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Revision 1.98 by root, Sat Dec 22 06:10:25 2007 UTC vs.
Revision 1.245 by root, Tue Jun 30 06:24:38 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
56		84
57	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	87	these event sources and provide your program with events.
60		88
…		…
65	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	96	watcher.
69		97
70	=head1 FEATURES	98	=head2 FEATURES
71		99
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
82		110
83	It also is quite fast (see this	111	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	112	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	113	for example).
86		114
87	=head1 CONVENTIONS	115	=head2 CONVENTIONS
88		116
89	Libev is very configurable. In this manual the default configuration will	117	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	118	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	119	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	120	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	121	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	122	name C<loop> (which is always of type C<ev_loop *>) will not have
		123	this argument.
95		124
96	=head1 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
97		126
98	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
100	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
102	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
103	it, you should treat it as some floatingpoint value. Unlike the name	132	on it, you should treat it as some floating point value. Unlike the name
104	component C<stamp> might indicate, it is also used for time differences	133	component C<stamp> might indicate, it is also used for time differences
105	throughout libev.	134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
		155
106		156
107	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
108		158
109	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
110	library in any way.	160	library in any way.
…		…
119		169
120	=item ev_sleep (ev_tstamp interval)	170	=item ev_sleep (ev_tstamp interval)
121		171
122	Sleep for the given interval: The current thread will be blocked until	172	Sleep for the given interval: The current thread will be blocked until
123	either it is interrupted or the given time interval has passed. Basically	173	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	174	this is a sub-second-resolution C<sleep ()>.
125		175
126	=item int ev_version_major ()	176	=item int ev_version_major ()
127		177
128	=item int ev_version_minor ()	178	=item int ev_version_minor ()
129		179
…		…
142	not a problem.	192	not a problem.
143		193
144	Example: Make sure we haven't accidentally been linked against the wrong	194	Example: Make sure we haven't accidentally been linked against the wrong
145	version.	195	version.
146		196
147	assert (("libev version mismatch",	197	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
150		200
151	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
152		202
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	203	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	206	a description of the set values.
157		207
158	Example: make sure we have the epoll method, because yeah this is cool and	208	Example: make sure we have the epoll method, because yeah this is cool and
159	a must have and can we have a torrent of it please!!!11	209	a must have and can we have a torrent of it please!!!11
160		210
161	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
163		213
164	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
165		215
166	Return the set of all backends compiled into this binary of libev and also	216	Return the set of all backends compiled into this binary of libev and also
167	recommended for this platform. This set is often smaller than the one	217	recommended for this platform. This set is often smaller than the one
168	returned by C<ev_supported_backends>, as for example kqueue is broken on	218	returned by C<ev_supported_backends>, as for example kqueue is broken on
169	most BSDs and will not be autodetected unless you explicitly request it	219	most BSDs and will not be auto-detected unless you explicitly request it
170	(assuming you know what you are doing). This is the set of backends that	220	(assuming you know what you are doing). This is the set of backends that
171	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
172		222
173	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
174		224
…		…
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
179	recommended ones.	229	recommended ones.
180		230
181	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
182		232
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
184		234
185	Sets the allocation function to use (the prototype is similar - the	235	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	236	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
187	allocate and free memory (no surprises here). If it returns zero when	237	used to allocate and free memory (no surprises here). If it returns zero
188	memory needs to be allocated, the library might abort or take some	238	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	239	or take some potentially destructive action.
190	function.	240
		241	Since some systems (at least OpenBSD and Darwin) fail to implement
		242	correct C<realloc> semantics, libev will use a wrapper around the system
		243	C<realloc> and C<free> functions by default.
191		244
192	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	246	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	247	or even to sleep a while and retry until some memory is available.
195		248
196	Example: Replace the libev allocator with one that waits a bit and then	249	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	250	retries (example requires a standards-compliant C<realloc>).
198		251
199	static void *	252	static void *
200	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
201	{	254	{
202	for (;;)	255	for (;;)
…		…
211	}	264	}
212		265
213	...	266	...
214	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
215		268
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
217		270
218	Set the callback function to call on a retryable syscall error (such	271	Set the callback function to call on a retryable system call error (such
219	as failed select, poll, epoll_wait). The message is a printable string	272	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
221	callback is set, then libev will expect it to remedy the sitution, no	274	callback is set, then libev will expect it to remedy the situation, no
222	matter what, when it returns. That is, libev will generally retry the	275	matter what, when it returns. That is, libev will generally retry the
223	requested operation, or, if the condition doesn't go away, do bad stuff	276	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	277	(such as abort).
225		278
226	Example: This is basically the same thing that libev does internally, too.	279	Example: This is basically the same thing that libev does internally, too.
…		…
237		290
238	=back	291	=back
239		292
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
241		294
242	An event loop is described by a C<struct ev_loop *>. The library knows two	295	An event loop is described by a C<struct ev_loop *> (the C<struct>
243	types of such loops, the I<default> loop, which supports signals and child	296	is I<not> optional in this case, as there is also an C<ev_loop>
244	events, and dynamically created loops which do not.	297	I<function>).
245		298
246	If you use threads, a common model is to run the default event loop	299	The library knows two types of such loops, the I<default> loop, which
247	in your main thread (or in a separate thread) and for each thread you	300	supports signals and child events, and dynamically created loops which do
248	create, you also create another event loop. Libev itself does no locking	301	not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		302
253	=over 4	303	=over 4
254		304
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		306
…		…
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		311
262	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
263	function.	313	function.
264		314
		315	Note that this function is I<not> thread-safe, so if you want to use it
		316	from multiple threads, you have to lock (note also that this is unlikely,
		317	as loops cannot be shared easily between threads anyway).
		318
		319	The default loop is the only loop that can handle C<ev_signal> and
		320	C<ev_child> watchers, and to do this, it always registers a handler
		321	for C<SIGCHLD>. If this is a problem for your application you can either
		322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		324	C<ev_default_init>.
		325
265	The flags argument can be used to specify special behaviour or specific	326	The flags argument can be used to specify special behaviour or specific
266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	327	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
267		328
268	The following flags are supported:	329	The following flags are supported:
269		330
…		…
274	The default flags value. Use this if you have no clue (it's the right	335	The default flags value. Use this if you have no clue (it's the right
275	thing, believe me).	336	thing, believe me).
276		337
277	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
278		339
279	If this flag bit is ored into the flag value (or the program runs setuid	340	If this flag bit is or'ed into the flag value (or the program runs setuid
280	or setgid) then libev will I<not> look at the environment variable	341	or setgid) then libev will I<not> look at the environment variable
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	override the flags completely if it is found in the environment. This is	343	override the flags completely if it is found in the environment. This is
283	useful to try out specific backends to test their performance, or to work	344	useful to try out specific backends to test their performance, or to work
284	around bugs.	345	around bugs.
…		…
290	enabling this flag.	351	enabling this flag.
291		352
292	This works by calling C<getpid ()> on every iteration of the loop,	353	This works by calling C<getpid ()> on every iteration of the loop,
293	and thus this might slow down your event loop if you do a lot of loop	354	and thus this might slow down your event loop if you do a lot of loop
294	iterations and little real work, but is usually not noticeable (on my	355	iterations and little real work, but is usually not noticeable (on my
295	Linux system for example, C<getpid> is actually a simple 5-insn sequence	356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
296	without a syscall and thus I<very> fast, but my Linux system also has	357	without a system call and thus I<very> fast, but my GNU/Linux system also has
297	C<pthread_atfork> which is even faster).	358	C<pthread_atfork> which is even faster).
298		359
299	The big advantage of this flag is that you can forget about fork (and	360	The big advantage of this flag is that you can forget about fork (and
300	forget about forgetting to tell libev about forking) when you use this	361	forget about forgetting to tell libev about forking) when you use this
301	flag.	362	flag.
302		363
303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
304	environment variable.	365	environment variable.
305		366
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		368
308	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
309	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,
310	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
311	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
312	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).
313		385
314	=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)
315		387
316	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
317	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
318	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
319	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>.
320		397
321	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
322		399
323	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,
324	but it scales phenomenally better. While poll and select usually scale	401	but it scales phenomenally better. While poll and select usually scale
325	like O(total_fds) where n is the total number of fds (or the highest fd),	402	like O(total_fds) where n is the total number of fds (or the highest fd),
326	epoll scales either O(1) or O(active_fds). The epoll design has a number	403	epoll scales either O(1) or O(active_fds).
327	of shortcomings, such as silently dropping events in some hard-to-detect	404
328	cases and rewiring a syscall per fd change, no fork support and bad	405	The epoll mechanism deserves honorable mention as the most misdesigned
329	support for dup:	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.
330		421
331	While stopping, setting and starting an I/O watcher in the same iteration	422	While stopping, setting and starting an I/O watcher in the same iteration
332	will result in some caching, there is still a syscall per such incident	423	will result in some caching, there is still a system call per such
333	(because the fd could point to a different file description now), so its	424	incident (because the same I<file descriptor> could point to a different
334	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
335	very 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.
336		428
337	Please note that epoll sometimes generates spurious notifications, so you	429	Best performance from this backend is achieved by not unregistering all
338	need to use non-blocking I/O or other means to avoid blocking when no data	430	watchers for a file descriptor until it has been closed, if possible,
339	(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>.
340		446
341	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
342		448
343	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
344	was broken on I<all> BSDs (usually it doesn't work with anything but	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
345	sockets and pipes, except on Darwin, where of course it's completely	451	with anything but sockets and pipes, except on Darwin, where of course
346	useless. On NetBSD, it seems to work for all the FD types I tested, so it	452	it's completely useless). Unlike epoll, however, whose brokenness
347	is used by default there). For this reason it's not being "autodetected"	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
348	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
349	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
350	system like NetBSD.	457	system like NetBSD.
351		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.
		462
352	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
353	kernel is more efficient (which says nothing about its actual speed,	464	kernel is more efficient (which says nothing about its actual speed, of
354	of course). While stopping, setting and starting an I/O watcher does	465	course). While stopping, setting and starting an I/O watcher does never
355	never cause an extra syscall as with epoll, it still adds up to two event	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
356	changes per incident, support for C<fork ()> is very bad and it drops fds	467	two event changes per incident. Support for C<fork ()> is very bad (but
357	silently in similarly hard-to-detetc cases.	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>.
358		483
359	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
360		485
361	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.
362		490
363	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
364		492
365	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	493	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
366	it's really slow, but it still scales very well (O(active_fds)).	494	it's really slow, but it still scales very well (O(active_fds)).
367		495
368	Please note that solaris event ports can deliver a lot of spurious	496	Please note that Solaris event ports can deliver a lot of spurious
369	notifications, so you need to use non-blocking I/O or other means to avoid	497	notifications, so you need to use non-blocking I/O or other means to avoid
370	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>.
371		512
372	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
373		514
374	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
375	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
376	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	517	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
377		518
		519	It is definitely not recommended to use this flag.
		520
378	=back	521	=back
379		522
380	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
381	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
382	specified, most compiled-in backend will be tried, usually in reverse	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
383	order of their flag values :)
384		526
385	The most typical usage is like this:	527	Example: This is the most typical usage.
386		528
387	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
388	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
389		531
390	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
391	environment settings to be taken into account:	533	environment settings to be taken into account:
392		534
393	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
394		536
395	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
396	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
397	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
398		541
399	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
400		543
401	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
402		545
403	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
404	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
405	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
406	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
407		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
408	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.
409		556
410	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
411	if (!epoller)	558	if (!epoller)
412	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
413		560
414	=item ev_default_destroy ()	561	=item ev_default_destroy ()
415		562
416	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
417	etc.). None of the active event watchers will be stopped in the normal	564	etc.). None of the active event watchers will be stopped in the normal
418	sense, so e.g. C<ev_is_active> might still return true. It is your	565	sense, so e.g. C<ev_is_active> might still return true. It is your
419	responsibility to either stop all watchers cleanly yoursef I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
420	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
421	the easiest thing, you can just ignore the watchers and/or C<free ()> them	568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
422	for example).	569	for example).
423		570
424	Note that certain global state, such as signal state, will not be freed by	571	Note that certain global state, such as signal state (and installed signal
425	this function, and related watchers (such as signal and child watchers)	572	handlers), will not be freed by this function, and related watchers (such
426	would need to be stopped manually.	573	as signal and child watchers) would need to be stopped manually.
427		574
428	In general it is not advisable to call this function except in the	575	In general it is not advisable to call this function except in the
429	rare occasion where you really need to free e.g. the signal handling	576	rare occasion where you really need to free e.g. the signal handling
430	pipe fds. If you need dynamically allocated loops it is better to use	577	pipe fds. If you need dynamically allocated loops it is better to use
431	C<ev_loop_new> and C<ev_loop_destroy>).	578	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
435	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
436	earlier call to C<ev_loop_new>.	583	earlier call to C<ev_loop_new>.
437		584
438	=item ev_default_fork ()	585	=item ev_default_fork ()
439		586
		587	This function sets a flag that causes subsequent C<ev_loop> iterations
440	This function reinitialises the kernel state for backends that have	588	to reinitialise the kernel state for backends that have one. Despite the
441	one. Despite the name, you can call it anytime, but it makes most sense	589	name, you can call it anytime, but it makes most sense after forking, in
442	after forking, in either the parent or child process (or both, but that	590	the child process (or both child and parent, but that again makes little
443	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.
444		593
445	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
446	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
447	fork+exec, you don't have to call it.	596	you just fork+exec, you don't have to call it at all.
448		597
449	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
450	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
451	quite nicely into a call to C<pthread_atfork>:	600	quite nicely into a call to C<pthread_atfork>:
452		601
453	pthread_atfork (0, 0, ev_default_fork);	602	pthread_atfork (0, 0, ev_default_fork);
454		603
455	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
456	without calling this function, so if you force one of those backends you
457	do not need to care.
458
459	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
460		605
461	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
462	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
463	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.
464		615
465	=item unsigned int ev_loop_count (loop)	616	=item unsigned int ev_loop_count (loop)
466		617
467	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
468	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
…		…
483	received events and started processing them. This timestamp does not	634	received events and started processing them. This timestamp does not
484	change as long as callbacks are being processed, and this is also the base	635	change as long as callbacks are being processed, and this is also the base
485	time used for relative timers. You can treat it as the timestamp of the	636	time used for relative timers. You can treat it as the timestamp of the
486	event occurring (or more correctly, libev finding out about it).	637	event occurring (or more correctly, libev finding out about it).
487		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>).
		676
488	=item ev_loop (loop, int flags)	677	=item ev_loop (loop, int flags)
489		678
490	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
491	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
492	events.	681	events.
…		…
494	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
495	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.
496		685
497	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
498	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
499	finished (especially in interactive programs), but having a program that	688	finished (especially in interactive programs), but having a program
500	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
501	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.
502		692
503	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
504	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
505	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.
506		697
507	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
508	neccessary) and will handle those and any outstanding ones. It will block	699	necessary) and will handle those and any already outstanding ones. It
509	your process until at least one new event arrives, and will return after	700	will block your process until at least one new event arrives (which could
510	one iteration of the loop. This is useful if you are waiting for some	701	be an event internal to libev itself, so there is no guarantee that a
511	external event in conjunction with something not expressible using other	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
512	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
513	usually a better approach for this kind of thing.	708	usually a better approach for this kind of thing.
514		709
515	Here are the gory details of what C<ev_loop> does:	710	Here are the gory details of what C<ev_loop> does:
516		711
517	- Before the first iteration, call any pending watchers.	712	- Before the first iteration, call any pending watchers.
518	* If there are no active watchers (reference count is zero), return.	713	* If EVFLAG_FORKCHECK was used, check for a fork.
519	- Queue all prepare watchers and then call all outstanding watchers.	714	- If a fork was detected (by any means), queue and call all fork watchers.
		715	- Queue and call all prepare watchers.
520	- 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.
521	- Update the kernel state with all outstanding changes.	718	- Update the kernel state with all outstanding changes.
522	- Update the "event loop time".	719	- Update the "event loop time" (ev_now ()).
523	- 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.
524	- Block the process, waiting for any events.	724	- Block the process, waiting for any events.
525	- Queue all outstanding I/O (fd) events.	725	- Queue all outstanding I/O (fd) events.
526	- Update the "event loop time" and do time jump handling.	726	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
527	- Queue all outstanding timers.	727	- Queue all expired timers.
528	- Queue all outstanding periodics.	728	- Queue all expired periodics.
529	- If no events are pending now, queue all idle watchers.	729	- Unless any events are pending now, queue all idle watchers.
530	- Queue all check watchers.	730	- Queue all check watchers.
531	- 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).
532	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
533	be handled here by queueing them when their watcher gets executed.	733	be handled here by queueing them when their watcher gets executed.
534	- 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
535	were used, return, otherwise continue with step *.	735	were used, or there are no active watchers, return, otherwise
		736	continue with step *.
536		737
537	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
538	anymore.	739	anymore.
539		740
540	... queue jobs here, make sure they register event watchers as long	741	... queue jobs here, make sure they register event watchers as long
541	... as they still have work to do (even an idle watcher will do..)	742	... as they still have work to do (even an idle watcher will do..)
542	ev_loop (my_loop, 0);	743	ev_loop (my_loop, 0);
543	... jobs done. yeah!	744	... jobs done or somebody called unloop. yeah!
544		745
545	=item ev_unloop (loop, how)	746	=item ev_unloop (loop, how)
546		747
547	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
548	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
549	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
550	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.
551		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
552	=item ev_ref (loop)	757	=item ev_ref (loop)
553		758
554	=item ev_unref (loop)	759	=item ev_unref (loop)
555		760
556	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
557	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
558	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
559	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>
560	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
561	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
562	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
563	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
564	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
565	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).
566		778
567	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>
568	running when nothing else is active.	780	running when nothing else is active.
569		781
570	struct ev_signal exitsig;	782	ev_signal exitsig;
571	ev_signal_init (&exitsig, sig_cb, SIGINT);	783	ev_signal_init (&exitsig, sig_cb, SIGINT);
572	ev_signal_start (loop, &exitsig);	784	ev_signal_start (loop, &exitsig);
573	evf_unref (loop);	785	evf_unref (loop);
574		786
575	Example: For some weird reason, unregister the above signal handler again.	787	Example: For some weird reason, unregister the above signal handler again.
576		788
577	ev_ref (loop);	789	ev_ref (loop);
578	ev_signal_stop (loop, &exitsig);	790	ev_signal_stop (loop, &exitsig);
579		791
580	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	792	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
581		793
582	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	794	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
583		795
584	These advanced functions influence the time that libev will spend waiting	796	These advanced functions influence the time that libev will spend waiting
585	for events. Both are by default C<0>, meaning that libev will try to	797	for events. Both time intervals are by default C<0>, meaning that libev
586	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	798	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		799	latency.
587		800
588	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	801	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
589	allows libev to delay invocation of I/O and timer/periodic callbacks to	802	allows libev to delay invocation of I/O and timer/periodic callbacks
590	increase efficiency of loop iterations.	803	to increase efficiency of loop iterations (or to increase power-saving
		804	opportunities).
591		805
592	The background is that sometimes your program runs just fast enough to	806	The idea is that sometimes your program runs just fast enough to handle
593	handle one (or very few) event(s) per loop iteration. While this makes	807	one (or very few) event(s) per loop iteration. While this makes the
594	the program responsive, it also wastes a lot of CPU time to poll for new	808	program responsive, it also wastes a lot of CPU time to poll for new
595	events, especially with backends like C<select ()> which have a high	809	events, especially with backends like C<select ()> which have a high
596	overhead for the actual polling but can deliver many events at once.	810	overhead for the actual polling but can deliver many events at once.
597		811
598	By setting a higher I<io collect interval> you allow libev to spend more	812	By setting a higher I<io collect interval> you allow libev to spend more
599	time collecting I/O events, so you can handle more events per iteration,	813	time collecting I/O events, so you can handle more events per iteration,
600	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	814	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
601	C<ev_timer>) will be not affected.	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. The
		817	sleep time ensures that libev will not poll for I/O events more often then
		818	once per this interval, on average.
602		819
603	Likewise, by setting a higher I<timeout collect interval> you allow libev	820	Likewise, by setting a higher I<timeout collect interval> you allow libev
604	to spend more time collecting timeouts, at the expense of increased	821	to spend more time collecting timeouts, at the expense of increased
605	latency (the watcher callback will be called later). C<ev_io> watchers	822	latency/jitter/inexactness (the watcher callback will be called
606	will not be affected.	823	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		824	value will not introduce any overhead in libev.
607		825
608	Many (busy) programs can usually benefit by setting the io collect	826	Many (busy) programs can usually benefit by setting the I/O collect
609	interval to a value near C<0.1> or so, which is often enough for	827	interval to a value near C<0.1> or so, which is often enough for
610	interactive servers (of course not for games), likewise for timeouts. It	828	interactive servers (of course not for games), likewise for timeouts. It
611	usually doesn't make much sense to set it to a lower value than C<0.01>,	829	usually doesn't make much sense to set it to a lower value than C<0.01>,
612	as this approsaches the timing granularity of most systems.	830	as this approaches the timing granularity of most systems. Note that if
		831	you do transactions with the outside world and you can't increase the
		832	parallelity, then this setting will limit your transaction rate (if you
		833	need to poll once per transaction and the I/O collect interval is 0.01,
		834	then you can't do more than 100 transations per second).
		835
		836	Setting the I<timeout collect interval> can improve the opportunity for
		837	saving power, as the program will "bundle" timer callback invocations that
		838	are "near" in time together, by delaying some, thus reducing the number of
		839	times the process sleeps and wakes up again. Another useful technique to
		840	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		841	they fire on, say, one-second boundaries only.
		842
		843	Example: we only need 0.1s timeout granularity, and we wish not to poll
		844	more often than 100 times per second:
		845
		846	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		847	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		848
		849	=item ev_loop_verify (loop)
		850
		851	This function only does something when C<EV_VERIFY> support has been
		852	compiled in, which is the default for non-minimal builds. It tries to go
		853	through all internal structures and checks them for validity. If anything
		854	is found to be inconsistent, it will print an error message to standard
		855	error and call C<abort ()>.
		856
		857	This can be used to catch bugs inside libev itself: under normal
		858	circumstances, this function will never abort as of course libev keeps its
		859	data structures consistent.
613		860
614	=back	861	=back
615		862
616		863
617	=head1 ANATOMY OF A WATCHER	864	=head1 ANATOMY OF A WATCHER
		865
		866	In the following description, uppercase C<TYPE> in names stands for the
		867	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		868	watchers and C<ev_io_start> for I/O watchers.
