ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.53 by root, Tue Nov 27 20:15:02 2007 UTC vs.
Revision 1.248 by root, Wed Jul 8 04:14:34 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	/* this is the only header you need */
8	#include <ev.h>	7	#include <ev.h>
9		8
10	/* what follows is a fully working example program */	9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
11	ev_io stdin_watcher;	18	ev_io stdin_watcher;
12	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
13		20
14	/* 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
15	static void	23	static void
16	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
17	{	25	{
18	/* puts ("stdin ready"); */	26	puts ("stdin ready");
19	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
20	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);
21	}	33	}
22		34
		35	// another callback, this time for a time-out
23	static void	36	static void
24	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
25	{	38	{
26	/* puts ("timeout"); */	39	puts ("timeout");
27	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);
28	}	42	}
29		43
30	int	44	int
31	main (void)	45	main (void)
32	{	46	{
		47	// use the default event loop unless you have special needs
33	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
34		49
35	/* 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
36	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);
37	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
38		54
		55	// initialise a timer watcher, then start it
39	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
40	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
41	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
42		59
43	/* loop till timeout or data ready */	60	// now wait for events to arrive
44	ev_loop (loop, 0);	61	ev_loop (loop, 0);
45		62
		63	// unloop was called, so exit
46	return 0;	64	return 0;
47	}	65	}
48		66
49	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
50		84
51	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
52	file descriptor being readable or a timeout occuring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
53	these event sources and provide your program with events.	87	these event sources and provide your program with events.
54		88
55	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
56	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
57	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
59	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
60	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
61	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
62	watcher.	96	watcher.
63		97
64	=head1 FEATURES	98	=head2 FEATURES
65		99
66	Libev supports select, poll, the linux-specific epoll and the bsd-specific	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
67	kqueue mechanisms for file descriptor events, relative timers, absolute	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
68	timers with customised rescheduling, signal events, process status change	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
69	events (related to SIGCHLD), and event watchers dealing with the event	103	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
70	loop mechanism itself (idle, prepare and check watchers). It also is quite	104	with customised rescheduling (C<ev_periodic>), synchronous signals
		105	(C<ev_signal>), process status change events (C<ev_child>), and event
		106	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		107	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		108	file watchers (C<ev_stat>) and even limited support for fork events
		109	(C<ev_fork>).
		110
		111	It also is quite fast (see this
71	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	112	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
72	it to libevent for example).	113	for example).
73		114
74	=head1 CONVENTIONS	115	=head2 CONVENTIONS
75		116
76	Libev is very configurable. In this manual the default configuration	117	Libev is very configurable. In this manual the default (and most common)
77	will be described, which supports multiple event loops. For more info	118	configuration will be described, which supports multiple event loops. For
78	about various configuration options please have a look at the file	119	more info about various configuration options please have a look at
79	F<README.embed> in the libev distribution. If libev was configured without	120	B<EMBED> section in this manual. If libev was configured without support
80	support for multiple event loops, then all functions taking an initial	121	for multiple event loops, then all functions taking an initial argument of
81	argument of name C<loop> (which is always of type C<struct ev_loop *>)	122	name C<loop> (which is always of type C<ev_loop *>) will not have
82	will not have this argument.	123	this argument.
83		124
84	=head1 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
85		126
86	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
87	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
88	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
89	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
90	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
91	it, you should treat it as such.	132	on it, you should treat it as some floating point value. Unlike the name
		133	component C<stamp> might indicate, it is also used for time differences
		134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
		155
92		156
93	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
94		158
95	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
96	library in any way.	160	library in any way.
…		…
101		165
102	Returns the current time as libev would use it. Please note that the	166	Returns the current time as libev would use it. Please note that the
103	C<ev_now> function is usually faster and also often returns the timestamp	167	C<ev_now> function is usually faster and also often returns the timestamp
104	you actually want to know.	168	you actually want to know.
105		169
		170	=item ev_sleep (ev_tstamp interval)
		171
		172	Sleep for the given interval: The current thread will be blocked until
		173	either it is interrupted or the given time interval has passed. Basically
		174	this is a sub-second-resolution C<sleep ()>.
		175
106	=item int ev_version_major ()	176	=item int ev_version_major ()
107		177
108	=item int ev_version_minor ()	178	=item int ev_version_minor ()
109		179
110	You can find out the major and minor version numbers of the library	180	You can find out the major and minor ABI version numbers of the library
111	you linked against by calling the functions C<ev_version_major> and	181	you linked against by calling the functions C<ev_version_major> and
112	C<ev_version_minor>. If you want, you can compare against the global	182	C<ev_version_minor>. If you want, you can compare against the global
113	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	183	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
114	version of the library your program was compiled against.	184	version of the library your program was compiled against.
115		185
		186	These version numbers refer to the ABI version of the library, not the
		187	release version.
		188
116	Usually, it's a good idea to terminate if the major versions mismatch,	189	Usually, it's a good idea to terminate if the major versions mismatch,
117	as this indicates an incompatible change. Minor versions are usually	190	as this indicates an incompatible change. Minor versions are usually
118	compatible to older versions, so a larger minor version alone is usually	191	compatible to older versions, so a larger minor version alone is usually
119	not a problem.	192	not a problem.
120		193
121	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
122	version:	195	version.
123		196
124	assert (("libev version mismatch",	197	assert (("libev version mismatch",
125	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
126	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
127		200
128	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
129		202
130	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_*>
131	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
133	a description of the set values.	206	a description of the set values.
134		207
135	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
136	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
137		210
138	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
139	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
140		213
141	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
142		215
143	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
144	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
145	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
146	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
147	(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
148	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
149		222
150	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
151		224
…		…
155	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
156	recommended ones.	229	recommended ones.
157		230
158	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
159		232
160	=item ev_set_allocator (void *(*cb)(void *ptr, size_t size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
161		234
162	Sets the allocation function to use (the prototype and semantics are	235	Sets the allocation function to use (the prototype is similar - the
163	identical to the realloc C function). It is used to allocate and free	236	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
164	memory (no surprises here). If it returns zero when memory needs to be	237	used to allocate and free memory (no surprises here). If it returns zero
165	allocated, the library might abort or take some potentially destructive	238	when memory needs to be allocated (C<size != 0>), the library might abort
166	action. The default is your system realloc function.	239	or take some potentially destructive action.
		240
		241	Since some systems (at least OpenBSD and Darwin) fail to implement
		242	correct C<realloc> semantics, libev will use a wrapper around the system
		243	C<realloc> and C<free> functions by default.
167		244
168	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
169	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,
170	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.
171		248
172	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
173	retries: better than mine).	250	retries (example requires a standards-compliant C<realloc>).
174		251
175	static void *	252	static void *
176	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
177	{	254	{
178	for (;;)	255	for (;;)
…		…
187	}	264	}
188		265
189	...	266	...
190	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
191		268
192	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
193		270
194	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
195	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
196	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
197	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
198	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
199	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
200	(such as abort).	277	(such as abort).
201		278
202	Example: do the same thing as libev does internally:	279	Example: This is basically the same thing that libev does internally, too.
203		280
204	static void	281	static void
205	fatal_error (const char *msg)	282	fatal_error (const char *msg)
206	{	283	{
207	perror (msg);	284	perror (msg);
…		…
213		290
214	=back	291	=back
215		292
216	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
217		294
218	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>
219	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>
220	events, and dynamically created loops which do not.	297	I<function>).
221		298
222	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
223	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
224	create, you also create another event loop. Libev itself does no locking	301	not.
225	whatsoever, so if you mix calls to the same event loop in different
226	threads, make sure you lock (this is usually a bad idea, though, even if
227	done correctly, because it's hideous and inefficient).
228		302
229	=over 4	303	=over 4
230		304
231	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
232		306
…		…
236	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
237		311
238	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
239	function.	313	function.
240		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
241	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
242	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>).
243		328
244	The following flags are supported:	329	The following flags are supported:
245		330
…		…
250	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
251	thing, believe me).	336	thing, believe me).
252		337
253	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
254		339
255	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
256	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
257	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
258	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
259	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
260	around bugs.	345	around bugs.
261		346
		347	=item C<EVFLAG_FORKCHECK>
		348
		349	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		350	a fork, you can also make libev check for a fork in each iteration by
		351	enabling this flag.
		352
		353	This works by calling C<getpid ()> on every iteration of the loop,
		354	and thus this might slow down your event loop if you do a lot of loop
		355	iterations and little real work, but is usually not noticeable (on my
		356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		357	without a system call and thus I<very> fast, but my GNU/Linux system also has
		358	C<pthread_atfork> which is even faster).
		359
		360	The big advantage of this flag is that you can forget about fork (and
		361	forget about forgetting to tell libev about forking) when you use this
		362	flag.
		363
		364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		365	environment variable.
		366
262	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
263		368
264	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
265	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,
266	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
267	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
268	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).
269		385
270	=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)
271		387
272	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
273	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
274	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
275	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>.
276		397
277	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
278		399
279	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,
280	but it scales phenomenally better. While poll and select usually scale like	401	but it scales phenomenally better. While poll and select usually scale
281	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	402	like O(total_fds) where n is the total number of fds (or the highest fd),
282	either O(1) or O(active_fds).	403	epoll scales either O(1) or O(active_fds).
283		404
		405	The epoll mechanism deserves honorable mention as the most misdesigned
		406	of the more advanced event mechanisms: mere annoyances include silently
		407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
		421
284	While stopping and starting an I/O watcher in the same iteration will	422	While stopping, setting and starting an I/O watcher in the same iteration
285	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
286	(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
287	best to avoid that. Also, dup()ed file descriptors might not work very	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
288	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.
289		428
290	Please note that epoll sometimes generates spurious notifications, so you	429	Best performance from this backend is achieved by not unregistering all
291	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,
292	(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>.
293		446
294	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
295		448
296	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
297	was broken on all BSDs except NetBSD (usually it doesn't work with	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
298	anything but sockets and pipes, except on Darwin, where of course its	451	with anything but sockets and pipes, except on Darwin, where of course
299	completely useless). For this reason its not being "autodetected"	452	it's completely useless). Unlike epoll, however, whose brokenness
		453	is by design, these kqueue bugs can (and eventually will) be fixed
		454	without API changes to existing programs. For this reason it's not being
300	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
301	C<EVBACKEND_KQUEUE>).	456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		457	system like NetBSD.
		458
		459	You still can embed kqueue into a normal poll or select backend and use it
		460	only for sockets (after having made sure that sockets work with kqueue on
		461	the target platform). See C<ev_embed> watchers for more info.
302		462
303	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
304	kernel is more efficient (which says nothing about its actual speed, of	464	kernel is more efficient (which says nothing about its actual speed, of
305	course). While starting and stopping an I/O watcher does not cause an	465	course). While stopping, setting and starting an I/O watcher does never
306	extra syscall as with epoll, it still adds up to four event changes per	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
307	incident, so its best to avoid that.	467	two event changes per incident. Support for C<fork ()> is very bad (but
		468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
		470
		471	This backend usually performs well under most conditions.
		472
		473	While nominally embeddable in other event loops, this doesn't work
		474	everywhere, so you might need to test for this. And since it is broken
		475	almost everywhere, you should only use it when you have a lot of sockets
		476	(for which it usually works), by embedding it into another event loop
		477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		478	also broken on OS X)) and, did I mention it, using it only for sockets.
		479
		480	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		482	C<NOTE_EOF>.
308		483
309	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
310		485
311	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.
312		490
313	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
314		492
315	This uses the Solaris 10 port mechanism. As with everything on Solaris,	493	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
316	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)).
317		495
318	Please note that solaris ports can result in a lot of spurious	496	Please note that Solaris event ports can deliver a lot of spurious
319	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
320	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>.
321		512
322	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
323		514
324	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
325	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
326	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	517	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
327		518
		519	It is definitely not recommended to use this flag.
		520
328	=back	521	=back
329		522
330	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
331	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
332	specified, most compiled-in backend will be tried, usually in reverse	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
333	order of their flag values :)
334		526
335	The most typical usage is like this:	527	Example: This is the most typical usage.
336		528
337	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
338	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
339		531
340	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
341	environment settings to be taken into account:	533	environment settings to be taken into account:
342		534
343	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
344		536
345	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
346	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
347	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):
348		541
349	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
350		543
351	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
352		545
353	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
354	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
355	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
356	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
357		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
358	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.
359		556
360	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
361	if (!epoller)	558	if (!epoller)
362	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
363		560
364	=item ev_default_destroy ()	561	=item ev_default_destroy ()
365		562
366	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
367	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
368	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
369	responsibility to either stop all watchers cleanly yoursef I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
370	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
371	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
372	for example).	569	for example).
		570
		571	Note that certain global state, such as signal state (and installed signal
		572	handlers), will not be freed by this function, and related watchers (such
		573	as signal and child watchers) would need to be stopped manually.
		574
		575	In general it is not advisable to call this function except in the
		576	rare occasion where you really need to free e.g. the signal handling
		577	pipe fds. If you need dynamically allocated loops it is better to use
		578	C<ev_loop_new> and C<ev_loop_destroy>).
373		579
374	=item ev_loop_destroy (loop)	580	=item ev_loop_destroy (loop)
375		581
376	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
377	earlier call to C<ev_loop_new>.	583	earlier call to C<ev_loop_new>.
378		584
379	=item ev_default_fork ()	585	=item ev_default_fork ()
380		586
		587	This function sets a flag that causes subsequent C<ev_loop> iterations
381	This function reinitialises the kernel state for backends that have	588	to reinitialise the kernel state for backends that have one. Despite the
382	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
383	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
384	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.
385		593
386	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
387	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
388	fork+exec, you don't have to call it.	596	you just fork+exec, you don't have to call it at all.
389		597
390	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
391	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
392	quite nicely into a call to C<pthread_atfork>:	600	quite nicely into a call to C<pthread_atfork>:
393		601
394	pthread_atfork (0, 0, ev_default_fork);	602	pthread_atfork (0, 0, ev_default_fork);
395		603
396	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
397	without calling this function, so if you force one of those backends you
398	do not need to care.
399
400	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
401		605
402	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
403	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
404	after fork, and how you do this is entirely your own problem.	608	after fork that you want to re-use in the child, and how you do this is
		609	entirely your own problem.
		610
		611	=item int ev_is_default_loop (loop)
		612
		613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
		615
		616	=item unsigned int ev_loop_count (loop)
		617
		618	Returns the count of loop iterations for the loop, which is identical to
		619	the number of times libev did poll for new events. It starts at C<0> and
		620	happily wraps around with enough iterations.
		621
		622	This value can sometimes be useful as a generation counter of sorts (it
		623	"ticks" the number of loop iterations), as it roughly corresponds with
		624	C<ev_prepare> and C<ev_check> calls.
		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
405		637
406	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
407		639
408	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
409	use.	641	use.
…		…
412		644
413	Returns the current "event loop time", which is the time the event loop	645	Returns the current "event loop time", which is the time the event loop
414	received events and started processing them. This timestamp does not	646	received events and started processing them. This timestamp does not
415	change as long as callbacks are being processed, and this is also the base	647	change as long as callbacks are being processed, and this is also the base
416	time used for relative timers. You can treat it as the timestamp of the	648	time used for relative timers. You can treat it as the timestamp of the
417	event occuring (or more correctly, libev finding out about it).	649	event occurring (or more correctly, libev finding out about it).
		650
		651	=item ev_now_update (loop)
		652
		653	Establishes the current time by querying the kernel, updating the time
		654	returned by C<ev_now ()> in the progress. This is a costly operation and
		655	is usually done automatically within C<ev_loop ()>.
		656
		657	This function is rarely useful, but when some event callback runs for a
		658	very long time without entering the event loop, updating libev's idea of
		659	the current time is a good idea.
		660
		661	See also L<The special problem of time updates> in the C<ev_timer> section.
		662
		663	=item ev_suspend (loop)
		664
		665	=item ev_resume (loop)
		666
		667	These two functions suspend and resume a loop, for use when the loop is
		668	not used for a while and timeouts should not be processed.
		669
		670	A typical use case would be an interactive program such as a game: When
		671	the user presses C<^Z> to suspend the game and resumes it an hour later it
		672	would be best to handle timeouts as if no time had actually passed while
		673	the program was suspended. This can be achieved by calling C<ev_suspend>
		674	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		675	C<ev_resume> directly afterwards to resume timer processing.
		676
		677	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		678	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		679	will be rescheduled (that is, they will lose any events that would have
		680	occured while suspended).
		681
		682	After calling C<ev_suspend> you B<must not> call I<any> function on the
		683	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		684	without a previous call to C<ev_suspend>.
		685
		686	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		687	event loop time (see C<ev_now_update>).
418		688
419	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
420		690
421	Finally, this is it, the event handler. This function usually is called	691	Finally, this is it, the event handler. This function usually is called
422	after you initialised all your watchers and you want to start handling	692	after you initialised all your watchers and you want to start handling
…		…
425	If the flags argument is specified as C<0>, it will not return until	695	If the flags argument is specified as C<0>, it will not return until
426	either no event watchers are active anymore or C<ev_unloop> was called.	696	either no event watchers are active anymore or C<ev_unloop> was called.
427		697
428	Please note that an explicit C<ev_unloop> is usually better than	698	Please note that an explicit C<ev_unloop> is usually better than
429	relying on all watchers to be stopped when deciding when a program has	699	relying on all watchers to be stopped when deciding when a program has
430	finished (especially in interactive programs), but having a program that	700	finished (especially in interactive programs), but having a program
431	automatically loops as long as it has to and no longer by virtue of	701	that automatically loops as long as it has to and no longer by virtue
432	relying on its watchers stopping correctly is a thing of beauty.	702	of relying on its watchers stopping correctly, that is truly a thing of
		703	beauty.
433		704
434	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	705	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
435	those events and any outstanding ones, but will not block your process in	706	those events and any already outstanding ones, but will not block your
436	case there are no events and will return after one iteration of the loop.	707	process in case there are no events and will return after one iteration of
		708	the loop.
437		709
438	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	710	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
439	neccessary) and will handle those and any outstanding ones. It will block	711	necessary) and will handle those and any already outstanding ones. It
440	your process until at least one new event arrives, and will return after	712	will block your process until at least one new event arrives (which could
441	one iteration of the loop. This is useful if you are waiting for some	713	be an event internal to libev itself, so there is no guarantee that a
442	external event in conjunction with something not expressible using other	714	user-registered callback will be called), and will return after one
		715	iteration of the loop.
		716
		717	This is useful if you are waiting for some external event in conjunction
		718	with something not expressible using other libev watchers (i.e. "roll your
443	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	719	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
444	usually a better approach for this kind of thing.	720	usually a better approach for this kind of thing.
445		721
446	Here are the gory details of what C<ev_loop> does:	722	Here are the gory details of what C<ev_loop> does:
447		723
448	* If there are no active watchers (reference count is zero), return.	724	- Before the first iteration, call any pending watchers.
449	- Queue prepare watchers and then call all outstanding watchers.	725	* If EVFLAG_FORKCHECK was used, check for a fork.
		726	- If a fork was detected (by any means), queue and call all fork watchers.
		727	- Queue and call all prepare watchers.
450	- If we have been forked, recreate the kernel state.	728	- If we have been forked, detach and recreate the kernel state
		729	as to not disturb the other process.
451	- Update the kernel state with all outstanding changes.	730	- Update the kernel state with all outstanding changes.
452	- Update the "event loop time".	731	- Update the "event loop time" (ev_now ()).
453	- Calculate for how long to block.	732	- Calculate for how long to sleep or block, if at all
		733	(active idle watchers, EVLOOP_NONBLOCK or not having
		734	any active watchers at all will result in not sleeping).
		735	- Sleep if the I/O and timer collect interval say so.
454	- Block the process, waiting for any events.	736	- Block the process, waiting for any events.
455	- Queue all outstanding I/O (fd) events.	737	- Queue all outstanding I/O (fd) events.
456	- Update the "event loop time" and do time jump handling.	738	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
457	- Queue all outstanding timers.	739	- Queue all expired timers.
458	- Queue all outstanding periodics.	740	- Queue all expired periodics.
459	- If no events are pending now, queue all idle watchers.	741	- Unless any events are pending now, queue all idle watchers.
460	- Queue all check watchers.	742	- Queue all check watchers.
461	- Call all queued watchers in reverse order (i.e. check watchers first).	743	- Call all queued watchers in reverse order (i.e. check watchers first).
462	Signals and child watchers are implemented as I/O watchers, and will	744	Signals and child watchers are implemented as I/O watchers, and will
463	be handled here by queueing them when their watcher gets executed.	745	be handled here by queueing them when their watcher gets executed.
464	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	746	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
465	were used, return, otherwise continue with step *.	747	were used, or there are no active watchers, return, otherwise
		748	continue with step *.
466		749
467	Example: queue some jobs and then loop until no events are outsanding	750	Example: Queue some jobs and then loop until no events are outstanding
468	anymore.	751	anymore.
469		752
470	... queue jobs here, make sure they register event watchers as long	753	... queue jobs here, make sure they register event watchers as long
471	... as they still have work to do (even an idle watcher will do..)	754	... as they still have work to do (even an idle watcher will do..)
472	ev_loop (my_loop, 0);	755	ev_loop (my_loop, 0);
473	... jobs done. yeah!	756	... jobs done or somebody called unloop. yeah!
474		757
475	=item ev_unloop (loop, how)	758	=item ev_unloop (loop, how)
476		759
477	Can be used to make a call to C<ev_loop> return early (but only after it	760	Can be used to make a call to C<ev_loop> return early (but only after it
478	has processed all outstanding events). The C<how> argument must be either	761	has processed all outstanding events). The C<how> argument must be either
479	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	762	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
480	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	763	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
481		764
		765	This "unloop state" will be cleared when entering C<ev_loop> again.
		766
		767	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		768
482	=item ev_ref (loop)	769	=item ev_ref (loop)
483		770
484	=item ev_unref (loop)	771	=item ev_unref (loop)
485		772
486	Ref/unref can be used to add or remove a reference count on the event	773	Ref/unref can be used to add or remove a reference count on the event
487	loop: Every watcher keeps one reference, and as long as the reference	774	loop: Every watcher keeps one reference, and as long as the reference
488	count is nonzero, C<ev_loop> will not return on its own. If you have	775	count is nonzero, C<ev_loop> will not return on its own.
		776
489	a watcher you never unregister that should not keep C<ev_loop> from	777	If you have a watcher you never unregister that should not keep C<ev_loop>
490	returning, ev_unref() after starting, and ev_ref() before stopping it. For	778	from returning, call ev_unref() after starting, and ev_ref() before
		779	stopping it.
