ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.55 by root, Tue Nov 27 20:38:07 2007 UTC vs.
Revision 1.236 by root, Thu Apr 16 07:56:05 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
52		84
53	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
54	file descriptor being readable or a timeout occuring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
55	these event sources and provide your program with events.	87	these event sources and provide your program with events.
56		88
57	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
58	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
59	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
61	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
62	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
63	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
64	watcher.	96	watcher.
65		97
66	=head1 FEATURES	98	=head2 FEATURES
67		99
68	Libev supports C<select>, C<poll>, the linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
69	bsd-specific C<kqueue> and the solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
70	for file descriptor events (C<ev_io>), relative timers (C<ev_timer>),	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		103	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
71	absolute timers with customised rescheduling (C<ev_periodic>), synchronous	104	with customised rescheduling (C<ev_periodic>), synchronous signals
72	signals (C<ev_signal>), process status change events (C<ev_child>), and	105	(C<ev_signal>), process status change events (C<ev_child>), and event
73	event watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	watchers dealing with the event loop mechanism itself (C<ev_idle>,
74	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
75	file watchers (C<ev_stat>) and even limited support for fork events	108	file watchers (C<ev_stat>) and even limited support for fork events
76	(C<ev_fork>).	109	(C<ev_fork>).
77		110
78	It also is quite fast (see this	111	It also is quite fast (see this
79	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	112	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
80	for example).	113	for example).
81		114
82	=head1 CONVENTIONS	115	=head2 CONVENTIONS
83		116
84	Libev is very configurable. In this manual the default configuration will	117	Libev is very configurable. In this manual the default (and most common)
85	be described, which supports multiple event loops. For more info about	118	configuration will be described, which supports multiple event loops. For
86	various configuration options please have a look at B<EMBED> section in	119	more info about various configuration options please have a look at
87	this manual. If libev was configured without support for multiple event	120	B<EMBED> section in this manual. If libev was configured without support
88	loops, then all functions taking an initial argument of name C<loop>	121	for multiple event loops, then all functions taking an initial argument of
89	(which is always of type C<struct ev_loop *>) will not have this argument.	122	name C<loop> (which is always of type C<ev_loop *>) will not have
		123	this argument.
90		124
91	=head1 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
92		126
93	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing the
94	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	(fractional) number of seconds since the (POSIX) epoch (somewhere near
95	the beginning of 1970, details are complicated, don't ask). This type is	129	the beginning of 1970, details are complicated, don't ask). This type is
96	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	called C<ev_tstamp>, which is what you should use too. It usually aliases
97	to the C<double> type in C, and when you need to do any calculations on	131	to the C<double> type in C, and when you need to do any calculations on
98	it, you should treat it as such.	132	it, you should treat it as some floating point value. Unlike the name
		133	component C<stamp> might indicate, it is also used for time differences
		134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
		155
99		156
100	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
101		158
102	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
103	library in any way.	160	library in any way.
…		…
108		165
109	Returns the current time as libev would use it. Please note that the	166	Returns the current time as libev would use it. Please note that the
110	C<ev_now> function is usually faster and also often returns the timestamp	167	C<ev_now> function is usually faster and also often returns the timestamp
111	you actually want to know.	168	you actually want to know.
112		169
		170	=item ev_sleep (ev_tstamp interval)
		171
		172	Sleep for the given interval: The current thread will be blocked until
		173	either it is interrupted or the given time interval has passed. Basically
		174	this is a sub-second-resolution C<sleep ()>.
		175
113	=item int ev_version_major ()	176	=item int ev_version_major ()
114		177
115	=item int ev_version_minor ()	178	=item int ev_version_minor ()
116		179
117	You can find out the major and minor version numbers of the library	180	You can find out the major and minor ABI version numbers of the library
118	you linked against by calling the functions C<ev_version_major> and	181	you linked against by calling the functions C<ev_version_major> and
119	C<ev_version_minor>. If you want, you can compare against the global	182	C<ev_version_minor>. If you want, you can compare against the global
120	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	183	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
121	version of the library your program was compiled against.	184	version of the library your program was compiled against.
122		185
		186	These version numbers refer to the ABI version of the library, not the
		187	release version.
		188
123	Usually, it's a good idea to terminate if the major versions mismatch,	189	Usually, it's a good idea to terminate if the major versions mismatch,
124	as this indicates an incompatible change. Minor versions are usually	190	as this indicates an incompatible change. Minor versions are usually
125	compatible to older versions, so a larger minor version alone is usually	191	compatible to older versions, so a larger minor version alone is usually
126	not a problem.	192	not a problem.
127		193
128	Example: Make sure we haven't accidentally been linked against the wrong	194	Example: Make sure we haven't accidentally been linked against the wrong
129	version.	195	version.
130		196
131	assert (("libev version mismatch",	197	assert (("libev version mismatch",
132	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
133	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
134		200
135	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
136		202
137	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	203	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
138	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
140	a description of the set values.	206	a description of the set values.
141		207
142	Example: make sure we have the epoll method, because yeah this is cool and	208	Example: make sure we have the epoll method, because yeah this is cool and
143	a must have and can we have a torrent of it please!!!11	209	a must have and can we have a torrent of it please!!!11
144		210
145	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
146	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
147		213
148	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
149		215
150	Return the set of all backends compiled into this binary of libev and also	216	Return the set of all backends compiled into this binary of libev and also
151	recommended for this platform. This set is often smaller than the one	217	recommended for this platform. This set is often smaller than the one
152	returned by C<ev_supported_backends>, as for example kqueue is broken on	218	returned by C<ev_supported_backends>, as for example kqueue is broken on
153	most BSDs and will not be autodetected unless you explicitly request it	219	most BSDs and will not be auto-detected unless you explicitly request it
154	(assuming you know what you are doing). This is the set of backends that	220	(assuming you know what you are doing). This is the set of backends that
155	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
156		222
157	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
158		224
…		…
162	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
163	recommended ones.	229	recommended ones.
164		230
165	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
166		232
167	=item ev_set_allocator (void *(*cb)(void *ptr, size_t size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
168		234
169	Sets the allocation function to use (the prototype and semantics are	235	Sets the allocation function to use (the prototype is similar - the
170	identical to the realloc C function). It is used to allocate and free	236	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
171	memory (no surprises here). If it returns zero when memory needs to be	237	used to allocate and free memory (no surprises here). If it returns zero
172	allocated, the library might abort or take some potentially destructive	238	when memory needs to be allocated (C<size != 0>), the library might abort
173	action. The default is your system realloc function.	239	or take some potentially destructive action.
		240
		241	Since some systems (at least OpenBSD and Darwin) fail to implement
		242	correct C<realloc> semantics, libev will use a wrapper around the system
		243	C<realloc> and C<free> functions by default.
174		244
175	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
176	free some memory if it cannot allocate memory, to use a special allocator,	246	free some memory if it cannot allocate memory, to use a special allocator,
177	or even to sleep a while and retry until some memory is available.	247	or even to sleep a while and retry until some memory is available.
178		248
179	Example: Replace the libev allocator with one that waits a bit and then	249	Example: Replace the libev allocator with one that waits a bit and then
180	retries).	250	retries (example requires a standards-compliant C<realloc>).
181		251
182	static void *	252	static void *
183	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
184	{	254	{
185	for (;;)	255	for (;;)
…		…
194	}	264	}
195		265
196	...	266	...
197	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
198		268
199	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
200		270
201	Set the callback function to call on a retryable syscall error (such	271	Set the callback function to call on a retryable system call error (such
202	as failed select, poll, epoll_wait). The message is a printable string	272	as failed select, poll, epoll_wait). The message is a printable string
203	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
204	callback is set, then libev will expect it to remedy the sitution, no	274	callback is set, then libev will expect it to remedy the situation, no
205	matter what, when it returns. That is, libev will generally retry the	275	matter what, when it returns. That is, libev will generally retry the
206	requested operation, or, if the condition doesn't go away, do bad stuff	276	requested operation, or, if the condition doesn't go away, do bad stuff
207	(such as abort).	277	(such as abort).
208		278
209	Example: This is basically the same thing that libev does internally, too.	279	Example: This is basically the same thing that libev does internally, too.
…		…
220		290
221	=back	291	=back
222		292
223	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
224		294
225	An event loop is described by a C<struct ev_loop *>. The library knows two	295	An event loop is described by a C<struct ev_loop *> (the C<struct>
226	types of such loops, the I<default> loop, which supports signals and child	296	is I<not> optional in this case, as there is also an C<ev_loop>
227	events, and dynamically created loops which do not.	297	I<function>).
228		298
229	If you use threads, a common model is to run the default event loop	299	The library knows two types of such loops, the I<default> loop, which
230	in your main thread (or in a separate thread) and for each thread you	300	supports signals and child events, and dynamically created loops which do
231	create, you also create another event loop. Libev itself does no locking	301	not.
232	whatsoever, so if you mix calls to the same event loop in different
233	threads, make sure you lock (this is usually a bad idea, though, even if
234	done correctly, because it's hideous and inefficient).
235		302
236	=over 4	303	=over 4
237		304
238	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
239		306
…		…
243	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
244		311
245	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
246	function.	313	function.
247		314
		315	Note that this function is I<not> thread-safe, so if you want to use it
		316	from multiple threads, you have to lock (note also that this is unlikely,
		317	as loops cannot be shared easily between threads anyway).
		318
		319	The default loop is the only loop that can handle C<ev_signal> and
		320	C<ev_child> watchers, and to do this, it always registers a handler
		321	for C<SIGCHLD>. If this is a problem for your application you can either
		322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		324	C<ev_default_init>.
		325
248	The flags argument can be used to specify special behaviour or specific	326	The flags argument can be used to specify special behaviour or specific
249	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	327	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
250		328
251	The following flags are supported:	329	The following flags are supported:
252		330
…		…
257	The default flags value. Use this if you have no clue (it's the right	335	The default flags value. Use this if you have no clue (it's the right
258	thing, believe me).	336	thing, believe me).
259		337
260	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
261		339
262	If this flag bit is ored into the flag value (or the program runs setuid	340	If this flag bit is or'ed into the flag value (or the program runs setuid
263	or setgid) then libev will I<not> look at the environment variable	341	or setgid) then libev will I<not> look at the environment variable
264	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
265	override the flags completely if it is found in the environment. This is	343	override the flags completely if it is found in the environment. This is
266	useful to try out specific backends to test their performance, or to work	344	useful to try out specific backends to test their performance, or to work
267	around bugs.	345	around bugs.
268		346
		347	=item C<EVFLAG_FORKCHECK>
		348
		349	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		350	a fork, you can also make libev check for a fork in each iteration by
		351	enabling this flag.
		352
		353	This works by calling C<getpid ()> on every iteration of the loop,
		354	and thus this might slow down your event loop if you do a lot of loop
		355	iterations and little real work, but is usually not noticeable (on my
		356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		357	without a system call and thus I<very> fast, but my GNU/Linux system also has
		358	C<pthread_atfork> which is even faster).
		359
		360	The big advantage of this flag is that you can forget about fork (and
		361	forget about forgetting to tell libev about forking) when you use this
		362	flag.
		363
		364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		365	environment variable.
		366
269	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
270		368
271	This is your standard select(2) backend. Not I<completely> standard, as	369	This is your standard select(2) backend. Not I<completely> standard, as
272	libev tries to roll its own fd_set with no limits on the number of fds,	370	libev tries to roll its own fd_set with no limits on the number of fds,
273	but if that fails, expect a fairly low limit on the number of fds when	371	but if that fails, expect a fairly low limit on the number of fds when
274	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	372	using this backend. It doesn't scale too well (O(highest_fd)), but its
275	the fastest backend for a low number of fds.	373	usually the fastest backend for a low number of (low-numbered :) fds.
		374
		375	To get good performance out of this backend you need a high amount of
		376	parallelism (most of the file descriptors should be busy). If you are
		377	writing a server, you should C<accept ()> in a loop to accept as many
		378	connections as possible during one iteration. You might also want to have
		379	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		380	readiness notifications you get per iteration.
		381
		382	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		383	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		384	C<exceptfds> set on that platform).
276		385
277	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	386	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
278		387
279	And this is your standard poll(2) backend. It's more complicated than	388	And this is your standard poll(2) backend. It's more complicated
280	select, but handles sparse fds better and has no artificial limit on the	389	than select, but handles sparse fds better and has no artificial
281	number of fds you can use (except it will slow down considerably with a	390	limit on the number of fds you can use (except it will slow down
282	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	391	considerably with a lot of inactive fds). It scales similarly to select,
		392	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		393	performance tips.
		394
		395	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		396	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
283		397
284	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
285		399
286	For few fds, this backend is a bit little slower than poll and select,	400	For few fds, this backend is a bit little slower than poll and select,
287	but it scales phenomenally better. While poll and select usually scale like	401	but it scales phenomenally better. While poll and select usually scale
288	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	402	like O(total_fds) where n is the total number of fds (or the highest fd),
289	either O(1) or O(active_fds).	403	epoll scales either O(1) or O(active_fds).
290		404
		405	The epoll mechanism deserves honorable mention as the most misdesigned
		406	of the more advanced event mechanisms: mere annoyances include silently
		407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
		421
291	While stopping and starting an I/O watcher in the same iteration will	422	While stopping, setting and starting an I/O watcher in the same iteration
292	result in some caching, there is still a syscall per such incident	423	will result in some caching, there is still a system call per such
293	(because the fd could point to a different file description now), so its	424	incident (because the same I<file descriptor> could point to a different
294	best to avoid that. Also, dup()ed file descriptors might not work very	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
295	well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
		427	file descriptors.
296		428
297	Please note that epoll sometimes generates spurious notifications, so you	429	Best performance from this backend is achieved by not unregistering all
298	need to use non-blocking I/O or other means to avoid blocking when no data	430	watchers for a file descriptor until it has been closed, if possible,
299	(or space) is available.	431	i.e. keep at least one watcher active per fd at all times. Stopping and
		432	starting a watcher (without re-setting it) also usually doesn't cause
		433	extra overhead. A fork can both result in spurious notifications as well
		434	as in libev having to destroy and recreate the epoll object, which can
		435	take considerable time and thus should be avoided.
		436
		437	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		438	faster than epoll for maybe up to a hundred file descriptors, depending on
		439	the usage. So sad.
		440
		441	While nominally embeddable in other event loops, this feature is broken in
		442	all kernel versions tested so far.
		443
		444	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		445	C<EVBACKEND_POLL>.
300		446
301	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
302		448
303	Kqueue deserves special mention, as at the time of this writing, it	449	Kqueue deserves special mention, as at the time of this writing, it
304	was broken on all BSDs except NetBSD (usually it doesn't work with	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
305	anything but sockets and pipes, except on Darwin, where of course its	451	with anything but sockets and pipes, except on Darwin, where of course
306	completely useless). For this reason its not being "autodetected"	452	it's completely useless). Unlike epoll, however, whose brokenness
		453	is by design, these kqueue bugs can (and eventually will) be fixed
		454	without API changes to existing programs. For this reason it's not being
307	unless you explicitly specify it explicitly in the flags (i.e. using	455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
308	C<EVBACKEND_KQUEUE>).	456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		457	system like NetBSD.
		458
		459	You still can embed kqueue into a normal poll or select backend and use it
		460	only for sockets (after having made sure that sockets work with kqueue on
		461	the target platform). See C<ev_embed> watchers for more info.
309		462
310	It scales in the same way as the epoll backend, but the interface to the	463	It scales in the same way as the epoll backend, but the interface to the
311	kernel is more efficient (which says nothing about its actual speed, of	464	kernel is more efficient (which says nothing about its actual speed, of
312	course). While starting and stopping an I/O watcher does not cause an	465	course). While stopping, setting and starting an I/O watcher does never
313	extra syscall as with epoll, it still adds up to four event changes per	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
314	incident, so its best to avoid that.	467	two event changes per incident. Support for C<fork ()> is very bad (but
		468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
		470
		471	This backend usually performs well under most conditions.
		472
		473	While nominally embeddable in other event loops, this doesn't work
		474	everywhere, so you might need to test for this. And since it is broken
		475	almost everywhere, you should only use it when you have a lot of sockets
		476	(for which it usually works), by embedding it into another event loop
		477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		478	also broken on OS X)) and, did I mention it, using it only for sockets.
		479
		480	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		482	C<NOTE_EOF>.
315		483
316	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
317		485
318	This is not implemented yet (and might never be).	486	This is not implemented yet (and might never be, unless you send me an
		487	implementation). According to reports, C</dev/poll> only supports sockets
		488	and is not embeddable, which would limit the usefulness of this backend
		489	immensely.
319		490
320	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
321		492
322	This uses the Solaris 10 port mechanism. As with everything on Solaris,	493	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
323	it's really slow, but it still scales very well (O(active_fds)).	494	it's really slow, but it still scales very well (O(active_fds)).
324		495
325	Please note that solaris ports can result in a lot of spurious	496	Please note that Solaris event ports can deliver a lot of spurious
326	notifications, so you need to use non-blocking I/O or other means to avoid	497	notifications, so you need to use non-blocking I/O or other means to avoid
327	blocking when no data (or space) is available.	498	blocking when no data (or space) is available.
		499
		500	While this backend scales well, it requires one system call per active
		501	file descriptor per loop iteration. For small and medium numbers of file
		502	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		503	might perform better.
		504
		505	On the positive side, with the exception of the spurious readiness
		506	notifications, this backend actually performed fully to specification
		507	in all tests and is fully embeddable, which is a rare feat among the
		508	OS-specific backends (I vastly prefer correctness over speed hacks).
		509
		510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		511	C<EVBACKEND_POLL>.
328		512
329	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
330		514
331	Try all backends (even potentially broken ones that wouldn't be tried	515	Try all backends (even potentially broken ones that wouldn't be tried
332	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	516	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
333	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	517	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
334		518
		519	It is definitely not recommended to use this flag.
		520
335	=back	521	=back
336		522
337	If one or more of these are ored into the flags value, then only these	523	If one or more of these are or'ed into the flags value, then only these
338	backends will be tried (in the reverse order as given here). If none are	524	backends will be tried (in the reverse order as listed here). If none are
339	specified, most compiled-in backend will be tried, usually in reverse	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
340	order of their flag values :)
341		526
342	The most typical usage is like this:	527	Example: This is the most typical usage.
343		528
344	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
345	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
346		531
347	Restrict libev to the select and poll backends, and do not allow	532	Example: Restrict libev to the select and poll backends, and do not allow
348	environment settings to be taken into account:	533	environment settings to be taken into account:
349		534
350	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
351		536
352	Use whatever libev has to offer, but make sure that kqueue is used if	537	Example: Use whatever libev has to offer, but make sure that kqueue is
353	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
354	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
355		541
356	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
357		543
358	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
359		545
360	Similar to C<ev_default_loop>, but always creates a new event loop that is	546	Similar to C<ev_default_loop>, but always creates a new event loop that is
361	always distinct from the default loop. Unlike the default loop, it cannot	547	always distinct from the default loop. Unlike the default loop, it cannot
362	handle signal and child watchers, and attempts to do so will be greeted by	548	handle signal and child watchers, and attempts to do so will be greeted by
363	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
364		550
		551	Note that this function I<is> thread-safe, and the recommended way to use
		552	libev with threads is indeed to create one loop per thread, and using the
		553	default loop in the "main" or "initial" thread.
		554
365	Example: Try to create a event loop that uses epoll and nothing else.	555	Example: Try to create a event loop that uses epoll and nothing else.
366		556
367	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
368	if (!epoller)	558	if (!epoller)
369	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
370		560
371	=item ev_default_destroy ()	561	=item ev_default_destroy ()
372		562
373	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
374	etc.). None of the active event watchers will be stopped in the normal	564	etc.). None of the active event watchers will be stopped in the normal
375	sense, so e.g. C<ev_is_active> might still return true. It is your	565	sense, so e.g. C<ev_is_active> might still return true. It is your
376	responsibility to either stop all watchers cleanly yoursef I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
377	calling this function, or cope with the fact afterwards (which is usually	567	calling this function, or cope with the fact afterwards (which is usually
378	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
379	for example).	569	for example).
		570
		571	Note that certain global state, such as signal state (and installed signal
		572	handlers), will not be freed by this function, and related watchers (such
		573	as signal and child watchers) would need to be stopped manually.
		574
		575	In general it is not advisable to call this function except in the
		576	rare occasion where you really need to free e.g. the signal handling
		577	pipe fds. If you need dynamically allocated loops it is better to use
		578	C<ev_loop_new> and C<ev_loop_destroy>).
380		579
381	=item ev_loop_destroy (loop)	580	=item ev_loop_destroy (loop)
382		581
383	Like C<ev_default_destroy>, but destroys an event loop created by an	582	Like C<ev_default_destroy>, but destroys an event loop created by an
384	earlier call to C<ev_loop_new>.	583	earlier call to C<ev_loop_new>.
385		584
386	=item ev_default_fork ()	585	=item ev_default_fork ()
387		586
		587	This function sets a flag that causes subsequent C<ev_loop> iterations
388	This function reinitialises the kernel state for backends that have	588	to reinitialise the kernel state for backends that have one. Despite the
389	one. Despite the name, you can call it anytime, but it makes most sense	589	name, you can call it anytime, but it makes most sense after forking, in
390	after forking, in either the parent or child process (or both, but that	590	the child process (or both child and parent, but that again makes little
391	again makes little sense).	591	sense). You I<must> call it in the child before using any of the libev
		592	functions, and it will only take effect at the next C<ev_loop> iteration.
392		593
393	You I<must> call this function in the child process after forking if and	594	On the other hand, you only need to call this function in the child
394	only if you want to use the event library in both processes. If you just	595	process if and only if you want to use the event library in the child. If
395	fork+exec, you don't have to call it.	596	you just fork+exec, you don't have to call it at all.
396		597
397	The function itself is quite fast and it's usually not a problem to call	598	The function itself is quite fast and it's usually not a problem to call
398	it just in case after a fork. To make this easy, the function will fit in	599	it just in case after a fork. To make this easy, the function will fit in
399	quite nicely into a call to C<pthread_atfork>:	600	quite nicely into a call to C<pthread_atfork>:
400		601
401	pthread_atfork (0, 0, ev_default_fork);	602	pthread_atfork (0, 0, ev_default_fork);
402		603
403	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
404	without calling this function, so if you force one of those backends you
405	do not need to care.
406
407	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
408		605
409	Like C<ev_default_fork>, but acts on an event loop created by	606	Like C<ev_default_fork>, but acts on an event loop created by
410	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	607	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
411	after fork, and how you do this is entirely your own problem.	608	after fork that you want to re-use in the child, and how you do this is
		609	entirely your own problem.
		610
		611	=item int ev_is_default_loop (loop)
		612
		613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
		615
		616	=item unsigned int ev_loop_count (loop)
		617
		618	Returns the count of loop iterations for the loop, which is identical to
		619	the number of times libev did poll for new events. It starts at C<0> and
		620	happily wraps around with enough iterations.
		621
		622	This value can sometimes be useful as a generation counter of sorts (it
		623	"ticks" the number of loop iterations), as it roughly corresponds with
		624	C<ev_prepare> and C<ev_check> calls.
412		625
413	=item unsigned int ev_backend (loop)	626	=item unsigned int ev_backend (loop)
414		627
415	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	628	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
416	use.	629	use.
…		…
419		632
420	Returns the current "event loop time", which is the time the event loop	633	Returns the current "event loop time", which is the time the event loop
421	received events and started processing them. This timestamp does not	634	received events and started processing them. This timestamp does not
422	change as long as callbacks are being processed, and this is also the base	635	change as long as callbacks are being processed, and this is also the base
423	time used for relative timers. You can treat it as the timestamp of the	636	time used for relative timers. You can treat it as the timestamp of the
424	event occuring (or more correctly, libev finding out about it).	637	event occurring (or more correctly, libev finding out about it).