618		869
619	A watcher is a structure that you create and register to record your	870	A watcher is a structure that you create and register to record your
620	interest in some event. For instance, if you want to wait for STDIN to	871	interest in some event. For instance, if you want to wait for STDIN to
621	become readable, you would create an C<ev_io> watcher for that:	872	become readable, you would create an C<ev_io> watcher for that:
622		873
623	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	874	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
624	{	875	{
625	ev_io_stop (w);	876	ev_io_stop (w);
626	ev_unloop (loop, EVUNLOOP_ALL);	877	ev_unloop (loop, EVUNLOOP_ALL);
627	}	878	}
628		879
629	struct ev_loop *loop = ev_default_loop (0);	880	struct ev_loop *loop = ev_default_loop (0);
		881
630	struct ev_io stdin_watcher;	882	ev_io stdin_watcher;
		883
631	ev_init (&stdin_watcher, my_cb);	884	ev_init (&stdin_watcher, my_cb);
632	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	885	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
633	ev_io_start (loop, &stdin_watcher);	886	ev_io_start (loop, &stdin_watcher);
		887
634	ev_loop (loop, 0);	888	ev_loop (loop, 0);
635		889
636	As you can see, you are responsible for allocating the memory for your	890	As you can see, you are responsible for allocating the memory for your
637	watcher structures (and it is usually a bad idea to do this on the stack,	891	watcher structures (and it is I<usually> a bad idea to do this on the
638	although this can sometimes be quite valid).	892	stack).
		893
		894	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		895	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
639		896
640	Each watcher structure must be initialised by a call to C<ev_init	897	Each watcher structure must be initialised by a call to C<ev_init
641	(watcher *, callback)>, which expects a callback to be provided. This	898	(watcher *, callback)>, which expects a callback to be provided. This
642	callback gets invoked each time the event occurs (or, in the case of io	899	callback gets invoked each time the event occurs (or, in the case of I/O
643	watchers, each time the event loop detects that the file descriptor given	900	watchers, each time the event loop detects that the file descriptor given
644	is readable and/or writable).	901	is readable and/or writable).
645		902
646	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	903	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
647	with arguments specific to this watcher type. There is also a macro	904	macro to configure it, with arguments specific to the watcher type. There
648	to combine initialisation and setting in one call: C<< ev_<type>_init	905	is also a macro to combine initialisation and setting in one call: C<<
649	(watcher *, callback, ...) >>.	906	ev_TYPE_init (watcher *, callback, ...) >>.
650		907
651	To make the watcher actually watch out for events, you have to start it	908	To make the watcher actually watch out for events, you have to start it
652	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	909	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
653	*) >>), and you can stop watching for events at any time by calling the	910	*) >>), and you can stop watching for events at any time by calling the
654	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	911	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
655		912
656	As long as your watcher is active (has been started but not stopped) you	913	As long as your watcher is active (has been started but not stopped) you
657	must not touch the values stored in it. Most specifically you must never	914	must not touch the values stored in it. Most specifically you must never
658	reinitialise it or call its C<set> macro.	915	reinitialise it or call its C<ev_TYPE_set> macro.
659		916
660	Each and every callback receives the event loop pointer as first, the	917	Each and every callback receives the event loop pointer as first, the
661	registered watcher structure as second, and a bitset of received events as	918	registered watcher structure as second, and a bitset of received events as
662	third argument.	919	third argument.
663		920
…		…
717	=item C<EV_FORK>	974	=item C<EV_FORK>
718		975
719	The event loop has been resumed in the child process after fork (see	976	The event loop has been resumed in the child process after fork (see
720	C<ev_fork>).	977	C<ev_fork>).
721		978
		979	=item C<EV_ASYNC>
		980
		981	The given async watcher has been asynchronously notified (see C<ev_async>).
		982
		983	=item C<EV_CUSTOM>
		984
		985	Not ever sent (or otherwise used) by libev itself, but can be freely used
		986	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		987
722	=item C<EV_ERROR>	988	=item C<EV_ERROR>
723		989
724	An unspecified error has occured, the watcher has been stopped. This might	990	An unspecified error has occurred, the watcher has been stopped. This might
725	happen because the watcher could not be properly started because libev	991	happen because the watcher could not be properly started because libev
726	ran out of memory, a file descriptor was found to be closed or any other	992	ran out of memory, a file descriptor was found to be closed or any other
		993	problem. Libev considers these application bugs.
		994
727	problem. You best act on it by reporting the problem and somehow coping	995	You best act on it by reporting the problem and somehow coping with the
728	with the watcher being stopped.	996	watcher being stopped. Note that well-written programs should not receive
		997	an error ever, so when your watcher receives it, this usually indicates a
		998	bug in your program.
729		999
730	Libev will usually signal a few "dummy" events together with an error,	1000	Libev will usually signal a few "dummy" events together with an error, for
731	for example it might indicate that a fd is readable or writable, and if	1001	example it might indicate that a fd is readable or writable, and if your
732	your callbacks is well-written it can just attempt the operation and cope	1002	callbacks is well-written it can just attempt the operation and cope with
733	with the error from read() or write(). This will not work in multithreaded	1003	the error from read() or write(). This will not work in multi-threaded
734	programs, though, so beware.	1004	programs, though, as the fd could already be closed and reused for another
		1005	thing, so beware.
735		1006
736	=back	1007	=back
737		1008
738	=head2 GENERIC WATCHER FUNCTIONS	1009	=head2 GENERIC WATCHER FUNCTIONS
739
740	In the following description, C<TYPE> stands for the watcher type,
741	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
742		1010
743	=over 4	1011	=over 4
744		1012
745	=item C<ev_init> (ev_TYPE *watcher, callback)	1013	=item C<ev_init> (ev_TYPE *watcher, callback)
746		1014
…		…
752	which rolls both calls into one.	1020	which rolls both calls into one.
753		1021
754	You can reinitialise a watcher at any time as long as it has been stopped	1022	You can reinitialise a watcher at any time as long as it has been stopped
755	(or never started) and there are no pending events outstanding.	1023	(or never started) and there are no pending events outstanding.
756		1024
757	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1025	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
758	int revents)>.	1026	int revents)>.
		1027
		1028	Example: Initialise an C<ev_io> watcher in two steps.
		1029
		1030	ev_io w;
		1031	ev_init (&w, my_cb);
		1032	ev_io_set (&w, STDIN_FILENO, EV_READ);
759		1033
760	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1034	=item C<ev_TYPE_set> (ev_TYPE *, [args])
761		1035
762	This macro initialises the type-specific parts of a watcher. You need to	1036	This macro initialises the type-specific parts of a watcher. You need to
763	call C<ev_init> at least once before you call this macro, but you can	1037	call C<ev_init> at least once before you call this macro, but you can
…		…
766	difference to the C<ev_init> macro).	1040	difference to the C<ev_init> macro).
767		1041
768	Although some watcher types do not have type-specific arguments	1042	Although some watcher types do not have type-specific arguments
769	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1043	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
770		1044
		1045	See C<ev_init>, above, for an example.
		1046
771	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1047	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
772		1048
773	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1049	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
774	calls into a single call. This is the most convinient method to initialise	1050	calls into a single call. This is the most convenient method to initialise
775	a watcher. The same limitations apply, of course.	1051	a watcher. The same limitations apply, of course.
		1052
		1053	Example: Initialise and set an C<ev_io> watcher in one step.
		1054
		1055	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
776		1056
777	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1057	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
778		1058
779	Starts (activates) the given watcher. Only active watchers will receive	1059	Starts (activates) the given watcher. Only active watchers will receive
780	events. If the watcher is already active nothing will happen.	1060	events. If the watcher is already active nothing will happen.
781		1061
		1062	Example: Start the C<ev_io> watcher that is being abused as example in this
		1063	whole section.
		1064
		1065	ev_io_start (EV_DEFAULT_UC, &w);
		1066
782	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1067	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
783		1068
784	Stops the given watcher again (if active) and clears the pending	1069	Stops the given watcher if active, and clears the pending status (whether
		1070	the watcher was active or not).
		1071
785	status. It is possible that stopped watchers are pending (for example,	1072	It is possible that stopped watchers are pending - for example,
786	non-repeating timers are being stopped when they become pending), but	1073	non-repeating timers are being stopped when they become pending - but
787	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1074	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
788	you want to free or reuse the memory used by the watcher it is therefore a	1075	pending. If you want to free or reuse the memory used by the watcher it is
789	good idea to always call its C<ev_TYPE_stop> function.	1076	therefore a good idea to always call its C<ev_TYPE_stop> function.
790		1077
791	=item bool ev_is_active (ev_TYPE *watcher)	1078	=item bool ev_is_active (ev_TYPE *watcher)
792		1079
793	Returns a true value iff the watcher is active (i.e. it has been started	1080	Returns a true value iff the watcher is active (i.e. it has been started
794	and not yet been stopped). As long as a watcher is active you must not modify	1081	and not yet been stopped). As long as a watcher is active you must not modify
…		…
820	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1107	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
821	(default: C<-2>). Pending watchers with higher priority will be invoked	1108	(default: C<-2>). Pending watchers with higher priority will be invoked
822	before watchers with lower priority, but priority will not keep watchers	1109	before watchers with lower priority, but priority will not keep watchers
823	from being executed (except for C<ev_idle> watchers).	1110	from being executed (except for C<ev_idle> watchers).
824		1111
825	This means that priorities are I<only> used for ordering callback
826	invocation after new events have been received. This is useful, for
827	example, to reduce latency after idling, or more often, to bind two
828	watchers on the same event and make sure one is called first.
829
830	If you need to suppress invocation when higher priority events are pending	1112	If you need to suppress invocation when higher priority events are pending
831	you need to look at C<ev_idle> watchers, which provide this functionality.	1113	you need to look at C<ev_idle> watchers, which provide this functionality.
832		1114
833	You I<must not> change the priority of a watcher as long as it is active or	1115	You I<must not> change the priority of a watcher as long as it is active or
834	pending.	1116	pending.
835		1117
		1118	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1119	fine, as long as you do not mind that the priority value you query might
		1120	or might not have been clamped to the valid range.
		1121
836	The default priority used by watchers when no priority has been set is	1122	The default priority used by watchers when no priority has been set is
837	always C<0>, which is supposed to not be too high and not be too low :).	1123	always C<0>, which is supposed to not be too high and not be too low :).
838		1124
839	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1125	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
840	fine, as long as you do not mind that the priority value you query might	1126	priorities.
841	or might not have been adjusted to be within valid range.
842		1127
843	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1128	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
844		1129
845	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1130	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
846	C<loop> nor C<revents> need to be valid as long as the watcher callback	1131	C<loop> nor C<revents> need to be valid as long as the watcher callback
847	can deal with that fact.	1132	can deal with that fact, as both are simply passed through to the
		1133	callback.
848		1134
849	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1135	=item int ev_clear_pending (loop, ev_TYPE *watcher)
850		1136
851	If the watcher is pending, this function returns clears its pending status	1137	If the watcher is pending, this function clears its pending status and
852	and returns its C<revents> bitset (as if its callback was invoked). If the	1138	returns its C<revents> bitset (as if its callback was invoked). If the
853	watcher isn't pending it does nothing and returns C<0>.	1139	watcher isn't pending it does nothing and returns C<0>.
854		1140
		1141	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1142	callback to be invoked, which can be accomplished with this function.
		1143
855	=back	1144	=back
856		1145
857		1146
858	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1147	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
859		1148
860	Each watcher has, by default, a member C<void *data> that you can change	1149	Each watcher has, by default, a member C<void *data> that you can change
861	and read at any time, libev will completely ignore it. This can be used	1150	and read at any time: libev will completely ignore it. This can be used
862	to associate arbitrary data with your watcher. If you need more data and	1151	to associate arbitrary data with your watcher. If you need more data and
863	don't want to allocate memory and store a pointer to it in that data	1152	don't want to allocate memory and store a pointer to it in that data
864	member, you can also "subclass" the watcher type and provide your own	1153	member, you can also "subclass" the watcher type and provide your own
865	data:	1154	data:
866		1155
867	struct my_io	1156	struct my_io
868	{	1157	{
869	struct ev_io io;	1158	ev_io io;
870	int otherfd;	1159	int otherfd;
871	void *somedata;	1160	void *somedata;
872	struct whatever *mostinteresting;	1161	struct whatever *mostinteresting;
873	}	1162	};
		1163
		1164	...
		1165	struct my_io w;
		1166	ev_io_init (&w.io, my_cb, fd, EV_READ);
874		1167
875	And since your callback will be called with a pointer to the watcher, you	1168	And since your callback will be called with a pointer to the watcher, you
876	can cast it back to your own type:	1169	can cast it back to your own type:
877		1170
878	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1171	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
879	{	1172	{
880	struct my_io *w = (struct my_io *)w_;	1173	struct my_io *w = (struct my_io *)w_;
881	...	1174	...
882	}	1175	}
883		1176
884	More interesting and less C-conformant ways of casting your callback type	1177	More interesting and less C-conformant ways of casting your callback type
885	instead have been omitted.	1178	instead have been omitted.
886		1179
887	Another common scenario is having some data structure with multiple	1180	Another common scenario is to use some data structure with multiple
888	watchers:	1181	embedded watchers:
889		1182
890	struct my_biggy	1183	struct my_biggy
891	{	1184	{
892	int some_data;	1185	int some_data;
893	ev_timer t1;	1186	ev_timer t1;
894	ev_timer t2;	1187	ev_timer t2;
895	}	1188	}
896		1189
897	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1190	In this case getting the pointer to C<my_biggy> is a bit more
898	you need to use C<offsetof>:	1191	complicated: Either you store the address of your C<my_biggy> struct
		1192	in the C<data> member of the watcher (for woozies), or you need to use
		1193	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1194	programmers):
899		1195
900	#include <stddef.h>	1196	#include <stddef.h>
901		1197
902	static void	1198	static void
903	t1_cb (EV_P_ struct ev_timer *w, int revents)	1199	t1_cb (EV_P_ ev_timer *w, int revents)
904	{	1200	{
905	struct my_biggy big = (struct my_biggy *	1201	struct my_biggy big = (struct my_biggy *)
906	(((char *)w) - offsetof (struct my_biggy, t1));	1202	(((char *)w) - offsetof (struct my_biggy, t1));
907	}	1203	}
908		1204
909	static void	1205	static void
910	t2_cb (EV_P_ struct ev_timer *w, int revents)	1206	t2_cb (EV_P_ ev_timer *w, int revents)
911	{	1207	{
912	struct my_biggy big = (struct my_biggy *	1208	struct my_biggy big = (struct my_biggy *)
913	(((char *)w) - offsetof (struct my_biggy, t2));	1209	(((char *)w) - offsetof (struct my_biggy, t2));
914	}	1210	}
		1211
		1212	=head2 WATCHER PRIORITY MODELS
		1213
		1214	Many event loops support I<watcher priorities>, which are usually small
		1215	integers that influence the ordering of event callback invocation
		1216	between watchers in some way, all else being equal.
		1217
		1218	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1219	description for the more technical details such as the actual priority
		1220	range.
		1221
		1222	There are two common ways how these these priorities are being interpreted
		1223	by event loops:
		1224
		1225	In the more common lock-out model, higher priorities "lock out" invocation
		1226	of lower priority watchers, which means as long as higher priority
		1227	watchers receive events, lower priority watchers are not being invoked.
		1228
		1229	The less common only-for-ordering model uses priorities solely to order
		1230	callback invocation within a single event loop iteration: Higher priority
		1231	watchers are invoked before lower priority ones, but they all get invoked
		1232	before polling for new events.
		1233
		1234	Libev uses the second (only-for-ordering) model for all its watchers
		1235	except for idle watchers (which use the lock-out model).
		1236
		1237	The rationale behind this is that implementing the lock-out model for
		1238	watchers is not well supported by most kernel interfaces, and most event
		1239	libraries will just poll for the same events again and again as long as
		1240	their callbacks have not been executed, which is very inefficient in the
		1241	common case of one high-priority watcher locking out a mass of lower
		1242	priority ones.
		1243
		1244	Static (ordering) priorities are most useful when you have two or more
		1245	watchers handling the same resource: a typical usage example is having an
		1246	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1247	timeouts. Under load, data might be received while the program handles
		1248	other jobs, but since timers normally get invoked first, the timeout
		1249	handler will be executed before checking for data. In that case, giving
		1250	the timer a lower priority than the I/O watcher ensures that I/O will be
		1251	handled first even under adverse conditions (which is usually, but not
		1252	always, what you want).
		1253
		1254	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1255	will only be executed when no same or higher priority watchers have
		1256	received events, they can be used to implement the "lock-out" model when
		1257	required.
		1258
		1259	For example, to emulate how many other event libraries handle priorities,
		1260	you can associate an C<ev_idle> watcher to each such watcher, and in
		1261	the normal watcher callback, you just start the idle watcher. The real
		1262	processing is done in the idle watcher callback. This causes libev to
		1263	continously poll and process kernel event data for the watcher, but when
		1264	the lock-out case is known to be rare (which in turn is rare :), this is
		1265	workable.
		1266
		1267	Usually, however, the lock-out model implemented that way will perform
		1268	miserably under the type of load it was designed to handle. In that case,
		1269	it might be preferable to stop the real watcher before starting the
		1270	idle watcher, so the kernel will not have to process the event in case
		1271	the actual processing will be delayed for considerable time.
		1272
		1273	Here is an example of an I/O watcher that should run at a strictly lower
		1274	priority than the default, and which should only process data when no
		1275	other events are pending:
		1276
		1277	ev_idle idle; // actual processing watcher
		1278	ev_io io; // actual event watcher
		1279
		1280	static void
		1281	io_cb (EV_P_ ev_io *w, int revents)
		1282	{
		1283	// stop the I/O watcher, we received the event, but
		1284	// are not yet ready to handle it.
		1285	ev_io_stop (EV_A_ w);
		1286
		1287	// start the idle watcher to ahndle the actual event.
		1288	// it will not be executed as long as other watchers
		1289	// with the default priority are receiving events.
		1290	ev_idle_start (EV_A_ &idle);
		1291	}
		1292
		1293	static void
		1294	idle_cb (EV_P_ ev_idle *w, int revents)
		1295	{
		1296	// actual processing
		1297	read (STDIN_FILENO, ...);
		1298
		1299	// have to start the I/O watcher again, as
		1300	// we have handled the event
		1301	ev_io_start (EV_P_ &io);
		1302	}
		1303
		1304	// initialisation
		1305	ev_idle_init (&idle, idle_cb);
		1306	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1307	ev_io_start (EV_DEFAULT_ &io);
		1308
		1309	In the "real" world, it might also be beneficial to start a timer, so that
		1310	low-priority connections can not be locked out forever under load. This
		1311	enables your program to keep a lower latency for important connections
		1312	during short periods of high load, while not completely locking out less
		1313	important ones.
915		1314
916		1315
917	=head1 WATCHER TYPES	1316	=head1 WATCHER TYPES
918		1317
919	This section describes each watcher in detail, but will not repeat	1318	This section describes each watcher in detail, but will not repeat
…		…
943	In general you can register as many read and/or write event watchers per	1342	In general you can register as many read and/or write event watchers per
944	fd as you want (as long as you don't confuse yourself). Setting all file	1343	fd as you want (as long as you don't confuse yourself). Setting all file
945	descriptors to non-blocking mode is also usually a good idea (but not	1344	descriptors to non-blocking mode is also usually a good idea (but not
946	required if you know what you are doing).	1345	required if you know what you are doing).
947		1346
948	You have to be careful with dup'ed file descriptors, though. Some backends	1347	If you cannot use non-blocking mode, then force the use of a
949	(the linux epoll backend is a notable example) cannot handle dup'ed file	1348	known-to-be-good backend (at the time of this writing, this includes only
950	descriptors correctly if you register interest in two or more fds pointing	1349	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
951	to the same underlying file/socket/etc. description (that is, they share	1350	descriptors for which non-blocking operation makes no sense (such as
952	the same underlying "file open").	1351	files) - libev doesn't guarentee any specific behaviour in that case.
953
954	If you must do this, then force the use of a known-to-be-good backend
955	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
956	C<EVBACKEND_POLL>).
957		1352
958	Another thing you have to watch out for is that it is quite easy to	1353	Another thing you have to watch out for is that it is quite easy to
959	receive "spurious" readyness notifications, that is your callback might	1354	receive "spurious" readiness notifications, that is your callback might
960	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1355	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
961	because there is no data. Not only are some backends known to create a	1356	because there is no data. Not only are some backends known to create a
962	lot of those (for example solaris ports), it is very easy to get into	1357	lot of those (for example Solaris ports), it is very easy to get into
963	this situation even with a relatively standard program structure. Thus	1358	this situation even with a relatively standard program structure. Thus
964	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1359	it is best to always use non-blocking I/O: An extra C<read>(2) returning
965	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1360	C<EAGAIN> is far preferable to a program hanging until some data arrives.
966		1361
967	If you cannot run the fd in non-blocking mode (for example you should not	1362	If you cannot run the fd in non-blocking mode (for example you should
968	play around with an Xlib connection), then you have to seperately re-test	1363	not play around with an Xlib connection), then you have to separately
969	whether a file descriptor is really ready with a known-to-be good interface	1364	re-test whether a file descriptor is really ready with a known-to-be good
970	such as poll (fortunately in our Xlib example, Xlib already does this on	1365	interface such as poll (fortunately in our Xlib example, Xlib already
971	its own, so its quite safe to use).	1366	does this on its own, so its quite safe to use). Some people additionally
		1367	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1368	indefinitely.
		1369
		1370	But really, best use non-blocking mode.
972		1371
973	=head3 The special problem of disappearing file descriptors	1372	=head3 The special problem of disappearing file descriptors
974		1373
975	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1374	Some backends (e.g. kqueue, epoll) need to be told about closing a file
976	descriptor (either by calling C<close> explicitly or by any other means,	1375	descriptor (either due to calling C<close> explicitly or any other means,
977	such as C<dup>). The reason is that you register interest in some file	1376	such as C<dup2>). The reason is that you register interest in some file
978	descriptor, but when it goes away, the operating system will silently drop	1377	descriptor, but when it goes away, the operating system will silently drop
979	this interest. If another file descriptor with the same number then is	1378	this interest. If another file descriptor with the same number then is
980	registered with libev, there is no efficient way to see that this is, in	1379	registered with libev, there is no efficient way to see that this is, in
981	fact, a different file descriptor.	1380	fact, a different file descriptor.
982		1381
…		…
992	optimisations to libev.	1391	optimisations to libev.
