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Revision 1.30 by root, Fri Nov 23 04:36:03 2007 UTC vs.
Revision 1.172 by root, Wed Aug 6 07:01:25 2008 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
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_<type>
		16	ev_io stdin_watcher;
		17	ev_timer timeout_watcher;
		18
		19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
		21	static void
		22	stdin_cb (EV_P_ struct ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	struct ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
8		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	108	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	117	to the C<double> type in C, and when you need to do any calculations on
		118	it, you should treat it as some floating point value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 ERROR HANDLING
		123
		124	Libev knows three classes of errors: operating system errors, usage errors
		125	and internal errors (bugs).
		126
		127	When libev catches an operating system error it cannot handle (for example
		128	a system call indicating a condition libev cannot fix), it calls the callback
		129	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		130	abort. The default is to print a diagnostic message and to call C<abort
		131	()>.
		132
		133	When libev detects a usage error such as a negative timer interval, then
		134	it will print a diagnostic message and abort (via the C<assert> mechanism,
		135	so C<NDEBUG> will disable this checking): these are programming errors in
		136	the libev caller and need to be fixed there.
		137
		138	Libev also has a few internal error-checking C<assert>ions, and also has
		139	extensive consistency checking code. These do not trigger under normal
		140	circumstances, as they indicate either a bug in libev or worse.
		141
51		142
52	=head1 GLOBAL FUNCTIONS	143	=head1 GLOBAL FUNCTIONS
53		144
54	These functions can be called anytime, even before initialising the	145	These functions can be called anytime, even before initialising the
55	library in any way.	146	library in any way.
…		…
60		151
61	Returns the current time as libev would use it. Please note that the	152	Returns the current time as libev would use it. Please note that the
62	C<ev_now> function is usually faster and also often returns the timestamp	153	C<ev_now> function is usually faster and also often returns the timestamp
63	you actually want to know.	154	you actually want to know.
64		155
		156	=item ev_sleep (ev_tstamp interval)
		157
		158	Sleep for the given interval: The current thread will be blocked until
		159	either it is interrupted or the given time interval has passed. Basically
		160	this is a sub-second-resolution C<sleep ()>.
		161
65	=item int ev_version_major ()	162	=item int ev_version_major ()
66		163
67	=item int ev_version_minor ()	164	=item int ev_version_minor ()
68		165
69	You can find out the major and minor version numbers of the library	166	You can find out the major and minor ABI version numbers of the library
70	you linked against by calling the functions C<ev_version_major> and	167	you linked against by calling the functions C<ev_version_major> and
71	C<ev_version_minor>. If you want, you can compare against the global	168	C<ev_version_minor>. If you want, you can compare against the global
72	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	169	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
73	version of the library your program was compiled against.	170	version of the library your program was compiled against.
74		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
75	Usually, it's a good idea to terminate if the major versions mismatch,	175	Usually, it's a good idea to terminate if the major versions mismatch,
76	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
77	compatible to older versions, so a larger minor version alone is usually	177	compatible to older versions, so a larger minor version alone is usually
78	not a problem.	178	not a problem.
79		179
		180	Example: Make sure we haven't accidentally been linked against the wrong
		181	version.
		182
		183	assert (("libev version mismatch",
		184	ev_version_major () == EV_VERSION_MAJOR
		185	&& ev_version_minor () >= EV_VERSION_MINOR));
		186
		187	=item unsigned int ev_supported_backends ()
		188
		189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		190	value) compiled into this binary of libev (independent of their
		191	availability on the system you are running on). See C<ev_default_loop> for
		192	a description of the set values.
		193
		194	Example: make sure we have the epoll method, because yeah this is cool and
		195	a must have and can we have a torrent of it please!!!11
		196
		197	assert (("sorry, no epoll, no sex",
		198	ev_supported_backends () & EVBACKEND_EPOLL));
		199
		200	=item unsigned int ev_recommended_backends ()
		201
		202	Return the set of all backends compiled into this binary of libev and also
		203	recommended for this platform. This set is often smaller than the one
		204	returned by C<ev_supported_backends>, as for example kqueue is broken on
		205	most BSDs and will not be auto-detected unless you explicitly request it
		206	(assuming you know what you are doing). This is the set of backends that
		207	libev will probe for if you specify no backends explicitly.
		208
		209	=item unsigned int ev_embeddable_backends ()
		210
		211	Returns the set of backends that are embeddable in other event loops. This
		212	is the theoretical, all-platform, value. To find which backends
		213	might be supported on the current system, you would need to look at
		214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		215	recommended ones.
		216
		217	See the description of C<ev_embed> watchers for more info.
		218
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
81		220
82	Sets the allocation function to use (the prototype is similar to the	221	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
84	and free memory (no surprises here). If it returns zero when memory	223	used to allocate and free memory (no surprises here). If it returns zero
85	needs to be allocated, the library might abort or take some potentially	224	when memory needs to be allocated (C<size != 0>), the library might abort
86	destructive action. The default is your system realloc function.	225	or take some potentially destructive action.
		226
		227	Since some systems (at least OpenBSD and Darwin) fail to implement
		228	correct C<realloc> semantics, libev will use a wrapper around the system
		229	C<realloc> and C<free> functions by default.
87		230
88	You could override this function in high-availability programs to, say,	231	You could override this function in high-availability programs to, say,
89	free some memory if it cannot allocate memory, to use a special allocator,	232	free some memory if it cannot allocate memory, to use a special allocator,
90	or even to sleep a while and retry until some memory is available.	233	or even to sleep a while and retry until some memory is available.
91		234
		235	Example: Replace the libev allocator with one that waits a bit and then
		236	retries (example requires a standards-compliant C<realloc>).
		237
		238	static void *
		239	persistent_realloc (void *ptr, size_t size)
		240	{
		241	for (;;)
		242	{
		243	void *newptr = realloc (ptr, size);
		244
		245	if (newptr)
		246	return newptr;
		247
		248	sleep (60);
		249	}
		250	}
		251
		252	...
		253	ev_set_allocator (persistent_realloc);
		254
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg));
93		256
94	Set the callback function to call on a retryable syscall error (such	257	Set the callback function to call on a retryable system call error (such
95	as failed select, poll, epoll_wait). The message is a printable string	258	as failed select, poll, epoll_wait). The message is a printable string
96	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
97	callback is set, then libev will expect it to remedy the sitution, no	260	callback is set, then libev will expect it to remedy the situation, no
98	matter what, when it returns. That is, libev will generally retry the	261	matter what, when it returns. That is, libev will generally retry the
99	requested operation, or, if the condition doesn't go away, do bad stuff	262	requested operation, or, if the condition doesn't go away, do bad stuff
100	(such as abort).	263	(such as abort).
101		264
		265	Example: This is basically the same thing that libev does internally, too.
		266
		267	static void
		268	fatal_error (const char *msg)
		269	{
		270	perror (msg);
		271	abort ();
		272	}
		273
		274	...
		275	ev_set_syserr_cb (fatal_error);
		276
102	=back	277	=back
103		278
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		280
106	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<struct ev_loop *>. The library knows two
107	types of such loops, the I<default> loop, which supports signals and child	282	types of such loops, the I<default> loop, which supports signals and child
108	events, and dynamically created loops which do not.	283	events, and dynamically created loops which do not.
109		284
110	If you use threads, a common model is to run the default event loop
111	in your main thread (or in a separate thread) and for each thread you
112	create, you also create another event loop. Libev itself does no locking
113	whatsoever, so if you mix calls to the same event loop in different
114	threads, make sure you lock (this is usually a bad idea, though, even if
115	done correctly, because it's hideous and inefficient).
116
117	=over 4	285	=over 4
118		286
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	287	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		288
121	This will initialise the default event loop if it hasn't been initialised	289	This will initialise the default event loop if it hasn't been initialised
122	yet and return it. If the default loop could not be initialised, returns	290	yet and return it. If the default loop could not be initialised, returns
123	false. If it already was initialised it simply returns it (and ignores the	291	false. If it already was initialised it simply returns it (and ignores the
124	flags).	292	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		293
126	If you don't know what event loop to use, use the one returned from this	294	If you don't know what event loop to use, use the one returned from this
127	function.	295	function.
128		296
		297	Note that this function is I<not> thread-safe, so if you want to use it
		298	from multiple threads, you have to lock (note also that this is unlikely,
		299	as loops cannot bes hared easily between threads anyway).
		300
		301	The default loop is the only loop that can handle C<ev_signal> and
		302	C<ev_child> watchers, and to do this, it always registers a handler
		303	for C<SIGCHLD>. If this is a problem for your application you can either
		304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		306	C<ev_default_init>.
		307
129	The flags argument can be used to specify special behaviour or specific	308	The flags argument can be used to specify special behaviour or specific
130	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	309	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		310
132	It supports the following flags:	311	The following flags are supported:
133		312
134	=over 4	313	=over 4
135		314
136	=item C<EVFLAG_AUTO>	315	=item C<EVFLAG_AUTO>
137		316
138	The default flags value. Use this if you have no clue (it's the right	317	The default flags value. Use this if you have no clue (it's the right
139	thing, believe me).	318	thing, believe me).
140		319
141	=item C<EVFLAG_NOENV>	320	=item C<EVFLAG_NOENV>
142		321
143	If this flag bit is ored into the flag value (or the program runs setuid	322	If this flag bit is or'ed into the flag value (or the program runs setuid
144	or setgid) then libev will I<not> look at the environment variable	323	or setgid) then libev will I<not> look at the environment variable
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	override the flags completely if it is found in the environment. This is	325	override the flags completely if it is found in the environment. This is
147	useful to try out specific backends to test their performance, or to work	326	useful to try out specific backends to test their performance, or to work
148	around bugs.	327	around bugs.
149		328
		329	=item C<EVFLAG_FORKCHECK>
		330
		331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		332	a fork, you can also make libev check for a fork in each iteration by
		333	enabling this flag.
		334
		335	This works by calling C<getpid ()> on every iteration of the loop,
		336	and thus this might slow down your event loop if you do a lot of loop
		337	iterations and little real work, but is usually not noticeable (on my
		338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		339	without a system call and thus I<very> fast, but my GNU/Linux system also has
		340	C<pthread_atfork> which is even faster).
		341
		342	The big advantage of this flag is that you can forget about fork (and
		343	forget about forgetting to tell libev about forking) when you use this
		344	flag.
		345
		346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		347	environment variable.
		348
150	=item C<EVMETHOD_SELECT> (value 1, portable select backend)	349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		350
152	This is your standard select(2) backend. Not I<completely> standard, as	351	This is your standard select(2) backend. Not I<completely> standard, as
153	libev tries to roll its own fd_set with no limits on the number of fds,	352	libev tries to roll its own fd_set with no limits on the number of fds,
154	but if that fails, expect a fairly low limit on the number of fds when	353	but if that fails, expect a fairly low limit on the number of fds when
155	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	354	using this backend. It doesn't scale too well (O(highest_fd)), but its
156	the fastest backend for a low number of fds.	355	usually the fastest backend for a low number of (low-numbered :) fds.
157		356
		357	To get good performance out of this backend you need a high amount of
		358	parallelism (most of the file descriptors should be busy). If you are
		359	writing a server, you should C<accept ()> in a loop to accept as many
		360	connections as possible during one iteration. You might also want to have
		361	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		362	readiness notifications you get per iteration.
		363
158	=item C<EVMETHOD_POLL> (value 2, poll backend, available everywhere except on windows)	364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
159		365
160	And this is your standard poll(2) backend. It's more complicated than	366	And this is your standard poll(2) backend. It's more complicated
161	select, but handles sparse fds better and has no artificial limit on the	367	than select, but handles sparse fds better and has no artificial
162	number of fds you can use (except it will slow down considerably with a	368	limit on the number of fds you can use (except it will slow down
163	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	369	considerably with a lot of inactive fds). It scales similarly to select,
		370	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		371	performance tips.
164		372
165	=item C<EVMETHOD_EPOLL> (value 4, Linux)	373	=item C<EVBACKEND_EPOLL> (value 4, Linux)
166		374
167	For few fds, this backend is a bit little slower than poll and select,	375	For few fds, this backend is a bit little slower than poll and select,
168	but it scales phenomenally better. While poll and select usually scale like	376	but it scales phenomenally better. While poll and select usually scale
169	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	377	like O(total_fds) where n is the total number of fds (or the highest fd),
170	either O(1) or O(active_fds).	378	epoll scales either O(1) or O(active_fds). The epoll design has a number
		379	of shortcomings, such as silently dropping events in some hard-to-detect
		380	cases and requiring a system call per fd change, no fork support and bad
		381	support for dup.
171		382
172	While stopping and starting an I/O watcher in the same iteration will	383	While stopping, setting and starting an I/O watcher in the same iteration
173	result in some caching, there is still a syscall per such incident	384	will result in some caching, there is still a system call per such incident
174	(because the fd could point to a different file description now), so its	385	(because the fd could point to a different file description now), so its
175	best to avoid that. Also, dup()ed file descriptors might not work very	386	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
176	well if you register events for both fds.	387	very well if you register events for both fds.
177		388
		389	Please note that epoll sometimes generates spurious notifications, so you
		390	need to use non-blocking I/O or other means to avoid blocking when no data
		391	(or space) is available.
		392
		393	Best performance from this backend is achieved by not unregistering all
		394	watchers for a file descriptor until it has been closed, if possible, i.e.
		395	keep at least one watcher active per fd at all times.
		396
		397	While nominally embeddable in other event loops, this feature is broken in
		398	all kernel versions tested so far.
		399
178	=item C<EVMETHOD_KQUEUE> (value 8, most BSD clones)	400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
179		401
180	Kqueue deserves special mention, as at the time of this writing, it	402	Kqueue deserves special mention, as at the time of this writing, it
181	was broken on all BSDs except NetBSD (usually it doesn't work with	403	was broken on all BSDs except NetBSD (usually it doesn't work reliably
182	anything but sockets and pipes, except on Darwin, where of course its	404	with anything but sockets and pipes, except on Darwin, where of course
183	completely useless). For this reason its not being "autodetected" unless	405	it's completely useless). For this reason it's not being "auto-detected"
184	you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).	406	unless you explicitly specify it explicitly in the flags (i.e. using
		407	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		408	system like NetBSD.
		409
		410	You still can embed kqueue into a normal poll or select backend and use it
		411	only for sockets (after having made sure that sockets work with kqueue on
		412	the target platform). See C<ev_embed> watchers for more info.
185		413
186	It scales in the same way as the epoll backend, but the interface to the	414	It scales in the same way as the epoll backend, but the interface to the
187	kernel is more efficient (which says nothing about its actual speed, of	415	kernel is more efficient (which says nothing about its actual speed, of
188	course). While starting and stopping an I/O watcher does not cause an	416	course). While stopping, setting and starting an I/O watcher does never
189	extra syscall as with epoll, it still adds up to four event changes per	417	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
190	incident, so its best to avoid that.	418	two event changes per incident, support for C<fork ()> is very bad and it
		419	drops fds silently in similarly hard-to-detect cases.
191		420
		421	This backend usually performs well under most conditions.
		422
		423	While nominally embeddable in other event loops, this doesn't work
		424	everywhere, so you might need to test for this. And since it is broken
		425	almost everywhere, you should only use it when you have a lot of sockets
		426	(for which it usually works), by embedding it into another event loop
		427	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		428	sockets.
		429
192	=item C<EVMETHOD_DEVPOLL> (value 16, Solaris 8)	430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
193		431
194	This is not implemented yet (and might never be).	432	This is not implemented yet (and might never be, unless you send me an
		433	implementation). According to reports, C</dev/poll> only supports sockets
		434	and is not embeddable, which would limit the usefulness of this backend
		435	immensely.
195		436
196	=item C<EVMETHOD_PORT> (value 32, Solaris 10)	437	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
197		438
198	This uses the Solaris 10 port mechanism. As with everything on Solaris,	439	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
199	it's really slow, but it still scales very well (O(active_fds)).	440	it's really slow, but it still scales very well (O(active_fds)).
200		441
		442	Please note that Solaris event ports can deliver a lot of spurious
		443	notifications, so you need to use non-blocking I/O or other means to avoid
		444	blocking when no data (or space) is available.
		445
		446	While this backend scales well, it requires one system call per active
		447	file descriptor per loop iteration. For small and medium numbers of file
		448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		449	might perform better.
		450
		451	On the positive side, ignoring the spurious readiness notifications, this
		452	backend actually performed to specification in all tests and is fully
		453	embeddable, which is a rare feat among the OS-specific backends.
		454
201	=item C<EVMETHOD_ALL>	455	=item C<EVBACKEND_ALL>
202		456
203	Try all backends (even potentially broken ones that wouldn't be tried	457	Try all backends (even potentially broken ones that wouldn't be tried
204	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	458	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
205	C<EVMETHOD_ALL & ~EVMETHOD_KQUEUE>.	459	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		460
		461	It is definitely not recommended to use this flag.
206		462
207	=back	463	=back
208		464
209	If one or more of these are ored into the flags value, then only these	465	If one or more of these are or'ed into the flags value, then only these
210	backends will be tried (in the reverse order as given here). If none are	466	backends will be tried (in the reverse order as listed here). If none are
211	specified, most compiled-in backend will be tried, usually in reverse	467	specified, all backends in C<ev_recommended_backends ()> will be tried.
