954	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3291	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1955		3292
1956	Similar to the other two macros, this gives you the value of the default	3293	Similar to the other two macros, this gives you the value of the default
1957	loop, if multiple loops are supported ("ev loop default").	3294	loop, if multiple loops are supported ("ev loop default").
		3295
		3296	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3297
		3298	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3299	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3300	is undefined when the default loop has not been initialised by a previous
		3301	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3302
		3303	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3304	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
1958		3305
1959	=back	3306	=back
1960		3307
1961	Example: Declare and initialise a check watcher, utilising the above	3308	Example: Declare and initialise a check watcher, utilising the above
1962	macros so it will work regardless of whether multiple loops are supported	3309	macros so it will work regardless of whether multiple loops are supported
1963	or not.	3310	or not.
1964		3311
1965	static void	3312	static void
1966	check_cb (EV_P_ ev_timer *w, int revents)	3313	check_cb (EV_P_ ev_timer *w, int revents)
1967	{	3314	{
1968	ev_check_stop (EV_A_ w);	3315	ev_check_stop (EV_A_ w);
1969	}	3316	}
1970		3317
1971	ev_check check;	3318	ev_check check;
1972	ev_check_init (&check, check_cb);	3319	ev_check_init (&check, check_cb);
1973	ev_check_start (EV_DEFAULT_ &check);	3320	ev_check_start (EV_DEFAULT_ &check);
1974	ev_loop (EV_DEFAULT_ 0);	3321	ev_loop (EV_DEFAULT_ 0);
1975		3322
1976	=head1 EMBEDDING	3323	=head1 EMBEDDING
1977		3324
1978	Libev can (and often is) directly embedded into host	3325	Libev can (and often is) directly embedded into host
1979	applications. Examples of applications that embed it include the Deliantra	3326	applications. Examples of applications that embed it include the Deliantra
1980	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3327	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1981	and rxvt-unicode.	3328	and rxvt-unicode.
1982		3329
1983	The goal is to enable you to just copy the neecssary files into your	3330	The goal is to enable you to just copy the necessary files into your
1984	source directory without having to change even a single line in them, so	3331	source directory without having to change even a single line in them, so
1985	you can easily upgrade by simply copying (or having a checked-out copy of	3332	you can easily upgrade by simply copying (or having a checked-out copy of
1986	libev somewhere in your source tree).	3333	libev somewhere in your source tree).
1987		3334
1988	=head2 FILESETS	3335	=head2 FILESETS
1989		3336
1990	Depending on what features you need you need to include one or more sets of files	3337	Depending on what features you need you need to include one or more sets of files
1991	in your app.	3338	in your application.
1992		3339
1993	=head3 CORE EVENT LOOP	3340	=head3 CORE EVENT LOOP
1994		3341
1995	To include only the libev core (all the C<ev_*> functions), with manual	3342	To include only the libev core (all the C<ev_*> functions), with manual
1996	configuration (no autoconf):	3343	configuration (no autoconf):
1997		3344
1998	#define EV_STANDALONE 1	3345	#define EV_STANDALONE 1
1999	#include "ev.c"	3346	#include "ev.c"
2000		3347
2001	This will automatically include F<ev.h>, too, and should be done in a	3348	This will automatically include F<ev.h>, too, and should be done in a
2002	single C source file only to provide the function implementations. To use	3349	single C source file only to provide the function implementations. To use
2003	it, do the same for F<ev.h> in all files wishing to use this API (best	3350	it, do the same for F<ev.h> in all files wishing to use this API (best
2004	done by writing a wrapper around F<ev.h> that you can include instead and	3351	done by writing a wrapper around F<ev.h> that you can include instead and
2005	where you can put other configuration options):	3352	where you can put other configuration options):
2006		3353
2007	#define EV_STANDALONE 1	3354	#define EV_STANDALONE 1
2008	#include "ev.h"	3355	#include "ev.h"
2009		3356
2010	Both header files and implementation files can be compiled with a C++	3357	Both header files and implementation files can be compiled with a C++
2011	compiler (at least, thats a stated goal, and breakage will be treated	3358	compiler (at least, that's a stated goal, and breakage will be treated
2012	as a bug).	3359	as a bug).
2013		3360
2014	You need the following files in your source tree, or in a directory	3361	You need the following files in your source tree, or in a directory
2015	in your include path (e.g. in libev/ when using -Ilibev):	3362	in your include path (e.g. in libev/ when using -Ilibev):
2016		3363
2017	ev.h	3364	ev.h
2018	ev.c	3365	ev.c
2019	ev_vars.h	3366	ev_vars.h
2020	ev_wrap.h	3367	ev_wrap.h
2021		3368
2022	ev_win32.c required on win32 platforms only	3369	ev_win32.c required on win32 platforms only
2023		3370
2024	ev_select.c only when select backend is enabled (which is enabled by default)	3371	ev_select.c only when select backend is enabled (which is enabled by default)
2025	ev_poll.c only when poll backend is enabled (disabled by default)	3372	ev_poll.c only when poll backend is enabled (disabled by default)
2026	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3373	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2027	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3374	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2028	ev_port.c only when the solaris port backend is enabled (disabled by default)	3375	ev_port.c only when the solaris port backend is enabled (disabled by default)
2029		3376
2030	F<ev.c> includes the backend files directly when enabled, so you only need	3377	F<ev.c> includes the backend files directly when enabled, so you only need
2031	to compile this single file.	3378	to compile this single file.