993		1392
994	=head3 The special problem of dup'ed file descriptors	1393	=head3 The special problem of dup'ed file descriptors
995		1394
996	Some backends (e.g. epoll), cannot register events for file descriptors,	1395	Some backends (e.g. epoll), cannot register events for file descriptors,
997	but only events for the underlying file descriptions. That menas when you	1396	but only events for the underlying file descriptions. That means when you
998	have C<dup ()>'ed file descriptors and register events for them, only one	1397	have C<dup ()>'ed file descriptors or weirder constellations, and register
999	file descriptor might actually receive events.	1398	events for them, only one file descriptor might actually receive events.
1000		1399
1001	There is no workaorund possible except not registering events	1400	There is no workaround possible except not registering events
1002	for potentially C<dup ()>'ed file descriptors or to resort to	1401	for potentially C<dup ()>'ed file descriptors, or to resort to
1003	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1402	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1004		1403
1005	=head3 The special problem of fork	1404	=head3 The special problem of fork
1006		1405
1007	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1406	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
…		…
1011	To support fork in your programs, you either have to call	1410	To support fork in your programs, you either have to call
1012	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1411	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1013	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1412	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1014	C<EVBACKEND_POLL>.	1413	C<EVBACKEND_POLL>.
1015		1414
		1415	=head3 The special problem of SIGPIPE
		1416
		1417	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1418	when writing to a pipe whose other end has been closed, your program gets
		1419	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1420	this is sensible behaviour, for daemons, this is usually undesirable.
		1421
		1422	So when you encounter spurious, unexplained daemon exits, make sure you
		1423	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1424	somewhere, as that would have given you a big clue).
		1425
1016		1426
1017	=head3 Watcher-Specific Functions	1427	=head3 Watcher-Specific Functions
1018		1428
1019	=over 4	1429	=over 4
1020		1430
1021	=item ev_io_init (ev_io *, callback, int fd, int events)	1431	=item ev_io_init (ev_io *, callback, int fd, int events)
1022		1432
1023	=item ev_io_set (ev_io *, int fd, int events)	1433	=item ev_io_set (ev_io *, int fd, int events)
1024		1434
1025	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1435	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1026	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1436	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1027	C<EV_READ | EV_WRITE> to receive the given events.	1437	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1028		1438
1029	=item int fd [read-only]	1439	=item int fd [read-only]
1030		1440
1031	The file descriptor being watched.	1441	The file descriptor being watched.
1032		1442
1033	=item int events [read-only]	1443	=item int events [read-only]
1034		1444
1035	The events being watched.	1445	The events being watched.
1036		1446
1037	=back	1447	=back
		1448
		1449	=head3 Examples
1038		1450
1039	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1451	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1040	readable, but only once. Since it is likely line-buffered, you could	1452	readable, but only once. Since it is likely line-buffered, you could
1041	attempt to read a whole line in the callback.	1453	attempt to read a whole line in the callback.
1042		1454
1043	static void	1455	static void
1044	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1456	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1045	{	1457	{
1046	ev_io_stop (loop, w);	1458	ev_io_stop (loop, w);
1047	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1459	.. read from stdin here (or from w->fd) and handle any I/O errors
1048	}	1460	}
1049		1461
1050	...	1462	...
1051	struct ev_loop *loop = ev_default_init (0);	1463	struct ev_loop *loop = ev_default_init (0);
1052	struct ev_io stdin_readable;	1464	ev_io stdin_readable;
1053	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1465	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1054	ev_io_start (loop, &stdin_readable);	1466	ev_io_start (loop, &stdin_readable);
1055	ev_loop (loop, 0);	1467	ev_loop (loop, 0);
1056		1468
1057		1469
1058	=head2 C<ev_timer> - relative and optionally repeating timeouts	1470	=head2 C<ev_timer> - relative and optionally repeating timeouts
1059		1471
1060	Timer watchers are simple relative timers that generate an event after a	1472	Timer watchers are simple relative timers that generate an event after a
1061	given time, and optionally repeating in regular intervals after that.	1473	given time, and optionally repeating in regular intervals after that.
1062		1474
1063	The timers are based on real time, that is, if you register an event that	1475	The timers are based on real time, that is, if you register an event that
1064	times out after an hour and you reset your system clock to last years	1476	times out after an hour and you reset your system clock to January last
1065	time, it will still time out after (roughly) and hour. "Roughly" because	1477	year, it will still time out after (roughly) one hour. "Roughly" because
1066	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1478	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1067	monotonic clock option helps a lot here).	1479	monotonic clock option helps a lot here).
		1480
		1481	The callback is guaranteed to be invoked only I<after> its timeout has
		1482	passed (not I<at>, so on systems with very low-resolution clocks this
		1483	might introduce a small delay). If multiple timers become ready during the
		1484	same loop iteration then the ones with earlier time-out values are invoked
		1485	before ones with later time-out values (but this is no longer true when a
		1486	callback calls C<ev_loop> recursively).
		1487
		1488	=head3 Be smart about timeouts
		1489
		1490	Many real-world problems involve some kind of timeout, usually for error
		1491	recovery. A typical example is an HTTP request - if the other side hangs,
		1492	you want to raise some error after a while.
		1493
		1494	What follows are some ways to handle this problem, from obvious and
		1495	inefficient to smart and efficient.
		1496
		1497	In the following, a 60 second activity timeout is assumed - a timeout that
		1498	gets reset to 60 seconds each time there is activity (e.g. each time some
		1499	data or other life sign was received).
		1500
		1501	=over 4
		1502
		1503	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1504
		1505	This is the most obvious, but not the most simple way: In the beginning,
		1506	start the watcher:
		1507
		1508	ev_timer_init (timer, callback, 60., 0.);
		1509	ev_timer_start (loop, timer);
		1510
		1511	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1512	and start it again:
		1513
		1514	ev_timer_stop (loop, timer);
		1515	ev_timer_set (timer, 60., 0.);
		1516	ev_timer_start (loop, timer);
		1517
		1518	This is relatively simple to implement, but means that each time there is
		1519	some activity, libev will first have to remove the timer from its internal
		1520	data structure and then add it again. Libev tries to be fast, but it's
		1521	still not a constant-time operation.
		1522
		1523	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1524
		1525	This is the easiest way, and involves using C<ev_timer_again> instead of
		1526	C<ev_timer_start>.
		1527
		1528	To implement this, configure an C<ev_timer> with a C<repeat> value
		1529	of C<60> and then call C<ev_timer_again> at start and each time you
		1530	successfully read or write some data. If you go into an idle state where
		1531	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1532	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1533
		1534	That means you can ignore both the C<ev_timer_start> function and the
		1535	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1536	member and C<ev_timer_again>.
		1537
		1538	At start:
		1539
		1540	ev_init (timer, callback);
		1541	timer->repeat = 60.;
		1542	ev_timer_again (loop, timer);
		1543
		1544	Each time there is some activity:
		1545
		1546	ev_timer_again (loop, timer);
		1547
		1548	It is even possible to change the time-out on the fly, regardless of
		1549	whether the watcher is active or not:
		1550
		1551	timer->repeat = 30.;
		1552	ev_timer_again (loop, timer);
		1553
		1554	This is slightly more efficient then stopping/starting the timer each time
		1555	you want to modify its timeout value, as libev does not have to completely
		1556	remove and re-insert the timer from/into its internal data structure.
		1557
		1558	It is, however, even simpler than the "obvious" way to do it.
		1559
		1560	=item 3. Let the timer time out, but then re-arm it as required.
		1561
		1562	This method is more tricky, but usually most efficient: Most timeouts are
		1563	relatively long compared to the intervals between other activity - in
		1564	our example, within 60 seconds, there are usually many I/O events with
		1565	associated activity resets.
		1566
		1567	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1568	but remember the time of last activity, and check for a real timeout only
		1569	within the callback:
		1570
		1571	ev_tstamp last_activity; // time of last activity
		1572
		1573	static void
		1574	callback (EV_P_ ev_timer *w, int revents)
		1575	{
		1576	ev_tstamp now = ev_now (EV_A);
		1577	ev_tstamp timeout = last_activity + 60.;
		1578
		1579	// if last_activity + 60. is older than now, we did time out
		1580	if (timeout < now)
		1581	{
		1582	// timeout occured, take action
		1583	}
		1584	else
		1585	{
		1586	// callback was invoked, but there was some activity, re-arm
		1587	// the watcher to fire in last_activity + 60, which is
		1588	// guaranteed to be in the future, so "again" is positive:
		1589	w->repeat = timeout - now;
		1590	ev_timer_again (EV_A_ w);
		1591	}
		1592	}
		1593
		1594	To summarise the callback: first calculate the real timeout (defined
		1595	as "60 seconds after the last activity"), then check if that time has
		1596	been reached, which means something I<did>, in fact, time out. Otherwise
		1597	the callback was invoked too early (C<timeout> is in the future), so
		1598	re-schedule the timer to fire at that future time, to see if maybe we have
		1599	a timeout then.
		1600
		1601	Note how C<ev_timer_again> is used, taking advantage of the
		1602	C<ev_timer_again> optimisation when the timer is already running.
		1603
		1604	This scheme causes more callback invocations (about one every 60 seconds
		1605	minus half the average time between activity), but virtually no calls to
		1606	libev to change the timeout.
		1607
		1608	To start the timer, simply initialise the watcher and set C<last_activity>
		1609	to the current time (meaning we just have some activity :), then call the
		1610	callback, which will "do the right thing" and start the timer:
		1611
		1612	ev_init (timer, callback);
		1613	last_activity = ev_now (loop);
		1614	callback (loop, timer, EV_TIMEOUT);
		1615
		1616	And when there is some activity, simply store the current time in
		1617	C<last_activity>, no libev calls at all:
		1618
		1619	last_actiivty = ev_now (loop);
		1620
		1621	This technique is slightly more complex, but in most cases where the
		1622	time-out is unlikely to be triggered, much more efficient.
		1623
		1624	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1625	callback :) - just change the timeout and invoke the callback, which will
		1626	fix things for you.
		1627
		1628	=item 4. Wee, just use a double-linked list for your timeouts.
		1629
		1630	If there is not one request, but many thousands (millions...), all
		1631	employing some kind of timeout with the same timeout value, then one can
		1632	do even better:
		1633
		1634	When starting the timeout, calculate the timeout value and put the timeout
		1635	at the I<end> of the list.
		1636
		1637	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1638	the list is expected to fire (for example, using the technique #3).
		1639
		1640	When there is some activity, remove the timer from the list, recalculate
		1641	the timeout, append it to the end of the list again, and make sure to
		1642	update the C<ev_timer> if it was taken from the beginning of the list.
		1643
		1644	This way, one can manage an unlimited number of timeouts in O(1) time for
		1645	starting, stopping and updating the timers, at the expense of a major
		1646	complication, and having to use a constant timeout. The constant timeout
		1647	ensures that the list stays sorted.
		1648
		1649	=back
		1650
		1651	So which method the best?
		1652
		1653	Method #2 is a simple no-brain-required solution that is adequate in most
		1654	situations. Method #3 requires a bit more thinking, but handles many cases
		1655	better, and isn't very complicated either. In most case, choosing either
		1656	one is fine, with #3 being better in typical situations.
		1657
		1658	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1659	rather complicated, but extremely efficient, something that really pays
		1660	off after the first million or so of active timers, i.e. it's usually
		1661	overkill :)
		1662
		1663	=head3 The special problem of time updates
		1664
		1665	Establishing the current time is a costly operation (it usually takes at
		1666	least two system calls): EV therefore updates its idea of the current
		1667	time only before and after C<ev_loop> collects new events, which causes a
		1668	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1669	lots of events in one iteration.
1068		1670
1069	The relative timeouts are calculated relative to the C<ev_now ()>	1671	The relative timeouts are calculated relative to the C<ev_now ()>
1070	time. This is usually the right thing as this timestamp refers to the time	1672	time. This is usually the right thing as this timestamp refers to the time
1071	of the event triggering whatever timeout you are modifying/starting. If	1673	of the event triggering whatever timeout you are modifying/starting. If
1072	you suspect event processing to be delayed and you I<need> to base the timeout	1674	you suspect event processing to be delayed and you I<need> to base the
1073	on the current time, use something like this to adjust for this:	1675	timeout on the current time, use something like this to adjust for this:
1074		1676
1075	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1677	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1076		1678
1077	The callback is guarenteed to be invoked only when its timeout has passed,	1679	If the event loop is suspended for a long time, you can also force an
1078	but if multiple timers become ready during the same loop iteration then	1680	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1079	order of execution is undefined.	1681	()>.
1080		1682
1081	=head3 Watcher-Specific Functions and Data Members	1683	=head3 Watcher-Specific Functions and Data Members
1082		1684
1083	=over 4	1685	=over 4
1084		1686
1085	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1687	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1086		1688
1087	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1689	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1088		1690
1089	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1691	Configure the timer to trigger after C<after> seconds. If C<repeat>
1090	C<0.>, then it will automatically be stopped. If it is positive, then the	1692	is C<0.>, then it will automatically be stopped once the timeout is
1091	timer will automatically be configured to trigger again C<repeat> seconds	1693	reached. If it is positive, then the timer will automatically be
1092	later, again, and again, until stopped manually.	1694	configured to trigger again C<repeat> seconds later, again, and again,
		1695	until stopped manually.
1093		1696
1094	The timer itself will do a best-effort at avoiding drift, that is, if you	1697	The timer itself will do a best-effort at avoiding drift, that is, if
1095	configure a timer to trigger every 10 seconds, then it will trigger at	1698	you configure a timer to trigger every 10 seconds, then it will normally
1096	exactly 10 second intervals. If, however, your program cannot keep up with	1699	trigger at exactly 10 second intervals. If, however, your program cannot
1097	the timer (because it takes longer than those 10 seconds to do stuff) the	1700	keep up with the timer (because it takes longer than those 10 seconds to
1098	timer will not fire more than once per event loop iteration.	1701	do stuff) the timer will not fire more than once per event loop iteration.
1099		1702
1100	=item ev_timer_again (loop)	1703	=item ev_timer_again (loop, ev_timer *)
1101		1704
1102	This will act as if the timer timed out and restart it again if it is	1705	This will act as if the timer timed out and restart it again if it is
1103	repeating. The exact semantics are:	1706	repeating. The exact semantics are:
1104		1707
1105	If the timer is pending, its pending status is cleared.	1708	If the timer is pending, its pending status is cleared.
1106		1709
1107	If the timer is started but nonrepeating, stop it (as if it timed out).	1710	If the timer is started but non-repeating, stop it (as if it timed out).
1108		1711
1109	If the timer is repeating, either start it if necessary (with the	1712	If the timer is repeating, either start it if necessary (with the
1110	C<repeat> value), or reset the running timer to the C<repeat> value.	1713	C<repeat> value), or reset the running timer to the C<repeat> value.
1111		1714
1112	This sounds a bit complicated, but here is a useful and typical	1715	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1113	example: Imagine you have a tcp connection and you want a so-called idle	1716	usage example.
1114	timeout, that is, you want to be called when there have been, say, 60
1115	seconds of inactivity on the socket. The easiest way to do this is to
1116	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1117	C<ev_timer_again> each time you successfully read or write some data. If
1118	you go into an idle state where you do not expect data to travel on the
1119	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1120	automatically restart it if need be.
1121
1122	That means you can ignore the C<after> value and C<ev_timer_start>
1123	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1124
1125	ev_timer_init (timer, callback, 0., 5.);
1126	ev_timer_again (loop, timer);
1127	...
1128	timer->again = 17.;
1129	ev_timer_again (loop, timer);
1130	...
1131	timer->again = 10.;
1132	ev_timer_again (loop, timer);
1133
1134	This is more slightly efficient then stopping/starting the timer each time
1135	you want to modify its timeout value.
1136		1717
1137	=item ev_tstamp repeat [read-write]	1718	=item ev_tstamp repeat [read-write]
1138		1719
1139	The current C<repeat> value. Will be used each time the watcher times out	1720	The current C<repeat> value. Will be used each time the watcher times out
1140	or C<ev_timer_again> is called and determines the next timeout (if any),	1721	or C<ev_timer_again> is called, and determines the next timeout (if any),
1141	which is also when any modifications are taken into account.	1722	which is also when any modifications are taken into account.
1142		1723
1143	=back	1724	=back
1144		1725
		1726	=head3 Examples
		1727
1145	Example: Create a timer that fires after 60 seconds.	1728	Example: Create a timer that fires after 60 seconds.
1146		1729
1147	static void	1730	static void
1148	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1731	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1149	{	1732	{
1150	.. one minute over, w is actually stopped right here	1733	.. one minute over, w is actually stopped right here
1151	}	1734	}
1152		1735
1153	struct ev_timer mytimer;	1736	ev_timer mytimer;
1154	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1737	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1155	ev_timer_start (loop, &mytimer);	1738	ev_timer_start (loop, &mytimer);
1156		1739
1157	Example: Create a timeout timer that times out after 10 seconds of	1740	Example: Create a timeout timer that times out after 10 seconds of
1158	inactivity.	1741	inactivity.
1159		1742
1160	static void	1743	static void
1161	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1744	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1162	{	1745	{
1163	.. ten seconds without any activity	1746	.. ten seconds without any activity
1164	}	1747	}
1165		1748
1166	struct ev_timer mytimer;	1749	ev_timer mytimer;
1167	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1750	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1168	ev_timer_again (&mytimer); /* start timer */	1751	ev_timer_again (&mytimer); /* start timer */
1169	ev_loop (loop, 0);	1752	ev_loop (loop, 0);
1170		1753
1171	// and in some piece of code that gets executed on any "activity":	1754	// and in some piece of code that gets executed on any "activity":
1172	// reset the timeout to start ticking again at 10 seconds	1755	// reset the timeout to start ticking again at 10 seconds
1173	ev_timer_again (&mytimer);	1756	ev_timer_again (&mytimer);
1174		1757
1175		1758
1176	=head2 C<ev_periodic> - to cron or not to cron?	1759	=head2 C<ev_periodic> - to cron or not to cron?
1177		1760
1178	Periodic watchers are also timers of a kind, but they are very versatile	1761	Periodic watchers are also timers of a kind, but they are very versatile
1179	(and unfortunately a bit complex).	1762	(and unfortunately a bit complex).
1180		1763
1181	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1764	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1182	but on wallclock time (absolute time). You can tell a periodic watcher	1765	relative time, the physical time that passes) but on wall clock time
1183	to trigger "at" some specific point in time. For example, if you tell a	1766	(absolute time, the thing you can read on your calender or clock). The
1184	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1767	difference is that wall clock time can run faster or slower than real
1185	+ 10.>) and then reset your system clock to the last year, then it will	1768	time, and time jumps are not uncommon (e.g. when you adjust your
1186	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1769	wrist-watch).
1187	roughly 10 seconds later).
1188		1770
1189	They can also be used to implement vastly more complex timers, such as	1771	You can tell a periodic watcher to trigger after some specific point
1190	triggering an event on each midnight, local time or other, complicated,	1772	in time: for example, if you tell a periodic watcher to trigger "in 10
1191	rules.	1773	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1774	not a delay) and then reset your system clock to January of the previous
		1775	year, then it will take a year or more to trigger the event (unlike an
		1776	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1777	it, as it uses a relative timeout).
1192		1778
		1779	C<ev_periodic> watchers can also be used to implement vastly more complex
		1780	timers, such as triggering an event on each "midnight, local time", or
		1781	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1782	those cannot react to time jumps.
		1783
1193	As with timers, the callback is guarenteed to be invoked only when the	1784	As with timers, the callback is guaranteed to be invoked only when the
1194	time (C<at>) has been passed, but if multiple periodic timers become ready	1785	point in time where it is supposed to trigger has passed. If multiple
1195	during the same loop iteration then order of execution is undefined.	1786	timers become ready during the same loop iteration then the ones with
		1787	earlier time-out values are invoked before ones with later time-out values
		1788	(but this is no longer true when a callback calls C<ev_loop> recursively).
1196		1789
1197	=head3 Watcher-Specific Functions and Data Members	1790	=head3 Watcher-Specific Functions and Data Members
1198		1791
1199	=over 4	1792	=over 4
1200		1793
1201	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1794	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1202		1795
1203	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1796	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1204		1797
1205	Lots of arguments, lets sort it out... There are basically three modes of	1798	Lots of arguments, let's sort it out... There are basically three modes of
1206	operation, and we will explain them from simplest to complex:	1799	operation, and we will explain them from simplest to most complex:
1207		1800
1208	=over 4	1801	=over 4
1209		1802
1210	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1803	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1211		1804
1212	In this configuration the watcher triggers an event at the wallclock time	1805	In this configuration the watcher triggers an event after the wall clock
1213	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1806	time C<offset> has passed. It will not repeat and will not adjust when a
1214	that is, if it is to be run at January 1st 2011 then it will run when the	1807	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1215	system time reaches or surpasses this time.	1808	will be stopped and invoked when the system clock reaches or surpasses
		1809	this point in time.
1216		1810
1217	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1811	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1218		1812
1219	In this mode the watcher will always be scheduled to time out at the next	1813	In this mode the watcher will always be scheduled to time out at the next
1220	C<at + N * interval> time (for some integer N, which can also be negative)	1814	C<offset + N * interval> time (for some integer N, which can also be
1221	and then repeat, regardless of any time jumps.	1815	negative) and then repeat, regardless of any time jumps. The C<offset>
		1816	argument is merely an offset into the C<interval> periods.
1222		1817
1223	This can be used to create timers that do not drift with respect to system	1818	This can be used to create timers that do not drift with respect to the
1224	time:	1819	system clock, for example, here is an C<ev_periodic> that triggers each
		1820	hour, on the hour (with respect to UTC):
1225		1821
1226	ev_periodic_set (&periodic, 0., 3600., 0);	1822	ev_periodic_set (&periodic, 0., 3600., 0);
1227		1823
1228	This doesn't mean there will always be 3600 seconds in between triggers,	1824	This doesn't mean there will always be 3600 seconds in between triggers,
1229	but only that the the callback will be called when the system time shows a	1825	but only that the callback will be called when the system time shows a
1230	full hour (UTC), or more correctly, when the system time is evenly divisible	1826	full hour (UTC), or more correctly, when the system time is evenly divisible
1231	by 3600.	1827	by 3600.
1232		1828
1233	Another way to think about it (for the mathematically inclined) is that	1829	Another way to think about it (for the mathematically inclined) is that
1234	C<ev_periodic> will try to run the callback in this mode at the next possible	1830	C<ev_periodic> will try to run the callback in this mode at the next possible
1235	time where C<time = at (mod interval)>, regardless of any time jumps.	1831	time where C<time = offset (mod interval)>, regardless of any time jumps.