212	order of their flag values :)	468
		469	The most typical usage is like this:
		470
		471	if (!ev_default_loop (0))
		472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		473
		474	Restrict libev to the select and poll backends, and do not allow
		475	environment settings to be taken into account:
		476
		477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		478
		479	Use whatever libev has to offer, but make sure that kqueue is used if
		480	available (warning, breaks stuff, best use only with your own private
		481	event loop and only if you know the OS supports your types of fds):
		482
		483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
213		484
214	=item struct ev_loop *ev_loop_new (unsigned int flags)	485	=item struct ev_loop *ev_loop_new (unsigned int flags)
215		486
216	Similar to C<ev_default_loop>, but always creates a new event loop that is	487	Similar to C<ev_default_loop>, but always creates a new event loop that is
217	always distinct from the default loop. Unlike the default loop, it cannot	488	always distinct from the default loop. Unlike the default loop, it cannot
218	handle signal and child watchers, and attempts to do so will be greeted by	489	handle signal and child watchers, and attempts to do so will be greeted by
219	undefined behaviour (or a failed assertion if assertions are enabled).	490	undefined behaviour (or a failed assertion if assertions are enabled).
220		491
		492	Note that this function I<is> thread-safe, and the recommended way to use
		493	libev with threads is indeed to create one loop per thread, and using the
		494	default loop in the "main" or "initial" thread.
		495
		496	Example: Try to create a event loop that uses epoll and nothing else.
		497
		498	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		499	if (!epoller)
		500	fatal ("no epoll found here, maybe it hides under your chair");
		501
221	=item ev_default_destroy ()	502	=item ev_default_destroy ()
222		503
223	Destroys the default loop again (frees all memory and kernel state	504	Destroys the default loop again (frees all memory and kernel state
224	etc.). This stops all registered event watchers (by not touching them in	505	etc.). None of the active event watchers will be stopped in the normal
225	any way whatsoever, although you cannot rely on this :).	506	sense, so e.g. C<ev_is_active> might still return true. It is your
		507	responsibility to either stop all watchers cleanly yourself I<before>
		508	calling this function, or cope with the fact afterwards (which is usually
		509	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		510	for example).
		511
		512	Note that certain global state, such as signal state, will not be freed by
		513	this function, and related watchers (such as signal and child watchers)
		514	would need to be stopped manually.
		515
		516	In general it is not advisable to call this function except in the
		517	rare occasion where you really need to free e.g. the signal handling
		518	pipe fds. If you need dynamically allocated loops it is better to use
		519	C<ev_loop_new> and C<ev_loop_destroy>).
226		520
227	=item ev_loop_destroy (loop)	521	=item ev_loop_destroy (loop)
228		522
229	Like C<ev_default_destroy>, but destroys an event loop created by an	523	Like C<ev_default_destroy>, but destroys an event loop created by an
230	earlier call to C<ev_loop_new>.	524	earlier call to C<ev_loop_new>.
231		525
232	=item ev_default_fork ()	526	=item ev_default_fork ()
233		527
		528	This function sets a flag that causes subsequent C<ev_loop> iterations
234	This function reinitialises the kernel state for backends that have	529	to reinitialise the kernel state for backends that have one. Despite the
235	one. Despite the name, you can call it anytime, but it makes most sense	530	name, you can call it anytime, but it makes most sense after forking, in
236	after forking, in either the parent or child process (or both, but that	531	the child process (or both child and parent, but that again makes little
237	again makes little sense).	532	sense). You I<must> call it in the child before using any of the libev
		533	functions, and it will only take effect at the next C<ev_loop> iteration.
238		534
239	You I<must> call this function in the child process after forking if and	535	On the other hand, you only need to call this function in the child
240	only if you want to use the event library in both processes. If you just	536	process if and only if you want to use the event library in the child. If
241	fork+exec, you don't have to call it.	537	you just fork+exec, you don't have to call it at all.
242		538
243	The function itself is quite fast and it's usually not a problem to call	539	The function itself is quite fast and it's usually not a problem to call
244	it just in case after a fork. To make this easy, the function will fit in	540	it just in case after a fork. To make this easy, the function will fit in
245	quite nicely into a call to C<pthread_atfork>:	541	quite nicely into a call to C<pthread_atfork>:
246		542
…		…
250		546
251	Like C<ev_default_fork>, but acts on an event loop created by	547	Like C<ev_default_fork>, but acts on an event loop created by
252	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	548	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
253	after fork, and how you do this is entirely your own problem.	549	after fork, and how you do this is entirely your own problem.
254		550
		551	=item int ev_is_default_loop (loop)
		552
		553	Returns true when the given loop actually is the default loop, false otherwise.
		554
		555	=item unsigned int ev_loop_count (loop)
		556
		557	Returns the count of loop iterations for the loop, which is identical to
		558	the number of times libev did poll for new events. It starts at C<0> and
		559	happily wraps around with enough iterations.
		560
		561	This value can sometimes be useful as a generation counter of sorts (it
		562	"ticks" the number of loop iterations), as it roughly corresponds with
		563	C<ev_prepare> and C<ev_check> calls.
		564
255	=item unsigned int ev_method (loop)	565	=item unsigned int ev_backend (loop)
256		566
257	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
258	use.	568	use.
259		569
260	=item ev_tstamp ev_now (loop)	570	=item ev_tstamp ev_now (loop)
261		571
262	Returns the current "event loop time", which is the time the event loop	572	Returns the current "event loop time", which is the time the event loop
263	got events and started processing them. This timestamp does not change	573	received events and started processing them. This timestamp does not
264	as long as callbacks are being processed, and this is also the base time	574	change as long as callbacks are being processed, and this is also the base
265	used for relative timers. You can treat it as the timestamp of the event	575	time used for relative timers. You can treat it as the timestamp of the
266	occuring (or more correctly, the mainloop finding out about it).	576	event occurring (or more correctly, libev finding out about it).
267		577
268	=item ev_loop (loop, int flags)	578	=item ev_loop (loop, int flags)
269		579
270	Finally, this is it, the event handler. This function usually is called	580	Finally, this is it, the event handler. This function usually is called
271	after you initialised all your watchers and you want to start handling	581	after you initialised all your watchers and you want to start handling
272	events.	582	events.
273		583
274	If the flags argument is specified as 0, it will not return until either	584	If the flags argument is specified as C<0>, it will not return until
275	no event watchers are active anymore or C<ev_unloop> was called.	585	either no event watchers are active anymore or C<ev_unloop> was called.
		586
		587	Please note that an explicit C<ev_unloop> is usually better than
		588	relying on all watchers to be stopped when deciding when a program has
		589	finished (especially in interactive programs), but having a program that
		590	automatically loops as long as it has to and no longer by virtue of
		591	relying on its watchers stopping correctly is a thing of beauty.
276		592
277	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	593	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
278	those events and any outstanding ones, but will not block your process in	594	those events and any outstanding ones, but will not block your process in
279	case there are no events and will return after one iteration of the loop.	595	case there are no events and will return after one iteration of the loop.
280		596
281	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	597	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
282	neccessary) and will handle those and any outstanding ones. It will block	598	necessary) and will handle those and any outstanding ones. It will block
283	your process until at least one new event arrives, and will return after	599	your process until at least one new event arrives, and will return after
284	one iteration of the loop.	600	one iteration of the loop. This is useful if you are waiting for some
		601	external event in conjunction with something not expressible using other
		602	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		603	usually a better approach for this kind of thing.
285		604
286	This flags value could be used to implement alternative looping
287	constructs, but the C<prepare> and C<check> watchers provide a better and
288	more generic mechanism.
289
290	Here are the gory details of what ev_loop does:	605	Here are the gory details of what C<ev_loop> does:
291		606
292	1. If there are no active watchers (reference count is zero), return.	607	- Before the first iteration, call any pending watchers.
		608	* If EVFLAG_FORKCHECK was used, check for a fork.
		609	- If a fork was detected (by any means), queue and call all fork watchers.
293	2. Queue and immediately call all prepare watchers.	610	- Queue and call all prepare watchers.
294	3. If we have been forked, recreate the kernel state.	611	- If we have been forked, detach and recreate the kernel state
		612	as to not disturb the other process.
295	4. Update the kernel state with all outstanding changes.	613	- Update the kernel state with all outstanding changes.
296	5. Update the "event loop time".	614	- Update the "event loop time" (ev_now ()).
297	6. Calculate for how long to block.	615	- Calculate for how long to sleep or block, if at all
		616	(active idle watchers, EVLOOP_NONBLOCK or not having
		617	any active watchers at all will result in not sleeping).
		618	- Sleep if the I/O and timer collect interval say so.
298	7. Block the process, waiting for events.	619	- Block the process, waiting for any events.
		620	- Queue all outstanding I/O (fd) events.
299	8. Update the "event loop time" and do time jump handling.	621	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
300	9. Queue all outstanding timers.	622	- Queue all outstanding timers.
301	10. Queue all outstanding periodics.	623	- Queue all outstanding periodics.
302	11. If no events are pending now, queue all idle watchers.	624	- Unless any events are pending now, queue all idle watchers.
303	12. Queue all check watchers.	625	- Queue all check watchers.
304	13. Call all queued watchers in reverse order (i.e. check watchers first).	626	- Call all queued watchers in reverse order (i.e. check watchers first).
		627	Signals and child watchers are implemented as I/O watchers, and will
		628	be handled here by queueing them when their watcher gets executed.
305	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	629	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
306	was used, return, otherwise continue with step #1.	630	were used, or there are no active watchers, return, otherwise
		631	continue with step *.
		632
		633	Example: Queue some jobs and then loop until no events are outstanding
		634	anymore.
		635
		636	... queue jobs here, make sure they register event watchers as long
		637	... as they still have work to do (even an idle watcher will do..)
		638	ev_loop (my_loop, 0);
		639	... jobs done or somebody called unloop. yeah!
307		640
308	=item ev_unloop (loop, how)	641	=item ev_unloop (loop, how)
309		642
310	Can be used to make a call to C<ev_loop> return early (but only after it	643	Can be used to make a call to C<ev_loop> return early (but only after it
311	has processed all outstanding events). The C<how> argument must be either	644	has processed all outstanding events). The C<how> argument must be either
312	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	645	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
313	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	646	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		647
		648	This "unloop state" will be cleared when entering C<ev_loop> again.
314		649
315	=item ev_ref (loop)	650	=item ev_ref (loop)
316		651
317	=item ev_unref (loop)	652	=item ev_unref (loop)
318		653
…		…
323	returning, ev_unref() after starting, and ev_ref() before stopping it. For	658	returning, ev_unref() after starting, and ev_ref() before stopping it. For
324	example, libev itself uses this for its internal signal pipe: It is not	659	example, libev itself uses this for its internal signal pipe: It is not
325	visible to the libev user and should not keep C<ev_loop> from exiting if	660	visible to the libev user and should not keep C<ev_loop> from exiting if
326	no event watchers registered by it are active. It is also an excellent	661	no event watchers registered by it are active. It is also an excellent
327	way to do this for generic recurring timers or from within third-party	662	way to do this for generic recurring timers or from within third-party
328	libraries. Just remember to I<unref after start> and I<ref before stop>.	663	libraries. Just remember to I<unref after start> and I<ref before stop>
		664	(but only if the watcher wasn't active before, or was active before,
		665	respectively).
		666
		667	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		668	running when nothing else is active.
		669
		670	struct ev_signal exitsig;
		671	ev_signal_init (&exitsig, sig_cb, SIGINT);
		672	ev_signal_start (loop, &exitsig);
		673	evf_unref (loop);
		674
		675	Example: For some weird reason, unregister the above signal handler again.
		676
		677	ev_ref (loop);
		678	ev_signal_stop (loop, &exitsig);
		679
		680	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		681
		682	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		683
		684	These advanced functions influence the time that libev will spend waiting
		685	for events. Both time intervals are by default C<0>, meaning that libev
		686	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		687	latency.
		688
		689	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		690	allows libev to delay invocation of I/O and timer/periodic callbacks
		691	to increase efficiency of loop iterations (or to increase power-saving
		692	opportunities).
		693
		694	The background is that sometimes your program runs just fast enough to
		695	handle one (or very few) event(s) per loop iteration. While this makes
		696	the program responsive, it also wastes a lot of CPU time to poll for new
		697	events, especially with backends like C<select ()> which have a high
		698	overhead for the actual polling but can deliver many events at once.
		699
		700	By setting a higher I<io collect interval> you allow libev to spend more
		701	time collecting I/O events, so you can handle more events per iteration,
		702	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		703	C<ev_timer>) will be not affected. Setting this to a non-null value will
		704	introduce an additional C<ev_sleep ()> call into most loop iterations.
		705
		706	Likewise, by setting a higher I<timeout collect interval> you allow libev
		707	to spend more time collecting timeouts, at the expense of increased
		708	latency (the watcher callback will be called later). C<ev_io> watchers
		709	will not be affected. Setting this to a non-null value will not introduce
		710	any overhead in libev.
		711
		712	Many (busy) programs can usually benefit by setting the I/O collect
		713	interval to a value near C<0.1> or so, which is often enough for
		714	interactive servers (of course not for games), likewise for timeouts. It
		715	usually doesn't make much sense to set it to a lower value than C<0.01>,
		716	as this approaches the timing granularity of most systems.
		717
		718	Setting the I<timeout collect interval> can improve the opportunity for
		719	saving power, as the program will "bundle" timer callback invocations that
		720	are "near" in time together, by delaying some, thus reducing the number of
		721	times the process sleeps and wakes up again. Another useful technique to
		722	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		723	they fire on, say, one-second boundaries only.
		724
		725	=item ev_loop_verify (loop)
		726
		727	This function only does something when C<EV_VERIFY> support has been
		728	compiled in. It tries to go through all internal structures and checks
		729	them for validity. If anything is found to be inconsistent, it will print
		730	an error message to standard error and call C<abort ()>.
		731
		732	This can be used to catch bugs inside libev itself: under normal
		733	circumstances, this function will never abort as of course libev keeps its
		734	data structures consistent.
329		735
330	=back	736	=back
		737
331		738
332	=head1 ANATOMY OF A WATCHER	739	=head1 ANATOMY OF A WATCHER
333		740
334	A watcher is a structure that you create and register to record your	741	A watcher is a structure that you create and register to record your
335	interest in some event. For instance, if you want to wait for STDIN to	742	interest in some event. For instance, if you want to wait for STDIN to
336	become readable, you would create an C<ev_io> watcher for that:	743	become readable, you would create an C<ev_io> watcher for that:
337		744
338	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	745	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
339	{	746	{
340	ev_io_stop (w);	747	ev_io_stop (w);
341	ev_unloop (loop, EVUNLOOP_ALL);	748	ev_unloop (loop, EVUNLOOP_ALL);
342	}	749	}
343		750
344	struct ev_loop *loop = ev_default_loop (0);	751	struct ev_loop *loop = ev_default_loop (0);
345	struct ev_io stdin_watcher;	752	struct ev_io stdin_watcher;
346	ev_init (&stdin_watcher, my_cb);	753	ev_init (&stdin_watcher, my_cb);
347	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	754	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
348	ev_io_start (loop, &stdin_watcher);	755	ev_io_start (loop, &stdin_watcher);
349	ev_loop (loop, 0);	756	ev_loop (loop, 0);
350		757
351	As you can see, you are responsible for allocating the memory for your	758	As you can see, you are responsible for allocating the memory for your
352	watcher structures (and it is usually a bad idea to do this on the stack,	759	watcher structures (and it is usually a bad idea to do this on the stack,
353	although this can sometimes be quite valid).	760	although this can sometimes be quite valid).
354		761
355	Each watcher structure must be initialised by a call to C<ev_init	762	Each watcher structure must be initialised by a call to C<ev_init
356	(watcher *, callback)>, which expects a callback to be provided. This	763	(watcher *, callback)>, which expects a callback to be provided. This
357	callback gets invoked each time the event occurs (or, in the case of io	764	callback gets invoked each time the event occurs (or, in the case of I/O
358	watchers, each time the event loop detects that the file descriptor given	765	watchers, each time the event loop detects that the file descriptor given
359	is readable and/or writable).	766	is readable and/or writable).
360		767
361	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	768	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro
362	with arguments specific to this watcher type. There is also a macro	769	with arguments specific to this watcher type. There is also a macro
…		…
368	*) >>), and you can stop watching for events at any time by calling the	775	*) >>), and you can stop watching for events at any time by calling the
369	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	776	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
370		777
371	As long as your watcher is active (has been started but not stopped) you	778	As long as your watcher is active (has been started but not stopped) you
372	must not touch the values stored in it. Most specifically you must never	779	must not touch the values stored in it. Most specifically you must never
373	reinitialise it or call its set method.	780	reinitialise it or call its C<set> macro.
374
375	You can check whether an event is active by calling the C<ev_is_active
376	(watcher *)> macro. To see whether an event is outstanding (but the
377	callback for it has not been called yet) you can use the C<ev_is_pending
378	(watcher *)> macro.
379		781
380	Each and every callback receives the event loop pointer as first, the	782	Each and every callback receives the event loop pointer as first, the
381	registered watcher structure as second, and a bitset of received events as	783	registered watcher structure as second, and a bitset of received events as
382	third argument.	784	third argument.
383		785
…		…
407	The signal specified in the C<ev_signal> watcher has been received by a thread.	809	The signal specified in the C<ev_signal> watcher has been received by a thread.
408		810
409	=item C<EV_CHILD>	811	=item C<EV_CHILD>
410		812
411	The pid specified in the C<ev_child> watcher has received a status change.	813	The pid specified in the C<ev_child> watcher has received a status change.
		814
		815	=item C<EV_STAT>
		816
		817	The path specified in the C<ev_stat> watcher changed its attributes somehow.
412		818
413	=item C<EV_IDLE>	819	=item C<EV_IDLE>
414		820
415	The C<ev_idle> watcher has determined that you have nothing better to do.	821	The C<ev_idle> watcher has determined that you have nothing better to do.