2032		3379
2033	=head3 LIBEVENT COMPATIBILITY API	3380	=head3 LIBEVENT COMPATIBILITY API
2034		3381
2035	To include the libevent compatibility API, also include:	3382	To include the libevent compatibility API, also include:
2036		3383
2037	#include "event.c"	3384	#include "event.c"
2038		3385
2039	in the file including F<ev.c>, and:	3386	in the file including F<ev.c>, and:
2040		3387
2041	#include "event.h"	3388	#include "event.h"
2042		3389
2043	in the files that want to use the libevent API. This also includes F<ev.h>.	3390	in the files that want to use the libevent API. This also includes F<ev.h>.
2044		3391
2045	You need the following additional files for this:	3392	You need the following additional files for this:
2046		3393
2047	event.h	3394	event.h
2048	event.c	3395	event.c
2049		3396
2050	=head3 AUTOCONF SUPPORT	3397	=head3 AUTOCONF SUPPORT
2051		3398
2052	Instead of using C<EV_STANDALONE=1> and providing your config in	3399	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2053	whatever way you want, you can also C<m4_include([libev.m4])> in your	3400	whatever way you want, you can also C<m4_include([libev.m4])> in your
2054	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3401	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2055	include F<config.h> and configure itself accordingly.	3402	include F<config.h> and configure itself accordingly.
2056		3403
2057	For this of course you need the m4 file:	3404	For this of course you need the m4 file:
2058		3405
2059	libev.m4	3406	libev.m4
2060		3407
2061	=head2 PREPROCESSOR SYMBOLS/MACROS	3408	=head2 PREPROCESSOR SYMBOLS/MACROS
2062		3409
2063	Libev can be configured via a variety of preprocessor symbols you have to define	3410	Libev can be configured via a variety of preprocessor symbols you have to
2064	before including any of its files. The default is not to build for multiplicity	3411	define before including any of its files. The default in the absence of
2065	and only include the select backend.	3412	autoconf is documented for every option.
2066		3413
2067	=over 4	3414	=over 4
2068		3415
2069	=item EV_STANDALONE	3416	=item EV_STANDALONE
2070		3417
…		…
2072	keeps libev from including F<config.h>, and it also defines dummy	3419	keeps libev from including F<config.h>, and it also defines dummy
2073	implementations for some libevent functions (such as logging, which is not	3420	implementations for some libevent functions (such as logging, which is not
2074	supported). It will also not define any of the structs usually found in	3421	supported). It will also not define any of the structs usually found in
2075	F<event.h> that are not directly supported by the libev core alone.	3422	F<event.h> that are not directly supported by the libev core alone.
2076		3423
		3424	In stanbdalone mode, libev will still try to automatically deduce the
		3425	configuration, but has to be more conservative.
		3426
2077	=item EV_USE_MONOTONIC	3427	=item EV_USE_MONOTONIC
2078		3428
2079	If defined to be C<1>, libev will try to detect the availability of the	3429	If defined to be C<1>, libev will try to detect the availability of the
2080	monotonic clock option at both compiletime and runtime. Otherwise no use	3430	monotonic clock option at both compile time and runtime. Otherwise no
2081	of the monotonic clock option will be attempted. If you enable this, you	3431	use of the monotonic clock option will be attempted. If you enable this,
2082	usually have to link against librt or something similar. Enabling it when	3432	you usually have to link against librt or something similar. Enabling it
2083	the functionality isn't available is safe, though, althoguh you have	3433	when the functionality isn't available is safe, though, although you have
2084	to make sure you link against any libraries where the C<clock_gettime>	3434	to make sure you link against any libraries where the C<clock_gettime>
2085	function is hiding in (often F<-lrt>).	3435	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2086		3436
2087	=item EV_USE_REALTIME	3437	=item EV_USE_REALTIME
2088		3438
2089	If defined to be C<1>, libev will try to detect the availability of the	3439	If defined to be C<1>, libev will try to detect the availability of the
2090	realtime clock option at compiletime (and assume its availability at	3440	real-time clock option at compile time (and assume its availability
2091	runtime if successful). Otherwise no use of the realtime clock option will	3441	at runtime if successful). Otherwise no use of the real-time clock
2092	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3442	option will be attempted. This effectively replaces C<gettimeofday>
2093	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3443	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2094	in the description of C<EV_USE_MONOTONIC>, though.	3444	correctness. See the note about libraries in the description of
		3445	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3446	C<EV_USE_CLOCK_SYSCALL>.
		3447
		3448	=item EV_USE_CLOCK_SYSCALL
		3449
		3450	If defined to be C<1>, libev will try to use a direct syscall instead
		3451	of calling the system-provided C<clock_gettime> function. This option
		3452	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3453	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3454	programs needlessly. Using a direct syscall is slightly slower (in
		3455	theory), because no optimised vdso implementation can be used, but avoids
		3456	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3457	higher, as it simplifies linking (no need for C<-lrt>).
		3458
		3459	=item EV_USE_NANOSLEEP
		3460
		3461	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3462	and will use it for delays. Otherwise it will use C<select ()>.
		3463
		3464	=item EV_USE_EVENTFD
		3465
		3466	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3467	available and will probe for kernel support at runtime. This will improve
		3468	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3469	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3470	2.7 or newer, otherwise disabled.
2095		3471
2096	=item EV_USE_SELECT	3472	=item EV_USE_SELECT
2097		3473
2098	If undefined or defined to be C<1>, libev will compile in support for the	3474	If undefined or defined to be C<1>, libev will compile in support for the
2099	C<select>(2) backend. No attempt at autodetection will be done: if no	3475	C<select>(2) backend. No attempt at auto-detection will be done: if no
2100	other method takes over, select will be it. Otherwise the select backend	3476	other method takes over, select will be it. Otherwise the select backend
2101	will not be compiled in.	3477	will not be compiled in.
