ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.30 by root, Fri Nov 23 04:36:03 2007 UTC vs.
Revision 1.177 by root, Mon Sep 8 17:27:42 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).
		577
		578	=item ev_now_update (loop)
		579
		580	Establishes the current time by querying the kernel, updating the time
		581	returned by C<ev_now ()> in the progress. This is a costly operation and
		582	is usually done automatically within C<ev_loop ()>.
		583
		584	This function is rarely useful, but when some event callback runs for a
		585	very long time without entering the event loop, updating libev's idea of
		586	the current time is a good idea.
		587
		588	See also "The special problem of time updates" in the C<ev_timer> section.
267		589
268	=item ev_loop (loop, int flags)	590	=item ev_loop (loop, int flags)
269		591
270	Finally, this is it, the event handler. This function usually is called	592	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	593	after you initialised all your watchers and you want to start handling
272	events.	594	events.
273		595
274	If the flags argument is specified as 0, it will not return until either	596	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.	597	either no event watchers are active anymore or C<ev_unloop> was called.
		598
		599	Please note that an explicit C<ev_unloop> is usually better than
		600	relying on all watchers to be stopped when deciding when a program has
		601	finished (especially in interactive programs), but having a program that
		602	automatically loops as long as it has to and no longer by virtue of
		603	relying on its watchers stopping correctly is a thing of beauty.
276		604
277	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	605	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	606	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.	607	case there are no events and will return after one iteration of the loop.
280		608
281	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	609	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	610	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	611	your process until at least one new event arrives, and will return after
284	one iteration of the loop.	612	one iteration of the loop. This is useful if you are waiting for some
		613	external event in conjunction with something not expressible using other
		614	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		615	usually a better approach for this kind of thing.
285		616
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:	617	Here are the gory details of what C<ev_loop> does:
291		618
292	1. If there are no active watchers (reference count is zero), return.	619	- Before the first iteration, call any pending watchers.
		620	* If EVFLAG_FORKCHECK was used, check for a fork.
		621	- If a fork was detected (by any means), queue and call all fork watchers.
293	2. Queue and immediately call all prepare watchers.	622	- Queue and call all prepare watchers.
294	3. If we have been forked, recreate the kernel state.	623	- If we have been forked, detach and recreate the kernel state
		624	as to not disturb the other process.
295	4. Update the kernel state with all outstanding changes.	625	- Update the kernel state with all outstanding changes.
296	5. Update the "event loop time".	626	- Update the "event loop time" (ev_now ()).
297	6. Calculate for how long to block.	627	- Calculate for how long to sleep or block, if at all
		628	(active idle watchers, EVLOOP_NONBLOCK or not having
		629	any active watchers at all will result in not sleeping).
		630	- Sleep if the I/O and timer collect interval say so.
298	7. Block the process, waiting for events.	631	- Block the process, waiting for any events.
		632	- Queue all outstanding I/O (fd) events.
299	8. Update the "event loop time" and do time jump handling.	633	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
300	9. Queue all outstanding timers.	634	- Queue all outstanding timers.
301	10. Queue all outstanding periodics.	635	- Queue all outstanding periodics.
302	11. If no events are pending now, queue all idle watchers.	636	- Unless any events are pending now, queue all idle watchers.
303	12. Queue all check watchers.	637	- Queue all check watchers.
304	13. Call all queued watchers in reverse order (i.e. check watchers first).	638	- Call all queued watchers in reverse order (i.e. check watchers first).
		639	Signals and child watchers are implemented as I/O watchers, and will
		640	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	641	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
306	was used, return, otherwise continue with step #1.	642	were used, or there are no active watchers, return, otherwise
		643	continue with step *.
		644
		645	Example: Queue some jobs and then loop until no events are outstanding
		646	anymore.
		647
		648	... queue jobs here, make sure they register event watchers as long
		649	... as they still have work to do (even an idle watcher will do..)
		650	ev_loop (my_loop, 0);
		651	... jobs done or somebody called unloop. yeah!
307		652
308	=item ev_unloop (loop, how)	653	=item ev_unloop (loop, how)
309		654
310	Can be used to make a call to C<ev_loop> return early (but only after it	655	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	656	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	657	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.	658	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		659
		660	This "unloop state" will be cleared when entering C<ev_loop> again.
314		661
315	=item ev_ref (loop)	662	=item ev_ref (loop)
316		663
317	=item ev_unref (loop)	664	=item ev_unref (loop)
318		665
…		…
323	returning, ev_unref() after starting, and ev_ref() before stopping it. For	670	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	671	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	672	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	673	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	674	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>.	675	libraries. Just remember to I<unref after start> and I<ref before stop>
		676	(but only if the watcher wasn't active before, or was active before,
		677	respectively).
		678
		679	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		680	running when nothing else is active.
		681
		682	struct ev_signal exitsig;
		683	ev_signal_init (&exitsig, sig_cb, SIGINT);
		684	ev_signal_start (loop, &exitsig);
		685	evf_unref (loop);
		686
		687	Example: For some weird reason, unregister the above signal handler again.
		688
		689	ev_ref (loop);
		690	ev_signal_stop (loop, &exitsig);
		691
		692	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		693
		694	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		695
		696	These advanced functions influence the time that libev will spend waiting
		697	for events. Both time intervals are by default C<0>, meaning that libev
		698	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		699	latency.
		700
		701	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		702	allows libev to delay invocation of I/O and timer/periodic callbacks
		703	to increase efficiency of loop iterations (or to increase power-saving
		704	opportunities).
		705
		706	The background is that sometimes your program runs just fast enough to
		707	handle one (or very few) event(s) per loop iteration. While this makes
		708	the program responsive, it also wastes a lot of CPU time to poll for new
		709	events, especially with backends like C<select ()> which have a high
		710	overhead for the actual polling but can deliver many events at once.
		711
		712	By setting a higher I<io collect interval> you allow libev to spend more
		713	time collecting I/O events, so you can handle more events per iteration,
		714	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		715	C<ev_timer>) will be not affected. Setting this to a non-null value will
		716	introduce an additional C<ev_sleep ()> call into most loop iterations.
		717
		718	Likewise, by setting a higher I<timeout collect interval> you allow libev
		719	to spend more time collecting timeouts, at the expense of increased
		720	latency (the watcher callback will be called later). C<ev_io> watchers
		721	will not be affected. Setting this to a non-null value will not introduce
		722	any overhead in libev.
		723
		724	Many (busy) programs can usually benefit by setting the I/O collect
		725	interval to a value near C<0.1> or so, which is often enough for
		726	interactive servers (of course not for games), likewise for timeouts. It
		727	usually doesn't make much sense to set it to a lower value than C<0.01>,
		728	as this approaches the timing granularity of most systems.
		729
		730	Setting the I<timeout collect interval> can improve the opportunity for
		731	saving power, as the program will "bundle" timer callback invocations that
		732	are "near" in time together, by delaying some, thus reducing the number of
		733	times the process sleeps and wakes up again. Another useful technique to
		734	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		735	they fire on, say, one-second boundaries only.
		736
		737	=item ev_loop_verify (loop)
		738
		739	This function only does something when C<EV_VERIFY> support has been
		740	compiled in. It tries to go through all internal structures and checks
		741	them for validity. If anything is found to be inconsistent, it will print
		742	an error message to standard error and call C<abort ()>.
		743
		744	This can be used to catch bugs inside libev itself: under normal
		745	circumstances, this function will never abort as of course libev keeps its
		746	data structures consistent.
329		747
330	=back	748	=back
		749
331		750
332	=head1 ANATOMY OF A WATCHER	751	=head1 ANATOMY OF A WATCHER
333		752
334	A watcher is a structure that you create and register to record your	753	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	754	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:	755	become readable, you would create an C<ev_io> watcher for that:
337		756
338	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	757	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
339	{	758	{
340	ev_io_stop (w);	759	ev_io_stop (w);
341	ev_unloop (loop, EVUNLOOP_ALL);	760	ev_unloop (loop, EVUNLOOP_ALL);
342	}	761	}
343		762
344	struct ev_loop *loop = ev_default_loop (0);	763	struct ev_loop *loop = ev_default_loop (0);
345	struct ev_io stdin_watcher;	764	struct ev_io stdin_watcher;
346	ev_init (&stdin_watcher, my_cb);	765	ev_init (&stdin_watcher, my_cb);
347	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	766	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
348	ev_io_start (loop, &stdin_watcher);	767	ev_io_start (loop, &stdin_watcher);
349	ev_loop (loop, 0);	768	ev_loop (loop, 0);
350		769
351	As you can see, you are responsible for allocating the memory for your	770	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,	771	watcher structures (and it is usually a bad idea to do this on the stack,
353	although this can sometimes be quite valid).	772	although this can sometimes be quite valid).
354		773
355	Each watcher structure must be initialised by a call to C<ev_init	774	Each watcher structure must be initialised by a call to C<ev_init
356	(watcher *, callback)>, which expects a callback to be provided. This	775	(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	776	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	777	watchers, each time the event loop detects that the file descriptor given
359	is readable and/or writable).	778	is readable and/or writable).
360		779
361	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	780	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	781	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	787	*) >>), and you can stop watching for events at any time by calling the
369	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	788	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
370		789
371	As long as your watcher is active (has been started but not stopped) you	790	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	791	must not touch the values stored in it. Most specifically you must never
373	reinitialise it or call its set method.	792	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		793
380	Each and every callback receives the event loop pointer as first, the	794	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	795	registered watcher structure as second, and a bitset of received events as
382	third argument.	796	third argument.
383		797
…		…
407	The signal specified in the C<ev_signal> watcher has been received by a thread.	821	The signal specified in the C<ev_signal> watcher has been received by a thread.
408		822
409	=item C<EV_CHILD>	823	=item C<EV_CHILD>
410		824
411	The pid specified in the C<ev_child> watcher has received a status change.	825	The pid specified in the C<ev_child> watcher has received a status change.
		826
		827	=item C<EV_STAT>
		828
		829	The path specified in the C<ev_stat> watcher changed its attributes somehow.
412		830
413	=item C<EV_IDLE>	831	=item C<EV_IDLE>
414		832
415	The C<ev_idle> watcher has determined that you have nothing better to do.	833	The C<ev_idle> watcher has determined that you have nothing better to do.
416		834
…		…
424	received events. Callbacks of both watcher types can start and stop as	842	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	843	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	844	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
427	C<ev_loop> from blocking).	845	C<ev_loop> from blocking).
428		846
		847	=item C<EV_EMBED>
		848
		849	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		850
		851	=item C<EV_FORK>
		852
		853	The event loop has been resumed in the child process after fork (see
		854	C<ev_fork>).
		855
		856	=item C<EV_ASYNC>
		857
		858	The given async watcher has been asynchronously notified (see C<ev_async>).
		859
429	=item C<EV_ERROR>	860	=item C<EV_ERROR>
430		861
431	An unspecified error has occured, the watcher has been stopped. This might	862	An unspecified error has occurred, the watcher has been stopped. This might
432	happen because the watcher could not be properly started because libev	863	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	864	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	865	problem. You best act on it by reporting the problem and somehow coping
435	with the watcher being stopped.	866	with the watcher being stopped.
436		867
437	Libev will usually signal a few "dummy" events together with an error,	868	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	869	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	870	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	871	with the error from read() or write(). This will not work in multi-threaded
441	programs, though, so beware.	872	programs, though, so beware.
442		873
443	=back	874	=back
		875
		876	=head2 GENERIC WATCHER FUNCTIONS
		877
		878	In the following description, C<TYPE> stands for the watcher type,
		879	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		880
		881	=over 4
		882
		883	=item C<ev_init> (ev_TYPE *watcher, callback)
		884
		885	This macro initialises the generic portion of a watcher. The contents
		886	of the watcher object can be arbitrary (so C<malloc> will do). Only
		887	the generic parts of the watcher are initialised, you I<need> to call
		888	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		889	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		890	which rolls both calls into one.
		891
		892	You can reinitialise a watcher at any time as long as it has been stopped
		893	(or never started) and there are no pending events outstanding.
		894
		895	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		896	int revents)>.
		897
		898	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		899
		900	This macro initialises the type-specific parts of a watcher. You need to
		901	call C<ev_init> at least once before you call this macro, but you can
		902	call C<ev_TYPE_set> any number of times. You must not, however, call this
		903	macro on a watcher that is active (it can be pending, however, which is a
		904	difference to the C<ev_init> macro).
		905
		906	Although some watcher types do not have type-specific arguments
		907	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		908
		909	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		910
		911	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		912	calls into a single call. This is the most convenient method to initialise
		913	a watcher. The same limitations apply, of course.
		914
		915	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		916
		917	Starts (activates) the given watcher. Only active watchers will receive
		918	events. If the watcher is already active nothing will happen.
		919
		920	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		921
		922	Stops the given watcher again (if active) and clears the pending
		923	status. It is possible that stopped watchers are pending (for example,
		924	non-repeating timers are being stopped when they become pending), but
		925	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		926	you want to free or reuse the memory used by the watcher it is therefore a
		927	good idea to always call its C<ev_TYPE_stop> function.
		928
		929	=item bool ev_is_active (ev_TYPE *watcher)
		930
		931	Returns a true value iff the watcher is active (i.e. it has been started
		932	and not yet been stopped). As long as a watcher is active you must not modify
		933	it.
		934
		935	=item bool ev_is_pending (ev_TYPE *watcher)
		936
		937	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		938	events but its callback has not yet been invoked). As long as a watcher
		939	is pending (but not active) you must not call an init function on it (but
		940	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		941	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		942	it).