1236		1832
1237	For numerical stability it is preferable that the C<at> value is near	1833	For numerical stability it is preferable that the C<offset> value is near
1238	C<ev_now ()> (the current time), but there is no range requirement for	1834	C<ev_now ()> (the current time), but there is no range requirement for
1239	this value.	1835	this value, and in fact is often specified as zero.
1240		1836
		1837	Note also that there is an upper limit to how often a timer can fire (CPU
		1838	speed for example), so if C<interval> is very small then timing stability
		1839	will of course deteriorate. Libev itself tries to be exact to be about one
		1840	millisecond (if the OS supports it and the machine is fast enough).
		1841
1241	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1842	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1242		1843
1243	In this mode the values for C<interval> and C<at> are both being	1844	In this mode the values for C<interval> and C<offset> are both being
1244	ignored. Instead, each time the periodic watcher gets scheduled, the	1845	ignored. Instead, each time the periodic watcher gets scheduled, the
1245	reschedule callback will be called with the watcher as first, and the	1846	reschedule callback will be called with the watcher as first, and the
1246	current time as second argument.	1847	current time as second argument.
1247		1848
1248	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1849	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1249	ever, or make any event loop modifications>. If you need to stop it,	1850	or make ANY other event loop modifications whatsoever, unless explicitly
1250	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1851	allowed by documentation here>.
1251	starting an C<ev_prepare> watcher, which is legal).
1252		1852
		1853	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1854	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1855	only event loop modification you are allowed to do).
		1856
1253	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1857	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1254	ev_tstamp now)>, e.g.:	1858	*w, ev_tstamp now)>, e.g.:
1255		1859
		1860	static ev_tstamp
1256	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1861	my_rescheduler (ev_periodic *w, ev_tstamp now)
1257	{	1862	{
1258	return now + 60.;	1863	return now + 60.;
1259	}	1864	}
1260		1865
1261	It must return the next time to trigger, based on the passed time value	1866	It must return the next time to trigger, based on the passed time value
1262	(that is, the lowest time value larger than to the second argument). It	1867	(that is, the lowest time value larger than to the second argument). It
1263	will usually be called just before the callback will be triggered, but	1868	will usually be called just before the callback will be triggered, but
1264	might be called at other times, too.	1869	might be called at other times, too.
1265		1870
1266	NOTE: I<< This callback must always return a time that is later than the	1871	NOTE: I<< This callback must always return a time that is higher than or
1267	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1872	equal to the passed C<now> value >>.
1268		1873
1269	This can be used to create very complex timers, such as a timer that	1874	This can be used to create very complex timers, such as a timer that
1270	triggers on each midnight, local time. To do this, you would calculate the	1875	triggers on "next midnight, local time". To do this, you would calculate the
1271	next midnight after C<now> and return the timestamp value for this. How	1876	next midnight after C<now> and return the timestamp value for this. How
1272	you do this is, again, up to you (but it is not trivial, which is the main	1877	you do this is, again, up to you (but it is not trivial, which is the main
1273	reason I omitted it as an example).	1878	reason I omitted it as an example).
1274		1879
1275	=back	1880	=back
…		…
1279	Simply stops and restarts the periodic watcher again. This is only useful	1884	Simply stops and restarts the periodic watcher again. This is only useful
1280	when you changed some parameters or the reschedule callback would return	1885	when you changed some parameters or the reschedule callback would return
1281	a different time than the last time it was called (e.g. in a crond like	1886	a different time than the last time it was called (e.g. in a crond like
1282	program when the crontabs have changed).	1887	program when the crontabs have changed).
1283		1888
		1889	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1890
		1891	When active, returns the absolute time that the watcher is supposed
		1892	to trigger next. This is not the same as the C<offset> argument to
		1893	C<ev_periodic_set>, but indeed works even in interval and manual
		1894	rescheduling modes.
		1895
1284	=item ev_tstamp offset [read-write]	1896	=item ev_tstamp offset [read-write]
1285		1897
1286	When repeating, this contains the offset value, otherwise this is the	1898	When repeating, this contains the offset value, otherwise this is the
1287	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1899	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1900	although libev might modify this value for better numerical stability).
1288		1901
1289	Can be modified any time, but changes only take effect when the periodic	1902	Can be modified any time, but changes only take effect when the periodic
1290	timer fires or C<ev_periodic_again> is being called.	1903	timer fires or C<ev_periodic_again> is being called.
1291		1904
1292	=item ev_tstamp interval [read-write]	1905	=item ev_tstamp interval [read-write]
1293		1906
1294	The current interval value. Can be modified any time, but changes only	1907	The current interval value. Can be modified any time, but changes only
1295	take effect when the periodic timer fires or C<ev_periodic_again> is being	1908	take effect when the periodic timer fires or C<ev_periodic_again> is being
1296	called.	1909	called.
1297		1910
1298	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1911	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1299		1912
1300	The current reschedule callback, or C<0>, if this functionality is	1913	The current reschedule callback, or C<0>, if this functionality is
1301	switched off. Can be changed any time, but changes only take effect when	1914	switched off. Can be changed any time, but changes only take effect when
1302	the periodic timer fires or C<ev_periodic_again> is being called.	1915	the periodic timer fires or C<ev_periodic_again> is being called.
1303		1916
1304	=item ev_tstamp at [read-only]
1305
1306	When active, contains the absolute time that the watcher is supposed to
1307	trigger next.
1308
1309	=back	1917	=back
1310		1918
		1919	=head3 Examples
		1920
1311	Example: Call a callback every hour, or, more precisely, whenever the	1921	Example: Call a callback every hour, or, more precisely, whenever the
1312	system clock is divisible by 3600. The callback invocation times have	1922	system time is divisible by 3600. The callback invocation times have
1313	potentially a lot of jittering, but good long-term stability.	1923	potentially a lot of jitter, but good long-term stability.
1314		1924
1315	static void	1925	static void
1316	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1926	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1317	{	1927	{
1318	... its now a full hour (UTC, or TAI or whatever your clock follows)	1928	... its now a full hour (UTC, or TAI or whatever your clock follows)
1319	}	1929	}
1320		1930
1321	struct ev_periodic hourly_tick;	1931	ev_periodic hourly_tick;
1322	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1932	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1323	ev_periodic_start (loop, &hourly_tick);	1933	ev_periodic_start (loop, &hourly_tick);
1324		1934
1325	Example: The same as above, but use a reschedule callback to do it:	1935	Example: The same as above, but use a reschedule callback to do it:
1326		1936
1327	#include <math.h>	1937	#include <math.h>
1328		1938
1329	static ev_tstamp	1939	static ev_tstamp
1330	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1940	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1331	{	1941	{
1332	return fmod (now, 3600.) + 3600.;	1942	return now + (3600. - fmod (now, 3600.));
1333	}	1943	}
1334		1944
1335	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1945	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1336		1946
1337	Example: Call a callback every hour, starting now:	1947	Example: Call a callback every hour, starting now:
1338		1948
1339	struct ev_periodic hourly_tick;	1949	ev_periodic hourly_tick;
1340	ev_periodic_init (&hourly_tick, clock_cb,	1950	ev_periodic_init (&hourly_tick, clock_cb,
1341	fmod (ev_now (loop), 3600.), 3600., 0);	1951	fmod (ev_now (loop), 3600.), 3600., 0);
1342	ev_periodic_start (loop, &hourly_tick);	1952	ev_periodic_start (loop, &hourly_tick);
1343		1953
1344		1954
1345	=head2 C<ev_signal> - signal me when a signal gets signalled!	1955	=head2 C<ev_signal> - signal me when a signal gets signalled!
1346		1956
1347	Signal watchers will trigger an event when the process receives a specific	1957	Signal watchers will trigger an event when the process receives a specific
1348	signal one or more times. Even though signals are very asynchronous, libev	1958	signal one or more times. Even though signals are very asynchronous, libev
1349	will try it's best to deliver signals synchronously, i.e. as part of the	1959	will try it's best to deliver signals synchronously, i.e. as part of the
1350	normal event processing, like any other event.	1960	normal event processing, like any other event.
1351		1961
		1962	If you want signals asynchronously, just use C<sigaction> as you would
		1963	do without libev and forget about sharing the signal. You can even use
		1964	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1965
1352	You can configure as many watchers as you like per signal. Only when the	1966	You can configure as many watchers as you like per signal. Only when the
1353	first watcher gets started will libev actually register a signal watcher	1967	first watcher gets started will libev actually register a signal handler
1354	with the kernel (thus it coexists with your own signal handlers as long	1968	with the kernel (thus it coexists with your own signal handlers as long as
1355	as you don't register any with libev). Similarly, when the last signal	1969	you don't register any with libev for the same signal). Similarly, when
1356	watcher for a signal is stopped libev will reset the signal handler to	1970	the last signal watcher for a signal is stopped, libev will reset the
1357	SIG_DFL (regardless of what it was set to before).	1971	signal handler to SIG_DFL (regardless of what it was set to before).
		1972
		1973	If possible and supported, libev will install its handlers with
		1974	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1975	interrupted. If you have a problem with system calls getting interrupted by
		1976	signals you can block all signals in an C<ev_check> watcher and unblock
		1977	them in an C<ev_prepare> watcher.
1358		1978
1359	=head3 Watcher-Specific Functions and Data Members	1979	=head3 Watcher-Specific Functions and Data Members
1360		1980
1361	=over 4	1981	=over 4
1362		1982
…		…
1371		1991
1372	The signal the watcher watches out for.	1992	The signal the watcher watches out for.
1373		1993
1374	=back	1994	=back
1375		1995
		1996	=head3 Examples
		1997
		1998	Example: Try to exit cleanly on SIGINT.
		1999
		2000	static void
		2001	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2002	{
		2003	ev_unloop (loop, EVUNLOOP_ALL);
		2004	}
		2005
		2006	ev_signal signal_watcher;
		2007	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2008	ev_signal_start (loop, &signal_watcher);
		2009
1376		2010
1377	=head2 C<ev_child> - watch out for process status changes	2011	=head2 C<ev_child> - watch out for process status changes
1378		2012
1379	Child watchers trigger when your process receives a SIGCHLD in response to	2013	Child watchers trigger when your process receives a SIGCHLD in response to
1380	some child status changes (most typically when a child of yours dies).	2014	some child status changes (most typically when a child of yours dies or
		2015	exits). It is permissible to install a child watcher I<after> the child
		2016	has been forked (which implies it might have already exited), as long
		2017	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2018	forking and then immediately registering a watcher for the child is fine,
		2019	but forking and registering a watcher a few event loop iterations later or
		2020	in the next callback invocation is not.
		2021
		2022	Only the default event loop is capable of handling signals, and therefore
		2023	you can only register child watchers in the default event loop.
		2024
		2025	=head3 Process Interaction
		2026
		2027	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2028	initialised. This is necessary to guarantee proper behaviour even if
		2029	the first child watcher is started after the child exits. The occurrence
		2030	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2031	synchronously as part of the event loop processing. Libev always reaps all
		2032	children, even ones not watched.
		2033
		2034	=head3 Overriding the Built-In Processing
		2035
		2036	Libev offers no special support for overriding the built-in child
		2037	processing, but if your application collides with libev's default child
		2038	handler, you can override it easily by installing your own handler for
		2039	C<SIGCHLD> after initialising the default loop, and making sure the
		2040	default loop never gets destroyed. You are encouraged, however, to use an
		2041	event-based approach to child reaping and thus use libev's support for
		2042	that, so other libev users can use C<ev_child> watchers freely.
		2043
		2044	=head3 Stopping the Child Watcher
		2045
		2046	Currently, the child watcher never gets stopped, even when the
		2047	child terminates, so normally one needs to stop the watcher in the
		2048	callback. Future versions of libev might stop the watcher automatically
		2049	when a child exit is detected.
1381		2050
1382	=head3 Watcher-Specific Functions and Data Members	2051	=head3 Watcher-Specific Functions and Data Members
1383		2052
1384	=over 4	2053	=over 4
1385		2054
1386	=item ev_child_init (ev_child *, callback, int pid)	2055	=item ev_child_init (ev_child *, callback, int pid, int trace)
1387		2056
1388	=item ev_child_set (ev_child *, int pid)	2057	=item ev_child_set (ev_child *, int pid, int trace)
1389		2058
1390	Configures the watcher to wait for status changes of process C<pid> (or	2059	Configures the watcher to wait for status changes of process C<pid> (or
1391	I<any> process if C<pid> is specified as C<0>). The callback can look	2060	I<any> process if C<pid> is specified as C<0>). The callback can look
1392	at the C<rstatus> member of the C<ev_child> watcher structure to see	2061	at the C<rstatus> member of the C<ev_child> watcher structure to see
1393	the status word (use the macros from C<sys/wait.h> and see your systems	2062	the status word (use the macros from C<sys/wait.h> and see your systems
1394	C<waitpid> documentation). The C<rpid> member contains the pid of the	2063	C<waitpid> documentation). The C<rpid> member contains the pid of the
1395	process causing the status change.	2064	process causing the status change. C<trace> must be either C<0> (only
		2065	activate the watcher when the process terminates) or C<1> (additionally
		2066	activate the watcher when the process is stopped or continued).
1396		2067
1397	=item int pid [read-only]	2068	=item int pid [read-only]
1398		2069
1399	The process id this watcher watches out for, or C<0>, meaning any process id.	2070	The process id this watcher watches out for, or C<0>, meaning any process id.
1400		2071
…		…
1407	The process exit/trace status caused by C<rpid> (see your systems	2078	The process exit/trace status caused by C<rpid> (see your systems
1408	C<waitpid> and C<sys/wait.h> documentation for details).	2079	C<waitpid> and C<sys/wait.h> documentation for details).
1409		2080
1410	=back	2081	=back
1411		2082
1412	Example: Try to exit cleanly on SIGINT and SIGTERM.	2083	=head3 Examples
1413		2084
		2085	Example: C<fork()> a new process and install a child handler to wait for
		2086	its completion.
		2087
		2088	ev_child cw;
		2089
1414	static void	2090	static void
1415	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2091	child_cb (EV_P_ ev_child *w, int revents)
1416	{	2092	{
1417	ev_unloop (loop, EVUNLOOP_ALL);	2093	ev_child_stop (EV_A_ w);
		2094	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1418	}	2095	}
1419		2096
1420	struct ev_signal signal_watcher;	2097	pid_t pid = fork ();
1421	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2098
1422	ev_signal_start (loop, &sigint_cb);	2099	if (pid < 0)
		2100	// error
		2101	else if (pid == 0)
		2102	{
		2103	// the forked child executes here
		2104	exit (1);
		2105	}
		2106	else
		2107	{
		2108	ev_child_init (&cw, child_cb, pid, 0);
		2109	ev_child_start (EV_DEFAULT_ &cw);
		2110	}
1423		2111
1424		2112
1425	=head2 C<ev_stat> - did the file attributes just change?	2113	=head2 C<ev_stat> - did the file attributes just change?
1426		2114
1427	This watches a filesystem path for attribute changes. That is, it calls	2115	This watches a file system path for attribute changes. That is, it calls
1428	C<stat> regularly (or when the OS says it changed) and sees if it changed	2116	C<stat> on that path in regular intervals (or when the OS says it changed)
1429	compared to the last time, invoking the callback if it did.	2117	and sees if it changed compared to the last time, invoking the callback if
		2118	it did.
1430		2119
1431	The path does not need to exist: changing from "path exists" to "path does	2120	The path does not need to exist: changing from "path exists" to "path does
1432	not exist" is a status change like any other. The condition "path does	2121	not exist" is a status change like any other. The condition "path does not
1433	not exist" is signified by the C<st_nlink> field being zero (which is	2122	exist" (or more correctly "path cannot be stat'ed") is signified by the
1434	otherwise always forced to be at least one) and all the other fields of	2123	C<st_nlink> field being zero (which is otherwise always forced to be at
1435	the stat buffer having unspecified contents.	2124	least one) and all the other fields of the stat buffer having unspecified
		2125	contents.
1436		2126
1437	The path I<should> be absolute and I<must not> end in a slash. If it is	2127	The path I<must not> end in a slash or contain special components such as
		2128	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1438	relative and your working directory changes, the behaviour is undefined.	2129	your working directory changes, then the behaviour is undefined.
1439		2130
1440	Since there is no standard to do this, the portable implementation simply	2131	Since there is no portable change notification interface available, the
1441	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2132	portable implementation simply calls C<stat(2)> regularly on the path
1442	can specify a recommended polling interval for this case. If you specify	2133	to see if it changed somehow. You can specify a recommended polling
1443	a polling interval of C<0> (highly recommended!) then a I<suitable,	2134	interval for this case. If you specify a polling interval of C<0> (highly
1444	unspecified default> value will be used (which you can expect to be around	2135	recommended!) then a I<suitable, unspecified default> value will be used
1445	five seconds, although this might change dynamically). Libev will also	2136	(which you can expect to be around five seconds, although this might
1446	impose a minimum interval which is currently around C<0.1>, but thats	2137	change dynamically). Libev will also impose a minimum interval which is
1447	usually overkill.	2138	currently around C<0.1>, but that's usually overkill.
1448		2139
1449	This watcher type is not meant for massive numbers of stat watchers,	2140	This watcher type is not meant for massive numbers of stat watchers,
1450	as even with OS-supported change notifications, this can be	2141	as even with OS-supported change notifications, this can be
1451	resource-intensive.	2142	resource-intensive.
1452		2143
1453	At the time of this writing, only the Linux inotify interface is	2144	At the time of this writing, the only OS-specific interface implemented
1454	implemented (implementing kqueue support is left as an exercise for the	2145	is the Linux inotify interface (implementing kqueue support is left as an
1455	reader). Inotify will be used to give hints only and should not change the	2146	exercise for the reader. Note, however, that the author sees no way of
1456	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2147	implementing C<ev_stat> semantics with kqueue, except as a hint).
1457	to fall back to regular polling again even with inotify, but changes are	2148
1458	usually detected immediately, and if the file exists there will be no	2149	=head3 ABI Issues (Largefile Support)
1459	polling.	2150
		2151	Libev by default (unless the user overrides this) uses the default
		2152	compilation environment, which means that on systems with large file
		2153	support disabled by default, you get the 32 bit version of the stat
		2154	structure. When using the library from programs that change the ABI to
		2155	use 64 bit file offsets the programs will fail. In that case you have to
		2156	compile libev with the same flags to get binary compatibility. This is
		2157	obviously the case with any flags that change the ABI, but the problem is
		2158	most noticeably displayed with ev_stat and large file support.
		2159
		2160	The solution for this is to lobby your distribution maker to make large
		2161	file interfaces available by default (as e.g. FreeBSD does) and not
		2162	optional. Libev cannot simply switch on large file support because it has
		2163	to exchange stat structures with application programs compiled using the
		2164	default compilation environment.
		2165
		2166	=head3 Inotify and Kqueue
		2167
		2168	When C<inotify (7)> support has been compiled into libev and present at
		2169	runtime, it will be used to speed up change detection where possible. The
		2170	inotify descriptor will be created lazily when the first C<ev_stat>
		2171	watcher is being started.
		2172
		2173	Inotify presence does not change the semantics of C<ev_stat> watchers
		2174	except that changes might be detected earlier, and in some cases, to avoid
		2175	making regular C<stat> calls. Even in the presence of inotify support
		2176	there are many cases where libev has to resort to regular C<stat> polling,
		2177	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2178	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2179	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2180	xfs are fully working) libev usually gets away without polling.
		2181
		2182	There is no support for kqueue, as apparently it cannot be used to
		2183	implement this functionality, due to the requirement of having a file
		2184	descriptor open on the object at all times, and detecting renames, unlinks
		2185	etc. is difficult.
		2186
		2187	=head3 C<stat ()> is a synchronous operation
		2188
		2189	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2190	the process. The exception are C<ev_stat> watchers - those call C<stat
		2191	()>, which is a synchronous operation.
		2192
		2193	For local paths, this usually doesn't matter: unless the system is very
		2194	busy or the intervals between stat's are large, a stat call will be fast,
		2195	as the path data is usually in memory already (except when starting the
		2196	watcher).
		2197
		2198	For networked file systems, calling C<stat ()> can block an indefinite
		2199	time due to network issues, and even under good conditions, a stat call
		2200	often takes multiple milliseconds.
		2201
		2202	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2203	paths, although this is fully supported by libev.
		2204
		2205	=head3 The special problem of stat time resolution
		2206
		2207	The C<stat ()> system call only supports full-second resolution portably,
		2208	and even on systems where the resolution is higher, most file systems
		2209	still only support whole seconds.
		2210
		2211	That means that, if the time is the only thing that changes, you can
		2212	easily miss updates: on the first update, C<ev_stat> detects a change and
		2213	calls your callback, which does something. When there is another update
		2214	within the same second, C<ev_stat> will be unable to detect unless the
		2215	stat data does change in other ways (e.g. file size).
		2216
		2217	The solution to this is to delay acting on a change for slightly more
		2218	than a second (or till slightly after the next full second boundary), using
		2219	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2220	ev_timer_again (loop, w)>).
		2221
		2222	The C<.02> offset is added to work around small timing inconsistencies
		2223	of some operating systems (where the second counter of the current time
		2224	might be be delayed. One such system is the Linux kernel, where a call to
		2225	C<gettimeofday> might return a timestamp with a full second later than
		2226	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2227	update file times then there will be a small window where the kernel uses
		2228	the previous second to update file times but libev might already execute
		2229	the timer callback).
1460		2230
1461	=head3 Watcher-Specific Functions and Data Members	2231	=head3 Watcher-Specific Functions and Data Members
1462		2232
1463	=over 4	2233	=over 4
1464		2234
…		…
1470	C<path>. The C<interval> is a hint on how quickly a change is expected to	2240	C<path>. The C<interval> is a hint on how quickly a change is expected to
1471	be detected and should normally be specified as C<0> to let libev choose	2241	be detected and should normally be specified as C<0> to let libev choose
1472	a suitable value. The memory pointed to by C<path> must point to the same	2242	a suitable value. The memory pointed to by C<path> must point to the same
1473	path for as long as the watcher is active.	2243	path for as long as the watcher is active.
1474		2244
1475	The callback will be receive C<EV_STAT> when a change was detected,	2245	The callback will receive an C<EV_STAT> event when a change was detected,
1476	relative to the attributes at the time the watcher was started (or the	2246	relative to the attributes at the time the watcher was started (or the
1477	last change was detected).	2247	last change was detected).