		638
		639	=item ev_now_update (loop)
		640
		641	Establishes the current time by querying the kernel, updating the time
		642	returned by C<ev_now ()> in the progress. This is a costly operation and
		643	is usually done automatically within C<ev_loop ()>.
		644
		645	This function is rarely useful, but when some event callback runs for a
		646	very long time without entering the event loop, updating libev's idea of
		647	the current time is a good idea.
		648
		649	See also "The special problem of time updates" in the C<ev_timer> section.
		650
		651	=item ev_suspend (loop)
		652
		653	=item ev_resume (loop)
		654
		655	These two functions suspend and resume a loop, for use when the loop is
		656	not used for a while and timeouts should not be processed.
		657
		658	A typical use case would be an interactive program such as a game: When
		659	the user presses C<^Z> to suspend the game and resumes it an hour later it
		660	would be best to handle timeouts as if no time had actually passed while
		661	the program was suspended. This can be achieved by calling C<ev_suspend>
		662	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		663	C<ev_resume> directly afterwards to resume timer processing.
		664
		665	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		666	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		667	will be rescheduled (that is, they will lose any events that would have
		668	occured while suspended).
		669
		670	After calling C<ev_suspend> you B<must not> call I<any> function on the
		671	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		672	without a previous call to C<ev_suspend>.
		673
		674	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		675	event loop time (see C<ev_now_update>).
425		676
426	=item ev_loop (loop, int flags)	677	=item ev_loop (loop, int flags)
427		678
428	Finally, this is it, the event handler. This function usually is called	679	Finally, this is it, the event handler. This function usually is called
429	after you initialised all your watchers and you want to start handling	680	after you initialised all your watchers and you want to start handling
…		…
432	If the flags argument is specified as C<0>, it will not return until	683	If the flags argument is specified as C<0>, it will not return until
433	either no event watchers are active anymore or C<ev_unloop> was called.	684	either no event watchers are active anymore or C<ev_unloop> was called.
434		685
435	Please note that an explicit C<ev_unloop> is usually better than	686	Please note that an explicit C<ev_unloop> is usually better than
436	relying on all watchers to be stopped when deciding when a program has	687	relying on all watchers to be stopped when deciding when a program has
437	finished (especially in interactive programs), but having a program that	688	finished (especially in interactive programs), but having a program
438	automatically loops as long as it has to and no longer by virtue of	689	that automatically loops as long as it has to and no longer by virtue
439	relying on its watchers stopping correctly is a thing of beauty.	690	of relying on its watchers stopping correctly, that is truly a thing of
		691	beauty.
440		692
441	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	693	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
442	those events and any outstanding ones, but will not block your process in	694	those events and any already outstanding ones, but will not block your
443	case there are no events and will return after one iteration of the loop.	695	process in case there are no events and will return after one iteration of
		696	the loop.
444		697
445	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	698	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
446	neccessary) and will handle those and any outstanding ones. It will block	699	necessary) and will handle those and any already outstanding ones. It
447	your process until at least one new event arrives, and will return after	700	will block your process until at least one new event arrives (which could
448	one iteration of the loop. This is useful if you are waiting for some	701	be an event internal to libev itself, so there is no guarantee that a
449	external event in conjunction with something not expressible using other	702	user-registered callback will be called), and will return after one
		703	iteration of the loop.
		704
		705	This is useful if you are waiting for some external event in conjunction
		706	with something not expressible using other libev watchers (i.e. "roll your
450	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	707	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
451	usually a better approach for this kind of thing.	708	usually a better approach for this kind of thing.
452		709
453	Here are the gory details of what C<ev_loop> does:	710	Here are the gory details of what C<ev_loop> does:
454		711
455	* If there are no active watchers (reference count is zero), return.	712	- Before the first iteration, call any pending watchers.
456	- Queue prepare watchers and then call all outstanding watchers.	713	* If EVFLAG_FORKCHECK was used, check for a fork.
		714	- If a fork was detected (by any means), queue and call all fork watchers.
		715	- Queue and call all prepare watchers.
457	- If we have been forked, recreate the kernel state.	716	- If we have been forked, detach and recreate the kernel state
		717	as to not disturb the other process.
458	- Update the kernel state with all outstanding changes.	718	- Update the kernel state with all outstanding changes.
459	- Update the "event loop time".	719	- Update the "event loop time" (ev_now ()).
460	- Calculate for how long to block.	720	- Calculate for how long to sleep or block, if at all
		721	(active idle watchers, EVLOOP_NONBLOCK or not having
		722	any active watchers at all will result in not sleeping).
		723	- Sleep if the I/O and timer collect interval say so.
461	- Block the process, waiting for any events.	724	- Block the process, waiting for any events.
462	- Queue all outstanding I/O (fd) events.	725	- Queue all outstanding I/O (fd) events.
463	- Update the "event loop time" and do time jump handling.	726	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
464	- Queue all outstanding timers.	727	- Queue all expired timers.
465	- Queue all outstanding periodics.	728	- Queue all expired periodics.
466	- If no events are pending now, queue all idle watchers.	729	- Unless any events are pending now, queue all idle watchers.
467	- Queue all check watchers.	730	- Queue all check watchers.
468	- Call all queued watchers in reverse order (i.e. check watchers first).	731	- Call all queued watchers in reverse order (i.e. check watchers first).
469	Signals and child watchers are implemented as I/O watchers, and will	732	Signals and child watchers are implemented as I/O watchers, and will
470	be handled here by queueing them when their watcher gets executed.	733	be handled here by queueing them when their watcher gets executed.
471	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	734	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
472	were used, return, otherwise continue with step *.	735	were used, or there are no active watchers, return, otherwise
		736	continue with step *.
473		737
474	Example: Queue some jobs and then loop until no events are outsanding	738	Example: Queue some jobs and then loop until no events are outstanding
475	anymore.	739	anymore.
476		740
477	... queue jobs here, make sure they register event watchers as long	741	... queue jobs here, make sure they register event watchers as long
478	... as they still have work to do (even an idle watcher will do..)	742	... as they still have work to do (even an idle watcher will do..)
479	ev_loop (my_loop, 0);	743	ev_loop (my_loop, 0);
480	... jobs done. yeah!	744	... jobs done or somebody called unloop. yeah!
481		745
482	=item ev_unloop (loop, how)	746	=item ev_unloop (loop, how)
483		747
484	Can be used to make a call to C<ev_loop> return early (but only after it	748	Can be used to make a call to C<ev_loop> return early (but only after it
485	has processed all outstanding events). The C<how> argument must be either	749	has processed all outstanding events). The C<how> argument must be either
486	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	750	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
487	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	751	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
488		752
		753	This "unloop state" will be cleared when entering C<ev_loop> again.
		754
		755	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		756
489	=item ev_ref (loop)	757	=item ev_ref (loop)
490		758
491	=item ev_unref (loop)	759	=item ev_unref (loop)
492		760
493	Ref/unref can be used to add or remove a reference count on the event	761	Ref/unref can be used to add or remove a reference count on the event
494	loop: Every watcher keeps one reference, and as long as the reference	762	loop: Every watcher keeps one reference, and as long as the reference
495	count is nonzero, C<ev_loop> will not return on its own. If you have	763	count is nonzero, C<ev_loop> will not return on its own.
		764
496	a watcher you never unregister that should not keep C<ev_loop> from	765	If you have a watcher you never unregister that should not keep C<ev_loop>
497	returning, ev_unref() after starting, and ev_ref() before stopping it. For	766	from returning, call ev_unref() after starting, and ev_ref() before
		767	stopping it.
		768
498	example, libev itself uses this for its internal signal pipe: It is not	769	As an example, libev itself uses this for its internal signal pipe: It
499	visible to the libev user and should not keep C<ev_loop> from exiting if	770	is not visible to the libev user and should not keep C<ev_loop> from
500	no event watchers registered by it are active. It is also an excellent	771	exiting if no event watchers registered by it are active. It is also an
501	way to do this for generic recurring timers or from within third-party	772	excellent way to do this for generic recurring timers or from within
502	libraries. Just remember to I<unref after start> and I<ref before stop>.	773	third-party libraries. Just remember to I<unref after start> and I<ref
		774	before stop> (but only if the watcher wasn't active before, or was active
		775	before, respectively. Note also that libev might stop watchers itself
		776	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		777	in the callback).
503		778
504	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	779	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
505	running when nothing else is active.	780	running when nothing else is active.
506		781
507	struct ev_signal exitsig;	782	ev_signal exitsig;
508	ev_signal_init (&exitsig, sig_cb, SIGINT);	783	ev_signal_init (&exitsig, sig_cb, SIGINT);
509	ev_signal_start (loop, &exitsig);	784	ev_signal_start (loop, &exitsig);
510	evf_unref (loop);	785	evf_unref (loop);
511		786
512	Example: For some weird reason, unregister the above signal handler again.	787	Example: For some weird reason, unregister the above signal handler again.
513		788
514	ev_ref (loop);	789	ev_ref (loop);
515	ev_signal_stop (loop, &exitsig);	790	ev_signal_stop (loop, &exitsig);
		791
		792	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		793
		794	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		795
		796	These advanced functions influence the time that libev will spend waiting
		797	for events. Both time intervals are by default C<0>, meaning that libev
		798	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		799	latency.
		800
		801	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		802	allows libev to delay invocation of I/O and timer/periodic callbacks
		803	to increase efficiency of loop iterations (or to increase power-saving
		804	opportunities).
		805
		806	The idea is that sometimes your program runs just fast enough to handle
		807	one (or very few) event(s) per loop iteration. While this makes the
		808	program responsive, it also wastes a lot of CPU time to poll for new
		809	events, especially with backends like C<select ()> which have a high
		810	overhead for the actual polling but can deliver many events at once.
		811
		812	By setting a higher I<io collect interval> you allow libev to spend more
		813	time collecting I/O events, so you can handle more events per iteration,
		814	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		815	C<ev_timer>) will be not affected. Setting this to a non-null value will
		816	introduce an additional C<ev_sleep ()> call into most loop iterations.
		817
		818	Likewise, by setting a higher I<timeout collect interval> you allow libev
		819	to spend more time collecting timeouts, at the expense of increased
		820	latency/jitter/inexactness (the watcher callback will be called
		821	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		822	value will not introduce any overhead in libev.
		823
		824	Many (busy) programs can usually benefit by setting the I/O collect
		825	interval to a value near C<0.1> or so, which is often enough for
		826	interactive servers (of course not for games), likewise for timeouts. It
		827	usually doesn't make much sense to set it to a lower value than C<0.01>,
		828	as this approaches the timing granularity of most systems.
		829
		830	Setting the I<timeout collect interval> can improve the opportunity for
		831	saving power, as the program will "bundle" timer callback invocations that
		832	are "near" in time together, by delaying some, thus reducing the number of
		833	times the process sleeps and wakes up again. Another useful technique to
		834	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		835	they fire on, say, one-second boundaries only.
		836
		837	=item ev_loop_verify (loop)
		838
		839	This function only does something when C<EV_VERIFY> support has been
		840	compiled in, which is the default for non-minimal builds. It tries to go
		841	through all internal structures and checks them for validity. If anything
		842	is found to be inconsistent, it will print an error message to standard
		843	error and call C<abort ()>.
		844
		845	This can be used to catch bugs inside libev itself: under normal
		846	circumstances, this function will never abort as of course libev keeps its
		847	data structures consistent.
516		848
517	=back	849	=back
518		850
519		851
520	=head1 ANATOMY OF A WATCHER	852	=head1 ANATOMY OF A WATCHER
		853
		854	In the following description, uppercase C<TYPE> in names stands for the
		855	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		856	watchers and C<ev_io_start> for I/O watchers.
521		857
522	A watcher is a structure that you create and register to record your	858	A watcher is a structure that you create and register to record your
523	interest in some event. For instance, if you want to wait for STDIN to	859	interest in some event. For instance, if you want to wait for STDIN to
524	become readable, you would create an C<ev_io> watcher for that:	860	become readable, you would create an C<ev_io> watcher for that:
525		861
526	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	862	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
527	{	863	{
528	ev_io_stop (w);	864	ev_io_stop (w);
529	ev_unloop (loop, EVUNLOOP_ALL);	865	ev_unloop (loop, EVUNLOOP_ALL);
530	}	866	}
531		867
532	struct ev_loop *loop = ev_default_loop (0);	868	struct ev_loop *loop = ev_default_loop (0);
		869
533	struct ev_io stdin_watcher;	870	ev_io stdin_watcher;
		871
534	ev_init (&stdin_watcher, my_cb);	872	ev_init (&stdin_watcher, my_cb);
535	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	873	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
536	ev_io_start (loop, &stdin_watcher);	874	ev_io_start (loop, &stdin_watcher);
		875
537	ev_loop (loop, 0);	876	ev_loop (loop, 0);
538		877
539	As you can see, you are responsible for allocating the memory for your	878	As you can see, you are responsible for allocating the memory for your
540	watcher structures (and it is usually a bad idea to do this on the stack,	879	watcher structures (and it is I<usually> a bad idea to do this on the
541	although this can sometimes be quite valid).	880	stack).
		881
		882	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		883	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
542		884
543	Each watcher structure must be initialised by a call to C<ev_init	885	Each watcher structure must be initialised by a call to C<ev_init
544	(watcher *, callback)>, which expects a callback to be provided. This	886	(watcher *, callback)>, which expects a callback to be provided. This
545	callback gets invoked each time the event occurs (or, in the case of io	887	callback gets invoked each time the event occurs (or, in the case of I/O
546	watchers, each time the event loop detects that the file descriptor given	888	watchers, each time the event loop detects that the file descriptor given
547	is readable and/or writable).	889	is readable and/or writable).
548		890
549	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	891	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
550	with arguments specific to this watcher type. There is also a macro	892	macro to configure it, with arguments specific to the watcher type. There
551	to combine initialisation and setting in one call: C<< ev_<type>_init	893	is also a macro to combine initialisation and setting in one call: C<<
552	(watcher *, callback, ...) >>.	894	ev_TYPE_init (watcher *, callback, ...) >>.
553		895
554	To make the watcher actually watch out for events, you have to start it	896	To make the watcher actually watch out for events, you have to start it
555	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	897	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
556	*) >>), and you can stop watching for events at any time by calling the	898	*) >>), and you can stop watching for events at any time by calling the
557	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	899	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
558		900
559	As long as your watcher is active (has been started but not stopped) you	901	As long as your watcher is active (has been started but not stopped) you
560	must not touch the values stored in it. Most specifically you must never	902	must not touch the values stored in it. Most specifically you must never
561	reinitialise it or call its C<set> macro.	903	reinitialise it or call its C<ev_TYPE_set> macro.
562		904
563	Each and every callback receives the event loop pointer as first, the	905	Each and every callback receives the event loop pointer as first, the
564	registered watcher structure as second, and a bitset of received events as	906	registered watcher structure as second, and a bitset of received events as
565	third argument.	907	third argument.
566		908
…		…
620	=item C<EV_FORK>	962	=item C<EV_FORK>
621		963
622	The event loop has been resumed in the child process after fork (see	964	The event loop has been resumed in the child process after fork (see
623	C<ev_fork>).	965	C<ev_fork>).
624		966
		967	=item C<EV_ASYNC>
		968
		969	The given async watcher has been asynchronously notified (see C<ev_async>).
		970
		971	=item C<EV_CUSTOM>
		972
		973	Not ever sent (or otherwise used) by libev itself, but can be freely used
		974	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		975
625	=item C<EV_ERROR>	976	=item C<EV_ERROR>
626		977
627	An unspecified error has occured, the watcher has been stopped. This might	978	An unspecified error has occurred, the watcher has been stopped. This might
628	happen because the watcher could not be properly started because libev	979	happen because the watcher could not be properly started because libev
629	ran out of memory, a file descriptor was found to be closed or any other	980	ran out of memory, a file descriptor was found to be closed or any other
		981	problem. Libev considers these application bugs.
		982
630	problem. You best act on it by reporting the problem and somehow coping	983	You best act on it by reporting the problem and somehow coping with the
631	with the watcher being stopped.	984	watcher being stopped. Note that well-written programs should not receive
		985	an error ever, so when your watcher receives it, this usually indicates a
		986	bug in your program.
632		987
633	Libev will usually signal a few "dummy" events together with an error,	988	Libev will usually signal a few "dummy" events together with an error, for
634	for example it might indicate that a fd is readable or writable, and if	989	example it might indicate that a fd is readable or writable, and if your
635	your callbacks is well-written it can just attempt the operation and cope	990	callbacks is well-written it can just attempt the operation and cope with
636	with the error from read() or write(). This will not work in multithreaded	991	the error from read() or write(). This will not work in multi-threaded
637	programs, though, so beware.	992	programs, though, as the fd could already be closed and reused for another
		993	thing, so beware.
638		994
639	=back	995	=back
640		996
641	=head2 GENERIC WATCHER FUNCTIONS	997	=head2 GENERIC WATCHER FUNCTIONS
642
643	In the following description, C<TYPE> stands for the watcher type,
644	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
645		998
646	=over 4	999	=over 4
647		1000
648	=item C<ev_init> (ev_TYPE *watcher, callback)	1001	=item C<ev_init> (ev_TYPE *watcher, callback)
649		1002
…		…
655	which rolls both calls into one.	1008	which rolls both calls into one.
656		1009
657	You can reinitialise a watcher at any time as long as it has been stopped	1010	You can reinitialise a watcher at any time as long as it has been stopped
658	(or never started) and there are no pending events outstanding.	1011	(or never started) and there are no pending events outstanding.
659		1012
660	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1013	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
661	int revents)>.	1014	int revents)>.
		1015
		1016	Example: Initialise an C<ev_io> watcher in two steps.
		1017
		1018	ev_io w;
		1019	ev_init (&w, my_cb);
		1020	ev_io_set (&w, STDIN_FILENO, EV_READ);
662		1021
663	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1022	=item C<ev_TYPE_set> (ev_TYPE *, [args])
664		1023
665	This macro initialises the type-specific parts of a watcher. You need to	1024	This macro initialises the type-specific parts of a watcher. You need to
666	call C<ev_init> at least once before you call this macro, but you can	1025	call C<ev_init> at least once before you call this macro, but you can
…		…
669	difference to the C<ev_init> macro).	1028	difference to the C<ev_init> macro).
670		1029
671	Although some watcher types do not have type-specific arguments	1030	Although some watcher types do not have type-specific arguments
672	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1031	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
673		1032
		1033	See C<ev_init>, above, for an example.
		1034
674	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1035	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
675		1036
676	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1037	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
677	calls into a single call. This is the most convinient method to initialise	1038	calls into a single call. This is the most convenient method to initialise
678	a watcher. The same limitations apply, of course.	1039	a watcher. The same limitations apply, of course.
		1040
		1041	Example: Initialise and set an C<ev_io> watcher in one step.
		1042
		1043	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
679		1044
680	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1045	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
681		1046
682	Starts (activates) the given watcher. Only active watchers will receive	1047	Starts (activates) the given watcher. Only active watchers will receive
683	events. If the watcher is already active nothing will happen.	1048	events. If the watcher is already active nothing will happen.
684		1049
		1050	Example: Start the C<ev_io> watcher that is being abused as example in this
		1051	whole section.
		1052
		1053	ev_io_start (EV_DEFAULT_UC, &w);
		1054
685	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1055	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
686		1056
687	Stops the given watcher again (if active) and clears the pending	1057	Stops the given watcher if active, and clears the pending status (whether
		1058	the watcher was active or not).
		1059
688	status. It is possible that stopped watchers are pending (for example,	1060	It is possible that stopped watchers are pending - for example,
689	non-repeating timers are being stopped when they become pending), but	1061	non-repeating timers are being stopped when they become pending - but
690	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1062	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
691	you want to free or reuse the memory used by the watcher it is therefore a	1063	pending. If you want to free or reuse the memory used by the watcher it is
692	good idea to always call its C<ev_TYPE_stop> function.	1064	therefore a good idea to always call its C<ev_TYPE_stop> function.
693		1065
694	=item bool ev_is_active (ev_TYPE *watcher)	1066	=item bool ev_is_active (ev_TYPE *watcher)
695		1067
696	Returns a true value iff the watcher is active (i.e. it has been started	1068	Returns a true value iff the watcher is active (i.e. it has been started
697	and not yet been stopped). As long as a watcher is active you must not modify	1069	and not yet been stopped). As long as a watcher is active you must not modify
…		…
700	=item bool ev_is_pending (ev_TYPE *watcher)	1072	=item bool ev_is_pending (ev_TYPE *watcher)
701		1073
702	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1074	Returns a true value iff the watcher is pending, (i.e. it has outstanding
703	events but its callback has not yet been invoked). As long as a watcher	1075	events but its callback has not yet been invoked). As long as a watcher
704	is pending (but not active) you must not call an init function on it (but	1076	is pending (but not active) you must not call an init function on it (but
705	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1077	C<ev_TYPE_set> is safe), you must not change its priority, and you must
706	libev (e.g. you cnanot C<free ()> it).	1078	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1079	it).
707		1080
708	=item callback ev_cb (ev_TYPE *watcher)	1081	=item callback ev_cb (ev_TYPE *watcher)
709		1082
710	Returns the callback currently set on the watcher.	1083	Returns the callback currently set on the watcher.
711		1084
712	=item ev_cb_set (ev_TYPE *watcher, callback)	1085	=item ev_cb_set (ev_TYPE *watcher, callback)
713		1086
714	Change the callback. You can change the callback at virtually any time	1087	Change the callback. You can change the callback at virtually any time
715	(modulo threads).	1088	(modulo threads).
716		1089
		1090	=item ev_set_priority (ev_TYPE *watcher, priority)
		1091
		1092	=item int ev_priority (ev_TYPE *watcher)
		1093
		1094	Set and query the priority of the watcher. The priority is a small
		1095	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1096	(default: C<-2>). Pending watchers with higher priority will be invoked
		1097	before watchers with lower priority, but priority will not keep watchers
		1098	from being executed (except for C<ev_idle> watchers).
		1099
		1100	If you need to suppress invocation when higher priority events are pending
		1101	you need to look at C<ev_idle> watchers, which provide this functionality.
		1102
		1103	You I<must not> change the priority of a watcher as long as it is active or
		1104	pending.
		1105
		1106	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1107	fine, as long as you do not mind that the priority value you query might
		1108	or might not have been clamped to the valid range.
		1109
		1110	The default priority used by watchers when no priority has been set is
		1111	always C<0>, which is supposed to not be too high and not be too low :).
		1112
		1113	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1114	priorities.
		1115
		1116	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1117
		1118	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1119	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1120	can deal with that fact, as both are simply passed through to the
		1121	callback.
		1122
		1123	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1124
		1125	If the watcher is pending, this function clears its pending status and
		1126	returns its C<revents> bitset (as if its callback was invoked). If the
		1127	watcher isn't pending it does nothing and returns C<0>.
		1128
		1129	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1130	callback to be invoked, which can be accomplished with this function.
		1131
717	=back	1132	=back
718		1133
719		1134
720	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1135	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
721		1136
722	Each watcher has, by default, a member C<void *data> that you can change	1137	Each watcher has, by default, a member C<void *data> that you can change
723	and read at any time, libev will completely ignore it. This can be used	1138	and read at any time: libev will completely ignore it. This can be used
724	to associate arbitrary data with your watcher. If you need more data and	1139	to associate arbitrary data with your watcher. If you need more data and
725	don't want to allocate memory and store a pointer to it in that data	1140	don't want to allocate memory and store a pointer to it in that data
726	member, you can also "subclass" the watcher type and provide your own	1141	member, you can also "subclass" the watcher type and provide your own
727	data:	1142	data:
728		1143
729	struct my_io	1144	struct my_io
730	{	1145	{
731	struct ev_io io;	1146	ev_io io;
732	int otherfd;	1147	int otherfd;
733	void *somedata;	1148	void *somedata;
734	struct whatever *mostinteresting;	1149	struct whatever *mostinteresting;
735	}	1150	};
		1151
		1152	...