		780
491	example, libev itself uses this for its internal signal pipe: It is not	781	As an example, libev itself uses this for its internal signal pipe: It
492	visible to the libev user and should not keep C<ev_loop> from exiting if	782	is not visible to the libev user and should not keep C<ev_loop> from
493	no event watchers registered by it are active. It is also an excellent	783	exiting if no event watchers registered by it are active. It is also an
494	way to do this for generic recurring timers or from within third-party	784	excellent way to do this for generic recurring timers or from within
495	libraries. Just remember to I<unref after start> and I<ref before stop>.	785	third-party libraries. Just remember to I<unref after start> and I<ref
		786	before stop> (but only if the watcher wasn't active before, or was active
		787	before, respectively. Note also that libev might stop watchers itself
		788	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		789	in the callback).
496		790
497	Example: create a signal watcher, but keep it from keeping C<ev_loop>	791	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
498	running when nothing else is active.	792	running when nothing else is active.
499		793
500	struct dv_signal exitsig;	794	ev_signal exitsig;
501	ev_signal_init (&exitsig, sig_cb, SIGINT);	795	ev_signal_init (&exitsig, sig_cb, SIGINT);
502	ev_signal_start (myloop, &exitsig);	796	ev_signal_start (loop, &exitsig);
503	evf_unref (myloop);	797	evf_unref (loop);
504		798
505	Example: for some weird reason, unregister the above signal handler again.	799	Example: For some weird reason, unregister the above signal handler again.
506		800
507	ev_ref (myloop);	801	ev_ref (loop);
508	ev_signal_stop (myloop, &exitsig);	802	ev_signal_stop (loop, &exitsig);
		803
		804	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		805
		806	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		807
		808	These advanced functions influence the time that libev will spend waiting
		809	for events. Both time intervals are by default C<0>, meaning that libev
		810	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		811	latency.
		812
		813	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		814	allows libev to delay invocation of I/O and timer/periodic callbacks
		815	to increase efficiency of loop iterations (or to increase power-saving
		816	opportunities).
		817
		818	The idea is that sometimes your program runs just fast enough to handle
		819	one (or very few) event(s) per loop iteration. While this makes the
		820	program responsive, it also wastes a lot of CPU time to poll for new
		821	events, especially with backends like C<select ()> which have a high
		822	overhead for the actual polling but can deliver many events at once.
		823
		824	By setting a higher I<io collect interval> you allow libev to spend more
		825	time collecting I/O events, so you can handle more events per iteration,
		826	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		827	C<ev_timer>) will be not affected. Setting this to a non-null value will
		828	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		829	sleep time ensures that libev will not poll for I/O events more often then
		830	once per this interval, on average.
		831
		832	Likewise, by setting a higher I<timeout collect interval> you allow libev
		833	to spend more time collecting timeouts, at the expense of increased
		834	latency/jitter/inexactness (the watcher callback will be called
		835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		836	value will not introduce any overhead in libev.
		837
		838	Many (busy) programs can usually benefit by setting the I/O collect
		839	interval to a value near C<0.1> or so, which is often enough for
		840	interactive servers (of course not for games), likewise for timeouts. It
		841	usually doesn't make much sense to set it to a lower value than C<0.01>,
		842	as this approaches the timing granularity of most systems. Note that if
		843	you do transactions with the outside world and you can't increase the
		844	parallelity, then this setting will limit your transaction rate (if you
		845	need to poll once per transaction and the I/O collect interval is 0.01,
		846	then you can't do more than 100 transations per second).
		847
		848	Setting the I<timeout collect interval> can improve the opportunity for
		849	saving power, as the program will "bundle" timer callback invocations that
		850	are "near" in time together, by delaying some, thus reducing the number of
		851	times the process sleeps and wakes up again. Another useful technique to
		852	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		853	they fire on, say, one-second boundaries only.
		854
		855	Example: we only need 0.1s timeout granularity, and we wish not to poll
		856	more often than 100 times per second:
		857
		858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		860
		861	=item ev_loop_verify (loop)
		862
		863	This function only does something when C<EV_VERIFY> support has been
		864	compiled in, which is the default for non-minimal builds. It tries to go
		865	through all internal structures and checks them for validity. If anything
		866	is found to be inconsistent, it will print an error message to standard
		867	error and call C<abort ()>.
		868
		869	This can be used to catch bugs inside libev itself: under normal
		870	circumstances, this function will never abort as of course libev keeps its
		871	data structures consistent.
509		872
510	=back	873	=back
511		874
512		875
513	=head1 ANATOMY OF A WATCHER	876	=head1 ANATOMY OF A WATCHER
		877
		878	In the following description, uppercase C<TYPE> in names stands for the
		879	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		880	watchers and C<ev_io_start> for I/O watchers.
514		881
515	A watcher is a structure that you create and register to record your	882	A watcher is a structure that you create and register to record your
516	interest in some event. For instance, if you want to wait for STDIN to	883	interest in some event. For instance, if you want to wait for STDIN to
517	become readable, you would create an C<ev_io> watcher for that:	884	become readable, you would create an C<ev_io> watcher for that:
518		885
519	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	886	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
520	{	887	{
521	ev_io_stop (w);	888	ev_io_stop (w);
522	ev_unloop (loop, EVUNLOOP_ALL);	889	ev_unloop (loop, EVUNLOOP_ALL);
523	}	890	}
524		891
525	struct ev_loop *loop = ev_default_loop (0);	892	struct ev_loop *loop = ev_default_loop (0);
		893
526	struct ev_io stdin_watcher;	894	ev_io stdin_watcher;
		895
527	ev_init (&stdin_watcher, my_cb);	896	ev_init (&stdin_watcher, my_cb);
528	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	897	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
529	ev_io_start (loop, &stdin_watcher);	898	ev_io_start (loop, &stdin_watcher);
		899
530	ev_loop (loop, 0);	900	ev_loop (loop, 0);
531		901
532	As you can see, you are responsible for allocating the memory for your	902	As you can see, you are responsible for allocating the memory for your
533	watcher structures (and it is usually a bad idea to do this on the stack,	903	watcher structures (and it is I<usually> a bad idea to do this on the
534	although this can sometimes be quite valid).	904	stack).
		905
		906	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		907	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
535		908
536	Each watcher structure must be initialised by a call to C<ev_init	909	Each watcher structure must be initialised by a call to C<ev_init
537	(watcher *, callback)>, which expects a callback to be provided. This	910	(watcher *, callback)>, which expects a callback to be provided. This
538	callback gets invoked each time the event occurs (or, in the case of io	911	callback gets invoked each time the event occurs (or, in the case of I/O
539	watchers, each time the event loop detects that the file descriptor given	912	watchers, each time the event loop detects that the file descriptor given
540	is readable and/or writable).	913	is readable and/or writable).
541		914
542	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	915	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
543	with arguments specific to this watcher type. There is also a macro	916	macro to configure it, with arguments specific to the watcher type. There
544	to combine initialisation and setting in one call: C<< ev_<type>_init	917	is also a macro to combine initialisation and setting in one call: C<<
545	(watcher *, callback, ...) >>.	918	ev_TYPE_init (watcher *, callback, ...) >>.
546		919
547	To make the watcher actually watch out for events, you have to start it	920	To make the watcher actually watch out for events, you have to start it
548	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	921	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
549	*) >>), and you can stop watching for events at any time by calling the	922	*) >>), and you can stop watching for events at any time by calling the
550	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	923	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
551		924
552	As long as your watcher is active (has been started but not stopped) you	925	As long as your watcher is active (has been started but not stopped) you
553	must not touch the values stored in it. Most specifically you must never	926	must not touch the values stored in it. Most specifically you must never
554	reinitialise it or call its C<set> macro.	927	reinitialise it or call its C<ev_TYPE_set> macro.
555		928
556	Each and every callback receives the event loop pointer as first, the	929	Each and every callback receives the event loop pointer as first, the
557	registered watcher structure as second, and a bitset of received events as	930	registered watcher structure as second, and a bitset of received events as
558	third argument.	931	third argument.
559		932
…		…
613	=item C<EV_FORK>	986	=item C<EV_FORK>
614		987
615	The event loop has been resumed in the child process after fork (see	988	The event loop has been resumed in the child process after fork (see
616	C<ev_fork>).	989	C<ev_fork>).
617		990
		991	=item C<EV_ASYNC>
		992
		993	The given async watcher has been asynchronously notified (see C<ev_async>).
		994
		995	=item C<EV_CUSTOM>
		996
		997	Not ever sent (or otherwise used) by libev itself, but can be freely used
		998	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		999
618	=item C<EV_ERROR>	1000	=item C<EV_ERROR>
619		1001
620	An unspecified error has occured, the watcher has been stopped. This might	1002	An unspecified error has occurred, the watcher has been stopped. This might
621	happen because the watcher could not be properly started because libev	1003	happen because the watcher could not be properly started because libev
622	ran out of memory, a file descriptor was found to be closed or any other	1004	ran out of memory, a file descriptor was found to be closed or any other
		1005	problem. Libev considers these application bugs.
		1006
623	problem. You best act on it by reporting the problem and somehow coping	1007	You best act on it by reporting the problem and somehow coping with the
624	with the watcher being stopped.	1008	watcher being stopped. Note that well-written programs should not receive
		1009	an error ever, so when your watcher receives it, this usually indicates a
		1010	bug in your program.
625		1011
626	Libev will usually signal a few "dummy" events together with an error,	1012	Libev will usually signal a few "dummy" events together with an error, for
627	for example it might indicate that a fd is readable or writable, and if	1013	example it might indicate that a fd is readable or writable, and if your
628	your callbacks is well-written it can just attempt the operation and cope	1014	callbacks is well-written it can just attempt the operation and cope with
629	with the error from read() or write(). This will not work in multithreaded	1015	the error from read() or write(). This will not work in multi-threaded
630	programs, though, so beware.	1016	programs, though, as the fd could already be closed and reused for another
		1017	thing, so beware.
631		1018
632	=back	1019	=back
633		1020
634	=head2 GENERIC WATCHER FUNCTIONS	1021	=head2 GENERIC WATCHER FUNCTIONS
635
636	In the following description, C<TYPE> stands for the watcher type,
637	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
638		1022
639	=over 4	1023	=over 4
640		1024
641	=item C<ev_init> (ev_TYPE *watcher, callback)	1025	=item C<ev_init> (ev_TYPE *watcher, callback)
642		1026
…		…
648	which rolls both calls into one.	1032	which rolls both calls into one.
649		1033
650	You can reinitialise a watcher at any time as long as it has been stopped	1034	You can reinitialise a watcher at any time as long as it has been stopped
651	(or never started) and there are no pending events outstanding.	1035	(or never started) and there are no pending events outstanding.
652		1036
653	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1037	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
654	int revents)>.	1038	int revents)>.
		1039
		1040	Example: Initialise an C<ev_io> watcher in two steps.
		1041
		1042	ev_io w;
		1043	ev_init (&w, my_cb);
		1044	ev_io_set (&w, STDIN_FILENO, EV_READ);
655		1045
656	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1046	=item C<ev_TYPE_set> (ev_TYPE *, [args])
657		1047
658	This macro initialises the type-specific parts of a watcher. You need to	1048	This macro initialises the type-specific parts of a watcher. You need to
659	call C<ev_init> at least once before you call this macro, but you can	1049	call C<ev_init> at least once before you call this macro, but you can
…		…
662	difference to the C<ev_init> macro).	1052	difference to the C<ev_init> macro).
663		1053
664	Although some watcher types do not have type-specific arguments	1054	Although some watcher types do not have type-specific arguments
665	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1055	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
666		1056
		1057	See C<ev_init>, above, for an example.
		1058
667	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1059	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
668		1060
669	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1061	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
670	calls into a single call. This is the most convinient method to initialise	1062	calls into a single call. This is the most convenient method to initialise
671	a watcher. The same limitations apply, of course.	1063	a watcher. The same limitations apply, of course.
		1064
		1065	Example: Initialise and set an C<ev_io> watcher in one step.
		1066
		1067	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
672		1068
673	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1069	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
674		1070
675	Starts (activates) the given watcher. Only active watchers will receive	1071	Starts (activates) the given watcher. Only active watchers will receive
676	events. If the watcher is already active nothing will happen.	1072	events. If the watcher is already active nothing will happen.
677		1073
		1074	Example: Start the C<ev_io> watcher that is being abused as example in this
		1075	whole section.
		1076
		1077	ev_io_start (EV_DEFAULT_UC, &w);
		1078
678	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1079	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
679		1080
680	Stops the given watcher again (if active) and clears the pending	1081	Stops the given watcher if active, and clears the pending status (whether
		1082	the watcher was active or not).
		1083
681	status. It is possible that stopped watchers are pending (for example,	1084	It is possible that stopped watchers are pending - for example,
682	non-repeating timers are being stopped when they become pending), but	1085	non-repeating timers are being stopped when they become pending - but
683	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1086	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
684	you want to free or reuse the memory used by the watcher it is therefore a	1087	pending. If you want to free or reuse the memory used by the watcher it is
685	good idea to always call its C<ev_TYPE_stop> function.	1088	therefore a good idea to always call its C<ev_TYPE_stop> function.
686		1089
687	=item bool ev_is_active (ev_TYPE *watcher)	1090	=item bool ev_is_active (ev_TYPE *watcher)
688		1091
689	Returns a true value iff the watcher is active (i.e. it has been started	1092	Returns a true value iff the watcher is active (i.e. it has been started
690	and not yet been stopped). As long as a watcher is active you must not modify	1093	and not yet been stopped). As long as a watcher is active you must not modify
…		…
693	=item bool ev_is_pending (ev_TYPE *watcher)	1096	=item bool ev_is_pending (ev_TYPE *watcher)
694		1097
695	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1098	Returns a true value iff the watcher is pending, (i.e. it has outstanding
696	events but its callback has not yet been invoked). As long as a watcher	1099	events but its callback has not yet been invoked). As long as a watcher
697	is pending (but not active) you must not call an init function on it (but	1100	is pending (but not active) you must not call an init function on it (but
698	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1101	C<ev_TYPE_set> is safe), you must not change its priority, and you must
699	libev (e.g. you cnanot C<free ()> it).	1102	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1103	it).
700		1104
701	=item callback = ev_cb (ev_TYPE *watcher)	1105	=item callback ev_cb (ev_TYPE *watcher)
702		1106
703	Returns the callback currently set on the watcher.	1107	Returns the callback currently set on the watcher.
704		1108
705	=item ev_cb_set (ev_TYPE *watcher, callback)	1109	=item ev_cb_set (ev_TYPE *watcher, callback)
706		1110
707	Change the callback. You can change the callback at virtually any time	1111	Change the callback. You can change the callback at virtually any time
708	(modulo threads).	1112	(modulo threads).
709		1113
		1114	=item ev_set_priority (ev_TYPE *watcher, priority)
		1115
		1116	=item int ev_priority (ev_TYPE *watcher)
		1117
		1118	Set and query the priority of the watcher. The priority is a small
		1119	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1120	(default: C<-2>). Pending watchers with higher priority will be invoked
		1121	before watchers with lower priority, but priority will not keep watchers
		1122	from being executed (except for C<ev_idle> watchers).
		1123
		1124	If you need to suppress invocation when higher priority events are pending
		1125	you need to look at C<ev_idle> watchers, which provide this functionality.
		1126
		1127	You I<must not> change the priority of a watcher as long as it is active or
		1128	pending.
		1129
		1130	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1131	fine, as long as you do not mind that the priority value you query might
		1132	or might not have been clamped to the valid range.
		1133
		1134	The default priority used by watchers when no priority has been set is
		1135	always C<0>, which is supposed to not be too high and not be too low :).
		1136
		1137	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1138	priorities.
		1139
		1140	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1141
		1142	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1143	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1144	can deal with that fact, as both are simply passed through to the
		1145	callback.
		1146
		1147	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1148
		1149	If the watcher is pending, this function clears its pending status and
		1150	returns its C<revents> bitset (as if its callback was invoked). If the
		1151	watcher isn't pending it does nothing and returns C<0>.
		1152
		1153	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1154	callback to be invoked, which can be accomplished with this function.
		1155
710	=back	1156	=back
711		1157
712		1158
713	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1159	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
714		1160
715	Each watcher has, by default, a member C<void *data> that you can change	1161	Each watcher has, by default, a member C<void *data> that you can change
716	and read at any time, libev will completely ignore it. This can be used	1162	and read at any time: libev will completely ignore it. This can be used
717	to associate arbitrary data with your watcher. If you need more data and	1163	to associate arbitrary data with your watcher. If you need more data and
718	don't want to allocate memory and store a pointer to it in that data	1164	don't want to allocate memory and store a pointer to it in that data
719	member, you can also "subclass" the watcher type and provide your own	1165	member, you can also "subclass" the watcher type and provide your own
720	data:	1166	data:
721		1167
722	struct my_io	1168	struct my_io
723	{	1169	{
724	struct ev_io io;	1170	ev_io io;
725	int otherfd;	1171	int otherfd;
726	void *somedata;	1172	void *somedata;
727	struct whatever *mostinteresting;	1173	struct whatever *mostinteresting;
728	}	1174	};
		1175
		1176	...
		1177	struct my_io w;
		1178	ev_io_init (&w.io, my_cb, fd, EV_READ);
729		1179
730	And since your callback will be called with a pointer to the watcher, you	1180	And since your callback will be called with a pointer to the watcher, you
731	can cast it back to your own type:	1181	can cast it back to your own type:
732		1182
733	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1183	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
734	{	1184	{
735	struct my_io *w = (struct my_io *)w_;	1185	struct my_io *w = (struct my_io *)w_;
736	...	1186	...
737	}	1187	}
738		1188
739	More interesting and less C-conformant ways of catsing your callback type	1189	More interesting and less C-conformant ways of casting your callback type
740	have been omitted....	1190	instead have been omitted.
		1191
		1192	Another common scenario is to use some data structure with multiple
		1193	embedded watchers:
		1194
		1195	struct my_biggy
		1196	{
		1197	int some_data;
		1198	ev_timer t1;
		1199	ev_timer t2;
		1200	}
		1201
		1202	In this case getting the pointer to C<my_biggy> is a bit more
		1203	complicated: Either you store the address of your C<my_biggy> struct
		1204	in the C<data> member of the watcher (for woozies), or you need to use
		1205	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1206	programmers):
		1207
		1208	#include <stddef.h>
		1209
		1210	static void
		1211	t1_cb (EV_P_ ev_timer *w, int revents)
		1212	{
		1213	struct my_biggy big = (struct my_biggy *)
		1214	(((char *)w) - offsetof (struct my_biggy, t1));
		1215	}
		1216
		1217	static void
		1218	t2_cb (EV_P_ ev_timer *w, int revents)
		1219	{
		1220	struct my_biggy big = (struct my_biggy *)
		1221	(((char *)w) - offsetof (struct my_biggy, t2));
		1222	}
		1223
		1224	=head2 WATCHER PRIORITY MODELS
		1225
		1226	Many event loops support I<watcher priorities>, which are usually small
		1227	integers that influence the ordering of event callback invocation
		1228	between watchers in some way, all else being equal.
		1229
		1230	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1231	description for the more technical details such as the actual priority
		1232	range.
		1233
		1234	There are two common ways how these these priorities are being interpreted
		1235	by event loops:
		1236
		1237	In the more common lock-out model, higher priorities "lock out" invocation
		1238	of lower priority watchers, which means as long as higher priority
		1239	watchers receive events, lower priority watchers are not being invoked.
		1240
		1241	The less common only-for-ordering model uses priorities solely to order
		1242	callback invocation within a single event loop iteration: Higher priority
		1243	watchers are invoked before lower priority ones, but they all get invoked
		1244	before polling for new events.
		1245
		1246	Libev uses the second (only-for-ordering) model for all its watchers
		1247	except for idle watchers (which use the lock-out model).
		1248
		1249	The rationale behind this is that implementing the lock-out model for
		1250	watchers is not well supported by most kernel interfaces, and most event
		1251	libraries will just poll for the same events again and again as long as
		1252	their callbacks have not been executed, which is very inefficient in the
		1253	common case of one high-priority watcher locking out a mass of lower
		1254	priority ones.
		1255
		1256	Static (ordering) priorities are most useful when you have two or more
		1257	watchers handling the same resource: a typical usage example is having an
		1258	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1259	timeouts. Under load, data might be received while the program handles
		1260	other jobs, but since timers normally get invoked first, the timeout
		1261	handler will be executed before checking for data. In that case, giving
		1262	the timer a lower priority than the I/O watcher ensures that I/O will be
		1263	handled first even under adverse conditions (which is usually, but not
		1264	always, what you want).
		1265
		1266	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1267	will only be executed when no same or higher priority watchers have
		1268	received events, they can be used to implement the "lock-out" model when
		1269	required.
		1270
		1271	For example, to emulate how many other event libraries handle priorities,
		1272	you can associate an C<ev_idle> watcher to each such watcher, and in
		1273	the normal watcher callback, you just start the idle watcher. The real
		1274	processing is done in the idle watcher callback. This causes libev to
		1275	continously poll and process kernel event data for the watcher, but when
		1276	the lock-out case is known to be rare (which in turn is rare :), this is
		1277	workable.
		1278
		1279	Usually, however, the lock-out model implemented that way will perform
		1280	miserably under the type of load it was designed to handle. In that case,
		1281	it might be preferable to stop the real watcher before starting the
		1282	idle watcher, so the kernel will not have to process the event in case
		1283	the actual processing will be delayed for considerable time.
		1284
		1285	Here is an example of an I/O watcher that should run at a strictly lower
		1286	priority than the default, and which should only process data when no
		1287	other events are pending:
		1288
		1289	ev_idle idle; // actual processing watcher
		1290	ev_io io; // actual event watcher
		1291
		1292	static void
		1293	io_cb (EV_P_ ev_io *w, int revents)
		1294	{
		1295	// stop the I/O watcher, we received the event, but
		1296	// are not yet ready to handle it.
		1297	ev_io_stop (EV_A_ w);
		1298
		1299	// start the idle watcher to ahndle the actual event.
		1300	// it will not be executed as long as other watchers
		1301	// with the default priority are receiving events.
		1302	ev_idle_start (EV_A_ &idle);
		1303	}
		1304
		1305	static void
		1306	idle_cb (EV_P_ ev_idle *w, int revents)
		1307	{
		1308	// actual processing
		1309	read (STDIN_FILENO, ...);
		1310
		1311	// have to start the I/O watcher again, as
		1312	// we have handled the event
		1313	ev_io_start (EV_P_ &io);
		1314	}
		1315
		1316	// initialisation
		1317	ev_idle_init (&idle, idle_cb);
		1318	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1319	ev_io_start (EV_DEFAULT_ &io);
		1320
		1321	In the "real" world, it might also be beneficial to start a timer, so that
		1322	low-priority connections can not be locked out forever under load. This
		1323	enables your program to keep a lower latency for important connections
		1324	during short periods of high load, while not completely locking out less
		1325	important ones.