2102		3478
2103	=item EV_SELECT_USE_FD_SET	3479	=item EV_SELECT_USE_FD_SET
2104		3480
2105	If defined to C<1>, then the select backend will use the system C<fd_set>	3481	If defined to C<1>, then the select backend will use the system C<fd_set>
2106	structure. This is useful if libev doesn't compile due to a missing	3482	structure. This is useful if libev doesn't compile due to a missing
2107	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3483	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2108	exotic systems. This usually limits the range of file descriptors to some	3484	on exotic systems. This usually limits the range of file descriptors to
2109	low limit such as 1024 or might have other limitations (winsocket only	3485	some low limit such as 1024 or might have other limitations (winsocket
2110	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3486	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2111	influence the size of the C<fd_set> used.	3487	configures the maximum size of the C<fd_set>.
2112		3488
2113	=item EV_SELECT_IS_WINSOCKET	3489	=item EV_SELECT_IS_WINSOCKET
2114		3490
2115	When defined to C<1>, the select backend will assume that	3491	When defined to C<1>, the select backend will assume that
2116	select/socket/connect etc. don't understand file descriptors but	3492	select/socket/connect etc. don't understand file descriptors but
…		…
2118	be used is the winsock select). This means that it will call	3494	be used is the winsock select). This means that it will call
2119	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3495	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2120	it is assumed that all these functions actually work on fds, even	3496	it is assumed that all these functions actually work on fds, even
2121	on win32. Should not be defined on non-win32 platforms.	3497	on win32. Should not be defined on non-win32 platforms.
2122		3498
		3499	=item EV_FD_TO_WIN32_HANDLE
		3500
		3501	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3502	file descriptors to socket handles. When not defining this symbol (the
		3503	default), then libev will call C<_get_osfhandle>, which is usually
		3504	correct. In some cases, programs use their own file descriptor management,
		3505	in which case they can provide this function to map fds to socket handles.
		3506
2123	=item EV_USE_POLL	3507	=item EV_USE_POLL
2124		3508
2125	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3509	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2126	backend. Otherwise it will be enabled on non-win32 platforms. It	3510	backend. Otherwise it will be enabled on non-win32 platforms. It
2127	takes precedence over select.	3511	takes precedence over select.
2128		3512
2129	=item EV_USE_EPOLL	3513	=item EV_USE_EPOLL
2130		3514
2131	If defined to be C<1>, libev will compile in support for the Linux	3515	If defined to be C<1>, libev will compile in support for the Linux
2132	C<epoll>(7) backend. Its availability will be detected at runtime,	3516	C<epoll>(7) backend. Its availability will be detected at runtime,
2133	otherwise another method will be used as fallback. This is the	3517	otherwise another method will be used as fallback. This is the preferred
2134	preferred backend for GNU/Linux systems.	3518	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3519	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2135		3520
2136	=item EV_USE_KQUEUE	3521	=item EV_USE_KQUEUE
2137		3522
2138	If defined to be C<1>, libev will compile in support for the BSD style	3523	If defined to be C<1>, libev will compile in support for the BSD style
2139	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3524	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2152	otherwise another method will be used as fallback. This is the preferred	3537	otherwise another method will be used as fallback. This is the preferred
2153	backend for Solaris 10 systems.	3538	backend for Solaris 10 systems.
2154		3539
2155	=item EV_USE_DEVPOLL	3540	=item EV_USE_DEVPOLL
2156		3541
2157	reserved for future expansion, works like the USE symbols above.	3542	Reserved for future expansion, works like the USE symbols above.
2158		3543
2159	=item EV_USE_INOTIFY	3544	=item EV_USE_INOTIFY
2160		3545
2161	If defined to be C<1>, libev will compile in support for the Linux inotify	3546	If defined to be C<1>, libev will compile in support for the Linux inotify
2162	interface to speed up C<ev_stat> watchers. Its actual availability will	3547	interface to speed up C<ev_stat> watchers. Its actual availability will
2163	be detected at runtime.	3548	be detected at runtime. If undefined, it will be enabled if the headers
		3549	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3550
		3551	=item EV_ATOMIC_T
		3552
		3553	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3554	access is atomic with respect to other threads or signal contexts. No such
		3555	type is easily found in the C language, so you can provide your own type
		3556	that you know is safe for your purposes. It is used both for signal handler "locking"
		3557	as well as for signal and thread safety in C<ev_async> watchers.
		3558
		3559	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3560	(from F<signal.h>), which is usually good enough on most platforms.
2164		3561
2165	=item EV_H	3562	=item EV_H
2166		3563
2167	The name of the F<ev.h> header file used to include it. The default if	3564	The name of the F<ev.h> header file used to include it. The default if
2168	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3565	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2169	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3566	used to virtually rename the F<ev.h> header file in case of conflicts.
2170		3567
2171	=item EV_CONFIG_H	3568	=item EV_CONFIG_H
2172		3569
2173	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3570	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2174	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3571	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2175	C<EV_H>, above.	3572	C<EV_H>, above.
2176		3573
2177	=item EV_EVENT_H	3574	=item EV_EVENT_H
2178		3575
2179	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3576	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2180	of how the F<event.h> header can be found.	3577	of how the F<event.h> header can be found, the default is C<"event.h">.