		1153	struct my_io w;
		1154	ev_io_init (&w.io, my_cb, fd, EV_READ);
736		1155
737	And since your callback will be called with a pointer to the watcher, you	1156	And since your callback will be called with a pointer to the watcher, you
738	can cast it back to your own type:	1157	can cast it back to your own type:
739		1158
740	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1159	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
741	{	1160	{
742	struct my_io *w = (struct my_io *)w_;	1161	struct my_io *w = (struct my_io *)w_;
743	...	1162	...
744	}	1163	}
745		1164
746	More interesting and less C-conformant ways of casting your callback type	1165	More interesting and less C-conformant ways of casting your callback type
747	instead have been omitted.	1166	instead have been omitted.
748		1167
749	Another common scenario is having some data structure with multiple	1168	Another common scenario is to use some data structure with multiple
750	watchers:	1169	embedded watchers:
751		1170
752	struct my_biggy	1171	struct my_biggy
753	{	1172	{
754	int some_data;	1173	int some_data;
755	ev_timer t1;	1174	ev_timer t1;
756	ev_timer t2;	1175	ev_timer t2;
757	}	1176	}
758		1177
759	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1178	In this case getting the pointer to C<my_biggy> is a bit more
760	you need to use C<offsetof>:	1179	complicated: Either you store the address of your C<my_biggy> struct
		1180	in the C<data> member of the watcher (for woozies), or you need to use
		1181	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1182	programmers):
761		1183
762	#include <stddef.h>	1184	#include <stddef.h>
763		1185
764	static void	1186	static void
765	t1_cb (EV_P_ struct ev_timer *w, int revents)	1187	t1_cb (EV_P_ ev_timer *w, int revents)
766	{	1188	{
767	struct my_biggy big = (struct my_biggy *	1189	struct my_biggy big = (struct my_biggy *
768	(((char *)w) - offsetof (struct my_biggy, t1));	1190	(((char *)w) - offsetof (struct my_biggy, t1));
769	}	1191	}
770		1192
771	static void	1193	static void
772	t2_cb (EV_P_ struct ev_timer *w, int revents)	1194	t2_cb (EV_P_ ev_timer *w, int revents)
773	{	1195	{
774	struct my_biggy big = (struct my_biggy *	1196	struct my_biggy big = (struct my_biggy *
775	(((char *)w) - offsetof (struct my_biggy, t2));	1197	(((char *)w) - offsetof (struct my_biggy, t2));
776	}	1198	}
		1199
		1200	=head2 WATCHER PRIORITY MODELS
		1201
		1202	Many event loops support I<watcher priorities>, which are usually small
		1203	integers that influence the ordering of event callback invocation
		1204	between watchers in some way, all else being equal.
		1205
		1206	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1207	description for the more technical details such as the actual priority
		1208	range.
		1209
		1210	There are two common ways how these these priorities are being interpreted
		1211	by event loops:
		1212
		1213	In the more common lock-out model, higher priorities "lock out" invocation
		1214	of lower priority watchers, which means as long as higher priority
		1215	watchers receive events, lower priority watchers are not being invoked.
		1216
		1217	The less common only-for-ordering model uses priorities solely to order
		1218	callback invocation within a single event loop iteration: Higher priority
		1219	watchers are invoked before lower priority ones, but they all get invoked
		1220	before polling for new events.
		1221
		1222	Libev uses the second (only-for-ordering) model for all its watchers
		1223	except for idle watchers (which use the lock-out model).
		1224
		1225	The rationale behind this is that implementing the lock-out model for
		1226	watchers is not well supported by most kernel interfaces, and most event
		1227	libraries will just poll for the same events again and again as long as
		1228	their callbacks have not been executed, which is very inefficient in the
		1229	common case of one high-priority watcher locking out a mass of lower
		1230	priority ones.
		1231
		1232	Static (ordering) priorities are most useful when you have two or more
		1233	watchers handling the same resource: a typical usage example is having an
		1234	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1235	timeouts. Under load, data might be received while the program handles
		1236	other jobs, but since timers normally get invoked first, the timeout
		1237	handler will be executed before checking for data. In that case, giving
		1238	the timer a lower priority than the I/O watcher ensures that I/O will be
		1239	handled first even under adverse conditions (which is usually, but not
		1240	always, what you want).
		1241
		1242	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1243	will only be executed when no same or higher priority watchers have
		1244	received events, they can be used to implement the "lock-out" model when
		1245	required.
		1246
		1247	For example, to emulate how many other event libraries handle priorities,
		1248	you can associate an C<ev_idle> watcher to each such watcher, and in
		1249	the normal watcher callback, you just start the idle watcher. The real
		1250	processing is done in the idle watcher callback. This causes libev to
		1251	continously poll and process kernel event data for the watcher, but when
		1252	the lock-out case is known to be rare (which in turn is rare :), this is
		1253	workable.
		1254
		1255	Usually, however, the lock-out model implemented that way will perform
		1256	miserably under the type of load it was designed to handle. In that case,
		1257	it might be preferable to stop the real watcher before starting the
		1258	idle watcher, so the kernel will not have to process the event in case
		1259	the actual processing will be delayed for considerable time.
		1260
		1261	Here is an example of an I/O watcher that should run at a strictly lower
		1262	priority than the default, and which should only process data when no
		1263	other events are pending:
		1264
		1265	ev_idle idle; // actual processing watcher
		1266	ev_io io; // actual event watcher
		1267
		1268	static void
		1269	io_cb (EV_P_ ev_io *w, int revents)
		1270	{
		1271	// stop the I/O watcher, we received the event, but
		1272	// are not yet ready to handle it.
		1273	ev_io_stop (EV_A_ w);
		1274
		1275	// start the idle watcher to ahndle the actual event.
		1276	// it will not be executed as long as other watchers
		1277	// with the default priority are receiving events.
		1278	ev_idle_start (EV_A_ &idle);
		1279	}
		1280
		1281	static void
		1282	idle-cb (EV_P_ ev_idle *w, int revents)
		1283	{
		1284	// actual processing
		1285	read (STDIN_FILENO, ...);
		1286
		1287	// have to start the I/O watcher again, as
		1288	// we have handled the event
		1289	ev_io_start (EV_P_ &io);
		1290	}
		1291
		1292	// initialisation
		1293	ev_idle_init (&idle, idle_cb);
		1294	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1295	ev_io_start (EV_DEFAULT_ &io);
		1296
		1297	In the "real" world, it might also be beneficial to start a timer, so that
		1298	low-priority connections can not be locked out forever under load. This
		1299	enables your program to keep a lower latency for important connections
		1300	during short periods of high load, while not completely locking out less
		1301	important ones.
777		1302
778		1303
779	=head1 WATCHER TYPES	1304	=head1 WATCHER TYPES
780		1305
781	This section describes each watcher in detail, but will not repeat	1306	This section describes each watcher in detail, but will not repeat
…		…
805	In general you can register as many read and/or write event watchers per	1330	In general you can register as many read and/or write event watchers per
806	fd as you want (as long as you don't confuse yourself). Setting all file	1331	fd as you want (as long as you don't confuse yourself). Setting all file
807	descriptors to non-blocking mode is also usually a good idea (but not	1332	descriptors to non-blocking mode is also usually a good idea (but not
808	required if you know what you are doing).	1333	required if you know what you are doing).
809		1334
810	You have to be careful with dup'ed file descriptors, though. Some backends	1335	If you cannot use non-blocking mode, then force the use of a
811	(the linux epoll backend is a notable example) cannot handle dup'ed file	1336	known-to-be-good backend (at the time of this writing, this includes only
812	descriptors correctly if you register interest in two or more fds pointing	1337	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
813	to the same underlying file/socket/etc. description (that is, they share
814	the same underlying "file open").
815
816	If you must do this, then force the use of a known-to-be-good backend
817	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
818	C<EVBACKEND_POLL>).
819		1338
820	Another thing you have to watch out for is that it is quite easy to	1339	Another thing you have to watch out for is that it is quite easy to
821	receive "spurious" readyness notifications, that is your callback might	1340	receive "spurious" readiness notifications, that is your callback might
822	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1341	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
823	because there is no data. Not only are some backends known to create a	1342	because there is no data. Not only are some backends known to create a
824	lot of those (for example solaris ports), it is very easy to get into	1343	lot of those (for example Solaris ports), it is very easy to get into
825	this situation even with a relatively standard program structure. Thus	1344	this situation even with a relatively standard program structure. Thus
826	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1345	it is best to always use non-blocking I/O: An extra C<read>(2) returning
827	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1346	C<EAGAIN> is far preferable to a program hanging until some data arrives.
828		1347
829	If you cannot run the fd in non-blocking mode (for example you should not	1348	If you cannot run the fd in non-blocking mode (for example you should
830	play around with an Xlib connection), then you have to seperately re-test	1349	not play around with an Xlib connection), then you have to separately
831	wether a file descriptor is really ready with a known-to-be good interface	1350	re-test whether a file descriptor is really ready with a known-to-be good
832	such as poll (fortunately in our Xlib example, Xlib already does this on	1351	interface such as poll (fortunately in our Xlib example, Xlib already
833	its own, so its quite safe to use).	1352	does this on its own, so its quite safe to use). Some people additionally
		1353	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1354	indefinitely.
		1355
		1356	But really, best use non-blocking mode.
		1357
		1358	=head3 The special problem of disappearing file descriptors
		1359
		1360	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1361	descriptor (either due to calling C<close> explicitly or any other means,
		1362	such as C<dup2>). The reason is that you register interest in some file
		1363	descriptor, but when it goes away, the operating system will silently drop
		1364	this interest. If another file descriptor with the same number then is
		1365	registered with libev, there is no efficient way to see that this is, in
		1366	fact, a different file descriptor.
		1367
		1368	To avoid having to explicitly tell libev about such cases, libev follows
		1369	the following policy: Each time C<ev_io_set> is being called, libev
		1370	will assume that this is potentially a new file descriptor, otherwise
		1371	it is assumed that the file descriptor stays the same. That means that
		1372	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1373	descriptor even if the file descriptor number itself did not change.
		1374
		1375	This is how one would do it normally anyway, the important point is that
		1376	the libev application should not optimise around libev but should leave
		1377	optimisations to libev.
		1378
		1379	=head3 The special problem of dup'ed file descriptors
		1380
		1381	Some backends (e.g. epoll), cannot register events for file descriptors,
		1382	but only events for the underlying file descriptions. That means when you
		1383	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1384	events for them, only one file descriptor might actually receive events.
		1385
		1386	There is no workaround possible except not registering events
		1387	for potentially C<dup ()>'ed file descriptors, or to resort to
		1388	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1389
		1390	=head3 The special problem of fork
		1391
		1392	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1393	useless behaviour. Libev fully supports fork, but needs to be told about
		1394	it in the child.
		1395
		1396	To support fork in your programs, you either have to call
		1397	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1398	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1399	C<EVBACKEND_POLL>.
		1400
		1401	=head3 The special problem of SIGPIPE
		1402
		1403	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1404	when writing to a pipe whose other end has been closed, your program gets
		1405	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1406	this is sensible behaviour, for daemons, this is usually undesirable.
		1407
		1408	So when you encounter spurious, unexplained daemon exits, make sure you
		1409	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1410	somewhere, as that would have given you a big clue).
		1411
		1412
		1413	=head3 Watcher-Specific Functions
834		1414
835	=over 4	1415	=over 4
836		1416
837	=item ev_io_init (ev_io *, callback, int fd, int events)	1417	=item ev_io_init (ev_io *, callback, int fd, int events)
838		1418
839	=item ev_io_set (ev_io *, int fd, int events)	1419	=item ev_io_set (ev_io *, int fd, int events)
840		1420
841	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1421	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
842	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1422	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
843	C<EV_READ | EV_WRITE> to receive the given events.	1423	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
844		1424
845	=item int fd [read-only]	1425	=item int fd [read-only]
846		1426
847	The file descriptor being watched.	1427	The file descriptor being watched.
848		1428
849	=item int events [read-only]	1429	=item int events [read-only]
850		1430
851	The events being watched.	1431	The events being watched.
852		1432
853	=back	1433	=back
		1434
		1435	=head3 Examples
854		1436
855	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1437	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
856	readable, but only once. Since it is likely line-buffered, you could	1438	readable, but only once. Since it is likely line-buffered, you could
857	attempt to read a whole line in the callback.	1439	attempt to read a whole line in the callback.
858		1440
859	static void	1441	static void
860	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1442	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
861	{	1443	{
862	ev_io_stop (loop, w);	1444	ev_io_stop (loop, w);
863	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1445	.. read from stdin here (or from w->fd) and handle any I/O errors
864	}	1446	}
865		1447
866	...	1448	...
867	struct ev_loop *loop = ev_default_init (0);	1449	struct ev_loop *loop = ev_default_init (0);
868	struct ev_io stdin_readable;	1450	ev_io stdin_readable;
869	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1451	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
870	ev_io_start (loop, &stdin_readable);	1452	ev_io_start (loop, &stdin_readable);
871	ev_loop (loop, 0);	1453	ev_loop (loop, 0);
872		1454
873		1455
874	=head2 C<ev_timer> - relative and optionally repeating timeouts	1456	=head2 C<ev_timer> - relative and optionally repeating timeouts
875		1457
876	Timer watchers are simple relative timers that generate an event after a	1458	Timer watchers are simple relative timers that generate an event after a
877	given time, and optionally repeating in regular intervals after that.	1459	given time, and optionally repeating in regular intervals after that.
878		1460
879	The timers are based on real time, that is, if you register an event that	1461	The timers are based on real time, that is, if you register an event that
880	times out after an hour and you reset your system clock to last years	1462	times out after an hour and you reset your system clock to January last
881	time, it will still time out after (roughly) and hour. "Roughly" because	1463	year, it will still time out after (roughly) one hour. "Roughly" because
882	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1464	detecting time jumps is hard, and some inaccuracies are unavoidable (the
883	monotonic clock option helps a lot here).	1465	monotonic clock option helps a lot here).
		1466
		1467	The callback is guaranteed to be invoked only I<after> its timeout has
		1468	passed. If multiple timers become ready during the same loop iteration
		1469	then the ones with earlier time-out values are invoked before ones with
		1470	later time-out values (but this is no longer true when a callback calls
		1471	C<ev_loop> recursively).
		1472
		1473	=head3 Be smart about timeouts
		1474
		1475	Many real-world problems involve some kind of timeout, usually for error
		1476	recovery. A typical example is an HTTP request - if the other side hangs,
		1477	you want to raise some error after a while.
		1478
		1479	What follows are some ways to handle this problem, from obvious and
		1480	inefficient to smart and efficient.
		1481
		1482	In the following, a 60 second activity timeout is assumed - a timeout that
		1483	gets reset to 60 seconds each time there is activity (e.g. each time some
		1484	data or other life sign was received).
		1485
		1486	=over 4
		1487
		1488	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1489
		1490	This is the most obvious, but not the most simple way: In the beginning,
		1491	start the watcher:
		1492
		1493	ev_timer_init (timer, callback, 60., 0.);
		1494	ev_timer_start (loop, timer);
		1495
		1496	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1497	and start it again:
		1498
		1499	ev_timer_stop (loop, timer);
		1500	ev_timer_set (timer, 60., 0.);
		1501	ev_timer_start (loop, timer);
		1502
		1503	This is relatively simple to implement, but means that each time there is
		1504	some activity, libev will first have to remove the timer from its internal
		1505	data structure and then add it again. Libev tries to be fast, but it's
		1506	still not a constant-time operation.
		1507
		1508	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1509
		1510	This is the easiest way, and involves using C<ev_timer_again> instead of
		1511	C<ev_timer_start>.
		1512
		1513	To implement this, configure an C<ev_timer> with a C<repeat> value
		1514	of C<60> and then call C<ev_timer_again> at start and each time you
		1515	successfully read or write some data. If you go into an idle state where
		1516	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1517	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1518
		1519	That means you can ignore both the C<ev_timer_start> function and the
		1520	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1521	member and C<ev_timer_again>.
		1522
		1523	At start:
		1524
		1525	ev_timer_init (timer, callback);
		1526	timer->repeat = 60.;
		1527	ev_timer_again (loop, timer);
		1528
		1529	Each time there is some activity:
		1530
		1531	ev_timer_again (loop, timer);
		1532
		1533	It is even possible to change the time-out on the fly, regardless of
		1534	whether the watcher is active or not:
		1535
		1536	timer->repeat = 30.;
		1537	ev_timer_again (loop, timer);
		1538
		1539	This is slightly more efficient then stopping/starting the timer each time
		1540	you want to modify its timeout value, as libev does not have to completely
		1541	remove and re-insert the timer from/into its internal data structure.
		1542
		1543	It is, however, even simpler than the "obvious" way to do it.
		1544
		1545	=item 3. Let the timer time out, but then re-arm it as required.
		1546
		1547	This method is more tricky, but usually most efficient: Most timeouts are
		1548	relatively long compared to the intervals between other activity - in
		1549	our example, within 60 seconds, there are usually many I/O events with
		1550	associated activity resets.
		1551
		1552	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1553	but remember the time of last activity, and check for a real timeout only
		1554	within the callback:
		1555
		1556	ev_tstamp last_activity; // time of last activity
		1557
		1558	static void
		1559	callback (EV_P_ ev_timer *w, int revents)
		1560	{
		1561	ev_tstamp now = ev_now (EV_A);
		1562	ev_tstamp timeout = last_activity + 60.;
		1563
		1564	// if last_activity + 60. is older than now, we did time out
		1565	if (timeout < now)
		1566	{
		1567	// timeout occured, take action
		1568	}
		1569	else
		1570	{
		1571	// callback was invoked, but there was some activity, re-arm
		1572	// the watcher to fire in last_activity + 60, which is
		1573	// guaranteed to be in the future, so "again" is positive:
		1574	w->repeat = timeout - now;
		1575	ev_timer_again (EV_A_ w);
		1576	}
		1577	}
		1578
		1579	To summarise the callback: first calculate the real timeout (defined
		1580	as "60 seconds after the last activity"), then check if that time has
		1581	been reached, which means something I<did>, in fact, time out. Otherwise
		1582	the callback was invoked too early (C<timeout> is in the future), so
		1583	re-schedule the timer to fire at that future time, to see if maybe we have
		1584	a timeout then.
		1585
		1586	Note how C<ev_timer_again> is used, taking advantage of the
		1587	C<ev_timer_again> optimisation when the timer is already running.
		1588
		1589	This scheme causes more callback invocations (about one every 60 seconds
		1590	minus half the average time between activity), but virtually no calls to
		1591	libev to change the timeout.
		1592
		1593	To start the timer, simply initialise the watcher and set C<last_activity>
		1594	to the current time (meaning we just have some activity :), then call the
		1595	callback, which will "do the right thing" and start the timer:
		1596
		1597	ev_timer_init (timer, callback);
		1598	last_activity = ev_now (loop);
		1599	callback (loop, timer, EV_TIMEOUT);
		1600
		1601	And when there is some activity, simply store the current time in
		1602	C<last_activity>, no libev calls at all:
		1603
		1604	last_actiivty = ev_now (loop);
		1605
		1606	This technique is slightly more complex, but in most cases where the
		1607	time-out is unlikely to be triggered, much more efficient.
		1608
		1609	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1610	callback :) - just change the timeout and invoke the callback, which will
		1611	fix things for you.
		1612
		1613	=item 4. Wee, just use a double-linked list for your timeouts.
		1614
		1615	If there is not one request, but many thousands (millions...), all
		1616	employing some kind of timeout with the same timeout value, then one can
		1617	do even better:
		1618
		1619	When starting the timeout, calculate the timeout value and put the timeout
		1620	at the I<end> of the list.
		1621
		1622	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1623	the list is expected to fire (for example, using the technique #3).
		1624
		1625	When there is some activity, remove the timer from the list, recalculate
		1626	the timeout, append it to the end of the list again, and make sure to
		1627	update the C<ev_timer> if it was taken from the beginning of the list.
		1628
		1629	This way, one can manage an unlimited number of timeouts in O(1) time for
		1630	starting, stopping and updating the timers, at the expense of a major
		1631	complication, and having to use a constant timeout. The constant timeout
		1632	ensures that the list stays sorted.
		1633
		1634	=back
		1635
		1636	So which method the best?
		1637
		1638	Method #2 is a simple no-brain-required solution that is adequate in most
		1639	situations. Method #3 requires a bit more thinking, but handles many cases
		1640	better, and isn't very complicated either. In most case, choosing either
		1641	one is fine, with #3 being better in typical situations.
		1642
		1643	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1644	rather complicated, but extremely efficient, something that really pays
		1645	off after the first million or so of active timers, i.e. it's usually
		1646	overkill :)
		1647
		1648	=head3 The special problem of time updates
		1649
		1650	Establishing the current time is a costly operation (it usually takes at
		1651	least two system calls): EV therefore updates its idea of the current
		1652	time only before and after C<ev_loop> collects new events, which causes a
		1653	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1654	lots of events in one iteration.
884		1655
885	The relative timeouts are calculated relative to the C<ev_now ()>	1656	The relative timeouts are calculated relative to the C<ev_now ()>
886	time. This is usually the right thing as this timestamp refers to the time	1657	time. This is usually the right thing as this timestamp refers to the time
887	of the event triggering whatever timeout you are modifying/starting. If	1658	of the event triggering whatever timeout you are modifying/starting. If
888	you suspect event processing to be delayed and you I<need> to base the timeout	1659	you suspect event processing to be delayed and you I<need> to base the
889	on the current time, use something like this to adjust for this:	1660	timeout on the current time, use something like this to adjust for this:
890		1661
891	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1662	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
892		1663
893	The callback is guarenteed to be invoked only when its timeout has passed,	1664	If the event loop is suspended for a long time, you can also force an
894	but if multiple timers become ready during the same loop iteration then	1665	update of the time returned by C<ev_now ()> by calling C<ev_now_update
895	order of execution is undefined.	1666	()>.
		1667
		1668	=head3 Watcher-Specific Functions and Data Members
896		1669
897	=over 4	1670	=over 4
898		1671
899	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1672	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
900		1673
901	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1674	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
902		1675
903	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1676	Configure the timer to trigger after C<after> seconds. If C<repeat>
904	C<0.>, then it will automatically be stopped. If it is positive, then the	1677	is C<0.>, then it will automatically be stopped once the timeout is
905	timer will automatically be configured to trigger again C<repeat> seconds	1678	reached. If it is positive, then the timer will automatically be
906	later, again, and again, until stopped manually.	1679	configured to trigger again C<repeat> seconds later, again, and again,
		1680	until stopped manually.
907		1681
908	The timer itself will do a best-effort at avoiding drift, that is, if you	1682	The timer itself will do a best-effort at avoiding drift, that is, if
909	configure a timer to trigger every 10 seconds, then it will trigger at	1683	you configure a timer to trigger every 10 seconds, then it will normally
910	exactly 10 second intervals. If, however, your program cannot keep up with	1684	trigger at exactly 10 second intervals. If, however, your program cannot
911	the timer (because it takes longer than those 10 seconds to do stuff) the	1685	keep up with the timer (because it takes longer than those 10 seconds to
912	timer will not fire more than once per event loop iteration.	1686	do stuff) the timer will not fire more than once per event loop iteration.