741		1326
742		1327
743	=head1 WATCHER TYPES	1328	=head1 WATCHER TYPES
744		1329
745	This section describes each watcher in detail, but will not repeat	1330	This section describes each watcher in detail, but will not repeat
…		…
769	In general you can register as many read and/or write event watchers per	1354	In general you can register as many read and/or write event watchers per
770	fd as you want (as long as you don't confuse yourself). Setting all file	1355	fd as you want (as long as you don't confuse yourself). Setting all file
771	descriptors to non-blocking mode is also usually a good idea (but not	1356	descriptors to non-blocking mode is also usually a good idea (but not
772	required if you know what you are doing).	1357	required if you know what you are doing).
773		1358
774	You have to be careful with dup'ed file descriptors, though. Some backends	1359	If you cannot use non-blocking mode, then force the use of a
775	(the linux epoll backend is a notable example) cannot handle dup'ed file	1360	known-to-be-good backend (at the time of this writing, this includes only
776	descriptors correctly if you register interest in two or more fds pointing	1361	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
777	to the same underlying file/socket/etc. description (that is, they share	1362	descriptors for which non-blocking operation makes no sense (such as
778	the same underlying "file open").	1363	files) - libev doesn't guarentee any specific behaviour in that case.
779
780	If you must do this, then force the use of a known-to-be-good backend
781	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
782	C<EVBACKEND_POLL>).
783		1364
784	Another thing you have to watch out for is that it is quite easy to	1365	Another thing you have to watch out for is that it is quite easy to
785	receive "spurious" readyness notifications, that is your callback might	1366	receive "spurious" readiness notifications, that is your callback might
786	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1367	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
787	because there is no data. Not only are some backends known to create a	1368	because there is no data. Not only are some backends known to create a
788	lot of those (for example solaris ports), it is very easy to get into	1369	lot of those (for example Solaris ports), it is very easy to get into
789	this situation even with a relatively standard program structure. Thus	1370	this situation even with a relatively standard program structure. Thus
790	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1371	it is best to always use non-blocking I/O: An extra C<read>(2) returning
791	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1372	C<EAGAIN> is far preferable to a program hanging until some data arrives.
792		1373
793	If you cannot run the fd in non-blocking mode (for example you should not	1374	If you cannot run the fd in non-blocking mode (for example you should
794	play around with an Xlib connection), then you have to seperately re-test	1375	not play around with an Xlib connection), then you have to separately
795	wether a file descriptor is really ready with a known-to-be good interface	1376	re-test whether a file descriptor is really ready with a known-to-be good
796	such as poll (fortunately in our Xlib example, Xlib already does this on	1377	interface such as poll (fortunately in our Xlib example, Xlib already
797	its own, so its quite safe to use).	1378	does this on its own, so its quite safe to use). Some people additionally
		1379	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1380	indefinitely.
		1381
		1382	But really, best use non-blocking mode.
		1383
		1384	=head3 The special problem of disappearing file descriptors
		1385
		1386	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1387	descriptor (either due to calling C<close> explicitly or any other means,
		1388	such as C<dup2>). The reason is that you register interest in some file
		1389	descriptor, but when it goes away, the operating system will silently drop
		1390	this interest. If another file descriptor with the same number then is
		1391	registered with libev, there is no efficient way to see that this is, in
		1392	fact, a different file descriptor.
		1393
		1394	To avoid having to explicitly tell libev about such cases, libev follows
		1395	the following policy: Each time C<ev_io_set> is being called, libev
		1396	will assume that this is potentially a new file descriptor, otherwise
		1397	it is assumed that the file descriptor stays the same. That means that
		1398	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1399	descriptor even if the file descriptor number itself did not change.
		1400
		1401	This is how one would do it normally anyway, the important point is that
		1402	the libev application should not optimise around libev but should leave
		1403	optimisations to libev.
		1404
		1405	=head3 The special problem of dup'ed file descriptors
		1406
		1407	Some backends (e.g. epoll), cannot register events for file descriptors,
		1408	but only events for the underlying file descriptions. That means when you
		1409	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1410	events for them, only one file descriptor might actually receive events.
		1411
		1412	There is no workaround possible except not registering events
		1413	for potentially C<dup ()>'ed file descriptors, or to resort to
		1414	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1415
		1416	=head3 The special problem of fork
		1417
		1418	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1419	useless behaviour. Libev fully supports fork, but needs to be told about
		1420	it in the child.
		1421
		1422	To support fork in your programs, you either have to call
		1423	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1424	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1425	C<EVBACKEND_POLL>.
		1426
		1427	=head3 The special problem of SIGPIPE
		1428
		1429	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1430	when writing to a pipe whose other end has been closed, your program gets
		1431	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1432	this is sensible behaviour, for daemons, this is usually undesirable.
		1433
		1434	So when you encounter spurious, unexplained daemon exits, make sure you
		1435	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1436	somewhere, as that would have given you a big clue).
		1437
		1438
		1439	=head3 Watcher-Specific Functions
798		1440
799	=over 4	1441	=over 4
800		1442
801	=item ev_io_init (ev_io *, callback, int fd, int events)	1443	=item ev_io_init (ev_io *, callback, int fd, int events)
802		1444
803	=item ev_io_set (ev_io *, int fd, int events)	1445	=item ev_io_set (ev_io *, int fd, int events)
804		1446
805	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1447	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
806	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1448	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
807	C<EV_READ | EV_WRITE> to receive the given events.	1449	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
808		1450
809	=item int fd [read-only]	1451	=item int fd [read-only]
810		1452
811	The file descriptor being watched.	1453	The file descriptor being watched.
812		1454
…		…
814		1456
815	The events being watched.	1457	The events being watched.
816		1458
817	=back	1459	=back
818		1460
		1461	=head3 Examples
		1462
819	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1463	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
820	readable, but only once. Since it is likely line-buffered, you could	1464	readable, but only once. Since it is likely line-buffered, you could
821	attempt to read a whole line in the callback:	1465	attempt to read a whole line in the callback.
822		1466
823	static void	1467	static void
824	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1468	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
825	{	1469	{
826	ev_io_stop (loop, w);	1470	ev_io_stop (loop, w);
827	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1471	.. read from stdin here (or from w->fd) and handle any I/O errors
828	}	1472	}
829		1473
830	...	1474	...
831	struct ev_loop *loop = ev_default_init (0);	1475	struct ev_loop *loop = ev_default_init (0);
832	struct ev_io stdin_readable;	1476	ev_io stdin_readable;
833	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1477	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
834	ev_io_start (loop, &stdin_readable);	1478	ev_io_start (loop, &stdin_readable);
835	ev_loop (loop, 0);	1479	ev_loop (loop, 0);
836		1480
837		1481
838	=head2 C<ev_timer> - relative and optionally repeating timeouts	1482	=head2 C<ev_timer> - relative and optionally repeating timeouts
839		1483
840	Timer watchers are simple relative timers that generate an event after a	1484	Timer watchers are simple relative timers that generate an event after a
841	given time, and optionally repeating in regular intervals after that.	1485	given time, and optionally repeating in regular intervals after that.
842		1486
843	The timers are based on real time, that is, if you register an event that	1487	The timers are based on real time, that is, if you register an event that
844	times out after an hour and you reset your system clock to last years	1488	times out after an hour and you reset your system clock to January last
845	time, it will still time out after (roughly) and hour. "Roughly" because	1489	year, it will still time out after (roughly) one hour. "Roughly" because
846	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1490	detecting time jumps is hard, and some inaccuracies are unavoidable (the
847	monotonic clock option helps a lot here).	1491	monotonic clock option helps a lot here).
		1492
		1493	The callback is guaranteed to be invoked only I<after> its timeout has
		1494	passed (not I<at>, so on systems with very low-resolution clocks this
		1495	might introduce a small delay). If multiple timers become ready during the
		1496	same loop iteration then the ones with earlier time-out values are invoked
		1497	before ones of the same priority with later time-out values (but this is
		1498	no longer true when a callback calls C<ev_loop> recursively).
		1499
		1500	=head3 Be smart about timeouts
		1501
		1502	Many real-world problems involve some kind of timeout, usually for error
		1503	recovery. A typical example is an HTTP request - if the other side hangs,
		1504	you want to raise some error after a while.
		1505
		1506	What follows are some ways to handle this problem, from obvious and
		1507	inefficient to smart and efficient.
		1508
		1509	In the following, a 60 second activity timeout is assumed - a timeout that
		1510	gets reset to 60 seconds each time there is activity (e.g. each time some
		1511	data or other life sign was received).
		1512
		1513	=over 4
		1514
		1515	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1516
		1517	This is the most obvious, but not the most simple way: In the beginning,
		1518	start the watcher:
		1519
		1520	ev_timer_init (timer, callback, 60., 0.);
		1521	ev_timer_start (loop, timer);
		1522
		1523	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1524	and start it again:
		1525
		1526	ev_timer_stop (loop, timer);
		1527	ev_timer_set (timer, 60., 0.);
		1528	ev_timer_start (loop, timer);
		1529
		1530	This is relatively simple to implement, but means that each time there is
		1531	some activity, libev will first have to remove the timer from its internal
		1532	data structure and then add it again. Libev tries to be fast, but it's
		1533	still not a constant-time operation.
		1534
		1535	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1536
		1537	This is the easiest way, and involves using C<ev_timer_again> instead of
		1538	C<ev_timer_start>.
		1539
		1540	To implement this, configure an C<ev_timer> with a C<repeat> value
		1541	of C<60> and then call C<ev_timer_again> at start and each time you
		1542	successfully read or write some data. If you go into an idle state where
		1543	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1544	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1545
		1546	That means you can ignore both the C<ev_timer_start> function and the
		1547	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1548	member and C<ev_timer_again>.
		1549
		1550	At start:
		1551
		1552	ev_init (timer, callback);
		1553	timer->repeat = 60.;
		1554	ev_timer_again (loop, timer);
		1555
		1556	Each time there is some activity:
		1557
		1558	ev_timer_again (loop, timer);
		1559
		1560	It is even possible to change the time-out on the fly, regardless of
		1561	whether the watcher is active or not:
		1562
		1563	timer->repeat = 30.;
		1564	ev_timer_again (loop, timer);
		1565
		1566	This is slightly more efficient then stopping/starting the timer each time
		1567	you want to modify its timeout value, as libev does not have to completely
		1568	remove and re-insert the timer from/into its internal data structure.
		1569
		1570	It is, however, even simpler than the "obvious" way to do it.
		1571
		1572	=item 3. Let the timer time out, but then re-arm it as required.
		1573
		1574	This method is more tricky, but usually most efficient: Most timeouts are
		1575	relatively long compared to the intervals between other activity - in
		1576	our example, within 60 seconds, there are usually many I/O events with
		1577	associated activity resets.
		1578
		1579	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1580	but remember the time of last activity, and check for a real timeout only
		1581	within the callback:
		1582
		1583	ev_tstamp last_activity; // time of last activity
		1584
		1585	static void
		1586	callback (EV_P_ ev_timer *w, int revents)
		1587	{
		1588	ev_tstamp now = ev_now (EV_A);
		1589	ev_tstamp timeout = last_activity + 60.;
		1590
		1591	// if last_activity + 60. is older than now, we did time out
		1592	if (timeout < now)
		1593	{
		1594	// timeout occured, take action
		1595	}
		1596	else
		1597	{
		1598	// callback was invoked, but there was some activity, re-arm
		1599	// the watcher to fire in last_activity + 60, which is
		1600	// guaranteed to be in the future, so "again" is positive:
		1601	w->repeat = timeout - now;
		1602	ev_timer_again (EV_A_ w);
		1603	}
		1604	}
		1605
		1606	To summarise the callback: first calculate the real timeout (defined
		1607	as "60 seconds after the last activity"), then check if that time has
		1608	been reached, which means something I<did>, in fact, time out. Otherwise
		1609	the callback was invoked too early (C<timeout> is in the future), so
		1610	re-schedule the timer to fire at that future time, to see if maybe we have
		1611	a timeout then.
		1612
		1613	Note how C<ev_timer_again> is used, taking advantage of the
		1614	C<ev_timer_again> optimisation when the timer is already running.
		1615
		1616	This scheme causes more callback invocations (about one every 60 seconds
		1617	minus half the average time between activity), but virtually no calls to
		1618	libev to change the timeout.
		1619
		1620	To start the timer, simply initialise the watcher and set C<last_activity>
		1621	to the current time (meaning we just have some activity :), then call the
		1622	callback, which will "do the right thing" and start the timer:
		1623
		1624	ev_init (timer, callback);
		1625	last_activity = ev_now (loop);
		1626	callback (loop, timer, EV_TIMEOUT);
		1627
		1628	And when there is some activity, simply store the current time in
		1629	C<last_activity>, no libev calls at all:
		1630
		1631	last_actiivty = ev_now (loop);
		1632
		1633	This technique is slightly more complex, but in most cases where the
		1634	time-out is unlikely to be triggered, much more efficient.
		1635
		1636	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1637	callback :) - just change the timeout and invoke the callback, which will
		1638	fix things for you.
		1639
		1640	=item 4. Wee, just use a double-linked list for your timeouts.
		1641
		1642	If there is not one request, but many thousands (millions...), all
		1643	employing some kind of timeout with the same timeout value, then one can
		1644	do even better:
		1645
		1646	When starting the timeout, calculate the timeout value and put the timeout
		1647	at the I<end> of the list.
		1648
		1649	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1650	the list is expected to fire (for example, using the technique #3).
		1651
		1652	When there is some activity, remove the timer from the list, recalculate
		1653	the timeout, append it to the end of the list again, and make sure to
		1654	update the C<ev_timer> if it was taken from the beginning of the list.
		1655
		1656	This way, one can manage an unlimited number of timeouts in O(1) time for
		1657	starting, stopping and updating the timers, at the expense of a major
		1658	complication, and having to use a constant timeout. The constant timeout
		1659	ensures that the list stays sorted.
		1660
		1661	=back
		1662
		1663	So which method the best?
		1664
		1665	Method #2 is a simple no-brain-required solution that is adequate in most
		1666	situations. Method #3 requires a bit more thinking, but handles many cases
		1667	better, and isn't very complicated either. In most case, choosing either
		1668	one is fine, with #3 being better in typical situations.
		1669
		1670	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1671	rather complicated, but extremely efficient, something that really pays
		1672	off after the first million or so of active timers, i.e. it's usually
		1673	overkill :)
		1674
		1675	=head3 The special problem of time updates
		1676
		1677	Establishing the current time is a costly operation (it usually takes at
		1678	least two system calls): EV therefore updates its idea of the current
		1679	time only before and after C<ev_loop> collects new events, which causes a
		1680	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1681	lots of events in one iteration.
848		1682
849	The relative timeouts are calculated relative to the C<ev_now ()>	1683	The relative timeouts are calculated relative to the C<ev_now ()>
850	time. This is usually the right thing as this timestamp refers to the time	1684	time. This is usually the right thing as this timestamp refers to the time
851	of the event triggering whatever timeout you are modifying/starting. If	1685	of the event triggering whatever timeout you are modifying/starting. If
852	you suspect event processing to be delayed and you I<need> to base the timeout	1686	you suspect event processing to be delayed and you I<need> to base the
853	on the current time, use something like this to adjust for this:	1687	timeout on the current time, use something like this to adjust for this:
854		1688
855	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1689	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
856		1690
857	The callback is guarenteed to be invoked only when its timeout has passed,	1691	If the event loop is suspended for a long time, you can also force an
858	but if multiple timers become ready during the same loop iteration then	1692	update of the time returned by C<ev_now ()> by calling C<ev_now_update
859	order of execution is undefined.	1693	()>.
		1694
		1695	=head3 Watcher-Specific Functions and Data Members
860		1696
861	=over 4	1697	=over 4
862		1698
863	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1699	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
864		1700
865	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1701	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
866		1702
867	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1703	Configure the timer to trigger after C<after> seconds. If C<repeat>
868	C<0.>, then it will automatically be stopped. If it is positive, then the	1704	is C<0.>, then it will automatically be stopped once the timeout is
869	timer will automatically be configured to trigger again C<repeat> seconds	1705	reached. If it is positive, then the timer will automatically be
870	later, again, and again, until stopped manually.	1706	configured to trigger again C<repeat> seconds later, again, and again,
		1707	until stopped manually.
871		1708
872	The timer itself will do a best-effort at avoiding drift, that is, if you	1709	The timer itself will do a best-effort at avoiding drift, that is, if
873	configure a timer to trigger every 10 seconds, then it will trigger at	1710	you configure a timer to trigger every 10 seconds, then it will normally
874	exactly 10 second intervals. If, however, your program cannot keep up with	1711	trigger at exactly 10 second intervals. If, however, your program cannot
875	the timer (because it takes longer than those 10 seconds to do stuff) the	1712	keep up with the timer (because it takes longer than those 10 seconds to
876	timer will not fire more than once per event loop iteration.	1713	do stuff) the timer will not fire more than once per event loop iteration.
877		1714
878	=item ev_timer_again (loop)	1715	=item ev_timer_again (loop, ev_timer *)
879		1716
880	This will act as if the timer timed out and restart it again if it is	1717	This will act as if the timer timed out and restart it again if it is
881	repeating. The exact semantics are:	1718	repeating. The exact semantics are:
882		1719
		1720	If the timer is pending, its pending status is cleared.
		1721
883	If the timer is started but nonrepeating, stop it.	1722	If the timer is started but non-repeating, stop it (as if it timed out).
884		1723
885	If the timer is repeating, either start it if necessary (with the repeat	1724	If the timer is repeating, either start it if necessary (with the
886	value), or reset the running timer to the repeat value.	1725	C<repeat> value), or reset the running timer to the C<repeat> value.
887		1726
888	This sounds a bit complicated, but here is a useful and typical	1727	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
889	example: Imagine you have a tcp connection and you want a so-called	1728	usage example.
890	idle timeout, that is, you want to be called when there have been,
891	say, 60 seconds of inactivity on the socket. The easiest way to do
892	this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
893	C<ev_timer_again> each time you successfully read or write some data. If
894	you go into an idle state where you do not expect data to travel on the
895	socket, you can stop the timer, and again will automatically restart it if
896	need be.
897
898	You can also ignore the C<after> value and C<ev_timer_start> altogether
899	and only ever use the C<repeat> value:
900
901	ev_timer_init (timer, callback, 0., 5.);
902	ev_timer_again (loop, timer);
903	...
904	timer->again = 17.;
905	ev_timer_again (loop, timer);
906	...
907	timer->again = 10.;
908	ev_timer_again (loop, timer);
909
910	This is more efficient then stopping/starting the timer eahc time you want
911	to modify its timeout value.
912		1729
913	=item ev_tstamp repeat [read-write]	1730	=item ev_tstamp repeat [read-write]
914		1731
915	The current C<repeat> value. Will be used each time the watcher times out	1732	The current C<repeat> value. Will be used each time the watcher times out
916	or C<ev_timer_again> is called and determines the next timeout (if any),	1733	or C<ev_timer_again> is called, and determines the next timeout (if any),
917	which is also when any modifications are taken into account.	1734	which is also when any modifications are taken into account.
918		1735
919	=back	1736	=back
920		1737
		1738	=head3 Examples
		1739
921	Example: create a timer that fires after 60 seconds.	1740	Example: Create a timer that fires after 60 seconds.
922		1741
923	static void	1742	static void
924	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1743	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
925	{	1744	{
926	.. one minute over, w is actually stopped right here	1745	.. one minute over, w is actually stopped right here
927	}	1746	}
928		1747
929	struct ev_timer mytimer;	1748	ev_timer mytimer;
930	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1749	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
931	ev_timer_start (loop, &mytimer);	1750	ev_timer_start (loop, &mytimer);
932		1751
933	Example: create a timeout timer that times out after 10 seconds of	1752	Example: Create a timeout timer that times out after 10 seconds of
934	inactivity.	1753	inactivity.
935		1754
936	static void	1755	static void
937	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1756	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
938	{	1757	{
939	.. ten seconds without any activity	1758	.. ten seconds without any activity
940	}	1759	}
941		1760
942	struct ev_timer mytimer;	1761	ev_timer mytimer;
943	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1762	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
944	ev_timer_again (&mytimer); /* start timer */	1763	ev_timer_again (&mytimer); /* start timer */
945	ev_loop (loop, 0);	1764	ev_loop (loop, 0);
946		1765
947	// and in some piece of code that gets executed on any "activity":	1766	// and in some piece of code that gets executed on any "activity":
948	// reset the timeout to start ticking again at 10 seconds	1767	// reset the timeout to start ticking again at 10 seconds
949	ev_timer_again (&mytimer);	1768	ev_timer_again (&mytimer);
950		1769
951		1770
952	=head2 C<ev_periodic> - to cron or not to cron?	1771	=head2 C<ev_periodic> - to cron or not to cron?
953		1772
954	Periodic watchers are also timers of a kind, but they are very versatile	1773	Periodic watchers are also timers of a kind, but they are very versatile
955	(and unfortunately a bit complex).	1774	(and unfortunately a bit complex).
956		1775
957	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1776	Unlike C<ev_timer>, periodic watchers are not based on real time (or
958	but on wallclock time (absolute time). You can tell a periodic watcher	1777	relative time, the physical time that passes) but on wall clock time
959	to trigger "at" some specific point in time. For example, if you tell a	1778	(absolute time, the thing you can read on your calender or clock). The
960	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1779	difference is that wall clock time can run faster or slower than real
961	+ 10.>) and then reset your system clock to the last year, then it will	1780	time, and time jumps are not uncommon (e.g. when you adjust your
962	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1781	wrist-watch).
963	roughly 10 seconds later and of course not if you reset your system time
964	again).
965		1782
966	They can also be used to implement vastly more complex timers, such as	1783	You can tell a periodic watcher to trigger after some specific point
		1784	in time: for example, if you tell a periodic watcher to trigger "in 10
		1785	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1786	not a delay) and then reset your system clock to January of the previous
		1787	year, then it will take a year or more to trigger the event (unlike an
		1788	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1789	it, as it uses a relative timeout).
		1790
		1791	C<ev_periodic> watchers can also be used to implement vastly more complex
967	triggering an event on eahc midnight, local time.	1792	timers, such as triggering an event on each "midnight, local time", or
		1793	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1794	those cannot react to time jumps.
968		1795
969	As with timers, the callback is guarenteed to be invoked only when the	1796	As with timers, the callback is guaranteed to be invoked only when the
970	time (C<at>) has been passed, but if multiple periodic timers become ready	1797	point in time where it is supposed to trigger has passed. If multiple
971	during the same loop iteration then order of execution is undefined.	1798	timers become ready during the same loop iteration then the ones with
		1799	earlier time-out values are invoked before ones with later time-out values
		1800	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1801
		1802	=head3 Watcher-Specific Functions and Data Members
972		1803
973	=over 4	1804	=over 4
974		1805
975	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1806	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
976		1807
977	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1808	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
978		1809
979	Lots of arguments, lets sort it out... There are basically three modes of	1810	Lots of arguments, let's sort it out... There are basically three modes of
980	operation, and we will explain them from simplest to complex:	1811	operation, and we will explain them from simplest to most complex:
981		1812
982	=over 4	1813	=over 4
983		1814
984	=item * absolute timer (interval = reschedule_cb = 0)	1815	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
985		1816
986	In this configuration the watcher triggers an event at the wallclock time	1817	In this configuration the watcher triggers an event after the wall clock
987	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1818	time C<offset> has passed. It will not repeat and will not adjust when a
988	that is, if it is to be run at January 1st 2011 then it will run when the	1819	time jump occurs, that is, if it is to be run at January 1st 2011 then it
989	system time reaches or surpasses this time.	1820	will be stopped and invoked when the system clock reaches or surpasses
		1821	this point in time.