416		822
…		…
424	received events. Callbacks of both watcher types can start and stop as	830	received events. Callbacks of both watcher types can start and stop as
425	many watchers as they want, and all of them will be taken into account	831	many watchers as they want, and all of them will be taken into account
426	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	832	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
427	C<ev_loop> from blocking).	833	C<ev_loop> from blocking).
428		834
		835	=item C<EV_EMBED>
		836
		837	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		838
		839	=item C<EV_FORK>
		840
		841	The event loop has been resumed in the child process after fork (see
		842	C<ev_fork>).
		843
		844	=item C<EV_ASYNC>
		845
		846	The given async watcher has been asynchronously notified (see C<ev_async>).
		847
429	=item C<EV_ERROR>	848	=item C<EV_ERROR>
430		849
431	An unspecified error has occured, the watcher has been stopped. This might	850	An unspecified error has occurred, the watcher has been stopped. This might
432	happen because the watcher could not be properly started because libev	851	happen because the watcher could not be properly started because libev
433	ran out of memory, a file descriptor was found to be closed or any other	852	ran out of memory, a file descriptor was found to be closed or any other
434	problem. You best act on it by reporting the problem and somehow coping	853	problem. You best act on it by reporting the problem and somehow coping
435	with the watcher being stopped.	854	with the watcher being stopped.
436		855
437	Libev will usually signal a few "dummy" events together with an error,	856	Libev will usually signal a few "dummy" events together with an error,
438	for example it might indicate that a fd is readable or writable, and if	857	for example it might indicate that a fd is readable or writable, and if
439	your callbacks is well-written it can just attempt the operation and cope	858	your callbacks is well-written it can just attempt the operation and cope
440	with the error from read() or write(). This will not work in multithreaded	859	with the error from read() or write(). This will not work in multi-threaded
441	programs, though, so beware.	860	programs, though, so beware.
442		861
443	=back	862	=back
		863
		864	=head2 GENERIC WATCHER FUNCTIONS
		865
		866	In the following description, C<TYPE> stands for the watcher type,
		867	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		868
		869	=over 4
		870
		871	=item C<ev_init> (ev_TYPE *watcher, callback)
		872
		873	This macro initialises the generic portion of a watcher. The contents
		874	of the watcher object can be arbitrary (so C<malloc> will do). Only
		875	the generic parts of the watcher are initialised, you I<need> to call
		876	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		877	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		878	which rolls both calls into one.
		879
		880	You can reinitialise a watcher at any time as long as it has been stopped
		881	(or never started) and there are no pending events outstanding.
		882
		883	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		884	int revents)>.
		885
		886	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		887
		888	This macro initialises the type-specific parts of a watcher. You need to
		889	call C<ev_init> at least once before you call this macro, but you can
		890	call C<ev_TYPE_set> any number of times. You must not, however, call this
		891	macro on a watcher that is active (it can be pending, however, which is a
		892	difference to the C<ev_init> macro).
		893
		894	Although some watcher types do not have type-specific arguments
		895	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		896
		897	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		898
		899	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		900	calls into a single call. This is the most convenient method to initialise
		901	a watcher. The same limitations apply, of course.
		902
		903	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		904
		905	Starts (activates) the given watcher. Only active watchers will receive
		906	events. If the watcher is already active nothing will happen.
		907
		908	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		909
		910	Stops the given watcher again (if active) and clears the pending
		911	status. It is possible that stopped watchers are pending (for example,
		912	non-repeating timers are being stopped when they become pending), but
		913	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		914	you want to free or reuse the memory used by the watcher it is therefore a
		915	good idea to always call its C<ev_TYPE_stop> function.
		916
		917	=item bool ev_is_active (ev_TYPE *watcher)
		918
		919	Returns a true value iff the watcher is active (i.e. it has been started
		920	and not yet been stopped). As long as a watcher is active you must not modify
		921	it.
		922
		923	=item bool ev_is_pending (ev_TYPE *watcher)
		924
		925	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		926	events but its callback has not yet been invoked). As long as a watcher
		927	is pending (but not active) you must not call an init function on it (but
		928	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		929	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		930	it).
		931
		932	=item callback ev_cb (ev_TYPE *watcher)
		933
		934	Returns the callback currently set on the watcher.
		935
		936	=item ev_cb_set (ev_TYPE *watcher, callback)
		937
		938	Change the callback. You can change the callback at virtually any time
		939	(modulo threads).
		940
		941	=item ev_set_priority (ev_TYPE *watcher, priority)
		942
		943	=item int ev_priority (ev_TYPE *watcher)
		944
		945	Set and query the priority of the watcher. The priority is a small
		946	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		947	(default: C<-2>). Pending watchers with higher priority will be invoked
		948	before watchers with lower priority, but priority will not keep watchers
		949	from being executed (except for C<ev_idle> watchers).
		950
		951	This means that priorities are I<only> used for ordering callback
		952	invocation after new events have been received. This is useful, for
		953	example, to reduce latency after idling, or more often, to bind two
		954	watchers on the same event and make sure one is called first.
		955
		956	If you need to suppress invocation when higher priority events are pending
		957	you need to look at C<ev_idle> watchers, which provide this functionality.
		958
		959	You I<must not> change the priority of a watcher as long as it is active or
		960	pending.
		961
		962	The default priority used by watchers when no priority has been set is
		963	always C<0>, which is supposed to not be too high and not be too low :).
		964
		965	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		966	fine, as long as you do not mind that the priority value you query might
		967	or might not have been adjusted to be within valid range.
		968
		969	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		970
		971	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		972	C<loop> nor C<revents> need to be valid as long as the watcher callback
		973	can deal with that fact.
		974
		975	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		976
		977	If the watcher is pending, this function returns clears its pending status
		978	and returns its C<revents> bitset (as if its callback was invoked). If the
		979	watcher isn't pending it does nothing and returns C<0>.
		980
		981	=back
		982
444		983
445	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	984	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
446		985
447	Each watcher has, by default, a member C<void *data> that you can change	986	Each watcher has, by default, a member C<void *data> that you can change
448	and read at any time, libev will completely ignore it. This can be used	987	and read at any time, libev will completely ignore it. This can be used
449	to associate arbitrary data with your watcher. If you need more data and	988	to associate arbitrary data with your watcher. If you need more data and
450	don't want to allocate memory and store a pointer to it in that data	989	don't want to allocate memory and store a pointer to it in that data
451	member, you can also "subclass" the watcher type and provide your own	990	member, you can also "subclass" the watcher type and provide your own
452	data:	991	data:
453		992
454	struct my_io	993	struct my_io
455	{	994	{
456	struct ev_io io;	995	struct ev_io io;
457	int otherfd;	996	int otherfd;
458	void *somedata;	997	void *somedata;
459	struct whatever *mostinteresting;	998	struct whatever *mostinteresting;
460	}	999	}
461		1000
462	And since your callback will be called with a pointer to the watcher, you	1001	And since your callback will be called with a pointer to the watcher, you
463	can cast it back to your own type:	1002	can cast it back to your own type:
464		1003
465	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1004	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
466	{	1005	{
467	struct my_io *w = (struct my_io *)w_;	1006	struct my_io *w = (struct my_io *)w_;
468	...	1007	...
469	}	1008	}
470		1009
471	More interesting and less C-conformant ways of catsing your callback type	1010	More interesting and less C-conformant ways of casting your callback type
472	have been omitted....	1011	instead have been omitted.
		1012
		1013	Another common scenario is having some data structure with multiple
		1014	watchers:
		1015
		1016	struct my_biggy
		1017	{
		1018	int some_data;
		1019	ev_timer t1;
		1020	ev_timer t2;
		1021	}
		1022
		1023	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		1024	you need to use C<offsetof>:
		1025
		1026	#include <stddef.h>
		1027
		1028	static void
		1029	t1_cb (EV_P_ struct ev_timer *w, int revents)
		1030	{
		1031	struct my_biggy big = (struct my_biggy *
		1032	(((char *)w) - offsetof (struct my_biggy, t1));
		1033	}
		1034
		1035	static void
		1036	t2_cb (EV_P_ struct ev_timer *w, int revents)
		1037	{
		1038	struct my_biggy big = (struct my_biggy *
		1039	(((char *)w) - offsetof (struct my_biggy, t2));
		1040	}
473		1041
474		1042
475	=head1 WATCHER TYPES	1043	=head1 WATCHER TYPES
476		1044
477	This section describes each watcher in detail, but will not repeat	1045	This section describes each watcher in detail, but will not repeat
478	information given in the last section.	1046	information given in the last section. Any initialisation/set macros,
		1047	functions and members specific to the watcher type are explained.
479		1048
		1049	Members are additionally marked with either I<[read-only]>, meaning that,
		1050	while the watcher is active, you can look at the member and expect some
		1051	sensible content, but you must not modify it (you can modify it while the
		1052	watcher is stopped to your hearts content), or I<[read-write]>, which
		1053	means you can expect it to have some sensible content while the watcher
		1054	is active, but you can also modify it. Modifying it may not do something
		1055	sensible or take immediate effect (or do anything at all), but libev will
		1056	not crash or malfunction in any way.
		1057
		1058
480	=head2 C<ev_io> - is this file descriptor readable or writable	1059	=head2 C<ev_io> - is this file descriptor readable or writable?
481		1060
482	I/O watchers check whether a file descriptor is readable or writable	1061	I/O watchers check whether a file descriptor is readable or writable
483	in each iteration of the event loop (This behaviour is called	1062	in each iteration of the event loop, or, more precisely, when reading
484	level-triggering because you keep receiving events as long as the	1063	would not block the process and writing would at least be able to write
485	condition persists. Remember you can stop the watcher if you don't want to	1064	some data. This behaviour is called level-triggering because you keep
486	act on the event and neither want to receive future events).	1065	receiving events as long as the condition persists. Remember you can stop
		1066	the watcher if you don't want to act on the event and neither want to
		1067	receive future events.
487		1068
488	In general you can register as many read and/or write event watchers per	1069	In general you can register as many read and/or write event watchers per
489	fd as you want (as long as you don't confuse yourself). Setting all file	1070	fd as you want (as long as you don't confuse yourself). Setting all file
490	descriptors to non-blocking mode is also usually a good idea (but not	1071	descriptors to non-blocking mode is also usually a good idea (but not
491	required if you know what you are doing).	1072	required if you know what you are doing).
492		1073
493	You have to be careful with dup'ed file descriptors, though. Some backends
494	(the linux epoll backend is a notable example) cannot handle dup'ed file
495	descriptors correctly if you register interest in two or more fds pointing
496	to the same underlying file/socket etc. description (that is, they share
497	the same underlying "file open").
498
499	If you must do this, then force the use of a known-to-be-good backend	1074	If you must do this, then force the use of a known-to-be-good backend
500	(at the time of this writing, this includes only EVMETHOD_SELECT and	1075	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
501	EVMETHOD_POLL).	1076	C<EVBACKEND_POLL>).
		1077
		1078	Another thing you have to watch out for is that it is quite easy to
		1079	receive "spurious" readiness notifications, that is your callback might
		1080	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1081	because there is no data. Not only are some backends known to create a
		1082	lot of those (for example Solaris ports), it is very easy to get into
		1083	this situation even with a relatively standard program structure. Thus
		1084	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1085	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1086
		1087	If you cannot run the fd in non-blocking mode (for example you should not
		1088	play around with an Xlib connection), then you have to separately re-test
		1089	whether a file descriptor is really ready with a known-to-be good interface
		1090	such as poll (fortunately in our Xlib example, Xlib already does this on
		1091	its own, so its quite safe to use).
		1092
		1093	=head3 The special problem of disappearing file descriptors
		1094
		1095	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1096	descriptor (either by calling C<close> explicitly or by any other means,
		1097	such as C<dup>). The reason is that you register interest in some file
		1098	descriptor, but when it goes away, the operating system will silently drop
		1099	this interest. If another file descriptor with the same number then is
		1100	registered with libev, there is no efficient way to see that this is, in
		1101	fact, a different file descriptor.
		1102
		1103	To avoid having to explicitly tell libev about such cases, libev follows
		1104	the following policy: Each time C<ev_io_set> is being called, libev
		1105	will assume that this is potentially a new file descriptor, otherwise
		1106	it is assumed that the file descriptor stays the same. That means that
		1107	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1108	descriptor even if the file descriptor number itself did not change.
		1109
		1110	This is how one would do it normally anyway, the important point is that
		1111	the libev application should not optimise around libev but should leave
		1112	optimisations to libev.
		1113
		1114	=head3 The special problem of dup'ed file descriptors
		1115
		1116	Some backends (e.g. epoll), cannot register events for file descriptors,
		1117	but only events for the underlying file descriptions. That means when you
		1118	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1119	events for them, only one file descriptor might actually receive events.
		1120
		1121	There is no workaround possible except not registering events
		1122	for potentially C<dup ()>'ed file descriptors, or to resort to
		1123	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1124
		1125	=head3 The special problem of fork
		1126
		1127	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1128	useless behaviour. Libev fully supports fork, but needs to be told about
		1129	it in the child.
		1130
		1131	To support fork in your programs, you either have to call
		1132	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1133	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1134	C<EVBACKEND_POLL>.
		1135
		1136	=head3 The special problem of SIGPIPE
		1137
		1138	While not really specific to libev, it is easy to forget about SIGPIPE:
		1139	when reading from a pipe whose other end has been closed, your program
		1140	gets send a SIGPIPE, which, by default, aborts your program. For most
		1141	programs this is sensible behaviour, for daemons, this is usually
		1142	undesirable.
		1143
		1144	So when you encounter spurious, unexplained daemon exits, make sure you
		1145	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1146	somewhere, as that would have given you a big clue).
		1147
		1148
		1149	=head3 Watcher-Specific Functions
502		1150
503	=over 4	1151	=over 4
504		1152
505	=item ev_io_init (ev_io *, callback, int fd, int events)	1153	=item ev_io_init (ev_io *, callback, int fd, int events)
506		1154
507	=item ev_io_set (ev_io *, int fd, int events)	1155	=item ev_io_set (ev_io *, int fd, int events)
508		1156
509	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1157	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
510	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1158	receive events for and events is either C<EV_READ>, C<EV_WRITE> or
511	EV_WRITE> to receive the given events.	1159	C<EV_READ | EV_WRITE> to receive the given events.
		1160
		1161	=item int fd [read-only]
		1162
		1163	The file descriptor being watched.
		1164
		1165	=item int events [read-only]
		1166
		1167	The events being watched.
512		1168
513	=back	1169	=back
514		1170
		1171	=head3 Examples
		1172
		1173	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1174	readable, but only once. Since it is likely line-buffered, you could
		1175	attempt to read a whole line in the callback.
		1176
		1177	static void
		1178	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1179	{
		1180	ev_io_stop (loop, w);
		1181	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1182	}
		1183
		1184	...
		1185	struct ev_loop *loop = ev_default_init (0);
		1186	struct ev_io stdin_readable;
		1187	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1188	ev_io_start (loop, &stdin_readable);
		1189	ev_loop (loop, 0);
		1190
		1191
515	=head2 C<ev_timer> - relative and optionally recurring timeouts	1192	=head2 C<ev_timer> - relative and optionally repeating timeouts
516		1193
517	Timer watchers are simple relative timers that generate an event after a	1194	Timer watchers are simple relative timers that generate an event after a
518	given time, and optionally repeating in regular intervals after that.	1195	given time, and optionally repeating in regular intervals after that.
519		1196
520	The timers are based on real time, that is, if you register an event that	1197	The timers are based on real time, that is, if you register an event that
521	times out after an hour and you reset your system clock to last years	1198	times out after an hour and you reset your system clock to January last
522	time, it will still time out after (roughly) and hour. "Roughly" because	1199	year, it will still time out after (roughly) and hour. "Roughly" because
523	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1200	detecting time jumps is hard, and some inaccuracies are unavoidable (the
524	monotonic clock option helps a lot here).	1201	monotonic clock option helps a lot here).
525		1202
526	The relative timeouts are calculated relative to the C<ev_now ()>	1203	The relative timeouts are calculated relative to the C<ev_now ()>
527	time. This is usually the right thing as this timestamp refers to the time	1204	time. This is usually the right thing as this timestamp refers to the time
…		…
529	you suspect event processing to be delayed and you I<need> to base the timeout	1206	you suspect event processing to be delayed and you I<need> to base the timeout
530	on the current time, use something like this to adjust for this:	1207	on the current time, use something like this to adjust for this:
531		1208
532	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1209	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
533		1210
534	The callback is guarenteed to be invoked only when its timeout has passed,	1211	The callback is guaranteed to be invoked only after its timeout has passed,
535	but if multiple timers become ready during the same loop iteration then	1212	but if multiple timers become ready during the same loop iteration then
536	order of execution is undefined.	1213	order of execution is undefined.
537		1214
		1215	=head3 Watcher-Specific Functions and Data Members
		1216
538	=over 4	1217	=over 4
539		1218
540	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1219	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
541		1220
542	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1221	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
543		1222
544	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1223	Configure the timer to trigger after C<after> seconds. If C<repeat>
545	C<0.>, then it will automatically be stopped. If it is positive, then the	1224	is C<0.>, then it will automatically be stopped once the timeout is
546	timer will automatically be configured to trigger again C<repeat> seconds	1225	reached. If it is positive, then the timer will automatically be
547	later, again, and again, until stopped manually.	1226	configured to trigger again C<repeat> seconds later, again, and again,
		1227	until stopped manually.