913		1687
914	=item ev_timer_again (loop)	1688	=item ev_timer_again (loop, ev_timer *)
915		1689
916	This will act as if the timer timed out and restart it again if it is	1690	This will act as if the timer timed out and restart it again if it is
917	repeating. The exact semantics are:	1691	repeating. The exact semantics are:
918		1692
		1693	If the timer is pending, its pending status is cleared.
		1694
919	If the timer is started but nonrepeating, stop it.	1695	If the timer is started but non-repeating, stop it (as if it timed out).
920		1696
921	If the timer is repeating, either start it if necessary (with the repeat	1697	If the timer is repeating, either start it if necessary (with the
922	value), or reset the running timer to the repeat value.	1698	C<repeat> value), or reset the running timer to the C<repeat> value.
923		1699
924	This sounds a bit complicated, but here is a useful and typical	1700	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
925	example: Imagine you have a tcp connection and you want a so-called	1701	usage example.
926	idle timeout, that is, you want to be called when there have been,
927	say, 60 seconds of inactivity on the socket. The easiest way to do
928	this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
929	C<ev_timer_again> each time you successfully read or write some data. If
930	you go into an idle state where you do not expect data to travel on the
931	socket, you can stop the timer, and again will automatically restart it if
932	need be.
933
934	You can also ignore the C<after> value and C<ev_timer_start> altogether
935	and only ever use the C<repeat> value:
936
937	ev_timer_init (timer, callback, 0., 5.);
938	ev_timer_again (loop, timer);
939	...
940	timer->again = 17.;
941	ev_timer_again (loop, timer);
942	...
943	timer->again = 10.;
944	ev_timer_again (loop, timer);
945
946	This is more efficient then stopping/starting the timer eahc time you want
947	to modify its timeout value.
948		1702
949	=item ev_tstamp repeat [read-write]	1703	=item ev_tstamp repeat [read-write]
950		1704
951	The current C<repeat> value. Will be used each time the watcher times out	1705	The current C<repeat> value. Will be used each time the watcher times out
952	or C<ev_timer_again> is called and determines the next timeout (if any),	1706	or C<ev_timer_again> is called, and determines the next timeout (if any),
953	which is also when any modifications are taken into account.	1707	which is also when any modifications are taken into account.
954		1708
955	=back	1709	=back
956		1710
		1711	=head3 Examples
		1712
957	Example: Create a timer that fires after 60 seconds.	1713	Example: Create a timer that fires after 60 seconds.
958		1714
959	static void	1715	static void
960	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1716	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
961	{	1717	{
962	.. one minute over, w is actually stopped right here	1718	.. one minute over, w is actually stopped right here
963	}	1719	}
964		1720
965	struct ev_timer mytimer;	1721	ev_timer mytimer;
966	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1722	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
967	ev_timer_start (loop, &mytimer);	1723	ev_timer_start (loop, &mytimer);
968		1724
969	Example: Create a timeout timer that times out after 10 seconds of	1725	Example: Create a timeout timer that times out after 10 seconds of
970	inactivity.	1726	inactivity.
971		1727
972	static void	1728	static void
973	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1729	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
974	{	1730	{
975	.. ten seconds without any activity	1731	.. ten seconds without any activity
976	}	1732	}
977		1733
978	struct ev_timer mytimer;	1734	ev_timer mytimer;
979	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1735	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
980	ev_timer_again (&mytimer); /* start timer */	1736	ev_timer_again (&mytimer); /* start timer */
981	ev_loop (loop, 0);	1737	ev_loop (loop, 0);
982		1738
983	// and in some piece of code that gets executed on any "activity":	1739	// and in some piece of code that gets executed on any "activity":
984	// reset the timeout to start ticking again at 10 seconds	1740	// reset the timeout to start ticking again at 10 seconds
985	ev_timer_again (&mytimer);	1741	ev_timer_again (&mytimer);
986		1742
987		1743
988	=head2 C<ev_periodic> - to cron or not to cron?	1744	=head2 C<ev_periodic> - to cron or not to cron?
989		1745
990	Periodic watchers are also timers of a kind, but they are very versatile	1746	Periodic watchers are also timers of a kind, but they are very versatile
991	(and unfortunately a bit complex).	1747	(and unfortunately a bit complex).
992		1748
993	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1749	Unlike C<ev_timer>, periodic watchers are not based on real time (or
994	but on wallclock time (absolute time). You can tell a periodic watcher	1750	relative time, the physical time that passes) but on wall clock time
995	to trigger "at" some specific point in time. For example, if you tell a	1751	(absolute time, the thing you can read on your calender or clock). The
996	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1752	difference is that wall clock time can run faster or slower than real
997	+ 10.>) and then reset your system clock to the last year, then it will	1753	time, and time jumps are not uncommon (e.g. when you adjust your
998	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1754	wrist-watch).
999	roughly 10 seconds later and of course not if you reset your system time
1000	again).
1001		1755
1002	They can also be used to implement vastly more complex timers, such as	1756	You can tell a periodic watcher to trigger after some specific point
		1757	in time: for example, if you tell a periodic watcher to trigger "in 10
		1758	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1759	not a delay) and then reset your system clock to January of the previous
		1760	year, then it will take a year or more to trigger the event (unlike an
		1761	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1762	it, as it uses a relative timeout).
		1763
		1764	C<ev_periodic> watchers can also be used to implement vastly more complex
1003	triggering an event on eahc midnight, local time.	1765	timers, such as triggering an event on each "midnight, local time", or
		1766	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1767	those cannot react to time jumps.
1004		1768
1005	As with timers, the callback is guarenteed to be invoked only when the	1769	As with timers, the callback is guaranteed to be invoked only when the
1006	time (C<at>) has been passed, but if multiple periodic timers become ready	1770	point in time where it is supposed to trigger has passed. If multiple
1007	during the same loop iteration then order of execution is undefined.	1771	timers become ready during the same loop iteration then the ones with
		1772	earlier time-out values are invoked before ones with later time-out values
		1773	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1774
		1775	=head3 Watcher-Specific Functions and Data Members
1008		1776
1009	=over 4	1777	=over 4
1010		1778
1011	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1779	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1012		1780
1013	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1781	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1014		1782
1015	Lots of arguments, lets sort it out... There are basically three modes of	1783	Lots of arguments, let's sort it out... There are basically three modes of
1016	operation, and we will explain them from simplest to complex:	1784	operation, and we will explain them from simplest to most complex:
1017		1785
1018	=over 4	1786	=over 4
1019		1787
1020	=item * absolute timer (interval = reschedule_cb = 0)	1788	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1021		1789
1022	In this configuration the watcher triggers an event at the wallclock time	1790	In this configuration the watcher triggers an event after the wall clock
1023	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1791	time C<offset> has passed. It will not repeat and will not adjust when a
1024	that is, if it is to be run at January 1st 2011 then it will run when the	1792	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1025	system time reaches or surpasses this time.	1793	will be stopped and invoked when the system clock reaches or surpasses
		1794	this point in time.
1026		1795
1027	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1796	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1028		1797
1029	In this mode the watcher will always be scheduled to time out at the next	1798	In this mode the watcher will always be scheduled to time out at the next
1030	C<at + N * interval> time (for some integer N) and then repeat, regardless	1799	C<offset + N * interval> time (for some integer N, which can also be
1031	of any time jumps.	1800	negative) and then repeat, regardless of any time jumps. The C<offset>
		1801	argument is merely an offset into the C<interval> periods.
1032		1802
1033	This can be used to create timers that do not drift with respect to system	1803	This can be used to create timers that do not drift with respect to the
1034	time:	1804	system clock, for example, here is an C<ev_periodic> that triggers each
		1805	hour, on the hour (with respect to UTC):
1035		1806
1036	ev_periodic_set (&periodic, 0., 3600., 0);	1807	ev_periodic_set (&periodic, 0., 3600., 0);
1037		1808
1038	This doesn't mean there will always be 3600 seconds in between triggers,	1809	This doesn't mean there will always be 3600 seconds in between triggers,
1039	but only that the the callback will be called when the system time shows a	1810	but only that the callback will be called when the system time shows a
1040	full hour (UTC), or more correctly, when the system time is evenly divisible	1811	full hour (UTC), or more correctly, when the system time is evenly divisible
1041	by 3600.	1812	by 3600.
1042		1813
1043	Another way to think about it (for the mathematically inclined) is that	1814	Another way to think about it (for the mathematically inclined) is that
1044	C<ev_periodic> will try to run the callback in this mode at the next possible	1815	C<ev_periodic> will try to run the callback in this mode at the next possible
1045	time where C<time = at (mod interval)>, regardless of any time jumps.	1816	time where C<time = offset (mod interval)>, regardless of any time jumps.
1046		1817
		1818	For numerical stability it is preferable that the C<offset> value is near
		1819	C<ev_now ()> (the current time), but there is no range requirement for
		1820	this value, and in fact is often specified as zero.
		1821
		1822	Note also that there is an upper limit to how often a timer can fire (CPU
		1823	speed for example), so if C<interval> is very small then timing stability
		1824	will of course deteriorate. Libev itself tries to be exact to be about one
		1825	millisecond (if the OS supports it and the machine is fast enough).
		1826
1047	=item * manual reschedule mode (reschedule_cb = callback)	1827	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1048		1828
1049	In this mode the values for C<interval> and C<at> are both being	1829	In this mode the values for C<interval> and C<offset> are both being
1050	ignored. Instead, each time the periodic watcher gets scheduled, the	1830	ignored. Instead, each time the periodic watcher gets scheduled, the
1051	reschedule callback will be called with the watcher as first, and the	1831	reschedule callback will be called with the watcher as first, and the
1052	current time as second argument.	1832	current time as second argument.
1053		1833
1054	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1834	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1055	ever, or make any event loop modifications>. If you need to stop it,	1835	or make ANY other event loop modifications whatsoever, unless explicitly
1056	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1836	allowed by documentation here>.
1057	starting a prepare watcher).
1058		1837
		1838	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1839	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1840	only event loop modification you are allowed to do).
		1841
1059	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1842	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1060	ev_tstamp now)>, e.g.:	1843	*w, ev_tstamp now)>, e.g.:
1061		1844
		1845	static ev_tstamp
1062	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1846	my_rescheduler (ev_periodic *w, ev_tstamp now)
1063	{	1847	{
1064	return now + 60.;	1848	return now + 60.;
1065	}	1849	}
1066		1850
1067	It must return the next time to trigger, based on the passed time value	1851	It must return the next time to trigger, based on the passed time value
1068	(that is, the lowest time value larger than to the second argument). It	1852	(that is, the lowest time value larger than to the second argument). It
1069	will usually be called just before the callback will be triggered, but	1853	will usually be called just before the callback will be triggered, but
1070	might be called at other times, too.	1854	might be called at other times, too.
1071		1855
1072	NOTE: I<< This callback must always return a time that is later than the	1856	NOTE: I<< This callback must always return a time that is higher than or
1073	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1857	equal to the passed C<now> value >>.
1074		1858
1075	This can be used to create very complex timers, such as a timer that	1859	This can be used to create very complex timers, such as a timer that
1076	triggers on each midnight, local time. To do this, you would calculate the	1860	triggers on "next midnight, local time". To do this, you would calculate the
1077	next midnight after C<now> and return the timestamp value for this. How	1861	next midnight after C<now> and return the timestamp value for this. How
1078	you do this is, again, up to you (but it is not trivial, which is the main	1862	you do this is, again, up to you (but it is not trivial, which is the main
1079	reason I omitted it as an example).	1863	reason I omitted it as an example).
1080		1864
1081	=back	1865	=back
…		…
1085	Simply stops and restarts the periodic watcher again. This is only useful	1869	Simply stops and restarts the periodic watcher again. This is only useful
1086	when you changed some parameters or the reschedule callback would return	1870	when you changed some parameters or the reschedule callback would return
1087	a different time than the last time it was called (e.g. in a crond like	1871	a different time than the last time it was called (e.g. in a crond like
1088	program when the crontabs have changed).	1872	program when the crontabs have changed).
1089		1873
		1874	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1875
		1876	When active, returns the absolute time that the watcher is supposed
		1877	to trigger next. This is not the same as the C<offset> argument to
		1878	C<ev_periodic_set>, but indeed works even in interval and manual
		1879	rescheduling modes.
		1880
		1881	=item ev_tstamp offset [read-write]
		1882
		1883	When repeating, this contains the offset value, otherwise this is the
		1884	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1885	although libev might modify this value for better numerical stability).
		1886
		1887	Can be modified any time, but changes only take effect when the periodic
		1888	timer fires or C<ev_periodic_again> is being called.
		1889
1090	=item ev_tstamp interval [read-write]	1890	=item ev_tstamp interval [read-write]
1091		1891
1092	The current interval value. Can be modified any time, but changes only	1892	The current interval value. Can be modified any time, but changes only
1093	take effect when the periodic timer fires or C<ev_periodic_again> is being	1893	take effect when the periodic timer fires or C<ev_periodic_again> is being
1094	called.	1894	called.
1095		1895
1096	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1896	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1097		1897
1098	The current reschedule callback, or C<0>, if this functionality is	1898	The current reschedule callback, or C<0>, if this functionality is
1099	switched off. Can be changed any time, but changes only take effect when	1899	switched off. Can be changed any time, but changes only take effect when
1100	the periodic timer fires or C<ev_periodic_again> is being called.	1900	the periodic timer fires or C<ev_periodic_again> is being called.
1101		1901
1102	=back	1902	=back
1103		1903
		1904	=head3 Examples
		1905
1104	Example: Call a callback every hour, or, more precisely, whenever the	1906	Example: Call a callback every hour, or, more precisely, whenever the
1105	system clock is divisible by 3600. The callback invocation times have	1907	system time is divisible by 3600. The callback invocation times have
1106	potentially a lot of jittering, but good long-term stability.	1908	potentially a lot of jitter, but good long-term stability.
1107		1909
1108	static void	1910	static void
1109	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1911	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1110	{	1912	{
1111	... its now a full hour (UTC, or TAI or whatever your clock follows)	1913	... its now a full hour (UTC, or TAI or whatever your clock follows)
1112	}	1914	}
1113		1915
1114	struct ev_periodic hourly_tick;	1916	ev_periodic hourly_tick;
1115	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1917	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1116	ev_periodic_start (loop, &hourly_tick);	1918	ev_periodic_start (loop, &hourly_tick);
1117		1919
1118	Example: The same as above, but use a reschedule callback to do it:	1920	Example: The same as above, but use a reschedule callback to do it:
1119		1921
1120	#include <math.h>	1922	#include <math.h>
1121		1923
1122	static ev_tstamp	1924	static ev_tstamp
1123	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1925	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1124	{	1926	{
1125	return fmod (now, 3600.) + 3600.;	1927	return now + (3600. - fmod (now, 3600.));
1126	}	1928	}
1127		1929
1128	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1930	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1129		1931
1130	Example: Call a callback every hour, starting now:	1932	Example: Call a callback every hour, starting now:
1131		1933
1132	struct ev_periodic hourly_tick;	1934	ev_periodic hourly_tick;
1133	ev_periodic_init (&hourly_tick, clock_cb,	1935	ev_periodic_init (&hourly_tick, clock_cb,
1134	fmod (ev_now (loop), 3600.), 3600., 0);	1936	fmod (ev_now (loop), 3600.), 3600., 0);
1135	ev_periodic_start (loop, &hourly_tick);	1937	ev_periodic_start (loop, &hourly_tick);
1136		1938
1137		1939
1138	=head2 C<ev_signal> - signal me when a signal gets signalled!	1940	=head2 C<ev_signal> - signal me when a signal gets signalled!
1139		1941
1140	Signal watchers will trigger an event when the process receives a specific	1942	Signal watchers will trigger an event when the process receives a specific
1141	signal one or more times. Even though signals are very asynchronous, libev	1943	signal one or more times. Even though signals are very asynchronous, libev
1142	will try it's best to deliver signals synchronously, i.e. as part of the	1944	will try it's best to deliver signals synchronously, i.e. as part of the
1143	normal event processing, like any other event.	1945	normal event processing, like any other event.
1144		1946
		1947	If you want signals asynchronously, just use C<sigaction> as you would
		1948	do without libev and forget about sharing the signal. You can even use
		1949	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1950
1145	You can configure as many watchers as you like per signal. Only when the	1951	You can configure as many watchers as you like per signal. Only when the
1146	first watcher gets started will libev actually register a signal watcher	1952	first watcher gets started will libev actually register a signal handler
1147	with the kernel (thus it coexists with your own signal handlers as long	1953	with the kernel (thus it coexists with your own signal handlers as long as
1148	as you don't register any with libev). Similarly, when the last signal	1954	you don't register any with libev for the same signal). Similarly, when
1149	watcher for a signal is stopped libev will reset the signal handler to	1955	the last signal watcher for a signal is stopped, libev will reset the
1150	SIG_DFL (regardless of what it was set to before).	1956	signal handler to SIG_DFL (regardless of what it was set to before).
		1957
		1958	If possible and supported, libev will install its handlers with
		1959	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1960	interrupted. If you have a problem with system calls getting interrupted by
		1961	signals you can block all signals in an C<ev_check> watcher and unblock
		1962	them in an C<ev_prepare> watcher.
		1963
		1964	=head3 Watcher-Specific Functions and Data Members
1151		1965
1152	=over 4	1966	=over 4
1153		1967
1154	=item ev_signal_init (ev_signal *, callback, int signum)	1968	=item ev_signal_init (ev_signal *, callback, int signum)
1155		1969
…		…
1162		1976
1163	The signal the watcher watches out for.	1977	The signal the watcher watches out for.
1164		1978
1165	=back	1979	=back
1166		1980
		1981	=head3 Examples
		1982
		1983	Example: Try to exit cleanly on SIGINT.
		1984
		1985	static void
		1986	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1987	{
		1988	ev_unloop (loop, EVUNLOOP_ALL);
		1989	}
		1990
		1991	ev_signal signal_watcher;
		1992	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1993	ev_signal_start (loop, &signal_watcher);
		1994
1167		1995
1168	=head2 C<ev_child> - watch out for process status changes	1996	=head2 C<ev_child> - watch out for process status changes
1169		1997
1170	Child watchers trigger when your process receives a SIGCHLD in response to	1998	Child watchers trigger when your process receives a SIGCHLD in response to
1171	some child status changes (most typically when a child of yours dies).	1999	some child status changes (most typically when a child of yours dies or
		2000	exits). It is permissible to install a child watcher I<after> the child
		2001	has been forked (which implies it might have already exited), as long
		2002	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2003	forking and then immediately registering a watcher for the child is fine,
		2004	but forking and registering a watcher a few event loop iterations later is
		2005	not.
		2006
		2007	Only the default event loop is capable of handling signals, and therefore
		2008	you can only register child watchers in the default event loop.
		2009
		2010	=head3 Process Interaction
		2011
		2012	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2013	initialised. This is necessary to guarantee proper behaviour even if
		2014	the first child watcher is started after the child exits. The occurrence
		2015	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2016	synchronously as part of the event loop processing. Libev always reaps all
		2017	children, even ones not watched.
		2018
		2019	=head3 Overriding the Built-In Processing
		2020
		2021	Libev offers no special support for overriding the built-in child
		2022	processing, but if your application collides with libev's default child
		2023	handler, you can override it easily by installing your own handler for
		2024	C<SIGCHLD> after initialising the default loop, and making sure the
		2025	default loop never gets destroyed. You are encouraged, however, to use an
		2026	event-based approach to child reaping and thus use libev's support for
		2027	that, so other libev users can use C<ev_child> watchers freely.
		2028
		2029	=head3 Stopping the Child Watcher
		2030
		2031	Currently, the child watcher never gets stopped, even when the
		2032	child terminates, so normally one needs to stop the watcher in the
		2033	callback. Future versions of libev might stop the watcher automatically
		2034	when a child exit is detected.
		2035
		2036	=head3 Watcher-Specific Functions and Data Members
1172		2037
1173	=over 4	2038	=over 4
1174		2039
1175	=item ev_child_init (ev_child *, callback, int pid)	2040	=item ev_child_init (ev_child *, callback, int pid, int trace)
1176		2041
1177	=item ev_child_set (ev_child *, int pid)	2042	=item ev_child_set (ev_child *, int pid, int trace)
1178		2043
1179	Configures the watcher to wait for status changes of process C<pid> (or	2044	Configures the watcher to wait for status changes of process C<pid> (or
1180	I<any> process if C<pid> is specified as C<0>). The callback can look	2045	I<any> process if C<pid> is specified as C<0>). The callback can look
1181	at the C<rstatus> member of the C<ev_child> watcher structure to see	2046	at the C<rstatus> member of the C<ev_child> watcher structure to see
1182	the status word (use the macros from C<sys/wait.h> and see your systems	2047	the status word (use the macros from C<sys/wait.h> and see your systems
1183	C<waitpid> documentation). The C<rpid> member contains the pid of the	2048	C<waitpid> documentation). The C<rpid> member contains the pid of the
1184	process causing the status change.	2049	process causing the status change. C<trace> must be either C<0> (only
		2050	activate the watcher when the process terminates) or C<1> (additionally
		2051	activate the watcher when the process is stopped or continued).
1185		2052
1186	=item int pid [read-only]	2053	=item int pid [read-only]
1187		2054
1188	The process id this watcher watches out for, or C<0>, meaning any process id.	2055	The process id this watcher watches out for, or C<0>, meaning any process id.
1189		2056
…		…
1196	The process exit/trace status caused by C<rpid> (see your systems	2063	The process exit/trace status caused by C<rpid> (see your systems
1197	C<waitpid> and C<sys/wait.h> documentation for details).	2064	C<waitpid> and C<sys/wait.h> documentation for details).
1198		2065
1199	=back	2066	=back
1200		2067
1201	Example: Try to exit cleanly on SIGINT and SIGTERM.	2068	=head3 Examples
1202		2069
		2070	Example: C<fork()> a new process and install a child handler to wait for
		2071	its completion.
		2072
		2073	ev_child cw;
		2074
1203	static void	2075	static void
1204	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2076	child_cb (EV_P_ ev_child *w, int revents)
1205	{	2077	{
1206	ev_unloop (loop, EVUNLOOP_ALL);	2078	ev_child_stop (EV_A_ w);
		2079	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1207	}	2080	}
1208		2081
1209	struct ev_signal signal_watcher;	2082	pid_t pid = fork ();
1210	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2083
1211	ev_signal_start (loop, &sigint_cb);	2084	if (pid < 0)
		2085	// error
		2086	else if (pid == 0)
		2087	{
		2088	// the forked child executes here
		2089	exit (1);
		2090	}
		2091	else
		2092	{
		2093	ev_child_init (&cw, child_cb, pid, 0);
		2094	ev_child_start (EV_DEFAULT_ &cw);
		2095	}
1212		2096
1213		2097
1214	=head2 C<ev_stat> - did the file attributes just change?	2098	=head2 C<ev_stat> - did the file attributes just change?
1215		2099
1216	This watches a filesystem path for attribute changes. That is, it calls	2100	This watches a file system path for attribute changes. That is, it calls
1217	C<stat> regularly (or when the OS says it changed) and sees if it changed	2101	C<stat> on that path in regular intervals (or when the OS says it changed)
1218	compared to the last time, invoking the callback if it did.	2102	and sees if it changed compared to the last time, invoking the callback if
		2103	it did.
1219		2104
1220	The path does not need to exist: changing from "path exists" to "path does	2105	The path does not need to exist: changing from "path exists" to "path does
1221	not exist" is a status change like any other. The condition "path does	2106	not exist" is a status change like any other. The condition "path does not
1222	not exist" is signified by the C<st_nlink> field being zero (which is	2107	exist" (or more correctly "path cannot be stat'ed") is signified by the
1223	otherwise always forced to be at least one) and all the other fields of	2108	C<st_nlink> field being zero (which is otherwise always forced to be at
1224	the stat buffer having unspecified contents.	2109	least one) and all the other fields of the stat buffer having unspecified
		2110	contents.