990		1822
991	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1823	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
992		1824
993	In this mode the watcher will always be scheduled to time out at the next	1825	In this mode the watcher will always be scheduled to time out at the next
994	C<at + N * interval> time (for some integer N) and then repeat, regardless	1826	C<offset + N * interval> time (for some integer N, which can also be
995	of any time jumps.	1827	negative) and then repeat, regardless of any time jumps. The C<offset>
		1828	argument is merely an offset into the C<interval> periods.
996		1829
997	This can be used to create timers that do not drift with respect to system	1830	This can be used to create timers that do not drift with respect to the
998	time:	1831	system clock, for example, here is an C<ev_periodic> that triggers each
		1832	hour, on the hour (with respect to UTC):
999		1833
1000	ev_periodic_set (&periodic, 0., 3600., 0);	1834	ev_periodic_set (&periodic, 0., 3600., 0);
1001		1835
1002	This doesn't mean there will always be 3600 seconds in between triggers,	1836	This doesn't mean there will always be 3600 seconds in between triggers,
1003	but only that the the callback will be called when the system time shows a	1837	but only that the callback will be called when the system time shows a
1004	full hour (UTC), or more correctly, when the system time is evenly divisible	1838	full hour (UTC), or more correctly, when the system time is evenly divisible
1005	by 3600.	1839	by 3600.
1006		1840
1007	Another way to think about it (for the mathematically inclined) is that	1841	Another way to think about it (for the mathematically inclined) is that
1008	C<ev_periodic> will try to run the callback in this mode at the next possible	1842	C<ev_periodic> will try to run the callback in this mode at the next possible
1009	time where C<time = at (mod interval)>, regardless of any time jumps.	1843	time where C<time = offset (mod interval)>, regardless of any time jumps.
1010		1844
		1845	For numerical stability it is preferable that the C<offset> value is near
		1846	C<ev_now ()> (the current time), but there is no range requirement for
		1847	this value, and in fact is often specified as zero.
		1848
		1849	Note also that there is an upper limit to how often a timer can fire (CPU
		1850	speed for example), so if C<interval> is very small then timing stability
		1851	will of course deteriorate. Libev itself tries to be exact to be about one
		1852	millisecond (if the OS supports it and the machine is fast enough).
		1853
1011	=item * manual reschedule mode (reschedule_cb = callback)	1854	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1012		1855
1013	In this mode the values for C<interval> and C<at> are both being	1856	In this mode the values for C<interval> and C<offset> are both being
1014	ignored. Instead, each time the periodic watcher gets scheduled, the	1857	ignored. Instead, each time the periodic watcher gets scheduled, the
1015	reschedule callback will be called with the watcher as first, and the	1858	reschedule callback will be called with the watcher as first, and the
1016	current time as second argument.	1859	current time as second argument.
1017		1860
1018	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1861	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1019	ever, or make any event loop modifications>. If you need to stop it,	1862	or make ANY other event loop modifications whatsoever, unless explicitly
1020	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1863	allowed by documentation here>.
1021	starting a prepare watcher).
1022		1864
		1865	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1866	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1867	only event loop modification you are allowed to do).
		1868
1023	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1869	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1024	ev_tstamp now)>, e.g.:	1870	*w, ev_tstamp now)>, e.g.:
1025		1871
		1872	static ev_tstamp
1026	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1873	my_rescheduler (ev_periodic *w, ev_tstamp now)
1027	{	1874	{
1028	return now + 60.;	1875	return now + 60.;
1029	}	1876	}
1030		1877
1031	It must return the next time to trigger, based on the passed time value	1878	It must return the next time to trigger, based on the passed time value
1032	(that is, the lowest time value larger than to the second argument). It	1879	(that is, the lowest time value larger than to the second argument). It
1033	will usually be called just before the callback will be triggered, but	1880	will usually be called just before the callback will be triggered, but
1034	might be called at other times, too.	1881	might be called at other times, too.
1035		1882
1036	NOTE: I<< This callback must always return a time that is later than the	1883	NOTE: I<< This callback must always return a time that is higher than or
1037	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1884	equal to the passed C<now> value >>.
1038		1885
1039	This can be used to create very complex timers, such as a timer that	1886	This can be used to create very complex timers, such as a timer that
1040	triggers on each midnight, local time. To do this, you would calculate the	1887	triggers on "next midnight, local time". To do this, you would calculate the
1041	next midnight after C<now> and return the timestamp value for this. How	1888	next midnight after C<now> and return the timestamp value for this. How
1042	you do this is, again, up to you (but it is not trivial, which is the main	1889	you do this is, again, up to you (but it is not trivial, which is the main
1043	reason I omitted it as an example).	1890	reason I omitted it as an example).
1044		1891
1045	=back	1892	=back
…		…
1049	Simply stops and restarts the periodic watcher again. This is only useful	1896	Simply stops and restarts the periodic watcher again. This is only useful
1050	when you changed some parameters or the reschedule callback would return	1897	when you changed some parameters or the reschedule callback would return
1051	a different time than the last time it was called (e.g. in a crond like	1898	a different time than the last time it was called (e.g. in a crond like
1052	program when the crontabs have changed).	1899	program when the crontabs have changed).
1053		1900
		1901	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1902
		1903	When active, returns the absolute time that the watcher is supposed
		1904	to trigger next. This is not the same as the C<offset> argument to
		1905	C<ev_periodic_set>, but indeed works even in interval and manual
		1906	rescheduling modes.
		1907
		1908	=item ev_tstamp offset [read-write]
		1909
		1910	When repeating, this contains the offset value, otherwise this is the
		1911	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1912	although libev might modify this value for better numerical stability).
		1913
		1914	Can be modified any time, but changes only take effect when the periodic
		1915	timer fires or C<ev_periodic_again> is being called.
		1916
1054	=item ev_tstamp interval [read-write]	1917	=item ev_tstamp interval [read-write]
1055		1918
1056	The current interval value. Can be modified any time, but changes only	1919	The current interval value. Can be modified any time, but changes only
1057	take effect when the periodic timer fires or C<ev_periodic_again> is being	1920	take effect when the periodic timer fires or C<ev_periodic_again> is being
1058	called.	1921	called.
1059		1922
1060	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1923	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1061		1924
1062	The current reschedule callback, or C<0>, if this functionality is	1925	The current reschedule callback, or C<0>, if this functionality is
1063	switched off. Can be changed any time, but changes only take effect when	1926	switched off. Can be changed any time, but changes only take effect when
1064	the periodic timer fires or C<ev_periodic_again> is being called.	1927	the periodic timer fires or C<ev_periodic_again> is being called.
1065		1928
1066	=back	1929	=back
1067		1930
		1931	=head3 Examples
		1932
1068	Example: call a callback every hour, or, more precisely, whenever the	1933	Example: Call a callback every hour, or, more precisely, whenever the
1069	system clock is divisible by 3600. The callback invocation times have	1934	system time is divisible by 3600. The callback invocation times have
1070	potentially a lot of jittering, but good long-term stability.	1935	potentially a lot of jitter, but good long-term stability.
1071		1936
1072	static void	1937	static void
1073	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1938	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1074	{	1939	{
1075	... its now a full hour (UTC, or TAI or whatever your clock follows)	1940	... its now a full hour (UTC, or TAI or whatever your clock follows)
1076	}	1941	}
1077		1942
1078	struct ev_periodic hourly_tick;	1943	ev_periodic hourly_tick;
1079	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1944	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1080	ev_periodic_start (loop, &hourly_tick);	1945	ev_periodic_start (loop, &hourly_tick);
1081		1946
1082	Example: the same as above, but use a reschedule callback to do it:	1947	Example: The same as above, but use a reschedule callback to do it:
1083		1948
1084	#include <math.h>	1949	#include <math.h>
1085		1950
1086	static ev_tstamp	1951	static ev_tstamp
1087	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1952	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1088	{	1953	{
1089	return fmod (now, 3600.) + 3600.;	1954	return now + (3600. - fmod (now, 3600.));
1090	}	1955	}
1091		1956
1092	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1957	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1093		1958
1094	Example: call a callback every hour, starting now:	1959	Example: Call a callback every hour, starting now:
1095		1960
1096	struct ev_periodic hourly_tick;	1961	ev_periodic hourly_tick;
1097	ev_periodic_init (&hourly_tick, clock_cb,	1962	ev_periodic_init (&hourly_tick, clock_cb,
1098	fmod (ev_now (loop), 3600.), 3600., 0);	1963	fmod (ev_now (loop), 3600.), 3600., 0);
1099	ev_periodic_start (loop, &hourly_tick);	1964	ev_periodic_start (loop, &hourly_tick);
1100		1965
1101		1966
1102	=head2 C<ev_signal> - signal me when a signal gets signalled!	1967	=head2 C<ev_signal> - signal me when a signal gets signalled!
1103		1968
1104	Signal watchers will trigger an event when the process receives a specific	1969	Signal watchers will trigger an event when the process receives a specific
1105	signal one or more times. Even though signals are very asynchronous, libev	1970	signal one or more times. Even though signals are very asynchronous, libev
1106	will try it's best to deliver signals synchronously, i.e. as part of the	1971	will try it's best to deliver signals synchronously, i.e. as part of the
1107	normal event processing, like any other event.	1972	normal event processing, like any other event.
1108		1973
		1974	If you want signals asynchronously, just use C<sigaction> as you would
		1975	do without libev and forget about sharing the signal. You can even use
		1976	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1977
1109	You can configure as many watchers as you like per signal. Only when the	1978	You can configure as many watchers as you like per signal. Only when the
1110	first watcher gets started will libev actually register a signal watcher	1979	first watcher gets started will libev actually register a signal handler
1111	with the kernel (thus it coexists with your own signal handlers as long	1980	with the kernel (thus it coexists with your own signal handlers as long as
1112	as you don't register any with libev). Similarly, when the last signal	1981	you don't register any with libev for the same signal). Similarly, when
1113	watcher for a signal is stopped libev will reset the signal handler to	1982	the last signal watcher for a signal is stopped, libev will reset the
1114	SIG_DFL (regardless of what it was set to before).	1983	signal handler to SIG_DFL (regardless of what it was set to before).
		1984
		1985	If possible and supported, libev will install its handlers with
		1986	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1987	interrupted. If you have a problem with system calls getting interrupted by
		1988	signals you can block all signals in an C<ev_check> watcher and unblock
		1989	them in an C<ev_prepare> watcher.
		1990
		1991	=head3 Watcher-Specific Functions and Data Members
1115		1992
1116	=over 4	1993	=over 4
1117		1994
1118	=item ev_signal_init (ev_signal *, callback, int signum)	1995	=item ev_signal_init (ev_signal *, callback, int signum)
1119		1996
…		…
1126		2003
1127	The signal the watcher watches out for.	2004	The signal the watcher watches out for.
1128		2005
1129	=back	2006	=back
1130		2007
		2008	=head3 Examples
		2009
		2010	Example: Try to exit cleanly on SIGINT.
		2011
		2012	static void
		2013	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2014	{
		2015	ev_unloop (loop, EVUNLOOP_ALL);
		2016	}
		2017
		2018	ev_signal signal_watcher;
		2019	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2020	ev_signal_start (loop, &signal_watcher);
		2021
1131		2022
1132	=head2 C<ev_child> - watch out for process status changes	2023	=head2 C<ev_child> - watch out for process status changes
1133		2024
1134	Child watchers trigger when your process receives a SIGCHLD in response to	2025	Child watchers trigger when your process receives a SIGCHLD in response to
1135	some child status changes (most typically when a child of yours dies).	2026	some child status changes (most typically when a child of yours dies or
		2027	exits). It is permissible to install a child watcher I<after> the child
		2028	has been forked (which implies it might have already exited), as long
		2029	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2030	forking and then immediately registering a watcher for the child is fine,
		2031	but forking and registering a watcher a few event loop iterations later or
		2032	in the next callback invocation is not.
		2033
		2034	Only the default event loop is capable of handling signals, and therefore
		2035	you can only register child watchers in the default event loop.
		2036
		2037	Due to some design glitches inside libev, child watchers will always be
		2038	handled at maximum priority (their priority is set to EV_MAXPRI by libev)
		2039
		2040	=head3 Process Interaction
		2041
		2042	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2043	initialised. This is necessary to guarantee proper behaviour even if
		2044	the first child watcher is started after the child exits. The occurrence
		2045	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2046	synchronously as part of the event loop processing. Libev always reaps all
		2047	children, even ones not watched.
		2048
		2049	=head3 Overriding the Built-In Processing
		2050
		2051	Libev offers no special support for overriding the built-in child
		2052	processing, but if your application collides with libev's default child
		2053	handler, you can override it easily by installing your own handler for
		2054	C<SIGCHLD> after initialising the default loop, and making sure the
		2055	default loop never gets destroyed. You are encouraged, however, to use an
		2056	event-based approach to child reaping and thus use libev's support for
		2057	that, so other libev users can use C<ev_child> watchers freely.
		2058
		2059	=head3 Stopping the Child Watcher
		2060
		2061	Currently, the child watcher never gets stopped, even when the
		2062	child terminates, so normally one needs to stop the watcher in the
		2063	callback. Future versions of libev might stop the watcher automatically
		2064	when a child exit is detected.
		2065
		2066	=head3 Watcher-Specific Functions and Data Members
1136		2067
1137	=over 4	2068	=over 4
1138		2069
1139	=item ev_child_init (ev_child *, callback, int pid)	2070	=item ev_child_init (ev_child *, callback, int pid, int trace)
1140		2071
1141	=item ev_child_set (ev_child *, int pid)	2072	=item ev_child_set (ev_child *, int pid, int trace)
1142		2073
1143	Configures the watcher to wait for status changes of process C<pid> (or	2074	Configures the watcher to wait for status changes of process C<pid> (or
1144	I<any> process if C<pid> is specified as C<0>). The callback can look	2075	I<any> process if C<pid> is specified as C<0>). The callback can look
1145	at the C<rstatus> member of the C<ev_child> watcher structure to see	2076	at the C<rstatus> member of the C<ev_child> watcher structure to see
1146	the status word (use the macros from C<sys/wait.h> and see your systems	2077	the status word (use the macros from C<sys/wait.h> and see your systems
1147	C<waitpid> documentation). The C<rpid> member contains the pid of the	2078	C<waitpid> documentation). The C<rpid> member contains the pid of the
1148	process causing the status change.	2079	process causing the status change. C<trace> must be either C<0> (only
		2080	activate the watcher when the process terminates) or C<1> (additionally
		2081	activate the watcher when the process is stopped or continued).
1149		2082
1150	=item int pid [read-only]	2083	=item int pid [read-only]
1151		2084
1152	The process id this watcher watches out for, or C<0>, meaning any process id.	2085	The process id this watcher watches out for, or C<0>, meaning any process id.
1153		2086
…		…
1160	The process exit/trace status caused by C<rpid> (see your systems	2093	The process exit/trace status caused by C<rpid> (see your systems
1161	C<waitpid> and C<sys/wait.h> documentation for details).	2094	C<waitpid> and C<sys/wait.h> documentation for details).
1162		2095
1163	=back	2096	=back
1164		2097
1165	Example: try to exit cleanly on SIGINT and SIGTERM.	2098	=head3 Examples
1166		2099
		2100	Example: C<fork()> a new process and install a child handler to wait for
		2101	its completion.
		2102
		2103	ev_child cw;
		2104
1167	static void	2105	static void
1168	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2106	child_cb (EV_P_ ev_child *w, int revents)
1169	{	2107	{
1170	ev_unloop (loop, EVUNLOOP_ALL);	2108	ev_child_stop (EV_A_ w);
		2109	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1171	}	2110	}
1172		2111
1173	struct ev_signal signal_watcher;	2112	pid_t pid = fork ();
1174	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2113
1175	ev_signal_start (loop, &sigint_cb);	2114	if (pid < 0)
		2115	// error
		2116	else if (pid == 0)
		2117	{
		2118	// the forked child executes here
		2119	exit (1);
		2120	}
		2121	else
		2122	{
		2123	ev_child_init (&cw, child_cb, pid, 0);
		2124	ev_child_start (EV_DEFAULT_ &cw);
		2125	}
1176		2126
1177		2127
1178	=head2 C<ev_stat> - did the file attributes just change?	2128	=head2 C<ev_stat> - did the file attributes just change?
1179		2129
1180	This watches a filesystem path for attribute changes. That is, it calls	2130	This watches a file system path for attribute changes. That is, it calls
1181	C<stat> regularly (or when the OS says it changed) and sees if it changed	2131	C<stat> on that path in regular intervals (or when the OS says it changed)
1182	compared to the last time, invoking the callback if it did.	2132	and sees if it changed compared to the last time, invoking the callback if
		2133	it did.
1183		2134
1184	The path does not need to exist: changing from "path exists" to "path does	2135	The path does not need to exist: changing from "path exists" to "path does
1185	not exist" is a status change like any other. The condition "path does	2136	not exist" is a status change like any other. The condition "path does not
1186	not exist" is signified by the C<st_nlink> field being zero (which is	2137	exist" (or more correctly "path cannot be stat'ed") is signified by the
1187	otherwise always forced to be at least one) and all the other fields of	2138	C<st_nlink> field being zero (which is otherwise always forced to be at
1188	the stat buffer having unspecified contents.	2139	least one) and all the other fields of the stat buffer having unspecified
		2140	contents.
1189		2141
1190	Since there is no standard to do this, the portable implementation simply	2142	The path I<must not> end in a slash or contain special components such as
1191	calls C<stat (2)> regulalry on the path to see if it changed somehow. You	2143	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1192	can specify a recommended polling interval for this case. If you specify	2144	your working directory changes, then the behaviour is undefined.
1193	a polling interval of C<0> (highly recommended!) then a I<suitable,	2145
1194	unspecified default> value will be used (which you can expect to be around	2146	Since there is no portable change notification interface available, the
1195	five seconds, although this might change dynamically). Libev will also	2147	portable implementation simply calls C<stat(2)> regularly on the path
1196	impose a minimum interval which is currently around C<0.1>, but thats	2148	to see if it changed somehow. You can specify a recommended polling
1197	usually overkill.	2149	interval for this case. If you specify a polling interval of C<0> (highly
		2150	recommended!) then a I<suitable, unspecified default> value will be used
		2151	(which you can expect to be around five seconds, although this might
		2152	change dynamically). Libev will also impose a minimum interval which is
		2153	currently around C<0.1>, but that's usually overkill.
1198		2154
1199	This watcher type is not meant for massive numbers of stat watchers,	2155	This watcher type is not meant for massive numbers of stat watchers,
1200	as even with OS-supported change notifications, this can be	2156	as even with OS-supported change notifications, this can be
1201	resource-intensive.	2157	resource-intensive.
1202		2158
1203	At the time of this writing, no specific OS backends are implemented, but	2159	At the time of this writing, the only OS-specific interface implemented
1204	if demand increases, at least a kqueue and inotify backend will be added.	2160	is the Linux inotify interface (implementing kqueue support is left as an
		2161	exercise for the reader. Note, however, that the author sees no way of
		2162	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2163
		2164	=head3 ABI Issues (Largefile Support)
		2165
		2166	Libev by default (unless the user overrides this) uses the default
		2167	compilation environment, which means that on systems with large file
		2168	support disabled by default, you get the 32 bit version of the stat
		2169	structure. When using the library from programs that change the ABI to
		2170	use 64 bit file offsets the programs will fail. In that case you have to
		2171	compile libev with the same flags to get binary compatibility. This is
		2172	obviously the case with any flags that change the ABI, but the problem is
		2173	most noticeably displayed with ev_stat and large file support.
		2174
		2175	The solution for this is to lobby your distribution maker to make large
		2176	file interfaces available by default (as e.g. FreeBSD does) and not
		2177	optional. Libev cannot simply switch on large file support because it has
		2178	to exchange stat structures with application programs compiled using the
		2179	default compilation environment.
		2180
		2181	=head3 Inotify and Kqueue
		2182
		2183	When C<inotify (7)> support has been compiled into libev and present at
		2184	runtime, it will be used to speed up change detection where possible. The
		2185	inotify descriptor will be created lazily when the first C<ev_stat>
		2186	watcher is being started.
		2187
		2188	Inotify presence does not change the semantics of C<ev_stat> watchers
		2189	except that changes might be detected earlier, and in some cases, to avoid
		2190	making regular C<stat> calls. Even in the presence of inotify support
		2191	there are many cases where libev has to resort to regular C<stat> polling,
		2192	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2193	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2194	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2195	xfs are fully working) libev usually gets away without polling.
		2196
		2197	There is no support for kqueue, as apparently it cannot be used to
		2198	implement this functionality, due to the requirement of having a file
		2199	descriptor open on the object at all times, and detecting renames, unlinks
		2200	etc. is difficult.
		2201
		2202	=head3 C<stat ()> is a synchronous operation
		2203
		2204	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2205	the process. The exception are C<ev_stat> watchers - those call C<stat
		2206	()>, which is a synchronous operation.
		2207
		2208	For local paths, this usually doesn't matter: unless the system is very
		2209	busy or the intervals between stat's are large, a stat call will be fast,
		2210	as the path data is usually in memory already (except when starting the
		2211	watcher).
		2212
		2213	For networked file systems, calling C<stat ()> can block an indefinite
		2214	time due to network issues, and even under good conditions, a stat call
		2215	often takes multiple milliseconds.
		2216
		2217	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2218	paths, although this is fully supported by libev.
		2219
		2220	=head3 The special problem of stat time resolution
		2221
		2222	The C<stat ()> system call only supports full-second resolution portably,
		2223	and even on systems where the resolution is higher, most file systems
		2224	still only support whole seconds.
		2225
		2226	That means that, if the time is the only thing that changes, you can
		2227	easily miss updates: on the first update, C<ev_stat> detects a change and
		2228	calls your callback, which does something. When there is another update
		2229	within the same second, C<ev_stat> will be unable to detect unless the
		2230	stat data does change in other ways (e.g. file size).
		2231
		2232	The solution to this is to delay acting on a change for slightly more
		2233	than a second (or till slightly after the next full second boundary), using
		2234	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2235	ev_timer_again (loop, w)>).
		2236
		2237	The C<.02> offset is added to work around small timing inconsistencies
		2238	of some operating systems (where the second counter of the current time
		2239	might be be delayed. One such system is the Linux kernel, where a call to
		2240	C<gettimeofday> might return a timestamp with a full second later than
		2241	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2242	update file times then there will be a small window where the kernel uses
		2243	the previous second to update file times but libev might already execute
		2244	the timer callback).