1478		2248
1479	=item ev_stat_stat (ev_stat *)	2249	=item ev_stat_stat (loop, ev_stat *)
1480		2250
1481	Updates the stat buffer immediately with new values. If you change the	2251	Updates the stat buffer immediately with new values. If you change the
1482	watched path in your callback, you could call this fucntion to avoid	2252	watched path in your callback, you could call this function to avoid
1483	detecting this change (while introducing a race condition). Can also be	2253	detecting this change (while introducing a race condition if you are not
1484	useful simply to find out the new values.	2254	the only one changing the path). Can also be useful simply to find out the
		2255	new values.
1485		2256
1486	=item ev_statdata attr [read-only]	2257	=item ev_statdata attr [read-only]
1487		2258
1488	The most-recently detected attributes of the file. Although the type is of	2259	The most-recently detected attributes of the file. Although the type is
1489	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2260	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1490	suitable for your system. If the C<st_nlink> member is C<0>, then there	2261	suitable for your system, but you can only rely on the POSIX-standardised
		2262	members to be present. If the C<st_nlink> member is C<0>, then there was
1491	was some error while C<stat>ing the file.	2263	some error while C<stat>ing the file.
1492		2264
1493	=item ev_statdata prev [read-only]	2265	=item ev_statdata prev [read-only]
1494		2266
1495	The previous attributes of the file. The callback gets invoked whenever	2267	The previous attributes of the file. The callback gets invoked whenever
1496	C<prev> != C<attr>.	2268	C<prev> != C<attr>, or, more precisely, one or more of these members
		2269	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2270	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1497		2271
1498	=item ev_tstamp interval [read-only]	2272	=item ev_tstamp interval [read-only]
1499		2273
1500	The specified interval.	2274	The specified interval.
1501		2275
1502	=item const char *path [read-only]	2276	=item const char *path [read-only]
1503		2277
1504	The filesystem path that is being watched.	2278	The file system path that is being watched.
1505		2279
1506	=back	2280	=back
1507		2281
		2282	=head3 Examples
		2283
1508	Example: Watch C</etc/passwd> for attribute changes.	2284	Example: Watch C</etc/passwd> for attribute changes.
1509		2285
1510	static void	2286	static void
1511	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2287	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1512	{	2288	{
1513	/* /etc/passwd changed in some way */	2289	/* /etc/passwd changed in some way */
1514	if (w->attr.st_nlink)	2290	if (w->attr.st_nlink)
1515	{	2291	{
1516	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2292	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1517	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2293	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1518	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2294	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1519	}	2295	}
1520	else	2296	else
1521	/* you shalt not abuse printf for puts */	2297	/* you shalt not abuse printf for puts */
1522	puts ("wow, /etc/passwd is not there, expect problems. "	2298	puts ("wow, /etc/passwd is not there, expect problems. "
1523	"if this is windows, they already arrived\n");	2299	"if this is windows, they already arrived\n");
1524	}	2300	}
1525		2301
1526	...	2302	...
1527	ev_stat passwd;	2303	ev_stat passwd;
1528		2304
1529	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2305	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1530	ev_stat_start (loop, &passwd);	2306	ev_stat_start (loop, &passwd);
		2307
		2308	Example: Like above, but additionally use a one-second delay so we do not
		2309	miss updates (however, frequent updates will delay processing, too, so
		2310	one might do the work both on C<ev_stat> callback invocation I<and> on
		2311	C<ev_timer> callback invocation).
		2312
		2313	static ev_stat passwd;
		2314	static ev_timer timer;
		2315
		2316	static void
		2317	timer_cb (EV_P_ ev_timer *w, int revents)
		2318	{
		2319	ev_timer_stop (EV_A_ w);
		2320
		2321	/* now it's one second after the most recent passwd change */
		2322	}
		2323
		2324	static void
		2325	stat_cb (EV_P_ ev_stat *w, int revents)
		2326	{
		2327	/* reset the one-second timer */
		2328	ev_timer_again (EV_A_ &timer);
		2329	}
		2330
		2331	...
		2332	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2333	ev_stat_start (loop, &passwd);
		2334	ev_timer_init (&timer, timer_cb, 0., 1.02);
1531		2335
1532		2336
1533	=head2 C<ev_idle> - when you've got nothing better to do...	2337	=head2 C<ev_idle> - when you've got nothing better to do...
1534		2338
1535	Idle watchers trigger events when no other events of the same or higher	2339	Idle watchers trigger events when no other events of the same or higher
1536	priority are pending (prepare, check and other idle watchers do not	2340	priority are pending (prepare, check and other idle watchers do not count
1537	count).	2341	as receiving "events").
1538		2342
1539	That is, as long as your process is busy handling sockets or timeouts	2343	That is, as long as your process is busy handling sockets or timeouts
1540	(or even signals, imagine) of the same or higher priority it will not be	2344	(or even signals, imagine) of the same or higher priority it will not be
1541	triggered. But when your process is idle (or only lower-priority watchers	2345	triggered. But when your process is idle (or only lower-priority watchers
1542	are pending), the idle watchers are being called once per event loop	2346	are pending), the idle watchers are being called once per event loop
…		…
1553		2357
1554	=head3 Watcher-Specific Functions and Data Members	2358	=head3 Watcher-Specific Functions and Data Members
1555		2359
1556	=over 4	2360	=over 4
1557		2361
1558	=item ev_idle_init (ev_signal *, callback)	2362	=item ev_idle_init (ev_idle *, callback)
1559		2363
1560	Initialises and configures the idle watcher - it has no parameters of any	2364	Initialises and configures the idle watcher - it has no parameters of any
1561	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2365	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1562	believe me.	2366	believe me.
1563		2367
1564	=back	2368	=back
1565		2369
		2370	=head3 Examples
		2371
1566	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2372	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1567	callback, free it. Also, use no error checking, as usual.	2373	callback, free it. Also, use no error checking, as usual.
1568		2374
1569	static void	2375	static void
1570	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2376	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1571	{	2377	{
1572	free (w);	2378	free (w);
1573	// now do something you wanted to do when the program has	2379	// now do something you wanted to do when the program has
1574	// no longer asnything immediate to do.	2380	// no longer anything immediate to do.
1575	}	2381	}
1576		2382
1577	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2383	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1578	ev_idle_init (idle_watcher, idle_cb);	2384	ev_idle_init (idle_watcher, idle_cb);
1579	ev_idle_start (loop, idle_cb);	2385	ev_idle_start (loop, idle_watcher);
1580		2386
1581		2387
1582	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2388	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1583		2389
1584	Prepare and check watchers are usually (but not always) used in tandem:	2390	Prepare and check watchers are usually (but not always) used in pairs:
1585	prepare watchers get invoked before the process blocks and check watchers	2391	prepare watchers get invoked before the process blocks and check watchers
1586	afterwards.	2392	afterwards.
1587		2393
1588	You I<must not> call C<ev_loop> or similar functions that enter	2394	You I<must not> call C<ev_loop> or similar functions that enter
1589	the current event loop from either C<ev_prepare> or C<ev_check>	2395	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1592	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2398	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1593	C<ev_check> so if you have one watcher of each kind they will always be	2399	C<ev_check> so if you have one watcher of each kind they will always be
1594	called in pairs bracketing the blocking call.	2400	called in pairs bracketing the blocking call.
1595		2401
1596	Their main purpose is to integrate other event mechanisms into libev and	2402	Their main purpose is to integrate other event mechanisms into libev and
1597	their use is somewhat advanced. This could be used, for example, to track	2403	their use is somewhat advanced. They could be used, for example, to track
1598	variable changes, implement your own watchers, integrate net-snmp or a	2404	variable changes, implement your own watchers, integrate net-snmp or a
1599	coroutine library and lots more. They are also occasionally useful if	2405	coroutine library and lots more. They are also occasionally useful if
1600	you cache some data and want to flush it before blocking (for example,	2406	you cache some data and want to flush it before blocking (for example,
1601	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2407	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1602	watcher).	2408	watcher).
1603		2409
1604	This is done by examining in each prepare call which file descriptors need	2410	This is done by examining in each prepare call which file descriptors
1605	to be watched by the other library, registering C<ev_io> watchers for	2411	need to be watched by the other library, registering C<ev_io> watchers
1606	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2412	for them and starting an C<ev_timer> watcher for any timeouts (many
1607	provide just this functionality). Then, in the check watcher you check for	2413	libraries provide exactly this functionality). Then, in the check watcher,
1608	any events that occured (by checking the pending status of all watchers	2414	you check for any events that occurred (by checking the pending status
1609	and stopping them) and call back into the library. The I/O and timer	2415	of all watchers and stopping them) and call back into the library. The
1610	callbacks will never actually be called (but must be valid nevertheless,	2416	I/O and timer callbacks will never actually be called (but must be valid
1611	because you never know, you know?).	2417	nevertheless, because you never know, you know?).
1612		2418
1613	As another example, the Perl Coro module uses these hooks to integrate	2419	As another example, the Perl Coro module uses these hooks to integrate
1614	coroutines into libev programs, by yielding to other active coroutines	2420	coroutines into libev programs, by yielding to other active coroutines
1615	during each prepare and only letting the process block if no coroutines	2421	during each prepare and only letting the process block if no coroutines
1616	are ready to run (it's actually more complicated: it only runs coroutines	2422	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1619	loop from blocking if lower-priority coroutines are active, thus mapping	2425	loop from blocking if lower-priority coroutines are active, thus mapping
1620	low-priority coroutines to idle/background tasks).	2426	low-priority coroutines to idle/background tasks).
1621		2427
1622	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2428	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1623	priority, to ensure that they are being run before any other watchers	2429	priority, to ensure that they are being run before any other watchers
		2430	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2431
1624	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2432	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1625	too) should not activate ("feed") events into libev. While libev fully	2433	activate ("feed") events into libev. While libev fully supports this, they
1626	supports this, they will be called before other C<ev_check> watchers did	2434	might get executed before other C<ev_check> watchers did their job. As
1627	their job. As C<ev_check> watchers are often used to embed other event	2435	C<ev_check> watchers are often used to embed other (non-libev) event
1628	loops those other event loops might be in an unusable state until their	2436	loops those other event loops might be in an unusable state until their
1629	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2437	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1630	others).	2438	others).
1631		2439
1632	=head3 Watcher-Specific Functions and Data Members	2440	=head3 Watcher-Specific Functions and Data Members
…		…
1637		2445
1638	=item ev_check_init (ev_check *, callback)	2446	=item ev_check_init (ev_check *, callback)
1639		2447
1640	Initialises and configures the prepare or check watcher - they have no	2448	Initialises and configures the prepare or check watcher - they have no
1641	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2449	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1642	macros, but using them is utterly, utterly and completely pointless.	2450	macros, but using them is utterly, utterly, utterly and completely
		2451	pointless.
1643		2452
1644	=back	2453	=back
		2454
		2455	=head3 Examples
1645		2456
1646	There are a number of principal ways to embed other event loops or modules	2457	There are a number of principal ways to embed other event loops or modules
1647	into libev. Here are some ideas on how to include libadns into libev	2458	into libev. Here are some ideas on how to include libadns into libev
1648	(there is a Perl module named C<EV::ADNS> that does this, which you could	2459	(there is a Perl module named C<EV::ADNS> that does this, which you could
1649	use for an actually working example. Another Perl module named C<EV::Glib>	2460	use as a working example. Another Perl module named C<EV::Glib> embeds a
1650	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2461	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1651	into the Glib event loop).	2462	Glib event loop).
1652		2463
1653	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2464	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1654	and in a check watcher, destroy them and call into libadns. What follows	2465	and in a check watcher, destroy them and call into libadns. What follows
1655	is pseudo-code only of course. This requires you to either use a low	2466	is pseudo-code only of course. This requires you to either use a low
1656	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2467	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1657	the callbacks for the IO/timeout watchers might not have been called yet.	2468	the callbacks for the IO/timeout watchers might not have been called yet.
1658		2469
1659	static ev_io iow [nfd];	2470	static ev_io iow [nfd];
1660	static ev_timer tw;	2471	static ev_timer tw;
1661		2472
1662	static void	2473	static void
1663	io_cb (ev_loop *loop, ev_io *w, int revents)	2474	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1664	{	2475	{
1665	}	2476	}
1666		2477
1667	// create io watchers for each fd and a timer before blocking	2478	// create io watchers for each fd and a timer before blocking
1668	static void	2479	static void
1669	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2480	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1670	{	2481	{
1671	int timeout = 3600000;	2482	int timeout = 3600000;
1672	struct pollfd fds [nfd];	2483	struct pollfd fds [nfd];
1673	// actual code will need to loop here and realloc etc.	2484	// actual code will need to loop here and realloc etc.
1674	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2485	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1675		2486
1676	/* the callback is illegal, but won't be called as we stop during check */	2487	/* the callback is illegal, but won't be called as we stop during check */
1677	ev_timer_init (&tw, 0, timeout * 1e-3);	2488	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1678	ev_timer_start (loop, &tw);	2489	ev_timer_start (loop, &tw);
1679		2490
1680	// create one ev_io per pollfd	2491	// create one ev_io per pollfd
1681	for (int i = 0; i < nfd; ++i)	2492	for (int i = 0; i < nfd; ++i)
1682	{	2493	{
1683	ev_io_init (iow + i, io_cb, fds [i].fd,	2494	ev_io_init (iow + i, io_cb, fds [i].fd,
1684	((fds [i].events & POLLIN ? EV_READ : 0)	2495	((fds [i].events & POLLIN ? EV_READ : 0)
1685	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2496	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1686		2497
1687	fds [i].revents = 0;	2498	fds [i].revents = 0;
1688	ev_io_start (loop, iow + i);	2499	ev_io_start (loop, iow + i);
1689	}	2500	}
1690	}	2501	}
1691		2502
1692	// stop all watchers after blocking	2503	// stop all watchers after blocking
1693	static void	2504	static void
1694	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2505	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1695	{	2506	{
1696	ev_timer_stop (loop, &tw);	2507	ev_timer_stop (loop, &tw);
1697		2508
1698	for (int i = 0; i < nfd; ++i)	2509	for (int i = 0; i < nfd; ++i)
1699	{	2510	{
1700	// set the relevant poll flags	2511	// set the relevant poll flags
1701	// could also call adns_processreadable etc. here	2512	// could also call adns_processreadable etc. here
1702	struct pollfd *fd = fds + i;	2513	struct pollfd *fd = fds + i;
1703	int revents = ev_clear_pending (iow + i);	2514	int revents = ev_clear_pending (iow + i);
1704	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2515	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1705	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2516	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1706		2517
1707	// now stop the watcher	2518	// now stop the watcher
1708	ev_io_stop (loop, iow + i);	2519	ev_io_stop (loop, iow + i);
1709	}	2520	}
1710		2521
1711	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2522	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1712	}	2523	}
1713		2524
1714	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2525	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1715	in the prepare watcher and would dispose of the check watcher.	2526	in the prepare watcher and would dispose of the check watcher.
1716		2527
1717	Method 3: If the module to be embedded supports explicit event	2528	Method 3: If the module to be embedded supports explicit event
1718	notification (adns does), you can also make use of the actual watcher	2529	notification (libadns does), you can also make use of the actual watcher
1719	callbacks, and only destroy/create the watchers in the prepare watcher.	2530	callbacks, and only destroy/create the watchers in the prepare watcher.
1720		2531
1721	static void	2532	static void
1722	timer_cb (EV_P_ ev_timer *w, int revents)	2533	timer_cb (EV_P_ ev_timer *w, int revents)
1723	{	2534	{
1724	adns_state ads = (adns_state)w->data;	2535	adns_state ads = (adns_state)w->data;
1725	update_now (EV_A);	2536	update_now (EV_A);
1726		2537
1727	adns_processtimeouts (ads, &tv_now);	2538	adns_processtimeouts (ads, &tv_now);
1728	}	2539	}
1729		2540
1730	static void	2541	static void
1731	io_cb (EV_P_ ev_io *w, int revents)	2542	io_cb (EV_P_ ev_io *w, int revents)
1732	{	2543	{
1733	adns_state ads = (adns_state)w->data;	2544	adns_state ads = (adns_state)w->data;
1734	update_now (EV_A);	2545	update_now (EV_A);
1735		2546
1736	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2547	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1737	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2548	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1738	}	2549	}
1739		2550
1740	// do not ever call adns_afterpoll	2551	// do not ever call adns_afterpoll
1741		2552
1742	Method 4: Do not use a prepare or check watcher because the module you	2553	Method 4: Do not use a prepare or check watcher because the module you
1743	want to embed is too inflexible to support it. Instead, youc na override	2554	want to embed is not flexible enough to support it. Instead, you can
1744	their poll function. The drawback with this solution is that the main	2555	override their poll function. The drawback with this solution is that the
1745	loop is now no longer controllable by EV. The C<Glib::EV> module does	2556	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1746	this.	2557	this approach, effectively embedding EV as a client into the horrible
		2558	libglib event loop.
1747		2559
1748	static gint	2560	static gint
1749	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2561	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1750	{	2562	{
1751	int got_events = 0;	2563	int got_events = 0;
1752		2564
1753	for (n = 0; n < nfds; ++n)	2565	for (n = 0; n < nfds; ++n)
1754	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2566	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1755		2567
1756	if (timeout >= 0)	2568	if (timeout >= 0)
1757	// create/start timer	2569	// create/start timer
1758		2570
1759	// poll	2571	// poll
1760	ev_loop (EV_A_ 0);	2572	ev_loop (EV_A_ 0);
1761		2573
1762	// stop timer again	2574	// stop timer again
1763	if (timeout >= 0)	2575	if (timeout >= 0)
1764	ev_timer_stop (EV_A_ &to);	2576	ev_timer_stop (EV_A_ &to);
1765		2577
1766	// stop io watchers again - their callbacks should have set	2578	// stop io watchers again - their callbacks should have set
1767	for (n = 0; n < nfds; ++n)	2579	for (n = 0; n < nfds; ++n)
1768	ev_io_stop (EV_A_ iow [n]);	2580	ev_io_stop (EV_A_ iow [n]);
1769		2581
1770	return got_events;	2582	return got_events;
1771	}	2583	}
1772		2584
1773		2585
1774	=head2 C<ev_embed> - when one backend isn't enough...	2586	=head2 C<ev_embed> - when one backend isn't enough...
1775		2587
1776	This is a rather advanced watcher type that lets you embed one event loop	2588	This is a rather advanced watcher type that lets you embed one event loop
1777	into another (currently only C<ev_io> events are supported in the embedded	2589	into another (currently only C<ev_io> events are supported in the embedded
1778	loop, other types of watchers might be handled in a delayed or incorrect	2590	loop, other types of watchers might be handled in a delayed or incorrect
1779	fashion and must not be used). (See portability notes, below).	2591	fashion and must not be used).
1780		2592
1781	There are primarily two reasons you would want that: work around bugs and	2593	There are primarily two reasons you would want that: work around bugs and
1782	prioritise I/O.	2594	prioritise I/O.
1783		2595
1784	As an example for a bug workaround, the kqueue backend might only support	2596	As an example for a bug workaround, the kqueue backend might only support
1785	sockets on some platform, so it is unusable as generic backend, but you	2597	sockets on some platform, so it is unusable as generic backend, but you
1786	still want to make use of it because you have many sockets and it scales	2598	still want to make use of it because you have many sockets and it scales
1787	so nicely. In this case, you would create a kqueue-based loop and embed it	2599	so nicely. In this case, you would create a kqueue-based loop and embed
1788	into your default loop (which might use e.g. poll). Overall operation will	2600	it into your default loop (which might use e.g. poll). Overall operation
1789	be a bit slower because first libev has to poll and then call kevent, but	2601	will be a bit slower because first libev has to call C<poll> and then
1790	at least you can use both at what they are best.	2602	C<kevent>, but at least you can use both mechanisms for what they are
		2603	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1791		2604
1792	As for prioritising I/O: rarely you have the case where some fds have	2605	As for prioritising I/O: under rare circumstances you have the case where
1793	to be watched and handled very quickly (with low latency), and even	2606	some fds have to be watched and handled very quickly (with low latency),
1794	priorities and idle watchers might have too much overhead. In this case	2607	and even priorities and idle watchers might have too much overhead. In
1795	you would put all the high priority stuff in one loop and all the rest in	2608	this case you would put all the high priority stuff in one loop and all
1796	a second one, and embed the second one in the first.	2609	the rest in a second one, and embed the second one in the first.
1797		2610
1798	As long as the watcher is active, the callback will be invoked every time	2611	As long as the watcher is active, the callback will be invoked every
1799	there might be events pending in the embedded loop. The callback must then	2612	time there might be events pending in the embedded loop. The callback
1800	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2613	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1801	their callbacks (you could also start an idle watcher to give the embedded	2614	sweep and invoke their callbacks (the callback doesn't need to invoke the
1802	loop strictly lower priority for example). You can also set the callback	2615	C<ev_embed_sweep> function directly, it could also start an idle watcher
1803	to C<0>, in which case the embed watcher will automatically execute the	2616	to give the embedded loop strictly lower priority for example).
1804	embedded loop sweep.
1805		2617
1806	As long as the watcher is started it will automatically handle events. The	2618	You can also set the callback to C<0>, in which case the embed watcher
1807	callback will be invoked whenever some events have been handled. You can	2619	will automatically execute the embedded loop sweep whenever necessary.
1808	set the callback to C<0> to avoid having to specify one if you are not
1809	interested in that.
1810		2620
1811	Also, there have not currently been made special provisions for forking:	2621	Fork detection will be handled transparently while the C<ev_embed> watcher
1812	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2622	is active, i.e., the embedded loop will automatically be forked when the
1813	but you will also have to stop and restart any C<ev_embed> watchers	2623	embedding loop forks. In other cases, the user is responsible for calling
1814	yourself.	2624	C<ev_loop_fork> on the embedded loop.
1815		2625
1816	Unfortunately, not all backends are embeddable, only the ones returned by	2626	Unfortunately, not all backends are embeddable: only the ones returned by
1817	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2627	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1818	portable one.	2628	portable one.
1819		2629
1820	So when you want to use this feature you will always have to be prepared	2630	So when you want to use this feature you will always have to be prepared
1821	that you cannot get an embeddable loop. The recommended way to get around	2631	that you cannot get an embeddable loop. The recommended way to get around
1822	this is to have a separate variables for your embeddable loop, try to	2632	this is to have a separate variables for your embeddable loop, try to
1823	create it, and if that fails, use the normal loop for everything:	2633	create it, and if that fails, use the normal loop for everything.