1225		2111
1226	Since there is no standard to do this, the portable implementation simply	2112	The path I<must not> end in a slash or contain special components such as
1227	calls C<stat (2)> regulalry on the path to see if it changed somehow. You	2113	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1228	can specify a recommended polling interval for this case. If you specify	2114	your working directory changes, then the behaviour is undefined.
1229	a polling interval of C<0> (highly recommended!) then a I<suitable,	2115
1230	unspecified default> value will be used (which you can expect to be around	2116	Since there is no portable change notification interface available, the
1231	five seconds, although this might change dynamically). Libev will also	2117	portable implementation simply calls C<stat(2)> regularly on the path
1232	impose a minimum interval which is currently around C<0.1>, but thats	2118	to see if it changed somehow. You can specify a recommended polling
1233	usually overkill.	2119	interval for this case. If you specify a polling interval of C<0> (highly
		2120	recommended!) then a I<suitable, unspecified default> value will be used
		2121	(which you can expect to be around five seconds, although this might
		2122	change dynamically). Libev will also impose a minimum interval which is
		2123	currently around C<0.1>, but that's usually overkill.
1234		2124
1235	This watcher type is not meant for massive numbers of stat watchers,	2125	This watcher type is not meant for massive numbers of stat watchers,
1236	as even with OS-supported change notifications, this can be	2126	as even with OS-supported change notifications, this can be
1237	resource-intensive.	2127	resource-intensive.
1238		2128
1239	At the time of this writing, no specific OS backends are implemented, but	2129	At the time of this writing, the only OS-specific interface implemented
1240	if demand increases, at least a kqueue and inotify backend will be added.	2130	is the Linux inotify interface (implementing kqueue support is left as an
		2131	exercise for the reader. Note, however, that the author sees no way of
		2132	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2133
		2134	=head3 ABI Issues (Largefile Support)
		2135
		2136	Libev by default (unless the user overrides this) uses the default
		2137	compilation environment, which means that on systems with large file
		2138	support disabled by default, you get the 32 bit version of the stat
		2139	structure. When using the library from programs that change the ABI to
		2140	use 64 bit file offsets the programs will fail. In that case you have to
		2141	compile libev with the same flags to get binary compatibility. This is
		2142	obviously the case with any flags that change the ABI, but the problem is
		2143	most noticeably displayed with ev_stat and large file support.
		2144
		2145	The solution for this is to lobby your distribution maker to make large
		2146	file interfaces available by default (as e.g. FreeBSD does) and not
		2147	optional. Libev cannot simply switch on large file support because it has
		2148	to exchange stat structures with application programs compiled using the
		2149	default compilation environment.
		2150
		2151	=head3 Inotify and Kqueue
		2152
		2153	When C<inotify (7)> support has been compiled into libev and present at
		2154	runtime, it will be used to speed up change detection where possible. The
		2155	inotify descriptor will be created lazily when the first C<ev_stat>
		2156	watcher is being started.
		2157
		2158	Inotify presence does not change the semantics of C<ev_stat> watchers
		2159	except that changes might be detected earlier, and in some cases, to avoid
		2160	making regular C<stat> calls. Even in the presence of inotify support
		2161	there are many cases where libev has to resort to regular C<stat> polling,
		2162	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2163	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2164	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2165	xfs are fully working) libev usually gets away without polling.
		2166
		2167	There is no support for kqueue, as apparently it cannot be used to
		2168	implement this functionality, due to the requirement of having a file
		2169	descriptor open on the object at all times, and detecting renames, unlinks
		2170	etc. is difficult.
		2171
		2172	=head3 C<stat ()> is a synchronous operation
		2173
		2174	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2175	the process. The exception are C<ev_stat> watchers - those call C<stat
		2176	()>, which is a synchronous operation.
		2177
		2178	For local paths, this usually doesn't matter: unless the system is very
		2179	busy or the intervals between stat's are large, a stat call will be fast,
		2180	as the path data is usually in memory already (except when starting the
		2181	watcher).
		2182
		2183	For networked file systems, calling C<stat ()> can block an indefinite
		2184	time due to network issues, and even under good conditions, a stat call
		2185	often takes multiple milliseconds.
		2186
		2187	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2188	paths, although this is fully supported by libev.
		2189
		2190	=head3 The special problem of stat time resolution
		2191
		2192	The C<stat ()> system call only supports full-second resolution portably,
		2193	and even on systems where the resolution is higher, most file systems
		2194	still only support whole seconds.
		2195
		2196	That means that, if the time is the only thing that changes, you can
		2197	easily miss updates: on the first update, C<ev_stat> detects a change and
		2198	calls your callback, which does something. When there is another update
		2199	within the same second, C<ev_stat> will be unable to detect unless the
		2200	stat data does change in other ways (e.g. file size).
		2201
		2202	The solution to this is to delay acting on a change for slightly more
		2203	than a second (or till slightly after the next full second boundary), using
		2204	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2205	ev_timer_again (loop, w)>).
		2206
		2207	The C<.02> offset is added to work around small timing inconsistencies
		2208	of some operating systems (where the second counter of the current time
		2209	might be be delayed. One such system is the Linux kernel, where a call to
		2210	C<gettimeofday> might return a timestamp with a full second later than
		2211	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2212	update file times then there will be a small window where the kernel uses
		2213	the previous second to update file times but libev might already execute
		2214	the timer callback).
		2215
		2216	=head3 Watcher-Specific Functions and Data Members
1241		2217
1242	=over 4	2218	=over 4
1243		2219
1244	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2220	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1245		2221
…		…
1249	C<path>. The C<interval> is a hint on how quickly a change is expected to	2225	C<path>. The C<interval> is a hint on how quickly a change is expected to
1250	be detected and should normally be specified as C<0> to let libev choose	2226	be detected and should normally be specified as C<0> to let libev choose
1251	a suitable value. The memory pointed to by C<path> must point to the same	2227	a suitable value. The memory pointed to by C<path> must point to the same
1252	path for as long as the watcher is active.	2228	path for as long as the watcher is active.
1253		2229
1254	The callback will be receive C<EV_STAT> when a change was detected,	2230	The callback will receive an C<EV_STAT> event when a change was detected,
1255	relative to the attributes at the time the watcher was started (or the	2231	relative to the attributes at the time the watcher was started (or the
1256	last change was detected).	2232	last change was detected).
1257		2233
1258	=item ev_stat_stat (ev_stat *)	2234	=item ev_stat_stat (loop, ev_stat *)
1259		2235
1260	Updates the stat buffer immediately with new values. If you change the	2236	Updates the stat buffer immediately with new values. If you change the
1261	watched path in your callback, you could call this fucntion to avoid	2237	watched path in your callback, you could call this function to avoid
1262	detecting this change (while introducing a race condition). Can also be	2238	detecting this change (while introducing a race condition if you are not
1263	useful simply to find out the new values.	2239	the only one changing the path). Can also be useful simply to find out the
		2240	new values.
1264		2241
1265	=item ev_statdata attr [read-only]	2242	=item ev_statdata attr [read-only]
1266		2243
1267	The most-recently detected attributes of the file. Although the type is of	2244	The most-recently detected attributes of the file. Although the type is
1268	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2245	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1269	suitable for your system. If the C<st_nlink> member is C<0>, then there	2246	suitable for your system, but you can only rely on the POSIX-standardised
		2247	members to be present. If the C<st_nlink> member is C<0>, then there was
1270	was some error while C<stat>ing the file.	2248	some error while C<stat>ing the file.
1271		2249
1272	=item ev_statdata prev [read-only]	2250	=item ev_statdata prev [read-only]
1273		2251
1274	The previous attributes of the file. The callback gets invoked whenever	2252	The previous attributes of the file. The callback gets invoked whenever
1275	C<prev> != C<attr>.	2253	C<prev> != C<attr>, or, more precisely, one or more of these members
		2254	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2255	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1276		2256
1277	=item ev_tstamp interval [read-only]	2257	=item ev_tstamp interval [read-only]
1278		2258
1279	The specified interval.	2259	The specified interval.
1280		2260
1281	=item const char *path [read-only]	2261	=item const char *path [read-only]
1282		2262
1283	The filesystem path that is being watched.	2263	The file system path that is being watched.
1284		2264
1285	=back	2265	=back
1286		2266
		2267	=head3 Examples
		2268
1287	Example: Watch C</etc/passwd> for attribute changes.	2269	Example: Watch C</etc/passwd> for attribute changes.
1288		2270
1289	static void	2271	static void
1290	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2272	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1291	{	2273	{
1292	/* /etc/passwd changed in some way */	2274	/* /etc/passwd changed in some way */
1293	if (w->attr.st_nlink)	2275	if (w->attr.st_nlink)
1294	{	2276	{
1295	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2277	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1296	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2278	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1297	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2279	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1298	}	2280	}
1299	else	2281	else
1300	/* you shalt not abuse printf for puts */	2282	/* you shalt not abuse printf for puts */
1301	puts ("wow, /etc/passwd is not there, expect problems. "	2283	puts ("wow, /etc/passwd is not there, expect problems. "
1302	"if this is windows, they already arrived\n");	2284	"if this is windows, they already arrived\n");
1303	}	2285	}
1304		2286
1305	...	2287	...
1306	ev_stat passwd;	2288	ev_stat passwd;
1307		2289
1308	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2290	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1309	ev_stat_start (loop, &passwd);	2291	ev_stat_start (loop, &passwd);
		2292
		2293	Example: Like above, but additionally use a one-second delay so we do not
		2294	miss updates (however, frequent updates will delay processing, too, so
		2295	one might do the work both on C<ev_stat> callback invocation I<and> on
		2296	C<ev_timer> callback invocation).
		2297
		2298	static ev_stat passwd;
		2299	static ev_timer timer;
		2300
		2301	static void
		2302	timer_cb (EV_P_ ev_timer *w, int revents)
		2303	{
		2304	ev_timer_stop (EV_A_ w);
		2305
		2306	/* now it's one second after the most recent passwd change */
		2307	}
		2308
		2309	static void
		2310	stat_cb (EV_P_ ev_stat *w, int revents)
		2311	{
		2312	/* reset the one-second timer */
		2313	ev_timer_again (EV_A_ &timer);
		2314	}
		2315
		2316	...
		2317	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2318	ev_stat_start (loop, &passwd);
		2319	ev_timer_init (&timer, timer_cb, 0., 1.02);
1310		2320
1311		2321
1312	=head2 C<ev_idle> - when you've got nothing better to do...	2322	=head2 C<ev_idle> - when you've got nothing better to do...
1313		2323
1314	Idle watchers trigger events when there are no other events are pending	2324	Idle watchers trigger events when no other events of the same or higher
1315	(prepare, check and other idle watchers do not count). That is, as long	2325	priority are pending (prepare, check and other idle watchers do not count
1316	as your process is busy handling sockets or timeouts (or even signals,	2326	as receiving "events").
1317	imagine) it will not be triggered. But when your process is idle all idle	2327
1318	watchers are being called again and again, once per event loop iteration -	2328	That is, as long as your process is busy handling sockets or timeouts
		2329	(or even signals, imagine) of the same or higher priority it will not be
		2330	triggered. But when your process is idle (or only lower-priority watchers
		2331	are pending), the idle watchers are being called once per event loop
1319	until stopped, that is, or your process receives more events and becomes	2332	iteration - until stopped, that is, or your process receives more events
1320	busy.	2333	and becomes busy again with higher priority stuff.
1321		2334
1322	The most noteworthy effect is that as long as any idle watchers are	2335	The most noteworthy effect is that as long as any idle watchers are
1323	active, the process will not block when waiting for new events.	2336	active, the process will not block when waiting for new events.
1324		2337
1325	Apart from keeping your process non-blocking (which is a useful	2338	Apart from keeping your process non-blocking (which is a useful
1326	effect on its own sometimes), idle watchers are a good place to do	2339	effect on its own sometimes), idle watchers are a good place to do
1327	"pseudo-background processing", or delay processing stuff to after the	2340	"pseudo-background processing", or delay processing stuff to after the
1328	event loop has handled all outstanding events.	2341	event loop has handled all outstanding events.
1329		2342
		2343	=head3 Watcher-Specific Functions and Data Members
		2344
1330	=over 4	2345	=over 4
1331		2346
1332	=item ev_idle_init (ev_signal *, callback)	2347	=item ev_idle_init (ev_idle *, callback)
1333		2348
1334	Initialises and configures the idle watcher - it has no parameters of any	2349	Initialises and configures the idle watcher - it has no parameters of any
1335	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2350	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1336	believe me.	2351	believe me.
1337		2352
1338	=back	2353	=back
1339		2354
		2355	=head3 Examples
		2356
1340	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2357	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1341	callback, free it. Also, use no error checking, as usual.	2358	callback, free it. Also, use no error checking, as usual.
1342		2359
1343	static void	2360	static void
1344	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2361	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1345	{	2362	{
1346	free (w);	2363	free (w);
1347	// now do something you wanted to do when the program has	2364	// now do something you wanted to do when the program has
1348	// no longer asnything immediate to do.	2365	// no longer anything immediate to do.
1349	}	2366	}
1350		2367
1351	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2368	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1352	ev_idle_init (idle_watcher, idle_cb);	2369	ev_idle_init (idle_watcher, idle_cb);
1353	ev_idle_start (loop, idle_cb);	2370	ev_idle_start (loop, idle_cb);
1354		2371
1355		2372
1356	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2373	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1357		2374
1358	Prepare and check watchers are usually (but not always) used in tandem:	2375	Prepare and check watchers are usually (but not always) used in pairs:
1359	prepare watchers get invoked before the process blocks and check watchers	2376	prepare watchers get invoked before the process blocks and check watchers
1360	afterwards.	2377	afterwards.
1361		2378
1362	You I<must not> call C<ev_loop> or similar functions that enter	2379	You I<must not> call C<ev_loop> or similar functions that enter
1363	the current event loop from either C<ev_prepare> or C<ev_check>	2380	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1366	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2383	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1367	C<ev_check> so if you have one watcher of each kind they will always be	2384	C<ev_check> so if you have one watcher of each kind they will always be
1368	called in pairs bracketing the blocking call.	2385	called in pairs bracketing the blocking call.
1369		2386
1370	Their main purpose is to integrate other event mechanisms into libev and	2387	Their main purpose is to integrate other event mechanisms into libev and
1371	their use is somewhat advanced. This could be used, for example, to track	2388	their use is somewhat advanced. They could be used, for example, to track
1372	variable changes, implement your own watchers, integrate net-snmp or a	2389	variable changes, implement your own watchers, integrate net-snmp or a
1373	coroutine library and lots more. They are also occasionally useful if	2390	coroutine library and lots more. They are also occasionally useful if
1374	you cache some data and want to flush it before blocking (for example,	2391	you cache some data and want to flush it before blocking (for example,
1375	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2392	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1376	watcher).	2393	watcher).
1377		2394
1378	This is done by examining in each prepare call which file descriptors need	2395	This is done by examining in each prepare call which file descriptors
1379	to be watched by the other library, registering C<ev_io> watchers for	2396	need to be watched by the other library, registering C<ev_io> watchers
1380	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2397	for them and starting an C<ev_timer> watcher for any timeouts (many
1381	provide just this functionality). Then, in the check watcher you check for	2398	libraries provide exactly this functionality). Then, in the check watcher,
1382	any events that occured (by checking the pending status of all watchers	2399	you check for any events that occurred (by checking the pending status
1383	and stopping them) and call back into the library. The I/O and timer	2400	of all watchers and stopping them) and call back into the library. The
1384	callbacks will never actually be called (but must be valid nevertheless,	2401	I/O and timer callbacks will never actually be called (but must be valid
1385	because you never know, you know?).	2402	nevertheless, because you never know, you know?).
1386		2403
1387	As another example, the Perl Coro module uses these hooks to integrate	2404	As another example, the Perl Coro module uses these hooks to integrate
1388	coroutines into libev programs, by yielding to other active coroutines	2405	coroutines into libev programs, by yielding to other active coroutines
1389	during each prepare and only letting the process block if no coroutines	2406	during each prepare and only letting the process block if no coroutines
1390	are ready to run (it's actually more complicated: it only runs coroutines	2407	are ready to run (it's actually more complicated: it only runs coroutines
1391	with priority higher than or equal to the event loop and one coroutine	2408	with priority higher than or equal to the event loop and one coroutine
1392	of lower priority, but only once, using idle watchers to keep the event	2409	of lower priority, but only once, using idle watchers to keep the event
1393	loop from blocking if lower-priority coroutines are active, thus mapping	2410	loop from blocking if lower-priority coroutines are active, thus mapping
1394	low-priority coroutines to idle/background tasks).	2411	low-priority coroutines to idle/background tasks).
1395		2412
		2413	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2414	priority, to ensure that they are being run before any other watchers
		2415	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2416
		2417	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2418	activate ("feed") events into libev. While libev fully supports this, they
		2419	might get executed before other C<ev_check> watchers did their job. As
		2420	C<ev_check> watchers are often used to embed other (non-libev) event
		2421	loops those other event loops might be in an unusable state until their
		2422	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2423	others).
		2424
		2425	=head3 Watcher-Specific Functions and Data Members
		2426
1396	=over 4	2427	=over 4
1397		2428
1398	=item ev_prepare_init (ev_prepare *, callback)	2429	=item ev_prepare_init (ev_prepare *, callback)
1399		2430
1400	=item ev_check_init (ev_check *, callback)	2431	=item ev_check_init (ev_check *, callback)
1401		2432
1402	Initialises and configures the prepare or check watcher - they have no	2433	Initialises and configures the prepare or check watcher - they have no
1403	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2434	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1404	macros, but using them is utterly, utterly and completely pointless.	2435	macros, but using them is utterly, utterly, utterly and completely
		2436	pointless.
1405		2437
1406	=back	2438	=back
1407		2439
1408	Example: To include a library such as adns, you would add IO watchers	2440	=head3 Examples
1409	and a timeout watcher in a prepare handler, as required by libadns, and	2441
		2442	There are a number of principal ways to embed other event loops or modules
		2443	into libev. Here are some ideas on how to include libadns into libev
		2444	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2445	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2446	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2447	Glib event loop).
		2448
		2449	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1410	in a check watcher, destroy them and call into libadns. What follows is	2450	and in a check watcher, destroy them and call into libadns. What follows
1411	pseudo-code only of course:	2451	is pseudo-code only of course. This requires you to either use a low
		2452	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2453	the callbacks for the IO/timeout watchers might not have been called yet.
1412		2454
1413	static ev_io iow [nfd];	2455	static ev_io iow [nfd];
1414	static ev_timer tw;	2456	static ev_timer tw;
1415		2457
1416	static void	2458	static void
1417	io_cb (ev_loop *loop, ev_io *w, int revents)	2459	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1418	{	2460	{
1419	// set the relevant poll flags
1420	// could also call adns_processreadable etc. here
1421	struct pollfd *fd = (struct pollfd *)w->data;
1422	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1423	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1424	}	2461	}
1425		2462
1426	// create io watchers for each fd and a timer before blocking	2463	// create io watchers for each fd and a timer before blocking
1427	static void	2464	static void
1428	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2465	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1429	{	2466	{
1430	int timeout = 3600000;truct pollfd fds [nfd];	2467	int timeout = 3600000;
		2468	struct pollfd fds [nfd];
1431	// actual code will need to loop here and realloc etc.	2469	// actual code will need to loop here and realloc etc.
1432	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2470	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1433		2471
1434	/* the callback is illegal, but won't be called as we stop during check */	2472	/* the callback is illegal, but won't be called as we stop during check */
1435	ev_timer_init (&tw, 0, timeout * 1e-3);	2473	ev_timer_init (&tw, 0, timeout * 1e-3);
1436	ev_timer_start (loop, &tw);	2474	ev_timer_start (loop, &tw);
1437		2475
1438	// create on ev_io per pollfd	2476	// create one ev_io per pollfd
1439	for (int i = 0; i < nfd; ++i)	2477	for (int i = 0; i < nfd; ++i)
1440	{	2478	{
1441	ev_io_init (iow + i, io_cb, fds [i].fd,	2479	ev_io_init (iow + i, io_cb, fds [i].fd,
1442	((fds [i].events & POLLIN ? EV_READ : 0)	2480	((fds [i].events & POLLIN ? EV_READ : 0)
1443	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2481	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1444		2482
1445	fds [i].revents = 0;	2483	fds [i].revents = 0;
1446	iow [i].data = fds + i;
1447	ev_io_start (loop, iow + i);	2484	ev_io_start (loop, iow + i);
1448	}	2485	}
1449	}	2486	}
1450		2487
1451	// stop all watchers after blocking	2488	// stop all watchers after blocking
1452	static void	2489	static void
1453	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2490	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1454	{	2491	{
1455	ev_timer_stop (loop, &tw);	2492	ev_timer_stop (loop, &tw);
1456		2493
1457	for (int i = 0; i < nfd; ++i)	2494	for (int i = 0; i < nfd; ++i)
		2495	{
		2496	// set the relevant poll flags
		2497	// could also call adns_processreadable etc. here
		2498	struct pollfd *fd = fds + i;
		2499	int revents = ev_clear_pending (iow + i);
		2500	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2501	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2502
		2503	// now stop the watcher
1458	ev_io_stop (loop, iow + i);	2504	ev_io_stop (loop, iow + i);
		2505	}
1459		2506
1460	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2507	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1461	}	2508	}
		2509
		2510	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2511	in the prepare watcher and would dispose of the check watcher.
		2512
		2513	Method 3: If the module to be embedded supports explicit event
		2514	notification (libadns does), you can also make use of the actual watcher
		2515	callbacks, and only destroy/create the watchers in the prepare watcher.
		2516
		2517	static void
		2518	timer_cb (EV_P_ ev_timer *w, int revents)
		2519	{
		2520	adns_state ads = (adns_state)w->data;
		2521	update_now (EV_A);
		2522
		2523	adns_processtimeouts (ads, &tv_now);
		2524	}
		2525
		2526	static void
		2527	io_cb (EV_P_ ev_io *w, int revents)
		2528	{
		2529	adns_state ads = (adns_state)w->data;
		2530	update_now (EV_A);
		2531
		2532	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2533	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2534	}
		2535
		2536	// do not ever call adns_afterpoll
		2537
		2538	Method 4: Do not use a prepare or check watcher because the module you
		2539	want to embed is not flexible enough to support it. Instead, you can
		2540	override their poll function. The drawback with this solution is that the
		2541	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2542	this approach, effectively embedding EV as a client into the horrible
		2543	libglib event loop.
		2544
		2545	static gint
		2546	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2547	{
		2548	int got_events = 0;
		2549
		2550	for (n = 0; n < nfds; ++n)
		2551	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2552
		2553	if (timeout >= 0)
		2554	// create/start timer
		2555
		2556	// poll
		2557	ev_loop (EV_A_ 0);
		2558
		2559	// stop timer again
		2560	if (timeout >= 0)
		2561	ev_timer_stop (EV_A_ &to);
		2562
		2563	// stop io watchers again - their callbacks should have set
		2564	for (n = 0; n < nfds; ++n)
		2565	ev_io_stop (EV_A_ iow [n]);
		2566
		2567	return got_events;
		2568	}
1462		2569
1463		2570
1464	=head2 C<ev_embed> - when one backend isn't enough...	2571	=head2 C<ev_embed> - when one backend isn't enough...
1465		2572
1466	This is a rather advanced watcher type that lets you embed one event loop	2573	This is a rather advanced watcher type that lets you embed one event loop
…		…
1472	prioritise I/O.	2579	prioritise I/O.