		2245
		2246	=head3 Watcher-Specific Functions and Data Members
1205		2247
1206	=over 4	2248	=over 4
1207		2249
1208	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2250	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1209		2251
…		…
1213	C<path>. The C<interval> is a hint on how quickly a change is expected to	2255	C<path>. The C<interval> is a hint on how quickly a change is expected to
1214	be detected and should normally be specified as C<0> to let libev choose	2256	be detected and should normally be specified as C<0> to let libev choose
1215	a suitable value. The memory pointed to by C<path> must point to the same	2257	a suitable value. The memory pointed to by C<path> must point to the same
1216	path for as long as the watcher is active.	2258	path for as long as the watcher is active.
1217		2259
1218	The callback will be receive C<EV_STAT> when a change was detected,	2260	The callback will receive an C<EV_STAT> event when a change was detected,
1219	relative to the attributes at the time the watcher was started (or the	2261	relative to the attributes at the time the watcher was started (or the
1220	last change was detected).	2262	last change was detected).
1221		2263
1222	=item ev_stat_stat (ev_stat *)	2264	=item ev_stat_stat (loop, ev_stat *)
1223		2265
1224	Updates the stat buffer immediately with new values. If you change the	2266	Updates the stat buffer immediately with new values. If you change the
1225	watched path in your callback, you could call this fucntion to avoid	2267	watched path in your callback, you could call this function to avoid
1226	detecting this change (while introducing a race condition). Can also be	2268	detecting this change (while introducing a race condition if you are not
1227	useful simply to find out the new values.	2269	the only one changing the path). Can also be useful simply to find out the
		2270	new values.
1228		2271
1229	=item ev_statdata attr [read-only]	2272	=item ev_statdata attr [read-only]
1230		2273
1231	The most-recently detected attributes of the file. Although the type is of	2274	The most-recently detected attributes of the file. Although the type is
1232	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2275	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1233	suitable for your system. If the C<st_nlink> member is C<0>, then there	2276	suitable for your system, but you can only rely on the POSIX-standardised
		2277	members to be present. If the C<st_nlink> member is C<0>, then there was
1234	was some error while C<stat>ing the file.	2278	some error while C<stat>ing the file.
1235		2279
1236	=item ev_statdata prev [read-only]	2280	=item ev_statdata prev [read-only]
1237		2281
1238	The previous attributes of the file. The callback gets invoked whenever	2282	The previous attributes of the file. The callback gets invoked whenever
1239	C<prev> != C<attr>.	2283	C<prev> != C<attr>, or, more precisely, one or more of these members
		2284	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2285	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1240		2286
1241	=item ev_tstamp interval [read-only]	2287	=item ev_tstamp interval [read-only]
1242		2288
1243	The specified interval.	2289	The specified interval.
1244		2290
1245	=item const char *path [read-only]	2291	=item const char *path [read-only]
1246		2292
1247	The filesystem path that is being watched.	2293	The file system path that is being watched.
1248		2294
1249	=back	2295	=back
1250		2296
		2297	=head3 Examples
		2298
1251	Example: Watch C</etc/passwd> for attribute changes.	2299	Example: Watch C</etc/passwd> for attribute changes.
1252		2300
1253	static void	2301	static void
1254	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2302	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1255	{	2303	{
1256	/* /etc/passwd changed in some way */	2304	/* /etc/passwd changed in some way */
1257	if (w->attr.st_nlink)	2305	if (w->attr.st_nlink)
1258	{	2306	{
1259	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2307	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1260	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2308	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1261	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2309	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1262	}	2310	}
1263	else	2311	else
1264	/* you shalt not abuse printf for puts */	2312	/* you shalt not abuse printf for puts */
1265	puts ("wow, /etc/passwd is not there, expect problems. "	2313	puts ("wow, /etc/passwd is not there, expect problems. "
1266	"if this is windows, they already arrived\n");	2314	"if this is windows, they already arrived\n");
1267	}	2315	}
1268		2316
1269	...	2317	...
1270	ev_stat passwd;	2318	ev_stat passwd;
1271		2319
1272	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2320	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1273	ev_stat_start (loop, &passwd);	2321	ev_stat_start (loop, &passwd);
		2322
		2323	Example: Like above, but additionally use a one-second delay so we do not
		2324	miss updates (however, frequent updates will delay processing, too, so
		2325	one might do the work both on C<ev_stat> callback invocation I<and> on
		2326	C<ev_timer> callback invocation).
		2327
		2328	static ev_stat passwd;
		2329	static ev_timer timer;
		2330
		2331	static void
		2332	timer_cb (EV_P_ ev_timer *w, int revents)
		2333	{
		2334	ev_timer_stop (EV_A_ w);
		2335
		2336	/* now it's one second after the most recent passwd change */
		2337	}
		2338
		2339	static void
		2340	stat_cb (EV_P_ ev_stat *w, int revents)
		2341	{
		2342	/* reset the one-second timer */
		2343	ev_timer_again (EV_A_ &timer);
		2344	}
		2345
		2346	...
		2347	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2348	ev_stat_start (loop, &passwd);
		2349	ev_timer_init (&timer, timer_cb, 0., 1.02);
1274		2350
1275		2351
1276	=head2 C<ev_idle> - when you've got nothing better to do...	2352	=head2 C<ev_idle> - when you've got nothing better to do...
1277		2353
1278	Idle watchers trigger events when there are no other events are pending	2354	Idle watchers trigger events when no other events of the same or higher
1279	(prepare, check and other idle watchers do not count). That is, as long	2355	priority are pending (prepare, check and other idle watchers do not count
1280	as your process is busy handling sockets or timeouts (or even signals,	2356	as receiving "events").
1281	imagine) it will not be triggered. But when your process is idle all idle	2357
1282	watchers are being called again and again, once per event loop iteration -	2358	That is, as long as your process is busy handling sockets or timeouts
		2359	(or even signals, imagine) of the same or higher priority it will not be
		2360	triggered. But when your process is idle (or only lower-priority watchers
		2361	are pending), the idle watchers are being called once per event loop
1283	until stopped, that is, or your process receives more events and becomes	2362	iteration - until stopped, that is, or your process receives more events
1284	busy.	2363	and becomes busy again with higher priority stuff.
1285		2364
1286	The most noteworthy effect is that as long as any idle watchers are	2365	The most noteworthy effect is that as long as any idle watchers are
1287	active, the process will not block when waiting for new events.	2366	active, the process will not block when waiting for new events.
1288		2367
1289	Apart from keeping your process non-blocking (which is a useful	2368	Apart from keeping your process non-blocking (which is a useful
1290	effect on its own sometimes), idle watchers are a good place to do	2369	effect on its own sometimes), idle watchers are a good place to do
1291	"pseudo-background processing", or delay processing stuff to after the	2370	"pseudo-background processing", or delay processing stuff to after the
1292	event loop has handled all outstanding events.	2371	event loop has handled all outstanding events.
1293		2372
		2373	=head3 Watcher-Specific Functions and Data Members
		2374
1294	=over 4	2375	=over 4
1295		2376
1296	=item ev_idle_init (ev_signal *, callback)	2377	=item ev_idle_init (ev_idle *, callback)
1297		2378
1298	Initialises and configures the idle watcher - it has no parameters of any	2379	Initialises and configures the idle watcher - it has no parameters of any
1299	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2380	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1300	believe me.	2381	believe me.
1301		2382
1302	=back	2383	=back
1303		2384
		2385	=head3 Examples
		2386
1304	Example: dynamically allocate an C<ev_idle>, start it, and in the	2387	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1305	callback, free it. Alos, use no error checking, as usual.	2388	callback, free it. Also, use no error checking, as usual.
1306		2389
1307	static void	2390	static void
1308	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2391	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1309	{	2392	{
1310	free (w);	2393	free (w);
1311	// now do something you wanted to do when the program has	2394	// now do something you wanted to do when the program has
1312	// no longer asnything immediate to do.	2395	// no longer anything immediate to do.
1313	}	2396	}
1314		2397
1315	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2398	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1316	ev_idle_init (idle_watcher, idle_cb);	2399	ev_idle_init (idle_watcher, idle_cb);
1317	ev_idle_start (loop, idle_cb);	2400	ev_idle_start (loop, idle_watcher);
1318		2401
1319		2402
1320	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2403	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1321		2404
1322	Prepare and check watchers are usually (but not always) used in tandem:	2405	Prepare and check watchers are usually (but not always) used in pairs:
1323	prepare watchers get invoked before the process blocks and check watchers	2406	prepare watchers get invoked before the process blocks and check watchers
1324	afterwards.	2407	afterwards.
1325		2408
1326	You I<must not> call C<ev_loop> or similar functions that enter	2409	You I<must not> call C<ev_loop> or similar functions that enter
1327	the current event loop from either C<ev_prepare> or C<ev_check>	2410	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1330	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2413	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1331	C<ev_check> so if you have one watcher of each kind they will always be	2414	C<ev_check> so if you have one watcher of each kind they will always be
1332	called in pairs bracketing the blocking call.	2415	called in pairs bracketing the blocking call.
1333		2416
1334	Their main purpose is to integrate other event mechanisms into libev and	2417	Their main purpose is to integrate other event mechanisms into libev and
1335	their use is somewhat advanced. This could be used, for example, to track	2418	their use is somewhat advanced. They could be used, for example, to track
1336	variable changes, implement your own watchers, integrate net-snmp or a	2419	variable changes, implement your own watchers, integrate net-snmp or a
1337	coroutine library and lots more. They are also occasionally useful if	2420	coroutine library and lots more. They are also occasionally useful if
1338	you cache some data and want to flush it before blocking (for example,	2421	you cache some data and want to flush it before blocking (for example,
1339	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2422	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1340	watcher).	2423	watcher).
1341		2424
1342	This is done by examining in each prepare call which file descriptors need	2425	This is done by examining in each prepare call which file descriptors
1343	to be watched by the other library, registering C<ev_io> watchers for	2426	need to be watched by the other library, registering C<ev_io> watchers
1344	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2427	for them and starting an C<ev_timer> watcher for any timeouts (many
1345	provide just this functionality). Then, in the check watcher you check for	2428	libraries provide exactly this functionality). Then, in the check watcher,
1346	any events that occured (by checking the pending status of all watchers	2429	you check for any events that occurred (by checking the pending status
1347	and stopping them) and call back into the library. The I/O and timer	2430	of all watchers and stopping them) and call back into the library. The
1348	callbacks will never actually be called (but must be valid nevertheless,	2431	I/O and timer callbacks will never actually be called (but must be valid
1349	because you never know, you know?).	2432	nevertheless, because you never know, you know?).
1350		2433
1351	As another example, the Perl Coro module uses these hooks to integrate	2434	As another example, the Perl Coro module uses these hooks to integrate
1352	coroutines into libev programs, by yielding to other active coroutines	2435	coroutines into libev programs, by yielding to other active coroutines
1353	during each prepare and only letting the process block if no coroutines	2436	during each prepare and only letting the process block if no coroutines
1354	are ready to run (it's actually more complicated: it only runs coroutines	2437	are ready to run (it's actually more complicated: it only runs coroutines
1355	with priority higher than or equal to the event loop and one coroutine	2438	with priority higher than or equal to the event loop and one coroutine
1356	of lower priority, but only once, using idle watchers to keep the event	2439	of lower priority, but only once, using idle watchers to keep the event
1357	loop from blocking if lower-priority coroutines are active, thus mapping	2440	loop from blocking if lower-priority coroutines are active, thus mapping
1358	low-priority coroutines to idle/background tasks).	2441	low-priority coroutines to idle/background tasks).
1359		2442
		2443	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2444	priority, to ensure that they are being run before any other watchers
		2445	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2446
		2447	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2448	activate ("feed") events into libev. While libev fully supports this, they
		2449	might get executed before other C<ev_check> watchers did their job. As
		2450	C<ev_check> watchers are often used to embed other (non-libev) event
		2451	loops those other event loops might be in an unusable state until their
		2452	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2453	others).
		2454
		2455	=head3 Watcher-Specific Functions and Data Members
		2456
1360	=over 4	2457	=over 4
1361		2458
1362	=item ev_prepare_init (ev_prepare *, callback)	2459	=item ev_prepare_init (ev_prepare *, callback)
1363		2460
1364	=item ev_check_init (ev_check *, callback)	2461	=item ev_check_init (ev_check *, callback)
1365		2462
1366	Initialises and configures the prepare or check watcher - they have no	2463	Initialises and configures the prepare or check watcher - they have no
1367	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2464	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1368	macros, but using them is utterly, utterly and completely pointless.	2465	macros, but using them is utterly, utterly, utterly and completely
		2466	pointless.
1369		2467
1370	=back	2468	=back
1371		2469
1372	Example: To include a library such as adns, you would add IO watchers	2470	=head3 Examples
1373	and a timeout watcher in a prepare handler, as required by libadns, and	2471
		2472	There are a number of principal ways to embed other event loops or modules
		2473	into libev. Here are some ideas on how to include libadns into libev
		2474	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2475	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2476	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2477	Glib event loop).
		2478
		2479	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1374	in a check watcher, destroy them and call into libadns. What follows is	2480	and in a check watcher, destroy them and call into libadns. What follows
1375	pseudo-code only of course:	2481	is pseudo-code only of course. This requires you to either use a low
		2482	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2483	the callbacks for the IO/timeout watchers might not have been called yet.
1376		2484
1377	static ev_io iow [nfd];	2485	static ev_io iow [nfd];
1378	static ev_timer tw;	2486	static ev_timer tw;
1379		2487
1380	static void	2488	static void
1381	io_cb (ev_loop *loop, ev_io *w, int revents)	2489	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1382	{	2490	{
1383	// set the relevant poll flags
1384	// could also call adns_processreadable etc. here
1385	struct pollfd *fd = (struct pollfd *)w->data;
1386	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1387	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1388	}	2491	}
1389		2492
1390	// create io watchers for each fd and a timer before blocking	2493	// create io watchers for each fd and a timer before blocking
1391	static void	2494	static void
1392	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2495	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1393	{	2496	{
1394	int timeout = 3600000;truct pollfd fds [nfd];	2497	int timeout = 3600000;
		2498	struct pollfd fds [nfd];
1395	// actual code will need to loop here and realloc etc.	2499	// actual code will need to loop here and realloc etc.
1396	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2500	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1397		2501
1398	/* the callback is illegal, but won't be called as we stop during check */	2502	/* the callback is illegal, but won't be called as we stop during check */
1399	ev_timer_init (&tw, 0, timeout * 1e-3);	2503	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1400	ev_timer_start (loop, &tw);	2504	ev_timer_start (loop, &tw);
1401		2505
1402	// create on ev_io per pollfd	2506	// create one ev_io per pollfd
1403	for (int i = 0; i < nfd; ++i)	2507	for (int i = 0; i < nfd; ++i)
1404	{	2508	{
1405	ev_io_init (iow + i, io_cb, fds [i].fd,	2509	ev_io_init (iow + i, io_cb, fds [i].fd,
1406	((fds [i].events & POLLIN ? EV_READ : 0)	2510	((fds [i].events & POLLIN ? EV_READ : 0)
1407	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2511	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1408		2512
1409	fds [i].revents = 0;	2513	fds [i].revents = 0;
1410	iow [i].data = fds + i;
1411	ev_io_start (loop, iow + i);	2514	ev_io_start (loop, iow + i);
1412	}	2515	}
1413	}	2516	}
1414		2517
1415	// stop all watchers after blocking	2518	// stop all watchers after blocking
1416	static void	2519	static void
1417	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2520	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1418	{	2521	{
1419	ev_timer_stop (loop, &tw);	2522	ev_timer_stop (loop, &tw);
1420		2523
1421	for (int i = 0; i < nfd; ++i)	2524	for (int i = 0; i < nfd; ++i)
		2525	{
		2526	// set the relevant poll flags
		2527	// could also call adns_processreadable etc. here
		2528	struct pollfd *fd = fds + i;
		2529	int revents = ev_clear_pending (iow + i);
		2530	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2531	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2532
		2533	// now stop the watcher
1422	ev_io_stop (loop, iow + i);	2534	ev_io_stop (loop, iow + i);
		2535	}
1423		2536
1424	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2537	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1425	}	2538	}
		2539
		2540	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2541	in the prepare watcher and would dispose of the check watcher.
		2542
		2543	Method 3: If the module to be embedded supports explicit event
		2544	notification (libadns does), you can also make use of the actual watcher
		2545	callbacks, and only destroy/create the watchers in the prepare watcher.
		2546
		2547	static void
		2548	timer_cb (EV_P_ ev_timer *w, int revents)
		2549	{
		2550	adns_state ads = (adns_state)w->data;
		2551	update_now (EV_A);
		2552
		2553	adns_processtimeouts (ads, &tv_now);
		2554	}
		2555
		2556	static void
		2557	io_cb (EV_P_ ev_io *w, int revents)
		2558	{
		2559	adns_state ads = (adns_state)w->data;
		2560	update_now (EV_A);
		2561
		2562	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2563	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2564	}
		2565
		2566	// do not ever call adns_afterpoll
		2567
		2568	Method 4: Do not use a prepare or check watcher because the module you
		2569	want to embed is not flexible enough to support it. Instead, you can
		2570	override their poll function. The drawback with this solution is that the
		2571	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2572	this approach, effectively embedding EV as a client into the horrible
		2573	libglib event loop.
		2574
		2575	static gint
		2576	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2577	{
		2578	int got_events = 0;
		2579
		2580	for (n = 0; n < nfds; ++n)
		2581	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2582
		2583	if (timeout >= 0)
		2584	// create/start timer
		2585
		2586	// poll
		2587	ev_loop (EV_A_ 0);
		2588
		2589	// stop timer again
		2590	if (timeout >= 0)
		2591	ev_timer_stop (EV_A_ &to);
		2592
		2593	// stop io watchers again - their callbacks should have set
		2594	for (n = 0; n < nfds; ++n)
		2595	ev_io_stop (EV_A_ iow [n]);
		2596
		2597	return got_events;
		2598	}
1426		2599
1427		2600
1428	=head2 C<ev_embed> - when one backend isn't enough...	2601	=head2 C<ev_embed> - when one backend isn't enough...
1429		2602
1430	This is a rather advanced watcher type that lets you embed one event loop	2603	This is a rather advanced watcher type that lets you embed one event loop
…		…
1436	prioritise I/O.	2609	prioritise I/O.
1437		2610
1438	As an example for a bug workaround, the kqueue backend might only support	2611	As an example for a bug workaround, the kqueue backend might only support
1439	sockets on some platform, so it is unusable as generic backend, but you	2612	sockets on some platform, so it is unusable as generic backend, but you
1440	still want to make use of it because you have many sockets and it scales	2613	still want to make use of it because you have many sockets and it scales
1441	so nicely. In this case, you would create a kqueue-based loop and embed it	2614	so nicely. In this case, you would create a kqueue-based loop and embed
1442	into your default loop (which might use e.g. poll). Overall operation will	2615	it into your default loop (which might use e.g. poll). Overall operation
1443	be a bit slower because first libev has to poll and then call kevent, but	2616	will be a bit slower because first libev has to call C<poll> and then
1444	at least you can use both at what they are best.	2617	C<kevent>, but at least you can use both mechanisms for what they are
		2618	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1445		2619
1446	As for prioritising I/O: rarely you have the case where some fds have	2620	As for prioritising I/O: under rare circumstances you have the case where
1447	to be watched and handled very quickly (with low latency), and even	2621	some fds have to be watched and handled very quickly (with low latency),
1448	priorities and idle watchers might have too much overhead. In this case	2622	and even priorities and idle watchers might have too much overhead. In
1449	you would put all the high priority stuff in one loop and all the rest in	2623	this case you would put all the high priority stuff in one loop and all
1450	a second one, and embed the second one in the first.	2624	the rest in a second one, and embed the second one in the first.
1451		2625
1452	As long as the watcher is active, the callback will be invoked every time	2626	As long as the watcher is active, the callback will be invoked every
1453	there might be events pending in the embedded loop. The callback must then	2627	time there might be events pending in the embedded loop. The callback
1454	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2628	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1455	their callbacks (you could also start an idle watcher to give the embedded	2629	sweep and invoke their callbacks (the callback doesn't need to invoke the
1456	loop strictly lower priority for example). You can also set the callback	2630	C<ev_embed_sweep> function directly, it could also start an idle watcher
1457	to C<0>, in which case the embed watcher will automatically execute the	2631	to give the embedded loop strictly lower priority for example).
1458	embedded loop sweep.
1459		2632
1460	As long as the watcher is started it will automatically handle events. The	2633	You can also set the callback to C<0>, in which case the embed watcher
1461	callback will be invoked whenever some events have been handled. You can	2634	will automatically execute the embedded loop sweep whenever necessary.
1462	set the callback to C<0> to avoid having to specify one if you are not
1463	interested in that.
1464		2635
1465	Also, there have not currently been made special provisions for forking:	2636	Fork detection will be handled transparently while the C<ev_embed> watcher
1466	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2637	is active, i.e., the embedded loop will automatically be forked when the
1467	but you will also have to stop and restart any C<ev_embed> watchers	2638	embedding loop forks. In other cases, the user is responsible for calling
1468	yourself.	2639	C<ev_loop_fork> on the embedded loop.
1469		2640
1470	Unfortunately, not all backends are embeddable, only the ones returned by	2641	Unfortunately, not all backends are embeddable: only the ones returned by
1471	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2642	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1472	portable one.	2643	portable one.
1473		2644
1474	So when you want to use this feature you will always have to be prepared	2645	So when you want to use this feature you will always have to be prepared
1475	that you cannot get an embeddable loop. The recommended way to get around	2646	that you cannot get an embeddable loop. The recommended way to get around
1476	this is to have a separate variables for your embeddable loop, try to	2647	this is to have a separate variables for your embeddable loop, try to
1477	create it, and if that fails, use the normal loop for everything:	2648	create it, and if that fails, use the normal loop for everything.
1478		2649
1479	struct ev_loop *loop_hi = ev_default_init (0);	2650	=head3 C<ev_embed> and fork
1480	struct ev_loop *loop_lo = 0;
1481	struct ev_embed embed;
1482
1483	// see if there is a chance of getting one that works
1484	// (remember that a flags value of 0 means autodetection)
1485	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1486	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1487	: 0;
1488		2651
1489	// if we got one, then embed it, otherwise default to loop_hi	2652	While the C<ev_embed> watcher is running, forks in the embedding loop will
1490	if (loop_lo)	2653	automatically be applied to the embedded loop as well, so no special
1491	{	2654	fork handling is required in that case. When the watcher is not running,
1492	ev_embed_init (&embed, 0, loop_lo);	2655	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1493	ev_embed_start (loop_hi, &embed);	2656	as applicable.