2181		3578
2182	=item EV_PROTOTYPES	3579	=item EV_PROTOTYPES
2183		3580
2184	If defined to be C<0>, then F<ev.h> will not define any function	3581	If defined to be C<0>, then F<ev.h> will not define any function
2185	prototypes, but still define all the structs and other symbols. This is	3582	prototypes, but still define all the structs and other symbols. This is
…		…
2206	When doing priority-based operations, libev usually has to linearly search	3603	When doing priority-based operations, libev usually has to linearly search
2207	all the priorities, so having many of them (hundreds) uses a lot of space	3604	all the priorities, so having many of them (hundreds) uses a lot of space
2208	and time, so using the defaults of five priorities (-2 .. +2) is usually	3605	and time, so using the defaults of five priorities (-2 .. +2) is usually
2209	fine.	3606	fine.
2210		3607
2211	If your embedding app does not need any priorities, defining these both to	3608	If your embedding application does not need any priorities, defining these
2212	C<0> will save some memory and cpu.	3609	both to C<0> will save some memory and CPU.
2213		3610
2214	=item EV_PERIODIC_ENABLE	3611	=item EV_PERIODIC_ENABLE
2215		3612
2216	If undefined or defined to be C<1>, then periodic timers are supported. If	3613	If undefined or defined to be C<1>, then periodic timers are supported. If
2217	defined to be C<0>, then they are not. Disabling them saves a few kB of	3614	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2224	code.	3621	code.
2225		3622
2226	=item EV_EMBED_ENABLE	3623	=item EV_EMBED_ENABLE
2227		3624
2228	If undefined or defined to be C<1>, then embed watchers are supported. If	3625	If undefined or defined to be C<1>, then embed watchers are supported. If
2229	defined to be C<0>, then they are not.	3626	defined to be C<0>, then they are not. Embed watchers rely on most other
		3627	watcher types, which therefore must not be disabled.
2230		3628
2231	=item EV_STAT_ENABLE	3629	=item EV_STAT_ENABLE
2232		3630
2233	If undefined or defined to be C<1>, then stat watchers are supported. If	3631	If undefined or defined to be C<1>, then stat watchers are supported. If
2234	defined to be C<0>, then they are not.	3632	defined to be C<0>, then they are not.
…		…
2236	=item EV_FORK_ENABLE	3634	=item EV_FORK_ENABLE
2237		3635
2238	If undefined or defined to be C<1>, then fork watchers are supported. If	3636	If undefined or defined to be C<1>, then fork watchers are supported. If
2239	defined to be C<0>, then they are not.	3637	defined to be C<0>, then they are not.
2240		3638
		3639	=item EV_ASYNC_ENABLE
		3640
		3641	If undefined or defined to be C<1>, then async watchers are supported. If
		3642	defined to be C<0>, then they are not.
		3643
2241	=item EV_MINIMAL	3644	=item EV_MINIMAL
2242		3645
2243	If you need to shave off some kilobytes of code at the expense of some	3646	If you need to shave off some kilobytes of code at the expense of some
2244	speed, define this symbol to C<1>. Currently only used for gcc to override	3647	speed, define this symbol to C<1>. Currently this is used to override some
2245	some inlining decisions, saves roughly 30% codesize of amd64.	3648	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3649	much smaller 2-heap for timer management over the default 4-heap.
2246		3650
2247	=item EV_PID_HASHSIZE	3651	=item EV_PID_HASHSIZE
2248		3652
2249	C<ev_child> watchers use a small hash table to distribute workload by	3653	C<ev_child> watchers use a small hash table to distribute workload by
2250	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3654	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2251	than enough. If you need to manage thousands of children you might want to	3655	than enough. If you need to manage thousands of children you might want to
2252	increase this value (I<must> be a power of two).	3656	increase this value (I<must> be a power of two).
2253		3657
2254	=item EV_INOTIFY_HASHSIZE	3658	=item EV_INOTIFY_HASHSIZE
2255		3659
2256	C<ev_staz> watchers use a small hash table to distribute workload by	3660	C<ev_stat> watchers use a small hash table to distribute workload by
2257	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3661	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2258	usually more than enough. If you need to manage thousands of C<ev_stat>	3662	usually more than enough. If you need to manage thousands of C<ev_stat>
2259	watchers you might want to increase this value (I<must> be a power of	3663	watchers you might want to increase this value (I<must> be a power of
2260	two).	3664	two).
2261		3665
		3666	=item EV_USE_4HEAP
		3667
		3668	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3669	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3670	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3671	faster performance with many (thousands) of watchers.
		3672
		3673	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3674	(disabled).
		3675
		3676	=item EV_HEAP_CACHE_AT
		3677
		3678	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3679	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3680	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3681	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3682	but avoids random read accesses on heap changes. This improves performance
		3683	noticeably with many (hundreds) of watchers.
		3684
		3685	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3686	(disabled).
		3687
		3688	=item EV_VERIFY
		3689
		3690	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3691	be done: If set to C<0>, no internal verification code will be compiled
		3692	in. If set to C<1>, then verification code will be compiled in, but not
		3693	called. If set to C<2>, then the internal verification code will be
		3694	called once per loop, which can slow down libev. If set to C<3>, then the
		3695	verification code will be called very frequently, which will slow down
		3696	libev considerably.
		3697
		3698	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3699	C<0>.
		3700
2262	=item EV_COMMON	3701	=item EV_COMMON
2263		3702
2264	By default, all watchers have a C<void *data> member. By redefining	3703	By default, all watchers have a C<void *data> member. By redefining
2265	this macro to a something else you can include more and other types of	3704	this macro to a something else you can include more and other types of
2266	members. You have to define it each time you include one of the files,	3705	members. You have to define it each time you include one of the files,
2267	though, and it must be identical each time.	3706	though, and it must be identical each time.