1473		2580
1474	As an example for a bug workaround, the kqueue backend might only support	2581	As an example for a bug workaround, the kqueue backend might only support
1475	sockets on some platform, so it is unusable as generic backend, but you	2582	sockets on some platform, so it is unusable as generic backend, but you
1476	still want to make use of it because you have many sockets and it scales	2583	still want to make use of it because you have many sockets and it scales
1477	so nicely. In this case, you would create a kqueue-based loop and embed it	2584	so nicely. In this case, you would create a kqueue-based loop and embed
1478	into your default loop (which might use e.g. poll). Overall operation will	2585	it into your default loop (which might use e.g. poll). Overall operation
1479	be a bit slower because first libev has to poll and then call kevent, but	2586	will be a bit slower because first libev has to call C<poll> and then
1480	at least you can use both at what they are best.	2587	C<kevent>, but at least you can use both mechanisms for what they are
		2588	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1481		2589
1482	As for prioritising I/O: rarely you have the case where some fds have	2590	As for prioritising I/O: under rare circumstances you have the case where
1483	to be watched and handled very quickly (with low latency), and even	2591	some fds have to be watched and handled very quickly (with low latency),
1484	priorities and idle watchers might have too much overhead. In this case	2592	and even priorities and idle watchers might have too much overhead. In
1485	you would put all the high priority stuff in one loop and all the rest in	2593	this case you would put all the high priority stuff in one loop and all
1486	a second one, and embed the second one in the first.	2594	the rest in a second one, and embed the second one in the first.
1487		2595
1488	As long as the watcher is active, the callback will be invoked every time	2596	As long as the watcher is active, the callback will be invoked every
1489	there might be events pending in the embedded loop. The callback must then	2597	time there might be events pending in the embedded loop. The callback
1490	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2598	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1491	their callbacks (you could also start an idle watcher to give the embedded	2599	sweep and invoke their callbacks (the callback doesn't need to invoke the
1492	loop strictly lower priority for example). You can also set the callback	2600	C<ev_embed_sweep> function directly, it could also start an idle watcher
1493	to C<0>, in which case the embed watcher will automatically execute the	2601	to give the embedded loop strictly lower priority for example).
1494	embedded loop sweep.
1495		2602
1496	As long as the watcher is started it will automatically handle events. The	2603	You can also set the callback to C<0>, in which case the embed watcher
1497	callback will be invoked whenever some events have been handled. You can	2604	will automatically execute the embedded loop sweep whenever necessary.
1498	set the callback to C<0> to avoid having to specify one if you are not
1499	interested in that.
1500		2605
1501	Also, there have not currently been made special provisions for forking:	2606	Fork detection will be handled transparently while the C<ev_embed> watcher
1502	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2607	is active, i.e., the embedded loop will automatically be forked when the
1503	but you will also have to stop and restart any C<ev_embed> watchers	2608	embedding loop forks. In other cases, the user is responsible for calling
1504	yourself.	2609	C<ev_loop_fork> on the embedded loop.
1505		2610
1506	Unfortunately, not all backends are embeddable, only the ones returned by	2611	Unfortunately, not all backends are embeddable: only the ones returned by
1507	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2612	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1508	portable one.	2613	portable one.
1509		2614
1510	So when you want to use this feature you will always have to be prepared	2615	So when you want to use this feature you will always have to be prepared
1511	that you cannot get an embeddable loop. The recommended way to get around	2616	that you cannot get an embeddable loop. The recommended way to get around
1512	this is to have a separate variables for your embeddable loop, try to	2617	this is to have a separate variables for your embeddable loop, try to
1513	create it, and if that fails, use the normal loop for everything:	2618	create it, and if that fails, use the normal loop for everything.
1514		2619
1515	struct ev_loop *loop_hi = ev_default_init (0);	2620	=head3 C<ev_embed> and fork
1516	struct ev_loop *loop_lo = 0;
1517	struct ev_embed embed;
1518
1519	// see if there is a chance of getting one that works
1520	// (remember that a flags value of 0 means autodetection)
1521	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1522	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1523	: 0;
1524		2621
1525	// if we got one, then embed it, otherwise default to loop_hi	2622	While the C<ev_embed> watcher is running, forks in the embedding loop will
1526	if (loop_lo)	2623	automatically be applied to the embedded loop as well, so no special
1527	{	2624	fork handling is required in that case. When the watcher is not running,
1528	ev_embed_init (&embed, 0, loop_lo);	2625	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1529	ev_embed_start (loop_hi, &embed);	2626	as applicable.
1530	}	2627
1531	else	2628	=head3 Watcher-Specific Functions and Data Members
1532	loop_lo = loop_hi;
1533		2629
1534	=over 4	2630	=over 4
1535		2631
1536	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2632	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1537		2633
…		…
1539		2635
1540	Configures the watcher to embed the given loop, which must be	2636	Configures the watcher to embed the given loop, which must be
1541	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2637	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1542	invoked automatically, otherwise it is the responsibility of the callback	2638	invoked automatically, otherwise it is the responsibility of the callback
1543	to invoke it (it will continue to be called until the sweep has been done,	2639	to invoke it (it will continue to be called until the sweep has been done,
1544	if you do not want thta, you need to temporarily stop the embed watcher).	2640	if you do not want that, you need to temporarily stop the embed watcher).
1545		2641
1546	=item ev_embed_sweep (loop, ev_embed *)	2642	=item ev_embed_sweep (loop, ev_embed *)
1547		2643
1548	Make a single, non-blocking sweep over the embedded loop. This works	2644	Make a single, non-blocking sweep over the embedded loop. This works
1549	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2645	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1550	apropriate way for embedded loops.	2646	appropriate way for embedded loops.
1551		2647
1552	=item struct ev_loop *loop [read-only]	2648	=item struct ev_loop *other [read-only]
1553		2649
1554	The embedded event loop.	2650	The embedded event loop.
1555		2651
1556	=back	2652	=back
		2653
		2654	=head3 Examples
		2655
		2656	Example: Try to get an embeddable event loop and embed it into the default
		2657	event loop. If that is not possible, use the default loop. The default
		2658	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2659	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2660	used).
		2661
		2662	struct ev_loop *loop_hi = ev_default_init (0);
		2663	struct ev_loop *loop_lo = 0;
		2664	ev_embed embed;
		2665
		2666	// see if there is a chance of getting one that works
		2667	// (remember that a flags value of 0 means autodetection)
		2668	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2669	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2670	: 0;
		2671
		2672	// if we got one, then embed it, otherwise default to loop_hi
		2673	if (loop_lo)
		2674	{
		2675	ev_embed_init (&embed, 0, loop_lo);
		2676	ev_embed_start (loop_hi, &embed);
		2677	}
		2678	else
		2679	loop_lo = loop_hi;
		2680
		2681	Example: Check if kqueue is available but not recommended and create
		2682	a kqueue backend for use with sockets (which usually work with any
		2683	kqueue implementation). Store the kqueue/socket-only event loop in
		2684	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2685
		2686	struct ev_loop *loop = ev_default_init (0);
		2687	struct ev_loop *loop_socket = 0;
		2688	ev_embed embed;
		2689
		2690	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2691	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2692	{
		2693	ev_embed_init (&embed, 0, loop_socket);
		2694	ev_embed_start (loop, &embed);
		2695	}
		2696
		2697	if (!loop_socket)
		2698	loop_socket = loop;
		2699
		2700	// now use loop_socket for all sockets, and loop for everything else
1557		2701
1558		2702
1559	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2703	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1560		2704
1561	Fork watchers are called when a C<fork ()> was detected (usually because	2705	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1564	event loop blocks next and before C<ev_check> watchers are being called,	2708	event loop blocks next and before C<ev_check> watchers are being called,
1565	and only in the child after the fork. If whoever good citizen calling	2709	and only in the child after the fork. If whoever good citizen calling
1566	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2710	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1567	handlers will be invoked, too, of course.	2711	handlers will be invoked, too, of course.
1568		2712
		2713	=head3 Watcher-Specific Functions and Data Members
		2714
1569	=over 4	2715	=over 4
1570		2716
1571	=item ev_fork_init (ev_signal *, callback)	2717	=item ev_fork_init (ev_signal *, callback)
1572		2718
1573	Initialises and configures the fork watcher - it has no parameters of any	2719	Initialises and configures the fork watcher - it has no parameters of any
…		…
1575	believe me.	2721	believe me.
1576		2722
1577	=back	2723	=back
1578		2724
1579		2725
		2726	=head2 C<ev_async> - how to wake up another event loop
		2727
		2728	In general, you cannot use an C<ev_loop> from multiple threads or other
		2729	asynchronous sources such as signal handlers (as opposed to multiple event
		2730	loops - those are of course safe to use in different threads).
		2731
		2732	Sometimes, however, you need to wake up another event loop you do not
		2733	control, for example because it belongs to another thread. This is what
		2734	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2735	can signal it by calling C<ev_async_send>, which is thread- and signal
		2736	safe.
		2737
		2738	This functionality is very similar to C<ev_signal> watchers, as signals,
		2739	too, are asynchronous in nature, and signals, too, will be compressed
		2740	(i.e. the number of callback invocations may be less than the number of
		2741	C<ev_async_sent> calls).
		2742
		2743	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2744	just the default loop.
		2745
		2746	=head3 Queueing
		2747
		2748	C<ev_async> does not support queueing of data in any way. The reason
		2749	is that the author does not know of a simple (or any) algorithm for a
		2750	multiple-writer-single-reader queue that works in all cases and doesn't
		2751	need elaborate support such as pthreads.
		2752
		2753	That means that if you want to queue data, you have to provide your own
		2754	queue. But at least I can tell you how to implement locking around your
		2755	queue:
		2756
		2757	=over 4
		2758
		2759	=item queueing from a signal handler context
		2760
		2761	To implement race-free queueing, you simply add to the queue in the signal
		2762	handler but you block the signal handler in the watcher callback. Here is
		2763	an example that does that for some fictitious SIGUSR1 handler:
		2764
		2765	static ev_async mysig;
		2766
		2767	static void
		2768	sigusr1_handler (void)
		2769	{
		2770	sometype data;
		2771
		2772	// no locking etc.
		2773	queue_put (data);
		2774	ev_async_send (EV_DEFAULT_ &mysig);
		2775	}
		2776
		2777	static void
		2778	mysig_cb (EV_P_ ev_async *w, int revents)
		2779	{
		2780	sometype data;
		2781	sigset_t block, prev;
		2782
		2783	sigemptyset (&block);
		2784	sigaddset (&block, SIGUSR1);
		2785	sigprocmask (SIG_BLOCK, &block, &prev);
		2786
		2787	while (queue_get (&data))
		2788	process (data);
		2789
		2790	if (sigismember (&prev, SIGUSR1)
		2791	sigprocmask (SIG_UNBLOCK, &block, 0);
		2792	}
		2793
		2794	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2795	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2796	either...).
		2797
		2798	=item queueing from a thread context
		2799
		2800	The strategy for threads is different, as you cannot (easily) block
		2801	threads but you can easily preempt them, so to queue safely you need to
		2802	employ a traditional mutex lock, such as in this pthread example:
		2803
		2804	static ev_async mysig;
		2805	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2806
		2807	static void
		2808	otherthread (void)
		2809	{
		2810	// only need to lock the actual queueing operation
		2811	pthread_mutex_lock (&mymutex);
		2812	queue_put (data);
		2813	pthread_mutex_unlock (&mymutex);
		2814
		2815	ev_async_send (EV_DEFAULT_ &mysig);
		2816	}
		2817
		2818	static void
		2819	mysig_cb (EV_P_ ev_async *w, int revents)
		2820	{
		2821	pthread_mutex_lock (&mymutex);
		2822
		2823	while (queue_get (&data))
		2824	process (data);
		2825
		2826	pthread_mutex_unlock (&mymutex);
		2827	}
		2828
		2829	=back
		2830
		2831
		2832	=head3 Watcher-Specific Functions and Data Members
		2833
		2834	=over 4
		2835
		2836	=item ev_async_init (ev_async *, callback)
		2837
		2838	Initialises and configures the async watcher - it has no parameters of any
		2839	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2840	trust me.
		2841
		2842	=item ev_async_send (loop, ev_async *)
		2843
		2844	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2845	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2846	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2847	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2848	section below on what exactly this means).
		2849
		2850	Note that, as with other watchers in libev, multiple events might get
		2851	compressed into a single callback invocation (another way to look at this
		2852	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2853	reset when the event loop detects that).
		2854
		2855	This call incurs the overhead of a system call only once per event loop
		2856	iteration, so while the overhead might be noticeable, it doesn't apply to
		2857	repeated calls to C<ev_async_send> for the same event loop.
		2858
		2859	=item bool = ev_async_pending (ev_async *)
		2860
		2861	Returns a non-zero value when C<ev_async_send> has been called on the
		2862	watcher but the event has not yet been processed (or even noted) by the
		2863	event loop.
		2864
		2865	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2866	the loop iterates next and checks for the watcher to have become active,
		2867	it will reset the flag again. C<ev_async_pending> can be used to very
		2868	quickly check whether invoking the loop might be a good idea.
		2869
		2870	Not that this does I<not> check whether the watcher itself is pending,
		2871	only whether it has been requested to make this watcher pending: there
		2872	is a time window between the event loop checking and resetting the async
		2873	notification, and the callback being invoked.
		2874
		2875	=back
		2876
		2877
1580	=head1 OTHER FUNCTIONS	2878	=head1 OTHER FUNCTIONS
1581		2879
1582	There are some other functions of possible interest. Described. Here. Now.	2880	There are some other functions of possible interest. Described. Here. Now.
1583		2881
1584	=over 4	2882	=over 4
1585		2883
1586	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2884	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1587		2885
1588	This function combines a simple timer and an I/O watcher, calls your	2886	This function combines a simple timer and an I/O watcher, calls your
1589	callback on whichever event happens first and automatically stop both	2887	callback on whichever event happens first and automatically stops both
1590	watchers. This is useful if you want to wait for a single event on an fd	2888	watchers. This is useful if you want to wait for a single event on an fd
1591	or timeout without having to allocate/configure/start/stop/free one or	2889	or timeout without having to allocate/configure/start/stop/free one or
1592	more watchers yourself.	2890	more watchers yourself.
1593		2891
1594	If C<fd> is less than 0, then no I/O watcher will be started and events	2892	If C<fd> is less than 0, then no I/O watcher will be started and the
1595	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2893	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1596	C<events> set will be craeted and started.	2894	the given C<fd> and C<events> set will be created and started.
1597		2895
1598	If C<timeout> is less than 0, then no timeout watcher will be	2896	If C<timeout> is less than 0, then no timeout watcher will be
1599	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2897	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1600	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2898	repeat = 0) will be started. C<0> is a valid timeout.
1601	dubious value.
1602		2899
1603	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2900	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1604	passed an C<revents> set like normal event callbacks (a combination of	2901	passed an C<revents> set like normal event callbacks (a combination of
1605	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2902	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1606	value passed to C<ev_once>:	2903	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2904	a timeout and an io event at the same time - you probably should give io
		2905	events precedence.
1607		2906
		2907	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2908
1608	static void stdin_ready (int revents, void *arg)	2909	static void stdin_ready (int revents, void *arg)
1609	{	2910	{
1610	if (revents & EV_TIMEOUT)
1611	/* doh, nothing entered */;
1612	else if (revents & EV_READ)	2911	if (revents & EV_READ)
1613	/* stdin might have data for us, joy! */;	2912	/* stdin might have data for us, joy! */;
		2913	else if (revents & EV_TIMEOUT)
		2914	/* doh, nothing entered */;
1614	}	2915	}
1615		2916
1616	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2917	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1617		2918
1618	=item ev_feed_event (ev_loop *, watcher *, int revents)	2919	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1619		2920
1620	Feeds the given event set into the event loop, as if the specified event	2921	Feeds the given event set into the event loop, as if the specified event
1621	had happened for the specified watcher (which must be a pointer to an	2922	had happened for the specified watcher (which must be a pointer to an
1622	initialised but not necessarily started event watcher).	2923	initialised but not necessarily started event watcher).
1623		2924
1624	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2925	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1625		2926
1626	Feed an event on the given fd, as if a file descriptor backend detected	2927	Feed an event on the given fd, as if a file descriptor backend detected
1627	the given events it.	2928	the given events it.
1628		2929
1629	=item ev_feed_signal_event (ev_loop *loop, int signum)	2930	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1630		2931
1631	Feed an event as if the given signal occured (C<loop> must be the default	2932	Feed an event as if the given signal occurred (C<loop> must be the default
1632	loop!).	2933	loop!).
1633		2934
1634	=back	2935	=back
1635		2936
1636		2937
…		…
1652		2953
1653	=item * Priorities are not currently supported. Initialising priorities	2954	=item * Priorities are not currently supported. Initialising priorities
1654	will fail and all watchers will have the same priority, even though there	2955	will fail and all watchers will have the same priority, even though there
1655	is an ev_pri field.	2956	is an ev_pri field.
1656		2957
		2958	=item * In libevent, the last base created gets the signals, in libev, the
		2959	first base created (== the default loop) gets the signals.
		2960
1657	=item * Other members are not supported.	2961	=item * Other members are not supported.
1658		2962
1659	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2963	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1660	to use the libev header file and library.	2964	to use the libev header file and library.
1661		2965
1662	=back	2966	=back
1663		2967
1664	=head1 C++ SUPPORT	2968	=head1 C++ SUPPORT
1665		2969
1666	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2970	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1667	you to use some convinience methods to start/stop watchers and also change	2971	you to use some convenience methods to start/stop watchers and also change
1668	the callback model to a model using method callbacks on objects.	2972	the callback model to a model using method callbacks on objects.
1669		2973
1670	To use it,	2974	To use it,
1671		2975
1672	#include <ev++.h>	2976	#include <ev++.h>
1673		2977
1674	(it is not installed by default). This automatically includes F<ev.h>	2978	This automatically includes F<ev.h> and puts all of its definitions (many
1675	and puts all of its definitions (many of them macros) into the global	2979	of them macros) into the global namespace. All C++ specific things are
1676	namespace. All C++ specific things are put into the C<ev> namespace.	2980	put into the C<ev> namespace. It should support all the same embedding
		2981	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1677		2982
1678	It should support all the same embedding options as F<ev.h>, most notably	2983	Care has been taken to keep the overhead low. The only data member the C++
1679	C<EV_MULTIPLICITY>.	2984	classes add (compared to plain C-style watchers) is the event loop pointer
		2985	that the watcher is associated with (or no additional members at all if
		2986	you disable C<EV_MULTIPLICITY> when embedding libev).
		2987
		2988	Currently, functions, and static and non-static member functions can be
		2989	used as callbacks. Other types should be easy to add as long as they only
		2990	need one additional pointer for context. If you need support for other
		2991	types of functors please contact the author (preferably after implementing
		2992	it).
1680		2993
1681	Here is a list of things available in the C<ev> namespace:	2994	Here is a list of things available in the C<ev> namespace:
1682		2995
1683	=over 4	2996	=over 4
1684		2997
…		…
1700		3013
1701	All of those classes have these methods:	3014	All of those classes have these methods:
1702		3015
1703	=over 4	3016	=over 4
1704		3017
1705	=item ev::TYPE::TYPE (object *, object::method *)	3018	=item ev::TYPE::TYPE ()
1706		3019
1707	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	3020	=item ev::TYPE::TYPE (struct ev_loop *)
1708		3021
1709	=item ev::TYPE::~TYPE	3022	=item ev::TYPE::~TYPE
1710		3023
1711	The constructor takes a pointer to an object and a method pointer to	3024	The constructor (optionally) takes an event loop to associate the watcher
1712	the event handler callback to call in this class. The constructor calls	3025	with. If it is omitted, it will use C<EV_DEFAULT>.
1713	C<ev_init> for you, which means you have to call the C<set> method	3026
1714	before starting it. If you do not specify a loop then the constructor	3027	The constructor calls C<ev_init> for you, which means you have to call the
1715	automatically associates the default loop with this watcher.	3028	C<set> method before starting it.
		3029
		3030	It will not set a callback, however: You have to call the templated C<set>
		3031	method to set a callback before you can start the watcher.
		3032
		3033	(The reason why you have to use a method is a limitation in C++ which does
		3034	not allow explicit template arguments for constructors).
1716		3035
1717	The destructor automatically stops the watcher if it is active.	3036	The destructor automatically stops the watcher if it is active.
		3037
		3038	=item w->set<class, &class::method> (object *)
		3039
		3040	This method sets the callback method to call. The method has to have a
		3041	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3042	first argument and the C<revents> as second. The object must be given as
		3043	parameter and is stored in the C<data> member of the watcher.
		3044
		3045	This method synthesizes efficient thunking code to call your method from
		3046	the C callback that libev requires. If your compiler can inline your
		3047	callback (i.e. it is visible to it at the place of the C<set> call and
		3048	your compiler is good :), then the method will be fully inlined into the
		3049	thunking function, making it as fast as a direct C callback.
		3050
		3051	Example: simple class declaration and watcher initialisation
		3052
		3053	struct myclass
		3054	{
		3055	void io_cb (ev::io &w, int revents) { }
		3056	}
		3057
		3058	myclass obj;
		3059	ev::io iow;
		3060	iow.set <myclass, &myclass::io_cb> (&obj);
		3061
		3062	=item w->set (object *)
		3063
		3064	This is an B<experimental> feature that might go away in a future version.
		3065
		3066	This is a variation of a method callback - leaving out the method to call
		3067	will default the method to C<operator ()>, which makes it possible to use
		3068	functor objects without having to manually specify the C<operator ()> all
		3069	the time. Incidentally, you can then also leave out the template argument
		3070	list.
		3071
		3072	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3073	int revents)>.
		3074
		3075	See the method-C<set> above for more details.
		3076
		3077	Example: use a functor object as callback.
		3078
		3079	struct myfunctor
		3080	{
		3081	void operator() (ev::io &w, int revents)
		3082	{
		3083	...
		3084	}
		3085	}
		3086
		3087	myfunctor f;
		3088
		3089	ev::io w;
		3090	w.set (&f);
		3091
		3092	=item w->set<function> (void *data = 0)
		3093
		3094	Also sets a callback, but uses a static method or plain function as
		3095	callback. The optional C<data> argument will be stored in the watcher's
		3096	C<data> member and is free for you to use.
		3097
		3098	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3099
		3100	See the method-C<set> above for more details.
		3101
		3102	Example: Use a plain function as callback.
		3103
		3104	static void io_cb (ev::io &w, int revents) { }
		3105	iow.set <io_cb> ();
1718		3106
1719	=item w->set (struct ev_loop *)	3107	=item w->set (struct ev_loop *)
1720		3108
1721	Associates a different C<struct ev_loop> with this watcher. You can only	3109	Associates a different C<struct ev_loop> with this watcher. You can only
1722	do this when the watcher is inactive (and not pending either).	3110	do this when the watcher is inactive (and not pending either).
1723		3111
1724	=item w->set ([args])	3112	=item w->set ([arguments])
1725		3113
1726	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3114	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1727	called at least once. Unlike the C counterpart, an active watcher gets	3115	called at least once. Unlike the C counterpart, an active watcher gets
1728	automatically stopped and restarted.	3116	automatically stopped and restarted when reconfiguring it with this
		3117	method.
1729		3118
1730	=item w->start ()	3119	=item w->start ()
1731		3120
1732	Starts the watcher. Note that there is no C<loop> argument as the	3121	Starts the watcher. Note that there is no C<loop> argument, as the
1733	constructor already takes the loop.	3122	constructor already stores the event loop.
1734		3123
1735	=item w->stop ()	3124	=item w->stop ()
1736		3125
1737	Stops the watcher if it is active. Again, no C<loop> argument.	3126	Stops the watcher if it is active. Again, no C<loop> argument.
1738		3127
1739	=item w->again () C<ev::timer>, C<ev::periodic> only	3128	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1740		3129
1741	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3130	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1742	C<ev_TYPE_again> function.	3131	C<ev_TYPE_again> function.