1824		2634
1825	struct ev_loop *loop_hi = ev_default_init (0);	2635	=head3 C<ev_embed> and fork
1826	struct ev_loop *loop_lo = 0;
1827	struct ev_embed embed;
1828
1829	// see if there is a chance of getting one that works
1830	// (remember that a flags value of 0 means autodetection)
1831	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1832	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1833	: 0;
1834		2636
1835	// if we got one, then embed it, otherwise default to loop_hi	2637	While the C<ev_embed> watcher is running, forks in the embedding loop will
1836	if (loop_lo)	2638	automatically be applied to the embedded loop as well, so no special
1837	{	2639	fork handling is required in that case. When the watcher is not running,
1838	ev_embed_init (&embed, 0, loop_lo);	2640	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1839	ev_embed_start (loop_hi, &embed);	2641	as applicable.
1840	}
1841	else
1842	loop_lo = loop_hi;
1843
1844	=head2 Portability notes
1845
1846	Kqueue is nominally embeddable, but this is broken on all BSDs that I
1847	tried, in various ways. Usually the embedded event loop will simply never
1848	receive events, sometimes it will only trigger a few times, sometimes in a
1849	loop. Epoll is also nominally embeddable, but many Linux kernel versions
1850	will always eport the epoll fd as ready, even when no events are pending.
1851
1852	While libev allows embedding these backends (they are contained in
1853	C<ev_embeddable_backends ()>), take extreme care that it will actually
1854	work.
1855
1856	When in doubt, create a dynamic event loop forced to use sockets (this
1857	usually works) and possibly another thread and a pipe or so to report to
1858	your main event loop.
1859		2642
1860	=head3 Watcher-Specific Functions and Data Members	2643	=head3 Watcher-Specific Functions and Data Members
1861		2644
1862	=over 4	2645	=over 4
1863		2646
…		…
1867		2650
1868	Configures the watcher to embed the given loop, which must be	2651	Configures the watcher to embed the given loop, which must be
1869	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2652	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1870	invoked automatically, otherwise it is the responsibility of the callback	2653	invoked automatically, otherwise it is the responsibility of the callback
1871	to invoke it (it will continue to be called until the sweep has been done,	2654	to invoke it (it will continue to be called until the sweep has been done,
1872	if you do not want thta, you need to temporarily stop the embed watcher).	2655	if you do not want that, you need to temporarily stop the embed watcher).
1873		2656
1874	=item ev_embed_sweep (loop, ev_embed *)	2657	=item ev_embed_sweep (loop, ev_embed *)
1875		2658
1876	Make a single, non-blocking sweep over the embedded loop. This works	2659	Make a single, non-blocking sweep over the embedded loop. This works
1877	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2660	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1878	apropriate way for embedded loops.	2661	appropriate way for embedded loops.
1879		2662
1880	=item struct ev_loop *other [read-only]	2663	=item struct ev_loop *other [read-only]
1881		2664
1882	The embedded event loop.	2665	The embedded event loop.
1883		2666
1884	=back	2667	=back
		2668
		2669	=head3 Examples
		2670
		2671	Example: Try to get an embeddable event loop and embed it into the default
		2672	event loop. If that is not possible, use the default loop. The default
		2673	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2674	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2675	used).
		2676
		2677	struct ev_loop *loop_hi = ev_default_init (0);
		2678	struct ev_loop *loop_lo = 0;
		2679	ev_embed embed;
		2680
		2681	// see if there is a chance of getting one that works
		2682	// (remember that a flags value of 0 means autodetection)
		2683	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2684	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2685	: 0;
		2686
		2687	// if we got one, then embed it, otherwise default to loop_hi
		2688	if (loop_lo)
		2689	{
		2690	ev_embed_init (&embed, 0, loop_lo);
		2691	ev_embed_start (loop_hi, &embed);
		2692	}
		2693	else
		2694	loop_lo = loop_hi;
		2695
		2696	Example: Check if kqueue is available but not recommended and create
		2697	a kqueue backend for use with sockets (which usually work with any
		2698	kqueue implementation). Store the kqueue/socket-only event loop in
		2699	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2700
		2701	struct ev_loop *loop = ev_default_init (0);
		2702	struct ev_loop *loop_socket = 0;
		2703	ev_embed embed;
		2704
		2705	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2706	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2707	{
		2708	ev_embed_init (&embed, 0, loop_socket);
		2709	ev_embed_start (loop, &embed);
		2710	}
		2711
		2712	if (!loop_socket)
		2713	loop_socket = loop;
		2714
		2715	// now use loop_socket for all sockets, and loop for everything else
1885		2716
1886		2717
1887	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2718	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1888		2719
1889	Fork watchers are called when a C<fork ()> was detected (usually because	2720	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1892	event loop blocks next and before C<ev_check> watchers are being called,	2723	event loop blocks next and before C<ev_check> watchers are being called,
1893	and only in the child after the fork. If whoever good citizen calling	2724	and only in the child after the fork. If whoever good citizen calling
1894	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2725	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1895	handlers will be invoked, too, of course.	2726	handlers will be invoked, too, of course.
1896		2727
		2728	=head3 The special problem of life after fork - how is it possible?
		2729
		2730	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2731	up/change the process environment, followed by a call to C<exec()>. This
		2732	sequence should be handled by libev without any problems.
		2733
		2734	This changes when the application actually wants to do event handling
		2735	in the child, or both parent in child, in effect "continuing" after the
		2736	fork.
		2737
		2738	The default mode of operation (for libev, with application help to detect
		2739	forks) is to duplicate all the state in the child, as would be expected
		2740	when I<either> the parent I<or> the child process continues.
		2741
		2742	When both processes want to continue using libev, then this is usually the
		2743	wrong result. In that case, usually one process (typically the parent) is
		2744	supposed to continue with all watchers in place as before, while the other
		2745	process typically wants to start fresh, i.e. without any active watchers.
		2746
		2747	The cleanest and most efficient way to achieve that with libev is to
		2748	simply create a new event loop, which of course will be "empty", and
		2749	use that for new watchers. This has the advantage of not touching more
		2750	memory than necessary, and thus avoiding the copy-on-write, and the
		2751	disadvantage of having to use multiple event loops (which do not support
		2752	signal watchers).
		2753
		2754	When this is not possible, or you want to use the default loop for
		2755	other reasons, then in the process that wants to start "fresh", call
		2756	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2757	the default loop will "orphan" (not stop) all registered watchers, so you
		2758	have to be careful not to execute code that modifies those watchers. Note
		2759	also that in that case, you have to re-register any signal watchers.
		2760
1897	=head3 Watcher-Specific Functions and Data Members	2761	=head3 Watcher-Specific Functions and Data Members
1898		2762
1899	=over 4	2763	=over 4
1900		2764
1901	=item ev_fork_init (ev_signal *, callback)	2765	=item ev_fork_init (ev_signal *, callback)
…		…
1905	believe me.	2769	believe me.
1906		2770
1907	=back	2771	=back
1908		2772
1909		2773
		2774	=head2 C<ev_async> - how to wake up another event loop
		2775
		2776	In general, you cannot use an C<ev_loop> from multiple threads or other
		2777	asynchronous sources such as signal handlers (as opposed to multiple event
		2778	loops - those are of course safe to use in different threads).
		2779
		2780	Sometimes, however, you need to wake up another event loop you do not
		2781	control, for example because it belongs to another thread. This is what
		2782	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2783	can signal it by calling C<ev_async_send>, which is thread- and signal
		2784	safe.
		2785
		2786	This functionality is very similar to C<ev_signal> watchers, as signals,
		2787	too, are asynchronous in nature, and signals, too, will be compressed
		2788	(i.e. the number of callback invocations may be less than the number of
		2789	C<ev_async_sent> calls).
		2790
		2791	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2792	just the default loop.
		2793
		2794	=head3 Queueing
		2795
		2796	C<ev_async> does not support queueing of data in any way. The reason
		2797	is that the author does not know of a simple (or any) algorithm for a
		2798	multiple-writer-single-reader queue that works in all cases and doesn't
		2799	need elaborate support such as pthreads.
		2800
		2801	That means that if you want to queue data, you have to provide your own
		2802	queue. But at least I can tell you how to implement locking around your
		2803	queue:
		2804
		2805	=over 4
		2806
		2807	=item queueing from a signal handler context
		2808
		2809	To implement race-free queueing, you simply add to the queue in the signal
		2810	handler but you block the signal handler in the watcher callback. Here is
		2811	an example that does that for some fictitious SIGUSR1 handler:
		2812
		2813	static ev_async mysig;
		2814
		2815	static void
		2816	sigusr1_handler (void)
		2817	{
		2818	sometype data;
		2819
		2820	// no locking etc.
		2821	queue_put (data);
		2822	ev_async_send (EV_DEFAULT_ &mysig);
		2823	}
		2824
		2825	static void
		2826	mysig_cb (EV_P_ ev_async *w, int revents)
		2827	{
		2828	sometype data;
		2829	sigset_t block, prev;
		2830
		2831	sigemptyset (&block);
		2832	sigaddset (&block, SIGUSR1);
		2833	sigprocmask (SIG_BLOCK, &block, &prev);
		2834
		2835	while (queue_get (&data))
		2836	process (data);
		2837
		2838	if (sigismember (&prev, SIGUSR1)
		2839	sigprocmask (SIG_UNBLOCK, &block, 0);
		2840	}
		2841
		2842	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2843	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2844	either...).
		2845
		2846	=item queueing from a thread context
		2847
		2848	The strategy for threads is different, as you cannot (easily) block
		2849	threads but you can easily preempt them, so to queue safely you need to
		2850	employ a traditional mutex lock, such as in this pthread example:
		2851
		2852	static ev_async mysig;
		2853	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2854
		2855	static void
		2856	otherthread (void)
		2857	{
		2858	// only need to lock the actual queueing operation
		2859	pthread_mutex_lock (&mymutex);
		2860	queue_put (data);
		2861	pthread_mutex_unlock (&mymutex);
		2862
		2863	ev_async_send (EV_DEFAULT_ &mysig);
		2864	}
		2865
		2866	static void
		2867	mysig_cb (EV_P_ ev_async *w, int revents)
		2868	{
		2869	pthread_mutex_lock (&mymutex);
		2870
		2871	while (queue_get (&data))
		2872	process (data);
		2873
		2874	pthread_mutex_unlock (&mymutex);
		2875	}
		2876
		2877	=back
		2878
		2879
		2880	=head3 Watcher-Specific Functions and Data Members
		2881
		2882	=over 4
		2883
		2884	=item ev_async_init (ev_async *, callback)
		2885
		2886	Initialises and configures the async watcher - it has no parameters of any
		2887	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2888	trust me.
		2889
		2890	=item ev_async_send (loop, ev_async *)
		2891
		2892	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2893	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2894	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2895	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2896	section below on what exactly this means).
		2897
		2898	Note that, as with other watchers in libev, multiple events might get
		2899	compressed into a single callback invocation (another way to look at this
		2900	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2901	reset when the event loop detects that).
		2902
		2903	This call incurs the overhead of a system call only once per event loop
		2904	iteration, so while the overhead might be noticeable, it doesn't apply to
		2905	repeated calls to C<ev_async_send> for the same event loop.
		2906
		2907	=item bool = ev_async_pending (ev_async *)
		2908
		2909	Returns a non-zero value when C<ev_async_send> has been called on the
		2910	watcher but the event has not yet been processed (or even noted) by the
		2911	event loop.
		2912
		2913	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2914	the loop iterates next and checks for the watcher to have become active,
		2915	it will reset the flag again. C<ev_async_pending> can be used to very
		2916	quickly check whether invoking the loop might be a good idea.
		2917
		2918	Not that this does I<not> check whether the watcher itself is pending,
		2919	only whether it has been requested to make this watcher pending: there
		2920	is a time window between the event loop checking and resetting the async
		2921	notification, and the callback being invoked.
		2922
		2923	=back
		2924
		2925
1910	=head1 OTHER FUNCTIONS	2926	=head1 OTHER FUNCTIONS
1911		2927
1912	There are some other functions of possible interest. Described. Here. Now.	2928	There are some other functions of possible interest. Described. Here. Now.
1913		2929
1914	=over 4	2930	=over 4
1915		2931
1916	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2932	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1917		2933
1918	This function combines a simple timer and an I/O watcher, calls your	2934	This function combines a simple timer and an I/O watcher, calls your
1919	callback on whichever event happens first and automatically stop both	2935	callback on whichever event happens first and automatically stops both
1920	watchers. This is useful if you want to wait for a single event on an fd	2936	watchers. This is useful if you want to wait for a single event on an fd
1921	or timeout without having to allocate/configure/start/stop/free one or	2937	or timeout without having to allocate/configure/start/stop/free one or
1922	more watchers yourself.	2938	more watchers yourself.
1923		2939
1924	If C<fd> is less than 0, then no I/O watcher will be started and events	2940	If C<fd> is less than 0, then no I/O watcher will be started and the
1925	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2941	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1926	C<events> set will be craeted and started.	2942	the given C<fd> and C<events> set will be created and started.
1927		2943
1928	If C<timeout> is less than 0, then no timeout watcher will be	2944	If C<timeout> is less than 0, then no timeout watcher will be
1929	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2945	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1930	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2946	repeat = 0) will be started. C<0> is a valid timeout.
1931	dubious value.
1932		2947
1933	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2948	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1934	passed an C<revents> set like normal event callbacks (a combination of	2949	passed an C<revents> set like normal event callbacks (a combination of
1935	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2950	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1936	value passed to C<ev_once>:	2951	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2952	a timeout and an io event at the same time - you probably should give io
		2953	events precedence.
1937		2954
		2955	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2956
1938	static void stdin_ready (int revents, void *arg)	2957	static void stdin_ready (int revents, void *arg)
1939	{	2958	{
1940	if (revents & EV_TIMEOUT)
1941	/* doh, nothing entered */;
1942	else if (revents & EV_READ)	2959	if (revents & EV_READ)
1943	/* stdin might have data for us, joy! */;	2960	/* stdin might have data for us, joy! */;
		2961	else if (revents & EV_TIMEOUT)
		2962	/* doh, nothing entered */;
1944	}	2963	}
1945		2964
1946	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2965	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1947		2966
1948	=item ev_feed_event (ev_loop *, watcher *, int revents)	2967	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1949		2968
1950	Feeds the given event set into the event loop, as if the specified event	2969	Feeds the given event set into the event loop, as if the specified event
1951	had happened for the specified watcher (which must be a pointer to an	2970	had happened for the specified watcher (which must be a pointer to an
1952	initialised but not necessarily started event watcher).	2971	initialised but not necessarily started event watcher).
1953		2972
1954	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2973	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1955		2974
1956	Feed an event on the given fd, as if a file descriptor backend detected	2975	Feed an event on the given fd, as if a file descriptor backend detected
1957	the given events it.	2976	the given events it.
1958		2977
1959	=item ev_feed_signal_event (ev_loop *loop, int signum)	2978	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1960		2979
1961	Feed an event as if the given signal occured (C<loop> must be the default	2980	Feed an event as if the given signal occurred (C<loop> must be the default
1962	loop!).	2981	loop!).
1963		2982
1964	=back	2983	=back
1965		2984
1966		2985
…		…
1982		3001
1983	=item * Priorities are not currently supported. Initialising priorities	3002	=item * Priorities are not currently supported. Initialising priorities
1984	will fail and all watchers will have the same priority, even though there	3003	will fail and all watchers will have the same priority, even though there
1985	is an ev_pri field.	3004	is an ev_pri field.
1986		3005
		3006	=item * In libevent, the last base created gets the signals, in libev, the
		3007	first base created (== the default loop) gets the signals.
		3008
1987	=item * Other members are not supported.	3009	=item * Other members are not supported.
1988		3010
1989	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3011	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1990	to use the libev header file and library.	3012	to use the libev header file and library.
1991		3013
1992	=back	3014	=back
1993		3015
1994	=head1 C++ SUPPORT	3016	=head1 C++ SUPPORT
1995		3017
1996	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3018	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1997	you to use some convinience methods to start/stop watchers and also change	3019	you to use some convenience methods to start/stop watchers and also change
1998	the callback model to a model using method callbacks on objects.	3020	the callback model to a model using method callbacks on objects.
1999		3021
2000	To use it,	3022	To use it,
2001		3023
2002	#include <ev++.h>	3024	#include <ev++.h>
2003		3025
2004	This automatically includes F<ev.h> and puts all of its definitions (many	3026	This automatically includes F<ev.h> and puts all of its definitions (many
2005	of them macros) into the global namespace. All C++ specific things are	3027	of them macros) into the global namespace. All C++ specific things are
2006	put into the C<ev> namespace. It should support all the same embedding	3028	put into the C<ev> namespace. It should support all the same embedding
2007	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3029	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2074	your compiler is good :), then the method will be fully inlined into the	3096	your compiler is good :), then the method will be fully inlined into the
2075	thunking function, making it as fast as a direct C callback.	3097	thunking function, making it as fast as a direct C callback.
2076		3098
2077	Example: simple class declaration and watcher initialisation	3099	Example: simple class declaration and watcher initialisation
2078		3100
2079	struct myclass	3101	struct myclass
2080	{	3102	{
2081	void io_cb (ev::io &w, int revents) { }	3103	void io_cb (ev::io &w, int revents) { }
2082	}	3104	}
2083		3105
2084	myclass obj;	3106	myclass obj;
2085	ev::io iow;	3107	ev::io iow;
2086	iow.set <myclass, &myclass::io_cb> (&obj);	3108	iow.set <myclass, &myclass::io_cb> (&obj);
		3109
		3110	=item w->set (object *)
		3111
		3112	This is an B<experimental> feature that might go away in a future version.
		3113
		3114	This is a variation of a method callback - leaving out the method to call
		3115	will default the method to C<operator ()>, which makes it possible to use
		3116	functor objects without having to manually specify the C<operator ()> all
		3117	the time. Incidentally, you can then also leave out the template argument
		3118	list.
		3119
		3120	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3121	int revents)>.
		3122
		3123	See the method-C<set> above for more details.
		3124
		3125	Example: use a functor object as callback.
		3126
		3127	struct myfunctor
		3128	{
		3129	void operator() (ev::io &w, int revents)
		3130	{
		3131	...
		3132	}
		3133	}
		3134
		3135	myfunctor f;
		3136
		3137	ev::io w;
		3138	w.set (&f);
2087		3139
2088	=item w->set<function> (void *data = 0)	3140	=item w->set<function> (void *data = 0)
2089		3141
2090	Also sets a callback, but uses a static method or plain function as	3142	Also sets a callback, but uses a static method or plain function as
2091	callback. The optional C<data> argument will be stored in the watcher's	3143	callback. The optional C<data> argument will be stored in the watcher's
…		…
2093		3145
2094	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3146	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2095		3147
2096	See the method-C<set> above for more details.	3148	See the method-C<set> above for more details.
2097		3149
2098	Example:	3150	Example: Use a plain function as callback.
2099		3151
2100	static void io_cb (ev::io &w, int revents) { }	3152	static void io_cb (ev::io &w, int revents) { }
2101	iow.set <io_cb> ();	3153	iow.set <io_cb> ();
2102		3154
2103	=item w->set (struct ev_loop *)	3155	=item w->set (struct ev_loop *)
2104		3156
2105	Associates a different C<struct ev_loop> with this watcher. You can only	3157	Associates a different C<struct ev_loop> with this watcher. You can only
2106	do this when the watcher is inactive (and not pending either).	3158	do this when the watcher is inactive (and not pending either).
2107		3159
2108	=item w->set ([args])	3160	=item w->set ([arguments])
2109		3161
2110	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3162	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2111	called at least once. Unlike the C counterpart, an active watcher gets	3163	called at least once. Unlike the C counterpart, an active watcher gets
2112	automatically stopped and restarted when reconfiguring it with this	3164	automatically stopped and restarted when reconfiguring it with this
2113	method.	3165	method.
2114		3166
2115	=item w->start ()	3167	=item w->start ()
…		…
2139	=back	3191	=back
2140		3192
2141	Example: Define a class with an IO and idle watcher, start one of them in	3193	Example: Define a class with an IO and idle watcher, start one of them in
2142	the constructor.	3194	the constructor.
2143		3195
2144	class myclass	3196	class myclass
2145	{	3197	{
2146	ev_io io; void io_cb (ev::io &w, int revents);	3198	ev::io io ; void io_cb (ev::io &w, int revents);
2147	ev_idle idle void idle_cb (ev::idle &w, int revents);	3199	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2148		3200
2149	myclass ();	3201	myclass (int fd)
2150	}	3202	{
2151
2152	myclass::myclass (int fd)
2153	{
2154	io .set <myclass, &myclass::io_cb > (this);	3203	io .set <myclass, &myclass::io_cb > (this);
2155	idle.set <myclass, &myclass::idle_cb> (this);	3204	idle.set <myclass, &myclass::idle_cb> (this);
2156		3205
2157	io.start (fd, ev::READ);	3206	io.start (fd, ev::READ);
		3207	}
2158	}	3208	};
		3209
		3210
		3211	=head1 OTHER LANGUAGE BINDINGS
		3212
		3213	Libev does not offer other language bindings itself, but bindings for a
		3214	number of languages exist in the form of third-party packages. If you know
		3215	any interesting language binding in addition to the ones listed here, drop
		3216	me a note.
		3217
		3218	=over 4
		3219
		3220	=item Perl
		3221
		3222	The EV module implements the full libev API and is actually used to test
		3223	libev. EV is developed together with libev. Apart from the EV core module,
		3224	there are additional modules that implement libev-compatible interfaces
		3225	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3226	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3227	and C<EV::Glib>).
		3228
		3229	It can be found and installed via CPAN, its homepage is at
		3230	L<http://software.schmorp.de/pkg/EV>.
		3231
		3232	=item Python
		3233
		3234	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3235	seems to be quite complete and well-documented.
		3236
		3237	=item Ruby
		3238
		3239	Tony Arcieri has written a ruby extension that offers access to a subset
		3240	of the libev API and adds file handle abstractions, asynchronous DNS and
		3241	more on top of it. It can be found via gem servers. Its homepage is at
		3242	L<http://rev.rubyforge.org/>.
		3243
		3244	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3245	makes rev work even on mingw.