2268		3707
2269	For example, the perl EV module uses something like this:	3708	For example, the perl EV module uses something like this:
2270		3709
2271	#define EV_COMMON \	3710	#define EV_COMMON \
2272	SV *self; /* contains this struct */ \	3711	SV *self; /* contains this struct */ \
2273	SV *cb_sv, *fh /* note no trailing ";" */	3712	SV *cb_sv, *fh /* note no trailing ";" */
2274		3713
2275	=item EV_CB_DECLARE (type)	3714	=item EV_CB_DECLARE (type)
2276		3715
2277	=item EV_CB_INVOKE (watcher, revents)	3716	=item EV_CB_INVOKE (watcher, revents)
2278		3717
2279	=item ev_set_cb (ev, cb)	3718	=item ev_set_cb (ev, cb)
2280		3719
2281	Can be used to change the callback member declaration in each watcher,	3720	Can be used to change the callback member declaration in each watcher,
2282	and the way callbacks are invoked and set. Must expand to a struct member	3721	and the way callbacks are invoked and set. Must expand to a struct member
2283	definition and a statement, respectively. See the F<ev.v> header file for	3722	definition and a statement, respectively. See the F<ev.h> header file for
2284	their default definitions. One possible use for overriding these is to	3723	their default definitions. One possible use for overriding these is to
2285	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3724	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2286	method calls instead of plain function calls in C++.	3725	method calls instead of plain function calls in C++.
		3726
		3727	=back
		3728
		3729	=head2 EXPORTED API SYMBOLS
		3730
		3731	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3732	exported symbols, you can use the provided F<Symbol.*> files which list
		3733	all public symbols, one per line:
		3734
		3735	Symbols.ev for libev proper
		3736	Symbols.event for the libevent emulation
		3737
		3738	This can also be used to rename all public symbols to avoid clashes with
		3739	multiple versions of libev linked together (which is obviously bad in
		3740	itself, but sometimes it is inconvenient to avoid this).
		3741
		3742	A sed command like this will create wrapper C<#define>'s that you need to
		3743	include before including F<ev.h>:
		3744
		3745	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3746
		3747	This would create a file F<wrap.h> which essentially looks like this:
		3748
		3749	#define ev_backend myprefix_ev_backend
		3750	#define ev_check_start myprefix_ev_check_start
		3751	#define ev_check_stop myprefix_ev_check_stop
		3752	...
2287		3753
2288	=head2 EXAMPLES	3754	=head2 EXAMPLES
2289		3755
2290	For a real-world example of a program the includes libev	3756	For a real-world example of a program the includes libev
2291	verbatim, you can have a look at the EV perl module	3757	verbatim, you can have a look at the EV perl module
…		…
2296	file.	3762	file.
2297		3763
2298	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3764	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2299	that everybody includes and which overrides some configure choices:	3765	that everybody includes and which overrides some configure choices:
2300		3766
2301	#define EV_MINIMAL 1	3767	#define EV_MINIMAL 1
2302	#define EV_USE_POLL 0	3768	#define EV_USE_POLL 0
2303	#define EV_MULTIPLICITY 0	3769	#define EV_MULTIPLICITY 0
2304	#define EV_PERIODIC_ENABLE 0	3770	#define EV_PERIODIC_ENABLE 0
2305	#define EV_STAT_ENABLE 0	3771	#define EV_STAT_ENABLE 0
2306	#define EV_FORK_ENABLE 0	3772	#define EV_FORK_ENABLE 0
2307	#define EV_CONFIG_H <config.h>	3773	#define EV_CONFIG_H <config.h>
2308	#define EV_MINPRI 0	3774	#define EV_MINPRI 0
2309	#define EV_MAXPRI 0	3775	#define EV_MAXPRI 0
2310		3776
2311	#include "ev++.h"	3777	#include "ev++.h"
2312		3778
2313	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3779	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2314		3780
2315	#include "ev_cpp.h"	3781	#include "ev_cpp.h"
2316	#include "ev.c"	3782	#include "ev.c"
2317		3783
		3784	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2318		3785
		3786	=head2 THREADS AND COROUTINES
		3787
		3788	=head3 THREADS
		3789
		3790	All libev functions are reentrant and thread-safe unless explicitly
		3791	documented otherwise, but libev implements no locking itself. This means
		3792	that you can use as many loops as you want in parallel, as long as there
		3793	are no concurrent calls into any libev function with the same loop
		3794	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3795	of course): libev guarantees that different event loops share no data
		3796	structures that need any locking.
		3797
		3798	Or to put it differently: calls with different loop parameters can be done
		3799	concurrently from multiple threads, calls with the same loop parameter
		3800	must be done serially (but can be done from different threads, as long as
		3801	only one thread ever is inside a call at any point in time, e.g. by using
		3802	a mutex per loop).
		3803
		3804	Specifically to support threads (and signal handlers), libev implements
		3805	so-called C<ev_async> watchers, which allow some limited form of
		3806	concurrency on the same event loop, namely waking it up "from the
		3807	outside".
		3808
		3809	If you want to know which design (one loop, locking, or multiple loops
		3810	without or something else still) is best for your problem, then I cannot
		3811	help you, but here is some generic advice:
		3812
		3813	=over 4
		3814
		3815	=item * most applications have a main thread: use the default libev loop
		3816	in that thread, or create a separate thread running only the default loop.