548		1228
549	The timer itself will do a best-effort at avoiding drift, that is, if you	1229	The timer itself will do a best-effort at avoiding drift, that is, if
550	configure a timer to trigger every 10 seconds, then it will trigger at	1230	you configure a timer to trigger every 10 seconds, then it will normally
551	exactly 10 second intervals. If, however, your program cannot keep up with	1231	trigger at exactly 10 second intervals. If, however, your program cannot
552	the timer (because it takes longer than those 10 seconds to do stuff) the	1232	keep up with the timer (because it takes longer than those 10 seconds to
553	timer will not fire more than once per event loop iteration.	1233	do stuff) the timer will not fire more than once per event loop iteration.
554		1234
555	=item ev_timer_again (loop)	1235	=item ev_timer_again (loop, ev_timer *)
556		1236
557	This will act as if the timer timed out and restart it again if it is	1237	This will act as if the timer timed out and restart it again if it is
558	repeating. The exact semantics are:	1238	repeating. The exact semantics are:
559		1239
		1240	If the timer is pending, its pending status is cleared.
		1241
560	If the timer is started but nonrepeating, stop it.	1242	If the timer is started but non-repeating, stop it (as if it timed out).
561		1243
562	If the timer is repeating, either start it if necessary (with the repeat	1244	If the timer is repeating, either start it if necessary (with the
563	value), or reset the running timer to the repeat value.	1245	C<repeat> value), or reset the running timer to the C<repeat> value.
564		1246
565	This sounds a bit complicated, but here is a useful and typical	1247	This sounds a bit complicated, but here is a useful and typical
566	example: Imagine you have a tcp connection and you want a so-called idle	1248	example: Imagine you have a TCP connection and you want a so-called idle
567	timeout, that is, you want to be called when there have been, say, 60	1249	timeout, that is, you want to be called when there have been, say, 60
568	seconds of inactivity on the socket. The easiest way to do this is to	1250	seconds of inactivity on the socket. The easiest way to do this is to
569	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1251	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
570	time you successfully read or write some data. If you go into an idle	1252	C<ev_timer_again> each time you successfully read or write some data. If
571	state where you do not expect data to travel on the socket, you can stop	1253	you go into an idle state where you do not expect data to travel on the
572	the timer, and again will automatically restart it if need be.	1254	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1255	automatically restart it if need be.
		1256
		1257	That means you can ignore the C<after> value and C<ev_timer_start>
		1258	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1259
		1260	ev_timer_init (timer, callback, 0., 5.);
		1261	ev_timer_again (loop, timer);
		1262	...
		1263	timer->again = 17.;
		1264	ev_timer_again (loop, timer);
		1265	...
		1266	timer->again = 10.;
		1267	ev_timer_again (loop, timer);
		1268
		1269	This is more slightly efficient then stopping/starting the timer each time
		1270	you want to modify its timeout value.
		1271
		1272	=item ev_tstamp repeat [read-write]
		1273
		1274	The current C<repeat> value. Will be used each time the watcher times out
		1275	or C<ev_timer_again> is called and determines the next timeout (if any),
		1276	which is also when any modifications are taken into account.
573		1277
574	=back	1278	=back
575		1279
		1280	=head3 Examples
		1281
		1282	Example: Create a timer that fires after 60 seconds.
		1283
		1284	static void
		1285	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1286	{
		1287	.. one minute over, w is actually stopped right here
		1288	}
		1289
		1290	struct ev_timer mytimer;
		1291	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1292	ev_timer_start (loop, &mytimer);
		1293
		1294	Example: Create a timeout timer that times out after 10 seconds of
		1295	inactivity.
		1296
		1297	static void
		1298	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1299	{
		1300	.. ten seconds without any activity
		1301	}
		1302
		1303	struct ev_timer mytimer;
		1304	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1305	ev_timer_again (&mytimer); /* start timer */
		1306	ev_loop (loop, 0);
		1307
		1308	// and in some piece of code that gets executed on any "activity":
		1309	// reset the timeout to start ticking again at 10 seconds
		1310	ev_timer_again (&mytimer);
		1311
		1312
576	=head2 C<ev_periodic> - to cron or not to cron	1313	=head2 C<ev_periodic> - to cron or not to cron?
577		1314
578	Periodic watchers are also timers of a kind, but they are very versatile	1315	Periodic watchers are also timers of a kind, but they are very versatile
579	(and unfortunately a bit complex).	1316	(and unfortunately a bit complex).
580		1317
581	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1318	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
582	but on wallclock time (absolute time). You can tell a periodic watcher	1319	but on wall clock time (absolute time). You can tell a periodic watcher
583	to trigger "at" some specific point in time. For example, if you tell a	1320	to trigger after some specific point in time. For example, if you tell a
584	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1321	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
585	+ 10.>) and then reset your system clock to the last year, then it will	1322	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1323	clock to January of the previous year, then it will take more than year
586	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1324	to trigger the event (unlike an C<ev_timer>, which would still trigger
587	roughly 10 seconds later and of course not if you reset your system time	1325	roughly 10 seconds later as it uses a relative timeout).
588	again).
589		1326
590	They can also be used to implement vastly more complex timers, such as	1327	C<ev_periodic>s can also be used to implement vastly more complex timers,
591	triggering an event on eahc midnight, local time.	1328	such as triggering an event on each "midnight, local time", or other
		1329	complicated, rules.
592		1330
593	As with timers, the callback is guarenteed to be invoked only when the	1331	As with timers, the callback is guaranteed to be invoked only when the
594	time (C<at>) has been passed, but if multiple periodic timers become ready	1332	time (C<at>) has passed, but if multiple periodic timers become ready
595	during the same loop iteration then order of execution is undefined.	1333	during the same loop iteration then order of execution is undefined.
		1334
		1335	=head3 Watcher-Specific Functions and Data Members
596		1336
597	=over 4	1337	=over 4
598		1338
599	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1339	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
600		1340
…		…
603	Lots of arguments, lets sort it out... There are basically three modes of	1343	Lots of arguments, lets sort it out... There are basically three modes of
604	operation, and we will explain them from simplest to complex:	1344	operation, and we will explain them from simplest to complex:
605		1345
606	=over 4	1346	=over 4
607		1347
608	=item * absolute timer (interval = reschedule_cb = 0)	1348	=item * absolute timer (at = time, interval = reschedule_cb = 0)
609		1349
610	In this configuration the watcher triggers an event at the wallclock time	1350	In this configuration the watcher triggers an event after the wall clock
611	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1351	time C<at> has passed and doesn't repeat. It will not adjust when a time
612	that is, if it is to be run at January 1st 2011 then it will run when the	1352	jump occurs, that is, if it is to be run at January 1st 2011 then it will
613	system time reaches or surpasses this time.	1353	run when the system time reaches or surpasses this time.
614		1354
615	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1355	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
616		1356
617	In this mode the watcher will always be scheduled to time out at the next	1357	In this mode the watcher will always be scheduled to time out at the next
618	C<at + N * interval> time (for some integer N) and then repeat, regardless	1358	C<at + N * interval> time (for some integer N, which can also be negative)
619	of any time jumps.	1359	and then repeat, regardless of any time jumps.
620		1360
621	This can be used to create timers that do not drift with respect to system	1361	This can be used to create timers that do not drift with respect to system
622	time:	1362	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1363	the hour:
623		1364
624	ev_periodic_set (&periodic, 0., 3600., 0);	1365	ev_periodic_set (&periodic, 0., 3600., 0);
625		1366
626	This doesn't mean there will always be 3600 seconds in between triggers,	1367	This doesn't mean there will always be 3600 seconds in between triggers,
627	but only that the the callback will be called when the system time shows a	1368	but only that the callback will be called when the system time shows a
628	full hour (UTC), or more correctly, when the system time is evenly divisible	1369	full hour (UTC), or more correctly, when the system time is evenly divisible
629	by 3600.	1370	by 3600.
630		1371
631	Another way to think about it (for the mathematically inclined) is that	1372	Another way to think about it (for the mathematically inclined) is that
632	C<ev_periodic> will try to run the callback in this mode at the next possible	1373	C<ev_periodic> will try to run the callback in this mode at the next possible
633	time where C<time = at (mod interval)>, regardless of any time jumps.	1374	time where C<time = at (mod interval)>, regardless of any time jumps.
634		1375
		1376	For numerical stability it is preferable that the C<at> value is near
		1377	C<ev_now ()> (the current time), but there is no range requirement for
		1378	this value, and in fact is often specified as zero.
		1379
		1380	Note also that there is an upper limit to how often a timer can fire (CPU
		1381	speed for example), so if C<interval> is very small then timing stability
		1382	will of course deteriorate. Libev itself tries to be exact to be about one
		1383	millisecond (if the OS supports it and the machine is fast enough).
		1384
635	=item * manual reschedule mode (reschedule_cb = callback)	1385	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
636		1386
637	In this mode the values for C<interval> and C<at> are both being	1387	In this mode the values for C<interval> and C<at> are both being
638	ignored. Instead, each time the periodic watcher gets scheduled, the	1388	ignored. Instead, each time the periodic watcher gets scheduled, the
639	reschedule callback will be called with the watcher as first, and the	1389	reschedule callback will be called with the watcher as first, and the
640	current time as second argument.	1390	current time as second argument.
641		1391
642	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1392	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
643	ever, or make any event loop modifications>. If you need to stop it,	1393	ever, or make ANY event loop modifications whatsoever>.
644	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
645	starting a prepare watcher).
646		1394
		1395	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1396	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1397	only event loop modification you are allowed to do).
		1398
647	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1399	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
648	ev_tstamp now)>, e.g.:	1400	*w, ev_tstamp now)>, e.g.:
649		1401
650	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1402	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
651	{	1403	{
652	return now + 60.;	1404	return now + 60.;
653	}	1405	}
…		…
655	It must return the next time to trigger, based on the passed time value	1407	It must return the next time to trigger, based on the passed time value
656	(that is, the lowest time value larger than to the second argument). It	1408	(that is, the lowest time value larger than to the second argument). It
657	will usually be called just before the callback will be triggered, but	1409	will usually be called just before the callback will be triggered, but
658	might be called at other times, too.	1410	might be called at other times, too.
659		1411
660	NOTE: I<< This callback must always return a time that is later than the	1412	NOTE: I<< This callback must always return a time that is higher than or
661	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1413	equal to the passed C<now> value >>.
662		1414
663	This can be used to create very complex timers, such as a timer that	1415	This can be used to create very complex timers, such as a timer that
664	triggers on each midnight, local time. To do this, you would calculate the	1416	triggers on "next midnight, local time". To do this, you would calculate the
665	next midnight after C<now> and return the timestamp value for this. How	1417	next midnight after C<now> and return the timestamp value for this. How
666	you do this is, again, up to you (but it is not trivial, which is the main	1418	you do this is, again, up to you (but it is not trivial, which is the main
667	reason I omitted it as an example).	1419	reason I omitted it as an example).
668		1420
669	=back	1421	=back
…		…
673	Simply stops and restarts the periodic watcher again. This is only useful	1425	Simply stops and restarts the periodic watcher again. This is only useful
674	when you changed some parameters or the reschedule callback would return	1426	when you changed some parameters or the reschedule callback would return
675	a different time than the last time it was called (e.g. in a crond like	1427	a different time than the last time it was called (e.g. in a crond like
676	program when the crontabs have changed).	1428	program when the crontabs have changed).
677		1429
		1430	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1431
		1432	When active, returns the absolute time that the watcher is supposed to
		1433	trigger next.
		1434
		1435	=item ev_tstamp offset [read-write]
		1436
		1437	When repeating, this contains the offset value, otherwise this is the
		1438	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1439
		1440	Can be modified any time, but changes only take effect when the periodic
		1441	timer fires or C<ev_periodic_again> is being called.
		1442
		1443	=item ev_tstamp interval [read-write]
		1444
		1445	The current interval value. Can be modified any time, but changes only
		1446	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1447	called.
		1448
		1449	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1450
		1451	The current reschedule callback, or C<0>, if this functionality is
		1452	switched off. Can be changed any time, but changes only take effect when
		1453	the periodic timer fires or C<ev_periodic_again> is being called.
		1454
678	=back	1455	=back
679		1456
		1457	=head3 Examples
		1458
		1459	Example: Call a callback every hour, or, more precisely, whenever the
		1460	system clock is divisible by 3600. The callback invocation times have
		1461	potentially a lot of jitter, but good long-term stability.
		1462
		1463	static void
		1464	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1465	{
		1466	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1467	}
		1468
		1469	struct ev_periodic hourly_tick;
		1470	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1471	ev_periodic_start (loop, &hourly_tick);
		1472
		1473	Example: The same as above, but use a reschedule callback to do it:
		1474
		1475	#include <math.h>
		1476
		1477	static ev_tstamp
		1478	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1479	{
		1480	return fmod (now, 3600.) + 3600.;
		1481	}
		1482
		1483	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1484
		1485	Example: Call a callback every hour, starting now:
		1486
		1487	struct ev_periodic hourly_tick;
		1488	ev_periodic_init (&hourly_tick, clock_cb,
		1489	fmod (ev_now (loop), 3600.), 3600., 0);
		1490	ev_periodic_start (loop, &hourly_tick);
		1491
		1492
680	=head2 C<ev_signal> - signal me when a signal gets signalled	1493	=head2 C<ev_signal> - signal me when a signal gets signalled!
681		1494
682	Signal watchers will trigger an event when the process receives a specific	1495	Signal watchers will trigger an event when the process receives a specific
683	signal one or more times. Even though signals are very asynchronous, libev	1496	signal one or more times. Even though signals are very asynchronous, libev
684	will try it's best to deliver signals synchronously, i.e. as part of the	1497	will try it's best to deliver signals synchronously, i.e. as part of the
685	normal event processing, like any other event.	1498	normal event processing, like any other event.
…		…
689	with the kernel (thus it coexists with your own signal handlers as long	1502	with the kernel (thus it coexists with your own signal handlers as long
690	as you don't register any with libev). Similarly, when the last signal	1503	as you don't register any with libev). Similarly, when the last signal
691	watcher for a signal is stopped libev will reset the signal handler to	1504	watcher for a signal is stopped libev will reset the signal handler to
692	SIG_DFL (regardless of what it was set to before).	1505	SIG_DFL (regardless of what it was set to before).
693		1506
		1507	If possible and supported, libev will install its handlers with
		1508	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1509	interrupted. If you have a problem with system calls getting interrupted by
		1510	signals you can block all signals in an C<ev_check> watcher and unblock
		1511	them in an C<ev_prepare> watcher.
		1512
		1513	=head3 Watcher-Specific Functions and Data Members
		1514
694	=over 4	1515	=over 4
695		1516
696	=item ev_signal_init (ev_signal *, callback, int signum)	1517	=item ev_signal_init (ev_signal *, callback, int signum)
697		1518
698	=item ev_signal_set (ev_signal *, int signum)	1519	=item ev_signal_set (ev_signal *, int signum)
699		1520
700	Configures the watcher to trigger on the given signal number (usually one	1521	Configures the watcher to trigger on the given signal number (usually one
701	of the C<SIGxxx> constants).	1522	of the C<SIGxxx> constants).
702		1523
		1524	=item int signum [read-only]
		1525
		1526	The signal the watcher watches out for.
		1527
703	=back	1528	=back
704		1529
		1530	=head3 Examples
		1531
		1532	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1533
		1534	static void
		1535	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1536	{
		1537	ev_unloop (loop, EVUNLOOP_ALL);
		1538	}
		1539
		1540	struct ev_signal signal_watcher;
		1541	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1542	ev_signal_start (loop, &sigint_cb);
		1543
		1544
705	=head2 C<ev_child> - wait for pid status changes	1545	=head2 C<ev_child> - watch out for process status changes
706		1546
707	Child watchers trigger when your process receives a SIGCHLD in response to	1547	Child watchers trigger when your process receives a SIGCHLD in response to
708	some child status changes (most typically when a child of yours dies).	1548	some child status changes (most typically when a child of yours dies). It
		1549	is permissible to install a child watcher I<after> the child has been
		1550	forked (which implies it might have already exited), as long as the event
		1551	loop isn't entered (or is continued from a watcher).
		1552
		1553	Only the default event loop is capable of handling signals, and therefore
		1554	you can only register child watchers in the default event loop.
		1555
		1556	=head3 Process Interaction
		1557
		1558	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1559	initialised. This is necessary to guarantee proper behaviour even if
		1560	the first child watcher is started after the child exits. The occurrence
		1561	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1562	synchronously as part of the event loop processing. Libev always reaps all
		1563	children, even ones not watched.
		1564
		1565	=head3 Overriding the Built-In Processing
		1566
		1567	Libev offers no special support for overriding the built-in child
		1568	processing, but if your application collides with libev's default child
		1569	handler, you can override it easily by installing your own handler for
		1570	C<SIGCHLD> after initialising the default loop, and making sure the
		1571	default loop never gets destroyed. You are encouraged, however, to use an
		1572	event-based approach to child reaping and thus use libev's support for
		1573	that, so other libev users can use C<ev_child> watchers freely.
		1574
		1575	=head3 Watcher-Specific Functions and Data Members
709		1576
710	=over 4	1577	=over 4
711		1578
712	=item ev_child_init (ev_child *, callback, int pid)	1579	=item ev_child_init (ev_child *, callback, int pid, int trace)
713		1580
714	=item ev_child_set (ev_child *, int pid)	1581	=item ev_child_set (ev_child *, int pid, int trace)
715		1582
716	Configures the watcher to wait for status changes of process C<pid> (or	1583	Configures the watcher to wait for status changes of process C<pid> (or
717	I<any> process if C<pid> is specified as C<0>). The callback can look	1584	I<any> process if C<pid> is specified as C<0>). The callback can look
718	at the C<rstatus> member of the C<ev_child> watcher structure to see	1585	at the C<rstatus> member of the C<ev_child> watcher structure to see
719	the status word (use the macros from C<sys/wait.h> and see your systems	1586	the status word (use the macros from C<sys/wait.h> and see your systems
720	C<waitpid> documentation). The C<rpid> member contains the pid of the	1587	C<waitpid> documentation). The C<rpid> member contains the pid of the
721	process causing the status change.	1588	process causing the status change. C<trace> must be either C<0> (only
		1589	activate the watcher when the process terminates) or C<1> (additionally
		1590	activate the watcher when the process is stopped or continued).
