ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.99 by root, Sat Dec 22 06:16:36 2007 UTC vs.
Revision 1.157 by root, Tue May 20 23:49:41 2008 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_<type>
13	ev_io stdin_watcher;	16	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	17	ev_timer timeout_watcher;
15		18
		19	// all watcher callbacks have a similar signature
16	/* called when data readable on stdin */	20	// this callback is called when data is readable on stdin
17	static void	21	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	22	stdin_cb (EV_P_ struct ev_io *w, int revents)
19	{	23	{
20	/* puts ("stdin ready"); */	24	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	25	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	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);
23	}	31	}
24		32
		33	// another callback, this time for a time-out
25	static void	34	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	35	timeout_cb (EV_P_ struct ev_timer *w, int revents)
27	{	36	{
28	/* puts ("timeout"); */	37	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	40	}
31		41
32	int	42	int
33	main (void)	43	main (void)
34	{	44	{
		45	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	46	struct ev_loop *loop = ev_default_loop (0);
36		47
37	/* initialise an io watcher, then start it */	48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	51	ev_io_start (loop, &stdin_watcher);
40		52
		53	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	54	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	56	ev_timer_start (loop, &timeout_watcher);
44		57
45	/* loop till timeout or data ready */	58	// now wait for events to arrive
46	ev_loop (loop, 0);	59	ev_loop (loop, 0);
47		60
		61	// unloop was called, so exit
48	return 0;	62	return 0;
49	}	63	}
50		64
51	=head1 DESCRIPTION	65	=head1 DESCRIPTION
52		66
53	The newest version of this document is also available as a html-formatted	67	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	68	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
56		70
57	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
58	file descriptor being readable or a timeout occurring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	73	these event sources and provide your program with events.
60		74
…		…
65	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
66	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	82	watcher.
69		83
70	=head1 FEATURES	84	=head2 FEATURES
71		85
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
82		96
83	It also is quite fast (see this	97	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	99	for example).
86		100
87	=head1 CONVENTIONS	101	=head2 CONVENTIONS
88		102
89	Libev is very configurable. In this manual the default configuration will	103	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	104	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	105	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	106	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	107	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	108	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		109	this argument.
95		110
96	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
97		112
98	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
100	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
101	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
…		…
181	See the description of C<ev_embed> watchers for more info.	196	See the description of C<ev_embed> watchers for more info.
182		197
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
184		199
185	Sets the allocation function to use (the prototype is similar - the	200	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	201	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
187	allocate and free memory (no surprises here). If it returns zero when	202	used to allocate and free memory (no surprises here). If it returns zero
188	memory needs to be allocated, the library might abort or take some	203	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	204	or take some potentially destructive action.
190	function.	205
		206	Since some systems (at least OpenBSD and Darwin) fail to implement
		207	correct C<realloc> semantics, libev will use a wrapper around the system
		208	C<realloc> and C<free> functions by default.
191		209
192	You could override this function in high-availability programs to, say,	210	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	211	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	212	or even to sleep a while and retry until some memory is available.
195		213
196	Example: Replace the libev allocator with one that waits a bit and then	214	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	215	retries (example requires a standards-compliant C<realloc>).
198		216
199	static void *	217	static void *
200	persistent_realloc (void *ptr, size_t size)	218	persistent_realloc (void *ptr, size_t size)
201	{	219	{
202	for (;;)	220	for (;;)
…		…
241		259
242	An event loop is described by a C<struct ev_loop *>. The library knows two	260	An event loop is described by a C<struct ev_loop *>. The library knows two
243	types of such loops, the I<default> loop, which supports signals and child	261	types of such loops, the I<default> loop, which supports signals and child
244	events, and dynamically created loops which do not.	262	events, and dynamically created loops which do not.
245		263
246	If you use threads, a common model is to run the default event loop
247	in your main thread (or in a separate thread) and for each thread you
248	create, you also create another event loop. Libev itself does no locking
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252
253	=over 4	264	=over 4
254		265
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	266	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		267
257	This will initialise the default event loop if it hasn't been initialised	268	This will initialise the default event loop if it hasn't been initialised
…		…
259	false. If it already was initialised it simply returns it (and ignores the	270	false. If it already was initialised it simply returns it (and ignores the
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	271	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		272
262	If you don't know what event loop to use, use the one returned from this	273	If you don't know what event loop to use, use the one returned from this
263	function.	274	function.
		275
		276	Note that this function is I<not> thread-safe, so if you want to use it
		277	from multiple threads, you have to lock (note also that this is unlikely,
		278	as loops cannot bes hared easily between threads anyway).
		279
		280	The default loop is the only loop that can handle C<ev_signal> and
		281	C<ev_child> watchers, and to do this, it always registers a handler
		282	for C<SIGCHLD>. If this is a problem for your app you can either
		283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		284	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		285	C<ev_default_init>.
264		286
265	The flags argument can be used to specify special behaviour or specific	287	The flags argument can be used to specify special behaviour or specific
266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	288	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
267		289
268	The following flags are supported:	290	The following flags are supported:
…		…
290	enabling this flag.	312	enabling this flag.
291		313
292	This works by calling C<getpid ()> on every iteration of the loop,	314	This works by calling C<getpid ()> on every iteration of the loop,
293	and thus this might slow down your event loop if you do a lot of loop	315	and thus this might slow down your event loop if you do a lot of loop
294	iterations and little real work, but is usually not noticeable (on my	316	iterations and little real work, but is usually not noticeable (on my
295	Linux system for example, C<getpid> is actually a simple 5-insn sequence	317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
296	without a syscall and thus I<very> fast, but my Linux system also has	318	without a syscall and thus I<very> fast, but my GNU/Linux system also has
297	C<pthread_atfork> which is even faster).	319	C<pthread_atfork> which is even faster).
298		320
299	The big advantage of this flag is that you can forget about fork (and	321	The big advantage of this flag is that you can forget about fork (and
300	forget about forgetting to tell libev about forking) when you use this	322	forget about forgetting to tell libev about forking) when you use this
301	flag.	323	flag.
…		…
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		329
308	This is your standard select(2) backend. Not I<completely> standard, as	330	This is your standard select(2) backend. Not I<completely> standard, as
309	libev tries to roll its own fd_set with no limits on the number of fds,	331	libev tries to roll its own fd_set with no limits on the number of fds,
310	but if that fails, expect a fairly low limit on the number of fds when	332	but if that fails, expect a fairly low limit on the number of fds when
311	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	333	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	the fastest backend for a low number of fds.	334	usually the fastest backend for a low number of (low-numbered :) fds.
		335
		336	To get good performance out of this backend you need a high amount of
		337	parallelity (most of the file descriptors should be busy). If you are
		338	writing a server, you should C<accept ()> in a loop to accept as many
		339	connections as possible during one iteration. You might also want to have
		340	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		341	readiness notifications you get per iteration.
313		342
314	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
315		344
316	And this is your standard poll(2) backend. It's more complicated than	345	And this is your standard poll(2) backend. It's more complicated
317	select, but handles sparse fds better and has no artificial limit on the	346	than select, but handles sparse fds better and has no artificial
318	number of fds you can use (except it will slow down considerably with a	347	limit on the number of fds you can use (except it will slow down
319	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	348	considerably with a lot of inactive fds). It scales similarly to select,
		349	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		350	performance tips.
320		351
321	=item C<EVBACKEND_EPOLL> (value 4, Linux)	352	=item C<EVBACKEND_EPOLL> (value 4, Linux)
322		353
323	For few fds, this backend is a bit little slower than poll and select,	354	For few fds, this backend is a bit little slower than poll and select,
324	but it scales phenomenally better. While poll and select usually scale	355	but it scales phenomenally better. While poll and select usually scale
325	like O(total_fds) where n is the total number of fds (or the highest fd),	356	like O(total_fds) where n is the total number of fds (or the highest fd),
326	epoll scales either O(1) or O(active_fds). The epoll design has a number	357	epoll scales either O(1) or O(active_fds). The epoll design has a number
327	of shortcomings, such as silently dropping events in some hard-to-detect	358	of shortcomings, such as silently dropping events in some hard-to-detect
328	cases and rewiring a syscall per fd change, no fork support and bad	359	cases and requiring a syscall per fd change, no fork support and bad
329	support for dup:	360	support for dup.
330		361
331	While stopping, setting and starting an I/O watcher in the same iteration	362	While stopping, setting and starting an I/O watcher in the same iteration
332	will result in some caching, there is still a syscall per such incident	363	will result in some caching, there is still a syscall per such incident
333	(because the fd could point to a different file description now), so its	364	(because the fd could point to a different file description now), so its
334	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	365	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
…		…
336		367
337	Please note that epoll sometimes generates spurious notifications, so you	368	Please note that epoll sometimes generates spurious notifications, so you
338	need to use non-blocking I/O or other means to avoid blocking when no data	369	need to use non-blocking I/O or other means to avoid blocking when no data
339	(or space) is available.	370	(or space) is available.
340		371
		372	Best performance from this backend is achieved by not unregistering all
		373	watchers for a file descriptor until it has been closed, if possible, i.e.
		374	keep at least one watcher active per fd at all times.
		375
		376	While nominally embeddeble in other event loops, this feature is broken in
		377	all kernel versions tested so far.
		378
341	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
342		380
343	Kqueue deserves special mention, as at the time of this writing, it	381	Kqueue deserves special mention, as at the time of this writing, it
344	was broken on I<all> BSDs (usually it doesn't work with anything but	382	was broken on all BSDs except NetBSD (usually it doesn't work reliably
345	sockets and pipes, except on Darwin, where of course it's completely	383	with anything but sockets and pipes, except on Darwin, where of course
346	useless. On NetBSD, it seems to work for all the FD types I tested, so it
347	is used by default there). For this reason it's not being "autodetected"	384	it's completely useless). For this reason it's not being "autodetected"
348	unless you explicitly specify it explicitly in the flags (i.e. using	385	unless you explicitly specify it explicitly in the flags (i.e. using
349	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	386	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
350	system like NetBSD.	387	system like NetBSD.
351		388
		389	You still can embed kqueue into a normal poll or select backend and use it
		390	only for sockets (after having made sure that sockets work with kqueue on
		391	the target platform). See C<ev_embed> watchers for more info.
		392
352	It scales in the same way as the epoll backend, but the interface to the	393	It scales in the same way as the epoll backend, but the interface to the
353	kernel is more efficient (which says nothing about its actual speed,	394	kernel is more efficient (which says nothing about its actual speed, of
354	of course). While stopping, setting and starting an I/O watcher does	395	course). While stopping, setting and starting an I/O watcher does never
355	never cause an extra syscall as with epoll, it still adds up to two event	396	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
356	changes per incident, support for C<fork ()> is very bad and it drops fds	397	two event changes per incident, support for C<fork ()> is very bad and it
357	silently in similarly hard-to-detetc cases.	398	drops fds silently in similarly hard-to-detect cases.
		399
		400	This backend usually performs well under most conditions.
		401
		402	While nominally embeddable in other event loops, this doesn't work
		403	everywhere, so you might need to test for this. And since it is broken
		404	almost everywhere, you should only use it when you have a lot of sockets
		405	(for which it usually works), by embedding it into another event loop
		406	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		407	sockets.
358		408
359	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
360		410
361	This is not implemented yet (and might never be).	411	This is not implemented yet (and might never be, unless you send me an
		412	implementation). According to reports, C</dev/poll> only supports sockets
		413	and is not embeddable, which would limit the usefulness of this backend
		414	immensely.