1494	}	2657
1495	else	2658	=head3 Watcher-Specific Functions and Data Members
1496	loop_lo = loop_hi;
1497		2659
1498	=over 4	2660	=over 4
1499		2661
1500	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2662	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1501		2663
…		…
1503		2665
1504	Configures the watcher to embed the given loop, which must be	2666	Configures the watcher to embed the given loop, which must be
1505	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2667	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1506	invoked automatically, otherwise it is the responsibility of the callback	2668	invoked automatically, otherwise it is the responsibility of the callback
1507	to invoke it (it will continue to be called until the sweep has been done,	2669	to invoke it (it will continue to be called until the sweep has been done,
1508	if you do not want thta, you need to temporarily stop the embed watcher).	2670	if you do not want that, you need to temporarily stop the embed watcher).
1509		2671
1510	=item ev_embed_sweep (loop, ev_embed *)	2672	=item ev_embed_sweep (loop, ev_embed *)
1511		2673
1512	Make a single, non-blocking sweep over the embedded loop. This works	2674	Make a single, non-blocking sweep over the embedded loop. This works
1513	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2675	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1514	apropriate way for embedded loops.	2676	appropriate way for embedded loops.
1515		2677
1516	=item struct ev_loop *loop [read-only]	2678	=item struct ev_loop *other [read-only]
1517		2679
1518	The embedded event loop.	2680	The embedded event loop.
1519		2681
1520	=back	2682	=back
		2683
		2684	=head3 Examples
		2685
		2686	Example: Try to get an embeddable event loop and embed it into the default
		2687	event loop. If that is not possible, use the default loop. The default
		2688	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2689	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2690	used).
		2691
		2692	struct ev_loop *loop_hi = ev_default_init (0);
		2693	struct ev_loop *loop_lo = 0;
		2694	ev_embed embed;
		2695
		2696	// see if there is a chance of getting one that works
		2697	// (remember that a flags value of 0 means autodetection)
		2698	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2699	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2700	: 0;
		2701
		2702	// if we got one, then embed it, otherwise default to loop_hi
		2703	if (loop_lo)
		2704	{
		2705	ev_embed_init (&embed, 0, loop_lo);
		2706	ev_embed_start (loop_hi, &embed);
		2707	}
		2708	else
		2709	loop_lo = loop_hi;
		2710
		2711	Example: Check if kqueue is available but not recommended and create
		2712	a kqueue backend for use with sockets (which usually work with any
		2713	kqueue implementation). Store the kqueue/socket-only event loop in
		2714	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2715
		2716	struct ev_loop *loop = ev_default_init (0);
		2717	struct ev_loop *loop_socket = 0;
		2718	ev_embed embed;
		2719
		2720	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2721	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2722	{
		2723	ev_embed_init (&embed, 0, loop_socket);
		2724	ev_embed_start (loop, &embed);
		2725	}
		2726
		2727	if (!loop_socket)
		2728	loop_socket = loop;
		2729
		2730	// now use loop_socket for all sockets, and loop for everything else
1521		2731
1522		2732
1523	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2733	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1524		2734
1525	Fork watchers are called when a C<fork ()> was detected (usually because	2735	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1528	event loop blocks next and before C<ev_check> watchers are being called,	2738	event loop blocks next and before C<ev_check> watchers are being called,
1529	and only in the child after the fork. If whoever good citizen calling	2739	and only in the child after the fork. If whoever good citizen calling
1530	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2740	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1531	handlers will be invoked, too, of course.	2741	handlers will be invoked, too, of course.
1532		2742
		2743	=head3 The special problem of life after fork - how is it possible?
		2744
		2745	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2746	up/change the process environment, followed by a call to C<exec()>. This
		2747	sequence should be handled by libev without any problems.
		2748
		2749	This changes when the application actually wants to do event handling
		2750	in the child, or both parent in child, in effect "continuing" after the
		2751	fork.
		2752
		2753	The default mode of operation (for libev, with application help to detect
		2754	forks) is to duplicate all the state in the child, as would be expected
		2755	when I<either> the parent I<or> the child process continues.
		2756
		2757	When both processes want to continue using libev, then this is usually the
		2758	wrong result. In that case, usually one process (typically the parent) is
		2759	supposed to continue with all watchers in place as before, while the other
		2760	process typically wants to start fresh, i.e. without any active watchers.
		2761
		2762	The cleanest and most efficient way to achieve that with libev is to
		2763	simply create a new event loop, which of course will be "empty", and
		2764	use that for new watchers. This has the advantage of not touching more
		2765	memory than necessary, and thus avoiding the copy-on-write, and the
		2766	disadvantage of having to use multiple event loops (which do not support
		2767	signal watchers).
		2768
		2769	When this is not possible, or you want to use the default loop for
		2770	other reasons, then in the process that wants to start "fresh", call
		2771	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2772	the default loop will "orphan" (not stop) all registered watchers, so you
		2773	have to be careful not to execute code that modifies those watchers. Note
		2774	also that in that case, you have to re-register any signal watchers.
		2775
		2776	=head3 Watcher-Specific Functions and Data Members
		2777
1533	=over 4	2778	=over 4
1534		2779
1535	=item ev_fork_init (ev_signal *, callback)	2780	=item ev_fork_init (ev_signal *, callback)
1536		2781
1537	Initialises and configures the fork watcher - it has no parameters of any	2782	Initialises and configures the fork watcher - it has no parameters of any
…		…
1539	believe me.	2784	believe me.
1540		2785
1541	=back	2786	=back
1542		2787
1543		2788
		2789	=head2 C<ev_async> - how to wake up another event loop
		2790
		2791	In general, you cannot use an C<ev_loop> from multiple threads or other
		2792	asynchronous sources such as signal handlers (as opposed to multiple event
		2793	loops - those are of course safe to use in different threads).
		2794
		2795	Sometimes, however, you need to wake up another event loop you do not
		2796	control, for example because it belongs to another thread. This is what
		2797	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2798	can signal it by calling C<ev_async_send>, which is thread- and signal
		2799	safe.
		2800
		2801	This functionality is very similar to C<ev_signal> watchers, as signals,
		2802	too, are asynchronous in nature, and signals, too, will be compressed
		2803	(i.e. the number of callback invocations may be less than the number of
		2804	C<ev_async_sent> calls).
		2805
		2806	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2807	just the default loop.
		2808
		2809	=head3 Queueing
		2810
		2811	C<ev_async> does not support queueing of data in any way. The reason
		2812	is that the author does not know of a simple (or any) algorithm for a
		2813	multiple-writer-single-reader queue that works in all cases and doesn't
		2814	need elaborate support such as pthreads.
		2815
		2816	That means that if you want to queue data, you have to provide your own
		2817	queue. But at least I can tell you how to implement locking around your
		2818	queue:
		2819
		2820	=over 4
		2821
		2822	=item queueing from a signal handler context
		2823
		2824	To implement race-free queueing, you simply add to the queue in the signal
		2825	handler but you block the signal handler in the watcher callback. Here is
		2826	an example that does that for some fictitious SIGUSR1 handler:
		2827
		2828	static ev_async mysig;
		2829
		2830	static void
		2831	sigusr1_handler (void)
		2832	{
		2833	sometype data;
		2834
		2835	// no locking etc.
		2836	queue_put (data);
		2837	ev_async_send (EV_DEFAULT_ &mysig);
		2838	}
		2839
		2840	static void
		2841	mysig_cb (EV_P_ ev_async *w, int revents)
		2842	{
		2843	sometype data;
		2844	sigset_t block, prev;
		2845
		2846	sigemptyset (&block);
		2847	sigaddset (&block, SIGUSR1);
		2848	sigprocmask (SIG_BLOCK, &block, &prev);
		2849
		2850	while (queue_get (&data))
		2851	process (data);
		2852
		2853	if (sigismember (&prev, SIGUSR1)
		2854	sigprocmask (SIG_UNBLOCK, &block, 0);
		2855	}
		2856
		2857	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2858	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2859	either...).
		2860
		2861	=item queueing from a thread context
		2862
		2863	The strategy for threads is different, as you cannot (easily) block
		2864	threads but you can easily preempt them, so to queue safely you need to
		2865	employ a traditional mutex lock, such as in this pthread example:
		2866
		2867	static ev_async mysig;
		2868	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2869
		2870	static void
		2871	otherthread (void)
		2872	{
		2873	// only need to lock the actual queueing operation
		2874	pthread_mutex_lock (&mymutex);
		2875	queue_put (data);
		2876	pthread_mutex_unlock (&mymutex);
		2877
		2878	ev_async_send (EV_DEFAULT_ &mysig);
		2879	}
		2880
		2881	static void
		2882	mysig_cb (EV_P_ ev_async *w, int revents)
		2883	{
		2884	pthread_mutex_lock (&mymutex);
		2885
		2886	while (queue_get (&data))
		2887	process (data);
		2888
		2889	pthread_mutex_unlock (&mymutex);
		2890	}
		2891
		2892	=back
		2893
		2894
		2895	=head3 Watcher-Specific Functions and Data Members
		2896
		2897	=over 4
		2898
		2899	=item ev_async_init (ev_async *, callback)
		2900
		2901	Initialises and configures the async watcher - it has no parameters of any
		2902	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2903	trust me.
		2904
		2905	=item ev_async_send (loop, ev_async *)
		2906
		2907	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2908	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2909	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2910	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2911	section below on what exactly this means).
		2912
		2913	Note that, as with other watchers in libev, multiple events might get
		2914	compressed into a single callback invocation (another way to look at this
		2915	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2916	reset when the event loop detects that).
		2917
		2918	This call incurs the overhead of a system call only once per event loop
		2919	iteration, so while the overhead might be noticeable, it doesn't apply to
		2920	repeated calls to C<ev_async_send> for the same event loop.
		2921
		2922	=item bool = ev_async_pending (ev_async *)
		2923
		2924	Returns a non-zero value when C<ev_async_send> has been called on the
		2925	watcher but the event has not yet been processed (or even noted) by the
		2926	event loop.
		2927
		2928	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2929	the loop iterates next and checks for the watcher to have become active,
		2930	it will reset the flag again. C<ev_async_pending> can be used to very
		2931	quickly check whether invoking the loop might be a good idea.
		2932
		2933	Not that this does I<not> check whether the watcher itself is pending,
		2934	only whether it has been requested to make this watcher pending: there
		2935	is a time window between the event loop checking and resetting the async
		2936	notification, and the callback being invoked.
		2937
		2938	=back
		2939
		2940
1544	=head1 OTHER FUNCTIONS	2941	=head1 OTHER FUNCTIONS
1545		2942
1546	There are some other functions of possible interest. Described. Here. Now.	2943	There are some other functions of possible interest. Described. Here. Now.
1547		2944
1548	=over 4	2945	=over 4
1549		2946
1550	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2947	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1551		2948
1552	This function combines a simple timer and an I/O watcher, calls your	2949	This function combines a simple timer and an I/O watcher, calls your
1553	callback on whichever event happens first and automatically stop both	2950	callback on whichever event happens first and automatically stops both
1554	watchers. This is useful if you want to wait for a single event on an fd	2951	watchers. This is useful if you want to wait for a single event on an fd
1555	or timeout without having to allocate/configure/start/stop/free one or	2952	or timeout without having to allocate/configure/start/stop/free one or
1556	more watchers yourself.	2953	more watchers yourself.
1557		2954
1558	If C<fd> is less than 0, then no I/O watcher will be started and events	2955	If C<fd> is less than 0, then no I/O watcher will be started and the
1559	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2956	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1560	C<events> set will be craeted and started.	2957	the given C<fd> and C<events> set will be created and started.
1561		2958
1562	If C<timeout> is less than 0, then no timeout watcher will be	2959	If C<timeout> is less than 0, then no timeout watcher will be
1563	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2960	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1564	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2961	repeat = 0) will be started. C<0> is a valid timeout.
1565	dubious value.
1566		2962
1567	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2963	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1568	passed an C<revents> set like normal event callbacks (a combination of	2964	passed an C<revents> set like normal event callbacks (a combination of
1569	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2965	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1570	value passed to C<ev_once>:	2966	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2967	a timeout and an io event at the same time - you probably should give io
		2968	events precedence.
1571		2969
		2970	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2971
1572	static void stdin_ready (int revents, void *arg)	2972	static void stdin_ready (int revents, void *arg)
1573	{	2973	{
1574	if (revents & EV_TIMEOUT)
1575	/* doh, nothing entered */;
1576	else if (revents & EV_READ)	2974	if (revents & EV_READ)
1577	/* stdin might have data for us, joy! */;	2975	/* stdin might have data for us, joy! */;
		2976	else if (revents & EV_TIMEOUT)
		2977	/* doh, nothing entered */;
1578	}	2978	}
1579		2979
1580	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2980	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1581		2981
1582	=item ev_feed_event (ev_loop *, watcher *, int revents)	2982	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1583		2983
1584	Feeds the given event set into the event loop, as if the specified event	2984	Feeds the given event set into the event loop, as if the specified event
1585	had happened for the specified watcher (which must be a pointer to an	2985	had happened for the specified watcher (which must be a pointer to an
1586	initialised but not necessarily started event watcher).	2986	initialised but not necessarily started event watcher).
1587		2987
1588	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2988	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1589		2989
1590	Feed an event on the given fd, as if a file descriptor backend detected	2990	Feed an event on the given fd, as if a file descriptor backend detected
1591	the given events it.	2991	the given events it.
1592		2992
1593	=item ev_feed_signal_event (ev_loop *loop, int signum)	2993	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1594		2994
1595	Feed an event as if the given signal occured (C<loop> must be the default	2995	Feed an event as if the given signal occurred (C<loop> must be the default
1596	loop!).	2996	loop!).
1597		2997
1598	=back	2998	=back
1599		2999
1600		3000
…		…
1616		3016
1617	=item * Priorities are not currently supported. Initialising priorities	3017	=item * Priorities are not currently supported. Initialising priorities
1618	will fail and all watchers will have the same priority, even though there	3018	will fail and all watchers will have the same priority, even though there
1619	is an ev_pri field.	3019	is an ev_pri field.
1620		3020
		3021	=item * In libevent, the last base created gets the signals, in libev, the
		3022	first base created (== the default loop) gets the signals.
		3023
1621	=item * Other members are not supported.	3024	=item * Other members are not supported.
1622		3025
1623	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3026	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1624	to use the libev header file and library.	3027	to use the libev header file and library.
1625		3028
1626	=back	3029	=back
1627		3030
1628	=head1 C++ SUPPORT	3031	=head1 C++ SUPPORT
1629		3032
1630	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3033	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1631	you to use some convinience methods to start/stop watchers and also change	3034	you to use some convenience methods to start/stop watchers and also change
1632	the callback model to a model using method callbacks on objects.	3035	the callback model to a model using method callbacks on objects.
1633		3036
1634	To use it,	3037	To use it,
1635		3038
1636	#include <ev++.h>	3039	#include <ev++.h>
1637		3040
1638	(it is not installed by default). This automatically includes F<ev.h>	3041	This automatically includes F<ev.h> and puts all of its definitions (many
1639	and puts all of its definitions (many of them macros) into the global	3042	of them macros) into the global namespace. All C++ specific things are
1640	namespace. All C++ specific things are put into the C<ev> namespace.	3043	put into the C<ev> namespace. It should support all the same embedding
		3044	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1641		3045
1642	It should support all the same embedding options as F<ev.h>, most notably	3046	Care has been taken to keep the overhead low. The only data member the C++
1643	C<EV_MULTIPLICITY>.	3047	classes add (compared to plain C-style watchers) is the event loop pointer
		3048	that the watcher is associated with (or no additional members at all if
		3049	you disable C<EV_MULTIPLICITY> when embedding libev).
		3050
		3051	Currently, functions, and static and non-static member functions can be
		3052	used as callbacks. Other types should be easy to add as long as they only
		3053	need one additional pointer for context. If you need support for other
		3054	types of functors please contact the author (preferably after implementing
		3055	it).
1644		3056
1645	Here is a list of things available in the C<ev> namespace:	3057	Here is a list of things available in the C<ev> namespace:
1646		3058
1647	=over 4	3059	=over 4
1648		3060
…		…
1664		3076
1665	All of those classes have these methods:	3077	All of those classes have these methods:
1666		3078
1667	=over 4	3079	=over 4
1668		3080
1669	=item ev::TYPE::TYPE (object *, object::method *)	3081	=item ev::TYPE::TYPE ()
1670		3082
1671	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	3083	=item ev::TYPE::TYPE (struct ev_loop *)
1672		3084
1673	=item ev::TYPE::~TYPE	3085	=item ev::TYPE::~TYPE
1674		3086
1675	The constructor takes a pointer to an object and a method pointer to	3087	The constructor (optionally) takes an event loop to associate the watcher
1676	the event handler callback to call in this class. The constructor calls	3088	with. If it is omitted, it will use C<EV_DEFAULT>.
1677	C<ev_init> for you, which means you have to call the C<set> method	3089
1678	before starting it. If you do not specify a loop then the constructor	3090	The constructor calls C<ev_init> for you, which means you have to call the
1679	automatically associates the default loop with this watcher.	3091	C<set> method before starting it.
		3092
		3093	It will not set a callback, however: You have to call the templated C<set>
		3094	method to set a callback before you can start the watcher.
		3095
		3096	(The reason why you have to use a method is a limitation in C++ which does
		3097	not allow explicit template arguments for constructors).
1680		3098
1681	The destructor automatically stops the watcher if it is active.	3099	The destructor automatically stops the watcher if it is active.
		3100
		3101	=item w->set<class, &class::method> (object *)
		3102
		3103	This method sets the callback method to call. The method has to have a
		3104	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3105	first argument and the C<revents> as second. The object must be given as
		3106	parameter and is stored in the C<data> member of the watcher.
		3107
		3108	This method synthesizes efficient thunking code to call your method from
		3109	the C callback that libev requires. If your compiler can inline your
		3110	callback (i.e. it is visible to it at the place of the C<set> call and
		3111	your compiler is good :), then the method will be fully inlined into the
		3112	thunking function, making it as fast as a direct C callback.
		3113
		3114	Example: simple class declaration and watcher initialisation
		3115
		3116	struct myclass
		3117	{
		3118	void io_cb (ev::io &w, int revents) { }
		3119	}
		3120
		3121	myclass obj;
		3122	ev::io iow;
		3123	iow.set <myclass, &myclass::io_cb> (&obj);
		3124
		3125	=item w->set (object *)
		3126
		3127	This is an B<experimental> feature that might go away in a future version.
		3128
		3129	This is a variation of a method callback - leaving out the method to call
		3130	will default the method to C<operator ()>, which makes it possible to use
		3131	functor objects without having to manually specify the C<operator ()> all
		3132	the time. Incidentally, you can then also leave out the template argument
		3133	list.
		3134
		3135	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3136	int revents)>.
		3137
		3138	See the method-C<set> above for more details.
		3139
		3140	Example: use a functor object as callback.
		3141
		3142	struct myfunctor
		3143	{
		3144	void operator() (ev::io &w, int revents)
		3145	{
		3146	...
		3147	}
		3148	}
		3149
		3150	myfunctor f;
		3151
		3152	ev::io w;
		3153	w.set (&f);
		3154
		3155	=item w->set<function> (void *data = 0)
		3156
		3157	Also sets a callback, but uses a static method or plain function as
		3158	callback. The optional C<data> argument will be stored in the watcher's
		3159	C<data> member and is free for you to use.
		3160
		3161	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3162
		3163	See the method-C<set> above for more details.
		3164
		3165	Example: Use a plain function as callback.
		3166
		3167	static void io_cb (ev::io &w, int revents) { }
		3168	iow.set <io_cb> ();
1682		3169
1683	=item w->set (struct ev_loop *)	3170	=item w->set (struct ev_loop *)
1684		3171
1685	Associates a different C<struct ev_loop> with this watcher. You can only	3172	Associates a different C<struct ev_loop> with this watcher. You can only
1686	do this when the watcher is inactive (and not pending either).	3173	do this when the watcher is inactive (and not pending either).
1687		3174
1688	=item w->set ([args])	3175	=item w->set ([arguments])
1689		3176
1690	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3177	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1691	called at least once. Unlike the C counterpart, an active watcher gets	3178	called at least once. Unlike the C counterpart, an active watcher gets
1692	automatically stopped and restarted.	3179	automatically stopped and restarted when reconfiguring it with this
		3180	method.
1693		3181
1694	=item w->start ()	3182	=item w->start ()
1695		3183
1696	Starts the watcher. Note that there is no C<loop> argument as the	3184	Starts the watcher. Note that there is no C<loop> argument, as the
1697	constructor already takes the loop.	3185	constructor already stores the event loop.
1698		3186
1699	=item w->stop ()	3187	=item w->stop ()
1700		3188
1701	Stops the watcher if it is active. Again, no C<loop> argument.	3189	Stops the watcher if it is active. Again, no C<loop> argument.
1702		3190
1703	=item w->again () C<ev::timer>, C<ev::periodic> only	3191	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1704		3192
1705	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3193	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1706	C<ev_TYPE_again> function.	3194	C<ev_TYPE_again> function.
1707		3195
1708	=item w->sweep () C<ev::embed> only	3196	=item w->sweep () (C<ev::embed> only)
1709		3197
1710	Invokes C<ev_embed_sweep>.	3198	Invokes C<ev_embed_sweep>.
1711		3199
1712	=item w->update () C<ev::stat> only	3200	=item w->update () (C<ev::stat> only)
1713		3201
1714	Invokes C<ev_stat_stat>.	3202	Invokes C<ev_stat_stat>.
1715		3203
1716	=back	3204	=back
1717		3205
1718	=back	3206	=back
1719		3207
1720	Example: Define a class with an IO and idle watcher, start one of them in	3208	Example: Define a class with an IO and idle watcher, start one of them in
1721	the constructor.	3209	the constructor.
1722		3210
1723	class myclass	3211	class myclass
1724	{	3212	{
1725	ev_io io; void io_cb (ev::io &w, int revents);	3213	ev::io io ; void io_cb (ev::io &w, int revents);
1726	ev_idle idle void idle_cb (ev::idle &w, int revents);	3214	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1727		3215
1728	myclass ();	3216	myclass (int fd)
1729	}	3217	{
		3218	io .set <myclass, &myclass::io_cb > (this);
		3219	idle.set <myclass, &myclass::idle_cb> (this);
1730		3220
1731	myclass::myclass (int fd)
1732	: io (this, &myclass::io_cb),
1733	idle (this, &myclass::idle_cb)
1734	{
1735	io.start (fd, ev::READ);	3221	io.start (fd, ev::READ);
		3222	}
1736	}	3223	};
		3224
		3225
		3226	=head1 OTHER LANGUAGE BINDINGS
		3227
		3228	Libev does not offer other language bindings itself, but bindings for a
		3229	number of languages exist in the form of third-party packages. If you know
		3230	any interesting language binding in addition to the ones listed here, drop
		3231	me a note.