		1591
		1592	=item int pid [read-only]
		1593
		1594	The process id this watcher watches out for, or C<0>, meaning any process id.
		1595
		1596	=item int rpid [read-write]
		1597
		1598	The process id that detected a status change.
		1599
		1600	=item int rstatus [read-write]
		1601
		1602	The process exit/trace status caused by C<rpid> (see your systems
		1603	C<waitpid> and C<sys/wait.h> documentation for details).
722		1604
723	=back	1605	=back
724		1606
		1607	=head3 Examples
		1608
		1609	Example: C<fork()> a new process and install a child handler to wait for
		1610	its completion.
		1611
		1612	ev_child cw;
		1613
		1614	static void
		1615	child_cb (EV_P_ struct ev_child *w, int revents)
		1616	{
		1617	ev_child_stop (EV_A_ w);
		1618	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1619	}
		1620
		1621	pid_t pid = fork ();
		1622
		1623	if (pid < 0)
		1624	// error
		1625	else if (pid == 0)
		1626	{
		1627	// the forked child executes here
		1628	exit (1);
		1629	}
		1630	else
		1631	{
		1632	ev_child_init (&cw, child_cb, pid, 0);
		1633	ev_child_start (EV_DEFAULT_ &cw);
		1634	}
		1635
		1636
		1637	=head2 C<ev_stat> - did the file attributes just change?
		1638
		1639	This watches a file system path for attribute changes. That is, it calls
		1640	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1641	compared to the last time, invoking the callback if it did.
		1642
		1643	The path does not need to exist: changing from "path exists" to "path does
		1644	not exist" is a status change like any other. The condition "path does
		1645	not exist" is signified by the C<st_nlink> field being zero (which is
		1646	otherwise always forced to be at least one) and all the other fields of
		1647	the stat buffer having unspecified contents.
		1648
		1649	The path I<should> be absolute and I<must not> end in a slash. If it is
		1650	relative and your working directory changes, the behaviour is undefined.
		1651
		1652	Since there is no standard to do this, the portable implementation simply
		1653	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1654	can specify a recommended polling interval for this case. If you specify
		1655	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1656	unspecified default> value will be used (which you can expect to be around
		1657	five seconds, although this might change dynamically). Libev will also
		1658	impose a minimum interval which is currently around C<0.1>, but thats
		1659	usually overkill.
		1660
		1661	This watcher type is not meant for massive numbers of stat watchers,
		1662	as even with OS-supported change notifications, this can be
		1663	resource-intensive.
		1664
		1665	At the time of this writing, only the Linux inotify interface is
		1666	implemented (implementing kqueue support is left as an exercise for the
		1667	reader, note, however, that the author sees no way of implementing ev_stat
		1668	semantics with kqueue). Inotify will be used to give hints only and should
		1669	not change the semantics of C<ev_stat> watchers, which means that libev
		1670	sometimes needs to fall back to regular polling again even with inotify,
		1671	but changes are usually detected immediately, and if the file exists there
		1672	will be no polling.
		1673
		1674	=head3 ABI Issues (Largefile Support)
		1675
		1676	Libev by default (unless the user overrides this) uses the default
		1677	compilation environment, which means that on systems with large file
		1678	support disabled by default, you get the 32 bit version of the stat
		1679	structure. When using the library from programs that change the ABI to
		1680	use 64 bit file offsets the programs will fail. In that case you have to
		1681	compile libev with the same flags to get binary compatibility. This is
		1682	obviously the case with any flags that change the ABI, but the problem is
		1683	most noticeably disabled with ev_stat and large file support.
		1684
		1685	The solution for this is to lobby your distribution maker to make large
		1686	file interfaces available by default (as e.g. FreeBSD does) and not
		1687	optional. Libev cannot simply switch on large file support because it has
		1688	to exchange stat structures with application programs compiled using the
		1689	default compilation environment.
		1690
		1691	=head3 Inotify
		1692
		1693	When C<inotify (7)> support has been compiled into libev (generally only
		1694	available on Linux) and present at runtime, it will be used to speed up
		1695	change detection where possible. The inotify descriptor will be created lazily
		1696	when the first C<ev_stat> watcher is being started.
		1697
		1698	Inotify presence does not change the semantics of C<ev_stat> watchers
		1699	except that changes might be detected earlier, and in some cases, to avoid
		1700	making regular C<stat> calls. Even in the presence of inotify support
		1701	there are many cases where libev has to resort to regular C<stat> polling.
		1702
		1703	(There is no support for kqueue, as apparently it cannot be used to
		1704	implement this functionality, due to the requirement of having a file
		1705	descriptor open on the object at all times).
		1706
		1707	=head3 The special problem of stat time resolution
		1708
		1709	The C<stat ()> system call only supports full-second resolution portably, and
		1710	even on systems where the resolution is higher, many file systems still
		1711	only support whole seconds.
		1712
		1713	That means that, if the time is the only thing that changes, you can
		1714	easily miss updates: on the first update, C<ev_stat> detects a change and
		1715	calls your callback, which does something. When there is another update
		1716	within the same second, C<ev_stat> will be unable to detect it as the stat
		1717	data does not change.
		1718
		1719	The solution to this is to delay acting on a change for slightly more
		1720	than a second (or till slightly after the next full second boundary), using
		1721	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1722	ev_timer_again (loop, w)>).
		1723
		1724	The C<.02> offset is added to work around small timing inconsistencies
		1725	of some operating systems (where the second counter of the current time
		1726	might be be delayed. One such system is the Linux kernel, where a call to
		1727	C<gettimeofday> might return a timestamp with a full second later than
		1728	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1729	update file times then there will be a small window where the kernel uses
		1730	the previous second to update file times but libev might already execute
		1731	the timer callback).
		1732
		1733	=head3 Watcher-Specific Functions and Data Members
		1734
		1735	=over 4
		1736
		1737	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1738
		1739	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1740
		1741	Configures the watcher to wait for status changes of the given
		1742	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1743	be detected and should normally be specified as C<0> to let libev choose
		1744	a suitable value. The memory pointed to by C<path> must point to the same
		1745	path for as long as the watcher is active.
		1746
		1747	The callback will receive C<EV_STAT> when a change was detected, relative
		1748	to the attributes at the time the watcher was started (or the last change
		1749	was detected).
		1750
		1751	=item ev_stat_stat (loop, ev_stat *)
		1752
		1753	Updates the stat buffer immediately with new values. If you change the
		1754	watched path in your callback, you could call this function to avoid
		1755	detecting this change (while introducing a race condition if you are not
		1756	the only one changing the path). Can also be useful simply to find out the
		1757	new values.
		1758
		1759	=item ev_statdata attr [read-only]
		1760
		1761	The most-recently detected attributes of the file. Although the type is
		1762	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1763	suitable for your system, but you can only rely on the POSIX-standardised
		1764	members to be present. If the C<st_nlink> member is C<0>, then there was
		1765	some error while C<stat>ing the file.
		1766
		1767	=item ev_statdata prev [read-only]
		1768
		1769	The previous attributes of the file. The callback gets invoked whenever
		1770	C<prev> != C<attr>, or, more precisely, one or more of these members
		1771	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1772	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1773
		1774	=item ev_tstamp interval [read-only]
		1775
		1776	The specified interval.
		1777
		1778	=item const char *path [read-only]
		1779
		1780	The file system path that is being watched.
		1781
		1782	=back
		1783
		1784	=head3 Examples
		1785
		1786	Example: Watch C</etc/passwd> for attribute changes.
		1787
		1788	static void
		1789	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1790	{
		1791	/* /etc/passwd changed in some way */
		1792	if (w->attr.st_nlink)
		1793	{
		1794	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1795	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1796	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1797	}
		1798	else
		1799	/* you shalt not abuse printf for puts */
		1800	puts ("wow, /etc/passwd is not there, expect problems. "
		1801	"if this is windows, they already arrived\n");
		1802	}
		1803
		1804	...
		1805	ev_stat passwd;
		1806
		1807	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1808	ev_stat_start (loop, &passwd);
		1809
		1810	Example: Like above, but additionally use a one-second delay so we do not
		1811	miss updates (however, frequent updates will delay processing, too, so
		1812	one might do the work both on C<ev_stat> callback invocation I<and> on
		1813	C<ev_timer> callback invocation).
		1814
		1815	static ev_stat passwd;
		1816	static ev_timer timer;
		1817
		1818	static void
		1819	timer_cb (EV_P_ ev_timer *w, int revents)
		1820	{
		1821	ev_timer_stop (EV_A_ w);
		1822
		1823	/* now it's one second after the most recent passwd change */
		1824	}
		1825
		1826	static void
		1827	stat_cb (EV_P_ ev_stat *w, int revents)
		1828	{
		1829	/* reset the one-second timer */
		1830	ev_timer_again (EV_A_ &timer);
		1831	}
		1832
		1833	...
		1834	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1835	ev_stat_start (loop, &passwd);
		1836	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1837
		1838
725	=head2 C<ev_idle> - when you've got nothing better to do	1839	=head2 C<ev_idle> - when you've got nothing better to do...
726		1840
727	Idle watchers trigger events when there are no other events are pending	1841	Idle watchers trigger events when no other events of the same or higher
728	(prepare, check and other idle watchers do not count). That is, as long	1842	priority are pending (prepare, check and other idle watchers do not
729	as your process is busy handling sockets or timeouts (or even signals,	1843	count).
730	imagine) it will not be triggered. But when your process is idle all idle	1844
731	watchers are being called again and again, once per event loop iteration -	1845	That is, as long as your process is busy handling sockets or timeouts
		1846	(or even signals, imagine) of the same or higher priority it will not be
		1847	triggered. But when your process is idle (or only lower-priority watchers
		1848	are pending), the idle watchers are being called once per event loop
732	until stopped, that is, or your process receives more events and becomes	1849	iteration - until stopped, that is, or your process receives more events
733	busy.	1850	and becomes busy again with higher priority stuff.
734		1851
735	The most noteworthy effect is that as long as any idle watchers are	1852	The most noteworthy effect is that as long as any idle watchers are
736	active, the process will not block when waiting for new events.	1853	active, the process will not block when waiting for new events.
737		1854
738	Apart from keeping your process non-blocking (which is a useful	1855	Apart from keeping your process non-blocking (which is a useful
739	effect on its own sometimes), idle watchers are a good place to do	1856	effect on its own sometimes), idle watchers are a good place to do
740	"pseudo-background processing", or delay processing stuff to after the	1857	"pseudo-background processing", or delay processing stuff to after the
741	event loop has handled all outstanding events.	1858	event loop has handled all outstanding events.
742		1859
		1860	=head3 Watcher-Specific Functions and Data Members
		1861
743	=over 4	1862	=over 4
744		1863
745	=item ev_idle_init (ev_signal *, callback)	1864	=item ev_idle_init (ev_signal *, callback)
746		1865
747	Initialises and configures the idle watcher - it has no parameters of any	1866	Initialises and configures the idle watcher - it has no parameters of any
748	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1867	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
749	believe me.	1868	believe me.
750		1869
751	=back	1870	=back
752		1871
		1872	=head3 Examples
		1873
		1874	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1875	callback, free it. Also, use no error checking, as usual.
		1876
		1877	static void
		1878	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1879	{
		1880	free (w);
		1881	// now do something you wanted to do when the program has
		1882	// no longer anything immediate to do.
		1883	}
		1884
		1885	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1886	ev_idle_init (idle_watcher, idle_cb);
		1887	ev_idle_start (loop, idle_cb);
		1888
		1889
753	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1890	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
754		1891
755	Prepare and check watchers are usually (but not always) used in tandem:	1892	Prepare and check watchers are usually (but not always) used in tandem:
756	prepare watchers get invoked before the process blocks and check watchers	1893	prepare watchers get invoked before the process blocks and check watchers
757	afterwards.	1894	afterwards.
758		1895
		1896	You I<must not> call C<ev_loop> or similar functions that enter
		1897	the current event loop from either C<ev_prepare> or C<ev_check>
		1898	watchers. Other loops than the current one are fine, however. The
		1899	rationale behind this is that you do not need to check for recursion in
		1900	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1901	C<ev_check> so if you have one watcher of each kind they will always be
		1902	called in pairs bracketing the blocking call.
		1903
759	Their main purpose is to integrate other event mechanisms into libev. This	1904	Their main purpose is to integrate other event mechanisms into libev and
760	could be used, for example, to track variable changes, implement your own	1905	their use is somewhat advanced. This could be used, for example, to track
761	watchers, integrate net-snmp or a coroutine library and lots more.	1906	variable changes, implement your own watchers, integrate net-snmp or a
		1907	coroutine library and lots more. They are also occasionally useful if
		1908	you cache some data and want to flush it before blocking (for example,
		1909	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1910	watcher).
762		1911
763	This is done by examining in each prepare call which file descriptors need	1912	This is done by examining in each prepare call which file descriptors need
764	to be watched by the other library, registering C<ev_io> watchers for	1913	to be watched by the other library, registering C<ev_io> watchers for
765	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1914	them and starting an C<ev_timer> watcher for any timeouts (many libraries
766	provide just this functionality). Then, in the check watcher you check for	1915	provide just this functionality). Then, in the check watcher you check for
767	any events that occured (by checking the pending status of all watchers	1916	any events that occurred (by checking the pending status of all watchers
768	and stopping them) and call back into the library. The I/O and timer	1917	and stopping them) and call back into the library. The I/O and timer
769	callbacks will never actually be called (but must be valid nevertheless,	1918	callbacks will never actually be called (but must be valid nevertheless,
770	because you never know, you know?).	1919	because you never know, you know?).
771		1920
772	As another example, the Perl Coro module uses these hooks to integrate	1921	As another example, the Perl Coro module uses these hooks to integrate
…		…
776	with priority higher than or equal to the event loop and one coroutine	1925	with priority higher than or equal to the event loop and one coroutine
777	of lower priority, but only once, using idle watchers to keep the event	1926	of lower priority, but only once, using idle watchers to keep the event
778	loop from blocking if lower-priority coroutines are active, thus mapping	1927	loop from blocking if lower-priority coroutines are active, thus mapping
779	low-priority coroutines to idle/background tasks).	1928	low-priority coroutines to idle/background tasks).
780		1929
		1930	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1931	priority, to ensure that they are being run before any other watchers
		1932	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1933	too) should not activate ("feed") events into libev. While libev fully
		1934	supports this, they might get executed before other C<ev_check> watchers
		1935	did their job. As C<ev_check> watchers are often used to embed other
		1936	(non-libev) event loops those other event loops might be in an unusable
		1937	state until their C<ev_check> watcher ran (always remind yourself to
		1938	coexist peacefully with others).
		1939
		1940	=head3 Watcher-Specific Functions and Data Members
		1941
781	=over 4	1942	=over 4
782		1943
783	=item ev_prepare_init (ev_prepare *, callback)	1944	=item ev_prepare_init (ev_prepare *, callback)
784		1945
785	=item ev_check_init (ev_check *, callback)	1946	=item ev_check_init (ev_check *, callback)
…		…
787	Initialises and configures the prepare or check watcher - they have no	1948	Initialises and configures the prepare or check watcher - they have no
788	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1949	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
789	macros, but using them is utterly, utterly and completely pointless.	1950	macros, but using them is utterly, utterly and completely pointless.
790		1951
791	=back	1952	=back
		1953
		1954	=head3 Examples
		1955
		1956	There are a number of principal ways to embed other event loops or modules
		1957	into libev. Here are some ideas on how to include libadns into libev
		1958	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1959	use as a working example. Another Perl module named C<EV::Glib> embeds a
		1960	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		1961	Glib event loop).
		1962
		1963	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1964	and in a check watcher, destroy them and call into libadns. What follows
		1965	is pseudo-code only of course. This requires you to either use a low
		1966	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1967	the callbacks for the IO/timeout watchers might not have been called yet.
		1968
		1969	static ev_io iow [nfd];
		1970	static ev_timer tw;
		1971
		1972	static void
		1973	io_cb (ev_loop *loop, ev_io *w, int revents)
		1974	{
		1975	}
		1976
		1977	// create io watchers for each fd and a timer before blocking
		1978	static void
		1979	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1980	{
		1981	int timeout = 3600000;
		1982	struct pollfd fds [nfd];
		1983	// actual code will need to loop here and realloc etc.
		1984	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1985
		1986	/* the callback is illegal, but won't be called as we stop during check */
		1987	ev_timer_init (&tw, 0, timeout * 1e-3);
		1988	ev_timer_start (loop, &tw);
		1989
		1990	// create one ev_io per pollfd
		1991	for (int i = 0; i < nfd; ++i)
		1992	{
		1993	ev_io_init (iow + i, io_cb, fds [i].fd,
		1994	((fds [i].events & POLLIN ? EV_READ : 0)
		1995	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1996
		1997	fds [i].revents = 0;
		1998	ev_io_start (loop, iow + i);
		1999	}
		2000	}
		2001
		2002	// stop all watchers after blocking
		2003	static void
		2004	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		2005	{
		2006	ev_timer_stop (loop, &tw);
		2007
		2008	for (int i = 0; i < nfd; ++i)
		2009	{
		2010	// set the relevant poll flags
		2011	// could also call adns_processreadable etc. here
		2012	struct pollfd *fd = fds + i;
		2013	int revents = ev_clear_pending (iow + i);
		2014	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2015	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2016
		2017	// now stop the watcher
		2018	ev_io_stop (loop, iow + i);
		2019	}
		2020
		2021	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2022	}
		2023
		2024	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2025	in the prepare watcher and would dispose of the check watcher.