362		415
363	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
364		417
365	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
366	it's really slow, but it still scales very well (O(active_fds)).	419	it's really slow, but it still scales very well (O(active_fds)).
367		420
368	Please note that solaris event ports can deliver a lot of spurious	421	Please note that solaris event ports can deliver a lot of spurious
369	notifications, so you need to use non-blocking I/O or other means to avoid	422	notifications, so you need to use non-blocking I/O or other means to avoid
370	blocking when no data (or space) is available.	423	blocking when no data (or space) is available.
371		424
		425	While this backend scales well, it requires one system call per active
		426	file descriptor per loop iteration. For small and medium numbers of file
		427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		428	might perform better.
		429
		430	On the positive side, ignoring the spurious readiness notifications, this
		431	backend actually performed to specification in all tests and is fully
		432	embeddable, which is a rare feat among the OS-specific backends.
		433
372	=item C<EVBACKEND_ALL>	434	=item C<EVBACKEND_ALL>
373		435
374	Try all backends (even potentially broken ones that wouldn't be tried	436	Try all backends (even potentially broken ones that wouldn't be tried
375	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	437	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
376	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	438	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
377		439
		440	It is definitely not recommended to use this flag.
		441
378	=back	442	=back
379		443
380	If one or more of these are ored into the flags value, then only these	444	If one or more of these are ored into the flags value, then only these
381	backends will be tried (in the reverse order as given here). If none are	445	backends will be tried (in the reverse order as listed here). If none are
382	specified, most compiled-in backend will be tried, usually in reverse	446	specified, all backends in C<ev_recommended_backends ()> will be tried.
383	order of their flag values :)
384		447
385	The most typical usage is like this:	448	The most typical usage is like this:
386		449
387	if (!ev_default_loop (0))	450	if (!ev_default_loop (0))
388	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
402		465
403	Similar to C<ev_default_loop>, but always creates a new event loop that is	466	Similar to C<ev_default_loop>, but always creates a new event loop that is
404	always distinct from the default loop. Unlike the default loop, it cannot	467	always distinct from the default loop. Unlike the default loop, it cannot
405	handle signal and child watchers, and attempts to do so will be greeted by	468	handle signal and child watchers, and attempts to do so will be greeted by
406	undefined behaviour (or a failed assertion if assertions are enabled).	469	undefined behaviour (or a failed assertion if assertions are enabled).
		470
		471	Note that this function I<is> thread-safe, and the recommended way to use
		472	libev with threads is indeed to create one loop per thread, and using the
		473	default loop in the "main" or "initial" thread.
407		474
408	Example: Try to create a event loop that uses epoll and nothing else.	475	Example: Try to create a event loop that uses epoll and nothing else.
409		476
410	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	477	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
411	if (!epoller)	478	if (!epoller)
…		…
435	Like C<ev_default_destroy>, but destroys an event loop created by an	502	Like C<ev_default_destroy>, but destroys an event loop created by an
436	earlier call to C<ev_loop_new>.	503	earlier call to C<ev_loop_new>.
437		504
438	=item ev_default_fork ()	505	=item ev_default_fork ()
439		506
		507	This function sets a flag that causes subsequent C<ev_loop> iterations
440	This function reinitialises the kernel state for backends that have	508	to reinitialise the kernel state for backends that have one. Despite the
441	one. Despite the name, you can call it anytime, but it makes most sense	509	name, you can call it anytime, but it makes most sense after forking, in
442	after forking, in either the parent or child process (or both, but that	510	the child process (or both child and parent, but that again makes little
443	again makes little sense).	511	sense). You I<must> call it in the child before using any of the libev
		512	functions, and it will only take effect at the next C<ev_loop> iteration.
444		513
445	You I<must> call this function in the child process after forking if and	514	On the other hand, you only need to call this function in the child
446	only if you want to use the event library in both processes. If you just	515	process if and only if you want to use the event library in the child. If
447	fork+exec, you don't have to call it.	516	you just fork+exec, you don't have to call it at all.
448		517
449	The function itself is quite fast and it's usually not a problem to call	518	The function itself is quite fast and it's usually not a problem to call
450	it just in case after a fork. To make this easy, the function will fit in	519	it just in case after a fork. To make this easy, the function will fit in
451	quite nicely into a call to C<pthread_atfork>:	520	quite nicely into a call to C<pthread_atfork>:
452		521
453	pthread_atfork (0, 0, ev_default_fork);	522	pthread_atfork (0, 0, ev_default_fork);
454		523
455	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
456	without calling this function, so if you force one of those backends you
457	do not need to care.
458
459	=item ev_loop_fork (loop)	524	=item ev_loop_fork (loop)
460		525
461	Like C<ev_default_fork>, but acts on an event loop created by	526	Like C<ev_default_fork>, but acts on an event loop created by
462	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	527	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
463	after fork, and how you do this is entirely your own problem.	528	after fork, and how you do this is entirely your own problem.
		529
		530	=item int ev_is_default_loop (loop)
		531
		532	Returns true when the given loop actually is the default loop, false otherwise.
464		533
465	=item unsigned int ev_loop_count (loop)	534	=item unsigned int ev_loop_count (loop)
466		535
467	Returns the count of loop iterations for the loop, which is identical to	536	Returns the count of loop iterations for the loop, which is identical to
468	the number of times libev did poll for new events. It starts at C<0> and	537	the number of times libev did poll for new events. It starts at C<0> and
…		…
513	usually a better approach for this kind of thing.	582	usually a better approach for this kind of thing.
514		583
515	Here are the gory details of what C<ev_loop> does:	584	Here are the gory details of what C<ev_loop> does:
516		585
517	- Before the first iteration, call any pending watchers.	586	- Before the first iteration, call any pending watchers.
518	* If there are no active watchers (reference count is zero), return.	587	* If EVFLAG_FORKCHECK was used, check for a fork.
519	- Queue all prepare watchers and then call all outstanding watchers.	588	- If a fork was detected, queue and call all fork watchers.
		589	- Queue and call all prepare watchers.
520	- If we have been forked, recreate the kernel state.	590	- If we have been forked, recreate the kernel state.
521	- Update the kernel state with all outstanding changes.	591	- Update the kernel state with all outstanding changes.
522	- Update the "event loop time".	592	- Update the "event loop time".
523	- Calculate for how long to block.	593	- Calculate for how long to sleep or block, if at all
		594	(active idle watchers, EVLOOP_NONBLOCK or not having
		595	any active watchers at all will result in not sleeping).
		596	- Sleep if the I/O and timer collect interval say so.
524	- Block the process, waiting for any events.	597	- Block the process, waiting for any events.
525	- Queue all outstanding I/O (fd) events.	598	- Queue all outstanding I/O (fd) events.
526	- Update the "event loop time" and do time jump handling.	599	- Update the "event loop time" and do time jump handling.
527	- Queue all outstanding timers.	600	- Queue all outstanding timers.
528	- Queue all outstanding periodics.	601	- Queue all outstanding periodics.
529	- If no events are pending now, queue all idle watchers.	602	- If no events are pending now, queue all idle watchers.
530	- Queue all check watchers.	603	- Queue all check watchers.
531	- Call all queued watchers in reverse order (i.e. check watchers first).	604	- Call all queued watchers in reverse order (i.e. check watchers first).
532	Signals and child watchers are implemented as I/O watchers, and will	605	Signals and child watchers are implemented as I/O watchers, and will
533	be handled here by queueing them when their watcher gets executed.	606	be handled here by queueing them when their watcher gets executed.
534	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	607	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
535	were used, return, otherwise continue with step *.	608	were used, or there are no active watchers, return, otherwise
		609	continue with step *.
536		610
537	Example: Queue some jobs and then loop until no events are outsanding	611	Example: Queue some jobs and then loop until no events are outstanding
538	anymore.	612	anymore.
539		613
540	... queue jobs here, make sure they register event watchers as long	614	... queue jobs here, make sure they register event watchers as long
541	... as they still have work to do (even an idle watcher will do..)	615	... as they still have work to do (even an idle watcher will do..)
542	ev_loop (my_loop, 0);	616	ev_loop (my_loop, 0);
…		…
546		620
547	Can be used to make a call to C<ev_loop> return early (but only after it	621	Can be used to make a call to C<ev_loop> return early (but only after it
548	has processed all outstanding events). The C<how> argument must be either	622	has processed all outstanding events). The C<how> argument must be either
549	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	623	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
550	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	624	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		625
		626	This "unloop state" will be cleared when entering C<ev_loop> again.
551		627
552	=item ev_ref (loop)	628	=item ev_ref (loop)
553		629
554	=item ev_unref (loop)	630	=item ev_unref (loop)
555		631
…		…
560	returning, ev_unref() after starting, and ev_ref() before stopping it. For	636	returning, ev_unref() after starting, and ev_ref() before stopping it. For
561	example, libev itself uses this for its internal signal pipe: It is not	637	example, libev itself uses this for its internal signal pipe: It is not
562	visible to the libev user and should not keep C<ev_loop> from exiting if	638	visible to the libev user and should not keep C<ev_loop> from exiting if
563	no event watchers registered by it are active. It is also an excellent	639	no event watchers registered by it are active. It is also an excellent
564	way to do this for generic recurring timers or from within third-party	640	way to do this for generic recurring timers or from within third-party
565	libraries. Just remember to I<unref after start> and I<ref before stop>.	641	libraries. Just remember to I<unref after start> and I<ref before stop>
		642	(but only if the watcher wasn't active before, or was active before,
		643	respectively).
566		644
567	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	645	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
568	running when nothing else is active.	646	running when nothing else is active.
569		647
570	struct ev_signal exitsig;	648	struct ev_signal exitsig;
…		…
596	overhead for the actual polling but can deliver many events at once.	674	overhead for the actual polling but can deliver many events at once.
597		675
598	By setting a higher I<io collect interval> you allow libev to spend more	676	By setting a higher I<io collect interval> you allow libev to spend more
599	time collecting I/O events, so you can handle more events per iteration,	677	time collecting I/O events, so you can handle more events per iteration,
600	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	678	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
601	C<ev_timer>) will be not affected. Setting this to a non-null bvalue will	679	C<ev_timer>) will be not affected. Setting this to a non-null value will
602	introduce an additional C<ev_sleep ()> call into most loop iterations.	680	introduce an additional C<ev_sleep ()> call into most loop iterations.
603		681
604	Likewise, by setting a higher I<timeout collect interval> you allow libev	682	Likewise, by setting a higher I<timeout collect interval> you allow libev
605	to spend more time collecting timeouts, at the expense of increased	683	to spend more time collecting timeouts, at the expense of increased
606	latency (the watcher callback will be called later). C<ev_io> watchers	684	latency (the watcher callback will be called later). C<ev_io> watchers
…		…
718		796
719	=item C<EV_FORK>	797	=item C<EV_FORK>
720		798
721	The event loop has been resumed in the child process after fork (see	799	The event loop has been resumed in the child process after fork (see
722	C<ev_fork>).	800	C<ev_fork>).
		801
		802	=item C<EV_ASYNC>
		803
		804	The given async watcher has been asynchronously notified (see C<ev_async>).
723		805
724	=item C<EV_ERROR>	806	=item C<EV_ERROR>
725		807
726	An unspecified error has occured, the watcher has been stopped. This might	808	An unspecified error has occured, the watcher has been stopped. This might
727	happen because the watcher could not be properly started because libev	809	happen because the watcher could not be properly started because libev
…		…
945	In general you can register as many read and/or write event watchers per	1027	In general you can register as many read and/or write event watchers per
946	fd as you want (as long as you don't confuse yourself). Setting all file	1028	fd as you want (as long as you don't confuse yourself). Setting all file
947	descriptors to non-blocking mode is also usually a good idea (but not	1029	descriptors to non-blocking mode is also usually a good idea (but not
948	required if you know what you are doing).	1030	required if you know what you are doing).