		943
		944	=item callback ev_cb (ev_TYPE *watcher)
		945
		946	Returns the callback currently set on the watcher.
		947
		948	=item ev_cb_set (ev_TYPE *watcher, callback)
		949
		950	Change the callback. You can change the callback at virtually any time
		951	(modulo threads).
		952
		953	=item ev_set_priority (ev_TYPE *watcher, priority)
		954
		955	=item int ev_priority (ev_TYPE *watcher)
		956
		957	Set and query the priority of the watcher. The priority is a small
		958	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		959	(default: C<-2>). Pending watchers with higher priority will be invoked
		960	before watchers with lower priority, but priority will not keep watchers
		961	from being executed (except for C<ev_idle> watchers).
		962
		963	This means that priorities are I<only> used for ordering callback
		964	invocation after new events have been received. This is useful, for
		965	example, to reduce latency after idling, or more often, to bind two
		966	watchers on the same event and make sure one is called first.
		967
		968	If you need to suppress invocation when higher priority events are pending
		969	you need to look at C<ev_idle> watchers, which provide this functionality.
		970
		971	You I<must not> change the priority of a watcher as long as it is active or
		972	pending.
		973
		974	The default priority used by watchers when no priority has been set is
		975	always C<0>, which is supposed to not be too high and not be too low :).
		976
		977	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		978	fine, as long as you do not mind that the priority value you query might
		979	or might not have been adjusted to be within valid range.
		980
		981	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		982
		983	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		984	C<loop> nor C<revents> need to be valid as long as the watcher callback
		985	can deal with that fact.
		986
		987	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		988
		989	If the watcher is pending, this function returns clears its pending status
		990	and returns its C<revents> bitset (as if its callback was invoked). If the
		991	watcher isn't pending it does nothing and returns C<0>.
		992
		993	=back
		994
444		995
445	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	996	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
446		997
447	Each watcher has, by default, a member C<void *data> that you can change	998	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	999	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	1000	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	1001	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	1002	member, you can also "subclass" the watcher type and provide your own
452	data:	1003	data:
453		1004
454	struct my_io	1005	struct my_io
455	{	1006	{
456	struct ev_io io;	1007	struct ev_io io;
457	int otherfd;	1008	int otherfd;
458	void *somedata;	1009	void *somedata;
459	struct whatever *mostinteresting;	1010	struct whatever *mostinteresting;
460	}	1011	}
461		1012
462	And since your callback will be called with a pointer to the watcher, you	1013	And since your callback will be called with a pointer to the watcher, you
463	can cast it back to your own type:	1014	can cast it back to your own type:
464		1015
465	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1016	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
466	{	1017	{
467	struct my_io *w = (struct my_io *)w_;	1018	struct my_io *w = (struct my_io *)w_;
468	...	1019	...
469	}	1020	}
470		1021
471	More interesting and less C-conformant ways of catsing your callback type	1022	More interesting and less C-conformant ways of casting your callback type
472	have been omitted....	1023	instead have been omitted.
		1024
		1025	Another common scenario is having some data structure with multiple
		1026	watchers:
		1027
		1028	struct my_biggy
		1029	{
		1030	int some_data;
		1031	ev_timer t1;
		1032	ev_timer t2;
		1033	}
		1034
		1035	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		1036	you need to use C<offsetof>:
		1037
		1038	#include <stddef.h>
		1039
		1040	static void
		1041	t1_cb (EV_P_ struct ev_timer *w, int revents)
		1042	{
		1043	struct my_biggy big = (struct my_biggy *
		1044	(((char *)w) - offsetof (struct my_biggy, t1));
		1045	}
		1046
		1047	static void
		1048	t2_cb (EV_P_ struct ev_timer *w, int revents)
		1049	{
		1050	struct my_biggy big = (struct my_biggy *
		1051	(((char *)w) - offsetof (struct my_biggy, t2));
		1052	}
473		1053
474		1054
475	=head1 WATCHER TYPES	1055	=head1 WATCHER TYPES
476		1056
477	This section describes each watcher in detail, but will not repeat	1057	This section describes each watcher in detail, but will not repeat
478	information given in the last section.	1058	information given in the last section. Any initialisation/set macros,
		1059	functions and members specific to the watcher type are explained.
479		1060
		1061	Members are additionally marked with either I<[read-only]>, meaning that,
		1062	while the watcher is active, you can look at the member and expect some
		1063	sensible content, but you must not modify it (you can modify it while the
		1064	watcher is stopped to your hearts content), or I<[read-write]>, which
		1065	means you can expect it to have some sensible content while the watcher
		1066	is active, but you can also modify it. Modifying it may not do something
		1067	sensible or take immediate effect (or do anything at all), but libev will
		1068	not crash or malfunction in any way.
		1069
		1070
480	=head2 C<ev_io> - is this file descriptor readable or writable	1071	=head2 C<ev_io> - is this file descriptor readable or writable?
481		1072
482	I/O watchers check whether a file descriptor is readable or writable	1073	I/O watchers check whether a file descriptor is readable or writable
483	in each iteration of the event loop (This behaviour is called	1074	in each iteration of the event loop, or, more precisely, when reading
484	level-triggering because you keep receiving events as long as the	1075	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	1076	some data. This behaviour is called level-triggering because you keep
486	act on the event and neither want to receive future events).	1077	receiving events as long as the condition persists. Remember you can stop
		1078	the watcher if you don't want to act on the event and neither want to
		1079	receive future events.
487		1080
488	In general you can register as many read and/or write event watchers per	1081	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	1082	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	1083	descriptors to non-blocking mode is also usually a good idea (but not
491	required if you know what you are doing).	1084	required if you know what you are doing).
492		1085
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	1086	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	1087	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
501	EVMETHOD_POLL).	1088	C<EVBACKEND_POLL>).
		1089
		1090	Another thing you have to watch out for is that it is quite easy to
		1091	receive "spurious" readiness notifications, that is your callback might
		1092	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1093	because there is no data. Not only are some backends known to create a
		1094	lot of those (for example Solaris ports), it is very easy to get into
		1095	this situation even with a relatively standard program structure. Thus
		1096	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1097	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1098
		1099	If you cannot run the fd in non-blocking mode (for example you should not
		1100	play around with an Xlib connection), then you have to separately re-test
		1101	whether a file descriptor is really ready with a known-to-be good interface
		1102	such as poll (fortunately in our Xlib example, Xlib already does this on
		1103	its own, so its quite safe to use).
		1104
		1105	=head3 The special problem of disappearing file descriptors
		1106
		1107	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1108	descriptor (either by calling C<close> explicitly or by any other means,
		1109	such as C<dup>). The reason is that you register interest in some file
		1110	descriptor, but when it goes away, the operating system will silently drop
		1111	this interest. If another file descriptor with the same number then is
		1112	registered with libev, there is no efficient way to see that this is, in
		1113	fact, a different file descriptor.
		1114
		1115	To avoid having to explicitly tell libev about such cases, libev follows
		1116	the following policy: Each time C<ev_io_set> is being called, libev
		1117	will assume that this is potentially a new file descriptor, otherwise
		1118	it is assumed that the file descriptor stays the same. That means that
		1119	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1120	descriptor even if the file descriptor number itself did not change.
		1121
		1122	This is how one would do it normally anyway, the important point is that
		1123	the libev application should not optimise around libev but should leave
		1124	optimisations to libev.
		1125
		1126	=head3 The special problem of dup'ed file descriptors
		1127
		1128	Some backends (e.g. epoll), cannot register events for file descriptors,
		1129	but only events for the underlying file descriptions. That means when you
		1130	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1131	events for them, only one file descriptor might actually receive events.
		1132
		1133	There is no workaround possible except not registering events
		1134	for potentially C<dup ()>'ed file descriptors, or to resort to
		1135	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1136
		1137	=head3 The special problem of fork
		1138
		1139	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1140	useless behaviour. Libev fully supports fork, but needs to be told about
		1141	it in the child.
		1142
		1143	To support fork in your programs, you either have to call
		1144	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1145	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1146	C<EVBACKEND_POLL>.
		1147
		1148	=head3 The special problem of SIGPIPE
		1149
		1150	While not really specific to libev, it is easy to forget about SIGPIPE:
		1151	when writing to a pipe whose other end has been closed, your program gets
		1152	send a SIGPIPE, which, by default, aborts your program. For most programs
		1153	this is sensible behaviour, for daemons, this is usually undesirable.
		1154
		1155	So when you encounter spurious, unexplained daemon exits, make sure you
		1156	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1157	somewhere, as that would have given you a big clue).
		1158
		1159
		1160	=head3 Watcher-Specific Functions
502		1161
503	=over 4	1162	=over 4
504		1163
505	=item ev_io_init (ev_io *, callback, int fd, int events)	1164	=item ev_io_init (ev_io *, callback, int fd, int events)
506		1165
507	=item ev_io_set (ev_io *, int fd, int events)	1166	=item ev_io_set (ev_io *, int fd, int events)
508		1167
509	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1168	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 |	1169	receive events for and events is either C<EV_READ>, C<EV_WRITE> or
511	EV_WRITE> to receive the given events.	1170	C<EV_READ | EV_WRITE> to receive the given events.
		1171
		1172	=item int fd [read-only]
		1173
		1174	The file descriptor being watched.
		1175
		1176	=item int events [read-only]
		1177
		1178	The events being watched.
512		1179
513	=back	1180	=back
514		1181
		1182	=head3 Examples
		1183
		1184	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1185	readable, but only once. Since it is likely line-buffered, you could
		1186	attempt to read a whole line in the callback.
		1187
		1188	static void
		1189	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1190	{
		1191	ev_io_stop (loop, w);
		1192	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		1193	}
		1194
		1195	...
		1196	struct ev_loop *loop = ev_default_init (0);
		1197	struct ev_io stdin_readable;
		1198	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1199	ev_io_start (loop, &stdin_readable);
		1200	ev_loop (loop, 0);
		1201
		1202
515	=head2 C<ev_timer> - relative and optionally recurring timeouts	1203	=head2 C<ev_timer> - relative and optionally repeating timeouts
516		1204
517	Timer watchers are simple relative timers that generate an event after a	1205	Timer watchers are simple relative timers that generate an event after a
518	given time, and optionally repeating in regular intervals after that.	1206	given time, and optionally repeating in regular intervals after that.
519		1207
520	The timers are based on real time, that is, if you register an event that	1208	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	1209	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	1210	year, it will still time out after (roughly) and hour. "Roughly" because
523	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1211	detecting time jumps is hard, and some inaccuracies are unavoidable (the
524	monotonic clock option helps a lot here).	1212	monotonic clock option helps a lot here).
		1213
		1214	The callback is guaranteed to be invoked only after its timeout has passed,
		1215	but if multiple timers become ready during the same loop iteration then
		1216	order of execution is undefined.
		1217
		1218	=head3 The special problem of time updates
		1219
		1220	Establishing the current time is a costly operation (it usually takes at
		1221	least two system calls): EV therefore updates its idea of the current
		1222	time only before and after C<ev_loop> polls for new events, which causes
		1223	a growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1224	lots of events.
525		1225
526	The relative timeouts are calculated relative to the C<ev_now ()>	1226	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	1227	time. This is usually the right thing as this timestamp refers to the time
528	of the event triggering whatever timeout you are modifying/starting. If	1228	of the event triggering whatever timeout you are modifying/starting. If
529	you suspect event processing to be delayed and you I<need> to base the timeout	1229	you suspect event processing to be delayed and you I<need> to base the
530	on the current time, use something like this to adjust for this:	1230	timeout on the current time, use something like this to adjust for this:
531		1231
532	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1232	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
533		1233
534	The callback is guarenteed to be invoked only when its timeout has passed,	1234	If the event loop is suspended for a long time, you can also force an
535	but if multiple timers become ready during the same loop iteration then	1235	update of the time returned by C<ev_now ()> by calling C<ev_now_update
536	order of execution is undefined.	1236	()>.
		1237
		1238	=head3 Watcher-Specific Functions and Data Members
537		1239
538	=over 4	1240	=over 4
539		1241
540	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1242	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
541		1243
542	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1244	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
543		1245
544	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1246	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	1247	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	1248	reached. If it is positive, then the timer will automatically be
547	later, again, and again, until stopped manually.	1249	configured to trigger again C<repeat> seconds later, again, and again,
		1250	until stopped manually.
548		1251
549	The timer itself will do a best-effort at avoiding drift, that is, if you	1252	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	1253	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	1254	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	1255	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.	1256	do stuff) the timer will not fire more than once per event loop iteration.
554		1257
555	=item ev_timer_again (loop)	1258	=item ev_timer_again (loop, ev_timer *)
556		1259
557	This will act as if the timer timed out and restart it again if it is	1260	This will act as if the timer timed out and restart it again if it is
558	repeating. The exact semantics are:	1261	repeating. The exact semantics are:
559		1262
		1263	If the timer is pending, its pending status is cleared.
		1264
560	If the timer is started but nonrepeating, stop it.	1265	If the timer is started but non-repeating, stop it (as if it timed out).
561		1266
562	If the timer is repeating, either start it if necessary (with the repeat	1267	If the timer is repeating, either start it if necessary (with the
563	value), or reset the running timer to the repeat value.	1268	C<repeat> value), or reset the running timer to the C<repeat> value.
564		1269
565	This sounds a bit complicated, but here is a useful and typical	1270	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	1271	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	1272	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	1273	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	1274	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	1275	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	1276	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.	1277	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1278	automatically restart it if need be.