		3232
		3233	=over 4
		3234
		3235	=item Perl
		3236
		3237	The EV module implements the full libev API and is actually used to test
		3238	libev. EV is developed together with libev. Apart from the EV core module,
		3239	there are additional modules that implement libev-compatible interfaces
		3240	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3241	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3242	and C<EV::Glib>).
		3243
		3244	It can be found and installed via CPAN, its homepage is at
		3245	L<http://software.schmorp.de/pkg/EV>.
		3246
		3247	=item Python
		3248
		3249	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3250	seems to be quite complete and well-documented.
		3251
		3252	=item Ruby
		3253
		3254	Tony Arcieri has written a ruby extension that offers access to a subset
		3255	of the libev API and adds file handle abstractions, asynchronous DNS and
		3256	more on top of it. It can be found via gem servers. Its homepage is at
		3257	L<http://rev.rubyforge.org/>.
		3258
		3259	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3260	makes rev work even on mingw.
		3261
		3262	=item Haskell
		3263
		3264	A haskell binding to libev is available at
		3265	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3266
		3267	=item D
		3268
		3269	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3270	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3271
		3272	=item Ocaml
		3273
		3274	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3275	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3276
		3277	=back
1737		3278
1738		3279
1739	=head1 MACRO MAGIC	3280	=head1 MACRO MAGIC
1740		3281
1741	Libev can be compiled with a variety of options, the most fundemantal is	3282	Libev can be compiled with a variety of options, the most fundamental
1742	C<EV_MULTIPLICITY>. This option determines wether (most) functions and	3283	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1743	callbacks have an initial C<struct ev_loop *> argument.	3284	functions and callbacks have an initial C<struct ev_loop *> argument.
1744		3285
1745	To make it easier to write programs that cope with either variant, the	3286	To make it easier to write programs that cope with either variant, the
1746	following macros are defined:	3287	following macros are defined:
1747		3288
1748	=over 4	3289	=over 4
…		…
1751		3292
1752	This provides the loop I<argument> for functions, if one is required ("ev	3293	This provides the loop I<argument> for functions, if one is required ("ev
1753	loop argument"). The C<EV_A> form is used when this is the sole argument,	3294	loop argument"). The C<EV_A> form is used when this is the sole argument,
1754	C<EV_A_> is used when other arguments are following. Example:	3295	C<EV_A_> is used when other arguments are following. Example:
1755		3296
1756	ev_unref (EV_A);	3297	ev_unref (EV_A);
1757	ev_timer_add (EV_A_ watcher);	3298	ev_timer_add (EV_A_ watcher);
1758	ev_loop (EV_A_ 0);	3299	ev_loop (EV_A_ 0);
1759		3300
1760	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3301	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1761	which is often provided by the following macro.	3302	which is often provided by the following macro.
1762		3303
1763	=item C<EV_P>, C<EV_P_>	3304	=item C<EV_P>, C<EV_P_>
1764		3305
1765	This provides the loop I<parameter> for functions, if one is required ("ev	3306	This provides the loop I<parameter> for functions, if one is required ("ev
1766	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3307	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1767	C<EV_P_> is used when other parameters are following. Example:	3308	C<EV_P_> is used when other parameters are following. Example:
1768		3309
1769	// this is how ev_unref is being declared	3310	// this is how ev_unref is being declared
1770	static void ev_unref (EV_P);	3311	static void ev_unref (EV_P);
1771		3312
1772	// this is how you can declare your typical callback	3313	// this is how you can declare your typical callback
1773	static void cb (EV_P_ ev_timer *w, int revents)	3314	static void cb (EV_P_ ev_timer *w, int revents)
1774		3315
1775	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3316	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1776	suitable for use with C<EV_A>.	3317	suitable for use with C<EV_A>.
1777		3318
1778	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3319	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1779		3320
1780	Similar to the other two macros, this gives you the value of the default	3321	Similar to the other two macros, this gives you the value of the default
1781	loop, if multiple loops are supported ("ev loop default").	3322	loop, if multiple loops are supported ("ev loop default").
1782		3323
		3324	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3325
		3326	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3327	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3328	is undefined when the default loop has not been initialised by a previous
		3329	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3330
		3331	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3332	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3333
1783	=back	3334	=back
1784		3335
1785	Example: Declare and initialise a check watcher, working regardless of	3336	Example: Declare and initialise a check watcher, utilising the above
1786	wether multiple loops are supported or not.	3337	macros so it will work regardless of whether multiple loops are supported
		3338	or not.
1787		3339
1788	static void	3340	static void
1789	check_cb (EV_P_ ev_timer *w, int revents)	3341	check_cb (EV_P_ ev_timer *w, int revents)
1790	{	3342	{
1791	ev_check_stop (EV_A_ w);	3343	ev_check_stop (EV_A_ w);
1792	}	3344	}
1793		3345
1794	ev_check check;	3346	ev_check check;
1795	ev_check_init (&check, check_cb);	3347	ev_check_init (&check, check_cb);
1796	ev_check_start (EV_DEFAULT_ &check);	3348	ev_check_start (EV_DEFAULT_ &check);
1797	ev_loop (EV_DEFAULT_ 0);	3349	ev_loop (EV_DEFAULT_ 0);
1798
1799		3350
1800	=head1 EMBEDDING	3351	=head1 EMBEDDING
1801		3352
1802	Libev can (and often is) directly embedded into host	3353	Libev can (and often is) directly embedded into host
1803	applications. Examples of applications that embed it include the Deliantra	3354	applications. Examples of applications that embed it include the Deliantra
1804	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3355	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1805	and rxvt-unicode.	3356	and rxvt-unicode.
1806		3357
1807	The goal is to enable you to just copy the neecssary files into your	3358	The goal is to enable you to just copy the necessary files into your
1808	source directory without having to change even a single line in them, so	3359	source directory without having to change even a single line in them, so
1809	you can easily upgrade by simply copying (or having a checked-out copy of	3360	you can easily upgrade by simply copying (or having a checked-out copy of
1810	libev somewhere in your source tree).	3361	libev somewhere in your source tree).
1811		3362
1812	=head2 FILESETS	3363	=head2 FILESETS
1813		3364
1814	Depending on what features you need you need to include one or more sets of files	3365	Depending on what features you need you need to include one or more sets of files
1815	in your app.	3366	in your application.
1816		3367
1817	=head3 CORE EVENT LOOP	3368	=head3 CORE EVENT LOOP
1818		3369
1819	To include only the libev core (all the C<ev_*> functions), with manual	3370	To include only the libev core (all the C<ev_*> functions), with manual
1820	configuration (no autoconf):	3371	configuration (no autoconf):
1821		3372
1822	#define EV_STANDALONE 1	3373	#define EV_STANDALONE 1
1823	#include "ev.c"	3374	#include "ev.c"
1824		3375
1825	This will automatically include F<ev.h>, too, and should be done in a	3376	This will automatically include F<ev.h>, too, and should be done in a
1826	single C source file only to provide the function implementations. To use	3377	single C source file only to provide the function implementations. To use
1827	it, do the same for F<ev.h> in all files wishing to use this API (best	3378	it, do the same for F<ev.h> in all files wishing to use this API (best
1828	done by writing a wrapper around F<ev.h> that you can include instead and	3379	done by writing a wrapper around F<ev.h> that you can include instead and
1829	where you can put other configuration options):	3380	where you can put other configuration options):
1830		3381
1831	#define EV_STANDALONE 1	3382	#define EV_STANDALONE 1
1832	#include "ev.h"	3383	#include "ev.h"
1833		3384
1834	Both header files and implementation files can be compiled with a C++	3385	Both header files and implementation files can be compiled with a C++
1835	compiler (at least, thats a stated goal, and breakage will be treated	3386	compiler (at least, that's a stated goal, and breakage will be treated
1836	as a bug).	3387	as a bug).
1837		3388
1838	You need the following files in your source tree, or in a directory	3389	You need the following files in your source tree, or in a directory
1839	in your include path (e.g. in libev/ when using -Ilibev):	3390	in your include path (e.g. in libev/ when using -Ilibev):
1840		3391
1841	ev.h	3392	ev.h
1842	ev.c	3393	ev.c
1843	ev_vars.h	3394	ev_vars.h
1844	ev_wrap.h	3395	ev_wrap.h
1845		3396
1846	ev_win32.c required on win32 platforms only	3397	ev_win32.c required on win32 platforms only
1847		3398
1848	ev_select.c only when select backend is enabled (which is by default)	3399	ev_select.c only when select backend is enabled (which is enabled by default)
1849	ev_poll.c only when poll backend is enabled (disabled by default)	3400	ev_poll.c only when poll backend is enabled (disabled by default)
1850	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3401	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1851	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3402	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1852	ev_port.c only when the solaris port backend is enabled (disabled by default)	3403	ev_port.c only when the solaris port backend is enabled (disabled by default)
1853		3404
1854	F<ev.c> includes the backend files directly when enabled, so you only need	3405	F<ev.c> includes the backend files directly when enabled, so you only need
1855	to compile this single file.	3406	to compile this single file.
1856		3407
1857	=head3 LIBEVENT COMPATIBILITY API	3408	=head3 LIBEVENT COMPATIBILITY API
1858		3409
1859	To include the libevent compatibility API, also include:	3410	To include the libevent compatibility API, also include:
1860		3411
1861	#include "event.c"	3412	#include "event.c"
1862		3413
1863	in the file including F<ev.c>, and:	3414	in the file including F<ev.c>, and:
1864		3415
1865	#include "event.h"	3416	#include "event.h"
1866		3417
1867	in the files that want to use the libevent API. This also includes F<ev.h>.	3418	in the files that want to use the libevent API. This also includes F<ev.h>.
1868		3419
1869	You need the following additional files for this:	3420	You need the following additional files for this:
1870		3421
1871	event.h	3422	event.h
1872	event.c	3423	event.c
1873		3424
1874	=head3 AUTOCONF SUPPORT	3425	=head3 AUTOCONF SUPPORT
1875		3426
1876	Instead of using C<EV_STANDALONE=1> and providing your config in	3427	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1877	whatever way you want, you can also C<m4_include([libev.m4])> in your	3428	whatever way you want, you can also C<m4_include([libev.m4])> in your
1878	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3429	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1879	include F<config.h> and configure itself accordingly.	3430	include F<config.h> and configure itself accordingly.
1880		3431
1881	For this of course you need the m4 file:	3432	For this of course you need the m4 file:
1882		3433
1883	libev.m4	3434	libev.m4
1884		3435
1885	=head2 PREPROCESSOR SYMBOLS/MACROS	3436	=head2 PREPROCESSOR SYMBOLS/MACROS
1886		3437
1887	Libev can be configured via a variety of preprocessor symbols you have to define	3438	Libev can be configured via a variety of preprocessor symbols you have to
1888	before including any of its files. The default is not to build for multiplicity	3439	define before including any of its files. The default in the absence of
1889	and only include the select backend.	3440	autoconf is documented for every option.
1890		3441
1891	=over 4	3442	=over 4
1892		3443
1893	=item EV_STANDALONE	3444	=item EV_STANDALONE
1894		3445
…		…
1896	keeps libev from including F<config.h>, and it also defines dummy	3447	keeps libev from including F<config.h>, and it also defines dummy
1897	implementations for some libevent functions (such as logging, which is not	3448	implementations for some libevent functions (such as logging, which is not
1898	supported). It will also not define any of the structs usually found in	3449	supported). It will also not define any of the structs usually found in
1899	F<event.h> that are not directly supported by the libev core alone.	3450	F<event.h> that are not directly supported by the libev core alone.
1900		3451
		3452	In stanbdalone mode, libev will still try to automatically deduce the
		3453	configuration, but has to be more conservative.
		3454
1901	=item EV_USE_MONOTONIC	3455	=item EV_USE_MONOTONIC
1902		3456
1903	If defined to be C<1>, libev will try to detect the availability of the	3457	If defined to be C<1>, libev will try to detect the availability of the
1904	monotonic clock option at both compiletime and runtime. Otherwise no use	3458	monotonic clock option at both compile time and runtime. Otherwise no
1905	of the monotonic clock option will be attempted. If you enable this, you	3459	use of the monotonic clock option will be attempted. If you enable this,
1906	usually have to link against librt or something similar. Enabling it when	3460	you usually have to link against librt or something similar. Enabling it
1907	the functionality isn't available is safe, though, althoguh you have	3461	when the functionality isn't available is safe, though, although you have
1908	to make sure you link against any libraries where the C<clock_gettime>	3462	to make sure you link against any libraries where the C<clock_gettime>
1909	function is hiding in (often F<-lrt>).	3463	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
1910		3464
1911	=item EV_USE_REALTIME	3465	=item EV_USE_REALTIME
1912		3466
1913	If defined to be C<1>, libev will try to detect the availability of the	3467	If defined to be C<1>, libev will try to detect the availability of the
1914	realtime clock option at compiletime (and assume its availability at	3468	real-time clock option at compile time (and assume its availability
1915	runtime if successful). Otherwise no use of the realtime clock option will	3469	at runtime if successful). Otherwise no use of the real-time clock
1916	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3470	option will be attempted. This effectively replaces C<gettimeofday>
1917	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3471	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
1918	in the description of C<EV_USE_MONOTONIC>, though.	3472	correctness. See the note about libraries in the description of
		3473	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3474	C<EV_USE_CLOCK_SYSCALL>.
		3475
		3476	=item EV_USE_CLOCK_SYSCALL
		3477
		3478	If defined to be C<1>, libev will try to use a direct syscall instead
		3479	of calling the system-provided C<clock_gettime> function. This option
		3480	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3481	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3482	programs needlessly. Using a direct syscall is slightly slower (in
		3483	theory), because no optimised vdso implementation can be used, but avoids
		3484	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3485	higher, as it simplifies linking (no need for C<-lrt>).
		3486
		3487	=item EV_USE_NANOSLEEP
		3488
		3489	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3490	and will use it for delays. Otherwise it will use C<select ()>.
		3491
		3492	=item EV_USE_EVENTFD
		3493
		3494	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3495	available and will probe for kernel support at runtime. This will improve
		3496	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3497	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3498	2.7 or newer, otherwise disabled.
1919		3499
1920	=item EV_USE_SELECT	3500	=item EV_USE_SELECT
1921		3501
1922	If undefined or defined to be C<1>, libev will compile in support for the	3502	If undefined or defined to be C<1>, libev will compile in support for the
1923	C<select>(2) backend. No attempt at autodetection will be done: if no	3503	C<select>(2) backend. No attempt at auto-detection will be done: if no
1924	other method takes over, select will be it. Otherwise the select backend	3504	other method takes over, select will be it. Otherwise the select backend
1925	will not be compiled in.	3505	will not be compiled in.
1926		3506
1927	=item EV_SELECT_USE_FD_SET	3507	=item EV_SELECT_USE_FD_SET
1928		3508
1929	If defined to C<1>, then the select backend will use the system C<fd_set>	3509	If defined to C<1>, then the select backend will use the system C<fd_set>
1930	structure. This is useful if libev doesn't compile due to a missing	3510	structure. This is useful if libev doesn't compile due to a missing
1931	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3511	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
1932	exotic systems. This usually limits the range of file descriptors to some	3512	on exotic systems. This usually limits the range of file descriptors to
1933	low limit such as 1024 or might have other limitations (winsocket only	3513	some low limit such as 1024 or might have other limitations (winsocket
1934	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3514	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
1935	influence the size of the C<fd_set> used.	3515	configures the maximum size of the C<fd_set>.
1936		3516
1937	=item EV_SELECT_IS_WINSOCKET	3517	=item EV_SELECT_IS_WINSOCKET
1938		3518
1939	When defined to C<1>, the select backend will assume that	3519	When defined to C<1>, the select backend will assume that
1940	select/socket/connect etc. don't understand file descriptors but	3520	select/socket/connect etc. don't understand file descriptors but
…		…
1942	be used is the winsock select). This means that it will call	3522	be used is the winsock select). This means that it will call
1943	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3523	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1944	it is assumed that all these functions actually work on fds, even	3524	it is assumed that all these functions actually work on fds, even
1945	on win32. Should not be defined on non-win32 platforms.	3525	on win32. Should not be defined on non-win32 platforms.
1946		3526
		3527	=item EV_FD_TO_WIN32_HANDLE
		3528
		3529	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3530	file descriptors to socket handles. When not defining this symbol (the
		3531	default), then libev will call C<_get_osfhandle>, which is usually
		3532	correct. In some cases, programs use their own file descriptor management,
		3533	in which case they can provide this function to map fds to socket handles.
		3534
1947	=item EV_USE_POLL	3535	=item EV_USE_POLL
1948		3536
1949	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3537	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1950	backend. Otherwise it will be enabled on non-win32 platforms. It	3538	backend. Otherwise it will be enabled on non-win32 platforms. It
1951	takes precedence over select.	3539	takes precedence over select.
1952		3540
1953	=item EV_USE_EPOLL	3541	=item EV_USE_EPOLL
1954		3542
1955	If defined to be C<1>, libev will compile in support for the Linux	3543	If defined to be C<1>, libev will compile in support for the Linux
1956	C<epoll>(7) backend. Its availability will be detected at runtime,	3544	C<epoll>(7) backend. Its availability will be detected at runtime,
1957	otherwise another method will be used as fallback. This is the	3545	otherwise another method will be used as fallback. This is the preferred
1958	preferred backend for GNU/Linux systems.	3546	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3547	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1959		3548
1960	=item EV_USE_KQUEUE	3549	=item EV_USE_KQUEUE
1961		3550
1962	If defined to be C<1>, libev will compile in support for the BSD style	3551	If defined to be C<1>, libev will compile in support for the BSD style
1963	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3552	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
1976	otherwise another method will be used as fallback. This is the preferred	3565	otherwise another method will be used as fallback. This is the preferred
1977	backend for Solaris 10 systems.	3566	backend for Solaris 10 systems.
1978		3567
1979	=item EV_USE_DEVPOLL	3568	=item EV_USE_DEVPOLL
1980		3569
1981	reserved for future expansion, works like the USE symbols above.	3570	Reserved for future expansion, works like the USE symbols above.
		3571
		3572	=item EV_USE_INOTIFY
		3573
		3574	If defined to be C<1>, libev will compile in support for the Linux inotify
		3575	interface to speed up C<ev_stat> watchers. Its actual availability will
		3576	be detected at runtime. If undefined, it will be enabled if the headers
		3577	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3578
		3579	=item EV_ATOMIC_T
		3580
		3581	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3582	access is atomic with respect to other threads or signal contexts. No such
		3583	type is easily found in the C language, so you can provide your own type
		3584	that you know is safe for your purposes. It is used both for signal handler "locking"
		3585	as well as for signal and thread safety in C<ev_async> watchers.
		3586
		3587	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3588	(from F<signal.h>), which is usually good enough on most platforms.
1982		3589
1983	=item EV_H	3590	=item EV_H
1984		3591
1985	The name of the F<ev.h> header file used to include it. The default if	3592	The name of the F<ev.h> header file used to include it. The default if
1986	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3593	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
1987	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3594	used to virtually rename the F<ev.h> header file in case of conflicts.
1988		3595
1989	=item EV_CONFIG_H	3596	=item EV_CONFIG_H
1990		3597
1991	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3598	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
1992	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3599	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
1993	C<EV_H>, above.	3600	C<EV_H>, above.
1994		3601
1995	=item EV_EVENT_H	3602	=item EV_EVENT_H
1996		3603
1997	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3604	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
1998	of how the F<event.h> header can be found.	3605	of how the F<event.h> header can be found, the default is C<"event.h">.
1999		3606
2000	=item EV_PROTOTYPES	3607	=item EV_PROTOTYPES
2001		3608
2002	If defined to be C<0>, then F<ev.h> will not define any function	3609	If defined to be C<0>, then F<ev.h> will not define any function
2003	prototypes, but still define all the structs and other symbols. This is	3610	prototypes, but still define all the structs and other symbols. This is
…		…
2010	will have the C<struct ev_loop *> as first argument, and you can create	3617	will have the C<struct ev_loop *> as first argument, and you can create
2011	additional independent event loops. Otherwise there will be no support	3618	additional independent event loops. Otherwise there will be no support
2012	for multiple event loops and there is no first event loop pointer	3619	for multiple event loops and there is no first event loop pointer
2013	argument. Instead, all functions act on the single default loop.	3620	argument. Instead, all functions act on the single default loop.
2014		3621
		3622	=item EV_MINPRI
		3623
		3624	=item EV_MAXPRI
		3625
		3626	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3627	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3628	provide for more priorities by overriding those symbols (usually defined
		3629	to be C<-2> and C<2>, respectively).
		3630
		3631	When doing priority-based operations, libev usually has to linearly search
		3632	all the priorities, so having many of them (hundreds) uses a lot of space
		3633	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3634	fine.
		3635
		3636	If your embedding application does not need any priorities, defining these
		3637	both to C<0> will save some memory and CPU.
		3638
2015	=item EV_PERIODIC_ENABLE	3639	=item EV_PERIODIC_ENABLE
2016		3640
2017	If undefined or defined to be C<1>, then periodic timers are supported. If	3641	If undefined or defined to be C<1>, then periodic timers are supported. If
2018	defined to be C<0>, then they are not. Disabling them saves a few kB of	3642	defined to be C<0>, then they are not. Disabling them saves a few kB of
2019	code.	3643	code.
2020		3644
		3645	=item EV_IDLE_ENABLE
		3646
		3647	If undefined or defined to be C<1>, then idle watchers are supported. If
		3648	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3649	code.
		3650
2021	=item EV_EMBED_ENABLE	3651	=item EV_EMBED_ENABLE
2022		3652
2023	If undefined or defined to be C<1>, then embed watchers are supported. If	3653	If undefined or defined to be C<1>, then embed watchers are supported. If
2024	defined to be C<0>, then they are not.	3654	defined to be C<0>, then they are not. Embed watchers rely on most other
		3655	watcher types, which therefore must not be disabled.
2025		3656
2026	=item EV_STAT_ENABLE	3657	=item EV_STAT_ENABLE
2027		3658
2028	If undefined or defined to be C<1>, then stat watchers are supported. If	3659	If undefined or defined to be C<1>, then stat watchers are supported. If
2029	defined to be C<0>, then they are not.	3660	defined to be C<0>, then they are not.
…		…
2031	=item EV_FORK_ENABLE	3662	=item EV_FORK_ENABLE
2032		3663
2033	If undefined or defined to be C<1>, then fork watchers are supported. If	3664	If undefined or defined to be C<1>, then fork watchers are supported. If
2034	defined to be C<0>, then they are not.	3665	defined to be C<0>, then they are not.
2035		3666
		3667	=item EV_ASYNC_ENABLE
		3668
		3669	If undefined or defined to be C<1>, then async watchers are supported. If
		3670	defined to be C<0>, then they are not.