949		1031
950	You have to be careful with dup'ed file descriptors, though. Some backends
951	(the linux epoll backend is a notable example) cannot handle dup'ed file
952	descriptors correctly if you register interest in two or more fds pointing
953	to the same underlying file/socket/etc. description (that is, they share
954	the same underlying "file open").
955
956	If you must do this, then force the use of a known-to-be-good backend	1032	If you must do this, then force the use of a known-to-be-good backend
957	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1033	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
958	C<EVBACKEND_POLL>).	1034	C<EVBACKEND_POLL>).
959		1035
960	Another thing you have to watch out for is that it is quite easy to	1036	Another thing you have to watch out for is that it is quite easy to
961	receive "spurious" readyness notifications, that is your callback might	1037	receive "spurious" readiness notifications, that is your callback might
962	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1038	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
963	because there is no data. Not only are some backends known to create a	1039	because there is no data. Not only are some backends known to create a
964	lot of those (for example solaris ports), it is very easy to get into	1040	lot of those (for example solaris ports), it is very easy to get into
965	this situation even with a relatively standard program structure. Thus	1041	this situation even with a relatively standard program structure. Thus
966	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1042	it is best to always use non-blocking I/O: An extra C<read>(2) returning
…		…
994	optimisations to libev.	1070	optimisations to libev.
995		1071
996	=head3 The special problem of dup'ed file descriptors	1072	=head3 The special problem of dup'ed file descriptors
997		1073
998	Some backends (e.g. epoll), cannot register events for file descriptors,	1074	Some backends (e.g. epoll), cannot register events for file descriptors,
999	but only events for the underlying file descriptions. That menas when you	1075	but only events for the underlying file descriptions. That means when you
1000	have C<dup ()>'ed file descriptors and register events for them, only one	1076	have C<dup ()>'ed file descriptors or weirder constellations, and register
1001	file descriptor might actually receive events.	1077	events for them, only one file descriptor might actually receive events.
1002		1078
1003	There is no workaorund possible except not registering events	1079	There is no workaround possible except not registering events
1004	for potentially C<dup ()>'ed file descriptors or to resort to	1080	for potentially C<dup ()>'ed file descriptors, or to resort to
1005	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1081	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1006		1082
1007	=head3 The special problem of fork	1083	=head3 The special problem of fork
1008		1084
1009	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1085	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
…		…
1013	To support fork in your programs, you either have to call	1089	To support fork in your programs, you either have to call
1014	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1090	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1015	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1091	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1016	C<EVBACKEND_POLL>.	1092	C<EVBACKEND_POLL>.
1017		1093
		1094	=head3 The special problem of SIGPIPE
		1095
		1096	While not really specific to libev, it is easy to forget about SIGPIPE:
		1097	when reading from a pipe whose other end has been closed, your program
		1098	gets send a SIGPIPE, which, by default, aborts your program. For most
		1099	programs this is sensible behaviour, for daemons, this is usually
		1100	undesirable.
		1101
		1102	So when you encounter spurious, unexplained daemon exits, make sure you
		1103	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1104	somewhere, as that would have given you a big clue).
		1105
1018		1106
1019	=head3 Watcher-Specific Functions	1107	=head3 Watcher-Specific Functions
1020		1108
1021	=over 4	1109	=over 4
1022		1110
…		…
1035	=item int events [read-only]	1123	=item int events [read-only]
1036		1124
1037	The events being watched.	1125	The events being watched.
1038		1126
1039	=back	1127	=back
		1128
		1129	=head3 Examples
1040		1130
1041	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1131	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1042	readable, but only once. Since it is likely line-buffered, you could	1132	readable, but only once. Since it is likely line-buffered, you could
1043	attempt to read a whole line in the callback.	1133	attempt to read a whole line in the callback.
1044		1134
…		…
1061		1151
1062	Timer watchers are simple relative timers that generate an event after a	1152	Timer watchers are simple relative timers that generate an event after a
1063	given time, and optionally repeating in regular intervals after that.	1153	given time, and optionally repeating in regular intervals after that.
1064		1154
1065	The timers are based on real time, that is, if you register an event that	1155	The timers are based on real time, that is, if you register an event that
1066	times out after an hour and you reset your system clock to last years	1156	times out after an hour and you reset your system clock to january last
1067	time, it will still time out after (roughly) and hour. "Roughly" because	1157	year, it will still time out after (roughly) and hour. "Roughly" because
1068	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1069	monotonic clock option helps a lot here).	1159	monotonic clock option helps a lot here).
1070		1160
1071	The relative timeouts are calculated relative to the C<ev_now ()>	1161	The relative timeouts are calculated relative to the C<ev_now ()>
1072	time. This is usually the right thing as this timestamp refers to the time	1162	time. This is usually the right thing as this timestamp refers to the time
…		…
1074	you suspect event processing to be delayed and you I<need> to base the timeout	1164	you suspect event processing to be delayed and you I<need> to base the timeout
1075	on the current time, use something like this to adjust for this:	1165	on the current time, use something like this to adjust for this:
1076		1166
1077	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1078		1168
1079	The callback is guarenteed to be invoked only when its timeout has passed,	1169	The callback is guarenteed to be invoked only after its timeout has passed,
1080	but if multiple timers become ready during the same loop iteration then	1170	but if multiple timers become ready during the same loop iteration then
1081	order of execution is undefined.	1171	order of execution is undefined.
1082		1172
1083	=head3 Watcher-Specific Functions and Data Members	1173	=head3 Watcher-Specific Functions and Data Members
1084		1174
…		…
1086		1176
1087	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1177	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1088		1178
1089	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1179	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1090		1180
1091	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1181	Configure the timer to trigger after C<after> seconds. If C<repeat>
1092	C<0.>, then it will automatically be stopped. If it is positive, then the	1182	is C<0.>, then it will automatically be stopped once the timeout is
1093	timer will automatically be configured to trigger again C<repeat> seconds	1183	reached. If it is positive, then the timer will automatically be
1094	later, again, and again, until stopped manually.	1184	configured to trigger again C<repeat> seconds later, again, and again,
		1185	until stopped manually.
1095		1186
1096	The timer itself will do a best-effort at avoiding drift, that is, if you	1187	The timer itself will do a best-effort at avoiding drift, that is, if
1097	configure a timer to trigger every 10 seconds, then it will trigger at	1188	you configure a timer to trigger every 10 seconds, then it will normally
1098	exactly 10 second intervals. If, however, your program cannot keep up with	1189	trigger at exactly 10 second intervals. If, however, your program cannot
1099	the timer (because it takes longer than those 10 seconds to do stuff) the	1190	keep up with the timer (because it takes longer than those 10 seconds to
1100	timer will not fire more than once per event loop iteration.	1191	do stuff) the timer will not fire more than once per event loop iteration.
1101		1192
1102	=item ev_timer_again (loop)	1193	=item ev_timer_again (loop, ev_timer *)
1103		1194
1104	This will act as if the timer timed out and restart it again if it is	1195	This will act as if the timer timed out and restart it again if it is
1105	repeating. The exact semantics are:	1196	repeating. The exact semantics are:
1106		1197
1107	If the timer is pending, its pending status is cleared.	1198	If the timer is pending, its pending status is cleared.
…		…
1142	or C<ev_timer_again> is called and determines the next timeout (if any),	1233	or C<ev_timer_again> is called and determines the next timeout (if any),
1143	which is also when any modifications are taken into account.	1234	which is also when any modifications are taken into account.
1144		1235
1145	=back	1236	=back
1146		1237
		1238	=head3 Examples
		1239
1147	Example: Create a timer that fires after 60 seconds.	1240	Example: Create a timer that fires after 60 seconds.
1148		1241
1149	static void	1242	static void
1150	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1243	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1151	{	1244	{
…		…
1180	Periodic watchers are also timers of a kind, but they are very versatile	1273	Periodic watchers are also timers of a kind, but they are very versatile
1181	(and unfortunately a bit complex).	1274	(and unfortunately a bit complex).
1182		1275
1183	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1276	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
1184	but on wallclock time (absolute time). You can tell a periodic watcher	1277	but on wallclock time (absolute time). You can tell a periodic watcher
1185	to trigger "at" some specific point in time. For example, if you tell a	1278	to trigger after some specific point in time. For example, if you tell a
1186	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1279	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
1187	+ 10.>) and then reset your system clock to the last year, then it will	1280	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1281	clock to january of the previous year, then it will take more than year
1188	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1282	to trigger the event (unlike an C<ev_timer>, which would still trigger
1189	roughly 10 seconds later).	1283	roughly 10 seconds later as it uses a relative timeout).
1190		1284
1191	They can also be used to implement vastly more complex timers, such as	1285	C<ev_periodic>s can also be used to implement vastly more complex timers,
1192	triggering an event on each midnight, local time or other, complicated,	1286	such as triggering an event on each "midnight, local time", or other
1193	rules.	1287	complicated, rules.
1194		1288
1195	As with timers, the callback is guarenteed to be invoked only when the	1289	As with timers, the callback is guarenteed to be invoked only when the
1196	time (C<at>) has been passed, but if multiple periodic timers become ready	1290	time (C<at>) has passed, but if multiple periodic timers become ready
1197	during the same loop iteration then order of execution is undefined.	1291	during the same loop iteration then order of execution is undefined.
1198		1292
1199	=head3 Watcher-Specific Functions and Data Members	1293	=head3 Watcher-Specific Functions and Data Members
1200		1294
1201	=over 4	1295	=over 4
…		…
1209		1303
1210	=over 4	1304	=over 4
1211		1305
1212	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1306	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1213		1307
1214	In this configuration the watcher triggers an event at the wallclock time	1308	In this configuration the watcher triggers an event after the wallclock
1215	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1309	time C<at> has passed and doesn't repeat. It will not adjust when a time
1216	that is, if it is to be run at January 1st 2011 then it will run when the	1310	jump occurs, that is, if it is to be run at January 1st 2011 then it will
1217	system time reaches or surpasses this time.	1311	run when the system time reaches or surpasses this time.
1218		1312
1219	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1313	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1220		1314
1221	In this mode the watcher will always be scheduled to time out at the next	1315	In this mode the watcher will always be scheduled to time out at the next
1222	C<at + N * interval> time (for some integer N, which can also be negative)	1316	C<at + N * interval> time (for some integer N, which can also be negative)
1223	and then repeat, regardless of any time jumps.	1317	and then repeat, regardless of any time jumps.
1224		1318
1225	This can be used to create timers that do not drift with respect to system	1319	This can be used to create timers that do not drift with respect to system
1226	time:	1320	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1321	the hour:
1227		1322
1228	ev_periodic_set (&periodic, 0., 3600., 0);	1323	ev_periodic_set (&periodic, 0., 3600., 0);
1229		1324
1230	This doesn't mean there will always be 3600 seconds in between triggers,	1325	This doesn't mean there will always be 3600 seconds in between triggers,
1231	but only that the the callback will be called when the system time shows a	1326	but only that the the callback will be called when the system time shows a
…		…
1236	C<ev_periodic> will try to run the callback in this mode at the next possible	1331	C<ev_periodic> will try to run the callback in this mode at the next possible
1237	time where C<time = at (mod interval)>, regardless of any time jumps.	1332	time where C<time = at (mod interval)>, regardless of any time jumps.