		1279
		1280	That means you can ignore the C<after> value and C<ev_timer_start>
		1281	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1282
		1283	ev_timer_init (timer, callback, 0., 5.);
		1284	ev_timer_again (loop, timer);
		1285	...
		1286	timer->again = 17.;
		1287	ev_timer_again (loop, timer);
		1288	...
		1289	timer->again = 10.;
		1290	ev_timer_again (loop, timer);
		1291
		1292	This is more slightly efficient then stopping/starting the timer each time
		1293	you want to modify its timeout value.
		1294
		1295	=item ev_tstamp repeat [read-write]
		1296
		1297	The current C<repeat> value. Will be used each time the watcher times out
		1298	or C<ev_timer_again> is called and determines the next timeout (if any),
		1299	which is also when any modifications are taken into account.
573		1300
574	=back	1301	=back
575		1302
		1303	=head3 Examples
		1304
		1305	Example: Create a timer that fires after 60 seconds.
		1306
		1307	static void
		1308	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1309	{
		1310	.. one minute over, w is actually stopped right here
		1311	}
		1312
		1313	struct ev_timer mytimer;
		1314	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1315	ev_timer_start (loop, &mytimer);
		1316
		1317	Example: Create a timeout timer that times out after 10 seconds of
		1318	inactivity.
		1319
		1320	static void
		1321	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
		1322	{
		1323	.. ten seconds without any activity
		1324	}
		1325
		1326	struct ev_timer mytimer;
		1327	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1328	ev_timer_again (&mytimer); /* start timer */
		1329	ev_loop (loop, 0);
		1330
		1331	// and in some piece of code that gets executed on any "activity":
		1332	// reset the timeout to start ticking again at 10 seconds
		1333	ev_timer_again (&mytimer);
		1334
		1335
576	=head2 C<ev_periodic> - to cron or not to cron	1336	=head2 C<ev_periodic> - to cron or not to cron?
577		1337
578	Periodic watchers are also timers of a kind, but they are very versatile	1338	Periodic watchers are also timers of a kind, but they are very versatile
579	(and unfortunately a bit complex).	1339	(and unfortunately a bit complex).
580		1340
581	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1341	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	1342	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	1343	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 ()	1344	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	1345	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1346	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	1347	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	1348	roughly 10 seconds later as it uses a relative timeout).
588	again).
589		1349
590	They can also be used to implement vastly more complex timers, such as	1350	C<ev_periodic>s can also be used to implement vastly more complex timers,
591	triggering an event on eahc midnight, local time.	1351	such as triggering an event on each "midnight, local time", or other
		1352	complicated, rules.
592		1353
593	As with timers, the callback is guarenteed to be invoked only when the	1354	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	1355	time (C<at>) has passed, but if multiple periodic timers become ready
595	during the same loop iteration then order of execution is undefined.	1356	during the same loop iteration then order of execution is undefined.
		1357
		1358	=head3 Watcher-Specific Functions and Data Members
596		1359
597	=over 4	1360	=over 4
598		1361
599	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1362	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
600		1363
…		…
603	Lots of arguments, lets sort it out... There are basically three modes of	1366	Lots of arguments, lets sort it out... There are basically three modes of
604	operation, and we will explain them from simplest to complex:	1367	operation, and we will explain them from simplest to complex:
605		1368
606	=over 4	1369	=over 4
607		1370
608	=item * absolute timer (interval = reschedule_cb = 0)	1371	=item * absolute timer (at = time, interval = reschedule_cb = 0)
609		1372
610	In this configuration the watcher triggers an event at the wallclock time	1373	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,	1374	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	1375	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.	1376	run when the system time reaches or surpasses this time.
614		1377
615	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1378	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
616		1379
617	In this mode the watcher will always be scheduled to time out at the next	1380	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	1381	C<at + N * interval> time (for some integer N, which can also be negative)
619	of any time jumps.	1382	and then repeat, regardless of any time jumps.
620		1383
621	This can be used to create timers that do not drift with respect to system	1384	This can be used to create timers that do not drift with respect to system
622	time:	1385	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1386	the hour:
623		1387
624	ev_periodic_set (&periodic, 0., 3600., 0);	1388	ev_periodic_set (&periodic, 0., 3600., 0);
625		1389
626	This doesn't mean there will always be 3600 seconds in between triggers,	1390	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	1391	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	1392	full hour (UTC), or more correctly, when the system time is evenly divisible
629	by 3600.	1393	by 3600.
630		1394
631	Another way to think about it (for the mathematically inclined) is that	1395	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	1396	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.	1397	time where C<time = at (mod interval)>, regardless of any time jumps.
634		1398
		1399	For numerical stability it is preferable that the C<at> value is near
		1400	C<ev_now ()> (the current time), but there is no range requirement for
		1401	this value, and in fact is often specified as zero.
		1402
		1403	Note also that there is an upper limit to how often a timer can fire (CPU
		1404	speed for example), so if C<interval> is very small then timing stability
		1405	will of course deteriorate. Libev itself tries to be exact to be about one
		1406	millisecond (if the OS supports it and the machine is fast enough).
		1407
635	=item * manual reschedule mode (reschedule_cb = callback)	1408	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
636		1409
637	In this mode the values for C<interval> and C<at> are both being	1410	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	1411	ignored. Instead, each time the periodic watcher gets scheduled, the
639	reschedule callback will be called with the watcher as first, and the	1412	reschedule callback will be called with the watcher as first, and the
640	current time as second argument.	1413	current time as second argument.
641		1414
642	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1415	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,	1416	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		1417
		1418	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1419	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1420	only event loop modification you are allowed to do).
		1421
647	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1422	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
648	ev_tstamp now)>, e.g.:	1423	*w, ev_tstamp now)>, e.g.:
649		1424
650	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1425	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
651	{	1426	{
652	return now + 60.;	1427	return now + 60.;
653	}	1428	}
…		…
655	It must return the next time to trigger, based on the passed time value	1430	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	1431	(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	1432	will usually be called just before the callback will be triggered, but
658	might be called at other times, too.	1433	might be called at other times, too.
659		1434
660	NOTE: I<< This callback must always return a time that is later than the	1435	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.	1436	equal to the passed C<now> value >>.
662		1437
663	This can be used to create very complex timers, such as a timer that	1438	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	1439	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	1440	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	1441	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).	1442	reason I omitted it as an example).
668		1443
669	=back	1444	=back
…		…
673	Simply stops and restarts the periodic watcher again. This is only useful	1448	Simply stops and restarts the periodic watcher again. This is only useful
674	when you changed some parameters or the reschedule callback would return	1449	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	1450	a different time than the last time it was called (e.g. in a crond like
676	program when the crontabs have changed).	1451	program when the crontabs have changed).
677		1452
		1453	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1454
		1455	When active, returns the absolute time that the watcher is supposed to
		1456	trigger next.
		1457
		1458	=item ev_tstamp offset [read-write]
		1459
		1460	When repeating, this contains the offset value, otherwise this is the
		1461	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1462
		1463	Can be modified any time, but changes only take effect when the periodic
		1464	timer fires or C<ev_periodic_again> is being called.
		1465
		1466	=item ev_tstamp interval [read-write]
		1467
		1468	The current interval value. Can be modified any time, but changes only
		1469	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1470	called.
		1471
		1472	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1473
		1474	The current reschedule callback, or C<0>, if this functionality is
		1475	switched off. Can be changed any time, but changes only take effect when
		1476	the periodic timer fires or C<ev_periodic_again> is being called.
		1477
678	=back	1478	=back
679		1479
		1480	=head3 Examples
		1481
		1482	Example: Call a callback every hour, or, more precisely, whenever the
		1483	system clock is divisible by 3600. The callback invocation times have
		1484	potentially a lot of jitter, but good long-term stability.
		1485
		1486	static void
		1487	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
		1488	{
		1489	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1490	}
		1491
		1492	struct ev_periodic hourly_tick;
		1493	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1494	ev_periodic_start (loop, &hourly_tick);
		1495
		1496	Example: The same as above, but use a reschedule callback to do it:
		1497
		1498	#include <math.h>
		1499
		1500	static ev_tstamp
		1501	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		1502	{
		1503	return fmod (now, 3600.) + 3600.;
		1504	}
		1505
		1506	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1507
		1508	Example: Call a callback every hour, starting now:
		1509
		1510	struct ev_periodic hourly_tick;
		1511	ev_periodic_init (&hourly_tick, clock_cb,
		1512	fmod (ev_now (loop), 3600.), 3600., 0);
		1513	ev_periodic_start (loop, &hourly_tick);
		1514
		1515
680	=head2 C<ev_signal> - signal me when a signal gets signalled	1516	=head2 C<ev_signal> - signal me when a signal gets signalled!
681		1517
682	Signal watchers will trigger an event when the process receives a specific	1518	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	1519	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	1520	will try it's best to deliver signals synchronously, i.e. as part of the
685	normal event processing, like any other event.	1521	normal event processing, like any other event.
…		…
689	with the kernel (thus it coexists with your own signal handlers as long	1525	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	1526	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	1527	watcher for a signal is stopped libev will reset the signal handler to
692	SIG_DFL (regardless of what it was set to before).	1528	SIG_DFL (regardless of what it was set to before).
693		1529
		1530	If possible and supported, libev will install its handlers with
		1531	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1532	interrupted. If you have a problem with system calls getting interrupted by
		1533	signals you can block all signals in an C<ev_check> watcher and unblock
		1534	them in an C<ev_prepare> watcher.
		1535
		1536	=head3 Watcher-Specific Functions and Data Members
		1537
694	=over 4	1538	=over 4
695		1539
696	=item ev_signal_init (ev_signal *, callback, int signum)	1540	=item ev_signal_init (ev_signal *, callback, int signum)
697		1541
698	=item ev_signal_set (ev_signal *, int signum)	1542	=item ev_signal_set (ev_signal *, int signum)
699		1543
700	Configures the watcher to trigger on the given signal number (usually one	1544	Configures the watcher to trigger on the given signal number (usually one
701	of the C<SIGxxx> constants).	1545	of the C<SIGxxx> constants).
702		1546
		1547	=item int signum [read-only]
		1548
		1549	The signal the watcher watches out for.
		1550
703	=back	1551	=back
704		1552
		1553	=head3 Examples
		1554
		1555	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1556
		1557	static void
		1558	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1559	{
		1560	ev_unloop (loop, EVUNLOOP_ALL);
		1561	}
		1562
		1563	struct ev_signal signal_watcher;
		1564	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1565	ev_signal_start (loop, &sigint_cb);
		1566
		1567
705	=head2 C<ev_child> - wait for pid status changes	1568	=head2 C<ev_child> - watch out for process status changes
706		1569
707	Child watchers trigger when your process receives a SIGCHLD in response to	1570	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).	1571	some child status changes (most typically when a child of yours dies). It
		1572	is permissible to install a child watcher I<after> the child has been
		1573	forked (which implies it might have already exited), as long as the event
		1574	loop isn't entered (or is continued from a watcher).
		1575
		1576	Only the default event loop is capable of handling signals, and therefore
		1577	you can only register child watchers in the default event loop.
		1578
		1579	=head3 Process Interaction
		1580
		1581	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1582	initialised. This is necessary to guarantee proper behaviour even if
		1583	the first child watcher is started after the child exits. The occurrence
		1584	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1585	synchronously as part of the event loop processing. Libev always reaps all
		1586	children, even ones not watched.
		1587
		1588	=head3 Overriding the Built-In Processing
		1589
		1590	Libev offers no special support for overriding the built-in child
		1591	processing, but if your application collides with libev's default child
		1592	handler, you can override it easily by installing your own handler for
		1593	C<SIGCHLD> after initialising the default loop, and making sure the
		1594	default loop never gets destroyed. You are encouraged, however, to use an
		1595	event-based approach to child reaping and thus use libev's support for
		1596	that, so other libev users can use C<ev_child> watchers freely.
		1597
		1598	=head3 Stopping the Child Watcher
		1599
		1600	Currently, the child watcher never gets stopped, even when the
		1601	child terminates, so normally one needs to stop the watcher in the
		1602	callback. Future versions of libev might stop the watcher automatically
		1603	when a child exit is detected.
		1604
		1605	=head3 Watcher-Specific Functions and Data Members
709		1606
710	=over 4	1607	=over 4
711		1608
712	=item ev_child_init (ev_child *, callback, int pid)	1609	=item ev_child_init (ev_child *, callback, int pid, int trace)
713		1610
714	=item ev_child_set (ev_child *, int pid)	1611	=item ev_child_set (ev_child *, int pid, int trace)
715		1612
716	Configures the watcher to wait for status changes of process C<pid> (or	1613	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	1614	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	1615	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	1616	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	1617	C<waitpid> documentation). The C<rpid> member contains the pid of the
721	process causing the status change.	1618	process causing the status change. C<trace> must be either C<0> (only
		1619	activate the watcher when the process terminates) or C<1> (additionally
		1620	activate the watcher when the process is stopped or continued).
		1621
		1622	=item int pid [read-only]
		1623
		1624	The process id this watcher watches out for, or C<0>, meaning any process id.
		1625
		1626	=item int rpid [read-write]
		1627
		1628	The process id that detected a status change.
		1629
		1630	=item int rstatus [read-write]
		1631
		1632	The process exit/trace status caused by C<rpid> (see your systems
		1633	C<waitpid> and C<sys/wait.h> documentation for details).
722		1634
723	=back	1635	=back
724		1636
		1637	=head3 Examples
		1638
		1639	Example: C<fork()> a new process and install a child handler to wait for
		1640	its completion.