		3246
		3247	=item Haskell
		3248
		3249	A haskell binding to libev is available at
		3250	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3251
		3252	=item D
		3253
		3254	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3255	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3256
		3257	=item Ocaml
		3258
		3259	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3260	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3261
		3262	=back
2159		3263
2160		3264
2161	=head1 MACRO MAGIC	3265	=head1 MACRO MAGIC
2162		3266
2163	Libev can be compiled with a variety of options, the most fundamantal	3267	Libev can be compiled with a variety of options, the most fundamental
2164	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3268	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2165	functions and callbacks have an initial C<struct ev_loop *> argument.	3269	functions and callbacks have an initial C<struct ev_loop *> argument.
2166		3270
2167	To make it easier to write programs that cope with either variant, the	3271	To make it easier to write programs that cope with either variant, the
2168	following macros are defined:	3272	following macros are defined:
…		…
2173		3277
2174	This provides the loop I<argument> for functions, if one is required ("ev	3278	This provides the loop I<argument> for functions, if one is required ("ev
2175	loop argument"). The C<EV_A> form is used when this is the sole argument,	3279	loop argument"). The C<EV_A> form is used when this is the sole argument,
2176	C<EV_A_> is used when other arguments are following. Example:	3280	C<EV_A_> is used when other arguments are following. Example:
2177		3281
2178	ev_unref (EV_A);	3282	ev_unref (EV_A);
2179	ev_timer_add (EV_A_ watcher);	3283	ev_timer_add (EV_A_ watcher);
2180	ev_loop (EV_A_ 0);	3284	ev_loop (EV_A_ 0);
2181		3285
2182	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3286	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2183	which is often provided by the following macro.	3287	which is often provided by the following macro.
2184		3288
2185	=item C<EV_P>, C<EV_P_>	3289	=item C<EV_P>, C<EV_P_>
2186		3290
2187	This provides the loop I<parameter> for functions, if one is required ("ev	3291	This provides the loop I<parameter> for functions, if one is required ("ev
2188	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3292	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2189	C<EV_P_> is used when other parameters are following. Example:	3293	C<EV_P_> is used when other parameters are following. Example:
2190		3294
2191	// this is how ev_unref is being declared	3295	// this is how ev_unref is being declared
2192	static void ev_unref (EV_P);	3296	static void ev_unref (EV_P);
2193		3297
2194	// this is how you can declare your typical callback	3298	// this is how you can declare your typical callback
2195	static void cb (EV_P_ ev_timer *w, int revents)	3299	static void cb (EV_P_ ev_timer *w, int revents)
2196		3300
2197	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3301	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2198	suitable for use with C<EV_A>.	3302	suitable for use with C<EV_A>.
2199		3303
2200	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3304	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2201		3305
2202	Similar to the other two macros, this gives you the value of the default	3306	Similar to the other two macros, this gives you the value of the default
2203	loop, if multiple loops are supported ("ev loop default").	3307	loop, if multiple loops are supported ("ev loop default").
		3308
		3309	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3310
		3311	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3312	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3313	is undefined when the default loop has not been initialised by a previous
		3314	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3315
		3316	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3317	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2204		3318
2205	=back	3319	=back
2206		3320
2207	Example: Declare and initialise a check watcher, utilising the above	3321	Example: Declare and initialise a check watcher, utilising the above
2208	macros so it will work regardless of whether multiple loops are supported	3322	macros so it will work regardless of whether multiple loops are supported
2209	or not.	3323	or not.
2210		3324
2211	static void	3325	static void
2212	check_cb (EV_P_ ev_timer *w, int revents)	3326	check_cb (EV_P_ ev_timer *w, int revents)
2213	{	3327	{
2214	ev_check_stop (EV_A_ w);	3328	ev_check_stop (EV_A_ w);
2215	}	3329	}
2216		3330
2217	ev_check check;	3331	ev_check check;
2218	ev_check_init (&check, check_cb);	3332	ev_check_init (&check, check_cb);
2219	ev_check_start (EV_DEFAULT_ &check);	3333	ev_check_start (EV_DEFAULT_ &check);
2220	ev_loop (EV_DEFAULT_ 0);	3334	ev_loop (EV_DEFAULT_ 0);
2221		3335
2222	=head1 EMBEDDING	3336	=head1 EMBEDDING
2223		3337
2224	Libev can (and often is) directly embedded into host	3338	Libev can (and often is) directly embedded into host
2225	applications. Examples of applications that embed it include the Deliantra	3339	applications. Examples of applications that embed it include the Deliantra
…		…
2232	libev somewhere in your source tree).	3346	libev somewhere in your source tree).
2233		3347
2234	=head2 FILESETS	3348	=head2 FILESETS
2235		3349
2236	Depending on what features you need you need to include one or more sets of files	3350	Depending on what features you need you need to include one or more sets of files
2237	in your app.	3351	in your application.
2238		3352
2239	=head3 CORE EVENT LOOP	3353	=head3 CORE EVENT LOOP
2240		3354
2241	To include only the libev core (all the C<ev_*> functions), with manual	3355	To include only the libev core (all the C<ev_*> functions), with manual
2242	configuration (no autoconf):	3356	configuration (no autoconf):
2243		3357
2244	#define EV_STANDALONE 1	3358	#define EV_STANDALONE 1
2245	#include "ev.c"	3359	#include "ev.c"
2246		3360
2247	This will automatically include F<ev.h>, too, and should be done in a	3361	This will automatically include F<ev.h>, too, and should be done in a
2248	single C source file only to provide the function implementations. To use	3362	single C source file only to provide the function implementations. To use
2249	it, do the same for F<ev.h> in all files wishing to use this API (best	3363	it, do the same for F<ev.h> in all files wishing to use this API (best
2250	done by writing a wrapper around F<ev.h> that you can include instead and	3364	done by writing a wrapper around F<ev.h> that you can include instead and
2251	where you can put other configuration options):	3365	where you can put other configuration options):
2252		3366
2253	#define EV_STANDALONE 1	3367	#define EV_STANDALONE 1
2254	#include "ev.h"	3368	#include "ev.h"
2255		3369
2256	Both header files and implementation files can be compiled with a C++	3370	Both header files and implementation files can be compiled with a C++
2257	compiler (at least, thats a stated goal, and breakage will be treated	3371	compiler (at least, that's a stated goal, and breakage will be treated
2258	as a bug).	3372	as a bug).
2259		3373
2260	You need the following files in your source tree, or in a directory	3374	You need the following files in your source tree, or in a directory
2261	in your include path (e.g. in libev/ when using -Ilibev):	3375	in your include path (e.g. in libev/ when using -Ilibev):
2262		3376
2263	ev.h	3377	ev.h
2264	ev.c	3378	ev.c
2265	ev_vars.h	3379	ev_vars.h
2266	ev_wrap.h	3380	ev_wrap.h
2267		3381
2268	ev_win32.c required on win32 platforms only	3382	ev_win32.c required on win32 platforms only
2269		3383
2270	ev_select.c only when select backend is enabled (which is enabled by default)	3384	ev_select.c only when select backend is enabled (which is enabled by default)
2271	ev_poll.c only when poll backend is enabled (disabled by default)	3385	ev_poll.c only when poll backend is enabled (disabled by default)
2272	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3386	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2273	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3387	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2274	ev_port.c only when the solaris port backend is enabled (disabled by default)	3388	ev_port.c only when the solaris port backend is enabled (disabled by default)
2275		3389
2276	F<ev.c> includes the backend files directly when enabled, so you only need	3390	F<ev.c> includes the backend files directly when enabled, so you only need
2277	to compile this single file.	3391	to compile this single file.
2278		3392
2279	=head3 LIBEVENT COMPATIBILITY API	3393	=head3 LIBEVENT COMPATIBILITY API
2280		3394
2281	To include the libevent compatibility API, also include:	3395	To include the libevent compatibility API, also include:
2282		3396
2283	#include "event.c"	3397	#include "event.c"
2284		3398
2285	in the file including F<ev.c>, and:	3399	in the file including F<ev.c>, and:
2286		3400
2287	#include "event.h"	3401	#include "event.h"
2288		3402
2289	in the files that want to use the libevent API. This also includes F<ev.h>.	3403	in the files that want to use the libevent API. This also includes F<ev.h>.
2290		3404
2291	You need the following additional files for this:	3405	You need the following additional files for this:
2292		3406
2293	event.h	3407	event.h
2294	event.c	3408	event.c
2295		3409
2296	=head3 AUTOCONF SUPPORT	3410	=head3 AUTOCONF SUPPORT
2297		3411
2298	Instead of using C<EV_STANDALONE=1> and providing your config in	3412	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2299	whatever way you want, you can also C<m4_include([libev.m4])> in your	3413	whatever way you want, you can also C<m4_include([libev.m4])> in your
2300	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3414	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2301	include F<config.h> and configure itself accordingly.	3415	include F<config.h> and configure itself accordingly.
2302		3416
2303	For this of course you need the m4 file:	3417	For this of course you need the m4 file:
2304		3418
2305	libev.m4	3419	libev.m4
2306		3420
2307	=head2 PREPROCESSOR SYMBOLS/MACROS	3421	=head2 PREPROCESSOR SYMBOLS/MACROS
2308		3422
2309	Libev can be configured via a variety of preprocessor symbols you have to define	3423	Libev can be configured via a variety of preprocessor symbols you have to
2310	before including any of its files. The default is not to build for multiplicity	3424	define before including any of its files. The default in the absence of
2311	and only include the select backend.	3425	autoconf is documented for every option.
2312		3426
2313	=over 4	3427	=over 4
2314		3428
2315	=item EV_STANDALONE	3429	=item EV_STANDALONE
2316		3430
…		…
2318	keeps libev from including F<config.h>, and it also defines dummy	3432	keeps libev from including F<config.h>, and it also defines dummy
2319	implementations for some libevent functions (such as logging, which is not	3433	implementations for some libevent functions (such as logging, which is not
2320	supported). It will also not define any of the structs usually found in	3434	supported). It will also not define any of the structs usually found in
2321	F<event.h> that are not directly supported by the libev core alone.	3435	F<event.h> that are not directly supported by the libev core alone.
2322		3436
		3437	In stanbdalone mode, libev will still try to automatically deduce the
		3438	configuration, but has to be more conservative.
		3439
2323	=item EV_USE_MONOTONIC	3440	=item EV_USE_MONOTONIC
2324		3441
2325	If defined to be C<1>, libev will try to detect the availability of the	3442	If defined to be C<1>, libev will try to detect the availability of the
2326	monotonic clock option at both compiletime and runtime. Otherwise no use	3443	monotonic clock option at both compile time and runtime. Otherwise no
2327	of the monotonic clock option will be attempted. If you enable this, you	3444	use of the monotonic clock option will be attempted. If you enable this,
2328	usually have to link against librt or something similar. Enabling it when	3445	you usually have to link against librt or something similar. Enabling it
2329	the functionality isn't available is safe, though, although you have	3446	when the functionality isn't available is safe, though, although you have
2330	to make sure you link against any libraries where the C<clock_gettime>	3447	to make sure you link against any libraries where the C<clock_gettime>
2331	function is hiding in (often F<-lrt>).	3448	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2332		3449
2333	=item EV_USE_REALTIME	3450	=item EV_USE_REALTIME
2334		3451
2335	If defined to be C<1>, libev will try to detect the availability of the	3452	If defined to be C<1>, libev will try to detect the availability of the
2336	realtime clock option at compiletime (and assume its availability at	3453	real-time clock option at compile time (and assume its availability
2337	runtime if successful). Otherwise no use of the realtime clock option will	3454	at runtime if successful). Otherwise no use of the real-time clock
2338	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3455	option will be attempted. This effectively replaces C<gettimeofday>
2339	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3456	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2340	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3457	correctness. See the note about libraries in the description of
		3458	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3459	C<EV_USE_CLOCK_SYSCALL>.
		3460
		3461	=item EV_USE_CLOCK_SYSCALL
		3462
		3463	If defined to be C<1>, libev will try to use a direct syscall instead
		3464	of calling the system-provided C<clock_gettime> function. This option
		3465	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3466	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3467	programs needlessly. Using a direct syscall is slightly slower (in
		3468	theory), because no optimised vdso implementation can be used, but avoids
		3469	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3470	higher, as it simplifies linking (no need for C<-lrt>).
2341		3471
2342	=item EV_USE_NANOSLEEP	3472	=item EV_USE_NANOSLEEP
2343		3473
2344	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3474	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2345	and will use it for delays. Otherwise it will use C<select ()>.	3475	and will use it for delays. Otherwise it will use C<select ()>.
2346		3476
		3477	=item EV_USE_EVENTFD
		3478
		3479	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3480	available and will probe for kernel support at runtime. This will improve
		3481	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3482	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3483	2.7 or newer, otherwise disabled.
		3484
2347	=item EV_USE_SELECT	3485	=item EV_USE_SELECT
2348		3486
2349	If undefined or defined to be C<1>, libev will compile in support for the	3487	If undefined or defined to be C<1>, libev will compile in support for the
2350	C<select>(2) backend. No attempt at autodetection will be done: if no	3488	C<select>(2) backend. No attempt at auto-detection will be done: if no
2351	other method takes over, select will be it. Otherwise the select backend	3489	other method takes over, select will be it. Otherwise the select backend
2352	will not be compiled in.	3490	will not be compiled in.
2353		3491
2354	=item EV_SELECT_USE_FD_SET	3492	=item EV_SELECT_USE_FD_SET
2355		3493
2356	If defined to C<1>, then the select backend will use the system C<fd_set>	3494	If defined to C<1>, then the select backend will use the system C<fd_set>
2357	structure. This is useful if libev doesn't compile due to a missing	3495	structure. This is useful if libev doesn't compile due to a missing
2358	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3496	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2359	exotic systems. This usually limits the range of file descriptors to some	3497	on exotic systems. This usually limits the range of file descriptors to
2360	low limit such as 1024 or might have other limitations (winsocket only	3498	some low limit such as 1024 or might have other limitations (winsocket
2361	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3499	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2362	influence the size of the C<fd_set> used.	3500	configures the maximum size of the C<fd_set>.
2363		3501
2364	=item EV_SELECT_IS_WINSOCKET	3502	=item EV_SELECT_IS_WINSOCKET
2365		3503
2366	When defined to C<1>, the select backend will assume that	3504	When defined to C<1>, the select backend will assume that
2367	select/socket/connect etc. don't understand file descriptors but	3505	select/socket/connect etc. don't understand file descriptors but
…		…
2369	be used is the winsock select). This means that it will call	3507	be used is the winsock select). This means that it will call
2370	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3508	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2371	it is assumed that all these functions actually work on fds, even	3509	it is assumed that all these functions actually work on fds, even
2372	on win32. Should not be defined on non-win32 platforms.	3510	on win32. Should not be defined on non-win32 platforms.
2373		3511
		3512	=item EV_FD_TO_WIN32_HANDLE
		3513
		3514	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3515	file descriptors to socket handles. When not defining this symbol (the
		3516	default), then libev will call C<_get_osfhandle>, which is usually
		3517	correct. In some cases, programs use their own file descriptor management,
		3518	in which case they can provide this function to map fds to socket handles.
		3519
2374	=item EV_USE_POLL	3520	=item EV_USE_POLL
2375		3521
2376	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3522	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2377	backend. Otherwise it will be enabled on non-win32 platforms. It	3523	backend. Otherwise it will be enabled on non-win32 platforms. It
2378	takes precedence over select.	3524	takes precedence over select.
2379		3525
2380	=item EV_USE_EPOLL	3526	=item EV_USE_EPOLL
2381		3527
2382	If defined to be C<1>, libev will compile in support for the Linux	3528	If defined to be C<1>, libev will compile in support for the Linux
2383	C<epoll>(7) backend. Its availability will be detected at runtime,	3529	C<epoll>(7) backend. Its availability will be detected at runtime,
2384	otherwise another method will be used as fallback. This is the	3530	otherwise another method will be used as fallback. This is the preferred
2385	preferred backend for GNU/Linux systems.	3531	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3532	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2386		3533
2387	=item EV_USE_KQUEUE	3534	=item EV_USE_KQUEUE
2388		3535
2389	If defined to be C<1>, libev will compile in support for the BSD style	3536	If defined to be C<1>, libev will compile in support for the BSD style
2390	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3537	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2403	otherwise another method will be used as fallback. This is the preferred	3550	otherwise another method will be used as fallback. This is the preferred
2404	backend for Solaris 10 systems.	3551	backend for Solaris 10 systems.
2405		3552
2406	=item EV_USE_DEVPOLL	3553	=item EV_USE_DEVPOLL
2407		3554
2408	reserved for future expansion, works like the USE symbols above.	3555	Reserved for future expansion, works like the USE symbols above.
2409		3556
2410	=item EV_USE_INOTIFY	3557	=item EV_USE_INOTIFY
2411		3558
2412	If defined to be C<1>, libev will compile in support for the Linux inotify	3559	If defined to be C<1>, libev will compile in support for the Linux inotify
2413	interface to speed up C<ev_stat> watchers. Its actual availability will	3560	interface to speed up C<ev_stat> watchers. Its actual availability will
2414	be detected at runtime.	3561	be detected at runtime. If undefined, it will be enabled if the headers
		3562	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3563
		3564	=item EV_ATOMIC_T
		3565
		3566	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3567	access is atomic with respect to other threads or signal contexts. No such
		3568	type is easily found in the C language, so you can provide your own type
		3569	that you know is safe for your purposes. It is used both for signal handler "locking"
		3570	as well as for signal and thread safety in C<ev_async> watchers.
		3571
		3572	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3573	(from F<signal.h>), which is usually good enough on most platforms.
2415		3574
2416	=item EV_H	3575	=item EV_H
2417		3576
2418	The name of the F<ev.h> header file used to include it. The default if	3577	The name of the F<ev.h> header file used to include it. The default if
2419	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3578	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2420	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3579	used to virtually rename the F<ev.h> header file in case of conflicts.
2421		3580
2422	=item EV_CONFIG_H	3581	=item EV_CONFIG_H
2423		3582
2424	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3583	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2425	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3584	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2426	C<EV_H>, above.	3585	C<EV_H>, above.
2427		3586
2428	=item EV_EVENT_H	3587	=item EV_EVENT_H
2429		3588
2430	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3589	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2431	of how the F<event.h> header can be found.	3590	of how the F<event.h> header can be found, the default is C<"event.h">.
2432		3591
2433	=item EV_PROTOTYPES	3592	=item EV_PROTOTYPES
2434		3593
2435	If defined to be C<0>, then F<ev.h> will not define any function	3594	If defined to be C<0>, then F<ev.h> will not define any function
2436	prototypes, but still define all the structs and other symbols. This is	3595	prototypes, but still define all the structs and other symbols. This is
…		…
2457	When doing priority-based operations, libev usually has to linearly search	3616	When doing priority-based operations, libev usually has to linearly search
2458	all the priorities, so having many of them (hundreds) uses a lot of space	3617	all the priorities, so having many of them (hundreds) uses a lot of space
2459	and time, so using the defaults of five priorities (-2 .. +2) is usually	3618	and time, so using the defaults of five priorities (-2 .. +2) is usually
2460	fine.	3619	fine.
2461		3620
2462	If your embedding app does not need any priorities, defining these both to	3621	If your embedding application does not need any priorities, defining these
2463	C<0> will save some memory and cpu.	3622	both to C<0> will save some memory and CPU.
2464		3623
2465	=item EV_PERIODIC_ENABLE	3624	=item EV_PERIODIC_ENABLE
2466		3625
2467	If undefined or defined to be C<1>, then periodic timers are supported. If	3626	If undefined or defined to be C<1>, then periodic timers are supported. If
2468	defined to be C<0>, then they are not. Disabling them saves a few kB of	3627	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2475	code.	3634	code.
2476		3635
2477	=item EV_EMBED_ENABLE	3636	=item EV_EMBED_ENABLE
2478		3637
2479	If undefined or defined to be C<1>, then embed watchers are supported. If	3638	If undefined or defined to be C<1>, then embed watchers are supported. If
2480	defined to be C<0>, then they are not.	3639	defined to be C<0>, then they are not. Embed watchers rely on most other
		3640	watcher types, which therefore must not be disabled.
2481		3641
2482	=item EV_STAT_ENABLE	3642	=item EV_STAT_ENABLE
2483		3643
2484	If undefined or defined to be C<1>, then stat watchers are supported. If	3644	If undefined or defined to be C<1>, then stat watchers are supported. If
2485	defined to be C<0>, then they are not.	3645	defined to be C<0>, then they are not.
…		…
2487	=item EV_FORK_ENABLE	3647	=item EV_FORK_ENABLE
2488		3648
2489	If undefined or defined to be C<1>, then fork watchers are supported. If	3649	If undefined or defined to be C<1>, then fork watchers are supported. If
2490	defined to be C<0>, then they are not.	3650	defined to be C<0>, then they are not.
2491		3651
		3652	=item EV_ASYNC_ENABLE
		3653
		3654	If undefined or defined to be C<1>, then async watchers are supported. If
		3655	defined to be C<0>, then they are not.
		3656
2492	=item EV_MINIMAL	3657	=item EV_MINIMAL
2493		3658
2494	If you need to shave off some kilobytes of code at the expense of some	3659	If you need to shave off some kilobytes of code at the expense of some
2495	speed, define this symbol to C<1>. Currently only used for gcc to override	3660	speed, define this symbol to C<1>. Currently this is used to override some
2496	some inlining decisions, saves roughly 30% codesize of amd64.	3661	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3662	much smaller 2-heap for timer management over the default 4-heap.
2497		3663
2498	=item EV_PID_HASHSIZE	3664	=item EV_PID_HASHSIZE
2499		3665
2500	C<ev_child> watchers use a small hash table to distribute workload by	3666	C<ev_child> watchers use a small hash table to distribute workload by
2501	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3667	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2502	than enough. If you need to manage thousands of children you might want to	3668	than enough. If you need to manage thousands of children you might want to
2503	increase this value (I<must> be a power of two).	3669	increase this value (I<must> be a power of two).
2504		3670
2505	=item EV_INOTIFY_HASHSIZE	3671	=item EV_INOTIFY_HASHSIZE
2506		3672
2507	C<ev_staz> watchers use a small hash table to distribute workload by	3673	C<ev_stat> watchers use a small hash table to distribute workload by
2508	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3674	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2509	usually more than enough. If you need to manage thousands of C<ev_stat>	3675	usually more than enough. If you need to manage thousands of C<ev_stat>
2510	watchers you might want to increase this value (I<must> be a power of	3676	watchers you might want to increase this value (I<must> be a power of
2511	two).	3677	two).
2512		3678
		3679	=item EV_USE_4HEAP
		3680
		3681	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3682	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3683	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3684	faster performance with many (thousands) of watchers.
		3685
		3686	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3687	(disabled).