1238		1333
1239	For numerical stability it is preferable that the C<at> value is near	1334	For numerical stability it is preferable that the C<at> value is near
1240	C<ev_now ()> (the current time), but there is no range requirement for	1335	C<ev_now ()> (the current time), but there is no range requirement for
1241	this value.	1336	this value, and in fact is often specified as zero.
1242		1337
1243	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1338	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1244		1339
1245	In this mode the values for C<interval> and C<at> are both being	1340	In this mode the values for C<interval> and C<at> are both being
1246	ignored. Instead, each time the periodic watcher gets scheduled, the	1341	ignored. Instead, each time the periodic watcher gets scheduled, the
1247	reschedule callback will be called with the watcher as first, and the	1342	reschedule callback will be called with the watcher as first, and the
1248	current time as second argument.	1343	current time as second argument.
1249		1344
1250	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1345	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1251	ever, or make any event loop modifications>. If you need to stop it,	1346	ever, or make ANY event loop modifications whatsoever>.
1252	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1253	starting an C<ev_prepare> watcher, which is legal).
1254		1347
		1348	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1349	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1350	only event loop modification you are allowed to do).
		1351
1255	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1352	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
1256	ev_tstamp now)>, e.g.:	1353	*w, ev_tstamp now)>, e.g.:
1257		1354
1258	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1355	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1259	{	1356	{
1260	return now + 60.;	1357	return now + 60.;
1261	}	1358	}
…		…
1263	It must return the next time to trigger, based on the passed time value	1360	It must return the next time to trigger, based on the passed time value
1264	(that is, the lowest time value larger than to the second argument). It	1361	(that is, the lowest time value larger than to the second argument). It
1265	will usually be called just before the callback will be triggered, but	1362	will usually be called just before the callback will be triggered, but
1266	might be called at other times, too.	1363	might be called at other times, too.
1267		1364
1268	NOTE: I<< This callback must always return a time that is later than the	1365	NOTE: I<< This callback must always return a time that is higher than or
1269	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1366	equal to the passed C<now> value >>.
1270		1367
1271	This can be used to create very complex timers, such as a timer that	1368	This can be used to create very complex timers, such as a timer that
1272	triggers on each midnight, local time. To do this, you would calculate the	1369	triggers on "next midnight, local time". To do this, you would calculate the
1273	next midnight after C<now> and return the timestamp value for this. How	1370	next midnight after C<now> and return the timestamp value for this. How
1274	you do this is, again, up to you (but it is not trivial, which is the main	1371	you do this is, again, up to you (but it is not trivial, which is the main
1275	reason I omitted it as an example).	1372	reason I omitted it as an example).
1276		1373
1277	=back	1374	=back
…		…
1281	Simply stops and restarts the periodic watcher again. This is only useful	1378	Simply stops and restarts the periodic watcher again. This is only useful
1282	when you changed some parameters or the reschedule callback would return	1379	when you changed some parameters or the reschedule callback would return
1283	a different time than the last time it was called (e.g. in a crond like	1380	a different time than the last time it was called (e.g. in a crond like
1284	program when the crontabs have changed).	1381	program when the crontabs have changed).
1285		1382
		1383	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1384
		1385	When active, returns the absolute time that the watcher is supposed to
		1386	trigger next.
		1387
1286	=item ev_tstamp offset [read-write]	1388	=item ev_tstamp offset [read-write]
1287		1389
1288	When repeating, this contains the offset value, otherwise this is the	1390	When repeating, this contains the offset value, otherwise this is the
1289	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1391	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
1290		1392
…		…
1301		1403
1302	The current reschedule callback, or C<0>, if this functionality is	1404	The current reschedule callback, or C<0>, if this functionality is
1303	switched off. Can be changed any time, but changes only take effect when	1405	switched off. Can be changed any time, but changes only take effect when
1304	the periodic timer fires or C<ev_periodic_again> is being called.	1406	the periodic timer fires or C<ev_periodic_again> is being called.
1305		1407
1306	=item ev_tstamp at [read-only]
1307
1308	When active, contains the absolute time that the watcher is supposed to
1309	trigger next.
1310
1311	=back	1408	=back
		1409
		1410	=head3 Examples
1312		1411
1313	Example: Call a callback every hour, or, more precisely, whenever the	1412	Example: Call a callback every hour, or, more precisely, whenever the
1314	system clock is divisible by 3600. The callback invocation times have	1413	system clock is divisible by 3600. The callback invocation times have
1315	potentially a lot of jittering, but good long-term stability.	1414	potentially a lot of jittering, but good long-term stability.
1316		1415
…		…
1356	with the kernel (thus it coexists with your own signal handlers as long	1455	with the kernel (thus it coexists with your own signal handlers as long
1357	as you don't register any with libev). Similarly, when the last signal	1456	as you don't register any with libev). Similarly, when the last signal
1358	watcher for a signal is stopped libev will reset the signal handler to	1457	watcher for a signal is stopped libev will reset the signal handler to
1359	SIG_DFL (regardless of what it was set to before).	1458	SIG_DFL (regardless of what it was set to before).
1360		1459
		1460	If possible and supported, libev will install its handlers with
		1461	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
		1462	interrupted. If you have a problem with syscalls getting interrupted by
		1463	signals you can block all signals in an C<ev_check> watcher and unblock
		1464	them in an C<ev_prepare> watcher.
		1465
1361	=head3 Watcher-Specific Functions and Data Members	1466	=head3 Watcher-Specific Functions and Data Members
1362		1467
1363	=over 4	1468	=over 4
1364		1469
1365	=item ev_signal_init (ev_signal *, callback, int signum)	1470	=item ev_signal_init (ev_signal *, callback, int signum)
…		…
1373		1478
1374	The signal the watcher watches out for.	1479	The signal the watcher watches out for.
1375		1480
1376	=back	1481	=back
1377		1482
		1483	=head3 Examples
		1484
		1485	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1486
		1487	static void
		1488	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1489	{
		1490	ev_unloop (loop, EVUNLOOP_ALL);
		1491	}
		1492
		1493	struct ev_signal signal_watcher;
		1494	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1495	ev_signal_start (loop, &sigint_cb);
		1496
1378		1497
1379	=head2 C<ev_child> - watch out for process status changes	1498	=head2 C<ev_child> - watch out for process status changes
1380		1499
1381	Child watchers trigger when your process receives a SIGCHLD in response to	1500	Child watchers trigger when your process receives a SIGCHLD in response to
1382	some child status changes (most typically when a child of yours dies).	1501	some child status changes (most typically when a child of yours dies). It
		1502	is permissible to install a child watcher I<after> the child has been
		1503	forked (which implies it might have already exited), as long as the event
		1504	loop isn't entered (or is continued from a watcher).
		1505
		1506	Only the default event loop is capable of handling signals, and therefore
		1507	you can only rgeister child watchers in the default event loop.
		1508
		1509	=head3 Process Interaction
		1510
		1511	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1512	initialised. This is necessary to guarantee proper behaviour even if
		1513	the first child watcher is started after the child exits. The occurance
		1514	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1515	synchronously as part of the event loop processing. Libev always reaps all
		1516	children, even ones not watched.
		1517
		1518	=head3 Overriding the Built-In Processing
		1519
		1520	Libev offers no special support for overriding the built-in child
		1521	processing, but if your application collides with libev's default child
		1522	handler, you can override it easily by installing your own handler for
		1523	C<SIGCHLD> after initialising the default loop, and making sure the
		1524	default loop never gets destroyed. You are encouraged, however, to use an
		1525	event-based approach to child reaping and thus use libev's support for
		1526	that, so other libev users can use C<ev_child> watchers freely.
1383		1527
1384	=head3 Watcher-Specific Functions and Data Members	1528	=head3 Watcher-Specific Functions and Data Members
1385		1529
1386	=over 4	1530	=over 4
1387		1531
1388	=item ev_child_init (ev_child *, callback, int pid)	1532	=item ev_child_init (ev_child *, callback, int pid, int trace)
1389		1533
1390	=item ev_child_set (ev_child *, int pid)	1534	=item ev_child_set (ev_child *, int pid, int trace)
1391		1535
1392	Configures the watcher to wait for status changes of process C<pid> (or	1536	Configures the watcher to wait for status changes of process C<pid> (or
1393	I<any> process if C<pid> is specified as C<0>). The callback can look	1537	I<any> process if C<pid> is specified as C<0>). The callback can look
1394	at the C<rstatus> member of the C<ev_child> watcher structure to see	1538	at the C<rstatus> member of the C<ev_child> watcher structure to see
1395	the status word (use the macros from C<sys/wait.h> and see your systems	1539	the status word (use the macros from C<sys/wait.h> and see your systems
1396	C<waitpid> documentation). The C<rpid> member contains the pid of the	1540	C<waitpid> documentation). The C<rpid> member contains the pid of the
1397	process causing the status change.	1541	process causing the status change. C<trace> must be either C<0> (only
		1542	activate the watcher when the process terminates) or C<1> (additionally
		1543	activate the watcher when the process is stopped or continued).
1398		1544
1399	=item int pid [read-only]	1545	=item int pid [read-only]
1400		1546
1401	The process id this watcher watches out for, or C<0>, meaning any process id.	1547	The process id this watcher watches out for, or C<0>, meaning any process id.
1402		1548
…		…
1409	The process exit/trace status caused by C<rpid> (see your systems	1555	The process exit/trace status caused by C<rpid> (see your systems
1410	C<waitpid> and C<sys/wait.h> documentation for details).	1556	C<waitpid> and C<sys/wait.h> documentation for details).
1411		1557
1412	=back	1558	=back
1413		1559
1414	Example: Try to exit cleanly on SIGINT and SIGTERM.	1560	=head3 Examples
		1561
		1562	Example: C<fork()> a new process and install a child handler to wait for
		1563	its completion.
		1564
		1565	ev_child cw;
1415		1566
1416	static void	1567	static void
1417	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1568	child_cb (EV_P_ struct ev_child *w, int revents)
1418	{	1569	{
1419	ev_unloop (loop, EVUNLOOP_ALL);	1570	ev_child_stop (EV_A_ w);
		1571	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1420	}	1572	}
1421		1573
1422	struct ev_signal signal_watcher;	1574	pid_t pid = fork ();
1423	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1575
1424	ev_signal_start (loop, &sigint_cb);	1576	if (pid < 0)
		1577	// error
		1578	else if (pid == 0)
		1579	{
		1580	// the forked child executes here
		1581	exit (1);
		1582	}
		1583	else
		1584	{
		1585	ev_child_init (&cw, child_cb, pid, 0);
		1586	ev_child_start (EV_DEFAULT_ &cw);
		1587	}
1425		1588
1426		1589
1427	=head2 C<ev_stat> - did the file attributes just change?	1590	=head2 C<ev_stat> - did the file attributes just change?
1428		1591
1429	This watches a filesystem path for attribute changes. That is, it calls	1592	This watches a filesystem path for attribute changes. That is, it calls
…		…
1452	as even with OS-supported change notifications, this can be	1615	as even with OS-supported change notifications, this can be
1453	resource-intensive.	1616	resource-intensive.