		1641
		1642	ev_child cw;
		1643
		1644	static void
		1645	child_cb (EV_P_ struct ev_child *w, int revents)
		1646	{
		1647	ev_child_stop (EV_A_ w);
		1648	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		1649	}
		1650
		1651	pid_t pid = fork ();
		1652
		1653	if (pid < 0)
		1654	// error
		1655	else if (pid == 0)
		1656	{
		1657	// the forked child executes here
		1658	exit (1);
		1659	}
		1660	else
		1661	{
		1662	ev_child_init (&cw, child_cb, pid, 0);
		1663	ev_child_start (EV_DEFAULT_ &cw);
		1664	}
		1665
		1666
		1667	=head2 C<ev_stat> - did the file attributes just change?
		1668
		1669	This watches a file system path for attribute changes. That is, it calls
		1670	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1671	compared to the last time, invoking the callback if it did.
		1672
		1673	The path does not need to exist: changing from "path exists" to "path does
		1674	not exist" is a status change like any other. The condition "path does
		1675	not exist" is signified by the C<st_nlink> field being zero (which is
		1676	otherwise always forced to be at least one) and all the other fields of
		1677	the stat buffer having unspecified contents.
		1678
		1679	The path I<should> be absolute and I<must not> end in a slash. If it is
		1680	relative and your working directory changes, the behaviour is undefined.
		1681
		1682	Since there is no standard to do this, the portable implementation simply
		1683	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1684	can specify a recommended polling interval for this case. If you specify
		1685	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1686	unspecified default> value will be used (which you can expect to be around
		1687	five seconds, although this might change dynamically). Libev will also
		1688	impose a minimum interval which is currently around C<0.1>, but thats
		1689	usually overkill.
		1690
		1691	This watcher type is not meant for massive numbers of stat watchers,
		1692	as even with OS-supported change notifications, this can be
		1693	resource-intensive.
		1694
		1695	At the time of this writing, only the Linux inotify interface is
		1696	implemented (implementing kqueue support is left as an exercise for the
		1697	reader, note, however, that the author sees no way of implementing ev_stat
		1698	semantics with kqueue). Inotify will be used to give hints only and should
		1699	not change the semantics of C<ev_stat> watchers, which means that libev
		1700	sometimes needs to fall back to regular polling again even with inotify,
		1701	but changes are usually detected immediately, and if the file exists there
		1702	will be no polling.
		1703
		1704	=head3 ABI Issues (Largefile Support)
		1705
		1706	Libev by default (unless the user overrides this) uses the default
		1707	compilation environment, which means that on systems with large file
		1708	support disabled by default, you get the 32 bit version of the stat
		1709	structure. When using the library from programs that change the ABI to
		1710	use 64 bit file offsets the programs will fail. In that case you have to
		1711	compile libev with the same flags to get binary compatibility. This is
		1712	obviously the case with any flags that change the ABI, but the problem is
		1713	most noticeably disabled with ev_stat and large file support.
		1714
		1715	The solution for this is to lobby your distribution maker to make large
		1716	file interfaces available by default (as e.g. FreeBSD does) and not
		1717	optional. Libev cannot simply switch on large file support because it has
		1718	to exchange stat structures with application programs compiled using the
		1719	default compilation environment.
		1720
		1721	=head3 Inotify
		1722
		1723	When C<inotify (7)> support has been compiled into libev (generally only
		1724	available on Linux) and present at runtime, it will be used to speed up
		1725	change detection where possible. The inotify descriptor will be created lazily
		1726	when the first C<ev_stat> watcher is being started.
		1727
		1728	Inotify presence does not change the semantics of C<ev_stat> watchers
		1729	except that changes might be detected earlier, and in some cases, to avoid
		1730	making regular C<stat> calls. Even in the presence of inotify support
		1731	there are many cases where libev has to resort to regular C<stat> polling.
		1732
		1733	(There is no support for kqueue, as apparently it cannot be used to
		1734	implement this functionality, due to the requirement of having a file
		1735	descriptor open on the object at all times).
		1736
		1737	=head3 The special problem of stat time resolution
		1738
		1739	The C<stat ()> system call only supports full-second resolution portably, and
		1740	even on systems where the resolution is higher, many file systems still
		1741	only support whole seconds.
		1742
		1743	That means that, if the time is the only thing that changes, you can
		1744	easily miss updates: on the first update, C<ev_stat> detects a change and
		1745	calls your callback, which does something. When there is another update
		1746	within the same second, C<ev_stat> will be unable to detect it as the stat
		1747	data does not change.
		1748
		1749	The solution to this is to delay acting on a change for slightly more
		1750	than a second (or till slightly after the next full second boundary), using
		1751	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1752	ev_timer_again (loop, w)>).
		1753
		1754	The C<.02> offset is added to work around small timing inconsistencies
		1755	of some operating systems (where the second counter of the current time
		1756	might be be delayed. One such system is the Linux kernel, where a call to
		1757	C<gettimeofday> might return a timestamp with a full second later than
		1758	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1759	update file times then there will be a small window where the kernel uses
		1760	the previous second to update file times but libev might already execute
		1761	the timer callback).
		1762
		1763	=head3 Watcher-Specific Functions and Data Members
		1764
		1765	=over 4
		1766
		1767	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1768
		1769	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1770
		1771	Configures the watcher to wait for status changes of the given
		1772	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1773	be detected and should normally be specified as C<0> to let libev choose
		1774	a suitable value. The memory pointed to by C<path> must point to the same
		1775	path for as long as the watcher is active.
		1776
		1777	The callback will receive C<EV_STAT> when a change was detected, relative
		1778	to the attributes at the time the watcher was started (or the last change
		1779	was detected).
		1780
		1781	=item ev_stat_stat (loop, ev_stat *)
		1782
		1783	Updates the stat buffer immediately with new values. If you change the
		1784	watched path in your callback, you could call this function to avoid
		1785	detecting this change (while introducing a race condition if you are not
		1786	the only one changing the path). Can also be useful simply to find out the
		1787	new values.
		1788
		1789	=item ev_statdata attr [read-only]
		1790
		1791	The most-recently detected attributes of the file. Although the type is
		1792	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1793	suitable for your system, but you can only rely on the POSIX-standardised
		1794	members to be present. If the C<st_nlink> member is C<0>, then there was
		1795	some error while C<stat>ing the file.
		1796
		1797	=item ev_statdata prev [read-only]
		1798
		1799	The previous attributes of the file. The callback gets invoked whenever
		1800	C<prev> != C<attr>, or, more precisely, one or more of these members
		1801	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1802	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1803
		1804	=item ev_tstamp interval [read-only]
		1805
		1806	The specified interval.
		1807
		1808	=item const char *path [read-only]
		1809
		1810	The file system path that is being watched.
		1811
		1812	=back
		1813
		1814	=head3 Examples
		1815
		1816	Example: Watch C</etc/passwd> for attribute changes.
		1817
		1818	static void
		1819	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1820	{
		1821	/* /etc/passwd changed in some way */
		1822	if (w->attr.st_nlink)
		1823	{
		1824	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1825	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1826	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1827	}
		1828	else
		1829	/* you shalt not abuse printf for puts */
		1830	puts ("wow, /etc/passwd is not there, expect problems. "
		1831	"if this is windows, they already arrived\n");
		1832	}
		1833
		1834	...
		1835	ev_stat passwd;
		1836
		1837	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1838	ev_stat_start (loop, &passwd);
		1839
		1840	Example: Like above, but additionally use a one-second delay so we do not
		1841	miss updates (however, frequent updates will delay processing, too, so
		1842	one might do the work both on C<ev_stat> callback invocation I<and> on
		1843	C<ev_timer> callback invocation).
		1844
		1845	static ev_stat passwd;
		1846	static ev_timer timer;
		1847
		1848	static void
		1849	timer_cb (EV_P_ ev_timer *w, int revents)
		1850	{
		1851	ev_timer_stop (EV_A_ w);
		1852
		1853	/* now it's one second after the most recent passwd change */
		1854	}
		1855
		1856	static void
		1857	stat_cb (EV_P_ ev_stat *w, int revents)
		1858	{
		1859	/* reset the one-second timer */
		1860	ev_timer_again (EV_A_ &timer);
		1861	}
		1862
		1863	...
		1864	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1865	ev_stat_start (loop, &passwd);
		1866	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1867
		1868
725	=head2 C<ev_idle> - when you've got nothing better to do	1869	=head2 C<ev_idle> - when you've got nothing better to do...
726		1870
727	Idle watchers trigger events when there are no other events are pending	1871	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	1872	priority are pending (prepare, check and other idle watchers do not
729	as your process is busy handling sockets or timeouts (or even signals,	1873	count).
730	imagine) it will not be triggered. But when your process is idle all idle	1874
731	watchers are being called again and again, once per event loop iteration -	1875	That is, as long as your process is busy handling sockets or timeouts
		1876	(or even signals, imagine) of the same or higher priority it will not be
		1877	triggered. But when your process is idle (or only lower-priority watchers
		1878	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	1879	iteration - until stopped, that is, or your process receives more events
733	busy.	1880	and becomes busy again with higher priority stuff.
734		1881
735	The most noteworthy effect is that as long as any idle watchers are	1882	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.	1883	active, the process will not block when waiting for new events.
737		1884
738	Apart from keeping your process non-blocking (which is a useful	1885	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	1886	effect on its own sometimes), idle watchers are a good place to do
740	"pseudo-background processing", or delay processing stuff to after the	1887	"pseudo-background processing", or delay processing stuff to after the
741	event loop has handled all outstanding events.	1888	event loop has handled all outstanding events.
742		1889
		1890	=head3 Watcher-Specific Functions and Data Members
		1891
743	=over 4	1892	=over 4
744		1893
745	=item ev_idle_init (ev_signal *, callback)	1894	=item ev_idle_init (ev_signal *, callback)
746		1895
747	Initialises and configures the idle watcher - it has no parameters of any	1896	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,	1897	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
749	believe me.	1898	believe me.
750		1899
751	=back	1900	=back
752		1901
		1902	=head3 Examples
		1903
		1904	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		1905	callback, free it. Also, use no error checking, as usual.
		1906
		1907	static void
		1908	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
		1909	{
		1910	free (w);
		1911	// now do something you wanted to do when the program has
		1912	// no longer anything immediate to do.
		1913	}
		1914
		1915	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1916	ev_idle_init (idle_watcher, idle_cb);
		1917	ev_idle_start (loop, idle_cb);
		1918
		1919
753	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1920	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
754		1921
755	Prepare and check watchers are usually (but not always) used in tandem:	1922	Prepare and check watchers are usually (but not always) used in tandem:
756	prepare watchers get invoked before the process blocks and check watchers	1923	prepare watchers get invoked before the process blocks and check watchers
757	afterwards.	1924	afterwards.
758		1925
		1926	You I<must not> call C<ev_loop> or similar functions that enter
		1927	the current event loop from either C<ev_prepare> or C<ev_check>
		1928	watchers. Other loops than the current one are fine, however. The
		1929	rationale behind this is that you do not need to check for recursion in
		1930	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1931	C<ev_check> so if you have one watcher of each kind they will always be
		1932	called in pairs bracketing the blocking call.
		1933
759	Their main purpose is to integrate other event mechanisms into libev. This	1934	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	1935	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.	1936	variable changes, implement your own watchers, integrate net-snmp or a
		1937	coroutine library and lots more. They are also occasionally useful if
		1938	you cache some data and want to flush it before blocking (for example,
		1939	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1940	watcher).
762		1941
763	This is done by examining in each prepare call which file descriptors need	1942	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	1943	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	1944	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	1945	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	1946	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	1947	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,	1948	callbacks will never actually be called (but must be valid nevertheless,
770	because you never know, you know?).	1949	because you never know, you know?).
771		1950
772	As another example, the Perl Coro module uses these hooks to integrate	1951	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	1955	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	1956	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	1957	loop from blocking if lower-priority coroutines are active, thus mapping
779	low-priority coroutines to idle/background tasks).	1958	low-priority coroutines to idle/background tasks).
780		1959
		1960	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1961	priority, to ensure that they are being run before any other watchers
		1962	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1963	too) should not activate ("feed") events into libev. While libev fully
		1964	supports this, they might get executed before other C<ev_check> watchers
		1965	did their job. As C<ev_check> watchers are often used to embed other
		1966	(non-libev) event loops those other event loops might be in an unusable
		1967	state until their C<ev_check> watcher ran (always remind yourself to
		1968	coexist peacefully with others).
		1969
		1970	=head3 Watcher-Specific Functions and Data Members
		1971
781	=over 4	1972	=over 4
782		1973
783	=item ev_prepare_init (ev_prepare *, callback)	1974	=item ev_prepare_init (ev_prepare *, callback)
784		1975
785	=item ev_check_init (ev_check *, callback)	1976	=item ev_check_init (ev_check *, callback)
…		…
787	Initialises and configures the prepare or check watcher - they have no	1978	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>	1979	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.	1980	macros, but using them is utterly, utterly and completely pointless.
790		1981
791	=back	1982	=back
		1983
		1984	=head3 Examples
		1985
		1986	There are a number of principal ways to embed other event loops or modules
		1987	into libev. Here are some ideas on how to include libadns into libev
		1988	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1989	use as a working example. Another Perl module named C<EV::Glib> embeds a
		1990	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		1991	Glib event loop).
		1992
		1993	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1994	and in a check watcher, destroy them and call into libadns. What follows
		1995	is pseudo-code only of course. This requires you to either use a low
		1996	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1997	the callbacks for the IO/timeout watchers might not have been called yet.