1743		3132
1744	=item w->sweep () C<ev::embed> only	3133	=item w->sweep () (C<ev::embed> only)
1745		3134
1746	Invokes C<ev_embed_sweep>.	3135	Invokes C<ev_embed_sweep>.
1747		3136
1748	=item w->update () C<ev::stat> only	3137	=item w->update () (C<ev::stat> only)
1749		3138
1750	Invokes C<ev_stat_stat>.	3139	Invokes C<ev_stat_stat>.
1751		3140
1752	=back	3141	=back
1753		3142
1754	=back	3143	=back
1755		3144
1756	Example: Define a class with an IO and idle watcher, start one of them in	3145	Example: Define a class with an IO and idle watcher, start one of them in
1757	the constructor.	3146	the constructor.
1758		3147
1759	class myclass	3148	class myclass
1760	{	3149	{
1761	ev_io io; void io_cb (ev::io &w, int revents);	3150	ev::io io ; void io_cb (ev::io &w, int revents);
1762	ev_idle idle void idle_cb (ev::idle &w, int revents);	3151	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1763		3152
1764	myclass ();	3153	myclass (int fd)
1765	}	3154	{
		3155	io .set <myclass, &myclass::io_cb > (this);
		3156	idle.set <myclass, &myclass::idle_cb> (this);
1766		3157
1767	myclass::myclass (int fd)
1768	: io (this, &myclass::io_cb),
1769	idle (this, &myclass::idle_cb)
1770	{
1771	io.start (fd, ev::READ);	3158	io.start (fd, ev::READ);
		3159	}
1772	}	3160	};
		3161
		3162
		3163	=head1 OTHER LANGUAGE BINDINGS
		3164
		3165	Libev does not offer other language bindings itself, but bindings for a
		3166	number of languages exist in the form of third-party packages. If you know
		3167	any interesting language binding in addition to the ones listed here, drop
		3168	me a note.
		3169
		3170	=over 4
		3171
		3172	=item Perl
		3173
		3174	The EV module implements the full libev API and is actually used to test
		3175	libev. EV is developed together with libev. Apart from the EV core module,
		3176	there are additional modules that implement libev-compatible interfaces
		3177	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3178	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3179	and C<EV::Glib>).
		3180
		3181	It can be found and installed via CPAN, its homepage is at
		3182	L<http://software.schmorp.de/pkg/EV>.
		3183
		3184	=item Python
		3185
		3186	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3187	seems to be quite complete and well-documented.
		3188
		3189	=item Ruby
		3190
		3191	Tony Arcieri has written a ruby extension that offers access to a subset
		3192	of the libev API and adds file handle abstractions, asynchronous DNS and
		3193	more on top of it. It can be found via gem servers. Its homepage is at
		3194	L<http://rev.rubyforge.org/>.
		3195
		3196	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3197	makes rev work even on mingw.
		3198
		3199	=item Haskell
		3200
		3201	A haskell binding to libev is available at
		3202	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3203
		3204	=item D
		3205
		3206	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3207	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3208
		3209	=item Ocaml
		3210
		3211	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3212	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3213
		3214	=back
1773		3215
1774		3216
1775	=head1 MACRO MAGIC	3217	=head1 MACRO MAGIC
1776		3218
1777	Libev can be compiled with a variety of options, the most fundemantal is	3219	Libev can be compiled with a variety of options, the most fundamental
1778	C<EV_MULTIPLICITY>. This option determines wether (most) functions and	3220	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1779	callbacks have an initial C<struct ev_loop *> argument.	3221	functions and callbacks have an initial C<struct ev_loop *> argument.
1780		3222
1781	To make it easier to write programs that cope with either variant, the	3223	To make it easier to write programs that cope with either variant, the
1782	following macros are defined:	3224	following macros are defined:
1783		3225
1784	=over 4	3226	=over 4
…		…
1787		3229
1788	This provides the loop I<argument> for functions, if one is required ("ev	3230	This provides the loop I<argument> for functions, if one is required ("ev
1789	loop argument"). The C<EV_A> form is used when this is the sole argument,	3231	loop argument"). The C<EV_A> form is used when this is the sole argument,
1790	C<EV_A_> is used when other arguments are following. Example:	3232	C<EV_A_> is used when other arguments are following. Example:
1791		3233
1792	ev_unref (EV_A);	3234	ev_unref (EV_A);
1793	ev_timer_add (EV_A_ watcher);	3235	ev_timer_add (EV_A_ watcher);
1794	ev_loop (EV_A_ 0);	3236	ev_loop (EV_A_ 0);
1795		3237
1796	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3238	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1797	which is often provided by the following macro.	3239	which is often provided by the following macro.
1798		3240
1799	=item C<EV_P>, C<EV_P_>	3241	=item C<EV_P>, C<EV_P_>
1800		3242
1801	This provides the loop I<parameter> for functions, if one is required ("ev	3243	This provides the loop I<parameter> for functions, if one is required ("ev
1802	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3244	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1803	C<EV_P_> is used when other parameters are following. Example:	3245	C<EV_P_> is used when other parameters are following. Example:
1804		3246
1805	// this is how ev_unref is being declared	3247	// this is how ev_unref is being declared
1806	static void ev_unref (EV_P);	3248	static void ev_unref (EV_P);
1807		3249
1808	// this is how you can declare your typical callback	3250	// this is how you can declare your typical callback
1809	static void cb (EV_P_ ev_timer *w, int revents)	3251	static void cb (EV_P_ ev_timer *w, int revents)
1810		3252
1811	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3253	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1812	suitable for use with C<EV_A>.	3254	suitable for use with C<EV_A>.
1813		3255
1814	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3256	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1815		3257
1816	Similar to the other two macros, this gives you the value of the default	3258	Similar to the other two macros, this gives you the value of the default
1817	loop, if multiple loops are supported ("ev loop default").	3259	loop, if multiple loops are supported ("ev loop default").
1818		3260
		3261	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3262
		3263	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3264	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3265	is undefined when the default loop has not been initialised by a previous
		3266	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3267
		3268	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3269	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3270
1819	=back	3271	=back
1820		3272
1821	Example: Declare and initialise a check watcher, working regardless of	3273	Example: Declare and initialise a check watcher, utilising the above
1822	wether multiple loops are supported or not.	3274	macros so it will work regardless of whether multiple loops are supported
		3275	or not.
1823		3276
1824	static void	3277	static void
1825	check_cb (EV_P_ ev_timer *w, int revents)	3278	check_cb (EV_P_ ev_timer *w, int revents)
1826	{	3279	{
1827	ev_check_stop (EV_A_ w);	3280	ev_check_stop (EV_A_ w);
1828	}	3281	}
1829		3282
1830	ev_check check;	3283	ev_check check;
1831	ev_check_init (&check, check_cb);	3284	ev_check_init (&check, check_cb);
1832	ev_check_start (EV_DEFAULT_ &check);	3285	ev_check_start (EV_DEFAULT_ &check);
1833	ev_loop (EV_DEFAULT_ 0);	3286	ev_loop (EV_DEFAULT_ 0);
1834
1835		3287
1836	=head1 EMBEDDING	3288	=head1 EMBEDDING
1837		3289
1838	Libev can (and often is) directly embedded into host	3290	Libev can (and often is) directly embedded into host
1839	applications. Examples of applications that embed it include the Deliantra	3291	applications. Examples of applications that embed it include the Deliantra
1840	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3292	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1841	and rxvt-unicode.	3293	and rxvt-unicode.
1842		3294
1843	The goal is to enable you to just copy the neecssary files into your	3295	The goal is to enable you to just copy the necessary files into your
1844	source directory without having to change even a single line in them, so	3296	source directory without having to change even a single line in them, so
1845	you can easily upgrade by simply copying (or having a checked-out copy of	3297	you can easily upgrade by simply copying (or having a checked-out copy of
1846	libev somewhere in your source tree).	3298	libev somewhere in your source tree).
1847		3299
1848	=head2 FILESETS	3300	=head2 FILESETS
1849		3301
1850	Depending on what features you need you need to include one or more sets of files	3302	Depending on what features you need you need to include one or more sets of files
1851	in your app.	3303	in your application.
1852		3304
1853	=head3 CORE EVENT LOOP	3305	=head3 CORE EVENT LOOP
1854		3306
1855	To include only the libev core (all the C<ev_*> functions), with manual	3307	To include only the libev core (all the C<ev_*> functions), with manual
1856	configuration (no autoconf):	3308	configuration (no autoconf):
1857		3309
1858	#define EV_STANDALONE 1	3310	#define EV_STANDALONE 1
1859	#include "ev.c"	3311	#include "ev.c"
1860		3312
1861	This will automatically include F<ev.h>, too, and should be done in a	3313	This will automatically include F<ev.h>, too, and should be done in a
1862	single C source file only to provide the function implementations. To use	3314	single C source file only to provide the function implementations. To use
1863	it, do the same for F<ev.h> in all files wishing to use this API (best	3315	it, do the same for F<ev.h> in all files wishing to use this API (best
1864	done by writing a wrapper around F<ev.h> that you can include instead and	3316	done by writing a wrapper around F<ev.h> that you can include instead and
1865	where you can put other configuration options):	3317	where you can put other configuration options):
1866		3318
1867	#define EV_STANDALONE 1	3319	#define EV_STANDALONE 1
1868	#include "ev.h"	3320	#include "ev.h"
1869		3321
1870	Both header files and implementation files can be compiled with a C++	3322	Both header files and implementation files can be compiled with a C++
1871	compiler (at least, thats a stated goal, and breakage will be treated	3323	compiler (at least, that's a stated goal, and breakage will be treated
1872	as a bug).	3324	as a bug).
1873		3325
1874	You need the following files in your source tree, or in a directory	3326	You need the following files in your source tree, or in a directory
1875	in your include path (e.g. in libev/ when using -Ilibev):	3327	in your include path (e.g. in libev/ when using -Ilibev):
1876		3328
1877	ev.h	3329	ev.h
1878	ev.c	3330	ev.c
1879	ev_vars.h	3331	ev_vars.h
1880	ev_wrap.h	3332	ev_wrap.h
1881		3333
1882	ev_win32.c required on win32 platforms only	3334	ev_win32.c required on win32 platforms only
1883		3335
1884	ev_select.c only when select backend is enabled (which is by default)	3336	ev_select.c only when select backend is enabled (which is enabled by default)
1885	ev_poll.c only when poll backend is enabled (disabled by default)	3337	ev_poll.c only when poll backend is enabled (disabled by default)
1886	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3338	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1887	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3339	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1888	ev_port.c only when the solaris port backend is enabled (disabled by default)	3340	ev_port.c only when the solaris port backend is enabled (disabled by default)
1889		3341
1890	F<ev.c> includes the backend files directly when enabled, so you only need	3342	F<ev.c> includes the backend files directly when enabled, so you only need
1891	to compile this single file.	3343	to compile this single file.
1892		3344
1893	=head3 LIBEVENT COMPATIBILITY API	3345	=head3 LIBEVENT COMPATIBILITY API
1894		3346
1895	To include the libevent compatibility API, also include:	3347	To include the libevent compatibility API, also include:
1896		3348
1897	#include "event.c"	3349	#include "event.c"
1898		3350
1899	in the file including F<ev.c>, and:	3351	in the file including F<ev.c>, and:
1900		3352
1901	#include "event.h"	3353	#include "event.h"
1902		3354
1903	in the files that want to use the libevent API. This also includes F<ev.h>.	3355	in the files that want to use the libevent API. This also includes F<ev.h>.
1904		3356
1905	You need the following additional files for this:	3357	You need the following additional files for this:
1906		3358
1907	event.h	3359	event.h
1908	event.c	3360	event.c
1909		3361
1910	=head3 AUTOCONF SUPPORT	3362	=head3 AUTOCONF SUPPORT
1911		3363
1912	Instead of using C<EV_STANDALONE=1> and providing your config in	3364	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1913	whatever way you want, you can also C<m4_include([libev.m4])> in your	3365	whatever way you want, you can also C<m4_include([libev.m4])> in your
1914	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3366	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1915	include F<config.h> and configure itself accordingly.	3367	include F<config.h> and configure itself accordingly.
1916		3368
1917	For this of course you need the m4 file:	3369	For this of course you need the m4 file:
1918		3370
1919	libev.m4	3371	libev.m4
1920		3372
1921	=head2 PREPROCESSOR SYMBOLS/MACROS	3373	=head2 PREPROCESSOR SYMBOLS/MACROS
1922		3374
1923	Libev can be configured via a variety of preprocessor symbols you have to define	3375	Libev can be configured via a variety of preprocessor symbols you have to
1924	before including any of its files. The default is not to build for multiplicity	3376	define before including any of its files. The default in the absence of
1925	and only include the select backend.	3377	autoconf is documented for every option.
1926		3378
1927	=over 4	3379	=over 4
1928		3380
1929	=item EV_STANDALONE	3381	=item EV_STANDALONE
1930		3382
…		…
1932	keeps libev from including F<config.h>, and it also defines dummy	3384	keeps libev from including F<config.h>, and it also defines dummy
1933	implementations for some libevent functions (such as logging, which is not	3385	implementations for some libevent functions (such as logging, which is not
1934	supported). It will also not define any of the structs usually found in	3386	supported). It will also not define any of the structs usually found in
1935	F<event.h> that are not directly supported by the libev core alone.	3387	F<event.h> that are not directly supported by the libev core alone.
1936		3388
		3389	In stanbdalone mode, libev will still try to automatically deduce the
		3390	configuration, but has to be more conservative.
		3391
1937	=item EV_USE_MONOTONIC	3392	=item EV_USE_MONOTONIC
1938		3393
1939	If defined to be C<1>, libev will try to detect the availability of the	3394	If defined to be C<1>, libev will try to detect the availability of the
1940	monotonic clock option at both compiletime and runtime. Otherwise no use	3395	monotonic clock option at both compile time and runtime. Otherwise no
1941	of the monotonic clock option will be attempted. If you enable this, you	3396	use of the monotonic clock option will be attempted. If you enable this,
1942	usually have to link against librt or something similar. Enabling it when	3397	you usually have to link against librt or something similar. Enabling it
1943	the functionality isn't available is safe, though, althoguh you have	3398	when the functionality isn't available is safe, though, although you have
1944	to make sure you link against any libraries where the C<clock_gettime>	3399	to make sure you link against any libraries where the C<clock_gettime>
1945	function is hiding in (often F<-lrt>).	3400	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
1946		3401
1947	=item EV_USE_REALTIME	3402	=item EV_USE_REALTIME
1948		3403
1949	If defined to be C<1>, libev will try to detect the availability of the	3404	If defined to be C<1>, libev will try to detect the availability of the
1950	realtime clock option at compiletime (and assume its availability at	3405	real-time clock option at compile time (and assume its availability
1951	runtime if successful). Otherwise no use of the realtime clock option will	3406	at runtime if successful). Otherwise no use of the real-time clock
1952	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3407	option will be attempted. This effectively replaces C<gettimeofday>
1953	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3408	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
1954	in the description of C<EV_USE_MONOTONIC>, though.	3409	correctness. See the note about libraries in the description of
		3410	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3411	C<EV_USE_CLOCK_SYSCALL>.
		3412
		3413	=item EV_USE_CLOCK_SYSCALL
		3414
		3415	If defined to be C<1>, libev will try to use a direct syscall instead
		3416	of calling the system-provided C<clock_gettime> function. This option
		3417	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3418	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3419	programs needlessly. Using a direct syscall is slightly slower (in
		3420	theory), because no optimised vdso implementation can be used, but avoids
		3421	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3422	higher, as it simplifies linking (no need for C<-lrt>).
		3423
		3424	=item EV_USE_NANOSLEEP
		3425
		3426	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3427	and will use it for delays. Otherwise it will use C<select ()>.
		3428
		3429	=item EV_USE_EVENTFD
		3430
		3431	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3432	available and will probe for kernel support at runtime. This will improve
		3433	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3434	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3435	2.7 or newer, otherwise disabled.
1955		3436
1956	=item EV_USE_SELECT	3437	=item EV_USE_SELECT
1957		3438
1958	If undefined or defined to be C<1>, libev will compile in support for the	3439	If undefined or defined to be C<1>, libev will compile in support for the
1959	C<select>(2) backend. No attempt at autodetection will be done: if no	3440	C<select>(2) backend. No attempt at auto-detection will be done: if no
1960	other method takes over, select will be it. Otherwise the select backend	3441	other method takes over, select will be it. Otherwise the select backend
1961	will not be compiled in.	3442	will not be compiled in.
1962		3443
1963	=item EV_SELECT_USE_FD_SET	3444	=item EV_SELECT_USE_FD_SET
1964		3445
1965	If defined to C<1>, then the select backend will use the system C<fd_set>	3446	If defined to C<1>, then the select backend will use the system C<fd_set>
1966	structure. This is useful if libev doesn't compile due to a missing	3447	structure. This is useful if libev doesn't compile due to a missing
1967	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3448	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
1968	exotic systems. This usually limits the range of file descriptors to some	3449	on exotic systems. This usually limits the range of file descriptors to
1969	low limit such as 1024 or might have other limitations (winsocket only	3450	some low limit such as 1024 or might have other limitations (winsocket
1970	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3451	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
1971	influence the size of the C<fd_set> used.	3452	configures the maximum size of the C<fd_set>.
1972		3453
1973	=item EV_SELECT_IS_WINSOCKET	3454	=item EV_SELECT_IS_WINSOCKET
1974		3455
1975	When defined to C<1>, the select backend will assume that	3456	When defined to C<1>, the select backend will assume that
1976	select/socket/connect etc. don't understand file descriptors but	3457	select/socket/connect etc. don't understand file descriptors but
…		…
1978	be used is the winsock select). This means that it will call	3459	be used is the winsock select). This means that it will call
1979	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3460	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1980	it is assumed that all these functions actually work on fds, even	3461	it is assumed that all these functions actually work on fds, even
1981	on win32. Should not be defined on non-win32 platforms.	3462	on win32. Should not be defined on non-win32 platforms.
1982		3463
		3464	=item EV_FD_TO_WIN32_HANDLE
		3465
		3466	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3467	file descriptors to socket handles. When not defining this symbol (the
		3468	default), then libev will call C<_get_osfhandle>, which is usually
		3469	correct. In some cases, programs use their own file descriptor management,
		3470	in which case they can provide this function to map fds to socket handles.
		3471
1983	=item EV_USE_POLL	3472	=item EV_USE_POLL
1984		3473
1985	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3474	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1986	backend. Otherwise it will be enabled on non-win32 platforms. It	3475	backend. Otherwise it will be enabled on non-win32 platforms. It
1987	takes precedence over select.	3476	takes precedence over select.
1988		3477
1989	=item EV_USE_EPOLL	3478	=item EV_USE_EPOLL
1990		3479
1991	If defined to be C<1>, libev will compile in support for the Linux	3480	If defined to be C<1>, libev will compile in support for the Linux
1992	C<epoll>(7) backend. Its availability will be detected at runtime,	3481	C<epoll>(7) backend. Its availability will be detected at runtime,
1993	otherwise another method will be used as fallback. This is the	3482	otherwise another method will be used as fallback. This is the preferred
1994	preferred backend for GNU/Linux systems.	3483	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3484	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1995		3485
1996	=item EV_USE_KQUEUE	3486	=item EV_USE_KQUEUE
1997		3487
1998	If defined to be C<1>, libev will compile in support for the BSD style	3488	If defined to be C<1>, libev will compile in support for the BSD style
1999	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3489	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2012	otherwise another method will be used as fallback. This is the preferred	3502	otherwise another method will be used as fallback. This is the preferred
2013	backend for Solaris 10 systems.	3503	backend for Solaris 10 systems.
2014		3504
2015	=item EV_USE_DEVPOLL	3505	=item EV_USE_DEVPOLL
2016		3506
2017	reserved for future expansion, works like the USE symbols above.	3507	Reserved for future expansion, works like the USE symbols above.
		3508
		3509	=item EV_USE_INOTIFY
		3510
		3511	If defined to be C<1>, libev will compile in support for the Linux inotify
		3512	interface to speed up C<ev_stat> watchers. Its actual availability will
		3513	be detected at runtime. If undefined, it will be enabled if the headers
		3514	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3515
		3516	=item EV_ATOMIC_T
		3517
		3518	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3519	access is atomic with respect to other threads or signal contexts. No such
		3520	type is easily found in the C language, so you can provide your own type
		3521	that you know is safe for your purposes. It is used both for signal handler "locking"
		3522	as well as for signal and thread safety in C<ev_async> watchers.
		3523
		3524	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3525	(from F<signal.h>), which is usually good enough on most platforms.
2018		3526
2019	=item EV_H	3527	=item EV_H
2020		3528
2021	The name of the F<ev.h> header file used to include it. The default if	3529	The name of the F<ev.h> header file used to include it. The default if
2022	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3530	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2023	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3531	used to virtually rename the F<ev.h> header file in case of conflicts.
2024		3532
2025	=item EV_CONFIG_H	3533	=item EV_CONFIG_H
2026		3534
2027	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3535	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2028	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3536	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2029	C<EV_H>, above.	3537	C<EV_H>, above.
2030		3538
2031	=item EV_EVENT_H	3539	=item EV_EVENT_H
2032		3540
2033	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3541	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2034	of how the F<event.h> header can be found.	3542	of how the F<event.h> header can be found, the default is C<"event.h">.
2035		3543
2036	=item EV_PROTOTYPES	3544	=item EV_PROTOTYPES
2037		3545
2038	If defined to be C<0>, then F<ev.h> will not define any function	3546	If defined to be C<0>, then F<ev.h> will not define any function
2039	prototypes, but still define all the structs and other symbols. This is	3547	prototypes, but still define all the structs and other symbols. This is
…		…
2046	will have the C<struct ev_loop *> as first argument, and you can create	3554	will have the C<struct ev_loop *> as first argument, and you can create
2047	additional independent event loops. Otherwise there will be no support	3555	additional independent event loops. Otherwise there will be no support
2048	for multiple event loops and there is no first event loop pointer	3556	for multiple event loops and there is no first event loop pointer
2049	argument. Instead, all functions act on the single default loop.	3557	argument. Instead, all functions act on the single default loop.
2050		3558
		3559	=item EV_MINPRI
		3560
		3561	=item EV_MAXPRI
		3562
		3563	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3564	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3565	provide for more priorities by overriding those symbols (usually defined
		3566	to be C<-2> and C<2>, respectively).
		3567
		3568	When doing priority-based operations, libev usually has to linearly search
		3569	all the priorities, so having many of them (hundreds) uses a lot of space
		3570	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3571	fine.
		3572
		3573	If your embedding application does not need any priorities, defining these
		3574	both to C<0> will save some memory and CPU.
		3575
2051	=item EV_PERIODIC_ENABLE	3576	=item EV_PERIODIC_ENABLE
2052		3577
2053	If undefined or defined to be C<1>, then periodic timers are supported. If	3578	If undefined or defined to be C<1>, then periodic timers are supported. If
2054	defined to be C<0>, then they are not. Disabling them saves a few kB of	3579	defined to be C<0>, then they are not. Disabling them saves a few kB of
2055	code.	3580	code.
2056		3581
		3582	=item EV_IDLE_ENABLE
		3583
		3584	If undefined or defined to be C<1>, then idle watchers are supported. If
		3585	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3586	code.
		3587
2057	=item EV_EMBED_ENABLE	3588	=item EV_EMBED_ENABLE
2058		3589
2059	If undefined or defined to be C<1>, then embed watchers are supported. If	3590	If undefined or defined to be C<1>, then embed watchers are supported. If
2060	defined to be C<0>, then they are not.	3591	defined to be C<0>, then they are not. Embed watchers rely on most other
		3592	watcher types, which therefore must not be disabled.