1454		1617
1455	At the time of this writing, only the Linux inotify interface is	1618	At the time of this writing, only the Linux inotify interface is
1456	implemented (implementing kqueue support is left as an exercise for the	1619	implemented (implementing kqueue support is left as an exercise for the
		1620	reader, note, however, that the author sees no way of implementing ev_stat
1457	reader). Inotify will be used to give hints only and should not change the	1621	semantics with kqueue). Inotify will be used to give hints only and should
1458	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1622	not change the semantics of C<ev_stat> watchers, which means that libev
1459	to fall back to regular polling again even with inotify, but changes are	1623	sometimes needs to fall back to regular polling again even with inotify,
1460	usually detected immediately, and if the file exists there will be no	1624	but changes are usually detected immediately, and if the file exists there
1461	polling.	1625	will be no polling.
		1626
		1627	=head3 ABI Issues (Largefile Support)
		1628
		1629	Libev by default (unless the user overrides this) uses the default
		1630	compilation environment, which means that on systems with optionally
		1631	disabled large file support, you get the 32 bit version of the stat
		1632	structure. When using the library from programs that change the ABI to
		1633	use 64 bit file offsets the programs will fail. In that case you have to
		1634	compile libev with the same flags to get binary compatibility. This is
		1635	obviously the case with any flags that change the ABI, but the problem is
		1636	most noticably with ev_stat and largefile support.
		1637
		1638	=head3 Inotify
		1639
		1640	When C<inotify (7)> support has been compiled into libev (generally only
		1641	available on Linux) and present at runtime, it will be used to speed up
		1642	change detection where possible. The inotify descriptor will be created lazily
		1643	when the first C<ev_stat> watcher is being started.
		1644
		1645	Inotify presence does not change the semantics of C<ev_stat> watchers
		1646	except that changes might be detected earlier, and in some cases, to avoid
		1647	making regular C<stat> calls. Even in the presence of inotify support
		1648	there are many cases where libev has to resort to regular C<stat> polling.
		1649
		1650	(There is no support for kqueue, as apparently it cannot be used to
		1651	implement this functionality, due to the requirement of having a file
		1652	descriptor open on the object at all times).
		1653
		1654	=head3 The special problem of stat time resolution
		1655
		1656	The C<stat ()> syscall only supports full-second resolution portably, and
		1657	even on systems where the resolution is higher, many filesystems still
		1658	only support whole seconds.
		1659
		1660	That means that, if the time is the only thing that changes, you can
		1661	easily miss updates: on the first update, C<ev_stat> detects a change and
		1662	calls your callback, which does something. When there is another update
		1663	within the same second, C<ev_stat> will be unable to detect it as the stat
		1664	data does not change.
		1665
		1666	The solution to this is to delay acting on a change for slightly more
		1667	than a second (or till slightly after the next full second boundary), using
		1668	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1669	ev_timer_again (loop, w)>).
		1670
		1671	The C<.02> offset is added to work around small timing inconsistencies
		1672	of some operating systems (where the second counter of the current time
		1673	might be be delayed. One such system is the Linux kernel, where a call to
		1674	C<gettimeofday> might return a timestamp with a full second later than
		1675	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1676	update file times then there will be a small window where the kernel uses
		1677	the previous second to update file times but libev might already execute
		1678	the timer callback).
1462		1679
1463	=head3 Watcher-Specific Functions and Data Members	1680	=head3 Watcher-Specific Functions and Data Members
1464		1681
1465	=over 4	1682	=over 4
1466		1683
…		…
1472	C<path>. The C<interval> is a hint on how quickly a change is expected to	1689	C<path>. The C<interval> is a hint on how quickly a change is expected to
1473	be detected and should normally be specified as C<0> to let libev choose	1690	be detected and should normally be specified as C<0> to let libev choose
1474	a suitable value. The memory pointed to by C<path> must point to the same	1691	a suitable value. The memory pointed to by C<path> must point to the same
1475	path for as long as the watcher is active.	1692	path for as long as the watcher is active.
1476		1693
1477	The callback will be receive C<EV_STAT> when a change was detected,	1694	The callback will receive C<EV_STAT> when a change was detected, relative
1478	relative to the attributes at the time the watcher was started (or the	1695	to the attributes at the time the watcher was started (or the last change
1479	last change was detected).	1696	was detected).
1480		1697
1481	=item ev_stat_stat (ev_stat *)	1698	=item ev_stat_stat (loop, ev_stat *)
1482		1699
1483	Updates the stat buffer immediately with new values. If you change the	1700	Updates the stat buffer immediately with new values. If you change the
1484	watched path in your callback, you could call this fucntion to avoid	1701	watched path in your callback, you could call this function to avoid
1485	detecting this change (while introducing a race condition). Can also be	1702	detecting this change (while introducing a race condition if you are not
1486	useful simply to find out the new values.	1703	the only one changing the path). Can also be useful simply to find out the
		1704	new values.
1487		1705
1488	=item ev_statdata attr [read-only]	1706	=item ev_statdata attr [read-only]
1489		1707
1490	The most-recently detected attributes of the file. Although the type is of	1708	The most-recently detected attributes of the file. Although the type is
1491	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	1709	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1492	suitable for your system. If the C<st_nlink> member is C<0>, then there	1710	suitable for your system, but you can only rely on the POSIX-standardised
		1711	members to be present. If the C<st_nlink> member is C<0>, then there was
1493	was some error while C<stat>ing the file.	1712	some error while C<stat>ing the file.
1494		1713
1495	=item ev_statdata prev [read-only]	1714	=item ev_statdata prev [read-only]
1496		1715
1497	The previous attributes of the file. The callback gets invoked whenever	1716	The previous attributes of the file. The callback gets invoked whenever
1498	C<prev> != C<attr>.	1717	C<prev> != C<attr>, or, more precisely, one or more of these members
		1718	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1719	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1499		1720
1500	=item ev_tstamp interval [read-only]	1721	=item ev_tstamp interval [read-only]
1501		1722
1502	The specified interval.	1723	The specified interval.
1503		1724
1504	=item const char *path [read-only]	1725	=item const char *path [read-only]
1505		1726
1506	The filesystem path that is being watched.	1727	The filesystem path that is being watched.
1507		1728
1508	=back	1729	=back
		1730
		1731	=head3 Examples
1509		1732
1510	Example: Watch C</etc/passwd> for attribute changes.	1733	Example: Watch C</etc/passwd> for attribute changes.
1511		1734
1512	static void	1735	static void
1513	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	1736	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
…		…
1526	}	1749	}
1527		1750
1528	...	1751	...
1529	ev_stat passwd;	1752	ev_stat passwd;
1530		1753
1531	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	1754	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1532	ev_stat_start (loop, &passwd);	1755	ev_stat_start (loop, &passwd);
		1756
		1757	Example: Like above, but additionally use a one-second delay so we do not
		1758	miss updates (however, frequent updates will delay processing, too, so
		1759	one might do the work both on C<ev_stat> callback invocation I<and> on
		1760	C<ev_timer> callback invocation).
		1761
		1762	static ev_stat passwd;
		1763	static ev_timer timer;
		1764
		1765	static void
		1766	timer_cb (EV_P_ ev_timer *w, int revents)
		1767	{
		1768	ev_timer_stop (EV_A_ w);
		1769
		1770	/* now it's one second after the most recent passwd change */
		1771	}
		1772
		1773	static void
		1774	stat_cb (EV_P_ ev_stat *w, int revents)
		1775	{
		1776	/* reset the one-second timer */
		1777	ev_timer_again (EV_A_ &timer);
		1778	}
		1779
		1780	...
		1781	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1782	ev_stat_start (loop, &passwd);
		1783	ev_timer_init (&timer, timer_cb, 0., 1.02);
1533		1784
1534		1785
1535	=head2 C<ev_idle> - when you've got nothing better to do...	1786	=head2 C<ev_idle> - when you've got nothing better to do...
1536		1787
1537	Idle watchers trigger events when no other events of the same or higher	1788	Idle watchers trigger events when no other events of the same or higher
…		…
1563	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1814	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1564	believe me.	1815	believe me.
1565		1816
1566	=back	1817	=back
1567		1818
		1819	=head3 Examples
		1820
1568	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	1821	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1569	callback, free it. Also, use no error checking, as usual.	1822	callback, free it. Also, use no error checking, as usual.
1570		1823
1571	static void	1824	static void
1572	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	1825	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1573	{	1826	{
1574	free (w);	1827	free (w);
1575	// now do something you wanted to do when the program has	1828	// now do something you wanted to do when the program has
1576	// no longer asnything immediate to do.	1829	// no longer anything immediate to do.
1577	}	1830	}
1578		1831
1579	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	1832	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1580	ev_idle_init (idle_watcher, idle_cb);	1833	ev_idle_init (idle_watcher, idle_cb);
1581	ev_idle_start (loop, idle_cb);	1834	ev_idle_start (loop, idle_cb);
…		…
1623		1876
1624	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	1877	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1625	priority, to ensure that they are being run before any other watchers	1878	priority, to ensure that they are being run before any other watchers
1626	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	1879	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
1627	too) should not activate ("feed") events into libev. While libev fully	1880	too) should not activate ("feed") events into libev. While libev fully
1628	supports this, they will be called before other C<ev_check> watchers did	1881	supports this, they might get executed before other C<ev_check> watchers
1629	their job. As C<ev_check> watchers are often used to embed other event	1882	did their job. As C<ev_check> watchers are often used to embed other
1630	loops those other event loops might be in an unusable state until their	1883	(non-libev) event loops those other event loops might be in an unusable
1631	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	1884	state until their C<ev_check> watcher ran (always remind yourself to
1632	others).	1885	coexist peacefully with others).
1633		1886
1634	=head3 Watcher-Specific Functions and Data Members	1887	=head3 Watcher-Specific Functions and Data Members
1635		1888
1636	=over 4	1889	=over 4
1637		1890
…		…
1643	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1896	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1644	macros, but using them is utterly, utterly and completely pointless.	1897	macros, but using them is utterly, utterly and completely pointless.
1645		1898
1646	=back	1899	=back
1647		1900
		1901	=head3 Examples
		1902
1648	There are a number of principal ways to embed other event loops or modules	1903	There are a number of principal ways to embed other event loops or modules
1649	into libev. Here are some ideas on how to include libadns into libev	1904	into libev. Here are some ideas on how to include libadns into libev
1650	(there is a Perl module named C<EV::ADNS> that does this, which you could	1905	(there is a Perl module named C<EV::ADNS> that does this, which you could
1651	use for an actually working example. Another Perl module named C<EV::Glib>	1906	use as a working example. Another Perl module named C<EV::Glib> embeds a
1652	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	1907	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1653	into the Glib event loop).	1908	Glib event loop).
1654		1909
1655	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	1910	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1656	and in a check watcher, destroy them and call into libadns. What follows	1911	and in a check watcher, destroy them and call into libadns. What follows
1657	is pseudo-code only of course. This requires you to either use a low	1912	is pseudo-code only of course. This requires you to either use a low
1658	priority for the check watcher or use C<ev_clear_pending> explicitly, as	1913	priority for the check watcher or use C<ev_clear_pending> explicitly, as
…		…
1776	=head2 C<ev_embed> - when one backend isn't enough...	2031	=head2 C<ev_embed> - when one backend isn't enough...