		1998
		1999	static ev_io iow [nfd];
		2000	static ev_timer tw;
		2001
		2002	static void
		2003	io_cb (ev_loop *loop, ev_io *w, int revents)
		2004	{
		2005	}
		2006
		2007	// create io watchers for each fd and a timer before blocking
		2008	static void
		2009	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		2010	{
		2011	int timeout = 3600000;
		2012	struct pollfd fds [nfd];
		2013	// actual code will need to loop here and realloc etc.
		2014	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2015
		2016	/* the callback is illegal, but won't be called as we stop during check */
		2017	ev_timer_init (&tw, 0, timeout * 1e-3);
		2018	ev_timer_start (loop, &tw);
		2019
		2020	// create one ev_io per pollfd
		2021	for (int i = 0; i < nfd; ++i)
		2022	{
		2023	ev_io_init (iow + i, io_cb, fds [i].fd,
		2024	((fds [i].events & POLLIN ? EV_READ : 0)
		2025	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2026
		2027	fds [i].revents = 0;
		2028	ev_io_start (loop, iow + i);
		2029	}
		2030	}
		2031
		2032	// stop all watchers after blocking
		2033	static void
		2034	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		2035	{
		2036	ev_timer_stop (loop, &tw);
		2037
		2038	for (int i = 0; i < nfd; ++i)
		2039	{
		2040	// set the relevant poll flags
		2041	// could also call adns_processreadable etc. here
		2042	struct pollfd *fd = fds + i;
		2043	int revents = ev_clear_pending (iow + i);
		2044	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2045	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2046
		2047	// now stop the watcher
		2048	ev_io_stop (loop, iow + i);
		2049	}
		2050
		2051	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2052	}
		2053
		2054	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2055	in the prepare watcher and would dispose of the check watcher.
		2056
		2057	Method 3: If the module to be embedded supports explicit event
		2058	notification (libadns does), you can also make use of the actual watcher
		2059	callbacks, and only destroy/create the watchers in the prepare watcher.
		2060
		2061	static void
		2062	timer_cb (EV_P_ ev_timer *w, int revents)
		2063	{
		2064	adns_state ads = (adns_state)w->data;
		2065	update_now (EV_A);
		2066
		2067	adns_processtimeouts (ads, &tv_now);
		2068	}
		2069
		2070	static void
		2071	io_cb (EV_P_ ev_io *w, int revents)
		2072	{
		2073	adns_state ads = (adns_state)w->data;
		2074	update_now (EV_A);
		2075
		2076	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2077	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2078	}
		2079
		2080	// do not ever call adns_afterpoll
		2081
		2082	Method 4: Do not use a prepare or check watcher because the module you
		2083	want to embed is too inflexible to support it. Instead, you can override
		2084	their poll function. The drawback with this solution is that the main
		2085	loop is now no longer controllable by EV. The C<Glib::EV> module does
		2086	this.
		2087
		2088	static gint
		2089	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2090	{
		2091	int got_events = 0;
		2092
		2093	for (n = 0; n < nfds; ++n)
		2094	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2095
		2096	if (timeout >= 0)
		2097	// create/start timer
		2098
		2099	// poll
		2100	ev_loop (EV_A_ 0);
		2101
		2102	// stop timer again
		2103	if (timeout >= 0)
		2104	ev_timer_stop (EV_A_ &to);
		2105
		2106	// stop io watchers again - their callbacks should have set
		2107	for (n = 0; n < nfds; ++n)
		2108	ev_io_stop (EV_A_ iow [n]);
		2109
		2110	return got_events;
		2111	}
		2112
		2113
		2114	=head2 C<ev_embed> - when one backend isn't enough...
		2115
		2116	This is a rather advanced watcher type that lets you embed one event loop
		2117	into another (currently only C<ev_io> events are supported in the embedded
		2118	loop, other types of watchers might be handled in a delayed or incorrect
		2119	fashion and must not be used).
		2120
		2121	There are primarily two reasons you would want that: work around bugs and
		2122	prioritise I/O.
		2123
		2124	As an example for a bug workaround, the kqueue backend might only support
		2125	sockets on some platform, so it is unusable as generic backend, but you
		2126	still want to make use of it because you have many sockets and it scales
		2127	so nicely. In this case, you would create a kqueue-based loop and embed it
		2128	into your default loop (which might use e.g. poll). Overall operation will
		2129	be a bit slower because first libev has to poll and then call kevent, but
		2130	at least you can use both at what they are best.
		2131
		2132	As for prioritising I/O: rarely you have the case where some fds have
		2133	to be watched and handled very quickly (with low latency), and even
		2134	priorities and idle watchers might have too much overhead. In this case
		2135	you would put all the high priority stuff in one loop and all the rest in
		2136	a second one, and embed the second one in the first.
		2137
		2138	As long as the watcher is active, the callback will be invoked every time
		2139	there might be events pending in the embedded loop. The callback must then
		2140	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2141	their callbacks (you could also start an idle watcher to give the embedded
		2142	loop strictly lower priority for example). You can also set the callback
		2143	to C<0>, in which case the embed watcher will automatically execute the
		2144	embedded loop sweep.
		2145
		2146	As long as the watcher is started it will automatically handle events. The
		2147	callback will be invoked whenever some events have been handled. You can
		2148	set the callback to C<0> to avoid having to specify one if you are not
		2149	interested in that.
		2150
		2151	Also, there have not currently been made special provisions for forking:
		2152	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		2153	but you will also have to stop and restart any C<ev_embed> watchers
		2154	yourself.
		2155
		2156	Unfortunately, not all backends are embeddable, only the ones returned by
		2157	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2158	portable one.
		2159
		2160	So when you want to use this feature you will always have to be prepared
		2161	that you cannot get an embeddable loop. The recommended way to get around
		2162	this is to have a separate variables for your embeddable loop, try to
		2163	create it, and if that fails, use the normal loop for everything.
		2164
		2165	=head3 Watcher-Specific Functions and Data Members
		2166
		2167	=over 4
		2168
		2169	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2170
		2171	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2172
		2173	Configures the watcher to embed the given loop, which must be
		2174	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2175	invoked automatically, otherwise it is the responsibility of the callback
		2176	to invoke it (it will continue to be called until the sweep has been done,
		2177	if you do not want that, you need to temporarily stop the embed watcher).
		2178
		2179	=item ev_embed_sweep (loop, ev_embed *)
		2180
		2181	Make a single, non-blocking sweep over the embedded loop. This works
		2182	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2183	appropriate way for embedded loops.
		2184
		2185	=item struct ev_loop *other [read-only]
		2186
		2187	The embedded event loop.
		2188
		2189	=back
		2190
		2191	=head3 Examples
		2192
		2193	Example: Try to get an embeddable event loop and embed it into the default
		2194	event loop. If that is not possible, use the default loop. The default
		2195	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2196	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2197	used).
		2198
		2199	struct ev_loop *loop_hi = ev_default_init (0);
		2200	struct ev_loop *loop_lo = 0;
		2201	struct ev_embed embed;
		2202
		2203	// see if there is a chance of getting one that works
		2204	// (remember that a flags value of 0 means autodetection)
		2205	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2206	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2207	: 0;
		2208
		2209	// if we got one, then embed it, otherwise default to loop_hi
		2210	if (loop_lo)
		2211	{
		2212	ev_embed_init (&embed, 0, loop_lo);
		2213	ev_embed_start (loop_hi, &embed);
		2214	}
		2215	else
		2216	loop_lo = loop_hi;
		2217
		2218	Example: Check if kqueue is available but not recommended and create
		2219	a kqueue backend for use with sockets (which usually work with any
		2220	kqueue implementation). Store the kqueue/socket-only event loop in
		2221	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2222
		2223	struct ev_loop *loop = ev_default_init (0);
		2224	struct ev_loop *loop_socket = 0;
		2225	struct ev_embed embed;
		2226
		2227	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2228	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2229	{
		2230	ev_embed_init (&embed, 0, loop_socket);
		2231	ev_embed_start (loop, &embed);
		2232	}
		2233
		2234	if (!loop_socket)
		2235	loop_socket = loop;
		2236
		2237	// now use loop_socket for all sockets, and loop for everything else
		2238
		2239
		2240	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2241
		2242	Fork watchers are called when a C<fork ()> was detected (usually because
		2243	whoever is a good citizen cared to tell libev about it by calling
		2244	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2245	event loop blocks next and before C<ev_check> watchers are being called,
		2246	and only in the child after the fork. If whoever good citizen calling
		2247	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2248	handlers will be invoked, too, of course.
		2249
		2250	=head3 Watcher-Specific Functions and Data Members
		2251
		2252	=over 4
		2253
		2254	=item ev_fork_init (ev_signal *, callback)
		2255
		2256	Initialises and configures the fork watcher - it has no parameters of any
		2257	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2258	believe me.
		2259
		2260	=back
		2261
		2262
		2263	=head2 C<ev_async> - how to wake up another event loop
		2264
		2265	In general, you cannot use an C<ev_loop> from multiple threads or other
		2266	asynchronous sources such as signal handlers (as opposed to multiple event
		2267	loops - those are of course safe to use in different threads).
		2268
		2269	Sometimes, however, you need to wake up another event loop you do not
		2270	control, for example because it belongs to another thread. This is what
		2271	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2272	can signal it by calling C<ev_async_send>, which is thread- and signal
		2273	safe.
		2274
		2275	This functionality is very similar to C<ev_signal> watchers, as signals,
		2276	too, are asynchronous in nature, and signals, too, will be compressed
		2277	(i.e. the number of callback invocations may be less than the number of
		2278	C<ev_async_sent> calls).
		2279
		2280	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2281	just the default loop.
		2282
		2283	=head3 Queueing
		2284
		2285	C<ev_async> does not support queueing of data in any way. The reason
		2286	is that the author does not know of a simple (or any) algorithm for a
		2287	multiple-writer-single-reader queue that works in all cases and doesn't
		2288	need elaborate support such as pthreads.
		2289
		2290	That means that if you want to queue data, you have to provide your own
		2291	queue. But at least I can tell you would implement locking around your
		2292	queue:
		2293
		2294	=over 4
		2295
		2296	=item queueing from a signal handler context
		2297
		2298	To implement race-free queueing, you simply add to the queue in the signal
		2299	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2300	some fictitious SIGUSR1 handler:
		2301
		2302	static ev_async mysig;
		2303
		2304	static void
		2305	sigusr1_handler (void)
		2306	{
		2307	sometype data;
		2308
		2309	// no locking etc.
		2310	queue_put (data);
		2311	ev_async_send (EV_DEFAULT_ &mysig);
		2312	}
		2313
		2314	static void
		2315	mysig_cb (EV_P_ ev_async *w, int revents)
		2316	{
		2317	sometype data;
		2318	sigset_t block, prev;
		2319
		2320	sigemptyset (&block);
		2321	sigaddset (&block, SIGUSR1);
		2322	sigprocmask (SIG_BLOCK, &block, &prev);
		2323
		2324	while (queue_get (&data))
		2325	process (data);
		2326
		2327	if (sigismember (&prev, SIGUSR1)
		2328	sigprocmask (SIG_UNBLOCK, &block, 0);
		2329	}
		2330
		2331	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2332	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2333	either...).
		2334
		2335	=item queueing from a thread context
		2336
		2337	The strategy for threads is different, as you cannot (easily) block
		2338	threads but you can easily preempt them, so to queue safely you need to
		2339	employ a traditional mutex lock, such as in this pthread example:
		2340
		2341	static ev_async mysig;
		2342	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2343
		2344	static void
		2345	otherthread (void)
		2346	{
		2347	// only need to lock the actual queueing operation
		2348	pthread_mutex_lock (&mymutex);
		2349	queue_put (data);
		2350	pthread_mutex_unlock (&mymutex);
		2351
		2352	ev_async_send (EV_DEFAULT_ &mysig);
		2353	}
		2354
		2355	static void
		2356	mysig_cb (EV_P_ ev_async *w, int revents)
		2357	{
		2358	pthread_mutex_lock (&mymutex);
		2359
		2360	while (queue_get (&data))
		2361	process (data);
		2362
		2363	pthread_mutex_unlock (&mymutex);
		2364	}
		2365
		2366	=back
		2367
		2368
		2369	=head3 Watcher-Specific Functions and Data Members
		2370
		2371	=over 4
		2372
		2373	=item ev_async_init (ev_async *, callback)
		2374
		2375	Initialises and configures the async watcher - it has no parameters of any
		2376	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2377	believe me.
		2378
		2379	=item ev_async_send (loop, ev_async *)
		2380
		2381	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2382	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2383	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2384	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2385	section below on what exactly this means).
		2386
		2387	This call incurs the overhead of a system call only once per loop iteration,
		2388	so while the overhead might be noticeable, it doesn't apply to repeated
		2389	calls to C<ev_async_send>.
		2390
		2391	=item bool = ev_async_pending (ev_async *)
		2392
		2393	Returns a non-zero value when C<ev_async_send> has been called on the
		2394	watcher but the event has not yet been processed (or even noted) by the
		2395	event loop.
		2396
		2397	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2398	the loop iterates next and checks for the watcher to have become active,
		2399	it will reset the flag again. C<ev_async_pending> can be used to very
		2400	quickly check whether invoking the loop might be a good idea.
		2401
		2402	Not that this does I<not> check whether the watcher itself is pending, only
		2403	whether it has been requested to make this watcher pending.
		2404
		2405	=back
		2406
792		2407
793	=head1 OTHER FUNCTIONS	2408	=head1 OTHER FUNCTIONS
794		2409
795	There are some other functions of possible interest. Described. Here. Now.	2410	There are some other functions of possible interest. Described. Here. Now.