2061		3593
2062	=item EV_STAT_ENABLE	3594	=item EV_STAT_ENABLE
2063		3595
2064	If undefined or defined to be C<1>, then stat watchers are supported. If	3596	If undefined or defined to be C<1>, then stat watchers are supported. If
2065	defined to be C<0>, then they are not.	3597	defined to be C<0>, then they are not.
…		…
2067	=item EV_FORK_ENABLE	3599	=item EV_FORK_ENABLE
2068		3600
2069	If undefined or defined to be C<1>, then fork watchers are supported. If	3601	If undefined or defined to be C<1>, then fork watchers are supported. If
2070	defined to be C<0>, then they are not.	3602	defined to be C<0>, then they are not.
2071		3603
		3604	=item EV_ASYNC_ENABLE
		3605
		3606	If undefined or defined to be C<1>, then async watchers are supported. If
		3607	defined to be C<0>, then they are not.
		3608
2072	=item EV_MINIMAL	3609	=item EV_MINIMAL
2073		3610
2074	If you need to shave off some kilobytes of code at the expense of some	3611	If you need to shave off some kilobytes of code at the expense of some
2075	speed, define this symbol to C<1>. Currently only used for gcc to override	3612	speed, define this symbol to C<1>. Currently this is used to override some
2076	some inlining decisions, saves roughly 30% codesize of amd64.	3613	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3614	much smaller 2-heap for timer management over the default 4-heap.
2077		3615
2078	=item EV_PID_HASHSIZE	3616	=item EV_PID_HASHSIZE
2079		3617
2080	C<ev_child> watchers use a small hash table to distribute workload by	3618	C<ev_child> watchers use a small hash table to distribute workload by
2081	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3619	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2082	than enough. If you need to manage thousands of children you might want to	3620	than enough. If you need to manage thousands of children you might want to
2083	increase this value.	3621	increase this value (I<must> be a power of two).
		3622
		3623	=item EV_INOTIFY_HASHSIZE
		3624
		3625	C<ev_stat> watchers use a small hash table to distribute workload by
		3626	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3627	usually more than enough. If you need to manage thousands of C<ev_stat>
		3628	watchers you might want to increase this value (I<must> be a power of
		3629	two).
		3630
		3631	=item EV_USE_4HEAP
		3632
		3633	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3634	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3635	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3636	faster performance with many (thousands) of watchers.
		3637
		3638	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3639	(disabled).
		3640
		3641	=item EV_HEAP_CACHE_AT
		3642
		3643	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3644	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3645	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3646	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3647	but avoids random read accesses on heap changes. This improves performance
		3648	noticeably with many (hundreds) of watchers.
		3649
		3650	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3651	(disabled).
		3652
		3653	=item EV_VERIFY
		3654
		3655	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3656	be done: If set to C<0>, no internal verification code will be compiled
		3657	in. If set to C<1>, then verification code will be compiled in, but not
		3658	called. If set to C<2>, then the internal verification code will be
		3659	called once per loop, which can slow down libev. If set to C<3>, then the
		3660	verification code will be called very frequently, which will slow down
		3661	libev considerably.
		3662
		3663	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3664	C<0>.
2084		3665
2085	=item EV_COMMON	3666	=item EV_COMMON
2086		3667
2087	By default, all watchers have a C<void *data> member. By redefining	3668	By default, all watchers have a C<void *data> member. By redefining
2088	this macro to a something else you can include more and other types of	3669	this macro to a something else you can include more and other types of
2089	members. You have to define it each time you include one of the files,	3670	members. You have to define it each time you include one of the files,
2090	though, and it must be identical each time.	3671	though, and it must be identical each time.
2091		3672
2092	For example, the perl EV module uses something like this:	3673	For example, the perl EV module uses something like this:
2093		3674
2094	#define EV_COMMON \	3675	#define EV_COMMON \
2095	SV *self; /* contains this struct */ \	3676	SV *self; /* contains this struct */ \
2096	SV *cb_sv, *fh /* note no trailing ";" */	3677	SV *cb_sv, *fh /* note no trailing ";" */
2097		3678
2098	=item EV_CB_DECLARE (type)	3679	=item EV_CB_DECLARE (type)
2099		3680
2100	=item EV_CB_INVOKE (watcher, revents)	3681	=item EV_CB_INVOKE (watcher, revents)
2101		3682
2102	=item ev_set_cb (ev, cb)	3683	=item ev_set_cb (ev, cb)
2103		3684
2104	Can be used to change the callback member declaration in each watcher,	3685	Can be used to change the callback member declaration in each watcher,
2105	and the way callbacks are invoked and set. Must expand to a struct member	3686	and the way callbacks are invoked and set. Must expand to a struct member
2106	definition and a statement, respectively. See the F<ev.v> header file for	3687	definition and a statement, respectively. See the F<ev.h> header file for
2107	their default definitions. One possible use for overriding these is to	3688	their default definitions. One possible use for overriding these is to
2108	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3689	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2109	method calls instead of plain function calls in C++.	3690	method calls instead of plain function calls in C++.
		3691
		3692	=back
		3693
		3694	=head2 EXPORTED API SYMBOLS
		3695
		3696	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3697	exported symbols, you can use the provided F<Symbol.*> files which list
		3698	all public symbols, one per line:
		3699
		3700	Symbols.ev for libev proper
		3701	Symbols.event for the libevent emulation
		3702
		3703	This can also be used to rename all public symbols to avoid clashes with
		3704	multiple versions of libev linked together (which is obviously bad in
		3705	itself, but sometimes it is inconvenient to avoid this).
		3706
		3707	A sed command like this will create wrapper C<#define>'s that you need to
		3708	include before including F<ev.h>:
		3709
		3710	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3711
		3712	This would create a file F<wrap.h> which essentially looks like this:
		3713
		3714	#define ev_backend myprefix_ev_backend
		3715	#define ev_check_start myprefix_ev_check_start
		3716	#define ev_check_stop myprefix_ev_check_stop
		3717	...
2110		3718
2111	=head2 EXAMPLES	3719	=head2 EXAMPLES
2112		3720
2113	For a real-world example of a program the includes libev	3721	For a real-world example of a program the includes libev
2114	verbatim, you can have a look at the EV perl module	3722	verbatim, you can have a look at the EV perl module
…		…
2117	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	3725	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
2118	will be compiled. It is pretty complex because it provides its own header	3726	will be compiled. It is pretty complex because it provides its own header
2119	file.	3727	file.
2120		3728
2121	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3729	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2122	that everybody includes and which overrides some autoconf choices:	3730	that everybody includes and which overrides some configure choices:
2123		3731
		3732	#define EV_MINIMAL 1
2124	#define EV_USE_POLL 0	3733	#define EV_USE_POLL 0
2125	#define EV_MULTIPLICITY 0	3734	#define EV_MULTIPLICITY 0
2126	#define EV_PERIODICS 0	3735	#define EV_PERIODIC_ENABLE 0
		3736	#define EV_STAT_ENABLE 0
		3737	#define EV_FORK_ENABLE 0
2127	#define EV_CONFIG_H <config.h>	3738	#define EV_CONFIG_H <config.h>
		3739	#define EV_MINPRI 0
		3740	#define EV_MAXPRI 0
2128		3741
2129	#include "ev++.h"	3742	#include "ev++.h"
2130		3743
2131	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3744	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2132		3745
2133	#include "ev_cpp.h"	3746	#include "ev_cpp.h"
2134	#include "ev.c"	3747	#include "ev.c"
2135		3748
		3749	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2136		3750
		3751	=head2 THREADS AND COROUTINES
		3752
		3753	=head3 THREADS
		3754
		3755	All libev functions are reentrant and thread-safe unless explicitly
		3756	documented otherwise, but libev implements no locking itself. This means
		3757	that you can use as many loops as you want in parallel, as long as there
		3758	are no concurrent calls into any libev function with the same loop
		3759	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3760	of course): libev guarantees that different event loops share no data
		3761	structures that need any locking.
		3762
		3763	Or to put it differently: calls with different loop parameters can be done
		3764	concurrently from multiple threads, calls with the same loop parameter
		3765	must be done serially (but can be done from different threads, as long as
		3766	only one thread ever is inside a call at any point in time, e.g. by using
		3767	a mutex per loop).
		3768
		3769	Specifically to support threads (and signal handlers), libev implements
		3770	so-called C<ev_async> watchers, which allow some limited form of
		3771	concurrency on the same event loop, namely waking it up "from the
		3772	outside".
		3773
		3774	If you want to know which design (one loop, locking, or multiple loops
		3775	without or something else still) is best for your problem, then I cannot
		3776	help you, but here is some generic advice:
		3777
		3778	=over 4
		3779
		3780	=item * most applications have a main thread: use the default libev loop
		3781	in that thread, or create a separate thread running only the default loop.
		3782
		3783	This helps integrating other libraries or software modules that use libev
		3784	themselves and don't care/know about threading.
		3785
		3786	=item * one loop per thread is usually a good model.
		3787
		3788	Doing this is almost never wrong, sometimes a better-performance model
		3789	exists, but it is always a good start.
		3790
		3791	=item * other models exist, such as the leader/follower pattern, where one
		3792	loop is handed through multiple threads in a kind of round-robin fashion.
		3793
		3794	Choosing a model is hard - look around, learn, know that usually you can do
		3795	better than you currently do :-)
		3796
		3797	=item * often you need to talk to some other thread which blocks in the
		3798	event loop.
		3799
		3800	C<ev_async> watchers can be used to wake them up from other threads safely
		3801	(or from signal contexts...).
		3802
		3803	An example use would be to communicate signals or other events that only
		3804	work in the default loop by registering the signal watcher with the
		3805	default loop and triggering an C<ev_async> watcher from the default loop
		3806	watcher callback into the event loop interested in the signal.
		3807
		3808	=back
		3809
		3810	=head3 COROUTINES
		3811
		3812	Libev is very accommodating to coroutines ("cooperative threads"):
		3813	libev fully supports nesting calls to its functions from different
		3814	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3815	different coroutines, and switch freely between both coroutines running the
		3816	loop, as long as you don't confuse yourself). The only exception is that
		3817	you must not do this from C<ev_periodic> reschedule callbacks.
		3818
		3819	Care has been taken to ensure that libev does not keep local state inside
		3820	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3821	they do not call any callbacks.
		3822
		3823	=head2 COMPILER WARNINGS
		3824
		3825	Depending on your compiler and compiler settings, you might get no or a
		3826	lot of warnings when compiling libev code. Some people are apparently
		3827	scared by this.
		3828
		3829	However, these are unavoidable for many reasons. For one, each compiler
		3830	has different warnings, and each user has different tastes regarding
		3831	warning options. "Warn-free" code therefore cannot be a goal except when
		3832	targeting a specific compiler and compiler-version.
		3833
		3834	Another reason is that some compiler warnings require elaborate
		3835	workarounds, or other changes to the code that make it less clear and less
		3836	maintainable.
		3837
		3838	And of course, some compiler warnings are just plain stupid, or simply
		3839	wrong (because they don't actually warn about the condition their message
		3840	seems to warn about). For example, certain older gcc versions had some
		3841	warnings that resulted an extreme number of false positives. These have
		3842	been fixed, but some people still insist on making code warn-free with
		3843	such buggy versions.
		3844
		3845	While libev is written to generate as few warnings as possible,
		3846	"warn-free" code is not a goal, and it is recommended not to build libev
		3847	with any compiler warnings enabled unless you are prepared to cope with
		3848	them (e.g. by ignoring them). Remember that warnings are just that:
		3849	warnings, not errors, or proof of bugs.
		3850
		3851
		3852	=head2 VALGRIND
		3853
		3854	Valgrind has a special section here because it is a popular tool that is
		3855	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3856
		3857	If you think you found a bug (memory leak, uninitialised data access etc.)
		3858	in libev, then check twice: If valgrind reports something like:
		3859
		3860	==2274== definitely lost: 0 bytes in 0 blocks.
		3861	==2274== possibly lost: 0 bytes in 0 blocks.
		3862	==2274== still reachable: 256 bytes in 1 blocks.
		3863
		3864	Then there is no memory leak, just as memory accounted to global variables
		3865	is not a memleak - the memory is still being referenced, and didn't leak.
		3866
		3867	Similarly, under some circumstances, valgrind might report kernel bugs
		3868	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3869	although an acceptable workaround has been found here), or it might be
		3870	confused.
		3871
		3872	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3873	make it into some kind of religion.
		3874
		3875	If you are unsure about something, feel free to contact the mailing list
		3876	with the full valgrind report and an explanation on why you think this
		3877	is a bug in libev (best check the archives, too :). However, don't be
		3878	annoyed when you get a brisk "this is no bug" answer and take the chance
		3879	of learning how to interpret valgrind properly.
		3880
		3881	If you need, for some reason, empty reports from valgrind for your project
		3882	I suggest using suppression lists.
		3883
		3884
		3885	=head1 PORTABILITY NOTES
		3886
		3887	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3888
		3889	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3890	requires, and its I/O model is fundamentally incompatible with the POSIX
		3891	model. Libev still offers limited functionality on this platform in
		3892	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3893	descriptors. This only applies when using Win32 natively, not when using
		3894	e.g. cygwin.
		3895
		3896	Lifting these limitations would basically require the full
		3897	re-implementation of the I/O system. If you are into these kinds of
		3898	things, then note that glib does exactly that for you in a very portable
		3899	way (note also that glib is the slowest event library known to man).
		3900
		3901	There is no supported compilation method available on windows except
		3902	embedding it into other applications.
		3903
		3904	Not a libev limitation but worth mentioning: windows apparently doesn't
		3905	accept large writes: instead of resulting in a partial write, windows will
		3906	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3907	so make sure you only write small amounts into your sockets (less than a
		3908	megabyte seems safe, but this apparently depends on the amount of memory
		3909	available).
		3910
		3911	Due to the many, low, and arbitrary limits on the win32 platform and
		3912	the abysmal performance of winsockets, using a large number of sockets
		3913	is not recommended (and not reasonable). If your program needs to use
		3914	more than a hundred or so sockets, then likely it needs to use a totally
		3915	different implementation for windows, as libev offers the POSIX readiness
		3916	notification model, which cannot be implemented efficiently on windows
		3917	(Microsoft monopoly games).
		3918
		3919	A typical way to use libev under windows is to embed it (see the embedding
		3920	section for details) and use the following F<evwrap.h> header file instead
		3921	of F<ev.h>:
		3922
		3923	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3924	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3925
		3926	#include "ev.h"
		3927
		3928	And compile the following F<evwrap.c> file into your project (make sure
		3929	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3930
		3931	#include "evwrap.h"
		3932	#include "ev.c"
		3933
		3934	=over 4
		3935
		3936	=item The winsocket select function
		3937
		3938	The winsocket C<select> function doesn't follow POSIX in that it
		3939	requires socket I<handles> and not socket I<file descriptors> (it is
		3940	also extremely buggy). This makes select very inefficient, and also
		3941	requires a mapping from file descriptors to socket handles (the Microsoft
		3942	C runtime provides the function C<_open_osfhandle> for this). See the
		3943	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3944	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3945
		3946	The configuration for a "naked" win32 using the Microsoft runtime
		3947	libraries and raw winsocket select is:
		3948
		3949	#define EV_USE_SELECT 1
		3950	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3951
		3952	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3953	complexity in the O(n²) range when using win32.
		3954
		3955	=item Limited number of file descriptors
		3956
		3957	Windows has numerous arbitrary (and low) limits on things.
		3958
		3959	Early versions of winsocket's select only supported waiting for a maximum
		3960	of C<64> handles (probably owning to the fact that all windows kernels
		3961	can only wait for C<64> things at the same time internally; Microsoft
		3962	recommends spawning a chain of threads and wait for 63 handles and the
		3963	previous thread in each. Great).
		3964
		3965	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3966	to some high number (e.g. C<2048>) before compiling the winsocket select
		3967	call (which might be in libev or elsewhere, for example, perl does its own
		3968	select emulation on windows).
		3969
		3970	Another limit is the number of file descriptors in the Microsoft runtime
		3971	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3972	or something like this inside Microsoft). You can increase this by calling
		3973	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3974	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3975	libraries.
		3976
		3977	This might get you to about C<512> or C<2048> sockets (depending on
		3978	windows version and/or the phase of the moon). To get more, you need to
		3979	wrap all I/O functions and provide your own fd management, but the cost of
		3980	calling select (O(n²)) will likely make this unworkable.
		3981
		3982	=back
		3983
		3984	=head2 PORTABILITY REQUIREMENTS
		3985
		3986	In addition to a working ISO-C implementation and of course the
		3987	backend-specific APIs, libev relies on a few additional extensions:
		3988
		3989	=over 4
		3990
		3991	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3992	calling conventions regardless of C<ev_watcher_type *>.
		3993
		3994	Libev assumes not only that all watcher pointers have the same internal
		3995	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3996	assumes that the same (machine) code can be used to call any watcher
		3997	callback: The watcher callbacks have different type signatures, but libev
		3998	calls them using an C<ev_watcher *> internally.
		3999
		4000	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4001
		4002	The type C<sig_atomic_t volatile> (or whatever is defined as
		4003	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4004	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4005	believed to be sufficiently portable.
		4006
		4007	=item C<sigprocmask> must work in a threaded environment
		4008
		4009	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4010	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4011	pthread implementations will either allow C<sigprocmask> in the "main
		4012	thread" or will block signals process-wide, both behaviours would
		4013	be compatible with libev. Interaction between C<sigprocmask> and
		4014	C<pthread_sigmask> could complicate things, however.
		4015
		4016	The most portable way to handle signals is to block signals in all threads
		4017	except the initial one, and run the default loop in the initial thread as
		4018	well.
		4019
		4020	=item C<long> must be large enough for common memory allocation sizes
		4021
		4022	To improve portability and simplify its API, libev uses C<long> internally
		4023	instead of C<size_t> when allocating its data structures. On non-POSIX
		4024	systems (Microsoft...) this might be unexpectedly low, but is still at
		4025	least 31 bits everywhere, which is enough for hundreds of millions of
		4026	watchers.
		4027
		4028	=item C<double> must hold a time value in seconds with enough accuracy
		4029
		4030	The type C<double> is used to represent timestamps. It is required to
		4031	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4032	enough for at least into the year 4000. This requirement is fulfilled by
		4033	implementations implementing IEEE 754 (basically all existing ones).
		4034
		4035	=back
		4036
		4037	If you know of other additional requirements drop me a note.
		4038
		4039
2137	=head1 COMPLEXITIES	4040	=head1 ALGORITHMIC COMPLEXITIES
2138		4041
2139	In this section the complexities of (many of) the algorithms used inside	4042	In this section the complexities of (many of) the algorithms used inside
2140	libev will be explained. For complexity discussions about backends see the	4043	libev will be documented. For complexity discussions about backends see
2141	documentation for C<ev_default_init>.	4044	the documentation for C<ev_default_init>.
		4045
		4046	All of the following are about amortised time: If an array needs to be
		4047	extended, libev needs to realloc and move the whole array, but this
		4048	happens asymptotically rarer with higher number of elements, so O(1) might
		4049	mean that libev does a lengthy realloc operation in rare cases, but on
		4050	average it is much faster and asymptotically approaches constant time.
2142		4051
2143	=over 4	4052	=over 4
2144		4053
2145	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4054	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2146		4055
		4056	This means that, when you have a watcher that triggers in one hour and
		4057	there are 100 watchers that would trigger before that, then inserting will
		4058	have to skip roughly seven (C<ld 100>) of these watchers.
		4059
2147	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4060	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2148		4061
		4062	That means that changing a timer costs less than removing/adding them,
		4063	as only the relative motion in the event queue has to be paid for.
		4064
2149	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4065	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2150		4066
		4067	These just add the watcher into an array or at the head of a list.
		4068
2151	=item Stopping check/prepare/idle watchers: O(1)	4069	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2152		4070
2153	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))	4071	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2154		4072
		4073	These watchers are stored in lists, so they need to be walked to find the
		4074	correct watcher to remove. The lists are usually short (you don't usually
		4075	have many watchers waiting for the same fd or signal: one is typical, two
		4076	is rare).
		4077
2155	=item Finding the next timer per loop iteration: O(1)	4078	=item Finding the next timer in each loop iteration: O(1)
		4079
		4080	By virtue of using a binary or 4-heap, the next timer is always found at a
		4081	fixed position in the storage array.
2156		4082
2157	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4083	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2158		4084
2159	=item Activating one watcher: O(1)	4085	A change means an I/O watcher gets started or stopped, which requires
		4086	libev to recalculate its status (and possibly tell the kernel, depending
		4087	on backend and whether C<ev_io_set> was used).
		4088
		4089	=item Activating one watcher (putting it into the pending state): O(1)
		4090
		4091	=item Priority handling: O(number_of_priorities)
		4092
		4093	Priorities are implemented by allocating some space for each
		4094	priority. When doing priority-based operations, libev usually has to
		4095	linearly search all the priorities, but starting/stopping and activating
		4096	watchers becomes O(1) with respect to priority handling.
		4097
		4098	=item Sending an ev_async: O(1)
		4099
		4100	=item Processing ev_async_send: O(number_of_async_watchers)
		4101
		4102	=item Processing signals: O(max_signal_number)
		4103
		4104	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4105	calls in the current loop iteration. Checking for async and signal events
		4106	involves iterating over all running async watchers or all signal numbers.
2160		4107
2161	=back	4108	=back
2162		4109
2163		4110
		4111	=head1 GLOSSARY
		4112
		4113	=over 4
		4114
		4115	=item active
		4116
		4117	A watcher is active as long as it has been started (has been attached to
		4118	an event loop) but not yet stopped (disassociated from the event loop).
		4119
		4120	=item application
		4121
		4122	In this document, an application is whatever is using libev.
		4123
		4124	=item callback
		4125
		4126	The address of a function that is called when some event has been
		4127	detected. Callbacks are being passed the event loop, the watcher that
		4128	received the event, and the actual event bitset.
		4129
		4130	=item callback invocation
		4131
		4132	The act of calling the callback associated with a watcher.
		4133
		4134	=item event
		4135
		4136	A change of state of some external event, such as data now being available
		4137	for reading on a file descriptor, time having passed or simply not having
		4138	any other events happening anymore.
		4139
		4140	In libev, events are represented as single bits (such as C<EV_READ> or
		4141	C<EV_TIMEOUT>).
		4142
		4143	=item event library
		4144
		4145	A software package implementing an event model and loop.
		4146
		4147	=item event loop
		4148
		4149	An entity that handles and processes external events and converts them
		4150	into callback invocations.
		4151
		4152	=item event model
		4153
		4154	The model used to describe how an event loop handles and processes
		4155	watchers and events.
		4156
		4157	=item pending
		4158
		4159	A watcher is pending as soon as the corresponding event has been detected,
		4160	and stops being pending as soon as the watcher will be invoked or its
		4161	pending status is explicitly cleared by the application.
		4162
		4163	A watcher can be pending, but not active. Stopping a watcher also clears
		4164	its pending status.
		4165
		4166	=item real time
		4167
		4168	The physical time that is observed. It is apparently strictly monotonic :)
		4169
		4170	=item wall-clock time
		4171
		4172	The time and date as shown on clocks. Unlike real time, it can actually
		4173	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4174	clock.
		4175
		4176	=item watcher
		4177
		4178	A data structure that describes interest in certain events. Watchers need
		4179	to be started (attached to an event loop) before they can receive events.
		4180
		4181	=item watcher invocation
		4182
		4183	The act of calling the callback associated with a watcher.
		4184
		4185	=back
		4186
2164	=head1 AUTHOR	4187	=head1 AUTHOR
2165		4188
2166	Marc Lehmann <libev@schmorp.de>.	4189	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2167		4190

Diff Legend

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