1777		2032
1778	This is a rather advanced watcher type that lets you embed one event loop	2033	This is a rather advanced watcher type that lets you embed one event loop
1779	into another (currently only C<ev_io> events are supported in the embedded	2034	into another (currently only C<ev_io> events are supported in the embedded
1780	loop, other types of watchers might be handled in a delayed or incorrect	2035	loop, other types of watchers might be handled in a delayed or incorrect
1781	fashion and must not be used). (See portability notes, below).	2036	fashion and must not be used).
1782		2037
1783	There are primarily two reasons you would want that: work around bugs and	2038	There are primarily two reasons you would want that: work around bugs and
1784	prioritise I/O.	2039	prioritise I/O.
1785		2040
1786	As an example for a bug workaround, the kqueue backend might only support	2041	As an example for a bug workaround, the kqueue backend might only support
…		…
1820	portable one.	2075	portable one.
1821		2076
1822	So when you want to use this feature you will always have to be prepared	2077	So when you want to use this feature you will always have to be prepared
1823	that you cannot get an embeddable loop. The recommended way to get around	2078	that you cannot get an embeddable loop. The recommended way to get around
1824	this is to have a separate variables for your embeddable loop, try to	2079	this is to have a separate variables for your embeddable loop, try to
1825	create it, and if that fails, use the normal loop for everything:	2080	create it, and if that fails, use the normal loop for everything.
		2081
		2082	=head3 Watcher-Specific Functions and Data Members
		2083
		2084	=over 4
		2085
		2086	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2087
		2088	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2089
		2090	Configures the watcher to embed the given loop, which must be
		2091	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2092	invoked automatically, otherwise it is the responsibility of the callback
		2093	to invoke it (it will continue to be called until the sweep has been done,
		2094	if you do not want thta, you need to temporarily stop the embed watcher).
		2095
		2096	=item ev_embed_sweep (loop, ev_embed *)
		2097
		2098	Make a single, non-blocking sweep over the embedded loop. This works
		2099	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2100	apropriate way for embedded loops.
		2101
		2102	=item struct ev_loop *other [read-only]
		2103
		2104	The embedded event loop.
		2105
		2106	=back
		2107
		2108	=head3 Examples
		2109
		2110	Example: Try to get an embeddable event loop and embed it into the default
		2111	event loop. If that is not possible, use the default loop. The default
		2112	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		2113	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		2114	used).
1826		2115
1827	struct ev_loop *loop_hi = ev_default_init (0);	2116	struct ev_loop *loop_hi = ev_default_init (0);
1828	struct ev_loop *loop_lo = 0;	2117	struct ev_loop *loop_lo = 0;
1829	struct ev_embed embed;	2118	struct ev_embed embed;
1830		2119
…		…
1841	ev_embed_start (loop_hi, &embed);	2130	ev_embed_start (loop_hi, &embed);
1842	}	2131	}
1843	else	2132	else
1844	loop_lo = loop_hi;	2133	loop_lo = loop_hi;
1845		2134
1846	=head2 Portability notes	2135	Example: Check if kqueue is available but not recommended and create
		2136	a kqueue backend for use with sockets (which usually work with any
		2137	kqueue implementation). Store the kqueue/socket-only event loop in
		2138	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
1847		2139
1848	Kqueue is nominally embeddable, but this is broken on all BSDs that I	2140	struct ev_loop *loop = ev_default_init (0);
1849	tried, in various ways. Usually the embedded event loop will simply never	2141	struct ev_loop *loop_socket = 0;
1850	receive events, sometimes it will only trigger a few times, sometimes in a	2142	struct ev_embed embed;
1851	loop. Epoll is also nominally embeddable, but many Linux kernel versions	2143
1852	will always eport the epoll fd as ready, even when no events are pending.	2144	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2145	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2146	{
		2147	ev_embed_init (&embed, 0, loop_socket);
		2148	ev_embed_start (loop, &embed);
		2149	}
1853		2150
1854	While libev allows embedding these backends (they are contained in	2151	if (!loop_socket)
1855	C<ev_embeddable_backends ()>), take extreme care that it will actually	2152	loop_socket = loop;
1856	work.
1857		2153
1858	When in doubt, create a dynamic event loop forced to use sockets (this	2154	// now use loop_socket for all sockets, and loop for everything else
1859	usually works) and possibly another thread and a pipe or so to report to
1860	your main event loop.
1861
1862	=head3 Watcher-Specific Functions and Data Members
1863
1864	=over 4
1865
1866	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1867
1868	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
1869
1870	Configures the watcher to embed the given loop, which must be
1871	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1872	invoked automatically, otherwise it is the responsibility of the callback
1873	to invoke it (it will continue to be called until the sweep has been done,
1874	if you do not want thta, you need to temporarily stop the embed watcher).
1875
1876	=item ev_embed_sweep (loop, ev_embed *)
1877
1878	Make a single, non-blocking sweep over the embedded loop. This works
1879	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1880	apropriate way for embedded loops.
1881
1882	=item struct ev_loop *other [read-only]
1883
1884	The embedded event loop.
1885
1886	=back
1887		2155
1888		2156
1889	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2157	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1890		2158
1891	Fork watchers are called when a C<fork ()> was detected (usually because	2159	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1907	believe me.	2175	believe me.
1908		2176
1909	=back	2177	=back
1910		2178
1911		2179
		2180	=head2 C<ev_async> - how to wake up another event loop
		2181
		2182	In general, you cannot use an C<ev_loop> from multiple threads or other
		2183	asynchronous sources such as signal handlers (as opposed to multiple event
		2184	loops - those are of course safe to use in different threads).
		2185
		2186	Sometimes, however, you need to wake up another event loop you do not
		2187	control, for example because it belongs to another thread. This is what
		2188	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2189	can signal it by calling C<ev_async_send>, which is thread- and signal
		2190	safe.
		2191
		2192	This functionality is very similar to C<ev_signal> watchers, as signals,
		2193	too, are asynchronous in nature, and signals, too, will be compressed
		2194	(i.e. the number of callback invocations may be less than the number of
		2195	C<ev_async_sent> calls).
		2196
		2197	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2198	just the default loop.
		2199
		2200	=head3 Queueing
		2201
		2202	C<ev_async> does not support queueing of data in any way. The reason
		2203	is that the author does not know of a simple (or any) algorithm for a
		2204	multiple-writer-single-reader queue that works in all cases and doesn't
		2205	need elaborate support such as pthreads.
		2206
		2207	That means that if you want to queue data, you have to provide your own
		2208	queue. But at least I can tell you would implement locking around your
		2209	queue:
		2210
		2211	=over 4
		2212
		2213	=item queueing from a signal handler context
		2214
		2215	To implement race-free queueing, you simply add to the queue in the signal
		2216	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2217	some fictitiuous SIGUSR1 handler:
		2218
		2219	static ev_async mysig;
		2220
		2221	static void
		2222	sigusr1_handler (void)
		2223	{
		2224	sometype data;
		2225
		2226	// no locking etc.
		2227	queue_put (data);
		2228	ev_async_send (EV_DEFAULT_ &mysig);
		2229	}
		2230
		2231	static void
		2232	mysig_cb (EV_P_ ev_async *w, int revents)
		2233	{
		2234	sometype data;
		2235	sigset_t block, prev;
		2236
		2237	sigemptyset (&block);
		2238	sigaddset (&block, SIGUSR1);
		2239	sigprocmask (SIG_BLOCK, &block, &prev);
		2240
		2241	while (queue_get (&data))
		2242	process (data);
		2243
		2244	if (sigismember (&prev, SIGUSR1)
		2245	sigprocmask (SIG_UNBLOCK, &block, 0);
		2246	}
		2247
		2248	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2249	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2250	either...).
		2251
		2252	=item queueing from a thread context
		2253
		2254	The strategy for threads is different, as you cannot (easily) block
		2255	threads but you can easily preempt them, so to queue safely you need to
		2256	employ a traditional mutex lock, such as in this pthread example:
		2257
		2258	static ev_async mysig;
		2259	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2260
		2261	static void
		2262	otherthread (void)
		2263	{
		2264	// only need to lock the actual queueing operation
		2265	pthread_mutex_lock (&mymutex);
		2266	queue_put (data);
		2267	pthread_mutex_unlock (&mymutex);
		2268
		2269	ev_async_send (EV_DEFAULT_ &mysig);
		2270	}
		2271
		2272	static void
		2273	mysig_cb (EV_P_ ev_async *w, int revents)
		2274	{
		2275	pthread_mutex_lock (&mymutex);
		2276
		2277	while (queue_get (&data))
		2278	process (data);
		2279
		2280	pthread_mutex_unlock (&mymutex);
		2281	}
		2282
		2283	=back
		2284
		2285
		2286	=head3 Watcher-Specific Functions and Data Members
		2287
		2288	=over 4
		2289
		2290	=item ev_async_init (ev_async *, callback)
		2291
		2292	Initialises and configures the async watcher - it has no parameters of any
		2293	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2294	believe me.
		2295
		2296	=item ev_async_send (loop, ev_async *)
		2297
		2298	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2299	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2300	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2301	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2302	section below on what exactly this means).
		2303
		2304	This call incurs the overhead of a syscall only once per loop iteration,
		2305	so while the overhead might be noticable, it doesn't apply to repeated
		2306	calls to C<ev_async_send>.
		2307
		2308	=item bool = ev_async_pending (ev_async *)
		2309
		2310	Returns a non-zero value when C<ev_async_send> has been called on the
		2311	watcher but the event has not yet been processed (or even noted) by the
		2312	event loop.
		2313
		2314	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2315	the loop iterates next and checks for the watcher to have become active,
		2316	it will reset the flag again. C<ev_async_pending> can be used to very
		2317	quickly check wether invoking the loop might be a good idea.
		2318
		2319	Not that this does I<not> check wether the watcher itself is pending, only
		2320	wether it has been requested to make this watcher pending.
		2321
		2322	=back
		2323
		2324
1912	=head1 OTHER FUNCTIONS	2325	=head1 OTHER FUNCTIONS
1913		2326
1914	There are some other functions of possible interest. Described. Here. Now.	2327	There are some other functions of possible interest. Described. Here. Now.
1915		2328
1916	=over 4	2329	=over 4
…		…
1984		2397
1985	=item * Priorities are not currently supported. Initialising priorities	2398	=item * Priorities are not currently supported. Initialising priorities
1986	will fail and all watchers will have the same priority, even though there	2399	will fail and all watchers will have the same priority, even though there
1987	is an ev_pri field.	2400	is an ev_pri field.
1988		2401
		2402	=item * In libevent, the last base created gets the signals, in libev, the
		2403	first base created (== the default loop) gets the signals.
		2404
1989	=item * Other members are not supported.	2405	=item * Other members are not supported.
1990		2406
1991	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2407	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1992	to use the libev header file and library.	2408	to use the libev header file and library.
1993		2409
…		…
2143	Example: Define a class with an IO and idle watcher, start one of them in	2559	Example: Define a class with an IO and idle watcher, start one of them in
2144	the constructor.	2560	the constructor.