		3671
2036	=item EV_MINIMAL	3672	=item EV_MINIMAL
2037		3673
2038	If you need to shave off some kilobytes of code at the expense of some	3674	If you need to shave off some kilobytes of code at the expense of some
2039	speed, define this symbol to C<1>. Currently only used for gcc to override	3675	speed, define this symbol to C<1>. Currently this is used to override some
2040	some inlining decisions, saves roughly 30% codesize of amd64.	3676	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3677	much smaller 2-heap for timer management over the default 4-heap.
2041		3678
2042	=item EV_PID_HASHSIZE	3679	=item EV_PID_HASHSIZE
2043		3680
2044	C<ev_child> watchers use a small hash table to distribute workload by	3681	C<ev_child> watchers use a small hash table to distribute workload by
2045	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3682	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2046	than enough. If you need to manage thousands of children you might want to	3683	than enough. If you need to manage thousands of children you might want to
2047	increase this value.	3684	increase this value (I<must> be a power of two).
		3685
		3686	=item EV_INOTIFY_HASHSIZE
		3687
		3688	C<ev_stat> watchers use a small hash table to distribute workload by
		3689	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3690	usually more than enough. If you need to manage thousands of C<ev_stat>
		3691	watchers you might want to increase this value (I<must> be a power of
		3692	two).
		3693
		3694	=item EV_USE_4HEAP
		3695
		3696	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3697	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3698	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3699	faster performance with many (thousands) of watchers.
		3700
		3701	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3702	(disabled).
		3703
		3704	=item EV_HEAP_CACHE_AT
		3705
		3706	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3707	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3708	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3709	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3710	but avoids random read accesses on heap changes. This improves performance
		3711	noticeably with many (hundreds) of watchers.
		3712
		3713	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3714	(disabled).
		3715
		3716	=item EV_VERIFY
		3717
		3718	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3719	be done: If set to C<0>, no internal verification code will be compiled
		3720	in. If set to C<1>, then verification code will be compiled in, but not
		3721	called. If set to C<2>, then the internal verification code will be
		3722	called once per loop, which can slow down libev. If set to C<3>, then the
		3723	verification code will be called very frequently, which will slow down
		3724	libev considerably.
		3725
		3726	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3727	C<0>.
2048		3728
2049	=item EV_COMMON	3729	=item EV_COMMON
2050		3730
2051	By default, all watchers have a C<void *data> member. By redefining	3731	By default, all watchers have a C<void *data> member. By redefining
2052	this macro to a something else you can include more and other types of	3732	this macro to a something else you can include more and other types of
2053	members. You have to define it each time you include one of the files,	3733	members. You have to define it each time you include one of the files,
2054	though, and it must be identical each time.	3734	though, and it must be identical each time.
2055		3735
2056	For example, the perl EV module uses something like this:	3736	For example, the perl EV module uses something like this:
2057		3737
2058	#define EV_COMMON \	3738	#define EV_COMMON \
2059	SV *self; /* contains this struct */ \	3739	SV *self; /* contains this struct */ \
2060	SV *cb_sv, *fh /* note no trailing ";" */	3740	SV *cb_sv, *fh /* note no trailing ";" */
2061		3741
2062	=item EV_CB_DECLARE (type)	3742	=item EV_CB_DECLARE (type)
2063		3743
2064	=item EV_CB_INVOKE (watcher, revents)	3744	=item EV_CB_INVOKE (watcher, revents)
2065		3745
2066	=item ev_set_cb (ev, cb)	3746	=item ev_set_cb (ev, cb)
2067		3747
2068	Can be used to change the callback member declaration in each watcher,	3748	Can be used to change the callback member declaration in each watcher,
2069	and the way callbacks are invoked and set. Must expand to a struct member	3749	and the way callbacks are invoked and set. Must expand to a struct member
2070	definition and a statement, respectively. See the F<ev.v> header file for	3750	definition and a statement, respectively. See the F<ev.h> header file for
2071	their default definitions. One possible use for overriding these is to	3751	their default definitions. One possible use for overriding these is to
2072	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3752	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2073	method calls instead of plain function calls in C++.	3753	method calls instead of plain function calls in C++.
		3754
		3755	=back
		3756
		3757	=head2 EXPORTED API SYMBOLS
		3758
		3759	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3760	exported symbols, you can use the provided F<Symbol.*> files which list
		3761	all public symbols, one per line:
		3762
		3763	Symbols.ev for libev proper
		3764	Symbols.event for the libevent emulation
		3765
		3766	This can also be used to rename all public symbols to avoid clashes with
		3767	multiple versions of libev linked together (which is obviously bad in
		3768	itself, but sometimes it is inconvenient to avoid this).
		3769
		3770	A sed command like this will create wrapper C<#define>'s that you need to
		3771	include before including F<ev.h>:
		3772
		3773	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3774
		3775	This would create a file F<wrap.h> which essentially looks like this:
		3776
		3777	#define ev_backend myprefix_ev_backend
		3778	#define ev_check_start myprefix_ev_check_start
		3779	#define ev_check_stop myprefix_ev_check_stop
		3780	...
2074		3781
2075	=head2 EXAMPLES	3782	=head2 EXAMPLES
2076		3783
2077	For a real-world example of a program the includes libev	3784	For a real-world example of a program the includes libev
2078	verbatim, you can have a look at the EV perl module	3785	verbatim, you can have a look at the EV perl module
…		…
2081	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	3788	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
2082	will be compiled. It is pretty complex because it provides its own header	3789	will be compiled. It is pretty complex because it provides its own header
2083	file.	3790	file.
2084		3791
2085	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3792	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2086	that everybody includes and which overrides some autoconf choices:	3793	that everybody includes and which overrides some configure choices:
2087		3794
		3795	#define EV_MINIMAL 1
2088	#define EV_USE_POLL 0	3796	#define EV_USE_POLL 0
2089	#define EV_MULTIPLICITY 0	3797	#define EV_MULTIPLICITY 0
2090	#define EV_PERIODICS 0	3798	#define EV_PERIODIC_ENABLE 0
		3799	#define EV_STAT_ENABLE 0
		3800	#define EV_FORK_ENABLE 0
2091	#define EV_CONFIG_H <config.h>	3801	#define EV_CONFIG_H <config.h>
		3802	#define EV_MINPRI 0
		3803	#define EV_MAXPRI 0
2092		3804
2093	#include "ev++.h"	3805	#include "ev++.h"
2094		3806
2095	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3807	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2096		3808
2097	#include "ev_cpp.h"	3809	#include "ev_cpp.h"
2098	#include "ev.c"	3810	#include "ev.c"
2099		3811
		3812	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2100		3813
		3814	=head2 THREADS AND COROUTINES
		3815
		3816	=head3 THREADS
		3817
		3818	All libev functions are reentrant and thread-safe unless explicitly
		3819	documented otherwise, but libev implements no locking itself. This means
		3820	that you can use as many loops as you want in parallel, as long as there
		3821	are no concurrent calls into any libev function with the same loop
		3822	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3823	of course): libev guarantees that different event loops share no data
		3824	structures that need any locking.
		3825
		3826	Or to put it differently: calls with different loop parameters can be done
		3827	concurrently from multiple threads, calls with the same loop parameter
		3828	must be done serially (but can be done from different threads, as long as
		3829	only one thread ever is inside a call at any point in time, e.g. by using
		3830	a mutex per loop).
		3831
		3832	Specifically to support threads (and signal handlers), libev implements
		3833	so-called C<ev_async> watchers, which allow some limited form of
		3834	concurrency on the same event loop, namely waking it up "from the
		3835	outside".
		3836
		3837	If you want to know which design (one loop, locking, or multiple loops
		3838	without or something else still) is best for your problem, then I cannot
		3839	help you, but here is some generic advice:
		3840
		3841	=over 4
		3842
		3843	=item * most applications have a main thread: use the default libev loop
		3844	in that thread, or create a separate thread running only the default loop.
		3845
		3846	This helps integrating other libraries or software modules that use libev
		3847	themselves and don't care/know about threading.
		3848
		3849	=item * one loop per thread is usually a good model.
		3850
		3851	Doing this is almost never wrong, sometimes a better-performance model
		3852	exists, but it is always a good start.
		3853
		3854	=item * other models exist, such as the leader/follower pattern, where one
		3855	loop is handed through multiple threads in a kind of round-robin fashion.
		3856
		3857	Choosing a model is hard - look around, learn, know that usually you can do
		3858	better than you currently do :-)
		3859
		3860	=item * often you need to talk to some other thread which blocks in the
		3861	event loop.
		3862
		3863	C<ev_async> watchers can be used to wake them up from other threads safely
		3864	(or from signal contexts...).
		3865
		3866	An example use would be to communicate signals or other events that only
		3867	work in the default loop by registering the signal watcher with the
		3868	default loop and triggering an C<ev_async> watcher from the default loop
		3869	watcher callback into the event loop interested in the signal.
		3870
		3871	=back
		3872
		3873	=head3 COROUTINES
		3874
		3875	Libev is very accommodating to coroutines ("cooperative threads"):
		3876	libev fully supports nesting calls to its functions from different
		3877	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3878	different coroutines, and switch freely between both coroutines running the
		3879	loop, as long as you don't confuse yourself). The only exception is that
		3880	you must not do this from C<ev_periodic> reschedule callbacks.
		3881
		3882	Care has been taken to ensure that libev does not keep local state inside
		3883	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3884	they do not call any callbacks.
		3885
		3886	=head2 COMPILER WARNINGS
		3887
		3888	Depending on your compiler and compiler settings, you might get no or a
		3889	lot of warnings when compiling libev code. Some people are apparently
		3890	scared by this.
		3891
		3892	However, these are unavoidable for many reasons. For one, each compiler
		3893	has different warnings, and each user has different tastes regarding
		3894	warning options. "Warn-free" code therefore cannot be a goal except when
		3895	targeting a specific compiler and compiler-version.
		3896
		3897	Another reason is that some compiler warnings require elaborate
		3898	workarounds, or other changes to the code that make it less clear and less
		3899	maintainable.
		3900
		3901	And of course, some compiler warnings are just plain stupid, or simply
		3902	wrong (because they don't actually warn about the condition their message
		3903	seems to warn about). For example, certain older gcc versions had some
		3904	warnings that resulted an extreme number of false positives. These have
		3905	been fixed, but some people still insist on making code warn-free with
		3906	such buggy versions.
		3907
		3908	While libev is written to generate as few warnings as possible,
		3909	"warn-free" code is not a goal, and it is recommended not to build libev
		3910	with any compiler warnings enabled unless you are prepared to cope with
		3911	them (e.g. by ignoring them). Remember that warnings are just that:
		3912	warnings, not errors, or proof of bugs.
		3913
		3914
		3915	=head2 VALGRIND
		3916
		3917	Valgrind has a special section here because it is a popular tool that is
		3918	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3919
		3920	If you think you found a bug (memory leak, uninitialised data access etc.)
		3921	in libev, then check twice: If valgrind reports something like:
		3922
		3923	==2274== definitely lost: 0 bytes in 0 blocks.
		3924	==2274== possibly lost: 0 bytes in 0 blocks.
		3925	==2274== still reachable: 256 bytes in 1 blocks.
		3926
		3927	Then there is no memory leak, just as memory accounted to global variables
		3928	is not a memleak - the memory is still being referenced, and didn't leak.
		3929
		3930	Similarly, under some circumstances, valgrind might report kernel bugs
		3931	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3932	although an acceptable workaround has been found here), or it might be
		3933	confused.
		3934
		3935	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3936	make it into some kind of religion.
		3937
		3938	If you are unsure about something, feel free to contact the mailing list
		3939	with the full valgrind report and an explanation on why you think this
		3940	is a bug in libev (best check the archives, too :). However, don't be
		3941	annoyed when you get a brisk "this is no bug" answer and take the chance
		3942	of learning how to interpret valgrind properly.
		3943
		3944	If you need, for some reason, empty reports from valgrind for your project
		3945	I suggest using suppression lists.
		3946
		3947
		3948	=head1 PORTABILITY NOTES
		3949
		3950	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3951
		3952	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3953	requires, and its I/O model is fundamentally incompatible with the POSIX
		3954	model. Libev still offers limited functionality on this platform in
		3955	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3956	descriptors. This only applies when using Win32 natively, not when using
		3957	e.g. cygwin.
		3958
		3959	Lifting these limitations would basically require the full
		3960	re-implementation of the I/O system. If you are into these kinds of
		3961	things, then note that glib does exactly that for you in a very portable
		3962	way (note also that glib is the slowest event library known to man).
		3963
		3964	There is no supported compilation method available on windows except
		3965	embedding it into other applications.
		3966
		3967	Sensible signal handling is officially unsupported by Microsoft - libev
		3968	tries its best, but under most conditions, signals will simply not work.
		3969
		3970	Not a libev limitation but worth mentioning: windows apparently doesn't
		3971	accept large writes: instead of resulting in a partial write, windows will
		3972	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3973	so make sure you only write small amounts into your sockets (less than a
		3974	megabyte seems safe, but this apparently depends on the amount of memory
		3975	available).
		3976
		3977	Due to the many, low, and arbitrary limits on the win32 platform and
		3978	the abysmal performance of winsockets, using a large number of sockets
		3979	is not recommended (and not reasonable). If your program needs to use
		3980	more than a hundred or so sockets, then likely it needs to use a totally
		3981	different implementation for windows, as libev offers the POSIX readiness
		3982	notification model, which cannot be implemented efficiently on windows
		3983	(due to Microsoft monopoly games).
		3984
		3985	A typical way to use libev under windows is to embed it (see the embedding
		3986	section for details) and use the following F<evwrap.h> header file instead
		3987	of F<ev.h>:
		3988
		3989	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3990	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3991
		3992	#include "ev.h"
		3993
		3994	And compile the following F<evwrap.c> file into your project (make sure
		3995	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3996
		3997	#include "evwrap.h"
		3998	#include "ev.c"
		3999
		4000	=over 4
		4001
		4002	=item The winsocket select function
		4003
		4004	The winsocket C<select> function doesn't follow POSIX in that it
		4005	requires socket I<handles> and not socket I<file descriptors> (it is
		4006	also extremely buggy). This makes select very inefficient, and also
		4007	requires a mapping from file descriptors to socket handles (the Microsoft
		4008	C runtime provides the function C<_open_osfhandle> for this). See the
		4009	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4010	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4011
		4012	The configuration for a "naked" win32 using the Microsoft runtime
		4013	libraries and raw winsocket select is:
		4014
		4015	#define EV_USE_SELECT 1
		4016	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4017
		4018	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4019	complexity in the O(n²) range when using win32.
		4020
		4021	=item Limited number of file descriptors
		4022
		4023	Windows has numerous arbitrary (and low) limits on things.
		4024
		4025	Early versions of winsocket's select only supported waiting for a maximum
		4026	of C<64> handles (probably owning to the fact that all windows kernels
		4027	can only wait for C<64> things at the same time internally; Microsoft
		4028	recommends spawning a chain of threads and wait for 63 handles and the
		4029	previous thread in each. Sounds great!).
		4030
		4031	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4032	to some high number (e.g. C<2048>) before compiling the winsocket select
		4033	call (which might be in libev or elsewhere, for example, perl and many
		4034	other interpreters do their own select emulation on windows).
		4035
		4036	Another limit is the number of file descriptors in the Microsoft runtime
		4037	libraries, which by default is C<64> (there must be a hidden I<64>
		4038	fetish or something like this inside Microsoft). You can increase this
		4039	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4040	(another arbitrary limit), but is broken in many versions of the Microsoft
		4041	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4042	(depending on windows version and/or the phase of the moon). To get more,
		4043	you need to wrap all I/O functions and provide your own fd management, but
		4044	the cost of calling select (O(n²)) will likely make this unworkable.
		4045
		4046	=back
		4047
		4048	=head2 PORTABILITY REQUIREMENTS
		4049
		4050	In addition to a working ISO-C implementation and of course the
		4051	backend-specific APIs, libev relies on a few additional extensions:
		4052
		4053	=over 4
		4054
		4055	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4056	calling conventions regardless of C<ev_watcher_type *>.
		4057
		4058	Libev assumes not only that all watcher pointers have the same internal
		4059	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4060	assumes that the same (machine) code can be used to call any watcher
		4061	callback: The watcher callbacks have different type signatures, but libev
		4062	calls them using an C<ev_watcher *> internally.
		4063
		4064	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4065
		4066	The type C<sig_atomic_t volatile> (or whatever is defined as
		4067	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4068	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4069	believed to be sufficiently portable.
		4070
		4071	=item C<sigprocmask> must work in a threaded environment
		4072
		4073	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4074	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4075	pthread implementations will either allow C<sigprocmask> in the "main
		4076	thread" or will block signals process-wide, both behaviours would
		4077	be compatible with libev. Interaction between C<sigprocmask> and
		4078	C<pthread_sigmask> could complicate things, however.
		4079
		4080	The most portable way to handle signals is to block signals in all threads
		4081	except the initial one, and run the default loop in the initial thread as
		4082	well.
		4083
		4084	=item C<long> must be large enough for common memory allocation sizes
		4085
		4086	To improve portability and simplify its API, libev uses C<long> internally
		4087	instead of C<size_t> when allocating its data structures. On non-POSIX
		4088	systems (Microsoft...) this might be unexpectedly low, but is still at
		4089	least 31 bits everywhere, which is enough for hundreds of millions of
		4090	watchers.
		4091
		4092	=item C<double> must hold a time value in seconds with enough accuracy
		4093
		4094	The type C<double> is used to represent timestamps. It is required to
		4095	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4096	enough for at least into the year 4000. This requirement is fulfilled by
		4097	implementations implementing IEEE 754, which is basically all existing
		4098	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4099	2200.
		4100
		4101	=back
		4102
		4103	If you know of other additional requirements drop me a note.
		4104
		4105
2101	=head1 COMPLEXITIES	4106	=head1 ALGORITHMIC COMPLEXITIES
2102		4107
2103	In this section the complexities of (many of) the algorithms used inside	4108	In this section the complexities of (many of) the algorithms used inside
2104	libev will be explained. For complexity discussions about backends see the	4109	libev will be documented. For complexity discussions about backends see
2105	documentation for C<ev_default_init>.	4110	the documentation for C<ev_default_init>.
		4111
		4112	All of the following are about amortised time: If an array needs to be
		4113	extended, libev needs to realloc and move the whole array, but this
		4114	happens asymptotically rarer with higher number of elements, so O(1) might
		4115	mean that libev does a lengthy realloc operation in rare cases, but on
		4116	average it is much faster and asymptotically approaches constant time.
2106		4117
2107	=over 4	4118	=over 4
2108		4119
2109	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4120	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2110		4121
		4122	This means that, when you have a watcher that triggers in one hour and
		4123	there are 100 watchers that would trigger before that, then inserting will
		4124	have to skip roughly seven (C<ld 100>) of these watchers.
		4125
2111	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4126	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2112		4127
		4128	That means that changing a timer costs less than removing/adding them,
		4129	as only the relative motion in the event queue has to be paid for.
		4130
2113	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4131	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2114		4132
		4133	These just add the watcher into an array or at the head of a list.
		4134
2115	=item Stopping check/prepare/idle watchers: O(1)	4135	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2116		4136
2117	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))	4137	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2118		4138
		4139	These watchers are stored in lists, so they need to be walked to find the
		4140	correct watcher to remove. The lists are usually short (you don't usually
		4141	have many watchers waiting for the same fd or signal: one is typical, two
		4142	is rare).
		4143
2119	=item Finding the next timer per loop iteration: O(1)	4144	=item Finding the next timer in each loop iteration: O(1)
		4145
		4146	By virtue of using a binary or 4-heap, the next timer is always found at a
		4147	fixed position in the storage array.
2120		4148
2121	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4149	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2122		4150
2123	=item Activating one watcher: O(1)	4151	A change means an I/O watcher gets started or stopped, which requires
		4152	libev to recalculate its status (and possibly tell the kernel, depending
		4153	on backend and whether C<ev_io_set> was used).
		4154
		4155	=item Activating one watcher (putting it into the pending state): O(1)
		4156
		4157	=item Priority handling: O(number_of_priorities)
		4158
		4159	Priorities are implemented by allocating some space for each
		4160	priority. When doing priority-based operations, libev usually has to
		4161	linearly search all the priorities, but starting/stopping and activating
		4162	watchers becomes O(1) with respect to priority handling.
		4163
		4164	=item Sending an ev_async: O(1)
		4165
		4166	=item Processing ev_async_send: O(number_of_async_watchers)
		4167
		4168	=item Processing signals: O(max_signal_number)
		4169
		4170	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4171	calls in the current loop iteration. Checking for async and signal events
		4172	involves iterating over all running async watchers or all signal numbers.
2124		4173
2125	=back	4174	=back
2126		4175
2127		4176
		4177	=head1 GLOSSARY
		4178
		4179	=over 4
		4180
		4181	=item active
		4182
		4183	A watcher is active as long as it has been started (has been attached to
		4184	an event loop) but not yet stopped (disassociated from the event loop).
		4185
		4186	=item application
		4187
		4188	In this document, an application is whatever is using libev.
		4189
		4190	=item callback
		4191
		4192	The address of a function that is called when some event has been
		4193	detected. Callbacks are being passed the event loop, the watcher that
		4194	received the event, and the actual event bitset.
		4195
		4196	=item callback invocation
		4197
		4198	The act of calling the callback associated with a watcher.
		4199
		4200	=item event
		4201
		4202	A change of state of some external event, such as data now being available
		4203	for reading on a file descriptor, time having passed or simply not having
		4204	any other events happening anymore.
		4205
		4206	In libev, events are represented as single bits (such as C<EV_READ> or
		4207	C<EV_TIMEOUT>).
		4208
		4209	=item event library
		4210
		4211	A software package implementing an event model and loop.
		4212
		4213	=item event loop
		4214
		4215	An entity that handles and processes external events and converts them
		4216	into callback invocations.
		4217
		4218	=item event model
		4219
		4220	The model used to describe how an event loop handles and processes
		4221	watchers and events.
		4222
		4223	=item pending
		4224
		4225	A watcher is pending as soon as the corresponding event has been detected,
		4226	and stops being pending as soon as the watcher will be invoked or its
		4227	pending status is explicitly cleared by the application.
		4228
		4229	A watcher can be pending, but not active. Stopping a watcher also clears
		4230	its pending status.
		4231
		4232	=item real time
		4233
		4234	The physical time that is observed. It is apparently strictly monotonic :)
		4235
		4236	=item wall-clock time
		4237
		4238	The time and date as shown on clocks. Unlike real time, it can actually
		4239	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4240	clock.
		4241
		4242	=item watcher
		4243
		4244	A data structure that describes interest in certain events. Watchers need
		4245	to be started (attached to an event loop) before they can receive events.
		4246
		4247	=item watcher invocation
		4248
		4249	The act of calling the callback associated with a watcher.
		4250
		4251	=back
		4252
2128	=head1 AUTHOR	4253	=head1 AUTHOR
2129		4254
2130	Marc Lehmann <libev@schmorp.de>.	4255	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2131		4256

Diff Legend

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