		3817
		3818	This helps integrating other libraries or software modules that use libev
		3819	themselves and don't care/know about threading.
		3820
		3821	=item * one loop per thread is usually a good model.
		3822
		3823	Doing this is almost never wrong, sometimes a better-performance model
		3824	exists, but it is always a good start.
		3825
		3826	=item * other models exist, such as the leader/follower pattern, where one
		3827	loop is handed through multiple threads in a kind of round-robin fashion.
		3828
		3829	Choosing a model is hard - look around, learn, know that usually you can do
		3830	better than you currently do :-)
		3831
		3832	=item * often you need to talk to some other thread which blocks in the
		3833	event loop.
		3834
		3835	C<ev_async> watchers can be used to wake them up from other threads safely
		3836	(or from signal contexts...).
		3837
		3838	An example use would be to communicate signals or other events that only
		3839	work in the default loop by registering the signal watcher with the
		3840	default loop and triggering an C<ev_async> watcher from the default loop
		3841	watcher callback into the event loop interested in the signal.
		3842
		3843	=back
		3844
		3845	=head3 COROUTINES
		3846
		3847	Libev is very accommodating to coroutines ("cooperative threads"):
		3848	libev fully supports nesting calls to its functions from different
		3849	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3850	different coroutines, and switch freely between both coroutines running the
		3851	loop, as long as you don't confuse yourself). The only exception is that
		3852	you must not do this from C<ev_periodic> reschedule callbacks.
		3853
		3854	Care has been taken to ensure that libev does not keep local state inside
		3855	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3856	they do not call any callbacks.
		3857
		3858	=head2 COMPILER WARNINGS
		3859
		3860	Depending on your compiler and compiler settings, you might get no or a
		3861	lot of warnings when compiling libev code. Some people are apparently
		3862	scared by this.
		3863
		3864	However, these are unavoidable for many reasons. For one, each compiler
		3865	has different warnings, and each user has different tastes regarding
		3866	warning options. "Warn-free" code therefore cannot be a goal except when
		3867	targeting a specific compiler and compiler-version.
		3868
		3869	Another reason is that some compiler warnings require elaborate
		3870	workarounds, or other changes to the code that make it less clear and less
		3871	maintainable.
		3872
		3873	And of course, some compiler warnings are just plain stupid, or simply
		3874	wrong (because they don't actually warn about the condition their message
		3875	seems to warn about). For example, certain older gcc versions had some
		3876	warnings that resulted an extreme number of false positives. These have
		3877	been fixed, but some people still insist on making code warn-free with
		3878	such buggy versions.
		3879
		3880	While libev is written to generate as few warnings as possible,
		3881	"warn-free" code is not a goal, and it is recommended not to build libev
		3882	with any compiler warnings enabled unless you are prepared to cope with
		3883	them (e.g. by ignoring them). Remember that warnings are just that:
		3884	warnings, not errors, or proof of bugs.
		3885
		3886
		3887	=head2 VALGRIND
		3888
		3889	Valgrind has a special section here because it is a popular tool that is
		3890	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3891
		3892	If you think you found a bug (memory leak, uninitialised data access etc.)
		3893	in libev, then check twice: If valgrind reports something like:
		3894
		3895	==2274== definitely lost: 0 bytes in 0 blocks.
		3896	==2274== possibly lost: 0 bytes in 0 blocks.
		3897	==2274== still reachable: 256 bytes in 1 blocks.
		3898
		3899	Then there is no memory leak, just as memory accounted to global variables
		3900	is not a memleak - the memory is still being referenced, and didn't leak.
		3901
		3902	Similarly, under some circumstances, valgrind might report kernel bugs
		3903	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3904	although an acceptable workaround has been found here), or it might be
		3905	confused.
		3906
		3907	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3908	make it into some kind of religion.
		3909
		3910	If you are unsure about something, feel free to contact the mailing list
		3911	with the full valgrind report and an explanation on why you think this
		3912	is a bug in libev (best check the archives, too :). However, don't be
		3913	annoyed when you get a brisk "this is no bug" answer and take the chance
		3914	of learning how to interpret valgrind properly.
		3915
		3916	If you need, for some reason, empty reports from valgrind for your project
		3917	I suggest using suppression lists.
		3918
		3919
		3920	=head1 PORTABILITY NOTES
		3921
		3922	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3923
		3924	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3925	requires, and its I/O model is fundamentally incompatible with the POSIX
		3926	model. Libev still offers limited functionality on this platform in
		3927	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3928	descriptors. This only applies when using Win32 natively, not when using
		3929	e.g. cygwin.
		3930
		3931	Lifting these limitations would basically require the full
		3932	re-implementation of the I/O system. If you are into these kinds of
		3933	things, then note that glib does exactly that for you in a very portable
		3934	way (note also that glib is the slowest event library known to man).
		3935
		3936	There is no supported compilation method available on windows except
		3937	embedding it into other applications.
		3938
		3939	Not a libev limitation but worth mentioning: windows apparently doesn't
		3940	accept large writes: instead of resulting in a partial write, windows will
		3941	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3942	so make sure you only write small amounts into your sockets (less than a
		3943	megabyte seems safe, but this apparently depends on the amount of memory
		3944	available).
		3945
		3946	Due to the many, low, and arbitrary limits on the win32 platform and
		3947	the abysmal performance of winsockets, using a large number of sockets
		3948	is not recommended (and not reasonable). If your program needs to use
		3949	more than a hundred or so sockets, then likely it needs to use a totally
		3950	different implementation for windows, as libev offers the POSIX readiness
		3951	notification model, which cannot be implemented efficiently on windows
		3952	(Microsoft monopoly games).