2145		2561
2146	class myclass	2562	class myclass
2147	{	2563	{
2148	ev_io io; void io_cb (ev::io &w, int revents);	2564	ev::io io; void io_cb (ev::io &w, int revents);
2149	ev_idle idle void idle_cb (ev::idle &w, int revents);	2565	ev:idle idle void idle_cb (ev::idle &w, int revents);
2150		2566
2151	myclass ();	2567	myclass (int fd)
2152	}
2153
2154	myclass::myclass (int fd)
2155	{	2568	{
2156	io .set <myclass, &myclass::io_cb > (this);	2569	io .set <myclass, &myclass::io_cb > (this);
2157	idle.set <myclass, &myclass::idle_cb> (this);	2570	idle.set <myclass, &myclass::idle_cb> (this);
2158		2571
2159	io.start (fd, ev::READ);	2572	io.start (fd, ev::READ);
		2573	}
2160	}	2574	};
		2575
		2576
		2577	=head1 OTHER LANGUAGE BINDINGS
		2578
		2579	Libev does not offer other language bindings itself, but bindings for a
		2580	numbe rof languages exist in the form of third-party packages. If you know
		2581	any interesting language binding in addition to the ones listed here, drop
		2582	me a note.
		2583
		2584	=over 4
		2585
		2586	=item Perl
		2587
		2588	The EV module implements the full libev API and is actually used to test
		2589	libev. EV is developed together with libev. Apart from the EV core module,
		2590	there are additional modules that implement libev-compatible interfaces
		2591	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2592	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2593
		2594	It can be found and installed via CPAN, its homepage is found at
		2595	L<http://software.schmorp.de/pkg/EV>.
		2596
		2597	=item Ruby
		2598
		2599	Tony Arcieri has written a ruby extension that offers access to a subset
		2600	of the libev API and adds filehandle abstractions, asynchronous DNS and
		2601	more on top of it. It can be found via gem servers. Its homepage is at
		2602	L<http://rev.rubyforge.org/>.
		2603
		2604	=item D
		2605
		2606	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2607	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2608
		2609	=back
2161		2610
2162		2611
2163	=head1 MACRO MAGIC	2612	=head1 MACRO MAGIC
2164		2613
2165	Libev can be compiled with a variety of options, the most fundamantal	2614	Libev can be compiled with a variety of options, the most fundamantal
…		…
2201		2650
2202	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	2651	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2203		2652
2204	Similar to the other two macros, this gives you the value of the default	2653	Similar to the other two macros, this gives you the value of the default
2205	loop, if multiple loops are supported ("ev loop default").	2654	loop, if multiple loops are supported ("ev loop default").
		2655
		2656	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2657
		2658	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2659	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2660	is undefined when the default loop has not been initialised by a previous
		2661	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2662
		2663	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2664	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2206		2665
2207	=back	2666	=back
2208		2667
2209	Example: Declare and initialise a check watcher, utilising the above	2668	Example: Declare and initialise a check watcher, utilising the above
2210	macros so it will work regardless of whether multiple loops are supported	2669	macros so it will work regardless of whether multiple loops are supported
…		…
2306		2765
2307	libev.m4	2766	libev.m4
2308		2767
2309	=head2 PREPROCESSOR SYMBOLS/MACROS	2768	=head2 PREPROCESSOR SYMBOLS/MACROS
2310		2769
2311	Libev can be configured via a variety of preprocessor symbols you have to define	2770	Libev can be configured via a variety of preprocessor symbols you have to
2312	before including any of its files. The default is not to build for multiplicity	2771	define before including any of its files. The default in the absense of
2313	and only include the select backend.	2772	autoconf is noted for every option.
2314		2773
2315	=over 4	2774	=over 4
2316		2775
2317	=item EV_STANDALONE	2776	=item EV_STANDALONE
2318		2777
…		…
2344	=item EV_USE_NANOSLEEP	2803	=item EV_USE_NANOSLEEP
2345		2804
2346	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	2805	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2347	and will use it for delays. Otherwise it will use C<select ()>.	2806	and will use it for delays. Otherwise it will use C<select ()>.
2348		2807
		2808	=item EV_USE_EVENTFD
		2809
		2810	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2811	available and will probe for kernel support at runtime. This will improve
		2812	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2813	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2814	2.7 or newer, otherwise disabled.
		2815
2349	=item EV_USE_SELECT	2816	=item EV_USE_SELECT
2350		2817
2351	If undefined or defined to be C<1>, libev will compile in support for the	2818	If undefined or defined to be C<1>, libev will compile in support for the
2352	C<select>(2) backend. No attempt at autodetection will be done: if no	2819	C<select>(2) backend. No attempt at autodetection will be done: if no
2353	other method takes over, select will be it. Otherwise the select backend	2820	other method takes over, select will be it. Otherwise the select backend
…		…
2371	be used is the winsock select). This means that it will call	2838	be used is the winsock select). This means that it will call
2372	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	2839	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2373	it is assumed that all these functions actually work on fds, even	2840	it is assumed that all these functions actually work on fds, even
2374	on win32. Should not be defined on non-win32 platforms.	2841	on win32. Should not be defined on non-win32 platforms.
2375		2842
		2843	=item EV_FD_TO_WIN32_HANDLE
		2844
		2845	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2846	file descriptors to socket handles. When not defining this symbol (the
		2847	default), then libev will call C<_get_osfhandle>, which is usually
		2848	correct. In some cases, programs use their own file descriptor management,
		2849	in which case they can provide this function to map fds to socket handles.
		2850
2376	=item EV_USE_POLL	2851	=item EV_USE_POLL
2377		2852
2378	If defined to be C<1>, libev will compile in support for the C<poll>(2)	2853	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2379	backend. Otherwise it will be enabled on non-win32 platforms. It	2854	backend. Otherwise it will be enabled on non-win32 platforms. It
2380	takes precedence over select.	2855	takes precedence over select.
2381		2856
2382	=item EV_USE_EPOLL	2857	=item EV_USE_EPOLL
2383		2858
2384	If defined to be C<1>, libev will compile in support for the Linux	2859	If defined to be C<1>, libev will compile in support for the Linux
2385	C<epoll>(7) backend. Its availability will be detected at runtime,	2860	C<epoll>(7) backend. Its availability will be detected at runtime,
2386	otherwise another method will be used as fallback. This is the	2861	otherwise another method will be used as fallback. This is the preferred
2387	preferred backend for GNU/Linux systems.	2862	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2863	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2388		2864
2389	=item EV_USE_KQUEUE	2865	=item EV_USE_KQUEUE
2390		2866
2391	If defined to be C<1>, libev will compile in support for the BSD style	2867	If defined to be C<1>, libev will compile in support for the BSD style
2392	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	2868	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2411		2887
2412	=item EV_USE_INOTIFY	2888	=item EV_USE_INOTIFY
2413		2889
2414	If defined to be C<1>, libev will compile in support for the Linux inotify	2890	If defined to be C<1>, libev will compile in support for the Linux inotify
2415	interface to speed up C<ev_stat> watchers. Its actual availability will	2891	interface to speed up C<ev_stat> watchers. Its actual availability will
2416	be detected at runtime.	2892	be detected at runtime. If undefined, it will be enabled if the headers
		2893	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2894
		2895	=item EV_ATOMIC_T
		2896
		2897	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2898	access is atomic with respect to other threads or signal contexts. No such
		2899	type is easily found in the C language, so you can provide your own type
		2900	that you know is safe for your purposes. It is used both for signal handler "locking"
		2901	as well as for signal and thread safety in C<ev_async> watchers.
		2902
		2903	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2904	(from F<signal.h>), which is usually good enough on most platforms.
2417		2905
2418	=item EV_H	2906	=item EV_H
2419		2907
2420	The name of the F<ev.h> header file used to include it. The default if	2908	The name of the F<ev.h> header file used to include it. The default if
2421	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	2909	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2422	can be used to virtually rename the F<ev.h> header file in case of conflicts.	2910	used to virtually rename the F<ev.h> header file in case of conflicts.
2423		2911
2424	=item EV_CONFIG_H	2912	=item EV_CONFIG_H
2425		2913
2426	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	2914	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2427	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	2915	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2428	C<EV_H>, above.	2916	C<EV_H>, above.
2429		2917
2430	=item EV_EVENT_H	2918	=item EV_EVENT_H
2431		2919
2432	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	2920	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2433	of how the F<event.h> header can be found.	2921	of how the F<event.h> header can be found, the default is C<"event.h">.
2434		2922
2435	=item EV_PROTOTYPES	2923	=item EV_PROTOTYPES
2436		2924
2437	If defined to be C<0>, then F<ev.h> will not define any function	2925	If defined to be C<0>, then F<ev.h> will not define any function
2438	prototypes, but still define all the structs and other symbols. This is	2926	prototypes, but still define all the structs and other symbols. This is
…		…
2489	=item EV_FORK_ENABLE	2977	=item EV_FORK_ENABLE
2490		2978
2491	If undefined or defined to be C<1>, then fork watchers are supported. If	2979	If undefined or defined to be C<1>, then fork watchers are supported. If
2492	defined to be C<0>, then they are not.	2980	defined to be C<0>, then they are not.
2493		2981
		2982	=item EV_ASYNC_ENABLE
		2983
		2984	If undefined or defined to be C<1>, then async watchers are supported. If
		2985	defined to be C<0>, then they are not.
		2986
2494	=item EV_MINIMAL	2987	=item EV_MINIMAL
2495		2988
2496	If you need to shave off some kilobytes of code at the expense of some	2989	If you need to shave off some kilobytes of code at the expense of some
2497	speed, define this symbol to C<1>. Currently only used for gcc to override	2990	speed, define this symbol to C<1>. Currently this is used to override some
2498	some inlining decisions, saves roughly 30% codesize of amd64.	2991	inlining decisions, saves roughly 30% codesize of amd64. It also selects a
		2992	much smaller 2-heap for timer management over the default 4-heap.
2499		2993
2500	=item EV_PID_HASHSIZE	2994	=item EV_PID_HASHSIZE
2501		2995
2502	C<ev_child> watchers use a small hash table to distribute workload by	2996	C<ev_child> watchers use a small hash table to distribute workload by
2503	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	2997	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2504	than enough. If you need to manage thousands of children you might want to	2998	than enough. If you need to manage thousands of children you might want to
2505	increase this value (I<must> be a power of two).	2999	increase this value (I<must> be a power of two).
2506		3000
2507	=item EV_INOTIFY_HASHSIZE	3001	=item EV_INOTIFY_HASHSIZE
2508		3002
2509	C<ev_staz> watchers use a small hash table to distribute workload by	3003	C<ev_stat> watchers use a small hash table to distribute workload by
2510	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3004	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2511	usually more than enough. If you need to manage thousands of C<ev_stat>	3005	usually more than enough. If you need to manage thousands of C<ev_stat>
2512	watchers you might want to increase this value (I<must> be a power of	3006	watchers you might want to increase this value (I<must> be a power of
2513	two).	3007	two).
		3008
		3009	=item EV_USE_4HEAP
		3010
		3011	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3012	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3013	to C<1>. The 4-heap uses more complicated (longer) code but has
		3014	noticably faster performance with many (thousands) of watchers.
		3015
		3016	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3017	(disabled).
		3018
		3019	=item EV_HEAP_CACHE_AT
		3020
		3021	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3022	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3023	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3024	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3025	but avoids random read accesses on heap changes. This improves performance
		3026	noticably with with many (hundreds) of watchers.
		3027
		3028	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3029	(disabled).
2514		3030
2515	=item EV_COMMON	3031	=item EV_COMMON
2516		3032
2517	By default, all watchers have a C<void *data> member. By redefining	3033	By default, all watchers have a C<void *data> member. By redefining
2518	this macro to a something else you can include more and other types of	3034	this macro to a something else you can include more and other types of
…		…
2592		3108
2593	#include "ev_cpp.h"	3109	#include "ev_cpp.h"
2594	#include "ev.c"	3110	#include "ev.c"
2595		3111
2596		3112
		3113	=head1 THREADS AND COROUTINES
		3114
		3115	=head2 THREADS
		3116
		3117	Libev itself is completely threadsafe, but it uses no locking. This
		3118	means that you can use as many loops as you want in parallel, as long as
		3119	only one thread ever calls into one libev function with the same loop
		3120	parameter.