		2026
		2027	Method 3: If the module to be embedded supports explicit event
		2028	notification (libadns does), you can also make use of the actual watcher
		2029	callbacks, and only destroy/create the watchers in the prepare watcher.
		2030
		2031	static void
		2032	timer_cb (EV_P_ ev_timer *w, int revents)
		2033	{
		2034	adns_state ads = (adns_state)w->data;
		2035	update_now (EV_A);
		2036
		2037	adns_processtimeouts (ads, &tv_now);
		2038	}
		2039
		2040	static void
		2041	io_cb (EV_P_ ev_io *w, int revents)
		2042	{
		2043	adns_state ads = (adns_state)w->data;
		2044	update_now (EV_A);
		2045
		2046	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2047	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2048	}
		2049
		2050	// do not ever call adns_afterpoll
		2051
		2052	Method 4: Do not use a prepare or check watcher because the module you
		2053	want to embed is too inflexible to support it. Instead, you can override
		2054	their poll function. The drawback with this solution is that the main
		2055	loop is now no longer controllable by EV. The C<Glib::EV> module does
		2056	this.
		2057
		2058	static gint
		2059	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2060	{
		2061	int got_events = 0;
		2062
		2063	for (n = 0; n < nfds; ++n)
		2064	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2065
		2066	if (timeout >= 0)
		2067	// create/start timer
		2068
		2069	// poll
		2070	ev_loop (EV_A_ 0);
		2071
		2072	// stop timer again
		2073	if (timeout >= 0)
		2074	ev_timer_stop (EV_A_ &to);
		2075
		2076	// stop io watchers again - their callbacks should have set
		2077	for (n = 0; n < nfds; ++n)
		2078	ev_io_stop (EV_A_ iow [n]);
		2079
		2080	return got_events;
		2081	}
		2082
		2083
		2084	=head2 C<ev_embed> - when one backend isn't enough...
		2085
		2086	This is a rather advanced watcher type that lets you embed one event loop
		2087	into another (currently only C<ev_io> events are supported in the embedded
		2088	loop, other types of watchers might be handled in a delayed or incorrect
		2089	fashion and must not be used).
		2090
		2091	There are primarily two reasons you would want that: work around bugs and
		2092	prioritise I/O.
		2093
		2094	As an example for a bug workaround, the kqueue backend might only support
		2095	sockets on some platform, so it is unusable as generic backend, but you
		2096	still want to make use of it because you have many sockets and it scales
		2097	so nicely. In this case, you would create a kqueue-based loop and embed it
		2098	into your default loop (which might use e.g. poll). Overall operation will
		2099	be a bit slower because first libev has to poll and then call kevent, but
		2100	at least you can use both at what they are best.
		2101
		2102	As for prioritising I/O: rarely you have the case where some fds have
		2103	to be watched and handled very quickly (with low latency), and even
		2104	priorities and idle watchers might have too much overhead. In this case
		2105	you would put all the high priority stuff in one loop and all the rest in
		2106	a second one, and embed the second one in the first.
		2107
		2108	As long as the watcher is active, the callback will be invoked every time
		2109	there might be events pending in the embedded loop. The callback must then
		2110	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2111	their callbacks (you could also start an idle watcher to give the embedded
		2112	loop strictly lower priority for example). You can also set the callback
		2113	to C<0>, in which case the embed watcher will automatically execute the
		2114	embedded loop sweep.
		2115
		2116	As long as the watcher is started it will automatically handle events. The
		2117	callback will be invoked whenever some events have been handled. You can
		2118	set the callback to C<0> to avoid having to specify one if you are not
		2119	interested in that.
		2120
		2121	Also, there have not currently been made special provisions for forking:
		2122	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2123	but you will also have to stop and restart any C<ev_embed> watchers
		2124	yourself.
		2125
		2126	Unfortunately, not all backends are embeddable, only the ones returned by
		2127	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2128	portable one.
		2129
		2130	So when you want to use this feature you will always have to be prepared
		2131	that you cannot get an embeddable loop. The recommended way to get around
		2132	this is to have a separate variables for your embeddable loop, try to
		2133	create it, and if that fails, use the normal loop for everything.
		2134
		2135	=head3 Watcher-Specific Functions and Data Members
		2136
		2137	=over 4
		2138
		2139	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2140
		2141	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2142
		2143	Configures the watcher to embed the given loop, which must be
		2144	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2145	invoked automatically, otherwise it is the responsibility of the callback
		2146	to invoke it (it will continue to be called until the sweep has been done,
		2147	if you do not want that, you need to temporarily stop the embed watcher).
		2148
		2149	=item ev_embed_sweep (loop, ev_embed *)
		2150
		2151	Make a single, non-blocking sweep over the embedded loop. This works
		2152	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2153	appropriate way for embedded loops.
		2154
		2155	=item struct ev_loop *other [read-only]
		2156
		2157	The embedded event loop.
		2158
		2159	=back
		2160
		2161	=head3 Examples
		2162
		2163	Example: Try to get an embeddable event loop and embed it into the default
		2164	event loop. If that is not possible, use the default loop. The default
		2165	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2166	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2167	used).
		2168
		2169	struct ev_loop *loop_hi = ev_default_init (0);
		2170	struct ev_loop *loop_lo = 0;
		2171	struct ev_embed embed;
		2172
		2173	// see if there is a chance of getting one that works
		2174	// (remember that a flags value of 0 means autodetection)
		2175	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2176	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2177	: 0;
		2178
		2179	// if we got one, then embed it, otherwise default to loop_hi
		2180	if (loop_lo)
		2181	{
		2182	ev_embed_init (&embed, 0, loop_lo);
		2183	ev_embed_start (loop_hi, &embed);
		2184	}
		2185	else
		2186	loop_lo = loop_hi;
		2187
		2188	Example: Check if kqueue is available but not recommended and create
		2189	a kqueue backend for use with sockets (which usually work with any
		2190	kqueue implementation). Store the kqueue/socket-only event loop in
		2191	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2192
		2193	struct ev_loop *loop = ev_default_init (0);
		2194	struct ev_loop *loop_socket = 0;
		2195	struct ev_embed embed;
		2196
		2197	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2198	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2199	{
		2200	ev_embed_init (&embed, 0, loop_socket);
		2201	ev_embed_start (loop, &embed);
		2202	}
		2203
		2204	if (!loop_socket)
		2205	loop_socket = loop;
		2206
		2207	// now use loop_socket for all sockets, and loop for everything else
		2208
		2209
		2210	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2211
		2212	Fork watchers are called when a C<fork ()> was detected (usually because
		2213	whoever is a good citizen cared to tell libev about it by calling
		2214	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2215	event loop blocks next and before C<ev_check> watchers are being called,
		2216	and only in the child after the fork. If whoever good citizen calling
		2217	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2218	handlers will be invoked, too, of course.
		2219
		2220	=head3 Watcher-Specific Functions and Data Members
		2221
		2222	=over 4
		2223
		2224	=item ev_fork_init (ev_signal *, callback)
		2225
		2226	Initialises and configures the fork watcher - it has no parameters of any
		2227	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2228	believe me.
		2229
		2230	=back
		2231
		2232
		2233	=head2 C<ev_async> - how to wake up another event loop
		2234
		2235	In general, you cannot use an C<ev_loop> from multiple threads or other
		2236	asynchronous sources such as signal handlers (as opposed to multiple event
		2237	loops - those are of course safe to use in different threads).
		2238
		2239	Sometimes, however, you need to wake up another event loop you do not
		2240	control, for example because it belongs to another thread. This is what
		2241	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2242	can signal it by calling C<ev_async_send>, which is thread- and signal
		2243	safe.
		2244
		2245	This functionality is very similar to C<ev_signal> watchers, as signals,
		2246	too, are asynchronous in nature, and signals, too, will be compressed
		2247	(i.e. the number of callback invocations may be less than the number of
		2248	C<ev_async_sent> calls).
		2249
		2250	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2251	just the default loop.
		2252
		2253	=head3 Queueing
		2254
		2255	C<ev_async> does not support queueing of data in any way. The reason
		2256	is that the author does not know of a simple (or any) algorithm for a
		2257	multiple-writer-single-reader queue that works in all cases and doesn't
		2258	need elaborate support such as pthreads.
		2259
		2260	That means that if you want to queue data, you have to provide your own
		2261	queue. But at least I can tell you would implement locking around your
		2262	queue:
		2263
		2264	=over 4
		2265
		2266	=item queueing from a signal handler context
		2267
		2268	To implement race-free queueing, you simply add to the queue in the signal
		2269	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2270	some fictitious SIGUSR1 handler:
		2271
		2272	static ev_async mysig;
		2273
		2274	static void
		2275	sigusr1_handler (void)
		2276	{
		2277	sometype data;
		2278
		2279	// no locking etc.
		2280	queue_put (data);
		2281	ev_async_send (EV_DEFAULT_ &mysig);
		2282	}
		2283
		2284	static void
		2285	mysig_cb (EV_P_ ev_async *w, int revents)
		2286	{
		2287	sometype data;
		2288	sigset_t block, prev;
		2289
		2290	sigemptyset (&block);
		2291	sigaddset (&block, SIGUSR1);
		2292	sigprocmask (SIG_BLOCK, &block, &prev);
		2293
		2294	while (queue_get (&data))
		2295	process (data);
		2296
		2297	if (sigismember (&prev, SIGUSR1)
		2298	sigprocmask (SIG_UNBLOCK, &block, 0);
		2299	}
		2300
		2301	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2302	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2303	either...).
		2304
		2305	=item queueing from a thread context
		2306
		2307	The strategy for threads is different, as you cannot (easily) block
		2308	threads but you can easily preempt them, so to queue safely you need to
		2309	employ a traditional mutex lock, such as in this pthread example:
		2310
		2311	static ev_async mysig;
		2312	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2313
		2314	static void
		2315	otherthread (void)
		2316	{
		2317	// only need to lock the actual queueing operation
		2318	pthread_mutex_lock (&mymutex);
		2319	queue_put (data);
		2320	pthread_mutex_unlock (&mymutex);
		2321
		2322	ev_async_send (EV_DEFAULT_ &mysig);
		2323	}
		2324
		2325	static void
		2326	mysig_cb (EV_P_ ev_async *w, int revents)
		2327	{
		2328	pthread_mutex_lock (&mymutex);
		2329
		2330	while (queue_get (&data))
		2331	process (data);
		2332
		2333	pthread_mutex_unlock (&mymutex);
		2334	}
		2335
		2336	=back
		2337
		2338
		2339	=head3 Watcher-Specific Functions and Data Members
		2340
		2341	=over 4
		2342
		2343	=item ev_async_init (ev_async *, callback)
		2344
		2345	Initialises and configures the async watcher - it has no parameters of any
		2346	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2347	believe me.
		2348
		2349	=item ev_async_send (loop, ev_async *)
		2350
		2351	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2352	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2353	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2354	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2355	section below on what exactly this means).
		2356
		2357	This call incurs the overhead of a system call only once per loop iteration,
		2358	so while the overhead might be noticeable, it doesn't apply to repeated
		2359	calls to C<ev_async_send>.
		2360
		2361	=item bool = ev_async_pending (ev_async *)
		2362
		2363	Returns a non-zero value when C<ev_async_send> has been called on the
		2364	watcher but the event has not yet been processed (or even noted) by the
		2365	event loop.
		2366
		2367	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2368	the loop iterates next and checks for the watcher to have become active,
		2369	it will reset the flag again. C<ev_async_pending> can be used to very
		2370	quickly check whether invoking the loop might be a good idea.
		2371
		2372	Not that this does I<not> check whether the watcher itself is pending, only
		2373	whether it has been requested to make this watcher pending.
		2374
		2375	=back
		2376
792		2377
793	=head1 OTHER FUNCTIONS	2378	=head1 OTHER FUNCTIONS
794		2379
795	There are some other functions of possible interest. Described. Here. Now.	2380	There are some other functions of possible interest. Described. Here. Now.
796		2381
…		…
804	or timeout without having to allocate/configure/start/stop/free one or	2389	or timeout without having to allocate/configure/start/stop/free one or
805	more watchers yourself.	2390	more watchers yourself.
806		2391
807	If C<fd> is less than 0, then no I/O watcher will be started and events	2392	If C<fd> is less than 0, then no I/O watcher will be started and events
808	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2393	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
809	C<events> set will be craeted and started.	2394	C<events> set will be created and started.
810		2395
811	If C<timeout> is less than 0, then no timeout watcher will be	2396	If C<timeout> is less than 0, then no timeout watcher will be
812	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2397	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
813	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2398	repeat = 0) will be started. While C<0> is a valid timeout, it is of
814	dubious value.	2399	dubious value.
…		…
816	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2401	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
817	passed an C<revents> set like normal event callbacks (a combination of	2402	passed an C<revents> set like normal event callbacks (a combination of
818	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2403	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
819	value passed to C<ev_once>:	2404	value passed to C<ev_once>:
820		2405
821	static void stdin_ready (int revents, void *arg)	2406	static void stdin_ready (int revents, void *arg)
822	{	2407	{
823	if (revents & EV_TIMEOUT)	2408	if (revents & EV_TIMEOUT)
824	/* doh, nothing entered */;	2409	/* doh, nothing entered */;
825	else if (revents & EV_READ)	2410	else if (revents & EV_READ)
826	/* stdin might have data for us, joy! */;	2411	/* stdin might have data for us, joy! */;
827	}	2412	}
828		2413
829	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2414	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
830		2415
831	=item ev_feed_event (loop, watcher, int events)	2416	=item ev_feed_event (ev_loop *, watcher *, int revents)
832		2417
833	Feeds the given event set into the event loop, as if the specified event	2418	Feeds the given event set into the event loop, as if the specified event
834	had happened for the specified watcher (which must be a pointer to an	2419	had happened for the specified watcher (which must be a pointer to an
835	initialised but not necessarily started event watcher).	2420	initialised but not necessarily started event watcher).
836		2421
837	=item ev_feed_fd_event (loop, int fd, int revents)	2422	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
838		2423
839	Feed an event on the given fd, as if a file descriptor backend detected	2424	Feed an event on the given fd, as if a file descriptor backend detected
840	the given events it.	2425	the given events it.
841		2426
842	=item ev_feed_signal_event (loop, int signum)	2427	=item ev_feed_signal_event (ev_loop *loop, int signum)
843		2428
844	Feed an event as if the given signal occured (loop must be the default loop!).	2429	Feed an event as if the given signal occurred (C<loop> must be the default
		2430	loop!).
845		2431
846	=back	2432	=back
		2433
847		2434
848	=head1 LIBEVENT EMULATION	2435	=head1 LIBEVENT EMULATION
849		2436
850	Libev offers a compatibility emulation layer for libevent. It cannot	2437	Libev offers a compatibility emulation layer for libevent. It cannot
851	emulate the internals of libevent, so here are some usage hints:	2438	emulate the internals of libevent, so here are some usage hints:
…		…
863		2450
864	=item * Priorities are not currently supported. Initialising priorities	2451	=item * Priorities are not currently supported. Initialising priorities
865	will fail and all watchers will have the same priority, even though there	2452	will fail and all watchers will have the same priority, even though there
866	is an ev_pri field.	2453	is an ev_pri field.
867		2454
		2455	=item * In libevent, the last base created gets the signals, in libev, the
		2456	first base created (== the default loop) gets the signals.
		2457
868	=item * Other members are not supported.	2458	=item * Other members are not supported.
869		2459
870	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2460	=item * The libev emulation is I<not> ABI compatible to libevent, you need
871	to use the libev header file and library.	2461	to use the libev header file and library.
872		2462
873	=back	2463	=back
874		2464
875	=head1 C++ SUPPORT	2465	=head1 C++ SUPPORT
876		2466
877	TBD.	2467	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2468	you to use some convenience methods to start/stop watchers and also change
		2469	the callback model to a model using method callbacks on objects.
		2470
		2471	To use it,
		2472
		2473	#include <ev++.h>
		2474
		2475	This automatically includes F<ev.h> and puts all of its definitions (many
		2476	of them macros) into the global namespace. All C++ specific things are
		2477	put into the C<ev> namespace. It should support all the same embedding
		2478	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2479
		2480	Care has been taken to keep the overhead low. The only data member the C++
		2481	classes add (compared to plain C-style watchers) is the event loop pointer
		2482	that the watcher is associated with (or no additional members at all if
		2483	you disable C<EV_MULTIPLICITY> when embedding libev).
		2484
		2485	Currently, functions, and static and non-static member functions can be
		2486	used as callbacks. Other types should be easy to add as long as they only
		2487	need one additional pointer for context. If you need support for other
		2488	types of functors please contact the author (preferably after implementing
		2489	it).
		2490
		2491	Here is a list of things available in the C<ev> namespace:
		2492
		2493	=over 4
		2494
		2495	=item C<ev::READ>, C<ev::WRITE> etc.
		2496
		2497	These are just enum values with the same values as the C<EV_READ> etc.
		2498	macros from F<ev.h>.
		2499
		2500	=item C<ev::tstamp>, C<ev::now>
		2501
		2502	Aliases to the same types/functions as with the C<ev_> prefix.
		2503
		2504	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2505
		2506	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2507	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2508	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2509	defines by many implementations.