796		2411
…		…
804	or timeout without having to allocate/configure/start/stop/free one or	2419	or timeout without having to allocate/configure/start/stop/free one or
805	more watchers yourself.	2420	more watchers yourself.
806		2421
807	If C<fd> is less than 0, then no I/O watcher will be started and events	2422	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	2423	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
809	C<events> set will be craeted and started.	2424	C<events> set will be created and started.
810		2425
811	If C<timeout> is less than 0, then no timeout watcher will be	2426	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	2427	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	2428	repeat = 0) will be started. While C<0> is a valid timeout, it is of
814	dubious value.	2429	dubious value.
…		…
816	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2431	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	2432	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>	2433	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
819	value passed to C<ev_once>:	2434	value passed to C<ev_once>:
820		2435
821	static void stdin_ready (int revents, void *arg)	2436	static void stdin_ready (int revents, void *arg)
822	{	2437	{
823	if (revents & EV_TIMEOUT)	2438	if (revents & EV_TIMEOUT)
824	/* doh, nothing entered */;	2439	/* doh, nothing entered */;
825	else if (revents & EV_READ)	2440	else if (revents & EV_READ)
826	/* stdin might have data for us, joy! */;	2441	/* stdin might have data for us, joy! */;
827	}	2442	}
828		2443
829	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2444	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
830		2445
831	=item ev_feed_event (loop, watcher, int events)	2446	=item ev_feed_event (ev_loop *, watcher *, int revents)
832		2447
833	Feeds the given event set into the event loop, as if the specified event	2448	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	2449	had happened for the specified watcher (which must be a pointer to an
835	initialised but not necessarily started event watcher).	2450	initialised but not necessarily started event watcher).
836		2451
837	=item ev_feed_fd_event (loop, int fd, int revents)	2452	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
838		2453
839	Feed an event on the given fd, as if a file descriptor backend detected	2454	Feed an event on the given fd, as if a file descriptor backend detected
840	the given events it.	2455	the given events it.
841		2456
842	=item ev_feed_signal_event (loop, int signum)	2457	=item ev_feed_signal_event (ev_loop *loop, int signum)
843		2458
844	Feed an event as if the given signal occured (loop must be the default loop!).	2459	Feed an event as if the given signal occurred (C<loop> must be the default
		2460	loop!).
845		2461
846	=back	2462	=back
		2463
847		2464
848	=head1 LIBEVENT EMULATION	2465	=head1 LIBEVENT EMULATION
849		2466
850	Libev offers a compatibility emulation layer for libevent. It cannot	2467	Libev offers a compatibility emulation layer for libevent. It cannot
851	emulate the internals of libevent, so here are some usage hints:	2468	emulate the internals of libevent, so here are some usage hints:
…		…
863		2480
864	=item * Priorities are not currently supported. Initialising priorities	2481	=item * Priorities are not currently supported. Initialising priorities
865	will fail and all watchers will have the same priority, even though there	2482	will fail and all watchers will have the same priority, even though there
866	is an ev_pri field.	2483	is an ev_pri field.
867		2484
		2485	=item * In libevent, the last base created gets the signals, in libev, the
		2486	first base created (== the default loop) gets the signals.
		2487
868	=item * Other members are not supported.	2488	=item * Other members are not supported.
869		2489
870	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2490	=item * The libev emulation is I<not> ABI compatible to libevent, you need
871	to use the libev header file and library.	2491	to use the libev header file and library.
872		2492
873	=back	2493	=back
874		2494
875	=head1 C++ SUPPORT	2495	=head1 C++ SUPPORT
876		2496
877	TBD.	2497	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2498	you to use some convenience methods to start/stop watchers and also change
		2499	the callback model to a model using method callbacks on objects.
		2500
		2501	To use it,
		2502
		2503	#include <ev++.h>
		2504
		2505	This automatically includes F<ev.h> and puts all of its definitions (many
		2506	of them macros) into the global namespace. All C++ specific things are
		2507	put into the C<ev> namespace. It should support all the same embedding
		2508	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2509
		2510	Care has been taken to keep the overhead low. The only data member the C++
		2511	classes add (compared to plain C-style watchers) is the event loop pointer
		2512	that the watcher is associated with (or no additional members at all if
		2513	you disable C<EV_MULTIPLICITY> when embedding libev).
		2514
		2515	Currently, functions, and static and non-static member functions can be
		2516	used as callbacks. Other types should be easy to add as long as they only
		2517	need one additional pointer for context. If you need support for other
		2518	types of functors please contact the author (preferably after implementing
		2519	it).
		2520
		2521	Here is a list of things available in the C<ev> namespace:
		2522
		2523	=over 4
		2524
		2525	=item C<ev::READ>, C<ev::WRITE> etc.
		2526
		2527	These are just enum values with the same values as the C<EV_READ> etc.
		2528	macros from F<ev.h>.
		2529
		2530	=item C<ev::tstamp>, C<ev::now>
		2531
		2532	Aliases to the same types/functions as with the C<ev_> prefix.
		2533
		2534	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2535
		2536	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2537	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2538	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2539	defines by many implementations.
		2540
		2541	All of those classes have these methods:
		2542
		2543	=over 4
		2544
		2545	=item ev::TYPE::TYPE ()
		2546
		2547	=item ev::TYPE::TYPE (struct ev_loop *)
		2548
		2549	=item ev::TYPE::~TYPE
		2550
		2551	The constructor (optionally) takes an event loop to associate the watcher
		2552	with. If it is omitted, it will use C<EV_DEFAULT>.
		2553
		2554	The constructor calls C<ev_init> for you, which means you have to call the
		2555	C<set> method before starting it.
		2556
		2557	It will not set a callback, however: You have to call the templated C<set>
		2558	method to set a callback before you can start the watcher.
		2559
		2560	(The reason why you have to use a method is a limitation in C++ which does
		2561	not allow explicit template arguments for constructors).
		2562
		2563	The destructor automatically stops the watcher if it is active.
		2564
		2565	=item w->set<class, &class::method> (object *)
		2566
		2567	This method sets the callback method to call. The method has to have a
		2568	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2569	first argument and the C<revents> as second. The object must be given as
		2570	parameter and is stored in the C<data> member of the watcher.
		2571
		2572	This method synthesizes efficient thunking code to call your method from
		2573	the C callback that libev requires. If your compiler can inline your
		2574	callback (i.e. it is visible to it at the place of the C<set> call and
		2575	your compiler is good :), then the method will be fully inlined into the
		2576	thunking function, making it as fast as a direct C callback.
		2577
		2578	Example: simple class declaration and watcher initialisation
		2579
		2580	struct myclass
		2581	{
		2582	void io_cb (ev::io &w, int revents) { }
		2583	}
		2584
		2585	myclass obj;
		2586	ev::io iow;
		2587	iow.set <myclass, &myclass::io_cb> (&obj);
		2588
		2589	=item w->set<function> (void *data = 0)
		2590
		2591	Also sets a callback, but uses a static method or plain function as
		2592	callback. The optional C<data> argument will be stored in the watcher's
		2593	C<data> member and is free for you to use.
		2594
		2595	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2596
		2597	See the method-C<set> above for more details.
		2598
		2599	Example:
		2600
		2601	static void io_cb (ev::io &w, int revents) { }
		2602	iow.set <io_cb> ();
		2603
		2604	=item w->set (struct ev_loop *)
		2605
		2606	Associates a different C<struct ev_loop> with this watcher. You can only
		2607	do this when the watcher is inactive (and not pending either).
		2608
		2609	=item w->set ([arguments])
		2610
		2611	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2612	called at least once. Unlike the C counterpart, an active watcher gets
		2613	automatically stopped and restarted when reconfiguring it with this
		2614	method.
		2615
		2616	=item w->start ()
		2617
		2618	Starts the watcher. Note that there is no C<loop> argument, as the
		2619	constructor already stores the event loop.
		2620
		2621	=item w->stop ()
		2622
		2623	Stops the watcher if it is active. Again, no C<loop> argument.
		2624
		2625	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2626
		2627	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2628	C<ev_TYPE_again> function.
		2629
		2630	=item w->sweep () (C<ev::embed> only)
		2631
		2632	Invokes C<ev_embed_sweep>.
		2633
		2634	=item w->update () (C<ev::stat> only)
		2635
		2636	Invokes C<ev_stat_stat>.
		2637
		2638	=back
		2639
		2640	=back
		2641
		2642	Example: Define a class with an IO and idle watcher, start one of them in
		2643	the constructor.
		2644
		2645	class myclass
		2646	{
		2647	ev::io io; void io_cb (ev::io &w, int revents);
		2648	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2649
		2650	myclass (int fd)
		2651	{
		2652	io .set <myclass, &myclass::io_cb > (this);
		2653	idle.set <myclass, &myclass::idle_cb> (this);
		2654
		2655	io.start (fd, ev::READ);
		2656	}
		2657	};
		2658
		2659
		2660	=head1 OTHER LANGUAGE BINDINGS
		2661
		2662	Libev does not offer other language bindings itself, but bindings for a
		2663	number of languages exist in the form of third-party packages. If you know
		2664	any interesting language binding in addition to the ones listed here, drop
		2665	me a note.
		2666
		2667	=over 4
		2668
		2669	=item Perl
		2670
		2671	The EV module implements the full libev API and is actually used to test
		2672	libev. EV is developed together with libev. Apart from the EV core module,
		2673	there are additional modules that implement libev-compatible interfaces
		2674	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2675	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2676
		2677	It can be found and installed via CPAN, its homepage is at
		2678	L<http://software.schmorp.de/pkg/EV>.
		2679
		2680	=item Python
		2681
		2682	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2683	seems to be quite complete and well-documented. Note, however, that the
		2684	patch they require for libev is outright dangerous as it breaks the ABI
		2685	for everybody else, and therefore, should never be applied in an installed
		2686	libev (if python requires an incompatible ABI then it needs to embed
		2687	libev).
		2688
		2689	=item Ruby
		2690
		2691	Tony Arcieri has written a ruby extension that offers access to a subset
		2692	of the libev API and adds file handle abstractions, asynchronous DNS and
		2693	more on top of it. It can be found via gem servers. Its homepage is at
		2694	L<http://rev.rubyforge.org/>.
		2695
		2696	=item D
		2697
		2698	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2699	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2700
		2701	=back
		2702
		2703
		2704	=head1 MACRO MAGIC
		2705
		2706	Libev can be compiled with a variety of options, the most fundamental
		2707	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2708	functions and callbacks have an initial C<struct ev_loop *> argument.
		2709
		2710	To make it easier to write programs that cope with either variant, the
		2711	following macros are defined:
		2712
		2713	=over 4
		2714
		2715	=item C<EV_A>, C<EV_A_>
		2716
		2717	This provides the loop I<argument> for functions, if one is required ("ev
		2718	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2719	C<EV_A_> is used when other arguments are following. Example:
		2720
		2721	ev_unref (EV_A);
		2722	ev_timer_add (EV_A_ watcher);
		2723	ev_loop (EV_A_ 0);
		2724
		2725	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2726	which is often provided by the following macro.
		2727
		2728	=item C<EV_P>, C<EV_P_>
		2729
		2730	This provides the loop I<parameter> for functions, if one is required ("ev
		2731	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2732	C<EV_P_> is used when other parameters are following. Example:
		2733
		2734	// this is how ev_unref is being declared
		2735	static void ev_unref (EV_P);
		2736
		2737	// this is how you can declare your typical callback
		2738	static void cb (EV_P_ ev_timer *w, int revents)
		2739
		2740	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2741	suitable for use with C<EV_A>.
		2742
		2743	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2744
		2745	Similar to the other two macros, this gives you the value of the default
		2746	loop, if multiple loops are supported ("ev loop default").
		2747
		2748	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2749
		2750	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2751	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2752	is undefined when the default loop has not been initialised by a previous
		2753	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2754
		2755	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2756	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2757
		2758	=back
		2759
		2760	Example: Declare and initialise a check watcher, utilising the above
		2761	macros so it will work regardless of whether multiple loops are supported
		2762	or not.
		2763
		2764	static void
		2765	check_cb (EV_P_ ev_timer *w, int revents)
		2766	{
		2767	ev_check_stop (EV_A_ w);
		2768	}
		2769
		2770	ev_check check;
		2771	ev_check_init (&check, check_cb);
		2772	ev_check_start (EV_DEFAULT_ &check);
		2773	ev_loop (EV_DEFAULT_ 0);
		2774
		2775	=head1 EMBEDDING
		2776
		2777	Libev can (and often is) directly embedded into host
		2778	applications. Examples of applications that embed it include the Deliantra
		2779	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2780	and rxvt-unicode.
		2781
		2782	The goal is to enable you to just copy the necessary files into your
		2783	source directory without having to change even a single line in them, so
		2784	you can easily upgrade by simply copying (or having a checked-out copy of
		2785	libev somewhere in your source tree).
		2786
		2787	=head2 FILESETS
		2788
		2789	Depending on what features you need you need to include one or more sets of files
		2790	in your application.
		2791
		2792	=head3 CORE EVENT LOOP
		2793
		2794	To include only the libev core (all the C<ev_*> functions), with manual
		2795	configuration (no autoconf):
		2796
		2797	#define EV_STANDALONE 1
		2798	#include "ev.c"
		2799
		2800	This will automatically include F<ev.h>, too, and should be done in a
		2801	single C source file only to provide the function implementations. To use
		2802	it, do the same for F<ev.h> in all files wishing to use this API (best
		2803	done by writing a wrapper around F<ev.h> that you can include instead and
		2804	where you can put other configuration options):
		2805
		2806	#define EV_STANDALONE 1
		2807	#include "ev.h"
		2808
		2809	Both header files and implementation files can be compiled with a C++
		2810	compiler (at least, thats a stated goal, and breakage will be treated
		2811	as a bug).