		3688
		3689	=item EV_HEAP_CACHE_AT
		3690
		3691	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3692	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3693	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3694	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3695	but avoids random read accesses on heap changes. This improves performance
		3696	noticeably with many (hundreds) of watchers.
		3697
		3698	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3699	(disabled).
		3700
		3701	=item EV_VERIFY
		3702
		3703	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3704	be done: If set to C<0>, no internal verification code will be compiled
		3705	in. If set to C<1>, then verification code will be compiled in, but not
		3706	called. If set to C<2>, then the internal verification code will be
		3707	called once per loop, which can slow down libev. If set to C<3>, then the
		3708	verification code will be called very frequently, which will slow down
		3709	libev considerably.
		3710
		3711	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3712	C<0>.
		3713
2513	=item EV_COMMON	3714	=item EV_COMMON
2514		3715
2515	By default, all watchers have a C<void *data> member. By redefining	3716	By default, all watchers have a C<void *data> member. By redefining
2516	this macro to a something else you can include more and other types of	3717	this macro to a something else you can include more and other types of
2517	members. You have to define it each time you include one of the files,	3718	members. You have to define it each time you include one of the files,
2518	though, and it must be identical each time.	3719	though, and it must be identical each time.
2519		3720
2520	For example, the perl EV module uses something like this:	3721	For example, the perl EV module uses something like this:
2521		3722
2522	#define EV_COMMON \	3723	#define EV_COMMON \
2523	SV *self; /* contains this struct */ \	3724	SV *self; /* contains this struct */ \
2524	SV *cb_sv, *fh /* note no trailing ";" */	3725	SV *cb_sv, *fh /* note no trailing ";" */
2525		3726
2526	=item EV_CB_DECLARE (type)	3727	=item EV_CB_DECLARE (type)
2527		3728
2528	=item EV_CB_INVOKE (watcher, revents)	3729	=item EV_CB_INVOKE (watcher, revents)
2529		3730
…		…
2534	definition and a statement, respectively. See the F<ev.h> header file for	3735	definition and a statement, respectively. See the F<ev.h> header file for
2535	their default definitions. One possible use for overriding these is to	3736	their default definitions. One possible use for overriding these is to
2536	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3737	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2537	method calls instead of plain function calls in C++.	3738	method calls instead of plain function calls in C++.
2538		3739
		3740	=back
		3741
2539	=head2 EXPORTED API SYMBOLS	3742	=head2 EXPORTED API SYMBOLS
2540		3743
2541	If you need to re-export the API (e.g. via a dll) and you need a list of	3744	If you need to re-export the API (e.g. via a DLL) and you need a list of
2542	exported symbols, you can use the provided F<Symbol.*> files which list	3745	exported symbols, you can use the provided F<Symbol.*> files which list
2543	all public symbols, one per line:	3746	all public symbols, one per line:
2544		3747
2545	Symbols.ev for libev proper	3748	Symbols.ev for libev proper
2546	Symbols.event for the libevent emulation	3749	Symbols.event for the libevent emulation
2547		3750
2548	This can also be used to rename all public symbols to avoid clashes with	3751	This can also be used to rename all public symbols to avoid clashes with
2549	multiple versions of libev linked together (which is obviously bad in	3752	multiple versions of libev linked together (which is obviously bad in
2550	itself, but sometimes it is inconvinient to avoid this).	3753	itself, but sometimes it is inconvenient to avoid this).
2551		3754
2552	A sed command like this will create wrapper C<#define>'s that you need to	3755	A sed command like this will create wrapper C<#define>'s that you need to
2553	include before including F<ev.h>:	3756	include before including F<ev.h>:
2554		3757
2555	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3758	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2572	file.	3775	file.
2573		3776
2574	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3777	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2575	that everybody includes and which overrides some configure choices:	3778	that everybody includes and which overrides some configure choices:
2576		3779
2577	#define EV_MINIMAL 1	3780	#define EV_MINIMAL 1
2578	#define EV_USE_POLL 0	3781	#define EV_USE_POLL 0
2579	#define EV_MULTIPLICITY 0	3782	#define EV_MULTIPLICITY 0
2580	#define EV_PERIODIC_ENABLE 0	3783	#define EV_PERIODIC_ENABLE 0
2581	#define EV_STAT_ENABLE 0	3784	#define EV_STAT_ENABLE 0
2582	#define EV_FORK_ENABLE 0	3785	#define EV_FORK_ENABLE 0
2583	#define EV_CONFIG_H <config.h>	3786	#define EV_CONFIG_H <config.h>
2584	#define EV_MINPRI 0	3787	#define EV_MINPRI 0
2585	#define EV_MAXPRI 0	3788	#define EV_MAXPRI 0
2586		3789
2587	#include "ev++.h"	3790	#include "ev++.h"
2588		3791
2589	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3792	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2590		3793
2591	#include "ev_cpp.h"	3794	#include "ev_cpp.h"
2592	#include "ev.c"	3795	#include "ev.c"
2593		3796
		3797	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2594		3798
		3799	=head2 THREADS AND COROUTINES
		3800
		3801	=head3 THREADS
		3802
		3803	All libev functions are reentrant and thread-safe unless explicitly
		3804	documented otherwise, but libev implements no locking itself. This means
		3805	that you can use as many loops as you want in parallel, as long as there
		3806	are no concurrent calls into any libev function with the same loop
		3807	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3808	of course): libev guarantees that different event loops share no data
		3809	structures that need any locking.
		3810
		3811	Or to put it differently: calls with different loop parameters can be done
		3812	concurrently from multiple threads, calls with the same loop parameter
		3813	must be done serially (but can be done from different threads, as long as
		3814	only one thread ever is inside a call at any point in time, e.g. by using
		3815	a mutex per loop).
		3816
		3817	Specifically to support threads (and signal handlers), libev implements
		3818	so-called C<ev_async> watchers, which allow some limited form of
		3819	concurrency on the same event loop, namely waking it up "from the
		3820	outside".
		3821
		3822	If you want to know which design (one loop, locking, or multiple loops
		3823	without or something else still) is best for your problem, then I cannot
		3824	help you, but here is some generic advice:
		3825
		3826	=over 4
		3827
		3828	=item * most applications have a main thread: use the default libev loop
		3829	in that thread, or create a separate thread running only the default loop.
		3830
		3831	This helps integrating other libraries or software modules that use libev
		3832	themselves and don't care/know about threading.
		3833
		3834	=item * one loop per thread is usually a good model.
		3835
		3836	Doing this is almost never wrong, sometimes a better-performance model
		3837	exists, but it is always a good start.
		3838
		3839	=item * other models exist, such as the leader/follower pattern, where one
		3840	loop is handed through multiple threads in a kind of round-robin fashion.
		3841
		3842	Choosing a model is hard - look around, learn, know that usually you can do
		3843	better than you currently do :-)
		3844
		3845	=item * often you need to talk to some other thread which blocks in the
		3846	event loop.
		3847
		3848	C<ev_async> watchers can be used to wake them up from other threads safely
		3849	(or from signal contexts...).
		3850
		3851	An example use would be to communicate signals or other events that only
		3852	work in the default loop by registering the signal watcher with the
		3853	default loop and triggering an C<ev_async> watcher from the default loop
		3854	watcher callback into the event loop interested in the signal.
		3855
		3856	=back
		3857
		3858	=head3 COROUTINES
		3859
		3860	Libev is very accommodating to coroutines ("cooperative threads"):
		3861	libev fully supports nesting calls to its functions from different
		3862	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3863	different coroutines, and switch freely between both coroutines running the
		3864	loop, as long as you don't confuse yourself). The only exception is that
		3865	you must not do this from C<ev_periodic> reschedule callbacks.
		3866
		3867	Care has been taken to ensure that libev does not keep local state inside
		3868	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3869	they do not call any callbacks.
		3870
		3871	=head2 COMPILER WARNINGS
		3872
		3873	Depending on your compiler and compiler settings, you might get no or a
		3874	lot of warnings when compiling libev code. Some people are apparently
		3875	scared by this.
		3876
		3877	However, these are unavoidable for many reasons. For one, each compiler
		3878	has different warnings, and each user has different tastes regarding
		3879	warning options. "Warn-free" code therefore cannot be a goal except when
		3880	targeting a specific compiler and compiler-version.
		3881
		3882	Another reason is that some compiler warnings require elaborate
		3883	workarounds, or other changes to the code that make it less clear and less
		3884	maintainable.
		3885
		3886	And of course, some compiler warnings are just plain stupid, or simply
		3887	wrong (because they don't actually warn about the condition their message
		3888	seems to warn about). For example, certain older gcc versions had some
		3889	warnings that resulted an extreme number of false positives. These have
		3890	been fixed, but some people still insist on making code warn-free with
		3891	such buggy versions.
		3892
		3893	While libev is written to generate as few warnings as possible,
		3894	"warn-free" code is not a goal, and it is recommended not to build libev
		3895	with any compiler warnings enabled unless you are prepared to cope with
		3896	them (e.g. by ignoring them). Remember that warnings are just that:
		3897	warnings, not errors, or proof of bugs.
		3898
		3899
		3900	=head2 VALGRIND
		3901
		3902	Valgrind has a special section here because it is a popular tool that is
		3903	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3904
		3905	If you think you found a bug (memory leak, uninitialised data access etc.)
		3906	in libev, then check twice: If valgrind reports something like:
		3907
		3908	==2274== definitely lost: 0 bytes in 0 blocks.
		3909	==2274== possibly lost: 0 bytes in 0 blocks.
		3910	==2274== still reachable: 256 bytes in 1 blocks.
		3911
		3912	Then there is no memory leak, just as memory accounted to global variables
		3913	is not a memleak - the memory is still being referenced, and didn't leak.
		3914
		3915	Similarly, under some circumstances, valgrind might report kernel bugs
		3916	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3917	although an acceptable workaround has been found here), or it might be
		3918	confused.
		3919
		3920	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3921	make it into some kind of religion.
		3922
		3923	If you are unsure about something, feel free to contact the mailing list
		3924	with the full valgrind report and an explanation on why you think this
		3925	is a bug in libev (best check the archives, too :). However, don't be
		3926	annoyed when you get a brisk "this is no bug" answer and take the chance
		3927	of learning how to interpret valgrind properly.
		3928
		3929	If you need, for some reason, empty reports from valgrind for your project
		3930	I suggest using suppression lists.
		3931
		3932
		3933	=head1 PORTABILITY NOTES
		3934
		3935	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3936
		3937	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3938	requires, and its I/O model is fundamentally incompatible with the POSIX
		3939	model. Libev still offers limited functionality on this platform in
		3940	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3941	descriptors. This only applies when using Win32 natively, not when using
		3942	e.g. cygwin.
		3943
		3944	Lifting these limitations would basically require the full
		3945	re-implementation of the I/O system. If you are into these kinds of
		3946	things, then note that glib does exactly that for you in a very portable
		3947	way (note also that glib is the slowest event library known to man).
		3948
		3949	There is no supported compilation method available on windows except
		3950	embedding it into other applications.
		3951
		3952	Sensible signal handling is officially unsupported by Microsoft - libev
		3953	tries its best, but under most conditions, signals will simply not work.
		3954
		3955	Not a libev limitation but worth mentioning: windows apparently doesn't
		3956	accept large writes: instead of resulting in a partial write, windows will
		3957	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3958	so make sure you only write small amounts into your sockets (less than a
		3959	megabyte seems safe, but this apparently depends on the amount of memory
		3960	available).
		3961
		3962	Due to the many, low, and arbitrary limits on the win32 platform and
		3963	the abysmal performance of winsockets, using a large number of sockets
		3964	is not recommended (and not reasonable). If your program needs to use
		3965	more than a hundred or so sockets, then likely it needs to use a totally
		3966	different implementation for windows, as libev offers the POSIX readiness
		3967	notification model, which cannot be implemented efficiently on windows
		3968	(due to Microsoft monopoly games).
		3969
		3970	A typical way to use libev under windows is to embed it (see the embedding
		3971	section for details) and use the following F<evwrap.h> header file instead
		3972	of F<ev.h>:
		3973
		3974	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3975	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3976
		3977	#include "ev.h"
		3978
		3979	And compile the following F<evwrap.c> file into your project (make sure
		3980	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3981
		3982	#include "evwrap.h"
		3983	#include "ev.c"
		3984
		3985	=over 4
		3986
		3987	=item The winsocket select function
		3988
		3989	The winsocket C<select> function doesn't follow POSIX in that it
		3990	requires socket I<handles> and not socket I<file descriptors> (it is
		3991	also extremely buggy). This makes select very inefficient, and also
		3992	requires a mapping from file descriptors to socket handles (the Microsoft
		3993	C runtime provides the function C<_open_osfhandle> for this). See the
		3994	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3995	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3996
		3997	The configuration for a "naked" win32 using the Microsoft runtime
		3998	libraries and raw winsocket select is:
		3999
		4000	#define EV_USE_SELECT 1
		4001	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4002
		4003	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4004	complexity in the O(n²) range when using win32.
		4005
		4006	=item Limited number of file descriptors
		4007
		4008	Windows has numerous arbitrary (and low) limits on things.
		4009
		4010	Early versions of winsocket's select only supported waiting for a maximum
		4011	of C<64> handles (probably owning to the fact that all windows kernels
		4012	can only wait for C<64> things at the same time internally; Microsoft
		4013	recommends spawning a chain of threads and wait for 63 handles and the
		4014	previous thread in each. Sounds great!).
		4015
		4016	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4017	to some high number (e.g. C<2048>) before compiling the winsocket select
		4018	call (which might be in libev or elsewhere, for example, perl and many
		4019	other interpreters do their own select emulation on windows).
		4020
		4021	Another limit is the number of file descriptors in the Microsoft runtime
		4022	libraries, which by default is C<64> (there must be a hidden I<64>
		4023	fetish or something like this inside Microsoft). You can increase this
		4024	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4025	(another arbitrary limit), but is broken in many versions of the Microsoft
		4026	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4027	(depending on windows version and/or the phase of the moon). To get more,
		4028	you need to wrap all I/O functions and provide your own fd management, but
		4029	the cost of calling select (O(n²)) will likely make this unworkable.
		4030
		4031	=back
		4032
		4033	=head2 PORTABILITY REQUIREMENTS
		4034
		4035	In addition to a working ISO-C implementation and of course the
		4036	backend-specific APIs, libev relies on a few additional extensions:
		4037
		4038	=over 4
		4039
		4040	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4041	calling conventions regardless of C<ev_watcher_type *>.
		4042
		4043	Libev assumes not only that all watcher pointers have the same internal
		4044	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4045	assumes that the same (machine) code can be used to call any watcher
		4046	callback: The watcher callbacks have different type signatures, but libev
		4047	calls them using an C<ev_watcher *> internally.
		4048
		4049	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4050
		4051	The type C<sig_atomic_t volatile> (or whatever is defined as
		4052	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4053	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4054	believed to be sufficiently portable.
		4055
		4056	=item C<sigprocmask> must work in a threaded environment
		4057
		4058	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4059	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4060	pthread implementations will either allow C<sigprocmask> in the "main
		4061	thread" or will block signals process-wide, both behaviours would
		4062	be compatible with libev. Interaction between C<sigprocmask> and
		4063	C<pthread_sigmask> could complicate things, however.
		4064
		4065	The most portable way to handle signals is to block signals in all threads
		4066	except the initial one, and run the default loop in the initial thread as
		4067	well.
		4068
		4069	=item C<long> must be large enough for common memory allocation sizes
		4070
		4071	To improve portability and simplify its API, libev uses C<long> internally
		4072	instead of C<size_t> when allocating its data structures. On non-POSIX
		4073	systems (Microsoft...) this might be unexpectedly low, but is still at
		4074	least 31 bits everywhere, which is enough for hundreds of millions of
		4075	watchers.
		4076
		4077	=item C<double> must hold a time value in seconds with enough accuracy
		4078
		4079	The type C<double> is used to represent timestamps. It is required to
		4080	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4081	enough for at least into the year 4000. This requirement is fulfilled by
		4082	implementations implementing IEEE 754 (basically all existing ones).
		4083
		4084	=back
		4085
		4086	If you know of other additional requirements drop me a note.
		4087
		4088
2595	=head1 COMPLEXITIES	4089	=head1 ALGORITHMIC COMPLEXITIES
2596		4090
2597	In this section the complexities of (many of) the algorithms used inside	4091	In this section the complexities of (many of) the algorithms used inside
2598	libev will be explained. For complexity discussions about backends see the	4092	libev will be documented. For complexity discussions about backends see
2599	documentation for C<ev_default_init>.	4093	the documentation for C<ev_default_init>.
2600		4094
2601	All of the following are about amortised time: If an array needs to be	4095	All of the following are about amortised time: If an array needs to be
2602	extended, libev needs to realloc and move the whole array, but this	4096	extended, libev needs to realloc and move the whole array, but this
2603	happens asymptotically never with higher number of elements, so O(1) might	4097	happens asymptotically rarer with higher number of elements, so O(1) might
2604	mean it might do a lengthy realloc operation in rare cases, but on average	4098	mean that libev does a lengthy realloc operation in rare cases, but on
2605	it is much faster and asymptotically approaches constant time.	4099	average it is much faster and asymptotically approaches constant time.
2606		4100
2607	=over 4	4101	=over 4
2608		4102
2609	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4103	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2610		4104
2611	This means that, when you have a watcher that triggers in one hour and	4105	This means that, when you have a watcher that triggers in one hour and
2612	there are 100 watchers that would trigger before that then inserting will	4106	there are 100 watchers that would trigger before that, then inserting will
2613	have to skip those 100 watchers.	4107	have to skip roughly seven (C<ld 100>) of these watchers.
2614		4108
2615	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4109	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2616		4110
2617	That means that for changing a timer costs less than removing/adding them	4111	That means that changing a timer costs less than removing/adding them,
2618	as only the relative motion in the event queue has to be paid for.	4112	as only the relative motion in the event queue has to be paid for.
2619		4113
2620	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4114	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2621		4115
2622	These just add the watcher into an array or at the head of a list.	4116	These just add the watcher into an array or at the head of a list.
		4117
2623	=item Stopping check/prepare/idle watchers: O(1)	4118	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2624		4119
2625	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4120	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2626		4121
2627	These watchers are stored in lists then need to be walked to find the	4122	These watchers are stored in lists, so they need to be walked to find the
2628	correct watcher to remove. The lists are usually short (you don't usually	4123	correct watcher to remove. The lists are usually short (you don't usually
2629	have many watchers waiting for the same fd or signal).	4124	have many watchers waiting for the same fd or signal: one is typical, two
		4125	is rare).
2630		4126
2631	=item Finding the next timer per loop iteration: O(1)	4127	=item Finding the next timer in each loop iteration: O(1)
		4128
		4129	By virtue of using a binary or 4-heap, the next timer is always found at a
		4130	fixed position in the storage array.
2632		4131
2633	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4132	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2634		4133
2635	A change means an I/O watcher gets started or stopped, which requires	4134	A change means an I/O watcher gets started or stopped, which requires
2636	libev to recalculate its status (and possibly tell the kernel).	4135	libev to recalculate its status (and possibly tell the kernel, depending
		4136	on backend and whether C<ev_io_set> was used).
2637		4137
2638	=item Activating one watcher: O(1)	4138	=item Activating one watcher (putting it into the pending state): O(1)
2639		4139
2640	=item Priority handling: O(number_of_priorities)	4140	=item Priority handling: O(number_of_priorities)
2641		4141
2642	Priorities are implemented by allocating some space for each	4142	Priorities are implemented by allocating some space for each
2643	priority. When doing priority-based operations, libev usually has to	4143	priority. When doing priority-based operations, libev usually has to
2644	linearly search all the priorities.	4144	linearly search all the priorities, but starting/stopping and activating
		4145	watchers becomes O(1) with respect to priority handling.
		4146
		4147	=item Sending an ev_async: O(1)
		4148
		4149	=item Processing ev_async_send: O(number_of_async_watchers)
		4150
		4151	=item Processing signals: O(max_signal_number)
		4152
		4153	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4154	calls in the current loop iteration. Checking for async and signal events
		4155	involves iterating over all running async watchers or all signal numbers.
2645		4156
2646	=back	4157	=back
2647		4158
2648		4159
		4160	=head1 GLOSSARY
		4161
		4162	=over 4
		4163
		4164	=item active
		4165
		4166	A watcher is active as long as it has been started (has been attached to
		4167	an event loop) but not yet stopped (disassociated from the event loop).
		4168
		4169	=item application
		4170
		4171	In this document, an application is whatever is using libev.
		4172
		4173	=item callback
		4174
		4175	The address of a function that is called when some event has been
		4176	detected. Callbacks are being passed the event loop, the watcher that
		4177	received the event, and the actual event bitset.
		4178
		4179	=item callback invocation
		4180
		4181	The act of calling the callback associated with a watcher.
		4182
		4183	=item event
		4184
		4185	A change of state of some external event, such as data now being available
		4186	for reading on a file descriptor, time having passed or simply not having
		4187	any other events happening anymore.
		4188
		4189	In libev, events are represented as single bits (such as C<EV_READ> or
		4190	C<EV_TIMEOUT>).
		4191
		4192	=item event library
		4193
		4194	A software package implementing an event model and loop.
		4195
		4196	=item event loop
		4197
		4198	An entity that handles and processes external events and converts them
		4199	into callback invocations.
		4200
		4201	=item event model
		4202
		4203	The model used to describe how an event loop handles and processes
		4204	watchers and events.
		4205
		4206	=item pending
		4207
		4208	A watcher is pending as soon as the corresponding event has been detected,
		4209	and stops being pending as soon as the watcher will be invoked or its
		4210	pending status is explicitly cleared by the application.
		4211
		4212	A watcher can be pending, but not active. Stopping a watcher also clears
		4213	its pending status.
		4214
		4215	=item real time
		4216
		4217	The physical time that is observed. It is apparently strictly monotonic :)
		4218
		4219	=item wall-clock time
		4220
		4221	The time and date as shown on clocks. Unlike real time, it can actually
		4222	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4223	clock.
		4224
		4225	=item watcher
		4226
		4227	A data structure that describes interest in certain events. Watchers need
		4228	to be started (attached to an event loop) before they can receive events.
		4229
		4230	=item watcher invocation
		4231
		4232	The act of calling the callback associated with a watcher.
		4233
		4234	=back
		4235
2649	=head1 AUTHOR	4236	=head1 AUTHOR
2650		4237
2651	Marc Lehmann <libev@schmorp.de>.	4238	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2652		4239

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