		2510
		2511	All of those classes have these methods:
		2512
		2513	=over 4
		2514
		2515	=item ev::TYPE::TYPE ()
		2516
		2517	=item ev::TYPE::TYPE (struct ev_loop *)
		2518
		2519	=item ev::TYPE::~TYPE
		2520
		2521	The constructor (optionally) takes an event loop to associate the watcher
		2522	with. If it is omitted, it will use C<EV_DEFAULT>.
		2523
		2524	The constructor calls C<ev_init> for you, which means you have to call the
		2525	C<set> method before starting it.
		2526
		2527	It will not set a callback, however: You have to call the templated C<set>
		2528	method to set a callback before you can start the watcher.
		2529
		2530	(The reason why you have to use a method is a limitation in C++ which does
		2531	not allow explicit template arguments for constructors).
		2532
		2533	The destructor automatically stops the watcher if it is active.
		2534
		2535	=item w->set<class, &class::method> (object *)
		2536
		2537	This method sets the callback method to call. The method has to have a
		2538	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2539	first argument and the C<revents> as second. The object must be given as
		2540	parameter and is stored in the C<data> member of the watcher.
		2541
		2542	This method synthesizes efficient thunking code to call your method from
		2543	the C callback that libev requires. If your compiler can inline your
		2544	callback (i.e. it is visible to it at the place of the C<set> call and
		2545	your compiler is good :), then the method will be fully inlined into the
		2546	thunking function, making it as fast as a direct C callback.
		2547
		2548	Example: simple class declaration and watcher initialisation
		2549
		2550	struct myclass
		2551	{
		2552	void io_cb (ev::io &w, int revents) { }
		2553	}
		2554
		2555	myclass obj;
		2556	ev::io iow;
		2557	iow.set <myclass, &myclass::io_cb> (&obj);
		2558
		2559	=item w->set<function> (void *data = 0)
		2560
		2561	Also sets a callback, but uses a static method or plain function as
		2562	callback. The optional C<data> argument will be stored in the watcher's
		2563	C<data> member and is free for you to use.
		2564
		2565	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2566
		2567	See the method-C<set> above for more details.
		2568
		2569	Example:
		2570
		2571	static void io_cb (ev::io &w, int revents) { }
		2572	iow.set <io_cb> ();
		2573
		2574	=item w->set (struct ev_loop *)
		2575
		2576	Associates a different C<struct ev_loop> with this watcher. You can only
		2577	do this when the watcher is inactive (and not pending either).
		2578
		2579	=item w->set ([arguments])
		2580
		2581	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2582	called at least once. Unlike the C counterpart, an active watcher gets
		2583	automatically stopped and restarted when reconfiguring it with this
		2584	method.
		2585
		2586	=item w->start ()
		2587
		2588	Starts the watcher. Note that there is no C<loop> argument, as the
		2589	constructor already stores the event loop.
		2590
		2591	=item w->stop ()
		2592
		2593	Stops the watcher if it is active. Again, no C<loop> argument.
		2594
		2595	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2596
		2597	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2598	C<ev_TYPE_again> function.
		2599
		2600	=item w->sweep () (C<ev::embed> only)
		2601
		2602	Invokes C<ev_embed_sweep>.
		2603
		2604	=item w->update () (C<ev::stat> only)
		2605
		2606	Invokes C<ev_stat_stat>.
		2607
		2608	=back
		2609
		2610	=back
		2611
		2612	Example: Define a class with an IO and idle watcher, start one of them in
		2613	the constructor.
		2614
		2615	class myclass
		2616	{
		2617	ev::io io; void io_cb (ev::io &w, int revents);
		2618	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2619
		2620	myclass (int fd)
		2621	{
		2622	io .set <myclass, &myclass::io_cb > (this);
		2623	idle.set <myclass, &myclass::idle_cb> (this);
		2624
		2625	io.start (fd, ev::READ);
		2626	}
		2627	};
		2628
		2629
		2630	=head1 OTHER LANGUAGE BINDINGS
		2631
		2632	Libev does not offer other language bindings itself, but bindings for a
		2633	number of languages exist in the form of third-party packages. If you know
		2634	any interesting language binding in addition to the ones listed here, drop
		2635	me a note.
		2636
		2637	=over 4
		2638
		2639	=item Perl
		2640
		2641	The EV module implements the full libev API and is actually used to test
		2642	libev. EV is developed together with libev. Apart from the EV core module,
		2643	there are additional modules that implement libev-compatible interfaces
		2644	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2645	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2646
		2647	It can be found and installed via CPAN, its homepage is at
		2648	L<http://software.schmorp.de/pkg/EV>.
		2649
		2650	=item Python
		2651
		2652	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2653	seems to be quite complete and well-documented. Note, however, that the
		2654	patch they require for libev is outright dangerous as it breaks the ABI
		2655	for everybody else, and therefore, should never be applied in an installed
		2656	libev (if python requires an incompatible ABI then it needs to embed
		2657	libev).
		2658
		2659	=item Ruby
		2660
		2661	Tony Arcieri has written a ruby extension that offers access to a subset
		2662	of the libev API and adds file handle abstractions, asynchronous DNS and
		2663	more on top of it. It can be found via gem servers. Its homepage is at
		2664	L<http://rev.rubyforge.org/>.
		2665
		2666	=item D
		2667
		2668	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2669	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2670
		2671	=back
		2672
		2673
		2674	=head1 MACRO MAGIC
		2675
		2676	Libev can be compiled with a variety of options, the most fundamental
		2677	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2678	functions and callbacks have an initial C<struct ev_loop *> argument.
		2679
		2680	To make it easier to write programs that cope with either variant, the
		2681	following macros are defined:
		2682
		2683	=over 4
		2684
		2685	=item C<EV_A>, C<EV_A_>
		2686
		2687	This provides the loop I<argument> for functions, if one is required ("ev
		2688	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2689	C<EV_A_> is used when other arguments are following. Example:
		2690
		2691	ev_unref (EV_A);
		2692	ev_timer_add (EV_A_ watcher);
		2693	ev_loop (EV_A_ 0);
		2694
		2695	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2696	which is often provided by the following macro.
		2697
		2698	=item C<EV_P>, C<EV_P_>
		2699
		2700	This provides the loop I<parameter> for functions, if one is required ("ev
		2701	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2702	C<EV_P_> is used when other parameters are following. Example:
		2703
		2704	// this is how ev_unref is being declared
		2705	static void ev_unref (EV_P);
		2706
		2707	// this is how you can declare your typical callback
		2708	static void cb (EV_P_ ev_timer *w, int revents)
		2709
		2710	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2711	suitable for use with C<EV_A>.
		2712
		2713	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2714
		2715	Similar to the other two macros, this gives you the value of the default
		2716	loop, if multiple loops are supported ("ev loop default").
		2717
		2718	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2719
		2720	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2721	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2722	is undefined when the default loop has not been initialised by a previous
		2723	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2724
		2725	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2726	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2727
		2728	=back
		2729
		2730	Example: Declare and initialise a check watcher, utilising the above
		2731	macros so it will work regardless of whether multiple loops are supported
		2732	or not.
		2733
		2734	static void
		2735	check_cb (EV_P_ ev_timer *w, int revents)
		2736	{
		2737	ev_check_stop (EV_A_ w);
		2738	}
		2739
		2740	ev_check check;
		2741	ev_check_init (&check, check_cb);
		2742	ev_check_start (EV_DEFAULT_ &check);
		2743	ev_loop (EV_DEFAULT_ 0);
		2744
		2745	=head1 EMBEDDING
		2746
		2747	Libev can (and often is) directly embedded into host
		2748	applications. Examples of applications that embed it include the Deliantra
		2749	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2750	and rxvt-unicode.
		2751
		2752	The goal is to enable you to just copy the necessary files into your
		2753	source directory without having to change even a single line in them, so
		2754	you can easily upgrade by simply copying (or having a checked-out copy of
		2755	libev somewhere in your source tree).
		2756
		2757	=head2 FILESETS
		2758
		2759	Depending on what features you need you need to include one or more sets of files
		2760	in your application.
		2761
		2762	=head3 CORE EVENT LOOP
		2763
		2764	To include only the libev core (all the C<ev_*> functions), with manual
		2765	configuration (no autoconf):
		2766
		2767	#define EV_STANDALONE 1
		2768	#include "ev.c"
		2769
		2770	This will automatically include F<ev.h>, too, and should be done in a
		2771	single C source file only to provide the function implementations. To use
		2772	it, do the same for F<ev.h> in all files wishing to use this API (best
		2773	done by writing a wrapper around F<ev.h> that you can include instead and
		2774	where you can put other configuration options):
		2775
		2776	#define EV_STANDALONE 1
		2777	#include "ev.h"
		2778
		2779	Both header files and implementation files can be compiled with a C++
		2780	compiler (at least, thats a stated goal, and breakage will be treated
		2781	as a bug).
		2782
		2783	You need the following files in your source tree, or in a directory
		2784	in your include path (e.g. in libev/ when using -Ilibev):
		2785
		2786	ev.h
		2787	ev.c
		2788	ev_vars.h
		2789	ev_wrap.h
		2790
		2791	ev_win32.c required on win32 platforms only
		2792
		2793	ev_select.c only when select backend is enabled (which is enabled by default)
		2794	ev_poll.c only when poll backend is enabled (disabled by default)
		2795	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2796	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2797	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2798
		2799	F<ev.c> includes the backend files directly when enabled, so you only need
		2800	to compile this single file.
		2801
		2802	=head3 LIBEVENT COMPATIBILITY API
		2803
		2804	To include the libevent compatibility API, also include:
		2805
		2806	#include "event.c"
		2807
		2808	in the file including F<ev.c>, and:
		2809
		2810	#include "event.h"
		2811
		2812	in the files that want to use the libevent API. This also includes F<ev.h>.
		2813
		2814	You need the following additional files for this:
		2815
		2816	event.h
		2817	event.c
		2818
		2819	=head3 AUTOCONF SUPPORT
		2820
		2821	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		2822	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2823	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2824	include F<config.h> and configure itself accordingly.
		2825
		2826	For this of course you need the m4 file:
		2827
		2828	libev.m4
		2829
		2830	=head2 PREPROCESSOR SYMBOLS/MACROS
		2831
		2832	Libev can be configured via a variety of preprocessor symbols you have to
		2833	define before including any of its files. The default in the absence of
		2834	autoconf is noted for every option.
		2835
		2836	=over 4
		2837
		2838	=item EV_STANDALONE
		2839
		2840	Must always be C<1> if you do not use autoconf configuration, which
		2841	keeps libev from including F<config.h>, and it also defines dummy
		2842	implementations for some libevent functions (such as logging, which is not
		2843	supported). It will also not define any of the structs usually found in
		2844	F<event.h> that are not directly supported by the libev core alone.
		2845
		2846	=item EV_USE_MONOTONIC
		2847
		2848	If defined to be C<1>, libev will try to detect the availability of the
		2849	monotonic clock option at both compile time and runtime. Otherwise no use
		2850	of the monotonic clock option will be attempted. If you enable this, you
		2851	usually have to link against librt or something similar. Enabling it when
		2852	the functionality isn't available is safe, though, although you have
		2853	to make sure you link against any libraries where the C<clock_gettime>
		2854	function is hiding in (often F<-lrt>).
		2855
		2856	=item EV_USE_REALTIME
		2857
		2858	If defined to be C<1>, libev will try to detect the availability of the
		2859	real-time clock option at compile time (and assume its availability at
		2860	runtime if successful). Otherwise no use of the real-time clock option will
		2861	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2862	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2863	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2864
		2865	=item EV_USE_NANOSLEEP
		2866
		2867	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2868	and will use it for delays. Otherwise it will use C<select ()>.
		2869
		2870	=item EV_USE_EVENTFD
		2871
		2872	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2873	available and will probe for kernel support at runtime. This will improve
		2874	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2875	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2876	2.7 or newer, otherwise disabled.
		2877
		2878	=item EV_USE_SELECT
		2879
		2880	If undefined or defined to be C<1>, libev will compile in support for the
		2881	C<select>(2) backend. No attempt at auto-detection will be done: if no
		2882	other method takes over, select will be it. Otherwise the select backend
		2883	will not be compiled in.
		2884
		2885	=item EV_SELECT_USE_FD_SET
		2886
		2887	If defined to C<1>, then the select backend will use the system C<fd_set>
		2888	structure. This is useful if libev doesn't compile due to a missing
		2889	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		2890	exotic systems. This usually limits the range of file descriptors to some
		2891	low limit such as 1024 or might have other limitations (winsocket only
		2892	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2893	influence the size of the C<fd_set> used.
		2894
		2895	=item EV_SELECT_IS_WINSOCKET
		2896
		2897	When defined to C<1>, the select backend will assume that
		2898	select/socket/connect etc. don't understand file descriptors but
		2899	wants osf handles on win32 (this is the case when the select to
		2900	be used is the winsock select). This means that it will call
		2901	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2902	it is assumed that all these functions actually work on fds, even
		2903	on win32. Should not be defined on non-win32 platforms.
		2904
		2905	=item EV_FD_TO_WIN32_HANDLE
		2906
		2907	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2908	file descriptors to socket handles. When not defining this symbol (the
		2909	default), then libev will call C<_get_osfhandle>, which is usually
		2910	correct. In some cases, programs use their own file descriptor management,
		2911	in which case they can provide this function to map fds to socket handles.
		2912
		2913	=item EV_USE_POLL
		2914
		2915	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2916	backend. Otherwise it will be enabled on non-win32 platforms. It
		2917	takes precedence over select.
		2918
		2919	=item EV_USE_EPOLL
		2920
		2921	If defined to be C<1>, libev will compile in support for the Linux
		2922	C<epoll>(7) backend. Its availability will be detected at runtime,
		2923	otherwise another method will be used as fallback. This is the preferred
		2924	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2925	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2926
		2927	=item EV_USE_KQUEUE
		2928
		2929	If defined to be C<1>, libev will compile in support for the BSD style
		2930	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2931	otherwise another method will be used as fallback. This is the preferred
		2932	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2933	supports some types of fds correctly (the only platform we found that
		2934	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2935	not be used unless explicitly requested. The best way to use it is to find
		2936	out whether kqueue supports your type of fd properly and use an embedded
		2937	kqueue loop.
		2938
		2939	=item EV_USE_PORT
		2940
		2941	If defined to be C<1>, libev will compile in support for the Solaris
		2942	10 port style backend. Its availability will be detected at runtime,
		2943	otherwise another method will be used as fallback. This is the preferred
		2944	backend for Solaris 10 systems.
		2945
		2946	=item EV_USE_DEVPOLL
		2947
		2948	Reserved for future expansion, works like the USE symbols above.
		2949
		2950	=item EV_USE_INOTIFY
		2951
		2952	If defined to be C<1>, libev will compile in support for the Linux inotify
		2953	interface to speed up C<ev_stat> watchers. Its actual availability will
		2954	be detected at runtime. If undefined, it will be enabled if the headers
		2955	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2956
		2957	=item EV_ATOMIC_T
		2958
		2959	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2960	access is atomic with respect to other threads or signal contexts. No such
		2961	type is easily found in the C language, so you can provide your own type
		2962	that you know is safe for your purposes. It is used both for signal handler "locking"
		2963	as well as for signal and thread safety in C<ev_async> watchers.
		2964
		2965	In the absence of this define, libev will use C<sig_atomic_t volatile>
		2966	(from F<signal.h>), which is usually good enough on most platforms.
		2967
		2968	=item EV_H
		2969
		2970	The name of the F<ev.h> header file used to include it. The default if
		2971	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2972	used to virtually rename the F<ev.h> header file in case of conflicts.
		2973
		2974	=item EV_CONFIG_H
		2975
		2976	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2977	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2978	C<EV_H>, above.
		2979
		2980	=item EV_EVENT_H
		2981
		2982	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2983	of how the F<event.h> header can be found, the default is C<"event.h">.
		2984
		2985	=item EV_PROTOTYPES
		2986
		2987	If defined to be C<0>, then F<ev.h> will not define any function
		2988	prototypes, but still define all the structs and other symbols. This is
		2989	occasionally useful if you want to provide your own wrapper functions
		2990	around libev functions.
		2991
		2992	=item EV_MULTIPLICITY
		2993
		2994	If undefined or defined to C<1>, then all event-loop-specific functions
		2995	will have the C<struct ev_loop *> as first argument, and you can create
		2996	additional independent event loops. Otherwise there will be no support
		2997	for multiple event loops and there is no first event loop pointer
		2998	argument. Instead, all functions act on the single default loop.
		2999
		3000	=item EV_MINPRI
		3001
		3002	=item EV_MAXPRI
		3003
		3004	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3005	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3006	provide for more priorities by overriding those symbols (usually defined
		3007	to be C<-2> and C<2>, respectively).
		3008
		3009	When doing priority-based operations, libev usually has to linearly search
		3010	all the priorities, so having many of them (hundreds) uses a lot of space
		3011	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3012	fine.
		3013
		3014	If your embedding application does not need any priorities, defining these both to
		3015	C<0> will save some memory and CPU.
		3016
		3017	=item EV_PERIODIC_ENABLE
		3018
		3019	If undefined or defined to be C<1>, then periodic timers are supported. If
		3020	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3021	code.
		3022
		3023	=item EV_IDLE_ENABLE
		3024
		3025	If undefined or defined to be C<1>, then idle watchers are supported. If
		3026	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3027	code.
		3028
		3029	=item EV_EMBED_ENABLE
		3030
		3031	If undefined or defined to be C<1>, then embed watchers are supported. If
		3032	defined to be C<0>, then they are not.
		3033
		3034	=item EV_STAT_ENABLE
		3035
		3036	If undefined or defined to be C<1>, then stat watchers are supported. If
		3037	defined to be C<0>, then they are not.