		2812
		2813	You need the following files in your source tree, or in a directory
		2814	in your include path (e.g. in libev/ when using -Ilibev):
		2815
		2816	ev.h
		2817	ev.c
		2818	ev_vars.h
		2819	ev_wrap.h
		2820
		2821	ev_win32.c required on win32 platforms only
		2822
		2823	ev_select.c only when select backend is enabled (which is enabled by default)
		2824	ev_poll.c only when poll backend is enabled (disabled by default)
		2825	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2826	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2827	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2828
		2829	F<ev.c> includes the backend files directly when enabled, so you only need
		2830	to compile this single file.
		2831
		2832	=head3 LIBEVENT COMPATIBILITY API
		2833
		2834	To include the libevent compatibility API, also include:
		2835
		2836	#include "event.c"
		2837
		2838	in the file including F<ev.c>, and:
		2839
		2840	#include "event.h"
		2841
		2842	in the files that want to use the libevent API. This also includes F<ev.h>.
		2843
		2844	You need the following additional files for this:
		2845
		2846	event.h
		2847	event.c
		2848
		2849	=head3 AUTOCONF SUPPORT
		2850
		2851	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		2852	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2853	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2854	include F<config.h> and configure itself accordingly.
		2855
		2856	For this of course you need the m4 file:
		2857
		2858	libev.m4
		2859
		2860	=head2 PREPROCESSOR SYMBOLS/MACROS
		2861
		2862	Libev can be configured via a variety of preprocessor symbols you have to
		2863	define before including any of its files. The default in the absence of
		2864	autoconf is noted for every option.
		2865
		2866	=over 4
		2867
		2868	=item EV_STANDALONE
		2869
		2870	Must always be C<1> if you do not use autoconf configuration, which
		2871	keeps libev from including F<config.h>, and it also defines dummy
		2872	implementations for some libevent functions (such as logging, which is not
		2873	supported). It will also not define any of the structs usually found in
		2874	F<event.h> that are not directly supported by the libev core alone.
		2875
		2876	=item EV_USE_MONOTONIC
		2877
		2878	If defined to be C<1>, libev will try to detect the availability of the
		2879	monotonic clock option at both compile time and runtime. Otherwise no use
		2880	of the monotonic clock option will be attempted. If you enable this, you
		2881	usually have to link against librt or something similar. Enabling it when
		2882	the functionality isn't available is safe, though, although you have
		2883	to make sure you link against any libraries where the C<clock_gettime>
		2884	function is hiding in (often F<-lrt>).
		2885
		2886	=item EV_USE_REALTIME
		2887
		2888	If defined to be C<1>, libev will try to detect the availability of the
		2889	real-time clock option at compile time (and assume its availability at
		2890	runtime if successful). Otherwise no use of the real-time clock option will
		2891	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2892	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2893	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2894
		2895	=item EV_USE_NANOSLEEP
		2896
		2897	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2898	and will use it for delays. Otherwise it will use C<select ()>.
		2899
		2900	=item EV_USE_EVENTFD
		2901
		2902	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2903	available and will probe for kernel support at runtime. This will improve
		2904	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2905	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2906	2.7 or newer, otherwise disabled.
		2907
		2908	=item EV_USE_SELECT
		2909
		2910	If undefined or defined to be C<1>, libev will compile in support for the
		2911	C<select>(2) backend. No attempt at auto-detection will be done: if no
		2912	other method takes over, select will be it. Otherwise the select backend
		2913	will not be compiled in.
		2914
		2915	=item EV_SELECT_USE_FD_SET
		2916
		2917	If defined to C<1>, then the select backend will use the system C<fd_set>
		2918	structure. This is useful if libev doesn't compile due to a missing
		2919	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		2920	exotic systems. This usually limits the range of file descriptors to some
		2921	low limit such as 1024 or might have other limitations (winsocket only
		2922	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2923	influence the size of the C<fd_set> used.
		2924
		2925	=item EV_SELECT_IS_WINSOCKET
		2926
		2927	When defined to C<1>, the select backend will assume that
		2928	select/socket/connect etc. don't understand file descriptors but
		2929	wants osf handles on win32 (this is the case when the select to
		2930	be used is the winsock select). This means that it will call
		2931	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2932	it is assumed that all these functions actually work on fds, even
		2933	on win32. Should not be defined on non-win32 platforms.
		2934
		2935	=item EV_FD_TO_WIN32_HANDLE
		2936
		2937	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2938	file descriptors to socket handles. When not defining this symbol (the
		2939	default), then libev will call C<_get_osfhandle>, which is usually
		2940	correct. In some cases, programs use their own file descriptor management,
		2941	in which case they can provide this function to map fds to socket handles.
		2942
		2943	=item EV_USE_POLL
		2944
		2945	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2946	backend. Otherwise it will be enabled on non-win32 platforms. It
		2947	takes precedence over select.
		2948
		2949	=item EV_USE_EPOLL
		2950
		2951	If defined to be C<1>, libev will compile in support for the Linux
		2952	C<epoll>(7) backend. Its availability will be detected at runtime,
		2953	otherwise another method will be used as fallback. This is the preferred
		2954	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2955	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2956
		2957	=item EV_USE_KQUEUE
		2958
		2959	If defined to be C<1>, libev will compile in support for the BSD style
		2960	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2961	otherwise another method will be used as fallback. This is the preferred
		2962	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2963	supports some types of fds correctly (the only platform we found that
		2964	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2965	not be used unless explicitly requested. The best way to use it is to find
		2966	out whether kqueue supports your type of fd properly and use an embedded
		2967	kqueue loop.
		2968
		2969	=item EV_USE_PORT
		2970
		2971	If defined to be C<1>, libev will compile in support for the Solaris
		2972	10 port style backend. Its availability will be detected at runtime,
		2973	otherwise another method will be used as fallback. This is the preferred
		2974	backend for Solaris 10 systems.
		2975
		2976	=item EV_USE_DEVPOLL
		2977
		2978	Reserved for future expansion, works like the USE symbols above.
		2979
		2980	=item EV_USE_INOTIFY
		2981
		2982	If defined to be C<1>, libev will compile in support for the Linux inotify
		2983	interface to speed up C<ev_stat> watchers. Its actual availability will
		2984	be detected at runtime. If undefined, it will be enabled if the headers
		2985	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2986
		2987	=item EV_ATOMIC_T
		2988
		2989	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2990	access is atomic with respect to other threads or signal contexts. No such
		2991	type is easily found in the C language, so you can provide your own type
		2992	that you know is safe for your purposes. It is used both for signal handler "locking"
		2993	as well as for signal and thread safety in C<ev_async> watchers.
		2994
		2995	In the absence of this define, libev will use C<sig_atomic_t volatile>
		2996	(from F<signal.h>), which is usually good enough on most platforms.
		2997
		2998	=item EV_H
		2999
		3000	The name of the F<ev.h> header file used to include it. The default if
		3001	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3002	used to virtually rename the F<ev.h> header file in case of conflicts.
		3003
		3004	=item EV_CONFIG_H
		3005
		3006	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3007	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3008	C<EV_H>, above.
		3009
		3010	=item EV_EVENT_H
		3011
		3012	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3013	of how the F<event.h> header can be found, the default is C<"event.h">.
		3014
		3015	=item EV_PROTOTYPES
		3016
		3017	If defined to be C<0>, then F<ev.h> will not define any function
		3018	prototypes, but still define all the structs and other symbols. This is
		3019	occasionally useful if you want to provide your own wrapper functions
		3020	around libev functions.
		3021
		3022	=item EV_MULTIPLICITY
		3023
		3024	If undefined or defined to C<1>, then all event-loop-specific functions
		3025	will have the C<struct ev_loop *> as first argument, and you can create
		3026	additional independent event loops. Otherwise there will be no support
		3027	for multiple event loops and there is no first event loop pointer
		3028	argument. Instead, all functions act on the single default loop.
		3029
		3030	=item EV_MINPRI
		3031
		3032	=item EV_MAXPRI
		3033
		3034	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3035	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3036	provide for more priorities by overriding those symbols (usually defined
		3037	to be C<-2> and C<2>, respectively).
		3038
		3039	When doing priority-based operations, libev usually has to linearly search
		3040	all the priorities, so having many of them (hundreds) uses a lot of space
		3041	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3042	fine.
		3043
		3044	If your embedding application does not need any priorities, defining these both to
		3045	C<0> will save some memory and CPU.
		3046
		3047	=item EV_PERIODIC_ENABLE
		3048
		3049	If undefined or defined to be C<1>, then periodic timers are supported. If
		3050	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3051	code.
		3052
		3053	=item EV_IDLE_ENABLE
		3054
		3055	If undefined or defined to be C<1>, then idle watchers are supported. If
		3056	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3057	code.
		3058
		3059	=item EV_EMBED_ENABLE
		3060
		3061	If undefined or defined to be C<1>, then embed watchers are supported. If
		3062	defined to be C<0>, then they are not.
		3063
		3064	=item EV_STAT_ENABLE
		3065
		3066	If undefined or defined to be C<1>, then stat watchers are supported. If
		3067	defined to be C<0>, then they are not.
		3068
		3069	=item EV_FORK_ENABLE
		3070
		3071	If undefined or defined to be C<1>, then fork watchers are supported. If
		3072	defined to be C<0>, then they are not.
		3073
		3074	=item EV_ASYNC_ENABLE
		3075
		3076	If undefined or defined to be C<1>, then async watchers are supported. If
		3077	defined to be C<0>, then they are not.
		3078
		3079	=item EV_MINIMAL
		3080
		3081	If you need to shave off some kilobytes of code at the expense of some
		3082	speed, define this symbol to C<1>. Currently this is used to override some
		3083	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3084	much smaller 2-heap for timer management over the default 4-heap.
		3085
		3086	=item EV_PID_HASHSIZE
		3087
		3088	C<ev_child> watchers use a small hash table to distribute workload by
		3089	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3090	than enough. If you need to manage thousands of children you might want to
		3091	increase this value (I<must> be a power of two).
		3092
		3093	=item EV_INOTIFY_HASHSIZE
		3094
		3095	C<ev_stat> watchers use a small hash table to distribute workload by
		3096	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3097	usually more than enough. If you need to manage thousands of C<ev_stat>
		3098	watchers you might want to increase this value (I<must> be a power of
		3099	two).
		3100
		3101	=item EV_USE_4HEAP
		3102
		3103	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3104	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3105	to C<1>. The 4-heap uses more complicated (longer) code but has
		3106	noticeably faster performance with many (thousands) of watchers.
		3107
		3108	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3109	(disabled).
		3110
		3111	=item EV_HEAP_CACHE_AT
		3112
		3113	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3114	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3115	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3116	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3117	but avoids random read accesses on heap changes. This improves performance
		3118	noticeably with with many (hundreds) of watchers.
		3119
		3120	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3121	(disabled).
		3122
		3123	=item EV_VERIFY
		3124
		3125	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3126	be done: If set to C<0>, no internal verification code will be compiled
		3127	in. If set to C<1>, then verification code will be compiled in, but not
		3128	called. If set to C<2>, then the internal verification code will be
		3129	called once per loop, which can slow down libev. If set to C<3>, then the
		3130	verification code will be called very frequently, which will slow down
		3131	libev considerably.
		3132
		3133	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3134	C<0.>
		3135
		3136	=item EV_COMMON
		3137
		3138	By default, all watchers have a C<void *data> member. By redefining
		3139	this macro to a something else you can include more and other types of
		3140	members. You have to define it each time you include one of the files,
		3141	though, and it must be identical each time.
		3142
		3143	For example, the perl EV module uses something like this:
		3144
		3145	#define EV_COMMON \
		3146	SV *self; /* contains this struct */ \
		3147	SV *cb_sv, *fh /* note no trailing ";" */
		3148
		3149	=item EV_CB_DECLARE (type)
		3150
		3151	=item EV_CB_INVOKE (watcher, revents)
		3152
		3153	=item ev_set_cb (ev, cb)
		3154
		3155	Can be used to change the callback member declaration in each watcher,
		3156	and the way callbacks are invoked and set. Must expand to a struct member
		3157	definition and a statement, respectively. See the F<ev.h> header file for
		3158	their default definitions. One possible use for overriding these is to
		3159	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3160	method calls instead of plain function calls in C++.
		3161
		3162	=head2 EXPORTED API SYMBOLS
		3163
		3164	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3165	exported symbols, you can use the provided F<Symbol.*> files which list
		3166	all public symbols, one per line:
		3167
		3168	Symbols.ev for libev proper
		3169	Symbols.event for the libevent emulation
		3170
		3171	This can also be used to rename all public symbols to avoid clashes with
		3172	multiple versions of libev linked together (which is obviously bad in
		3173	itself, but sometimes it is inconvenient to avoid this).
		3174
		3175	A sed command like this will create wrapper C<#define>'s that you need to
		3176	include before including F<ev.h>:
		3177
		3178	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3179
		3180	This would create a file F<wrap.h> which essentially looks like this:
		3181
		3182	#define ev_backend myprefix_ev_backend
		3183	#define ev_check_start myprefix_ev_check_start
		3184	#define ev_check_stop myprefix_ev_check_stop
		3185	...
		3186
		3187	=head2 EXAMPLES
		3188
		3189	For a real-world example of a program the includes libev
		3190	verbatim, you can have a look at the EV perl module
		3191	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3192	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3193	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3194	will be compiled. It is pretty complex because it provides its own header
		3195	file.