		3121
		3122	Or put differently: calls with different loop parameters can be done in
		3123	parallel from multiple threads, calls with the same loop parameter must be
		3124	done serially (but can be done from different threads, as long as only one
		3125	thread ever is inside a call at any point in time, e.g. by using a mutex
		3126	per loop).
		3127
		3128	If you want to know which design is best for your problem, then I cannot
		3129	help you but by giving some generic advice:
		3130
		3131	=over 4
		3132
		3133	=item * most applications have a main thread: use the default libev loop
		3134	in that thread, or create a seperate thread running only the default loop.
		3135
		3136	This helps integrating other libraries or software modules that use libev
		3137	themselves and don't care/know about threading.
		3138
		3139	=item * one loop per thread is usually a good model.
		3140
		3141	Doing this is almost never wrong, sometimes a better-performance model
		3142	exists, but it is always a good start.
		3143
		3144	=item * other models exist, such as the leader/follower pattern, where one
		3145	loop is handed through multiple threads in a kind of round-robbin fashion.
		3146
		3147	Chosing a model is hard - look around, learn, know that usually you cna do
		3148	better than you currently do :-)
		3149
		3150	=item * often you need to talk to some other thread which blocks in the
		3151	event loop - C<ev_async> watchers can be used to wake them up from other
		3152	threads safely (or from signal contexts...).
		3153
		3154	=back
		3155
		3156	=head2 COROUTINES
		3157
		3158	Libev is much more accomodating to coroutines ("cooperative threads"):
		3159	libev fully supports nesting calls to it's functions from different
		3160	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3161	different coroutines and switch freely between both coroutines running the
		3162	loop, as long as you don't confuse yourself). The only exception is that
		3163	you must not do this from C<ev_periodic> reschedule callbacks.
		3164
		3165	Care has been invested into making sure that libev does not keep local
		3166	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3167	switches.
		3168
		3169
2597	=head1 COMPLEXITIES	3170	=head1 COMPLEXITIES
2598		3171
2599	In this section the complexities of (many of) the algorithms used inside	3172	In this section the complexities of (many of) the algorithms used inside
2600	libev will be explained. For complexity discussions about backends see the	3173	libev will be explained. For complexity discussions about backends see the
2601	documentation for C<ev_default_init>.	3174	documentation for C<ev_default_init>.
…		…
2610		3183
2611	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3184	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2612		3185
2613	This means that, when you have a watcher that triggers in one hour and	3186	This means that, when you have a watcher that triggers in one hour and
2614	there are 100 watchers that would trigger before that then inserting will	3187	there are 100 watchers that would trigger before that then inserting will
2615	have to skip those 100 watchers.	3188	have to skip roughly seven (C<ld 100>) of these watchers.
2616		3189
2617	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3190	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2618		3191
2619	That means that for changing a timer costs less than removing/adding them	3192	That means that changing a timer costs less than removing/adding them
2620	as only the relative motion in the event queue has to be paid for.	3193	as only the relative motion in the event queue has to be paid for.
2621		3194
2622	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3195	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2623		3196
2624	These just add the watcher into an array or at the head of a list.	3197	These just add the watcher into an array or at the head of a list.
		3198
2625	=item Stopping check/prepare/idle watchers: O(1)	3199	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2626		3200
2627	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3201	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2628		3202
2629	These watchers are stored in lists then need to be walked to find the	3203	These watchers are stored in lists then need to be walked to find the
2630	correct watcher to remove. The lists are usually short (you don't usually	3204	correct watcher to remove. The lists are usually short (you don't usually
2631	have many watchers waiting for the same fd or signal).	3205	have many watchers waiting for the same fd or signal).
2632		3206
2633	=item Finding the next timer per loop iteration: O(1)	3207	=item Finding the next timer in each loop iteration: O(1)
		3208
		3209	By virtue of using a binary or 4-heap, the next timer is always found at a
		3210	fixed position in the storage array.
2634		3211
2635	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3212	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2636		3213
2637	A change means an I/O watcher gets started or stopped, which requires	3214	A change means an I/O watcher gets started or stopped, which requires
2638	libev to recalculate its status (and possibly tell the kernel).	3215	libev to recalculate its status (and possibly tell the kernel, depending
		3216	on backend and wether C<ev_io_set> was used).
2639		3217
2640	=item Activating one watcher: O(1)	3218	=item Activating one watcher (putting it into the pending state): O(1)
2641		3219
2642	=item Priority handling: O(number_of_priorities)	3220	=item Priority handling: O(number_of_priorities)
2643		3221
2644	Priorities are implemented by allocating some space for each	3222	Priorities are implemented by allocating some space for each
2645	priority. When doing priority-based operations, libev usually has to	3223	priority. When doing priority-based operations, libev usually has to
2646	linearly search all the priorities.	3224	linearly search all the priorities, but starting/stopping and activating
		3225	watchers becomes O(1) w.r.t. priority handling.
		3226
		3227	=item Sending an ev_async: O(1)
		3228
		3229	=item Processing ev_async_send: O(number_of_async_watchers)
		3230
		3231	=item Processing signals: O(max_signal_number)
		3232
		3233	Sending involves a syscall I<iff> there were no other C<ev_async_send>
		3234	calls in the current loop iteration. Checking for async and signal events
		3235	involves iterating over all running async watchers or all signal numbers.
2647		3236
2648	=back	3237	=back
2649		3238
2650		3239
		3240	=head1 Win32 platform limitations and workarounds
		3241
		3242	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3243	requires, and its I/O model is fundamentally incompatible with the POSIX
		3244	model. Libev still offers limited functionality on this platform in
		3245	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3246	descriptors. This only applies when using Win32 natively, not when using
		3247	e.g. cygwin.
		3248
		3249	Lifting these limitations would basically require the full
		3250	re-implementation of the I/O system. If you are into these kinds of
		3251	things, then note that glib does exactly that for you in a very portable
		3252	way (note also that glib is the slowest event library known to man).
		3253
		3254	There is no supported compilation method available on windows except
		3255	embedding it into other applications.
		3256
		3257	Due to the many, low, and arbitrary limits on the win32 platform and
		3258	the abysmal performance of winsockets, using a large number of sockets
		3259	is not recommended (and not reasonable). If your program needs to use
		3260	more than a hundred or so sockets, then likely it needs to use a totally
		3261	different implementation for windows, as libev offers the POSIX readiness
		3262	notification model, which cannot be implemented efficiently on windows
		3263	(microsoft monopoly games).
		3264
		3265	=over 4
		3266
		3267	=item The winsocket select function
		3268
		3269	The winsocket C<select> function doesn't follow POSIX in that it requires
		3270	socket I<handles> and not socket I<file descriptors>. This makes select
		3271	very inefficient, and also requires a mapping from file descriptors
		3272	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		3273	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		3274	symbols for more info.
		3275
		3276	The configuration for a "naked" win32 using the microsoft runtime
		3277	libraries and raw winsocket select is:
		3278
		3279	#define EV_USE_SELECT 1
		3280	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3281
		3282	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3283	complexity in the O(n²) range when using win32.
		3284
		3285	=item Limited number of file descriptors
		3286
		3287	Windows has numerous arbitrary (and low) limits on things.
		3288
		3289	Early versions of winsocket's select only supported waiting for a maximum
		3290	of C<64> handles (probably owning to the fact that all windows kernels
		3291	can only wait for C<64> things at the same time internally; microsoft
		3292	recommends spawning a chain of threads and wait for 63 handles and the
		3293	previous thread in each. Great).
		3294
		3295	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3296	to some high number (e.g. C<2048>) before compiling the winsocket select
		3297	call (which might be in libev or elsewhere, for example, perl does its own
		3298	select emulation on windows).
		3299
		3300	Another limit is the number of file descriptors in the microsoft runtime
		3301	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3302	or something like this inside microsoft). You can increase this by calling
		3303	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3304	arbitrary limit), but is broken in many versions of the microsoft runtime
		3305	libraries.
		3306
		3307	This might get you to about C<512> or C<2048> sockets (depending on
		3308	windows version and/or the phase of the moon). To get more, you need to
		3309	wrap all I/O functions and provide your own fd management, but the cost of
		3310	calling select (O(n²)) will likely make this unworkable.
		3311
		3312	=back
		3313
		3314
		3315	=head1 PORTABILITY REQUIREMENTS
		3316
		3317	In addition to a working ISO-C implementation, libev relies on a few
		3318	additional extensions:
		3319
		3320	=over 4
		3321
		3322	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3323
		3324	The type C<sig_atomic_t volatile> (or whatever is defined as
		3325	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3326	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3327	believed to be sufficiently portable.
		3328
		3329	=item C<sigprocmask> must work in a threaded environment
		3330
		3331	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3332	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3333	pthread implementations will either allow C<sigprocmask> in the "main
		3334	thread" or will block signals process-wide, both behaviours would
		3335	be compatible with libev. Interaction between C<sigprocmask> and
		3336	C<pthread_sigmask> could complicate things, however.
		3337
		3338	The most portable way to handle signals is to block signals in all threads
		3339	except the initial one, and run the default loop in the initial thread as
		3340	well.
		3341
		3342	=item C<long> must be large enough for common memory allocation sizes
		3343
		3344	To improve portability and simplify using libev, libev uses C<long>
		3345	internally instead of C<size_t> when allocating its data structures. On
		3346	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3347	is still at least 31 bits everywhere, which is enough for hundreds of
		3348	millions of watchers.
		3349
		3350	=item C<double> must hold a time value in seconds with enough accuracy
		3351
		3352	The type C<double> is used to represent timestamps. It is required to
		3353	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3354	enough for at least into the year 4000. This requirement is fulfilled by
		3355	implementations implementing IEEE 754 (basically all existing ones).
		3356
		3357	=back
		3358
		3359	If you know of other additional requirements drop me a note.
		3360
		3361
		3362	=head1 VALGRIND
		3363
		3364	Valgrind has a special section here because it is a popular tool that is
		3365	highly useful, but valgrind reports are very hard to interpret.
		3366
		3367	If you think you found a bug (memory leak, uninitialised data access etc.)
		3368	in libev, then check twice: If valgrind reports something like:
		3369
		3370	==2274== definitely lost: 0 bytes in 0 blocks.
		3371	==2274== possibly lost: 0 bytes in 0 blocks.
		3372	==2274== still reachable: 256 bytes in 1 blocks.
		3373
		3374	then there is no memory leak. Similarly, under some circumstances,
		3375	valgrind might report kernel bugs as if it were a bug in libev, or it
		3376	might be confused (it is a very good tool, but only a tool).
		3377
		3378	If you are unsure about something, feel free to contact the mailing list
		3379	with the full valgrind report and an explanation on why you think this is
		3380	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3381	no bug" answer and take the chance of learning how to interpret valgrind
		3382	properly.
		3383
		3384	If you need, for some reason, empty reports from valgrind for your project
		3385	I suggest using suppression lists.
		3386
		3387
2651	=head1 AUTHOR	3388	=head1 AUTHOR
2652		3389
2653	Marc Lehmann <libev@schmorp.de>.	3390	Marc Lehmann <libev@schmorp.de>.
2654		3391

Diff Legend

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