		3038
		3039	=item EV_FORK_ENABLE
		3040
		3041	If undefined or defined to be C<1>, then fork watchers are supported. If
		3042	defined to be C<0>, then they are not.
		3043
		3044	=item EV_ASYNC_ENABLE
		3045
		3046	If undefined or defined to be C<1>, then async watchers are supported. If
		3047	defined to be C<0>, then they are not.
		3048
		3049	=item EV_MINIMAL
		3050
		3051	If you need to shave off some kilobytes of code at the expense of some
		3052	speed, define this symbol to C<1>. Currently this is used to override some
		3053	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3054	much smaller 2-heap for timer management over the default 4-heap.
		3055
		3056	=item EV_PID_HASHSIZE
		3057
		3058	C<ev_child> watchers use a small hash table to distribute workload by
		3059	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3060	than enough. If you need to manage thousands of children you might want to
		3061	increase this value (I<must> be a power of two).
		3062
		3063	=item EV_INOTIFY_HASHSIZE
		3064
		3065	C<ev_stat> watchers use a small hash table to distribute workload by
		3066	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3067	usually more than enough. If you need to manage thousands of C<ev_stat>
		3068	watchers you might want to increase this value (I<must> be a power of
		3069	two).
		3070
		3071	=item EV_USE_4HEAP
		3072
		3073	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3074	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3075	to C<1>. The 4-heap uses more complicated (longer) code but has
		3076	noticeably faster performance with many (thousands) of watchers.
		3077
		3078	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3079	(disabled).
		3080
		3081	=item EV_HEAP_CACHE_AT
		3082
		3083	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3084	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3085	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3086	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3087	but avoids random read accesses on heap changes. This improves performance
		3088	noticeably with with many (hundreds) of watchers.
		3089
		3090	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3091	(disabled).
		3092
		3093	=item EV_VERIFY
		3094
		3095	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3096	be done: If set to C<0>, no internal verification code will be compiled
		3097	in. If set to C<1>, then verification code will be compiled in, but not
		3098	called. If set to C<2>, then the internal verification code will be
		3099	called once per loop, which can slow down libev. If set to C<3>, then the
		3100	verification code will be called very frequently, which will slow down
		3101	libev considerably.
		3102
		3103	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3104	C<0.>
		3105
		3106	=item EV_COMMON
		3107
		3108	By default, all watchers have a C<void *data> member. By redefining
		3109	this macro to a something else you can include more and other types of
		3110	members. You have to define it each time you include one of the files,
		3111	though, and it must be identical each time.
		3112
		3113	For example, the perl EV module uses something like this:
		3114
		3115	#define EV_COMMON \
		3116	SV *self; /* contains this struct */ \
		3117	SV *cb_sv, *fh /* note no trailing ";" */
		3118
		3119	=item EV_CB_DECLARE (type)
		3120
		3121	=item EV_CB_INVOKE (watcher, revents)
		3122
		3123	=item ev_set_cb (ev, cb)
		3124
		3125	Can be used to change the callback member declaration in each watcher,
		3126	and the way callbacks are invoked and set. Must expand to a struct member
		3127	definition and a statement, respectively. See the F<ev.h> header file for
		3128	their default definitions. One possible use for overriding these is to
		3129	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3130	method calls instead of plain function calls in C++.
		3131
		3132	=head2 EXPORTED API SYMBOLS
		3133
		3134	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3135	exported symbols, you can use the provided F<Symbol.*> files which list
		3136	all public symbols, one per line:
		3137
		3138	Symbols.ev for libev proper
		3139	Symbols.event for the libevent emulation
		3140
		3141	This can also be used to rename all public symbols to avoid clashes with
		3142	multiple versions of libev linked together (which is obviously bad in
		3143	itself, but sometimes it is inconvenient to avoid this).
		3144
		3145	A sed command like this will create wrapper C<#define>'s that you need to
		3146	include before including F<ev.h>:
		3147
		3148	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3149
		3150	This would create a file F<wrap.h> which essentially looks like this:
		3151
		3152	#define ev_backend myprefix_ev_backend
		3153	#define ev_check_start myprefix_ev_check_start
		3154	#define ev_check_stop myprefix_ev_check_stop
		3155	...
		3156
		3157	=head2 EXAMPLES
		3158
		3159	For a real-world example of a program the includes libev
		3160	verbatim, you can have a look at the EV perl module
		3161	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3162	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3163	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3164	will be compiled. It is pretty complex because it provides its own header
		3165	file.
		3166
		3167	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3168	that everybody includes and which overrides some configure choices:
		3169
		3170	#define EV_MINIMAL 1
		3171	#define EV_USE_POLL 0
		3172	#define EV_MULTIPLICITY 0
		3173	#define EV_PERIODIC_ENABLE 0
		3174	#define EV_STAT_ENABLE 0
		3175	#define EV_FORK_ENABLE 0
		3176	#define EV_CONFIG_H <config.h>
		3177	#define EV_MINPRI 0
		3178	#define EV_MAXPRI 0
		3179
		3180	#include "ev++.h"
		3181
		3182	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3183
		3184	#include "ev_cpp.h"
		3185	#include "ev.c"
		3186
		3187
		3188	=head1 THREADS AND COROUTINES
		3189
		3190	=head2 THREADS
		3191
		3192	Libev itself is completely thread-safe, but it uses no locking. This
		3193	means that you can use as many loops as you want in parallel, as long as
		3194	only one thread ever calls into one libev function with the same loop
		3195	parameter.
		3196
		3197	Or put differently: calls with different loop parameters can be done in
		3198	parallel from multiple threads, calls with the same loop parameter must be
		3199	done serially (but can be done from different threads, as long as only one
		3200	thread ever is inside a call at any point in time, e.g. by using a mutex
		3201	per loop).
		3202
		3203	If you want to know which design (one loop, locking, or multiple loops
		3204	without or something else still) is best for your problem, then I cannot
		3205	help you. I can give some generic advice however:
		3206
		3207	=over 4
		3208
		3209	=item * most applications have a main thread: use the default libev loop
		3210	in that thread, or create a separate thread running only the default loop.
		3211
		3212	This helps integrating other libraries or software modules that use libev
		3213	themselves and don't care/know about threading.
		3214
		3215	=item * one loop per thread is usually a good model.
		3216
		3217	Doing this is almost never wrong, sometimes a better-performance model
		3218	exists, but it is always a good start.
		3219
		3220	=item * other models exist, such as the leader/follower pattern, where one
		3221	loop is handed through multiple threads in a kind of round-robin fashion.
		3222
		3223	Choosing a model is hard - look around, learn, know that usually you can do
		3224	better than you currently do :-)
		3225
		3226	=item * often you need to talk to some other thread which blocks in the
		3227	event loop - C<ev_async> watchers can be used to wake them up from other
		3228	threads safely (or from signal contexts...).
		3229
		3230	=back
		3231
		3232	=head2 COROUTINES
		3233
		3234	Libev is much more accommodating to coroutines ("cooperative threads"):
		3235	libev fully supports nesting calls to it's functions from different
		3236	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3237	different coroutines and switch freely between both coroutines running the
		3238	loop, as long as you don't confuse yourself). The only exception is that
		3239	you must not do this from C<ev_periodic> reschedule callbacks.
		3240
		3241	Care has been invested into making sure that libev does not keep local
		3242	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3243	switches.
		3244
		3245
		3246	=head1 COMPLEXITIES
		3247
		3248	In this section the complexities of (many of) the algorithms used inside
		3249	libev will be explained. For complexity discussions about backends see the
		3250	documentation for C<ev_default_init>.
		3251
		3252	All of the following are about amortised time: If an array needs to be
		3253	extended, libev needs to realloc and move the whole array, but this
		3254	happens asymptotically never with higher number of elements, so O(1) might
		3255	mean it might do a lengthy realloc operation in rare cases, but on average
		3256	it is much faster and asymptotically approaches constant time.
		3257
		3258	=over 4
		3259
		3260	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3261
		3262	This means that, when you have a watcher that triggers in one hour and
		3263	there are 100 watchers that would trigger before that then inserting will
		3264	have to skip roughly seven (C<ld 100>) of these watchers.
		3265
		3266	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3267
		3268	That means that changing a timer costs less than removing/adding them
		3269	as only the relative motion in the event queue has to be paid for.
		3270
		3271	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3272
		3273	These just add the watcher into an array or at the head of a list.
		3274
		3275	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3276
		3277	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3278
		3279	These watchers are stored in lists then need to be walked to find the
		3280	correct watcher to remove. The lists are usually short (you don't usually
		3281	have many watchers waiting for the same fd or signal).
		3282
		3283	=item Finding the next timer in each loop iteration: O(1)
		3284
		3285	By virtue of using a binary or 4-heap, the next timer is always found at a
		3286	fixed position in the storage array.
		3287
		3288	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3289
		3290	A change means an I/O watcher gets started or stopped, which requires
		3291	libev to recalculate its status (and possibly tell the kernel, depending
		3292	on backend and whether C<ev_io_set> was used).
		3293
		3294	=item Activating one watcher (putting it into the pending state): O(1)
		3295
		3296	=item Priority handling: O(number_of_priorities)
		3297
		3298	Priorities are implemented by allocating some space for each
		3299	priority. When doing priority-based operations, libev usually has to
		3300	linearly search all the priorities, but starting/stopping and activating
		3301	watchers becomes O(1) w.r.t. priority handling.
		3302
		3303	=item Sending an ev_async: O(1)
		3304
		3305	=item Processing ev_async_send: O(number_of_async_watchers)
		3306
		3307	=item Processing signals: O(max_signal_number)
		3308
		3309	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3310	calls in the current loop iteration. Checking for async and signal events
		3311	involves iterating over all running async watchers or all signal numbers.
		3312
		3313	=back
		3314
		3315
		3316	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3317
		3318	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3319	requires, and its I/O model is fundamentally incompatible with the POSIX
		3320	model. Libev still offers limited functionality on this platform in
		3321	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3322	descriptors. This only applies when using Win32 natively, not when using
		3323	e.g. cygwin.
		3324
		3325	Lifting these limitations would basically require the full
		3326	re-implementation of the I/O system. If you are into these kinds of
		3327	things, then note that glib does exactly that for you in a very portable
		3328	way (note also that glib is the slowest event library known to man).
		3329
		3330	There is no supported compilation method available on windows except
		3331	embedding it into other applications.
		3332
		3333	Not a libev limitation but worth mentioning: windows apparently doesn't
		3334	accept large writes: instead of resulting in a partial write, windows will
		3335	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3336	so make sure you only write small amounts into your sockets (less than a
		3337	megabyte seems safe, but thsi apparently depends on the amount of memory
		3338	available).
		3339
		3340	Due to the many, low, and arbitrary limits on the win32 platform and
		3341	the abysmal performance of winsockets, using a large number of sockets
		3342	is not recommended (and not reasonable). If your program needs to use
		3343	more than a hundred or so sockets, then likely it needs to use a totally
		3344	different implementation for windows, as libev offers the POSIX readiness
		3345	notification model, which cannot be implemented efficiently on windows
		3346	(Microsoft monopoly games).
		3347
		3348	A typical way to use libev under windows is to embed it (see the embedding
		3349	section for details) and use the following F<evwrap.h> header file instead
		3350	of F<ev.h>:
		3351
		3352	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3353	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3354
		3355	#include "ev.h"
		3356
		3357	And compile the following F<evwrap.c> file into your project (make sure
		3358	you do I<not> compile the F<ev.c> or any other embedded soruce files!):
		3359
		3360	#include "evwrap.h"
		3361	#include "ev.c"
		3362
		3363	=over 4
		3364
		3365	=item The winsocket select function
		3366
		3367	The winsocket C<select> function doesn't follow POSIX in that it
		3368	requires socket I<handles> and not socket I<file descriptors> (it is
		3369	also extremely buggy). This makes select very inefficient, and also
		3370	requires a mapping from file descriptors to socket handles (the Microsoft
		3371	C runtime provides the function C<_open_osfhandle> for this). See the
		3372	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3373	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3374
		3375	The configuration for a "naked" win32 using the Microsoft runtime
		3376	libraries and raw winsocket select is:
		3377
		3378	#define EV_USE_SELECT 1
		3379	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3380
		3381	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3382	complexity in the O(n²) range when using win32.
		3383
		3384	=item Limited number of file descriptors
		3385
		3386	Windows has numerous arbitrary (and low) limits on things.
		3387
		3388	Early versions of winsocket's select only supported waiting for a maximum
		3389	of C<64> handles (probably owning to the fact that all windows kernels
		3390	can only wait for C<64> things at the same time internally; Microsoft
		3391	recommends spawning a chain of threads and wait for 63 handles and the
		3392	previous thread in each. Great).
		3393
		3394	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3395	to some high number (e.g. C<2048>) before compiling the winsocket select
		3396	call (which might be in libev or elsewhere, for example, perl does its own
		3397	select emulation on windows).
		3398
		3399	Another limit is the number of file descriptors in the Microsoft runtime
		3400	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3401	or something like this inside Microsoft). You can increase this by calling
		3402	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3403	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3404	libraries.
		3405
		3406	This might get you to about C<512> or C<2048> sockets (depending on
		3407	windows version and/or the phase of the moon). To get more, you need to
		3408	wrap all I/O functions and provide your own fd management, but the cost of
		3409	calling select (O(n²)) will likely make this unworkable.
		3410
		3411	=back
		3412
		3413
		3414	=head1 PORTABILITY REQUIREMENTS
		3415
		3416	In addition to a working ISO-C implementation, libev relies on a few
		3417	additional extensions:
		3418
		3419	=over 4
		3420
		3421	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3422	calling conventions regardless of C<ev_watcher_type *>.
		3423
		3424	Libev assumes not only that all watcher pointers have the same internal
		3425	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3426	assumes that the same (machine) code can be used to call any watcher
		3427	callback: The watcher callbacks have different type signatures, but libev
		3428	calls them using an C<ev_watcher *> internally.
		3429
		3430	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3431
		3432	The type C<sig_atomic_t volatile> (or whatever is defined as
		3433	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3434	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3435	believed to be sufficiently portable.
		3436
		3437	=item C<sigprocmask> must work in a threaded environment
		3438
		3439	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3440	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3441	pthread implementations will either allow C<sigprocmask> in the "main
		3442	thread" or will block signals process-wide, both behaviours would
		3443	be compatible with libev. Interaction between C<sigprocmask> and
		3444	C<pthread_sigmask> could complicate things, however.
		3445
		3446	The most portable way to handle signals is to block signals in all threads
		3447	except the initial one, and run the default loop in the initial thread as
		3448	well.
		3449
		3450	=item C<long> must be large enough for common memory allocation sizes
		3451
		3452	To improve portability and simplify using libev, libev uses C<long>
		3453	internally instead of C<size_t> when allocating its data structures. On
		3454	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3455	is still at least 31 bits everywhere, which is enough for hundreds of
		3456	millions of watchers.
		3457
		3458	=item C<double> must hold a time value in seconds with enough accuracy
		3459
		3460	The type C<double> is used to represent timestamps. It is required to
		3461	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3462	enough for at least into the year 4000. This requirement is fulfilled by
		3463	implementations implementing IEEE 754 (basically all existing ones).
		3464
		3465	=back
		3466
		3467	If you know of other additional requirements drop me a note.
		3468
		3469
		3470	=head1 COMPILER WARNINGS
		3471
		3472	Depending on your compiler and compiler settings, you might get no or a
		3473	lot of warnings when compiling libev code. Some people are apparently
		3474	scared by this.
		3475
		3476	However, these are unavoidable for many reasons. For one, each compiler
		3477	has different warnings, and each user has different tastes regarding
		3478	warning options. "Warn-free" code therefore cannot be a goal except when
		3479	targeting a specific compiler and compiler-version.
		3480
		3481	Another reason is that some compiler warnings require elaborate
		3482	workarounds, or other changes to the code that make it less clear and less
		3483	maintainable.
		3484
		3485	And of course, some compiler warnings are just plain stupid, or simply
		3486	wrong (because they don't actually warn about the condition their message
		3487	seems to warn about).
		3488
		3489	While libev is written to generate as few warnings as possible,
		3490	"warn-free" code is not a goal, and it is recommended not to build libev
		3491	with any compiler warnings enabled unless you are prepared to cope with
		3492	them (e.g. by ignoring them). Remember that warnings are just that:
		3493	warnings, not errors, or proof of bugs.
		3494
		3495
		3496	=head1 VALGRIND
		3497
		3498	Valgrind has a special section here because it is a popular tool that is
		3499	highly useful, but valgrind reports are very hard to interpret.
		3500
		3501	If you think you found a bug (memory leak, uninitialised data access etc.)
		3502	in libev, then check twice: If valgrind reports something like:
		3503
		3504	==2274== definitely lost: 0 bytes in 0 blocks.
		3505	==2274== possibly lost: 0 bytes in 0 blocks.
		3506	==2274== still reachable: 256 bytes in 1 blocks.
		3507
		3508	Then there is no memory leak. Similarly, under some circumstances,
		3509	valgrind might report kernel bugs as if it were a bug in libev, or it
		3510	might be confused (it is a very good tool, but only a tool).
		3511
		3512	If you are unsure about something, feel free to contact the mailing list
		3513	with the full valgrind report and an explanation on why you think this is
		3514	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3515	no bug" answer and take the chance of learning how to interpret valgrind
		3516	properly.
		3517
		3518	If you need, for some reason, empty reports from valgrind for your project
		3519	I suggest using suppression lists.
		3520
878		3521
879	=head1 AUTHOR	3522	=head1 AUTHOR
880		3523
881	Marc Lehmann <libev@schmorp.de>.	3524	Marc Lehmann <libev@schmorp.de>.
882		3525

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