		3196
		3197	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3198	that everybody includes and which overrides some configure choices:
		3199
		3200	#define EV_MINIMAL 1
		3201	#define EV_USE_POLL 0
		3202	#define EV_MULTIPLICITY 0
		3203	#define EV_PERIODIC_ENABLE 0
		3204	#define EV_STAT_ENABLE 0
		3205	#define EV_FORK_ENABLE 0
		3206	#define EV_CONFIG_H <config.h>
		3207	#define EV_MINPRI 0
		3208	#define EV_MAXPRI 0
		3209
		3210	#include "ev++.h"
		3211
		3212	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3213
		3214	#include "ev_cpp.h"
		3215	#include "ev.c"
		3216
		3217
		3218	=head1 THREADS AND COROUTINES
		3219
		3220	=head2 THREADS
		3221
		3222	Libev itself is completely thread-safe, but it uses no locking. This
		3223	means that you can use as many loops as you want in parallel, as long as
		3224	only one thread ever calls into one libev function with the same loop
		3225	parameter.
		3226
		3227	Or put differently: calls with different loop parameters can be done in
		3228	parallel from multiple threads, calls with the same loop parameter must be
		3229	done serially (but can be done from different threads, as long as only one
		3230	thread ever is inside a call at any point in time, e.g. by using a mutex
		3231	per loop).
		3232
		3233	If you want to know which design (one loop, locking, or multiple loops
		3234	without or something else still) is best for your problem, then I cannot
		3235	help you. I can give some generic advice however:
		3236
		3237	=over 4
		3238
		3239	=item * most applications have a main thread: use the default libev loop
		3240	in that thread, or create a separate thread running only the default loop.
		3241
		3242	This helps integrating other libraries or software modules that use libev
		3243	themselves and don't care/know about threading.
		3244
		3245	=item * one loop per thread is usually a good model.
		3246
		3247	Doing this is almost never wrong, sometimes a better-performance model
		3248	exists, but it is always a good start.
		3249
		3250	=item * other models exist, such as the leader/follower pattern, where one
		3251	loop is handed through multiple threads in a kind of round-robin fashion.
		3252
		3253	Choosing a model is hard - look around, learn, know that usually you can do
		3254	better than you currently do :-)
		3255
		3256	=item * often you need to talk to some other thread which blocks in the
		3257	event loop - C<ev_async> watchers can be used to wake them up from other
		3258	threads safely (or from signal contexts...).
		3259
		3260	=back
		3261
		3262	=head2 COROUTINES
		3263
		3264	Libev is much more accommodating to coroutines ("cooperative threads"):
		3265	libev fully supports nesting calls to it's functions from different
		3266	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3267	different coroutines and switch freely between both coroutines running the
		3268	loop, as long as you don't confuse yourself). The only exception is that
		3269	you must not do this from C<ev_periodic> reschedule callbacks.
		3270
		3271	Care has been invested into making sure that libev does not keep local
		3272	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3273	switches.
		3274
		3275
		3276	=head1 COMPLEXITIES
		3277
		3278	In this section the complexities of (many of) the algorithms used inside
		3279	libev will be explained. For complexity discussions about backends see the
		3280	documentation for C<ev_default_init>.
		3281
		3282	All of the following are about amortised time: If an array needs to be
		3283	extended, libev needs to realloc and move the whole array, but this
		3284	happens asymptotically never with higher number of elements, so O(1) might
		3285	mean it might do a lengthy realloc operation in rare cases, but on average
		3286	it is much faster and asymptotically approaches constant time.
		3287
		3288	=over 4
		3289
		3290	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3291
		3292	This means that, when you have a watcher that triggers in one hour and
		3293	there are 100 watchers that would trigger before that then inserting will
		3294	have to skip roughly seven (C<ld 100>) of these watchers.
		3295
		3296	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3297
		3298	That means that changing a timer costs less than removing/adding them
		3299	as only the relative motion in the event queue has to be paid for.
		3300
		3301	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3302
		3303	These just add the watcher into an array or at the head of a list.
		3304
		3305	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3306
		3307	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3308
		3309	These watchers are stored in lists then need to be walked to find the
		3310	correct watcher to remove. The lists are usually short (you don't usually
		3311	have many watchers waiting for the same fd or signal).
		3312
		3313	=item Finding the next timer in each loop iteration: O(1)
		3314
		3315	By virtue of using a binary or 4-heap, the next timer is always found at a
		3316	fixed position in the storage array.
		3317
		3318	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3319
		3320	A change means an I/O watcher gets started or stopped, which requires
		3321	libev to recalculate its status (and possibly tell the kernel, depending
		3322	on backend and whether C<ev_io_set> was used).
		3323
		3324	=item Activating one watcher (putting it into the pending state): O(1)
		3325
		3326	=item Priority handling: O(number_of_priorities)
		3327
		3328	Priorities are implemented by allocating some space for each
		3329	priority. When doing priority-based operations, libev usually has to
		3330	linearly search all the priorities, but starting/stopping and activating
		3331	watchers becomes O(1) w.r.t. priority handling.
		3332
		3333	=item Sending an ev_async: O(1)
		3334
		3335	=item Processing ev_async_send: O(number_of_async_watchers)
		3336
		3337	=item Processing signals: O(max_signal_number)
		3338
		3339	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3340	calls in the current loop iteration. Checking for async and signal events
		3341	involves iterating over all running async watchers or all signal numbers.
		3342
		3343	=back
		3344
		3345
		3346	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3347
		3348	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3349	requires, and its I/O model is fundamentally incompatible with the POSIX
		3350	model. Libev still offers limited functionality on this platform in
		3351	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3352	descriptors. This only applies when using Win32 natively, not when using
		3353	e.g. cygwin.
		3354
		3355	Lifting these limitations would basically require the full
		3356	re-implementation of the I/O system. If you are into these kinds of
		3357	things, then note that glib does exactly that for you in a very portable
		3358	way (note also that glib is the slowest event library known to man).
		3359
		3360	There is no supported compilation method available on windows except
		3361	embedding it into other applications.
		3362
		3363	Not a libev limitation but worth mentioning: windows apparently doesn't
		3364	accept large writes: instead of resulting in a partial write, windows will
		3365	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3366	so make sure you only write small amounts into your sockets (less than a
		3367	megabyte seems safe, but thsi apparently depends on the amount of memory
		3368	available).
		3369
		3370	Due to the many, low, and arbitrary limits on the win32 platform and
		3371	the abysmal performance of winsockets, using a large number of sockets
		3372	is not recommended (and not reasonable). If your program needs to use
		3373	more than a hundred or so sockets, then likely it needs to use a totally
		3374	different implementation for windows, as libev offers the POSIX readiness
		3375	notification model, which cannot be implemented efficiently on windows
		3376	(Microsoft monopoly games).
		3377
		3378	A typical way to use libev under windows is to embed it (see the embedding
		3379	section for details) and use the following F<evwrap.h> header file instead
		3380	of F<ev.h>:
		3381
		3382	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3383	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3384
		3385	#include "ev.h"
		3386
		3387	And compile the following F<evwrap.c> file into your project (make sure
		3388	you do I<not> compile the F<ev.c> or any other embedded soruce files!):
		3389
		3390	#include "evwrap.h"
		3391	#include "ev.c"
		3392
		3393	=over 4
		3394
		3395	=item The winsocket select function
		3396
		3397	The winsocket C<select> function doesn't follow POSIX in that it
		3398	requires socket I<handles> and not socket I<file descriptors> (it is
		3399	also extremely buggy). This makes select very inefficient, and also
		3400	requires a mapping from file descriptors to socket handles (the Microsoft
		3401	C runtime provides the function C<_open_osfhandle> for this). See the
		3402	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3403	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3404
		3405	The configuration for a "naked" win32 using the Microsoft runtime
		3406	libraries and raw winsocket select is:
		3407
		3408	#define EV_USE_SELECT 1
		3409	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3410
		3411	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3412	complexity in the O(n²) range when using win32.
		3413
		3414	=item Limited number of file descriptors
		3415
		3416	Windows has numerous arbitrary (and low) limits on things.
		3417
		3418	Early versions of winsocket's select only supported waiting for a maximum
		3419	of C<64> handles (probably owning to the fact that all windows kernels
		3420	can only wait for C<64> things at the same time internally; Microsoft
		3421	recommends spawning a chain of threads and wait for 63 handles and the
		3422	previous thread in each. Great).
		3423
		3424	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3425	to some high number (e.g. C<2048>) before compiling the winsocket select
		3426	call (which might be in libev or elsewhere, for example, perl does its own
		3427	select emulation on windows).
		3428
		3429	Another limit is the number of file descriptors in the Microsoft runtime
		3430	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3431	or something like this inside Microsoft). You can increase this by calling
		3432	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3433	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3434	libraries.
		3435
		3436	This might get you to about C<512> or C<2048> sockets (depending on
		3437	windows version and/or the phase of the moon). To get more, you need to
		3438	wrap all I/O functions and provide your own fd management, but the cost of
		3439	calling select (O(n²)) will likely make this unworkable.
		3440
		3441	=back
		3442
		3443
		3444	=head1 PORTABILITY REQUIREMENTS
		3445
		3446	In addition to a working ISO-C implementation, libev relies on a few
		3447	additional extensions:
		3448
		3449	=over 4
		3450
		3451	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3452	calling conventions regardless of C<ev_watcher_type *>.
		3453
		3454	Libev assumes not only that all watcher pointers have the same internal
		3455	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3456	assumes that the same (machine) code can be used to call any watcher
		3457	callback: The watcher callbacks have different type signatures, but libev
		3458	calls them using an C<ev_watcher *> internally.
		3459
		3460	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3461
		3462	The type C<sig_atomic_t volatile> (or whatever is defined as
		3463	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3464	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3465	believed to be sufficiently portable.
		3466
		3467	=item C<sigprocmask> must work in a threaded environment
		3468
		3469	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3470	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3471	pthread implementations will either allow C<sigprocmask> in the "main
		3472	thread" or will block signals process-wide, both behaviours would
		3473	be compatible with libev. Interaction between C<sigprocmask> and
		3474	C<pthread_sigmask> could complicate things, however.
		3475
		3476	The most portable way to handle signals is to block signals in all threads
		3477	except the initial one, and run the default loop in the initial thread as
		3478	well.
		3479
		3480	=item C<long> must be large enough for common memory allocation sizes
		3481
		3482	To improve portability and simplify using libev, libev uses C<long>
		3483	internally instead of C<size_t> when allocating its data structures. On
		3484	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3485	is still at least 31 bits everywhere, which is enough for hundreds of
		3486	millions of watchers.
		3487
		3488	=item C<double> must hold a time value in seconds with enough accuracy
		3489
		3490	The type C<double> is used to represent timestamps. It is required to
		3491	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3492	enough for at least into the year 4000. This requirement is fulfilled by
		3493	implementations implementing IEEE 754 (basically all existing ones).
		3494
		3495	=back
		3496
		3497	If you know of other additional requirements drop me a note.
		3498
		3499
		3500	=head1 COMPILER WARNINGS
		3501
		3502	Depending on your compiler and compiler settings, you might get no or a
		3503	lot of warnings when compiling libev code. Some people are apparently
		3504	scared by this.
		3505
		3506	However, these are unavoidable for many reasons. For one, each compiler
		3507	has different warnings, and each user has different tastes regarding
		3508	warning options. "Warn-free" code therefore cannot be a goal except when
		3509	targeting a specific compiler and compiler-version.
		3510
		3511	Another reason is that some compiler warnings require elaborate
		3512	workarounds, or other changes to the code that make it less clear and less
		3513	maintainable.
		3514
		3515	And of course, some compiler warnings are just plain stupid, or simply
		3516	wrong (because they don't actually warn about the condition their message
		3517	seems to warn about).
		3518
		3519	While libev is written to generate as few warnings as possible,
		3520	"warn-free" code is not a goal, and it is recommended not to build libev
		3521	with any compiler warnings enabled unless you are prepared to cope with
		3522	them (e.g. by ignoring them). Remember that warnings are just that:
		3523	warnings, not errors, or proof of bugs.
		3524
		3525
		3526	=head1 VALGRIND
		3527
		3528	Valgrind has a special section here because it is a popular tool that is
		3529	highly useful, but valgrind reports are very hard to interpret.
		3530
		3531	If you think you found a bug (memory leak, uninitialised data access etc.)
		3532	in libev, then check twice: If valgrind reports something like:
		3533
		3534	==2274== definitely lost: 0 bytes in 0 blocks.
		3535	==2274== possibly lost: 0 bytes in 0 blocks.
		3536	==2274== still reachable: 256 bytes in 1 blocks.
		3537
		3538	Then there is no memory leak. Similarly, under some circumstances,
		3539	valgrind might report kernel bugs as if it were a bug in libev, or it
		3540	might be confused (it is a very good tool, but only a tool).
		3541
		3542	If you are unsure about something, feel free to contact the mailing list
		3543	with the full valgrind report and an explanation on why you think this is
		3544	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3545	no bug" answer and take the chance of learning how to interpret valgrind
		3546	properly.
		3547
		3548	If you need, for some reason, empty reports from valgrind for your project
		3549	I suggest using suppression lists.
		3550
878		3551
879	=head1 AUTHOR	3552	=head1 AUTHOR
880		3553
881	Marc Lehmann <libev@schmorp.de>.	3554	Marc Lehmann <libev@schmorp.de>.
882		3555

Diff Legend

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