		3953
		3954	A typical way to use libev under windows is to embed it (see the embedding
		3955	section for details) and use the following F<evwrap.h> header file instead
		3956	of F<ev.h>:
		3957
		3958	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3959	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3960
		3961	#include "ev.h"
		3962
		3963	And compile the following F<evwrap.c> file into your project (make sure
		3964	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3965
		3966	#include "evwrap.h"
		3967	#include "ev.c"
		3968
		3969	=over 4
		3970
		3971	=item The winsocket select function
		3972
		3973	The winsocket C<select> function doesn't follow POSIX in that it
		3974	requires socket I<handles> and not socket I<file descriptors> (it is
		3975	also extremely buggy). This makes select very inefficient, and also
		3976	requires a mapping from file descriptors to socket handles (the Microsoft
		3977	C runtime provides the function C<_open_osfhandle> for this). See the
		3978	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3979	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3980
		3981	The configuration for a "naked" win32 using the Microsoft runtime
		3982	libraries and raw winsocket select is:
		3983
		3984	#define EV_USE_SELECT 1
		3985	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3986
		3987	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3988	complexity in the O(n²) range when using win32.
		3989
		3990	=item Limited number of file descriptors
		3991
		3992	Windows has numerous arbitrary (and low) limits on things.
		3993
		3994	Early versions of winsocket's select only supported waiting for a maximum
		3995	of C<64> handles (probably owning to the fact that all windows kernels
		3996	can only wait for C<64> things at the same time internally; Microsoft
		3997	recommends spawning a chain of threads and wait for 63 handles and the
		3998	previous thread in each. Great).
		3999
		4000	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4001	to some high number (e.g. C<2048>) before compiling the winsocket select
		4002	call (which might be in libev or elsewhere, for example, perl does its own
		4003	select emulation on windows).
		4004
		4005	Another limit is the number of file descriptors in the Microsoft runtime
		4006	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		4007	or something like this inside Microsoft). You can increase this by calling
		4008	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		4009	arbitrary limit), but is broken in many versions of the Microsoft runtime
		4010	libraries.
		4011
		4012	This might get you to about C<512> or C<2048> sockets (depending on
		4013	windows version and/or the phase of the moon). To get more, you need to
		4014	wrap all I/O functions and provide your own fd management, but the cost of
		4015	calling select (O(n²)) will likely make this unworkable.
		4016
		4017	=back
		4018
		4019	=head2 PORTABILITY REQUIREMENTS
		4020
		4021	In addition to a working ISO-C implementation and of course the
		4022	backend-specific APIs, libev relies on a few additional extensions:
		4023
		4024	=over 4
		4025
		4026	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4027	calling conventions regardless of C<ev_watcher_type *>.
		4028
		4029	Libev assumes not only that all watcher pointers have the same internal
		4030	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4031	assumes that the same (machine) code can be used to call any watcher
		4032	callback: The watcher callbacks have different type signatures, but libev
		4033	calls them using an C<ev_watcher *> internally.
		4034
		4035	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4036
		4037	The type C<sig_atomic_t volatile> (or whatever is defined as
		4038	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4039	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4040	believed to be sufficiently portable.
		4041
		4042	=item C<sigprocmask> must work in a threaded environment
		4043
		4044	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4045	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4046	pthread implementations will either allow C<sigprocmask> in the "main
		4047	thread" or will block signals process-wide, both behaviours would
		4048	be compatible with libev. Interaction between C<sigprocmask> and
		4049	C<pthread_sigmask> could complicate things, however.
		4050
		4051	The most portable way to handle signals is to block signals in all threads
		4052	except the initial one, and run the default loop in the initial thread as
		4053	well.
		4054
		4055	=item C<long> must be large enough for common memory allocation sizes
		4056
		4057	To improve portability and simplify its API, libev uses C<long> internally
		4058	instead of C<size_t> when allocating its data structures. On non-POSIX
		4059	systems (Microsoft...) this might be unexpectedly low, but is still at
		4060	least 31 bits everywhere, which is enough for hundreds of millions of
		4061	watchers.
		4062
		4063	=item C<double> must hold a time value in seconds with enough accuracy
		4064
		4065	The type C<double> is used to represent timestamps. It is required to
		4066	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4067	enough for at least into the year 4000. This requirement is fulfilled by
		4068	implementations implementing IEEE 754 (basically all existing ones).
		4069
		4070	=back
		4071
		4072	If you know of other additional requirements drop me a note.
		4073
		4074
2319	=head1 COMPLEXITIES	4075	=head1 ALGORITHMIC COMPLEXITIES
2320		4076
2321	In this section the complexities of (many of) the algorithms used inside	4077	In this section the complexities of (many of) the algorithms used inside
2322	libev will be explained. For complexity discussions about backends see the	4078	libev will be documented. For complexity discussions about backends see
2323	documentation for C<ev_default_init>.	4079	the documentation for C<ev_default_init>.
2324		4080
2325	All of the following are about amortised time: If an array needs to be	4081	All of the following are about amortised time: If an array needs to be
2326	extended, libev needs to realloc and move the whole array, but this	4082	extended, libev needs to realloc and move the whole array, but this
2327	happens asymptotically never with higher number of elements, so O(1) might	4083	happens asymptotically rarer with higher number of elements, so O(1) might
2328	mean it might do a lengthy realloc operation in rare cases, but on average	4084	mean that libev does a lengthy realloc operation in rare cases, but on
2329	it is much faster and asymptotically approaches constant time.	4085	average it is much faster and asymptotically approaches constant time.
2330		4086
2331	=over 4	4087	=over 4
2332		4088
2333	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4089	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2334		4090
2335	This means that, when you have a watcher that triggers in one hour and	4091	This means that, when you have a watcher that triggers in one hour and
2336	there are 100 watchers that would trigger before that then inserting will	4092	there are 100 watchers that would trigger before that, then inserting will
2337	have to skip those 100 watchers.	4093	have to skip roughly seven (C<ld 100>) of these watchers.
2338		4094
2339	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4095	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2340		4096
2341	That means that for changing a timer costs less than removing/adding them	4097	That means that changing a timer costs less than removing/adding them,
2342	as only the relative motion in the event queue has to be paid for.	4098	as only the relative motion in the event queue has to be paid for.
2343		4099
2344	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4100	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2345		4101
2346	These just add the watcher into an array or at the head of a list.	4102	These just add the watcher into an array or at the head of a list.
		4103
2347	=item Stopping check/prepare/idle watchers: O(1)	4104	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2348		4105
2349	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4106	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2350		4107
2351	These watchers are stored in lists then need to be walked to find the	4108	These watchers are stored in lists, so they need to be walked to find the
2352	correct watcher to remove. The lists are usually short (you don't usually	4109	correct watcher to remove. The lists are usually short (you don't usually
2353	have many watchers waiting for the same fd or signal).	4110	have many watchers waiting for the same fd or signal: one is typical, two
		4111	is rare).
2354		4112
2355	=item Finding the next timer per loop iteration: O(1)	4113	=item Finding the next timer in each loop iteration: O(1)
		4114
		4115	By virtue of using a binary or 4-heap, the next timer is always found at a
		4116	fixed position in the storage array.
2356		4117
2357	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4118	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2358		4119
2359	A change means an I/O watcher gets started or stopped, which requires	4120	A change means an I/O watcher gets started or stopped, which requires
2360	libev to recalculate its status (and possibly tell the kernel).	4121	libev to recalculate its status (and possibly tell the kernel, depending
		4122	on backend and whether C<ev_io_set> was used).
2361		4123
2362	=item Activating one watcher: O(1)	4124	=item Activating one watcher (putting it into the pending state): O(1)
2363		4125
2364	=item Priority handling: O(number_of_priorities)	4126	=item Priority handling: O(number_of_priorities)
2365		4127
2366	Priorities are implemented by allocating some space for each	4128	Priorities are implemented by allocating some space for each
2367	priority. When doing priority-based operations, libev usually has to	4129	priority. When doing priority-based operations, libev usually has to
2368	linearly search all the priorities.	4130	linearly search all the priorities, but starting/stopping and activating
		4131	watchers becomes O(1) with respect to priority handling.
		4132
		4133	=item Sending an ev_async: O(1)
		4134
		4135	=item Processing ev_async_send: O(number_of_async_watchers)
		4136
		4137	=item Processing signals: O(max_signal_number)
		4138
		4139	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4140	calls in the current loop iteration. Checking for async and signal events
		4141	involves iterating over all running async watchers or all signal numbers.
2369		4142
2370	=back	4143	=back
2371		4144
2372		4145
		4146	=head1 GLOSSARY
		4147
		4148	=over 4
		4149
		4150	=item active
		4151
		4152	A watcher is active as long as it has been started (has been attached to
		4153	an event loop) but not yet stopped (disassociated from the event loop).
		4154
		4155	=item application
		4156
		4157	In this document, an application is whatever is using libev.
		4158
		4159	=item callback
		4160
		4161	The address of a function that is called when some event has been
		4162	detected. Callbacks are being passed the event loop, the watcher that
		4163	received the event, and the actual event bitset.
		4164
		4165	=item callback invocation
		4166
		4167	The act of calling the callback associated with a watcher.
		4168
		4169	=item event
		4170
		4171	A change of state of some external event, such as data now being available
		4172	for reading on a file descriptor, time having passed or simply not having
		4173	any other events happening anymore.
		4174
		4175	In libev, events are represented as single bits (such as C<EV_READ> or
		4176	C<EV_TIMEOUT>).
		4177
		4178	=item event library
		4179
		4180	A software package implementing an event model and loop.
		4181
		4182	=item event loop
		4183
		4184	An entity that handles and processes external events and converts them
		4185	into callback invocations.
		4186
		4187	=item event model
		4188
		4189	The model used to describe how an event loop handles and processes
		4190	watchers and events.
		4191
		4192	=item pending
		4193
		4194	A watcher is pending as soon as the corresponding event has been detected,
		4195	and stops being pending as soon as the watcher will be invoked or its
		4196	pending status is explicitly cleared by the application.
		4197
		4198	A watcher can be pending, but not active. Stopping a watcher also clears
		4199	its pending status.
		4200
		4201	=item real time
		4202
		4203	The physical time that is observed. It is apparently strictly monotonic :)
		4204
		4205	=item wall-clock time
		4206
		4207	The time and date as shown on clocks. Unlike real time, it can actually
		4208	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4209	clock.
		4210
		4211	=item watcher
		4212
		4213	A data structure that describes interest in certain events. Watchers need
		4214	to be started (attached to an event loop) before they can receive events.
		4215
		4216	=item watcher invocation
		4217
		4218	The act of calling the callback associated with a watcher.
		4219
		4220	=back
		4221
2373	=head1 AUTHOR	4222	=head1 AUTHOR
2374		4223
2375	Marc Lehmann <libev@schmorp.de>.	4224	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2376		4225

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines